JP2002055504A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and accurately measure a color slurring measuring pattern without causing cost rise by relating the shape of the color slurring measuring pattern to the shape of the light receiving area of an image detection sensor in the case of performing color slurring correction. SOLUTION: A line 95a perpendicular to the moving direction of a carrying belt and a line 95b inclined by +45 deg. are set as the color slurring measuring pattern for each color, and a parallelogram diamond having a side perpendicular to the carrying direction and a side inclined by +45 deg., which have equal length, is set as the pattern detection area 92 of the sensor. The line 95a is used for detecting the color slurring in a subscanning direction and the line 95b is used for detecting the color slurring in a main scanning direction with the line 95a. When the lines 95a and 95b cross the area 92 at the same speed, they have equal covering area per unit time from starting covering the area 92 until perfectly covering it up, and detection output from the sensor becomes trapezoidal waveform and a boundary between a belt surface and a pattern surface is sharp, whereby detecting accuracy is improved.

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 using an electrophotographic process, and more particularly to a color image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as a color image forming apparatus for forming a color image at high speed, yellow (Y), magenta (M), cyan (C), A photosensitive drum is arranged for each color of black (Bk), and the toner images of each color formed on the photosensitive drum are sequentially superimposed on a recording material conveyed by a conveyance belt and transferred, or are sequentially superimposed on an intermediate transfer belt. An in-line type is known, in which a color image is transferred onto a recording material conveyed to an intermediate transfer belt and then collectively transferred to a recording material.

One of the main problems in the in-line type color image forming apparatus is a color shift between colors of a color image. The components of the color shift include a shift in the scanning direction (main scanning direction) by the laser, a shift in the belt moving direction (sub-scanning direction), expansion and contraction of an image in the main scanning direction, and an angular shift in the main scanning direction.

[0004] The deviation of each color is adjusted so as to be below the allowable value at the time of shipment of the apparatus. Due to distortion, displacement of the photosensitive drum due to replacement of a cartridge, or the like, color displacement exceeding an allowable value may occur.

Therefore, a color misregistration measuring pattern is formed at a predetermined interval on a conveyor belt or an intermediate transfer belt as appropriate, and this pattern is detected by an image detecting sensor.
2. Description of the Related Art An amount of color misregistration is calculated based on a detection result, and an image forming position is corrected based on the calculation result.

The color misregistration measurement pattern is composed of a straight line for each color. A plurality of such patterns are formed at regular intervals in the moving direction, and the amount of color misregistration is obtained by calculating from the measured values to obtain the color misregistration amount. Correct the misalignment. By such color misregistration correction, the color misregistration amount can be suppressed to within an allowable value, and a color image with optimum image quality can be always maintained.

An image detection sensor used for detecting the color misregistration measurement pattern is composed of an optical photosensor having a light emitting element and a light receiving element, and reflects a belt surface and a toner surface on the belt to light emitted from the light emitting element. Since the difference in the rate causes a difference in the output voltage of the light receiving element that has received the reflected light, the position of the pattern is detected.

At this time, as the inclination of the change in the output voltage of the light receiving element is larger, the difference between the toner surface and the belt surface becomes clearer, and the pattern detection accuracy is improved. For this reason, a method of increasing the light amount of the detection sensor or reducing the light receiving area of the sensor to detect sharper has been adopted.

[0009]

However, in the conventional method, in order to increase the amount of light of the image detection sensor, it is necessary to increase the performance of the light emitting element, which is disadvantageous in cost. In addition, reducing the light receiving area of the sensor causes a problem that the amount of light decreases.

Accordingly, an object of the present invention is to relate the shape of the color misregistration measurement pattern to the shape of the light receiving area of the image detection sensor without increasing the cost.
It is an object of the present invention to provide an image forming apparatus capable of easily performing accurate measurement of a pattern, performing color shift correction, and obtaining a color image with optimum image quality.

[0011]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image forming unit that forms a toner image of a plurality of colors; a conveying belt that carries and conveys a recording material; and an image detecting unit that detects a color misregistration measurement pattern formed on the conveying belt. The measurement pattern is formed of two straight lines for each color formed along the movement direction of the belt, and the image detection unit detects the pattern by detecting that the straight line crosses the detection area, In the image forming apparatus in which color shift correction is performed based on the detection result, two straight lines of each color of the color shift measurement pattern are
An image characterized by two substantially non-parallel straight lines for each color, and the detection area of the image detecting means is divided into a parallelogram having sides substantially parallel to the two straight lines. It is a forming device.

The present invention further comprises an image forming means for forming a plurality of color toner images, an intermediate transfer belt, and an image detecting means for detecting a color misregistration measuring pattern formed on the belt, The measurement pattern is formed of two straight lines for each color formed along the movement direction of the belt, and the image detection unit detects the pattern by detecting that the straight line crosses the detection area, In the image forming apparatus in which color shift correction is performed based on the detection result, two straight lines of each color of the color shift measurement pattern are
An image characterized by two substantially non-parallel straight lines for each color, and the detection area of the image detecting means is divided into a parallelogram having sides substantially parallel to the two straight lines. It is a forming device.

According to the present invention, one of the two straight lines is a vertical line substantially perpendicular to the moving direction of the belt, and the other straight line is the moving direction of the belt. Is a straight line inclined with respect to. The other straight line is
It is a straight line inclined at + 45 ° or −45 ° with respect to the moving direction of the belt. The parallelogram is a rhombus whose adjacent sides are equal in length. Alternatively, both of the two straight lines are straight lines inclined with respect to the moving direction of the transport belt. One straight line of the two straight lines is inclined at + 45 ° with respect to the moving direction of the conveyor belt, and the other straight line is −4 °.
Incline to 5 °. The parallelogram is a rectangle having different lengths of adjacent sides. The parallelogram is a square whose adjacent sides are equal in length.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic sectional view showing an embodiment of the image forming apparatus of the present invention. In this embodiment, the image forming apparatus is configured as a color laser printer.

The printer has a recording material transport belt 61 therein.
Along the image forming portions Pa, Pb, P of yellow (Y), magenta (M), cyan (C), and black (Bk).
c, Pd, and the image forming units Pa, Pb, Pc, Pd
Has rotatable photosensitive drums (drum-shaped electrophotographic photosensitive members) 21, 22, 23, and 24 as image carriers, and has charging rollers 31, 32, 33, 3 around them.
4, scanner units 11, 12, 13, 14, developing units 41, 42, 43, 44, transfer rollers 51, 52, 5,
3, 54, and cleaning blades 71, 72, 7
3, 74 are provided, and these photosensitive drums, charging rollers,
The scanner unit, the developing device, the transfer roller and the cleaner constitute an image forming unit.

The transport belt 61 is a recording material transporting member for carrying a recording material (paper for printing) and transporting it to each image forming unit. The transport belt 61 is wound around a driven roller 62 and a driving roller 63 and rotates in the direction of the arrow. It is installed freely. The image forming unit Pa at the uppermost stream in the recording material conveyance direction by the conveyance belt 61
The manual feed tray 82 and its pickup roller 64b are installed on the upstream side of the
5. A suction roller 66 is provided. Conveyor belt 61
A paper cassette 81 and a pickup roller 64a thereof are provided below the paper cassette 81. Also, the most downstream image forming unit P
Downstream of d, image detection sensors 90 and 91 and a fixing device 71 are provided.

In order to form a four-color full-color image using this color laser printer, first, each of the image forming units Pa to
The surfaces of the Pd photosensitive drums 21 to 24 are charged to a desired potential by respective charging rollers 31 to 34, and image exposure is performed by the scanner units 11 to 14, and the photosensitive drums 21 to 24 are exposed.
The electrostatic latent images for yellow, magenta, cyan, and black are formed on the surface of the toner image, and the latent images are developed by developing units 41 to 44 to form yellow, magenta, cyan, and black toner images.

Next, the toner images of the respective colors formed on the respective photosensitive drums 21 to 24 are transferred onto a recording material which is held on a transport belt 61 and sequentially transported to a transfer section facing the respective photosensitive drums 21 to 24. The images are superimposed and transferred one after another by the rollers 51 to 54. The recording material is fed from a paper feed cassette 81 or a manual feed cassette 82 by a pickup roller 64a or 64b, and is held on a transport belt 61 via a registration roller 65 and a suction roller 66.

Next, the recording material onto which the four color toner images have been transferred is separated from the conveyor belt 61 and sent to a fixing device 71, where it is heated and pressed to melt and mix and fix the four color toners. After forming a full-color permanent image on the recording material, the recording material is discharged outside the printer.

The color laser printer is provided with a color misregistration correction mechanism, and generates a color misregistration measurement pattern by a pattern generating means before forming an image on a recording material. 24, the pattern is exposed, the latent image is developed, and the obtained pattern toner image is directly transferred to the conveyor belt 61 to form a color misregistration measurement pattern on the surface of the conveyor belt 61. Is measured and color shift correction is performed.

In the present invention, the pattern for measuring color misregistration is
Each color of yellow (Y), magenta (M), cyan (C), and black (Bk) is composed of two straight lines, and the pattern of these lines is moved in two rows at intervals in the width direction of the belt 61. A plurality of sets are formed in the direction.

Correspondingly, two image detecting sensors 9 are provided at an upper position on the downstream side of the image forming portion Pd of the final color of the conveyor belt 61 with a space in the width direction of the conveyor belt 61.
0 and 91 are arranged. As shown in FIG. 2, the sensors 90 and 91 irradiate the surface of the conveyor belt 61 with light and receive the reflected light. 90,
At the position of 91, the pattern is detected as a light intensity distribution by a change in the amount of received light reflected from the pattern,
Output as voltage.

The output voltage is input to the image position detection circuit 104 of the control circuit board 100 of the color misregistration correction mechanism.
The position detection circuit 104 detects the position of each color line of each pattern from the input voltage waveform, and outputs the detection result to the control circuit 1.
Enter 03. The control circuit 103 measures the interval between the colors, that is, the amount of color shift between the colors from the position of the line of each color. This is performed for all of the plural sets of patterns, and the average value of the color shift amounts for each color is calculated, and the difference between the average value of the color shift amounts (intervals between the colors) for each color and a desired value is calculated. , The amount of color shift of each color.

The control circuit 103 controls the photosensitive drums 21 by the scanner units 11 to 14 based on the amount of color misregistration.
The exposure start position of the image to -24, i.e., the image writing position (writing timing) is corrected and changed, and the changed image writing is performed to form an image, and the color image finally formed on the paper The color misregistration of each color is eliminated.

In the present invention, the shape of the pattern is related to the shape of the light receiving area of the image detection sensor in order to easily and accurately measure the color misregistration measurement pattern without increasing the cost.

First, problems in the conventional case will be described. FIG. 3 shows a conceptual diagram of a conventional color misregistration measurement pattern and a pattern detection area of an image detection sensor.

The color misregistration measurement pattern 95 has a straight line 95a extending in the vertical direction (belt width direction) perpendicular to the recording material conveyance direction of the conveyance belt 61 (belt movement direction), and inclined by + 45 ° with respect to the conveyance direction. A straight line 95b is formed for each color. Vertical straight line 95
a is used to detect a color shift in the sub-scanning direction of the image, and a straight line 95b inclined at + 45 ° is a vertical straight line 95.
It is used to detect a color shift in the main scanning direction of the image from the interval from a.

The pattern detecting area 92 is a light receiving area of the image detecting sensor 90 and is divided into a square having no inclination with respect to the conveying direction of the conveying belt. The image detection sensor 91 also defines a square pattern detection area 93 that is not inclined with respect to the conveyance direction of the conveyance belt. Hereinafter, the same applies to the pattern detection area 93.
Will be described.

In the pattern detection area 92, the side perpendicular to the transport direction is parallel to the straight line 95a forming the pattern. Therefore, when the straight line 95a crosses the detection area at the same speed, as shown in FIG.
The area to cover per unit time is the same from the start of covering until it is completely covered. For this reason, the detection output output from the sensor 90 changes linearly with time, and FIG.
As shown in (a), a trapezoidal output waveform is obtained.

On the other hand, an inclined straight line 9 constituting a pattern
5b, none of the sides of the pattern detection area 92 are parallel, and as shown in FIG.
From the start of the covering until the covering is completed, the covering area per unit time is not equal, and the detection output outputted from the sensor 90 changes quadratically with respect to time.
As shown in (a), the output waveform is a quadratic curve.

The accuracy of detecting the amount of color misregistration is affected by the sharpness of the boundary between the conveyor belt 61 and the pattern surface on the conveyor belt. Therefore, the detection waveform of the quadratic curve of the straight line 95b has a sharper boundary than the trapezoidal detection waveform of the straight line 95a, and the detection accuracy is reduced.

Therefore, in the present invention, two straight lines of each color of the color misregistration measurement pattern are set to two straight lines which are not parallel to each other, and the detection area of the image detection sensor is defined by a side parallel to the two straight lines. Into parallelograms. The parallelogram is formed in such a size that any two straight lines can be covered.

The two non-parallel straight lines may be a combination of a straight line extending perpendicular to the belt conveying direction and a straight line inclined with respect to the conveying direction, or a non-parallel two line inclined with respect to the conveying direction. There are combinations of book straight lines. In the former case, the color shift in the sub-scanning direction is detected from the interval between the reference color of the vertical straight line and the other measurement colors, and the reference color of the interval between the inclined straight line and the vertical straight line and each measurement color are detected. A color shift in the main scanning direction can be detected from the difference. In the latter case, the midpoint of the two inclined straight lines is determined, the color shift in the sub-scanning direction is detected from the interval between the midpoints of the measurement colors with respect to the midpoint of the reference color, and the two slanted straight lines are detected. The color shift in the main scanning direction can be detected from the difference between the reference color and the measured color at the interval of the straight line.

Although the inclination of the straight line inclined with respect to the belt conveyance direction may be any number in principle, if the inclination is ± 45 °, the number of dots detected with respect to the deviation amount in the main scanning direction is equal. (From tan45 ゜ = 1), it becomes easier on the calculation. Therefore, it is preferable that the two straight lines are a straight line and a straight line inclined at + 45 ° or −45 ° or a straight line inclined at approximately ± 45 ° from the viewpoint of easy handling.

In this embodiment, as shown in FIG. 6, the color misregistration measurement pattern of each color is a straight line 95a perpendicular to the belt conveyance direction and a straight line 95b inclined at + 45 °, and the pattern detection area 92 of the image detection sensor is set. And a side parallel to the transport direction and a side inclined by + 45 °, and each side was a parallelogram, that is, a rhombus of the same size. The vertical straight line 95a is used for detecting color shift in the sub-scanning direction, and the straight line 95b inclined at + 45 ° is used for detecting color shift in the main scanning direction together with the vertical straight line 95a.

In order to divide the pattern detection area 92 of the image detection sensor 90 into a parallelogram, the shape of the light receiving element of the sensor 90 must be a parallelogram or a parallelogram slit should be placed in front of the light receiving element. Can be realized. Alternatively, a parallelogram slit may be provided in front of the light emitting element of the sensor to make the light emission distribution parallelogram.

According to FIG. 6, if the straight lines 95a and 95b cross the detection area 92 at the same speed,
8 (b), as shown in FIG. 8 (b), the area to be covered per unit time is the same from the start of covering the detection area 92 to the completion of covering, so that the detection output outputted from the sensor 90 is , Changing linearly with time, FIG.
8A, a trapezoidal output waveform is obtained as shown in FIG.

That is, the detected waveform of the straight line 95a, the straight line 9
In the detection waveform 5b, the boundary lines are both clear, and the detection accuracy of the pattern by the sensor 90 is improved. Sensor 9
For the same reason, the detection accuracy of the pattern detection by the method No. 1 is improved.

In this embodiment, as described above, the shape of the color misregistration measurement pattern and the shape of the light receiving area of the image detection sensor are associated with each other, so that the pattern can be easily formed without requiring extra cost for measurement. Can be measured accurately. Therefore, it is possible to obtain a color image having an optimum image quality by performing a favorable color shift correction.

Embodiment 2 FIG. 9 is an explanatory view showing a color misregistration measurement pattern and a pattern detection area of an image detection sensor according to another embodiment of the present invention. Hereinafter, the image detection sensor 90 in FIG. 2 will be described, but the same applies to the image detection sensor 91.

In this embodiment, the color misregistration measurement pattern of each color is represented by a straight line 95 inclined at -45 ° with respect to the belt conveyance direction.
a and a straight line 95b inclined at + 45 °, the pattern detection area 92 of the image detection sensor 90 in FIG. 2 has a side inclined at −45 ° and a side inclined at + 45 ° in the transport direction, A parallelogram, that is, a rectangle, having a longer side inclined to ゜, was used. Straight lines 95a, 95 inclined ± 45 °
b is used for detecting a color shift in the sub-scanning direction and the main scanning direction.

According to FIG. 9, if the straight lines 95a and 95b cross the detection area 92 at the same speed,
11 (b), as shown in FIG. 11 (b), the area to be covered per unit time is equal between the time when the detection area 92 is covered and the time when the detection area 92 is completely covered, so that the detection output from the sensor 90 is , Changing linearly with time, FIG.
0 (a) and a trapezoidal output waveform as shown in FIG. 11 (a).

That is, the detected waveform of the straight line 95a, the straight line 9
In the detection waveform 5b, the boundary lines are both clear, and the detection accuracy of the pattern by the sensor 90 is improved. The detection accuracy of the pattern detection by the sensor 91 in FIG. 2 is also improved for the same reason.

According to this embodiment, the pattern can be easily and accurately measured without requiring extra cost for the measurement. Therefore, it is possible to obtain a color image having an optimum image quality by performing a favorable color shift correction.

Embodiment 3 FIG. 12 is an explanatory diagram showing a color misregistration measurement pattern and a pattern detection area of an image detection sensor according to another embodiment of the present invention. Hereinafter, the image detection sensor 90 in FIG. 2 will be described, but the same applies to the image detection sensor 91.

In this embodiment, the color misregistration measurement pattern of each color is represented by a straight line 95 inclined at -45 ° with respect to the belt conveyance direction.
a and a straight line 95b inclined at + 45 °, the pattern detection area 92 of the image detection sensor 90 in FIG. 2 has a side inclined at −45 ° and a side inclined at + 45 ° in the transport direction. Are parallelograms of the same size, that is, squares. The straight lines 95a and 95b inclined by ± 45 ° are both used for detecting a color shift in the sub-scanning direction and the main scanning direction.

As in the second embodiment, the pattern detection area 92
When the lengths of the adjacent sides of the pattern are not equal, that is, in the case of a rectangle, the rising and falling slopes of the output waveform differ depending on whether the pattern straight line cuts the longitudinal direction or the short direction of the detection area 92. Come. That is, when the pattern straight line 95b cuts the longitudinal direction of the detection area 92 (FIG. 11), the output waveform rises and falls compared to the case where the pattern straight line 95a cuts the short direction of the area 92 (FIG. 10). Becomes gentler, which causes a difference in detection accuracy. Therefore, in the present embodiment, in order to eliminate this, as described above, the pattern detection area 92 is formed as a parallelogram having adjacent sides equal and an inclination angle of ± 45 °.

FIG. 12 shows that when the straight lines 95a and 95b cross the detection area 92 at the same speed,
3 (b), as shown in FIG. 14 (b), the area to be covered per unit time is equal between the time when the detection area 92 is covered and the time when the detection area 92 is completely covered. Changes linearly with time, resulting in a trapezoidal output waveform as shown in FIGS. 13 (a) and 14 (a).

That is, the detected waveform of the straight line 95a, the straight line 9
In the detection waveform 5b, the boundary lines are both clear, and the detection accuracy of the pattern by the sensor 90 is improved. The detection accuracy of the pattern detection by the sensor 91 in FIG. 2 is also improved for the same reason.

According to this embodiment, the pattern can be easily and accurately measured without requiring extra cost for the measurement. Therefore, it is possible to obtain a color image having an optimum image quality by performing a favorable color shift correction.

In each of the above embodiments, in an image forming apparatus having a recording material conveying belt, a pattern for measuring color misregistration is transferred from an image forming means to the conveying belt, and the pattern is detected by an image detecting sensor. However, the present invention can also be applied to an image forming apparatus having an intermediate transfer belt, and transfers and forms a color misregistration measurement pattern from an image forming unit to the intermediate transfer belt, and the pattern is used as an image detection sensor. , The same effect can be obtained by doing the same.

[0053]

As described above, in the image forming apparatus of the present invention, the shape of the color misregistration measurement pattern formed on the recording material conveying belt or the intermediate transfer belt and the shape of the light receiving area of the image detection sensor are set to predetermined values. Because we related to the relationship,
It is possible to easily and accurately measure the pattern without increasing the cost, and therefore, it is possible to perform good color shift correction and obtain a color image with optimum image quality.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a schematic diagram illustrating a measurement and control system of a color misregistration measurement pattern formed on a recording material conveyance belt of the image forming apparatus of FIG. 1;

FIG. 3 is a conceptual diagram showing a conventional color misregistration measurement pattern and a pattern detection area of an image detection sensor.

FIG. 4 is a conceptual diagram showing a state when one line of the pattern of FIG. 3 covers a detection area and an output waveform of a sensor.

FIG. 5 is a conceptual diagram showing a state when the other line of the pattern of FIG. 3 covers a detection area and an output waveform of a sensor.

FIG. 6 is a conceptual diagram showing a color misregistration measurement pattern and a pattern detection area of an image detection sensor in the embodiment of FIG. 1;

FIG. 7 is a conceptual diagram showing a state when one line of the pattern of FIG. 6 covers a detection area and an output waveform of a sensor.

FIG. 8 is a conceptual diagram showing a state when the other line of the pattern of FIG. 6 covers a detection area and an output waveform of a sensor.

FIG. 9 is a conceptual diagram showing a color misregistration measurement pattern and a pattern detection area of an image detection sensor according to another embodiment of the present invention.

FIG. 10 is a conceptual diagram showing a state when one line of the pattern in FIG. 9 covers a detection area and an output waveform of a sensor.

11 is a conceptual diagram showing a state when the other line of the pattern of FIG. 9 covers a detection area and an output waveform of a sensor.

FIG. 12 is a conceptual diagram showing a color misregistration measurement pattern and a pattern detection area of an image detection sensor according to still another embodiment of the present invention.

FIG. 13 is a conceptual diagram showing a state when one line of the pattern of FIG. 12 covers a detection area and an output waveform of a sensor.

FIG. 14 is a conceptual diagram showing a state when the other line of the pattern of FIG. 12 covers a detection area and an output waveform of a sensor.

[Explanation of symbols]

 11-14 Scanner Unit 21-24 Photosensitive Drum 41-44 Developing Device 51-54 Transfer Roller 61 Recording Material Conveying Belt 90-91 Image Detection Sensor 92-93 Pattern Detection Area 95 Pattern for Measuring Color Shift 95a, 95b Straight Line 103 Control Circuit 104 Image position detection circuit

Claims (9)

[Claims] An image forming means for forming a toner image of a plurality of colors, a conveying belt for carrying and conveying a recording material, and an image detecting means for detecting a color misregistration measuring pattern formed on the belt. The color misregistration measurement pattern is composed of two straight lines for each color formed along the moving direction of the belt, and the image detecting means detects that the straight line crosses the detection area and detects the pattern. In the image forming apparatus for detecting color shift and correcting color shift based on the detection result, two straight lines of each color of the color shift measuring pattern are replaced with two straight lines that are substantially the same for each color and are not parallel. Wherein the detection area of the image detection means is partitioned into a parallelogram having sides substantially parallel to the two straight lines. 2. An image forming means for forming a toner image of a plurality of colors, an intermediate transfer belt, and an image detecting means for detecting a color misregistration measurement pattern formed on the belt, wherein the color misregistration measurement pattern is provided. Is formed of two straight lines for each color formed along the movement direction of the belt, and the image detecting means detects that the straight line crosses the detection area to detect the pattern, and the detection result In the image forming apparatus in which color misregistration is corrected based on the following, two straight lines of each color of the color misregistration measurement pattern are set to two non-parallel straight lines that are substantially the same for each color. An image forming apparatus, wherein a detection area is divided into a parallelogram having sides substantially parallel to the two straight lines. 3. One of the two straight lines is:
3. The image forming apparatus according to claim 1, wherein the straight line is a vertical line substantially perpendicular to the moving direction of the belt, and the other straight line is a straight line inclined with respect to the moving direction of the belt. 4. The image forming apparatus according to claim 3, wherein the other straight line is a straight line inclined at + 45 ° or −45 ° with respect to the moving direction of the belt. 5. The image forming apparatus according to claim 4, wherein said parallelogram is a rhombus whose adjacent sides are substantially equal in length. 6. The straight line which is inclined with respect to the moving direction of the conveyor belt.
Image forming apparatus. 7. The image forming apparatus according to claim 6, wherein one of the two straight lines is inclined at + 45 ° with respect to the moving direction of the transport belt, and the other straight line is inclined at −45 °. 8. The image forming apparatus according to claim 7, wherein the parallelogram is a rectangle having adjacent sides having different lengths. 9. The image forming apparatus according to claim 7, wherein said parallelogram is a square whose adjacent sides are substantially equal in length.