Study on a Method of Horizontal Position Measurement for Suspended Target Based on Single Camera

The low gravity test is an indispensable test for space manipulators before launching into the outer space. This paper aims to propose a position measurement method for the suspended target, which is a component of a low gravity test system. In order to obtain the position of lower hanging point in real time, an active target is designed with 7 infrared LEDs. A single camera is employed to acquire images of the feature points on the target. After that, the region growing, centroid extracting and locally searching methods are adopted to get the feature points location on the imagine plane. And then the perspective-n-point pose determination method (PnP) is used to calculate the relative position of the upper and lower hanging points. Experimental results show that this method can measure the horizontal position accurately and efficiently, and the maximum error is 0.128mm.