JPH0635290A - Image forming device - Google Patents

Abstract

PURPOSE:To perfectly eliminate the positional deviation and the distortion of a transferred image to an endless belt and to obtain a high-quality image (mainly a color image). CONSTITUTION:This device is provided with a mark image writing control means 4 intermittently writing a mark image M for correcting the positional deviation at intervals of specified time on the circularly rotating endless belt 1 by using one or plural monochrome image forming unit 2 (2a to 2d), a mark image position detecting means 5 detecting the position of the mark image M or pitch length between the mark images M written on the belt 1, a pitch fluctuation correcting means 6 calculating the pitch fluctuation of the mark image M based on positional information from the means 5 and controlling a belt driving means 3 so that the picth fluctuation may be corrected, and a cleaning means 7 erasing the mark image M processed as the correction object of the means 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image by an electrophotographic method, and more particularly, to a recording sheet directly or held on an image forming portion of an endless belt. Alternatively, the present invention relates to improvement of an image forming apparatus that transfers each single color image formed by a plurality of single color image forming units.

[0002]

2. Description of the Related Art Conventionally, as a color image forming apparatus of this type, for example, a plurality of single color image forming units for forming a single color image corresponding to a plurality of color components by an electrophotographic method are provided and held on an endless belt. It is known that a single color image is transferred by the above single color image forming unit onto the formed recording sheet.

In such a color image forming apparatus, unless the positions of the transfer images from the single color image forming units are accurately aligned, the positions of the transfer images are displaced from each other and the quality of the full color image is impaired. Therefore, in the related art, the overall positional deviation amount of the transfer image on the endless belt is detected, and an electrostatic latent image is written on, for example, a photoconductor for each single-color image forming unit. A method of correcting the writing timing of an optical system such as a laser scanning unit (see, for example, Japanese Patent Application Laid-Open No. 1-126881),
Alternatively, a method of transferring a registration mark together with a transfer image in each monochromatic image forming unit onto an endless belt and superimposing the transfer images on the basis of the registration mark (for example, Japanese Patent Laid-Open No. 63- 300263
(See Japanese Patent Publication).

[0004]

However, in such a color image forming apparatus, it is certainly possible to match the transfer positions of the images of the respective color systems as a whole, but the color image forming unit Distortion of the transferred image due to rotation fluctuations of the photoconductor and speed fluctuations of the endless belt, in other words, fluctuations in image magnification cannot be accurately corrected,
It was still insufficient to completely avoid the color shift.

The present invention has been made in order to solve the above technical problems, and completely eliminates the positional deviation and distortion of the transferred image on the endless belt, and provides a high quality image (mainly a color image). ) Is provided.

[0006]

That is, the present invention is
As shown in FIG. 1, a monochromatic image corresponding to one or a plurality of color components is formed by an electrophotographic method, and is directly formed on an image forming portion of the endless belt 1 or on a recording sheet held at the image forming portion. One or a plurality of single color image forming units 2 (for example, 2a to 2d) for transferring the single color image.
And an image forming apparatus including a belt driving unit 3 that circulates and rotates the endless belt 1, and an endless belt that is circulated and rotated by using one or a plurality of single-color image forming units 2 (2a to 2d). 1, the mark image writing control means 4 for intermittently writing the mark image M for positional deviation correction at a constant time interval, and the position of the mark image M written on the endless belt 1 or the pitch length between the mark images M. Of the mark image position detecting means 5 for detecting the position of the mark image M, the pitch variation of the mark image M is calculated based on the position information from the mark image position detecting means 5, and the belt driving means 3 is controlled so as to correct the pitch variation. Pitch fluctuation correcting means 6 and cleaning means 7 for erasing the mark image M for positional deviation correction processed as a correction target of the pitch fluctuation correcting means 6. The is characterized in that it comprises.

In such a technical means, the mark image writing control means 4 can be selected as appropriate as long as it writes one or a plurality of mark images M at a predetermined writing timing. , Is appropriately selected according to the image magnification correction accuracy of the transferred image. Further, from the viewpoint of more accurately correcting the pitch variation of the transferred image, it is preferable to design so that the mark image M is formed by the single-color image forming unit 2 on the side closer to the driving portion of the endless belt 1. .

Further, as the mark image detecting means 5, if the mark image M of a predetermined color component can be detected,
A reflective or transmissive optical sensor (bar code reader, CCD sensor, etc.) may be selected as appropriate. Further, the position of the mark image detecting means 5 is not particularly limited, but if the ease of correction by the pitch variation correcting means 6 is taken into consideration, the mark image detecting means 5 will be described.
The distance from the mark image transfer portion to the mark image transfer portion is set to an integral multiple of the peripheral length of the photoconductor or the like of the single-color image forming unit 2 or the driving portion (roll diameter or the like) of the endless belt 1, in other words, a synchronous relationship. It is preferable that if there is no synchronous relationship, it is necessary to correct and correct only the shifted phase. However, since it is necessary to superimpose the transfer image formed by each monochromatic image forming unit 2 at a fixed timing, a synchronous relationship is required between the photoconductors and the like of each monochromatic image forming unit 2. Is.

Further, as the pitch variation correcting means 6, the written mark image M is written in one image forming cycle.
The position of the mark image M is detected from the detected position, the pitch variation correction amount of the mark image M based on the detection information is stored in a memory or the like in advance, and the endless belt is based on the pitch variation correction amount in the next image forming cycle. Belt driving means 3 of 1
May be controlled, or the belt driving means 3 of the endless belt 1 may be sequentially controlled in the same image forming cycle.

Further, from the viewpoint of further improving the accuracy of image magnification correction of a transfer image in the type in which a plurality of monochromatic image forming units 2 are provided, the mark image writing control means 4 has at least two monochromatic image forming units. Two
The color component mark images M of (2a to 2d) are written so as not to overlap each other, the mark image position detection means 5 detects the position information of the written color component mark images M, respectively, and the pitch variation correction means 6 makes each color component. Based on the position information of the mark image M, the pitch variation of each color component mark image M is calculated and averaged, and the belt driving means 3 is controlled so as to correct this average pitch variation. preferable. In this case, regarding the writing of the color component mark images M, the phase may be shifted along the movement direction of the endless belt 1, or the color component mark images M may be arranged side by side along the width direction of the endless belt 1. Good.

The cleaning means 7 may also serve as the original cleaning means for the endless belt 1, or may be provided separately. Here, when the mark image writing control means 4 writes the mark image M on the end portion in the width direction of the endless belt 1, the cleaning means 7 includes:
At least the blade 7a that comes into contact with the endless belt 1 at the time of cleaning is provided so that the mark image M to be erased along with the movement of the endless belt 1 is removed and guided outward in the width direction of the endless belt 1. It is preferable that the blade 7a is arranged in an inclined manner. However, when the cleaning means for the endless belt 1 which is originally used also serves as the so-called endless belt 1, if the blades 7a that contact the entire width direction of the endless belt 1 are simply inclined, the endless belt 1 is displaced in the width direction. Since the belt walk phenomenon is likely to occur, it is preferable that the endless belt 1 is designed so that the inclination direction is changed symmetrically (so-called V-shape) with the center line portion in the width direction as a boundary.

[0012]

According to the technical means as described above, the mark image writing control means 4 uses the one or a plurality of single color image forming units 2 (2a to 2d) for the endless belt 1 which is circulatingly rotated. The mark image M for positional deviation correction is intermittently written at regular time intervals. Then, the mark image position detecting means 5 detects the position of the mark image M written on the endless belt 1 or the pitch length between the mark images M. Then, the pitch fluctuation correcting means 6 calculates the pitch fluctuation of the mark image M based on the position information from the mark image position detecting means 5, and controls the belt driving means 3 so as to correct this pitch fluctuation. On the other hand, the cleaning unit 7 erases the mark image M for positional deviation correction processed as the correction target of the pitch fluctuation correcting unit 6.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the accompanying drawings. Example 1 FIGS. 2 and 3 show an example of a so-called tandem type color printer to which the present invention is applied. In the figure, reference numerals 20a to 20d (the whole is indicated by 20) are yellow (Y), magenta (M), cyan (C), and black (K) toner images formed by an electrophotographic process. Forming unit, each single-color image forming unit 2
Reference numeral 0 denotes a photosensitive drum 21, a charging corotron 22 that charges the surface of the photosensitive drum 21 in advance, a semiconductor laser 23 that writes an electrostatic latent image on the charged photosensitive drum 21, yellow, magenta, cyan, and black color systems. Of the developing device 24 in which the toner is stored, a pre-transfer corotron 25 that removes the surface potential of the photosensitive drum 21 before the transfer process in order to maintain good transferability of the toner image, and the residual toner on the photosensitive drum 21. And a cleaner 26 for removal.

Further, reference numeral 30 is a sheet conveying system for conveying the recording sheet 36, and a driving roll 31 rotated by a driving motor 37 and an alignment adjusting mechanism (not shown) arranged in parallel to the driving roll 31. The steering roll 32, which is aligned and adjusted by an appropriate number of driven rolls 33, and these rolls 31, 32.
It is provided with an endless conveyance belt 35 which is stretched between 33 and holds the recording sheet 36 by electrostatic attraction. In addition, in this embodiment, the tension roll 34 applies a predetermined tension to the conveyor belt 35 to stably convey the conveyor belt 35. Reference numeral 38 indicates the recording sheet 36 and the transfer belt 35 after the transfer processing.
A charge-removing corotron for removing the excessively charged electric charges of 39, a peeling corotron 39 for removing the electrostatic charge of the recording sheet 36 and the conveying belt 35 after the final transfer process is completed, and weakening the electrostatic attraction force of the recording sheet 36 to the conveying belt 35 40
Is a static elimination corotron that removes residual charges on the conveyor belt 35, 41 is a belt cleaner that removes paper dust and the like adhering to the conveyor belt 35, and 42 is a home sensor that detects the home position of the conveyor belt 35.

Further, reference numeral 45 is a sheet accommodating cassette for accommodating the recording sheet 36, and the recording sheet 36 delivered from the sheet accommodating cassette 45 is a transport roll 46.
Is conveyed to the tacking point of the conveyor belt 35, and the recording sheet 36 is electrostatically adsorbed to the conveyor belt 35 by the adsorption corotron 47 installed corresponding to the tacking point. Furthermore, the recording sheet 36 on the conveyor belt 35 is separated from the conveyor belt 35 at a corner portion corresponding to the steering roll 32, and the separated recording sheet 36 passes through the fixing device 28 and the discharge tray 4.
It is designed to be discharged to 8.

Further, a transfer corotron 27 is provided on the back surface side of the conveyor belt 35 corresponding to each monochromatic image forming unit 20, and each corotron wire is supplied with a voltage of a positive polarity from a high voltage power supply (not shown) to a predetermined level. Is applied, the transfer corotron 27 electrostatically transfers the toner image formed on the photosensitive drum 21 to the recording sheet 36 on the conveying belt 35.

The standard image writing control system 5
0 is the semiconductor laser 23 of each monochromatic image forming unit 20.
The image data (normal image data) of each color component to be supplied to the mark image writing control system 51 is generated by the mark image writing control system 51 in each image forming cycle.
Mark image data is written only on the semiconductor laser 23 of the yellow single-color image forming unit 20a (in this embodiment, a line-shaped mark image M [written on the one side in the width direction of the conveyor belt 35 at predetermined time intervals). [See FIG. 3]].

Further, a mark sensor 60 for detecting the mark image M on the conveyor belt 35 is disposed on the rear side of the final black monochromatic image forming unit 20d, and the mark sensor 60 detects the mark image M. The signal passes through the belt control system 70 and the drive motor 37 of the conveyor belt 35.
Is converted into a drive control signal for.

In this embodiment, the conveyor belt 3 is
5 is made of a transparent material, the mark sensor 60 has a light emitting element 61 and a light receiving element 62 arranged to face each other with the conveyor belt 35 interposed therebetween, as shown in FIG.
The mark image M is detected according to the change in the light amount of 2. Then, the pulse output corresponding to the mark image M of the light receiving element 62 is counted by the counter 71, and the mark image pitch detection circuit 72 detects the count output time difference of the counter 71 to detect the pitch p of the mark image M. The difference calculation circuit 73 uses the mark image pitch detection circuit 72.
From the difference calculation circuit 73, the correction amount setting circuit 74 calculates speed correction data of the drive motor 37 of the conveyor belt 35 based on the difference from the difference calculation circuit 73, The speed correction data based on each mark image pitch error during one image forming cycle is temporarily stored in the memory 75, and the speed of the conveyor belt 35 in the next image forming cycle is kept constant so that the speed of the conveyor belt 3 becomes constant.
The drive motor 37 of No. 5 is controlled. According to this example,
The conveyance belt 35 is moved and conveyed so that the pitch p of the mark image M is always constant, and accordingly, the transfer image due to the uneven rotation of the photosensitive drum of the single-color image forming unit 20a and the speed fluctuation of the conveyance belt 35. The positional deviation and the change in image magnification are effectively eliminated.

Further, in this embodiment, a cleaning device 80 for cleaning the mark image is provided. This cleaning device 80, as shown in FIG. 3 and FIG.
The cleaning blade 81 has a cleaning blade 81 that comes into contact with the mark image forming area portion of the transport belt 35 on the front side of the first monochromatic image forming unit 20a.
Is inclined with respect to the width direction of the conveyor belt 35 so that the outer end thereof faces the direction opposite to the moving direction of the conveyor belt 35. Incidentally, reference numeral 82 is a toner recovery box arranged below the cleaning blade 81. According to this embodiment, the mark image M detected by the mark sensor 60 collides with the cleaning blade 81 as the conveyor belt 35 moves,
The mark image M colliding with the cleaning blade 81 moves along the cleaning blade 81 to the outside in the width direction of the conveyor belt 35, and is collected in the toner collecting box 82 from the end portion in the width direction of the conveyor belt 35.

Example 2 This example has basically the same configuration as that of Example 1, but is different from Example 1 in the method of forming the mark image M, the method of detecting the mark image, and the belt control system. That is,
In the present embodiment, the mark image writing control system 51 uses two, for example, the line-shaped mark images M1 and M2 for each predetermined time interval in the yellow and magenta single-color image forming units 20a and 20b, respectively. It is designed such that the mark sensor
0 consists of a pair of members 60a and 60b for detecting the mark images M1 and M2 of the respective color systems.
0a and 60b include a light emitting element 61 and a light receiving element 62 as in the first embodiment, but additionally include a filter 63 for detecting only the mark images M1 and M2 of the respective color systems.

The output pulse corresponding to the mark image M1 from one mark sensor 60a is counted by the counter 91, and the mark image pitch detection circuit 92 is counted by the counter 9.
The pitch p1 of the mark image M1 is detected from the counting time difference of 1. The output pulse corresponding to the mark image M2 from the other mark sensor 60b is shifted to the position corresponding to the mark image M1 position by the phase shift circuit 93, and then counted by the counter 94, and the mark image pitch detection circuit 95. Is the mark image M from the counting time difference of the counter 94.
2 pitch p2 is detected. Then, the averaging circuit 96 averages the detection pitches p1 and p2 from the respective mark image pitch detection circuits 92 and 95, and the difference calculation circuit 97 calculates the difference between the averaged detection pitch p and a predetermined reference pitch. The correction amount setting circuit 98 calculates the speed correction data of the drive motor 37 of the conveyor belt 35 based on the difference from the difference calculation circuit 97, and the speed based on each mark image pitch error during one image forming cycle. The correction data is temporarily stored in the memory 99 and is adjusted so that the speed of the conveyor belt 35 becomes constant in the next image forming cycle.
Control the drive motor 37.

According to this embodiment, the mark images M1 and M2 are respectively formed in the plurality of single color image forming units 20a and 20b.
Is formed, and the conveyance belt 35 is moved and conveyed so that the average value of the pitches 1 and p2 of these mark images is always constant. Therefore, the plurality of single-color image forming units 20
The positional deviation of the transferred image and the fluctuation of the image magnification due to the uneven rotation of the photosensitive drum 21 of a and 20b are corrected on average, and compared with the first embodiment, the single color image forming unit 20b.
Since the influence of is also taken into consideration, the speed correction accuracy of the conveyor belt 35 becomes higher. In this embodiment, a plurality of mark sensors 60a and 60b are used. However, when marks of a plurality of color systems are lined up in the belt transport direction, one mark sensor is used and each color system is filtered by a filter. The marks may be identified, or each mark may be identified in order. However, when the marks of a plurality of color systems are separated in the direction orthogonal to the belt transport direction, a plurality of mark sensors for detecting the marks are necessary. Further, when the mark images are formed by the single-color image forming units 20a to 20d and the drive motor 37 of the conveyor belt 35 is controlled so that the average value of the mark image pitches becomes constant, the conveyor belt 35 can be controlled. The speed correction accuracy is extremely high.

Modified Example In each of the above-described embodiments, the cleaning device 80 for cleaning the mark image M is provided separately from the ordinary belt cleaner 41, but the invention is not limited to this and the belt cleaner 4 is not limited thereto.
The mark image M may also be cleaned at 1. The structure of the belt cleaner 41 in this case is shown in FIG.
Those of (a) to (d) are preferable. That is, FIG.
(A) The cleaning blades 101 in the shape of a dogleg are arranged symmetrically with respect to the center in the width direction of the conveyor belt 35. According to this, the position variation of the conveyor belt 35 in the width direction (so-called belt walk) is shown. ) Is effectively suppressed, the mark image M can be pushed out along the cleaning blade 101 to the end portion in the width direction of the conveyor belt 35 to be removed. It should be noted that FIG. 2B shows the arrangement of the cleaning blade 101 in FIG. 1A reversed, and FIG. 1C shows the cleaning blade 101 in order to further improve the peelability of the cleaning blade 101. The conveyor belt 3
The cleaning blade 101 is inclined at an acute angle θ with respect to the five surfaces, and further, a brush 102 is provided at the tip of the cleaning blade 101 in FIG.

[0025]

As described above, according to the first aspect of the invention, a line-shaped mark image is formed by the single-color image forming unit at predetermined time intervals, and the pitch of the mark image is constant. The endless belt is driven and controlled so that the transfer image can be accurately aligned, and uneven rotation of the photosensitive member on the single-color image forming unit side and uneven speed of the endless belt can be prevented. It is possible to effectively correct the variation of the image magnification that accompanies, and it is possible to obtain a high-quality color image with no color misregistration, especially when the color images are superposed.

According to the second aspect of the present invention, a plurality of monochromatic image forming units form linear mark images at predetermined time intervals so that the average value of the mark image pitches becomes constant. Since the endless belt is driven and controlled, it is possible to averagely correct the causes of variations in the plurality of single-color image forming units, and more accurately realize the alignment of the transfer image and the variation correction of the image magnification. You can

Further, according to the third aspect of the invention, the mark image is formed in the area other than the normal image forming area by the single color image forming unit, and the cleaning means is devised so that the mark image is surely erased. I got it, so
In forming the mark image, since it is not necessary to change the normal image forming process, it is possible not only to reduce the cost of the device by directly following the conventional device configuration, but also because the mark image remains due to the mark image remaining. It is possible to effectively prevent a situation in which the speed correction accuracy of the endless belt is reduced due to erroneous detection.

[Brief description of drawings]

FIG. 1A is an explanatory diagram showing a configuration of an image forming apparatus according to the present invention, and FIG. 1B is a view seen from a direction B in FIG.

FIG. 2 is an explanatory diagram showing a first embodiment of a color printer to which the invention is applied.

FIG. 3 is a plan view of FIG.

FIG. 4 is an explanatory diagram showing a specific example of the belt control system according to the first embodiment.

FIG. 5 is an explanatory diagram showing an example of a cleaning device according to the first embodiment.

FIG. 6 is an explanatory diagram showing a specific example of a belt control system according to a second embodiment.

FIG. 7 is an explanatory diagram showing a modification of the cleaning device according to the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Endless belt, 2 (2a to 2d) ... Monochromatic image forming unit, 3 ... Belt driving means, 4 ... Mark image writing control means, 5 ... Mark image position detecting means, 6 ... Pitch fluctuation correcting means, 7 ... Cleaning Means, 7a ... Blade

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03G 21/00 111 119

Claims (3)

[Claims] 1. A monochromatic image corresponding to one or a plurality of color components is formed by an electrophotographic method, and is directly on an image forming portion of an endless belt (1) or on a recording sheet held at the image forming portion. One or a plurality of single color image forming units (2: 2a to 2d) for transferring the single color image;
In an image forming apparatus provided with a belt driving means (3) for circulatingly rotating the endless belt (1), one or a plurality of single color image forming units (2: 2a to 2d) are used to rotate the endless belt. A mark image writing control means (4) for intermittently writing a mark image (M) for positional deviation correction on the belt (1) at regular intervals, and a mark image (() for the endless belt (1). M) position or mark image position detecting means (5) for detecting the pitch length between the mark images (M), and pitch variation of the mark image (M) based on the position information from the mark image position detecting means (5). Is calculated and the pitch fluctuation correcting means (6) for controlling the belt driving means (3) so as to correct the pitch fluctuation, and the position processed as the correction target of the pitch fluctuation correcting means (6). Is an image forming apparatus characterized by comprising a cleaning means (7) for erasing the mark image (M) for correction. 2. A type having a plurality of monochromatic image forming units (2) according to claim 1,
The mark image writing control means (4) writes the color component mark images (M) of at least two or more single color image forming units (2: 2a to 2d) so as not to overlap each other, and the mark image position detection means (5) writes. The pitch variation correction means (6) detects the positional information of each color component mark image (M), and the pitch variation correction means (6) individually detects the pitch variation of each color component mark image (M) based on the positional information of each color component mark image (M). An image forming apparatus characterized by calculating and averaging, and controlling the belt driving means (3) so as to correct the average pitch variation. 3. The mark image writing control means (4) according to claim 1, wherein the mark image (M) is written on an end portion in the width direction of the endless belt (1), and the cleaning means (7). Has a blade (7a) that contacts the endless belt (1) at least during cleaning,
The blade (7a) is arranged so as to be inclined so that the mark image (M) to be erased is guided outward in the width direction of the endless belt (1) as the endless belt (1) moves. An image forming apparatus characterized by.