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train is divided into low-speed and high-speed gear trains. The high-speed gear train consists of two reductions of spur gearing (G-1) and the low-speed gear train consists of two reductions of planetary type gears (G-2) (Figure 3). The G-2 gear ratio is the same for each joint, while the G-1 gear ratio varies from joint to joint. The encoder is an electro-optical device attached to the gearbox output of each joint to sense the angular position of the joint.

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Figure 3 RMS Gear Schematic

The shoulder joint assembly is depicted by Figure 4. The Shoulder Yaw joint is attached at its base to the Orbiter Manipulator Positioning Mechaism (designed and supplied by Rockwell International). The Shoulder Pitch joint is connected to the Shoulder Yaw joint by a transition piece. The Electronics Compartment is a tubular structure accommodating the Shoulder Yaw and Shoulder Pitch Servo Power Amplifiers, Shoulder and Elbow Joint Power Conditioner and Back-Up Drive Amplifier. The Shoulder Brace is designed to limit loading on

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Figure 4 Shoulder Joint Assembly

the Shoulder Pitch gear train during launch. The Shoulder Cable Harness is looped over the shoulder joints to allow for full shoulder yaw and pitch rotations.

Figure 5 shows the elbow joint assembly. The elbow joint is attached at its forward end to the Elbow Electronics Compartment via a transition piece, and at its aft end to the lower arm booms via another transition piece. The 'dog-leg' structure at the elbow, where the joint drive axis is offset by 0.1524m from the arm boom centreline, is designed to permit 160 degree travel of the elbow joint in a low weight/high stiffness design. The Elbow Electronics Dompartment is similar to, although smaller than, the Shoulder Electronics compartment. It accommodates the Elbow Servo Power Amplifier and has a retention fitting striker to attach to the Orbiter Latching Mechanism.

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Figure 5 Elbow Joint Assembly

The wrist joint assembly is shown in Figure 6. The Wrist Roll joint is designed to accommodate its required ±447 degree angular travel. The inner shaft of the joint in non-rotating; the outer shaft is mounted on a single row ball bearing and a roller bearing, and carries the G-2 output gear train. The Wrist Forward Electronics Compartment is the longest, whereas the Wrist Aft Electronics Compartment is the smallis in diameter and length, of all the others. The Wrist Pitch and Wrist Yaw Servo Power Amplifiers and the Wrist Joint Power Conditioner are located in the Wrist Forward Electronics Compartment. The Wrist Roll Servo Power Amplifier is located in the Wrist Aft Electronics Compartment.

Arm Booms

The arm boom assemblies comprise two thin-walled graphite-epoxy circular sections called the upper and lower arms. The end flanges are made of aluminum alloy and are bonded and bolted to graphite-epoxy sections. Internal stabilization rings are povided [[provided]] in both arm booms to maintain ovalization frequencies above 180 Hz. These rings also resist local shell buckling. Electrical cable harness assemblies are installed along the length of each arm. A bumper system is bonded to the graphite-epoxy booms to protect them against accidental damage in handling. Adjacent to the lower arm and elbow joint interface, a mounting provision exists for the installation of an optional CCTV camera and pan/tilt unit.

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