JP2010002753A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excellent transferred image by determining a proper transfer voltage, without lowering productivity. <P>SOLUTION: In an image forming apparatus, when a job is started, ATVC (Auto Transfer Voltage Control) for obtaining an optimum secondary transfer voltage by monitoring the voltage of a secondary transfer roller under certain conditions is executed (step S1:YES and steps S2 and S3), then, a transfer voltage is corrected on the basis of a temperature change amount Δt in the vicinity of the secondary transfer roller (steps S4 and S5), and when the temperature change amount Δt is a predetermined threshold Ta or more, the ATVC is executed again to prevent occurrence of transfer failure due to the increase of a correction error and secure the excellent transferred image (step S12:YES and the steps S2 and S3). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly, to a technique for determining an appropriate transfer voltage without reducing image forming productivity.

In an image forming apparatus such as a copying machine, a toner image formed on an image bearing member such as a photosensitive drum or an intermediate transfer belt is transferred to a sheet using an electrostatic force generated by a transfer voltage applied to a transfer member such as a transfer roller. An image is formed by transferring to a transfer medium.
The transfer roller is usually configured to form a layer of conductive elastic material around a metal shaft core and apply a necessary transfer voltage to the shaft core. In particular, an elastic material containing an ionic conductor to ensure conductivity has a large variation in resistance value due to temperature, and it is necessary to frequently adjust the transfer voltage applied to the shaft core in order to obtain a good transfer image. .

Therefore, for example, in Patent Document 1, during execution of an image forming job, a section (hereinafter referred to as “non-transfer”) after the trailing edge of the previous sheet passes the transfer position and then reaches the leading edge of the next sheet. In this section, the transfer roller resistance value is measured to determine the optimum transfer voltage (optimum transfer voltage determination process), and the process of alternately switching the transfer voltage in the next non-transfer section is performed. It is disclosed.
JP 2003-287966 A JP 11-258923 A

  However, it is desirable to measure the resistance value of the transfer roller to obtain an average value of resistance values measured at a plurality of locations in the circumferential direction by at least one rotation in order to avoid a measurement error. It is necessary to delay the conveyance timing and increase the non-transfer section. If this is done for every other non-transfer section as in Patent Document 1, the productivity of image formation is remarkably increased. It will decline.

  The present invention has been made in view of the above problems, and provides an image forming apparatus capable of determining an appropriate transfer voltage and obtaining a good transfer image without reducing productivity in image formation as much as possible. For the purpose.

  In order to achieve the above object, the transfer means according to the present invention allows a toner image on an image carrier to be transferred onto another image carrier or recording sheet by an electrostatic force generated by a transfer member to which a transfer voltage is applied. An image forming apparatus provided with a transfer means for transferring, an optimum transfer voltage determining means for obtaining an optimum transfer voltage by obtaining a resistance value of the transfer member, and at least the temperature and humidity in the apparatus as an index Environmental information acquisition means for acquiring parameters to be environmental information, transfer voltage correction means for correcting the optimum transfer voltage based on the environment information, and the temperature of the environmental information is predetermined from the time of the previous optimum transfer voltage determination process. The optimum transfer voltage is determined by the optimum transfer voltage determining means, and if not, the corrected transfer voltage obtained by the transfer voltage correcting means is obtained. The to the provisional transfer voltage, characterized in that it comprises a control means for controlling the transfer means.

  As described above, the optimum transfer voltage determination process based on the resistance value of the transfer member is not executed until the temperature change changes by a predetermined threshold value or more, and during that time, the transfer voltage correction is performed based on the environmental information including the in-machine temperature. A process for correcting the optimum transfer voltage by means is executed. The correction processing when the correction transfer voltage is used as a provisional transfer voltage does not require actual measurement of the resistance value of the transfer member, and therefore can be performed quickly only by calculation, thereby affecting the productivity of image formation. Therefore, it is possible to determine an appropriate transfer voltage according to the temperature change.

Here, an acquisition unit that acquires the type of the recording sheet to which the toner image is to be transferred may be provided, and the optimum voltage correction unit may execute a different transfer voltage correction process depending on the type of the recording sheet.
Thereby, a good transfer image is always obtained regardless of the type of sheet.
In addition, here, in the case of continuously forming an image on a plurality of recording sheets, it is provided with a sheet interval determination unit that determines a sheet interval to be conveyed, and the control unit determines whether the sheet interval is the optimum transfer voltage determination process. When the time required for the execution of the image is equal to or longer than the predetermined time, the optimum transfer voltage determination process is executed even if the temperature change in the environmental information is less than the predetermined value. And an image forming unit that forms a toner image on the image carrier based on the processed image data, and the sheet interval determination unit processes unprocessed image data to be continuously formed. The size of the sheet interval may be determined with reference to the time required for the sheet.

As a result, the optimum transfer voltage determination process can be executed without lowering the productivity, and a good transfer image can be secured.
In addition, an image determination unit that determines the type of an image to be formed is provided, and the control unit determines whether or not the optimum transfer voltage determination process is required by the optimum transfer voltage determination unit using a threshold value that varies depending on the image type. You may make it do.

Thus, in the case of an image such as text that is difficult to manifest the influence of the transfer voltage, a threshold value that reduces the frequency of performing the optimum transfer voltage determination process is selected, and in the case of an image such as a photo that is easily manifested, By selecting a threshold value that increases the frequency with which the optimum transfer voltage determination process is performed, productivity can be improved without impairing a good transfer image.
Here, the image determination means counts the number of dots to which the toner is to be attached and the number of rising or falling edges of the dot to which the toner is to be attached as the number of edges in one page of image data to be image-formed. A counting unit may be provided, and the determination of the type of image may be performed based on the number of dots and the number of edges.

Thereby, it is possible to easily determine the type of image to be formed.
The image forming apparatus further includes a receiving unit configured to receive selection of one image forming mode from a plurality of image forming modes, and the control unit uses an optimum transfer voltage determined by the optimum transfer voltage determining unit using a threshold value that differs depending on the selected image forming mode. You may make it determine the necessity of a determination process.
Thus, for example, for an image that does not require high image quality, productivity can be improved by selecting a threshold value that reduces the frequency of performing the optimum transfer voltage determination process.

  In addition, when image formation is continuously performed, a remaining number determination unit that determines whether or not the remaining number of image formations is within a predetermined number is provided, and the remaining number of image formations is within a predetermined number. If it is determined that there is, the control means determines the optimum transfer voltage in the optimum transfer voltage determination means even if the amount of change in temperature has exceeded a predetermined threshold since the previous optimum transfer voltage decision processing. The processing may not be executed.

  As a result, it is possible to avoid a situation in which the optimum transfer voltage determination process is executed and the job issuer is kept waiting despite the small number of remaining image formations.

Hereinafter, an embodiment according to the present invention will be described with reference to the drawings, taking as an example a case where the embodiment is applied to a tandem type digital color printer. (Hereafter, simply called “printer”)
<1> Overall Configuration of Printer FIG. 1 is a schematic cross-sectional view showing the overall configuration of a printer 100 according to an embodiment of the present invention, and includes an image forming unit 10, a paper feeding unit 20, a transfer unit 30, a fixing device 40, The control unit 50 and the environment sensors 71 and 72 are provided.

When this printer 100 is connected to a network (for example, LAN: Local Area Network) and receives an instruction to execute a print job from an external terminal device (not shown), cyan, magenta, yellow, and black are received based on the instruction. The toner images of the respective colors are formed, and these are multiplex-transferred to form a full-color image.
Hereinafter, the reproduction colors of cyan, magenta, yellow, and black are represented as C, M, Y, and K, and the C, M, Y, and K are added as subscripts to the numbers of the components related to the reproduction colors.

The image forming unit 10 includes image forming units 1C, 1M, 1Y, and 1K, an optical unit 15, an intermediate transfer belt 31, and the like.
The image forming unit 1C includes a photosensitive drum 11C, a charger 12C, a developing unit 13C, a primary transfer roller 34C, and a cleaner 14C for cleaning the photosensitive drum 11C disposed around the photosensitive drum 11C. A C-color toner image is formed on the photosensitive drum 11C. The other image forming units 3M to 3K have the same structure as the image forming unit 3C except that the toner colors are different from each other. However, in order to prevent the drawing from becoming complicated, The sign of is not shown.

The intermediate transfer belt 31 is an endless belt, is stretched around a driving roller 32 and a driven roller 33 and is driven to rotate in the direction of arrow A.
The optical unit 15 includes a light emitting element such as a laser diode, emits a laser beam L for image formation of C to K colors in accordance with a drive signal from the control unit 50, and scans the photosensitive drums 11C to 11K.

By this exposure scanning, electrostatic latent images are formed on the photosensitive drums 11C to 11K charged by the chargers 12C to 12K. The electrostatic latent images are developed by the developing units 13C to 13K so that toner images of colors C to K are primarily transferred onto the photosensitive drums 11C to 11K at the same position on the intermediate transfer belt 31. It is executed at different timings.
The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 31 by the electrostatic force acting on the primary transfer rollers 34C to 34K to form a full color toner image, and further move toward the secondary transfer position 36.

  On the other hand, the paper feeding unit 20 includes a paper feeding cassette 21 that accommodates the sheets S, a feeding roller 22 that feeds the sheets S in the paper feeding cassette 21 one by one onto the conveying path 23, and a second feeding of the fed sheets S. A timing roller pair 24 and the like for taking the timing to send to the transfer position 36 are provided, and the sheet S is fed from the paper feeding unit 20 to the secondary transfer position in accordance with the movement timing of the toner image on the intermediate transfer belt 31. The toner images on the intermediate transfer belt 31 are secondarily transferred onto the sheet S all at once by the action of electrostatic force by the secondary transfer roller 35.

The sheet S that has passed through the secondary transfer position 36 is further conveyed to the fixing device 40, and after the toner image (unfixed image) on the sheet S is fixed to the sheet S by heating and pressing in the fixing device 40, The paper is discharged onto the discharge tray 62 via the discharge roller pair 61.
In addition, the control unit 50 executes communication with an external terminal, image processing, drive control of the above-described units, and the like.

  FIG. 2 is a block diagram showing a configuration of the control unit 50. As shown in the drawing, the control unit 50 includes, as main components, a CPU (Central Processing Unit) 51, a communication interface (I / F) unit 52, a ROM (Read Only Memory) 53, a RAM (Random Access Memory) 54, An EEPROM (Electrically Erasable and Programmable Read Only Memory) 55 is provided.

The communication I / F unit 52 is an interface for connecting to a LAN, such as a LAN card or a LAN board, and receives print job data from the outside.
The CPU 51 reads a necessary program from the ROM 53, controls the operations of the image forming unit 10, the paper feeding unit 20, the transfer unit 30, and the fixing device 40 in a unified manner with timing, and the communication I / F unit 52 The printing operation based on the received print job data is smoothly executed. Further, the transfer voltage to be applied to the secondary transfer roller 35 is determined with reference to the detection value of the environment sensor 71. Details will be described later.

The EEPROM 55 is a storage unit composed of a nonvolatile memory, and stores acquired environmental information and information related to the transfer voltage.
<2> Outline of Secondary Transfer Voltage Control Transfer members such as the primary transfer rollers 34C to 34K and the secondary transfer roller 35 are generally formed of an elastic material having conductivity, and their resistance values are such as temperature and humidity. It is known that it fluctuates depending on the environmental conditions around, especially the temperature.

FIG. 3 shows that continuous printing is performed in a state where a constant current (10 μA) is supplied to the shaft core of the secondary transfer roller 35, the elapsed printing time and the temperature around the secondary transfer roller 35 (secondary transfer portion temperature). ) And a change in the voltage measurement value (secondary transfer measurement voltage) on the peripheral surface of the secondary transfer roller 35, L1 indicates a change in the secondary transfer portion temperature, and L2 indicates the secondary transfer measurement voltage. Showing change.
As shown in the graph, as the printing time elapses, the temperature of the secondary transfer unit gradually rises due to the heat generated by the motor of the driving system and the temperature of the fixing unit. The resistance value of the secondary transfer roller 35 fluctuates, and as a result, the secondary transfer measurement voltage decreases greatly at first, and then gradually decreases gradually.

When the toner image is transferred, the potential on the peripheral surface of the secondary transfer roller 35 that is in contact with the sheet surface greatly influences, so that the potential on the peripheral surface of the secondary transfer roller 35 does not change according to the temperature change as described above. In addition, by properly controlling the transfer voltage applied to the axis of the secondary transfer roller 35, a good transfer image can be obtained.
Therefore, in this embodiment, an appropriate secondary transfer voltage is obtained mainly as follows.
(A) Optimal Transfer Voltage Determination Process This process is to determine an optimum transfer voltage by actually measuring a value indicating the resistance value of the secondary transfer roller 35.

  Here, the “value indicating the resistance value” is not limited to the resistance value itself in the radial direction of the secondary transfer roller 35, and a value having a certain correlation with the resistance value, for example, a constant voltage is used as the secondary transfer roller. A constant current is supplied between the shaft core of the driving roller 32 of the intermediate transfer belt 31 and the current value when applied between the shaft core of the intermediate transfer belt 31 and the driving roller 32 of the intermediate transfer belt 31. It is a concept including the voltage measured when

A value indicating the resistance value of the secondary transfer roller 35 is actually measured, and an optimum transfer voltage is determined with reference to a table showing a correlation between the index value obtained in advance and the optimum transfer voltage value. (This process is hereinafter referred to as “ATVC (Auto Transfer Voltage Control)”).
In this embodiment, as an example, a constant current is applied to the axis of the secondary transfer roller 35, and the secondary transfer roller 35 is rotated at a predetermined sampling interval during one rotation of the roller (800 ms in this example). The voltage value obtained by measuring the voltage between the shaft centers of the driving roller 32 of the intermediate transfer belt 31 and the average is regarded as a value indicating the resistance value of the secondary transfer roller, and is correlated with this. ATVC processing is performed using a predetermined table.

(B) Transfer voltage correction process Since the above-described "value indicating the resistance value" requires a certain amount of time, if the ATVC process is executed every time the in-machine temperature changes, the image formation productivity can be improved. Incurs a decline.
Therefore, in this embodiment, instead of executing the ATVC process under a predetermined condition, the secondary transfer voltage correction according to the temperature change amount is executed.

However, even if the secondary transfer reference voltage is corrected by the temperature, if the temperature change exceeds a certain threshold, the resistance value change of the secondary transfer roller may increase and exceed the allowable range. Re-executes the ATVC process.
As described above, by using the ATVC process and the transfer voltage correction process in combination, it is possible to obtain a good transfer image by applying an appropriate secondary transfer voltage while suppressing a decrease in productivity as much as possible. .
(C) Details of Secondary Transfer Voltage Control FIG. 4 is a flowchart showing the contents of secondary transfer voltage control executed by the control unit 50 in the present embodiment.

First, when a print job is received from an external terminal via a LAN, an environmental step indicating the magnitude of the absolute humidity is acquired based on the temperature / humidity information detected by the environmental sensor 71 of the paper feed slot (step S1). : YES, step S2).
FIG. 5 shows a table for determining this environmental step. As shown in the table, in this embodiment, the magnitude of absolute humidity obtained according to the magnitude of temperature (° C.) and relative humidity (%) detected by the environmental sensor 71 of the paper feed port is used as an index. It is classified into 8 levels from 1 to 8.

In step S3, the above-described ATVC process is executed, and the secondary transfer roller 35 is subjected to secondary calculation using the following equation 1 based on the measured voltage value of the secondary transfer roller 35 (secondary transfer monitor voltage) and the environmental step. Acquire the transfer voltage.
Note that the secondary transfer voltage acquired here is an optimum transfer voltage to be applied at the time of execution of the ATVC, but is a reference voltage in the transfer voltage correction process described later. This is referred to as “secondary transfer reference voltage”.
(Expression 1) Secondary transfer reference voltage (V) = secondary transfer monitor voltage (V) × slope a + offset value In the above formula 1, the slope a and the offset value are optimal for each level of the environment step by repeating experiments in advance. Therefore, the secondary transfer reference voltage is required to be obtained.

FIG. 6 shows an example of a table when the sheet is plain paper, and is stored in the ROM 53. When actually transferring, the moisture absorption state of the sheet also greatly affects, and therefore, the slope a and the offset value are set using the environmental step having a certain correlation with the moisture absorption state as a parameter.
The secondary transfer reference voltage determined by the ATVC process as described above is stored in the EEPROM 55.

Next, the temperature change amount Δt in the secondary transfer portion is acquired (step S4). The control unit 50 monitors the temperature detected by the environment sensor 72, and obtains the amount of temperature change in the secondary transfer unit from the time of execution of the ATVC as Δt.
Then, based on the secondary transfer reference voltage determined in step S3 and the value of Δt, a corrected secondary transfer voltage is calculated by the arithmetic expression shown in the following expression 2 (transfer voltage correction process: step S5).
(Expression 2) Secondary transfer voltage (V) = secondary transfer reference voltage (V) + Δt (° C.) × slope s (V / ° C.)
Here, FIG. 7 is a table showing the value of the slope s, which is obtained in advance by experiments so that an optimum correction amount can be obtained according to the value of the secondary transfer reference voltage at that time and the level of the environmental step. And stored in the ROM 53.

The secondary transfer voltage corrected in this way is stored in the EEPROM 55.
The control unit 50 controls the application of the secondary transfer reference voltage to the secondary transfer roller 35 to perform a job execution process for forming an image on the sheet by the series of operations described above, and the job is completed. (Step S6, S7).
The header of the print job data received from the external terminal includes information related to the number of pages N1 to be printed. The control unit 50 counts the number of pages N2 where image formation has been completed, and the value of N1-N2 is Whether or not the job is completed can be determined based on whether or not it is “0”.

If the determination at step S7 is affirmative, the secondary transfer voltage control is terminated as it is, but if there is still a job, it is next determined whether or not the sheet interval is equal to or greater than a predetermined value (step S).
7: NO, step S8).
The sheet interval is normally constant. However, for example, when a large amount of print data is transmitted in Postscript format, the image data to be imaged next is RIP based on the relationship between the memory capacity and the processing speed of the CPU. In some cases, it takes time to develop the image. In this case, the control unit 50 controls the sheet feeding unit 20 to delay the timing of sheet feeding by the timing roller 24 in order to delay image formation on the next sheet.

  At this time, the sheet interval becomes longer than usual. Therefore, in step S8, the control unit 50 sets the sheet interval to a predetermined value, specifically, a value (system speed (cm / s) × 0 necessary for executing the time required for executing the ATVC (about 800 ms)). .8 (s)), and if so (step S8: YES), the ATVC process of steps S2 and S3 is executed. In this case, even if the ATVC process is executed, the image forming job is not delayed.

If it is determined in step S8 that the sheet interval is not greater than or equal to the predetermined value (step S8: NO), it is next determined whether or not the job is about to end (step S9). Specifically, when the number of remaining pages (N1-N2) of the image forming job is 3 or less, for example, it is determined that the job is about to end.
If the job is about to end, the process returns to step S5 without determining whether the ATVC process is necessary, and the secondary transfer voltage is obtained by correction. If the processing time is about 3 sheets, the temperature inside the machine will not fluctuate significantly, and it will be possible to cope with correction processing only by calculation without performing ATVC processing again. This is so as not to impair the expectation that the job will end.

In step S9, if it is negative (step S9: NO), that is, if it is determined that the job is not about to end, the process proceeds to step S10 to determine the type of image to be imaged next. I do.
The types of images determined by the image pattern determination are, for example, text images and other general images, and the latter general images include photographic images. Various known methods for analyzing received image data are used for image pattern determination. In this embodiment, determination is made based on the count values of dot count and edge count as a simpler method.

  Here, the dot count refers to a pixel (hereinafter referred to as a “black dot”) to which toner is attached by scanning image data that has been bitmap-developed in preparation for image formation on the next page in the main scanning direction. ) Is counted, and the edge count is a process of counting an edge that changes from a pixel (hereinafter referred to as “white dot”) that does not have any toner to a black dot, and an edge that changes from a black dot to a white dot. Say.

Specifically, for example, the dot count is executed by repeating the process of accumulating and integrating the signal value in the capacitor for each line of the video signal for one page, and the edge count is for each line of the video signal. The process of detecting and counting the change in the brightness of the dots is executed by repeating one page.
In the case of a text image, compared with general images such as photographs and illustrations, there is a tendency that the dot count number is small and the edge count number is large, so the dot count number and edge count number for one page are respectively Cd and Ce. Then, for example, in the conditional expression Cd <a1 and (Ce / Cd)> a2, the types of images can be determined by appropriately determining the values of a1 and a2 with experience values and experimental values.

In step S10, when the type of image to be imaged next is determined, the temperature change amount Δt (temperature change detected by the environmental sensor 72 after the most recent ATVC process is executed) is acquired, and A threshold Ta set in advance according to the type of image, the secondary transfer reference voltage at that time, and the environmental step is acquired (step S11).
Then, the temperature change amount Δt is compared with the threshold value Ta, and when Δt ≧ Ta (step S12: YES), the process returns to step S2 and the ATVC process is executed again.

  If the temperature change amount Δt becomes larger than necessary, the correction formula in step S5 can no longer be used, and a secondary transfer monitor voltage that indicates the resistance value of the transfer roller 35 is obtained again to accurately set the secondary transfer reference voltage. It is necessary. Since the ATVC process at this time is executed during the job process, image formation on the next sheet (the job execution process in step S6) is delayed until the ATVC process is completed.

FIG. 8 and FIG. 9 show examples of the table for determining the threshold value Ta for the general image and the text image, respectively, which are obtained in advance by experiments and stored in the ROM 53.
In both tables, since the amount of change in the resistance value of the secondary transfer roller 35 differs depending on the current secondary transfer voltage and the environmental step, the threshold value Ta for determining the re-execution of the ATVC process is determined as a parameter. It is comprised so that.

Further, the threshold value for the general image shown in FIG. 8 is set to be relatively smaller than the threshold value for the text image in FIG. 9. This is because it is conspicuous and it is necessary to execute ATVC processing more frequently than text images.
The two-transfer voltage control process as described above is repeatedly performed until the received print job is completed. When it is determined that the job has been completed (step S7: YES), the flowchart is ended, and then the job Wait for reception.

  As described above, according to the secondary transfer voltage control method according to the present embodiment, after performing the ATVC process before the start of execution of the job receiving the job, the transfer voltage correction by the temperature change amount Δt after the ATVC process is performed. Until the temperature change amount Δt becomes equal to or greater than the predetermined threshold Ta, the transfer voltage is corrected and compensated for by extension, so that the ATVC process can be performed while accurately preventing the transfer failure. Can be performed less frequently than before, and image forming productivity is not significantly reduced.

Further, the threshold value Ta for determining whether or not the ATVC process is necessary is obtained by referring to a different table depending on the type of image, and for an image such as a text image in which the deterioration of the transferred image is not noticeable, Since the execution frequency of the ATVC process is set to be lower, rational control is possible.
<Modification>
As described above, the present invention has been described based on the embodiment, but the present invention is not limited to the above-described embodiment, and the following modifications can be considered.

(1) In the above embodiment, in the image pattern determination process in step S10 of FIG. 4, the dot count number and edge count number methods are used to determine a text image and other general images. Other known image processing can also be used.
For example, when a density histogram of image data is generated for tone correction (γ correction), if the density distribution in the density histogram is relatively dispersed, there is a possibility of a general image. On the other hand, if it is concentrated in a specific density range, it may be judged as a text image.

(2) In addition to or instead of the image pattern determination, the table may be selected according to the image quality mode designated by the user.
That is, in a printer, for example, when printing is possible in a high image quality mode with a high resolution and a low image quality mode with a lower resolution, and the image quality mode can be selected from a panel of a computer or an image forming apparatus, the low image quality mode is selected. When the mode is selected, the execution frequency of the ATVC process is lowered by using a table in which Ta is set to be large, and productivity is prioritized. On the other hand, when the high image quality mode is selected, a table in which Ta is set low is used to increase the frequency of ATVC to prevent secondary transfer failure and ensure high image quality.

(3) In the flowchart of FIG. 4, step S8 (sheet interval determination processing), step S9 (job close-up determination), and step S10 (image pattern determination) are not necessarily performed. This is because even if these processes are not performed, the execution frequency of the ATVC process can be sufficiently reduced as compared with the prior art, and a decrease in productivity can be prevented.
When step S10 is omitted, a table for general images is preferably used as the Ta table.

  (4) Although the printer according to the above embodiment did not have a double-sided printing function, when an image is formed on the second side (back side) of the sheet, it is contained by thermal fixing at the time of image formation on the first side. Since the amount of moisture to be changed has changed, a table dedicated to the second surface is obtained in advance by experiments or the like and stored in the ROM 53 separately from the tables shown in FIGS. Then, it is determined whether or not the next sheet on which an image is to be formed is the second side printing. In the case of the second side printing, it is desirable to correct the transfer voltage using the dedicated table.

  (5) In the above embodiment, the control of the secondary transfer voltage has been described, but the above situation is the same even when transferring by the primary transfer roller, except that the contents of each specific table are different. However, in the case of primary transfer, since no sheet is interposed, there is not much need to consider sheet moisture absorption as in Equation 1, and the subsequent correction process is performed using the measured transfer monitor voltage as it is as the transfer reference voltage. You may do it.

  (6) In the above embodiment, in the ATVC process, the secondary transfer roller 35 is rotated once to monitor the transfer voltage. However, the secondary transfer voltage is monitored for one rotation of the intermediate transfer belt and the average is obtained. A value may be obtained. In this case, a secondary transfer reference voltage can be obtained in consideration of variations in resistance of the intermediate transfer belt. However, since this takes time, it may be limited to ATVC processing only before the start of execution of the print job.

(7) In the above embodiment, the case where the transfer roller is used as the transfer member has been described as an example. However, the present invention is not limited to the transfer roller, and other transfer members such as a transfer brush are used. Also good.
(8) In the above embodiment, the tandem type color printer has been described. However, the present invention is not limited to this. A monochrome printer may be used, a four-cycle color image forming apparatus, other copiers, fax machines, and the like. The present invention is generally applied to an image forming apparatus generally equipped with a transfer device such as a multifunction machine.

  It should be noted that the above-described embodiments and modifications can be combined as much as possible.

  INDUSTRIAL APPLICABILITY The present invention is useful as a technique for achieving both productivity and a good transfer image in an image forming apparatus including a transfer device.

Schematic sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the invention The block diagram which shows the structure of the control part of the said image forming apparatus. Graph showing temperature change of secondary transfer part and change of secondary transfer measurement voltage during continuous printing Secondary transfer voltage control flowchart Environmental step table Normal paper secondary transfer reference voltage calculation slope a, offset table Secondary transfer voltage correction slope s table ATVC re-execution temperature threshold Ta table for general images ATVC re-execution temperature threshold Ta table for text images

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming part 100 Tandem type digital color printer 20 Paper feed part 30 Transfer part 31 Intermediate transfer belt 35 Secondary transfer roller 40 Fixing device 50 Control part 71 Paper feed port part environmental sensor 72 Secondary transfer roller part environmental sensor

Claims (8)

An image forming apparatus comprising transfer means for applying a transfer voltage to a transfer member and transferring a toner image on the image carrier to another image carrier or a recording sheet by an electrostatic force generated thereby,
An optimum transfer voltage determining means for obtaining a value indicating the resistance value of the transfer member and determining an optimum transfer voltage;
Environmental information acquisition means for acquiring at least temperature as environmental information among the temperature and humidity in the apparatus;
Transfer voltage correction means for correcting the optimum transfer voltage based on the environmental information;
When the temperature in the environmental information has changed by more than a predetermined threshold from the previous optimum transfer voltage determination process, the optimum transfer voltage is determined again by the optimum transfer voltage determination means. Otherwise, the transfer voltage is determined. An image forming apparatus comprising: a control unit that controls the transfer unit so that the corrected transfer voltage obtained by the correction unit is a temporary transfer voltage. An acquisition means for acquiring the type of recording sheet to which the toner image is to be transferred;
The image forming apparatus according to claim 1, wherein the optimum voltage correction unit executes different transfer voltage correction processing depending on a type of the recording sheet. In the case of continuously forming an image on a plurality of recording sheets, a sheet interval determination unit that determines a sheet interval to be conveyed is provided,
When the sheet interval is equal to or longer than the time necessary for execution of the optimum transfer voltage determination process, the control means executes the optimum transfer voltage determination process even if the temperature change of the environmental information is less than the predetermined value. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: Image forming means for applying a predetermined process to the input image data and forming a toner image on the image carrier based on the processed image data;
4. The sheet interval determination unit determines the size of the sheet interval with reference to a time required to process unprocessed image data to be continuously formed. The image forming apparatus according to any one of the above. Image determining means for determining the type of image to be imaged;
5. The image according to claim 1, wherein the control unit determines whether or not an optimum transfer voltage determination process is required by the optimum transfer voltage determination unit using a threshold value that varies depending on an image type. Forming equipment. The image determination means includes counting means for counting the number of dots to which toner is to be attached and the number of rising or falling edges of the dots to which the toner is to be attached as the number of edges in one page of image data to be image-formed. Prepared,
The image forming apparatus according to claim 5, wherein the determination of the type of image is performed based on the number of dots and the number of edges. A receiving unit for receiving selection of one image forming mode from a plurality of image forming modes;
5. The control unit according to claim 1, wherein the control unit determines whether or not an optimum transfer voltage determination process is required by the optimum transfer voltage determination unit using a threshold value that differs depending on the selected image forming mode. The image forming apparatus described. In the case where image formation is continuously performed, a remaining number determination unit that determines whether or not the remaining number of times of image formation is within a predetermined number of times,
When it is determined that the remaining number of times of image formation is within a predetermined number of times, the control unit may determine that the amount of change in temperature has been equal to or greater than a predetermined threshold since the previous optimum transfer voltage determination process. The image forming apparatus according to claim 1, wherein the optimum transfer voltage determination unit does not execute an optimum transfer voltage determination process.

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