WO1983001842A1

WO1983001842A1 - Thermally isolated developer pump

Info

Publication number: WO1983001842A1
Application number: PCT/US1981/001529
Authority: WO
Inventors: Corporation Nashua
Original assignee: Faucher, Jerome, R.; Baptiste, Paul, J., Jr.
Priority date: 1981-11-18
Filing date: 1981-11-18
Publication date: 1983-05-26
Also published as: GB2122512A

Abstract

In the liquid developing system (24) for an electrostatic copier (10), the liquid developer (26) is ordinarily pumped to the developer electrode (30) through a conduit (86) from a storage tank (28). Generally, the motor (50) for the liquid pump housing (82) is located in the storage tank (28) above the level of the liquid developer, with motor shafts extending down into the developer to the pump housing. In this type of arrangement, the heat generated by the pump motor (50) is transferred to the liquid developer thereby raising the temperature of the developer to the point that it produces an undesirable "halo" effect on the developed image. In order to eliminate this "halo" effect, the heat generating pump motor (50) of the present device is thermally isolated from the liquid developer tank (28) for the electrostatic copier. In one embodiment, the pump impeller (90), with a first magnet (92) fixed to it, is magnetically coupled to a second magnet (70) disposed outside the tank. In this embodiment, the second magnet (70) is coupled to a pulley (72) driven by a belt (94) which is coupled to the remote motor (50) by pulley (62). In another embodiment, the second magnet (130) is mounted on the motor shaft.

Description

THERMALLY ISOLATED DEVELOPER PUMP

Background of the Invention This invention relates generally to photocopiers employing liquid toner developer, and particularly to pumps in the liquid toner developer tanks of the photocopiers.

In photocopiers using liquid toner developers, a rotating photosensitive drum surface is electrically charged and then exposed to the light pattern reflected from an original document to form a latent electrostatic image on the surface. The latent image is developed by liquid developers attracted to the latent image under the influences of the image change pattern, and the developed image is transferred onto copy material by a transfer process. The drum is thereafter cleaned and used again.

The liquid developer contacts the drum surface at a developer station. There is typically located at the developer station a development electrode, and liquid toner developer is provided in the gap between the electrode and the drum surface. Toner particles in the developer in the gap are attracted to, and electrostatically adhere to, the latent image in conformity with the electric field pattern that forms from the charge on the drum surface.

The liquid developer is ordinarily pumped to the developer electrode through a conduit from a liquid developer storage tank. Generally motors for such pumps are located in the storage tanks, above the level of the liquid developer, with motor shafts extending down into the developer to pump housings. In some liquid development systems, copy quality (density, sharpness, etc.) deteriorates in direct proportion to the total number of copies made with a given amount of solution. One of the common problems with copy quality in photocopiers is the so-called "halo" effect, in which a fine detached line surrounds characters in the copy. It appears that one cause of the halo effect is an increase in temperature of the liquid developer as the photocopier is continuously operated, presumably because of the increased conductivity of the liquid developer as its temperature rises.

It is an object of the invention to improve the clarity of photocopier copy images, and in particular to minimize the halo effect from copy images.

Summary of the Invention The developing apparatus of the invention comprises-in a photocopying apparatus having a movable member having a photosensitive surface, means for charging the photosensitive surface, means for selectively exposing the photosensitive surface to form an electrostatic latent image, means for developing the latent image with a liquid developer to form a developed image, and means for transferring the developed image to a transfer material-a container for liquid developer, driven means in the container for pumping the liquid developer from the container to the vicinity of the latent image, a heat generating motive power means, thermally isolated from the developer in the container, and means for drivingly coupling the motive power means to the driven means while maintaining said thermal isolation. The invention also features the heat generating motive power means comprising a rotary motor; providing means for mounting the motive power means remotely from the container; and the coupling means comprising a magnetic coupling means. Other features are that the driven means comprises a rotatable impeller; the coupling means comprises a first rotatable magnetic portion adjacent a wall of the container, a second rotatable magnetic portion outside the container wall, and means for directly coupling the impeller and the first magnetic portion along a first shaft, and means for directly coupling by a belt means the second magnetic portion to the motive power means, whereby the impeller is rotated when the second rotatable portion is rotated.

Brief Description of the Drawings Other features, objects and advantages of the invention will be described in, or be inherent in, the following description of preferred embodiments of the invention, including the drawings thereof, in which:

Fig. 1 is a schematic front elevation view of a photocopier in which one embodiment of the present invention is incorporated;

Fig. 2 is a schematic front elevation view of the liquid developer holding tank and pumping assembly of the photocopier of Fig. 1;

Fig. 3 is a schematic front elevation view like that of Fig. 2 showing a second embodiment of the invention; and Fig. 4 is a schematic front elevation view showing a pump impeller housing with a different arrangement for supporting the pump impeller.

Description of the Preferred Embodiments Referring to Fig. 1, a photocopier in which the present invention can be employed has a photosensitive element, preferably a drum 10 having a photosensitive selenium surface 12 deposited upon an aluminum substrate, rotating in a counter clockwise direction as indicated by the arrow 14. A charge corona 16 charges the drum 10 to about +1000 volts DC. The charged drum 10 is exposed to an image typically transmitted by a lens 18 from a scanning system 20, at an exposure station 22. The image is focused on the drum photosensitive surface 12 and thereupon the charge on the drum surface 12 is selectively discharged and forms an electrostatic latent image comprising a pattern of remaining electrical charges. The electrostatic latent image on the drum surface 12 is brought to a development station 24 where a liquid developer 26 having a negatively charged toner is drawn from a liquid developer holding tank 28 to the electrostatic image to develop the image. The development station 24 includes a development electrode 30. Liquid 26 is introduced between the development electrode 30 and the drum surface 12 to wet the surface 12 and develop the electrostatic image. The drum surface 12, now wetted and carrying the developed image, travels past a metering roll 32, which limits the thickness of the liquid on the drum surface 12. A transfer material, preferably a sheet 34, is fed to the drum surface 12 at a transfer station 36 by rollers 38. A positive charge from a transfer corona 40 is applied to the back side of the sheet 34, urging the transfer of toner particles from the developed image on the drum surface 12 to a copy sheet 34. The copy sheet 34 is then removed from the drum surface 12 and follows a path dictated by a set of rollers 42. After transfer, the residue of liquid developer on the drum is cleaned by a cleaning roller 44 and a cleaning blade 46. Finally, the drum surface 12 is electrically neutralized prior to the next charging step by a high AC neutralizing charge from discharge corona 48.

In the prior art, a pump motor is ordinarily mounted above the level of the liquid developer 26 in the liquid developer holding tank 28, with a shaft extending down to rotate a pump impeller located in a housing at the bottom. of the tank 28. The heat from the motor, however, heats up the liquid developer 26 as the photocopy machine is used, and the heating up of the liquid developer has as one result the halo effect on copies made by the photocopier.

In the development station 24 of the embodiment of the invention, shown in more detail in Fig. 2, therefore, a rotary pump motor 50 is relocated from inside the developer holding tank 28 to outside the tank. The motor 50 is mounted on the copier chassis 52, so that it is physically separated from, and thermally isolated from, the tank 28. Heat generated by the motor 50 at its outside location is not transmitted to the liquid developer 26, as it would be if the motor were located in the tank 28 where the heat normally generated by the motor would be transferred to the developer 26 by conduction through the impeller shaft, and by convection and radiation. The chassis 52 is raised above ground level by foot pads 54, and the pump motor 50 is mounted on the chassis 52 by a motor mountirig 56.

A rotatable shaft 58 driven by the pump motor 50 protrudes through a hole 60 in the chassis 52 to beneath the chassis, and a motor pulley 62 is mounted on the end of the shaft 58 below the chassis 52. At a location on the chassis 52 below the developer tank 28 and separated from the motor 50 there is mounted a drive magnet and pulley assembly 64. A bracket 66 is mounted underneath the chassis 52, and a vertical shaft 68 is rotatably mounted in the bracket 66. Fixed to the top of the shaft 68 and within the bracket 66 is an integrated four pole circular ceramic drive magnet 70; fixed to the bottom of the shaft 68 and beneath the bracket 66 is a magnetic coupling pulley 72. As a result, rotating the pulley 72 will rotate the directly coupled drive magnet 70. The periphery 74 of the bracket 66 surrounds a hole 76 that is cut in the chassis 52 so that the upper surface 78 of the drive magnet 70 can be flush with the upper surface 80 of the chassis 52.

Inside the holding tank 28, above the drive magnet and pulley assembly 64 is a pump impeller housing 82 with an inlet opening 84 at the top and an outlet conduit 86 at the side. Liquid developer 26 enters the inlet 84 and is pumped through the outlet conduit 86 to the developer electrode 30 (see Fig. 1), in the vicinity of the latent image on the photosensitive drum 10, for development of the image.

Inside the pump impeller housing 84, a vertical shaft 88 is mounted on the bottom of the tank 28 directly above and aligned with the shaft 68 of the magnet and pulley assembly 64 below. Rotatably mounted on the vertical shaft 88 is a pump impeller 90 with an integrated 4 pole circular ceramic pump magnet 92 fixed to the bottom of the impeller 90.

Finally, a thermally non-conductive belt 94 connects the motor pulley 62 and the driven pulley 72. As a result, when the pump motor 50 is energized, the motor pulley 62 is rotated; the belt 94, connecting the motor pulley 62 and the magnetic coupling pulley 72, causes the magnetic coupling pulley 72 to rotate. The drive magnet 70, fixed to the same shaft 68 as the driven pulley 72, also rotates. The pump magnet 92, magnetically coupled to the drive magnet 70, rotates when the drive magnet 70 rotates, so that the pump impeller 90 is driven, or rotates, operating the pump.

The gap 96 between the pump 92 and drive 70 magnets is held to less than one-quarter inch to maximize the coupling force. The gap 96 is determined by the thickness of the bottom 98 of the tank 28 and the necessary clearances between the magnets 70, 92 and the surfaces of the tank bottom 98 for bind free operation.

A second embodiment of the invention is shown in Fig. 3. A portion of a container for liquid developer 102, namely a tank 104, is shown, and inside the tank 104 is a pump housing 106 whose characteristics are like those of the pump housing 82 described in the first embodiment. The pump housing 106 has an inlet opening 108, an outlet conduit 110, and a rotatable pump impeller 112 rotatably mounted on a vertical shaft 114. An integrated 4 pole circular ceramic pump magnet 116 is fixed to the bottom of the impeller 112. The housing 106, and the impeller 112 and magnet 116, are arranged so that the pump magnet 116 is close to the bottom 118 of the tank 104.

The tank 104 rests on the photocopier chassis

120, the chassis 120 having foot pads 122. Directly below and aligned with the pump impeller 112, a rotary motor 124 is vertically mounted in a bracket 126 connected to the chassis 120. The rotatable motor shaft 128 extends upwardly from the motor 124, and fixed to the upper end of the shaft 128 is a drive magnet 130. A hole 132 cut in the chassis 120 allows the drive magnet 130 upper face 134 to be substantially flush with the upper surface 136 of the portion of the chassis 120 beneath the liquid developer tank 104, to provide for effective magnetic coupling of the pump magnet 116 and the drive magnet 130.

In operation, when the motor 124 is energized, the drive magnet 130 rotates, and rotates the pump magnet 116 by virtue of the magnetic coupling between the two aligned magnets 116, 130. When the pump magnet 116 rotates, so does the pump impeller 116 of which it is a part, and pumping action, moving liquid developer from the inlet opening 108 and through the outlet conduit 110 to the vicinity of the latent image on the photocopier drum, is effected.

Fig. 4 illustrates a pump impeller housing 150 with a different arrangement for supporting the impeller unit 152, comprising a pump impeller 154 and a pump magnet 156, than that shown in the embodiments described above. As in the previously described embodiments, however, the pump impeller housing.150 is located in the bottom of a liquid developer tank 158, over a rotatable drive magnet 160 that is driven by some means of motive power, not shown in Fig. 4.

The pump impeller housing 150 has an inlet opening 162 and an outlet conduit 164, and a bottom portion 166 that forms a conical cavity 168 with an inwardly sloping wall 170, in which the impeller unit 152 is loosely seated. The impeller unit 152 has an inwardly sloping conical surface 172 conforming to the wall 170 of the cavity 168. There is, however, about a 1/8" clearance between the cavity wall 170 and the impeller unit surface 172, to allow some self-aligning horizontal movement by the impeller unit 152.

The bottom portion 174 of the impeller unit

152 (or the floor 176 of the cavity 168 in which it is seated) is arranged, as by the application of a layer of appropriate material, to provide a low friction surface 178 so that the impeller unit 152 may rotate freely on the floor 176 of the cavity 168 in response to rotation of the drive magnet 160.

In this variation of the pump impeller housing 150, the vertical shaft 88, 114 of the previously described embodiments, around which the pump impeller rotated, has been omitted. The impeller unit 152 can be dropped into the housing cavity 168, where it will self-align with the drive magnet- 160 when the liquid developer tank 158 is installed. This will reduce problems of alignment between the tank 158 and the drive magnet 160, and eliminate the potential problem of the impeller 154 binding to a shaft on which it is mounted. Advantages and Non-Obviousness of the Invention

The apparatus of the invention accomplishes reduction of temperature in the liquid developer tank 28. Heat transfer from the pump motor to the developer solution is eliminated, and "haloing" is reduced, because of the thermal isolation of the pumping unit, the impeller 90, from the heat-generating motive power source, the pump motor 50.

Furthermore, since typical liquid developer 26 is flammable, greater safety is obtained by elimination of the heat source (the pump motor 50) and electrical power lines from the tank 28. This becomes especially important when shields are used to limit evaporation from the tank 28, since their presence increases the vapor pressure over the developer in the tank.

Patents such as U.S. Patent No. 2,941,477 and U.S. Patent No. 3,779,147 show magnetically coupled pumps. U.S. Patent No. 2,495,049 shows a temperature control for a continuous film dark tank and U.S. Patent No. 3,583,805 shows the use of an air curtain in an electrophotographic copier to prevent hot air in the drying and fixing portion of the copier from flowing to the developing unit. The prior art does not show, however, the use of a thermally isolated pump to prevent the build-up of heat in the liquid developer tank.

The preferred embodiment illustrates some structures for thermally isolating the pumping element from the motive power element, though other structural configurations may occur to those skilled within the art. Other additions, subtractions, or modifications of elements of the preferred embodiment will also occur to those skilled in the art and are within the spirit and scope of the invention, as defined by the following claims.

What is claimed is:

Claims

1. In a photocopying apparatus having a movable member having a photosensitive surface, means for charging said photosensitive surface, means for selectively exposing said photosensitive surface to form an electrostatic latent image, means for developing said latent image with a liquid developer to form a developed image, and means for transferring said developed image to a transfer material, developing apparatus comprising a container for liquid developer, driven means in said container for pumping said liquid developer from said container to the vicinity of said latent image, a heat generating motive power means, thermally isolated from said developer in said container, and means for drivingly coupling said motive power means to said driven means while maintaining said thermal isolation.

2. The developing apparatus of claim 1 further comprising means for mounting said heat generating means remotely from said container.

3. The developing apparatus of claim 1 or 2 wherein said heat generating means comprises a rotary motor.

4. The developing apparatus of claim 1 or 2 wherein said coupling means comprises a magnetic coupling means.

5. The developing apparatus of claim 1 or 2 wherein said driven means comprises a rotatable impeller, said coupling means comprises a first rotatable magnetic portion adjacent a wall of said container, and a second rotatable magnetic portion outside said container wall, means for directly coupling said impeller and said first magnetic portion along a first shaft, and means for directly coupling said second magnetic portion to said motive power means, whereby said impeller is rotated when said second rotatable portion is rotated.

6. In a photocopying apparatus having a movable member having a photosensitive surface, means for charging said photosensitive surface, means for selectively exposing said photosensitive surface to form an electrostatic latent image, means for developing said latent image with a liquid developer to form a developed image, and means for transferring said developed image to a transfer material, developer apparatus comprising means for containing liquid developer, means for pumping said liquid developer from said containing means to the vicinity of said latent image, motor means located remotely from, and thermally isolated from, said containing means, driving means located outside said containing means, means for magnetically coupling said driving means to said pumping means, and means for drivingly connecting said motor means to said driving means.

7. In a photocopying apparatus having a movable member having a photosensitive surface, means for charging said photosensitive surface, means for selectively exposing said photosensitive surfact to form an electrostatic latent image, means for developing said latent image with a liquid developer to form a developed image, and means for transferring said developed image to a transfer material, developer apparatus comprising means for containing liquid developer, means for pumping said liquid developer from said containing means to the vicinity of said latent image, said pumping means including pump impeller means located within said containing means, a rotatable driving means located outside said containing means, said pump impeller means being magnetically coupled to said driving means, a motor with a rotatable shaft located remotely from said driving means, and belt means for drivingly connecting said motor shaft means to said driving means.