JP5364693B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately recognize density of an evaluation pattern, thereby accurately adjusting writing timing of each of light emitting parts. <P>SOLUTION: An exposure controller makes an image forming part draw the evaluation patterns which are different in writing timing. At such a time, the exposure controller controls the image forming part so that light quantity can be larger compared to a case when forming a normal image. A controller makes a density sensor measure the density of the evaluation pattern, and calculates the density of the evaluation pattern on the basis of the result of measurement. Next, a writing timing determination part extracts the evaluation pattern whose density is the lowest or the evaluation pattern whose density is the highest in the densities of the respective evaluation patterns, and determines the writing timing obtained when drawing such an evaluation pattern as the writing timing of respective laser diodes. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus that accurately adjusts the writing timing of each light beam in a multi-beam image forming apparatus.

  2. Description of the Related Art Conventionally, in response to demands for high-speed image output, many multi-beam image forming apparatuses that simultaneously scan light beams from a multi-beam laser including a plurality of light emitting units on a photosensitive drum have been developed. In such an image forming apparatus, it is necessary to control the writing timing of each light beam so that the writing position in the main scanning direction on the photosensitive drum is exactly matched. Therefore, as described in Patent Document 1, a method is known in which an evaluation pattern is output from an apparatus, and a writing position is matched by detecting a phase shift in the main scanning direction based on the density of the evaluation pattern.

JP 2002-137447 A

  However, in the method of Patent Document 1, when density unevenness or density variation occurs due to development characteristics or jitter caused by a transfer system such as a transfer belt, the density of the evaluation pattern cannot be detected accurately, and each light is accurately detected. There was a possibility that the beam writing timing could not be matched.

  The present invention has been made to solve the above problem, and provides an image forming apparatus capable of accurately adjusting the writing timing in the main scanning direction by accurately grasping the density of the evaluation pattern. It is intended.

According to the first aspect of the present invention, there is provided an image forming apparatus that emits light corresponding to image data from a multi-beam laser having a plurality of light emitting units arranged in a line at a predetermined interval with a predetermined angle with respect to a main scanning direction. An image forming unit that emits an electrostatic latent image on the photosensitive member and visualizes the electrostatic latent image formed on the photosensitive member with toner to form a toner image; and detects the density of the toner image Between the detection means and the dots formed by irradiating light by repeatedly turning on and off a plurality of dots from each light emitting unit with an exposure light amount larger than the exposure light amount of the light emitting unit when forming a normal image. an evaluation pattern, the patterning system that performs control to form a plurality of the evaluation pattern was varied said predetermined write start timing of each light-emitting portion with respect to said image forming means And a writing timing adopted when the density of each evaluation pattern is detected by the detection means and the evaluation pattern with the lowest density or the evaluation pattern with the highest density is formed among the detected densities. Determining means for determining.

  According to the present invention, the amount of coupling between dots constituting the evaluation pattern increases, and the density of the evaluation pattern becomes clear. Accordingly, the difference in the detected density between the evaluation patterns by the detection means is also increased, so that the accuracy in discriminating the evaluation pattern with the lowest density or the evaluation pattern with the highest density is improved. Thereby, the determination means can accurately adjust the writing start timing of the light emitting unit.

  In the present invention, the amount of coupling between dots constituting the evaluation pattern increases, and the density of the evaluation pattern becomes clear. Accordingly, the difference in the detected density between the evaluation patterns by the detection means is also increased, so that the accuracy in discriminating the evaluation pattern with the lowest density or the evaluation pattern with the highest density is improved. Thereby, the determination means can accurately adjust the writing start timing of the light emitting unit.

1 is a schematic diagram of an internal structure of an image forming apparatus. 1 is a block diagram illustrating an electrical configuration of an image forming apparatus. The schematic diagram which shows the state which irradiated the light beam to the light deflection surface of the polygon mirror. The block diagram which shows the irradiation control system of a light beam. FIG. The figure which showed an example of the evaluation chart. The schematic diagram which expanded and showed the dot of the evaluation chart. The graph which compared the average density of the evaluation pattern. The figure which represented typically the dot formed when the light quantity of a light source is small. The figure which represented the dot to which this invention was applied typically. The flowchart which showed the flow of the adjustment process of the write-out timing of a laser diode.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an outline of the internal structure of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 can be applied to, for example, a digital multifunction machine having a copy, printer, and facsimile function. The image forming apparatus 1 is a tandem system, and includes an apparatus main body 100 and an image reading unit 200 disposed on the apparatus main body 100.

  The image reading unit 200 reads an image (character, figure, photograph, etc.) with a CCD (Charge Coupled Device) or the like and outputs it as image data. The image reading unit 200 has a function of reading a color image. As a result, copying and facsimile transmission can be performed.

  The apparatus main body 100 includes a sheet storage unit 110, an image forming unit 130, and a fixing unit 160.

  The paper storage unit 110 is disposed at the lowermost part of the apparatus main body 100 and includes a paper tray 111 that can store a bundle of paper P. The paper tray 111 is inserted into the apparatus main body 100 and attached. When the paper P is replenished, the paper tray 111 is pulled out from the apparatus main body 100. In the bundle of sheets P stored in the sheet tray 111, the uppermost sheet P is fed out toward the sheet conveyance path 115 by driving the pickup roller 113. The paper P is transported to the image forming unit 130 through the paper transport path 115.

  The image forming unit 130 forms a toner image on the conveyed paper P. The image forming unit 130 includes a magenta unit 133M, a cyan unit 133C, a yellow unit 133Y, and a black unit 133K, which are arranged in the order in which the toner images are transferred to the transfer belt 131. These units have the same configuration, and a magenta unit 133M will be described as an example.

  The magenta unit 133M includes a photosensitive drum 135 and an exposure device 137. Around the photosensitive drum 135, a charger 139, a developing device 141, and a cleaner 143 are arranged. The charger 139 uniformly charges the peripheral surface of the photosensitive drum 135. The exposure device 137 generates light corresponding to magenta data among image data (image data output from the image reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.), and uniformly. Irradiate the circumferential surface of the charged photosensitive drum 135. As a result, an electrostatic latent image having a magenta pattern is formed on the peripheral surface of the photosensitive drum 135. In this state, by supplying magenta toner from the developing device 141 to the peripheral surface of the photosensitive drum 135, a toner image having a magenta pattern is formed on the peripheral surface.

  The transfer belt 131 can move clockwise while being sandwiched between the photosensitive drum 135 and the primary transfer roller 145. A toner image having a magenta pattern is transferred from the photosensitive drum 135 to the transfer belt 131. The magenta toner remaining on the peripheral surface of the photosensitive drum 135 is removed by the cleaner 143. The above is the description of the magenta unit 133M.

  Above the magenta unit 133M, the cyan unit 133C, the yellow unit 133Y, and the black unit 133K, containers that accommodate corresponding color toners, that is, a magenta toner container 147M, a cyan toner container 147C, and a yellow toner. A container for toner 147Y and a container for black toner 147K are arranged. Each color developing device 141 is supplied with toner from a corresponding container.

  As described above, a magenta pattern toner image is transferred to the transfer belt 131, and a cyan pattern toner image is transferred onto the toner image. Similarly, a yellow pattern toner image and a black pattern toner are transferred. The image is transferred in layers. As a result, a color toner image is formed on the transfer belt 131. In this way, a color toner image is formed on the transfer belt 131 by transferring the toner image of each color pattern superimposed on the transfer belt 131. The color toner image is transferred by the secondary transfer roller 149 onto the paper P conveyed from the paper storage unit 110 described above.

  The sheet P on which the color toner image is transferred is sent to the fixing unit 160. The fixing unit 160 has a structure in which a fixing belt 165 is hung on a heating roller 161 and a fixing roller 163. The fixing belt 165 is sandwiched between the fixing roller 163 and the pressure roller 167. The paper P onto which the color toner image is transferred is sandwiched between these rollers. Thus, heat and pressure are applied to the color toner image and the paper P, and the color toner image is fixed to the paper P. The paper P is discharged to a paper discharge tray 169.

  The image forming unit 130 includes a density sensor 148. The density sensor 148 detects the optical density of the toner image transferred onto the transfer belt 131. The density sensor 148 is, for example, a specular reflection type sensor that detects reflected light, and includes an LED light source disposed at a predetermined angle with respect to a detection position on the surface of the transfer belt 131, a phototransistor as a light receiving element, and the like. Is done. The toner image on the transfer belt 131 is irradiated with light from an LED light source, and the phototransistor detects the amount of reflected light, thereby measuring the optical density (hereinafter simply referred to as “density”) of the toner image. To do. The density sensor 148 converts the measurement result into an electric signal and outputs it to the control unit 300 described later. The density sensor 148 may be any sensor that can detect density information of a toner image. For example, the density sensor 148 may be a sensor that can detect density from an image acquired by capturing a toner image.

  FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus 1 shown in FIG. The image forming apparatus 1 has a configuration in which an apparatus main body 100, an image reading unit 200, a control unit 300, an operation display unit 400, and a communication unit 500 are connected to each other by a bus. The apparatus main body 100 and the image reading unit 200 have been described with reference to FIG.

  The control unit 300 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an image memory, and the like. The CPU executes control necessary for operating the image forming apparatus 1 on the hardware constituting the image forming apparatus 1. The ROM stores software necessary for controlling the operation of the image forming apparatus 1. The RAM is used for temporary storage of data generated during execution of software, storage of application software, and the like. The image memory temporarily stores image data (image data output from the image reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.).

  The control unit 300 includes a storage unit 301, an exposure control unit 303, and a writing timing determination unit 307. The storage unit 301 stores image data of each color used for drawing an electrostatic latent image. In the present embodiment, magenta, cyan, yellow and black image data are stored.

  The exposure control unit 303 is provided corresponding to each color, and generates a light beam modulated by image data stored in the storage unit 301 in a light beam generation unit to be described later while rotating the polygon mirror by a motor. And reflect with a polygon mirror. That is, control is performed to draw an electrostatic latent image on the photosensitive drum 135 using the light beam modulated by the image data. The writing timing determination unit 307 determines the optimal writing timing of each light emitting unit included in the light source 21 based on the measurement result of the density sensor 148. A method for determining the writing timing will be described in detail later.

  The operation display unit 400 is provided with operation keys including hard keys. Specifically, a function key for switching between a start key, a numeric keypad, a stop key, a reset key, a copy, a printer, a scanner, and a facsimile are provided. The operation display unit 400 is provided with a touch panel. On the screen of the touch panel, various operations and details of operations are displayed and operation keys including soft keys are displayed.

  The communication unit 500 includes a facsimile communication unit 501 and a network I / F unit 503. The facsimile communication unit 501 includes an NCU (Network Control Unit) that controls connection of a telephone line with a destination facsimile and a modulation / demodulation circuit that modulates / demodulates a signal for facsimile communication. The facsimile communication unit 501 is connected to the telephone line 505.

  A network I / F unit 503 is connected to a LAN (Local Area Network) 507. A network I / F unit 503 is a communication interface circuit for executing communication with a terminal device such as a personal computer connected to the LAN 507.

  Next, a light beam irradiation control system that executes drawing of an electrostatic latent image will be described with reference to FIGS. FIG. 3 is a schematic diagram showing a state in which the light deflection surface 13 of the polygon mirror 11 is irradiated with the light beam LB in the present embodiment. FIG. 4 is a block diagram showing a light beam irradiation control system according to this embodiment. FIG. 5 is an external view of the light source 21.

  The irradiation control system shown in FIG. 4 is provided corresponding to each color constituting the color image. In the present embodiment, irradiation control systems are provided for magenta, cyan, yellow, and black. The optical components such as the collimator lens and the fθ lens are not shown. The irradiation control system includes a polygon mirror 11, a light beam generation unit 17, a timing signal generation unit 19, an exposure control unit 303, and the like.

  The light beam generation unit 17 includes a light source 21 that generates the light beam LB and emits the light beam LB, a drive circuit that drives the light source 21, and the like. As the light source 21, for example, a semiconductor laser is used. As shown in FIG. 5, the light source 21 is formed by unitizing a plurality of laser diodes LD <b> 1 and LD <b> 2 arranged in a line at a constant interval on the tip surface Y, and a normal passing through the center among the normals to the tip surface Y. It is configured to be rotatable in the direction of arrow X with G as the rotation axis. In this embodiment, a monolithic multi-laser diode provided with two laser diodes will be described as an example. However, any laser diode in which two or more laser diodes are arranged on the same chip may be used.

  When the light beams emitted from the laser diodes LD1 and LD2 irradiate the peripheral surface of the photosensitive drum 135, the arrangement direction of the irradiation positions (imaging positions) is the main scanning line that connects the laser diodes LD1 and LD2. By arranging so as to have a predetermined inclination angle with respect to the direction, a drawing operation on a plurality of drawing lines can be performed by one scan. Furthermore, the resolution in the sub-scanning direction can be adjusted by adjusting the tilt angle. Usually, the pitch in the sub-scanning direction is determined according to the specifications of the apparatus, and the pitch in the main scanning direction is determined by this determination.

  The polygon mirror 11 reflects the light beam LB generated by the light beam generator 17. The polygon mirror 11 is rotated by the motor 23 about the rotation shaft 25 in the rotation direction R1. The polygon mirror 11 has a regular hexagonal side surface. This side surface is composed of six light deflection surfaces 13.

  The exposure control unit 303 controls to draw an electrostatic latent image on the photosensitive drum 135 by irradiating the light beam LB. That is, the exposure control unit 303 sends the corresponding color image data stored in the storage unit 301 to the light beam generation unit 17 while rotating the polygon mirror 11 by the motor 23, and sends the image data to the light beam generation unit 17. To generate a light beam LB modulated by. The generated light beam, that is, the light beam LB emitted from the light source 21 is applied to the rotating polygon mirror 11, deflected by the light deflection surface 13 (reflected by the polygon mirror 11), and then on the photosensitive drum 135. The scanning line SL is drawn in the main scanning direction D1. One scanning line SL is drawn by one light deflection surface 13. By repeating the drawing of one scanning line SL on the photosensitive drum 135 thus rotated, an electrostatic latent image is drawn along the sub-scanning direction. The sub-scanning direction corresponds to the rotation direction R2 of the photosensitive drum 135.

  The timing signal generator 19 is provided for each color, and generates a timing signal BD called a BD (Beam Detect) signal. The timing signal BD is a reference signal for aligning the writing position in the main scanning direction D1 when an electrostatic latent image is drawn on the photosensitive drum 135. After the timing signal BD is output from the timing signal generator 19 and a predetermined period has elapsed, drawing of an electrostatic latent image on the photosensitive drum 135 is started by the light beam LB modulated by the image data.

  The configuration of the timing signal generator 19 will be described. The timing signal generation unit 19 includes a BD sensor 27 and a BD signal conversion unit 29. The light beam LB is repeatedly scanned in the main scanning direction D1 within a scanning range longer than the dimension of the photosensitive drum 135 in the main scanning direction D1. The BD sensor 27 is installed in a position where the light beam LB is received before the light beam LB starts scanning the photosensitive drum 135 in the scanning range.

  The BD sensor 27 is a photo sensor. When receiving the light beam LB generated by the light beam generation unit 17 and reflected by the light deflection surface 13 of the rotating polygon mirror 11, the BD sensor 27 outputs the received light signal to the BD signal conversion unit 29. The BD signal conversion unit 29 shapes the received light signal into a rectangular wave timing signal BD, and outputs the timing signal BD to the exposure control unit 303.

  In the case of the light source 21 using such a multi-laser diode, each laser diode is arranged obliquely with respect to the main scanning direction and the sub-scanning direction. The writing position in the main scanning direction on the body drum 135 is shifted. If the writing position is deviated, a positional shift occurs in each line in the main scanning direction, resulting in image quality deterioration. Therefore, it is necessary to control the emission timing (writing timing) of the emitted light beam so that the writing position in the main scanning direction can be accurately matched.

  As a method for adjusting the writing timing, a method using an evaluation chart is known. FIG. 6 is a diagram showing an example of an evaluation chart. Hereinafter, each pattern is referred to as an “evaluation pattern”, and the evaluation patterns PT1 to PT10 are collectively referred to as an “evaluation chart”. Further, among the evaluation patterns PT1 to PT10, when a specific pattern is not pointed out, it is simply referred to as “evaluation pattern PT”.

  The evaluation pattern will be described with reference to FIGS. Each evaluation pattern PT is common in that it is a pattern drawn by emitting an optical laser by repeating 2 dots on and 2 dots off from the laser diodes LD1 and LD2, and the difference is in the writing timing of the laser diode LD1. On the other hand, the writing timing of the laser diode LD2 is changed within a predetermined range. For this reason, they have different patterns.

  More specifically, first, an ideal writing start timing calculated from the beam pitches of the laser diodes LD1 and LD2 in the main scanning direction (a time difference between the writing timing of the laser diode LD2 and the writing timing of the laser diode LD1) is calculated. Then, with respect to the calculated ideal writing timing, the writing timing of the laser diode LD2 is changed in units of 0.1 [us], for example. In other words, if the ideal writing timing is 3.0 [us], 2.8, 2.9, 3.0, 3.1, 3.2, 3.3 [ us], and the writing timing of the laser diode LD2 is changed (changed) to draw the evaluation pattern.

  If the writing timings of the laser diodes LD1 and LD2 match, the dot rows of the lines corresponding to the laser diodes LD1 and LD2 match as shown in FIG. 7C. However, if the writing timings of the laser diodes LD1 and LD2 do not match, a positional deviation of dots occurs as shown in FIGS. Here, the pattern corresponding to FIG. 7C in which the dot rows match is PT5 in FIG. 6, and the pattern corresponding to FIG. 7A in which the positional deviation of the dots is generated is PT1, FIG. The pattern corresponding to b) corresponds to PT3.

  FIG. 8 is a graph comparing the densities of the respective evaluation patterns PT, where the vertical axis indicates the density and the horizontal axis indicates the pattern number. From FIG. 8, it can be seen that the evaluation patterns PT1 and PT10 having the largest dot positional deviation have the highest density, and the density decreases as the dot positional deviation decreases. This is because, as shown in FIG. 7C, when the dot rows match, a white line appears remarkably, so that the average density of the pattern is reduced accordingly. If this characteristic is used, it can be said that the writing timing of the laser diodes LD1 and LD2 when the pattern with the lowest density is drawn is the timing with the smallest dot misalignment.

  However, even when the writing timing is adjusted using the evaluation chart as shown in FIG. 6, the density unevenness or density variation in the evaluation chart is caused by the density unevenness or density variation caused by the development characteristics or jitter caused by the transfer system such as the transfer belt. Concentration variation may occur. Thus, if there is density unevenness or variation in the evaluation chart, an error occurs in the measured density of each evaluation pattern PT, and the writing timing of the laser diodes LD1 and LD2 cannot be adjusted with high accuracy simply by comparing the measured density. There was a possibility.

  Therefore, in the present invention, when outputting the evaluation chart, the light intensity of the light source 21 (hereinafter, simply referred to as “light quantity”) is increased to clarify the density of the pattern, and each evaluation pattern PT detected by the density sensor 148 is detected. A method for accurately adjusting the writing timing of the laser diodes LD1 and LD2 by increasing the accuracy of the detection density is proposed.

  FIG. 9 is a diagram schematically illustrating dots formed when the light amount of the light source 21 is small. As shown in this figure, when the light amount is small, the beam diameters of the laser diodes LD1 and LD2 are also small, so that they are isolated from adjacent dots or the coupling amount is small. Therefore, a difference in density is less likely to appear in the evaluation pattern PT, that is, a difference in detected density between the evaluation patterns PT by the density sensor 148 is also reduced. In this case, if the detected density includes an error due to slight density unevenness or variation, the accuracy in determining the evaluation pattern PT having the lowest density is lowered.

  FIG. 10 is a diagram schematically showing dots to which the present invention is applied. The exposure control unit 303 controls the image forming unit 130 so that the amount of light is larger when forming an evaluation chart than when forming a normal image. As shown in FIG. 10, as the amount of light increases, the amount of coupling between dots increases, and the density of the evaluation pattern PT becomes clear. Therefore, the difference in the detected density between the evaluation patterns PT by the density sensor 148 also increases, so that the accuracy in discriminating the evaluation pattern PT with the lowest density is improved.

  FIG. 11 is a flowchart showing a flow of adjustment processing of the writing timing of the laser diodes LD1 and LD2. First, as shown in FIG. 6, the exposure control unit 303 causes the image forming unit 130 to draw evaluation patterns PT1 to PT10 having different writing timings (step S11). At this time, the exposure control unit 303 controls the image forming unit 130 so that the amount of light is larger than when a normal image is formed. Then, the control unit 300 causes the density sensor 148 to measure the density of the evaluation patterns PT1 to PT10, and calculates the density Dpt of the evaluation pattern PT based on the measurement result (steps S13, S14, and S15).

  Next, the write timing determination unit 307 extracts the evaluation pattern PT having the lowest density from the density of each evaluation pattern PT, and sets the write timing when the evaluation pattern PT is drawn as the write timing of the laser diodes LD1 and LD2. (Step S16).

  As described above, the exposure control unit 303 controls the image forming unit 130 so that the amount of light is larger than when a normal image is formed when the evaluation chart is formed. As the amount of light increases, the amount of coupling between dots increases, and the density of the evaluation pattern PT becomes clear. Therefore, the difference in the detected density between the evaluation patterns PT by the density sensor 148 also increases, so that the accuracy in discriminating the evaluation pattern PT with the lowest density is improved. Thereby, the write-out timing of the laser diodes LD1 and LD2 can be accurately adjusted.

  In the present embodiment, the writing timing of the laser diodes LD1 and LD2 is determined using the writing timing when the evaluation pattern PT having the lowest density among the density of each evaluation pattern PT is drawn. . On the contrary, the evaluation pattern PT having the highest density may be extracted, and the writing timing of the laser diodes LD1 and LD2 may be determined using the writing timing when the evaluation pattern PT is drawn.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Polygon mirror 17 Light beam generation part 19 Timing signal generation part 100 Main body 130 Image formation part (image formation means)
131 Transfer Belt 135 Photosensitive Drum 137 Exposure Device 139 Charger 141 Development Device 143 Cleaner 148 Density Sensor (Detection Unit)
200 Image Reading Unit 21 Light Source 27 BD Sensor 29 BD Signal Conversion Unit 300 Control Unit 301 Storage Unit 303 Exposure Control Unit (Pattern Formation Control Unit)
307 Write timing determination unit (determination means)
LD1, LD2 Laser diode (light emitting part)

Claims (1)

A light corresponding to image data is emitted from a multi-beam laser having a plurality of light emitting portions arranged in a line at regular intervals with a predetermined angle with respect to the main scanning direction to form an electrostatic latent image on the photosensitive member. Image forming means for visualizing the electrostatic latent image formed on the photosensitive member with toner to form a toner image;
Detecting means for detecting the density of the toner image;
An evaluation pattern in which dots are combined, formed by repeatedly irradiating light by repeatedly turning on and off a plurality of dots from each light emitting unit with an exposure light amount larger than the exposure light amount of the light emitting unit when forming a normal image A pattern formation control unit that controls the image forming unit to form a plurality of the evaluation patterns in which the writing timing of each light emitting unit is changed within a predetermined range;
Determination that causes the detection means to detect the density of each evaluation pattern, and determines the write-out timing adopted when the evaluation pattern with the lowest density or the evaluation pattern with the highest density is formed among the detected densities Means,
An image forming apparatus.

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