This paper presents an in-depth performance analysis and validation of a correlation based stereo vision system being used as part of the ongoing 2003 Mars Exploration Rover flight mission. Our analysis includes the effects of correlation window size, pyramidal image down-sampling, vertical misalignment, focus, maximum disparity, stereo baseline, and range ripples. A key element of validation is to determine the stereo localization error both analytically and experimentally. We study both down-range and cross-range error and verify that while camera calibration inaccuracy contributes to both, stereo correlation error affects only the former. Error contributions of subpixel interpolation, vertical misalignment, and foreshortening on stereo correlation are examined carefully. A novel method using bricks with reflective metrology targets and a mast-mounted stereo camera system enabled experimental measurements of the stereo disparity error. The standard deviation of the down-range disparity error was measured at sigma=0.32 pixel for high-resolution 1024times768 camera images. The result is critical in evaluating accurate rover navigation and instrument placement within given error budgets

In October 1996, a research and development task was initiated at JPL to develop and demonstrate nonlinear contact control schemes for the dexterous robotic arms planned for the Space Station. This paper reports on the progress made to-date in this task. Specifically, the paper introduces a new class of contact controllers comprised of a nonlinear gain in cascade with a linear fixed-gain PI force controller and PD compliance controller. The nonlinear gains used are simple hyperbolic functions of force error and contact force, respectively. The stability of the closed-loop systems incorporating nonlinear PI and PD controllers are investigated using the Popov stability criterion. Experimental results are presented to demonstrate the efficacy of the nonlinear force and compliance control schemes for a dexterous 7-DOF arm. These results highlight the advantages of the proposed nonlinear contact controllers compared to conventional fixed-gain controllers.

The paper presents experimental results that demonstrate a new approach to real-time collision avoidance for 7-DOF arms. The collision avoidance problem is formulated and solved as a force control problem. Virtual forces opposing intrusion of the arm into the obstacle safety zone are computed in real time. These forces are then nullified by employing an outer feedback loop which perturbs the arm Cartesian commands for the inner position control system. The approach is implemented and tested on a 7-DOF RRC arm and a set of experiments are conducted in the laboratory. These experiments demonstrate perturbations of the end-effector position and orientation, as well as the arm configuration, in order to avoid impending collisions. The approach is simple, computationally fast, requires minimal modification to the arm control system, and applies to whole-arm collision avoidance.

The paper presents experimental results that demonstrate a new approach to real-time collision avoidance for 7-DOF arms. The collision avoidance problem is formulated and solved as a force control problem. Virtual forces opposing intrusion of the arm into the obstacle safety zone are computed in real time. These forces are then nullified by employing an outer feedback loop which perturbs the arm Cartesian commands for the inner position control system. The approach is implemented and tested on a 7-DOF RRC arm and a set of experiments are conducted in the laboratory. These experiments demonstrate perturbation of the end-effector position and orientation, as well as the arm configuration, in order to avoid impending collisions The approach is simple, computationally fast, requires minimal modification to the arm control system, and applies to whole-arm collision avoidance.