Development On Shape-adaptive Compliant Tool System For Free-form Surfaces

Nowadays industrial robots and many other CNC equipments are taken to replace the traditional labor's handwork, such as free-form surfaces polishing. It's prevalent to control the CNC equipments compliantly by integrating their end effectors with some passive compliant device. This kind of force/position hybrid control method has its disadvantages such as strong coupling of force and position space, nonlinearity, low control precision and bad stability. The high flexibility of producing discretionary force could not be reached by the polishing process in the condition of robots'high position and structure stiffness, it needs a new kind of compliant control strategy.A new shape-adaptive compliant tool system is developed in this thesis, which can be effectually integrated with industrial robots and five-axis NC machines. It can satisfy the compliant control requirements of tool's pose and normal force in free-form surfaces polishing. The position and force can be independently controlled after their hybrid space is decoupled into two independent subspaces in software programs. The main principle of this compliant tool system can be described as follows: a passive servo mechanism of bi-directional rotating sphere hinge, which works with the tool-path controlled by robots, is designed to realize the shape-adaptive capability on free-form surfaces, and the normal polishing force could be controlled by the designed linear stepping motor and column helix spring system.In chapter 3, the virtual prototyping of the tool system is created in ADAMS and the simulation on three typical free-form surfaces: sine surface, ellipsoide surface, and top cover surface of a kind of dust collectors is taken. In the simulation, the fitting states of the normal varying angle of the tool system and the workpiece surfaces are used to investigate the adaptive capability of the tool system in the process of feed movement.In chapter 4, the transfer function model of the control system is built in MATLAB. The regular PID controller and fuzzy-PID controller are designed, and the simulation in Simulink is taken to study their control performance of the tool system. Further more, an angle-adaptive PID controller is designed to improve the performance of the control system.In chapter 5, an experiment platform is built to investigate the shape-adaptive capacity and force control property of the tool system. And a set of LabVIEW software is programmed to accomplish acquisition data and control the polishing normal force. The compliant control experiments simulating the installation of the tool system on robots are taken, where three typical and representative free-form surfaces of the workpiece are used: convex surface, concave surface and plane surface. The experiments results indicate that the tool system developed in this thesis has good performance on shape-adaptive capacity for free-form surfaces, and superior property on normal force control.The investigation results of the theory and experiments both indicate that the compliant tool system developed in this thesis can realize the hybrid control of force and position, while it's tracking the free-form surfaces.