Visual positioning system for small-scaled spherical robot in underwater environment

Aiming at application requirements of our small-scaled spherical amphibious robots, a visual positioning system adopting the model of depth image and feature fusion was designed and implemented in this paper. Considering the narrow load space, the limited structure space and the specialized underwater application scenarios of the spherical robot (the diameter of the upper and lower hemisphere is 320 and 350 mm, respectively), a Time of Flight RGB-D camera was used, and the color image and depth image could be acquired, thus the position of objective could be calculated from image information, a calibration experiment for distance correction was designed to improve the accuracy of the positioning system. Based on the theoretical analysis and calculation, a series of underwater experiments were carried out to test the performance of the proposed positioning method. Experimental results confirmed the feasibility of the proposed visual positioning method, and the maximum error between the actual positioning result and the reference value is less than 7 mm, which could meet future demands of our amphibious spherical robot in biological monitoring and multi robot cooperation.