JPH09230672A - Electrostatic charging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make identical the discharging characteristics at the left end and right extremities of a plurality of projections provided in a charging device. SOLUTION: An electrostatically charging device 2 makes corona discharge by impressing a voltage on a discharge electrode 22, which is composed of an electrode plate and a number of projections provided at the ends of the electrode plate. The section of each projection across the plate thickness has a tip symmetrical to the left and right, and the discharging characteristics at the left and right extremities are made identical substantially. It may also be accepted that the contour of the section of a retaining member 24 for projections is symmetrical to the left and right.

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 charging, transferring, or removing charge from a recording medium for forming an image in electrostatic electrophotography, and more specifically to an image of a copying machine, a printer or the like. The present invention relates to a charging device for uniformly charging the surface of a recording medium in a forming apparatus by corona discharge, and relates to a charging device having a discharge electrode having a plurality of protrusions with respect to the rotation axis direction of the recording medium.

[0002]

2. Description of the Related Art As is well known, an image forming apparatus using an electrostatic electrophotographic system comprises process units for charging, exposing, developing, transferring, peeling, cleaning, and removing charge.

That is, in the process of recording an image, first, the surface of an image carrier, which is a recording medium having a photoconductive layer that is rotationally driven, formed on a conductive support such as an aluminum drum, is uniformly charged by a charging device. . Then, the surface of the charged image carrier is exposed with an optical image of the original image through an exposure optical device to record an electrostatic latent image corresponding to the optical image. Then, toner is electrostatically attached to the electrostatic latent image on the image carrier to develop it, and a toner image is formed on the image carrier. Then, the toner image on the image carrier is transferred onto the transfer material by the transfer device, and the toner image on the transfer material is fixed by the heat fixing device. Further, the residual transfer toner remaining on the surface of the image carrier is removed by a cleaning device and collected in a predetermined collecting unit, and the surface of the image carrier after cleaning is subjected to residual charge removal by a charge eliminating device to form the next image. Can be provided.

A recording medium which is an image carrier is, for example, an OPC.
(Organic Photo Conductor)
A corona discharge device is generally often used as a charging device for charging the surface of the recording medium with a photoconductive layer as a photoconductive layer on a conductive drum.

As a corona discharge device, a very thin conductive wire is covered with a conductive shield plate except for a portion facing the recording medium, and a high voltage is applied to the wire itself to generate a corona discharge. There is a device in which a charged electric charge is given by a current generated in the recording medium. In addition to this, as a charging device utilizing corona discharge, instead of a wire for corona discharge, a sawtooth discharge electrode having a large number of sharp protrusions in a row is provided to charge by corona discharge from the sharp protrusions. There is something to do.

A charging device using the sawtooth discharge electrode (hereinafter referred to as a sawtooth electrode) is disclosed in, for example, British Patent No. 1,388,084 (Japanese Patent Laid-Open No. 4684/1988).
-8241 / Corresponding Japan) Proposed in Japanese Patent Laid-Open No. 6-11947.

[0007] The one described is specified for a saw-toothed electrode, and in particular, a projection having a plate thickness of 0.1 mm and a pitch of 6 mm is formed from a projection having a plate thickness of 0.1 mm and a pitch of 1 mm, and the projections are formed in a staggered pattern. It is stipulated to be provided in.

It is specified that the above-mentioned one is provided with a plurality of protrusions in the plate thickness direction of the saw-tooth electrode.

[0009]

[Problems to be Solved by the Invention]

In the one described in (Problem / Purpose of claim 1), it is specified that the protrusions are provided in a zigzag manner, but in the plate thickness direction of the saw-toothed electrode, there is only one protrusion capable of corona discharge. Due to this, if the projections have a deterioration in discharge characteristics due to their own corona discharge, or if the tips of the projections are physically damaged due to inadequate handling of the sawtooth electrode during production or service maintenance, Corona discharge is not possible at the protrusions of this portion, and the photosensitive drum cannot be uniformly charged. Then, it causes a remarkable deterioration in image quality.

It is conceivable to increase the high-voltage current and voltage to the saw-tooth electrode in order to prevent the uneven charging due to the deterioration of the discharge characteristics and the physical defect at the tip of the projection, but as a result, the high-voltage power supply is required to be large. This causes an increase in the size of the device due to electric power consumption, an increase in the amount of ozone that is a harmful substance, and deterioration of the photosensitive drum due to ozone.

The above-mentioned one proposes a structure in which a plurality of protrusions are provided in the plate thickness direction of the saw-tooth electrode and the saw-tooth electrodes are simply overlapped. Since the manner of concentration of the electric field does not coincide with each other, a difference occurs in the discharge characteristic of each protrusion, that is, the discharge starting voltage. Also in another item described, it is proposed that the plurality of protrusions have different discharge characteristics due to different heights, and that the protrusions having a lower discharge start voltage are used in sequence. In any case, the one described is characterized in that the discharge starting voltages of the protrusions are varied and the protrusions having a lower discharge starting voltage are used in sequence. Therefore, in order to realize this, the high-voltage power supply supplied to the charging device requires a high-voltage, high-current, high-power power that can generate corona discharge even in a protrusion having a high discharge start voltage. Furthermore, even if some protrusions in the entire saw-tooth electrode are defective and one expects discharge at a protrusion with a high discharge start voltage, most normal protrusions will have the same low discharge start voltage. As a result, no matter how much current is supplied from the high-voltage power supply device, the supplied current steadily flows as a corona current from the protrusion having a low discharge start voltage. As a result, the output voltage does not rise, and corona discharge cannot be performed at the protrusion having a high discharge start voltage, resulting in uneven charging.

(Problem / Purpose of Claim 2) If the shape of the saw-tooth electrode holding member is made large in order to securely fix the saw-tooth electrode, the surface of the saw-tooth electrode holding member is removed by ions in the air due to corona discharge. The discharge is started by a change in the discharge start voltage due to the charging, and unevenness of the charge is caused by a large variation in the discharge start voltage.

(Problems / objects of claims 3, 4, and 5) The left and right symmetrical protrusions provided in the plate thickness direction have substantially the same shape and are provided with saw blade electrodes so that they have the same discharge starting voltage. Although created, the difference between the discharge start voltages on the left and right is not necessarily 0, and there is some voltage difference on the left and right. In addition, the discharge start voltage at the protrusion of the sawtooth electrode may vary due to variations in physical shape of the sawtooth electrode holding member, shield case, etc., variations in electrical characteristics such as dielectric constant and electrical resistance, and variations in assembly of the charging device. A change may occur and the variation in the discharge start voltage may become large, which may cause uneven charging.
Further, when the charging device is further miniaturized, the variation in the shape and the characteristic field more greatly affects the variation in the discharge starting voltage, which causes uneven charging and deterioration of the image quality.

[0014]

SUMMARY OF THE INVENTION The present invention has been made for the purpose of solving the above problems. In the invention according to claim 1, in a charging device for performing corona discharge by applying a voltage to a discharge electrode, The discharge electrode is composed of a plate-shaped electrode plate and a plurality of protrusions provided at the end of the electrode plate, and the protrusion has a tip whose cross-sectional shape is bilaterally symmetrical in the plate thickness direction of the electrode plate, The charging device has a characteristic that the discharge characteristics at the left and right ends are substantially the same.

According to a second aspect of the present invention, there is provided the charging device, wherein the cross-sectional outer shape of the holding member for the protrusion is symmetrical.

According to a third aspect of the present invention, there is provided the charging device including an adjusting member for adjusting the fixing position of the holding member on one side of the protrusion.

According to a fourth aspect of the present invention, there is provided the charging device including an adjusting member for adjusting the fixed position of the shield case on one side of the protrusion.

According to a fifth aspect of the present invention, there is provided the charging device, wherein the cross-sectional outer shape of the holding member of the protrusion and the cross-sectional shape of the shield case of the holding member are symmetrical.

According to the charging device of the present invention, when a high voltage for corona discharge is supplied to the saw-tooth discharge electrode, corona discharge is generated from each protruding portion, which causes a corona discharge current (total current) on the discharge current side. ) Flows. At this time, a part of the discharge current also flows on the recording medium side, so that the surface of the recording medium is charged to a predetermined polarity. Therefore, in the charging device according to the first aspect, since the cross-sectional shape of the tip of the saw blade is bilaterally symmetrical in the plate thickness direction, the directional characteristics of the left and right protrusions are substantially the same, so that at least one protrusion Corona discharge is generated at one portion, and even if one of the left and right protrusions is defective, the corona discharge can be continued at the other protrusion having substantially the same discharge starting voltage.

In the charging device according to the second aspect, the cross-sectional outer shape of the holding member of the saw blade near the protrusion is symmetrical, so that the discharge start voltage of the protrusion due to the charging of the holding member by corona discharge. The left and right discharge start voltages of the saw blade electrode protrusions are equal. The variation of the discharge start voltage does not change.

In the charging device according to the third aspect of the present invention, the surface of the saw blade holding member is charged to the same potential as the saw tooth electrode by corona discharge, but the charged holding member reduces the concentration of the electric field on the protrusions in the vicinity. Increase the discharge start voltage. Therefore, conversely, the discharge start voltage of the saw blade electrode can be set equal to the left and right by adjusting the fixed position of the saw blade holding member on one side with respect to the protrusion of the saw tooth electrode. Can be scrapped.

In the charging device according to the fourth aspect, the value of the discharge starting voltage of the protrusion of the saw-toothed electrode is determined by the spatial distance between the protrusion and the shield case in the vicinity. Therefore, by adjusting the fixed position of the shield case on one side with respect to the protrusion, the discharge start voltage on the left and right of the saw blade electrode can be set to be more equal, and therefore the range of variations in the discharge start voltage can be reduced.

In the charging device according to the fifth aspect, the cross-sectional shape of the holding member of the saw blade and the cross-sectional shape of the shield case are made symmetrical so that the influence of the charging of the holding member and the space between the shield case and the protruding portion are increased. By making the influence of distance the same on the left and right sides, the discharge characteristics on the left and right sides of the protrusions can be made equal, and therefore the range of variations in the discharge start voltage can be reduced.

[0024]

1 is a developed perspective view showing a specific structure of a charging device according to the present invention, and FIG. 2 shows an internal structure of an image forming apparatus (laser printer) equipped with the charging device according to the present invention. FIG. First, in the image forming apparatus of FIG. 2, a photosensitive drum (1 in FIG. 2) in which an OPC layer is formed as a photoconductive layer on an aluminum drum is arranged in the left center of the figure. The units composing the electrophotographic process are arranged to face each other with respect to 1). Reference numeral 2 in FIG. 2 arranged around the photosensitive drum (1 in FIG. 2) is a charging device utilizing corona discharge for uniformly charging the photosensitive drum (1 in FIG. 2) in the present invention,
Reference numeral 3 in FIG. 2 is an optical recording unit for irradiating with a laser beam for exposing and recording the original image on the surface of the photosensitive drum (1 in FIG. 2) uniformly charged by the charging device (2 in FIG. 2). Reference numeral 2-4 is a developing device for developing with toner the electrostatic latent image formed on the photosensitive drum (1 in FIG. 2) by the optical recording unit (3 in FIG. 2). 1)
A transfer device (8 in FIG. 2) that transfers the toner image formed on the surface of the transfer material fed from either the paper storage unit (5 or 6 in FIG. 2) is a transfer device (in FIG. 2). 7) does not transfer the toner image on the photosensitive drum (1 in FIG. 2)
This is a cleaning device that removes and collects the residual toner that remains. Also, the toner image of the original image transferred onto the transfer material by the transfer device (7 in FIG. 2) is a heat fixing device (9 in FIG. 2).
Then, the toner is fixed on the transfer material by heat and pressure, and is discharged onto a paper discharge tray (11 in FIG. 2) above the image forming apparatus via a paper discharge roller (10 in FIG. 2).

The paper storage unit (5 or 6 in FIG. 2) is detachably attached to the main body of the image forming apparatus, and the paper feed rollers (12 and 13 in FIG. 2) are provided to face each other. . The transfer material sent via the paper feed roller (12, 13 in FIG. 2) is sent to the registration roller (16 in FIG. 2) via the transport roller (14, 15 in FIG. 2). The registration roller (16 in FIG. 2) temporarily stops the fed transfer material and controls the conveyance start in synchronization with the rotation of the photosensitive drum (1 in FIG. 2). The conveyance start of the paper is controlled so that the leading edge of the image formed in 1) of FIG.

(Embodiment 1) FIG. 1 shows an example of a specific structure of a charging device (2 in FIG. 2) according to the present invention. 1 includes a conductive shield case (21 in FIG. 1), a saw-tooth electrode (22 in FIG. 1), a grid electrode (23 in FIG. 1) and an insulating saw-tooth electrode holding various electrodes. It is composed of a member (24 in FIG. 1).

In FIG. 1, the shield case (2 in FIG.
Reference numeral 1) is a conductive shield case plate having a length which substantially coincides with the width direction (rotational axis direction of the drum) of the photosensitive drum (1 in FIG. 1) and faces the surface of the photosensitive drum (1 in FIG. 1). The side is open. The saw-tooth electrode (22 in FIG. 1) has a plurality of sharp projections for discharge at a predetermined interval in the length direction, and is a strip of stainless steel (such as JIU standard 304) formed by etching. It consists of thin plates.

The saw-toothed electrode 22 is formed with a plurality of fixing openings. These openings are protrusions (24b in FIG. 1) formed in a planar shape portion (24a in FIG. 1) of a holding member (24 in FIG. 1) integrally formed of an insulating member.
Be inserted into. As a result, the sawtooth electrode (22 in FIG. 1)
Is positioned and held and fixed to the plane portion (24a in FIG. 1) of the holding member (24 in FIG. 1) while being electrically insulated from the shield case (21 in FIG. 1).

Further, a grid electrode (23 in FIG. 1) is electrically insulated from the holding case (24 in FIG. 1) with respect to the shield case (21 in FIG. 1) and the sawtooth electrode (22 in FIG. 1). A grid electrode holding portion (25 in FIG. 1) for holding is integrally formed. The grid electrode holding portion (25 in FIG. 1) has a locking barb formed corresponding to the openings (23a in FIG. 1) formed at both ends of the grid electrode (23 in FIG. 1). Stops (25a in FIG. 1) are formed respectively. This grid electrode holder (25 in FIG. 1)
By elastically deforming the grid electrode (23 in FIG. 1)
The locking portion (25a in FIG. 1) is inserted into the opening (23a in FIG. 1) and elastic deformation is released to hold the grid electrode (23 in FIG. 1) with a predetermined tension by elastic force.

In the grid electrode (23 in FIG. 1), a mesh-shaped opening is uniformly formed by etching a strip-shaped stainless thin plate like the saw-tooth electrode (22 in FIG. 1). The part indicated by reference numeral 26 in FIG. 1 integrally molded with the holding member (24 in FIG. 1) is located corresponding to both end edges of the shield case (21 in FIG. 1), and the holding member (24 in FIG. 1). Is a member for positioning inside the shield case (21 in FIG. 1).

In assembling the charging device having the above structure,
First, the plane portion (24a in FIG. 1) of the holding member (24 in FIG. 1)
An opening formed in the saw-tooth electrode (22 in FIG. 1) is fitted into and fixed to the protrusion of the projection, and a predetermined amount in the shield case (21 in FIG. 1) is held with the saw-tooth electrode (22 in FIG. 1) being held. Positioning member (26 in FIG. 1) is placed in the shield case (FIG. 1).
21). The opening (23a in FIG. 1) of the grid electrode (23 in FIG. 1) is provided in the locking portion (25a in FIG. 1) of the grid electrode holding member (25 in FIG. 1).
Is inserted and engaged. Reference numeral 27 in FIG. 1 is a spring terminal for power supply that electrically elastically contacts the end portion of the saw-tooth electrode (22 in FIG. 1) located on the holding member (24 in FIG. 1) protruding from the shield case. is there.

In the charging device of FIG. 1 having the above structure, when a predetermined high voltage is applied to the saw-tooth electrode (22 in FIG. 1),
At this time, corona discharge is generated from the tips of the sharp protrusions formed at equal pitch.
Flowing toward the side 1) of the photosensitive drum (1 in FIG. 2) is charged to a specific polarity. This charging potential can be set freely by controlling the voltage value supplied to the grid electrode (23 in FIG. 1), for example. Here, the tip of the sharpened projection according to the present invention is characterized in that it has a structure of a pair of projections whose cross-section is bilaterally symmetrical in the plate thickness direction.

FIG. 3 shows a perspective view of the saw-tooth electrode (22 in FIG. 1). The cross section along the plane indicated by the broken line in FIG. 3 means the cross section in the plate thickness direction of the saw-tooth electrode. 4A and 4B are examples of the cross section.

FIG. 4A is a cross-sectional view of the tip portion of the sharpened protrusion shown by the broken line in FIG. One electrode member (30 in FIG. 4A) has a protrusion (31 in FIG. 4A) as a discharge tip.
a, 31b) are formed symmetrically with respect to the center line (32 in FIG. 4A) of the electrode member (30 in FIG. 4A). Heights (HL and HR in FIG. 4A) of tips of projections (31a and 31b in FIG. 4A) and angles (FIG. 4A)
(A) AL, AR), ridgeline (SL, S in FIG. 4A)
Since R) is substantially the same on the left and right, the corona discharge characteristics and the corona discharge starting voltage are substantially the same value due to the symmetry of the shape of the protrusions (31a and 31b in FIG. 4A). FIG. 4B shows two electrode members (33 in FIG. 4B).
L and 33R) are overlapped to form one saw-tooth electrode (22 in FIG. 1), which shows a tip cross section at a sharp tip as in FIG. 4 (A). By stacking the front and back surfaces of the same member to form a saw-tooth electrode having a completely symmetrical shape on the left and right, the protrusions (34a, 34 in FIG. 4B) are formed.
b) Tip height (HL and HR in FIG. 4B), angle (AL and AR in FIG. 4B), ridge line (S in FIG. 4B)
The left and right sides of (L, SR) completely match. Therefore, the discharge characteristics and the discharge start voltage are the same due to the symmetry of the left and right protrusions. Alternatively, the variations in discharge characteristics and discharge start voltage are extremely small.

FIG. 5 is a functional cross-sectional view showing the discharging state of the charging device using the saw-tooth electrode shown in FIG. 4 (A).
The saw-toothed electrodes (22 in FIG. 5) arranged substantially in the center are the shield case (21 in FIG. 5) and the grid electrode (2 in FIG. 5).
3), by applying a high voltage to the drum (1 in FIG. 5), corona discharge is generated at the tips (31a and 31b in FIG. 5), the shield case (21 in FIG. 5), the grid electrode (FIG. 5). 23), and a current due to discharge flows through the drum (1 in FIG. 5). Here, the tips (31a and 31b in FIG. 5) have substantially the same shape, and the saw-tooth electrode (22 in FIG. 5).
Since the fixing position of is at the center in the width direction of the shield case 21 (L1 = L2 in FIG. 5A), the tip end portion (31 in FIG. 5) is fixed.
The electric field concentration in the vicinity of (a, 31b) is symmetrical with respect to the center line (32 in FIG. 5) and can be said to be the same or substantially the same. Therefore, the corona discharge characteristics and the discharge starting voltage at the tip portions (31a and 31b in FIG. 5) are also the same or substantially the same, and the voltage difference can be extremely reduced on the left and right, so that the tip portions can be supplied even if the high voltage current is a little. (31a of FIG. 5,
31b) can be discharged at the same time. Alternatively, even if there is a slight voltage difference, the discharge can be maintained at the tip portion where the discharge start voltage is low. Alternatively, even if one of the left and right tips (31a and 31b in FIG. 5) is missing and the discharge start voltage becomes high and the discharge cannot be performed, the discharge can be maintained at the remaining tips.

From the above, the tip of the sawtooth electrode (see FIG.
31a, 31b) of the left and right sides suppress the variation of the discharge start voltage of the left and right tips (31a, 31b in FIG. 5), which reduces the voltage, current and power of the high voltage power supply. It can be seen that even if the tip portion on one side is damaged, the alternative function of maintaining the discharge on the other tip portion works.

With this alternative function, the drum (Fig.
In 1), the uneven charging is eliminated, and the image quality can be stabilized. FIG. 5 has described the charging device using the saw-tooth electrode shown in FIG. 4A, but using the saw-tooth electrode having the two-sheet structure shown in FIG. It is needless to say that the effect of preventing uneven charging can be further enhanced because the completeness can be achieved.

(Embodiment 2) In FIG. 5, the saw-tooth electrode (22 in FIG. 5) is fixed to the electrode holding member (24 in FIG. 5), but the electrode holding member is improved to improve productivity and serviceability. It is required to enlarge the shape of (24 in FIG. 5) and securely fix the saw-tooth electrode (22 in FIG. 5). FIG. 6 shows a functional cross section of the charging device which satisfies this requirement. In FIG. 6, the height (H4 in FIG. 6) of the electrode holding member (22 in FIG. 6) is shown in FIG. 2 of 5
It is higher than the height of 2) (H4 in FIG. 5), and by increasing the contact area with the sawtooth electrode (22 in FIG. 6),
It secures the fixation. For example, when a negative high-voltage power supply is supplied to the saw-tooth electrode (22 in FIG. 6) in FIG. 6, corona discharge is generated at the protrusions (31a, 31b in FIG. 6), but oxygen, nitrogen, nitrogen oxides, etc. in the air are generated. The gas molecules become negative ions having the same polarity as the high-voltage power supply, and a current flows as a corona discharge current through the shield case (21 in FIG. 6), the grid (23 in FIG. 6), and the drum (1 in FIG. 6). At the same time, in the vicinity of the protrusions (31a and 31b in FIG. 6), the surface of the holding member (24 in FIG. 6) molded of an insulating material adsorbs the ionic molecules in the air, and the surface is the same as the sawtooth electrode. The electrodes are charged to the same voltage (35 in FIG. 6). The surface of the holding member (24 in FIG. 6) is thus charged (35 in FIG. 6).
Then, the protrusion (31 in FIG. 6) closest to the charged area is
In the vicinity of b), the negative electric potential of the same polarity appears in the vicinity, so that the electric field distribution becomes gentle and corona discharge is less likely to occur. Therefore, the protrusion (31b in FIG. 6) is not
31a), the discharge start voltage becomes relatively higher. Since the discharge start voltages of the left and right protrusions (31a and 31b in FIG. 6) are different, the corona discharge concentrates only on the protrusion (31a in FIG. 6) having a low discharge start voltage, and the corona discharge is discharged in the protrusion (31b in FIG. 6). Can not. Therefore, even if a defect occurs in the protrusion (31a in FIG. 6), the protrusion (31b in FIG. 6) cannot discharge because the discharge start voltage is high and uneven charging occurs in this portion.

In order to eliminate the above-mentioned problem, FIG. 7 shows a charging device in which a holding member (70 in FIG. 7) formed of the same insulating material for holding a charge is provided on the opposite side of the holding member (24 in FIG. 7). is there. The shape of the holding member (70 in FIG. 7) is centered around the saw-tooth electrode (22 in FIG. 7) and has a saw-tooth projection (31a in FIG. 7,
31b) Cross-section outline ridgeline (72, 73 in FIG. 7)
The surfaces of the holding members 24 and 70 are bilaterally symmetrical and are charged in the same state (74 and 75 in FIG. 7) by making (line shown by a solid thick line in the figure) bilaterally symmetrical. Therefore, the protrusion (31 in FIG. 7)
There is no relative change in the discharge characteristics of a and 31b) and the discharge start voltage.

Accordingly, even if the shape of the electrode holding member is increased, by making the shape of the saw-tooth electrode symmetrical,
There is no difference between the left and right discharge characteristics and the discharge start voltage of the left and right protrusions of the saw-tooth electrode. Then, both of the left and right sides of the protrusion can be discharged at the same time, and even if the other is lost, the remaining one can maintain the discharge and the replacement function works.

FIG. 8 is an assembly view of the holding member (24, 70 in FIG. 8) and the saw-tooth electrode (22 in FIG. 8). The insulating fixing screw (74 in FIG. 8) is a holding member (70 in FIG. 8) and a holding member (76 in FIG. 8) provided with tapping holes (22 in FIG. 8) through the sawtooth electrode (22 in FIG. 8). Fasten these parts by fastening them to 24 of 8).

(Embodiment 3) In FIG. 7, the left and right discharge starting voltages of the protrusions (31a, 31b in FIG. 7) of the saw-tooth electrode (22 in FIG. 7) are slight, but the factors that change are
Protrusions (31a, 3 in FIG. 7) of the sawtooth electrode (22 in FIG. 7)
1b) in the etching production process, the shape difference between the protrusions (31a, 31b in FIG. 7), the shape difference between the shield case (21 in FIG. 7), the holding member (80, 24 in FIG. 7). There may be a case where the electric field is not concentrated at the tips of the protrusions (31a and 31b in FIG. 7) symmetrically due to a difference in shape between the left and right and variations in assembly of the charging device.

FIG. 9 shows an embodiment of a charging device capable of adjusting the fixing position of the holding member in the height direction. A holding member (80 in FIG. 9) for correcting the charge is provided with a tap hole (85 in FIG. 9) at one end thereof for fastening through a long hole (84 in FIG. 9) of the shield case (21 in FIG. 9). It is fixed with a screw (81 in FIG. 9). By loosening the screw (81 in FIG. 9), the holding member (80 in FIG. 9) becomes a sawtooth electrode (22 in FIG. 9).
The protrusion is moved vertically (← → in FIG. 9) to adjust its height, and after adjustment, tighten the fastening screw. On the other hand, the cross-sectional outer shape (82 in FIG. 9) of the charging correction holding member (80 in FIG. 9) is centered around the cross-sectional outer shape (83 in FIG. 9) of the holding member (24 in FIG. 9) and the saw-tooth electrode. The shape is symmetrical.

In the present invention, the protrusion (31a in FIG. 9,
31b) by vertically moving the fixing position of the holding member (80 in FIG. 9) to adjust the protrusions (31a, 31 in FIG. 9).
The discharge starting voltages on the left and right of b) are adjusted and matched. That is, the holding member (2 in FIG. 9) is generated by the occurrence of corona discharge.
4) A charge due to charging (86 in FIG. 9) is generated on the surface of the cross-sectional contour shape (83 in FIG. 9), and similarly, a cross-sectional contour shape (82 in FIG. 9) of the holding member (80 in FIG. 9). Electric charges (87 in FIG. 9) are also generated on the surface of the. Here, moving the holding member (80 in FIG. 9) up and down with respect to the protrusion (31a in FIG. 9) means that the cross-sectional outer shape (82 in FIG. 9) of the holding member (80 in FIG. 9) is charged. This means (87 in FIG. 9) to move the electric charge closer to or farther from the protrusion 31a, which changes the manner of concentration of the electric field at the tip of the protrusion 31a. That is, by bringing them closer to each other, the discharge start voltage of the protrusion (31a in FIG. 9) can be made higher than the discharge start voltage of the protrusion (31b in FIG. 9). On the contrary, it can be made lower than the discharge start voltage by increasing the distance. Therefore, even if the discharge starting voltage and the discharge characteristic are different from each other on the left and right sides, the left and right sides can be matched by adjusting the fixed position of the holding member.

A specific method for adjusting the vertical position of the holding member (80 in FIG. 9) is to adjust the corona of the protrusions (31a, 31b in FIG. 9) while applying a high voltage to the charging device to generate corona discharge. The intensity of light emission due to discharge is equal on the left and right, or the left column, that is, the column of the protrusions (31a in FIG. 9) and the right column, with respect to all the protrusions of the sawtooth electrode (22 in FIG. 9), that is, The light emission rate of the row of protrusions (31b in FIG. 9) is about 50%.

FIG. 10 shows a correction holding member (80 in FIG. 9).
Shows the assembly of. The shield case (21 in FIG. 10) is opened at the opening indicated by the broken line, bent 90 degrees outward, and is used as a bent portion (83 in FIG. 10) for fixing the correction holding member (80 in FIG. 10) with screws. Bending part (Fig. 1
No. 83 of No. 0) is provided with an elongated hole 84 for screw fixing adjustment. The holding member (80 in FIG. 10) has a screw tap hole (8 in FIG. 10).
5) is provided, and a long hole (84 in FIG. 10) of the sawtooth electrode bent portion (83 in FIG. 10) of the shield case (21 in FIG. 10) is provided.
Fixed to the shield case via. The procedure for assembling the charging device is as follows: a holding member (24 in FIG. 1), a saw-tooth electrode (22 in FIG. 1), and a grid electrode (23 in FIG. 1).
After pre-assembling the spring terminal (27 in FIG. 1), the holding member (80 in FIG. 10) shown in FIG. 10 is inserted from the bottom of the shield case (21 in FIG. 10), and the screw (FIG. 1) is inserted.
It is fixed at 81) of 0.

In this embodiment, the holding member was moved in the vertical direction. However, the holding member may be moved in a direction perpendicular to the vertical direction for adjustment, or the height of the holding member may be set lower beforehand. Instead of moving it, it is also possible to adjust the height by attaching a necessary number of insulating materials such as a polyester film to the surface of the holding member.

(Embodiment 4) In FIG. 6, the left and right discharge starting voltages of the protrusions (31a, 31b) differ depending on the charge (35 in FIG. 6) of the holding member (24 in FIG. 6). As described above, in this figure, the protrusion (31 in FIG.
By adjusting any of the intervals (L1, L2 in FIG. 6) from a, 31b) to the shield case (21 in FIG. 6), the left and right discharge starting voltages can be matched. In this figure, the protrusion (31b in FIG. 6) is changed to the protrusion (31 in FIG. 6) by charging (35 in FIG. 6) of the holding member (24 in FIG. 6).
The discharge starting voltage is higher than that in a), but at intervals (L1 in FIG. 6)
The discharge start voltage of the protrusion (31b of FIG. 6) can be made lower than that of the protrusion (31a of FIG. 6) by widening or narrowing the interval (L2 of FIG. 6). By canceling and further adjusting either of the intervals (L1 and L2 in FIG. 6), the left and right discharge start voltages can be matched or the difference between the discharge start voltages can be reduced.

FIG. 11 shows the interval in FIG. 6 (L1 in FIG. 6).
FIG. 3 is a cross-sectional view of a charging device that can adjust the. The shield case is composed of a shield case (90 in FIG. 11) and a shield case (91 in FIG. 11), and a saw-tooth electrode (2 in FIG. 11).
2), the shield case (90 in FIG. 11) can be moved horizontally (arrow ← →). By moving the shield case (90 in FIG. 11) to the right, the protrusion (31a in FIG. 11) and the shield case (90 in FIG. 11)
Since the distance between the two becomes narrower, the discharge start voltage of the protrusion (31a in FIG. 11) can be adjusted to the lower direction. By moving the shield case (90 in FIG. 11) to the left, the protrusion (FIG.
31a) and the shield case (90 in FIG. 11) are widened, the discharge starting voltage of the protrusion (31a in FIG. 11) can be adjusted to a lower direction.

The method of adjusting the left and right positions of the shield case (90 in FIG. 11) is the same as the method of the third embodiment.

FIG. 12 shows an assembly drawing of the above and the shield case (91, 91 in FIG. 11). The screw hole portion of the shield case (90 in FIG. 12) for movement adjustment is provided with an elongated hole (93 in FIG. 12) for movement. Shield case (9 in Fig. 12)
1) is provided with a tap hole (94 in FIG. 12) for fixing the shield case (90 in FIG. 12), and the metal fastening screw (95 in FIG. 12) is provided in the shield case (90 in FIG. 12).
Is sandwiched between and fixed to the shield case (91 in FIG. 12). The shield case (90 in FIG. 12) is moved by loosening the screw (95 in FIG. 12).

Although the shield case is moved in the present embodiment, a method of moving the saw-tooth electrode (22 in FIG. 11) horizontally with respect to the shield case is also possible. Further, the shield case (90 in FIG. 11) is moved in the vertical direction to bend the shield case (92 in FIG. 11).
It is also possible to adjust the interval between the protrusions (31a and 31b in FIG. 11).

(Embodiment 5) FIG. 13 shows a left and right symmetrical saw-tooth discharge electrode (22 in FIG. 13) and a symmetrical outer cross-sectional shape around the saw-tooth discharge electrode (22 in FIG. 12). The charging device is composed of a holding member (24 and 26 in FIG. 13) and a shield case (21 in FIG. 13) which is symmetrical with respect to the saw-tooth discharge electrode (22 in FIG. 13). By locating the shield case and the holding member symmetrically with respect to the saw-tooth electrode (22 in FIG. 13), the electric field distribution at the tips of the protrusions (31a, 31b in FIG. 13) is also symmetrical. Therefore, the protrusion (Fig. 1
There is no difference in the discharge start voltages on the left and right of 3a of 31a and 31b), and the charging device can be formed within the same or a very small variation range, and uneven charging can be eliminated.

[0054]

【The invention's effect】

(Effect of Claim 1) By using the saw-tooth electrode symmetrically shaped in the plate thickness direction, the corona discharge inception voltages on the left and right of the protrusions of the saw-tooth electrode can be made to coincide with each other or their variations can be extremely reduced. As a result, the output voltage and output current of the high-voltage power supply device can be reduced, and the device can be downsized. Further, even if the protrusion on one side is missing, the other protrusion functions to maintain the discharge, thereby eliminating uneven charging of the drum and stabilizing the image quality. Alternatively, it is possible to obtain a remarkable effect in stabilizing the quality such as prolonging the life of the saw-tooth electrode due to changes over time in actual use. Or, in the production process of the charging device and the sawtooth electrode, since it has an alternative function, it was necessary to replace the sawtooth electrode in the past with the lack of protrusions, but since it can be used as it is, the yield and productivity are improved. Can contribute to the improvement of

(Effect of claim 2) Even if the shape of the holding member is increased, the left and right shapes are made symmetrical so that the charging performance is not affected, so that the saw-tooth electrode is held and fixed securely, and the assembly is completed. Cleaning of the sawtooth electrode inside the charging device with a brush or ultrasonic waves should be easy. Further, by making the height of the holding member the same as or higher than the height of the protrusion, it is possible to protect the protrusion from physical damage and prevent a serviceman or a production worker from being injured by the protrusion.

(Effect of Claim 3) By having the function of adjusting the discharge start voltage, the production of the saw-toothed electrode and the assembly of the charging device are facilitated, and at the same time the performance of preventing uneven charging is improved.

(Effect of Claim 4) Since there is no restriction on the shape of the holding member, the degree of designing is increased. The function of adjusting the discharge start voltage facilitates production of the saw-tooth electrode and assembly of the charging device, and at the same time improves performance of preventing uneven charging.

(Effect of Claim 5) The apparatus can be downsized without deteriorating the performance of the charging apparatus.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a charging device of the present invention.

FIG. 2 is a sectional view of the printer of the present invention.

FIG. 3 is a perspective view of a saw-toothed electrode protrusion of the present invention.

FIG. 4 is a sectional view of a saw-toothed electrode protrusion of the present invention.

FIG. 5 is a sectional view of the charging device of the present invention.

FIG. 6 is a sectional view of the charging device of the present invention.

FIG. 7 is a sectional view of the charging device of the present invention.

FIG. 8 is an assembly view of a holding portion of the present invention.

FIG. 9 is a sectional view of the charging device of the present invention.

FIG. 10 is an assembly view of a holding portion of the present invention.

FIG. 11 is a sectional view of the charging device of the present invention.

FIG. 12 is an assembly diagram of the shield case of the present invention.

FIG. 13 is a sectional view of the charging device of the present invention.

[Explanation of symbols]

 2 Charging Device 21 Shield Case 22 Sawtooth Discharge Electrode (Sawtooth Electrode) 24 Holding Member 31a, 31b, 34a, 34b Tip (Protrusion)

Claims (5)

[Claims] 1. A charging device for performing corona discharge by applying a voltage to a discharge electrode, wherein the discharge electrode comprises a plate-shaped electrode plate and a plurality of protrusions provided at an end of the electrode plate, The charging device is characterized in that the projecting portion has a tip whose cross-sectional shape is bilaterally symmetric in the plate thickness direction of the electrode plate, and the discharge characteristics at the left and right tips are substantially the same. 2. The charging device according to claim 1, wherein a cross-sectional outer shape of the holding member for the protrusion is symmetrical. 3. An adjusting member for adjusting the fixing position of the holding member on one side of the protrusion portion.
The charging device described. 4. The charging device according to claim 1, further comprising an adjusting member for adjusting a fixing position of the shield case on one side of the protrusion. 5. The charging device according to claim 1, wherein the cross-sectional outer shape of the holding member of the protrusion and the cross-sectional shape of the shield case of the holding member are symmetrical.