Exposure apparatus

Abstract

 An electro-photographic machine has a light source 21 and a reflector 22 to illuminate a line on an original to be copied and carried on a movable table 9. Light is absorbed by text on the original and reflected by non-text background through an optical lens 5 and a slit between stops 6 onto the photosensitive surface 7 of a revolving drum. The surface is previously charged at 23 and subsequently toner 25 is applied to adhere to the non-exposed areas. This is then transferred to plain paper by a transfer charger 28 and fixed in rollers 30. The invention replaces the original by a reflective type optical modulation element 10 having a liquid crystal material between a common electrode and a series of separately energisable electrodes, so that electric signals applied to the electrodes change the reflection characteristics of the liquid crystal to reflect light through the lens 5 or not, in accordance with the desired images for reproduction.

Description

[0001] The present invention relates to apparatus for exposing photosensitive material.

[0002] In a copying machine comprising a light source to light an original to be copied and means to optically direct light reflected from the original onto photosensitive material, the present invention provides an additional function of exposure control using electric signals by installing a reflection type optical modulation element where the original would be located.

[0003] In the prior art example of an electro-­photographic copying machine shown in the Japanese Patent Laid-Open No. 238078/1986, the addition of the exposure control function using electric signals to an exposing apparatus which exposes photo-sensitive material to light reflected from originals to be copied, required a section including a light source, a light converging means and an optical modulation element, in addition to the section that uses reflected light from the original.

[0004] Such apparatus is large in size and complicated in structure because, in addition to a section to expose photosensitive material to light reflected from the original, it has an exposure control section that uses electric signals and which consists of a light source, a light converging means and an optical modulation element. This drawback inevitably leads to other disadvantages of higher cost and larger power consumption.

[0005] To overcome the above drawbacks, this invention adds an exposure control function to the existing function of exposing the photosensitive material to reflected light from the original by simply adding to where the original is located a reflection type optical modulation element that has its reflectivity changed by electric signals.

[0006] According to the invention, therefore, apparatus for exposing photosensitive material in a copying machine comprising a light source to light an original to be copied and means to optically direct light reflected from the original onto the photosensitive material, is characterised by comprising a reflective type optical modulation element installed where the original would be, and means to change by electric signals the reflection characteristics of the element so as to control the exposure of the photosensitive material.

[0007] The invention is further characterised in that the reflective type optical modulation element is a liquid crystal device having transparent electrodes between which liquid crystal material is sandwiched, and to which electric signals are supplied by drive means.

[0008] In this case,the apparatus may be characterised in that there is a common electrode and a multiplicity of spaced individually energisable electrodes in a line across the path of light from the light source.

[0009] Alternatively, the invention may be characterised in that there is a common electrode and a multiplicity of spaced individually energisable electrodes in three lines across the path of light from the light source, the lines being provided with different colour filters, respectively.

[0010] The reflective type optical element may be a piezo-electric device in which piezo-electric material is sandwiched between a common electrode and a multiplicity of reflective plates which are individually energisable.

[0011] How the invention may be carried into effect is hereinafter particularly described with reference to the accompanying drawings in which:-

Figures 1a and 1b show diagrammatically the principles involved in exposing photosensitive material to reflected light modulated in accordance with text on an original;

Figures 2a and 2b show diagrammatically the principles involved in the use of a reflection type optical modulation element with liquid crystal material in apparatus according to the invention;

Figures 3a and 3b show diagrammatically the principles involved in the use of a reflection type optical modulation element with piezo-electric device in apparatus according to the invention;

Figure 4 is a diagrammatic cross-section of an electro-photographic copying machine incorporating the present invention,

Figures 5a and 5b are facing views in opposite directions of the electrodes in the liquid crystal device used in the machine of Figure 4; and

Figure 6 is a diagrammatic cross-section of a photographic copying machine incorporating the invention.

[0012] An explanation of the principles behind the present invention will now be given, referring to Figures 1a, 1b, 2a, 2b, 3a and 3c. In known reprographic apparatus in which an original 3 to be copied passes over a rotating drum 7 of photosensitive material, there is an exposure apparatus for selectively exposing the photosensitive material to light reflected from the original 3. Incident light 1 coming from a light source is absorbed where it strikes an optically dense part 4 (such as ink) (Figure 1a) of the original 3 to be copied (such as text). On the other hand, when the incident light 1 strikes a part whose optical density is low (such as the background of the text on original 3), light is reflected and scattered in general and a part of the scattered light 2 (Figure 1b) passes through an optical lens 5 and through a slit formed between two stops 6 to expose the photosensitive material 7.

[0013] In accordance with the present invention, such an original is replaced by a reflection type optical modulation element 10 (Figures 2a and 2b), the reflection characteristics of which are changed by electric signals applied to transparent electrodes 13 and 14 between which liquid crystal material 15 is located. The electrodes 13 and 14 are mounted on spaced transparent substrates 11 and 12, respectively with a reflective plate 16 on the outer face of the substrate 11. A drive circuit 17 is connectible across the electrodes 13 and 14 to provide signals. When the electric signal is switched off (Figure 2a), the incident light 1 either passes through the element 10 or is reflected by the plate 16 without reaching the photosensitive material 7. When the electric signal is on (Figure 2b), the liquid crystal material 15 takes up such a disposition that the incident light 1 is scatter reflected before reaching the plate 16 and part of the scattered light 2 passes through the optical lens 5 and slit to expose the photosensitive material 7.

[0014] In another example of the invention, the reflection type optical modulation element 10 (Figure 3a) takes the form of a thin plate 19, piezo-electric device 18 and an electrode 20, the drive circuit 17 being connectible across the thin plate 19 and electrode 20 to provide electric signals to the piezo-electric device 18. In this case, when the electric signal is off (Figure 3a) incident light is reflected by the plate 19 as light 2 to pass through the optical lens 5 and slit to expose the photosensitive material 7. When the electric signal is on (Figure 3b) the piezo-electric device 18 deforms and changes the attitude of the plate 19 so that the direction in which the reflected light 2 travels is so changed that it will not pass through the lens 5 and exposure of the photosensitive material 7 is stopped. By appropriate application and non-application of the electric signals, exposure of the photosensitive material 7 is controlled.

[0015] In a specific embodiment of the invention (Figure 4) an electrophotographic copying machine is used as a device to expose the photosensitive material to the reflected light from an original (such as text), and a scatter type liquid crystal device is used as the reflection type optical modulation element to be installed where an original would otherwise be located.

[0016] The electrophotographic copying machine includes an original support table 9 linearly movable over the top of the machine in correspondence with the rotation of the drum 7 of photosensitive material. A light source 21 has a reflective element 22 by which light is incident upon an original carried by the table 9 in a thin band transverse to the direction of movement of the table. The incident light is then reflected or absorbed or reflected (as described above in reference to Figures 1a and 1b) through the lens 5 and the slit between stops 6 onto the photosensitive material of the drum 7. Just prior to such exposure position, the surface of the drum has been charged by a charger 23, and thereafter toner 25 is applied to the surface of the drum. Toner adheres to the surface of the drum at locations determined by the exposure or non-exposure of the drum, and is transferred to paper by a transfer charger 28. Thereafter, the surface of the drum is cleaned by a cleaner 31 before being charged again by the charger 23. Paper is fed by supply rollers 27 from a cassette 26 to between the drum 7 and the transfer charger 28 and thereafter onto a conveyor belt 29. Thereafter, the paper passes through fixing rollers 30 which fix the adhering toner to the surface of the paper. The paper is finally discharged by rollers 27.

[0017] In accordance with the invention, a reflection type optical modulation element 10 is located in a stationary position to be able to reflect incident light from the source 21 onto the lens 5. Such position may necessitate the removal of the table 9, or the disablement of its movement. The optical modulation element 10 takes the form of a liquid crystal device, similar to that shown in Figures 2a and 2b. The device consists of two opposed and spaced transparent substrates 11 and 12 on which are formed transparent electrodes 13 and 14. The transparent electrodes 13 (Figure 5a) on the substrate 11 consist of separately energisable electrodes, of about 0.1mm width to give 240 electrodes per inch (25.4mm). On the substrate 12 (Figure 5b) is a single common transparent electrode 14. A liquid crystal material 15 which is located between the electrodes and which has a dynamic dispersion effect on light is sealed between the substrates. The transparent electrodes on the two opposing substrates are thus formed into a pattern consisting of a line of dots at a density of 240 dots per inch (25.4mm). The liquid crystal section corresponding to each dot is separately electrically connected to the drive circuit 17 through the transparent electrodes 13 and the common electrode 14.

[0018] The electric voltage signals applied to the individual transparent electrodes 13 are selected to give the exposure to the photosensitive material which is required to achieve the copy desired, which may, for example, be a page of text and/or drawings. Such signals may conveniently be derived from data stored in a computer and delivered to the electrodes in accordance with instructions therefrom. When the voltage of the signal applied to an electrode 13 is below threshold value (OFF), the incident light 1 (Figure 2a) passes through the layer of liquid crystal material 15, which is transparent and is then reflected by the reflective plate 16 provided on the other side of the transparent substrate 11. In this case, the reflected light 2 does not reach the optical lens 5, which may be a self-convergent rod lens array, so that the photosensitive material on the drum 7 is not exposed. When the voltage of the signal applied to a transparent electrode 13 is above the threshold value (ON), the layer of liquid crystal material 15 (Figure 2b)goes into a dynamically dispersing state and scatters the incident light 1. A part of the reflected and scattered light 2 enters the optical lens 5 passing through the slit between the stops 6 and exposing the photosensitive material on the drum 7. By making the liquid crystal layer a few micrometers thick or less and setting the applied voltage at 10V to 20V, the liquid crystal can be driven to display the dynamic dispersion effect within a time of the order of milliseconds, thereby permitting the exposure of one text page of A4 size to be performed in a few seconds.

[0019] It is also possible to use a phase transfer type liquid crystal as the crystal liquid material 15 to be sealed in the crystal liquid device. This type of crystal liquid layer can also be switched between transparent state and scatter state by controlling the applied voltage. The use of the transparent and the scatter states of a strong dielectric crystal liquid enables exposure switching in a few 1 hundred microseconds.

[0020] The same effect can be also obtained if a piezo-electric device is used as the reflection type optical modulation element 10. The piezo-electric device uses the deformation in the crystal structure produced by voltage application to generate deflecting motion of the device. In such a device, illustrated in Figures 3a and 3b, the individual devices are about 0.1mm in width and there are 240 per inch (25.4mm). The electrode 20 is common and the individual plates 19 are separately driven from the drive circuit 17. Each thin plate 19 is of metal and doubles as an electrode and a mirror, having one side facing the incident light finished to form a mirror which, by the deflecting motion of the piezo-electric device 18, changes the path of the reflected light 2, as shown in Figures 2a, and 2b, thereby performing the exposure switching. The drive frequency suited to the piezo-electric device is several kHz and switching is performed in a few hundred microseconds.

[0021] With the embodiment of Figure 4, colour reproduction is possible. In this case, an image of a first of three colours is reproduced upon the photosensitive material on the drum 7 and toner of the first colour is applied to the drum surface and transferred to paper. The toned paper is passed through the machine or another one again, and an image of the second colour is reproduced upon the photosensitive material on the drum and toner of the second colour applied to be transferred to the paper. The same steps are repeated with an image of the third colour and toner of the third colour, so that images of the three colours are superimposed to reproduce the full colour image.

[0022] In the embodiment illustrated in Figure 4, images are reproduced by exposure of photosensitive material and subsequent application of toner, followed by transfer of toner and fixing on paper or other medium. In a second embodiment (Figure 6), images are reproduced by exposure of photosensitive material in the form of sensitized paper or negative film, so that xerography is not involved.

[0023] In the second embodiment (Figure 6) a reflection type liquid crystal device is used as the reflection type optical modulation element 10, a fluorescent lamp as the light source 21 to light the reflection type liquid crystal device, and a self-convergent rod lens array as the optical lens 5, to radiate the reflected light from the reflection type liquid crystal device onto photosensitive paper 32, which is passed through the machine by supply rollers 27 and a conveyor belt 29. The photosensitive paper 32 passes below the slit between the stops 6, where it is exposed to the reflected light radiated by the lens 5.

[0024] The second embodiment is particularly suitable for colour reproduction, in which case the two transparent electrodes on the two opposing transparent substrates of the liquid crystal device are combined to form a pattern consisting of three lines of dots at a density of 240 dots per inch (25.4mm). The three lines of dots are provided with cyan (C), magenta (M) and yellow (Y) filters, respectively. Colour photosensitive paper 32 is used and in synchronism with the movement of the photosensitive paper, the three lines of dots are switched between a transparent and scatter state. A colour image is obtained by controlling the switching between the transparent and the scatter states of the dots in the lines and the photosensitive paper is passed through the machine only once. Subsequent to exposure, the paper is developed in a developer 24.

[0025] As photosensitive material, a negative film and a sensitized paper on which direct writing is possibly permitted and commonly used for photography, are satisfactory.

[0026] Experiments show that it is possible to use as a colour copying machine, an apparatus in which an original on a movable table 9 replaces the reflection type liquid crystal device 10 and in which the movement of the original is synchronized with that of the photosensitive paper.

[0027] The present invention enables the addition of an exposure control function using electric signals simply by adding a reflection type optical modulation element to an apparatus which exposes photosensitive material to reflected light from an original to be copied. Further, as explained in the embodiments, the reflection type optical modulation element may be formed of the reflection type liquid crystal device or piezo-electric device and hence is small and light, and also consumes only a small amount of power. Because the light source and the light converging means are shared by the two functions, modification to existing apparatus when implementing this invention is not necessary or, if so, is only minor with small extra cost.

[0028] The invention allows a copying machine to be used as the printer of a computer and word processor, or as the output device of a facsimile machine. Not only does this widen the range of use of a copying machine, but also make it possible with small extra cost to integrate various kinds of equipment into a multi-purpose one.

Claims

1. Apparatus for exposing photosensitive material (7,32) in a copying machine comprising a light source (21) to light an original (3) to be copied and means (5,6) to optically direct light reflected from the original (3) onto the photosensitive material (7,32), characterised by comprising a reflective type optical modulation element (10) installed where the original (3) would be, and means to change by electric signals the reflection characteristics of the element (10) so as to control the exposure of the photosensitive material (7,32).

2. Apparatus as claimed in claim 1, characterised in that the reflective type optical modulation element (10) is a liquid crystal device having transparent electrodes (13,14) between which liquid crystal material (15) is sandwiched, and to which electric signals are supplied by drive means (17).

3. Apparatus as claimed in claim 2 characterised in that there is a common electrode (14) and a multiplicity of spaced individually energisable electrodes (13) in a line across the path of light from the light source (21).

4. Apparatus as claimed in claim 2, characterised in that there is a common electrode (14) and a multiplicity of spaced individually energisable electrodes (13) in three lines across the path of light from the light source (21), the lines being provided with different colour filters, respectively.

5. Apparatus as claimed in claim 1, characterised in that the reflective type optical modulation element (10) is a piezo-electric device in which piezo-electric material (18) is sandwiched between a common electrode (20) and a multiplicity of reflective plates (19) which are individually energisable.

6. An exposing apparatus having a copying function and consisting of a light source (21) to light originals (3) to be copied and a means (5) to optically direct the reflected light from the original onto photosensitive material (7,32), further comprising a reflection type optical modulation element (10) installed where the original (3) is located in order to provide an additional function of controlling the exposure of the photosensitive material (7,32), the reflection type optical modulation element (10) being adapted to have its reflection characteristic changed by electric signals.

Drawing