JP5600643B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer or a copying machine.

  In an image forming apparatus to which electrophotographic technology is applied, a charging member is arranged in contact with or close to the surface of an image carrier, and an image voltage is applied by applying an oscillating voltage in which an AC voltage and a DC voltage are superimposed on the charging member. A contact charging method is used in which the surface of the carrier is charged to a predetermined potential.

  In such a contact charging type image forming apparatus, as shown in the timing chart of FIG. 4, when an image forming operation start signal (main motor ON signal) is input, all the unit units sequentially operate. Start. That is, simultaneously with the input of the ON signal of the main motor, an erase lamp as a charge removal member for removing the charged potential on the surface of the image carrier is turned on (ON). Subsequently, by applying an oscillating voltage to the charging member (charging ON), a charge is applied to the surface of the image carrier, and the surface of the image carrier is raised to a predetermined potential. Thereafter, exposure is performed (exposure ON), and an electrostatic latent image is formed on the surface of the image carrier. Next, the electrostatic latent image on the surface of the image carrier is developed by a developing device (development ON), and a visible image (toner image) is formed. Further, a reverse bias is applied to the transfer portion, and then a positive bias is applied to the transfer portion, and the toner image is transferred to a transfer material such as paper.

As described above, in an image forming apparatus in which static elimination, charging, exposure, development, and transfer are performed in one cycle of image formation, when the image carrier is in an initial use state, the image is formed immediately after the start of the image forming operation. It is possible to raise the surface potential of the carrier to a predetermined potential.
However, by repeating the image forming cycle process due to long-term use of the image forming apparatus, the image bearing member becomes fatigued over time due to film abrasion on the surface of the image bearing member, electrical fatigue, light fatigue, etc. ,to degrade. When the image carrier is fatigued and deteriorates, the surface potential of the image carrier immediately after the start of the image forming operation becomes lower than a predetermined potential. As a result, as shown by the line B in FIG. 5, it takes a long time t2 to rise to a predetermined surface potential (potential at which fog does not occur) V1 or more after applying the charge, and the image forming operation starts. Immediately after that, image defects such as image fog are likely to occur. The time t2 required for the surface potential of the image carrier to rise to the predetermined surface potential V1 takes longer as the degree of fatigue or deterioration of the image carrier increases.

  Even when the image carrier is continuously loaded and then temporarily stopped and the image forming operation is started again, the surface potential of the image carrier is not changed between the first and several images. Is lower than a predetermined potential. As a result, image defects such as image fog may occur immediately after the start of the image forming operation.

  Therefore, a detection circuit for detecting the charging current value applied to the image carrier is provided, the difference between the previous detection current value and the current detection current value by this detection circuit is obtained, and the surface potential is lowered from the obtained difference. By calculating the minutes and feedback-controlling the voltage applied to the charging member, the surface potential of the image carrier immediately after the start of the image forming operation is maintained at a predetermined potential, thereby suppressing the occurrence of image defects such as image fogging. A possible image forming apparatus has been proposed (see, for example, Patent Document 1).

JP 2009-8828 A

  However, the image forming apparatus disclosed in Patent Document 1 includes a detection circuit (detection sensor) that detects a charging current value applied to the image carrier, an arithmetic circuit that calculates a difference between the detected current values, and feedback of an applied voltage. A relatively complicated circuit configuration such as a control circuit is required, and there is a problem that the cost of the apparatus is easily increased.

  The present invention does not require a complicated circuit configuration or the like, and can suppress the occurrence of image defects such as image fog by bringing the surface potential of the image carrier immediately after the start of the image forming operation close to a predetermined potential. An object is to provide a forming apparatus.

  The present invention is an image carrier, a charging member that is disposed to face the image carrier, and charges the surface of the image carrier, and generates an oscillating voltage by superimposing an alternating voltage and a direct voltage, An oscillating voltage generator that applies the oscillating voltage to the charging member; a neutralizing member that neutralizes the surface of the image carrier; and an operation control unit that controls operations of the oscillating voltage generator and the neutralizing member. The operation control unit controls the vibration voltage generation unit to apply a vibration voltage to the charging member as a control mode so as to temporarily raise the surface potential of the image carrier above a predetermined potential, and then Further, the present invention relates to an image forming apparatus having a surface potential adjustment control mode for controlling the operation of the charge eliminating member so that the surface of the image carrier is neutralized to bring the surface potential close to the predetermined potential.

  The operation control unit preferably shifts the control mode to the surface potential adjustment control mode after the operation time of the image carrier or the number of images formed by the image carrier exceeds a predetermined value.

  Further, it is preferable that the operation control unit shifts the control mode to the surface potential adjustment control mode before the image carrier rotates once for image formation.

  The image carrier is preferably composed of a single layer type electrophotographic photosensitive member having a single layer type photosensitive layer.

  Further, it is preferable not to include means for measuring a current value by the oscillating voltage applied to the charging member and means for measuring the surface potential of the image carrier.

  It is preferable that the image forming apparatus further includes a developing unit that develops the electrostatic latent image formed on the image carrier with a one-component developer.

  According to the present invention, it is possible to suppress the occurrence of image defects such as image fog by making the surface potential of the image carrier immediately after the start of the image forming operation close to a predetermined potential without requiring a complicated circuit configuration. An image forming apparatus that can be used can be provided.

FIG. 2 is a diagram for explaining an arrangement of each component of the printer. 3 is a functional block diagram relating to operations of the charging device 10 and the erase lamp 12. FIG. 7 is a timing chart showing the operation timing of each unit when the control mode of the operation control unit 65 is shifted to a control mode 82 for surface potential adjustment. 7 is a timing chart showing the operation timing of each unit when the control mode of the operation control unit 65 is shifted to a normal control mode 81. 5 is a graph for explaining the transition (temporal change) of the surface potential of the photosensitive drum 2 when the mode is shifted to the surface potential adjustment control mode 82 and when the mode is shifted to the normal control mode 81. 4 is a flowchart illustrating an operation flow of the printer 1 including control mode transition control.

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, the printer 1 according to the present embodiment includes an apparatus main body M, and 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. A paper supply / discharge unit KH that supplies the paper T to the image forming 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 device 10, a laser scanner unit 4, a developing device 16, a toner cartridge 5, and a toner. A supply unit 6, a drum cleaning unit 11, an erase lamp 12 as a charge removal member, a transfer roller 8, and a fixing unit 9 are provided.

  As shown in FIG. 1, the paper feed / discharge unit KH includes a paper feed cassette 52, a manual paper feed unit 164, a conveyance path L for 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 device 10, exposure by the laser scanner unit 4, development by the developing device 16, transfer by the transfer roller 8. Then, cleaning by the drum cleaning unit 11 and static elimination by the erase lamp 12 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 composed of a single layer type electrophotographic photosensitive member having a single layer type photosensitive layer on the surface of an aluminum cylinder. The photosensitive drum 2 is arranged so as to be capable of rotating at a constant speed 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 is formed on the surface of the photosensitive drum 2.

The charging device 10 is disposed to face the surface of the photosensitive drum 2. The charging device 10 charges the surface of the photosensitive drum 2 uniformly negatively (minus polarity) or positively (plus polarity).
Details of the charging device 10 will be described later.

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). The scanning exposure by the laser scanner unit 4 removes the charge of the exposed portion on the surface of the photosensitive drum 2. 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 develops a single color toner image on the surface of the photosensitive drum 2 by attaching a single color (usually black) toner to the electrostatic latent image formed on the photosensitive 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 is a one-component developer made of magnetic toner having magnetism.

  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 to the paper T.

  The drum cleaning unit 11 is disposed to face the surface of the photosensitive drum 2. The drum cleaning unit 11 removes (cleans) toner remaining on the surface of the photosensitive drum 2 and adhering matter (including moisture), and transports the removed toner to a predetermined recovery mechanism for recovery. .

  The erase lamp 12 is disposed to face the surface of the photosensitive drum 2. The erase lamp 12 irradiates the surface of the photoconductive drum 2 with light, thereby neutralizing the surface of the photoconductive drum 2 after being transferred and cleaned (removes charges).

  The fixing unit 9 melts and presses the toner constituting the toner image transferred onto the paper T to fix it 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 160 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 160. The paper T placed on the placement plate 160 is sent out to the transport path L by the cassette paper feed unit 51 disposed at the paper feed side end of the paper feed cassette 52 (the right end in FIG. 1). The cassette paper feeding unit 51 includes a forward feed roller 161 for taking out the paper T on the loading plate 160 and a paper feed roller pair 163 for feeding the paper T to the transport path L one by one. Is provided.

  A manual paper feed unit 164 is provided on the right side of the apparatus main body M (right side in FIG. 1). The manual paper feed unit 164 is provided mainly for supplying the apparatus main body M with a paper T having a size and type different from the paper T set in the paper feed cassette 52. The manual paper feed unit 164 includes a manual feed tray 165 that forms part of the front surface of the apparatus main body M in the closed state, and a paper feed roller 166. The manual feed tray 165 is attached to the apparatus main body M near the paper feed roller 166 at its lower end so as to be rotatable (openable and closable). The paper T is placed on the open manual feed tray 165. The paper feed roller 166 feeds the paper T placed on the open manual feed tray 165 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. The third conveyance path L3 up to the section 50, the manual conveyance path La that joins the paper supplied from the manual sheet feeding unit 164 to the first conveyance path L1, and the third conveyance path L3 from the downstream side to the upstream side. And a return transport path Lb that reverses the paper and returns it 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 shared.

  A sensor (not shown) for detecting the paper T and a skew of the paper T (oblique feeding) are provided in the middle of the first transport path L1 (specifically, between the second junction P2 and the transfer roller 8). A pair of registration rollers 80 for adjusting the timing of paper (paper) correction and toner image formation in the image forming unit GK and the conveyance of the paper T are arranged. 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 at the transfer nip N to the unprinted surface of the paper T that has been turned 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 164 side). The paper discharge unit 50 discharges the paper T transported through the third transport 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 on which a predetermined toner image is formed and discharged from the paper discharge unit 50 are stacked and stacked.
A sheet detection sensor is disposed at a predetermined position in each conveyance path.

Next, the operation of the printer 1 according to the present embodiment 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 161 and the paper feed roller pair 163, 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 melts in the fixing nip, and the toner is fixed on the paper T.

Next, the paper T is conveyed to the paper discharge unit 50 through the third conveyance 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.

  In the case of performing single-sided printing on the paper T placed on the manual feed tray 165, the paper T placed on the manual feed tray 165 is sent out to the manual feed path La by the paper feed roller 166, 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 structure of the characteristic part of the present invention will be described with reference to FIGS. FIG. 2 is a functional block diagram relating to the operation of the charging device 10 and the erase lamp 12. FIG. 3 is a timing chart showing the operation timing of each unit when the control mode of the operation control unit 65 is shifted to the surface potential adjustment control mode 82. FIG. 4 is a timing chart showing the operation timing of each unit when the control mode of the operation control unit 65 is shifted to the normal control mode 81. FIG. 5 is a graph for explaining the transition (temporal change) of the surface potential of the photosensitive drum 2 when the mode is shifted to the surface potential adjustment control mode 82 and when the mode is shifted to the normal control mode 81.

  As illustrated in FIG. 2, the printer 1 includes a charging device 10, an erase lamp 12, an oscillating voltage generation unit 61, a voltage control unit 62, an environment measurement unit 63, a storage unit 64, and an operation control unit 65. . The printer 1 does not include a unit that measures a current value based on an oscillating voltage and a unit that measures the surface potential of the photosensitive drum 2.

As shown in FIG. 2, the charging device 10 is disposed to face the photosensitive drum 2. The charging device 10 includes a charging roller 60 and a brush roll 67.
The charging roller 60 is a charging member that charges the surface of the photosensitive drum 2.
The brush roll 67 is disposed above the charging roller 60 (at a position away from the surface of the photosensitive drum 2). The brush roll 67 rotates in contact with the surface of the charging roller 60 to remove deposits on the surface of the charging roller 60.

  As shown in FIG. 2, the erase lamp 12 is disposed to face the photosensitive drum 2. The erase lamp 12 can be switched between a lighting (ON) state and a non-lighting (OFF) state. In the ON state, the erase lamp 12 discharges the surface of the photosensitive drum 2 by irradiating the surface of the photosensitive drum 2 with light.

The oscillating voltage generator 61 generates an oscillating voltage by superimposing an alternating voltage and a dc voltage, and applies the generated oscillating voltage to the charging roller 60 of the charging device 10.
Specifically, the oscillating voltage generator 61 includes an AC constant voltage power supply 68 and a DC constant voltage power supply 69.
The AC constant voltage power supply 68 generates a predetermined sinusoidal AC voltage from a low-voltage DC voltage modulated in a pulse shape by using a step-up transformer (not shown). The DC constant voltage power source 69 generates a predetermined sine wave AC voltage from a low-voltage DC voltage modulated in a pulse shape using a step-up transformer (not shown), and the generated AC voltage is rectified (not shown). ) To generate a predetermined DC voltage.

  The voltage control unit 62 controls the AC constant voltage power supply 68 to control the peak-to-peak voltage and the DC voltage of the AC voltage superimposed in the vibration voltage generation unit 61. The voltage control unit 62 acquires information on the peak-to-peak voltage from the table data 72 of the storage unit 64 based on environmental condition information acquired from the environment measurement unit 63 described later.

The environment measuring unit 63 measures environmental conditions. The environment measuring unit 63 measures, for example, environmental temperature and environmental humidity as environmental conditions.
The environment measurement unit 63 includes a temperature sensor 70 and a humidity sensor 71 installed in the printer 1. The environment measurement unit 63 outputs the acquired environmental temperature information and environmental humidity information to the voltage control unit 62.

  In the table data 72, a peak-to-peak voltage is set in advance in association with the in-machine environmental temperature and the environmental humidity, which are the factors that change the charging characteristics of the charging roller 60. The table data 72 is stored in the storage unit 64. The table data 72 is referred to when the voltage controller 62 determines the peak-to-peak voltage applied from the vibration voltage generator 61 to the charging roller 60.

The operation control unit 65 includes a timer 73, a mode selection unit 74, an oscillating voltage generation unit control unit 75, and an erase lamp turn-on / off control unit 76.
The timer 73 measures the operation (drive) time of the photosensitive drum 2 and outputs a control signal S1 related to the operation time to the mode selection unit 74 when the measured operation time T exceeds a predetermined value T0.

  The mode selection unit 74 has a surface potential adjustment control mode 82 and a normal control mode 81 as control modes. When the control signal S1 from the timer 73 is not input, the mode selection unit 74 shifts the control mode to the normal control mode 81 (selects the normal control mode 81 as the control mode). On the other hand, when the control signal S1 from the timer 73 is input, the mode selection unit 74 shifts the control mode to the surface potential adjustment control mode 82 (selects the surface potential adjustment control mode 82 as the control mode). . The mode selection unit 74 outputs a selection signal S2 related to the selected control mode to the vibration voltage generation unit control unit 75 and the erase lamp turn-off control unit 76.

  In the surface potential adjustment control mode 82, as shown in the timing chart of FIG. 3, the ON signal of the main motor (not shown) is input, the vibration voltage is applied to the charging roller 60 by the vibration voltage generator 61 (charging ON), In this mode, the operation proceeds in the order of lighting of the erase lamp 12 (ON), start of operation of the developing device 16 (development ON) simultaneously with application of the reverse transfer bias, and start of exposure by the laser scanner unit 4 (exposure ON).

Specifically, in the surface potential adjustment control mode 82, first, as shown by a line A in FIG. 5, first, an oscillating voltage is applied from the oscillating voltage generator 61 to the charging roller 60, and the surface of the photosensitive drum 2. The oscillating voltage generator controller 75 starts the operation of the oscillating voltage generator 61 so that the potential is once increased to a predetermined potential V1 or higher (charging ON). In the present embodiment, the predetermined potential V1 is a potential at which fog does not occur. Further, the surface potential is once more than 100 V higher than the predetermined potential V1. In the control mode 82 for adjusting the surface potential, thereafter, the erase lamp 12 is turned on (ON) by the erase lamp turn-off control unit 76 so as to bring the surface potential of the photosensitive drum 2 close to the predetermined potential V1, thereby performing static elimination. .
Further, the mode selection unit 74 of the operation control unit 65 shifts the control mode to the surface potential adjustment control mode 82 before the photosensitive drum 2 rotates once for image formation.

  In the normal control mode 81, as shown in the timing chart of FIG. 4, simultaneously with the input of the ON signal of the main motor (not shown), the erase lamp 12 is turned on (ON), and the charging roller 60 is driven by the vibration voltage generator 61. In this mode, the operation proceeds in the order of the application of the vibration voltage (charging ON), the application of the reverse transfer bias, the operation start of the developing device 16 (development ON), and the exposure start (exposure ON) by the laser scanner unit 4.

Next, the operation of the printer 1 including the control mode transition control in the operation control unit 65 will be briefly described. FIG. 6 is a flowchart illustrating an operation flow of the printer 1 including control mode transition control.
First, in step ST1, the printer 1 is turned on.

  Next, in step ST2, it is determined whether or not the operating time T measured by the timer 73 has exceeded a predetermined value T0 (T ≧ T0?). If it is determined that the operating time T has exceeded the predetermined value T0 (YES), the process proceeds to step ST3. If it is determined that the operation time T does not exceed the predetermined value T0 (NO), the process proceeds to step ST5.

  When it is determined that the operation time T exceeds the predetermined value T0 (step ST2, YES), in step ST3, the mode selection unit 74 of the operation control unit 65 sets the surface potential adjustment control mode 82 as the control mode. select.

  Subsequently, in step ST4, based on the selected surface potential adjustment control mode 82, the respective units are connected via the vibration voltage generation unit control unit 75 and the erase lamp turn-off control unit 76 in the operation control unit 65. The operation proceeds in the order as shown in the timing chart of FIG.

  On the other hand, when it is determined that the operation time T does not exceed the predetermined value T0 (step ST2, NO), in step ST5, the mode selection unit 74 of the operation control unit 65 sets the normal control mode as the control mode. 81 is selected.

  Next, in step ST6, based on the selected normal control mode 81, each unit is configured as shown in FIG. 3 via the vibration voltage generation unit control unit 75 and the erase lamp turn-off control unit 76 in the operation control unit 65. The operation proceeds in the order shown in the timing chart.

  Finally, in step ST7, a predetermined image is formed by the printer 1.

According to this embodiment, the following effects are produced, for example.
The printer 1 according to the present embodiment is disposed to face the photosensitive drum 2, and generates a vibration voltage by superimposing an AC voltage and a DC voltage on the charging roller 60 that charges the surface of the photosensitive drum 2, and An oscillating voltage generator 61 that applies an oscillating voltage to the charging roller 60; an erase lamp 12 that neutralizes the surface of the photosensitive drum 2; an operation controller 65 that controls operations of the oscillating voltage generator 61 and the erase lamp 12; The operation control unit 65 controls the vibration voltage generation unit 61 to apply a vibration voltage to the charging roller 60 and temporarily raise the surface potential of the photosensitive drum 2 to a predetermined potential or higher as a control mode. Thereafter, the surface potential adjustment control mode 8 for controlling the lighting operation of the erase lamp 12 so that the surface of the photosensitive drum 2 is neutralized to bring the surface potential closer to a predetermined potential. Having.

  Therefore, according to the present embodiment, when the photosensitive drum 2 is fatigued or deteriorated over time due to film scraping on the surface of the photosensitive drum 2, electrical fatigue, light fatigue, or the like, the operation control unit 65. , The surface potential of the photosensitive drum 2 is once increased to a predetermined potential or higher, and thereafter, the surface potential adjustment control mode 82 is performed in which the surface of the photosensitive drum 2 is discharged to bring the surface potential closer to the predetermined potential. . As a result, the surface potential of the photosensitive drum 2 can be brought close to a predetermined potential immediately after the start of the image forming operation. Accordingly, it is possible to suppress the occurrence of image defects such as image fogging immediately after the start of image formation, regardless of fatigue or deterioration of the photosensitive drum 2.

  Moreover, the operation control unit 65 shifts to the surface potential adjustment control mode 82 only by changing the timing of application of the vibration voltage from the vibration voltage generation unit 61 to the charging roller 60 and the lighting operation of the erase lamp 12. The occurrence of image defects such as image fog can be suppressed. Therefore, compared with the case where the charging current value applied to the photosensitive drum 2 or the surface potential of the photosensitive drum 2 is detected and the voltage applied to the charging roller 60 is feedback controlled based on the detection result, A complicated circuit configuration such as a feedback control circuit is not required, and the cost of the apparatus can be reduced.

In the printer 1 of the present embodiment, the operation control unit 65 shifts the control mode to the surface potential adjustment control mode 82 after the operation time T of the photosensitive drum 2 exceeds the predetermined value T0.
Therefore, when the operation time T of the photosensitive drum 2 is less than the predetermined value T0 and there is no deterioration in characteristics due to fatigue or deterioration of the photosensitive drum 2, the operation control unit 65 shifts the control mode to the normal control mode 81. . Thereby, application of an excessive voltage to the photosensitive drum 2 can be reduced, power consumption can be reduced, and deterioration of the photosensitive drum 2 and the charging roller 60 can be suppressed.

In the printer 1 of this embodiment, the operation control unit 65 shifts the control mode to the surface potential adjustment control mode 82 before the photosensitive drum 2 makes one rotation for image formation.
For this reason, the surface potential of the photosensitive drum 2 once increased to a predetermined potential or more can be rapidly lowered to a vicinity of the predetermined potential, and the surface potential of the photosensitive drum 2 can be reduced to a predetermined potential at the time of image formation. It is easy to stabilize in the vicinity. As a result, it is possible to form a good image without fog.

The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and can be implemented in various forms.
For example, in the above-described embodiment, the operation time T of the photosensitive drum 2 is used as a determination factor for shifting to the surface potential adjustment control mode 82 by the operation control unit 65, but the present invention is not limited to this. As the determination element, the number of images formed by the printer 1 (number of printed sheets) may be used.
Further, using either the operation time T of the photosensitive drum 2 or the number of formed images (number of printed sheets), after either one (time or number) exceeds a predetermined value, the mode shifts to the surface potential adjustment control mode 82. You may let them.

  In the above-described embodiment, the photosensitive drum 2 is composed of a single-layer electrophotographic photosensitive member having a single-layered photosensitive layer on the surface of an aluminum cylinder, but is not limited thereto. As the photosensitive drum 2, a photosensitive drum formed by vapor-depositing an amorphous silicon layer as a positively chargeable photoconductor on the surface of an aluminum cylinder may be used.

  The type of the image forming apparatus according to the present invention is not particularly limited, and may be a copier, a printer, a facsimile, or a complex machine thereof.

  DESCRIPTION OF SYMBOLS 1 ... Printer (image forming apparatus), 2 ... Photosensitive drum (image carrier), 10 ... Charging device, 12 ... Erase lamp (static elimination member), 16 ... Developer, 60 ... Charging roller ( Charging member), 61... Vibration voltage generation unit, 65... Operation control unit, 68... AC constant voltage power source, 69... DC constant voltage power source, 73. Oscillating voltage generator control unit 76... Erase lamp turn-off control unit 81... Normal control mode 82... Surface potential adjustment control mode T T. Operation time T 0.

Claims (5)

An image carrier;
A charging member disposed opposite to the image carrier and charging the surface of the image carrier;
An oscillating voltage is generated by superimposing an alternating voltage and a dc voltage, and the oscillating voltage is applied to the charging member;
A static elimination member for neutralizing the surface of the image carrier;
An operation control unit for controlling the operation of the vibration voltage generation unit and the static elimination member,
The operation control unit, as a control mode according to the operation time of the image carrier, applies a vibration voltage to the charging member to temporarily increase the surface potential of the image carrier above a predetermined potential. A control mode for adjusting the surface potential, which controls the operation of the static eliminating member so as to control the vibration voltage generation unit and thereafter neutralize the surface of the image carrier to bring the surface potential close to the predetermined potential; With
The operation control unit shifts the control mode to the surface potential adjustment control mode after the operation time of the image carrier or the number of images formed by the image carrier exceeds a predetermined value. apparatus. The image forming apparatus according to claim 1 , wherein the operation control unit shifts a control mode to the surface potential adjustment control mode before the image carrier rotates once for image formation. It said image bearing member, an image forming apparatus according to claim 1 or 2 consisting of a single layer type electrophotographic photoreceptor having a photosensitive layer of single layer type. Said means for measuring the current value by the oscillating voltage applied to the charging member, and an image forming apparatus according to any one of claims 1-3 which is not provided with means for measuring the surface potential of said image bearing member . The image forming apparatus according to any one of the developing device for developing, from claim 1, further comprising 4 to the electrostatic latent image formed on the image bearing member by a one-component developer.

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