Instantaneous Speed Observer with Improved Disturbance Rejection Performance based on Higher Order Dynamics.

We propose the instantaneous speed observer for high performance control of servomotors which use inexpensive low precision shaft encoders. Due to the recent development of DSP (Digital Signal Processors), we have been able to control servomotors with a very short sampling period. We usually obtain the speed information from the increased pulse number of a shaft encoder in a sampling period. However, in this simple method, we lose the speed resolution easily. If we get accurate speed information by clocking the period of encoder pulse, the system will be easily unstable in the lower speed range because a long deadtime is inserted in the feedback loop. To overcome these problems, we propose the novel estimation technique of the instantaneous speed by utilizing the armature current together with the encoder information. As this observer inherently includes the disturbance observer. We can use it for the effective disturbance rejection control. We implement this system by using a DSP, and prove through laboratory experiments that it can greatly improve the system stability and achieves the excellent disturbance rejection performance.