JP2003200609A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide one rotary polygon mirror and one BD sensor with respect to a plurality of laser beam generators to reduce the cost on an image forming apparatus having a plurality of image carrier bodies. <P>SOLUTION: This image forming apparatus comprises a laser beam detecting means which is provided on a scanning path of a first laser beam and outputs a signal representing the detection of the laser beam when the laser beam is inputted, a first horizontal synchronizing signal generating means for generating a first horizontal synchronizing signal which becomes a reference for determining an image output timing of the first laser beam, and a second laser beam timing signal generating means that generates a signal for determining the image output timing of a second laser beam by delaying the horizontal synchronizing signal of the first laser beam by a predetermined time period. When the shift between the first and second laser beams on a reflection face of the rotary polygon mirror is (n), the delay time is set to be (n) times of an average cycle of the first horizontal synchronizing signal. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus using an electrophotographic process, and more particularly to a color image forming method for forming different color images by using a plurality of laser beams. Regarding the device.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic system, a laser beam modulated by an image signal is reflected by a scanner having a polygon mirror (hereinafter sometimes abbreviated as polygon mirror). Then, the image is formed by scanning the photoconductor. A drum-shaped photosensitive member is often used and is called a photosensitive drum. When this method is applied to a color laser printer, different colors (for example, yellow (Y), magenta (M), cyan (C), black (B
k) four colors) A plurality of developed color images are superposed on a sheet-shaped medium to form a color image. There are the following configurations for achieving this superposition technique.

In one method, one photosensitive drum is sequentially used for each developing color as one configuration. The photosensitive drum is scanned with a first developing color image signal to form a latent image on the photosensitive drum. To make the image visible, a developer is attached to the photosensitive drum to form a visible image, the visible image is transferred to recording paper, and then the photosensitive drum is cleaned, and again on the same photosensitive drum with the second development color image signal. A latent image is formed by scanning, and the same steps as the first step are performed. However, the developer of the second color is used. This is repeated for the third development color image signal and the fourth development color image signal.
In this way, one color image recording is performed by superimposing images developed with different developing colors a plurality of times on the same recording paper.

In another configuration, the same number of photosensitive drums for a plurality of developed color images, that is, a plurality of photosensitive drums are provided, and one for each developed color image signal.
A latent image is formed on the photosensitive drum corresponding to pair 1, visualized development is performed with developers of respective corresponding colors, and then sequentially transferred to recording paper. In this case, one laser for one developed color image, one scanner, and one BD (Beam D) for detecting the image writing timing of the laser.
(eect) sensor, one photosensitive drum is generally prepared, and therefore, when there are a plurality of color images to be superimposed, the same number of lasers, scanners, photosensitive drums and BD sensors as the color images are required.

In the first construction, a series of electrophotographic processes of charging-exposure-developing-transfer-cleaning are performed on a first developing color image signal and then again on a second developing color image signal. The same process must be performed, and the third development color image signal and the fourth development color image signal must be performed in series in time series. Therefore, it has a drawback that the printing time for one sheet is very long.

The second configuration has an advantage over the first configuration in that it is possible to print in a short time because the processing of each developing color can be overlapped and processed. However, as mentioned above, lasers, scanners,
It is necessary to prepare the same number of photosensitive drums and BD sensors as the number of developing colors, which has a drawback that the apparatus becomes large and expensive.

Since images of respective developing colors are superposed in both configurations, so-called color misregistration, which occurs when the image positions of the respective developing colors are not aligned, is likely to occur. Particularly, in the latter configuration, since different color images are formed by using different scanners and photosensitive drums, there is a problem that registration for each color is difficult to match. Therefore, registration is performed for each color. For example, an intermediate transfer belt (Intermediate
Transfer belt: abbreviated as ITB) or electrostatic transfer belt (abbreviated as ETB), a resist detection pattern image is formed on the transfer surface, read by the resist detection sensor, and an image writing position. A means for making a correction by feeding back to the above is used.

The resist detection sensor is ITB or ET.
The image pattern for resist detection formed on B is irradiated by the light source, the reflected light is focused and read by the light receiving sensor, and the temporal intensity change of the signal of the light receiving sensor when the resist detecting pattern passes is output. To do. The output signal is electrically processed to obtain the positional deviation information.

In order to shorten the printing time of a laser printer, it is usually done by increasing the rotation speed of the scanner. The conventional scanner rotation speed of a laser printer is usually a high speed rotation of 20,000 rpm or more. Furthermore, the mirror used in the scanner is a polygonal mirror, which is a polygonal mirror, and the error in the deflection angle causes a positional change on the photosensitive drum depending on the optical path length of the laser beam, so the scanner has a tilt error on each surface. It needs to be very small, and it is also necessary that there be little vibration due to high speed rotation. Therefore, in order to obtain a stable high-speed rotation of the polygon mirror, the motor becomes large, and it is necessary to limit the tilt error on each surface of the mirror. Therefore, precision processing technology is required for the scanner manufacturing process. Therefore, the manufacturing yield is poor and the cost is very high.

A device having a plurality of scanners as described above becomes large and expensive.

Therefore, in order to reduce the cost, a common scanner is used for each of a plurality of developing colors (Japanese Patent Publication No. 4-51829). Among a plurality of light sources provided in correspondence with colors, one in which a BD sensor is provided for only one light source (JP-A-4-313776) has been devised.

[0012] To briefly describe JP-A-4-313776, a plurality of (two) light sources are configured so that the photosensitive member is simultaneously scanned by different surfaces of a polygon, and other than the light source provided with a BD sensor. Since the rotational phase difference (angle difference) of the polygons of other light sources is known in advance, it can be estimated from the BD signal of the light source provided with the BD sensor.

[0013]

However, among the above proposals, in Japanese Patent Publication No. 4-51829, the polygon mirror and the scanner motor are unified into one. However, since the BD sensor must be prepared for each color, an increase in cost is inevitable.

Further, in the first embodiment of Japanese Patent Laid-Open No. 4-313776, the BD sensor is set to one, and the image of the first C (cyan) developed color in the image forming order C, M, Y, Bk. The cost can be reduced because it is provided on the scanning path of the laser beam for forming the. However, regarding the BD of the light source without the BD sensor, it is premised that the rotational phase difference of the polygon, that is, the surface division accuracy is accurate. That is, since the rotational phase difference is known in advance, the laser scanning position of the laser without the BD sensor is known from the BD signal of the laser with the BD sensor.

An example in which a common scanner is used for a plurality of colors will be described with reference to FIGS. 11 and 12. FIG. 11 shows laser diodes LD1 and LD2 that are point-symmetric with respect to the center of rotation of the polygon mirror 1103.
FIG. 7 is a diagram showing a state in which each is arranged and is scanned upward and downward. Reference numerals 1104 and 1105 denote BD sensors, which detect a laser beam scanned prior to a scanning period for writing an image in each scan. Here, the BD sensors 1104 and 1105 are also arranged at positions symmetrical with respect to the rotation center of the polygon mirror 1103. In addition, FIG. 12 shows laser diodes LD1 and L when configured as shown in FIG.
It is a figure which shows the timing relationship between the detection signal of the BD sensor corresponding to the image modulation period of D2. In FIG. 11, L
The BD sensor 1104 exists on the scan path of D1 (1101). The BD signal from the normal BD sensor 1104 is set to B
If it is D1, as shown by reference numerals 1201 and 1202 in FIG.
c) By writing out the image later, the image is formed at the correct position. On the other hand, the BD sensor 1105 is also present on the scanning path of the LD2 (1102), and if the position is completely symmetrical to the LD1, BD2 (BD from the BD sensor 1105 as shown by reference numerals 1203 and 1204 in FIG. By writing the image after tc from (the signal is BD2), the image is formed at the correct position.

The two lasers 1101 and 1102 are arranged at positions that are completely line-symmetric with respect to the center axis of rotation of the polygon mirror, and the polygon mirror 1103 is also a square having an ideal 90 ° angle. , BD sensor 11
Since 04 and 1105 output BD signals at exactly the same timing, it means that only one of the BD sensors 1104 needs to be used.

However, in reality, it is impossible to make the surface division accuracy of each mirror surface of the polygon mirror the same, and there is always an error α as shown in FIG.
(Α is usually an angle of about several tens to several hundreds of seconds) Next, the BD cycle when such a polygon mirror is used will be introduced.

As shown in FIG. 11, a polygon mirror 11
The laser diode
Laser beam output from the LD1 (1101)
Is reflected by the polygon mirror 1103, and BD
Measures the BD signal cycle when it enters the sensor 1104 every time.
Set. The graph shown in FIG. 14 plots the BD cycle.
It was done. In FIG. 14, t_1-2Is a polygon
Time from detecting BD on the surface to detecting BD on the surface
Indicates the interval, t_2-3, T_3-4, T_4-1Has a similar meaning for
Is. Δt₁Is t_1-2And the average BD cycle (in the present embodiment,
(1/4 rotation period) and Δt₂, Δ
t₃, Δt_FourHas the same meaning. This situation
The horizontal axis represents the timing shown in Fig. 15
It is a chart. The BD detected on the polygon surface is used as a reference
And, the upper side is the BD for an ideal polygon mirror
The cycle is shown below and the BD cycle of the actual polygon mirror is shown below.
t_{1- 2}Is Δt with respect to the ideal BD cycle.₁Only the cycle is short.
t_2-3Is Δt with respect to the ideal BD cycle.₂Only the cycle is long.
The error is cumulative and Δt₁+ Δt₂Becomes (Δt₁Is negative, Δ
t₂In this way, if the polygon makes one round, the error
Is cumulative and Δt₁+ Δt ₂+ Δt₃+ Δt_FourBecomes this is
Is equal to zero. The above uses an actual polygon mirror
It is the characteristic of the BD cycle when used.

Since BD is always detected on each side of the polygon, the error on each side of the polygon is not affected and the image writing start position does not shift. However, as shown in FIG. 11, two lasers are simultaneously scanned by one polygon, and only one scanning path of one laser is BD.
If the sensor is arranged and the BD detection for the scanning of the other laser is configured to be detected from the BD signal of the laser with the BD sensor, the BD cycle deviation for each surface as shown in FIG. 14 and FIG. And the scanning surface of the laser with BD and the scanning surface of the laser without BD are different, the writing timing of the image of the laser without BD does not match, and the writing position shift appears.
In order to avoid this, the surface accuracy of the polygon should be raised to the limit. However, in order to improve the surface accuracy of the polygon mirror, advanced precision processing technology is essential. This has a problem that the manufacturing yield is low and the cost becomes very expensive.

The present invention has been made in view of the above problems, and an object thereof is to provide a laser beam to each laser beam of each developing color without providing a BD sensor for each laser beam independently generated. An object of the present invention is to provide a method for obtaining an image writing timing, that is, to provide a high-quality image forming apparatus that reduces the number of BD sensors, is low in cost, and has high accuracy in the image registration position of each color.

[0021]

In order to achieve such an object, the present invention provides an image forming apparatus according to the first aspect of the invention, wherein two laser beams, a first laser beam and a second laser beam, are provided. Generating means, first and second image carriers provided corresponding to the laser beam generating means, and first and second laser beams generated by the two laser beam generating means. One rotary polygon mirror for deflecting and scanning a beam on the surface of the corresponding image carrier at different planes at the same time, and the laser beam is input on the scanning path of the first laser beam. And a signal from the laser beam detection means for outputting a signal indicating that a beam has been detected, and a signal from the laser beam detection means are input to determine an image writing timing of the first laser beam. A first horizontal synchronizing signal generation means for generating a first horizontal synchronizing signal as a reference at the time of the first
A second signal for determining an image writing timing of the second laser beam by inputting a horizontal synchronizing signal of the second laser beam and delaying the same for a predetermined time.
Laser beam timing signal generating means.

According to a second aspect of the present invention, there is provided an image forming apparatus, which is provided corresponding to each of the first and second laser beam generating means and the laser beam generating means. Different first and second image carriers, and the first and second laser beams generated by the two laser beam generating means are simultaneously directed to the surfaces of the corresponding image carriers to form different surfaces. One rotating polygon mirror for deflecting and scanning by the laser beam and laser beam detecting means for outputting a signal indicating that the beam has been detected when the laser beam is input on the scanning path of the first laser beam. And a signal from the laser beam detecting means to input a first horizontal synchronizing signal which serves as a reference when determining the image writing timing of the first laser beam. A horizontal sync signal generating means, said first
The second horizontal synchronizing signal generating means for generating the horizontal synchronizing signal of the second laser beam by inputting the horizontal synchronizing signal of the laser beam and delaying the same for a predetermined time.

The invention described in claim 3 is the same as claim 1
Or the image forming apparatus according to 2, wherein a setting value for setting an amount of delaying the first horizontal synchronizing signal in the second laser beam timing signal generating means or the second horizontal synchronizing signal generating means. Is characterized by being variable.

The invention according to claim 4 is the same as claim 2
The image forming apparatus according to claim 1, wherein the first laser
After n faces of the surface of the rotating polygon mirror for deflecting and scanning the beam,
In a configuration in which there is a surface of the rotary polygon mirror that deflects and scans the second laser beam, the set value that sets the amount by which the first horizontal synchronizing signal is delayed is the average period of the first horizontal synchronizing signal. Is a value representing n times the time.

The invention described in claim 5 is the same as claim 3
The image forming apparatus according to claim 1, wherein each of the resist detection pattern images formed on the image carrier by the first and second laser beams and further transferred onto the intermediate transfer member is read, An image registration detecting unit for detecting each image registration position is provided, and the set value is changed based on a detection result of the image registration detecting unit.

The invention according to claim 6 is the same as claim 1.
5. The image forming apparatus according to any one of 1 to 5, wherein the laser beam detecting means is provided on a scanning path of a laser beam generating means for generating a laser beam for scanning an image carrier carrying a black toner image. It is characterized by being provided.

According to a seventh aspect of the present invention, the laser beam detecting means is provided on the scanning path of the laser beam generating means for generating a laser beam for scanning the image carrier carrying the yellow toner image. It is characterized by not having.

The invention described in claim 8 is the same as claim 1.
8. The image forming apparatus according to any one of 1 to 7, which has a plurality of the optical systems and is used as a light source for image formation of a plurality of colors, and the images of the plurality of colors are superimposed to form a color image on a sheet-like medium. It is characterized by doing.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram for explaining the present embodiment, which is a four-drum type color laser indicated by reference numeral 101 including two scanner units 105 and 106.
Shows a printer. Reference numeral 102 is a host computer. The color laser printer is provided with a four-color image forming unit for forming a color image in which images of four colors (yellow Y, magenta M, cyan C, and black Bk) are superimposed.

The image forming unit comprises toner cartridges 107 to 110 having a photosensitive drum as an image carrier and scanner units 105 and 106, and the scanner unit generates a laser beam as a light source for image exposure. It has a laser diode. Of these, the toner cartridge has one for each of the four color developing colors. However, the scanner unit is characterized in that it has one in common for yellow and magenta and two in common for cyan and black. This scanner unit will be described in detail later.

Upon receiving the image data from the host computer 102, the video controller 103 in the laser printer expands the image data into bitmap data to generate a video signal for image formation. The video controller and the engine controller perform serial communication to send and receive information. The video signal is transmitted to the engine controller 104, and the engine controller drives a laser diode (not shown) in the scanner units 105 and 106 in response to the video signal, and finally the toner cartridge (207).
Each of the developed color images is formed on a photosensitive drum (not shown) in the (-210). The photosensitive drum is the intermediate transfer belt I.
Each developed color image formed on the photosensitive drum in contact with the TB111 is transferred onto the ITB111 and sequentially (Y, M,
A color image is formed by superposing them in the order of C and Bk. The image forming process will be described later in detail.

Further, an image registration position detection sensor (registration detection sensor) 112 is provided for monitoring the registration position of the image on the ITB 111, in other words, the registration detection pattern image formed on the ITB 111.

FIG. 2 is a sectional view showing the structure of the color laser printer. The same parts as those in FIG. 1 are designated by the same reference numerals. The video controller and engine controller described in FIG. 1 are not shown. Reference numerals 201 to 204 are photosensitive drums. The photosensitive drum 201 is used for forming a black development image, the photosensitive drum 202 is cyan, the photosensitive drum 203 is magenta, and the photosensitive drum 204 is for forming a yellow development color image. In this figure, ITB
On the 111, yellow Y is transferred first, then magenta M, cyan C, and black Bk in this order, respectively, and the developed color images are transferred. In the figure, reference numerals 105 and 106 are scanner units,
Latent images are formed on the photosensitive drums of yellow Y and magenta M, cyan C and black Bk, respectively.

FIG. 3 is a diagram showing details of the scanner units 105 and 106 in FIG. First, the configuration of the scanner unit 105 will be described with reference to FIG. Since the scanner unit 106 has the same configuration as the scanner unit 105, the description thereof will be omitted. In FIG. 3, reference numerals 301 and 302 denote laser diodes (hereinafter sometimes abbreviated as lasers), which are driven and controlled by a control signal from an engine controller (not shown). For convenience, the laser diodes denoted by reference numerals 301 and 302 are referred to as LD1 and LD2, respectively.
Reference numeral 303 is a polygon mirror, which is rotated by a scanner motor (not shown) in the direction of the arrow at a constant speed,
Scanning is performed while reflecting the laser beams emitted from LD1 and LD2. In this embodiment, the laser beam from LD1 is emitted from the right side of the figure to the left direction, and the laser beam from LD2 is emitted from the left side of the figure to the right direction, and both are irradiated on the polygon mirror 303.

The photodiode 306 is an optical sensor which is on the laser beam scanning path from the LD 2 and generates a signal when the laser beam is incident.
(BeamDetect) This is called a sensor. This BD sensor 306 is only on the scanning path of the laser beam from LD2,
It does not exist on the laser beam scanning path of the other LD1. The laser beam emitted from the LD 2 is scanned while being reflected by the polygon mirror 303 and further reflected by the folding mirror 305, and scans the photosensitive drum 202 from left to right in the figure.

Actually, the laser beam is passed through various lenses (not shown) for focusing on the photosensitive drum or for converting the laser beam from diffused light to parallel light. However, the explanation is omitted this time.

The LD 2 generates a laser beam modulated by a video signal generated by the video controller 104, which is a video signal representing a cyan C image in this case, and scans the photosensitive drum. . On the other hand, the photosensitive drum 202 is rotated in the direction of the arrow shown in FIG. 3 at a constant speed by a drum motor (not shown). Photosensitive drum 2
The surface of 02 is uniformly charged by the charging roller 206 of FIG. 2, and the surface is invisible because the laser beam modulated by the video data generated by the video controller scans the surface. An electrostatic latent image is formed. This electrostatic latent image is visualized as a toner image, in this case, a cyan C toner image by the developing device 210 of FIG.

Usually, the video controller transmits the video signal to the engine controller a predetermined time after detecting the output signal of the BD sensor. By making the time from the output signal of the BD sensor to the start of the video signal constant, the writing start positions of the image by the laser beam on the photosensitive drum are always in agreement.

On the other hand, the LD1 also forms an electrostatic latent image on the photosensitive drum 201 in the same manner as the LD2.

Since there is no BD sensor on the scanning path of LD1, the BD signal for LD1 cannot be obtained. Therefore, as the BD signal for LD1 positioned the same as the BD signal from the BD sensor for LD2, a signal obtained by delaying the BD signal of LD2 by a predetermined time is generated. The details will be described later.

As described above, the cyan (C) color image formed by the LD2 is formed on the photosensitive drum 202 and the LD1 is formed.
A black (Bk) color image is formed on the photosensitive drum 201.

As described above, the scanner unit 1 in FIG.
I explained 05. The scanner unit 106 is exactly the same as 105. That is, the photosensitive drum 20
A magenta (M) color image is formed on the photosensitive drum 204 and a yellow (Y) color image is formed on the photosensitive drum 204.

Each color image formed on each photosensitive drum is
The images are sequentially transferred (primary transfer) onto the ITB 111 conveyed at a constant speed so as to overlap each other. That is, a yellow (Y) image is first transferred to the ITB, and then magenta (M), cyan (C), and black (Bk) are transferred in this order so as to be superposed thereon, and a color image is formed on the ITB. It

The color image formed on the ITB is the IT
It is transported by B. On the other hand, the sheet in the cassette 214 is picked up by the pickup roller 216 at the position of the transfer roller 218 so as to be in time with the image on the ITB. Then, the sheet is pressed by the transfer roller 218, and the color image is transferred from the ITB to the sheet (secondary transfer). The image-transferred sheet is fixed by the fixing device 213 by heat and pressure, and then discharged onto the paper discharge tray 217 above the printer. The above is a series of image forming processes.

Next, the image registration position detecting sensor (hereinafter referred to as the registration detecting sensor) will be described.

Reference numeral 112 in FIG. 2 indicates the position of the registration detection sensor. This sensor controls the image registration position of each color by reading the position of each color image formed on the ITB and feeding back the data to the video controller or engine controller to prevent color misregistration. Is.

FIG. 5 is a diagram showing the ITB extracted. The same parts as those in FIG. 2 are designated by the same reference numerals. Four
It is a widely used sensor in so-called in-line type color laser printers, in which color images are formed on four independent photosensitive drums and four color images are superimposed to form a color image. The structure of a registration check sensor is shown in FIG. In FIG. 4, the registration detection sensor 112 includes an LED 401 that is a light emitting unit and an optical sensor 402 that is a light receiving unit. The light from the LED 401 is reflected on the ITB 111, and the reflected light is focused to form an image on the optical sensor 402.
The second light receiving section detects the amount of incident light. The difference between the light amount of the reflected light on the ITB in the state where the toner image is not formed and the light amount of the reflected light of the toner image is detected, and the toner image 4 is detected from the detected timing and the ITB transport speed.
No. 03 registration position, the position of the registration detection pattern in the horizontal (main scanning) direction and the vertical (sub scanning) direction is detected.

For example, to detect the registration position in the vertical direction of the toner image (referred to as the ITB transport direction or the sub-scanning direction), a horizontal line of one line is drawn on the ITB by the laser, and the horizontal line image is detected by the registration detection sensor. Check the timing for detecting. The registration position in the sub-scanning direction of the image can be detected by detecting early or late with respect to the predetermined timing.

To detect the registration position of the toner image in the lateral direction (vertical to the ITB transport direction, referred to as the main scanning direction), as shown by reference numerals 501 to 504 in FIG. The time it takes to print an "" character and the registration detection sensor detects the image once, and then detects the image again,
That is, it is sufficient to check the time required to cross the "U" character in the vertical direction. If the image detection interval is shorter than the specified time,
It can be determined that the image is formed by being shifted to the right side on the ITB in FIG. 5, and conversely, when the image detection interval is longer than the predetermined time, it is determined that the image is formed by being shifted to the left side. can do.

Such resist detection is performed before the printing operation, and is usually a reference color such as black (B
This is performed to prevent color misregistration by aligning the positions of the remaining colors, that is, yellow (Y), cyan (C), and magenta (M) with the position of color k). for that reason,
In the in-line type color laser printer using the independent photosensitive drum for each color as in the present embodiment, the registration detection sensor is always present.

Next, BD detection will be described. The BD signal of LD2, that is, the BD signal for LD2 corresponding to the BD signal from the BD sensor of LD1 is
The BD signal is generated by delaying it by a predetermined time. The details will be described.

In FIG. 11, reference numeral 1105 is the position where the BD sensor for the LD 2 according to the conventional method is arranged. Normally, if the BD sensor is arranged at this position and the image is written after a predetermined timing tc from the output signal of the BD sensor, the image is written from the correct position. However, the BD signal of LD1 is used as it is for LD2
When it is used as a BD for a disc, the image writing position of the LD2 in the main scanning direction deviates from the image writing position of the LD1 in the main scanning direction due to the error of each surface of the polygon. Therefore, the BD signal of LD1 is delayed by two BD cycles to obtain the BD signal of LD2.
Here, the BD cycle is an average cycle of the BD signal cycles of the LD1. By writing the image at the timing delayed by tc from the BD signal for LD2 (referred to as BD2) generated in this way, the image writing can be performed at the correct position. With such a configuration, from the BD signal generated on the LD1 side on the same polygonal surface as that on which the LD2 scans the photosensitive drum 201,
The BD2 signal for LD2 can be generated.

This state will be described with reference to the timing chart of FIG. 6 and the block diagram of FIG. FIG. 6 shows FIG.
It is a figure which shows the BD signal which the BD sensor 306 in the scanner structure shown in FIG. Outputs. In FIG. 6, S1001 shown in the upper stage is a virtual BD signal when the surface division error is ideal, and S1002 in the middle stage is the actual BD sensor 30.
6 shows the BD signal output by S6, and S1003 shows the BD signal for the LD2 of the first embodiment shown in FIG. These BD signals are true when they are Low, which means that BD signal detection is performed. Also, in this figure, the phase of S1001 in the upper stage is the B of the LD1 laser.
The phase of the left end of the output signal of the D sensor is matched. In this embodiment, the BD signal of the LD1 laser is converted into two BD signals.
A signal delayed by two cycles, namely, the average cycle of the BD signal of the LD1 laser is generated as the BD signal of the LD2 laser. In this case, LD1
Is scanning the photosensitive drum 202 on the third polygonal surface, the LD 2 detects the photosensitive drum 201 on the first polygonal surface.
Are scanning. The BD signal for LD2 at that time is
The first polygonal surface is generated with reference to the timing when the BD sensor 306 is scanned. By doing so, even if the surface division error of the polygon surface is large, the image writing can be performed at an appropriate timing.

Therefore, in FIG. 6, the signal phase at the left end of the virtual BD signal S1001 having the average BD period shown in the upper part is made to coincide with the output phase of the BD sensor by the first polygonal surface, so that it is delayed. Generated LD
The signal for the first polygon surface of the BD signal for 2 is also S1001.
Will match the phase of.

FIG. 7 shows B for LD2 in this embodiment.
3 is a block diagram of a BD signal generation unit that generates a D signal. FIG.
The output of the BD sensor 306 is input to the block 701. In block 701, the BD sensor 3 which has an analog amount as it is and has analog timing
The output of 06 is compared with a predetermined reference value by a comparator. The output of this comparator is sampled with a clock that is at least four times the pixel clock frequency and is output as a BD digital signal, that is, a BD signal (BD1) S1002 for LD1. This signal is also input to the delay circuit 702. The delay circuit 702 delays the input signal S1002 by two cycles of the average cycle of the two BD signals, and outputs the LD2
The BD signal S1003 is generated. LD1 and LD
The digital BD signals S1002 and S1003 for 2 are output to the video controller. Although not shown, since the output of the BD sensor actually has analog timing, it is converted into a digital signal by being sampled with a clock that is four times as large as the pixel clock or more, for example. It becomes S1002. Delay circuit 70
2 includes, for example, a count circuit capable of counting a time corresponding to twice the average BD cycle, loads the counter together with the input of S1002, down-counts every clock, and outputs S1003 when the count value becomes 0. It is also possible to make a circuit that does. The delay circuit 702 is not limited to the counter circuit as described above,
Any circuit can be used as long as it can be delayed by a predetermined time.

By performing such processing, the relationship between the digital BD signal S1002 of the LD1 and its image writing timing, and the digital BD signal S1003 for the LD2.
And the image writing start timing can be made equal. In other words, the BD sensor is arranged on the laser beam scanning path of the LD2, and the B
This can be equivalent to the case where the D signal is obtained.

The image writing position on the photosensitive member is related to the optical arrangement of the folding mirror with respect to the photosensitive drum and the polygon mirror, but here, for simplification of the description, for example, the arrangement shown in FIG. In this case, the folding mirror and the photosensitive drum are arranged in line symmetry with respect to the rotation axis of the polygon mirror. In other words,
It is assumed that the characteristics of the optical systems for LD1 and LD2 are the same. On the contrary, if they do not match, a mismatch occurs in the image position, the image size, and the deformation amount of the image, and the color misregistration cannot be eliminated only by adjusting the timing.

As described above, even if there is only one BD sensor, it is possible to generate the reference signal for keeping the image registration position of the LD 2 in the main scanning direction constant. This makes it possible to read the registration detection pattern image and effectively operate the image registration detection unit that detects each image registration position.

Although the present invention has been described based on the embodiment of the four-sided polygon, the present invention is not limited to the four-sided polygon. It can be applied to three or five surfaces, or even more. In the case of 3 surfaces, the surface next to the surface that reflects the laser beam of RD1 is the laser of LD2.
When the beam is reflected, the period of one cycle of the average BD cycle,
In the case of five surfaces, if the surface next to the surface that reflects the laser beam of RD1 reflects the laser beam of LD2, the period of two cycles of the average BD cycle may be delayed. In this delay or in acquisition of the average period, for example, by using a clock having a frequency of multiple times (preferably four times or more) of the pixel clock, the accuracy of the average period and the delay period to be acquired is divided into a plurality of pixel clocks. It can be 1. This means that the Nth surface from the reflection surface of the laser beam received by the BD sensor is
When it becomes a reflecting surface of the beam, the BD signal for the other laser beam may be delayed by N periods of the average period.

In the present embodiment, the present invention has been described by exemplifying an image forming apparatus which has an ITB and forms an image.
It is also applicable to a TB type image forming apparatus.

(Second Embodiment) FIG. 8 is a timing chart for explaining the second embodiment, and FIG. 9 is a block diagram for explaining the second embodiment.

In this embodiment, the delay circuit 70 shown in FIG.
This is different from the first embodiment in that the set amount of the delay time of 3 is made variable so that the engine controller or the video controller shown by reference numeral 704 can freely set it. Other configurations and operations are similar to those of the first embodiment, and detailed description thereof will be omitted.

In this embodiment, as a result of the resist inspection, that is, a registration detecting pattern image is formed on the ITB at a predetermined timing, the image is detected by the image registration position detecting sensor 112, and the image is detected on the photoconductor corresponding to each color. Based on the result of examining the state of registration,
To minimize the color shift in the main scanning direction,
The delay time tv shown in FIG. 8 is adjusted. The method will be described below.

According to the method described in the first embodiment, in order to detect the registration position of the toner image in the main scanning direction,
As indicated by reference numerals 501 to 504 in FIG. 5, the time until the image is detected again after the registration detection sensor once detects the image by printing the character “registration” of the hiragana, that is, , You can check the time to cross the "ku" character in the vertical direction. Therefore, when the black and cyan resist detection patterns are formed by the method shown in the above-described first embodiment and the deviation amount between the two is detected, to be precise, in the case shown in FIG. Detect the amount. Shift amount ΔCB having the sign at that time
The image writing timing of main scanning is changed by the time corresponding to the correction. If the time is ΔtCB, Δt
CB can be easily calculated from the deviation amount and the scanning speed Vs of the laser beam on the photosensitive drum, and ΔtCB = ΔCB
/ Vs.

The value obtained by adding this ΔtCB to the original delay time 2tBD when the registration check pattern is created is t.
Let v. By using this tv as the delay time, the black writing start position can be accurately aligned with the cyan writing end position in the main scanning direction.

In the present embodiment, when the BD signal of LD1 is delayed to generate the BD signal of LD2, the set amount of delay time is made variable, and from the initially set 2BD period,
The system is configured so that the delay amount is finally set again as found from the result of the registration inspection. Therefore, for example, in FIG. 3, even when the laser diodes 1101 and 1102 deviate from the symmetrical positions with respect to the polygon mirror 1103 by a small amount, the deviation of the BD signal is accurately detected, and the deviation is detected by the variable delay unit 703. Can be corrected.

In other words, by setting the delay amount in the above-described first embodiment as the initial setting, the registration position inspection is executed, and then the second embodiment is executed, so that the writing start position is adjusted with high accuracy. be able to.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG. 10 having the same functions as those in FIG. 3 are denoted by the same reference numerals as those in FIG. As shown in FIG. 10, the present embodiment is different from FIG. 1 in that the LD 1 having the BD sensor 306 on the scanning path is used to scan the black photosensitive drum 201. Also in this configuration, as in the first and second embodiments, the two laser beams are scanned on different surfaces of the polygon, and the photosensitive drums are scanned in opposite directions.

Such an arrangement has the following advantages. First, in a so-called monochrome mode in which monochrome printing is performed using a black station, that is, without using a mechanism related to developing colors other than black, a cyan pseudo BD signal is generated to generate a pseudo BD signal for black. You don't have to light your laser diode.
Therefore, it is not necessary to turn on the unnecessary laser diode in the monochrome mode. Further, since the black station can generate the writing timing by scanning the BD sensor with its own laser, it uses the pseudo BD signal using the delay circuit as shown in the first and second embodiments. There is no need, and therefore, there is an advantage that the writing start position can be adjusted with high accuracy without being influenced by the uneven rotation of the polygon.

(Fourth Embodiment) A fourth embodiment of the present invention will be described with reference to FIG. 16 having the same functions as those in FIG. 2 are denoted by the same reference numerals as those in FIG. In the present embodiment, as shown in FIG. 16, the LD 3 having the BD sensor 406 on the scanning path is used to scan the magenta photosensitive drum 203 and scan the yellow photosensitive drum 204 with the BD sensor on the scanning path. It is not configured. Also in this configuration, as in the first and second embodiments,
The two laser beams are scanned on different sides of the polygon, scanning the photosensitive drum in opposite directions.

This arrangement has the following advantages. A station without a BD sensor is slightly less accurate in writing position than a station with a BD sensor. In the configuration of this embodiment, the station that forms a yellow image does not have the BD sensor.
Therefore, the accuracy of the writing start position of the main scanning of yellow is slightly worse than the accuracy of magenta. However, since the yellow image is less noticeable, there is an advantage that the deterioration of the image can be made less noticeable as compared with the case where the writing position accuracy of magenta deteriorates.

[0073]

As described above, according to the first embodiment of the present invention, the first and second laser beam generators are provided corresponding to the laser beam generators. The first and second image carriers, and the first and second laser beams generated by the two laser beam generators, are simultaneously directed onto the corresponding image carrier surfaces, and on different surfaces. One rotating polygon mirror for deflection scanning and a laser beam on the scanning path of the first laser beam
When the beam is input, the laser beam detection unit that outputs a signal indicating that the beam has been detected and the signal from the laser beam detection unit are input, and the image writing timing of the first laser beam is determined. The second laser beam is generated by inputting the first horizontal synchronization signal portion that generates the first horizontal synchronization signal that serves as a reference when performing the operation and the horizontal synchronization signal of the first laser beam and delaying the same for a predetermined time. Second laser beam timing signal generator that generates a signal for determining the image writing timing of the second laser beam, or by inputting the horizontal synchronization signal of the first laser beam and delaying it by a predetermined time. Since the second horizontal synchronizing signal generating means for generating the horizontal synchronizing signal of the beam is provided, the scanner motor and the BD sensor can be integrated. , It is possible to achieve cost down, including mounting structure of the BD sensor.

Further, in the structure in which there is the surface of the rotary polygon mirror for deflecting and scanning the second laser beam after the n surface of the surface of the rotary polygon mirror for deflecting and scanning the first laser beam, the first horizontal synchronization is performed. Since the set value for setting the signal delay amount is set to a value that represents a time that is n times the average period of the first horizontal synchronization signal, the image for detecting the registration detection pattern image and detecting each image registration position is read. It becomes possible to effectively function the resist detection unit.

Further, according to the second embodiment of the present invention,
In addition to the above, in the second laser beam timing signal generating means or the second horizontal synchronizing signal generating means, it is possible to change the set value for setting the amount of delaying the first horizontal synchronizing signal. The second laser, which has no laser beam detection means
It is possible to provide a high-quality image forming apparatus with good image writing position accuracy even when the position of the beam deviates from the symmetrical position with respect to the first laser beam position and the center of the rotary polygon mirror.

Further, according to the third embodiment of the present invention, in addition to the above, a laser beam generating means for generating a laser beam for scanning an image carrier carrying a black toner image is further provided. Since the laser beam detection means is provided on the scanning path, there is an effect that it is not necessary to light an unnecessary laser diode when performing monochrome printing, and the black BK laser beam itself for monochrome printing is provided. Since the laser beam detecting means can be scanned by the laser, it is less affected by polygonal rotation unevenness, and the image writing position can be adjusted with high accuracy. Further, even if another laser beam fails, the image forming apparatus can perform monochrome printing.

Further, according to the fourth embodiment of the present invention, BD is provided on the scanning path for scanning the yellow photosensitive drum.
The sensor is not provided. With this arrangement, the accuracy of the yellow main scanning write position is slightly worse than that of magenta. However, since the yellow image is less noticeable, there is an advantage that the deterioration of the image can be made less noticeable as compared with the case where the writing position accuracy of magenta deteriorates.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a laser printer illustrating a first embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a relationship between a scanner unit and a photoconductor according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between a configuration of an image registration position detection sensor and an intermediate transfer body (ITB).

FIG. 5 is a diagram illustrating a relationship between a resist detection pattern on an intermediate transfer body (ITB) and an image registration position detection sensor.

FIG. 6 is a timing chart explaining the operation of the first embodiment of the present invention.

FIG. 7 is a block diagram illustrating a first embodiment of the present invention.

FIG. 8 is a timing chart explaining the operation of the second embodiment of the present invention.

FIG. 9 is a block diagram illustrating a second embodiment of the present invention.

FIG. 10 illustrates a scanner for explaining a third embodiment of the present invention.
It is a schematic diagram of a unit.

FIG. 11 is a diagram illustrating a relationship between a scanner unit and laser beam scanning.

FIG. 12 is a timing chart illustrating a relationship between a BD signal and image writing.

FIG. 13 is a diagram illustrating a division error for each surface of a polygon mirror.

FIG. 14 is a diagram illustrating a deviation of the cycle of a BD signal output from a BD sensor due to a division error for each surface of a polygon mirror.

FIG. 15 is a timing chart for explaining the deviation of the BD cycle, similar to FIG.

FIG. 16 is a schematic diagram of a scanner unit illustrating a fourth embodiment of the present invention.

[Explanation of symbols]

101 laser printer 102 host computer 103 video controller 104 engine controller 105 Scanner (Cyan, Black) 106 Scanner (yellow, magenta) 107 cartridge (black) 108 cartridge (cyan) 109 cartridge (magenta) 110 cartridges (yellow) 111 ITB 112 Registration position detection sensor 201 Photosensitive drum (black) 202 Photosensitive drum (cyan) 203 Photosensitive drum (magenta) 204 Photosensitive drum (yellow) 301 First laser diode 302 Second laser diode 303 polygon mirror 304 First folding mirror 305 Second folding mirror 306 BD sensor 701 Digital BD signal signal generator 702 delay circuit S1001 Virtual BD signal S1002 LD1 digital BD signal S1003 LD2 digital BD signal

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/036 B41J 3/00 D 5C072 1/113 H04N 1/04 104A (72) Inventor Kenichi Tomita Tokyo 3-30-2 Shimomaruko, Ota-ku Canon Inc. F-term (reference) 2C362 AA10 BA04 BA47 BA50 BA51 BA70 BA89 BB32 BB38 BB43 CA23 CA39 2H030 AA01 AA06 AB02 BB02 BB16 2H045 BA22 BA34 CA88 CA98 2H076 AB06 AB08 AB12 AB18 AB18 AB12 AB18 AB67 EA01 5C051 AA02 CA07 DA02 DB02 DB08 DB22 DB24 DB30 DC03 DE02 EA01 5C072 AA03 BA02 HA02 HA06 HA13 HB08 HB11 HB13 QA14 XA05

Claims (8)

[Claims] 1. A first and a second laser beam generating means, a first and a second image carrier provided corresponding to each of the laser beam generating means, and the two lasers. The first and second laser beams generated by the beam generating means are simultaneously deflected and scanned on different surfaces toward the surface of the corresponding image carrier.
Two rotating polygon mirrors, laser beam detection means for outputting a signal indicating that the beam has been detected when the laser beam is input on the scanning path of the first laser beam; Input the signal from the beam detection means,
First horizontal synchronizing signal generating means for generating a first horizontal synchronizing signal which is a reference when determining the image writing start timing of the first laser beam, and a horizontal synchronizing signal of the first laser beam are inputted. And delaying for a predetermined time, the second laser
An image forming apparatus, comprising: a second laser beam timing signal generating unit that generates a signal that determines a beam image writing timing. 2. A first and a second laser beam generating means, a first and a second image carrier provided corresponding to each of the laser beam generating means, and the two lasers. The first and second laser beams generated by the beam generating means are simultaneously deflected and scanned on different surfaces toward the surface of the corresponding image carrier.
Two rotating polygon mirrors, laser beam detection means for outputting a signal indicating that the beam has been detected when the laser beam is input on the scanning path of the first laser beam; Input the signal from the beam detection means,
First horizontal synchronizing signal generating means for generating a first horizontal synchronizing signal which is a reference when determining the image writing start timing of the first laser beam, and a horizontal synchronizing signal of the first laser beam are inputted. Then, the image forming apparatus is provided with a second horizontal synchronizing signal generating means for generating a horizontal synchronizing signal of the second laser beam by delaying for a predetermined time. 3. A set value for setting an amount of delaying the first horizontal synchronizing signal in the second laser beam timing signal generating means or the second horizontal synchronizing signal generating means is variable. The image forming apparatus according to claim 1, wherein: 4. A structure in which there is a surface of the rotary polygon mirror for deflecting and scanning the second laser beam after n surfaces of the surface of the rotary polygon mirror for deflecting and scanning the first laser beam, 3. The set value for setting the delay amount of the first horizontal synchronizing signal is a value representing a time that is n times the average period of the first horizontal synchronizing signal.
The image forming apparatus according to item 1. 5. The respective resist detection pattern images formed on the image carrier by the first and second laser beams and further transferred onto the intermediate transfer member are read, and respective image resist positions are read. The image forming apparatus according to claim 3, further comprising: an image registration detecting unit that detects a change of the set value based on a detection result of the image registration detecting unit. 6. The laser beam detecting means is provided on the scanning path of a laser beam generating means for generating a laser beam for scanning an image carrier carrying a black toner image. The image forming apparatus according to any one of 5 above. 7. The laser beam detecting means is not provided on the scanning path of a laser beam generating means for generating a laser beam for scanning an image bearing member carrying a yellow toner image. 7. The image forming apparatus according to any one of 1 to 6. 8. A color image is formed on a sheet-shaped medium by using a plurality of the optical systems as a light source for image formation of a plurality of colors and superimposing images of a plurality of colors on each other. 7. The image forming apparatus according to any one of 7.