In this paper, we develop a monocular vision system for online pose measurement of a 3-RRR planar parallel manipulator (PPM). By combining with a camera with global shutter, an active marker array, an industrial personal computer, and a degenerated perspective-n-points (DPnP) algorithm, a monocular vision measurement system (MVMS) is established. To improve measuring accuracy of the MVMS, factors that cause inaccuracy including the lens distortion, non-perpendicular angle, and input parameters’ uncertainty are analyzed and modeled in detail. In the simulation, effects of these error factors on the accuracy of the MVMS are quantitatively displayed, and comparisons between the DPnP algorithms and other state-of-art PnP algorithms are conducted. Experimental tests on the constructed MVMS demonstrate that it not only can accurately and efficiently measure pose of the 3RRR PPM, but possesses a higher operability and stability compared to the laser tracker.
