Planning And Control Of Mobile Manipulator Operating Constrained Mechanism

The home service robot with manipulator can enhance people’s convenience by realizing a set of tasks; for example, interact with the environment such as grabbing, lifting or passing through a door. While, in order to serve human in domestic environment, the robot should have the ability to open doors. If the doors can be opened successfully, it will not only widen the working area of the robot but also increase the utility of it since the robot will not be constrained in a particular room and can achieve many more tasks.The problem of door opening is very fundamental for mobile manipulators operating in domestic environments. However, doors vary in its size, shape and types and the wheeled-manipulator is a redundant system. Therefore, opening door with mobile manipulator is a challenging problem: it’s hard to locate the doors and grasp the handle, the trajectory to open doors must be generated online, and finally it is hard to compute the coordinated arm-base motion that opens the door. In order to successfully achieve the door opening task with wheeled mobile redundant manipulators, a manipulability improving scheme is proposed and investigated in this paper. The scheme treats the wheelchair and the manipulator as a whole system and can improve the manipulator’s manipulability when opening the door. And thus remedy the manipulator’s manipulability decreasing and/or joint variable’ abrupt change as well as the workspace limitations during opening the doors. What’s more, the control scheme can drive the wheelchair to move according to the end-effector so as not to collide with the door, and can open door smoothly. The control system mainly contains three controllers. Firstly, the velocity of the end-effector is generated with the hybrid position/force control for opening doors, and then the coordinated motion control of mobile platform and the manipulator is adopted to drive the whole system moving to a suitable position to open doors successfully. This control scheme can be used by any mobile manipulator that can be velocity controlled. For verifying the performance of the proposed scheme during opening doors, both simulations and physical experiment are performed on a wheelchair mounted with a 6-DOF robot arm.