Research On The Kinematics System And Polishing System Of Small Polishing Robot

The automation for the manufacturing of large-scaled freeform surface has been critical in the field of Aeronautics and Astronautics industry as well as automobile industry, in order to enhance the producing efficiency, cut down the costs, and promote the industry. Finishing processing plays a significant role in the mould's producing. Such, the research on the automation of finishing processing is necessary.Our group has proposed a totally new idea for the automation of finishing processing: using small equipment to work on large-scaled work pieces. Researches based on this method combine knowledge of robot and polishing together. The small robot polishes on large-scaled surface, moving agilely according to the geometric information of the work piece. In the light of this idea, a small polishing robot has been developed, which has the ability of self-location.This paper, based on the results of former researches, pays more attention on the kinematic and polishing system of the small polishing robot. A method for the robot's moving with a high efficiency when the target point was set as the navigation mark is proposed and testified by experiments. Also, this paper presents a flexible polishing system. This system combines the positive and passive flexibility with both pneumatic control and a flexible polishing tool. Experiments are designed for the tests of moving ability and polishing ability as well as the most fitted parameters of the robot when polishing .In the research of kinematics system, the configuration of wheels has been fixed firstly: two standard wheels as positive wheels and two casters as passive ones, considering the characters of each kind of wheels, such as Figure 1. Fig. 1 Configuration of wheels on chassisThe motion equations of the robot are deduced through each wheel of the robot and the configuration of the wheels: is provided by the location system; v1 , v2indicate the speed of the two standard wheels. Equation 1 shows the kinematic model of the robot, telling the relations between the robot's movement and the characters of each wheel.However, the inverse kinematics based on Equation 1 could not meet the need of path-tracking, because the moving efficiency of the robot should be considered as an important factor since the robot's low moving speed when polishing. For higher efficiency, as the path is already determined, we set the tracing mode of the robot as'forwardâ†'change lineâ†'backwardâ†'change lineâ†'forward…'. So the kinematic model and the inverse kinematic are modified for each section of tracking.The paper provides with the angular velocity factor k to illustrate the relation between angular velocity of the robot and the angle which is between the robot's gesture angle and target's azimuth angle in the coordinate system:ω= kΔγ. The analysis of the relation shows that the path-tracking of the robot could be stable when when k belongs to (-1/t,0), shown in Figure 2. Fig. 2 Relation between k and angle-differenceAccording to the tracking modes and the inverse kinematic of the robots, a C++ program is compiled for moving controlling in order to output the parameters of two standard wheels. This program integrates the results in the kinematic research, the method of path-tracking, and the transformation matrix, solving the limitations of the robot.Experiments are designed for the verification of the kinematic model and the program. The position information of the robot when tracking the path was collected at the interval of 200ms. Different kinds of paths-tracking on a plane and a freeform surface prove that the model and the program are correct. Figure 3 shows the result of path-tracking of the robot on the freeform surface. Fig. 3 Path-tracking resultIn the research of polishing system, polishing equipment with flexibility installed with a flexible polishing tool was designed for this robot. This polishing system has a high adaptability on the surface. With the easy-change equipment, this tool shows a processing flexibility.In order for a better polishing traces on the work-piece's surface as well as a higher polishing efficiency, the distance between two lines of the path should be adjusted of 40mm, as shown in Figure 4. (a) macro-trace (b) micro-trace Fig. 4 Polishing trace of the robot , e=40mmResults of polishing experiments verify the polishing ability of the robot. After polishing, Ra of the work piece has decreased from 1.5μm~1.6μm to 0.2μm~0.4μm.To test the polishing effect, 3-factors, 3-levels orthogonal test is designed including the polishing parameters of the robot, as shown in Table 1.Through the visual analysis and the analysis of variance, results are obtained: the sequence of the significance of all the polishing parameters is: rotation speed > feed rate > pressure; The best result could obtained when the rotation speed=4300rpm, feed rate=3.0mm/s, pressure=20N; rotation speed is very significant for the polishing result, and the feed rate is very significant. As shown in Table 2.