Parker Trilogy Reference Manual

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Trilogy Linear Motor
Engineering Reference Guide

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Parker Hannifi n Corporation

Electromechanical Automation Division

1

Engineering
Reference

1. Advantages of linear motors

1.1 What are linear motors?

Simply stated, a linear motor is the same as a rotary motor that has been
“unwrapped.” They operate exactly the same as rotary motors, where
the same electromagnetic equations that describe how a rotary motor
produces torque now describe how a linear motor produces a direct
force.

In many applications, linear motors offer distinct advantages over
conventional rotary drive systems. When using a linear motor, there
is no need to couple the motor to the load by means of intermediate
mechanical components such as gears, ballscrews, or belt drives. The
load is directly connected to the motor. Therefore, there is no backlash or
elasticity from the moving elements. Thus, the dynamic behavior of the
servo control is improved and higher levels of accuracy are achieved.

The absence of a mechanical transmission component results in a drive
system with low inertia and noise. In addition, mechanical wear only
occurs in the guidance system. As a result, linear motors have better
reliability and lower frictional losses than traditional rotary drive systems.

1.2 Differences in construction

The differences in construction between a direct-drive linear motor and
a conventional rotary drive system are shown in (Fig. 1 and Fig. 2,) using
the examples of a linear motor drive and a ballscrew drive. Due to the
absence of mechanical transmission elements converting rotary move­ment into linear movement, the axis fi tted with a linear motor has a much
simpler mechanical construction, resulting in a low-inertia drive for highly
dynamic applications. Though not always required, the linear motor table
is equipped with a linear encoder, which provides extremely accurate
positional feedback.

Though the linear encoder in (Fig. 2) can be considered a high-cost
component, the selection of the feedback system can be optimally
suited to the requirements of the application. For instance, Parker
offers extremely high-resolution optical encoders for applications with
demanding precision requirements. In addition, Parker offers lower­resolution, low-cost magnetic encoders for applications where overall
system cost is a concern. Actually, it is not uncommon for a linear motor
with an economical form of feedback to outperform and actually cost
the same or even less than a rotary system using a precision ground
ballscrew.

Linear Motor Engineering Reference Guide

Encoder Motor

Coupling

Motor Mount

Carriage

Drive Screw

Linear Bearing

Base

Encoder Motor

Coupling

Motor Mount

Carriage

Drive Screw

Linear Bearing

Encoder Motor

Coupling

Motor Mount

Carriage

Drive Screw

Linear Bearing

Base

Fig. 1: Precision table fi tted with ballscrew drive

Carriage

Base

Linear Motor

Linear Encoder

Carriage

BaseBase

Linear Motor

Linear Encoder

Fig. 2: Precision table fi tted with linear motor

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2

2.0 Types of linear motors

There are many different types of linear motors. Each type exhibits its
inherent advantages and benefi ts to the user. Parker manufactures 3 styles
of linear motors – ironless, ironcore, and an interesting variant known as
the “slotless” design.

Linear motors are either offered as individual components or complete
systems. Components, or “kits” (Fig. 3), consist of a motor coil and separate
magnet rail. The coil assembly is known as the “forcer” or sometimes as
the “primary” element. The forcer generally consists of the motor coil and
an attachment plate or mounting bar which allows the coil to connect to the
carriage.

The motor cables typically exit from one side of the package. The magnet
track is sometimes referred to as the “secondary” element. Depending on
the type of linear motor used, the magnet track can either be a single row
of magnets or a double-sided confi guration offering balanced attraction
forces.

A complete linear motor system (Fig. 4) is typically made up of the
individual motor components, base, bearings, feedback elements, and
cable management.

By selecting linear motor components, the user is given an economical
solution and is allowed complete fl exibility with respect to integration into
the machine. However, this requires a high degree of specifi c knowledge
on the part of the machine builder. The designing engineer must have an
understanding of the motor characteristics, linear feedback technology,
cooling methods, and the performance of the servo amplifi er and control
system.

By selecting integrated linear motor positioning systems, the design
engineer is given a pre-engineered, robustly designed, fully tested package.
This takes the worry out of designing and aligning bearings, encoders, heat
sinks, cables, connectors, travel stops, and limit / home sensors. Parker
linear motor tables provide all this and more in easily mounted and
ready-to-run packages.

Fig. 3: Linear motor components include a

separate coil and magnet rail

Fig. 4: Linear motor positioning systems include a base, bearings,

carriage, feedback and typically cable management

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3

Engineering
Reference

2.1 Ironcore motors

Ironcore motors consist of a forcer which rides over a single magnet
rail (Fig. 5). The forcer is made of copper windings wrapped around iron
laminations. The back iron provides an effi cient path for the magnetic fl ux
to circulate between the motor and the magnet rail. In addition, there is
an effi cient path for heat to escape the motor. This ironcore design allows
for extremely high forces and effi cient cooling. In fact, the ironcore design
offers the highest force available per unit volume. Finally, the ironcore
design is economically attractive because only one row of magnet
material is required.

One of the drawbacks of the ironcore design is that the motor has a high
attractive force between the forcer and the magnet track. The attractive
force can range from 5 – 13 times the rated force of the motor. This force
must be supported by the bearing system of the motor. In addition, the
high attractive force makes installation more challenging than other linear
motor designs.

Another drawback of the ironcore design is the presence of cogging
forces. Cogging occurs when the iron laminations exert a horizontal force
on the motor in order to line up with their preferred positions over the
magnets. Cogging limits the smoothness of motion systems because
the force generated by the motor must change with position in order to
maintain a constant velocity.

Parker Trilogy has developed a patent-pending Anti-Cog technology that
virtually eliminates cogging and allows ironcore motors to be used in
applications where only ironless motors were considered before. This
offers the machine builder a powerful combination of extremely high
force and smooth operation in an economical package.

To summarize the advantages and disadvantages of ironcore motors:

Ironcore advantages:

• High Force per Size - Uses laminations to concentrate the
fl ux fi eld.

• Lower Cost - Open face design only uses one row of magnets.

• Good Heat Dissipation - Because of laminations and large
surface area, heat can be removed easily.

Ironcore disadvantages:

• Normal attractive force – 5 to 13 times greater than force
generated.

• Cogging – Limits the smoothness of motion and creates velocity
ripple. This is counteracted by Parker Trilogy’s patent pending

Anti-Cog technology.

Fig. 5: Ironcore linear motor

Fig. 7: Parker Trilogy’s TR Series Ironcore Linear Motor Positioner

Fig. 6: Ripped Series Ironcore Linear Motor

Parker Trilogy offers ironcore motors both as components and as
pre-engineered, fully integrated positioning systems. Please refer to the
catalog for the RIPPED Series Ironcore Linear Motors and the TR Series
Ironcore Linear Motor Positioners (Fig. 6 and Fig. 7).

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4

2.2 Ironless Motors

Ironless motors consist of a forcer which rides between dual magnet rails
(Fig. 8). They are also known as “aircore” or “U-channel” motors. The
forcer does not have any iron laminations in the coil – hence the name
ironless. Instead, the copper windings are encapsulated and located in
the air gap between the two rows of magnets. Because the motors are
ironless, there are no attractive forces or cogging forces between the
forcer and the magnet track.

In addition, the forcers have lower mass than their ironcore counterparts.
What results is a motor design that allows for extremely high accelerations
and overall dynamic performance. The ironless design has zero cogging
and the lack of attractive force allows for extended bearing life and, in
some applications, the ability to use smaller bearings.

While the high dynamic performance and zero cogging motion make the
ironless motors a powerful design, they are not as thermally effi cient
as their ironcore counterparts. A small contacting surface area and a
long thermal path from the winding base to the cooling plate makes the
full-load power of these motors low. In addition, the dual row of magnets
increases the overall cost of these motors in relation to the generated force
and stroke length.

Fig. 8: Ironless Linear Motor

Parker Trilogy’s patented I-beam shape and overlapping winding design
provides very high forces in a compact package. In addition, the design
is more thermally effi cient than tradition ironless motor designs.

By overlapping the windings (Fig. 9) instead of arranging them side-by­side, Parker Trilogy is able to provide a motor with a very high power
density. The result is a package size considerably smaller than competitive
motors with similar force capabilities.

Overlapping windings for
shorter overall length

Non-overlapped windings
result in longer package length

Fig. 9: Overlapping Windings

Parker Trilogy creates the I-beam shape by fl aring out the end turns of
the motor at a 90-degree angle. The end turns of a linear motor coil do
not contribute to the horizontal force component of the motor. Instead
of producing force, the end turns simply produce heat. Parker’s I-beam
shaped design allows for better heat transfer between the motor coils
and the heat sink by increasing the contacting surface area between
components (Fig. 10). The combination of overlapped windings and the
I-Beam shape creates a more thermally effi cient motor than most
traditional ironless motors. As a result, the payload will experience
less thermal expansion due to heat from the motor. In high precision
applications, thermal expansion can adversely affect the overall system
accuracy. Parker Trilogy motors will help maintain system accuracy by
running at lower operating temperatures than our competitors. In addition,
there are added benefi ts of the I-beam shape by lowering the overall
profi le height and creating a stiffer mechanical structure.

What results is a compact motor design with high force and extraordinary
thermal characteristics.

Fig. 10: Parker Trilogy’s Patented I-Beam Design

Good surface area for

efficient heat transfer

Dual rows of magnetsDual rows of magnets

Vacuum encapsulated

inronless coil with

I-beam shape

I-beam shaped coil for

lowerprofile, better

thermalefficiency and

higher structural stiffness

U-Shaped

magnet track

Non I-beam (T shaped)

coil with larger profile size,

less thermal efficiency

and less rigidity

acts as heat sink/

adapater plate

Small surface area for

poor heat transfer

Trilogy I-beam design

Competitive designs

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Parker Hannifi n Corporation

Electromechanical Automation Division

5

Engineering
Reference

Fig. 11: ML50 Ironless Linear Motor

Fig. 12: T2D Series Linear Motor Positioner

2.3 Slotless Motors

Slotless motors are an interesting variant of linear motor which com­bines several of the design elements of ironcore and ironless motors. In
a slotless motor (Fig. 13), the forcer has no iron toothed laminations. The
coils are wound without iron and are located underneath a “back iron”
plate. The forcer then operates along a single magnet row. The slotless
motor design can be thought of as a sort of hybrid between ironcore and
ironless linear motor designs.

What results is a motor with the following characteristics:

Slotless linear motor advantages:

• Single-row magnet bar

• Lower cost (compared to ironless design)

• Better heat dissipation (compared to ironless design)

• More force per package size (compared to ironless design)

• Lighter weight and lower inertia forcer (compared to
ironcore design)

• Lower attractive forces (compared to ironcore designs) –
extended bearing life and smaller bearings in some applications

• Less cogging (compared to ironcore designs)

Slotless linear motor disadvantages:

• Some attractive force and cogging

• Air gap is critical

• Less effi cient than both ironcore and ironless –
more heat to do the same job

Fig. 13: Slotless Linear Motor

To summarize the advantages and disadvantages of ironless motor
designs:

Ironless advantages:

• No Attractive Force - Balanced dual magnet track. Safe and easy to
handle. No forces to deal with during assembly.

• No Cogging - Ironless forcer for zero cogging and ultimate
smoothness.

• Low Weight Forcer - No iron means higher acceleration and
deceleration rates, higher mechanical bandwidth.

• Air Gap Forgiving - easy to align and install.

Ironless disadvantages:

• Heat dissipation - Higher thermal resistance. Parker Trilogy’s I-beam
design helps mitigate this issue.

• Power per package - Lower RMS power when compared to ironcore
designs.

• Higher cost - Uses twice as many magnets.

Parker Trilogy offers ironless motors in both component kits and complete
pre-engineered positioning systems. Please refer to the catalog for the
“I-Force” and “ML50” ironless linear motors and the “T Series” linear
motors positioners (Fig. 11 and 12).

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Parker Hannifi n Corporation
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Fig 16(b): Servo Motor Control (position sensor located at load)

Fig 16(a): Servo Motor Control (position sensor located at motor)

4.0 Servo Control and Feedback

Linear motors can offer the ultimate in high precision and motion
dynamics. However, overall system performance is dependent on other
components – particularly the servo controller and feedback mechanism
used. In this section, we will examine how linear motors are commutated,
how their position is sensed, and how it is important to have an adequate
controller to optimize system performance.

Figure 16 shows the traditional cascaded structure of servo motor control.
The same structure can be applied to linear motors. One advantage is that
the position sensor can typically be located right at or closer to the load,
thus improving the overall accuracy of the system.

One drawback is that the lack of a traditional mechanical transmission
results in the effects of external forces being signifi cantly greater. For this
reason, the quality of the position signal (resolution and accuracy) and
the performance of the servo controller (sampling time, trajectory update,
and control algorithms used) are of prime importance in determining the
degree of “positional stiffness” that can be achieved.

Servo Controller Amplifier Motor Load

Commutation

Sensor

Position Sensor

Servo Controller Amplifier Motor Load

Commutation

Sensor

Position Sensor

Servo Controller Amplifier Motor Load

Commutation

Sensor

Position Sensor

Servo Controller Amplifier Motor Load

Commutation

Sensor

Position Sensor

3.0 Guide Systems

Even though a linear motor system lacks the rotary transmission com­ponents of traditional positioning systems, the user is still required to
provide some sort of linear guide / bearing. Typically, a linear bearing must
be selected based on high speed and acceleration capability, long service
life, high accuracy, low maintenance costs, high stiffness, and low noise.
Other considerations may include, for example, the site space available,
the mounting accuracy (fl atness, parallelism, inclination), and the thermal
expansion.

Different guide systems are available to fulfi ll these requirements:

• Slide bearings (dry running or hydrodynamic)

• Hydrostatic bearings

• Aerostatic bearings (air bearings)

• Track rollers (steel or plastic roller wheels)

• Rolling-contact bearings (square rail, cross roller, or round rail)

• Magnetic bearings

In practice, slide bearings, rolling-contact bearings, and air bearings
are the most popular. For applications with low demands on precision
and load-bearing capacity, dry-running slide bearings may be a suitable
option. Guide systems based on rolling-contact like square rail and cross
roller bearings exhibit good stiffness and excellent load-bearing capability.
In addition, they offer excellent straightness and fl atness over the length
of travel. Air bearings offer the ultimate in performance. With practically no
limits to max speed and acceleration and virtually no breakaway forces,
air bearings are the best solution for ultra-high precision applications.

Parker offers slotless motors in both component kits and precision
positioning systems. Please refer to this catalog under 400LXR Positioners
or to the “SL Series” linear motor section on www.parkermotion.com
(Fig. 14 and 15).

Fig. 15: 404LXR Slotless

Linear Motor Positioning System

Fig. 14: SL Series Slotless Linear Motors

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Parker Hannifi n Corporation

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Engineering
Reference

4.1 Commutation of the motor

In traditional rotary servo systems, it is important for the amplifi er to
know the position of the rotor. This way it can properly switch current
through the motor phases in order to achieve the desired rotation of the
shaft. Many times, three digital Hall effect sensors (spaced 60 degrees or
120 degrees apart) are used in order to provide positional information of
the shaft within 6 states.

The same principle applies to linear motors. The amplifi er must know the
position of the forcer in relationship to the magnet rail in order to properly
switch the windings. Rather than aligning the Hall effect devices (HEDs)
within one complete revolution of the shaft, the Halls are matched to the
magnetic pole pitch of the motor. The “pole pitch” is the linear distance
traveled within one electrical cycle of the motor and is analogous to one
revolution of a rotary motor.

Once the amplifi er establishes the position of the forcer within the
electrical cycle, it will then switch the motor phases whenever a transition
occurs in the Hall states. This is known as trapezoidal commutation.

In most modern servo amplifi ers, the position of the forcer need only be
determined upon power up and enabling of the drive. Once the initial
position is recognized, the drive can commutate off of the position sensor,
which provides signifi cantly higher resolution feedback than the digital
HEDs. This allows the motor to be sinusoidally commutated. Sinusoidal
commutation provides a smoother switching sequence resulting in less
disturbances and less heat.

Another method of sinusoidal commutation is through the use of analog
Hall effect devices. Analog Halls produce a sinusoidal signal as they pass
over the magnetic poles of the magnet track. Analog Halls have also been
used as an inexpensive method of providing positional feedback as well
as commutation feedback. However, these devices are susceptible to
picking up noise which can affect commutation – which in turn, affects
smoothness of travel.

In some applications, HEDs are not desired – either from a cost savings
standpoint, reduced wiring / component count, or other application spe­cifi c standpoint. However, the servo drive must still be able to recognize
the position of the motor forcer. In this case, automatic commutation
can be achieved with a properly equipped servo drive. Parker’s Com-
pax3 drive/control has an “auto-commutation with test movement” func­tion that automatically establishes the commutation angle. In this system,
the Compax3 applies a test signal which induces small movements in the
motor upon power up. The physical size of these movements can be quite
small – as small as 10 electrical degrees (less than 2 mm on many linear
motors), so there is no need to worry about the motor “jumping.” In addi­tion, the test signals are “softened” such that system jerk is minimized.

4.2 Positional Feedback

There are a variety of methods to provide linear positional feedback to
the motion controller. There are analog transducers, rack-and-pinion
style potentiometers, and laser interferometers, to name a few. Each has
its own level of accuracy and cost. But far and away the most popular
feedback device for linear motor positioning systems is the linear
encoder.

Most linear encoders provide an incremental pulse train that provides
discrete “counts” back to the motion controller as the encoder “read
head” moves along a “linear scale.” Typically, the read head is mounted
close to the load and the linear scale is applied to the positioner base.
There are two popular styles of linear encoders – optical and magnetic.

Optical encoders use refl ected light scanning techniques to provide
feedback with extremely high resolution and accuracy. Optical encoders
are capable of providing feedback in the nanometer resolutions. Magnetic
encoders use inductive scanning techniques to offer signifi cantly more
economical feedback, but have considerably lower accuracy and resolu­tion. Magnetic encoders can typically offer resolutions down between the
1 to 5 micron range.

A third variation of linear encoder is the Sine encoder. The Sine encoder
produces analog sine and cosine signals instead of discrete pulses.
Many modern motion controllers have the ability to interpolate these
analog signals into extremely fi ne resolutions. For example, the Compax3
controller can interpolate a 1 Vpp signal into 14 bits, i.e., the sine/cosine
signal period is divided into 16,384 counts. A typical pitch period of a Sine
encoder is 1mm, thus the resolution can be interpolated down to 62 nm
in the controller.

All of these encoders provide incremental positioning information.
Hence, it is necessary to establish a home position any time positional
information is lost by the controller, i.e., power down. In some
applications it is necessary to have absolute feedback where the actual
position of the motor is known immediately and no homing sequence
is required. Some encoder manufacturers are now making absolute
linear encoders that transfer data using a synchronous serial interface
(SSI). Parker’s Aries family of servo drives support absolute feedback
transmitted via SSI. Please contact your Parker representative for further
details.

Fig. 17: Parker ACR Controller

and Aries Drives

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When using linear encoders it is critically important to have proper
mounting of the scanner (read) head. Inadequate mounting may cause
mechanical resonance effects and errors in the measured position
caused by vibration of the sensor head. In this case, the achievable
bandwidth of the control loop – and hence, the maximum positioning
stiffness – is reduced considerably. In some cases, large gaps of
positional information are lost entirely, rendering the system totally
inaccurate.

If the linear scale is not aligned straight with the guide bearings,
accuracy can be affected in the form of “cosine errors.” (Fig. 18) shows
a representation of how linear encoder scale misalignment can cause
cosine errors.

The actual distance traveled will be L, where L=Lenc(cosΘ). The size
of the error will be error = Lenc(1 – cosΘ). Thus, it is important to pay
attention to the mounting of the read head as well as providing robust
attachment and accurate alignment of the linear scale.

Fig. 19: Parker’s ACR Controller Gantry Lock Feature

Θ

L

enc

L

)(cosLL

enc

Θ=

Linear bearings

Encoder scale

Carriage

Θ

L

enc

L

)(cosLL

enc

Θ=

Θ

L

enc

L

)(cosLL

enc

Θ=

L

enc

L

)(cosLL

enc

Θ=

L

)(cosLL

enc

Θ=

Linear bearings

Encoder scale

Carriage

Fig. 18: Cosine errors caused by encoder scale misalignment

4.3 Servo Control –

Due to the direct drive nature of linear motors, there are no intermediate
mechanical components or gear reductions to absorb external disturbances
or shock loading. As a result, these disturbances have a signifi cantly
greater impact on the control loop than they would when using other
technologies. For this reason, it is extremely important to have a controller
with fast trajectory update rates. In addition, it is important to have a
controller which allows you manipulate “feedforward” control of speed,
acceleration, and jerk. These parameters allow the user to minimize
tracking errors during acceleration, deceleration, and during external
disturbances.

By defi ning parameters like jerk within your move profi le, the tracking
accuracy of highly dynamic moves can be improved, stresses on the
mechanical system can be reduced, and excitation of mechanical
resonances can be minimized. In addition, payloads that must
be handled gently can still have optimized move profi les with the
implementation of jerk-limited setpoint generation. Parker’s ACR and
Compax3 families of controllers allow optimization of all feedforward
parameters and provide extremely fast trajectory update rates for
superior control of linear motors.

Another common control challenge of linear motor systems is the control
of gantry robots. Unlike belt- and screw-driven gantries where the
transmissions of parallel axes can be mechanically connected, linear
motor gantries have no mechanical coupling whatsoever. If tight control
is not provided between these axes, binding and mechanical damage
can occur. Traditional “master – follower” control schemes do not work
well with gantries because the follower axis can bind but the master axis
will be unable to recognize it.

Parker’s ACR series of controllers have a gantry lock function which pro­vides skew compensation for gantry systems. By locking the feedback of
each axis into the servo loop of the other, perfect coordination between
axes is established to prevent binding and mechanical damage.

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Engineering
Reference

Fig. 20: MX80L Miniature Linear Motor Stage

5.0 Packaged Linear Motor Positioners

As we have learned here, there are a lot of elements that affect precision
in a linear motor system. Accuracy is affected by the bearing technology,
structural stability, mounting and precision of the feedback system, and
the capabilities of the controller. In addition, other variables such as
mechanical stiffness and vibration can play a large part in the overall
error budget of a machine.

As a result, it takes a reasonable amount of expertise to integrate all the
components into a precision linear motor system. Many machine builders
and laboratory equipment users tend to have expertise in their particular
processes rather than in the integration of components. In addition, many
systems integrators do not have the time to model, analyze, and
implement linear motor designs.

For these reasons, several designers have chosen to purchase pre­packaged, pre-engineered linear motor positioners. By leaving the design
and integration work to their vendors, they can deliver cost effective
precision motion control solutions to their customers in an extremely
short time to market. Components are performance matched for fast
response, high acceleration, smooth translation, high velocity, and
quick settling time. In addition, positioners can have a variety of fl exible
connectorization options, cable tracks, and mounting options – including
multi-axis compatibility.

Parker offers a variety of packaged linear motor positioners to fi t most
any application.

• Industrial-grade positioners for high force, high motion dynamics,
and high precision

• Precision-grade positioners for extremely high positional accuracy

• Miniature precision-grade positioners for lab automation, photonics,
electronics and other applications requiring high accuracy in a small
form factor

6.0 Linear motors compared against other technologies

It has been well established that linear motors offer the ultimate in high
dynamics and high precision. However, many machine builders have
cost sensitive budgets and will often look to common rotary-to-linear
technologies to solve their positioning needs. This section will take a
hard look at these competing technologies and will show the long-term
benefi ts switching to linear motors.

6.1 Belt Drives

Belts and pulleys are the workhorses of the automation world. They
provide high speeds and reasonable positioning repeatability for an
economical component cost. But there are inherent limitations to using
belt drives. A belt drive system will typically consist of the following
components:

• High tensile strength belt

• Pulleys

• Gearbox, for inertia matching

• Motor and coupling

• Carriage attached to belt

• Roller bearings or slider element

All the torsional windup, backlash, and belt stretching of these
components contribute to inaccuracies in the system. Typical repeatability
of a belt drive system is around ± 0.2 mm whereas repeatability for a
common linear motor system can be ± 1µ. Even then, the belts must be
optimally tensioned and the bearings preloaded. Also, the feedback is
connected to the motor and not the load. This contributes to even further
inaccuracies in the system.

Additionally, all of these components are “spring like” by nature and
cause ringing and delays in settling time. So while belt drive systems
can operate at high speeds, they can be diffi cult to tune for dampening
and quick settling. This problem only gets worse at longer lengths, as
belts tend to sag the longer they have to span. Eventually, the belt drives
become limited in how long they can travel due to the unavoidable sag.

Finally, belt-driven systems can be maintenance intensive. Belts can lose
tensioning over time and even skip teeth. Sliding bearings can break
down. Couplings can slip or be misaligned. All of these problems force
the user to shut down valuable production time in order to maintain the
actuator.

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Linear motors, by their direct-drive nature, are virtually maintenance free.
As long as the bearings are properly lubricated, there is little else to do in
order to maintain the positioner. Because all of the mechanical transmis­sion components are gone, linear motor positioners do not suffer from
torsional windup, backlash, belt stretch, or settling problems. They are
extremely responsive and settle extraordinarily quick. They can match or
exceed the acceleration and speed characteristics of a belt drive while
positioning far more accurately. Finally, there are no limitations as to how
long a linear motor travels. The dynamic performance stays exactly the
same, no matter what the distance traversed.

6.2 Screw Drives

Screw driven positioning systems are very common for relatively high­precision positioning applications. They are cost-effective and offer varying
degrees of precision depending on the needs of the application. A screw­driven system typically consists of the following components:

• Ballscrew or leadscrew that is precision ground or rolled

• Ball nut or sliding nut

• Motor

• Motor block and coupling

• Carriage

• Linear guide – typically square rail, cross roller, or round rail

Leadscrews are typically ineffi cient, less than 50% in most cases. While
they are cost effective, the nut tends to wear due to friction. In addition,
the accuracy and repeatability can suffer with leadscrews as most are
not precision ground. Ballscrews, approaching 90% effi ciency, come in
precision ground or rolled packages. However, they still wear over time,
suffer from torsional windup, and have a tendency to exhibit backlash.
These problems factor into lost precision and slower settling times. In both
cases, speeds are limited by the thread pitch and the length of the screw.
As screws become longer, they tend to “whip” at higher speeds. Thus, they
come nowhere near the speed and acceleration capabilities of linear
motors. Eventually, there comes a point where screws become so long,
they are diffi cult and unwieldy to manufacture.

Finally, like belt drives, screw-driven systems must be maintained.
Eventually nuts wear, couplings slip, and screws need to be replaced

- again, shutting down production and costing the user valuable time
and money.

Since linear motor positioners have no intermediate mechanical
transmissions, they do not suffer from the drawbacks of screw drives.
In addition, they are not limited by length or by the dynamic performance
related to length. One drawback to linear motors is that they are not
inherently suffi cient for vertical applications that require braking. Typically,
this problem can be overcome by adding a pneumatic, spring-based, or
weight-based counterbalance.

6.3 Comparing Costs

In most cases, the upfront cost of purchasing a linear motor system
will be more expensive than belt- or screw-driven systems. However,
in certain cases the cost can be similar or even less. Many machine
builders requiring an extra degree of accuracy will buy a precision-ground
ballscrew and add linear encoder feedback. Typically, the added cost of
these components will drive the overall cost of the positioner to be higher
than that of a linear motor system. In addition, improved manufacturing
methods and increased volumes are driving down the cost of linear
motors. Over time, users will see the price gap close dramatically. Finally,
when comparing the overall cost of ownership (factoring in maintenance
and down time), linear motors become considerably less expensive.

7.0 The Future of Linear Motors

The fi eld of linear motors will develop dynamically in the future. As costs
continue to fall and as innovations continue to rise, more and more
industries will begin to adopt linear motor technology. Their high dynamics,
high precision, and virtually maintenance-free operation will appeal to
traditional users of rotary-to-linear transmissions.

In the early days of linear motors, only the high-tech industries like
semiconductor and electronics adopted the technology. Eventually,
industries like machine tool latched on to the inherent benefi ts of direct
drives and now account for nearly 1/3rd of all linear motor sales. Now
we are seeing new markets like material handling, packaging, medical,
and food processing begin to switch out the belts, screws, and even
pneumatics for linear motors. All of these new customers are beginning to
push the technology to a critical mass and widespread acceptance. Indeed,
it looks like linear motors will be making a breakthrough impact on the
entire world of manufacturing.

Parker Hannifi n Corporation

Electromechanical Automation
5500 Business Park Drive
Rohnert Park, CA 94928
Phone: [phone]
Fax: [phone]
Web site: www.parkermotion.com
www.trilogysystems.com

Australia

Parker Hannifi n (Australia)

Pty Limited
9 Carrington Road
Castle Hill NSW 2154
Australia
Tel: [phone]
Fax: [phone]

Brazil

Parker Hannifi n Ind. Com Ltda.

Av. Lucas Nogueira Garcez 2181
Esperança
12325-900 Jacareí, SP
Tel: [phone]
Fax: [phone]
[email protected]

China

Parker Hannifi n Motion & Control
(Shanghai) Co., Ltd

280 Yunqiao Rd, Jin Qiao Export
Processing Zone
Shanghai 201206, China
Tel: [phone]
Fax: [phone]

France

Parker SSD Parvex

8 avenue du Lac
B.P. 249
F-21007 Dijon Cedex
Tel: [phone]
Fax: [phone]

India

Parker Hannifi n India Pvt. Ltd.

EL-26,TTC. Industrial Area.
Mahape, Navi-Mumbai.-400 709.
Tel: [phone] 85, 65137050-03
Fax: [phone]

Italy

Parker Hannifi n SpA
(SSD Drives Division)

Via Gran Sasso, 7
20030 Lentate sul Seveso ­MI - Italy
Tel: [phone]
Fax: [phone]

Korea

Parker Hannifi n Korea

6th Floor Daehwa Building
169 Samsung-dong Kangnam-gu
Seoul 135-882, South Korea
Tel: [phone]
Fax: [phone]

Scotland and
Northern Ireland

Unit 59
Stirling Enterprise Park
Player Road
Stirling FK7 7RP
Tel: [phone]
Fax: [phone]

Singapore

Parker Hannifi n
Singapore Pte Ltd

11, Fourth ChinBee Road
Singapore 619702
Tel: [phone]
Fax: [phone] 4929

Singapore Pte Ltd
(Branch Offi ce)

Lot 558A, Jalan Subang 3
Off Persiaran Subang
Sungai Penaga Industrial Park
47610 Subang Jaya Malaysia
Tel: [phone]
Fax: [phone]

Taiwan

Parker Hannifi n Taiwan Co., Ltd

No. 40, Wuchiuan 3rd Road
Wuku Industrial Park
Taipei County, Taiwan 248
ROC
Tel: [phone]
Fax: [phone]

Thailand

Parker Hannifi n (Thailand) Co., Ltd.

1023, 3rd Floor, TPS Building,
Pattanakarn Road,
Suanluang, Bangkok 10250
Thailand
Tel: [phone]
Fax: [phone]

UK

Parker Hannifi n (Main Offi ce)

New Courtwick Lane
Littlehampton
West Sussex BN17 7RZ
United Kingdom
Tel: [phone]
Fax: [phone]

Germany

Electromechanical Europe
Parker Hannifi n GmbH & Co KG

Robert-Bosch-Strasse 22
D-77656 Offenburg
Germany
Tel: [phone]
Fax: [phone]

USA

Parker Hannifi n
Electromechanical Automation Division Main
Offi ce/Compumotor

5500 Business Park Drive
Rohnert Park, CA 94928 USA
Tel: [phone]
800-358-9070
Fax: [phone]
Email: [email protected]

Parker Hannifi n
Electromechanical Automation
Division/CTC

50 West TechneCenter Dr.
Milford, OH 45150
Tel: [phone]
800-233-3329
Fax: [phone]
Email: [email protected]

Parker Hannifi n
Electromechanical Automation
Division/Bayside

27 Seaview Boulevard
Port Washington, NY 11050
Tel: [phone]
800-305-4555
Fax: [phone]
Email: [email protected]

Parker Hannifi n
Electromechanical Automation
Division/

Daedal

1140 Sandy Hill Road
Irwin, PA 15642
Tel: [phone]
800-245-6903
Fax: [phone]
Email: [email protected]

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