JP2009020465A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for preventing toner dust or irregularity on a toner image or transfer paper caused by a large amount of toner adhering to a developing roller, and preventing toner dust or irregularity on the toner image or the transfer paper due to an edge effect. <P>SOLUTION: The image forming apparatus is provided with a remaining amount detection means 28 for detecting that only a small amount of toner remaining remains in a developer storing part 27a, or provided with an adhesive amount detection means for detecting toner adhesive amount on a photoreceptor 3, or provided with a width detection means for detecting the width of a toner image in a main scanning direction from a write signal for forming a latent image on the photoreceptor 3 on the signal. The image forming apparatus is provided with a controller to substantially reduce the amount of toner flying from the developing roller 31 to the photoreceptor 3 rotated at constant speed by decreasing linear velocity of the developing roller 31 when only a small amount of toner remains, when the toner adhesive amount on the photoreceptor 3 exceeds the predetermined amount or when determining that a signal of a small-width line image exists in the write signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus such as a printer, a copier, or a fax machine, and more specifically, a nonmagnetic toner and an external additive that improves the fluidity of the nonmagnetic toner. The present invention relates to an image forming apparatus using a component developer.

Developers used in electrophotographic image forming apparatuses include two-component developers composed of toner and carrier and one-component developers composed of toner.
In particular, the latter one-component developer includes, for example, a magnetic toner containing a magnetic material of black magnetite powder in the toner, and external additives such as hydrophobic silica and styrene-acrylic resin fine particles for improving fluidity. In some cases, an agent and a nonmagnetic toner composed of a color pigment are blended.
A one-component developer containing this external additive can form a clear multicolor image that cannot be obtained with a magnetic toner containing black magnetite powder.
By the way, an electrophotographic image forming apparatus using such a developer is capable of extending the lifespan of the photoconductor and the developing roller and superimposing toner images of respective colors, so that a latent image is formed. The photosensitive member and the developing roller are arranged so as to face each other so that the surface of the photosensitive member and the developer layer on the surface of the developing roller are not in contact with each other.
Then, by applying a DC bias to these, a one-component developer (only toner in the case of a two-component developer) flies from the developing roller toward the photoreceptor, and the latent image is developed as a toner image. A non-contact development method is generally used.

Thus, in order to fly a one-component developer (only toner in the case of a two-component developer), a direct current bias is applied, but when a one-component developer containing an external additive is used, Such a problem has occurred.
That is, the styrene-acrylic resin fine particles in the external additive are charged up over time due to their physical properties, the amount of charge per unit weight increases and the adhesion becomes strong, and as a result, the inner wall of the cabinet of the developer unit Furthermore, styrene-acrylic resin fine particles are filmed and accumulated.
As the styrene-acrylic resin fine particles adhere and accumulate on the inner wall of the developing device cabinet, naturally, the styrene-acrylic resin fine particles in the one-component developer are reduced and the fluidity is lowered. The amount of nonmagnetic toner adhering to the roller increases.
If the amount of non-magnetic toner adhering to the developing roller increases, the amount of non-magnetic toner that is developed into the latent image also increases, so that the discharge discharge when the transfer material is peeled off from the transfer device, the transfer material guide member, The toner image (including the fixed image after fixing) is liable to generate dust and unevenness due to static electricity due to sliding of the transfer material, moisture evaporation of the transfer material due to fixing heat at the fixing unit, and the like.
Even if the amount of nonmagnetic toner adhering to the developing roller is at a level at which no dust or unevenness occurs, it may occur depending on the image shape. That is, when there is a line image with a small image width in the main scanning direction, the amount of adhesion per unit area is larger in the line image than in the reference pattern due to the so-called edge effect. Dust and unevenness are likely to occur in the later fixed image).
Conventionally, to solve the dust and unevenness that occurs in toner images (including fixed images after fixing), for example, the charge amount of toner on the photoconductor is calculated, and if the charge amount is low, the transfer high-voltage power supply is controlled. The toner charge amount on the transfer paper is increased to a level at which image degradation does not occur due to disturbance after transfer, and the adhesion between the toner and the transfer paper is electrostatically increased, so that the image after transfer is free from dust and unevenness. There is an image forming apparatus in which the occurrence of the above is reduced (see, for example, Patent Document 1).
Japanese Patent Laying-Open No. 2005-140902 (first page, FIG. 1)

The technique for preventing the occurrence of dust and unevenness disclosed in Patent Document 1 is very suitable. However, as described above, styrene-acrylic resin fine particles adhere and accumulate on the inner wall of the cabinet of the developing device. In the case where the flowability of the one-component developer is lowered due to this, no fundamental solution has been achieved.
In other words, if the absolute amount of one-component developer on the transfer paper increases, no matter how much the transfer high-voltage power supply is controlled, the peeling discharge when the transfer material is peeled off from the transfer device after transfer or the transfer material guide member and transfer The generation of image dust and unevenness due to external disturbances such as static electricity due to the rubbing of the material and moisture evaporation of the transfer material due to fixing heat at the fixing portion could not be completely suppressed.
Even if the amount of non-magnetic toner adhering to the developing roller is at a level at which no dust or unevenness occurs, if there is a line image with a small image width in the main scanning direction, the so-called edge effect is applied. In this case, although the problem can be solved by controlling the transfer high-voltage power supply, the same technical means is used to prevent the occurrence of dust and unevenness due to such a case and the prevention of dust and unevenness due to the above case. Could not be solved.
Accordingly, the present invention has been made in view of such a situation, and the amount of toner adhering to the developing roller is excessive, and toner is generated due to dust or unevenness generated on a toner image or transfer paper, or an edge effect. An object of the present invention is to provide an image forming apparatus that prevents dust and unevenness generated on an image and transfer paper.

In order to achieve the above technical problem, the image forming apparatus according to the present invention employs the following technical means.
That is, the image forming apparatus according to claim 1 includes a rotatable developing roller to which a one-component developer composed of a nonmagnetic toner and an external additive for improving the fluidity of the nonmagnetic toner is attached, a latent roller, and a latent image. The photosensitive member on which an image is formed is disposed so that the one-component developer adhered to the surface of the developing roller can fly toward the latent image, and the linear velocity of the developing roller is reduced. A developing roller control means is provided for adjusting the amount of the one-component developer adhered to the developing roller.
According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the amount of the one-component developer is detected in a developer containing portion that contains the one-component developer and supplies the one-component developer to the developing roller. And a developing roller control unit that determines whether the detected value of the remaining amount detecting unit is a toner end, and decelerates the developing roller when the toner end is determined. And
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the developing roller control means integrates the number of times the one-component developer is replenished into the developer accommodating portion, and the accumulated number of replenishments is a predetermined number. When it reaches, the control of the deceleration is stopped.

According to a fourth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to third aspects, further comprising an adhesion amount detection unit that detects an amount of the one-component developer adhered to the photoconductor, and the development roller control unit. Is characterized in that the developing roller is decelerated based on the adhesion amount of the one-component developer detected by the adhesion amount detection means.
An image forming apparatus according to a fifth aspect is the image forming apparatus according to the fourth aspect, wherein the developing roller control unit is configured such that the development amount of the one-component developer detected by the adhesion amount detection unit is 0.8 mg / cm ² or more. The roller is decelerated.
According to a sixth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to fifth aspects, further comprising a width detecting unit that detects a toner image width in a main scanning direction from a write signal for forming a latent image on the photoconductor. The developing roller control means decelerates the developing roller when the width detecting means detects the toner image having a small width.
An image forming apparatus according to a seventh aspect is the image forming apparatus according to the sixth aspect, further comprising: an adhesion amount detection unit that detects an amount of the one-component developer adhered to the photoconductor; The developing roller is decelerated when the adhesion amount of the one-component developer detected by the detecting means is 0.6 mg / cm ² or more.

According to the present invention, even if the external additive in the one-component developer is reduced and the fluidity is lowered, and the amount of nonmagnetic toner adhering to the developing roller increases, the developing roller control means can The amount of one-component developer flying from the developing roller toward the photoreceptor is substantially reduced, so that the amount of non-magnetic toner for developing the latent image can be maintained at an optimum state. it can. Therefore, since the absolute amount of the one-component developer on the transfer paper is always substantially constant, it is possible to suppress the occurrence of image dust and unevenness due to excessive nonmagnetic toner.
Further, when a toner image having a small width in the main scanning direction is detected from a write signal for forming a latent image on the photoconductor, the developing roller control means decelerates the linear velocity of the developing roller and moves from the developing roller toward the photoconductor. The amount of one-component developer that flies is reduced substantially, so the occurrence of dust and unevenness is suppressed even for images that tend to increase the amount of non-magnetic toner attached due to edge effects such as line images. be able to.

Next, an embodiment of an image forming apparatus according to the present invention will be described with reference to the accompanying drawings. The image forming apparatus according to the present embodiment includes a two-component developer (hereinafter referred to as “black toner”) composed of black toner and a carrier, hydrophobic silica and styrene-acrylic resin fine particles for improving fluidity, and the like. And a one-component developer (hereinafter referred to as “red toner”) in which a non-magnetic toner comprising a red pigment and a non-magnetic toner are blended to form a red-black two-color image. Illustrated.
First, an outline of the image forming apparatus according to the present embodiment will be described.
As shown in FIG. 1, the image forming apparatus according to the present embodiment is electrically connected to a document reader 1 that optically reads a document and outputs it as electrical image data, and the document reader 1. An image memory unit 2 for storing image data output by the document reader 1, a rotatable drum-shaped photoconductor 3 on which a latent image and a toner image are formed, and a black toner image is formed on the photoconductor 3. A first image forming unit 4; a second image forming unit 5 for forming a red toner image on the photosensitive member 3 so as to be superimposed on the black toner image; and the first image forming unit 4 and the second image forming unit 5 A controller 6 that is electrically connected to both of the image memory unit 2 and performs overall control of image formation, and a transfer sheet sent from the paper feed tray 7 is put on standby, and a transfer belt, which will be described later, via a paper feed guide 8. 11 and a predetermined timing between the photosensitive member 3 Thus, a registration roller 9 to be sent out, a transfer belt 11 hung on a pair of rollers 10, and a bias roller 12 pivotally supported on the back surface of the transfer belt 11 are provided, and the bias roller 12 sandwiches the transfer belt 11. A transfer current is supplied to the photoconductor 3 to transfer the toner image on the photoconductor 3 onto the transfer paper, and the transfer device 13 that transports the transfer paper to a fixing device (not shown) and the bias roller 12 are electrically connected. The transfer voltage applying unit 14 that outputs a transfer voltage while keeping the current flowing to the photoconductor 3 constant, and the separation claw 15 that peels the transfer paper from the photoconductor 3 when the transfer paper is attached to the photoconductor 3. And a cleaner 16 for removing the toner remaining on the photoconductor 3 after transferring the two-color toner image onto the transfer paper, and a charge eliminating for removing the charge of the photoconductor 3 in preparation for the next image formation. Configured with a 17.

The outline of the operation of the image forming apparatus configured as described above will be described. First, a document reader 1 on which a desired document is set is optically read and stored in the image memory unit 2 as electrical image data. accumulate.
Next, at the same time as the rotational movement of the photosensitive member 3 is started, image formation by the first image forming unit 4 and the second image forming unit 5 is started. Although the first developing unit 21 and the second developing unit 25 constituting the first image forming unit 4 and the second image forming unit 5 have different configurations and development methods, the image forming process itself is an electrophotographic method. Are well known.
That is, the surface of the photosensitive member 3 is uniformly charged, the charged surface of the photosensitive member 3 is exposed based on image data, and the latent image on the photosensitive member 3 formed by the exposure is developed with toner. Visualize in the image. This image formation is continuously performed by the first image forming unit 4 and the second image forming unit 5 so that the red toner image is superimposed on the black toner image on the photoreceptor 3.
The two-color toner image formed on the photoreceptor 3 in this manner moves to a position facing the transfer belt 11. At the same time, the registration roller 9 feeds the transfer paper between the transfer belt 11 and the photosensitive member 3, and a transfer current is passed through the transfer belt 11 to transfer the toner image on the photosensitive member 3 to the transfer paper.
Then, the transfer paper carrying the two-color toner image is moved to a fixing device (not shown) by the transfer belt 11, and the fixing device pressurizes and heats the transfer paper carrying the two-color toner image to transfer the two-color toner image. Fix on paper. The transfer paper on which the two-color toner image is fixed in this way moves to a carry-out section (not shown), and a series of operations ends.

The main part of the present invention is the deceleration control of the second developing roller 31, and the detailed description thereof will be described later in each embodiment. The configuration and operation of the first image forming unit 4 which is a set with the second image forming unit 5 are as follows.
That is, the first image forming unit 4 includes a first charger 18 that uniformly charges the surface of the photoconductor 3 and a first exposure device that forms a latent image of a black image on the photoconductor 3 based on image data. 19 and a first developing roller 21 provided with a first developing roller 20 provided with a magnet roller inside a sleeve rotatably supported by the shaft, and developing a latent image of a black image into a black toner image using black toner. And a first bias applying unit 22 that applies a DC bias to the sleeve. The first developing device 21 is configured to supply black toner to the first developing device 21 via a toner cartridge (not shown) filled with black toner.
In the first image forming unit 4 configured as described above, first, the first charger 18 uniformly charges the surface of the photoreceptor 3. Then, the first exposure device 19 irradiates the photosensitive member 3 with strong or weak light based on the image data to form a latent image of a black image on the surface of the photosensitive member 3.
Then, the latent image of the black image formed on the photoconductor 3 moves to a position facing the first developing device 21 by the rotation of the photoconductor 3. At this time, a direct current bias is applied to the sleeve rotating at a linear velocity ratio of about 2.0 with respect to the photosensitive member 3 to form a magnetic brush by a carrier on the surface of the sleeve.
The black toner is electrostatically attached to the latent image of the black image on the photoconductor 3 through the magnetic brush, thereby forming a black toner image on the photoconductor 3. Thus, the first image forming unit 4 is a so-called magnetic brush DC bias developing method.

(Embodiment 1)
The image forming apparatus according to the first embodiment includes a second image forming unit 5 and a controller 6 (developing roller control means).
The second image forming unit 5 includes a second charger 23 that uniformly charges the surface of the photoconductor 3, and a second exposure device 24 that forms a latent image of a red image on the photoconductor 3 based on the image data. A second developing unit 25 that develops the latent image of the red image into a red toner image using red toner, and a second bias applying unit 26 that applies a DC bias to the second developing roller 31 of the second developing unit 25; It is configured with.
As shown in FIG. 2, the second developing device 25 includes the cabinet 27, the remaining amount detecting means 28, the agitator 29, the toner supply roller 30, the second developing roller 31, and the second developing device 25, as shown in FIG. The developing roller drive motor 32 and the thin layer blade 33 are provided. The second developing device 25 is detachable from a toner cartridge (not shown) filled with red toner, and the red toner is supplied into the developer accommodating portion 27a via the toner cartridge. It is like that.
The cabinet 27 includes a developer container 27a in a hermetically sealed container shape having a convexly curved bottom portion 27b formed on the right bottom surface and a bottom surface formed substantially stepped from the bottom portion 27b to the left. Is formed. Further, the cabinet 27 has a supply hole (not shown) for supplying red toner from the toner cartridge into the developer accommodating portion 27a, and a slit-like opening for exposing a part of the second developing roller 31 described later. A portion 27c is provided at the left end.
In addition, as described above, this red toner is a single component obtained by blending an external additive such as hydrophobic silica and fine particles of styrene-acrylic resin and a non-magnetic toner composed of a red pigment in order to improve fluidity. Developer.
The remaining amount detecting means 28 is electrically connected to the controller 6 and is provided on the inner bottom surface of the lowermost portion 27b of the developer accommodating portion 27a according to the weight (pressure) of the red toner in the developer accommodating portion 27a. A piezoelectric sensor having a known configuration is provided so that a voltage can be output. That is, the voltage value output from the piezoelectric sensor is replaced by the controller 6 with the amount of red toner in the developer container 27a. Note that the voltage value output from the piezoelectric sensor constantly fluctuates because the red toner in the developer accommodating portion 27a is agitated by an agitator 29 described later.

The agitator 29 is composed of a pair of shafts supported on the upper surface of the lowermost portion 27b of the cabinet 27 and on the left side thereof. The pair of agitators 29 both rotate in the clockwise direction, and the red toner is directed toward the toner supply roller 30 described later while stirring so as to dig up the red toner in the developer containing portion 27a. Is supposed to be transported.
The toner supply roller 30 includes a sponge roller that is pivotally supported to the left of the left agitator 29.
The second developing roller 31 is formed such that a small-area dielectric portion and a small-area conductor portion are regularly (or irregularly) distributed on the peripheral surface, and an opening formed in the cabinet 27. It is pivotally supported by the cabinet 27 so that a part of the peripheral surface is exposed from 27 c and is in contact with the toner supply roller 30.

A spacer roller 36 having a required diameter larger than the diameter of the second developing roller 31 is rotatably engaged with both shaft ends of the second developing roller 31. 36 is disposed in the image forming apparatus so that a minute gap C is formed between the surface of the second developing roller 31 and the surface of the photosensitive member 3 by contacting the end of the photosensitive member 3.
The second developing roller drive motor 32 is composed of an electric motor such as a brushless DC motor, a pulse motor, an ultrasonic motor, or a direct drive motor, and is mechanically engaged with one end of the second developing roller 31 and a controller. 6 (developing roller control means) is electrically connected. Under the control of the controller 6, the second developing roller 31 can be rotated counterclockwise with a linear speed ratio of about 1.2 with respect to the photosensitive member 3 under normal conditions and when a predetermined condition is satisfied. The linear speed of the second developing roller 31 can be rotated at a reduced speed.
The thin layer blade 33 is a belt-like member formed along the axial direction of the second developing roller 31, the closest portion between the second developing roller 31 and the photosensitive member 3, the toner supply roller 30, and the second developing roller 31. The second development is performed so that the red toner adhering to the second developing roller 31 is leveled between the contact portion with the developing roller 31 and a middle portion downstream of the contact portion in the rotation direction of the second developing roller 31. A predetermined distance is provided from the surface of the roller 31.

The controller 6 records a predetermined threshold value for determining the toner end, and compares the threshold value with the voltage value output from the remaining amount detection means 28 to determine whether the toner end is reached. When the determination is made, the drive command value to the second developing roller drive motor 32 (which varies depending on the type of motor) is adjusted to decelerate the linear velocity of the second developing roller 31. The voltage value is detected when the transfer paper passes the registration roller 9.
Further, the controller 6 determines that the toner end is detected when the toner end is detected five times continuously at the detection timing described above, and the toner end is determined when the toner end is determined as the near end when the toner end is repeated twice. Thus, the linear velocity of the second developing roller 31 is decelerated. This is because the voltage value output from the piezoelectric sensor may instantaneously reach the threshold value by the stirring by the agitator 29 even though there is sufficient red toner in the developer containing portion 27a, and the above-described control is performed. This is to avoid malfunction.
Further, even when the red toner at the arrangement position reaches the toner end by the remaining amount detecting means 28 provided at the lowermost portion 27b of the developer containing portion 27a, as shown in FIG. Since the bottom surface is formed in a substantially stepped shape toward the second developing roller 31, a considerable number of images can be formed in the developer containing portion 27a.
Further, the controller 6 accumulates the number of times the red toner has been replenished into the developer accommodating portion 27a, and the accumulated number of replenishments is a predetermined number of times (external additive adhering to the inner wall of the developer accommodating portion 27a). In this case, the linear velocity of the second developing roller 31 is not reduced.
As an example of inputting the number of times of replenishment, for example, a sensor or switch that responds to the setting operation of the toner cartridge is provided so that it can be automatically input, or it is configured to allow the user to input that toner has been replenished. An example is given.

A series of operations of the second image forming unit 5 configured as described above will be described.
First, similarly to the first image forming unit 4, the second charger 23 uniformly charges the surface of the photoreceptor 3 including the black toner image forming surface, and the second exposure unit 24 converts the image data into image data. Based on this, the photosensitive member 3 is irradiated with strong or weak light to form a latent image of a red image on the surface of the photosensitive member 3.
Then, the latent image of the red image formed on the photoconductor 3 moves to a position facing the second developing device 25 by the rotation of the photoconductor 3. At the same time, the red toner moves toward the toner supply roller 30 while being charged by stirring by the agitator 29, electrostatically adheres to the rotating toner supply roller 30, and collides with the second developing roller 31. Move towards the part.
The red toner that has reached the abutting portion is charged with the same polarity as that of the photosensitive member 3 by the sliding of the second developing roller 31 and the toner supply roller 30, and adheres to the second developing roller 31 and rotates toward the photosensitive member 3 side. Moving. During this rotational movement, the thin layer blade 33 levels the red toner layer so as to have a constant layer thickness. At this time, due to the bearing effect of the external additive interposed between the non-magnetic toners, the excess red toner adhering to the second developing roller 31 is not pressed as if it was pressed and hardened, but at the thin layer blade 33 portion. The red toner layer having a constant layer thickness is formed by staying or dropping into the developer containing portion 27a.
When the latent image of the red image has moved to a position facing the second developing device 25, a DC bias is applied to the second developing roller 31 that is rotating at a linear velocity ratio of about 1.2 with respect to the photoreceptor 3. Apply. By this application, the red toner on the second developing roller 31 that is not in contact with the surface of the photoreceptor 3 flies toward the latent image of the red image, and electrostatically adheres from above the black toner image. A red toner image is formed.
As described above, the second image forming unit 5 performs development by a jumping method in which the toner is allowed to fly toward the latent image so as not to destroy the black toner image.

The second image forming unit 5 forms a red toner image on the photosensitive member 3 in this way, and when the image is formed, the external additive in the red toner is also charged. It adheres to the inner wall of the developer accommodating portion 27a of the second developing device 25. This adhesion phenomenon occurs every time an image is formed, and the amount of the external additive in the red toner gradually decreases, resulting in a loss of the blending balance.
As the amount of the external additive decreases, the nonmagnetic toner gradually aggregates due to the decrease in the external additive that plays a bearing effect, and the fluidity of the red toner decreases. When the fluidity of the red toner decreases in this way, when the thin layer blade 33 leveles the red toner layer, the excess red toner attached to the second developing roller 31 is pressed as if it were pressed and hardened. As a result, a substantial amount of red toner adheres to the surface of the second developing roller 31.
When a lot of red toner adheres to the second developing roller 31, it is a matter of course that a lot of red toner adheres to the latent image and the transfer paper.
In the first place, in the jumping method of the one-component developer, the toner charge amount tends to be low and the holding force of the transfer paper and the toner tends to be weak. In addition, the peeling discharge when the transfer paper is peeled off from the transfer device 13, Dust and unevenness are likely to occur in the image after fixing due to disturbances such as static electricity due to sliding contact between the guide member for transfer paper guide and the transfer paper provided as appropriate, or due to disturbance such as moisture evaporation of the transfer paper due to fixing heat in the fixing device. Since a large amount of red toner is placed on the second developing roller 31, the problem becomes remarkable.

Here, the relationship between the number of replenishment of the red toner, which is a one-component developer, to the developer accommodating portion 27a, that is, the number of times the toner cartridge is used, the amount of red toner attached to the second developing roller 31, and the number of image formations This will be described with reference to FIG. The horizontal axis represents the number of formed images, and the vertical axis represents the amount of red toner attached on the second developing roller 31. In addition, FIG. 3 is a diagram in which a plurality of upwardly rising mountain-shaped portions gradually decreases to the right.
First, the upper right portion of the first mountain shows the state of the amount of toner attached to the second developing roller 31 from the start of red toner replenishment until the red toner runs out, using the first toner cartridge. That is, as described above, each time the number of image formations is repeated, the flowability of the red toner decreases due to the decrease in the external additive, and the toner adhesion amount to the two developing rollers increases due to the decrease in fluidity. Note that at the first time of image formation using the first toner cartridge, the inner wall of the developer accommodating portion 27a is clean, so that more external additives adhere.

The right upper portion of the second mountain indicates the amount of toner attached to the second developing roller 31 from the start of red toner replenishment until the red toner disappears, using the second toner cartridge. Basically, as described above, each time the number of image formations is repeated, the fluidity of the red toner decreases due to the decrease in the external additive, and the amount of toner adhering to the second developing roller 31 due to the decrease in fluidity. However, as compared with the time of image formation using the first toner cartridge, a large amount of external additive has already adhered to the inner wall of the developer containing portion 27a. Is limited (reduced). Therefore, the flowability of the red toner is slightly better than when the first toner cartridge is used, and the amount of red toner attached to the second developing roller 31 decreases (a plurality of upwardly rising mountain-shaped portions gradually increase). Down to the right).
The right-up part after the third mountain reaches the second right-up part until the amount of the external additive adhering to the inner wall of the developer containing portion 27a reaches an attachable amount (saturation amount). While the amount of toner adhering to the developing roller 31 decreases as a whole, the flow of red toner decreases due to a decrease in the external additive each time the number of image formations is repeated. The toner adhesion amount to 31 increases.
If the amount of the external additive adhering to the inner wall of the developer accommodating portion 27a reaches an adherable amount and no longer adheres, the above-mentioned problems are solved without reducing the fluidity of the red toner.

Next, a series of operations of the second developing roller 31 according to the first embodiment will be described in detail with reference to FIG. In FIG. 4, the vertical axis represents the amount of red toner per unit area adhering to the surface of the photoconductor 3, and the horizontal axis represents the linear speed ratio of the second developing roller 31 to the photoconductor 3 immediately after the red toner supply ( The example illustrates three states: when the toner cartridge is replaced, when image formation is stabilized after a predetermined number of times, and when the toner end is reached. FIG. 4 illustrates the case of the first toner cartridge.
First, the remaining amount detecting means 28 and the controller 6 provided at the lowermost portion 27b of the developer containing portion 27a detect the presence or absence of red toner at the timing when the rear end of the transfer paper passes through the registration roller 9. As described above, this detection is determined as the toner end when the toner end is detected five times in succession and when the toner end is determined as the near end when the toner end is twice and the two ends are accumulated 20 times.
If the controller 6 determines that the toner end is not reached, the rotation of the second developing roller 31 is maintained at a linear speed ratio of about 1.2 with respect to the photoreceptor 3. As shown in FIG. 4, when the red toner is replenished, the red toner adhesion amount on the photosensitive member 3 is 0.5 mg / cm ² , and when stable, the red toner adhesion amount is 0.7 mg / cm 2. ² and the above-mentioned problem due to a large amount of red toner adhering to the latent image or transfer paper does not occur.

When the controller 6 determines that the toner end is reached, the controller 6 proceeds to a deceleration control that reduces the linear speed of the second developing roller 31. That is, the drive command value to the second developing roller drive motor 32 (which varies depending on the type of motor) is adjusted, and the linear velocity ratio of about 1. with respect to the photosensitive member 3 is normally obtained as shown in FIG. 2, the linear speed ratio of the second developing roller 31 rotating counterclockwise is set to 1.0. By this deceleration control, the red toner adhesion amount on the photoreceptor 3 of 0.9 mg / cm ² (the amount that causes the above-mentioned problems) is changed to the adhesion amount of 0.7 mg / cm ² so that it does not change from the stable time. To. This deceleration control is performed until the red toner is replenished in the developer accommodating portion 27a (until the toner cartridge is replaced).
When the toner cartridge is replaced, the controller 6 records the number of replacements, and controls the rotation of the second developing roller 31 at a linear speed ratio of about 1.2 with respect to the photoreceptor 3 during image formation. The linear speed ratio of the second developing roller 31 is controlled to 1.0. In the case of the second toner cartridge, as described above, the flowability of the red toner is slightly better than when the first toner cartridge is used, so that each line shown in FIG. shift.
The controller 6 indicates that the number of times the red toner has been replenished into the developer accommodating portion 27a (the number of replacements of the toner cartridge) has reached the amount of external additive adhering to the inner wall of the developer accommodating portion 27a. When the number of times that can be assumed is reached, no further external additive adheres to the inner wall of the developer accommodating portion 27a, so that the second developing roller 31 is moved to the photosensitive member 3 without reducing the linear velocity of the second developing roller 31. However, the linear speed ratio of about 1.2 is maintained.

As described above, in the image forming apparatus according to the first embodiment, when the controller 6 determines that the toner has ended, the external additive in the corresponding red toner adheres to the inner wall of the developer accommodating portion 27a, and the developer accommodating portion. Assuming that the fluidity of the red toner remaining in 27a is lowered, deceleration control is performed to lower the linear speed ratio of the second developing roller 31 relative to the photoreceptor 3.
By this deceleration control, the amount of red toner flying from the second developing roller 31 toward the photoconductor 3 rotating at a constant speed is substantially reduced, and a non-magnetic material composed of a red pigment that develops a latent image of a red image. The toner amount can be optimized.
Accordingly, since the amount of nonmagnetic toner on the transfer paper does not become an amount that adversely affects the image, it is possible to suppress the occurrence of dust and unevenness in the image due to excessive nonmagnetic toner.
Further, the controller 6 records the number of times red toner is replenished into the developer accommodating portion 27a, that is, the number of replacements of the toner cartridge, and the number of times red toner is replenished into the developer accommodating portion 27a is a predetermined number of times ( When the number of external additives adhering to the inner wall of the developer containing portion 27a reaches the possible number of adhering times (the number of toner cartridge replacements), the deceleration control of the second developing roller 31 is stopped. Contrary to the above, it is possible to avoid a decrease in the amount of non-magnetic toner on the transfer paper and obtain an image with an appropriate density.

(Embodiment 2)
In the first embodiment, the deceleration control trigger is the toner end, but the image forming apparatus according to the second embodiment is an example based on the amount of red toner attached to the photoconductor 3. A detailed description of the configuration common to the first embodiment will be omitted, and only the main part will be described in detail.
The image forming apparatus according to the second embodiment includes an adhesion amount detection unit and a controller 6.
As shown in FIG. 1, the adhering amount detection means includes a reflective photosensor 34 that includes a light emitting element and a light receiving element and is disposed between the second developing device 25 and the paper feed guide 8, and the reflective photosensor. An adhesion amount measurement circuit 35 electrically connected to both the sensor 34 and the controller 6 is provided.
In this adhesion amount detection means, the reflection type photosensor 34 irradiates the red toner image on the photoconductor 3 with a certain amount of light, photoelectrically converts the reflected light of the light, and measures the photoelectrically converted voltage value. An output signal that can be input to the controller 6 is adjusted by the circuit 35, and the controller 6 detects the amount of red toner adhering to the photoreceptor 3 (the density of the red toner image) based on the output signal.
The red toner adhesion amount is determined in advance (determined from the test result) based on the output value of the reflection type photosensor 34, and is, for example, a diagram shown in FIG. FIG. 5 shows the output value (v) of the reflection type photosensor 34 on the vertical axis, and the amount of red toner adhering (mg / cm ² ) on the photosensitive member 3 on the horizontal axis.

As shown in FIG. 5, when the output value of the reflection type photosensor 34 is high, that is, when the reflected light is strong, as shown in FIG. If the amount of red toner attached on the photoreceptor 3 is small and, conversely, the output value of the reflective photosensor 34 is low, that is, if the reflected light is weak, the amount of red toner attached on the photoreceptor 3 is large. From the test results, it has been found that the amount of red toner adhering to the image where dust or unevenness occurs is 0.8 mg / cm ² or more.
The controller 6 uses only red toner before normal image formation, for example, when the image forming apparatus main body is turned on after the power is turned on, or after a certain operation suspension or after a continuous operation. The formed test image is executed.
Further, the controller 6 records a threshold value for determining an appropriate amount of red toner (an amount that does not cause image dust or unevenness due to excessive nonmagnetic toner, that is, less than 0.8 mg / cm ² ). The threshold value is compared with the output value of the reflection type photosensor 34 to determine whether or not the density is excessive. When it is determined that the density is excessive (red toner adhesion amount: 0.8 mg / cm ² or more) In addition, the linear velocity of the second developing roller 31 is decelerated by adjusting a drive command value to the second developing roller drive motor 32 (which varies depending on the type of motor).

In the image forming apparatus according to the second embodiment configured as described above, the controller 6 starts forming a test image using only red toner before performing normal image formation, and includes an adhesion amount detection unit. Are linked together to detect the amount of red toner adhering to the photoreceptor 3. If the controller 6 determines that the red toner adhesion amount is less than 0.8 mg / cm ² , the controller 6 rotates the second developing roller 31 at a normal time with a linear speed ratio of about 1.2 with respect to the photoreceptor 3. maintain.
Contrary to the above, when the controller 6 determines that the red toner adhesion amount is 0.8 mg / cm ² or more, the rotation of the second developing roller 31 is reduced to a linear speed ratio of about 1.0 with respect to the photoreceptor 3. Thus, it is desired for the image formation.
According to the image forming apparatus according to the second embodiment, the trigger for deceleration control is performed based on the amount of red toner adhering to the photoconductor 3, thereby preventing image dust caused by excessive nonmagnetic toner. The occurrence of unevenness can be suppressed with higher accuracy.
The image forming apparatus according to the second embodiment is applicable even when a two-component developer composed of toner and carrier is used.

(Embodiment 3)
In the image forming apparatus according to the third embodiment, when there is a line image with a small image width in the main scanning direction, the amount of nonmagnetic toner adhering to the second developing roller 31 is at a level at which no dust or unevenness occurs. However, the so-called edge effect may cause dust and unevenness, which is solved. A detailed description of the configuration common to the above-described embodiment will be omitted, and only the main part will be described in detail.
The image forming apparatus according to the third embodiment includes a width detection unit and a controller 6.
The width detecting means detects the toner image width in the main scanning direction on the signal from a writing signal for forming a red latent image on the photosensitive member 3.
The controller 6 decelerates the second developing roller 31 when it is determined by the width detection means that a line image signal having a small width exists in the write signal.
In the image forming apparatus according to the third embodiment configured as described above, the width detecting unit detects the toner image width in the main scanning direction on the signal, and the controller 6 has a line with a small width in the write signal. If it is determined that there is no image signal, the rotation of the second developing roller 31 is maintained at a normal time with a linear speed ratio of about 1.2 with respect to the photoreceptor 3.
Contrary to the above, if the controller 6 determines that a line image signal having a small width is present in the writing signal, the rotation of the second developing roller 31 is caused to rotate with respect to the photoreceptor 3 with a linear velocity ratio of about 1. Decelerate to zero.

According to the image forming apparatus according to the third embodiment, the deceleration control is triggered based on the presence of the signal of the line image having a small width in the write signal, thereby generating the image dust and unevenness due to the edge effect. Can be suppressed.
Further, the image forming apparatus according to the third embodiment is applicable even when a two-component developer composed of toner and carrier is used.
In addition to the configuration of the fourth embodiment, the adhesion amount detection means exemplified in the second embodiment is added, the trigger for the deceleration control is present, the signal of the line image with a small width exists in the write signal, and the adhesion amount detection The linear velocity of the second developing roller 31 may be reduced only when the adhesion amount of the red toner on the photosensitive member 3 detected by the means is 0.6 mg / cm ² or more.
This is because, when the amount of red toner attached is less than 0.6 mg / cm ² , the image is hardly affected by the edge effect. Although it is necessary to form a test image using only red toner before, it is possible to form an image with good density.

The image forming apparatus according to the present embodiment has been described above. However, the above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto. Various modifications can be made without departing from the scope of the invention.
For example, two triggers, a trigger for deceleration control of the second developing roller 31 exemplified in the first embodiment and a trigger for deceleration control of the second developing roller 31 exemplified in the second embodiment, may be used simultaneously. A configuration in which a trigger for deceleration control according to the third embodiment is added thereto may be used. In this case, when either the detection of the toner end (Embodiment 1) or the determination that the amount of red toner adhering on the photoreceptor 3 is 0.8 mg / cm ² or more (Embodiment 2) is detected first. Therefore, it is preferable to shift to the deceleration control and to make the control separated from the deceleration control trigger of the third embodiment.
The gist of the present invention is to reduce the linear velocity of the second developing roller 31 with respect to the photoreceptor 3 as a solution for suppressing the occurrence of image dust and unevenness in the image forming apparatus. If the toner adhesion amount is insufficient, technical means for adjusting the density by increasing the linear speed of the second developing roller 31 with respect to the photoreceptor 3, or the line of the second developing roller 31 as necessary to maintain a constant density. It can be diverted to technical means for accelerating / decelerating the speed.

1 is a schematic diagram of an image forming apparatus according to an exemplary embodiment. FIG. 3 is a longitudinal front view of a second developing device 25. FIG. 6 is a diagram showing the relationship between the number of image formations and the amount of red toner attached on the second developing roller. FIG. 6 is a diagram illustrating a relationship between a linear speed ratio of a second developing roller to a photosensitive member and a red toner adhesion amount on the photosensitive member. It is a diagram showing the relationship between the output value of the adhesion amount detection means and the amount of adhesion of red toner on the photoreceptor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Document reader, 2 Image memory part, 3 Photoconductor, 4 1st image forming part, 5 2nd image forming part, 6 Controller, 7 Paper feed tray, 8 Paper feed guide, 9 Registration roller, 10 Roller, 11 Transfer Belt, 12 Bias roller, 13 Transfer device, 14 Transfer voltage application section, 15 Separation claw, 16 Cleaning device, 17 Charger, 18 First charger, 19 First exposure device, 20 First development roller, 21 First development , 22 1st bias application unit, 23 2nd charger, 24 2nd exposure device, 25 2nd development device, 26 2nd bias application unit, 27 cabinet, 27a developer storage unit, 27b bottom part, 27c opening 28, remaining amount detecting means, 29 agitator, 30 toner supply roller, 31 second developing roller, 32 second developing roller drive motor, 33 thin layer blade, 34 Morphism photosensor, C small gap

Claims (7)

  A rotatable developing roller to which a one-component developer composed of a non-magnetic toner and an external additive for improving the fluidity of the non-magnetic toner is attached, and a photosensitive member on which a latent image is formed include the developing unit. The one-component developer adhering to the surface of the roller is disposed so as to be able to fly toward the latent image, and the one-component developer adhering to the developing roller by decelerating the linear velocity of the developing roller. An image forming apparatus comprising developing roller control means for adjusting the amount.   A developer storage unit for storing the one-component developer and supplying the one-component developer to the developing roller is provided with a remaining amount detecting means for detecting the amount of the one-component developer, and the developing roller control means 2. The image forming apparatus according to claim 1, wherein it is determined whether or not a detected value of the remaining amount detecting means is a toner end, and the developing roller is decelerated when it is determined that the toner end.   The developing roller control means accumulates the number of replenishments of the one-component developer to the developer accommodating portion, and stops the deceleration control when the accumulated number of replenishments reaches a predetermined number. The image forming apparatus according to claim 2.   Adhesion amount detection means for detecting the amount of the one-component developer adhering to the photoconductor is provided, and the developing roller control means determines the adhesion amount of the one-component developer detected by the adhesion amount detection means. 4. The image forming apparatus according to claim 1, wherein the developing roller is decelerated based on the speed. 5. The image according to claim 4, wherein the developing roller control means decelerates the developing roller when the adhesion amount of the one-component developer detected by the adhesion amount detection means is 0.8 mg / cm ² or more. Forming equipment.   Width detecting means for detecting a toner image width in the main scanning direction from a writing signal for forming a latent image on the photosensitive member is provided, and the developing roller control means detects the toner image having a small width. 6. The image forming apparatus according to claim 1, wherein the developing roller is decelerated in the event of a failure. Adhesion amount detection means for detecting the amount of the one-component developer adhering to the photosensitive member is provided, and the developing roller control means is configured to detect the adhesion amount of the one-component developer detected by the adhesion amount detection means. The image forming apparatus according to claim 6, wherein the developing roller is decelerated at 0.6 mg / cm ² or more.

Images