JP4164271B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using a plurality of light beams.
[0002]
[Prior art]
As a conventional technique, an optical beam scanning device disclosed in Japanese Patent Application Laid-Open No. 2000-187171 scans two writing systems with one deflecting means, and connects them together to form a compact scanning optical with a wide scanning width. Realize the system.
[0003]
In addition, the optical scanning device and the image forming apparatus disclosed in Japanese Patent Laid-Open No. 2000-267027 detect the position of the joint portion of the two beams in the sub-scanning direction, and correct the position. In this technique, since the accuracy of adjustment of the light beam is determined by the accuracy of the position detection sensor (including peripheral circuits), a highly accurate sensor is required (and only in the sub-scanning direction).
[0004]
[Problems to be solved by the invention]
In the technique described in the above Japanese Patent Laid-Open No. 2000-267027, two writing systems are scanned with one polygon, optical beam scanning is started from almost the center of the image, and optical beam is scanned in the main scanning direction. A method for connecting the two systems has been proposed. As a result, a low-cost, compact and wide writing system has been achieved. Further, a light beam passage position detecting means (one one-dimensional CCD) is provided in the sub-scanning direction, and the scanning line shifts in the sub-scanning direction caused by temperature fluctuations (the optical path due to thermal expansion of the housing or the lens system). It has been proposed to correct the displacement of the two joints. In adjusting the shift of the joint, it is important that the positions of the two light beams (writing start positions) can be accurately detected and adjusted easily.
[0005]
The present invention has been made in view of the above points, and provides an image forming apparatus capable of easily and accurately adjusting a shift between joints in the main and sub directions of two light beams. For the purpose.
[0006]
In particular, the main object of the present invention is that the position of an optical beam can be detected with high accuracy even if a sensor having a relatively low linearity is used. In the technique of Japanese Patent Laid-Open No. 2000-267027, since the accuracy of adjustment of the light beam is determined by the accuracy of the position detection sensor (including peripheral circuits), a highly accurate sensor is required (and only in the sub-scanning direction).
[0007]
Another object of the present invention is to display a plurality of connection states of two optical beams at different times (conditions (control values)) at once, and to easily visually recognize the connection state.
[0008]
Another object of the present invention is to make it easy to find and input conditions when the connection state of two optical beams is optimal, and to simplify connection adjustment.
[0009]
Also, other objects, two light bi - is that it does not require subsequent adjustment be determined once the control value of the beam lighting means - arm ties degree bicycloalkyl when optimum.
[0010]
[Means for Solving the Problems]
In order to achieve such an object, the invention described in claim 1 corresponds to each light beam in an image forming apparatus that scans by dividing two light beams on the photosensitive member in the main scanning direction. Synchronization detecting means for detecting a reference position of the light beam, and a light beam lighting means for lighting a dot and moving the dot lighting position and the image writing position between the synchronization detecting means and the image writing position, Position detection means for detecting the position of the lit dot between the synchronization detection means and the image writing position, and the difference between the detected dot position and the regular dot position ( ΔX1), and the smallest integer N that satisfies N * P> ΔX1 is calculated (where P is the pitch interval of the light beam), and the image writing position by the light beam is N * P−ΔX1 later Las adjustment, and, you store the light beam position adjustment control for adjusting shifting forward by N * P, the output value of the position detecting means when the measurement accuracy is lit dots with high positional in memory Then, the output value stored in the memory is called for each image writing, and the light beam lighting means is used until the output value of the position detection means becomes the output value stored in the memory. And an image writing position adjustment control for moving the image writing position .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, a basic configuration / operation as a premise of the image forming apparatus according to the embodiment of the present invention will be described. In the following, the same parts are distinguished by being given the same symbols.
[0016]
First, with reference to FIG. 11 and the subsequent figures, a description will be given of an “optical scanning device that scans a scanning region on a surface to be scanned by dividing it into two in the main scanning direction by two beams” to which the present invention is applied. As shown in FIG. 11, the optical scanning device has a first writing system and a second writing system.
[0017]
The first writing system will be described. A laser beam whose intensity is modulated in accordance with an image signal is emitted from the semiconductor laser 1-1 as a “light source”. The emitted beam is made into a parallel beam by the collimating action of the coupling lens 2-1, and is given a tendency to converge only in the sub-scanning direction by the cylinder lens 3-1, and one deflection reflection of the polygon mirror 4 as a "deflecting means". A line image that is long in the main scanning direction is formed near the surface. The beam deflected at a constant angular velocity by the rotation of the polygon mirror 4 is transmitted through the lenses 5-1 and 6-1 constituting the fθ lens as “image forming means”, and the mirrors 7-1 and 8-1 and the folding mirror. A beam spot is formed on the photosensitive surface of the photoconductive photoconductor 10 (substantially the surface to be scanned) that is sequentially reflected by the light-sensitive photoconductor 10-1, and scans the first scanning region S1 of the photoconductor 10 at a constant speed. To do.
[0018]
The second writing system is arranged at a position where the “first writing system” is rotated 180 degrees around the rotation axis of the polygon mirror 4. A laser beam whose intensity is modulated in accordance with an image signal is emitted from the semiconductor laser 1-2 as a “light source”, is converted into a parallel beam by the coupling lens 2-2, and is sub-scanned by the cylinder lens 3-2. As a result, the image is formed as a long line image in the main scanning direction in the vicinity of another deflecting reflection surface of the polygon mirror 4. The beam deflected at a constant angular velocity by the rotation of the polygon mirror 4 is transmitted through the lenses 5-2 and 6-2 constituting the fθ lens as the “imaging means”, and the mirrors 7-2 and 8-2 and the folding mirror. The beam spot is sequentially reflected by 9-2 to form a beam spot on the photosensitive surface of the photoconductor 10, and the second scanning region S2 of the photoconductor 10 is scanned at a constant speed.
[0019]
The first and second writing systems are optically equivalent. Writing by the first and second writing systems is performed in opposite directions from the junction of the first and second scanning regions S1 and S2, that is, the central portion S0 of all the scanning regions, that is, both end portions of the scanning region. Done to the side.
[0020]
The first and second writing systems have synchronization detection units 11-1 and 11-2, respectively. Each of the synchronization detection units 11-1 and 11-2 is provided outside the image area of each scanning beam, and determines the scanning start timing of each scanning beam for each scan. A “write control circuit” (not shown) starts writing from the writing start position (the above-described central portion S0 of all scanning regions) according to the determined timing. In this way, the writing start position S0 of each scanning beam is common to each other and is controlled well by the synchronization detection unit 11, so that the seam portion of each scanning beam in the main scanning direction can be easily and satisfactorily aligned. .
[0021]
The first and second scanning regions S1 and S2 are to be connected to each other as one straight line, and are designed to be “fixed in the apparatus space” in terms of design. The ideal scanning line fixedly set in the apparatus space in this way is a “line to be scanned simultaneously by two beams” on the surface to be scanned and a “surface to be scanned”. That is, the first and second scanning regions S1 and S2 should ideally be “both coincide with the scanned surface axis and be connected to each other at the central portion S0”.
[0022]
FIG. 12 shows a state where the optical scanning device shown in FIG. 11 is viewed from the direction of the rotation axis of the polygon mirror 4. The aforementioned “beam deflection surface” is a surface parallel to the drawing in FIG. FIG. 13 shows a state in which the state of FIG. 12 is viewed from the axial direction of the photoconductor 10 constituting the surface to be scanned. Although not shown in FIG. 12, the optical scanning device is hermetically sealed and fixed and arranged with high precision in order to prevent “attachment of dust and the like”. In FIG. 13, reference numerals 12-1 and 12-2 indicate “dust-proof glass” that blocks the beam emission opening formed in the optical box.
[0023]
As shown in FIG. 14, the mirrors 7-1 and 8-1 in the first writing system are arranged so as to “spatially overlap in the sub-scanning direction (vertical direction in the drawing)”. As shown in the figure, “inclination angles with respect to the beam deflection surface” of the mirrors 7-1 and 8-1 are angles: α and β (both measured from the beam deflection surface, with clockwise being “positive” and counterclockwise being “negative”. The inclination angle: α, β satisfies the relationship: | α−β | = 90 degrees. That is, the mirrors 7-1 and 8-1 constitute a so-called “dach mirror”, and the surface on which the deflection beam sequentially reflected by the mirrors 7-1 and 8-1 sweeps becomes “parallel to the beam deflection surface”. The mirrors 7-2 and 8-2 in the second writing system are similarly configured.
[0024]
In order that the first and second writing systems can equivalently scan a common scanning line (“scanned surface axis”), generally, the optical axes of the first and second writing systems are scanned surface axes (photosensitive). The optical path lengths of the imaging means of each writing system must be equal to each other. If this is the case, the beam spot diameter is uniform and good scanning can be realized, and a good image can be obtained.
[0025]
In the example described above, the imaging means is composed of an fθ lens. As shown in FIG. 12, the optical axis of the fθ lens composed of the lenses 5-1 and 6-1 has an inclination angle θ1 with respect to the scanned surface axis S, and the lenses 5-2 and 6-2. The optical axis of the fθ lens configured as follows has an inclination angle: θ2 with respect to the scanned surface axis S. Therefore, in order to make the optical axis of each fθ lens perpendicular to the scanning surface axis S, two mirrors (mirrors 7-1 and 8-1 in the first writing system, mirror 7- in the second writing system). 2, 8-2).
[0026]
In the first writing system, an angle formed by the optical axis of the fθ lens “in the beam deflection plane with respect to the mirror 7-1”: γ1, and an angle formed by the optical axis with respect to the scanned surface axis S: θ1. Satisfies | θ1 | +2 | γ1 | = 90 °. Similarly, in the second writing system, an angle formed by the optical axis of the fθ lens “within the beam deflection surface with respect to the mirror 7-2”: γ2, and an angle formed by the optical axis with respect to the scanned surface axis S. : Θ2 satisfies | θ1 | +2 | γ1 | = 90 °.
[0027]
In this way, the principal ray of the beam matching the optical axis of each fθ lens is reflected by the mirror 8-1 or the mirror 8-2 (when projected onto the beam deflection surface) and is projected onto the beam deflection surface. It is orthogonal to the scanning plane axis. The beams reflected by the mirrors 8-1 and 8-2 are folded back by the folding mirrors 9-1 and 9-2 in the sub-scanning direction, and finally made orthogonal to each beam scanning surface axis S.
[0028]
FIG. 12 shows the optical arrangement described with reference to FIG. 2 and subsequent drawings, and is the case where θ1 = θ2 and γ1 = γ2. The arrangement of the first and second writing systems is not limited to the case of FIG. FIG. 15 shows another arrangement example. The optical arrangement in FIG. 15 is an example in which θ1 ≠ θ2 and γ1 ≠ γ2. In this case, the “scanning length” of the first writing system and the second writing system is not the same. The angles γ1 and γ2 are uniquely determined according to the angles θ1 and θ2, respectively. The scanning lengths of the first and second writing systems are determined according to the angle: θ1 and the angle: θ2. Therefore, the effective scanning width can be maximized by setting the angles θ1 and θ2 to optimum values.
[0029]
As described above, in the “optical scanning device that scans the scanning area on the surface to be scanned in two in the main scanning direction using two beams”, the scanning beams of the two writing systems are connected together with high accuracy. One scan line is scanned. That is, the scanning lines of the scanning beams of the first and second writing systems are ideally “should match the scanning surface axis”. The optical arrangement of the first and second writing systems is adjusted so that the scanning beam of each writing system is aligned with the scanned surface axis after assembly. However, due to a rise in the internal temperature of the image forming apparatus equipped with the optical scanning device or heat generated by the deflecting means, it is possible to change the writing of each The phenomenon that the scanning position of the scanning beam of the system is shifted in the sub-scanning direction occurs. Therefore, it is necessary to detect and automatically correct such a “scan position shift amount”.
[0030]
Based on the above basic description, the characteristic configuration and operation of the present invention will be described next. First, the correction of the two-dimensional position sensor is completed, the position of the light beam (laser beam) position adjustment with the sensor will be described, and then the sensor correction method will be described.
[0031]
<Light Beam Position Adjustment> FIG. 1 is a block diagram of an image forming apparatus including an optical scanning device according to an embodiment of the present invention. Laser beam by the first writing system is deflected by the rotation of the polygon mirror 4 is first incident on the virtual photosensitive disposed on a body surface the synchronization detection plate 11-1 (synchronization detection unit described above). At this time, the laser beam is incident on the synchronous detection in the continuous lighting state as referred to the LD lighting signal (a) in FIG. When a continuously lit laser beam is incident upon synchronization detection, a synchronization detection signal (b) for horizontal synchronization of the laser beam is generated, the LD lighting signal is temporarily turned OFF, and the LD is turned off.
[0032]
In the synchronization detection plate 11-1, there are a synchronization detection sensor 11-1-1 and a two-dimensional position sensor 11-1-2 arranged between the synchronization detection sensor 11-1-1 and the image writing start position. Has been placed. In this example, they are arranged on the same substrate, but may not be on the same substrate as long as they are between the synchronization detection and the image writing position.
[0033]
In the present example, the two-dimensional position detection element is configured to use a two-dimensional PSD (which is a known technique; details are omitted). Also for the second writing system, a synchronization detection plate 11-2, a synchronization detection sensor 11-2-1 and a position sensor 11-2-2 included therein are arranged.
[0034]
2 and 3 are diagrams showing the relationship between the synchronization detection sensors (11-1-1 and 11-2-1), the position sensors (11-1-2 and 11-2-2), the laser beam dots and each signal. It is. Although the first writing system and the second writing system are written, if only one explanation can be found, the first writing system will be described. After the LD is turned off once, the LD is turned on again after a predetermined number of pixel clocks (No clock in this example) from the synchronization detection signal (b), and one dot is generated on the position sensor. As a result, the laser beam is equivalently stationary on the position sensor, and the laser beam positions for main scanning and sub-scanning can be detected simultaneously. The pixel clock (c) is generated based on the synchronization detection signal (b), and modulation based on the image data is started after a predetermined number of clocks (Ng clock in this example) from the synchronization detection.
[0035]
Signals from the position sensors (11-1-2, 11-2-2) generate X1 and Y1 voltages based on the X (main scanning) direction position and the Y (sub-scanning) direction position via the control unit. Then, it is converted into position information by an AD converter (not shown) (in the write control unit in FIG. 10), a control calculation unit, or the like.
[0036]
Even in the second writing system, only the scanning direction is reversed, the operation is the same as in the first writing system, and position detection is performed.
[0037]
Next, FIGS. 4, 5 and 6 show conceptual diagrams when dots are shifted in the main direction and sub-scanning direction due to a signal delay due to a temperature rise in synchronization detection and a temperature rise in the writing system. First, to describe the main scanning direction of the shift, until the laser beam is incident on the detection sync, the laser beam is continuous light. As shown in FIGS. 2 and 3 (FIG. 5b) in the case of room temperature, if the synchronization detection signal is generated almost simultaneously with the incidence of the synchronization detection (actually, the time lag is not 0), the temperature in FIG. In the case of rising, the phenomenon that the generation of the synchronization detection signal is delayed by Δt (ΔX1 in terms of distance) occurs. In addition, the phenomenon that the magnification changes due to the temperature rise of the lens system and the dots shift in the main scanning direction also overlaps.
[0038]
When the synchronization detection signal is delayed, writing is started after a predetermined clock (Ng) based on the synchronization detection, so that the image writing position is also shifted by ΔX1, and the beam position on the position sensor is also shifted by ΔX1. . Considering the influence of the magnification error of the optical system, the shift amount on the position sensor and the shift amount at the writing position are not the same, but are omitted here for simplification.
[0039]
As an example, FIG. 6 shows an example of a correction method in the case where there is a deviation in the main scanning direction by ΔX1. FIG. 6A shows dot positions when there is no regular deviation. FIG. 6B shows the dot position when it is shifted by ΔX1.
[0040]
If the dot is shifted on the two-dimensional position detection element by ΔX1, the phase of the pixel clock corresponding to the distance of N * P−ΔX1 is delayed by a laser beam lighting control unit not shown in FIG. 6C. Here, N is the smallest integer that satisfies N * P> ΔX1, and P is the beam pitch interval.
[0041]
As a result, the fourth pixel at the normal dot position is the same as the first dot position in the main scanning direction of (c). Next, as shown in FIG. 6D, N dots (3 dots in this example) are added in front of the first dot, and the image data is further shifted to the N dot front side. Actually, this is the same as setting the number of clocks (Ng) from the synchronization detection signal to the writing position to Ng−N.
[0042]
By performing the above processing in the second writing system in the same manner, the joint in the main scanning direction can be aligned with a predetermined position.
[0043]
Next, correction in the sub-scanning direction will be described. In FIG. 8, a shift of ΔY1 in the sub-scanning direction is detected on the two-dimensional position detection element in the first writing system and ΔY2 in the second writing system. Correspondingly, deviations of ΔY1 and ΔY2 also occur at the writing position, and the laser beam is relatively separated in the sub-scanning direction by ΔY.
[0044]
The main cause of the shift in the sub-scanning direction is that the position of the optical component such as the mirror is slightly displaced due to the thermal expansion of the housing.
[0045]
The stepping motor 14 in FIG. 1 is rotated by an amount corresponding to the detected deviation in the sub-scanning direction to displace the angle of the folding mirrors (9-1, 9-2), and the deviation in the sub-scanning direction is corrected. ing.
[0046]
<Adjustment of Image Writing Start Position> A case where image writing start points are adjacent to each other when two laser beams are connected to form one scanning line will be described. Two dots at adjacent start points are designed so that writing is performed at a specified interval, but the desired interval is not achieved due to variations in the structure and components. In the case of 600 DPI writing, the specified interval is 42.3 μm. For example, even if the desired interval is determined to be 42.3 μm ± 20 μm, the interval is actually 115 μm and the desired interval is not achieved.
[0047]
Here, two types of adjustment are required. The initial adjustment and the adjustment for making the amount of deviation of the writing start position due to temperature and time after the initial adjustment to be a desired interval.
[0048]
The initial adjustment will be described. FIG. 7A shows a synchronous detection plate 11-1 including a position sensor 11-1-2 for the first writing system laser beam, and FIG. 7C shows a laser beam for the second writing system left scanning laser beam. The synchronous detection board 11-2 containing the position sensor 11-2-2 is shown.
[0049]
In FIG. 8, the position of the writing start dot (second writing system side number 1) of the second writing system is initially fixed, and the position of the writing start dot (first writing system side number 1) of the first writing system is fixed. Are sequentially moved in the main scanning direction. ~ No8. These are the adjustment sheets that were produced and printed out. The movement interval is the smallest possible control. As an example of the identification symbol or character corresponding to the line segment on the adjustment sheet, in FIG. ~ No8. Is described. In FIG. 8, the two laser beams are drawn while being shifted in the sub-scanning (up and down) direction (there is a shift both in practice and after adjustment in the sub-scanning direction) for easy understanding. 1 ′ on the second writing system side indicates the ideal position (position error is zero) of the writing start dot on the first writing system side. No6. Is found to be optimal (closest to the ideal position).
[0050]
This No6. Is input by an input means (not shown) (located in the operation unit in FIG. 10), and No. 6 on the apparatus side. Recognize that is optimal. No6. Assume that the dot positions on the position sensor at (1) and (2) are (1) and (2), respectively. (1) on the position sensor 11-2-1 is within the broken-line rectangle (center) where the measurement accuracy of the sensor described later is high, while (2) on the position sensor 11-1-2 is outside the broken-line rectangle ( It is in the main scanning direction ΔX1-1) from the center. When {circle around (2)} is outside the rectangle of the broken line, the fact that adjustment is necessary is displayed on a display unit (not shown) in the operation unit. If (2) is within the dashed rectangle at this point, the X1 voltage corresponding to the position (4) in this state and the X2 voltage corresponding to the position (3) are converted into digital values, and then the non-volatile memory (FIG. 10). ).
[0051]
When {circle around (2)} is outside the broken rectangle, the writing start position of the second writing system is shifted by ½ of ΔX1-1. The dot position on the position sensor 11-2-2 moves from (1) to (3). Note that ΔX2≈1 / 2 (ΔX1-1). In this way, the adjustment sheet is output again with the writing position of the second writing system shifted. Corresponding to the display indicating that the operation unit needs to be adjusted again, the optimal connection state is input from the latter adjustment sheet. In this state, the dot on the position sensor 11-1-2 approaches the center of the position sensor 11-1-2 by approximately ½ (ΔX1-1), and the position within the broken line rectangle where the measurement accuracy of the sensor is high (4) Move to ▼.
[0052]
When (2) is within the broken line rectangle, the values corresponding to (1) and (2) are stored in the memory, but when (2) is outside the broken line rectangle, the position in this state is set to (4). The corresponding X1 voltage and the X2 voltage corresponding to the position (3) (moved from the position (2)) are converted into digital values and stored in the nonvolatile memory.
[0053]
FIG. 9 shows the characteristics of the position sensor 11-1-2 (same for the position sensor 11-2-2). Measurement can be performed up to a distance ΔXH from the center, but if the distance is larger than ΔXL (corresponding to the broken-line rectangle in FIGS. 7A and 7B), the measurement accuracy (linearity) of the sensor is deteriorated. By moving the position from (2) to (4), the measurement accuracy can be increased (refer to other known documents for the principle and accuracy of the sensor).
[0054]
Adjustment for making a desired interval the amount by which the writing start position has shifted due to temperature or time is automatically performed as follows. Each time writing, the value corresponding to (3), (4) (or (1), (2)) stored in the non-volatile memory is recalled, and the dot is lit up until the image writing position and the dot is lit. The position sensor output is controlled to be a value corresponding to (3), (4) (or (1), (2)) by the light beam lighting means capable of moving the position and the image writing position. .
[0055]
Although the above description is mainly made in the main scanning direction, the joint adjustment can be performed in the sub-scanning direction as well. FIG. 10 is an overall block diagram. The numbers in each block correspond to the numbers in the sentence. The writing control unit includes means for outputting an identification symbol or a character corresponding to the images of a plurality of connected portions.
[0056]
The embodiment of the present invention has been described above. The above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto, and various modifications can be made without departing from the scope of the invention. .
[0057]
【The invention's effect】
As is clear from the above description, according to the present invention , the light beam position can be measured at a portion with a small error on the position sensor, so that even a sensor with partially poor positional accuracy can perform high-precision light beam position measurement. .
[0058]
Further, according to the present invention , since the connection state of two light beams with different conditions (control values) is displayed at a time, the connection state can be easily confirmed.
[0059]
In addition, according to the present invention , while viewing an output sheet displayed at a plurality of times, which is identified by an identification symbol or a character, an example of the connection state of two optical beams with different conditions (control values), Since adjustment can be performed by selecting and inputting an optimal connection, adjustment can be facilitated.
[0060]
Further, according to the present invention , the control value of the beam lighting means when the connection state of the two light beams is optimum is stored, and the connection value is always maintained by using the control value for each writing. Write in the optimal state.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus including an optical scanning device according to an embodiment of the present invention.
FIG. 2 is a diagram showing a relationship among synchronization detection sensors (11-1-1, 11-2-1), position sensors (11-1-2, 11-2-2), and laser beam dots.
FIG. 3 is a diagram illustrating a relationship between signals in FIG. 2;
FIG. 4 is a diagram illustrating a case where a dot is shifted in a main direction and a sub-scanning direction due to a signal delay due to a temperature rise in synchronization detection or a temperature rise in a writing system; It is a figure which shows a relationship.
FIG. 5 is a diagram illustrating a relationship between signals in FIG. 4;
FIG. 6 is a diagram illustrating an example of a correction method in a case where a deviation is caused in the main scanning direction by ΔX1.
FIG. 7 is a diagram showing the synchronization detection plates 11-1 and 11-2 for explaining the initial adjustment.
FIG. 8 is a diagram illustrating an adjustment sheet for explaining correction in the sub-scanning direction.
FIG. 9 is a diagram illustrating characteristics of the position sensor 11-1-2 (the same applies to the position sensor 11-2-2).
FIG. 10 is a diagram illustrating an overall configuration of an image forming apparatus including an optical scanning device according to an embodiment of the present invention.
FIG. 11 is a diagram showing a configuration of an optical scanning device that scans a scanning region on a surface to be scanned in two in the main scanning direction using two beams.
12 is a diagram showing a configuration of the optical scanning device of FIG. 11 viewed from the rotation axis direction of a polygon mirror 4. FIG.
13 is a diagram showing the state of FIG. 12 as viewed from the axial direction of the photoconductor 10 that is the substance of the surface to be scanned.
14 is a diagram showing the arrangement of mirrors in the optical scanning device of FIG. 11. FIG.
15 is a diagram showing another arrangement of the first and second writing systems in the optical scanning device of FIG. 11. FIG.
[Explanation of symbols]
1-1, 1-2 Semiconductor lasers 2-1, 2-2 Coupling lens 3-1, 3-2 Cylinder lens 4 Polygon motor 5-1, 5-2 Lens 6-1, 6-2 Lens 7-1 7-2 Mirror 8-1, 8-2 Mirror 9-1, 9-2 Folding mirror 10 Photoreceptor 11-1, 11-2 Synchronization detection unit 11-1-1, 11-2-1 Synchronization detection sensor 11 -1-2, 11-2-2 Position sensors 12-1, 12-2 Dust-proof glass 14 Stepping motor S0 Scanning region center S1 First scanning region S2 Second scanning region 30 Control means

Claims (1)

In an image forming apparatus that scans by dividing two light beams on a photosensitive member in the main scanning direction,
Synchronization detecting means for detecting the reference position of the light beam corresponding to each light beam;
A light beam lighting means for lighting dots between the synchronization detection means and the image writing position and moving the dot lighting position and the image writing position;
A position detection means for detecting the position of the lit dot between the synchronization detection means and the image writing position;
Calculate the difference (denoted as ΔX1) between the detected dot position and the regular dot position;
Calculate the smallest integer N such that N * P> ΔX1 (where P is the pitch interval of the light beam),
A light beam position adjustment control for adjusting the image writing position by the light beam to shift by N * P−ΔX1 and to adjust to shift the image writing position by N * P ;
After storing the output value of the position detection means in the memory when the dot is lit at a position with high measurement accuracy,
Each time the image is written, the output value stored in the memory is called, and the light beam lighting means is used to set the image write position until the output value of the position detecting means becomes the output value stored in the memory. An image forming apparatus that performs image writing position adjustment control to be moved .

Images