Patent ID: 7872733

Claim:
A tracking type laser interferometer that detects displacement of a retroreflector being an object to be measured by utilizing interference of a laser beam that defines a Z axis and is irradiated onto the retroreflector and reflected by the retroreflector in the returning direction, and carries out tracking by means of a two-axis turning mechanism using displacement in the position of an optical axis of the laser beam; wherein the two-axis turning mechanism comprises a combination of two one-axis turning mechanisms, being driven by a first and a second motor that rotate to define a Y axis and an X axis, respectively; the same tracking type laser interferometer, comprising; a light irradiator that emits a fan-shaped laser light with a center axis, wherein the fan-shaped laser light includes the optical axis of the laser beam and the light irradiator is disposed between the first and the second motor of the two-axis turning mechanism, and wherein the light irradiator is interlocked with turning movements of the two-axis turning mechanism such that the center axis of the fan-shaped laser light and the laser beam share a plane that is orthogonal to the X axis so as to be aligned with the Y axis a light receptor that has a specific positional relationship with the retroreflector or the light irradiator and receives the fan-shaped laser light; and a PC that instructs the two-axis turning mechanism to stop tracking the retroreflector when an amount of light from the laser beam detected by a quadruplicate divisional photo diode of the interferometer becomes 0, wherein the PC also stops measuring the displacement of the retroreflector and instructs the light irradiator to emit the fan-shaped laser light when the amount of light from the laser beam that is detected by the quadruplicate divisional photo diode becomes 0.