Abstract: To provide a measuring apparatus of positions and postures of a machine for correcting positions and postures of an end effecter by means of an actuator, and an error correcting method for correcting errors thereof. At least three universal joint fixing members 2 are attached onto a base 1 that comprises a measuring reference; steel balls 3 are fixed to the respective universal joint fixing members 2 as universal joints; a steel ball 5 is fixed to a universal joint fixing member 9 as a universal joint; a universal joint fixing member 4 is attached to an object to be measured 7 that is supported by means of another member; and a measuring device 6 is attached to between the steel balls B3 and the steel ball 5. By using such a measuring apparatus, geometrical errors of a mechanism in a machine are estimated and corrected based on measured values on positions and postures of the end effecter.

Abstract: A universal joint having two or three degrees of freedom in rotation is disclosed which exhibits a small size, great rigidity and satisfactory accuracy. An end of a first node is connected to a base through a rolling bearing. A plurality of circular-arc guide bearings are disposed at positions opposite to the center line of the first node opposite to the base. A circular-arc rail formed around a cylindrical base is engaged to the circular-arc guide bearings. A shaft is disposed in a direction of the diameter which passes through the center of the circular arc of the circular-arc rail of the cylindrical base. A second node is, through a rolling bearing, joined to the shaft such that the center of rotation is positioned on the axis of rotation of the base.