A swashplate is a device used in mechanical engineering to translate the motion of a rotating shaft into reciprocating motion. Conversely it can translate a reciprocating motion into a rotating one and can be used to replace the crankshaft in engine designs.
The swashplate consists of a disk attached to a shaft. If the disk is aligned squarely on the shaft then rotation of the shaft will turn the disk with it and no swashplate effect will be seen. Even a slight displacement of the disk from the square position, however , will cause the disk edge to appear to describe an oscillating linear path when viewed from a non-rotating point of view away from the shaft. The greater the angle of the plate to the shaft the more exaggerated the apparent linear motion will be. The apparent linear motion can be turned into an actual linear motion by having a follower, stationary with respect to the shaft but which presses against the top or bottom edge of the plate. The device has many similarities to the cam.
The swashplate engine uses a swashplate in place of a crankshaft to translate the motion of a piston into rotary motion. Internal combustion engines and Stirling engines have been built using this mechanism.
The axial piston pump drives a series of pistons aligned coaxially with a shaft through a swashplate to pump a fluid.
A helicopter swashplate is a pair of plates, one rotating and one fixed, that are centered on the main rotor shaft. The rotating plate is linked to the rotor head, and the fixed plate is linked to the operator controls. Displacement of the alignment of the fixed plate transferred to the rotating plate, where it becomes reciprocal motion of the rotor blade linkages. This type of pitch control, known as cyclic pitch, allows the helicopter rotor to provide selective lift in any direction.
Nutating flowmeters and pumps have similar motions to the wobble of a swashplate, but do not necessarilly transform the motion to a reciprocating motion at any time.