The swashplate changes the pilot's linear cyclic (and often collective) control inputs into rotary blade pitch angle changes in the main rotor. It is the position of the swashplate that determines which direction the rotor disk will move in.
The swashplate is usually made up of two halves. The top half rotates with the rotor (usually pulled around by the washout and washout guide), while the bottom half does not (aligned with the helicopter body by the anti-rotation bracket). Due to the use of a spherical bearing in the center, the swashplate is free to tilt in response to control inputs, and transfers those inputs through the linkages to the rotor blades.
In mechanical terms, the lower (non-rotating) part of the swashplate forms a cam, and the upper rotating part its cam follower. This is slightly unusual, as it is normally the cam that is thought of as rotating, and its follower that is held stationary.
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