JPH04233558A - Blade-type corona charging device without arc - Google Patents

Abstract

PURPOSE: To supply/distribute a largest number of electric charges to a charge receptor, while suppressing the generation of an arc as little as possible. CONSTITUTION: This corona electrifier for electrifying the surface of the charge receptor includes a ribbon type corona electrode 91 with electric field correcting electrodes 92 and 93, these electric field correcting electrodes 92 and 93 are installed in parallel with a ribbon surface and the possibility of the generation of the arc can be suppressed as little as possible.

Description

[Detailed description of the invention]

FIELD OF THE INVENTION This invention relates to charging devices for applying a charge to adjacent surfaces. In particular, it relates to anti-arc blade type corona charging devices used in such devices. This device is useful in electrophotographic reproduction systems for generating a flow of ions toward an adjacent image surface to alter or change the electrostatic charge on that surface.

[Background of the Invention] In electrophotographic copying technology, electrostatic charges are uniformly distributed on an image surface, and these charges are sequentially applied to produce an electrostatic latent image according to information including an optical image by exposure to light. It is necessary to be selectively distributed. The electrostatic latent image is then developed and the developed image is transferred to a support surface to produce the final copy of the original document.

In addition to precharging the image plane of an electrophotographic system prior to exposure, corona devices are used to perform a variety of other functions in the electrophotographic process. Corona devices can be used, for example, to transfer electrostatic toner images from a reusable photoreceptor to a transfer member, or to load and unload paper from an image member to improve the quality of electrophotographic reproductions. It is also useful for adjusting the image surface before, during, and after toner adhesion.

Both direct current and alternating current type corona devices are used to perform many of the above functions.

A conventional type of corona charging device used in reproduction systems of the type described above is disclosed in US Pat. No. 2,836,72.
No. 5, in which a conductive corona charging device in the form of a tapered wire is connected to a DC power source for corona generation. This wire is partially surrounded by a conductive shield, which is usually grounded. The surface to be charged rests on the opposite side of the shield, away from the wire, and on a grounded substrate. Additionally, corona devices of the type described above have been biased in the manner described in US Pat. No. 2,879,395. According to this patent, a potential difference that generates an alternating current corona is applied to a conductive wire electrode, and a direct current potential difference is applied to a conductive shield that partially surrounds the electrode to regulate the flow of ions from the electrode toward the surface to be charged. is being applied. Although there are other methods of applying bias that are known as prior art, they will not be discussed here.

Among the problems with these devices, there is the problem that the wires tend to vibrate, producing vibration noise and becoming droopy. It is difficult to use these wires in close proximity to the surface to be charged. Another problem is that these wires are easily damaged and difficult to install.

Various attempts have been made to solve these problems. For example, U.S. Pat.
, 711,710 discloses a corona charging system that includes a plurality of ion discharge corona electrodes made of thin conductive strips that charge the surface of a light-receiving medium in a document reproduction machine. U.S. Pat. No. 3,959,690 discloses a corona charging element for an electrophotographic copier that includes a corona electrode element in the form of a metal strip, in which a protrusion is provided in the plane of one side of the metal strip. Alternating and further on the other side are tetrahedral pyramid-shaped protrusions, one side of which rests on the surface of a metal strip that discharges an ionic charging current directly onto the conductive photoreceptor surface. This charges the surface of the photoreceptor.

[Summary of the Invention] Accordingly, a charging device is disclosed that employs a ribbon-shaped corona charging device that discharges an ion charging current onto the surface of a photoreceptor. The ribbon-shaped corona charging device is arranged vertically and has an electric field correction electrode parallel to the ribbon, which is known to have a tendency to reduce the occurrence of arc discharge, placed beside the ribbon. The field correction electrode also plays a major role in improving the broad corona distribution from the ribbon to the charge receptor surface.

BRIEF DESCRIPTION OF THE DRAWINGS The prior art and other aspects of the present invention will become more apparent from the following features, reading the claims, and the following drawings.

FIG. 1 is a schematic plan view of an electrophotographic copying machine that adopts the idea that characterizes the present invention.

FIG. 2 is a side view of the charging device of FIG. 1, showing that the present invention is used as a charging unit.

FIG. 3 shows another embodiment of a charging device according to the present invention.

FIG. 4 is a graph illustrating the charge uniformity obtained with a charging device according to the invention for various processing distances and processing speeds.

DETAILED DESCRIPTION OF THE DRAWINGS The drawings are incorporated herein by reference in order to provide an overview of the features of the present invention. Reference numbers in the figures are used throughout the text to refer to the same elements. FIG. 1 is a schematic diagram for explaining each member of an electrophotographic copying machine incorporating an improved charging device according to the present invention.

Since electrophotographic copying machine technology is well known, each processing section used in the copying machine shown in FIG. 1 will be schematically shown below, and a brief explanation will be given with reference to it.

In FIG. 1, the illustrated electrophotographic printing machine employs a belt 10 having a photoconductive surface. This photoconductive surface is preferably made of a selenium alloy. Belt 10 is indicated by arrow 12
The photoconductive surface is moved in the direction shown in FIG.

First, a portion of the photoconductive surface passes through the charging section A. In charging station A, a corona generating device according to the invention, indicated by the reference numeral 90, charges the photoconductive surface to a substantially uniform, relatively high potential difference.

The charged portion of the photoconductive surface then advances past image area B. In the image section B, a document handling unit, indicated by the reference numeral 15, positions an original document 16 with its copy side facing down above an exposure system 17. The exposure system, designated by the reference numeral 17, includes a transparent platen 1.
Lamp 2 irradiating the original document 16 positioned on 8
Contains 0. Light rays reflected from original document 16 pass through lens 22 . Lens 22 focuses an image of original document 16 onto the charged portion of the photoconductive surface of belt 10 to selectively distribute charge thereon. This records an electrostatic latent image on the photoconductive surface that corresponds to the informational areas contained in the document. Belt 10 then advances to transfer the electrostatic latent image recorded on the photoconductive surface to developer station C. Platen 18 is movably mounted and is set to move in the direction of arrow 24 to adjust the magnification of the original document to be copied. Lens 22 moves synchronously to image an optical image of original document 16 onto the charged portion of the photoconductive surface of belt 10.

The document handling unit 15 sequentially feeds the documents from the stack of documents stacked by the operator to the document stack holding tray in the normal progression order. The documents are sequentially fed from the holding tray to the platen 18. The document handling unit returns the document to the document stack held in the tray. It is desirable that the document handling unit has the function of smoothly and sequentially feeding paper or plastic on which information to be printed is written even if the size and weight of the paper or plastic is diverse. The dimensions of the original document in the holding tray and the dimensions of the copy paper have been measured.

Having described the original handling unit, those skilled in the art will recognize that it is better to measure the dimensions of the original document at the platen portion than within the original handling unit. This also applies to copiers or printers that do not have a document handling unit, and the A3 document handling unit is lifted from the platen and oversized documents must be manually placed onto the copying platen. Or 11″ x 17″
This is also necessary when copying a (28 cm x 43 cm) original.

Continuing to refer to FIG. 1, in developer station C a pair of magnetic brush developer rollers, generally indicated by reference numerals 26 and 28, advance developer material into contact with the electrostatically charged latent image. There is. The latent image attracts toner particles from the developer carrier particles to form a toner powder image on the photoconductive surface of belt 10.

After the electrostatic latent image recorded on the photoconductive surface of belt 10 is developed, belt 10 advances to transport the toner particle image to transfer station D. At transfer station D, the copy sheet is moved into contact with the toner particle image. The transfer section D includes a corona generating device 30, which emits ions to the back side of the copy paper. As a result of this process, the toner particle image is drawn from the photoconductive surface of belt 10 to the copy sheet. When the transfer is completed, the conveyor 32 transports the copy sheet to the fixing section E.

The copy paper is fed from the tray 34 to the transfer section D. The tray senses the size of the copy sheet and sends a sensed electrical signal to a microprocessor within controller 38. Similarly, the holding tray of the document handling unit 15 has a switch thereon which senses the size of the document and generates a sensed electrical signal which is also transmitted to the microprocessor controller 38.

Fusing station E is provided with a fuser assembly, generally indicated by the reference numeral 40, for completely fusing the transferred particle image to the copy sheet. The fixing device 40 includes a heat fixing roller 4.
2 and a support roller 44. The copy paper comes into contact with the particle image on the fixing roller 42 while passing between the fixing roller 42 and the support roller 44 . In this way, the particle image is completely fused to the copy sheet.

After fusing, conveyor 46 transfers the copy sheet to gate 48, which operates as an inverter selector. Depending on the position of gate 48, the copy sheet is either inverted into paper inverter 50 or bypassed paper inverter 50 and fed directly to second judgment gate 52. Thus, the copy sheet that bypasses the inverter 50 turns 90 degrees into the paper path before reaching the gate 52. The gate 48 serves to direct the side of the paper with the transferred and fixed image upward. The opposite occurs if inverter path 50 is used. In other words, the finished printed surface faces downward. The second judgment gate 52 determines whether the paper is directly put into the output tray 54 or not.
Alternatively, the paper may be directed to a transport path that transports the paper to the third judgment gate 56 without inputting the paper. The gate 56 either transfers the paper directly to the output path of the copier without inverting it, or
Or inverter roller drive mechanism 58 for double-sided printing of paper
Transfer to. The reversing drive mechanism 58 reverses and stacks the paper onto the duplex printing tray 60 when the gate 56 is activated in that direction. The duplex printing tray 60 is used to finish printing on one side and continue printing on the back side, and is an intermediate so-called buffer storage place for sheets to be printed on both sides. As the sheets are being inverted by rollers 58, the sheets stored in this buffer storage are stacked face down in duplex tray 60. These sheets are stacked on top of each other in the duplex printing tray 60 in the order in which they will be copied.

To complete duplex printing, the paper in the tray 60 on which the first side has already been printed is fed to the conveyor 59 and returned to the transfer section D sequentially by the final feeder 62, and toner is applied to the back side of the paper. Transfer the particle image. Conveyor 100 and 66
moves the paper along a reversing motion path. However, as the bottom paper is fed from the duplex printing tray 60, the unprinted side of the copy paper comes into contact with the belt 10 at the transfer station D, so that the toner particle image on the belt is transferred. become. Next, the sheets that have been printed on both sides are fed along the same path as the sheets that have been printed on the first side and stacked on the tray 54, and are successively carried away by the printing operator.

Turning now to the operation of a printing press, some amount of toner particles always remain attached to the belt 10 after the copy sheet is separated from the photoconductive surface of the belt 10. The remainder of these particles are removed from the photoconductive surface in cleaning station F. A fiber brush 68 in contact with the photoconductive surface of the belt 10 is rotatably attached to the cleaning section F. Particles are removed from the photoconductive surface of belt 10 by rotation of brush 68 in contact with the belt. Following cleaning, the photoconductive surface is illuminated with a discharge lamp (not shown) to dissipate any remaining particles and allow charging of the belt for the next imaging cycle.

Returning now to the present invention, in FIG. 2, corotron 90 is positioned in a plane perpendicular to charge receptor 10 and includes a thin (approximately 1 to 3 mil thick) conductive ribbon 91 that is grounded. It is equipped with a corona electrode in the shape of a . Electrodes 92 and 93, which have roles to be described later, face the ribbon 91. The ribbon-shaped electrode 91 is much more advantageous than the wire-shaped electrode. The ribbon type, i.e., the blade 91, has a rigid structure, and is not as difficult to install as wire tension, nor is it easily broken, and does not generate oscillating noise, droop, or other troubles that thin wire type corona charging devices cause. be. However, ribbon or blade types tend to arc. This is probably due to the higher capacitance of this type of electrode, as well as the fact that the proportion of the electric field emanating from the corona emission edge is smaller than that of the wire type. The electric field from the wire-type electrode reaches the Paschen limit (P
(aschen limit) is exceeded only in a very small area surrounding the surface of the wire. In the case of a blade, the ionization area is much wider and in fact the extent of the electric field reaching the charge acceptor across the gap is unnecessarily high. That is, the extra conductive surface with a high potential difference extending above the corona emission edge increases the potential difference across the space around the edge of the ribbon. Therefore, the voltage required for corona generation must be high,
The second derivative with respect to distance of the voltage taken toward the earth's surface also decreases. In other words, a high electric field will spread further towards the charge acceptor, whereas in the case of a wire electric field it will decrease more rapidly with increasing distance from the corona electrode.

[0029] A solution to the problem that arcs are more likely to occur due to blade charging is to use (
Ground electrodes 92 and 93 (of substantially the same value and opposite polarity) are incorporated on both sides of the ribbon 91. The electrode is adjustable in position and electrically biased so that all lines of force extending from the sides of the ribbon 91 are concentrated on this electrode, while
Electric field lines emanating from the tip of the corona active region extend directly to the charge receiving member. This electric field then spreads across the charge receptor plate, lowering the electric field in the vicinity of the charge receptor plate, thereby reducing the tendency for arcing. This corona charging unit (91, 92
and 93) (alternating current or direct current) can be applied not only to such specific embodiments but also to charging operations in general. This method can be used in a corotron or scorotron (screen type or slit type scorotron),
In the case of corotron it is 100% effective.

In the corotron 90, the presence of conductors 92 and 93 allows a wide distribution of the corona or ions to the charge receptors. Typically, in an electrophotographic copier employing a wire/conductor type corotron, less than 15% of the ions travel to the charge acceptor. In contrast, conductors 92 and 93 as depicted in FIG. This reduces the probability of occurrence. Conductors 92 and 93 are placed at suitable locations to draw barely detectable currents. This current verifies that all subsequent current from ribbon 91 is flowing into the charge receptor.

FIG. 3 shows another embodiment of the charging device of the present invention, which includes a wedge-shaped ribbon corona electrode 301 flanked by ground electrodes 302 and 303. The wedge-shaped ribbon corona electrode 301 tapers at an approximately 40 degree slope and is coupled to a high voltage power source 304 . This structure of the corona electrode is far more advantageous than the wire type in that it does not suffer from problems such as vibration noise and movement that are likely to occur with a normal wire type corona electrode, and its positioning can be performed extremely accurately. Furthermore, the corona electrode can be extended to the mating connector of the high voltage power supply of the printing press. In other words, the wedge, that is, the thick wedge-shaped boss, has the same strength as a connector. This reduces the number of parts and assembly time of the charging unit, thus lowering manufacturing costs and increasing the strength of the unit.

FIG. 4 shows the uniformity of the charge distribution obtained by the charge receptor using the charging unit. Here, the processing speeds are 6, 12, and 24 inches/second when the distance is 8 inches, and the fluctuation range of the surface potential difference is plus or minus 21/2% at a processing speed of 12 inches/second. and comparable to a typical corotron with a conductive shielding device.

A novel charging device is disclosed in which the corona electrode includes a small active area conductive strip which may take the form of a wedge and has electrodes placed opposite the conductive strip. It is now clear that the charge receptors are arranged vertically (or perpendicularly to the charge receptor surface). This arrangement is particularly important, as it results in the field lines being distributed in such a way that maximum charge is delivered to the charge receptors while minimizing arcing.

Although the present invention has been described with reference to the structure disclosed herein, the present invention is not limited to the details detailed above, but includes modifications and variations that fall within the scope of the claims. .

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of an electrophotographic copying machine that adopts the idea that characterizes the present invention.

FIG. 2 is a side view of the charging device of FIG. 1, and is a diagram showing that the present invention is used in the charging device.

FIG. 3 is another embodiment of the charging device according to the invention.

FIG. 4 is a graph representing the charge uniformity obtained with a charging device according to the invention for various processing distances and processing speeds;

[Explanation of symbols]

10 belt, 15 document handling unit,
16 Manuscript document, 18 Platen, 30 Corona generator, 90 Corotron, 91 Ribbon-shaped electrode, 92 Ground electrode, 93 Ground electrode

Claims (4)

[Claims] 1. A charging device for uniformly applying a charge to a charging surface, comprising: a corona generating means in the form of a strip placed vertically so that a small diameter portion appears on the surface to be charged; , electrode means placed on opposite sides of said conductive strip, connected to said corona generating means and applying a voltage sufficient to cause corona ions to be emitted from said corona generating means towards the surface to be charged. and a high voltage generating means for applying a high voltage to the electrode means to generate an electric field from the conductive strip in such a manner as to provide maximum charge to the surface to be charged while minimizing the occurrence of arc discharge. A charging device characterized by adjusting the distribution of lines of force. 2. The charging device of claim 1, wherein the conductive strip has a thickness of about 1 to 20 mils. 3. The charging device of claim 1, wherein the conductive strip has a thickness of about 2 to 3 mils. 4. The charging device of claim 1, wherein said conductive strip is wedge-shaped to provide a relatively robust corona charging device.