Patent Application
20050207778
1. Field of the Invention
This invention relates to an image forming apparatus which forms an image on a transfer material by use of an electrophotographic process, and a charger installed in this image forming apparatus.
2. Description of the Related Art
A corona discharge type fixing device installed in an image forming apparatus using an electrophotographic process is classified broadly into a wire electric discharge type (Corotron, Scorotron, etc.) or pin discharge type (pin electrode, sawtooth electrode, etc.).
In a method generally known, a cleaning member such as felt provided to wrap around a wire electrode is moved in a longitudinal direction (axial direction of a photoconductor drum) of a charger, as a means to clean the wire electric discharge type wire electrode.
Another method is known in which a cylindrical cleaning member provided movably along the sawtooth electrode is moved while being pressed against the edge of the sawtooth electrode, as a means to clean the pin discharge type sawtooth electrode (Jpn. Pat. Appln. KOKAI Publication No. 9-211940).
Still another method is known in which the sawtooth electrode is rotatably provided, and electric discharge products deposited on the edge of the sawtooth electrode are scraped against the cleaning member (Jpn. Pat. Appln. KOKAI Publication No. 11-327265).
Furthermore, apparatuses or methods are known in which a driving force generator such as a motor is used to automatically clean the electrode of the charger (Jpn. Pat. Appln. KOKAI Publication No. 6-194934, Jpn. Pat. Appln. KOKAI Publication No. 7-49606, U.S. Pat. No. 3,842,273).
However, the abovementioned method using the cylindrical cleaning member in which cleaning is achieved by the rolling and contacting of a roller has the disadvantage that the electric discharge products, toner, dust and the like deposited on the edge of the sawtooth electrode are not adequately removed because of insufficient cleaning power.
Moreover, the problem of the above-described method of cleaning the rotatably provided sawtooth electrode is that the edge of the sawtooth electrode warps and deforms when it contacts the cleaning member, and the cleaning power decreases as the cleaning is performed time and time again. Further, the warping and deforming of the sawtooth edge cause improper corona discharge and insufficient electric discharge to an image carrier.
According to an aspect of the present invention, there is provided a charger comprising:
According to another aspect of the present invention, there is provided a charger comprising:
According to further another aspect of the present invention, there is provided an image forming apparatus comprising:
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.
One example of a charger installed in an image forming apparatus to which embodiments of this invention are applied will hereinafter be described with reference to the drawings.
As shown in
The scanner 100 comprises an original table 101, an illumination lamp 103, a reflector 104, a first carriage 105, a first mirror 106, a second carriage 107, a second mirror 108, a third mirror 109, a lens 110, photoelectric transfer element (CCD sensor) 102 and an image processor 111.
The original table 101 is made of a light transmitting material, and holds a copy target (original) P which is a solid body such as a book or a sheet-shaped original.
The illumination lamp 103 irradiates light from under the original table 101.
The reflector 104 condenses the light emitted by the illumination lamp 103 at a predetermined position of the original table 101.
The illumination lamp 103 and the reflector 104 are fixed to the first carriage 105, and the first carriage 105 moves back and forth along a surface of the original table 101.
The first mirror 106 guides, into a predetermined direction (the second carriage 107), a reflected light from the original P illuminated by an illumination light from the illumination lamp 103 and the reflector 104, that is, image information on the original P. The reflected light from the original P will hereinafter be referred to as an image light, for description.
The second carriage 107 moves the second mirror 108 and the third mirror 109 held by the second carriage 107 along the surface of the original table 101 in conjunction with the first carriage 105.
The second mirror 108 bends the image light reflected by the first mirror 106 at 90°, and guides it to the third mirror 109.
The third mirror 109 bends the image light reflected by the second mirror 108 at 90°, and guides it to the lens 110.
The lens 110 gives a predetermined image formation magnification to the guided image light, and forms an image on the CCD sensor 102 disposed at a focal position of the lens 110.
The CCD sensor 102 converts the image information (image light) concerning the original P into an electrical signal, and outputs the first image signal.
The image processor 111 subjects the first image signal output by the CCD sensor 102 to predetermined image processing, and outputs the image information as the second image signal.
The image forming section 120 comprises a charger 1, an exposure device 122, a photoconductor drum 2, a development device 3, a sheet cassette 125, a pickup roller 126, a conveying path 127, an aligning roller 128, a transfer device 129, a fixing device 130, a delivery roller 131, a tray 132 and a cleaning device 4.
The charger 1 discharges electricity at a predetermined discharge position, and supplies a predetermined electric charge to an outer peripheral surface of the photoconductor drum 2.
The exposure device 122 outputs a laser beam whose light intensity is changed, on the basis of the second image signal output by the image processor 111. This laser beam is incident on the outer peripheral surface of the photoconductor drum 2 which is charged with a predetermined potential in an axial direction by the charger 1.
The photoconductor drum 2 is irradiated with the laser beam and holds an electrostatic image corresponding to the image of the original P, that is, an electrostatic latent image.
The development device 3 provides a developer (e.g., toner) to the photoconductor drum 2 that rotates in a direction of an arrow A, and the unshown electrostatic latent image is converted into a toner image.
The sheet cassette 125 contains paper Q.
The pickup roller 126 takes out the paper Q one by one from the sheet cassette 125, and guides it to the conveying path 127.
The conveying path 127 has a plurality of rollers, and guides the paper Q to the photoconductor drum 2.
The aligning roller 128 once stops the paper Q guided by the conveying path 127 to align the unshown toner image with a position on the paper Q on which the toner image is to be transferred, and then conveys the paper Q to the photoconductor drum 2 with predetermined timing.
The transfer device 129 electrostatically transfers the toner image onto the paper Q at a transfer position opposite to the photoconductor drum 2, that is, at a predetermined position on a downstream side of a rotation direction of the development device 3.
The fixing device 130 secures or fixes the unshown toner image, which has been transferred onto the paper Q, to the paper Q.
The delivery roller 131 discharges, to the image output media holder (tray) 132, the paper Q on which the unshown toner image has been fixed by the fixing device 130, that is, an image corresponding to the image information on the original P is formed.
The tray 132 is located in a space defined between the scanner 100 and the sheet cassette 125.
The cleaning device 4 is located downstream of the rotation direction of the photoconductor drum 2 from the transfer position and upstream from the discharge position, and removes the remaining toner, which has not been transferred, from the surface of the photoconductor drum 2.
In addition, the charger 1, the photoconductor drum 2, the development device 3 and the cleaning device 4 are provided as one unit (process unit) in the image forming section 120.
When instructed to read or form the image of the original P, the scanner 100 outputs the first image signal based on the original P to the image processor 111. The image processor 111 outputs the second image signal to the exposure device 122. The exposure device 122 applies the laser beam to the photoconductor drum 2, and forms an electrostatic image. The electrostatic image is converted into a toner image by the development device 3. The toner image is transferred onto the paper Q by the transfer device 129. The fixing device 130 fixes the toner to the paper Q, that is, the image of the original P is formed on the paper Q.
As shown in
The charger 1 discharges electricity at the predetermined discharge position, and supplies the predetermined electric charge to the outer peripheral surface of the photoconductor drum 2.
The photoconductor drum 2 is given a predetermined potential by the charger 1 and irradiated with the laser beam whose intensity is modulated in accordance with the image information from the exposure device 122, thereby retaining an electrostatic latent image corresponding to the image to be copied.
The development device 3 provides the developer (e.g., toner) to the photoconductor drum 2, and the electrostatic latent image formed on the photoconductor drum 2 is converted into a toner image. This toner image is transferred, by an electric field provided from the transfer device 129, onto transfer paper conveyed almost vertically from under the process unit. The toner image transferred onto the transfer paper is conveyed to the fixing device 130 where the toner is melted and fixed to the transfer paper.
The cleaning device 4 is located downstream of the rotation direction of the photoconductor drum 2 from the transfer position and upstream from the discharge position, and removes the remaining toner, which has not been transferred, from the surface of the photoconductor drum 2.
As shown in
As shown in
The support members 12 and 13 are respectively fixed at both ends of the shield plate 11 in a predetermined manner (e.g., by screws). In addition, the support members 12 and 13 are preferably made of an insulating material.
The electrode 14 is made of a conductive material, for example, stainless steel having a predetermined length in the axial direction, that is, longitudinal direction (lateral direction) of the photoconductor drum 2, and has a shape in which a plurality of charging needles 14a is formed on one side as shown in
In addition, the charging needle preferably has a sharper edge for more efficient electric discharge. However, as in the present embodiment, the charging needle 14a has a certain degree of curvature at the edge to reduce manufacturing labor and deterioration of the charging needles 14a due to the electric discharge, thereby ensuring a longer life. Therefore, in the present invention, a plurality of charging needles having an acute angle may be formed in the electrode.
The electrode 14 is disposed at a predetermined position by protrusions 12a, 12b and 13a (see
The electrode cleaning device 20 is usually located at one end of the electrode 14, for example, on the side of the holding member 12 so as not to affect the electric discharge to the photoconductor drum 2 (see
In addition, the holding members 12 and 13 and the fixing plate 17 are made of an insulating resin, for example, polypropylene (PP) resin in the present embodiment.
As shown in
The plate 21 is made of the insulating resin, for example, polypropylene (PP) resin, and has such a shape as to be able to move the shield plate 11 in the longitudinal direction without contacting the electrode 14. More specifically, the plate 21 has a locking portion 21a protruding from the upper opening 11A, and the hooked plate 21 can move in the upper opening 11A in the longitudinal direction sliding along the shield plate 11.
The cleaning sheet 22 is a film-like elastic sheet made of polyester, polyimide, polyamide or the like as represented by a Mylar sheet (trademark) or Kapton sheet (trademark), and is held at a predetermined position of the plate 21. In other words, the cleaning sheet 22 has a hardness lower than that of the electrode 14 made of stainless steel. The cleaning sheet 22 is positioned by protrusions 21b, and adhesively bonded to the plate 21, for example, via double-sided tape. In addition, the protrusions 21b can be melted to prevent the cleaning sheet 22 from being peeled from the plate 21.
More specifically, the cleaning sheet 22 has a thickness ranging from 10 to 100 μm, and preferably 25 to 75 μm. In the present embodiment, the cleaning sheet having a thickness of 50 μm is used. Further, an abrasive may be applied to the surface of the cleaning sheet 22. This makes it possible to more effectively remove the electric discharge products and the like deposited on the electrode 14.
For example, silicon carbide, silicon nitride, cerium oxide, ferric oxide, chromic oxide and alumina can be used as the abrasive, and the particle diameter is 0.01 to 2 μm, preferably 0.01 to 1 μm.
The cleaning sheet 22 includes a first sheet portion 22a fixed to the plate 21, and a second sheet portion 22b that is moved to contact the electrode 14, as described above.
The second sheet portion 22b has such a shape as to be able to contact the side of the electrode 14 where the charging needles 14a are formed with a predetermined amount X (hereinafter referred to as an encroaching amount), and the second sheet portion 22b deforms due to a cut portion 22c formed between the second sheet portion 22b and the first sheet portion 22a, as the contacting electrode 14 moves, that is, as a predetermined stress is provided (see
It should be noted that the encroaching amount X is the amount in design in which the cleaning sheet 22 overlaps the edge of the charging needles 14a of the electrode 14 in an undeformed state in a sectional view, as shown in
Furthermore, the second sheet portion 22b of the cleaning sheet 22 has a second plane including a straight line in a direction of an arrow P (see
The moving bar 23 has a predetermined length in a longitudinal direction of the charger 1, and one end of which is fixed by the locking portion 21a of the plate 21, while the other end is utilized as a drawing portion for a user to draw the moving bar 23 from a front side of the apparatus. In addition, the present embodiment concerns a manual type in which movement force of the electrode cleaning mechanism 20 is provided by the user, and the moving bar 23 may be modified in accordance with the apparatus as long as it is placed at a position where the user can operate.
The holding plate 24 is disposed outside the shield plate 11, and serves as a shield plate to regulate an area where the electrode 14 discharges electricity so that the electric discharge does not influence circuits or the like disposed in the proximity thereof. In addition, the holding plate 24 may have a configuration such that deposits such as the toner, dust and waste thread removed by the electrode cleaning device 20 can be stored.
It should be noted that in the present embodiment, the charger is obliquely disposed (see
Next, an operation of the electrode cleaning mechanism 20 will be described.
As shown in
Continuously, the moving bar 23 is moved in an arrow B direction, so as to place the cleaning sheet 22 at the home position HP. Accordingly, the cleaning sheet 22 moved in the arrow A direction contacts the charging needles 14a, and stuck contamination is further cleaned.
More specifically, an image to be copied including a blank image and a halftone image is obtained by, for example, the scanner 120, and the exposure device 122 is used to form the electrostatic latent image, corresponding to the image to be copied, on the surface of the photoconductor drum 2, and then the image is fixed on the transfer paper as described above with reference to
It should be noted that the image forming apparatus equipped with the charger that supplies a current of about 700 μA to 500 μA has been used in the present embodiment, but because this current value varies depending upon the apparatus in which the charger is used, a current of 300 μA to 900 μA has been experimentally used.
For example, the same current is supplied to the charger and the same number of electrostatic latent images of the same image is formed on the photoconductor drum, thereby preparing, as the samples, the electrodes 14 having the same degree of contamination such as the electric discharge products, dust and toner deposited on the charging needles 14a. For example, the samples used include (1) a sample 1 as the electrode which is not cleaned and has contamination stuck thereto, (2) a sample 2 as the electrode having the charging needles cleaned in a conventional cleaning method, and (3) a sample 3 as the electrode having the charging needles cleaned by use of the electrode cleaning mechanism 20 of the present invention.
As shown in
Furthermore, when heavier contamination is stuck and a copied image has unevenness or the like even though the cleaning has been performed, the cleaning can naturally be performed again by again moving the moving bar 23.
As described above, according to the first embodiment of the present invention, the film-like elastic sheet is used as the cleaning sheet, and the film-like elastic sheet is provided in such a manner that it can deform in accordance with movement, so that the edge of the charging needles of the electrode can be prevented from being damaged or buckling, and adequate cleaning effects can be obtained.
Next, the charger to which the second embodiment is applied will be described.
As shown in
The electrode cleaning mechanism 30 includes the plate 21 and the cleaning sheet 22 that constitute the electrode cleaning mechanism 20 described above, and additionally has a moving mechanism 31 which holds the plate 21 and can move the plate 21 with an electrical signal. It is to be noted that the same components as in the first embodiment have the same functions in the present embodiment, and will not be described.
The moving mechanism 31 includes a configuration to move the plate 21 in the longitudinal direction (arrow A, B directions) of the electrode 14, for example, a conveying means 31A in a shape of a wire, rail or belt to fix the plate 21 at a predetermined position, a motor 31M which provides power to the conveying means 31A, and an electrode cleaning mechanism position detecting sensor 31B for detecting the position of the plate 21 moved by the moving mechanism 31.
When the conveying means 31A is provided with power by the motor 31M, the plate 21 which has been positioned at the home position is moved in the arrow A direction, and the cleaning sheet 22 is also moved in the arrow A direction contacting the electrode 14. The electrode cleaning mechanism position detecting sensor 31B is located, for example, at one end of the movement direction (arrow A, B directions) of the plate 21, and detects a sensor 31C provided on a home position side of the conveying means 31A, for example, when the plate 21 is not moved, thus informing a printer CPU 420, which will be described later, that the cleaning sheet 22 has been moved from end to end in the longitudinal direction of the electrode 14. In this way, the printer CPU 420 instructs a drive circuit 424 so that predetermined power to move the plate 21 in the arrow B direction will be provided from the motor 31M to the conveying means 31A. Accordingly, the cleaning sheet 22 is moved in the arrow B direction contacting the electrode 14, and placed at an initial position (home position).
As shown in
The main CPU 410 totally controls parts of the image forming apparatus.
The printer CPU 420 totally controls parts of the image forming section 120.
The control panel 430 comprises an operation portion 431, and communicates instructions from the user to the main CPU 410 and the printer CPU 420.
When instructed to form an image from the operation portion 431 by the user, the printer CPU 420 outputs a charging signal for the plurality of charging needles 14a of the electrode 14 to start discharging electricity.
The main CPU 410 outputs a high-voltage generating signal when the charging signal is input from the printer CPU 420.
Moreover, when instructed to remove the deposits, the printer CPU 420 outputs a drive signal to drive the drive circuit 424 with predetermined timing.
The main CPU 410 is connected to the high-voltage generating mechanism 411 and a main motor 412.
The high-voltage generating mechanism 411 is connected to an electric power supply section (not shown) which supplies electric power to operate the image forming apparatus, and supplied with predetermined electric power. When the high-voltage generating signal is input from the main CPU 410, the high-voltage generating mechanism 411 generates high-voltage electric power required for the electric discharge of the electrode 14 to charge the photoconductor drum 2 with a predetermined potential, and supplies electric power to the supply portion 18 connected to the electrode 14.
The main motor 412 operates parts included in the scanner 100, the image forming section 120 and the like, for example, the first and second carriages 105 and 107 or the photoconductor drum 2.
The printer CPU 420 is connected to a ROM 421, a RAM 422, a counter 423 and the drive circuit 424.
The counter 423 counts the number of output media (paper Q) on which the image has been formed in the image forming section 120, and informs the printer CPU 420 of the number.
The ROM 421 stores a program to totally control the parts of the image forming section 120, and a dedicated program to control the electric discharge of the electrode 14 or to control the motor 31M. Further, in the present embodiment, the ROM 421 stores such a program that when a number NQ1 of output media counted by the counter 423 reaches a print stipulated value NQ2 (e.g., 1000 sheets) which might cause an unsatisfactory image to be formed, the printer CPU 420 outputs the drive signal.
The RAM 422 has a work area necessary for the printer CPU 420 to perform a predetermined processing operation.
The drive signal is input to the drive circuit 424 from the printer CPU 420, and the drive circuit 424 operates the motor 31M connected thereto.
Next, operation of the electrode cleaning mechanism 30 will be described.
As shown in
When the counted number NQ1 of output media is 1000 or more (S1—YES), the printer CPU 420 continuously monitors a motor drive signal of an unshown motor driver circuit, and judges whether or not the main motor 412 is operating (S2). When the main motor 412 is not operating (S2—NO), the drive signal is output (S3).
When the drive signal is input to the drive circuit 424, the motor 31M is driven as described above, and the cleaning sheet 22 moves back and forth in the directions of arrows A and B, and then the deposits are shaken off by contact or vibration and impact, and removed.
In addition, when the main motor 412 is operating, that is the time when both or one of the scanner 100 and the image reading section 120 are/is operating. Therefore, when the image forming section 120 is forming an image, that is, when the toner image is being formed on the photoconductor drum 2, there is no possibility that the deposits are shaken off on the surface of the photoconductor drum 2. Moreover, when the scanner 100 is operating, the vibration generated by the motor 31M is transmitted, so that there is no possibility of trouble caused to a reading operation.
Furthermore, it has been described in the present embodiment that the time to operate the drive circuit 424 of the electrode cleaning mechanism 30 is when the number of output media becomes a predetermined number or more, to which the present invention is not limited, and this time may be when an instruction is given from the control panel 430 (operation portion 431).
