EP0022175B2 - Elektrophotographisches Kopiergerät mit variabler Vergrösserung des Originaldokuments im Verhältnis zur Kopie - Google Patents

Elektrophotographisches Kopiergerät mit variabler Vergrösserung des Originaldokuments im Verhältnis zur Kopie Download PDF

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Publication number
EP0022175B2
EP0022175B2 EP19800103074 EP80103074A EP0022175B2 EP 0022175 B2 EP0022175 B2 EP 0022175B2 EP 19800103074 EP19800103074 EP 19800103074 EP 80103074 A EP80103074 A EP 80103074A EP 0022175 B2 EP0022175 B2 EP 0022175B2
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EP
European Patent Office
Prior art keywords
platen
document
image
light
lens
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Expired
Application number
EP19800103074
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English (en)
French (fr)
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EP0022175A1 (de
EP0022175B1 (de
Inventor
Edwin Langford Libby
Randall Adrian Maddox
Douglas James Roberts
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International Business Machines Corp
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International Business Machines Corp
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Publication of EP0022175B2 publication Critical patent/EP0022175B2/de
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/04—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material
    • G03G15/041—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material with variable magnification

Definitions

  • the present invention is directed to electrophotographic copiers with variable original document to image size ratios.
  • One particularly desirable feature which has been introduced with commercial electrostatic copiers is the capability of varying the object image so that the copied image is varied in size with respect to the object image.
  • the advent of copiers capable of this function required the solution of several problems, i.e., those particularly caused by changes induced as a result of the changes in the optical configuration required to reduce the image. While the solution of these problems in a laboratory environment may be trivial, the constraints imposed by practical manufacture of these devices made the solution to these problems more difficult.
  • the commercial device had to exhibit the same image sharpness and consistency of image intensity for all ratios of document and image sizes with desirably little or no increase in equipment size, cost or maintenance difficulty.
  • the copied image produced by a copier is uniform in intensity, and the achievement of this requires careful design. Even if one assumed uniform object illumination (which is usually not actually the case due to size limitations), the presence of a lens in the optical path results in image intensity reduction for that portion of the image passed off the lens or optical centre line, i.e., so-called COS4 losses. In the prior art, solutions to this difficulty have been achieved by shaping the object illumination so as to compensate for the image intensity falloff, and similar shaping has been used to compensate for otherwise uneven object illumination.
  • the centre line is not changed, i.e., the objects are centre-referenced; obviously, this causes no additional difficulties.
  • the objects to be copied are corner referenced, and as a result, as the object to be copied increases in size, and the ratio is correspondingly changed, the centre line moves or changes in position relative to centre line of a smaller object to be copied.
  • This "corner-referencing" serves to increase the difficulties associated with cos4 losses and drum curvature distortions, since more of the image to be reproduced falls in the edge areas whose intensity would be reduced absent some special attention.
  • U.S. Patent Specification No. 4,057,342 This discloses a copying system with a pair of apertures located in the optical path and capable of operating in a base mode and a reduction mode.
  • the patentee recognized that additional reduction modes could be employed and, while image intensity variations would occur, the exposure system would provide a degree of correction.
  • the patentee also indicates, however, that a slit appropriate for a base mode or non-reduction mode of operation would probably not be adequate for reduction mode of operation and correspondingly, a slit provided for uniform illumination in a reduction mode of operation would not provide proper operation in a base of non-reduction mode or in a different reduction mode.
  • an electrophotographic copier comprising an exposure station including a platen for supporting an original document to be copied, an illumination source adapted to produce a line of light and to direct it towards the platen to scan a document thereon, an optical system adapted to direct a line of light reflected from a document on the platen on to an imaging element, said optical system including a lens for focussing the reflected light on to the imaging element and mounted for movement relative to the imaging element to effect variation of the ratio of original document to image size on the imaging element between one to one and one to a predetermined value less than one, and a single mask positioned adjacent the platen and having a fixed stop aperture in the form of an elongate slit therein to receive and pass said reflected light to said optical system, said slit having a length substantially equal to that of the reflected line of light, characterised in that said slit has a width profile defined by a predetermined width at a reference position and widths at points along the aperture calculated, relative to
  • FIG. 1 A preferred embodiment of the invention is illustrated in the accompanying drawings, in connection with an essentially continuously variable reducing copying machine which can be of the type shown in Figure 1, and in more detail in U.K. Patent Specificatin No. 152518.
  • a transparent platen or document support 50 is arranged to support a document to be copied. Illumination for the copying process is provided by the lamp 40, and reflectors 41, 44 are provided to reflect the illumination to impinge on the support 50.
  • the source 40, the elliptical reflector 41 and the dichroic reflector 44 are arranged so that the illumination on the platen describes a focused line of light 45. Light reflected by the object to be copied, is directed to a mirror 46, and from thence to mirrors 47-48.
  • Illumination reflected from the mirror 48 passes through a lens 9, is reflected by a further mirror 49, passes through a slit 51 in a wall of the machine and impinges on the surface of a drum 13.
  • the image produced by the line of light 45 is reproduced on the surface of the drum 13 as a line of light 45'.
  • a first carriage supporting the light source 40, reflector 41 and mirrors 44, 46 and a second carriage supporting the mirrors 47-48 are moved parallel to the longer dimension of the platen 50. As the carriages are so moved, the line of light 45 scans the document to be copied and produces a corresponding image thereon the surface of the drum 13, as that drum rotates.
  • a latent image of the object to be copied is produced on the drum 13, and this latent image is developed and the developed image later transferred to the copy paper so that the image which the object bears is reproduced on the copy paper.
  • the electrophotographic copying machine shown in Figure 1 achieves a unique reduction ratio, and thus, the machine is capable of a range of reduction ratios or reduction modes within the range of movement of the lens 9. In a preferred embodiment of the invention, the machine is capable of reducing modes in the range 1:1 to 1:0.647.
  • Figure 2 illustrates the illumination source including lamp 40, reflectors 41 and 44, in relation to the platen 50 and an image-bearing object 50' whose image is desired to be copied.
  • the illumination from the illumination source is reflected by the document in accordance with the image on the document 50', and is coupled through the lens 9 to be focussed on the surface of the drum 13. If we assume that the distance along the optical centre line of the lens 9 from the object to the lens is equal to the distance from the lens to the surface of the drum 13, then the image at the drum 13 will be of the same size as is the image on the object 50', i.e., no reduction will be produced. With most practical illumination sources, the distribution of object light intensity is non-uniform. A typical profile is reproduced by the curve 52 in Figure 2.
  • 1/S' + 1/S 1/f
  • S' mS
  • m the magnification or reduction mode
  • f the focal length of the lens.
  • S' f(m + 1) and therefore, the irradiance H equals in units of watts per square centimetre, indicating that the irradiance varies in accordance with reduction mode m.
  • a mask 25, acting as a field stop is located to limit the reflection from the object 50' to a width h o .
  • exposure energy density (joules per cm 2 ) is the quantity of interest, and that is merely the irradiance multiplied by the exposure time.
  • the exposure time is the height h, of the illuminated image area divided by the drum tangential velocity v.
  • h i mh o .
  • E the exposure energy density
  • the energy exposure density can be written as
  • the exposure energy density ratio E l /E 2 is equal to For the parameter of m equal to 0.647, this expression indicates a change in energy exposure density of about 5%, which is an acceptable variation.
  • the preceding discussion is applicable only along the centre line, and does not treat edge effects or reduction in intensity off the optical centre line.
  • the image illumination E is equal to TBWcos 4 ⁇ ), where T is a function of the lens (and any mirror) transmittance and B is the object brightness, and ⁇ is the angle between the image position and the lens centre line, and W (omega) is the solid angle subtended by the lens aperture to a given point in the image.
  • K K A ⁇ K III , where K is the brightness coefficient which is variable, K A is the aperture width ratio and K III , is the object illumination intensity ratio.
  • E i TWK A K III B o cos 4 ⁇ .
  • Figure 4 is the object illumination profile for a practical illumination package. It can be seen that, for example, the illumination changes by a factor or more than two from the reference edge across the object width.
  • Table I reproduced below illustrates object illumination as a function of image positions or distance from the reference edge, with the first two columns of Table I merely reproducing the information shown in Figure 4.
  • the third column illustrates relative illumination, Kill, normalized to the reference edge.
  • the next column corrects for cos4 losses by multiplying the factor Kill by cos4 of the appropriate angle, depending upon image position.
  • the factor K A is the reciprocal of that product.
  • the last column shows the aperture width which is obtained by starting with an aperture width, for example, 10 m.m., and dividing that quantity by the associated factor K A to determine a given factor, in this example, 9.017, that is used to multiply all K A factors to obtain related widths along the aperture.
  • Figure 5 shows a field stop mask including an aperture having a configuration, from the reference edge up to 200 m.m. therefrom, which conforms to the width dimensions shown in Table 1.
  • the chosen starting aperture width is selected to provide a consistent field angle for all ratios of the object to image size to be employed as explained above with reference to Figure 3.
  • the K A values correct for cos 4 ⁇ losses when the lens remains on a constant axis. If, however, the lens axis is changed for different reduction modes, then the cos 4 ⁇ values will also change somewhat.
  • the illumination package with the Figure 4 profile it was found that the calculated aperture size from the reference edge up to 200 m.m. provided substantially even illumination throughout the reduction range. However, for 225 m.m. from the reference edge and greater, the calculated sizes had to be determined empirically to obtain good results throughout the reduction range.
  • the mask In the machine shown in Figure 1, the mask must be mounted to avoid the illuminating rays from source 40, via mirror 44, towards the document glass, and to intercept the reflected light passing between the document glass and mirror 46. It must, therefore, be mounted for movement with mirrors 44 and 46 in a direction along the document glass.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Exposure Or Original Feeding In Electrophotography (AREA)
  • Light Sources And Details Of Projection-Printing Devices (AREA)

Claims (2)

1. Elektrophotographisches Kopiergerät mit einer Belichtungsstation, in der eine Auflagefläche (50) für das zu kopierende Originaldokument vorgesehen ist, mit einer Belichtungsquelle (40, 41) die ein Lichtband erzeugt und es auf die Auflagefläche richtet, um das dort aufliegende Dokument abzutasten, mit einem optischen System, das ein von dem Dokument auf der Auflagefläche reflektiertes Lichtband auf ein Abbildungselement (13) richtet und eine Linse (9) zum Fokussieren des reflektierten Lichts auf das abbildende Element enthält, die relativ dazu beweglich montiert ist, so daß das Verhältnis des Originaldokuments zur Bildgröße auf dem abbildenden Element zwischen Eins und einem vorbestimmten Wert kleiner Eins geändert werden kann und mit einer einzelnen Maske (Fig. 5), die benachbart zur Auflagefläche angebracht ist und eine feste Blende in Form eines länglichen Schlitzes aufweist, um das reflektierte Licht aufzunehmen und an das optische System weiterzuleiten, wobei der Schlitz eine Länge aufweist, die im wesentlichen gleich der des reflektierten Lichtbandes ist, dadurch gekennzeichnet, daß der Schlitz in Breitenrichtung ein Profil aufweist, das durch eine vorbestimmte Breite bei einer Bezugsposition und Breiten an Punkten längs der Öffnung bestimmt ist, die relativ zur vorbestimmten Breite so berechnet sind, daß an diesen Punkten eine Kompensation der Intensitätsänderungen der Lichtquelle und der Kosinus4- Verluste der Linse beim Eins-zu-Eins-Verhältnis erfolgt und daß die vorbestimmte Breite so gewählt ist, daß die Kompensation bei allen Verhältnissen wirksam ist.
2. Kopiergerät nach Anspruch 1 mit Vorrichtungen zur seitlichen Ausrichtung eines Dokuments auf der Auflagefläche, dadurch gekennzeichnet, daß die Bezugsposition ein Ende des Schlitzes darstellt, das der ausgerichteten Seite eines Dokuments auf der Auflagefläche entspricht.
EP19800103074 1979-06-21 1980-06-03 Elektrophotographisches Kopiergerät mit variabler Vergrösserung des Originaldokuments im Verhältnis zur Kopie Expired EP0022175B2 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US5084979A 1979-06-21 1979-06-21
US50849 1979-06-21

Publications (3)

Publication Number Publication Date
EP0022175A1 EP0022175A1 (de) 1981-01-14
EP0022175B1 EP0022175B1 (de) 1983-04-13
EP0022175B2 true EP0022175B2 (de) 1985-10-09

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EP19800103074 Expired EP0022175B2 (de) 1979-06-21 1980-06-03 Elektrophotographisches Kopiergerät mit variabler Vergrösserung des Originaldokuments im Verhältnis zur Kopie

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EP (1) EP0022175B2 (de)
DE (1) DE3062716D1 (de)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5964810A (ja) * 1982-10-05 1984-04-12 Canon Inc 変倍投影装置

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1097439A (fr) * 1954-03-29 1955-07-05 Verrerie Scient Perfectionnements aux machines à reproduire les plans
GB1079231A (en) * 1963-10-14 1967-08-16 Hall Harding Ltd Improvements in or relating to photographic reproducing apparatus
FR2099191A5 (de) * 1970-06-23 1972-03-10 Ibm
US3720465A (en) * 1970-11-20 1973-03-13 Ibm Electrophotographic apparatus with synchronized document illumination and scanning feature
DE2553665C2 (de) * 1975-11-28 1984-10-18 Agfa-Gevaert Ag, 5090 Leverkusen Bildfeldblende in einem Kopiergerät
US4057342A (en) * 1976-05-27 1977-11-08 Xerox Corporation Illumination slit for a reproducing machine
GB1525218A (en) * 1976-09-07 1978-09-20 Ibm Electrophotographic copying machine
JPS5455821U (de) * 1977-09-27 1979-04-18

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Publication number Publication date
EP0022175A1 (de) 1981-01-14
EP0022175B1 (de) 1983-04-13
DE3062716D1 (en) 1983-05-19

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