KR20170088426A - Image forming apparatus - Google Patents

Abstract

A constant voltage element connected between the inner circumferential surface of the intermediate transfer body and the ground potential and configured to generate a predetermined voltage, a first power source for forming a secondary transfer electric field, and a second transfer electric field And controls the first power source during at least a part of a period in which a primary transfer electric field is formed in the primary transfer portion to form an electric field in a direction opposite to the secondary transfer electric field in the secondary transfer portion.

Description

[0001] IMAGE FORMING APPARATUS [0002]

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

In the image forming apparatus based on the electrophotographic system, a toner image is transferred (primary transfer) from the photosensitive member to the intermediate transfer member, and the toner image is transferred from the intermediate transfer member to the recording material (secondary transfer) The intermediate transfer method is proposed.

However, in the case of using the primary transfer power source and the primary transfer roller separately from the secondary transfer roller or the secondary transfer power source, this configuration can increase the cost and increase the size of the intermediate transfer unit. In view of the above, Patent Document 1 proposes a configuration for reducing the size of the intermediate transfer unit. In this configuration, the resistance of the inner surface of the intermediate transfer belt is reduced, and the intermediate transfer belt is grounded through the constant voltage element without providing the primary transfer roller and the primary transfer power source Lease-system ").

However, in the above-described primary transfer member-less system, when the photoconductor is worn and thinned by use, the amount of current flowing into the primary transfer portion among the currents supplied from the power source increases, and the amount of current flowing through the constant- There may be cases in which it is reduced. As a result, there is a problem that the constant voltage element can not generate a predetermined voltage and primary transfer failure occurs due to insufficient primary transfer electric field.

There is a case where an electric field in a direction opposite to the secondary transfer electric field is formed in the secondary transfer portion in order to return fogging toner or flying toner accumulated in the secondary transfer member to the intermediate transfer body and clean it. Further, in order to suppress the adherence of the image for adjustment formed between images to the secondary transfer member, there is a case where an electric field in the reverse direction is formed in the secondary transfer portion.

In addition, in order to increase the productivity of the image, the image toner and the adjustment toner can be transferred at the same time at the timing of performing the cleaning and the timing at which the adjustment image passes through the secondary transfer portion.

However, in the above-described primary transfer member-less system, since both the secondary transfer electric field and the primary transfer electric field are generated by flowing the current supplied to the secondary transfer member from the power source to the constant-voltage element, There is a problem that an electric field in the direction opposite to the secondary transfer electric field can not be formed in the secondary transfer portion during the period in which the primary transfer electric field is formed in the secondary transfer portion.

Japanese Patent Laid-Open Publication No. 1-137733

In view of the above, according to an aspect of the present invention, an image forming apparatus includes: an image bearing member that carries a toner image having a predetermined charging polarity; An intermediate transferring member for supporting the toner image primarily transferred from the primary transferring portion from the image bearing member; A transfer member disposed so as to abut the outer circumferential surface of the intermediate transfer member and configured to transfer the toner image from the intermediate transfer member to the recording material in the secondary transfer portion; A constant voltage element electrically connected between the inner circumferential surface of the intermediate transfer member and the ground potential and configured to generate a predetermined voltage by flowing an electric current; A first power source for applying a voltage to the transfer member and forming a secondary transfer electric field in the secondary transfer portion in which a toner image having a charging polarity is moved from the intermediate transfer member toward the recording material; A second power source for generating a primary transfer electric field in which the toner image having a charge polarity is moved from the image carrier toward the intermediate transfer member is formed in the primary transfer portion by electrically connecting the inner peripheral surface of the intermediate transfer member and flowing a current through the constant voltage element, ; And a control unit configured to control the first power source and form an electric field in a direction opposite to the secondary transfer electric field in the secondary transfer unit during at least a part of a period in which the primary transfer electric field is formed in the primary transfer unit.

Additional features of the invention will become apparent from the following description of illustrative embodiments with reference to the accompanying drawings.

1 is a view for explaining the basic configuration of a primary transfer member-less system.
Fig. 2 is a view for explaining a device configuration according to the first exemplary embodiment.
3 is a view for explaining an equivalent circuit in the first exemplary embodiment.
4 shows the relationship between the transfer potential and the electrostatic image potential in the first exemplary embodiment.
5 shows the current-voltage characteristics of the zener diode.
6 is a block diagram according to a first exemplary embodiment.
7 is a flow chart according to the first exemplary embodiment.
8 is a timing chart according to the first exemplary embodiment.
9 is a view for explaining a device configuration according to the second exemplary embodiment.
10 is a view for explaining a toner image for adjustment (patch image) in the second exemplary embodiment.
11A is a view for explaining a configuration according to the second exemplary embodiment.
11B is a view for explaining a configuration according to the second exemplary embodiment.
12A is a diagram for explaining control according to a comparative example.
12B is a diagram for explaining control according to a comparative example.
13 is a block diagram of a control system of the transfer voltage according to the second exemplary embodiment.
14 is a flowchart of the control according to the second exemplary embodiment.
15 is a timing chart according to the second exemplary embodiment.
16A is a diagram according to a third exemplary embodiment.
16B is a diagram according to a third exemplary embodiment.
17 is a timing chart according to the third exemplary embodiment.

In the following, exemplary embodiments of the present invention will be described with reference to the drawings. It should be noted that the components having the same reference numerals in the respective drawings have the same configuration or function, and the redundant description of these components is appropriately omitted.

The first exemplary Example

The image forming apparatus 1

2 shows a tandem type image forming apparatus using an intermediate transfer body according to the first exemplary embodiment.

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

Each of the image forming units 101a, 101b, 101c, and 101d is provided with photoconductors 1a, 1b, 1c, and 1d as an image bearing member on which a toner image is formed and supported. The charging rollers 2a, 2b, 2c, and 2d are charging units configured to charge the surfaces of the respective photoconductors 1a, 1b, 1c, and 1d. The exposure apparatuses 3a, 3b, 3c and 3d are equipped with laser scanners and expose the photoreceptors 1a, 1b, 1c and 1d charged by the charging rollers 2a, 2b, 2c and 2d. The electric power of the laser scanner is turned on / off based on the image information, so that an electrostatic image corresponding to the image is formed on each of the photoconductors 1a, 1b, 1c and 1d. That is, the charging rollers 2a, 2b, 2c, and 2d and the exposing devices 3a, 3b, 3c, and 3d function as electrostatic image forming units configured to form electrostatic images on the photoreceptors 1a, 1b, 1c, and 1d . The developing devices 4a, 4b, 4c and 4d are each provided with a receptacle for receiving toners of respective colors of yellow, magenta, cyan and black, and the electrostatic image on the photoconductors 1a, 1b, 1c and 1d is used Thereby developing the image.

The toner images formed on the photosensitive members 1a, 1b, 1c, and 1d are primarily transferred to the intermediate transfer belt 7 by the primary transfer portions N1a, N1b, N1c, and N1d. Therefore, the toner images of the four colors are superimposed and transferred onto the intermediate transfer belt 7.

The intermediate transfer belt 7 is a movable intermediate transfer member that transfers the toner image from the photoconductors 1a, 1b, 1c and 1d. The intermediate transfer belt 7 has a two-layer structure including a base layer (inner peripheral surface side) and a surface layer (outer peripheral surface side). It should be noted that the intermediate transfer belt 7 may have a structure of two or more layers in which another layer is disposed between the base layer and the surface layer.

As the base layer, a layer obtained by adding an appropriate amount of an antistatic agent such as carbon black to a resin such as polyimide or polyamide, PEN, PEEK, or various rubbers is used.

The base layer of the intermediate transfer belt 7 is formed so that the surface resistivity of the base layer is set to 10 ² to 10 ⁸ Ω / □ (conductive). As the base layer in the first exemplary embodiment, a film-shaped endless belt formed of polyimide and having a center thickness of about 45 to 150 mu m is used.

The surface layer includes an acrylic coating having a volume resistivity in the film thickness direction including the base layer of from 10 ⁹ to 10 ¹³ Ω · cm, which is resistance-regulated. 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 mu m. Of course, these figures are not intended to limit the thickness.

The intermediate transfer belt 7 is held against the inner peripheral surface of the intermediate transfer belt 7 by support rollers 10, 11, 12, 13 as support members. The idler roller 12 supports the intermediate transfer belt 7 extending in the arrangement direction of the photoconductors 1a, 1b, 1c and 1d.

The tension roller 11 is a roller for applying a predetermined tension to the intermediate transfer belt 7. Further, the tension roller 11 functions as a correction roller for preventing the intermediate transfer belt 7 from skewing. The tension roller 11 is configured such that the belt tension is set to approximately 5 to 12 kgf. By applying the belt tension, nips are formed between the intermediate transfer belt 7 and the photoconductors 1a, 1b, 1c, and 1d as the primary transfer portions N1a, N1b, N1c, and N1d.

The secondary transfer inner roller 10 functions as a drive roller configured to be driven by a motor having a good positive property and to drive the intermediate transfer belt 7 in a circulating manner.

The second power source 21 is connected to the tension roller 11 and is a power source for flowing current in the circumferential direction of the intermediate transfer belt 7. [ The second power source 21 does not necessarily have to be connected to the tension roller 11 and the second power source 21 can be connected to any one of the support rollers 10, 11, 12, Be careful.

The recording material P is accommodated in the paper tray. The recording material P is taken out by the pickup roller at a predetermined timing from the paper tray, and is led to a registration roller (not shown). The recording material P is fed by the registration roller to the secondary transfer portion N2, which is transferred from the intermediate transfer belt 7 to the recording material P, in synchronization with the conveyance of the toner image on the intermediate transfer belt 7. [

The secondary transfer outer roller 14 abuts the intermediate transfer belt 7 and presses the secondary transfer inner roller 10 through the intermediary transfer belt 7 to form the secondary transfer inner roller 10 To form a secondary transfer portion N2.

The first power source 22 is a power source that functions as a voltage applying unit that is electrically connected to the secondary transfer outside roller 14 (transfer roller) and applies a voltage to the secondary transfer outside roller 14. [

When the recording material P is conveyed to the secondary transferring portion N2, a secondary transferring voltage having a polarity opposite to that of the toner is applied to the secondary transferring / non-transferring roller 14 to form a secondary transferring electric field, Image is transferred to the recording material P.

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

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

On the downstream side with respect to the secondary transferring portion N2 in the moving direction of the intermediate transferring belt 7, the intermediate transfer belt cleaning device 15 is provided. The intermediate transfer belt cleaning device 15 is configured to remove residual toner and paper dust remaining on the intermediate transfer belt 7 without transferring the recording material P to the secondary transfer portion N2.

The patch detection sensor 207 (toner image detection unit) is provided at a position where the patch detection sensor 207 is opposed to the intermediate transfer belt portion supported by the support roller 12. [ The patch detection sensor 207 is configured to optically detect reflected light or scattered light of the light irradiated onto the adjustment toner image (patch image) formed on the intermediate transfer belt 7. [

Primary warrior Field  formation

Formation of the primary transfer electric field according to the first exemplary embodiment 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.

11, 12 and 13 so as to generate a primary transfer electric field by using a current from the first power source 22 for secondary transferring the toner image from the intermediate transfer belt 7 to the recording material, And a constant-voltage element is disposed between the ground and the ground.

As a result, as shown in Fig. 3, the potential of the intermediary transfer belt 7 is increased, and a primary transfer electric field is realized between the intermediary transfer belt 7 and the photoconductors 1a, 1b, 1c and 1d.

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

4 shows a state in which the potential of the surface of the photoreceptor is set to Vd (here, -678 V) while the surface of the photoreceptor is charged by the charging roller, and the photoreceptor surface is Vl (-240 V here) while the charged photoreceptor surface is exposed by the exposing unit .

The potential Vd is the potential of the non-image portion to which the toner is not attached, and the potential V1 is the potential of the image portion to which the toner on the photoreceptor is attached. Vitb represents the potential of the intermediate transfer belt.

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

The potential sensor detects the potential of the non-image portion on the photoconductor surface and the potential of the image portion. The potential sensor controls the charging potential of the charging unit based on the potential of the non-forming portion, and controls the exposure intensity of the exposure unit based on the potential of the image portion.

With the above-described control, both the potential of the image portion and the potential of the non-image portion can be set to appropriate values in relation to the surface potential of the photoconductor.

The electrostatic image contrast Vcb corresponding to the difference between the potential Vl of the image portion and the potential Vd of the non-image portion is set to -240 (V) - (- 678 (V)) = 438 (V).

The primary transfer contrast Vtr corresponding to the difference between the potential Vl of the image portion of the photosensitive member and the potential Vitb (300 V in this case) of the intermediate transfer belt is set to 300 (V) - (-240 (V)) = 540 (V).

Zener  Diode Voltage-Current Characteristics

The primary transfer is determined by the primary transfer contrast corresponding to the difference between the potential of the intermediate transfer belt and the potential of the photoconductor. Therefore, in order to form the primary transfer contrast stably, it is desirable to keep the potential of the intermediate transfer belt constant.

In view of the foregoing, according to the first exemplary embodiment, a zener diode is used as a constant-voltage element disposed between a support roller and a ground potential (ground). It should be noted that a varistor can be used instead of a zener diode.

5 shows the current-voltage characteristics of the zener diode. The Zener diode has almost no current until a voltage exceeding the zener breakdown voltage Vbr is generated, but has a characteristic in which a current abruptly 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).

The potential of the intermediate transfer belt 7 is kept substantially constant at a predetermined voltage by using the current-voltage characteristic of the zener diode described above.

That is, according to the first exemplary embodiment, the zener diodes 16 are electrically connected between all the support rollers 10, 11, 12, 13 and the ground potential (ground).

According to the exemplary embodiment of the present invention, by providing the second power source 21 so that the voltage generated in the zener diode 16 can maintain a predetermined voltage, the belt potential of the intermediate transfer belt 7 is kept constant .

According to the first exemplary embodiment, twelve zener diodes 16 having a zener breakdown voltage Vbr of 25 V are connected in series between the support roller and the ground potential (ground). The potential of the intermediate transfer belt is kept constant at the sum of the zener breakdown voltages of the respective Zener diodes, that is, 25 x 12 = 300V.

Of course, the present invention is not intended to limit the present invention to a configuration using a plurality of Zener diodes. It is also possible to use a configuration in which only one Zener diode is used.

Of course, the present invention is not intended to limit the present invention to a configuration in which the surface potential of the intermediate transfer belt is set to 300V. It is preferable to appropriately set the surface potential according to the type of the toner to be used and the characteristics of the photoconductor.

Zener  Circuit for detecting the current flowing through the diode

According to a first exemplary embodiment, there is provided a first current detection circuit 204 (first current detection circuit unit, current detection unit) configured to detect a current flowing through a zener diode 16 to ground.

When the current detected by the first current detection circuit 204 is less than 5 [micro] A, the voltage generated in the Zener diode 16 is less than a predetermined voltage. When the detected current is 5 A or more, the voltage generated in the zener diode 16 is a predetermined voltage.

controller

A configuration of a controller for controlling the entire image forming apparatus according to the first exemplary embodiment will be described with reference to Fig. The controller includes a CPU circuit unit 150 (control unit), as shown in Fig. A CPU (not shown), a ROM 151 and a RAM 152 are incorporated in the CPU circuit unit 150.

The first current detection circuit 204 is a circuit configured to detect a current flowing from the zener diode 16 to the ground potential. The second current detection circuit 205 (second current detection unit) is a circuit configured to detect a current flowing from the first power source 22 to the secondary transfer portion. A potential sensor 206 not shown in Fig. 2 is a sensor configured to detect the potential of the surface of the photoreceptor.

The patch detection sensor 207 is a sensor configured to optically detect a patch image on the intermediate transfer belt.

Here, the patch image includes the following types. (1) Patch image for setting the exposure output: The electrostatic image in which the laser beam intensity is made different in a plurality of steps is developed to form a patch-like adjusting toner image. (2) Pitch image for gradation correction: An electrostatic image in which the halftone gradation is made different in a plurality of steps is developed to form a patch-like adjustment toner image. (3) Patch image for developer replenishment: A patch toner image for adjustment is formed at an image interval of several tens of image forming operations. (4) Image for correction of misalignment of each color: A plurality of stripe-shaped adjusting toner images arranged in the carrying direction with respect to the rotating direction of the photosensitive drum are formed.

The first exemplary embodiment relates to an exemplary embodiment of a patch image whose length is relatively long (a plurality of patches are continuous) in the rotational direction of the photosensitive drum as in (1), (2), and (4) .

The CPU circuit unit 150 (adjusting toner image forming unit) is configured to adjust the image forming conditions such as the image density and the image forming timing, in the middle of a period other than the period of the primary transfer of the secondary- Thereby forming an adjustment toner image (patch image) on the transfer belt.

The CPU circuit unit 150 receives information from the first current detection circuit 204, the second current detection circuit 205, the potential sensor 206, and the patch detection sensor 207. The CPU circuit unit 150 drives the second power source 21, the first power source 22, the developing high voltage power source 201, the exposure power source 202 and the charging high voltage power source (not shown) in accordance with a control program stored in the ROM 151 203).

The CPU circuit unit 150 (adjustment unit) changes the image forming conditions such as the charging condition, the exposure condition, and the developing condition of the photoreceptor in accordance with the detection result of the patch detection sensor 207.

The RAM 152 temporarily holds the control data, and is also used as a work area for the arithmetic processing accompanying the control.

Control when patch image is detected

Control when the patch image is continuously formed on the intermediate transfer belt will be described with reference to Fig.

Here, the patch image corresponds to a single patch image or a series of patch images divided into a plurality of in the traveling direction of the intermediate transfer belt. A series of patch lengths from the most upstream side position to the most downstream side position in the traveling direction of the intermediate transfer belt is set to be equal to or longer than the path length from the primary transferring portion to the secondary transferring portion on the intermediate transferring belt. When a patch image is continuously formed, there may be a case where a patch image formed in advance passes through the secondary transfer portion when the patch image is transferred to the intermediate transfer belt in the primary transfer portion. When the patch image passes through the secondary transfer portion, there is no recording material in the secondary transfer portion. Therefore, it is necessary to form a non-electric field different from the electric field at the secondary transfer in the secondary transfer portion so that the contact patch image is not electrostatically adhered to the secondary transfer outside roller.

However, in the primary transfer member-less system, the first power source 22 that forms an electric field in the secondary transfer portion is used to form the electric field of the primary transfer portion. Even when a non-electric field is formed in the secondary transfer portion, it is necessary that an appropriate primary transfer electric field is formed in the primary transfer portion.

The CPU circuit unit 150 sets the detection current of the first current detection circuit 204 to the second power supply 21 ). This control is continuously executed in the next steps S102 and S103.

With this control, +300 V can be generated in the zener diode without flowing current more than necessary, and a proper primary transfer electric field can be formed in the primary transfer portion. The voltage of the second power source 21 at this time is substantially equal to + 300V and corresponds to a voltage slightly lower than + 300V.

Next, in step S102, the CPU circuit unit 150 determines whether or not the second current detection circuit 205 for detecting the current flowing through the secondary transferring-out roller during the period in which at least the patch image passes through the secondary transferring part is set to -25 [ And controls the first power source 22 to indicate the first power source.

Here, the target current value is not limited to -25 [micro] A. The target current can be set in advance according to the state in which the toner is attached. For example, when the amount of the attached toner is not large, the target current is set to 0 to -5 (μA), and when the amount of the attached toner is large, the target current is set to -15 to -30 do.

Next, in S103, after the last patch image of the subsequently formed patch image passes through the secondary transfer portion, the voltage applied to the secondary transfer outside roller is controlled as follows. That is, the detection current of the second current detection circuit 205 is set to be +25 (μA) and -25 (μA) alternately in a period interval corresponding to one rotation of the circumferential length of the secondary transfer / Thereby controlling the voltage applied to the outer roller.

Here, the target current value is not limited thereto. Also, the number of times of alternate application is not limited to one time of the constant current and the sub-current, but may be set in advance in consideration of the degree of cleaning performance and the like.

By the above-described control, even when the patch image is being transferred by the primary transferring section, toner adherence to the surface of the secondary transferring-out roller is suppressed and toner adhered to the surface of the secondary transferring- It can be returned to the intermediate transfer belt side from the roller.

Next, the timing of high voltage switching of the second power source 21 and the first power source 22 will be described.

8 is a timing chart at the time of detecting a patch image. Here, t0 indicates the timing at which the control of the second power source 21 is started, t1 indicates the timing at which the front end of the patch image enters the primary transfer section, t2 indicates timing at which the control of the first power source 22 is started Lt; / RTI > Next, t3 indicates the timing at which the front end of the patch image enters the secondary transfer section, t4 indicates that the trailing end of the patch image passes through the secondary transfer section, and the polarity of the target current value for control of the second power source 21 is Indicates the timing of switching. Next, t5 indicates the timing for switching the polarity of the target current value for control of the second power source 21, and t6 indicates the timing for terminating the electrostatic cleaning of the secondary transferring / non-transferring roller.

First, the control of the second power source 21 is started so that the detection current of the first current detection circuit 204 is set to +5 (μA) at t0 before t1 when the front end of the patch image enters the primary transfer portion

Next, the control of the first power source 22 is started so that the second current detection circuit 205 is set to -25 (μA) at t2 before the timing t3 when the front end of the patch image enters the secondary transfer portion. By this control, an electric field in a direction opposite to the secondary transfer electric field is formed in the secondary transfer portion.

Then, at t4 when the trailing end of the patch image passes through the secondary transfer portion, the target value polarity of the current of the second current detection circuit 205 is switched to +25 (μA) of positive polarity. By this control, an electric field in the same direction as the secondary transfer electric field is formed in the secondary transfer portion.

t4, the target value polarity of the current of the second current detection circuit 205 is switched to negative (-A) of negative polarity at time t5 after a lapse of a time for one rotation of the rollers outside the secondary transfer roller. By this control, an electric field in a direction opposite to the secondary transfer electric field is formed in the secondary transfer portion.

After t5, the first power source 22 is turned off at time t6 after a lapse of a time for one rotation of the secondary transfer outside roller.

With the above-described configuration, contamination of the secondary transferring outside roller can be prevented when forming a continuous patch image in the primary transferring member -less system.

Second Exemplary Embodiment

The image forming apparatus 2

9 is a view for explaining the configuration of the image forming apparatus. 9, the image forming apparatus 100 is a full-color printer based on a tandem-type intermediate transfer system in which image forming units Pa, Pb, Pc, and Pd are arrayed along the downward surface of the intermediate transfer belt 56 to be.

In the image forming unit Pa, a yellow toner image is formed on the photosensitive drum 50a and transferred to the intermediate transfer belt 56. [ In the image forming unit Pb, a magenta toner image is formed on the photosensitive drum 50b and transferred to the intermediate transfer belt 56. [ In the image forming units Pc and Pd, a cyan toner image and a black toner image are formed on the photosensitive drums 50c and 50d, respectively, and transferred to the intermediate transfer belt 56. [

The image forming unit

As shown in Fig. 9, the image forming units Pa, Pb, Pc, and Pd have substantially the same configuration except that the toner colors used in the developing devices 53a, 53b, 53c, and 53d are yellow, magenta, cyan, . In the following description, the image forming unit Pa will be described, and redundant description of other image forming units Pb, Pc, and Pd will be omitted.

9, the intermediate transfer belt 56 is supported over the tension roller 63, the secondary transfer inward roller 62 and the idler rollers 60, 61, and the secondary transfer inward roller 62, And moves in the direction of arrow R2.

The secondary transfer roller 62 is disposed so as to function also as a drive roller of the intermediate transfer belt 56 and sandwiches the intermediate transfer belt 56 between the secondary transfer outside roller 64 and the toner image Thereby forming a secondary transfer portion T2. The secondary transfer roller 62 is driven by a motor having excellent constant speed.

Secondary Transfer part

The secondary transfer outer roller 64 disposed on the toner image bearing surface side of the intermediate transfer belt 56 and the secondary transfer inner roller 62 disposed on the inner peripheral surface of the intermediate transfer belt 56 are disposed on the intermediate transfer belt 56, The secondary transfer portion T2 is formed. The secondary transfer outer roller 64 forms the secondary transfer portion T2 by abutting the inner peripheral surface supported by the secondary transfer inner roller 62 against the intermediate transfer belt 56. [

The secondary transfer power source 210 outputs a variable voltage to the secondary transfer outside roller 64. The secondary transfer power source 210 applies a DC voltage of positive polarity larger than the secondary transfer inner roller 62 to the secondary transfer outer roller 64 and transfers the DC voltage of the positive polarity from the intermediate transfer belt 56 to the recording material P . An electric field is also formed in the portions where the photosensitive drums 50a, 50b, 50c and 50d come into contact with each other through the conductive intermediate transfer belt 56 and the toner image carried on the intermediate transfer belt 56 is transferred onto the intermediary transfer belt 56, And electrostatically moved to be transferred first.

As described above, the exposure apparatus 52a and the developing apparatus 53a, which are an example of the toner image forming unit, use the charged toner having a predetermined charge polarity to image the photosensitive drum 50a, which is an example of the image carrier, Thereby forming a normal toner image and an adjusting toner image according to the information. The intermediate transfer belt 56, which is an example of a conductive endless belt, carries a toner image transferred from the photosensitive drum 50a to the outer peripheral surface and moves. The secondary transfer outer roller 64, which is an example of the first rotary member, forms a secondary transfer portion T2 which is an example of a transfer portion abutting the outer peripheral surface of the intermediate transfer belt 56. [ The secondary transfer inner roller 62, which is an example of the second rotary member, is opposed to the secondary transfer outer roller 64 and abuts against the inner peripheral surface of the intermediate transfer belt 56. [

Adjusting Toner Image (Patch Image)

10 is a view for explaining a toner image for adjustment in the second exemplary embodiment. The second exemplary embodiment relates to an exemplary embodiment of a patch image whose length is short in the rotational direction of the photosensitive drum as in the item 3 among the four kinds of patch images described above.

And an optical sensor 59 is disposed so as to face the intermediate transfer belt 56 supported by the idler roller 61. [ The optical sensor 59 irradiates infrared light onto the toner carried on the intermediate transfer belt 56 from the light emitting diode 59a and the photodiode 59b detects the reflected light according to the toner adhesion amount on the toner.

The image forming apparatus 100 forms a patch image between toner images (image intervals) of an image formed on the photosensitive drum 50a.

After the reflected light is measured by the optical sensor 59, the patch image passes through the secondary transfer portion T2 and is conveyed to the belt cleaning device 65 and removed from the intermediate transfer belt 56 by the cleaning blade. However, when a patch image carried on the intermediate transfer belt 56 passes through the secondary transfer portion T2, and a voltage opposite in polarity to the charge polarity of the toner is applied to the secondary transfer outside roller 64, And transferred to the outside roller 64 of the car. When the toner image is adhered to the secondary transfer outer roller 64, toner adheres to the back surface of the recording material at the time of the next image formation and is fixed, thereby causing contamination of the recording material.

According to the second exemplary embodiment, while the patch image is passing through the secondary transfer portion T2, a voltage that is opposite in polarity to the charge polarity of the toner is applied to the secondary transfer inner roller 62, Thereby preventing the patch image from moving to the outside roller 64 of the car.

Secondary transfer power

11A and 11B are views for explaining the control of the second exemplary embodiment. Fig. 11A corresponds to the case where the toner image of the image at the secondary transfer portion T2 is transferred, and Fig. 11B corresponds to the case where the patch image passes through the secondary transfer portion T2.

As shown in Fig. 11A, the image forming apparatus 100 does not include the primary transfer roller 73 for each of the photosensitive drums 50a, 50b, 50c, and 50d. The photosensitive drums 50a, 50b, 50c, and 50d are driven by the intermediate transfer belt 56 from the photosensitive drums 50a, 50b, 50c, and 50d while using the idler rollers 60 and 61 to set the conductive intermediate transfer belt 56 at a constant potential, 56 to transfer the toner image.

The idler rollers 60 and 61 form a supporting surface of the intermediate transfer belt 56 and equally contact the photosensitive drums 50a, 50b, 50c and 50d. The idler roller 60 and the tension roller 63 are electrically connected to the idler roller 61 and are grounded via the zener diode circuit 71. Therefore, when the secondary transferring voltage is applied to the secondary transferring / non-transferring roller 64, the area supported by the idler rollers 60 and 61 of the intermediate transferring belt 56 is transferred to the intermediate transferring belt 56 via the idler rollers 60 and 61, And the potential is held constant by the diode circuit 71.

The Zener diode circuit 71 is configured such that a plurality of Zener elements having a breakdown voltage Vbr of 25 V are connected in series in a total of 12 Zener breakdown voltages Vbr so that the Zener breakdown voltage Vbr is 300 V in total. As a zener diode, a Sanken electrophotographic material SJPZ-N33 was used as a result of selecting a device having a small influence of the temporal reaction on image uniformity.

The output of the power source 310 is controlled so that the detection current of the first current detection circuit 510, which is an example of the detection result of the detection unit, is set to +5 [mu] A at which the Zener diode circuit 71 can sufficiently maintain the breakdown voltage. The voltage Vc of the power source 310 at this time is set to 300V which is equal to the zener breakdown voltage Vbr.

11A, the secondary transfer power source 210 applies the transfer voltage Vt used for moving the toner image to the recording material from the intermediate transfer belt 56 to the secondary transfer outside roller 64. [

The voltage required for moving the toner image from the photosensitive drum 50a to the intermediate transfer belt 56 is substantially constant voltage Vc. On the other hand, since the voltage required for moving the toner image from the intermediate transfer belt 56 to the recording material P largely changes according to the kind of the recording material and the degree of hygroscopicity, the secondary transfer power source 210 is variable in the range of 1200 V to 1500 V And outputs a DC constant voltage.

The control unit 110 is configured to control the secondary transfer power source 210. [ In the case of a recording material having a large resistance value in the thickness direction, the control unit 110 outputs a higher transfer voltage Vt to the secondary transfer outer roller 64 than in the case of the recording material having a small resistance value in the thickness direction. For example, in the case of a plain paper (CS-814) having a weight per unit area of 81 [g / m 2], the control unit 110 controls the secondary transfer power source 210 And a voltage of about 1300 V is applied to the roller 64. A potential of 300 V, which is the potential of the secondary transfer inner roller 62, is supplied between the secondary transfer inner roller 62 and the secondary transfer outer roller 64 when a constant voltage of 1300 V is applied to the secondary transfer outer roller 64 A voltage of 1000 V is applied.

11A, when the toner image of the image passes through the secondary transfer portion T2, the control unit 110 transfers the transfer voltage Vt from the secondary transfer power source 210 to the secondary transfer outside roller 64 . At this time, since the zener diode circuit 71 holds the potential of the intermediate transfer belt 56 supported by the idler rollers 60 and 61 to be the zener breakdown voltage Vbr, the potential difference between the photosensitive drum 50a and the intermediate transfer belt 56 The toner image is stably transferred.

As shown in Fig. 11B, the control unit 110 stops the output of the secondary transfer power source 210 when the patch image passes through the secondary transfer portion T2. Next, the switch SW1 is operated to connect the secondary transfer outside roller 64 to the ground potential. At this time, the control unit 110 also uses the first current detection circuit 510 to control the power source 310 so that a constant current flows through the Zener diode circuit 71. As a result, since the constant voltage Vc is applied to the secondary transfer roller 62, the difference between the potential of the photosensitive drum 50a and the potential of the intermediary transfer belt 56 is such that when the toner image passes through the secondary transfer portion T2 . ≪ / RTI >

Therefore, during the period in which the toner image is primarily transferred from the photosensitive drum 50a to the intermediate transfer belt 56, the patch image passes through the secondary transfer portion T2 and the secondary transfer outside roller 64 is connected to the ground potential , The toner image continues to be transferred to the intermediate transfer belt 56 normally.

As described above, the zener diode circuit 71, which is an example of the constant voltage element, holds the voltage of the intermediate transfer belt 56, which is contacted with the photosensitive drum 50a, at a predetermined voltage.

The idler roller 61, which is an example of the abutting member, abuts against the inner peripheral surface of the intermediate transfer belt 56 between the photosensitive drum 50a and the secondary transfer portion T2 in the moving direction of the intermediate transfer belt 56. [ The zener diode circuit 71, which is an example of the constant voltage element, is connected to the idler roller 61 to maintain the voltage of the intermediate transfer belt 56 at the zener breakdown voltage Vbr.

(Comparative Example)

12A and 12B are views for explaining control according to a comparative example. Fig. 12A corresponds to the case where the toner image of the image is transferred in the secondary transfer portion T2, and Fig. 12B corresponds to the case where the patch image passes through the secondary transfer portion T2.

12A, in the image forming apparatus 100H according to the comparative example, the secondary transfer inner roller 62, the idler rollers 60 and 61, and the tension roller 63 are connected to the Zener diode circuit 71 And maintains the potential at the Zener breakdown voltage Vbr.

The secondary transfer power source 210 applies the positive transfer voltage Vt necessary for transferring the toner image from the intermediary transfer belt 56 to the recording material P to the secondary transfer outside roller 64. [ The potential of the intermediate transfer belt 56 supported by the idler rollers 60 and 61 is simultaneously supplied to the zener diode 71 by the Zener breakdown voltage Vbr ≪ / RTI > Therefore, the toner image can be primarily transferred from the photosensitive drum 50a to the intermediate transfer belt 56 while the toner image is secondarily transferred from the intermediate transfer belt 56 to the recording material.

12B, in the image forming apparatus 100H according to the comparative example, when the patch image passes through the secondary transfer portion T2, the polarity of the voltage applied to the secondary transferring / 56 to transfer the toner image to the recording material P. The control unit 110 applies the negative polarity direct current voltage to the secondary transferring / non-transferring roller 64 when the patch image passes through the secondary transferring portion T2 so that the patch image carried on the intermediate transferring belt 56 is transferred to the secondary transferring / And is prevented from being transferred to the outside roller 64 of the car. The patch image is not transferred to the secondary transferring outside roller 64 but passes through the secondary transferring portion T2 and is collected by the belt cleaning device 65. [

According to the comparative example, since the charge polarity of the toner is negative, in order to apply the forward voltage to the secondary transfer outside roller 64 at the time of normal transfer, the potential of the secondary transfer outside roller 64 is changed to the secondary It is required to be higher than the potential of the roller 62 inside the transfer. On the other hand, when the patch image passes through the secondary transfer portion T2, the electric potential of the secondary transfer outer roller 64 is changed to the secondary (secondary) transfer portion T2 in order to form an electric field in the direction opposite to the direction at the time of transferring the toner image in the secondary transfer portion T2. It is necessary to make it lower than the potential of the roller 62 in the transfer.

At this time, since the potential of the intermediate transfer belt 56 supported by the idler rollers 60 and 61 is set to the ground potential due to the characteristic of the Zener diode, the toner image is transferred from the photosensitive drum 50a to the intermediate transfer belt 56 It is not transferred. Therefore, as shown in Fig. 10, a patch image can not be formed at intervals between toner images of an image. Therefore, it is necessary to stop the formation of the toner image on the photosensitive drums 50a, 50b, 50c, and 50d and the transfer to the intermediate transfer belt 56 before forming the patch image. Therefore, it is necessary to start image formation on the photosensitive drum 50a and transfer to the intermediate transfer belt 56 only after the patch image has passed through the secondary transfer portion T2.

The second exemplary In the embodiment  Control according to

13 is a block diagram of a control system of the transfer voltage according to the second exemplary embodiment. 14 is a control flow diagram according to the second exemplary embodiment. 15 is a timing chart of control according to the second exemplary embodiment. In the second exemplary embodiment, with respect to the potential of the support rollers 62, 63, 60, 61 supporting the intermediate transfer belt 56, the period during which the toner image passes through the secondary transfer portion, And a period during which the vehicle passes through the car transfer portion are individually described in detail.

As shown in Fig. 13, in the second exemplary embodiment, control relating to the primary transfer and the secondary transfer on the toner image of the image is performed using the secondary transfer power source 210 and the power source 310. [ The digital signal transmitted from the DC controller 111 of the control unit 110 is converted into an analog signal by the D / A converters 200 and 300 and output to the secondary transfer power source 210 and the power source 310 . The second current detection circuit 410 outputs a current corresponding to the transfer voltage Vt output from the secondary transfer power source 210. [ The analog signal obtained by the second current detection circuit 410 is converted into a digital signal by the A / D converter 400 and fed back to the control unit 110.

14, when the operation of the image forming apparatus 100 is started, the control unit 110 operates the image forming units Pa, Pb, Pc, and Pd, (50a, 50b, 50c, 50d). In the forward rotation, for example, after various adjustments related to the charging potential, development potential, and laser beam intensity are performed, the gradation control of the output image is performed (S1).

The control unit 110 executes control to obtain a current value when a plurality of test voltages are applied and applies a transfer voltage to the secondary transferring outside roller 64 so that a predetermined target current flows through the secondary transferring portion T2 The voltage Vt is determined (S2).

The control unit 110 starts continuous image formation as a unitary operation received as a job (S3).

The control unit 110 starts forming the patch image for controlling the density of the output image at the interval between the toner images of the image (S4), transfers it to the intermediate transfer belt 56, and detects it by the optical sensor 59. [ The detection result of the patch image is fed back to the control unit 110 to adjust the density of the output image.

When the image interval does not pass through the secondary transfer portion T2 (S5: NO), that is, while the toner image of the image passes through the secondary transfer portion T2, the control unit 110 sets the transfer voltage Vt to 2 The secondary transfer inner roller 62 is connected to the secondary transfer power source 210 (S6). 12A, the difference voltage between the transfer voltage Vt output from the secondary transfer power source 210 to the secondary transfer outside roller 64 and the output voltage Vc of the power supply 310 causes the intermediate transfer belt 56 The secondary transfer of the toner image of the image to the recording material P is performed.

The control unit 110 turns off the secondary transfer power source 210 while the image interval passes through the secondary transfer portion T2 (S5: YES), that is, while the patch image is passing through the secondary transfer portion T2 And the secondary transfer roller 62 is connected to the ground potential (S7). The voltage Vc is applied to the secondary transfer inward roller 62 and the intermediate transfer belt 56 from the power supply 310 and the electric field in the reverse direction to the direction in the case of transferring the toner image of the image Is formed in the secondary transfer portion T2. Therefore, the patch image on the intermediary transfer belt 56 is prevented from being transferred to the secondary transfer outside roller 64. [

The control unit 110 executes the reverse rotation to stop the image forming apparatus 100 (S9) when continuous image formation is completed as one unit operation received as the image forming operation (S8: YES). In the reverse rotation, gamma correction control and the like are executed. Therefore, the operation of the image forming apparatus 100 is ended.

As shown in Fig. 15, both the secondary transfer power source 210 and the power source 310 are in the ON state at the timing when the toner image of the image is located at the secondary transfer portion T2.

The power source 310 maintains the ON state at the timing when the image interval corresponding to the interval between the toner images of the image and another toner image is located in the secondary transfer portion T2 but the secondary transfer power source 210 is off (OFF), and the secondary transfer outside roller 64 is connected to the ground potential. Therefore, the patch image is prevented from being transferred to the secondary transferring / At the timing when the patch image passes through the secondary transfer portion T2, the secondary transferring / outward roller 64 is connected to the secondary transferring power source 210, and the secondary transferring power source 210 is turned on.

Since the potential of the idler roller 61 is maintained by the zener diode circuit 71 even if a series of operations is repeated for each image, the potential of the intermediate transfer belt 56 abutting against the photosensitive drum 50a is steadily maintained at 300V .

Therefore, in the configuration of the intermediate transfer system in which the primary transfer roller is not provided, reverse bias is applied from the secondary transfer inner roller to the secondary transfer outer roller to clean the secondary transfer outer roller, It is possible to perform image formation in the transfer portion.

The secondary transferring outside roller 64 can be connected to the ground potential at the margin portion of the rear end portion of the recording material as shown by the broken line in Fig. 15, and the secondary transfer power source 210 is connected at the margin portion at the leading end of the next recording material It is possible to output the transfer voltage Vt.

As described above, according to the second exemplary embodiment, the secondary transfer power source 210, which is an example of the first power source, supplies the intermediate transfer belt 56 with the zener breakdown voltage Vbr It is possible to apply the first voltage capable of transferring the toner image from the intermediary transfer belt 56 to the recording material while the voltage is applied. The power source 310 which is an example of the second power source is connected to the intermediate transfer belt 56 which is in contact with the secondary transferring outside roller 64 through the secondary transferring inner roller 62, The Zener breakdown voltage Vbr and a second voltage less than a value of the first voltage. The control unit 110, which is an example of the control unit, controls the secondary transfer power source 210 and the power source 310 to form an electric field necessary for the secondary transfer portion T2.

The control unit 110 applies a voltage to the intermediate transfer belt 56 to transfer the toner from the intermediate transfer belt 56 to the intermediate transfer belt 56 when the normal toner image carried on the intermediate transfer belt 56 passes the secondary transfer portion T2. Thereby forming an electric field for directing the recording material. Specifically, the first voltage is applied to the secondary transferring / non-transferring roller 64 and the second voltage is applied to the secondary transferring inner roller 62.

The control unit 110 applies a voltage to the intermediate transfer belt 56 to transfer the toner to the secondary transfer outside roller 64 when the patch image carried on the intermediate transfer belt 56 passes the secondary transfer portion T2. To the intermediate transfer belt 56. As shown in Fig. Specifically, the potential of the secondary transfer outside roller 64 is set to the potential on the side of the charging polarity of the toner rather than the potential of the secondary transfer in-roller 62, and the second voltage is supplied to the secondary transfer in- .

The second exemplary Example  effect

According to the second exemplary embodiment, when the normal toner image carried on the intermediary transfer belt 56 passes through the secondary transfer portion T2, the control unit 110 generates a current that is not less than the zener breakdown voltage Vbr The second voltage is applied to the secondary transfer roller 62 so as to flow through the unit. Therefore, even when the resistance value of the secondary transfer portion T2 at the time of transferring the toner image onto the recording material P changes, the potential of the intermediate transfer belt 56 does not drop below the Zener breakdown voltage Vbr. The potential difference between the photosensitive drum 50a and the intermediate transfer belt 56 is stabilized and the transfer of the toner image is hardly disturbed.

According to the second exemplary embodiment, the power source 310 applies the second voltage to the in-secondary transfer roller 62. [ Therefore, the transfer electric field can be formed in the same manner as the whole of the transfer nip opposed to the secondary transfer outside roller 64.

According to the second exemplary embodiment, since the image forming apparatus 100 is based on the intermediate transfer method having no primary transfer roller, omission of the primary transfer roller makes it possible to reduce the cost And downsizing of the apparatus is realized. In addition, unlike the conventional intermediate transfer method, the transfer failure due to toner agglomeration due to the increase of the local transfer pressure, that is, the so-called hollow image, occurs at the center of the toner attaching area when passing through the primary transfer portion Hardly occurs.

According to the second exemplary embodiment, since none of the support rollers 63, 60, 61 is grounded, current is supplied from the intermediate transfer belt 56 through the support rollers 63, 60, 61 to the ground potential It does not flow. Therefore, it is possible to apply the primary transfer voltage from the secondary transfer inner roller 62. [

According to the second exemplary embodiment, since the support rollers 63, 60, 61 for supporting the intermediate transfer belt 56 are grounded via the Zener diode circuit 71, which is an example of the voltage generating unit, , 60, and 61 of the image forming apparatus 100 are prevented from unnecessarily flowing out. Since the support rollers 63, 60 and 61 are grounded via the zener diode circuit 71, the potential of the intermediate transfer belt 56 is maintained at a proper potential necessary for primary transfer of the image on the toner.

According to the second exemplary embodiment, since the intermediate transfer belt 56 having a lower resistance value than the conventional intermediate transfer method is used, the high voltage applied to the secondary transfer portion T2 through the intermediate transfer belt 56 is And can act substantially equally to a plurality of primary transfer portions. The charge supplied from the secondary transfer power source 210 flows into the photosensitive drum 50a through the intermediary transfer belt 56 to perform the primary transfer of the image on the toner image as in the conventional intermediate transfer method.

According to the second exemplary embodiment, while the patch image is located at the secondary transfer portion T2, the positive voltage is applied to the secondary transfer inward roller 62 to change the potential of the secondary transfer outside roller 64 to the secondary Lower than the in-transfer roller 62, and forms an electric field in the secondary transfer portion T2 in the direction opposite to the direction at the time of transfer. A positive voltage is applied from the secondary transfer inner roller 62 by the power source 310 to clean the contaminated secondary transfer outer roller 64 by contacting the patch image. Since the power source 310 continuously applies the forward voltage to the primary transfer portion, the formation of the toner image on the photosensitive drums 50a, 50b, 50c, and 50d and the primary transfer can be performed seamlessly.

Example 3 Example

11A, according to the second exemplary embodiment, the power source 310 continuously outputs 300 V to the in-secondary transfer roller 62 even while the toner image of the image passes through the secondary transfer portion T2 . 16A, according to the third exemplary embodiment, while the toner image of the image passes through the secondary transfer portion T2, the power source 310 is turned off and the secondary transfer in-roller 62 is turned off, A zener diode circuit 71 is connected. Therefore, power consumption of the power source 310 during the period of transferring the toner image of the image to the recording material is reduced.

Example 3 Example  Control

16A and 16B are diagrams for explaining control according to the third exemplary embodiment. 17 is a timing chart of control according to the third exemplary embodiment. Fig. 16A corresponds to the case of transferring the toner image of the image in the secondary transfer portion T2, and Fig. 16B corresponds to the case where the patch image passes through the secondary transfer portion T2.

As shown in Fig. 16A, the secondary transfer outside roller 64 switches between the secondary transfer power source 210 and the ground potential by the switch SW1, as in the second exemplary embodiment. On the other hand, the secondary transfer roller 62 switches between the power supply 310 and the zener diode circuit 71 by the switch SW2. The switch SW2, which is an example of the switching unit, switches the connection state and the blocking state of the electrical connection between the inner circumferential surface of the intermediate transfer belt 56 and the power source 310. [

As shown in Fig. 16B, while the patch image passes through the secondary transfer portion T2, the control unit 110 connects the secondary transfer outside roller 64 to the ground potential by the switch SW1, and the switch SW2 And the secondary transfer inner roller 62 is connected to the power source 310. The control unit 110 controls the power source 310 such that the detection current of the first current detection circuit 510 is set to +5 [mu] A so that the zener diode circuit 71 can sufficiently maintain the breakdown voltage. Therefore, a voltage Vc equal to 300V of the zener breakdown voltage Vbr is applied to the secondary transfer inner roller 62, and an electric field in the direction opposite to the direction in the case where the toner image of the image is transferred to the recording material in the secondary transfer portion T2 . The toner image on the intermediate transfer belt 56 is subjected to the Coulomb force on the side of the intermediate transfer belt 56 and the adhesion of the toner image onto the secondary transfer outside roller 64 is prevented.

17, the secondary transfer power source 210 is turned off after the power source 310 is turned on when the blank region (5 mm) of the trailing edge of the recording material passes the secondary transfer portion T2. Thereafter, the switch SW1 is switched from the secondary transfer power source 210 to the ground potential. Therefore, the patch image formed so as to correspond to the interval of the recording material is not transferred to the secondary transferring /

16A, while transferring the toner image of the image onto the recording material, the control unit 110 connects the secondary transferring / outgoing roller 64 to the secondary transferring power source 210 by the switch SW1, And the secondary transfer inner roller 62 is connected to the Zener diode circuit 71 by the switch SW2.

17, when the blank space (5 mm) at the tip of the next recording material passes through the secondary transfer portion T2, the switch SW1 is switched from the ground potential to the secondary transfer power source 210, (210). Thereafter, the power source 310 is turned off. Next, the switch SW2 is switched from the power source 310 to the Zener diode circuit 71 to maintain the voltage of the secondary transfer in-roller 62. [ Therefore, even after the power source 310 is turned off, the potential of the secondary transferring / non-transferring roller 64 is maintained at 300 V, and 1300 V-300 V = 300 V is applied between the secondary transferring inner roller 62 and the secondary transferring / A stable transfer voltage of 1000 V is continuously applied.

Example 3 Example  effect

According to the third exemplary embodiment, as shown in Fig. 17, timing for applying the reverse bias for cleaning the secondary transferring / non-transferring roller 64 from the secondary transferring inner roller 62 is controlled. Therefore, even when cleaning the secondary transferring / non-transferring roller 64, image formation can be performed in the photosensitive drum 50a, and at the same time, the cost can be further reduced as compared with the second exemplary embodiment.

According to the second exemplary embodiment, 300 V is continuously output from the power source 310 to the in-secondary transfer roller 62. In this state, when the patch image passes through the secondary transfer portion T2, 1300 V is output from the secondary transfer power source 210 to the secondary transfer outside roller 64. [ Therefore, the secondary transfer contrast is set to 1000V.

According to the third exemplary embodiment, by preparing the switch SW2, the time for turning off the power source 310 is longer than that in the second exemplary embodiment, so that the power consumption can be reduced accordingly.

Other Example

The present invention is not limited to the configuration and control according to the first, second and third exemplary embodiments. The numerical values and the like used in the explanation according to the first, second and third exemplary embodiments are merely examples, and the present invention is not limited by these numerical values.

The control unit controls the second power supply such that a current at which the inter-terminal voltage of the constant-voltage element is maintained at the predetermined voltage is detected by the detection unit. The second power source may be an analog power source that continuously feeds back the analog current output from the detection unit to continuously change the output voltage. The second power source may be a digitally controlled analog power source that outputs the calculated output voltage as a constant voltage based on the current value measured by the detection unit. In any case, since the current measured by the detection unit is within an appropriate range, an excessive current can be prevented from flowing to the constant-voltage element while securing the primary transfer voltage as necessary.

The method of controlling the output voltages of the first power source and the second power source may be different from each other. The control unit for controlling the first power source and the control unit for controlling the second power source may be implemented by independent separate control units.

The image forming apparatus can employ an image carrier other than the photosensitive drum, and can be implemented in other types of image forming apparatus employing an endless belt. A constant voltage element is used in addition to the Zener diode, the support rollers may be provided with a configuration which is grounded through a constant-voltage element such as a (63, 60, 61) is 10 ⁸ [Ω] or more resistors or varistors.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims priority to Japanese Patent Application No. 2014-246568, filed December 5, 2014, and Japanese Patent Application No. 2014-247333, filed December 5, 2014, the contents of which are incorporated herein by reference in their entirety .

Claims (17)

An image forming apparatus comprising:
An image bearing member carrying a toner image having a predetermined charging polarity;
An intermediate transferring member for supporting the toner image primarily transferred from the primary transferring portion from the image carrier;
A transfer member arranged to abut the outer peripheral surface of the intermediate transfer member and configured to transfer the toner image from the intermediate transfer member to the recording material in the secondary transfer portion;
A constant voltage element electrically connected between the inner circumferential surface of the intermediate transfer member and the ground potential and configured to generate a predetermined voltage by flowing an electric current;
A first power source for applying a voltage to the transfer member and forming a secondary transfer electric field in the secondary transfer unit in which the toner image having the charging polarity is moved from the intermediate transfer member toward the recording material;
A primary transfer electric field in which the toner image having the charging polarity is moved from the image carrier toward the intermediate transfer member is supplied to the primary transfer portion A second power source formed on the first power source; And
And a control unit configured to control the first power source and form an electric field in a direction opposite to the secondary transfer electric field in the secondary transfer unit during at least a part of the period in which the primary transfer electric field is formed in the primary transfer unit To the image forming apparatus. The method according to claim 1,
Wherein the control unit performs control to set the first power source to the ground potential or to apply a voltage having the same polarity as the charging polarity to the first power source to cause the secondary transfer unit And forms an electric field in a reverse direction. The method according to claim 1,
Wherein the control unit forms an electric field in a direction opposite to the secondary transfer electric field in the secondary transfer unit during a period in which at least the toner secondaryly transferred to the recording material is not present in the secondary transfer unit. The method according to claim 1,
Wherein when the primary transfer electric field is formed in the primary transfer section during a period in which an electric field in the direction opposite to the secondary transfer electric field is formed in the secondary transfer section, the control unit controls the constant- The control unit controls the second power source to generate the second power. 5. The method of claim 4,
And a current detecting member configured to detect a current flowing through the constant-voltage element,
Wherein the control unit controls the second power supply based on the detection result of the current detection member such that the constant voltage element generates the predetermined voltage. The method according to claim 1,
An execution unit configured to execute a test mode for forming an adjusting toner image on the intermediate transfer member in a period other than a period during which the toner image that is secondarily transferred to the recording material is primarily transferred to the intermediate transfer member;
A toner image detecting member configured to detect the adjusting toner image formed on the intermediate transfer member; And
Further comprising an adjustment unit configured to adjust an image forming condition on a toner image to be transferred to the recording material based on the detection result of the toner image detecting member,
Wherein the control unit controls the first power source to form an electric field in a direction opposite to the secondary transfer electric field in the secondary transfer unit during a period in which the adjustment toner image is present in the secondary transfer unit, . The method according to claim 6,
Wherein the control unit controls the second power source for a period in which the toner image for adjustment exists in the secondary transfer unit and the toner image to be transferred to the recording material exists in the primary transfer unit, Thereby forming a secondary transfer electric field. The method according to claim 6,
The control unit controls the second power source for a period in which a part of the toner image for adjustment exists in the secondary transfer unit and another part of the toner image for adjustment exists in the primary transfer unit, To form the primary transfer electric field. The method according to claim 1,
Wherein a plurality of image carriers are arranged along an outer circumferential surface of the intermediate transfer member and the second power source is an image transfer member which forms the primary transfer electric field in each of the plurality of primary transfer members corresponding to each of the plurality of image carriers, Forming device. The method according to claim 1,
Wherein the transferring member includes a transferring roller and the control unit is configured to transfer the toner to the transferring member during a period during which the transferring roller is rotated at least once during a period in which the toner image to be transferred to the recording material is not present in the secondary transferring portion, 2 power source to form an electric field in the same direction as the secondary transfer electric field in the secondary transfer portion. 9. The method of claim 8,
Wherein the control unit controls the second power source for a period of time in which the transfer roller is rotated one or more times after the electric field in the same direction as the secondary transfer electric field is formed in the secondary transfer unit, And forms an electric field in a direction opposite to the secondary transfer electric field. The method according to claim 1,
Further comprising a switching unit configured to switch between a connection state in which an electrical connection between the inner peripheral surface of the endless belt and the second power source is established and a cutoff state in which electrical connection is blocked,
Wherein the control unit causes the switching unit to be switched to the connection state during a period in which the electric field in the direction opposite to the secondary transfer electric field is formed in the secondary transfer unit and the secondary transfer electric field is formed in the secondary transfer unit The switching unit causes the switching unit to switch to the blocking state. 13. The method of claim 12,
Wherein the control unit sets the first power source to the ground potential while causing the switching unit to switch to the connection state during a period in which an electric field in the direction opposite to the secondary transfer electric field is formed in the secondary transfer unit, . The method according to claim 1,
Wherein the intermediate transfer member has a structure including two or more layers, and the volume resistivity of the layer on the outer circumferential surface side is higher than the volume resistivity of the layer on the inner circumferential surface side. The method according to claim 1,
Further comprising a plurality of support members,
Wherein the intermediate transfer member includes an intermediate transfer belt,
And the plurality of support members abut against the inner circumferential surface of the intermediate transfer belt to support the intermediate transfer belt. 16. The method of claim 15,
Wherein the support member includes a conductive support roller, and the intermediate transfer member and the constant-voltage element are electrically connected to each other when the support roller is electrically connected to the constant-voltage element. The method according to claim 1,
Wherein the constant voltage element includes a zener diode or a varistor.

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