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motors. Table 1 lists the torque/speed characteristics of various joints together with their gear ratios and motor current limits. The joints are all backdrive-able; and due to the lower gearbox efficiency when the input is driven by the output, the deceleration torques are controlled by implementing a lower value of current limit than in the forward drive condition. 

TABLE 1
JOINT CHARACTERISTICS
|Joint | Min Torque ft. lbs. | Max Speed rad/sec. | Gear Ratio | Current Limit Amps |
| --- | --- | --- | --- | --- |
| Shoulder | 772 | .04 | 1842 | 4.4 |
| Elbow | 528 | .056 | 1260 | 4.4 |
| Wrist | 231 | .083 | 740 | 3.3 |

The joint servo control system is implemented by joint electronics packages located strategically within the manipulator arm structure. Each electronics package consists of a Servo Power Amplifier (SPA) which produces a drive signal proportional to the demanded speed, attenuated by the tachometer feedback signal. The motor drive amplifier within the SPA uses the pulse width modulation technique to provide an average voltage to the relevant motor phase in response to signals received from the commutator. All six SPAs are identical and incorporate circuitry enabling motor current limits to be tailored to each joint via external cable connections. Included within the electronics package are two identical Joint Power Conditioners (JPCs) to convert the +28V Orbiter supply into regulated voltage levels for use by the electronic components, each JPC supplying three joints.
This mechanism for the end effector essentially consists of three steel snare cables mounted on a retracting carriage as shown in Figure 5. The snares close around the shaft of a compatible grapple fixture on the payload. This shaft is then drawn into the end effector to rigidize the interface. During capture and rigidization, the joint motors implement zero current limits to allow the arm to take out up to ±4 in. misalignment in each translational axis and ±15° misalignment in each rotational axis. The snare and retracting carriage mechanisms are both driven from a single three-phase brushless DC motor with

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Fig. 5 End Effector Configuration

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Fig. 6 End Effector Drive Train Configuration

isolation brake and clutch units in each mechanism as shown in Figure 6. The drive to the motor and actuation of the appropriate break and clutch are controlled by the End Effector Electronics unit (EEEU) located within the end effector.
The space environment dictates protection of the RMS electromechanical devices and electronics packages against both hot and cold conditions. For each manipulator arm, twelve strategically located thermistors allow the astronaut to monitor control temperatures during hot conditions and when necessary to initiate temperature control strategy; cold cases being automatically managed by thermostatically controlled heaters. The manipulator arm uses white paint and multi-layer insulation optimized to maintain an acceptable thermal balance.

MAN-MACHINE INTERFACE

The operator interface with the RMS is provided by the Translational (THC) and Rotational (RHC) Hand Controllers designed for the left and right handed operation respectively, and the RMS D&C panel augmented by the Orbiter CCTV monitors and GPC interactive displays. The manipulator arm has the option of incorporating two CCTV cameras; the one at the elbow mounted on a pan and tilt assembly facilitates payload stowage, and the other mounted on the wrist roll joint is used during payload capture tasks. 
The man-in-the-loop control system is designed for instinctive operation, minimizing fatigue in a zero - g environment. The astronaut commands end point rates using the two hand controllers without consciously controlling individual joints. Operations are conducted with the aid of out-of-window views or CCTV monitor scenes; in both cases, the control algorithms provide end point motions compatible with hand controller movements. During handling of payloads, the payload center is used as the point of resolution.
The end point position control is implemented by the astronaut executing preprogrammed auto trajectories via a single discrete command from the RMS D&C panel. The system includes the capability to pause at any point in the auto trajectory and subsequently continue to move along the preprogrammed path. The arm joints may also be driven on a joint-by-joint basis to facilitate certain operations, such as restowing the arm. 
The operator's visual information is augmented by selectable displays of end point coordinates, arm status parameters, and system health warnings at the D&C Panel.

DATA COMMUNICATION SYSTEM

The RMS operation in primary modes requires the 

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