JP2007148248A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently create a patch for correction at the same position of a photoreceptor drum at all times, by using a home position sensor of the photoreceptor drum, in an image forming apparatus having a plurality of photoreceptor drums. <P>SOLUTION: The image forming apparatus 1 detects the home position of the photoreceptor drum by the home position sensor 39 for each photoreceptor drum, when correction operation is performed, and creates the patch for correction at the timing that the home position is detected. Then, the apparatus detects the density of each created patch for correction by a density detection sensor 30, and corrects the maximum density of each patch for correction on the basis of the detection results. A photoreceptor drum control part 40 performs control for making the stop or the start position of rotation synchronized in each photoreceptor drum, on the basis of an output signal of the home position sensor 39. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a plurality of photosensitive drums.

In an image forming apparatus such as a copying machine or a printer, a correction operation is performed to keep the image quality at a certain level. In an image forming apparatus capable of forming a color image, a change in image quality such as color and density is easily recognized on a sheet, so that higher level image quality and stability are required. Conventionally, when patches are created by a correction operation, correction patches are created simultaneously on a plurality of photosensitive drums. However, in this method, since correction patches are created at random positions on the photosensitive drum, it is necessary to eliminate the influence of periodic unevenness on the photosensitive drum and perform correction with higher accuracy. Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for performing correction by always creating a correction patch used in a correction operation at the same position on the photosensitive drum using a position detection unit.
JP-A-6-51551

  A method using a means for detecting the home position of the photosensitive drum has been conventionally used in order to always create a correction patch at the same position on the photosensitive drum. However, in an image forming apparatus having a plurality of photosensitive drums, it is necessary to create a correction patch by detecting the home position for each photosensitive drum. Therefore, the time for waiting for the detection timing of each home position Loss may occur. Further, in an image forming apparatus having an intermediate transfer belt, it is necessary to control so that correction patches created on the respective photosensitive drums do not overlap on the intermediate transfer belt.

  An object of the present invention is to make it possible to efficiently create a correction patch at the same position on the photosensitive drum by using the home position sensor of the photosensitive drum in an image forming apparatus having a plurality of photosensitive drums. is there.

In order to solve the above problem, the invention described in claim 1 includes a plurality of photosensitive drums,
Home position detecting means for detecting a home position of each of the plurality of photosensitive drums;
Creating means for creating a correction patch on each photosensitive drum;
Density detecting means for detecting the density of the correction patch created by the creating means;
Correction means for correcting the image quality of the output image based on the detection result by the density detection means;
Control means for performing control to synchronize the rotation stop position or start position of each photosensitive drum based on the output signal of the home position detection means.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the creation unit is configured to perform the correction patch adjustment based on a home position of each photosensitive drum detected by the home position detection unit. It is characterized by controlling the creation timing.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the image forming apparatus includes an intermediate transfer belt that primarily transfers an image formed on each photosensitive drum or a correction patch,
The creating means controls the correction patches created on the respective photosensitive drums so as not to overlap on the intermediate transfer belt.

  According to the present invention, based on the output signal of the home position detection means, it is possible to efficiently create a correction patch at the same position of the photosensitive drum, and to improve the accuracy and productivity of the correction operation. It becomes.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the configuration in the present embodiment will be described.

  FIG. 1 shows an internal configuration of an image forming apparatus 1 according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 1 includes an image reading unit 10 and an image forming unit 20.

  The image reading unit 10 includes an automatic document feeder 11 and a document image scanning device 12. The automatic document feeder 11 conveys the document d placed on the document table by the conveyance mechanism and sends it to the document image scanning device 12. The document image scanning device 12 optically scans the conveyed document d, The original image is read by photoelectric conversion by the line image density detection sensor 30CD.

  A document image (analog image signal) read by the image reading unit 10 is output to an image processing unit described later, and various images such as analog processing, A / D conversion processing, shading processing, and image compression processing are processed in the image processing unit. After the processing, the color separation is performed for each color of Y (yellow), M (magenta), C (cyan), and K (black), and the exposure units 2Y, 2M, and 2C of the image forming unit 20 are used as output image data. 2K.

  The automatic document feeder 11 has a conveyance mechanism for reading both sides of the document, and continuously reads images (including both sides) of a large number of documents d conveyed from the document table all at once. Is possible. The read document image data is stored in an image memory inside the image forming unit 20, and is sequentially read as output data at the time of output, and is output to the exposure units 2Y, 2M, 2C, and 2K. This function can be used when copying a large number of original images by the copying function, or when transmitting data of a large number of originals d by the facsimile function.

  The image forming unit 20 performs tandem image formation, and for each of Y, M, C, and K colors, the exposure units 2Y, 2M, 2C, and 2K that are exposure units, and the development unit 3Y that is a development unit. 3M, 3C, 3K, photosensitive drums 4Y, 4M, 4C, 4K as photosensitive members, primary transfer rollers 7Y, 7M, 7C, 7K as transfer means, and an intermediate transfer belt 8. Around the photosensitive drums 4Y, 4M, 4C, and 4K, charging units 5Y, 5M, 5C, and 5K that perform charging, and cleaning units 6Y and 6M that remove residual toner on the photosensitive drums 4Y, 4M, 4C, and 4K. , 6C, 6K are provided.

  The intermediate transfer belt 8 is wound around a plurality of rollers and is rotatably supported. A cleaning unit 9 and a density detection sensor 30 for removing residual toner on the intermediate transfer belt 8 are provided facing the intermediate transfer belt 8.

  Further, the image forming unit 20 includes a secondary transfer roller 21 that is a transfer unit, a fixing unit 22, paper feed trays T <b> 1 to T <b> 3, and a density detection sensor 30. The fixing unit 22 includes a fixing heater and the like, and heat-treats the output paper on which the toner image is transferred to fix the toner image on the output paper. The paper feed trays T1 to T3 can store output papers of various paper sizes.

Hereinafter, an image forming process by the image forming unit 20 will be described.
First, exposure is performed by the exposure unit 2Y based on the input output image data, and an electrostatic latent image of the output image is formed on the photosensitive drum 4Y. Next, the developing unit 3Y blows toner onto the photosensitive drum 4Y for development, and a toner image is formed on the photosensitive drum 4Y. The development is performed by a reversal phenomenon in which a development bias in which an AC voltage is superimposed on a DC voltage having the same polarity as the polarity of the toner to be used is applied.

  The toner image formed on the photosensitive drum 4Y is transferred onto the rotating intermediate transfer belt 8 by the primary transfer roller 7Y to which a primary transfer bias having a polarity opposite to that of the used toner is applied (this is transferred to the primary transfer roller 8Y). A Y toner image is formed on the intermediate transfer belt 8. Such processing is sequentially performed for each of the colors M, C, and K, and a color image in which the toner images of the respective colors are combined is formed on the intermediate transfer belt 8.

  On the other hand, output paper is fed from the paper feed trays T1 to T3 and is conveyed onto the secondary transfer roller 21 by the conveyance mechanism. In the secondary transfer roller 21, the color image formed on the intermediate transfer belt 8 is collectively transferred onto one surface of the output paper (this is called secondary transfer). The output sheet on which the color image has been transferred is subjected to a fixing process by the fixing unit 22 and is output to a discharge tray outside the apparatus by the transport mechanism.

  When the image forming cycle for one image is completed, the toner remaining on the photosensitive drums 4Y, 4M, 4C, 4K and the intermediate transfer belt 8 after the transfer is removed by the cleaning units 6Y, 6M, 6C, 6K, and 9. Then, the process proceeds to the image forming cycle of the next image.

Next, the density detection sensor 30 will be described.
As shown in FIG. 1, the density detection sensor 30 faces the intermediate transfer belt 8 and is installed on the downstream side of the exposure unit, the development unit, and the like. The density detection sensor 30 measures (detects) the density of the toner image primarily transferred onto the intermediate transfer belt 8 in order to detect an image forming state after image formation. As the density detection sensor 30, for example, an optical sensor including a phototransistor and an LED (Light Emitting Diode) can be applied, and the intermediate transfer belt 8 is irradiated with inspection light to detect the amount of reflected light. A density value can be obtained by performing log conversion on the measured value of the amount of reflected light.

  FIG. 2 shows a main configuration of a control system in the image forming apparatus 1. As shown in FIG. 2, the image forming apparatus 1 includes an overall control unit 31, an operation unit 32, a display unit 33, a communication unit 34, a storage unit 35, an engine control unit 36, an image processing unit 37, an image memory 38, a home position. The sensor 39, the photosensitive drum control unit 40, the correction operation execution unit 41, the image reading unit 10, the image forming unit 20, and the density detection sensor 30 are configured. Since the image reading unit 10, the image forming unit 20, and the density detection sensor 30 are as described above, description thereof is omitted here.

  The overall control unit 31 performs various calculations according to a control program stored in the storage unit 35 and controls each unit such as the operation unit 32, the display unit 33, and the communication unit 34. The overall control unit 31 generates various control information such as instruction information related to output and setting information related to the correction operation based on an operation signal input from the operation unit 32, and outputs the control information to the engine control unit 36.

  The operation unit 32 includes various function keys such as numeric keys and a start key, a touch panel configured integrally with the display unit 33, an operation signal corresponding to the operated key, and an input operation on the touch panel. An operation signal corresponding to the above is generated and output to the overall control unit 31.

  The display unit 33 includes a display such as an LCD (Liquid Crystal Display), and displays various display information such as various operation screens, processing results of the overall control unit 31, and output results of the image forming unit 20.

  The communication unit 34 includes a communication interface such as a network interface card or a fax modem, and transmits / receives information to / from an external device such as another image forming apparatus or a user terminal. For example, data to be output can be received from the user terminal, or image data read by the image reading unit 10 can be transmitted by facsimile to another image forming apparatus.

  The storage unit 35 stores various setting information, parameters necessary for execution of processing by the program, processing result data, and the like in addition to various control programs executed by the overall control unit 31 or the engine control unit 36.

  The engine control unit 36 is a unit that mainly controls each unit related to the image forming operation such as the image reading unit 10 and the image forming unit 20, and comprehensively controls output processing according to control information input from the overall control unit 31. To do.

  The image processing unit 37 performs various processes on the analog image signal input from the image reading unit 10 to generate digital image data, and performs compression or expansion processing on data stored in the image memory 38. In addition, various image processing such as rotation / reversal processing, gradation processing, sharpness adjustment processing, and the like is performed on the output target data in accordance with an instruction from the engine control unit 36.

  The image memory 38 is composed of a DRAM (Dynamic Random Access Memory) or the like, and stores data to be output such as image data read by the image reading unit 10 and output data received via the communication unit 34. .

  As shown in FIG. 3A, the home position sensor 39 is provided for each photosensitive drum on a wheel provided on the rotating shaft of the photosensitive drum, and the home position (reference position) of the photosensitive drum is detected by the photosensor. ) And outputs the detection result to the engine control unit 36. As shown in FIG. 3A, the home position (reference position) of the photosensitive drum is a correction patch creation start position.

  When the home position of the photosensitive drum is detected by the home position sensor 39, the photosensitive drum control unit 40 performs control to synchronize the rotation stop position or start position of each photosensitive drum (see FIGS. 4 and 5). .)

  The correction operation execution unit 41 performs a plurality of correction operations under the control of the engine control unit 36 in order to obtain a stable output image satisfied by the user. A correction operation called stabilization control is performed. In the stabilization control, surface potential correction for matching the surface potential of the photosensitive drum, Dmax correction for correcting the maximum density by creating a correction patch, and gradation correction are performed. Among these three types of correction, a correction patch is created on the photosensitive drum when performing Dmax correction and gradation correction. In these correction operations, when the number of output sheets reaches a predetermined number (for example, 1000 sheets), or when a pause time (idling time or power-off time) has elapsed (for example, 360 minutes), the operation unit 32 is operated by the user. This is executed when an instruction to execute a correction operation is issued.

  In the surface potential correction, the correction operation execution unit 41 corrects the surface potential of the photosensitive drums 4Y, 4M, 4C, and 4K. Specifically, the surface potentials of the photosensitive drums 4Y, 4M, 4C, and 4K are measured using a surface potentiometer, and correction is performed so that the surface potential of a portion that is not exposed to light and is not exposed is within the reference. Do.

  In the Dmax correction, the correction operation execution unit 41 corrects the development bias in the development units 3Y, 3M, 3C, and 3K so that the maximum density at the time of output becomes a specified value. Specifically, the correction operation execution unit 41 forms an image of the correction patch at the timing when the home position (reference position) is detected by the home position sensor 39 of each photosensitive drum, and based on the generation start timing, The time for the correction patch to reach the density detection sensor 30 is calculated for each color, and the correction patch for each color is sampled in accordance with the calculated arrival time. Then, the density of the correction patch for each color is corrected based on the result detected by the density detection sensor 30.

  As shown in FIG. 3B, the order in which the created correction patches are transferred onto the intermediate transfer belt 8 and reach the density detection sensor 30 is changed from K (black) → Although C (cyan) → M (magenta) → Y (yellow), if the correction patch creation start timing differs for each color, the interval between the correction patches transferred onto the intermediate transfer belt 8 is not constant. . Therefore, as in the present embodiment, by calculating the time for the correction patch to reach the density detection sensor 30 for each color, it is possible to sample the correction patch for each color from the correct position.

  In the gradation correction, the correction operation execution unit 41 corrects the conditions for the gradation conversion process in the image processing unit 37. First, a correction image is formed in stages from a light gradation to a dark gradation, and the density is read by the density detection sensor 30 to obtain gradation characteristics. Then, a gradation correction curve is calculated so that the obtained gradation characteristic becomes the target gradation characteristic, and this is applied during the gradation conversion process.

Next, the operation in this embodiment will be described.
First, the drum rotation start control process executed in the photosensitive drum control unit 40 will be described with reference to the flowchart of FIG.

  When rotation of the photosensitive drums for each color is started (step S1), it is determined whether or not the rotation state is stable (step S2). If it is determined in step S2 that the rotation state of each photosensitive drum is stable (step S2; YES), the phase difference state between the photosensitive drums is checked (step S3), and the phase difference is always constant. The drum rotation start control process is terminated. In step S3, the home position is detected in what state the photosensitive drums of the other three colors are rotating with reference to a photosensitive drum of one color (for example, photosensitive drum 4K) (several millimeters earlier or later). Is confirmed).

  Next, the drum rotation stop control process executed in the photosensitive drum control unit 40 will be described with reference to the flowchart of FIG.

  When stopping the photosensitive drum, first, for each color, it is determined whether or not the home position of the photosensitive drum is detected by the home position sensor 39 (step S10). In step S10, when the home position of the photosensitive drum is detected (step S10; YES), the photosensitive drum is stopped at a predetermined reference position (step S11), and the drum rotation stop control process ends.

  As shown in FIG. 5, when the photosensitive drums are stopped, the home positions of the photosensitive drums of all colors are detected and stopped at the reference position, so that the phase difference of each photosensitive drum greatly changes at the time of activation. However, as shown in step S3 of FIG. 4, the accuracy of the correction operation is checked by checking whether or not the phase difference has changed and controlling the phase difference to be always constant. Can be improved. This is also effective for a configuration in which some errors occur in the stop position and rise time of the photosensitive drum depending on the type of motor to be controlled and the control method.

  Next, the Dmax control process among the correction operations executed by the correction operation execution unit 41 will be described with reference to the flowchart of FIG. In the normal Dmax control process, a predetermined number of correction patches are created for each color, and the correction operation is performed using the correction patches. However, in FIG. A case where correction patches are created one by one will be described.

  First, it is determined whether or not it is necessary to create correction patches for all colors (step S20). If it is determined in step S20 that the correction patch creation determination has not been completed for all colors (step S20; NO), it is necessary to create a correction patch for each color (correction patch). Is determined) (step S21).

  If it is determined in step S21 that a correction patch needs to be created (step S21; YES), does the correction patch for the corresponding color overlap the correction patch for other colors on the intermediate transfer belt 8? It is determined whether or not (step S22). In step S <b> 22, whether or not it overlaps with correction patches of other colors is determined based on a value considering a margin from the pitch distance between the photosensitive drums.

  If it is determined in step S22 that the correction patch for the color to be determined does not overlap with the correction patches for other colors (step S22; YES), it is necessary to create a correction patch for that color. Is determined (step S23), and the process returns to step S20.

  If it is determined in step S21 that the creation of a correction patch is not necessary (that is, the correction patch has been created) (step S21; NO), or in step S22, the correction patch of the corresponding color is found. If it is determined that the correction patch overlaps with another color correction patch (step S22; NO), it is determined that it is not necessary to create a correction patch for that color (step S24), and the process returns to step S20. If it is determined in step S22 that the correction patch overlaps with another color correction patch, the correction patch for that color is created later (created after the correction patch for another color is created).

  When it is determined in step S20 that the correction patch creation determination has been completed for all colors (step S20; YES), it is necessary to create a correction patch for each color based on the determination in step S23 or S24. It is determined whether the color is correct (step S25). If it is determined in step S25 that it is not necessary to create a correction patch for the corresponding color (step S25; NO), the process proceeds to step S31 described later.

  In step S25, when it is determined that the color needs to be corrected (step S25; YES), the home position sensor 39 detects the home position of the photosensitive drum of that color (step S26; YES), a correction patch is created at the detected timing (step S27). Then, based on the timing when the creation of the correction patch is started, the time (sampling start timing) for the color correction patch to reach the density detection sensor 30 is calculated, and the calculated arrival time (sampling start timing). ) Is stored in the storage unit 35 (step S28).

  Next, it is determined whether or not the check for the creation of the correction patch has been completed for all the colors that need to be created (step S29). If it is determined in step S29 that the check has not been completed (step S29; NO), the process returns to step S25, and the processes in steps S25 to S29 are repeated for the color for which no correction patch has been created.

  If it is determined in step S29 that the check has been completed (step S29; YES), the correction operation execution unit 41 samples a correction patch for each color in accordance with the sampling start timing stored in step S28. A Dmax correction operation is performed (step S30).

  After completion of the Dmax correction operation in step S30, or when it is determined in step S25 that it is not necessary to create a correction patch (step S25; NO), the correction patch generation and correction operations have been completed for all colors. Is determined (step S31). If it is determined in step S31 that the correction patch creation and correction operations for all colors have not been completed (there is a color that has been delayed in the creation of the correction patch) (step S31; NO), the process proceeds to step S20. Returning to step S27, the intermediate transfer belt 8 is moved to a position where it does not overlap with the other color correction patches that have been created, and correction patch creation and correction operations are performed. If it is determined in step S31 that the correction patch creation and correction operations for all colors have been completed (step S31; YES), the Dmax control process ends.

  With the above operation, it is possible to efficiently create a correction patch at the same position of the photosensitive drum based on the output signal of the home position sensor 39, and to improve the accuracy and productivity of the correction operation. Become.

1 is a diagram illustrating an internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a block diagram showing a main part configuration of a control system in the image forming apparatus. FIG. 4 is a diagram illustrating correction patches formed on a photosensitive drum and correction patches transferred to an intermediate transfer belt. The flowchart which shows a drum rotation start control process. The flowchart which shows a drum rotation stop control process. The flowchart which shows the Dmax control process for correct | amending the highest density of the correction patch.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image reading part 20 Image forming part 2Y, 2M, 2C, 2K Exposure unit 3Y, 3M, 3C, 3K Developing unit 4Y, 4M, 4C, 4K Photosensitive drum 8 Intermediate transfer belt 21 Secondary transfer roller 22 Fixing unit 30 Density detection sensor (density detection means)
31 Overall Control Unit 32 Operation Unit 33 Display Unit 36 Engine Control Unit 37 Image Processing Unit 38 Image Memory 39 Home Position Sensor (Home Position Detection Means)
40 Photosensitive drum control section (control means)
41 Correction operation execution unit (creation means, correction means)

Claims (3)

A plurality of photosensitive drums;
Home position detecting means for detecting a home position of each of the plurality of photosensitive drums;
Creating means for creating a correction patch on each photosensitive drum;
Density detecting means for detecting the density of the correction patch created by the creating means;
Correction means for correcting the image quality of the output image based on the detection result by the density detection means;
Control means for performing control to synchronize the stop position or start position of rotation of each photosensitive drum based on the output signal of the home position detection means;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the creation unit controls the creation timing of the correction patch based on a home position of each photosensitive drum detected by the home position detection unit. An intermediate transfer belt that primarily transfers an image formed on each photosensitive drum or a correction patch;
3. The image forming apparatus according to claim 1, wherein the creating unit controls the correction patches formed on the photosensitive drums so as not to overlap on the intermediate transfer belt. 4.

Images