Development of a Gravity Compensation Device for Rotary Joint Using Magnetic Force

The torque required for the driving part of a rotary joint is divided into a static torque for supporting mass and payload and dynamic torque used for acceleration and deceleration of the rotary joint. The static torque occupies a large part of the required torque and energy consumption. In this study, a gravity compensator was developed that generates a torque of the same magnitude as the static torque in the opposite direction in the 360 degrees range using permanent magnets (PMs). The shape of the PMs were designed to generate a sinusoidal wave gravity compensation torque according to the rotation angle. The profile of the gravity compensation torques generated according to the shape of the PMs were analyzed using a finite element analysis. A prototype was manufactured, and its performance was verified through experiments.