US3893414A

US3893414A - Method and apparatus for varying developer bandwidth

Info

Publication number: US3893414A
Application number: US464864A
Authority: US
Inventors: Frederick W Hudson
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1974-04-29
Filing date: 1974-04-29
Publication date: 1975-07-08
Anticipated expiration: 1992-07-08
Also published as: JPS50147720A; GB1498830A; NL7504311A; CA1049770A; DE2516433A1

Abstract

An electrostatic copying machine is provided utilizing a magnetic brush development system. The magnetic brush presents a band of developer to a latent electrostatic image, the width of the developer band being changed in accordance with the size of copy paper used. This is effected by utilizing a variable length magnet inside a non-magnetic rotatable roller which carries developer thereon. The length of the magnet is varied in accordance with the size of the copy paper used to accordingly change the length of the magnetic field emanating therefrom thereby effecting a corresponding change in the bandwidth of the developer transported to the image. An alternate method for effecting the same result is to utilize a shunt which may be swung into a position surrounding one end of the magnet to prevent the magnet field emanating from that end of the magnet from being effective to attract developer to the roller thereby decreasing the developer bandwidth.

Description

United States Patent 11 1 Hudson METHOD AND APPARATUS FOR VARYING DEVELOPER BANDWIDTH Frederick W. Hudson, West Henrietta, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Apr. 29, 1974 [2]] Appl. No.: 464,864

[75] Inventor:

521 U.S. c1 118/637; 117/175; 355/3 DD 51 1111.121 G03g 13/08 581 Field of Search 118/637; 117/175; 355/15,

[56] References Cited UNITED STATES PATENTS 6/1962 118/637 3/1972 Ogawa 118/637 1111 3,893,414 1451 July 8, 1975 [57] ABSTRACT An electrostatic copying machine is provided utilizing a magnetic brush development system. The magnetic brush presents a band of developer to a latent electrostatic image, the width of the developer band being changed in accordance with the size of copy paper used. This is effected by utilizing a variable length magnet inside a non-magnetic rotatable roller which carries developer thereon. The length of the magnet is varied in accordance with the size of the copy paper used to accordingly change the length of the magnetic field emanating therefrom thereby effecting a corresponding change in the bandwidth of the developer transported to the image. An alternate method for effecting the same result is to utilize a shunt which may be swung into a position surrounding one end of the magnet to prevent the magnet field emanating from that end of the magnet from being effective to attract developer to the roller thereby decreasing the developer bandwidth.

6 Claims, 6 Drawing Figures mes MTEFQ'TEDJUL 8 I975 SHEEI Iii/11111;

METHOD AND APPARATUS FOR VARYING DEVELOPER BANDWIDTH DESCRIPTION OF THE INVENTION In an electrostatic copier system. it has been found that developer (carrier and toner particles) life is related to the function of the number of times the developer is cycled through the development system; the more times cycled, the shorter the life.

In known systems, it is the custom to present developer to a photoconductive surface carrying a latent image over the same width regardless of the size of the final image desired. For instance, developer may be presented to a surface carrying a latent image over a 14-inch bandwidth for copying an image onto either an 11 X 14-inch paper or an 8V2X 1 linch paper. The bandwidth coincides with the length of the paper as the paper is fed through the machine. For the latter size paper, developer is presented to a latent image over an extra 3-inch bandwidth and is, therefore, needlessly circulated with resultant shortening of developer life.

It is, therefore, an object of this invention to stop needless circulation of excess developer and thus improve developer life.

It is a further object of this invention to limit developer presentation to a surface carrying a latent image over a bandwidth equal to the length of paper on which the developed image is to be transferred.

Furthermore, in some systems the photoconductive surface is developed beyond the borders of an original and copy sheet resulting in removal of excess toner particles from the areas of the surface which taxes the cleaning system.

It is, therefore. an additional object of the invention to prevent needless cleaning of toner particles from a photoconductive surface.

Other objects of the invention will become apparent from the following description with reference to the drawing wherein:

FIG. 1 is a schematic view of a copying apparatus; FIG. 2 is a view taken along section line 22 of FIG.

FIG. 3 is a view of modification of the embodiment of FIGS. 1 and 2;

FIG. 4 is a view taken along section line 44 of FIG.

FIG. 5 is a top view of a copy paper receptacle adjuster; and

FIG. 6 is a partial view taken along section line 6-6 of FIG. 5.

Referring to FIGS. 1 and 2, there is shown a drum 10 on which a photoconductive layer 12 is formed. Arranged about the drum 10 are a charging station A, an imaging station B, a development station C, an image transfer and fixing station D and a cleaning station E. All of the functions of these stations are well known in the art. An electrostatic latent image may be formed on the layer 12 and developed with xerographic toner particles. The invention resides in the developing station to which particular attention is directed.

The development station comprises a developer sump 14 containing developer 16 therein. The developer is a mixture of toner particles and ferromagnetic carrier particles. The toner particles are triboelectrically attached to the carrier particles. One side wall of the sump has a stationary hub I8 affixed thereto which receives one end of a cylinder or roller 20 therein which is of non-magnetic material.

A bearing race 22 is secured to the hub 18 to allow the cylinder 20 to rotate relative to the hub and sump. The other end of the cylinder 20 is operably secured to a motor (not shown) by a gear train (not shown) for driving the cylinder. A keeper member 24 of magnetic material is secured to the hub l8 and has secured thereto a developer pickup magnet 26, a development magnet 28 and a residual developer transport magnet 30, all of which are located within the confines of the cylinder 20. Attached to the keeper 24 is a guide portion 31 having an upper surface 32, a lower surface 34 and a side surface 36 surrounding the magnet 26 for purposes to be hereinafter described. The guide portion 31 is of a non-magnetic material and the

magnets

26, 28 and 30 are permanent.

The magnet 26 is split into two sections, a stationary section 38 and a slidable section 40. Surfaces 42 and 44 of

sections

38 and 40, respectively, are complementary to each other and slidably engage each other. A leaf spring 46 is secured to the side wall 36 and engages the slidable section 40 to maintain the section 40 in contact with the section 38. A flexible cable assembly is provided and comprises a tubular sheath 48, secured at one end to the hub 18 and at the other end to a portion 50 of the copier frame, and a flexible twisted wire 52 slidable within the sheath 48. The wire 52 is connected at one end to the slidable magnet section 40 and the other end has a knob 54 which may be manually engaged to slide the wire back and forth. Upon pushing the knob in, the wire 52 pushes the magnet section 40 inwards to the phantom position to shorten the effective magnetic field emanating from the magnet 26. These movements are guided by the

guide surfaces

32 and 34. The leaf spring 46 ensures engagement of the section 40 with section 38. Upon pulling the knob out, the wire 52 pulls the magnet section 40 back to the position as shown in FIG. 2.

The split magnet has its applicability to copiers in the following manner: Assume the axial length a' of fixed section 38 is 11 inches and the axial length "b of movable section 40 is 3 inches and assume the combined axial length of the magnets 28 and 30 is 14 inches. With the section 40 in the full line position, shown in FIG. 2, the total length of the magnet 26 is 14 inches. As the roller 20 rotates in the direction of the arrow it will magnetically pick up developer material in the magnetic field of magnet 26 across a 14inch axial band and present a l4-inch band of developer to the photoconductive surface 12. When the section 40 is in the phantom position, as shown in FIG. 2, the total length of the magnet 26 is 11 inches, thus decreasing the magnetic field emanating therefrom by 3 inches. As the roller 20 rotates in the direction of arrow A, it will magnetically pick up developer material in the magnetic field of magnet 26 across an 11-inch axial band and present approximately an 11-inch band (allowing for slight spreading) of developer to the photoconductive surface 12. The magnet 40 may also be moved into positions intermediate the full line and phantom positions shown in FIG. 2 wherein a developer hand between 11 and 14 inches may be presented to the photoconductive surface 12.

The length of a copy sheet usually corresponds to the axial length of a developed image carried by a photoconductive drum. For instance, the image may be over an ll-inch or a 14-inch axial length of the drum to be transferred to an 11-inch or a 14-inch length copy paper, respectively. Developer life is a function of circulation through the development system; the more times cycled, the shorter the life. Thus, if developer is presented to the photoconductor 12 over a 14-inch bandwidth when an ll-inch image and copy sheet are used, a 3-inch bandwidth of developer is unnecessarily circulated resulting in shorter developer life. However, if the length of the magnet 26 is decreased so the roller 20 will only pick up an 11-inch bandwidth of developer which is then presented to the photoconductor, only the necessary amount of developer is presented to the photoconductor resulting in an increase in developer life. If an 13-inch length copy sheet is used, the section 40 may be moved inwards one inch from its position shown in FIG. 2 by pushing the knob 54 accordingly. An indicator may be provided to guide an operator on how far to move the knob for various paper sizes. Obviously, various paper sizes may be designed for by changing the length of and the number of the stationary and movable sections of the pick-up magnet 26.

Referring to FIGS. 3 and 4, a modification of the embodiment of FIGS. 1 and 2 is shown. The same elements as in the previous embodiment are designated with the same reference numeral with an a affixed thereto. In this embodiment, a shunt 100 is pivotally connected to the keeper member 24a. A torsion spring 101 is wrapped around the pivot connection and urges the shunt in a clockwise direction to surround a permanent magnet 103. The flexible wire 52a is wrapped around a pulley 104 and connected at the other end to the shunt 100. The shunt may be approximately 3 inches in axial length and is of a material, such as thin gauge steel, to decrease the axial length of the magnetic field of the magnetic bar 103 by approximately 3 inches when the shunt is in the full line positions shown in FIG. 3. If a l4-inch copy paper is used, the knob 54a is pulled out to lift the shunt 100 into the phantom position shown in FIG. 3 whereby the axial length of the magnetic field of the magnetic bar 103 will extend the full length of the magnet, Le, 14 inches. If an ll-inch copy paper is used, the knob 54a is pushed in which allows spring 101 to rotate the shunt 100 in a clockwise direction into the full line position shown in FIG. 3.

Obviously, any number of shunts could be used and the length thereof could vary according to the results desired.

In the above embodiments, the magnetic bar section 40 and the shunt 100 have been shown as being selectively manually actuated. However, the cable 52 or 52a may be connected to a selector which adjusts a paper tray to the length of paper used. In this manner, the axial magnetic field of the pick-up

magnet

26 or 103 will be automatically adjusted to copy paper size when the paper tray is adjusted. FIGS. 5 and 6 show an overall view of such a selector and the wire 52 or 52a could be connected to a selector 200 depicted therein. For a detailed operation of the selector, reference is made to US. Pat. No. 3,251,594 (.l.W. Wagner), which discloses and describes a similar such selector 348. The description of this patent is incorporated herein by reference.

While the pick-up magnet has been disclosed in a combined pick-up and development roller, the invention could be employed in a system using any number of rollers; the main feature being to employ this invention in a roller prior to the developer being presented to the photoconductive surface. However, it will be most advantageous to employ the invention in the initial developer pick-up roller.

What is claimed is:

1. A copying machine comprising: a member having a developable image thereon, a developer sump containing developer therein having magnetic properties, means for transporting a band of developer from said sump to the image for developing the same, means for selectively changing the width of the developer band, a copy paper supply receptacle, means for changing the size of said receptacle to accommodate various sizes of copy paper, said selective means being operably connected to said last named means to be controlled thereby.

2. A copying machine comprising: a member having a developable image thereon, a developer sump containing developer therein having magnetic properties, means for transporting a bandwidth of the developer from said sump to the image for developing the same, said means comprising a rotatable non-magnetic member surrounding at least one magnetic member, said magnetic member being so constructed to vary in length, and means to selectively increase or decrease the length of said magnetic member to effect a corresponding change in the magnetic field emanating therefrom thereby effecting a corresponding change in the bandwidth of the developer transported to the image.

3. The structure as recited in claim 2 further comprising a copy paper supply receptacle, means for changing the size of said receptacle to accommodate various sizes of copy paper, said selective means being operably connected to said last named means to be controlled thereby.

4. A copying machine comprising: a member having a developable image thereon; a developer sump containing developer therein having magnetic properties, means for transporting a band of developer from said sump to the image for developing the same, said means comprising a rotatable non-magnetic member surrounding at least one magnetic member; a shunt, said shunt being located adjacent one end of said magnetic member, means for moving said shunt into a position to surround one end of said magnetic member and for withdrawing said shunt from said position, said shunt being of a material to prevent the magnetic field emanating from the end of the magnetic member surrounded thereby from being effective to attract developer to said non-magnetic member.

5. The structure as recited in claim 4 wherein said magnetic member is supported by a stationary support member, and means for pivotably connecting said shunt to said support member.

6. The structure as recited in claim 4 further comprising a copy paper supply receptacle, means for changing the size of said receptacle to accommodate various sizes of copy paper, said means for moving said shunt being operably connected to said last named means to be controlled thereby.