Intrinsic vs. Extrinsic Actuation (Proximal Actuator Placement)

Whether a motor sits right at the joint, or is placed near the torso and drives the joint remotely.

This pair of terms describes where the actuator (the motor) is placed. Intrinsic actuation means the motor is mounted right inside the part it drives — for example, motors packed into the palm and fingers of a dexterous hand. Extrinsic actuation means the motor sits somewhere closer to the torso, such as the forearm, and power is transmitted out to the fingers via tendons, linkages, or a timing belt, the same way most of the muscles that move a human hand actually sit in the forearm. Placing heavy motors closer to the body like this is called proximal placement, and it reduces the weight and rotational inertia at the far end, letting an arm or leg swing faster and more efficiently. The trade-off is a longer transmission chain, which brings friction, backlash, and tension-management problems. Both dexterous-hand design and humanoid leg and arm design have to weigh this trade-off.

ExampleThe Shadow Dexterous Hand keeps its motors in the forearm and pulls the fingers via tendons (extrinsic); the LEAP Hand mounts its servos directly at the finger joints (intrinsic).

Also called

Intrinsic / Extrinsic Actuation, Proximal Actuator Placement

Related

Dexterous Hand · Tendon-Driven Actuation · Hybrid-Drive Dexterous Hand · Reflected Inertia · Linkage Transmission · Timing Belt Drive

Sources

Shadow Dexterous Hand Series - Shadow Robot Company
LEAP Hand