Focus detection system with zero crossing detection for use in optical measuring systems
US4952816A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | May 22, 1989 |
| Grant date | Aug 28, 1990 |
| Priority date | — |
| Expiry date | May 22, 2009 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG02B7/32
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
The invention concerns a focus detection circuit for an optical trigger probe. The probe has a laser light source, a beam splitter and a focusing lens system. The probe produces a light beam focused to a point at a distance d from the probe. Light reflected from the surface is reflected from the beam splitter onto two pairs of photosensitive detectors. 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 which is passed to a zero crossing detector. When the light beam is focused on the surface, the difference between the sums of the detector signals will be zero and the zero crossing detector circuit emits an output pulse. To eliminate false trigger signals when the probe is some distance from the workpiece and the reflected light is minimal, a validating signal is generated by measuring the intensity of the relected light at a detector. The validating signal so produced, based upon the reflected light, is passed to an AND gate along with the output pulse. The AND gate only transmits a trigger signal when a validating signal and an output pulse are present at the same time…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.