JP6699202B2 - Image forming device - Google Patents

Description

  The present invention relates to an image forming apparatus including a transfer unit.

  In the image forming apparatus, a toner image is formed on an image carrier based on image information, the toner image is transferred onto a recording material such as paper or an OHP sheet, and the recording material carrying the toner image is passed through a fixing device. The toner image is fixed on the recording material by heat and pressure.

  In a transfer unit as a transfer unit that transfers a toner image, if the load increases due to deterioration of the transfer roller over time, an abnormal voltage may be output and an abnormal image due to discharge may occur.

  On the other hand, a method of applying a predictive current, detecting the current-voltage characteristics, and controlling to an appropriate current according to the type of paper and the usage environment, etc. is adopted before the start of paper passing (for example, See Patent Document 1).

  The image forming apparatus described in Patent Document 1 applies constant currents of different magnitudes to the transfer roller when the paper is not passed, and measures the voltage when each is applied to calculate the current-voltage characteristic of the transfer roller. There is.

  By the way, the current values having different magnitudes are set near the minimum value and the maximum value which flow to the transfer roller when the paper is passed.

  Therefore, in the image forming apparatus described in Patent Document 1, when the load is increased due to deterioration of the transfer roller over time or the like, by applying a current near the maximum value, an excessive voltage is applied even when a predictive current is applied before the start of sheet passing. Is output, and there is a problem that discharge occurs.

  It is an object of the present invention to provide an image forming apparatus that does not cause an abnormality when a current is applied over time.

In order to solve the above-mentioned problems, the image forming apparatus according to claim 1 of the present invention is
An image forming apparatus having a transfer means for transferring a toner image on an image carrier onto a transfer material,
The output voltage from the transfer power source output to the transfer unit, has a control unit for controlling according to a predetermined condition ,
The control means is
At the time of non-paper passing, at least two different currents are applied with a current value lower than the current value at the time of paper passing,
Based on the detection voltage detected by the application, predict the output voltage during paper passing ,
When the predicted output voltage does not exceed the predetermined limiter voltage, the output voltage is controlled to be the value calculated by the predetermined condition,
If the predicted output voltage exceeds the predetermined limiter voltage, the output voltage is controlled to be the limiter voltage , and
Among the at least two currents having different values, a current having a larger value is first applied .

  According to the present invention, it is possible to provide an image forming apparatus that does not cause an abnormality when a current is applied over time.

FIG. 1 is a configuration diagram schematically showing an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a configuration diagram schematically showing an image forming unit of the image forming apparatus shown in FIG. 1. FIG. 3 is an explanatory diagram illustrating prediction of an output voltage when the image forming apparatus illustrated in FIG. 1 passes a sheet. FIG. 3 is an explanatory diagram illustrating prediction of an output voltage when the image forming apparatus illustrated in FIG. 1 passes a sheet. FIG. 3 is an explanatory diagram illustrating prediction of an output voltage when the image forming apparatus illustrated in FIG. 1 passes a sheet. 2 is a block diagram illustrating a functional configuration of a control unit of the image forming apparatus illustrated in FIG. 6 is a flowchart illustrating a printing process of the first embodiment of the image forming apparatus illustrated in FIG. 1. FIG. 9 is an explanatory diagram illustrating a modified example of the image forming apparatus illustrated in FIG. 1. FIG. 9 is an explanatory diagram illustrating a modified example of the image forming apparatus illustrated in FIG. 1. FIG. 9 is an explanatory diagram illustrating a modified example of the image forming apparatus illustrated in FIG. 1. FIG. 9 is an explanatory diagram illustrating a modified example of the image forming apparatus illustrated in FIG. 1. 9 is a flowchart illustrating a printing process according to the second embodiment. 7 is a graph showing an output voltage when a conventional printing process is performed. 6 is a graph showing an output voltage when the printing process of the first embodiment is performed. 7 is a graph showing an output voltage when the printing process of the second embodiment is performed.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In each of the drawings for explaining the present embodiment, components such as members or components having the same function or shape are given the same reference numerals as far as possible to distinguish them from each other. Is omitted.

  FIG. 1 shows a monochrome printer as an example of an image forming apparatus according to an embodiment of the present invention, and a description will be given based on this, of course, the present invention is similarly applied to a known color image forming apparatus. It is possible.

  First, the configuration and operation of the entire image forming apparatus will be described with reference to FIGS. FIG. 1 is a configuration diagram showing a printer as an image forming apparatus, and FIG. 2 is an enlarged view showing an image forming unit thereof.

  As shown in FIG. 1, an intermediate transfer belt device 15 is installed at the center of the image forming apparatus 100. One image forming unit 6 corresponding to black is detachably arranged so as to face the image carrier and the intermediate transfer belt 8 as a transfer material. Further, a paper feeding unit 10 is installed below the image forming apparatus. Further, a fixing device 20 as a fixing unit is provided at the end of the paper conveyance path along which the recording medium P as the transfer material from the paper feeding unit 10 is conveyed.

  The intermediate transfer belt device 15 includes an endless intermediate transfer belt 8 and a plurality of roller members. The intermediate transfer belt 8 is stretched and supported by a plurality of roller members, and is moved by rotationally driving one roller member 1.

  As shown in FIG. 2, the image forming unit 6 includes a photoconductor drum 1 as an image carrier, a charging unit 4, a developing unit 5, a cleaning unit 2, a charge eliminating unit, etc. arranged around the photoconductor drum 1. It is composed of. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on the photosensitive drum 1, and an image (toner image) is formed on the photosensitive drum 1.

  As shown in FIG. 1, the sheet feeding unit 10 sequentially feeds the sheet feeding tray 26 in which sheets P serving as recording media are stored and the sheets P accommodated in the sheet feeding tray 26 in order from the top. It has a paper feed roller 27 and the like for separating and feeding the sheets one by one.

  The fixing device 20 includes a fixing roller and a pressure roller.

  As shown in FIG. 2, the photosensitive drum 1 is rotationally driven counterclockwise by a drive motor. Then, the surface of the photosensitive drum 1 is uniformly charged at the position of the charging unit 4 (charging step). In the present embodiment, the contact type charging roller that comes into contact with the photosensitive drum 1 is used as the charging unit 4. However, the non-contact type charging roller that faces the photosensitive drum 1 with a predetermined gap is used as the charging unit. A charging roller may be used, or a corona discharge type charging charger may be used. After that, the surface of the photoconductor drum 1 reaches the irradiation position of the laser beam L emitted from the exposure unit 7, and an electrostatic latent image is formed by exposure scanning at this position (exposure step).

  After that, the surface of the photosensitive drum 1 reaches a position facing the developing unit 5, and the electrostatic latent image is developed at this position to form a toner image (developing step). After that, the surface of the photosensitive drum 1 reaches a position facing the intermediate transfer belt 8 and the primary transfer roller 9 as a transfer unit, and at this position, the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 8. Transferred (primary transfer process).

  After that, the surface of the photoconductor drum 1 reaches a position facing the cleaning unit 2, and the untransferred toner remaining on the photoconductor drum 1 at this position is collected in the cleaning unit 2 by the cleaning blade 2a (cleaning). Process). Then, the surface of the photoconductor drum 1 reaches a position facing the charge eliminating portion, and the residual potential on the photoconductor drum 1 is removed at this position.

  The primary transfer roller 9 sandwiches the intermediate transfer belt 8 with the photosensitive drum 1 to form a primary transfer nip. To the primary transfer roller 9, a control unit 50, which will be described later as control means, controls the primary transfer power supply 41, and a predetermined transfer voltage opposite to the polarity of the toner is applied. Then, the intermediate transfer belt 8 travels in the direction of the arrow, and the toner image on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 8 at the position of the primary transfer nip of the primary transfer roller 9. ..

  The intermediate transfer belt 8 to which the toner image is primarily transferred reaches a position facing a secondary transfer roller 19 as a transfer unit, as shown in FIG. At this position, the secondary transfer counter roller 16 sandwiches the intermediate transfer belt 8 with the secondary transfer roller 19 to form a secondary transfer nip. The controller 50 controls the secondary transfer power source 42 to apply the transfer voltage having the same polarity as the normal charging polarity to the secondary transfer counter roller 16. A transfer voltage having a polarity opposite to the normal charging polarity of toner may be applied to the secondary transfer roller 19. The secondary transfer roller 19 is electrically grounded.

  A plurality of recording media P such as transfer papers are stacked and housed in the paper supply unit 10. When the paper feed roller 27 is driven to rotate counterclockwise in FIG. 1, the uppermost recording medium P is fed between the registration roller pair (timing roller pair) 28.

  The recording medium P conveyed to the pair of registration rollers 28 is temporarily stopped at the position of the roller nip of the pair of registration rollers 28 whose rotation has been stopped. Then, the registration roller pair 28 is rotationally driven in synchronization with the image on the intermediate transfer belt 8 to convey the recording medium P toward the secondary transfer nip, and the desired image is transferred onto the recording medium P. To be done.

  The untransferred toner remaining on the intermediate transfer belt 8 without being transferred at the secondary transfer nip reaches the position of the intermediate transfer cleaning portion as the intermediate transfer belt 8 runs, and the untransferred toner on the intermediate transfer belt 8 is removed. To be removed.

  The recording medium P on which the image is transferred at the position of the secondary transfer nip is conveyed to the fixing device 20. Then, at this position, the image transferred to the surface is fixed on the recording medium P by heat and pressure by the fixing roller and the pressure roller. The recording medium P on which the image is transferred is ejected out of the apparatus by the pair of paper ejection rollers. The recording media P ejected outside the apparatus by the pair of paper ejection rollers are sequentially stacked as an output image on the stack unit.

Next, the functional configuration of the control unit 50 will be described.
As shown in FIG. 6, the control unit 50 has a CPU 50a as an arithmetic unit, a ROM 50b as a storage unit, a RAM 50c as a non-volatile memory, and the like. As shown in FIG. 1, the image forming apparatus 100 includes an operation panel 17 on the top of the apparatus. The operation panel 17 includes an input unit 18 for inputting the paper type and paper thickness of the paper (transfer material) to be used. The control unit 50 is connected to the input unit 18, and acquires the information on the paper type and the paper thickness input by the user or the like. The image forming apparatus 100 also includes a temperature/humidity sensor 45 that detects temperature and humidity. The control unit 50 is connected to the temperature/humidity sensor 45 and acquires information on the temperature/humidity detected by the temperature/humidity sensor 45. The control unit 50 applies the result to the secondary transfer facing roller 16 based on the image information, the detection result of the temperature and humidity by the temperature/humidity sensor 45, the acquisition result of the information of the paper type and the paper thickness from the input unit 18, and the like. The transfer current value I(T2) is calculated. Note that a sensor for detecting the paper type and the paper thickness is provided in the image forming apparatus instead of the configuration for acquiring the information on the paper type and the paper thickness from the input unit 18, and the information about the paper type and the paper thickness is detected by the sensor. It may be configured to acquire. The same control may be applied to the transfer current value applied to the primary transfer roller 9. The control unit 50 controls the entire apparatus, and controls the drive of each device based on a control program stored in the RAM 50c or the ROM 50b.

The transfer current value I(T2) is calculated as follows.
[Transfer current value (standard control value)] (μA)=standard value (μA)×linear velocity correction coefficient (%)×environmental correction coefficient (%)×paper size correction coefficient (%)
Standard value: 100 μA
Linear velocity correction coefficient: The coefficient is determined by the set linear velocity (=surface moving velocity of the photosensitive drum 1 and the intermediate transfer belt 8). Example: Type-a: 432 mm/s 68%, Type-b: 500 mm/s 78%, Type-c: 640 mm/s 100%
Environmental correction coefficient: Determined based on the temperature and humidity detection result of the sensor 45 installed in the machine. Example: 100% in a standard environment (MM environment; 23° C., 50% RH) and 80% in a low temperature and low humidity environment (LL environment, 10° C., 15% RH). The environment may be classified into three or more stages.
Paper size correction coefficient: Determined based on the width of the paper used. Example: Output of 95% for A4Y (A4 paper is passed horizontally. 297 mm width), and 82% for A4T (A4 paper is passed vertically, width 210 mm). The division may be made into three or more stages.
That is, the control unit 50 calculates the transfer current value I(T2) according to predetermined conditions such as the linear velocity, temperature and humidity environment, paper size, paper type, paper thickness, and resistance of the secondary transfer unit. The predetermined conditions are linear velocity, temperature or humidity, size of transfer material, type of transfer material, thickness of transfer material, resistance of transfer section for transferring toner image from image carrier to transfer material, and transfer material. At least one of the positions on the transfer material in the transport direction is included.

Next, the prediction of the output voltage when the paper is passed will be described.
As shown in FIG. 3, the control unit 50 calculates a transfer current value I(T2), a current T2(FB1) corresponding to a voltage smaller than the output voltage V(T2) at the time of sheet passing, and a voltage smaller than this. The current T2 (FB2) corresponding to is applied when paper is not passing. The control unit 50 calculates the voltage detected by this application. That is, the control unit 50, the voltage _V T2 (FB1) that corresponds to the current T2 (FB1), and calculates the voltage _V T2 (FB2) which corresponds to the current T2 (FB2). Then, the current-voltage characteristic of the secondary transfer portion is calculated based on this detected voltage. That is, the slope/intercept is calculated from the relationship between the current and the voltage at the two points, and the current I(T2) during paper passing and the output voltage V(T2) during paper passing are predicted. The secondary transfer portion is a position (a core of the secondary transfer roller 19) from a position (a core metal of the secondary transfer counter roller 16) where the secondary transfer voltage is output by the secondary transfer power source 42 to a ground. It is a part that forms a current path that is formed up to (gold). That is, as shown in FIG. 1, the secondary transfer portion is a portion composed of the secondary transfer counter roller 16, the intermediate transfer belt 8 and the secondary transfer roller 19.

  The application of T2(FB1) and T2(FB2) is performed when the paper is not passed, but the polarity opposite to that at the time of transfer is applied to clean the toner and the like adhering to the secondary transfer roller 19 before the application of T2(FB1). A (positive polarity) bias may be applied. In order to quickly raise the bias of T2(FB1), the bias may be set to zero (=not applied) before the application of T2(FB1). Further, the current applied when the paper is not passed is not limited to two times, and may be three times or more.

Regarding the application of the electric current T2(FB1) and the electric current T2(FB2) smaller than this, the following will be supplemented.
Example: While the standard value of the transfer current value is -100 μA, -40 μA is applied as the current T2 (FB1) and -20 μA is applied as the T2 (FB2). T2(FB1) and T2(FB2) are preferably set to a value of 10% to 50% of the transfer current value.
In the device of the present embodiment, T2(FB1) and T2(FB2) use fixed values regardless of the usage state (cumulative usage time) of the device.

  In addition, by setting the upper limit voltage set during sheet passing, that is, the limiter voltage V(lmt) that is the upper limit of the output voltage in advance, it is possible to avoid the occurrence of abnormal images such as discharge and leaks due to the output voltage becoming too large. To do.

  Specifically, the control unit 50 determines whether or not the output voltage predicted when the paper is not passed exceeds the limiter voltage V(lmt). When the control unit 50 determines that the output voltage V(T2)>the limiter voltage V(lmt), as shown in FIG. 4, the output voltage V(T2) becomes the limiter voltage V(lmt). The control unit 50 applies the limiter current value T2′(l(lmt)). The limiter current is the upper limit of the supplied current, and the limiter voltage is the upper limit of the supplied voltage.

  On the other hand, when the control unit 50 determines that the output voltage V(T2)<the limiter voltage V(lmt), as shown in FIG. 5, the output voltage V(T2) is the paper type, the paper thickness, the machine environment. The controller 50 applies the current value T2 so that the value becomes a value calculated from a predetermined condition such as.

  Next, from the signal of the print start performed by the control unit 50, regarding the voltage prediction before passing the sheet, and the printing process regarding the correction and application of the current value based on the predicted value, the first embodiment formation, the flowchart shown in FIG. Will be described. It should be noted that the flow charts are merely explanations of an example of a routine capable of exhibiting the action of the present invention in the present embodiment, and other flow charts can be applied as long as the action of the present invention can be exerted. Needless to say.

  First, the control unit 50 calculates the transfer current value I(T2) as described above before starting the printing process and before the sheet reaches the primary transfer nip and/or the secondary transfer nip (step S30). . Next, as described above, the output voltage prediction during sheet passing is executed (step S31). Next, the control unit 50 determines whether or not the predicted output voltage V(T2)>limiter voltage V(lmt) is satisfied (step S32).

When it is determined that the predicted output voltage V(T2)>the limiter voltage V(lmt), the control unit 50 applies the limiter current value T2′(I(lmt)) as the transfer current output and outputs the output voltage V(T2). ) Is corrected to the limiter voltage V(lmt) (step S33).
On the other hand, when it is determined that the predicted output voltage V(T2)>limiter voltage is not satisfied, the control unit 50 uses the transfer current value T2(I) calculated from a predetermined condition such as the paper type, the paper thickness, and the machine environment as the transfer current output. (Def)) is applied to control the output voltage V(T2) (step S34).

  Next, the control unit 50 determines whether or not the actual output voltage>the limiter voltage V(lmt) (step S35). The actual output voltage is the output voltage when the paper is passed.

  If it is determined that the actual output voltage>the limiter voltage V(lmt), the process proceeds to step S37. On the other hand, when it is determined that the actual output voltage>limiter voltage V(lmt) is not satisfied, it is determined whether or not the actual output current<current value I(def) calculated from predetermined conditions such as paper type, paper thickness and environment. The control unit 50 determines (step S36). The actual output current refers to the output current during sheet passing.

  If it is determined that the actual output current is smaller than the current value I(def) calculated from the predetermined conditions such as the paper type, the paper thickness, and the environment, the process proceeds to step S37. On the other hand, if it is determined that the actual output current is less than the current value I(def) calculated from a predetermined condition such as paper type, paper thickness, environment, etc., the process returns to step S35.

  Next, the control unit 50 determines whether or not the actual output voltage>the limiter voltage V(lmt) (step S37).

  When it is determined that the actual output voltage>the limiter voltage V(lmt), the control unit 50 corrects the control current value to be smaller than the current value and converges to the limiter voltage (step S38). On the other hand, when it is determined that the actual output voltage>limiter voltage V(lmt) is not satisfied, it is determined whether or not the actual output current>current value I(def) calculated from predetermined conditions such as paper type, paper thickness and environment. The control unit 50 determines (step S39).

  If it is determined that the actual output current>current value I(def) calculated from a predetermined condition such as paper type, paper thickness, environment, etc., the control current value is made larger than the current value and the limiter voltage is focused. The control unit 50 makes a correction (step S40). On the other hand, when it is determined that the actual output current>the current value I(def) calculated from the predetermined conditions such as paper type, paper thickness, environment, etc., the control current value is determined from the predetermined conditions such as paper type, paper thickness, environment, etc. The control unit 50 controls the calculated current value I(def) (step S41).

  Then, it is determined whether or not to end the printing process (step S42). If the print process is not to be ended, the process returns to step S37, and if the print process is to be ended, the process is ended.

  Next, the operation of the image forming apparatus according to this exemplary embodiment will be described.

  By the control unit 50 of the image forming apparatus 100 of the present embodiment performing the control as described above, the voltage output at the time of sheet passing can be predicted, so that an appropriate transfer current can be obtained. Further, since the predicted current is smaller than that at the time of passing the paper, an excessive voltage is output at the time of applying the predictive current before the start of the paper passing, and the discharge does not occur. Further, even when the paper is passed, an excessive voltage is output and a discharge does not occur when a current value corrected as necessary based on the output prediction is applied.

  Further, when the control unit 50 predicts that the output voltage exceeds the limiter voltage when the paper is not passed, and applies a current obtained by correcting the output voltage to a current value corresponding to the limiter voltage, the actual output voltage is higher than the limiter voltage. When it is low, the control unit 50 controls the current so that the output voltage becomes the value calculated under the predetermined condition. Therefore, it can be avoided that the output voltage becomes lower than the limiter voltage.

  In addition, when the control unit 50 predicts that the output voltage does not exceed the limiter voltage when the paper is not passed and applies a current obtained by correcting the output voltage to a current value corresponding to the voltage calculated under the predetermined condition, the actual When the output voltage exceeds the limiter voltage, the control unit 50 controls the current so that the output voltage converges to the limiter voltage. Therefore, the current value can be increased so that the desired voltage output can be obtained, and even if the current value is increased by correction, a voltage exceeding the limiter voltage is not applied, so an appropriate voltage can be applied. ..

  By the way, a device having a high linear velocity such as a production printer is designed to apply a current value larger than that applied to a device having a slow linear velocity. When the control of the present embodiment is applied to such an apparatus, if the current value at the time of prediction before the start of sheet passing is small, there is a problem that the rise is delayed.

  The image forming apparatus according to the present embodiment first applies a large current, and then applies a smaller current.

  Specifically, description will be made using actual measurement values. It should be noted that 90% of the output target of the power supply is the rising output. The time required to reach the rising output is defined as the rising time.

  For example, as shown in FIG. 8, when the target output is -20 μA, the rising time is 149 ms.

  On the other hand, as shown in FIG. 9, the rise time when the target output is -40 μA is 58.4 ms.

  From this relationship, it can be seen that the higher the target output, the faster the rise time. Therefore, when applying the predictive current before the start of paper feeding, by applying the larger current value of the set multiple predictive current values first, and then applying the smaller current value, You can save time. In addition, stable output can be obtained, and highly accurate prediction can be performed with a low current that does not cause discharge. Also, when applying the predictive current before the start of paper feeding, the current value lower than that during paper feeding is used for prediction, but one of the multiple current values for prediction that is closer to the current value used during paper feeding is used. By first applying the current value of 1, the rise time and the time until it stabilizes can be shortened.

  Also, when switching the target output, a large current is switched to a smaller current.

  For example, as shown in FIG. 10, when the target output is set to -20 μA and then the target output is switched from -20 μA to -40 μA, the time from the switching from -20 μA to -40 μA to the rising time is 134 ms. Has become.

  On the other hand, as shown in FIG. 11, when the target output is set to −40 μA and then the target output is switched from −40 μA to −20 μA, the time from the switching from −40 μA to −20 μA to the rising time is 18 ms. Has become.

  From such a relationship, it is understood that the rising time is faster when the target output is switched from the higher one to the lower one. Therefore, more accurate prediction is possible.

  Next, from the signal of the print start performed by the control unit 50, the voltage prediction before passing the paper, and the printing process regarding the correction and application of the current value based on the predicted value, the second embodiment, the flowchart shown in FIG. It will be described with reference to FIG.

  First, the control unit 50 calculates the transfer current value I(T2) as described above before starting the printing process and before the sheet reaches the primary transfer nip and/or the secondary transfer nip (step S130). .. Next, as described above, the output voltage prediction during sheet passing is executed (step S131). Next, the control unit 50 determines whether or not the predicted output voltage V(T2)>limiter voltage V(lmt) is satisfied (step S132).

When it is determined that the predicted output voltage V(T2)>the limiter voltage V(lmt), the control unit 50 applies the limiter current value T2′(I(lmt)) as the transfer current output and outputs the output voltage V(T2). ) Is corrected to the limiter voltage V(lmt) (step S133).
On the other hand, when it is determined that the predicted output voltage V(T2)>limiter voltage is not satisfied, the control unit 50 outputs the transfer current value T2(I) calculated from a predetermined condition such as the paper type, the paper thickness and the machine environment as the transfer current output. (Def)) is applied to control the output voltage V(T2) (step S134).

  Next, the control unit 50 determines whether or not the actual output voltage>the limiter voltage V(lmt) (step S135). The actual output voltage refers to the output voltage during sheet feeding.

  If it is determined that the actual output voltage>the limiter voltage V(lmt), the process proceeds to step S137. On the other hand, when it is determined that the actual output voltage>limiter voltage V(lmt) is not satisfied, it is determined whether or not the actual output current<current value I(def) calculated from predetermined conditions such as paper type, paper thickness and environment. The control unit 50 determines (step S136). The actual output current refers to the output current during sheet passing.

  When it is determined that the actual output current is smaller than the current value I(def) calculated from the predetermined conditions such as the paper type, the paper thickness, the environment, etc., the process proceeds to step S137. On the other hand, when it is determined that the actual output current is less than the current value I(def) calculated from a predetermined condition such as paper type, paper thickness, environment, etc., the process returns to step S135.

  Next, the control unit 50 determines whether or not the actual output voltage>the limiter voltage V(lmt) (step S137).

  When it is determined that the actual output voltage>the limiter voltage V(lmt), the control unit 50 corrects so that the control current value is made smaller than the current current value and is focused on the limiter voltage (step S138). On the other hand, when it is determined that the actual output voltage>limiter voltage V(lmt) is not satisfied, it is determined whether or not the actual output current>current value I(def) calculated from predetermined conditions such as paper type, paper thickness and environment. The control unit 50 determines (step S139).

  If it is determined that the actual output current>current value I(def) calculated from a predetermined condition such as paper type, paper thickness, environment, etc., the control current value is made larger than the current value and the limiter voltage is focused. The control unit 50 makes the correction (step S140). On the other hand, when it is determined that the actual output current>the current value I(def) calculated from the predetermined conditions such as paper type, paper thickness, environment, etc., the control current value is determined from the predetermined conditions such as paper type, paper thickness, environment, etc. The control unit 50 controls the calculated current value I(def) (step S141).

  Then, it is determined whether or not to end the printing process (step S142).

  When ending the print processing, the print processing ends. On the other hand, when the printing process is not completed, the control current value T2″ corrected in step S138, step S140, and step S141 is updated as the limiter current value I(lmt) (step S144).

  Next, the control unit 50 determines whether to change the transfer condition (output type) (step S144).

  When the output condition is not changed, the process returns to step S137. On the other hand, when changing the output condition, the process proceeds to step S145.

  In step S145, the control unit 50 determines whether or not current value I(def)>limiter current value I(lmt) calculated from predetermined conditions such as paper type, paper thickness, environment, etc. (step S145).

  When it is determined that the current value I(def)>limiter current value I(lmt) calculated from predetermined conditions such as paper type, paper thickness, environment, etc., the control unit 50 outputs the limiter current value T2″( as the transfer current output. I(lmt)) is applied (step S146), and the process returns to step S135. On the other hand, current value I(def)>limiter current value I(lmt) calculated from predetermined conditions such as paper type, paper thickness and environment is not satisfied. If the controller 50 determines that the transfer current output is the limiter current value T2″(I(def)) (step S147), the process returns to step S135.

  As a result, even if there is an error in the predicted value before the start of sheet passing, and even if a voltage exceeding the limiter voltage is applied during the print job, the limiter current value I(lmt corresponding to the limiter voltage is ) Is corrected and updated, an appropriate current value can be obtained. Further, even if the state such as the machine temperature changes during a print job due to the passage of a large number of sheets or the like, the limiter current value I(lmt) corresponding to the limiter voltage is updated. A large current value can be obtained.

  Next, the output voltage when the control of the first embodiment or the control of the second embodiment is performed and when the control is not performed will be described.

  14 is a graph showing the output voltage when the control of the first embodiment is performed, FIG. 15 is a graph showing the output voltage when the control of the second embodiment is performed, and FIG. 13 does not perform these controls. It is a graph which shows an output voltage in a case.

  When the control of the first embodiment or the control of the second embodiment is not performed, when the resistance value increases due to deterioration over time, environmental changes, and other factors, control is performed with a constant current. Therefore, as shown in FIG. 13, there is a possibility that an excessive output may be generated in excess of the output voltage in the proper range and a defect such as discharge may occur. As a result, there is a possibility that not only the occurrence of an abnormal image but also the occurrence of machine down may occur.

  On the other hand, when the control of the first embodiment is performed, if the resistance value increases due to deterioration over time, environmental changes, and other factors, it is determined from the prediction before the paper is passed that the initial output voltage is large, and the output voltage is Is corrected. Therefore, as shown in FIG. 14, an excessive output is not generated by exceeding the output voltage in the proper range. Further, when the output is changed at the leading edge, the image portion, the trailing edge, or the like of one sheet that is passed, the output voltage is corrected from the predicted value before passing when changing the output type. You may do the same. As a result, the output is suppressed below the preset limiter voltage.

  By the way, when the control of the first embodiment is performed, an error may occur in the output due to variations in prediction and changes in the state of the machine. This error may occur every time the output type changes. Therefore, even if an excessive output is suppressed, an abnormal image or the like may be generated each time the output type changes.

  Therefore, in the case of performing the control of the second embodiment, when the control for converging to the limiter voltage is performed after the prediction before passing the sheet, the correction value (corrected control current value) immediately before the output type is switched is set. Remember and update. Therefore, as shown in FIG. 15, no error occurs every time the output type changes. Thereby, the output error can be minimized. Further, even when the state such as the temperature inside the machine changes, the optimum value for each condition can be obtained by updating the limiter current.

  In the control of the second embodiment, the comparison between the output voltage in step S137 of FIG. 12 and the limiter voltage V(lmt) is performed at short intervals, for example, every 20 milliseconds. The correction of the control current value is also performed at the same intervals (20 milliseconds). The correction of the control current value is executed in real time on the sheet conveyed to the transfer nip at a high linear velocity such as in a production printer.

  In the control of the second embodiment, the correction value (corrected control current value) is stored/updated in real time, and until immediately before the output type is switched (timing within 20 milliseconds before the time when the output type is switched). The error can be minimized by storing and updating the correction value of (corrected control current value).

  Although the embodiment of the present invention has been described above, the present invention is not limited to this. For example, the control of the above-described embodiment has been described with respect to the secondary transfer portion, but is not limited to this aspect and may be applied to the primary transfer portion. The materials and dimensions of the components introduced in the above-described embodiments are merely examples, and it goes without saying that various materials and dimensions can be selected within the range in which the effects of the present invention can be exerted.

1 Photoconductor drum (an example of image carrier)
8 Intermediate transfer belt (an example of image carrier and transfer material)
9 Primary transfer roller (an example of transfer means)
19 Secondary transfer roller (an example of transfer means)
50 Control unit (an example of control means)
P recording medium (an example of transfer material)

JP 2002-351234A

Claims (6)

An image forming apparatus having a transfer means for transferring a toner image on an image carrier onto a transfer material,
The output voltage from the transfer power source output to the transfer unit, has a control unit for controlling according to a predetermined condition ,
The control means is
At the time of non-paper passing, at least two different currents are applied with a current value lower than the current value at the time of paper passing,
Based on the detection voltage detected by the application, predict the output voltage during paper passing ,
When the predicted output voltage does not exceed the predetermined limiter voltage, the output voltage is controlled to be the value calculated by the predetermined condition,
If the predicted output voltage exceeds the predetermined limiter voltage, the output voltage is controlled to be the limiter voltage , and
An image forming apparatus, wherein a current having a larger value is first applied among the at least two currents having different values . The image according to claim 1, wherein the control unit corrects the output voltage to a value calculated under the predetermined condition when the output voltage at the time of passing the paper is lower than the limiter voltage. Forming equipment. 3. The image forming apparatus according to claim 1 , wherein the control unit corrects the output voltage so that the output voltage converges to the limiter voltage when the output voltage during sheet feeding is higher than the limiter voltage. The image forming apparatus according to claim 1 , wherein the control unit controls an output voltage by controlling a current. When the output voltage at the time of paper feeding is higher than the limiter voltage and the output voltage is corrected so as to converge to the limiter voltage, the control means outputs the corrected output voltage until the predetermined condition changes. The image forming apparatus according to claim 4 , wherein the corresponding output current is updated as a limiter current. The predetermined conditions are linear velocity, temperature or humidity, size of transfer material, type of transfer material, thickness of transfer material, resistance of transfer unit for transferring toner image from image carrier to transfer material, and transfer material transport. The image forming apparatus according to claim 1 , further comprising at least one of a position on the transfer material in the direction.