JPH1191159A - Writing head focus position adjusting method and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust the focus position of a writing head without detaching a photosensitive member by relatively recognizing the positions of the writing head and the photosensitive member when a toner image cannot be visualized, and finding the intermediate point of the two points. SOLUTION: With the position of a writing head 4 adjusted to the photosensitive member 2 side with respect to the anticipated focal point, an image pattern for test is written with the writing head 4 and developed with a writing developer 5, with the exposure time shortened until judgment is made that a visualized toner image is not found. When it is judged that a visualized toner image is not found, the writing head 4 is positioned away from the photosensitive member 2 by a predetermined distance so as to judge whether a visualized toner image is found. If it is judged that a visualized toner image is found, the present position A1 of the writing head 4 is stored. Then, the writing head 4 is positioned away from the photosensitive member 2 with respect to the focal point by a predetermined distance. When it is judged that a visualized toner image is not found, the position B1 is stored. Then, the writing head 4 is moved to the intermediate point calculated from the positions A1, B1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a write head focal position adjusting method for determining a focal position of a write head for writing an electrostatic latent image on a photoreceptor, and an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, there is an image forming apparatus in which an electrostatic latent image is written by forming a beam emitted from an LED array on a photosensitive member by a lens array. In such an image forming apparatus, it is important that the beam is focused on the photoconductor at a correct focal position. The beam diameter emitted from the LED array and imaged on the photoconductor by the lens array is smallest at the true focal position, and increases as the focal length changes.

Therefore, as described in, for example, Japanese Patent Application Laid-Open No. 5-134158, the beam diameter and the beam irradiation area emitted from the LED are measured at the position of the image plane, and the measured values are minimized. In addition, the position of an LED array or a lens array is adjusted.

[0004]

Conventionally, in order to analyze the beam diameter and beam irradiation area at the position of the image plane,
Although the beam is received by a CCD camera arranged at the position of the image plane instead of the photoconductor, the structure is complicated because the CCD camera is used. Moreover, in order to adjust the variation in the position in the focal direction of the LEDs arranged in a direction parallel to the axis of the photoreceptor (hereinafter referred to as the main scanning direction), a plurality of CCD cameras are arranged in the main scanning direction or This requires a structure for moving the camera in the main scanning direction, and further complicates the structure.

[0005] Further, even if the position of an LED array or a lens array is determined by analyzing a beam diameter or the like using a CCD camera,
When assembling the photoconductor at the position of the CCD camera, the position of the photoconductor must be accurately determined, so that the assembling work is not easy.

According to the present invention, when a beam is formed on a photoreceptor, as the distance between the photoreceptor and the writing head approaches or departs from the focal length, the exposure potential is less likely to drop, and the toner image is visualized. Focusing on the tendency to disappear, the critical write head position at which the toner image is not visualized on the photoconductor is determined at two places sandwiching the expected in-focus position for forming a true focus on the photoconductor. It is intended to easily adjust the focus position of the write head with respect to the photoreceptor by setting an intermediate point between the positions of the two write heads as the focal point.

[0007]

According to a first aspect of the present invention, there is provided a method for adjusting a focal position of a write head, wherein an electrostatic latent image is formed on a surface of a photoreceptor by a write head having a plurality of point light source elements arranged in an array. In the image forming apparatus, the electrostatic latent image is formed into a toner image and transferred to a sheet by changing the position of the writing head relative to the photosensitive member in the focal length direction. Exposure and development of the test image pattern by the writing head are performed to form a toner image, and the critical position of the writing head at which the toner image is not visualized on the photoconductor is determined with respect to the photoconductor. The focal point of the write head relative to the photoreceptor is set with the intermediate point between the two positions of the write head as the focal point. And this setting So as to adjust the relative position of the write head relative to the photosensitive member in accordance with the position.

Therefore, by recognizing two relative positions of the writing head with respect to the photoconductor when the toner image is no longer visualized, and obtaining an intermediate point between the recognized positions, the photoconductor can be removed and attached. The focus position of the write head can be easily adjusted.

According to a second aspect of the present invention, there is provided a write head focal position adjusting method according to the first aspect, wherein the position of the write head relative to the photosensitive member in the focal length direction is relatively changed, and the writing is performed at each position. When exposing the image pattern by the head, the exposing efficiency is set lower than that in normal image formation.

Therefore, the toner image of the image pattern is hard to be visualized, so that when the relative position between the photosensitive member and the writing head is changed, the range in which the toner image is visualized becomes short. As a result, it is possible to quickly recognize two positions where the toner image is not visualized.

According to a third aspect of the present invention, in the method of the first aspect, the position of the write head relative to the photosensitive member in the direction of the focal length is relatively changed, and the write head is changed at each position. When a toner image is formed by exposing and developing an image pattern according to the above, the developing bias is set lower than during normal image formation.

Accordingly, it becomes difficult to visualize the toner image of the image pattern, so that when the relative position between the photosensitive member and the writing head is changed, the visible range of the toner image is shortened. As a result, it is possible to quickly recognize two positions where the toner image is not visualized.

According to a fourth aspect of the present invention, there is provided a write head focal position adjusting method according to the first aspect, wherein the position of the write head relative to the photosensitive member in the focal length direction is relatively changed, and the writing is performed at each position. When exposing the image pattern by the head, the image pattern is formed by dots.

Therefore, since the dot image has a small image area and is hard to be visualized, when the relative position between the photosensitive member and the writing head is changed, the range in which the toner image is visualized becomes short. As a result, it is possible to quickly recognize two positions where the toner image is not visualized.

According to a fifth aspect of the present invention, in the method of adjusting the focal position of the write head, the position of the write head relative to the photosensitive member in the focal length direction is relatively changed, and the writing is performed at each position. When exposing the image pattern by the head, the image pattern is formed along the rotation direction of the photoconductor.

Therefore, every time the photosensitive member is rotated by a predetermined angle, the focus position of the writing head with respect to the photosensitive member is recognized, thereby making it possible to measure the variation in the roundness of the photosensitive member.

According to a sixth aspect of the present invention, in the method of the first aspect, the position of the writing head relative to the photosensitive member in the direction of the focal length is relatively changed, and the writing is performed at each position. When exposing the image pattern by the head, the image pattern is formed along the axial direction of the photoconductor.

Therefore, it is possible to recognize the parallelism between the photosensitive member and the write head by recognizing the state in which the visualization state of the toner image of the image pattern changes at a position along the axial direction of the photosensitive member. .

According to a seventh aspect of the present invention, there is provided a writing head focal position adjusting method according to the first aspect of the present invention, wherein the critical position of the writing head at which a toner image is not formed on the photosensitive member is determined. The presence or absence of an image is determined based on a transferred image on a sheet.

Accordingly, the presence or absence of the visualized toner image can be recognized by silent observation.

According to the image forming apparatus of the present invention, an electrostatic latent image is formed on the surface of a photoreceptor by a writing head having a plurality of point light source elements arranged in an array, and the electrostatic latent image is formed by toner. In an image forming apparatus that develops an image and transfers the image to a sheet, a driving unit that moves the writing head relative to the photoconductor in a focal length direction is expected with respect to the photoconductor. Focus position changing means for controlling the operation of the drive unit so as to move the write head relatively to the photoconductor to a plurality of positions where the focus position of the write head is symmetrical; An image for forming a toner image on the photoconductor by exposing and developing a test image pattern by the writing head at each position of the writing head whose relative position with respect to the photoconductor has been changed by the control of the changing unit; Pa Image image output means, visible toner image presence / absence detection means for detecting the presence / absence of the visualized toner image, and Imageless head position storage means for storing a critical position of the write head at which a toner image is not visualized on the photoreceptor, and an intermediate position between the two write head positions stored in the imageless head position storage means An intermediate point calculating means for calculating a point, and driving the drive unit based on a calculated value of the intermediate point calculating means to move the writing head relatively to the photoconductor to be positioned at a focal point. And a focus position correcting means for performing the correction.

Accordingly, the operation of the drive section is controlled by the focal position changing means, and the write head is moved relative to the photosensitive member at a plurality of positions which make the expected focusing position of the write head relative to the photosensitive member. At the respective positions of the writing head whose relative position with respect to the photoreceptor has been changed by the movement, a toner image is output by the image pattern image output means, and the presence or absence of the visualized toner image is determined by a visible toner image. The position of the critical write head at which the toner image is not visualized on the photoreceptor at two places sandwiching the expected focus point of the write head with respect to the photoreceptor is detected by the presence / absence detection means, and the image-free head position is stored. Means for calculating an intermediate point between the two stored positions of the write head by the intermediate point calculating means, and operating the drive unit by the focal position correcting means based on the calculated value. By relatively moving the writing head relative to the photosensitive member control to, it is possible to automatically perform to define the write head at the focal point position with respect to the photosensitive member.

[0023]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG. First, an outline of the image forming apparatus 1 will be described with reference to FIG. In the figure, reference numeral 2 denotes a photoconductor that is driven to rotate. Around this photoconductor 2,
Charger 3, writing head 4, developing device 5, transfer device 6
And a cleaning unit 7 are arranged. Below the developing device 5, there are provided a paper feed roller 9 for separating and pulling out the paper in the paper feed cassette 8 one by one, and a registration roller 10 driven in synchronization with the rotation of the photoreceptor 2 for cleaning. Below the unit 7, a belt 12 that conveys the sheet passing through the transfer unit 6 toward the fixing unit 11 is rotatably provided.

In such an image forming apparatus 1, the photosensitive member 2
In the process of rotating clockwise, the surface of the photoreceptor 2 is charged by the charger 3, the charged portion is exposed by the writing head 4 to write an electrostatic latent image, and the developing device 5 forms the electrostatic latent image. Visualize as a toner image. During this time, the paper in the paper feed cassette 8 is pulled out by the paper feed roller 9, the leading ends thereof are aligned at the nip portion of the stopped registration roller 10, and the registration roller 10 is driven in synchronization with the rotation of the photoconductor 2. Is transferred between the photoconductor 2 and the transfer device 6. The toner image on the photoreceptor 2 is transferred to a sheet by a transfer unit 6. The fixing device 11 fixes the image transferred to the paper in the process of transporting the paper.

FIG. 3 is a side view showing the photoreceptor 2 and the write head 4. The write head 4 has a large number of Ls which are point light source elements.
An LED array 14 in which EDs 13 (see FIG. 4) are arranged along the axial direction of the photoconductor 2, and a number of lenses 15 that form light beams emitted from the individual LEDs 13 on the photoconductor 2
4 (see FIG. 4) in the axial direction of the photoconductor 2. The writing head 4 is supported so as to be freely movable toward and away from the photosensitive member 2 in the focal length direction. That is, screws 18 screwed to the fixing base 17 are inserted through both ends in the longitudinal direction of the writing head 4, and are supported by the flanges 19 fixedly formed at the lower ends of these screws 18. Therefore, when the screw 18 is tightened to the fixing base 17, the writing head 4 is separated from the photoconductor 2, and when the screw 18 is loosened from the fixing base 17, the writing head 4 is attached to the photoconductor 2 by its own weight or the urging force of a spring (not shown). It is configured to approach. Further, near the both ends in the longitudinal direction of the write head 4, a reflection type density sensor 20 for detecting the optical density of the surface of the photoconductor 2 is fixedly provided.

Next, an electronic circuit of a control system relating to the write head 4 is shown in FIG. The electronic circuits of the control system of the other process units are omitted. When normal image data to be output as printed matter is input, the data correction unit 21 corrects output data to be output to each LED 13 by using correction data stored in the first ROM 22. The LED drive circuit 23 drives the LED 13 of the write head 4 based on the result of this correction.

In FIG. 5, reference numeral 24 denotes a drive unit for moving the writing head 4 relative to the photosensitive member 2 in the direction of the focal length. In this example, since the writing head 4 is moved without moving the photoconductor 2, the head driving unit 24 will be described. The head drive unit 24 is, specifically, a motor capable of rotating forward and reverse. The head drive unit (motor) 24 rotates the screw 18 shown in FIG. Bring it to and away from the body 2. This operation is realized by meshing a gear (not shown) driven by the head drive unit (motor) 24 with the flange (gear) 19 of the screw 18, but is not limited to such a configuration. . As shown in FIG. 5, such a head drive section (motor) 24 is connected to a head drive circuit 25, and a second ROM 26 is connected to the head drive circuit 25. As will be described later, data for positioning the writing head 4 at the focal point position with respect to the photoconductor 2 is recorded in the second ROM 26.

Here, FIG. 4 shows a change in the beam due to a difference in the distance between the LED 13 and the image plane. a shows the beam diameter at the in-focus position, and b shows the beam diameter at the non-focus position. FIG. 6 shows the relationship between the focal length and the dot diameter on the photosensitive member 2 when an electrostatic latent image of dots is formed on the photosensitive member 2 with a constant output, and the electrostatic latent image is developed under constant conditions. Is a graph showing by experiment. In FIG. 6, 0 on the horizontal axis is
Position of the write head 4 when focusing on a true focus, -10,-
Reference numerals 20... Move the writing head 4 from the focal point to the photosensitive member 2 side.
Positions approaching every 0 μm, 10, 20,.
When the writing head 4 is moved by 10 μm in the out-of-focus direction with respect to the photoconductor 2 at a position separated from the in-focus position by 10 μm toward the photoconductor 2 side, the dot diameter on the photoconductor 2 becomes a little. It can be seen that the size becomes larger gradually. In this case, a change in the dot diameter due to a difference of 10 μm from the in-focus position is small, and it can be determined that such a positional error is within an allowable range. As the write head 4 moves away from the focal point, the dot diameter increases, but if it exceeds 20 μm, the exposure potential on the photoreceptor 2 is less likely to be lower than at the focal point, so that it is difficult to visualize. Understood.

Utilizing such a phenomenon, the write head 4 is positioned at an intermediate point between the two positions of the write head 4 with respect to the photosensitive member 2 when the toner image is not visualized across the focal point. Thus, the write head 4 can be fixed at the focal point.

Hereinafter, the processing will be described with reference to the flowchart shown in FIG. In the present embodiment, a description will be given assuming that the focus position is adjusted at the time of final adjustment work at a factory that manufactures the image forming apparatus 1 or at the time of adjustment work by maintenance after shipment from the factory.

First, the position of the writing head 4 is adjusted from the expected focal point to the photosensitive member 2 (S1). In this example, since the distance from the surface of the photoconductor 2 to the LED 13 is assumed to be 400 μm, the focus position is adjusted to 150 μm from the focus position to the photoconductor 2 side. For this adjustment, the write head drive circuit 25 rotates the head drive unit (motor) 24 forward by a predetermined angle to move the write head 4 to the photoconductor 2 side. At this out-of-focus position, a test image pattern is written by the write head 4, and the image pattern is developed by the developing device 5 (S2), and it is determined whether or not the toner image visualized at this time is present (S3). . The determination of the presence or absence of the toner image is performed by detecting the output of the density sensor 20. If it is determined in step S3 that there is a toner image visualized, the efficiency of exposure by the writing head 4 is reduced. In this example, the exposure time of the write head 4 is reduced by 0.5 μsec from the time of normal image formation (S4). Such processing is repeated until it is determined in step S3 that there is no visualized toner image. When it is determined that there is no visualized toner image, the position of the writing head 4 is set to 10
It is moved away from the photoconductor 2 by μm (S5). The writing head 4 is moved away from the photoconductor 2 by reversing the head driving unit (motor) 24 by a predetermined angle by the head driving circuit 25.

Subsequently, at that position, a test image pattern is written by the writing head 4 and the image pattern is developed by the developing device 5 (S6), and it is determined whether or not there is a toner image visualized at this time. (S7). The processes of steps S5 and S6 are repeated until it is determined in step S7 that the visualized toner image is present.
When it is determined that there is a visualized toner image, the current position A1 of the write head 4 is stored in a RAM (not shown) (S8). The stored data of A1 is data indicating a critical position where the toner image is visualized or stopped in a direction in which the writing head 4 is closer to the photoconductor 2 side than the focus position.

Subsequently, in order to detect a critical position where the toner image is visualized or not in a direction in which the writing head 4 is farther from the photosensitive member 2 than the focal point, the writing head 4 is detected.
Is moved away from the photoconductor 2 by 10 μm (S9), and at that position, a test image pattern is written by the writing head 4 and the image pattern is developed by the developing device 5 (S9).
10) It is determined whether there is a toner image visualized at this time (S11). The processes of steps S9 and S10 are repeated until it is determined in step S11 that there is no visualized toner image. When it is determined that there is no visualized toner image, the current position B1 of the write head 4 is not shown. It is stored in the RAM (S12).

In this manner, the critical position A1 of the write head 4 at which the toner image is not visualized on the photoconductor 2 at two positions sandwiching the expected focal point of the write head 4 with respect to the photoconductor 2 , B1 are called from the RAM, and A1, B
1 is calculated, and the calculated value D1 is stored in the second ROM 2
6 (S13). The data D1 stored in the second ROM 26 is fixed data determined by the assembly state of each image forming apparatus 1. Then, the head driving circuit (motor) 24 is driven by the head driving circuit 25 based on the data of D1, and the writing head 4 is moved to the in-focus position (S14). Thereby, the focal position of the writing head 4 can be automatically adjusted.

In the present embodiment, the writing head 4 is moved when the writing head 4 is relatively moved with respect to the photosensitive member 2, but the photosensitive member 2 may be moved. Good. Also, when moving the write head 4,
Either the LED array 14 or the lens array 16 constituting the writing head 4 may be moved.

Here, S1, S5, and S9 are positions of the writing head 4 relative to the photosensitive member 2 at a plurality of positions where the expected focal position of the writing head 4 with respect to the photosensitive member 2 is symmetrical. Corresponds to a focal position changing unit that controls the operation of the head driving unit 24 so as to move the head.

In steps S2, S6 and S10, a test image pattern is exposed by the write head 4 at each position of the write head 4 whose relative position with respect to the photosensitive member 2 has been changed by the control of the above-mentioned focus position changing means. And an image pattern image output unit that forms a toner image on the photoconductor 2 by performing development.

The density sensor 20 functions as a visible toner image presence / absence detecting means for detecting the presence / absence of a visualized toner image.

In step S12, the photosensitive member 2 is positioned at two positions sandwiching the expected focal point of the write head 4 with respect to the photosensitive member 2.
Image head position storing means for storing the critical positions A1 and B1 of the write head 4 at which the toner image is no longer visualized.

Step S13 corresponds to an intermediate point calculating means for calculating an intermediate point between the two positions of the write head 4 stored in the imageless head position storing means.

In step S14, the head driving unit 24 is driven based on the calculated value D1 of the above-mentioned intermediate point calculating means to move the writing head 4 relatively to the photosensitive member 2 and position it at the focal point. It corresponds to a focal position correcting means.

As described above, when the beam is imaged on the photosensitive member 2, as the distance between the photosensitive member 2 and the writing head 4 approaches or separates from the focal point as a center, the exposure potential becomes less likely to decrease, and the toner Focusing on the tendency of the image not to be visualized, the critical write head positions A1 and B1 at which the toner image is not visualized on the photoconductor 2 are set to the expected in-focus positions where the true focus is formed on the photoconductor 2. Are determined at two positions sandwiching the position of the write heads A1 and B1, and the intermediate point between the positions of the two write heads A1 and B1 is set as the focal point position D1, so that the focus position of the write head with respect to the photosensitive member 2 is adjusted. The focus position of the write head 4 can be easily adjusted without attaching and detaching the head. In addition, since the position of the writing head 4 is adjusted while the photoconductor 2 is mounted, the trouble of remounting the photoconductor 2 can be eliminated.

The toner image on the photoreceptor 2 is detected by the density sensor 20, and based on the detection result, charging,
Forming an image with a constant density by setting image conditions such as exposure and development has been conventionally performed, but in the present embodiment, in order to detect whether or not the toner image is no longer visualized, Since the density sensor 20 is used, CC
Other light receiving devices such as a D camera can be omitted. Also, when the presence or absence of a visualized toner image is determined without using another reading element by transferring the toner image to a sheet of paper and silently looking at it, other light receiving devices are omitted and the structure is further increased. Simplification can be achieved.

Further, if the efficiency of the exposure of the writing head 4 is increased to detect the position A1 where the first toner image is not visualized, the distance for moving the writing head 4 to the in-focus position becomes longer. Then, the writing head 4 is moved to a predetermined out-of-focus position, and when there is a toner image visualized at this time, the efficiency of the exposure by the writing head 4 is reduced, so that the writing head 4 is further moved to a non-focused position. It is possible to recognize a position where the toner image is no longer visualized without moving the focus position. When the exposure efficiency is reduced, the exposure power of the LED 13 may be reduced as well as the exposure time of the write head 4 as in the process in step S4 of FIG. Further, the same effect can be obtained by lowering the developing bias from that at the time of normal image formation and performing development. Further, the same effect can be obtained even if an image pattern is formed by dots having a small area ratio.

Further, the position of the write head 4 in the direction of the focal length with respect to the photosensitive member 2 is relatively changed, and when the image pattern is exposed by the write head 4 at each position, the position of the write head 4 in the axial direction of the photosensitive member 2 is changed. When the image pattern is formed along the image pattern, it is possible to recognize a state where the visualization state of the toner image of the image pattern changes at a position along the axial direction of the photoconductor 2. Thereby, the write head 4 can be correctly positioned after recognizing the degree of parallelism between the photoconductor 2 and the write head 4.

Next, a second embodiment of the present invention will be described with reference to FIG. The parts described with reference to FIGS. 2 to 6 are the same in the present embodiment. In the previous embodiment, the description has been made on the assumption that the focal position of the writing head 4 is adjusted at the time of factory shipment and maintenance.
In this embodiment, each time the printing operation is started, the writing head 4
It is assumed that the focal position is adjusted. Further, in this example, the focal position of the writing head 4 is adjusted in accordance with the rotation angle of the photoconductor 2 in consideration of the variation in the roundness of the photoconductor 2. For this purpose, a counter (not shown) for counting the rotation angle data of the photoconductor 2 is provided. FIG. 7 shows the process of adjusting the focal position.

First, the counter indicates the rotation angle n =
0 is set (S21). Subsequently, the number of samples in the sub-scanning direction (the rotation direction of the photoconductor 2) is determined (S22). In this example, the number of samples is set to 360 in order to adjust the focal position every time the photoconductor 2 is rotated by 1 °. Subsequently, by the same processing as in steps S1 to S13 in FIG. 1, the critical writing head positions An and Bn at which the toner image is not visualized on the photoconductor 2 are focused on the photoconductor 2 with a true focus. At the two positions sandwiching the expected in-focus position. The intermediate point between the two positions An and Bn of the write head 4 is determined as the in-focus position D.
n is stored in the second ROM 26 (S23). This process is performed each time the photoconductor 2 is rotated by 1 °, and the counter is incremented each time (S24), and the process proceeds to step S2.
5, the processes of steps S23 and S24 are repeated until the state where the number of samples reaches 360 is recognized, and the counter is cleared when the number of samples reaches 360 (S
26). That is, the data of n of An, Bn, and Dn has the number of samples. In the processes of S21 to S26, it can be recognized that the photoconductor 2 is a perfect circle if the value of Dn is constant, and is not a perfect circle if the value of Dn is not constant.

Subsequently, based on the given image data, a charger 3, a write head 4, a developing unit 5, a transfer unit 6, and a fixing unit 11
The operation shifts to printing by the operation of each process unit.
In this case, before exposing the photosensitive member 2 with the writing head 4 (forming an electrostatic latent image), data Dn of the in-focus position is called from the second ROM 25 (S27), and based on Dn, the data for the photosensitive member 2 is read. Adjust the focal position of the write head 4 (S2
8). The processing in step S28 is the same as the processing in step S14 described in FIG. Thereafter, the photoconductor 2 is exposed by the writing head 4 (S29), and an electrostatic latent image for one scanning line is formed. This step S27-
The process of step S29 is executed until it is determined in step S30 that the image data (print data) is completed, and the counter is incremented each time (step S31). Step S
In S32, unless it is recognized that the value of the counter has reached 360, the processes of steps S27 to S31 are executed. However, when it is recognized that the value of 360 has reached 360, the counter is cleared (S26).

As described above, when outputting image data for printing, the focal position of the writing head 4 can be adjusted in accordance with the rotation angle of the photoconductor 2, so that the roundness of the photoconductor 2 can be adjusted. Even if the image does not appear, it is possible to prevent unevenness in image quality in the sub-scanning direction.

In the exposure step, if the rotation angle of the photosensitive member 2 increases, the exposure position reaches the position of the developing device 5 or the transfer device 6, and therefore, depending on the progress of the rotation of the photosensitive member 2, step S29 is performed. Then, development and transfer are also performed.

[0051]

According to the first aspect of the present invention, there is provided a method for adjusting a focus position of a write head, wherein the position of the write head relative to the photosensitive member is relatively changed to form a toner image at each position, and the toner image is visualized on the photosensitive member. Critical write head position,
A true focal point is formed on the photoreceptor at two positions sandwiching an expected in-focus position. By setting the position, the focal position of the writing head can be easily adjusted without attaching / detaching the photoconductor. Further, since the position of the writing head is adjusted while the photoconductor is mounted, the trouble of remounting the photoconductor can be eliminated.

According to a second aspect of the present invention, in the method of adjusting the focal position of the write head, the position of the write head in the direction of the focal length with respect to the photosensitive member is relatively changed, and the writing is performed at each position. When exposing the image pattern by the head, by lowering the exposure efficiency compared to the normal image formation, the toner image of the image pattern is hardly visualized. When the relative position with respect to the head is changed, the range in which the toner image is visualized becomes short. As a result, two positions where the toner image cannot be visualized can be recognized in a short time.

According to a third aspect of the present invention, in the method of the first aspect, the position of the writing head relative to the photosensitive member in the direction of the focal length is relatively changed, and the writing head is changed at each position. When a toner image is formed by performing exposure and development of an image pattern according to the present invention, by lowering the developing bias from the time of normal image formation and performing development, it becomes difficult to visualize the toner image of the image pattern. When the relative position between the photoconductor and the writing head is changed, the range in which the toner image is visualized becomes short. As a result, two positions where the toner image cannot be visualized can be recognized in a short time.

According to a fourth aspect of the present invention, there is provided a write head focal position adjusting method according to the first aspect, wherein the position of the write head relative to the photosensitive member in the focal length direction is relatively changed, and the writing is performed at each position. When exposing the image pattern by the head, by forming the image pattern with dots, the dot image has a small image area and is hard to be visualized, so the relative position between the photosensitive member and the writing head is reduced. Is changed, the range in which the toner image is visualized becomes shorter. As a result, two positions where the toner image cannot be visualized can be recognized in a short time.

According to a fifth aspect of the present invention, in the method of the first aspect, the position of the write head relative to the photosensitive member in the focal length direction is relatively changed, and the writing is performed at each position. When exposing the image pattern by the head, by forming the image pattern along the rotation direction of the photoconductor, the focus position of the writing head with respect to the photoconductor every time the photoconductor is rotated by a predetermined angle. Can be recognized. This makes it possible to measure variations in the roundness of the photoconductor.

According to a sixth aspect of the present invention, in the method of adjusting the focal position of the write head, the position of the write head relative to the photosensitive member in the direction of the focal length is relatively changed, and the writing is performed at each position. When exposing the image pattern by the head, the visualization state of the toner image of the image pattern changes at a position along the axial direction of the photoconductor by forming the image pattern along the axial direction of the photoconductor. It is possible to recognize the state of doing. Thereby, the parallelism between the photoconductor and the write head can be recognized.

According to a seventh aspect of the present invention, there is provided a writing head focal position adjusting method according to the first aspect, wherein the critical position of the writing head at which a toner image is not formed on the photosensitive member is determined. By determining the presence / absence of an image based on the transferred image on the paper, the presence / absence of the visualized toner image can be recognized by silent observation without using another light receiving element, thereby simplifying the structure. be able to.

In the image forming apparatus according to the present invention, the operation of the driving section is controlled by the focal position changing means, and writing is performed at a plurality of positions where the expected focal position of the write head with respect to the photosensitive member is symmetrical. The head was moved relative to the photoconductor, and at each position of the writing head whose relative position to the photoconductor was changed by this movement, a toner image was output by the image pattern image output means, and this visualization was performed. Critical write head in which the presence or absence of a toner image is detected by a visible toner image presence / absence detecting means, and the toner image is not visualized on the photoreceptor at two places sandwiching the expected focusing position of the write head with respect to the photoreceptor. Is stored in the imageless head position storage means, the intermediate point between the two stored write head positions is calculated by the intermediate point calculation means, and the focal position is corrected based on the calculated value. Since the operation of the drive unit is controlled by the step to move the write head relatively to the photoconductor, the focal position of the write head can be automatically adjusted without attaching / detaching the photoconductor. Further, since the position of the write head is adjusted while the photoconductor is mounted, the trouble of remounting the photoconductor can be eliminated.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a write head focus position adjustment process according to a first embodiment of the present invention.

FIG. 2 is a front view illustrating a schematic configuration of the image forming apparatus.

FIG. 3 is a side view showing a photoconductor and a write head.

FIG. 4 is an explanatory diagram showing an imaging state of a beam emitted from an LED.

FIG. 5 is a block diagram showing an electronic circuit.

FIG. 6 is a graph experimentally showing a relationship between a position of a write head with respect to a photoconductor and a dot diameter.

FIG. 7 is a flowchart illustrating a printing process according to a second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 2 photoconductor 4 write head 13 point light source element 20 visible toner image presence / absence detection means 24 drive unit S1, S5, S9 focal position change means S2, S6, S10 image pattern image output means S12 imageless head position storage means S13 intermediate point Calculation means S14 Focus position correction means

Claims (8)

[Claims] An electrostatic latent image is formed on a surface of a photoreceptor by a writing head having a plurality of point light source elements arranged in an array, and the electrostatic latent image is developed into a toner image and transferred to a sheet. In the image forming apparatus, the position of the writing head in the direction of the focal length with respect to the photoconductor is relatively changed, and the writing image is exposed and developed by the writing head at each position. The critical position of the writing head at which the toner image is formed and the toner image is not visualized on the photoconductor is defined by two points sandwiching an expected in-focus position for forming a true focus on the photoconductor. The focus position of the write head with respect to the photoconductor is set using the intermediate point between the two positions of the write head as the focal point position, and the writing to the photoconductor is adjusted in accordance with the set position. Head relative A focus position adjusting method for adjusting a focal position of a write head. 2. The method according to claim 1, wherein the position of the write head relative to the photoreceptor in the direction of the focal length is relatively changed, and when the image pattern is exposed by the write head at each position, the efficiency of the exposure is reduced by normal image formation. 2. The method according to claim 1, wherein the exposure is performed at a time lower than the exposure time. 3. A developing bias for forming a toner image by relatively changing the position of the write head relative to the photoreceptor in the direction of the focal length and exposing and developing an image pattern by the write head at each position. 2. The method according to claim 1, wherein the developing operation is performed while lowering the image forming temperature than during normal image formation. 4. A method according to claim 1, wherein the position of the writing head relative to the photosensitive member in the direction of the focal length is relatively changed, and when the image pattern is exposed by the writing head at each position, the image pattern is formed by dots. 2. The method according to claim 1, wherein the focus position is adjusted. 5. A method according to claim 1, wherein the position of the writing head relative to the photosensitive member in the direction of the focal length is relatively changed, and the exposure of the image pattern by the writing head at each position is performed along the rotation direction of the photosensitive member. 2. The method according to claim 1, wherein an image pattern is formed. 6. When the position of the writing head in the direction of the focal length with respect to the photosensitive member is relatively changed, and the image pattern is exposed by the writing head at each position, the position is changed along the axial direction of the photosensitive member. 2. The method according to claim 1, wherein an image pattern is formed. 7. The method according to claim 1, wherein the presence or absence of the visualized toner image is determined based on a transfer image on a sheet in order to determine a critical position of the write head at which a toner image is not formed on the photosensitive member. Item 2. The write head focal position adjusting method according to Item 1. 8. An electrostatic latent image is formed on the surface of a photoreceptor by a writing head having a plurality of point light source elements arranged in an array, and the electrostatic latent image is developed into a toner image and transferred to a sheet. A driving unit that moves the writing head relative to the photoconductor in a focal length direction, and an expected focal point of the writing head with respect to the photoconductor. Focus position changing means for controlling the operation of the drive unit so as to move the write head relatively to the photosensitive member to a plurality of positions symmetrical with each other; Image pattern image output means for performing exposure and development of a test image pattern by the write head at each position of the write head whose relative position with respect to has been changed to form a toner image on a photoreceptor; A visible toner image presence / absence detecting means for detecting the presence / absence of the toner image, and a toner image visualized on the photoconductor at two places sandwiching an expected focal point of the writing head with respect to the photoconductor. Imageless head position storage means for storing the position of the write head at a critical point, and intermediate point calculation means for calculating an intermediate point between the two positions of the write head stored in the imageless head position storage means Focus position correcting means for driving the drive unit based on the calculated value of the intermediate point calculating means to move the write head relatively to the photoconductor to be positioned at a focal point;
An image forming apparatus comprising: