JP2005300906A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent the occurrence of ghosts in an image forming apparatus for forming an image, by developing an electrostatic latent image formed on a photoreceptor. <P>SOLUTION: A control part 90 forms a test pattern on a sheet of recording paper 3 by performing image forming operation for transferring a toner image on the recording paper 3, and then at least in an area for a portion worth a single period of a photoreceptor drum 62, forms a non-plotting area, on which the toner image is not formed on the recording paper 3. Then a density detection sensor 71 detects the presence of the toner in the non-plotting area. Further a control part 90 sets an image forming condition in any one of transfer rollers 61, on the basis of a detection result of the density detection sensor 71 so as not to cause ghosts to be generated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that forms an image by developing an electrostatic latent image formed on a photoreceptor.

  Conventionally, an electrostatic latent image is formed on a photosensitive member, and the electrostatic latent image is developed with toner to form a visible image. The visible image (developer image) is transferred onto a sheet to form an image. An image forming apparatus for forming is known.

In particular, this image forming apparatus includes a sensor for detecting a transfer residual toner remaining on the surface of the photosensitive member after the developer image is transferred to the sheet. The sensor detects the transfer residual toner on the surface of the photoconductor, and controls the bias applied to the developing roller (development bias) from which the transfer residual toner is collected by the simultaneous development cleaning system based on the detection result. In this way, by increasing the collection efficiency of the transfer residual toner, the toner is prevented from being transferred (a ghost is generated) to an area where an image should not be formed on the paper (see, for example, Patent Document 1).
JP 2003-233253 A

  However, in the image forming apparatus, since the density of the transfer residual toner is generally low, if the color of the surface of the photoconductor changes due to aging, the density of the surface of the photoconductor may be measured by a sensor. Therefore, there is a possibility that it cannot be accurately detected whether or not there is transfer residual toner. In addition, unnecessary toner density such as residual toner remaining on the photoconductor and the so-called ghost phenomenon in which an image is formed in an area where an image should not be formed on the paper are not necessarily the same. There was also a problem of not.

  Therefore, in view of such problems, in an image forming apparatus that forms an image by developing an electrostatic latent image formed on a photoconductor, unnecessary developer is accurately detected, and ghosting is surely generated. It is an object of the present invention to prevent this from occurring.

  In order to achieve the above object, the invention according to claim 1 is formed on the photoconductor, a charging unit for charging the photoconductor, an exposure unit for forming an electrostatic latent image on the photoconductor. A developing unit that visualizes the electrostatic latent image with a developer to form a developer image; and a transfer unit that transfers the developer image on the photosensitive member to a member to be transferred at a predetermined transfer position. An image forming apparatus comprising: an image forming unit including: an image forming unit configured to transfer a developer image onto the transfer member or a transfer member for transferring the transfer target member using the image formation unit; To form a developer image as a test pattern on the transfer member or the transport member, and then using at least a part of the area where the developer image is formed on the photoreceptor, On transferred member or transport member A non-drawing area based on a detection result by the ghost detection means, a test pattern forming means for forming a non-drawing area where a developer image is not formed, a ghost detection means for detecting the presence or absence of the developer in the non-drawing area. An image forming condition setting unit that sets an image forming condition for at least one of the charging unit, the exposure unit, the developing unit, and the transfer unit so that a visible image is not formed in the region. It is characterized by having prepared.

  That is, the test pattern forming unit forms a test pattern and a non-image area on the transfer member or the conveying member, and the ghost detection unit detects the presence or absence of the developer in the non-image area. Then, based on the detection result, the image forming condition is set by the image forming condition setting means.

  Therefore, according to such an image forming apparatus, it is possible to detect whether or not a ghost is generated in an image actually formed on the transferred member or the conveying member, and thus it is possible to more accurately set the image forming condition. Can be set.

Note that the member to be transferred in the present invention corresponds to a recording medium such as a recording sheet or an OHP sheet, and an intermediate transfer medium such as an intermediate transfer belt or an intermediate transfer drum.
Further, when the photoconductor has an endless structure having a predetermined circumference, the presence or absence of the developer may be detected in a non-drawing area formed when the photoconductor is rotated two or more times. As described in Item 2, it is preferable to detect the presence or absence of a developer in a non-drawing region formed when the photosensitive member is rotated by one rotation.

According to such an image forming apparatus, more developer can be detected in the non-drawing area, so that the measurement accuracy of the developer can be improved.
Furthermore, the test pattern forming means may form any test pattern, but it is desirable to form a plurality of test patterns periodically as described in claim 3. In particular, in this case, the image forming condition setting means detects the developer on the member to be transferred or the conveying member when the developer is detected at a cycle that coincides with the test pattern formation cycle, as detected by the ghost detector. It is preferable that the image forming conditions are set assuming that there is an image.

  According to such an image forming apparatus, it is possible to determine that a ghost is generated when the developer is detected in the non-image area at the same cycle as the cycle of the test pattern. It is possible to easily and accurately detect the occurrence of a ghost by clearly distinguishing it from dirt or the like of a member or a conveying member.

  By the way, on the surface of the photoreceptor of the image forming apparatus according to any one of claims 1 to 3, the transfer unit applies a transfer bias to the photoreceptor at the transfer position, whereby a developer image is obtained. In the case where the image is transferred onto the transfer member or the conveyance member, the test pattern forming means has a length in a direction parallel to the relative movement direction in the photosensitive position at the transfer position. It is preferable to form a test pattern larger than the length in the same direction of the contact portion between the body and the member to be transferred or the conveying member.

  That is, when the test pattern as described in the present invention is formed, a large amount of developer is attached to the transfer nip portion where the photoconductor and the transfer target member or the transport member are in contact with each other. At this time, for example, when a positively chargeable developer is used and the transfer bias is controlled at a constant current, the transfer bias has a potential applied to the transfer means in order to secure a constant current. Controlled to go down. For this reason, the potential difference between the potential of the portion where the developer adheres on the surface of the photoreceptor and the potential of the transfer member or the transport member becomes large.

  Therefore, according to such an image forming apparatus, when a positively chargeable developer is used, the upper limit of the transfer bias to be applied between the transfer unit and the photosensitive member can be grasped. Even when a negatively chargeable developer is used, the polarity is opposite to that described above, but the upper limit of the transfer bias to be applied to the photoreceptor can be grasped.

  In particular, in the image forming apparatus according to claim 4, the test pattern forming unit includes a developer whose length in a direction perpendicular to the relative movement direction can be formed on the transfer member as described in claim 5. It is preferable to form a test pattern having a size that occupies almost the entire area of the maximum width of the image.

According to such an image forming apparatus, the upper limit of the transfer bias can be grasped more strictly.
Note that “substantially the entire area” in the present invention only needs to occupy an area of 80% or more of the entire area because most of the maximum width capable of forming a developer image is exposed. Shall.

  Further, in the image forming apparatus according to claim 4 or 5, the image forming condition setting unit includes a developer in the non-drawing area based on the detection result by the ghost detecting unit. When it is determined that there is a transfer bias, it is preferable to control so that the transfer bias applied to the photosensitive member at the transfer position is reduced.

According to such an image forming apparatus, it is possible to set a transfer bias so that a developer image is not formed in a non-image area.
Further, in the image forming apparatus according to any one of claims 1 to 3, the test pattern forming unit has a length in a direction parallel to the relative movement direction at the transfer position as described in claim 7. It may be configured to form a plurality of test patterns that are shorter than the length in the same direction of the contact portion between the photoconductor and the member to be transferred or the transport member, and are arranged substantially in parallel.

  That is, when the test pattern as described in the present invention is formed, the developer is only slightly attached to the transfer nip portion. At this time, for example, when a positively chargeable developer is used and the transfer bias is controlled at a constant current, the potential applied to the transfer unit is controlled to increase. For this reason, the potential difference between the portion where the developer adheres on the surface of the photosensitive member and the potential of the transfer member or the transport member is reduced.

  Therefore, according to such an image forming apparatus, the lower limit of the transfer bias to be applied between the transfer unit and the photosensitive member can be grasped. Even when a negatively charged developer is used, the polarity is opposite to that described above, but the lower limit of the transfer bias to be applied to the photosensitive member can be grasped.

  In particular, in the image forming apparatus according to claim 7, the test pattern forming means has a length in a direction orthogonal to the relative movement direction as defined in claim 8, wherein the length of the photoconductor and the member to be transferred is Alternatively, it is preferable to form a test pattern having a size that occupies a part of the length in the same direction of the contact portion with the conveying member.

According to such an image forming apparatus, the lower limit of the transfer bias can be grasped more strictly.
Furthermore, in the image forming apparatus according to claim 7 or 8, the image forming condition setting unit includes a developer in the non-drawing area based on the detection result by the ghost detecting unit. When it is determined that there is, it is preferable to control so that the transfer bias applied to the photosensitive member at the transfer position is increased.

According to such an image forming apparatus, it is possible to set an appropriate transfer bias so that the developer is not detected in the non-drawing area.
Further, in the image forming apparatus according to claim 9, the image forming condition setting means controls the transfer bias as described in claim 10, and then uses the test pattern forming means again with the controlled transfer bias. When the image forming operation is repeatedly executed and it is determined that there is no developer in the non-drawing area, it is preferable to set the transfer bias at this time to the transfer bias value when the image forming unit performs image formation.

According to such an image forming apparatus, a more appropriate transfer bias can be set without unnecessarily increasing the transfer bias.
Furthermore, in the image forming apparatus according to claim 7 or 8, the image forming condition setting means includes a developer in the non-drawing area based on the detection result by the ghost detecting means as described in claim 11. If it is determined that there is no transfer bias, it is desirable that the transfer bias applied to the photosensitive member at the transfer position is controlled to be small.

According to such an image forming apparatus, an appropriate transfer bias can be set without increasing the transfer bias unnecessarily.
Further, in the image forming apparatus according to claim 11, the image forming condition setting means controls the transfer bias as described in claim 12 and then again uses the test pattern forming means with the controlled transfer bias. When the image forming operation is repeatedly executed and it is determined that there is a developer in the non-drawing area, the transfer bias at the time when it is determined that there is no developer at the end is set to the transfer bias value when the image forming unit performs image formation. It is preferable to set.

According to such an image forming apparatus, a more appropriate transfer bias can be set without unnecessarily increasing the transfer bias.
The image forming apparatus according to any one of claims 1 to 12, wherein the image forming means includes at least a plurality of developing means, each developer means forms a developer image, and the test pattern forming means includes an image When the image forming operation by each developing unit is set to be performed sequentially using the forming unit, the ghost detecting unit detects the presence or absence of the developer in each non-drawing area as described in claim 13. The image forming condition setting unit includes a charging unit, an exposure unit, a developing unit, and a transfer unit that constitute the image forming unit that performs the image forming operation in the non-drawing area based on the detection result by the ghost detecting unit. It is desirable that the image forming condition is set for at least one of them.

According to such an image forming apparatus, for example, even if a plurality of developing units are provided like a color printer, it is possible to appropriately prevent the occurrence of ghosts.
In the image forming apparatus according to claim 13, the test pattern forming unit may create any test pattern as a test pattern formed by each developing unit. 14, it is preferable to form a test pattern in which at least a part is formed by overlapping a plurality of developers using an image forming unit.

  That is, when a test pattern as in the present invention is formed, when another developer image is formed on the transfer medium at the position where the developer image is formed, the developer already on the transfer member is used. Due to the influence of the applied electric charge, the developer is hardly transferred. Further, a ghost that occurs when the transfer bias is too large (too strong) is likely to occur.

Therefore, according to such an image forming apparatus, it is possible to set a transfer bias that does not generate ghost even under more severe conditions.
Further, in the image forming apparatus according to claim 14, the test pattern forming means is developed by a developing means using the image forming means as described in claim 15, and the photosensitive member and the transfer member or the transporting member are conveyed. A plurality of test patterns that are arranged substantially in parallel with each other at the contact portion with the member, and a test pattern that is developed by different developing means before drawing the test pattern and has a size that fills the plurality of test patterns are formed. It is preferable.

According to such an image forming apparatus, conditions for forming a test pattern can be made stricter.
Further, in the image forming apparatus according to any one of claims 13 to 15, when the image forming unit is configured to form an image by sequentially superimposing developer images by the developing units, As described in Item 16, the test pattern forming unit selects a developing unit to be used first when forming an image from among the developing units to be set as image forming conditions, and the developing unit to be used first. After the detection by the ghost detecting means is completed, the next developing means to be used is sequentially selected, and the image forming operation using the developing means to be used next is performed. It is preferable that the image forming operation using each developing unit is configured to detect the presence or absence of developer in each non-drawing area.

  According to such an image forming apparatus, it is possible to perform image formation in the same order as the actual image forming operation. Therefore, transfer is performed in consideration of the effect when the developer images actually formed by different developing units are superimposed. A bias can be set.

  Note that the test pattern forming means preferably detects all the developing means used for image formation, and the ghost detection means detects the presence or absence of the developer. For example, in the case where there is little occurrence of ghost in the developing unit that is used at the time of image formation, the developing unit that is used first may be excluded from the target. When a ghost is generated in the developing unit used later in image formation, the image forming conditions are reset only for the developing unit used thereafter including the developing unit. It may be.

  Furthermore, in the image forming apparatus according to claim 16, when setting the transfer bias for each transfer unit, the ghost detection unit transfers the developer image after the transfer unit (positioned on the downstream side). It is desirable to detect the developer in a state where the influence of the means is excluded.

  Specifically, for example, when the image forming condition setting unit detects the presence or absence of the developer image in the non-drawing area by the ghost detecting unit, the test pattern forming unit forms a test pattern as described in claim 17. It is conceivable that the transfer bias applied between the photoconductor located downstream of the photoconductor to be transferred and the transfer means is made smaller than the originally set bias.

  Alternatively, as described in claim 18, when the presence or absence of the developer in the non-image area is detected by the ghost detection unit, the photoconductor located downstream from the photoconductor on which the test pattern is formed by the test pattern formation unit. It is also conceivable to include a separating means for separating the transfer target member or the transport member.

  Therefore, according to such an image forming apparatus, when the ghost detection unit detects the developer, only the influence of the transfer unit positioned on the upstream side is considered, and the influence of the transfer unit positioned on the downstream side is excluded. Therefore, it is possible to set an appropriate transfer bias for each transfer unit. In particular, according to the image forming apparatus of the eighteenth aspect, since the developer attached to the non-image area can be prevented from being contacted before being detected by the ghost detection means, An appropriate transfer bias can be set.

  Furthermore, in the image forming apparatus according to any one of claims 1 to 18, as described in claim 19, the ghost detection means emits light irradiated from the light emitting unit onto the transfer member or the transport member. It is preferable to include an optical sensor that detects the presence or absence of the developer by irradiating and receiving the reflected light by the light receiving unit.

  According to such an image forming apparatus, the optical sensor constituting the ghost detection means does not contact the sensor and the member to be transferred or the transport member, so that the developer is not damaged without damaging the member to be transferred or the transport member. Detection can be performed.

  Further, in the image forming apparatus according to claim 19, the optical sensor has a function of a registration sensor for detecting a positional deviation of the developer image formed by each developing device as described in claim 20. Is desirable.

According to such an image forming apparatus, it is not necessary to further provide a registration sensor, so that cost can be reduced.
Furthermore, in the image forming apparatus according to claim 19 or 20, the optical sensor includes a test pattern formed to correct the density of an image formed by the image forming unit as described in claim 21. It is desirable to have the function of a concentration detection sensor for measuring the concentration.

According to such an image forming apparatus, it is not necessary to further provide a density detection sensor, so that cost can be reduced.
Further, in the image forming apparatus according to any one of claims 1 to 21, when the test pattern forming unit performs a process of correcting the density of an image formed by the image forming unit as described in claim 22. It is desirable to perform an image forming operation for ghost detection.

That is, when density correction is performed, the transfer bias conditions and the like are often changed, so that the test pattern is formed at this time.
Therefore, according to such an image forming apparatus, since the transfer bias is adjusted when density correction is performed, an appropriate transfer bias can be efficiently set.

  According to a twenty-third aspect of the present invention, there is provided a charging means for charging an endless photoconductor having a predetermined circumference, an exposure means for forming an electrostatic latent image on the photoconductor, and formed on the photoconductor. The developer image is transferred to a transfer member that moves relative to the circumferential direction of the photosensitive member at a predetermined transfer position with a developing unit that visualizes the electrostatic latent image thus formed to form a developer image. An image forming means having a transfer means, a test pattern forming means for forming a test pattern as the developer on the photosensitive member using the image forming means, and a proximity of the photosensitive member. And a developer presence / absence detecting means for detecting the presence / absence of the developer on the photoreceptor after the developer image on the photoreceptor is transferred using the image forming means, and a detection result by the developer presence / absence detecting means. And the developer image is detected. An image forming apparatus including at least an image forming condition setting unit for setting an image forming condition for any one of the charging unit, the exposure unit, the developing unit, and the transfer unit, The test pattern forming unit periodically forms a plurality of test patterns each arranged in the relative movement direction, and the image forming condition setting unit detects the test pattern by detecting the developer presence / absence detecting unit. When the developer is detected in a cycle that coincides with the formation cycle, it is considered that the developer is present on the photoconductor.

  That is, the test pattern forming unit periodically forms a plurality of test patterns, each of which is arranged in the relative movement direction, and the image forming condition setting unit detects the test pattern forming cycle based on the detection by the developer presence / absence detecting unit. When the developer is detected at the coincident period, it is considered that the developer is on the photoconductor, and the image forming conditions are set.

  Therefore, according to such an image forming apparatus, it is possible to easily distinguish whether the developer remaining on the photoconductor after transfer is based on the test pattern, clearly distinguishing it from noise, contamination of the photoconductor, and the like. Judgment can be made.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view showing a schematic configuration of a printer 1 to which the present invention is applied.
In FIG. 1, a printer 1 is a so-called horizontal type tandem color laser printer in which four image forming units 20 (image forming means referred to in the present invention) to be described later are arranged in a horizontal direction. A paper feed unit 9 for feeding the recording paper 3, an image forming unit 4 for forming an image on the fed recording paper 3, and the recording paper 3 on which the image is formed are discharged to the main body casing 5. And a controller 90 for controlling the operation of the printer 1.

  The paper feed unit 9 is provided at the bottom of the main casing 5 so as to be detachably attached to the main casing 5 from the front side, and above one end (upper front) of the paper feed tray 12. A sheet feed roller 83 and a position above the sheet feed roller 83 and downstream of the sheet feed roller 83 in the conveyance direction of the recording paper 3 (hereinafter, the conveyance direction downstream side of the recording sheet 3 is referred to as a conveyance direction downstream side). 3 in the conveyance direction may be omitted as upstream in the conveyance direction.).

  The recording paper 3 is stacked in the paper feed tray 12, and the uppermost recording paper 3 is fed toward the transport roller 14 one by one by the rotation of the paper feeding roller 83, The toner is sequentially fed from the conveyance roller 14 to the space between the conveyance belt 68 and each photosensitive drum 62 (transfer position).

  A guide member 15 disposed in the vertical direction is provided between the paper feed roller 83 and the transport roller 14, and the recording paper 3 fed by the paper feed roller 83 is fed by the guide member 15. The paper is sequentially fed between the conveyance belt 68 and the photosensitive drum 62 (transfer position).

  The image forming unit 4 transfers the images formed by the four image forming units 20Y, 20M, 20C, and 20K that form images and the image forming units 20 to the recording paper 3 in the intermediate portion in the main body casing 5. The image forming apparatus includes a transfer unit 17 and a fixing unit 8 that heats and presses an image transferred onto the recording paper 3 and fixes the image on the recording paper 3.

  Each image forming unit 20 includes a photosensitive drum 62, a charger 31 (charging means in the present invention) for charging the photosensitive drum 62 around the photosensitive drum 62, and an electrostatic latent image on the photosensitive drum 62. And a developing cartridge 51 for forming a toner image (developer image) by attaching toner (developer) to the photosensitive drum 62. The

  The charger 31 is, for example, a scorotron charger for positive charging that generates corona discharge from a charging wire made of tungsten or the like and uniformly charges the surface of the photosensitive drum 62 to positive polarity.

The scanner unit 41 includes a laser generator that generates laser light for forming an electrostatic latent image on the surface of the photosensitive drum 62, a lens (none of which are shown), and the like.
In the scanner unit 41, laser light emitted from the laser light emitting unit is scanned and irradiated on the photosensitive drum 62 to form an electrostatic latent image on the surface of the photosensitive drum 62.

The developing cartridge 51 includes a developer hopper 56, a supply roller 32, and a developing roller 52 (developing means referred to in the present invention) in a developing casing 55.
The developer hopper 56 is formed as an internal space of the developing casing 55. The developer hopper 56 accommodates yellow (Y), magenta (M), cyan (C), and black (K) developers for each image forming unit 20.

  That is, the four developing cartridges 51 described above are the developing cartridge 51Y in which the developer hopper 56 contains yellow (Y) developer, and the developing cartridge in which the developer hopper 56 contains magenta (M) developer. 51M, a developer cartridge 51C in which a developer hopper 56 contains cyan (C) developer, and a developer cartridge 51K in which developer (hopper) 56 contains black (K) developer.

  The supply roller 32 is disposed on the developer hopper 56 obliquely rearwardly downward, and a metal roller shaft is covered with a roller portion made of a conductive sponge member. The supply roller 32 is rotatably supported so as to rotate in a direction opposite to the developing roller 52 at a nip portion facing and contacting the developing roller 52.

  The developing roller 52 is rotatably disposed below the supply roller 32 at a position facing and in contact with the supply roller 32. The developing roller 52 is formed by covering a metal roller shaft with a roller portion made of an elastic member such as a conductive rubber material.

  The transfer unit 17 is provided on the opposite side of the developing cartridge 51 in the main body casing 5 so as to face the photosensitive drum 62. The transfer unit 17 includes a transport belt driving roller 63, a transport belt driven roller 64, a transport belt 68 that is an endless belt, and a transfer roller 61 (transfer means in the present invention).

  Further, in the vicinity of the conveyance belt driving roller 63, a density detection sensor 71 (ghost detection means and developer presence / absence detection means in the present invention) for measuring the density of the recording paper 3 conveyed on the conveyance belt 68 is provided. Is provided. The density detection sensor 71 is used not only for measuring the density of the recording paper 3 but also for detecting a positional shift of the toner image formed by each image forming unit 20.

  The conveyance belt driven roller 64 is disposed in front of the photosensitive drum 62 of the image forming unit 20 </ b> Y on the most upstream side with respect to the conveyance direction of the recording paper 3 and on the upper rear side of the paper supply roller 83. Further, the conveyance belt drive roller 63 is disposed behind the photosensitive drum 62 of the black image forming unit 20K on the most downstream side with respect to the conveyance direction of the recording paper 3 and obliquely below and below the fixing unit 8. Has been.

  The conveyor belt 68 is wound between the conveyor belt driving roller 63 and the conveyor belt driven roller 64. The conveyor belt 68 is disposed such that the outer surface around which it is wound is in opposed contact with all the photosensitive drums 62 of each image forming unit 20.

  The conveyance belt driven roller 64 is driven by the driving of the conveyance belt driving roller 63, and the conveyance belt 68 is interposed between the conveyance belt driving roller 63 and the conveyance belt driven roller 64 and the photosensitive drum 62 of each image forming unit 20. And rotates counterclockwise so as to rotate in the same direction as the photosensitive drum 62 on the contact surface facing and facing.

  Further, the transfer roller 61 is disposed inside the wound conveyance belt 68 so as to face the photosensitive drum 62 of each image forming unit 20 with the conveyance belt 68 interposed therebetween. The transfer roller 61 is formed by covering a metal roller shaft with a roller portion made of an elastic member such as a conductive rubber material.

  The transfer roller 61 is provided so as to be able to rotate counterclockwise so as to rotate in the same direction as the circumferential movement direction of the conveyor belt 68 on the contact surface facing the conveyor belt 68. A predetermined voltage is applied from a power source (not shown) in the direction in which the developer image carried on the photosensitive drum 62 is transferred (transferred) to the recording paper 3, and the transfer roller 61, the photosensitive drum 62, and the like are controlled by constant current control. An appropriate transfer bias is applied during this period.

  The fixing unit 8 is disposed behind the image forming unit 20 and the transfer unit 17 and on the downstream side in the transport direction. The fixing unit 8 includes a heating roller 81 and a pressing roller 82. The heating roller 81 is made of a metal base tube having a release layer formed on the surface thereof, and a halogen lamp is provided along the axial direction thereof. Then, the surface of the heating roller 81 is heated to the fixing temperature by the halogen lamp. The pressing roller 82 is disposed so as to press the heating roller 81.

  The paper discharge unit 6 is disposed on the downstream side in the transport direction of the fixing unit 8 in the upper part of the main body casing 5. The paper discharge unit 6 is provided with a pair of paper discharge rollers 11 for discharging the recording paper 3 on which image fixing has been completed to the paper discharge tray 10, and a downstream side of the paper discharge rollers 11. A paper discharge tray 10 for accumulating all the recording sheets 3 that have been completed is provided.

  Next, while describing the electrical configuration of the printer 1 with reference to FIG. 2, a color image is formed on the recording paper 3 in the normal printing (printing) mode by the printer 1 by the cooperative operation of each unit in the apparatus described above. Each process until it will be described. FIG. 2 is a block diagram schematically showing the electrical configuration of the printer 1.

  As shown in FIG. 2, the printer 1 includes a control unit 90 (including a CPU, a ROM, a RAM, and the like) that performs overall control of each unit of the apparatus, and the control unit 90 performs an image forming operation in a normal print mode. And a toner density correction operation in the toner density correction mode.

  In the normal print mode, when receiving the input image data from the outside, the control unit 90 of the printer 1 drives the paper feed mechanism unit 77 by the paper transport processing unit (program). The paper feed roller 83, the developing roller 52, and the transport roller 14 are driven by the paper feed mechanism 77 and start feeding the recording paper 3 stacked on the top of the paper feed tray 12.

  The control unit 90 performs initial setting of each unit to be controlled at the time of image formation by a main control processing unit (program) and inputs a control signal to the main drive unit 79 to prepare for the main drive unit 79. The developing cartridge mechanism 72 is driven by the motor thus driven, and the supply roller 32 and the photosensitive drum 62 are rotated in a certain direction. At this time, the control unit 90 also drives the transfer mechanism driving unit 76 to rotate the transfer roller 61 in synchronization with the photosensitive drum 62. At the same time, the control unit 90 operates the bias applying unit 54 to apply a predetermined potential to the transfer roller 61 so that a predetermined transfer bias is applied to the photosensitive drum 62, and to charge the charger 31. Is given a predetermined charging voltage. At this time, the surface of the photosensitive drum 62 before forming the electrostatic latent image is uniformly charged positively, and a predetermined transfer bias is applied between the transfer roller 61 and the photosensitive drum 62.

  Then, the control unit 90 controls the control signal based on the input image data at a predetermined timing based on the origin position (marker) of the conveyance belt 68 detected by the origin sensor 75 (see FIG. 2) by the latent image formation processing unit (program). Is input to the scanner unit 41, and the scanner unit 41 is driven.

  That is, the printer 1 irradiates the surface of the photosensitive drum 62 after positive charging with laser light from the scanner unit 41 at a predetermined exposure point by such an operation of the control unit 90, thereby Is changed from the state immediately after charging to form an electrostatic latent image on the surface of the photosensitive drum 62 based on the input image data. Further, the printer 1 conveys the electrostatic latent image formed in this way to the developing roller 52 side that is located downstream of the exposure point in the rotation direction of the photosensitive drum 62 by the rotation of the photosensitive drum 62.

  The electrostatic latent image formed on the specific photosensitive drum 62 is brought into contact with the developing roller 52. As a result, the electrostatic latent image is developed with toner supplied from the developing roller 52 in contact with the photosensitive drum 62, and a toner image is formed on the surface of the photosensitive drum 62.

  When the toner image is formed, the printer 1 causes the rotation of the photosensitive drum 62 to transfer the toner image to a transfer point (transfer position: the photosensitive drum 62 and the transfer roller) located downstream from the development point by the developing roller 52. 61 or a contact position with the recording paper 3), and the toner image is transferred to the surface of the recording paper 3 at the transfer point.

  In addition, the control unit 90 performs the series of operations from the electrostatic latent image forming process to the transfer process described above for each color toner, and the formed toner image of each color according to the rotation of the conveyance belt 68. In this way, a multi-color toner image formed by superimposing the respective color toner images is formed on the surface of the recording paper 3.

  As a result, the control unit 90 first develops the yellow electrostatic latent image with yellow toner using the yellow image forming unit 20Y to form a yellow toner image, and further, at the transfer point, the yellow toner image is formed. The toner image is transferred onto the surface of the recording paper 3.

Similarly, the control unit 90 sequentially superimposes color images of magenta (M), cyan (C), and black (K) on the recording paper 3.
In order to superimpose the toner images in this way, the control unit 90 of the printer 1 uses the latent image formation processing unit based on the rotation period of the conveyance belt 68 and the arrangement interval of the image forming units 20. The timing for driving each scanner unit 41 is controlled. Then, the control unit 90 forms an electrostatic latent image on each photosensitive drum 62, forms a toner image of each color, and further transfers the toner image to the recording paper 3 at each color transfer point.

In this way, a color image is formed on the recording paper 3.
When executing the density correction mode, test pattern formation data from the test pattern latent image formation processing unit (program) is used instead of the image data input in the normal print mode described above. A toner image (hereinafter referred to as a test pattern) 73 as a test pattern is formed on the recording paper 3 by the same procedure as in the print mode.

  Then, the control unit 90 reads the density of the test pattern 73 by the density detection sensor 71 shown in FIG. 1 by the toner amount correction processing unit (program). Specifically, the density detection sensor 71 converts the density of the test pattern 73 formed on the recording paper 3 or the recording paper 3 itself into a voltage value and outputs the voltage value. The output from the density detection sensor 71 is a density detection sensor. After AD conversion by the circuit 74, the signal is input to the control unit 90.

  Then, the control unit 90 determines whether or not the toner density of each color is accurately reproduced based on the density of the toner supplied by each developing cartridge 51C, 51M, 51Y, 51K detected by the density detection sensor 71, When it is considered that the toner density of each color is not accurately reproduced, the toner amount attached to the photosensitive drum 62 is corrected based on the toner amount correction processing unit (program). The toner amount correction performed by the control unit 90 is performed by controlling, for example, a developing bias (potential difference between the developing roller 52 and the photosensitive drum 62). At this time, it is set so that the positional deviation of the toner image is also corrected by the detection of the density detection sensor 71.

  Further, after correcting the toner amount, the control unit 90 reads the density of the recording paper 3 using the density detection sensor 71 by a ghost correction processing unit (program). At this time, the density detection sensor 71 on the recording paper 3 is located at a position (non-notified) behind the recording paper 3 in the transport direction by the circumference of the photosensitive drum 62 from the position where the test pattern 73 is formed. Measure the density of the image area. At this time, the control unit 90 performs only the transfer operation of transferring the toner image from the photosensitive drum 62 to the recording paper 3 by the transfer roller 61.

  Note that the image forming unit 4 in the present embodiment is configured such that the toner remaining on the surface of the photosensitive drum 62 after transfer (transfer residual toner) or the toner (transferred back from the recording paper 3 to the photosensitive drum 62 at the time of transfer). A so-called cleaner-less method (development simultaneous cleaning method) in which no cleaning means for removing the reverse transfer toner) is provided, and the transfer drum 17 transfers the toner image onto the recording paper 3 and then the photosensitive drum. The toner adhering to 62 is collected in the developing cartridge 51 and again used for development.

  That is, when the photosensitive drum 62 is further rotated while the toner that cannot be completely transferred in the transfer portion 17 (transfer residual toner) or the reversely transferred toner (reverse transfer toner) is attached to the photosensitive drum 62, the charging is performed. The surface of the photosensitive drum 62 is charged again at the charging position facing the device 31. The toner that has not been exposed by the scanner unit 41 and has adhered to the portion where the charged potential is maintained has a lower potential than the surface of the photosensitive drum 62 when facing the developing roller 52. The toner is attracted to and collected by the developing roller 52, but some toner may pass through without being collected.

At this time, the toner that has not been collected by the developing roller 52 is transferred to the recording paper 3 and becomes a transfer residual ghost.
The reverse transfer toner is used for the second and subsequent magenta (M), cyan (C), and black (K) from the upstream side when the visible image is transferred to the recording paper 3 in the image forming unit 20 of each color. The toner already transferred to the recording paper 3 in each image unit 51 on the upstream side of the image forming unit 20 is transferred to the photosensitive drum 62 of the image forming unit 20, and is generated once. The toner transferred to the recording paper 3 is considered to be generated by charging with a polarity opposite to the original charging polarity, and the mechanism of the generation has not been clarified accurately, but the transfer bias is not The stronger the toner is, the more reverse transfer toner is generated, and the charge amount of the toner already transferred to the recording paper 3 is high (the transfer bias of the image forming unit 20 on the upstream side is strong). A throat charge amount increases), it has been found that generation of reverse transcription toner increases.

Then, the developer reversely transferred to the photosensitive drum 62 may not be collected by the developing roller 52 but may be transferred to the recording paper 3 at the time of transfer after the next rotation of the photosensitive drum 62.
That is, in the above case, the toner image is formed at a position where the toner image should not be originally formed. It should be noted that the toner image formed at a position where it should not be formed is generally referred to as a ghost (if the transfer residual toner is the cause, the transfer residual ghost is the cause, and the reverse transfer toner is the cause. This is called reverse transfer ghost) or ghost image.

  The position where the ghost image is formed is an area (non-image area) that is rearward from the position where the test pattern 73 is formed with respect to the conveyance direction of the recording paper 3 by an integral multiple of the circumferential length of the photosensitive drum 62. . Then, the position where the ghost image with the highest density is formed is considered to be an area located behind the recording sheet 3 in the conveyance direction by the circumference of the photosensitive drum from the position where the test pattern 73 is formed. Therefore, in the printer 1, in the transfer bias setting process (see FIGS. 4 and 5) described later, density measurement for ghost detection is performed in this region.

  By the way, a predetermined potential necessary for transferring the toner to the recording paper 3 is applied to the developing roller 52, the photosensitive drum 62, and the transfer roller 61. For example, the surface of the photosensitive drum 62 is charged to +700 V by the charger 31. A developing bias of +550 V is applied to the developing roller 52, although not shown in FIG. Further, the surface of the photosensitive drum 62 is irradiated with a laser beam, and the potential of the exposed portion is reduced to about + 200V.

It should be noted that a potential at which a preset developing bias is generated between the developing roller 52 and the photosensitive drum 62 is applied to the developing roller 52 by constant voltage control.
On the other hand, the transfer roller 61 is not subjected to constant voltage control but is subjected to constant current control so that the current flowing to the transfer roller 61 is constant. Here, the constant bias voltage is not applied to the transfer bias applied to the transfer roller 61. When the toner image formed on the photosensitive drum 62 is transferred, recording is performed between the photosensitive drum 62 and the transfer roller 61. This is because there is a possibility that the sheet 3 exists and the thickness of the recording sheet 3 is not constant. That is, if the thickness of the recording paper 3 is different, the value of the current flowing from the photosensitive drum 62 to the transfer roller 61 is different, so that the image quality of the transferred toner image changes. Further, when the resistance value of the transfer roller 61, the conveyance belt 68, or the like changes due to environmental changes or durable changes, the transferability (transfer performance) changes accordingly.

  Therefore, in order to prevent the image quality of the transferred toner image from changing even if the thickness of the recording paper 3 changes, the control unit 90 in the printer 1 applies the transfer roller 61 via the bias application unit 54. The transfer bias is controlled by constant current control. The current value for controlling the transfer bias is configured to be capable of being stepwise (for example, five steps in units of 1 μA).

Next, a mechanism for transferring the toner image onto the recording paper 3 will be described with reference to FIG. FIG. 3 is an explanatory diagram showing potentials at various rollers.
The toner attached to the developing roller 52 in this embodiment is a positively charged toner, and therefore has a characteristic of moving from a higher potential to a lower potential. For this reason, as shown in FIG. 3A, when the surface of the photosensitive drum 62 is contacted, the surface of the photosensitive drum 62 is moved to an exposed position. This toner is recorded by the potential difference between the exposed portion (+200 V) of the photosensitive drum 62 and the surface potential of the recording paper 3 when the photosensitive drum 62 rotates and contacts the recording paper 3 that contacts the transfer roller 61. It is transferred to the paper 3.

Note that the potential on the surface of the recording paper 3 varies in conjunction with the variation of the transfer bias.
As described above, the transfer bias is controlled so that the value of the current flowing through the transfer roller 61 is constant. For this reason, the potential of the transfer roller 61 is affected by the average potential of the contact portion of the photosensitive drum 62 with the transfer roller 61 (specifically, the recording paper 3). That is, if the average potential of the contact portion of the photosensitive drum 62 with the transfer roller 61 is low, the potential of the transfer roller 61 is also low. If the average potential of the contact portion of the photosensitive drum 62 with the transfer roller 61 is high, the transfer is performed. The potential of the roller 61 is also increased.

  For example, as shown in FIG. 3A, the potential of the transfer roller 61 is increased when the exposed area on the surface of the photosensitive drum 62 is narrow. In this case, since the potential difference between the exposed portion of the surface of the photosensitive drum 62 and the potential of the transfer roller 61 is small, the toner image formed on the photosensitive drum 62 is hardly transferred to the recording paper 3. Further, when the pattern is a thin line or the like, compared with a wide pattern having the same total area, the portion of the transfer roller 61 facing the exposed portion of the photosensitive drum 62 even if the shaft potential of the transfer roller 61 is the same. Since the surface potential of the film increases, it becomes more difficult to transfer. This also occurs when the transfer bias is controlled at a constant voltage. For this reason, if the test pattern 73 of a thin line is formed, the ghost image is detected, and the current value (constant current) flowing from the photosensitive drum 62 to the transfer roller 61 is set based on the detection result, the toner is surely obtained. A transfer bias (lower limit of transfer bias) at which an image can be transferred can be set.

  On the other hand, the lowering of the potential of the transfer roller 61 corresponds to the case where all the areas are exposed on the surface of the photosensitive drum 62 as shown in FIG. In this case, the potential difference between the exposed portion (+200 V) of the surface of the photosensitive drum 62 and the transfer roller 61 becomes large. For this reason, a test pattern 73 occupying the entire contact portion between the photosensitive drum 62 and the transfer roller 61 is formed, and the ghost image is detected, thereby detecting a ghost that is caused when the transfer bias is too large (too strong). can do.

  Next, processing for setting a transfer current value will be described with reference to FIGS. FIG. 4 is a flowchart showing a transfer bias setting process performed by the control unit 90 using a ghost correction processing unit (program), and FIG. 5 is a flowchart showing a transfer bias optimization process in the transfer bias setting process. In the transfer bias setting process, the processes of S180 and S190 correspond to the image forming condition setting means in the present invention. In addition, the processing of S120, S150, S340, and S390 corresponds to the test pattern forming means in the present invention.

  As shown in FIG. 4, in the transfer bias setting process, first, in S120, a transfer residual ghost is generated in each of the image forming units 20Y, 20M, 20C, and 20K under the currently set transfer bias conditions. Check whether or not. That is, a test pattern for detecting a yellow transfer residual ghost prepared in advance to determine whether or not the transfer bias in the yellow image forming unit 20Y is appropriate, for example, a test pattern shown in FIG. The toner image (developer image) is drawn on the recording paper 3, and a non-drawing area is formed in which nothing is drawn for at least one rotation of the photosensitive drum 62 thereafter. Next, a magenta transfer residual ghost detection test pattern prepared in advance for determining whether or not the transfer bias in the magenta image forming unit 20M is appropriate, for example, a test pattern shown in FIG. A toner image (developer image) is drawn on the recording paper 3, and a non-drawing area where nothing is drawn is formed for at least one rotation of the photosensitive drum 62 thereafter. In the same manner, drawing of a test pattern for detecting a cyan transfer residual ghost shown in FIG. 6C and formation of a non-drawing area, and a test for detecting a transfer residual ghost of a plaque shown in FIG. Pattern drawing and non-drawing area formation are performed.

  In the test patterns for detecting the transfer residual ghost for each color shown in FIGS. 6A to 6D, the transfer bias set in the transfer portion of each image forming unit 20Y, 20M, 20C, 20K is appropriate. Of course, it should be set within the range, but in order to prevent color change and color mixing due to reverse transfer, and also reverse transfer ghost, a smaller (weak) transfer bias within the proper range. Is considered to be set.

  FIG. 6A shows an example of a test pattern for detecting a yellow transfer residual ghost, and a plurality of elongate yellow test patterns are generated in a direction orthogonal to the conveyance direction of the recording paper 3. This test pattern only needs to be detectable by the density detection sensor 71. For example, the length (the length in the direction orthogonal to the conveyance direction of the recording paper 3) is about 30 mm and the width (the conveyance direction of the recording paper 3). Is a length that is considerably narrower than the transfer nip width (about 2 mm) and is set to about 0.15 mm. Then, a total of about 20 test patterns are arranged at 1 mm intervals.

  FIG. 6B shows an example of a test pattern for detecting a residual magenta transfer ghost, and uses the entire area of the maximum width (maximum print width) of the toner image that can be formed on the recording paper 3. A yellow test pattern (solid pattern) is generated, and a plurality of magenta test patterns from above the yellow test pattern (solid pattern) in a partial intermediate region in a direction orthogonal to the conveyance direction of the recording paper 3 As a result, a plurality of elongated red (R = Y + M) test patterns are generated in parallel with the conveyance direction of the recording paper 3. Note that the plurality of red test patterns have the same form as the plurality of yellow test patterns shown in FIG. The reason why the plurality of magenta test patterns are overlapped on the yellow full-width solid pattern is to increase the charge amount of the toner during yellow transfer. That is, as the potential difference increases, the charge is easily accumulated in the toner, so that ghosts are generated under more severe conditions than simply forming a plurality of magenta test patterns or overlaying narrow solid patterns. You can check.

  FIG. 6C shows an example of a test pattern for detecting a cyan transfer residual ghost. A yellow test pattern (in a middle region in a direction orthogonal to the conveyance direction of the recording paper 3) A plurality of red (R = Y + M) test patterns (vertical stripes) formed by superimposing a plurality of elongated magenta test patterns parallel to the conveyance direction of the recording paper 3 from above the solid paper), and the recording paper 3 A lattice pattern (pattern) composed of a plurality of green (G = M + C) test patterns (horizontal stripes) formed by superimposing a plurality of elongated cyan test patterns in a direction perpendicular to the conveyance direction is generated. The magenta test pattern (solid pattern) was superimposed on the yellow test pattern (solid pattern) on both sides of the intermediate area. Head (R = Y + M) of the test pattern (solid pattern) is generated. A plurality of green test patterns (horizontal stripes) are a plurality of yellow test patterns shown in FIG. 6A and a plurality of red (R = Y + M) tests shown in FIG. 6B. It has the same form as the pattern, and the multiple red test patterns (vertical stripes) are the same as the multiple green test patterns, regardless of whether they are vertical or horizontal. It is.

  In the intermediate region, a test pattern Y + M + C is formed at a point where a plurality of test patterns (horizontal stripes) of green (G = M + C) and a plurality of test patterns (vertical stripes) of red (R = Y + M) intersect. Although it is generated, it is originally intended for use up to a secondary color (a color obtained by superimposing two colors), that is, when there is no tertiary color (a color obtained by superimposing three colors), Such a test pattern is generated assuming that the three colors overlap due to color misregistration or the like. Therefore, if there is no problem such as color misregistration, for example, a plurality of green test patterns and a plurality of red test patterns may be formed as horizontal stripes (patterns) alternately arranged.

  FIG. 6D shows an example of a test pattern for detecting a black transfer residual ghost. In some intermediate regions in the direction orthogonal to the conveyance direction of the recording paper 3, yellow, magenta, cyan A black test pattern (solid pattern) is formed by superimposing black at a density of 60% and black at a density of 100%, and a yellow pattern is formed on both sides of the intermediate region. A red (R = Y + M) test pattern (solid pattern) is generated by superimposing a magenta test pattern (solid pattern) on the test pattern (solid pattern).

  In S120, the control unit 90 controls the image forming operation (particularly, the electrostatic latent image forming operation based on the exposure of the scanner unit 41) by each of the image forming units 20Y, 20M, 20C, and 20K. a) a test pattern (toner image) for detecting a transfer residual ghost shown in FIG. 6 (d) is formed on the recording paper 3 in sequence, and immediately after each test pattern (toner image) is formed in sequence. At least in one section of the photosensitive drum 62, a non-image area where no toner image is formed is formed.

  Next, in S130, the density detection sensor 71 performs an operation for detecting a ghost (transfer residual ghost) due to each test pattern in a region (non-image region) behind each test pattern.

  Then, the process proceeds to S140. In S140, it is determined whether or not there is a ghost. Here, for yellow, magenta, and cyan test patterns, when a ghost for the target color is detected, the control unit 90 acquires a waveform (pulse wave) having a periodic output level from the density detection sensor 71. it can. Therefore, particularly in the printer 1, when the output waveform from the density detection sensor 71 is subjected to discrete Fourier transform (frequency analysis) and a frequency that matches the frequency at the time of generating the test pattern is detected in the output waveform, the ghost is detected. Judge that there is. Further, regarding the black test pattern, it is determined that there is a ghost when the period of the dither pattern of Y, M, C is detected or when there is a change in density exceeding a certain level.

  In S140, if any one of the yellow, magenta, cyan, and black test patterns is detected, the process proceeds to S190. If no ghost is detected, the process proceeds to S150.

In S150, the test pattern latent image formation processing unit forms a test pattern for detecting the reverse transfer ghost, and the process proceeds to S160.
In this embodiment, whether or not a transfer residual ghost is generated is confirmed based on a test pattern for detecting a transfer residual ghost for each color shown in FIGS. 6A to 6D. If no residual transfer ghost is detected in any of magenta, cyan, and black, it is further checked whether a reverse transfer ghost has occurred.

  For example, a toner image (developer image) of a test pattern for detecting reverse transfer ghost shown in FIGS. 7A and 7B is drawn on the recording paper 3 and at least one of the photosensitive drums 62 immediately after that is drawn. A non-drawing area in which nothing is drawn is formed in the rotation section.

  As a test pattern for detecting a reverse transfer ghost, it is preferable to perform a check with a color pattern in which reverse transfer is likely to occur. Therefore, in this embodiment, a primary color (any one of yellow, magenta, and cyan) is used. Also, based on the fact that reverse transfer is likely to occur in secondary (ie, red (R), green (G), and blue (B) image areas obtained by combining a plurality of color toners (developers). The secondary color reverse transfer ghost detection test pattern shown in FIGS. 7A and 7B is used.

  FIG. 7A shows an example of a test pattern for detecting a reverse transfer ghost. Two types of yellow, magenta, and cyan are sequentially selected, and the most toner image that can be formed on the recording paper 3 is shown. Three areas of red (R = Y + M), green (G = Y + C), and blue (B = M + C) having a predetermined length in the conveyance direction of the recording paper 3 using the entire area of the large (maximum printing width). A test pattern (solid pattern) is generated.

  The length of each test pattern in the conveyance direction of the recording paper 3 is set to, for example, about 17 mm. However, when the three test patterns do not fit into the entire circumference of the photosensitive drum 62, The length of the recording sheet 3 in the conveyance direction may be shortened, or a non-image area for one turn of the photosensitive drum 62 may be formed between the test patterns.

  FIG. 7B shows a test pattern suitable for a case where the reverse transfer phenomenon tends to occur as the boundary between the portion where the toner image is formed and the portion where the toner image is not formed increases. An example is shown, and each test pattern of red, green, and blue is divided into a plurality (for example, three) and formed. In this case, the length of each test pattern in the conveyance direction of the recording paper 3 is, for example, about 4 mm, and it may be arranged in rows at the same interval (4 mm). In the case of the test pattern of FIG. 7B, there is also an effect that occurrence of a ghost can be accurately detected by using discrete Fourier transform or the like.

  In S160, a detection operation of a ghost (reverse transfer ghost) caused by the test pattern for detecting the reverse transfer ghost is performed. In this case, similarly to the detection of the black transfer residual ghost in S140, it is determined that there is a ghost when there is a change in density of a certain level or more.

  Next, the process proceeds to S170, where it is determined whether or not a ghost is detected. If a ghost is detected, the process proceeds to S190. If no ghost is detected, the process proceeds to S180.

  In S180, assuming that the currently set transfer bias (transfer current value) of each color is appropriate (no adjustment is necessary), the transfer bias is set as it is, and the processing is completed.

  In S190, transfer bias optimization processing for eliminating the occurrence of ghost is performed, and the process proceeds to S200. In this transfer bias optimization process, a transfer current value (constant current) is determined (corrected), and control is performed to set a current value that optimizes the transfer bias.

  By the way, the transfer residual ghost records all the toner (developer) on the photoconductive drum 62 when the toner image (developer image) formed on the photoconductive drum 62 is transferred to the recording paper 3 at the transfer position. This is caused by the fact that a part of the toner remains on the photosensitive drum 62 after the transfer without being transferred to the paper 3, and the toner remaining on the photosensitive drum 62 after the transfer. Is generally referred to as “transfer residual toner”, but as the transfer bias applied to the transfer portion is smaller (weaker), the transfer residual toner is more likely to occur, and accordingly, the transfer residual ghost tends to occur. However, when the transfer bias is large (strong) beyond the appropriate range, the transfer bias is too large, and thus a reversely charged toner (toner charged to a polarity opposite to the original charged polarity) is generated. The transfer residue increases.

  On the other hand, the reverse transfer ghost is generated due to the toner (reverse transfer toner) reversely transferred to the photosensitive rest drum 62 at the time of transfer. Even in the case of plus) or negative (minus), the potential (charge amount) of the toner image already transferred to the recording paper 3 is high, and the transfer applied to the transfer portion As the bias is larger (stronger), the reverse transfer toner is more likely to be generated, and accordingly, the reverse transfer ghost tends to occur.

  For this reason, as an appropriate value of the transfer bias to be applied to the transfer portion, a transfer residual ghost does not occur even when the transfer bias is applied by any method of constant current control or constant voltage control (occurrence The transfer residual ghost and the reverse transfer ghost do not occur (there is no problem even if they occur), and are below the upper limit. It is necessary. Therefore, in this sense, the test pattern for detecting the residual transfer ghost shown in FIGS. 6A to 6D is mainly for checking whether or not the transfer bias is too small. Thus, the test pattern for “under-transfer bias detection” is used, and the test pattern for reverse transfer ghost detection shown in FIGS. 7A and 7B is mainly based on whether or not the transfer bias is too large. Can be rephrased as a test pattern for “transfer bias excess detection”.

  FIG. 5 shows details of the transfer bias optimization processing in S190 in the transfer bias setting processing of FIG. As shown in FIG. 5, in the transfer bias optimizing process, first, in S110, yellow, which is the color of the image forming unit 20 that is initially selected when a color image is generated in the normal print mode, is selected. In the present embodiment, the yellow image forming unit 20Y is located on the most upstream side with respect to the conveyance direction of the regular recording paper 3.

  Next, in S310, the transfer bias of the color transfer roller 61 positioned downstream in the conveyance direction of the recording paper 3 is set to be smaller (weaker) than the currently selected color. Specifically, the transfer current value is reduced to about one third (for example, from 15 μA to 5 μA).

  Then, the process proceeds to S315. In S315, the test pattern latent image formation processing unit draws a test pattern for detecting the transfer residual toner shown in FIG. 4 as a test pattern, and then at least one rotation of the photosensitive drum 62. A non-drawing area where no toner image is formed is formed in the minute area.

  When the test pattern is formed, the test pattern shown in FIG. 4A is selected when yellow is selected using the image forming unit 20 of the currently selected color and its upstream color. When magenta is selected, the test pattern shown in FIG. 4B is selected. When cyan is selected, the test pattern shown in FIG. 4C is selected. When black is selected, the test pattern shown in FIG. ) Is formed.

Next, in S317, the density detection sensor 71 performs an operation for detecting a ghost (transfer residual ghost) generated in a region behind the test pattern (non-image region).
Then, the process proceeds to S320, and in S320, it is determined whether or not a ghost is detected in S317. If a ghost is detected in S317, the process proceeds to S380, and if no ghost is detected in S317, the process proceeds to S330.

  In S330, if no ghost is detected in S320, the transfer current value is within an appropriate range, but the transfer bias is smaller (weak) in order to prevent reverse transfer more effectively. Therefore, the transfer current value is decreased by one step, the changed current value is set to a new transfer current value, and the process proceeds to S340.

  In S340 to S360, the same process as in S315 to S320 is performed again. If no ghost is detected in S360, the process returns to S330, and if a ghost is detected in S360, the process proceeds to S370.

  In S370, if a ghost is generated as a result of reducing the transfer current value by one step in S330, it means that the transfer current value is reduced too much, so that the currently set transfer current value is returned by one step ( The increased current value is set to a constant current value in the normal printing mode, and the process proceeds to S200.

  On the other hand, in S380 which is shifted when a ghost is detected in S320, the transfer current value is increased by one level in order to prevent the ghost from being generated, the changed current value is set as a new transfer current value, and S390 is set. Migrate to

  And in S390-S410, the same process as S315-S320 is performed again. If a ghost is detected in S410, the process returns to S380. If a ghost is not detected in S410, the process proceeds to S420 assuming that the transfer current value is within an appropriate range.

In S420, the currently set transfer current value is set to a constant current value in the normal print mode, and the process proceeds to S200.
In S200, it is determined whether or not black, which is the color of the image forming unit 20 to be selected last when the color image is generated in the normal printing mode, is selected. When black is not selected, the process proceeds to S210, and when a color image is generated in the normal print mode, a color located immediately downstream of the currently selected color is selected. Next, in S215, The transfer bias in the image forming unit 20 of the color selected in S210 is returned to the original set value. That is, in S310, the transfer current value reduced to about one third is returned to the original set value. Then, the process proceeds to S315 again, and the same processing as described above is repeated.

  As described above, when the color newly selected in S210 is magenta, the magenta transfer residual ghost detection test pattern shown in FIG. 4B is drawn in S315, whereby the magenta image forming unit. When the optimum transfer bias at 20M is set, and then cyan is selected in S210, a test pattern for detecting a cyan transfer residual ghost shown in FIG. 4C is drawn in S315. When an optimum transfer bias is set in the cyan image forming unit 20C, and finally black is selected in S210, a test pattern for black transfer residual ghost detection shown in FIG. 4D is drawn in S315. As a result, an optimum transfer bias in the black image forming unit 20K is set.

  As described above, when the transfer bias optimization processing for all the image forming units 20Y, 20M, 20C, and 20K is completed, the determination of YES is made in S200 because black is finally selected in S210. The process shown in FIG.

  In the printer 1 described in detail above, the control unit 90 performs an image forming operation for transferring the toner image onto the recording paper 3, thereby generating a toner image as a transfer residual toner detection pattern on the recording paper 3. A non-drawing area where the toner image is not formed is formed at least in an area of one circumference of the photosensitive drum 62 immediately after the toner image is formed. The density detection sensor 71 detects the presence or absence of toner in the non-drawing area. Further, the control unit 90 sets image forming conditions (transfer bias) for the image forming units 20Y, 20M, 20C, and 20K based on the detection result by the density detection sensor 71 so that no transfer residual ghost is generated.

  Therefore, according to such a printer 1, it is possible to detect whether or not a ghost is generated in an image actually formed on the recording paper 3, so that more optimal image forming conditions can be set. .

  In addition, since the presence or absence of toner is detected in the non-drawing area immediately after the toner image formed as a test pattern for detecting the residual transfer ghost, more toner can be detected in the non-image area, improving the toner measurement system. Can be made.

  Further, the control unit 90 periodically forms a plurality of test patterns, and the control unit 90 detects, by the detection by the density detection sensor 71, when toner is detected at a cycle that matches the test pattern formation cycle. The recording paper 3 is regarded as having toner, and image forming conditions are set.

  Therefore, according to such a printer 1, when toner is detected in the non-image area, it is detected according to the cycle in which the test pattern is formed. Can be identified. For this reason, the control unit 90 only needs to analyze the detection result detected from the specified position, and therefore can easily and reliably detect the toner present in the non-drawing area.

  The transfer roller 61 is configured to transfer the toner image onto the recording paper 3 by applying a transfer bias to the photosensitive drum 62 at the transfer position. Further, the control unit 90 is configured to form a test pattern in which the length in the direction parallel to the relative movement direction is larger than the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position. ing.

Therefore, according to such a printer 1, the upper limit of the transfer bias to be applied between the transfer roller 61 and the photosensitive drum 62 can be grasped.
Further, the controller 90 forms a test pattern in which the length in the direction parallel to the relative movement direction is larger than the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position. The test pattern is configured such that the length in the direction orthogonal to the relative movement direction occupies almost the entire area of the maximum width of the toner image (developer image) that can be formed on the recording paper 3.

Therefore, according to such a printer 1, the upper limit of the transfer bias can be grasped more strictly.
In addition, the control unit 90 has a test pattern in which the length in the direction parallel to the relative movement direction is larger than the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position, and further the relative movement. The detection result by the density detection sensor 71 when a test pattern having a size in which the length in the direction orthogonal to the direction occupies almost the entire width of the maximum width of the toner image (developer image) that can be formed on the recording paper 3 is formed. If it is determined that there is toner in the non-drawing area, the transfer bias applied to the photosensitive drum 62 at the transfer position is controlled to be small.

Therefore, according to such a printer 1, it is possible to set a transfer bias so that a toner image is not formed in a non-image area.
Further, the control unit 90 has a length in a direction parallel to the conveyance direction of the recording paper 3 shorter than the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position, and each is substantially parallel. Are formed so as to form a plurality of test patterns.

Therefore, according to such a printer 1, the lower limit of the transfer bias to be applied between the transfer roller 61 and the photosensitive drum 62 can be grasped.
In particular, the control unit 90 has a length in the direction parallel to the conveyance direction of the recording paper 3 shorter than the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position. When forming a plurality of test patterns arranged in parallel, the length in the direction orthogonal to the relative movement direction is the same length of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position. A test pattern having a size occupying a part is formed.

According to such a printer 1, the lower limit of the transfer bias can be grasped more strictly.
Further, the control unit 90 has a length in a direction parallel to the conveyance direction of the recording paper 3 shorter than the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position, and each is substantially parallel. The plurality of test patterns arranged on the recording medium and the length in the direction perpendicular to the relative movement direction occupy a part of the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position. When the test pattern is formed, if it is determined that there is toner in the non-drawing area based on the detection result by the density detection sensor 71, it is applied to the photosensitive drum 62 at the transfer position. The transfer bias is controlled to increase.

Therefore, according to such a printer 1, it is possible to set an appropriate transfer bias so that toner is not detected in the non-drawing area.
Further, the control unit 90 has a length in a direction parallel to the conveyance direction of the recording paper 3 shorter than the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position, and each is substantially parallel. The plurality of test patterns arranged on the recording medium and the length in the direction perpendicular to the relative movement direction occupy a part of the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position. When the test pattern is formed, after the transfer bias is controlled, the image forming operation by the control unit 90 is repeatedly executed again with the controlled transfer bias, and it is determined that there is no toner in the non-drawing area. The transfer bias at this time is set to a transfer bias value when image formation is performed by the image forming means.

Therefore, according to such a printer 1, a more appropriate transfer bias can be set without increasing the transfer bias unnecessarily.
Further, the control unit 90 has a length in a direction parallel to the conveyance direction of the recording paper 3 shorter than the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position, and each is substantially parallel. The plurality of test patterns arranged on the recording medium and the length in the direction perpendicular to the relative movement direction occupy a part of the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position. When the test pattern is formed, if it is determined that there is no toner in the non-drawing area based on the detection result by the density detection sensor 71, it is applied to the photosensitive drum 62 at the transfer position. It is desirable to control the transfer bias to be small.

Therefore, according to such a printer 1, an appropriate transfer bias can be set without increasing the transfer bias unnecessarily.
Further, the control unit 90 has a length in a direction parallel to the conveyance direction of the recording paper 3 shorter than the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position, and each is substantially parallel. The plurality of test patterns arranged on the recording medium and the length in the direction perpendicular to the relative movement direction occupy a part of the length in the same direction of the contact portion between the photosensitive drum 62 and the recording paper 3 at the transfer position. When the test pattern is formed, if it is determined that there is no toner in the non-drawing area based on the detection result by the density detection sensor 71, it is applied to the photosensitive drum 62 at the transfer position. After controlling the transfer bias so as to reduce the transfer bias, the controller 90 repeatedly performs the image forming operation again with the controlled transfer bias, and determines that there is toner in the non-drawing area. If, it is configured to set the transfer bias value when the image formed by the image forming means a transfer bias of the last time is determined that there is no toner.

Therefore, according to such a printer 1, a more appropriate transfer bias can be set without increasing the transfer bias unnecessarily.
The image forming unit includes at least a plurality of developing rollers 52, and each developing roller 52 forms a toner image. The controller 90 sequentially performs image forming operations by the developing rollers 52 using the image forming unit. Is set. Further, the density detection sensor 71 detects the presence / absence of toner in each non-drawing area, and the control unit 90 performs image forming operation in the non-drawing area based on the detection result by the density detection sensor 71. The image forming conditions for at least one of the charger 31, the scanner unit 41, the developing roller 52, and the transfer roller 61 are set.

  Therefore, according to such a printer 1, even if a plurality of developing rollers 52 are provided as in a color printer, for example, occurrence of transfer residual ghost or reverse transfer ghost can be prevented appropriately.

Further, the control unit 90 forms a test pattern in which at least a part is formed by overlapping a plurality of toners.
Therefore, according to such a printer 1, it is possible to set a transfer bias so that toner is not detected in the non-image area even under more severe conditions.

  In addition, the control unit 90 is developed by a certain developing roller 52 using an image forming unit, and a plurality of test patterns each arranged substantially in parallel at a contact portion between the photosensitive drum 62 and the recording paper 3, and The test pattern is developed by different developing rollers 52 before the test pattern is drawn, and a test pattern having a size for filling a plurality of test patterns is formed.

Therefore, according to such a printer 1, conditions for forming a test pattern can be made stricter.
In addition, the image forming unit is configured to form an image by sequentially superimposing the toner images from the developing rollers 52, and the control unit 90 selects the developing roller 52 to be used at the beginning of the image formation, The image forming operation is performed a plurality of times using the developing roller 52 that is used first, and after the detection by the density detection sensor 71, the developing roller 52 that is used next is sequentially selected, and the developing roller that is used next. 52 is configured to perform an image forming operation using 52. The density detection sensor 71 is preferably configured to detect the presence or absence of toner in each non-drawing region every time the image forming operation using each developing roller 52 is completed.

  According to such a printer 1, it is possible to perform image formation in the same order as the actual image forming operation. Therefore, the transfer bias is taken into consideration when the toner images actually formed by different developing rollers 52 are superimposed. Can be set.

  Further, when the control unit 90 detects the presence / absence of a toner image in a non-drawing area by the density detection sensor 71, the control unit 90 includes a photosensitive drum 62 positioned downstream of the photosensitive drum 62 on which a test pattern is formed. The transfer bias applied between the transfer roller 61 and the transfer roller 61 is configured to be smaller than the originally set bias.

  Therefore, according to such a printer 1, when the density detection sensor 71 detects toner, only the influence of the transfer roller 61 located on the upstream side is considered, and the influence of the transfer roller 61 located on the downstream side is considered. Since it can be eliminated, an appropriate transfer bias for each transfer roller 61 can be set.

  Furthermore, the density detection sensor 71 includes an optical sensor that detects the presence or absence of toner by irradiating the recording sheet 3 with light emitted from the light emitting unit and receiving the reflected light by the light receiving unit.

  Therefore, according to such a printer 1, the optical sensor constituting the density detection sensor 71 does not come into contact with the recording paper 3, so that the toner can be detected without damaging the recording paper 3. it can.

The optical sensor also has a function of a registration sensor that detects a positional shift of a toner image formed by each developing device.
Therefore, according to such a printer 1, it is not necessary to further provide a registration sensor, so that the cost can be reduced.

Furthermore, the optical sensor also has a function of a density detection sensor that measures the density of the test pattern formed to correct the density of the image formed by the image forming unit.
Therefore, according to such a printer 1, it is not necessary to further provide a density detection sensor, so that the cost can be reduced.

The control unit 90 is configured to perform an image forming operation for ghost detection when performing processing for correcting the density of an image formed by the image forming unit.
Therefore, according to such a printer 1, since the transfer bias is adjusted when density correction is performed, an appropriate transfer bias can be efficiently set.

The embodiment of the present invention is not limited to the above-described embodiment, and can take various forms as long as it belongs to the technical scope of the present invention.
For example, the transfer residual ghost detection test patterns shown in FIGS. 6A to 6D are not necessarily limited to the test patterns shown in the figure. For example, yellow, magenta, cyan, black The patterns may be such that each of these patterns fits on one revolution of the photosensitive drum 62. Further, the pattern need not necessarily be a test-specific pattern, and may be any pattern as long as ghost detection is possible.

  In this embodiment, the transfer bias optimization process is configured to repeatedly form a test pattern until the current value for controlling the transfer bias becomes an appropriate current value in the processes of S320 to S420. However, it is not necessary to configure in this way, and an appropriate bias may be calculated based on the ghost density of two types of test patterns. For example, in the ghost detection process in S320, a ghost generation amount is detected, and a transfer bias is referred to by referring to a table (database: stored in the ghost correction processing unit) based on the detection result. You may comprise so that the electric current value for setting may be set. More specifically, instead of performing the transfer bias optimization process in S190, a table for correcting the transfer bias is referred to according to the ghost generation amount, and a bias control current value based on the reference result is set. What is necessary is just to process.

In this way, the transfer bias optimization process can be simplified, and the number of recording sheets 3 used in the transfer bias setting process can be saved.
Further, in the present embodiment, the present invention is applied to a horizontal type direct tandem color laser printer. However, the present invention is not limited to such a configuration. For example, the photosensitive drum 62 is configured in a belt shape. Alternatively, the toner image may be transferred from the photosensitive drum 62 to the recording paper 3 via an intermediate transfer medium such as an intermediate transfer belt or an intermediate transfer drum.

  In the present embodiment, the density detection sensor 71 is configured to read more the density of the recording paper 3 positioned on the conveyance belt 68. However, the present invention is not limited to this configuration. For example, in the direct tandem method, the recording paper is used. Instead of 3, the test pattern may be transferred onto the conveying belt 68, and the occurrence of ghost may be detected by the density sensor 71. If the intermediate transfer medium is provided, The density detection sensor 71 may be arranged in the vicinity of the intermediate transfer medium, and the density detection sensor 71 may be configured to read the density of a ghost generated on the intermediate transfer body. Further, the above control method is not limited to the generation of ghosts. For example, as shown in FIG. 8, a density detection sensor 71 is disposed in the vicinity of the photosensitive drums 62 and is transferred onto each photosensitive drum 62 after transfer. The present invention can also be applied to the case where residual transfer residual toner is detected.

  In the present embodiment, the printer 1 is configured as a color laser printer. However, the present invention is not limited to this configuration. For example, if only the transfer residual ghost is targeted, the printer 1 may be configured as a monochrome laser printer.

  Further, the printer 1 according to the present embodiment is configured to set the image forming conditions by controlling the transfer bias applied to the transfer roller 61. However, the present invention is not limited to this configuration. The image forming conditions may be set by controlling the electrical characteristics of the unit 41, the developing roller 52, and the like.

In this embodiment, a positively chargeable toner is used as the developer. However, the developer is not limited to a positively chargeable toner, and for example, a negatively chargeable toner may be used.
Further, in the present embodiment, when occurrence of ghost is detected in any one of yellow, magenta, cyan, and black, transfer bias is applied to all the image forming units 20Y, 20M, 20C, and 20K. However, it is not always necessary to target all the developing means. For example, when ghosting is detected in yellow, all image formation is performed. The transfer bias optimization processing (resetting of image forming conditions) is performed on the unit 20. If a ghost is detected in cyan, the yellow and magenta image forming unit 20Y positioned upstream of the cyan is detected. , 20M, the transfer bias optimization process is not performed, and the currently set transfer current value is kept as it is. Lifting and, cyan and black image forming units 20C, only it may be performed to optimize the process of the transfer bias for 20K.

  In the case where the ghost is hardly generated in the first image forming unit used for image formation, for example, the image forming unit located at the most upstream in the case of the tandem method, the ghost detection process is performed. In particular, it may be excluded from the transfer bias optimization process.

  Next, another type of printer 2 will be described. The printer 2 described in the present embodiment (Example 2) is different from the printer 1 of Example 1 only in the configuration of each image forming unit 20, and the other configuration is the same as that of the printer 1 of Example 1. It is the composition. Therefore, in the present embodiment (second embodiment), the printer 2 of the present embodiment (second embodiment) details only the portions different from the printer 1 of the first embodiment, and the same portions are denoted by the same reference numerals. A description thereof will be omitted.

First, the image forming unit 20 in the present embodiment will be described with reference to FIG.
Each image forming unit 20 in this embodiment is configured to be movable in the vertical direction so that the photosensitive drum 62 provided in each image forming unit 20 can be brought into and out of contact with the transport belt 68. Each unit 20 is configured such that the entire unit including the photosensitive drum 62 and the developing cartridge 51 can be moved integrally.

  That is, these image forming units 20 include a moving member 65 having two shafts inserted through the guide hole 65a, a link 66 connected to the moving member 65 and rotatable with respect to the moving member 65, and A motor (which may be a rotating solenoid) 67 is provided to move the moving member 65 in a substantially horizontal direction (left and right in FIG. 9) by rotating the link 66. Note that the description of the moving member 65, the link 66, and the motor 67 is omitted for the black image forming unit 20K.

  Next, each motor 67 is configured as a part of the developing cartridge mechanism 72 shown in FIG. For this reason, the control unit 90 controls the drive of the motor 67 via the main drive unit 79.

  Here, when the controller 90 drives the motor 67, the moving member 65 is moved in a substantially horizontal direction (leftward in FIG. 9) via the link 66. Then, the two shafts provided in the image forming unit 20 move in the guide hole 65a and move upward. For this reason, the photosensitive drum 62 is separated from the transport belt 68.

  As described above, the operation in which the control unit 90 moves the photosensitive drum 62 and the supply roller 32 in the upward direction is executed instead of the processing of S310 by the ghost correction processing unit. That is, the process for reducing the bias control current to 1/3, which is performed in S310 of the first embodiment, is not necessary.

This operation is performed only for the image forming unit 20 located on the downstream side of the selected color.
In the printer 2 described above, when the presence or absence of toner in the non-image area is detected by the density detection sensor 71, the photosensitive unit located downstream of the photosensitive drum 62 on which the test pattern is formed by the control unit 90. The body drum 62 and the recording paper 3 are separated from each other.

  Therefore, according to such a printer 2, since it is possible to employ a configuration in which the toner adhering to the non-image area is not contacted until the toner is detected by the density detection sensor 71, a more appropriate transfer bias can be achieved. Can be set.

1 is a side cross-sectional view illustrating a main part of a printer according to a first embodiment to which the present invention is applied. 2 is a block diagram schematically illustrating an electrical configuration of a printer. FIG. It is explanatory drawing which shows the electric potential in various rollers. It is a flowchart which shows a transfer bias setting process. It is a flowchart which shows the transfer bias optimization process in a transfer bias setting process. FIG. 6 is an explanatory diagram illustrating a test pattern for detecting a transfer residual toner. It is explanatory drawing which shows the test pattern for reverse transfer toner detection. FIG. 10 is a cross-sectional view illustrating details of a developing cartridge according to a modification. 6 is a cross-sectional view illustrating details of a developing cartridge according to Embodiment 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Printer, 3 ... Recording paper, 4 ... Image formation part, 5 ... Main body casing, 6 ... Paper discharge part, 8 ... Fixing part, 9 ... Paper feed part, 10 ... Paper discharge tray, 11 ... Paper discharge roller , 12 ... paper feed tray, 14 ... transport roller, 15 ... guide member, 17 ... transfer unit, 20, 20C, 20K, 20M, 20Y ... image forming unit, 31 ... charger, 32 ... supply roller, 33a ... roller shaft , 41 ... Scanner unit, 51, 51C, 51K, 51M, 51Y ... Developing cartridge, 52 ... Developing roller, 54 ... Bias applying unit, 55 ... Developing casing, 56 ... Developer hopper, 61 ... Transfer roller, 62 ... Photoconductor Drum, 63 ... conveying belt drive roller, 64 ... conveying belt driven roller, 65 ... moving member, 65a ... guide hole, 66 ... link, 67 ... motor, 68 ... conveying belt, 71 ... concentration detection sensor , 72 ... developing cartridge mechanism, 73 ... test pattern, 74 ... density detection circuit, 75 ... origin sensor, 76 ... transfer mechanism drive, 77 ... paper feed mechanism, 79 ... main drive, 81 ... heating roller, 82 ... Pressing roller, 83 ... Feeding roller, 90 ... Control section.

Claims (23)

Charging means for charging the photoreceptor;
Exposure means for forming an electrostatic latent image on the photoreceptor;
Developing means for visualizing the electrostatic latent image formed on the photoreceptor with a developer to form a developer image;
Transfer means for transferring the developer image on the photosensitive member to a transfer member at a predetermined transfer position;
An image forming apparatus comprising image forming means having
By using the image forming means to perform an image forming operation for transferring a developer image onto the transfer member or a transfer member for transferring the transfer member, a test pattern is formed on the transfer member or the transfer member. Then, a developer image is not formed on the transfer member or the transport member by using at least a part of a region where the developer image is formed on the photosensitive member. Test pattern forming means for forming a drawing region;
Ghost detection means for detecting the presence or absence of developer in the non-drawing area;
Based on the detection result of the ghost detection means, at least one of the charging means, the exposure means, the developing means, and the transfer means is used so that a visible image is not formed in the non-drawing area. An image forming apparatus comprising: image forming condition setting means for setting image forming conditions for The photosensitive surface of the photoreceptor has an endless structure having a predetermined circumference,
The transfer unit is configured to transfer a developer image onto a transfer target member or a transport member that relatively moves in a circumferential direction of the photoconductor,
The ghost detection means detects the presence or absence of the developer in a non-drawing region located behind the transfer member or the conveyance member in the relative movement direction by the circumferential length of the photoconductor from the test pattern formation position. The image forming apparatus according to claim 1, wherein: The test pattern forming means periodically forms a plurality of test patterns,
The image forming condition setting means detects the developer on the member to be transferred or the conveying member when the developer is detected at a period that coincides with the formation period of the test pattern as detected by the ghost detecting means. The image forming apparatus according to claim 1, wherein the image forming condition is set assuming that the image forming condition is present. The transfer unit is configured to transfer the developer image onto the transfer target member or the transport member by applying a transfer bias between the transfer member and the photoconductor at the transfer position,
The test pattern forming means has a test pattern in which the length in the direction parallel to the relative movement direction is larger than the length in the same direction of the contact portion between the photoconductor and the transfer target member or the transport member at the transfer position. The image forming apparatus according to claim 1, wherein the image forming apparatus is formed. The test pattern forming unit forms a test pattern whose length in the direction orthogonal to the relative movement direction occupies almost the entire area of the maximum width of the developer image that can be formed on the transfer member. The image forming apparatus according to claim 4. When the image forming condition setting unit determines that there is a developer in the non-drawing area based on the detection result by the ghost detection unit, the image forming condition setting unit applies the image forming condition setting unit to the photoconductor at the transfer position. The image forming apparatus according to claim 4, wherein the transfer bias is controlled to be small. The transfer unit is configured to transfer the developer image to the transfer target member or the transport member by applying a transfer bias between the transfer member and the photosensitive member at the transfer position.
In the test pattern forming means, the length in the direction parallel to the relative movement direction is shorter than the length in the same direction of the contact portion between the photosensitive member and the transferred member or the transport member at the transfer position. The image forming apparatus according to claim 1, wherein a plurality of test patterns arranged substantially in parallel are formed. In the test pattern forming means, the length in the direction orthogonal to the relative movement direction occupies a part of the length in the same direction of the contact portion between the photoconductor and the transfer target member or the transport member at the transfer position. The image forming apparatus according to claim 7, wherein a test pattern is formed. When the image forming condition setting unit determines that there is a developer in the non-drawing area based on the detection result by the ghost detection unit, the image forming condition setting unit applies the image forming condition setting unit to the photoconductor at the transfer position. The image forming apparatus according to claim 7, wherein the transfer bias is controlled to increase. The image forming condition setting unit repeatedly performs the image forming operation by the test pattern forming unit again with the controlled transfer bias after controlling the transfer bias, and determines that there is no developer in the non-drawing area. 10. The image forming apparatus according to claim 9, wherein in this case, the transfer bias at this time is set to a transfer bias value when image formation is performed by the image forming unit. When the image forming condition setting unit determines that there is no developer in the non-drawing area based on the detection result by the ghost detecting unit, the image forming condition setting unit applies the image forming condition setting unit to the photoconductor at the transfer position. The image forming apparatus according to claim 7, wherein the transfer bias is controlled to be small. The image forming condition setting unit, after controlling the transfer bias, repeatedly executes the image forming operation by the test pattern forming unit again with the controlled transfer bias, and determines that there is a developer in the non-drawing area. 12. The image forming apparatus according to claim 11, wherein the transfer bias when the image forming unit performs image formation is set to a transfer bias when it is finally determined that there is no developer. The image forming unit includes at least a plurality of developing units, and each of the developing units is set to form a developer image.
The test pattern forming unit sequentially performs image forming operations by the developing units using the image forming unit,
The ghost detection means detects the presence or absence of the developer in each non-drawing area,
The image forming condition setting means comprises a charging means, an exposure means, a developing means, and a transfer means constituting an image forming means that has performed an image forming operation in the non-drawing area based on a detection result by the ghost detecting means. The image forming apparatus according to claim 1, wherein an image forming condition is set for at least one of the image forming apparatus and the image forming apparatus. The image forming apparatus according to claim 13, wherein the test pattern forming unit forms a test pattern at least partially formed by overlapping a plurality of developers using the image forming unit.   The test pattern forming means is developed by a developing means using the image forming means, and a plurality of tests are arranged substantially in parallel at the contact portion between the photoconductor and the transfer member or the transport member. The image forming apparatus according to claim 14, wherein a pattern and a test pattern having a size that is developed by different developing means before the test pattern is drawn and fills the plurality of test patterns are formed. The image forming means is configured to form an image by sequentially superimposing developer images by the developing means,
The test pattern forming unit selects a developing unit to be used first when forming the mixed color image among the developing units to be set with image forming conditions, and forms an image using the developing unit to be used first. After the detection by the ghost detection means, sequentially select the next development means to be used, and perform the image forming operation using the development means to be used next,
The ghost detection means detects the presence or absence of a developer in each non-drawing region every time an image forming operation using each of the development means is completed. The image forming apparatus described in 1.   The image forming condition setting unit includes a photoconductor positioned downstream of a photoconductor on which a test pattern is formed by the test pattern forming unit when the ghost detecting unit detects the presence or absence of a developer image in a non-drawing area. The image forming apparatus according to claim 16, wherein a transfer bias applied between the transfer unit and the transfer unit is made smaller than an originally set bias.   When the presence or absence of the developer in the non-image area is detected by the ghost detection unit, the photosensitive member positioned downstream from the photosensitive member on which the test pattern is formed by the test pattern forming unit and the transfer member or the conveyance member are separated from each other. The image forming apparatus according to claim 16, further comprising a separating unit that moves the image forming apparatus.   The ghost detection unit includes an optical sensor that detects the presence or absence of the developer by irradiating the transfer member or the transport member with light emitted from the light emitting unit and receiving the reflected light by the light receiving unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 19, wherein the optical sensor also has a function of a registration sensor that detects a positional deviation of a developer image formed by each developing device. The optical sensor also has a function of a density detection sensor that measures the density of a test pattern formed to correct the density of an image formed by the image forming unit. The image forming apparatus described.   The test pattern forming unit performs an image forming operation for ghost detection when performing a process of correcting a density of an image formed by the image forming unit. An image forming apparatus according to claim 1. Charging means for charging an endless photoconductor having a predetermined circumference;
Exposure means for forming an electrostatic latent image on the photoreceptor;
Developing means for visualizing the electrostatic latent image formed on the photoreceptor to form a developer image;
Transfer means for transferring the developer image to a member to be transferred that moves relative to the circumferential direction of the photosensitive member at a predetermined transfer position;
Image forming means having
A test pattern forming unit that forms a developer image as a test pattern on the photoreceptor using the image forming unit;
A developer presence / absence detecting means which is disposed in the vicinity of the photoreceptor and detects the presence / absence of the developer on the photoreceptor after the developer image on the photoreceptor is transferred using the image forming means;
An image for at least one of the charging unit, the exposure unit, the development unit, and the transfer unit so that the developer image is not detected based on the detection result of the developer presence / absence detection unit. An image forming apparatus comprising: an image forming condition setting unit that sets a forming condition;
The test pattern forming means periodically forms a plurality of test patterns each arranged in the relative movement direction,
The image forming condition setting means has the developer on the photoconductor when the developer is detected at a cycle that coincides with the test pattern formation cycle by detection by the developer presence / absence detector. An image forming apparatus characterized by being regarded as a thing.