Prismatic Joint

A single-degree-of-freedom joint that lets two parts slide relative to each other along one straight axis, with no rotation.

The prismatic joint is one of the two most basic robot joints, alongside the revolute joint: it constrains two links to slide relative to each other along a shared axis only, with no rotation, giving 1 translational degree of freedom, and its joint variable is a displacement rather than an angle. In mechanism theory, it's classified as a lower pair, also called a sliding pair; in shorthand notation it's written P, as in RRP for two revolute joints plus a prismatic joint. It's usually driven by a linear actuator, such as a motor-and-ball-screw electric cylinder, a hydraulic cylinder, or a linear motor. The three axes of a Cartesian robot, a SCARA robot's vertical lift axis, a hybrid robot's lift column, and the opening and closing motion of a parallel-jaw two-finger gripper are all prismatic joints. In URDF, this joint type is written prismatic, with an axis direction and upper/lower travel limits specified.

ExampleA SCARA robot is typically two horizontal revolute joints plus one vertical prismatic joint: the revolute joints position the tool within a plane, and the prismatic joint plunges it down or lifts it up.

Also called

Slider Joint, Sliding Pair, P Joint

Related

Revolute Joint · Linear Actuator (Electric Cylinder) · Cartesian Robot · Selective Compliance Assembly Robot Arm · Kinematic Pair · Unified Robot Description Format

Sources

Wikipedia: Prismatic joint
Wikipedia: Linear actuator