JP2007163534A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively suppress the quantity of toner consumed for the formation of a patch image, and also, to highly accurately control image density based on the density detection result of the patch image. <P>SOLUTION: The belt-like patch image Ip1 extending in an oblique direction to the relative moving direction (arrow direction) of the detection spot Sd of a density sensor is formed on the intermediate transfer belt 71, and the density of the patch image is detected by the density sensor. The relative positional deviation of the detection spot Sd to the patch image is estimated based on the mean value of the rise time t1 and fall time t2 of the density detection value, and also, the width of the detection spot Sd is estimated based on a difference between the rise time and the fall time. The width and formation position of the density control patch image are decided based on the estimation results. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method for forming an image while controlling the image density based on the density detection result of a patch image.

  Some image forming apparatuses that use toner to form an image, such as a printer, a copying machine, or a facsimile machine, detect the density of a patch image with a sensor and control the image density based on the detection result. For example, in the image forming apparatus described in Patent Document 1, the density of a patch image formed at a predetermined position on the image carrier is detected by a patch sensor at a plurality of locations, and the operating conditions of the apparatus are optimized based on the result. Yes.

  In this type of apparatus, in order to prevent erroneous detection of the patch image density due to relative positional deviation or distance variation between the patch image and the sensor, the size of the patch image is set to the detection spot (detected region of the sensor). In general, it is a size having a sufficient margin for the size of).

Japanese Patent Laying-Open No. 2003-255628 (paragraph 0031, FIG. 8)

  By providing the margin as described above, the problem of erroneous detection of density due to mismatch between the patch image and the detection spot is avoided. However, in this case, the amount of toner consumed for forming the patch image increases. In particular, in the apparatus configured to improve the detection accuracy by detecting the density at a plurality of locations in the patch image as in the above-described prior art, toner consumption due to the formation of the patch image becomes a problem.

  In other words, while it is desirable to keep the width of the patch image as small as possible in order to reduce the toner consumption, as described above, there is a conflicting demand for increasing the size of the patch image in order to prevent erroneous detection of density. In the prior art, it was difficult to achieve both.

  The present invention has been made in view of the above problems, and is consumed for forming a patch image in an image forming apparatus and an image forming method for forming an image while controlling the image density based on the density detection result of the patch image. It is an object of the present invention to provide a technique capable of effectively suppressing the amount of toner and controlling the image density with high accuracy based on the density detection result of the patch image.

  In order to achieve the above object, an image forming apparatus according to the present invention includes an image forming unit that forms a toner image, and an image carrier that supports the toner image formed by the image forming unit and moves in a predetermined moving direction. A detecting means for detecting a toner density in a detection area on the image carrier, and a control unit formed on the image carrier by the image forming means. And a control unit that executes density control processing for controlling the density of an image formed by the image forming unit based on a detection result of the toner unit as a patch image by the detection unit. The image forming unit forms a predetermined positioning image on the image carrier, and the control unit has a width orthogonal to the moving direction based on a detection result of the positioning unit on the positioning image. A positioning process for determining a relative position between the detection means and the control patch image in the direction is executed.

  In the invention configured as described above, the formation position of the control patch image used for the density control processing is determined based on the detection result of the positioning image by the detection means. In this way, by determining the control patch image formation position based on the actual measurement result, it is not necessary to provide an extra margin for the width of the control patch image, and the toner area can be reduced by minimizing the area of the control patch image. The amount can be suppressed. Further, since a control patch image is formed at a necessary position, the possibility of erroneous detection of density is reduced, and density control can be performed with high accuracy. In addition, by forming an image under such a density-controlled condition, it is possible to stably form an image with good image quality.

  Here, in the positioning process, a formation position in the width direction of the control patch image on the image carrier may be determined. To change the relative position between the control patch image and the detection means, it is only necessary to move either the control patch image or the detection means in the width direction, but it is easier to change the formation position of the control patch image. is there.

  More specifically, for example, the image forming unit forms a belt-like image extending obliquely with respect to the moving direction as the positioning image, and the control unit detects a toner density equal to or higher than a predetermined value by the detection unit. The relative position between the detection means and the control patch image may be determined based on at least one of the time when the detection is started and the time when the detection ends. When an image that extends obliquely is used, the relative positional variation between the detection unit and the image appears as a change in timing at which the image reaches the detection area of the detection unit. Therefore, both the time when the toner density starts to be detected by the detection unit and the time when the detection ends can be used as information for determining the formation position of the control patch image.

  Further, for example, the image forming unit forms the positioning image including a plurality of image pieces having the same image pattern and different positions in the moving direction and the width direction, and the control unit includes: The relative position between the detection unit and the control patch image may be determined based on at least one of a time when the detection unit starts detecting a toner density of a predetermined value or more and a time when the detection ends. In the invention configured as above, some toner density is detected when at least one of the plurality of image pieces is applied to the detection area. Therefore, the positional relationship in the width direction between the image and the detection means can be estimated by checking at which timing the toner density starts to be detected (or when the detection ends).

  Further, for example, the positioning image is polygonal, and one of the sides of the polygon that first reaches the detection area by moving the image carrier is inclined with respect to the width direction. The control unit may determine a relative position between the detection unit and the control patch image based on a time when the detection unit starts detecting a toner density of a predetermined value or more. In the invention configured as described above, since the timing at which the toner density starts to be detected changes depending on the positional relationship between the image and the detection unit, the positional relationship between the image and the detection unit in the width direction can be estimated from the timing. .

  In addition, when the image forming unit has a plurality of developing units each storing toner, the positioning process is performed using only one of the plurality of developing units. It may be. This is because the relative positional relationship between the control patch image and the detection means is the same regardless of which developing device is used.

  In the case where the image forming unit includes a plurality of developing units that store toners of different colors, the positioning process includes a developing unit that stores toner of a specific color among the plurality of developing units. May be executed using only Here, the “specific color” is not limited to one color. For example, in a device incorporating toner of N colors (N is a natural number of 2 or more), a toner color of (N−1) or less can be a specific color. In an apparatus configured to detect the density of each color toner by the same detection means, the above-described positioning process may be performed with only one of the toner colors as a specific color. Further, for example, in an apparatus configured to perform density detection using a detection unit that is different between a black color and another color, the black color and the other color may be set as a specific color.

  The image forming apparatus configured as described above further includes an adjusting unit that adjusts the width of the control patch image in the width direction based on a detection result of the positioning unit for the positioning image. You may do it. By doing so, both the width and the formation position of the control patch image are optimized, so that it is possible to further enhance the effect of the present invention of performing density control with high accuracy while suppressing toner consumption. .

  In the image forming method according to the present invention, a predetermined positioning image is formed on the image carrier by the image forming means, the density is formed by the detecting means, and the image is formed on the image carrier based on the detection result. A positioning step for determining the position of the control patch image to be formed, a control patch image is formed on the image carrier at the position determined in the positioning step, and the density is formed by the detection means, and the detection result A density control step for controlling the density of the image by adjusting the operating conditions of the image forming means based on the image forming step, and an image forming step for forming an image by the image forming means under the operating conditions adjusted in the density control step It is characterized by comprising.

  In the invention configured as described above, similarly to the above-described apparatus, it is possible to form a control patch image without providing an extra margin, so that it is possible to reduce toner consumption. In addition, it is possible to prevent concentration detection and to perform concentration control with high accuracy. Furthermore, by forming an image under the conditions in which density is controlled in this way, it is possible to stably form an image with good image quality.

  FIG. 1 is a view showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus 1 forms a full color image by superposing four color toners (developers) of yellow (Y), cyan (C), magenta (M), and black (K), or black (K) toner. This is an image forming apparatus that forms a monochrome image using only the image forming apparatus. In the image forming apparatus 1, when an image signal is given to the main controller 11 from an external device such as a host computer, the engine controller 10 controls each part of the engine unit EG in accordance with a command from the main controller 11 to obtain a predetermined image. The forming operation is executed, and an image corresponding to the image signal is formed on the sheet S.

  In the engine unit EG, the photosensitive member 22 is provided to be rotatable in the arrow direction D1 in FIG. A charging unit 23, a rotary developing unit 4 and a cleaning unit 25 are arranged around the photosensitive member 22 along the rotation direction D1. The charging unit 23 is applied with a predetermined charging bias, and uniformly charges the outer peripheral surface of the photoconductor 22 to a predetermined surface potential. The cleaning unit 25 removes the toner remaining on the surface of the photosensitive member 22 after the primary transfer, and collects it in a waste toner tank provided inside. The photosensitive member 22, the charging unit 23, and the cleaning unit 25 integrally constitute the photosensitive member cartridge 2, and this photosensitive member cartridge 2 is detachably attached to the main body of the apparatus 1 as a whole.

  Then, the light beam L is irradiated from the exposure unit 6 toward the outer peripheral surface of the photosensitive member 22 charged by the charging unit 23. The exposure unit 6 exposes the light beam L onto the photosensitive member 22 in accordance with an image signal given from an external device, and forms an electrostatic latent image corresponding to the image signal.

  The electrostatic latent image thus formed is developed with toner by the developing unit 4. That is, in this embodiment, the developing unit 4 is configured as a support frame 40 that is rotatably provided about a rotation axis center orthogonal to the paper surface of FIG. A yellow developing device 4Y, a cyan developing device 4C, a magenta developing device 4M, and a black developing device 4K are provided. The developing unit 4 is controlled by the engine controller 10. Based on the control command from the engine controller 10, the developing unit 4 is driven to rotate, and the developing units 4Y, 4C, 4M, and 4K are selectively brought into contact with the photoreceptor 22 or have a predetermined gap. When positioned at a predetermined developing position facing each other, the photosensitive member 22 is provided from the metal developing roller 44 which is provided in the developing unit and carries charged toner of a selected color and to which a predetermined developing bias is applied. Toner is applied to the surface. As a result, the electrostatic latent image on the photosensitive member 22 is visualized with the selected toner color.

  Each of the developing devices 4Y, 4C, 4M, and 4K is provided with non-volatile memories 91 to 94 for storing information related to the developing devices. One of the connectors 49Y, 49C, 49M, and 49K provided in each developing device is selected as necessary, and the connector 109 provided on the main body side is connected to each other, and the CPU 101 of the engine controller 10 and the memory Communication is performed with 91-94. In this way, information about each developing device is transmitted to the CPU 101, and information in each of the memories 91 to 94 is updated and stored. Note that the communication between the CPU 101 and each of the memories 91 to 94 is not limited to that performed by mechanical contact using a connector as described above, and may be non-contact communication means such as wireless communication.

  The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. The transfer unit 7 includes an intermediate transfer belt 71 stretched between a plurality of rollers 72 to 75, and a drive unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction D2 by rotationally driving the roller 73. It has. When a color image is transferred to the sheet S, each color toner image formed on the photosensitive member 22 is superimposed on the intermediate transfer belt 71 to form a color image and taken out from the cassette 8 one by one. The color image is secondarily transferred onto the sheet S conveyed to the secondary transfer region TR2 along the conveyance path F.

  At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet S, the timing of feeding the sheet S to the secondary transfer region TR2 is managed. Specifically, a gate roller 81 is provided on the transport path F on the front side of the secondary transfer region TR2, and the gate roller 81 rotates in accordance with the timing of the circumferential movement of the intermediate transfer belt 71. S is sent to the secondary transfer region TR2 at a predetermined timing.

  Further, the sheet S on which the color image is thus formed is conveyed to the discharge tray portion 89 provided on the upper surface portion of the apparatus main body via the fixing unit 9, the pre-discharge roller 82 and the discharge roller 83. Further, when images are formed on both sides of the sheet S, when the rear end portion of the sheet S on which the image is formed on one side as described above is conveyed to the reversal position PR behind the pre-discharge roller 82. The rotation direction of the discharge roller 83 is reversed, whereby the sheet S is conveyed in the direction of the arrow D3 along the reverse conveyance path FR. Then, the sheet is again placed on the transport path F before the gate roller 81. At this time, the surface of the sheet S to which the image is transferred by contacting the intermediate transfer belt 71 in the secondary transfer region TR2 is first transferred. It is the opposite surface. In this way, images can be formed on both sides of the sheet S.

  Further, a density sensor 60 and a cleaner 76 are provided in the vicinity of the roller 75. The density sensor 60 optically detects the amount of toner constituting the toner image formed on the intermediate transfer belt 71 as necessary. That is, the density sensor 60 irradiates light toward the toner image, receives reflected light from the toner image, and outputs a signal corresponding to the reflected light amount. The cleaner 76 is configured to be able to come into contact with and separate from the intermediate transfer belt 71, and scrapes the residual toner on the belt 71 by contacting the intermediate transfer belt 71 as necessary.

  In addition, the apparatus 1 includes a display unit 12 controlled by the CPU 111 of the main controller 11 as shown in FIG. The display unit 12 is constituted by, for example, a liquid crystal display, and in accordance with a control command from the CPU 111, the operation guidance to the user, the progress of the image forming operation, the occurrence of an abnormality in the apparatus, the replacement timing of any unit, etc. A predetermined message for notification is displayed.

  In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112. Reference numeral 106 is a ROM for storing a calculation program executed by the CPU 101, control data for controlling the engine unit EG, and the like. Reference numeral 107 is a RAM for temporarily storing calculation results in the CPU 101 and other data. is there.

  FIG. 3 is a diagram showing the configuration of the density sensor. The density sensor 60 is disposed opposite to the surface of the intermediate transfer belt 71 and includes a light emitting element 601 made of, for example, a light emitting diode that emits light with a predetermined light amount. Irradiation light from the light emitting element 601 passes through the polarization beam splitter 603 to become a polarization beam Lp having only a predetermined polarization component, and is applied to the patch image Icp formed on the surface of the intermediate transfer belt 71. The light reflected from the patch image Icp is decomposed by the polarization beam splitter 671 into a p-wave component having the same polarization plane as the incident light and an s-wave component having a polarization plane orthogonal to the incident light, and receiving the p-wave component. The respective polarization components are received by the element 672p and the light receiving element 672s that receives the s-wave component. The light receiving elements 672p and 672s each output a signal corresponding to the amount of received light.

  The density of the patch image formed with the black toner is obtained based on the light amount of the p-wave component received by the light receiving element 672p in the reflected light from the patch image. Further, the density of the patch image formed with other toner colors (yellow, magenta, cyan) is the amount of the p-wave component received by the light receiving element 672p and the amount of the s-wave component received by the light receiving element 672s. Determined based on both values.

  In the image forming apparatus configured as described above, the density of the patch image Icp formed under a predetermined condition is detected by the density sensor 60, and the image forming operation is executed based on the density detection result. Operating conditions such as development bias and exposure power are determined. Therefore, in order to optimize the operating conditions of the apparatus and form an image with a predetermined image quality, it is necessary that the density of the formed patch image Icp be correctly detected by the density sensor 60.

  FIG. 4 is a diagram showing the relationship between the detection spot size of the density sensor and the patch image. The density sensor 60 is provided so as to anticipate a predetermined area (detection spot) on the intermediate transfer belt 71. That is, it is provided so as to receive light emitted from the detection spot. This detection spot moves in the direction indicated by the arrow in FIG. 4 on the intermediate transfer belt 71 in accordance with the relative movement between the density sensor 60 and the intermediate transfer belt 71. As shown in FIG. 4, the density sensor 60 can correctly detect the density of the patch image Ipa formed with an appropriate size and position with respect to the detection spot Sd1.

  However, due to variations in the attachment positions of the intermediate transfer belt 71 and the density sensor 60, the relative positions of both in the width direction (vertical direction in FIG. 4) perpendicular to the moving direction of the intermediate transfer belt 71 vary. As a result, the relative position between the patch image and the detection spot Sd1 may be shifted in the width direction, for example, as indicated by the symbol Ipb in FIG. If such a shift occurs, the density of the patch image Ipb cannot be detected correctly, and as a result, the operating conditions of the apparatus cannot be optimized. In addition, the size of the detection spot varies mainly due to variations in the distance between the density sensor 60 and the intermediate transfer belt 71. If the size of the detection spot Sd2 is larger than the size of the patch image Ipc, the patch image density cannot be detected correctly.

  In order to avoid such a problem, in the conventional image forming apparatus, the width Wp of the patch image is set in consideration of variations in the position and size of the detection spot. That is, the width Wp of the patch image is set so as to be larger than the width of the designed detection spot width plus a tolerance taking into account variations in allowable density sensor dimensions, mounting positions, and distances as margins. It was. As a result, the detection spot is prevented from being deviated from the patch image, but as a result, the area of the patch image is increased and excessive toner is consumed.

  Therefore, in the density control process of the image forming apparatus, the width and the formation position of the patch image are optimized prior to adjusting the operating conditions of the apparatus based on the density detection result of the patch image. By doing so, in this image forming apparatus, the area of the patch image is minimized, and consumption of excess toner is prevented.

  FIG. 5 is a flowchart showing the density control process. This density control process is executed by the engine controller 10 at a predetermined timing, such as when the number of images formed reaches a certain number immediately after the apparatus is turned on or after returning from sleep mode. Since the density sensor 60 and the intermediate transfer belt 71 constitute an integral transfer unit 7, the relative position between the density sensor 60 and the intermediate transfer belt 71 fluctuates because the transfer unit 7 is different from that in the apparatus. When is attached. Therefore, in the density control processing of this apparatus, it is determined whether or not the transfer unit 7 has been replaced (step S101). If the unit has just been replaced, processing for determining the width and forming position of the patch image ( Steps S102 to S105) are performed.

  In this process, first, one developing device, for example, the black developing device 4K is moved to the developing position (step S102). This processing is performed using only one developing device. Since the relative position between the density sensor 60 and the intermediate transfer belt 71 is the same regardless of which developing device is used as long as the same transfer unit is used, the width of the patch image is typically determined by using one developing device. If the formation position is determined, the result can be used for other developing units. Subsequently, for example, a width / positioning patch image as shown in FIG. 6 is formed using the developing device (step S103), and the density is detected by the density sensor 60 (step S104).

  FIG. 6 is a diagram showing a first example of a width / positioning patch image. This width / positioning patch image Ip1 is a belt-like image having a width smaller than the diameter of the detection spot Sd and extending obliquely with respect to the moving direction of the detection spot Sd (the arrow direction in FIG. 6). When the toner density is detected while moving the density sensor 60 relative to the intermediate transfer belt 71 in the direction of the arrow, as shown in FIG. 6, the density detection value is detected at time t1 when a part of the detection spot Sd is applied to the patch image Ip1. Rises and returns to zero again at time t2 when the detection spot Sd leaves the patch image. Note that the “density detection value” here is not a raw output value of the density sensor 60 but a value obtained by converting the output value (for example, corresponding to the p-wave component) into a toner density. Therefore, in this example, the density detection value is zero if no toner adheres to the detection spot, and the density detection value increases as the toner adhesion amount in the detection spot increases.

  At this time, if the position of the detection spot Sd with respect to the intermediate transfer belt 71 is shifted in the width direction, that is, upward or downward in FIG. 6, the output waveform of the density sensor 60 fluctuates back and forth on the time axis. For example, when the detection spot Sd is shifted upward in FIG. 6, toner is detected at an earlier timing, so that the sensor output rises earlier than the time t1. Further, when the size of the detection spot Sd is increased, the toner is detected over a longer time, so that the width of the sensor output waveform becomes wider. Thus, by monitoring the output of the density sensor 60, the relative position and size of the detection spot Sd with respect to the intermediate transfer belt 71 can be estimated.

  Therefore, in this apparatus, the formation position and width of the patch image for operating condition control described later on the intermediate transfer belt 71 are determined so as to match the position and size of the detection spot Sd thus estimated (step). S105). More specifically, as follows. The formation position of the patch image is determined based on the average value ((t1 + t2) / 2) of the rising time t1 and the falling time t2 of the sensor output waveform. That is, when the average value is smaller than the reference time determined corresponding to the rotation of the intermediate transfer belt 71, that is, when the waveform is shifted forward on the time axis, the detected spot position is shown in FIG. Since it is considered that the position is shifted upward, the patch image formation position is determined above a predetermined reference position. Conversely, when the average value is later than the reference time, the patch image formation position is set below the reference position.

  Further, for example, the width of the sensor output waveform represented by (t2-t1) corresponds to the detected spot size, so that the width of the patch image is increased as the width is increased. For example, the detected spot size is obtained from the width (t2−t1) of the sensor output waveform and the moving speed of the intermediate transfer belt 71, and a value obtained by adding a slight margin to the size can be used as the width of the patch image.

  Note that the width and formation position of the control patch image obtained as described above do not need to be changed unless the transfer unit 7 is replaced. Accordingly, in the density control process performed at a timing other than immediately after the transfer unit 7 is replaced, a control patch image is formed in the already obtained width and formation position, thereby performing the width / positioning process (step S102 to S105) can be omitted. Thereby, wasteful toner consumption can be further suppressed.

  When the patch image formation position and width are thus determined, the operating conditions of the apparatus are subsequently optimized. In this apparatus, the image density is controlled to a predetermined target density by optimizing the developing bias and the exposure power. More specifically, a solid patch image is sequentially formed with each bias value while changing and setting the development bias in multiple stages, and an optimum development bias for setting the solid image to a predetermined target density is calculated based on the density detection result. (Step S106). Subsequently, a halftone patch image is formed while changing and setting the exposure power in multiple stages, and an optimum exposure power for setting the halftone image to a predetermined target density is calculated based on the density detection result (step S107). ). There are many known techniques for optimizing the developing bias and exposure power based on the patch image density, and since these techniques can be applied to this apparatus, detailed description thereof is omitted here.

  However, in this apparatus, all patch images (control patch images) are formed at the previously determined formation position and width. For this reason, in this apparatus, the detection error due to the positional deviation of the detection spot relative to the intermediate transfer belt 71 and the size variation does not occur, and the optimum operating condition of the apparatus can be obtained with high accuracy. In addition, since the margin provided in the patch image width can be minimized, it is possible to reduce the area of the patch image and effectively suppress wasteful toner consumption.

  FIG. 7 is a diagram showing a second example of the width / positioning patch image. In the width / positioning patch image Ip2 shown in FIG. 7, one side that first reaches the detection spot Sd among the sides that form the peripheral edge thereof is oblique with respect to the moving direction of the detection spot Sd (the arrow direction in FIG. 7). It is configured to intersect. In this case, a part of the detection spot Sd gradually increases after the sensor output rises at time t3 applied to the patch image Ip2, but when the entire detection spot Sd is applied to the patch image Ip2, the density detection value is saturated (time t4). At time t5 when the image leaves the image, the output sharply decreases. By using such an image, the width and the formation position of the control patch image can be determined. That is, the relative position of the detection spot Sd with respect to the intermediate transfer belt 71 can be estimated by comparing the time t3, t4 or an average value thereof with the reference time, and the control patch image formation position can be determined from the result. . Further, since the width of the detection spot Sd can be estimated from the difference between the time t3 and the time t4, the width of the control patch image can be determined from the result. Note that one side of the patch image on the rear end side may be oblique to the moving direction of the detection spot Sd.

  FIG. 8 is a diagram showing a third example of the width / positioning patch image. FIG. 9 is a diagram showing a fourth example of the width / positioning patch image. Of these, the width / positioning patch image Ip3 shown in FIG. 8 is a step-type image in which the width of the image gradually increases along the moving direction of the detection spot Sd. Further, the width / positioning patch image Ip4 shown in FIG. 9 is composed of a plurality of image pieces that are slightly different in position in the moving direction of the detection spot Sd and in the width direction perpendicular thereto. By using these pattern images Ip3 or Ip4, the formation position and width of the control patch image can be appropriately determined as in the above example.

  As described above, in the image forming apparatus of this embodiment, the width and the formation position of the control patch image are determined prior to optimizing the operation conditions of the apparatus based on the density detection result of the control patch image. Execute the process. Therefore, in this apparatus, the width of the control patch image can be minimized, and the amount of toner consumed for forming the control patch image can be reduced. In addition, the density of the control patch image can be detected correctly regardless of variations in the mounting position of the density sensor 60 and the detection spot size, so that density control can be performed with high accuracy. Furthermore, the effect of reducing the device cost can be obtained by relaxing the demands on the size and mounting accuracy of the density sensor 60.

  Then, by forming an image under conditions where the density is appropriately controlled in this way, this image forming apparatus can stably form an image with good image quality.

  As described above, in this embodiment, the engine unit EG functions as the “image forming unit” of the present invention, and the intermediate transfer belt 71 functions as the “image carrier” of the present invention. Further, the density sensor 60 functions as the “detecting means” of the present invention. The engine controller 10, more specifically, the CPU 101 functions as the “control unit” and “adjustment unit” of the present invention. Furthermore, in this embodiment, the width / positioning patch images Ip1, Ip2, etc. correspond to the “positioning image” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the shape of the above-described width / positioning patch image is an example, and is not limited thereto. In the above-described embodiment, processing for determining the width and formation position of the control patch image is performed, and the shape of the width / positioning patch image is determined in accordance with this purpose. However, in the present invention, processing for determining the width of the control patch image is not essential.

  In the embodiment, the width / positioning patch image is formed using only the black developing device 4K. This is because the positional relationship between the density sensor 60 and the intermediate transfer belt 71 is the same regardless of the toner color. From this point of view, the width / positioning patch image may be formed with toner of other colors. Further, the width / positioning patch image may be formed with two colors, black toner and one of the other toner colors. This is because in the density sensor 60 of this embodiment, as described above, the black toner is based on the received light amount of the p-wave component, and the color toner is based on the received light amount of the p-wave component and the s-wave component. This is because the relative positional relationship between the sensor and the patch image may be slightly different between the black toner and the color toner. This is also desirable when using different sensors for black toner and color toner.

  Further, in the above-described embodiment, the formation position of the control patch image Icp is changed in order to adjust the relative positional relationship between the density sensor 60 and the control patch image Icp. The position of the density sensor 60 may be changed and controlled by an actuator.

  In the above embodiment, the density of the image developed on the photosensitive member 22 and transferred onto the intermediate transfer belt 71 is detected by the density sensor 60. Instead of this, the surface of the photosensitive member 22 is detected. It is also possible to detect the image density on the photoconductor 22 by arranging density sensors facing each other.

  In the above-described embodiment, the present invention is applied to a color image forming apparatus including four color toners and having an intermediate transfer belt. However, the present invention is not limited to this. For example, the present invention is not limited to this. The present invention can also be applied to an image forming apparatus that does not include a transfer belt.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. The figure which shows the structure of a density sensor. The figure which shows the relationship between the detection spot size of a density sensor, and a patch image. The flowchart which shows density | concentration control processing. The figure which shows the 1st example of the patch image for width and positioning. The figure which shows the 2nd example of the patch image for width and positioning. The figure which shows the 3rd example of the patch image for width and positioning. The figure which shows the 4th example of the patch image for width and positioning.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine controller (control means, adjustment means) 60 ... Density sensor (detection means) 71 ... Intermediate transfer belt (image carrier), EG ... Engine part (image forming means), Ip1-Ip4 ... For width and positioning Patch image (positioning image)

Claims (9)

An image forming means for forming a toner image;
An image carrier that carries the toner image formed by the image forming means and moves in a predetermined movement direction;
A detecting means arranged so as to face the surface of the image carrier and detecting a toner density in a detection area on the image carrier;
Density control for controlling the density of an image formed by the image forming unit based on a detection result of the detection unit for a toner image as a control patch image formed on the image carrier by the image forming unit. Control means for executing processing,
The image forming unit forms a predetermined positioning image on the image carrier, and based on a detection result of the positioning unit on the positioning image, the control unit is configured in a width direction orthogonal to the moving direction. An image forming apparatus that executes a positioning process for determining a relative position between the detection unit and the control patch image.   The image forming apparatus according to claim 1, wherein in the positioning process, a formation position in the width direction of the control patch image on the image carrier is determined. The image forming means forms a band-like image extending obliquely with respect to the moving direction as the positioning image,
The control means determines a relative position between the detection means and the control patch image based on at least one of a time when the detection means starts detecting a toner density equal to or higher than a predetermined value and a time when the detection ends. The image forming apparatus according to claim 1. The image forming unit forms the positioning image including a plurality of image pieces having the same image pattern and different positions in the moving direction and the width direction;
The control means determines a relative position between the detection means and the control patch image based on at least one of a time when the detection means starts detecting a toner density equal to or higher than a predetermined value and a time when the detection ends. The image forming apparatus according to claim 1. The positioning image is polygonal, and one of the sides of the polygon that first reaches the detection area by the movement of the image carrier is inclined with respect to the width direction.
3. The image according to claim 1, wherein the control unit determines a relative position between the detection unit and the control patch image based on a time when a toner density of a predetermined value or more starts to be detected by the detection unit. Forming equipment. The image forming means has a plurality of developing units each storing toner;
The image forming apparatus according to claim 1, wherein the positioning process is executed using only one of the plurality of developing devices. The image forming means has a plurality of developing units for storing toners of different colors;
The image forming apparatus according to claim 1, wherein the positioning process is executed using only a developing unit that stores toner of a specific color among the plurality of developing units.   The image forming apparatus according to claim 1, further comprising an adjusting unit that adjusts a width of the control patch image in the width direction based on a detection result of the positioning unit with respect to the positioning image. Positioning for forming a predetermined positioning image on the image carrier by the image forming means and forming the density by the detecting means, and determining the position of the control patch image to be formed on the image carrier based on the detection result Process,
A control patch image is formed on the image carrier at the position determined in the positioning step, the density is formed by the detection means, and the operating condition of the image formation means is adjusted based on the detection result. A density control step for controlling the density of the image with,
And an image forming step of forming an image by the image forming means under the operating conditions adjusted in the density control step.

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