Compliance Control

柔顺控制Common

Control methods that let a robot yield to some set degree instead of fighting back when it contacts the environment.

Compliance control is the umbrella term for methods that let a robot yield to external force by a designed amount when it contacts the environment. A purely position-controlled arm is very stiff: in a peg-in-hole task, even a small misalignment can jam the parts or crush them. Compliance comes in two forms. Passive compliance comes from the mechanical structure itself — such as a remote center compliance (RCC) device mounted on the wrist, or the spring inside a series elastic actuator — and needs no sensing or computation, but once its characteristics are built in, they can't be changed. Active compliance comes from measuring force or torque and feeding it back through control, commonly in the form of impedance control (making the robot behave like a mass-spring-damper system with tunable parameters), admittance control (correcting a position command after measuring force), or hybrid force/position control (controlling force along some directions and position along others), with parameters that can be adjusted per task. Hogan pointed out in 1985 that controlling position alone or force alone isn't enough — what should be controlled is the dynamic relationship between the two — and this is the theoretical basis for active compliance. Sanding, assembly, wiping, and human-robot collaboration all depend on it.

ExampleDuring peg-in-hole assembly, the robot arm keeps position control along the insertion direction but lowers the stiffness in the perpendicular directions: if the peg catches the edge of the hole, it gets pushed sideways and slides on into the hole, instead of jamming or crushing the part.

Also called: Compliant Control, Active Compliance Control
Related: Impedance Control · Admittance Control · Hybrid Force/Position Control · Compliance · Remote Center Compliance (RCC) Device · Series Elastic Actuator (SEA)
Sources: Wikipedia: Force control（passive / active compliance）
Wikipedia: Impedance control
Hogan, Impedance Control: An Approach to Manipulation, Part I (1985)