Abstract:
A circulating mechanism includes a moving member, e.g. a chain or a belt, which travels along a circulating path and is looped about at least one deflecting member for reversing a travel direction of the moving member. Disposed in a section of the circulating path is a guide assembly for guiding the moving member. A magnetic field generating device is provided for applying a magnetic force upon the moving member at least in an area of the guide assembly so as to draw the moving member against the guide assembly and thereby enhance the travel behavior of the moving member.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
         [0001]    This application claims the priority of German Patent Application, Serial No. 103 23 910.3, filed May 23, 2003, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates, in general, to a circulating mechanism such a circulating chain mechanism or circulating belt mechanism, and to a method of operating such a circulating mechanism.  
           [0003]    Circulating mechanisms of a type involved here include a moving member, such as for example a transport chain or transport belt, which is moved about a circulating path that is oftentimes split into two path portions whereby the path portions form in particular components of a machine frame. By splitting the circulating path, the moving member can be mechanically tensioned. In case of a circulating chain mechanism, tensioning is normally implemented by using a spring force to urge the path portions of the circulating path against one another so that the chain, which is looped about the path portions and composed of plural chain links, becomes taut. As a consequence, also the chain links of the chain are tensioned. The chain links of the chain may hereby be configured in the form of chain carriages having guide wheels. As the chain is maintained under tension by the spring action, the chain is subjected to vibrations or oscillations that strain the chain and cause wear which adversely affects also parts of the circulating chain mechanism. The chain and its guidance are subjected to shocks and vibrations in particular in the transition zone between the path portions of the circulating path, causing noise and significant wear.  
           [0004]    It would therefore be desirable and advantageous to provide an improved circulating mechanism to obviate prior art shortcomings.  
         SUMMARY OF THE INVENTION  
         [0005]    According to one aspect of the present invention, a circulating mechanism includes a moving member traveling along a circulating path and looped about at least one deflecting member for reversing a travel direction of the moving member, a guide assembly disposed in a section of the circulating path for guiding the moving member, and a magnetic field generating device for applying a magnetic force upon the moving member at least in an area of the guide assembly.  
           [0006]    The present invention resolves prior art problems by providing the circulating mechanism with a magnetic field generating device by which the moving member, e.g. a chain or a belt, is drawn to and bears upon the guide assembly. As a result, the guide assembly is able to guide the moving member along a path while the moving member circulates. In the event the moving member includes guide wheels and the guide wheels roll on the guide assembly, the magnetic field generating device provides a connection at all times between the guide wheels of the moving member and the guide assembly.  
           [0007]    When the moving member is a chain comprised of plural chain links, the magnetic field generating device is able to influence at least some or all chain links by a magnetic field and a magnetic force. Hereby, the magnetic field generating device may be realized by magnetized material that is integrated in the chain links. Examples of magnetizable material include a permanent magnet or a remagnetizable material, i.e. soft-magnetic material, such as ferrous material, which can be magnetized and has a slight coercive force and which looses a substantial part of magnetization, once the magnetic field is removed. In other words, a material with slight remanence.  
           [0008]    The advantageous effect of the magnetic field can be realized through repulsive action as well as attractive action of the magnetic field. When using repulsive action, the chain includes, e.g. a permanent magnet or an electromagnet which has a magnetic field that opposes a further magnetic field. The repulsion pushes hereby the chain against the guide assembly.  
           [0009]    According to another feature of the present invention, the magnetic field generating device applies a force upon the chain to urge the chain against the guide assembly. The magnetic field generating device may hereby be a permanent magnet or electromagnet, and represent a part that is separate from the chain whereby the magnetic field travels across the chain.  
           [0010]    A circulating mechanism according to the present invention is cost-efficient to manufacture when the chain includes a magnetic material which is remagnetizable, and thus has a slight coercive force and small remanence, such as soft-magnetic ferrous material, and when a magnetic field is generated which does not have to interact with another magnetic field to produce a magnetic force. Shocks, vibrations and excessive wear are eliminated or at least significantly reduced by the magnetic attraction of individual chain links against the guide assembly which forms a guide path. The provision of the magnetic field generating device is also advantageous in connection with a mechanical play between individual chain links of a chain. Even, when encountering such a mechanical play between individual chain links, the chain can no longer detach from the guide assembly. The guide assembly may extend over single portions of the circulating path, or over several portions, or over the entire circulating chain path. As the chain links of the chain are pressed individually against the guide assembly through magnetic force and thus can no longer detach from the guide assembly, it is no longer necessary to mechanically maintain the chain under tension on its circulating path, or at least the need for re-tensioning the chain mechanism is eliminated. Thus, the circulating mechanism is easier to operate and less complicated to manufacture, thereby reducing overall costs. The circulating chain path can now be made in one piece, thereby eliminating the problem caused by vibrations and arrangement of a tensioning spring.  
           [0011]    In particular, when transporting chain mechanisms are involved which operate at high speed of the chain, wear of the chain and the guide assembly is significantly reduced so that replacement thereof is less frequent, resulting in longer operating times and shorter standstill periods.  
           [0012]    According to another feature of the present invention, a flux conductor may be provided for directing a magnetic flux of the magnetic field. The flux conductor may hereby be positioned adjacent to an air gap, with the magnetic flux conducted across the air gap. By using one or more flux conductors, which may include remagnetizable ferrous material, the generated magnetic field can be conducted in such a manner as to realize a high magnetic force. The air gap is sized as small as possible and may even approach zero, in which case the flux conductor thus closes the magnetic field without provision of an air gap.  
           [0013]    According to another feature of the present invention, the magnetic field generating device may be integrated in the moving member, and/or the magnetic field generating device may be fixed in place in relation to the guide assembly. Integration of the magnetic field generating device in the moving member has the advantage that a magnetic flux is generated and a magnetic force is applied during travel of the moving member over the entire circulating path. Disposing the magnetic field generating device in fixed relation to the guide assembly simplifies installation and does not increase the inertia of the moving member, thereby positively affecting the dynamic behavior of the circulating mechanism.  
           [0014]    According to another feature of the present invention, the magnetic field generating device may be disposed in an area of the deflecting member, in particular in an area of an entry zone of the moving member. The guide assembly is subject to wear in particular in the area of the deflecting member or entry zone which is further increased when the deflecting member, also called chain wheel head in the event of a chain as moving member, is resiliently supported by a portion of the machine frame. In this case, the resilient deflecting member has several vibrations modes. The resilient construction, heretofore required to tension the chain, results between the deflecting member and the machine frame in a jointed area which excites additional vibrations.  
           [0015]    In accordance with the present invention, pretensioning of the moving member, e.g. by a spring, can be omitted when the moving member is tensioned electrically. As a consequence, the deflecting member, i.e. chain wheel head, can be securely fixed to the machine frame. The moving member can be maintained under tension by means of a biasing torque or braking moment for the drive of the deflecting member. Thus, the tendency of the deflecting member to vibrate is reduced to a minimum. Moreover, there is no jointed area between the deflecting member and the machine frame. As a result, the moving member such as a chain, can be held on the circulating path without a single jointed area between the deflecting member and the machine frame. Vibrating or rattling of the chain is thus avoided.  
           [0016]    According to another feature of the present invention, the magnetic field generating device may be made of magnetized material, e.g. a permanent magnet, e.g. of hardened carbon steel with high remanence, or an electromagnet which generates a magnetic flux when electric current is applied.  
           [0017]    According to another feature of the present invention, the air gap may be made variable in size. In this way, the magnetic force acting upon the moving member can also be varied accordingly. Suitably, a controller is provided to control the size of the air gap in dependence on, e.g., a circulating speed of the moving member. When high speeds are involved, a reduction of the air gap size increases the magnetic force so that the moving member is drawn at all times against the guide assembly despite the increase in centrifugal forces. On the other hand, when the moving member circulates at reduced speed, the air gap can be enlarged to such an extent that the magnetic force is still sufficient to maintain the moving member against the guide assembly. In this way, wear is less as friction is reduced.  
           [0018]    According to another aspect of the present invention, a method of guiding a moving member of a circulating mechanism includes the step of applying a magnetic force upon the moving member to thereby draw the moving member to a guide assembly. The moving member may hereby be a chain or a belt. The magnetic force upon the moving member can be controlled by directing the magnetic field across an air gap and varying the size of the air gap in dependence on, e.g., the speed of the moving member.  
           [0019]    According to another feature of the present invention, the moving member is maintained under tension electrically, e.g. by a biasing torque or a braking moment, predefined in a control unit of a drive for propelling the deflecting members of the circulating mechanism.  
           [0020]    A circulating mechanism according to the present invention, such as a circulating chain mechanism or a circulating belt mechanism, is applicable in a production machine or machine tool having a sensor for ascertaining wear of the moving member and/or guide assembly and/or deflecting member. Such a sensor is, e.g., provided for measuring the magnetic field and includes means for changing the magnetic field in dependence on the extent of wear.  
           [0021]    The circulating mechanism in production machines or machine tools is oftentimes propelled by means of an electric drive which can be controlled by power converters to produce a mechanical tension. Thus, the mechanical tension of the moving member can be combined with the magnetic field generating device for guiding the moving member free of wear.  
           [0022]    A circulating mechanism according to the present invention is also applicable in a crawler vehicle having a superstructure, and a base for supporting the superstructure, with the base having a circulating chain mechanism with a chain traveling along a circulating path and looped about at least one deflecting member for reversing a travel direction of the moving member, a guide assembly disposed in a section of the circulating path for guiding the moving member, and a magnetic field generating device for applying a magnetic force upon the moving member at least in an area of the guide assembly. Examples of a crawler vehicle includes construction vehicles, such as a crane, an excavator, a caterpillar, which have a crawler-based drive unit.  
           [0023]    Also a robot may be equipped with a circulating chain mechanism according to the present invention for movement. Likewise, armored vehicles or other transport vehicles may be constructed as crawler vehicles, including a bucket wheel excavator or an excavator for transporting brown coal or hard coal.  
           [0024]    The use of a circulating chain mechanism in a crawler vehicle reduces vibration, oscillations and wear. This is especially true when high speeds of the chain are involved in view of the improved guidance of the chain so that the chain can be operated at maximum speed. Also, when the crawler vehicle operates a lower speed of the chain, previously experienced problems as a result of dirty chains, statically unbalanced load of the crawler vehicle, or irregularities in the road surface, and leading to oscillations or vibrations can be significantly reduced. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0025]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:  
         [0026]    [0026]FIG. 1 is a perspective view of a circulating mechanism according to the present invention, constructed in the form of a circulating chain mechanism in combination with a circulating belt mechanism;  
         [0027]    [0027]FIG. 2 is a cutaway view in perspective illustration of the circulating chain mechanism of FIG. 1, showing in detail the area of a deflecting member of the circulating chain mechanism;  
         [0028]    [0028]FIG. 3 is a cutaway view in top perspective illustration of the circulating chain mechanism of FIG. 1, showing in detail the area of a guide assembly of the circulating chain mechanism;  
         [0029]    [0029]FIG. 4 is a schematic illustration of a modified embodiment of a circulating chain mechanism according to the present invention;  
         [0030]    [0030]FIG. 5 is a cutaway view of the circulating chain mechanism of FIG. 4 with modified deflecting member;  
         [0031]    [0031]FIG. 6 is a schematic illustration of a circulating chain mechanism according to the present invention depicting the course of a generated magnetic field;  
         [0032]    [0032]FIG. 7 is a schematic illustration of another circulating chain mechanism according to the present invention depicting the course of a generated magnetic field;  
         [0033]    [0033]FIG. 8 is a schematic illustration of a guide wheel of a chain link of a circulating chain mechanism according to the present invention;  
         [0034]    [0034]FIG. 9 is a detailed view of an arrangement of a permanent magnet in a circulating chain mechanism according to the present invention;  
         [0035]    [0035]FIG. 10 is a schematic illustration of a template for positioning magnets on a circulating chain mechanism according to the present invention;  
         [0036]    [0036]FIG. 11 is a schematic illustration of another template for positioning magnets on a circulating chain mechanism according to the present invention;  
         [0037]    [0037]FIG. 12 is a schematic illustration of still another template for positioning magnets on a circulating chain mechanism according to the present invention;  
         [0038]    [0038]FIG. 13 is a schematic illustration of a flux conductor for a circulating chain mechanism according to the present invention; and  
         [0039]    [0039]FIG. 13 a  is a cross sectional view of the flux conductor of FIG. 13. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0040]    Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.  
         [0041]    Turning now to the drawing, and in particular to FIG. 1, there is shown a perspective view of a circulating mechanism according to the present invention, constructed in the form of a circulating chain mechanism, generally designated by reference numeral  1 , in combination with a circulating belt mechanism, generally designated by reference numeral  41 . The circulating chain mechanism  1  includes a chain  3  composed of a plurality of interconnected chain links  5 . The chain  3  moves about a circulating path  6  which defines a closed loop and is shown in more detail in FIG. 1 only over a section of the circulating chain mechanism  1  for sake of simplicity. The circulating path  6  of the chain  3  is guided about deflecting members  17  on opposite ends of the circulating path  6  (only one deflecting member  17  on the left-hand side is shown in FIG. 1). The deflecting member  17 , also referred to as chain wheel head, is formed about its perimeter with grooves  19  for engagement of engagement arms  21  of the chain  3 . The chain  3  is guided about guide wheels  7  which include the engagement arms  21  and are guided by guide assemblies  14 ,  15 ,  16 . The guide assemblies  15 ,  16  form hereby a track for the guide wheels  7 , with the guide assembly  15  having a circular configuration in the area of the deflecting member  17 , as indicated by the dashed line.  
         [0042]    The deflecting member  17  is rotatably supported by a tensioning member  35  which is connected by cylinders  37  to a machine frame  9 . A spring  39  urges the tensioning member  35  via the cylinders  37  in a direction away from the machine frame  9  so that the applied spring force maintains the chain  3  under tension. Depending on the transport direction of the chain  3 , as indicated by arrows  23 ,  24 , chain entry and chain exit  29 ,  30  are defined in the area of the deflecting member  17 . The area of the deflecting member  17  is shown in greater detail in FIG. 2, which shows in particular the guide assembly  15  providing a track for the guide wheels  7  with their engagement arms  21 .  
         [0043]    Although not shown in detail, at least the one of the deflecting members  17 , which is securely fixed to the machine frame  9 , is normally propelled electrically while the other deflecting member  17  provides only proper guidance of the chain  3  and is also spring-biased in a direction away from the machine frame  9  to maintain the chain  3  under tension. Of course, it is certainly conceivable to propel more than one of the deflecting members  17 .  
         [0044]    The circulating chain mechanism  1  and the circulating belt mechanism  41  may be used together to transport therebetween an article (not shown), e.g. a wooden panels for a parquet floor, for precise positioning. The circulating belt mechanism  41  includes a belt  42  which is looped about primary deflecting members  18  on opposite ends and secondary deflecting members  22 . At least one of the deflecting members  18  is mechanically connected to a drive, e.g. an electric drive, for propelling the belt  42  which is further guided along its circulating path by guide wheels  20 . The guide assembly  14  is hereby also provided to guide the belt  42  so that the belt  42  can easily enter or exit the deflecting member  18  at area  28 .  
         [0045]    [0045]FIG. 3 shows in more detail the chain entry zone  29  of the chain  3  into the deflecting member  17 , when the chain  3  moves in direction of arrow  23 . In addition to the illustration of the interconnected chain links  5 , FIG. 3 also illustrates the problem associated to shocks, vibrations and oscillations in the entry zone  29 . As a result of the suspension of the tensioning body  35  via the cylinders  37 , oscillations and vibrations are encountered in relation to the machine frame  9 . Thus, the guide wheels  7  bang against the guide assembly  15 , leading to wear. In accordance with the present invention, this problem is addressed and overcome by providing magnets  11 , such as permanent magnets or electromagnets and shown e.g. in FIG. 6, in the area of the guide assembly  14  as well as in the area of the guide assemblies  15  and  16  in order to draw the guide wheels  7  and thus the chain  3  and belt  42  through magnetic force against the guide assemblies  14 ,  15 ,  16 , respectively during their advance. As a consequence, the movement of the chain  3  is relatively quiet and smooth.  
         [0046]    Turning now to FIG. 4, there is shown a schematic illustration a modified embodiment of a circulating chain mechanism  1  according to the present invention, having deflecting members  17  on opposite ends. Parts corresponding with those in FIG. 1 are denoted by identical reference numerals and not explained again. Both deflecting members  17  are propelled here by separate drives which are shown here by way of example only. Each belt drive includes a belt  25  for operatively connecting a motor  31 , in particular a controllable electric motor, with the deflecting member  17 . As further shown in FIG. 4, a plurality of magnets  11  is disposed in the area of the entry zone  29  along the circular path about the deflecting member  17 . The circulating chain mechanism  1  is here of single-piece construction without circulating belt mechanism  41  and without arrangement of spring  39  for maintaining the chain  3  under tension. As a consequence, the problem associated with vibrations and oscillations is eliminated or at least significantly reduced because the need for the tensioning member  35  is also eliminated.  
         [0047]    The guide wheels  7  are configured as rollers and maintained by the attractive magnetic force of the magnets  11  on a track defined by the guide assemblies (not shown in FIG. 4) so that the deflecting members  17  can be rotatably connected to the machine frame  9 . Thus, there is no need for a jointed area between machine frame  9  and a tensioning member. The magnets  11  assume hereby also the function to maintain the chain  3  under tension so that the need for re-tensioning is eliminated. The positive effect of drawing the chain links  5  to the track further assists the mutual tensioning between the defecting members  17 . It is hereby possible to apply a biasing torque upon one of the deflecting members  17  in relation to the other one of the deflecting members  17 . As an alternative, it is also possible to bias the other one of the deflecting members  17  by a drive with a predetermined braking moment, or by a brake which executes a braking moment.  
         [0048]    As shown in FIG. 4, the magnetic attraction of the guide wheels  7  at the lower chain entry zone  29  draws the chain links  5  (chain carriages) firmly against the guide, thereby preventing bouncing of the chain  3 . By making the guides of elastic material, e.g. steel band which is able to absorb the bouncing energy, wear is further reduced.  
         [0049]    The circulating chain mechanism as shown in FIG. 4 does not require a manual tensioning of the chain  3  because both deflecting members  17  are securely fixed to the machine frame  9  and the chain  3  is guided about the entire circulating path in the absence of any jointed areas.  
         [0050]    In FIG. 5, the deflecting member  17 , unlike the construction shown in FIG. 4, is provided with magnets  11  in the chain entry zone  29  as well as in the chain exit zone  30  to draw and guide the chain  3  during its advance.  
         [0051]    Referring now to FIG. 6, there is shown is a fragmentary schematic illustration of the circulating chain mechanism  1 , depicting in detail the pattern of a generated magnetic field in the area of a guide wheel  7  having engagement arm  21  and disposed upon the guide assembly  15 . A magnet  11  is positioned at the guide assembly  15 . A flux conductor  43  is hereby provided to properly direct the magnetic flux or magnetic field, as shown by magnetic field lines  13 , across an air gap  45 .  
         [0052]    [0052]FIG. 7 shows another embodiment of a circulating mechanism according to the present invention which differs from the embodiment of FIG. 6 by providing a flux conductor  44  which is so configured as to provide a running surface for the guide wheel  7  in the absence of an air gap, in addition to the running surface formed by the guide assembly  15 .  
         [0053]    [0053]FIG. 8 shows in more detail the configuration of the guide wheel  7  with engagement arm  21  which defines a wheel axis  8 . The magnet  11  is shown here also by the magnetic pole distribution with N designating the north pole and S designating the south pole. Reference numeral  10  designates the bearing for the guide wheel  7  upon the guide assembly  15 .  
         [0054]    Referring now to FIG. 9, there is shown the use of a template  47  for proper positioning of magnets  11  in the circulating mechanism  1 . The template  47  is configured as expendable template  47  to assist a proper positioning of individual magnets  11 , whereby the template  47  may remain in the circulating mechanism after installation of the magnets  11 . The magnetic poles may hereby, for example, be aligned in such a manner that the north pole is always directed to the outside. The use of template  47  is desired because poles of same sign repel one another so that the magnets  11  have a tendency to move apart, complicating otherwise the gluing operation for attachment of the magnets  11 . The magnetic circuit is so configured that a major part of the width of the running surface of the guide wheel  7  is maintained. Advantageously, the magnetic yoke is shifted substantially to the side surface  12  of the guide wheel  7 .  
         [0055]    [0055]FIG. 10 shows a straight template  49  for use with a guide assembly of straight configuration. The dashed line represents the track  57  for the guide wheels  7 . Recesses  55  are provided for receiving the magnets  11 . FIG. 11 shows a curved template  51 , used in particular for the area of the deflecting members  17 ,  18 . FIG. 12 shows a half-curved template  53  having a curved portion  59  as well as a straight portion  61 . The half-curved template  53  is used in particular for the area of the chain entry  29  or belt entry as well as chain exit  30  or belt exit  28 . The template  53  may be made of non-magnetic special steel, such as V2a, and has a material thickness of 1.5 mm.  
         [0056]    [0056]FIG. 13 shows a schematic longitudinal view of the flux conductor  43  and illustrates the positions of the magnets  11  by dashed line. FIG. 13 a  shows a cross section of the flux conductor  43 .  
         [0057]    While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.  
         [0058]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: