Design and Testing of a Variable Effective Compliance Transmission With an MR Damper

This paper describes the design and experimental testing of a variable effective compliance transmission for use with revolute joints in robotic systems. The transmission consists of a parallel arrangement of a torsional spring and a rotary magnetorheological (MR) fluid damper and is placed between a brush–less DC gearmotor and an end-effector. While the stiffness of the torsional spring is constant, the damping of the MR damper can be adjusted by changing the applied current, which alters the apparent rigidity of the system. Hence, the transmission exhibits a variable “effective compliance”. Experimental results show that increasing the damping can reduce position errors during acceleration and deceleration phases of motion. Impact tests indicate that for small currents applied to the damper (low damping), the presence of the torsional spring reduces impact loads during constant velocity motion. In combination, these results indicate that the variable effective compliance transmission can improve safety without sacrificing precise motion control.© 2009 ASME