JP2017072635A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can reduce power loss at primary transfer during the execution of monochrome printing.SOLUTION: During the execution of color printing, an image forming apparatus drives a primary transfer power supply part 60 and supplies a primary transfer voltage Va output from the primary transfer power supply part 60 to each of primary transfer rollers 24Y to 24K, and during the execution of monochrome printing, stops the drive of the primary transfer power supply part 60 and supplies a voltage stepped down by a step-down circuit 80 from a secondary transfer voltage Vb2 of a secondary transfer power supply part 70 to a voltage Vd necessary for primary transfer only to the primary transfer roller 24K used for the monochrome printing.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for reducing power loss during transfer.

An image forming apparatus such as an electrophotographic printer includes a so-called tandem color image forming apparatus.
In this color image forming apparatus, for example, photosensitive drums for each color of yellow (Y), magenta (M), cyan (C), and black (K) are arranged outside the circulation path of the intermediate transfer belt along the circumferential direction of the belt. And a Y-K color primary transfer roller is disposed at a position facing the Y-K color photosensitive drum with the intermediate transfer belt sandwiched inside the intermediate transfer belt. In general, a secondary transfer roller is provided on the outer side of the circulation path and downstream of the most downstream photosensitive drum and in contact with the outer peripheral surface of the intermediate transfer belt at the secondary transfer position.

In such a configuration, color image formation is performed by the following operation.
That is, the primary transfer voltage is supplied to the primary transfer rollers for Y to K colors, and the secondary transfer voltage is supplied to the secondary transfer roller. A Y to K color toner image was formed on the Y to K color photosensitive drum, and a primary transfer voltage was applied to the Y to K color toner image formed on the Y to K color photosensitive drum. Electrostatic multiple transfer is performed on the rotating intermediate transfer belt by the electrostatic action of the primary transfer rollers for Y to K colors (primary transfer).

Then, the sheet is conveyed to the secondary transfer position in accordance with the timing at which the Y to K color toner images multiplex-transferred onto the intermediate transfer belt reach the secondary transfer position, and the sheet is transferred to the intermediate transfer belt and the secondary transfer roller. During the passage, the toner images of Y to K on the intermediate transfer belt are transferred to the sheet by the electrostatic action of the secondary transfer roller to which the secondary transfer voltage is applied (secondary transfer).
Although the color image forming operation has been described above, the tandem color image forming apparatus can also perform monochrome image formation.

  For example, in the case of K-color monochrome image formation, a K-color toner image is formed using only the K-color photosensitive drum, and the K-color toner image is subjected to primary transfer voltage application to the K-color primary image. Primary transfer is performed on the intermediate transfer belt by the electrostatic action of the transfer roller. While the sheet passes between the intermediate transfer belt and the secondary transfer roller, the K-color toner image on the intermediate transfer belt is transferred to the sheet by the electrostatic action of the secondary transfer roller to which the secondary transfer voltage is applied. Next transfer.

Since the primary transfer voltage is a high voltage such as about 1000 V, for example, a voltage obtained by boosting a voltage from a power source with a transfer transformer is usually used as the primary transfer voltage.
Although it is possible to adopt a configuration in which this transfer transformer is provided corresponding to each of the primary transfer rollers for Y to K colors, a total of four transfer transformers are required, resulting in high costs. In many cases, a single transfer transformer common to the primary transfer roller is disposed in the primary transfer power supply unit.

International Publication WO2002 / 56119

In the configuration in which one transfer transformer common to the primary transfer rollers for Y to K colors is arranged, in the case of monochrome image formation, the transfer transformer is driven to supply the primary transfer voltage to the primary transfer roller for K colors.
However, primary transfer voltages are also supplied to the primary transfer rollers for Y, M, and C colors other than K color, and wasteful transfer currents flow to the primary transfer rollers for Y, M, and C colors that are not used. Therefore, there is a problem that it leads to power loss at the time of primary transfer. Such a problem is not limited to a configuration using a transfer transformer, and can generally occur in a configuration using a circuit that boosts a voltage from a power source to a primary transfer voltage.

  The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus capable of reducing power loss during primary transfer.

  In order to achieve the above object, an image forming apparatus according to the present invention uses a primary transfer member provided with images of different colors carried on a plurality of image carriers corresponding to the respective image carriers. Color image formation in which each color image on the intermediate transfer member is secondarily transferred onto a sheet using a secondary transfer member after being primary transferred in an overlapping manner on the intermediate transfer member, and one of the plurality of image carriers. After the image carried on the image carrier is primarily transferred onto the intermediate transfer member using a primary transfer member corresponding to the image carrier, the image on the intermediate transfer member is sheeted using the secondary transfer member. An electrophotographic image forming apparatus capable of switching between monochrome image formation for secondary transfer on the image forming apparatus and provided in common to the plurality of primary transfer members for primary transfer during color image formation Boosted to the primary transfer voltage required for After that, a primary transfer power supply unit that supplies the primary transfer voltage to each of the plurality of primary transfer members, and a secondary transfer voltage necessary for the secondary transfer in the case of color and monochrome image formation. A secondary transfer power supply unit that generates and supplies the generated secondary transfer voltage to the secondary transfer member; and receives the secondary transfer voltage generated by the secondary transfer power supply unit to form a monochrome image. In the case of color image formation, the step-down circuit that supplies a voltage stepped down to a voltage required for primary transfer to a primary transfer member used for monochrome image formation, the primary transfer power supply unit, and the step-down circuit are controlled. Control means for driving the power supply unit and stopping the operation of the step-down circuit, and in the case of monochrome image formation, stopping the drive of the primary transfer power supply unit and operating the step-down circuit. To.

Further, the secondary transfer power supply unit can switch the secondary transfer voltage to Vb1 during the color image formation and the secondary transfer voltage to Vb2 during the monochrome image formation, and is necessary for the primary transfer during the monochrome image formation. When the voltage is Vd, the relationship Vd <Vb2 <Vb1 may be satisfied.
Further, after the monochrome image formation is performed on the Nth sheet among the plurality of continuously conveyed sheets, the color image formation can be performed by switching the (N + 1) th sheet. Each of the plurality of image carriers is arranged along the moving direction of the intermediate transfer member, and the control unit stops the operation of the step-down circuit upon completion of primary transfer during execution of the monochrome image formation. To the position where the image carried on the most upstream image carrier in the moving direction of the intermediate transfer member reaches the position where it is primarily transferred to the intermediate transfer member by the color image formation. In the meantime, driving of the primary transfer power supply unit may be started.

  A first power line electrically connecting the output terminal of the primary transfer power supply unit and the primary transfer member used for monochrome image formation; and an output of the step-down circuit branched from the middle of the first power line. A first power supply line electrically connected to the terminal; and the first power supply line inserted into the output terminal side of the primary transfer power supply unit from a branch position where the second power supply line branches. A first diode that passes only a transfer current in the direction from the output terminal of the power supply unit to the branch position, and a transfer current that is inserted into the second power supply line and that is in the direction from the output terminal of the step-down circuit to the branch position. And a second diode that allows the light to pass therethrough.

  Further, the primary transfer power supply unit includes a transfer transformer for boosting an input voltage to the primary transfer voltage, and in the case of color image formation, the control unit stops driving the transfer transformer to form a monochrome image. In this case, the transfer transformer may be driven.

  According to the above configuration, in the case of monochrome image formation, since the drive of the primary transfer power supply unit is stopped, power is not consumed in the primary transfer power supply unit, and the primary transfer member that is not used in monochrome image formation. In other words, useless power is not consumed by supplying a primary transfer voltage to a useless transfer current. Therefore, in the case of monochrome image formation, it is possible to reduce power loss during primary transfer as compared with a configuration in which a primary transfer voltage is supplied to each primary transfer member from a common primary transfer power supply unit.

1 is a schematic diagram illustrating an overall configuration of a printer. It is a figure for demonstrating the relationship between a control part, a primary transfer power supply part, a secondary transfer power supply part, a pressure | voltage fall circuit, a primary transfer roller, and a secondary transfer roller. It is a block diagram which shows schematic structure of a primary transfer power supply part. (A) is a figure which shows the mode at the time of color printing in an Example, (b) is a figure which shows the mode at the time of monochrome printing in an Example. (A) is a block diagram illustrating a circuit configuration in a comparative example, and (b) is a diagram illustrating a state during monochrome printing in the comparative example. (A) is a diagram showing a timing chart of a primary transfer signal, a secondary transfer signal, and a step-down instruction signal at the time of color printing on one sheet S, and (b) at the time of monochrome printing on one sheet S. FIG. 10 is a diagram illustrating a timing chart of a primary transfer signal, a secondary transfer signal, and a step-down instruction signal in FIG. 6 is a flowchart illustrating control of output of a primary transfer signal, a secondary transfer signal, and a step-down instruction signal when a print job is executed. It is a figure which shows the flowchart of primary transfer switching control.

Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described by taking a tandem color printer (hereinafter simply referred to as “printer”) as an example.
FIG. 1 is a schematic diagram illustrating the overall configuration of the printer 1.
As shown in the figure, the printer 1 forms an image by a well-known electrophotographic method, and includes an image processing unit 10, an intermediate transfer unit 20, a feeding unit 30, a fixing unit 40, and a control unit 50. A primary transfer power supply unit 60, a secondary transfer power supply unit 70, and a step-down circuit 80, and a color or monochrome print job execution request from an external terminal device (not shown) via a network (for example, LAN). Based on the above, color or monochrome image formation is executed.

The image processing unit 10 includes image forming units 10Y, 10M, 10C, and 10K corresponding to yellow (Y), magenta (M), cyan (C), and black (K), respectively.
The image forming unit 10Y includes a photosensitive drum 11Y that rotates in a direction indicated by an arrow, and a cleaner for cleaning the surfaces of the charging unit 12Y, the exposure unit 13Y, the developing unit 14Y, and the photosensitive drum 11Y disposed around the photosensitive drum 11Y. 15Y and the like, and a Y-color toner image is formed on the photosensitive drum 11Y through charging, exposure, and development processes. This configuration is the same for the other image forming units 10M to 10K. The image forming units 10M, 10C, and 10K are charged units 12M, 12C, and 12K, exposure units 13M, 13C, and 13K, and developing units 14M, 14C, and 14K. Further, cleaners 15M, 15C, and 15K for cleaning the surface of the photosensitive drum 11Y are provided, and toner images of corresponding colors are formed on the photosensitive drums 11M, 11C, and 11K.

The intermediate transfer unit 20 includes an intermediate transfer belt 21, a driving roller 22, a driven roller 23, primary transfer rollers 24Y, 24M, 24C, and 24K, a secondary transfer roller 25, and the like. The intermediate transfer belt 21 is an endless belt.
The driving roller 22, the driven roller 23, and the primary transfer rollers 24 </ b> Y to 24 </ b> K are arranged on the inner side of the belt rotation path (traveling path) of the intermediate transfer belt 21.

The drive roller 22 is located on one end side in the direction in which the image forming units 10Y to 10K are arranged (the left-right direction in the figure), and the driven roller 23 is located on the other end side. The primary transfer rollers 24Y to 24K are between the driving roller 22 and the driven roller 23, and are disposed to face the corresponding photosensitive drums 11Y to 11K with the intermediate transfer belt 21 interposed therebetween.
The intermediate transfer belt 21 is stretched by these rollers along the direction in which the image forming units 10Y to 10K are arranged, and is driven to rotate in the belt rotating direction indicated by the arrow in FIG. .

The secondary transfer roller 25 is pressed against the driving roller 22 via the intermediate transfer belt 21 at a position on the outer side of the belt circulation path and on the downstream side in the belt rotation direction with respect to the image forming unit 10K disposed on the most downstream side in the belt rotation direction. A transfer nip N is formed between the intermediate transfer belt 21 and the outer peripheral surface.
The feeding unit 30 includes a paper feed cassette 31, a feeding roller 32, a transport roller pair 33, and a timing roller pair 34.

The paper feed cassette 31 stores a plurality of sheets, here, paper S, and the feed roller 32 feeds the paper S stored in the paper feed cassette 31 one by one onto the transport path 35.
The transport roller pair 33 transports the paper S fed by the feed roller 32 to the timing roller pair 34. The timing roller pair 34 conveys the sheet S conveyed from the conveyance roller pair 33 toward the transfer nip N according to the image forming operation by the image forming units 10Y to 10K.

The fixing unit 40 includes a fixing roller 41 and a pressure roller 42 pressed against the fixing roller 41.
The control unit 50 comprehensively controls the operations of the image processing unit 10 to the fixing unit 40 to execute a smooth job.
Specifically, when color image formation (color printing) is performed, the surfaces of the photosensitive drums 11Y to 11K are charged by the charging units 12Y to 12K in the image forming units 10Y to 10K, and the charged photosensitive members. The surfaces of the drums 11Y to 11K are exposed and scanned by the exposure units 13Y to 13K to form latent images, and the latent images on the photosensitive drums 11Y to 11K are developed by the developing units 14Y to 14K, so that Y to K are obtained. A color toner image is formed.

Then, each color toner image formed on the photosensitive drums 11Y to 11K is generated between the photosensitive drums 11Y to 11K and the primary transfer rollers 24Y to 24K by the primary transfer voltage applied to the primary transfer rollers 24Y to 24K. The primary transfer is electrostatically performed on the intermediate transfer belt 21 by the action of the electric field.
The image forming operations for the respective colors Y to K are timed from the upstream side toward the downstream side in the belt circumferential direction so that the toner images of the respective colors are primary-transferred superimposed on the same position of the circulating intermediate transfer belt 21. It is executed by shifting. The Y to K color toner images (hereinafter referred to as “color toner images”) transferred onto the intermediate transfer belt 21 in a multiple transfer manner are conveyed toward the transfer nip N as the intermediate transfer belt 21 rotates.

The sheet S is conveyed toward the transfer nip N by the timing roller pair 34 so that the color toner image on the intermediate transfer belt 21 reaches the transfer nip N.
When the sheet S passes through the transfer nip N, the secondary transfer voltage applied to the secondary transfer roller 25 causes the electric field generated between the intermediate transfer belt 21 and the secondary transfer roller 25 to act on the intermediate transfer belt 21. The color toner images are secondarily transferred electrostatically to the sheet S at once.

The sheet S after the color toner image is secondarily transferred is conveyed to the fixing unit 40 and heated and pressed when passing between the fixing roller 41 and the pressure roller 42 of the fixing unit 40. The toner particles of the color toner image on the paper S are fused and fixed to the paper S. The paper S that has passed through the fixing unit 40 is discharged onto a paper discharge tray 39 by a paper discharge roller 38.
On the other hand, when performing monochrome (here, K-color image formation) (monochrome printing), only the image forming unit 10K among the image forming units 10Y to 10K is used, and the same charging, exposing, and developing steps as described above are used for photosensitivity. A K-color toner image is formed on the body drum 11K. The K-color toner image on the photosensitive drum 11K is statically transferred onto the intermediate transfer belt 21 by the action of an electric field generated between the photosensitive drum 11K and the primary transfer roller 24K by the primary transfer voltage applied to the primary transfer roller 24K. Electrically primary transferred. The K-color toner image on the intermediate transfer belt 21 is conveyed toward the transfer nip N as the intermediate transfer belt 21 rotates.

The sheet S is conveyed toward the transfer nip N by the timing roller pair 34 so that the timing at which the K-color toner image on the intermediate transfer belt 21 reaches the transfer nip N is matched.
When the sheet S passes through the transfer nip N, the secondary transfer voltage applied to the secondary transfer roller 25 causes the electric field generated between the intermediate transfer belt 21 and the secondary transfer roller 25 to act on the intermediate transfer belt 21. The K toner image is secondarily transferred electrostatically to the paper S.

The sheet S after the K-color toner image is secondarily transferred is conveyed to the fixing unit 40 and heated and pressurized when passing between the fixing roller 41 and the pressure roller 42 of the fixing unit 40. As a result, the toner particles of the K-color toner image on the paper S are fused and fixed to the paper S. The paper S that has passed through the fixing unit 40 is discharged onto a paper discharge tray 39 by a paper discharge roller 38.
The primary transfer power supply unit 60 is a power supply unit that generates and outputs a primary transfer voltage by boosting an input voltage (for example, DC 24 V) to a voltage (for example, DC 1000 V) necessary for primary transfer during color image formation. .

The secondary transfer power supply unit 70 boosts the input voltage (for example, DC 24V) to a voltage necessary for the secondary transfer (for example, DC 1500V) at the time of color image formation and monochrome image formation, respectively. A power supply unit that generates and outputs a voltage.
The step-down circuit 80 is a circuit that receives the secondary transfer voltage generated by the secondary transfer power supply unit 70, and steps down and outputs the voltage to a voltage required for primary transfer during monochrome image formation.

FIG. 2 is a diagram for explaining the relationship among the control unit 50, the primary transfer power supply unit 60, the secondary transfer power supply unit 70, the step-down circuit 80, the primary transfer rollers 24Y to 24K, and the secondary transfer roller 25. The image processing unit 10 and the feeding unit 30 other than the unit 20 are omitted.
As shown in the figure, the control unit 50 outputs a primary transfer signal that instructs the primary transfer power supply unit 60 to switch between driving (ON) and stopping (OFF). When the primary transfer power supply unit 60 receives a drive instruction from the primary transfer signal from the control unit 50, the primary transfer power supply unit 60 generates a primary transfer voltage Va and outputs the primary transfer voltage Va from the output terminal 60a. Here, the primary transfer voltage Va is a positive DC voltage.

FIG. 3 is a block diagram illustrating a schematic configuration of the primary transfer power supply unit 60.
As shown in FIG. 3, the primary transfer power supply unit 60 includes a transfer transformer 61, a rectifying / smoothing circuit 62, and a switching unit 63.
The switching unit 63 intermittently (switches) the DC voltage input from the power source to generate a high-frequency AC voltage, and supplies it to the primary coil of the transfer transformer 61. Examples of the power supply include a power supply circuit that converts an AC voltage input from a commercial power supply into a DC voltage and outputs the DC voltage.

The transfer transformer 61 boosts the AC voltage supplied from the switching unit 63 to the primary coil to a predetermined magnitude and outputs the boosted voltage from the secondary coil. The rectifying / smoothing circuit 62 smoothes the AC voltage output from the secondary coil of the transfer transformer 61, rectifies it into a DC voltage, and outputs the DC voltage. This output voltage becomes the primary transfer voltage Va when forming a color image.
The switching unit 63 performs a switching operation when the primary transfer signal from the control unit 50 is a drive (ON) instruction. As a result, an alternating current flows through the primary coil of the transfer transformer 61 to perform boosting, and the primary transfer voltage Va is output from the rectifying and smoothing circuit 62.

  On the other hand, when the primary transfer signal from the control unit 50 is a stop (OFF) instruction, the switching unit 63 stops the switching operation. As a result, no alternating current flows through the primary coil of the transfer transformer 61, and the output of the primary transfer voltage Va from the rectifying and smoothing circuit 62 is stopped. The secondary transfer power supply unit 70 has the same switching power supply configuration as the primary transfer power supply unit 60.

It should be noted that both the primary transfer power supply unit 60 and the secondary transfer power supply unit 70 may be any circuit capable of boosting the input voltage to a voltage necessary for transfer and outputting it. It may be used.
Returning to FIG. 2, the primary transfer voltage Va output from the output terminal 60 a of the primary transfer power supply unit 60 is simultaneously applied to each of the metal rotation shafts 26 </ b> Y to 26 </ b> K of the primary transfer rollers 24 </ b> Y to 24 </ b> K via the power supply line 91. Supplied. In the present embodiment, constant voltage control is performed so that a constant primary transfer voltage Va is output from the primary transfer power supply unit 60. The transfer current flowing from the primary transfer power supply unit 60 to the primary transfer rollers 24Y to 24K via the power supply line 91 has a magnitude of, for example, several μA to several tens of μA.

On the other hand, when receiving a stop instruction from the control unit 50, the primary transfer power supply unit 60 stops generating the primary transfer voltage Va. Thereby, the supply of the primary transfer voltage Va to the rotation shafts 26Y to 26K of the primary transfer rollers 24Y to 24K is stopped.
Further, the control unit 50 outputs a secondary transfer signal for instructing switching between driving (ON) and stop (OFF) to the secondary transfer power source unit 70 and an output voltage instruction signal for instructing the magnitude of the output voltage. To do. When the secondary transfer power supply unit 70 receives a drive instruction from the secondary transfer signal from the control unit 50 and receives an output voltage level from the output voltage instruction signal, the secondary transfer power supply unit 70 generates the secondary transfer voltage Vb having the specified level. And output. Here, the secondary transfer voltage Vb is a positive DC voltage, which is Vb1 during color printing and Vb2 during monochrome printing, and is set to a value larger than the primary transfer voltage Va.

The secondary transfer voltage Vb output from the secondary transfer power supply unit 70 is supplied to the metal rotary shaft 27 of the secondary transfer roller 25 via the power supply line 92. In the present embodiment, a constant secondary transfer voltage Vb is output from the secondary transfer power supply unit 70, and the secondary transfer roller 25 is controlled at a constant voltage.
The transfer current flowing from the secondary transfer power supply unit 70 toward the secondary transfer roller 25 via the power supply line 92 is, for example, several μA to several tens μA.

A power supply line 93 that branches in the middle of the power supply line 92 is connected to the step-down circuit 80, and the secondary transfer voltage Vb is connected to the input terminal 80 a of the step-down circuit 80 through a diode 89 disposed on the power supply line 93. Supplied.
The step-down circuit 80 is a so-called shunt circuit that steps down the input voltage of the input terminal 80 a and outputs the voltage from the output terminal 80 b, and includes a PNP transistor 81 and a resistor 82.

The emitter terminal of the transistor 81 is connected to the power supply line 93 via the input terminal 80a, and the secondary transfer voltage Vb from the power supply line 93 is input thereto. The collector terminal of the transistor 81 is connected to the output terminal 80 b through the resistor 82. The resistor 82 is provided for protecting the transistor 81, and is several MΩ, for example.
A power line 94 is connected to the output terminal 80 b of the step-down circuit 80. The power supply line 94 is an electric wire branched from a portion 99 (position between the diode 88 and the rotating shaft 26K of the primary transfer roller 24K; hereinafter referred to as “branch position”) in the middle of the power supply line 91.

A diode 83 is inserted in the power line 94. The diode 83 is inserted on the power supply line 94 in such a direction that only a current in a direction from the output terminal 80b of the step-down circuit 80 toward the branch position 99 of the power supply line 91 flows.
The base terminal of the transistor 81 is connected to the signal terminal 80c, and the step-down instruction signal output from the control unit 50 is input to the signal terminal 80c. The step-down instruction signal is a signal for instructing switching between driving (ON) and stopping (OFF) of the step-down circuit 80. Here, the step-down instruction signal becomes L (low) level when driving and H (high) level when stopping. Switch to

  When the secondary transfer voltage Vb is input to the step-down circuit 80, the transistor 81 is turned on when the step-down instruction signal becomes L level. As a result, a transfer current flows from the secondary transfer power supply unit 70 to the primary transfer roller 24K via the diode 89, the transistor 81, the resistor 82, and the diode 83. This transfer current has a magnitude of, for example, several μA to several tens of μA. The transfer current does not flow to the other primary transfer rollers 24Y to 24C due to the rectification action of the diode 88 disposed on the power supply line 91.

  Due to the voltage drop of the resistor 82 when the transfer current flows through the step-down circuit 80, the voltage applied to the primary transfer roller 24K is a voltage (primary transfer voltage) Vd necessary for primary transfer during monochrome image formation, which is the same as Va here. The resistance value R of the resistor 82 is set in advance so that the voltage of Specifically, the magnitude of the transfer current is measured in advance through experiments or the like, and the magnitude of the resistance value R is determined from the measured current value and the magnitudes of the primary transfer voltage Vd and the secondary transfer voltage Vb determined in advance. Is decided.

  In this sense, the power supply line 91 can be said to be a common power supply line for supplying the primary transfer voltage Va from the primary transfer power supply unit 60 and the voltage Vd from the step-down circuit 80 to the primary transfer roller 24K. In addition, a diode 88 inserted in the power supply line 91 on the primary transfer power supply unit 60 side and a power supply line 94 on the secondary transfer power supply unit 70 side are inserted across a branching position 99 on the middle of the power supply line 91. It can be said that the diode 83 constitutes a maximum value selection circuit that selects the maximum value among the voltage output from the primary transfer power supply unit 60 and the voltage output from the step-down circuit 80.

In the above description, the voltage Vd has the same magnitude as Va. However, the present invention is not limited to this, and there may be a value in the range of Vd <Vb depending on the device configuration.
Further, the circuit configuration of the step-down circuit 80 is not limited to that shown in FIG. Any circuit capable of stepping down the secondary transfer voltage Vb to the voltage Vd necessary for primary transfer may be used. For example, a configuration in which a plurality of transistors 81 are provided in multiple stages without providing the resistor 82 may be employed.

Although the primary transfer power supply unit 60 generates the primary transfer voltage Va as described above, the step-down circuit 80 is also configured to generate the voltage Vd necessary for the primary transfer during the primary transfer. This is because by stopping the driving of the power supply unit 60, the power consumption can be reduced as compared with the conventional equivalent configuration in which the primary transfer power supply unit 60 is kept driven.
Hereinafter, the difference in power consumption during monochrome printing between the embodiment and the conventional equivalent (comparative example) will be described with reference to FIGS. 4 and 5. FIG.

4A and 4B are diagrams showing the configuration of the embodiment. FIG. 4A shows a state during color printing, and FIG. 4B shows a state during monochrome printing.
As shown in FIG. 4A, during color printing, the primary transfer power supply unit 60 is driven (ON), and the drive of the step-down circuit 80 is stopped (OFF). The secondary transfer power supply unit 70 is driven (ON) during color printing and monochrome printing.

  The primary transfer power supply unit 60 outputs a primary transfer voltage Va from the primary transfer power supply unit 60. The value of the primary transfer voltage Va is 1000 V, for example. The primary transfer voltage Va output from the primary transfer power supply unit 60 is supplied to each of the primary transfer rollers 24Y to 24K via the power supply line 91. Accordingly, the primary transfer current Ia flows from the primary transfer power supply unit 60 to the primary transfer rollers 24Y to 24K via the power supply line 91.

  Further, the secondary transfer power supply unit 70 outputs the secondary transfer voltage Vb <b> 1 by driving the secondary transfer power supply unit 70. The value of the secondary transfer voltage Vb1 is, for example, 1500V. The secondary transfer voltage Vb <b> 1 output from the secondary transfer power supply unit 70 is supplied to the secondary transfer roller 25 via the power supply line 92. As a result, the secondary transfer current Ib1 flows from the secondary transfer power supply unit 70 to the secondary transfer roller 25 through the power supply line 92.

Since the step-down circuit 80 is stopped during color printing, no transfer current flows from the secondary transfer power supply unit 70 to the primary transfer roller 24K via the step-down circuit 80, and power is consumed in the step-down circuit 80. There is no.
On the other hand, as shown in FIG. 4B, during monochrome printing, the driving of the primary transfer power supply unit 60 is stopped (OFF), and the step-down circuit 80 is driven (ON).

The primary transfer power supply unit 60 stops outputting the primary transfer voltage Va when the primary transfer power supply unit 60 stops driving.
Further, the secondary transfer power supply unit 70 outputs the secondary transfer voltage Vb <b> 2 by driving the secondary transfer power supply unit 70. The value of the secondary transfer voltage Vb2 is smaller by a predetermined amount than Vb1 during color printing. Specifically, for example, when Vb1 = 1500V, Vb2 = 1300V. The reason why the secondary transfer voltage is thus differentiated is as follows.

  That is, in color printing, a maximum of Y to K toner images may be transferred onto the intermediate transfer belt 21 by primary transfer. In order to move these four color toner images collectively from the intermediate transfer belt 21 to the sheet S with electrostatic force, it is necessary that a large electrostatic force acts between the intermediate transfer belt 21 and the secondary transfer roller 25. In order to apply a large electrostatic force, it is necessary to increase the secondary transfer voltage.

  On the other hand, in monochrome printing, only one color toner image is primarily transferred onto the intermediate transfer belt 21, so that an electrostatic force smaller than that of a color print is sufficient, and a secondary transfer voltage is also small. On the contrary, when the secondary transfer voltage becomes excessive in monochrome printing, the electrostatic force becomes excessive, and the toner image on the intermediate transfer belt 21 from the intermediate transfer belt 21 immediately before a part of the toner particles reaches the transfer nip N. The so-called toner scattering that scatters and adheres on the paper S is likely to occur. This toner scattering is a position different from the original transfer position on the paper S because the toner particles to be secondarily transferred onto the paper S at the transfer nip N scatter from the intermediate transfer belt 21 immediately before reaching the transfer nip N. This is a phenomenon that adheres to the image, which causes a reduction in image quality.

Therefore, the value of the secondary transfer voltage Vb2 at the time of monochrome printing is smaller than the secondary transfer voltage Vb1 at the time of color printing, and a voltage value suitable for the secondary transfer of the monochrome print is set in advance by experiments or the like. It has become so.
When the secondary transfer voltage Vb <b> 2 is output from the secondary transfer power supply unit 70, the secondary transfer current Ib <b> 2 flows to the secondary transfer roller 25 through the power supply line 92.

Further, since the step-down circuit 80 is driven, the transfer current Ia flows only from the secondary transfer power supply unit 70 to the primary transfer roller 24K via the step-down circuit 80, and primary transfer at the time of monochrome image formation only to the primary transfer roller 24K. Is supplied with a voltage Vd required for.
As a result, the primary transfer roller 24K can perform primary transfer of K color in a state where driving of the primary transfer power supply unit 60 is stopped. Since the drive of the primary transfer power supply unit 60 is stopped, power is not consumed by the transfer transformer 61, the switching unit 63, and the like.

FIG. 5A is a block diagram illustrating a circuit configuration in the comparative example, and FIG. 5B is a diagram illustrating a state during monochrome printing in the comparative example.
As shown in FIG. 5A, in the comparative example, there is nothing equivalent to the step-down circuit of the embodiment, and the primary transfer voltage Va output from the primary transfer power supply unit 600 is supplied to each of the primary transfer rollers 24Y to 24K. The secondary transfer voltage Vb output from the secondary transfer power supply unit 700 is supplied only to the secondary transfer roller 25.

For this reason, as shown in FIG. 5B, it is necessary to drive the primary transfer power supply unit 600 during monochrome printing, and the primary transfer voltage Va output from the primary transfer power supply unit 600 is used during monochrome printing. Not only the roller 24K but also the primary transfer rollers 24Y, 24M, and 24C that are not used in monochrome printing are supplied.
Therefore, in the comparative example, power is consumed to drive the primary transfer power supply unit 600, and power is consumed by the primary transfer current Ia flowing through the primary transfer rollers 24Y, 24M, and 24C that are not necessary for monochrome printing. End up.

On the other hand, in the embodiment, as shown in FIG. 4B, the primary transfer power supply unit 60 is not driven during monochrome printing, and only the primary transfer roller 24K is supplied from the secondary transfer power supply unit 70 via the step-down circuit 80. A transfer current is supplied, and the primary transfer current does not flow through the primary transfer rollers 24Y, 24M, and 24C.
In the experimental machine having the same configuration as that of the printer 1 according to the embodiment, when the circuit of the comparative example is used, the power loss at the time of primary transfer at the time of monochrome printing is 0.4 W. In the case of this circuit, it has been confirmed by experiments that the power consumed by the step-down circuit 80 (this corresponds to a power loss) has been reduced to 0.2 W. From this result, in the embodiment, 0 is compared to the comparative example. It was found that reduction of 2W power loss was realized.

FIG. 6A is a timing chart of the primary transfer signal, the secondary transfer signal, and the step-down instruction signal during color printing on one sheet S, and FIG. FIG. 7 is a timing chart of a primary transfer signal, a secondary transfer signal, and a step-down instruction signal during monochrome printing with respect to FIG.
As shown in FIG. 6A, at the time of color printing, each of the primary transfer signal and the secondary transfer signal is turned on (driven) at the start of the print job (time point t0). When the primary transfer of the last K color among Y to K colors is completed during execution of the print job for one sheet S (time t1), the primary transfer signal is turned off (stopped). Thereafter, when the sheet S passes through the transfer nip N and the secondary transfer is completed (time t2), the secondary transfer signal is turned off (stopped). The step-down instruction signal remains OFF (stopped) from the start to the end of the print job, and the step-down circuit 80 is not driven.

  On the other hand, as shown in FIG. 6B, during monochrome printing, each of the secondary transfer signal and the step-down instruction signal is turned on (driven) at the start of the print job (time point t0). When the primary transfer of the last K color among Y to K colors is completed during execution of the print job for one sheet S (time t1), the step-down instruction signal is turned off (stopped). Thereafter, when the sheet S passes through the transfer nip N and the secondary transfer is completed (time t2), the secondary transfer signal is turned off (stopped). The primary transfer signal remains OFF (stopped) from the start to the end of the print job, and the primary transfer power supply unit 60 is not driven.

FIG. 7 is a flowchart showing the output control of the primary transfer signal, the secondary transfer signal, and the step-down instruction signal when the print job is executed. This control is performed when a print job for one sheet S is performed by the control unit 50. To be executed.
As shown in the figure, the control unit 50 determines whether or not the job to be executed is a color print (step S1). If it is determined that the print is a color print (“Yes” in step S1), the step-down instruction signal output to the step-down circuit 80 is turned off (stopped) (step S2), and the primary transfer signal output to the primary transfer power supply unit 60 is turned on. (Drive) (step S3), turn on (drive) the secondary transfer signal output to the secondary transfer power supply unit 70, set the output voltage of the output voltage instruction signal to Vb1 (step S4), and go to step S5. move on. As a result, the primary transfer power supply unit 60 and the secondary transfer power supply unit 70 are driven, and the operation of the step-down circuit 80 is stopped.

  On the other hand, if it is determined that the print is monochrome printing (“No” in step S1), the step-down instruction signal output to the step-down circuit 80 is turned on (driven) (step S6), and the primary transfer signal output to the primary transfer power supply unit 60. Is turned off (stopped) (step S7), the secondary transfer signal output to the secondary transfer power supply unit 70 is turned on (driven), and the output voltage of the output voltage instruction signal is set to Vb2 (step S8). Proceed to S5.

As a result, the step-down circuit 80 operates while the secondary transfer power supply unit 70 is driven, and the drive of the primary transfer power supply unit 60 is stopped. In the figure, the secondary transfer signal is turned on (step S8) after the step-down instruction signal is turned on (step S6). However, the step-down circuit 80 only needs to operate, for example, after the secondary transfer signal is turned on. It may be a control to turn on the instruction signal.
In step S5, it is determined whether or not the primary transfer of K color is completed. When the end of the primary transfer of the K color is determined (“Yes” in step S5), if the primary transfer signal is currently ON (“Yes” in step S9), the primary transfer signal is turned off (stopped). (Step S10), the process proceeds to Step S11. On the other hand, if the primary transfer signal is currently OFF (“No” in step S9), step S10 is skipped (not executed) and the process proceeds to step S11.

Subsequently, if the step-down instruction signal is currently ON (“Yes” in step S11), the step-down instruction signal is turned off (stopped) (step S12), and the process proceeds to step S13. On the other hand, if the step-down instruction signal is currently OFF (“No” in step S11), step S12 is skipped and the process proceeds to step S13.
In step S13, it is determined whether the secondary transfer has been completed. The end of the secondary transfer is determined by determining that the trailing edge of the conveyed paper S has passed through the transfer nip N. Whether the trailing edge of the sheet S has passed through the transfer nip N is determined by a sheet detection sensor (not shown) provided near the transfer nip N and downstream of the transfer nip N in the sheet conveying direction. This is performed by detecting.

When the end of the secondary transfer is determined (“Yes” in step S13), the secondary transfer signal is turned off (stopped) (step S14), and the control ends.
In FIGS. 6 and 7, an example in which color printing and monochrome printing are executed in separate jobs has been described. For example, a plurality of sheets S are continuously conveyed one by one and printing is performed on each sheet S. When performing monochrome printing on the Nth sheet S and switching to color printing for the next (N + 1) th sheet S in the job to be performed, supply of the primary transfer voltage to the primary transfer roller 24K Primary transfer switching control for switching the voltage from the step-down circuit 80 to the primary transfer power supply unit 60 is required.

  FIG. 8 is a diagram illustrating a flowchart of primary transfer switching control, which is executed by the control unit 50. As shown in the figure, the control unit 50 receives an instruction to switch to color printing for the (N + 1) th sheet S during monochrome printing on the Nth sheet S (step S21). It is determined whether or not the primary transfer of the K color has been completed during monochrome printing on the first sheet S (step S22).

When this end is determined (“Yes” in step S22), first, the step-down instruction signal to the step-down circuit 80 is turned off (stopped) (step S23), and then the primary transfer signal to the primary transfer power supply unit 60 is turned on ( After driving) (step S24), the control is terminated.
The primary transfer signal is turned on when the drive of the step-down circuit 80 is stopped by turning off the step-down instruction signal (the transistor 81 of the step-down circuit 80 is turned off), and then the most upstream of the color image formation on the (N + 1) th sheet S. Any point in time until the Y-color toner image carried on the photosensitive drum 11Y reaches the position (primary transfer position 241: FIG. 1) at which the Y-color toner image is primarily transferred to the intermediate transfer belt 21 is set in advance. The

In the present embodiment, as shown in FIG. 2, one power supply line 91 is connected to the power supply line for supplying the primary transfer voltage Va from the primary transfer power supply unit 60 to the primary transfer roller 24K, and from the step-down circuit 80 to the primary transfer roller 24K. The power supply line for supplying the primary transfer voltage Vd is commonly used.
Therefore, when the print mode is switched from monochrome printing to color printing as shown in FIG. 8, the primary transfer switching is stopped after the operation of the step-down circuit 80 is stopped, and then the primary transfer power supply unit 60 is started to drive. Simultaneous application of the primary transfer voltage from the step-down circuit 80 and the primary transfer voltage from the primary transfer power supply unit 60 to the line 91 is prevented.

This prevents an excessive current from flowing through the primary transfer roller 24K, even temporarily when the print mode is switched, and eliminates unnecessary power consumption without placing a burden on the primary transfer roller 24K due to excessive current. Is possible.
In the above description, the example in which the print mode is switched from monochrome print to color print during execution of one print job has been described. However, the present invention is not limited to this, and the same applies to the case in which the print mode is switched from color print to monochrome print. It is possible to take control to start the operation of the step-down circuit 80 after the driving of the primary transfer power supply unit 60 is stopped.

As described above, in the present embodiment, since the drive of the primary transfer power supply unit 60 is stopped during monochrome printing, the primary transfer roller 24Y, which consumes power by driving the primary transfer power supply unit 60 and is unnecessary for monochrome printing, Since the primary transfer current flows through 24M and 24C, power is not consumed, and power loss during primary transfer can be reduced.
In addition, since it is not necessary to change the configuration of the primary transfer power supply unit 60 and the secondary transfer power supply unit 70, a conventional one can be used.

  Further, the primary transfer voltage Vd during monochrome printing, the secondary transfer voltage Vb2 during monochrome printing, and the secondary transfer voltage Vb1 during color printing have a relationship of Vd <Vb2 <Vb1. As a result, compared to the case of Vb1 = Vb2, the magnitude of the voltage to be stepped down by the step-down circuit 80 (= Vb2-Vd) during monochrome printing becomes a small value, and the power consumed by the resistor 82 can be reduced accordingly. Reduction of power loss during primary transfer can be achieved.

Depending on the device configuration of the printer 1, Vb1 = Vb2 may be possible. In this case, the effect of reducing the power loss may be lower than the above, but from the comparative example in which the primary transfer power supply unit 60 is driven during monochrome printing. Can also reduce power loss.
The present invention is not limited to the image forming apparatus, and may be a switching control method for driving and stopping the primary transfer power supply unit, the secondary transfer power supply unit, and the step-down circuit in color printing and monochrome printing. Furthermore, the method may be a program executed by a computer. The program according to the present invention includes, for example, a magnetic disk such as a magnetic tape and a flexible disk, an optical recording medium such as a DVD-ROM, DVD-RAM, CD-ROM, CD-R, MO, and PD, and a flash memory recording medium. It can be recorded on various computer-readable recording media, and may be produced, transferred, etc. in the form of the recording medium, wired and wireless various networks including the Internet in the form of programs, In some cases, the data is transmitted and supplied via broadcasting, telecommunication lines, satellite communications, or the like.
<Modification>
As described above, the present invention has been described based on the embodiment, but the present invention is not limited to the above-described embodiment, and the following modifications can be considered.

(1) In the above-described embodiment, the primary transfer voltage and the secondary transfer voltage are set to DC. However, the present invention is not limited to this, and for example, AC may be superimposed on DC.
In this case, in color printing, the superimposed primary transfer voltage is supplied from the primary transfer power supply unit 60 to each of the primary transfer rollers 24Y to 24K, and in monochrome printing, the superimposed secondary transfer voltage is supplied from the secondary transfer power supply unit 70. Is supplied to only the primary transfer roller 24K via the step-down circuit 80, and a circuit different from the above is configured that can switch the supply path of the primary transfer voltage to the primary transfer roller 24K.

In the above embodiment, the primary transfer voltage and the secondary transfer voltage are positive voltages. However, the present invention is not limited to this, and depending on the apparatus configuration, for example, a negative voltage may be obtained.
(2) In the above embodiment, an example in which monochrome image formation is K color has been described. However, the present invention is not limited to this, and image formation of any one of Y to M can be made a monochrome image. For example, when monochrome image formation is selected in the case of an apparatus configuration capable of forming a Y-color monochrome image, a Y-color toner image is formed using only the Y-color photosensitive drum 11Y. In this apparatus configuration, when a monochrome image is formed, the output voltage Vd of the step-down circuit 80 is supplied only to the primary transfer roller 24Y for Y color.

(3) In the above-described embodiment, the configuration example in which the primary transfer power supply unit 60 includes the transfer transformer 61 for boosting the voltage from the power supply to the primary transfer voltage Va has been described.
Any booster circuit capable of boosting to the primary transfer voltage Va may be used. For example, a booster chopper circuit or the like may be provided. Similarly, the step-down circuit 80 is not limited to the above configuration, and can be designed to reduce the power loss during the primary transfer according to the configuration of the printer.

(4) Although the printer has been described in the above embodiment, the present invention is not limited to this.
Intermediate transfer of images such as toner images carried on a plurality of image carriers (photosensitive drums, etc.) using a primary transfer member (primary transfer roller, etc.) provided corresponding to each image carrier After primary transfer electrostatically so as to be superimposed on the body (intermediate transfer belt, etc.), each color image transferred onto the intermediate transfer body is transferred onto the sheet using a secondary transfer member (secondary transfer roller, etc.). Forming a color image that is electrostatically secondary-transferred onto the intermediate transfer member using a primary transfer member corresponding to the image carrier. After transfer, an electrophotographic printer, copier, etc. that can be switched between monochrome image formation that electrostatically transfers the image on the intermediate transfer member onto a sheet using a secondary transfer member Application to general image forming apparatus It can be.

  Further, the above-described embodiment and each modification may be used in combination as much as possible.

  In the present invention, an image carried on each of a plurality of image carriers is primary-transferred electrostatically by superimposing on an intermediate transfer member using a primary transfer member provided corresponding to each image carrier. Thereafter, the present invention can be widely applied to an image forming apparatus having a configuration in which each color image multiple-transferred onto an intermediate transfer member is electrostatically secondary-transferred onto a sheet using a secondary transfer member.

DESCRIPTION OF SYMBOLS 1 Printer 11Y, 11M, 11C, 11K Photosensitive drum 21 Intermediate transfer belt 24Y, 24M, 24C, 24K Primary transfer roller 25 Secondary transfer roller 50 Control part 60 Primary transfer power supply part 60a Output terminal of primary transfer power supply part 61 Transfer transformer 63 Switching section 70 Secondary transfer power supply section 80 Step-down circuit 80b Output terminal of step-down circuit 81 Transistor 82 Resistor 83, 88, 89 Diode 91, 92, 93, 94 Power supply line 99 Branch position 241 The most upstream photosensitive drum Primary transfer position in N Transfer nip Va Primary transfer voltage during color image formation Vb Secondary transfer voltage Vd Primary transfer voltage during monochrome image formation

Claims (5)

After the primary transfer of images of different colors carried on each of the plurality of image carriers on the intermediate transfer member using a primary transfer member provided corresponding to each image carrier, the intermediate transfer member Color image formation in which each color image is secondarily transferred onto a sheet using a secondary transfer member, and an image carried on one image carrier among the plurality of image carriers is associated with the image carrier. It is possible to perform switching between monochrome image formation in which an image on the intermediate transfer body is transferred onto the sheet using the secondary transfer member after the primary transfer onto the intermediate transfer body using the primary transfer member. An electrophotographic image forming apparatus,
Provided in common to the plurality of primary transfer members, and after boosting the input voltage to a primary transfer voltage necessary for primary transfer during color image formation, the primary transfer voltage is supplied to each of the plurality of primary transfer members. A primary transfer power supply unit,
A secondary transfer power supply unit that generates a secondary transfer voltage necessary for the secondary transfer and supplies the generated secondary transfer voltage to the secondary transfer member in the case of color and monochrome image formation; ,
A step-down circuit that receives a secondary transfer voltage generated by the secondary transfer power supply unit and supplies a voltage that is stepped down to a voltage required for primary transfer during monochrome image formation to a primary transfer member used for monochrome image formation; ,
In the case of color image formation, the primary transfer power supply unit and the step-down circuit are controlled, the primary transfer power supply unit is driven and the operation of the step-down circuit is stopped, and in the case of monochrome image formation, the primary transfer power supply unit Control means for stopping driving and operating the step-down circuit;
An image forming apparatus comprising: The secondary transfer power supply unit
The secondary transfer voltage can be switched to Vb1 when the color image is formed, and the secondary transfer voltage can be switched to Vb2 when the monochrome image is formed.
2. The image forming apparatus according to claim 1, wherein when a voltage required for primary transfer at the time of monochrome image formation is Vd, a relationship of Vd <Vb2 <Vb1 is satisfied. Among a plurality of continuously conveyed sheets, after executing monochrome image formation on the Nth sheet, color image formation can be switched and executed on the (N + 1) th sheet,
Each of the plurality of image carriers is arranged along the moving direction of the intermediate transfer member,
The control means includes
The operation of the step-down circuit is stopped by the end of primary transfer during the execution of the monochrome image formation, and then the most upstream image carrier in the moving direction of the intermediate transfer member among the plurality of image carriers by the color image formation. 3. The image formation according to claim 1, wherein the driving of the primary transfer power supply unit is started before reaching the position where the image carried thereon is primarily transferred to the intermediate transfer member. apparatus. A first power supply line for electrically connecting an output terminal of the primary transfer power supply unit and a primary transfer member used for monochrome image formation;
A second power line branched from the middle of the first power line and electrically connected to the output terminal of the step-down circuit;
The first power supply line is inserted closer to the output terminal side of the primary transfer power supply unit than the branch position where the second power supply line branches, and the transfer in the direction from the output terminal of the primary transfer power supply unit toward the branch position A first diode that passes only current;
A second diode inserted into the second power supply line and passing only a transfer current in a direction from the output terminal of the step-down circuit toward the branch position;
The image forming apparatus according to claim 1, further comprising: The primary transfer power supply unit
A transfer transformer for boosting the input voltage to the primary transfer voltage;
The control means includes
5. The image forming apparatus according to claim 1, wherein in the case of color image formation, the drive of the transfer transformer is stopped, and in the case of monochrome image formation, the transfer transformer is driven.

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