Abstract:
A tensioning apparatus for a circulating element, such as a belt or a band, has a basic body in which a first chamber is formed. A piston is positioned in the first chamber and carries a piston rod. The piston can be displaced in the first chamber by the use of a pressure fluid. Either the piston rod or the base body is attached to the carrier for the belt or band. Either the piston rod or the basic body carries a head piece which can be moved in contact with the circulating element. A locking mechanism for the piston rod can be engaged and disengaged by the use of fluid pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase, under 35 USC 371, of PCT/EP2007/052668, filed Mar. 21, 2007; published as WO 2007/107581 A1 on Sep. 27, 2007 and claiming priority from DE 10 2006 013 635.7, filed Mar. 22, 2006 and from DE 10 2006 060 236.6, filed Dec. 20, 2006, the disclosures of which are expressly incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention is directed to tensioning mechanisms for a circulating element. A main body has a first chamber that receives a displaceable piston. A piston rod is driven by movement of the piston in response to the introduction of a pressurized fluid into the first chamber. The main body is mounted on a support and the piston rod supports a head piece, typically a pulley that can be moved into contact with a circulating element. 
     BACKGROUND OF THE INVENTION 
     Endless belts, which are utilized as circulating elements, are used in production systems to transport workpieces. For transport of such workpieces in a substantially horizontal direction, the workpieces can lie loosely on an endless belt or can lie loosely on a plurality of endless belts which are arranged side by side. For transport of such workpieces in any direction, they can be clamped between cooperating circulating endless belts that are arranged opposite one another. In either of these configurations, and in order to accurately convey the workpieces, it is important for the endless belts to each have a predetermined degree of tension. Such tension is needed either to limit the sagging of the belts, under the weight of the workpieces, to a predetermined level, or to ensure an adequately secure clamping of the workpieces between the cooperating belts which are arranged opposite one another. 
     A tensioning mechanism, that can be used to implement a desired tension to a circulating endless belt, generally comprises a main body, which is stationary in relation to a frame that supports the belt, and a head piece, such as a pulley, which is in contact with the belt. The pulley can typically be displaced, in relation to the main body, for the purpose of varying the path length of the belt, thereby varying its tension. 
     The technique of using a threaded spindle, for the purpose of displacing the pulley, is generally known. The rotation of such a threaded spindle causes the pulley to be displaced in relation to the main body. However, adjusting the belt tension using such a threaded spindle is laborious and time-consuming. Each time the pulley is adjusted, the belt tension must be measured to determine whether it is correct and to thus determine if further displacement of the pulley in one or the other direction is necessary. If a conveyor belt device has a plurality of circulating endless belts which are arranged in parallel, this belt tensioning process must be performed separately for each endless belt. Moreover, in an assembly comprising a plurality of tensioning mechanisms for use in the tensioning of a plurality of belts, it is difficult to transfer the adjusting motion to the threaded spindle of each individual adjustment mechanism within a compact structure. 
     The tensioning process can be simplified by the use of a tensioning mechanism that is actuated using a pressurized fluid. The pressure of the pressurized fluid applied to the tensioning mechanism determines the belt tension to be achieved rather than a position of the movable pulley. In other words, the application of the same pressure of the pressurized fluid to a tensioning mechanism can result in different positions for the pulley, depending upon the length and the elasticity of the endless belt to be tensioned. The requirement of measuring belt tension is thus eliminated. Moreover, a plurality of tensioning mechanisms, for use with a plurality of belts having the same transport direction, can be acted upon by pressurized fluid in parallel, in order to generate the same belt tension in all of the belts, regardless of potential variations in their lengths and/or elasticity. 
     However, it has been found that such a pressurized fluid or pneumatically driven belt tensioning mechanism produces greater wear and tear on the endless belts than does a mechanical tensioning mechanism. 
     DE 35 31 552 A1 discloses a tensionable belt reversal unit for a conveyor belt used in mining and tunnel construction. The tensionable belt reversal unit can be moved and locked in position via an actuator cylinder. 
     A chain conveyor for underground mining is known from DE 83 17 386 U1. A hoisting cylinder and a locking device are provided. 
     DE 18 01 522 A describes a tensioning mechanism for endless chain or belt mechanisms. This mechanism is provided with a pressurized medium cylinder. 
     DE 38 35 524 A1 discloses a reversing station for a scraper chain conveyor. A tensioning mechanism for the scraper chain belt is provided. 
     DE 25 54 785 A1, DE 100 14 700 A1, DE 43 15 504 A1, DE 42 30 781 C2, DE 35 40 880 A1 and DE 90 05 350 U1 all describe pressure actuated drives. 
     DE 31 13 894 A1 describes a pressure actuated operating cylinder. A piston rod is steplessly fixed in position via a pressure actuated, stationary device. 
     EP 0 890 532 A1 relates to a device for tensioning systems for transporting flat products in a folding unit. The device for transporting the flat products includes a plurality of individual belts. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a device that is usable as a tensioning mechanism for a circulating element such as an endless belt. 
     The object of the present invention is attained with the provision of a tensioning mechanism having a main body in which a first chamber is provided. A piston is positioned in the first chamber and can be displaced by the application of a fluid under pressure to that first chamber. A piston rod is driven by movement of the piston. The main body is securely mounted on a support and the piston rod carries a head piece, such as a pulley that is movable into contact with the circulating element. A mechanism for locking the piston rod in a certain position can be controlled also using pressurized fluid. The main body has at least one second chamber which is usable to control the piston rod locking mechanism. 
     One advantage of the tensioning mechanism in accordance with the present invention is that it enables a rapid and precise adjustment of belt tension while also enabling a wear-resistant operation of the endless belts. Locking the piston rod in place prevents the pulley from shifting back from its adjusted position as a result of any decrease in belt tension that may occur during operation, for example when a conveyed product is delivered. This would cause the belt to be increasingly stretched over time. 
     Preferably, at least one second chamber of the main body, which at least one second chamber can also be pressurized with pressurized fluid, is used to control the locking mechanism for the piston rod. 
     In accordance with one preferred embodiment of the present invention, every second chamber contains a displaceable second chamber piston, which is forced against the piston rod attached to the first chamber piston when the second chamber is pressurized with pressurized fluid. This will lock the piston rod in place. 
     In accordance with a second preferred embodiment of the present invention, every second chamber can be bounded by a membrane, which membrane is forced against the piston rod that is connected to the first chamber piston when the second chamber is pressurized with pressurized fluid. This second arrangement is also used to lock the piston rod of the first chamber piston in place. 
     To prevent the piston rod from yielding or deforming under the pressure which is exerted upon it by the second chamber, the piston rod is preferably conducted through an opening in the main body. The second chamber is arranged on one side of the opening. A second side of the opening, which is opposite the first side, is formed by an abutment, which abutment is securely connected to the main body. 
     To prevent the piston rod from yielding or deforming, it is also expedient for the forces exerted on the piston rod to be provided or exerted by a plurality of second chambers, each pressurized with pressurized fluid. In order to compensate for one another, it is especially beneficial to arrange the plurality of second chambers with the membranes or pistons of the plurality of second chambers executing movements in opposite directions when pressurized, and all exerting forces of substantially the same level on the piston rod. 
     It is particularly expedient for the piston rod to be divided into a plurality of branches, and for an area of the main body which contains the second chambers to be arranged between these branches. This is beneficial for the application of balanced locking forces to the piston rod by the several secondary chambers. 
     To ensure adequate rigidity, each of the branches is preferably connected at two ends to a frame that encompasses the respective area of the main body. 
     To keep the structure compact, the first chamber can also be situated in an area of the main body which is located between the branches. 
     The piston of the first chamber is preferably a dual action piston. Both an extending movement and a retracting movement of the head piece can be controlled by the use of the dual action piston. 
     Supply couplings, for use in supplying the first and the second chamber with pressurized fluid are preferably attached, aligned in pairs and in communication with one another, to opposite sides of the main body. This arrangement significantly simplifies the side by side assembly of a plurality of tensioning mechanisms for use in tensioning a plurality of belts in the same conveyor belt device. 
     To attach the tensioning mechanism to the support, the main body can be equipped with a bore hole. The bore hole can then be configured to hold the support. 
     This bore hole preferably extends parallel to the direction of alignment of the communicating supply couplings. This will facilitate a compact, organized positioning of the main body and the supply couplings. 
     The chambers in the main body, and the head piece attached to the piston rod are preferably arranged on diametrically opposite sides of the bore hole. The support can accordingly support the tensioning mechanism close to its center of gravity. At the most, levels of torque will occur between the support and the tensioning mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present invention are detailed in the following detailed description of the preferred embodiments, taken in conjunction with reference to the accompanying set of drawing figures. 
       The drawings show in: 
         FIG. 1  a perspective view of a tensioning mechanism for a circulating element in accordance with the present invention; in 
         FIG. 2A-D  schematic representations of variations of the tensioning mechanism; in 
         FIG. 3  a cross-sectional view of the tensioning mechanism in accordance with the present invention; in 
         FIG. 4  a locking device for the tensioning mechanism; in 
         FIG. 5  an arrangement of a plurality of tensioning mechanisms combined to form an assembly; in 
         FIG. 6  an enlarged partial sectional view of tensioning mechanisms combined to form an assembly; in 
         FIG. 7  an enlarged partial sectional view of a head piece of the tensioning mechanism in accordance with the present invention; in 
         FIG. 8  a schematic representation of a folding unit with belt systems; and in 
         FIG. 9  a schematic representation of a belt tensioning system. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to  FIG. 1 , there may be seen a preferred embodiment of a tensioning mechanism for a circulating element in accordance with the present invention. The tensioning mechanism which is depicted in  FIG. 1  is shown mounted on a rod-shaped support  01 , which support  01  is configured having an out-of-round cross-section. An ovoid cross-section is depicted in  FIG. 1 . It will be understood that other out-of-round cross-sections, such as square, rectangular, elliptical and the like could also be used as the shape for the support  01 . A main body  02  of the tensioning mechanism is broken down, in the longitudinal direction of travel of the circulating element, which is not specifically shown in  FIG. 1 , into a base section  03 , a cylindrical section  04 , and a head section  09 . The support  01  extends through a transverse bore hole in the base section  03 . A first chamber  06  is formed in the cylindrical section  04  of the main body  02 , as seen in  FIG. 3 . A piston rod  07  is connected to a piston  08 , both of which are disposed in the first chamber  06 . The piston rod  07  emerges at the head section  09  of the main body  02 . The piston rod  07  is extended by or is joined to a head of a U-shaped yoke  11 , which is preferably formed from a metal strip. Two legs  12 ,  13  of the U-shaped yoke  11  lead back, parallel to the piston rod  07 , on opposite sides of the main body  02 , to the side of the support  01  which is remote from the head section  09 . Each of the legs  12 ,  13  of the U-shaped yoke is fed through an opening, which is bounded by the head section  09  and by a bracket  17  that is attached to the head section, as seen in  FIG. 1 . Each leg  12 ,  13  then extends through a groove or channel  18  which is formed on an upper narrow side, or on a lower narrow side of the base section  03  of the main body  02 . At their open ends, the two legs  12 ,  13  of the U-shaped yoke  11  are securely connected, to form a rigid, rectangular frame, via a block  14 . The block  14 , in turn, supports a head piece in the form of a rotatable pulley  16 , which pulley  16  is configured to be wrapped by an endless belt whose tension is to be adjusted. The piston rod  07 , the yoke  11  and the block  14  can together be conceived of, in a broader sense, as a compound piston rod which connects the pulley  16  to the piston  08 , in order to accomplish an adjusting movement of the pulley  16 . 
     Two pairs of ribs  19 , as may also be seen in  FIG. 1 , and which are adjacent the main body base section  03 , have end surfaces  21  that lie within the same plane. That rib end surface plane is perpendicular to the longitudinal direction of the support  01 . These ribs  19  are formed on the cylindrical section  04  of the main body  02 . Threaded bore holes  22  are formed in the end surfaces  21  and are situated to enable the attachment of an arm  23  that supports one or more additional pulleys. One such attachment arm  23  and its additional pulley is illustrated in  FIG. 1  by a dashed line because it is optional. 
     The diameter of the piston  16  is preferably from 25 mm to 40 mm, and preferably is 32 mm. With this pulley  16 , belts that are 25 mm to 35 mm in width, and which preferably are 30 mm in width, can be tensioned. 
     As is illustrated schematically in  FIG. 2A , the tensioning mechanism, in accordance with the present invention, can use the pulley  16  as the sole pulley, and can tension a belt  24 , which wraps around the pulley  16  on a section of its periphery that faces away from the main body. Such tensioning of belt  24  is accomplished by pushing the pulley  16  away from the main body  02 . The aforementioned optional arm  23  can be equipped with an additional pulley  26 , around which additional pulley  26  the belt  24  is wrapped, as seen in  FIG. 2B . The arm or arms  23  can project outward from the main body  02  in opposite directions, and can support a pulley  26  at each open end, as seen in  FIG. 2C . Moreover, an arrangement, in accordance with  FIG. 2D  is also possible in which only the displaceable pulley  16  is provided, but it is wrapped by the belt  24  to be tensioned on its side that faces the main body  02 . 
       FIG. 3  shows a detailed sectional view of the tensioning mechanism, in accordance with the present invention, in the arrangement depicted schematically in  FIG. 2C . A first stop configuration, in which the pulley  16  is spaced as far as possible from the main body  02 , is represented by solid lines. In this first stop configuration, the piston  08  is located in the first chamber  06  in direct proximity to a first chamber end surface  27  of the chamber  06 , which is adjacent to the support  01 . The piston rod  07  extends through the chamber  06  and through a bore hole in the head section  09 , up to a point of connection with the yoke  11 , which lies outside of the main body  02 . The two legs  12 ,  13  of the yoke extend parallel to the piston rod  07  in the opposite direction between the head section  09  and the brackets  17  which are attached to the head section  09 , as seen in  FIG. 1 . In the head section  09 , opposite the brackets  17 , two locking chambers  28  can be seen in  FIG. 2 , which locking chambers  28  can be pressurized with compressed air via a bore hole  29  that extends through the head section  09  parallel to the support  01 . Each of the locking chambers  28  contains a membrane or a piston plate, not specifically seen, which membrane or piston plate, when the locking chambers  28  are pressurized with compressed air, force the legs  12 ,  13  against the brackets  17 , thereby fixing them in their position. When the locking chambers  28  are in the pressureless state, the legs  12 ,  13  are freely displaceable with respect to the brackets  17 . 
     In another embodiment of the present invention, depicted for example according to  FIG. 4 , clamping pads  66  are arranged in the locking chambers  28 . These clamping pads  66  force the legs  12 ,  13  of the yoke  11  against the brackets  17  in response to forces exerted on them by compression springs  67 . When the locking chambers  28  are pressurized with pressure medium, the clamping pads  28  are retracted against the force of springs  67 , and therefore the locking mechanisms, are released. To lock the individual tension pulley  16  in position, a spring-loaded clamping pad  66 , with a finely toothed radial outer surface is used, which spring-loaded clamping pad  66  prevents movement of the U-shaped yoke  11 , whose legs  12  and  13  may also each have a finely toothed surface, for example, via mating engagement with the clamping pads  66 . To enable an adjustment of a tensioning of the tension pulley, the spring pressure on the clamping pad  66  is pneumatically released. When the pneumatic pressurization is removed, and the spring pressure is re-established the form-closure locking again takes effect, and the tension pulley  16  is now fixed in a new position. 
     In another preferred embodiment of the present invention, when the locking chambers  28  are in the unpressurized state, a residual holding force may be provided by frictional resistance. This frictional residual holding force remains, in particular, even when the tensioning mechanisms  37 , which are shown in  FIGS. 5 and 6 , are in an unfavorable assembling position. In this case, each pulley  16  maintains its position, causing the belts  24  to also remain on track when the pressure medium is shut off. 
     A second bore hole  31 , which is parallel to the support  01 , extends through the base section  03 , as may be seen in  FIGS. 1 and 3 . It communicates with the first chamber  06  via a radial bore hole  32 , which is seen in  FIG. 3  and which opens up, or passes into the first chamber end surface  27  of the chamber  06 . If the locking chambers  28  are pressureless and the bore hole  31  is pressurized with compressed air, the compressed air flowing through the bore hole  31  into the chamber  06  forces the piston  08  out of the stopped position, as represented by continuous lines in  FIG. 3 , and into an opposite stopped position, which is represented by dotted-dashed lines in  FIG. 3 , in which the piston  08  is situated in direct proximity to the opposite second end surface  33  of the chamber  06 . 
     A third bore hole  34  is formed in the head section  09  and communicates with the chamber  06  via a radial bore hole  36  that opens up adjacent to the second chamber end surface  33 . By pressurizing the third bore hole  34 , while simultaneously releasing the pressure on the second bore hole  31 , the piston  08  can be forced back into the tensioning configuration, which is represented by the continuous lines in  FIG. 3 . 
     When the belt  24  is wrapped around the pulley  16 , as shown in  FIG. 3 , the tension of the belt  24  can prevent the piston from returning to the fully extended configuration, which is represented by continuous lines in  FIG. 3 . Instead, the piston  24  now comes to rest in an intermediate position, which is not specifically shown, in which intermediate position, the pressure acting on the piston  08  and the tensioning of the belt  24  compensate for one another. 
     This invention enables the easy and rapid adjustment of a plurality of tensioning mechanisms  37 , which are mounted side by side on the same support  01 , as shown in  FIG. 5 , for example. All of the tensioning mechanisms  37  are acted upon by an equal level of pressure at each one of their respective third bore hole  34 , or at their second bore hole  31 , if the belt  24  is arranged as shown in  FIG. 2D . The adjusting movement of each pulley  16 , that is executed as a result of the pressurization, can differ from one tensioning mechanism  37  to another. However, the generated belt tension is the same for all tensioning mechanisms  37 . After the belt tension has been adjusted, the bore hole  29  is pressurized in order to lock the tensioning mechanisms  37  of the configuration depicted in  FIG. 3  in the adjusted configuration. Alternatively, the bore holes  29  of  FIG. 4  can be depressurized thereby locking each respective tensioning mechanism in its locked position under the force applied to each clamping pad by its associated spring  67 . The first chamber  06  can then be left pressureless until the next adjustment process. 
     The adjusting movement range, of, for example, 55 mm to 65 mm, of a single tensioning mechanism  37  is preferably greater than a radius, and especially is greater than a diameter, of the pulley  16 . 
     As is shown, for example, in  FIG. 5 , the tensioning mechanisms  37  are positioned on the support  01  closely enough in adjacency to each other that the base sections  03  and head sections  09  of their respective main bodies are in mutual contact with one another. To pressurize homologous bore holes  29 ,  31  or  34  of the individual tensioning mechanisms  37  simultaneously with compressed gas, it is sufficient, as shown in the partial cross-sectional view of  FIG. 6 , by the example of the bore holes  31 , to provide a groove, situated on one side of each main body  02  and encompassing the respective bore hole  31 , which groove is equipped with a sealing ring  38 . Each sealing ring  38  between adjacent ones of the main bodies  02  of the tensioning mechanisms  37  is compressed when the tensioning mechanisms  37  are assembled. A stopper  39  is positioned at one end of the assembled bore holes  31  which are aligned with one another, with stopper  39  being located in the far end of the last bore  31 , which is facing away from the compressed gas source. Thus, a single compressed gas source, combined with a directional valve or with two shut-off valves, is sufficient for adjusting the plurality of adjoining tensioning mechanisms  37  and for fixing them in their adjusted configuration. 
     The tensioning mechanism can be used for tensioning circulating endless belts  24  for any of a wide variety of applications. The support  01  is generally attached to the same frame on which guide rollers that guide the endless belts  24  are mounted. The tensioning mechanism of the present invention permits the endless belts  24  to be adjusted either at rest or in motion. One preferred area of application of the present invention is for use with endless belts which are used to transport printed products to be folded in a generally known folding unit  41 , as is depicted in  FIG. 8 . 
       FIG. 7  shows a pulley  16 , which is arranged on the block  14  by the use of roller bearings. The pulley  16  can have different widths, such as 6.5 mm, 9 mm, 18 mm, 20 mm or 22 mm and can also have shapes for its belt-engaging bearing surfaces, such as flat or convex. 
       FIG. 8  shows, by way of example, a folding unit  41  with corresponding belts  24 . A cross-cutting device  42  is positioned upstream, in the path of travel of a paper web, in the folding unit  41 , and is used to cross-cut a printed paper web, for example, into product sections, before the printed web is taken up onto the surface of a transport or folding blade cylinder  43 , where it is held by pins or grippers, for example, is then cross-folded in the gap by a folding jaw cylinder  44 , and is taken over by the folding jaw cylinder  44 . Between the cross-cutting device  42  and the folding blade cylinder  43 , a belt  24 , which is configured as an accelerating belt, can be provided for use in guiding the product sections. Downstream from the folding jaw cylinder  44 , the now folded product is taken over, for example, by a belt system which may be comprised of at least one belt  24 , and is conveyed, for example, to one or more delivery fans  46  or to another optional unit of a folding unit, such as for formation of a second longitudinal fold and/or a second cross fold, which is not specifically shown here. The belt system, which is situated downstream from the folding jaw cylinder  44 , is configured, for example, as a dual system comprising two belts  24 , between which the product sections are conveyed. A delivery belt  47 , for example, is situated downstream from the delivery fan  46 . In  FIG. 8 , in the belt system which is situated upstream from the folding blade cylinder  43 , and in a belt system which is situated downstream from the folding jaw cylinder  44 , a corresponding tensioning mechanism, in accordance with the present invention, is indicated, by way of example, by a pulley  16 . One or more tensioning mechanisms in accordance with the present invention can be provided in each belt system. 
     In a further preferred embodiment of the present invention, in place of the single pulley  16  for use in the diversion of the plurality of belts  24 , a continuous guide roller  51  may be provided, which continuous guide roller  51  is extending crosswise to the direction of travel of the conveyor belts, as depicted in  FIG. 9 . At least one such shared guide roller  51  is provided for a plurality of tensioning mechanisms  37 . In the preferred embodiment, which is shown in  FIG. 9 , a first guide roller  51  and a second guide roller  52  are provided for all of the tensioning mechanisms  37 . 
     The tensioning mechanisms  37  are all arranged on a single support  01  and are all fixed in place by first and second end plates  53 ;  54  which end plates  53 ;  54  are situated at each end in the longitudinal direction of the support  01 , as seen in  FIG. 9 . The two end plates  53 ;  54  are secured to each other by the use of tie rods, for example. The two end plates  53 ;  54  can also support screw-connected bearings, for example, and especially can support roller bearings, which are configured to hold the respective ends of the guide rollers  51 ;  52 . 
     At least one of the first and second end plates  53 ;  54  is connected to at least one coupling  57 ;  58  for use in supplying the pressurized fluid that is required for the tensioning and/or the slackening of the endless belt  24 , via the piston  08  and/or with a coupling  59  for use in locking the endless belt  24  or the piston  08  in position. 
     In one advantageous preferred embodiment of the present invention, for example, a sensor  61  may be arranged on at least one of the first and second end plates  53 ;  54 . This sensor  61  is usable to detect the position of at least one tensioning mechanism  37 , and especially is usable to detect the position of a part of the tensioning mechanism  37  that cooperates with the pulley  16 , preferably the yoke  11 . 
     In addition, a reference element  62 , such as, for example, a pin  62  is arranged on each tensioning mechanism  37  and is capable of moving together with the respective pulley  16  of each tensioning mechanism  37 . The reference element  62  can also be arranged inside the U-shaped yoke  11 . The sensor  61 , which is embodied, for example, as a photodiode, detects the position of the pulley  16  and thus signals an end of the tensioning path and/or wear and tear on the endless belts  24 . 
     While preferred embodiments of a tensioning mechanism for a circulating element, in accordance with the present invention, have been set forth fully and completely hereinabove, it will be apparent to one of skill in the art the various changes in, for example, the source of the fluid under pressure, the specific types of printing presses used to print the web, and the like could be made without departing from the true spirit and scope of the present invention which accordingly is to be limited only by the appended claims.