The principal components of our laser tracking system are:The optical reference to be fixed close to the tool of the machine-tool.A laser interferometer to measure the distance to the reference reflector.A deflection unit with two motorized mirrors to bend the laser beam towards the reference.A Position Sensitive Detector (PSD) for estimating the tracking error.A Personal Computer (PC) for commanding the mirrors to track the reference and to estimate its position.A converter for translating in real-time the position estimations into a format that the Machine-Tool can understand.2.2. The Optical ReferenceThe optical reference used to track the machine-tool position is a retroreflector. It returns back the incoming laser beam through a path that must be coaxial or parallel to the incident one.

This reference is a totally passive component, i.e., it does not need any cabling for power supply.Solid-glass and hollow corner cube retro-reflectors were initially used, but their performance was not ideal. Considering we operate at vertex incidence, i.e., the system tries to keep the laser beam pointing on the vertex or center of the retro-reflector, then after a reflection it generates undesirable star-like laser beam cross-sections. In addition, solid-glass reflectors suffered from a secondary reflection on the first facet of the glass. We finally used a cat-eye reflector, which has a smooth spherical reflection surface and therefore provides an unaltered laser beam cross-section which results beneficial for the interferometer measurements.

2.3.

The Interferometer with Vertex Incidence for Range EstimationThe ranging measurement system is based AV-951 on the interferometric Michelson-Morley principle. The design and components have been selected to operate with vertex incidence on the retro-reflector. This is necessary to unambiguously determine the position Dacomitinib of the retro-reflector. As a consequence the optical arrangement considers a coaxial beam propagation.Figure 3 shows the implemented optical arrangement. An helium-neon (632.8 nm) laser source (1) with a long coherent length (Limtek LS 10.3) is used as emitter having a 45-degrees polarized beam directed to a polarizing cube (2) which splits the beam in two orthogonally polarized beams: the transmission beam in the reference arm with a vertical state of polarization, and the reflected beam in the measurement arm with a horizontal state of polarization. As it is known, a reflecting element for each arm is necessary in a Michelson-Morley interferometer.