Impact dynamics of a differential gears based underactuated robotic arm for moving target capturing

This paper presents impact dynamic analysis of a differential gears based underactuated robotic arm colliding with a moving target. The robotic arm employs a set of one-input-dual-output planetary gears to distribute driving torque of the underactuated joints, which takes advantage of the underactuation to cope with collision. Based on an analysis of the movement relation of three joints, the driving torque is resolved into generalized force corresponding to coordinates of two underactuated joints for establishing a dynamic model of the underactuated robotic arm. Along with the dynamic equation, impulse-momentum equations involving the restitution coefficient of the system (arm and target) are used to establish the impact dynamic model which can extrapolate the impact momentum on the drive component. With the impact dynamic model, the impact-absorbing capability of the underactuated robotic arm is illustrated that the impact momentum on the drive component is reduced by a factor of three compared with a 2-DOF fully actuated rigid robotic arm. Impact experiments were carried out to validate the inference results presented in this paper by using of a prototype of the proposed arm.