| 摘要 |
The invention concerns a focus detection circuit for an optical trigger probe. In figure 4 there is shown a probe having laser light source (4), a beam splitter (8) and a focussing lens system (10). The probe produces a light beam (6) focussed to a point at a distance d from the probe. Light reflected from the surface (12) is reflected from the beam splitter (8) onto two pairs of photo-sensitive detectors (16, 18). The signals from the two outer detectors are added as are the signals from the two inner detectors, and the two sums are subtracted to provide a focus error signal (23) which is passed to a zero crossing detector (25). When the light beam is focussed on the surface (12) the difference between the sums of the detector signals will be zero and the zero crossing detector circuit emits an output pulse (26). To eliminate false trigger signals when the probe is some distance from the workpiece and the reflected light is minimal, a validating signal (39) is generated by measuring the intensity of the reflected light at a detector (32), and this signal is passed to an AND gate (27) along with the output (26) which only transmits a trigger signal (28) when a validating signal and an output pulse are received simultaneously. |
