JP2005266063A - Image forming apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and an image forming method by which a bias determination precision can be enhanced without adding an extra sequence for a resistance detection even when there is uneven resistance in the peripheral direction of a rotary member. <P>SOLUTION: In steps S12 and S14, a voltage applied to a transfer roll is varied, and also the voltage applied to the transfer roll is adjusted while a current is detected at predetermined time intervals. In step S16 during the voltage adjustment period, the resistances of at least two circumferential parts of the transfer roll are measured from changes in voltage and current during the voltage adjustment. Based upon the results of the measurement, a voltage before or for transfer is determined. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile, and an image forming method.

  For example, in an electrophotographic image forming apparatus, a transfer roll, which is a rotating member, faces a photoconductor, which is an image carrier, and a toner image formed on the photoconductor is transferred to the photoconductor by a bias applied to the transfer roll. It is transferred to a recording medium that passes between the rolls.

  The transfer performance of the transfer roll varies greatly with changes in environmental conditions such as temperature and humidity. For this reason, it is known to control the bias voltage or current of the transfer roll in response to changes in environmental conditions. For example, Patent Document 1 discloses that a resistance value of a transfer roll is detected at the time of pre-rotation of the transfer roll, and then a reverse polarity bias is applied. Patent Document 2 discloses that the output voltage is controlled by measuring the resistance value of the transfer roll from the detection circuit during constant voltage control. Patent Document 3 discloses that the resistance value of the transfer roll is directly detected by measuring the current flowing from the charging unit to the transfer roll when the power is turned on. Patent Document 4 discloses that, for example, a constant current is supplied to the transfer roll during a cleaning cycle to calculate the impedance of the transfer roll, and an appropriate current is calculated. Patent Document 5 discloses that resistance detection is performed a plurality of times during the pre-rotation process, and when the resistance is lower than a desired value, a different transfer constant voltage bias is determined for each resistance detection process. Patent Document 6 discloses that a transfer bias is determined by detecting a resistance value of a member involved in transfer when the sheet is not passed through a transfer unit.

  On the other hand, the transfer roll may have uneven resistance in the rotational direction (circumferential direction) due to uneven material distribution during manufacture, dirt adhesion during use, deterioration, or the like. For this reason, it is known to control the transfer bias in consideration of uneven resistance values in the circumferential direction of the transfer roll. For example, Patent Document 7 discloses that the resistance value distribution in the rotation direction of the transfer roll is detected immediately before the printing operation of the image forming apparatus to determine the bias of the transfer roll. Patent Document 8 discloses that the voltage is variably controlled within one rotation of the transfer roll around the target voltage during printing by the image forming apparatus. Patent Document 9 discloses that the voltage / current of the transfer roll at the time of non-printing is read and the bias applied to the transfer roll is calculated.

Japanese Patent Laid-Open No. 05-181373 JP 05-31522 A Japanese Patent Laid-Open No. 08-115000 JP-A-10-301408 Japanese Patent Laid-Open No. 2000-075694 JP 2003-057969 A JP 05-297740 A Japanese Patent Laid-Open No. 06-186867 Japanese Patent Laid-Open No. 08-186867

In order to adjust the bias of the rotating member such as the transfer roll in response to the influence of the environment, a predetermined sequence is performed.
However, in the above-described conventional example, the sequence for adjusting the bias of the rotating member and the correction due to the uneven circumferential resistance of the rotating member are performed regardless of the sequence. Therefore, when both are performed, it takes time to perform a sequence for adjusting the bias and time to perform a sequence for correcting the resistance unevenness, and it takes a long time to determine the bias. There is.

  An object of the present invention is to provide an image forming apparatus and an image forming method capable of improving bias determination accuracy without adding an extra sequence for resistance detection even when the rotating member has uneven resistance in the circumferential direction. It is to provide.

  The first feature of the present invention is that the image carrier, a rotating member that rotates against the image carrier, a bias applying unit that applies a bias to the rotating member, and the non-printing operation during the non-printing operation. Adjustment means for adjusting the voltage or current applied to the rotating member by rotating the rotating member, and measurement for measuring a change in voltage and current between at least two points in the circumferential direction of the rotating member during adjustment by the adjusting means And an image forming apparatus having setting means for setting the voltage or current value of the bias means before or during the printing operation based on the measurement result of the measuring means.

  Here, the image carrier includes a photosensitive member (photosensitive drum, photosensitive belt) and an intermediate transfer member (intermediate transfer drum, intermediate transfer belt). The rotating member is mainly a transfer roll or a transfer belt, but also includes a charging roll and a developing roll.

  Preferably, the measurement means divides a region including one rotation of the rotating member into at least two, and measures resistance values at two points in each of the divided regions.

  Preferably, the measuring unit divides one rotation of the rotating member into two parts, a first half and a second half, and measures resistance values at two points in each of the divided areas.

  Preferably, the setting unit places more weight on the resistance value in the second half than the resistance value in the first half by the measuring unit.

  Preferably, the measurement means obtains the maximum and minimum resistance values.

  Preferably, the adjustment means finely adjusts the voltage or current applied to the rotating member after the adjustment by the first adjusting means for roughly adjusting the voltage or current applied to the rotating member, and the adjustment by the first adjusting means. Second adjusting means.

  The second feature of the present invention is that the rotating member facing the image carrier is rotated during the non-printing operation to adjust either the voltage or the current applied to the rotating member, and this adjustment is in progress. In addition, an image forming method for measuring a resistance value of at least two points in the circumferential direction of the rotating member and setting a voltage or a current value to be applied to the rotating member before or during a printing operation based on the measurement result. is there.

  Therefore, for example, when the voltage / current adjustment sequence requires a time corresponding to 1.5 rotations of the transfer roll, adding one rotation of the resistance unevenness detection sequence transfer roll requires a total of 2.5 rotations. According to the present invention, 1.5 laps can be completed.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an outline of an image forming apparatus 10 according to an embodiment of the present invention. The image forming apparatus 10 includes a photoreceptor 12, and a charging roll 14, a laser exposure device 16, a developing device 18, a transfer roll 20, and a cleaner 22 are disposed around the photoreceptor 12.

  In the photoreceptor 12, a photosensitive layer 26 is formed around the drum base 24. The drum base 24 is made of a conductor such as aluminum and is grounded. The photosensitive layer 26 is composed of an inorganic or organic photoconductor. The charging roll 14 is pressed against the photoconductor 12 with a predetermined pressing force, and is driven to rotate as the photoconductor 12 rotates. By applying a predetermined charging bias to the charging roll 14, the peripheral surface of the rotating photoreceptor 12 is uniformly charged to a predetermined polarity and potential. The laser exposure device 16 emits laser light corresponding to the image signal to the photosensitive member 12 to form a latent image on the photosensitive layer 26 of the photosensitive member 12. The developing unit 18 includes a developing roll 28 that rotates with a toner layer formed thereon, and applies a predetermined bias to transfer the toner to the photoconductor 12 to form a toner image on the photoconductor 12.

The transfer roll 20 includes a conductive rotating shaft 30 and a conductive rubber layer 32 formed on the outer periphery thereof. The rubber layer 32 is adjusted so that conductive particles are dispersed in a relatively soft rubber material such as EPDM, urethane, silicon, etc., and the volume resistance is about 10 ⁵ to 10 ¹⁰ Ω. Further, the transfer roll 20 is pressed against the photoconductor 12 to form a nip portion 34 with the photoconductor 12. The transfer roll 20 is in contact with the photoconductor 12 via the tracking roll 36, and rotates with a slightly faster peripheral speed with respect to the photoconductor 12 as the photoconductor 12 rotates by a gear. A paper guide 38 is provided in front of the nip portion 34, and the paper P is guided to the nip portion 34 by the paper guide 38, and the toner image is transferred to the paper P by passing through the nip portion 34. The toner image is fixed on the paper P by the fixing device that does not.

  A rotary shaft 30 of the transfer roll 20 is connected to a high voltage power source 42 via a current detector 40. The high voltage power source 42 has a variable voltage and outputs a constant voltage V set by the controller 44. The current detector 40 detects a current supplied from the high voltage power source 42 to the transfer roll 20 and outputs the detected current I to the controller 44.

  In FIG. 2, the circuit configuration of the controller 44 is shown. The controller 44 is configured by connecting a current detector interface 46, a CPU 48, a motor interface 50, a voltage setting circuit 52, a memory 54 constituting storage means, and the like to a bus 56. A detection current I from the current detector 40 is input at predetermined intervals via the current detector interface 46 in accordance with a command from the CPU 48, and each value is stored in the memory 54. Further, the drive motor 58 is controlled through the motor interface 50 in accordance with a command from the CPU 48. The drive motor 58 rotates the photoconductor 12. In addition, a constant voltage is set in the voltage setting circuit 52 by a command from the CPU 48, and the applied voltage V is determined by the voltage setting circuit 52.

  FIG. 3 shows a control flow related to transfer by the CPU 48 of the controller 44. First, step S10 is preprocessing, for example, a drive signal is output to the drive motor 52 via the motor interface 50, the photoconductor 12 is rotated, and the photoconductor 12 and the transfer roll 20 have a predetermined peripheral speed. Further, the contents stored in the memory 54 are cleared, and each member is checked for failure.

The next step S12 is a first voltage adjustment process, in which the applied voltage V of the high-voltage power supply 42 is roughly adjusted based on the detected current I detected from the current detector 40.
That is, when the applied voltage Vn-1 at a certain time tn-1, the detected current In-1 and the constant at this time is A, the applied voltage Vn for the next time tn is obtained according to the equation (1), and this processing is performed. Is repeated at predetermined time intervals over a predetermined period to adjust the applied voltage.
Vn = Vn-1 * (A / In-1) (1)

The next step S14 is a second voltage adjustment process, in which the applied voltage V of the high voltage power source 42 is finely adjusted based on the detected current I detected from the current detector 40.
That is, when the applied voltage Vn-1 at a certain time, the detected current In-1 and the constant at this time are B, the next applied voltage Vn is obtained according to the equation (2), and this process is performed at predetermined time intervals. The applied voltage is adjusted repeatedly over a period of time.
Vn = Vn-1 * (B / In-1) (2)

During the processing of step S12 and step S14, that is, during the first voltage adjustment period and the second voltage adjustment period, as step S16, at least two points of the transfer roll 20 from the relationship with the voltage current. Measure the resistance value at.
In this embodiment, a time that is one round of the transfer roll 20 from the time when the second voltage adjustment period ends is divided into two, and the area is divided into the first half and the second half of the transfer roll 20. . Then, the maximum and minimum resistance values in each region are obtained. In order to obtain the maximum and minimum resistance values, all the resistance values measured at predetermined times may be stored in the memory 54 for comparison, or the previously measured resistance value and the currently measured resistance value may be compared with each other. May be stored, and only the larger or smaller one may be stored.
Here, the maximum resistance value of the first half is Rmin_f, the minimum resistance value of the first half is Rmax_f, the maximum resistance value of the second half is Rmin_b, the minimum resistance value of the second half is Rmax_b, and the overall average resistance value R is expressed by the following (3) to ( 4) Determined by the equation.
Rmin = (α · Rmin_f + β · Rmin_b) / (α + β) (3)
Rmax = (α · Rmax_f + β · Rmax_b) / (α + β) (4)
R = (Rmin + Rmax) / 2 (5)
However, 0 <α <β is set, and the resistance value measured in the latter half is emphasized.

In the next step S18, the final applied voltage Ve before transfer is determined.
The final applied voltage Ve before transfer is obtained by the following equation (6).
Ve = Id · R (6)
However, Id is a constant, and may be set to Id = B by using B of the second voltage adjustment processing in step S14.

Next, examples will be described.
In the first embodiment, the image forming apparatus having the above-described configuration is used, the rotational speed of the above-described photoconductor 12 is 141 mm / sec, the diameter of the transfer roll 20 is 16.15 mm, and the diameter of the tracking roll 36. Is 15.85 mm. The transfer roll 20 is driven by a gear at a peripheral speed 1.056 times that of the photoreceptor 12. Therefore, the rotation period of the transfer roll 20 in this embodiment is 334 msec.

  FIG. 4A shows the result of measuring the resistance value change in the rotation direction (circumferential direction) of the transfer roll (BTR) 20. The vertical axis represents the BTR resistance value (MΩ), and the horizontal axis represents the time (sec). As described above, the transfer roll 20 has uneven resistance in the rotation direction (circumferential direction) due to uneven material distribution during manufacture, dirt adhesion, deterioration during use, and the like. Process speed, transfer roll diameter, tracking From the roll diameter and the peripheral speed ratio between the photoconductor 12 and the transfer roll 20, the maximum resistance portion and the minimum resistance portion pass through the nip portion 34 at a cycle of 334 msec (0.334 sec).

  FIG. 4B shows the result of performing voltage control on the transfer roll 20 in accordance with the control flow shown in FIG. The vertical axis represents voltage (V), and the horizontal axis represents time t (sec). The first voltage adjustment starts at time 0.00 sec and ends at time 0.30 sec. During the first voltage adjustment period, the current was detected from the current detector 40 to the controller 44 every 20 msec, and voltage adjustment was performed according to the equation (1). Here, A = 6.0.

  The second voltage adjustment starts at time 0.40 sec and ends at time 0.60 sec. During the second voltage adjustment period, the current was detected from the current detector 40 to the controller 44 every 20 msec, and the voltage adjustment was performed according to the equation (2). Here, B = 9.0.

  The region is divided into the first half and the second half retrospectively (0.334 sec) from the time 0.60 sec when the second voltage adjustment ends. The first half starts at time 0.28 sec and ends at time 0.42 sec. The second half starts at time 0.44 and ends at time 0.60. In the first half period, 8 times of applied voltage Vn and detection current In were used every 20 msec, and the minimum value and the maximum value of Vn / In were set to Rmin_f and Rmax_f, respectively. Similarly, in the latter half period, nine times of applied voltage Vn and detection current In are used every 20 msec, and the minimum value and the maximum value of Vn / In are set to Rmin_b and Rmax_b, respectively.

  FIG. 4-3 shows the relationship between the time change of Vn / In and the maximum value and minimum value of the resistance value. The vertical axis represents Vn / In (MΩ), and the horizontal axis represents time t (sec). Compared to FIG. 4A, it can be seen that the change in the resistance value in the circumferential direction of the transfer roll 20 is reflected in the maximum and minimum resistance values obtained from Vn / In.

Rmin_f, Rmax_f, Rmin_b, and Rmax_b obtained as described above were put into Equations (3) and (4), and an overall average resistance value R was obtained from Equation (5). Here, α = 1.0 and β = 3.0.
Then, the average resistance value R was put into the equation (6) to determine the final applied voltage Ve before transfer. Here, Id = B, that is, Id = 9.0. As a result, the final applied voltage Ve before transfer was determined to be 2556V. The applied voltage at the time of transfer is obtained by multiplying the final applied voltage Ve before transfer by a coefficient.

Example 2 is shown in FIGS. 5-1 to 5-3.
The first embodiment described above is a case where the second voltage adjustment period ends at the time when the resistance of the nip portion 34 is at the minimum value. On the other hand, the second embodiment is performed when the second voltage adjustment period ends at the time when the resistance of the nip portion 34 is at the maximum value. In Example 2, the same control as in Example 1 was performed. As a result, the final applied voltage Ve before transfer was determined to be 2475V.

Comparative Example 1 is shown in FIGS. A comparative example 2 is shown in FIGS. In Comparative Example 1 and Comparative Example 2, the resistance value measurement of the nip portion is not performed, and the voltage when the second voltage adjustment period ends is directly used as the final applied voltage Ve before transfer. Comparative Example 1 is a case where the second voltage adjustment period ends at the time when the resistance of the nip portion 34 is at the minimum value, and Comparative Example 2 is the case where the resistance of the nip portion 34 is at the maximum value. This is performed when the voltage adjustment period 2 ends. In Comparative Example 1, the final applied voltage before transfer Ve = 2151V is determined, and in Comparative Example 2, the final applied voltage Ve before transfer is determined to be 2706V, and the difference is 551V.
On the other hand, according to Example 1 and Example 2 described above, the difference was 2556V-2475V = 91V, and the variation could be reduced to 1/6 or less as compared with the comparative example.

  In the above-described embodiments and examples, the current is detected by changing the voltage. Conversely, the voltage may be detected by changing the current.

1 is a schematic view of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a controller used in an image forming apparatus according to an embodiment of the present invention. 3 is a flowchart illustrating a control flow of the image forming apparatus according to the embodiment of the present invention. It is a figure which shows the time change of the transfer nip part resistance in Example 1 which concerns on this invention. It is a figure which shows the time change of the voltage V and the electric current I in Example 1 which concerns on this invention. . It is a figure which shows the time change of Vn / In and the maximum value minimum value of resistance in Example 1 which concerns on this invention. It is a figure which shows the time change of the transfer nip part resistance in Example 2 which concerns on this invention. It is a figure which shows the time change of the voltage V and the electric current I in Example 2 which concerns on this invention. . It is a figure which shows the time change of Vn / In and the maximum value minimum value of resistance in Example 2 which concerns on this invention. FIG. 10 is a diagram illustrating a change over time in transfer nip portion resistance in Comparative Example 1; It is a figure which shows the time change of the voltage V and the electric current I in the comparative example 1. FIG. . FIG. 9 is a diagram showing a change over time in transfer nip portion resistance in Comparative Example 2. It is a figure which shows the time change of the voltage V and the electric current I in the comparative example 2. FIG. .

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photoconductor 14 Charging roll 20 Transfer roll 28 Developing roll 34 Nip part 40 Current detector 42 High voltage power supply 44 Controller 54 Memory

Claims (7)

An image carrier;
A rotating member that rotates against the image carrier;
Bias applying means for applying a bias to the rotating member;
An adjusting means for rotating the rotating member during a non-printing operation to adjust a voltage or current applied to the rotating member;
Measuring means for measuring resistance values of at least two points in the circumferential direction of the rotating member during adjustment by the adjusting means;
Setting means for setting the voltage or current value of the bias means before or during the printing operation based on the measurement result of the measuring means;
An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein the measurement unit divides an area including one rotation of the rotating member into at least two areas and measures resistance values at two points in each of the divided areas. apparatus.   3. The image according to claim 2, wherein the measuring means divides one rotation of the rotating member into two parts, a first half and a second half, and measures resistance values at two points in each of the divided areas. Forming equipment.   The image forming apparatus according to claim 3, wherein the setting unit places more weight on the resistance value in the latter half than the resistance value in the first half by the measuring unit.   The image forming apparatus according to claim 1, wherein the measuring unit obtains the maximum and minimum resistance values.   The adjustment means includes a first adjustment means for roughly adjusting a voltage or current applied to the rotating member, and a second adjustment for finely adjusting the voltage or current applied to the rotating member after adjustment by the first adjusting means. The image forming apparatus according to claim 1, further comprising: an adjusting unit. An image bearing member rotating a rotating member facing the image bearing member during a non-printing operation to adjust a voltage or current applied to the rotating member;
During this adjustment, the resistance values of at least two points in the circumferential direction of the rotating member are measured,
Based on this measurement result, the voltage or current value to be applied to the rotating member before or during the printing operation is set.
An image forming method.

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