Tech Briefs

Monitoring and Controlling an Underwater Robotic Arm

The SSRMS Module 1 software is part of a system for monitoring an adaptive, closed-loop control of the motions of a robotic arm in NASA’s Neutral Buoyancy Laboratory, where buoyancy in a pool of water is used to simulate the weightlessness of outer space. This software is so named because the robot arm is a replica of the Space Shuttle Remote Manipulator System (SSRMS).

This software is distributed, running on remote joint processors (RJPs), each of which is mounted in a hydraulic actuator comprising the joint of the robotic arm and communicating with a pool-side processor denoted the Direct Control Rack (DCR). Each RJP executes the feedback joint-motion control algorithm for its joint and communicates with the DCR. The DCR receives joint-angular-velocity commands either locally from an operator or remotely from computers that simulate the flight like SSRMS and perform coordinated motion calculations based on hand-controller inputs. The received commands are checked for validity before they are transmitted to the RJPs. The DCR software generates a display of the statuses of the RJPs for the DCR operator and can shut down the hydraulic pump when excessive joint-angle error or failure of a RJP is detected.

This work was done by John Haas and Brian Keith Todd of Johnson Space Center, Larry Woodcock and Fred M. Robinson of Oceaneering Space Systems, and Thomas (Jay) Costales of Raytheon Co. MSC-24165-1

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Monitoring and Controlling an Underwater Robotic Arm (reference MSC-24165-1) is currently available for download from the TSP library.

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