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Types of Motion Control


There are mainly two types for motion control;

1) Open Loop, No Feedback Required
The stepper, also known as step or stepper motor, is used.


2) Closed Loop, Feedback Required
The DC brush type or brushless motor with a feedback device is used. The most commonly feedback device is an optical encoder.

Stepper Motor

Advantages

Disadvantages

Inexpensive relative to other motion control systems. Low efficiency. Motor draws substantial power regardless of load.
Needs no feedback. The motor is also the position transducer. Torque drops rapidly with speed (torque is the inverse of speed).
Stable. Can drive a wide range of frictional and inertial loads. Low accuracy. 1:200 at full load, 1:2000 at light loads.
Standardized frame size and performance. Prone to resonance. Requires micro-stepping to move smoothly.
Plug and play. Easy to setup and use. No feedback to indicate missed steps.
Safe. If anything breaks, the motor stops. Low torque to inertia ratio. Cannot accelerate loads very rapidly.
Long life. Bearings are the only wear-out mechanism. Motor gets very hot in high performance configurations.
Excellent low speed torque. Can drive many loads without gearing. Motor will not "pick up" after momentary overload.
Excellent repeatability. Returns to the same location accurately. Motor is audibly very noisy at moderate to high speeds.
Overload safe. Motor cannot be damaged by mechanical overload. Low output power for size and weight.

 

DC Motor

Advantages

Disadvantages

High output power relative to motor size and weight. Higher cost.
Encoder determines accuracy and resolution. Motor "runs away" when something breaks. Safety circuits required.
High efficiency. Can approach 90% at light loads. Complex. Requires encoder.
High torque to inertia ratio. Can rapidly accelerate loads. Brush wear limits life to 2,000 hrs. Service is then required.
Has "reserve" power. 2-3 times continuous power for short periods. Peak torque is limited to a 1% duty cycle.
Has "reserve" torque. 5-10 times rated torque for short periods. Motor can be damaged by sustained overload.
Motor stays cool. Current draw proportional to load. Requires "tuning" to stabilize feedback loop.
Usable high speed torque. Maintains rated torque to 90% of NL RPM. Power supply current 10 times average to use peak torque.
Audibly quiet at high speeds. Motor develops peak power at higher speeds. Gearing often required.
Resonance and vibration free operation. Poor motor cooling. Ventilated motors are easily contaminated.

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