CA1165158A - Compact laser beam monitor - Google Patents
Compact laser beam monitorInfo
- Publication number
- CA1165158A CA1165158A CA000385852A CA385852A CA1165158A CA 1165158 A CA1165158 A CA 1165158A CA 000385852 A CA000385852 A CA 000385852A CA 385852 A CA385852 A CA 385852A CA 1165158 A CA1165158 A CA 1165158A
- Authority
- CA
- Canada
- Prior art keywords
- grating
- retro
- scanner
- laser
- monitor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
ABSTRACT OF THE DISCLOSURE
A laser recording device comprising a laser beam monitor (LBM) which can be utilized to generate a pulse train the pulses of which can be correlated with instantaneous beam position. Alternatively, the pulse train may be used as a controlling "clock" for the output shift registers of a CCD array. The LBM is characterized by the provision of a retro-reflective light pulse generator which allows a pulse detector of the monitor to be positioned adjacent the focus of another component of the recording device, for example, a ploygon scanner whereby the LBM is compact.
A laser recording device comprising a laser beam monitor (LBM) which can be utilized to generate a pulse train the pulses of which can be correlated with instantaneous beam position. Alternatively, the pulse train may be used as a controlling "clock" for the output shift registers of a CCD array. The LBM is characterized by the provision of a retro-reflective light pulse generator which allows a pulse detector of the monitor to be positioned adjacent the focus of another component of the recording device, for example, a ploygon scanner whereby the LBM is compact.
Description
~ ~65~
BACKGROUND OF THE IN~ENIION
This invention relates to xerographic reproducing apparatus utilizing a laser recording system responsive to an electronic digital computer and more particularly to a laser beam monitor therefor.
The interfacing of electronic digital computers in xerographic reprod-5 ucing apparatus for converting binary coded intelligence to graphic symbols on hardcopy output is highly desirable since by this means it is possible to produce xerographic reproducing apparatus which can generate copies ~t higher rates thanheretofore possible. TQ accomplish the foregoing it is necessary to synchronize a scanning array with the changing position of a non-uniformly scanned laser beam.To synchronize a scanning array with the changing position of a non-uniformly scanned laser beam, a standard practice is to place a binary grating structure (e.g. a Ronchi ruling~ at or very near the beam focus to intercept a portion of the beam to thereby produce an optical pulse train. The pulse train correlates with the beam positions during scanning and therefore serves as a laser 15 beam monitor (LBM). The detected pulses from an LBM can be used to control a pulse-train driven scanner, for example, a CCD array. The output shift registers of the CCD array can be clocked by the detected pulses produced by the LBM.
How the optical pulses from the grating are collected greatly affects the overall size of the LBM. Heretofore, the detector that collects the pulses has 20 been placed at a beam focus which occupies a position different from all other foci of the optical path traversed by the light beam generated by the laser. ~ one such devise of the prior art as illustated in U.S. Patent 3,898,627 the beam generated by a laser is split by a conventional beam splitter into two beams, one of which is used to discharge a uniformly charged photoreceptor drum in accordance with intel-Z5 ligence contained in a computer used to modulate said one beam. The other beamwhich is used to monitor the position of said one beam is directed through a Ronchi ruling or grating having an elliptical reflector dispose there behind such that said other beam is intercepted by a photodetector pasitioned at one focus of the elliptical reflector which focus is spatially different from all other foci occupied 30 by other components of the recording apparatus. Thus, as can be seen the position of the detector is such that it does not lend itself to a compact arrangement ofelements.
., '~
BACKGROUND OF THE IN~ENIION
This invention relates to xerographic reproducing apparatus utilizing a laser recording system responsive to an electronic digital computer and more particularly to a laser beam monitor therefor.
The interfacing of electronic digital computers in xerographic reprod-5 ucing apparatus for converting binary coded intelligence to graphic symbols on hardcopy output is highly desirable since by this means it is possible to produce xerographic reproducing apparatus which can generate copies ~t higher rates thanheretofore possible. TQ accomplish the foregoing it is necessary to synchronize a scanning array with the changing position of a non-uniformly scanned laser beam.To synchronize a scanning array with the changing position of a non-uniformly scanned laser beam, a standard practice is to place a binary grating structure (e.g. a Ronchi ruling~ at or very near the beam focus to intercept a portion of the beam to thereby produce an optical pulse train. The pulse train correlates with the beam positions during scanning and therefore serves as a laser 15 beam monitor (LBM). The detected pulses from an LBM can be used to control a pulse-train driven scanner, for example, a CCD array. The output shift registers of the CCD array can be clocked by the detected pulses produced by the LBM.
How the optical pulses from the grating are collected greatly affects the overall size of the LBM. Heretofore, the detector that collects the pulses has 20 been placed at a beam focus which occupies a position different from all other foci of the optical path traversed by the light beam generated by the laser. ~ one such devise of the prior art as illustated in U.S. Patent 3,898,627 the beam generated by a laser is split by a conventional beam splitter into two beams, one of which is used to discharge a uniformly charged photoreceptor drum in accordance with intel-Z5 ligence contained in a computer used to modulate said one beam. The other beamwhich is used to monitor the position of said one beam is directed through a Ronchi ruling or grating having an elliptical reflector dispose there behind such that said other beam is intercepted by a photodetector pasitioned at one focus of the elliptical reflector which focus is spatially different from all other foci occupied 30 by other components of the recording apparatus. Thus, as can be seen the position of the detector is such that it does not lend itself to a compact arrangement ofelements.
., '~
2~
BRIEF SUMMARY OF THE INVENTION
Thus, in accordance with the present teachings, an improvement is provided in a laser recording apparatus which includes means ~or scanning a modulated light beam relative to a uniformly charged photosensitive surface for selectively discharging the surface in accordace with intelligence to be recorded and further including a laser beam monitor including a photodetector. The improvement which is provided comprises a compact laser monitor which comprises a retro-reflective grating for generating a plurality of light pulses which are reflected in the direction of the photodetector for collection thereby.
Accordingly, the present invention incorporates a retro-reflective pulse generator ~i.e. a grating or Ronchi ruling withretro-reflective properties~ as part of a laser beam monitor which allows photodetector to be positioned at or adjacent a common focus with a scanning reflector such as a polygon scanner or an oscillating galvo-mirror. The retro-reflective ruling is positioned such that the light pulses there~y are returned essentially along the instante-ous scan direction. If all scan eman~te from a fixed aperture location, then a fixed detector essent:ially at ~his same location, will generate the desired electrical pulse train. Hence the use of a retro~reflective ruling permits t:he laser beam monitor to be arranged compactly.
To make an ordinary transmis~;ion-ty~e Ronchi ruling act in a retro-reflective mode, a retro-reflective strip (e.g. 3 M's Scotchlite type) ~7as placed on the back side of the ruling. The scotchlite comprises a glass beaded reflector construction. Slight divergence of the reflected light, due to the small size and imper-fections of the reflectors, facilitates detection. Alternati~el~r~
a gxating with alternate slits composed of small retro-reflective cells (corner-reflectors~ can be used. Having the cells ~rom a surface relief structure allo~s inexpensive mass production of the grating through replication.
'' * Trademark -~ 2a Another form of relief that is retro reflective in one plane, .say, the scanning plane, would be reflecting, right-angle grooves (dispersed in alternate grating slits) parallel to the slits. The right-angle grooves comprise a pair of mirrors dis-posed at right-angles to each other. This form has the advantage that a small tilt of the grating about its longitudinal axis permits the reflected pulses to be collected conveniently just above or below the fixed scanning aperture. The "opaque" slits or lines in the grating may be either clear or absorbing, for both cases will yield pulsing of the retro-reflected light as the beam traverses the grating.
..
s~a DETAILED DESCRIPTION OF T~IE DRAWINGS
Fig. 1 is a schematic illustration of a recording device utilizing a laser beam scanner and a compact laser beam monitor therefor;
Fig. 2 is a schematic illustPation of a modified embodiment of the recording device shown in Fig. l; and Fig 3 is a schematic illustration of another embodiment of the recording device shown in Fig.l.
DETAILED DESCRIPTION OF THE PREFERED
EMBODIMENTS OF THE INVENTION
~n accordance with the invention as illustrated in Fig. 1, a controlled light beam is generated from a source of high energy coherent light such as a continuous mode laser 12. The beam 10 is projected along an optical path which includes a beam spliter 14. A beam 16 emerging from the beam spliter 14 travels through a light modulator 18 of the type well known in the art. The modulator 18responds to the binary states 1 or 0 of electrical information bits transmitted on an input line Z0. The modulator emits the beam 16 along either of two closely adjacent but slightly different output paths 22 and 24. When the beam is emittedalong the output path 22 it eventually travels past a knife edge 26 and strikes a photoconductive surface 28 at a spot 30. The surface 28 is herein disclosed in the form of a drum. The beam discharges the surface which had previously been uniformly charged in accordance with well known techniques used in xerography.
When the beam is emitted along the path 24 it strikes the knife edge 26 and therefore~ does not effect the discharging of the photosensitive surface at thatparticular spot.
As will be appreciated, when the uniformly charged photosensive surface 28 has been discharged in accordance with information to be printed, toner material presented to the drum in accordance with well known xerographic techniques, will adhere to the areas that have not been discharged thereby 3Q rendering the latent image visible.
The beam 16 impinges on a scan mirror 3Z after passing through lens system 34 and is thereby directed along a line corresponding to the longitudinalaxis of the photosensive drum 28. Drive means 36 serves to rotate the drum Z8 sothat when a subsequent scan takes place another line of latent information is "4 ~1~5~
formed on the drum. The scan mirror 3Z comprises a galvo-mirror which is oscillated by a motor 38 which is synchronised with the rotational speed of the drum 28. The beam splitter 14 produces a second beam 40 which is directed by - means of a reflecting mirror 42 through a lens system 44 so that it too impinges on 5 the scan mirror 32 but at a difEerent angle than the beam 16. A second reflecting mirror 46 is positioned to intercept the beam 40 and reflect it in the direction of a retro-reflective grating 48. The grating 48 comprises retro-reflective cells forming relief structures disposed at right-angles with respect to each other toform what is commonly referred to as grooved reflectoPs which are indicated by 10 the reference character 50. The grooved reflectors are disposed in alternate slits in the grating intermediate opaque slits or lines 52.
The beam 40 is reflected by the grating 48 back to the mirror 46 such that the mirror redirects the beam generally back in the direction of the grating but at an angle that enables the beam to impinge on a photodetector 54 which is 15 adjacent the scan mirror 32. Suitable tilting of the grating 48 with respect to the mirror 46 permits positioning of the detector 54 above the scanning mirror 3Z. It will appreciated that the grading could also be tilted such that the detector 54could be positioned below the mirror 32.
As shown in Fig. 2, a modified form of the invention comprises a Z number of components which are similar to those found in the embodiment of Fig.
1. Accordingly, like components will be referred to in the drawings with the same reference characters.
The primary differences of the embodiment of Fig. 2 reside in the scanner, detector and the pulse generator. The galvo mirror 32 of Fig. 1 is Z5 replaced by a polygon scanner 60 which is rotated by means of a motor and drive indicated schematically by reference character 6Z. The pulse generating device or grating 48 is replaced by a corner reflector type grating 64 and the detector 54 is replaced by a ring detector 66.
As shown, one facet 70 of the polygon scanner is employed to generate 30 a clock signal from the corner reflector type grating, retro-reflected light being sampled by the ring-shaped detector 66 located adjacent the facet 70. Another facet 68 is used to reflect the light beam 16 toward the photorecepter 28 in a horizontal scanning motion.
Reference is now made to Fig. 3 wherein there is disclosed another 35 modified form of the invention. Components which are common with Fig. 1 and Zhave the same reference characters. In this embodiment, the galvo-mirror 70 ~16515~
which could also be a polygon scanner uses one surface thereof for the writing beam (i.e. beam that discharges the photoreceptor~ and the opposite surface for the clock signal beam. The grating 48 comprises a grooved type grating the same as the grating of the embodiment of Fig. 1. The grooved type grating allows 5 collection of the light beam above or below the galvo-mirror sirrlply by tilting thereof at a very small angle.
BRIEF SUMMARY OF THE INVENTION
Thus, in accordance with the present teachings, an improvement is provided in a laser recording apparatus which includes means ~or scanning a modulated light beam relative to a uniformly charged photosensitive surface for selectively discharging the surface in accordace with intelligence to be recorded and further including a laser beam monitor including a photodetector. The improvement which is provided comprises a compact laser monitor which comprises a retro-reflective grating for generating a plurality of light pulses which are reflected in the direction of the photodetector for collection thereby.
Accordingly, the present invention incorporates a retro-reflective pulse generator ~i.e. a grating or Ronchi ruling withretro-reflective properties~ as part of a laser beam monitor which allows photodetector to be positioned at or adjacent a common focus with a scanning reflector such as a polygon scanner or an oscillating galvo-mirror. The retro-reflective ruling is positioned such that the light pulses there~y are returned essentially along the instante-ous scan direction. If all scan eman~te from a fixed aperture location, then a fixed detector essent:ially at ~his same location, will generate the desired electrical pulse train. Hence the use of a retro~reflective ruling permits t:he laser beam monitor to be arranged compactly.
To make an ordinary transmis~;ion-ty~e Ronchi ruling act in a retro-reflective mode, a retro-reflective strip (e.g. 3 M's Scotchlite type) ~7as placed on the back side of the ruling. The scotchlite comprises a glass beaded reflector construction. Slight divergence of the reflected light, due to the small size and imper-fections of the reflectors, facilitates detection. Alternati~el~r~
a gxating with alternate slits composed of small retro-reflective cells (corner-reflectors~ can be used. Having the cells ~rom a surface relief structure allo~s inexpensive mass production of the grating through replication.
'' * Trademark -~ 2a Another form of relief that is retro reflective in one plane, .say, the scanning plane, would be reflecting, right-angle grooves (dispersed in alternate grating slits) parallel to the slits. The right-angle grooves comprise a pair of mirrors dis-posed at right-angles to each other. This form has the advantage that a small tilt of the grating about its longitudinal axis permits the reflected pulses to be collected conveniently just above or below the fixed scanning aperture. The "opaque" slits or lines in the grating may be either clear or absorbing, for both cases will yield pulsing of the retro-reflected light as the beam traverses the grating.
..
s~a DETAILED DESCRIPTION OF T~IE DRAWINGS
Fig. 1 is a schematic illustration of a recording device utilizing a laser beam scanner and a compact laser beam monitor therefor;
Fig. 2 is a schematic illustPation of a modified embodiment of the recording device shown in Fig. l; and Fig 3 is a schematic illustration of another embodiment of the recording device shown in Fig.l.
DETAILED DESCRIPTION OF THE PREFERED
EMBODIMENTS OF THE INVENTION
~n accordance with the invention as illustrated in Fig. 1, a controlled light beam is generated from a source of high energy coherent light such as a continuous mode laser 12. The beam 10 is projected along an optical path which includes a beam spliter 14. A beam 16 emerging from the beam spliter 14 travels through a light modulator 18 of the type well known in the art. The modulator 18responds to the binary states 1 or 0 of electrical information bits transmitted on an input line Z0. The modulator emits the beam 16 along either of two closely adjacent but slightly different output paths 22 and 24. When the beam is emittedalong the output path 22 it eventually travels past a knife edge 26 and strikes a photoconductive surface 28 at a spot 30. The surface 28 is herein disclosed in the form of a drum. The beam discharges the surface which had previously been uniformly charged in accordance with well known techniques used in xerography.
When the beam is emitted along the path 24 it strikes the knife edge 26 and therefore~ does not effect the discharging of the photosensitive surface at thatparticular spot.
As will be appreciated, when the uniformly charged photosensive surface 28 has been discharged in accordance with information to be printed, toner material presented to the drum in accordance with well known xerographic techniques, will adhere to the areas that have not been discharged thereby 3Q rendering the latent image visible.
The beam 16 impinges on a scan mirror 3Z after passing through lens system 34 and is thereby directed along a line corresponding to the longitudinalaxis of the photosensive drum 28. Drive means 36 serves to rotate the drum Z8 sothat when a subsequent scan takes place another line of latent information is "4 ~1~5~
formed on the drum. The scan mirror 3Z comprises a galvo-mirror which is oscillated by a motor 38 which is synchronised with the rotational speed of the drum 28. The beam splitter 14 produces a second beam 40 which is directed by - means of a reflecting mirror 42 through a lens system 44 so that it too impinges on 5 the scan mirror 32 but at a difEerent angle than the beam 16. A second reflecting mirror 46 is positioned to intercept the beam 40 and reflect it in the direction of a retro-reflective grating 48. The grating 48 comprises retro-reflective cells forming relief structures disposed at right-angles with respect to each other toform what is commonly referred to as grooved reflectoPs which are indicated by 10 the reference character 50. The grooved reflectors are disposed in alternate slits in the grating intermediate opaque slits or lines 52.
The beam 40 is reflected by the grating 48 back to the mirror 46 such that the mirror redirects the beam generally back in the direction of the grating but at an angle that enables the beam to impinge on a photodetector 54 which is 15 adjacent the scan mirror 32. Suitable tilting of the grating 48 with respect to the mirror 46 permits positioning of the detector 54 above the scanning mirror 3Z. It will appreciated that the grading could also be tilted such that the detector 54could be positioned below the mirror 32.
As shown in Fig. 2, a modified form of the invention comprises a Z number of components which are similar to those found in the embodiment of Fig.
1. Accordingly, like components will be referred to in the drawings with the same reference characters.
The primary differences of the embodiment of Fig. 2 reside in the scanner, detector and the pulse generator. The galvo mirror 32 of Fig. 1 is Z5 replaced by a polygon scanner 60 which is rotated by means of a motor and drive indicated schematically by reference character 6Z. The pulse generating device or grating 48 is replaced by a corner reflector type grating 64 and the detector 54 is replaced by a ring detector 66.
As shown, one facet 70 of the polygon scanner is employed to generate 30 a clock signal from the corner reflector type grating, retro-reflected light being sampled by the ring-shaped detector 66 located adjacent the facet 70. Another facet 68 is used to reflect the light beam 16 toward the photorecepter 28 in a horizontal scanning motion.
Reference is now made to Fig. 3 wherein there is disclosed another 35 modified form of the invention. Components which are common with Fig. 1 and Zhave the same reference characters. In this embodiment, the galvo-mirror 70 ~16515~
which could also be a polygon scanner uses one surface thereof for the writing beam (i.e. beam that discharges the photoreceptor~ and the opposite surface for the clock signal beam. The grating 48 comprises a grooved type grating the same as the grating of the embodiment of Fig. 1. The grooved type grating allows 5 collection of the light beam above or below the galvo-mirror sirrlply by tilting thereof at a very small angle.
Claims (5)
1. In a laser recording apparatus including means for scanning a modulated light beam relative to a uniformly charged photosensive surface for selectively discharging said surface in accordance with intelligence to be recorded and further including a laser beam monitor including a photo-detector, the improvement comprising:
a compact laser monitor comprising a retro-reflective grating for generating a plurality of light pulses which are reflected in the direction of said photodetector for collection thereby.
a compact laser monitor comprising a retro-reflective grating for generating a plurality of light pulses which are reflected in the direction of said photodetector for collection thereby.
2. In a laser recording apparatus including a scanner for scanning a light modulated light beam relative to a uniformly charged photosensitive surface for selectively discharging said surface in accordance for intelligence to be scanned, the improvement comprising:
a compact laser monitor comprising a retro-reflective grating for generating a plurality of light pulses; and a photodetector for collecting said light pulses, said photo-detector being positioned adjacent said scanner whereby light beams re-flected from said scanner are retro-reflected by said grating back along essentially the same path as the beam is reflected from said scanner.
a compact laser monitor comprising a retro-reflective grating for generating a plurality of light pulses; and a photodetector for collecting said light pulses, said photo-detector being positioned adjacent said scanner whereby light beams re-flected from said scanner are retro-reflected by said grating back along essentially the same path as the beam is reflected from said scanner.
3. Apparatus according the claims 1 or 2 wherein said grating comprises glass beaded reflectors disposed in the spaces intermediate lines of said grating.
4. Apparatus according to claims 1 or 2 where in said grating comprises corner reflectors disposed in the spaces intermediate lines of said grating.
5. Apparatus according to claims 1 or 2 wherein said grating comprises grooved reflectors disposed in spaces intermediate lines of said grating.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US20632280A | 1980-11-12 | 1980-11-12 | |
| US206,322 | 1980-11-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1165158A true CA1165158A (en) | 1984-04-10 |
Family
ID=22765860
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000385852A Expired CA1165158A (en) | 1980-11-12 | 1981-09-14 | Compact laser beam monitor |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS57112766A (en) |
| CA (1) | CA1165158A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0564178A1 (en) * | 1992-04-01 | 1993-10-06 | The Regents Of The University Of California | Scanning confocal microscope |
-
1981
- 1981-09-14 CA CA000385852A patent/CA1165158A/en not_active Expired
- 1981-11-04 JP JP17777881A patent/JPS57112766A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0564178A1 (en) * | 1992-04-01 | 1993-10-06 | The Regents Of The University Of California | Scanning confocal microscope |
| US5296703A (en) * | 1992-04-01 | 1994-03-22 | The Regents Of The University Of California | Scanning confocal microscope using fluorescence detection |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS57112766A (en) | 1982-07-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |