Manipulator System for a Robotic Vehicle

NASA's Jet Propulsion Laboratory, Pasadena, California

A prototype manipulator system that includes two different arms has been tentatively selected for use on a semiautonomous robotic vehicle called Rocky 7 (see figure). [A previous version of this vehicle with a single manipulator arm was described in "High-Performance Robotic Vehicle" (NPO-19921) NASA Tech Briefs, Vol. 21, No. 1 (January 1997), page 67.] Rocky 7 is the most recent one in a series of such vehicles that are candidates for use in future remotely controlled scientific exploration of the surface of Mars. In comparison with the Sojourner vehicle deployed on Mars from the Mars Pathfinders pacecraft in July 1997, Rocky 7 would carry more scientific instrumentation and would function with greater autonomy, mobility, and capability for manipulation. The basic design of Rocky 7 and the other vehicles in the series could also be adapted to such terrestrial uses as remote surveillance and/or manipulation in remote and/or hostile environments.

The joints in the two manipulator arms are back-driveable and feature modular, lightweight, high-torque, gearmotor-type actuators, which were described in "Actuators for Rapid Development of Prototypes of Robots" (NPO-20054), NASA Tech Briefs, Vol. 21, No. 3 (March 1997), page 94. Both the actuators and the arm segments are hollow; this makes it possible to use the insides of the actuators and arms as optical paths and to hold electrical wires for actuators and for scientific instruments.

The Two Manipulator Arms perform different functions. The shorter arm can dig, grasp an object, or aim a spectrometer. The longer arm serves as a mast for stereoscopic, multispectral imaging, and as a mechanism for positioning a scientific instrument.

Mounted on the outer end of the shorter arm are two scoops and an optical assembly. The scoops can be used to dig (to a depth of 10 cm), hold, and dump soil samples; they can also be used to grasp an instrument canister; e.g., for burying a seismometer. The total mass of the arm is 0.65 kg. The arm can carry a payload of as much as 1 kg in normal Earth gravity.

The optical assembly includes two mirrors, with a fiber-optic connection along the arm to a spectrometer housed in the vehicle chassis. The optical assembly constitutes the input optical device of the spectrometer, and is aimed by turning the arm. The optical aperture is open only when the scoops are rotated to the back-to-back position. A spectrometer-calibration target can be rotated into or out of the spectrometer field of view by rotating both scoops together through a full circle.

Mounted on the outer end of the longer arm is an integrated sensor package that contains the following: (1) two stereoscopic video cameras with counter-rotating filter wheels, and (2) an instrument canister that can be outfitted with either a gimballed close-focus camera, Mössbauer spectrometer, nuclear magnetic resonance spectrometer, or other science instrument. The arm can be extended to a height of 1.4 m above ground; it can be used to rotate the cameras through a complete circle for panoramic imaging of the surrounding terrain, to position the cameras for viewing objects of scientific interest from above, or to position the cameras to inspect the vehicle. The total mass of the longer arm is 0.7 kg. The arm can carry a scientific instrument as massive as 0.5 kg in normal Earth gravity.

Both arms can be stowed compactly, without interfering with the suspension and wheel-drive mechanisms, with a solar photovoltaic panel that supplies the power for the vehicle, or with another stereoscopic camera system that is used to guide the vehicle across the terrain as well as image the activities of the arms. An onboard electronic control system is used to operate both the vehicle drive motors and the actuators in the manipulator arms; this system provides variable-rate motor control, detects errors in joint angles, prevents collisions of the arms with objects in the vicinity, controls contact of mast instruments with the target rock, analyzes images of potential digging areas to prevent futile attempts to dig in rock, and visually verifies successful manipulator operations.

This work was done by Richard Volpe, Timothy Ohm, Richard Petras, Richard Welch, J. (Bob) Balaram, and Robert Ivlev of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Machinery/Automation category, or circle no. 152 on the TSP Order card in this issue to receive a copy by mail ($5 charge).

NPO-20162