Experimental Verification of Impact Absorbing Property of Wire Driven Joint with Synthetic Fiber Rope

In a quadruped robot, the impact force applied to the leg mechanism by falling or stepping over is a problem that may cause damage to the mechanism. Therefore, various systems to increase impact resistance have been studied. In order to have high impact resistance, there are methods to withstand the impact by using a high-rigidity drive system, such as hydraulic cylinders which is heavy and large, or methods to absorb it by control using back-drivable actuators which is low energy efficient for quadruped robot. On the other hand, various series elastic actuators have been studied, which can absorb impact. Meanwhile, we have been studying synthetic fiber wire drive system. Synthetic fiber wire drive system is lightweight and can handle actuator arrangement freely. Also, synthetic fiber rope has elasticity, and if the elongation of the wire is measured and the force is estimated by its elastic characteristic, impact absorption and torque control can be performed. In this paper, we firstly compare the impact absorption of wire drive mechanism to that of harmonic drive mechanism as a typical reduction mechanism. For comparison, we build a 1 DoF link mechanism for both drive mechanism, and compare impact absorption by drop weight test. Then, a control to absorb the impact by measuring the elongation of the wire and estimating the force applied to the link is performed and evaluated with the link mechanism with fix axis replaced with a motor. The gain of position control was regulated by the estimated force applied to the link in order to back drive the motor and to absorb impact force. As the result, comparing with the harmonic drive link mechanism, the wire driven link mechanism can reduce impact force by approximately 66%. Also, the impact force can be reduced by approximately 10% by the impact absorption system.