Robot control
Impedance control
Definition
Impedance control shapes the dynamic relationship between a robot’s motion and the forces it exchanges with its environment. A common goal is for the robot to respond like a chosen mass, spring, and damper at a joint or end effector.
Also known as: Robot impedance control
Updated
Programming how the robot yields
Instead of insisting on an exact hand position during contact, an impedance controller can make position error produce a spring-like restoring force and motion produce damping. MIT's manipulation notes explain this using a virtual spring, mass, and damper. Setting only stiffness and damping is often called stiffness control, a subset of the broader idea.
For example, a robot inserting a peg can allow lateral motion when the peg touches the hole's edge. The desired response depends on the task: yielding in one direction can help alignment while stiffness in another direction maintains useful pressure.
Relation to force and admittance control
Force control targets a contact force directly. Impedance control specifies how force and displacement interact, so the resulting force also depends on the environment. A common torque-based implementation calculates joint commands from motion error.
Admittance control commonly implements the complementary arrangement: measured force drives a motion reference that another loop tracks. Both can aim for a similar external mechanical response.
Performance depends on the implementation
Selected stiffness is not a promise of safe contact. Sensor quality, actuator bandwidth, sampling, and transmission dynamics limit the behavior the robot can realize. MIT's discussion emphasizes these details and the role of passivity when reasoning about contact stability.
Sources
Related terms
Admittance control
Admittance control converts measured or estimated interaction forces into a desired robot motion through a specified dynamic model. An inner motion controller then follows that reference.
Force control
Force control regulates the force or wrench a robot applies to its environment. It may use a robot model, measured interaction forces, or both to produce joint commands that achieve a desired contact load.
Operational-space control
Operational-space control formulates a robot’s motion and force behavior in task coordinates, such as the position and orientation of its hand, while accounting for the robot’s dynamics. Secondary joint objectives can be coordinated with the primary task.
Torque control
Torque control regulates the turning effort delivered by an actuator or robot joint. It provides an actuation interface from which motion, force, and impedance controllers can produce the joint torques their tasks require.