Analysis and design of semi-direct-drive robot arms

Two major improvements are incorporated into a lightweight arm mechanism for direct-drive robots. To avoid the mounting of heavy motors at the serial links, the serial link mechanism is replaced by a four-bar-link mechanism. High performance brushless motors were developed to obtain large torques with relatively small power dissipation. A basic model for the Pulse Width Modulated 'H' bridge-type driving amplifiers with current feedback and brushless motor was set up and experimentally verified. Analytic relations were derived to evaluate static and dynamic characteristics and actuator-load matching for multi-degree of freedom actuating systems. For the cross configuration of the semi-direct-drive arm, a maximum payload of 33 kg was obtained based on a total power of 1 kW.