EP0578190A2

EP0578190A2 - Developing device for use in image forming apparatus

Info

Publication number: EP0578190A2
Application number: EP93110760A
Authority: EP
Inventors: Takayuki Konica Corporation Miyamoto
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 1992-07-08
Filing date: 1993-07-06
Publication date: 1994-01-12
Also published as: JP3094255B2; JPH0627795A; EP0578190A3

Abstract

A developing device (6) of an image forming machine, by which an electrostatic latent image formed on an image carrier (3) is developed with toner. The developing device (6) includes at least one exhaust hole (30) formed in a portion of the housing of the developing device, and an air filter (31), provided in the air exhaust hole (30), to prevent the leakage of developer. In another embodiment the developing device comprises a developing sleeve (26) and at least one grove is provided in the surface of the housing facing the sleeve for preventing developer scattering. Developer scattering prevention members could also be provided to both sides of said housing. A developer layer forming member (28) is attracted by the magnetic force of a magnet in the sleeve to the sleeve (26) and said force is reduced when the gap between member (28) and the sleeve (26) is decreased.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a developer leakage preventing means for a developing device provided in an image forming apparatus such as a copier and printer.
In general, an electrophotographic image forming apparatus such as a copier and printer includes: a platen on which a document is set; an optical scanning system composed of a document illumination lamp reciprocating under the platen, reflection mirrors and a stationary projection lens; a rotational photoreceptor drum electrically charged by a charging electrode at a predetermined potential; a developing device to develop an electrostatic latent image formed on the surface of the photoreceptor drum, using toner; a transfer electrode to transfer the toner image onto a recording sheet conveyed toward a lower portion of the drum surface; a separation electrode and a discharge electrode; a fixing unit to fix the toner image transferred onto the surface of the recording paper; and a cleaning unit to remove residual toner and paper dust deposited on the photoreceptor surface.
A predetermined toner image is successively formed on a recording paper intermittently conveyed through a predetermined recording paper conveyance passage.
Fig. 4 is a sectional view showing a primary portion of the developing device 6. In the drawing, numeral 20 is a developing device frame forming a housing of the developing device 6, numeral 22 is a first stirring member, numeral 23 is a second stirring member, numeral 24 is a supply roller, numeral 26 is a developing sleeve, numeral 28 is a rigid cylindrical rod to regulate an amount of developer provided on the circumferential surface of the developing sleeve 26, the cylindrical rod 28 being a thin developer layer forming means, and numeral 28a is a spring plate to restrict an amount of developer, and the cylindrical rod 28 is always pressed against the developing sleeve 26 with a predetermined force by the spring plate 28a. Numeral 27 is a scraper to cut bristles of developer, numeral 25 is a stirring separation plate, and numeral 21 is an upper cover integrally provided on the upper surface of the developing device frame.
Toner is supplied into the developing device 6. The supplied toner is sufficiently mixed with carrier by the second stirring member 23 rotated in the arrowed direction and the first stirring member 22 rotated in an opposite direction to that of the second stirring member 23. In this manner, the toner and carrier are formed into developer D and sent to the developing sleeve 26 through the supply roller 24.
The first and second stirring members 22 and 23 are screw members rotated in the opposite direction to each other as shown by arrows in the drawing, and their spiral angles are formed counterclockwise with respect to the rotating direction. Toner and carrier are conveyed by the first stirring member 22 away from the viewer's side, and successively overflows the stirring separation plate 25, the upper edge of which is inclined downward in the direction opposite to the viewer's side, so that the toner and carrier are moved onto the side of the second stirring member 23. Then, the toner and carrier are conveyed to the viewer's side by the thrust generated by the second stirring member 23. While the toner and carrier are mixed in the aforementioned manner, they are triboelectrically charged and formed into uniform developer D. After that, developer D is deposited on the circumferential surface of the developing sleeve 26 rotated clockwise in the arrowed direction when the sponge-like supply roller 24 is rotated in the arrowed direction, whereby a layer of developer D is formed on the circumferential surface of the developing sleeve 26.
Then, the toner conveyed by the developing sleeve 26 is deposited on an electrostatic latent image formed on the circumferential surface of the photoreceptor drum located close to the developing sleeve 26 so that a predetermined gap is formed between the surface of the developing sleeve 26 and that of the photoreceptor drum 3. In this manner, the electrostatic image is developed. The first and second stirring members 22 and 23, supply roller 24, and developing sleeve 26 are respectively driven by a drive transmission mechanism provided on the side of the frame of the developing device 20.
Airborne toner particles inside the image forming apparatus are sucked through appropriately provided suction holes.
However, when the bristles of developer are cut by the scraper 27 disposed in a right upper diagonal position of the developing sleeve 26 as shown in Fig. 4, the developer is gradually accumulated, and finally developer clog D₁ shown in the drawing is formed in a relatively small space formed by the developing sleeve 26, scraper 27 and lower surface of the cover 21. When the developing sleeve 26 is rotated at high speed, an air flow is generated in the arrowed direction. When this air flow collides with developer clog D₁, convection is generated in an opposite direction. By the action of this convection, toner particles separated from developer clog D₁ and developer bristles that have been cut by the scraper 27 leak out from an opening 120 formed between the lower surface of the cover 21 and the circumferential surface of the developing sleeve 26. Therefore, toner particles are scattered inside the image forming apparatus in all directions. The airborne toner particles stain a developed toner image and affect the gears of the transmission mechanism.
Moreover, as shown in Fig. 6, a thin layer of developer D is formed on the circumferential surface of the developing sleeve 26 by the cylindrical rod 28 disposed in the lower jaw portion of the developing device frame 20. After that, bristles of developer D are formed again on the surface of the developing sleeve 26.
An air flow S is always generated between the lower circumferential surface of the developing sleeve 26 rotated clockwise at high speed and the upper surface 20b of the lower jaw portion opposed to the lower circumferential surface of the developing sleeve 26. Toner particles separated from bristles of developer D are scattered by the pressure of this air flow S. Therefore, the toner particles leak out from the developing device and scatter inside the image forming apparatus. As a result, the optical scanning system is stained and formed images are deteriorated. Moreover, the gears of the transmission mechanism are affected by the airborne toner particles.
Moreover, as shown in Fig. 6, a thin layer of developer D, the thickness of which is about 50 µm, is formed between the circumferential surface of the developing sleeve 26 and that of the cylindrical rod 28 that is a thin developer layer forming means. Therefore, a gap is necessarily formed outside the thin developer layer. Moreover, gaps are formed between both end portions of the cylindrical rod 28 and the developing device frame 20 that supports the end portions of the cylindrical rod 28. Accordingly, when the developing sleeve 26 is rotated at high speed, toner particles separated from developer D leak out and scatter from the developing device 6 through the aforementioned gaps. In order to solve those problems, a resilient member made of rubber or Moltopren is provided into the gaps formed between the end portions of the cylindrical rod 28 and the developing device frame 20. When a member made of Moltopren is used, it is pinched between the circumferential surface of the developing sleeve 26 and that of the cylindrical rod 28. When a member made of rubber is used, it is not slippery, and moreover the circumferential surface of the developing sleeve 26 and the side edge surface of the cylindrical rod 28 are pushed too strongly, which affects the operations of the developing sleeve 26 and the cylindrical rod 28, and a predetermined thin developer layer is not formed on the circumferential surface of the developing sleeve 26. The structure shown in Fig. 6 has the aforementioned disadvantages.
Moreover, the present invention relates to a developer scatter prevention means for a developing device provided in a color image forming means such as a copier and printer.
In general, a color image forming apparatus includes: a yellow toner developing device in which yellow toner is accommodated; a magenta developing device in which magenta toner is accommodated; a cyan developing device in which cyan toner is accommodated; a black developing unit in which black toner is accommodated, wherein the developing devices are provided around the photoreceptor drum that is an image carrier, and they are opposed to the circumferential surface of the photoreceptor drum forming a respectively predetermined gap. Yellow, magenta, cyan and black toners are successively superimposed on the electrostatic latent image formed on the circumferential surface of the photoreceptor drum so that a required color image can be formed.
As described above, the gap formed between the end portion of each of the yellow, magenta, cyan and black developing devices is determined according to the developing characteristics of each developing device.
In the process of development, toner leaks and scatters from the gaps formed on both sides of the end portion of each developing device opposed to the circumferential surface of the photoreceptor drum. The airborne toner particles stain the optical systems for image reading and image writing. Therefore, the gears of the drive mechanism are affected, and quality of formed color images is deteriorated.
Moreover, the present invention relates to a countermeasure to prevent the occurrence of scratches caused on the developing sleeve surface and further relates to a counter measure to prevent the occurrence of white spots on the image.
As described above, the cylindrical rod 28 that is a thin developer layer forming member is pressed against the developing sleeve 26 by the spring plate 28a. Therefore, when a gap is formed between the cylindrical rod 28 and the developing sleeve 26, resisting the resilient force of the spring plate 28a, the spring force applied to the cylindrical rod 28 is necessarily increased. In the conventional structure, the cylindrical rod 28 is rotated in accordance with the rotation of the developing sleeve 26, so that the cylindrical rod 28 is relatively strongly contacted with the circumferential surface of the developing sleeve 26 in order to form a thin developer layer, the thickness of which is 50 µm, on the developing sleeve. In the case where a foreign object such as a chip is included in developer D, it is pinched between the developing sleeve 26 and the cylindrical rod 28, and then a strong resilient force is applied to the chip when the cylindrical rod 28 is separated from the developing sleeve 26. As a result of the foregoing, the chip is strongly pressed against the developing sleeve 26, and the circumferential surface of the developing sleeve 26 is damaged, wherein a ring-shaped mark is formed on the circumferential surface. When the developing sleeve 26, the surface of which has been scratched, is used, a white stripe is formed on the image provided by the developing device. Therefore, the image quality is seriously deteriorated.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide a developing device from which developer is not leaked inside the image forming apparatus.
The second object of the present invention is to provide a developing device in which developer to be deposited on the developing sleeve is prevented from leaking from a lower portion of the developing device and scattering inside the image forming apparatus.
The third object of the present invention is to provide a developing device in which leakage of developer from both sides of the thin developer forming means (cylindrical rod) can be prevented.
The fourth object of the present invention is to provide a developing device in which toner particles are not scattered from both sides of the developing device opposed to the circumferential surface of the photoreceptor drum.
The fifth object of the present invention is to provide a developing device in which the developing sleeve is not scratched even when a foreign object is included in the developing device.
The objects of the present invention can be accomplished by the following embodiments (a), (b) and (c).

(a) In a developing device of an image forming apparatus in which developing is carried out when toner is deposited on an electrostatic latent image formed on an image carrier, an air exhaust hole is formed in a portion of the developing device frame that forms a housing of the developing device, and an air filter to prevent the leakage of developer is provided in the air exhaust hole.
(b) Furhter to the aforementioned item (a), the air exhaust hole is formed in the developing device frame opposed to the upper circumferential surface of the developing sleeve, or the air exhaust hole is formed on the upper cover of the developing device frame.
(c) Furhter to item (a), a narrow path is formed between the circumferential surface of the image carrier and the upper end portion of the developing device frame opposed to this circumferential surface, and the width of the narrow path is 3 mm.
The objects of the present invention are accomplished by either of the following embodiments (d) and (e).
(d) In a developing device of an image forming apparatus in which developing is carried out when toner is deposited on an electrostatic latent image formed on an image carrier, at least one developer scattering prevention groove to prevent the developer from scattering is provided on a surface of the developing device opposed to the circumferential surface of the developing sleeve pivotally supported by the developing device frame that is a housing of the developing device.
(e) Further to item (d), a narrow path is formed between the circumferential surface of the image carrier and the lower end portion of the developing device opposed to the circumferential surface of the image carrier, wherein the width of the narrow path is not more than 3 mm.
The objects of the present invention are accomplished by either of the following embodiments (f) and (g).
(f) In a developing device of an image forming apparatus in which developing is carried out by depositing toner on an electrostatic latent image formed on an image carrier, a thin developer layer forming means supported by the developing device frame is provided so that a thin developer layer is formed on the circumferential surface of the developing sleeve, and a developer leakage prevention member, one surface of which comes into pressure contact with the circumferential surface of the developing sleeve, and the other surface of which is slidably contacted with the side surface of the thin developer layer forming means, is provided between both side portions of this thin developer layer forming means and the developing device frame.
(g) Further to item (f), the phase of both side edge portions of the thin developer layer forming means is aligned with that of both side portions of a magnet of the developing sleeve.
The objects of the present invention are accomplished by either of the following embodiments (h) and (i).
(h) In a developing device of a color image forming apparatus in which development is carried out by depositing toners of a plurality of colors on an electrostatic latent image formed on the image carrier, a developer scattering prevention member to prevent the scatter of developer is provided on both sides of the developing device so that the developer scattering prevention member is opposed to the circumferential surface of the image carrier outside of the image forming region.
(i) Further to item (h), the developer scattering prevention member is composed of 2 layers, one layer is constituted of a flexible and resilient member, and the other layer is constituted of a member having sliding properties.
The objects of the present invention are accomplished by either of the following embodiments (j) and (k).
(j) In a developing device of an image forming apparatus in which development is carried out by depositing toner on an electrostatic latent image formed on the image carrier, the developing device includes a thin developer layer forming member that comes into contact with a developing sleeve so as to form a thin developer layer on the surface of the developing sleeve, wherein the thin developer layer forming member can be slidably contacted with and separated from the developing sleeve by the magnetic force of the developing sleeve.
(k) Further to item (j), the thin developer layer forming member provided to the developing device frame includes a rotation prevention member to prevent the rotation of the member.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a sectional side view showing the arrangement of the air exhausting hole and filtering member provided in the developing device of the first example of the present invention;
Fig. 2 is an upper view showing the aforementioned arrangement;
Fig. 3 is a schematic view showing the structure of an image forming apparatus;
Fig. 4 is a sectional side view showing the primary structure of a conventional developing device;
Fig. 5 is a sectional side view showing the arrangement and configuration of the developer scatter preventing slot provided in the developing device of the second example of the present invention;
Fig. 6 is a sectional side view showing a primary structure of a conventional developing device;
Fig. 7 is a sectional side view showing the structure and arrangement of the developer leakage preventing member of the third example of the present invention;
Fig. 8 is a front view showing the structure and arrangement of the developer leakage preventing member of the third example of the present invention;
Fig. 9 is a sectional side view showing a condition in which the developer scatter preventing member is provided to the developing device of the fourth example of the present invention;
Fig. 10 is an upper view showing the condition in which the developer scatter preventing member is provided to the developing device of the fourth example of the present invention;
Fig. 11 is a sectional side view showing a primary structure of a developing device;
Fig. 12 is a schematic view showing the structure of a color image forming apparatus; and
Fig. 13 is a sectional side view of a developing device to which the thin developer layer forming member (cylindrical rod) of the fifth example of the present invention is provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to Figs. 1, 2, 3 and 4, the first example of the present invention will be explained as follows, wherein Fig. 1 is a sectional side view showing the arrangement of the air exhausting hole and filtering member provided in the developing device of the first example of the present invention, Fig. 2 is an upper view showing the aforementioned arrangement, Fig. 3 is a schematic view showing the structure of an image forming apparatus, and Fig. 4 is a sectional side view showing the primary structure of a conventional developing device. Like parts of a developing device in each of the examples of the present invention are identified by the same reference character as that of the conventional example.
The function and operation of the developing device 6 are the same as those of the conventional example. Therefore, the explanation will be omitted, and only different points will be explained here.
As shown in Fig. 3, the electrophotographic image forming apparatus 18 is provided with a platen glass P on which a document M is set, wherein platen glass P is mounted on the upper surface of the electrophotographic image forming apparatus 18, and an optical scanning unit 2 is provided under this platen glass P. The optical scanning device 2 includes a document illumination lamp 2a and a first mirror 2b that are reciprocated, and also includes second and third mirrors 2c that are arranged in a V-shape, and further includes a lens 2d and a fourth mirror 2e that are fixed. In the center of the image forming apparatus body 1, a photoreceptor drum 3 is rotatably provided so that it can be rotated in the arrowed direction. Around the photoreceptor drum 3, there are successively provided a charging electrode 4 that uniformly charges a photoreceptor 3a in the rotational direction, a developing device 6 having a developing sleeve 26 to which toner is supplied, a transfer electrode 7, a separation electrode 8, a discharge electrode 9, and a cleaning unit 10. Paper feed cassettes 11 and 11' respectively accommodating recording papers of different sizes are provided to the image forming apparatus body 1. Numeral 12 is a first paper feed roller that conveys a recording paper accommodated in the paper feed cassette 11 to a waiting position located before a second paper feed roller 13. The first paper feed roller 12 includes rollers 12a and 12a rotated through a belt to prevent multiple-feed of recording papers, and a stop roller (referred to as a separation roller) 12b. Numeral 13 is a second paper feed roller that temporarily stops a recording paper sent by the first paper feed roller 12 at the aforementioned waiting position, and feeds it to a transfer position in an appropriate timed relation so that the leading edge of a visualized image formed on the photoreceptor 3a and the leading edge of the recording paper can coincide with each other. Numeral 14 is a guide plate that guides a recording paper fed by the first paper feed roller 12 to the second paper feed roller 13. When a lever (not shown) is manipulated, the guide can be opened and closed so as to remove a jammed paper by hand. Numeral 15 is a conveyance unit that conveys a recording paper onto which an image has been transferred to a fixing position. A fixing unit 16 is composed of a heat roller 16a and press roller 16b. Numeral 17 is a paper discharge roller that discharges a recording paper outside of the image forming apparatus after fixing.
When a copy button is pressed in the aforementioned image forming apparatus, document M on platen glass P is scanned by the optical scanning system 2, and an electrostatic latent image of document M is formed on the photoreceptor drum 3. This electrostatic latent image is visualized by the developing device 6, and the visualized image is transferred on a recording paper sent from one of the paper feed cassettes 11 and 11' provided to the image forming apparatus body 1. After the image has been transferred, the recording paper is separated from the photoreceptor 3a by the action of the separation electrode 8, and conveyed to the fixing unit 16 by the conveyance unit 15. In the fixing unit, the developed image is fixed, and then the recording paper is discharged by the paper discharge roller 17. In the aforementioned manner, required toner images are successively formed on the recording papers.
Air exhausting holes and a filter, which are the developer leakage preventing means of the developing device of the invention, are constituted in the following manner.
As shown in Figs. 1 and 2, a number of square air exhausting holes 30, which are formed with predetermined dimensions, are provided in positions of the upper cover 21 opposed to the circumferential surface of the developing sleeve 26, wherein the air exhausting holes are aligned in the longitudinal direction of the upper cover 21 at regular intervals, that is, the air exhausting holes are aligned in the vertical direction with respect to the surface of the drawing.
The filter member 31 is a long and slender sheet-shaped member made of polyester fiber. The filter member 31 is adhered onto the upper surfaces of the air exhausting holes 30 formed on the upper cover 21 by a double-sided tape so that all the air exhausting holes 30 are airtightly covered.
As shown in Fig. 1, the end portion of the upper cover 21 opposed to the circumferential surface of the photoreceptor drum 3 is extended in the circumferential direction of the photoreceptor drum 3 compared with a conventional upper cover, and the extended portion is formed concentrically with the circumferential surface of the developing sleeve 26, and a predetermined gap is formed between the extended portion of the upper cover 21 and the circumferential surface of the developing sleeve 26. As shown in Fig. 1, the developer leakage preventing wall 21a, which is approximately concentric with the circumferential surface of the photoreceptor drum 3, is provided to the end of the extended portion in the longitudinal direction of the upper cover 21 in such a manner that the leakage preventing wall 21a is opposed to the circumferential surface of the photoreceptor drum 3. Developer D and toner contained in the developing device 6 are leaked out through the narrow path 32 formed between the outer side wall of the leakage preventing wall 21a and the circumferential surface of the photoreceptor drum 3. The width of this narrow path 32 is set at not more than 3 mm, and preferably set at about 1.3 mm. By the actions of the air exhausting holes 30, filter member 31 and developer leakage preventing wall 21a, developer D that has been scattered by the aforementioned air flow and the scraper 27 to cut the bristles of developer is completely collected by the filter member 31, so that only clean air is exhausted from the developing device 6 in the arrowed direction.
Accordingly, leakage of developer D and toner from the developing device 6 is prevented, so that the inside of the image forming apparatus 18 can be always maintained clean. Even when the aforementioned developer clog D₁ is not formed in the developing device, the air exhausting holes 30 and the filter member 31 are very effective to prevent the leakage of developer D and toner when toner is scattered by the scraper 27 in the case where the bristles of developer are cut. The air exhausting holes 30 and filter member 31 are not necessarily disposed in the aforementioned positions, but they may be disposed in appropriate positions corresponding to the characteristics of the developing device 6. In this connection, it is possible to replace the filter member 31 for the maintenance of the device.
In this manner, an excellent toner image can always be developed on the circumferential surface of the photoreceptor drum 3.
By the action of the air exhausting holes and filter member provided to the developing device of the present invention, developer D scattered by the developer clog and the scraper in the case where the bristles of developer are cut, is collected by the filter member, so that the leakage of developer inside of the image forming apparatus can be prevented. The narrow path of an appropriate width is formed between the developer leakage preventing wall provided at the front side portion of the upper cover and the circumferential surface the photoreceptor drum. Therefore, the leakage of developer can be further prevented.
With reference to Figs. 5 and 6, the second example of the present invention will be explained as follows, wherein Fig. 5 is a sectional side view showing the arrangement and configuration of the developer scatter preventing slot provided in the developing device of the second example of the present invention, and Fig. 6 is a sectional side view showing a primary structure of a conventional developing device.
In the present invention, the developer scatter preventing slot is provided in the developing device body in the following manner. As shown in Fig. 5, the lower jaw portion 20a including the developer scatter preventing slot of the present invention is provided to the developing device body 20, wherein the developing device body 20 is extended in the circumferential surface direction of the photoreceptor drum 3 so as to form the lower jaw portion 20a, and the lower jaw portion 20a is provided in the direction vertical to the surface of the drawing so that the lower jaw portion 20a covers all the photoreceptor drum 3 surface with respect to the direction vertical to the drawing. As shown in Fig. 5, the lower jaw portion 20a is constituted in the following manner: the upper surface 20b of the lower jaw portion 20a opposed to the circumferential surface of the developing sleeve 26 is disposed so that a predetermined gap is formed between the upper surface 20b of the lower jaw portion 20a and the circumferential surface of the developing sleeve 26; and the upper surface 20b is formed concentrically with the circumferential surface of the developing sleeve 26.
As shown in the drawing, two rows of developer scatter preventing slots (referred to as scatter preventing slots hereinafter) 130 having predetermined width and depth are provided in parallel in the longitudinal direction of the lower jaw portion 20a, wherein the scatter preventing slots extend across the entire lower jaw portion 20a.
When the developing sleeve 26 is rotated at high speed, an air flow S is generated toward the circumferential surface of the photoreceptor drum 3 between the circumferential surface of the developing sleeve 26 and the upper surface 20b of the lower jaw portion 20a. This air flow S enters each developer scatter preventing slot 130, and as shown by the arrow in the enlarged view encircled by a chain line in Fig. 5, a turbulent flow is formed counterclockwise. By the action of this air flow S, toner separated from developer D formed into bristles in a position close to the cylindrical rod 28 is dragged into the developer scatter preventing slot 130. Accordingly, scatter of toner to the outside of the developing device 6 can be effectively prevented. Developer D in each developer scatter preventing slot 130 is carried toward the circumferential surface of the developing sleeve 26 by the action of the turbulent flow and Coulomb's force or magnetic force, so that developer D is deposited on the circumferential surface of the developing sleeve 26. Developer D that has not been deposited on the circumferential surface of the developing sleeve 26 enters the developer scatter preventing slot 130 again by the action of air flows. When the aforementioned operation is repeated, leakage of airborne toner from the developing device 6 can be prevented, and it does not accumulate in the developer scatter preventing slot 130. The number of the rows of the developer scatter preventing slots is not limited to two. The larger the number of the rows of the developer scatter preventing slots is, the more effect can be provided, however, when the number is two, toner leakage can be sufficiently prevented.
As shown in the drawing, the curved surface 20c concentric with the circumferential surface of the photoreceptor drum 3 is provided at the end of the lower jaw portion 20a opposed to the circumferential surface of the photoreceptor drum 3. The narrow path 131 is formed by this curved surface 20c and the circumferential surface of the photoreceptor drum 3. The width of this narrow path 131 is set at not more than 3 mm, and preferably set at about 1.3 mm.
Airborne developer D and toner that have passed through the gap between the upper surface 20b of the lower jaw 20a and the developing sleeve 26 are not leaked outside the developing device 6 by this narrow path 131. As described above, leakage of developer D and toner to the outside of the developing device 6 can be prevented by the developer scatter preventing slot 130 provided in the lower jaw portion 20a of the developing device body 20, and also by the narrow path 131 formed by the circumferential surface of the photoreceptor drum 3 and the curved surface 20c of the lower jaw portion 20a. Accordingly, an excellent toner image can be always developed on the circumferential surface of the photoreceptor drum 3.
In the present invention, the developer scatter preventing slot is provided in the lower jaw portion of the developing device body opposed to the circumferential surface of the developing sleeve. Accordingly, even when developer is scattered by the air flow generated by the developing sleeve rotated at high speed, the airborne developer is not carried outside the developing device, so that leakage of developer can be very effectively prevented.
In the present invention, the narrow path is formed between the circumferential surface of the photoreceptor drum and the curved surface of the end portion of the lower jaw. Therefore, leakage of developer to the outside of the developing device can be further prevented.
With reference to Figs. 7 and 8, the third example of the present invention will be explained as follows, wherein Fig. 7 is a side view showing the structure and arrangement of the developer leakage preventing member, and Fig. 8 is a front view of the developer leakage preventing member.
The developer leakage preventing member provided in both side edge portions of the thin developer layer forming means (cylindrical rod) of the present invention is constituted and disposed in the following manner.
As shown in Figs. 7 and 8, a developer leakage preventing unit 230 is composed of a developer leakage preventing member (referred to as leakage preventing member hereinafter) 231 and a resilient member 232. The leakage preventing member 231 is a molded member made of polyacetal resin having high lubricating properties. The upper surface of the leakage preventing member 231 is formed into a curved surface 231a, wherein the curved surface 231a includes an arc, the radius of curvature of which is the same as that of the outer circumference of the developing sleeve 26, and also includes thickness "t" shown in Fig. 7,and width "d" shown in Fig. 8. The resilient member 232 is made of foamed urethane, and adhered to the leakage preventing member 231 by a double-sided tape in the following manner: the resilient member 232 is adhered to the bottom surface of the leakage preventing member 231, which is a surface opposite to the curved surface 231a; and the resilient member 232 is adhered to the left side surface of the leakage preventing member 231, which is a surface opposite to the flat surface portion 231b. As shown in Fig. 7, the resilient member 232 is adhered, being formed into an L-shape.
As described above, the developer leakage preventing unit 230 is composed of the leakage preventing member 231 and the resilient member 232 that have been previously adhered to each other. The developer leakage preventing unit 230 is provided to a predetermined position in the developing device body 20 in the following manner: the curved surface 231a of the leakage preventing member 231 is opposed to the circumferential surface of the developing sleeve 26 as if the curved surface 231a of the leakage preventing member 231 were engaged with the circumferential surface of the developing sleeve 26; and the flat surface portion 231b is slidably contacted with the left side surface of the cylindrical rod 28. By the resilience of the adhered resilient member 232, the developer leakage preventing unit 230 embedded in the developing device body 20 is pushed in the following manner: the developer leakage preventing unit 230 is pushed by a predetermined pushing force to the circumferential surface of the developing sleeve 26 in the arrowed direction; and the developer leakage preventing unit 230 is lightly contacted with the right side surface of the cylindrical rod 28 as shown by the arrow. Although not shown in the drawing, the same developer leakage preventing unit 230 as described above is embedded in a space formed between the left side surface of the cylindrical rod 28 and the right side portion of the developing sleeve 26 in the developing device body 20.
Consequently, the developer leakage preventing units 230 symmetrically provided to both side portions of the cylindrical rod 28 seal the gap between the developing sleeve 26 and the cylindrical rod 28 pushing the developing sleeve 26, and also seal both side portions of the cylindrical rod 28. Therefore, leakage of developer D and toner can be effectively prevented.
The developing sleeve 26 and the cylindrical rod 28 are assembled in such a manner that: both side portions of the magnetic region of the developing sleeve and both side surfaces of the cylindrical rod 28 are aligned on the line P - P₁ shown in the drawing. Accordingly, the flat surface portion 231b of the leakage preventing member 231 shown in Fig. 7 coincides with the left side of a thin layer of developer D formed on the circumferential surface of the developing sleeve 26. Consequently, the leakage preventing member 231 is embedded without leaving a gap, so that leakage of developer D and toner can be more positively prevented. In order to maintain the accuracy, the flat surface portion 231b of the leakage preventing member 231 is preferably located in the magnetic region of the developing sleeve 26.
Since the leakage preventing member 231 molded of polyacetal resin having high lubricating properties is slidably contacted with the circumferential surface of the developing sleeve 26 and both side surfaces of the cylindrical rod 28 with a predetermined contacting force, the units can be very smoothly operated without affecting the rotation of the developing sleeve 26 and the cylindrical rod 28. As explained above, leakage of developer D and toner from both end portions of the cylindrical rod can be prevented. Therefore, an excellent toner image can be always developed on the circumferential surface of the photoreceptor drum 3. The present invention has been explained above, taking a developing device of a monochromatic image forming apparatus for example. Of course, the present invention can be applied to a developing device of a color image forming apparatus.
In the present invention, the developer leakage preventing unit is provided so that it can act on both side surfaces of the thin developer layer forming means (cylindrical rod) and the circumferential surface of the developing sleeve. Therefore, leakage of developer into the image forming apparatus can be prevented, and the unit can be very smoothly operated without affecting the operation of the developing sleeve and the cylindrical rod.
With reference to Figs. 9, 10. 11 and 12, the fourth example of the present invention will be explained as follows. wherein Fig. 9 is a sectional side view showing a condition in which the developer scatter preventing member is provided to the developing device of the fourth example of the present invention, Fig. 10 is an upper view showing the condition in which the developer scatter preventing member is provided to the developing device of the fourth example of the present invention, Fig. 11 is a sectional side view showing a primary structure of a developing device, and Fig. 12 is a schematic view showing the structure of a color image forming apparatus.
Fig. 12 is a sectional view showing the primary structure of a copier that is a color image forming apparatus 101. This copier includes an image reading system A, laser writing system unit B, image forming section C, and paper supply section E. In this color image forming apparatus, a color image can be formed by the following process.
First, in image reading system A, a document set on the platen glass 111 is irradiated by the halogen lamp 113 mounted on the horizontally sliding carriage 112 of the optical scanning system 110. The mirrors 116 and 116a are mounted on the movable mirror unit 115 in such a manner that the two mirrors form a V-shape. The mirror 114 is mounted on the carriage 112 and slid horizontally. An optical image of the document is sent to the image reading section 117 by the combination of the aforementioned mirrors.
The carriage 112 and the movable mirror unit 115 are driven through a wire (not shown) connected with a stepping motor (not shown), and respectively slid in the same direction at a speed of V and 1/2V.
The image reading section 117 includes the lens 118 and the color CCD 119 disposed in the image forming position right behind the lens 118. The color CCD 119 is used for color separation when the document on the platen glass 111 is read. The color CCD 119 is composed of a 3-line CCD having filters through which light of red, green and blue passes. A color signal on which color-correction has been conducted in accordance with the toner colors of yellow (Y), magenta (M), cyan (C) and black (B). Then, the corrected color signal is inputted into laser writing system unit B that is an exposure means.
In laser writing system unit B, a laser beam generated by a semiconductor laser (not shown) conducts rotary scanning by the action of the polygonal mirror 52 rotated by the drive motor 51. Then, the optical path of the laser beam is curved by the action of the mirror 54 through the fϑ lens 53, and then the laser beam is projected on the circumferential surface of the photoreceptor drum 3 that has been uniformly charged and given a predetermined electrical charge. Therefore, a bright line is formed by the laser beam on the drum surface.
On the other hand, concerning the auxiliary scanning direction, an index (not shown in the drawing) provided in a specific position on the photoreceptor drum 3 is detected, and on the basis of this detection signal, the laser beam generated by the semiconductor is modulated by an image signal, and the primary scanning direction is determined. After the scanning operation has been started, the laser beam is detected by the index sensor with respect to the primary scanning direction, and the modulated laser beam scans the circumferential surface of the photoreceptor drum 3. Consequently, a latent image corresponding to the first color is formed on the circumferential surface of the photoreceptor drum 3 by the primary scanning conducted by the laser beam and the auxiliary scanning conducted by the rotation of the photoreceptor drum 3. In this example, this latent image is developed by the yellow developing device 6Y in which yellow toner (Y) is accommodated, wherein the yellow developing device 6Y is one of a plurality of developing means disposed in parallel with each other. In this way, a Y toner image is formed on the surface of the photoreceptor drum 3. While the developed toner image is held on the surface of the photoreceptor drum 3, the image passes under the cleaning unit 59 that is separate from the circumferential surface of the photoreceptor drum 3. Successively, a copy cycle of the second color is started.
The photoreceptor drum 3 on which the Y toner image has already been formed is charged again by the charger 55. Then the second color signal outputted from reading system A is inputted into writing system unit B, and a writing operation is conducted on the surface of the photoreceptor drum 3 in the same manner as the first color signal described above, so that a latent image of the second color is formed. The latent image of the second color is developed by the magenta developing device 6M in which magenta (M) toner is accommodated. This M toner image is formed on the aforementioned Y toner image.
In the same manner, a latent image formed by the third image signal is developed by the cyan developing unit 6C in which cyan (C) toner is accommodated. Then the photoreceptor drum 3 is charged again, and a latent image of the fourth color is formed by the fourth image signal, and the latent image is developed by the black developing device 6B in which black (B) toner is accommodated. In this way, the B toner image is formed on the C toner image on the circumferential surface of the photoreceptor drum 3.
A bias voltage of AC and/or DC is impressed upon each developing sleeve of the developing devices 6Y, 6M, 6C and 6B, and the photoreceptor drum 3, the base of which is grounded, is subjected to reversal-development under a non-contact condition, that is, what is called jumping development is conducted. At this time, the developing sleeves of the developing devices that are not participating in development are stopped and the supply of bias voltage to those developing sleeves is cut off so as to protect the toner image formed on the photoreceptor drum 3 and not to supply unnecessary toner to the latent image.
The color toner image formed on the circumferential surface of the photoreceptor drum 3 in the aforementioned manner is transferred onto a recording paper by the action of the transfer pole 56 that is a transfer means, wherein the recording paper is fed from paper feed section E by the paper feed belt and sent to the transfer section by the timing roller in timed relation with the color toner image. This transfer operation is conducted by the transfer electrode 56 when a high voltage, the polarity of which is reverse to that of toner, is impressed upon the recording paper.
In this way, the color toner image is transferred onto the recording paper, and then the recording paper is separated from the surface of the photoreceptor drum 3 by the action of the separation electrode 57 and conveyed to the belt fixing device 58 through the conveyance belt. After the color toner image on the recording paper has been fixed, the recording paper is discharged.
After the color toner image has been transferred onto the recording paper, the recording paper is separated from the photoreceptor drum 3. Then the photoreceptor drum is rotated clockwise, and the blade 59A of the cleaning unit 59 is contacted with the surface of the photoreceptor drum 3 with pressure so that the residual toner on the photoreceptor drum surface can be removed. After the cleaning operation has been completed, the cleaning blade 59A is separated from the photoreceptor drum 3, and a new color image forming process is started.
Fig. 11 is a sectional view showing the primary portion of the yellow developing device 6Y. Numeral 20 is a developing device body composing the housing of the yellow developing device 6Y. Numeral 22 is a first stirring member. Numeral 23 is a second stirring member. Numeral 24 is a supply roller. Numeral 26 is a developing sleeve. Numeral 28 is a rigid cylindrical rod that is a thin developer layer forming means to regulate the amount of developer to be fed onto the circumferential surface of the developing sleeve 26. Numeral 28a is a spring plate to regulate the conveyance amount of developer, and the cylindrical rod 28 is pushed against the developing sleeve 26 by a constant resilient force of the spring plate 28a when there is no developer on the surface of the developing sleeve 26. Numeral 27 is a scraper to cut the bristles of developer. Numeral 25 is a separation plate used in the process of stirring. Numeral 21 is an upper cover mounted on the upper surface of the developer body.
Toner supplied to the yellow developing device 6Y is sufficiently stirred and mixed with carrier by the action of the second stirring member 23 rotated in the arrowed direction and the first stirring member 22 rotated in the opposite direction. Developer D including toner and carrier sufficiently mixed in the aforementioned manner is sent to the developing sleeve 26 through the supply roller 24.
The first and second stirring members 22 and 23 are screw members rotated in the opposite direction to each other as shown by arrows in the drawing, and their spiral angles are formed counterclockwise with respect to the rotating direction. Toner and carrier are conveyed by the first stirring member 22 in the direction away from the viewer's side, and successively overflows the stirring separation plate 25, the upper edge of which is inclined downward in the direction away from the viewer's side, so that the toner and carrier are moved onto the side of the second stirring member 23. Then, the toner and carrier are conveyed to the viewer's side by the thrust generated by the second stirring member 23. While the toner and carrier are mixed in the aforementioned manner, they are triboelectrically charged and formed into uniform developer D. After that, developer D is deposited on the circumferential surface of the developing sleeve 26 rotated clockwise in the arrowed direction when the sponge-like supply roller 24 is rotated in the arrowed direction, whereby a layer of developer D is formed on the circumferential surface of the developing sleeve 26.
Then, the toner conveyed by the developing sleeve 26 is deposited on an electrostatic latent image formed on the circumferential surface of photoreceptor drum located close to the developing sleeve 26 so that a predetermined gap is formed between the surface of the developing sleeve 26 and that of the photoreceptor drum 3. In this manner, the electrostatic image is developed. The first and second stirring members 22 and 23, supply roller 24, and developing sleeve 26 are respectively driven by a drive transmission mechanism provided on the side of the frame of the developing device 20. Other developing devices 6M, 6C and 6B are constituted and operated in the same manner as the aforementioned yellow developing device 6Y.
The developer leakage preventing member provided to the developing device of the present invention is disposed in the following manner. As shown in Figs. 9 and 10, the developing devices 6Y, 6M and 6C respectively accommodating yellow, magenta and cyan toners are provided in the case 70 from the upper to the lower positions at regular intervals, and the black developing device 6B is provided in the case 70a that is separately disposed under the case 70. As shown in Fig. 9, each of the developing devices 6Y, 6M, 6C and 6B is provided with a spacing roller 6a that is disposed at the end portion of the developing device so that the spacing roller 6a can be contacted with the circumferential surface of the photoreceptor drum 3 outside of the image forming region. The pushing spring 80 is provided between the right side of each of the developing devices 6Y, 6M, 6C, 6B and each of the cases 70, 70a, wherein the spring 80 pushes each developing device toward the photoreceptor drum 3 so that the spacing roller 6a is pressed against the photoreceptor drum 3. As a result of the foregoing, a predetermined gap is formed between the end portion of each developing device and the circumferential surface of the photoreceptor drum 3.
In order to prevent developer D and toner from scattering outside from a gap on both sides of the end portion of each of the developing devices 6Y, 6M, 6C and 6B, the following measure is taken. As shown in Figs. 9 and 10, the developer scatter preventing members 90 are integrally adhered by a double-sided tape to both sides of the end portion of each of the developing devices 6Y, 6, 6C in the case 70, wherein the developer scatter preventing members 90 are provided so that they are opposed to the circumferential surface of the photoreceptor drum 3 outside of the image forming region L (shown in Fig. 10). In this case, the developer scatter preventing member 90 is a strip-shaped member of 2 mm thick constituted of a flexible and resilient member made of Moltopren and a slidable member made of high density polyethylene. The member made of high density polyethylene having high sliding properties is opposed to the circumferential surface of the photoreceptor drum 3, and as shown in Fig. 9, the end portion of the developer scatter preventing member 90 is folded and adhered on both sides at the upper surface portion of the yellow developing device 6Y disposed at the uppermost position. Then, the developer scatter preventing member 90 is adhered to the end on both sides of each of the developing devices 6Y, 6M, 6C. After that, the rear end portion of the developer scatter preventing member 90 is folded and adhered on both sides to the bottom portion of the cyan developing device 6C. Accordingly, one strip-shaped developer scatter preventing member 90 is continuously adhered to the end portions of the developing devices 6Y, 6M, 6C on both sides without leaving any gaps as shown in Fig. 9.
Although the positions of the end portions of the developing devices 6Y, 6M, 6C are different from each other, the developer scatter preventing member 90 can be adhered to the developing devices in accordance with their profiles since the developer scatter preventing member 90 is flexible. In the case of the black developing device 6B disposed in the lowermost position, the developer scatter preventing member 90 is adhered by the same procedure as described above, and as shown in Fig. 9, the upper and lower portions of the developer scatter preventing member 90 are folded and adhered on both sides to the end portion of the developing device 6B. In this example, this black developing device 6B is independent of other developing devices 6Y, 6M, 6C from the reason of the specification of the image forming apparatus, however, the black developing device 6B may be integrated into the case 70. In this case, all the developing devices are adhered to one developer scatter preventing member 90. When each of the developing devices 6Y, 6M, 6C, 6B, to which the developer scatter preventing member 90 is adhered, is pressed against the circumferential surface of the photoreceptor drum by each pushing spring 80, the developer scatter preventing member 90 is compressed approximately to a half of its thickness, that is, the developer scatter preventing member 90 is compressed to about 1 mm, so that the gaps between the circumferential surface of the photoreceptor drum 3 and the end portion on both sides of each of developing devices 6Y, 6M, 6B are completely sealed.
As described above, the developer scatter preventing member 90 can be very easily adhered to the developing devices 6Y, 6M, 6C and 6B, so that the scatter of developer D and toner from the end portion on both sides of each developing device can be prevented. Accordingly, an excellent color toner image can be always formed on the circumferential surface of the photoreceptor drum 3.
The present invention can be applied to not only the developing device of a color image forming apparatus but also the developing device of a monochromatic image forming apparatus.
By the developer scatter preventing member of the present invention, which can be very easily provided to the apparatus, the gap between the circumferential surface of the photoreceptor drum and the end portion on both sides of each developing device can be sealed without leaving any gaps. Therefore, the scatter of developer from the end portion on both sides of each of the developing devices 6Y, 6M, 6C, 6B can be prevented.
The fifth example of the present invention will be explained with reference to Fig. 13 that is a sectional side view of a developing device to which the thin developer layer forming member (cylindrical rod) of the fifth example of the present invention is provided.
In order to prevent the developing sleeve of the invention from being damaged, the following countermeasure is taken.
As shown in Fig. 13 and the enlarged view, a pin 29, which is a rotation preventing member to prevent the rotation of the cylindrical rod 28, is provided in the center of the cylindrical rod 28 in the longitudinal direction (perpendicular to the surface of the drawing), and moreover a hole 220c that slidably engages with the pin 29 is provided on the surface 220b of the lower jaw portion 220a of the developing device body 20 in the longitudinal direction. Then, the cylindrical rod 28, the pin 29 of which is engaged with the hole 220c, is positioned on the sliding surface 220d. As a result of the foregoing structure, when the cylindrical rod 28 is rotated, it is slid through the restricted pin 29 along the sliding surface 220d, so that the cylindrical rod 28 is moved in the left upper direction as shown by the arrow in the drawing, and comes into contact with the circumferential surface of the developing sleeve 26. Accordingly, the rotation of the cylindrical rod 28 is restricted by the pin 29, and also the conventional spring plate 28a is omitted in this constitution.
The number of holes 220c and pins 29 is not limited to one, but an optional number of holes and pins may be provided in optional positions.
In order to cause the cylindrical rod 28 to be contacted with the circumferential surface of the developing sleeve 26, the cylindrical rod 28 is attracted by the magnetic force of the developing sleeve 26. Even when the cylindrical rod 28 is contacted with the developing sleeve 26 with a pushing force lower than that of a conventional structure, a thin developer layer can be formed because the rotation of the cylindrical rod 28 is restricted. The cylindrical rod 28 is positioned on the sliding surface 220d of the lower jaw portion 220a of the developing device body 20, the pin 29 is inserted into the hole 220c, and the developing sleeve 26 is provided in a predetermined position of the developing device body 20. Then, the cylindrical rod 28 is slid through the pin 29 in the left upper direction by the magnetic force of the developing sleeve 26, and comes into contact with the circumferential surface of the developing sleeve 26 with a predetermined pushing force.
Since the cylindrical rod 28 is contacted with the developing sleeve 26 by the magnetic force, the pushing force of the cylindrical rod 28 is reduced when the gap between the cylindrical rod 28 and the developing sleeve 26 is increased, which is contrary to the conventional structure.
The cylindrical rod 28 is contacted with the developing sleeve 26 in the aforementioned manner. Therefore, even when a foreign object F is pinched between the cylindrical rod 28 and the developing sleeve 26, the cylindrical rod 28 is moved from the circumferential surface of the developing sleeve 26 in the arrowed direction as shown by a chain line, so that the pushing force is reduced. Accordingly, foreign object F passes through between the developing sleeve 26 and the cylindrical rod 28 without damaging the circumferential surface of the developing sleeve 26.
Of course, the present invention can be appropriately applied to not only a monochromatic image forming apparatus but also a color image forming apparatus.
In the present invention, the thin developer layer forming member (cylindrical rod) is contacted with the developing sleeve by the magnetic force of the developing sleeve. Accordingly, even when a foreign object is pinched between the developing sleeve and the cylindrical rod, the cylindrical rod is separated from the circumferential surface of the developing sleeve without damaging the surface, and the foreign object passes through without causing any problems.
Consequently, the occurrence of white stripes deteriorating the quality of toner images formed on the circumferential surface of the photoreceptor drum can be prevented.

Claims

A developing device for use in an image forming apparatus, by which an electrostatic latent image formed on an image carrier is developed with toner, said developing device comprising:
(a) a housing of said developing device, having at least one air exhaust hole through which air inside said housing is exhausted; and

(b) a filter provided on said hole for preventing developer inside said housing being exhausted.
The developing device of claim 1 further comprising a developing sleeve provided inside said housing and an upper cover attached to said housing, wherein said hole is provided on either part of said housing which faces the upper circumferential surface of said developing sleeve or said upper cover.
The developing device of claim 1, wherein the circumferential surface of said image carrier and the upper end portion of said housing which faces said circumferential surface have a gap therebetween of not more than 3 mm.
A developing device for use in an image forming apparatus, by which an electrostatic latent image formed on an image carrier is developed with toner, said developing device comprising:
(a) a housing of said developing device;

(b) a developing sleeve pivotally supported by said housing; and

(c) at least one groove provided in the surface of said housing which faces the circumferential surface of said developing sleeve, for preventing developer inside said housing from scattering outside.
The developing device of claim 4, wherein the circumferential surface of said image carrier and the lower end portion of said housing which faces said circumferential surface have a gap therebetween of not more than 3 mm.
A developing device for use in an image forming apparatus, by which an electrostatic latent image formed on an image carrier is developed with toner, said developing device comprising:
(a) a housing of said developing device;

(b) a developing sleeve having a magnet therein;

(c) developer layer forming means supported by said housing, for forming a thin developer layer on the circumferential surface of said sleeve; and

(d) developer leakage prevention members provided between both side portions of said developer layer forming means and said housing, each of said developer leakage prevention members having a surface slidingly in pressure contact with the circumferential surface of said developing sleeve at a side end portion between said developer layer forming means and said housing, and a surface in slidable contact with the side surface of said developer layer forming means.
The developing device of claim 6, wherein a phase of the both side portions of said developer layer forming means are aligned with both side portions of said magnet in said developing sleeve.
A developing device for use in a color image forming apparatus, by which electrostatic latent images formed on an image carrier are developed with a plurality of color toners, said developing device comprising:
(a) a housing of said developing device, said housing containing developer therein; and

(b) developer scattering prevention members provided to both sides of said housing which face non-image areas of the circumferential surface of said image carrier, for preventing scatter of developer outside said housing.
The developing device of claim 8, wherein said developer scattering prevention members comprise two layers, one layer being a flexible and resilient member and the other layer being a member with high slidability.
A developing device for use in an image forming apparatus, by which an electrostatic latent image formed on an image carrier is developed with toner, said developing device comprising:
(a) a housing of said developing device;

(b) a developing sleeve provided in said housing, having a magnet therein, for supplying toner to said image carrier; and

(c) a developer layer forming member provided in said housing, for forming a thin developer layer on the circumferential surface of said sleeve by being in pressure contact with the circumferential surface of said developing sleeve, said developer layer forming member being in slidably contact with and separated from the circumferential surface of said developing sleeve by the magnetic force of said magnet in said developing sleeve.
The developing device of claim 10, wherein said developer layer forming member further comprises a rotation prevention member for preventing said member from rotating.