JP5629649B2 - 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 electrophotographic image forming apparatus, a charging member is disposed in contact with or close to the surface of the image carrier, and an image voltage is applied to the charging member by applying a vibration voltage in which an AC voltage and a DC voltage are superimposed. A contact charging method is used in which the surface is charged to a predetermined potential.

In such a contact charging method, discharge products such as nitrogen oxides and ozone are generated by the discharge phenomenon, and the discharge products may easily adhere to the surface of the image carrier. The discharge product adhering to the surface of the image carrier changes to a conductive substance by reacting with moisture, and as a result, the electrical resistance of the surface of the image carrier is reduced, and the potential of the surface of the image carrier is reduced. May not be held at the potential required for forming the electrostatic latent image.
If development is performed in this state, an image flow phenomenon including bleeding and blurring may occur in the obtained toner image, and image quality may be significantly deteriorated.

The image flow phenomenon occurs not only due to fluctuations in environmental conditions (temperature and humidity), but also due to secular changes in characteristics of the image carrier and charging member.
In view of this, an image forming apparatus including a voltage control unit that can accurately set an appropriate peak-to-peak voltage of an AC voltage regardless of changes in environmental conditions and changes in characteristics of an image carrier or a charging member has been proposed. (For example, refer to Patent Document 1).

  As shown in FIG. 3, the voltage control unit disclosed in Patent Document 1 is a two-way device that represents the relationship between the peak-to-peak voltage value Vpp of the AC voltage and the DC current value Idc between the charging member and the image carrier. Two low-voltage side peak-to-peak voltage values Vpp (A) and Vpp that are assumed to be lower than the voltage value of the inflection point P that appears when the peak-to-peak voltage Vpp is boosted with respect to the assumed characteristic curve on the dimensional coordinates. Coordinates A {Vpp (A), Idc (A)}, B {Vpp obtained based on two DC current values Idc (A) and Idc (B) detected by the current detector when (B) is applied (B), Idc (B)} is detected by the current detection unit when a high-voltage peak-to-peak voltage value Vpp (C) that is assumed to be higher than the voltage value at the inflection point P is applied. Coordinates C {obtained based on the direct current value Idc (C) The peak-to-peak voltage Vpp corresponding to the intersection P1 with the straight line L2 passing through pp (V), Idc (C)} and parallel to the coordinate axis representing the peak-to-peak voltage Vpp is selected as the appropriate peak-to-peak voltage value Vpp (O). To do.

In addition, in the image forming apparatus, with the diversification of user needs, it is possible to form an image on a wide variety of sheets such as cardboard and OHP, and when forming an image on a wide variety of sheets, There is a demand to prevent the image density from changing.
In order to meet this requirement, the operation speed (linear speed) of the image carrier can be selected from a normal operation speed and at least one low speed slower than the normal operation speed, and the selected operation speed is selected. An image forming apparatus for forming an image has been developed.

JP 2007-199094 A

  The voltage control method by the voltage control unit disclosed in Patent Document 1 can set the appropriate peak-to-peak voltage value Vpp of the AC voltage with high accuracy at a normal operation speed. However, when a low speed slower than the normal operation speed is selected, the direct current value Idc between the charging member and the image carrier is small as shown in FIG. That is, the direct current value Idc has a dependency on the operation speed, and the direct current value Idc decreases as the operation speed decreases.

  Therefore, when the low speed is selected as the operation speed of the image carrier, the DC current value Idc detected to select the appropriate peak-to-peak voltage value Vpp is small. If the appropriate peak-to-peak voltage value Vpp is set using the small DC current value Idc, the setting accuracy of the appropriate peak-to-peak voltage value Vpp is lower than that at the normal operating speed. As a result, the peak-to-peak voltage Vpp is lower than an appropriate value, and the uniformity of the surface potential of the image carrier is deteriorated. On the other hand, when the peak-to-peak voltage Vpp is higher than an appropriate value, there is a problem in that an increase in discharge products causes an image flow and an increase in the surface friction force of the image carrier.

  An object of the present invention is to provide an image forming apparatus capable of accurately setting an appropriate peak-to-peak voltage value regardless of the selection of the operation speed of the image carrier.

  The present invention includes an image carrier, and an operation speed selection unit capable of selecting an operation speed of the image carrier as a normal image formation speed and at least one low speed lower than the normal image formation speed, A charging member disposed opposite to the image carrier and charging the surface of the image carrier and an alternating voltage and a DC voltage Vdc are superimposed to generate a vibration voltage, and the vibration voltage is applied to the charging member. A vibration voltage generator to be applied; a voltage controller for controlling the peak-to-peak voltage value Vpp of the AC voltage and the DC voltage Vdc superimposed in the vibration voltage generator; and between the image carrier and the charging member. And a target DC current value for storing a target DC current value that is a target DC current value when the surface of the image carrier is charged to a predetermined surface potential. An information storage unit; The voltage control unit controls the peak-to-peak voltage value Vpp based on the normal image forming speed when the operation speed of the image carrier is selected to be the low speed by the operation speed selection unit. After the operation, the operation speed of the image carrier is switched to the selected low speed so that the target DC current value stored in the target DC current value information storage unit is obtained. The present invention relates to an image forming apparatus that performs control.

  In addition, the voltage control unit is configured to calculate the relationship between the peak-to-peak voltage value Vpp and a direct current value Idc between the charging member and the image carrier with respect to an assumed characteristic curve on a two-dimensional coordinate. The current detection when two low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) that are assumed to be lower than the voltage value at the inflection point appearing when the peak-to-peak voltage value Vpp is boosted are applied. Coordinates A {Vpp (A), Idc (A)}, B {Vpp (B), Idc (B)} obtained based on the two DC current values Idc (A) and Idc (B) detected by the unit And a DC current value Idc (C) detected by the current detector when a high-voltage peak-to-peak voltage value Vpp (C) assumed to be higher than the voltage value at the inflection point is applied. The coordinates C {Vpp (V), Id obtained based on (C) through}, it is preferable to select the peak-to-peak voltage value Vpp corresponding to the intersection of the straight line L2 parallel to the coordinate axis representing the peak-to-peak voltage value Vpp as the proper peak voltage value Vpp (O).

  The low voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and the high voltage side peak-to-peak voltage value Vpp (C) are set in advance based on the variation factors of the charging characteristics of the charging member. The voltage control unit preferably selects the low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and the high-voltage-side peak-to-peak voltage value Vpp (C) according to the table data.

  The normal image forming speed is preferably the maximum operating speed set for the image carrier.

  The charging member is preferably a charging roller formed by coating an outer peripheral portion of a metal core with a conductive elastic material layer.

  The image carrier is preferably a photosensitive drum formed by depositing an amorphous silicon layer on the surface of an aluminum cylinder.

  According to the present invention, it is possible to provide an image forming apparatus capable of accurately setting an appropriate peak-to-peak voltage value regardless of the selection of the operation speed of the image carrier.

FIG. 2 is a diagram for explaining an arrangement of each component of the printer. 3 is a functional block diagram showing a configuration around a charging device 10. FIG. 2 shows an assumed characteristic curve on a two-dimensional coordinate representing the relationship between the peak-to-peak voltage value Vpp of the AC voltage and the DC current value Idc between the charging member (charging roller 60) and the image carrier (photosensitive drum 2). It is a graph. It is a graph explaining the relationship between the straight lines L1 and L2 calculated | required by this invention, the coordinate A, B, and C, and appropriate peak-to-peak voltage value Vpp (O). 5 is a graph showing an example of table data 73. It is a flowchart which shows the flow of the image output preparation operation | movement of the printer 1 including control of the voltage value Vpp between peaks. 3 is a graph for explaining a relationship between a rotation speed of a photosensitive drum 2 and a target direct current value. 6 is a flowchart illustrating an operation flow after the printer 1 is shifted to an actual image output operation after the image output preparation operation.

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, a static eliminator 12, 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, 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 formed by depositing an amorphous silicon layer, which is a positively chargeable photoconductor, 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 can be 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 uniformly charges the surface of the photosensitive drum 2 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 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 to 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 (including moisture) 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 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 arranged at the end of the paper feed cassette 52 on the paper feed side (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 sheet T conveyed from the first branching section Q1 to the sheet 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. Thus, it can be transported to the upstream side of the registration roller pair 80 disposed 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 of the first 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, referring to FIGS. 2 to 5, the charging device 10 and the configuration for applying a voltage to the charging device 10 will be described. FIG. 2 is a functional block diagram showing a configuration around the charging device 10. FIG. 3 shows a two-dimensional coordinate assumption representing the relationship between the peak-to-peak voltage value Vpp of the AC voltage and the DC current value Idc between the charging member (charging roller 60) and the image carrier (photosensitive drum 2). It is a graph which shows a characteristic curve. FIG. 4 is a graph for explaining the relationship between the straight lines L1 and L2, the coordinates A, B, and C obtained by the present invention and the appropriate peak-to-peak voltage value Vpp (O). FIG. 5 is a graph showing an example of the table data 73.

  As shown in FIG. 2, the printer 1 includes a charging device 10, an oscillating voltage generation unit 61, a voltage control unit 62, a current detection unit 63, a rotation speed selection unit 64 as an operation speed selection unit, and an environment measurement. Unit 65 and storage unit 66.

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 charging roller 60 includes a cored bar 601 and an epichlorohydrin rubber layer 602 that covers the surface of the cored bar 601. The epichlorohydrin rubber layer 602 is made of an elastic material layer having conductivity.
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 removes deposits attached to the surface of the charging roller 60 by rotating in contact with the surface of the charging roller 60.

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 current detector 63 detects a direct current value Idc between the photosensitive drum 2 and the charging roller 60. The current detection unit 63 outputs information regarding the detected DC current value Idc to the rotation speed selection unit 64.

The voltage control unit 62 controls the peak-to-peak voltage value Vpp of the alternating voltage superimposed on the oscillating voltage generation unit 61. The voltage control unit 62 controls the AC constant voltage power supply 68 to control the peak-to-peak voltage value Vpp and the DC voltage Vdc of the AC voltage superimposed in the vibration voltage generation unit 61.
The voltage control unit 62 converts the peak-to-peak voltage value Vpp of the AC voltage into two low-voltage side peak-to-peak voltage values Vpp (A), second peak-to-peak voltage value Vpp (B), and high-voltage-side peak-to-peak voltage value Vpp (C ). The two low-voltage side peak-to-peak voltage values Vpp (A) and the second peak-to-peak voltage value Vpp (B) are peak-to-peak voltage values that are assumed to be lower than the peak-to-peak voltage value Vpp at an inflection point P described later. is there. The high-voltage side peak-to-peak voltage value Vpp (C) is a peak-to-peak voltage value that is assumed to be higher than the peak-to-peak voltage value Vpp at the inflection point P.

  Specifically, as shown in FIGS. 3 and 4, the voltage control unit 62 is a two-dimensional representation of the relationship between the peak-to-peak voltage value Vpp and the DC current value Idc between the photosensitive drum 2 and the charging roller 60. The peak-to-peak voltage value Vpp corresponding to the intersection P1 between the straight line L1 and the straight line L2 is selected as the appropriate peak-to-peak voltage value Vpp (O) for the assumed characteristic curve on the coordinates. The straight line L1 has coordinates A {Vpp (A), Idc (A)} and coordinates B {Vpp (B), Idc (B)} obtained based on the two DC current values Idc (A) and Idc (B). A straight line passing through The two DC current values Idc (A) and Idc (B) are detected by the current detection unit 63 when the two low-voltage peak-to-peak voltage values Vpp (A) and the second peak-to-peak voltage value Vpp (B) are applied. Is done. The straight line L2 is a straight line that passes through the coordinates C {Vpp (C), Idc (C)} obtained based on the direct current value Idc (C) and is parallel to the coordinate axis representing the peak-to-peak voltage value Vpp. The direct current value Idc (C) is detected by the current detection unit 63 when the high voltage side peak-to-peak voltage value Vpp (C) is applied.

  Information about the two low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and the high-voltage-side peak-to-peak voltage value Vpp (C) is acquired from the table data 73 stored in the storage unit 66. Specifically, the voltage control unit 62 acquires information on the two low-voltage peak-to-peak voltage values Vpp (A), Vpp (B) and the high-voltage-side peak voltage value Vpp (C) from the environment measurement unit 65 described later. Based on the environmental condition information, it is obtained from the table data 73 of the storage unit 66.

The environment measuring unit 65 measures environmental conditions. The environment measuring unit 65 measures, for example, an environmental temperature and an environmental humidity as environmental conditions.
The environment measurement unit 65 includes a temperature sensor 70 and a humidity sensor 71 installed in the printer 1. The environment measurement unit 65 (temperature sensor 70, humidity sensor 71) outputs the acquired environmental condition information (environment temperature information, environment humidity information) to the voltage control unit 62.

The two low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and the high-voltage-side peak-to-peak voltage value Vpp (C) are set in advance in the table data 73 in association with the charging factor of the charging roller 60. Is done. The table data 73 is stored in the storage unit 66.
Large fluctuation factors in the charging characteristics of the charging roller 60 are the environmental temperature and the environmental humidity.

In the present embodiment, in the table data 73, two low voltage side peak-to-peak voltage values Vpp (A) and Vpp ( B) and the high-voltage side peak-to-peak voltage value Vpp (C) are set.
As a specific example, as shown in FIG. 5, two low-voltage side peak-to-peak voltage values Vpp (A) associated with the in-machine temperature (° C.) and the in-machine relative humidity (%) as peak-to-peak voltage values Vpp (V). , Vpp (B) and high-voltage peak-to-peak voltage value Vpp (C) are set as an example.

  The table data 73 shown in FIG. 5 includes the in-machine temperature and peak-to-peak voltage when the in-machine relative humidity is less than 35%, the in-machine relative humidity is less than 35 to 65%, and the in-machine relative humidity is 65% or more. The relationship with the value Vpp (V) is tabulated.

  The table data 73 includes two low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and a high-voltage-side peak-to-peak voltage value Vpp (C) applied by the voltage control unit 62 from the vibration voltage generation unit 61 to the charging roller 60. It is referred to when determining.

The rotation speed selection unit 64 sets the rotation speed of the photosensitive drum 2, which is a main factor for determining the operation speed of the photosensitive drum 2, to a normal image forming speed and a normal image forming speed by a user operation. It is possible to choose a slow low speed. The rotational speed of the photosensitive drum 2 is switched between a normal image forming speed and a low speed via the rotational speed control unit 72 according to the selection operation in the rotational speed selection unit 64.
Here, the normal image forming speed is, as shown in FIG. 7, out of the rotational speeds set on the photosensitive drum 2, the most frequently used thickness, type of paper T or normal paper T The maximum speed Vmax corresponding to the image quality. The low speeds are two low speeds V1 and V2 which are slower than the maximum speed Vmax corresponding to the paper T which is not frequently used, paper T such as OHP, and high image quality.

  In the storage unit 66, two low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and a high-voltage-side peak-to-peak voltage value Vpp (C) are stored in advance in association with the variation factors of the charging characteristics of the charging roller 60. Table data 73 that has been set and target DC current value data 74 corresponding to a target DC current value when the surface of the photosensitive drum 2 is charged to a predetermined surface potential are stored in advance. .

  The voltage control unit 62 controls the peak-to-peak voltage value Vpp based on the maximum speed Vmax when the rotation speed selection unit 64 selects the rotation speed of the photosensitive drum 2 to be the low speed V1 or V2. The rotational speed of the photosensitive drum 2 is switched to the low speed V1 or V2 selected by the rotational speed control unit 72 so that the target current value stored in the target DC current value data 74 of the storage unit 66 is obtained. The DC voltage Vdc is controlled.

Next, the operation of the printer 1 including the selection control of the appropriate peak-to-peak voltage value Vpp (O) of the oscillating voltage applied to the charging device 10 will be briefly described. FIG. 6 is a flowchart showing the flow of the image output preparation operation of the printer 1 including the control of the peak-to-peak voltage value Vpp.
First, in step ST1, the printer 1 is turned on.

Next, in step ST2, the temperature sensor 70 of the environment measuring unit 65 measures the environmental temperature, and the humidity sensor 71 measures the environmental humidity. Information on the measured environmental temperature and environmental humidity is input to the voltage controller 62.
Subsequently, in step ST3, the voltage control unit 62 determines the two low-voltage peak-to-peak voltage values set in the table data 73 of the storage unit 66 in association with the environmental temperature based on the input environmental temperature information. Vpp (A), Vpp (B), and high-voltage side peak-to-peak voltage value Vpp (C) are selected.

  Subsequently, in step ST <b> 4, the vibration voltage generation unit 61 generates a vibration voltage in which the AC voltage value and the DC voltage are superimposed, and applies the generated vibration voltage to the charging roller 60. In the oscillating voltage generator 61, the voltage control unit 62 controls the peak-to-peak voltage value Vpp, and the peak-to-peak voltage value Vpp is divided into two low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and the high-voltage side peak. A vibration voltage in the case of the voltage value Vpp (C) is generated, and the generated vibration voltage is applied to the charging roller 60.

  Subsequently, in step ST5, the current detection unit 63 determines the DC current values Idc (A) and Idc (A) when the peak-to-peak voltage value Vpp is two low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B). B) and the DC current value Idc (C) when the peak-to-peak voltage value Vpp is the high-voltage side peak-to-peak voltage value Vpp (C) are detected.

  Subsequently, in step ST6, the voltage controller 62 determines the coordinates A {Vpp (A), Idc (A) obtained based on the two DC current values Idc (A) and Idc (B) detected by the current detector 63. A)}, a straight line L1 passing through the coordinates B {Vpp (B), Idc (B)}, and a coordinate C {Vpp (C) obtained based on the direct current value Idc (C) detected by the current detector 63. , Idc (C)}, the peak-to-peak voltage value Vpp corresponding to the intersection P1 with the straight line L2 parallel to the coordinate axis representing the peak-to-peak voltage value Vpp is selected as the appropriate peak-to-peak voltage value Vpp (O).

Next, in step ST7, the voltage control unit 62 refers to the target DC current value data 74 in the storage unit 66, and controls the DC voltage Vdc so that the target DC current value Idc is obtained.
In step ST8, the printer 1 shifts to an image output preparation operation.

As described above, in the image output preparation operation of the printer 1, selection control of the appropriate peak-to-peak voltage value Vpp (O) of the oscillating voltage applied to the charging roller 60 is performed. According to the selection control of the appropriate peak-to-peak voltage value Vpp (O), the rotational speed of the photosensitive drum 2 is set to the thickness, type of paper T and normal image quality that are most frequently used for normal image formation. Even when the corresponding maximum speed Vmax is selected, when the rotational speed of the photosensitive drum 2 is selected to be a low speed V1 or V2 lower than the maximum speed Vmax, as shown in FIG. The direct current value Idc (C) detected by the current detector 63 is small.
As a result, when the appropriate peak-to-peak voltage value Vpp (O) is selected using a small DC current value Idc, the peak-to-peak voltage value Vpp becomes lower than the appropriate value, and the uniformity of the surface potential of the photosensitive drum 2 is deteriorated. Or the peak-to-peak voltage value Vpp becomes higher than the appropriate value, and the image flow and the surface frictional force of the photosensitive drum 2 due to the increase of the discharge products increase.

  In the present embodiment, when the rotational speed of the photosensitive drum 2 is selected to be a low speed V1 or V2 that is slower than the maximum speed Vmax, the direct current value Idc depends on the rotational speed of the photosensitive drum 2. On the other hand, the appropriate peak-to-peak voltage value Vpp (O) is controlled as follows in view of not depending on the rotational speed of the photosensitive drum 2. Specifically, in a state where the DC current value Idc is large, that is, under the condition where the rotational speed of the photosensitive drum 2 is selected as the maximum speed Vmax, the voltage control unit 62 sets the appropriate peak-to-peak voltage value Vpp (O). Then, based on the input information on the rotational speed of the photosensitive drum 2, the target DC current value Idc stored in the target DC current value data 74 of the storage unit 66 corresponding to the rotational speed is obtained. The DC voltage Vdc by the DC constant voltage power source 69 of the oscillating voltage generator 61 is controlled as described above.

  Next, an actual image output operation by the printer 1 will be briefly described. FIG. 8 is a flowchart showing an operation flow after the printer 1 is shifted to an actual image output operation after the image output preparation operation.

First, in step ST11, an image output operation by the printer 1 is started.
Next, in step ST <b> 12, the voltage control unit 62 applies the appropriate peak-to-peak voltage value Vpp (O) to the charging roller 60.

  Next, in step ST13, it is determined whether or not the rotation speed of the photosensitive drum 2 by the rotation speed selection unit 64 is selected as the maximum speed Vmax (selected as the low speed V1 or V2). If it is determined that the maximum speed Vmax is selected (YES), the process proceeds to step ST15. On the other hand, when it is determined that the maximum speed Vmax is not selected (NO), the process proceeds to step ST14.

  In step ST14, the rotation speed control unit 72 switches the rotation speed of the photosensitive drum 2 to the selected low speed V1 or V2.

  After it is determined in step ST13 that the maximum speed Vmax is selected (YES) or after step ST14, in step ST15, the voltage control unit 62 determines the rotational speed of the input photosensitive drum 2. Based on the information, the DC voltage by the DC constant voltage power source 69 of the oscillating voltage generating unit 61 is obtained so that the target DC current value stored in the target DC current value data 74 of the storage unit 66 corresponding to the rotational speed is obtained. Vdc is controlled.

After step ST15, in step ST16, the appropriate peak-to-peak voltage value Vpp (O) and the controlled DC voltage Vdc are applied to the charging roller 60, and the printer 1 shifts to a predetermined image output operation (image formation).
Next, in step ST17, the printer 1 shifts to an image output preparation operation.

According to this embodiment, the following effects are produced, for example.
In the present embodiment, when the rotation speed of the photosensitive drum 2 is selected to be the low speed V1 or V2 by the rotation speed selection unit 64, the voltage control unit 62 sets the peak-to-peak voltage value Vpp based on the maximum speed Vmax. After performing the control, the rotational speed of the photosensitive drum 2 is switched to the selected low speed V1 or V2 so that the target DC current value stored in the target DC current value data 74 can be obtained. Take control.

Therefore, according to the present embodiment, when the rotational speed of the photosensitive drum 2 is selected as the maximum speed Vmax or the low speed V1, V2 according to the thickness or type of paper used or the image quality. Also, it is possible to select an appropriate peak-to-peak voltage value Vpp (O) at the maximum speed Vmax with a large DC current value. Thereby, it is possible to accurately set the appropriate peak-to-peak voltage value Vpp (O) regardless of the selection of the rotational speed of the photosensitive drum 2.
In addition, after setting the appropriate peak-to-peak voltage value Vpp (O), the photosensitive drum is controlled by switching to the selected low speeds V1 and V2 and controlling the DC voltage Vdc so as to obtain the target DC current value. The two surfaces can be charged to a predetermined surface potential corresponding to the selected rotational speed.

  Therefore, regardless of the selection of the rotational speed of the photosensitive drum 2, the appropriate peak-to-peak voltage value Vpp (O) and the surface potential are ensured, the surface potential of the photosensitive drum 2 is excellent in uniformity, and a high-quality image is obtained. As a result, it is possible to suppress an image flow and an increase in the surface friction force of the image carrier due to an increase in discharge products.

  Further, in the printer 1 of the present embodiment, the voltage control unit 62 assumes a two-dimensional coordinate representing the relationship between the peak-to-peak voltage value Vpp and the direct current value Idc between the charging roller 60 and the photosensitive drum 2. Two low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) that are assumed to be lower than the voltage value of the inflection point P that appears when the peak-to-peak voltage value Vpp is boosted with respect to the characteristic curve. Coordinates A {Vpp (A), Idc (A)}, B {Vpp (B) obtained based on the two DC current values Idc (A) and Idc (B) detected by the current detector 63 when applied. ), Idc (B)} and the high voltage side peak-to-peak voltage value Vpp (C) assumed to be higher than the voltage value at the inflection point P, are detected by the current detection unit 63. Based on the DC current value Idc (C) The peak-to-peak voltage value Vpp corresponding to the intersection P1 with the straight line L2 passing through the coordinates C {Vpp (V), Idc (C)} and parallel to the coordinate axis representing the peak-to-peak voltage value Vpp Select as (O).

  Therefore, in obtaining the appropriate peak-to-peak electrode value Vpp (O), a single sampling point (high-voltage-side peak-to-peak voltage value Vpp (C)) from the inflection point P is sufficient. Therefore, the appropriate peak voltage value Vpp (O) can be quickly obtained as compared with the case where the approximate straight line is obtained by sampling a plurality of points on the high voltage side from the inflection point P. In addition, it is possible to select a value slightly higher than the inflection point P of the assumed characteristic curve as the peak-to-peak voltage value Vpp to be applied. Therefore, it is possible to suppress deterioration of the photosensitive drum 2 and the charging roller 60 due to generation of discharge products due to excessive voltage application.

In the printer 1 of the present embodiment, the low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and the high-voltage-side peak-to-peak voltage value Vpp (C) based on the variation factors of the charging characteristics of the charging roller 60. Is set in advance, and the voltage control unit 62 selects the low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and the high-voltage-side peak-to-peak voltage value Vpp (C) according to the table data 73. .
Therefore, even if the position of the inflection point P on the assumed characteristic curve may fluctuate due to various factors such as environmental changes, the low voltage side peak voltage value Vpp (A ), The appropriate peak-to-peak voltage value Vpp (O) can be obtained by selecting the sampling voltage based on Vpp (B) and the high-voltage side peak voltage value Vpp (C).

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, there are two characteristic curves on the two-dimensional coordinate representing the relationship between the peak-to-peak voltage value Vpp and the direct current value Idc between the charging roller 60 and the photosensitive drum 2. Coordinates A {obtained based on the two DC current values Idc (A) and Idc (B) detected by the current detector 63 when the low-voltage peak-to-peak voltage values Vpp (A) and Vpp (B) are applied. Detected by the current detector 63 when the straight line L1 passing through Vpp (A), Idc (A)}, B {Vpp (B), Idc (B)} and the high-voltage side peak-to-peak voltage value Vpp (C) are applied. Corresponding to the intersection point P1 with the straight line L2 that passes through the coordinates C {Vpp (V), Idc (C)} obtained based on the DC current value Idc (C) and is parallel to the coordinate axis representing the peak-to-peak voltage value Vpp. Appropriate peak-to-peak voltage value Vpp Although during it is selected as a voltage value Vpp (O), but is not limited thereto. A value obtained by multiplying the peak-to-peak voltage value Vpp corresponding to the intersection P1 between the straight line L1 and the straight line L2 by a coefficient for correcting an error may be selected as the appropriate peak-to-peak voltage value Vpp (O).

In the above-described embodiment, the rotational speed (peripheral speed) of the photosensitive drum 2 is used as the operation speed of the photosensitive drum 2, but the present invention is not limited to this. As the operation speed of the photosensitive drum 2, the rotational speed (rps, rpm, 1 / s, 1 / m), angular velocity (rad / s), linear velocity (mm / s), or the like of the photosensitive drum 2 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, 11 ... Cleaning unit, 60 ... Charging roller (charging member), 61 ... Vibration voltage generation , 62... Voltage control unit, 63... Current detection unit, 64... Rotational speed selection unit (operation speed selection unit), 66... Storage unit, 68. Power source, 73 ... Table data, 74 ... Target DC current value data, 601 ... Core metal, 602 ... Epichlorohydrin rubber layer (elastic material layer), P ... Inflection point, Vpp ... AC voltage Peak-to-peak voltage value, Vpp (A), Vpp (B) ... Low-voltage side peak-to-peak voltage value, Vpp (C) ... High-voltage-side peak-to-peak voltage value, Vdc ... DC voltage, Idc, Idc (O1), Idc (O2) ... DC current value, Vmax ... maximum speed, 1, V2 ...... low speed

Claims (6)

An image carrier;
An operation speed selection unit capable of selecting an operation speed of the image carrier as a normal image formation speed and at least one low speed lower than the normal image formation speed;
A charging member disposed opposite to the image carrier and charging the surface of the image carrier;
An oscillating voltage generator configured to superimpose an alternating voltage and a dc voltage Vdc to generate an oscillating voltage, and to apply the oscillating voltage to the charging member;
A voltage control unit for controlling the peak-to-peak voltage value Vpp of the AC voltage and the DC voltage Vdc superimposed in the vibration voltage generation unit;
A current detector for detecting a direct current value Idc between the image carrier and the charging member;
When the surface of the image carrier is a target direct current value that is a target direct current value when the surface of the image carrier is charged to a predetermined surface potential, and corresponds to the rotational speed of the image carrier, the rotational speed becomes slow. A target DC current value information storage unit that stores a target DC current value that decreases ,
The voltage control unit controls the peak-to-peak voltage value Vpp based on the normal image forming speed when the operation speed of the image carrier is selected to be the low speed by the operation speed selection unit. Later, the DC voltage Vdc is controlled so that the target DC current value stored in the target DC current value information storage unit is obtained by switching the operation speed of the image carrier to the selected low speed. An image forming apparatus to perform. The voltage control unit performs a peak-to-peak operation with respect to an assumed characteristic curve on a two-dimensional coordinate representing a relationship between the peak-to-peak voltage value Vpp and a direct current value Idc between the charging member and the image carrier. When the two low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) that are assumed to be lower than the voltage value at the inflection point appearing when the voltage value Vpp is boosted are applied by the current detection unit. Passes the coordinates A {Vpp (A), Idc (A)}, B {Vpp (B), Idc (B)} obtained based on the two detected DC current values Idc (A) and Idc (B). Based on the straight line L1 and the DC current value Idc (C) detected by the current detector when the high-voltage peak-to-peak voltage value Vpp (C) assumed to be higher than the voltage value at the inflection point is applied. Coordinates C {Vpp (V), Idc (C }, The peak-to-peak voltage value Vpp corresponding to the intersection with the straight line L2 parallel to the coordinate axis representing the peak-to-peak voltage value Vpp is selected as the appropriate peak-to-peak voltage value Vpp (O). Forming equipment. Table data in which the low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and the high-voltage-side peak-to-peak voltage value Vpp (C) are set in advance based on a variation factor of the charging characteristics of the charging member is provided. 3. The image formation according to claim 2, wherein the voltage control unit selects the low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and the high-voltage-side peak-to-peak voltage value Vpp (C) according to the table data. apparatus. 4. The image forming apparatus according to claim 1, wherein the normal image forming speed is a maximum operating speed set for the image carrier. 5. 5. The image forming apparatus according to claim 1, wherein the charging member is a charging roller formed by coating an outer peripheral portion of a cored bar with a conductive elastic material layer. 6. The image forming apparatus according to claim 1, wherein the image carrier is a photosensitive drum formed by depositing an amorphous silicon layer on a surface of an aluminum cylinder.

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