JP2003295598A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize the accurate control of the toner concentration of developer. <P>SOLUTION: In the image forming apparatus equipped with an electrifying device to electrify a photoreceptor drum by a magnetic brush, the variation of a control voltage value for adjusting the detection signal of a toner concentration sensor to the number of image forming times is made to differ for each environment so as to solve a problem that the amount of magnetic particles intruded in a developing device is different according to the environment. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer, a recorded image display for developing an electrostatic latent image formed on an image carrier by an electrophotographic system, an electrostatic recording system or the like to form a visible image. Image forming apparatus such as a device and a facsimile,
In particular, the present invention relates to an image forming apparatus equipped with a developer concentration control device that appropriately controls the toner concentration of a two-component developer.

[0002]

2. Description of the Related Art Generally, a two-component developer containing toner particles and carrier particles as a main component is used in a developing device provided in an electrophotographic or electrostatic recording type image forming apparatus. Particularly, in a color image forming apparatus that forms a full-color image or a multi-color image by an electrophotographic method, most developing apparatuses use a two-component developer from the viewpoint of image tint and the like. As is well known, the toner concentration of this two-component developer (that is, the ratio of the weight of toner particles to the total weight of carrier particles and toner particles; hereinafter referred to as T / D ratio) is extremely important for stabilizing image quality. It is an element. The toner particles of the developer are consumed during development, and the toner concentration changes. Therefore, the developer concentration control device (AT
It is necessary to accurately detect the toner concentration of the developer by using R), to replenish the toner according to the change, to constantly control the toner concentration, and to maintain the image quality.

In order to correct such a change in the developer concentration in the developing device due to development, that is, to control the amount of toner replenished to the developing device, the toner concentration in the developing container is detected and the toner concentration is detected. Conventionally, various types of control devices have been proposed and put into practical use.

For example, a developer carrying member (generally referred to as a "developing sleeve" in the following description since a developing sleeve is generally used) or a developer carrying path of a developing container is carried onto the developing sleeve. The developer concentration control device that detects and controls the toner concentration by utilizing the fact that the reflectance when the developer or the developer in the developer container is exposed to light varies depending on the toner concentration, or on the side wall of the developing device. An inductance head is installed to detect the apparent magnetic permeability due to the mixing ratio of the magnetic carrier and the non-magnetic toner and convert it into an electric signal, and the toner concentration of the developer in the developing device is detected by the detection signal from this inductance head,
An inductance detection type developer concentration control device is used in which toner is replenished by comparison with a reference value.

An image carrier (photosensitive drum is generally used in many cases, so in the following description, "photosensitive drum")
The density of the patch image formed above is read by a light source provided at a position facing the surface and a sensor for receiving the reflected light, converted into a digital signal by an analog-digital converter, and then sent to the CPU, and the CPU If the density is higher than the initial setting value, toner supply is stopped until the initial setting value is returned, and if the density is lower than the initial setting value, toner is forcibly supplied until the initial setting value is returned. As a result, there is a method in which the toner concentration is indirectly maintained at a desired value.

However, in the method of detecting the toner density from the reflectance when the developer conveyed on the developing sleeve or the developer in the developing container is irradiated with light, the detecting means is contaminated due to toner scattering or the like. In this case, there is a problem that the toner density cannot be accurately detected. Further, the method of indirectly controlling the toner density from the patch image density has a problem in that a space for forming a patch image and a space for installing a detection unit cannot be secured due to downsizing of a copying machine or an image forming apparatus.

On the other hand, the inductance detection method is
In addition to the low cost of the sensor alone, it is not affected by the above-mentioned space problems and dirt problems due to toner scattering, so it is the optimum toner for low-cost, small-space copiers or image forming apparatuses. It can be said to be a concentration detection method.

The above-mentioned inductance detecting type developer concentration control device (hereinafter referred to as "inductance detecting type ATR"), for example, when it is detected that the apparent magnetic permeability of the developer is high, Toner replenishment is started because it means that the ratio of the carrier particles is high and the toner concentration is low.On the contrary, when the apparent magnetic permeability is low, the ratio of the carrier in the developer in a certain volume is small. This means that the toner density has decreased and the toner density has increased. Therefore, the toner density is controlled based on control such as stopping the toner supply.

In general, a corona charger is generally used as a charging means for an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric, which is included in an electrophotographic or electrostatic recording type image forming apparatus. Came. In recent years, because of advantages such as low ozone and low power consumption, a contact charging device, that is, a device of a type in which a charging member to which a voltage is applied is brought into contact with an object to be charged, is put into practical use. Has been done. In particular, a roller charging type device using a conductive roller as a charging member is preferably used from the viewpoint of charging stability.

However, in the roller charging method described above, charging is performed by discharging from the charging member to the member to be charged,
The surface potential of the photoconductor also fluctuates due to changes in the electrical resistance of the charging roller and the electrophotographic photoconductor due to changes in the environment.

Therefore, recently, as a charging method with less environmental fluctuation, a voltage is applied to a conductive contact charging member (charging fur brush, charging magnetic brush, charging roller, etc.) in Japanese Patent Application No. 5-66150. , A method of injecting electric charges having the same polarity as the electric potential of the photoconductor to a photoconductor having a charge injection layer on the surface of which a conductive powder (SnO2 or the like) serving as a trap level is dispersed to perform contact charging.

This injection charging system is not only environmentally dependent and does not use discharge, so that the applied voltage is sufficient at the same level as the photoconductor potential, and ozone that shortens the life of the photoconductor is not generated. There is.

Further, in the contact charging using discharge, in order to obtain a desired charging potential Vs on the body to be charged, the discharge start voltage Vth (DC voltage is applied to the contact charging member is applied to the desired charging potential Vs. DC bias Vs + Vt added with (applied voltage of contact charging member when charging of member starts)
Although it is necessary to apply h to the charging member, the charge injection charging can obtain the charging potential Vs that is almost the same as the DC bias applied to the charging member, so that the cost of the charging power source can be reduced. As the contact charging member in the case of such a charge injection method, a magnetic brush charging member or a fur brush charging member is preferably used in terms of stability of charging and contact.

The magnetic brush charging member has a magnetic brush of conductive magnetic particles (charging magnetic carrier) formed and held by magnetically restraining it on a carrier that also serves as a power feeding electrode, and the magnetic brush contacts the member to be charged. The power is supplied to the carrier. More specifically, the conductive magnetic particles are magnetically restrained and held as a magnetic brush directly on the magnet or on the sleeve containing the magnet, and the magnetic brush portion is covered while the magnetic brush charging member is stopped or rotated. The charged body is charged by bringing it into contact with the charged body and applying a voltage.

The fur brush charging member has a brush portion (fur brush portion) of conductive fibers carried on a carrier which also serves as a power feeding electrode, and the conductive fiber brush is brought into contact with a member to be charged to carry the carrier. It supplies power to.

In comparison between the magnetic brush charging member and the fur brush charging member, the charging property of the fur brush charging member is deteriorated when the hair collapses due to long-term use or long-term storage, and the charging uniformity is uniform. However, such a phenomenon does not occur with the magnetic brush charging member, and uniform and stable charging can be performed.

By the way, in recent years, the downsizing of the apparatus has been advanced, but there is a limit to downsizing the steps of charging, exposing, developing, transferring, fixing and cleaning, which are the steps of a general copying machine. there were. Also, the above-mentioned transfer residual toner is collected by a cleaner, but this waste toner is
It is preferable that there is no environmental protection.

The above-mentioned cleaner is detached, the transfer residual toner on the photosensitive drum is collected by the contact charger, the photosensitive drum is charged to a desired potential, and the collected toner is discharged onto the photosensitive drum and simultaneously developed by the developing device. A cleanerless device for cleaning is also proposed.

Simultaneous development cleaning referred to here is a method in which a small amount of toner remaining on the photosensitive drum at the time of transfer is collected by the contact charging member and discharged onto the photosensitive drum, and is collected by the fog removing bias (Vback) at the developing position. Is.

Also in this case, if the magnetic brush charger is used as the contact charging member, it is advantageous in collecting the transfer residual toner.
In the magnetic brush charger, magnetic particles 94 having a relatively low resistance are formed in a brush shape by a magnetic field on a rotatable non-magnetic sleeve 93 having a fixed magnet 92 provided therein as shown in FIG. The magnetic particles are conveyed with the rotation of. Then, by applying a charging voltage to the non-magnetic sleeve, charges are applied from the magnetic particles onto the photosensitive drum, and the photosensitive drum is charged to a potential according to the charging voltage. When magnetic particles are used, the transfer residual toner once collected is surely charged by frictional charging, so that the toner discharged onto the photosensitive drum is not only surely attached to the photosensitive drum but also the developing unit. It is possible to make the state easy to collect. According to this method
The transfer residual toner is collected and reused at the time of development, so that the waste toner can be eliminated. In addition, there is a great advantage in terms of space, and the size can be greatly reduced.

However, a problem with the magnetic brush charging device as described above is that the charge carrier forming the charging magnetic brush may adhere to or flow out from the surface of the image carrier. When it is collected in the developing device, in the developing device using the inductance detection type sensor, even if a small amount of the charged carrier adheres which is not particularly problematic in terms of image, the number of copies increases and the accumulated in the developing device. When the magnetic permeability of the developing carrier is different from that of the charging carrier, the apparent magnetic permeability of the developer as a whole may change, and an error may occur in the T / D ratio control by the inductance detection type sensor.

That is, when the magnetic permeability of the charge carrier is higher than that of the developing carrier, the toner concentration in the developing container is at the same level as the reference toner concentration, but the charge carrier is mixed in the developer, so that the average of the developer is increased. If the magnetic permeability is large, it is detected by the inductance detection sensor, and this is because the ratio of carrier particles in the developer in a certain volume is large, and it is erroneously detected that the T / D ratio is low, and toner supply is started. , The concentration control higher than the proper T / D ratio will be performed. On the contrary, if the magnetic permeability of the charge carrier is smaller than that of the development carrier, if the charge carrier is mixed in the developer, the average magnetic permeability of the developer becomes small and the output value of the inductance detection sensor is detected lower than the reference value. However, this means that the ratio of the carrier in the developer within a certain volume has decreased and the T / D ratio has increased, so toner supply is stopped and the concentration is controlled to be lower than the proper T / D ratio. Problems such as being lost occur. In the former case, there is a problem that the image density becomes dark due to excessive toner supply, a problem that the developer amount increases as the toner amount increases and the developer overflows from the developer container, or a toner ratio in the developer increases. As a result, the toner charge amount decreases, which causes problems such as toner scattering and image fog. On the other hand, in the latter case, problems such as image deterioration and low image density due to a decrease in the amount of toner in the developer occur.

For example, as shown in FIG. 15B, when the optimum T / D ratio of the developer is 8%, the initial value of the detection signal from the inductance head 20 is 2.5 V, and the T / D is
It is assumed that the initial value is set to the reference value so that the ratio can be maintained. However, when the charge carrier gradually accumulates in the developing device as the image forming operation is repeated, if the permeability of the charge carrier is higher than that of the developer carrier, the apparent permeability of the developer is as shown in FIG. When the magnetic permeability of the charge carrier is smaller than the magnetic permeability of the developing carrier as shown in FIG.
(A) It becomes gradually smaller as indicated by the dotted line in (ii). Accordingly, the output of the inductance detection sensor in accordance with the change in the magnetic permeability is as shown in FIG. 15 when the magnetic permeability of the charging carrier is larger than the magnetic permeability of the developing carrier.
(B) It gradually increases as shown by the dotted line in (i),
When the magnetic permeability of the charging carrier is smaller than the magnetic permeability of the developing carrier, it gradually decreases as shown by the dotted line in FIG. 15 (b) (ii). However, the actual value of the inductance detection sensor is 2.5V.
As shown in FIG. 15C, when the magnetic permeability of the charging carrier is larger than that of the developing carrier, as shown in FIG. c) As shown by the dotted line in (i), the T / D ratio gradually increases, and when the magnetic permeability of the charge carrier is smaller than the magnetic permeability of the developing carrier, the T / D ratio is as shown by the dotted line in FIG. 15 (c) (ii). Therefore, the T / D ratio will gradually decrease.

Details will be described below. The amount of charge carriers mixed in the developing device during image formation with 5% duty is about 20.
At about g / 50000 times, the detection sensitivity of the inductance detection sensor mounted on the developing device (change in sensor output with respect to change in T / D ratio) changes by 0.5 V with respect to a change in T / D ratio of 1%. Use the sensor. Here, when the detection signal of the inductance detection sensor is set to 2.5 V with respect to the reference T / D ratio, if the charge carrier 20 g is forcibly mixed into the developer, the apparent magnetic permeability of the developer is obtained. , The optimum T / D at the initial stage
When the ratio was maintained, the detection signal of the inductance detection sensor had increased by 1 V from the initial reference value of 2.5 V to 3.5 V. Therefore, the toner is actually replenished so that the detection signal becomes 2.5 V, so that the toner is replenished excessively, and the image forming operation is repeated 50,000 times. The toner density deviated from 8% by 2% and was controlled to 10%.

To solve this problem, the amount of charge carriers collected in the developing device is predicted from the number of image formations and the number of sheets, and the initial reference value of the inductance detection sensor is set when the image forming operation is repeated for a certain time or a certain number of times. Instructions are set in advance in the CPU 25 (FIG. 6) so that the processing is repeated,
A method has been proposed in which the CPU 25 sets a new reference signal value at a predetermined timing.

Specifically, when the image forming operation is repeated 25,000 times in the above-mentioned developing device, if the mixing amount of the charging carrier is proportional to the image forming operation, the amount is 20 g / 50000 times, so 10 g / It becomes 25,000 times. The value of the inductance detection sensor changes by 1 V when 20 g of the charge carrier is mixed, so that the value changes by 0.5 V when about 5 g of the charge carrier is mixed. Therefore, a command is set in advance in the CPU 25 so that the reference signal value for T / D ratio control is reset to 3.0 V when the image formation is repeated 25000 times. When the setting is reset, toner replenishment is stopped until the detection signal reaches 3.0V, so the error in the toner density that has occurred up to that point is eliminated, and the initial T / D ratio is 8%.
Will be controlled again. As a result, when the image forming operation is repeated 50,000 times, the reference value is similarly changed to reduce the error in toner density control as compared with the case where the detection signal is not corrected for the T / D ratio after 50,000 times of image formation. be able to.

[0027]

However, as described above, the amount of charge carriers collected in the developing device is predicted based on the number of image formations and the number of copies, and the reference value for the reference toner density is set as a new reference value. If the toner density is controlled by the resetting method, the following problems occur.

FIG. 16A is a graph showing the relationship of the sensor detection signal with respect to the developer toner concentration change of the inductance detection sensor. Further, FIG. 16B shows a change in the reference value with respect to the number of image-formed sheets by means of resetting the reference value with respect to the reference toner density as a new reference value with respect to the number of image-formed sheets described in [Prior Art]. It shows the history of. As shown in FIG. 16A, the inductance detection sensor has a detection signal output range of 0 to 5V.
In the case of 2.5V, which is the central value, the lower limit is 1V, and the upper limit is around 4V, the output change amount of the sensor (hereinafter referred to as sensor sensitivity) shows a 1: 1 inclination with respect to the toner concentration change amount. As a result, the sensitivity becomes dull, and the sensor sensitivity does not show a constant slope. In the inductance detection sensor having such characteristics, if the means for resetting the reference value for the reference toner density as a new reference value for the number of image formed is executed, the number of images is increased and the toner is collected in the developing container. When the carrier amount increases and the reference value is reset again, the sensor sensitivity is not constant and the toner concentration must be controlled in a region where the sensitivity is low.

For example, in the area B in the figure, the detection signal value of the 0.5V sensor fluctuates with respect to the change of the toner density of 1%.
On the other hand, in the areas A and C, the detection value of the sensor fluctuates only by 0.25 V with respect to the change of the toner concentration of 1%. In other words, even if the toner concentration deviates by 1%, only 0.25 V fluctuates, so that the detection signal outputs a signal for supplying 0.25 V (0.5% of toner concentration).
Since the replenishment amount is smaller than the consumed toner amount in this way, in the regions A and C, it takes time to restore the developer whose toner concentration has decreased due to toner consumption to the reference toner concentration in the region B. It will be late. In such a case, if high-density originals continue, the toner replenishment cannot keep up with the consumption of toner in the developer, and the developer toner concentration becomes extremely low, causing an image defect of a light original image.

Such a problem occurs because the number of images to be formed increases and the magnetic carrier of the charging magnetic brush accumulates in the developing container. Therefore, the image carrying member is charged by the magnetic brush injection charging method. This is a serious problem in achieving a long life of the developing device of the forming apparatus. In the example of [Prior Art], the amount of charge carriers mixed into the developing device at the time of image formation with 5% Duty is about 20 g / 50000 times, and the detection sensitivity (T / D ratio) of the inductance detection sensor used. The sensor output change amount for the change amount is T
The one that changes by 0.5 V with respect to the change of the / D ratio of 1% is used. Here, when the detection signal of the inductance detection sensor is set to 2.5 V with respect to the reference T / D ratio, if the charge carrier 20 g is forcibly mixed into the developer, the apparent magnetic permeability of the developer is obtained. , The detection signal of the inductance detection sensor when the initial optimum T / D ratio is maintained is 2.5V from the initial reference value 2.5V.
It had risen by 1V to 5V. The number of times of image formation of the developing device of such an image forming apparatus is 75000 times, 1000 times
If the number is increased to 00, the initial value of the inductance detection sensor will exceed 4.0V, and the newly set reference value will also exceed 4.0V.

In addition, an upper limit value and a lower limit value (for example, an upper limit value of 4.0 V and a lower limit value of 1.0 V in the figure) are set within the output range of the detection signal of the inductance detection sensor to serve as an abnormality detecting means for the developer toner concentration. The method to use is proposed. This is because "the toner concentration is abnormally increased due to the excessive toner supply of the toner supply means, and the detection signal of the sensor is 1.0
V ”or“ a large amount of magnetic particles forming the charging magnetic brush adhere to the surface of the image carrier and are collected by the developing device, and the detection signal value of the sensor becomes 4.0 V or more. For an accident such as "," the image forming operation is stopped when an abnormality is detected. Even for such a proposal, by using a means for resetting the reference value for the reference toner density, when the number of image forming sheets increases and the reference value is set near 4.0V, the normal toner density is obtained. Nevertheless, the detection signal value exceeds the upper limit value, a malfunction that detects an abnormality occurs, and there is a problem that it cannot be used as an abnormality detection unit.

Further, according to the study by the present inventors, it has been found that the amount of charge carriers adhering to the photosensitive drum changes depending on the environment in which it is used.

For example, in a low-humidity environment, both the charging carrier and the photosensitive drum have high resistance, and the efficiency of injecting charges into the photosensitive drum by the charging carrier is reduced. However, the charging potential on the surface of the photoconductor drum is lowered. Therefore, there is a potential difference between the tip of the charging carrier and the surface of the photosensitive drum, and the charging carrier is likely to adhere to the photosensitive drum.

Therefore, an object of the present invention is to provide an image forming apparatus which predicts the mixed amount of charge carriers different for each environment and does not change the reference value of the toner concentration control of the inductance detection sensor and has a small error. is there.

[0035]

The above object can be achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to a charging device for charging an image carrier by bringing a charging member composed of magnetic particles facing the image carrier into contact with the image carrier and applying a charging bias to the charging member. And an exposure device for forming an electrostatic latent image on the charged image carrier, and a two-component developing device for forming the electrostatic latent image from toner particles and magnetic carrier particles having different magnetic permeability from the magnetic particles used for the charging member. Forming a visible image using an agent, and detecting the apparent magnetic permeability of the two-component developer, has a toner concentration sensor that outputs a detection signal, a detection signal based on the detection result, and its reference value. From the comparison result of 1., a developing device having a developer toner density control device for operating the toner replenishing means based on the reference value of the toner replenishment control, and a transfer device for transferring the visible image to a transfer material are provided, Is the inspection The control unit has a control unit that can adjust the signal by changing the control signal value input to the toner concentration sensor, and the magnetic particles of the charging member attached to the image carrier are developed in the developing container according to the operating time of the image forming apparatus. In the image forming apparatus that changes the control signal value of the control unit in response to the change in the detection signal of the toner concentration sensor due to the accumulation inside, the change amount of the control signal value corrected by the control value changing unit is An image forming apparatus, which is different depending on the environment judged by an attached temperature and humidity sensor.

[0036]

According to the present invention, when the charge carrier used for the magnetic brush charging is charged in the developing device due to the adhesion of the charge carrier due to the repeated image forming operation, the charge carrier is charged. Even if the average magnetic permeability of the entire developer, which is the optimum toner concentration, gradually changes due to the difference in magnetic permeability between the carrier and the developing carrier, the control means adjusts the detection signal of the inductance detection sensor by changing the control value. By adjusting the detection signal, the toner reference value for initial toner density control is not changed, and toner replenishment is always performed properly even when the image forming operation is repeated. /
D ratio control becomes possible. Further, by having a control table of the detection signal of the inductance detection sensor for each environment, accurate toner concentration control can be performed even if the mixing amount of the charge carrier in the developing device is different for each environment.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIGS. 1 and 2 are schematic configuration diagrams of an electrophotographic image forming apparatus to which the present invention can be applied. The image forming apparatus includes a photosensitive drum 1 that rotates in the direction of the arrow, and a charger 2, a transfer discharger 3, and a laser beam scanner (not shown) disposed above the photosensitive drum around the photosensitive drum 1. And an image forming unit. A document reading device having a photoelectric conversion element such as a CCD outputs an image signal corresponding to monochrome image information of a document. The semiconductor laser built in the laser beam scanner is controlled according to this image signal and emits the laser beam 5. The output signal from the electronic computer can also be printed out.

In the sequence of the entire image forming apparatus, the photosensitive drum is first uniformly charged by the charger.
The photoconductor is 150 mm / sec. In the clockwise direction indicated by the arrow. It rotates at the process speed (peripheral speed) of.

Next, scanning exposure is performed by the laser beam 5 modulated by the image signal, an electrostatic latent image is formed on the photosensitive drum 1, and the electrostatic latent image is reversely developed by the developing device 6. In this embodiment, the two-component contact developing method using a developer in which a non-magnetic toner and a magnetic carrier are mixed as the developer is used to improve the collectability of the toner discharged from the magnetic brush charger. In addition, a full-color image can be obtained by performing the above steps on images of four colors of yellow, magenta, cyan, and black.

The toner image on the photosensitive drum is taken out from the paper feed cassette 7, and transferred onto a transfer material 8 such as paper which has advanced through a paper feed roller and a paper feed guide by a transfer charger (corona charger) 3. Transcribed. The toner remaining on the surface of the photosensitive drum 1 without being transferred is temporarily collected by the magnetic brush charger 2. After that, the photosensitive drum 1 is de-charged by pre-exposure to form an electrostatic latent image again.

On the other hand, the transfer material 8 on which the toner has been transferred is sent to a fixing device (heat roller fixing device) 9 by a conveyor belt and the image is fixed.

Next, the charger used in the present invention will be described with reference to FIG.

The charger 2 includes a container 10 and a fixed magnet 1 inside.
1, a sleeve 12 made of a non-magnetic material, magnetic particles 13 that contact the photoreceptor 1 to inject charges, and a regulating blade 14 that coats the magnetic particles with a uniform thickness on the sleeve surface. There is.

The sleeve 12 made of non-magnetic stainless steel is 225 mm / sec. It is rotating at the peripheral speed of.

Regulation blade 14 made of non-magnetic stainless steel
Are arranged so that the gap with the sleeve surface is about 900 μm.

Magnet 11 fixedly arranged in the sleeve
Has a magnetic pole (main pole) 10 degrees upstream from the closest position of the sleeve and the photosensitive drum in the rotation direction of the photosensitive drum. It is desirable that the angle of the main pole with the closest position (θ in the figure) falls within the range of 20 ° upstream to 10 ° downstream in the rotation direction of the photosensitive drum, and more preferably 15 ° to 0 ° upstream. . If it is downstream from that, magnetic particles are attracted to the main pole position, and it becomes easy for magnetic particles to accumulate on the downstream side of the charging nip in the direction of rotation of the photosensitive drum. Deteriorates, and retention easily occurs. Further, when there is no magnetic pole in the charging nip portion, it is obvious that the force exerted by the magnetic particles on the sleeve is weakened, and the magnetic particles tend to adhere to the photosensitive drum. The charging nip described here indicates a region where the magnetic particles are in contact with the photosensitive drum during charging.

In the present embodiment, magnetic particles obtained by subjecting a sintered ferromagnetic material (ferrite) to a reduction treatment are used, but in addition to this, a resin and ferromagnetic powder are kneaded to form particles, Alternatively, a mixture of conductive carbon or the like for adjusting the resistance value and a surface-treated one may be used in the same manner. These magnetic particles have a role of favorably injecting electric charges into the photoconductor, and have a role of preventing the electrification of the charging member and the photoconductor caused by the concentration of the charging current on defects such as pinholes formed on the photoconductor. It must also have a protective role.

Therefore, the resistance value of the charging member is 1 × 10 ⁴ Ω.
˜1 × 10 ⁹ Ω is preferable, and especially 1 × 10 ⁹ Ω.
It is preferably ⁴ Ω to 1 × 10 ⁷ Ω. If the resistance value of the charging member is less than 1 × 10 ⁴ Ω, pinhole leak tends to occur, and if it exceeds 1 × 10 ⁹ Ω, good charge injection tends to be difficult. Further, in order to control the resistance value within the above range, the volume resistance value of the magnetic particles of the present invention is preferably 1 × 10 ⁴ Ω · cm to 1 × 10 ⁹ Ω · cm, and particularly 1 ×. 10 ⁴ Ω · cm to 1 ×
It is preferably 10 ⁷ Ω · cm.

The peak in the measurement of the average particle size and particle size distribution of the magnetic particles of the present invention is preferably in the range of 5 to 100 μm from the viewpoint of preventing charge deterioration due to contamination of the particle surface. The resistance value of the charging member is 1 × 10 ⁶ Ω · cm.
Therefore, by applying -700v as the DC component of the charging bias, the surface potential of the photosensitive drum also became about -700v.

Next, the developing device described in this embodiment will be described with reference to FIG.

The developing device 44 is arranged so as to face the photosensitive drum 1, and the inside thereof is a partition wall 51 extending in the vertical direction.
The first chamber (developing chamber) 52 and the second chamber (stirring chamber) 53
It is divided into and. A non-magnetic developing sleeve 54 that rotates in the arrow direction is arranged in the first chamber 52, and a magnet 55 is fixedly arranged in the developing sleeve 54. The developing sleeve 54 carries and conveys a layer of a two-component developer (including a magnetic carrier and a non-magnetic toner) whose layer thickness is regulated by a blade 56, and transfers the developer to the photosensitive drum 1 in a developing area facing the photosensitive drum 1. To develop the electrostatic latent image. In order to improve the developing efficiency, that is, the rate of applying toner to the latent image, a developing bias voltage in which a DC voltage is superimposed on an AC voltage is applied from a power source 57 to the developing sleeve 54.

Developer stirring screws 58 and 59 are arranged in the first chamber 52 and the second chamber 53, respectively. The screw 58 stirs and transports the developer in the first chamber 52, and the screw 59 and the toner 63 supplied by the rotation of the transport screw 62 from the toner discharge port 61 of the toner replenishing tank, which will be described later, are already in the developing device. A certain developer 43 is stirred and conveyed to make the toner concentration uniform. In the partition wall 51, a developer passage (not shown) that allows the first chamber 52 and the second chamber 53 to communicate with each other at the front and rear ends in FIG.
Is formed, and the developer in the first chamber 52, in which the toner is consumed by the development and the toner concentration is lowered, is moved from one passage into the second chamber 53 by the conveying force of the screws 58 and 59. The developer whose toner concentration has recovered in the second chamber 53 moves from the other passage into the first chamber 52.

In the present embodiment, in order to correct the change in the developer density in the developing device 44 due to the development of the electrostatic latent image, that is, in order to control the toner amount replenished to the developing device 44, the development is performed. The inductance head 20 is installed on the bottom wall of the first chamber (developing chamber) 52 of the developing device 44, and a developing signal in the developing device 44, specifically, in the first developing chamber 52 is detected by a detection signal from the inductance head 20. An inductance detection system ATR is provided which detects the actual toner concentration of the agent 43 and supplies toner by comparing it with a reference value.

The toner particles used in the present invention are spherical polymerized toners. The method for producing the toner particles is, in the present embodiment, a monomer composition obtained by adding a colorant and a charge control agent to the monomer of the polymerization method in an aqueous system. Spherical toner particles were obtained by suspending and polymerizing in a medium. This method is suitable for inexpensively producing spherical toner.

The developer carrier particles used in the present invention are:
A low-magnetization carrier is used, and high image quality is achieved in combination with the spherical polymer toner. The advantage of using a low-magnetization carrier is that the magnetic interaction between adjacent magnetic brushes is small due to the low amount of magnetization, and as a result, the ears of the magnetic brushes become dense and short, which causes the magnetic brushes to become toner on the latent image. Since the adhesion surface is softly peeled off, so-called scavenging, which is scratched off of the developing toner, can be prevented, and an image with high resolution can be provided.

The non-resistance of the developing carrier particles used in this embodiment is 1 × 10 with respect to the magnetic particles used in the charger to prevent power supply to the photosensitive drum in the developing section.
Use a high resistance material of about ¹³ Ω · cm.

In this embodiment, the magnetic permeability of the developing carrier particles is different from that of the charging carrier particles, and the magnetic permeability of the charging carrier particles is twice that of the developing carrier particles.

As described above, the two-component developer contains the magnetic carrier and the non-magnetic toner as the main components, and the developer 4
When the toner concentration of No. 3 (ratio of the weight of toner particles to the total weight of carrier particles and toner particles) changes, the apparent magnetic permeability changes depending on the mixing ratio of the magnetic carrier and the non-magnetic toner. When this apparent magnetic permeability is detected by the inductance head 20 and converted into an electric signal, the electric signal changes substantially linearly according to the toner concentration, as shown in FIG. That is, the output electric signal from the inductance head 20 corresponds to the toner concentration of the two-component developer in the developing device 44. The processing of the output electric signal from the inductance head 20 will be described with reference to FIG. The output electric signal from the inductance head 20 is compared with the comparator 2
1 to one input. To the other input of the comparator 21, the reference voltage signal source 22 receives a reference electric signal corresponding to the apparent magnetic permeability of the developer 43 at the specified toner concentration (toner concentration at the initial setting value). . Therefore, since the comparator 21 compares the specified toner density with the actual toner density in the developing device, the detection signal of the comparator 21 is the CPU as the comparison result of both input signals.
Is supplied to 67.

The CPU 67 controls so as to correct the next toner supply time based on the detection signal from the comparator 21. For example, when the actual toner concentration of the developer 43 detected by the inductance head 20 is lower than the specified value, that is, when the toner is insufficiently supplied, the CPU 67 supplies the insufficient toner to the developing device. The conveying screw 62 of the toner replenishing tank 60 is operated so as to replenish the toner to the toner supplying tank 44. That is, the screw rotation time required to replenish the developing device 44 with the insufficient toner is calculated based on the detection signal from the comparator 21, and the motor drive circuit 69 is controlled to rotationally drive the motor 70 for that time. , Shortage toner is supplied to the developing device 44. When the actual toner concentration of the developer 43 detected by the inductance head 20 is higher than the specified value, that is, when the toner is excessively replenished, the CPU 67 causes the detection signal from the comparator 21 to be detected. The excess toner amount in the developer is calculated based on. Then, in the subsequent image formation by the original, the toner is replenished so as to eliminate the excess toner amount, or the image is formed without replenishing the toner until the excess toner amount is consumed, that is, there is no toner. Replenishment forms an image to consume the excess toner amount, and when the excess toner amount is consumed, the toner replenishing operation is performed as described above.

Next, the above operation will be further described with reference to the flowchart of FIG.

First, when the image forming apparatus is started, toner density detection is started in block S502. The detected voltage signal a from the inductance head is input to the comparator 21 in block S503, is compared with the reference voltage signal b from the reference voltage signal source 22 in the comparator 21 in block S504, and the detected signal difference is detected in block S505. (A-
b) is sent to the CPU 67. In block S506, the CPU
In 67, it is determined whether (ab)> 0, and if the toner density is lower than the reference value (YES), block S50
In 7, the toner replenishment time is determined. After the copy operation is started in block S508, toner is replenished between the images for the toner replenishment time determined in block S507 in block S509, and the process returns to the start. Also, block S506
If the toner concentration is higher than the reference value (NO), the copy operation of block S510 is started, and the process returns to the start without supplying toner. The toner density detection timing may be immediately before the copy operation is restarted or during the copy operation. For example, the operation of the first sheet of the image forming apparatus may be detected immediately before the copy operation is resumed, and thereafter, it may be detected during the copy operation.

In the inductance detection ATR used in this embodiment, the optimum toner density (8% in this embodiment. If it is higher than this value, toner scattering occurs, and if it is too low, the image density becomes low. A problem such as thinning may occur).
If the detection signal of the sensor is larger than the reference value (for example, 3.0 V), the toner is replenished, and if the detection signal of the sensor is small (for example, 2.0 V).
V) Toner supply is to be stopped, but the present invention is not limited to the above signal processing, and the circuit configuration may be changed to a reference value other than 2.5V. Well, when the toner concentration is lower than the optimum value, the detection signal of the sensor should be smaller than the reference value of the sensor.
The detection signal of the sensor may be increased when the toner density is higher than the optimum value.

The inductance detecting sensor used in the present invention has the following functions.
FIG. 8 shows a DC voltage (hereinafter referred to as a control voltage, Vc in the figure) for adjusting the detection signal value of the toner concentration sensor used in the present invention.
6 is a graph showing the relationship between the output voltage (Vout) of the toner concentration sensor and the output voltage (Vout). As described above, the inductance detection sensor used in the present invention can change the detection signal value of the toner concentration sensor within the output range of the sensor by changing the control voltage value even if the toner concentration is constant.

As described above in the problems to be solved by the invention, the above-mentioned structure has a problem in the magnetic brush charging device, which has a problem in that the surface of the image carrier of the magnetic particles forming the charging magnetic brush. The magnetic carrier may adhere to or flow out of the magnetic carrier. When it is collected in the developing device, the developing device using the inductance detection type sensor accumulates in the developing device as the number of copies increases even if a small amount of injected carrier adheres, which is not particularly problematic for the image. As a result, the apparent magnetic permeability of the developer as a whole changes when the magnetic permeability of the developing carrier differs from that of the injection carrier, which may cause an error in toner concentration control by the inductance detection type sensor.

Further, as described above, according to the study by the present inventors, it has been found that the image forming apparatus shown in the present embodiment has a different amount of charged carriers mixed into the developing device for each environment.

More specifically, as shown in FIG. 9, the lower the humidity, and strictly speaking, the smaller the absolute water content in the air, the higher the resistance of the charging carrier and the photosensitive drum becomes. Carrier adhesion and incorporation into the developer will increase.

The present invention will be specifically described below with respect to the above problem. A feature of the present invention is that the control voltage value for adjusting the detection signal of the inductance detection sensor is set to the image forming time,
Alternatively, it is characterized in that it is newly set according to the number of times of image formation.

For example, as shown in FIG. 10A, the detection signal of the sensor is 0.2 when the control voltage value changes by 0.1V.
When the toner density changes by 5V, the detection signal of the toner density sensor changes by 0.5V with respect to the change of the toner density of 1% (FIG. 10).
(B)) Use an inductance detection sensor. This inductance detection sensor, temperature 25 ℃ / humidity 50
In a developing device of the image forming apparatus, the amount of charge carriers mixed into the developing device at the time of image formation of 5% Duty under the environment of 5% is about 20 g / 50000 times. The initial value (reference value) of toner concentration control is the optimum toner concentration of the developer of 8%.
The control signal value is adjusted so that the detection signal from the inductance head 20 becomes 2.5V. When 20 g of the charge carrier is forcibly mixed into the developer in the developing container having the inductance detection sensor set in this way, the apparent magnetic permeability of the developer increases and the initial optimum T / D ratio is maintained. In this case, the detection signal of the inductance detection sensor changes from the initial reference value of 2.5V to 3.5V 1
V will rise. Therefore, the detection signal is actually 2.5V
As a result, the toner is replenished so that the toner is replenished excessively, and the sensitivity of the inductance detection sensor used in the image forming apparatus is 0.5 V /% (see FIG. 10).
(B)) Therefore, as a result of repeating the image forming operation 50,000 times, the final toner concentration is 8%.
It deviated by 2% and was controlled to 10%.

In response to this malfunction, when the initial reference value of the inductance detection sensor was 2.5 V and the image forming operation was repeated 25,000 times, if the mixing amount of the charge carriers was proportional to the image forming operation. Then, since the amount is 20 g / 50000 times, it becomes 10 g / 25000 times. Inductance detection sensor has 2 charge carriers
When 0 g is mixed, the value changes by 1 V, and when about 10 g of charged carriers are mixed, the value changes by 0.5 V. At this point, the toner density has an error of 1%. Since the detection signal of the inductance detection sensor changes by 0.25V when the control voltage value changes by 0.1V, the output value is reduced by decreasing the control voltage value by 0.2V to 12.3V at the timing of 25,000 times of image formation. Make sure to set the CP from 2.5V to 2V beforehand.
Set a command in U25. By setting the detection signal of the inductance detection sensor to 2.0V, toner replenishment is not performed until the detection signal reaches the reference value of toner concentration control, which is 2.5V, so that the error of 1% of toner is eliminated, The initial toner density will be adjusted back to 8%. Further, when the control voltage value is further lowered by 0.2 V when the image forming operation is repeated 50,000 times, the toner density after the image forming operation 50,000 times is about 8% which is the reference toner density and the detection signal is not corrected. (Fig. 11i
Compared to i)), the error in toner density control can be eliminated (FIG. 11 (i)).

Further, when the image formation is carried out in the image forming apparatus under the environment of 23 ° C./5%, the mixing amount of the charge carrier into the developing device is about 30 g / 50,000 sheets as shown in FIG. Therefore, in this environment, the charge carrier mixing amount of 25,000 sheets is 15 g, and the output change amount of the inductance detecting sensor is 0.75 V due to the mixing of the charge carrier 15 g, so the control voltage correction amount of the inductance detecting sensor is 0.3 V. An instruction to lower the control voltage value by 0.3V is set in the CPU 25 when 50,000 sheets are printed.

As described above, in the present invention, a command is set in advance in the CPU 25 so that the control voltage value of the inductance detecting sensor is reset when the image forming operation is repeated for a certain time or a certain number of times. The correction amount when resetting the control voltage value is set to be different for each environment, and the CPU 25 newly sets the control voltage value output from the control voltage signal source at a predetermined timing.

A more accurate toner density control can be performed by setting a correction amount of the control voltage for the number of times of image formation for each environment in the CPU 25 and selecting the control voltage correction amount based on the output from an environment sensor (not shown). You can do it.

In the above embodiment, the timing for resetting the control voltage with respect to the number of images is set to once every 25,000 sheets, but it is not specified, and the toner timing can be controlled more accurately by advancing the timing. You can also do

Further, in the present embodiment, the number of images formed is set as the control voltage setting timing, but the operation time of the image forming apparatus may be set as the control voltage setting timing.

(Embodiment 2) The control voltage value newly set by the control voltage signal source 22 in the above-described Embodiment 1 is set as appropriate depending on the image forming time and the number of image formed, as shown in FIG.
As shown in (a), it is possible to control toner density with higher accuracy by newly setting linearly. (Fig. 12
(B)).

(Embodiment 3) The charge carrier has a certain degree of spread in the particle size distribution, and it has been found by the inventors of the present invention that the charge carrier tends to adhere to even minute particles. It is considered that such a minutely charged carrier adheres to the carrier especially when the time or the number of times of the image forming operation is early and the apparent change in the magnetic permeability of the initial developer becomes large. After that, when the minute charge carriers are reduced in the charging device, the apparent change in the magnetic permeability of the developer is gradually reduced and may be changed in a non-linear manner (FIG. 13A).

Therefore, the control voltage value newly set by the control voltage signal source 22 in the above-described first embodiment is properly set again as shown in FIG. 13B depending on the image forming time and the number of image formed. With this, it becomes possible to control the toner density with higher accuracy. (FIG.13 (c)).

In each of the embodiments described so far, the case where the present invention is applied to the electrophotographic digital copying machine is shown. However, the present invention is not limited to the electrophotographic method, the electrostatic recording method and the like. Can be applied equally to various image forming apparatuses such as various copying machines and printers. For example, the present invention can be applied to an image forming apparatus that performs grayscale representation of an image by a dither method, and also to an image forming apparatus that forms a toner image based on an image information signal output from a computer or the like, instead of copying a document. The present invention can also be applied. Further, it goes without saying that various modifications and changes can be made to the configurations of the image forming apparatus and the control system as necessary.

[0079]

As described above, according to the present invention, the above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to a charging device for charging an image carrier by bringing a charging member composed of magnetic particles facing the image carrier into contact with the image carrier and applying a charging bias to the charging member. And an exposure device for forming an electrostatic latent image on the charged image carrier, and a two-component developing device for forming the electrostatic latent image from toner particles and magnetic carrier particles having different magnetic permeability from the magnetic particles used for the charging member. Forming a visible image using an agent, and detecting the apparent magnetic permeability of the two-component developer,
A developer toner concentration control device that has a toner concentration sensor that outputs a detection signal, and operates a toner replenishing means based on a reference value of toner replenishment control based on a comparison result of the detection signal based on the detection result and the reference value. And a transfer device for transferring the visible image onto a transfer material, and the toner concentration sensor can control the detection signal by changing the control signal value input to the toner concentration sensor. And a control signal of the control unit in response to a change in the detection signal of the toner concentration sensor due to the magnetic particles of the charging member attached to the image carrier accumulating in the developing container with the operation time of the image forming apparatus. In the image forming apparatus for changing the value, the change amount of the control signal value corrected by the control value changing unit is determined by the temperature / humidity sensor attached to the image forming apparatus. By being different from the, the charging carrier is used in the magnetic brush charging,
When the charge carrier adheres to the developing device due to the repeated image forming operation and the charge carrier is mixed in the developing device, the difference in the magnetic permeability between the charge carrier and the developer carrier causes the optimum toner concentration of the entire developer Even if the average magnetic permeability changes gradually, the control signal that adjusts the detection signal of the inductance detection sensor by changing its control value is adjusted by the detection signal to adjust the toner density control standard set initially. Without changing the value,
Even if the image forming operation is repeated, the toner is always replenished properly, so that the T / D ratio control with less error becomes possible. Further, by having a control table of the detection signal of the inductance detection sensor for each environment, accurate toner concentration control can be performed even if the mixing amount of the charge carrier in the developing device is different for each environment.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of an image forming apparatus according to the present invention.

FIG. 2 is a detailed view of an image forming unit in the image forming apparatus according to the present invention.

FIG. 3 is a schematic cross-sectional view showing a schematic configuration of a charger included in the image forming unit of FIG.

FIG. 4 is a schematic cross-sectional view showing a schematic configuration of a developing device included in the image forming unit of FIG.

FIG. 5 is a characteristic diagram showing a state in which a detection signal from the inductance head changes due to a change in toner concentration of the developer.

FIG. 6 is a diagram illustrating toner replenishment control by the inductance detection sensor of the present invention.

FIG. 7 is a flow chart for explaining the basic operation of the embodiment of the present invention.

FIG. 8 is a diagram illustrating a relationship between a control voltage and a sensor output by the inductance detection sensor of the present invention.

FIG. 9 is a graph showing the number of operations of the image forming apparatus in Embodiment 1 and the amount of charge carriers mixed in the developing device for each environment.

FIG. 10 shows the relationship between the control voltage value of the toner concentration sensor and the detection signal of the toner concentration sensor and the relationship of the toner concentration sensor with respect to the toner concentration change in the first embodiment.

FIG. 11 is a diagram simply showing the relationship between the number of operations of the image forming apparatus and the toner concentration of the developer in the first embodiment.

FIG. 12 is a diagram simply showing the relationship between the number of operations of the image forming apparatus according to the second embodiment, the reference signal value of the inductance detection sensor, and the toner concentration of the developer.

FIG. 13 is a diagram simply showing the relationship between the operating time of the image forming apparatus, the apparent magnetic permeability of the developer, the reference signal value of the inductance detection sensor, and the toner concentration of the developer according to the third embodiment.

FIG. 14 is a schematic sectional view showing a schematic configuration of a magnetic brush charger.

FIG. 15 is a graph showing a change in developer permeability, a change in sensor output, and a change in toner concentration due to mixing of charge carriers in a conventional technique.

FIG. 16 shows changes in the toner concentration sensor detection signal with respect to changes in the toner concentration and transitions of the reference signal with respect to the number of times of image formation in the related art.

Continued front page    F-term (reference) 2H027 DA01 DA11 DA14 DA39 DA45                       DD07 DE04 DE07 DE10 EA06                       EC06 EC10 EC14 ED10 EF09                       EF12                 2H077 AA14 AB02 AC02 AD06 AD36                       DA10 DA22 DA24 DA42 DA52                       DB01 DB22 EA03                 2H200 FA16 GA23 GA34 GA45 GA47                       GA57 GB25 HA03 HB12 HB17                       HB20 HB22 HB46 HB48 MB04                       MB06 MC15 NA02

Claims (8)

[Claims] 1. A charging device for charging an image carrier by bringing a charging member made of magnetic particles facing the image carrier into contact with the image carrier and applying a charging bias to the charging member; And an exposure device for forming an electrostatic latent image on the image carrier, and a two-component developer comprising the electrostatic latent image composed of toner particles, magnetic particles used for the charging member, and magnetic carrier particles having different magnetic permeability. A toner image sensor that forms a visible image by detecting the apparent magnetic permeability of the two-component developer and outputs a detection signal, and compares the detection signal based on the detection result with its reference value. From a toner replenishment control reference value, a developing device having a developer toner concentration control device for operating the toner replenishing means, and a transfer device for transferring the visible image to a transfer material. The detection signal Having a control means that can be adjusted by changing the control signal value input to the concentration sensor,
An image in which the control signal value of the control unit is changed in response to a change in the detection signal of the toner concentration sensor caused by the accumulation of magnetic particles of the charging member attached to the image carrier in the developing container with the operation time of the image forming apparatus. In the image forming apparatus, the change amount of the control signal value corrected by the control value changing unit varies depending on the environment judged by the temperature / humidity sensor attached to the image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the operating time of the image forming apparatus includes the operating time of the image forming apparatus other than the image forming operation. 3. The image forming apparatus according to claim 1, wherein the control value changing unit gradually changes and sets the control value of the control unit. 4. The image forming apparatus according to claim 1, wherein the control value changing unit linearly changes and sets the control value of the control unit. 5. The control value changing means nonlinearly changes and sets the control value of the control means.
The image forming apparatus according to item 1. 6. The image forming apparatus according to claim 1, wherein the image forming operation time is determined based on the operation time of the charging member by the magnetic brush. 7. The image forming apparatus according to claim 1, wherein the time of the image forming operation is determined from the video count number of the image density signal in the image information signal. 8. The image forming apparatus according to claim 1, wherein the change amount of the control signal value is determined from the video count number of the image density signal in the image information signal.