JP5740880B2 - Image forming apparatus and program - Google Patents

Description

  The present invention relates to an image forming apparatus having an optical writing device composed of a plurality of light emitting element array units that perform division exposure in the main scanning direction, and a program for adjusting a joint position of the light emitting element array units.

  In an image forming apparatus such as a wide copying machine or a wide printer using an electrophotographic method, an inexpensive A3 or A4 size light emitting element array unit, for example, a plurality of LED print heads whose light emitting elements are LEDs (light emitting diodes) is provided. An optical writing device that is arranged in the main scanning direction and supports divided writing by using divided exposure is used.

  Here, the positions of the LED print heads adjacent to each other in the main scanning direction are made different in the sub scanning direction, the end portions are overlapped in the main scanning direction, and a predetermined light emitting element at the end portion is connected to perform main scanning of the image. Connected in the direction.

  For example, when the first LED print head and the second LED print head are arranged in this order so as to be adjacent to each other from the start end side in the main scanning direction, and the number of overlapping pixels is 10, for example, the first LED print head The fifth overlap pixel from the start end side in the main scanning direction in the head and the sixth overlap pixel from the start end side in the main scanning direction in the second LED print head are connected as a joint.

  For this reason, if the positional relationship between adjacent LED print heads shifts due to the assembly accuracy or physical variations of the LED print heads, the number of overlapping pixels increases and the joint position becomes the expected position (theoretical position). ) May cause the images to overlap in the main scanning direction or vice versa.

  As a device to deal with this problem, the light emission output of LED print heads arranged in a staggered pattern in the main scanning direction is detected by a light receiving element such as a CCD camera and processed by a computer, thereby shifting the joint position of the LED print head. There is a light emitting element array position detection device that can adjust the joint position by detecting the amount and moving the dot lighting position of one of the adjacent LED print heads by the amount of shift (patent) Reference 1).

  However, in this light emitting element array position detection device, since adjustment is performed by an external device (a jig) different from the optical writing device, there is a shift in the joints due to replacement or aging of some LED print heads after shipment. If it does, it must be adjusted in the market. Therefore, there is a problem that adjustment is difficult and man-hours are required.

  The present invention has been made to solve such a problem, and an object of the present invention is to make the positions of a plurality of light emitting element array units different in the sub-scanning direction and to overlap the ends in the main scanning direction. In an image forming apparatus having an optical writing device with the light emitting element at the end as a joint, the position of the joint can be easily adjusted even in the market after shipment by mounting simple and inexpensive means on the image forming apparatus main body. Is to do.

An image forming apparatus according to the present invention is an optical writing device in which the positions of a plurality of light emitting element array units in the sub-scanning direction are made different, the end portions are overlapped in the main scanning direction, and the light emitting elements at the end portions are connected. In the image forming apparatus, a plurality of test pattern latent images are formed on the photosensitive member by sequentially writing a plurality of test pattern data to at least the light emitting elements at the ends of two light emitting element array units adjacent in the main scanning direction. Print head control means for sequentially forming; and test pattern image forming means for sequentially forming a plurality of test pattern images on the photoreceptor by operating a single developing device to develop the latent images of the plurality of test patterns. A density detecting means for operating the density sensor to detect the density of the plurality of test pattern images; and the plurality of test patterns Storage means for storing the output of each of said density detecting means down image based on the pattern of change of the plurality of outputs stored in said storage means, the number of light-emitting elements are overlapped by the end A plurality of overlapping pixel number determining means for determining, and a joint pixel determining means for determining a pixel of a joint of the two light emitting element array units based on a determination result of the overlapping pixel number determining means, The test pattern data is to alternately turn on and off the light emitting elements of one light emitting element array unit every predetermined number, and alternately turn on and off the light emitting elements of the other light emitting element array unit every predetermined number of times, An image form characterized by sequentially shifting the lighting and extinguishing positions of the light emitting elements of the other light emitting element array unit for each test pattern It is a device.
The program of the present invention is a program for causing a computer to function as each unit of the image forming apparatus of the present invention.

  According to the present invention, an image having an optical writing device in which the positions of a plurality of light emitting element array units in the sub-scanning direction are made different, the ends are overlapped in the main scanning direction, and the light emitting elements at the ends are connected. In the forming apparatus, by installing simple and inexpensive means on the image forming apparatus main body, the joint position can be easily adjusted even in the market after shipment.

1 is a diagram schematically illustrating a main part of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an internal configuration of a control device included in the image forming apparatus according to the embodiment of the present invention. In the image forming apparatus of the embodiment of the present invention, it is a diagram showing the relationship between two print heads adjacent in the main scanning direction, a test pattern formed on a photosensitive drum, and a density sensor. FIG. 5A is a diagram showing a first test pattern image formed on the photosensitive drum when the number of overlapping pixels is 100, and FIG. 5B is a diagram showing an output obtained by detecting the test pattern image with a density sensor. . FIG. 6A is a diagram showing a second test pattern image formed on the photosensitive drum when the number of overlapping pixels is 100, and FIG. 6B is a diagram showing an output obtained by detecting the test pattern image with a density sensor. . FIG. 7A is a diagram showing a third test pattern image formed on the photosensitive drum when the number of overlapping pixels is 100, and FIG. 7B is a diagram showing an output obtained by detecting the test pattern image with a density sensor. . FIG. 8A is a diagram showing an eleventh test pattern image formed on the photosensitive drum when the number of overlapping pixels is 100, and FIG. 8B is a diagram showing an output obtained by detecting the test pattern image with a density sensor. . It is a figure which shows the relationship between the 1st thru | or 11th test pattern image in case an overlap pixel number is 100, and the output detected by the density sensor. FIG. 10A is a diagram showing a first test pattern image formed on the photosensitive drum when the number of overlapping pixels is 99, and FIG. 10B is a diagram showing an output obtained by detecting the test pattern image with a density sensor. . FIG. 11A is a diagram showing a second test pattern image formed on the photosensitive drum when the number of overlapping pixels is 99, and FIG. 11B is a diagram showing an output obtained by detecting the test pattern image with a density sensor. . FIG. 12A is a diagram showing an eleventh test pattern image formed on the photosensitive drum when the number of overlapping pixels is 99, and FIG. 12B is a diagram showing an output obtained by detecting the test pattern image with a density sensor. . It is a figure which shows the relationship between the 1st thru | or 11th test pattern image in case an overlap pixel number is 99, and the output detected with the density sensor. It is a figure which shows the example of the pattern of the output change of a density sensor in case the overlap pixel number of Table 3 is 95 thru | or 105. It is a figure which shows the relationship between the 1st thru | or 11th test pattern image in case the overlap pixel number of Table 3 is 95 thru | or 105, and the output detected by the density sensor. 6 is a flowchart illustrating a procedure for determining the number of overlapping pixels and adjusting a joint position in the image forming apparatus according to the embodiment of the present invention.

FIG. 1 is a diagram schematically showing a main part of an image forming apparatus according to an embodiment of the present invention.
As shown in the figure, the image forming apparatus G includes a photosensitive drum 9 that is a photosensitive member formed in a drum shape, and a rotation driving device (not shown) that rotates the photosensitive drum 9 at a predetermined speed around an axis. It has. In addition, the image forming apparatus G surrounds the photosensitive drum 9 and is sequentially arranged in the rotation direction (sub-scanning direction: see arrow), and the charger 1, the first print head 2, and the second print head 3. , A developing device 4, a density sensor 10 as density detecting means, a transfer charger 5, a separation charger 6, a cleaning unit 7, and a static elimination lamp 8.

  The separation charger 6 separates the transfer paper from the photosensitive drum 9. The cleaning unit 7 cleans transfer residual toner remaining on the surface of the photosensitive drum 9. The neutralization lamp 8 neutralizes and removes the residual potential on the photosensitive drum 9 after cleaning. The density sensor 10 is a sensor for measuring (detecting) the density (toner density) of the image formed on the photosensitive drum 9, for example, a sensor such as a reflective photosensor. In order to determine the number of overlapping pixels of the second print heads 2 and 3, it is used when detecting the density of the test pattern image formed on the photosensitive drum 9.

  Here, the first and second print heads 2 and 3 are spaced apart from each other along the width direction (main scanning direction) of the photosensitive drum 9 and in the rotation direction (sub-scanning direction) of the photosensitive drum 9. Is opened and placed. In addition, the first and second print heads 2 and 3 are arranged in different ranges in the main scanning direction set on the photosensitive drum 9, and the arrangement ranges so that some arrangement ranges overlap. On the boundary side, the respective end portions are arranged so as to overlap in the main scanning direction. As a result, the first and second print heads 2 and 3 overlap each other along the main scanning direction of the photosensitive drum 9 so that the joint (boundary of the arrangement range) overlaps the photosensitive drum 9 in the width direction. It is arranged in the range divided into. The first and second print heads 2 and 3 are arranged over the entire photosensitive range of the photosensitive drum 9 in the main scanning direction, with a part (end) of each of them overlapping in the main scanning direction.

  The first and second print heads 2 and 3 are arrayed (row-shaped) light emitting elements in which a plurality of light emitting elements are arranged one-dimensionally. Here, LED print heads using LEDs as light emitting elements. Consists of. The first and second print heads 2 and 3 irradiate the photosensitive drum 9 with light generated when the respective light emitting elements are turned on to form an electrostatic latent image on the surface of the photosensitive drum 9. At that time, the image forming apparatus G divides the main scanning direction of the photosensitive drum 9 by the first and second print heads 2 and 3 and exposes them, and connects them in the main scanning direction to form one electrostatic charge. After forming the latent image, the electrostatic latent image is developed with the toner of the developing device 4.

  FIG. 2 is a block diagram illustrating a schematic configuration of the image forming apparatus G, and FIG. 3 is a block diagram illustrating an internal configuration of a control device included in the image forming apparatus G. In the drawings, the print head is represented as LPH.

  As shown in FIG. 2, the image forming apparatus G includes a reading unit 100 that is a unit for reading a document, an image processing unit 200 that performs image processing on an image (image information) of the read document, and a copy of the document. Has a writing unit 500 for writing an image to. The image forming apparatus G includes a control device 300 that controls the entire apparatus, and an operation unit 400 that is an operation unit that performs key input and the like to the control device 300. The density sensor 10 described above is connected to the control device 300. Yes.

  As shown in FIG. 3, the control device 300 includes a CPU (Central Processing Unit) 301 for executing various arithmetic processes, and a ROM (Read Only Memory) that stores various setting information, programs, data, and the like used by the CPU 301. ) 302 and a computer having a RAM (Random Access Memory) 303 for temporarily storing data directly accessed by the CPU 301. In the present embodiment, each means of the present invention is realized by causing a computer to execute a program.

  The writing unit 500 (see FIG. 2) converts the image data signal transferred from the image processing unit 200 into 1-pixel unit bits by the print head control circuit 501, and the first and second print heads 2 and 3. It is converted into light (here, infrared light) and output. At this time, the print head control circuit 501 divides the image in a direction corresponding to the width direction of the photosensitive drum 9, and the divided image data is divided into the first print head 2 and the second print head 3. In parallel. The second print head 3 is disposed downstream of the first print head 2 in the rotation direction of the photosensitive drum 9. For this reason, the print head control circuit 501 passes the delay between the second print head 3 and the interval between the first print head 2 and the second print head 3 in the sub-scanning line direction and the photosensitive drum 9. Data is transferred with a delay of a delay time determined by the peripheral speed. As a result, the image written by the second print head 3 on the photosensitive drum 9 is combined with the image written by the first print head 2 into one line.

  Here, in the image forming apparatus G, if the positions of the first and second print heads 2 and 3 are displaced in the main scanning direction due to the assembling accuracy and physical variations, the number of overlapping pixels is increased. As a result of the increase / decrease from the predetermined number, the joint position may deviate from the planned position (theoretical position), so that the images may overlap in the main scanning direction or vice versa.

  If the number of overlapping pixels is known, the joint position can be determined. Therefore, in the present embodiment, as shown in FIG. 4, the overlap portions 21 and 31 at the ends of the first and second print heads 2 and 3 are driven by the test pattern data, so A test pattern image 11 for detecting the number of overlapping pixels is formed, and its density is detected by the density sensor 10 to determine the number N of overlapping pixels. Using the determination result, the first and second test pattern images 11 are detected. The joint position of the print heads 2 and 3 is determined. In this figure, in order to suppress toner consumption, the test pattern image 11 is formed only on the overlapped portion, but a wider range than the overlapped portion, for example, the first and second print heads 2, The test pattern image 11 can also be formed in the entire main scanning direction 3. However, the detection range of the density sensor 10 is only the overlapping portion.

Hereinafter, a method (algorithm) for detecting the number N of overlapping pixels will be described.
First, a detection example when the number of overlap pixels is 100 is shown. Even when the theoretical number of overlapping pixels is 100, if a deviation of about ± 0.2 mm occurs due to an attachment accuracy error or the like, a deviation of about ± 5 pixels (600 dpi conversion) occurs, and the overlap region is approximately It can be estimated that it is between 95 and 105 pixels. Here, it is assumed that the deviation variation range is not more than the above value. In the present embodiment, it is assumed that the positions of the dots of the first and second print heads 2 and 3 are matched by a known dot position misalignment method not described in the present embodiment.

  5 to 9 are diagrams showing different test pattern images formed on the photosensitive drum 9 when the number of overlapping pixels is 100, and outputs obtained by detecting the test pattern images by the density sensor 10. FIG. Hereinafter, it demonstrates in order.

  5A shows a first test pattern image, and FIG. 5B shows an output obtained by detecting the test pattern image with the density sensor 10. In FIG. 5A, 100 pixels (overlap pixels) of the overlap portion 21 of the first print head 2 are numbered “n” to “n-99” in order from the right end, and the second print head 3. 100 pixels (overlapping pixels) in the overlap portion 31 are numbered from “1” to “100” in order from the left end. Then, test pattern data is written into the overlap pixels of the first print head 2 every 10 dots from the nth pixel. That is, 10 dots are alternately turned on and 10 dots are turned off from the right end. Further, test pattern data is written into the overlapping pixels of the second print head 3 every 10 dots from the first pixel. That is, 10 dots are alternately turned on and 10 dots are turned off from the left end. In the figure, black represents a dot that is lit and white represents a dot that is not lit. These are the first test pattern data.

  At this time, a test pattern image (first test pattern) formed by developing the latent image of the test pattern formed on the photosensitive drum 9 by both the first print head 2 and the second print head 3. Image) 11_1 is a black solid image. Further, as shown in FIG. 5B, the output value of the density sensor 10 at that time is a Vmin value. This output value Vmin is stored in the RAM 303 or the like. Note that the amount of reflected light is maximized when the density sensor 10 detects a portion of the photosensitive drum 9 where no toner is attached. At this time, the output value of the density sensor 10 (the drum surface density in FIG. 5B) is the maximum value. Take.

  Next, as shown in FIG. 6A, the second test pattern data is written to the first print head 2 and the second print head 3 to form a second test pattern image 11_2 on the photosensitive drum 9. The second test pattern data is the same as the data written to the first print head 2 with respect to the first test pattern data, and the data to be written to the second print head 3 is one pixel rightward (main scanning end direction). ). The second test pattern image 11_2 is an image having a one-dot width and a portion 11_2a where toner is not applied, and the output value of the density sensor 10 at that time is Va (Va> Vmin) as shown in FIG. 6B. . The density sensor output value Va at this time is stored in the RAM 303 or the like.

  Next, as shown in FIG. 7A, the third test pattern data is written to the first print head 2 and the second print head 3 to form a third test pattern image 11_3 on the photosensitive drum 9. The third test pattern data is obtained by making the data written to the first print head 2 the same as the first test pattern data and shifting the data written to the second print head 3 to the right by two pixels. . The third test pattern image 11_3 is an image having a portion 11_3a having a 2-dot width and no toner, and the output value of the density sensor at that time is Vb (Vb> Va) as shown in FIG. 7B.

  Thereafter, the fourth to eleventh test pattern data are sequentially written on the first print head 2 and the second print head 3 to form fourth to eleventh test pattern images on the photosensitive drum 9. In the fourth to eleventh test pattern data, the data to be written to the first print head 2 is the same as the first test pattern data, and the data to be written to the second print head 3 is 3 pixels to 10 pixels to the right. It has been shifted to. FIG. 8A shows an eleventh test pattern image 11_11. The eleventh test pattern image 11_11 is the thinnest image having a 10-dot width and a portion 11_11a where toner is not applied. As shown in FIG. 8B, the output value of the density sensor 10 at that time is the highest Vmax. Become. Output values when the density sensors 10 detect the fourth to eleventh test pattern images 11_4 to 11_11 are stored in the RAM 303 or the like.

  As described above, the density sensor output when the test pattern data written to the second print head 3 is sequentially changed is as shown in Table 1 below. In this table, “Vmin <Va <Vb <Vc <Vd <Ve <Vf <Vg <Vh <Vi <Vmax”.

  From this table, when the number of overlapping pixels N is 100, the density sensor output when the test pattern data written to the second print head 3 is sequentially shifted to the right by 1 to 10 pixels is shown in FIG. Thus, it can be seen that the value changes from Vmin to Vmax.

  Next, different test pattern images formed on the photosensitive drum 9 when the number of overlapping pixels N is set to 99, and outputs detected by the density sensor 10 will be described.

  In FIG. 10A, 99 pixels (overlap pixels) in the overlap portion 21 of the first print head 2 are numbered “n” to “n−98” in order from the right end, and the second print head 3. 99 pixels (overlap pixels) in the overlap portion 31 are numbered from “1” to “99” in order from the left end. Then, test pattern data is written into the overlap portion 21 of the first print head 2 every 10 dots from the nth pixel. That is, 10 dots are alternately turned on and 10 dots are turned off from the right end. Further, test pattern data is written into the overlap portion 31 of the second print head 3 every 10 dots from the first pixel. That is, 10 dots are alternately turned on and 10 dots are turned off from the left end. In the figure, black represents a dot that is lit and white represents a dot that is not lit. These are the first test pattern data.

  At this time, a test pattern image (first test pattern) formed by developing the latent image of the test pattern formed on the photosensitive drum 9 by both the first print head 2 and the second print head 3. (Image) 12_1 is an image having a portion 12_1a with a dot width of 1 dot, and the output value of the density sensor 10 at that time is Va as shown in FIG. 10B. The density sensor output value Va at this time is stored in the RAM 303 or the like.

  Next, as shown in FIG. 11A, the second test pattern data is written into the first print head 2 and the second print head 3 to form a second test pattern image 12_2 on the photosensitive drum 9. The second test pattern data is obtained by making the data to be written to the first print head 2 the same as the first test pattern data and shifting the data to be written to the second print head 3 to the right by one pixel. . The second test pattern image 12_2 is an image having a 2-dot width and a portion 12_2a where toner is not applied, and the output value of the density sensor at that time is Vb (Vb> Va) as shown in FIG. 11B. The density sensor output value Vb at this time is stored in the RAM 303 or the like.

  Thereafter, the third to eleventh test pattern data are sequentially written on the first print head 2 and the second print head 3 to form third to eleventh test pattern images on the photosensitive drum 9. In the third to eleventh test pattern data, the data to be written to the first print head 2 is the same as the first test pattern data, and the data to be written to the second print head 3 is 2 pixels to 10 pixels to the right. It has been shifted to. FIG. 12A shows an eleventh test pattern image 12_11. In the eleventh test pattern image 12_11, the images formed by the first print head 2 and the second print head 3 overlap each other and have a portion 12_11a with a 9-dot width and no toner, and the density at that time The output value of the sensor is Vi (Vi> Vb). Output values when the third to eleventh test pattern images 11_3 to 11_11 are detected by the density sensor 10 are stored in the RAM 303 or the like.

  As described above, the density sensor output when the test pattern data written to the second print head 3 is sequentially changed is as shown in Table 2 below. In this table, “(Vmin) <Va <Vb <Vc <Vd <Ve <Vf <Vg <Vh <Vi <Vmax”.

  From this table, when the number of overlapping pixels N is 99, the density sensor output when the test pattern data written to the second print head 3 is sequentially shifted to the right by 1 to 10 pixels is shown in FIG. Thus, it can be seen that the voltage decreases to Vi after changing from Va to Vmax.

  Similarly, when the overlap pixel numbers are 90 to 98 and 101 to 110, the first to eleventh test pattern images are formed and the density is detected by the density sensor 10 to obtain the data shown in Table 3 below.

  From Table 3, since the output change of the density sensor 10 varies depending on the number of overlap pixels, the number of overlap pixels can be determined by checking how the output of the density sensor 10 is changing. That is, for example, when the sensor change is Vmin → Vmax, it is determined that the number of overlapping pixels is 100.

  Here, when the number of overlap pixels is 90 or less and 110 or more, the output change of the density sensor 10 overlaps. Therefore, in the case of 10-dot test pattern data, the detection of the overlap region fluctuation amount up to ± 9 dots is performed. Is possible. When the variation in the number of overlap pixels is large or small, the detectable overlap region can be changed by changing the pattern width.

  A part of the output change pattern of the density sensor 10 of Table 3 is shown in FIG. The output change pattern when the number of overlapping pixels is 95 to 105 in order from the left side of the figure is illustrated. FIG. 15 is a graph showing the relationship between the first to eleventh test pattern images and the output detected by the density sensor when the number of overlapping pixels in Table 3 is 95 to 105.

Processing for determining the number of overlapping pixels in the procedure described above and adjusting the joint position using the determination result will be described with reference to the flowchart shown in FIG.
In step S1, the photosensitive drum 9 is rotated, the density of the photosensitive drum 9 is read by the density sensor 10, and Vsg adjustment (calibration) is executed.

In step S2, the pattern number n of the test pattern data output to the first print head 2 and the second print head 3 is initialized (n = 1).
In step S3, the nth test pattern data is written to the first print head 2 and the second print head 3. Since n = 1 here, the first test pattern data, that is, the lighting data of 10 dots wide and 10 dots apart from the right side of the overlap portion 21 is supplied to the first print head 2 to the second print head 3. Writes lighting data of 10 dots wide and 10 dots apart from the left side of the overlap portion 31. Thereby, a latent image of the first test pattern is formed on the photosensitive drum 9. By developing this latent image with the developing device 4, a first test pattern image is formed on the photosensitive drum 9.

  In step S <b> 4, the image density of the nth test pattern is measured by the density sensor 10 and stored in the RAM 303.

  In step S5, it is determined whether or not all predetermined test pattern data (here, first to eleventh test pattern data) has been written in the first print head 2 and the second print head 3.

  If the writing is not completed as a result of the determination (step S5: No), the pattern number n is incremented by 1 (step S8), and the process returns to step S3. On the other hand, when the writing up to the eleventh test pattern data has been completed (step S5: Yes), the process proceeds to step S6.

  In step S6, the density data of each test pattern image stored in the RAM 303 is read out, the data is compared by the CPU 301, and the number of overlap pixels is determined from the result of confirming the data change transition.

  In the last step S7, the joint position is determined based on the number of overlapping pixels determined in step S6. That is, for example, when the number of overlapping pixels is 100, the joint pixel of the first print head 2 is set as the “n-50” pixel, and the joint pixel of the second print head 3 is set as the 51st pixel. And set.

  As described above in detail, according to the image forming apparatus of this embodiment, simple and inexpensive means (such as the density sensor 10 and a program for executing the procedure shown in FIG. 16) are mounted on the apparatus body. The joint position can be easily adjusted even in the market after shipment.

  In the above embodiment, the detection range in the main scanning direction of the density sensor 10 is only the overlap portion, but the overlap portion is wider than the detection range of the density sensor 10 (the detection range of the density sensor 10 overlaps). It is good also as a structure narrower than a part. Thereby, the density of the test pattern image of the overlap portion can be read without being affected by the mounting error of the density sensor 10.

  Further, since the test pattern image formed on the photosensitive drum 9 is thickened by development with toner, the light quantity of the first print head 2 and the second print head 3 is adjusted (suppressed) so that the test pattern image It is preferable to improve the output characteristics of the density sensor 10 by adjusting the line width.

  The above embodiment is directed to an image forming apparatus that divides and exposes the main scanning direction with two print heads. However, the image forming apparatus divides and exposes the main scanning direction with three or more print heads. For the two adjacent print heads, the joint positions of the overlap portions can be adjusted by sequentially or simultaneously executing the procedure shown in FIG.

  In the above embodiment, data to be written to the second print head 3 is sequentially shifted to the right one pixel at a time. Initially, a plurality of pixels are shifted, and after an approximate position is known, one pixel at a time. It may be shifted. Accordingly, for example, since the amount of deviation is large, if the amount of wasted toner is increased by shifting pixel by pixel, the amount of wasted toner can be reduced.

  DESCRIPTION OF SYMBOLS 2 ... 1st print head, 3 ... 2nd print head, 4 ... Developing device, 9 ... Photosensitive drum, 10 ... Density sensor, 300 ... Control apparatus, 301 ... CPU, 302 ... ROM, 303 ... RAM.

JP 2005-88371 A

Claims (7)

In the image forming apparatus having the optical writing device in which the positions of the plurality of light emitting element array units in the sub-scanning direction are made different and the end portions are overlapped in the main scanning direction, and the light emitting elements at the end portions are connected.
Print head control that sequentially forms a plurality of test pattern latent images on the photosensitive member by sequentially writing a plurality of test pattern data to at least the light emitting elements at the end of two light emitting element array units adjacent in the main scanning direction. Means,
A test pattern image forming means for sequentially forming a plurality of test pattern images on the photosensitive member by operating a single developing device to develop latent images of the plurality of test patterns;
A density detecting means for operating the density sensor to detect the density of the plurality of test pattern images;
Storage means for storing the output of the density detection means for each of the plurality of test pattern images ;
Based on a plurality of output change patterns stored in the storage unit, an overlap pixel number determination unit that determines the number of light emitting elements overlapping at the end;
A joint pixel determining unit that determines a pixel of a joint of the two light emitting element array units based on a determination result of the overlap pixel number determining unit;
The plurality of test pattern data alternately turns on and off the light emitting elements of one light emitting element array unit every predetermined number, and turns on and off the light emitting elements of the other light emitting element array unit alternately every predetermined number of times. And an on / off position of the light emitting element of the other light emitting element array unit is sequentially shifted for each test pattern. The image forming apparatus according to claim 1,
An image forming apparatus comprising means for changing the predetermined number. The image forming apparatus according to claim 1 or 2,
An image forming apparatus comprising means for adjusting a light amount of the light emitting element. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, wherein a length in the main scanning direction of the overlapping portion of the end portion is longer than a length in the main scanning direction of a detection range of the density sensor. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the print head control means writes the plurality of test pattern data into light emitting elements only at the ends of the two light emitting element array units. The image forming apparatus according to claim 1,
An image forming apparatus, wherein one pixel is sequentially shifted for each test pattern.   A program for causing a computer to function as each unit of the image forming apparatus according to any one of claims 1 to 6.

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