JP3597933B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in a method for detecting a shift in a printing position of an image of each color in an image forming apparatus capable of multicolor printing.
[0002]
[Prior art]
In an image forming apparatus such as a color copying machine, a color printer, and a color facsimile apparatus, which can print in multiple colors, an electrostatic latent image for each color of black, yellow, magenta, and cyan is formed on a photoreceptor. Each color is developed separately using toner of each color, and each color is superimposed on a transfer paper to express a multi-color.
That is, for example, in a multiplex image forming apparatus described in JP-A-63-271275, an image forming unit for each color (photosensitive drum, charger, optical writing unit, (Developing unit, transfer unit, etc.) are sequentially arranged, so that the toner images of each color are individually superimposed and transferred from each image forming unit onto the transfer belt, and the toner images that have been superimposed are collectively transferred onto transfer paper. There is disclosed a technique for transferring the image to a computer.
When this image forming principle is used, if even one of the four colors shifts the transfer position, the originally desired image color quality cannot be obtained. Therefore, as a means for detecting the displacement, Japanese Patent Application Laid-Open No. 63-271275 proposes a method using a CCD as a detecting means.
[0003]
[Problems to be solved by the invention]
As described above, in the conventional image forming apparatus capable of multicolor printing, the four colors of black, yellow, magenta, and cyan are separately developed, and the multicolor is expressed by superimposing each color on the transfer paper. However, if even one of the four colors is displaced from the overlapping position, the originally desired image color quality cannot be obtained. In order to solve such a problem, Japanese Patent Application Laid-Open No. 63-271275 discloses a method using a CCD as a means for detecting the positional deviation.
However, when a CCD is used, a large-scale lens optical system is inevitable to form an image on the light-receiving surface of the CCD, which complicates the mechanism, resulting in an increase in size and cost of the apparatus. Was.
The present invention has been made in view of the above, and simplification of the mechanism and miniaturization by applying an optical pickup device widely used as a recording / reproducing means of an optical disc as a means for detecting a positional deviation between toner images. The purpose is to reduce the cost and cost.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an image forming apparatus capable of multicolor printing using a transfer belt,
An objective lens for condensing the laser light emitted from the laser diode on the optical disc to a radial interval between tracks formed on the disc surface of the optical disc, and a change in reflected light of the laser light condensed by the objective lens; An optical pickup device for detecting the position of each toner image is disposed at an appropriate position opposed to the surface of the transfer belt as a detecting unit for detecting a displacement of each toner image,
A beam having a reduced beam diameter emitted from the detection unit is condensed on the transfer belt, and a deviation of a printing position of each color toner pattern on the transfer belt is detected.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the drawings.
FIG. 1 is a schematic configuration diagram of a four-drum type image forming apparatus as an example of an image forming apparatus capable of multicolor printing according to the present invention, and reference numerals 1a to 1d denote black image (K), Optical writing units for magenta image (M), yellow image (Y), and cyan image (C), 2a to 2d are photosensitive members and image forming process units for K, M, Y, and C, respectively. (E.g., a charger, a developing unit, a transfer unit, and a cleaning unit). Reference numeral 3 denotes a printing paper feeding unit, 4 denotes a transfer belt which is stretched endlessly by a plurality of rollers 4a and is driven in the direction of arrow A, and 5 denotes a heat fixing unit. The configuration and operation of each of these components are well known and will not be described in detail.
Optical color image data obtained by reading an image of a document (not shown) by a scanner (not shown) is finally converted into a black component, a magenta component, a yellow component, and a cyan component by an image processing unit (not shown). Are written on the photoconductors of the respective image forming process units by the respective optical writing units 1a to 1d, and the respective electrostatic latent images written on the respective photoconductors are formed by toner from the respective developing units. Each color image is formed.
On the other hand, the printing paper fed from the paper feeding unit 3 is conveyed in the direction of arrow A by the transfer belt 4, and the toner of each color is transferred by being superposed by the respective image forming process units 2a to 2d. After the transfer of the toners of all colors is completed, the image is fixed by the fixing unit 5.
With the above configuration, if the transfer position of the toner image of each color with respect to the transfer belt 4 is shifted, the desired color cannot be expressed even in the finally obtained image on the printing paper as described above. is there.
Possible causes of the displacement include variations in component tolerances, variations in accuracy during assembly due to the stroke, mechanical vibrations, environmental changes such as temperature rise, and the like.
The characteristic configuration of the present invention resides in that the optical pickup device 10 is disposed as a means for detecting a displacement of each toner image at an appropriate position facing the surface of the transfer belt 4.
[0006]
FIG. 2 is a schematic diagram of an example of an optical pickup device used in an optical disk recording / reproducing apparatus such as a CD-ROM player. 11 is a laser diode as a light source, 12 is a beam splitter for passing only an electric field component parallel to the incident surface, 13 is a collimating lens, 14 is a prism, 15 is an objective lens, and 16 is an objective lens. The object to be detected (in this case, the optical disk surface). Light emitted from the laser diode 11 travels straight through the beam splitter 12, is collimated by the collimating lens 13, is deflected by the prism 14, and is focused on the disk surface 16 by the objective lens 15. . The light reflected from the disk surface 16 passes through the objective lens 15, the prism 14, and the collimating lens 13 and is deflected by the beam splitter 12 to be incident on the photo diode, contrary to the incident path. Since information is recorded on the track formed on the optical disc surface 16 in the form of irregularities, the light reflected by the track changes, and the output of the photodiode also changes by that amount. Since the radial spacing between the tracks formed on the disk surface is about 1.6 μm, the beam can be condensed less than that.
[0007]
In the example shown in FIG. 1, the position of the optical pickup device 10 as a means for detecting a displacement is set to a position facing the roller 4a downstream of each image forming process unit. This is because, in consideration of the fact that the transfer belt 4 that is wound around the roller 4a with a certain tension is unlikely to bend and erroneous detection due to the bend does not occur, this is an example. If the position is a position at which the positional deviation of the toner image can be detected, the layout is not limited to the illustrated position and may be laid out anywhere.
In the present invention, what is to be detected by the detecting means 10 is a predetermined toner pattern formed on the transfer belt 4, and this toner pattern is formed on the photoreceptor for each color. Above, by transferring this onto the transfer belt 4, detection becomes possible.
[0008]
FIG. 3 shows an example of the pattern.
FIG. 3A shows a pattern for detecting a shift of the print data in the transport direction (a shift in the sub-scanning direction). As shown in the figure, the patterns of the respective colors are straight lines arranged in parallel at predetermined intervals. It is. FIG. 3B shows a pattern for detecting a shift in the writing direction of print data (a shift in the main scanning direction). These are merely examples, and any pattern may be used as long as the pattern can be detected. This pattern is formed as a reference pattern during non-image formation.
The toner pattern of each color transferred onto the transfer belt 4 moves to the position of the detecting means 10 by driving the transfer belt 4 in the direction of the arrow. Since each toner pattern is formed by attaching toner on the flat surface of the transfer belt 4, a portion with toner is protruding, and therefore, a portion with toner and a portion without toner (transfer belt surface). ) Is formed.
[0009]
In the present invention, the control unit can determine the positional deviation between the patterns by detecting the presence / absence of the unevenness and the deviation of the position of the step by the detecting means 10 comprising an optical pickup. The position at which the beam emitted from the detecting means 10 converges on the transfer belt 4 is determined by the passing path of each pattern when the deviation between the patterns in the sub-scanning direction is observed as shown in FIG. When the pattern is shifted upward in the main scanning direction as shown in (b), each pattern is set so as to be located on the outer side (on the transfer belt) from one end edge of the row composed of each pattern. Therefore, when the position of each pattern is normal as shown in FIG. 3B, the detecting means 10 does not detect anything (projection, that is, toner portion).
[0010]
That is, in the case of FIG. 3 (a), the detection means 10 first detects the pattern (the pattern of black toner in this example) which first enters the detection position, and then detects the magenta, The pattern of each color is sequentially detected in the order of yellow and cyan. The positions of the pattern data sent from the detection means 10 are sequentially stored in a memory of a control unit (not shown), and the positional relationship between the patterns of the respective colors is compared with each other. It is determined how much the position is deviated in the sub-scanning direction from the position.
In the case of FIG. 3B, first, patterns are formed so that the patterns of the respective colors are located on one line along the paper transport direction.
As described above, the detection position of the detection means 10 is set in advance so as to be located immediately beside this linear line. The distance from the edge L of the pattern line to the irradiation position of the beam from the detection means is set to the beam spot diameter, for example, 1.5 μm. In the drawings, the distance is shown too large for easy understanding, but the purpose is as described above.
[0011]
As shown in FIG. 4 (a), in the case of FIG. 3 (b), one of the patterns is shifted in the main scanning direction, and the direction of the shifting is the outer edge of the pattern line. If it is on the detecting means 10 side from the edge L, the unevenness can be detected at that part. In this case, if a specific pattern is displaced, the direction of the displacement can be detected. However, it is not possible to determine the degree of displacement (displacement amount) only with this data. Thus, in the present embodiment, the second detection operation (pattern formation, pattern detection) is subsequently performed, and the detection is performed again in a direction opposite to the direction in which the pattern has shifted, with the writing start position deliberately shifted (FIG. b)). At this time, the smaller the shift amount, the higher the accuracy of detection. The shift amount is, for example, an amount corresponding to one beam diameter, and the shift amount is set as one step, and the position is shifted by one step until the shift cannot be detected. That is, this detection operation is sequentially repeated until no deviation is detected. When the deviation is no longer detected, the positional deviation can be corrected (FIG. 4C). This detection operation is performed at an interval between regular image forming processes.
[0012]
Next, when the detection beam is not detected from the beginning to the end as a result of relatively passing the detection beam along all the patterns, there is no displacement, or one of the patterns is a line detection means. There is a possibility that it is shifted in the opposite direction to the 10 side. Therefore, this time, the pattern forming step of intentionally shifting the writing start position toward the line detecting means 10 side and the detecting step of detecting the pattern are performed again (FIGS. 5A to 5D). In the detection process performed later, pattern formation is performed by shifting the position one by one from the pattern on the near side, in this example, the black pattern, and detection is performed, and this is performed for all four colors.
[0013]
First, as shown in FIG. 5 (a), one pattern (the second M pattern in this example) is shifted to the opposite side to the detection means 10, but only one detection work is performed by this detection means 10. Then, it is impossible to know the presence or absence of a shift, which pattern is shifted, and the shift amount. Therefore, in the present embodiment, the presence / absence of a shift is detected for all patterns for the first time from the pattern K on the near side. In this case, first, a pattern is formed by shifting only the pattern K by one step toward the detection means 10 and then detection is performed by the detection means 10. At this time, if the pattern K is detected by the detection means 10, the normal position is detected. It is determined that there is. In the next detection step, the pattern K is returned to the position shown in FIG. 5A and the next pattern M is moved to the detection means 10 by one step. At this time, since the pattern M is shifted on the opposite side to the detecting means, it is not detected by the detecting means 10 only by moving the pattern M by one step. Here, it is found that the pattern M is shifted on the opposite side, but in order to correct the shift, the position is further shifted by one step in the same direction, and the pattern M is shifted as shown in FIG. Pattern formation and detection are repeated until detected by the detection means. When the pattern M is detected for the first time as shown in (c), the state one step before that, that is, the state shown in FIG. In the pattern formation described above, a pattern in which the pattern M is returned to the side opposite to the detection means by one step is formed. By performing this pattern formation, detection, and correction work for all the remaining color patterns, a normal pattern line as shown in FIG. 3B can be finally formed.
[0014]
The detection method of the present invention makes full use of the characteristic of the optical pickup device, that is, the characteristic that the beam diameter can be reduced. That is, when the writing density of the digital image forming apparatus is, for example, 600 dpi, the width of one line to be written is about 40 μm. On the other hand, since the beam diameter of the optical pickup is as small as about 1.5 μm, it is possible to correct a deviation of about 1/25 dot with respect to the writing line width.
Further, since the optical pickup device itself is widely used in relation to an optical disk, it is more advantageous in terms of cost than using other detecting means.
Note that the pattern formation, detection, and correction operations according to the present invention may be automatically performed based on a program stored in the ROM of the control unit, or may be performed by a key operation or the like when a color shift occurs. It may be.
[0015]
【The invention's effect】
As described above, according to the present invention, simplification of the mechanism, miniaturization, and cost reduction can be achieved by using an optical pickup device as a position shift detecting unit between a plurality of toner images superimposedly transferred on a transfer belt. It can be carried out.
Generally, the cause of the deviation of the position of the toner of each color on the transfer belt is considered to be a variation in component tolerance, a variation in accuracy during assembly due to a process, a mechanical vibration, an environmental change such as a rise in temperature, etc. Any positional deviation due to any cause can be automatically corrected and the image quality can be maintained.
[Brief description of the drawings]
FIG. 1 is a schematic view of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of an optical pickup device.
FIGS. 3A and 3B are schematic diagrams showing an example of a detection method according to the present invention.
4 (a), (b) and (c) are diagrams showing a specific example of a detection method corresponding to FIG. 3 (b).
5 (a) to 5 (d) are diagrams showing another specific example of the detection method corresponding to FIG. 3 (b).
[Explanation of symbols]
1a to 1d optical writing unit, 2a to 2d image forming process unit, 3 printing paper feeding unit, 4 transfer belt, 5 heat fixing unit, 10 optical pickup device (detection means), 11 laser diode, 12 Beam splitter, 13 collimating lens, 14 prism, 15 objective lens, 16 detection object,

Claims (1)

In an image forming apparatus capable of multicolor printing using a transfer belt,
An objective lens for condensing the laser light emitted from the laser diode on the optical disc to a radial interval between tracks formed on the disc surface of the optical disc, and a change in reflected light of the laser light condensed by the objective lens; An optical pickup device for detecting the position of each toner image is disposed at an appropriate position opposed to the surface of the transfer belt as a detecting unit for detecting a displacement of each toner image,
An image forming apparatus for detecting a deviation of a printing position of a toner pattern of each color on the transfer belt by condensing a beam having a reduced beam diameter emitted from the detection unit on the transfer belt. .

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