| Summary: | 碩士 === 中原大學 === 機械工程研究所 === 100 === The purpose of this study is to increase the hit rate of a ball-pitching robotic arm based on stereo vision. The robotic arm has four degrees of freedom and a four fingers robot hand designed for grabbing and throwing a ball. The target is fixed on an XZ two-axis motorized mechanical stage, so the position of the target can be changed arbitrarily. The robotic arm is equipped with a pair of CCD cameras to calculate the relative position between the target and cameras in three-dimensional space. The work in this study is firstly to reduce the vibration phenomenon of the robotic arm and to accurately set the target for ball throwing using an XZ two-axis motorized mechanical stage. The objective of the first step is to minimize errors caused by hardware. Secondly, we set some grid points in three-dimensional space as pitching targets and move these grid points in sequence. When the target location is calculated by the stereo vision system and converted to control parameters of the robotic arm by inverse dynamics, the robotic arm can throw a ball toward the target. After the robotic arm throwing several times, we can estimate these hitting locations by using the stereo vision system and then to record the average value. Therefore, as the pitching target is moved arbitrarily, we can use these previously collected grid parameters for spline interpolation to improve throwing accuracy. Due to the presence of camera barrel distortion, the hit rate is low in some positions. So we finally do a compensation of these control parameters to solve this problem. After the above procedures, the experimental results in this study show that the hit rate is increased to about 60% and average error is 6 cm from the front of the robot 150 to 180 cm and cross-section range 20 cm × 20 cm of three-dimensional space.
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