The kinematic parameters of a 3-PRR planar parallel manipulator driven by linear ultrasonic motors are calibrated based on visual measurement technology. Firstly, the structure of the 3-PRR manipulator is introduced, and then the kinematic model of the manipulator and the error function are deduced. To realize kinematic calibration of parallel manipulator, charge coupled device (CCD) camera is adopted as the external measurement device. By using the technologies of image processing, the center of the artificial features fixed on the moving platform is located to realize accurate pose measurement of the moving platform. Finally, particle swarm optimization (PSO) algorithm is employed to optimize and calibrate the kinematic parameters of parallel manipulator. Calibration experiments show that the trajectory of the moving platform is an ellipse with 16 mm major axis and 10 mm minor axis, the maximum trajectory error is greater than 800 μm before calibration, but the trajectory error is reduced to within 20 μm after calibration. As a result, the accuracy of the parallel manipulator is greatly improved, and the proposed calibration approach is further proved to be effective.
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