SCARA Type Robot Arm with Mechanically Adjustable Compliant Joints

A new SCARA type robot arm with passive compliance for contact or constraint tasks is presented. It utilizes a leaf spring and the joint stiffness can be adjusted by rotating this spring, i.e. changing its bending direction. A joint actuator moves an arm link via a connection hollow cylinder and a leaf spring. This mechanism is compact to add in a joint and it can change the stiffness rapidly and stably. We discuss the relationship between the angle of the leaf spring and the joint stiffness and also analyze the relationship between the joint stiffness and the stiffness at the end-effector. Since 4 joints are necessary to make arbitrary stiffnesses in plane motion, a 4 D.O.F. robot arm with proposed compliant joints was developed and tested.