Abstract:
A drum ( 10 ) usable as an intermediate transfer member or fuser in a copier or printer, comprising: an outer cylinder ( 16 ) for contact with a toner image; an inner cylinder ( 18 ); and a quantity of liquid ( 12 ) between and in contact with said inner and outer cylinders; wherein the inner cylinder is stationary or rotatable at one or both of a different rotation direction and a different rotation rate from that of the outer cylinder.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is related to the field of printers and copiers and more particularly to printers or copiers that utilize fusers, intermediate transfer members and/or elements that function as both fusers and intermediate transfer members.  
         BACKGROUND OF THE INVENTION  
         [0002]    Printers and copiers are well known. Modern copiers that utilize powder or liquid toners comprising toner particles to form visible images generally form a latent electrostatic image on an image forming surface (such as a photoreceptor), develop the image utilizing a toner (such as the aforementioned powder or liquid toners) to form a developed image and transfer the developed image to a final substrate. The transfer may be direct, i.e., the image is transferred directly to the final substrate from the image forming surface, or indirect, i.e., the image is transferred to the final substrate via one or more intermediate transfer members.  
           [0003]    In general, the image on the final substrate must be fused and fixed to the substrate. This step is achieved in most copiers and printers by heating the toner image on the substrate. In some copiers and printers the fusing and fixing of the image is performed simultaneously with the transfer of the image to the substrate. This is achieved by utilizing a heated intermediate transfer member to perform the transfer and by pressing the intermediate transfer member against the final substrate. This combination of heat and pressure softens the toner particles and fixes them to the substrate. In other copiers and printers, the image is first transferred to the final substrate, and then fused by a separate fuser.  
           [0004]    In several prior art devices, a drum used as an intermediate transfer member or fuser contains water or another fluid in its interior. These include devices described in PCT Publication WO 00/31593, EP 0 772 100 A2, JP Publication 08320625, U.S. Pat. No. 4,172,976, and PCT Application PCT/IL00/00652 filed Oct. 13, 2000, the disclosures of all of which are incorporated herein by reference. There are two reasons for including fluid inside the drum. The first reason is that the fluid can keep the outer surface of the drum at a uniform temperature. This is important for obtaining good image quality, and especially for avoiding “short-term memory” effects, in which an image can be affected by the previous image. Such short-term memory effects are believed to be caused by lower surface temperatures in regions where the drum previously had liquid toner, which cools the surface locally when it evaporates. Having fluid inside the drum has been found to practically eliminate short-term memory. The second reason for using fluid, described in WO 00/31593, is that when the fluid gets hot, the vapor pressure of the fluid inside the drum can support a thin membrane, allowing it to conform slightly to the surface of the substrate that it is in contact with, when transferring images or fixing images. That could also be accomplished by maintaining air under pressure inside the drum, or by including a layer of compliant spongy material underlying the outer surface of a drum whose interior is rigid. But maintaining air under pressure inside the drum would require a pumping system, and a spongy layer can easily become damaged, and thermally insulates the surface from the source of heat inside the drum. Another advantage of using a thin membrane supported by gas pressure is that the heat capacity on transfer is low, so the image cools and hardens during transfer.  
           [0005]    A disadvantage of using fluid inside the drum is that it takes longer to heat the drum up to its operating temperature when the copier or printer is first turned on. In order to minimize this problem, WO 00/31593 describes an inner cylinder inside the drum, concentric with the outer surface. The fluid is confined to the relatively small volume between the inner and outer cylinders. The relatively small volume of fluid does not take as long to heat up, but it is still effective at keeping the outer surface of the drum at a uniform temperature. With this configuration, it may be convenient to heat the fluid by first heating the inner cylinder, for example resistively or by a halogen lamp located inside it, and using the inner cylinder to heat the fluid. Alternatively, the inner cylinder could be made of quartz or some other transparent material, and a lamp inside the inner cylinder could directly heat the fluid and/or the outer cylinder radiatively. Alternatively, a heating element of some other kind could directly heat the fluid.  
         SUMMARY OF INVENTION  
         [0006]    Whether the fluid is heated by the inner cylinder or by some other means, it is desirable to induce turbulence as the drum rotates. That is to say, it is desirable for the fluid to exhibit some vortex motion, even if it does not exhibit fully developed turbulence. Such vortex motion will increase the heat transfer rate for a given temperature differential across the fluid, since heat will be transferred by convection as well as by conduction. Since the required heat transfer rate is fixed by conduction of heat from the outer surface of the drum to the substrate that it is in contact with, this means that the temperature differential across the fluid can be smaller if the fluid flow is non-laminar. Keeping the fluid flow non-laminar also means that the outer surface of the drum will be heated more uniformly, even if the fluid is heated very locally.  
           [0007]    For a given gap between the inner and outer cylinders, vortices will develop at a lower rotation rate of the drum (i.e. the outer cylinder) if the inner cylinder is rotating in a direction opposite to the outer cylinder, rather than rotating in the same direction. Further, for a given speed of rotation of the outer cylinder, counter-rotating the inner cylinder will increase any turbulence that is present. In an embodiment of the invention, the inner cylinder rotates in a direction opposite to the outer cylinder, in order to induce or intensify turbulence.  
           [0008]    In an embodiment of the invention, the fusing/intermediate transfer drum comprises a hollow outer cylinder, an inner cylinder within and coaxial with the outer cylinder, a heater, fluid located in the space between the inner and outer cylinders, and end caps on each end of the outer cylinder to keep the fluid from leaking out. Bearings on each end of the inner cylinder are mounted in the end caps, supporting the inner cylinder while allowing it to rotate with respect to the outer cylinder.  
           [0009]    In some embodiments of the invention, the bearing on one end is located entirely inside the outer cylinder, but the bearing on the other end consists of a shaft which goes through the end cap, surrounded by a rotating seal to keep the fluid from leaking out. On the outside of that end cap, the shaft is surrounded by a cylindrical housing, coaxial with the shaft but with some space between them, and fixed to the end cap. A roller is positioned on one side of the shaft, between the shaft and the housing. The axis of the roller is fixed in place by attaching it to the frame of the copier or printer, but the roller is free to rotate. There is sufficient friction between the roller and the inner surface of the housing, and between the roller and the outer surface of the shaft, that the roller surface will not slide with respect to these surfaces. Alternatively, there are teeth on the roller and on these surfaces to prevent them from sliding. When the outer cylinder rotates, the housing will rotate with it, and this will cause the roller to rotate, which in turn will cause the shaft and the inner cylinder to rotate in the opposite direction.  
           [0010]    In other embodiments, both bearings of the inner cylinder are located entirely within the end caps of the outer cylinder. The shaft, housing and roller are also located within the outer cylinder. In some of these embodiments, the axis of the roller is held in place magnetically, by a holder located near it but on the other side of the end cap. However, it is free to roll. In others of these embodiments, the roller is heavy enough and free enough to roll that it always remains at the bottom of the housing as the drum turns.  
           [0011]    In other embodiments, there is no roller, and the shaft of the inner cylinder extends outside one of the end caps, and it is caused to rotate in one direction by one motor, while another motor causes the outer cylinder to rotate in the other direction. Alternatively, both cylinders could be driven by the same motor, using belts or gears.  
           [0012]    In other embodiments, there is no roller, and both bearings are located entirely within the end-caps of the outer cylinder. A motor compromising a rotor and a stator is used to drive the inner cylinder. The rotor is mounted on the inner cylinder close to one of the end caps, and the stator is located just outside that end cap. Alternatively, a disk, located just outside one of the end caps, could be made to rotate by a motor. The disk could be coupled magnetically to the inner cylinder, causing it to rotate at the same rate. In both these cases, another motor drives the outer cylinder in the opposite direction.  
           [0013]    In embodiments where there is no roller, it is possible to make the inner cylinder rotate in the same direction but at a different rate than the outer cylinder, or to make the inner cylinder remain stationary while the outer cylinder rotates. In these situations, the fluid will still become turbulent at a lower rotation rate of the outer cylinder, than it would if the inner and outer cylinders were rotating in the same direction at the same rate.  
           [0014]    There is thus provided, in accordance with an embodiment of the invention, a drum usable as an intermediate transfer member or fuser in a copier or printer, comprising:  
           [0015]    an outer cylinder for contact with a toner image;  
           [0016]    an inner cylinder; and  
           [0017]    a quantity of liquid between and in contact with said inner and outer cylinders;  
           [0018]    wherein the inner cylinder is stationary or rotatable at one or both of a different rotation direction and a different rotation rate from that of the outer cylinder.  
           [0019]    In an embodiment of the invention, the different rotation rate or different rotation direction of the inner and outer cylinders induces or intensifies turbulence in the liquid.  
           [0020]    In an embodiment of the invention, the turbulence in the liquid leads to increased heat transport between the inner and outer cylinders.  
           [0021]    In an embodiment of the invention, the turbulence in the liquid leads to more uniform heating of the outer cylinder.  
           [0022]    Optionally, a roller, operatively associated with the inner and outer cylinders operates to cause the inner cylinder to rotate in a direction opposite to the direction of rotation of the outer cylinder. Optionally, the roller is located in the interior of the drum. Alternatively, the roller may be located exterior to the drum.  
           [0023]    Optionally, the roller axis is held substantially at a constant location, while the roller is free to rotate about its axis. Optionally, the roller axis is anchored in place. Alternatively, the roller axis may be held in place magnetically. Alternatively, the roller axis may be held in place by gravity.  
           [0024]    In an embodiment of the invention, a first motor drives the inner cylinder and a second motor drives the outer cylinder. Optionally, the inner cylinder has a drive shaft that extends to the exterior of the drum. Alternatively, the inner cylinder could be magnetically coupled to a drive shaft that is located outside the drum. Alternatively, the motor driving the inner cylinder could be have a rotor located inside the drum, and a stator located outside the drum. Optionally, the motor driving the inner cylinder is a permanent magnet motor. Alternatively, the motor driving the inner cylinder may be an induction motor, or any other kind of motor known to the art.  
           [0025]    In an embodiment of the invention, a single motor drives both the inner and outer cylinders. Optionally, the inner cylinder has a drive shaft that extends to the exterior of the drum. Alternatively, the inner cylinder could be magnetically coupled to a drive shaft that is located outside the drum.  
           [0026]    Optionally, the single motor directly drives the outer cylinder, and drives the inner cylinder by means of gears. Alternatively, the single motor could drive both cylinders by means of gears, or could drive one or more cylinders by means of belts.  
           [0027]    In an embodiment of the invention, a single motor drives the outer cylinder, and the inner cylinder substantially does not rotate. Optionally, the inner cylinder is prevented from rotating by a shaft which extends to the outside of the drum. Alternatively, the inner cylinder could be prevented from rotating by means of magnetic force. Alternatively, the inner cylinder could be prevented from rotating by means of gravity.  
           [0028]    In an embodiment of the invention, the outer cylinder has a thin wall. Optionally, the wall of the outer cylinder is supported by gas pressure.  
           [0029]    In an embodiment of the invention, there is a heater within the inner cylinder. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    Exemplary embodiments of the invention are described in the following sections with reference to the drawings. The drawings are generally not to scale and the same or similar reference numbers are used for the same or related features on different drawings.  
         [0031]    [0031]FIG. 1 is a schematic axial view of a drum with counter-rotating inner cylinder in accordance with an embodiment of the invention;  
         [0032]    [0032]FIGS. 2A, 2B, and  2 C are side views of two different embodiments of the drum of FIG. 1;  
         [0033]    [0033]FIG. 3 is a side view of an alternative embodiment of a drum, in accordance with an embodiment of the invention;  
         [0034]    [0034]FIGS. 4A is a side view, and  4 B and  4 C are perspective views, of still other embodiments of a drum;  
         [0035]    [0035]FIG. 5 is a side view of another embodiment of a drum; and  
         [0036]    [0036]FIG. 6 is a side view of the drum, showing a different method of coupling to the inner cylinder, in accordance with an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0037]    [0037]FIG. 1 is a schematic axial view of a drum  10 , in accordance with an embodiment of the invention. Drum  10  comprises a heating element  11 , a roller  12 , in contact with both a housing  14  (FIG. 2) of an outer cylinder  16 , and an inner cylinder  18 . Heating element  11  could be a halogen lamp located on the axis of the inner cylinder, as suggested in FIG. 1, or it could be a resistive heater in the wall of the inner cylinder, or any other kind of heater known to the art. Although free to rotate on its axis, the axis of the roller is fixed in place. This forces the inner cylinder to rotate at the same speed but in the opposite direction as the housing. In some embodiments, the roller is in contact not with inner cylinder  18 , but with a shaft that is connected to inner cylinder  18 . However, the principle of operation is the same as shown in FIG. 1.  
         [0038]    [0038]FIGS. 2A, 2B and  2 C show side views of the drum  10  for three different embodiments that use a roller to drive counter-rotation of the outer and inner cylinders. In all these embodiments, there is fluid  20  filling up at least part of the space between outer cylinder  16  and inner cylinder  18 , as in the prior art described, for example, in PCT Application PCT/IL00/00652 filed Oct. 13, 2000. There are two end caps,  22  and  24 , at the ends of outer cylinder  16 , which prevent the fluid from leaking out. Optionally, end caps  22  and  24  could also allow air or another gas between the outer and inner cylinders to remain at an elevated pressure. Optionally, the wall of outer cylinder  16  could consist of a thin membrane, supported by such gas pressure. In FIG. 2A, roller  12  is located outside end cap  22 , and housing  14  is attached to the outside of end cap  22 . The inner cylinder has two shafts  26  and  28 . Shaft  26  extends beyond end cap  22 , and roller  12  stays in contact with the outside of shaft  26  and the inner surface of housing  14 . Friction or teeth prevent the roller from sliding with respect to these surfaces, but the rolleris free to rotate about its axis  30 . A rotating seal  32  surrounding shaft  26  keeps the fluid from leaking out of the interior of the drum, and keeps a higher pressure inside the drum in the case of a drum whose surface compliance is maintained by gas pressure. Roller axis  30  is held in place simply by attaching it to the frame of the copier or printer. In FIG. 2A, shaft  28 , which is the other shaft of inner cylinder  18 , is shown mounted on a bearing  34  against the inside of end cap  24 . However, shaft  28  could also extend outside end cap  24  with its own rotating seal, similar to rotating seal  32 . Any method known to the art could be used to rotate outer cylinder  16 . For example, FIG. 2A shows a shaft  35  attached to end cap  24 , which can be attached to a motor (not shown in FIG. 2A) which causes it to rotate.  
         [0039]    [0039]FIG. 2A shows heating element  11  in the interior of inner cylinder  18 , where it could heat inner cylinder  18  radiantly. Optionally, inner cylinder  18  could be made of quartz or another transparent material, and heating element  11  could directly heat fluid  20  and/or outer cylinder  16  radiatively. Optionally, heating element  11  could instead use resistive heating, or any other method of heating known to the art, and it could be located in the wall of inner cylinder  18  rather than in the interior of inner cylinder  18 . It could also be located in the fluid. Electric power could be supplied to heating element  11  from outside the drum, by means of slip rings, or inductively, or by any other means known to the art. In some embodiments, where inner cylinder  18  is not rotating and is connected to a shaft that extends outside the drum, electric power could be supplied to heating element  11  by a direct electrical connection. Heating element  11  is present also in the embodiments shown in all of the following drawings, but it is not shown in those drawings.  
         [0040]    In FIG. 2B, roller  12  is located just inside end cap  22 . Inner cylinder  18  is located entirely inside drum  10 , rotating freely on bearings  34  and  36  that are located inside end caps  24  and  22  respectively, so there is no need for a rotating seal. Housing  14  is attached to the inside of end cap  22 , and roller  12  is in contact with the inner surface of housing  14 , and the outer surface of inner cylinder  18 . Roller  12  is made at least partly of iron or some other magnetic material. A holder  38 , consisting at least partly of a magnet, is located just outside end cap  22 , close to roller  12 , and keeps the axis of roller  12  from moving with outer cylinder  16  and housing  14  as they rotate. FIG. 2B shows a track  40  on the outer surface of inner cylinder  18 , which keeps roller  12  from moving axially, preventing roller  12  from moving up to end cap  22  and rubbing against it, which might impede its rotating, and also preventing roller  12  from accidentally moving away from the magnet in holder  38  and consequently ceasing to be held in place by the magnet, or moving past the end of housing  14  and losing contact with it. This could also be accomplished by having a track on the inner surface of housing  14 , or two tracks, one on each surface. Other methods could also be used to keep roller  12  from moving axially. For example, roller axis  30  could extend axially to both end cap  22  and end cap  24 , and slide around races in the end caps as outer cylinder  16  (together with end caps  22  and  24 ) rotates. Whatever mechanism is used to prevent roller  12  from moving axially, it must not seriously impede roller  12  from rotating freely, and it must not seriously impede outer cylinder  16  and inner cylinder  18  from rotating freely.  
         [0041]    Instead of making roller  12  out of iron or another soft magnetic material, it could be made at least partly of a magnet, and holder  38  could be made at least partly of iron or another magnetic material. In still another embodiment, both roller  12  and the holder  38  could be made at least partly of magnets.  
         [0042]    If the magnetic field turns out to significantly impede roller  12  from rotating about its axis, then the central part of roller  12  could consist of a roller bearing  39  made at least partly of a magnetic material, and the rest of roller  12  could be non-magnetic. The friction between roller bearing  39  and roller  12  could be low enough so that roller  12  can rotate freely even if roller bearing  39  is not rotating. Then it will not matter if the magnetic field impedes roller bearing  39  from turning.  
         [0043]    The embodiment shown in FIG. 2C is like that in FIG. 2B, but roller  12  is not magnetic, and there is no holder. Instead, roller  12  is heavy enough, and free enough to roll, that it always remains at the lowest point on housing  14 , as outer cylinder  16  rotates. The force of gravity plays the same role in keeping the roller in place that magnetic force plays in the embodiment shown in FIG. 2B. If roller  12  and holder  38  were located at the bottom of housing  14  in the embodiment shown in FIG. 2B, then both gravity and magnetic force would contribute to keeping roller  12  in place as outer cylinder  16  rotates.  
         [0044]    In FIGS. 2B and 2C, as in FIG. 2A, any means could be used to rotate outer cylinder  16 . For example, any kind of motor could cause shaft  35  to rotate, thereby causing the outer cylinder to rotate.  
         [0045]    Another embodiment of the invention is shown in FIG. 3. In this embodiment, there is no roller. Instead, a separate motor  42 , comprising a rotor  44  and a stator  46 , turns inner cylinder  18 . As in FIG. 2B, inner cylinder  18  is located entirely inside drum  10 , with bearings  34  and  36  on the inside of end caps  24  and  22  respectively, so there is no need for a rotating seal. Rotor  42  could consist of a set of magnets spaced at intervals azimuthally around inner cylinder  18 , near end cap  22 . Stator  46  consists of a set of coils located just outside end cap  22 . By applying AC current to the coils of stator  46  with appropriate phase, or by applying DC current with a commutator, stator  46  will interact magnetically with rotor  44 , causing inner cylinder  18  to rotate. Any other standard or nonstandard type of rotor and stator could also be used to make inner cylinder  18  rotate. For example, instead of using magnets for rotor  44 , a “squirrel cage” could be used, with AC current induced in it inductively by stator  46 , as is done in an induction motor.  
         [0046]    As in FIGS. 2A, 2B, and  2 C, any means can be used to make outer cylinder  16  rotate. For example, any kind of motor can be used to rotate shaft  35 , thereby causing outer cylinder  16  to rotate.  
         [0047]    Another embodiment of the invention is shown in FIG. 4A. Shaft  26  extends past end cap  22 , as in FIG. 2A, and rotating seal  32  keeps fluid  20  inside drum  10 , and maintains the gas pressure there, if there is any gas pressure. Shaft  26  is then caused to rotate by any kind of motor, which causes inner cylinder  18  to rotate. Another motor causes outer cylinder  16  to rotate, for example by means of shaft  35 , as in FIGS. 2A, 2B, and  3 . Although this embodiment requires the use of a rotating seal, the motor driving inner cylinder  18  could be more efficient, and perhaps more reliable and cheaper, than motor  42  in the embodiment shown in FIG. 3, since there is no need for the rotor and the stator to be on opposite sides of end cap  22 . In particular, an off-the-shelf motor could be used in this embodiment, while in the embodiment shown in FIG. 3 it might be necessary to design and manufacture a new motor. As in FIGS. 2A, 2B,  2 C, and  3 , any means can be used to rotate outer cylinder  16 , for example another motor attached to shaft  35 .  
         [0048]    In fact, inner cylinder  18  could be driven by the same motor which drives outer cylinder  16 , using mechanisms such as belts and gears. An exemplary embodiment of this method is shown in FIG. 4B. A motor  48 , which can be any kind of motor known to the art, has a shaft  50  which it causes to rotate. An outer cylinder drive belt  52  in contact with shaft  50  and shaft  35  causes shaft  35  and outer cylinder  16  to rotate in the same direction as shaft  50 . An inner cylinder drive belt  54 , with a twist in it, is in contact with shaft  50  and shaft  26 . Because it is twisted, belt  54  causes shaft  26  and inner cylinder  18  to rotate in a direction opposite to shaft  50 .  
         [0049]    [0049]FIG. 4C shows another exemplary embodiment of a method of driving inner cylinder  18  and outer cylinder  16  by the same motor. A motor  48  directly drives shaft  35 . A gear  56 , attached to shaft  35 , meshes with a gear  58 , causing gear  58  to turn in the opposite direction of gear  56  and shaft  35 . Gear  58  is attached to a shaft  60 , which is attached to a gear  62 , causing gear  62  to turn in the opposite direction to shaft  35 . Gear  62  is enmeshed with a gear  64 , and gear  64  is enmeshed with a gear  66 , which is attached to shaft  26 . Thus shaft  26  turns in the same direction as gear  62 , and in the opposite direction to shaft  35 .  
         [0050]    In other embodiments of the invention, inner cylinder  18  could be rotating in the same direction as outer cylinder  16 , but at a different rate. If inner cylinder  18  and outer cylinder  16  are driven by two different motors, as in FIG. 4A, then the two motors could be rotating in the same direction at different rates. It is also possible for inner cylinder  18  and outer cylinder  16  to rotate in the same direction at different rates even if they are driven indirectly by the same motor. For example, if gear  62  in FIG. 4C were directly enmeshed with gear  66 , rather than indirectly through gear  64 , then gear  66  and shaft  26  would rotate in the same direction as shaft  35 . But, depending on the ratios of the diameters of gears  56 ,  58 ,  62 , and  66 , shaft  26  could be rotating at a different rate than shaft  35 .  
         [0051]    In other embodiments of the invention, inner cylinder  18  is stationary while outer cylinder  16  is rotating. For example, if shaft  26  in FIG. 4A is attached to the frame of the copier or printer, rather than attached to a motor, then inner cylinder  18  would remain stationary while outer cylinder  16  rotates. FIG. 5 shows another embodiment of the invention in which inner cylinder  18  remains stationary while outer cylinder  16  rotates. In FIG. 5, as in FIG. 3, inner cylinder  18  is mounted on bearings  34  and  36  inside end caps  24  and  22 . A weight  68 , at the bottom of inner cylinder  18 , keeps inner cylinder  18  from rotating when outer cylinder  16  rotates. Optionally, there could be a magnetic piece  70 , made at least partly of a magnetic material, attached to inner cylinder  18 , in addition to or instead of weight  68 , and there could be a holder  72 , made at least partly of a magnet, located outside outer cylinder  16  but near magnetic piece  70 , and attached to the frame of the printer or copier. The magnetic attraction between magnetic piece  70  and holder  72  would also keep inner cylinder  18  from rotating when outer cylinder  16  rotates. Optionally, magnetic piece  70  and weight  68  could be the same piece. Optionally, magnetic piece  70  could include a magnet, and holder  72  could be made at least partly of a magnetic material. Optionally, both magnetic piece  70  and holder  72  could include magnets, oriented so as to attract each other. In any of the embodiments in which magnetic force is used to keep inner cylinder  18  from rotating, drum  10  should preferably be designed so that magnetic forces do not unduly inhibit outer cylinder  16  from rotating, and so that any magnetic materials used in outer cylinder  16  and end caps  22  and  24  do not magnetically shield magnetic piece  70  from holder  72  too much.  
         [0052]    In any of the embodiments in which shaft  26  extends from inner cylinder  18  through end cap  22  to the outside (for example, the embodiments shown in FIGS. 2A, 4A and  4 B), inner cylinder  18  could instead be coupled magnetically to the outside, as show in FIG. 6. Shaft  26  does not extend through end cap  22 , but rests on bearing  36  inside end cap  22 . At least one magnet  74  is attached to the end of inner cylinder  18  near end cap  22 , and a disk  76 , with at least one magnet  78 , is located just outside end cap  22 . Alternatively, either magnet  74  or magnet  78  could be replaced by a piece of magnetic material. When disk  76  rotates, inner cylinder  18  is made to rotate by magnetic force. Disk  76  is attached to shaft  80 , which serves the same function as shaft  26  does in FIGS. 2A, 4A, and  4 B.  
         [0053]    In the claims of the present application, the verbs “comprise” and “include” and conjugates thereof mean “include but are not necessarily limited to.” 
         [0054]    While the invention has been described with reference to certain exemplary embodiments, various modifications will be readily apparent to and may be readily accomplished by persons skilled in the art without departing from the spirit and scope of the above teachings. Furthermore, features found in one embodiment may be used in other embodiments. In some embodiments, fewer elements may be present. For example, while the invention is described with reference to a thin-walled pressure-supported drum, in some embodiments of the invention the wall of the drum may be thick enough to be self-supporting. Furthermore, while an internal heater is described, in some embodiments external heating may be used with the liquid acting to distribute the heat uniformly on the drum. Therefore, it is understood that the invention may be practiced other than as specifically described herein without departing from the scope of the following claims: