JP5382519B2 - Image forming apparatus - Google Patents

Description

  In the present invention, the developer conveyed along a predetermined circulation path is supported on the moving surface of the developer carrier and contributes to development, and then returned from the surface of the developer carrier to the circulation path. The present invention relates to an image forming apparatus using a developing unit.

  As this type of developing means, one shown in FIG. 25 is known. In the drawing, a developing device 900 has a circulation path for circulating and conveying a developer (not shown) containing toner and a magnetic carrier in a casing, a developing roll 910 as a developer carrier, and the like. The circulation path includes a first agent storage chamber 901 and a second agent storage chamber 903 arranged so as to be aligned in the short direction. The developer stored in the first agent storage chamber 901 that is a part of the circulation path is rotated in the direction of the arrow A in the figure along the longitudinal direction of the indoor space by the rotational drive of the first transport screw 902. Be transported. The first agent storage chamber 901 and the second agent storage chamber 903 adjacent to the first agent storage chamber 901 communicate with each other at both ends in the longitudinal direction. The developer transported to the end in the direction of arrow A in the figure in the first agent storage chamber 901 as the first transport screw 902 is driven passes through the communicating portion and enters the second agent storage chamber 903. To do. Then, in the second agent storage chamber 903, the second transport screw 904 is driven to rotate in the direction of arrow B opposite to the direction of arrow A by the rotational drive. Thereafter, when transported to the end in the arrow B direction in the second agent storage chamber 903, the second agent storage chamber 903 enters the most upstream portion in the first agent storage chamber 901 in the direction of arrow A through the communicating portion. In this way, the developer is circulated and conveyed in the first agent storage chamber 901 and the second agent storage chamber 903.

  A developing roll 910 is disposed on the lateral side of the second agent storage chamber 903 in the short direction. The developing roll 910 includes a developing sleeve made of a non-magnetic pipe that is driven to rotate, and a magnet roller (not shown) that is housed in the developing sleeve so as not to rotate. The developer in the second agent storage chamber 903 is carried on the surface of the rotating developing sleeve by the magnetic force generated by the magnet roller, and is transported to the developing area where the developing sleeve and the photoconductor 920 face each other. Thereafter, the latent image on the photoconductor 920 is developed with the developer on the surface of the sleeve, and then the developer contributing to the development is returned to the second agent storage chamber 903 as the surface of the sleeve moves. The returned developer reduces the toner concentration. In the first agent storage chamber 901, the developer whose toner concentration has been reduced in this way is sent from the second agent storage chamber 903, so that the toner concentration of the developer becomes lower than the target value. The first agent storage chamber 901 is provided with a toner concentration sensor (not shown) including a magnetic permeability sensor. A control unit (not shown) drives a toner supply unit (not shown) based on the detection result of the toner density sensor. Then, the toner is supplied to the first agent storage chamber 901 through the toner supply port 915 provided in the vicinity of the upstream end of the first agent storage chamber 901 in the developer transport direction, and the toner concentration of the developer is recovered. .

  By such toner replenishment control, the toner concentration of the developer in the developing device 900 can be maintained within a certain range. However, it is not possible to obtain a stable image density over a long period of time alone. This is for the reason explained below. That is, in the image forming apparatus, when the environment changes, the charging characteristics of the photosensitive member and the charging characteristics of the toner change accordingly. As a result, the image forming capability of the image forming apparatus also varies. For this reason, even if the toner density is maintained within a certain range, if the environment fluctuates, the image density fluctuates accordingly.

  As an image forming apparatus capable of suppressing this kind of fluctuation in image density, the one described in Patent Document 1 is known. This image forming apparatus performs the following image forming condition correction process every time a predetermined number of prints are performed. That is, predetermined toner images are formed on both ends in the axial direction of the photosensitive member as a latent image carrier. Then, after detecting the image density of each toner image, the developing capability of the apparatus is grasped based on the average value of the image densities. Next, after grasping the excess or deficiency of the developing ability based on the grasped developing ability, the developing bias as the image forming condition is corrected to a value at which a desired developing ability is obtained. By correcting the development bias in this manner, a target image density can be obtained even if the environment changes.

  The image forming apparatus can also provide the following effects. That is, even if the developing gap between the photosensitive member and the developing roll has an error between one end side and the other end side in the photosensitive member axial direction, it is possible to suppress the occurrence of insufficient image density and excessive image density. Specifically, when one of the photosensitive member and the developing roll is assembled with a slight inclination with respect to the other, the developing gap gradually increases from one end side to the other end side in the photosensitive member axial direction. (Hereinafter, one end side is referred to as a small gap side, and the other end side is referred to as a large gap side). When there is such a development gap deviation, the image density gradually decreases from one end side to the other end side in the photosensitive member axial direction. If the development bias is corrected in accordance with the image density on the small gap side in this state, the desired image density can be obtained on the small gap side, but the developing ability is insufficient on the large gap side, which may cause insufficient image density. It will be high. Conversely, if the development bias is corrected in accordance with the image density on the large gap side, the desired image density can be obtained on the large gap side, but on the small gap side, there is a possibility of causing excessive image density due to excessive development capability. It will be high. On the other hand, in the image forming apparatus described in Patent Document 1, the image density at the center in the photosensitive member axial direction is grasped by obtaining the average of the image density on the small gap side and the image density on the large gap side. Based on the result, the development bias is corrected so that a desired image density can be obtained at the central portion, thereby causing an excessive image density in the small gap and an insufficient image density on the large gap side. It can be suppressed.

  However, in a low-stress specification developing device, it has been found that even if the developing bias is corrected in this way, image density deficiency tends to be caused at the end on the large gap side at both ends in the photosensitive member axial direction. . Specifically, in recent years when the development apparatus is being reduced in size, the amount of developer contained in the development apparatus has decreased compared to the conventional one. In such a low-capacity developing device, the mechanical stress on the toner in the developer is increased compared to the conventional case, and the deterioration of the toner is likely to be accelerated. Therefore, it has become common to avoid the early deterioration of the toner by using a low-stress specification that conveys the developer with a smaller stress than in the past. However, in such a low-stress specification developing device, when images with a relatively high area ratio are continuously output, a large amount of toner replenished to the developing device with a large amount of toner consumption is charged in a state of poor charging. May be sent to the second agent storage chamber opposite to the container. The charging failure referred to here is a state where the charge amount of the toner is below an appropriate range. Within the proper range, the image density is almost constant regardless of the fluctuation of the charge amount within the range, but when the charge amount is below the proper range, the image density becomes higher than the constant value. . The poorly charged toner that increases the image density in this way increases the charge amount to an appropriate range in the process of being transported toward the downstream side in the transport direction in the second agent storage chamber. When there is such a charge amount behavior, the image density corresponds to the development gap only at the end corresponding to the upstream side in the developer transport direction and the area in the vicinity thereof at both ends in the photosensitive member axial direction. It will be higher than the original value. More specifically, in a normal state in which poorly charged toner is not fed into the second agent storage chamber, as described above, the development gap gradually increases from the small gap side toward the large gap side. As the image density gradually decreases. However, when poorly charged toner is fed to the upstream end in the developer transport direction in the second agent storage chamber, the upstream end is on the small gap side or on the large gap side. The density becomes higher than the original value corresponding to the development gap. That is, when an image having a relatively high area ratio is output continuously, or immediately after the output, the end corresponding to the upstream side in the developer transport direction among the both ends in the photosensitive member axial direction The image density of the toner image formed in the above becomes higher than the value corresponding to the development gap at the end. At this time, if the above-described image forming condition correction processing is performed, the average of the image densities of the toner images respectively formed at both ends in the photosensitive member axial direction depends on the size of the developing gap in the central portion in the photosensitive member axial direction. Therefore, the developing bias is set to a value smaller than the value corresponding to the developing gap in the central portion. If such a setting is made, the developing potential is insufficient at the end portion on the large gap side, and the image density is likely to be insufficient. If the image forming condition correction process is performed at a timing different from that after the continuous output of the high area ratio image, the developing bias can be set to a value corresponding to the developing gap at the center in the photosensitive member axial direction. Such occurrence of insufficient image density can be avoided. However, the image forming condition correction processing is generally performed at a regular timing such as every predetermined number of prints or every predetermined time, and the regular timing and continuous output of a high area ratio image are performed. It is inevitable that the latter will be accidentally synchronized.

  Further, in a low-stress developing device, even if there is no deviation in the developing gap, the image density may differ between one end side and the other end side in the photosensitive member axial direction. For example, when an image with a relatively large amount of toner consumption such as a photographic image is continuously output, the charge amount of the newly supplied toner is not in time, and the charge amount of the toner is increased from one end side to the other end side. In some cases, the image density decreases as the time goes. Even in such a case, if the average of the image densities of the toner images respectively formed at one end and the other end in the photosensitive member axial direction is obtained and the developing bias is set based on the result, the image at the one end side is obtained. The occurrence of excessive density and the occurrence of insufficient image density on the other end side can be suppressed. However, when an image with a relatively small amount of toner consumption is output, the toner in the second storage chamber facing the developing roll is sufficiently charged, so that there is no difference in image density between the one end side and the other end side. . Nevertheless, if toner images are formed at both ends and the respective image densities are measured, the toner is wasted.

The present invention has been made in view of the above background, it is an purpose of that is, be carried out image forming condition correcting process an image of the high area ratio after continuous output, the latent image bearing member It is an object of the present invention to provide an image forming apparatus capable of suppressing the occurrence of insufficient image density at the end of the large gap.

To achieve the above Symbol purpose, the invention of claim 1 includes a latent image bearing member for bearing a latent image on its moving surface, a latent image forming means for forming a latent image on said surface, toner and While the developer containing the carrier is transported along a predetermined circulation path, the developer transported in the predetermined transport direction in a region facing the developer support in the circulation path is moved by the developer carrier. And the developer is moved to a development region facing the latent image carrier, and the developer toner is attached to the latent image on the latent image carrier in the development region to develop the latent image; and A developing means for returning the developer that has contributed to development in the development area to the opposing area of the circulation path as the developer carrier moves to the surface, and a surface of the latent image carrier. Each in two different areas After the toner images are formed, the image forming unit is provided with a control unit that performs image forming condition correction processing for correcting the image forming conditions in the image forming unit based on the results of detection of the two toner images by the image detecting unit. In the apparatus, an image detecting unit capable of detecting the image density of the toner image is used, and in the image forming condition correction process, as one of the two regions, the surface of the latent image carrier in the transport direction is used. While forming a toner image with respect to the downstream end region in the transport direction in both end regions, as the other of the two regions, from the upstream end portion in the transport direction in the both end regions. even a toner image is formed to the central side of the area, based on the previous SL downstream end region, and a result of detecting the image density of the toner image formed respectively on the inboard region, various work Of the conditions, so as to correct the image forming conditions capable of changing the image density of the toner image, it is characterized in that constitutes the control means.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the image detection is performed on the toner images formed in the downstream side end region and the central region in the image forming condition correction process. The control means is configured to correct an image forming condition that can change a formation position of a toner image on the latent image carrier among various image forming conditions based on a timing detected by the means. To do.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect , in the image forming condition correction processing, a gradation pattern image having a plurality of toner images having different image densities is displayed on the downstream end portion. And the downstream side of the imaging means based on the result of detecting the image density of each toner image in the gradation pattern image formed in each of the region and the central region, and formed in the downstream end region. While grasping the developing ability in the end region, the central region in the image forming means based on the result of detecting the image density of each toner image in the gradation pattern image formed in the central region The control means is configured so as to grasp the developing ability of the printer.
According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect , the developing ability in the downstream end region of the image forming means and the developing ability in the region near the center of the image forming means Based on the image forming means, grasp the developing ability in the central region of the developer conveying direction in the image forming means, and based on the result, to correct the image forming conditions that can change the image density of the toner image, The control means is configured.
According to a fifth aspect of the present invention, in the image forming apparatus according to the third or fourth aspect , the control means is configured to correct the development potential as an image forming condition capable of changing the image density of the toner image. It is a feature.
According to a sixth aspect of the present invention, in the image forming apparatus of the third, fourth, or fifth aspect , the latent image carrier and the developing unit for forming toner images of different colors are used as the image forming unit. A transfer means for obtaining a multicolor image by transferring toner images of different colors formed on the latent image carrier onto the surface of the intermediate transfer body, respectively, as the image detection means, Each toner image of the gradation pattern image formed on each of the regions near the center of the plurality of latent image carriers and then transferred to one end side in the direction perpendicular to the surface movement direction on the surface of the intermediate transfer member. A first image detecting means for detecting the first image detecting means, and a plurality of latent image carriers, respectively, on the other end side in a direction perpendicular to the surface movement direction on the surface of the intermediate transfer body. Transcribed In which characterized in that a second image detecting means for detecting the toner images of the gradation pattern images.
The invention according to claim 7 is the image forming apparatus according to claim 6 , wherein each of the gradation pattern images formed on the plurality of latent image carriers has a plurality of lengths in the moving direction of the surface of the intermediate transfer member. The control means is configured so as to form the latent image carrier shorter than the arrangement pitch of the latent image carriers.
According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth or seventh aspect , the first image detection unit and the second image detection unit detect both the regular reflection light amount and the diffuse reflection light amount on the surface of the intermediate transfer member. It is characterized by using what to do.
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the image forming condition correction process includes any one of the downstream end region and the central region. A mode in which a toner image is formed only in the region and a process for correcting the image forming condition based on a result of detecting the toner image by the image detecting unit, and a toner image is formed in each of the regions. The control unit is configured to select and execute a mode corresponding to a predetermined parameter from among modes in which processing for correcting the imaging condition is performed based on a result detected by the image detection unit. It is characterized by .

請 Motomeko intended to provide all of the first subject matter, when an image of high area ratio and continuous output, among the region opposed to the developer carrying member in the circulation path of the developing means, upstream of the developer carrying direction Even if the poorly charged toner is fed into the side end region, the charge amount of the toner is increased to an appropriate range in the region closer to the center than the upstream end region and in the downstream end region. Therefore, on the surface of the latent image carrier, a toner image is formed in each of the region near the center in the developer conveyance direction and the downstream end region, and the image forming condition is determined based on the result of detecting the image density. to correct. In such a configuration, one of the one end side and the other end side of the surface of the latent image carrier is immediately after a high area ratio image is continuously output on the side corresponding to the upstream side in the developer transport direction. Even in a state where the image density is higher than the value corresponding to the development gap in the edge region, the toner image for detecting the image density is near the center where the image density corresponding to the development gap is obtained. Formed in the region. Then, by correcting the image forming condition based on the detection result of the image density of the toner image, even if the image forming condition correction process is performed after the high area ratio image is continuously output, the latent image carrier is large. The occurrence of insufficient image density at the end on the gap side can be suppressed.

1 is a schematic configuration diagram illustrating a printer according to a first embodiment. FIG. 3 is a configuration diagram showing a process unit and a control unit for generating a Y toner image in the printer. The perspective view which shows the external appearance of the process unit. FIG. 3 is an exploded perspective view showing a developing device of the process unit. FIG. 3 is an enlarged perspective view showing a part of an intermediate transfer belt of the printer together with an optical sensor. The schematic diagram which shows a part of image for position shift detection. The schematic diagram which shows the other part of the image for the same position shift detection. 6 is a flowchart showing a control flow of development potential correction processing performed by the control unit of the printer. 6 is a graph showing the relationship between the output voltage of the optical sensor and the toner adhesion amount. Sensitivity correction coefficient α and regular reflection differential voltage ΔVsp_reg. [N] and the diffuse reflection differential voltage ΔVsp_dif. The graph which shows an example of a relationship with [n]. Regular reflection light differential voltage ΔVsp_reg. The graph explaining the extraction method of the regular reflection light component from [n]. The graph which shows an example of the relationship between the diffuse reflection component (DELTA) Vsp_dif 'after correction | amendment of background part fluctuation | variation, and the normalized value (beta). 6 is a graph showing the relationship between the development potential at the time of forming each toner image in the gradation pattern image and the toner adhesion amount. FIG. 4 is a schematic diagram for explaining an image density shortage that occurs when a development potential correction process is performed with reference to a rear end. FIG. 6 is a schematic diagram illustrating excessive image density that occurs when developing potential correction processing is performed with reference to the front side end. FIG. 6 is a schematic diagram illustrating a state of an image density deviation when a development potential correction process is performed with a belt center as a reference. FIG. 3 is a schematic diagram illustrating an intermediate transfer belt of the printer, a gradation pattern image of each color formed on the surface of the intermediate transfer belt, and a misregistration detection image. The graph which shows the relationship between the development potential on the rear side, the development potential on the front side, and the central development potential. The schematic diagram for demonstrating the length of the gradation pattern image Py, Pc, Pm, and Pk for Y, C, M, and K. FIG. The graph explaining the detection error of an optical sensor. The graph explaining the detection error of two optical sensors. FIG. 10 is a schematic diagram illustrating an intermediate transfer belt, a gradation pattern image of each color formed on a surface of the intermediate transfer belt, and a position shift detection image in the printer according to the second embodiment. 6 is a graph showing a relationship between a toner charge amount in a first agent storage chamber of a developing device and an area ratio of an output image in each color process unit of the printer according to the first embodiment. The graph which shows the relationship between the image density deviation of a front side edge part and a rear side edge part, and the area ratio of an output image. The expanded block diagram which shows the conventional image development apparatus. FIG. 10 is a schematic diagram illustrating an intermediate transfer belt in a conventional image forming apparatus, a gradation pattern image of each color formed on the surface of the intermediate transfer belt, and a misregistration detection image.

A first embodiment in which the present invention is applied to an electrophotographic printer (hereinafter simply referred to as “printer”) as an image forming apparatus will be described below.
First, the basic configuration of the printer according to the first embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating the printer according to the first embodiment. This printer includes four process units 1Y, 1C, 1M, and 1K for yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K). These use Y, C, M, and K toners of different colors as image forming substances for forming an image, but the other configurations are the same.

  FIG. 2 is a configuration diagram showing a process unit 1Y and a control unit for generating a Y toner image. FIG. 3 is a perspective view showing the appearance of the process unit 1Y. In these drawings, the process unit 1Y has a photoreceptor unit 2Y and a developing device 7Y. As shown in FIG. 3, the photosensitive unit 2Y and the developing device 7Y are configured to be detachable as a process unit 1Y integrally with the printer main body. However, in a state where it is detached from the printer main body, the developing device 7Y can be attached to and detached from a photosensitive unit (not shown).

  The photoreceptor unit 2Y includes a drum-shaped photoreceptor 3Y as a latent image carrier, a drum cleaning device 4Y, a static eliminator (not shown), a charging device 5Y, and the like. The charging device 5Y as a charging unit uniformly charges the surface of the photosensitive member 3Y, which is driven to rotate clockwise in FIG. 2 by a driving unit (not shown), by the charging roller 6Y. Specifically, in FIG. 2, a charging bias is applied from a power source (not shown) to the rotationally driven charging roller 6Y, and the charging roller 6Y is brought close to or in contact with the photoconductor 3Y, thereby uniformly aligning the photoconductor 3Y. Charge. Instead of the charging roller 6Y, another charging member such as a charging brush may be used in proximity or contact. Further, a charger that uniformly charges the photosensitive member 3Y by a charger method, such as a scorotron charger, may be used. The surface of the photoreceptor 3Y uniformly charged by the charging device 5Y is exposed and scanned by a laser beam emitted from an optical writing unit 20 serving as a latent image forming unit, which will be described later, and carries an electrostatic latent image for Y.

  FIG. 4 is an exploded perspective view showing the inside of the developing device 7Y. As shown in FIGS. 2 and 4, the developing device 7 </ b> Y as a developing unit has a first agent storage chamber 9 </ b> Y in which a first conveying screw 8 </ b> Y as a developer conveying unit is disposed. Further, it also has a second agent storage chamber 10Y in which a second conveying screw 11Y as a developer conveying means, a developing roll 12Y as a developer carrying member, a doctor blade 13Y as a developer regulating member, and the like are disposed. . In these two agent storage chambers forming the circulation path, a Y developer (not shown) which is a two-component developer composed of a magnetic carrier and a negatively chargeable Y toner is contained. The first conveying screw 8Y is rotationally driven by a driving means (not shown), so that the Y developer in the first agent storage chamber 9Y is moved to the rear side of the printer main body (the side in the direction perpendicular to the drawing sheet in FIG. 2). Transport toward Then, the Y developer transported to the end of the first agent storage chamber 9Y by the first transport screw 8Y enters the second agent storage chamber 10Y through the communication port.

  The second conveying screw 11Y in the second agent storage chamber 10Y is driven to rotate by a driving means (not shown), so that the Y developer is fed to the front side of the printer body (the front side in the direction perpendicular to the drawing sheet in FIG. 2). Transport toward In this manner, the developing roll 12Y is arranged in a posture parallel to the second transport screw 11Y above the second transport screw 11Y that transports the Y developer. The developing roll 12Y includes a magnet roller 16Y fixedly disposed in a developing sleeve 15Y made of a nonmagnetic sleeve that is driven to rotate clockwise in the drawing. A part of the Y developer conveyed by the second conveying screw 11Y is pumped up to the surface of the developing sleeve 15Y by the magnetic force generated by the magnet roller 16Y. Then, after the layer thickness is regulated by a doctor blade 13Y disposed so as to maintain a predetermined gap from the surface of the developing sleeve 15Y, the layer is conveyed to a developing region facing the photosensitive member 3Y, and is transferred onto the photosensitive member 3Y. Y toner is adhered to the electrostatic latent image for Y. This adhesion forms a Y toner image on the photoreceptor 3Y. The Y developer that has consumed Y toner by the development is returned to the second transport screw 11Y as the developing sleeve 15Y rotates. Then, the Y developer transported to the end of the second agent storage chamber 10Y by the second transport screw 11Y returns to the first agent storage chamber 9Y through the communication port. In this way, the Y developer is circulated and conveyed in the developing device.

  In FIG. 2, the control unit 100 includes an I / O unit 100a, a CPU (Central Processing Unit) 100b as a calculation means, a RAM (Random Access Memory) 100c as a data storage means, a ROM (Read Only Memory) 100d, and the like. ing. Various arithmetic processes and control programs can be executed. The Y toner image formed on the photoreceptor 3Y is intermediately transferred to an intermediate transfer belt that is an intermediate transfer body. The drum cleaning device 4Y of the photoreceptor unit 2Y removes toner remaining on the surface of the photoreceptor 3Y after the intermediate transfer process. As a result, the surface of the photoreceptor 3Y subjected to the cleaning process is neutralized by a neutralizing device (not shown). By this charge removal, the surface of the photoreceptor 3Y is initialized and prepared for the next image formation. Similarly, in the process units (1C, 1M, 1K) for other colors, C toner images, M toner images, and K toner images are formed on the photoconductors (3C, 3M, 3K), and then on the intermediate transfer belt. Intermediate transfer.

  A toner concentration sensor 14Y including a magnetic permeability sensor is disposed on the bottom wall of the first agent storage chamber 9Y, and detects the toner concentration of the developer in the first agent storage chamber 9Y.

  The control unit 100 stores the target voltage Vtref for Y, which is the target value of the output voltage from the toner density sensor 14Y, in the RAM 100c or the ROM 100d, and C and C mounted on other developing devices (7C, 7M, 7K). Data of target voltages Vtref for C, M, and K, which are target values of output voltages from the toner density sensors for M and K, are stored. For the developing device 7Y for Y, the value of the output voltage from the toner density sensor 14Y is compared with the target voltage Vtref for Y, and an amount of Y toner corresponding to the comparison result is supplied from the toner supply port 17Y. The toner supply motor for Y is controlled. By this control, an appropriate amount of Y toner is supplied in the first agent storage chamber 9Y to the Y developer whose Y toner density has decreased due to consumption of Y toner accompanying development. As a result, the toner density of the Y developer is maintained within the target toner density range. The same applies to the developers in the developing devices (7C, 7M, 7K) for other colors.

  1, the optical writing unit 20 is disposed below the process units 1Y, C, M, and K in FIG. The optical writing unit 20 irradiates the photoconductors 3Y, C, M, and K of the process units 1Y, C, M, and K with laser light L emitted based on the image information. As a result, electrostatic latent images for Y, C, M, and K are formed on the photoreceptors 3Y, 3C, 3M, and 3K, respectively. The optical writing unit 20 deflects the laser light L emitted from the light source by the polygon mirror 21 that is rotationally driven by a motor, and passes through the photosensitive members 3Y, 3C, 3M, and 3K via a plurality of optical lenses and mirrors. Is irradiated. Instead of such a configuration, an LED array may be used.

  A first paper feed cassette 31 and a second paper feed cassette 32 are disposed below the optical writing unit 20 so as to overlap in the vertical direction. In each of these paper feed cassettes, a plurality of recording papers P, which are recording materials, are stored in a stack of recording papers, and a first paper feed roller is placed on the top recording paper P. 31a and the second paper feed roller 32a are in contact with each other. When the first paper feed roller 31a is driven to rotate counterclockwise in FIG. 1 by driving means (not shown), the uppermost recording paper P in the first paper feed cassette 31 is vertically oriented on the right side of the cassette in FIG. The paper is discharged toward the paper feed path 33 arranged so as to extend. When the second paper feed roller 32a is rotated counterclockwise in FIG. 1 by driving means (not shown), the uppermost recording paper P in the second paper feed cassette 32 is discharged toward the paper feed path 33. The A plurality of transport roller pairs 34 are arranged in the paper feed path 33, and the recording paper P fed into the paper feed path 33 is sandwiched between the rollers of the transport roller pair 34 while being fed between the paper feed paths 33. 1 is conveyed from the lower side to the upper side in FIG. A registration roller pair 35 is disposed at the end of the paper feed path 33. The registration roller pair 35 temporarily stops the rotation of both rollers as soon as the recording paper P sent from the conveyance roller pair 34 is sandwiched between the rollers. Then, the recording paper P is sent out toward a later-described secondary transfer nip at an appropriate timing.

  Above each process unit 1Y, C, M, and K in FIG. 1, a transfer unit 40 is disposed to endlessly move the intermediate transfer belt 41 counterclockwise in FIG. In addition to the intermediate transfer belt 41, the transfer unit 40 includes a belt cleaning unit 42, a first bracket 43, a second bracket 44, and the like. Further, four primary transfer rollers 45Y, 45C, 45M, 45K, a secondary transfer backup roller 46, a drive roller 47, an auxiliary roller 48, a tension roller 49, and the like are also provided. The intermediate transfer belt 41 is endlessly moved counterclockwise in FIG. 1 by the rotational driving of the driving roller 47 while being stretched around these rollers. The four primary transfer rollers 45Y, 45C, 45C, 45M, 45K, and 45K sandwich the endlessly moving intermediate transfer belt 41 between the photoreceptors 3Y, 3C, 3M, and 3K to form primary transfer nips. Yes. A transfer bias having a polarity opposite to that of the toner (plus polarity in the first embodiment) is applied to the inner peripheral surface of the intermediate transfer belt 41. The intermediate transfer belt 41 sequentially passes through the primary transfer nips for Y, C, M, and K along with its endless movement, and each color on the photoreceptors 3Y, 3C, 3M, and 3K is disposed on the outer peripheral surface thereof. Primary transfer is performed so that the toner images overlap. As a result, a four-color superimposed toner image (hereinafter referred to as “four-color toner image”) is formed on the intermediate transfer belt 41.

  The secondary transfer backup roller 46 sandwiches the intermediate transfer belt 41 with the secondary transfer roller 50 disposed outside the loop of the intermediate transfer belt 41 to form a secondary transfer nip. The registration roller pair 35 described above feeds the recording paper P sandwiched between the rollers toward the secondary transfer nip at a timing at which the recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 41. The four-color toner image on the intermediate transfer belt 41 is affected by the secondary transfer electric field formed between the secondary transfer roller 50 to which the secondary transfer bias is applied and the secondary transfer backup roller 46, and the influence of the nip pressure. The secondary transfer is batch-transferred onto the recording paper P in the secondary transfer nip. Then, combined with the white color of the recording paper P, a full color toner image is obtained.

  Untransferred toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 41 after passing through the secondary transfer nip. This is cleaned by the belt cleaning unit 42. In the belt cleaning unit 42, the cleaning blade 42a is brought into contact with the front surface of the intermediate transfer belt 41, whereby the transfer residual toner on the belt is scraped off and removed.

  The first bracket 43 of the transfer unit 40 swings at a predetermined rotation angle about the rotation axis of the auxiliary roller 48 as the solenoid (not shown) is turned on / off. In the case of forming a monochrome image, the printer of the first embodiment rotates the first bracket 43 a little counterclockwise in the drawing by driving the solenoid described above. This rotation causes the Y, C, M primary transfer rollers 45Y, C, M to revolve counterclockwise in the drawing around the rotation axis of the auxiliary roller 48, thereby causing the intermediate transfer belt 41 to move in the Y, C direction. , M is separated from the photoconductors 3Y, 3C, 3M. Of the four process units 1Y, 1C, 1M, and 1K, only the K process unit 1K is driven to form a monochrome image. As a result, it is possible to avoid exhaustion of the process units due to wastefully driving the process units for Y, C, and M during monochrome image formation.

  A fixing unit 60 as a fixing unit is disposed above the secondary transfer nip in the figure. The fixing unit 60 includes a pressure heating roller 61 that includes a heat source such as a halogen lamp, and a fixing belt unit 62. The fixing belt unit 62 includes a fixing belt 64, a heating roller 63 containing a heat source such as a halogen lamp, a tension roller 65, a driving roller 66, a temperature sensor (not shown), and the like. Then, the endless fixing belt 64 is endlessly moved in the counterclockwise direction in FIG. 2 while being stretched by the heating roller 63, the tension roller 65, and the driving roller 66. In the process of endless movement, the fixing belt 64 is heated from the back side by the heating roller 63. A pressure heating roller 61 that is driven to rotate in the clockwise direction in FIG. 1 is in contact with the surface of the fixing belt 64 that is heated in this manner. Thereby, a fixing nip where the pressure heating roller 61 and the fixing belt 64 abut is formed.

  Outside the loop of the fixing belt 64, a temperature sensor (not shown) is disposed so as to face the front surface of the fixing belt 64 with a predetermined gap, and the fixing belt 64 just before entering the fixing nip. Detect surface temperature. This detection result is sent to a fixing power supply circuit (not shown). The fixing power supply circuit performs on / off control of power supply to the heat generation source included in the heating roller 63 and the heat generation source included in the pressure heating roller 61 based on the detection result of the temperature sensor. As a result, the surface temperature of the fixing belt 64 is maintained at about 140.degree. The recording paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 41 and then fed into the fixing unit 60. Then, in the process of being conveyed from the lower side to the upper side in the drawing while being sandwiched by the fixing nip in the fixing unit 60, the full-color toner image is applied to the recording paper P by being heated or pressed by the fixing belt 64. To settle.

  The recording paper P subjected to the fixing process in this manner is discharged outside the apparatus after passing between the rollers of the paper discharge roller pair 67. A stack unit 68 is formed on the upper surface of the housing of the printer main body, and the recording paper P discharged to the outside by the discharge roller pair 67 is sequentially stacked on the stack unit 68.

  Above the transfer unit 40, toner bottles 72Y, C, M, and K, which are four toner containers that respectively store Y, C, M, and K toners, are disposed. The color toners in the toner bottles 72Y, 72C, 72M, and 72K are appropriately supplied to the developing devices 7Y, 7C, 7M, and 7K of the process units 1Y, 1C, 1M, and 1K by the toner supply device 70 as described above. The toner bottles 72Y, 72C, 72M, and 72K are detachable from the printer main body independently of the process units 1Y, 1C, 1M, and 1K.

  FIG. 5 is an enlarged perspective view showing a part of the intermediate transfer belt 41 together with an optical sensor as an image detecting means. As shown in the figure, the first optical sensor 101 and the second optical sensor 102 are opposed to each other with a predetermined gap at a place where the intermediate transfer belt 41 is wound around the secondary transfer backup roller 46. The control unit 100 (see FIG. 2) performs color misregistration correction processing and development potential correction processing as image forming condition correction processing immediately after a power switch (not shown) is turned on or every time a predetermined number of prints are performed. It is supposed to be. In the color misregistration correction process, as shown in FIG. 5, a misregistration detection image PV made up of a plurality of toner images called chevron patches on one end side and the other end side in the width direction of the intermediate transfer belt 41, respectively. Form.

  The first optical sensor 101 passes the light emitted from the light emitting means through the condensing lens, reflects it on the surface of the intermediate transfer belt 20, receives the reflected light by the light receiving means, and outputs a voltage corresponding to the amount of light received To do. The toner image in the misregistration detection image PV formed on the rear side of the printer main body among the both ends in the width direction of the intermediate transfer belt 41 passes directly under the first optical sensor 101 as the belt moves. . At this time, the amount of light received by the light receiving means of the first optical sensor 101 changes greatly. Accordingly, the control unit 100 can detect each toner image in the position shift detection image PV formed on the rear side in the width direction of the intermediate transfer belt 41. Similarly, each toner image in the misregistration detection image PV formed on the front side in the width direction of the intermediate transfer belt 41 can be detected based on the output from the second optical sensor 102. As described above, the first optical sensor 101 and the second optical sensor 102 function as image detection means in combination with the control unit 100. As the light emitting means, an LED or the like having an amount of light that can generate reflected light necessary for detecting a toner image is used. Two light receiving means are used, one that receives specularly reflected light and one that receives diffusely reflected light.

  The control unit 100 detects each toner image in the misregistration detection image PV formed on each end of the intermediate transfer belt 41 in the width direction, thereby detecting the position in the main scanning direction and the sub-scanning direction ( Belt position direction), magnification error in the main scanning direction, and skew from the main scanning direction are detected. The main scanning direction here refers to the direction in which the laser light is phased on the surface of the photosensitive member as it is reflected by the polygon mirror. As shown in FIG. 6, the misregistration detection image PV has a posture in which the toner images of the respective colors Y, C, M, and K are inclined by about 45 [°] from the main scanning direction, and the belt moving direction that is the sub scanning direction. Are arranged at a predetermined pitch. Further, as shown in FIG. 7, there is also provided a pattern in which toner images of respective colors Y, C, M, and K are arranged in a posture extending in the main scanning direction. Color misregistration correction processing is processing for reducing registration misalignment and skew misalignment by adjusting optical writing start timing as an image forming condition for each color based on the timing for detecting these toner images.

  In the development potential correction process, a gradation pattern image for image density detection is formed on the intermediate transfer belt 41. As the gradation pattern images for image density detection, those for Y, C, M, and K are formed. Each gradation pattern image is composed of 10 to 15 toner images each having a predetermined pixel pattern. Each toner image is formed to have a different toner adhesion amount (image density).

  For example, taking a K gradation pattern image as an example, this is composed of about 10 K toner images in which the toner adhesion amount gradually increases. These K toner images are formed on the front surface of the belt so as to be arranged at a predetermined interval in the traveling direction of the intermediate transfer belt 41. The amount of toner adhesion per unit area for each K toner image is detected by an optical sensor.

  26 is a schematic diagram showing an intermediate transfer belt 41 in a conventional image forming apparatus, a gradation pattern image of each color formed on the surface thereof, and a position deviation detection image PV. In the conventional image forming apparatus, as shown in the figure, each toner image of the misregistration detection image PV formed on one end portion (rear side end portion) of the intermediate transfer belt 41 in the width direction is obtained by the first optical sensor 101. It was detected. Further, each toner image of the misregistration detection image PV formed at the other end portion (front side end portion) in the width direction of the intermediate transfer belt 41 is detected by the second optical sensor 102. In addition to these optical sensors (101, 102), the conventional image forming apparatus has optical sensors 109Y, C, M, K for individually detecting Y, C, M, K gradation pattern images. Was. Then, Y, C, M, and K gradation pattern images are formed side by side in the belt width direction with respect to a region closer to the center than both ends of the belt as shown in the figure. In such a configuration, since the formation of the gradation pattern image and the detection of the toner image in the gradation pattern image can be performed in parallel for each color, the development potential is more than that performed by shifting the time for each color. The correction process can be completed quickly.

  However, in addition to the first optical sensor 101 and the second optical sensor 102, it is necessary to add four optical sensors for individually detecting the gradation pattern images of the respective colors. is there. Further, if there is a development gap deviation that gradually decreases or increases from one end to the other end of the photoreceptor in the axial direction, a density difference occurs between the gradation pattern images of each color. This may cause a difference in image density between the colors.

  Therefore, in the printer according to the first embodiment, gradation pattern images of each color are formed at the detection position by the first optical sensor 101 and the detection position by the second optical sensor 101 on the intermediate transfer belt 41, respectively. It has become. In such a configuration, the first optical sensor 101 or the second optical sensor 102 that detects the misregistration detection image PV detects the gradation pattern image of each color, thereby reducing the cost. Further, by forming the gradation pattern images of the respective colors at the same position in the width direction of the intermediate transfer belt 41, it is possible to detect a gradation pattern image having no image density difference between the colors.

  FIG. 8 is a flowchart showing a control flow of the development potential correction process performed by the control unit 100. In the printer according to the first embodiment, as described above, gradation pattern images are formed at the detection position by the first optical sensor 101 and the detection position by the second optical sensor 101 on the surface of the intermediate transfer belt 41, respectively. Detect. For these gradation pattern images, the illustrated control flow is performed in parallel.

  In the development potential correction process, first, the first optical sensor 101 and the second optical sensor 102 are calibrated (step 1: hereinafter, step is referred to as S). Specifically, the amount of light emitted from the light emitting element (the voltage to the light emitting element) is set so that the output from the light receiving element when receiving regular reflection light on the surface of the intermediate transfer belt 41 without toner adhesion is 4 [V]. ). When the calibration of the optical sensor is completed, a gradation pattern image of each color is formed at the detection position by the first optical sensor 101 and the detection position by the second optical sensor 102 on the surface of the intermediate transfer belt 41 (S2). Specifically, a gradation pattern image composed of a plurality of toner images developed with different development potentials is formed by adjusting the development bias and the charging bias on each color photoconductor 3Y, 3C, 3M, and 3K. Instead of adjusting the developing bias and the charging bias, the developing potential may be changed by changing the optical writing amount by adjusting the optical writing duty and power. In this case, it is possible to accurately adjust the developing potential by confirming the latent image potential by providing a potential sensor for measuring the potential of the optical writing unit.

  Thereafter, the toner adhesion amount (image density) per unit area of the toner image in the formed gradation pattern image is detected by the optical sensor (S3). Specifically, the toner image on the belt surface is irradiated with light from the light emitting element of the optical sensor, and the amount of reflected light is detected by the light receiving element. For the K toner image, only the regular reflection light amount is detected, while for the Y, C, and M toner images, both the regular reflection light amount and the diffuse reflection light amount are detected. This is because the Y, C, and M toner images use these two reflected light amounts in the color toner adhesion amount conversion algorithm.

  Hereinafter, the output voltage from the optical sensor that receives the reflected light on the surface of the intermediate transfer belt 41 where the toner is not attached is referred to as a background portion detection output voltage Vsg. Further, the output voltage from the light receiving element that receives the specularly reflected light obtained on the surface of the toner image is referred to as a regular reflection output voltage Vsp_reg during image detection. Further, the output voltage from the light receiving element that receives the diffuse reflection light obtained on the surface of the toner image is referred to as a diffuse reflection output voltage Vsp_dif at the time of image detection. The output voltage from the light receiving element when light emission by the light emitting element is stopped is referred to as an offset voltage Voffset. The order from the top of each toner image in the gradation pattern image is indicated by “n”.

For each K toner image in the K gradation pattern image, the output voltage is converted into the toner adhesion amount as follows. That is, first, the offset potential Voffset_reg is subtracted from the regular reflection output voltage Vsp_reg at the time of image detection based on the following equations 1 and 2.

Next, the diffuse reflection output voltage Vsp_dif at the time of image detection is normalized using the following equation (3). Thereafter, the normalized value is converted into the toner adhesion amount using a lookup data table constructed in advance.

For Y, C, and M toner images in the Y, C, and M gradation pattern images, the output voltage is converted into the toner adhesion amount as follows. That is, for each toner image, using the following equations (4) and (5), the difference between the regular reflection output voltage Vsp_reg at the time of image detection and the diffuse reflection output voltage Vsp_dif at the time of image detection is the difference from the offset potential Voffset_reg. Conversion into a certain regular reflection differential voltage ΔVsp_reg and diffuse reflection differential voltage ΔVsp_dif. This is because the increase in the sensor output is represented only by the increase in the toner adhesion amount. For reference, FIG. 9 shows the relationship between the output voltage before conversion and the toner adhesion amount.

The obtained regular reflection differential voltage ΔVsp_reg. [N], diffuse reflection differential voltage ΔVsp_dif. From [n], ΔVsp_reg. [N] / ΔVsp_dif. [N] is calculated. Then, based on the calculation result, a sensitivity correction coefficient α to be multiplied by the diffuse reflection differential voltage ΔVsp_dif is calculated by the following equation (6). For reference, the sensitivity correction coefficient α and the regular reflection differential voltage ΔVsp_reg. [N] and the diffuse reflection differential voltage ΔVsp_dif. An example of the relationship with [n] is shown in FIG.

  Note that the ratio of the sensitivity correction coefficient α is obtained from the minimum value because of the diffuse reflection differential voltage ΔVsp_dif. This is because the minimum value of [n] is almost zero and is known to be a positive value.

Next, the regular reflection differential voltage ΔVsp_reg. [N] diffused light component ΔVsp_reg. _Dif [n] is obtained. Further, the regular reflection differential voltage ΔVsp_reg. [N] specular reflection component ΔVsp_reg. _Reg [n] is obtained.

  In this way, the specular reflection light differential voltage ΔVsp_reg. If the diffused light component is separated from [n], only a pure specularly reflected light component can be extracted as shown in FIG.

Next, the regular reflection component ΔVsp_reg. The ratio between _reg [n] and the output voltage Vsg at the time of detecting the background portion is calculated to obtain a normalized value β [n] in the range of 0-1.

この一例のように、正規化値βと地肌部変動補正後の拡散反射成分△Ｖｓｐ＿ｄｉｆ’との関係を２次元平面にプロットし、そのプロット線を近似することで、拡散光出力の感度を求める。そして、この感度があらかじめ定めた狙いの感度となるように、補正を行う。プロット点を近似する方法としては、多項式近似（２次近似）を用いる。 Next, the diffuse reflection component ΔVsp_dif ′ after the background portion variation correction is obtained by the mathematical expression of Formula 10. For reference, FIG. 12 shows an example of the relationship between the diffuse reflection component ΔVsp_dif ′ after the background fluctuation correction and the normalized value β.

As in this example, the relationship between the normalized value β and the diffuse reflection component ΔVsp_dif ′ after the background fluctuation correction is plotted on a two-dimensional plane, and the sensitivity of the diffused light output is obtained by approximating the plot line. . Then, correction is performed so that the sensitivity becomes a predetermined target sensitivity. As a method of approximating the plot points, polynomial approximation (secondary approximation) is used.

In the polynomial approximation, first, a plot line obtained by plotting the diffuse reflection component ΔVsp_dif ′ after the background portion fluctuation correction is normalized with respect to the normalized value β by a polynomial approximation (in the first embodiment, a quadratic expression approximation), A sensitivity correction coefficient η is calculated. More specifically, first, the plot line is approximated by a quadratic approximate expression (y = ξ1x2 + ξ2x + ξ3), and coefficients ξ1, ξ2, and ξ3 are obtained by the least square method as shown in the following equation (11).

  In Equation 11, m is the number of data. X [i] is a normalized value of the regular reflection light_regular reflection component. Further, y [i] is the diffuse reflection component ΔVsp_dif ′ after the background portion fluctuation correction. The range of x used for the calculation is 0.1 ≦ x ≦ 1.00. The coefficients ξ1, ξ2, and ξ3 can be obtained by solving the simultaneous equations (1), (2), and (3) in Equation 11.

A sensitivity correction coefficient η is calculated by the mathematical expression 12 so that a certain normalized value a calculated from the approximated plot line becomes a certain value b.

By multiplying the diffuse reflection component ΔVsp_dif ′ after the background portion fluctuation correction obtained by Equation 10 by the sensitivity correction coefficient η obtained by Equation 12, the relationship between the toner adhesion amount and the diffused light output is determined in advance. A diffused light output ΔVsp_dif ″ after sensitivity correction is obtained.

  The above is the correction process of the optical sensor output value with respect to the temporal variation of the optical sensor output caused by the decrease in the light emission amount of the light emitting element. By performing such correction, it is possible to correct the relationship between the output value of the light receiving element and the toner adhesion amount to a unique relationship with respect to fluctuations in the output value of the light emitting element and the light receiving element due to temperature change, deterioration with time, etc. it can. The output value of the optical sensor can be converted into the toner adhesion amount by referring to the adhesion amount conversion table based on the corrected optical sensor output value. As a result, good toner adhesion amount detection can be performed using an optical sensor even over time.

  In the flow shown in FIG. 8, when the toner adhesion amount of each toner image is obtained (S4), next, development γ is calculated (S5). FIG. 13 is a graph showing the relationship between the development potential at the time of forming each toner image in the gradation pattern image and the toner adhesion amount. A linear expression obtained by linearly approximating each plot point in the figure by the least square method represents the developing ability. This linear inclination is the development γ. Further, the value of the intersection of this linear equation and the X axis is the development start voltage Vk. Although linear approximation is used, quadratic curve approximation may be adopted. However, the development γ when the quadratic linear approximation is adopted is a linear differential value at the point where the target adhesion amount is obtained. In the first embodiment, since the gradation pattern images are formed at the detection position by the first optical sensor 101 and the detection position by the second optical sensor 102, two approximate lines based on the respective detection results are obtained.

  After the development γ is calculated based on the two approximate lines (S5), the development potential for obtaining the target toner adhesion amount for each development γ is obtained based on the approximate lines in FIG. 13 (S6).

Next, a characteristic configuration of the printer according to the first embodiment will be described.
In the process units of the respective colors, it is assumed that one is slightly inclined with respect to the other without being exactly parallel to each other due to an assembly error of the developing roll or the photosensitive member. Then, a deviation occurs in the developing gap between the developing roll and the photoconductor. For example, the deviation is such that the development gap at the rear end in the axial direction of the photosensitive member is the smallest, and the development gap gradually increases toward the front. Hereinafter, a case where there is such a deviation will be described as an example.

  When there is a deviation in the development gap, a deviation occurs in the image density in the photosensitive body axial direction. With the development gap deviation as described above, the image density of the image formed at the rear end is the highest. Then, the image density gradually decreases as going to the front side.

  Assume that the image density (ID) is higher at the rear side end portion by 0.1 than at the front side end portion. Further, it is assumed that there is a toner adhesion amount detection error corresponding to an image density of plus or minus 0.05 due to the limit of toner adhesion amount measurement accuracy. It is assumed that development potential correction processing is executed for each color based on the toner adhesion amount of the toner image formed at the rear side end under such conditions. Then, as shown in FIG. 14, in the subsequent print jobs, there is a possibility that the image density of the toner image formed on the front side end will fall below the lower limit value (ID = 1.25).

  On the contrary, it is assumed that the development potential correction process is executed based on the toner adhesion amount of the toner image formed on the front side end. Then, as shown in FIG. 15, in subsequent print jobs, the image density of the toner image formed on the rear side end may exceed the upper limit (ID = 1.55).

  On the other hand, as shown in FIG. 16, based on the toner adhesion amount of the toner image formed at the rear side end portion and the toner adhesion amount of the toner image formed at the front side end portion, It is assumed that the toner adhesion amount is obtained and the development potential correction process is executed based on the result. Then, as shown in FIG. 16, the probability that the image density is lower than the lower limit or higher than the upper limit is lower than in the two examples described above.

However, it has been found that with a low-stress developing device, even if the development potential correction process is performed in this way, the image density tends to be insufficient at the front side end, which is the large gap side. This is for the reason explained below. That is, in the developing device, additives such as silica (SiO ₂ ) and titanium oxide (TiO ₂ ) added to the toner in order to obtain good toner fluidity are buried in the toner particles by mechanical stress. Or may be detached from the surface to cause toner deterioration. In the low-stress specification, the mechanical stress on the developer is reduced as much as possible in order to make it difficult to cause such toner deterioration. In such a low-stress specification, when images with a relatively high area ratio are continuously output, a large amount of toner replenished to the developing device as a large amount of toner is consumed is not sufficiently charged in the first agent storage chamber. , It may be fed into the second agent storage chamber facing the developing roll. The poorly charged toner fed into the second agent storage chamber is sufficiently charged as it is transported from the rear side, which is the downstream side in the transport direction, toward the front side. If it is pumped up to the development area, it may adhere excessively to the electrostatic latent image on the photoreceptor and cause an excessive image density.

  Therefore, in the printer according to the first embodiment, since the toner charge amount rises sufficiently on the front side corresponding to the downstream side in the developer transport direction in the photosensitive member axial direction, A gradation pattern image is formed. On the other hand, on the rear side corresponding to the upstream side in the developer conveyance direction, a gradation pattern image is formed closer to the center than the rear side end portion because there is a possibility that toner with poor charging will be sent.

  FIG. 17 is a schematic diagram showing the intermediate transfer belt 41 in the printer according to the first embodiment, a gradation pattern image of each color formed on the surface thereof, and a misregistration detection image PV. In the drawing, the width direction of the intermediate transfer belt 41 is the same as the axial direction of a photoreceptor not shown. In the belt width direction, the front side end corresponds to the downstream side end in the developer transport direction of the photoreceptor. A position shift detection image PV and color gradation pattern images (Py, Pc, Pm, Pk) are formed on the front side end. Then, the respective toner images provided in them are detected by the second optical sensor 102. The distance between the center portion and the end portion of the intermediate transfer belt 41 is da. On the front side, image formation and detection are performed at the front side end portion shifted from the central portion by the distance da.

  On the other hand, in the belt width direction, the rear side end corresponds to the upstream side end in the developer transport direction of the photosensitive member. At the rear side end, excessively charged image density is likely to occur due to the poorly charged toner being fed into the second agent storage chamber of the developing device. Therefore, on the rear side, the position shift detection image PV and each color gradation pattern image (Py, Pc, Pm, Pk) are formed in a region closer to the center than the rear end. Then, the first optical sensor 101 detects each toner image provided in them. The distance between the central portion of the intermediate transfer belt 41 and the region closer to the center is db (da> db).

In the development potential correction process, the control unit 100 approximates the straight line obtained based on the gradation pattern image formed at the front side end, and the gradation formed in the region closer to the center than the rear side end on the rear side. Based on the approximate straight line obtained based on the pattern image, a central development potential Vpot (center), which is a development potential suitable for the central portion of the belt, is calculated. This calculation is performed according to the mathematical formula (14). In this equation, Vpot1 represents the developing potential at the front side end. Vpot2 represents the developing potential in a region closer to the center than the end on the rear side.

  For reference, FIG. 18 shows the relationship among the development potential on the rear side, the development potential on the front side, and the central development potential.

When the central developing potential Vpot (center) is obtained, the developing bias is obtained based on the mathematical formula 15 or the charging bias is obtained based on the mathematical formula 16. Then, the developing bias and the charging bias that have been employed in the print job are corrected to the values obtained by the mathematical formulas (15) and (16). Such processing is performed for each color. Since the potential of the electrostatic latent image is approximately 50 [−V], 50 [−V] is subtracted from the development potential in the mathematical expression of Formula 15. Further, 200 [−V] in Equation 16 is the background potential. The background potential is a potential that is set offset from the development bias in order to prevent background contamination.

  The optical writing intensity is changed in the range of 80 to 120 [%] according to the photosensitive member charging potential, but the detailed description is omitted.

  As the gradation pattern images Py, Pc, Pm, and Pk for Y, C, M, and K, those that are shorter than the photoreceptor arrangement pitch L1 are formed as shown in FIG. With such a configuration, it is possible to simultaneously start the formation of gradation pattern images of the respective colors, thereby shortening the pattern image formation time.

  In addition, the following merit can also be acquired by using two optical sensors (101, 102). That is, a detection error unique to each product occurs in the optical sensor. This detection error shows a normal distribution as shown in FIG. 20, for example, but the deviation varies depending on the product. As shown in the drawing, if the optical sensor has a detection error of plus or minus 10 [%], the detection result may include an error of plus or minus 10 [%]. On the other hand, if the optical sensor has a detection error of less than plus or minus 10 [%], for example, the normal distribution of the dotted line in FIG. 21 is shown. On the other hand, when calculating the image density at the center based on the detection results of the two optical sensors, the detection error indicates, for example, a normal distribution of dotted lines in FIG. Although the maximum error is the same as that detected by one optical sensor, it can be seen that the frequency at which the error is maximized decreases. In order to maximize the error, there is only a sensor combination having a detection error of +10 [%] or a sensor combination having a detection error of −10 [%]. However, the probability of such a combination is low. is there. Moreover, the frequency of the range with a small detection error is increasing. This is also an advantage of performing the averaging process.

Next, a modification of the printer according to the first embodiment will be described.
When a gradation pattern image is formed in each of the front end portion of the intermediate transfer belt 41 and a region closer to the center than the end portion on the rear side, the central development potential Vpot (center) is obtained based on the results. As described above, it is possible to suppress the occurrence of excessive image density at the rear end and the occurrence of insufficient image density at the front end. On the other hand, since two gradation pattern images are formed, there is a demerit that the toner consumption increases.

Therefore, in the printer according to the modified example, a gradation pattern image is formed on the front side end and the end closer to the center than the end on the rear side only at the time of the initial operation for the user after factory shipment. To do. Then, when the central development potential Vpot (center) is calculated based on the detection result of each gradation pattern image, the calculation result and the front-side development potential Vpot1 are substituted into the equation 17 to obtain the potential correction coefficient. Vcoef is obtained.

When the potential correction coefficient Vcoef is obtained in this way, in the subsequent development potential correction processing, gradation is applied only to the front side end portion of the front side end portion and the region closer to the center than the rear end portion. A pattern image is formed. Then, the front developing potential Vpot1 obtained based on the detection result and the potential correction coefficient Vcoef are substituted into the following equation 18 to obtain the central developing potential Vpot (center).

Instead of the mathematical expression 17 using the front development potential Vpot1 and the potential correction coefficient Vcoef, the mathematical expression 19 using the central development potential Vpot (center) and the rear development potential Vpot2 may be used. In this case, the rear-side development potential Vpot2 is used instead of the front-side development potential Vpot1 in the mathematical formula (18).

  In this printer having such a configuration, after the initial development potential correction process is performed under the user, either the front-side end portion or the region closer to the center than the rear-side end portion is selected. An appropriate development potential at the center can be obtained simply by forming a gradation pattern image.

  Although an example in which the image density deviation from the front side to the rear side is caused by the development gap deviation has been described, it is not caused by the development gap deviation, and the toner charging as in the third embodiment described later is performed. The present invention can also be applied to cases caused by deviations in quantity. In this case, as in the third embodiment, if necessary, a second mode in which a gradation pattern image is formed in both the front end and the region closer to the center than the end on the rear side, You may make it switch as needed the 1st mode which forms a gradation pattern image only in one side.

Next, a printer according to the second embodiment will be described. Note that the configuration of the printer according to the second embodiment is the same as that of the first embodiment unless otherwise specified.
In the printer according to the second embodiment, in each color process unit, the charge amount of the toner replenished in the first agent storage chamber of the developing device sufficiently rises in the first agent storage chamber. For this reason, even if an image with a high area ratio is continuously output, a large amount of poorly charged toner is not fed to the rear side end in the second agent storage chamber.

  FIG. 22 is a schematic diagram showing the intermediate transfer belt 41 in the printer according to the second embodiment, a gradation pattern image of each color formed on the surface of the intermediate transfer belt 41, and a position deviation detection image PV. In the same figure, the misalignment detection image PV and the gradation pattern images (Py, Pc, Pm, Pk) of each color are formed on the front side end of the intermediate transfer belt 41 in the first embodiment. It is the same as the form. On the other hand, the aspect on the rear side is different from the first embodiment. Specifically, on the rear side, as shown in the figure, a position shift detection image PV and gradation pattern images (Py, Pc, Pm, Pk) of each color are formed on the rear side end.

In the development potential correction process, the following formula 20 is used for the central development potential Vpot (center) instead of the formula 14 described above.

  As in the modification example of the printer according to the first embodiment, the control unit 100 performs the front side end and the rear side end as shown in FIG. A gradation pattern image is formed on both. When the potential correction coefficient Vcoef is obtained, a gradation pattern image is formed on only one of the front end and the rear end in the subsequent development potential correction process. Then, based on the result of detection by the optical sensor and the potential correction coefficient Vcoef, the central development potential Vpot (center) is obtained.

  Next, a printer according to a third embodiment to which the invention is applied will be described. Unless otherwise specified, the configuration of the printer according to the third embodiment is the same as that of the first embodiment.

  As in the first embodiment, the printer according to the third embodiment has a front-side end portion of the intermediate transfer belt 41 and a region closer to the center than the end portion on the rear side during the development potential correction process. A gradation pattern image is formed for each. Alternatively, as in the second embodiment, gradation pattern images are formed at the front end and the rear end of the intermediate transfer belt 41 during the development potential correction process.

  In this printer, unlike the first embodiment, there is no deviation in image density in the belt width direction due to deviation in the development gap. Instead, in each color process unit, a deviation in image density in the belt width direction may occur due to a deviation in toner charge amount from the rear side to the front side in the second agent storage chamber of the developing device. The deviation may or may not occur depending on predetermined conditions such as the area ratio of the output image and the environment. Alternatively, the deviation amount is large or small depending on a predetermined condition. When there is no deviation or the deviation is small, there is no merit for obtaining an appropriate central development potential Vpot (center) by forming gradation pattern images on both ends in the belt width direction. Nevertheless, if the gradation pattern images are formed on both ends, wasteful toner consumption is caused.

  Therefore, the control unit 100 of the printer appropriately switches between the first mode and the second mode as the development potential correction process according to a predetermined parameter indicating the magnitude of the image density deviation in the belt width direction, for example, the environment. It is supposed to be implemented. Specifically, it is assumed that the predetermined parameter is a value indicating that the image density deviation in the belt width direction is relatively small or almost none. In this case, as the development potential correction process, a first mode is executed in which a gradation pattern image is formed on only one of the front side and the rear side of the intermediate transfer belt 41. On the other hand, it is assumed that the predetermined parameter is a relatively large value for the image density deviation in the belt width direction. In this case, as a development potential correction process, a second mode is performed in which gradation pattern images are formed on both the front side and the rear side of the intermediate transfer belt 41 to obtain the central development potential Vpot (center).

  In this configuration, when the predetermined parameter is a value indicating that no image density deviation occurs between the upstream region and the downstream region in the developer transport direction on the surface of the latent image carrier, By executing the mode, it is possible to avoid unnecessary toner consumption.

Next, printers according to examples in which a more characteristic configuration is added to the printer according to the third embodiment will be described.
[First embodiment]
FIG. 23 is a graph showing the relationship between the toner charge amount in the first agent storage chamber of the developing device and the area ratio of the output image in each color process unit of the printer according to the first embodiment. 100 sheets per image area ratio under the condition that the toner density in each color developing device is kept constant by toner replenishment in the standard linear speed mode in which the linear speed of the photosensitive member or belt is driven at the standard linear speed (120 mm / sec). It is the graph produced based on the experiment which performed continuous printing one by one. As shown in the figure, it can be seen that the charge amount of the toner in the first agent storage chamber decreases as the area ratio of the continuously output image increases.

  FIG. 24 is a graph showing the relationship between the image density deviation between the front side end and the rear side end and the area ratio of the output image. The image density deviation was measured as follows. That is, three toner images for image density measurement are formed on the front side edge and the rear side edge of the recording paper, respectively, and the image density of these toner images is measured. Then, after calculating the average value of the image density at the front end and the average value of the image density at the rear end, the result of subtracting the average value of the front end from the average value of the rear end. The image density deviation was taken.

  As shown in the figure, it can be seen that the image density deviation increases with an increase in the image area ratio in the range of the image area ratio from 10 [%] to 60 [%]. As described above, the difference in the image density deviation is caused by the fact that when a relatively high area ratio image such as a photographic image is continuously output, the poorly charged toner is sent to the second agent storage chamber. This is because the amount increases as the image area ratio increases. There is a difference of 0.2 in the deviation amount between the image area ratio of 10 [%] and 60 [%].

  There are individual differences in the average output image area ratio of users. The average output image area ratio is relatively high for users who mainly output graphics such as photographic images, while the average output image area ratio is relatively low for users who mainly output text images. Because it becomes. Here, since the former user has a relatively large image density deviation as shown in the figure, it is desirable to measure the above-described central development potential Vpot (center). On the other hand, since there is almost no image density deviation for the latter user, there is not much difference between the above-described central development potential Vpot and the front side development potential Vpot1 and the rear side development potential Vpot2. Nevertheless, it is not desirable from the viewpoint of wasteful toner consumption to perform the second mode and obtain the central development potential Vpot (center).

  Therefore, when executing the development potential correction process, the control unit 100 first calculates the average output image area ratio from the present time to the past predetermined number of outputs. When the average output image area ratio exceeds a predetermined upper limit value or exceeds the upper limit value, the second mode is performed. On the other hand, when the average output image area ratio does not exceed the predetermined upper limit value or becomes lower than the upper limit value, the first mode is performed. This avoids unnecessary toner consumption.

  Note that the same effect can be obtained by using the average toner replenishment amount per one sheet output as a predetermined parameter instead of the average output image area ratio.

[Second Embodiment]
In the printer according to the second embodiment, the leaving time (power OFF time) is used as a parameter indicating the magnitude of the image density deviation between the front side and the rear side. This is because, when the leaving time is long, the image density deviation is almost eliminated, whereas when the leaving time is relatively short, there is a high possibility of causing the image density deviation. Specifically, when the leaving time is relatively long, almost all toners are poorly charged in the developing device of each color process unit regardless of the position of the circulation path. There is almost no difference in charge amount. When the power is turned on in this state and stirring of the developer is started, the charge amount of the toner gradually increases, but the stirring time is the same regardless of the position in the circulation path. The toner at the position has almost the same charge amount. Thereafter, in the development potential correction process prior to the print job, gradation pattern images are simultaneously formed on the rear side and the front side, so that each gradation pattern image is developed with toner having no difference in charge amount. Become. Therefore, the image density deviation hardly occurs even from the rear side to the front side.

  On the other hand, if the neglected time is relatively short, the situation that the toner charge amount on the rear side is smaller than that on the front side during the print job may still remain in the second agent storage chamber. . Then, an image density deviation occurs from the rear side to the front side.

  In the case where the standing time is smaller than the predetermined lower limit value, the necessity for executing the development potential correction process is low. In this printer, the development potential correction process is executed for every predetermined number of prints. If the standing time is smaller than the lower limit value, it is highly likely that the effect of the previous development potential correction process still remains. It is.

Therefore, when the standing time is shorter than the predetermined lower limit value, the control unit 100 does not perform the development potential correction process immediately after the power is turned on as shown in Table 1 below. On the other hand, when the standing time is not less than the predetermined lower limit value and less than the predetermined upper limit value, the second mode is performed as the development potential correction process to obtain the central development potential Vpot (center). This is because there is a possibility that a situation in which “the toner charge amount on the rear side is smaller than that on the front side” still remains in the second agent storage chamber before the power is turned off. If the standing time is equal to or greater than a predetermined upper limit, the first mode is implemented as the development potential correction process, and only one of the front side development potential Vpot1 and the rear side development potential Vpot2 is measured.

  An example of the lower limit of the standing time is 1 hour. Moreover, as an upper limit of leaving time, 6 hours can be illustrated, for example.

Note that just because the standing time is not less than the lower limit and less than the upper limit does not necessarily cause an image density deviation. If the image density deviation does not occur immediately before the power is turned off due to the relatively small average image area ratio (or toner supply amount) immediately before the power is turned off, the image density deviation does not occur even when the power is turned on thereafter. Because. Therefore, as shown in Table 2 below, as the predetermined parameter, the cumulative number of prints when the power is turned on last time is used in addition to the neglecting time, and the neglecting time is not less than the lower limit value and less than the upper limit value. It is more effective to execute the second mode only when the number of sheets exceeds the threshold value.

[Third embodiment]
In the printer according to the third embodiment, absolute humidity [g / m ³ ], which is an environmental parameter, is used as a parameter indicating the magnitude of the image density deviation between the front side and the rear side. This is for the reason explained below. That is, the developing device of each color process unit of the printer according to the third embodiment, when the absolute humidity is below a predetermined upper limit, depends on the amount of toner newly supplied to the first agent storage chamber. The developer agitating ability to such an extent that it is surely charged and then fed into the second agent storage chamber is exhibited. For this reason, when the absolute humidity is below the upper limit, no image density deviation occurs from the rear side to the front side. On the other hand, when the absolute humidity exceeds the upper limit value, the developer stirring ability is lowered, and the toner with poor charging may be fed into the second agent storage chamber. This causes an image density deviation from the rear side to the front side.

Therefore, when the absolute humidity is lower than the predetermined upper limit value, the control unit 100 performs the first mode as the development potential correction process as shown in the following Table 3, and either the front side development potential Vpot1 or the rear side. Only one of the side development potential Vpot2 is measured. On the other hand, when the absolute humidity is equal to or higher than the predetermined upper limit value, the central development potential Vpot (center) is obtained by executing the second mode as the development potential correction process.

In addition, as an upper limit of absolute humidity, 4 [g / m < ³ >] can be illustrated, for example.

  As described above, in the printer according to the first embodiment, the first optical sensor 101 or the second optical sensor 102 that can detect the image density of the toner image is used as the image detection unit, and downstream in the development potential correction process. Of the various image forming conditions, the image of the toner image is based on the detection result of the image density of the toner image formed in each of the front end and the end closer to the center than the rear end. The control unit 100 serving as a control unit is configured to correct the development potential, which is an image forming condition that can change the density. In such a configuration, the image density can be stabilized over a long period of time by correcting the development potential.

  Further, in the printer according to the first embodiment, the toner images formed in the front side end portion and the central region in the color misregistration correction processing, which is the image forming condition correction processing, are detected by the optical sensors (101, 102). Based on the detection timing, the control unit 100 corrects the optical writing start timing, which is an image forming condition that can change the formation position of the toner image with respect to the photosensitive member as the latent image carrier, among various image forming conditions. Is configured. In such a configuration, it is possible to form an image with no positional deviation over a long period of time by correcting the optical writing start timing.

  In the printer according to the first embodiment, in the development potential correction process, the gradation pattern image including a plurality of toner images having different image densities is respectively displayed on the front side edge and the central area. Based on the result of detecting the image density of each toner image in the gradation pattern image formed and formed on the front side edge, the developing ability in the front side edge region of the image forming means comprising a process unit or the like is grasped On the other hand, on the basis of the result of detecting the image density of each toner image in the gradation pattern image formed in the central area, the control unit 100 so as to grasp the developing ability in the central area of the image forming means. Is configured. In such a configuration, the developing ability can be more accurately grasped based on the result of detecting the image density of various toner images in the gradation pattern image, not the result of detecting the image density of one toner image.

  In the printer according to the first embodiment, the developer in the image forming unit is based on the developing capability in the front side end region of the image forming unit and the developing capability in the region near the center of the image forming unit. The control unit 100 is configured to grasp the developing capability in the central region in the transport direction and correct the central developing potential Vpot (center), which is an image forming condition that can change the image density of the toner image, based on the result. It is composed. In this configuration, as described above, the image density on the rear side is excessive as compared with the case where the developing potential is corrected based only on the developing ability in the front end region or the developing ability in the rear end region. And the occurrence of insufficient image density on the front side can be suppressed.

  In the printer according to the first embodiment, the control unit 100 is configured to correct the development potential as an image forming condition that can change the image density of the toner image. The image density can be stabilized.

  In the printer according to the first embodiment, the image forming means includes a combination of a photoconductor and a developing device for forming different color toner images, and the photoconductors formed on the photoconductors are mutually connected. A transfer unit 40 is provided as transfer means for transferring different color toner images onto the surface of the intermediate transfer belt 41 as an intermediate transfer body to obtain a multicolor image, and the center of a plurality of photoconductors is used as image detection means. A first image that detects each toner image of the gradation pattern image that has been formed in each of the close regions and then transferred to one end in the width direction that is a direction orthogonal to the surface movement direction on the surface of the intermediate transfer belt 41. After the first optical sensor 101 serving as the detection means and the front side end region of the plurality of photoconductors are respectively formed, the intermediate transfer belt 41 is respectively provided on the other end side in the width direction. It is provided and the second optical sensor 102 serving as a second image detecting means for detecting the respective toner images transferred gradation pattern images. With this configuration, the first optical sensor 101 can detect the gradation pattern image in the region near the center, and the second optical sensor 102 can detect the gradation pattern image in the front side end region.

  In the printer according to the first embodiment, the length of the intermediate transfer belt surface movement direction is set to be larger than the arrangement pitch L1 of the plurality of photoconductors as the gradation pattern images formed on the plurality of photoconductors. The control unit 100 is configured to form a shortened one. In such a configuration, as already described, the formation of the gradation pattern images of the respective colors can be started simultaneously to shorten the pattern image formation time.

  In the printer according to the first embodiment, since the first optical sensor 101 and the second optical sensor 102 detect both the regular reflection light amount and the diffuse reflection light amount on the surface of the intermediate transfer belt, respectively. In addition to the K toner image, the image density (toner adhesion amount) of the Y, C, and M toner images can be detected with high accuracy.

  In the printer according to the first embodiment, as a development potential correction process, a toner image is formed only in one of the front side end region and the central region, and this is used as an optical sensor. A first mode in which processing for correcting the development potential is performed based on the result detected by the image forming method, and processing for correcting the development potential based on the result of forming toner images in both areas and detecting them by the optical sensor. Of the second mode to be implemented, the control unit 100 is configured to select and execute the one corresponding to the parameter indicating whether or not it is the first development potential correction process. In this configuration, as described above, in the second and subsequent development potential correction processes, it is possible to suppress the toner density consumption by omitting the formation of the gradation pattern image for either one of the two areas. .

  Further, in the second example of the printer according to the third embodiment, a leaving time which is an apparatus stop period is adopted as a predetermined parameter. Then, the control unit 100 is configured to execute the first mode when the leaving time exceeds a predetermined upper limit value, and to execute the second mode when it is equal to or lower than the upper limit value. In such a configuration, unnecessary toner consumption due to the execution of the second mode despite the absence of the image density difference from the rear side to the front side due to the long standing time is avoided. be able to. It should be noted that the same effect can be obtained by adopting an elapsed time after processing, which is a period from the execution of the development potential correction processing to the current time, instead of the standing time.

  In the third example of the printer according to the third embodiment, absolute humidity, which is one of the environmental parameters indicating the environmental conditions, is employed as the predetermined parameter. The control unit 100 is configured to execute the second mode when the absolute humidity exceeds a predetermined upper limit value, and to execute the first mode when the absolute humidity is equal to or lower than the upper limit value. In such a configuration, due to the relatively low absolute humidity, wasteful toner consumption is caused by performing the second mode even though there is no difference in image density from the rear side to the front side. It can be avoided. Note that the same effect can be obtained by using relative humidity or temperature as the environmental parameter instead of absolute humidity.

  In the first example of the printer according to the third embodiment, an average output image area ratio in a predetermined period is adopted as a predetermined parameter. When the average output image area ratio exceeds a predetermined upper limit value or is equal to or higher than the upper limit value, the second mode is executed. On the other hand, when the average output image area ratio is equal to or lower than the upper limit value or lower than the upper limit value, the first mode is executed. Thus, the control unit is configured. In such a configuration, wasteful toner consumption due to the execution of the second mode even though there is no difference in image density from the rear side to the front side due to the relatively low average output image area ratio. Can be avoided. Note that the same effect can be obtained by using a toner replenishment amount per unit time instead of the average output image area ratio as a parameter.

3Y, C, M, K: photoconductor (latent image carrier)
7Y: Developing device (developing means)
20: Optical writing unit (latent image forming means)
40: Transfer unit (transfer means)
41: Intermediate transfer belt (intermediate transfer member)
100: Control unit (control means, calculation means)
101: 1st optical sensor (1st image detection means)
102: Second optical sensor (second image detection means)

JP-A-11-143144

Claims (9)

A latent image carrier that carries a latent image on its moving surface;
Latent image forming means for forming a latent image on the surface;
While the developer containing the toner and the carrier is transported along a predetermined circulation path, the developer transported in a predetermined transport direction in the region facing the developer support in the circulation path Is moved to a developing area facing the latent image carrier, and developer toner is attached to the latent image on the latent image carrier in the developing area to develop the latent image. And an image forming means having a developing means for returning the developer that contributed to the development in the developing area to the opposing area of the circulation path in accordance with the movement of the surface of the developer carrier.
After forming predetermined toner images in two different areas on the surface of the latent image carrier, the image forming conditions in the image forming means are based on the results of detecting the two toner images by the image detecting means, respectively. In an image forming apparatus including a control unit that performs image forming condition correction processing for correcting
Using the image detecting means capable of detecting the image density of the toner image,
In the image forming condition correction process, as one of the two regions, a toner image is applied to a downstream end region in the transport direction among both end regions in the transport direction on the surface of the latent image carrier. On the other hand, as the other of the two regions, a toner image is formed on a region closer to the center than the upstream end portion in the transport direction as the other end region, and the downstream end region, And the control to correct an image forming condition that can change the image density of the toner image among various image forming conditions based on the result of detecting the image density of the toner image formed in each of the regions near the center. An image forming apparatus comprising a means . The image forming apparatus 請 Motomeko 1,
Based on the timing at which the image detection means detects the toner images formed in the downstream end region and the central region in the image forming condition correction process, the latent image is selected from among the various image forming conditions. An image forming apparatus comprising the control means so as to correct an image forming condition capable of changing a position where a toner image is formed on an image carrier. The image forming apparatus according to claim 1 .
In the image forming condition correction process, gradation pattern images including a plurality of toner images having different image densities are formed in the downstream end region and the central region, respectively, and the downstream end Based on the result of detecting the image density of each toner image in the gradation pattern image formed in the partial area, the developing ability in the downstream end area of the image forming means is grasped, while the area closer to the center The control means is configured to grasp the developing ability in the region near the center of the image forming means based on the result of detecting the image density of each toner image in the gradation pattern image formed in An image forming apparatus. The image forming apparatus according to claim 3 .
Based on the developing ability in the downstream end region of the image forming means and the developing ability of the image forming means in the region closer to the center, in the central region of the image forming means in the developer transport direction. An image forming apparatus characterized in that the control means is configured to ascertain the developing ability of the toner image and to correct an image forming condition capable of changing the image density of the toner image based on the result. The image forming apparatus according to claim 3 or 4 ,
An image forming apparatus, wherein the control means is configured to correct a developing potential as an image forming condition capable of changing an image density of a toner image. The image forming apparatus according to claim 3, 4 or 5 .
As the image forming means, one comprising a combination of the latent image carrier and developing means for forming toner images of different colors from each other,
Transfer means for transferring multi-color images by transferring toner images of different colors formed on these latent image carriers to the surface of the intermediate transfer member,
Further, as the image detection means, each of the latent image carriers is formed in the region near the center, and then transferred to one end side in a direction orthogonal to the surface movement direction on the surface of the intermediate transfer body. First image detecting means for detecting each toner image of the gradation pattern image, and formed on the downstream end region of each of the plurality of latent image carriers, and then orthogonal to the surface movement direction on the surface of the intermediate transfer member An image forming apparatus comprising: a second image detecting unit configured to detect each toner image of the gradation pattern image transferred to the other end side in the direction in which the toner image is transferred. The image forming apparatus according to claim 6 .
As the gradation pattern images to be formed on the plurality of latent image carriers, respectively, the length of the intermediate transfer member surface movement direction is made shorter than the arrangement pitch of the plurality of latent image carriers. An image forming apparatus comprising the control means. The image forming apparatus according to claim 6 or 7 ,
An image forming apparatus using the first image detecting means and the second image detecting means for detecting both the regular reflection light quantity and the diffuse reflection light quantity on the surface of the intermediate transfer member. The image forming apparatus according to claim 1 to 8,
As the image forming condition correction process, based on a result of forming a toner image only in one of the downstream end region and the central region and detecting the toner image by the image detecting unit. A mode for performing processing for correcting the image forming conditions, and a mode for performing processing for correcting the image forming conditions based on the results of forming toner images in both areas and detecting them by the image detecting means. An image forming apparatus characterized in that the control means is configured to select and execute a method according to a predetermined parameter .

Images