Design World Motion_Systems_Handbook August 2022

AUGUST 2022 DESIGNWORLDONLINE.COM MOTIONCONTROLTIPS.COM

MOTION
SYSTEMS

HANDBOOK
Compact & Light Wave Springs

WORLD-CLASS LINEAR

MOTION

LOCAL

MANUFACTURING

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extremely cost-effective package: Pre-matched LS Electric gearboxes offer easy mounting
to the servo motor. Use these gearboxes to increase the
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NEW! Motio System Handboo

4 AXIS SERVO HOW ENGINEERING
from CAN CLEAR THE AIR

2.25” Earl in the COVID-19 pandemic way back in 2020, we here at Design World did
quite a number of stories on companies designing and building ventilators and
- brushed or bldc motors
- 5 amps per axis other medical devices to accommodate the rapid uptick in need in the face of the COVID surge.
- 16 analog inputs
- 16 on/off drivers This was still in the emergency phase of the pandemic, with much uncertainty and the sudden
- home and limit in
- live tech support and surging need for all sorts of medical supplies, including PPE of various types for front-line
- made in the USA
medical workers as well as the ventilators that were in short supply.
See the
Now, two years later, we are far removed from those early emergency days and know a lot more NIOR EDITOR
EZQUAD SERVO about the virus and how it spreads. We also have many more effective ways to both combat the
in action! spread of the virus, including a number of highly effective vaccines which also lessen disease
severity, as well as treatments should one get infected.
WWW.ALLMOTION.COM
Other mitigation strategies, including the by now all-too-familiar social distancing and
(510) 471-4000 masking, can also be effective. However, there is still one huge area of impact that is often
overlooked or just not covered in the media much at all. And this is where engineering comes
30097 Ahern Avenue in. From almost the beginning of the pandemic, we’ve known that the virus spreads primarily
Union City, CA 94587 through the air, either in aerosol form or in droplets. The truth of the matter is that engineering
can play a central role in dealing with COVID-19 and other respiratory diseases by focusing on air
Technical Support quality, something that HVAC engineers know all about.
(408) 460-1345
Air quality is perhaps the single most important environmental factor that engineering can
control in order to reduce the risk of illness. This can include better air filtration and air flow
rates from building HVAC systems that increase supplies of fresh air, to something as low tech as
opening windows to let in fresh outside air.

A number of studies including from the EPA and the NIH as well as published studies in
journals of building design and engineering conclude that HVAC systems play a central role in
indoor air quality and what steps need to be taken to help reduce the risk of viral transmission
and spread. Key areas include air movement in buildings including exchange rates for fresh air.
Other factors include filter design in HVAC systems and using high quality filters to clear the air of
contaminants such as bacteria and viruses. This means not only the coronavirus but other viruses
that cause respiratory illnesses like the common cold and the flu.

Anyone who’s ever worked in a building with poor air quality, where people were always
sneezing or catching colds or other respiratory ailments, knows
the importance of good indoor air quality. In this sense,
improving HVAC systems in the ways suggested can
not only decrease the spread of pathogens such as
the coronavirus but also others that make people
sick, making for a better and healthier indoor
environment all around.

The world learned these lessons once
before in the wake of the 1918 flu pandemic,
which caused a shift in thinking in terms of
building design and ventilation. A lot has
already been done, but we can (and should)
push to do more.

4 DESIGN WORLD — MOTION MILES BUDIMIR • SE

8 • 2022

ISO 9001 + AS9100
CERTIFIED

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Content
VOLUME 8 NUMBER 3

4 EDITORIAL
8 STAFF
10 ACTUATORS — PNEUMATIC & ELECTRIC
14 BELTS & PULLEYS
17 BRAKES & CLUTCHES
18 CABLES & CONNECTIVITY
22 CONTROLLERS
24 CONVEYORS
26 COUPLINGS
31 DRIVES
33 ENCODERS & SENSORS
37 GEARING & GEARMOTORS
48 LINEAR GUIDES & RAILS • SLIDES & WAYS
52 SCREWS — BALL & ROLLER
54 MOTORS
58 SHOCK ABSORBERS • DAMPERS • GAS SPRINGS
63 SPRINGS
65 TABLES & STAGES • CARTESIAN ROBOTS • GANTRIES
68 AD INDEX

OP RNE CT HI SE I OCNO VL IENRE: AASURETRDOVROMIVACETSOEADUNPADLSINSPEGRMOS BFCILLYOE-EMRQAPUILLIEPMLMINEEENNATTR.
GUIDES IN THIS OF PHOTOMALL

| COURTESY

6 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com

The right gearmotor
for your application.

With over 1,400 standard products to choose from you
can count on the engineers at Bodine to help you find a
gearmotor with the right torque, power and speed for your
application. We’ll get your design moving.

bodine-electric.com

visit us at bodine-electric.com | [email protected] | 773.478.3515 (USA)

Desig W l
FOLLOW THE WHOLE TEAM ON TWITTER @DESIGNWORLD

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Motion Control Classroom PRINT PRODUCTION 2014- 2016
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stay up-to-date @wtwh_mariel Halle Kirsh
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learn more at: www.designworldonline.com/mc2 [email protected]
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8 DESIGN WORLD — MOTION 8 • 2022

TOPJOB® S MINI CTAECGPHEUN-SCOHLLOA-IGMNYP ®
TERMINAL BLOCK

A REAL SPACE GENIUS

The compact design of WAGO’s TopJob® S Mini Rail-Mount Terminal Blocks makes them
ideal for work in tight spaces. Various mounting and actuation variants are also available
for maximum flexibility; allowing you to choose your Mini terminal blocks based on use
and convenience. Thanks to spring pressure connection technology, they can be used in
junction boxes and are also suitable for vibration-proof connections.

www.wago.us/
discover-terminal-blocks/mini-rail-mount-terminal-blocks

Motion Systems Handbook

COMPARING ACTUATOR TYPES
Pneumatic cylinders and actuators are sometimes
called bang-bang devices — making quick travel. In addition to obtaining feedback on position, servo pneumatics
also monitor and regulate air pressure, which enables precise control of
moves from one end of their stroke to the other, with limited regulation the force that’s produced.

of the force or move profile. On the other hand, electromechanical One drawback (real or perceived) to traditional pneumatics is air
consumption. Air preparation and delivery costs money, and pneumatics
actuators with servo controls offer high levels of refinement in positioning, can use a significant amount of air even when they’re not working.
Servo pneumatics, on the other hand, control air flow based on the
force/torque, and accuracy. Pneumatics offers a cost-effective solution required position and force. This leads to less air consumption than
standard pneumatics, by as much as 30%. It’s important to note that
for rather crude point-to-point moves while electromechanical actuators servo pneumatics require higher quality air than standard pneumatics.
In addition to industry-standard filtration, a 5- mm filter is typically
provide high precision, at a higher cost. recommended for servo pneumatic systems.

However, there’s a spot between these two solutions where a relatively Servo pneumatics versus electromechanical actuators
high level of control is needed, but without the complexity and cost
of electromechanical servo driven systems. Bridging this gap are Of course, electromechanical actuators can provide accurate position
pneumatics that operate in a closed-loop system—in other words, and force control, but servo pneumatics have a much higher power
servo pneumatics. density—that is, force capability for a given size. A servo pneumatic
cylinder or actuator typically provides many times the force capability
A servo system is one that uses a feedback device and a controller to of an electromechanical actuator of a similar body size, which is a
monitor and correct the system’s error (in position, speed, or torque/force). significant advantage in pressing, inserting, and tightening applications.
Hence, integrating a pneumatic cylinder or actuator with a feedback Servo pneumatics also operate with 24 Vdc power supplies, which
system and a controller that can issue commands based on that feedback, allows them to be used in low-power applications. Lower power also
gives us a servo pneumatic device. Another key component of a servo reduces heat generation and thermal build-up, so they perform well in
pneumatic system is a proportional valve, which precisely regulates air continuous-duty applications and high-temperature environments.
delivery to ensure that the commanded position and/or force is achieved.
While electromechanical servo systems have been in use for decades,
Traditional pneumatics enable rapid, high-force, point-to- the adoption of servo pneumatics in industrial applications hinged on
point motion. Servo pneumatics provide the same speed and force advancements in controls and software. Air is compressible, and this
capabilities, with the advantage of higher accuracy positioning, not
only at the ends of the stroke, but also at intermediate points along the

| COURTESY OF VIOREL DUDAU

10 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com



Motion Systems Handbook

variable is much more difficult to define and convert it into controlled motion. That motion THE NEW AVENTICS SERIES SPRA ELECTRIC ROD-STYLE
model than the compliance, or backlash, can be for a variety of functions — including
in an electromechanical system. Before blocking, clamping, or ejecting. LINEAR ACTUATOR IS A COST-EFFECTIVE PERFORMANCE
servo pneumatics could be commercialized,
pneumatic control algorithms capable of Pneumatic actuators are mechanical SOLUTION. THE SERIES SPRA PROVIDES ENHANCED LOAD
considering this nonlinearity had to be created. devices that use compressed air acting on a
But the past ten years or so have seen the piston inside a cylinder to move a load along a CAPACITY, ACCURACY AND RELIABILITY, AS WELL AS
development and integration of high-response linear path. Unlike their hydraulic alternatives,
valves and digital signal processors (DSPs) the operating fluid in a pneumatic actuator OUTSTANDING PRECISION AND REPEATABILITY. EMERSON
that can perform high-speed computations, is simply air, so leakage doesn’t drip and
making servo pneumatic systems a reality, contaminate surrounding areas. There are OFFERS THE SERIES SPRA WITH THREE DIFFERENT SCREW
capable of providing accurate, highly responsive many styles of pneumatic actuators, including
positioning and force control. diaphragm cylinders, rodless cylinders, TECHNOLOGIES THAT ALLOW IMPLEMENTATION WITHIN A
telescoping cylinders and through-rod cylinders.
Pneumatic actuator benefits WIDE RANGE OF APPLICATIONS — MAKING IT A VERSATILE
The most popular style of pneumatic
Pneumatics is the technology of compressed actuator consists of a piston and rod moving AND FLEXIBLE SOLUTION.
air. Pressurized gas — generally air that is inside a closed cylinder. This actuator style
dry or lubricated — actuates an end effector can be sub-divided into two types based on If the load connected to the rod is less
and do work. End effectors in this context the operating principle: single acting and than the resultant force, the piston and rod
can range from the common cylinder to more double acting. will extend and move the machine element.
application-specific devices such as grippers Reversing the valving and the compressed
or air springs. Vacuum systems, also in the Single-acting cylinders use one air port to air flow will cause the assembly to retract
pneumatic realm, use vacuum generators and let compressed air enter the cylinder to move back to the home position. Pneumatic
cups to handle delicate operations, such as the piston to the desired position, as well as an actuators are at the working end of a fluid
lifting and moving large sheets of glass or internal spring to return the piston to the home power system. Upstream of these units, which
delicate objects such as eggs. Pneumatics is position when the air pressure is removed. produce the visible work of moving a load,
common in industries that include medical, Double-acting cylinders have an air port at are compressors, filters, pressure regulators,
packaging, material handling, entertainment each end and move the piston forward and lubricators, on/off control valves and flow
and even robotics. back by alternating the port that receives the controls. Connecting all these components
high pressure air. together is a network of piping or tubing
By its nature, air is easily compressible, (either rigid or flexible) and fittings.
and so pneumatic systems tend to absorb In a typical application, the actuator body
excessive shock, a feature useful in some connects to a support frame and the end of the Pressure and flow requirements of the
applications. Most pneumatic systems operate rod is connected to a machine element that is actuators in a system must be considered when
at a pressure of about 100 psi, a small fraction to be moved. An on/off control valve is used to selecting these upstream system components.
of the 3,000 to 5,000 psi that some hydraulic direct compressed air into the extended port Undersized upstream components can cause
systems see. As such, pneumatics is generally while opening the retract port to atmosphere. pneumatic actuators to perform poorly, or even
used when much smaller loads are involved. The difference in pressure on the two sides make them incapable of moving their loads.
of the piston results in a force equal to the
A pneumatic system generally uses an pressure differential multiplied by the surface
air compressor to reduce the volume of the area of the piston.
air, thereby increasing the pressure of the gas.
The pressurized gas travels through pneumatic
hoses and is controlled by valves on the way
to the actuator. The air supply itself must be
filtered and monitored constantly to keep the
system operating efficiently and the various
components working properly. This also helps
to ensure long system life.

How do these fluid-power actuators work?
Many industrial applications require linear
motion during their operating sequence. One
of the simplest and most cost-effective ways to
accomplish this is with a pneumatic actuator,
often referred to as an air cylinder. An actuator
is a device that translates a source of static
power into useful output motion. It can also be
used to apply a force. Actuators are typically
mechanical devices that take energy and

12 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com

Flexibility to Meet
Your Needs

Steel, Stainless Steel, and
Aluminum Shafting cut to
length and optimized for
use with LEE Linear bearings.

LEE Linear has the ability to manufacture
custom shafting to required standards in a
short amount of time, eliminating downtime
and increasing profits for our customers.

Special machining capabilities include
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Motio System Handboo

KEEPING BELT AND PULLEY
DRIVES ON TRACK

BELT-DRIVEN LINEAR ACTUATORS, SUCH AS THE SMART
SYSTEM FROM ROLLON SHOWN HERE, CAN SUPPORT
HEAVY LOADS AND OFFER LOW MAINTENANCE IN A RANGE
OF APPLICATIONS IN AUTOMATED MANUFACTURING.

Linea motion actuation can take pulleys that keep the belt taut and on track.
many forms; from the latest The tensile members of many of today’s

linear motor designs to mechanical means belts – cords embedded into the belt rubber that
carry the majority of the belt load – are stronger
involving screw actuators. Mechanical drive than ever. Made of polyester, aramid, fiberglass
or carbon fiber, these tensile cords make
systems involving chains or belts and pulleys can today’s belt drives thoroughly modern power
transmission devices.
also be a reliable option.
The pulleys used in belt drives are typically
Belts can either be the source of motion metal or plastic, and the most suitable depends MISALIGNMENT OF THE BELT PULLEYS CAN
themselves or transmit power or motion, on a number of factors including the required CAUSE SEVERAL ISSUES, INCLUDING BELT
depending on the setup. A typical belt drive precision, price, inertia, color, magnetic WEAR AND THE BELT “JUMPING” OFF THE
includes the belt and a number of pulleys, properties and the engineers’ preference based PULLEY DURING OPERATION.
as well as clutches and mechanisms for ratio on experience. Plastic pulleys with metal inserts
variation. In some cases belt drives function as or metal hubs are a good compromise. | COURTESY OF TIMKEN
a conveyor, with the load riding on the belt. In
other situations such as in actuators or machine- Engineers use belt drives in motion systems
axis coupling, belt drives function as the device for a number of reasons. For starters, belt drives
to convert rotary motion of an electric motor to are simple and relatively inexpensive compared
linear motion. with other drive technologies. Plus, modern belt
drives require little if any maintenance and are
Industrial belt drives include a number of relatively quiet and efficient, even up to 95% or
variations, including the common design of a more in some cases. Another plus is that they are
rubber belt that wraps around drive pulleys, more tolerant of shaft misalignment, meaning
which are in turn driven by electric motors. The that they do not require axially aligned shafts.
belt also typically wraps around one or more idler

14 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com

Custom
Synchronous
Drives

You’ve created a unique design.
Now relax.
We’ll take it from here.
Custom precision manufacturing.

Manufacturer of Power Transmission and Motion Control Components

Precise. Reliable. Trusted. American Engineering | American Made

© 2017 Custom Machine & Tool Co., Inc.

Motio System Handboo

Focu o V-bel troubleshootin the sheave during installation. In extreme cases, foreign objects in the
drive can damage the belt severely enough to cause breakage.
The earliest belt iteration — and one that’s still economical today — is
the friction-based V-belt design. These pair a belt with a pulley (often on Edg c damag
an electric motor’s geared output shaft) to provide reliable operation in a
variety of end-user and industrial designs. Edge cord damage or failure can be a product of sheave misalignment,
which causes the belt to track unevenly and, in some cases, twist during
Modern V belts are rubber, urethane synthetic, and neoprene operation. Damaged tensile cords can also lead to edge cord damage
designs with either a V or trapezoidal profile. The latter increases the or failure.
amount of contact between V belts and pulleys to minimize tension
needed to transmit torque. Even so, polyurethane outperforms Bel come o th sheav
rubber thanks to its higher resistance to chemicals and adaptability to
specialized profiles. During operation, if the belt comes off the sheave or turns over, this
can indicate misaligned pulleys or contamination in the drive. Other
Although there are more than a dozen symptoms of premature conditions that can cause the belt to jump off the sheave or turn over
wear and impending failure for V-belts — ranging from visible include insufficient belt tension, significant vibrations in the drive, and
damage to audible noise — there are a few key ways that these shock loads.
friction-based belts can fail during operation. To help users determine
the root cause of a failure or signs of potential failure, V-belt Failur t carr th loa
manufacturers provide troubleshooting guides that suggest causes
and remedies for a wide range of issues. Here, we’ll look at five A belt that’s unable to carry the designed load will often slip and is an
common ways that V-belts can fail and the most probable causes of indication that the drive is improperly sized or has insufficient tension. If
each condition. sizing and tension are found to be sufficient, other potential causes are
damaged tensile cords or worn sheave grooves.
B oke bel
Abn ma wea
The clearest sign of accelerated belt wear or failure is a broken belt,
which typically indicates that the tensile cords have been damaged. Any abnormal wear – whether on the top, bottom, sides, or grooves of
Damage to these load-carrying members can be caused by severe the belt – can indicate a problem in the application. Wear on the top or
shock loads during operation or by using a belt that’s under-sized for bottom corners of the belt is often caused by a poor fit between the belt
the application. and the sheaves, due to incorrect sizing or due to wear on the sheaves.
Wear on the bottom of the belt is also a sign of poor fit between the
Tensile cord damage can also occur if the belt is pried or rolled onto
belt and the sheaves, although debris in the drive can also cause
POWER TRANSMISSION-PART CONVEYING bottom surface wear.

PYRATHANE® BELTS If belt surfaces — especially the belt sidewalls or the top
Lifetime Warranty Against Manufacturing Defects surface — become hard or stiff, this can indicate that the belt is
slipping (which increases heat and friction), or that it has been
exposed to excessive heat from the environment or the process.
Similarly, contamination from oil other chemicals can cause
the belt — in this case, typically the top surface — to swell or
become flaky or sticky.

LINE SHAFT CONVEYOR BELTS SHOWN HERE IS THE DIFFERENCE BETWEEN FRICTION BELTS AND SYNCHRONOUS
BELTS – THE FORMER USE FRICTION AND HAVE MORE POTENTIAL FOR ERROR IN
Original Equipment and Connectable POSITIONING, WHILE THE LATTER MAKE USE OF TOOTHED PULLEY ENGAGEMENT.
CUSTOM MADE IN INCH, METRIC & O-RING SIZES
16 DESIGN WORLD — MOTION 8 • 2022
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B ake & clutche

ELECTROMAGNETIC
MAGNETIC-PARTICLE ACTION

Magneti -particl clutches and Magnetic-particle clutches are
brakes include useful in paper-feeding applications
a profiled magnet-studded wheel (rotor) half and a cup half that such as printers and ATMs, as they
(when assembled) enclose an internal ring-shaped cavity — or (for slip upon detection of the feeding
higher-torque units) multiple arc-shaped cavities. During assembly, of muliple plys or sheets.
the component manufacturer fills this cavity (or cavities) with

DC POWER INPUTmagnetic particles. Then during operation, these particles respond

to the application of direct current fed to an electromagnetic coil
embedded in the component’s outer assembly half.

More specifically, the particles within the cavity lock into chains to ROTOR INPUT SHAFT
drag against the steel housing. Maximum torque of components thus OUTPUT SHAFT
locked depends in large part on the quantity of particles as well as MAGNETIC
the magnitude of applied electrical power — with full power causing PARTICLES
the particles to lock as a solid drag mass and lower input power
allowing the particles to slip somewhat. FLUX PATH
FIELD COIL
Strengths: Unlike friction-element-based units that can shed dust
as their friction elements wear, magnetic-particle clutches and brakes When the stator coil is energized, the
run clean. That’s exceptionally helpful on machines manufacturing magnetic particles in the cavity align
electronics or optical components … or medical products such as
pharmaceuticals or sterile bandages. into chains to drag on the stator.

Magnetic-particle clutches and brakes also excel in web- INPUT SHAFT
processing applications and other machines involving tension control
or torque limiting. That’s because converting and general web and MAGNETIC-PARTICLE CLUTCHES AND BRAKES ARE TORQUE DENSE.
cable-tensioning processes usually need smooth and adjustable THAT’S HELPFUL WHEN THEY’RE MOUNTED TO MOTORS REQUIRING
torque. Here it’s magnetic-particle clutches and brakes can engage MINIMAL ADDITION OF INERTIA — WHEN DRIVING AXES NEEDING QUICK
across myriad input-power values for adjustable and smooth-running ACCELERATIONS AND REVERSALS FOR EXAMPLE.
(cog-free) slipping even down to very low rpm … as their particles
can (as mentioned above) slip past each other. In contrast, friction-
based components tend to exhibit stick-slip behavior during most
low-force low-speed engagement.

Constraints: Magnetic-particle brakes and clutches are typically
used on horizontal applications, as vertical arrangements can
cause the particles to fall to the bottom of their cavity and degrade
torque capacity. That’s especially true where machinery is subject
to vibration. Though usually quite smooth running, a faint stiction
of these units at near-zero rpm may render them inappropriate for
exceptionally slow axes.

At the other end of the spectrum, these brakes and clutches
don’t do particularly well on axes involving exceptionally fast slip
speeds … as such situations tend to make magnetic-particle units
exceed their heat-dissipation limits.

In fact, magnetic-particle components must be sized to
accommodate the application’s torque and heat-dissipation
requirements. Another caveat is that eventually the magnetic particles
can indeed wear out … though usually that’s only a risk on tensioning
axes involving constant slip and heat sufficient to eventually degrade
the particles’ magnetic capacity. In-field serviceability is also limited
for magnetic-particle clutches and brakes.

motioncontroltips.com | designworldonline.com 8 • 2022 DESIGN WORLD — MOTION 17

Motio System Handboo

HELUKABEL’S TRAYCONTROL PRODUCT FAMILY IS A
VERSATILE, HIGHLY FLEXIBLE LINE OF INDUSTRIAL CONTROL,
POWER AND INSTRUMENTATION CABLES CAPABLE OF
BEING USED IN VARIOUS APPLICATIONS AND INDUSTRIES. 

THE IMPORTANCE OF FLEXIBILITY

IN INDUSTRIAL CONTROL CABLES

Mult -axi machines and are then enclosed in an extruded tube-shaped Fla cable o e compac desig
robots are always jacket. In the case of shielded cables, the cores
are wrapped up with fleece or foils. However, An alternative to flexible cabling in some
in continuous operation, featuring repetitive this type of construction means that during the motion applications are flat cables. These
bending process the inner radius compresses cables can incorporate any variety of power,
motions that can stress all the moving parts of and the outer radius stretches as the cable signal, and video conductors in a single
core moves. This can work quite well because compact cable. In addition to every type of
the machine. Electrical data, power and signal the elasticity of the material is still sufficient, electrical conductor, flat cables can also include
but material fatigue can set in and cause tubing for air or liquids, and even fiber optics.
cables — critical components in these designs permanent deformations. The cores move and
begin to make their own compressing and By incorporating all these elements into
— must be considered with care. Standard stretching zones, which can lead to a corkscrew a single flat cable, motion equipment can be
shape and even core rupture. significantly smaller, quieter, and more energy
cables can fail prematurely, so it is necessary to efficient. Flat cables are best for continuous
The other construction technique involves flexing. Their wire conductors can individually
select the right type of high-flex motion control braiding conductors around a tension-proof flex in a single plane, which provides optimum
center instead of layering them. Eliminating flex life.
cables for your industrial motion application. multiple layers guarantees a uniform bend
radius across each conductor. At any point Some motion control systems may encase
Designed and manufactured to cope with the where the cable flexes, the path of any core separate wires, cables, and tubes in a carrier
tight bending radii and physical stress associated moves quickly from the inside to the outside track to contain and manage the separate
with motion applications, these highly flexible or of the cable. The result is that no single core elements and to constrain their motion. These
continuous-flex cables have long service lives, compresses near the inside of the bend or tracks are usually made of plastic and have
especially if run inside protective cable carriers. stretches near the outside of the bend, which a rather large bend radius. These tracks do
Standard cables typically manage 50,000 cycles, reduces overall stresses. An outer jacket is still not add performance to the motion device or
but a flexible cable can complete between one required to prevent the cores from untwisting. machine, as they are simply cable management
and three million cycles. devices. Cable tracks can add bulk, mass and
A pressure-filled jacket fills all the inertia to the motion system, and moving this
Commo desig type gussets around the cores and ensures that extra mass requires more energy. While certain
the cores cannot untwist. The resulting motion systems such as robotic applications
Flexible cables fall into two categories — flexible cable is often stiffer than a standard may require this design, others may not and
those with conductors stranded in layers cable, but lasts longer in applications where can use standard flat cabling instead to save
inside the cable and those with bundled or it must constantly flex. weight and cost.
braided conductors.
Some flat-cable manufacturers offer cables
Cables with stranded layers are easier to
produce so usually less expensive. The cable
cores are stranded firmly and left relatively
long in several layers around the center and

18 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com

INDUSTRIAL AUTOMATION

HELUKABEL is a global cable system solutions provider specializing in the production of cables, wires, cable assemblies,
robotic dress packs, and drag chains. Our electrical solutions consistently and reliably bring power and transmit data
to our customer’s applications in various automation-focused industries including machine building, automotive
manufacturing, material handling, food and beverage, wood, pulp, and paper processing, oil and gas, and robotics.

With a comprehensive product portfolio of more than 33,000 stock items, and the capabilities to design and build custom solutions,
HELUKABEL is your one-stop source for electrical connection technology.

HELUKABEL® USA, Inc. | West Dundee, IL | www.helukabel.com | [email protected]

Motio System Handboo MULTIFLEX 512-PUR UL/CSA, WITH OR WITHOUT A SHIELD FROM

WHY SHOULD ONE WORRY IGUS , IS A DRAG CHAIN-RATED CONTROL AND POWER CABLE
ABOUT VOLTAGE DROP?
SUITABLE FOR NOMINAL VOLTAGES UP TO 1,000 V (UL AWM).
T pu i simpl , excess voltage drop can reduce the operating efficiency of motors,
with silicone jacketing. These types of flat cables are
lights, appliances, and other electrical equipment. If too much voltage is lost while durable and need no external armor for protection.
passing through wires, equipment may not function properly, or at all. For certain They resist abrasion and will even self-heal minor nicks.
equipment such as pumps, large motors, or machines that use compressors, even Silicone encapsulation also provides protection against
a small loss of voltage can be problematic. Keep in mind that voltage drop also oils, acids, ozone, steam, and extreme temperatures.
generates heat, which can build up in wires or cables and damage the insulation,
ultimately leading to safety issues such as fire and shock. Let’s take a look at the four Selectin th igh cabl
main factors that affect voltage drop, and how to keep it to an acceptable minimum
— defined by the National Electrical Code (NEC) as 5% at the furthest receptacle in a Selecting the right cable for an application starts with
branch wiring circuit. For example, in a 120 V/15 A circuit, there should be no greater fundamental parameters. First, determine whether the
than a 6 V drop (to 114 V) at the furthest outlet, with the circuit fully loaded. cable will be moving. Does the motion induce cable
flexing or twisting? Or does the application induce
When current passes through wire, it is pushed along by electrical potential, or voltage, flexing and torsion? Cables exist for all three situations.
which must exceed a certain level of opposing pressure from the wire itself. Voltage
drop is defined as the amount of electrical potential loss that is caused by the contrary If the application is only bending, determine the
pressure of the wire. The four chief variables involved in voltage drop include the wiring cable’s worst-case bend radius. Bend radius depends
material, diameter, and length, and the amount of current being carried. The current on the cable wire gauge and the kind of conductors
carrying capacity of a wire is often called ampacity, which stands for ampere capacity. in the cable. Cable size is determined by the gauge
of wire which in turn is dependent on current
With regard to the wiring material, copper and aluminum are widely used due requirements (and the number of conductors the
to their excellent electrical conductivity and relatively low price compared with application needs). As a general rule, finer conductor
more expensive options such as silver or gold. Copper will experience less voltage gauge allows tighter bend radii. Flat cables with PTFE
drop than aluminum for the same wire length and diameter, as copper is a better jackets can have a larger bend radius than cables with
conductor. Next, a larger wire size (diameter) will have less voltage drop than a silicone jacketing for a given number of conductors.
smaller size of the same length. Wire length is also a key factor. A shorter wire will
have less voltage drop than a longer wire of the same diameter. Finally, the amount For cabling in flexing applications, two key
of current being carried will affect voltage drop levels. An increase in current leads factors are wire conductors and the cable jacket. With
to increased voltage drop, but just how much depends on the wire’s ampacity, continuous flexing, conductors containing multiple
which in turn depends on variables such as wire material and temperature. strands of fine-gauge wire generally last the longest.

One of the easiest ways to decrease voltage drop is to increase the size The most suitable choice of cable material
(diameter) of your wires or cables, which will lower the resistance of the overall wire depends on application needs, and can include PVC
length. Take into consideration that a larger copper or aluminum cable will add and halogen-free to Neoprene, rubber, silicone and
cost, so be sure to calculate voltage drop in order to specify a properly sized wire. other materials. Also, do the cables require electrical
Online voltage drop calculators and wire manufacturers are a good place to start. shielding? Tip: Consider any approvals that the cables
may need to meet such as UL, CSA, CE, and RoHS.

Chief environmental factors dictating the most
suitable cable choice include exposure to harsh
conditions such as temperature and humidity and
required resistance to environmental contaminants
such as oil or corrosive materials. For instance, what
is the operating temperature for the application? Will
the cables be in cold (freezing and below freezing)
or hot environments? Will the cables need to endure
exposure to oil? Here, other cables can resist full
immersion for days. In the same way, cables also have
varying degrees of flame resistance.

20 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com



Motion Systems Handbook

PACSYSTEMS RSTI-EP CPE 200 PROGRAMMABLE AUTOMATION
CONTROLLERS (PAC) FROM EMERSON ARE HELPING DESIGNERS
MINIMIZE THE NEED FOR SPECIALIZED SOFTWARE ENGINEERING. THE
CONTROLLERS OFFER OPEN COMMUNICATIONS THROUGH NATIVE,
PRE-LICENSED SUPPORT FOR OPC UA SECURE AND OTHER COMMON
INDUSTRIAL PROTOCOLS FOR FLEXIBLE CONNECTIVITY OVER HIGH-
SPEED GIGABIT ETHERNET. IEC 61131 PROGRAMMING LANGUAGES HELP
ENGINEERS WRITE AND RUN HIGH-PERFORMANCE ALGORITHMS FOR
ADVANCED AUTOMATION FUNCTIONS.

EMBEDDED CONTROLLERS FOR MOTION
Controllers are at the heart
of every motion controllers) include a basic PC motherboard Still, PACs differentiate themselves
system, issuing motion commands to a motor or ruggedized industrial PC as well as PC- from PLCs by employing a more open
or actuator. The controllers available to motion type hardware components and a high-speed architecture and modular design. They’re
dedicated bus that transmits data to and from also more capable than PLCs at monitoring
the processor. Inputs and outputs from the and controlling a large number of I/O, such
as in a large processing plant or a complex
design engineers today are more powerful controller board provide interfaces to factory automation system. They do this because
data can be exchanged between devices and
and offer better performance than ever floor devices such as motors, actuators, and applications in different domains, such as
before. Many of them feature built-in functions sensors and feedback. motion and process control.
adaptable to a range of applications, making
A familiar type of controller is the Spotlight on embedded control
programmable logic controller (PLC). These
Over the past several years, embedded
them more versatile. devices serve as the programmable smarts solutions have found their way into the motion
control space, with terms such as embedded
for a host of applications, from simple motion, embedded motion control, and
embedded motion controller now commonly
Typically, controllers are categorized in one of machine control up to advanced multi-axis used in product descriptions. Although there
are no standard definitions for these terms,
several ways. They can be divided by physical motion control. they all refer to some level of integration of
motion control components for the purpose
format (plug-in board, stand-alone, embedded) The next step in evolution beyond PLCs of making end devices better-suited for
applications in which size, performance, and
or by function (PLC, PAC, motion controller) or are programmable automation controllers or efficiency are paramount.

even by architecture (distributed vs. centralized.) PACs. These industrial controllers combine The term “embedded motion” is most
often used when referring to a motor that is
Of course, the right controller will always the functionality of a PLC with the processing an integrated part of the mechatronic system,
rather than a separately coupled mechanism.
depend on the particular application needs. power of a PC. Note; because there is no

For example, standalone controllers industry-standard definition for a PAC the

are complete control units that include distinction between PACs and PLCs can be a

control circuitry, power supplies and external bit fuzzy. For instance, higher-end PLCs now

connections that mount to one physical incorporate some of the features considered

enclosure. Such control units fit into machines PAC territory. In fact, many PLCs now include

in applications that consist of a single motion standard programming languages, the ability

axis up to multiple axes of motion. to expand functionality through add-on

On the other hand, plug-in board modules, and connectivity to a range of the

controllers (sometimes called PC-based most common data bus systems.

22 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com

Controllers

THE CM-CPB3-44 ETHERCAT CONTROLLER FROM NANOTEC
CONTROLS FOUR BRUSHLESS DC OR STEPPER MOTORS WITH A
RATED POWER OF UP TO 150 W PER AXIS. FEEDBACK ON THE MOTOR
POSITION IS PROVIDED BY HALL SENSORS OR INCREMENTAL OR SSI
ENCODERS. FEATURES SUCH AS FIELD-ORIENTED TORQUE, SPEED AND
POSITION CONTROL, COMBINED WITH OTHER FEATURES SUCH AS
ACCELERATION FEEDFORWARD AND JERK-LIMITED RAMPS, ENSURES
OPTIMUM DYNAMIC PERFORMANCE AND CYCLE TIME.

For example, frameless motors (sometimes referred Looking for cost effective
to as “kit” motors) can be integrated into a robot and energy efficient
joint, with the load directly coupled to the motor or positioning?
even integrated into the motor itself. Embedded
motion reduces the number of transmission The simplicity of pneumatics combined with the
components required, which in turn provides higher advantages of electric automation
efficiency and reliability. And in many cases, the drive The Simplified Motion Series axes are ideal for simple
and control electronics are also integrated into the positioning and pressing/clamping movements.
end device, rather than being mounted remotely on • Quick and easy commissioning using the integrated
the machine or in a separate control cabinet.
buttons on the motor or via IO-Link
Where embedded motion commonly refers • Connection via IO-Link for enhanced functionality
to the mechanical part of the motion system (the
motor), the term “embedded motion controller” including diagnostics
typically refers to PCB-mounted motion control • Simple control with 2 digital inputs for basic functions
modules that are integrated directly into the
machine. These modules take care of all motion or enhanced control with IO-Link for additional
controller functions, such as servo path planning functions, multi position download with speed and
and motion profile generation. The primary torque data
benefit of an embedded motion controller is that
the system no longer requires remote-mounted festo.us
drives and PLCs (or other controllers), significantly
reducing the length of encoder and feedback
cables between the motor and the controller. This
means less wiring, better signal integrity, fewer
failure points, and better machine performance.

The term “embedded motion control” refers to
an embedded system that includes the mechanical
devices (motor, actuator); sensors or encoders;
motion control hardware, software, and firmware;
and a network interface. In other words, embedded
motion control combines mechanical and electrical
components and functionality into one device that
has been optimized for size, performance, and
efficiency. Because they’re purpose-built (rather
than general purpose, like a PLC or industrial PC),
embedded controllers and embedded motion
control systems significantly reduce development
time and simplify programming, allowing designers
to focus on the specific motion application and how
it operates within the system, rather than designing
the motion system from scratch.

DESIGN WORLD — MOTION 23

Motion Systems Handbook

BELT-DRIVEN CONVEYORS TAKE CENTER STAGE
Conveyors are systems
used to and weight of the product being handled exceed rated load, speed, or acceleration,
and on the process requirements, such as and the product can move, or slip, on the belt
deliver bulk or discrete materials through conveying distance and route, transport speed, during starts and stops or any time there’s a
and positioning accuracy. For assembly and change in acceleration.
processing operations or along assembly lines. automation applications, the most common
conveying media are belts, chains, flat-top Also referred to as synchronous or
Advances in materials, controls, and modular chains, and powered rollers. toothed belts, timing belts have toothed
surfaces that engage with matching,
subcomponents have spurred advancements Of these media choices, belts are arguably toothed pulleys. This positive engagement
the most versatile. They can be manufactured in between belt and pulley, together with
in conveyor systems including new large virtually any width and can span long conveying pre-tension (force applied to the belt in the
distances, and they operate with lower noise direction of motion) eliminates the problem
conveyors for bulk material transport, miniature and less required maintenance than chains or of belt slipping. And timing belt conveyors
rollers. Belts and their mating rollers (or pulleys) typically use belts that are reinforced with
conveyors for discrete sorting, and a host of are also available in many different materials steel or Kevlar tensile cords to provide
and finishes to meet specific application increased load carrying capability and
other innovations. requirements and environmental conditions. enable high acceleration rates (which result
in high forces on the belt) without causing
Conveyors come in a range of shapes and sizes Traditional belt-driven conveyors use the belt to stretch.
to accommodate the many diverse uses they flat belts that rely on friction between the
can be put to. For instance, conveyor widths belt and rollers to transmit power. They also To improve grip, the top (carrier) side
can range from less than 2 in. for moving rely on friction between the belt surface and of the belt can be coated to increase friction
extremely small parts to several feet wide for the product to hold the product at a specific between the product and the belt surface and
handling boxes in packaging applications. location on the conveyor. This friction-based reduce the possibility of the product slipping
design is flexible and economical, but it leads on the belt. Belt and pulley materials and
Most conveyors in light to medium duty to a potentially variable product positioning finishes can also be selected to meet specific
discrete transport applications use belts that and orientation. Case in point; the belt can application requirements and environmental
wrap around two or more pulleys. A motor slip on its drive rollers if working conditions conditions, such as ESD-compatible, food-
powers the pulleys that in turn engage the grade, or clean environments.
conveyor belt. A range of styles and materials
are available to meet specific applications.
Some belts are low friction, so products can
slide a bit for accumulation. In contrast, high-
friction belts have more grip to better hold
products to the belt.

One of the most common types of
conveyors are belt-driven. Here, servo
drives can accurately start and stop belt
conveyors to provide precise part location.
They also let engineers control acceleration
and deceleration, and thus are most suitable
for conveyors used in assembly operations.
Manufacturers often mount encoders to a
conveyor’s drive shaft to sense shaft rotation
or count pulley revolutions for accurate control
of the belt in feeding or indexing applications.
Single drive, multi-belt conveyors are set up
to run off of a single gearmotor or driveshaft
of coupled shafts. In some arrangements, the
belts even mount to a single conveyor frame.

Focus on timing belt conveyors INTERROLL’S LIGHT CONVEYOR PLATFORM (LCP) IS
DESIGNED TO TRANSPORT SMALLER CONVEYED GOODS,
A common type of conveyor drive setup is based AS WELL AS BOXES OR POLYBAGS WEIGHING UP TO 50
on timing belts. Timing-belt conveyors use KILOGRAMS. THE SYSTEMS ARE DESIGNED TO INCREASE
toothed belts that engage synchronous drive PRODUCTIVITY OF PRODUCTION CELLS AS WELL AS
pulleys while serving as the conveyor surface as ASSEMBLY AND PACKAGING STATIONS THROUGH
well. These provide excellent belt movement EFFICIENT MATERIAL FEED AND DISCHARGE.
control for accurate part or fixture positioning.

When designing a conveyor, one of the
first considerations is the conveying media to
be used, which depends on the size, shape,

24 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com

Conveyors

These conveyors are used to move work piece devices to further manipulate the work piece
pallets from one assembly station to another. pallet. Typical applications involve some type of
orientation change to the work piece pallet as it
One of the things that differentiates this moves about the system. Another common task
style of conveyance from a traditional large is to precisely locate the work piece pallet for a
diameter roller or flat belt conveyor is the robotic application.
ability to easily add additional components and

PALLET CONVEYORS, SUCH AS THIS EXAMPLE FROM better products. better solutions.

GLIDE LINE, SHOWS THE COMPONENTS IN THE DRIVE Recirculating Over-Under Conveyors

MECHANISM INCLUDING THE MOTOR AND GEARBOX Streamline Over-Under Conveyor Applications
with the SPU 2040 from mk North America, Inc.
DRIVING THE BELT DRIVES ON BOTH SIDES OF THE
mk’s SPU 2040 conveyor system is a powerful alternative to
CONVEYOR WITH THE PALLET ON TOP. traditional over-under conveyor systems.

When application requirements call for No Vertical Transfer Units | Less System Controls | Faster Deliveries
accurate product location with no loss of
position, cleats or fixtures can be attached (860) 769-5500 | [email protected]
to the belt carrier surface to hold the
product in a specific location and with the www.mknorthamerica.com/SPU
correct orientation.

Another option to ensure precise location
and orientation is to transport the product on
a pallet. Locating the product on a fixed pallet,
together with the accurate, no-slip conveying
of the timing belt, provides the highest level of
position accuracy and certainty.

A further benefit of timing belt conveyors
is that the movements — and, therefore,
the products being carried — of multiple
conveyors can be synchronized. This makes
timing belt designs ideal for dual- or multiple-
line configurations and allows large, heavy
loads to be transported, even when accurate
positioning is required.

Other conveyor types

Some key industry trends are shaping conveyor
technology as well. For instance, the push to
automate assembly, distribution operations,
and material handling are leading to
innovations in conveyor design, as is the drive
for more energy-efficient designs in general.

In terms of conveyor technology, systems
based on belt and roller designs are the
most common, with pallet conveyors gaining
ground. These conveyor types consist of
individual pallets on conveyors that typically
hold a single product. The conveyor itself is
belt driven with a dc motor and they are smart
in that they can be controlled individually,
which also eliminates accumulation of
products on a conveyor belt.

Some conveyors for pallet handling include
a basic timing belt or roller-chain conveyor.

DESIGN WORLD — MOTION 25

Motion Systems Handbook

COUPLING SELECTION FUNDAMENTALS

Couplings are motion system Additionally, other factors like STEEL DISC COUPLINGS LIKE THESE FROM RINGFEDER
devices that handling the vacuum of space,
extreme temperatures, and PROVIDE BACKLASH-FREE TORQUE TRANSMISSION AND
connect two shafts and are found in countless no outgassing would need to
be examined. In this specific EXCELLENT POSITIONING ACCURACY IN MACHINES THAT
motion systems. Mechanical couplings are example, Ruland chose 316
stainless steel Oldham hubs and INVOLVE SYNCHRONOUS OPERATION, FREQUENT STARTS
often found on rotating equipment like motors a special non-outgassing PEEK
Oldham insert. AND STOPS, OR REVERSING OPERATIONS.
to transmit several motion parameters. These
Another application Windup is dampening. It’s dampening or
parameters include the transmission of angular example would be a coupling cushioning. It is not an error in the coupling
in an autoclave’s environment. — It’s not “play.” A jaw coupling provides
positioning, velocity, and torque. Here, we For an application like this, a perfect example of windup: The spider
a coupling must survive high compresses, rebounds, and absorbs shock
look at a few of the most frequently asked temperatures for short intervals. and dampens — that’s wind up, not error.
A bellows coupling might be an option, but Some couplings have different amounts of
questions about mechanical coupling selection autoclave temperatures will often exceed the wind up. A bellows coupling or disc coupling,
temperature capability of the epoxy in the for example, has little windup. They have
fundamentals and more. Oldham. To work around this, an Oldham high torsional stiffness. Rigid couplings have
coupling with a PEEK disk might work. The almost no windup. Windup is a good thing
Coupling selection fundamentals disk not only does not outgas, but it can also to have in your coupling design. Especially
withstand high temperatures. for applications where frequent shock loads
Temperature are expected and a jaw coupling has been
Speed selected. Windup is your friend at that point
The environment where the coupling will in the jaw coupling. 
operate is one of the first questions to be Certain applications are relatively easy to solve
answered when selecting a coupling for with most any coupling at 5,000 or even up to Duty cycle
an application. Understanding the myriad 10,000 RPM. Occasionally, couplings may get
environmental variables a coupling might up near 25,000 RPM or even higher — 75,000, Duty cycle is a critical but often overlooked
encounter is crucial during the early design 80,000 RPM. The consideration engineers consideration during the coupling selection
stages of your motion system. need to factor in is not just torque capacity process. Essential elements like types of
but how well balanced the coupling is for motion, potential shock load scenarios, and
Environmental considerations include the type of speed they expect the coupling start/stop situations should all be evaluated
moisture, temperature, chemicals, and to encounter. If the coupling is not either when selecting a coupling for your next motion
vacuum — all important things to consider balanced or symmetrical by nature, a vibration system application.
at the time of selection. The question to problem is likely because of the imbalance of
ask yourself is “What are we dealing with Duty cycle, types of motion, continuous
in all these different issues?” For example, the weight. This is an important and start/stop and reversing, and asking, “how
an aerospace application where engineers often overlooked consideration. As often is the system running?” These all come
are using a coupling to control the aperture positioning devices accelerate faster into play with selection. Selection error
on a telescope. In this situation, a coupling and faster, coupling balance is more often occurs when the type of motion is not
that can survive the vibration of an actual important than ever. accounted for or when the number of cycles is
spacecraft during takeoff would be necessary. not understood. Talk to the manufacturer and
Windup give them your duty cycle.

Often confused with backlash, windup A system running at full speed, that does
is easy to overlook when selecting not stop or reverse abruptly, will often have a jaw
couplings for a motion system. But coupling selected for the application. Gradual
windup is an important consideration
that can cause real problems if not
factored in early in the design process.

Windup and backlash are often
confused. They are not the same.

SHAFT COLLARS AND COUPLINGS, LIKE THESE FROM

STAFFORD WITH DIFFERENT BORES, ARE OFTEN AVAILABLE IN

STANDARD INCH AND METRIC SIZES FROM 1/8 TO 10-IN. I.D.

(COUPLINGS TO 6-IN. I.D) TO PRECISELY MATCH DIFFERENT

SHAFTS AND POSITIVE DRIVE SYSTEMS.

26 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com

WHAT’S NEW froRmULAND All products available directly on
RULAND.COM

TOOL-LESS ADJUSTMENT COMPONENTS

• Adjustable handles and knobs replace standard hardware
and can be used to torque components without tools.

• Levers can be used with Ruland shaft collars for quick
installation and adjustment.

Adjustable Handle Star Knob Shaft Collar with Lever Ruland Manufacturing is proud to
support the FIRST Robotics Competition
SLIT AND CONTROLFLEX COUPLINGS
as a Gold Supplier of precision
• Slit couplings are available in short and long styles giving shaft collars & couplings.
designers a variety of body sizes to choose from to t
application envelope and performance requirements. MODULAR MOUNTING
SYSTEMS
• Control ex is a highly exible encoder coupling designed
for applications with high speed, low torque, and wide • Assortment of components
differences in shaft sizes (up to a 4:1 small to large ratio). that allow users to build small
assemblies for mounting sensors,
• Slit couplings are available in bore sizes from 1.5mm conveyor rails, machine guards,
to 12mm (1/8” to 1/2”) and control ex couplings are and more.
available in sizes from 6mm to 40mm (1/4” to 1-1/2”).
• Optional pre-designed kits make
Slit Coupling Control ex Coupling it easier to select the right
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Motion Systems Handbook

start/stop — systems running at full speed then handle the hard stop and start shock loads.
slowly coming to a stop or reverses — often have For dampening, frequent starts and
beam couplings. Beam couplings can work well in
these applications. Many of the coupling types like stops, or high shock load applications, the
the bellows type, and in most cases the disc types, applications may require a coupling that
are also used, however. This gradual start/stop can dampen the impulse load; again, jaw
cycle is a must for coupling life because they can’t couplings are a good option. Selection
error occurs when this is not accounted for.

BOOTH 134043 MECHANICAL COUPLINGS ARE OFTEN FOUND ON ROTATING

Maximize EQUIPMENT LIKE MOTORS TO TRANSMIT SEVERAL MOTION
your performance
PARAMETERS. THESE PARAMETERS INCLUDE THE TRANSMISSION
with the widest range of precision couplings
OF ANGULAR POSITIONING, VELOCITY, AND TORQUE.
®
| COURTESY OF RULAND
NBK
In that type of application, beam couplings are
www.nbk1560.com common. When asking for increased dampening,
choose a jaw coupling.
307 East Church Road, Suite 7, King of Prussia, PA 19406
phone: 484-685-7500 fax: 484-685-7600 e-mail: [email protected] Dampening application examples where
there are different materials available —different
hardness of material to change the dampening
characteristics — are common in food processing
OEM applications.

What are slit couplings?

Slit couplings are mechanical couplings and can
offer zero-backlash, reduced weight, and are
manufactured with intermittent slit cuts, making
them a good starting point for designers of robotic
systems. While they are visually similar to multiple
beam couplings, the slit cut design gives them
higher torque and torsional stiffness capabilities
and numerous length options in the same outer
diameter, allowing coupling performance to be
tailored to system requirements.

Slit couplings have torque comparable to
a single disc coupling, torsional stiffness like a
stainless-steel beam coupling, and misalignment
consistent with an aluminum beam coupling.
This combination of specifications allows a slit
coupling to be used in place of one of these
styles, which all have limitations such as no
accommodation of parallel misalignment in a
single disc coupling. Along with low mass and
inertia, these characteristics make slit couplings a
good choice for robotic systems.

Robotic applications such as those found
in medical, surgical, factory, and warehouse
environments often require a zero-backlash
coupling with high torque, torsional rigidity,
and speed. These robots can start, stop, and
reverse constantly, necessitating a responsive
coupling. Along with other performance benefits,
slit couplings have a moderate amount of
dampening, which is useful in robots requiring
vibration control, such as material handling and
articulating robots.

28 DESIGN WORLD — MOTION

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D ive

FOCUS ON VARIABLE FREQUENCY DRIVES

I motion control systems, drives are Drives are generally split into dc and ac. lower energy losses, which allows for less
the interface between control signals One of the most common type of ac drives cooling and smaller designs. IGBTs also permit
and an electric motor, delivering the signals are variable frequency drives (VFD). VFDs the VFD to use a higher carrier frequency for
operate by switching output devices on and sending output voltage pulses to the motor,
which reduces audible motor noise and
in the form of voltage and current that cause off, which can be transistors, IGBTs (insulated provides the motor with reduced harmonics
and lower peak current. Lower peak current
the motor to move. Sometimes drives are gate bipolar transistors), or thyristors. VFDs can enables the motor to run cooler and develop
referred to as amplifiers because they amplify be either constant voltage or constant current, more torque-producing current throughout the
with constant voltage types being more speed range.

the voltage signals that come from the common. They use pulse width modulation On the flip side, IGBTs have brought to
light the phenomenon of reflected waves. Also
controller, which are too low to drive sufficient (PWM) to control both the frequency and the known as transmission line effects or standing
current through the motor windings to cause voltage applied to the motor. waves, reflected waves are over-voltages that
can damage motor insulation and cables.
One of the reasons why VFDs are
Cause o eflecte wave
meaningful speed or torque. becoming more common are for their energy
Most VFDs today operate via PWM, with
savings. By controlling the amount of current the inverter producing a continuous train of
pulses rather than sinusoidal wave forms.
Modern digital drives have internal processing drawn by the motor, energy costs can be These voltage pulses are transmitted to the
motor terminals through the motor cable. The
capabilities that allow them to not only decreased due to the motor not running at full cable’s inductance (a factor of impedance)
is proportional to the length of the cable.
manage position, velocity and torque loops load all of the time. This is especially important High inductance, due to long cable lengths,
increases the amount of time it takes to charge
but also take over high-level functions such as as motor efficiency and energy savings the capacitance of the motor, which increases
the amount of energy in the cables.
trajectory generation. Digital drives also allow become top design priorities. VFDs also
Inductance is a conductor’s resistance to
tuning to be done via software, and they’re provide an advantage on motor start-up. For change in electric current, and capacitance is
the ability to store an electrical charge. Both
able to monitor internal functions and provide motors operated without a VFD, an induction are impeding mechanisms and present an
opposition to current when voltage is applied.
detailed fault diagnostics. motor on start-up has to handle a high initial The collective impedance caused by inductance
and capacitance is known as reactance.
in-rush current. As the motor speeds up and
Additionally, when the voltage pulses
approaches a constant speed, the current reach the motor, they encounter a different
(higher) impedance than in the cable, causing
levels off from the peak in-rush the pulses to be reflected back to the drive.
Under certain conditions, a pulse from the VFD
VFDS, LIKE THIS MODEL FROM BISON, SIGNIFICANTLY REDUCE values. With a VFD, the can add to a pulse reflected back from the
ENERGY CONSUMPTION BY ENABLING ELECTRIC MOTORS TO motor’s input starts off with motor, resulting in a doubling of the voltage
OPERATE AT LESS THAN FULL SPEED. SUCH NEWER MODELS low voltage and a low level. The greater the length of the cable (i.e.
ARE ALSO DESIGNED TO BE EASY TO COMMISSION AND frequency, avoiding the the distance between the motor and the VFD),
OPERATE. THIS PANEL-MOUNTED VFD IS OUTDOOR-RATED, the greater the over-voltage, or reflected wave.

WASHDOWN-READY AND DUST-TIGHT, MAKING IT SUITABLE problem of high in-rush Together with cable length, the rise time
FOR MANY ENVIRONMENTS. currents. Eliminating the of the switching device also has an effect on
reflected waves and the amount of voltage
in-rush currents upon overshoot. If the turn-on time of the switching
device is slow, the capacitance of the motor
start-up also gets rid of has time to charge and discharge in step with
the switching device. But if the switching
the excessive torque on device’s turn-on time is fast, the voltage

components, increasing

the life of the motor and

reducing maintenance

costs and the need for

repair.

Sepfoletlcitgeh wo avVeFD

Reflected waves, also
known as transmission
line effects or standing
waves, are over-voltages
that can damage the motor
and cable. The use of IGBTs
in variable frequency drives
has helped to improve VFD
performance in several ways.
First, their quick switching time (also
referred to as rise time, or dV/dt) means

motioncontroltips.com | designworldonline.com 8 • 2022 DESIGN WORLD — MOTION 31

Motio System Handboo

Precision Motion. THE SCHEMATIC SHOWS THE ELECTRICAL LAYOUT OF A
TYPICAL VARIABLE FREQUENCY DRIVE, WITH 3-PHASE INPUT AT
Made Easy. LEFT, THE BRIDGE RECTIFIER AND FILTER SECTION, FOLLOWED BY
THE INVERTER SECTION AND THE PWM OUTPUT TO THE MOTOR.
Aerotech’s Automation1 motion control
platform powers some of the most precise applied across the cable increases, and more
processes in operation all over the world. energy is stored, resulting in a higher over-voltage.
Yet, it is very simple to use and easy to
integrate. Reduce your risk with the variety E ect o eflecte wave
of software, controller and high-performance
drive options available with Automation1. The problem with reflected waves is that the
voltage spikes can ionize the air in the air gap
Make your precision motion easier between motor windings, as well as the air
between the cable insulation and cable jacket,
at aerotech.com/automation1 causing partial discharge, or corona. The point
at which this ionization causes arcing across
the motor windings (or across the conductors
in the cable) is known as the corona inception
voltage (CIV). When the motor CIV is reached, the
insulation in the motor windings can be damaged
or even fail. When the cable CIV is reached,
a short-circuit can occur and the cable can be
permanently damaged.

Although reflected waves can occur regardless
of the type of switching device—IGBT, GTO (gate
turn off), or BJT (bipolar junction transistor)—the
fast switching capability (rise time) of IGBTs makes
this phenomenon more prevalent. Case in point:
current IGBTs have turn-on times as fast as 0.1
msec, where BJTs switch at 0.5 to 1.0 msec, and
GTOs switch at 15.0 to 20.0 msec.

Damage due to reflected waves is more
prevalent with 460-V and 575-V IGBT-based
drives. Drives that operate on 230 volts are rarely
damaged due to voltage overshoot because the
reflected waves have amplitudes that are lower
than the motor CIV.

The most effective way to prevent the
occurrence of reflected waves and over-
voltage is to keep the cable length shorter than
manufacturer’s recommended maximum. In cases
where reducing the cable length isn’t feasible,
there are hardware solutions, such as output
reactors, filters, and terminator devices, that can
reduce or eliminate reflected waves, protecting the
motor and cable from damage.

32 DESIGN WORLD — MOTION

Encoders & sensors

| COURTESY OF VLADIMIR TIMOFEEV

LINEAR SENSING BASED
ON INDUCTIVE TECHNOLOGY
Most design engineers
involved in motion We’ve covered several different magnetism-based linear-sensor technologies in past Design World
system engineering are intimately familiar Motion Handbooks … and one induction-based variable-reluctance linear sensor (VR sensor) type as
with the function of induction motors. well — that of LVDTs. In fact, there are several other types of linear sensors based on induction. Two
Most are also familiar with proximity that are particularly common in motion applications are:
sensors that use induction for metal-
object presence detection. But there’s a Linear variable-reluctance transducers (LVRTs) — another VR sensor type — and differential
third design leveraging induction for its variable-reluctance transducers (DVRTs) along with related variations on traditional LVDTs
operation. Called inductive linear sensors,
these use field induction (in a conductive Linear-variable-inductance transducers — also called LVITs
subcomponent) for linear-motion feedback.
These linear sensors actually track inductance variations — disturbances made by a conductive target
through a magnetic field. The latter is made by primary winding transformer that’s been energized
… sans permanent magnets needed with magnetism-based linear sensors. LVRTs resemble LVDTs
but include a continuous core winding and not a segmented winding as in LVDTs. In contrast, LVITs
contain an inductive sensing coil connected to onboard sensor electronics. Upon axis traversal, a
conductive cylinder called a spoiler coupled to the axis’ end effector travels axially through the coil —
in turn changing the inductance and prompting the sensor electronics to generate an output signal
proportional to axis’ move.

motioncontroltips.com | designworldonline.com 8 • 2022 DESIGN WORLD — MOTION 33

Motio System Handboo AMPÈRE’S LAW SOLENOID
MAGNETIC
Anothe inductio -base technolog = FIELD

There are also more sophisticated technologies based = Line integral of B around CONDUCTIVE
on inductive operation and advanced electronics to a closed path WIRE
offer OEMs accuracy, speed, and reliability exceeding
those of other linear-sensing options. = Permeability of free space

In one proprietary design, the physics described = Current
in both Ampère’s law and Faraday’s law are put to
work. Conductive sine and cosine-patterned traces RIGHT-HAND RULE MAGNETIC
are manufactured onto a circuit board. 90° phase- FIELD FROM CURRENT
shifted alternating current on these traces function
as a coil to generate twin fields perpendicular to the AMPÈRE’S LAW STATES THAT
traces’ 2D plane. A CURRENT THROUGH A
CONDUCTOR CAUSES A
An active position marker (which attaches to the PROPORTIONAL MAGNETIC FIELD
moving carriage or component of the motion axis — AROUND THAT CONDUCTOR.
but needs no external wiring) passes over the traces.
Summing the resulting signal yields:

H · sin(x) · cos(w·t) + H · cos(x) · sin(w·t) = H · sin(w·t + x)

Where x = Marker position
t = Time and w = Applied waveform frequency
H = Signal strength.

In other words, the phase of the signals’ sum at
each location is proportional to marker position x.
Amplitude is modulated along the travel, and sin(w·t) is
the reference signal. First the electronics phase shift the

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first signal 90° to get the second with sin(w·t + 90°) = cos(w·t). Then the addition theorem is applied,
and amplitude information is converted into phase information:

sin(w·t + x) = sin(w·t) · cos(x) + cos(w·t) · sin(x)

Finally, the sensor electronics compare the phase information with the reference signal. The
marker returns summed signals back to the circuit board; tracking phase shift between outgoing and
returned sinusoidal signals produces a dc voltage proportional to their phase shift — which serves to
inform motion controls of the marker’s positional change.

In another patented variation, linear sensors employing this technology integrate both
transmission and receiver coils on a common circuit board protected by a ruggedized housing.

During operation, the position marker receives an alternating field from the transmission coil.
In response, the marker induces current in the receiver coil … a current that varies with location.
Receiver-coil sine and cosine structures include coarse and fine tracks for both approximate and
high-precision position tracking. The position marker’s position is reflected in the signals’ phase
relationship — converted to a usable position signal by the linear sensor’s electronics.

8 • 2022 DESIGN WORLD — MOTION 35

Motion Systems Handbook

BESIDES STROKE LENGTH, ANOTHER IMPORTANT FACTORS FOR SELECTING A LINEAR-POSITION
SENSOR OR ENCODER INCLUDE THE APPLICATION’S REQUIREMENTS FOR LINEAR POSITION-SENSOR
OUTPUT TYPE — WHETHER ANALOG (0 TO 20 mA, 4 TO 20 ma, OR 0 TO 10 V) OR DIGITAL.

Despite what is essentially electromagnetic
operation, these induction-based linear sensors are
immune to external magnetic fields — including EMI
from electric motors and inverters. That’s because they
operate within an exceptionally narrow frequency range
and reject any signals at frequencies outside that tight
range. That also avoids the problems associated with
sensing components that rely on magnetic markers
(such as magnetostrictive sensors) that can collect metal
shavings during normal operation ... as in machine-tool
and assembly settings, for example.

More sophisticated linear-feedback components
based on inductive measurement are readily
programmable, as the microprocessor electronics for
deriving position from marker-induced signals can
also accept programmable settings. These include
status reporting as well as customizing the electrical
measurement range, slope, and positions for minimum
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Gears & gearmotors

CONSIDERING GEAR GEOMETRIES,
INERTIA, AND USUAL LOAD CONDITIONS

The limits of a gearmotor include those • Bring attached loads to a full stop before as mentioned … as well as attached system
related to unusual loads, load reversing or components and workpieces.
arrangements, and duty cycles. Durability and
(gear) strength ratings are the limiting factors • Will fully disengage load attached to the Sudden or erratic and large peaks in torque
when a gearmotor is subject to cyclical loads. gearmotor before such changes. called shock loading present similar modes of
Note however that these load types differ from potential gearmotor damage. Such loading is
the rapid stops or reversals that can damage One common solution is to include a in some cases unavoidable: After all, punches,
most gearmotors … especially inertial-load plug clutch or brake in the assembly to prevent presses, and extruders subject their components
reversals — rapid switches in rotational direction large inertial loads from driving the gearmotor to necessarily powerful strokes during normal
sans intermediate stopping. That’s why properly backward through axis backlash … or forward operation; professional-grade crushers and
designed gearmotor axes will either: after de-energization. Another common power tools must sometimes power past
solution is the employ drives and controls temporary obstacles and jams; debarking,
capable of electronic compensation to grinding, and chopping axes must sometimes
prevent such backdriving and overrunning, drive through unusually dense material volumes;
which can otherwise damage gearmotors and hoists and conveyors must sometimes

| COURTESY OF NIKONAFT

motioncontroltips.com | designworldonline.com 8 • 2022 DESIGN WORLD — MOTION 37

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Gear & gearmot

HIGH-TORQUE GEARBOX-
MOTOR PAIRING

| COURTESY OF STEFAN11

overcome sudden additions of payload — necessitating resistance to this force by both loads. That’s especially true during the
as when unexpectedly large products are the shaft itself as well as its support bearings. acceleration and deceleration portions of the
dropped on conveyances, for example. motion profile.
In fact, any mechanical belt, cable,
Shock loading is generally quantified or chain drive directly mounted on the In this context, the inertia to which we’re
by its severity as well as its switching duty — gearmotor’s shaft will exert some bending referring is mass moment of inertia, sometimes
the frequency with which the torque peaks force. Mounting such drives as close as called rotational inertia — an object’s
occur. Most gearmotor manufacturers publish possible to the gearmotor body helps resistance to change in rotational speed. An
figures on maximum gearmotor shock-loading minimize the effects of overhung load on the object’s mass moment of inertia depends on
capabilities according to a grading system or bearings and shaft. Overhung load Ō can be its mass and geometry … usually the radius
as a percentage of running load. calculated: defined by the object’s center of mass and the
point around which the object rotates.
For example, a heavily ruggedized unit Where T = Torque; r = Radius of
may be capable of withstanding shock that mechanical output-shaft component; and If the load’s inertia significantly exceeds
is 300% greater than the typical continuous- x = Power-transmission adjustment factor. the motor’s inertia, that load will essentially
running load for the axis. However, especially In some rating systems, the latter is unity for try to drive the motor … and the motor will
challenging inertia ratios and duty along with chain drives, 1.3 for timing-belt drives, and struggle to get the load to its target position,
significant shock-load conditions (as well as 2.5 for flat-belt drives. Once the (unavoidable) speed, or torque.
shock-amplifying mechanical components such overhung load requirement for a given axis is
as chain in the drivetrain) can often necessitate calculated, the design engineer should consult That in turn will prompt the motor to
further upsizing of the gearmotor. overhung-load limits in charts supplied by draw higher current … which decreases
gearmotor manufacturers ... or communicate efficiency and increases wear on the motor
Yet another extenuating condition is that the details of the overhung load during the and electrical components.
of overhung loads — those which occur when specification process.
some load exerts a perpendicular force (or On the other hand, if the motor’s inertia
hangs off) a gearmotor’s output shaft. These Usin gearin t optimiz significantly exceeds the load’s inertia, it’s
loads can be: mot -syste inerti ati likely that the motor is oversized. That in turn
has negative implications throughout the
(Most commonly) attached power- Any system using a motor to drive a load system — including higher initial cost, higher
transmission components (including cable, with precise positioning, velocity, or torque operating cost, larger footprint, and the
belt-drive pulley, or chain sprocket) requires consideration of inertia. That’s need to oversize other components such as
because the ratio of load inertia to motor mounting hardware, couplings, and cables.
• (Less commonly) the payload itself inertia significantly impacts a motor’s ability
• Shaft misalignment, often addressed with to effectively and efficiently control attached If the inertia ratio is too high, the load
inertia is much higher than the motor inertia
the addition of a flexible coupling and will cause problems with positioning
accuracy, settling time, or control of velocity
Overhung loading can cause detrimental or torque.
bending in the gearmotor output shaft —
If this is the situation at hand, load inertia

motioncontroltips.com | designworldonline.com 8 • 2022 DESIGN WORLD — MOTION 39

Motion Systems Handbook

that is seen by (reflected to) the motor can be decreased by adding a gearset or gearbox
between the motor and the load:

Where JL = Inertia of the load reflected to motor and JM = Inertia of the motor. Adding
a gearset or a gearbox to a motor-driven system reduces the load inertia by the inverse
square of the gear ratio, meaning that even a relatively low gear ratio can have a significant
effect on the inertia ratio:

Where JL = Inertia of load reflected to motor; JD = Inertia of drive — whether ball
screw, belt, or rack-and-pinion set; JE = Inertia of external (moved) load; JC = Inertia of the
coupling; JG = Inertia of gearset or gearbox; and i = Gear ratio.

Note that the inertia of the gearset or gearbox JG is added to the load inertia, but its
effect is typically small compared to the reduction provided by the gear ratio.

In addition to optimizing the load-motor inertia ratio, gearboxes are often used in
motion control applications to increase the torque delivered to the load from the motor,
but they also decrease the rotational speed delivered to the driven component from the
motor, by an amount equal to the gear ratio. Therefore gearboxes are often called gear
reducers or speed reducers.

In other words, if a motor running at 1,200 rpm is driving a load through a 3:1
gearbox, the rotational speed delivered to the load will be 1,200 ÷ 3 = 400 rpm. This
reduction in speed can enable the system to operate at a more favorable location on the
motor’s speed-torque curve.

Although it is possible to use a gearbox or gearset that is configured to reduce torque
(and increase speed) in motion control applications, a more typical solution here is to
choose a smaller motor.

Special requirements for servogearing

Servo systems are precision-motion setups with feedback and (in most cases) stringent
accuracy demands. So for these designs, engineers should pick servogear reducers with
good torsional stiffness, reliable output torque, and minimal backlash. OEMs tasked with
integrating servo systems should look for quiet reducers that easily mount to the motor
and require little or (if possible) no maintenance. In fact, advanced machinery often
integrates servogears into application-specific electromechanical arrangements … and
several of these arrangements are common enough to have specific labels. Here is a look
at some of the most widespread.

Gearmotor: This complete motion component is a gear reducer integrated with an
ac or dc electric motor. Usually the motor includes the gears on its output (typically in
the form of an assembled gearbox) to reduce speed and boost available output torque.
Engineers use gearmotors in machines that must move heavy objects. Speed specifications
for gearmotors are normal speed and stall-speed torque.

Gearbox: This is a fully integrated mechanical component consisting of a series of
mating gears contained in a housing with shafts and bearings (to support and resolve
loads) and in many cases a flange for motor mounting.

Gearhead: Most of the motion industry makes no differentiation between the terms
gearhead and gearbox. But in a few contexts, the term gearbox specifically refers to
housed gearing as described above while the more general term gearhead also refers to
assemblies of otherwise open gearing that installs within some existing machine frame.
The latter are often targeted to compact, consumer-grade, or battery-powered mobile
designs necessitating especially tight integration and omission of potentially redundant
subcomponents. In one variation, a series of parallel plates might support gear-train shafts
(and bearings) and allow bolting to a motor face.

Other open gearing simply mounts to the electric-motor output and operates
exposed to the environment. Some such open gearing is self-lubricating — constructed
of dimensionally stable polyamides or similar materials engineered to meet stringent
cleanliness, vibration, weight, and cost requirements.

40 DESIGN WORLD — MOTION 8 • 2022

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Motion Systems Handbook PLANETARY GEARSET
| COURTESY OF JACEK JĘDRZEJOWSKI
More on planetary gearsets
GEARMOTORS DRIVE CONVEYORS IN A WIDE
Particularly common in servo systems, planetary gearsets ARRAY OF LOGISTICS APPLICATIONS.
consist of one or more outer planet gears that revolve
about a central sun gear. Typically the planet gears | COURTESY OF NORD DRIVESYSTEMS
mount on a movable arm or carrier that rotates relative
to the sun gear. The sets often use an outer ring gear, or
annulus, that meshes with the planet gears.

The gear ratio of a planetary set requires
calculation, because there are several ways they can
convert an input rotation to an output rotation.

Typically, one of these three gear wheels stays
stationary; another is an input that provides power
to the system, and the last acts as an output that
receives power from the driving motor. The ratio
of input rotation to output rotation depends on
the number of teeth in each gear and on which
component is held stationary.

Planetary gearsets offer several advantages over
other gearsets. These include high power density, the
ability to get large reductions from a small volume,
multiple kinematic combinations, pure torsional reactions
and coaxial shafting. Another advantage to planetary
gearbox arrangements is power-transmission efficiency.
Losses are typically less than 3% per stage, so rather than
waste energy on mechanical losses inside the gearbox,
these gearboxes transmit a high proportion of the energy
for productive motion output.

Planetary gearbox arrangements distribute load
efficiently, too.

Multiple planets share transmitted load, which
greatly increases torque density. The more planets in
the system, the greater load ability and the higher the
torque density. This arrangement is also very stable
due to the even distribution of mass and increased
rotational stiffness. Disadvantages include high bearing
loads, inaccessibility and design complexity.

In servo systems, besides boosting output
torque, gearboxes impart another benefit — reducing
settling time. Settling time is a problem when motor
inertia is low compared to load inertia … an issue
that’s the source of constant debate (and regular
improvement) in the industry. Gearboxes reduce the
reflected inertia at the controls by a factor equal to
the gear reduction squared.

More on hypoid gearsets

Hypoid gearboxes are a type of spiral bevel gearbox —
with the difference that hypoid gears have axes that are
non-intersecting and not parallel. In other words, the
axes of hypoid gears are offset from one another. The
basic geometry of the hypoid gear is hyperbolic rather
than having the conical geometry of a spiral bevel gear.

In a hypoid gearbox, the spiral angle of the pinion
is larger than the spiral angle of the gear, so the pinion
diameter can be larger than that of a bevel gear pinion.
This provides more contact area and better tooth
strength, which allows more torque to be transmitted
and high gear ratios (up to 200:1) to be used.

42 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com

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Because the shafts of hypoid gears don’t intersect, bearings can be operation. But it also requires special extreme pressure (EP) gear oil to
used on both sides of the gear to provide extra rigidity. maintain effective lubrication due to the pressure between the teeth.

The difference in spiral angles between the pinion and the crown Hypoid gearboxes are generally used where speeds exceed 1,000
(larger gear) causes some sliding along the teeth, but the sliding is rpm ... although above 8,000 rpm ground gears are recommended.
uniform, both in the direction of the tooth profile and longitudinally.
This gives hypoid gearboxes very smooth-running properties and quiet However, hypoid gearing is also useful for lower speed applications
that require extreme smoothness of motion or quiet operation. In multi-
From Concept
stage gearboxes, hypoid gears are often used for
the output stage, where lower speeds and high
torques are required.

The most common application for hypoid
gearboxes is in the automotive industry, where
they are used in rear axles — especially for large
trucks. With a left-hand spiral angle on the pinion
and a right-hand spiral angle on the crown, these
applications have what is known as a below-center
offset ... which allows the driveshaft to be located
lower in the vehicle. This lowers the vehicle’s center
of gravity and in some cases reduces interference
with the interior vehicle space.

To Creation Industria -grad plasti gearin

Bison Gear & Engineering is an industry leader in Plastic gears are primarily recognized for their
designing and manufacturing custom gearmotors quiet operation and resistance to rust — attributes
for the fractional horsepower market. Our engineering that are important the food processing, medical
team will work with you to find the perfect solution equipment, and chemical processing industries, as
for your power transmission needs. well as in consumer applications. But plastic gears
Challenge us today with offer many other benefits, and advances in materials
your custom project and manufacturing processes are helping to close
the remaining performance gap between plastics
and metals in gearing applications.

When determining whether a plastic gear
will be suitable for a particular application, the
most critical factor is environment. Some though
not all plastics maintain less dimensional stability
than metals ... and in a few cases, their strength
and stiffness characteristics are dependent on
temperature and exposure to water or chemicals.
When properly specified, plastic gears will exhibit no
swelling or shrinking.

Plastic and metal gears also experience
different types of contact under load. Metal gears
have primarily line contact, with one tooth in mesh
at a time. But plastic gear teeth have an involute
surface that deforms under load, distributing the
contact pressure across a larger surface and allowing
contact between adjacent teeth. This provides load
sharing among teeth and helps to improve the life
of plastic gears in some applications — especially
those with high impact loads and relatively low
continuous loads.

The lighter weight of plastic gears means they
have lower inertia than their metal counterparts,
which is essential for aerospace and some military
applications. In addition, most plastic gears can run
without lubrication ... or can be embedded with
lubricating materials such as graphite, silicone, or
PTFE. However, some operating conditions benefit

www.bisongear.com 44 DESIGN WORLD — MOTION



Motion Systems Handbook

WORM-GEAR
| COURTESY OF

DMITRY KALINOVSKY

LENGTH INCREASE (%) 3.5 from (or even require) lubrication. Choosing a lubricant for plastic gears should take into
consideration the environmental, load, and speed conditions in which the gears will operate.
POLYAMID GEARS IN MOISTURE If the lubricant isn’t compatible with the plastic material, stress cracking or even failure of the
plastic can result.
3
Due to sliding contact, plastic worm gears can in some cases experience heating which in
2.5 NYLON 6 turn decreases strength and accelerates wear. Speed capability is limited for such plastic worm
gears, and lubrication is typically recommended.
2 NYLON 6.6
The variety of plastics that are suitable for gear applications is extensive, but common
CAST NYLON 12 choices include nylon, acetal, polycarbonate, polyphenylene sulfide, and polyurethane. The
1.5 addition of glass fiber can improve the stiffness and heat conductivity of some materials, although
it reduces the material’s fatigue endurance. Plastic gears can be processed by injection molding
NYLON 11 for lower cost than machined plastic gears. However, machined plastic gears typically offer better
1 tooth strength and can be produced to meet higher AGMA quality levels than can be achieved
with injection-molded versions.
0.5
A metal hub — either molded into the gear or assembled after manufacturing — can help
TENSILE STRENGTH (KILO LB/SQ IN.) 0123456789 in heat dissipation. It can also increase the rigidity of the gear and provide a secure surface for
WATER ABSORPTION (%) fastening the gear to the shaft.

MOISTURE ABSORPTION SOME PLASTICS USED IN THE CONSTRUCTION OF GEARS EXCEL IN WET SETTINGS.
12 AFFECTS TENSILE STRENGTH FOR EXAMPLE, CAST NYLON (POLYAMIDE-12) GEARS THAT ARE SUBMERGED
DURING OPERATION NEVER SWELL BEYOND A TENTH OF A PERCENT. THAT’S FAR
10 NYLON 6.6 LESS MOISTURE ABSORPTION THAN OTHER NYLONS USED IN CONSTRUCTING
8 PLASTIC GEARS — FOR MAINTENANCE OF DIMENSIONS AS WELL AS RATED
6 TENSILE STRENGTH.
4 CAST NYLON 12

2 NYLON 6

0
01 234567 89
MOISTURE (%)

46 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com

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Motion Systems Handbook

SPLINES TO SERVE
LINEAR-GUIDE FUNCTIONS
As covered in earlier Motion Handbook exclusively used in dual-shaft configurations handling. In contrast, ball splines for combined
installments, ball splines are a type to prevent the bearings from rotating as they linear and rotary motion abound in pick-and-
of rolling-bearing linear guide. They’re much ride on the shafts. But since ball splines are place robotics, water jets, automatic tool
like linear bushing (round shaft and bushing) inherently anti-rotation, they can be used in changers, laboratory equipment needing quick
assemblies but with a critical distinction in their single-shaft configurations. And replacing transfers of pipettes and other test samples,
two shafts with one also means a smaller and packaging equipment.

operation. The ball-spline shaft is much like a footprint, less weight, and easier alignment Ball splines for torque transfer: A ball spline
linear-guide shaft except that the spline shaft and assembly. Linear and rotary motion in is essentially a linear bushing and shaft pairing
has grooves along its length. The spline nut one: Rotary ball splines also provide excellent … except with both the axial shaft and the nut
(analogous to the bearing, or bushing, of a solutions for Z-theta axes on SCARA robots. ID sporting axial grooves … hence the term
The spline shaft provides the Z (vertical) spline. Load-carrying balls recirculate within the

traditional rolling bearing guide) contains circuits movement. The rotary bearing on the spline nut just as they do in a linear bushing. However,

of recirculating balls. But instead of the spline nut then provides the ϴ rotational movement. the grooves in the shaft prevent rotation and
nut riding freely on the shaft with the ability to These properties also make rotary ball facilitate the transmission of torque. This allows
rotate during linear travel, the load-carrying ball splines to withstand overhung loads and
balls ride in the shaft grooves that constrain the splines suitable for automatic tool changers in moment loads, unlike linear bushings, which can
CNC machine tools. only support radial loads.

Pick-and-place or assembly applications

spline nut and totally prevent rotation. also make copious use of rotary ball splines. The ball-spline assembly’s part housing

Consider how transferring a workpiece from one the recirculating balls is called a nut — and not

Another version of the ball spline is the rotary ball station or conveyor to another might involve: usually called a bushing. Even this terminology

spline, which incorporates a rotating element — is somewhat imperfect though … as a ball-

such as an angular contact ball bearing, crossed • Picking the part from the first station — spline nut’s functionality is indeed different

rollers, or gear teeth — on the outer diameter of with vertical motion from that of a ballscrew’s recirculating-ball nut.

the nut. This adds the capability of rotary motion • Rotating to the position of the second Because the design of a ball spline

to the linear motion provided by the ball spline conveyor — with rotary motion affords much greater contact area between

— somewhat like a cross between a recirculating • Placing the part on the second conveyor the balls and the grooves than that of standard

linear guide and a ballscrew. — with vertical motion bushings, ball splines have significantly higher

Because the recirculating balls of the load capacities. Ball splines typically have

spline nut ride in grooves, the contact area is In this case, a rotary ball spline can be two, three, or four grooves … although some

greater than for ball bushings, giving ball splines driven by a pneumatic cylinder (for the linear designs have up to six grooves. Like the

much higher load capacities than ball bushing motion) in conjunction with a belt-and-pulley raceways of profiled rail bearings, the grooves

assemblies of the same size. But even though system for the rotary motion. in a ball spline can be designed with either:

higher load capacity is a benefit, the primary Ball-spline designs fall into two categories Circular arch geometry for two-point

reason many designers and engineers use ball — those for torque transfer and those for contact on each ball

splines is their ability to prevent rotation or (in combined linear and rotary motion. Ball splines or

the case of rotary ball splines) to provide both for torque transfer abound in machinery for Gothic-arch geometry for four-point contact on

linear and rotary motion in one device. product assembly, welding and plating, wire each ball.

Traditional linear bushings are almost winding, paper processing, and material Essentially, Gothic arch geometry provides

higher rigidity but also contributes to higher

| COURTESY OF VIOREL DUDAU friction. In contrast, circular arch geometry
has lower friction and smoother running

characteristics. Torque capacity is determined

by the number of contact points, so a ball spline

with four Gothic arch grooves will have 16

contact points and transmit more torque than an

otherwise identical component with two Gothic

arch grooves and just eight contact points.

Sizing and selection of ball splines

combines technical considerations from both

linear recirculating bearings and ballscrews.

Life is calculated via the standard bearing life

equation, using both radial loads and torque

48 DESIGN WORLD — MOTION 8 • 2022 motioncontroltips.com | designworldonline.com