JP7449488B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

2. Description of the Related Art Conventionally, image forming apparatuses are known that include an intermediate transfer member to which a toner image on an image carrier is transferred, and a secondary transfer member to secondarily transfer the toner image on the intermediate transfer member to a recording medium.
For example, Patent Document 1 describes such an image forming apparatus that includes an optical sensor disposed opposite to a secondary transfer roller (secondary transfer body) and the following control means. This is a control means that forms a toner pattern (toner image for measurement) on a photoreceptor (on an image carrier) at a predetermined timing, transfers it to a secondary transfer roller via an intermediate transfer belt, and detects it with an optical sensor. It is said that the following problems can be solved by transferring the toner pattern to a secondary transfer roller and detecting it on the secondary transfer roller. An intermediate transfer body whose surface is made of an elastic material generally has a low surface gloss, so an optical sensor detects the density of the toner pattern formed on the intermediate transfer body to determine the density of the toner image. When performing control, there is a problem in that sufficient toner concentration detection accuracy cannot be obtained.

It is desired that the device be made smaller.

In order to solve the above problems, the present invention provides an intermediate transfer member to which a toner image on an image carrier is transferred, and a secondary transfer member to secondarily transfer the toner image on the intermediate transfer member to a recording medium. In the image forming apparatus, a measurement transfer body is arranged to face the intermediate transfer body in a surface movement region of the intermediate transfer body from the secondary transfer body toward the image carrier; Optical sensors arranged to face each other and a measurement toner image are formed on the image carrier at a predetermined timing, are transferred to the measurement transfer body via the intermediate transfer body, and are detected by the optical sensor. means, an electrostatic cleaning device disposed opposite to the intermediate transfer member in a surface movement region of the intermediate transfer member from the measurement transfer member to the image carrier, and after the toner image is secondarily transferred; During the period when the residual toner remaining on the surface of the intermediate transfer body faces the measurement transfer body, an electric field is formed on the measurement transfer body to facilitate electrostatic removal of the residual toner by the cleaning device. The present invention is characterized in that it includes a bias applying means for applying a bias .

According to the present invention, it is possible to downsize the device.

A schematic configuration diagram of a printer. FIG. 3 is an explanatory diagram of an example of a toner pattern. FIG. 3 is an explanatory diagram showing an example of a measurement transfer unit. FIG. 7 is an explanatory diagram showing another example of the measurement transfer unit. A block diagram of the electrical equipment section of the printer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic tandem color printer (hereinafter referred to as a printer) as an image forming apparatus will be described below.
FIG. 1 is a schematic configuration diagram of a printer 100. The basic configuration includes an intermediate transfer belt 20 as an intermediate transfer member to which a toner image on a photoreceptor 10 as an image carrier is transferred. The intermediate transfer belt 20 is supported from the back side by a plurality of support rollers 21, 22, 23, and 24, and is also supported from the front side by a support roller 25, so that the movement trajectory of the front side is determined. It also includes a secondary transfer unit 30 that includes a secondary transfer roller 31 as a secondary transfer body that secondary transfers the toner image on the intermediate transfer belt 20 onto a sheet P as a recording medium.

This printer 100 is a device that forms one image from five color toners: special color (hereinafter referred to as S), yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M), cyan (hereinafter referred to as C), and black (hereinafter referred to as K). This printer includes five drum-shaped photoreceptors 1S, 1Y, 1M, 1C, and 1K for each color. Each photoreceptor 1 is rotationally driven so that its surface moves in the same direction as the intermediate transfer belt 20, which moves in the direction indicated by A in the figure while contacting the intermediate transfer belt 20, respectively. S and K do not need to be provided.

The five photoreceptors 1 are arranged in the order of S, Y, M, C, and K from the left in the figure. A toner image is formed on each photoreceptor 1 in the following manner. The photoreceptor 1, which has been uniformly charged in advance by the charging device 11, is exposed and scanned with laser light by the writing unit 26, and an electrostatic latent image is created on the photoreceptor 1. Each electrostatic latent image is developed by a developing device 12 for each color, thereby forming toner images of special colors, yellow, magenta, cyan, and black, on the surface of the photoreceptor 1. Each developing device 12 is supplied with a predetermined amount of toner of each color via a conveyance path from a toner bottle filled with toner.

The toner images on each photoreceptor 1 are sequentially transferred onto the intermediate transfer belt 20 by applying a voltage to the primary transfer roller 13 . The image forming operations for each color are performed at different timings from the upstream side to the downstream side so that the toner images are transferred to the same position on the intermediate transfer belt 20 in an overlapping manner. The toner images formed overlappingly on the intermediate transfer belt 20 are secondarily transferred onto the sheet P that is conveyed to the position of the secondary transfer roller 31 . The sheet P is fed by a paper feed roller 41 and conveyed to a secondary transfer nip between a secondary transfer roller 31 and an intermediate transfer belt 20 .

The sheet P onto which the toner images of each color have been transferred is conveyed to a fixing device 50, where it is thermally fixed and discharged by a paper discharge roller 60. The remaining toner on the photoreceptor 1 is removed by a photoreceptor cleaning device 14. Further, residual toner on the intermediate transfer belt 20 is removed by an intermediate transfer belt cleaning device 70.

A measuring transfer unit 80 is arranged between the secondary transfer roller 31 and the intermediate transfer belt cleaning device 70 and facing the intermediate transfer belt 20 . This is a unit for transferring a toner pattern, which is a toner image for measurement for image density adjustment control, etc. from the intermediate transfer belt 20 and optically detecting the toner pattern. This unit will be detailed later.

FIG. 2 is an explanatory diagram of an example of a toner pattern. FIG. 2A is an explanatory diagram of toner patterns formed on each photoreceptor 1 and transferred to the intermediate transfer belt 20 for image density adjustment. The following toner pattern similar to that described in Patent Document 2 can be employed. The image forming apparatus described in Patent Document 2 transfers a toner pattern for measurement from an intermediate transfer belt 20 to a secondary transfer belt, and detects the toner pattern on the secondary transfer belt with an optical sensor. Gradation patterns Sk, Sm, Sc, Sy, and Ss of each color as toner patterns are formed so as to be lined up at predetermined intervals in the width direction (main scanning direction) of the intermediate transfer belt 20. The gradation pattern of each color consists of ten toner patches having different image densities, for example, with an area of 2 [cm] x 2 [cm], and are formed side by side in the sub-scanning direction (belt movement direction). Based on the result of detecting this pattern for image density adjustment, the developing bias potential, charging potential, etc. are adjusted.

FIG. 2B is an explanatory diagram of toner patterns formed on each photoreceptor 1 and transferred to the intermediate transfer belt 20 for color misregistration correction. The following toner pattern similar to that described in Patent Document 2 can be employed. At one end and the other end in the width direction of the secondary transfer belt 204, a toner pattern consisting of Y, M, C, and K color toner images called a chevron patch PV as shown in FIG. 2(b) is formed. Form an image for color shift detection. It is preferable to add S color. The chevron patches PV are a group of line patterns arranged at a predetermined pitch in the belt movement direction, which is the sub-scanning direction, in an attitude inclined by about 45 degrees from the main-scanning direction. The amount of adhered chevron patch PV is, for example, about 0.3 [mg/cm2].

Image density adjustment and color misregistration correction that involve formation and detection of such toner patterns are performed at a predetermined timing, such as when the power is turned on or every time a predetermined number of sheets are printed.

In this embodiment, a measurement transfer body that transfers a toner pattern formed on the photoreceptor 1 and transferred onto the intermediate transfer belt 20 at a predetermined timing for image density adjustment, color misregistration correction, etc., and an optical sensor are used. The measurement transfer unit 80 is equipped with a measurement transfer unit 80. The measurement transfer unit 80 is arranged at a position opposite to the intermediate transfer belt 20 in the area where the surface of the intermediate transfer belt 20 moves from the secondary transfer roller 31 toward the photoreceptor 1S, which is the most upstream image carrier. In other words, this is a surface movement area of the intermediate transfer belt 20 that is downstream of the portion facing the secondary transfer roller 31 and upstream of the portion facing the photoreceptor 1 . In the illustrated example, it is arranged between the secondary transfer roller 31 and the intermediate transfer belt cleaning device 70.

In Patent Document 1, a toner pattern is transferred from an intermediate transfer member with low surface gloss and insufficient toner density detection accuracy of a toner pattern for measurement to a secondary transfer roller, and the toner pattern is transferred on the secondary transfer roller. Instead of detecting the toner pattern with an optical sensor, the toner pattern is transferred to a measurement transfer body provided in the surface movement area of the intermediate transfer belt 20 downstream of the area facing the secondary transfer roller and upstream of the area facing the photoreceptor. The toner pattern is detected on the measurement transfer body using an optical sensor.

According to this, as image forming apparatuses become smaller, it becomes difficult to arrange optical sensors around the secondary transfer roller due to the smaller diameter of the secondary transfer roller and constraints on the surrounding layout. By utilizing the extra space in the surface movement area of the intermediate transfer belt 20 downstream of the secondary transfer roller facing portion and upstream of the photoreceptor facing portion, it is possible to detect toner patterns with high accuracy. As the measurement transfer body, one is used that has surface optical characteristics that allow the optical sensor to detect toner density patterns with better accuracy than the intermediate transfer body.

FIG. 3 is an explanatory diagram showing an example of the measurement transfer unit 80. 2 is an enlarged view of the range from the secondary transfer unit 30 to the intermediate transfer belt cleaning device 70 in the printer 100 of FIG. 1. FIG. The measuring transfer unit 80 in this example includes a measuring transfer roller 81 as a measuring transfer member disposed opposite to the intermediate transfer belt 20. The measuring transfer roller 81 is arranged so as to be in contact with the intermediate transfer belt 20, and is driven so that the surfaces thereof move in the same direction at the opposing portions. As the measuring transfer body, a belt member can be used instead of a roller. As the surface material of the measurement transfer body, polyimide, which is also an example of the material of the secondary transfer belt in Patent Document 2, can be used. To electrostatically transfer a toner pattern, the base layer is a conductor for a roller, the base layer is a conductor for a belt, or the backup roller is a conductor. Apply voltage to these conductors. A configuration similar to that of a photoreceptor can also be adopted from the optical specification of the surface.

The measuring transfer unit 80 also includes an optical sensor unit 82 arranged opposite to the measuring transfer roller 81 . The optical sensor unit 82 includes an optical sensor consisting of a pair of light receiving and emitting elements for each color, corresponding to the position in the width direction of each toner pattern shown in FIG. 2(a). For example, a removal blade 83 is provided to remove toner from the surface of the measurement transfer roller 81 after being measured by the optical sensor unit 82 . A screw 84 is also provided to collect the removed toner. A case 85 for housing these items is also provided.

A measurement power supply circuit 87 is connected to the measurement transfer roller 81 . A counter roller 86 is arranged at a location facing the measurement transfer roller 81 with the intermediate transfer belt 20 interposed therebetween. This counter roller 86 is connected to ground. The measurement power supply circuit 87 applies a bias to form an electric field for electrostatically transferring the toner image on the intermediate transfer belt 20 during a period when the measurement toner pattern is transferred to the measurement transfer roller 81. do. Assuming that the normal charge polarity of the toner used for development in the developing device 12 is negative, a positive voltage is applied.

The secondary transfer unit 30 in the example shown in FIG. 3 includes a secondary transfer cleaning blade 32 as a secondary transfer cleaning means for removing residual toner on the secondary transfer roller 31, a lubricant application member 33, a removed toner collection screw 34, A secondary transfer unit case 35 is provided. A cleaning brush roller may be provided instead of or in addition to the secondary transfer cleaning blade 32. The secondary transfer roller 31 is grounded, and a bias for forming a secondary transfer electric field is applied from the secondary transfer bias power supply circuit 36 to the support roller 23 that opposes the secondary transfer roller 31 with the intermediate transfer belt 20 in between. There is. During the period when the toner image of the normal image is secondarily transferred onto the sheet P, if the normally charged toner is negative, a negative bias is applied.

During the period when the toner pattern for measurement on the intermediate transfer belt 20 faces the secondary transfer roller 31, the toner pattern is allowed to pass through the portion facing the secondary transfer roller 31 as it is. To this end, as shown by arrow B in FIG. 1, the secondary transfer roller 31 is made movable between a transfer position where the toner image is transferred to the sheet P and a retracted position where it is retracted from the transfer position.

For example, only the secondary transfer roller 31 may be configured to be movable, or the entire secondary transfer unit may be configured to be movable. For this purpose, a known mechanism for separating the secondary transfer member for preventing shock jitter can be used, with modifications such as increasing the amount of separation as necessary. Such a configuration corresponds to a moving means for moving the secondary transfer body. Then, it controls the drive of a separation drive motor that rotationally drives, for example, a cam of the separation mechanism. During the period when the toner pattern for measurement passes through the opposing portion, the driving control is performed so that the toner pattern takes the retracted position.

Instead of or in addition to causing the secondary transfer roller 31 to take the retracted position as described above, the secondary transfer bias power supply circuit 36 may be configured as follows. That is, between the intermediate transfer belt 20 and the secondary transfer roller 31, there is an electric field in a direction that directs the toner image on the intermediate transfer belt 20 toward the secondary transfer roller 31, and an electric field in the opposite direction. is configured as an electric field forming means that can be selectively formed. Then, the period during which the toner pattern for measurement passes through the portion facing the secondary transfer roller 31 is controlled so as to form an electric field in the opposite direction. The secondary transfer bias power supply circuit 36 in FIG. 3 schematically shows that bias can be selectively applied using a changeover switch.

The intermediate transfer belt cleaning device 70 shown in FIG. 3 includes a cleaning member 71, a removed toner collection screw 72, and an intermediate transfer belt cleaning device case 73. A backup roller 74 is provided on the back side of the intermediate transfer belt 20 facing the cleaning member 71. The cleaning member may be one that performs mechanical cleaning or electrostatic cleaning. You can also serve both together.

FIG. 4 is an explanatory diagram showing an example of the measurement transfer unit 80. The difference from the measurement transfer unit 80 in the example of FIG. 3 is that in the example of FIG. This is a point that brings together the following. The components of the measurement transfer unit 80 and the intermediate transfer belt cleaning device 70 are arranged in a common case 90. For example, a pair of side plates that hold both ends of each component in the width direction may also be used in common, so that the whole can be assembled into the printer 100, or only the case 90 may be used in common. In any case, by sharing parts, it is possible to downsize the device.

The structure of the intermediate transfer belt cleaning device 70 shown in FIG. 4 includes two sets of cleaning units each having an electrostatic cleaning member that performs electrostatic cleaning. The configuration is basically the same as the two sets of cleaning units in the cleaning device described in Patent Document 2, and the applied voltage for electrostatic cleaning is also the same.

Specifically, each cleaning unit includes cleaning brush rollers 71 a and 71 b that are electrostatic cleaning members that scrape off transfer residual toner from the surface of the intermediate transfer belt 20 . In addition, collection rollers 75a and 75b are collection members that rotate while contacting cleaning brush rollers 71a and 71b and collect the transfer residual toner from the brush rollers, and collection removal that scrapes the transfer residual toner from the surfaces of the collection rollers 75a and 75b. It has scraping blades 76a and 76b which are members. It also includes trays 73a and 73b for receiving the transfer residual toner scraped off from the collection rollers 75a and 75b, and conveyance screws 72a and 72b for discharging the toner to the outside of the case 90.

Of the two cleaning units, in the cleaning unit located on the upstream side, a first cleaning bias of negative polarity, which is the same polarity as the normal charging polarity of the toner, is applied to the cleaning brush roller 71a by the cleaning bias power supply circuit 77a. Ru. As a result, among the transfer residual toner, the oppositely charged toner that is charged to the opposite polarity (positive polarity) to the normal charging polarity is electrostatically captured in the brush of the cleaning brush roller 71a. A collection bias of negative polarity, which is larger than the above-mentioned cleaning bias, is applied to the collection roller 75a by a collection power supply 78a. Note that the cleaning brush roller 71a injects a negative polarity charge, which is a normal charging polarity, to the oppositely charged toner, which is charged with a polarity opposite to the normal charging polarity on the surface of the intermediate transfer belt 20, to reversely charge the toner. It also functions as a polarity control means for returning the toner particles to their normal polarity.

In the cleaning unit located on the downstream side, a cleaning bias with a positive polarity opposite to the normal charging polarity of the toner is applied to the cleaning brush roller 71b by a cleaning bias power supply circuit 77b. As a result, the normally charged toner among the transfer residual toner is electrostatically captured within the brush of the cleaning brush roller 71a. A recovery bias of positive polarity, which is larger than the above-mentioned cleaning bias, is applied to the recovery roller 75b by a recovery power source 78b.

Grounded backup rollers 74a and 74b are provided on the back surface of the intermediate transfer belt 20 facing the two cleaning brush rollers 71a and 71b. Note that reference numeral 85a in the figure is a tray that receives transfer residual toner scraped off from the measurement transfer roller 81 by the measurement transfer unit.

In the example of FIG. 4, the measurement transfer roller 81 may perform the following function similarly to the cleaning brush roller 71a in the upstream cleaning unit. A polarity that returns the reversely charged toner particles to the normal polarity by injecting a negative charge, which is the normal charging polarity, into the oppositely charged toner particles that are charged to the opposite polarity to the normal charging polarity on the surface of the intermediate transfer belt 20. It functions as a control means. It can also be said that the charging polarity of toner containing both positive and negative electrodes is unified.

Specifically, during a period when the normal secondary transfer residual toner faces the measurement transfer roller 81, a bias is applied to the measurement transfer roller 81 to inject negative polarity charge, which is a normal charging polarity, into the secondary transfer residual toner. to be applied. In this case, the measurement transfer roller 81 collects the oppositely charged toner from the intermediate transfer belt 20 in the same way as the cleaning brush roller 71a.

If the number of cleaning units is one set instead of two and the measurement transfer roller 81 is to perform the above function, one set of cleaning units will clean the regularly charged toner in the same way as the downstream cleaning unit. The unit configuration is as follows. The configuration of the cleaning unit in Patent Document 2 is based on the following device configuration. Most of the secondary transfer residual toner input to the intermediate transfer belt cleaning device (approximately 80%) has a polarity opposite to the normal charging polarity of the toner (positive polarity) due to charge injection at the primary transfer nip and secondary transfer nip. It is charged toner.

Unlike such a device configuration, if the proportion of secondary transfer residual toner is higher than that of normally charged toner, the bias applied to the measurement transfer roller 81 by the measurement power supply circuit 87 is based on this assumption. Set. The point is to apply a bias to form an electric field that facilitates electrostatic removal in downstream electrostatic cleaning. The measurement power supply circuit 87 uses a cleaning device to electrostatically remove residual toner remaining on the surface of the intermediate transfer body after the toner image has been secondarily transferred, while the residual toner remains on the surface of the intermediate transfer body faces the measurement transfer body. This corresponds to a bias applying means that applies a bias to the measurement transfer body so as to form an electric field that facilitates the measurement. Alternatively, the voltage may not be applied during the period in which the secondary transfer residual toner faces, or the toner may be separated from the intermediate transfer belt 20.

FIG. 5 is a block diagram of the electrical components of the printer 100 when the configuration of the intermediate transfer belt cleaning device shown in FIG. 4 is adopted. The control unit 200 is a controller that controls the entire printer 100 of the embodiment shown in FIG. 1, and includes a microcomputer including a CPU, ROM, RAM, input/output circuits, and the like. The control unit 200 drives and controls each unit shown in FIG. 1 to execute image formation (printing) processing on the sheet P during printing. Further, when the power is turned on or every time a predetermined number of images are formed, processing for adjusting image quality such as image density adjustment and color shift correction is also performed.

When the control unit 200 brings the display unit 201, intermediate transfer belt drive circuit 27, secondary transfer bias power supply circuit 36, measurement power supply circuit 87, cleaning bias power supply circuits 77a and 77b, and the secondary transfer roller 31 into contact with and separates from each other, The contact/separation motor drive circuit 37 and other controlled parts 202 are also controlled. A detection signal from the optical sensor unit 82 is input to this control section 200 . The control unit 200 functions as a control unit that forms a measurement toner image on the image carrier at a predetermined timing, transfers it to the measurement transfer member via an intermediate transfer member, and detects it with an optical sensor. .

In the above embodiments, the secondary transfer body has a roller shape, but it can also be applied to a belt shape. This is effective in cases where it is difficult to arrange an optical sensor due to the belt shape due to the layout around the belt, or where the material of the belt is such that it is difficult to detect toner images with an optical sensor.

1: Photoreceptor 11: Charging device 12: Developing device 13: Primary transfer roller 14: Photoreceptor cleaning device 20: Intermediate transfer belt 21: Support roller 22: Support roller 23: Support roller 24: Support roller 25: Support roller 26: Writing unit 27 : Intermediate transfer belt drive circuit 30 : Secondary transfer unit 31 : Secondary transfer roller 32 : Secondary transfer cleaning blade 33 : Lubricant application member 34 : Removed toner collection screw 35 : Secondary transfer unit case 36 : 2 Next transfer bias power supply circuit 37 : Contact/separation motor drive circuit 41 : Paper feed roller 50 : Fixing device 60 : Paper discharge roller 70 : Intermediate transfer belt cleaning device 71 : Cleaning member 71a : Cleaning brush roller 71b : Cleaning brush roller 72 : Collection Screw 72a: Conveyance screw 72b: Conveyance screw 73: Intermediate transfer belt cleaning device case 73a: Tray 73b: Tray 74: Backup roller 74a: Backup roller 74b: Backup roller 75a: Collection roller 75b: Collection roller 76a: Scraping blade 76b: Scraping blade 77a: Cleaning bias power supply circuit 77b: Cleaning bias power supply circuit 78a: Recovery power supply 78b: Recovery power supply 80: Measurement transfer unit 81: Measurement transfer roller 82: Optical sensor unit 83: Removal blade 84: Screw 85: Case 86: Opposing roller 87: Measuring power supply circuit 90: Case 100: Printer 200: Control section 201: Display section 202: Controlled section 204: Secondary transfer belt P: Sheet PV: Chevron patch Sc: Gradation pattern Sk: Gradation Tone pattern Sm: Tone pattern Ss: Tone pattern Sy: Tone pattern

Japanese Patent Application Publication No. 2010-265282 Japanese Patent Application Publication No. 2016-142879

Claims (7)

an intermediate transfer member to which the toner image on the image carrier is transferred;
An image forming apparatus comprising: a secondary transfer member that secondarily transfers the toner image on the intermediate transfer member to a recording medium;
a measurement transfer member disposed opposite to the intermediate transfer member in a surface movement area of the intermediate transfer member from the secondary transfer member to the image carrier;
an optical sensor arranged opposite to the measuring transfer body;
a control unit that forms a measurement toner image on the image carrier at a predetermined timing, transfers it to the measurement transfer body via the intermediate transfer body, and detects it with the optical sensor;
an electrostatic cleaning device disposed opposite to the intermediate transfer member in a surface movement area of the intermediate transfer member from the measurement transfer member to the image carrier;
During a period when residual toner remaining on the surface of the intermediate transfer body after the toner image has been secondarily transferred faces the measurement transfer body, an electric field is formed to facilitate electrostatic removal of the residual toner by the cleaning device. bias applying means for applying a bias to the measurement transfer body so as to
An image forming apparatus characterized by being provided with . The image forming apparatus according to claim 1 ,
An image forming apparatus characterized in that the cleaning device and the measurement transfer body are provided in a common case facing the intermediate transfer body. an intermediate transfer member to which the toner image on the image carrier is transferred;
An image forming apparatus comprising: a secondary transfer member that secondarily transfers the toner image on the intermediate transfer member to a recording medium;
a measurement transfer member disposed opposite to the intermediate transfer member in a surface movement area of the intermediate transfer member from the secondary transfer member to the image carrier;
an optical sensor arranged opposite to the measuring transfer body;
a control unit that forms a measurement toner image on the image carrier at a predetermined timing, transfers it to the measurement transfer body via the intermediate transfer body, and detects it with the optical sensor;
a cleaning device disposed opposite to the intermediate transfer body in a surface movement area of the intermediate transfer body from the measurement transfer body toward the image carrier ;
established,
An image forming apparatus characterized in that the cleaning device and the measurement transfer body are arranged in a common case facing the intermediate transfer body. The image forming apparatus according to any one of claims 1 to 3,
providing a moving means for moving the secondary transfer body between a transfer position where the toner image is transferred to the recording medium and a retreat position where the toner image is evacuated from the transfer position;
The image forming apparatus is characterized in that the control means controls the moving means to take the retracted position during a period in which the measurement toner image passes through a portion facing the secondary transfer body. The image forming apparatus according to any one of claims 1 to 4 ,
An electric field is selectively applied between the intermediate transfer body and the secondary transfer body in a direction that directs the toner image on the intermediate transfer body toward the secondary transfer body and an electric field in the opposite direction. Providing an electric field forming means that can be formed,
The control means controls the electric field forming means so as to form an electric field in the opposite direction during a period in which the measurement toner image passes through a portion facing the secondary transfer body. Forming device. The image forming apparatus according to any one of claims 1 to 5 ,
An image forming apparatus characterized in that the measurement toner image is electrostatically transferred to the measurement transfer body. The image forming apparatus according to any one of claims 1 to 6 ,
An image forming apparatus comprising a cleaning device for removing the measurement toner image detected by the optical sensor from the measurement transfer body.

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