Length measuring apparatus based on the dual laser beam interferometer principle

Claim 1

Length measuring apparatus with position sensor means comprising: a laser light beam source comprising a laser diode for the production of simultaneously laterally, transversely and longitudinally monomodal laser light with a coherence length which corresponds at least to the length to be measured, a beam splitter diposed in the optical axis of said laser light beam source for dividing the light beam into a measuring light beam and a reference light beam aligned at an angle thereto, a movable mirror connected to the position sensor means and reflecting the measuring light beam with transverse offset parallel to the optical axis, additional at least partially reflecting optical means for reflecting at least a portion of the reference light beam to provide an interference range of the beam paths of the reflected portion of the reference light beam and the reflected measuring light beam, at least one photodetector lying in said interference range of the beam paths, evaluating circuit means coupled to said at least one photodetector and having counting means for counting the light/dark sequences including direction recognition, said laser diode having a system for the stabilization of its operating temperature, the length measuring apparatus comprising a current-stabilized, controllable power source and said laser diode being connected to said current-stabilized, controllable power source, the length measuring apparatus including an additional photodetector, an analog-to-digital converter, a microcomputer, a digital-to-analog converter, said laser diode for intensity measurement being associated with said additional photodetector whose output signal is connected through said analog-to-digital converter to said microcomputer in which a comparison can be made with a given standard intensity value to provide an output signal, and the output signal of said microcomputer corresponding to said output signal of said additional photodetector being fed as a correction signal through said digital-to-analog converter to said power source, the length measuring apparatus including sensors for temperature, pressure and humidity in the beam path and providing output signals, and the output signals of the sensors for temperature, pressure and humidity being coupled by said analog-to-digital converter to said microcomputer in which a compensation operation is performed for the magnitudes of temperature, pressure and humidity.