Computers Elect. Engng Vol. 17, No. 3, pp. vii-viii, 1991 0045-7906/91 $3.00 + 0.00 Printed in Great Britain Pergamon Press pie

GUEST EDITORIAL

R O B O T I C S R E S E A R C H A T T H E N A S A / G O D D A R D

S P A C E F L I G H T C E N T E R

Exploration of space has been successful and exciting in the first 25 years of the U.S. Space Program. However, new times bring new challenges. A new era in space begins as NASA moves into the second 25 years of the Space Program and commits itself to establish a permanent manned presence in space with the Space Station supporting in-space scientific and commercial endeavors. The Space Station Program has served as a medium to promote a new generation of machine intelligence and robotics technology, developed on recent advances in AI and robotics, microelectronics and computer science. The advances in automation and robotics stimulated by the Space Station Program will: (i) increase productivity in space for commerce and science; (ii) transfer new technology back to earth-based industries; and (iii) maintain the U.S. leadership both in space and at the cutting edge of technology.

Space operations outside of life-supporting environments such as the Space Station are considered relatively dangerous. Astronauts performing space operations are required to possess the ability to work in an environment which is not precisely controllable and completely understood a priori as an earth-based factory environment. Consequently NASA has focused on developing space robots which will assist or replace astronauts in performing extravehicular activities such as assembly, repair, construction or inspection. Using its intelligence and smart sensors, a space robot will be able to adapt to the frequently changing space environment, react to unforeseen events and to solve unexpected problems. The Goddard Space Flight Center has been one of the key NASA centers which develops advanced robotics and related technologies for the implementation of space robots.

The objective of this special issue on Robotics Research at the NASA/Goddard Space Flight Center is to present some research activities in robotics and related areas, which are currently conducted by its employees, industry and universities at the Goddard Space Flight Center (GSFC). The first versions of the majority of the papers in this issue were presented at the Third Biannual International Symposium on Robotics and Manufacturing (ISRAM) held on 18-20 July 1990 in Burnaby, British Columbia, Canada. GSFC has a wide range of research activites in robotics and related areas, including vision, path planning, obstacle avoidance sensors, redundant manipu- lators, force-reflecting teleoperation, adaptive control, Stewart Platform-based manipulators, high-speed computers, etc. A brief description of the papers in this issue is given below.

Ollendorf and Nguyen present in an overview fashion, two major robotic facilities at GSFC, the Development, Integration and Test Facility (DITFAC) and the Intelligent Robotics Laboratory (IRL), in which most research activities presented in this issue are performed. Also described are the Flight Telerobotic Servicer (FTS) Program and its mission.

Leake discusses the development and implementation of coordinate transformations for a dual-arm teleoperation system with Cartesian force-reflecting capability, which is part of the DITFAC at GSFC. The teleoperation system consisting of a slave arm and a master hand controller, has been developed at GSFC for studying the feasibility of teleoperation in space. The transformations are implemented on a 386-based Multibus-I system using Ada language. The system has been used to successfully demonstrate basic teleoperation tasks such as peg-in-hole and contour tracing.

Nguyen, Zhou and Mosier, in their paper, present the mathematical developments needed in the computer simulation study and real-time motion control of a 7-degree-of-freedom (DOF) kinematically redundant slave arm of the DITFAC teleoperation system. The forward kinematic transformation and the Jacobian matrix of the slave arm are derived. Results of computer simulation performed to evaluate the conversion efficiency of the developed kinematic and differential transformations are presented, Three adaptive control schemes are proposed to control

vii

viii Guest Editorial

the positions/orientations and/or forces/torques of the slave arm, and latest computer simulation results of the control schemes are reported.

Campbell develops a path planning scheme for a 3 DOF robot, which avoids collision. Heuristic algorithms are obtained to relax the slide-jump trajectory defined as a sequence of edges which are alternately traversed and then linked by line segment paths, to a jump-jump trajectory defined as two consecutive jump trajectories. The concept of pseudo-obstacles is introduced to convert the 3 DOF manipulator problem to a point robot problem. The path planning scheme is evaluated for several cases using a Silicon Graphics workstation.

Vranish, McConnell and Mahalingam present the ongoing research and development of a capactive proximity sensor, called Capaciflector. The Capaciflector is a capacitive sensing element backed by a reflector which is driven at the same voltage as, and in phase with, the sensor, to reflect the field lines away from a grounded robot arm and therefore can be mounted on a robot arm to avoid collision with obstacles during a teleoperation task. A single-element Capaciflector has been successfully demonstrated on a Puma robot at GSFC. Latest experimental results on the Capaciflector are presented.

Lerner and Morelli develop an algebraic image operator which uses an accurate method for deriving gradient component information in model-based vision. In addition, a robust method of linear feature extraction is derived by combining the techniques of a Hough transform and a line follower, and then optimized by capitalizing on the spatially reconfigurable nature of the edge detector/gradient component operator. Results of several test cases are presented.

Nguyen, Antrazi, Zhou and Campbell present the kinematic analysis and implementation of a 6 DOF robot wrist of the IRL, whose design is based on the Stewart Platform mechanism. The robot wrist which is capable of performing very precise motion is proposed to be mounted on a general manipulator such as the space shuttle arm to perform autonomous assembly of NASA hardwares in space. Forward and inverse kinematic transformations and a modified Jacobian matrix and derived for the wrist. Computer simulation results of the conversion efficiency between joint and Cartesian spaces of the developed transformations and the Jacobian matrix are presented.

Shaffer, in his paper, discusses the role of real-time collision detection algorithms in telerobotics applications. The use of collision detection systems based on proximity sensors is compared with collision detection systems based on simulation of the robots' workspace in terms of cost, complexity and available information on collision. One simulation-based system for a multi-robot environment based on a variant of the octree is described and computer simulation results for a dual 7 DOF robot arm system are presented and discussed.

In the final paper of this issue, Smiarowski and Anderson deal with a computer system implemented by off-the-shelf fast processor chips, for control of space robots. The Robotic Arm Control System (RACS) proposed by the authors incorporates not only position/orientation control but also force/torque feedback control, resulting in a flexible tool for research in the area of compliant control. All the RACS modules housed in plug-in boards are used to replace the existing low-level servo controller of the PUMA 562 VAL-II Mk III controller. The selection of processors for the RACS is explained and calculations of the control sampling rate are given for several control schemes.

The Guest Editors would like to thank Professor Mo Jamshidi, Editor of Computers & Electrical Engineering for the opportunity to edit this special issue and for his help in the paper review process. They also wish to express their appreciation to the authors for their contributions to this special issue. The Guest Editors also would like to thank Professor Yao-Bin Chen of Purdue University, Professor Yuan F. Zheng of Ohio State University, Professor Robert Meister of Catholic University of America, Dr R. L. Andersson of AT&T Bell Laboratories, Dr Peter Kanzanzides of Integrated Surgical Systems for their enthusiasm in reviewing the issue papers. Finally the financial support of the NASA/Goddard Space Flight Center for this special issue is greatly appreciated.

Department of Electrical Engineering CHARLES C. NGUYEN Catholic University of America Washington, DC 20064, U.S.A.

NASA/Goddard Space Flight Center STANFORD OLLENDORF Greenbelt, MD 20771, U.S.A.