Hardware

4-Bar Linkage

A 4-bar linkage is a closed-chain mechanism of four rigid links joined by four revolute joints with one link fixed as ground, the simplest one-degree-of-freedom closed kinematic chain. By choosing link lengths, designers shape the coupler curve and mechanical advantage, which is why four-bars appear in gripper jaws, robot leg designs that keep actuator mass proximal, prosthetic knees, and countless latching and toggle mechanisms.

Why it matters for physical AI

Clever passive kinematics can replace actuators, sensors, and control effort outright; linkage design is a reminder that in physical AI, intelligence embedded in mechanism trades directly against intelligence required in software.