US3924944A

US3924944A - Split developer housing

Info

Publication number: US3924944A
Application number: US525532A
Authority: US
Inventors: Richard E Smith; Herbert L Bresnick
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1974-11-20
Filing date: 1974-11-20
Publication date: 1975-12-09
Anticipated expiration: 1992-12-09
Also published as: DE2548452C3; DE2548452A1; IT1048748B; FR2292274A1; NL7513053A; CA1058395A; JPS5852584B2; SE7512760L; DE2548452B2; JPS5174642A; CH593504A5; GB1527083A

Abstract

A development system for developing latent electrostatic images carried by a substrate has a split housing, whereby internal portions of the system may be accessed for maintenance purposes and the like, without disturbing the interface between the development system and the image bearing substrate. For example, a cascade development system having a development electrode is provided with a split housing so that the critical spacing between the development electrode and the image bearing substrate need not be altered to internally access the system.

Description

United States Patent 1 Smith et al.

Dec. 9, 1975 SPLIT DEVELOPER HOUSING [75] Inventors: Richard E. Smith, Webster; Herbert L. Bresnick, Rochester, both of NY.

Xerox Corporation, Stamford, Conn.

Filed: Nov. 20, 1974 Appl. No.: 525,532

[73] Assignee:

US. Cl. 355/3 DD; 118/637; 1l8/DIG. 24; 427/20 Int. Cl. G03G 15/08 Field of Search 355/3 R, 3 DD, 14; 222/DIG. 1; 118/637, DIG. 24; 96/1 SD;

References Cited UNITED STATES PATENTS Ulrich 118/637 3,011,474 l2/l96l 3,721,209 3/1973 Szostak et al 118/637 X Primary Examiner-Robert P. Greiner [57] ABSTRACT A development system for developing latent electrostatic images carried by a substrate has a split housing,

,whereby internal portions of the system may be accessed for maintenance purposes and the like, without disturbing the interface between the development system and the image bearing substrate. For example, a cascade development system having a development electrode is provided with a split housing so that the critical spacing between the development electrode and the image bearing substrate need not be altered to internally access the system.

10 Claims, 6 Drawing Figures U.S. Patent Dec. 9, 1975 Sheet 10f4 3,924,944

US. Patent Dec. 9, 1975 Sheet 2 of4 3,924,944

FIG. 2

US. Patent Dec. 9, 1975 Sheet 3 of4 3,924,944

m QPx L? k .L: i

US. Patent Dec. 9, 1975 Sheet 4 of4 3,924,944

SPLIT DEVELOPER HOUSING BACKGROUND OF THE INVENTION This invention relates to development systems for electrostatic processors and, more particularly, to housings for those systems.

In a conventional electrostatic printing process of the type described in Carlsons US. Pat. No. 2,297,691 on Electrophotography, a uniformly charged photoconductor is selectively discharged in an image configuration to provide a latent electrostatic image which is then developed through the application of a finely divided marking material, called toner. As is known, that process has enjoyed outstanding commercial success, especially in plain paper copiers and duplicators. Nevertheless, substantial effort and expense are still being devoted to the perfection of the process, including the development step.

The modern practice is to carry out the development step on the fly viz., as the photoconductor moves through a development zone. For that reason, development systems now in use generally employ a multi-component developer and include means for circulating the developer from a sump, through the development zone, and then back to the sump.

Characteristically, multi-component developers comprise relatively coarse, granular carrier particles in addition to the aforementioned toner particles. The toner and carrier (or, sometimes, carrier coating) are formed from materials which are separated from one another in the triboelectric series so that electrical charges of opposite polarities tend to be imparted to the toner and carrier particles by a triboelectric charging process. Consideration is given to the ranking of the materials in the triboelectric series inasmuch as the aim is to have the polarity of the charge on the toner particles oppose the polarity of the charge of the latent image. Consequently, in operation, there are competing electrostatic forces acting on the toner particles, whereby those particles at least initially tend to be attracted to the carrier particles, but are subject to being electrostatically stripped therefrom whenever the developer is brought into the immediate proximity of or actual contact with an image bearing photoconductor.

There are various techniques for circulating the developer. For example, in a cascade development system, the developer is typically transported to a position above the development zone and then released to cascade across the photoconductor while falling back toward the sump under the influence of gravity. In a magnetic brush-type system, on the other hand, the developer is characteristically magnetically entrained on one or more rotatably driven rolls as it passes through the development zone.

Regardless, however, of the technique employed, the development process is sensitive to any dimensional change in the interface between the development system and the photoconductor (i.e., the development zone). Magnetic brush-type systems and cascade systems with development electrodes are especially sensitive to such change because they rely on supplemental electrostatic fields to enhance the development process. However, other types of development systems, such as simple cascade types, are also affected by such changes, inasmuch as there is an interrelationship between the dimensions of the development zone and the 2 electrostatic force the image bearing photoconductor exerts on the toner particles.

Unfortunately, conventional development systems have to be internally accessed from time-to-time for maintenance purposes and the like. As an example, fresh developer is periodically needed to replace exhausted developer since there otherwise ultimately is a significant reduction in the quality of the copies produced. Heretofore, however, the general practice has been to design development systems so that they can be internally accessed only after being physically displaced from the photoconductor. As a result, it has been difficult to maintain precise dimensions for the development zone or, in other words, the development system/photoconductor interface.

SUMMARY OF THE INVENTION Accordingly, a primary aim of this invention is to provide means for internally accessing a development system for an electrostatic processor, without affecting the development zone. In more detail, an object is to provide a split housing for such a development system.

More specifically, an important object of the present invention is to provide a split housing for a cascade development system having a development electrode so that the system may be internally accessed without moving the development electrode.

To carry out these and other objects of the invention, the development system of an electrostatic processor has a split housing with a stationary section adjacent the image bearing substrate of the processor and a movable section releasably engaged with the stationary section. To internally access the development system, a catch is released and the movable section of the housing is then moved away from the stationary section. A cascade development system having a development electrode is desirably provided with a split housing of this type because the development electrode can be mounted in the stationary section of the housing, thereby permitting the system to be internally accessed, without altering the critical spacing between the development electrode and the image bearing substrate.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the invention will become apparent when the following detailed description is read in conjunction with the attached drawings, in which:

FIG. 1 is a simplified schematic diagram of an electrostatic processor having a cascade development system housing in accordance with this invention;

FIG. 2 is an enlarged, fragmentary view of the housing for the development system of FIG. 1, with certain parts broken away in the interest of clarity;

FIG. 3 is another enlarged, fragmentary view of the 'housing as split to provide internal access to the development system;

FIGS. 4 and 5 are enlarged fragmentary views showing the catch for the housing in engaged and disengaged states, respectively; and

FIG. 6 is an exploded view of the catch shown in FIGS. 4 and 5.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT While the invention is described in some detail hereinafter with reference to a specific embodiment, it is to be understood that there is no desire to limit it to that 3 embodiment. On the contrary, the intent is to cover all modifications, alternatives and equivalents falling within the spirit and scope of the invention as defined by the appended claims.

Turning now to the drawings, and at this point especially to FIG. 1, it will be seen that the invention is embodied in a development system 11 which is used in an electrostatic processor 12 to develop latent electrostatic images carried by a photoconductor 13 on the fly as the photoconductor 13 moves through a development zone 14. In this instance, the photoconductor 13 is coated on the surface of a rotatable drum 15. It will be apparent, however, that there are other suitable machine configurations, including one wherein a flexible photoconductor is supported by a belt-like substrate.

There is no reason to dwell at length on the processor 12. It is simply an exemplary environment for the invention, and it closely resembles a commercially available 4000 copier of Xerox Corporation as modified to include the new development system 11. Thus, anyone interested in the specific details of that copier can inspect one of the commercially available units and refer to the published literature describing it, such as US. Pat. No. 3,724,019, which issued Apr. 3, 1973 in the name of Alan L. Shanly. Nevertheless, a brief functional description may be helpful.

Considering the processor 12 on that level, it will be observed that the drum 15 and its related components are enclosed within a base frame 16 which has a transparent platen 17 for supporting a document or other object (i.e., subject copy) image side down in position to be copied. The drum 15 is rotatably driven in the direction of the arrow (counterclockwise as shown) so that the photoconductor 13 is sequentially advanced during each copying cycle through a charging station 18, an exposure station 19, the development zone 14, a transfer station 21, and a cleaning station 22.

At the outset of each copying cycle, the photoconductor 13 is uniformly charged by a corona generator 23 as it advances through the charging station 18 and then selectively discharged in response to light reflected from the subject copy as it advances through the exposure station 19. There is, therefore, a latent electrostatic image of the subject copy on the photoconductor 13 when it reaches the development zone 14.

To carry out the exposure step, this particular copier comprises a scanning lamp 24 which is driven from one side to the other of the platen 17 during each copying cycle by a double helix auger drive 25 to illuminate successive lines or strips of the subject copy from below. The light reflected from the subject copy is intensity modulated in accordance with the image to be copied and is focused on the photoconductor 13 by a movable lens 26, a pair of stationary mirrors 2'7 and 28, and an exposure slit 29. To maintain the focus, the movable lens 26 is laterally driven in timed synchronism with the scanning lamp 24. That is accomplished by means of a linkage 31 which has a follower 32 riding on a camming surface 33 which, in turn, is mounted for rotation with the drum 15.

As described in detail hereinbelow, the development system 1 1 applies toner to develop the image carried by the photoconductor 13 as it advances through the development zone 14. The toner charge is then partially neutralized by a pre-transfer corona generator 30, thereby conditioning the toner image for transfer to a 4 copy sheet under the influence of transfer corona generator 34 at the transfer station 21. The copy sheet is selectively fed from one of two

supply trays

35 and 36 and is brought into contact with the photoconductor 13 by a sheet feeding and registration mechanism schematically shown at 37.

After the image has been transferred, the drum 15 rotates beneath a detack corona generator 38, which at least partially neutralizes the charge previously provided by the transfer corona generator 34, and then beneath a vacuum-type stripper 39. The stripper 39 removes the copy sheet from the photoreceptor l3 and transports it into a nip between a pair of heated fuser rolls 41 and 42.

The fuser rolls 41 and 42 supply heat and pressure for fixing the toner image to the copy sheet so that the copy which is ultimately fed into the output tray 43 has a substantial degree of permanence. To minimize the tendency for toner to offset during the fusing process, there is a reservoir 44 with a wick 45 for applying a release agent, such as silicone oil, to the lower fuser roll 41, which is the one that engages the image bearing side of the subject copy.

While fusing is taking place, the photoreceptor 13 continues to advance into the cleaning station 22 wherein there is a pre-cleaning corona generator 46 for at least partially neutralizing the change tending to hold residual toner on the photoconductor 13, followed by a resilient cleaning blade 47 for wiping the residual toner from the photoconductor 13in preparation for the next copying cycle.

Referring to FIGS. 2 and.3, it will be apparent that the development system 11 is similar to prior so-called cascade systems, with the principal exception being this system is housed in a split housing 51 consistantly with the present invention.

Briefly, in keeping with accepted practices, the development system 11 comprises a hopper 52 for guiding developer into the development zone 14, a buckettype conveyor 53 for transporting developer from a sump 54 in the lower reaches of the housing 51 to a position above the hopper 52, and a chute 55 for recovering developer from the development zone 14 and returning it to the sump 54. The hopper 52 and the chute 55 are positioned immediately above and below, respectively, the development zone 14. Accordingly, in operation, developer circulates in a more or less conventional path which runs upwardly from the sump 54 along the conveyor 53 and then downwardly through the hopper 52, then the development zone 14, andfinally back to the sump 54 via the chute 55.

Development occurs because the developer falling through the development zone 14 cascades across the photoconductor 13. As is known, a development electrode 56 is often included in a system of this type on the opposite side of the development zone 14 from the photoconductor 13 (i.e., so that there is a predetermined space or gap between therebetween). Typically,

the development electrode 56 is used to suppress background development. To accomplish that, in operation, it is electrically biased (by means not shown) relative to the drum 15 to provide an electrostatic field which tends to neutralize the electrostatic forces which might otherwise tend to attract toner to the non-image or background areas of the photoconductor 13. 2

Usually, there are seals 57-59 between the developer housing 51 and the photoconductor 13 to block developer from passing beyond the top, bottom, and sides,

respectively, of the development zone 14. Hence, there is little, if any, leakage of developer from the development zone 14. Some toner is, however, necessarily consummed in the development process. Consequently, there normally is a toner dispenser (not shown) for adding additional toner to the developer from time-totime so that its toner concentration remains at a suitably high level. 1

As will be appreciated, a development zone of substantially constant dimensions is a basic requirement for obtaining consistant performance from this or most any other development system. Here, for example, the density of developed image and the amount of background development are dependent on several factors,

including (1) the length of the development zone 14 (i.e., the span between the hopper 52 and the chute 55, as measured along the surface of the photoconductor 13) and (2) the depth of the development zone 14 (i.e., the distance or gap between the photoconductor 13 and the development electrode 56).

Prior attempts to maintain a development zone of substantially constant dimensions have not been altogether successful. The practice of moving the complete development system away from the photoconductor for routine servicing has generally frustrated those attempts. Indeed, it has been customary to accept slight changes in the dimensions of the development zone in the interest of expediting the maintenance procedures. This compromise has been struck simply because precise positioning of a development system is a time consuming task, at best. I

In accordance with this invention, however, the housing 51 is split so that the development system 11 may be internally accessed for maintenance purposes and the like, without disturbing its interface with the photoconductor 13 (i.e., without altering, or even temporally upsetting, any of the dimensions of the development zone 14). As a result, there is little, if any, need to rely on the aforementioned compromise inasmuch as the components defining the development zone 14 may generally be held in place while the development system 11 is being serviced.

More particularly, to carry out the invention, the housing 51 comprises an outboard movable section 61 which is releasably secured to an inboard stationary section 62 by a catch mechanism 63. The stationary section 62 is more or less permanently held in a position immediately adjacent the photoconductor 13 and includes at least those components of the development system 11 which participate in defining the development zone 14. Here, for example, the hopper 52, the chute 55, and the development electrode 56 are mounted within the stationary section 62 which, in turn, is rigidly attached (by means not shown) to the base frame 16 of the processor 12 (FIG. 1). The mov-- able section 61, on the other hand, houses the conveyor 53 and the sump 54 and is supported on, say a pair of generally horizontal rails 64 (only one can be seen) for sliding movement toward and away from the stationary section 62. As shown, there are forward and

rearward bearings

65 and 66, respectively, extending outwardly from each side of the movable section 61 to bridge that section between the rails 64. The rails 64 are, of course, anchored (by means not shown) to the processor base frame 16.

As best shown in FIGS. 4-6, the catch mechanism 63 for this particular embodiment includes a stop 71 which is selectively moved into and out of interfering relationship with, say, the rearward bearing 66 for the movable section 61 of the housing 51. A similar catch (not shown) is provided for the opposite side of the housing. Therefore, it should be understood that the following description of the one that can be seen is equally applicable to the other.

'In this instance, there is an extender 73 pivotally connected as at to the outer end of each of the rails 64. Ordinary maintenance procedures for the development system 11 require that the extender 73 be manually swung downwardly from a generally upright storage position so that it aligns with the rail 64 when there is maintenance to be performed and then upwardly back to its storage position after the maintenance has been completed. Advantageously, that motion is employed to engage and disengage the catch 63. Accordingly, the stop 71 is a shoulder formed by the upper edge of a latch plate 74. The latch plate 74 is pivotally connected as at 75 to a channel-like backing plate 76 which is anchored on the rail 64. The motion of the rail extension 73 is transmitted to the latch plate 74 by a link 77 so that the stop 71 is raised and lowered as the extender 73 is swing upwardly and downwardly, respectively. To that end, one end of the link 77 is pivotally connected as at 78 to the extender 73 and its opposite end is secured to a pin 79 which extends through a profiled cam track 81 in the latch plate 74 and a generally horizontal guide track 82 in the backing plate 76. The path of travel of the stop 71 is, of course, dictated by the offset between the

pivots

75 and 78 and by the profile of the cam track 81.

Indeed, in keeping with one of the more detailed aspects of this invention, the stop 71 is used to insure that a gasket 83 between the movable and

stationary sections

61 and 62 of the housing 51 is compressed under operating conditions to provide a seal. As will be appreciated, the gasket 83 may be mounted on either one of the

sections

61 or 62. As illustrated, to provide the force necessary to compress the gasket 83, the bearing 66 is generally cylindrical and is positioned when the movable section 61 of the housing 51 is manually placed against the stationary section 62 so that its axis is just slightly in front of the path of travel for the stop 71. Consequently, as the stop -71 is raised, it bears against the rear of the bearing 66 to urge the movable section 61 forwardly, thereby compressing the gasket 83.

CONCLUSION In view of the foregoing, it will now be understood that a development system for an electrostatic processor is advantageously equipped with a split housing so that the development system may be internally accessed for maintenance purposes and the like, without disturbing the development zone of the processor. Also, it will be appreciated that the split housing provides additional design freedom, whereby the position sensitive components of the development system (e.g., the development electrode in the exemplary embodiment) may be configured to have substantial rigidity and ruggedness, independent of any concern for their mobility.

What is claimed is:

1. A development system for developing latent electrostatic images carried by a substrate in an electrostatic processor: said system comprising a housing having a sump for storing a supply of developer; means for circulating developer along a path running from said movable section is outboard of said stationary section and is mounted for movement toward and away from said stationary section.

3. The development system of claim 2 wherein said movable section is mounted on rails having extensions pivotally connected thereto, and said movable section is releasably secured to said stationary section by at least one catch mechanism which is engaged and disengaged in response to movement of one of said extensions toward and away from, respectively, a storage position.

4. The development system of claim 3 further including means between said stationary and movable sections for sealing said housing when said catch mechanism is engaged.

5. The development system of claim 4 wherein said means for sealing said housing comprises a gasket which is subjected to a compressive force generated by engaging said catch mechanism.

6. In an electrostatic processor having a photoconductor for carrying latent electrostatic images, and a development system for applying toner laden developer to said photoconductor to develop said images, the improvement comprising a split housing for said development system; said housing including a stationary section positioned immediately adjacent said photoconductor to define a development zone, a movable section mounted for movement relative to said stationary section, and means for releasably securing said movable section to said stationary section; said stationary section containing means above and means below said development zone for guiding developer into and out of, respectively, said development zone; said movable section containing a sump for storing a supply of developer, and a conveyor for transporting developer from said sump to said means for guiding developer into said development zone.

7. The processor of claim 6 wherein said sump is formed by a lower portion of said movable section, and the developer guided away from said development zone is returned to said sump.

8. The processor of claim 6 further including a development electrode mounted within said stationary section at a predetermined distance from said photoconductor so that there is a gap permitting developer to flow between said electrode and said photoconductor.

9. The processor of claim 8 wherein said movable section is mounted for sliding movement toward and away from said stationary section.

10. The processor of claim 9 wherein said movable section is releasably secured to said stationary section by at least one catch mechanism, and further including means for selectively engaging and disengaging said catch mechanism to secure and release, respectively, said movable section to and from said stationary section.

Claims

1. A development system for developing latent electrostatic images carried by a substrate in an electrostatic processor: said system comprising a housing having a sump for storing a supply of developer; means for circulating developer along a path running from said sump, through a development zone, and then back into said sump; a stationary section mounted immediately adjacent said substrate to define said development zone; a movable section mounted for movement relative to said stationary section; and means for releasably securing said movable section to said stationary section; said movable section including said sump, whereby said sump may be accessed without disturbing said development zone.

2. The development system of claim 1 wherein said movable section is outboard of said stationary section and is mounted for movement toward and away from said stationary section.