JP2014081553A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of improving accuracy in correcting image formation conditions by predicting a change in transfer amount of toner generated due to disturbance.SOLUTION: An image forming apparatus 1 includes an image carrier 50, a transfer unit 60, a density detection sensor 91, and a control unit 100. The density detection sensor 91 is arranged on the downstream side of the transfer unit 60 on the image carrier 50 to detect the density of a toner image P1 for a correction patch. The control unit 100 corrects image formation conditions on the basis of a detection value detected by the density detection sensor 91. The control unit 100 further corrects the detection value by using at least one or more pieces of information of the charge amount of toner and the resistance value of the transfer unit.

Description

  The present invention relates to an image forming apparatus that corrects an image forming condition for forming an image by detecting a correction patch formed on an image carrier with a density detection sensor.

  In order to form an image on a sheet, the image forming apparatus forms a toner image on an image carrier such as a photoreceptor or an intermediate transfer belt, and transfers the formed toner image onto the sheet by a transfer unit. The toner image transferred to the paper is fixed on the paper by the fixing unit, thereby forming an image on the paper.

  2. Description of the Related Art Conventionally, an image forming apparatus is known in which a density detection sensor is disposed on the downstream side of a transfer portion of an intermediate transfer belt in order to stabilize image quality. This image forming apparatus corrects image forming conditions for forming an image by creating a correction patch formed of toner on an intermediate transfer belt and detecting the density of the correction patch with a density detection sensor. For example, the correction using the correction patch is performed every time the predetermined image forming process is executed.

  In addition, when the correction patch passes between the intermediate transfer belt and the transfer roller of the transfer portion (transfer nip portion), the intermediate transfer belt is used to prevent a part of the toner of the correction patch from adhering to the transfer roller. The transfer roller is separated from After the correction patch passes through the transfer nip portion, the transfer roller is again brought into contact with the intermediate transfer belt. In this case, it is necessary to interrupt the image forming process for the time required for the separation operation and the contact operation of the transfer roller, and the productivity is lowered.

  In order to suppress the decrease in productivity, Patent Document 1 discloses an image forming apparatus that passes a correction patch to a transfer nip portion in a state where an image carrier and a transfer roller are in contact with each other. In the image forming apparatus described in Patent Document 1, in order to prevent the toner of the correction patch from being transferred to the transfer roller, when the correction patch passes through the transfer unit, the transfer roller has the same toner as the correction patch. Polarity bias is applied.

JP 2006-47779 A

  However, in the image forming apparatus described in Patent Document 1, although the toner image of the correction patch can be prevented from being disturbed, the toner has been transferred to the transfer roller. Note that the amount of toner transferred to the transfer roller (hereinafter referred to as “toner transfer amount”) varies depending on disturbances such as the toner charge amount and the resistance value of the transfer roller. However, the transfer amount of the toner which fluctuates due to disturbance is not taken into consideration. For this reason, when the transfer amount of toner fluctuates due to disturbance, the output value of the density detection sensor also fluctuates, resulting in a problem that accuracy in correcting the image forming condition is lowered.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of predicting fluctuations in the amount of toner transfer caused by a disturbance and improving the correction accuracy of image forming conditions in consideration of the actual situation in the prior art. .

  In order to solve the above problems and achieve the object of the present invention, an image forming apparatus of the present invention includes an image carrier, an image forming unit, a transfer unit, a density detection sensor, and a control unit. The image forming unit includes a developing unit, and forms toner images for correction patches or image formation by attaching toner to the image carrier. The transfer unit is disposed in contact with the image carrier, and (secondarily) transfers the toner image to the sheet. The density detection sensor is disposed on the downstream side of the transfer portion of the image carrier and detects the toner density of the toner image for the correction patch formed on the image carrier. The control unit corrects the image forming condition of the image forming unit based on the detection value detected by the density detection sensor. The control unit corrects the image forming condition of the image forming unit by correcting the detection value detected by the density detection sensor based on at least one of the charge amount of the toner and the resistance value of the transfer unit.

  In the image forming apparatus of the present invention, the signal from the density detection sensor is corrected using at least one piece of information among the toner charge amount and the transfer portion resistance value, which are disturbances that change the toner transfer amount. Yes. As a result, fluctuations in the amount of toner transfer can be predicted, correction can be performed in consideration of disturbances, and image forming conditions can be corrected more accurately.

  According to the image forming apparatus having the above-described configuration, it is possible to predict a change in the toner transfer amount caused by a disturbance, and it is possible to improve the accuracy when correcting the image forming conditions. As a result, it is possible to stably create high-quality images.

1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a hardware configuration of each unit of an image forming apparatus according to an exemplary embodiment of the present invention. 6 is a flowchart illustrating a stabilization batch correction process of the image forming apparatus according to the exemplary embodiment of the present invention. 6 is a flowchart illustrating inter-image stabilization correction processing of the image forming apparatus according to the exemplary embodiment of the present invention. FIG. 4 is an explanatory diagram showing, in an enlarged manner, main portions in inter-image stabilization correction of the image forming apparatus according to the embodiment of the present invention. 4 is a graph showing the relationship between the output and density of a density detection sensor of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is an explanatory diagram illustrating a toner charge amount distribution. 4 is a graph showing a relationship between a toner charge amount and a charge amount correction value of the image forming apparatus according to the embodiment of the present invention. 6 is a graph showing a relationship between a resistance value and a resistance correction value of a transfer body including an intermediate transfer belt or a secondary transfer roller of an image forming apparatus according to an exemplary embodiment of the present invention. It is a graph which shows the relationship between coverage information and a toner charge amount. 5 is a graph showing a relationship between developer usage progress information and toner charge amount. 6 is a graph showing a relationship between toner temperature or humidity information and toner charge amount. 6 is a graph showing the relationship between development stop time and toner charge amount. 6 is a graph showing a relationship between toner density information and toner charge amount. 6 is a graph showing a relationship between a development DC bias and a toner charge amount. 6 is a graph showing a relationship between a resistance value of a transfer member formed of an intermediate transfer belt or a secondary transfer roller and the number of rotations of the intermediate transfer belt or the secondary transfer roller. 6 is a graph showing a relationship between a resistance value of a transfer member including an intermediate transfer belt or a secondary transfer roller and temperature or humidity information.

  Hereinafter, embodiments for implementing the image forming apparatus will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the common member in each figure.

1. Configuration Example of Image Forming Apparatus First, a configuration example of an image forming apparatus according to an embodiment will be described with reference to FIG.
FIG. 1 is an overall configuration diagram illustrating an image forming apparatus according to the first embodiment.

  As shown in FIG. 1, the image forming apparatus 1 forms an image on a sheet by an electrophotographic method, and has four colors of yellow (Y), magenta (M), cyan (C), and black (K). This is a tandem color image forming apparatus that superimposes toner. The image forming apparatus 1 includes an original transport unit 10, a paper storage unit 20, an image reading unit 30, an image forming unit 40, an intermediate transfer belt 50 as an image carrier, a secondary transfer unit 60, and a fixing unit. Part 80 and a control board 90.

  The document transport unit 10 includes a document feeder 11 on which a document G is set, a plurality of rollers 12, a transport drum 13, a transport guide 14, a document discharge roller 15, and a document discharge tray 16. . The documents G set on the document feeder 11 are conveyed one by one to the reading position of the image reading unit 30 by the plurality of rollers 12 and the conveying drum 13. The conveyance guide 14 and the document discharge roller 15 discharge the document G conveyed by the plurality of rollers 12 and the conveyance drum 13 to the document discharge tray 16.

  The image reading unit 30 reads an image of the document G transported by the document transport unit 10 or the document placed on the document table 31 and generates image data. Specifically, the image of the original G is irradiated by the lamp L. The reflected light from the document G is guided in the order of the first mirror unit 32, the second mirror unit 33, and the lens unit 34 and forms an image on the light receiving surface of the image sensor 35. The image sensor 35 photoelectrically converts incident light and outputs a predetermined image signal. The output image signal is created as image data by A / D conversion.

  The image reading unit 30 has an image reading control unit 36. The image reading control unit 36 performs processing such as shading correction, dither processing, and compression on the image data created by the A / D conversion, and stores it in the RAM 103 (see FIG. 2) of the control board 90. The image data is not limited to data output from the image reading unit 30 and may be data received from an external device such as a personal computer connected to the image forming apparatus 1 or another image forming apparatus.

  The paper storage unit 20 is disposed in the lower part of the apparatus main body, and a plurality of paper storage units 20 are provided according to the size and type of the paper S. The sheet S is fed by the sheet feeding unit 21 and sent to the transport unit 23, and is transported by the transport unit 23 to the secondary transfer unit 60 that is a transfer unit having a transfer position. Further, a manual feed portion 22 is provided in the vicinity of the paper storage portion 20. From the manual feed section 22, paper of a size not stored in the paper storage section 20, tag paper having a tag, special paper such as an OHP (Overhead projector) sheet is sent to the transfer position.

  An image forming unit 40 and an intermediate transfer belt 50 are disposed between the image reading unit 30 and the paper storage unit 20. The image forming unit 40 includes four image forming units 40Y, 40M, 40C, and 40K in order to form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). . That is, the image forming unit 40 attaches toner to the intermediate transfer belt 50 to form a toner image for correction patch or a toner image for image formation.

  The first image forming unit 40Y forms a yellow toner image, and the second image forming unit 40M forms a magenta toner image. The third image forming unit 40C forms a cyan toner image, and the fourth image forming unit 40K forms a black toner image. Since these four image forming units 40Y, 40M, 40C, and 40K have the same configuration, the configuration of the first image forming unit 40Y will be described here.

  The first image forming unit 40Y includes a drum-shaped photoconductor 41, a charging unit 42 arranged around the photoconductor 41, an exposure unit 43, a developing unit 44, and a cleaning unit 45. The photoreceptor 41 is rotated by a drive motor (not shown). The charging unit 42 applies a charge to the photoconductor 41 and uniformly charges the surface of the photoconductor 41. The exposure unit 43 performs an exposure operation on the surface of the photoconductor 41 based on image data read from the original G or image data transmitted from an external device, thereby forming an electrostatic latent image on the photoconductor 41. Form.

  The developing unit 44 develops the electrostatic latent image formed on the photoconductor 41 using a two-component developer composed of toner and carrier stored inside. The developing unit 44 includes a stirring unit 44 a that stirs the toner and frictionally charges it, and a developing roller 44 b that transports the charged toner and adheres it to the electrostatic latent image formed on the photoreceptor 41. The developing unit 44 attaches yellow toner to the electrostatic latent image formed on the photoreceptor 41. As a result, a yellow toner image is formed on the surface of the photoreceptor 41.

  A predetermined voltage, so-called development DC bias, is applied between the photoconductor 41 and the developing unit 44 when toner is attached to the photoconductor 41 to form a toner image. By adjusting this development DC bias, the amount of toner adhering to the photoreceptor 41 can be adjusted, and the image density can be adjusted.

  The developing unit 44 of the second image forming unit 40M attaches magenta toner to the photoconductor 41 to form a magenta toner image on the surface of the photoconductor 41. In addition, the developing unit 44 of the third image forming unit 40 </ b> C attaches cyan toner to the photoconductor 41 to form a cyan toner image on the surface of the photoconductor 41. Then, the developing unit 44 of the fourth image forming unit 40K attaches black toner to the photoconductor 41 and forms a black toner image on the surface of the photoconductor 41.

  The toner image formed on the photoconductor 41 is primarily transferred to an intermediate transfer belt 50 showing an example of an intermediate transfer member. The cleaning unit 45 removes toner remaining on the surface of the photoreceptor 41 after the toner image is primarily transferred to the intermediate transfer belt 50.

  An intermediate transfer belt 50 showing an example of an image carrier is formed in an endless shape and is stretched around a plurality of rollers. The intermediate transfer belt 50 is rotationally driven in a direction opposite to the rotation (movement) direction of the photoconductor 41 by a drive motor (not shown).

  A primary transfer portion 51 is provided at a position on the intermediate transfer belt 50 that faces the photoreceptor 41 of each of the image forming units 40Y, 40M, 40C, and 40K. The primary transfer unit 51 primarily transfers the toner image formed on the photoreceptor 41 to the intermediate transfer belt 50 by applying a voltage having a polarity opposite to that of the toner to the intermediate transfer belt 50.

  When the intermediate transfer belt 50 is driven to rotate, toner images formed by the four image forming units 40Y, 40M, 40C, and 40K are sequentially primary-transferred onto the surface of the intermediate transfer belt 50 sequentially. As a result, yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 50 to form a color toner image.

  A belt cleaning device 53 faces the intermediate transfer belt 50. The belt cleaning device 53 cleans the surface of the intermediate transfer belt 50 that has finished transferring the toner image onto the paper S.

  In the vicinity of the intermediate transfer belt 50 and downstream of the conveyance unit 23 in the sheet conveyance direction, a secondary transfer unit 60 showing an example of the transfer unit of the present invention is disposed. The secondary transfer unit 60 brings the paper S sent by the transport unit 23 into contact with the intermediate transfer belt 50 and secondarily transfers the toner image formed on the outer peripheral surface of the intermediate transfer belt 50 onto the paper S. .

  The secondary transfer unit 60 has a secondary transfer roller 61. The secondary transfer roller 61 is in pressure contact with the counter roller 52. A portion where the secondary transfer roller 61 and the intermediate transfer belt 50 come into contact becomes a secondary transfer nip portion 62. The secondary transfer nip portion 62 is a secondary transfer position where the toner image formed on the outer peripheral surface of the intermediate transfer belt 50 is secondarily transferred to the paper S.

  A fixing unit 80 is provided on the discharge side of the sheet S in the secondary transfer unit 60. The fixing unit 80 pressurizes and heats the paper S to fix the toner image that has been secondarily transferred to the paper S. The fixing unit 80 includes, for example, a fixing upper roller 81 and a fixing lower roller 82 which are a pair of fixing members. The upper fixing roller 81 and the lower fixing roller 82 are arranged in pressure contact with each other, and the pressure contact portion between the upper fixing roller 81 and the lower fixing roller 82 is a fixing nip portion that pressurizes and heats the sheet S.

  A heating unit is provided inside the fixing upper roller 81. The outer peripheral portion of the fixing upper roller 81 is warmed by the radiant heat from the heating portion. Then, the heat of the outer peripheral portion of the fixing upper roller 81 is transmitted to the sheet S, whereby the toner image on the sheet S is thermally fixed.

  The sheet S is conveyed so that the surface on which the toner image is transferred by the secondary transfer unit 60 (the surface to be fixed) faces the fixing upper roller 81 and passes through the fixing nip portion. Accordingly, the sheet S passing through the fixing nip is subjected to pressure by the fixing upper roller 81 and the fixing lower roller 82 and heating by the heat of the roller portion of the fixing upper roller 81.

  A switching gate 24 is disposed downstream of the fixing unit 80 in the sheet conveyance direction. The switching gate 24 switches the transport path of the paper S that has passed through the fixing unit 80. That is, the switching gate 24 advances the paper S straight when performing face-up paper discharge in which the image forming surface in single-sided image formation is discharged upward. As a result, the paper S is discharged by the pair of paper discharge rollers 25. The switching gate 24 guides the paper S downward when performing face-down paper discharge and double-sided image formation in which the image forming surface in single-sided image formation is discharged downward.

When face-down paper discharge is performed, the paper S is guided downward by the switching gate 24, and then the front and back sides are reversed by the paper reverse conveyance unit 26 and conveyed upward. As a result, the paper S whose front and back sides are reversed and whose image forming surface faces downward is discharged by the pair of paper discharge rollers 25.
When double-sided image formation is performed, the sheet S is guided downward by the switching gate 24, the front and back sides are reversed by the sheet reversing conveyance unit 26, and sent again to the transfer position by the refeed path 27.

  A post-processing device that folds the paper S or performs stapling processing or the like on the paper S may be disposed on the downstream side of the pair of paper discharge rollers 25.

  An IDC (Image Density Controller) sensor 91 that is an image density detection sensor is disposed between the belt cleaning device 53 and the secondary transfer unit 60 in the intermediate transfer belt 50. . That is, the IDC sensor 91 is disposed on the downstream side of the secondary transfer unit 60 in the rotation direction of the intermediate transfer belt 50. The IDC sensor 91 includes a light emitting unit that irradiates light toward the surface of the intermediate transfer belt 50 and a light receiving unit that receives reflected light from the intermediate transfer belt 50. Further, the light receiving portion and the light emitting portion of the IDC sensor 91 are opposed to the surface of the intermediate transfer belt 50.

[Hardware Configuration of Each Part of Image Forming Apparatus]
Next, a hardware configuration of each unit of the image forming apparatus 1 will be described with reference to FIG.
FIG. 2 is a block diagram illustrating a hardware configuration of each unit of the image forming apparatus 1.

  As illustrated in FIG. 2, the image forming apparatus 1 includes a control unit 100. The control unit 100 is configured on the control board 90 (see FIG. 1) described above.

  The control unit 100 includes, for example, a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102 for storing programs executed by the CPU 101, and a RAM (Random Access Memory) used as a work area of the CPU 101. 103. As the ROM 102, for example, a programmable ROM that is normally electrically erasable is used.

  The CPU 101 controls the entire apparatus. The CPU 101 is connected to the HDD 104, the operation display unit 105, and the communication unit 108 via the system bus 107, respectively. The CPU 101 is connected to a thermometer 97 and a hygrometer 98 via a system bus 107. Further, the CPU 101 is connected to the image reading unit 30, the image processing unit 106, the image forming unit 40, the paper feeding unit 21, the fixing unit 80, the secondary transfer unit 60, and the IDC sensor 91 via the system bus 107.

  The HDD 104 stores image data of an original image obtained by reading by the image reading unit 30, or stores output image data and the like. The operation display unit 105 is a touch panel including a display such as a liquid crystal display (LCD) or an organic ELD (Electro Luminescence Display). The operation display unit 105 displays an instruction menu for the user, information about the acquired image data, and the like. Further, the operation display unit 105 includes a plurality of keys, receives input of various instructions, data such as characters and numbers, and outputs an input signal to the control unit 100.

  The communication unit 108 receives job information transmitted from an external information processing apparatus PC (personal computer) 120 via a communication line. The received job information is sent to the control unit 100 via the system bus 107. The job information includes image data of an image to be formed and information such as the type and number of sheets to be used associated with the image data.

  In this embodiment, an example in which a personal computer is applied as an external device has been described. However, the present invention is not limited to this, and various other devices such as a facsimile device can be applied as the external device.

  The thermometer 97 and the hygrometer 98 are disposed in the image forming apparatus 1. The thermometer 97 detects the temperature in the apparatus and transmits the detection result to the control unit 100. The hygrometer 98 detects the humidity in the apparatus and transmits the detection result to the control unit 100.

  In addition, a thermometer that measures the temperature of the toner stored in the developing unit 44 and a hygrometer that measures humidity, a thermometer that measures the temperature around the intermediate transfer belt 50 and the secondary transfer unit 60, and a hygrometer that measures humidity are provided. May be. The thermometer for measuring the temperature of the toner and the hygrometer for measuring the humidity may be provided at the intake port for taking in the air for cooling the toner on the side surface of the image forming apparatus 1.

  The IDC sensor 91 irradiates the intermediate transfer belt 50 with light and receives light reflected from the intermediate transfer belt 50. The IDC sensor 91 detects the density of toner adhering to the intermediate transfer belt 50 and transmits the detection result to the control unit 100. Based on information from the IDC sensor 91, the control unit 100 corrects the image forming conditions when the image forming unit 40 forms an image. The details of the image forming condition correction method will be described later.

  The image reading unit 30 optically reads a document image and converts it into an electrical signal. For example, when reading a color original, image data having luminance information of 10 bits for each of RGB per pixel is generated. Image data generated by the image reading unit 30 and image data transmitted from the PC 120 showing an example of an external device connected to the image forming apparatus 1 are sent to the image processing unit 106 and subjected to image processing. The image processing unit 106 performs processes such as analog processing, A / D conversion, shading correction, and image compression on the received image data.

  For example, when a color image is formed by the image forming apparatus 1, R, G, B image data generated by the image reading unit 30 or the like is input to a color conversion LUT (Look up Table) in the image processing unit 106. Then, the image processing unit 106 performs color conversion of the R, G, and B data into Y, M, C, and K image data. Then, correction of gradation reproduction characteristics, screen processing such as halftone dots with reference to the density correction LUT, or edge processing for emphasizing thin lines is performed on the color-converted image data.

  The image forming unit 40 is driven and controlled by the control unit 100 and forms a toner image on the paper S. The fixing unit 80 is driven and controlled by the control unit 100 and pressurizes and heats the paper S to fix the toner image on the paper S.

2. Next, a method for correcting the image forming condition according to the image forming apparatus 1 described above will be described.
In order to stabilize the density of the formed image, the image forming apparatus 1 corrects the image forming conditions using the IDC sensor 91. The image forming condition correction method includes a stabilization batch correction process and an inter-image stabilization correction process. The stabilization collective correction process is performed, for example, when the image forming process is not performed for a long time or when the environment changes. Further, the inter-image stabilization correction process is performed every predetermined number of image forming executions or every predetermined time.

[Stabilized batch correction]
FIG. 3 is a flowchart showing the stabilization batch correction process.
The stabilization collective correction processing is performed for each color of yellow (Y), magenta (M), cyan (C), and black (K). The stabilization batch correction process is performed in a state where the secondary transfer roller 61 of the secondary transfer unit 60 is separated from the intermediate transfer belt 50.

  As shown in FIG. 3, first, the control unit 100 performs a base correction process for correcting the surface property of the intermediate transfer belt 50 and the contamination of the IDC sensor 91 (step S <b> 11). In the base correction according to step S11, the light emitting portion of the IDC sensor 91 is caused to emit light, and light is irradiated to the intermediate transfer belt 50 on which no toner image, correction patch or the like is formed. The IDC sensor 91 receives the light reflected from the intermediate transfer belt 50 by the light receiving unit and transmits the detection value to the control unit 100. The control unit 100 corrects the light amount of the light emitting unit of the IDC sensor 91 so that the detection value becomes a predetermined value.

  When the base correction process shown in step S11 ends, the control unit 100 performs a Dmax correction process for correcting the developability of the image forming unit 40 (step S12). In the Dmax correction process in step S12, a solid image patch that is a single color solid image is formed on the intermediate transfer belt 50. Next, the density of the solid image patch is detected by the IDC sensor 91.

  When the density of the solid image patch is higher than the predetermined density, that is, when the toner charge amount is high and a large amount of toner adheres to the photoreceptor 41, the control unit 100 sets the development DC bias in the image forming unit 40. Decrease the value. Further, when the density of the solid image patch is lower than the predetermined density, that is, when the charge amount of the toner is low and the toner hardly adheres to the photosensitive member 41, the control unit 100 sets the development DC bias in the image forming unit 40. Increase the value.

  Next, the control unit 100 performs dot diameter correction processing for correcting halftone, dot diameter, and line width (step S13). In the dot diameter correction process in step S13, a line correction patch including a halftone line pattern is formed on the intermediate transfer belt 50, and the density of the line correction patch is detected by the IDC sensor 91. The control unit 100 corrects the light amount of the exposure unit 43 so that the line width becomes a predetermined thickness.

  When the dot diameter correction process in step S13 ends, the control unit 100 performs a γ correction process (step S14). The γ correction process in step S14 is for correcting the toner density gradation. Then, the control unit 100 corrects the gradation of the toner density so that it is smooth. Thereby, the stabilization collective correction process ends.

[Image stabilization]
Next, the inter-image stabilization correction process, which is an object of the present invention, will be described with reference to FIGS.
FIG. 4 is a flowchart showing the inter-image stabilization correction process, FIG. 5 is an explanatory diagram showing an enlarged main part in the inter-image stabilization correction process, and FIG. 6 shows the relationship between the output of the IDC sensor 91 and the density. It is a graph.

  As shown in FIGS. 4 and 5, the control unit 100 creates an inter-image correction patch P <b> 1 for each color of yellow (Y), magenta (M), cyan (C), and black (K) on the intermediate transfer belt 50. (Step S21). The inter-image correction patch P1 for each color is formed between toner images for image formation formed on the intermediate transfer belt 50. That is, the inter-image stabilization correction process is performed in a process of continuously forming images on a plurality of sheets.

  As shown in FIG. 5, the inter-image correction patch P1 passes through the secondary transfer nip portion 62 where the intermediate transfer belt 50 and the secondary transfer roller 61 are in contact. At this time, the secondary transfer roller 61 is in contact with the intermediate transfer belt 50. Thereby, the operation of separating and contacting the secondary transfer roller 61 with respect to the intermediate transfer belt 50 can be omitted, and the productivity of the image forming process can be prevented from being lowered.

  Further, in order to reduce the amount of toner of the correction patch transferred to the secondary transfer roller 61, the bias having the same polarity as the toner of the correction patch is applied to the secondary transfer unit 60. In other words, a reverse bias is applied to the secondary transfer portion 60 as compared with the normal secondary transfer, and the amount of transfer patch toner transferred to the secondary transfer roller 61 by the repulsive force is reduced.

  Next, as shown in FIGS. 4 and 5, the density of the inter-image correction patch P1 that has passed through the secondary transfer nip 62 is detected by the IDC sensor 91 (step S22). As shown in FIG. 6, for example, when the detection value Q2 that is the correction patch detection value detected by the IDC sensor 91 is higher than the target value Q1, it can be seen that the density of the inter-image correction patch P1 is thinner than the standard density. . Then, as shown in FIG. 4, the control unit 100 calculates a difference value Q3 between the detection value Q2 and the target value Q1 (step S23).

  Further, as shown in FIG. 5, when the inter-image correction patch P1 passes through the secondary transfer nip portion 62, the toner P2 of the inter-image correction patch P1 adheres to the secondary transfer roller 61. The amount of toner P2 adhering to the secondary transfer roller 61 varies depending on disturbances such as the toner charge amount and the transfer member resistance. Therefore, as shown in FIG. 4, the control unit 100 calculates a fluctuation amount (hereinafter referred to as “toner transfer fluctuation amount”) P3 of the toner transferred to the secondary transfer roller 61 (step S24).

  The toner transfer fluctuation amount P3 is at least one of a charge amount correction value calculated from the toner charge amount and a resistance correction value calculated from the resistance value of the transfer member including the intermediate transfer belt 50 or the secondary transfer roller 61. Calculated from information. A detailed calculation method of the toner transfer fluctuation amount P3 will be described later.

Next, the control unit 100 corrects the difference value Q3 between the target value calculated in step S23 and the sensor output value using the toner transfer fluctuation amount P3 calculated in step S24, as shown in the following formula 1. A correction value Q4 for the image forming condition is calculated (step S25). The correction value Q4 is the exposure amount of the exposure unit 43, for example.
[Formula 1]
Correction value Q4 = (difference value Q3—toner transfer fluctuation amount P3) × correction coefficient W1
The correction coefficient W1 is a coefficient for converting the sensor output value of the IDC sensor 91 into a light amount.

  Next, the control unit 100 feeds back the calculated correction value Q4 to the image forming conditions of the image forming unit 40 (step S26). Thereby, the inter-image stabilization correction of the image forming apparatus 1 is completed.

  The step of calculating the toner transfer fluctuation amount P3 performed in step S24 may be performed when the inter-image correction patch P1 is generated in step S21, or may be performed when the difference value Q3 is calculated in step 23. .

[Calculation method of toner transfer fluctuation amount]
Next, a method for calculating the toner transfer fluctuation amount P3 will be described with reference to FIGS.
FIG. 7 is a diagram showing the toner charge amount distribution, and FIG. 8 is a graph showing the relationship between the toner charge amount and the charge amount correction value. The toner charge amount shown in FIG. 8 and subsequent figures is an average value of the charge amount of the entire toner.

  In the state having the toner charge distribution as indicated by the solid line R1 shown in FIG. 7, when the charge amount of the toner increases, that is, the charge amount of the whole toner increases, as shown by the dotted line R2, the charge is low or reverse charged. The number of toners is reduced. Here, a bias having the same polarity as the toner of the correction patch is applied to the secondary transfer roller 61. Therefore, as shown in FIG. 8, when the toner charge amount increases, the number of low-charged toners or reversely charged toners that are easily affected by bias decreases, so the amount of toner transfer to the secondary transfer roller 61 is reduced. The charge amount correction value decreases.

  Further, as shown by the dotted line R3 in FIG. 7, when the charge amount of the toner is decreased, that is, the charge amount of the whole toner is decreased, the amount of low-charged or reversely charged toner is increased. Therefore, as shown in FIG. 8, when the toner charge amount is decreased, the number of toners oppositely charged to the low charge toner is increased, so that the toner transfer amount to the secondary transfer roller 61 is increased and the charge amount correction is performed. The value increases.

FIG. 9 is a graph showing the relationship between the resistance value and the resistance correction value of the transfer member composed of the intermediate transfer belt 50 or the secondary transfer roller 61.
As shown in FIG. 9, when the resistance value of the transfer body increases, a constant current value is applied to the secondary transfer roller 61, so that the voltage value of the secondary transfer roller 61 increases. Then, the potential difference between the secondary transfer roller 61 and the low-charge toner or the reverse-charge toner in the toner of the inter-image correction patch P1 increases. For this reason, the secondary transfer roller 61 has a stronger force to attract the low-charged toner or the reversely-charged toner. As a result, the amount of toner transferred to the secondary transfer roller 61 increases and the resistance correction value increases.

  Further, when the resistance value of the transfer body is lowered, the voltage of the secondary transfer roller 61 is lowered, so that the force of the secondary transfer roller 61 to attract the low-charged or reverse-charged toner is weakened. As a result, the amount of toner transferred to the secondary transfer roller 61 decreases, and the resistance correction value decreases.

  As described above, the charge amount correction value can be calculated by detecting the charge amount of the toner, and the resistance correction value can be calculated by detecting the resistance value of the transfer body. Further, the toner transfer fluctuation amount P3 is calculated from at least one piece of information among the charge amount correction value and the resistance correction value. Therefore, the control unit 100 can calculate the toner transfer fluctuation amount P3 by detecting at least one piece of information among the charge amount of the toner and the resistance value of the transfer body.

[First calculation method of toner charge amount]
Next, a first calculation method of the toner charge amount will be described with reference to FIGS.
FIG. 10 is a graph showing the relationship between coverage information and toner charge amount, and FIG. 11 is a graph showing the relationship between developer usage information and toner charge amount. FIG. 12 is a graph showing the relationship between temperature or humidity and toner charge amount, and FIG. 13 is a graph showing the relationship between development stop time and toner charge amount.

  In the first toner charge amount calculation method, the control unit 100 acquires coverage information, developer usage history information, temperature or humidity information, and development stop time information. The coverage information indicates the ratio of the image area formed on the paper. This coverage information is an average value of the predetermined number of image forming processes. The coverage information may be an integrated value of a predetermined number of image forming processes.

  The usage history information of the developer is detected from, for example, the rotational speed of the stirring unit 44a or the developing roller 44b provided in the developing unit 44. Further, the development stop time information indicates a time during which the image forming process is stopped, that is, a time during which the stirring operation of the stirring unit 44a in the developing unit 44 is stopped. The control unit 100 acquires development stop time information by measuring the time from when the image forming process is stopped to when it is started next. In addition, the control unit 100 acquires temperature information and humidity information from a thermometer 97 and a hygrometer 98 disposed in the apparatus.

  Then, the control unit 100 calculates the toner charge amount from at least one of the acquired coverage information, developer usage progress information, temperature or humidity information, and development stop time information.

  Here, as the coverage, that is, the ratio of the image area formed on the paper increases, the amount of toner used for image formation also increases. When the amount of toner used increases, the amount of toner supplied to the developing unit 44 from a toner storage unit (not shown) increases. The toner just supplied from the toner container is not charged. As a result, as shown in FIG. 10, when coverage information increases and toner replacement is frequently performed, the toner charge amount decreases.

  Furthermore, if the developer is used for a long period of time, the developer itself deteriorates and is difficult to be charged. Therefore, as shown in FIG. 11, the toner charge amount decreases as the developer usage progresses longer.

  As shown in FIG. 12, it can be seen that the toner charge amount increases as the temperature or humidity decreases. The temperature information and the humidity information may be acquired from a thermometer and a hygrometer provided at an intake port that takes in air for cooling the toner in the side surface portion of the image forming apparatus 1.

  Further, when the time during which the developing unit 44 is stopped becomes long, the toner stored in the developing unit 44 is discharged. As a result, as shown in FIG. 13, as the development stop time becomes longer, the toner charge amount decreases.

  Thus, according to the first calculation method, a plurality of pieces of information related to the toner charge amount such as coverage information, developer usage progress information, temperature or humidity information, and development stop time information are used. Thereby, the toner transfer fluctuation amount P3 at the time of inter-image stabilization correction can be accurately calculated, and the stability of the image density can be improved.

  In addition, since a real-time value related to the toner charge amount can be used during the inter-image stabilization correction, it is possible to immediately cope with fluctuations in the toner transfer amount.

[Second method of calculating toner charge amount]
Next, a second method for calculating the toner charge amount will be described with reference to FIG.
FIG. 14 is a graph showing the relationship between toner density information and toner charge amount.
In the second calculation method, the developing unit 44 is provided with a magnetic permeability sensor (TCR sensor) that detects the ratio of the carrier and the toner contained per unit volume of the developer. The toner density is detected. The magnetic permeability sensor transmits the detected toner density information to the control unit 100. Then, the control unit 100 calculates the toner charge amount from the toner density information detected by the magnetic permeability sensor. Here, as shown in FIG. 14, when the toner density decreases, the toner charge amount increases.

  According to the second calculation method, since a real-time value related to the toner charge amount can be used during the inter-image stabilization correction, it is possible to immediately cope with a change in the toner transfer amount, and to reduce the image density. It can be stabilized. Furthermore, since the actual measurement value by the magnetic permeability sensor can be used during the inter-image stabilization correction, the toner transfer fluctuation amount P3 can be calculated more accurately.

  In the second calculation method, the example in which the magnetic permeability sensor is used as an example of the toner density sensor in the developing unit for detecting the toner density information has been described. However, the present invention is not limited to this. As the toner density sensor in the developing section, for example, a sensor that optically detects the toner density may be used.

[Third calculation method of toner charge amount]
Next, a third method for calculating the toner charge amount will be described with reference to FIGS.
In the third calculation method, the control unit 100 calls the value of the development DC bias set at the time of Dmax correction in step S12 shown in FIG. Then, the control unit 100 calculates the toner charge amount using the called development DC bias value.

FIG. 15 is a graph showing the relationship between the development DC bias and the toner charge amount.
As shown in FIG. 15, when the development DC bias increases, the potential when the toner adheres to the photoconductor 41 increases, so the toner charge amount also increases. Since the fluctuation factor of the development DC bias is mainly the toner charge amount, the toner charge amount calculated from the development DC bias approximates the actual measurement value. As a result, according to the third calculation method, a more accurate toner transfer fluctuation amount P3 can be calculated, and the stability of the image density can be improved.

[Fourth Calculation Method of Toner Charge Amount]
Next, a fourth method for calculating the toner charge amount will be described.
In the fourth calculation method, the control unit 100 determines, for example, the value of the current flowing through the developing unit 44 when the secondary transfer roller 61 and the intermediate transfer belt 50 are separated from each other during the stabilization batch correction. Measure by. The control unit 100 calculates the toner charge amount from the current value and the toner adhesion amount per unit area on the intermediate transfer belt. The toner adhesion amount per unit area is obtained from a value detected by the IDC sensor 91 based on a toner image formed on the intermediate transfer belt 50 in a state where the secondary transfer roller 61 and the intermediate transfer belt 50 are separated from each other. .

  Specifically, the control unit 100 integrates the measured current value and obtains the total charge amount of the toner moved when developing the toner image. Then, the control unit 100 calculates the toner charge amount from the obtained total charge amount and the toner adhesion amount per unit area.

  The toner charge amount calculated by the fourth calculation method is an actual measurement value when performing the inter-image stabilization correction process. Therefore, more accurate correction can be performed.

  The toner charge amount calculation method may be performed by combining the first to fourth calculation methods described above.

[First Calculation Method of Resistance Value of Transfer Member]
Next, a first calculation method of the resistance value of the transfer body will be described with reference to FIGS.
FIG. 16 is a graph showing the relationship between the resistance value of the transfer member and the rotation speed of the intermediate transfer belt 50 or the secondary transfer roller 61, and FIG. 17 is a graph showing the relationship between the resistance value of the transfer member and temperature or humidity information. It is.

  In the first calculation method, the control unit 100 counts the number of rotations of the intermediate transfer belt 50 or the secondary transfer roller 61. Further, the control unit 100 acquires temperature information from the thermometer 97 or acquires humidity information from the hygrometer 98. Then, the control unit 100 calculates the resistance value of the transfer body using at least one information among the temperature or humidity information and the rotation speed information of the intermediate transfer belt 50 or the secondary transfer roller 61.

  Here, when the rotation speed of the intermediate transfer belt 50 or the secondary transfer roller 61 increases, the intermediate transfer belt 50 or the secondary transfer roller 61 deteriorates over time. For this reason, as shown in FIG. 16, it becomes difficult for current to flow to the intermediate transfer belt 50 or the secondary transfer roller 61 due to aging, and the resistance value of the transfer body increases.

  Further, as shown in FIG. 17, it can be seen that the resistance value of the transfer body decreases as the temperature or humidity increases. The temperature information and the humidity information may be acquired from the same thermometer and hygrometer used in the first toner charge amount calculation method. Further, a thermometer and a hygrometer may be provided in the vicinity of the intermediate transfer belt 50 or the secondary transfer roller 61. Thereby, the temperature information and humidity information of the intermediate transfer belt 50 or the secondary transfer roller 61 can be acquired more accurately.

  As described above, according to the first calculation method, a plurality of pieces of information relating to the resistance value of the transfer body such as the temperature or humidity information and the rotation speed information of the intermediate transfer belt 50 or the secondary transfer roller 61 are used. Thereby, the toner transfer fluctuation amount P3 at the time of inter-image stabilization correction can be accurately calculated, and the stability of the image density can be improved and a high-quality image can be stably formed.

  In addition, since a real-time value related to the resistance value of the transfer member can be used during the inter-image stabilization correction, it is possible to immediately cope with fluctuations in the toner transfer amount.

[Second calculation method of resistance value of transfer member]
Next, a second calculation method of the resistance value of the transfer body will be described.
In the second calculation method, the control unit 100 applies a constant current to the secondary transfer roller 61. And the control part 100 calculates resistance value from the change of the voltage value in that case. Since the resistance value calculated by the second calculation method is a measured value of the resistance value of the transfer body, the correction value can be calculated more accurately.

  The method for calculating the resistance value of the transfer member may be performed by combining the first calculation method and the second calculation method described above. Further, the first to fourth calculation methods for the toner charge amount may be combined with the first to second calculation methods for the resistance value of the transfer member.

  According to the image forming apparatus 1 of this example, the difference value Q3 between the detection value Q2 of the IDC sensor and the target value Q1 is corrected using the toner charge amount that is a disturbance that changes the toner transfer amount and the resistance value of the transfer body. ing. As a result, it is possible to predict the amount of toner transfer and perform correction in consideration of disturbance. As a result, it is possible to improve the calculation accuracy of the correction value Q4 for correcting the image forming condition, improve the stability of the image density, and stably form a high quality image.

  The embodiment of the image forming apparatus has been described above including its effects. However, the image forming apparatus of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention described in the claims.

  In the above-described embodiment, the color image is formed using the four sets of image forming units 40Y, 40M, 40C, and 40K. However, the image forming apparatus according to the present invention includes one image forming unit. It may be configured to form a monochromatic image by using it.

  Further, the image forming apparatus 1 described above has an intermediate transfer belt as a transfer material for transferring a toner image formed on the photosensitive member, and is configured to secondarily transfer an image from the intermediate transfer belt to a sheet. However, the image forming apparatus according to the present invention may have a configuration in which a toner image is directly transferred from a photosensitive member to a sheet conveyed by a belt member.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Document conveying part, 20 ... Paper storage part, 30 ... Image reading part, 40 ... Image forming part, 41 ... Photoconductor, 42 ... Charging part, 43 ... Exposure part, 44 ... Developing part, 44a ... Stirring unit 44b ... Developing roller 45 ... Cleaning unit 50 ... Intermediate transfer belt (image carrier) 51 ... Primary transfer unit 60 ... Secondary transfer unit (transfer unit) 61 ... Secondary transfer roller (Transfer roller), 62 ... secondary transfer nip part (transfer nip part), 80 ... fixing part, 91 ... IDC sensor (concentration detection sensor), 97 ... thermometer, 98 ... hygrometer, 100 ... control part, P1 ... Inter-image correction patch (correction patch toner image), P3 ... toner transfer fluctuation amount, Q1 ... target value, Q2 ... detection value (correction patch detection value), Q3 ... difference value, Q4 ... correction value

Claims (9)

An image carrier;
An image forming unit that has a developing unit and forms a toner image for a correction patch or an image by attaching toner to the image carrier;
A transfer unit disposed in contact with the image carrier;
A density detection sensor that is disposed downstream of the transfer portion in the image carrier and detects a toner density of the toner image for the correction patch formed on the image carrier;
A control unit that corrects an image forming condition of the image forming unit based on a detection value detected by the density detection sensor;
The controller is
An image forming apparatus for correcting an image forming condition of the image forming unit by correcting a detection value detected by the density detection sensor based on at least one of a charge amount of the toner and a resistance value of the transfer unit. The charge amount of the toner includes coverage information that is a ratio of an image area formed on a sheet, developer usage information of the developing unit, temperature information of the toner, humidity information of the toner, and information on the image forming unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is calculated from at least one or more pieces of development stop time information. The image forming apparatus according to claim 2, wherein the coverage information is an integration value or an average value of the number of executions of predetermined image formation performed by the image forming unit. The image forming apparatus according to claim 1, wherein the charge amount of the toner is calculated from toner density information obtained by a toner density sensor in a developing unit provided in the developing unit. The image forming apparatus according to claim 1, wherein the charge amount of the toner is calculated from a preset development DC bias of the image forming unit. The toner charge amount is calculated from the current value in the step of developing the correction patch toner image detected by the developing current detection unit and the toner amount of the correction patch toner image detected by the density detection sensor. The image forming apparatus according to claim 1. The transfer section has a transfer roller that contacts the image carrier,
The resistance value of the transfer unit is at least one of rotation number information of the image carrier or the transfer roller, temperature information of the image carrier or the transfer roller, and humidity information of the image carrier or the transfer roller. The image forming apparatus according to claim 1, wherein the image forming apparatus is calculated from the information. The image forming apparatus according to claim 1, wherein the resistance value of the transfer unit is calculated from a voltage value when a constant current value is applied to the transfer unit. The control unit calculates a fluctuation amount of toner transferred from the correction patch toner image to the transfer unit using at least one or more information of the charge amount of the toner and the resistance value of the transfer unit. Item 9. The image forming apparatus according to any one of Items 1 to 8.

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