A direct-drive arm is an innovative mechanical arm in which no reducers are used between motors and their loads. Because the motor rotors are directly coupled to the loads, the drive systems have no backlash, small friction, and high mechanical stiffness, which are all important features for fast and accurate positioning and dexterous handling using sophisticated torque control.
The goal of the MIT direct-drive arm project is to achieve arm speeds of 10 m/s [15]. The arm has torques of up to 660 N m (475 ft lb). Feedback and a set of position and velocity sensors are used with each motor. The frequency response of one joint of the arm is shown in Figure P9.6 (a).The two poles appear at 3.7 Hz and 68 Hz. Figure P9.6 (b) shows the step response with position and velocity feedback used. The time constant of the closed-loop system is 82 ms. Develop the block diagram of the drive system and prove that 82 ms is a reasonable result.
