Non-contact measurement of run-out and torque in rotating shafts using enhanced function rotary encoders


A method of measurement of run out in rotating shafts which is non contact and digital. Suitable for short term testing and long term since the system is stable over time.

Standard rotary encoders usually have a single sensor point which generates signals as features on the encoder wheel rotate past. The signals may be counted to indicate the angular displacement. If the signals are compared with a time base the speed of rotation may be calculated.

The Encoder used in this method has at least three sensor points distributed around the encoder disk. As each feature rotates past a signal is generated. These signals are sent to a signal processor where they are accurately time stamped. The timings are further transmitted to a computer, where they are processed by algorithms. A signal arriving early at one of the sensors means that the centre of rotation has moved towards the sensor. Conversely a signal arriving late means that the centre of rotation has moved away from the sensor. Three sensors are sufficient to calculate the two axes of radial movement of the centre.

Practical applications in the marine and industrial fields have shown that accuracies of measurement down to ± 0.1 microns at speeds over a range from 1 rpm to 10,000 rpm are achievable.

Results from testing a 7Mw wind turbine nacelle.