Abstract:
A positive drive mechanism for use in a sheet folding apparatus includes a motor drive, a torque-limiting device coupled to the motor drive, a drive pulley coupled to the torque-limiting device, and a plurality of idler pulleys. Each of the idler pulleys is coupled to a drive shaft which supports a fold roller. A non-slip positive drive member operatively engages portions of the drive pulley and the plurality of idler pulleys. A sheet is fed into the folder and between the fold rollers in order to fold the sheet. In the event that the sheet becomes jammed between the fold rollers, the torque-limiting device operates to release the torque transmitted from the motor drive to the drive pulley.

Description:
TECHNICAL FIELD 
     The present invention is relates generally to apparatuses utilized for automatically folding paper sheets, and more particularly to the drive mechanisms utilized in conjunction with such folding apparatuses. 
     BACKGROUND ART 
     Buckle folders are used to take a sheet of paper and fold it into any of a number of conventional user-selected formats, such as half or z-folds. Examples of conventional buckle folders can be found in U.S. Pat. Nos. 2,669,331; 3,796,423; 3,797,196; 3,841,621; 4,032,133; 4,099,710; 4,125,254; 4,586,704; 4,781,367; 5,048,809; 5,178,383; 5,269,744; 5,350,170; and 5,797,319 whose contents are hereby incorporated by reference into the instant patent application. 
     Currently, conventional buckle folders include a belt drive mechanism for transmitting rotational energy from the drive source (motor) to the various fold rollers. The belt drive used, however, is not a positive drive and after some usage, slippage occurs between the drive belt and the various drive and idler pulleys. This results in degradation in the operation of the folder. 
     In the past, alternative designs implementing a positive drive of some type in a folder have been proposed. For example, chain and sprocket drives have been proposed. However, chain and sprocket drives are very noisy and excessive noise is already an issue in the use of buckle folders. Also, this type of design does not incorporate a torque limiting device. Without this device, when a material jam occurs, the folder may get damaged. 
     Accordingly, there is room for improvement within the art. 
     DISCLOSURE OF THE INVENTION 
     In one embodiment according to the present invention, a drive mechanism is provided for use in a folder. The drive mechanism comprises a motor drive, a torque-limiting device coupled to the motor drive, a drive pulley coupled to the torque-limiting device, and a plurality of idler pulleys. Each of the idler pulleys is coupled to a drive shaft which supports a fold roller. A non-slip positive drive member operatively engages portions of the drive pulley and the plurality of idler pulleys. 
     The present invention also provides a method for automatically folding sheets. The method comprises the steps of providing a sheet folder including a plurality of fold rollers and providing a drive mechanism. The drive mechanism includes a motor drive, a torque-limiting device coupled to the motor drive, a drive pulley coupled to the torque-limiting device, and a plurality of idler pulleys coupled to a drive shaft supporting the fold roller. In addition, a non-slip positive drive member operatively engages portions of the drive pulley and the idler pulleys in order to positively drive the drive pulley. A sheet is fed into the folder and between the fold rollers in order to fold the sheet. In the event that the sheet becomes jammed between the fold rollers, the torque-limiting device operates to release the torque transmitted from the motor drive to the drive pulley. 
     Accordingly, it is an object of the invention to provide a positive drive mechanism for a buckle folder. 
     It is another object of the invention to provide a positive drive mechanism for a buckle folder that does not result in excessive noise. 
     It is a further object of the invention to provide a positive drive mechanism for a buckle folder that is better capable of handling the machine forces generated by jammed sheets. 
     Some of the objects of the invention having been stated hereinabove, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevation view of a conventional prior art fold roller support and adjusting mechanism for a buckle folder. 
     FIG. 2 is an elevation view depicting the details of a portion of the positive drive mechanism for a buckle folder according to the invention and employing a flat metal belt. 
     FIG. 3 is a plan view depicting a portion of the flat metal belt according to the invention. 
     FIG. 4 is a plan view of the positive drive mechanism for a buckle folder of FIG. 3 according to the invention. 
     FIG. 5 is an elevation view depicting the details of a portion of the positive drive mechanism for a buckle folder according to the invention and employing a double-sided timing belt. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the above-mentioned figures, an example of a drive mechanism for a folder that meets and achieves the various objects of the invention set forth above will now be described. 
     FIG. 1 is an elevation view of a conventional prior art fold roller support and adjusting mechanism for a buckle folder  10  having a top support panel  11 . Paper sheets are fed at a location generally indicated by arrow P. 
     Buckle folder  10  is provided with a plurality of fold roller support and adjusting mechanisms  100 . Each folder roller will be supported at each of its ends by one of the plurality of fold roller support and adjusting mechanisms  100  (and only one is shown in the drawings herein for simplicity) so that the vertical position of each end of the fold roller can be adjusted. While each fold roller support and adjusting mechanism  100  is slightly different in design due to its position within folder  10 , they all have common elements. In particular, each fold roller support and adjusting mechanism  100  includes: vertical fold roller support and adjusting bar  110  having thread portion  111  at its upper end and pivot point  112  at its lower end; pivoting roller support  114  pivotally mounted via axle  113  to pivot point  112  and pivotable about second pivot point  115 ; fold roller  122  rotatably mounted to pivoting roller support  114  via second axle  121 ; spring mechanism  125  for biasing vertical fold roller support and adjusting bar  110  in a downward position; and adjustment knobs  130  for adjusting the vertical position of vertical fold roller support and adjusting bar  110 , the pivotal position of pivoting roller support  114 , and therefore the position of fold roller  122 . 
     To drive folder  10 , drive pulley  55  is driven by a drive motor  55   a , which can be conventionally positioned on drive shaft  55   b  or at various other locations based upon the manufacturer of the folder, and feeds drive forces to fold rollers  122  via drive belt  56 . Take-up idler rollers  60   a ,  60   b  prevent slack in drive belt  56 . A stationary exit fold roller  150  is also provided to produce an exit drive couple with the last adjustable fold roller  122 . Hand wheel  80  allows a human operator to rotate all the fold rollers  122  at a slow rate and in either direction so that jammed sheets can be removed from folder  10 . 
     Finally, it should be noted that various folder structures not relevant to the instant invention have been left out of FIG. 1 for simplicity. Examples of such conventional structures include fold plates and fold deflectors. 
     Competing problems are involved in conventional buckle-folders. In particular, belt slippage and folder jams are typical problems. 
     Belt slippage is a common problem in most belt-driven mechanical systems. Belt slippage results, from among other reasons, because of belt stretching and wear resulting from rubbing between the inner belt surface and its pulleys. To counteract or minimize the effects of belt stretching it is common to use take-up pulleys, which provide for a relatively constant tension on the belt as well as increase the amount of wrap of a belt around a pulley so as to reduce slippage. Furthermore, in some applications, belts are provided with thick rubber teeth (e.g., timing belts) that mate with similarly toothed pulleys. The belt teeth-pulley teeth interaction provides a positive drive that is less conducive to the effects of belt slippage. 
     However, sheet jamming can also be a pervasive problem in all sheethandling machines and especially buckle folders. Buckle folders, as can be seen in FIG. 1, provide for multiple roller gaps through which one or more sheets will simultaneously pass. Additionally, with the sheet(s) set to be both injected at high speed into one buckle-chute and then removed from the chute at a similarly high speed, precision handling is required. When this precision is deviated from, jams result. 
     Jams typically result in a machine “seizing” or coming to an abrupt and immediate stop as the sheet wedges itself within or around the various rollers, etc. To absorb the shock to the folder drive mechanism caused by the seizure, relative rotation/movement is allowed between the drive belt and the various pulleys, i.e., a positive drive is not used. Thus, while belt slippage is undesirable when the folder is working properly, it is desirable when a jam occurs. Slippage allows the energy produced by a machine jam to be dissipated rather than totally absorbed by the machine mechanism. 
     Accordingly, it can be seen that as one reduces the tendency of the belt system to slip, such as by using toothed belts and pulleys, one is also reducing the ability of the belt system to absorb the forces commensurate with a sheet jam. 
     The instant invention overcomes these conflicting problems by providing a positive drive system having torque-limiting capability, as will now be described. 
     In particular, as shown in FIG. 4, a torque-limiting device  200  is added to the folder drive system between drive motor  55   a  and drive pulley  155 . As a result, the drive shaft is separated into two drive shaft portions  155   b . Torque-limiting device  200 , typically in the form of a clutch of some type, is set to release the drive couple between drive motor  55   a  and drive pulley  155  when the torque reaches a predetermined limit that exceeds the normal expected torque. A suitable torque-limiting device is available from MAYR GMBH &amp; CO. and designated as Model No. EAS-compact 01/490.520.1 S O.    
     Providing the system with torque-limiting device  200  allows a positive belt drive system to be employed. If folder  10  then jams, rather than dissipating the jam forces through slippage, the torque-limiting device releases the jam forces. Thus, there is no downside to then using a positive drive system in connection with the present invention. 
     While a positive drive system such as a chain and corresponding sprocket may be used, as described above, the noises resulting from the chain/sprocket interaction and the chain itself are often unacceptable. As a folder is typically already the noisiest component in a sheet handling system, additional noise is undesirable. The present invention, however, provides two alternatives to chain drive systems. 
     As shown in the first preferred embodiment of FIGS. 2 and 3, a flat metal belt  156  with holes  157  therein that interact with pins or teeth  158  on drive pulley  155  is preferred. Holes  157  of flat metal belt  156  interact with teeth  158  on drive pulley  155  to create the positive drive. Flat metal belt  156  is about 0.003 inches thick. Holes  157  are of 0.115 inches diameter and approximately 0.25 to 0.50 inches apart along the length of the flat metal belt  156 . Pins/teeth  158  are about 0.057 inches high and spaced approximately about 0.25 to 0.50 inches apart, corresponding to the distance between holes  157  in flat metal belt  156 . The belts are typically made from steel. For this embodiment, similar pulleys provided with pins/teeth  158  could then be substituted for the pulley or drum portions that support fold rollers  122 , take-up idler rollers  60   a  and  60   b , and/or exit fold roller  150  shown in FIG.  1 . 
     It is possible for flat metal belt  156  and drive pulley  155  with pins/teeth  158  to be replaced by a double-sided, notched timing belt  256  and toothed drive pulley  255 , respectively, as shown in the second preferred embodiment of FIG.  5 . Double-sided timing belt  256  is provided with notches  257  on both sides thereof; notches  257  mate with teeth  258  on drive pulley  255 . 
     As in the case of flat metal belt  156 , the use of double-sided timing belt  256  in conjunction with torque limiting device  200  according to the present invention represents an improvement over convention drive systems. However, observation has shown that rubber timing belts in general wear down much faster than flat metal belts and have less uniform thickness along their lengths. Accordingly, in most implementations of the present invention, the first embodiment disclosed herein incorporating flat metal belts  156  is preferred over the second embodiment incorporating double-sided timing belt  256 . This is because flat metal belt  156  will in most cases be considered as allowing folder  10  to attain the degree of precision necessary for proper sheet handling and operation. 
     It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims.