Adjustable Lever Mechanism with Double Parallel Link Platforms for Robotic Limbs

For universal robotic limbs, having a large workspace with high stiffness and adjustable output properties is important to adapt to various situations. A combination of parallel mechanisms that can change output characteristics is promising to meet these demands. As such, we propose a lever mechanism with double parallel link platforms. This mechanism is composed of a lever mechanism with the effort point and the pivot point; each is supported by a parallel link mechanism. First, we calculated the differential kinematics of this mechanism. Next, we investigated the workspace of the mechanism. The proposed mechanism can reach nearer positions than the posture with the most shrinking actuators thanks to the three-dimensional movable effort point. Then, we confirmed that this mechanism could change the output force profile at the end-effector by changing the lever ratio. The main change is the directional change of the maximum output force. The change range is larger when the squatting depth is larger. The changing tendency of the shape of the maximum output force profile by the position of the pivot plate depends on the force balance of the actuators. These analytical results show the potential of the proposed mechanism and would aid in the design of this mechanism for robotic limbs.