JP6136518B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly to an electrophotographic image forming apparatus and an image forming method.

  In an electrophotographic image forming apparatus, due to the property of forming an image using static electricity, fluctuations in environmental conditions such as temperature and humidity in the environment in which the image forming apparatus is used, and deterioration over time of the photoconductor and developer, etc. That is, there is a case where a stable image cannot be formed due to a change in durability.

  In order to prevent this, environmental condition information, durability information, and image adjustment pattern image information are detected to form an image forming condition (hereinafter referred to as “image forming condition”). Control for stabilizing the image by feedback (hereinafter referred to as “image stabilization control”) is performed.

  For example, by using a sensor that detects the color (reflection density) of the test pattern on the paper before fixing by the fixing device and a sensor that detects the color of the test pattern on the paper after fixing, the deterioration level of the fixing unit is determined. The determination is performed (see, for example, FIG. 6 of Patent Document 1).

  Also, the color of the toner image on the paper after fixing is measured, and based on the color space coordinates of the measured color (reflection density), the image forming conditions are set so that the toner adhesion amount on the paper is optimized, Alternatively, fixing conditions are controlled (see, for example, FIG. 7 of Patent Document 2).

JP 2011-59308 A JP 2010-164891 A

  By the way, the relationship between the toner adhesion amount on the paper (hereinafter also referred to as “the toner adhesion amount on paper”) and the reflection density is not necessarily constant. This is because the reflection density is a characteristic value obtained by combining the internal reflection component of the toner color material and the surface reflection component generated by fixing. Therefore, even if the toner adhesion amount on the paper is controlled by the image forming apparatus and the toner adhesion amount on the paper is adjusted to an appropriate value (target value), the reflection of the image formed on the paper due to a change in the fixing temperature generated at the time of fixing. Concentration is not appropriate (within target range).

  On the other hand, even if the reflection density becomes appropriate, it cannot be determined whether the toner adhesion amount on paper and the fixing temperature are appropriate. For this reason, there are problems that toner is excessively consumed, and that glossiness is increased and image quality is deteriorated. FIG. 9A is an explanatory diagram for glossiness, and FIG. 9B is an explanatory diagram for reflection density. As shown in FIG. 9A, the glossiness is calculated by detecting regular reflection light of light incident on the paper. Further, as shown in FIG. 9B, the reflection density is calculated by detecting irregularly reflected light of light incident on the paper. The irregular reflection light tends to be weak when the regular reflection light is strong, and tends to be strong when the regular reflection light is weak.

  From the above situation, in order to form a high-quality image, there has been a demand for a method for adjusting both the reflection density and the glossiness of an image formed on a sheet to be within a target range.

In one aspect of the present invention, the toner amount of the toner image attached to the sheet before fixing by the fixing unit is detected by a toner adhesion amount sensor disposed upstream of the fixing unit included in the image forming apparatus in the sheet conveyance direction.
Next, the reflection density of the toner image on the sheet after fixing is detected by a reflection density sensor arranged on the downstream side of the fixing unit in the sheet conveyance direction.
Next, based on the detection value of the toner adhesion amount sensor and the detection value of the reflection density sensor, the determination unit determines whether the toner amount and the reflection density of the toner image attached to the sheet are within the target range.
Then, based on the determination result of the determination unit, the control unit sets the toner amount of the toner image to be attached to the paper as the image forming condition and the target value of the fixing temperature of the fixing unit.

  In the above configuration, when it is determined that the toner amount of the toner image attached to the paper detected by the determination unit is not within the target range, the control unit sets the target value of the toner amount of the toner image attached to the paper. To change. When the determination unit determines that the reflection density is not within the target range, the control unit changes the target value of the fixing temperature. If the determination unit determines that the toner amount and reflection density of the toner image attached to the sheet are not within the target range, the control unit sets the target toner amount and fixing temperature of the toner image attached to the sheet. Change the value.

  According to the above configuration, based on the toner amount of the toner image attached to the paper before fixing and the reflection density of the paper after fixing, whether the toner amount and reflection density of the toner image attached to the paper are within the target range. It is determined whether or not. Based on the determination result, the toner amount of the toner image to be attached to the paper and the target value of the fixing temperature are set as image forming conditions. By appropriately setting the target value of the toner amount of the toner image to be attached to the sheet and controlling the fixing temperature so that the reflection density is within the target range, the glossiness can be adjusted within the target range.

  According to the present invention, both the reflection density and the glossiness of an image formed on a sheet can be adjusted to be within a target range.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. It is explanatory drawing of arrangement | positioning of the toner adhesion amount sensor and reflection density sensor which concern on one embodiment of this invention. 2 is a block diagram illustrating a hardware configuration of each unit of the image forming apparatus according to the embodiment of the present disclosure. FIG. It is a graph which shows an example of the characteristic of the toner adhesion amount and reflection density on paper. 6 is a graph showing an example of characteristics of toner adhesion amount and glossiness on paper. 6 is a graph showing an example of the relationship between the toner adhesion amount on paper and the glossiness. It is the flowchart which showed the image adjustment process which concerns on one embodiment of this invention. 6 is a determination table in which a detected value of toner adhesion amount on paper and a detected value of reflection density are combined. FIG. 9A is an explanatory diagram for glossiness, and FIG. 9B is an explanatory diagram for reflection density.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the common member in each figure.

[Configuration example of image forming apparatus]
First, an outline of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a plan view showing the arrangement of the toner adhesion amount sensor and the reflection density sensor according to the embodiment of the present invention.

  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 (Bk). This is a tandem color image forming apparatus that superimposes toner. The image forming apparatus 1 includes a document transport unit 10, a paper storage unit 20, an image reading unit 30, an image forming unit 40, an intermediate transfer belt 50, a secondary transfer unit 60, and a fixing unit 80. .

  The document transport unit 10 includes a document feed table 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. Yes. 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 the image data in the RAM 103 (see FIG. 3) of the control unit 100. 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 at 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 paper. The sheet 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 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 sheet is sent to the transfer position. In FIG. 1, a sheet S fed by the sheet feeding unit 21 is denoted by a symbol “S”.

  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 (Bk). .

  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, only 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 attaches yellow toner to the electrostatic latent image formed on the photoconductor 41 using, for example, a two-component developer composed of toner and carrier. As a result, a yellow toner image (toner image) is formed on the surface of the photoreceptor 41.

  The developing unit 44 of the second image forming unit 40M attaches magenta toner to the photoconductor 41, and the developing unit 44 of the third image forming unit 40C attaches cyan toner to the photoconductor 41. Then, the developing unit 44 of the fourth image forming unit 40K adheres black toner to the photoconductor 41.

The toner image formed on the photoreceptor 41 is transferred to an intermediate transfer belt 50 that is an example of an image carrier. The intermediate transfer belt 50 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).
The cleaning unit 45 removes the toner remaining on the surface of the photoreceptor 41 after the toner image is transferred to the intermediate transfer belt 50.

  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, the toner images formed by the four image forming units 40Y, 40M, 40C, and 40K are sequentially transferred onto the surface of the intermediate transfer belt 50. As a result, on the intermediate transfer belt 50, yellow, magenta, cyan, and black toner images are overlapped 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.

  A secondary transfer unit 60 is disposed in the vicinity of the intermediate transfer belt 50 and downstream of the transport unit 23 in the sheet transport direction. The secondary transfer unit 60 brings the paper 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. The secondary transfer unit 60 has a secondary transfer roller 61. The secondary transfer roller 61 is pressed against the opposing roller 52 with the intermediate transfer belt 50 interposed therebetween. 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 transfer position where the toner image formed on the outer peripheral surface of the intermediate transfer belt 50 is transferred to the paper S.

  A fixing unit 80 is provided on the paper discharge side of the secondary transfer unit 60. The fixing unit 80 pressurizes and heats the paper to fix the transferred toner image on the paper. 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 a fixing nip portion is formed as a pressing portion at a position where the upper fixing roller 81 and the lower fixing roller 82 are in contact with each other.

  A heating unit is provided inside the fixing upper roller 81. The roller portion on 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 roller portion of the fixing upper roller 81 is transmitted to the sheet, whereby the toner image on the sheet is thermally fixed.

  The sheet 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. Accordingly, the sheet passing through the fixing nip portion is pressed by the upper fixing roller 81 and the lower fixing roller 82 and heated by the heat of the roller portion of the upper fixing 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 conveyance path of the sheet that has passed through the fixing unit 80. That is, the switching gate 24 moves the paper straight when performing face-up paper discharge in which the image forming surface is discharged upward in single-sided image formation. As a result, the paper is discharged by the pair of paper discharge rollers 25. Further, the switching gate 24 guides the sheet 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, after the sheet is guided downward by the switching gate 24, the sheet reverse transport unit 26 reverses the front and back and transports the sheet upward. As a result, the sheet whose front and back sides are reversed and whose image forming surface faces downward is discharged by the pair of discharge rollers 25.
When double-sided image formation is performed, after the sheet is guided downward by the switching gate 24, the front and back 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 or performs stapling processing or the like on the paper may be disposed on the downstream side of the pair of paper discharge rollers 25.

In this embodiment, as shown in FIGS. 1 and 2, a toner adhesion amount sensor 111 is disposed on the downstream side of the secondary transfer nip portion 62 and on the upstream side of the fixing portion 80 in the sheet conveyance direction. . The toner adhesion amount sensor 111 detects the amount of toner (the amount of toner adhesion on paper) that has adhered to the paper S before being conveyed to the fixing unit 80.
As the toner adhesion amount sensor 111, for example, a transmissive photosensor in which a light emitting member and a light receiving member are arranged to face each other, a reflective photosensor that detects reflected light from an object of emitted light, or the like can be used. Alternatively, a line sensor in which a light emitting member and a plurality of photoelectric conversion elements are arranged linearly over a part or the entire area in the paper width direction, or an image sensor in which photoelectric conversion elements are arranged in a matrix form is used. As the line sensor and the image sensor, a CCD type image sensor or a CMOS type (including MOS type) image sensor can be used.

A reflection density sensor 112 is disposed downstream of the fixing unit 80 in the sheet conveyance direction. The reflection density sensor 112 detects the reflection density of the toner fixed on the paper S on which the fixing process has been performed by the fixing unit 80.
The reflection density sensor 112 uses a line sensor in which a plurality of photoelectric conversion elements are linearly arranged over the entire area in the paper width direction, or an image sensor in which photoelectric conversion elements are arranged in a matrix. The detection information of the reflection density sensor 112 includes toner density and color information, and the fixing state can be estimated from the information.

[Configuration of control system of image forming apparatus]
Next, a control system of the image forming apparatus 1 will be described with reference to FIG.
FIG. 3 is a block diagram illustrating a control system of the image forming apparatus 1.

  As illustrated in FIG. 3, the image forming apparatus 1 includes a control unit 100. The control unit 100 is connected to the communication unit 108, the image reading unit 30, the image processing unit 106, the image forming unit 40, the paper feeding unit 21, the secondary transfer unit 60, and the fixing unit 80 via the system bus 107. . Further, the control unit 100 is connected to the HDD 104, the operation display unit 105, the toner adhesion amount sensor 111, the reflection density sensor 112, the temperature sensor 113, and the humidity sensor 114 via the system bus 107.

  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. Note that, as the ROM 102 (an example of a storage unit), for example, a programmable ROM that is normally electrically erasable is used. The control unit 100 is an example of a determination unit that determines whether or not the detection values output from the toner adhesion amount sensor 111 and the reflection density sensor 112 are appropriate. The control unit 100 controls each block, that is, controls the entire apparatus.

  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.

  Image data generated by the image reading unit 30 and image data transmitted from a PC (personal computer) 120 which is an example of an external device connected to the image forming apparatus 1 are sent to the image processing unit 106 for image processing. Is done. The image processing unit 106 performs processes such as analog processing, A / D conversion, shading correction, and image compression on the received image data.

  The communication unit 108 receives job information transmitted from the PC 120 which is an external information processing apparatus via a communication line. The received job information is sent to the control unit 100 via the system bus 107.

  The control unit 100 controls driving of the image forming unit 40, the paper feeding unit 21, the secondary transfer unit 60, and the fixing unit 80 based on the job information.

  Under the control of the control unit 100, the toner adhesion amount sensor 111 turns on the light emitting member with a preset reference light emission setting value, receives the reflected light from the paper before fixing the toner image, and outputs it as a detection value. To do. The control unit 100 calculates the toner adhesion amount of the toner image (toner image) on the sheet before fixing based on the toner adhesion amount characteristic information that associates the detection value of the toner adhesion amount sensor 111 with the toner adhesion amount. Then, the control unit 100 applies the calculated toner adhesion amount to determination means (determination table, conversion formula, etc.) described later, and determines the toner amount of the toner image (toner image) to be adhered to the paper S in the image forming unit 40. Control. The toner adhesion amount characteristic information and the data relating to the determination unit are stored in the ROM 102 or the HDD 104 in advance.

  As control factors of the toner adhesion amount, for example, toner density in the developing unit 44, developing bias, exposure light amount to the photosensitive member 41 by the exposing unit 43, charging voltage to the photosensitive member 41 by the charging unit 42, contents of image data Etc. The ROM 102 holds a table for associating the toner adhesion amount with its control factor, and the control unit 100 controls the toner adhesion amount as an image forming condition with reference to the table.

  Under the control of the control unit 100, the reflection density sensor 112 lights the light emitting member with a preset reference light emission setting value, receives the reflected light from the paper after fixing the toner image, and outputs it as a detection value. . The control unit 100 calculates the reflection density of the toner image on the fixed paper based on the reflection density characteristic information that associates the detection value of the reflection density sensor 112 with the reflection density. Then, the control unit 100 controls the fixing temperature of the fixing unit 80 by applying the calculated reflection density to a determination unit (determination table, conversion formula, etc.) described later. The reflection density characteristic information and the data relating to the determination unit are stored in the ROM 102 or the HDD 104 in advance.

  The temperature sensor 113 is provided in the image forming apparatus 1 and detects the temperature in the image forming apparatus 1. The temperature sensor 113 is provided in the vicinity of the toner adhesion amount sensor 111 or the reflection density sensor 112, for example.

  The humidity sensor 114 is provided in the image forming apparatus 1 and detects the humidity in the image forming apparatus 1. The humidity sensor 114 is provided in the vicinity of the toner adhesion amount sensor 111 or the reflection density sensor 112, for example. The temperature sensor 113 and the humidity sensor 114 are an example of an environment sensor that detects an environment in the image forming apparatus 1.

  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. .

[Relationship between reflection density and gloss]
Here, the relationship between the reflection density and the glossiness will be described with reference to FIGS.
FIG. 4 is a graph showing an example of the characteristics of the toner adhesion amount on paper and the reflection density. In the drawing, the horizontal axis represents the toner adhesion amount (g / m ² ) on the paper, and the vertical axis represents the reflection density. In the figure, “□” indicates a fixing temperature of 190 ° C., “◯” indicates a fixing temperature of 180 ° C., “Δ” indicates a fixing temperature of 170 ° C., and “◇” indicates a fixing temperature of 160 ° C. The straight line in the figure is a regression line by the least square method with respect to the plot points.
As shown by the arrows in the figure, even if the toner adhesion amount detected by the toner adhesion amount sensor 111 is the same, the reflection density detected becomes higher as the fixing temperature is higher. For this reason, even if the reflection density is the same, it cannot be distinguished whether the toner adhesion amount on paper is small and the fixing temperature is high, or whether the toner adhesion amount on paper is large and the fixing temperature is low.

The following is the data of the plot points of the broken-line circles in the graph shown in FIG. 4 (and FIG. 5).
Amount of toner on paper: 5.5 (g / m ² ), fixing temperature: 190 ° C, reflection density: 1.95 (glossiness: 80)
Amount of toner on paper: 6.5 (g / m ² ), fixing temperature: 170 ° C, reflection density: 1.95 (glossiness: 70)

FIG. 5 is a graph showing an example of characteristics of toner adhesion amount and glossiness on paper. In the figure, the horizontal axis represents the toner adhesion amount (g / m ² ) on the paper, and the vertical axis represents the glossiness. In the figure, the plot points with the same symbols as those in FIG. 4 indicate the same fixing temperature. The straight line in the figure is a regression line by the least square method with respect to the plot points.
As shown by the arrows in the figure, the glossiness increases if the fixing temperature is high even if the toner adhesion amount detected by the toner adhesion sensor 111 is small, and if the fixing temperature is low even if the toner adhesion amount is large. Glossiness is lowered. Therefore, even if only the reflection density detected by the reflection density sensor 112 is controlled to be appropriate (within the target range), the glossiness is not appropriate (within the target range). Here, the reflection density or glossiness being within the target range means a state in which the reflection density or glossiness is within a predetermined range from a preset threshold value.

FIG. 6 is a graph showing an example of the relationship between the toner adhesion amount on paper and the glossiness.
In the figure, the horizontal axis indicates glossiness and the vertical axis indicates reflection density. In the figure, the plotted points with the same symbols as those in FIG. 4 are the same fixing temperature. In addition, the straight line in the figure is a regression line with respect to plot points of data measured under the same toner adhesion amount on paper. In this example, the straight line 121 is a regression line with a toner density on paper of 7.0 g / m ² , the straight line 122 is 5.9 g / m ² , the straight line 123 is 5.5 g / m ² , and the straight line 124 is 4.7 g / m ² . m ² is represented.
As shown in FIG. 6, under the same toner adhesion amount on paper, regular reflection light increases as glossiness increases, so irregular reflection light decreases and reflection density increases, so the reflection density and glossiness are constant. It becomes the relationship. Therefore, if the target value of the toner amount of the toner image to be attached to the paper is appropriately set and the fixing temperature is controlled so that the reflection density is within the target range, the glossiness can be adjusted within the target range. it can.

[Operation of image forming apparatus]
Hereinafter, the operation of the image forming apparatus 1 will be described.
FIG. 7 is a flowchart showing image adjustment processing by the image forming apparatus 1.
First, the control unit 100 of the image forming apparatus 1 (see FIG. 1) performs image adjustment related to image formation based on an operation signal input from the operation display unit 105 or job information transmitted from the PC 120 via the communication unit 108. Detects the start of a job. When the control unit 100 detects the start of the image adjustment job, for example, the control unit 100 operates the paper supply unit 21 to supply the selected paper S from the paper storage unit 20 and start passing the paper. In the following processing, as an example of image adjustment, an example will be described in which image adjustment is performed so that an image having a default (initial setting) reflection density and glossiness of a sheet is obtained.

  After starting the paper feeding, the control unit 100 controls the image forming unit 40 to control the toner amount of the toner image to be attached to the paper S based on the initial target value stored in the ROM 102 (step S1). . In parallel with the control of the toner adhesion amount, the fixing temperature of the fixing unit 80 is controlled based on the initial target value stored in the ROM 102 (step S2). Thereafter, the control unit 100 forms an image adjustment pattern image on the paper S (step S3).

  The control unit 100 detects the toner adhesion amount on the paper S before fixing on which the image adjustment pattern image is formed by the toner adhesion amount sensor 111 (step S4). Further, the control unit 100 detects the reflection density of the fixed sheet S on which the image adjustment pattern image is formed by the reflection density sensor 112 (step S5).

  The control unit 100 determines whether or not the toner adhesion amount on the paper before fixing is appropriate based on the detection value of the toner adhesion amount sensor 111 thus obtained. Further, the control unit 100 determines whether or not the reflection density is appropriate based on the detection value of the reflection density sensor 112 (step S6). That is, the control unit 100 determines whether or not the detected toner adhesion amount and reflection density on the paper are within the target range.

The control unit 100 determines which of the toner adhesion amount on the paper and the reflection density is not appropriate (within the target range) from the determination result of step S6 (step S7).
In the determination process of step S7, when the control unit 100 determines that the toner adhesion amount on paper is not appropriate, the control unit 100 controls the toner adhesion amount on the paper by changing the target value of the toner amount of the toner image to be adhered to the paper (step S8).
In the determination process of step S7, when the control unit 100 determines that the reflection density (that is, the fixing temperature) is not appropriate, the control unit 100 controls the fixing temperature by changing the target value of the fixing temperature (step S9).
Further, in the determination process of step S7, when the control unit 100 determines that the toner adhesion amount on the paper and the reflection density (that is, the fixing temperature) are not appropriate, the toner amount of the toner image to be adhered to the paper and the target value of the fixing temperature are set. The toner amount and fixing temperature of the toner image to be changed and attached to the paper are controlled (steps S10 and S11).

  When the processes of steps S8, S9, and S11 are completed, the control unit 100 ends the image adjustment process. Thereafter, when the target value of the toner amount of the toner image to be attached to the paper is changed, the control unit 100 performs the above-described image adjustment process again. When the target value of the toner amount of the toner image attached to the sheet is not changed, the control unit 100 changes only the target value of the fixing temperature and does not perform the image adjustment process again. Then, the control unit 100 forms an image on the sheet based on the toner amount and / or the fixing temperature target value of the toner image to be attached to the changed sheet, and performs the image adjustment process again. The control unit 100 acquires the detection value of the toner adhesion amount sensor 111 and the detection value of the reflection density sensor 112 based on the changed target value, and both the reflection density and glossiness of the paper are within appropriate ranges (that is, the target value). It is more desirable to adjust so that it is within the range.

[Target values for the toner amount and reflection density of the toner image to be attached to the paper after the change]
In steps S8 and S10, the control unit 100 performs a predetermined determination as to how much the target value of the toner amount of the toner image to be attached should be changed from the target value of the toner amount of the toner image to be attached to the paper before the change. It is determined using means (determination reference information). Similarly, in steps S9 and S11, how much the target value of the fixing temperature should be changed from the target value of the fixing temperature before the change is determined using predetermined determination means (determination reference information). As the determination means, a determination table including a detection value of the toner adhesion amount on paper and a detection value of reflection density, a conversion formula, or the like can be applied.

  FIG. 8 is a determination table in which the detected value of the toner adhesion amount on paper and the detected value of reflection density are combined. The vertical direction corresponds to the detection value of the toner adhesion amount sensor 111, and the horizontal direction corresponds to the detection value of the reflection density sensor 112. The detected value of the toner adhesion amount on the paper increases from the top to the bottom of the determination table, and the detection value of the reflection density increases from the right to the left of the determination table. The stabilization target value in the determination table is a target value of the toner amount of the toner image attached to the paper. The target value of the toner amount and fixing temperature of the toner image to be adhered to the paper is determined according to which cell in the determination table the detected value of the toner adhesion amount and reflection density on the paper corresponds to.

  For example, in the determination table, the hatched cells in the center are hatched detection values within the target range set in advance for both the toner adhesion amount on paper and the reflection density. Both the toner adhesion amount on paper and the detected value of reflection density are within the target range means a state where the toner adhesion amount and reflection density on paper are within a predetermined range from a preset threshold value. In this case, both the stabilization target value and the fixing temperature are appropriate (within the target range), and the reflection density and glossiness of the paper are also within the target range. Therefore, the control unit 100 does not change the target value of the toner amount and the fixing temperature of the toner image attached to the paper.

  In the determination table, the upper-left cell 131 has a small amount of toner adhesion on paper and a detected value of reflection density. In this case, the control unit 100 increases the target value of the toner adhesion amount, which is the stabilization target value, by three levels. Regarding the fixing temperature, the detection value of the reflection density is small, but the detection value of the toner adhesion amount on the paper is also small, so the target value is lowered by one step. It should be noted that for each toner amount and fixing temperature of the toner image to be attached to the paper, how much the toner image is to be raised or lowered in one step is set in advance, and the setting information is stored in the ROM 102.

  In the determination table, the upper right cell 132 has a small detection value of the toner adhesion amount on the paper and a large detection value of the reflection density. In this case, the control unit 100 raises the target value of the toner amount of the toner image to be adhered to the paper, which is the stabilization target value, by three levels. Regarding the fixing temperature, the detection value of the reflection density is large despite the small detection value of the toner adhesion amount on the paper, so the target value is lowered by five steps.

  Further, in the determination table, the lower right cell 133 has a large amount of toner adhesion on the paper and a detected value of reflection density. In this case, the control unit 100 lowers the target value of the toner amount of the toner image to be attached to the sheet, which is the stabilization target value, by three levels. Regarding the fixing temperature, the detected value of the toner adhesion amount on the paper is large although the detected value of the fixing temperature is large, and therefore the target value is raised by one step.

  In the determination table, the lower left cell 134 has a large detection value of the toner adhesion amount on the paper and a small detection value of the reflection density. In this case, the control unit 100 lowers the target value of the toner amount of the toner image to be attached to the sheet, which is the stabilization target value, by three levels. Regarding the fixing temperature, the detection value of the reflection density is small despite the large detection value of the toner adhesion amount on the paper, so the target value is raised by five levels.

  As shown in FIG. 8, in the present embodiment, the target value of the toner amount of the toner image attached to the paper is set according to the detection value of the toner attachment amount sensor 111. That is, if the detection value of the toner adhesion amount sensor 111 is small, the target value of the toner amount of the toner image to be adhered to the paper is set to a larger value, and if the detection value of the toner adhesion amount sensor 111 is large, the target value of the toner adhesion amount is increased. Set to a smaller value.

  On the other hand, the target value of the fixing temperature is also set according to the detection value of the reflection density sensor 112. However, the detection value of the toner adhesion amount on paper is reflected in the target value of the fixing temperature. That is, when the detection value of the reflection density sensor 112 is large, the target value of the fixing temperature is greatly increased if the detection value of the toner adhesion amount sensor 111 is small, and the fixing temperature is increased if the detection value of the toner adhesion amount sensor 111 is large. The target value is close to the current target value. When the detection value of the reflection density sensor 112 is small, if the detection value of the toner adhesion amount sensor 111 is small, the target value of the fixing temperature is close to the current target value, and the detection value of the toner adhesion amount sensor 111 is If it is larger, the target value of the fixing temperature is greatly increased.

  When the detection value of the toner adhesion amount sensor 111 is appropriate (the cell at the center of the determination table), if the detection value of the reflection density sensor 112 is small, the reflection density target value is set to a larger value, and the reflection density sensor 112 is detected. If the detected value is large, the target value of the reflection density is set to a smaller value.

  As described above, the control unit 100 uses the determination table to determine the toner amount of the toner image to be attached to the changed paper and the target value of the fixing temperature based on the detected values of the toner adhesion amount and the reflection density on the paper. can do.

  Furthermore, in this embodiment, a conversion formula can be used as the determination means. For example, as shown in the following conversion formula, by inputting the detected value of the toner adhesion amount on paper and the detection value of reflection density into the conversion formula, how many steps (how many steps) the target value after the change is from the current target value It is required to change the target value to be increased or decreased.

<Conversion formula>
Stabilization target value step = F (detection value of toner adhesion amount on paper, detection value of reflection density)
Fixing temperature step = G (detection value of toner adhesion on paper, detection value of reflection density)
Where F (x, y) and G (x, y) are two variable expressions.
x = detection value of toner adhesion on paper, y = detection value of reflection density

  According to the present embodiment configured as described above, in addition to the reflection density sensor 112 disposed on the downstream side of the fixing unit 80 in the paper conveyance direction, the toner adheres to the upstream side of the fixing unit 80 in the paper conveyance direction. A quantity sensor 111 is provided. Then, the reflection density detection value of the paper after the toner image fixing by the reflection density sensor 112 and the toner adhesion amount of the paper before the toner image fixing by the toner adhesion amount sensor 111 are detected. As shown in FIG. 6, if the target value of the toner amount of the toner image to be adhered to the paper is appropriately set and the fixing temperature is controlled so that the reflection density is within the target range, the glossiness is also set to the target value. Can be adjusted within the range. Therefore, the control unit 100 appropriately changes the target value of the toner amount and / or fixing temperature of the toner image to be attached to the paper based on these detection values. Therefore, the image forming apparatus 1 can obtain an image in which the reflection density and glossiness of the paper are adjusted so as to be within the target range.

In the present embodiment, the control unit 100 performs adjustment to change the target value of the toner amount of the toner image to be attached to the paper to a larger value as the detection value of the toner adhesion amount sensor 111 is smaller.
On the other hand, with respect to the target value of the fixing temperature, the target value of the fixing temperature is changed according to the level of the detection value of the toner adhesion amount sensor 111. That is, when the detection value of the reflection density sensor 112 is large, the control unit 100 sets the target value of the fixing temperature to a relatively smaller value than the target value of the fixing temperature when the detection value of the reflection density sensor 112 is small. Set.

  The embodiment to which the invention made by the present inventor is applied has been described above. However, the present invention is not limited by the description and drawings which form part of the disclosure of the invention according to the above-described embodiments, and various modifications may be made without departing from the spirit of the invention described in the claims. Is possible.

  For example, in the above-described embodiment, an example in which image adjustment is performed so that an image having a default (initial setting) reflection density and glossiness is obtained has been described, but the reflection density and gloss indicated by the operation display unit 105 or the like. Image adjustment may be performed so that a certain degree of image can be obtained.

  In image formation, image forming conditions are changed so that an optimal image can be obtained according to the paper type. Examples of the paper type include paper size, basis weight, and paper thickness. Therefore, the control unit 100 uses the toner adhesion amount sensor 111 and the reflection density sensor 112 to detect the toner amount of the toner image to be adhered to the paper according to the paper type and the target value of the fixing temperature. You may make it set the toner amount of the toner image to adhere, and the target value of fixing temperature. The control unit 100 sets the target value of the toner amount of the toner image to be attached to the paper and the fixing temperature in advance according to the paper type. Thereby, for each paper type, an image in which the reflection density and glossiness of the paper are adjusted within the target range is obtained.

  Further, the control unit 100 uses the detection values of the toner adhesion amount sensor 111 and the reflection density sensor 112 as a reference based on the target amount of toner and the fixing temperature of the toner image to be attached to the paper according to the front and back surfaces of the paper. Alternatively, the toner amount of the toner image attached to the paper and the target value of the fixing temperature may be set. The control unit 100 sets a target value for the toner amount of the toner image to be attached to the paper and the fixing temperature for each of the front and back surfaces of the paper in advance. Thus, an image in which the reflection density and glossiness of the paper are adjusted within the target range is obtained for each of the front and back surfaces of the paper.

  Since the information on the unevenness of the paper is reflected in the detection value of the reflection density sensor 112, the control unit 100 can detect the unevenness of the paper from the detection value of the reflection density sensor 112. Therefore, based on the detection values of the toner adhesion amount sensor 111 and the reflection density sensor 112, the control unit 100 uses the toner amount of the toner image to be adhered to the sheet according to the degree of unevenness of the sheet and the target value of the fixing temperature as a reference. You may make it set the target value of the toner amount of the toner image adhering to a paper, and fixing temperature. The control unit 100 sets in advance the toner amount of the toner image to be attached to the paper and the target value of the fixing temperature in accordance with the degree of unevenness of the paper. As a result, an image in which the reflection density and glossiness of the paper are adjusted within the target range according to the unevenness of the paper can be obtained.

  Further, the control unit 100 adheres to the sheet based on the detection values of the toner adhesion amount sensor 111 and the reflection density sensor 112 based on the toner amount of the toner image to be adhered to the sheet and the target value of the fixing temperature according to the environment. A target value of the toner amount and fixing temperature of the toner image to be set may be set. The control unit 100 sets in advance the toner amount of the toner image to be attached to the paper and the target value of the fixing temperature according to the environment. For example, a temperature sensor 113 and a humidity sensor 114 (see FIG. 3) are used as means for detecting the environment. Thereby, for example, an image in which the reflection density and glossiness of the paper are adjusted within the target range according to the temperature and humidity in the image forming apparatus 1 is obtained.

  Further, it is possible to detect the moisture content of the sheet from the detection value of the toner adhesion amount sensor 111. Therefore, based on the detection values of the toner adhesion amount sensor 111 and the reflection density sensor 112, the control unit 100 uses the toner amount of the toner image to be adhered to the sheet according to the moisture content of the sheet and the target value of the fixing temperature as a reference. You may make it set the target value of the toner amount of the toner image adhering to a paper, and fixing temperature. The control unit 100 sets a target value of the toner amount of the toner image to be attached to the paper and the fixing temperature in advance according to the moisture content of the paper. As a result, an image in which the reflection density and glossiness of the paper are adjusted within the target range according to the moisture content of the paper is obtained.

  In the above-described embodiment, the example in which the present invention is applied to the image forming apparatus 1 including the intermediate transfer belt 50 has been described. For example, a photoconductor is provided as an image carrier, and a toner image is transferred from the photoconductor to a sheet. It can also be applied to an image forming apparatus.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 40 ... Image forming part, 50 ... Intermediate transfer belt, 60 ... Secondary transfer part, 80 ... Fixing part, 100 ... Control part, 102 ... ROM, 103 ... RAM, 111 ... Toner adhesion amount sensor, 110: reflection density sensor, S: paper

Claims (8)

An image forming unit for forming a toner image to be attached to a sheet based on image forming conditions;
A fixing unit for fixing the toner image on a sheet;
A toner adhesion amount sensor that is disposed upstream of the fixing unit in the sheet conveyance direction and detects a toner amount of the toner image adhered to the sheet before fixing;
A reflection density sensor that is disposed downstream of the fixing unit in the paper conveyance direction and detects the reflection density of the toner image of the paper after fixing;
A determination unit that determines whether the toner amount and the reflection density of the toner image attached to the paper are within a target range based on the detection value of the toner adhesion amount sensor and the detection value of the reflection density sensor;
An image forming apparatus comprising: a controller configured to set a toner amount of a toner image to be attached to the sheet as the image forming condition and a target value of a fixing temperature of the fixing unit based on a determination result of the determining unit. When it is determined that the toner amount of the toner image attached to the sheet detected by the determination unit is not within the target range, the control unit sets the target value of the toner amount of the toner image attached to the sheet. Change
When the determination unit determines that the reflection density is not within a target range, the control unit changes the target value of the fixing temperature,
When the determination unit determines that the toner amount of the toner image attached to the paper and the reflection density are not within the target range, the control unit sets the target of the toner amount of the toner image attached to the paper. The image forming apparatus according to claim 1, wherein the value is changed. The image forming apparatus according to claim 1, wherein the control unit sets a toner amount of a toner image to be attached to the paper and a target value of the fixing temperature according to a paper type. The image forming apparatus according to claim 1, wherein the control unit sets a toner amount of a toner image to be attached to the paper and a target value of the fixing temperature for each of the front surface and the back surface of the paper. The unevenness degree of the paper is detected using the reflection density sensor, and the control unit determines a toner amount of the toner image to be attached to the paper and a target value of the fixing temperature according to a detection result of the paper unevenness. The image forming apparatus according to claim 1, wherein the image forming apparatus is set. An environmental sensor for measuring the environment in the image forming apparatus;
The image forming apparatus according to claim 1, wherein the control unit sets a toner amount of a toner image to be attached to the sheet and a target value of the fixing temperature based on a detection value of the environment sensor. The control unit calculates a moisture content of the paper based on a detection value of the toner adhesion amount sensor, and sets a toner amount of the toner image to be adhered to the paper and a target of the fixing temperature according to the moisture content of the paper. The image forming apparatus according to claim 1, wherein a value is set. In an image forming method of an image forming apparatus including an image forming unit that forms a toner image to be attached to a sheet based on image forming conditions,
A process of detecting the toner amount of the toner image attached to the paper before fixing by the fixing unit by a toner adhesion amount sensor disposed upstream of the fixing unit in the paper conveyance direction;
A process of detecting the reflection density of the toner image on the paper after fixing by a reflection density sensor disposed on the downstream side in the paper conveyance direction of the fixing unit;
The determination unit determines whether the toner amount and the reflection density of the toner image attached to the paper are within a target range based on the detection value of the toner adhesion amount sensor and the detection value of the reflection density sensor. Processing,
An image forming method in which a control unit performs a process of setting a toner amount of a toner image to be attached to the sheet as the image forming condition and a target value of a fixing temperature of the fixing unit based on a determination result of the determining unit.

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