This paper proposes an algorithm that estimates a reaction torque loading the grasping jaws of wire-actuated robotic forceps and compensates for subsequent wire elongation. The algorithm is constructed by the combination of the Reaction Force Observer (RFOB) and an optimization problem based on a gradient descent method. The conventional RFOB is used to estimate an external torque that includes not only the reaction torque but also the acceleration of wire elongation. The wire elongation is directly obtained from the differential equation of wire elongation. Then, as a solution of the optimization problem, the acceleration of the wire elongation is obtained. Thus, the reaction torque is derived by subtracting the acceleration of wire elongation from the external torque estimated by the RFOB. Our previous algorithm required an assumption that the motor torque and reaction torque are constant, although they fluctuate in practice. The new algorithm eliminates this assumption, resulting much improved accuracy in estimating the reaction torque. The improvement was verified through simulation.
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