412LXR Series Product Manual
Appendix A – Understanding Linear Motors
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Appendix A – Understanding Linear Motors
The Linear Motor Concept
Linear Motors are basically a conventional rotary servo motor unwrapped. So now what was the
stator is now called a forcer and the rotor becomes a magnet rail. With this design, the load is
connected directly to the motor. No more need for a rotary to linear transmission device.
Linear Motor Benefits
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High speeds:
Only the bus voltage and the speed of the control electronics limit the maximum speed of
a linear motor. Typical speeds for linear motors are 3 meters per second with 1 micron resolution and
over 5 meters per second with courser resolution.
Note: Motors must be sized for specific loading conditions.
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High Precision:
The feedback device controls the accuracy, resolution, and repeatability of a linear
motor driven device. And with the wide range of linear feedback devices available today, resolution and
accuracy are primarily limited to budget and control system bandwidth.
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Fast Response:
The response rate of a linear motor driven device can be over 100 times faster than
some mechanical transmissions. This is simply because there is no mechanical linkage. This means
faster accelerations and settling times, thus more throughput.
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Stiffness:
Because there is no mechanical linkage in a linear motor, increasing the stiffness is simply a
matter of gain and current. Thus the spring rate of a linear motor driven system can be many times that
of a ball screw driven device. However it must be noted that this is limited by the motor’s peak force, the
current available, and the resolution of the feedback.
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Zero Backlash: Since there are no mechanical components there is no backlash. There are however,
resolution considerations which effect the repeatability of the positioner (See Chapter 2, General Table
Specifications, Chapter 3, Setting Home Sensor and Z Channel Position Reference)
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Maintenance Free Drive Train: Because linear motors of today have no contacting parts, in contrast
with screw and belt driven positioners, there is no wear on the drive mechanism.
Slotless Linear Motor Design
The Linear Motor inside the 412LXR is a Slotless Linear Motor. The following will give a brief
description of the motor design and construction:
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Construction: Designed by the Compumotor and Daedal Divisions of Parker Hannifin, the motor takes
its operating principle from Parker’s slotless rotary motors which have grown popular over the past few
years. The magnetic rail is simply a flat iron plate with magnets bonded to it. The forcer is unique. It
begins with a coil and a “backiron” plate, which is placed behind the coil. This assembly is placed inside
an aluminum housing with an open bottom. The housing is then filled with epoxy, securing the winding
and “backiron” into the housing. The thermal sensors and hall effect sensors are mounted to the
housing.
