Focusing error detection apparatus using a first and second knife edge at different positions
US5231280A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Sep 27, 1991 |
| Grant date | Jul 27, 1993 |
| Priority date | — |
| Expiry date | Sep 27, 2011 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B7/0916
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A focusing error detection apparatus for detecting a focusing error of a converging light beam on a surface of a recording medium in an image forming system. The apparatus includes a pair of mutually opposed first and second knife edges placed adjacent to the recording medium, a photodetector for outputting a signal indicative of a quantity of light received by the photodetector, a differentiation circuit for outputting a signal proportional to a derivative of the signal inpuuted from the photodetector with respect to time, a detection circuit having a first peak voltage part outputting a first signal indicative of a first peak voltage and a second peak voltage part outputting a second signal indicative of a second peak voltage, and a comparison circuit for comparing the first peak voltage with the second peak voltage, so that a deviation of the converging light beam from an intended position on the surface of the recording medium is detected on the basis of a difference between the first and second peak voltages.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.