Parallel Mechanism

A mechanism connecting a base to an end platform through several kinematic chains at once — stiff and fast, but with a small workspace.

A parallel mechanism has its end platform connected to the base by two or more independent kinematic chains at the same time, forming closed loops; its counterpart, a serial mechanism, has just one chain running from base to tip — an ordinary 6-axis arm is serial. Classic examples include the Stewart platform, which holds up a platform on six extendable struts (used in flight simulators), and the Delta robot — nicknamed the “spider robot” — invented in the early 1980s by Reymond Clavel's team at EPFL (the Swiss Federal Institute of Technology in Lausanne), widely used for high-speed pick-and-place sorting of food and electronics. A parallel mechanism's motors are mostly mounted on the base, keeping the moving parts light, and the load is shared across several chains, giving high stiffness, high precision, and high speed; the tradeoffs are a small workspace, hard-to-solve forward kinematics, and extra singular configurations that a serial arm doesn't have. Many humanoid robots also use a parallel structure for their ankle joints.

ExampleA Delta robot's three actively driven arms each carry a parallelogram linkage, so the end platform can only translate, never rotate; according to Wikipedia, it can complete up to about 300 pick-and-place cycles per minute.

Also called

Parallel Manipulator, Parallel Robot

Related

Serial Mechanism · Delta Robot · Parallel Ankle Mechanism · Kinematic Chain · Singular Configuration (Kinematic Singularity) · Four-Bar Linkage

Sources

Wikipedia: Parallel manipulator
Wikipedia: Delta robot