Force Sensing Strategy for the Antagonistic Variable Stiffness Hand

This research proposes the design, sensor modeling, and application of the force sensors for an antagonistic variable stiffness (AVS) hand. The AVS hand is a multi-fingered hand designed to achieve in-hand manipulation and also possess physical impact absorption capabilities. The key design feature of the hand is the finger module developed based on the principle of variable stiffness actuation. Combining the structural features, control requirements and low-cost requirements, the finger force sensing is achieved through joint torque sensors instead of expensive multi-axis force/torque (F/T) sensors. From the mechanical design of the AVS hand, it can be observed that the actuations of the finger joints are highly coupled and have a very compact structure, which makes the torque sensor design challenging. This article proposes two types of torque sensor designs, including a strain-based torque (SBT) sensor and a torque sensor for measuring elastic deformation in the series elastic actuator (SEA), which not only simplifies the wiring and electronics of the hand, but also enhances reliability. The linearity and hysteresis of the SBT sensor do not exceed 2.37% and 0.41%, respectively. The linearity and hysteresis of elastic-deformation based torque sensor do not exceed 10.12% and 11.32%, respectively. We validated the effectiveness of the proposed torque sensing method through impedance control.