Parallel manipulator

A parallel manipulator consists of a fixed "base" platform, connected to an end effector platform by means of a number of "legs". These legs often consist of an actuated prismatic joint, connected to the platforms through passive (i.e. not actuated) spherical and/or universal joints. Hence, the links feel only traction or compression, not bending, which increases their position accuracy and allows a lighter construction.The actuators for the prismatic joints can be placed in the motionless base platform, so that their mass does not have to be moved, which again makes the construction lighter.
Parallel manipulators have (in principle) high structural stiffness, since the end effector is supported in several places at the same time.All these features result in manipulators with a wide range of motion capability.Their major drawback is their limited workspace, because the legs can collide and, in addition, each leg has five passive joints that each have their own mechanical limits. Another drawback of Parallel Robots is that they lose stiffness in singular positions completely (The robot gains finite or infinite degrees of freedom which are uncontrolable; it becomes shaky or mobile). This means that the Jacobian matrix, which is the mapping from joint space to euclidian space, becomes singular (the rank decreases from six).

Applications

Major industrial applications of these devices are
* airplane simulators
* automobile simulators
* in work processes
* photonics / fiber alignment http://www.pb.izm.fhg.de/p2sa/020_Technologies/Optik/FundE_Faserjustage.htmlThey also become more popular
* in high speed, high-accuracy positioning with limited workspaces, such as in assembly of PCBs
* as micro manipulators mounted on the end effector of larger but slower serial manipulators
* as high speed/high-precision milling machines

ee also

* Serial Manipulator
* Robot kinematics