A microstep controller of a DC servomotor

A microstep controller of a DC servomotor has been developed for accurate positioning and smooth movement at low-speed rotation. It consists of digital and analog positioning loops. Dividing one period of quadrature sinusoidal signals, generated by an incremental encoder attached to a motor shaft, into four quarter sections, the digital loop controls the movement between the sections. The analog loop divides each section further into N equiangle segments, to control the movement within it. The effective angle resolution is thus 90°/MN, with M being the number of slits etched on an incremental encoder. A prototype controller, assembled using monolithic and hybrid integrated components, has confirmed the principles of operation. Experimental results are presented to demonstrate its capabilities. The positioning accuracy of the prototype controller was 0.009°±0.002°