JP5648445B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an intermediate transfer type image forming apparatus that can superimpose a plurality of color toners on an intermediate transfer member and collectively transfer the toner onto a recording medium such as paper or film is known. Some intermediate transfer type image forming apparatuses are provided with a transfer device having an elastic layer on the surface of an intermediate transfer member from the viewpoint of improving the paper compatibility. By using an intermediate transfer member having an elastic layer, the toner image transfer followability with respect to the irregularities on the surface of the recording medium is improved, and good toner transfer can be performed on various recording media. As an apparatus using an intermediate transfer member having such an elastic layer, for example, Patent Document 1 can be cited.

An intermediate transfer member having a surface made of an elastic material generally has a low glossiness on the surface. Therefore, when the density of a toner pattern formed on the intermediate transfer member is detected by an optical sensor, the density of a toner image is controlled. Therefore, there is a problem that sufficient toner density detection accuracy cannot be obtained.
As a means for solving such a problem, a method of transferring a toner pattern to a secondary transfer member and detecting the toner density on the secondary transfer member can be considered. When the toner density is detected on the secondary transfer member, the secondary transfer unit that transfers the toner pattern on the intermediate transfer member from the intermediate transfer member to the secondary transfer member is always predetermined in order to accurately detect the toner concentration. It is desirable to detect the density by transferring to a secondary transfer body under the transfer bias conditions. However, since the secondary transfer bias conditions are variously set depending on the type and thickness of the recording medium, the secondary printing bias condition is between the recording medium printed first and the recording medium printed next (hereinafter referred to as “inter-paper”). When detecting the toner pattern, it is necessary to switch the setting of the secondary transfer bias at the inter-paper portion and the setting of the secondary transfer bias applied to the recording medium at the time of printing for each paper interval. In this case, in order to properly transfer the toner pattern to the secondary transfer body under a predetermined bias condition, a sufficient interval between the sheets is set for the response performance of the rising / falling of the high voltage power source serving as the bias supply source. There is a need to. In consideration of such bias condition switching timing, the gap between the sheets must be set longer than that in the conventional method (density detection method on the intermediate transfer member), which may lead to a decrease in productivity of the apparatus. Absent.

Patent Document 1 discloses a technique related to mark detection of an intermediate transfer member having an elastic layer. However, the mark detection unit is configured to be movable in a direction orthogonal to the moving direction of the intermediate transfer member. It is necessary to provide a moving drive device or the like in the mark detection unit, which is not desirable from the viewpoint of downsizing and cost reduction of the device.
An object of the present invention is to provide an image forming apparatus capable of obtaining toner density detection accuracy and obtaining a good image without degrading the productivity of the apparatus.

An image forming apparatus according to the present invention includes an intermediate transfer member to which a toner image on an image carrier is transferred, and a toner image on the intermediate transfer member to a recording medium by applying a transfer bias. A transfer device that transfers the density-adjusting toner pattern formed on the inter-paper portion to the surface of the secondary transfer member; and a detection unit that detects the density of the toner pattern transferred to the surface of the secondary transfer member; And a control means for obtaining an inter-paper transfer bias condition Tp at the inter-paper portion when the toner pattern is transferred to the secondary transfer body according to the bias condition applied to the recording medium.
In the image forming apparatus according to the present invention, the control means sets a fixed reference bias condition Ti for transferring the toner pattern to the secondary transfer member in advance, and generates a print image in response to an image formation start signal. Before image formation, a toner pattern is formed on the intermediate transfer body under both the inter-paper transfer bias condition Tp and the fixed reference bias condition Ti, and the density of the toner pattern is detected by the detection means, and the detection results are respectively determined. Dp and Di are sampled, the toner pattern after printing is started is transferred to the secondary transfer body under the inter-paper transfer bias condition Tp, and the toner density detection result detected by the detecting means is calculated from the sampling data before printing is started. mark corrects the density detection result of the toner pattern by multiplying the Di / Dp, the inter-sheet transfer bias condition Tp, the leading edge of the recording medium to be So as to approach the bias conditions Tb to be applied to the rear end portion of the bias conditions Tf and a recording medium which is characterized by a higher than the fixed reference bias condition Ti.
In the image forming apparatus according to the present invention, the control unit executes the initial adjustment operation when the apparatus is started up and the density adjustment control when printing is completed, and is fixed when performing at least one of the initial adjustment operation and the density adjustment control. It is characterized in that density adjustment is performed by transferring a toner pattern onto a secondary transfer body under a reference bias condition Ti.
In the image forming apparatus according to the present invention, the control unit sets the inter-sheet transfer bias condition Tp by the bias condition Tf applied to the leading end portion of the recording medium and the bias condition Tb applied to the trailing end portion of the recording medium. The set value is calculated by Equation 1 represented by Tp = (Tf + Tb) / 2.
In the image forming apparatus according to the present invention, the intermediate transfer member is characterized in that at least the surface is formed of an elastic layer.

  According to the present invention, the inter-paper transfer bias condition Tp at the inter-paper portion on the intermediate transfer body when the toner pattern is transferred to the secondary transfer body is determined according to the bias condition applied to the recording medium. Since the time required for switching between the bias condition applied to the medium and the bias condition applied to the inter-paper portion can be shortened, the toner density detection accuracy can be obtained without deteriorating the productivity of the apparatus, and a good image can be obtained. Is obtained.

1 is an overall view showing an embodiment of an image forming apparatus to which the present invention is applied. (A)-(c) is a figure which shows the form of control of the inter paper transfer bias conditions by a control means. It is a figure which shows the form of control of the transfer bias conditions between sheets by a control means.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The image forming apparatus shown in FIG. 1 illustrates a full-color copying machine. The copying machine includes a printer unit 100, a paper feeding unit 200 disposed below the printer unit 100, a scanner unit 300 disposed above the printer unit 100, and an automatic document feed disposed above the scanner unit 300. And an apparatus (hereinafter referred to as “ADF”) ADF400. The image forming apparatus is not limited to a copying machine, but may be a printer, a facsimile machine, or a multifunction machine having a plurality of these functions.

  The printer unit 100 includes an endless belt-shaped intermediate transfer belt 10 as an intermediate transfer member. The intermediate transfer belt 10 is formed of an elastic layer on the surface, and is wound around the driving roller 14, the driven roller 15, and the secondary transfer counter roller 16 in a posture in which the side view is an inverted triangular shape. The endless movement of the driving roller 14 in the clockwise direction in FIG. Above the intermediate transfer belt 10, four image forming units 18Y, 18M, 18C, and 18K for forming toner images of Y (yellow), M (magenta), C (cyan), and K (black) are provided. Arranged along the belt moving direction.

  The image forming units 18Y, 18M, 18C, and 18K are photoreceptors 20Y, 20M, 20C, and 20K as image carriers, developing units 61Y, 61M, 61C, and 61K, and photoreceptor cleaning devices 63Y, 63M, 63C, and 63K. have. The photoconductors 20Y, 20M, 20C, and 20K are in contact with the intermediate transfer belt 10 to form primary transfer nips for Y, M, C, and K, respectively, and are rotated counterclockwise in the drawing by driving means (not shown). It can be driven to rotate. The developing units 61Y, 61M, 61C, and 61K are for developing the electrostatic latent images formed on the photoreceptors 20Y, 20M, 20C, and 20K with toners of Y, M, C, and K. The photoconductor cleaning devices 63Y, 63M, 63C, and 63K clean the transfer residual toner adhering to the photoconductors 20Y, 20M, 20C, and 20K after passing through the primary transfer nip. In this copying machine, the tandem image forming unit 11 is configured by four image forming units 18Y, 18M, 18C, and 18K arranged in the belt moving direction.

  In the printer unit 100, an optical writing unit 21 is disposed above the tandem image forming unit. The optical writing unit 21 performs an optical writing process by optical scanning on the surfaces of the photoconductors 20Y, 20M, 20C, and 20K that are driven to rotate counterclockwise in the drawing to form an electrostatic latent image. Is. Prior to the optical writing process, the surfaces of the photoreceptors 20Y, 20M, 20C, and 20K are uniformly charged by charging means of the image forming units 18Y, 18M, 18C, and 18K, respectively.

  The transfer unit 12 as an intermediate transfer unit including the intermediate transfer belt 10 and the like has primary transfer rollers 62Y, 62M, 62C, and 62K inside the loop of the intermediate transfer belt 10. These primary transfer rollers 62Y, 62M, 62C, and 62K press the intermediate transfer belt 10 toward the photoreceptors 20Y, 20M, 20C, and 20K behind the primary transfer nips for Y, M, C, and K. Yes.

  A secondary transfer roller 24 serving as a secondary transfer body is disposed below the intermediate transfer belt 10. The secondary transfer roller 24 is in contact with a portion of the intermediate transfer belt 10 that is wound around the secondary transfer counter roller 16 from the belt surface side to form a secondary transfer nip. The secondary transfer counter roller 16 is connected to a voltage applying means 160 composed of a high voltage power source, and a transfer bias (repulsive force bias) having the same polarity as the charging polarity of the toner constituting the toner image is applied to the backup roller 16. As a result, a transfer electric field is formed between the secondary transfer roller 24 and the ground. As a result, the unfixed toner image carried on the intermediate transfer belt 10 is collectively secondary transferred to a sheet-like recording medium P (hereinafter referred to as recording sheet P) fed at a predetermined timing at the secondary transfer position. At the same time, a toner pattern used for image density adjustment described later is transferred to the surface of the secondary transfer roller 24. In the present embodiment, the secondary transfer counter roller 16 and the voltage applying unit 160 constitute a secondary transfer device 600.

  The recording sheet P onto which the unfixed toner image has been transferred moves from the secondary transfer roller 24 to the conveyance belt 22 and is conveyed to the fixing device 25 while being attracted to the conveyance belt 22, and heat and pressure are applied by the fixing device 25. The toner image is fixed. The recording paper that has passed through the fixing device 25 is discharged to a paper discharge tray 57 by a discharge roller 56 and stacked.

  The scanner unit 300 reads image information of a document placed on the contact glass 32 by the reading sensor 36 and transmits the read image information to the control unit 500 of the printer unit 100. Based on the image information received from the scanner unit 300, the control unit 500 controls a light source such as a laser diode or an LED in the optical writing unit 21 of the printer unit 100 to perform laser writing for Y, M, C, and K. Light is emitted, and the photoconductors 20Y, 20M, 20C, and 20K are optically scanned. By this optical scanning, electrostatic latent images are formed on the surfaces of the photoreceptors 20Y, 20M, 20C, and 20K, and the latent images are developed into Y, M, C, and K toner images through a predetermined development process. The control unit 500 controls the toner pattern for density adjustment formed on the inter-paper portion on the intermediate transfer belt 10 described later, and the toner pattern formed on the inter-paper portion on the surface of the secondary transfer roller 24. Controls the transfer bias for transfer.

  The paper feed unit 200 includes a paper feed roller 42 that feeds recording sheets P from paper feed cassettes 44 arranged in multiple stages in the paper bank 43, and a separation roller that separates the sent recording sheets P and guides them to a paper feed path 46. 45, a conveyance roller 47 for conveying the recording sheet P to the paper feed path 48 of the printer unit 100, and the like. In addition to the paper feed unit 200, manual paper feed is also possible, and the manual feed tray 51 for manual feed and the recording sheet P on the manual feed tray 51 toward the manual feed path 53 one by one. A separation roller 52 for separation is also provided. In the printer unit 100, the manual paper feed path 53 joins the paper feed path 48.

  Near the end of the paper feed path 48, a registration roller pair 49 is disposed. The registration roller pair 49 sandwiches the recording sheet P conveyed in the paper feed path 48 between the rollers, and then feeds it toward the secondary transfer nip at a predetermined timing.

  In the copying machine according to the present embodiment, when copying a color image, an original is set on the original table 30 of the ADF 400, or the original is set on the contact glass 32 of the scanner unit 300 by opening the ADF 400. Press to close the document. Then, a start switch (not shown) is pressed. Then, when the document is set on the ADF 400, the document is conveyed onto the contact glass 32. Thereafter, the scanner unit 300 starts driving, and the first traveling body 33 and the second traveling body 34 start traveling along the document surface. Then, the light emitted from the light source by the first traveling body 33 is emitted on the original surface, and the obtained reflected light is folded and directed to the second traveling body 34. The folded light is further folded by the mirror of the second traveling body 34 and then incident on the reading sensor 36 through the imaging lens 35. Thereby, the content of the original is read.

  When the printer unit 100 receives image information from the scanner unit 300, the printer unit 100 feeds a recording sheet having a size corresponding to the image information to the paper feed path 48. Along with this, the drive roller 14 is rotationally driven by a drive motor (not shown) to move the intermediate transfer belt 10 endlessly in the clockwise direction in the drawing. At the same time, after the rotational driving of the photoconductors 20Y, 20M, 20C, and 20K of the image forming units 18Y, 18M, 18C, and 18K is started, charging processing, optical writing processing, and development processing are performed on the photoconductors 20Y, 20M, 20C, and 20K. And so on. The Y, M, C, and K toner images formed on the surfaces of the photoconductors 20Y, 20M, 20C, and 20K by these processes are sequentially overlapped at the Y, M, C, and K primary transfer nips to be intermediate. Primary transfer is performed on the transfer belt 10 to form a four-color superimposed toner image.

  In the paper feeding unit 200, one of the paper feeding rollers 42 is selectively rotated according to the recording sheet size, and the recording sheet P is sent out from one of the three paper feeding cassettes 44. The fed recording sheets P are separated one by one by the separation roller 45, introduced into the paper feed path 46, and then sent to the paper feed path 48 in the printer unit 100 via the conveyance roller 47. When the manual feed tray 51 is used, the paper feed roller of the tray is driven to rotate, and the recording sheet P on the tray is fed to the manual paper feed path 53 while being separated by the separation roller 52. Near the end. In the vicinity of the end of the paper feed path 48, the recording sheet P stops by abutting the leading edge against the registration roller pair 49. Thereafter, when the registration roller pair 49 is rotationally driven at a timing that can be synchronized with the four-color superimposed toner image on the intermediate transfer belt 10, the registration roller pair 49 is fed into the secondary transfer nip and is in close contact with the four-color superimposed toner image on the belt. . Then, secondary transfer is performed collectively on the recording sheet P due to the influence of nip pressure, secondary transfer bias, and the like.

  The recording sheet P onto which the four-color superimposed toner image has been secondarily transferred at the secondary transfer nip is fed into the fixing device 25 by the paper transport belt 22. When the fixing device 25 is sandwiched between the fixing nip between the pressure roller 27 and the fixing belt 26, the four-color superimposed toner image is fixed on the surface by pressure or heat treatment. The recording sheet P on which the color image is formed in this manner is stacked on a discharge tray 57 outside the apparatus via a discharge roller pair 56.

  When an image is also formed on the other surface of the recording sheet P, the recording sheet P is discharged from the fixing device 25 and then sent to the sheet reversing device 57 by the path switching by the switching claw 55. Then, after being turned upside down, it is returned to the registration roller pair 49 again, and then goes through the secondary transfer nip and the fixing device 25 again.

  After passing through the secondary transfer nip, the belt cleaning device 17 abuts on the surface of the intermediate transfer belt 10 before entering the Y primary transfer nip where the primary transfer process is the most upstream of the four colors. ing. This belt cleaning device 17 cleans transfer residual toner adhering to the belt surface.

Next, features of the present invention will be described.
This copier has a detecting means 310 for detecting the density of the toner pattern, and when the paper-to-paper transfer bias condition at the paper-to-paper portion when transferring the toner pattern to the secondary transfer member is Tp, this paper-to-paper transfer The control unit 500 obtains the bias condition Tp according to the bias condition applied to the recording sheet P. The secondary transfer device 600 has a function of transferring a toner pattern for density adjustment formed on the inter-sheet portion of the intermediate transfer belt 10 to the surface of the secondary transfer member.

  The detection unit 310 includes one light emitting element and two light receiving elements, and the intermediate transfer belt 10 is irradiated with light from the light emitting elements, and the regular reflection component of the reflected light from the intermediate transfer belt 10 is received by the light receiving element. This is a known reflection density detection sensor that receives diffuse reflection components with a light receiving element.

  The toner density transferred to the surface of the secondary transfer roller 24 serving as a secondary transfer body is detected by the detection unit 310 shown in FIG. FIG. 2A shows an example of the bias switching timing applied between the recording sheet P and the paper when the method of detecting the density of the toner pattern on the secondary transfer body is adopted. This bias switching timing is executed by the control means 500.

  The secondary transfer bias is constant-current controlled by the control unit 500 and is applied to each of the leading end portion (sheet leading end portion), the image portion, the recording sheet P trailing end portion (sheet trailing end portion), and the inter-paper portion of the recording sheet P. Corresponding current conditions are set. A predetermined reference current is set as a paper gap bias condition when the toner pattern is transferred to the secondary transfer body (secondary transfer roller 24). As shown in FIG. 2A, for example, when there is a gap between the current setting value applied to the leading end of the sheet and the reference current value between the sheets, the responsiveness of the high-voltage power source constituting the voltage applying unit 160 It is necessary to provide a predetermined length between papers in consideration of the above.

  In order to apply an appropriate transfer bias to the very leading end of the recording sheet P, it is necessary to apply a bias before the sheet leading end enters the secondary transfer nip. is there. Furthermore, due to the electrical resistance of the recording sheet P, the combined electrical resistance from the repulsive roller to the secondary transfer body increases rapidly immediately after the recording sheet P enters the secondary transfer nip. When is applied to the leading edge of the sheet, there may be a problem that the transfer bias acting on the leading edge of the sheet instantaneously decreases and the image density at the leading edge of the sheet decreases. For this reason, it is desirable that the transfer current value Tf, which is a bias condition applied to the leading edge of the sheet, be set to a higher value than the current value Tg of the normal image area. That is, in the present embodiment, the control unit 500 sets the inter-paper transfer bias condition Tp to a condition equal to the bias condition Tf applied to the sheet leading edge.

  Also for the sheet rear end portion, a current setting value Tb serving as a bias condition to be applied to the sheet rear end portion higher than the image portion is provided in order to cope with a change in electric resistance when the sheet rear end portion passes through the secondary transfer nip. There is a case. Furthermore, since it is desirable that the bias condition applied to the recording sheet P including the sheet front end portion, the sheet rear end portion, and the image portion is set to an appropriate current for each paper type and paper thickness of the recording sheet P, the recording sheet The set current conditions vary for each P paper type and are not uniquely determined.

  Here, a description will be given of bias application at the inter-paper portion when the toner pattern is transferred to the secondary transfer body by the control unit 500. The control unit 500 has a function of obtaining the inter-paper transfer bias condition Tp according to the bias condition applied to the recording sheet P. That is, the control unit 500 sets the current value applied between the sheets as shown in FIG. 2B, for example, according to the current value applied to the leading end of the sheet. As shown in FIG. 2B, the rise time of the high-voltage power supply is shortened by setting the inter-sheet current setting Tp, which is the inter-sheet transfer bias condition, closer to the transfer current value Tf at the leading end of the sheet. Can be shortened.

  Desirably, an intermediate value between the sheet current setting Tb and the transfer current value Tf, which is a bias condition applied to the leading edge of the sheet, is set as the sheet current setting Tp. More preferably, by setting the transfer current value Tf and the sheet interval Tp at the sheet leading end to Tf = Tp, the power supply response time from the sheet interval to the sheet leading end becomes zero as shown in FIG. It is possible to shorten the space between the limit sheets.

  That is, the control unit 500 sets the inter-sheet transfer bias condition Tp by the bias condition Tf applied to the leading end of the sheet and the bias condition Tb applied to the trailing end of the sheet, and the set value is Tp = (Tf + Tb). It calculates by the formula 1 shown by / 2.

  However, as described above, the set values of the bias conditions Tf and Tb applied to the recording sheet P differ depending on the paper type and thickness of the recording sheet P. May be different. In order to solve this problem, a reference current value Ti for detecting the toner density is determined in advance, and before the image formation of the print image is started, for example, a bias is applied as shown in FIG. The density of the toner mark transferred under the secondary transfer bias conditions of the value Ti and the inter-paper bias Tp is individually sampled, and the toner density detection result when the inter-paper bias Tp is applied is corrected based on this sampling data. That's fine.

  That is, the control unit 500 sets a fixed reference bias condition Ti for transferring the toner pattern to the secondary transfer roller 24 (secondary transfer body) in advance, and generates a print image in response to an image formation start signal. Before the image is formed, a toner pattern is formed on the intermediate transfer belt 10 under both the inter-paper transfer bias condition Tp and the fixed reference bias condition Ti, and the density of the toner pattern is detected by the detection unit 310, and the detection result Are sampled as Dp and Di, respectively. Then, the toner pattern after the start of printing is transferred to the secondary transfer roller 24 (secondary transfer body) under the inter-paper transfer bias condition Tp, and the toner density detection result detected by the detection unit 310 is sampled before the start of printing. The density detection result of the toner pattern is corrected by multiplying Di / Dp calculated from the data.

  As in this embodiment, a fixed reference bias condition Ti for transferring the toner pattern to the secondary transfer roller 24 is set in advance in the control unit 500, and before a print image is formed upon receipt of an image formation start signal. Then, a toner pattern is formed on the intermediate transfer belt 10 under both the inter-paper transfer bias condition Tp and the fixed reference bias condition Ti, the density of the toner pattern is detected by the detection means 310, and the detection results are Dp, Di is sampled, the toner pattern after the start of printing is transferred to the secondary transfer roller 24 under the inter-paper transfer bias condition Tp, and the toner density detection result detected by the detecting means 310 is calculated from the sampling data before the start of printing. By changing Di / Dp, the density detection result of the toner pattern is corrected to change the paper gap bias condition at the paper gap Concentration change amount of the toner pattern to be transferred onto the secondary transfer roller 24 due to the can be corrected, thereby enabling more stable density control.

  As in the present embodiment, the control unit 500 executes the initial adjustment operation when the apparatus is started up and the density adjustment control at the end of printing, and also performs at least one of the initial adjustment operation and the density adjustment control. Toner pattern density detection when a regular density adjustment operation such as initial adjustment operation or density adjustment control is performed by transferring the toner pattern onto the secondary transfer roller 24 under the condition Ti and performing density adjustment. The error between the result and the density detection result between papers can be suppressed to a minimum, and more stable density control can be performed.

  As in this embodiment, when the control unit 500 sets the inter-sheet transfer bias condition Tp to a condition equal to the bias condition Tf applied to the leading end of the sheet, the bias condition from the inter-sheet portion to the leading end of the sheet becomes the same, There is no need to consider the rising response of the voltage application means 160, the length between the sheets can be shortened, and the productivity of the apparatus can be further improved.

  As in this embodiment, the control unit 500 sets the sheet-to-sheet transfer bias condition Tp by the bias condition Tf applied to the sheet leading end and the bias condition Tb applied to the sheet trailing end, and the set value is Tp = ( By calculating using Equation 1 shown by (Tf + Tb) / 2, it is possible to minimize the amount of change in the bias condition setting across the trailing edge of the sheet, the gap between the sheets, and the leading edge of the sheet, and shorten the length between the sheets. It is possible to improve the productivity of the apparatus.

  By forming at least the surface of the intermediate transfer belt 10 with an elastic layer as in this embodiment, it is possible to achieve good image quality independent of the surface property of the recording sheet P, and the toner density on the intermediate transfer belt 10 can be reduced. In this case, the density of the toner pattern can be detected with high accuracy on the secondary transfer roller 24. Therefore, the density stability is excellent, and more stable density control is possible.

  In this embodiment, the secondary transfer roller 24 is used as the secondary transfer body, and a toner pattern for density detection is transferred to the surface 24a and the density of this toner pattern is detected. Is not limited to this configuration. For example, the secondary transfer member may be a secondary transfer belt member stretched around a plurality of rollers. In this case, it is preferable to use a belt member made of a polyimide resin having excellent surface gloss from the viewpoint of density detection stability in an optical sensor.

DESCRIPTION OF SYMBOLS 10 Intermediate transfer body 20 (Y, M, C, K) Image carrier 24 Secondary transfer body 24a Surface of secondary transfer body 310 Detection means 500 Control means 600 Transfer device P Recording medium Tp Inter-paper transfer bias condition Ti Fixed reference Bias condition Tf Bias condition applied to the leading end of the recording medium Tb Bias condition applied to the trailing end of the recording medium

JP 2010-44098 A

Claims (4)

An intermediate transfer member to which a toner image on the image carrier is transferred;
By applying a transfer bias, the toner image on the intermediate transfer member is transferred to a recording medium, and the toner pattern for density adjustment formed on the intermediate sheet on the intermediate transfer member is transferred onto the surface of the secondary transfer member. A transfer device for transferring to,
Detection means for detecting the density of the toner pattern transferred to the surface of the secondary transfer member ;
Control means for obtaining an inter-paper transfer bias condition Tp at an inter-paper portion when the toner pattern is transferred to the secondary transfer body according to a bias condition applied to the recording medium ;
The control means includes
A fixed reference bias condition Ti for transferring the toner pattern to the secondary transfer body is set in advance, and before forming a print image upon receiving an image formation start signal, the inter-paper transfer bias condition Tp And the fixed reference bias condition Ti, the toner pattern is formed on the intermediate transfer member, the density of the toner pattern is detected by the detection means, and the detection results are sampled as Dp and Di,
The toner pattern after the start of printing is transferred to the secondary transfer body under the inter-paper transfer bias condition Tp, and the toner density detection result detected by the detecting means is calculated from the sampling data before the start of printing. Multiply Di / Dp to correct the toner pattern density detection result,
The inter-paper transfer bias condition Tp is set higher than the fixed reference bias condition Ti so as to approach the bias condition Tf applied to the leading end portion of the recording medium and the bias condition Tb applied to the trailing end portion of the recording medium. An image forming apparatus. The image forming apparatus according to claim 1.
The control means executes initial adjustment operation when the apparatus is started up and density adjustment control at the end of printing, and at the time of performing at least one of the initial adjustment operation or the density adjustment control, the control means sets the fixed reference bias condition Ti. An image forming apparatus that adjusts density by transferring the toner pattern onto the secondary transfer body . The image forming apparatus according to claim 1 , wherein
The control means sets the inter-paper transfer bias condition Tp by a bias condition Tf applied to the leading end portion of the recording medium and a bias condition Tb applied to the trailing end portion of the recording medium, and the set value is Tp = An image forming apparatus, wherein the image forming apparatus is calculated by Formula 1 represented by (Tf + Tb) / 2 . The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus intermediate transfer member at least the surface is characterized that you have formed of an elastic layer.

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