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Test Facilities Guide

Engineering Test Facilities Guide

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Dexterous Manipulator Testbed

    Dexterous Manipulator Testbed (DMT)Dexterous Manipulator Testbed (DMT) Facility
    Photo credit: NASA

    The Dexterous Manipulator Testbed (DMT) consists of two six-joint, hydraulic manipulators mounted on a seven foot high pedestal It is designed to grasp and precisely position small payloads of up to 240lbs for task specific, close-in work site operations concentrating on hardware contact. The arms can be manually controlled with inputs from two joysticks (also referred to as Hand Controllers (HCs)) or autonomously driven through a specified script. Each arm has an ORU Tool Changeout Mechanism Emulator as its end effector, but these can be replaced with standard or custom grippers, if desired. A model following, closed loop control system, allows the DMT to emulate any motion within its rate and travel limits as well as the contact dynamics associated with installing/removing payloads into/from receptacles.

    DMT Director Console/Computing InterfaceDMT Director Console/Computing Interface
    Photo credit: NASA

    The DMT was used as a Special Purpose Dexterous Manipulator (SPDM) training facility, utilizing a computer model of the SPDM and a functional equivalent of the ORU Tool Changeout Mechanism (OTCM), the SPDM end effector. The system consists of two Schilling robots mounted on an approximately 7 ft high pedestal. The manipulator arms have a maximum reach of 72 inches with the OTCM and a maximum payload capacity of 240 pounds. The manipulator arm joint configuration is yaw, pitch, pitch, pitch, yaw and roll. The system can be controlled from both a Test Director Console (TDC) and a shared Cupola workstation. A force-moment sensor capable of reading torque up to 50 foot-pounds and force-moment accommodation software allows the system to perform insertion/removal tasks with small tolerance interfaces. An 8-camera Closed Circuit Television System provides video surveillance of all test operations that occur within the DMT facility.

    How the System Works

    A Hydraulic Power Supply (HPS) supplies hydraulic pressure to the two Schilling manipulators. There is one pump to pressurize both manipulators. Under normal operating conditions, only one manipulator will be operated at a time.

    Control software resides on a single Host computer that interfaces with system processors and controllers. Automated system monitoring detects off-nominal conditions in robot control, communications and system health, and takes action to safe the system.

    Computer Interfacing

    DMT Cupola Computing InterfaceDMT Cupola Computing Interface
    Photo credit: NASA

    The control architecture is identical for each manipulator. The two duplicate systems are referred to as Alpha and Beta respectively. The control architecture of the DMT relies on a Host computer to interface with system processors and controllers. The Host runs the Graphical User Interface (GUI) at the TDC to control the manipulators. It accepts operator commands through the GUI, including solenoid open/close commands. It receives commands from and sends feedback to the TWS . There are two Digital Signal Processor (DSP) boards in the DMT control system. DSPA performs the forward kinematics, coordinate transformations, inverse kinematics, gravity compensation, and Force Moment Accommodation (FMA). DSPB performs the joint control and sends solenoid valve commands and servo commands to the manipulator controller. A Titan III controller is the low level manipulator controller. It directly controls the solenoid valve to activate and deactivate the manipulator. The OTCME controller controls all OTCME functions. It receives serial data commands from the Host computer and provides feedback.

    DMT Specification Table

    Name Values
    Discrete Manipulator Arm Reach Limit 72 inches
    Discrete Manipulator Arm Lift Capacity 240 lbs  mass
    Discrete Degrees of Freedom  6 dof
    Discrete Shoulder Yaw Arm Rotary Joint 135/-135 degrees
    Range Shoulder pitch Arm Rotary Joint 82/-27 degrees
    Range Elbow pitch Arm Rotary Joint 135/-135 degrees
    Range Wrist pitch Arm Rotary Joint 90/-90 degrees
    Range Wrist yaw Arm Rotary Joint 90/-90 degrees
    Range Wrist roll Arm Rotary Joint 180/-180 degrees
    Range Arm Joint Rotational Velocity 0.08-5 degrees/second
    Range Maximum Gripper Closing force 1000 lbs
    Discrete OTCM Rotary Drive Extend force 5-15 lbs
    Range OTCM Rotary Drive Retract force Up to 15 lbs
    Range OTCM Rotary Drive Torque Up to 50 ft-lb
    Range OTCM Lighting Maximum Illumination >275 lux
    Discrete OTCM Lighting Uniformity Ratio <3:1 uniformity ratio
    Discrete OTCM Camera Viewing Vertical Distance ~3.4" WFOV /
    ~3.3" NFOV field of view
    Discrete OTCM Camera Viewing Horizontal Distance ~2.5" WFOV /
    ~2.3" NFOV field of view

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