The upper and lower arm links of each arm have redundant actuation mechanism that act in concert to provide both payload capacity and safety in unstructured environments: a gravity compensation system and joint torque actuators.
The gravity compensation system, grounded in the base of the arm, passively floats the arm and payload throughout workspace of the arm. This reduces the ned for large joint motors in the arm segments and enables the use of backdrivable transmissions, which is imperative for human and robot safety in unstructured environments.
This gravity compensation system uses compression springs, highly-geared, small motors and steel cables mounted to the arm segments in an innovative kinematic arrangement that provides passive gravity compensation throughout all arm configurations with a one degree of freedom payload set point adjustment, similar in concept to other mechanisms in rehabilitation and human service robot designs.
The gravity compensation system uses a geometry-based principle to linearize the force required to counter the angle-dependent effect of gravity of a mass on a rotating joint, effectively allowing the arm to passively float throughout its workspace. The system achieves as effect similar to that of a mass counter balance without the additional inertia, utilizing springs instead of masses to store the required potential energy. Each arm counter balance mechanism has an additional actuated degree of freedom to adjust for the payload to be counter-balanced.
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