Compliance

How readily a robot yields to an external force; numerically, the inverse of stiffness.

In mechanics, compliance is the inverse of stiffness: stiffness k is how much force it takes to produce a unit of deformation (N/m), and compliance 1/k is how much deformation a unit of force produces (m/N). In robotics, it describes whether an arm or joint gives way under an external push: a purely position-controlled arm is “stiff” and generates a large force if it hits a table or a person, while a compliant robot yields like a spring instead. Compliance can be passive, built into the mechanism's own elasticity — a series elastic actuator, the twisting flex of a harmonic reducer's flexspline, or the remote center compliance (RCC) device invented at Draper Laboratory in the 1970s — or active, where impedance control or admittance control simulates a virtual spring in software. Contact-rich tasks like peg-in-hole assembly, wiping a table, and working alongside people all depend on it.

ExampleDuring peg-in-hole assembly, a slight misalignment will jam a rigid arm's peg against the edge of the hole; adding an RCC device between the wrist and the gripper lets the peg, once it touches the hole's chamfered edge, get pushed sideways and slide itself into alignment automatically.

Related

Stiffness · Impedance Control · Admittance Control · Compliance Control · Series Elastic Actuator (SEA) · Peg-in-Hole Insertion

Sources

Stiffness - Wikipedia（Compliance 为刚度的倒数） (Chinese)
Remote center compliance - Wikipedia
Modern Robotics（Lynch & Park, 2017 预印本）第 11 章 Robot Control (Chinese)