JP2007245448A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize image quality without reference to a change in the quantity of light to a synchronization detecting means (synchronization detecting part). <P>SOLUTION: A synchronization-detecting and light quantity-computing part 301 measures the pulse width (the quantity of the light on a light detecting surface of the synchronization detecting part 123) of a synchronization detection signal output from the synchronization detecting part 123. A light-quantity comparing part 302 prestores the pulse width of the synchronization detection signal when the light is emitted from an LD 121 in preset light quantities, compares the pulse width with that of the subsequent synchronization detection signal so as to compute the ratio between both the pulse widths, and determines the quantity of the light depending on the result of computation. An LD light-quantity control part 304 variably controls the quantity of the light from the LD 121 along the fluctuation of the pulse width of the synchronization detection signal by generating an LD driving signal depending on the quantity of the light, so as to output it to the LD 121. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical scanning device for writing an electrostatic image by light on an image carrier, and an electrophotographic color copying machine (PPC), a color multifunction peripheral (MFP), and a color facsimile (FAX) provided with the same. The present invention relates to a color image forming apparatus such as an apparatus and a color printer.

As an image forming apparatus using the optical scanning device as described above, for example, there is one that performs the control shown in the following (1) and (2).
(1) The rotation of the scanner motor driver is controlled at the start of the apparatus, and it is confirmed that the rotation speed (rotation speed) converges to a predetermined value, and the semiconductor laser is forced to emit light in the timing period of the non-image area of the line cycle. . APC control is performed so that the amount of light emitted from the semiconductor laser becomes a target value, and at the timing of forced light emission for APC control, the synchronization detection unit (BD monitor photodiode) generates a timing BD synchronization signal in the main scanning direction. Output to the control unit. The timing in the printer engine is controlled by the BD synchronization signal. Further, by controlling the increase / decrease of the reference bias value, the light emission power emitted from the semiconductor laser element is varied, and the control is repeated so that the amount of light on the surface of the photoreceptor becomes a target value (see Patent Document 1).

(2) A polygon mirror that deflects and scans a beam generated from an LD unit that is modulated based on an image signal, and an image that focuses the laser beam from the LD unit at a predetermined interval in the rotational direction on the photosensitive drum. In the image forming apparatus comprising the means and a synchronization detection unit (synchronization detection sensor) that detects a plurality of laser beams deflected and scanned by the polygon mirror at a predetermined position, the light amounts of the plurality of laser beams detected by the synchronization detection sensor Is provided, and the amount of light is set for each beam (see Patent Document 2).
Japanese Patent Laid-Open No. 2002-248806 JP 2002-29089 A

  In the conventional example shown in (1) above, the maximum deviation level and slice level of the analog light quantity of the synchronization detection unit are detected to control the light amount on the photosensitive member surface. The light amount control of the sensor part is not sufficiently performed. As a result, the amount of light input to the synchronization detection sensor becomes insufficient due to the occurrence of optical contamination on the polygon mirror surface, etc., and as a result, the synchronization detection output becomes unstable and eventually becomes a pixel in the main scanning direction. Deviation will occur. When such a phenomenon occurs, particularly in the case of a color image forming apparatus, the color shifts become the color shifts of each other, leading to a decrease in image quality, or a system error due to a decrease in the amount of light with respect to the synchronization detection portion. become.

  Actually, dirt may occur on the reflection surface of the polygon motor mirror. This is due to the difference in wind pressure generated around the polygon mirror that rotates at high speed, so that minute dust and toner generated in the machine become dirty and adhere to the end of the reflective surface of the polygon mirror through various factors such as temperature and humidity. To do. When this dirt portion on the reflection surface of the polygon mirror overlaps the scan position input to the synchronization detection unit, sufficient light is not irradiated to the synchronization detection unit, causing the above-mentioned problem due to insufficient light quantity. .

In the conventional example shown in the above (2), the amount of light can be set for each beam. However, as in the conventional example shown in the above (2), the factors over time and the environment inside the unit If the output of the synchronous detector becomes unstable compared to the initial state due to contamination of the reflective surface of the polygon mirror due to, there is sufficient means such as light amount control for the feedback system with the state of the reflective surface of the polygon mirror as a factor It is the current situation that is not done.
The present invention has been made in view of the above points, and an object of the present invention is to stabilize the image quality regardless of the change in the light amount to the synchronization detection means (synchronization detection unit).

In order to achieve the above object, the present invention provides the following optical scanning device and color image forming apparatus.
In the optical scanning device according to the first aspect of the present invention, the light emitted from the light emitting element is repeatedly scanned in the main scanning direction, whereby the light is applied onto the image carrier that rotates in the sub-scanning direction orthogonal to the main scanning direction. An optical scanning device for writing an electrostatic image, wherein the light emitting element is driven in a modulated manner in accordance with image data, thereby emitting light corresponding to the light emitting element, and the image carrier Synchronization detection means for detecting the light in the main scanning direction and generating and outputting a synchronization detection signal for defining the image writing start position by the light in the main scanning direction; and on the light detection surface of the synchronization detection means Synchronous detection surface light amount setting means for setting the light amount, and synchronous detection surface light amount calculation means for calculating the light amount on the light detection surface of the synchronous detection means when light is emitted from the light emitting element by the light emitting element driving means. A light amount comparison unit that compares the light amount calculated by the synchronization detection surface light amount calculation unit with a light amount set by the synchronization detection surface light amount setting unit, and a light amount of the light emitting element based on a comparison result by the light amount comparison unit And a light amount variable control means for variably controlling the light intensity.

An optical scanning device according to a second aspect of the present invention is the optical scanning device according to the first aspect, further comprising image carrier surface light amount setting means for setting a light amount on a light irradiation surface of the image carrier, wherein the light amount variable control means is The light amount of the light emitting element is variably controlled so that the light amount calculated by the synchronization detection surface light amount calculating means matches the light amount set by the image carrier surface light amount setting means.
According to a third aspect of the present invention, there is provided the optical scanning device according to the first or second aspect, wherein the light amount variable control means executes variable control of the light amount of the light emitting element according to the type of image data from the outside. Select to stop.

  According to a fourth aspect of the present invention, there is provided an optical scanning device according to the present invention, wherein the light emitted from the light emitting element is repeatedly scanned in the main scanning direction, whereby the light is applied onto the image carrier that rotates in the sub scanning direction orthogonal to the main scanning direction. An optical scanning device for writing an electrostatic image, wherein the light emitting element is driven in a modulated manner in accordance with image data, thereby emitting light corresponding to the light emitting element, and the image carrier Synchronization detection means for detecting the light in the main scanning direction and generating and outputting a synchronization detection signal for defining the image writing start position by the light in the main scanning direction; and on the light detection surface of the synchronization detection means Synchronous detection surface light amount setting means for setting the light amount, and synchronous detection surface light amount calculation means for calculating the light amount on the light detection surface of the synchronous detection means when light is emitted from the light emitting element by the light emitting element driving means. The light quantity comparison means for comparing the light quantity calculated by the synchronization detection surface light quantity calculation means with the light quantity set by the synchronization detection face light quantity setting means, and the difference between both light quantities by the light quantity comparison means exceeds a predetermined value. In this case, a warning stage for outputting a warning signal to the outside is provided.

  According to a fifth aspect of the present invention, there is provided a color image forming apparatus comprising: the optical scanning device according to any one of the first to fourth aspects; and each electrostatic image sequentially written on the image carrier by the optical scanning device. A developing device that sequentially develops toner images to form toner images, and each toner image that is sequentially formed on the image carrier by the developing device is sequentially superimposed and transferred onto another image carrier. An image is formed.

  According to a sixth aspect of the present invention, there is provided a color image forming apparatus comprising: the optical scanning device according to any one of the first to third aspects; and the electrostatic images sequentially written on the image carrier by the optical scanning device. A developing device that sequentially develops toner images to form toner images, and each toner image that is sequentially formed on the image carrier by the developing device is sequentially superimposed and transferred onto another image carrier. In the color image forming apparatus for forming an image, the synchronization detection surface light amount setting unit of the optical scanning device determines the light amount of the light emitting element with reference to the end timing of writing of the electrostatic image of the final color on the image carrier. It is a means for variably controlling.

  According to this invention, the optical scanning device presets the light amount on the light detection surface of the synchronization detection unit, and the light amount on the light detection surface of the synchronization detection unit when the light emission from the light emitting element by the light emitting element driving unit is performed. Calculate and compare the calculated light amount with a preset light amount, and variably control the light amount of the light emitting element based on the comparison result, or when the difference between both light amounts exceeds a predetermined value, Since the warning signal is output to the outside and the subsequent operation can be stopped, the image quality can be stabilized regardless of the change in the light amount to the synchronization detection means (synchronization detection sensor).

Hereinafter, the best mode for carrying out the present invention will be specifically described with reference to the drawings.
[First embodiment]
FIG. 1 is a block diagram showing a configuration example of a control system of a color image forming apparatus according to the first embodiment of the present invention.
This color image forming apparatus includes a FAX interface (hereinafter, “interface” is also referred to as “I / F”) 1, a FAX control unit 2, a host I / F 3, a printer control unit 4, a document reading unit 5, and an input image processing unit 6. , Key operation unit 7, main control unit 8, memory unit 9, write control unit 10, and image printing unit 11.

The FAX I / F 1 is a part that interfaces with a FAX apparatus (or an electronic apparatus such as a digital multi-function peripheral having a FAX function), and transfers FAX transmission / reception data.
The FAX control unit 2 performs processing on FAX transmission / reception data (image data) between the FAX I / F 1 and the main control unit 8 according to the communication specifications of each FAX apparatus. This process can be realized by a FAX application.
The host I / F 3 is a part that interfaces with other electronic devices on the network such as a host (personal computer or the like) or a LAN (local area network), and exchanges data such as image data.

The printer control unit 4 processes data between the host I / F 3 and the main control unit 8 via the controller. This process can be realized by a printer application.
The document reading unit 5 reads an image of a document set on a contact glass or an image of a document being fed by an ADF (automatic document feeder).
The input image processing unit 6 performs input processing on the image data of the document read by the document reading unit (scanner) 5 and passes it to the main control unit 8. The input process can be realized by a scanner application.

The key operation unit 7 instructs or sets selection or setting of an application, number of prints, paper size, scaling (enlargement / reduction), user program (UP), service program (SP), etc. in the color image forming apparatus. Various keys for instructing to clear the mode, start or stop each operation, and a display unit for displaying various information are provided.
The main control unit 8 performs overall control of data transfer between each unit (other than the main control unit 8) in the color image forming apparatus, and communicates with a control circuit that controls each peripheral unit such as a CPU. Controls timing control and command I / F.

The memory unit 9 is a storage unit such as a RAM or an HDD (hard disk device), and stores the image data from the FAX control unit 2, the printer control unit 4, and the input image processing unit 6 via the main control unit 8.
The writing control unit 10 sets an image area in accordance with the paper size for the image data from the main control unit 8 or performs conversion processing into an LD drive signal (LD modulation data) to generate an image. It is passed to the printing unit 11.
The image printing unit 11 prints (forms) an image on a sheet (transfer sheet) via a photoreceptor (OPC) and an intermediate transfer belt.

Here, in the first embodiment, each unit can be controlled in accordance with a signal from the key operation unit 7 and a printing operation can be started by a command signal from the main control unit 8, but the key operation unit 7 is used. Therefore, it aims at releasing the stepwise change operation of the polygon clock frequency to the outside and giving the change timing flexibility.
FIG. 2 is a diagram illustrating a configuration example of a printer engine in the color image forming apparatus.

  This color image forming apparatus uses a laser diode (hereinafter abbreviated as “LD”) as a light emitting element to form a tandem type electrophotographic apparatus (electrophotographic color copying machine, color composite apparatus, A color facsimile apparatus, a color printer, etc.) around the plurality of photosensitive drums 21 (21B, 21M, 21C, 21Y), in addition to the primary transfer rollers 22 (22B, 22M, 22C, 22Y), respectively. A charging device, a developing device, a cleaning device, etc. are provided.

Further, the intermediate transfer belt 23 and a mark sensor 24 for detecting a plurality of marks (which may be slits or through holes) (not shown) formed so as to be continuous at equal intervals along the circumferential direction of the surface thereof are provided. .
Each primary transfer roller 22 can selectively contact the corresponding photosensitive drum 21 via the intermediate transfer belt 23.

The color image forming apparatus also includes an engine control unit 101, an application control unit 102, an image writing control unit 103, and a laser writing device 104. Among them, the image writing control unit 103 and the laser writing device 104 constitute an optical scanning device.
The engine control unit 101 comprehensively controls the entire printer engine, such as controlling the laser writing device 104 via the image writing control unit 103. The engine control unit 101 corresponds to the main control unit 8 in FIG. 1 and has a function of interfacing with the memory unit 9.

  The application control unit 102 performs processing by a corresponding application on image data input from a FAX apparatus, a host, a scanner, or the like that is a higher-level apparatus. The application control unit 102 functions as the FAX control unit 2, the printer control unit 4, and the input image processing unit 6 in FIG. 1, and is independent of the FAXI / F 1, the host I / F 3, and the document reading unit 5. is doing.

The image writing control unit 103 corresponds to the writing control unit 10 in FIG. 1, and includes a pixel clock generation unit 111, a multiplication circuit 112, an image signal generation unit 113, a writing position control unit 114, and an LD driving unit. 115. The image writing control unit 103 has functions as a synchronization detection surface light amount setting unit, an image carrier surface light amount setting unit, a synchronization detection surface light amount calculation unit, a light amount comparison unit, and a light amount variable control unit. Fulfill.
The pixel clock generation unit 111 generates a pixel clock vclk based on the source oscillation clock CLKREF based on a register setting value from the engine control unit 101 and outputs it to the multiplication circuit 112.

The multiplication circuit 112 divides the pixel clock vclk from the pixel clock generation unit 111 by a predetermined setting value and outputs the divided clock to the writing position control unit 114.
The image signal generation unit 113 uses the source oscillation clock CLKREF to perform image processing such as scaling or edge processing on the image data from the application control unit 102, thereby outputting an image to be output to the writing position control unit 114. Generate a signal.
The write position control unit 114 uses the source oscillation clock CLKREF, synchronizes the image signal from the image signal generation unit 113 with the pixel clock vclk from the multiplication circuit 112, and outputs it to the LD drive unit 115 as an LD drive signal. The image writing position (image area) by the laser beam is controlled.

The LD driving unit 115 is a light emitting element driving unit using, for example, CML (Current Mode Logic), and modulates and drives the LD 121 in the laser writing device 104 in accordance with an LD driving signal from the writing position control unit 114. Thus, the corresponding laser beam is emitted.
Note that the polygon motor clock CLKPM is supplied with the source oscillation clock CLKREF from the engine control unit 101 to the image signal generation unit 113 and the write position control unit 114 in the image write control unit 103 in the same manner as the pixel clock vclk. The position control unit 114 generates a predetermined frequency division ratio set by a register or the like.

Laser light emitted from the LD 121 by modulation driving by the LD driving unit 115 is collimated by a collimator lens (not shown), and is irradiated onto one surface of the polygon mirror 122 a rotated by the polygon motor driving unit 122.
The laser beam applied to one surface of the polygon mirror 122a is deflected thereby, and the synchronization detector 123 disposed on the front side of the photosensitive drum 21 outside the main scanning writing area (outside the effective image area in the main scanning direction). Is incident on the light detection surface.

The synchronization detection unit 123 is a synchronization detection unit using a synchronization detection sensor including a photoelectric conversion element such as a photodiode and a signal waveform shaping circuit. The synchronization detection unit 123 photoelectrically converts the laser light incident on the light detection surface to generate a synchronization detection signal DETP_N. To the image signal generation unit 113.
Here, the signals input to the polygon motor driving unit 122 are a polygon clock CLKPM and a polygon motor ON / OFF signal PMON. Further, a polygon ready signal (not shown) indicating a locked state accompanying the rotation of the polygon mirror 122 a is fed back from the polygon motor driving unit 122 to the image writing control unit 103.
The laser writing device 104 including the polygon motor driving unit 122 and the synchronization detection unit 123, the photosensitive drum 21, the intermediate transfer belt 23, and the mark sensor 24 constitute the image printing unit 11 of FIG.

  The laser beam applied to one surface of the polygon mirror 122a is incident on the light detection surface of the synchronization detection unit 123, and is then rotated by the fθ lens 124 and the like by the rotation of the polygon mirror 122a. An image is formed by irradiating on a certain photosensitive drum 21 (a surface charged in advance). The imaging spot is repeatedly moved and scanned (scanned) in the main scanning direction, which is the width direction of the photosensitive drum 21 (the direction orthogonal to the sub-scanning direction), by the rotation of the polygon mirror 122a. An electronic image) is formed.

For convenience of illustration, FIG. 2 shows only a configuration for forming an electrostatic latent image for one color on the photosensitive drum 21 (for example, 21B) by one laser beam (for example, for B) from the LD 121. Although not shown, in reality, there are four LDs 121, and the four laser beams from the four LDs 121 generate four-color electrostatic latent images on the photosensitive drums 21B, 21M, 21C, and 21Y, respectively. It is the structure for forming.
Here, for example, when the image data input from the application control unit 102 to the image writing control unit 103 is image data for performing full color copying, the printer engine including the laser writing device 104 performs the following operation. Do.

First, the laser writing device 104 charges the surface of the photosensitive drum 21B with a corresponding charging device, writes a B electrostatic latent image on the charging surface with B laser light, and handles the B electrostatic latent image. The toner is developed with B toner from the developing device to form a B toner image on the photosensitive drum 21B.
The B toner image is intermediately transferred onto the intermediate transfer belt 23 by the primary transfer roller 22B.

  Thereafter, the B toner remaining on the photosensitive drum 21B is removed by the corresponding cleaning device, and then the above-described cycle starting with charging by the corresponding charging device again, laser writing, development, intermediate transfer, cleaning, etc. is repeated. As a result, four toner images of B, M, C, and Y, which are sequentially formed on the photosensitive drums 21B, 21M, 21C, and 21Y, are transferred onto the intermediate transfer belt 23 while being sequentially aligned, thereby superimposing four colors. A secondary transfer roller (not shown) is brought into contact with the intermediate transfer belt 23 via the paper and is collectively transferred onto the paper fed from a paper feeding unit (not shown).

  Therefore, when the B process for forming the B toner image on the intermediate transfer belt 23 is completed, the process proceeds to the M process for forming the M toner image on the intermediate transfer belt 23. The timing of starting laser writing for the M latent image by the laser writing device 104 is adjusted so that the leading end of the B toner image on the belt 23 matches. At this time, the toner image alignment is performed by feeding back and using the output signal of the mark sensor 24 for detecting a plurality of marks formed so as to be continuous at equal intervals along the circumferential direction of the surface of the intermediate transfer belt 23. Control is performed. That is, a sub-scanning position reference signal is generated, timing is determined from the sub-scanning reference signal, and laser writing for the M latent image by the laser writing device 104 is started.

Similarly, the C process and the Y process are performed, and a four-color superimposed color image is formed on the intermediate transfer belt 23. However, the image forming order is not limited to the order of B, M, C, and Y as described above, but is determined according to the characteristics of the toner and the finishing effect of the color image finally formed on the paper. Has been.
The paper on which the four-color superimposed color images are collectively transferred by the secondary transfer roller is sent to a fixing unit (not shown), and the color image is thermally fixed by the fixing roller and the pressure roller, and is discharged.
After batch transfer by the secondary transfer roller, the secondary transfer roller is separated from the intermediate transfer belt 23, and then the toner remaining on the intermediate transfer belt 23 is removed by a cleaning device (not shown).

Next, APC (Automatic Power Control) which is LD light quantity control in an image forming apparatus using an electrophotographic method will be described with reference to FIG.
APC is widely known, and its function is provided in the LD driving unit 115 which is a light emitting element driving means. APC is a series of operations in which information of a PD (photodiode) arranged in the vicinity of the LD 121 is detected, and the light amount of the LD 121 is controlled from this information so as to become the standard light amount. This control is used to keep the accompanying light quantity decrease constant.

FIG. 3 is a block diagram illustrating a basic configuration example of the LD driving unit 115 of FIG.
The LD driving unit 115 includes a comparator 201, a reference bias unit 202, an S & H (sample and hold) circuit 203, a current source 204, and a current switching circuit 205.

  The comparator 201 receives a monitor signal from the PD 131 that monitors the light amount of the LD 121 and a target light amount setting bias signal from the reference bias unit 202. The value of the target light amount setting bias signal is related so that the light amount of the LD 121 becomes the target light amount. The volume VR1 adjusts the gain of the APC feedback loop so that the light amount of the LD 121 becomes the target light amount with respect to the target light amount setting bias.

The operation timing of the S & H circuit 203 is controlled by a laser ENB signal from the outside. Then, the output value of the comparator 201 is held in the capacitor C1 at the timing of the S & H control signal input from the outside.
The current source 204 sets the LD drive current amount according to the held value.
The current switching circuit 205 causes the LD driving current of the amount set by the current source 204 described above to flow through either the LD 121 or the resistor R2 in accordance with the LD driving signal.

Here, during the APC control period, the LD drive signal is set so that the LD drive current flows only through the LD 121. The S & H circuit 203 samples the output value of the comparator 201 at this time in the capacitor C1. During the sample period, the values sampled by successive updating are held until the next sample timing when the hold mode is entered. During the hold period, the LD drive current is determined according to the held value, and flows through either the LD 121 or the resistor R2.
By performing such control at a predetermined interval, for example, in the timing period of the non-image region of the line cycle, the light amount of the LD 121 is controlled to the target light amount.

The feedback control that makes the light amount of the LD 121 constant by the APC described above is an operation that can obtain a predetermined standard light amount on the light emitting surface (chip surface) of the LD 121, but is actually required in the electrophotographic process. These are the light amounts on the light detection surface of the synchronization detection unit 123 and the light irradiation surface of the photosensitive drum 21.
However, the APC operation alone does not completely control the deterioration of the light amount with time on the light detection surface of the synchronization detection unit 123 and the light irradiation surface of the photosensitive drum 21, and the optical from the LD 121 to the photosensitive drum 21 is not perfect. Since there are scanning optical system components such as a collimator lens, a cylindrical lens, a polygon mirror 122a, a spherical lens, an Fθ lens, and a reflection mirror in the path, the standard light amount of the LD 121 controlled by the APC is used for subsequent scanning optics. It is necessary to control in consideration of changes in the system over time.

For example, the amount of light obtained from the light detection surface of the synchronization detection unit 123 and the light irradiation surface of the photosensitive drum 21 via the scanning optical system is such that dirt such as dust adheres to the components constituting the scanning optical system over time. If this is the case, it will be lower than the initial stage of device manufacture, and as a result, a predetermined image density cannot be obtained.
Examples of errors that occur when dirt such as dust adheres to the components of the scanning optical system include misalignment due to dirt on the reflecting surface of the polygon mirror 122a, which has been a concern, and system errors.

  In an image forming apparatus that forms an image using a polygon mirror, such as a digital color copying machine, dirt may occur on the reflecting surface of the polygon mirror. Due to the difference in wind pressure, minute dust and toner generated in the machine are generated over time due to the combination of various factors such as temperature and humidity, and this dirty part is the light of the synchronization detection unit (synchronization detection sensor). If it overlaps with the timing (scan position) at which the laser beam is incident on the detection surface, a sufficient amount of laser beam is not irradiated to the synchronization detection unit, resulting in insufficient light amount.

As a result, the synchronization position in the main scanning direction becomes unstable, and in a color image formed with a plurality of colors, a color shift in the main scanning direction due to the position shift occurs. Furthermore, a system error accompanying a decrease in the amount of light with respect to the synchronization detection unit is also induced, leading to a significant decrease in the reliability of the apparatus.
In this way, due to the occurrence of partial contamination on the reflection surface of the polygon mirror, the light amount on the light detection surface of the synchronization detection unit may fluctuate even if the light amount on the photoconductor surface maintains a constant value. As a result, the above-described color shift in the main scanning direction and a system error may be caused. Therefore, in the first embodiment, focusing on this point, dirt generated on the reflection surface of the polygon mirror, etc. Means shall be provided to eliminate the effects of.

  In consideration of the above-described problems, in the first embodiment, apart from APC generally used for LD light amount control, a function for setting the light amount on the light detection surface of the synchronization detection unit 123, and the photosensitive drum 21 And a function for setting the amount of light on the light irradiation surface. When controlling the amount of light, a shading correction function (not shown) provided in the LD drive unit 115 is used.

  The shading correction function is a generally known method for controlling the LD light quantity in the main scanning direction. The synchronization detection surface light quantity setting function and the photoconductor surface light quantity setting function are independent of each other, that is, the synchronization detection unit and the photoconductor. The feature is that each item is divided. This is for the purpose of controlling the difference between the light amount on the light detection surface of the synchronization detection unit and the light amount on the light irradiation surface of the photosensitive member so as not to occur as much as possible, for example, as shown in FIG.

FIG. 4 is a timing chart for explaining the shading correction function provided in the LD driving unit 115.
As can be seen from FIG. 4, the LD 121 light quantity control analog voltage (shading output) LDLVL by the shading correction function is changed in accordance with an arbitrary position in the main scanning direction, so that the light quantity of the LD 121 corresponds to the image height. Can be changed to a value.
The level change point of the shading output LDLVL output to the LD driver in the LD driver 115 in FIG. 2 is controlled by the register setting value. This is an example when a divided PWM (pulse width modulation) method is adopted, and is a case where the PWM cycle is set to 8 divisions.

  Here, the area 0 is set as an offset period based on the synchronization detection signal DETP_N (N means Low active), and thereafter, the areas 1, 2, 3,... The shading output LDLVL to the LD driver is controlled by changing the corresponding amount of light corresponding to the data (shlutt # 1 to shdlut # 8) of the latch (LUT) arranged in the image writing control unit 103 in FIG. . Further, the remaining area in the main scanning direction is given as area 9.

In the first embodiment, the LD light quantity for area 0 and area 1 is controlled by the same latch (shudlt # 1), and each area has a pixel clock vclk or a clock having a frequency equivalent thereto. It is assumed that the area is controlled by
Since the light amount changes following the shading output LDLVL based on this control, the light amount can be controlled at a desired image height (optical main scanning position) in the main scanning direction. That is, it is possible to freely control the amount of light on the light detection surface of the synchronization detection unit 123 and the amount of light on the actual image area (light irradiation surface of the photosensitive drum 21).

Next, a function for feeding back and calculating the light amount on the light detection surface of the synchronization detection unit 123 and a configuration for comparing the calculated light amount with a preset light amount on the light detection surface of the synchronization detection unit 123 will be described.
FIG. 5 is a diagram showing a configuration example of a main part related to the present invention of the LD driving unit 115 of FIG. 2 and an optical system of the laser writing device 104. In FIG.
FIG. 6 is a diagram for explaining the relationship between the scanning position of the laser beam on the reflection surface and the contamination when the reflection surface of the polygon mirror 122a in FIG. 5 is normal and when the contamination is attached.

FIG. 7 is a diagram for explaining the difference in pulse width of the synchronization detection signal output from the synchronization detection unit 123 when the reflection surface of the polygon mirror 122a of FIG. 5 is normal and when dirt is attached.
FIG. 8 is a timing chart for explaining the counting of the pulse width of the synchronization detection signal DETP_N by the synchronization detection light quantity calculation unit 301 of FIG.
FIG. 9 is a diagram illustrating the relationship between the count value of the pulse width of the synchronization detection signal DETP_N by the synchronization detection light amount calculation unit 301 in FIG. 5 and the light amount on the light detection surface of the synchronization detection unit 123.

As a method for calculating by feeding back the amount of light on the light detection surface of the synchronization detection unit 123 when the LD 121 of FIG. 2 emits laser light, the synchronization detection unit 123 is based on the waveform of the synchronization detection signal DETP_N output from the synchronization detection unit 123. There is a method of calculating the amount of light on the light detection surface.
The laser beam reflected by the polygon mirror 122a is input to the image signal generation unit 113 and the writing position control unit 114 as the synchronization detection signal DETP_N by the synchronization detection unit 123. In this first embodiment, the writing position control is performed. The following determination is performed on the synchronization detection signal DETP_N by the unit 114, and the light amount of the LD 121 is variably controlled by the LD driving unit 115 at the next stage according to the result.

  The determination method is such that the synchronization detection signal DETP_N is input to the synchronization detection light amount calculation unit 301 in FIG. 5, and the light amount on the light detection surface of the synchronization detection unit 123 calculated by the synchronization detection light amount calculation unit 301 (actually proportional thereto). (The pulse width count value of the synchronization detection signal DETP_N to be performed) is compared with the light amount on the light detection surface of the synchronization detection unit 123 set in advance by the light amount comparison unit 302.

  For example, when the reflection surface of the polygon mirror 122a is normal as shown in FIG. 6A, the pulse width of the synchronization detection signal DETP_N, which is the output signal of the synchronization detection unit 123, is shown in FIG. An initial width (normal width) tvo as shown in FIG. 6 is set in advance, and then dirt is attached to the reflecting surface of the polygon mirror 122a as shown in FIG. As the amount of light decreases, the pulse width of the synchronization detection signal DETP_N becomes tvo ′ as shown in FIG. 7B, and becomes narrower than the initial width tvo. At this time, in the configuration in which each line synchronization is controlled using the falling edge of the synchronization detection signal DETP_N, the line synchronization timing is shifted in the main scanning direction, and as a result, the image forming position in the main scanning direction is shifted and the color shift is shifted. It will be affected.

  In such a variation in pulse width, the amount of light on the light detection surface of the synchronization detection unit 123 is compared by comparing the initial pulse width of the synchronization detection signal DETP_N output from the synchronization detection unit 123 with the subsequent pulse width. Can be estimated. As a result, it can be estimated how much the light quantity has been reduced or increased.

For example, as illustrated in FIG. 8, the synchronization detection light amount calculation unit 301 calculates the pulse width of the synchronization detection signal DETP_N output from the synchronization detection unit 123 (proportional to the light amount on the light detection surface of the synchronization detection unit 123) as the pixel clock. Measurement is performed by counting (sampling measurement) vclk, and the measurement value, that is, the count value is output to the light quantity comparison unit 302.
Regarding the configuration of the synchronization detection light quantity calculation unit 301, it is desired to count, such as by performing initialization by register setting at an arbitrary timing and further performing a count operation by inputting a count enable signal at an arbitrary timing. As long as the pulse width of the synchronization detection signal DETP_N can be counted at the timing, the content of the configuration does not matter.

  The light quantity comparison unit 302 prepares, for example, data having a relationship as shown in FIG. 9 as look-up table (LUT) data, and at the time of emitting laser light from the LD 121 with a preset light quantity (initially set light quantity). The count value of the pulse width (initial width) tvo of the synchronization detection signal DETP_N output from the synchronization detection light quantity calculation unit 301 is stored as a reference count value, and then the value is output from the synchronization detection light quantity calculation unit 301. The ratio of each count value is calculated by comparing the count value of the pulse width tvo ′ of the synchronization detection signal DETP_N, and the light quantity corresponding to the calculation result is obtained from the lookup table.

The image data identification unit 303 identifies whether the image data input to the image writing control unit 103 is image data for a mono color mode or image data for a full color mode, and uses the identification result as an LD light amount control. To the unit 304.
The LD light amount control unit 304 generates an LD drive signal corresponding to the light amount obtained by the light amount comparison unit 302 and outputs the LD drive signal to the LD 121, whereby the light amount of the LD 121 associated with the fluctuation of the pulse width of the synchronization detection signal DETP_N, that is, synchronization. Variable control of the amount of light on the light detection surface of the detection unit 123 is performed. At this time, the control is switched according to the identification result by the image data identification unit 303, which will be described in detail later.

FIG. 10 is a circuit diagram illustrating a configuration example of the synchronization detection unit (synchronization detection sensor) 123 of FIG.
The amount of light on the light detection surface of the synchronization detection unit 123 is between an external gain resistor Ro inserted between the power supply terminal Vcc and the terminal (Ro) of the photosensor, and between the power supply terminal Vcc and the output terminal (Vo). It is determined by the value of the external load resistance RL to be inserted. Here, the gain resistance Ro = 5.1 kΩ and the load resistance RL = 510Ω are set, but these values may be flexibly changed and used in accordance with specifications required for the image forming apparatus.

  In the first embodiment, an example in which the amount of fluctuation of the light amount on the light detection surface of the synchronization detection unit 123 is calculated by paying attention to the pulse width of the synchronization detection signal DETP_N output from the output terminal (Vo) is described. You may make it obtain | require the fluctuation amount of the light quantity based on the fluctuation amount of the voltage level of the detection signal DETP_N. In FIG. 10, not only the output of the output terminal (Vo) but also the analog level of the output of the terminal (Ro) may be compared.

  Here, a method for presetting the light amounts on the light detection surface of the synchronization detection unit 123 and the light irradiation surface of the photosensitive drum 21 is obtained by a calculation formula that takes into consideration the light utilization efficiency of the optical system as shown in FIG. And The arrangement of the optical system components shown in FIG. 11 is for explaining an example of light amount calculation, and is different from the configuration shown in FIG.

In the configuration of FIG. 11, the laser beam emitted from the LD 121 is
Collimating lens → ・ ・ ・ → Second mirror → Third mirror → Dust-proof glass → Path to reach the photosensitive drum 21,
Collimating lens → ・ ・ ・ → Second mirror → Synchronous mirror → Cylindrical lens (CY lens) → Path to reach synchronous detector (synchronous detection sensor) 123 and after the second mirror The transmittance of the lens and the reflectance of the mirror in the part. Third mirror ... R3m
Dust-proof glass ... Rg
Synchronous mirror ... Rdm
CY lens ... Rcy
Assuming that the amount of light on the light irradiation surface of the photosensitive drum 21 is Popc, the amount of light Pa at point A (after the second folding mirror) is
Pa = Popc / Rg / R3m
Similarly, the light amount Pdet up to the point B (before the CY lens) with respect to the light amount on the light irradiation surface of the synchronization detection unit 123 is
Pdet = Popc × Rdm × Rcy
It is represented by

In this way, if the amount of light on the light irradiation surface of the photosensitive drum 21 is known, the required amount of light can be obtained from any component by calculating the light transmittance and light reflectance of each component constituting the optical system. The position can be calculated.
Based on this principle, in the first embodiment, the light amount on the light irradiation surface of the synchronization detection unit 123 and the light amount on the light irradiation surface of the photosensitive drum 21 are respectively calculated in advance, and these are originally used for the optical system. In consideration of the shading characteristics (about 0.9 to 1.0) possessed by, the amount of light at an arbitrary position is uniquely determined.

The light transmittance and light reflectance of each of the above-mentioned components are generally in the range of about 0.8 to 1.0, and further, typ., Min., Max due to external factors such as temperature conditions. Each light quantity shall be set by calculation considering the value.
As described above, the light quantity of the LD 121 is compared with the laser light incident on the synchronization detection unit 123 by comparing the calculated light quantity with a preset light quantity and feeding back the comparison result, using the above-described shading correction function. The variable control is the control related to the present invention.

With this configuration, the calculation on the light detection surface of the synchronization detection unit 123 can be performed even when the light amount on the light detection surface of the synchronization detection unit 123 is caused by contamination due to environmental changes over time on the reflection surface of the polygon mirror 122a. Since the light quantity of the LD 121 is corrected based on the comparison result between the light quantity and the preset light quantity, it is possible to always provide a stable light quantity.
As a result, even if the reflection surface of the polygon mirror 122a becomes dirty over time, the amount of light of the LD 121 is controlled so that the synchronization detection position is always constant. Therefore, it is possible to continue providing a stable image.

In the first embodiment, the shading correction function is provided in the LD driving unit 115 in FIG. 2, but there is no limitation on the function as long as the function is arranged in the image writing control unit 103.
Further, although the photosensor constituting the synchronization detection unit 123 has been described using the 1PD type (FIG. 10), even if the existing 2PD type is used, the first means for calculating the feedback light amount is the first. The present invention can be applied in the same manner as the embodiment.

[Second Embodiment]
Next explained is the second embodiment of the invention. Note that only a slight difference from the first embodiment will be described.
In the second embodiment, the amount of light on the light detection surface of the synchronization detection unit 123 is calculated by feeding back the laser light emitted from the LD 121 in FIG. 2, and the light amount and the light amount on the light irradiation surface of the photosensitive drum 21 set in advance are calculated. So that the light quantity of the LD 121 is variably controlled.

  That is, in the first embodiment, as described with reference to FIG. 11, with respect to the light amount on the light detection surface of the synchronization detection unit 123 and the light amount on the light irradiation surface of the photosensitive drum 21, the reflectance of mirrors and lenses in each optical path. , The amount of light taking into account the transmittance can be calculated, and using these values, the amount of light on the light irradiation surface of the photosensitive drum 21 is obtained and temporarily stored in a register or the like provided in the LD light amount controller 304. Then, the LD light amount control unit 304 variably controls the light amount of the LD 121 so that the light amount obtained from the lookup table matches the light amount as in the first embodiment.

  By doing so, the light amount at an arbitrary image height is feedback-controlled based on the synchronization detection signal from the synchronization detection unit 123 regardless of the presence or absence of dirt on the reflection surface of the polygon mirror 122a. The light quantity on the light detection surface of the synchronization detection unit 123 and the light quantity on the light irradiation surface of the photosensitive drum 21 can be made constant.

[Third embodiment]
Next explained is the third embodiment of the invention. Note that only a slight difference from the first embodiment or the second embodiment will be described.
In the third embodiment, the light amount setting timing on the light detection surface of the synchronization detection unit 123 is based on the writing end timing of the electrostatic image of the final color (Y) on the photosensitive drum 21Y (sub-scanning on the photosensitive drum 21Y). Control from the end of the image area. In other words, the LD light amount control unit 304 in FIG. 5 determines the end of the sub-scanning image area of the final color of the image to be printed as the light amount on the light detection surface of the synchronization detection unit 123 calculated in the same manner as in the first embodiment. The negated edge of the sub-scanning gate signal (which may be another signal) is detected and reflected at that timing.

  In consideration of printing a full-color image, etc., the end of image printing for one page is detected and reliably reflected from the image data of the next page so as not to increase or decrease the corresponding LD light quantity in the middle of the color. This is to aim to be done. By performing such control, the amount of light of the LD 121 is reliably changed for each color, so that the occurrence of variations in the amount of light for each color can be suppressed and the influence on the image can be minimized. Become.

FIG. 12 is a timing chart showing an example of the control timing.
In FIG. 12, the final color state flag is given from the writing position control unit 114 in FIG. 2 to the LD light amount control unit 304 in FIG. 5, and the LD light amount control unit 304 negates the final color state flag and the sub-scanning gate signal. An example of timing when the light amount is changed from P0 to P1 calculated after feedback is shown.

[Fourth embodiment]
Next explained is the fourth embodiment of the invention. Note that only a slight difference from any of the first to third embodiments will be described.
In the fourth embodiment, the image data identification unit 303 in FIG. 5 receives the mono color mode / full color mode status flag from the engine control unit 101 in FIG. Whether the image data is for color mode or full color mode is identified.

  The LD light amount control unit 304 selects execution / stop of variable control of the light amount of the LD 121 according to the identification result according to the type of image data from the host device (external). That is, the difference between the calculated light amount on the light detection surface of the synchronization detection unit 123 and a preset light amount and the type of image data are used as parameters, and the combination is used to variably control the light amount of the LD 121 to continue printing. Or whether to continue printing with the current value.

  For example, the difference between the calculated light amount on the light detection surface of the synchronization detection unit 123 and a preset light amount is within a certain value range, and the image data to be printed is centered on characters and is monochromatic (single color). In mode printing, it can be determined that the effect of color misregistration and the like is low and the effect on image quality is small, so printing is continued with the light amount of the LD 121 remaining at the current value. On the other hand, even if the light intensity difference is within the same range, if the image data to be printed is full-color photographic data including a person or a fine object, the color misregistration in the main scanning direction is greatly reduced in image quality. Influence. In such a case, that is, in the case of full-color mode printing, the light amount of the LD 121 is variably controlled so that the light amount on the light detection surface of the synchronization detection unit 123 matches, for example, the light amount on the light irradiation surface of the photosensitive drum 21. To do.

These execution timings may be controlled starting from the end of the sub-scanning image area of the final color as shown in the third embodiment.
By doing in this way, in order to perform light quantity control corresponding to the target image, even for image quality deterioration due to light quantity reduction on the light detection surface of the synchronization detection unit 123 due to dirt generated on the reflection surface of the polygon mirror 122a. Thus, the variable control of the light quantity of the LD 121 can be performed under optimum conditions.

[Fifth embodiment]
Next explained is the fifth embodiment of the invention. In addition to the controls of the first to fourth embodiments, the following control is performed.
The LD light amount control unit 304 counts the pulse width when the synchronization detection signal DETP_N output from the synchronization detection unit 123 compared by the light amount comparison unit 302 is initially set (calculated light amount on the light detection surface of the synchronization detection unit 123). Polygon mirror and other optical systems constituting the optical system when the difference between the count value of the pulse width and the subsequent pulse width count value (calculated light amount on the light detection surface of the synchronization detection unit 123) exceeds a predetermined value (when it is significantly different) It is determined that some serious abnormality such as dirt has occurred in the component, and a warning signal indicating the abnormality content is output to the engine control unit 101.

When the engine control unit 101 (main control unit 8) receives the warning signal, the engine control unit 101 (main control unit 8) outputs the warning signal to an external operation unit (key operation unit 7), and displays the abnormality content on the display. Therefore, the user who sees the display can stop the subsequent operation in the color image forming apparatus.
Alternatively, the engine control unit 101 automatically stops the subsequent operation when receiving the warning signal.
Therefore, it is not necessary to print an abnormal image.

As described above, the embodiment in which the present invention is applied to a color image forming apparatus using a photosensitive drum and an intermediate transfer belt as a combination of image bearing members for image formation has been described. However, the present invention is not limited to this. The present invention can also be applied to color image forming apparatuses using other image carrier combinations such as a combination of a photosensitive belt and an intermediate transfer drum, or a combination of a photosensitive drum and a transfer conveyance belt.
That is, an example in which the present invention is applied to a tandem type color image forming apparatus in which a plurality of photosensitive drums are arranged side by side on an intermediate transfer belt has been described. However, a color image forming apparatus to which the present invention can be applied has this configuration. It is not limited to.

In the above-described embodiment, the present invention is applied to an indirect transfer type color image forming apparatus that transfers toner images of four colors onto an intermediate transfer belt, superimposes the four colors, and transfers them onto a transfer sheet at once. Although applied, the present invention can also be applied to a direct transfer type color image forming apparatus that transports transfer paper by a transfer transport belt and sequentially transfers four color toner images from the photosensitive drum onto the transfer paper. .
Further, in the above-described embodiment, laser light is used as the exposure light source, but the present invention is not limited to this.

  As is apparent from the above description, according to the present invention, it is possible to stabilize the image quality regardless of the change in the light amount to the synchronization detecting means. Therefore, by using the present invention, it is possible to provide an optical scanning device capable of acquiring a high-quality image and a color image forming device capable of forming a color composite image without color misregistration.

1 is a block diagram illustrating a configuration example of a control system of a color image forming apparatus according to a first embodiment of the present invention. FIG. FIG. 2 is a diagram illustrating a configuration example of a printer engine in the color image forming apparatus illustrated in FIG. 1. FIG. 3 is a block diagram illustrating a basic configuration example of an LD driving unit 115 in FIG. 2. FIG. 3 is a timing diagram for explaining a shading correction function provided in the LD driving unit 115 of FIG. 2.

FIG. 3 is a diagram illustrating a configuration example of a main part of the LD driving unit 115 of FIG. 2 according to the present invention and an optical system of a laser writing device 104; FIG. 6 is a diagram for explaining the relationship between the scanning position of the laser beam on the reflection surface and the contamination when the reflection surface of the polygon mirror 122a of FIG. 5 is normal and when the contamination is attached.

FIG. 6 is a diagram for explaining a difference in pulse width of a synchronization detection signal output from the synchronization detection unit 123 when the reflection surface of the polygon mirror 122a of FIG. 5 is normal and when dirt is attached. FIG. 6 is a timing diagram for explaining the counting of the pulse width of the synchronization detection signal DETP_N by the synchronization detection light quantity calculation unit 301 of FIG. 5.

6 is a diagram showing the relationship between the pulse width count value of the synchronization detection signal DETP_N by the synchronization detection light amount calculation unit 301 of FIG. 5 and the light amount on the light detection surface of the synchronization detection unit 123. FIG. FIG. 6 is a circuit diagram illustrating a configuration example of a synchronization detection unit (synchronization detection sensor) 123 in FIG. 5. It is a figure for demonstrating the relationship between arrangement | positioning of the components which comprise the optical system of a laser writing apparatus, and a light quantity. FIG. 6 is a timing chart showing an example of control timing of the LD light amount control unit 304 in FIG. 5.

Explanation of symbols

1: FAX I / F 2: FAX control unit 3: Host I / F 4: Printer control unit 5: Document reading unit 6: Input image processing unit 7: Key operation unit 8: Main control unit 9: Memory unit 10: Write Control unit 21 (21B, 21M, 21C, 21Y): photosensitive drum 22 (22B, 22M, 22C, 22Y): primary transfer roller 23: intermediate transfer belt 24: mark sensor 101: engine control unit 102: application control unit 103: Image writing control unit 104: Laser writing device 111: Pixel clock generation unit 112: Multiplication circuit 113: Image signal generation unit 114: Writing position control unit 115: LD driving unit 121: LD 122: Polygon motor driving unit 122a: Polygon mirror 123: Synchronization detection unit 124: fθ lens 201: Comparator 202: Reference bias unit 203: S & H times Path 204: Current source 205: Current switching circuit 301: Synchronization detection light quantity calculation unit 302: Light quantity comparison unit 303: Image data identification unit 304: LD light quantity control unit

Claims (6)

An optical scanning device that writes an electrostatic image with light on an image carrier that rotates in a sub-scanning direction orthogonal to the main scanning direction by repeatedly scanning light emitted from a light emitting element in the main scanning direction. There,
A light emitting element driving means for emitting light corresponding to the light emitting element by modulating and driving the light emitting element according to image data;
Synchronization detecting means for detecting light in the main scanning direction with respect to the image carrier and generating and outputting a synchronization detection signal for defining an image writing start position by the light in the main scanning direction;
Synchronization detection surface light amount setting means for setting the light amount on the light detection surface of the synchronization detection means;
A synchronization detection surface light amount calculating means for calculating a light amount on a light detection surface of the synchronization detection means when light is emitted from the light emitting element by the light emitting element driving means;
A light amount comparison unit that compares the light amount calculated by the synchronization detection surface light amount calculation unit with the light amount set by the synchronization detection surface light amount setting unit;
An optical scanning apparatus comprising: a light amount variable control unit that variably controls the light amount of the light emitting element based on a comparison result by the light amount comparison unit. The optical scanning device according to claim 1,
An image carrier surface light amount setting means for setting the light amount on the light irradiation surface of the image carrier is provided,
The light quantity variable control means is a means for variably controlling the light quantity of the light emitting element so that the light quantity calculated by the synchronization detection surface light quantity calculating means matches the light quantity set by the image carrier surface light quantity setting means. There is provided an optical scanning device. The optical scanning device according to claim 1 or 2,
The light amount variable control means selects execution / stop of variable control of the light amount of the light emitting element according to the type of image data from the outside. An optical scanning device that writes an electrostatic image with light on an image carrier that rotates in a sub-scanning direction orthogonal to the main scanning direction by repeatedly scanning light emitted from a light emitting element in the main scanning direction. There,
A light emitting element driving means for emitting light corresponding to the light emitting element by modulating and driving the light emitting element according to image data;
Synchronization detecting means for detecting light in the main scanning direction with respect to the image carrier and generating and outputting a synchronization detection signal for defining an image writing start position by the light in the main scanning direction;
Synchronization detection surface light amount setting means for setting the light amount on the light detection surface of the synchronization detection means;
A synchronization detection surface light amount calculating means for calculating a light amount on a light detection surface of the synchronization detection means when light is emitted from the light emitting element by the light emitting element driving means;
A light amount comparison unit that compares the light amount calculated by the synchronization detection surface light amount calculation unit with the light amount set by the synchronization detection surface light amount setting unit;
An optical scanning device comprising a warning stage for outputting a warning signal to the outside when a difference between both light amounts by the light amount comparing means exceeds a predetermined value.   5. The optical scanning device according to claim 1, and the electrostatic images sequentially written on the image carrier by the optical scanning device are sequentially developed with different color toners to form toner images. A color image forming apparatus comprising: a developing device that forms the toner image; and a toner image that is sequentially formed on the image carrier by the developing device is sequentially superimposed and transferred onto another image carrier to form a composite color image. . The optical scanning device according to any one of claims 1 to 3 and electrostatic images sequentially written on the image carrier by the optical scanning device are sequentially developed with different color toners to form toner images. A color image forming apparatus comprising: a developing device that forms the toner image; and a toner image that is sequentially formed on the image carrier by the developing device is sequentially superimposed and transferred onto another image carrier to form a composite color image. In
The synchronization detection surface light amount setting unit of the optical scanning device is a unit that variably controls the light amount of the light emitting element with reference to the end timing of writing of the electrostatic image of the final color on the image carrier. A color image forming apparatus.

Images