Method and apparatus for measuring dynamic balance

Apparatus for measuring the rotational imbalance of a test member comprising:

• a rotational support portion for supporting the test member;
• means for rotating the member;
• a rotation sensor arranged to detect the rotational angular position of the test member and produce a position signal;
• a vibrating sensor arranged to detect the amount of vibration of the member through the support portion and produce an analogue vibration signal;
• a memory storing digital dummy data corresponding to a predetermined imbalance to remain in the member;
• a digital to analogue converter for converting the digital dummy data read from the memory, based on the rotational position from the rotation sensor, into an analogue dummy signal;
• a wave synthesizing circuit arranged to receive the analogue vibration signal from the vibration sensor, and the analogue dummy signal from the digital to analogue converter, and to subtract the dummy signal from the vibration signal to produce an analogue initial imbalance signal;
• and
• an analogue to digital converter arranged to receive the analogue initial imbalance signal from the wave synthesizing circuit and convert the analogue initial imbalance signal into a digital initial imbalance signal.