Digital control of direct drive robot manipulators

This paper proposes design and implementation of a digital control system to drive a two-link robotic manipulator. Our process adopting a completely digital control system design, to avoid using an ordinary ADDA card. A permanent magnet DC servo drive with a gear set is chosen to be as an actuator driven by a high frequency Darlington transistor in an H-bridge configuration. A four quadrant control using CMOS switches is achieved to control the output of the power driver and to provide motor speed and torque control in two different directions. It is designed to use a constant frequency variable duty cycle pulse width modulation (PWM). PWM signal is generated using a combination of multiple semiconductor component technologies, TTL, LS, HS, and CMOS depending on what is available in our local market. The semiconductor components used in this work are all not exotic to avoid ordering any component from abroad. PWM signal drives CMOS switch to control the average of the output DC voltage applied to the actuator. A novel unusual incremental encoder technique is implemented to design an accurate digital 16 bit shaft encoder circuit to serve as a feedback arm position. ISA bus is chosen to be our PC interface to the manipulator's drives. The feasibility of the digital control system is investigated by experimental results using a digital PID-controller.