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Kollmorgen
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Response
•
Stability
In a broad sense, the performance of a system is characterized by its noise susceptibility, response, and stability.
These quantities tend to be mutually exclusive. The system designer must decide what noise susceptibility (in the
form of a "busy" motor) is acceptable.
"Busyness" is random activity in the motor and can often be felt on the motor shaft. Busyness in a motor should not
be confused with PWM noise. PWM noise is high pitched, relatively constant noise and cannot be felt on the motor
shaft.
Response is a measure of the system's quickness. Response can also be characterized by bandwidth and by rise time
in response to a step command. Normally, designers want high bandwidth, though sometimes the response is
purposely degraded to reduce stress on mechanical components. This is called detuning. Typical current loop
bandwidths range from 1000 to 2500 Hz. Typical velocity loop bandwidths range from 20 to 60 Hz.
Stability measures the level of control in the system. Stability can be measured with damping ratio or with overshoot
in response to a step command. A discussion of different levels of stability follows.
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Commissioning
5-7
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