JP7216890B2 - 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. 5 is a diagram illustrating a general relationship between toner charge amount and toner concentration 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. 5, 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 measurement 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. 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, and increases the transfer current of the transfer roller during transfer of the print image. A transfer current of the transfer roller during transfer of the toner patch image is controlled so that the height of the toner patch image is lower than that of the transfer current of the transfer roller.

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 illustrating a general relationship between toner charge amount and toner concentration measurement value.

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

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, and a transfer bias circuit 33. As shown in FIG.

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.

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, the controller 41 reduces the transfer current of the primary transfer roller 9a to 1 when transferring the toner patch image 2i (here, i=1, . . . , 5) when transferring a normal print image. The transfer current of the next transfer roller 9a is increased.

At this time, the higher the density of the toner patch image 2i, the higher the control unit 41 increases the transfer current of the transfer roller when transferring the toner patch image 2i. That is, the higher the toner density, the more easily the sensor output value of the density sensor 8 is saturated, so the transfer current value is increased.

In addition, the control unit 41 controls the primary current during transfer of the toner patch image 2i so that the height of the toner patch image 2i becomes lower than the transfer current of the primary transfer roller 9a during transfer of the print image. It controls the transfer current of the 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.

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.

The toner charge amount specifying unit 42 performs calibration based on the development current value of the toner patch image 2i detected by the development current detection unit 32a and the density measurement value of the toner patch image 2i detected by the density sensor 8. Identify the toner charge amount of the toner.

Specifically, the toner charge amount specifying unit 42 derives the charge Q of the toner used for development from the development current value, and derives the weight M of the toner used for development from the density measurement value of the toner patch image 2i. 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.

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.

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

In calibration, 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. to form a predetermined toner patch image 2i and 1 Execute the next transfer. At this time, the control unit 41 acquires the measured value of the development current, controls the transfer current value to be higher than the above reference value, and intentionally places the toner patch image 2i having a large stacking height around it. Disperse and reduce its height.

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. The control unit 41 receives the sensor signal as a sensor output value corresponding to the density of the toner patch image 2i.

Then, the toner charge amount specifying section 42 specifies the toner charge amount of the toner based on the development current value and the density measurement value of the toner patch image 2i. Note that when a plurality of toner patch images 21 to 25 having different 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 specified as the toner charge amount of the toner. be done.

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.

As described above, according to the above embodiment, in the calibration, the controller 41 controls the transfer currents of the primary transfer rollers 9a to 9d during the transfer of the print image (that is, during the normal printing operation). The transfer current of the primary transfer rollers 9a to 9d is increased when the toner patch image 2i is transferred. The toner charge amount specifying unit 42 specifies the toner charge amount of the toner based on the development current value of the toner patch image 2i and the density of the toner patch image 2i detected by the density sensor 8 in calibration.

As a result, the height of the toner patch image 2i on the intermediate transfer belt 5 is 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.

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 (2)

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,
The control unit makes the transfer current of the transfer roller when the toner patch image is transferred higher than the transfer current of the transfer roller when the print image is transferred, and the transfer current when the print image is transferred. controlling the transfer current of the transfer roller during transfer of the toner patch image such that the height of the toner patch image is lower than the transfer current of the roller;
An image forming apparatus characterized by: 2. The image forming apparatus according to claim 1, wherein the higher the density of the toner patch image, the higher the transfer current of the transfer roller when the toner patch image is transferred.

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