Alternative design for optical incremental encoder measurement systems

An encoder system is commonly used as a passive device within a controller system. It is sampled by the controller with the same sampling time as that of the control system. Control loop requires time to execute set of commands hence sampling time of control system cannot be very small and is generally fixed. This limitation made utilization of M/T method unavoidable to measure high and low speeds by switching between M and T method at certain point. Error analysis conducted in this paper showed high-valued errors at the switching instance. Inherent error associated with M-Method, i.e. yielding average speed, is also pointed out. To overcome these problems, an alternative encoder system is proposed, in which sampling time for the measurement system is made independent from control system. Therefore, there will not be any restriction on using high sampling frequency for measurement system. Proposed strategy made it possible to use T-Method, only, for entire range of speed measurement without compromising accuracy. Hence, sources of errors usually encountered by using M/T Method can be avoided. Error analysis of proposed strategy showed notable improvement in measurements.