JPS6249625B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic copying machine, and more particularly to an improvement in a charging device.

In electronic copying machines, it is well known that a photoreceptor is charged with a charging device before a document image is exposed to light. Conventionally, the above-mentioned charging device employs corona charging by corona discharge, or contact charging by pressing a conductive brush or charging roller against the photoreceptor. The above-mentioned corona charging has the advantage of simple structure and stable performance, but from 5KV to
Since it uses a high-voltage power source of 10KV, it has safety issues and is not economical. Another disadvantage is that ozone is generated during corona discharge, and this ozone significantly deteriorates the properties of the photoreceptor, developer, and other materials. In addition, contact charging means requires only a small power source of 0.5KV to 1KV, and since there is no corona discharge, no ozone is generated. However, in this case, there is a drawback that it is difficult to obtain continuous and uniform charging, and the reliability is low.
In other words, in the conventional contact charging method, the voltage necessary for charging the photoreceptor is applied in a pulsed manner in one step, and the maximum voltage is applied at the point where the photoreceptor starts contacting the conductive brush or charging roller. I end up. For this reason, the applied voltage changes rapidly at the point of contact with the photoreceptor, the charge on the photoreceptor is not uniform, and the photoreceptor is likely to be electrically damaged.

The present invention has been made in view of the above-mentioned circumstances, and its object is to bring a plurality of contact band electrons into contact with a photoreceptor and apply different voltages to them from a power supply means. It is an object of the present invention to provide a charging device for an electronic copying machine that can continuously obtain uniform charging performance, has high safety, and is economical.

An electronic copying machine suitable for employing the apparatus of the present invention will be described below with reference to FIG. A document placement table 2 is provided on the top surface of the main body 1, and this
It is designed to reciprocate by a drive motor 3 disposed inside. A drum-shaped zinc oxide-resin dispersant photoreceptor 4 that rotates synchronously with the original document mounting table 2 is pivotally supported approximately at the center of the main body 1 . Photoreceptor 4
An exposure system 7 consisting of a lamp 5, an optical fiber lens 6, etc. is provided between the document table 2 and the original table 2.
The document placed on the document table 2 is irradiated with light, and the reflected light is guided to the photoreceptor 4 to form an image of the document. A developing device 8, a transfer device 9, a cleaning device 10, and a charging device 11, which will be described later, are arranged in this order along the rotational direction of the photoreceptor 4 from this image forming position.
The developing device 8 visualizes the latent image of the document formed on the surface of the photoreceptor 4 by the action of the exposure system 7. The transfer device 9 is for transferring the original toner image formed on the photoconductor 4 onto the copy paper P, and the cleaning device 10 is for removing toner remaining on the surface of the photoconductor 4. At the bottom of the main body 1 is a removable cassette 12 for storing copy paper P.
A paper feeding device 14 is provided, which includes a paper feeding roller 13 for feeding the copy paper P. This paper feeding device 14, the transfer device 9, and a tray 15 protruding from the side of the main body 1 opposite to the paper feeding device are communicated by a conveyance path 16 made of rollers and guide plates. Therefore, the conveyance path 16 carries the copy paper P fed from the paper feed device 14.
is guided between the transfer device 9 and the photoreceptor 4 to transfer the copy paper P.
The original image is transferred onto the tray 15 and then discharged onto the tray 15. A fixing device 17 is arranged opposite to a conveyance path 16 between the transfer device 9 and the tray 15. This fixing device 17 fixes the original image formed on the copy paper P.

Next, the charging device 11 will be explained. As shown in FIG.
and a third charging roller 22, and a power supply means 24 that applies different voltages to the first to third charging rollers 21, 22, and 23, respectively. The charging rollers 21, 22, and 23 are all electrically conductive rollers of the same diameter made of foamed urethane rubber material, for example, and have a certain contact width with the peripheral wall of the photoreceptor 4, and are spaced at predetermined intervals along the rotational direction. It exists and transfers. Furthermore, each roller 21, 22,
23 is connected to a drive mechanism 25 consisting of a gear pulley, a belt, etc., so that the drive mechanism 25 rotates in the same direction. In addition, each roller 21, 22, 23
There is a removable substrate 27 constituting the cleaning means 26.
Brushes 28, 28, 28 provided on the rollers 21, 22, 23 are rubbed against each other to remove residual toner adhering to the rollers 21, 22, 23, respectively.

The power feeding means 24 is connected to each charging roller 2.
1, 22, 23 and are electrically connected to the respective rotating shafts 20a, 21a, 22a, power supply brushes 29a, which are provided in the electric circuit described later,
29b and 29c are in contact. FIG. 3 shows a power supply device 30 that applies voltage to the power supply brushes 29a, 29b, and 29c. That is, 31 is an iron resonant transformer, and 32 is a rectifier circuit having a diode 33a, a capacitor 33b, and the like. Therefore, the ferro-resonant transformer 31 applies the AC voltage applied to the input terminals 34 and 35 to the output terminal 37 and the rectifier circuit 32,
This is adapted to apply a transformed AC power to the output terminal 37.

The output terminal 37 is electrically connected to the first to third charging rollers 20, 21, 22 as shown in FIG. That is, the output terminal 37 is grounded via a plurality of resistors 38, 39, 40, 36, and the power supply brushes 29a, 29b,
Connect to 29c.

By electrically connecting in this way, the first to third charging rollers 20, 21, 22 are connected to the fifth charging roller.
A potential as shown in the figure is applied. That is, the first
The charging roller 20 has a potential of about 200V, the second charging roller 21 has a potential of about 350V, and the third charging roller 22 has a potential of about 500V. Moreover, each of these potentials is superimposed with a DC voltage and an AC voltage component whose peak-to-peak value is about 20% or less with respect to the DC voltage.

Taking the third charging roller 22 as an example, the sixth
As shown in the figure, the DC component is approximately 500V and the AC component is approximately 80V.
will be superimposed. According to the experimental results, if the AC voltage exceeds 100V, the photoconductor 4 becomes overcharged.
It was shown that a fatigue phenomenon appeared when the voltage was lower than 50V, and that it was not effective in recovering from fatigue due to continuous use. Therefore, the optimum range of the alternating current to be superimposed is about 80V to about 100V.

Note that the seventh characteristic of the iron resonant transformer 31 is
As shown in the figure, the predetermined voltage is temporarily exceeded immediately after input, and the predetermined voltage is maintained after about 500 ms. In other words, the rise of the output takes approximately
Since it takes 500 ms, there is a risk that a stable potential may not be applied to a part of the photoreceptor 4, so timing control is carried out so that no image is placed on this part.

As shown in FIG. 8, the charging device 11 has first, second, and third charging rollers 20, 21, and 22 that sequentially roll into contact with the photoreceptor 4 along the traveling direction of the photoreceptor ₄ . Apply higher voltages in sequence: 2V ₀ and 3V ₀ . If these voltages are graphed, they will show a linear upward slope, and in the end the potential will be the same as before.
In contrast, conventionally, as shown in FIG. 9, a single electric device instantly rises and applies a predetermined potential, resulting in one-step charging.

By placing an original on the original placing table 2 and pressing a copy button (not shown), each device performs the above-described operations, and the copy paper P on which the original copy image has been obtained is ejected onto the tray 15. In the charging device 11, as the photoreceptor 4 rotates, the drive mechanism 25
operates to charge the first, second and third charging rollers 20,
21 and 22 are rotated in the opposite direction to the photoreceptor 4 and at a slightly slower circumferential speed. Therefore, the rollers 20, 21, 22 will come into frictional contact with the photoreceptor 4, but it is possible to make uniform contact, and in the unlikely event that a part of the rollers 20, 21, 22 has a defect (such as staining with toner). can be sufficiently compensated for in other areas. At the same time, each roller 20, 2 is connected to the power supply device 30.
1 and 22 are applied with a voltage in which alternating current is superimposed on direct current, and higher voltages are applied in order. Therefore, the photoreceptor 4 is sequentially charged as it rotates, and the third charging roller 2
2, the necessary charging can be obtained without excessive current flowing. By superimposing alternating current on direct current, the effect of space charges generated on the photoreceptor 4 can be prevented and sufficient charging can be achieved in a short time.
All residual toner adhering to each roller 20, 21, 22 is scraped off by brushes 28, 28, 28, thereby preventing charging failure and eliminating the risk of changing electrical resistance.

In the above embodiment, the first, second, and third charging rollers 20, 21, and 22 each have an AC voltage superimposed on a DC voltage, but the present invention is not limited to this, and as shown in FIG. The first and second charging rollers 20 and 21 may apply a DC voltage, and only the third charging roller 22 may have an AC voltage of 20% superimposed on the DC voltage. In this case, a power supply device 30a as shown in FIG. 11 is provided, which is composed of an iron resonant transformer 31a, a rectifier circuit 32a, and a voltage dividing circuit 38 having a resistor. 34a and 35a are input terminals, and 39, 40, and 41 are output terminals. Although not shown, the output terminal 39 is connected to the first charging roller 2
0, the output terminal 40 is connected to the second charging roller 21,
The output terminals 41 are electrically connected to the third charging roller 22, respectively. In both this case and the above embodiments, it is effective for the alternating current to range from 200 to 600 Hz.

Note that in the above embodiment, each charging roller 20,
Although 21 and 22 are rotated at a circumferential speed slightly slower than the circumferential speed of the photoreceptor 4, the present invention is not limited to this, and for example, they may be rotated at the same circumferential speed. In this case, it rolls into contact with the photoreceptor 4 and there is no friction. Therefore, even when the surface of the photoreceptor 4 is relatively soft, such as a selenium photoreceptor, it is less likely to be scratched, which is advantageous.

Note that the drive mechanism 25 for rotationally driving the first, second, and third charging rollers 20, 21, and 22 in the above embodiment is not necessarily necessary, and the drive mechanism 25 for rotating each of the rollers 20, 21, and 22 on the photoreceptor 4 is not necessarily required. Press the
A secondary rotation may be performed along with this rotation. In this case, since there is no drive mechanism, the structure is simple and costs can be reduced, and the roller contacts the photoreceptor 4 by rolling so that the surface thereof is not damaged.

Further, although the photoreceptor 4 is formed into a drum shape, it may be formed into a flat plate shape.

In the above embodiment, the first, second and third charging rollers 20, 21, 22 are used as the contact band electrons.
applied, but is not limited to
It may be arranged as shown in FIGS. 12 to 14. That is, FIG. 12 shows an electronic copying machine equipped with a charging device 50, and the same parts as in the above embodiment are given the same numbers and the explanation will be omitted. Figures 13 and 14
The figure shows a contact charging section 5 used in the charging device 50.
1 is shown. This contact charging section 51 connects mounting flanges 52a, 52a provided on a case 52 made of aluminum, for example, to grooves 53a, 5 of a support frame 53.
3a so that it can be inserted and removed freely. The case 52 has a substantially U-shaped cross section, and a handle 54 is integrally provided at one end thereof, and a power receiving piece 58 having input terminals 55, 56, and 57 is protruded from the other end. The case 52 is filled with a first rubber gasket 59 and a second rubber gasket 60 that are fitted into each other. These rubber gaskets 5
First, second and third charging brushes 61, 62 and 63, which are contact band electrons, are attached to 9 and 60. These charging brushes 61, 62, and 63 are conductive and made of, for example, carbon fiber (trade name: Trading Card), and are spaced apart at predetermined intervals in the rotational direction of the photoconductor 4, and their bristles are attached to the photoconductor 4. contact with the peripheral wall along the axial direction. Furthermore, they are tilted in the direction of rotation of the photoreceptor 4, and their contact area with each other is large. The end portions of the charging brushes 61, 62, 63 on the side of the first rubber packing 59 are bound by fittings 64, 64, 64 made of conductive material, respectively.
They are electrically connected to the input terminals 55, 56, and 57, respectively. In addition, each charging brush 61, 62, 6
3 is held between both sides by insulating thin plates 65, 65, which are holding plates, over the insertion portion of the second rubber packing 60 and a portion of the protruding portion thereof.
This insulating thin plate 65 has a thickness of about 20 μm, is about 1.5 mm shorter than the bristles of the charging brushes 61, 62, and 63, and is made of a resin such as Mylar (trade name).

The main body 1 is provided with a power feeding section (not shown), and when the case 52 is inserted into the support frame 53 by holding the handle 54, the power receiving piece 5
8 is located at the power feeding section. That is, input terminal 5
5, 56, and 57 are electrically connected to a power supply device 30a as shown in FIG. 11, for example. When a copying operation is performed in this state, the first, second, and third charging brushes 61, 62, and 63 apply higher voltages in order as the photoreceptor 4 rotates. Specifically, if the same amount of voltage as in the above embodiment is applied, the same effect can be obtained. In addition, each charging brush 61, 62, 6
Since the bristles 3 are inclined in the direction of rotation of the photoreceptor 4, a sufficient contact area can be obtained even if the lengths are uneven, and the rigidity of the brush ensures sliding contact with the photoreceptor 4. And since it is a brush, even if some of the bristles are defective (broken, bent, etc.), other bristles can compensate for this. Furthermore, the carbon fibers forming the charging brushes 61, 62, and 63 have stable electrical resistance, do not vary from lot to lot, and have strong resilience against repeated bending.

During such a charging action, the insulating thin plates 65, 65 hold the charging brushes 61, 62, 63 from both sides with a certain degree of rigidity, thereby preventing bending and the like, and also preventing the brushes from shooting each other. It can be prevented.

Each time a predetermined number of copies are made or a predetermined period of time elapses, the operator pulls out the case 52 from the main body 1 by holding the handle 54 and attaches it to the first, second, and third charging brushes 61, 62, and 63. It is a good idea to remove toner etc.

Further, in this embodiment, input terminals 55, 56, and 57 are provided on the power receiving piece 58, and these are electrically connected to the first, second, and third charging brushes 61, 62, and 63, respectively. The present invention is not limited to this, and the second rubber gasket 60 may be replaced with a conductive rubber material. In this case, the conductive rubber acts as a resistor interposed between the input terminals, and the power supply device 30 or 30a can be simplified. That is, by inputting a predetermined amount of a predetermined voltage to the first charging brush 61, each brush 6
2 and 63 are sequentially supplied with a predetermined voltage that decreases in voltage, the charging voltage difference becomes about 150 V, and when the current flowing into the photoreceptor 4 is about 15 μA, each resistance value becomes about 10 MΩ.

Further, in this embodiment, the first, second, and third charging brushes 61, 62, and 63 were used as contact band electrons, but the invention is not limited to this, and conductive rubber blades as shown in FIG. A plurality of contact band electrons consisting of 66 may be used. In this case, the conductive rubber blade 66 is held by replacing the charging brushes 61, 62, 63 shown in FIGS. 13 and 14 with the conductive rubber blade 66. The advantage of the conductive rubber blade 66 is that desired rigidity can be freely obtained by selecting the hardness and thickness of the material, and it can be provided at a low cost.

The end of the conductive rubber blade 66 is tilted in the forward direction of the rotational direction of the photoreceptor 4, and the second rubber gasket 60 is replaced with conductive rubber so as to act as a resistor. Needless to say, a modification similar to the case using a brush can be applied.

In addition, according to the above embodiment, since the contact band electrons are rollers, the width of contact with the photoreceptor can be made small, and friction can be suppressed to improve the durability of the photoreceptor.
Further, since the contact band consisting of the roller is cleaned by the cleaning means, the contact band is not contaminated with, for example, toner and its electrical resistance is not changed, thereby improving reliability.

As explained above, according to the present invention, since a plurality of contact band electrons are brought into contact with the photoreceptor and a voltage is applied to these contact band electrons via the power supply means, uniform and continuous charging is possible. At this time, no ozone is generated and safety is good. Furthermore, by using multiple contact band electrons, it is possible to optimally compensate for the characteristics of the photoreceptor, such as its sensitivity, inflow current/voltage, and fatigue characteristics, and to obtain stable charging performance even during continuous use. play.

In addition, the power feeding means applies a voltage in which the absolute value of the DC component increases sequentially to a plurality of contact band electrons that come into contact with the photoconductor in the rotating direction, so that the photoconductor is not charged like a conventional contact charging method. Therefore, the photoreceptor is protected from damage caused by the inflow of excessive current, and the required amount of charging can be performed.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal sectional view of an electronic copying machine showing an embodiment of the present invention, FIG. 2 is a perspective view of a charging device, FIG. 3 is an electric circuit diagram of a power supply device as a power supply means, and FIG. 4 is an electric circuit diagram of the power supply means, FIG. 5 is a waveform diagram thereof, FIG. 6 is a waveform diagram of only the power supply state to the third charging roller, FIG. 7 is a diagram showing the characteristics of the iron resonant transformer, and FIG. FIG. 9 is an explanatory diagram of a conventional power supply state, FIG. 10 is a waveform diagram of a power supply means showing another embodiment of the present invention, and FIG. 11 is an electric circuit diagram of a power supply device that is the power supply means. , FIG. 12 is a schematic vertical cross-sectional view of an electronic copying machine showing still another embodiment of the present invention, FIG. 13 is a perspective view of a contact charging section used in the charging device, and FIG. 14 is a vertical cross-sectional view thereof. , FIG. 15 is a longitudinal sectional view of a contact band electron showing still another embodiment. 4... Photoreceptor, 20, 21, 22... Contact band electron (first, second, third charging roller), 24...
Power feeding means, 26...Cleaning means.

Claims (1)

[Scope of Claims] 1. A plurality of contact band electrons in contact with a photoreceptor, and a power supply means for applying a voltage to these contact band electrons, the absolute value of which is a direct current component increasing sequentially in the direction of movement of the photoreceptor. A charging device for an electronic copying machine, characterized by comprising: 2. The charging device for an electronic copying machine according to claim 1, wherein each of the contact band electrons is a roller. 3. Claim 2, characterized in that the contact band consisting of the roller is cleaned by a cleaning means.
A charging device for an electronic copying machine as described in .