JP7501330B2 - CONTROL DEVICE AND IMAGE FORMING APPARATUS - Google Patents

Description

The present invention relates to a control device and an image forming device.

A transfer FF control technology is known that improves transfer efficiency by using an image controller to change the transfer bias according to the amount of toner in each divided area of a print image divided in the sub-scanning direction.

Patent document 1 discloses a technology that detects temperature and humidity to predict the electrical resistance of recording paper and corrects the DC bias of the transfer FF control to improve transfer efficiency.

However, the secondary transfer load contains a capacitive component, and the optimal secondary transfer bias varies depending on the capacitive component. Therefore, there was a problem in that the transfer efficiency could not be improved when the capacitive component changed.

The present invention has been made in consideration of the above, and aims to provide a control device and an image forming device that can improve transfer efficiency even when the capacitance component of the load on the transfer section changes.

In order to solve the above-mentioned problems and achieve the object, the present invention provides a control device for a transfer bias unit that outputs a transfer bias that is a superimposed transfer DC bias and transfer AC bias, and is characterized by comprising a prediction unit that predicts the capacitance component of the transfer unit, a calculation unit that calculates correction information corresponding to the capacitance component of the transfer unit for each specified area of an image, and a control unit that controls the transfer bias using the correction information.

The present invention has the effect of improving transfer efficiency even when the capacitance component of the load on the transfer section changes.

FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment. FIG. 2 is a detailed explanatory diagram of the image forming unit. FIG. 3 is a diagram showing an example of the relationship between a toner image and the timing of changing the bias value of the secondary transfer bias. FIG. 4 is a diagram showing an example of the relationship of timing for changing the secondary transfer bias when the change in density of a toner image is large. FIG. 5 is a diagram showing the relationship between capacity and frequency. FIG. 6 is a diagram showing the relationship between the DC bias and the rate of change of the capacitance component. FIG. 7 is a diagram showing an example of settings of DC bias correction coefficients, which is an example of correction information. FIG. 8 is a diagram showing an example of a control result when control is performed using the DC bias correction coefficient. FIG. 9 is a diagram showing an example of the result when the divided region width is increased according to the control of the first modification. FIG. 10 is a diagram showing an example of settings of correction coefficients for AC bias, which is an example of correction information according to the second modification. FIG. 11 is a circuit diagram showing an example of the configuration of a secondary transfer power supply including a secondary transfer bias.

The following describes in detail the embodiments of the control device and image forming device with reference to the attached drawings.

(Embodiment)
FIG. 1 is a diagram showing an example of the configuration of an image forming apparatus according to an embodiment. The image forming apparatus is, for example, a printer or a multifunction peripheral (MFP). FIG. 1 shows an image forming apparatus 1 called an MFP having multiple functions as an example. The image forming apparatus 1 shown in FIG. 1 has a reading device main body 50 which is an image reading scanner, an image forming unit 80, and a paper feeding unit 90. An ADF (Automatic Document Feeder) 60 is provided on the upper part of the reading device main body 50, and a document set in the ADF 60 is read by automatic conveyance. The image forming apparatus 1 has a control circuit inside and controls the entire apparatus.

The image forming device 1 prints print data sent from a client PC and images read by the reading device main body 50 onto a recording medium such as transfer paper using the image forming unit 80.

Specifically, the image forming section 80 has an optical writing device 81, tandem imaging units (Y, M, C, K) 82, an intermediate transfer belt 83, and a secondary transfer belt 84. In the image forming section 80, the optical writing device 81 writes an image to be printed onto the photoconductor drum 820 of the imaging unit 82 by optical scanning, and the toner image of each plate is transferred from each photoconductor drum 820 onto the intermediate transfer belt 83.

In the example shown in FIG. 1, the imaging unit (Y, M, C, K) 82 has four rotatable photoconductor drums (Y, M, C, K) 820, and around each photoconductor drum 820, imaging elements including a charging roller, a developer, a primary transfer roller, a cleaner unit, and a static eliminator are provided. Around each photoconductor drum 820, each imaging element operates in a predetermined imaging process to form an image on each photoconductor drum 820, and the image formed on each photoconductor drum 820 is transferred as a toner image onto the intermediate transfer belt 83 by the primary transfer roller.

The intermediate transfer belt 83 is stretched across a drive roller and a driven roller in the nip between each photoconductor drum 820 and each primary transfer roller. Each toner image that has been primarily transferred onto the intermediate transfer belt 83 is secondarily transferred to a recording medium on the secondary transfer belt 84 at a secondary transfer section as the intermediate transfer belt 83 moves. The recording medium is transported to the fixing device 85 as the secondary transfer belt 84 moves, and the image is fixed onto the recording medium. The recording medium is then discharged to a paper discharge tray outside the machine.

The recording medium is, for example, a paper feed unit 90 that feeds out a specific recording paper from paper feed cassettes 91 and 92 that store recording paper of different sizes, and transports the paper using a transport means 93 consisting of various rollers to supply it to the secondary transfer belt 84.

Figure 2 is a detailed explanatory diagram of the image forming unit 80. As shown in Figure 2, the image forming unit 80 forms an image based on the image (pixel data) after RIP processing by the image processing controller 10.

The laser driver 13 drives a semiconductor laser, which is the light source of the optical writing device 81 (see FIG. 1). Specifically, the laser driver 13 scans a light beam on the surface of the charged photoconductor drum 820 to optically write an image. The light beam from the light source is deflected by a polygon mirror or the like to scan the surface of the photoconductor drum 820. The electrostatic charge on the photoconductor drum 820 is image-wise exposed by this light beam, forming an electrostatic latent image. Note that the light source may be a single light source, or a multi-beam light source having multiple light sources.

The photoconductor drum 820 is provided with a photoconductive layer including at least a charge generation layer and a charge transport layer on a conductive drum such as aluminum. The photoconductor drum 820 rotates in the direction of the arrow, and the charging bias 14 applies a bias to the charging roller, causing electrostatic charges to be applied to the surface of the photoconductor drum 820. The electrostatic latent image formed on the photoconductor drum 820 is developed by the developing bias 12 applying a bias to the developer, and a developer image 31 is formed on the surface of the photoconductor drum 820.

The developer image 31 carried on the photosensitive drum is transferred onto the intermediate transfer belt 83, which runs by a transport roller or the like. The intermediate transfer belt 83 runs in the direction of the arrow and transports the toner image to the secondary transfer section. In addition, a recording medium 32, such as high-quality paper or a plastic sheet, is supplied to the secondary transfer section from a paper feed cassette or the like. The secondary transfer section has a repulsive roller 86 and a secondary transfer roller 87, and the toner image on the intermediate transfer belt 83 is transferred to the recording medium 32 in the gap between the repulsive roller 86 and the secondary transfer roller 87.

The secondary transfer bias (secondary transfer bias section) 17 controls the application of a bias to the repulsive roller 86 by transfer FF control. The secondary transfer bias 17 applies a bias that is a superposition of an AC (alternating current) bias and a DC (direct current) bias to the repulsive roller 86. The toner image on the intermediate transfer belt 83 is transferred to the recording medium 32 by applying a bias from the secondary transfer bias 17 to the repulsive roller 86. The recording medium 32 is then supplied to the fixing device 85, where the image is fixed to the recording medium 32 by pressure and heat.

The control device shown in FIG. 2 includes a pixel counter 21, a prediction unit 22, a calculation unit 23, and a control unit 24. The control device is composed of an arithmetic unit including a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). Some or all of the pixel counter 21, the prediction unit 22, the calculation unit 23, and the control unit 24 may be realized as functional units by the CPU executing a program in the ROM, or may be provided by hardware such as an ASIC (Application Specific Integrated Circuit).

Note that in the following, "secondary transfer unit" is an example of application to the "transfer unit" in this electrophotographic system configuration, and if there is a transfer unit in other configurations that transfers an image to recording paper, it may be applied to that transfer unit, not just the secondary transfer unit. Also, in this configuration, to show an example of application to the secondary transfer unit, "transfer bias (unit)" will be referred to as "secondary transfer bias (unit)," "transfer DC bias" as "secondary transfer DC bias," and "transfer AC bias" as "secondary transfer AC bias," etc.

The pixel counter 21 inputs pixel data from the image processing controller 10 and counts the pixels.

The prediction unit 22 predicts the capacitance component of the secondary transfer unit. The calculation unit 23 calculates correction information corresponding to the capacitance component of the secondary transfer unit for each specified area of the image. Note that this example shows an example in which calculation is performed for each divided area of the image.

The control unit 24 controls the secondary transfer bias 17 based on the correction information. In this example, the bias value applied by the secondary transfer bias 17 to the repulsive roller 86 is controlled according to the amount of toner for each divided area.

In other words, the control device divides the image in the sub-scanning direction of the paper transport direction based on the pixel data 30 output by the image processing controller, and calculates the amount of toner for each divided area from the count value of the pixel counter 21. The amount of toner is calculated by monitoring the pixel count output by the pixel counter 21.

More specifically, the control device stores in advance in a memory the image transport speed during printing and the length of the image transport path (for example, the image transport speed of the intermediate transfer belt 83 and the length of the image transport path). The control device then measures the timing at which the leading edge of each divided area of the toner image reaches the position of the secondary transfer roller 87 from the image transport speed and the length of the image transport path. When the leading edge of a divided area reaches the position of the secondary transfer roller 87, the control device controls the secondary transfer bias value according to the toner amount determined in advance for that divided area. When the leading edge of the next divided area reaches the position of the secondary transfer roller 87, the control device controls the secondary transfer bias value according to the toner amount corresponding to that divided area.

Figure 3 is a diagram showing an example of the relationship between a toner image and the timing of changing the bias value of the secondary transfer bias 17. The toner image I shown in Figure 3 shows an example of the density distribution of a toner image transferred to the recording medium 32 at the position of the secondary transfer roller 87 shown in Figure 2. The density of the toner image I shown in Figure 3 gradually changes in the transport direction. The control device changes the bias value of the secondary transfer bias 17 at the tip of the divided region according to the change in the density distribution of the toner image I in the transport direction, if there is a large change in density. In other words, if the change in density is small, the bias value of the secondary transfer bias 17 is maintained, and if the change in density becomes large, the bias value is changed.

Therefore, for toner image I, in which the change in density is small, the time span for changing the bias value of secondary transfer bias 17 shown in FIG. 3 becomes longer, so that even if the bias value is changed, secondary transfer bias 17 reaches the target value.

Next, we will explain the case where the bias value of the secondary transfer bias 17 does not reach the target value. Figure 4 is a diagram showing an example of the relationship of the timing of changing the secondary transfer bias 17 when there is a large change in the density of the toner image. The toner image I shown in Figure 4 shows an image with a larger change in density in the transport direction than the toner image I shown in Figure 3. Here, a large change in density means that the time width of the density change is shorter at the same speed during transfer.

The control device controls the bias value of the secondary transfer bias 17 at the beginning of each divided area in the same manner as in FIG. 3 according to the density distribution in the transport direction of this toner image I. The difference from FIG. 3 is that the time width for changing the bias value of the secondary transfer bias 17 is shorter than the time width shown in FIG. 3 due to the large density change. In FIG. 4, the target value of the secondary transfer bias 17 shown in FIG. 3 is superimposed, but in reality it takes the value indicated by the curve and does not follow the target value. The cause of this is related to the capacitive component of the image forming unit 80. For example, there is the capacitive component of the components of the secondary transfer unit (such as the gap between the intermediate transfer belt 83 and the secondary transfer roller 87). In addition, the capacitor on the circuit of the secondary transfer unit (such as the bypass capacitor of AC transfer) also becomes a capacitive component.

Figures 5 and 6 are diagrams showing the characteristics of the capacitance component. Figure 5 is a diagram showing the relationship between capacitance and frequency, and Figure 6 is a graph showing the relationship between DC bias and the rate of change of the capacitance component. As shown in Figure 5, the capacitance component has frequency characteristics. As the frequency increases, the capacitance decreases. Figure 6 shows that the rate of change of the capacitance component decreases by increasing the DC bias value. This shows that the effect of the capacitance component can be suppressed by correcting the DC bias of the transfer FF control.

Figure 7 shows an example of setting a DC bias correction coefficient, which is an example of correction information. Figure 7(a) shows an example of the relationship between the capacitance component and the AC bias frequency. Figure 7(b) shows an example of the relationship between the capacitance component and the DC bias correction coefficient. Note that the curve shown in Figure 7(a) shows an example of the relationship in which the capacitance component decreases as the AC bias frequency increases. Also, the curve shown in Figure 7(b) shows an example of the relationship in which the capacitance component increases as the DC bias correction coefficient increases. It is not intended that the change will follow the curve shown in Figure 7(a) or the curve shown in Figure 7(b).

In the secondary transfer section, a capacitive component exists because there is a gap between the intermediate transfer belt and the secondary transfer roller. Therefore, using the relationship shown in Figure 7, the control device predicts the capacitive component as follows and controls the bias value of the secondary transfer bias 17. Note that the control device is assumed to know the output frequency of the AC bias.

The control device predicts the capacitive component of the load of the secondary transfer section (called the secondary transfer load) from the AC bias frequency using the relationship shown in FIG. 7(a). The control device calculates a DC bias correction coefficient from the capacitive component of the secondary transfer load using the relationship shown in FIG. 7(b). The control device sets the secondary transfer DC bias value as the value obtained by multiplying the secondary transfer DC bias setting value by the calculated DC bias correction coefficient.

Figure 8 shows an example of the control results when control is performed using the DC bias correction coefficient. In this control, the bias setting value at the tip of each divided region is increased by control using the DC bias correction coefficient. As a result, as shown in Figure 8, the bias value tracks the target value more closely than in Figure 6.

The control device may increase the bias at the tip of the divided region when the predicted value of the capacitive component of the secondary transfer load exceeds a threshold value. This can improve the transfer efficiency when the capacitive component of the secondary transfer load is larger than a predetermined threshold value.

With the above configuration, the image forming device and the calculation device of this embodiment can improve the transfer efficiency even when the capacitance component of the secondary transfer load changes.

(Variation 1)
The division area width may be increased for division. Alternatively, it may be used in combination with the configuration of the embodiment. If the load capacity of the secondary transfer is larger than predicted, it may be possible that the target secondary transfer bias value for the division area is not reached. For this reason, when the predicted value of the capacity component of the secondary transfer load exceeds the threshold, the control device may perform division by increasing the division area width.

Figure 9 is a diagram showing an example of the results when the division area width is increased and divided, which is the control according to the first modified example. The division area width refers to the division width in the transport direction of the toner image I shown in Figure 9. As shown in Figure 9, by increasing the division area width, the time interval between the timings at which the bias value is changed increases, and the bias value follows the target value as shown in Figure 9. Note that by combining this with the configuration of the embodiment, it is possible to increase the division area width to a minimum extent and cause the bias value to follow the target value with high accuracy. The division area width may also be increased only in some areas that exceed the prediction.

(Variation 2)
In the embodiment, an example has been shown in which the DC bias of the transfer FF control is corrected by the DC bias correction coefficient, but the AC bias of the transfer FF control may be corrected by the AC bias correction coefficient.

Figure 10 is a diagram showing an example of the setting of the AC bias correction coefficient, which is an example of the correction information according to the second modification. Figure 10(a) shows an example of the relationship between the capacitance component and the DC bias setting value. Figure 10(b) shows an example of the relationship between the capacitance component and the AC bias correction coefficient. Note that the curve shown in Figure 10(a) shows an example of the relationship in which the capacitance component decreases as the DC bias setting value increases. Also, the curve shown in 10(b) shows an example of the relationship in which the capacitance component increases as the AC bias correction coefficient increases. It is not intended that the change will follow the curve shown in Figure 10(a) or the curve shown in Figure 10(b).

In the second modification, the control device controls the bias value of the secondary transfer bias 17 as follows, using the relationship shown in FIG. 10. Note that the control device is assumed to know the output setting value of the DC bias.

The control device predicts the capacitive component of the secondary transfer load from the DC bias using the relationship shown in FIG. 10(a). The control device calculates an AC bias correction coefficient from the capacitive component of the secondary transfer load using the relationship shown in FIG. 10(b). The control device sets the secondary transfer AC bias as a value obtained by multiplying the setting of the secondary transfer AC bias by the calculated AC bias correction coefficient.

By using the above control, it is possible to obtain the same effect of improving transfer efficiency even when the capacitive component of the secondary transfer load changes.

(Circuit of the secondary transfer power supply 100 including the secondary transfer bias 17 applicable to each embodiment and modification)
When AC bias and DC bias are superimposed, it is necessary to connect an AC bypass capacitor to secure a path for the AC bias circuit. In order to pass a high-voltage secondary transfer current, a capacitor with a large capacity may be selected for the AC bypass capacitor. In this case, the capacity of the AC bypass capacitor becomes dominant as the capacitance component of the secondary transfer load. The AC bypass capacitor has more stable frequency characteristics and DC bias characteristics than the capacitance component due to the gap between the intermediate transfer belt and the secondary transfer roller. Therefore, the control device can accurately predict the capacitance component of the secondary transfer load.

Here, there may be individual differences and variations in the secondary transfer capacity load of the actual machine. There may be a mode for detecting the frequency characteristics and DC bias characteristics of the secondary transfer load capacity during operation of the actual machine. For example, a detection circuit for AC bias current is provided in the secondary transfer bias 17. The frequency characteristics can be grasped by changing the frequency of the AC bias in multiple steps and monitoring the AC bias current when the AC bias is output. The DC bias characteristics can be grasped by changing the DC bias in multiple steps and monitoring the AC bias current when the AC bias is output.

Figure 11 is a circuit diagram showing an example of the configuration of the secondary transfer power supply 100 including the secondary transfer bias 17. The DC (-)_PWM signal is input from the power supply control unit 200 to the DC power supply 110, and the input DC (-)_PWM signal is integrated and input to the current control circuit 122 (comparator). The value of the integrated DC (-)_PWM signal becomes the reference voltage in the current control circuit 122. In addition, the DC current detection circuit 128 detects the DC current output by the DC power supply 110 on the output line of the secondary transfer power supply 100, and inputs the output value of the detected DC current to the current control circuit 122. Then, the current control circuit 122 actively drives the DC drive circuit 123 of the DC high-voltage transformer when the DC current is small relative to the reference voltage, and regulates the drive of the DC drive circuit 123 of the DC high-voltage transformer when the DC current is large relative to the reference voltage. This ensures that the DC power supply 110 has a constant current characteristic.

The DC voltage detection circuit 126 detects the DC voltage output by the DC power supply 110 and inputs the detected DC voltage output value to the voltage control circuit 121 (comparator). When the DC voltage output value reaches an upper limit, the voltage control circuit 121 regulates the drive of the DC drive circuit 123 of the DC high-voltage transformer. The DC voltage detection circuit 127 feeds back the DC voltage output value detected by the DC voltage detection circuit 126 to the power supply control unit 200 as an FB_DC(-) signal.

By driving the DC drive circuit 123 under the control of the current control circuit 122 and the voltage control circuit 121, the output generated by the primary winding N1_DC(-) 124 of the DC high-voltage transformer and the secondary winding N2_DC(-) 125 of the DC high-voltage transformer is smoothed by a diode and a capacitor, and then input as a DC voltage from the AC power supply input unit 157 to the AC power supply 140, and applied to the secondary winding N2_AC 156 of the AC high-voltage transformer.

An AC_PWM signal is input from the power supply control unit 200 to the AC power supply 140 and input to the voltage control circuit 151 (comparator). The value of the input AC_PWM signal becomes the reference voltage in the voltage control circuit 151. In addition, the AC voltage detection circuit 162 predicts the output value of the AC voltage from the mutual induction voltage generated by the primary winding N3_AC155 of the AC high-voltage transformer, and inputs the predicted output value of the AC voltage to the voltage control circuit 151. This is because it is difficult to detect only the output (AC voltage) of the AC power supply 140 itself on the output line of the secondary transfer power supply 100 because the AC voltage is superimposed on the DC voltage. Then, the voltage control circuit 151 actively drives the AC drive circuit 153 of the AC high-voltage transformer when the AC voltage is smaller than the reference voltage, and regulates the drive of the AC drive circuit 153 of the AC high-voltage transformer when the AC voltage is larger than the reference voltage. This ensures that the AC power supply 140 has a constant voltage.

The AC current detection circuit 160 detects the AC current on the low-voltage side of the AC bypass capacitor 159, which is the output line of the secondary transfer power supply 100, and inputs the detected AC current output value to the current control circuit 152 (comparator). This AC bypass capacitor 159 corresponds to the AC bypass capacitor described above. When the AC current output value reaches an upper limit, the current control circuit 152 regulates the drive of the AC drive circuit 153 of the AC high-voltage transformer. The AC current detection circuit 161 also feeds back the detected AC current output value to the power supply control unit 200 as an FB_AC signal.

The AC drive circuit 153 of the AC high-voltage transformer is driven according to the AND logic of the AC_CLK signal input from the power supply control unit 200 and the voltage control circuit 151 and current control circuit 152, and generates an output with the same period as AC_CLK.

When the AC drive circuit 153 is driven, the AC voltage generated in the primary winding N1_AC154 of the AC high-voltage transformer is superimposed on the DC voltage applied to the secondary winding N2_AC156, and is output (applied) as a superimposed voltage from the high-voltage output unit 158 to the repulsive roller 86. However, when the AC power supply 140 is not driven, the DC voltage applied to the secondary winding N2_AC156 is output (applied) as is from the high-voltage output unit 158 to the repulsive roller 86.

Generally, the secondary winding of the step-up transformer is connected to the ground and the high voltage output terminal, so it is not expected that the low voltage side (input side) of the secondary winding will be at a high voltage. However, in the first embodiment, when the secondary transfer power supply 100 outputs a superimposed voltage, the high DC voltage generated by the DC power supply 110 is input to the low voltage side (input side) of the secondary winding N2_AC156 of the AC high voltage transformer, and an AC voltage is further superimposed on it, so that the low voltage side (input side) of the secondary winding will be at a higher voltage than usual. As a result, if a general AC high voltage transformer is used, the secondary winding will not be insulated, and there is a risk of current leakage inside the AC high voltage transformer.

For this reason, the voltage resistance of the AC high-voltage transformer has been improved so that it can withstand not only the maximum output voltage of the secondary transfer power supply 100 (maximum value of the superimposed voltage), i.e., the maximum output voltage of the AC power supply 140, but also the maximum output voltage of the AC power supply 140 and the maximum output voltage of the DC power supply 110.

Specifically, the spacing between the windings on the low voltage side (input side) of the secondary winding N2_AC156 of the AC high voltage transformer is made wider than that of a typical AC high voltage transformer, so that it can withstand the maximum output voltage of the secondary transfer power supply 100.

To explain in more detail, normally, the voltage on the output side of a step-up transformer is higher than that on the input side, so the spacing between the windings becomes wider as you move closer to the output side. For this reason, in the first embodiment, the spacing between the windings on the low-voltage side (input side) of the secondary winding N2_AC156 is set to a spacing that can withstand the maximum output voltage of the DC power supply 110, and the spacing between the windings on the high-voltage side (output side) of the secondary winding N2_AC156 is set to a spacing that can withstand the maximum output voltage (maximum value of the superimposed voltage) of the secondary transfer power supply 100.

The target value of the DC current when only the DC voltage is output (corresponding to the reference voltage in the current control circuit 122) is several tens of percent higher than the target value of the DC current when the DC voltage is superimposed on the AC voltage and output. Similarly, the value of the DC voltage when the output of the DC current reaches the target value is also higher when only the DC voltage is output than when the DC voltage is superimposed on the AC voltage and output.

For this reason, at first glance, the maximum output voltage of the AC power supply 140 and the maximum output voltage of the DC power supply 110 are not applied to the AC high-voltage transformer at the same time, and it does not seem that the AC high-voltage transformer is required to have a voltage resistance sufficient to withstand the application of the maximum output voltage of the AC power supply 140 and the maximum output voltage of the DC power supply 110.

However, even when an AC voltage is superimposed on a DC voltage, depending on conditions such as the resistance of the paper, the maximum output voltage of the AC power supply 140 and the maximum output voltage of the DC power supply 110 may be temporarily applied to the AC high-voltage transformer simultaneously. For this reason, in the first embodiment, the voltage resistance of the AC high-voltage transformer is improved so that it can withstand the application of the maximum output voltage of the AC power supply 140 and the maximum output voltage of the DC power supply 110.

In addition to the secondary winding N2_AC156 of the AC high-voltage transformer, the voltage resistance has also been improved for the peripheral circuits of the secondary winding N2_AC156, such as the AC drive circuit 153, the primary winding N1_AC154, and the primary winding N3_AC155.

Specifically, the peripheral circuits of the secondary winding N2_AC156 are arranged with an insulation distance sufficient to withstand the maximum output voltage of the secondary transfer power supply 100 being output to the secondary winding N2_AC156 of the AC high-voltage transformer. In the first embodiment, the AC high-voltage transformer is composed of the AC drive circuit 153, the primary winding N1_AC154, the primary winding N3_AC155, and the secondary winding N2_AC156, and therefore are arranged with a sufficient insulation distance within the AC high-voltage transformer. The specific insulation distance can be determined according to the maximum output voltage of the secondary transfer power supply 100, the structure and material of the AC high-voltage transformer, the number of turns of the secondary winding N2_AC156, and the thickness and material of the insulator within the AC high-voltage transformer.

In addition, because both the DC voltage and the AC voltage are output through an AC high-voltage transformer, the resistance value of the secondary winding N2_AC156 is reduced by using a winding of an appropriate thickness for the maximum output voltage of the secondary transfer power supply 100, and the generation of large amounts of heat is also prevented.

As described above, the secondary transfer power supply 100 has a DC power supply 110 and an AC power supply 140 connected in series with the DC power supply 110, and the AC power supply 140 selectively outputs a superimposed voltage in which an AC voltage is superimposed on the DC voltage output from the DC power supply 110, or the DC voltage output from the DC power supply 110, and transfers the toner to the paper using the voltage output from the AC power supply 140.

Although the embodiments and modifications of the present invention have been described above, they are presented as examples and are not intended to limit the scope of the invention. These novel embodiments and modifications can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents as set forth in the claims.

REFERENCE SIGNS LIST 1 Image forming apparatus 10 Image processing controller 12 Development bias 13 Laser driving unit 14 Charging bias 15 Primary transfer bias 17 Secondary transfer bias 21 Pixel counter 22 Prediction unit 23 Calculation unit 24 Control unit 30 Image data (pixel data)
32 Recording medium 80 Image forming unit 83 Intermediate transfer belt 86 Repulsion roller 87 Secondary transfer roller 820 Photoconductor drum

JP 2012-042835 A

Claims (7)

A control device for a transfer bias unit that outputs a transfer bias obtained by superimposing a transfer DC bias and a transfer AC bias,
A prediction unit that predicts a capacitance component of a transfer unit;
a calculation unit that calculates correction information corresponding to a capacitance component of the transfer unit for each predetermined area of an image;
a control unit for controlling the transfer bias based on the correction information;
A control device comprising: the calculation unit calculates the correction information for each divided region by counting the amount of toner for each divided region in an image based on image data;
The control device according to claim 1 . the prediction unit predicts the capacitance component based on a frequency of the transfer AC bias.
3. The control device according to claim 1 or 2. the prediction unit predicts the capacitance component based on a bias setting value of the transfer DC bias;
3. The control device according to claim 1 or 2. the control unit performs control to change the transfer bias at the leading end of the divided region based on the correction information.
5. A control device according to claim 2, wherein the control device is a control unit. the calculation unit changes a division region width of the division region based on the predicted value of the capacitance component.
6. The control device according to claim 2, wherein the control device is a control unit. A control device according to any one of claims 1 to 6;
an image forming unit that forms an image on a recording medium by the transfer unit;
An image forming apparatus comprising:

Images