An aerostatic spherical bearing has been developed for parallel kinematic machines. The design is based on a ball and socket configuration and is preloaded by permanent magnets arranged about the socket. High pressure air is injected through three orifices into the cavity between the ball and socket to produce a low friction, high accuracy interface. Joint accuracy is measured using a coordinate measurement machine and found to be 16 μm throughout the joint working range; this can be reduced to 11 μm through calibration of the joint error parameters. The flow properties are modeled using a Navier-Stokes flat-plate approximation and agree with measurements to 10% within the joint operating range.
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