How do impedance control and admittance control differ in rehabilitation robotics?

• A. Impedance control modulates resistive dynamics; admittance control modulates movement in response to external forces; both adjust assistive force.
• B. Impedance control modulates movement in response to external forces; admittance control modulates resistive dynamics; both adjust assistive force.
• C. Both methods modulate only resistive damping; not movement or force.
• D. Admittance control modifies device hardware; impedance control modifies software only.

Answer: (A)

Impedance control and admittance control differ in what the controller uses to shape the interaction and how it generates motion or force. Impedance control modulates resistive dynamics—the robot is programmed to present a desired impedance (stiffness, damping, and inertia) so that when a user moves, the forces the device exerts follow that impedance, shaping how much it resists or assists motion. Admittance control, by contrast, modulates movement in response to external forces—the controller measures the user’s applied force and then drives motion according to a defined admittance, so the user’s push or pull directly determines the robot’s movement. Both approaches adjust the assistive force during therapy, but impedance control controls force via a specified motion–force relationship, while admittance control controls motion via the user’s force.