JP2020126136A - Image forming apparatus - Google Patents

Abstract

To obtain an image forming apparatus that appropriately controls a fixing temperature.SOLUTION: A developing device attaches a toner to an electrostatic latent image on a photoreceptor drum to develop a toner image. An intermediate transfer belt carries the toner image. A density sensor 8 optically detects the density of a toner patch image as a toner image for calibration. In calibration, a toner charge amount specification unit 42 specifies the amount of charge of toner based on a developing current value of the toner patch image and the density of the toner patch image detected by the density sensor 8. A control unit 41 controls a fixing temperature of a fixing unit based on the specified amount of charge of toner.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming apparatus.

An image forming apparatus detects the number of edges in an image, determines whether to correct the transfer toner amount according to the number of edges, and controls the fixing temperature according to the transfer toner amount (for example, patent document Reference 1).

JP-A-5-333728

In the above-described image forming apparatus, the transfer toner amount is controlled according to the number of edges, but the increase amount of the toner adhesion amount at the edge portion varies depending on the toner charge amount, and thus the fixing temperature may not be properly controlled. is there.

The present invention has been made in view of the above problems, and an object thereof is to obtain an image forming apparatus that appropriately controls the fixing temperature.

An image forming apparatus according to the present invention includes a photoconductor drum, a developing device that develops a toner image by attaching toner to an electrostatic latent image on the photoconductor drum, and an image carrier that carries the toner image. A fixing device that fixes the toner image on the print sheet onto which the toner image is transferred, a density sensor that optically detects the density of a toner patch image as the toner image for calibration, and the calibration in the calibration, 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, and the toner charge amount specifying unit based on the toner charge amount. And a control unit that controls the fixing temperature of the fixing device.

According to the present invention, an image forming apparatus capable of appropriately controlling the fixing temperature can be obtained.

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

FIG. 1 is a side view showing a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing a 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 illustrating a difference between the relationship between the toner charge amount and the toner adhesion amount in the solid portion and the relationship between the toner charge amount and the toner adhesion amount in the thin line portion. FIG. 5 is a flow chart for explaining the operation of the image forming apparatus shown in FIGS.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

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

The image forming apparatus of this embodiment has a tandem type color developing device. This color developing device has photoconductor drums 1a to 1d, an exposure device 2 and developing devices 3a to 3d. The photoconductor drums 1a to 1d are photoconductors of four colors of cyan, magenta, yellow and black, and electrostatic latent images are formed on the photoconductor drums 1a to 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, which is a light source of laser light, and an optical element (lens, mirror, polygon mirror, etc.) that guides the laser light to the photosensitive drums 1a to 1d.

The developing devices 3a to 3d develop the toner image by adhering the toner in the toner cartridge to the electrostatic latent image on the photoconductor drums 1a to 1d. The photosensitive drum 1a and the developing device 3a perform magenta development, the photosensitive drum 1b and the developing device 3b perform cyan development, and the photosensitive drum 1c and the developing device 3c perform yellow development. Black is developed by the photoconductor drum 1d and the developing device 3d.

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

The secondary transfer roller 7 brings a conveyed print sheet (print paper or the like) into contact with the intermediate transfer belt 5, and secondarily transfers the toner image on the intermediate transfer belt 5 onto the print sheet. The print sheet to which the toner image is secondarily transferred is conveyed to the fixing device 10. The fixing device 10 includes a heater, and fixes the toner image on the print sheet by a heating and pressing method using the heater.

The density sensor 8 irradiates the intermediate transfer belt 5 with light, receives the reflected light (for example, specularly reflected light and diffusely reflected light), and outputs an electric signal corresponding to the amount of the received reflected light. It is a 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 calibration toner image is primarily transferred to the intermediate transfer belt 5.

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

FIG. 2 is a block diagram showing a 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 developing bias circuit 32, a transfer bias circuit 33, and a fixing control circuit 34.

The controller 31 electrically controls each unit in the image forming apparatus. The controller 31 includes an ASIC (Application Specific Integrated Circuit), a microcomputer, and the like, 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 the control signal between the developing device 3a and the photosensitive drum 1a. The developing bias circuit 32 includes a developing current detector 32a that detects a developing current value (DC current value) at the time of developing the toner patch image.

The transfer bias circuit 33 applies a primary transfer bias having a voltage designated by the control signal between the photosensitive drum 1a and the primary transfer roller 9a.

The fixing control circuit 34 energizes the heater of the fixing device 10 to control the fixing temperature of the fixing device 10 to the temperature designated by the controller 31.

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

The control unit 41 controls the mechanical configuration shown in FIG. 1, the developing bias circuit 32, the transfer bias circuit 33, the fixing control circuit 34, and the like to execute printing and calibration.

In the calibration, the control unit 41 controls the photosensitive drum 1a, the exposure device 2, the developing device 3a, the primary transfer roller 9a, and the like to form a toner patch image (a toner image having a predetermined density and a predetermined shape) and a primary toner image. 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 the position corresponding to the 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, the toner dot density). That is, in the toner patch images 21 to 25, the pixel positions having toner dots and the pixel positions having no toner dots coexist.

The control unit 41 supplies a control signal to the developing bias circuit 32 to control the developing bias and the developing current, and supplies a control signal to the transfer bias circuit 33 to control the primary transfer bias and the transfer current.

Although the functions of the controller 31 with respect to the photosensitive drum 1a, the developing device 3a, and the primary transfer roller 9a will be described here, the other photosensitive drums 1b to 1d, the developing devices 3b to 3d, and the primary transfer roller are described. The function of the controller 31 for 9b to 9d is also the same.

In the calibration, the toner charge amount specifying unit 42, 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, The toner charge amount of the toner is specified.

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. Then, the ratio Q/M of the two is derived as the toner charge amount.

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

Further, the control unit 41 uses the fixing control circuit 34 to control the fixing temperature of the fixing device 10 based on the toner charge amount specified by the toner charge amount specifying unit 42. Specifically, the control unit 41 controls the fixing temperature of the fixing device 10 during printing of a user image and the like until the next calibration, based on the toner charge amount specified by the calibration.

Specifically, the control unit 41 specifies the toner adhesion amount on the edge portion of the toner image corresponding to the toner charge amount using (a) a table or a relational expression, and (b) identifies the toner adhesion amount on the specified edge portion. The fixing temperature (particularly, the lower limit value of the fixing temperature) required for is specified, and the specified fixing temperature is set as the fixing temperature of the fixing device 10. At that time, the control unit 41 sets the fixing temperature to be lower as the toner charge amount is higher.

FIG. 4 is a diagram illustrating a difference between the relationship between the toner charge amount and the toner adhesion amount in the solid portion and the relationship between the toner charge amount and the toner adhesion amount in the thin line portion. As shown in FIG. 4, the toner adhesion amount in the solid portion (that is, the toner consumption amount per unit area of the dot area) does not change much depending on the toner charge amount, but the toner adhesion amount in the thin line portion (that is, the edge portion) is Changes with the toner charge amount, and specifically, as the toner charge amount decreases, the toner adhesion amount increases.

Therefore, the control unit 41 sets the fixing temperature to be lower as the toner charge amount is higher, because the toner adhesion amount to the edge portion is smaller as the toner charge amount is higher.

For example, the control unit 41 holds in advance a relational expression (or lookup table) between the toner adhesion amount at the edge portion corresponding to the toner charge amount and the fixing temperature decrease amount (or increase amount), and the relational expression. (Or look-up table) is used to identify the increment/decrement of the fixing temperature with respect to the reference temperature (fixing temperature corresponding to the predetermined maximum or minimum value of the toner charge amount), and the increment/decrement is used to determine the fixing temperature from the reference temperature. Change and set.

The reference temperature may be dynamically set based on the toner loading amount on the entire print sheet to be fixed and the environmental temperature.

Further, the increase/decrease in the fixing temperature may be set stepwise at predetermined intervals, for example, by 5 degrees each time the toner adhesion amount at the edge portion increases by a predetermined value. Alternatively, it may be set with a predetermined characteristic (non-linear function or the like) with respect to the toner charge amount.

In this embodiment, for example, the photosensitive drums 1a to 1d are made of amorphous silicon having a relatively high dielectric constant, and the developing rollers of the developing devices 3a to 3d are the photosensitive drums 1a. If the linear velocity of the developing roller is higher than the linear velocity of the photoconductor drums 1a to 1d after the trail rotation with respect to 1d to 1d, not only the toner adhesion amount on the edge portion due to the edge effect but also the edge portion due to the rear end accumulation is An increase in the toner adhesion amount also occurs. Therefore, from the edge of the dot area in the image, a portion (for example, a range of a predetermined number of pixels from the edge) where the toner adhesion amount increases due to the edge effect or the trailing edge accumulation is regarded as the above-mentioned edge portion. In the dot area in the image, a portion other than the edge portion is regarded as a non-edge portion.

Next, the operation of the image forming apparatus will be described. FIG. 5 is a flow chart for explaining the operation of the image forming apparatus shown in FIGS.

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

In the calibration, the control unit 41 controls the photoconductor drums 1a to 1d, the exposure device 2, the developing devices 3a to 3d, the primary transfer rollers 9a to 9d, and the like to obtain a predetermined toner patch image 2i (test pattern). Formation and primary transfer are performed (step S1). At that time, the control section 41 detects the developing current by the developing current detecting section 32a (step S2).

The toner patch image 2i thus transferred onto the intermediate transfer belt 5 moves as the intermediate transfer belt 5 advances, and when the toner patch image 2i reaches the measurement position of the density sensor 8, the density sensor 8 A sensor signal corresponding to the density of the patch image 2i is output. The control unit 41 receives the sensor signal as a density measurement value corresponding to the density of the toner patch image 2i (step S3).

Then, the toner charge amount identifying unit 42 identifies the toner charge amount of the toner based on the charge of the toner patch image 2i based on the developing current value and the toner adhesion amount based on the toner density measurement value (step S4). ). 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. To be done.

As described above, the control unit 41 specifies the toner adhesion amount at the edge portion corresponding to the toner charge amount (step S5), and increases or decreases the fixing temperature (that is, the toner amount) corresponding to the toner adhesion amount at the edge portion. The amount of increase/decrease in fixing temperature corresponding to the charge amount is specified (step S6).

In this way, the increase/decrease in the fixing temperature corresponding to the toner charge amount is specified in the calibration.

In the normal printing operation (that is, when printing the print image designated by the user), the control unit 41 controls the photoconductor drums 1a to 1d, the exposure device 2, the developing devices 3a to 3d, the primary transfer rollers 9a to 9d, and the like. Control is performed to form the toner image corresponding to the user image and perform the primary transfer based on the image data.

Further, the controller 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 the fixing device 10. After that, the print sheet is discharged as a printed matter. At this time, the control unit 41 uses the fixing control circuit 34 to change the fixing temperature of the fixing device 10 from the reference temperature by an increase/decrease in the fixing temperature specified by the calibration, and fix the toner image. It is executed by the container 10 (step S7).

As described above, according to the above-described embodiment, the developing devices 3a to 3d develop toner images by attaching toner to the electrostatic latent images on the photoconductor drums 1a to 1d. The intermediate transfer belt 5 carries the toner image. The density sensor 8 optically detects the density of a toner patch image as a calibration toner image. The toner charge amount specifying unit 42 specifies the toner charge amount of toner based on the developing current value of the toner patch image and the density of the toner patch image detected by the density sensor 8 in the calibration. Then, the control unit 41 controls the fixing temperature of the fixing device 10 based on the specified toner charge amount.

Thereby, the fixing temperature is appropriately controlled in consideration of the toner charge amount. Therefore, power consumption due to insufficient fixing in the fixing device 10 when the toner charging rate is low and power consumption due to an excessive fixing temperature in the fixing device 10 when the toner charging rate is high are suppressed.

Various changes and modifications to the above-described embodiment will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. Such changes and modifications are intended to be included within the scope of the following claims.

For example, in the above embodiment, the control unit 41 makes the transfer current of the transfer rollers 9a to 9d at the time of transferring the toner patch image 2i higher than the transfer current of the transfer rollers 9a to 9d at the time of transferring the print image. You may do it. In that case, the control unit 41 may increase the transfer current of the transfer rollers 9a to 9d when transferring the toner patch image 2i as the density of the toner patch image 2i increases. As a result, even if 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. The toner patch image 2i is dispersed on the transfer belt 5 to reduce its height. Therefore, the sensor output value of the density sensor 8 is less likely to be saturated, and the measurement error of the density measurement value is reduced. As a result, the measurement error of the toner weight M, and consequently the error of the toner charge amount Q/M, also becomes small.

Further, the image forming apparatus according to the above embodiment is a color image forming apparatus, but may be a monochrome image forming apparatus.

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

1a to 1d Photoreceptor drums 3a to 3d Developing device 5 Intermediate transfer belt (an example of an image carrier)
8 Density sensor 41 Control unit 42 Toner charge amount specification unit

Claims (3)

A photoconductor drum,
A developing device for developing a toner image by attaching toner to the electrostatic latent image on the photosensitive drum,
An image carrier for carrying the toner image;
A fixing device for fixing the toner image on the print sheet onto which the toner image has been transferred;
A density sensor that optically detects the density of a toner patch image as the toner image for calibration,
In the calibration, based on the development current value of the toner patch image and the density of the toner patch image detected by the density sensor, a toner charge amount specifying unit that specifies the toner charge amount of the toner,
A control unit that controls the fixing temperature of the fixing device based on the toner charge amount;
An image forming apparatus comprising: The control unit specifies (a) a toner adhesion amount at an edge portion of the toner image corresponding to the toner charge amount, and (b) a fixing temperature required for the specified toner adhesion amount at the edge portion, The image forming apparatus according to claim 1, wherein the fixing temperature of the fixing device is set. The image forming apparatus according to claim 1, wherein the control unit lowers the fixing temperature as the toner charge amount increases.