A capacitance based ultra-precision spindle error analyser

The measurement of errors in the axis of rotation is of increasing interest, and considerable work has been done to improve understanding of the effects of these errors on machined workpieces. In an attempt to simplify the measurements, and to increase their accuracy, a multiple capacitive transducer has been developed. Use of large-area sensors reduces the effects of out-of-roundness and misalignment of the master cylinder. Instrument errors less than 10 nm have been demonstrated. A combination of digital and analogue circuitry reduces set-up time to a minimum, and facilitates rejection of the once-per-revolution components at any speed.