JP2001255594A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of obtaining a full color print of higher image quality by moving a photoreceptor at a fixed speed relatively with a shutter array. SOLUTION: A pixel array constituted of plural pixels are arranged in a direction orthogonal to a direction of moving relatively with the photoreceptor, and the photoreceptor is repeatedly exposed at every line while continuously and relatively moving the pixel array with reference to the photoreceptor, and the exposure area of the optional line of the photoreceptor and the exposure area of another adjacent line are exposed in the overlaid state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color printer, and more particularly to an image forming apparatus having a shutter array for optically writing a color image on a photosensitive member.

[0002]

2. Description of the Related Art A liquid crystal shutter array will be described below as an example of a shutter array. The liquid crystal shutter array turns on a plurality of liquid crystal pixels arranged in one or more rows,
This is a device that is turned off to control the amount of light transmission for each pixel. A method of performing full-color printing of a color image on photosensitive paper using the liquid crystal shutter array is described in, for example, Japanese Patent Application Laid-Open No. 62-134624. This method uses a black and white liquid crystal shutter array 11 as shown in FIG.
And red, green and blue color filters 10r, 10g, 1
A full-color print is obtained on the photosensitive paper 13 by combining a rotating plate having 0b and rotated by a motor or the like, and an exposure device 9 positioned above the rotating plate and irradiating white light.

However, in this method, when the exposure light of each color is to be overlaid on one pixel, the relative movement of the photosensitive paper 13 and the liquid crystal shutter array 11 is stopped for each color, and the opening / closing timing of the pixels of the liquid crystal shutter array is stopped. Therefore, a precise moving mechanism including the rotation period of the rotating body including the color filter is required, and it is difficult to obtain a full-color image with high accuracy. In addition, the intermittent movement stop time causes a reduction in print speed.

[0004] Further, as a liquid crystal color printer for obtaining a full color print on photosensitive paper by eliminating the above problems,
There is a method described in JP-A-2-169271. This method uses three types of monochromatic light sources 9r, 9g, 9 that emit red, green, and blue light, as shown in FIG.
b, a three-color separation liquid crystal shutter array 19 is arranged between the photosensitive paper 13 and the light source, and light transmitted therethrough is passed through the liquid crystal shutter array 11 again to form an image on the photosensitive paper 13. Met. FIG. 9B shows the incident path of light of each color and the state of light irradiation on the photosensitive paper 13 at this time. The light incident path differs depending on the color of the incident light, and the focus position on the photosensitive paper 13 changes depending on each color. While moving the photosensitive paper 13 without interruption, light of three colors from the liquid crystal shutter array 11 is superimposed to obtain a full-color image on the photosensitive paper 13.

[0005]

However, in this method, the use of three types of monochromatic light sources leads to an increase in the number of components and an increase in the size of the color printing apparatus. 3
Due to the dual use of liquid crystal shutters for color separation and image formation, the amount of exposure on photosensitive paper has been reduced, which has caused the cost of the exposure equipment to increase or the printing speed to slow down. . Further, in order to superimpose light precisely, adjustment of incident angles of light in three directions becomes a problem. This is because, unlike the case where exposure light is incident on the liquid crystal shutter array from the vertical direction, light with an angle enters from the surface of the liquid crystal shutter array and the transmitted light is exposed on photosensitive paper at an angle. In this case, the change in the refractive index due to the temperature of each of the liquid crystal elements such as glass and liquid crystal elements cannot be ignored. This causes color shift and defocus on the image.

The present invention solves the above-mentioned problems, and precisely shifts the red light, green light, and blue light while moving the photosensitive member and the shutter array at a relatively constant speed, thereby shortening the color shift in a shorter time. It is an object of the present invention to provide an image forming apparatus capable of obtaining a high-quality full-color print without defocus.

[0007]

In order to achieve the above object, the present invention is characterized in that the image forming apparatus has the following configuration. The shutter array and the photoreceptor move relative to each other, and the shutter array includes a pixel row composed of a plurality of pixels in a direction orthogonal to the direction of movement with respect to the photoreceptor. Then, the exposure of the photosensitive member for each line while repeating the relative movement is repeated to form an image on the photosensitive member. The present invention is characterized in that an exposure area of an arbitrary line and an exposure area of an adjacent line on the photoconductor are overlapped and exposed. The light source sequentially emits at least three types of color light. Here, as three types of color light emitted from the exposure apparatus,
Red, green and blue light can be used. The three types of color light are sequentially emitted in a predetermined order. Further, the shutter array has a plurality of pixel rows, and these pixel rows are arranged orthogonal to the moving direction of the photosensitive paper. Further, a preferable relative speed between the shutter array and the photoconductor is a speed at which the photoconductor moves by one pixel row with respect to the shutter array during the exposure time of one type of color light.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 2 is a schematic view showing one embodiment of the color image forming apparatus of the present invention. FIG. 2 omits a converging optical system, a slit, and the like from the exposure apparatus. The exposure light source 9 has a wide exposure amount in the visible light region. A cylindrical rotating body (not shown, for example, a rotating motor) surrounding it is covered with three color filters, 10r transmitting red light, 10g transmitting green light, and 10b transmitting blue light. I have. The color light emitted from the exposure light source 9 passes through the color filter, slit, optical lens, etc.
The light reaches a liquid crystal shutter array 11 which is a shutter array having a row of pixels as substantially parallel light.

FIG. 1 schematically shows the exposure and driving method (selection state) of a liquid crystal shutter array to be incorporated in the image forming apparatus of the present invention into which parallel light that has arrived is incident, with the lapse of time. FIGS. 1A to 1D show cells 1 corresponding to the pixels of the liquid crystal shutter array, respectively, and the hatched portions indicate that all the cells in the pixel column are closed (non-selected state). It indicates that The outside 2 of the cell is an ITO space, covered with a chromium film, and does not transmit exposure light. In the figure, for the sake of simplicity, the cells are arranged vertically with time, but actually the same cell is
Are translated in the direction indicated by the arrow 3 of FIG.
(A) and (d) show red light R, (b) show green light G,
The blue light B is incident on (c). One pixel on the photosensitive paper, which is a photosensitive member, is formed by the open / closed state of the liquid crystal shutter array of (a) to (c). FIG. 1D shows a second pixel in the traveling direction. Further, in FIG. 1, in order to express the superposition, all the three pixel columns in the liquid crystal shutter array selected respectively are shown in an open state. FIGS. 4A to 4C show the state of this selection as the state of the entire liquid crystal shutter array, and correspond to FIGS. 1A to 1C, respectively.

The light incident on the liquid crystal shutter array from the state shown in FIG. 1A to the state shown in FIG. 1B is red light R, and the selected state of the three rows does not change. At this time, the shape of the exposure area of the line viewed from the exposure direction (top) on the photosensitive paper is as shown by the solid line 4 in FIG. A solid line 6 in FIG. 1F shows a graph in which the energy of the exposure light is plotted on the vertical axis and the traveling direction is plotted on the horizontal axis.
However, broken lines 5 and 7 in (e) and (f) show the second line, respectively.

The exposure time for each color is comprehensively determined by the relative speed of the photosensitive paper and the liquid crystal shutter array, the sensitivity of the photosensitive paper, the amount of exposure, and the like. Here, each color filter 10 and the exposure light source 9 perform simultaneous exposure,
It is adjusted so that the required density of each color is obtained. Explaining the exposure time of each color in detail, the exposure time is a time for relatively moving one liquid crystal pixel width and one ITO space width shown in FIG. At this time, the exposure module up to the cell hook lens 12 including the exposure light source 9 shown in FIG. 2 is driven to move. By repeating the exposure for the above-described exposure time by selecting the liquid crystal shutter row as shown in FIG. 1 for each color, all the R, G, and B exposure pixel shapes are accurately displayed on the solid line 4 in FIG. Superimposed. In addition, the first line and the second line have an overlapping area corresponding to one liquid crystal pixel width, so that a non-exposed portion on the photosensitive paper does not occur. In the overlapping area, the energy of the exposure light itself is reduced as a first line, as shown in FIG.
The energy increase portion as the second line is overlapped, and the total amount of the energy is different from the portion always exposed (the portion parallel to the solid line portion 6 and the broken line portion 7 in (f)). And no streaks are formed on the photosensitive paper.

One pixel on the photosensitive paper formed as described above has a width in the traveling direction from the center of the overlapping portion to the center (range of arrow 8 in FIG. 1F) and a width perpendicular to the traveling direction to the liquid crystal. This can be determined as the width of one pixel of the liquid crystal in the shutter row direction.
Therefore, in order for one pixel on the photosensitive paper to form a square pixel, the vertical and horizontal shape ratio of one pixel of the liquid crystal needs to be approximately 1: 3, and the relative traveling direction between the photosensitive paper and the liquid crystal shutter array needs to be shorter. However, this is not the case when using a lens of variable magnification in the horizontal and vertical directions between the liquid crystal shutter array and the photosensitive paper.

As described above, the liquid crystal shutter array having the liquid crystal pixel shape as described above, the selection of the liquid crystal shutter array row as shown in FIG. 1, the closing of the non-selected array row, the relative driving speed of the photosensitive paper and the liquid crystal shutter array. With this adjustment, it is possible to obtain a color image forming apparatus having a liquid crystal shutter array capable of obtaining a high-quality full-color print without color shift and defocus in a short time. Less than,
Driving methods such as the pixel arrangement of the liquid crystal used, the applied voltage and the open / closed state will be described in detail with reference to examples.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 3, a pixel of a liquid crystal has scanning electrodes 15 corresponding to pixel rows, five rows of T1 to T5, signal electrodes 16,
S1 to S640 are arranged in 640 rows, and the IT
The O space is covered with a chromium film so that exposure light is blocked. The black-and-white liquid crystal shutter array having the above pixel arrangement uses a super-twisted nematic liquid crystal having a liquid crystal layer thickness of 6 μm and a twist angle of 225 degrees, and is constituted by a micro shutter having 3200 pixels.

FIG. 7 shows the relationship between the transmittance of light passing through the liquid crystal and the polarizing plate and the voltage applied to the liquid crystal. The voltage applied to the liquid crystal is shown as a composite voltage of the voltage waveform input to the scanning electrode 15 and the voltage waveform input to the signal electrode 16 shown in FIG. As shown in FIG. 7, here, a polarizing plate is arranged so that a dark state is selected when a high voltage is applied. Each liquid crystal pixel becomes dark when it exceeds VM in FIG. The voltage applied in the bright state is for suppressing the display color that is likely to occur in the super twisted nematic liquid crystal and preventing coloring of transmitted light.

FIG. 4 shows an example of selecting a liquid crystal shutter array for each exposure light when the liquid crystal shutter array is viewed from above as described above. Here, when the red light R arrives, T3, T4, and T5 of the scanning electrode 15 are selected, opened and closed, and T
1, T2 is not selected and all the liquid crystal pixels in this column are in a closed state. However, when opening and closing the Sn row of the signal electrode 16, all of T3 to T5 perform the same operation. Next, when the green light G arrives,
T2, T3, and T4 are selected, and T1 and T5 are not selected.
Further, when blue light arrives, T1, T2, and T3 are selected.
4. T5 is not selected. Since the cylindrical rotating body is rotating at a constant speed around the exposure light source 9, the R, G, and B exposures are sequentially repeated toward the liquid crystal shutter array. At that time, the liquid crystal shutter row is always set to T1 to T of R, G, and B.
In the same manner as the selection method of No. 5, one-to-one correspondence is selected. This is repeated for the number of divisions, here 480 lines, in the traveling direction 14 shown in FIG.

The scanning electrode 1 for making the above selections
FIG. 5 shows an example of the input voltage waveform to the reference numeral 5. VH in FIG. 5 is sufficiently larger than VL. Here, VH indicates the voltage value of the column non-selection signal, and VL indicates the voltage value of the column selection signal. The one shown to the left of T5 in FIG.
The signal shown to the left of T1 is a signal input to T1, which corresponds to exposure light of three colors of R, G, and B for each time, and selects or deselects each column corresponding to each color. This is an input signal for one pixel to be determined.

Since the voltage applied to the liquid crystal is represented by a composite voltage of the input voltage to the scanning electrode 15 and the input voltage to the signal electrode 16, the open / close state of the liquid crystal shutter array is determined by the input voltage to the scanning electrode 15 described above. In addition, it is necessary to consider the signal of the input voltage to the signal electrode. FIG. 6 shows each input voltage waveform to both electrodes and a composite voltage thereof. VO is the voltage value of the input signal in the open state, and VS is the voltage value of the input signal in the closed state. VM in FIG. 6 is a branch voltage value that determines the open / closed state in the liquid crystal shutter array as in FIG. Therefore, the liquid crystal shutter is opened in FIG. 7 only when the scan electrode input voltage waveform is a column selection signal and the signal electrode input waveform is an open signal. In order to maintain this relationship, it is necessary to set a voltage that satisfies the following equation. VH> VL VH−VO> VM VH−VS> VM VL−VO <VM VL−VS> VM VH: Scan electrode input signal, AC voltage value when column is not selected VL: Scan electrode input signal, when column is selected VO: The signal electrode input signal, the AC voltage value in the open state VS: The signal electrode input signal, the AC voltage value in the open state VM: The AC voltage value at the branch point of the open / close state of the liquid crystal shutter array However, VO and VS may have only inverted phases.

The liquid crystal shutter array is opened and closed by signals satisfying the above conditions, and the exposure system module is moved at the following speed and timing so that the R, G, and B exposure light can be accurately overlapped on the photosensitive paper. . At the same time as the exposure light from the slit becomes light passing through the color filter 10r, the selection of the liquid crystal shutter row is as shown in FIG. 4A, and the liquid crystal shutter row starts to move at a constant speed in the direction of arrow 14 shown in FIG. . At this time, the liquid crystal shutter array is
Start from the uppermost end of the image forming area. With the exposure light and the selection and opening / closing state of the liquid crystal shutter row, parallel movement is performed while exposing by a distance corresponding to the width of one pixel of the liquid crystal in the traveling direction and one width of the ITO space. Here, a red pixel is written on the photosensitive paper. Although the open / closed state is described here, this is for writing red in order to make the overlay easy to see, and this is not the case when forming a halftone as an image.

At this time, the shape of the exposure area on the photosensitive paper is shown in FIG.
(E) The shape shown by the solid line 4 is obtained, and the width in the line direction is the same as the width in the line direction of one liquid crystal pixel, and the width in the traveling direction is four widths in the traveling direction of one liquid crystal pixel and three ITO spaces. . However, the density appearing on the photosensitive paper is determined by the energy of light. Assuming that the amount of light energy is simply multiplied by the amount of exposure and the exposure time, a graph 6 shown in FIG. 1F is obtained. However, in this case, the opening is performed so as to maintain the open state until the parallel movement is completed in order to obtain the superimposed white, but this is not the case when obtaining the halftone of each color. In this graph, the vertical axis indicates the amount of light energy, and the horizontal axis indicates the position on the photosensitive paper. Therefore, it is considered that the density is reduced toward the both ends before and after the exposure region by one width in the liquid crystal traveling direction.

The cylindrical rotating body continues to rotate during the translation, and at the moment when the translation completes the distance, the color filter is switched from red light to green light in the region of 10r to 10g. Fig. 4
As shown in (b), the speed of the parallel movement is maintained while maintaining the speed of the parallel movement, and the width of the liquid crystal in the traveling direction of one pixel and IT
The parallel movement is performed while exposing for one width of the O space.
Here, green pixels are written on the photosensitive paper. At this time, the red exposure area and the green exposure area are completely overlapped because the selected liquid crystal shutter row for opening and closing is shifted by the amount of movement of the exposure module. That is, at the start of red light exposure, the position of the photosensitive paper corresponding to the position of T3 on the scanning electrode is immediately below the scanning electrode T2 at the start of green light exposure. In this selection state, the parallel movement by the same distance causes the shape of the exposure area to exactly overlap. The same is true at the moment when the color filter 10g switches from green light to blue light to 10b. From this moment, the selection of the liquid crystal shutter row is as shown in FIG. 4C, and the blue pixel is written to the area where the red and green pixels have already been written at a constant speed. Thus, writing three times on one line is completed.

Next, the writing of the second line is continued. Positionally, as shown in FIG. 1D, three pixels in the traveling direction of one pixel of the liquid crystal from the time of writing the red light on the first line,
It is translated by three ITO spaces. As described above, the parallel movement is performed while exposing by the width of one pixel of the liquid crystal in the traveling direction and the width of one ITO space. At this time, the exposure area on the photosensitive paper is as shown by a broken line 5 in FIG. 1E, and there is an area that overlaps the exposure area 4 of the first line by the width in the liquid crystal one pixel traveling direction. However, the actual color density on the photosensitive paper is determined by the amount of light energy, and as can be seen from FIG. The amount of energy is equal to the non-overlapping area. This makes it possible to obtain a high-quality print sample having no lines between lines.

Next, the liquid crystal shutter array and the pixel shape on the photosensitive paper will be described. The pixel size depends on the image forming range and the resolution of the photosensitive paper. In the embodiment, an instant film and a spectro film manufactured by Polaroid Co., Ltd. are used as the photosensitive paper, and the long side is 640 dots and the short side is 48.
Disassembled into 0 lines. Since the shape of one pixel on the photosensitive paper is a square, the length ratio of the image forming area is 4:
It becomes 3. The spectrum film used this time has a long side of 90.8 mm and a short side of 73.5 mm in the image forming area,
The ratio is not 4: 3. Therefore, the total length of the long side is 64
Although the dot is decomposed into 0 dots, the short side represents the area of the unexposed portion as 5.
About 4 mm remains. The image from the liquid crystal shutter array is formed on the photosensitive paper 13 by the cell hook lens 12 shown in FIG. 2 at a ratio of 1: 1. Therefore, the long side 90.90 is determined by the sum of 639 ITO spaces and 640 liquid crystal pixel widths.
8 mm is configured. Since the ITO space was 4 μm here, the liquid crystal pixel width in the line direction was 138 μm. One pixel width in the traveling direction is considered to be the center of the overlapping area of the first line exposure area and the second line exposure area,
This is considered to be the length of the arrow indicated by 8 in FIG. This width is equal to the sum of three liquid crystal one pixel traveling direction widths and three ITO spaces. If one pixel on the photosensitive paper forms a square and the ITO space is 4 μm, the liquid crystal pixel width in the traveling direction is 43 μm.

In a color printer having a liquid crystal shutter array having the above-described shape and driving method, the amount of exposure was adjusted, and the cylindrical rotating body was rotated at 160 rps. Since the superposition of one line of R, G, and B is completed in one rotation, it took three seconds from the start to the end of image formation. The obtained full-color print was also an extremely high-quality sample without streaks.

[0025]

As described in the above embodiment, when performing optical writing of full-color printing using an optical shutter array, writing can be performed line by line at a constant speed without interruption. Since there is no need to repeat stop and move accurately, and there is no stop time, writing can be completed at high speed. In addition, the superposition of each pixel of each color, the red pixel, the green pixel, and the blue pixel is performed without displacement, and the entire area of the photosensitive paper area is subjected to the superposition of three colors. It is possible to obtain a very high quality full color print without any.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the operation of a liquid crystal shutter array which is a component of the device of the present invention.

FIG. 2 is a schematic view of the apparatus of the present invention.

FIG. 3 is a diagram showing an arrangement of scanning electrodes and signal electrodes of a liquid crystal shutter array according to an embodiment of the present invention.

FIG. 4 is a diagram showing a column selection state corresponding to exposure light of a liquid crystal shutter array according to the embodiment of the present invention.

FIG. 5 is a diagram showing an input voltage waveform for one pixel input to a scanning electrode of the liquid crystal shutter array according to the embodiment of the present invention.

FIG. 6 is a diagram showing input voltage waveforms input to scanning electrodes and signal electrodes of a liquid crystal shutter array according to an embodiment of the present invention, and a composite voltage waveform applied to liquid crystal as a combination thereof.

FIG. 7 is a graph showing transmittance corresponding to an applied voltage of the liquid crystal shutter array according to the embodiment of the present invention.

FIG. 8 is a schematic view of a conventional color image forming apparatus.

FIG. 9 is a schematic view of a conventional color image forming apparatus.

[Explanation of symbols]

Reference Signs List 1 liquid crystal cell 2 ITO space 3 relative movement direction of liquid crystal shutter array 4 exposure area on first line photosensitive paper 5 exposure area on second line photosensitive paper 6 light energy amount and position on first line photosensitive paper Curve of relationship 7 Curve of relationship between amount of light energy and position on photosensitive paper on second line 8 Substantial pixel width per line 9 Exposure light source 9r Red exposure light source 9g Green exposure light source 9b Blue exposure light source 10r Red color filter 10g Green color filter 10b Blue color filter 11 Liquid crystal shutter array 12 Selfoc lens array 13 Photosensitive paper 14 Moving direction of exposure optical system module 15 Scanning electrodes (T1 to T5) 16 Signal electrodes (S1 to S640) 17 Non-selection not operating as shutter Row 18 Selection row 193 to act as shutter Separated liquid crystal shutter array R Red light G Green light B Blue light VH Scan electrode input signal, AC voltage value when column is not selected VL Scan electrode input signal, AC voltage value when column is selected VO Open with signal electrode input signal AC voltage value in the state VS signal electrode input signal, AC voltage value in the open state VM AC voltage value which becomes the branch point of the open / close state of the liquid crystal shutter array

Claims (10)

[Claims] 1. An image forming apparatus for forming an image on a photoconductor by controlling a transmission amount of light emitted from a light source by a shutter array relatively moving with respect to the photoconductor, wherein the shutter array is Comprises a pixel row composed of a plurality of pixels in a direction orthogonal to the direction of relative movement with respect to the photoconductor, and moving the pixel row continuously relative to the photoconductor while moving the photoconductor. An image forming apparatus wherein exposure is repeated for each line, and an exposure area of an arbitrary line on the photoconductor overlaps an exposure area of another adjacent line. 2. The method according to claim 1, wherein an overlapping width of an exposure area of an arbitrary line on the photosensitive member and an exposure area of another adjacent line is a width in a relative movement direction of one pixel in a shutter array. The image forming apparatus as described in the above. 3. The pixel width of an image formed on a photosensitive member formed by exposure from a center position of an overlapping exposure area of a line to a center position of a next overlapping exposure area. 2. The image forming apparatus according to 1. 4. The shutter array according to claim 1, wherein the shutter array includes a plurality of pixel columns.
Alternatively, the image forming apparatus according to claim 3. 5. The image forming apparatus according to claim 1, wherein the light source emits a plurality of types of color light. 6. The image forming apparatus according to claim 5, wherein the plurality of types of color light are red, blue, and green light. 7. The image forming apparatus according to claim 5, wherein the light source emits the color light in a time-division manner. 8. The image forming apparatus according to claim 5, wherein the color light is simultaneously incident on a plurality of pixel columns of the shutter array. 9. The image forming apparatus according to claim 1, wherein the shutter array is a liquid crystal shutter. 10. The image forming apparatus according to claim 1, wherein the photoconductor is an instant film.