JP7177984B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

An image forming apparatus calculates the toner charge amount ( charge per unit weight) is derived (see, for example, Patent Document 1).

JP 2010-19969 A

FIG. 7 is a diagram for explaining a general relationship between toner charge amount and toner density measurement value.

In general, with the optical toner density sensor as described above, the sensor output value saturates when the height of the toner image (that is, the height of the toner stack) increases to some extent. On the other hand, as shown in FIG. 7, the lower the toner charge amount, the higher the height of the transferred toner image. Therefore, in the image forming apparatus described above, when the toner charge amount is low, the sensor output value is saturated, and there is a possibility that the measurement error of the toner density (corresponding to the toner adhesion density described above) increases. If the measurement error of the toner concentration is large, the estimation error of the toner weight derived from the toner concentration also becomes large, so the measurement error of the toner charge amount also becomes large.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of reducing toner charge amount measurement errors.

An image forming apparatus according to the present invention includes a photosensitive drum, a developing device that develops a toner image by attaching toner to an electrostatic latent image on the photosensitive drum, and an image carrier that carries the toner image. a transfer roller for transferring the toner image from the photoreceptor drum to the image carrier; a density sensor that optically detects the density of the toner patch image; A toner charge amount specifying unit that specifies the toner charge amount, and a control unit that controls the transfer current of the transfer roller.

In the calibration, the controller (a) sets the initial value of the toner charge amount measurement mode to the first mode, and (b1) uses the density sensor when the mode switching condition is not satisfied. (b2) if the mode switching condition is satisfied, change the toner charge amount measurement mode to the second mode, and use the density sensor; Then, the density of the toner patch image transferred in the second mode is measured.

In the first mode, the controller sets the transfer current of the transfer roller when transferring the toner patch image to be the same as the transfer current of the transfer roller when transferring the print image. and the control section makes the transfer current of the transfer roller during transfer of the toner patch image higher than the transfer current of the transfer roller during transfer of the print image.

The mode switching condition is that the toner charge amount specified in the current calibration is out of the allowable range set based on the toner charge amount specified in the previous calibration.

According to the present invention, it is possible to obtain an image forming apparatus that reduces the measurement error of the toner charge amount.

The above and other objects, features and advantages of the present invention will become further apparent from the following detailed description together with the accompanying drawings.

FIG. 1 is a side view showing the mechanical internal configuration of an image forming apparatus according to an embodiment of the invention. FIG. 2 is a block diagram showing part of the electrical configuration of the image forming apparatus shown in FIG. FIG. 3 is a diagram showing an example of a toner patch image. FIG. 4 is a diagram for explaining the relationship between the toner charge amount and the toner density measurement value during calibration in the image forming apparatus shown in FIGS. 1 and 2. In FIG. FIG. 5 is a diagram for explaining switching of the toner charge amount measurement mode during calibration in the image forming apparatus shown in FIGS. FIG. 6 is a flowchart for explaining calibration in the image forming apparatus shown in FIGS. 1 and 2. FIG. FIG. 7 is a diagram for explaining a general relationship between toner charge amount and toner density measurement value.

Embodiments of the present invention will be described below based on the drawings.

Embodiment 1.

FIG. 1 is a side view showing the mechanical internal configuration of an image forming apparatus according to an embodiment of the invention. This image forming apparatus is an apparatus having an electrophotographic printing function, such as a printer, a facsimile machine, a copier, a multifunction machine, or the like.

The image forming apparatus of this embodiment has a tandem color developing device. This color developing device has photosensitive drums 1a to 1d, an exposure device 2 and developing devices 3a to 3d. The photoreceptor drums 1a-1d are four-color photoreceptors of cyan, magenta, yellow and black, and electrostatic latent images are formed on the photoreceptor drums 1a-1d. The exposure device 2 is a device that irradiates the photosensitive drums 1a to 1d with laser light to form an electrostatic latent image. The exposure device 2 has a laser diode as a light source of laser light, and optical elements (lenses, mirrors, polygon mirrors, etc.) for guiding the laser light to the photosensitive drums 1a to 1d.

The developing devices 3a to 3d attach toner in the toner cartridges to the electrostatic latent images on the photosensitive drums 1a to 1d to develop toner images. The photoreceptor drum 1a and developing device 3a develop magenta, the photoreceptor drum 1b and developing device 3b perform cyan development, and the photoreceptor drum 1c and developing device 3c perform yellow development. , the photosensitive drum 1d and the developing device 3d, black development is performed.

The intermediate transfer belt 5 is an annular image bearing member that contacts the photoreceptor drums 1a to 1d and transfers and carries the toner images on the photoreceptor drums 1a to 1d. The intermediate transfer belt 5 is stretched around a driving roller 6a and a tension roller 6b, and is rotated in the direction from the contact position with the photosensitive drum 1a to the contact position with the photosensitive drum 1d by the driving force from the driving roller 6a. To go.

The secondary transfer roller 7 brings the conveyed print sheet (print paper, etc.) into contact with the intermediate transfer belt 5 and secondarily transfers the toner image on the intermediate transfer belt 5 to the print sheet. The print sheet on which the toner image is secondarily transferred is conveyed to a fixing device (not shown), and the toner image is fixed on the print sheet.

The density sensor 8 is a reflective optical type that irradiates the intermediate transfer belt 5 with light, receives the reflected light (for example, regular reflected light and diffuse reflected light), and outputs an electric signal corresponding to the amount of the received reflected light. sensor. The density sensor 8 optically detects the density of the toner patch image on the intermediate transfer belt 5 after the toner patch image as the toner image for calibration is primarily transferred to the intermediate transfer belt 5 .

The primary transfer rollers 9a to 9d are arranged to face the photoreceptor drums 1a to 1d, respectively, with the intermediate transfer belt 5 interposed therebetween, and transfer the toner images on the photoreceptor drums 1a to 1d from the photoreceptor drums 1a to 1d. Primary transfer is performed onto the intermediate transfer belt 5 .

FIG. 2 is a block diagram showing part of the electrical configuration of the image forming apparatus shown in FIG. As shown in FIG. 2, the image forming apparatus shown in FIG. 1 further includes a controller 31, a development bias circuit 32, a transfer bias circuit 33, and a storage device .

The controller 31 electrically controls each section in the image forming apparatus. The controller 31 includes an ASIC (Application Specific Integrated Circuit), a microcomputer, etc., and operates as various processing units that perform one or both of hardware processing and software processing.

The developing bias circuit 32 applies a developing bias having a voltage designated by a control signal between the developing device 3a and the photosensitive drum 1a. The development bias circuit 32 includes a development current detection section 32a for detecting a development current value (direct current value) during development of the toner patch image.

A transfer bias circuit 33 applies a primary transfer bias having a voltage designated by a control signal between the photosensitive drum 1a and the primary transfer roller 9a. The transfer bias circuit 33 includes a transfer current detector 33a for detecting a transfer current value during primary transfer of the toner patch image.

The storage device 34 is a non-volatile storage device such as flash memory, and stores history data 34a. The history data 34a includes the toner charge amount specified in the previous calibration, the environmental measurement value, the average stirring time of the toner in the developing devices 3a to 3d, and the like.

Here, the environmental measurement values are temperature, humidity, etc. measured by a sensor (not shown). The average stirring time is the average value of the toner stirring operation time for the toner staying in the developing devices 3a to 3d at that time.

Here, the controller 31 operates as a control section 41 and a toner charge amount specifying section 42 .

The control unit 41 controls the mechanical configuration, the development bias circuit 32, the transfer bias circuit 33, and the like shown in FIG. 1 to execute printing and calibration.

In calibration, the control unit 41 controls the photosensitive drum 1a, the exposure device 2, the development device 3a, the primary transfer roller 9a, and the like to form a toner patch image (a toner image of a predetermined shape with a constant density) and a primary transfer roller 9a. Perform transcription.

FIG. 3 is a diagram showing an example of a toner patch image. For example, as shown in FIG. 3, a plurality of toner patch images 21 to 25 having different densities are transferred to the intermediate transfer belt 5 . The toner patch images 21 to 25 are transferred to positions corresponding to the arrangement position of the density sensor 8 in the width direction of the intermediate transfer belt 5 .

Note that the densities of the toner patch images 21 to 25 are expressed by the printing rate (that is, toner dot density). That is, in the toner patch images 21 to 25, pixel positions with toner dots and pixel positions without toner dots are mixed.

The control unit 41 supplies control signals to the development bias circuit 32 to control the development bias and development current, and supplies control signals to the transfer bias circuit 33 to control the primary transfer bias and transfer current.

In particular, in the calibration, the controller 41 (a) sets the initial value of the toner charge amount measurement mode to the first mode (normal mode), and (b1) uses the density sensor 8 when the mode switching condition is not satisfied. Then, the density of the toner patch image 2i (here, i=1, . . . , 5) transferred in the first mode is measured. is changed to the second mode (high precision mode), and the density sensor 8 is used to measure the density of the toner patch image 2i transferred in the second mode.

In the first mode, the controller 41 makes the transfer current of the primary transfer roller 9a for transferring the toner patch image the same as the transfer current for the primary transfer roller 9a for transferring the normal print image.

In the second mode, the controller 41 makes the transfer current of the primary transfer roller 9a during transfer of the toner patch image 2i higher than the transfer current of the primary transfer roller 9a during transfer of the print image. At that time, the control unit 41 controls the transfer current of the primary transfer roller 9a during the transfer of the print image so that the height of the toner patch image 2i becomes lower than the transfer current of the primary transfer roller 9a. It controls the transfer current of the next transfer roller 9a.

FIG. 4 is a diagram for explaining the relationship between the toner charge amount and the toner density measurement value during calibration in the image forming apparatus shown in FIGS. 1 and 2. In FIG. As shown in FIG. 4, even under conditions where the stacking height of the toner patch image 2i is high (such as when the toner charge amount is low), the transfer current value is controlled to be high. of toner is dispersed on the intermediate transfer belt 5, and the height of the toner patch image 2i is reduced. Therefore, saturation of the sensor output value of the density sensor 8 is less likely to occur, and the measurement error of the density measurement value is reduced. As a result, the measurement error of the toner weight M and the error of the toner charge amount Q/M are also reduced.

FIG. 5 is a diagram for explaining switching of the toner charge amount measurement mode during calibration in the image forming apparatus shown in FIGS. As shown in FIG. 5, in this calibration, when the mode switching condition is met after the toner charge amount is measured in the first mode, the toner charge amount is measured in the second mode and then measured in the first mode. The toner charge measured in the second mode is used instead of the toner charge.

Alternatively, in the current calibration, if the mode switching condition is met after the toner charge amount is measured in the first mode, the toner charge amount measured in the first mode is used, and in the next calibration, the toner charge amount is measured in the first mode. The toner charge amount may be measured in two modes.

Here, the functions of the controller 31 for the photosensitive drum 1a, the developing device 3a, and the primary transfer roller 9a will be described, but other photosensitive drums 1b to 1d, the developing devices 3b to 3d, and the primary transfer roller The function of the controller 31 for 9b-9d is similar.

In both the first mode and the second mode, the toner charge amount specifying section 42 determines the development current value detected by the development current detection section 32a and the density detected by the density sensor 8 for the toner patch image 2i. It is specified as the toner charge amount of the toner based on the measured value.

Specifically, the toner charge amount specifying unit 42 derives the charge Q of the toner used for development from the development current value, and calculates the weight M of the toner used for development as the density measurement value of the toner patch images 21 to 25. and the ratio Q/M between the two is derived as the toner charge amount.

Note that the correspondence between the development current value and the charge Q and the correspondence between the density measurement value and the charge Q are specified in advance by experiments or the like, and are implemented in the toner charge amount specifying unit 42 as a table, a conversion formula, or the like. Then, the toner charge amount specifying unit 42 derives the charge Q from the development current value and derives the weight M from the density measurement value using the table, conversion formula, and the like.

Here, the above mode switching conditions will be described.

The mode switching condition described above is that the toner charge amount specified in the current calibration falls outside the allowable range set based on the toner charge amount specified in the previous calibration. Note that the toner charge amount specified in the previous calibration is specified based on the history data 34a.

In other words, since the actual toner charge amount does not change abruptly, when the measured value of the toner charge amount changes abruptly, it is conceivable that the measurement error of the toner weight (that is, the toner density) has increased. Therefore, the toner charge amount measurement mode is switched.

This allowable range (that is, at least one of the upper limit threshold and the lower limit threshold) is defined by (a) the upper limit of the difference between the toner charge amount specified in the current calibration and the toner charge amount specified in the previous calibration; (b) at least one of the upper limit and the lower limit of the ratio between the toner charge amount specified in the current calibration and the toner charge amount specified in the previous calibration; and (c ) between the toner charge amount specified in this calibration and the toner charge amount specified in the previous calibration (that is, the difference between the two is the at least one of the upper limit value and the lower limit value obtained by dividing by the elapsed time of ).

Furthermore, this allowable range may be adjusted based on the environmental measurement values measured in the current calibration and the environmental measurement values measured in the previous calibration.
In that case, the environmental measurement values measured in the previous calibration are identified based on the historical data 34a, for example, the environmental measurement values measured in the current calibration and the environmental measurement values measured in the previous calibration. The allowable range is adjusted so that the amount of change in the toner charge amount due to the environmental change is allowed based on the difference, ratio, temporal slope, and the like.

For example, when the humidity increases, the charge on the toner particles decreases, so the amount of toner required to satisfy the total charge of the toner corresponding to the developing bias increases, and the weight of the toner used for development increases. Therefore, fluctuations in the measured toner charge due to humidity changes are appropriate.

Furthermore, this allowable range is based on the average stirring time of the toner in the developing device 3a at the time of the current calibration and the average stirring time of the toner in the developing device 3a at the time of the previous calibration. It may be adjusted. In that case, the average stirring time at the previous calibration is specified based on the history data 34a. For example, the average stirring time at the current calibration and the average stirring time at the previous calibration The allowable range is adjusted so that the amount of change in the toner charge amount due to the difference in the stirring time is allowed based on the difference, the ratio, the temporal inclination, and the like.

If the toner consumption is slow, the toner stays in the developing devices 3a to 3d for a long time, resulting in a long average stirring time. On the other hand, when the toner is consumed quickly, the toner is consumed in the developing devices 3a to 3d in a short time, so the average stirring time is shortened. When the average stirring time is long, the external additive is buried in the toner body, which changes the charging characteristics of the toner. Therefore, the variation in the measured value of the toner charge amount due to the difference in the average stirring time is appropriate.

Next, the operation of the image forming apparatus will be described.

In a normal print operation (that is, when printing an image designated by the user), the control unit 41 controls the photosensitive drums 1a to 1d, the exposure device 2, the development devices 3a to 3d, the primary transfer rollers 9a to 9d, and the like. Under control, formation and primary transfer of a toner image corresponding to an image designated by the user are executed.

At this time, the controller 41 controls the transfer current value to a reference value that does not cause the transferred toner to scatter on the intermediate transfer belt 5 so that the image quality does not deteriorate.

Then, the control unit 41 causes the secondary transfer roller 7 to secondarily transfer the toner image on the intermediate transfer belt 5 onto the print sheet. After the secondary transfer, the toner image is fixed on the print sheet by a fixing device (not shown). After that, the print sheet is discharged as printed matter.

In this manner, a normal print operation is performed.

The control unit 41 performs calibration automatically at a predetermined timing or when manually instructed by a user or a service person.

FIG. 6 is a flowchart for explaining calibration in the image forming apparatus shown in FIGS. 1 and 2. FIG.

When the calibration is started (step S1), the control section 41 first uses the toner charge amount specifying section 42 to measure the toner charge amount in the first mode (step S2).

Next, the control unit 41 specifies a mode switching condition based on the history data 34a (step S3), and determines whether the mode switching condition is satisfied for the toner charge amount measured in step S2 (step S4). ).

When the mode switching condition is satisfied, the control unit 41 uses the toner charge amount specifying unit 42 to measure the toner charge amount in the second mode, and uses this toner charge amount instead of the toner charge amount in the first mode. (step S5). Note that if the mode switching condition is not satisfied, the controller 41 does not measure the toner charge amount in the second mode.

The control unit 41 updates the currently set toner charge amount with the toner charge amount specified in this calibration, and uses the updated toner charge amount to adjust the process such as the voltage value of the developing bias. Update the conditions and apply them to subsequent normal print operations.

Then, the controller 41 updates the history data 34a with the toner charge amount measured in the first mode or the second mode (step S6). At this time, the environment measurement value, average stirring time, etc. in the history data 34a are also updated with the current environment measurement value and average stirring time, if necessary.

A specific measurement operation will now be described.

The control unit 41 controls the photosensitive drums 1a to 1d, the exposure device 2, the development devices 3a to 3d, the primary transfer rollers 9a to 9d, etc., and executes the formation and primary transfer of the toner patch image 2i. At that time, the control unit 41 obtains the measured value of the development current for the toner patch image 2i, and performs the primary transfer of the toner patch image 2i with the transfer current value according to the toner charge amount measurement mode.

The toner patch image 2i thus transferred onto the intermediate transfer belt 5 moves as the intermediate transfer belt 5 advances. When the toner patch image 2i reaches the measurement position of the density sensor 8, the density sensor 8 detects the toner A sensor signal corresponding to the density of the patch image 2i is output. Control unit 41 receives the sensor signal as a sensor output value corresponding to the density of toner patch images 21-25.

Then, the toner charge amount specifying section 42 specifies the toner charge amount based on the development current value and density measurement value of each toner patch image 2i.

Note that when a plurality of toner patch images 21 to 25 having different densities (actual densities) are used, for example, the average value of the toner charge amounts obtained for the plurality of toner patch images 21 to 25 is the amount of toner. It is specified as the toner charge amount.

As described above, according to the first embodiment, in the calibration, the control unit 41 (a) sets the initial value of the toner charge amount measurement mode to the first mode, and (b1) satisfies the mode switching condition. If not, the density sensor 8 is used to measure the density of the toner patch image 2i transferred in the first mode, and (b2) if the mode switching condition is satisfied, the toner charge amount measurement mode is changed to the second mode. Then, using the density sensor 8, the density of the toner patch image 2i transferred in the second mode is measured. In the first mode, the controller 41 sets the transfer current of the primary transfer roller 9a when transferring the toner patch image 2i to be the same as the transfer current of the primary transfer roller 9a when transferring the print image. In the mode, the controller 41 makes the transfer current of the primary transfer roller 9a during transfer of the toner patch image 2i higher than the transfer current of the primary transfer roller 9a during transfer of the print image. The mode switching condition is that the toner charge amount specified in the current calibration is outside the allowable range set based on the toner charge amount specified in the previous calibration.

As a result, the toner charge amount is measured in the second mode only when the measurement error in the first mode is large. In the second mode, the heights of the toner patch images 21 to 25 on the intermediate transfer belt 5 are suppressed, and the sensor output value of the density sensor 8 is less likely to saturate. As a result, the measurement error of the toner charge amount is reduced.

Embodiment 2.

In the second embodiment, a plurality of mutually identical toner patch images 2i are primarily transferred with a plurality of transfer current values different from each other, and the maximum value of the density measurement values of these toner patch images 2i is used to transfer the toner. A charge amount is derived.

The degree of dispersion of the toner in the toner patch image 2i differs depending on the transfer current value. When the transfer current value is small, toner dispersion is small, so some toner dots in the toner patch image 2i have a stacking height that saturates the sensor output value. On the other hand, when the transfer current value is large, the toner is dispersed too much, and some toner dots in the toner patch image 2i disappear. Therefore, when the transfer current value is such that some of the toner dots in the toner patch image 2i do not disappear and the stacking height of the toner dots is sufficiently lowered, an appropriate density measurement value (that is, the maximum density measurement value ) is obtained.

In the second embodiment, specifically, in the second mode, the control unit 41 controls the transfer current of the primary transfer roller 9a when transferring a plurality of toner patch images 2i of the same (that is, the same coverage rate). are different from each other, and the transfer current of the primary transfer roller 9a when transferring the toner patch image 2i is made higher than the transfer current of the primary transfer roller 9a when transferring the print image, and the toner charge amount is specified The unit 42 selects the toner based on the maximum value among the density measurement values detected by the density sensor 8 for each of the plurality of toner patch images 2i and the development current of the toner patch image 2i having the maximum density measurement value. Identify the amount of charge.

Other configurations and operations of the image forming apparatus according to Embodiment 2 are the same as those in Embodiment 1, so description thereof will be omitted.

As described above, according to the second embodiment, in the second mode, the toner charge amount is derived from the density measurement value in which the measurement error is reduced by a more appropriate transfer current. is reduced.

Embodiment 3.

In Embodiment 3, the mode switching conditions are as follows: (a) the toner charge amount specified in the current calibration is outside the above-described allowable range; is set to exceed

Other configurations and operations of the image forming apparatus according to Embodiment 3 are the same as those in Embodiments 1 and 2, and therefore descriptions thereof are omitted.

As described above, according to the third embodiment, when the density of the toner patch image 2i is low (that is, when the measurement error of the density sensor 8 is small), the toner charge amount increases in a relatively short time in the first mode. When it is specified and the density of the toner patch image 2i is high, the toner charge amount is specified accurately in the second mode.

Various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of its subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the claims.

For example, although the image forming apparatus according to the above embodiment is a color image forming apparatus, it may be a monochrome image forming apparatus.

The present invention is applicable to, for example, an electrophotographic image forming apparatus.

1a to 1d photosensitive drum 2 exposure device 3a to 3d developing device 5 intermediate transfer belt (an example of an image carrier)
9a to 9d primary transfer rollers (an example of transfer rollers)
41 control unit 42 toner charge amount specifying unit

Claims (7)

a photoreceptor drum;
a developing device that develops a toner image by attaching toner to the electrostatic latent image on the photosensitive drum;
an image carrier that carries the toner image;
a transfer roller for transferring the toner image from the photosensitive drum to the image carrier;
a density sensor that optically detects the density of the toner patch image on the image carrier after the toner patch image as the toner image for calibration is transferred to the image carrier;
a toner charge amount specifying unit that specifies the toner charge amount of the toner based on the development current value of the toner patch image and the density of the toner patch image detected by the density sensor in the calibration;
a control unit that controls the transfer current of the transfer roller,
In the calibration, the control section (a) sets the initial value of the toner charge amount measurement mode to the first mode, and (b1) uses the density sensor to set the first mode if the mode switching condition is not satisfied. (b2) when the mode switching condition is satisfied, changing the toner charge amount measurement mode to the second mode, using the density sensor, measuring the density of the toner patch image transferred in the second mode;
In the first mode, the control unit sets the transfer current of the transfer roller when transferring the toner patch image to be the same as the transfer current of the transfer roller when transferring the print image,
In the second mode, the control unit makes the transfer current of the transfer roller during transfer of the toner patch image higher than the transfer current of the transfer roller during transfer of the print image,
The mode switching condition is that the toner charge amount specified in the current calibration is out of the allowable range set based on the toner charge amount specified in the previous calibration;
An image forming apparatus characterized by: The allowable range includes (a) at least one of an upper limit value and a lower limit value of the difference between the toner charge amount specified in the current calibration and the toner charge amount specified in the previous calibration; At least one of the upper limit value and the lower limit value of the ratio between the toner charge amount specified in the current calibration and the toner charge amount specified in the previous calibration, and (c) the ratio specified in the current calibration 2. The setting is set as at least one of an upper limit value and a lower limit value of a temporal gradient between the toner charge amount and the toner charge amount specified in the previous calibration. 1. The image forming apparatus according to 1. 3. The allowable range is adjusted based on the environmental measurement value measured in the current calibration and the environmental measurement value measured in the previous calibration. image forming device. The allowable range is the average stirring time of the toner in the developing device at the time of the current calibration and the average stirring time of the toner in the developing device at the time of the previous calibration. 4. The image forming apparatus according to any one of claims 1 to 3, wherein adjustment is performed based on the image forming apparatus. In the second mode, the control unit makes the transfer currents of the transfer rollers different from each other when transferring the same plurality of toner patch images, and sets the transfer current of the transfer rollers when transferring the print image. Therefore, the transfer current of the transfer roller is increased when the toner patch images are transferred, and the toner charge amount specifying unit determines the maximum density among the densities detected by the density sensor for each of the plurality of toner patch images. 2. The image forming apparatus according to claim 1, wherein the toner charge amount is specified based on the value and the development current of the toner patch image having the density of the maximum value. The mode switching condition is that (a) the toner charge amount specified in the current calibration is outside the allowable range, and (b) the density in the first mode exceeds a predetermined threshold. 2. The image forming apparatus according to claim 1, wherein: In the second mode, the controller controls the transfer of the plurality of toner patch images so that the height of the toner patch images is lower than the transfer current of the transfer roller during transfer of the print image. 2. The image forming apparatus according to claim 1, wherein a transfer current of said transfer roller is controlled during printing.

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