Developmental And Experimental Research On Small Robot For Polishing Large Freeform Susrface

With the development of automobile industry , aeronautics and astronautics industry and some new high-tech industries, high-quality, high-performance and low-cost manufacture of large-scale dies are widely concerned by researchers. And large free-form surfaces of the mold is the most important manufacturing content. Based on the traditional processing model, a large free-form surface must be polished by large equipment. But the large-scale polishing equipment is costliness and there is some contradictory between processing and precision, stiffness, stability and rapid movement. Therefore, in order to break the limitations using traditional numerical control machine tools and industrial robots, it should be searched that new ideas and technical means of polishing equipment.This paper study put forward a new idea. A wheeled mobile robot for polishing the large free-form surface has been researched and developed. The small robot with polishing device can move on the surface of the large free-form surface. On the basis of the geometric information of the free-form surface, the robot may achieve polishing process automaticly. In this paper, theoretical and experimental researches were done on the small polishing robot. It mainly includes the followings:Firstly, the frame of the small polishing robot was constructed. The mobile device of the robot was designed to be a wheeled configuration that consists of two driving wheels and a all-direction wheel. The polishing device was loaded by mobile device. Then, the three-dimensional model of the robot is established by CATIA platform. A virtual model of the robot was founded and the interference test were done. The results show that the design of the robot is reasonable. The small polishing robot has been manufactured as a whole.Secondly, the kinematic reseach on small polishing robot was done.Small polishing robot is a kind of wheeled mobile robot, which is different from other robot systems. Wheeled mobile robot have kinematic constraints that limits the movement of the wheel. the kinematic equations of the robot were foundeded by the vector coordinates. Then, the overall kinematic model in the robot's movement coordinates were established. The kinematics simulating was done. It shows that the kinematic relationship of the robot is correct and the robot can move alone the anticipative track. According to the robot polishing tool, the work coordinates of the polishing point is researched. The path of movement and attitude controlof the robot is due to the processing requirements.Then, the movement trajectory planning problems of the robot was studied. When the robot polished on large free-form surface, it should be mainly used equidistant method of longitudinal trajectory planning. The robot moved and polished on free-form surface alone y direction. The distance of every two movement trajectory was always equation. by this way it can be completed most of the surface processing tasks. When the surface appears a small area of the local processes, it should be used circular cut-law trajectory planning. It should be adjusted the location of the robot and the angle of the polishing tools to keep a rational gesture moving in the planning trajectory.The robot's movement capability experiment was done.The robot moved on the tilt surface. The results show that the robot can move well and truly on the tilt surface in the 0°~ 22°angle of inclination. The robot begins to slip when the angle are greater than 22°. Then, the movement experimenn is done. The robot moves along the planning trajectory which speed is 1mm / s. The results show that the Y offset error is about 1.0 mm ~ 1.5 mm. At the same time it was contrasted to the Y error at different speeds within the same section of track, it can be seen that the speed of the robot has no obvious influence on the accuracy of moving track.The results also approve that the kinematic model of the robot is correct and equidistant method of longitudinal trajectory planning is feasible.In addition, the system dynamics of the robot was researched. Small polishing robot was limited by both nonholonomic constraint and holonomic constraint at the same time. It can not be established dynamic equations by lagrangian approach. In this paper, it was from the overall point of view. The adoption of additional constraint equations was input. Then, the dynamics of multi-body systems were established. The dynamic equations solving process wre clarified by Gear-correction algorithm and Newton-Laffer's iterative methods. Then the movement simulation is proceed. The results of the robot's visual simulation show that dynamic analysis of the robot is correct. And velocity and acceleration curve and its joint drive torque simulation curve is reasonable. The simulation results show that more stable and rational dynamics curve. can be get by adjusting the driver's joint of the robot.A dual-processor open control system based on programmable controller PMAC and IPC is designed. In the control system, IPC is a core controller and PMAC motion controller as the next crew. PMAC, IPC and DPRAM form the core of the control system. This is based on an inclusive structure of the three-tier structure of the hybrid system. The control system accords with the important open structure thinking. According as the hardware structure of the control system was established, the software system was designed. Then, a robot pneumatic system hardware platform was built. So the pneumatic system control model of the robot was founded. The pneumatic system were make up of oscillation tache and differential tache. when the input is the unit step signal, the system response a damping oscillation frequency vibration attenuation. The output signal is stabilized. the pneumatic system can be remained polishing powe of the cylinder stably in a certain range.Lastly, The machining experiment of small polishing robot was done. A large free-form surface of JETTA car was conducted a test workpiece. In the surface of the workpiece it was designated a regional ABJK as polishing processing zone. The region is flat similar to the plane. In this region, the original surface roughness value were about Ra1.5μm- Ra1.6μm. The results of the machining experiment showed that the surface roughness value had been about Ra 0.1μm-Ra0.2μm after machined by flexible tool. Three main factors affected the surface quality obviously. They are spindle speed, polishing pressure and moving speed. Among the three factors, the influencing trend can be concluded: the greater the polishing pressure becomes, the better the quality of processing gets; moving speed is more slowly, the better the quality of the surface obtains; the greater the spindle speed inputs, the better the quality is. And second polishing experimental results show that the surface roughness value reached about Ra0.06μm. The surface quality has been further improved. And the three factor affect processing quality indistinctively. And the machining experiment by rigid tools was done too. It can be contrasted between the rigid tools and the flexible tools. The results show that the surface roughness value were about Ra 0.35μm– Ra 0.6μm by rigid tools. It vibrated obviously and its wiping fficiency was better than flexible tools. Polished by rigid pole tool , the surface roughness was better than rigid ball tools, but the wiping depth was worse than rigid ball tools. So the robot is practicable and valid.