Hybrid image-plane/stereo (HIPS) for orientation control of manipulators

Planetary exploration systems, operating under severe environmental and operating conditions, have thus far successfully employed carefully calibrated stereo cameras and manipulators to achieve desired precision in instrument placement activities. However, the environmental and functional restrictions imposed by the remote operation of semi-autonomous robots in a harsh planetary atmosphere for long periods of time limit the ultimate operational accuracy of this approach. This paper builds on an algorithm, referred to as Hybrid Image-Plane/Stereo (HIPS), developed to optimize the positioning accuracy of a manipulator. The HIPS method generates camera models through direct visual sensing of the manipulator end-effector. It estimates and subsequently uses these models to position the manipulator at a target location specified in the image-planes of a stereo camera pair using stereo correlation and triangulation. While positioning control of manipulation systems is important, orientation control of these systems is also crucial. Many planetary manipulation tasks being considered for the Mars Science Laboratory rover, due to launch in 2009, and subsequent missions, will require precise orientation control of manipulators. This paper studies the effect of using HIPS models to control the position and orientation of manipulator end-effector. As seen in previous position control experiments, the static version of the HIPS technique reduces position error by almost an order of magnitude. This paper additionally shows that orientation error is reduced by almost a factor of two.