Patent ID: 8704129

Claim:
A positioning device for positioning a focusing or imaging lens to a working datum position at a predetermined distance relative to a first surface of a work piece in micro-machining by a laser beam, said laser beam being focused by the focusing or imaging lens onto the first surface of the work piece, said positioning device comprising a distance sensing device comprising a body member riding on a fluid cushion on the first surface of the work piece, said fluid cushion being established by a flow of fluid such as to maintain the body member at a predetermined distance from said first surface, wherein the body member is incorporated into a closed circuit gas system by which the body member is used to establish said flow of fluid to provide said fluid cushion, a heat transfer means is provided which is incorporated in the closed circuit gas system to provide for heat exchange between the heat transfer means and gas flowing around the closed circuit gas system for controlling a temperature of the surface of the work piece during the micro-machining and said positioning device being configured such that, in the event that the body member is displaced due to a variation in thickness of the work piece, any change in position of said body member, Perpendicular to the first surface, moves the focusing or imaging lens so as to cause a corresponding change in a current datum position of the focusing or imaging lens to restore the current datum position to the working datum position.