JP2008015268A - Image forming apparatus, its control method, and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive and small image forming apparatus, wherein occurrence of charging failure is prevented even in the simple configuration of a power source, and charge control to minimize wear of a photoreceptor is made possible. <P>SOLUTION: The image forming apparatus has a current detection circuit 26 for detecting a current flowing in a photoreceptor drum 1 according to a charging voltage. In an image non-formation step, the apparatus sets a charging voltage range so as to use a charging voltage in the previous image formation step, stored in a memory 90, as a reference voltage. Within the set range, a detection charging voltage for detecting a charging current is set to the charging voltage supply part 53. When the set detection charging voltage is supplied from the charging voltage supply part 53, a current value detected by the current detection circuit 26 is compared with a threshold. A detection charging voltage corresponding to the minimum current value of a current value determined to be greater than the threshold is determined as a charging voltage used for an image formation step. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a laser beam printer, a copying machine, and a facsimile, a control method therefor, and a process cartridge mounted on the image forming apparatus. Here, the process cartridge is a cartridge in which at least one of a charging unit, a developing unit, and a cleaning unit and an electrophotographic photosensitive member are integrally formed, and the cartridge can be attached to and detached from the image forming apparatus main body. Or at least the developing means and the electrophotographic photosensitive member are integrated into a cartridge, and the cartridge can be attached to and detached from the image forming apparatus main body.

  FIG. 22 is a diagram showing a schematic configuration of a recording unit of an image forming apparatus such as an electrophotographic copying machine or printer.

  The photosensitive drum 100 is a rotating drum type electrophotographic photosensitive member as a latent image carrier, and is driven to rotate at a predetermined peripheral speed in the clockwise direction of an arrow. The surface of the photosensitive drum 100 is uniformly charged with a predetermined polarity and potential by the charger 101 during the rotation process. Next, the exposure unit 102 receives image exposure according to the image. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 100. The electrostatic latent image is developed with toner supplied from the developing device 103. The toner image on the photosensitive drum 100 is transferred by a transfer roller 105 to a recording medium 104 such as paper fed from a paper feeding unit (not shown). The recording medium 104 onto which the toner image has been transferred in this manner is separated from the photosensitive drum 100 and introduced into the fixing device 106, where the toner image is fixed. After the recording medium 104 is separated, the surface of the photosensitive drum 100 is cleaned by scraping off the transfer residual toner by the cleaning device 107 and repeatedly used for image formation. Such an image forming apparatus uses the above-mentioned means to perform image formation by repeating the steps of charging, exposure, development, transfer, fixing, and cleaning.

  As the charger 101, a contact charging method in which a charging member such as a roller type or a blade type is brought into contact with the surface of the photosensitive drum 100 and a voltage is applied to the charged charging member to charge the surface of the photosensitive drum 100. Is widely adopted. In particular, the contact charging method using a roller-type charging member (charging roller) is characterized in that stable charging can be performed over a long period of time. A charging bias voltage is applied from the charging bias applying means to the charging roller as the contact charging member. The charging bias voltage may be only a DC voltage, but the DC voltage Vdc corresponding to the dark potential Vd on the desired drum 100 has a peak-to-peak voltage (Vpp) that is at least twice the discharge start voltage when the DC voltage is applied. A bias voltage on which an alternating voltage is superimposed is used (see Patent Document 1). This charging method is excellent in that the surface of the photosensitive drum can be uniformly charged, and there is an advantage that local potential unevenness on the photosensitive drum can be eliminated by applying an AC voltage superimposed on a DC voltage. is there. As a result, the charging potential Vd on the surface of the photosensitive drum uniformly converges to the DC applied voltage value Vdc. However, this method increases the amount of discharge to the photosensitive drum. For this reason, compared with the case where only the DC component is applied as the charging bias voltage, there is a tendency that the surface deterioration such as the surface of the photosensitive drum being worn by the cleaning device 107 is easily promoted. In order to cope with this, it is necessary to suppress the AC peak-to-peak voltage Vpp of the charging bias voltage as small as possible to prevent the charging roller from being excessively discharged to the photosensitive drum.

  The relationship between the AC peak-to-peak voltage (Vpp) and the discharge amount varies depending on the film thickness of the photosensitive layer on the surface of the photosensitive drum, the usage environment, and the like, and is not always constant. For example, even when the same peak-to-peak voltage is applied to the charging roller, the impedance of the charging roller increases in a low temperature / low humidity environment, so the amount of discharge decreases. On the contrary, the discharge amount increases in a high temperature / humidity environment where the impedance decreases. Even when the usage environment is the same, if the surface of the photosensitive drum is scraped due to wear, the impedance decreases compared to the initial usage, and the amount of discharge increases.

  In order to avoid this problem, a method of controlling the AC component of the charging bias with a constant current has been proposed. In this method, the AC current Iac flowing through the photosensitive drum is detected and controlled to be constant. When this method is used, the AC peak-to-peak voltage can be freely changed with respect to changes in impedance due to environmental fluctuations or photoconductor drum scraping. For this reason, the discharge amount can always be kept substantially constant regardless of environmental fluctuations, the thickness of the photosensitive drum, and the like (see Patent Document 2).

  Furthermore, when the AC peak-to-peak voltage Vpp in the discharge area and the non-discharge area is applied to the charger during non-image formation, the AC current Iac flowing through the photosensitive drum is detected. A method has also been proposed in which the amount of discharge current is calculated from the relationship between the two and an alternating voltage that provides an appropriate amount of discharge is applied as a charging bias during image formation. Since this method controls the discharge current more directly, the discharge current can be controlled with higher accuracy than conventional constant current control (see Patent Document 3). These methods have a great effect in extending the life of the photosensitive drum and ensuring good chargeability.

  In addition, it has been proposed that the process cartridge use amount detecting and storing means is mounted on the process cartridge, and the AC peak-to-peak voltage has two or more constant voltage outputs. According to this, it is described that the film thickness of the photosensitive drum is predicted in accordance with the amount of use of the process cartridge, and the AC peak-to-peak voltage is lowered stepwise (see Patent Document 4).

  FIG. 23 is a diagram illustrating a circuit example for performing constant voltage control on the AC component of the charging bias.

The DC voltage is generated by connecting a capacitor C for creating DC voltage via a diode D from a boosting transformer T-AC (voltage boosting means) for AC output. Here, a DC voltage is generated by peak-charging the capacitor C. In this way, a configuration of a power source has been proposed that can output an AC and DC superimposed bias with only one voltage booster T-AC (see Patent Document 5). According to this, since a transformer dedicated to DC voltage can be omitted, the configuration of the power supply circuit can be greatly simplified as compared with the case of constant current control, and there are great advantages in terms of cost and space saving of the power supply circuit. In addition, a cartridge memory medium that stores information on the amount of process cartridge used and information on parameter values unique to the process cartridge has also been proposed (see Patent Document 6).
JP-A 63-149669 Japanese Examined Patent Publication No. 06-093150 (pages 4-5, FIG. 2) JP 2001-201920 (pages 11-14, FIG. 4) Japanese Unexamined Patent Publication No. 09-190143 (pages 4-5, FIG. 1) Japanese Patent Laid-Open No. 11-258957 (page 3, FIG. 16) JP 2001-117468 A (pages 6-7, FIG. 6)

  As described above, in order to control the amount of discharge from the charging means to the image carrier so as to be substantially constant regardless of the use situation, a constant current control method for alternating current components as in Patent Document 2, What is necessary is just to employ | adopt the discharge amount calculation system like patent document 3. FIG. However, these methods require highly accurate parts in the feedback circuit and the like, which increases costs. Further, as shown in FIG. 23 (Patent Document 5), in the example in which the superimposed voltage of alternating current and direct current is output by one voltage boosting means T-AC, the second half of the drum usage (drum The condition is such that the AC peak-to-peak voltage is reduced under conditions such as the amount of use increasing and the drum life approaching. For this reason, under such an environment or condition, a voltage for peak charging of the capacitor C for generating a DC voltage cannot be obtained, and the photosensitive member cannot be charged to a predetermined potential. Therefore, when the power source is constituted by one voltage boosting means, the range of the charging voltage can be restricted. Therefore, there is a limit in outputting a superimposed voltage of AC and DC with one voltage boosting means. Therefore, in order to obtain a stable charging bias voltage, it is necessary to divide the DC power supply T-DC and the AC power supply T-AC as shown in FIG. 24 and mount two voltage boosting means for DC and AC. there were.

  However, such voltage boosting means is expensive and large in size among the charge generation circuits. Therefore, particularly in a small and low-cost image forming apparatus, it is desirable to obtain a stable charging bias voltage with a single voltage booster from the viewpoint of space saving and cost reduction of the power supply circuit.

  In the method of Patent Document 4, voltage switching (AC peak-to-peak voltage reduction) is performed when a predetermined timing (photosensitive member usage amount) is reached. For this reason, for example, when the AC peak-to-peak voltage output is the tolerance lower limit, the voltage switching is performed even though the discharge amount is appropriate, and the discharge amount becomes insufficient, and charging failure may occur. Furthermore, when the AC peak-to-peak voltage output is at the upper limit of tolerance, it is conceivable that, although the discharge amount is excessive, the voltage is not switched until a predetermined timing, and the abrasion of the photosensitive drum is accelerated. Therefore, in this method, it is necessary to reduce the power supply tolerance of the charging bias generation circuit. Therefore, it is necessary to adjust the power supply, which is a disadvantage in terms of cost.

  Due to the circumstances described above, in a small and low-cost image forming apparatus, there has been a demand for charging control that does not cause charging failure even with a simple power supply configuration and minimizes wear abrasion of the photosensitive member.

  An object of the present invention is to solve the above-mentioned conventional problems.

  The feature of the present invention is to provide a technique capable of performing good charge control even if the charging voltage, the impedance of the charging means and the image carrier vary, and the like.

In order to achieve the above object, an image forming apparatus according to an aspect of the present invention has the following configuration. That is,
An image forming apparatus having an image carrier and a charging member for charging the image carrier, and a process cartridge provided with a storage medium is detachable.
Charging voltage supply means capable of supplying a plurality of alternating voltages as charging voltages to the charging member;
Current detection means for detecting a current flowing through the image carrier in accordance with a charging voltage supplied from the charging voltage supply means;
In a non-image forming step, range setting means for setting a charging voltage range using a charging voltage in the previous image forming step stored in the storage medium as a reference voltage;
Charging voltage setting means for setting a charging voltage for detection for detecting a charging current in the charging voltage supply means within the range set by the range setting means;
A comparison unit that compares a current value detected by the current detection unit with a threshold value when a charging voltage for detection set by the charging voltage setting unit is supplied from the charging voltage supply unit;
Control means for determining a charging voltage for detection corresponding to a minimum current value of a current value determined to be a current value larger than the threshold value by the comparison means as a charging voltage in the image forming step;
It is characterized by having.

In order to achieve the above object, an image forming apparatus according to an aspect of the present invention has the following configuration. That is,
A mounting means for mounting a process cartridge including at least an image carrier, a charging member for charging the image carrier, and a storage medium;
Charging voltage supply means capable of supplying a plurality of alternating voltages as charging voltages to the charging member;
Current detection means for detecting a current flowing through the image carrier in accordance with a charging voltage supplied from the charging voltage supply means;
In a non-image forming step, a range setting unit that sets a charging voltage range using a charging voltage in a previous image forming step stored in the storage medium of the process cartridge mounted on the mounting unit as a reference voltage;
Charging voltage setting means for setting a charging voltage for detection for detecting a charging current in the charging voltage supply means within the range set by the range setting means;
A comparison unit that compares a current value detected by the current detection unit with a threshold value when a charging voltage for detection set by the charging voltage setting unit is supplied from the charging voltage supply unit;
Control means for determining a charging voltage for detection corresponding to a minimum current value of a current value determined to be a current value larger than the threshold value by the comparison means as a charging voltage in the image forming step;
It is characterized by having.

In order to achieve the above object, a method for controlling an image forming apparatus according to an aspect of the present invention includes the following steps. That is,
A control method of an image forming apparatus for forming an image by mounting a process cartridge including at least an image carrier, a charging member for charging the image carrier, and a storage medium,
A current detection step of detecting a current flowing through the image carrier in accordance with a charging voltage supplied from a charging voltage supply unit capable of supplying a plurality of AC voltages as charging voltages to the charging member;
In a non-image forming step, a range setting step for setting a charging voltage range using a charging voltage in the previous image forming step stored in the storage medium of the process cartridge as a reference voltage;
A charging voltage setting step for setting a charging voltage for detection for charging current detection in the charging voltage supply unit within the range set in the range setting step;
A comparison step for comparing the current value detected in the current detection step with a threshold when the detection charging voltage set in the charging voltage setting step is supplied from the charging voltage supply unit;
A control step of determining a charging voltage for detection corresponding to a minimum current value of the current value determined to be a current value larger than the threshold value in the comparison step as a charging voltage in the image forming step;
It is characterized by having.

In order to achieve the above object, a process cartridge according to an aspect of the present invention has the following configuration. That is,
A process cartridge that is mounted on an image forming apparatus and includes at least an image carrier, a charging member that charges the image carrier, and a storage medium,
The storage medium is
A first storage area for storing a usage amount of the image carrier;
A second storage area for storing a threshold value to be compared with the usage amount of the image carrier stored in the first storage area;
A third storage area for storing data for specifying the charging voltage in the previous image forming process;
A fourth storage area for storing data for specifying a target value of a current to be compared with a current flowing through the image carrier;
Connection means for enabling access from the apparatus main body to the storage medium when the process cartridge is mounted in the image forming apparatus main body;
It is characterized by having.

  The means for solving this problem does not enumerate all the features of the present invention, and other claims described in the claims and combinations of these feature groups can also be the invention. .

  According to the present invention, it is possible to prevent charging failure due to variations in charging voltage and impedance between the charging unit and the image carrier, and to perform favorable charging control.

  Furthermore, since an appropriate charging voltage can be determined in a short time, the first printout time can be shortened.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the present embodiments are essential to the solution means of the present invention. Not exclusively.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. Note that the image forming apparatus according to the present embodiment is an electrophotographic type and a process cartridge detachable laser printer.

  Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (photosensitive drum) as a latent image carrier. This photosensitive drum 1 is a negatively charged organic photosensitive member, and is rotated at a predetermined peripheral speed in the clockwise direction of an arrow by a driving motor (not shown) rotated by a photosensitive drum driving circuit (FIG. 15). Driven. The photosensitive drum 1 is uniformly charged to a predetermined negative potential by a charger during its rotation. This charger is a contact charger using a charging roller 21 as a charging member. The charging roller 21 is driven to rotate with respect to the photosensitive drum 1. A bias voltage is applied to the charging roller 21 from a charging bias power source 98. As this bias voltage, a method is used in which a DC voltage Vdc corresponding to a desired on-drum potential Vd is superimposed and applied to an AC voltage having a peak-to-peak voltage (Vpp) that is twice or more the discharge start voltage. . This charging method eliminates local potential unevenness on the photosensitive drum 1 by applying an alternating voltage to the direct current voltage, and uniformly charges the photosensitive drum 1 to a potential Vd substantially equal to the direct current applied voltage Vdc. It aims to.

  Next, the image exposure by the exposure apparatus 30 is received. This exposure device 30 forms an electrostatic latent image on the surface of the uniformly charged photoreceptor drum 1, and in this example, a semiconductor laser scanner is used. The exposure device 30 outputs a laser beam b modulated in accordance with an image signal sent from a control unit 51 (FIG. 7) in the image forming apparatus. The laser beam b is reflected by the reflecting mirror 31, and scans and exposes (image exposures) the uniformly charged surface of the photosensitive drum 1 through an exposure window portion a of a process cartridge C described later. On the surface of the photosensitive drum 1, the absolute value of the potential of the portion exposed to the laser beam b is lower than the absolute value of the charging potential. In this way, electrostatic latent images corresponding to the image information are sequentially formed on the surface of the photosensitive drum 1.

  Next, the electrostatic latent image is developed by the reversal developing device 40 to be visualized as a toner image. In this embodiment, a jumping development method is used. In this method, a developing bias voltage in which alternating current and direct current are superimposed is applied from the developing bias power source 99 to the developing sleeve 41. As a result, the toner negatively charged by frictional charging at the contact portion between the developer layer thickness regulating member 42 and the developing sleeve 41 is applied to the electrostatic latent image on the surface of the photosensitive drum 1 and electrostatically applied. The latent image is reversely developed.

  The developed toner image on the photosensitive drum 1 is transferred by a transfer device to a recording medium (transfer material) P such as paper fed from the paper supply unit 87. In this embodiment, the transfer device is a contact transfer device using the transfer roller 5. The transfer roller 5 is pressed against the photosensitive drum 1 in the center direction of the photosensitive drum 1 by an urging means such as a pressing spring (not shown). When the transfer material P is thus conveyed and the transfer process is started, a positive transfer bias voltage is applied to the transfer roller 5 from the transfer bias power supply 88, and the negatively charged toner on the photosensitive drum 1 is transferred. And transferred onto the transfer material P.

  The transfer material P onto which the toner image has been transferred is separated from the surface of the photosensitive drum 1 and introduced into the fixing device 70 to fix the toner image, and then is discharged onto the paper discharge tray 85. The fixing device 70 fixes the toner image transferred to the transfer material P as an image using means such as heat and pressure.

  The surface of the photosensitive drum 1 after the transfer material P is separated is cleaned by scraping off the remaining toner without being transferred by the cleaning device 60, and the surface of the photosensitive drum 1 is repeatedly used for image formation. The The cleaning device 60 according to the present embodiment uses a cleaning blade 61. The cleaning blade 61 collects transfer residual toner that was not completely transferred from the photosensitive drum 1 to the transfer material P during the transfer process. The cleaning blade 61 is brought into contact with the photosensitive drum 1 with a constant pressure, and cleans the surface of the photosensitive drum 1 by collecting the transfer residual toner. After the completion of this cleaning process, the surface of the photosensitive drum 1 enters the charging process again. As described above, the image forming apparatus uses the above-described means to perform image formation by repeating the charging, exposure, development, transfer, fixing, and cleaning steps.

  The process cartridge C is a process cartridge that can be attached to and detached from the image forming apparatus main body L. The process cartridge C includes four process devices including a photosensitive drum 1 as a latent image carrier, a charging roller 21 as a contact charging member for the photosensitive drum 1, a developing device 40, and a cleaning device 60. As a process cartridge. Further, the process cartridge C is provided with a memory 90 as a storage unit. Information is read from and written to the memory 90 via the reading unit and writing unit (FIGS. 5 and 7) of the image forming apparatus main body L.

  The process cartridge C is attached to and detached from the image forming apparatus main body L by opening and closing a door (cartridge door) 86 of the image forming apparatus main body L. The process cartridge C is mounted by opening the door 86, inserting and mounting the process cartridge C in the image forming apparatus main body L, and closing the main body door 86. The transmission means of the process cartridge C includes a positioning portion 97 and a metal contact 96. Thus, when the process cartridge C is properly attached to the image forming apparatus main body L, the memory 90 is electrically connected to the reading unit and the writing unit of the apparatus main body L, and data writing to the memory 90 is performed. In addition, data can be read from the memory 90. The process cartridge C is detached from the image forming apparatus main body L by opening the door 86 and pulling out the process cartridge C from the image forming apparatus main body L.

  FIG. 2 is a structural sectional view showing the configuration of the process cartridge C according to the present embodiment. Here, a state where the process cartridge C is removed from the main body L is shown.

  In this state, the drum cover 11 is moved to a closed position, and the exposed lower surface of the photosensitive drum 1 is concealed and protected. The exposure window portion a is also held closed by the shutter plate 12. When the process cartridge C is mounted on the image forming apparatus main body L, the drum cover 11 and the shutter plate 12 are respectively moved to the open position and held.

  Further, according to the present embodiment, the amount of use of the photosensitive drum 1 is written and stored in the memory 90. If the image forming apparatus can determine the usage amount of the photosensitive drum 1 stored in the memory 90, the meaning or configuration of the data is not particularly limited. For example, the rotation time of the photosensitive drum 1, the application time of a bias voltage such as charging, development, and transfer, the number of printed sheets, and a value obtained by weighting each usage amount may be used.

  Further, threshold information to be compared with the stored usage amount of the photosensitive drum 1 and data specifying process conditions to be set when the usage amount reaches the threshold value are stored in advance at the time of factory shipment or the like. 90 is information to be stored. This threshold information is information relating to timing for switching process conditions. This information includes, for example, the rotation time of the photosensitive drum 1, the application time of the bias voltage, and a value obtained by combining the respective usage amounts. The threshold information is a value corresponding to the usage amount of the photosensitive drum 1, and the threshold information can be used as a timing for switching process conditions.

  FIG. 3 is a diagram for explaining information stored in the memory 90 according to the present embodiment.

  The usage amount W (90a) of the photosensitive drum 1 and threshold information Wi (90b) of the usage amount are stored. Further, process condition specifying data Bwi (90d) for specifying the target current value Iwi is stored as a process condition that is changed when the usage amount W reaches the threshold information Wi. Further, in the process cartridge C, data Am (90c) for specifying the charging voltage Vppm applied during image formation is stored. Note that k (90e) is a calculation coefficient.

  The usage amount W (drum scraping amount) of the photosensitive drum 1 in this image forming apparatus is represented by W = tp + k × td. Here, tp is the total application time of the charging AC bias voltage, and td is the total rotation time of the photosensitive drum 1. This calculation method is obtained based on the result of the study of the contribution of the rotation time of the photosensitive drum and the voltage application time with respect to the amount of wear of the photosensitive drum 1 in the sequence according to the present embodiment. The target current value Iwi is an alternating current value that does not generate a black spot image (sandy image) generated in a portion where the charging of the photosensitive drum 1 is not sufficiently performed when the discharge amount of the charging roller 21 is small. is there.

  The previous charging voltage data Am stored in the memory 90 is data for the controller 51 of the image forming apparatus to specify the charging voltage Vppm. The process condition specifying data Bwi is a value for comparing the detected current value Iacm with a value (Cm) A / D converted by the control unit 51 after converting the detected current value Iacm to a voltage of 0 to 3.4 V. is there. Therefore, these values are all hexadecimal data.

  FIG. 4 is a diagram for explaining an outline of an operation sequence in the image forming apparatus according to the present embodiment.

  First, when the image forming apparatus is powered on, an initial process 401 is started. In the initial step 401, the presence / absence of the process cartridge C is detected and the transfer roller 5 is cleaned while the photosensitive drum 1 is driven to rotate. When the initial process 401 is completed and no image information (print signal) is sent from the host computer (not shown) to the image forming apparatus, the apparatus enters a standby (standby) state and waits for reception of the image information. . When image information is sent during the initial step 401, the rotation of the photosensitive drum 1 is continued, and the pre-image formation step 402 is continued from the initial step 401. In this pre-image formation step 402, preparatory operations for various process devices are performed. Mainly, the photosensitive drum 1 is precharged, the laser scanner 30 is started, the transfer print bias is determined, the temperature of the fixing device 70 is adjusted, and the like. Is called.

  When the pre-image formation process 402 is thus completed, the first image formation process 403 is started. In this image forming step 403, feeding of the transfer material P, exposure of laser light onto the photosensitive drum 1, development, and the like are performed at a predetermined timing. When this image forming process 403 is completed, if there is next image information, the process enters a paper gap process 404 until the next transfer material P arrives, and waits for the next image forming operation.

  If there is no next image information after the end of the image forming operation, the image forming apparatus enters a post-image forming step 405. In this post-image formation step 405, processes such as charge removal on the surface of the photosensitive drum 1 and discharging of toner adhering to the transfer roller 5 to the photosensitive drum 1 (cleaning of the transfer roller 5) are performed. When the post-image formation step 405 is completed in this manner, the image forming apparatus again enters a standby (standby) state and waits for the next image information (print signal).

  FIG. 5 is a block diagram illustrating a configuration of a charging bias power supply circuit that generates a charging bias voltage according to the present embodiment.

  In the present embodiment, the charging bias power supply circuit 98 is supplied from the AC oscillation output unit 53 by Vppm (m = 1 to 8: Vpp1> Vpp2> Vpp3> Vpp4> Vpp5> Vpp6) which are eight different AC peak-to-peak voltages. > Vpp7> Vpp8). The output of the AC peak charging voltage Vppm from the AC oscillation output unit 23 is selectively performed when the control unit 51 controls the charging voltage selection unit 52.

  First, the output voltage output from the AC oscillation output unit 53 is amplified by the amplifier circuit 23 and converted into a sine wave voltage by the sine voltage conversion circuit 24 including an operational amplifier, a resistor, a capacitor, and the like. The sine wave voltage is input to the step-up transformer T1 after the DC component is cut to zero by the capacitor C1. The voltage input to the step-up transformer T1 is boosted to a sine voltage corresponding to the number of turns of the transformer. The secondary side capacitor C2 of the step-up transformer T1 is peak-charged after the boosted sine voltage is rectified by the rectifier circuit D1. As a result, a constant DC voltage Vdc1 is generated.

  Further, the DC voltage oscillation output unit 54 outputs an output voltage determined by the density to be printed. This output voltage is rectified by the rectifier circuit 25 and then input to the negative (inverted) input terminal of the operational amplifier IC1 as a constant voltage Va. At the same time, a voltage Vb obtained by dividing one terminal voltage of the step-up transformer T1 by the resistors R1 and R2 is input to the positive input (non-inverted) terminal of the operational amplifier IC1. The output of the operational amplifier IC1 is inputted to the base of the transistor Q1, and the capacitor C2 and the rectifier circuit D1 are connected to the collector of the transistor Q1. As a result, the voltage Vb is controlled so as not to exceed the constant voltage Va. Thus, the transistor Q1 is driven so that the voltage values of both (Va and Vb) are equal. As a result, a current flows through the resistors R1 and R2, causing a voltage drop, and a DC voltage Vdc2 is generated.

  A desired DC voltage can be obtained by adding the DC voltages Vdc1 and Vdc2 described above. This DC voltage is superimposed on the AC voltage described above on the secondary side of the step-up transformer T1 and applied to the charging roller 21 of the process cartridge C.

  In the system according to the present embodiment, since the DC voltage is created using the step-up transformer T1, the DC voltage is dependent on the AC peak-to-peak voltage Vpp. That is, in order to obtain a desired DC voltage Vdc for making the charging potential uniform, it is necessary to charge the capacitor C2 with a certain level of charge by the step-up transformer T1. As in the present embodiment, in the method of charging with a voltage in which a DC voltage and an AC voltage are superimposed, as shown in FIG. 6, in order to obtain a desired DC voltage Vdc ′, the AC peak-to-peak voltage Vpp is Must be greater than or equal to 2 × | Vdc ′ |.

  FIG. 6 is a diagram showing the relationship between the AC peak-to-peak voltage Vpp and the output DC voltage Vdc in the circuit of FIG.

  In the region where the AC peak-to-peak voltage Vpp is smaller than 2 × | Vdc ′ |, the capacitor C2 cannot be fully charged. For this reason, a desired DC voltage Vdc ′ cannot be obtained. Therefore, in this state, the potential Vd on the photosensitive drum 1 cannot be charged to a desired value, and a good image cannot be obtained.

  As described above, the AC peak-to-peak voltage Vpp is set to a different value depending on the use environment. Particularly in a high temperature and high humidity environment, the AC peak-to-peak voltage Vpp is set to a small value. In that case, the capacitor C2 is not sufficiently charged, and a situation in which a desired DC voltage cannot be obtained occurs.

  Therefore, in the present embodiment, the minimum value Vpp-min of the output range of the AC peak-to-peak voltage Vpp that can be output from the AC oscillation output unit 53 is Vpp-min ≧ with respect to a desired DC voltage Vdc ′ that does not cause charging unevenness. The relationship 2 × | Vdc ′ | is established.

  Next, processing for determining an appropriate charging bias voltage will be described.

  In the present embodiment, in the initial step 401, the current value that flows when the charging voltage Vpp that is the detection voltage is applied is compared with the process condition specifying data Bwi corresponding to the set target current value Iwi. The charging voltage at the time of image formation is determined. Here, a part of the charge voltage range Vppm that can be output is made a detection voltage range, and the charge voltage is switched according to the usage amount W of the photosensitive drum 1. Specifically, the range of the detection voltage is set to a charging voltage that is stored in the memory 90 and is before or after the previous charging voltage data Am.

  In FIG. 5, when a charging bias voltage is applied to the charging roller 21, the alternating current Iacm flows through the charging roller 21 and the photosensitive drum 1 to GND. At this time, the alternating current detection circuit 26 extracts only the alternating current having a frequency equal to the charging frequency from the alternating current by a filter circuit (not shown) including a resistor, a capacitor, and the like. Then, the alternating current is converted into a voltage signal 22 in the range of 0 to 3.4 V and input to the control unit 51. This AC current value may vary with the period of the charging roller 21 or the photosensitive drum 1. In particular, the photosensitive drum 1 may have uneven film thickness in the circumferential direction due to uneven coating during manufacture or uneven shaving due to eccentricity, and the impedance may vary in the circumferential direction. As a result, the alternating current Iacm varies even when the same charging voltage Vppm is applied. Therefore, it is desirable to improve the detection accuracy by performing arithmetic processing such as detecting the alternating current for a period of one cycle or more of the photosensitive drum 1 and obtaining the average.

  The controller 51 performs A / D conversion on the input voltage signal 22 and recognizes it as a detected current value Cm corresponding to the detected current Iacm. On the other hand, the process condition specifying data Bwi (90d) corresponding to the target current value Iwi is stored in the memory 90 in advance. Therefore, the control unit 51 compares the detected current value (Cm) with the target current value (Bwi). That is, the detected current value Iacm is compared with the target current value Iwi. Further, when the usage amount W of the photosensitive drum 1 reaches the threshold value Wi (90b), the process condition specifying data (Bwi) (target current value Iwi) is selected. Further, Vppm + 2, Vppm + 1, and Vppm are selected as detection voltages from the previous charging voltage data Am (Vppm).

  FIG. 7 is a block diagram for explaining the relationship between the control unit 51, the charging bias power supply circuit 98, and the process cartridge C of the image forming apparatus according to the present embodiment, and the same parts as those in the above-described figure (FIG. 5) are the same. It is indicated by a symbol. Here, the control unit 51 has a CPU, a ROM storing a program executed by the CPU, and a RAM used as a work area. And the function of each part of the control part 51 is implement | achieved by cooperation with this program, CPU, RAM, etc.

  Next, a series of operations from the mounting of the process cartridge C to the end of image formation in the image forming apparatus according to the present embodiment will be described with reference to the flowcharts of FIGS. In this sequence, the charging voltage Vprn at the time of image formation is determined to be a voltage corresponding to the minimum current value among the current values larger than the target current value Iwi (Bwi). A program for executing this processing is stored in the ROM and is executed under the control of the CPU.

  First, in step S101, it is detected that the cartridge C is mounted on the image forming apparatus main body L, the process proceeds to step S102, and data stored in the memory 90 of the cartridge C is read. Next, in step S103, the usage amount W of the photosensitive drum stored in the memory 90 is compared with the threshold value Wi of the usage amount. Here, if Wi ≦ W <Wi + 1, the target current value Iwi (process condition specifying data Bwi) corresponding to the threshold value Wi is set. Further, the previous charging voltage data Am (Vppm) stored in the memory 90 is read, and Vppm + 2, Vppm + 1, and Vppm (Vppm + 2 <Vppm + 1 <Vppm) are selected as detection voltages.

  In step S104, rotation of the photosensitive drum 1 is started, and counting of the rotation time Δtd of the photosensitive drum 1 and the charging bias application time Δtp is started. The rotation time Δtd and the application time Δtp thus counted are added to the total rotation time td and the total application time tp, respectively. In step S105, the charging voltage Vprn at the time of image formation is set to Vppm-1 as an initial value. In step S106, the charging detection voltage Vppm is applied for one rotation (Δtc) of the photosensitive drum 1. Then, the current value data Cm (digital value of the detected current value Iacm) detected by the alternating current detection circuit 26 is compared with the target current value data Bwi. If the detected current value is larger than the target value (Cm ≧ Bwi), the process proceeds to step S107, the charging voltage Vprn at the time of image formation is reset to Vppm, and the process proceeds to step S108. On the other hand, if Cm ≧ Bwi is not satisfied in step S106, the process proceeds to step S108.

  In step S108, the charging detection voltage Vppm + 1 having a voltage lower than that in step S106 is applied for one rotation (Δtc) of the photosensitive drum 1. Then, the current value data Cm + 1 (digital value of the detected current value Iacm) detected by the alternating current detection circuit 26 is compared with the target current value data Bwi. If the detected current value is larger than the target value (Cm + 1 ≧ Bwi), the process proceeds to step S109, the charging voltage Vprn at the time of image formation is reset to Vppm + 1, and the process proceeds to step S110. On the other hand, if Cm + 1 ≧ Bwi is not satisfied in step S108, the process proceeds to step S110 as it is.

  In step S110, the charging detection voltage Vppm + 2 having a voltage lower than that in step S108 is applied for one rotation (Δtc) of the photosensitive drum 1. Then, the current value data Cm + 2 detected by the AC current detection circuit 26 is compared with the target current value data Bwi. If the detected current value is larger than the target value (Cm + 2 ≧ Bwi), the process proceeds to step S111, the charging voltage Vprn at the time of image formation is reset to Vppm + 2, and the process proceeds to step S112 (FIG. 9). . On the other hand, if Cm + 1 ≧ Bwi is not satisfied in step S110, the process proceeds to step S112 and print ready (print preparation is completed).

  Next, the process proceeds to step S113 in FIG. 9 to determine whether or not a print signal is input from the host computer. If the print signal is input, the process proceeds to step S114. If not, the process proceeds to step S119. In step S114, the pre-image formation process (402) is started. Next, in step S115, an image forming step (403) is started (the charging voltage at the time of image formation is Vprn set in steps S105 to S111 described above). Next, the process proceeds to step S116, where it is determined whether or not a print signal for the next page has been input, and if it has been input, the process proceeds to step S117, the inter-sheet process (404) is executed, and the process returns to step S115. On the other hand, when the print signal for the next page is not input in step S116, the process proceeds to step S118, the image forming post-process (405) is executed, and the process returns to step S113.

  If it is determined in step S113 that no print signal is input from the host computer, the process proceeds to step S119 to set the standby mode. In step S120, Vprn (previous charging voltage specifying data Am for specifying Vprn) is written in the memory 90. In step S121, the drum rotation time Δtd and the charging bias application time Δtp are counted. Then, the rotational driving of the photosensitive drum 1 is finished. In step S122, the usage amount data W = W + ΔW (ΔW = Δtp + k × Δtd) of the photosensitive drum 1 is written in the memory 90 to update the usage amount W of the photosensitive member.

  As described above, in the processing of the above-described embodiment, the detection voltage range is set to Vppm + 2 to Vppm. The charging voltage at the time of image formation is selected from voltages Vppm + 2 to Vppm-1. Further, the range of the charging detection voltage may be set so that the selection range of the charging voltage at the time of image formation is a range including the following upper and lower limit values.

  The upper limit of the charging voltage is within a voltage range in which sand is not generated under a low temperature / low humidity environment (temperature and humidity conditions where the charging roller 21 has high impedance), regardless of the resistance of the charging roller 21 or circuit tolerances. Set to the minimum value. The lower limit of the charging voltage is a voltage value at which no sand is generated even under conditions where the resistance of the charging roller 21 and circuit tolerances are the most likely to occur in a high temperature / high humidity environment.

  As described above, when a plurality of charge detection voltages are switched and applied to the image carrier (photosensitive drum 1) and the charging means (charging roller 21), the AC current value flowing through both is detected, and the target is detected. Compare with the current value of. In accordance with the comparison result, the charging voltage for image formation is determined to charge the image carrier. Accordingly, even if the charging voltage of the apparatus and the impedance of the photosensitive drum 1 and the charging unit vary, there is an effect that an image can be formed by determining an appropriate charging voltage.

  In this embodiment, in order to increase the detection accuracy of the charging current, the charging voltage can be switched and the voltage is generated in multiple stages. Thereby, an appropriate charging voltage can be determined in a short time without deteriorating the detection accuracy of the charging current. As a result, charging control can be performed with high accuracy, and there is an effect that the life of the photosensitive drum can be extended and the first printout time can be shortened.

  In order to clarify the effect of the present embodiment, the following evaluation was performed.

<Experiment 1>
For this embodiment and Comparative Examples 1 and 2, the charging current value, the life of the photosensitive drum, and the first printout time were measured.

<Evaluation conditions>
Environment: temperature 25 ° C, humidity 50% Rh
Process speed (moving speed of photosensitive drum surface): 94 mm / sec. Charging AC frequency: 900 Hz
Detection time: One round time of the photosensitive drum Diameter of the photosensitive drum: 30φ
Photosensitive drum surface layer film thickness: 25 μm
Contact pressure of cleaning blade to photosensitive drum: 40 gf / square cm
Evaluation Mode: Intermittent Printing Mode for Each Sheet Further, the target current value for charging control is shown in FIG.

  FIG. 10 is a diagram showing the relationship between the usage amount of the photosensitive drum and the target current value. Here, the amount used is the number of printed sheets.

<Example 1>
Applicable voltage: 1650V to 2000V (voltage interval 50V): 8 voltage Detection voltage: 3 voltages (standard value of charging voltage and charging voltage which is lower by 1 step and 2 steps)
For reference, a detection voltage range corresponding to each usage amount is shown in FIG.

  FIG. 11 is a diagram showing the relationship between the usage amount of the photosensitive drum and the standard value (detection voltage range) of the charging voltage.

<Comparative Example 1>
Applicable voltage: 1650 V to 2000 V (voltage interval 50 V): 8 voltages Detection voltage: 1650 V to 2000 V (voltage interval 50 V): 8 voltages <Comparative Example 2>
Applicable voltage: 1650 V to 2000 V (voltage interval 175 V): 3 voltages Detection voltage: 1650 V to 2000 V (voltage interval 175 V): 3 voltages <Result>
FIG. 12 is a diagram showing the transition of the alternating current value (effective value) flowing through the photosensitive drum. In FIG. 12, the abrasion of the photosensitive drum is particularly compared in Example 1 and Comparative Example 2. In the figure, in Comparative Example 2, a large current flows through the photosensitive drum immediately before the charging voltage is switched, and the abrasion of the photosensitive drum is promoted. In Comparative Example (Embodiment) 1, an appropriate current value is obtained through the usage amount of the photosensitive drum. However, since all the voltages that can be applied by the apparatus are used as the detection voltage, the process for determining the charging voltage during image formation becomes longer. Therefore, if printing is to be performed immediately after the process cartridge C is mounted or the power is turned on, the first print time becomes longer.

  On the other hand, in Example 1, it can be seen that the charging voltage is applied at a value close to the target current value throughout the usage period of the photoreceptor. Further, in the first embodiment, no sand image was generated during this period of use, and the first print time could be shortened as compared with the first comparative example. This evaluation is a result of paper passing and printing for several days as a practical mode, and the main body power is turned off after one day of evaluation.

  FIG. 13 is a diagram showing a comparative example of the life of the photosensitive drum and the first print time after the cartridge is mounted.

  As described above, according to the present embodiment, the first print time can be shortened by 6 seconds as compared with the second comparative example. Further, compared with Comparative Example 1, the life of the photosensitive drum could be extended by about 15%.

  In the present embodiment described above, the case where the determination of the charging voltage at the time of image formation is performed in the initial process has been described. However, it may be performed in the pre-image formation process by shortening the detection time, which is an effect of the present embodiment. It becomes possible.

  As described above, according to the present embodiment, in a power supply circuit that applies an AC and DC superimposed bias with a single voltage booster, the previous charging is performed at an arbitrary timing during an initial process or non-image formation. The charging voltage can be determined by applying a plurality of alternating voltages having the voltage as a reference voltage. That is, the AC current detecting means detects each current value flowing through the photoconductor corresponding to a plurality of AC voltages, and uses the optimum voltage value as a print bias, whereby the AC current flowing through the photoconductor is a value that is almost constant. Can be controlled.

  As a result, it is possible to perform highly accurate charging control by correcting the impedance change caused by the usage environment, the film thickness of the photosensitive drum, the tolerance of the charging power source, and the like. Thus, it was possible to achieve both cost reduction and space saving of the power supply circuit and high-precision discharge control.

[Embodiment 2]
In general, the film thickness of the photosensitive drum is reduced with the amount of use. Therefore, the charging voltage required to uniformly charge the photosensitive drum can be lowered with the film thickness. Therefore, the charging voltage is lowered step by step by setting the detection voltage to the charging voltage Vppm + 1 that is one step lower than the previous charging voltage and comparing it with the target process condition specifying data Bwi (target current value Iwi). It is also possible to do. In this case, since the time for applying the charging voltage for detection can be shortened, it can be performed in the process immediately before the image formation.

  On the other hand, in the case of a small image forming apparatus, the distance between the photosensitive drum and the charging roller and the fixing device is short, and there is a tendency that the temperature difference in the apparatus at the time of image formation immediately after the power is turned on becomes large.

  FIG. 14 is a diagram illustrating a temperature transition in the vicinity of the charging roller after the image forming apparatus is powered on.

  When the power is turned on, the fixing device is started up, so that the temperature inside the device rises. After that, the fixing device is controlled at a constant temperature, so that the temperature inside the device becomes saturated.

  According to the method of applying the detection charging voltage to the charging roller in the process immediately before the image formation, an appropriate charging voltage can be selected even when there is a difference in the internal temperature at the time of image formation immediately after the power is turned on. In addition, in the case of a printer apparatus using a fixing device having a heating surface made of a film having a small heat capacity, the main body is often turned on and used immediately before use. Even for such an apparatus, it is an effective control for determining a charging voltage by applying a charging voltage for detection and measuring a charging current in a process immediately before image formation. However, in rare cases, the temperature in the image forming apparatus main body may change greatly during image formation. Specifically, this is the case where images are printed before and after the indoor air conditioning is entered. In such a case, if the previous charging voltage Vppm is set to the reference voltage, the difference between the detected current value Iacm and the target current value Iwi increases, and if the detection charging voltage is small, an appropriate charging voltage cannot be selected. Therefore, in such a case, it is desirable to add a step of correcting the reference charging voltage.

  FIG. 15 is a block diagram illustrating the relationship between the control unit 51, the charging bias power supply circuit 98, and the process cartridge C of the image forming apparatus according to the second embodiment of the present invention, and the same parts as those in FIG. It is indicated by a symbol. Here, the control unit 51 has a CPU, a ROM storing a program executed by the CPU, and a RAM used as a work area. And each part of the control part 51 is implement | achieved by cooperation with this program, CPU, RAM, etc.

  The configuration of the image forming apparatus according to the second embodiment is the same as that of the first embodiment, and a series of operations from the mounting of the process cartridge C to the end of image formation in this image forming apparatus are shown in FIG. This will be described with reference to the flowcharts of FIGS.

  16 to 18 are flowcharts for explaining processing in the image forming apparatus according to Embodiment 2 of the present invention. A program for executing this processing is stored in the ROM of the control unit 51 and is executed under the control of the CPU.

  In this sequence, the charging voltage Vprn at the time of image formation is applied immediately before the image formation by applying one step of the detection voltage Vppm + 1 based on the previously applied charging voltage Vppm as a target current value Iwi (Bwi). It is decided by comparison. Further, when the difference between the target current value Iwi and the detected current value Iacm + 1 is large, the process automatically enters the reference voltage correction process to correct the reference voltage. In the second embodiment, a current threshold for determining correction is set to 100 μA (data ΔIth in the memory 90), and a correction process is performed based on the current threshold to select an appropriate charging voltage. is doing. Other set values are the same as those in the first embodiment, and the same numbers and symbols are used for those having the same functions and roles as those in the first embodiment.

  After the power is turned on, it is first determined in step S201 that the cartridge C is mounted on the image forming apparatus main body L. Next, the control part 51 reads the data of the memory 90 at the preparation process of step S202. In step S203, start-up processing of the scanner unit 30 and the fixing device 70 is started. In step S204, the print ready state is set. Next, in step S205, it is determined whether or not a print signal is input from a host computer (not shown). When the print signal is input, the process proceeds to step S206, and the pre-image formation process 402 (FIG. 4) is started. In step S207, the control unit 51 reads data stored in the memory 90. In step S208, the usage amount W of the photosensitive drum is compared with the usage threshold value Wi. If Wi ≦ W <Wi + 1, the target current value Iwi (process condition specifying data: Bwi). Further, Vppm + 1 (one step lower charging voltage) is selected as the detection voltage from the previous charging voltage Vppm (Am). Further, a current threshold value ΔIth is set for comparison with the difference between the target current value Bwi and the detected current value (Cm).

  In step S209, rotation of the photosensitive drum 1 is started, and time measurement of the rotation time Δtd of the drum 1 and charging bias application time Δtp is started. The rotation time Δtd and the application time Δtp thus counted are added to the total rotation time td and the total application time tp, respectively. In step S210, the charging voltage Vprn at the time of image formation is set to Vppm as an initial value. In step S211, the absolute value of the difference between the charging current data Cm + 1 detected by applying the charging voltage Vppm + 1 for detecting the charging current for one rotation (Δtc) of the photosensitive drum 1 and the target current data Bwi. Ask for. Then, it is determined whether or not the absolute value is larger than the current threshold value ΔIth (90f). Here, if | Cm + 1−Bwi | ≧ ΔIth, it is determined that correction of the reference value of the charging voltage is necessary, and the process proceeds to step S214 (FIG. 17). Otherwise, the process proceeds to step S212, and the detected charging is performed. The current data Cm + 1 is compared with the target current data Bwi. If Cm + 1 ≧ Bwi is not satisfied, the process proceeds to the image forming process in step S229 (FIG. 18A). If so, the process proceeds to step S213, and Vppm is obtained by reducing the charging voltage Vprn at the time of image formation by one step. Set it to +1 again. Then, the process proceeds to step S229 (FIG. 18A).

  Next, a process for correcting the reference value of the charging voltage will be described.

  In step S214, the charging voltage Vprn at the time of image formation is set to Vpp1 (the highest voltage value of the eight AC peak-to-peak voltages) as an initial value. In step S215, the charging voltage Vpp2 for detecting the charging current is applied for one rotation (Δtc) of the photosensitive drum 1, and the detected current data C2 at that time is compared with the target current data Bwi. If C2 <Bwi, the process proceeds to step S217. If C2 ≧ Bwi, the process proceeds to step S216, the charging voltage Vprn at the time of image formation is reset to Vpp2, and the process proceeds to step S217. In step S217, a charging voltage Vpp3 for detecting the charging current is applied for one rotation (Δtc) of the photosensitive drum 1, and the detected current data C3 at that time and the target current data Bwi are compared. If C3 <Bwi, the process proceeds to step S219. If C3 ≧ Bwi, the process proceeds to step S218, and the charging voltage Vprn at the time of image formation is reset to Vpp3, and the process proceeds to step S219.

  In step S219, the charging voltage Vpp4 for detecting the charging current is applied for one rotation (Δtc) of the photosensitive drum 1, and the detected current data C4 and the target current data Bwi at that time are compared. If C4 <Bwi, the process proceeds to step S221. If C4 ≧ Bwi, the process proceeds to step S220, and the charging voltage Vprn at the time of image formation is reset to Vpp4, and the process proceeds to step S221.

  In step S221, the charging voltage Vpp5 for detecting the charging current is applied for one rotation (Δtc) of the photosensitive drum 1, and the detected current data C5 at that time is compared with the target current data Bwi. If C5 <Bwi, the process proceeds to step S223. If C5 ≧ Bwi, the process proceeds to step S222, the charging voltage Vprn at the time of image formation is reset to Vpp5, and the process proceeds to step S223.

  In step S223, the charging voltage Vpp6 for detecting the charging current is applied for one rotation (Δtc) of the photosensitive drum 1, and the detected current data C6 at that time is compared with the target current data Bwi. If C6 <Bwi, the process proceeds to step S225, but if C6 ≧ Bwi, the process proceeds to step S224, the charging voltage Vprn at the time of image formation is reset to Vpp6, and the process proceeds to step S225.

  In step S225, the charging voltage Vpp7 for detecting the charging current is applied for one rotation (Δtc) of the photosensitive drum 1, and the detected current data C7 at that time is compared with the target current data Bwi. If C7 <Bwi, the process proceeds to step S227. If C7 ≧ Bwi, the process proceeds to step S226, the charging voltage Vprn at the time of image formation is reset to Vpp7, and the process proceeds to step S227.

  In step S227, the charging voltage Vpp8 for detecting the charging current is applied for one rotation (Δtc) of the photosensitive drum 1, and the detected current data C8 at that time is compared with the target current data Bwi. If C8 <Bwi, the process proceeds to the image forming process in step S229 (FIG. 18A). If C8 ≧ Bwi, the process proceeds to step S228, and the charging voltage Vprn at the time of image formation is reset to Vpp8. Proceed to step S229.

  In step S229, image formation is started (charging voltage Vprn at the time of image formation). In step S230, it is determined whether a print signal is input from the host computer. If there is a print signal, the process proceeds to step S231 to start the inter-sheet process (404).

  When the print signal is not input in step S230, the process proceeds to step S232, the image formation post-process (405) is executed, and the process proceeds to step S233. In step S233, the charging voltage Vprn at the time of image formation set at that time (data Am specifying Vprn) is written in the memory 90, and the process returns to step S205 (FIG. 16).

  If no print signal is input from the host computer in step S205 (FIG. 16), the process proceeds to step S234 to enter a standby mode. In step S235, the drum rotation time Δtd and the charging bias application time Δtp are counted, and the rotation of the photosensitive drum 1 is ended. In step S 236, the usage amount data W = W + ΔW (ΔW = Δtp + k × Δtd) of the photosensitive drum 1 is written in the memory 90.

  As described above, according to the second embodiment, the same effects as those of the first embodiment described above can be obtained, and the first print time after power-on can be shortened.

  Furthermore, by setting a minimum detection charging voltage range, a charging current detection step can be inserted immediately before the image forming step. As a result, the power supply of the main unit can be used only when performing image formation when using a small machine that has a large temperature / humidity difference immediately after turning on the power and when forming an image, or when using a fuser whose heating surface is made of a film with a small heat capacity. It is possible to set an optimum charging voltage with high accuracy even for an image forming apparatus that is often used after being charged.

  In the second embodiment, even in a rare case where there is a large temperature change in the room, the reference voltage of the charging voltage is corrected, so that an appropriate charging voltage can be set, and reduction in charging uniformity and drum scraping can be achieved. Note that the detection of the charging current accompanying the application of the charging voltage is preferably performed for one or more times of the photosensitive drum in order to suppress variations in the detected current value. Therefore, if the time is equal to or longer than one rotation of the photosensitive drum, for example, the charging current can be detected even during the inter-sheet process.

[Embodiment 3]
In the third embodiment, a series of operations from the mounting of a cartridge using an unused cartridge to the end of image formation will be described with reference to the flowcharts of FIGS.

  In the third embodiment, whether the process cartridge is used or not is determined based on the usage amount of the photosensitive drum stored in the memory 90. When the program cartridge is not used, the correction voltage is entered to determine the reference voltage. The configuration and other set values of the image forming apparatus and process cartridge according to the third embodiment are the same as those in the second embodiment, and the description thereof is omitted.

  19 to 21 are flowcharts for explaining a series of operations from the mounting of the process cartridge C to the end of image formation in the image forming apparatus according to Embodiment 3 of the present invention. A program for executing this processing is stored in the ROM of the control unit 51 and is executed under the control of the CPU.

  First, in step S301, when it is confirmed that the cartridge C is attached to the image forming apparatus main body L, the process proceeds to step S302, and whether or not the usage amount W (90a) of the photosensitive drum is “0” in the data of the memory 90. to decide. If “0”, the process proceeds to step S315 (FIG. 20). If not, the process proceeds to step S303 to execute a preparation process, and the data in the memory 90 is read by the control unit 51. In step S304, start-up of the scanner 30 and the fixing device 70 is started. In step S305, the printer is ready for printing.

  In step S306, it is determined whether a print signal is input from the host computer. When the print signal is input, the process proceeds to step S307 and the pre-image formation process is started. On the other hand, when the print signal is not input, the process proceeds to step S335 (FIG. 21B). Hereinafter, the processing in steps S307 to S314 in FIG. 19 is the same as the processing in steps S206 to S213 in FIG.

  After step S307, the process proceeds to step S308, and the controller 51 reads the data in the memory 90. In step S309, the drum usage amount W is compared with the usage threshold value Wi. If Wi ≦ W <Wi + 1, the target current value Iwi (process specific data: Bwi) corresponding to the threshold value Wi is established. ). Further, Vppm + 1 is selected as the charging voltage for detection from the previous charging voltage Vppm. Further, a current threshold value ΔIth is set for comparison with the difference between the target current value and the detected current value. In step S310, rotation of the photosensitive drum 1 is started, and counting of the drum rotation time Δtd and the charging bias application time Δtp is started. In step S311, the charging voltage Vprn at the time of image formation is set to Vppm as an initial value. In step S312, a charging voltage Vppm + 1 for detecting the charging current is applied for one rotation (Δtc) of the photosensitive drum 1. Then, it is determined whether or not the absolute value of the difference between the detected current data Cm + 1 and the target current data Bwi at this time is larger than the current threshold value ΔIth. If | Cm + 1−Bwi | ≧ ΔIth, the process proceeds to step S315 (FIG. 20). If not, the process proceeds to step S313, and the detected current data Cm + 1 is compared with the target current data Bwi. If Cm + 1 <Bwi, the process proceeds to the image forming process in step S330 (FIG. 21A). If Cm + 1 ≧ Bwi, the process proceeds to step S314, and the charging voltage Vprn at the time of image formation is set to Vppm +. The value is reset to 1 and the process proceeds to the image forming process in step S330.

  If | Cm + 1−Bwi | ≧ ΔIth in step S312, the process proceeds to step S315, and the charging voltage Vprn at the time of image formation is set to Vpp1 as an initial value. The processes in steps S315 to S329 in FIG. 20 are the same as the processes in steps S214 to S228 in FIG. In step S316, the detection voltage Vpp2 is applied for one rotation (Δtc) of the photosensitive drum 1, and the detection current data C2 is compared with the target current data Bwi. If C2 <Bwi, the process proceeds to step S318. If C2 ≧ Bwi, the process proceeds to step S317, the charging voltage Vprn at the time of image formation is reset to Vpp2, and the process proceeds to step S318. In step S318, the detection voltage Vpp3 is applied for one rotation (Δtc) of the photosensitive drum 1, and the detection current data C3 and the target current data Bwi are compared. If C3 <Bwi, the process proceeds to step S320. If C3 ≧ Bwi, the process proceeds to step S319, the charging voltage Vprn at the time of image formation is reset to Vpp3, and the process proceeds to step S320.

  Next, in step S320, the detection voltage Vpp4 is applied for one rotation (Δtc) of the photosensitive drum 1, and the detection current data C4 and the target current data Bwi are compared. If C4 <Bwi, the process proceeds to step S322. If C4 ≧ Bwi, the process proceeds to step S321, and the charging voltage Vprn at the time of image formation is reset to Vpp4, and the process proceeds to step S322. In step S322, the detection voltage Vpp5 is applied for one rotation (Δtc) of the photosensitive drum 1, and the detection current data C5 is compared with the target current data Bwi. If C5 <Bwi, the process proceeds to step S324. If C5 ≧ Bwi, the process proceeds to step S323, and the charging voltage Vprn at the time of image formation is reset to Vpp5, and the process proceeds to step S324.

  Next, in step S324, the detection voltage Vpp6 is applied for one rotation (Δtc) of the photosensitive drum, and the detection current data C6 and the target current data Bwi are compared. If C6 <Bwi, the process proceeds to step S326. If C6 ≧ Bwi, the process proceeds to step S325, the charging voltage Vprn at the time of image formation is reset to Vpp6, and the process proceeds to step S326. In step S326, the detection voltage Vpp7 is applied for one rotation (Δtc) of the photosensitive drum 1, and the detection current value data C7 and the target current value data Bwi are compared. If C7 <Bwi, the process proceeds to step S328. If C7 ≧ Bwi, the process proceeds to step S327, the charging voltage Vprn at the time of image formation is reset to Vpp7, and the process proceeds to step S328. In step S328, the detection voltage Vpp8 is applied for one rotation (Δtc) of the photosensitive drum, and the detection current data C8 is compared with the target current data Bwi. If C8 <Bwi, the process proceeds to step S328a. If C8 ≧ Bwi, the process proceeds to step S329, and the charging voltage Vprn at the time of image formation is reset to Vpp8, and the process proceeds to step S328a. In step S328a, it is determined whether the usage amount W of the photosensitive drum in the memory 90 is “0”, that is, whether a new cartridge is installed. If so, the process returns to step S303 to execute the preparation process. .

  On the other hand, if no new cartridge is installed, the process proceeds to the image forming process in step S330 (FIG. 21A), and image formation is started (charging voltage Vprn at the time of image formation). Next, in step SS331, it is determined whether or not a print signal has been input. If the print signal has been input, the process proceeds to step S332 to start the inter-sheet process and return to step S330. If no print signal is input in step S332, the process advances to step S333 to start a post-image formation process. In step S334, Vprn (data Am specifying Vprn) is written in the memory 90, and the process returns to step S306 (FIG. 19).

  Further, in step S335 in FIG. 21B, the standby mode is set, and then the process proceeds to step S336, where the counting of the drum rotation time Δtd and the charging bias application time Δtp is terminated. Thus, the rotational drive of the photosensitive drum 1 is completed. In step S 337, usage amount data W = W + ΔW (ΔW = Δtp + k × Δtd) of the photosensitive drum 1 is written in the memory 90. 21A and 21B show the same processing as that shown in FIGS. 18A and 18B.

  As described above, according to the third embodiment, an appropriate charging voltage can be selected even in the case of an unused cartridge, and the uniformity of charging of the photosensitive drum and the reduction of drum scraping can be achieved. In addition, since an appropriate charging voltage can be stored in the memory of the process cartridge, the next first print time can be shortened.

  Further, the unused / used discrimination flag in the memory can be substituted by the value of the usage amount W of the photosensitive drum.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is a structure sectional view showing the composition of the process cartridge concerning the embodiment of the invention. It is a figure explaining the memory | storage information of the memory which concerns on this Embodiment. It is a figure explaining the outline of the operation | movement sequence in the image forming apparatus which concerns on this Embodiment. It is a block diagram explaining the structure of the charging bias power supply circuit which generates the charging bias voltage based on this Embodiment. FIG. 6 is a diagram illustrating a relationship between an AC peak-to-peak voltage and a DC voltage that can be output in the circuit of FIG. 5. 3 is a block diagram illustrating a relationship among a control unit, a charging bias power supply circuit, and a process cartridge of the image forming apparatus according to the present embodiment. FIG. , 4 is a flowchart for explaining a series of operations from mounting of a process cartridge to completion of image formation in the image forming apparatus according to the present embodiment. It is a figure which shows the relationship between the usage-amount of a photoconductor drum, and a target electric current value. It is a figure which shows the relationship between the usage-amount of a photoconductor drum, and the standard value (detection voltage range) of a charging voltage. It is a figure which shows the transition corresponding to the usage-amount of a photoconductor drum of the alternating current value (effective value) which flowed to the photoconductor drum. FIG. 6 is a diagram showing a comparative example of the life of a photosensitive drum and the first print time after mounting the cartridge. It is a figure which shows the temperature transition of the charging roller vicinity after main body power activation. FIG. 10 is a block diagram illustrating a relationship among a control unit, a charging bias power supply circuit, and a process cartridge of the image forming apparatus according to the second embodiment. , , 6 is a flowchart illustrating a series of operations from mounting of a process cartridge to completion of image formation in the image forming apparatus according to the second embodiment. , , 10 is a flowchart illustrating a series of operations from mounting a process cartridge to ending image formation in the image forming apparatus according to Embodiment 3 of the present invention. FIG. 2 is a diagram illustrating a schematic configuration of a recording unit of an image forming apparatus such as a general electrophotographic copying machine or printer. It is a figure which shows the example of a circuit which carries out constant voltage control of the alternating current component of the conventional charging bias. It is a figure which shows the example of a circuit which mounts the voltage boosting means for DC and AC, separating the conventional DC power supply T-DC and AC power supply T-AC.

Claims (16)

An image forming apparatus having an image carrier and a charging member for charging the image carrier, and a process cartridge provided with a storage medium is detachable.
Charging voltage supply means capable of supplying a plurality of alternating voltages as charging voltages to the charging member;
Current detection means for detecting a current flowing through the image carrier in accordance with a charging voltage supplied from the charging voltage supply means;
In a non-image forming step, range setting means for setting a charging voltage range using a charging voltage in the previous image forming step stored in the storage medium as a reference voltage;
Charging voltage setting means for setting a charging voltage for detection for detecting a charging current in the charging voltage supply means within the range set by the range setting means;
A comparison unit that compares a current value detected by the current detection unit with a threshold value when a charging voltage for detection set by the charging voltage setting unit is supplied from the charging voltage supply unit;
Control means for determining a charging voltage for detection corresponding to a minimum current value of a current value determined to be a current value larger than the threshold value by the comparison means as a charging voltage in the image forming step;
An image forming apparatus comprising: A mounting means for mounting a process cartridge including at least an image carrier, a charging member for charging the image carrier, and a storage medium;
Charging voltage supply means capable of supplying a plurality of alternating voltages as charging voltages to the charging member;
Current detection means for detecting a current flowing through the image carrier in accordance with a charging voltage supplied from the charging voltage supply means;
In a non-image forming step, a range setting unit that sets a charging voltage range using a charging voltage in a previous image forming step stored in the storage medium of the process cartridge mounted on the mounting unit as a reference voltage;
Charging voltage setting means for setting a charging voltage for detection for detecting a charging current in the charging voltage supply means within the range set by the range setting means;
A comparison unit that compares a current value detected by the current detection unit with a threshold value when a charging voltage for detection set by the charging voltage setting unit is supplied from the charging voltage supply unit;
Control means for determining a charging voltage for detection corresponding to a minimum current value of a current value determined to be a current value larger than the threshold value by the comparison means as a charging voltage in the image forming step;
An image forming apparatus comprising: The charging voltage setting means sets a voltage lower than the reference voltage as the detection charging voltage,
When the current value detected by the current detection unit with respect to the detection charging voltage is larger than the threshold value, the control unit determines the detection charging voltage as a charging voltage in the image forming process,
2. The reference voltage is determined as a charging voltage in an image forming process when a current value detected by the current detection unit with respect to the detection charging voltage is smaller than the threshold value. The image forming apparatus according to 2.   The image forming apparatus according to claim 1, wherein the non-image forming step is a pre-image forming step immediately before the image forming step.   Further, it is determined whether or not the difference between the current value detected by the current detection means and the threshold value is larger than a predetermined value. If the difference is larger, the charging voltage is determined by the control means. 3. The image forming apparatus according to claim 1, further comprising means for determining a charging voltage for detection corresponding to a current value determined to be a current value larger than the threshold value as a charging voltage in the image forming process. .   The image forming apparatus according to claim 1, further comprising a writing unit that writes the charging voltage in the image forming step determined by the control unit to the storage medium.   The image forming apparatus according to claim 2, wherein the storage medium stores data for specifying a usage amount of the image carrier.   The image forming apparatus according to claim 2, further comprising an update unit configured to update a usage amount of the image carrier according to a usage state of the image carrier. A control method of an image forming apparatus for forming an image by mounting a process cartridge including at least an image carrier, a charging member for charging the image carrier, and a storage medium,
A current detection step of detecting a current flowing through the image carrier in accordance with a charging voltage supplied from a charging voltage supply unit capable of supplying a plurality of AC voltages as charging voltages to the charging member;
In a non-image forming step, a range setting step for setting a charging voltage range using a charging voltage in the previous image forming step stored in the storage medium of the process cartridge as a reference voltage;
A charging voltage setting step for setting a charging voltage for detection for charging current detection in the charging voltage supply unit within the range set in the range setting step;
A comparison step for comparing the current value detected in the current detection step with a threshold when the detection charging voltage set in the charging voltage setting step is supplied from the charging voltage supply unit;
A control step of determining a charging voltage for detection corresponding to a minimum current value of the current value determined to be a current value larger than the threshold value in the comparison step as a charging voltage in the image forming step;
A control method for an image forming apparatus, comprising: In the charging voltage setting step, a voltage lower than the reference voltage is set as the detection charging voltage,
In the control step, when the current value detected in the current detection step with respect to the detection charging voltage is larger than the threshold, the detection charging voltage is determined as the charging voltage in the image forming step,
10. The reference voltage is determined as a charging voltage in an image forming process when a current value detected in the current detecting process with respect to the detection charging voltage is smaller than the threshold value. A control method of the image forming apparatus described.   The method for controlling an image forming apparatus according to claim 9, wherein the non-image forming step is a pre-image forming step immediately before the image forming step.   Further, it is determined whether or not a difference between the current value detected in the current detection step and the threshold value is larger than a predetermined value. If the difference is larger, the charging voltage is determined by the control step. 12. The method according to claim 9, further comprising a step of determining a charging voltage for detection corresponding to a current value determined to be a current value larger than the threshold value as a charging voltage in the image forming step. The image forming apparatus described.   The control of the image forming apparatus according to claim 9, further comprising a writing step of writing the charging voltage in the image forming step determined in the control step into the storage medium. Method.   The method for controlling an image forming apparatus according to claim 9, wherein the storage medium stores data for specifying a usage amount of the image carrier.   The method for controlling an image forming apparatus according to claim 9, further comprising an update step of updating a usage amount of the image carrier according to a usage state of the image carrier. A process cartridge that is mounted on an image forming apparatus and includes at least an image carrier, a charging member that charges the image carrier, and a storage medium,
The storage medium is
A first storage area for storing a usage amount of the image carrier;
A second storage area for storing a threshold value to be compared with the usage amount of the image carrier stored in the first storage area;
A third storage area for storing data for specifying the charging voltage in the previous image forming process;
A fourth storage area for storing data for specifying a target value of a current to be compared with a current flowing through the image carrier;
Connection means for enabling access from the apparatus main body to the storage medium when the process cartridge is mounted in the image forming apparatus main body;
A process cartridge comprising:

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