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Test Facilities Guide

Engineering Test Facilities Guide

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Multi-Use Remote Manipulator Development

    Multi-Use Remote Manipulator DevelopmentMRMDF Facility with Shuttle Cargo Bay
    Photo credit: NASA

    The Multi-Use Remote Manipulator Development Facility (MRMDF) is a very large model following motion platform that is hydraulically actuated and computer controlled. It is designed to grapple and maneuver payloads of 500lbs or less at the end of a 60 foot long robotic arm. The arm can be manually controlled with inputs from two joysticks (also referred to as Hand Controllers (HCs)) or autonomously driven through a specified script. A force/moment sensor in the end effector provides system compliance when operating in constrained motion. The arm weighs approximately 15 tons and each joint has a maximum rotational velocity of 5 deg/second. A model following, closed loop control system allows the MRMDF to emulate any simulated system as long as the desired motions are within its rate and travel limits.

    MRMDF 7-Joint ClusterMRMDF 7-Joint Cluster
    Photo credit: NASA

    The MRMDF motion platform consists of a 60 foot long, hydraulically actuated, computer controlled robotic manipulator. Similar to a human arm, the manipulator has 3 shoulder joints, an elbow joint and 3 wrist joints, giving it a total of 7 degrees of freedom (DOF). An 8th DOF is provided by the end effector payload grappling mechanism. The arm is mounted on a reconfigurable base on top of a 16 foot tall pedestal and is capable of positioning payloads within an approximately 100 foot diameter spherical envelope, truncated in the nadir by the plane of the high bay floor. A Force Moment Sensor (FMS) located at the end effector provides force and moment data used in mating and installation procedures. The Air Bearing Floor (ABF) or "flat floor" is an ~70' X 100' epoxy surface used to support free floating mockups on air bearings in the facility and can be used independent of the MRMDF. A 16 camera Closed Circuit Television System covers every aspect of the MRMDF.

    The current configuration includes:

    • 5 cameras in a Payload Bay mockup
    • A camera on each of the 2 arm booms
    • An end effector camera
    • Various floor-based cameras
    • Several facility cameras located in the B9 rafters
    MRMDF with S1 Truss Payload Attached MRMDF with S1 Truss Payload Attached
    Photo credit: NASA

    All SD video cameras can be recorded on VHS or digitized for electronic archiving. The Arm to Payload Interface can provide an attached payload with a 62.5/125 graded index fiber-optic link as well as 24 VAC power through a Tyco Amp Series 1 CPC 4 Pin connector. Recording of arm position and orientation data collected at 30Hz is time stamped and can be correlated with data independently collected by the payload. Facility power can be made available, providing 110VAC or 3-Phase 220VAC at 30 amps via cables directly attached to the payload.

    How the System Works

    The MRMDF is driven by a 3000 PSI hydraulic system with Joint Based Control Electronics (JBCE) controlling the components at each joint, which consists of motors, brakes, hydraulic servos, and relief valves. The brakes are failsafe, meaning power must be applied to release the brakes. Once power is removed, the brakes are applied. The arm control software resides on two redundant Manipulator Control System Electronics (MCSE) computers. Should one computer fail, the other will automatically bring the system to a controlled stop and apply the brakes. Should the two MCSEs vary out of tolerance; a third computer known as the Facility Control System Electronics (FCSE) will shut the facility down.

    Computer Interfacing

    The Test Director Console (TDC) is the front end computer that links the other systems together. The Simulation Host (SIMHOST) computer transforms the simulated or desired motion commands into MRMDF joint commands. All the system computers (TDC, FCSE, MCSEs, and SIMHOST) communicate via Ethernet. The universal TCP/IP interfaces to and from the simulation model driving the arm simplify the exchange of one simulation for another. As long the simulation generates POR or joint angles rates within the facility specification limits as outlined in the MRMDF Specification Table, the arm can follow a user specified model. Safety features in the MRMDF software prevent the system from implementing any motion commands outside of its design limits.

    MRMDF Specification Table

    Feature  Unit of Measure 
    End Effector Translational Velocity,
    [configuration dependent]
    14 in/s
    End Effector Rotational Velocity,
    [configuration dependent]
    10 d/s
    Degrees of Freedom 8
    Number of Joints 7
    Joint Velocity 0.08 d/s - 5 d/s
    Joint Reach Limits +/- 270 degrees
    Arm Reach Limits 100 foot diameter hemisphere
    Payload Capacity 500 lbs
    FMS Data Collection Rate 150 Hz
    Full-Joint Position Data Collection Rate 30 Hz
    One-Joint Position Data Collection Rate 30 - 300 Hz
    Absolute POR Linear Position Accuracy +/- 3.04 in
    Model Following Capability Yes

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