JPH1184892A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently transfer a visible image on an image carrier onto a transfer material, without causing a failure in transfer, even if a grounded conductive member such as a destaticization needle is arranged in the vicinity of a transfer-electrifying means. SOLUTION: The grounded destaticization needle 210 for preventing a peeling discharge at the time of separating the transfer material P from a photoreceptive drum 3 is provided in the vicinity of the downstream side of a transfer electrifier 24, under a transfer belt. At the time of performing the transfer, a high voltage controlled with a constant current is applied to the transfer electrifier 24 by a constant current power source 216. At this time, the value Y of a current flowing into the destaticization needle 210 is measured by an ammeter 220 at any time. Then, the output of a power source 216 is controlled to obtain a current value obtained by adding the measured value Y of the inflow current to an initial stage value T, by a CPU 218, to be applied to the electrifier 24 and the value of the current contributing to the transfer, in the output current of the electrifier 24 is feedback-controlled to be the initial stage value T.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus which forms a visible image on an image carrier and electrostatically transfers the visible image to a transfer material. It can be suitably used for an electrophotographic image forming apparatus or the like.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus is provided with a plurality of image forming units, each of which forms a toner image of a different color, and superimposes the toner images sequentially on the same transfer material. Various electrophotographic recording devices that obtain a color image by transferring the image have been proposed.

An example of such a conventional color electrophotographic recording apparatus will be briefly described with reference to FIG. 4. First, second, third, and fourth image forming units Pa, Pb, P
c and Pd are arranged side by side, and in the respective image forming units Pa to Pd, toner images of different colors are formed through processes of charging, image exposure, development, and transfer.

The image forming units Pa, Pb, Pc, and Pd each have a dedicated image carrier, in this embodiment, an electrophotographic photosensitive drum 3.
a, 3b, 3c, 3d, and each of the photosensitive drums 3a-3
One transfer belt 130 is provided as a common transfer material carrier adjacent to the lower side of d. In this example, the photosensitive drums 3a to 3d and the transfer belt 130 have a process speed of 135 mm / sec.

[0005] Exposure lamps 111a, 111b and 111 are provided on the outer periphery of the photosensitive drums 3a, 3b, 3c and 3d, respectively.
c, 111d, drum charger (primary charger) 2a, 2
b, 2c, 2d, potential sensors 113a, 113b, 1
13c, 113d, developing devices 1a, 1b, 1c, 1d, transfer chargers 24a, 24b, 24c, 24d, and cleaners 4a, 4b, 4c, 4d are provided. A mirror 117 is further provided.

A laser light modulated by an image signal is generated from a light source device, the laser light is rotated and scanned by a polygon mirror 117, the light beam of the scanned light is deflected by a reflection mirror, and the photosensitive drums 3a, 3b, 3c, 3
By condensing and exposing on the generatrix d, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drums 3a, 3b, 3c and 3d. The photosensitive drums 3a, 3b, 3c, 3d
Prior to exposure, the drum chargers 2a, 2b, 2c, and 2d uniformly and primary charge a predetermined potential.

The developing devices 1a, 1b, 1c, and 1d are filled with a predetermined amount of cyan, magenta, yellow, and black toners, respectively, by a supply device (not shown). The developing devices 1a, 1b, 1c, and 1d develop the latent images on the photosensitive drums 3a, 3b, 3c, and 3d, and visualize the latent images as cyan, magenta, yellow, and black toner images, respectively. .

This toner image is transferred onto a transfer material P conveyed by a transfer belt 130. The transfer belt 130 includes a driving roller 13 and driven rollers 14 and 15.
And is disposed below the photosensitive drums 3a to 3d. The transfer material P is stored in a transfer material cassette 10 and is supplied onto the transfer belt 130 from the transfer material cassette 10 via a plurality of transport rollers and registration rollers 12.

The transfer belt 130 is made of polyethylene terephthalate resin (PET), polyvinylidene fluoride resin,
It is made of a sheet of a dielectric resin such as a polyurethane resin, and its both ends are overlapped and joined to form an endless shape, or a seamless (seamless) belt is used.

When the transfer belt 130 is rotated by the driving roller 13 and is confirmed to be at a predetermined position, the transfer material P is sent out from the registration roller 12 to the transfer belt 130, and the transfer material P is subjected to the first image formation. The sheet Pa is conveyed toward the transfer section facing the photosensitive drum 3a of the section Pa. At the same time, the image writing signal is turned on, and the above-described image formation is performed on the photosensitive drum 3a of the first image forming unit Pa at a certain timing based on the signal, thereby forming a cyan toner image. Then, the transfer charger 24a applies a transfer electric field or transfer charge in the lower transfer section of the photosensitive drum 3a, so that the first color cyan toner image formed on the photosensitive drum 3a is transferred onto the transfer material P. . Due to this transfer, the transfer material P is firmly held on the transfer belt 130 by electrostatic attraction, and is conveyed to the second image forming portion Pb and thereafter.

The second, third, and fourth image forming units Pb, Pc,
Also in Pd, image formation is performed in the same manner as in the first image forming unit Pa, and a magenta toner image, a yellow toner image, and a black toner image are superimposed and transferred on the transfer material P in a multiplex manner.

In this embodiment, the transfer chargers 24a to 24d are:
Although it is a contact charger made of a conductive blade in contact with the back surface of the transfer belt 130, a contact charger using a conductive roller, a brush, or the like, or a non-contact charger such as corona discharge should be used. Can be.

In addition, in the vicinity of the transfer portions of the image forming portions Pa to Pd, peeling discharge between the photosensitive drums 3 (3a to 3d) and the transfer material P is prevented to stabilize transferability. ,
As shown in FIG. 5, a grounded discharging needle 210 is provided in non-contact with the transfer belt 130. This static elimination needle 210
As shown in FIG. 6, a large number of needle electrodes 214 having a small radius of curvature at the distal end are provided on a conductive base 212, and each transfer charger 24 is provided below the transfer belt 130.
(24a to 24d) are arranged near the downstream side.

Particularly in a dry environment, the discharge limit voltage of the atmosphere rises, and discharge at a high voltage (several kV) often occurs. When the discharge at such a high voltage occurs, the toner image formed from the toner, which is the charged particles transferred to the transfer material P, is disturbed and the image quality is reduced.
A needle-like electrode having a small radius of curvature at the tip end, such as the static elimination needle 210, is placed near the discharge location, that is, the photosensitive drum 3 and the transfer material P.
In this case, the discharge limit voltage can be reduced so that the toner image transferred onto the transfer material P is not affected.

The transfer material P on which the toner images of the four colors have been superimposedly transferred as described above is then discharged by the separation charger 32 downstream of the transfer belt 130 in the transport direction, and electrostatically attracted to the transfer belt 130. By attenuating the force, the transfer belt 130 is separated from the end. Transferred material P removed
Is transported to the fixing device 9 by the transport unit 62.

The fixing device 9 includes a fixing roller 51, a pressure roller 52, heat-resistant cleaning members 54 and 55 for cleaning the fixing roller 51, heaters 56 and 57 installed in the rollers 51 and 52, and a fixing roller. An application roller 50 that applies a release agent oil such as dimethyl silicone oil to the surface 51, an oil reservoir 53, and a thermistor 58 that detects the temperature of the surface of the pressure roller 52 and controls the fixing temperature.
It is composed of

The transfer material P sent to the fixing device 9 is heated and pressed by a fixing roller 51 and a pressure roller 52 to fix the transfer material P, so that the four color toner images are mixed and fixed to the transfer material. After being formed into a full-color copy image, the image is discharged to the sheet discharge tray 63.

The photosensitive drums 3a, 3b, 3 after the transfer is completed
c, 3d are the respective cleaners 4a, 4b, 4c, 4
d removes and removes the transfer residual toner,
Subsequently, preparation is made for the formation of the next latent image. Further, the transfer belt 130 from which the transfer material has been separated is brought into contact with the conductive cleaning web (nonwoven fabric) 22 provided on the transfer material carrying side and the metal roller 21 provided on the opposite side thereof, so that the transfer belt 130 is placed on the transfer belt 130. The residual toner and other foreign substances are cleaned and removed, and static elimination is performed. A conductive fur brush may be used instead of the cleaning web.

[0019]

As described above, the static elimination needle 210 prevents peeling discharge when the transfer material P is separated from the photosensitive drum 3, so that the toner image transferred onto the transfer material P is disturbed. To prevent Therefore, it is effective to dispose the static elimination needle 210 at a position closer to the separation point between the photosensitive drum 3 and the transfer material P.

However, if the static elimination needle 210 is installed at a position closer to the separation point, the transfer may be performed on paper that has absorbed moisture in the atmosphere due to being left in a high-humidity environment, or paper that has reduced the resistance value by surface treatment. Since the electric resistance in the surface direction of the paper is low, the high-voltage electric field applied to the transfer charger 24 electrically interferes with the static elimination needle 210, and several% of the output current from the transfer charger 24 is directly discharged. It may flow into the needle 210. Such a phenomenon may occur even when only a high voltage is applied in a high humidity environment.

The output of the transfer charger 24 is usually such that a constant current power supply 216 is used as its high voltage power supply, and a constant current value is output by controlling the constant current power supply 216 with a control device. However, as described above, when a current flowing into the charge eliminating needle 210 is generated, the output of the transfer charger 24 outputs the toner image on the photosensitive drum 3 by the amount of the charge eliminating needle. You will lose the ability to electrostatic transfer onto it. As a result, a so-called transfer failure occurs in which the toner image is not sufficiently transferred to the transfer material P, and the transfer material P
The image obtained above has a reduced image quality.

An object of the present invention is to transfer a visible image formed on an image carrier onto a transfer material well even if a grounded conductive member such as a static elimination needle is arranged near the transfer charging means. It is another object of the present invention to provide an image forming apparatus capable of obtaining a high quality image without transfer failure.

[0023]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image carrier, a transfer charging unit for transferring a visible image formed on the image carrier to a transfer material conveyed to the image carrier, and a transfer device on which the visible image is transferred. An image forming apparatus having a non-contacting grounding static elimination unit which is in non-contact with the image carrier, in order to prevent peeling discharge due to separation of the transfer material in the vicinity of a position where the material and the image carrier separate from each other; An image forming apparatus comprising: a measuring unit for measuring a current value flowing into a charge removing unit by transfer; and a control unit for controlling an output current value of the transfer charging unit in accordance with the measured current value. Device.

According to the present invention, the output current value of the transfer charging means is controlled by a constant current, and the current value obtained by subtracting the inflow current value of the charge removing means from the output current value of the transfer charging means becomes a fixed specified value. Is controlled so that The control of the subtracted current value to a specified value is performed by updating the output current value of the transfer charging unit to a current value obtained by adding the inflow current value of the discharging unit to the output current value of the transfer charging unit, or This can be achieved by updating the output current value of the means to a current value obtained by multiplying a ratio of the output current value of the transfer charging means to the subtracted current value by a predetermined value. Further, the static elimination means is a static elimination needle.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 1 is an explanatory view showing a transfer section of an image forming section in an embodiment of the image forming apparatus of the present invention.

According to the present invention, when the transfer is performed by the transfer charging means provided in the transfer section of the image forming section, the value of the current flowing into the static elimination needle is measured, and the transfer charging means is compensated for the flowing current value. It is characterized by controlling the output current value of. Since other configurations of the image forming apparatus of the present invention are basically the same as those of the conventional image forming apparatus shown in FIG. 4, the present invention will be described below with reference to FIG.

Also in this embodiment, as shown in FIG. 1, the blade type contact charger 24 (2) is used as a transfer charging means in each of the transfer sections of the first to fourth image forming sections Pa to Pd in FIG.
4a to 24d) are installed, and a high voltage is applied by the constant current power supply 216 so that the output of the transfer charger 24 has a predetermined current value.

In this embodiment, the constant current power supply 216 is
Control device of image forming apparatus main body, more specifically, control CPU 2
18 controls the constant current. A high-voltage transformer is incorporated in the constant-current power supply 216, and a constant-current transformer having a value corresponding to a control signal given from the CPU 218 on a one-to-one basis is used as the high-voltage transformer.

As shown in FIG. 1, the transfer chargers 2 are provided below the transfer belt 130 in the transfer sections of the respective image forming sections.
In the vicinity of the downstream side of the transfer belt 4, a grounded discharging needle 210 is arranged in non-contact with the transfer belt 130. This static elimination needle 210
As shown in FIG. 6, a large number of needle-like electrodes 214 having a small radius of curvature at the tip end are provided on a conductive base 212, so that the transfer material P and the photosensitive drum 3 are separated from each other. On the downstream side of the first transfer nip, the occurrence of peeling discharge at a high voltage is prevented, and the scattering of the toner image on the transfer material P due to the peeling discharge is prevented.

In the present embodiment, the neutralization needle 210 is located 20 mm downstream from the contact point between the transfer charger 24 and the transfer belt 130 in the traveling direction of the transfer material P, and is located 7 mm directly below the transfer belt 130. At the position where the operation was performed, the static elimination needle 21
It was arranged so that the tip of 0 came. In addition, an ammeter 220 was inserted between the neutralization needle 201 and the ground in order to measure a current value flowing through the neutralization needle 210 during transfer.

When the transfer material P is left in a high-humidity environment, or in the case of a certain type of coated paper that has been subjected to surface treatment, the electrical resistance in the surface direction of the paper decreases, and the transfer charger in the transfer nip is used. The current flowing into the static elimination needle 210 changes the output current to the transfer charger 24 because of electrical interference between the static elimination needle 24 and the static elimination needle 210 and for the reason that only a high voltage is applied in a high humidity environment. It is observed at a rate of about 0-20%. As described above, since this phenomenon changes depending on the paper type, paper moisture absorption conditions, the atmosphere of the installation location of the image forming apparatus, and the like, the transfer becomes unstable even if a higher transfer current value is given in advance. Likely to be.

Therefore, in this embodiment, at the time of transfer, FIG.
As shown in (a), the current value Y flowing into the static elimination needle 210 is measured by the ammeter 220 as needed, and the information on the measured current value Y is sent to the control CPU 218.
By controlling the output of the constant current power supply 216 to a current value obtained by adding the inflow current measurement value Y to the initial set value, and applying the current value to the transfer charger 24, the output current value of the transfer charger 24 to be controlled is The feedback control is performed so that the current value contributing to the transfer of the image becomes a predetermined necessary current value T.

The current value T required for the transfer is roughly estimated as the amount of electric charge necessary for electrostatically transferring the toner image to the transfer material, and is obtained from the total amount of the toner constituting the toner image and the process speed. That is, the photosensitive drums 3 (3a to 3a)
d) The width of the upper image area is L (cm), the toner amount per unit area of the image area of the toner image is W (mg / cm ² ), and the charge amount per unit weight of the toner is Q (μC / g). ,
Assuming that the process speed is V (cm / sec), the current value T (μA) required for transfer is obtained as follows: T = 10 ⁻³ .Q.W.L.V

As an average value, Q = 36 μC / g, W
= 0.70 mg / cm ² , L = 30 cm, V = 13.5
By substituting cm / sec, T ≒ 10 μA, which indicates that a current value of 10 μA is required to transfer the toner image on the photosensitive drum 3. The constant current of 10 μA is transferred from the transfer charger 24 to the photosensitive drum 3. Is a necessary condition. Therefore, in the present embodiment, the current value required for transfer, 10 μA, is initially set as the target output current value.

The control device, that is, the control CPU 218,
First, as shown in FIG. 2B, a current value (output current control value) X to be output by the constant current power supply 216 is set as the CPU 2
18 or the initial value stored in the attached storage device, that is, the target output current value T = 10 μA (step S).
1) The power supply 216 is controlled at a constant current to output a constant current of X = T = 10 μA, which is applied to the transfer charger 24 (S).
2). Thus, the transfer charger 24 starts transferring the toner image on the photosensitive drum 3 to the transfer material P with an output current of 10 μA.

At the same time, the transfer needle 210 is transferred by transfer.
Is measured by the ammeter 220. When the CPU 218 receives the measured current value Y, the CP
U218 determines whether Y is greater than 0 (S3), and Y>
If 0, X is set as the initial set value T and the measured inflow current Y
(T + Y) is calculated, and the sum is substituted into the constant current power supply 2
The 16 output current values X are updated to X = T + Y (S4).
As a result, the process returns from step S4 to S2, where the transfer charger 24 outputs the changed current value X = T + Y, and continues the transfer at the current value T = 10 μA excluding the current Y flowing into the static elimination needle 210.

On the other hand, if Y <0 or Y = 0, the output current value X is stored as it is, and the process returns from step S3 to S2 to continue transfer to the transfer charger 24 with the current value X = T (= 10 μA). Let it.

In the present embodiment, as described above, at the time of transfer, feedback control is performed on the output current of the transfer charger 24, so that the feedback control is applied from the transfer charger 24 to the toner image on the photosensitive drum 3 during the transfer nip. Current can be compensated and maintained up to a current value of 10 μA required for transfer. Therefore, a good transfer image can be obtained without causing transfer failure.

Further, once the current value Y flowing into the neutralization needle 10 becomes Y> 0, and the value of the control value X exceeds T, if Y = 0 thereafter, X Since the control for returning to the initial value of = T is added, there is no problem even if an excessive current state occurs.

Second Embodiment In the first embodiment, the value obtained by adding the measured value of the inflow current Y to the initial value T is updated as the output current control value X in order to compensate for the amount of current flowing into the static elimination needle 210. In the embodiment, the output current control value X is calculated on the assumption that the inflow current component Y is a certain ratio of the current value output from the transfer charger 24. FIG. 3 shows a specific operation.

The control CPU 218 first sets an initial value (target output current value) stored in the CPU 218 (or an attached storage device) as an output current value (output current control value) X to be output from the constant current power supply 216. T = 10 μA is substituted (step S1), and the power supply 216 is controlled to X =
A constant current of T = 10 μA is output (S2), and the transfer charger 2
4 starts the transfer of the toner image on the photosensitive drum 3 to the transfer material P with an output current of 10 μA.

At the same time, the transfer needle 210 is transferred by transfer.
The ammeter 220 measures the current value Y flowing into the
18 obtains the measured value of the inflow current Y and determines whether or not Y is greater than 0 (S3). If Y> 0, the output current value of the power source 216, ie, the output current value of the power source 216 minus the static elimination needle The ratio of the output current value X to the inflow current Y is taken, and the required output current value, that is, the value multiplied by the initial value T, X = (X / (X−Y)) × T is calculated as a new output. It is updated as the current control value X (S5).

In this embodiment, since the above operation is performed as needed, the current applied from the transfer charger 24 to the toner image on the photosensitive drum 3 during the transfer nip is set to the required target value,
That is, it is possible to approach the initial value T of 10 μA.

However, the updated current control value X is
Since the current always increases until the static elimination needle inflow current value Y becomes 0, if the static elimination needle inflow current value Y is less than 10% of the initial value T, the process returns from step 4 to S2, where the current control value Get out of the update loop. When the discharge needle inflow current Y = 0 or Y <0, the output current control value X is returned to the initial set value T (S3).

On the other hand, as an extreme example, 50% or more of the output current may be measured as the current flowing into the static elimination needle on paper with extremely low resistance. In such a case, even if this control method is adopted, the output of the transfer high-voltage power supply becomes too large, and it is difficult to sufficiently supply a current to the toner image.
In addition, a situation may occur that affects other parts of the apparatus, such as an electric shock to the photosensitive drum. Therefore,
In such a case, it is preferable to display an error and stop the image forming operation.

[0047]

As described above, according to the present invention,
Even if a grounded conductive member such as a static elimination needle is arranged near the transfer charging means, the visible image formed on the image carrier can be transferred onto the transfer material satisfactorily. Up to this, a high-quality image free from transfer failure can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a transfer unit in an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a diagram illustrating a method of controlling an output current of a transfer charger at the time of transfer in the image forming apparatus of FIG. 1;

FIG. 3 is a diagram showing a method for controlling an output current of a transfer charger at the time of transfer in another embodiment of the present invention.

FIG. 4 is a schematic configuration diagram illustrating a conventional image forming apparatus.

FIG. 5 is an explanatory diagram illustrating a transfer unit of the image forming apparatus of FIG. 4;

FIG. 6 is a front view showing a static elimination needle installed near a transfer unit in FIG. 5;

[Explanation of symbols]

 3 photosensitive drum 24 transfer charger 130 transfer belt 210 static elimination needle 216 constant current power supply 218 CPU 212 ammeter

Claims (6)

[Claims] 1. An image carrier, a transfer charging means for transferring a visible image formed on the image carrier to a transfer material conveyed to the image carrier, and a transfer material on which the visible image is transferred and an image In the image forming apparatus, the image forming apparatus includes a grounding neutralization unit that is not in contact with the image carrier and that prevents the separation discharge due to the separation of the transfer material in the vicinity of a position where the transfer member separates from the image bearing member. An image forming apparatus comprising: a measuring unit that measures a current value flowing into the unit; and a control unit that controls an output current value of the transfer charging unit in accordance with the measured current value. 2. The image forming apparatus according to claim 1, wherein an output current value of said transfer charging means is controlled at a constant current. 3. The image forming apparatus according to claim 2, wherein a current value obtained by subtracting an inflow current value of the charge removing means from an output current value of the transfer charging means is controlled to a predetermined value. 4. The control of the subtracted current value to a specified value updates the output current value of the transfer charging unit to a current value obtained by adding the inflow current value of the charge removing unit to the output current value of the transfer charging unit. 4. The image forming apparatus according to claim 3, wherein the image forming is performed by the following. 5. The control of the subtracted current value to a specified value is performed by multiplying an output current value of the transfer charging unit by a ratio of an output current value of the transfer charging unit to the subtracted current value by a predetermined specified value. The image forming apparatus according to claim 3, wherein the updating is performed by updating the current value. 6. The static elimination means is a static elimination needle.
6. The image forming apparatus according to any one of items 5.