Simple circuit provides motor-feed control

摘要

Because we needed a small grinding machine, we modified an old milling machine that lacked a control system. The table of the grinding machine needed only to move back and forth with adjustable feed. Using an existing dc servoamplifier, a servo motor, and limit switches, we devised the circuit shown in Figure 1. Because the motor had no tachometer, we used part of the motor voltage as feedback. We reduced the feedback voltage from the motor to approximately 8V by using the resistors R_1 to R_3. (Motor voltage=60V, maximum amplifier input =10V, R_1=R_2=33 kΩ, and R_3=10 kΩ.) This feedback voltage feeds back to the speed-command differential-voltage input.