JP6540440B2 - Image forming device - Google Patents

Description

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

Examples of image forming apparatuses such as electrophotographic printers include so-called tandem color image forming apparatuses.
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 along the belt circulation direction outside the circulation path of the intermediate transfer belt. The primary transfer roller for Y to K color is disposed at a position facing the photosensitive drum for Y to K on both sides of the intermediate transfer belt, and the intermediate transfer belt is further provided. In general, a secondary transfer roller is disposed outside 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 a 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 roller for Y to K colors, and the secondary transfer voltage is supplied to the secondary transfer roller. A toner image of Y to K is formed on a photosensitive drum for Y to K, and a primary transfer voltage is applied to the toner image of Y to K formed on a photosensitive drum for Y to K By electrostatic action of the primary transfer roller for Y to K colors, electrostatically multiple transfer is performed on the circulating intermediate transfer belt (primary transfer).

Then, the sheet is conveyed to the secondary transfer position in synchronization with the timing at which the Y to K toner images 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. While passing between them, the toner image of Y to K colors on the intermediate transfer belt is transferred onto 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 forming a monochrome image of K color, a toner image of K color is formed using only a photosensitive drum for K color, and the toner image of K color is formed into a primary for K color to which a primary transfer voltage is applied. Primary transfer is performed on the intermediate transfer belt by the electrostatic action of the transfer roller. Then, while the sheet passes between the intermediate transfer belt and the secondary transfer roller, the electrostatic action of the secondary transfer roller to which the secondary transfer voltage is applied causes the toner image of K color on the intermediate transfer belt to be formed on the sheet. Next transfer.

Since the primary transfer voltage is a high voltage, for example, about 1000 V, usually, a voltage obtained by boosting a voltage from a power supply by a transfer transformer is used as a primary transfer voltage.
Although this transfer transformer may be provided corresponding to each of the primary transfer rollers for Y to K colors, a total of four transfer transformers are required, which increases the cost, so for Y to K colors. There are many configurations in which one 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 color.
However, the primary transfer voltage is also supplied to the primary transfer rollers for Y, M, and C colors other than K color, and unnecessary transfer current flows to the primary transfer rollers for Y, M, and C colors that are not used. As a result, there is a problem that it leads to power loss at the time of primary transfer. Such a problem is not limited to the configuration using the transfer transformer, but may occur in general in a configuration using a circuit for boosting the voltage from the power supply to the primary transfer voltage.

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

  In order to achieve the above object, the image forming apparatus according to the present invention uses a primary transfer member provided with images of different colors carried on each of a plurality of image carriers corresponding to the respective image carriers. A 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 overlapping and primary transfer on the intermediate transfer member, and one of the plurality of image carriers After primary transfer of the image carried on the image carrier onto the intermediate transfer body using a primary transfer member corresponding to the image carrier, the image on the intermediate transfer body is sheeted using the secondary transfer member An electrophotographic image forming apparatus capable of switching between monochrome image formation for secondary transfer onto the upper side and being provided in common to the plurality of primary transfer members, and performing primary voltage transfer for color image formation with an input voltage Up to the primary transfer voltage required for After that, the primary transfer power supply unit supplies the primary transfer voltage to each of the plurality of primary transfer members, and the secondary transfer voltage necessary for the secondary transfer in the case of image formation of color and monochrome, respectively. At the time of monochrome image formation by receiving a secondary transfer voltage generated and generated at the secondary transfer power supply unit, and a secondary transfer power supply unit for supplying the generated secondary transfer voltage to the secondary transfer member A step-down circuit for supplying to a primary transfer member used for monochrome image formation a voltage lowered to a voltage necessary for primary transfer, and controlling the primary transfer power supply unit and the step-down circuit to form a color image; A control unit configured to drive a power supply unit and stop the operation of the step-down circuit, and stop the driving of the primary transfer power supply unit and operate the step-down circuit in the case of monochrome image formation; To.

Further, the secondary transfer power supply unit can switch the secondary transfer voltage to Vb1 at the time of color image formation, and switch the secondary transfer voltage to Vb2 at the time of monochrome image formation, and is necessary for primary transfer at the time of monochrome image formation. When the voltage is Vd, the relationship Vd <Vb2 <Vb1 may be satisfied.
Furthermore, after performing monochrome image formation on the N-th sheet among a plurality of sheets conveyed continuously, color image formation can be switched and executed on the (N + 1) -th sheet, Each of the plurality of image carriers is arranged in a line along the moving direction of the intermediate transfer member, and the control means stops the operation of the step-down circuit by the completion of primary transfer during execution of the monochrome image formation. And the image carried on the uppermost image carrier in the moving direction of the intermediate transfer member among the plurality of image carriers by the color image formation reaches a position where the image is primarily transferred onto the intermediate transfer member. In the meantime, the driving of the primary transfer power supply unit may be started.

  Further, a first power supply line electrically connecting an output terminal of the primary transfer power supply section and a primary transfer member used for forming the monochrome image, and a branch of the first power supply line, and an output of the step-down circuit A second power supply line electrically connected to a terminal, and a first power supply line is inserted closer to the output terminal side of the primary transfer power supply than a branch position where the second power supply line branches, and the primary transfer Only the first diode that passes only the transfer current in the direction from the output terminal of the power supply unit toward the branch position, and the transfer current in the direction from the output terminal of the step-down circuit toward the branch position And a second diode that passes through.

Furthermore, the primary transfer power supply unit includes a transfer transformer for boosting an input voltage to the primary transfer voltage, and the control unit drives the transfer transformer in the case of color image formation, and in the case of monochrome image formation The driving of the transfer transformer may be stopped .

  According to the above configuration, in the case of monochrome image formation, the driving of the primary transfer power supply unit is stopped, so that the power is not consumed in the primary transfer power supply unit, and the primary transfer member is not used in monochrome image formation. There is no consumption of unnecessary power due to the use of unnecessary transfer current due to supply of the primary transfer voltage. Therefore, in the case of monochrome image formation, it is possible to reduce the power loss at the time of primary transfer as compared with the configuration in which the primary transfer voltage is supplied from the common primary transfer power supply unit to all of the primary transfer members.

FIG. 1 is a schematic view showing an entire configuration of a printer. FIG. 6 is a view for explaining the relationship among a control unit, a primary transfer power supply unit, a secondary transfer power supply unit, a step-down circuit, a primary transfer roller, and a secondary transfer roller. FIG. 2 is a block diagram showing a schematic configuration of a primary transfer power supply unit. (A) is a figure which shows the mode at the time of the color printing in an Example, (b) is a figure which shows the mode at the time of the monochrome printing in an Example. (A) is a block diagram which shows the circuit structure in a comparative example, (b) is a figure which shows the mode at the time of the monochrome printing in a comparative example. (A) is a diagram showing a timing chart of the primary transfer signal, the secondary transfer signal, and the step-down instruction signal at the time of color printing on one sheet S, and (b) is at the time of monochrome printing on one sheet S FIG. 16 is a timing chart of the primary transfer signal, the secondary transfer signal, and the step-down instruction signal in FIG. 5 is a flowchart showing control of output of a primary transfer signal, a secondary transfer signal, and a step-down instruction signal when a print job is executed. FIG. 7 is a diagram showing a 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-type color printer (hereinafter, simply referred to as “printer”) as an example.
FIG. 1 is a schematic view showing the entire 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) Perform color or monochrome imaging based on

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 rotating in a direction indicated by an arrow, and a cleaner for cleaning the surfaces of the charging unit 12Y, the exposing unit 13Y, the developing unit 14Y, and the photosensitive drum 11Y disposed around the photosensitive drum 11Y. A Y-toner image is formed on the photosensitive drum 11Y through charging, exposure, and developing steps. This configuration is the same for the other imaging units 10M to 10K, and the imaging units 10M, 10C, and 10K include the charging units 12M, 12C, and 12K, the exposure units 13M, 13C, and 13K, and the development units 14M, 14C, and 14K. , Cleaners 15M, 15C, and 15K for cleaning the surface of the photosensitive drum 11Y, 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 drive roller 22, a driven roller 23, primary transfer rollers 24Y, 24M, 24C, 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 disposed inside the belt circulation path (traveling path) of the intermediate transfer belt 21.

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

The secondary transfer roller 25 is in pressure contact with the drive roller 22 via the intermediate transfer belt 21 at a position downstream of the image forming unit 10K disposed outside the belt circulation path and downstream of the belt rotation direction in the belt circulation direction. The transfer nip N is formed with the outer peripheral surface of the intermediate transfer belt 21.
The feeding unit 30 includes a sheet feeding cassette 31, a delivery roller 32, a conveyance roller pair 33, and a timing roller pair 34.

The sheet feeding cassette 31 stores a plurality of sheets, in this case, the sheets S, and the feeding roller 32 feeds the sheets S stored in the sheet feeding cassette 31 one by one onto the transport path 35.
The transport roller pair 33 transports the sheet S fed out by the delivery 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 in accordance with 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 generally 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 photosensitive drums 11Y to 11K in the image forming units 10Y to 10K are charged by the charging units 12Y to 12K, and the photosensitive members are charged. The surface of the drums 11Y to 11K is 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 to Y to K A color toner image is formed.

The respective color toner images formed on the photosensitive drums 11Y to 11K are 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 toner is electrostatically primary-transferred onto the intermediate transfer belt 21 by the action of an electric field.
The image forming operation for each of the colors Y to K is performed from the upstream side to the downstream side in the belt rotation direction so that the toner images of the colors are primarily transferred on the same position of the rotating intermediate transfer belt 21. It is executed by shifting. The toner images of Y to K colors (hereinafter, referred to as “color toner images”), which are multi-transferred onto the intermediate transfer belt 21, are conveyed toward the transfer nip N as the intermediate transfer belt 21 circulates.

The sheet S is conveyed toward the transfer nip N by the timing roller pair 34 so as to match the timing when 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 move on the intermediate transfer belt 21. The color toner images are electrostatically collectively and secondarily transferred onto the sheet S.

After the color toner image is secondarily transferred, the sheet S is conveyed to the fixing unit 40, and is heated and pressurized 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 sheet S are fused and fixed to the sheet S. The sheet S having passed through the fixing unit 40 is discharged onto the sheet discharge tray 39 by the sheet discharge roller 38.
On the other hand, when performing monochrome (here, K-color image formation), only the image forming unit 10K of the image forming units 10Y to 10K is used, and exposure is performed by the same charging, exposure, and developing steps as described above. A K toner image is formed on the body drum 11K. Then, the K color toner image on the photosensitive drum 11K is stopped on the intermediate transfer belt 21 by the action of the 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. Primary transfer is performed electronically. The K-color toner image on the intermediate transfer belt 21 is conveyed toward the transfer nip N as the intermediate transfer belt 21 travels.

The sheet S is conveyed toward the transfer nip N by the timing roller pair 34 so as to match the timing when the K 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 move on the intermediate transfer belt 21. The toner image of color K is electrostatically secondarily transferred to the sheet S.

The sheet S on which the K-color toner image has been secondarily transferred is conveyed to the fixing unit 40, and is heated and pressurized when passing between the fixing roller 41 and the pressure roller 42 of the fixing unit 40. Thus, toner particles of the K-color toner image on the sheet S are fused and fixed to the sheet S. The sheet S having passed through the fixing unit 40 is discharged onto the sheet discharge tray 39 by the sheet 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 or the like) necessary for primary transfer during color image formation. .

The secondary transfer power supply unit 70 boosts an input voltage (for example, DC 24 V) to a voltage (for example, DC 1500 V or the like) necessary for the secondary transfer at the time of color image formation and at the time of monochrome image formation. It is 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, steps down the voltage to a voltage necessary for primary transfer at the time of monochrome image formation, and outputs the voltage.

FIG. 2 is a view for explaining the relationship between 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 drive (ON) and stop (OFF). When the primary transfer power source unit 60 receives a drive instruction from the control unit 50 in response to a primary transfer signal, it generates a primary transfer voltage Va and outputs it from the output terminal 60a. Here, the primary transfer voltage Va is a positive DC voltage.

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

The transfer transformer 61 boosts the alternating voltage supplied from the switching unit 63 to the primary coil to a predetermined magnitude and outputs the voltage from the secondary coil. The rectifying and 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 it. This output voltage becomes the primary transfer voltage Va at the time of color image formation.
The switching unit 63 performs 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 execute 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, alternating current does not flow to 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 also has a switching power supply configuration similar to that of the primary transfer power supply unit 60.

In both primary transfer power supply unit 60 and secondary transfer power supply unit 70, any circuit capable of boosting the input voltage to a voltage necessary for transfer and outputting can be used. You may use it.
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 the metal rotation shafts 26 Y to 26 K of the primary transfer rollers 24 Y to 24 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 toward each of the primary transfer rollers 24Y to 24K through the power supply line 91 is, for example, several μA to several tens of μA.

On the other hand, primary transfer power supply unit 60 stops the generation of primary transfer voltage Va when it receives a stop instruction from control unit 50. 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, control unit 50 outputs a secondary transfer signal instructing switching between drive (ON) and stop (OFF) to secondary transfer power supply unit 70 and an output voltage instruction signal instructing the magnitude of the output voltage. Do. Secondary transfer power supply unit 70 generates a secondary transfer voltage Vb of the instructed magnitude when the drive instruction is received by the secondary transfer signal from control unit 50 and the magnitude of the output voltage is received by the output voltage designation signal. Output. Here, the secondary transfer voltage Vb is a positive DC voltage, and is Vb1 at the time of color printing and Vb2 at the time of monochrome printing, and each has 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 subjected to constant voltage control.
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 of μA.

Further, the power supply line 93 branched in the middle of the power supply line 92 is connected to the step-down circuit 80, and the secondary transfer voltage Vb is input to the input terminal 80 a of the step-down circuit 80 via the diode 89 arranged 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 80a and outputs the voltage from the output terminal 80b, 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. The collector terminal of the transistor 81 is connected to the output terminal 80 b via the resistor 82. The resistor 82 is provided to protect the transistor 81, and is, for example, several MΩ.
A power supply 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 middle portion 99 of the power supply line 91 (a position between the diode 88 and the rotation shaft 26 K of the primary transfer roller 24 K. Hereinafter, referred to as “branching position”).

A diode 83 is inserted in the power supply line 94. The diode 83 is inserted in a direction in which only the current in the direction from the output terminal 80 b of the step-down circuit 80 to the branch position 99 of the power supply line 91 flows on the power supply line 94.
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 instructing switching between drive (ON) and stop (OFF) of the step-down circuit 80. Here, it becomes L (low) level in the case of drive and H (high) level in the case of stop Switch to

  When the secondary transfer voltage Vb is input to the step-down circuit 80, when the step-down instruction signal becomes L level, the transistor 81 is turned on. As a result, a transfer current flows from the secondary transfer power supply unit 70 to the primary transfer roller 24 K via the diode 89, the transistor 81, the resistor 82, and the diode 83. The transfer current is, 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 rectifying 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 in the step-down circuit 80, the applied voltage of the primary transfer roller 24K has the same magnitude as the voltage (primary transfer voltage) Vd necessary for primary transfer at the time of monochrome image formation. 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 by experiments etc., 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. Further, the diode 88 inserted in the power supply line 91 on the primary transfer power supply unit 60 side and the power supply line 94 on the secondary transfer power supply unit 70 side across the branch position 99 on the power supply line 91 side. 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.

Although the voltage Vd is assumed to have the same magnitude as Va in the above, the present invention is not limited to this, and the value may fall within 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 of 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 plurality of transistors 81 may be provided in multiple stages without providing the resistor 82.

Thus, while the primary transfer power supply unit 60 is configured to generate the primary transfer voltage Va, the step-down circuit 80 is configured to generate the voltage Vd necessary for the primary transfer in the case of monochrome printing. By stopping the driving of the power supply unit 60, power consumption can be reduced as compared with the conventional configuration in which the primary transfer power supply unit 60 is kept driven.
Hereinafter, differences in power consumption at the time of monochrome printing in each of the embodiment and the conventional equivalent (comparative example) will be described with reference to FIGS. 4 and 5.

FIG. 4 is a view showing the configuration of the embodiment, and FIG. 4 (a) shows a state at the time of color printing, and FIG. 4 (b) shows a state at the time of monochrome printing.
As shown in FIG. 4A, at the time of color printing, the primary transfer power supply unit 60 is driven (ON), and the driving of the step-down circuit 80 is stopped (OFF). The secondary transfer power supply unit 70 is driven (ON) in both color printing and monochrome printing.

  A primary transfer voltage Va is output from the primary transfer power supply unit 60 by the driving of the primary transfer power supply unit 60. The value of the primary transfer voltage Va is, for example, 1000V. The primary transfer voltage Va output from the primary transfer power supply unit 60 is supplied to each of the primary transfer rollers 24 </ b> Y to 24 </ b> K via the power supply line 91. Thereby, the primary transfer current Ia flows from the primary transfer power supply unit 60 to each of the primary transfer rollers 24Y to 24K through the power supply line 91.

  In addition, the secondary transfer voltage Vb1 is output from the secondary transfer power supply unit 70 by the driving of the secondary transfer power supply unit 70. The value of the secondary transfer voltage Vb1 is, for example, 1500V. The secondary transfer voltage Vb1 output from the secondary transfer power supply unit 70 is supplied to the secondary transfer roller 25 via the power supply line 92. Thus, the secondary transfer current Ib1 flows from the secondary transfer power supply unit 70 to the secondary transfer roller 25 via the power supply line 92.

Since the step-down circuit 80 is stopped at the time of color printing, the transfer current does not flow from the secondary transfer power supply unit 70 to the primary transfer roller 24 K via the step-down circuit 80, and power is consumed by the step-down circuit 80. There is no
On the other hand, as shown in FIG. 4B, in monochrome printing, the driving of the primary transfer power supply unit 60 is stopped (OFF), and the step-down circuit 80 is driven (ON).

When the driving of the primary transfer power supply unit 60 is stopped, the output of the primary transfer voltage Va from the primary transfer power supply unit 60 is stopped.
In addition, the secondary transfer voltage Vb2 is output from the secondary transfer power supply unit 70 by the drive of the secondary transfer power supply unit 70. The value of this secondary transfer voltage Vb2 is smaller than Vb1 at the time of color printing by a predetermined amount. Specifically, for example, when Vb1 = 1500 V, Vb2 = 1300 V. The reason for making the secondary transfer voltage different in this way is as follows.

  That is, in color printing, a toner image of Y to K colors at maximum may be multiply transferred onto the intermediate transfer belt 21 by primary transfer. In order to move the four color toner images collectively from the intermediate transfer belt 21 to the sheet S by electrostatic force, a large electrostatic force needs to be applied 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, since only a toner image of one color is primarily transferred onto the intermediate transfer belt 21, an electrostatic force smaller than that of color printing is sufficient, and the secondary transfer voltage also needs a small value. Conversely, when the secondary transfer voltage in monochrome printing becomes excessive, the electrostatic force becomes excessive, and some of the toner particles of the toner image on the intermediate transfer belt 21 reach the transfer nip N from the intermediate transfer belt 21. It becomes easy to generate so-called toner scattering that scatters and adheres onto the sheet S. The toner scattering is caused by the toner particles to be secondarily transferred onto the sheet S at the transfer nip N splattering from the intermediate transfer belt 21 immediately before reaching the transfer nip N, and the position different from the original transfer position on the sheet S Because it is a phenomenon that adheres to the image, it causes the image quality to deteriorate.

From this, the secondary transfer voltage Vb2 at the time of monochrome printing is set to a value 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 experiment. It has become so.
When the secondary transfer voltage Vb2 is output from the secondary transfer power supply unit 70, the secondary transfer current Ib2 flows to the secondary transfer roller 25 through the power supply line 92.

Since the step-down circuit 80 is driven, the transfer current Ia flows only from the secondary transfer power supply 70 through the step-down circuit 80 to the primary transfer roller 24K, and the primary transfer at the time of monochrome image formation only on the primary transfer roller 24K. The necessary voltage Vd is supplied.
As a result, in a state where the driving of the primary transfer power supply unit 60 is stopped, it is possible to execute the primary transfer of K color by the primary transfer roller 24K. Since the driving of the primary transfer power supply unit 60 is stopped, power consumption in the transfer transformer 61, the switching unit 63, and the like is not performed.

FIG. 5 (a) is a block diagram showing a circuit configuration in the comparative example, and FIG. 5 (b) is a diagram showing an appearance in 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.

Therefore, as shown in FIG. 5B, it is necessary to drive the primary transfer power supply unit 600 at the time of monochrome printing, and the primary transfer voltage Va output from the primary transfer power supply unit 600 is used at the time of monochrome printing. Not only the roller 24K but also the primary transfer rollers 24Y, 24M and 24C which 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 to the primary transfer rollers 24Y, 24M, and 24C unnecessary for monochrome printing. I will.

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

FIG. 6A is a timing chart of the primary transfer signal, the secondary transfer signal, and the step-down instruction signal at the time of color printing on one sheet S, and FIG. 7 is a timing chart of the primary transfer signal, the secondary transfer signal, and the step-down instruction signal at the time of monochrome printing with respect to FIG.
As shown in FIG. 6A, in 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 t0). Then, when the final transfer of the last K color among the colors Y to K 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 the transfer nip N and the secondary transfer is completed (at time t2), the secondary transfer signal is turned off (stopped). Note that 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, in 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 t0). Then, when the final transfer of the last K color among the colors Y to K 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 the transfer nip N and the secondary transfer is completed (at 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 flow chart showing the control of the output of the primary transfer signal, the secondary transfer signal, and the step-down instruction signal at the time of print job execution, and this control is performed when the print job for one sheet S is performed by To be executed.
As shown in the figure, the control unit 50 determines whether the job to be executed is color printing (step S1). If it is determined that it is a color print ("Yes" in step S1), the step-down instruction signal output to step-down circuit 80 is turned off (stopped) (step S2), and the primary transfer signal output to primary transfer power supply unit 60 is turned on. (Driving) (step S3), the secondary transfer signal to be 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 Vb1 (step S4). move on. Thereby, 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 it is a monochrome print ("No" in step S1), the step-down instruction signal output to step-down circuit 80 is turned on (driven) (step S6), and the primary transfer signal output to primary transfer power supply 60 Is turned off (step S7), and the secondary transfer signal to be output to the secondary transfer power supply 70 is turned on (driven) and the output voltage of the output voltage instruction signal is set to Vb2 (step S8). Go to S5.

Thereby, 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. Although the secondary transfer signal is turned on (step S8) after the step-down instruction signal is turned on (step S6) in the same figure, the step-down circuit 80 may operate, for example, step-down after the secondary transfer signal is turned on. It may be control to execute ON of the instruction signal.
In step S5, it is determined whether the primary transfer of the K color is completed. If it is determined that the primary transfer of K color is completed ("Yes" in step S5), and 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" at step S11), the process skips step S12 and proceeds to step S13.
In step S13, it is determined whether secondary transfer has ended. The determination as to the end of the secondary transfer is made by determining that the trailing edge of the sheet S being conveyed has passed the transfer nip N. The determination that the rear end of the sheet S has passed the transfer nip N is determined by the sheet detection sensor (not shown) provided near the transfer nip N and downstream of the transfer nip N in the sheet conveyance direction. It is done by the detection of

If it is determined that the secondary transfer is completed ("Yes" in step S13), the secondary transfer signal is turned off (stopped) (step S14), and the control is ended.
In the above-described FIGS. 6 and 7, an example in which color printing and monochrome printing are performed in separate jobs has been described. For example, printing is performed on each sheet S by continuously transporting a plurality of sheets S one by one When performing monochrome printing on the Nth sheet of paper S and switching to color printing on the next (N + 1) th sheet of paper S, supply of the primary transfer voltage to the primary transfer roller 24K The first transfer switching control to switch the step-down circuit 80 from the step-down circuit 80 to the first transfer power supply unit 60 is required.

  FIG. 8 is a flowchart of the primary transfer switching control, which is executed by the control unit 50. As shown in the figure, when the control unit 50 receives an instruction to switch to the (N + 1) th sheet S during the monochrome printing on the Nth sheet S (step S21), It is determined whether the primary transfer of the K color is completed during the monochrome printing on the 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 ends.
The ON timing of the primary transfer signal is the uppermost stream by forming a color image on the (N + 1) th sheet S after the driving of the step-down circuit 80 is stopped (the transistor 81 of the step-down circuit 80 is turned off) The point in time before the Y-color toner image carried on the photosensitive drum 11Y reaches the position (primary transfer position 241: FIG. 1) to be primarily transferred to the intermediate transfer belt 21 is preset. Ru.

In the present embodiment, as shown in FIG. 2, one power supply line 91 is supplied from the primary transfer power supply unit 60 to the primary transfer roller 24K to supply the primary transfer voltage Va, and 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 switching the printing mode from monochrome printing to color printing as shown in FIG. 8, after stopping the operation of the step-down circuit 80 for the primary transfer switching, driving of the primary transfer power source unit 60 is started, It is prevented that the primary transfer voltage from the step-down circuit 80 and the primary transfer voltage from the primary transfer power supply unit 60 are simultaneously applied to the line 91.

As a result, although temporary at the time of print mode switching, excessive current flow is prevented from flowing through the primary transfer roller 24K, and unnecessary power consumption is eliminated without burdening the primary transfer roller 24K with excessive current. Becomes possible.
In the above, an example in which the print mode is switched from monochrome printing to color print during execution of one print job has been described. However, the present invention is not limited to this. After stopping the driving of the primary transfer power supply unit 60, control can be taken to start the operation of the step-down circuit 80.

As described above, in the present embodiment, since driving of the primary transfer power supply unit 60 is stopped at the time of monochrome printing, power is consumed by driving of the primary transfer power supply unit 60, and the primary transfer roller 24Y unnecessary for monochrome printing. Since the primary transfer current flows to 24M and 24C, power is not consumed, and power loss at the time of primary transfer can be reduced.
Further, since it is not necessary to change the configurations of the primary transfer power supply unit 60 and the secondary transfer power supply unit 70, conventional ones can be used.

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

Depending on the device configuration of the printer 1, Vb1 = Vb2 may be applied. In this case, the reduction effect of the power loss may be lower than the above case, but the comparative example for driving the primary transfer power source unit 60 at the time of monochrome printing Can also reduce the power loss.
The present invention is not limited to the image forming apparatus, and may be a switching control method of driving and stopping of 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 may be, for example, a magnetic tape, a magnetic disk such as a flexible disk, a DVD-ROM, a DVD-RAM, a CD-ROM, an optical recording medium such as a CD-R, an MO, or a PD, and a flash memory recording medium. It can be recorded in various computer readable recording media, etc., and may be produced, transferred, etc. in the form of the recording media, and various wired and wireless networks including the Internet in the form of programs. It may be transmitted and supplied via broadcasting, telecommunication lines, satellite communication, etc.
<Modification>
As mentioned above, although this invention was demonstrated based on embodiment, it is needless to say that this invention is not limited to the above-mentioned embodiment, The following modifications can be considered.

(1) In the above embodiment, although the primary transfer voltage and the secondary transfer voltage are direct currents, the invention is not limited thereto. For example, an alternating current may be superimposed on a direct current.
In this case, in color printing, the superimposed primary transfer voltage is supplied from primary transfer power supply unit 60 to each of primary transfer rollers 24Y to 24K, and in monochrome printing, the superimposed secondary transfer voltage is supplied from secondary transfer power supply unit 70. In order to supply only the primary transfer roller 24K via the step-down circuit 80, a circuit different from the above is configured, which can switch the supply path of the primary transfer voltage to the primary transfer roller 24K.

Although the primary transfer voltage and the secondary transfer voltage are positive voltages in the above-described embodiment, the invention is not limited thereto. For example, the voltage may be negative depending on the device configuration.
(2) In the above embodiment, an example in which monochrome image formation is K color has been described, but the present invention is not limited thereto, and image formation of any one of Y to M can be monochrome image. For example, in the case of a device configuration capable of forming a monochrome image of Y color, when monochrome image formation is selected, a toner image of Y color is formed using only the photosensitive drum 11 Y for Y color. In this apparatus configuration, when forming a monochrome image, 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 embodiment, 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. However, the present invention is not limited to this.
Any booster circuit capable of boosting up to the primary transfer voltage Va may be used. For example, a configuration including a boost chopper circuit is also possible. Similarly, the step-down circuit 80 is not limited to the above configuration, and can be designed to reduce power loss at the time of 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.
An image such as a toner image carried on each of a plurality of image carriers (photosensitive drum etc.) is transferred to an intermediate transfer using a primary transfer member (primary transfer roller etc.) provided corresponding to each image carrier After electrostatically primary transfer so as to overlap on a body (such as an intermediate transfer belt), each color image multi-transferred on the intermediate transfer member is printed on a sheet using a secondary transfer member (such as a secondary transfer roller) Primary image formation on the intermediate transfer member electrostatically using the primary transfer member corresponding to the image carrier and color image formation electrostatically secondarily transfer to the image carrier and the image carried on any one image carrier An electrophotographic printer, copier, etc. that can be executed by switching between monochrome image formation in which the image on the intermediate transfer body is electrostatically secondarily transferred onto a sheet using a secondary transfer member after transfer. Apply to general image forming devices It can be.

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

  According to the present invention, an image carried on each of a plurality of image carriers is electrostatically primary-transferred by being superimposed 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 configured to electrostatically secondarily transfer, onto a sheet, each color image that has been multiply transferred onto an intermediate transfer member using a secondary transfer member.

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 unit 60 Primary transfer power supply unit 60a Output terminal of primary transfer power supply unit 61 Transfer transformer 63 switching unit 70 secondary transfer power supply unit 80 step-down circuit 80b output terminal of step-down circuit 81 transistor 82 resistance 83, 88, 89 diodes 91, 92, 93, 94 power supply line 99 branch position 241 most photosensitive drum in the belt circulation direction Primary transfer position at the position N Transfer nip Va Primary image transfer voltage Vb for color image formation Secondary image transfer voltage Vd Primary image transfer voltage for monochrome image formation

Claims (5)

After an image of different colors carried on each of a plurality of image carriers is superimposed and primarily transferred onto an intermediate transfer body using a primary transfer member provided corresponding to each of the image carriers, the intermediate transfer body Forming a color image by secondarily transferring each color image on the sheet by using the secondary transfer member, and corresponding to the image carrier the image carried on one of the plurality of image carriers. After primary transfer onto the intermediate transfer body using the primary transfer member, it is possible to switch between monochrome image formation in which the image on the intermediate transfer body is secondarily transferred onto the sheet using the secondary transfer member. An electrophotographic image forming apparatus,
The voltage is commonly provided to the plurality of primary transfer members, and after the input voltage is boosted to the primary transfer voltage necessary for primary transfer at the time of color image formation, the primary transfer voltage is supplied to each of the plurality of primary transfer members. Primary transfer power supply unit,
And 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, and ,
A step-down circuit which receives the secondary transfer voltage generated by the secondary transfer power supply unit and supplies a voltage, which is reduced to a voltage necessary for primary transfer at the time of monochrome image formation, to a primary transfer member used for monochrome image formation; ,
The primary transfer power supply unit and the step-down circuit are controlled, and in the case of color image formation, the primary transfer power supply unit is driven and the operation of the step-down circuit is stopped. In the case of monochrome image formation, the primary transfer power supply unit Control means for stopping the 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 at the time of color image formation, and the secondary transfer voltage can be switched to Vb2 at the time of monochrome image formation,
The image forming apparatus according to claim 1, wherein a relationship of Vd <Vb <b> 2 <Vb <b> 1 is satisfied, where Vd is a voltage necessary for primary transfer at the time of monochrome image formation. After performing monochrome image formation on the Nth sheet among a plurality of sheets conveyed continuously, color image formation can be switched and executed on the (N + 1) th sheet,
Each of the plurality of image carriers is arranged in a line along the movement direction of the intermediate transfer member,
The control means
After the operation of the step-down circuit is stopped at the end of primary transfer during execution of the monochrome image formation, the image carrier of the uppermost transfer direction of the intermediate transfer member among the plurality of image carriers is formed by the color image formation. 3. The image forming method according to claim 1, wherein driving of the primary transfer power source unit is started while the image carried on the upper side reaches a position where primary transfer is performed to the intermediate transfer member. apparatus. A first power supply line electrically connecting an output terminal of the primary transfer power supply unit and a primary transfer member used for forming the monochrome image;
A second power supply line branched from the middle of the first power supply 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 of the primary transfer power supply than the branch position where the second power supply line branches, and the transfer is performed in the direction from the output terminal of the primary transfer power supply toward the branch position. A first diode for passing only current;
A second diode inserted in the second power supply line and passing only the transfer current from the output terminal of the step-down circuit toward the branch position;
The image forming apparatus according to any one of claims 1 to 3, further comprising: The primary transfer power supply unit
A transfer transformer for boosting an input voltage to the primary transfer voltage;
The control means
The image forming apparatus according to any one of claims 1 to 4, wherein in the case of color image formation, the transfer transformer is driven , and in the case of monochrome image formation, the drive of the transfer transformer is stopped .

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