Computation of imbalance in rotatably mounted object in a motion control system

A motion control system including:

• an object mounting mechanism for holding and rotating an object about a first axis;
• an object positioning mechanism for displacing the object mounting mechanism;
• an object positioning drive for driving the object positioning mechanism;
• one or more rotation detection devices for generating an output signal indicative of the rotation of the object about the first axis;
• and
• a processor for computing an object rotation signal indicative of the speed and phase of the object about the first axis from the rotation detection devices output signal;
• demodulating an output signal from the drive with the object rotation signal to derive a demodulated output signal that is synchronous with rotation of the object about the first axis;
• and
• computing the magnitude and phase of the object imbalance from the demodulated output signal.

A processor for use in a motion control system, the motion control system including an object mounting mechanism for holding and rotating an object about a first axis;

• an object positioning mechanism for displacing the object mounting mechanism;
• an object positioning drive for driving the object positioning mechanism;
• and rotation detection means for generating an output signal indicative of the rotation of the object about the first axis, the processor acting to:
• compute an object rotation signal indicative of the speed and phase of the object about the first axis from the rotation detection devices output signal;
• demodulate an output signal from the drive with the object rotation signal to derive a demodulated output signal that is synchronous with rotation of the object about the first axis;
• and
• compute the magnitude and phase of the object imbalance from the demodulated output signal.