BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
FIG. 1 shows a roller and an associated cooling system in a longitudinal section;
FIG. 2 shows the roller and the cooling system of FIG. 1 in a condition when the roller is detached;
FIG. 3 shows a roller and a cooling system according to another embodiment;
FIG. 4 shows, in an enlarged longitudinal section, a roller according to yet another embodiment;
FIG. 5 shows, in longitudinal section, an end portion of a roller and an associated cooling system according to yet another embodiment; and
FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As is shown in FIG. 1, a roller 10 includes a stationary axle 12 that is rigidly and detachably flanged to a frame 14 of an image forming apparatus. A cylindrical drum 16 is rotatably supported on the axle 12 by means of bearings 18. It shall be assumed here that the peripheral wall of the drum 16 or at least the portion between the two bearings 18 needs to be temperature-controlled, e.g. cooled. To that end, the bearings 18 are configured as liquid-tight seals, so that an annular space formed between the two bearings 18 and between the outer peripheral surface of the axle 12 and the inner surface of the drum 16 defines a primary liquid circuit 20 that is filled with a liquid coolant, e.g., water. Thus, the heat generated at or transferred to the surface of the drum 16, e.g., because the drum 16 supports a belt or roller (not shown) that is heated in the course of the image forming process, is transferred from the peripheral wall of the drum 16 to the axle 12 through heat conductivity and/or the flow of the water in the primary liquid circuit 20.
One end of the stationary axle 12 (on the right side in FIG. 1) is connected to a heat exchanger 22, which transfers the heat from the thermally conductive axle 12 onto a secondary liquid circuit 24 that is defined inside of a stationary part 26 of the image forming apparatus, i.e. a part rigidly connected to a portion of the frame 14 that has not been shown here. The secondary liquid circuit 24 contains another coolant liquid, e.g. water, that circulates through the stationary part 26 and a cooling device 28, such as a radiator or an active cooling device (heat pump). The cooling device 28 may also include a pump that causes the liquid to circulate through the circuit 24. The cooling device 28 may be replaced or supplemented by a heating device (not shown), if necessary.
The heat exchanger 22 includes a first heat exchange member 30 formed by a flange at the end of the axle 12. A second heat exchange member 32 is formed by an end wall of the stationary part 26. The second heat exchange member 32 is in direct thermal contact with the secondary liquid circuit 24. The first and second heat exchange members 30, 32 form two parallel heat transfer surfaces 34, 36, that are opposed to one another, so that a heat transfer may occur through radiation and/or heat conduction. In the example shown, the heat transfer surfaces 34, 36 form a gap that is filled by a thermally conductive compensation member 38, e.g. a wire mesh, that compensates for any possible misalignment of the axle 12 of the roller 10. The compensation member 38 may also compensate for any possible deflection of the axle 12 when the drum 16 is subject to a mechanical load. Of course, in a modified embodiment, the compensation member 38 may be dispensed with, and the heat transfer surfaces 34, 36 may be in direct engagement with one another.
It will be appreciated that the primary liquid circuit 20 is a closed circuit, so that the liquid therein is permanently sealed inside of the roller 10. On the other hand, the secondary liquid circuit 24 may be an open circuit, but is in thermal contact with the roller 10 only through the heat exchanger 22. The liquid contained in the secondary liquid circuit 24 is nowhere in contact with any part of the roller 10. Thus, the roller 10 may easily be detached, as has been shown in FIG. 2, without any risk of leakage of liquid from the primary liquid circuit 20 or the secondary liquid circuit 24.
In the example shown, thermal contact between the primary liquid circuit 20 and the first heat exchange member 30 is established through the heat conductivity of the axle 12, which may be made of metal. Furthermore, the axle 12 is shown to have vertical bores 40 through which the liquid may circulate. Since the axle 12 is stationary, the bores 40 will retain their vertical orientation. The liquid in the left bore 40 in FIG. 1 will be cooled, because heat is dissipated towards the heat exchanger 22. As a result, a convective flow of the liquid will be established, as indicated by arrows in FIG. 1. In addition, the liquid may be stirred by the rotation of the drum 16. Of course, the bores 40 might be dispensed with, because the liquid may also flow around the axle 12 in the annular gap.
FIG. 3 shows a heat exchanger 22′ according to a modified embodiment. Here, the first heat exchange member is formed by a cylindrical end portion of the axle 12 that is inserted into a blind bore in the end of the stationary part 26 that forms the second heat exchange member. Thus, the end face and the peripheral wall of the end portion of the axle 12 form heat transfer surfaces 34a and 34b, respectively, that are opposed to heat transfer surfaces 36a and 36b, respectively, formed by the bottom and the internal peripheral wall of the blind bore in the stationary part 26. Again, a gap between the heat transfer surfaces is filled by a thermally conductive compensation member.
The secondary liquid circuit 24 includes helical passages that surround the blind bore in close proximity to the heat transfer surface 36b, so that a good thermal contact is achieved when the liquid circulates in the helical passage. In order to improve the thermal contact between the primary liquid circuit 20 and the heat exchanger 22′, the axle 12 according to this example accommodates a heat pipe 42.
FIG. 4 shows another example of a roller 10′, wherein impeller blades 44 are formed on the inner peripheral wall of the drum 16, and stationary impeller blades 46 are formed on the outer periphery of the axle 12. The impeller blades 44 and 46 are arranged alternatingly and are inclined in opposite directions, so that the water in the primary liquid circuit 20 will be propelled from right to left in FIG. 4 when the drum 16 rotates in the direction indicated by an arrow A. The stationary blades 46 prevent the water from co-rotating with the drum 10 when the latter is driven for a longer period of time.
The primary liquid circuit 20 extends into the interior of the axle 12 through radial bores 48 and a central axial bore 50, which extends into the first heat exchange member 30 that is shaped as a flange, as in FIG. 1. At the end of the axial bore 50 on the right side in FIG. 4, the liquid that has been pumped into the passage 50 by the blades 44, 46 impinges onto the wall of the first heat exchange member 30 forming the heat transfer surface 34 and is then radially spread into return ducts 52 that open into the annular space between the axle 12 and the drum 16, thus closing the primary liquid circuit 20.
In this embodiment, the coolant in the primary liquid circuit 20 is still permanently enclosed in the roller 10′, but is actively pumped through the first heat exchange member 30 of the heat exchanger 22, so that the heat transfer will be improved. Of course, this concept can also be used in combination with the heat exchanger 22′ shown in FIG. 3.
FIG. 5 illustrates an example of a roller 10″ that is arranged to rotate as a unit and is rotatably supported in the frame 14 by means of bearings 54. The primary liquid circuit 20 is formed by the hollow interior of the roller 10″. The heat exchanger 22′ is of the type shown in FIG. 3, that is, the first heat exchange member 30 is formed by an end portion of the roller 10″ engaged in a blind bore of the stationary part 26. The gap between the heat transfer surfaces 34a, 34b and 36a, 36b is in this case not filled by any member that would cause friction, because the roller 10″ rotates relative to the stationary part 26.
The secondary liquid circuit in the stationary part 26 is in this case formed by a lower supply passage 24a and an upper supply passage 24b that are both connected to an annular chamber 56 in the second heat exchange member 32. This annular chamber 56 surrounds the first heat exchange member 30, the interior of which forms a convection chamber 58.
The convection chamber 58 is connected to the primary liquid circuit 20 via three axial passages 60, the configuration of which is more clearly shown in FIG. 6. When the liquid in the convection chamber 58 is cooled because it is in thermal contact with the secondary liquid circuit, it will tend to sink down in the convection chamber 58 and flow out through the two lower passages 60 shown in FIG. 6, while new hot liquid is sucked in through the upper passage 60. Thus, a convective circulation of the liquid in the primary liquid circuit 20 is established. This convective flow may be disturbed when the roller 10″ rotates at relatively high speed, but will be established again as soon as the roller 10″ comes to rest. The arrangement of the three passages 60 assures that, in any angular position of the roller 10″, there will always be at least two of the passages 60 having a height difference that induces the convective flow.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
Patent Application
20080056749
