Development of an arm for collaborative robot equipped with gravity compensation mechanism according to payload

This paper describes a principle, a design and an evaluation of a light-weight safe arm equipped with 3-dimensional gravity compensation mechanism for a collaborating robot. This arm realizes the gravity compensation for 3-dimensional arm posture by the addition of a rotary joint to the base of a pantograph mechanism and arranging links and counterweights to balance the center of gravity. It is possible to reduce the weight of the arm by using joint driving motors as counterweights. Moreover, this arm is equipped with a compensation force adjustment mechanism using wires to make the mechanism compact. Since application of this mechanism makes it is possible to adjust the compensation force according to the payload, joint driving motors can be made smaller. Based on the simulation result and the experimental result of the developed arm, it was confirmed that the arm is able to reduce the joint torque by 75% - 85% by the effect of this gravity compensation mechanism.