Optical Kinematic State Estimation of Planetary Rovers using Downward-Facing Monocular Fisheye Camera

Knowledge of the kinematic state of rovers is critical to navigation, path reconstruction and exploration, especially on rugged terrain like planetary surfaces. Existing methods employ many encoders, potentiometers and hall sensors. These add components and wiring to moving parts. The components are susceptible to mechanical and electronic failures, add mass, and some require thermal regulation. In addition, the sensor wires are susceptible to bending, flexing and wear. Where miniaturization counts, the limitations on mass, size and power encourage elimination of sensors wherever possible. This paper presents a method to estimate the kinematic state of rovers using only a downward-facing fisheye camera. This novel approach implements a vision algorithm to obtain kinematic state information in planetary rovers. The two additional benefits of the technique are (1) redundancy to proprioceptive measurements, (2) means for perceptive visual odometry. The method uses a single camera to estimate 10 degrees-of-freedom (associated with steering, driving and suspension) on the AutoKrawler, a rover test platform for planetary exploration. Motions are estimated by self-perception combining fiducial marker tracking, optical flow techniques and the kinematic constraints of rover mechanics. Experimental results, obtained from the rover operating in an environment analogous to the lunar surface, are presented. The results obtained are compared with ground truth data to validate the approach.