JPH0915946A - Electrostatic charge device - Google Patents

Abstract

PURPOSE: To detect the soil of an electric discharge wire without using a special metallic wire for monitoring an electric discharge state. CONSTITUTION: This electrostatic charge device 31 for electrostatically charging a photoreceptor drum 32 is provided with the electric discharge wire 33 connected to a high-voltage power source 311, a first and a second metallic shields 35 and 36 being as the electric discharge shields divided into two at the central position and mutually insulated and resistors 38 and 39 changing currents flowing to the shields 35 and 36 to voltages and outputting them. When difference between the voltages becomes large to a certain extent, it is recognized that either side of the wire 33 is soiled 69.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for applying a high voltage to a discharge wire to cause discharge, as in the case of forming an image in an electronic copying machine, a printer or a facsimile machine of a certain type, In particular, the present invention relates to a charging device capable of detecting dirt on a discharge wire.

[0002]

2. Description of the Related Art In a predetermined image forming apparatus such as an electronic copying machine, an electric discharge wire (electrical wire for electric discharge) is used to apply an electric charge to a photoconductor or a predetermined paper. For example, in an electronic copier,
A corotron called a charge corotron uniformly charges the photoconductor such as the photoconductor drum and the photoconductor belt,
Next, an electrostatic latent image is formed by irradiating the photoconductor with an optical image corresponding to the image to eliminate the electric charge in the portion exposed to the light. This electrostatic latent image is developed with toner in a developing device, and a toner image corresponding to the image is created. This toner image on the photoconductor is transferred onto a sheet by a corotron called a transfer corotron and is fixed by heating or pressing.

In such an image forming apparatus, the amount of toner adsorbed on the photoconductor changes depending on the amount of electric charge discharged from the corotron, or the amount of toner transferred on the photoconductor onto a sheet changes. . Therefore, in order for the light and shade of the image to be reproduced correctly, it is necessary that the discharge of each part of the discharge wire is uniform. Therefore, there has been proposed a charging device capable of detecting when discharge becomes nonuniform and performing early cleaning.

FIG. 14 shows an outline of the charging device proposed in Japanese Patent Publication No. 6-1399. This charging device has a structure in which two metal wires 12 and 13 are stretched in parallel so as to be adjacent to a discharge wire 11 for discharging. One metal wire 12 is covered with an insulating member 14 on the right side in the figure from the center, and the other metal wire 13 is covered with an insulating member 15 on the left side in the figure from the center. The discharge wire 11 and the two metal wires 12 and 13 have a U-shaped metal shield 1 in cross section.
It is housed inside 6. A high voltage is applied to the discharge wire 11 from a DC high voltage power supply 17. As a result, a discharge current flows from the discharge wire 11 to the surface of the photoconductor (not shown) arranged on the front side in the figure, facing the metal shield 16 and the opening.

Each of the two metal wires 12 and 13 has a resistor 1
It is grounded via 8 and 19. Therefore, a current also flows through the metal wires 12 and 13 as the discharge wire 11 discharges. Along with this, a voltage is generated in the resistors 18 and 19. The amplifier 21 amplifies the difference between these voltages, and the comparator 22 compares the amplified output with the reference voltage 23. Then, when it is detected that the reference voltage is exceeded, the warning display circuit 24 displays a warning. That is, in this charging device, when any part of the discharge wire 11 is contaminated and the current flowing through the two metal wires 12 and 13 becomes non-uniform, the amplifier 21 amplifies this difference, and as a result, the comparator 22 is used as a reference. A voltage exceeding the voltage will be input and an alarm will be issued.

[0006]

In the charging device shown in FIG. 14, the discharge wires 11 and 2 are provided in the metal shield 16.
The metal wires 12 and 13 are arranged.
In such a structure, the discharge wire 11 and the two metal wires 1
If the distances 2 and 13 are close to each other, abnormal discharge or partial leakage of discharge occurs between them, so it is necessary to set the distance between them to a certain extent. As a result, there is a problem that the size of the entire charging device including the metal shield 16 increases.

Further, in this charging device, two metal wires 1
Discharge wire 11 by monitoring the discharge current to 2 and 13
The occurrence of dirt is detected. However, discharge wire 1
2 metal wires 1 even if there is no stain on 1
If any of the stains 2 and 13 is contaminated, the amount of discharge to them becomes unbalanced. That is, when the alarm is issued, it is not possible to determine whether the cause is the discharge wire 11 itself or one of the two metal wires 12 and 13 is contaminated. There was a problem that output reliability was low.

Further, in this charging device, both metal wires 12, 1
Since it is difficult to obtain a large difference in the detection voltage of 3,
The amplifier 21 is used to amplify the difference.
For this reason, the detection error is increased, and an erroneous alarm may be issued when electrical noise occurs, and similarly the reliability of the device cannot be increased.

Further, in the conventional charging device, when one of the two halves of the discharge wire is locally contaminated, it can be detected by the imbalance of the discharge current. When it became dirty, it could not be detected correctly, and it was not possible to instruct to clean or replace the discharge wire.

Therefore, an object of the present invention is to provide a charging device capable of detecting the occurrence of dirt on the discharge wire without using a special metal wire for monitoring the discharge state.

Another object of the present invention is to provide a charging device capable of finely indicating the location where the discharge wire is dirty.

Still another object of the present invention is to provide a charging device capable of detecting that the contamination of a discharge wire is out of an allowable range at a predetermined time when the contamination of the discharge wire progresses with time. To do.

[0013]

According to a first aspect of the present invention, (a) a discharge wire having a predetermined length, and (b) the wire is surrounded so as to shield discharge from the discharge wire. Discharge shields, which are arranged along the length of the wire in a uniform shape, are divided into a plurality of pieces of equal length in the length direction, and are electrically insulated from each other,
Current detecting means for detecting a current flowing between the respective discharge shields and the ground; and (d) comparing means for comparing the difference between the currents flowing through the discharge shields detected by the current detecting means with a predetermined reference value, (E) The charging device is provided with a dirt detecting means for detecting a partial dirt on the discharge wire when the difference between the currents is larger than the reference value.

That is, according to the first aspect of the invention, the discharge shield arranged so as to surround the periphery of the discharge wire is divided into two or three or more parts in the length direction of the discharge wire from the viewpoint of discharge characteristics. It is divided so that, ideally, the same discharge current flows in each of these discharge shields. Then, the difference between the currents flowing in these discharge shields is compared with a predetermined reference value, and when this value, which should ideally be zero, becomes a value larger than this reference value, it corresponds to one of the discharge shields. Localization of dirt in the area of the discharge wire is detected.

According to the second aspect of the invention, (a) the discharge wire having a predetermined length, and (b) the length of the wire so as to surround the circumference of the wire in order to shield discharge by the discharge wire. A plurality of discharge shields that are arranged along the vertical direction and are electrically isolated from each other by being divided at a plurality of positions in this length direction, and (c) detecting the current flowing between each of these discharge shields and ground. And (d) compare the ratio of the length of each of these discharge shields and the flowing current for each discharge shield, and in the area of the discharge wire corresponding to the discharge shield whose value is relatively different among these values. The charging device is provided with a dirt detection unit that detects the presence of dirt.

That is, according to the second aspect of the invention, a plurality of discharge shields are arranged so as to surround the circumference of the discharge wire so as to have an arbitrary length in the lengthwise direction of the discharge wire and to keep them insulated from each other. Split it. Since the longer the length, the larger the discharge current received from the discharge wire, the length of each discharge shield and the ratio of the flowing current should be compared for each discharge shield. The presence of dirt in the area of the discharge wire corresponding to the discharge shield is detected.

According to the third aspect of the invention, (a) the discharge wire having a predetermined length, and (b) the length of the wire so as to surround the periphery of the wire in order to shield discharge by the discharge wire. A plurality of discharge shields which are arranged along the vertical direction and are electrically isolated from each other at positions corresponding to the ends of a plurality of pre-selected size sheets for image recording in the length direction. , (C) Current detection means for detecting the current flowing between each of these discharge shields and ground, and (D) The ratio of the length of each of these discharge shields to the flowing current is compared for each discharge shield. Stain detection means for detecting the presence of stains in the area of the discharge wire corresponding to the discharge shield having a relatively different value in (4), and (e) the size of the paper used for recording the current image. And a recording propriety determining means for determining whether or not recording on the sheet can be completely performed in the area of the discharge wire corresponding to the discharge shield other than the discharge shield in which the dirt is detected by the dirt detecting means. ) The charging device is provided with cleaning instruction means for instructing the cleaning of the discharge wire when the recordability determination means determines NO.

That is, according to the third aspect of the invention, the discharge shields arranged so as to surround the circumference of the discharge wire respectively correspond to the end portions of a plurality of sizes of paper preselected in the length direction of the discharge wire. Arrange them so that they are separated by position, and keep them insulated from each other. Then, by comparing the ratio of the length of each discharge shield and the flowing current for each discharge shield, there is dirt in the region of the discharge wire corresponding to the discharge shield having a relatively different value among these values. To be able to detect things. On the other hand, the discharge area used by the charging device to form an image is obtained from the size information of the paper, and recording on this paper is performed in the area of the discharge wire other than the area of the discharge wire where the dirt is detected by the dirt detecting unit. It is determined whether or not the discharge can be completely performed, and only when it is impossible, the cleaning of the discharge wire is instructed. As a result, the minimum necessary cleaning can be performed so as not to interfere with the image forming process.

According to a fourth aspect of the invention, (a) high voltage applying means for applying a predetermined high voltage to the discharge wire, and (b)
Discharge state information storage means for storing, as discharge state information, a current flowing in the discharge shield when a high voltage is applied to the discharge wire or a voltage generated in a resistance component connected to the discharge shield by the current as discharge state information. ,
(C) The charging device is provided with a dirt detection means for comparing the discharge status information stored in the discharge status information storage means with the current discharge status and detecting dirt on the discharge wire when the discharge status information exceeds a predetermined range.

That is, in the invention described in claim 4, the discharge wire is used by storing the current flowing in the discharge shield in a new state or the voltage generated in the resistance connected to the discharge shield by this current. When the difference exceeds a predetermined range, the contamination of the discharge wire is detected.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

First Embodiment

FIG. 1 shows the relationship between the charging device and the photosensitive drum in the first embodiment of the present invention. The charging device 31 of this embodiment is arranged parallel to the rotation axis of the photoconductor drum 32 and at a predetermined distance from the drum surface.
A discharge wire 33, a high-voltage power supply 34 connected to one end of the discharge wire 33, and first and second metal shields 36 having a U-shaped cross section arranged so as to surround the discharge wire 33. There is. First and second metal shield 3
Reference numerals 5 and 36 are arranged so that their respective openings are opposed to the surface of the photosensitive drum 32, and a gap 37 is set between them so that they are electrically insulated. . One end of the first resistor 38 is connected to one end of the first metal shield 35, and the other end is grounded. One end of the second resistor 39 is connected to one end of the second metal shield 36, and the other end is similarly grounded. From the ends of the first resistor 38 and the second resistor 39 which are not on the ground side, respectively, the first and second detection voltage signals 41, 4 are outputted.
2 is output.

FIG. 2 shows a holding mechanism for the first and second metal shields. First and second metal shields 35, 36 are adhered to the inner surface of a resin-made shield holding member 44 having a U-shaped cross section with a gap 37 therebetween. The gap 37 may be about 1 to 2 mm.

FIG. 3 shows a processing circuit for the first and second detection voltage signals described in FIG. The first detection voltage signal 41 is input to the-side input terminal of the differential amplifier 52 via the first adjustment resistor 51, and the second detection voltage signal 42 is differentially input via the second adjustment resistor 53. Amplifier 52
It is designed to be input to the + input terminal of. The + side input terminal is grounded via the resistor 54. Also,
A series circuit of a fixed resistor 55 and a balance adjusting resistor 56 is connected between the negative input terminal and the output terminal.

Differential amplification output 58 output from the output terminal
Is input to the + side input terminal or the − side input terminal of the first and second comparators 61 and 62. A series circuit composed of three resistors 63 to 65 is arranged between the DC constant voltage sources + V _CC and −V _CC of this circuit to form a voltage dividing circuit. Of these, the first reference potential 6 output from the connection point of the two resistors 63 and 64
7 is input to the-input terminal of the first comparator 61,
The differential amplified output 58 is compared. Also, two resistors 6
The second reference potential 68 output from the connection point of Nos. 4 and 65 is input to the + input terminal of the second comparator 62 and similarly compared with the differential amplification output 58.

When dirt 69 due to toner or the like occurs at a relative level in any one of the regions with the center of the discharge wire 33 shown in FIG. 1 as a boundary, the differential amplification output 58 responds to the + side or Tilt to the − side. Therefore, when the degree exceeds a certain value, the first or second comparator 6
1, 62 change its output to a logic level representing dirt detection. First and second comparators 61, 62
The output side of is electrically connected, and a status signal 71 indicating normality or abnormality of the charging device is output from this.

That is, in this charging device, when the degree of contamination of the discharge wire 33 is nearly uniform on the left and right, the differential amplification output 58 exists between the potentials compared by the two comparators 61 and 62, and therefore the status signal 71. Is a logic indicating normality. Further, when the dirt 69 as shown in FIG. 1 is generated on a part of the discharge wire 33 and the discharge characteristics are greatly different between the right half part and the left half part in the figure, the two comparators 61 and 62 have different discharge characteristics. One of them detects an abnormality, and the status signal 71 changes to a logic indicating the abnormality. Of course, the first and second comparators 61, 6
It is also possible to use each of the two outputs individually as a status signal, which makes it possible to tell which side is dirty.

Second embodiment

FIG. 4 shows the relationship between the charging device and the photosensitive drum in the second embodiment of the present invention. 4, the same parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

In the second embodiment, first to fourth metal shields 81 to 84 having a U-shaped cross section are provided so as to surround the discharge wire 33. These are shown in Figure 2.
As described above, the one shield holding member 44 is arranged in a state in which it is insulated from the inner surface of the one shield holding member 44 with a predetermined gap. The openings of the first to fourth metal shields 81 to 84 are arranged so as to face the surface of the photosensitive drum 32. One end of the first resistor 85 is connected to one end of the first metal shield 81, and the other end is grounded. One end of the second resistor 86 is connected to one end of the second metal shield 82, and the other end is similarly grounded. The same applies to the one ends of the third metal shield 83 and the fourth metal shield 84, and the third and fourth resistors 8 and 8 respectively.
One ends of 7, 88 are connected, and the other ends thereof are grounded. These first to fourth resistors 85 to 88 each have a predetermined resistance value r, and the first to fourth detection voltage signals 9 are respectively provided from the ends not on the ground side.
1 to 94 are output.

FIG. 5 shows the relationship between the widths of the first to fourth metal shields and the paper. In a predetermined image forming apparatus such as an electronic copying machine using the charging device of the present embodiment, one side portion of each of the B5 size, A4 size, B4 size and A3 size papers 96 to 99 of the Japanese Industrial Standard is used as a photoconductor. Drum 32
The sheet is conveyed so as to be aligned with one end of (FIG. 4), and an image is recorded or copied on the sheet. The end portion of the fourth metal shield 84 is arranged on the one end side, and the length of the fourth metal shield 84 is the length in the direction orthogonal to the conveying direction of the B5 size paper 96 (paper width). )
Is set to almost match. The total length of the third metal shield 83 and the fourth metal shield 84 is set so as to be substantially the same as the length of the A4 size sheet 97 in the direction orthogonal to the transport direction. Furthermore, the second
The total length of the fourth metal shields 82 to 84 is B4.
It is set so as to substantially match the length of the plain paper 98 in the direction orthogonal to the transport direction. The total length of the first to fourth metal shields 81 to 84 is the A3 size sheet 9
It is set so as to substantially match the length of 9 in the direction orthogonal to the transport direction.

FIG. 6 shows an outline of the first to fourth detection voltage signal processing circuits shown in FIG. The detection voltage signals 91 to 94 representing the detection voltages are input to the data selector 101. Data selector 101
Are configured to alternately select these four detection voltage signals 91 to 94, and this is performed by the selection instruction signal 103 supplied from the control unit 102. The detection voltage signal 104 output from the data selector 101 is input to the A / D converter 105, and analog-digital conversion is performed. The converted detection voltage signal 106 is supplied to the control unit 102.
The control is performed so that the presence or absence of dirt on the discharge wire and the location of the dirt wire are identified.

FIG. 7 shows a circuit configuration of this control unit. The control unit 102 is a CPU (central processing unit)
It is equipped with 111. The CPU 111 is connected to the ROM 113, the RAM 114, the input circuit 115, and the output circuit 116 via a bus 112 such as a data bus. Of these, the ROM 113 is a read-only program that stores a program for performing control relating to detection of dirt on the charging device.
Memory. The RAM 114 is a random access memory that stores data used temporarily when performing this control.
Memory. The input circuit 115 uses the detection voltage signal 106
And the main body side of the image forming apparatus (not shown)
A predetermined control signal 121 such as a paper selection signal indicating the type of paper to be used is input. The output circuit 116 outputs the selection instruction signal 103 for performing the switching control of the data selector 101 shown in FIG. 6, and also determines whether or not the discharge wire is contaminated with respect to the CPU (not shown) on the main body side of the image forming apparatus. When it is generated, the status signal 122 indicating the location is transmitted.

The control unit 102 shown in FIG.
As a matter of course, it can be shared with a control unit including a CPU or the like prepared on the main body side of the image forming apparatus. In this case, the ROM 113 stores various control programs other than monitoring of dirt on the discharge wire 33.

FIG. 8 shows a state of control of generation of a selection instruction signal performed for switching control of the data selector. When high voltage is applied to the discharge wire 33 from the high voltage power source 34 (step S101; Y), C
The PU 111 initializes the numerical value m stored in a predetermined area of the RAM 114 to "1" (step S102). Then, in this state, the m-th selection signal 103 _m is generated.
In this case, since the numerical value m is "1", the first selection signal 103 ₁ is generated (step S103).
The data selector 101 selects the first detection voltage signal 91 based on this. This state is maintained until a relatively short time t elapses without ending the discharge (step S10).
4, S105; N) is performed.

When the time t has passed (step S104;
Y), the numerical value m is incremented by "1" (step S106), and if the value does not exceed "4" at this point (step S107; N), the m-th value corresponding to the updated numerical value m. The selection signal 103 _m is generated (step S103). In this case, ₂ second selection signal 103 is generated, the data selector 101 and the second detection voltage signal 9
2 will be selected. Similarly, the contents of the selection signal 103 are switched every time the time t elapses.
When the numerical value m is counted up and becomes a value exceeding "4" (step S107; Y),
Since it is initialized to "1" (step S102), the switching in the data selector 101 is cyclically performed during the discharging. When the discharge control of the discharge wire 33 ends (step S105; Y), the control of the generation of the selection instruction signal 103 also ends (END).

By the way, FIG. 9 shows the charging characteristics of the photosensitive member by the charging device. The discharge current i flowing from the charging device 131 attached with the discharge wire 33 to the photoconductor 132 shows a substantially constant value except for both ends of the discharge wire 33 when the length direction of the discharge wire 33 is taken as the x-axis. . Therefore, if the regions where the current value is insufficient at both ends are cut and the remaining region is set as the image forming region, that is, the region corresponding to the maximum sheet (A3 size) shown in FIG. Unless it's dirty
The discharge current ideally shows a constant value at any place.

Therefore, if the lengths of the metal shields 81 to 84 shown in FIG. 5 are L _{1 to} L _4, and the voltages of the first to fourth detection voltage signals 91 to 94 are V _{1 to} V ₄ , respectively. Ideally, the following expression (1) is established.

[0040]

(Equation 1)

The relationship of the equation (1) is that the metal shield 81
It is established even if a small amount of stain is generated on ~ 84.
The metal shields 81 to 84 have an extremely large relative area as compared with the discharge wire 33. Therefore, the contamination of the discharge wire 33 immediately has a great effect on the discharge current,
This is because even if the metal shields 81 to 84 are partially contaminated with paper powder or toner powder, the possibility that the metal shields 81 to 84 are visibly affected is reduced. When this equation (1) is disassembled with reference to the portion of the fourth metal shield 84 having the longest shield length, the following equation (2) is obtained.

[0042]

(Equation 2)

Therefore, the voltage V ₄ and the respective voltages V ₃ , V ₂ and V _{1 according} to the equation (2) are constantly monitored by the detection voltage signal 106 output from the A / D converter 105 while being selected by the data selector 101. Then, it is possible to detect the occurrence of partial contamination of the discharge wire 33. That is, since the lengths of the first to fourth metal shields 81 to 84 can be known in advance, the voltage V ₃ obtained by the equation (2),
The three parties of V _2, V _1, although two will be obtained of the values obtained by the measured value and the voltage V ₄ to the group. Therefore,
The control unit 102 can sequentially compare these values to determine where the discharge wire 33 is contaminated.

That is, the voltage V_Three, V_Two, V₁The three parties
When the calculated value is smaller than the measured value
Is attached to the fourth metal shield 84 of the discharge wire 33.
It can be determined that the corresponding area is dirty.
it can. Also, the voltage V_Three, V _Two, V₁Any of the three
When the measured value becomes smaller than the calculated value,
The shields 81-83 are
It is determined that the area of the corresponding discharge wire 33 has become dirty.
Can be Therefore, the status showing these
The signal 122 will be output.

FIG. 10 shows the status signal creating process of the charging device. This process is repeated at predetermined time intervals, and the status signal 122 is created each time. First, the detection voltage signal 106 is fetched for the first to fourth detection voltage signals 91 to 94 (step S
201), and based on this, three types of voltages V ₃ , V ₂ , V
₁ is calculated (step S202). Then, the measured value and the calculated value are compared with each other, and when the first to fourth metal shields 81 to 84 are contaminated, the status signal 122 that specifies the position is output. (Step S203).

FIG. 11 shows an example of control of the image forming apparatus which receives this status signal. If the status signal 122 sent from the charging device indicates that the discharge wire 133 is dirty (step S301; Y), the relationship between the currently selected paper size and the dirt position is checked, and this paper is It is determined whether or not the recording or copying of the image with respect to is affected (step S302). For example, when it is determined that the fourth metal shield 84 is soiled, all the papers are affected by the image, but it is considered that the first metal shield 81 is soiled. In the case of B4 size or smaller paper size, the image does not affect the paper.

If it is determined that the image will be affected in relation to the currently selected paper (step S3
02; Y), the image formation is temporarily interrupted, and the corresponding discharge wire 33 is automatically cleaned (step S30).
3). A known technique can be used for the automatic cleaning of the discharge wire 33, and a description thereof will be omitted here. For example, if it is determined that the image is not adversely affected on the sheet at this time, such as when the currently selected sheet is A4 size and the first metal shield 81 is soiled (step S302; N), the discharge wire 33 is not cleaned until the end of the current job, and this is executed at the end (step S304). In the case where the next copying operation or the like is programmed in advance, the cleaning of the discharge wire 33 may be delayed until A3 size paper is selected in this example. Step S30
When it is determined in 1 that the discharge wire 33 is not contaminated (N), the processing ends without performing the cleaning operation (END).

The second embodiment has been described on the premise that the dirt on the discharge wire 33 is automatically cleaned.
For example, a warning lamp may be turned on by the status signal 122, or a character or the like indicating a dirty portion may be displayed on the display to give an alarm to the operator to clean the discharge wire 33. Based on this, the operator will call a serviceman to clean the discharge wire by a manual cleaning mechanism or to receive service maintenance.

Further, in the second embodiment, the relation between the discharge wire 33 and the size of the paper is discriminated, and the copying work and the printing operation are made different depending on whether the dirt affects the image quality or not. , Based on the status signal 122, the size of the paper that cannot be copied or printed is positively displayed on the display or the like, when the size of the paper is selected, the selection is prohibited or the paper size is instructed to be reduced. It may be like this.

Modification of the second embodiment

The voltages V _{1 to} V _{4 of the first} to fourth detection voltage signals 91 to 94 and the metal shields 81 to 84 shown in FIG.
The ratio of the lengths L _{1 to} L ₄ of can be expressed by the following equation (3).

[0052]

(Equation 3)

As shown by the equation (1), these values k ₁ ,
Ideally, k ₂ , k ₃ and k ₄ are equal to each other. However, when the discharge wire 33 is uniformly soiled with time, these values k ₁ , k ₂ , k ₃ , and k ₄ gradually decrease.

FIG. 12 shows that these values k ₁ , k ₂ , k ₃ ,
This shows an example in which k ₄ changes with an increase in the number of recording sheets on the sheet. Discharge wire 33 over time
The values k ₁ , k ₂ , k ₃ , and k ₄ gradually decrease as the toner becomes dirty, but when the dirt locally rapidly progresses due to toner particles or the like, the value k sharply decreases at that point. . In this figure, it can be seen that the value k ₃ drastically decreases when about 5000 sheets of paper are used, and the position of the discharge wire 33 corresponding to the third metal shield 83 is extremely contaminated.

FIG. 13 shows how the CPU is controlled in the modification of the second embodiment. As a premise of this control, the CPU 111 (FIG. 7) indicates that the discharge wire 33 of the charging device has values k ₁ , k ₂ , k when the discharge wire 33 is new (initial state).
₃ , k ₄ is measured, and the values are stored in the RAM 114 in the nonvolatile memory area backed up by the battery. Then, at a predetermined timing such as when recording on the sheet is started, the current values k ₁ , k ₂ , k ₃ , k
₄ are measured, and the sum of these is calculated as the initial values k ₁ , k ₂ ,
It is compared with the total value of k ₃ and k ₄ (step S401).
As a result, if the ratio (k) of the voltage V and the length L is reduced by a predetermined amount by a% from the initial value (step S402; Y), the discharge wire 33 is wholly soiled and the discharge capability is deteriorated. Is displayed as an instruction (step S
403). The same result can be obtained by comparing the average values.

In FIG. 12, even if the portion of the discharge wire 33 corresponding to the third metal shield 83 is not locally contaminated, if the discharge wire 33 becomes totally contaminated, the discharge wire at that point is discharged. 33 will be instructed to be cleaned.

When it is determined that the work of the status 402 has not decreased by a% (N), the current values k ₁ , k ₂ , k
The variations in ₃ , k ₄ are checked. That is, the value _{k 1, k 2, k 3} , k 4 average value A of the current is calculated (step S404), the absolute value of the difference between the average value A and the current value k _{m (m} = 1~4) the value obtained by dividing the average value a to check whether there is a value k _m which is larger than the predetermined value b (step S405). If there is such a value k _m (step S406; N),
Proceeding to status 403, cleaning of the discharge wire 33 is instructed. The occurrence of contamination at the position of the discharge wire 33 corresponding to the third metal shield 83 in FIG. 12 corresponds to this.

[0058] On the other hand, the value k _m that was unevenly distributed in this way
Is not present (step S406; N), the charging device has sufficiently normal charging characteristics, and therefore no instruction to clean the discharge wire 33 is given (END).

In the first and second embodiments described above, a DC voltage is applied to the discharge wire 33, but an AC voltage is applied, or a combination of AC and DC is applied. The present invention can be similarly applied to the device. Further, in the embodiment, the charging device that charges or discharges the photosensitive drum has been described, but a charging device that charges or discharges the photosensitive member such as a photosensitive belt may be used. Needless to say, it may be a charging device used for charging an object or removing electricity.

[0060]

As described above, according to the first aspect of the present invention, the discharge shield is divided into two or three or more parts in the length direction of the discharge wire from the viewpoint of discharge characteristics, and these are divided. The difference between the currents flowing through the discharge shields is compared, and when the difference exceeds a predetermined reference value, it is detected that the dirt is localized in the area of the discharge wire. Therefore, it is possible to detect the dirt on the discharge wire with a simple configuration in which the discharge shield is divided and the discharge currents are compared with each other. Moreover, since the discharge shield has a stronger influence on dirt than the discharge wire, dirt on the discharge wire can be reliably detected.

Further, according to the second aspect of the invention, the discharge shield is divided into a plurality of pieces in the length direction of the discharge wire so as to keep an insulated state from each other with an arbitrary length. Can be diversified. In addition, since the ratio of the length of each discharge shield after splitting to the flowing current is compared for each discharge shield, it is possible to arbitrarily divide the discharge wires and detect the localization of dirt on these. Moreover, in the present invention, the dirt is detected based on the discharge current flowing through the discharge shield as in the first aspect of the invention, so that the dirt on the discharge wire can be reliably detected.

Further, according to the third aspect of the invention, the discharge shields are arranged in the lengthwise direction of the discharge wire so as to be divided at positions corresponding respectively to the end portions of the paper of a plurality of sizes selected in advance. Are kept insulated from each other. Therefore, the position of dirt on the discharge wire can be determined in accordance with the transport state of each sheet. Therefore, the discharge area used by the charging device to form an image is obtained from the size information of the paper, and the recording on the paper is completely performed in the area of the discharge wire other than the area of the discharge wire where the dirt is detected by the dirt detecting means. By determining whether or not the cleaning can be performed, the cleaning instruction can be given only when the area of the discharge wire that is directly related to the image formation of the paper is dirty, which hinders the current image formation processing. The minimum necessary cleaning can be done to prevent it. Moreover, in the present invention, the dirt is detected based on the discharge current flowing through the discharge shield as in the first aspect of the invention, so that the dirt on the discharge wire can be reliably detected.

According to the invention of claim 4, the current flowing in the discharge shield in a new state of the discharge wire or the voltage generated in the resistance connected to the discharge shield by this current is stored, and the discharge wire is stored. Since the dirt on the discharge wire is detected by comparing it with the value at the specified time when it is used, even if the dirt on the discharge wire is not localized and occurs uniformly, it is the discharge characteristic. If it has progressed to such an extent that it deteriorates, dirt can be detected and cleaning can be instructed. Also, when the discharge shield is divided, by comparing the initial value and the current value for these, even if the area of the discharge wire corresponding to some of the discharge shield is dirty, By detecting this, it is possible to instruct cleaning of the discharge wire. Of course, in the present invention as well, as in the first aspect of the invention, the dirt is detected based on the discharge current flowing through the discharge shield, so that the dirt on the discharge wire can be reliably detected.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a relationship between a charging device and a photosensitive drum in a first embodiment of the present invention.

FIG. 2 is a perspective view showing a holding mechanism for the first and second metal shields in the first embodiment.

FIG. 3 is a circuit diagram showing a processing circuit for the first and second detection voltage signals described in FIG.

FIG. 4 is a schematic configuration diagram showing a relationship between a charging device and a photosensitive drum in a second embodiment of the present invention.

FIG. 5 is an explanatory diagram showing the relationship between the width of a sheet and the first to fourth metal shields in the second embodiment.

6 is a block diagram showing an outline of a first to fourth detection voltage signal processing circuit shown in FIG. 4. FIG.

7 is a block diagram showing a circuit configuration of a control unit shown in FIG.

FIG. 8 is a flowchart showing a control state of selection instruction signal generation in the second embodiment.

FIG. 9 is a characteristic diagram showing charging characteristics of a photoconductor in a length direction of a discharge wire by a charging device according to a second exemplary embodiment.

FIG. 10 is a flowchart of a status signal creation process of the charging device according to the second exemplary embodiment.

FIG. 11 is a flowchart showing an example of control of the image forming apparatus that has received a status signal in the second embodiment.

FIG. 12 shows values k ₁ , k ₂ , k in the modification of the second embodiment.
FIG. 3 is a characteristic diagram showing an example of the relationship between ₃ , k ₄ and the number of recorded sheets.

FIG. 13 is a flowchart showing how the CPU is controlled in the modification of the second embodiment.

FIG. 14 is a schematic configuration diagram showing an outline of a conventionally proposed charging device.

[Explanation of symbols]

31 ... Charging device, 32 ... Photosensitive drum, 33 ... Discharge wire, 34 ... High voltage power supply, 35, 81 ... First metal shield, 36, 82 ... Second metal shield, 37 ... Gap, 3
8, 39, 85-88 ... Resistance, 41 ... First detection voltage signal, 42 ... Second detection voltage signal, 52 ... Differential amplifier, 6
1 ... 1st comparator, 62 ... 2nd comparator,
83 ... Third metal shield, 84 ... Fourth metal shield, 101 ... Data selector, 102 ... Control section, 105
... A / D converter, 111 ... CPU, 113 ... ROM, 1
14 ... RAM, 116 ... Output circuit

Claims (4)

[Claims] 1. A discharge wire having a predetermined length, and arranged along the length of the wire so as to surround the periphery of the wire so as to shield discharge by the discharge wire, and the length of the wire. A plurality of discharge shields that are divided into a plurality of parts each having the same length in the same direction and are electrically insulated from each other, a current detection unit that detects a current flowing between each discharge shield and the ground, and a current detection unit that detects the current. It comprises: comparing means for comparing the difference in current flowing through each discharge shield with a predetermined reference value; and dirt detecting means for detecting partial dirt on the discharge wire when the difference in current is larger than this reference value. A charging device characterized by the above. 2. A discharge wire having a predetermined length, and arranged along the length of the wire so as to surround the periphery of the wire so as to shield discharge by the discharge wire, and this length. Direction, a plurality of discharge shields that are divided at a plurality of positions in the direction and electrically insulated from each other, a current detection unit that detects a current flowing between each of the discharge shields and the ground, and a length and a flow of each of the discharge shields. A dirt detection unit is provided which compares the ratio of currents for each discharge shield and detects the presence of dirt in the region of the discharge wire corresponding to the discharge shields having relatively different values among these values. Characteristic charging device. 3. A discharge wire having a predetermined length, the discharge wire being arranged along the length of the wire so as to surround the periphery of the wire so as to shield the discharge from the discharge wire, and this length. Discharge shields electrically isolated from each other at positions corresponding to the edges of a plurality of preselected paper sizes for image recording in the direction, and the current flowing between each discharge shield and ground. And the ratio of the length of each of these discharge shields and the flowing current for each discharge shield are compared, and in the area of the discharge wire corresponding to the discharge shield whose value is relatively different among these values. Dirt detection means for detecting the presence of dirt and size information of the paper used for recording the image at the present time are obtained, and dirt is detected by the dirt detection means. Recording possibility determination means for determining whether or not recording on this paper can be completely performed in the area of the discharge wire corresponding to the discharge shield other than the discharge shield, and an instruction for cleaning the discharge wire when the recording possibility determination means determines no A charging device comprising: 4. A high voltage applying means for applying a predetermined high voltage to the discharge wire, and a current flowing through the discharge shield when the high voltage is applied to the discharge wire or a resistance component connected to the discharge shield by this current. The discharge state information storing means for storing the voltage generated at the discharge state information at a predetermined time and the discharge state information stored in the discharge state information storing means are compared with the current discharge state, and when this exceeds a predetermined range. A charging device, comprising: a dirt detection unit that detects dirt on the discharge wire.