Image Number 10 for United States Patent #6943894.
A laser distance measuring system has a simple optical structure with which abnormal return light can be removed. The laser distance measuring system includes a laser light source that generates at least two interferable light beams with different frequencies on a same optical axis, a parallel reflecting portion that includes a reflecting surface, which is included in an object that moves along a measurement axis and that is arranged on the measurement axis, and returns an incident light beam in a direction opposite that at which it is incident and at a certain spacing from and parallel to the incident light beam, and an interferometer that is positioned between the laser light source and the parallel reflecting portion and that is arranged on the measurement axis. The optical axes of the light beams are displaced parallel to one another from the measurement axis and one of the light beams is passed through the interferometer and guided to the parallel reflecting portion. The interferometer has a flat reflector that maintains a light path of the light beam that is returned by the parallel reflecting portion.