Abstract: A concentricity evaluating system has a stage supported by a hydrostatic bearing in at least one of radial and thrust directions. The angle of rotation of the stage is detected by a rotation angle detector. On the stage a hollow cylindrical member is fixed coaxially. Onto the upper end face of the hollow cylindrical member or into the hole thereof a light beam is applied from a light emitting means, whereby a clear image of the profile of the hole is formed. The image thus formed is enlarged by an optical system. The light beam passing through the optical system reaches a photodiode array which is positioned across a part of the enlarged image. The hollow cylindrical member is rotated, and a displacement meter is detected how the circumference of the hollow cylindrical member varies as the member rotates. Data from the displacement meter, photodiode array and the rotation angle detector are fed to an interface and processed.

Abstract: A precise feeding table apparatus which comprises an XY-table assembly including a Y-table and an X-table mounted thereon. Electric motors for supplying a driving force to feed the X- and Y-tables are set on a base of the table apparatus. A driving shaft of the electric motor for the Y-table takes the form of a ball screw to cause a guide carriage supported by the driving shaft to make a minute reciprocation. A moment derived from the reciprocation of the guide carraige is not directly transmitted to the Y-table. A connection rod moving jointly with the guide carriage is connected to an output shaft fitted to the Y-table by means of a coupling including a fluid bearing. The fluid bearing supports the connecting rod in contactless relationship, thereby preventing the vibrations and moments of the connecting rod from being transmitted to the output shaft.

Abstract: A bearing device comprising a rotatable shaft, a spherical body fixed to said shaft, a bearing body having a spherical concave bearing face corresponding to said spherical body, and a radial bearing for supporting said shaft at a position spaced apart from said bearing body.