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This paper addresses the problems of opening a door with a modular and reconfigurable robot (MRR) mounted on a wheeled mobile robot platform. The main concern of opening a door is how to prevent the occurrence of large internal forces that arise because of the positioning errors or imprecise modeling of the robot or its environment, specifically, the door parameters. Unlike previous methods that relied on compliance control, making the control design rather complicated, this paper presents a new concept that utilizes the multiple working modes of the MRR modules. The control design is significantly simplified by switching selected joints of the MRR to work in passive mode during door-opening operation. As a result, the occurrence of large internal forces is prevented. Different control schemes are used for control of the joint modules in different working modes. For the passive joint modules, a feedforward torque control approach is used to compensate the joint friction to ensure passive motion. For the active joint modules, a distributed control method based on torque sensing is used to facilitate the control of joint modules working under this mode. To enable autonomous door-opening, an online door parameter estimation algorithm is proposed on the basis of the least squares method, and a path planning algorithm is developed on the basis of Hermite cubic spline functions, with consideration of motion constraints of the mobile MRR. Simulation and experimental results are presented to show the effectiveness of the proposed approach.
Date of Publication: June 2013