JP2016024230A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration of an image quality generated accompanied with a change in the amount of a toner applied to a first face during the printing of a second face of a recording material.SOLUTION: An image forming apparatus includes control means in which, when printing is performed on a first face of a recording material, it is determined whether or not a current value of the current flowing to the nip part is fluctuated while the recording material is sandwiched and conveyed by the nip part from a detection result of the current detection means, and when determined that the current value is fluctuated, information relating to a position of a current fluctuating portion which is the portion sandwiched by the nip part in the recording material is obtained, and a timing at which the current fluctuating portion is sandwiched by the nip part is derived when printing is performed on a second face of the recording material based on the information, and control means for correcting a fluctuation portion setting voltage which is the setting voltage applied to a transfer member when the current fluctuating portion is sandwiched by the nip part in the case that printing is performed on a second face of the recording material.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer having a function of forming an image on a recording material such as a sheet.

As one of the electrophotographic image forming apparatuses, an image forming apparatus including an intermediate transfer member is known.
In such an apparatus, an image forming operation is performed as follows. First, a voltage is applied to the primary transfer member disposed at the photosensitive drum facing portion via the intermediate transfer member, so that a primary transfer potential is generated in the primary transfer portion in contact with the photosensitive drum of the intermediate transfer member. . Then, the toner image formed on the surface of the photosensitive drum is primarily transferred onto the intermediate transfer member by the potential difference formed between the photosensitive drum and the intermediate transfer member. Thereafter, a voltage is applied to the secondary transfer member, whereby the toner image formed on the surface of the intermediate transfer member is secondarily transferred collectively onto the surface of the recording material such as paper.
Conventionally, in transfer control, constant current control is performed to keep the current value during transfer control constant by changing the set voltage according to the difference between the target current value and the detected current value. . Patent Document 1 proposes changing the target current at the time of transfer control according to environmental information, the printing surface, and the type of recording material.

JP 2004-117920 A

However, in the conventional control as in Patent Document 1, when double-sided printing is performed with a recording material left in a high-temperature and high-humidity environment, the image quality of the second-side image is changed due to a change in the amount of toner on the first side of the recording material. There is concern about the decline.
This is considered to be caused by a steep change in current during secondary transfer constant current control to the recording material due to resistance fluctuation caused by a change in the amount of applied toner on the first side during backside printing. There is a concern that such a decrease in image quality may occur particularly when an image pattern having all white on the first surface is printed and a solid image pattern is printed on the second surface.
Since the deterioration in image quality on the second surface is caused by a change in the amount of toner applied on the first surface, there is a concern that the image quality may be deteriorated in an image printed in a region located on the back surface of the entire white region on the first surface. The same applies to an image pattern having a photograph and characters on the first side and a photograph on the second side.
As a means for solving such a problem, a method of shortening the control cycle during constant current control can be considered. However, if the control cycle during constant current control is shorter than the time required for the current to rise or fall, the next set voltage is determined and applied before the detected current value reaches the target current value. Oscillation may occur.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to suppress a decrease in image quality that occurs due to a change in the amount of applied toner on the first surface when the recording material is printed on the second surface. .

In order to achieve the above object, the present invention provides:
An image carrier for carrying a toner image;
A transfer member that forms a nip portion with the image carrier, wherein the transfer member transfers a toner image carried by the image carrier to a recording material that is nipped and conveyed by the nip portion;
Current detecting means for detecting a value of a current flowing through the nip portion;
Voltage application means for applying a set voltage, which is set according to a difference between a current value detected by the current detection means and a target current value, to the transfer member;
Have
In an image forming apparatus capable of printing on the second surface of the recording material after printing on the first surface of the recording material,
When printing is performed on the first surface of the recording material, it is determined from the detection result of the current detection means whether the current value of the current flowing through the nip portion fluctuates while the recording material is nipped and conveyed by the nip portion. Judgment
When it is determined that the current value has fluctuated, information on the position of the current fluctuation portion that is a portion of the recording material that is sandwiched by the nip portion is acquired,
Based on the information, when the printing is performed on the second surface of the recording material, the timing at which the current fluctuation portion is sandwiched by the nip portion is derived,
Control means for correcting a variable portion set voltage, which is the set voltage applied to the transfer member when the current variable portion is sandwiched between the nip portions when printing is performed on the second surface of the recording material. It is characterized by.

  According to the present invention, it is possible to suppress a decrease in image quality that occurs with a change in the amount of applied toner on the first surface during printing of the second surface of the recording material.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment. 1 is a block diagram of a CPU configuration and a control unit of an image forming system according to a first exemplary embodiment. The figure explaining the influence on the 2nd surface by the printing pattern of the 1st surface of Example 1 The figure explaining determination of the current fluctuation start / end timing of the 1st surface of Example 1 The figure explaining correction | amendment of the setting voltage of the 2nd surface of Example 1. FIG. The figure which shows the flowchart regarding the 1st surface constant current control of Example 1. FIG. The figure which shows the flowchart regarding the 2nd surface constant current control of Example 1. FIG. The figure explaining the switching to the constant voltage control of the 2nd surface of Example 2. The figure which shows a flowchart regarding the switch to the constant voltage control of the 2nd surface of Example 2. FIG.

  DETAILED DESCRIPTION Exemplary embodiments for carrying out the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

[Example 1]
Example 1 will be described below.
In this embodiment, the following method is employed as a method for preventing a sharp change in the current on the second surface due to a change in the amount of toner applied on the first surface. First, the current fluctuation start timing and end timing during constant current control at the time of printing the first page are detected (detected), and the current fluctuation start timing and end timing at the time of printing the second page are calculated from the current fluctuation timing at the time of printing the first page. . Then, constant current control is performed by correcting the set voltage at the current fluctuation start timing and end timing at the time of printing on the second side.

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus 100 according to the present exemplary embodiment.
The overall configuration of the image forming system of this embodiment will be described below. In the following description, the first station is a yellow (Y) toner image forming station (image forming unit), and the second station is a magenta (M) toner image forming station. The third station is a cyan (C) color toner image forming station, and the fourth station is a black (K) color toner image forming station. Here, the configuration and operation of each station are substantially the same except that the color of the toner used is different. Accordingly, in the following description, unless there is a particular distinction, the subscripts a, b, c, and d given to the reference numerals in FIG. 1 are omitted in order to indicate the elements provided for any color. The overall explanation is as follows.

(Image forming part)
The photosensitive drum (photoconductor) 1 is configured by applying an organic photoconductor layer (OPC) to the outer peripheral surface of an aluminum cylinder. More specifically, a plurality of functional organic materials including a carrier generation layer that generates charges upon exposure to light and a charge transport layer that transports the generated charges are laminated on a metal cylinder. The outer layer has low electrical conductivity and is almost in an insulating state. The photosensitive drum 1 is rotatably supported at both ends by flanges, and is driven to rotate counterclockwise with respect to FIG. 1 when a driving force is transmitted to one end from a driving motor (not shown). .
The charging roller (charging means) 2 is a conductive roller formed in a roller shape. The charging roller 2 is brought into contact with the surface of the photosensitive drum 1, and a charging bias voltage is applied by a charging bias power source 20, whereby the photosensitive drum 1. The surface is charged uniformly.

The developing unit (developing unit) 8 includes a developing roller 4, a toner storage unit that stores toner (nonmagnetic one-component developer) 5, a developer coating blade 7, and the like. Here, the developing roller 4 is adjacent to the surface of the photosensitive drum, is driven to rotate by a driving unit (not shown), and develops when a developing bias voltage is applied from a developing bias power source 21.
The cleaning unit 3 cleans the transfer residual toner on the photosensitive drum 1.
The photosensitive drum 1, the charging roller 2, the cleaning unit 3, and the developing unit 8 (the developing roller 4, the toner 5, and the developer coating blade 7) are detachable (detachable) from the main body of the image forming apparatus. Cartridge) 9a. The charging roller 2 and the developing roller 4 are connected to a charging bias power source 20 that is a voltage supply unit to the charging roller 2 and a developing bias power source 21 that is a voltage supply unit to the developing roller 4, respectively. Each station is configured in this way.

The exposure unit 11 includes a scanner unit or LED array that scans laser light with a polygon mirror (rotating polygon mirror), and irradiates the photosensitive drum 1 with a scanning beam 12 that is modulated based on an image signal.
An intermediate transfer member (hereinafter referred to as an intermediate transfer belt) 80 as an image carrier is stretched and supported by three rollers of a secondary transfer counter roller 86, a driving roller 14, and a tension roller 15 as a stretching member. Appropriate tension is maintained. By driving the drive roller 14, the intermediate transfer belt 80 moves in the forward direction at substantially the same speed with respect to the photosensitive drum 1.

Further, inside the intermediate transfer belt 80, a primary transfer roller 81 that is in contact with the intermediate transfer belt 80 is provided so as to face the four photosensitive drums 1, and the intermediate transfer belt 80 and each photosensitive drum 1 are connected to each other. They are in contact with each other at the primary transfer portion (transfer nip portion) N1. The primary transfer roller 81 is connected to a primary transfer bias power supply 84 that is a voltage supply unit to the primary transfer roller 81. Then, a positive charge is applied from the primary transfer roller 81 to the intermediate transfer belt 80, and each negative color toner image on the photosensitive drum 1 is sequentially transferred to the intermediate transfer belt 80 by the primary transfer portion N1. A multicolor image is formed.
In addition, a charge removal member 23 is disposed downstream of the primary transfer roller 81a in the rotation direction of the intermediate transfer belt 80. The driving roller 14, the tension roller 15, the neutralizing member 23, and the secondary transfer counter roller 86 are electrically grounded.

(Feeding department)
When the recording material P is fed from the main body cassette 16, the cassette pickup roller 17 is driven. By rotating the cassette pickup roller 17, the recording material P placed in the main body cassette 16 is separated and fed one by one and conveyed to the registration roller 18.
(Recording material controller)
The registration sensor 35 detects the front end of the main body cassette 16 and the recording material P fed through the conveyance path 90. The recording material P is detected according to the timing at which the registration sensor 35 detects the leading edge of the recording material P so that the leading edge of the recording material P conveyed by the registration roller 18 coincides with the leading edge of the image at a position 36 (hereinafter, merge point 36). Change the transport speed. Before the transported recording material P reaches the merge point 36, the transport speed is returned to the speed before the change and transported to the secondary transfer portion N2.

(Secondary transfer part)
The intermediate transfer belt 80 is circulated by the driving roller 14 and electrostatically adsorbs toner to the outer peripheral surface facing the photosensitive drum 1. As a result, a multicolor image is formed on the outer periphery of the intermediate transfer belt 80, and the image formed on the belt is a contact portion formed between the secondary transfer roller 82 serving as a transfer member and the intermediate transfer belt 80. It is conveyed to a secondary transfer portion (secondary transfer position) N2 which is a (nip portion). A voltage is applied to the secondary transfer roller 82 by a secondary transfer bias power source (voltage applying means) 85. As a result, an electric field is formed on the secondary transfer counter roller 86 disposed opposite to the secondary transfer roller 82, and dielectric polarization occurs between the intermediate transfer belt 80 and the conveyed recording material P, causing both to occur. An electrostatic attraction force is generated.
At this time, the current detection unit (current detection unit) detects the current flowing through the secondary transfer unit N2 in a predetermined cycle, and the secondary transfer is performed in the next cycle according to the difference between the target current value and the detected current value. Constant current control is performed by determining the voltage applied to the roller 82.

(Fixing part)
The fixing unit 19 fixes the toner image on the recording material P by applying heat and pressure to the toner image transferred and carried on the recording material P when the recording material P is nipped and conveyed by the secondary transfer portion N2. A fixing belt and an elastic pressure roller. The elastic pressure roller sandwiches the fixing belt, and forms a fixing nip portion having a predetermined width with a predetermined pressure contact force with the belt guide member.
In a state where the fixing nip portion rises to a predetermined temperature and is temperature-controlled, the recording material P on which the unfixed toner image conveyed from the image forming portion is formed is formed between the fixing belt of the fixing nip portion and the elastic pressure roller. In between, the image surface is introduced upward, that is, facing the fixing belt surface. Thereafter, the recording material P is nipped at the fixing nip portion in a state where the image surface is in close contact with the outer surface (front surface) of the fixing belt, and is conveyed by moving together with the fixing belt.
In the process in which the recording material P is nipped and conveyed through the fixing nip portion together with the fixing belt, the unfixed toner image on the recording material P is heated and fixed on the recording material P by being heated by the fixing belt. .

(Double-sided printing)
Hereinafter, a case where double-sided printing is performed on the recording material P will be described.
The heat-fixed recording material P is conveyed to the discharge roller 41 along the conveyance flapper 43a. Here, the conveyance flapper 43a is configured to be movable between a position indicated by 43a and a position indicated by 43b in FIG. The conveyance flapper 43a and the discharge roller 41 correspond to a reversing mechanism that reverses the conveyance direction with respect to the recording material P on which an image is printed on the first surface.
When the rear end of the recording material P is conveyed to the recording material reversal position 42, the conveyance flapper 43a moves to the position 43b, and the rotation direction of the discharge roller 41 is reversed. As a result, the recording material P conveyed to the recording material reversal position 42 changes its traveling direction (recording material conveyance direction), is conveyed from the rear end side to the double-sided conveyance path 40, and is conveyed by the double-sided conveyance rollers 44 and 45 to the conveyance path 90. It is conveyed to. The recording material P transported to the transport path 90 is transported so that the multicolor image formed on the intermediate transfer belt 80 is transferred at a predetermined position of the recording material P, and is transferred and fixed according to the process described above. And discharged outside the device (outside the machine).

FIG. 2 is a block diagram of the CPU configuration and the control unit of the image forming system constituting the control means.
The controller unit 201 can communicate with the host computer 200 and the engine control unit 202. The controller unit 201 receives image information and a print command from the host computer 200. The controller unit 201 analyzes the received image information and converts it into bit data, and sends a print reservation command, a print start command, and a video signal for each recording material to the CPU 211 and the image processing unit via the video interface unit 210. To 212. The controller unit 201 transmits a print reservation command to which print conditions are added according to a print command from the host computer 200 to the CPU 211 via the video interface unit 210. Further, the controller unit 201 transmits a print start command to the CPU 211 at a timing when printing is possible.

The CPU 211 prepares for execution of printing in the order of print reservation commands from the controller unit 201 and waits for a print start command from the controller unit 201. When receiving the print instruction, the CPU 211 instructs each control unit (the image control unit 213, the fixing control unit 214, and the recording material control unit 215) to start the print operation in accordance with the information of the print reservation command.
When receiving the start of the printing operation, the image control unit 213 starts preparation for the printing operation (image forming operation). When the CPU 211 receives from the image control unit 213 that preparation for image formation has been completed, the CPU 211 outputs a / TOP signal as a reference timing for outputting a video signal to the controller unit 201. When the controller unit 201 receives the / TOP signal from the CPU 211, the controller unit 201 outputs a video signal based on the / TOP signal. When receiving a video signal from the controller unit 201, the image processing unit 212 transmits image formation data to the image control unit 213. The image control unit 213 forms an image based on the image formation data received from the image processing unit 212.

  When the recording material control unit 215 receives the start of the printing operation, the recording material control unit 215 starts the feeding operation. The recording material control unit 215 rotates the cassette pickup roller 17 at the pickup timing of the recording material P and feeds the recording material P from the main body cassette 16. When the registration sensor 35 detects the leading edge of the recording material, the recording material control unit 215 accelerates or decelerates the feeding speed so that the leading edge of the recording material P and the leading edge of the image are aligned at the merge point 36 and reaches the merge point 36. Before returning to the original speed, the recording material P is conveyed to the secondary transfer portion N2.

  When the recording material reaches the secondary transfer portion N2, the CPU 211 determines a target current value and starts secondary transfer control. The CPU 211 instructs the ASIC 216 of a set value of a voltage to be applied to the transfer control unit 217 (voltage to be applied to the secondary transfer roller 82). The ASIC 216 applies a voltage corresponding to the instructed set value to the voltage application unit 220, and detects the current value of the transfer control unit 217 from the current detection unit 221. The CPU 211 acquires the current value detected by the ASIC 216 at a predetermined period, changes the set value of the voltage applied to the transfer control unit 217 according to the difference from the target current value, and instructs the ASIC 216.

The ASIC 216 performs constant current control by applying a voltage corresponding to the instructed set value to the voltage application unit 220 and detecting the current value of the transfer control unit 217 from the current detection unit 221. Thereafter, the constant current control is repeated until the trailing edge of the recording material P passes through the secondary transfer portion N2.
The fixing control unit 214 starts fixing preparation when it receives the start of the printing operation. The fixing control unit 214 starts temperature adjustment according to the information of the print reservation command in accordance with the timing when the recording material P is conveyed from the recording material control unit 215. The fixing control unit 214 fixes the image on the recording material P and conveys the recording material P to the outside of the apparatus (outside the apparatus).

FIG. 3 is a diagram for explaining the influence of the printing pattern on the first side on the second side.
The detection current in the figure indicates the secondary transfer current value when the second side printing is performed on the recording material P on which the illustrated first side printing pattern is formed, and the set voltage is the detection current as shown in the figure. The example of the setting voltage as a result of having performed constant current control with respect to the value is shown. That is, FIG. 3 shows the movement of the detected current and the set voltage during constant current control on the second side when an image having the all white area B on the first side is printed on the recording material P left in a high temperature and high humidity environment. Is shown. Here, in the recording material P shown in FIG. 3, the print areas (solid black portions) are indicated by C and D, and the area including the print areas C and D and the all white area B is the printable area A. It is. In the present embodiment, the print area C (first print area) and the print area D (second print area) are separated from each other in the recording material conveyance direction, and the recording material is included in the printable area A on the first surface of the recording material. An all white area B exists in the area between the print areas C and D in the transport direction. The all-white area B corresponds to a blank area that is an area where a toner image is not transferred from the intermediate transfer belt 80 (no toner image exists). The all-white area B shown in FIG. 3 can also be said to be an area where the toner image is not transferred from the intermediate transfer belt 80 in the printable area in the direction orthogonal to the recording material conveyance direction.
Further, in this embodiment, double-sided printing is performed using a reversing mechanism, and the recording material conveyance direction at the time of printing the first page is opposite to the recording material conveyance direction (reverse conveyance direction) at the time of printing the second page. ing.

In FIG. 3, reference numeral 300 denotes a constant current control start timing.
Reference numeral 301 denotes the timing at which the entire white area on the first surface reaches the secondary transfer portion N2. At this timing, the resistance due to the toner on the first surface rapidly decreases, so the current flowing through the secondary transfer portion N2 increases rapidly. Since the CPU 211 determines the voltage to be set from the difference between the detected current and the target current, when the detected current exceeds the target current, the set voltage is decreased and the current flowing through the secondary transfer unit N2 converges to the target current. Control to do.
302 is the timing when the all white area of the first surface is completed (the all white area end point of the all white area (the rear end, the upstream end in the recording material conveyance direction) has passed through the secondary transfer portion N2). At this timing, resistance due to the toner on the first surface is generated, so that the current flowing through the secondary transfer portion N2 rapidly decreases. Since the CPU 211 determines the voltage to be set from the difference between the detected current and the target current, when the detected current is lower than the target current, the CPU 211 increases the set voltage and the current flowing through the secondary transfer unit N2 converges to the target current. Control to do.

As described above, since the next set voltage is determined from the variation in the detection current, there is a concern that when the sudden resistance variation occurs, the current value of the secondary transfer portion N2 is not stabilized and the image quality of the image is degraded. The
In this embodiment, first, the current fluctuation start timing and end timing during constant current control at the time of printing the first page are detected, and the current fluctuation start timing and end timing at the time of printing the second page from the current fluctuation timing at the time of printing the first page. Is calculated. Then, constant current control is performed after correcting the set voltage at the current fluctuation start timing and end timing at the time of printing on the second side.

FIG. 4 is a diagram for explaining the means for determining the current fluctuation start / end timing during the first-surface constant current control of the present embodiment. FIG. 4 (a) shows an overall view, and FIG. (C) shows an enlarged view for explaining the detected current at a predetermined timing.
Reference numeral 400 denotes a constant current control start timing. The CPU 211 starts constant current control at this timing. 401 indicates the timing when the entire white area on the first surface reaches the secondary transfer portion N2. At this timing, the resistance due to the toner on the first surface drops rapidly,
The current flowing through the secondary transfer portion N2 increases rapidly. Reference numeral 402 denotes a timing when the all white area on the first surface is completed. At this timing, resistance due to the toner on the first surface is generated, so that the current flowing through the secondary transfer portion N2 rapidly decreases.
In addition, t1 indicates the time from the start of constant current control until the first white area start point reaches the secondary transfer portion N2, and t2 indicates that the first white area end point from the start of constant current control is the secondary transfer portion. The time required to reach N2 is shown.

Hereinafter, the determination means of time t1, t2 is demonstrated.
FIG. 4B is an enlarged view of the current fluctuation start timing during the first-surface constant current control, and is a diagram relating to a means for determining time t1. Reference numerals 403 and 404 indicate timings at which the CPU 211 detects current.
The CPU 211 detects current at a predetermined cycle, and the interval between 403 and 404 is defined by this cycle. ΔI1 represents the difference between the currents detected at 403 and 404. ΔIth1 is a current fluctuation start point determined by the environment and the type of the recording material P (current fluctuation portion,
This is a threshold value for determining the first end on the downstream side of the all white area B in the recording material conveyance direction during the first-surface constant current control.
The timing when ΔI1> ΔIth1 is satisfied during the constant current control is the timing (401, 403) when the time t1 has elapsed from the start of the constant current control, and this timing is hereinafter referred to as the current fluctuation start point (current change point). Sometimes referred to as t1.

As described above, when printing is performed on the first surface of the recording material, the CPU 211 determines that the current value of the current flowing through the secondary transfer portion N2 from the current detection result (detection result) is the recording material P is the secondary transfer portion. It is determined whether or not there has been a change while being held and conveyed at N2.
Then, the CPU 211 determines that the current value has fluctuated when ΔI1> ΔIth1 is satisfied, and at this time, information on the position of the portion of the recording material P sandwiched by the secondary transfer portion N2 (current fluctuating portion) is obtained. Have acquired. Here, as this information, the time t1 from the start of constant current control until the first white area start point on the first surface reaches the secondary transfer portion N2 is acquired, but the present invention is not limited to this. Any time from passing through the reference point to determining that the current value has changed may be used.

FIG. 4C is an enlarged view of the current fluctuation end timing at the time of the first-surface constant current control, and is a diagram relating to a means for determining time t2. Reference numerals 405 and 406 denote timings at which the CPU 211 detects current.
The CPU 211 detects current at a predetermined cycle, and the interval between 405 and 406 is defined by this cycle. ΔI2 represents the difference between the currents detected at 405 and 406. ΔIth2 is a current fluctuation end point determined by the environment and the type of the recording material P (current fluctuation portion,
This is a threshold value for determining the second end portion on the upstream side of the all white area B in the recording material conveyance direction during the first-surface constant current control. Here, the timing when ΔI2 <ΔIth2 is satisfied during the constant current control is the timing (402, 405) when the time t2 has elapsed from the start of the constant current control, and this timing is hereinafter referred to as the current fluctuation end point (current In some cases, the change point is t2. The CPU 211 determines that the current value has fluctuated when ΔI1> ΔIth1 is satisfied. As described above, the CPU 211 determines that the current value has changed when the absolute value of the fluctuation amount of the current value has become larger than the threshold value.
At this time, the CPU 211 calculates an average value Vave of the set voltage between the current fluctuation start point t1 and the current fluctuation end point t2 and an average value Vbase of the set voltage during the time t1, and corrects the set voltage on the second surface. (Average value difference) ΔV is calculated from the following equation.
ΔV = Vbase−Vave
Here, the average value Vbase is a set voltage applied while the following region of the recording material P is nipped and conveyed by the secondary transfer portion N2 in the recording material conveyance direction during the first-surface constant current control. Corresponds to the average value. That area is the downstream end (400) of the print area C downstream of the all white area B.
) To the downstream end (401, 403) of the all white area B.
The average value Vave is the average of the set voltages applied while the following region of the recording material P is nipped and conveyed by the secondary transfer portion N2 in the recording material conveyance direction during the first constant current control. Corresponds to the value. The region is a region from the downstream end (401, 403) to the upstream end (402, 405) in the all white region B.

FIG. 5 is a diagram for explaining the correction of the set voltage during the second-plane constant current control according to the present embodiment.
Reference numeral 500 denotes a constant current control start timing, and the CPU 211 starts constant current control at this timing. Reference numeral 501 denotes a timing for correcting the set voltage (variable part set voltage) by −ΔV, and 502 denotes a timing at which the entire white area on the first surface reaches the secondary transfer portion N2. Here, the timing for correcting the set voltage is before the timing at which the all white area reaches the secondary transfer portion N2. It takes time until the voltage is actually reflected after the set voltage is applied. Therefore, this time is set to Δtv.

The reason why the set voltage is corrected by -ΔV at the timing 501 is as follows. That is, when the entire white area on the first surface reaches the secondary transfer portion N2, the resistance of the toner on the first surface rapidly decreases, and the current flowing through the secondary transfer portion N2 increases rapidly (the absolute value of the current value). This is to suppress the fluctuation in the direction of increasing. Here, correcting the set voltage by -ΔV can be said in other words that correction is performed to reduce the absolute value of ΔV from the absolute value of the set voltage so that the absolute value of the set voltage becomes small.
In this way, by applying the set voltage in consideration of the resistance variation at the timing 501, it is possible to suppress the variation in the current value during the constant current control due to the resistance variation.

Reference numeral 503 denotes a timing for correcting the set voltage by + ΔV, and reference numeral 504 denotes a timing at which the entire white area on the first surface is finished. As described above, the timing for correcting the set voltage needs to be Δtv before the timing when the all white area ends.
The set voltage is corrected by + ΔV at the timing of 503. When the all white area on the first side is completed, resistance due to the toner on the first side is generated, and the current flowing through the secondary transfer portion N2 decreases rapidly (current value). This is to prevent the absolute value of fluctuating in the direction of decreasing). Here, correcting the set voltage by + ΔV can be said in other words as correcting to add the absolute value of ΔV to the absolute value of the set voltage so that the absolute value of the set voltage is increased.
Thus, also at the timing of 503, by applying the set voltage in consideration of the resistance variation, it is possible to suppress the variation in the current value during the constant current control due to the resistance variation.
Reference numeral 505 represents the timing of the constant current control end.

Hereinafter, the times t1 ′ and t2 ′ for determining these timings will be described.
Time t1 ′ indicates the time from the start of the constant current control on the second surface until the set voltage is corrected by −ΔV (the time from when the set voltage corrected by −ΔV is applied). Here, the timing 502 is a timing at which the current fluctuation end point t2 on the first surface is sandwiched by the secondary transfer portion N2 when printing on the second surface, and is downstream of the all white area B with respect to the reverse conveyance direction. It is also the timing at which the end portion is sandwiched by the secondary transfer portion N2.
That is, the time t1 ′ is calculated (derived) using the constant current control execution time T and the time t2 measured on the first surface by the following equation.
t1 ′ = T−t2−Δtv
t2 ′ indicates the time from the start of the constant current control on the second surface to the correction of the set voltage by + ΔV. Here, the timing of 504 is a timing at which the current fluctuation start point t1 on the first surface is sandwiched by the secondary transfer portion N2 when printing on the second surface, and is upstream of the all white area B with respect to the reverse conveyance direction. It is also the timing at which the end portion is sandwiched by the secondary transfer portion N2.
That is, t2 ′ is calculated by the following equation using the constant current control execution time T and the time t1 measured on the first surface.
t2 ′ = T−t1−Δtv

FIG. 6 is a flowchart illustrating the first-surface constant current control according to this embodiment.
The CPU 211 starts the first-surface constant current control at the timing when the recording material P reaches the secondary transfer portion N2 (S600), and starts time measurement (S601). The CPU 211 waits until the current detection cycle elapses (S602), and when the cycle time elapses, performs current detection and changes the set voltage (S603). The CPU 211 calculates an increase ΔI1 from the previous current detection result (S604). The CPU 211 determines whether or not the constant current control end timing has been reached (S605), and if it has not reached the end timing, compares it with the threshold value ΔIth1 (S606).
). When the end timing is reached, the CPU 211 ends the first-surface constant current control (S617). When ΔI1 is larger than ΔIth1 in S606, the CPU 211 obtains the elapsed time from S601, and determines the current fluctuation start point t1 (n) with n as the number of fluctuations (S607).

The CPU 211 waits until the current detection cycle elapses (S608), and when the cycle time elapses, performs current detection and changes the set voltage (S609). The CPU 211 calculates a decrease ΔI2 from the previous current detection result (S610). The CPU 211 determines whether or not the constant current control end timing has been reached (S611), and if it has not reached the end timing, it compares it with the threshold value ΔIth2 of the current fluctuation end point (S612). When the end timing is reached, the CPU 211 ends the first-surface constant current control (S617). When the CPU 211 determines in S612 that ΔI2 is smaller than ΔIth2 (the absolute value of the fluctuation amount of the current value is larger than the threshold value), the CPU 211 performs S60.
The elapsed time from 1 is acquired, and the current fluctuation end point t2 (n) is determined (S613). The CPU 211 calculates average values Vbase and Vave of the set voltage corresponding to the times t1 (n) to t2 (n) (S614), and determines a correction value ΔV (n) of the set voltage (S615). The CPU 211 repeats the control from S602 to S615 until the constant current control end timing (S616), and ends the first surface constant current control (S617).

FIG. 7 is a diagram showing a flowchart regarding the second-surface constant current control of the present embodiment.
The CPU 211 starts the second-surface constant current control at the timing when the recording material P reaches the secondary transfer portion N2 (S700), and starts time measurement (S701). The CPU 211 determines whether or not the first surface current fluctuation has occurred based on the presence or absence of the current fluctuation start point t1 (n) on the first face (S702). If the first face current fluctuation has occurred, the time t1 (n), Times t1 ′ (n) and t2 ′ (n) are calculated from t2 (n) (S703). When the first-surface current fluctuation has not occurred, the constant-current control is continued until the constant-current control end timing (S713), and the second-surface constant current control is ended (S714). Here, in the case of YES in S611 shown in FIG. 6 in the constant current control on the first surface, t2 is not set and the constant current control on the first surface is finished. In such a case, in S703, the control proceeds with “t1 ′ = 0”.

  After calculating the times t1 ′ (n) and t2 ′ (n) in S703, the CPU 211 waits until the current detection cycle elapses (S704), performs current detection when the cycle time elapses, and changes the set voltage (S705). ). The CPU 211 waits until the time t1 ′ (n) elapses (S706), and corrects the set voltage by −ΔV (n) when the time t1 ′ (n) elapses (S707). The CPU 211 waits until the current detection cycle elapses (S708), and when the cycle time elapses, performs current detection and changes the set voltage (S709). The CPU 211 waits until the time t2 ′ (n) elapses (S710), and corrects the set voltage by + ΔV (n) when the time t2 ′ (n) elapses (S711). The CPU 211 determines whether or not the fluctuation correction has been completed (S712). If the fluctuation correction has not been completed, the control of S703 to S711 is repeated. When the fluctuation correction is completed, the CPU 211 continues the constant current control until the constant current control end timing (S713), and ends the second surface constant current control (S714).

As described above, in this embodiment, the current fluctuation start timing and end timing during the constant current control during the first page printing are detected, and the current fluctuation start timing during the second page printing from the current fluctuation timing during the first page printing. And the end timing is calculated. Then, constant current control is performed by correcting the set voltage at the current fluctuation start timing and end timing at the time of printing the second side.
As a result, when the recording material P is printed on the second side, it is possible to prevent the image quality of the second side from being deteriorated due to resistance fluctuation caused by a change in the amount of applied toner on the first side.
In this embodiment, it is not necessary to shorten the control cycle during constant current control. Therefore, the oscillation that has been a concern when the control period is shortened does not occur, and the image quality of the second surface can be better prevented from being deteriorated.

Here, in this embodiment, the case where the current fluctuation is detected at the timing when the first image surface reaches the all white area where the toner image is not transferred in the recording material conveyance direction has been described. However, an image pattern in which current fluctuation is detected is not limited to an image pattern having all white, and a toner image may be formed (transferred) as long as current fluctuation is not detected. Good. That is, any recording material P may be used as long as it can suppress deterioration in image quality on the second surface due to resistance variation caused by a change in the amount of applied toner on the first surface. The threshold value to be determined may be set as appropriate.
In this embodiment, the correction value ΔV of the set voltage on the second surface is calculated using the average value Vave and the average value Vbase, but the present invention is not limited to this. For example, using the difference between the set voltage that was set before the current value was determined to be changed and the set voltage that was set after the current value was determined to be changed, The correction value ΔV may be obtained.
In the present embodiment, the configuration in which the recording material conveyance direction is reversed by the reversing mechanism to perform double-sided printing has been described. However, the present invention is not limited to this. For example, a configuration may be adopted in which the recording material that is fixed on the first side and stacked on the stacking unit is fed by the user with the hand facing the second side from the manual feed tray. Even in such a configuration, the present invention can be preferably applied.
In this embodiment, the intermediate transfer type image forming apparatus has been described. However, the present invention is not limited to this, and the present invention transfers the toner image directly from the photosensitive member to the recording material conveyed by the recording material conveying means. The method can also be suitably applied. Examples of this method include a method in which a recording material is carried and conveyed by a conveyance belt, and a toner image is transferred to the recording material at a nip portion formed between the photosensitive member and the transfer member via the conveyance belt.
In this embodiment, the case where the normal charging polarity of the toner is negative has been described. However, the present invention can be suitably applied even when the normal charging polarity of the toner is positive.

[Example 2]
Example 2 will be described below. In addition, the same code | symbol is attached | subjected about the component similar to Example 1, and the description is abbreviate | omitted. The first embodiment is characterized in that constant current control is performed over the entire surface by obtaining the correction value ΔV of the set voltage.
On the other hand, this embodiment is characterized in that the set voltage is corrected and switched to constant voltage control at the current fluctuation start timing and end timing at the time of printing the second side described in the first embodiment.
FIG. 8 is a diagram for explaining switching to the constant voltage control during the second-surface constant current control of the present embodiment.

In FIG. 8, 800 indicates a constant current control start timing, and the CPU 211 starts constant current control at this timing. Reference numeral 801 denotes timing for changing the set voltage to Va ′ and switching to constant voltage control. In the present embodiment, the set voltage Va ′ is obtained by the following expression, where Va is the immediately preceding set voltage, that is, the set voltage set before it is determined that the current value has changed.
Va ′ = Va−ΔV
Reference numeral 802 denotes the timing at which the first white area is reached. Reference numeral 803 denotes a timing at which the set voltage is changed (returned) to Va and switched to constant current control. Reference numeral 804 denotes the timing when the entire white area on the first surface is finished. Reference numeral 805 denotes a constant current control end timing. Further, t1 ′, t2 ′, and ΔV are determined by the same means as in the first embodiment.

FIG. 9 is a diagram illustrating a flowchart regarding switching to constant voltage control at the time of second-surface constant current control according to the present embodiment. The control for the first surface is the same as that shown in the first embodiment.
The CPU 211 starts the second surface constant current control at the timing when the recording material reaches the secondary transfer portion N2 (S900), and starts time measurement (S901). The CPU 211 determines whether or not the first side current fluctuation has occurred (S902). If the first side current fluctuation has occurred, the CPU 211 counts the fluctuation correction count N and calculates t1 ′ and t2 ′ (S903). If the first-surface current fluctuation has not occurred, the constant-current control is continued until the constant-current control end timing (S915), and the second-surface constant current control is ended (S916). After calculating t1 ′ and t2 ′ in S903, the CPU 211 waits until the current detection cycle elapses (S904), performs current detection when the cycle time elapses, and changes the set voltage (S905). The CPU 211 waits until t1 ′ elapses (S906), and after t1 ′ elapses, the set voltage is corrected by −ΔV (S907) and switched to constant voltage control (S908).

  The CPU 211 waits until the current detection cycle elapses (S909). When the cycle time elapses, the CPU 211 performs current detection and changes the set voltage (S910). The CPU 211 waits until t2 'elapses (S911). When t2' elapses, the CPU 211 corrects the set voltage by + ΔV (S912) and switches to constant current control (S913). The CPU 211 determines whether or not the fluctuation correction number N has reached the fluctuation number n counted on the first surface (S914). If the fluctuation correction number N has not reached the fluctuation number n, the control of S903 to S913 is repeated. When the fluctuation correction number N reaches the fluctuation number n, the CPU 211 continues the constant current control until the constant current control end timing (S915), and ends the second surface constant current control (S916).

  As described above, also in the present embodiment, the current fluctuation start timing and end timing during constant current control at the time of printing the first page are detected, and the current fluctuation start timing at the time of printing the second page from the current fluctuation timing at the time of printing the first page. And the end timing is calculated. In this embodiment, the constant voltage control is performed by correcting the set voltage at the current fluctuation start timing and end timing at the time of printing the second page.

80 ... intermediate transfer belt, 82 ... secondary transfer roller, 85 ... secondary transfer bias power source,
DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 202 ... Engine control part, 211 ... CPU, 221 ... Current detection part, N2 ... Secondary transfer part, P ... Recording material, t1, t2, t1 ', t2' ... Time

Claims (11)

An image carrier for carrying a toner image;
A transfer member that forms a nip portion with the image carrier, wherein the transfer member transfers a toner image carried by the image carrier to a recording material that is nipped and conveyed by the nip portion;
Current detecting means for detecting a value of a current flowing through the nip portion;
Voltage application means for applying a set voltage, which is set according to a difference between a current value detected by the current detection means and a target current value, to the transfer member;
Have
In an image forming apparatus capable of printing on the second surface of the recording material after printing on the first surface of the recording material,
When printing is performed on the first surface of the recording material, it is determined from the detection result of the current detection means whether the current value of the current flowing through the nip portion fluctuates while the recording material is nipped and conveyed by the nip portion. Judgment
When it is determined that the current value has fluctuated, information on the position of the current fluctuation portion that is a portion of the recording material that is sandwiched by the nip portion is acquired,
Based on the information, when the printing is performed on the second surface of the recording material, the timing at which the current fluctuation portion is sandwiched by the nip portion is derived,
Control means for correcting a variable portion set voltage, which is the set voltage applied to the transfer member when the current variable portion is sandwiched between the nip portions when printing is performed on the second surface of the recording material. An image forming apparatus.   The control means determines that the current value fluctuates when an absolute value of a fluctuation amount of a current value detected by the current detection means in a predetermined cycle becomes larger than a threshold value. The image forming apparatus according to 1.   The image forming apparatus according to claim 1, wherein the information is a time from when the recording material passes a reference point to when it is determined that the current value has changed. The control means includes
Using the difference between the set voltage set before determining that the current value has changed and the set voltage set after determining that the current value has changed, the variable unit set voltage is Correct,
When printing the second surface of the recording material, when the current fluctuation portion is sandwiched by the nip portion,
When the absolute value of the current value fluctuates in a direction that increases, correction is performed to reduce the absolute value of the difference from the absolute value of the variable part setting voltage so that the absolute value of the variable part setting voltage decreases. ,
When the absolute value of the current value fluctuates in a decreasing direction, correction is performed to add the absolute value of the difference to the absolute value of the fluctuating part setting voltage so that the absolute value of the fluctuating part setting voltage increases. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   On the first surface of the recording material, the first printing region and the second printing region are present apart from each other in the recording material conveyance direction, and the first printing region in the recording material conveyance direction among the printable regions on the first surface of the recording material. And the second print area, when there is a blank area where the toner image is not transferred from the image carrier, the control means is configured as the current fluctuation portion in the recording material conveyance direction. 5. The image forming apparatus according to claim 4, wherein information relating to positions of a first end on the downstream side and a second end on the upstream side of the blank area is acquired. A reversing mechanism for reversing the transport direction with respect to the recording material on which an image is printed on the first surface,
The recording material on which the image is printed on the first surface is reversed in the conveyance direction with respect to the recording material conveyance direction by the reversing mechanism, is conveyed again toward the nip portion, and is printed on the second surface. The image forming apparatus according to claim 5. The control means includes
In the recording material conveyance direction, a region of the recording material from the downstream end portion of the first printing area downstream of the blank area to the first end portion is nipped and conveyed by the nip portion. An average value of the applied set voltages;
Of the recording material, an area from the first end portion to the second end portion is an average value of the set voltage applied while being nipped and conveyed by the nip portion, and
The image forming apparatus according to claim 6, wherein the variation portion setting voltage is corrected using an average value difference which is a difference between the image forming apparatus and the image forming apparatus. The control means, when printing on the second side of the recording material,
With respect to the reverse conveyance direction reversed with respect to the recording material conveyance direction, the timing at which the downstream end portion and the upstream end portion of the blank area are sandwiched by the nip portion is determined when the second side is printed. Derived using the timing at which the end and the first end are sandwiched by the nip,
The absolute value of the average value difference from the absolute value of the variable part setting voltage is reduced so that the absolute value of the variable part setting voltage becomes small at the timing when the downstream end of the margin region is sandwiched by the nip part. Make a reduction correction,
The absolute value of the average value difference is set to the absolute value of the variable portion setting voltage so that the absolute value of the variable portion setting voltage becomes large at the timing when the upstream end portion of the margin area is sandwiched by the nip portion. The image forming apparatus according to claim 7, wherein correction to be added is performed. The control means, when printing on the second side of the recording material,
With respect to the reverse conveyance direction reversed with respect to the recording material conveyance direction, the timing at which the downstream end portion and the upstream end portion of the blank area are sandwiched by the nip portion is determined when the second side is printed. Derived using the timing at which the end and the first end are sandwiched by the nip,
Correction that subtracts the absolute value of the difference from the absolute value of the variable part setting voltage so that the absolute value of the variable part set voltage becomes small at the timing when the downstream end of the margin area is sandwiched by the nip part. And
From the time when the downstream end portion of the blank area is sandwiched by the nip portion to the time when the upstream end portion of the blank region is sandwiched by the nip portion, the set voltage is controlled at a constant voltage. Controlling the voltage application means;
Correction for adding the absolute value of the difference to the absolute value of the variable portion setting voltage so that the absolute value of the variable portion setting voltage becomes large at the timing when the upstream end portion of the margin area is sandwiched by the nip portion. The image forming apparatus according to claim 6, wherein: The image carrier is an intermediate transfer body on which a toner image is primarily transferred from the photoreceptor at a transfer nip portion provided between the image carrier and the photoreceptor.
The image forming apparatus according to claim 1, wherein the toner image primarily transferred to the intermediate transfer member is secondarily transferred to a recording material at the nip portion. The image carrier is a photoreceptor;
10. The image according to claim 1, wherein the nip portion is formed between the photoconductor and the transfer member via a conveyance belt that carries and conveys a recording material. Forming equipment.

Images