Microprocessor controlled d.c. motor for controlling print value

Abstract

In printing apparatus including structure for changing a value to be printed and structure for selecting a value to be printed, wherein the former includes a plurality of banks, each of which includes a print wheel having a plurality of print elements, and the latter includes structure for selecting each bank and structure for selecting each print element of a selected bank, and structure for driving the bank and print element selection structure, wherein the driving structure includes an output shaft, and structure for selectively coupling the shaft to the bank and print element selection structure, the improvement for controlling the value selection structure, the improvement comprising: the driving structure including a d.c. motor having the output shaft; structure for sensing angular displacement of the shaft; a microprocessor comprising clock structure for generating successive sampling time periods, structure for providing first counts respectively representative of successive desired angular displacements of the shaft, structure responsive to the sensing structure for providing second counts respectively representative of actual angular displacements of the shaft, and structure for compensating for the difference between the first and second counts during each successive sampling time period and generating a PWM signal causing the actual angular displacement of the shaft to substantially match the desired angular displacement thereof during successive sampling time periods; and signal amplifying structure operably coupling the signal to the motor.