JP2016114844A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can accurately adjust the density of an image formed on an image formation object.SOLUTION: There is provided an image forming apparatus comprising: image forming means, such as an image forming part 43 that forms an image on an image formation object, such as an intermediate transfer belt 51; a density sensor, such as a density sensor 40 that includes an image element, such as an image element 102 having a plurality of light receiving elements, such as light receiving elements 103 arranged side by side along the width direction of the image formation object, and detects the density of an image for adjustment, such as a toner image Tn for adjustment; and control means, such as a control part 41 for correcting the density of an image to be formed on the basis of an output from the density sensor, the image forming apparatus including moving means, such as an actuator 104 that moves the density sensor in the width direction of a transfer medium, where the control means controls to move the density sensor to detect the density of the image.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus.

  As an image forming apparatus, an apparatus that forms an image such as a toner image on an image forming object such as paper or a transfer medium is known.

  In Patent Document 1, in such an image forming apparatus, in order to adjust the image density, an image density (toner adhesion amount) of a toner image formed on a transfer medium is detected by a density sensor, and based on the detected information. Are described for controlling the image forming conditions. The density sensor has an image element (line sensor) in which a plurality of light receiving elements are arranged side by side along the width direction of the transfer medium.

  By detecting the image density with the image element, it is possible to obtain an image density distribution in the width direction of an image forming object such as a transfer medium. However, in the image forming apparatus of Patent Document 1, since the image density of the image on the image forming object cannot be detected at the interval portion between the light receiving elements, the accuracy in the width direction of the image forming object is high. The density distribution of the image cannot be obtained. For this reason, there has been a problem that the density of an image formed on the image forming object cannot be adjusted with high accuracy.

  In order to solve the above-described problems, the present invention includes an image forming unit that forms an image on an image forming object, and an image element in which a plurality of light receiving elements are arranged side by side along the width direction of the image forming object. In an image forming apparatus having a density sensor for detecting an image density and a control unit for correcting the density of an image formed based on an output of the density sensor, the movement for moving the density sensor in the width direction of the transfer medium And the control means controls to detect the image density while moving the density sensor.

  It is possible to accurately adjust the density of the image formed on the image forming object.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is a schematic configuration diagram of a density sensor of the printer. Explanatory drawing about the image element of the density sensor. FIG. 3 is an explanatory diagram of a formation position on an intermediate transfer belt of an adjustment toner image and a sensor position detection toner image that are formed when the printer starts an image density adjustment operation. 2 is a diagram illustrating a functional configuration of a control unit of the printer. FIG. FIG. 6 is a schematic diagram illustrating an example of a distribution of toner adhesion amount of an adjustment toner image in the belt width direction acquired by the density sensor. FIG. 6 is a schematic diagram illustrating an example of a distribution of toner adhesion amount of an adjustment toner image when a defect in which toner is not adhered is part of the adjustment toner image. FIG. 3 is an explanatory diagram of a pattern shape of a sensor position detection toner image formed when the printer starts an image density adjustment operation. FIG. 6 is a schematic diagram showing a state where a sensor position detection toner image is detected through a light receiving element of an image element in the density sensor. 6 is a graph showing an example of an output value of toner adhesion amount detected through a light receiving element. FIG. 9 is a schematic diagram illustrating a modified example of a sensor position detection toner image. FIG. 9 is a schematic diagram showing a state where a sensor position detection toner image according to a modification is detected through a light receiving element of an image element in a density sensor. The graph of the output value of the toner adhesion amount of each color of R, G, B detected through the light receiving element.

Hereinafter, an embodiment in which the present invention is applied to a printer which is an electrophotographic image forming apparatus will be described with reference to the drawings. The image forming apparatus to which the present invention can be applied is not limited to an electrophotographic system, and may be applied to other systems such as an ink jet system and a thermal transfer system.
FIG. 1 is a schematic configuration diagram illustrating a printer according to the present embodiment.
The printer includes a control unit 41, an image processing unit 42, an image forming unit 43, and the like.

  The control unit 41 includes, for example, a CPU (Central Processing Unit) and a memory, and controls the image forming unit 43. Specifically, the control unit 41 causes the image forming unit 43 to form an image according to the control parameter. This control parameter is used as a condition to be followed when the image forming unit 43 forms an image. The image processing unit 42 includes, for example, an application specific integrated circuit (ASIC) and a memory, and performs various types of image processing on image data input from a client device such as a PC (personal computer) or a scanner device.

The image forming unit 43 includes photoreceptors 1a, 1b, 1c, and 1d, charging devices 8a, 8b, 8c, and 8d, an exposure device 13, developing devices 12a, 12b, 12c, and 12d, an intermediate transfer belt 51, and a secondary transfer belt 61. And a fixing device 18.
Different color toner images are formed on the photoreceptors 1a, 1b, 1c, and 1d, respectively. Specifically, a black toner image, a magenta toner image, a cyan toner image, and a yellow toner image are formed on these photoreceptors 1a, 1b, 1c, and 1d, respectively. Note that each of the photoconductors 1a, 1b, 1c, and 1d in the present embodiment is formed in a drum shape, but an endless belt-like photoconductor wound around a plurality of rollers and driven to rotate can also be used.

  An intermediate transfer belt 51, which is an endless belt-like member, is disposed as an intermediate transfer member that is an image carrier, facing the four photosensitive members 1a, 1b, 1c, and 1d. The outer peripheral surfaces of the photoreceptors 1a, 1b, 1c, and 1d are in contact with the outer peripheral surface of the intermediate transfer belt 51, respectively. The intermediate transfer belt 51 according to the present embodiment is wound and stretched around a support roller (support rotary body) such as a tension roller 52, a drive roller 53, a repulsive roller 54, and an entrance roller 55. A driving roller 53, which is one of these support rollers, is rotationally driven by a driving source, and the intermediate transfer belt 51 travels in the direction of arrow A in the drawing by the rotational driving of the driving roller 53.

  The intermediate transfer belt 51 may have a multilayer structure or a single layer structure. When the belt is composed of a multilayer structure, for example, a base layer is formed of a less stretched fluororesin, PVDF sheet, or polyimide resin, and the belt outer peripheral surface is composed of a smooth coat layer such as a fluororesin. preferable. On the other hand, when a belt having a single layer structure is used, a material such as PVDF, PC, or polyimide is preferably used.

  The configuration and operation for forming each color toner image on each photoconductor 1a, 1b, 1c, 1d and the configuration and operation for primary transfer of each color toner image onto the intermediate transfer belt 51 are substantially the same and formed. Only the color of each color toner image is different. Therefore, hereinafter, a configuration and operation for forming a black toner image on the black photoconductor 1a and primarily transferring the toner image onto the intermediate transfer belt 51 will be described, and description of other colors will be omitted.

  The black photoconductor 1a is driven to rotate counterclockwise in FIG. The surface potential of the photosensitive member 1a is initialized by irradiating the outer peripheral surface of the photosensitive member 1a with light from the static eliminator. The initialized outer peripheral surface of the photoconductor is uniformly charged to a predetermined polarity (in this embodiment, a negative polarity) by the charging device 8a. The photoconductor outer peripheral surface charged in this way is irradiated with a light-modulated laser beam L emitted from the exposure device 13, whereby an electrostatic latent image is formed on the outer peripheral surface of the photoconductor 1a.

  In the present embodiment, the exposure device 13 that emits the laser beam L is constituted by a laser writing device. However, for example, an exposure device 13 having an LED array and an imaging means can be used. The electrostatic latent image formed on the photoconductor 1a is visualized as a black toner image when passing through a developing area facing the developing device 10a.

  On the inner peripheral surface side of the intermediate transfer belt 51, a primary transfer roller 11a is disposed at a position facing the photoreceptor 1a. When the primary transfer roller 11 a contacts the inner peripheral surface of the intermediate transfer belt 51, an appropriate primary transfer nip is ensured between the photoreceptor 1 a and the intermediate transfer belt 51. The primary transfer roller 11a is applied with a primary transfer voltage having a polarity opposite to the toner charging polarity of the toner image formed on the photoreceptor 1a (plus polarity in the present embodiment). As a result, a primary transfer electric field is formed between the photoreceptor 1a and the intermediate transfer belt 51, and the toner image on the photoreceptor 1a is statically transferred onto the intermediate transfer belt 51 that is driven to rotate in synchronization with the photoreceptor 1a. Electrically primary transferred. The transfer residual toner adhering to the outer peripheral surface of the photoconductor 1a after the toner image is primarily transferred to the intermediate transfer belt 51 is removed by the cleaning device 12a, and the outer peripheral surface of the photoconductor 1a is cleaned.

  In the full color mode using all four color toner images, magenta toner images, cyan toner images, and yellow toner images are similarly formed on the photoconductors 1b, 1c, and 1d of other colors. These color toner images are sequentially primary-transferred so as to be superimposed on the black toner image primarily transferred onto the intermediate transfer belt 51.

  On the other hand, in the black single color mode, the primary transfer rollers 11b, 11c, and 11d are separated from the photoreceptors 1b, 1c, and 1d by the contact / separation mechanism, thereby causing the photoreceptors 1b, 1c, and 1d for magenta, cyan, and yellow to be separated. Separated from the intermediate transfer belt 51. Only the black toner image is primarily transferred to the intermediate transfer belt 51 while only the black photosensitive member 1 a is in contact with the intermediate transfer belt 51.

  As shown in FIG. 1, a paper feeding device 14 is disposed at the lower part of the printer body. The paper feeding device 14 feeds the transfer paper P as a recording material in the direction of arrow B in the figure by the rotation of the paper feeding roller 15. The transferred transfer paper P is subjected to a contact between the intermediate transfer belt 51 wound around the repulsive roller 54 at a predetermined timing by the registration roller pair 16 and the secondary transfer belt 61 disposed opposite thereto. It is fed to the secondary transfer nip that is in contact. At this time, a predetermined secondary transfer voltage is applied to the repulsive roller 54 by a secondary transfer voltage power source as a transfer voltage output means, whereby the toner image on the intermediate transfer belt 51 is secondarily transferred to the transfer paper P. .

  The secondary transfer belt 61 is stretched between a secondary transfer roller 62 and a separation roller 63. The secondary transfer belt 61 travels in the direction indicated by the arrow C in the drawing by rotating one of the rollers (supporting rotating body) as a driving roller. The transfer paper P onto which the toner image has been secondarily transferred is conveyed as the secondary transfer belt 61 travels while being electrostatically attracted to the outer peripheral surface of the secondary transfer belt 61. The transfer paper P is separated from the outer peripheral surface of the secondary transfer belt 61 by the curvature of the portion of the secondary transfer belt 61 wound around the separation roller 63, and is disposed downstream of the secondary transfer belt 61 in the transfer paper transport direction. It is further conveyed downstream in the transfer sheet conveying direction by the conveying belt 17. When the transfer paper P passes through the fixing device 18, the toner image on the transfer paper P is fixed to the transfer paper P by the action of heat and pressure. The transfer paper P that has passed through the fixing device 18 is discharged out of the apparatus through a pair of paper discharge rollers 19 provided in the paper discharge unit.

  The printer includes a density sensor 40, a density correction unit 74, a reading control unit 71, and the like for correcting image density or density unevenness. The density correction unit 74 and the reading control unit 71 have the functions of the control unit 41. For example, the density correction unit 74 and the reading control unit 71 are realized by the CPU executing a program stored in the memory. This program may be a single program or a plurality of programs.

  The density sensor (line sensor) 40 optically reads the adjustment toner image Tn formed on the intermediate transfer belt 51. The density sensor 40 has a traveling direction of the intermediate transfer belt 51 (arrow A in the drawing) rather than the primary transfer roller 11a which is a primary transfer roller disposed at the most downstream side in the traveling direction of the intermediate transfer belt 51 (arrow A in the drawing). ) On the downstream side. Further, the density sensor 40 is disposed upstream of the secondary transfer roller 62 in the traveling direction of the intermediate transfer belt 51 (arrow A in the figure). In this embodiment, the adjustment toner image Tn is formed on the intermediate transfer belt 51 and is read by the density sensor 40. However, the present invention is not limited to this. For example, the adjustment toner image Tn is transferred to the transfer paper. P may be formed and read by the density sensor 40.

FIG. 2 is a diagram showing a schematic configuration of the density sensor 40.
As shown in FIG. 2, the density sensor 40 includes a light source 100, a lens array 101, and an image element 102 inside. Further, the density sensor 40 has an actuator 104 that can move the density sensor 40 in the belt width direction on the intermediate transfer belt 51 (a direction perpendicular to the traveling direction of the intermediate transfer belt 51 indicated by an arrow A in the figure). ing.

  As the light source 100, a light emitting element provided at the end of a light guide or an LED array can be used. The light source 100 emits RGB light. As the lens array 101, a SELFOC (registered trademark) lens is used. The image element 102 receives the light imaged by the lens array 101 and outputs a signal corresponding to the received light. As the image element 102, a CMOS sensor, a CCD sensor, or the like is used. Since the reading width of the density sensor 40 is longer than the image forming region in the belt width direction on the intermediate transfer belt 51 (the direction perpendicular to the traveling direction of the intermediate transfer belt 51 indicated by the arrow A in the drawing), It is possible to detect the toner adhesion amount of the toner image T over the entire area.

FIG. 3 is a diagram illustrating the image element 102.
As shown in FIG. 3A, the image element 102 has a plurality of small light receiving elements 103 arranged side by side. FIG. 3B is an enlarged view of a region D surrounded by a dotted line in FIG. 3A, but a gap E is generated between the light receiving element 103a and the light receiving element 103b. A gap such as a gap E is generated between adjacent light receiving elements, but the toner adhesion amount of the toner image cannot be read through these gaps. Therefore, the adjustment toner image Tn is read while moving the density sensor 40 including the image element 102 in the direction in which the light receiving elements 103 are arranged (arrow H in the figure). As a result, the toner adhesion amount of the toner image can be read even at a location on the intermediate transfer belt 51 that is located in the gap between the light receiving elements.

FIG. 4 is a diagram illustrating the formation positions on the intermediate transfer belt 51 of the adjustment toner image Tn and the sensor position detection toner image Tp that are formed when the image density adjustment operation is started.
In FIG. 4, the traveling direction of the intermediate transfer belt 51 is indicated by an arrow G, the belt width direction of the intermediate transfer belt 51 is indicated by an arrow F, and the moving direction of the density sensor 40 including the image element 102 is indicated by an arrow H. The adjustment toner image Tn includes density information patterns Tna, Tnb, Tnc, and Tnd for each color of black (K), magenta (M), cyan (C), and yellow (Y). A sensor position detecting toner image Tp for detecting the position of the density sensor 40 is formed on each of the density information patterns Tna, Tnb, Tnc, and Tnd on the upstream side and the downstream side in the running direction of the intermediate transfer belt 51.

  This printer performs an image density adjustment operation at a predetermined timing in order to stabilize the image density. The predetermined timing is, for example, when the printer is turned on, when image formation is started, between sheets during continuous image formation (between the recording material and the recording material), or when image formation is completed. The image density adjustment operation in this printer will be described below.

  FIG. 5 is a diagram illustrating a functional configuration of the control unit 41. The control unit 41 includes a pattern formation control unit 70, a reading control unit 71, a sensor position detection unit 72, a toner adhesion amount distribution calculation unit 73, a density correction unit 74, and the like. The pattern formation control unit 70 controls the formation of the adjustment toner image Tn and the sensor position detection toner image Tp. The reading control unit 71 reads the toner adhesion amount of the adjustment toner image Tn by the density sensor 40 and controls the actuator 104 that moves the density sensor 40. The sensor position detection unit 72 detects the position of the intermediate transfer belt 51 of the density sensor 40 in the belt width direction. The toner adhesion amount distribution calculation unit 73 determines the position of the density sensor 40 detected by the sensor position detection unit 72 in the belt width direction of the intermediate transfer belt 51 and the toner adhesion amount of the adjustment toner image Tn read by the density sensor 40. Based on this, the distribution of the toner adhesion amount of the adjustment toner image Tn is calculated. The density correction unit 74 adjusts various parameters for controlling the image forming conditions based on the distribution of the toner adhesion amount of the adjustment toner image Tn.

  When the image density adjustment operation is started, first, an adjustment toner image Tn and a sensor position detection toner image Tp are formed on the intermediate transfer belt 51. Then, the density sensor 40 reads the toner adhesion amount of the adjustment toner image Tn while moving in the belt width direction of the intermediate transfer belt 51. The density sensor 40 outputs a signal corresponding to the read toner adhesion amount. This signal is input to the density correction unit 74.

  If the moving speed of the density sensor 40 is known, the position of the density sensor 40 in the belt width direction of the intermediate transfer belt 51 when the density sensor 40 is detecting the adjustment toner image Tn can be detected. Based on the toner adhesion amount of the sensor position detection toner image Tp read by the density sensor 40, the sensor position detection unit 72 as sensor position detection means calculates the moving speed of the density sensor 40 and performs intermediate transfer of the density sensor 40. The position of the belt 51 in the belt width direction is detected. A method for calculating the moving speed of the density sensor 40 will be described later. Based on the toner adhesion amount of the sensor position detection toner image Tp read by the density sensor 40 and the moving speed of the density sensor 40, the toner adhesion amount distribution calculation unit 73 applies the toner adhesion amount of the adjustment toner image Tn in the belt width direction. The distribution of is calculated.

FIG. 6 is a schematic diagram illustrating an example of the distribution of the toner adhesion amount of the adjustment toner image Tn with respect to the belt width direction F (see FIG. 4) acquired by the density sensor 40.
When the density sensor 40 is not moved in the direction of the arrow H in FIG. 4, the toner adhesion amount of the adjustment toner image Tn cannot be read in the gap between the light receiving elements, and the distribution of the obtained toner adhesion amount is as shown in FIG. It becomes like this. On the other hand, when the density sensor 40 is moved in the direction of arrow H in FIG. 4, the toner adhesion amount of the adjustment toner image Tn can be read in the gap between the light receiving elements. Is as shown in FIG.

  FIG. 7 is a schematic diagram illustrating an example of the distribution of the toner adhesion amount of the adjustment toner image Tn when there is a defect in which toner is not attached to a part of the adjustment toner image Tn. If there is a defect in which toner does not adhere to a part of the adjustment toner image Tn, the output value of the toner adhesion amount at that position becomes lower than the output value at the adjacent position. By utilizing this, it is possible to detect defects in the sub-scanning direction (belt width direction F in FIG. 4). Specifically, at each position in the main scanning direction (traveling direction G of the intermediate transfer belt in FIG. 4), an output value of the toner adhesion amount at a certain position, and an output value of the toner adhesion amount at a position adjacent to the certain position, Calculate the difference. When the difference is equal to or greater than a predetermined threshold, it is determined that there is a defect at the certain position.

  Various parameters for controlling the image forming conditions are adjusted based on the obtained distribution of the toner adhesion amount. For example, when the toner adhesion amount distribution is large in the central portion on the intermediate transfer belt 51 in the main scanning direction, the amount of light written by the exposure device 13 is decreased in the central portion. By doing so, the toner adhesion amount on the intermediate transfer belt 51 in the belt direction can be made uniform.

  After the toner adhesion amount on the intermediate transfer belt 51 in the belt direction is made uniform, an adjustment toner image Tn is formed, and the toner adhesion amount detected from the adjustment toner image Tn is compared with the desired toner adhesion amount. Do. Various parameters for controlling image forming conditions are adjusted so that the toner adhesion amount becomes a desired toner adhesion amount.

Calculation of the moving speed of the density sensor 40 will be described below.
FIG. 8 is a diagram illustrating the pattern shape of the sensor position detection toner image Tp.
In FIG. 8, the traveling direction of the intermediate transfer belt 51 is indicated by an arrow G, and the sensor position detection toner image Tp located upstream in the traveling direction of the intermediate transfer belt 51 is replaced with the upstream sensor position detection toner image Tpu, the intermediate transfer belt. The sensor position detection toner image Tp located on the downstream side in the running direction 51 is defined as a downstream sensor position detection toner image Tpl.

  Both the upstream sensor position detection toner image Tpu and the downstream sensor position detection toner image Tpl have the same pattern shape and are aligned with each other along the belt width direction of the intermediate transfer belt 51 (arrow F in the figure). It is formed from a plurality of line segments having different widths. Line segments of the upstream sensor position detection toner image Tpu are denoted as Tpu_1, Tpu_2, Tpu_3, Tpu_4, and Tpu_5 from the left in the drawing. Line segments of the downstream sensor position detection toner image Tpl are denoted by Tpl_1, Tpl_2, Tpl_3, Tpl_4, and Tpl_5 from the left in the drawing. Tpu_1 and Tpl_1, Tpu_2 and Tpl_2, Tpu_3 and Tpl_3, Tpu_4 and Tpl_4, and Tpu_5 and Tpl_5 have the same shape.

  In FIG. 8, in the upstream sensor position detection toner image Tpu and the downstream sensor position detection toner image Tpl, the line segments are arranged in order of increasing width from the left in the figure, but the present invention is not limited to this. What is necessary is just to have a mutually different width | variety in the some line segment which comprises the toner image Tp for sensor position detection. The width of each line segment is set to be equal to or larger than the minimum width detectable by the light receiving element 103. Further, the number of line segments is not limited to five. The number of line segments is determined according to the light receiving element to be used and the length of the gap between adjacent light receiving elements.

  The length I in the belt width direction of the upstream sensor position detecting toner image Tpu and the downstream sensor position detecting toner image Tpl is the length E of the gap between the light receiving element 103a and the light receiving element 103b, and a density sensor 40 described later. Longer than the moving distance L. Further, the upstream sensor position detecting toner image Tpu is formed away from the downstream sensor position detecting toner image Tpl by a predetermined distance J.

FIG. 9 is a schematic diagram showing a state in which the sensor position detection toner image Tp is being detected via the light receiving element 103 of the image element 102 in the density sensor 40.
When the intermediate transfer belt 51 moves in the direction of arrow G in the figure, the density sensor 40 moves in the direction of arrow F in the figure, while the downstream sensor position detection toner image Tpl, the adjustment toner image Tn, and the upstream sensor position. The toner images are detected in the order of the detection toner image Tpu.

  FIG. 9A shows a state in which the light receiving elements 103a and 103b of the image element 102 in the density sensor 40 are detecting the downstream sensor position detecting toner image Tpl. FIG. 9B shows a state where the light receiving elements 103a and 103b of the image element 102 in the density sensor 40 are detecting the upstream sensor position detecting toner image Tpu. The left end of the light receiving element 103a is indicated by M1, and the right end is indicated by M2. The left end of the light receiving element 103b is indicated by N1, and the right end is indicated by N2.

In contrast to the state shown in FIG. 9A, in the state shown in FIG. 9B, the image element 102 has moved by the moving distance L in the belt width direction F. The moving distance L is set to be longer than the length E (see FIG. 8) of the gap between the light receiving element 103a and the light receiving element 103b. If the running speed of the intermediate transfer belt 51 is v _G , the time t required to change from the state shown in FIG. 9A to the state shown in FIG. 9B can be expressed by t = J / v _G.

FIG. 10 is a graph of the output value of the toner adhesion amount detected through the light receiving elements 103a and 103b. In the figure, the horizontal axis indicates the position of the light receiving element in the belt width direction F (see FIG. 9), and the vertical axis indicates an example of the output value of the toner adhesion amount.
10A-1 shows the toner adhesion amount detected through the light receiving element 103a in the state of FIG. 9A, and FIG. 10A-2 shows the light receiving element 103a in the state of FIG. 9B. The amount of toner adhesion detected via each is shown. FIG. 10B-1 shows the toner adhesion amount detected through the light receiving element 103b in the state of FIG. 9A, and FIG. 10B-2 shows the light receiving element in the state of FIG. 9B. The toner adhesion amounts detected via 103b are respectively shown.

  K1 in FIG. 10A-1 represents the left end portion of the line segment Tpl_1. As shown in FIG. 10A-1, the position of the left end portion of the line segment Tpl_1 in the light receiving element 103a in the belt width direction F is S1. Further, K2 in FIG. 10A-2 indicates the left end portion of the line segment Tpu_1. As shown in FIG. 10A-2, the position of the left end portion of the line segment Tpu_1 in the light receiving element 103a in the belt width direction F is S2. The moving distance L of the density sensor 40 can be calculated from the difference between the position S1 and the position S2.

  K3 in FIG. 10B-1 indicates the right end portion of the line segment Tpl_5. As shown in FIG. 10 (b-1), the position of the right end portion of the line segment Tpl_5 in the light receiving element 103b in the belt width direction F is S3. Moreover, K4 in FIG.10 (b-2) has shown the right end part of line segment Tpu_5. As shown in FIG. 10B-2, the position of the right end portion of the line segment Tpu_5 in the light receiving element 103b in the belt width direction F is S4. The moving distance L of the density sensor 40 can be calculated from the difference between the position S3 and the position S4.

  That is, in at least one line segment, the left end position of the line segment can be confirmed in either of the states shown in FIGS. 9A and 9B, or the right end position of the line segment is determined in FIG. If it can be confirmed in either of the states shown in FIGS. 9A and 9B, the moving distance L of the density sensor 40 can be calculated. If the moving distance L of the density sensor 40 is divided by the time t required to change from the state shown in FIG. 9A to the state shown in FIG. 9B, the moving speed of the density sensor 40 can be obtained. it can.

[Modification]
Next, a modified example of the sensor position detecting toner image Tp according to the embodiment will be described.
FIG. 11 is a schematic diagram illustrating an example of a sensor position detection toner image Tp according to the present modification.
In FIG. 11, the traveling direction of the intermediate transfer belt 51 is indicated by an arrow G, and the sensor position detecting toner image Tp located on the upstream side of the traveling direction of the intermediate transfer belt 51 is represented by the upstream sensor position detecting toner image Tpu, the intermediate transfer belt. The sensor position detection toner image Tp located on the downstream side in the running direction 51 is defined as a downstream sensor position detection toner image Tpl.

  Both the upstream sensor position detection toner image Tpu and the downstream sensor position detection toner image Tpl have the same pattern shape, and a plurality of different colors arranged in the belt width direction (arrow F in the figure). It is formed from line segments. For example, Tpu_6 and Tpl_6 are black, Tpu_7 and Tpl_7 are cyan, Tpu_8 and Tpl_8 are magenta, Tpu_9 and Tpl_9 are yellow, Tpu_10 and Tpl_10 are red, Tpu_11 and Tpl_11 are green, and Tpu_12 are green. , Formed with. As the light receiving element 103 of the image element 102 provided in the density sensor 40, an element capable of discriminating color information (RGB) is used. R: G: B = 0: 0: 0 is black, R: G: B = 0: 1: 1 is cyan, R: G: B = 1: 0: 1 is magenta, R: G: B = 1: 1: 0 for yellow, R: G: B = 1: 0: 0 for red, R: G: B = 0: 1: 0 for green, R: G: B = 0: 0: 1 for blue Become.

  In the sensor position detection toner image Tp in the embodiment described with reference to FIG. 8, the widths of the respective line segments are different from each other. However, in the sensor position detection toner image Tp of the present modification, the widths of the respective line segments are the same. It's okay. The width of each line segment may be equal to or greater than the minimum length that can be detected by the light receiving element 103. When the width of the line segment is set to the minimum length that can be detected by the light receiving element 103, the toner for forming the sensor position detecting toner image Tp with respect to the sensor position detecting toner image Tp in the embodiment described in FIG. Consumption can be reduced.

  The length I in the belt width direction of the upstream sensor position detecting toner image Tpu and the downstream sensor position detecting toner image Tpl is the length E of the gap between the light receiving element 103a and the light receiving element 103b, and a density sensor 40 described later. Longer than the moving distance L. Further, the upstream sensor position detecting toner image Tpu is formed away from the downstream sensor position detecting toner image Tpl by a predetermined distance J.

FIG. 12 is a schematic diagram showing a state in which the sensor position detection toner image Tp is being detected via the light receiving element 103 of the image element 102 in the density sensor 40.
When the intermediate transfer belt 51 moves in the direction of arrow G in the figure, the density sensor 40 moves in the direction of arrow F in the figure, while the downstream sensor position detection toner image Tpl, the adjustment toner image Tn, and the upstream sensor position. The toner images are detected in the order of the detection toner image Tpu.

  FIG. 12A shows a state where the light receiving elements 103a and 103b of the image element 102 in the density sensor 40 are detecting the downstream sensor position detecting toner image Tpl. FIG. 12B shows a state in which the light receiving elements 103a and 103b of the image element 102 in the density sensor 40 detect the upstream sensor position detection toner image Tpu. The left end of the light receiving element 103a is indicated by M1, and the right end is indicated by M2. The left end of the light receiving element 103b is indicated by N1, and the right end is indicated by N2.

In contrast to the state shown in FIG. 12A, in the state shown in FIG. 12B, the image element 102 moves in the belt width direction F by the moving distance L. The movement distance L is set to be longer than the length E (see FIG. 11) of the gap between the light receiving element 103a and the light receiving element 103b. If the running speed of the intermediate transfer belt 51 is v _G , the time t required to change from the state shown in FIG. 12A to the state shown in FIG. 12B can be expressed by t = J / v _G.

FIG. 13 is a graph of the output values of the toner adhesion amounts of the R, G, and B colors detected through the light receiving elements 103a and 103b. In the figure, the horizontal axis indicates the position of the light receiving element in the belt width direction F (see FIG. 9), and the vertical axis indicates the output value of the toner adhesion amount.
13A-1 shows the toner adhesion amount detected through the light receiving element 103a in the state of FIG. 12A, and FIG. 13A-2 shows the light receiving element 103a in the state of FIG. 12B. The amount of toner adhesion detected via each is shown. FIG. 13B-1 shows the toner adhesion amount detected through the light receiving element 103b in the state of FIG. 12A, and FIG. 13B-2 shows the light receiving element in the state of FIG. The toner adhesion amounts detected via 103b are respectively shown.

  K5 in FIG. 13B-1 indicates the right end portion of the line segment Tpl_12. As shown in FIG. 13 (b-1), the position of the right end portion of the line segment Tpl_12 in the light receiving element 103b in the belt width direction F is S5. Moreover, K6 in FIG.13 (b-2) has shown the right end part of line segment Tpu_12. As shown in FIG. 13B-2, the position of the right end portion of the line segment Tpu_1 in the light receiving element 103a in the belt width direction F is S6. The moving distance L of the density sensor 40 can be calculated from the difference between the position S5 and the position S6.

  That is, in at least one line segment, the left end position of the line segment can be confirmed in either of the states shown in FIGS. 12A and 12B, or the right end position of the line segment is shown in FIG. If it can be confirmed in either of the states shown in FIGS. 12A and 12B, the moving distance L of the density sensor 40 can be calculated. If the moving distance L of the density sensor 40 is divided by the time t required to change from the state shown in FIG. 12A to the state shown in FIG. 12B, the moving speed of the density sensor 40 can be obtained. it can.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
An image forming unit such as an image forming unit 43 that forms an image on an image forming object such as the intermediate transfer belt 51 and a plurality of light receiving elements such as a plurality of light receiving elements 103 are arranged along the width direction of the image forming object. A density sensor such as a density sensor 40 that includes an image element such as the image element 102 and detects the density of an adjustment image such as the adjustment toner image Tn, and a density for correcting the density of an image formed based on the output of the density sensor The image forming apparatus having a control unit such as the control unit 41 includes a moving unit such as an actuator 104 that moves the density sensor in the width direction of the transfer medium, and the control unit moves the density sensor. Control to detect image density.
By moving the density sensor in the width direction of the image forming object, it is possible to detect the image density by making the light receiving elements face each other even in the image portion corresponding to the gap between the light receiving elements before the movement. become able to. Since the image density can be detected also in the portion of the image corresponding to the gap portion, the image density distribution in the width direction of the image forming object can be obtained with high accuracy. If the image forming conditions are adjusted based on the image density distribution, the image density can be corrected with high accuracy.

(Aspect B)
In Aspect A, it has sensor position detecting means for detecting the position of the density sensor in the width direction of the image forming object, and the image forming means extends along a direction perpendicular to the width direction of the image forming object. A sensor position detecting toner image such as a sensor position detecting toner image Tp in which a plurality of line segments having different widths are arranged along the width direction of the image forming object is provided on an upstream side and a downstream side of the adjustment image. The sensor position detecting means is configured to detect the sensor position detection toner images formed on the upstream side and the downstream side of the adjustment image based on information detected by the density sensor. The position is specified.
The moving speed of the concentration sensor may change due to disturbance. The width direction of the transfer medium when the sensor position detection toner image is detected by arranging a plurality of line segments having different widths along the width direction of the transfer medium as the sensor position detection toner image. The position of the concentration sensor can be grasped. The density is determined by the difference between the position of the sensor position detection toner image formed on the upstream side of the adjustment toner image and the position of the sensor position detection toner image formed on the downstream side of the adjustment toner image. The movement distance of the sensor can be calculated. The moving speed of the transfer medium and the distance between the sensor position detection toner images formed on the upstream side and the downstream side of the adjustment toner image can be defined in advance. By dividing the distance between the sensor position detection toner images by the moving speed of the transfer medium, the sensor position detection formed when the sensor position detection toner image formed upstream is detected and the sensor position detection formed downstream. The time difference when the toner image is detected can be obtained. By dividing the moving distance of the concentration sensor by the time difference, the moving speed of the concentration sensor can be accurately obtained without depending on disturbance. When the moving speed of the density sensor is accurately known, the position of the density sensor in the width direction of the transfer medium can be accurately specified. The density of the adjustment toner image is determined by the position of the density sensor in the width direction of the transfer medium specified by the sensor position detection unit as described above and the toner adhesion amount of the adjustment toner image detected by the density sensor. Distribution can be obtained with high accuracy.

(Aspect C)
In the aspect A, the image forming unit includes a sensor position detecting unit that detects a position of the density sensor in the width direction of the image forming target, and a sensor capable of identifying color information is used as the density sensor. A sensor position detecting toner image in which a plurality of line segments extending in a direction perpendicular to the width direction of the image forming object and having different colors are arranged along the width direction of the image forming object is the adjustment image. The sensor position detecting means detects the sensor position detecting toner images formed on the upstream side and the downstream side of the adjustment image by the density sensor. Based on the above, the position of the density sensor is specified.
By reading the sensor position detecting toner image in which a plurality of line segments having different colors are arranged in the width direction of the transfer medium through the light receiving element capable of detecting color information, the width direction of the transfer medium The amount of movement of the concentration sensor can be grasped. This eliminates the need to make the widths of the plurality of line segments constituting the sensor position detecting toner image different from each other as in the case B. Therefore, the width of each line segment in the sensor position detection toner image can be set to the minimum length that can be detected by the light receiving element. Accordingly, it is possible to reduce the amount of toner consumed for forming the sensor position detection toner image.

(Aspect D)
In Aspects A to C, the distance for moving the density sensor in the width direction of the image forming object is longer than the gap between adjacent light receiving elements.
If the moving distance is shorter than the gap between the adjacent light receiving elements, a part of the toner image on the transfer medium located in the gap between the adjacent light receiving elements cannot be detected. By making the moving distance longer than the gap between the adjacent light receiving elements, it is possible to detect all the toner images of the transfer medium located in the gap between the adjacent light receiving elements.

(Aspect E)
In aspects A to D, a contact image sensor (CIS) was used as the concentration sensor.
The toner adhesion amount can be detected with a small size and at a low cost.

DESCRIPTION OF SYMBOLS 1 Photoconductor 40 Density sensor 41 Control part 42 Image processing part 43 Image formation part 51 Intermediate transfer belt 72 Sensor position detection part 102 Image element 103 Light receiving element Tn Toner image for adjustment

JP 2014-021248 A

Claims (5)

Image forming means for forming an image on an image forming object;
A density sensor that includes an image element in which a plurality of light receiving elements are arranged side by side along the width direction of the image forming object;
An image forming apparatus having control means for correcting the density of an image to be formed based on the output of the density sensor;
An image forming apparatus comprising: a moving unit that moves the density sensor in a width direction of the transfer medium; and the control unit performs control to detect an image density while moving the density sensor. The image forming apparatus according to claim 1.
Sensor position detecting means for detecting the position of the density sensor in the width direction of the image forming object, and the image forming means extend along a direction perpendicular to the width direction of the image forming object and have different widths. A sensor position detection image in which a plurality of line segments are arranged along the width direction of the image forming object is formed on the upstream side and the downstream side of the adjustment image, and the sensor position detection unit includes the sensor position detection unit, The density sensor is configured to specify the position of the density sensor based on information obtained by detecting the sensor position detection images formed on the upstream side and the downstream side of the adjustment image. Image forming apparatus. The image forming apparatus according to claim 1.
A sensor position detecting unit configured to detect a position of the density sensor in a width direction of the image forming target; a sensor capable of identifying color information is used as the density sensor; and the image forming unit includes the image forming target. A sensor position detection image in which a plurality of line segments extending in a direction perpendicular to the width direction of the object and having different colors are arranged along the width direction of the image forming object is provided on the upstream side and the downstream side of the adjustment image. And the sensor position detecting means detects the density sensor based on information obtained when the density sensor detects the sensor position detection images formed on the upstream side and the downstream side of the adjustment image. An image forming apparatus characterized by specifying the position of the image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The distance at which the density sensor is moved in the width direction of the image forming object is longer than the gap between adjacent light receiving elements. The image forming apparatus according to claim 1,
An image forming apparatus using a contact image sensor (CIS) as the density sensor.