Overcoming encoder quantisation noise in an adaptive position controller

In digital position controllers, it is common to derive velocity information from a digital position encoder signal, thereby alleviating the requirement for a tachometer sensor. However, the effect of quantisation noise present in the position feedback may become problematic in certain applications. A technique is presented for overcoming the undesirable effects of encoder quantisation, when the digital encoder signal is used to derive the velocity feedback. The technique was developed to overcome quantisation noise problems identified during testing of an adaptive controller. As such, the technique involves on-line design of a model-based filter, utilising the plant parameters identified as part of the adaptive control process. The material presented has relevance also to non-adaptive, fixed parameter control systems.