Control of a multijoint manipulator "Moray arm"

In this paper, we first introduce a multijoint manipulator that was named "Moray arm," which is a slider-integrating multijoint manipulator, where a powerful slider is installed at the base of the arm. The Moray arm emulates the motion of a Moray, thus, allowing it to easily enter a narrow space while avoiding obstacles. To elucidate the features of the Moray arm, we present new control methods named "Moray drive" and "two-degrees-of-freedom (2-DOF) Moray drive." The Moray drive control generates rotating motion of the joints in synchronization with linear motion of the slider while restricting the arm on the trajectory. The 2-DOF Moray drive control reduces the control problem of the hyper DOFs to the simple one of 2 DOFs: one of the control variables signifies the linear combination of the objective initial and final postures of the arm, while another expresses the amount of the pull-out-displacement when pulling the arm out of the housing. The Moray arm controlled by Moray drive or 2-DOF Moray drive has the basic properties: 1) possibility to use the lightweight joint-driving mechanism by subrogating most of the driving power to the slider; 2) simplicity of control in spite of the hyper-redundancy of the multijoint system; 3) feasibility to enter a narrow space while avoiding obstacles; and 4) little fluid resistance in operation in a fluid. Based on the 2-DOF Moray drive control, we also propose an obstacle avoidance scheme for the "Moray arm" to perform a pick-and-place task while avoiding the existing static obstacles in environment. The scheme is based on the Posture Space analysis and generates the obstacle collision-, free trajectory in the Posture Space. Computer simulations were executed as well to verify the proposed schemes. As a result, we conclude that the Moray arm controlled by the proposed schemes gives great possibility for the hyper-redundant manipulator to perform applications such as maintenance of nuclear reactors, collection of lumps of existing manganese under sea, and care of patients.