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[[image]]
Figure 6. Wrist Joint assembly
WRIST PITCH JOINT
WRIST YAW JOINT
WRIST AFT ELECTRONICS COMPARTMENT
TV/VIEWING LIGHT ENVELOPE
E/E ENVELOPE
WRIST ROLL JOINT
RETENTION FITTING STRIKER
WRIST FWD. ELECTRONICS COMPARTMENT
RETENTION FITTING

The SRMS arm design capability is summarized in Table 1 in terms of the joint output torques, the joint angular travels, etc.

Finite-Element Analysis

It is clear from the arm structural design that the arm mass and stiffness are not uniformly distributed along its length. Furthermore, the arm overall stiffness (hence the arm natural frequencies) varies with the arm geometry. In view of the complicated mass and stiffness distribution, finite-element analysis is considered appropriate to determine the arm overall stiffness, the arm natural frequencies and mode shapes and the structural loads induced by external disturbances. To this end, simple finite-element models have been developed as shown in Figures 7 and 9 and the commercially available finite-element program NASTRAN and STARDYNE have been used. It is to be kept in mind that in the following finite element study, the SRMS joints are considered to have brakes on (i.e. locked) and the SRMS servos are not operative since the SRMS control system cannot be simulated in NASTRAN and STARDYNE.

Figure 7 shows a finite-element model of the SRMS arm in stowed configuration, with the retention systems latched to the Cargo Bay. It consists of 64 nodes connected by beam elements whose masses are concentrated at the nodes. The

Table 1

Typical SRMS Arm Design Capability

[[7 column table]]

- | Shoulder Yaw | Shoulder Pitch | Elbow Pitch | Wrist Pitch | Wrist Yaw | Wrist Roll

Torque Output (Nm) | 1298. | 1298. | 888. | 389. | 389. | 389.

Gear Ratio | 1842. | 1843. | 1260. | 738. | 739. | 738.

Joint Travel (deg) - Mechanical Stop | +/- 180. | -2. 145. | -161.  2.4 | +/- 121.4 | +/- 121.3 | +/- 447.

Backlash (deg) | 0.057 | 0.086 | 0.12 | 0.12 | 0.12 | 0.12

Maximum joint rate - Unloaded arm (rad/sec) | 0.04 | 0.04 | 0.056 | 0.083 | 0.083 | 0.083

Maximum joint rate - arm loaded with baseline 14615 Kg payload (rad/sec) | 0.004 | 0.004 | 0.0056 | 0.0083 | 0.0083 | 0.0083
[[/table]]

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