US3678895A

US3678895A - Magnetic cascade development device for dry process electrophotography

Info

Publication number: US3678895A
Application number: US19360A
Authority: US
Inventors: Wasaburo Ohta; Kazuhiko Kasuya; Masayuki Yamauchi
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1969-03-15
Filing date: 1970-03-13
Publication date: 1972-07-25
Anticipated expiration: 1989-07-25
Also published as: FR2034969A1; GB1300865A; DE2012106A1

Abstract

Cascade development device for a dry process electrophotography includes a magnetic endless belt trained around a pair of rollers and a non-magnetic endless roller partially wrapped over the magnetic belt along its going pass and trained around a guide roller spaced apart from the upper one of the pair of rollers and adjacent to the upper end of an development of an electrophotographic recording medium in such a manner that the non-magnetic belt may be separate from the magnetic belt adjacent to the upper one of the pair of rollers. The developer is entrained and transported upon the non-magnetic belt and is freed from the magnetic field when the belts are separated so that the developer may be freely cascaded. Mixing means is provided for mixing the returned developer and guide roller oscillating means is also provided so as to uniformly cascade the developer.

Description

United States Patent Ohta et al.

[451 July25,1972

[54] MAGNETIC CASCADE DEVELOPMENT DEVICE FOR DRY PROCESS ELECTROPHOTOGRAPHY [72] Inventors: Wasaburo Ohta, Yokohama; Kazuhiko Kasuya; Masayuki Yamauchi, both of Kawasaki, all of Japan [73] Assignee: Kabushiki Kaisha Ricoh, Tokyo, Japan [22] Filed: March 13, 1970 21 Appl. No.: 19,360

[30] Foreign Application Priority Data March 15, 1969 Japan ..44/19813 [52] U.S.Cl ..ll8/637,l17/17.5

Primary Examiner-Mervin Stein Assistant Examiner-Leo Millstein Attorney-Burgess, Ryan and Wayne [5 7] ABSTRACT Cascade development device for a dry process electrophotography includes a magnetic endless belt trained around a pair of rollers and a non-magnetic endless roller partially wrapped over the magnetic belt along its going pass and trained around a guide roller spaced apart from the upper one of the pair of rollers and adjacent to the upper end of an development of an electrophotographic recording medium in such a manner that the non-magnetic belt may be separate from the magnetic belt adjacent to the upper one of the pair of rollers. The developer is entrained and transported upon the non-magnetic belt and is freed from the magnetic field when the belts are separated so that the developer may be freely cascaded. Mixing means is provided for mixing the returned developer and guide roller oscillating means is also provided so as to uniformly cascade the developer.

6 Claims, 5 Drawing Figures PitOhtOd July 25, 1972 BEST AVAILABLE GOPY 306780895 2 Shuts-Sheet 1 FIG. 2B

2lb 2lb 2| gmmmmmmmmmmmfi summmmmfil INVENTORS m W BY W/IP M ATTORNEYS Pltflltd July 25, B ABLE GOPY 2 Sheets-Sheet 2 FIG. 3

FIG. 4

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MAGNETIC CASCADE DEVELOPMENT DEVICE FOR DRY PROCESS ELECTROPIIOTOGRAPHY BACKGROUND OF THE INVENTION The present invention relates to a dry process electrophotographic development and more particularly a device for cascade development for a dry process electrophotography.

In the conventional cascade development of the type described, a developer consisting of a toner, a finely divided pigmented resinous powder and a carrier of glass beads, etc. is cascaded upon a recording medium bearing thereupon a latent electrostatic image so that the toner may be adhered to the latent electrostatic image, thereby forming a visible powder image. In a typical cascade development device as disclosed in Japanese Pat. Publication No.16596/1967 (US. Pat. No.3,062,109 to Mayo et al.) a bucket elevator is employed for moving the developer mixture from a sump region to an area elevated with respect to the image-bearing surface of a recording medium so as to cascade or pour the developer mixture upon the image-bearing surface. In this system, factors affecting the quantity of the developer to be supplied are the shapes, number, velocity, etc. of the buckets which scoop the developer, so that a number of buckets must be increased or the conveying velocity must be increased so as to continuously scooping and cascading the developer, thereby improving the development. This system becomes therefore large in size, complex in construction and expensive.

SUMMARY OF THE INVENTION It is therefor one object of the present invention to provide an improved cascade development system for dry process electrophotography which can substantially eliminate the defects encountered in the conventional system, can be operated in a simple manner at a less operation cost and can develop a high quality image having no edge effect. The novel feature which is believed to be characteristic of the present invention lies in the fact that an endless belt made of a non-magnetic material (non-magnetic belt) is wrapped over an endless belt made of a magnetic material (magnetic belt) so that the developer mixture consisting of a tonner and a carrier made of a magnetic material such as iron oxides may be attracted upon the surface of the non-magnetic belt and continuously entrained so as to be moved upwardly when at least the nonmagnetic belt is driven; and thereafter the non-magnetic belt is separated from the magnetic belt so that the magnetic force from the magnetic belt will not act upon the developer upon the non-magnetic belt when the developer is cascaded or poured upon the image-bearing surface of a recording medium.

Opposed to the conventional system, the system in accordance with the present invention can continuously and smoothly convey and cascade the developer so that the development can be continuously and smoothly carried out whereby a high quality image having no edge effect can be produced.

According to one aspect of the present invention, the nonmagnetic belt is so arranged as to be oscillated when the developer is cascaded upon the image-bearing surface of the recording medium so that the developer may be uniformly cascaded upon the surface whereby the non-uniform development due to the insufficient tonner supply can be eliminated.

According to another aspect of the present invention, the developer is mixed after it is dropped or removed away from the recording medium after developmentso that the concentration of the tonner and the charge imparted thereto may be uniformly maintained. Therefore, the developed image has no developing mark and the supply of the developer is much facilitated.

According to another aspect of the present invention, a thin non-magnetic metallic sheet is used as the non-magnetic belt so that a special electrostatic effect is attained, thereby improveing the quality of developed image.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of illustrative embodiments thereof taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a diagrammatic sectional view of one embodiment of the present invention;

FIG. 2 A and FIG. 2 B are fragmentary sectional views illustrating the construction of the magnetic belts used in the present invention;

FIG. 3 is a diagrammatic sectional view of an electrophotographic copying machine to which is applied the present invention in one form; and

FIG. 4 is a diagrammatic sectional view illustrating another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an electrostatic latent image formed by the exposure upon a recording medium 2 upon a rotary drum 1 rotating in the direction indicated by the arrow is directed toward the developing zone A. The recording medium 2 may be a photoconductive material material such as inorganic semiconductors (for example, selenium, zinc oxide, etc.) and organic semiconductors (for example, poly-N-vinyl carbazole) applied directly upon the surface of the rotary drum 1 or an insulating electrophotographic copy paper upon which is formed the above described photoconductive material in layer. The developing agent 4 in a developing agent tray 3 is a dry process developer consisting of the so-called tonner, a pigmented resinous powder, and a carrier made of ferromagnetic materials such as powder of iron oxides.

An endless belt 7 incorporating therein a plurality of magnet sections which will be referred to as magnetic belt" hereinafter is trained around a driving roller 5 and a driven roller 6 which rotate in the direction indicated by the arrow b. Another endless belt 9 made of a non-magnetic material such as fabrics, synthetic resins, aluminum, etc., so that it will be referred to as non-magnetic belt" hereinafter, is wrapped over the magnetic belt 7 and around a guide roller 8.

The developer 4 is adhered to the surface of the non-magnetic belt 9 adjacent to the roller 5 and is entrained toward the roller 6. The non-magnetic belt 9 is separated from the magnetic belt 7 adjacent to the roller 6 so that the developer 4 is cascaded or dropped adjacent to the guide roller 8 upon the recording medium in the developing zone A. The tonner is adhered to the latent electrostatic image upon the recording medium 2 in a manner well known in the art so that a visible powder image is developed. Thereafter the developer 4 is returned to the tray 3 and re-circulated in the manner as described hereinbefore. The excessively applied tonner is returned to the tray 3 by a fog preventive brush 10 which may comprise a roller having cotton fabrics, feathers, Japanese paper, etc. affixed thereto and more preferably may comprise silk fabric folded in the form of a brush with its free ends untwisted as disclosed in Japanese Utility Model Publication No.l2,558/l967.

The developed image is directed toward the transfer zone and after the transfer of the developed image to a suitable support, the residual tonner upon the recording medium is removed by a cleaning brush 11 having the same construction as the brush 10, but being pressed against the recording medium 2 with a pressure higher than that of the brush 10.

The magnetic belt 21 shown in FIG. 2-A comprises an endless belt 21a made of fabrics or rubber and a plurality of permanent magnet sections aflixed thereto in spaced apart relation with each other. The magnet belt 21 shown in FIG. 2- B comprises an endless belt 21a and a plurality of permanent magnet sections 21b incorporated therein. It is not necessarily required to train the magnetic belt and in one form of the present invention it may be in the form of a fixed plate.

FIG. 3 is a diagrammatic sectional view of a photocopying machine to which is applied the present invention in one form. A selenium sensitized member is vacuum deposited as a recording medium 32 upon a rotary drum 31 rotating in the direction indicated by the arrow 0. The recording medium 32 is imparted with the positive electrostatic charge by a charging device 34 to which is applied a high voltage of thousands of volts from a high voltage source 33 and a light image of an original 37 to be reproduced by light sources 35a and 36a is projected through a projection lens 38 upon the recording medium 32 thereby forming a latent electrostatic image corresponding to the configuration of the original 37 to be reproduced.

Reference numerals

33b and 36b designate reflectors for the light sources 35a and 36a respectively.

The latent electrostatic image thus formed upon the recording medium 32 is directed to the developing zone B. In a developing agent tray 39 is contained a developer 40 which is entrained upwardly by the cooperation of a magnetic belt 43 trained around a driving roller 41 being a regular polygon in cross section and a driven roller 42 being also a regular polygon in cross section and a non-magnetic belt 46 wrapped over the magnetic belt 43 and a guide roller 44 and a tension roller 45 which is biased by means of a spring 450. The developer 40 is cascaded or dropped adjacent to the guide roller 44 over the developing zone B so that the tonner is adhered to the latent electrostatic image upon the recording medium 32, thereby forming a visible powder image. A cover 47 which may enclose all of the developing device is fixed to the developer tray 39 so as to prevent the dispersion of the developer 40 during the operation.

The guide roller 44 has its shaft 44a fixed to an oscillating device-not shown so that the guide roller 44 may be oscillated during the developing operation, thereby facilitating the continuous and smooth cascade of the developer 40 upon the recording medium 32. The developer 40, after development, is mixed by a roller 48 having mixing blades or vanes 48a so that the concentration of the tonner in the developer may be equalized and directed toward the driving roller 41 for re-circulation. The excess tonner adhered to the recording medium 32 is removed by a fog preventative brush 49 and returned to the tray 39.

The powder image thus formed upon the recording medium 32 is transferred to a transfer sheet or the like 50 pressed against the recording medium 32 by means of a pair of pressure roller 51a and 51b. The sheet 50 may be advanced by a conveyor means not shown at the same velocity as that of the recording medium 32. When the sheet 50 is closely pressed against the recording medium 32, the powder image thereupon is transferred to the sheet 50 by the corona discharge ofa charging device 53 electrically connected to a high-voltage source 52. The transferred image is heated and fixed to the sheet 50 by an infra-red lamp 54 having a reflector 54a. Thereafter the residual tonner upon the recording medium 32 is removed by a cleaning brush 55 for preparation of the next operation. The cleaning brush 55 is surrounded by a shielding plate 550 for preventing the dispersion ofthe tonner.

FIG. 4 is a diagrammatic sectional view of a dry process developing device to which is applied the present invention in such a manner that a non-magnetic belt 146 is advanced in closely spaced apart relation with the recording medium 32 over the developing zone B so as to attain a special electrostatic conduction effect for development, thereby further improving the development. More particularly, the non-magnetic belt 146 comprises an endless belt made of fabrics or rubber and a thin non-magnetic metallic sheet such as aluminum, stainless steel, etc. laminated upon the endless belt, and is wrapped over the magnetic belt 43 and around a pair of guide rollers 144a and l44b disposed substantially at both ends of the developing zone B respectively and adjacent to the rotary drum 31. In order to space the non-magnetic belt 146 from the recording medium 32 by about 5 mm, a belt guide plate 147 is disposed as shown in FIG. 4. The non-magnetic belt 146 is advanced over the developing zone B along the rotary drum 31 so that the special electrostatic conduction effect for development may be attained, thereby substantially eliminating the edge effect of the developed image. The nonmagnetic belt 146 may be made only of a non-magnetic metallic sheet.

The present invention has been so far described with particular reference to the illustrative embodiments thereof, but it will be understood that variations and modifications can be effected without departing from the true spirit of the present invention as described hereinabove and a defined in the appended claims.

What is claimed is:

l. A device for a dry process electrophotographic cascade development comprising a developer sump,

a magnetic endless belt trained around a pair of spaced apart roller means,

a non-magnetic endless belt partially wrapped over said magnetic endless belt along its going pass and trained around a guide roller means disposed in spaced apart relation from the upper one of said pair of roller means and adjacent to the upper end of a development zone of an electrophotographic recording medium overlaid upon the peripheral surface of a rotary drum in such a manner that said non-magnetic belt may be separated from said magnetic belt adjacent to said upper roller means, and

drive means for driving at least said non-magnetic endless belt, said magnetic endless belt having means for generating the magnetic field through both of said magnetic and non-magnetic endless belts, whereby the developer in said sump is entrained upon said non-magnetic endless belt and transported to an area adjacent to said guide roller means and the free movement of said developer upon said non-magnetic endless belt being permitted upon said separation of said non-magnetic belt from said magnetic belt so that the developer may be freely cascaded over said development zone from an area adjacent to said guide roller reans.

2. A device as specified in claim 1 wherein means is provided for oscillating said guide roller means so as to oscillate said non-magnetic endless belt when the developer is cascaded.

3. A device as specified in claim 1 wherein mixing means is provided for mixing the developer returned from said cascade over said recording medium into said developer sump and for directing the developer toward the lower one of said pair of roller means.

4. A device as specified in claim 2 wherein mixing means is provided for mixing the developer returned from said cascade over said recording medium into said developer sump and for directing the developer toward the lower one of said pair of roller means.

5. A device for a dry process electrophotographic cascade development comprising a developer sump,

a magnetic endless belt trained around a pair of spaced apart roller means,

a non-magnetic metallic belt partially wrapped over said magnetic endless belt along its going pass and trained around a pair of mutually spaced apart guide roller means disposed substantially at both ends of a development zone of a recording medium overlaid upon the peripheral surface of a rotary drum in such a manner that said non-magnetic metallic belt may be separated from said magnetic belt adjacent to the upper one of said pair of roller means and pass along said development zone in closely spaced apart relation therewith,

a guide plate means for ensuring said pass of said non-magnetic metallic belt along said development zone in closely spaced apart relation therewith, and

drive means for driving at least said non-magnetic metallic belt,

mixing means for mixing the developer returned into said developer sump from said recording medium and for directing the developer toward the lower one of said pair of roller means,

said magnetic endless belt having means for generating the magnetic field through both of said magnetic and nonmagnetic metallic endless belts, whereby the developer in said sump is entrained upon said non-magnetic endless belt and transported to an area adjacent to the upper one of said pair of mutually spaced apart guide roller means, and

Claims

1. A device for a dry process electrophotographic cascade development comprising a developer sump, a magnetic endless belt trained around a pair of spaced apart roller means, a non-magnetic endless belt partially wrapped over said magnetic endless belt along its going pass and trained around a guide roller means disposed in spaced apart relation from the upper one of said pair of roller means and adjacent to the upper end of a development zone of an electrophotographic recording medium overlaid upon the peripheral surface of a rotary drum in such a manner that said non-magnetic belt may be separated from said magnetic belt adjacent to said upper roller means, and drive means for driving at least said non-magnetic endless belt, said magnetic endless belt having means for generating the magnetic field through both of said magnetic and non-magnetic endless belts, whereby the developer in said sump is entrained upon said non-magnetic endless belt and transported to an area adjacent to said guide roller means and the free movement of said developer upon said non-magnetic endless belt being permitted upon said separation of said non-magnetic belt from said magnetic belt so that the developer may be freely cascaded over said development zone from an area adjacent to said guide roller reans.

5. A device for a dry process electrophotographic cascade development comprising a developer sump, a magnetic endless belt trained around a pair of spaced apart roller means, a non-magnetic metallic belt partially wrapped over said magnetic endless belt along its going pass and trained around a pair of mutually spaced apart guide roller means disposed substantially at both ends of a development zone of a recording medium overlaid upon the peripheral surface of a rotary drum in such a manner that said non-magnetic metallic belt may be separated from said magnetic belt adjacent to the upper one of said pair of roller means and pass along said development zone in closely spaced apart relation therewith, a guide plate means for ensuring said pass of said non-magnetic metallic belt along said development zone in closely spaced apart relation therewith, and drive means for driving at least said non-magnetic metallic belt, mixing means for mixing the developer returned into said developer sump from said recording medium and for directing the developer toward the lower one of said pair of roller means, said magnetic endless belt having means for generating the magnetic field through both of said magnetic and non-magnetic metallic endless belts, whereby the developer in said sump is entrained upon said non-magnetic endless belt and transported to an area adjacent to the upper one of said pair of mutually spaced apart guide roller means, and the free movement of said developer upon said non-magnetic metallic endless belt being permitted when said non-magnetic metallic endless belt is separated from said magnetic endless belt so that the developer may be freely cascaded over said development zone from an area adjacent to the upper one of said pair of guide roller means.

6. A device as specified in claim 1 wherein said non-magnetic metallic endless belt comprises an endless belt made of fabrics or rubber with a thin non-magnetic metallic sheet laminated thereover.