JP2016109875A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve both acceleration and a cost reduction of a system omitting primary transfer.SOLUTION: An image forming apparatus causes a first power source and a second power source to flow a current in the circumferential direction of an intermediate transfer belt so that the current flows into the ground via a Zener diode, and adjusts the output of the power sources so that the Zener diode generates a predetermined voltage.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus using an electrophotographic technique such as a copying machine or a laser printer.

  In an electrophotographic image forming apparatus, an intermediate transfer system that forms an image by transferring a toner image from a photosensitive member to an intermediate transfer member (primary transfer) and then transferring the image from the intermediate transfer member to a recording material (secondary transfer). It has been known.

  However, if a power supply dedicated for primary transfer and a primary transfer roller are used separately from the secondary transfer roller and the power supply for secondary transfer, there is a risk that the cost increases and the intermediate transfer unit becomes large. Therefore, in order to reduce the size of the intermediate transfer unit, the resistance of the inner surface of the intermediate transfer belt is reduced, the primary transfer roller and the primary transfer power supply are omitted, and the intermediate transfer belt is grounded via a constant voltage element (hereinafter referred to as a single transfer). System) (see Patent Document 1).

JP 2012-137733 A

  However, in the above-mentioned one-turn-less system, when the photosensitive member is worn and thinned by use, the amount of current flowing from the power source that flows into the primary transfer portion increases, and the amount of current flowing through the constant voltage element. May be low. As a result, the constant voltage element cannot generate a predetermined voltage, and there is a problem that primary transfer failure occurs due to insufficient primary transfer electric field.

  In view of this, the image forming apparatus of the present invention contacts an image carrier that carries a toner image, an intermediate transfer member that carries a toner image transferred from the image carrier by a primary transfer unit, and an outer peripheral surface of the intermediate transfer member. A transfer member that is disposed in contact with the intermediate transfer member and transfers a toner image from the intermediate transfer member to a recording material at a secondary transfer portion; and is electrically connected between an inner peripheral surface of the intermediate transfer member and a ground potential. A constant voltage element that generates a generated voltage; a detection unit that detects a current flowing through the constant voltage element; and a voltage applied to the transfer member to cause the current to flow through the constant voltage element, and to the secondary transfer unit. A first power source that forms a transfer electric field, a second power source that is electrically connected to the inner peripheral surface of the intermediate transfer member and forms a primary transfer electric field in the primary transfer portion, and a detection result of the detection means And a control unit for controlling the second power source based on And features.

  According to the present invention, a predetermined voltage can be reliably generated in the constant voltage element, and primary transfer failure can be suppressed.

Diagram explaining a conventional one-turn-less system The figure explaining the basic composition in this embodiment The figure explaining the equivalent circuit in this embodiment The figure which shows the relationship between the transfer potential and electrostatic image potential in this embodiment Zener diode IV characteristics Block diagram in this embodiment

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, what attached | subjected the same code | symbol in each drawing has the same structure or effect | action, The duplication description about these was abbreviate | omitted suitably.

[Image forming apparatus]
FIG. 2 shows an image forming apparatus using a tandem type intermediate transfer member according to the first embodiment.

  The image forming units 101a, 101b, 101c, and 101d are image forming units that form yellow (Y), magenta (M), cyan (C), and black (K) toner images, respectively. These image forming units are arranged from the upstream side in the moving direction of the intermediate transfer belt 7 in the order of the image forming units 101a, 101b, 101c, and 101d, that is, in order of yellow, magenta, cyan, and black.

  Each of the image forming units 101a, 101b, 101c, and 101d includes a photoreceptor 1a, 1b, 1c, and 1d as an image carrier on which a toner image is formed. The charging rollers 2a, 2b, 2c, and 2d are charging units that charge the surfaces of the photoreceptors 1a, 1b, 1c, and 1d. The exposure devices 3a, 3b, 3c, and 3d include a laser scanner, and expose the photoreceptors 1a, 1b, 1c, and 1d charged by the charging rollers 2a, 2b, 2c, and 2d. When the output of the laser scanner is turned on / off based on the image information, electrostatic images corresponding to the images are formed on the respective photoreceptors 1a, 1b, 1c, and 1d. That is, the charging rollers 2a, 2b, 2c, and 2d and the exposure devices 3a, 3b, 3c, and 3d function as an electrostatic image forming unit that forms electrostatic images on the photoreceptors 1a, 1b, 1c, and 1d. Each of the developing devices 4a, 4b, 4c, and 4d includes a container that stores toner of each color of yellow, magenta, cyan, and black, and uses the electrostatic images on the photoreceptors 1a, 1b, 1c, and 1d with the toner. And developing means for developing.

  The toner images formed on the photoreceptors 1a, 1b, 1c, and 1d are primarily transferred to the intermediate transfer belt 7 by primary transfer portions N1a, N1b, N1c, and N1d. In this way, the four color toner images are superimposed and transferred onto the intermediate transfer belt 7.

  The intermediate transfer belt 7 is a movable intermediate transfer member to which toner images are transferred from the photoreceptors 1a, 1b, 1c, and 1d. The intermediate transfer belt 7 has a two-layer configuration of a base layer (inner peripheral surface side) and a surface layer (outer peripheral surface side). The intermediate transfer belt 7 may have a structure of two or more layers having another layer between the base layer and the surface layer.

The base layer is made of a resin such as polyimide or polyamide, PEN or PEEK, or various rubbers containing an appropriate amount of an antistatic agent such as carbon black.
The base layer of the intermediate transfer belt 7 is formed so that the surface resistivity of the base layer is 10 ² to 10 ⁸ Ω / □ (conductive). As the base layer in Example 1, a film-like endless belt made of polyimide and having a center thickness of about 45 to 150 μm is used.

Further, the surface layer is coated with an acrylic coat whose resistance in the film thickness direction including the base layer is adjusted to 10 ⁹ to 10 ¹³ Ω · cm. That is, the resistance of the base layer is lower than the resistance of the surface layer.

  The thickness of the surface layer is 1 to 10 um. Of course, it is not intended to limit to these numerical values.

  The intermediate transfer belt 7 is stretched in contact with the inner peripheral surface of the intermediate transfer belt 7 by various rollers 10, 11, 12, 13 as stretch members. The idler roller 12 stretches the intermediate transfer belt 7 extending along the arrangement direction of the photoreceptors 1a, 1b, 1c, and 1d.

  The tension roller 11 is a tension roller that applies a constant tension to the intermediate transfer belt 7. Further, the tension roller 11 also functions as a correction roller that prevents the intermediate transfer belt 7 from meandering. The belt tension with respect to the tension roller 11 is configured to be about 5 to 12 kgf. By applying this belt tension, nips are formed between the intermediate transfer belt 7 and the photoreceptors 1a, 1b, 1c, and 1d as primary transfer portions N1a, N1b, N1c, and N1d.

  The secondary transfer inner roller 10 functions as a driving roller that is driven by a motor excellent in constant speed and circulates and drives the intermediate transfer belt 7.

  The second power source 21 is connected to the tension roller 11 and is a power source for causing a current to flow in the circumferential direction of the intermediate transfer belt 7. Note that the second power source 21 is not necessarily connected to the tension roller 11, and may be configured to be connected to any one of the stretching rollers 10, 11, 12, and 13.

  The recording material P is accommodated in a paper tray. The recording material P is taken out from the paper tray by a pickup roller at a predetermined timing and guided to a registration roller (not shown). The recording material P is sent out by the registration roller to the secondary transfer portion N2 that transfers the toner image from the intermediate transfer belt 7 to the recording material P in synchronization with the toner image on the intermediate transfer belt 7 being conveyed.

  The secondary transfer outer roller 14 abuts on the intermediate transfer belt 7 and presses the secondary transfer inner roller 10 via the intermediate transfer belt 7 to form a secondary transfer portion N2 together with the secondary transfer inner roller 10. Next transfer member.

  The first power source 22 is electrically connected to the secondary transfer outer roller 14 and is a power source as a voltage application unit that applies a voltage to the secondary transfer outer roller 14.

  When the recording material P is conveyed to the secondary transfer portion N2, a secondary transfer voltage having a polarity opposite to that of the toner is applied to the secondary transfer outer roller 14, whereby the toner image is transferred from the intermediate transfer belt 7 to the recording material. To do.

  The secondary transfer inner roller 10 is made of EPDM rubber. The diameter of the secondary transfer inner roller 10 is set to 20 mm, the rubber thickness is set to 0.5 mm, and the hardness is set to 70 ° (Asker-C).

  The secondary transfer outer roller 14 is made of an elastic layer made of NBR rubber, EPDM rubber or the like and a cored bar. The diameter of the secondary transfer outer roller is formed to be 24 mm.

  For removing residual toner and paper dust remaining on the intermediate transfer belt 7 without being transferred to the recording material at the secondary transfer portion N2 on the downstream side of the secondary transfer portion N2 in the direction in which the intermediate transfer belt 7 moves. An intermediate transfer belt cleaning device 15 is provided.

[Primary transfer electric field formation]
The formation of the primary transfer electric field in Example 1 will be described with reference to the equivalent circuit of FIG. Here, ITB_b represents the base layer of the intermediate transfer belt 7, and ITB_s represents the surface layer of the intermediate transfer belt 7.

  The stretching rollers 10, 11, 12, and 13 are grounded so as to generate a primary transfer electric field by using a current from a first power source 22 for secondary transfer of the toner image from the intermediate transfer belt 7 to the recording material. A constant voltage element is disposed between the two.

  As a result, as shown in FIG. 3, the potential of the intermediate transfer belt 7 becomes high, and a primary transfer electric field acts between the photoreceptors 1 a, 1 b, 1 c, 1 d and the intermediate transfer belt 7.

  Next, the primary transfer contrast, which is the difference between the potential of the photoreceptor and the potential of the intermediate transfer belt, will be described with reference to FIG.

  In FIG. 4, the surface of the photosensitive member is charged by a charging roller to become a potential Vd of the surface of the photosensitive member (here, assumed to be −678 V), and the charged surface of the photosensitive member is exposed by an exposure unit. Is Vl (here, assumed to be −240 V).

  The potential Vd is the potential of the non-image area where the toner is not adhered, and the potential Vl is the potential of the image area where the toner on the photoreceptor is adhered. Vitb is the potential of the intermediate transfer belt.

  The surface potential of the photoconductor is controlled on the basis of the detection result of a potential sensor disposed close to the photoconductor on the downstream side of the charging and exposure unit and upstream of the developing unit.

  The potential sensor detects the non-image portion potential and the image portion potential on the surface of the photoreceptor, controls the charging potential of the charging unit based on the non-image portion potential, and controls the exposure light amount of the exposure unit based on the image portion potential. .

  By this control, the surface potential of the photoreceptor can be set to an appropriate value for both the image portion potential and the non-image portion potential.

The electrostatic image contrast Vcb, which is the potential difference between the image portion potential Vl and the non-image portion potential Vd, is
−240 (V) − (− 678 (V)) = 438 (V)
It becomes.

The primary transfer contrast Vtr, which is the potential difference between the image portion potential Vl of the photoreceptor and the potential Vitb (here, 300 V) of the intermediate transfer belt,
300 (V)-(-240 (V)) = 540 (V)
It becomes.

[Voltage-current characteristics of Zener diode]
The primary transfer is determined by the primary transfer contrast which is a potential difference between the potential of the intermediate transfer belt and the potential of the photosensitive member. Therefore, in order to stably form the primary transfer contrast, it is desirable to keep the potential of the intermediate transfer belt constant.

  Therefore, in the first embodiment, a Zener diode is used as a constant voltage element disposed between the stretching roller and the ground potential (earth). A varistor may be used instead of the Zener diode.

  FIG. 5 shows the current-voltage characteristics of the Zener diode. The Zener diode has a characteristic that current hardly flows until a voltage equal to or higher than the Zener breakdown voltage Vbr is generated, but current rapidly flows when the Zener breakdown voltage is generated. That is, when the voltage applied to the Zener diode 16 is equal to or higher than the Zener breakdown voltage, the voltage drop of the Zener diode 16 is kept constant at the Zener voltage (predetermined voltage).

  Utilizing such a current-voltage characteristic of the Zener diode, the potential of the intermediate transfer belt 7 is maintained substantially constant at a predetermined voltage.

  That is, in the first embodiment, the Zener diode 16 is electrically connected between all the stretching rollers 10, 11, 12, 13 and the ground potential (earth).

  Here, the reason why the current flowing through the constant voltage element is reduced when the photoreceptor is worn by use and the film thickness of the photosensitive layer is reduced will be described. Assuming that the primary transfer contrast is the same, the transfer current flowing through the primary transfer portion increases when the film thickness of the photoconductor is small compared to when it is thick. This is because the transfer current flows until the potential difference between the photoconductor and the intermediate transfer belt reaches a predetermined value. The thinner the photoconductor is, the higher the capacitance of the photoconductor. This is because the transfer charge to be changed to the same potential is required as the photoconductor is thinner.

  Note that when the process speed is high, the current flowing through the Zener diode 16 may decrease when the set potential of the photoconductor is high, compared to when it is low.

  When the photosensitive member is worn and thinned in this way, the amount of current flowing into the primary transfer portion among the current supplied from the first power supply increases, and the current flowing through the Zener diode 16 decreases. For this reason, the voltage generated in the Zener diode 16 may not reach a predetermined voltage.

  Therefore, in the present invention, the belt potential of the intermediate transfer belt 7 is kept constant by providing the second power source 21 so that the voltage generated in the Zener diode 16 can be maintained at a predetermined voltage.

  In Example 1, it is assumed that 12 Zener diodes 16 having a Zener breakdown voltage Vbr of 25V are connected in series between the stretching roller and the ground potential (earth). The potential of the intermediate transfer belt is kept constant at the total Zener breakdown voltage of each Zener diode, that is, 25 × 12 = 300V.

  Of course, the present invention is not intended to be limited to a configuration using a plurality of Zener diodes. A configuration in which only one Zener diode is used may be employed.

  Of course, the surface potential of the intermediate transfer belt is not intended to be limited to 300V. It is desirable to set appropriately according to the type of toner used and the characteristics of the photoreceptor.

[Circuit for detecting current flowing in Zener diode]
In the first embodiment, a first current detection circuit 204 (detection means) that detects a current flowing to the ground via the Zener diode 16 is provided.

  When the current detected by the first current detection circuit 204 is less than 5 μA, the voltage generated in the Zener diode 16 is less than a predetermined voltage, and when it is 5 μA or more, the voltage generated in the Zener diode 16 is The voltage is determined.

[controller]
A configuration of a controller that controls the entire image forming apparatus according to the first exemplary embodiment will be described with reference to FIG. As shown in FIG. 6, the controller includes a CPU circuit unit 150 (control unit). The CPU circuit unit 150 includes a CPU (not shown), a ROM 151, and a RAM 152.

  The first current detection circuit 204 is a circuit that detects a current flowing into the Zener diode 16. The second current detection circuit 205 is a circuit that detects a current flowing through the secondary transfer unit. The potential sensor 206 is a sensor that detects the potential of the photoreceptor surface. The temperature / humidity sensor 207 is a sensor for detecting temperature / humidity.

  Information from the first current detection circuit 204, the second current detection circuit 205, the potential sensor 206, and the temperature / humidity sensor 207 is input to the CPU circuit unit 150. The CPU circuit unit 150 comprehensively controls the second power source 21, the first power source 22, the development high-voltage power source 201, the exposure power source 202, and the charging high-voltage power source 203 in accordance with a control program stored in the ROM 151. . An environment table and a paper thickness correspondence table, which will be described later, are stored in the ROM 151 and reflected by being called by the CPU. The RAM 152 temporarily stores control data and is used as a work area for arithmetic processing associated with control.

[Control of first power source]
In order to optimize the secondary transfer electric field, the first power supply 22 is controlled by the CPU circuit unit 150.

  The appropriate secondary transfer electric field varies depending on the atmospheric environment and the type of recording material. Therefore, in the first embodiment, the adjustment process is executed by the CPU circuit unit 150 during the non-secondary transfer before the secondary transfer process for transferring the toner image to the recording material.

  The CPU circuit unit 150 measures the current flowing through the secondary transfer unit with the second current detection unit 205 when a plurality of adjustment voltages are applied by the first power supply 22, and calculates the correlation between the voltage and the current.

  The CPU circuit unit 150 calculates a voltage V1 for flowing the secondary transfer target current It necessary for the secondary transfer based on the calculated correlation between the current and the voltage.

  The CPU circuit unit 150 sets a voltage (V1 + V2) obtained by adding the recording material sharing voltage V2 to V1 for flowing the secondary transfer target current It as the target voltage Vt of the secondary transfer voltage.

[Power ON / OFF and control during primary transfer and secondary transfer]
From the viewpoint of whether or not the transfer is performed at each of the primary transfer portion and the secondary transfer portion during image formation, the timing is divided into the following three timings (a) to (c). The ON / OFF and control of the first power supply and the second power supply at each timing are summarized as follows.
(A) When primary transfer is being performed and secondary transfer is being performed The first power supply is turned on and the second power supply is turned on
(B) When primary transfer is performed and secondary transfer is not performed, the first power supply is turned off and the second power supply is turned on
(C) When the primary transfer is not performed and the secondary transfer is performed The first power supply is turned on and the second power supply is turned on
In the case of (a), the first power source is controlled to a constant voltage determined by ATVC, and the second power source 21 is controlled so that the detection current of the first current detection circuit 204 becomes 5 μA.
In the case of (a), the second power supply 21 is controlled so that the detection current of the first current detection circuit 204 becomes 5 μA.
In the case of (c), the first power source is controlled so as to have a constant voltage determined by ATVC, and the second power source is controlled so that the detection current of the first current detection circuit 204 becomes 5 μA.

  Here, it is possible to turn on the first power supply and turn off the second power supply at the timing (b). The reason for turning off the first power supply and turning on the second power supply is as follows. Street. The secondary transfer roller increases in resistance depending on the product of the energization time and the current value and reaches the end of its life. However, the first transfer is turned off to shorten the energization time to the secondary transfer roller and improve the life. This is to make it happen.

  It is also possible to turn on the first power supply 22 and turn off the second power supply 21 at the timing of (c). However, the first power supply 22 is turned on and the second power supply 21 is turned on. The reason for doing this is as follows. Since the timing of (c) is a period in which primary transfer is not performed, there is no problem in terms of primary transfer even if the constant voltage element is less than a predetermined voltage. However, since the potential generated in the constant voltage element is also the potential of the secondary transfer inner roller 10, the secondary transfer electric field is affected and a secondary transfer failure occurs due to a deviation from the appropriate value of the secondary transfer electric field. As a countermeasure against this secondary transfer failure, a predetermined voltage can be generated in the constant voltage element by lowering the set potential of the photoreceptor in accordance with the timing of (c) and relatively increasing the current flowing through the constant voltage element. However, when the set potential of the photosensitive member is lowered, the potential difference between the intermediate transfer belt 7 and the photosensitive member becomes large, and there is a possibility that memory is generated in the photosensitive member. Therefore, in the first embodiment, the first power supply 22 is turned on and the second power supply 21 is turned on at the timing of (c).

  According to the first embodiment, the constant voltage element can be reliably set to a predetermined voltage, primary transfer failure can be suppressed, the life of the secondary transfer roller can be improved, and the memory of the photoconductor can be avoided.

The basic configuration of the apparatus of the second embodiment is the same as that of the first embodiment.
In the first embodiment, the first power supply 22 is turned off and the second power supply 21 is turned on at the timing (a). However, the resistance increase due to energization does not become a problem due to the material of the secondary transfer roller and the set life. In some cases, the following configuration is possible.
(A) When primary transfer is being performed and secondary transfer is being performed The first power supply is turned on and the second power supply is turned on
(A) When primary transfer is being performed and secondary transfer is not being performed The first power supply is turned on and the second power supply is turned off
(C) When the primary transfer is not performed and the secondary transfer is performed The first power supply is turned on and the second power supply is turned on
In the case of (a), the first power source 22 is controlled to a constant voltage determined by ATVC, and the second power source 21 is controlled so that the detection current of the first current detection circuit 204 becomes 5 μA.
In the case of (a), the first power supply 22 is controlled so that the detection current of the first current detection circuit 204 becomes 5 μA.
In the case of (c), the first power supply 22 is controlled to a constant voltage determined by ATVC, and the second power supply 21 is controlled so that the detection current of the first current detection circuit 204 is 5 μA.

  According to the second embodiment, the constant voltage element can be reliably set to a predetermined voltage, primary transfer failure can be suppressed, and the memory of the photoconductor can be avoided.

The basic configuration of the apparatus of the third embodiment is the same as that of the first embodiment.
In the first and second embodiments, the first power source 22 is turned on and the second power source 21 is turned off at the timing of (c). However, the memory of the photoconductor becomes a problem due to the material of the photoconductor. If not, the following configuration can be used.
(A) When primary transfer is being performed and secondary transfer is being performed The first power supply is turned on and the second power supply is turned on
(A) When primary transfer is being performed and secondary transfer is not being performed The first power supply is turned on and the second power supply is turned off
(C) When the primary transfer is not performed and the secondary transfer is performed The first power supply is turned on and the second power supply is turned off.
In the case of (a), the first power source 22 is controlled to a constant voltage determined by ATVC, and the second power source 21 is controlled so that the detection current of the second current detection circuit 204 is 5 μA.
In the case of (a), the first power supply 22 is controlled so that the detection current of the first current detection circuit 204 becomes 5 μA.
In the case of (c), the first power supply 22 is controlled by a constant voltage determined by ATVC.

  Here, in Example 3, charging or exposure is controlled so that the potential of the photoconductor in the primary transfer portion becomes 0 V in accordance with the timing of (c). As a result, the current flowing through the Zener diode is increased and the potential of the secondary transfer inner roller 10 is suppressed from being lowered, and the secondary transfer electric field can be properly maintained.

  According to the third embodiment, the constant voltage element can be reliably set to a predetermined voltage, and primary transfer failure can be suppressed.

DESCRIPTION OF SYMBOLS 1 Photoconductor 7 Intermediate transfer belt 21 2nd power supply 22 1st power supply 14 Secondary transfer outer roller 150 CPU circuit part

Claims (7)

An image carrier for carrying a toner image;
An intermediate transfer member carrying a toner image transferred from the image carrier at a primary transfer portion;
A transfer member disposed in contact with the outer peripheral surface of the intermediate transfer member, and transferring a toner image from the intermediate transfer member to a recording material at a secondary transfer unit;
A constant voltage element that is electrically connected between the inner peripheral surface of the intermediate transfer member and a ground potential, and generates a predetermined voltage;
Detecting means for detecting a current flowing in the constant voltage element;
A first power source that applies a voltage to the transfer member to cause a current to flow through the constant voltage element to form a secondary transfer electric field in the secondary transfer portion;
A second power source electrically connected to the inner peripheral surface of the intermediate transfer member and forming a primary transfer electric field in the primary transfer portion;
A control unit for controlling the second power supply based on a detection result of the detection means;
An image forming apparatus comprising:   2. The control unit according to claim 1, wherein the control unit controls the second power supply so that a detection result of the detection unit becomes a current value at which the constant voltage element generates a predetermined voltage. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit controls the second power source based on a detection result of the detection unit when primary transfer is performed.   The controller supplies current only from the second power source when primary transfer is being performed and when secondary transfer is not being performed, and the second power source is based on the detection result of the detection means. 4. The image forming apparatus according to claim 3, wherein the image forming apparatus is controlled.   The intermediate transfer member has a structure of two or more layers, and the volume resistivity of the layer on the outer peripheral surface side is higher than the volume resistivity of the layer on the inner peripheral surface side. The image forming apparatus according to claim 1. The intermediate transfer member is an intermediate transfer belt;
The image forming apparatus according to claim 1, further comprising a plurality of stretching members that are in contact with an inner peripheral surface of the intermediate transfer belt and stretch the intermediate transfer belt. The tension member is a tension roller having conductivity,
The image forming apparatus according to claim 6, wherein the tension roller is electrically connected to the constant voltage element to electrically connect the intermediate transfer body and the constant voltage element.

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