JP5858863B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a transfer material.

  Image forming apparatuses such as printers, copiers, and multifunction machines include an image carrier (photosensitive drum), a charging roller that contacts the surface of the photosensitive drum and charges the surface of the photosensitive drum, and a photosensitive member Some include a laser scanner unit that forms an electrostatic latent image on the surface of the drum, and a developer that develops the electrostatic latent image formed on the surface of the photosensitive drum with toner. Such an image forming apparatus may be installed in a high-temperature and high-humidity environment or an environment where condensation is likely to occur. When the image forming apparatus is installed in such an environment, it is supplied from the charging roller to the photosensitive drum to charge the surface of the photosensitive drum due to the influence of moisture on the surface of the photosensitive drum or the surface of the charging roller. There is a possibility that the charging current increases and a leak occurs in the photosensitive drum. When the leak occurs, a pinhole is generated on the surface of the photosensitive drum. Due to the pinhole, black streaks or the like are generated in the image formed on the transfer material (paper).

  Therefore, in the image forming apparatus, even when a leak occurs in the photosensitive drum, by suppressing current from flowing into the leaked portion, black streaks or the like are prevented from being generated in the image formed on the paper. (See Patent Document 1).

JP-A-8-123149

  However, originally, it is necessary to prevent the occurrence of leakage in the image carrier (photosensitive drum).

  An object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of leakage in an image carrier.

  The present invention relates to an image forming apparatus for transferring a toner image formed by developing an electrostatic latent image with toner onto a transfer material and forming an image on the transfer material. An image carrier formed on the surface; a charging unit that charges the surface of the image carrier to form an electrostatic latent image on the surface of the image carrier; and a current supply that supplies current to the charging unit. And a limiting unit that restricts supply of a current of a predetermined current value or higher when current is supplied from the current supply unit to the charging unit. In the first case where the current is supplied from the current supply unit to the charging unit when an image is formed on the transfer material, the limiting unit is configured to use the image carrier and the charging unit as the predetermined current value. Is lower than the current value of the current supplied from the current supply unit to the charging unit when a leak occurs, and the charging unit can charge the surface of the image carrier. A first current value larger than the current value is set. In the second case where the current supply unit supplies a current having a value smaller than that in the first case from the current supply unit, the limiting unit has a second current smaller than the minimum current value as the predetermined current value. 2 Set the current value.

  According to the present invention, it is possible to provide an image forming apparatus capable of preventing the occurrence of leakage in the image carrier.

FIG. 4 is a diagram for explaining an arrangement of each component of the printer. It is a figure for demonstrating a control part, an electric current supply part, a limiter, and a time measuring part. It is a figure for demonstrating the setting of a 2nd electric current value. It is a figure which shows about the relationship between the drive time of a photoconductive drum, charging current, 1st electric current value, and the presence or absence of generation | occurrence | production of a leak. 6 is a flowchart for explaining a characteristic operation of the printer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
With reference to FIG. 1, the overall structure of a printer 1 as an image forming apparatus according to the present embodiment will be described. FIG. 1 is a diagram for explaining the arrangement of each component of the printer 1.

As shown in FIG. 1, a printer 1 as an image forming apparatus transfers a toner image formed by developing an electrostatic latent image with toner onto a paper T and forms an image on the paper T. Specifically, the printer 1 forms an image of the apparatus main body M, an image forming unit GK that forms a predetermined toner image on a sheet T as a sheet-like transfer material based on predetermined image information, and the sheet T. A paper supply / discharge unit KH that supplies paper to the unit GK and discharges the paper T on which the toner image is formed.
The outer shape of the apparatus main body M is configured by a case body BD as a casing.

  As shown in FIG. 1, the image forming unit GK includes a photosensitive drum 2 as an image carrier (photosensitive member), a charging unit 10, a laser scanner unit 4 as an exposure unit, a developing device 16, and a toner cartridge. 5, a toner supply unit 6, a drum cleaning unit 11, a static eliminator 12, a transfer roller 8, and a fixing unit 9.

  As shown in FIG. 1, the paper supply / discharge unit KH includes a paper feed cassette 52, a manual paper feed unit 64, a transport path L of the paper T, a registration roller pair 80, and a paper discharge unit 50.

Hereinafter, each configuration of the image forming unit GK and the paper supply / discharge unit KH will be described in detail.
First, the image forming unit GK will be described.
In the image forming unit GK, in order from the upstream side to the downstream side along the surface of the photosensitive drum 2, charging by the charging unit 10, exposure by the laser scanner unit 4, development by the developing device 16, transfer by the transfer roller 8. Then, static elimination by the static eliminator 12 and cleaning by the drum cleaning unit 11 are performed.

  The photosensitive drum 2 is made of a cylindrical member and functions as a photosensitive member or an image carrier. The photosensitive drum 2 is disposed so as to be rotatable in the direction of an arrow about a rotation axis extending in a direction orthogonal to the conveyance direction of the paper T in the conveyance path L. An electrostatic latent image can be formed on the surface of the photosensitive drum 2.

  The charging unit 10 is disposed to face the surface of the photosensitive drum 2. The charging unit 10 uniformly charges the surface of the photosensitive drum 2 to be negative (minus polarity) or positive (plus polarity) in order to form an electrostatic latent image on the surface of the photosensitive drum 2. Specifically, the charging unit 10 includes a charging roller 10 a (charging member) that is disposed in contact with or close to the surface of the photosensitive drum 2. The charging roller 10a charges the surface of the photosensitive drum 2 based on the application of a bias.

  The laser scanner unit 4 functions as an exposure unit, and is disposed apart from the surface of the photosensitive drum 2. The laser scanner unit 4 includes a laser light source (not shown), a polygon mirror, a polygon mirror driving motor, and the like.

  The laser scanner unit 4 scans and exposes the surface of the photosensitive drum 2 based on image information input from an external device such as a PC (personal computer). By performing scanning exposure with the laser scanner unit 4, the charge on the exposed portion of the surface of the photosensitive drum 2 is removed. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 2.

  The developing device 16 is provided corresponding to the photosensitive drum 2 and is disposed to face the surface of the photosensitive drum 2. The developing device 16 attaches a single color (usually black) toner to the electrostatic latent image formed on the photoconductive drum 2 to form a single color toner image on the surface of the photoconductive drum 2. The developing device 16 includes a developing roller 17 disposed opposite to the surface of the photosensitive drum 2, a stirring roller 18 for stirring the toner, and the like.

  The toner cartridge 5 is provided corresponding to the developing device 16 and stores toner supplied to the developing device 16.

  The toner supply unit 6 is provided corresponding to the toner cartridge 5 and the developing device 16, and supplies the toner contained in the toner cartridge 5 to the developing device 16. The toner supply unit 6 and the developing device 16 are connected by a toner supply path (not shown).

  The transfer roller 8 transfers the toner image developed on the surface of the photosensitive drum 2 to the paper T. A transfer bias for transferring the toner image formed on the photosensitive drum 2 to the paper T is applied to the transfer roller 8 by a transfer bias applying unit (not shown). The transfer roller 8 is configured to be rotatable while in contact with the photosensitive drum 2.

  A sheet T conveyed through the conveyance path L is sandwiched between the photosensitive drum 2 and the transfer roller 8. The sandwiched paper T is pressed against the surface of the photosensitive drum 2. A transfer nip N is formed between the photosensitive drum 2 and the transfer roller 8. In the transfer nip N, the toner image developed on the photosensitive drum 2 is transferred onto the paper T.

  The static eliminator 12 is disposed to face the surface of the photosensitive drum 2. The static eliminator 12 irradiates the surface of the photosensitive drum 2 with light, thereby neutralizing the surface of the photosensitive drum 2 after the transfer is performed (removing the electric charge).

  The drum cleaning unit 11 is disposed to face the surface of the photosensitive drum 2. The drum cleaning unit 11 removes toner and deposits remaining on the surface of the photosensitive drum 2, and transports the removed toner and the like to a predetermined recovery mechanism for recovery.

  The fixing unit 9 melts and presses the toner constituting the toner image transferred to the paper T and fixes the toner on the paper T. The fixing unit 9 includes a heating rotator 9a heated by a heater and a pressure rotator 9b pressed against the heating rotator 9a. The heating rotator 9a and the pressure rotator 9b sandwich and pressurize the paper T on which the toner image has been transferred, and convey the paper T. By transporting the paper T while being sandwiched between the heating rotator 9a and the pressure rotator 9b, the toner transferred onto the paper T is melted and pressurized, and is fixed to the paper T.

Next, the paper supply / discharge unit KH will be described.
As shown in FIG. 1, in the lower part of the apparatus main body M, a single paper feed cassette 52 that stores paper T is disposed. The paper feed cassette 52 is configured to be drawable in the horizontal direction from the right side (the right side in FIG. 1) of the apparatus main body M. In the paper feed cassette 52, a placement plate 60 on which the paper T is placed is disposed. In the paper feed cassette 52, the paper T is stored in a state of being stacked on the placement plate 60. The paper T placed on the placement plate 60 is sent out to the transport path L by the cassette paper feed unit 51 arranged at the paper feed side end of the paper feed cassette 52 (the right end in FIG. 1). The cassette paper feed unit 51 includes a forward feed roller 61 for taking out the paper T on the placement plate 60 and a paper feed roller pair 63 for feeding the paper T one by one to the transport path L. Is provided.

  On the right side (right side in FIG. 1) of the apparatus main body M, a manual paper feed unit 64 is provided. The manual paper feed unit 64 is provided mainly for supplying the apparatus main body M with a paper T of a size and type different from the paper T set in the paper feed cassette 52. The manual paper feed unit 64 includes a manual feed tray 65 that forms a part of the front surface of the apparatus main body M in the closed state, and a paper feed roller 66. The manual feed tray 65 is attached at its lower end to the apparatus body M in the vicinity of the paper feed roller 66 so as to be rotatable (openable and closable). The paper T is placed on the open manual feed tray 65. The paper feed roller 66 feeds the paper T placed on the open manual feed tray 65 to the manual feed path La.

  A paper discharge unit 50 is provided on the upper side of the apparatus main body M. The paper discharge unit 50 discharges the paper T to the outside of the apparatus main body M by the third roller pair 53. Details of the paper discharge unit 50 will be described later.

  The conveyance path L for conveying the paper T is a first conveyance path L1 from the cassette paper feeding unit 51 to the transfer nip N, a second conveyance path L2 from the transfer nip N to the fixing unit 9, and a discharge from the fixing unit 9. A third conveyance path L3 to the section 50, a manual conveyance path La that joins the paper supplied from the manual sheet feeding unit 64 to the first conveyance path L1, and a third conveyance path L3 from the downstream side to the upstream side. And a return transport path Lb that reverses the front and back and returns the sheet to the first transport path L1.

Moreover, the 1st junction part P1 and the 2nd junction part P2 are provided in the middle of the 1st conveyance path L1. A first branch portion Q1 is provided in the middle of the third transport path L3.
The first joining part P1 is a joining part where the manual feed path La joins the first transport path L1. The second junction P2 is a junction where the return conveyance path Lb merges with the first conveyance path L1.
The first branch portion Q1 is a branch portion where the return transport path Lb branches from the third transport path L3, and includes a first roller pair 54a and a second roller pair 54b. One roller of the first roller pair 54a and one roller of the second roller pair 54b are combined.

  In the middle of the first transport path L1 (specifically, between the second joining portion P2 and the transfer roller 8), a sensor for detecting the paper T, skew correction (diagonal paper feeding) of the paper T, and an image A registration roller pair 80 for aligning the timing of forming the toner image in the forming unit GK and the conveyance of the paper T is disposed. The sensor is disposed immediately before the registration roller pair 80 in the transport direction of the paper T (upstream in the transport direction). The registration roller pair 80 conveys the paper T by performing the above-described correction and timing adjustment based on detection signal information from the sensor.

The return conveyance path Lb is a conveyance path that is provided so that the opposite surface (unprinted surface) to the surface that has already been printed faces the photosensitive drum 2 when performing duplex printing on the paper T.
According to the return conveyance path Lb, the paper T conveyed from the first branching section Q1 to the paper discharge section 50 side by the first roller pair 54a is reversed and returned to the first conveyance path L1 by the second roller pair 54b. , And can be conveyed to the upstream side of the pair of registration rollers 80 arranged on the upstream side of the transfer roller 8. A predetermined toner image is transferred onto the unprinted surface at the transfer nip N on the paper T that is reversed upside down by the return conveyance path Lb.

  A paper discharge unit 50 is formed at the end of the third transport path L3. The paper discharge unit 50 is disposed on the upper side of the apparatus main body M. The paper discharge unit 50 opens toward the right side of the apparatus main body M (the right side in FIG. 1, the manual paper feed unit 64 side). The paper discharge unit 50 discharges the paper T conveyed through the third conveyance path L3 to the outside of the apparatus main body M by the third roller pair 53.

On the opening side of the paper discharge unit 50, a paper discharge stacking unit M1 is formed. The paper discharge stacking unit M1 is formed on the upper surface (outer surface) of the apparatus main body M. The paper discharge stacking unit M1 is a part formed by the upper surface of the apparatus main body M being depressed downward. The bottom surface of the paper discharge stacking unit M1 constitutes a part of the top surface of the apparatus main body M. In the paper discharge stacking unit M1, sheets T formed with a predetermined toner image and discharged from the paper discharge unit 50 are stacked and stacked.
A paper detection sensor is disposed at a predetermined position on each conveyance path.

  FIG. 2 is a diagram for explaining the control unit 100, the current supply unit 101, the limiter 102, and the time measuring unit 103. As shown in FIG. 2, the printer 1 further includes a control unit 100, a current supply unit 101, a limiter 102 as a limiting unit, and a time measuring unit 103.

  The control unit 100 controls the current supply unit 101 and the limiter 102. Further, the control unit 100 controls the image forming unit GK, the paper supply / discharge unit KH, and the like.

  The current supply unit 101 supplies current to the charging unit 10 based on the control of the control unit 100. That is, the current supply unit 101 supplies a current to the charging unit 10 (charging roller 10a) based on a bias applied to the charging unit 10 (charging roller 10a).

  When the current is supplied from the current supply unit 101 to the charging unit 10, the limiter 102 limits the supply of a current having a predetermined current value or more. That is, the limiter 102 is connected between the current supply unit 101 and the charging unit 10 and limits the current supplied to the charging unit 10. Therefore, the limiter 102 can also limit the inrush current to the charging unit 10.

The limiter 102 varies the current value to be limited in the first case and the second case based on the control of the control unit 100.
The first case is a case where current is supplied from the current supply unit 101 to the charging unit 10 when an image is formed on the paper T. That is, the first case is a case where an image is formed on the paper T using the photosensitive drum 2, the charging unit 10, the laser scanner unit 4, the developing device 16, the transfer roller 8, and the like.

  The second case is a case where a current having a value smaller than that in the first case is supplied from the current supply unit 101 to the charging unit 10. For example, the second case is a case where moisture attached to the photosensitive drum 2 or the charging unit 10 is removed. When a bias is applied to the charging roller 10a to charge the surface of the photosensitive drum 2 in a state where moisture is attached to the photosensitive drum 2 or the charging roller 10a, a leak may occur in the photosensitive drum 2. There is sex. Therefore, in the second case, when the printer 1 is turned on or when the printer 1 shifts from the sleep mode to the image forming mode, a weak current is supplied from the current supply unit 101 to the charging unit 10, The moisture attached to the photosensitive drum 2 or the charging roller 10a is removed.

  The image forming mode is a mode in which an image can be formed on the paper T, and the photosensitive drum 2, the laser scanner unit 4, the developing device 16, the transfer roller 8, and the like can be operated. The sleep mode is a mode in which the power consumed by the printer 1 is less than that in the image forming mode. That is, the power saving mode is a mode in which an image is not formed on the paper T, and the photosensitive drum 2, the laser scanner unit 4, the developing device 16, the transfer roller 8, and the like are not operated. The sleep mode may be referred to as a power saving mode.

  In the first case, the limiter 102 has a current value of a current supplied from the current supply unit 101 to the charging unit 10 when a leak occurs between the photosensitive drum 2 and the charging unit 10 as a predetermined current value. And a first current value that is lower than the minimum current value at which the surface of the photosensitive drum 2 can be charged by the charging unit 10 is set.

  That is, the first current value is lower than the current value corresponding to the current when the photosensitive drum 2 is broken down. Further, the first current value is larger than the current value of the current corresponding to the lowest voltage at which the surface of the photosensitive drum 2 can be charged by the charging unit 10 (charging roller 10a). As a specific example, the first current value is 1.1 to 1.5 times the charging current with respect to the voltage applied to the charging unit 10 for charging the surface of the photosensitive drum 2, more preferably 1.2. The current value is double.

  FIG. 3 is a diagram for explaining setting of the second current value. In the second case, the limiter 102 sets a second current value smaller than the minimum current value in the first case as the predetermined current value. The second current value is a value obtained by multiplying the current value of the current supplied from the current supply unit 101 to the charging unit 10 in the second case by a predetermined coefficient.

  For example, when a current having a current value A as a desired current value is supplied from the current supply unit 101 to the charging unit 10, as shown in FIG. 3, immediately after starting the supply of current, the current value A is supplied to the charging unit 10. A current having a larger current value is supplied. When the time for supplying current elapses, the current value of the current supplied to the charging unit 10 decreases and approaches the current value A. The second current value is, for example, a value obtained by multiplying the current value A by a predetermined coefficient. As a specific example, the predetermined coefficient is 1/45 to 1/2. More preferably, the predetermined coefficient is 1/2 in the initial stage (when the drive time is 0 min) and 1/5 in the second half of the endurance (when the drive time is 7000 min). When a voltage of about 400 to 600 V is applied to the charging unit 10 (charging roller 10a), the second current value is 15 to 25 μA, more preferably 20 μA. The second current value is constant regardless of the driving time of the photosensitive drum 2.

  The timer 103 counts the drive time of the photosensitive drum 2. As shown in FIG. 2, the photosensitive drum 2 rotates when the rotation drive of the motor 104 is transmitted. Therefore, for example, the time measuring unit 103 measures the time during which the motor 104 for rotating the photosensitive drum 2 is rotationally driven as the driving time of the photosensitive drum 2. The timing unit 103 supplies the timing result to the control unit 100.

  Here, based on the control of the control unit 100, the limiter 102 increases the first current value as the driving time measured by the time measuring unit 103 becomes longer. That is, when the film formed on the surface of the photosensitive drum 2 becomes thinner with durability, the current (charging current) supplied from the current supply unit 101 to the charging unit 10 (charging roller 10a) increases. For this reason, the limiter 102 increases the first current value as the current supplied to the charging unit 10 increases.

  FIG. 4 is a diagram illustrating the relationship between the driving time of the photosensitive drum 2, the charging current, the first current value, and whether or not leakage has occurred. As shown in FIG. 4, as the driving time of the photosensitive drum 2 becomes longer, the current (charging current) supplied from the current supply unit 101 to the charging unit 10 increases. The limiter 102 increases the first current value as the charging current increases. As an example, when the charging current is 45 μA, the limiter 102 sets 54 μA, which is 1.2 times the charging current, as the first current value. The limiter 102 has a charging current of 56 μA when the driving time of the photosensitive drum 2 reaches 3000 minutes. Therefore, 67 μA, which is 1.2 times the charging current, is set as the first current value.

  In the case where the limiter 102 is connected between the current supply unit 101 and the charging unit 10 (charging roller 10a) as in the present embodiment (in the case of “with current limiter”), the high-temperature and high-humidity environment and the condensation environment In either case, no leak occurred in the photosensitive drum 2 (in the case of “◯” in FIG. 4). On the other hand, when the limiter 102 is not connected between the current supply unit 101 and the charging unit 10 (in the case of “no current limiter”), the driving time of the photosensitive drum 2 is 4000 minutes or more in a high temperature and high humidity environment. Then, a leak occurred in the photosensitive drum 2 (in the case of “x” in FIG. 4). Furthermore, in the condensation environment without a current limiter, a leak occurred in the photosensitive drum 2 (in the case of “x” in FIG. 4).

Next, a general operation of the printer 1 will be briefly described with reference to FIG.
First, a case where single-sided printing is performed on the paper T stored in the paper feed cassette 52 will be described.
The paper T accommodated in the paper feed cassette 52 is sent out to the first transport path L1 by the forward feed roller 61 and the paper feed roller pair 63, and then the registration rollers via the first junction P1 and the first transport path L1. Transported to pair 80.
In the registration roller pair 80, skew correction of the paper T and timing adjustment with the toner image are performed.

The paper T discharged from the registration roller pair 80 is introduced between the photosensitive drum 2 and the transfer roller 8 (transfer nip N) via the first conveyance path L1. A toner image is transferred onto the paper T between the photosensitive drum 2 and the transfer roller 8.
Thereafter, the paper T is discharged from between the photosensitive drum 2 and the transfer roller 8, and the fixing nip between the heating rotator 9a and the pressure rotator 9b in the fixing unit 9 via the second conveyance path L2. To be introduced. Then, the toner TN is melted in the fixing nip, and the toner TN is fixed on the paper T.

Next, the paper T is transported to the paper discharge unit 50 through the third transport path L3 by the first roller pair 54a, and is discharged from the paper discharge unit 50 to the paper discharge stacking unit M1 by the third roller pair 53.
In this way, single-sided printing of the paper T stored in the paper feed cassette 52 is completed.

  When single-sided printing is performed on the paper T placed on the manual feed tray 65, the paper T placed on the manual feed tray 65 is sent out to the manual feed path La by the paper feed roller 66, and then the first joining portion. It is conveyed to the registration roller pair 80 via P1 and the first conveyance path L1. Subsequent operations are the same as the one-side printing operation of the paper T accommodated in the paper feed cassette 52 described above, and a description thereof will be omitted.

Next, the operation of the printer 1 when performing duplex printing will be described.
In the case of single-sided printing, as described above, the paper T on which single-sided printing has been performed is discharged from the paper discharge unit 50 to the paper discharge stacking unit M1, and the printing operation is completed.
On the other hand, when performing double-sided printing, the paper T on which single-sided printing has been performed is reversed from the time of single-sided printing and conveyed again to the registration roller pair 80 via the return conveyance path Lb. Then, double-sided printing is performed on the paper T.

  Specifically, the operation is the same as the above-described single-sided printing operation until the paper T on which single-sided printing is performed is discharged from the paper discharge unit 50 by the third roller pair 53. Thus, in the case of double-sided printing, the rotation of the third roller pair 53 is stopped and rotated in the reverse direction in a state where the paper T on which single-sided printing has been performed is held by the third roller pair 53. When the third roller pair 53 is thus rotated in the reverse direction, the paper T held by the third roller pair 53 moves in the reverse direction (from the paper discharge unit 50 to the first branching unit Q1) along the third transport path L3. Transported in the direction of heading).

  As described above, when the paper T is transported in the reverse direction on the third transport path L3, it is introduced into the second roller pair 54b (not the first roller pair 54a). Then, the paper T joins the first transport path L1 via the return transport path Lb and the second joining portion P2. Here, the paper T is turned upside down from the one-side printing.

  Further, the paper T is corrected or adjusted by the registration roller pair 80 and is introduced between the photosensitive drum 2 and the transfer roller 8 through the first conveyance path L1. Since the unprinted surface of the sheet T passes through the return conveyance path Lb and faces the photosensitive drum 2, the toner image is transferred to the unprinted surface, and as a result, duplex printing is performed.

  Next, a characteristic operation of the printer 1 will be described. FIG. 5 is a flowchart for explaining a characteristic operation of the printer 1.

  In step ST1, the control unit 100 determines whether or not the power is turned on or whether or not the sleep mode is restored. When the power is turned on or when returning from the sleep mode (YES), the control unit 100 advances the process to step ST2. When the power is not turned on and when the sleep mode is not restored (NO), the control unit 100 performs the determination in step ST1 again.

  In step ST <b> 2, the control unit 100 sets a second current value as a predetermined current value in the limiter 102.

  In step ST3, the control unit 100 supplies the charging unit 10 (charging roller 10a) with a weak current, that is, a current for supplying a current for removing moisture attached to the photosensitive drum 2 or the charging roller 10a for a predetermined time. Control the supply unit 101. The predetermined time is a time until moisture attached to the photosensitive drum 2 or the charging roller 10a is removed. The predetermined time is determined by conducting an experiment or the like in advance. Here, even if a large current (inrush current) is output from the current supply unit 101 immediately after supplying the current from the current supply unit 101 to the charging unit 10, the second current value is set in the limiter 102 in step ST2. Therefore, no large current is input to the charging unit 10.

  In step ST <b> 4, the control unit 100 determines whether to form an image on the paper T. That is, the control unit 100 determines whether image information has been received from an external device. When an image is formed (YES), the control unit 100 advances the process to step ST5. When the image is not formed (NO), the control unit 100 performs the determination in step ST4 again.

  In step ST <b> 5, the control unit 100 sets a first current value as a predetermined current value in the limiter 102.

  In step ST6, the control unit 100 supplies current to the charging unit 10 to supply a current for charging the surface of the photosensitive drum 2 in order to form an image based on the image information received from the external device on the paper T. The unit 101 is controlled. Even when a large current (inrush current) is output from the current supply unit 101 immediately after supplying the current from the current supply unit 101 to the charging unit 10, the first current value is set in the limiter 102 in step ST5. A large current is not input to the charging unit 10.

  In step ST7, the control unit 100 determines whether or not the image formation is completed. If the image formation has not ended (NO), the control unit 100 returns the process to step ST6. When the image formation is completed (YES), the control unit 100 ends the process.

According to this embodiment, the following effects are produced, for example.
In the first case where the current is supplied from the current supply unit 101 to the charging unit 10 when an image is formed on the paper T, the printer 1 has a predetermined current value between the photosensitive drum 2 and the charging unit 10. The minimum current value that is lower than the current value of the current supplied from the current supply unit 101 to the charging unit 10 when a leak occurs and is capable of charging the surface of the photosensitive drum 2 by the charging unit 10. A first current value that is larger than that is set in the limiter 102. In the second case in which the printer 1 supplies a current having a smaller value than the first case from the current supply unit 101 to the charging unit 10, the second current that is smaller than the above-described minimum current value as the predetermined current value. Set the value in the limiter 102.
As a result, the printer 1 sets the upper limit value of the current corresponding to each of the first case and the second case in the limiter 102. Therefore, in the first case and the second case, the printer 1 Leakage can be prevented.

  In the second case, moisture attached to the photosensitive drum 2 or the charging unit 10 (charging roller 10a) is removed. When moisture adheres to the photosensitive drum 2 or the charging unit 10, leakage is likely to occur in the photosensitive drum 2. For this reason, in the second case, the printer 1 can prevent a leak from occurring on the photosensitive drum 2 by setting the second current value in the limiter 102.

  The second current value is a value obtained by multiplying the current value of the current supplied from the current supply unit 101 to the charging unit 10 in the second case by a predetermined coefficient. Accordingly, the printer 1 can set the second current value set in the limiter 102 to an appropriate value.

  Further, the printer 1 increases the first current value as the driving time measured by the time measuring unit 103 becomes longer. Accordingly, the printer 1 can set the first current value to an appropriate value according to durability.

As mentioned above, although preferred embodiment was described, this invention can be implemented with a various form, without being limited to embodiment mentioned above.
For example, in the present embodiment, the monochrome printer 1 is described as the image forming apparatus. However, the present invention is not limited to this, and the image forming apparatus may be a color printer, a copier, a facsimile, or a complex machine thereof. Good.

DESCRIPTION OF SYMBOLS 1 ... Printer (image forming apparatus), 2 ... Photosensitive drum (image carrier), 10 ... Charging part, 101 ... Current supply part, 102 ... Limiter (limitation part), 103 ... Time measuring part

Claims (3)

An image forming apparatus for transferring a toner image formed by developing an electrostatic latent image with toner to a transfer material and forming an image on the transfer material,
An image carrier on which an electrostatic latent image is formed;
A charging unit that charges the surface of the image carrier in order to form an electrostatic latent image on the surface of the image carrier;
A current supply unit for supplying current to the charging unit;
A restriction unit that restricts supply of a current of a predetermined current value or more when current is supplied from the current supply unit to the charging unit;
The restriction unit is
In the first case where current is supplied from the current supply unit to the charging unit when an image is formed on the transfer material, a leak occurs between the image carrier and the charging unit as the predetermined current value. Lower than the current value of the current supplied from the current supply unit to the charging unit when generated, and lower than the minimum current value with which the surface of the image carrier can be charged by the charging unit. set the first current value has a size,
In the second case in which a current having a smaller value than that in the first case is supplied from the current supply unit to the charging unit, the predetermined current value is set to a size that prevents the image carrier from being charged by the charging unit. An image forming apparatus for setting a second current value. The image forming apparatus according to claim 1, wherein the second case is a case of removing moisture attached to the image carrier or the charging unit. A timing unit for measuring the driving time of the image carrier,
3. The image forming apparatus according to claim 1, wherein the limiting unit increases the first current value as the driving time measured by the timing unit becomes longer.

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