JP2002372676A - Image forming device by two-point synchronization detection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a clear multicolor image by performing modification in addition to the magnification error correction of an image formation optical system by taking that the positional interval of two synchronization detecting means of a two-point synchronization system causes image formation deviation due to the fluctuation of temperature at the inside of an image forming device into consideration. SOLUTION: In the image forming device to obtain a multicolor image by forming a latent image by performing image formation scanning with light beams from several image formation optical systems on a photoreceptor by using a polygon scanner, by visualizing it with the toner of different colors and performing the overlapping transfer of a visible image, an upstream side synchronization detecting means and a downstream side synchronization detecting means to detect the scanning start end and the scanning finish end of the light beams are provided, so that the deviation of the magnification error of the image formation optical system is detected by a signal from both synchronization detecting means so as to correct the deviation of the magnification error of the image formation optical system, and a temperature sensor to detect the temperature at a space between both synchronization detecting means is provided, so that the deviation of an image formation length on the photoreceptor is detected by a signal from the temperature sensor, and the deviation of the positional interval between the synchronization detecting means due to the temperature of the temperature sensor is modified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to correction of a magnification shift of an image forming apparatus, and more particularly to a technique of correcting a color shift caused by a magnification shift in a multicolor image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a multicolor image forming apparatus has a light beam scanning device comprising a plurality of image forming optical systems for scanning a photosensitive member with a plurality of light beams using a laser diode as a light source. A latent image obtained on the photoreceptor is visualized by scanning with a scanning device, and these visible images are superimposed and transferred on a transfer paper to obtain a multicolor image, which is then fixed to form a multicolor image. are doing. Then, various devices are devised so that the images formed by the respective image forming optical systems in the light beam scanning device are accurately overlapped to eliminate color shift and obtain a clear multicolor image.

[0003] The internal temperature of an image forming apparatus such as a copying machine or a laser printer varies depending on the location or with the operating time due to the influence of a fixing device that generates a large amount of heat. For this reason, as an imaging optical system of the light beam scanning device, an imaging optical system with small magnification error fluctuation due to temperature change,
For example, it is desirable to use a glass lens, but an imaging optical system using a plastic lens has been widely used from the viewpoint of easiness of processing, cost reduction, and the like.

When a plastic lens is used for the imaging optical system, magnification error fluctuation due to temperature change becomes large.
There is a possibility that a difference occurs in the magnification error of each of the plurality of imaging optical systems and a clear multicolor image cannot be obtained. In order to improve this, according to the technique described in Japanese Patent Application Laid-Open No. H10-307269, synchronization detection means are provided at the scanning start end and scanning end end of the light beam to be scanned, respectively. A two-point synchronization system is adopted in which the amount of error is detected and the frequency modulation of the laser diode (LD) is operated to correct the error.

[0005]

If all the imaging optical systems are provided with the two-point synchronization method in the prior art as described above, the deviation of the magnification error of each imaging optical system is detected and this deviation is detected. And a clear multicolor image can be obtained.

However, a situation arises in which the position interval between the synchronization detecting means provided at the scanning start end and the scanning end end of the light beam changes due to a change in the temperature inside the image forming apparatus.
Due to this situation, there has arisen a problem that the error in the image formation on the photoconductor is not properly corrected only by the above-described error correction of the magnification error by the two-point synchronization method based on the signal from the synchronization detecting means.

It is an object of the present invention to provide a two-point synchronous system.
Focusing on the fact that the position interval between the two synchronization detecting means changes due to a change in the temperature inside the image forming apparatus, the correction of the deviation of each magnification error of the imaging optical system due to the temperature change inside the apparatus and the synchronization An object of the present invention is to provide a light beam scanning apparatus capable of obtaining a clear multicolor image in consideration of a shift in image formation due to a temperature change in a position interval between detection means.

[0008]

In order to solve the above problems, the present invention mainly employs the following configuration.

An image forming apparatus for visualizing latent images obtained on a photoreceptor by scanning light beams from a plurality of image forming optical systems, and superimposing and transferring these visible images onto transfer paper to obtain an image. Based on a signal from the two-point synchronization detecting means of the light beam provided in each imaging optical system, the deviation of the magnification error of each of the imaging optical systems is corrected, and the temperature between the two-point synchronization detecting means is adjusted. An image forming apparatus that corrects a deviation of an image forming length on the photoconductor based on a signal from a temperature sensor to be detected.

A latent image is formed by scanning light beams from a plurality of imaging optical systems on a photosensitive member using a polygon scanner to form a latent image, and the latent image is visualized with toners of different colors. In an image forming apparatus for obtaining a multi-color image by superimposing and transferring the image on a transfer sheet, an upstream synchronization detecting unit and a downstream synchronization detecting unit for detecting a scanning start end and a scanning end end of the light beam are provided. And a temperature sensor for detecting a temperature difference between the two synchronous detection means while detecting a deviation of the magnification error by a signal from the two synchronous detection means, correcting a deviation of the magnification error of each imaging optical system. An image forming apparatus that detects a shift in the image forming length on the photoconductor by a signal from the temperature sensor and corrects a shift in a positional interval between the synchronization detecting units due to a temperature of the temperature sensor.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus based on two-point synchronization detection according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an overall configuration of a color printer including a light beam scanning device including a first imaging optical system and a second imaging optical system according to an embodiment of the present invention. FIG. 2 is a diagram showing a specific arrangement of a polygon scanner, a pair of image forming optical systems, a synchronization detecting unit, and a temperature sensor according to the present embodiment. FIG. 3 is a diagram showing a four-drum light beam scanning device including a plurality of photoconductors, a plurality of polygon scanners, and a plurality of imaging optical systems. FIG. 4 is a diagram showing an intermediate transfer type light beam scanning device including a plurality of photoconductors, a plurality of polygon scanners, and a plurality of imaging optical systems. FIG. 5 is a diagram showing the relationship between the average magnification error of each imaging optical system and the temperature between the synchronization detecting means according to the present embodiment. FIG. 6 is a diagram showing an operation system for correcting an image forming shift based on a change in the position interval between the synchronization detecting means in addition to the shift correction of the magnification error of the imaging optical system according to the embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a polygon scanner, reference numerals 2-1 and 2-2 denote a pair of imaging optical systems, a first imaging optical system and a second imaging optical system, and reference numeral 3-1.
Reference numerals a, 3-1b, 3-2a, and 3-2b denote folding mirrors, reference numeral 4 denotes a drum-shaped photoconductor, and reference numerals 5-1 and 5-1.
5-2, 6-1 and 6-2 are fθ lenses, reference numerals 7-1 and 7
-2 indicates a horizontal toroidal lens.

FIG. 2 shows the polygon scanner 1 shown in FIG.
FIG. 4 is a partial plan view showing an optically equivalent positional relationship excluding the return mirrors 3-1a and 3-1b in a component portion including a pair of imaging optical systems 2-1 and 2-2. FIG.
, The polygon scanner 1 rotates in the direction of the arrow, and the first imaging optical system 2-1 has two synchronization detecting means 15-1 and 15-2 at a scanning start end and a scanning end end. , Adopts a two-point synchronization method. Similarly, the second imaging optical system 2-2 also employs a two-point synchronization system in which synchronization detection means 15-3 and 15-4 are arranged at the scanning start end and scanning end end.

On one side of the polygon scanner 1,
In order to irradiate different mirror surfaces of the polygon scanner 1 with laser beams, a first laser light emitting device 11 and a second laser light emitting device 12 using LDs are arranged. The polygon scanner 1 scans the laser beam emitted from the first laser light emitting device 11 and the second laser light emitting device 12 on the photoconductor 4 in the main scanning direction.
Rotate in the sub-scanning direction orthogonal to the main scanning direction.

Further, in FIG. 2, the synchronization detecting means 15-
A temperature sensor 20-1 is provided at a central position between 1 and 15-2, and a temperature sensor 20-2 is similarly provided at an intermediate position between the synchronization detecting means 15-3 and 15-4. The arrangement of the temperature sensor is not limited to the above-described central position, and any temperature measurement point that can detect a change in the position interval between the synchronization detection means provided at both ends of the scanning end due to the temperature in the apparatus may be used. An appropriate place between the synchronization detecting means may be used.

The first laser light emitting device 11 and the second laser light emitting device 12 are driven based on image data input by an image data input device (not shown). In the light beam scanning device including the first imaging optical system 2-1 and the second imaging optical system 2-2, the first beam B1 emitted from the first laser light emitting device 11 in FIGS. The light passes through the cylindrical lens 13, is reflected by the polygon scanner 1, passes through the fθ lenses 5-1 and 6-1, is turned back by the turn-back mirror 3-1a, and is turned off by the toroidal lens 7-1.
, Is returned by the return mirror 3-1b, and scans the photoconductor 4.

On the other hand, the second beam B2 emitted from the second laser light emitting device 12 passes through the cylindrical lens 14, is reflected by the polygon scanner 1, passes through the fθ lenses 5-2, 6-2, and passes through the turning mirror 3 -2a, and scans the photoconductor 4 through the toroidal lens 7-2. The first beam B1 and the second beam B2 are scanned in directions opposite to each other in the main scanning direction by the rotation of the polygon scanner 1.

As described above, the beams B1 and B2 emitted from the two light emitting sources of the first laser light emitting device 11 and the second laser light emitting device 12 are simultaneously oscillated by the polygon scanner 1 in directions corresponding to the main scanning direction. By performing beam exposure on the surface of the photoconductor 4 rotating in the sub-scanning direction, electrostatic latent images are respectively formed at different positions on the surface of the photoconductor 4.

Next, toner particles of different colors are adhered to the respective electrostatic latent images formed at these different positions on the surface of the photosensitive member 4 by developing devices 9 and 10 so as to be visible as a toner image. The toner images are superimposed and transferred onto transfer paper (not shown) by the action of a transfer charger (not shown). The transfer paper after the transfer is transferred to the conveyor belt 11.
The toner image is fixed on the transfer paper by applying heat and pressure by the fixing device 16 while the toner image is fed toward the paper discharge unit side as indicated by an arrow by 0, thereby forming a multicolor image on the transfer paper. obtain.

In FIG. 1, reference numeral 8 denotes a charging charger for uniformly charging the surface of the photoconductor 4 before beam exposure, and reference numeral 120 denotes removal and recovery of residual toner remaining on the surface of the photoconductor 4 after transfer. Cleaning units for cleaning are shown.

The optical writing device based on the two-point synchronization detection according to the embodiment of the present invention can be applied to the four-drum light beam scanning device shown in FIG. 3 and the intermediate transfer type light beam scanning device shown in FIG. Is also applicable.

In FIG. 3, a polygon scanner 43a is provided.
The first imaging optical system 44a-
1, a second imaging optical system 44-b is arranged, and furthermore, the first imaging optical system 44a-1 and the second imaging optical system 44a-
The first imaging optical system 44b-1 and the second imaging optical system 44b-1 are located at positions optically symmetric with respect to the polygon
An imaging optical system 44b-2 is arranged. With this arrangement, two light beam scanning devices shown in FIG. 2 are arranged in parallel. The light beams emitted from the first imaging optical system 44a-1, the second imaging optical system 44a-2, the first imaging optical system 44b-1, and the second imaging optical system 44b-2 are Each of the drum-shaped photoconductors 42
a, 42b, 42c, and 42d, and finally a toner image is formed on each of the photoconductors, and is transferred onto the transfer paper conveyed in the direction of the arrow.

In FIG. 4, a first image forming optical system 48a-1 and a second image forming optical system are optically symmetrically arranged around a single drum-shaped photosensitive member 45 around a polygon scanner 46a. 48a-2, and a first imaging optical system 48 that is optically symmetric about the polygon scanner 46b.
b-1 and a second imaging optical system 48b-2 are provided.

In the above-described image forming apparatus, in particular, according to the apparatuses shown in FIGS. 1 and 2, the fθ lens and other optical members are thermally deformed by the influence of heat from the fixing device 16 which generates a large amount of heat. As a result, the magnification error of the first imaging optical system 2-1 changes, so that the image written by the first imaging optical system 2-1 and the image written by the second imaging optical system 2-2 are changed. Causes color misregistration. Therefore, synchronization detecting means 15-1 and 15-2 for correcting a magnification error are provided at the scanning start end and scanning end end positions of the first imaging optical system 2-1 in which the magnification error fluctuates due to temperature fluctuation. A two-point synchronization method using the detection signal from the STA (the details of the two-point synchronization method will be described later). Similarly, the second imaging optical system 2-2
Are provided with the synchronization detecting means 15-3 and 15-4.
Then, the synchronization detecting means 15-1 and 15-3 are also for setting the image writing time point. Then, the synchronization detecting means 15-1 or 15-3
-2 or 15-4 to enable a two-point synchronization scheme,
It has a function of detecting the deviation amount of the magnification error. Using this magnification error detection function, a laser diode as a light source is frequency-modulated to achieve a magnification error correction function.

In the two-point synchronization system, the synchronization detecting means 15-1
The control unit calculates the actual time required for scanning at a predetermined interval from the time of beam detection by the control unit to the synchronization detection unit 15-2, and compares the actual time with a reference time. Thus, a magnification error of the imaging optical system can be detected.
Based on the magnification error thus detected, the magnification error is corrected by operating the magnification error function by frequency modulation of the laser diode. The correction of the magnification error of the imaging optical system is larger in the imaging optical system whose temperature is higher due to the arrangement relationship with the fixing device.

Here, the correction based on the magnification error of the imaging optical system will be described again with a specific example. Referring to FIG. 2, the environmental temperature of the first imaging optical system 2-1 is influenced by the fixing device. When the magnification error becomes large, the length of the scanning line on the photoconductor, that is, the writing range becomes long. Then, the pixel pitch on the photoconductor becomes large, and the number of pixel clocks counted until the scanning line reaches the synchronization detection unit 15-2 from the synchronization detection unit 15-1 becomes small.

Accordingly, in a temperature environment where the temperature of the imaging optical system is within a predetermined value and the magnification error does not occur, the number of pixel clocks counted until the scanning line reaches the synchronization detecting means 15-2 is calculated. As a reference value, a ratio is determined by comparing and contrasting a small pixel clock count number when the magnification error is large in an environment of a temperature increase, and a reference pixel frequency is multiplied by the ratio to obtain a corrected pixel frequency. The length of one scanning line on the photoconductor, that is, the writing range is matched with the reference range. By using such a method, the correction of the magnification error of the imaging optical system due to the temperature rise has been conventionally performed.
It is possible to correct the color misregistration occurring in the optical system for forming the scanning beams of C, M, Y and K shown in FIG.

FIG. 5 shows the relationship between the average magnification error and the temperature between the synchronization detecting means, and shows the problem solving problem that led to the adoption of the embodiment of the present invention. More specifically, the vertical axis represents the average value of a number of image lengths on the photoreceptor per scanning line by the laser and represents the average value. The image length is represented by the error of the imaging optical system. It is converted to the magnification and displayed. The lowermost line in FIG. 5 (the line indicated by the black diamond and the black circle) is, for example, the temperature sensor 20-1 in FIG.
And the temperature at the central portion between the synchronization detection means measured with time and 20-2, which is shown as a temperature rise of the central wall of the KC synchronization detection means and a temperature rise of the central wall of the YM synchronization detection means. are doing.

Here, the image length shown on the vertical axis is the image length when the above-mentioned two-point synchronization method is operated. Originally, by setting the pixel frequency by the conventional two-point synchronization method, even if the temperature rises, the magnification error of the imaging optical system should be corrected and the image length should be the same. As a result of experiments and studies, it has been found that a magnification error as shown on the vertical axis of FIG. 5 occurs due to an increase in the length between the synchronization detection means at both ends due to the rise. . The CMYK codes represent cyan, magenta, yellow, and black, respectively. According to the example of FIG. 5, the image forming optical system at K and C has a scanning line image length corresponding to the temperature rise of the image forming optical system (the temperature at the center between the KC synchronization detecting means (graph indicated by black diamonds)). That is, the average magnification error increases. On the other hand, the average magnification error of the imaging optical system at M and Y separated from the fixing device that generates a large amount of heat indicates that the magnification error of the imaging optical system is relatively small without being significantly affected by the temperature rise.

FIG. 6 shows the operation of the optical writing apparatus according to the embodiment of the present invention for correcting the image forming deviation due to the change in the position interval between the synchronization detecting means in addition to the correction of the magnification error deviation of the two-point synchronization method. The system diagram is shown. The counter circuit 50 is a counter that starts counting with a signal from the upstream synchronization detecting unit and ends counting with a signal from the downstream synchronization detecting unit. The count value of the counter circuit is latched by the latch circuit 51. Then, the count value is input to the main CPU 53 via the parallel / serial conversion circuit 52. The main CPU 53 determines in advance what value the image frequency of the laser diode should be set based on the input count value so that the image length on the photoconductor per one scanning line becomes a predetermined reference length. Since it is stored as a design value,
The image frequency setting circuit 56 operates so as to give an instruction to output a predetermined image frequency by the calculation based on the input count value. The above operation is the correction of the deviation of the magnification error in the two-point synchronization method.

In the embodiment of the present invention, the correction by the position interval is also solved by focusing on the fact that the position interval between the start-end synchronization detection means and the end-end synchronization detection means of the two-point synchronization method expands and contracts depending on the temperature. As shown in FIG. 6, the temperature sensors 20-1 and 20-2 (the temperature detecting circuit 54 shown in FIG. -1 and 20-2) are provided, for example, at the center of both synchronization detecting means, and the temperature signal from the temperature detecting circuit 54 is input to the main CPU. Further, as shown in FIG. 5, the relationship between the temperature detected by the temperature detection circuit 54 and the image length of one scanning line (the image length can be converted into a magnification error of the imaging optical system) is formed in advance by image formation. The relationship is obtained for each device, and the relationship is stored in the memory 55 as a table.

The temperature-magnification error relation table (table) held in the memory 55 determines in advance how much the numerical value of the magnification error of the imaging optical system has occurred due to the temperature rise measured by the temperature detection circuit 54. The main CPU
The reference number 53 can determine the correction amount of the magnification error by referring to the table based on the temperature signal from the temperature detection circuit 54. The correction of the magnification error obtained in this way is
Even if the temperature of the temperature detecting circuit 54 rises, it is intended to correct the error so that a magnification error does not occur in the imaging optical system related to the rise.

Therefore, in the embodiment of the present invention shown in FIGS. 5 and 6, the deviation of the magnification error of the image formation by each imaging optical system is corrected by using the two-point synchronization method, and the temperature rise by the fixing device or the like is performed. In this case, the deviation of the magnification error caused by the change of the position interval between the synchronization detecting means due to the influence of the above-mentioned is intended to be corrected. For this reason, according to the present embodiment, in order to detect a temperature change that causes a change in the position interval between the synchronization detection units, using the deviation correction control device for the magnification error of the imaging optical system using the two-point synchronization method, A temperature sensor is installed, for example, at the center between the synchronization detecting means, and a memory 55 having a temperature-magnification error relation table is installed, and the image frequency is set so as to output a desired image frequency without image shift. A main CPU 53 for giving an instruction to a circuit 56 is connected to the temperature detection circuit 54 and the memory 55.

In FIG. 6, the parallel-serial conversion circuit 52 is not necessarily an indispensable configuration in the present embodiment. Further, the present embodiment has described the color misregistration in a color printer using a laser. However, the present invention is not limited to this and can be applied to a two-color image forming apparatus, and can be applied to a wide-area machine using a single-color multi-scanning beam. This is an applicable technique of an image forming apparatus having an image forming optical system for each of a plurality of light beams.

[0035]

According to the present invention, in an image forming apparatus, a temperature fluctuation inside the apparatus due to the influence of a fixing device, etc., a temperature fluctuation inside the apparatus over time due to the use time of the apparatus, and a temperature fluctuation inside the apparatus due to an installation environment of the apparatus. It is possible to correct a deviation of a magnification error caused by each imaging optical system due to a temperature change or the like.

In addition, even when the position interval between the two synchronization detecting means used in the two-point synchronization system changes due to the above-mentioned temperature fluctuation in the apparatus, it is possible to correct the deviation of the image formation.

[Brief description of the drawings]

FIG. 1 illustrates a first imaging optical system and a second imaging optical system according to an embodiment of the present invention.
FIG. 1 is a diagram illustrating an overall configuration of a color printer including a light beam scanning device including an imaging optical system.

FIG. 2 is a diagram illustrating a specific arrangement of a polygon scanner, a pair of imaging optical systems, a synchronization detecting unit, and a temperature sensor according to the embodiment.

FIG. 3 is a diagram illustrating a four-drum light beam scanning device including a plurality of photoconductors, a plurality of polygon scanners, and a plurality of imaging optical systems.

FIG. 4 is a diagram illustrating an intermediate transfer type light beam scanning device including a plurality of photoconductors, a plurality of polygon scanners, and a plurality of imaging optical systems.

FIG. 5 is a diagram illustrating a relationship between an average magnification error of each imaging optical system and a temperature between synchronization detection units according to the embodiment.

FIG. 6 is a diagram showing an operation system for correcting a shift in image formation based on a change in a position interval between synchronization detecting means in addition to a shift correction of a magnification error of the imaging optical system according to the embodiment of the present invention. .

[Explanation of symbols]

 Reference Signs List 1 polygon scanner 2-1 first imaging optical system 2-2 second imaging optical system 4 photoreceptor 5, 6 fθ lens 15-1, 15-3 upstream synchronization detection means 15-2, 15-4 downstream Synchronization detecting means 16 Fixing device 20-1, 20-2 Temperature sensor 50 Counter circuit 51 Latch circuit 52 Parallel-serial conversion circuit 53 Main CPU 54 Temperature detection circuit 55 Memory 56 Image frequency setting circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/04 G03G 15/04 120 5C072 15/043 B41J 3/00 M 5C074 H04N 1/04 H04N 1/04 104A 1/113 D 1/23 103 (72) Inventor Hiroho Shijo 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2C362 AA46 BA51 BA52 BA69 BA70 BB30 BB32 BB37 BB38 CA22 CA39 2H027 DA11 DB01 DE02 DE07 DE09 EA02 EB04 EB06 EC02 EC06 EC07 EC19 ED04 ZA07 2H030 AA01 AB02 AD17 BB02 BB16 BB23 2H045 BA22 BA34 CA88 CA99 DA41 2H076 AB05 AB06 AB08 AB12 AB22 AB33 DA41 5C072 AA13B13 HA13 A19B13 HA3 EE02 EE06 EE08 FF15 GG12 HH02

Claims (3)

[Claims] An image forming apparatus that visualizes latent images obtained on a photosensitive member by scanning light beams from a plurality of image forming optical systems, and superimposes these visible images on a transfer paper to obtain an image. In the above, based on the signal from the two-point synchronization detecting means of the light beam provided in each imaging optical system, the deviation of the magnification error of each of the imaging optical systems is corrected, and An image forming apparatus, wherein a deviation of an image forming length on the photoconductor is corrected based on a signal from a temperature sensor for detecting a temperature. 2. A latent image is formed by scanning light beams from a plurality of imaging optical systems on a photosensitive member using a polygon scanner to form a latent image, and the latent image is visualized with toners of different colors. An image forming apparatus for obtaining a multi-color image by superimposing and transferring the image on a transfer sheet, comprising: an upstream synchronization detection unit and a downstream synchronization detection unit for detecting a scanning start end and a scanning end end of the light beam; And a temperature sensor for detecting a temperature difference between the two synchronous detection means while detecting a deviation of the magnification error by a signal from the two synchronous detection means and correcting a deviation of the magnification error of each of the imaging optical systems. Image forming apparatus, wherein a deviation of an image forming length on the photoreceptor is detected by a signal from the temperature sensor, and a deviation of a position interval between the synchronization detecting means due to a temperature of the temperature sensor is corrected. apparatus. 3. A latent image is formed by forming light beams from a plurality of image forming optical systems on a photosensitive member using a polygon scanner to form a latent image, and visualizing the latent image with toners of different colors. In an image forming apparatus that obtains a multicolor image by over-transfer onto a transfer sheet, an upstream synchronization detection unit and a downstream synchronization detection unit that detect a scanning start end and a scanning end end of the light beam; A temperature detection circuit that processes a signal from a temperature sensor that detects a temperature between the counter, a counter circuit that counts the number of pixel clocks by a detection signal from the two synchronization detection units based on the light beam scanning, and that is detected by the temperature sensor. A memory having a table indicating the relationship between the temperature of the photosensitive member and the error of the image forming length on the photosensitive member; an image frequency setting circuit of the light beam light source; a count value from the counter circuit; And a main CPU that receives the temperature signal and the table of the memory as input, and provides an instruction of an image frequency to the image frequency setting circuit, wherein the main CPU detects a deviation of a magnification error of each imaging optical system. Correcting and correcting color misregistration in multiple colors by capturing the shift in the position interval between the synchronization detecting means due to the temperature of the temperature sensor by capturing the input count value and the signal from the temperature detection circuit and the table. An image forming apparatus comprising: