US3848988A - Moisture control device - Google Patents

Abstract

A thermodynamic system for use in a copier for removing excessive heat energy from a xerographic fusing station and discharging this energy into a support material supply area to control the moisture content contained therein. Further means are provided to augment the system during periods when the fuser is in a standby mode of operation or during periods when a low volume of copy is being produced.

Description

United States Patent [191 Thettu et al.

MOISTURE CONTROL DEVICE Inventors: Raghulinga R. Thettu; Haribhajan S. Kocher, both of Webster, NY.

Assignee: Xerox Corporation, Stamford,

Conn.

Filed: June 11, 1973 Appl. No.: 368,924

US. Cl 355/3 R, 219/216, 355/30 Int. Cl G03g 15/22 Field of Search 355/3, 10, 17,30; 219/216, 388; 165/105, 66; 432/58-62, 227, 228

References Cited UNITED STATES PATENTS 8/1960 Roeder 165/105 UX Schulze et a1. 355/3 R X Andrus et al. 355/3 R X 1 Nov. 19, 1974 3,592,538 7/1971 Takeshi Ukai 355/3 R 3,602,429 8/1971 Levedahl et al. 165/105 X 3,609,991 10/1971 Chu et al. 165/105 X 3,649,992 3/1972 Thettu 355/15 X 3,677,632 7/1972 MacDonald 355/3 R 3,765,828 10/1973 Lux 219/216 X 3,770,346 l1/l973 Jordan 219/216 X Primary ExaminerSamuel S. Matthews Assistant ExaminerKenneth C. Hutchison 57 ABSTRACT A thermodynamic system for use in a copier for removing excessive heat energy from a xerographic fusing station and discharging this energy into a support material supply area to control the moisture content contained therein. Further means are provided to augment the system during periods when the fuser is in a standby mode of operation or during periods when a low volume of copy is being produced.

7 Claims, 4 Drawing Figures PATENTEL .(UVI 91974 SHEET 2 OF 4 PATENIEL W 91914 3; 848.988

SHEET 30F 4 PATENTEL, RU! 1 91974 sum war 4 This invention relates to apparatus for controlling the moisture content within a supply station containing a quantity of final support material to be used in a copying machine.

In many copier environments and, in particular, in electrostatic copiers, controlling the moisture content contained in the final support material, upon which copies are produced, is extremely important in order to insure that constant high quality copy is produced. When the moisture level in the material is allowed to become excessively high, the copy material itself acts in a deleterious manner to effect the various processing systems. For example, excessive moisture carried by the support material can rob energy from a heat fuser and thus seriously reduce the quality of image fixing that is produced. Similarly, as in the reusable xerographic process where a toner image is electrically transferred from a photoconductive plate to the final support sheet, excessive moisture in the support material will degrade the electrical characteristics of the transfer system and result in relatively incomplete or non-uniform transferring of images to the final support material.

It is therefore an object of the present invention to improve the xerographic process.

It is a further object of the present invention to regulate the amount of moisture contained within a copy sheet supply station used in a copier environment.

A still further object of this invention is to facilitate the processing of copy material within an automatic xerographic copying machine.

These and other objects of the present invention are attained by apparatus for removing excessive or unused heat energy from one area of an automatic copying machine, such as a heat fusing system, and discharge this excessive energy into the support material supply area of the machine under controlled conditions to regulate the amount of moisture contained in the material prior to its being processed. A secondary source of energy is also herein provided to maintain the energy discharge into the supply region at a constant level during periods when the copier is in a standby mode of operation or during periods of low copy volume usage.

For a better understanding of the present invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings wherein:

FIG. 1 is a schematic drawing illustrating an automatic xerographic copying machine utilizing the teachings of the present invention, the automatic machine having the capability of producing copies containing toner images affixed to both sides thereof;

FIG. 2 is an enlarged plan view of a heat transfer device encompassing the teachings of the present invention;

FIG. 3 is an enlarged perspective view of an evaporator unit utilized in the heat transfer device shown in FIG. 2 illustrating means to equalize the work load distribution between the evaporator utilized therein; and

FIG. 4 is an enlarged perspective view of one of shown in FIG. 2 further illustrating an auxiliary heating means to augment the energy provided to the condenser by the evaporator unit.

Referring now to FIG. 1, there is illustrated a schematic representation of an automatic xerographic reproducing machine employing a heat transfer mechanism for removing heat energy from the xerographic fusing system and delivering the heat energy into the support material supply regions of said machine. It should be noted at the outset that the apparatus of the present invention will be explained in conjunction with the copying machine employing the readable xerographic process and having the ability to produce toner images on both sides of a single sheet of copy material. However, it should be clear to one skilled in the art that the apparatus of the present invention is not so limited in its usage and this invention has wide application in many copying environments in which it is desirous or even necessary to control the moisture content within the final support material. Similarly, the energy input to the present system is described in reference to a I heated pressure roll fusing system. It should be clear that the energy input could be provided by any type of heat fixing device or any other machine component which is capable of delivering sufficient energy to produce the desired results.

Because the xerographic process is well known and used in the art, the processing steps herein involved will be briefly described with reference to FIG. 1. A photosensitive plate 10, in drum configuration, is mounted upon a horizontally aligned shaft 12 and caused to rotate in the direction indicated so as to pass the drum surface sequentially through a series of processing stations. The xerographic plate consists of an outer layer 13 of photoconductive material, such as selenium or the like, which is placed over a grounded support material 14. In operation, the plate is initially charged to a uniform potential at a charging station A by means of a corona generator 15. The uniformly charged plate is then moved into an imaging station B wherein a flowing light image of an original, which is supported upon a transparent viewing platen 17, is projected onto the plate surface via a moving scanning lens element 18 and a pair of mirrors l9 and 20. As a result of this imaging process, a latent electrostatic image containing the original subject matter is recorded upon the photoconductive plate. The latent image is next transported on the plate surface through a developing station C wherein the latent image is rendered visible by the application of an especially prepared charged toner material to the imaged plate surface.

The visible image is then transported upon the drum surface into an image transfer station D. Sheets of final support material are fed from either one of two supply tray areas, an upper supply tray area 24 and a lower supply tray area 25, into the transfer station in synchronous moving contact with the visible image carried on the drum surface. The support sheet and the charged toner image are transported under a transfer corona generator 27 which serves to electrostatically transfer the toner images from the plate surface to the contacting side of the final support sheet. The sheet is then stripped from the drum surface by means of a picker finger 28 and directed via a vacuum transport 29 into the nip of the heat pressure roll fusing assembly F. For further details concerning this type of fuser assembly, reference is had to US. Pat. No. 3,498,596 which issued in the name of Moser.

As noted above, the automatic copier herein disclosed has the capability of producing either single sided copy, that is, copy bearing a toner image on one side thereof, or double sided copy. In the case of a single sided copy, the final support sheets can be fed from either the upper supply tray or the lower supply tray directly into the image transfer station. The imaged sheet is then passed through the fuser assembly and forwarded directly into a collecting tray 19 where the copies are stored and held until such time as the operator has need for them. On the other hand, when a two sided copy mode of operation is selected, movable transport 26 is lowered to the dotted line position as shown in FIG. 1 and the upper supply tray, which has been previously emptied of all support sheets, is automatically prepared to accept copy sheets directed therein by transport 26. The copy sheets are fed from the lower support tray through the image transfer and fusing stations and delivered into the upper tray where the once imaged copy sheets are stored until the machine is programmed for a second copy run. Upon the initialization of a second copy run, the movable transport is once again raised to the solid line position shown in FIG. 1 and the once imaged copy sheets are fed from the upper supply tray through the transfer and fusing stations wherein a second image is transferred onto the opposite or non-imaged side of the sheet. The two sided imaged copy sheet is then fused and fed directly into the copy tray in the manner described above.

Referring now more specifically to the fuser assembly F (FIG. 2), the fuser basically consists of a lower heated roll 30 and an upper back up roll 31. The heated roll is constructed of a support cylinder 32 over which is placed a relatively thick resilient silicone blanket 33 and a thin layer 34 of low surface energy material, such as triflouroethylene. Both the blanket and the outer layer placed thereover are formed of materials having low thermal conductivity, the purpose of which will be explained in greater detail below. The back up roll is formed of a relatively rigid core 36 over which is placed a relatively thick sleeve 37 of triflouroethylene.

The fuser rolls are supported within the machine frame (not shown) in horizontal axial alignment and I are arranged to be rotated at synchronous speeds in the direction indicated. The lower fuser roll is biased into deforming contact against the more rigid surface of the upper back up roll to provide an extended nip therebetween in which energy is transferred from the heated roll surface to the image bearing side of the copy sheet delivered therebetween. In operation, a radiant source of energy 35 (FIG. 1) is positioned to irradiate the outer surface of the lower roll just prior to the roll surface entering the fuser nip. Because the lower roll is constructed of a material exhibiting a low thermal conductivity, the rate at which energy flows into the roll is minimized. As a consequence, a preponderance of the total energy directed onto the roll by the lamp is stored upon the outer surface where it is readily available to be efficiently delivered to the toner image bearing side of a copy sheet brought into contact therewith.

During image fixing, it has been found desirous to minimize the transfer of energy from the lower fuser to the back up roll. To this end, the triflouroethylene sleeve 37 is constructed of a material having low thermal conductivity within the fusing temperature range of the system thus minimizing the ability of the back up roll to act as the heat sink in the fusing system. In this manner, most of the energy brought into the fuser nip on the lower roll surface is made available for use in the I fusing process rather than being conducted across the nip and wasted in heating the back up roll structure. It

- has been found that this particular arrangement not material to be dried in a curled position as it moves through the nip. The back up roll, because of its low thermal conductivity, acts as a barrier to retard the amount of heat energy fiowing'through the fuser nip and thus serves to keep the back up roll at a relatively low temperature. As a consequence, during two sided image processing, the first fused images passing through the fuser nip a second time contact the relatively cooler back up roll surface and are thus held below their melting temperature substantially minimizing the danger of the images from being disturbed or otherwise degraded.

During image fixing operations, it has been found advantageous to minimize the amount of heat energy conducted across the fuser nip into the back up roll structure. If a heat build up is allowed to occur in the back up roll, the back up roll will act to remelt previously fused toner images brought into contact therewith when two-sided image fusing is being accomplished. Remelting of these images is undesirous because it leads to loss of image definition and places the toner images in a condition whereby the toner can offset onto machine elements coming into contact therewith. Further more, overheating of the back up roll structure produces an excess of heat in the nip which also tends to dry out the copy sheets passing therethrough causing the sheets to be deformed in a curled condition.

The triflouroethylene sleeve, which is placed over the back up roll structure, acts as a barrier to impede the passage of heat across the fuser nip. When fusing most conventional toner materials to a sheet of plain paper, the surface temperature of the heated roll entering the nip is preferably held at or about 375 F. Under these operating conditions, it is desirous that the surface of the back up roll at the nip be maintained at somewhere close to 210 F in order to prevent unwanted image degradation. However, particularly during periods of continuous and extended machine usage, it has been found that the temperature of the back up roll is inadvertently increased to a point where it can no longer effectively function in a desired manner to accomplish high quality double sided image fixing. Also, when excessively high back up roll temperatures are encountered, the excessive heat in the fuser nip tends to drive off the natural moistures contained in the support material causing the sheet to be dried in an unwanted curled or otherwise deformed posture.

The apparatus of the present invention utilizes the excessive heat producer in the fusing station of the automatic machine as a means for controlling the amount of moisture contained within the sheet supply regions. The system basically consists of evaporator stage G which is placed in thermal communication with the back up roll structure, and a condenser stage H operatively attached thereto. As will be explained in greater detail below, the evaporator units are interconnected with the condenser units to provide a system whereby excessive heat energy is removed from the fusing system and is discharged into the supply tray areas to control the humidity content therein.

The fuser roll cooling assembly illustrated in FIGS. 2-4 includes an evaporator stage G made up of two evaporators 41 and 42 that are supported, in assembly, in close proximity with the back up roll surface. The two evaporators are substantially enclosed within a blanket 43 which rides in contact with a portion of the back up roll surface. The blanket is constructed of a material having a relatively high thermal coefficient of conductivity whereby the heat energy in the back up roll surface is rapidly and efficiently transferred to the evaporators. The blanket has the further characteristic of exhibiting a low coefficient of friction in regard to the back up roll surface thereby reducing the effect of friction between the two contacting bodies. Although any suitable material may be used to construct the blanket, it has been found that Grafoil which is a graphite based material having the desired thermal properties, manufactured by Union Carbide Corporation, 270 Park Avenue, New York, New York, will function quite well in his particular environment.

Both evaporators are axially aligned in a stacked configuration adjacent to the back up roll surface with each evaporator extending in a longitudinal direction across the surface of the roll. Normally, each evaporator is partially filled with a working substance, in this case a liquid, to a predetermined level line. When he surface temperature of the back up roll exceeds a predetermined operating level, the working substance is caused to vaporize and the vapors are collected in a chamber 44 which is provided within each evaporator above the liquid level line. It should be clear to one skilled in the art that the term vapor as herein used refers to a fluid which exists in a gaseous state at or near its particular condensation point. In this particular case, it is preferred that the vapor of the working substance be formed at a predetermined temperature under atmospheric conditions.

The vapor chamber 44 of each evaporator is connected to one of the two condensers by means of a vapor line. In practice, the upper evaporator 41 in the stack is connected to condenser 50 associated with the upper sheet supply station 24 via vapor line 51. Similarly, the vapor chamber of the lower evaporator 42 is connected to the second condenser 49 associated with the lower sheet supply station 25 via vapor line 48. It should be noted that each condenser is located at a higher elevation than the associated evaporator unit whereby the vapors collected in the vapor chambers are caused to flow upwardly, under natural flow conditions, into the associated condenser unit.

As shown in FIG. 2, each condenser is positioned directly above the sheet stack contained within the associated supply region. Although not clearly shown, each support station is preferably constructed to create a relatively enclosed, humidically isolated region within the machine into which heat energy given up by the condenser is discharged. As more clearly seen in FIG. 4, each condenser includes a horizontally aligned condensing coil 45 which is positioned substantially parallel to the support stack being serviced. Each condenser coil is provided with a series of perpendicularly aligned cooling fins 47 which serve to reduce the thermal resistance on the condenser side of the system thereby facilitating the discharge of energy into the support stack supply regions. As the vapors move through the condenser coils, the vapors are allowed to cool below their respective due point, thus giving up the latent energy of evaporation acquired. This energy, in turn, is discharged from the system directly into the sheet support regions where it is used to control the moisture or humidity content therein.

The condensate collected in the condenser stage is returned to the evaporator stage thus closing the thermodynamic system. In order to balance the work load between evaporator units, the condensate or liquid return lines are crossed to that the upper condenser delivers condensate to the lower evaporator and the lower condenser similarly delivers condensate to the upper evaporator. Condensate is returned under the force of gravity from the upper condenser via liquid return line 54 while liquid return line 55 services the upper condenser. lt should be noted that an expansion valve 59 is positioned in each of the liquid return lines to throttle the condensate before it is returned to the evaporators.

The apparatus herein described represents a closed thermodynamic system wherein energy is both absorbed and rejected from the system under isothermal conditions. The system further relies upon a natural flow of the working substance through the system thereby eliminating the need for pumps or the like. As noted above, it is desirous to maintain the back up roll surface at or about 210 F. As a consequence, it is possible to use water, which evaporates at about 212 F under atmospheric conditions as a working substance in the present invention. In practice, the amount of working substance within the system and/or the size of the lines connecting the evaporator and condenser stages are regulated so that the system; under normal working conditions provides about 500 watts into the support tray regions.

When the machine is held in a standby mode of operation, i.e., when the machine is on but no copies are being produced, the power to the fuser is reduced and thus the flow of energy into the sheet support regions is minimized. An auxiliary heating unit, associated with each. condenser, is herein provided to augment the energy output of the system during periods when the machine is in'a standby condition or during periods when a low volume of copy is being produced. As best seen in FIG. 4, an electrical resistance heater is positioned along the inner walls of each condenser coil. The terminal ends of the heater are connected to output terminals 71 and 72' and the output terminals, in turn, electrically connected to a source of power 75 (FIG. 1) via leads .76, 77. A thermal sensing device 79 is embedded within each condenser coil and is electrically connected to the power supply by means of a lead 80. In operation, the sensing element monitors the temperature of the condensate fluid within the condenser coils. The term fluid is herein used in reference to the working substance contained within the condensers and the fluid can exist as either a gas or a liquid or both. When the sensed temperature of the fluid falls below a predetermined level, the power supply is actuated thus providing energy to the heating elements which, in turn heats the fluid to a predetermined temperature. Auxiliary power the fluid to a predetermined temperature. Auxiliary power to the heaters will remain on until such time as the working substance begins to flow through the closed system indicating that energy is once again passing from the evaporator to the condenser. Although not shown, any sufficient device for measuring the flow of the working substance through the system can be so employed to inactivate the auxiliary power supply.

Under extreme operating conditions, wherein continuous copy is made over a prolonged period of time, steps must be taken to prevent the individual evaporators from becoming overworked and thus burning out. To this end, a series of equalizing devices, generally referenced 56,.are herein provided between the two evaporator units. As shown in FIGS. 3, each equalizer is made up of a hollow tubing 57 which enters the vapor chamber of each evaporator unit well above the normal fluid level line maintained therein. An absorptive wick 58 runs through the tubing and extends downwardly intothe fluid supply area of each evaporator unit. In operation, the wicks, through capillary action, function to equalize the fluid level contained in each unit. In the event that one evaporator unit becomes overworked, the wicks will deliver fluid from the opposite underworked evaporator unit into the fluid deplete overworked unit thus preventing the overworked unit from burning out or otherwise being damaged.

A similar interconnection 60 is also provided between the liquid inlet lines 54 and 55 prior to the lines entering the evaporators. As can best be seen in FIG. 3, the inlet interconnector is quite similar in construction to the equalizing devices extending between the evaporator units in that it consists of a hollow tube or connector 61 running between the two liquid return lines which contain a wick element 62. If a vapor of the working substance inadvertently passes the throttling valve, or otherwise enters one of the liquid return lines, the wick will automatically sense this condition and take corrective action to replenish the liquid in the vapor containing line by bringing liquid from the opposite line and thus returning the system to optimum operating conditions.

While this invention has been described with reference to the structure herein disclosed, it is not necessarily confined to the specific details as set forth and this application is intended to cover any modifications or changes as may come within the scope of the following claims.

What is claimed:

1. In a copying machine having a supply station for storing final support material upon which copies are to be produced and a heat fusing station for fixing said copies, the improvement comprising an evaporator, containing a working substance, which vaporizes at a predetermined temperature, for removing heat energy from the fuser system,

a condensor positioned in said support material supply station, being operatively connected in fluid flow communication with said evaporator means, for condensing said vapor of the working substance and discharging the latent energy into the supply region, and

means associated with said condenser for providing energy to the working substance in said condenser when the rate of discharge falls below a predetermined level.

2. The apparatus of claim 1 wherein said further means includes a sensor for detecting the temperature of the-working fluid within said condenser,

a heating means in thermal communication with said working substance contained within said condenser, and

control means for actuating said heater means when said sensor detects that the temperature level in the working fluid falls below a predetermined level.

3. The apparatus of claim 1 further-including means to return the condensate in said condenser back to the evaporator.

4. The apparatus of claim 3 wherein the vapors and condensate flow between the evaporator and condenser under natural flow conditions.

5. The apparatus of claim 3 wherien the means to return condensate to said evaporators has means to throttle thecondensate prior to the condensates entering the evaporator.

6. The apparatus of claim 1 wherein the working substance vaporizes at about 210 F.

7. The apparatus of claim 6 wherein the working substance is water.

Claims (7)

1. In a copying machine having a supply station for storing final support material upon which copies are to be produced and a heat fusing station for fixing said copies, the improvement comprising an evaporator, containing a working substance, which vaporizes at a predetermined temperature, for removing heat energy from the fuser system, a condensor positioned in said support material supply station, being operatively connected in fluid flow communication with said evaporator means, for condensing said vapor of the working substance and discharging the latent energy into the supply region, and means associated with said condenser for providing energy to the working substance in said condenser when the rate of discharge falls below a predetermined level.

2. The apparatus of claim 1 wherein said further means includes a sensor for detecting the temperature of the working fluid within said condenser, a heating means in thermal communication with said working substance contained within said condenser, and control means for actuating said heater means when said sensor detects that the temperature level in the working fluid falls below a predetermined level.

3. The apparatus of claim 1 further including means to return the condensate in said condenser back to the evaporator.

4. The apparatus of claim 3 wherein the vapors and condensate flow between the evaporator and condenser under natural flow conditions.

5. The apparatus of claim 3 wherien the means to return condensate to said evaporators has means to throttle the condensate prior to the condensates entering the evaporator.

6. The apparatus of claim 1 wherein the working substance vaporizes at about 210* F.

7. The apparatus of claim 6 wherein the working substance is water.

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