JP2010039071A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which reduces toner consumption when image quality is adjusted and detects an amount of toner adhered with high accuracy over a long period of time. <P>SOLUTION: A test pattern for correcting a main-scanning direction shape including n toner patches whose lengths in a main scanning line direction are different from each other is formed on an intermediate transfer belt. Each toner patch is detected by a reflection type photosensor, and the length in a main scanning direction of a toner patch for adjusting image quality is determined from the detection value of the reflection type photosensor. A test pattern for correcting a sub-scanning direction shape inclduing n toner patches whose lengths in a sub-scanning line direction are different from each other is formed on the intermediate transfer belt. Each toner patch is detected by the reflection type photosensor, and the length in a sub-scanning direction of the toner patch for adjusting image quality is determined from the detection value of the reflection type photosensor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer.

  In an electrophotographic image forming apparatus, when the properties of toner (for example, fluidity and bulk) change with environmental changes, the development density changes due to the change in image forming ability accordingly. Therefore, conventionally, after the amount of toner attached to a predetermined toner patch is detected by an optical sensor as an optical detection means, image quality adjustment processing is performed by adjusting image forming conditions such as development bias and optical writing intensity based on the detection result. An image forming apparatus that performs the above is known (for example, Patent Document 1). This type of image forming apparatus forms a toner patch as an image quality adjusting toner image on the surface of an image carrier such as an intermediate transfer belt at a predetermined timing. Then, light emitted from the light emitting element of the reflective photosensor toward the surface of the image carrier is reflected by the surface of the image carrier or the toner patch, and the amount of reflected light is detected by the light receiving element.

  The light applied to the surface of the image carrier is specularly reflected by specular reflection, and the light applied to the toner surface is diffusely reflected. When the toner adhesion amount of the toner patch is small, the exposure rate of the surface of the image carrier is high, so that the regular reflection light is large and the diffuse reflection light is small. On the other hand, when the toner adhesion amount of the toner patch increases, the exposure rate on the surface of the image carrier is low, regular reflection light decreases, and diffuse reflection light increases. Therefore, it is possible to know the toner adhesion amount of the toner patch by detecting the regular reflection light amount and the diffuse reflection light amount with the light receiving element.

In this manner, the change amount of the image forming ability of the image forming means is detected based on the comparison between the detection result detected by the optical sensor and the predetermined toner adhesion amount target value. Then, by adjusting the image forming ability of the image forming means based on the detection result, it is possible to stabilize the development density and maintain good image quality.
JP 2004-93972 A

  Conventionally, the length of the toner patch in the axial direction of the image carrier (hereinafter referred to as the main scanning direction) and the length of the image carrier surface movement direction (hereinafter referred to as the sub-scanning direction) have been determined in advance by experiments or the like. That is, as shown in FIG. 24, when the length of the toner patch T in the main scanning direction and the sub scanning line direction is smaller than the beam spot diameter S of the optical sensor, the surface of the peripheral image carrier 206 on which the toner patch T is formed. Also, the light from the optical sensor is irradiated. For this reason, the amount of specular reflection increases and an accurate amount of adhesion cannot be detected. Therefore, it is necessary to ensure that the toner patch T enters the beam spot diameter. Therefore, conventionally, as shown in FIG. 25, the length of the toner patch T in the main scanning direction and the length in the sub-scanning line direction are made sufficiently longer than the beam spot diameter S of the optical sensor, so that the toner patch T is securely attached. The beam spot diameter S was entered.

However, if the length of the toner patch T in the main scanning direction and the sub-scanning direction is too long with respect to the beam spot diameter S of the optical sensor, there is a problem that the amount of toner consumed during the image quality adjustment process increases. . In view of this, it is conceivable that the length of the toner patch T is made equal to or slightly larger than the beam spot diameter S of the optical sensor so that the size of the toner patch T is minimized.
However, due to use over time, the image carrier 206 may change in position in a direction orthogonal to the moving direction of the image carrier, or the writing position of the toner patch T in the main scanning direction may change. When a position change occurs in the image carrier 206 in a direction perpendicular to the moving direction of the image carrier, the distance between the optical sensor and the surface of the image carrier changes, and the beam spot diameter S of the optical sensor may increase. . As a result of the increase of the beam spot diameter S of the optical sensor, the beam spot diameter S becomes larger than the length of the toner patch T in the main scanning direction and the sub-scanning direction, and the surface of the image carrier other than the toner patch is detected. There is a problem that the toner adhesion amount cannot be detected. When the writing position of the toner patch T in the main scanning direction is changed, the toner patch is shifted in the main scanning direction with respect to the beam irradiation position of the optical sensor, and the optical sensor detects the surface of the image carrier other than the toner patch. End up. Therefore, there is a problem that an accurate toner adhesion amount cannot be detected even when the toner patch is displaced in the main scanning direction.

  The present invention has been made in view of the above problems, and an object of the present invention is to control an image forming apparatus capable of suppressing toner consumption during image quality adjustment control and performing highly accurate toner adhesion amount detection over time. Is to provide.

In order to achieve the above object, the invention of claim 1 is directed to an image carrier that carries a toner image on its moving surface, an optical detection means that detects reflected light from the toner image, and the image carrier. An image quality adjustment toner image is formed on the body surface, and the amount of toner adhesion of the image quality adjustment toner image is detected and detected based on a detection value when the optical detection means detects the image quality adjustment toner image. In the image forming apparatus including image quality adjustment control means for executing image quality adjustment control based on the toner adhesion amount formed, the detection results of the test toner images of the optical detection means having different shapes are formed, and the optical An image quality adjusting toner image determining means for determining the shape of the image quality adjusting toner image based on the detection result of each test toner image of the detecting means is provided.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, a test toner image group having the same detection result is identified from the detection result of each test toner image of the optical detection means. The image quality adjusting toner image determining means is configured to determine a test toner image having the smallest shape in the test toner image group as an image quality adjusting toner image.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the image quality adjusting toner image determining means forms each test toner image so that the lengths in the axial direction of the image carrier are different from each other. The image-bearing body axial length of the image quality adjusting toner image is determined.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the image forming apparatus further comprises a transfer unit that transfers the toner image on the image carrier to a recording medium. Is a non-image output area that does not contribute to image output to the recording medium, and the image quality adjustment toner image and the test toner image are transferred to the non-image output area. It is characterized by forming.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, when the image forming apparatus is used for the first time, the image quality adjusting toner image determining means is controlled to be executed. It is characterized by.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the image quality adjusting toner image determining means is controlled to be executed when the power is turned on.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the image quality adjusting toner image determination unit is controlled to be executed when the optical detection unit is replaced. It is.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the image quality adjusting toner image determining means is executed after correcting the positional deviation of the toner image on the image carrier. It is characterized by controlling.

According to the present invention, a plurality of test toner images having different shapes are formed, and the shape of the image quality adjustment toner image is determined based on the detection result of each test toner image of the optical detection means. In the case of a test toner image having a shape smaller than the beam spot diameter of the optical detection means, the detection result of the optical detection means varies depending on the shape of the test toner image. This is because in the case of a test toner image having a shape smaller than the beam spot diameter of the optical detection means, the optical detection means detects the toner and the surface of the image carrier. That is, since the exposure rate of the image carrier surface at the beam spot diameter varies depending on the shape of the test toner image, the detection result of the optical detection means varies depending on the shape of the test toner image.
On the other hand, in the case of a test toner image having a shape larger than the beam spot diameter of the optical detection means, the detection result of the optical detection means is the same even if the shape of the test toner image is different. In the case of a test toner image having a shape larger than the beam spot diameter, the optical detection means detects only the toner. Therefore, even if the shape of the test toner image is different, the optical detection means detects only the toner, so the detection result is the same.
Since the relationship between the shape of the test toner image and the optical detection means is as described above, when the relationship between the shape of the test toner image and the detection result of the optical detection means is examined, the test toner image becomes larger. As the result, the detection result of the optical detection means changes, and when the shape of the test toner image becomes a certain size, the detection result becomes the same value. Therefore, when the shape of the test toner image changes, the optical detection means changes from a region where the detection result of the optical detection means changes to a region where the detection result does not change even if the shape of the test toner image changes. It can be estimated that the shape of the test toner image is equal to or slightly larger than the beam spot diameter.
Therefore, an image quality adjustment toner image having an optimum shape that is equal to or slightly larger than the beam spot diameter of the optical detection means is determined from the relationship between the shape of the test toner image and the detection result of the optical detection means. Can do. Accordingly, it is possible to detect the toner adhesion amount with high accuracy and to suppress the toner consumption amount during the image quality adjustment control.
The image quality adjusting toner image determining means for determining the image quality adjusting toner image is provided, whereby the image quality adjusting toner image determining means is executed at a predetermined timing to adjust the shape of the image quality adjusting toner image. Can do. As a result, if the image quality adjustment toner image determination means is executed at a timing at which the beam spot diameter of the optical detection means may change or at a timing at which the image quality adjustment toner image may be shifted in the main scanning direction, over time. The toner image for image quality adjustment can be maintained in an optimum shape that is equal to or slightly larger than the beam spot diameter of the optical detection means. Accordingly, it is possible to detect the toner adhesion amount with high accuracy over time, and to suppress the toner consumption amount during the image quality adjustment control.

  According to the first to eighth aspects of the present invention, it is possible to detect the toner adhesion amount with high accuracy over time, and to suppress the toner consumption amount during the image quality adjustment control.

  First, a first embodiment of an electrophotographic printer will be described as an image forming apparatus to which the present invention is applied. FIG. 1 is a schematic configuration diagram showing an image forming process part (process engine part) that performs exposure, charging, development, transfer, and fixing in the printer according to the first embodiment.

  In addition to the components shown in FIG. 1, the printer includes a print controller (indicated by reference numeral 410 in FIG. 5 to be described later) that processes image data sent from a PC (personal computer) and converts it into exposure data, and a high pressure. A high pressure generator (denoted by reference numeral 416 in FIG. 5 to be described later), a control unit (indicated by reference numeral 406 in FIG. 5 to be described later) for controlling the image forming operation, and recording paper as a transfer material as a recording member. A paper supply device (not shown) for supplying P, a manual feed tray (not shown) for manually feeding the recording paper P, a paper discharge tray (not shown) for discharging the recording paper P on which an image has been formed, and the like are provided.

  In FIG. 1, what is indicated by reference numeral 200 is a transfer unit. The transfer unit 200 includes a driving roller 201, a cleaning backup roller 202, a primary transfer nip entrance roller 203, four primary transfer rollers 204Y, C, M, and K, a secondary transfer nip entrance roller 205, an intermediate transfer belt 206, A belt cleaning device 207, a secondary transfer roller 208, a cleaning roller 209, and the like are included. Then, the endless intermediate transfer belt 206 is endlessly moved in the counterclockwise direction in the figure by the rotational driving of the driving roller 201 while being stretched by a plurality of rollers disposed inside the belt loop. The subscripts Y, C, M, and K attached to the end of the reference numerals indicating the four primary transfer rollers indicate members for yellow, cyan, magenta, and black. The same applies to the subscripts Y, C, M, and K attached to the other symbols.

  The intermediate transfer belt 206 as an image carrier has a three-layer structure in which an elastic layer and a surface layer are sequentially laminated on the front surface of the belt base layer having the largest thickness. The belt base layer is made of, for example, a material obtained by combining a fluorine resin having a small elongation or a rubber material having a large elongation with a material that is difficult to stretch, such as canvas. The elastic layer is made of, for example, fluorine-based rubber or acrylonitrile-butadiene copolymer rubber, and is laminated on the front surface of the belt base layer. Further, the surface layer is formed by coating, for example, a fluorine resin on the front surface of the elastic layer.

  Below the transfer unit 200, four image forming units for Y, C, M, and K are arranged along the front surface of the lower stretched portion of the intermediate transfer belt 206. Each of these image forming units includes drum-shaped photoreceptors 101Y, 101C, M, and K, developing devices 103Y, 103M, and K, drum cleaning devices 120Y, 120C, 120M, and 120K. Then, the upper ends of the peripheral surfaces of the photoreceptors 101Y, 101C, 101M, and 101K as image carriers are brought into contact with the lower stretched portion front surface of the intermediate transfer belt 206, respectively, for Y, C, M, and K use. The primary transfer nip is formed.

  Above the transfer unit 200, Y, C, M, and K toner bottles 90Y, C, M, and K, which respectively store Y, C, M, and K toners (not shown), are intermediate transfer belts 206. It is arrange | positioned so that it may be located in a line along the front surface of the upper tension part. The Y, C, M, and K toners stored in the toner bottles 90Y, 90C, 90M, and 90K are respectively developed by developing devices 103Y, 103C, and M by driving toner supply devices for Y, C, M, and K (not shown). K is replenished. The toner bottles 90Y, 90C, 90M, and 90K can be individually attached to and detached from the main body of the image forming apparatus, and are replaced with new ones when the internal toner runs out.

  In the drawing, an optical writing unit 290 is provided below four image forming units arranged in a substantially horizontal direction. This optical writing unit 290 drives Y, C, M, K writing light by driving a semiconductor laser from a laser exposure unit (not shown) provided in the optical writing unit 290 based on image information. Lb is emitted. Then, the writing light Lb scans the photoconductors 101Y, 101C, 101M, and 101K as image carriers on the peripheral surfaces of the photoconductors 101Y, 101C, M, and K that are driven to rotate counterclockwise in the drawing. Write an electrostatic latent image. The emission of the writing light Lb is not limited to the laser, but may be, for example, an LED (light emitting diode).

  Next, the configuration of the image forming unit will be described by taking the image forming unit for K as an example. The image forming units for other colors (Y, C, M) have the same configuration except that the color of the toner to be used is different, and the description thereof will be omitted.

  FIG. 2 is an enlarged configuration diagram showing an image forming unit for K. Various members and devices constituting the image forming unit for K should be suffixed with K at the end of the reference numeral, but in the figure, the suffix is omitted for convenience. In the image forming unit for K, a charging device 102 for uniformly charging the photosensitive member 101, a developing device 103, a drum cleaning device 120, and the like are disposed around the drum-shaped photosensitive member 101.

  The charging device 102 is of a contact charging type in which a charging roller to which a charging bias is applied by a power source (not shown) is brought into contact with the photoconductor 101, and a discharge is generated between the charging roller and the photoconductor 101 to cause the photoconductor. The peripheral surface of 101 is uniformly charged. Instead of the contact charging method using a charging roller, a contact discharge method using a charging brush or a non-contact charging method using a scorotron charger may be used.

  The developing device 103 includes a stirring unit 104 that stirs a two-component developer containing a magnetic carrier (not shown) and a non-magnetic toner, and a developing unit 105 that houses a developing sleeve described later. . In the stirring unit 104, a two-component developer (hereinafter simply referred to as “developer”) is conveyed while being stirred. More specifically, in the stirring unit 104, a first screw member 106 and a second screw member 107 are arranged in parallel, and a partition plate is provided between the two screws. Although the space which accommodates both screws is divided individually by this partition plate, openings are formed at both ends of the partition plate in the screw axial direction. As a result, both spaces communicate with each other at both ends in the screw axis direction. Hereinafter, the space in which the first screw member 106 is accommodated is referred to as a first stirring chamber, and the space in which the second screw member 107 is accommodated is referred to as a second stirring chamber.

  The second screw member 107 is located below the developing unit 105, and the upper end side of its peripheral surface faces the lower end side of the developing sleeve 109 accommodated in the developing unit 105. Then, while being driven to rotate by a driving means (not shown), the developer in the second agitating chamber is supplied to the developing sleeve 109, which will be described later, in the course of transporting the developer from the back side to the front side in the direction orthogonal to the drawing sheet, The used developer is received from 109. The developer conveyed to the front side end in the drawing by the second screw member 107 enters the first stirring chamber through the opening of the partition plate.

  The first screw member 106 conveys the developer in the first stirring chamber from the near side to the far side in the direction orthogonal to the drawing surface while being driven to rotate by a driving means (not shown). A toner concentration sensor 108 is fixed to the bottom wall of the first stirring chamber, and detects the toner concentration of the developer conveyed by the first screw member 106. This detection result is sent to a control unit (not shown) as a toner density signal. Based on the toner density signal, the control unit appropriately drives a toner supply device for K (not shown) to supply an appropriate amount of toner into the first agitation chamber. As a result, the toner density of the developer whose toner density has been reduced accompanying development at the developing unit 105 is recovered. The developer conveyed to the far side end in the drawing by the first screw member 106 enters the second stirring chamber through the other opening provided in the partition plate. In this way, the developer in the developing device 103 is circulated and conveyed through a path of the first stirring chamber → the second stirring chamber → the developing unit → the second stirring chamber → the first stirring chamber. Then, the toner concentration is adjusted in the first stirring chamber.

  The developing unit 105 is provided with a cylindrical developing sleeve 109 that is rotationally driven by a driving unit (not shown). The developing sleeve 109 is provided on the peripheral surface of the developing unit 103 through an opening provided in the casing of the developing device 103. The part is exposed outside the casing. The exposed portion is made to face the photoconductor 101 with a development gap of about 0.9 mm. Further, the developing sleeve 109 includes a magnet roller (not shown) in the hollow. The magnet roller is fixed so that it cannot rotate with the developing sleeve 109 so as not to rotate.

  The developer conveyed by the second screw member 107 in the second stirring chamber described above is attracted to the surface of the developing sleeve 109 by the magnetic force generated by the magnet roller, and is pumped up to the sleeve surface. Then, as the sleeve rotates, the layer thickness on the sleeve is regulated when passing through the gap between the sleeve and the regulating blade 110, and then conveyed to the developing region facing the photoreceptor 110.

  A developing electrode (not shown) is disposed inside the developing sleeve 109 made of a nonmagnetic material, and a developing bias is applied thereto. In the developing area, a developing electric field is formed between the electrostatic latent image on the photoconductor 101 and the developing sleeve 109. The developer transported to the developing area is raised by a magnetic force generated by a developing magnetic pole (not shown) of the magnet roller to form a magnetic brush, and the tip of the brush is rubbed against the photoreceptor 101. Then, the toner in the magnetic brush is separated from the magnetic carrier by the action of the above-described developing electric field and transferred to the electrostatic latent image on the photosensitive member 101. By this transfer, the electrostatic latent image on the photoconductor 101 is developed into a toner image as a visible image.

  When the developer that has passed through the developing region with the rotation of the developing sleeve 109 comes to a position facing the second stirring chamber, the sleeve is caused by the action of a repulsive magnetic field formed by two homopolar magnetic poles (not shown) of the magnet roller. Detach from the surface and fall into the second stirring chamber.

  As a result, the toner in the developer is transferred to the electrostatic latent image portion on the photosensitive member 101, and the electrostatic latent image on the photosensitive member 101 is visualized to form a toner image. The developer that has passed through the development region is transported to a portion where the magnetic force of the magnet is weak, and is separated from the development sleeve 109 and returned to the agitation unit 104.

  Although the developing device 103 adopting the two-component developing method using the two-component developer has been described, a one-component developing method developing device using the one-component developer (toner) not including the magnetic carrier may be adopted. .

  The toner image formed on the peripheral surface of the photoconductor 101 enters the primary transfer nip due to the contact between the photoconductor 101 and the intermediate transfer belt 206 as the photoconductor 101 rotates in the clockwise direction in the drawing. Then, primary transfer is performed on the front surface of the intermediate transfer belt 206. The surface of the photoconductor 101 that has passed through the primary transfer nip enters a position facing the drum cleaning device 120.

  The drum cleaning device 120 has a cleaning blade 121 made of polyurethane rubber or the like, for example, and presses the tip of the cleaning blade 121 against the photoreceptor 101. A small amount of untransferred toner that has not been transferred to the intermediate transfer belt 206 adheres to the surface of the photoreceptor 101 that has passed through the primary transfer nip. This transfer residual toner is scraped off from the surface of the photoreceptor 101 by the cleaning blade 121 and collected in the drum cleaning device 120.

  In addition, the drum cleaning device 120 includes a conductive fur brush 122 that rotates while contacting the surface of the photoconductor 101 just before entering the contact position with the cleaning blade 121. Remove toner.

  The toner removed from the photosensitive member 101 by the cleaning blade 121 and the fur brush 122 is accommodated inside the drum cleaning device 120 and discharged outside the device by the discharge screw 123. The discharged toner is collected in a waste toner bottle (not shown).

  The photosensitive member 101 having a diameter of 40 [mm] is driven to rotate clockwise in the drawing at a linear speed of 200 [mm / sec]. The developing sleeve 109 having a diameter of 25 [mm] is driven to rotate counterclockwise in the drawing at a linear speed of 564 [mm / sec].

  The charge amount of the toner in the developer conveyed to the development region is preferably in the range of about −10 to −30 [μC / g]. The development gap, which is the gap between the photoconductor 101 and the development sleeve 109, is set in the range of 0.5 to 0.9 [mm], and the development efficiency can be improved by reducing this value. Is possible.

  In FIG. 1 described above, the thickness of the photosensitive layer of the photosensitive member 101 is 30 [μm], and the beam spot diameter of the optical writing unit 290 of the optical writing unit (290 in FIG. 1) is 50 × 60 [μm]. The amount of light is about 0.47 [mW]. As an example, the surface of the photosensitive member 101 is uniformly charged to −700 [V] by the charging device (102 in FIG. 2), and the potential of the electrostatic latent image portion irradiated with the laser beam by the optical writing unit 290 is − 120 [V]. On the other hand, the developing bias voltage applied to the developing sleeve (109 in FIG. 2) is −470 [V], which generates a developing potential of 350 [V]. Such process conditions are changed as appropriate according to the result of the potential control.

  The primary transfer rollers 204Y, C, M, and K of the transfer unit 200 are in contact with the back side of the primary transfer nip for Y, C, M, and K of the intermediate transfer belt 206. In this way, a primary transfer bias is applied to the primary transfer roller 204Y in contact with the back surface of the belt by a power source (not shown). Thus, the primary transfer electric field for electrostatically moving the toner images on the photoconductors 101Y, 101C, 101M, and 101K from the surface of the photoconductor toward the belt side in the primary transfer nips for Y, C, M, and K. Is formed. In this printer, the primary transfer rollers 204Y, 204C, 204M, and 204K are employed as the first transfer unit, but a conductive brush shape, a non-contact corona charger, or the like may be employed.

  The intermediate transfer belt 206 sequentially passes through the primary transfer nips for Y, C, M, and K along with the endless movement thereof. Then, Y, C, M, and K toner images are sequentially superimposed on the front surface and primarily transferred. As a result, a superimposed toner image is formed on the front surface of the intermediate transfer belt 206 after passing through the primary transfer nip for K by superimposing the Y, C, M, and K toner images.

  The secondary transfer roller 208 disposed outside the loop of the intermediate transfer belt 206 is in contact with the front surface of the belt so as to sandwich the belt with the driving roller 201 disposed inside the loop. A secondary transfer nip is formed. The drive roller 201 is grounded around the secondary transfer nip, whereas a secondary transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 208. As a result, a secondary transfer electric field is formed in the secondary transfer nip to electrostatically move the toner from the belt front surface side to the secondary transfer roller 208 side as the second transfer means.

  The printer includes a paper feed cassette (not shown), in which a plurality of recording papers are stored in a bundle of paper stacked in the thickness direction. The paper feed cassette sends out the uppermost recording paper in the paper bundle toward the paper feed path at a predetermined timing. The fed recording paper P is sandwiched between the rollers of the registration roller pair 250 disposed near the end of the paper feed path. The registration roller pair 250 sandwiches the leading end portion of the recording paper P between both rollers while rotating its own two rollers, but immediately after that, the rotation driving of both rollers is stopped. Then, at the timing when the recording paper P can be superimposed on the superimposed toner image on the intermediate transfer belt 206 at the secondary transfer nip, the rotational driving of both rollers is resumed. For the recording paper P sandwiched between the secondary transfer nips, the superimposed toner image on the intermediate transfer belt 206 is batch-transferred collectively by the action of the above-described secondary transfer electric field, and combined with the white color of the recording paper P, is full color. It becomes an image.

  As the second transfer means of the transfer unit 200, a system using a transfer charger may be employed instead of the system using the secondary transfer roller 208.

  FIG. 3 is a perspective view showing the transfer unit 200. In the drawing, the width (length in the width direction) of the intermediate transfer belt 206 is larger than the length in the axial direction of the roller portion of the secondary transfer roller 208. Further, the width (length in the direction orthogonal to the transport direction) of the maximum size recording paper P that can be accommodated in a paper feed cassette (not shown) is equal to or less than the axial length of the roller portion of the secondary transfer roller 208. An area of a dimensional difference between both ends in the width direction of the intermediate transfer belt 206 and both ends in the axial direction of the roller portion of the secondary transfer roller 208 is a non-image output area that does not contribute to image output on the recording paper P as a recording medium. It has become. The non-image output areas are test pattern formation areas A1 and A2 in which test patterns described later are formed, respectively. It should be noted that the test pattern includes patch-like Y, C, M, and K image quality adjustment toner patches respectively formed on both ends in the axial direction of the photosensitive member (101Y, C, M, and K in FIG. 1). It is obtained by primary transfer to both ends in the width direction 206.

  Since the secondary transfer roller 208 is in contact with the belt area inside the test pattern formation areas A1 and A2, it does not come into contact with the test pattern. Further, since the recording paper P is interposed between the surface of the roller and the intermediate transfer belt 206 at the time of secondary transfer, the toner image on the intermediate transfer belt 206 is not contacted.

  In FIG. 1 described above, a fixing device 260 is disposed above the secondary transfer nip. The fixing device 260 forms a fixing nip by bringing a fixing roller 261 containing a heat source such as a halogen lamp and a pressure roller 262 into contact with each other. Then, both rollers are rotationally driven so as to move the surfaces in the same direction at the fixing nip. The recording paper P that has passed through the secondary transfer nip enters the fixing device 260 and is then sandwiched by the fixing nip. Then, the full color image is fixed by nip pressure or heating.

  In FIG. 1 and FIG. 3, the optical detection means that faces the test pattern forming area A1 at one end in the belt width direction at a place where the intermediate transfer belt 206 is wound around the driving roller 201 with a predetermined gap. A first reflective photosensor 130 is provided. In addition, a second reflective photosensor 115 is disposed as an optical detection means that faces the test pattern formation region A2 at the other end in the belt width direction with a predetermined gap.

  A cleaning blade 210 of the belt cleaning device 207 is in contact with the cleaning transfer roller 202 on the intermediate transfer belt 206 from the front surface side. This cleaning blade 210 is for removing residual transfer toner remaining on the front surface of the intermediate transfer belt 206 after passing through the secondary transfer nip and the test pattern from the front surface of the belt. The belt is in contact with the entire width direction of the belt.

  FIG. 4 is an enlarged configuration diagram showing the first reflective photosensor 130 as optical detection means. In the figure, the first reflection type photosensor 130 includes an infrared LED 131 as a light emitting element, a regular reflection type light receiving element 132, a diffuse reflection type light receiving element 133, a condensing lens 134, a casing 135, and the like. As the light emitting element, a laser light emitting element or the like may be used instead of the infrared LED. In addition, as the regular reflection type light receiving element 111 and the diffuse reflection type light receiving element 112, phototransistors are used, but it is also possible to use a photodiode or an amplifier circuit.

  Infrared light emitted from the infrared LED 110 passes through the condenser lens 113 and then the test pattern forming region (A1 in FIG. 3) of the intermediate transfer belt 206 and the toner constituting the test pattern thereon. Reach the layer. A part of the infrared light is specularly reflected in the test pattern formation region to become specularly reflected light, and then retransmits through the condenser lens 113 and is received by the specular reflection type light receiving element 111. The other part of the infrared light is diffusely reflected by the test pattern formation region and the toner layer to become diffusely reflected light, and then retransmits through the condenser lens 113 and is received by the diffuse reflection type light receiving element 112. The The configuration of the second reflective photosensor 136 shown in FIG. 3 is the same as that of the first reflective photosensor 130.

  FIG. 5 is a block diagram showing a part of the electric circuit of the printer according to the first embodiment. In the figure, a control unit 406 of the printer performs drive control of various devices of the printer. A CPU (Central Processing Unit) 402 that executes various calculations and drive control of each unit, a ROM (Read Only Memory) 405 that stores in advance fixed data such as a computer program via the bus line 409, and various data A RAM (Random Access Memory) 403 that functions as a rewritable work area or the like, a non-volatile random access memory (NVRAM) 407, an analog / digital conversion circuit (hereinafter referred to as an A / D conversion circuit) 401 Etc.

  The ROM 405 includes a first reflection type photo for estimating the test pattern formation position and density information necessary for generating the test pattern, the bias condition for forming the test pattern gradation, and the test pattern adhesion amount. An adhesion amount conversion table (Look up table) of output voltage values from the sensor 109 and the second reflective photosensor 115 is stored.

  The NVRAM 407 stores information on the length of the intermediate transfer belt axial direction (hereinafter referred to as the main scanning direction) and the length of the intermediate transfer belt moving direction (hereinafter referred to as the sub scanning direction) of the image quality adjustment toner patch. Further, a developing bias Vb as an image forming condition is also stored.

  Further, a print controller 410 is connected to the control unit 406, which transmits image information from a PC (personal computer), a FAX (facsimile), a scanner, and the like as unified image data to the control unit 406. An A / D conversion circuit 401 that converts various sensor information into digital data, a drive circuit 414 that drives a motor and a clutch, a high voltage generator 416 that generates a voltage necessary for image formation, and the like are also connected.

Next, the operation of the printer according to the first embodiment will be described with reference to FIGS.
When printing with information from a PC using this printer, first, image information is transmitted using a printer driver on the PC. The print controller 410 receives print information from the printer driver and sends an exposure signal to the optical writing unit 290.

  Upon receiving the print command, the control unit 406 drives various drive motors (not shown) to move the intermediate transfer belt 206 endlessly. At the same time, the photoreceptors 101Y, 101C, 101M, and 101K of each image forming unit are also driven to rotate.

  Thereafter, based on the information from the print controller 410, the optical writing unit 290 irradiates the writing light Lb onto the photoreceptors 101Y, 101C, 101M, and 101K, respectively. As a result, electrostatic latent images are formed on the photoreceptors 101Y, 101C, 101M, and 101K, respectively, and are visualized by the developing devices 103Y, 103Y, 103M, and K. Then, Y, C, M, and K toner images are formed on the respective photoreceptors 101Y, 101C, 101M, and 101K. These Y, C, M, and K toner images are primarily transferred to the intermediate transfer belt 206 at the Y, C, M, and K primary transfer nips to form a superimposed toner image.

  On the other hand, in a paper feed cassette (not shown), the recording paper P is sent out by the rotational drive of the paper feed roller. The fed recording paper P is separated into one sheet by a separation roller (not shown) and enters the paper feed path, and is then sandwiched between the registration roller pair 250.

  When recording paper P not set in a paper feed cassette (not shown) is used, the recording paper P set in a manual feed tray (not shown) is sent out by a paper feed roller (not shown) and separated into one sheet by a separation roller (not shown). Thereafter, the sheet is fed into the registration roller pair 250.

  The registration roller pair 250 feeds the recording paper P toward the secondary transfer nip at a timing at which it can be superimposed on the superimposed toner image formed on the intermediate transfer belt 206. Note that the registration roller pair 250 is generally used while being grounded, but a bias may be applied to remove paper dust from the recording paper P.

  The superposed toner image on the intermediate transfer belt 206 is secondarily transferred collectively onto the recording paper P fed out by the registration roller pair 250 and sandwiched between the secondary transfer nips. Thereafter, the recording paper P passes through the fixing device 260 as described above and is then discharged outside the apparatus.

  When an image is also formed on the other side of the recording paper P on which the toner image is fixed on one side by the fixing device 260, the recording paper P that has passed through the fixing device 260 is first used by a switchback device (not shown). The image is retransmitted to the registration roller pair 250 while being reversed.

Next, an outline of the image quality adjustment process performed by the CPU 402 of the printer according to the first embodiment will be described. FIG. 6 is a flowchart showing a control flow in image quality adjustment processing. When a power switch of the main body (not shown) is powered on or a print command is received (Y in step 502, step is hereinafter referred to as S), the necessity of image quality adjustment processing is determined (S503).

  Immediately after power-on, the heating time of the fixing heater and the preparation time of the print controller are required. Using this time, image quality adjustment processing is performed as necessary. Specifically, the printer has a surface temperature sensor (not shown) that detects the surface temperature of the fixing roller (261 in FIG. 1). If the detection result by the surface temperature sensor is lower than the predetermined temperature, it means that the image forming operation has not been performed for a relatively long time, and the environment changes greatly compared to the previous image forming operation. There is a possibility. Therefore, when the detection result by the surface temperature sensor is equal to or lower than the predetermined temperature, image quality adjustment processing is performed.

  In addition, for users who do not turn on and off frequently, the environment and the like change during power-on. Therefore, during power-on, the photoreceptor stop time, in-machine temperature, and in-machine humidity are monitored. When the print command is received, the photosensitive member stop time is 6 hours or more, the in-machine temperature has changed by 10 ° C. or more from the end of the previous image forming operation, or the in-machine humidity has ended the previous image forming operation. When it is determined that the change has occurred by 50% or more from the time, image quality adjustment processing is performed.

  The stop time of the photosensitive member is obtained as follows. That is, when the photosensitive member is stopped, time information is acquired from the real-time clock mounted on the print controller 410 in FIG. Similarly, when receiving a print command, time information is acquired from the real-time clock, and the photosensitive member stop time is obtained from the difference.

  Further, changes in temperature and humidity are grasped as follows. That is, temperature information and relative humidity information are acquired from the in-machine temperature / humidity sensor 414 when the photoconductor is stopped, and temperature information and relative humidity information are acquired from the temperature / humidity sensor 414 in the same manner when a print command is received. The relative humidity change is determined.

  In FIG. 6, the flow is not shown for convenience, but in this printer, the cumulative number of prints is counted, and image quality adjustment processing is performed every time the cumulative number of prints increases by a predetermined number. The increased number of prints that triggers the start of image quality adjustment processing is set based on the amount of process variation obtained by a previous experiment. Instead of the increased number of prints, the travel distance of the developing sleeve (109 in FIG. 2) or the intermediate transfer belt (206 in FIG. 1) may be used as a trigger.

  If it is determined that the image quality adjustment process is necessary (Y in S503), the length information in the main scanning direction of the image quality adjustment toner patch stored in the NVRAM (407 in FIG. 5) and the sub-image of the image quality adjustment toner patch are stored. A gradation pattern is formed based on the scanning direction length information and the like (S504). FIG. 7 is a plan view showing the intermediate transfer belt 206 on which the gradation pattern is formed and the surrounding configuration from above. In this figure, the roller portion of the secondary transfer roller 208 is in contact with the front surface of the intermediate transfer belt 206 in a posture extending in the belt width direction to form a secondary transfer nip. The length of the portion in the axial direction is smaller than the belt width. For this reason, non-image output regions that are not in contact with the roller portions are formed on both sides of the roller portion of the secondary transfer roller 208 in the axial direction, and these regions are the test pattern formation regions A1 and A2. Yes. In the test pattern formation area A1 of the intermediate transfer belt 206, the Y gradation pattern TpY and the C gradation pattern TpC are formed so as to be aligned in the belt moving direction. Further, the M gradation pattern TpM and the K gradation pattern TpK are formed in the test pattern formation area A2 of the intermediate transfer belt 206 so as to be aligned in the belt moving direction.

  Each of these gradation patterns includes five image quality adjustment toner patches, which are five image quality adjustment toner images arranged in the belt moving direction. Further, the length in the main scanning direction and the length in the sub-scanning direction of the five image quality adjustment toner patches are determined by a toner patch adjustment process described later.

  The image forming conditions of the five image quality adjustment toner patches are different. Specifically, the first image quality adjusting toner patch is formed under the condition that the background potential (uniform charging potential) of the photoreceptor is −300 [V] and the developing bias is −100 [V]. The second image quality adjusting toner patch is formed under the condition that the background potential of the photosensitive member = −350 [V] and the developing bias = −150 [V]. The third image quality adjusting toner patch is formed under the condition of the background potential of the photoreceptor = −400 [V] and the developing bias = −200 [V]. The fourth image quality adjusting toner patch is formed under the conditions of the background potential of the photoreceptor = −450 [V] and the developing bias = −250 [V]. The fifth image quality adjusting toner patch is formed under the conditions of the background potential of the photoreceptor = −500 [V] and the developing bias −300 [V]. The developing potential condition of any image quality adjustment toner patch is 200 [V].

  Each of the image quality adjustment toner patches in the Y gradation pattern TpY and the C gradation pattern TpC formed in the test pattern formation area A1 of the intermediate transfer belt 206 is transferred to the first reflective type as the intermediate transfer belt 206 moves endlessly. Passes directly under the photo sensor 130. At this time, the first reflective photosensor 130 detects the amount of reflected light as an optical characteristic. In addition, each of the image quality adjustment toner patches in the M gradation pattern TpM and the K gradation pattern TpK formed in the test pattern formation area A2 of the intermediate transfer belt 206 has the second end as the intermediate transfer belt 206 moves endlessly. It passes directly under the reflective photosensor 136. At this time, the amount of reflected light is detected by the second reflective photosensor 136.

  Specifically, the analog output voltage value from the reflective photosensor (130, 136) is converted into digital data by the A / D conversion circuit (401 in FIG. 5), and then the control unit (406 in FIG. 5). CPU (402 in FIG. 5). The CPU stores the above-mentioned digital data in the RAM 403 every 2 [msec] in anticipation of the timing at which each image quality adjustment toner patch passes directly below the reflective photosensor. For example, when the size of the image quality adjustment toner patch is 15 [mm] and the belt moving speed is 200 [mm / sec], (15/200 × 1000) / 2≈38 per patch. Are sampled. For the purpose of removing noise at the time of measurement, the CPU excludes the upper 10 of the 38 values and the lower 10 of the lower values, and then averages the remaining 18 data. A value is obtained and stored in the RAM as an average sensor output value (average reflected light amount) for the toner patch.

  When the control unit (406 in FIG. 5) as the image quality adjustment control unit of the printer obtains the average sensor output value for each image quality adjustment toner patch in this way (S505 in FIG. 6), reflection is performed based on the result. The amount of received light R [n] is obtained. For each of the colors Y, M, C, and K, the received light amount R [n] for the five image quality adjustment toner patches, and the adhesion amount conversion table stored in the ROM (405 in FIG. 5), Based on the above, the toner adhesion amount per unit area for each image quality adjustment toner patch is obtained. Next, for each color, an approximate linear expression indicating the relationship between the developing bias Vb [n] corresponding to the image quality adjustment toner patch and the toner adhesion amount MA [n] is obtained by the least square method (S506 in FIG. 6). Then, based on the approximate linear equation and a predetermined target value of the toner adhesion amount, the development bias Vb as an image forming condition suitable for the environment at that time is specified and stored in the NVRAM. Further, by subtracting a predetermined developing potential (for example, 200 V) from the developing bias Vb, a photosensitive member uniform charging potential (background portion potential) as an image forming condition suitable for the environment at that time is obtained and stored in the NVRAM (FIG. 6 S507, S508). In the subsequent printing process, the image forming units of the respective colors are set to the image forming conditions stored in the NVRAM and operated.

  In this printer, the toner adhesion amount to the K image quality adjustment toner patch is obtained based on the amount of specularly reflected light received by the second reflective photosensor (136 in FIG. 7). Further, the toner adhesion amount to the M image quality adjustment toner patch is obtained based on the amount of diffusely reflected light received by the second reflective photosensor. Further, the amount of toner attached to the Y, C image quality adjustment toner patch is obtained based on the amount of diffusely reflected light received by the first reflective photosensor (130 in FIG. 7).

  The example of adjusting the developing bias Vb and the uniform charging potential of the photosensitive member has been described as the imaging condition. However, other imaging conditions such as optical writing intensity and toner density on the photosensitive member may be adjusted. Good.

  FIG. 8 is a graph showing the relationship between the amount of regular reflection light received by the regular reflection type light receiving element of the reflection type photosensor and the toner adhesion amount to the K image quality adjustment toner patch. In a K image quality adjustment toner patch made of K toner that does not have light reflectivity, almost all of the reflected light received by the regular reflection type light receiving element becomes regular reflected light that is regularly reflected by the surface of the intermediate transfer belt 206. . When the toner adhesion amount increases to an amount corresponding to the visual image density increase saturation point, the light reception amount of the regular reflection type light receiving element becomes substantially zero. With such characteristics, the toner adhesion amount can be obtained by directly substituting the average sensor output value Vsp_reg of the regular reflection type light receiving element into a conversion formula such as a proportional formula. However, it is necessary to calibrate the reflective photosensor prior to detecting the gradation pattern. The amount of light emitted from the light-emitting element of the reflective photosensor varies due to changes in the internal temperature (particularly due to the heat generated by the operation of the device), or the amount of light received by the light-receiving element depends on changes in the optical axis and directivity due to the internal temperature Because it fluctuates.

In this printer, the reflection type photosensor is calibrated as follows. That is, the background which is the average sensor output value of the regular reflection type light receiving element at the time when light is emitted from the light emitting element to the background where no toner is placed in the test pattern forming area (A1, A2) of the intermediate transfer belt 206. The light emission amount of the light emitting element is adjusted so that the output value Vsg_reg becomes a predetermined value. The background output value Vsg_reg is obtained by averaging 10 output values. Next, when the average sensor output value Vsp1_reg in the regular reflection type light receiving element is detected for the first of the five K image quality adjustment toner patches in the K gradation pattern, the received light amount R [n] is calculated based on the following equation. After that, the K toner adhesion amount corresponding to the received light amount R [n] is specified from the above-described adhesion amount conversion table. For the second, third, fourth, and fifth K image quality adjustment toner patches, the toner adhesion amount is specified in the same manner.
R [n] [Bk] = Vsp_REG / Vsg_REG

In this printer, the toner adhesion amount of each image quality adjustment toner patch in the Y, C, and M gradation patterns is obtained as follows.
FIG. 9 is a graph showing the relationship between the amount of diffusely reflected light received by the diffuse reflection type light receiving element of the reflection type photosensor and the amount of toner attached to the Y, C, M image quality adjustment toner patch. As shown in FIG. 8, in the regular reflection type light receiving element that uses the K image quality adjustment toner patch as a test object, as the toner adhesion amount increases, the regular reflection light obtained on the belt surface decreases. The output voltage value decreases. On the other hand, in the diffuse reflection type light receiving element in which the Y, C, M image quality adjustment toner patches are to be examined, as the adhesion amount of these color toners having diffuse reflection increases, as shown in FIG. Since the diffuse reflection light obtained on the particle surface increases, the amount of light received by the light receiving element increases. In the case of color toners, the amount of received light continues to increase monotonously even when the toner adhesion amount exceeds the amount corresponding to the visual image density increase saturation point. With such characteristics, it is difficult to accurately detect the color toner adhesion amount with the diffuse reflection type light receiving element alone.

  However, in this embodiment, the color toner adhesion amount can be accurately detected by the diffuse reflection type light receiving element alone by using the following method.

  In FIG. 7 described above, in the test pattern formation areas A1 and A2 of the intermediate transfer belt 206, standard reflection portions 206a as standard optical characteristic portions are formed at predetermined positions in the belt circumferential direction. The standard reflection portion 206a is formed in the test pattern formation areas A1 and A2 by sticking the seal to the belt surface, vapor deposition, printing, or the like, and the lightness of the Munsell color system is adjusted to 7.5. Yes. On the other hand, the background portion of the intermediate transfer belt 206 (the portion where the standard reflection portion 206a is not provided) has a blackish color and the lightness of the Munsell color system is adjusted to about 1-2.

  In addition, the control unit (406 in FIG. 5) of the printer stores the standard diffuse reflection output value Vtref_tgt obtained by a previous test in the ROM. This standard diffuse reflection output value Vtref_tgt is a sensor having the same configuration as that of the first reflective photosensor 130 shown in FIG. 4, and diffuse reflected light obtained on the surface of the standard reflective portion 206a under the condition of a predetermined light emission amount. This is the sensor output value obtained when detected.

To calculate the toner adhesion amount of each image quality adjustment toner patch in the Y, C, and M gradation patterns, first, the diffusion-type light reception of the reflection type photosensor (130, 136) having the standard reflection unit 206a as the test object. The average value of the output values from the elements is obtained in the same manner as the image quality adjustment toner patch, and stored in the RAM as the standard sensor output Vtref. Next, average sensor output values Vsp1_dif, Vsp2_dif, Vsp3_dif, Vsp4_dif, Vsp5_dif in the diffusion-type light receiving element for each image quality adjustment toner patch are acquired and stored in the RAM. Then, the diffuse reflection light amount R [n] for the toner patch is obtained by the following gain correction formula.
Each of the average sensor output values Vsp [n] _dif is gain-corrected.
R [n] = Vsp [n] _dif × (Vtref_tgt / Vtref)

  Assume that Vsp1_dif = 1 [V], Vsp2_dif = 2 [V], and Vsp3_dif = 3 [V] are obtained under the same conditions as in the test in which the standard diffuse reflection output value Vtref_tgt was obtained in the laboratory. . Under the user's circumstances, the environmental conditions fluctuate and the reflective photo sensor is different from the one used in the previous test. I can't. Even in such a situation, it is possible to accurately detect the amount of diffusely reflected light in the color image quality adjustment toner patch by performing gain correction as described above. For example, when the light emission amount of the light emitting element is 1.5 times that in the same test, Vsp1_dif = 1.5 [V], Vsp2_dif = 3 [V], Vsp3_dif = 4.5 [V]. However, since they are respectively corrected to 1 [V], 2 [V], and 3 [V] by gain correction, the diffuse reflection light amount is obtained with the same value as in the same test.

  In this printer, the image forming means is constituted by the image forming unit for Y, M, C, K shown in FIG. 1, the optical writing unit 290, the control unit (406 in FIG. 5), and the like. Then, this image forming means transfers the gradation pattern formed in the non-image output area of the photosensitive member to a position shifted from the standard reflecting portion 206a in the test pattern formation area (A1, A2) of the intermediate transfer belt 206. As described above, the latent image writing start timing (optical writing start timing) for obtaining the gradation pattern is determined. Specifically, based on the detection of the standard reflection portion 206a by the reflection type photo sensor for each belt revolution, the position of the standard reflection portion 206a on the belt track is grasped at each turn, and based on the grasp result. Thus, the gradation pattern starts to be formed at a position shifted from the standard reflecting portion 206a by a predetermined amount to the downstream side in the belt moving direction.

  Note that the toner adhesion amount of each image quality adjusting toner patch in the Y, C, and M gradation patterns can be obtained without providing the standard reflection portion 206a on the intermediate transfer belt. In this case, the toner adhesion amount of each image quality adjustment toner patch in the Y, C, and M gradation patterns is obtained using the output value of the regular reflection light receiving element.

First, the background output which is an average value of the output values from the regular reflection type light receiving elements in the background portion where the toner is not placed in the test pattern formation areas (A1, A2) of the intermediate transfer belt 206 after the light emission amount adjustment of the light emitting elements. The background output value Vsg_dif which is an average value of the value Vsg_reg and the output value from the diffused light receiving element is stored in the RAM.
Next, regular reflection is performed based on the relationship between the average sensor output value Vsp [1-5] _reg in the regular reflection type light receiving element in the color image quality adjustment toner patch and the average sensor output value Vsp [1-5] _dif in the diffuse reflection type light receiving element. The sensitivity correction coefficient (K2) of the light receiving element is obtained.
K2 = MIN (Vsp [n] _reg / Vsp [n] _dif)

Next, a value (K [n]) obtained by removing the toner diffuse reflection component from the output voltage of the regular reflection light receiving element is obtained. This value represents a regular reflection light component from the intermediate transfer belt 206 of each image quality adjustment toner patch.
K [n] = (Vsp [n] _reg−Vsp [n] _dif × K2) / (Vsg [n] _reg−Vsg [n] _dif × K2)

Next, the diffuse reflection component from the intermediate transfer belt 206 is removed from the output voltage of the diffuse reflection light receiving element, and only the diffuse reflection component from the color toner of each image quality adjustment toner patch is separated.
Vsp [n] _dif_dush = Vsp [n] _dif−Vsg [n] _dif × K [n]

Next, gain adjustment is performed to correct variations in the toner output of the diffuse reflection light receiving element. This gain adjustment is performed by obtaining a gain adjustment coefficient K5.
K5 = 1.63 / (α × 0.15 ^ 2 + β × 0.15 × γ)
(Α, β, and γ are coefficients of square terms obtained by quadratic approximation when the X axis is K [n] of each gradation pattern and the Y axis is Vsp [n] _dif_dush of each image quality adjustment toner patch. 1 represents the coefficient of the first power term and the y-intercept, and the approximate straight line is obtained by the least square method, and the constants in the equation are values obtained beforehand through experiments or the like.

Next, normalization calculation is performed.
R [n] [YCMK] = K5 × Vsp [n] _DIF_dush
At this point, sensor attachment and individual variation of the detection system and reflection characteristic change of the intermediate transfer belt 206 are substantially canceled and determined uniquely. Next, the relationship between the toner adhesion amount for the colors Y, C, M, and K obtained in advance through experiments or the like is determined, and the toner adhesion amount MA [n] is obtained from the table and R [n] and [YCMK].

  In addition, the printer according to the first embodiment performs misregistration correction control at a predetermined timing. In the following, an example of misregistration correction control performed by the CPU 402 will be described with reference to Japanese Patent Laid-Open No. 2002-207338.

  FIG. 10 is a flowchart showing a control flow in the misregistration correction process (color matching).

  The misregistration correction processing (color matching) is performed when (1) when the fixing temperature of the fixing device 260 is less than 60 ° C. and the power is turned on, (2) any of K, Y, C, and M units (image forming units). Is replaced with a new one, (3) When there is a color matching instruction from the operation display board or PC411, (4) When the specified number of printouts have been completed and the in-machine temperature is the previous color matching When the temperature has changed by more than 5 ° C, and (5) the specified number of printouts have been completed, and the number of color prints has increased by 200 or more than the value at the previous color matching. When to run.

  When color matching, which is a positional deviation correction process, is executed, the control unit 406 first performs a test on the intermediate transfer belt 206 as shown in FIG. 11 in “test pattern formation and measurement” (PFM). A start mark Msr and eight sets of misregistration correction test patterns are formed in the pattern formation area A1. Further, the start mark Msf and eight sets of misregistration correction test patterns are formed in the test pattern formation region A2. The misregistration correction test pattern is composed of an orthogonal mark group parallel to the main scanning direction and an oblique mark group forming an angle of 45 ° with respect to the main scanning direction. The orthogonal mark group includes a K-color orthogonal mark Akc, a Y-color orthogonal mark Ayc, a C-color orthogonal mark Acc, and an M-color orthogonal mark Amc. The oblique mark group includes the K-colored oblique mark Bkc. , Y color oblique mark Byc, C color oblique mark Bcc, and M color oblique mark Bmc. The start mark and eight sets of misalignment correction test patterns are detected by the reflection type photosensors (130, 136), and the detection signals Sdr, Sdf (output values of the regular reflection light receiving elements) are converted into the above-described A / D conversion circuit (FIG. 5 401) is converted into digital data Ddr and Ddf and read.

  The control unit 406 calculates the position (distribution) on the intermediate transfer belt 206 at the center point of each mark from the digital data Ddr and Ddf. Further, the control unit 406 calculates an average pattern (average group of patch positions) of the rear side test pattern group (eight sets of rear side positional deviation correction test patterns) and an average pattern of the front side test pattern group. Details of this “test pattern formation and measurement” (PFM) will be described later.

  When calculating the average pattern, the control unit 406 calculates an image formation shift amount by each of the K, Y, C, and M image forming units based on the average pattern (DAC), and calculates the calculated image formation. Based on the amount of displacement, adjustment is made to eliminate image formation displacement (DAD).

FIG. 12 is an execution flow of test pattern formation and measurement.
First, the control unit 402 simultaneously applies, for example, a width w in the sub-scanning direction (Y direction in FIG. 11) to each of the test pattern formation areas A1 and A2 of the intermediate transfer belt 206 driven at a constant speed of 200 [mm / sec]. Is 1 [mm], the length A in the main scanning direction (X direction in FIG. 11) is, for example, 10 [mm], the pitch d is, for example, 6 [mm], and the interval c between sets is, for example, 9 [mm]. Formation of the marks Msr and Msf and eight sets of misregistration correction test patterns is started. The timer T1 with a time limit value Tw1 is started (1) for the timing immediately before the start marks Msr and Msf arrive immediately below the reflection type photosensors (130, 136). ) Wait to do (2). When the timer T1 runs out of time (T1 = Tw1), the control unit 402 detects that the last misregistration correction toner patch of the test pattern group on each of the rear r and front f of the intermediate transfer belt 206 is a reflective photosensor (130, 136). ) To start the timer T2 whose time limit value is Tw2 for measuring the timing of finishing passing (3).

  When the K, Y, C, or M mark is not present in the visual field of the reflection type photosensor (130, 136), the output voltage of the regular reflection light receiving element of the photosensor reflection type photosensor (130, 136) is 4V. On the other hand, when the mark of the amount of adhesion corresponding to the visual image density increase saturation point fills the visual field of the reflection type photosensor (130, 136), the output voltage of the regular reflection light receiving element is 0V. For this reason, when the orthogonal mark or the oblique mark enters the field of view (beam spot diameter) of the reflection type photosensor (130, 136), the output voltage of the regular reflection light receiving element decreases. When the orthogonal mark or the oblique mark moves, the ratio of the surface of the intermediate transfer belt captured by the field of view of the reflective photosensor (130, 136) (the exposed portion of the intermediate transfer belt in the beam spot diameter) decreases. When the mark comes to the center of the field of view (the center of the beam spot diameter in the sub-scanning direction), the intermediate transfer belt portion captured by the field of view of the reflective photosensor (130, 136) is the smallest, and the output value is 0. It drops to around [V]. As the mark moves further, the portion of the intermediate transfer belt captured by the field of view of the reflective photosensor (130, 136) gradually increases, and when the mark falls out of the field of view of the reflective photosensor (130, 136) Since only the surface of the intermediate transfer belt is captured in the visual field of the type photosensor (130, 136), the output value is 4 [V]. As a result, the output voltage of the regular reflection light-receiving element varies in level as shown in FIG. 13 due to the constant speed movement of the intermediate transfer belt 206. FIG. 14A is an enlarged view of a part of the level fluctuation.

  In FIG. 15A, the descending region where the level of the output voltage of the regular reflection light receiving element is lowered corresponds to the leading edge region of the mark. The rising area where the level of the output voltage of the regular reflection light receiving element is rising corresponds to the trailing edge area of the mark. A width w in the sub-scanning direction of the mark is between the descending region and the ascending region.

The control unit 406 is provided with a window comparator (not shown) that transmits a determination signal from the output voltage of the regular reflection light receiving element of the reflection type photosensor (130, 136). This window comparator transmits an L determination signal when the output voltage of the regular reflection light receiving element is 2 to 3 [V], and transmits an H determination signal otherwise.
In the process in which the start marks Msr and Msf arrive in the field of view of the reflective photosensors (130, 136) and the output voltage of the regular reflection light receiving element changes from 5 [V] to 0 [V], the controller 406 It waits for the level determination signals Swr and Swf output from the window comparator shown to change from the H determination signal to the L determination signal.
As shown in FIG. 14B, the L determination signal output from the window comparator (not shown) when the output voltage of the regular reflection light receiving element is 2 to 3 [V] corresponds to the edge region of the mark. That is, the fact that the level determination signals Swr and Swf are L means that the mark edge has arrived in the field of view of the reflective photosensor (130, 136). That is, in Step 4, the control unit 406 monitors whether or not the tips of the start marks Msr and Msf have arrived in the field of view of the reflective photosensors (130, 136).

  When the edge region of the start marks Msr and Msf arrives in the field of view of the reflection type photosensor (130, 136), the timer T3 with a very short time (for example, 50 [μsec]) is started. The shorter the time limit value Tsp, the more accurately the position of the center point can be calculated, but the amount of data stored in the RAM increases. On the other hand, if the time limit value Tsp is lengthened, the amount of data stored in the RAM can be reduced, but the position of the center point of the patch cannot be accurately calculated. Therefore, the time limit value Tsp is determined in consideration of the capacity of the RAM and the accuracy of the position of the center point of the patch.

  When the timer T3 times out (becomes Tsp), the control unit 406 permits and executes “interrupt processing” (TIP) shown in FIG. 15 (5). Next, the control unit 406 initializes the sampling number value Nos of the sampling number register Nos to 0. Also, the write addresses Noar and Noaf of the r memory (rear mark read data storage area) and f memory (front mark read data storage area) allocated to the FIFO memory in the control unit are initialized to the start addresses (6). The control unit 406 waits for the timer T2 to time out (Tw2), that is, all of the eight sets of misregistration correction test patterns have passed through the field of view of the reflective photosensor (130, 136). (7)

  Here, the interrupt process will be described. FIG. 15 is an execution flow of “interrupt processing” (TIP). This "interrupt processing" (TIP) processing is executed every time the timer T3 whose time limit value is Tsp times out. First, the control unit 406 starts a timer T3 (11) and instructs the A / D conversion circuit 401 to perform A / D conversion (12). That is, the analog output voltage value Sdr from the reflective photosensor (130, 136) is converted into digital data by the A / D conversion circuit (401 in FIG. 5) and held in the data latch. Further, the control unit 406 increments one sampling number value Nos in the sampling number register Nos which is the number of A / D conversion instructions (13).

  Nos × Tsp is an elapsed time from the detection of the leading edge of one of the start marks Msr and Msf (= a reflective photosensor in the sub-scan line direction based on one of the start marks Msr and Msf). 130, 136) and the current position of the intermediate transfer belt 206).

  The control unit 406 checks whether or not the detection signal Swr from the window comparator (not shown) is L (the reflection type photosensor 130 is detecting the edge portion of the mark, and 2V <Sdr <3V) (14). . When the detection signal Swr from the window comparator is L (YES in S14), the sampling number value Nos of the sampling number register Nos and the A / D conversion data Ddr held in the data latch are written as write data to the address Noar of the r memory. (The digital value of the output value Sdr of the regular reflection light receiving element of the reflective photosensor 130) is written (15), and the write address Noar of the r memory is incremented by one (16).

  When the detection signal Swr from the window comparator (not shown) is H (Sdr <2V or 3V <Sdr), the control unit 406 does not write the A / D conversion data Ddr held in the data latch to the r memory. This is for reducing the amount of data written to the memory and simplifying subsequent data processing.

  Next, similarly, the control unit 406 checks whether the detection signal Swf from the window comparator (not shown) is L (the reflection type photosensor 136 is detecting the edge portion of the mark, and 2V <Sdf <3V). (17) If the detection signal Swf from the window comparator (not shown) is L, the sampling number value Nos of the sampling number register Nos and the A / D conversion data Ddf (reflection) are written to the address Noaf of the f memory as write data. The digital value of the output value Sdf of the regular reflection light receiving element of the photosensor 136 is written (18), and the write address Noaf of the f memory is incremented by one (19).

  Since such interruption processing is repeatedly executed at a period of time Tsp, the output values Sdr and Sdf of the regular reflection light receiving elements of the reflection type photosensors (130, 136) are high as shown in FIG. When changing to low, the r memory and f memory allocated to the FIFO memory in the control unit 406 include the digital data of the detection signals Sdr and Sdf within the range of 2V to 3V as shown in FIG. Only Ddr and Ddf are stored together with the sampling number value Nos. From the sampling number value Nos stored in each memory (r, f), the position in the sub-scanning direction from the start mark in each mark of the misregistration correction test pattern can be indicated (time Tsp × sampling number value Nos × intermediate). Transfer belt conveyance speed).

  After the last mark of the test pattern group (the M-color oblique marks Bmr, Bmf of the eighth misregistration correction test pattern) passes through the reflective photosensors (130, 136), the timer T2 times out (T2 = Tw2). As shown in the flow of FIG. 12, when the timer T2 is over (YES in 7), interrupt processing is prohibited (8). Next, the control unit 406 calculates the center position of each mark based on the detection data Ddr and Ddf of the r memory and f memory of the FIFO memory (CPA).

  The calculation of the center point position of the mark is performed as follows. The data written to the write addresses Noar and Noaf of each memory has a falling area where the level of the output voltage of the regular reflection light receiving element is reduced within the range of 2V to 3V shown in FIG. A plurality of data corresponding to the next rising area is stored. First, the center position a is calculated from a plurality of data corresponding to the descending area of the first K-color orthogonal mark Akr, and the center position b is calculated from the plurality of data corresponding to the K-color misregistration correction toner patch increasing area. Next, a K-color orthogonal mark center point (intermediate point Akrp) is calculated from the center position a and the center position b. Similarly, the center position c of the descending area of the next mark (Y color orthogonal mark Ayr) and the center position d of the ascending area that is ascending next are calculated from a plurality of data corresponding to each area. From this, the Y-color orthogonal mark center point (intermediate point Ayrp) is calculated. Such processing is performed for each misregistration correction toner patch.

  This will be specifically described below with reference to FIGS. 16 and 17. 16 and 17 are flowcharts of “calculation of mark center point position” (CPA). Here, “calculation of mark center point position of rear r” (CPAr) and “calculation of mark center point position of front f” (CPAf) are executed.

  In “calculation of mark center point position of rear r” (CPAr), first, the read address RNoar of the r memory allocated to the FIFO memory in the inside is initialized, and the data of the edge center point number register Noc is first stored. It is initialized to 1 which means an edge (21). This edge center point number register Noc corresponds to a, b, c, d... Shown in FIG. Next, the control unit 406 initializes the data Ct of the one-edge region sample number register Ct to 1, and initializes the data Cd and Cu of the descending number register Cd and the ascending number register Cu to 0 (22). Next, the control unit 406 writes the read address RNoar in the edge area data group start address register Sad (23). The above is preparation processing for data processing of the first edge region.

  Next, the control unit 406 reads data (position Nos: N · RNoar, detection level Ddr: D · RNoar in the sub-scanning direction) from the address RNoar of the r memory. The position Nos: N · RNoar in the sub-scanning direction is a value calculated by multiplying the time Tsp, the sampling number value Nos, and the conveyance speed of the intermediate transfer belt. The control unit 406 also reads data (sub-scanning direction position Nos: N · (RNoar + 1), detection level Ddr: D · (RNoar + 1)) from the next address RNoar + 1. The difference in the sub-scanning direction position (N · (RNoar + 1) −N · RNoar) between the read data is equal to or less than E (for example, E = w / 2 = for example 1/2 [mm] equivalent value) (on the same edge region). Is checked (24). If the difference in the sub-scanning direction position between the read data is E or less (24 YES), is the detection level difference between the read data (D · RNoar−D · (RNoar + 1)) 0 or more? It is determined whether or not (25). When the difference between the detection levels of both data is 0 or more (YES in 25), the data tends to decrease, so the data Cd of the decrease count register Cd is incremented by one (S27). On the other hand, when the difference between the detection levels of the two data is 0 or less (NO in 25), the data Cu in the ascending number register Cu is incremented by one (26) because there is a tendency to increase.

  Next, the control unit 406 increments the data Ct of the in-edge sample number register Ct by one (28). Then, the control unit 406 checks whether or not the r memory read address RNoar is the end address of the r memory (29). If the r memory read address RNoar is not the end address of the r memory (NO in S29) ) Increments the memory read address RNoar by one (30) and repeats the above processing (24-30).

  On the other hand, when the read data is changed from the first edge area to the next edge area, in step 24, the position difference (N · (RNoar + 1) −N · RNoar) of the respective position data of the preceding and following memory addresses becomes larger than E. (NO in S24), the process proceeds from step 24 to step 31 in FIG. By proceeding to Step 31, all the sampling data in one mark edge (leading edge or trailing edge) area have been checked for downward and upward trends.

  Next, the control unit 406 checks whether the sample number data Ct in the one-edge sample number register Ct at this time is an equivalent value in one edge region (31). That is, it is checked whether or not F ≦ Ct ≦ G. Here, F is a lower limit value of data written to the r memory when the leading edge or the trailing edge of a normally formed mark is detected, and G is the leading edge of the normally formed mark or This is the upper limit value (set value) of data written to the r memory when the trailing edge is detected.

  When Ct is F ≦ Ct ≦ G (YES in 31), it is determined that reading and data storage have been normally performed, and it is checked whether the first edge has a downward trend or an upward trend (32, 34). Specifically, the control unit 406 determines that the data Cd of the descending number register Cd is 70% or more of the sum Cd + Cu of the data Cd and the data Cu of the ascending number register Cu (Cd ≧ 0.7 (Cd + Cu)). (YES in 32) indicates the memory edge No. Information Down indicating down is written in the address addressed to Noc (33). Further, when the data Cu of the rising number register Cu is 70% or more of Cd + Cu (Cu ≧ 0.7 (Cd + Cu)) (YES in 34), the memory edge No. Information Up indicating an increase is written in the address addressed to Noc (35). Next, the control unit calculates the average value of the position data in the sub-scanning direction in the first edge area, that is, the center point position of the edge area (a in FIG. Write to the address addressed to Noc (36).

Next, the control unit 406 determines the edge number. Check whether Nos has reached 130 or more, that is, whether the calculation of the center positions of the leading edge area and trailing edge area in all marks of the start mark Msr and the eight sets of misregistration correction test patterns has been completed. (37). In the case of 130 or less, the data of the edge center point number register Noc means the first edge (the leading end of the K-color orthogonal mark Akr) to the second edge (the trailing edge of the K-color orthogonal mark Akr). Increment to 2 Similarly, the processing from steps 22 to S36 is performed for the second edge, and information indicating ascending or descending and the center point position of the edge region (b in FIG. 14B) are stored in memory. Edge No. Write to the address addressed to Noc. Such processing is repeated until the edge area (Bmr) at the rear end of the last mark in the eight sets of misregistration correction test patterns.
On the other hand, the calculation of the center position of each mark in the leading edge region and trailing edge region of all of the start mark Msr and the eight sets of misregistration correction test patterns is completed (YES in S37), or the r memory read address RNoar is r end. When the reading of stored data from the r memory is complete (YES in S29), the mark center point position is calculated based on the edge center point position data (sub-scanning direction position data calculated in step 36). (39).

  The calculation of the mark center point position starts with the memory edge number. Reads address data addressed to Noc (falling / rising data & edge center point position data). Next, it is checked whether or not the position difference between the center point position of the preceding descending edge region and the center point position of the immediately following rising edge region is within the range corresponding to the width w of the mark in the sub-scanning direction. If the position difference between the center point position of the preceding descending edge region and the center point position of the immediately following rising edge region is outside the range corresponding to the width w in the sub-scanning direction of the mark, these data are deleted. If the position difference between the center point position of the preceding falling edge area and the center point position of the immediately following rising edge area is within the range corresponding to the width w of the mark in the sub-scanning direction, the average value of these data is obtained. As the center point position of one mark. Write to memory addressed to. If mark formation, mark detection, and detection data processing are all appropriate, with respect to rear r, start mark Msr and 8 sets of misregistration correction test patterns (1 misregistration correction test pattern 8 marks × 8 sets = 64 marks) ), The center point position data of 65 marks are obtained and stored in the memory.

  Next, the control unit 406 executes “calculation of the mark center point position of the front f” CPAf in the same manner as the “calculation of mark center point position of the rear r” CPAr described above, and processes the measurement data on the memory. With respect to the front f, if mark formation, measurement and measurement data processing are all appropriate, the start mark Msf and 8 sets of misregistration correction test pattern marks (64 marks), a total of 65 mark center point position data Is obtained and stored in memory.

  When the calculation of the mark center point position is completed as described above, the control unit 406 next performs “verification of each set pattern” (SPC) as shown in FIG. “Verification of patterns in each set” (SPC) verifies whether or not the mark center point position data group written in the memory has a center point distribution corresponding to the mark distribution shown in FIG. First, the control unit 406 deletes data deviating from the mark distribution equivalent to the mark distribution shown in FIG. 11 from the mark center point position data group written in the memory in units of sets, and becomes a distribution pattern equivalent to the mark distribution shown in FIG. Only the set (one set is 8 position data groups) is left. If all are appropriate, the mark center point position data group written in the memory has 8 sets of data on the rear r side and 8 sets of data on the front f side.

  Next, the control unit 406 sets the K color orthogonal mark Akr center point position data, which is the first mark in each set after the second set of data sets on the rear r side, to the first set (first set). To the K-color orthogonal mark Akr center point position. The center point position data of the second to eighth marks is also changed by the changed difference value. In other words, the control unit 406 determines the center point position data group of each mark in each set after the second set so that the center point position of the top mark of each set matches the center point position of the first mark of the first set. Change to a value shifted in the scanning direction. The control unit 406 similarly changes the center point position data in each set after the second set on the front f side.

Next, the control unit 406 performs “average pattern calculation” (MPA). First, average values Mar to Mhr of the center point position data of each mark of all sets on the rear r side are calculated. Similarly, average values Mac to Mhc and Maf to Mhf of the center point position data of each mark of all sets on the front f side are calculated. These average values are virtual average position marks MAkr (representative of K rear-side orthogonal marks) distributed as shown in FIG.
MAyr (representative of Y side rear-side orthogonal mark),
MAcr (representative of C rear side orthogonal mark),
MAmr (representative of M rear side orthogonal mark),
MBkr (representative of the K rear-side oblique mark),
MByr (representative of Y side rear cross mark),
MBcr (representative of the rear diagonal mark of C),
MBmr (representative of M rear side oblique mark),
MAkf (representative of K front side orthogonal mark),
MAyf (representative of Y front side orthogonal mark),
MAcf (representative of C front side orthogonal mark),
MAmf (representative of M front side orthogonal mark),
MBkf (K's front side diagonal mark),
MByf (representative of Y front side oblique mark),
MBcf (representative of C front side oblique mark), and
The center point position of MBmr (representative of M front side oblique mark) is shown.

  When “test pattern formation and measurement” (PFM) is completed as described above, the control unit 406 executes “adjustment of deviation amount based on measurement data” (DAC) as shown in FIG. Then, the color misregistration amount is calculated. In this printer, the shift amount of each color of Y, M, and C is calculated for K color. Hereinafter, calculation of the color misregistration amount (Acy) of the Y color will be specifically described.

[Sub-scanning deviation amount: dyy]
Deviation amount dyy = (Mbr−Mar) −d of the difference (Mbr−Mar) of the center point position between the Bk orthogonal mark MAkr and the Y orthogonal mark MAyr on the rear r side with respect to the reference value d (FIG. 11). Of course, the amount of deviation of the center point position (Mbf−Maf) between the Bk orthogonal mark MAkf on the front f side and the Y orthogonal mark MAyf with respect to the reference value d may be used as the sub-scanning deviation amount, or the rear-side sub-scanning deviation. The average value of the amount and the front side sub-scanning deviation amount may be used as the sub-scanning deviation amount.

[Main scanning deviation amount dxy]
A deviation dxyr = (Mfr−Mbr) −4d of the difference (Mfr−Mbr) between the center point position of the rear r-side orthogonal mark MAyr and the oblique mark MByr with respect to the reference value 4d (FIG. 11), and the front f-side Average value dxy = (dxyr + dxyf) / difference dxyf = (Mff−Mbf) −4d with respect to the reference value 4d (FIG. 11) of the difference (Mff−Mbf) of the center point position between the orthogonal mark MAyf and the oblique mark MByf 2 = (Mfr−Mbr + Mff−Mbf−8d) / 2.

[Skew dSqy]
The difference dSqy = (Mbf−Mbr) between the center points of the rear R-side orthogonal mark MAyr and the front f-side orthogonal mark MAyf.

[Main scanning line length deviation dLxy]
A value dLxy = (Mff−Mfr) −, obtained by subtracting the skew dSqy = (Mff−Mfr) from the difference (Mff−Mfr) of the center point position between the rear r side oblique mark MByr and the front f side oblique mark MByf. dSqy = (Mff−Mfr) − (Mbf−Mbr).

  The other C and M image forming deviation amounts are calculated in the same manner as the calculation related to Y (Acc, Acm). Although Bk is substantially the same, in this embodiment, since color matching in the sub-scanning direction y is based on Bk, the positional deviation amount dyk in the sub-scanning direction is not calculated for Bk (Ack). .

  In the shift adjustment (DAD) shown in FIG. 10, the control unit 406 adjusts the image formation shift amount of each color as follows. The Y shift amount adjustment (Ady) is specifically shown below.

[Adjustment of sub-scanning deviation amount dy]
The start timing of image exposure (latent image formation) for forming a Y toner image is set by shifting the calculated shift amount dyy from the reference timing (sub-scanning direction).

[Adjustment of main scanning deviation amount dxy]
The transmission timing (main scanning direction) of the image data at the head of the line to the exposure laser modulator of the exposure device 109 in response to a line synchronization signal representing the head of the line for image exposure (latent image formation) for Y toner image formation. The shift amount dxy is calculated from the reference timing.

[Adjustment of skew dSqy]
The rear r side of the mirror extending in the axial direction is projected on the photosensitive drum 101 by reflecting the laser beam modulated by Y image data facing the photosensitive drum 101 of the exposure device 109, and the front f side is supported by the fulcrum. , And is supported by a block slidable in the sub-scanning direction. This block is driven back and forth in the sub-scanning direction by a sub-scanning drive mechanism mainly composed of a pulse motor and a screw to adjust the skew dSqy. In “adjustment of skew dSqy”, the pulse motor of the sub-scanning drive mechanism is driven to drive the block from the reference y position by an amount corresponding to the calculated skew dSqy.

[Adjustment of main scanning line length deviation dLxy]
The frequency of the pixel synchronization clock for allocating image data in units of pixels on the line is set to reference frequency × Ls / (Ls + dLxy). Ls is the reference line length.

  The other adjustments of C and M image formation shift amounts are adjusted in the same manner as the adjustment for Y (Adc, Adm). Although Bk is generally the same, in this embodiment, since color matching in the sub-scanning direction is based on K, the positional deviation amount dyk in the sub-scanning direction is not adjusted for K (Adk). Until the next “color matching”, a color image is formed under the adjusted conditions.

Next, a characteristic configuration of the printer will be described.
In the printer according to the first embodiment, the CPU 402 performs toner patch adjustment processing for adjusting the shape of the image quality adjustment toner patch.
FIG. 19 is a flowchart showing a control flow in toner patch adjustment processing. When a power switch of the main body (not shown) is powered on or the first print command is received, toner patch adjustment processing is performed.

  Immediately after the power is turned on, it is performed before the image adjustment processing is performed. Specifically, as described above, when the detection result by the surface temperature sensor is equal to or lower than a predetermined temperature and the execution of the image quality adjustment process is determined, the toner patch adjustment process is executed before the image adjustment process is executed. The If the detection result by this surface temperature sensor is below the predetermined temperature, it means that a relatively long time has passed without image forming operation, and the environment etc. changes significantly compared to the previous image quality adjustment processing. There is a possibility. If the environment fluctuates greatly, the writing start position may shift in the main scanning direction. As a result, the toner patch formation position is shifted in the axial direction of the intermediate transfer belt (main scanning direction), and the surface of the intermediate transfer belt other than the toner patch is also detected when the toner patch is detected by the reflective photosensor (130, 136). There is a possibility that an accurate toner adhesion amount cannot be calculated. Therefore, the toner patch adjustment process is executed immediately after power-on and before the image adjustment process is performed.

  In addition, for users who do not turn on and off frequently, the environment and the like change during power-on. Therefore, during power-on, the photoreceptor stop time, in-machine temperature, and in-machine humidity are monitored. When the print command is received, the photosensitive member stop time is 6 hours or more, the in-machine temperature has changed by 10 ° C. or more from the end of the previous image forming operation, or the in-machine humidity has ended the previous image forming operation. When it is determined that the change has occurred by 50% or more from the time, the toner patch adjustment processing is performed before the image adjustment processing is performed.

Further, when the first print command is received, a toner patch adjustment process may be executed to determine a toner patch for the image adjustment process. In this case, a flag is set in advance so that toner patch adjustment processing is executed when the first print command is received in the manufacturing stage.
In addition, before the first image adjustment process is performed, the toner patch adjustment process may be executed to determine a toner patch for the image adjustment process. In this case, it is only necessary to check whether or not the toner patch adjustment process execution flag is set when it is determined that the toner patch adjustment process is necessary.

Further, the toner patch adjustment process may be executed when the reflective photosensors (130, 136) are replaced. Replacing the reflective photosensors (130, 136) changes the beam spot diameter of the reflective photosensors (130, 136). As a result, the toner patch may be smaller than the beam spot diameter or may be larger than necessary with respect to the beam spot diameter. Therefore, toner patch adjustment processing is performed when the reflective photosensors (130, 136) are replaced.
When the reflective photosensors (130, 136) are replaced, a service person calls a hidden menu from an operation display panel (not shown) to instruct execution of toner patch adjustment processing.

  When the toner patch adjustment process is performed, a main scanning direction shape correction test pattern as shown in FIG. 20 is formed in the test pattern formation areas A1 and A2 of the intermediate transfer belt (S601). The main scanning direction shape correction test pattern is composed of n toner patches having different lengths in the main scanning line direction. The length of the toner patch in the main scanning direction on the upstream side in the intermediate transfer belt movement direction is longer than the length of the toner patch in the main scanning direction on the downstream side in the intermediate transfer belt movement direction. The length of each toner patch in the intermediate transfer belt moving direction (hereinafter referred to as sub-scanning direction) is sufficiently longer than the length of the beam spot diameter of the reflective photosensor (130, 136) in the sub-scanning direction. Each toner patch is formed under an image forming condition in which the adhesion amount of each toner patch is an adhesion amount that completely covers the surface of the intermediate transfer belt.

  Then, the average sensor output value (average reflected light amount) of each toner patch is stored in the RAM in association with the toner patch by the reflection type photo sensor (130, 136) (S602). Either one of the average sensor output value Vsp [n] _reg of the regular reflection light receiving element and the average sensor output value Vsp [n] _dif of the diffuse reflection light receiving element may be stored in the RAM.

Next, the control unit 406 determines the length of the image quality adjustment toner patch in the main scanning direction (S603).
FIG. 21 is a graph when the output voltage of the diffusely reflected light receiving element when the main scanning direction shape correction test pattern shown in FIG. 20 is detected is plotted on the vertical axis and the time is plotted on the horizontal axis.
As shown in FIG. 21, the output voltage of the diffusely reflected light receiving element when the first toner patch smaller than the beam spot diameter in the main scanning direction of the reflective photosensor (130, 136) is detected is low. However, it can be seen that the output voltage of the diffuse reflection light receiving element increases as the lengths of the second and third toner patches in the main scanning direction become longer. This is because the length of the second toner patch in the main scanning direction is longer than that of the first toner patch, so that the amount of light applied to the toner patch portion is increased and the diffused reflected light is increased. Even when the length of the toner patch in the main scanning direction is increased with a certain toner patch as a boundary, the value of the output voltage of the diffusely reflected light receiving element does not increase and becomes a constant value. This is because the length of the toner patch in the main scanning direction is longer than the length of the beam spot diameter of the reflective photosensor (130, 136) in the main scanning direction, and all of the infrared light of the reflective photosensor (130, 136). Is irradiated onto the toner patch. As a result, even if the length in the main scanning direction is increased, the value of the output voltage of the diffuse reflection light receiving element does not increase and becomes a constant value.

FIG. 22 is a graph when the average sensor output value Vsp [n] _dif of the diffuse reflection light receiving element stored in the RAM is plotted.
As shown in FIG. 22, as the length of the toner patch in the main scanning direction increases, the output voltage value of the diffusely reflected light receiving element increases, and even when the length of the toner patch in the main scanning direction increases. It can be seen that the output voltage value of the reflected light receiving element is almost constant. As shown in FIG. 22, from the region where the value of the output voltage of the diffuse reflection light receiving element increases as the length of the toner patch in the main scanning direction increases, even if the length of the toner patch in the main scanning direction increases. The main scanning direction length A when the value of the output voltage of the light receiving element is switched to a substantially constant region is the main scanning direction length of the beam spot diameter of the reflective photosensor (130, 136).

In the present embodiment, the length in the main scanning direction is specified as follows. The toner patch is a so-called solid image that completely covers the intermediate transfer belt. That is, when the toner patch is larger than the beam spot diameter of the reflective photosensor, the reflective photosensor detects only the toner. Therefore, the output value of the diffuse reflection light receiving element when a solid image is detected is examined in advance by experiments or the like, and the examined value is stored in a ROM or the like. Then, the output value of the diffuse reflection light receiving element when each toner patch is detected is checked, and the first toner patch in which the same output value as the output value stored in the ROM is detected is specified. The main scanning direction length is determined as the main scanning direction length of the image quality adjustment toner patch.
Further, the length of the image quality adjustment toner patch in the main scanning direction can be determined based on the output value of the regular reflection light receiving element. Since the output value of the regular reflection light receiving element when a solid image is detected is 0 [V], the first toner patch whose output value is 0 [V] is identified and identified. The main scanning direction length of the toner patch is determined as the main scanning direction length of the image quality adjusting toner patch.

  Further, a toner patch group having the same output value is identified from the output value of the reflection type photosensor when each toner patch stored in the RAM is detected, and the reflection type photo patch is first identified from the identified toner patch group. The toner patch detected by the sensor is specified. The length of the identified toner patch in the main scanning direction may be determined as the length of the image adjustment toner patch in the main scanning direction.

  Further, the output value of the reflection type photosensor when each toner patch stored in the RAM is detected is divided into a toner patch group having the same output value and a toner patch group having a different output value, and the output values are different. An approximate linear equation indicating the relationship between the output value corresponding to the toner patch from the toner patch group and the length in the main scanning direction corresponding to the toner patch is obtained by the method of least squares. Substitute the output value corresponding to the toner patch group with the same output value or the output value for a solid image obtained in advance in the experiment into the obtained approximate linear equation, and calculate the length in the main scanning direction of the image quality adjustment toner patch. You may ask for it.

  In addition, in order to provide some margin, a specified value α is added to the obtained main scanning line direction length, and the value obtained by adding the specified value α is used as the length of the image quality adjustment toner patch in the main scanning direction. Good.

  The above calculation is performed for the main scanning direction shape correction test pattern formed in the test pattern forming area A1 of the intermediate transfer belt, and the length of the toner patch corresponding to the first reflective photosensor is calculated in the main scanning direction. To do. Further, the main scanning direction shape correction test pattern formed in the test pattern forming area A2 of the intermediate transfer belt is performed, and the length of the toner patch corresponding to the second reflective photosensor is calculated in the main scanning direction. The main scanning direction length of the toner patch corresponding to the first reflective photosensor and the main scanning direction length of the toner patch corresponding to the second reflective photosensor are stored in NVRAM.

Once the main scanning direction lengths of the toner patches corresponding to the first and second reflective photosensors are obtained, the sub-scanning direction shape correction is then performed to determine the toner patch sub-scanning direction length for image adjustment processing. The test pattern is formed in the test pattern formation areas A1 and A2 of the intermediate transfer belt (S604). The sub-scanning direction shape correction test pattern is composed of n toner patches having different lengths in the sub-scanning line direction. The length of each toner patch in the main scanning direction is the length determined in advance.
Next, the average sensor output value (average reflected light amount) of each toner patch is stored in the RAM in association with the toner patch by the reflection type photosensor (130, 136) (S605). Then, the sub-scanning direction length of the image quality adjustment toner patch corresponding to the first reflection type photosensor 130 and the subscanning direction length of the image quality adjustment toner patch corresponding to the second reflection type photosensor 130 are determined (S606). ). Specifically, the image quality adjustment toner patch is calculated in the same manner as when the main scanning direction length is calculated.
The calculated sub-scanning direction length of the toner patch corresponding to the first reflective photosensor and the sub-scanning direction length of the toner patch corresponding to the second reflective photosensor are stored in the NVRAM.

  Such processing is performed for all the colors Y, M, C, and K.

  At the time of image quality adjustment processing, when creating a gradation pattern, the sub-scanning line direction length data and the main scanning direction length data of the image quality adjustment toner patch of each color are read from the NVRAM, and based on these data, Create a gradation pattern for each color.

  As described above, in the printer of this embodiment, the toner patch adjustment process is executed at a predetermined timing to adjust the shape of the image quality adjustment toner patch so that the image quality adjustment toner patch is attached to the reflective photosensor. It is possible to maintain an optimum shape that is equal to or slightly larger than the beam spot diameter over time. Accordingly, it is possible to detect the toner adhesion amount with high accuracy over time, and to suppress the toner consumption amount during the image quality adjustment control.

  Further, the toner patch for determining the length in the main scanning direction is not limited to the one shown in FIG. 20, and as shown in FIG. 23, the sub-scanning line whose width in the main scanning direction increases stepwise. One large toner patch that is long in the direction may be used. In this case, when the tip of the toner patch is detected by the reflective photosensor (130, 136), time measurement is started. Then, the time when the output value of the reflective photosensor (130, 136) reaches a predetermined value is measured. This predetermined value is an output value when a toner patch larger than the beam spot diameter is detected, and is obtained in advance by experiment and stored in the ROM. That is, the fact that the output value of the reflective photosensor (130, 136) has become a predetermined value means that the length in the main scanning direction at this time is larger than the length in the main scanning direction of the beam spot diameter of the reflective photosensor. . Therefore, the length in the main scanning direction is obtained from the measured time, and the obtained main scanning direction length is determined as the main scanning direction length of the toner patch for image adjustment processing. In addition to the shape shown in FIG. 23, a trapezoid or an isosceles triangle may be used.

Further, the toner patch adjustment process may be executed after the positional deviation correction process (color matching). After the misalignment correction, the main scanning line length misalignment amount and main scanning misalignment amount are adjusted. Therefore, by executing the toner patch adjustment processing after the misalignment correction processing (color matching), the main image quality adjusting toner main toner is adjusted. The length in the scanning direction can be further shortened, and toner consumption during image quality adjustment can be suppressed.
In addition, the toner patch adjustment process performed after the misregistration correction process may calculate only the length of the image quality adjustment toner in the main scanning direction.

  As described above, according to the image forming apparatus of the present embodiment, the control unit, which is an image quality adjustment toner image determination unit that determines the image quality adjustment toner image, forms toner patches that are a plurality of test toner images having different shapes, and optically A toner patch adjustment process for determining the shape of the image quality adjustment toner patch, which is the image quality adjustment toner image, can be executed based on the detection result of each toner patch of the reflection type photosensor as the target detection means. Therefore, if the toner patch adjustment process is executed at a timing at which the beam spot diameter of the reflective photosensor may change or at a timing at which the image quality adjustment toner patch may shift in the main scanning direction, the image quality adjustment over time The toner patch can have an optimum shape that is the same as or slightly larger than the beam spot diameter of the reflective photosensor. Accordingly, it is possible to detect the toner adhesion amount with high accuracy over time and to suppress the toner consumption amount during the image quality adjustment process.

  In addition, the control unit forms each toner patch so that the length in the axial direction of the intermediate transfer belt serving as an image carrier is different, and determines the length in the axial direction of the intermediate transfer belt (main scanning direction length) of the toner patch for image quality adjustment. To do. As a result, the length of the image quality adjustment toner patch in the main scanning direction can be set to an optimum length that is equal to or slightly larger than the length of the beam spot diameter of the reflective photosensor in the main scanning direction.

Also, a test pattern such as an image quality adjustment test pattern is formed in a test pattern area, which is a non-image output area of the intermediate transfer belt, so that a test pattern is formed in parallel with the image to be transferred onto the paper in the main scanning line direction. be able to. As a result, productivity does not decrease even when a test pattern is formed during continuous image formation and image quality adjustment processing and positional deviation correction processing are performed.
Further, in the present embodiment, the length of the toner patch in the main scanning direction can be suppressed to the extent that the beam spot diameter of the reflective photosensor is equal to or slightly larger than the main scanning direction, so that the main scanning direction of the test pattern region can be reduced. The length can be shortened. As a result, the length of the intermediate transfer belt in the main scanning direction can be shortened, and the length of the apparatus in the main scanning direction can be shortened.

  In addition, when the image forming apparatus is used for the first time, the toner patch adjustment process causes an assembly error of the reflective photosensor at the time of manufacture, and the beam spot diameter of the reflective photosensor varies. Even when the image quality adjustment processing is performed, the image quality adjustment can be executed with an image quality adjustment toner patch having an optimum shape.

  In addition, by performing toner patch adjustment processing when the power is turned on, even if the test pattern writing position is shifted due to external environment fluctuations, image quality adjustment can be performed with an optimally shaped image quality adjustment toner patch during image quality adjustment processing. it can.

  Also, by performing toner patch adjustment processing at the time of replacement of the reflective photosensor, even if the beam spot diameter of the reflective photosensor changes due to replacement of the reflective photosensor, an optimal shape can be obtained at the time of image quality adjustment processing. Image quality adjustment can be executed with the image quality adjustment toner patch.

  Further, by performing toner patch adjustment processing after correcting the positional deviation, the length of the image quality adjustment toner in the main scanning direction can be further shortened, and toner consumption during image quality adjustment can be suppressed.

FIG. 2 is a schematic configuration diagram illustrating an image forming process portion of the printer according to the first embodiment. FIG. 2 is a front view showing an image forming unit for K of the printer. FIG. 2 is a perspective view showing a transfer unit of the printer. FIG. 3 is an enlarged configuration diagram illustrating a first reflective photosensor of the printer. FIG. 2 is a block diagram showing a part of an electric circuit of the printer. 6 is a flowchart illustrating a control flow in image forming condition adjustment processing performed by the control unit of the printer. FIG. 3 is a plan view showing the intermediate transfer belt on which a test pattern is formed and the surrounding configuration from above. 6 is a graph showing the relationship between the amount of regular reflection light received by a regular reflection type light receiving element of a reflection type photosensor and the amount of toner attached to a K toner patch. 7 is a graph showing the relationship between the amount of diffusely reflected light received by a diffuse reflection type light receiving element of a reflection type photosensor and the amount of toner attached to Y, C, and M toner patches. The figure which shows the execution flow of a color matching. FIG. 3 is a diagram showing a misregistration correction test pattern group formed on an intermediate transfer belt. The figure which shows the execution flow of test pattern formation and measurement. The figure which shows the relationship between a test pattern and the level fluctuation | variation of detection signal Sdr, Sdf. (A) is a time chart of the detection signals Sdr and Sdf, and (b) shows only the range in which the A / D conversion data is written in the FIFO memory among the detection signals shown in a). It is a time chart. The figure which shows the execution flow of "interrupt processing" (TIP). The figure which shows a part of flow of "calculation of a mark center point position" (CPA). The figure which shows the other part of the flow of "calculation of a mark center point position" (CPA). The figure which shows a virtual average position mark. 7 is a flowchart illustrating a control flow in toner patch adjustment processing. FIG. 4 is a diagram illustrating a main scanning direction shape correction test pattern formed on an intermediate transfer belt. A graph when the output voltage of the diffusely reflected light receiving element when a main scanning direction shape correction test pattern is detected is plotted on the vertical axis and the time is plotted on the horizontal axis. The graph when the average sensor output value of the diffuse reflection light receiving element stored in RAM is plotted. FIG. 14 is a diagram showing another shape of the test pattern for shape correction in the main scanning direction formed on the intermediate transfer belt. The figure explaining a mode when a toner patch is smaller than the beam spot diameter of an optical sensor. The figure which shows the relationship between the conventional toner patch and the beam spot diameter of an optical sensor.

Explanation of symbols

101Y, C, M, K: Photoconductors 103Y, C, M, K: Developing device 130: First reflective photosensor 136: Second reflective photosensor 204Y, C, M, K: Primary transfer roller 206: Intermediate transfer belt 206a: Standard reflection unit 208: Secondary transfer roller 290: Optical writing unit 406: Control unit A1, A2: Test pattern formation region

Claims (8)

An image carrier that carries a toner image on its moving surface;
Optical detection means for detecting reflected light from the toner image;
Forming a toner image for image quality adjustment on the surface of the image carrier;
Based on the detection value when the image quality adjustment toner image is detected by the optical detection means, the toner adhesion amount of the image quality adjustment toner image is detected, and the image quality adjustment control is executed based on the detected toner adhesion amount. In an image forming apparatus comprising image quality adjustment control means for
The detection results of the test toner images of the optical detection means having different shapes are formed, and the shape of the image quality adjustment toner image is determined based on the detection results of the test toner images of the optical detection means. An image forming apparatus comprising a toner image determining means for adjusting image quality. The image forming apparatus according to claim 1.
From the detection results of the test toner images of the optical detection means, a test toner image group having the same detection result is specified, and the test toner image having the smallest shape among the test toner image groups is defined as the image quality. An image forming apparatus, wherein the image quality adjusting toner image determination means is configured to determine an adjustment toner image. The image forming apparatus according to claim 1 or 2,
The image quality adjusting toner image determining means is configured to form each test toner image so that the lengths in the image carrier axis direction are different, and to determine the image carrier axis length in the image carrier axis direction. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
A transfer means for transferring the toner image on the image carrier to a recording medium;
As the image carrier, a partial region in a direction orthogonal to the moving direction on its surface is a non-image output region that does not contribute to the output of the image to the recording medium,
An image forming apparatus, wherein the image quality adjusting toner image and the test toner image are formed in the non-image output area. The image forming apparatus according to claim 1,
An image forming apparatus that controls to execute the image quality adjusting toner image determining means when the image forming apparatus is used for the first time. The image forming apparatus according to claim 1,
An image forming apparatus that controls to execute the image quality adjusting toner image determining means when power is turned on. The image forming apparatus according to claim 1.
An image forming apparatus that controls to execute the image quality adjusting toner image determination unit when the optical detection unit is replaced. The image forming apparatus according to claim 1,
An image forming apparatus that controls to execute the image quality adjusting toner image determination unit after correcting the positional deviation of the toner image on the image carrier.

Images