Motion Control Systems Integrator
Motion Control Components and Applications

Motion Control Components

Motion control applications are generally considered a specialty subset of controls engineering.  Although they may fall under the responsibility of a Controls Engineer, motion control applications really do require a different way of thinking.  Controls Engineers may be experts in general machine control, but they generally lack the knowledge and experience to design and implement a robust motion control system.

It is imperative that the proper motion control components are chosen for a project that requires motion control.  The selection of motion control components really has to start with the mechanical side of the project.  The mechanical components, and their motion requirements, determine what other components are selected.  Your application may require a piezo stage for fine assembly work that has resolution measured in nanometers, or it could require a 1000HP motor to move a steel ingot down a conveyor.  Either way, the basic concepts are the same.

Is the required motion linear or rotary?

Does the final motion move something linearly?  If it does, at what speed and what is the load that is moving?  What is the mechanism that turns a motor’s rotary motion into linear motion?  This would typically be an acme or ball screw mechanism.  Does the motion required exceed the capabilities of a motor/screw system?  Then perhaps a linear motor is required.  Given the load and speed requirements, motor speed and torque requirements can be determined.

Does the final motion need to be rotary?  If so, then does it need to be an “endless” axis that moves in one direction for an infinite distance?  If it does, then encoder rollover needs to be taken into consideration.  Again, given the load and speed requirements, motor speed and torque requirements can be determined.  Don’t ignore rotary inertia, as this will determine motor selection.  A motor may meet the torque and speed requirements, but it may have too low of a rotary moment of inertia, and your motor will not be controllable.  Even with a linear motion system, inertias need to be determined and the motor needs to be selected with this in mind.

Do you need a stepper, servo, or induction motor?

A stepper motor is the least expensive option.  A stepper motor doesn’t have to use an encoder, and that means less cost for the motor, and less cost for a control system.  Stepper motors have some serious limitations that need to be accounted for.  The biggest problem with stepper motors is that they develop their peak torque at zero speed.  This means that as soon as a stepper motor starts moving, its torque capabilities drop off.   The faster you go, the lower the torque.  Running the stepper motor at higher voltages helps this situation, but no matter what, torque drops off with speed.  In general, stepper motors should not be used for applications that require more than 1000RPM.

A servo motor, by definition, is a motor with a feedback device.  Typically, servo motors are permanent magnet motors that are capable of high speed and/or high torque.  They usually use a resolver or encoder to provide position feedback to the control system.  A feedback device is also used by the drive (amplifier) to properly determine motor rotor position for commutation (current timing of the 3 phases).  Unlike a stepper motor, a servo motor can produce full torque at zero speed and at rated speed.

Historically, induction (standard AC) motors haven’t been used in motion control applications. That has changed with the advent of advanced drives.  With the addition of an encoder, induction motors can be used in motion control applications.  Servo motors will still give higher performance, but in many higher horsepower applications, a properly rated induction motor can be used instead of a servo motor, at a much lower cost.

Get select excerpts of our Motion Control Guide. Or, download our free guide 10 Ways to Make Your Best Moves with Motion Control Systems.

Highland Controls offers solutions for businesses in Northern Ohio (including Cleveland and Akron), Western Pennsylvania, Northeast Indiana, and Southeast Michigan.