Design Optimization of Y-Shaped Transmission System for Dual-Arm Concentric-Tube Robots

Abstract

Y-shaped transmission system of dual-arm concentric-tube robots (CTR) possesses advantage of convenient arrangement of its actuation units. However, the design optimization of such Y-shaped transmission system has not been systematically studied. This paper presents an optimal design framework of Y-shaped transmission system for dual-arm CTR. Each robotic arm consists of several telescoped tubes, and each tube is made by a pre-curved super-elastic NiTi tube bonded to a stainless steel (SS) tube that transmits rotations and translations to the distal NiTi tube. Geometric constraints of the transmission system, including the tube diameters, the Y-shaped configuration, and the collision of actuation units, are first deduced. Secondly, deformation constraints considering the bending and torsional twisting of SS tubes are derived. Lastly, the design problem has been formulated as a constrained nonlinear optimization problem whose objective function is to minimize the relative twist angle or length of SS tubes. According to the proposed framework, a dual-arm CTR prototype with the optimal Y-shaped transmission system has been built. Thorough analyses on the optimal designs by different objective functions have been presented. A performance test experiment has also been conducted to validate the modeling and optimization methods.