JP3717349B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is an electrophotographic copying machine using a two-component developer comprising a toner and a carrier, a laser beam printer, relates to an image forming apparatus such as a facsimile apparatus, stable especially correct bets toner specific concentration depending on the humidity change The present invention relates to an image forming apparatus that performs image formation.
[0002]
[Prior art]
A conventional image forming apparatus has a photosensitive drum for carrying an electrostatic latent image in the main body of the apparatus. After the surface of the photosensitive drum is uniformly charged by a charging device, the surface of the photosensitive drum is statically charged. An electrostatic latent image is formed. The electrostatic latent image formed on the surface of the photosensitive drum is developed by a developing device to form a toner image. This toner image is transferred to a sheet as a transfer medium that has been conveyed to a transfer device.
[0003]
Next, after the paper is peeled from the photosensitive drum by the peeling device, the toner image is fixed on the paper in the fixing device.
[0004]
Such a conventional developing device uses a two-component developer composed of toner and carrier as a developer.
[0005]
The toner is formed of colored thermosetting and thermoplastic particles. The carriers are formed of ferromagnetic particles such as iron powder.
[0006]
Among the two-component developer composed of the toner and the carrier, the weight ratio of the toner is several percent, and the toner in the developer is consumed every time the electrostatic latent image on the photosensitive drum is developed. . Therefore, it is necessary to replenish the consumed toner and maintain the weight ratio of the toner in the developer, that is, the toner specific density within a predetermined range.
[0007]
Next, a configuration for maintaining the toner specific density within a predetermined range will be described. FIG. 1 is a block diagram of a circuit unit for controlling the toner specific density, and FIG. 2 is an auto toner control sensor for the toner specific density. It is a characteristic view showing an output of (hereinafter referred to as ATC sensor).
[0008]
The toner specific concentration of the developer contained in the developing device 1 is detected by a magnetic ATC sensor 2, and the CPU 3 controls the replenishment of toner from the toner cartridge 3 in accordance with detection information of the ATC sensor 2.
[0009]
For example, as shown in FIG. 2, when the toner specific concentration of the developer in the developing device 1 decreases and the output voltage from the ATC sensor 2 increases and exceeds the set voltage Va, the toner cartridge 4 is replaced with the CPU 3. The toner is supplied to the developing device 1 in accordance with a control command from. As a result of the replenishment, when the toner specific density increases and the output voltage from the ATC sensor 2 falls below a reference value V0, for example, 2V, the CPU 3 stops the toner replenishment from the toner cartridge 4. As a result, the toner specific concentration of the developer in the developing device 1 is maintained at 4 wt%, for example.
[0010]
However, the two-component developer has an environment dependency, and when the humidity is in a high humidity state such as 70% or more, the toner specific concentration of the developer is increased and the charge amount is decreased. The image quality deteriorates due to the occurrence of crushing.
[0011]
On the other hand, when the humidity becomes a low humidity state of 40% or less, the toner specific density of the developer is decreased and the charge amount is increased. As a result, the density of the image is reduced, for example, character blurring occurs, and the image quality is lowered.
[0012]
In order to solve this problem, the image forming apparatus described in Japanese Patent Application Laid-Open No. 4-12380 is provided with a humidity sensor 5 as shown in FIG. 1, for example, when the humidity is 70% or more, the developing device 1 The toner replenishment amount is controlled so that the toner specific concentration of the developer in the developer becomes a first reference value, for example, 3.5 wt%. Conversely, when the humidity is 40% or less, the toner ratio of the developer in the developing device 1 There is a control device for controlling the toner replenishment amount so that the density becomes a second reference value 4.5 wt% higher than the first reference value.
[0013]
[Problems to be solved by the invention]
In the image forming apparatus as described above, as shown by the C line in FIG. 6, the humidity is controlled to a toner specific concentration of 4.5 wt% when the humidity is 40% or less, and the toner specific concentration is 3.5 wt% when the humidity is 70% or more. However, in reality, the toner specific density with respect to the humidity is as shown by line A in FIG. 6. The toner specific density is 4.5 wt% when the humidity is 40% or less, 4 wt% when the humidity is 40 to 70%, and 70% or higher. Is almost impossible to control at 3.5 wt%. For this reason, the following problems occur in the image forming apparatus having the above configuration.
[0014]
When the humidity for executing the correction of the toner specific density is preset to 40% or less and 70% or more, the behavior of the toner specific density when the humidity when the image forming apparatus is installed is 55% is shown in FIG. Although it can be expected that the A-line will appear, the toner specific density when the humidity at the time of installation is 69% can be expected to be the B-line in FIG.
[0015]
When the image forming apparatus is installed , the toner specific concentration is always stored by the CPU through the ATC sensor. When the image forming apparatus is stored at a humidity of 55%, the humidity is 55%, the toner specific concentration is 4 wt% of the reference value, and the humidity is 69%. When stored, the toner specific density is 4 wt% of the reference value at a humidity of 69%.
[0016]
Those result, if the both became 70% humidity, that stores the toner specific concentration humidity 55%, the toner specific density is adjusted to 3.5 wt%, which was stored in 69% since the only the same amount of correction humidity rises slightly performed, toner specific concentration becomes 3 wt%.
[0017]
Thus, when the installation of the humidity in the image forming apparatus in the vicinity of the boundary of the correction is not performed and the area made the region of the toner specific density, greatly deviates from the toner ratio density of the reference in some humidity change Will occur.
[0018]
When correcting the toner specific density according to the humidity change, if the humidity is near the boundary between the area where the correction of the toner specific density is performed and the area where the correction is not performed, the correction is performed with a slight humidity change, or There is a possibility that correction may not be performed with a slight change in humidity, and the toner specific density becomes very unstable, and it is difficult to obtain a stable image quality.
[0019]
For example, when it is set that the correction of the toner specific density is executed when the humidity is 70% or more, the humidity is 69% at one time, 70% at the next moment, and the toner specific density when the humidity is 69% after that. If this correction is performed or not performed, the toner specific density becomes very unstable.
[0020]
Referring to FIG. 6, for the toner specific density between 69% and 71% humidity, the difference in toner specific density is about 1 wt%, and the toner specific density is corrected every time the humidity changes by 1% or 2%. If it is broken or not done, the toner specific density becomes very unstable.
[0021]
The present invention has been made in view of the above problems, and even when the environmental condition (humidity) changes, it is possible to stably form a good image by keeping the toner specific density stable. It is an object of the present invention to provide an image forming apparatus that can be used.
[0022]
[Means for Solving the Problems]
An image forming apparatus according to the present invention includes a developing device that uses a two-component developer composed of toner and a carrier, a density detecting unit that detects a toner specific density of the two-component developer, a humidity detecting unit that detects humidity, Correction means for correcting the toner specific density value of the two-component developer in the developing device according to the humidity detected by the humidity detection means, and the two-component development to the toner specific density value corrected by the correction means. Control means for controlling the toner specific density of the agent, and when the image forming apparatus is installed, the toner specific density detected by the density detection means and the humidity detected as the humidity reference value by the humidity detection means. Storage means for storing is provided, and the correction means calculates a change amount of the humidity detected by the humidity detection means from the humidity reference value stored in the storage means, and the change amount is determined in advance. If the greater than or equal to a predetermined value, by setting the correction amount of the toner specific concentration value, is performed to correct the toner specific density of the two-component developer.
[0023]
According to the above configuration, the correction amount of the toner specific density value is set according to the amount of change from the reference humidity based on the humidity at the time of installation of the image forming apparatus . Accurate toner specific density correction is possible regardless of humidity.
[0025]
Further , according to the above configuration, the toner specific density value is not corrected or not corrected by a slight change in humidity, and stable toner specific density correction can be performed.
[0026]
The image forming apparatus of the present invention, an image density detecting means for detecting the concentration of toner pattern formed on the photosensitive member to hold the image density constant, the toner pattern concentration detected by the image density detecting means and an image density control means for performing a predetermined toner pattern density reference value and controls the development bias based on the result of comparison with the image density correction when said correction means is controlled by the image density control means The correction of the toner specific density value of the two-component developer is performed only when the correction direction of the development bias value from the previously controlled development bias value is the direction corresponding to the humidity change direction detected by the humidity detecting means. Is going.
[0027]
According to the above configuration, it is possible to accurately correct the toner specific density only when it is actually necessary to correct the specific toner density.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
An image forming apparatus according to an embodiment of the present invention will be described with a block diagram of a circuit unit for performing toner specific density correction of FIGS. 4 and 1.
[0029]
As shown in FIG. 4 , the image forming apparatus includes a photosensitive drum 11 that is rotatably supported. The photosensitive drum 11 is driven to rotate in the direction of an arrow by a driving device (not shown).
[0030]
In addition, around the photosensitive drum 11, a charging device 12 that uniformly charges the surface of the photosensitive drum 11 in order, an exposure unit 13 that exposes the surface of the photosensitive drum 11 to form an electrostatic latent image, and A developing device 1 that develops the electrostatic latent image to form a toner image, a transfer device 14 that transfers the toner image onto a sheet as a transfer material, and a cleaning device that cleans residual toner remaining on the surface of the photosensitive drum 11. 15 is arranged.
[0031]
On the other hand, four photosensitive drums 11 are arranged in series, and a developing device 1 having a toner cartridge having toners of Y, M, C, and Bk is provided, and each developing device 1 has a density. An ATC sensor 2 serving as detection means is provided, and the toner specific density is detected using the ATC sensor 2.
[0032]
The transfer device 14 includes a transfer belt 16 that runs while being stretched between a driving pulley and a driven pulley, and the transfer belt 16 runs in the direction of the arrow. The transfer belt 16 is made of modified polyimide or the like, and the paper is electrostatically held on the transfer belt 16.
[0033]
A transfer charger 17 is disposed inside the transfer belt 16 at a position facing the photosensitive drum 11 so as to transfer a toner image formed on the photosensitive drum 11. Although not shown, a cleaning member and a neutralizing member for removing charges accumulated on the belt are disposed inside and outside the transfer belt 16.
[0034]
The toner image is fixed by the fixing device 18 on the sheet on which the toner image of each color is transferred through the four photosensitive drums 11 on the transfer belt 16.
[0035]
The density detection sensor 19 is provided at an appropriate position below the transfer belt 17 so as to face the transfer belt 16, and the toner image formed by the developing device 1 is transferred onto the transfer belt 16. The density detection sensor 19 includes a light emitting element and a light receiving element. The density detection sensor 19 emits light to the toner image and receives reflected light to generate a voltage corresponding to the amount of light. Density correction is performed using the density detection sensor 19.
[0036]
Here, the developer in the developing device 1 is a two-component developer composed of a toner and a carrier, and the two-component developer has a property that its characteristics depend on humidity. If the corresponding toner specific density is not corrected, the toner specific density will increase as the humidity becomes higher, and conversely, the toner specific density will decrease as the humidity becomes lower.
[0037]
This is a phenomenon that occurs because the ATC sensor 2 controls the specific toner density by detecting the magnetic flux density. For example, when the humidity becomes high, the charge amount of the developer decreases, and the developer is tightly tightened as a whole. Accordingly, the ATC sensor 2 determines that the carrier density is high, that is, the toner specific density is low, and replenishes the toner.
[0038]
On the other hand, when the humidity becomes low, the charge amount of the developer increases and the developer becomes swollen. Therefore, the ATC sensor 2 determines that the density of the carrier is low, that is, the toner specific density is high, and replenishes the toner. It will stop doing.
[0039]
That is, the characteristic curve showing the ATC sensor output in FIG. 2 changes to a characteristic curve as shown in FIG. If this phenomenon is not corrected, a stable image cannot be obtained.
[0040]
In the image forming apparatus described above, correction of the toner specific density when the humidity changes will be described below.
[0041]
In the conventional technique, if the humidity is equal to or higher than a predetermined value, the toner specific density is corrected. However, in the present invention, the predetermined humidity is not set in advance, and the initial toner specific density is set to ATC when the image forming apparatus is installed. When detecting by the sensor 2 and storing in the storage device 3b of the CPU 3, the humidity is detected by the humidity sensor 5 and stored in the CPU 3, and the values are used as a reference, ± 0.2V, ± 0.4V, ± 0. The toner specific density is corrected by the control device 3a of the CPU 3 when it changes to a predetermined value or more such as 6V or more.
[0042]
For example, when the output value of the humidity sensor 5 when the initial toner specific density is stored is 0.5 V, the output value of the humidity sensor 5 changes from 0.7 V to 0.89 V as shown in FIG. The reference value V0 is corrected to move to Vb. When the output value of the humidity sensor 5 is 0.9 V or higher, the reference value V0 is corrected to an arbitrary value equal to or higher than Vb.
[0043]
Conversely, when the output value of the humidity sensor 5 changes from 0.11 V to 0.3 V, the reference value V0 is corrected to move to Vc, and when the output value of the humidity sensor 5 is 0.1 V or less, The reference value V0 is corrected to an arbitrary value equal to or less than Vc.
[0044]
This will be described using the straight line A in FIG. 6. The movement of the toner specific density does not discontinuously shift up and down at the position where the humidity is 40% or 70% depending on the humidity when the image forming apparatus is installed. It becomes the form which shifts to right and left continuously linearly.
[0045]
Thus, by determining the correction range based on the output value of the humidity sensor 5 at the time of installation of the image forming apparatus, the toner specific density is corrected only when the humidity actually changes from the initial state. Therefore, the value does not deviate significantly from the reference value of the toner specific density.
[0046]
Further, in the vicinity of the determined correction range and the boundary between the ranges, in the above example, the output value of the humidity sensor 5 is about 0.1 V, about 0.3 V, about 0.7 V, and about 0.9 V. For example, the toner ratio density correction is not executed unless the difference from the humidity sensor output value when the toner ratio density correction was executed last time is ± 0.1 V or more.
[0047]
That is, when the output value of the humidity sensor 5 changes from 0.68V to 0.72V, the correction of the toner specific density is not executed. This solves the problem that correction is performed or not performed with a slight change in humidity, and furthermore, correction of toner specific density is executed only when the humidity actually changes. A stable toner specific density can be obtained.
[0048]
Further, a predetermined toner pattern is formed on the photoconductor while changing the developer bias in order to keep the image density constant, and the density of the toner pattern is detected by a reflection type sensor which is an image density detecting means. comparing the toner pattern concentration reference value determined in advance and the detected value, and controls the developing bias value based on the comparison result by the image density control unit, an image forming apparatus to correct the image density, the correction of the toner specific concentration For example, when the environment is changed to a humid state, the development bias value is determined when the image density correction development bias value is used. Should change in the positive direction (in the direction of decreasing image density), but if the development bias value changes in the negative direction (in the direction of increasing image density) In image density it means that is in the state hard to leave, if that is running correction of the toner specific density lower the toner specific density, further, the image density becomes difficult state output. In order to solve this problem, when the environment changes to a high humidity state, the development bias value changes in the positive direction, and conversely when the environment changes to a low humidity state, the development bias value changes in the negative direction by a predetermined value (± 10 V) or more. Only when the toner density is corrected.
[0049]
From the above, even when the humidity changes, it is possible to keep the toner specific density stable and always obtain a stable image.
[0050]
Further, when the toner ratio density correction is performed, only when the average change amount of the developing bias value in the developing device corresponding to each color of Y, M, C, and Bk is changed by a predetermined value (± 10 V) or more, the toner ratio is corrected. Since the density is corrected, the toner ratio density correction can be performed only when the toner ratio density correction is actually required.
[0051]
Further, the toner specific density correction is performed for the developing devices of all colors.
[0052]
【The invention's effect】
In the image forming apparatus of the present invention, the humidity at the time of installation of the apparatus is used as a reference, and the correction amount of the toner specific density value is set according to the change from the reference humidity. Even if this occurs, accurate toner specific density correction can be performed.
[0053]
The image forming apparatus of the present invention corrects the toner specific density value only when the humidity changes by a predetermined value or more from the humidity detected by the humidity detecting means when the previous correction of the toner specific density value was performed. The toner specific density value is not corrected or not corrected by a slight change in humidity, and stable toner specific density correction can be performed.
[0054]
An image forming apparatus according to the present invention includes an image density detecting unit that detects a density of a toner pattern formed on a photosensitive member in order to maintain a constant image density, a toner pattern density detected by the image density detecting unit, and a toner. Image density control means for controlling the developing bias and correcting the image density based on the result of comparison with the pattern density reference value, and the correcting means is previously controlled of the developing bias value controlled by the image density control means. Since the toner specific density value is corrected only when the correction direction from the development bias value is the direction corresponding to the humidity change direction detected by the humidity detecting means, the toner specific density correction is actually performed. The toner specific density correction can be accurately performed only when necessary.
[Brief description of the drawings]
FIG. 1 is a block diagram of a circuit unit for correcting a toner specific density according to a change in humidity in an image forming apparatus.
FIG. 2 is a characteristic diagram illustrating an output of an ATC sensor with respect to a toner specific density of a developing device of an image forming apparatus.
FIG. 3 is a characteristic diagram showing an output change of an ATC sensor with respect to a toner specific density in a high humidity state and a low humidity state of the developing device of the image forming apparatus.
FIG. 4 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus.
FIG. 5 is a characteristic diagram showing an output change of an ATC sensor and a reference value correction amount with respect to a toner specific density in a high humidity state and a low humidity state of the developing device of the image forming apparatus.
FIG. 6 is a characteristic diagram illustrating a relationship between toner specific density and humidity depending on a difference in humidity when the image forming apparatus is installed.
[Explanation of symbols]
1 Developing device 2 ATC sensor 3 CPU
5 Humidity sensor

Claims (2)

A developing device using a two-component developer composed of toner and carrier, a density detecting means for detecting a specific toner density of the two-component developer, a humidity detecting means for detecting humidity, and the humidity detecting means Correcting means for correcting the toner specific density value of the two-component developer in the developing device according to the humidity, and controlling the toner specific density of the two-component developer to the toner specific density value corrected by the correcting means. Control means,
A storage unit is provided for storing the toner specific density detected by the density detection unit and the humidity detected as a humidity reference value by the humidity detection unit when the image forming apparatus is installed , and the correction unit includes the humidity A change amount of the humidity detected by the detection means from the humidity reference value stored in the storage means is calculated, and when the change amount is equal to or greater than a predetermined value, the toner specific density value is corrected. An image forming apparatus that corrects a toner specific density of the two-component developer by setting an amount.   Image density detecting means for detecting the density of the toner pattern formed on the photosensitive member in order to keep the image density constant, the toner pattern density detected by the image density detecting means and a predetermined toner pattern density reference Image density control means for correcting the image density by controlling the development bias value based on the result of comparison with the value, and the correction means is previously controlled for the development bias value controlled by the image density control means. The correction of the toner specific density value of the two-component developer is performed only when the direction of correction from the development bias value is a direction corresponding to the direction of change in humidity detected by the humidity detecting means. Item 2. The image forming apparatus according to Item 1.

Images