A robust downward-looking camera based velocity estimation with height compensation for mobile robots

Slip plays a vital role in traction control when a mobile robot traverses over soft soils. To estimate slip parameters, accurate measurement of robot velocity is particularly required. Previous related work done by the authors has adopted a single downward-looking single camera system for velocity and slip estimation [1][2]; however, such a single camera system is prone to lose accuracy when the distance between the camera and terrain is time-varying, such as traversing over uneven terrains [1]. To cope with the problem, this paper presents a robust downward-looking camera based velocity estimation approach, which can particularly be capable of identifying height variation and compensating for velocity estimation. A downward-looking stereo camera instead of previously used single camera is adopted. The camera-terrain distance can be estimated by matching same features in left and right frames. Robot velocity measured with height compensation can be more accurate, compared to estimates without it. The proposed approach has been validated through comprehensive experimental study on a lab-based test rig; and test results show good performance of the proposed approach. With the proposed method, slip estimation techniques given by [2][3] can be promisingly extended to non-flat terrains.