Abstract:
A reciprocated knife cuts pattern work material pieces without rotating a housing tube for orientation of the cutting knife. An integrated tangent axis drive motor orients the cutting knife, eliminating any inertia caused by the cutting housing tube and preventing the slowing of the angular acceleration and increasing the speed of the knife orientation. Alternative motor types are provided by various embodiments of the invention.

Description:
FIELD OF INVENTION 
     The present invention is generally directed to cutting shapes from sheet type work material and is more specifically related to cutting shapes using a computer controlled cutting table incorporating a reciprocated knife having a tangent axis orientation drive. 
     BACKGROUND OF THE INVENTION 
     Historically, a computer controlled cutting table incorporating a motor reciprocated knife has been used to cut a single-ply of flexible sheet type material, such as leather. For example, Zund Systemtechnik of Altstatten, Switzerland produces a motor reciprocated knife. A typical example of this type of cutting apparatus is schematically illustrated in  FIG. 1 . 
     In this example, a computer controlled tangent axis drive motor  1000  is coupled to a housing tube  1010  that is keyed to the reciprocating knife  1020 . Therefore, any movement of the housing tube generates movement of the knife. The knife is oriented tangent to the cut path by rotating the housing tube via the tangent axis motor drive. 
     A limitation of the existing art is that the inertia of the housing tube is oriented along with the knife. This extra inertia may slow the angular acceleration of orientation of the knife. To maximize the throughput of cut pieces, it is desirable to orient the knife as quickly as possible. 
     Another difficulty occurs when multiple changes in the cutting direction of the knife is required at very short time intervals. A series of changes of cutting direction can decrease the quality of the final cut sheet by having the cutting knife&#39;s orientation hampered by the inertia of the housing tube. The use of the housing tube to orient the cutting knife can greatly and detrimentally affect the amount of time it takes to cut a pattern piece from the work material. In addition, because of the need for multiple changes in cutting knife direction, the likelihood for errors can increase at higher throughput speeds. 
     Based on the foregoing, there is a need in the art to provide a cutting apparatus that improves upon or overcomes the drawbacks of prior art devices. 
     SUMMARY OF THE INVENTION 
     The present invention is directed in one aspect to an apparatus for cutting pattern pieces that eliminates the rotating housing tube, and consequently increases the speed of knife orientation. The invention is not limited to motor reciprocation. Other means of reciprocating the knife are possible, including but not limited to, a mass-spring system that is excited by an electromagnetic actuator. 
     In one embodiment of the present invention, a servomotor orients the heading of the knife in response to a controller. The reciprocating motion of the knife is performed by a second motor that causes rotational motion of a spool. The spool is coupled to a rod. A bushing at the end of the rod allows rotary and linear motion to the knife also at the distal end of the rod. 
     In another embodiment of the invention, the motor that reciprocates the knife has a crack shaft with an eccentric shaft connected to ball bearings disposed in the spool. A pressure distributor may be attached to the ball bearing to reduce contact stresses of the flanges of the spool. 
     In another form of the invention the servomotor and secondary motor are attached to a housing. The distal end of the housing has threading mated with a presser foot that is used to provide adjustment of the cutting depth of the knife. A spring loaded catch can be used to prevent the presser foot from rotating and changing the cutting depth during the cutting operation. 
     The present invention can be utilized in, but is not limited to, a mass-spring system implementation. In this embodiment, a servomotor orients the knife tangent to a cutting path. The servomotor can be an encoder, but is not limited to this implementation. The mass spring motion is produced by an electromagnetic actuator. 
     An advantage of the present invention is that the process of cutting can be performed quickly and automatically. 
     These aspects and other objects, features and advantages of the invention are described in the following Detailed Description, which is to be read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a cutting apparatus known in the art. 
         FIG. 2  is a perspective illustration of a cutting table incorporating the present invention. 
         FIG. 3  is a perspective view showing one embodiment of the invention. 
         FIG. 4  is a partial view showing internals of one embodiment of the present invention. 
         FIG. 5  is an exploded view showing portions of the internals of the embodiment of  FIG. 4 . 
         FIG. 6  is an enlarged view showing a ball bearing in a spool for converting rotary motion to linear motion. 
         FIG. 7  is an enlarged view showing the ball bearing of  FIG. 6  with a pressure distributor for reducing contact stress in the spool. 
         FIG. 8  is an enlarged partial perspective view showing a coupling for a tangent axis drive motor. 
         FIG. 9  is an enlarged partial perspective view showing a coupling for a reciprocation drive motor. 
         FIG. 10  is the present invention having a blade that is reciprocated by a mass spring system that has motion provided by an electromagnetic actuator. 
         FIG. 11  is a partial perspective view showing portions of the embodiment of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a cutting apparatus known in the art. A motor driven crank arm  1030  generates the reciprocation motion. At the end of the crank arm is a ball bearing whose outer race is captured between flanges of a spool. The spool motion is linear and is guided by linear ball bearings  1040  at each end. A computer controlled tangent axis drive motor  1000  is coupled to a housing tube  1010 . The housing tube is keyed to a reciprocating knife  1020  such that it may be oriented tangent to cut a path through work material. One limitation of this existing apparatus is that the inertia of the housing tube is oriented along with the knife. The extra inertia may slow the angular acceleration of the knife&#39;s orientation. 
     The present invention eliminates the need of a rotating housing tube and consequently increases the speed of knife orientation. Again, the present invention is not limited to driving the knife through a reciprocation drive motor. Other means of reciprocating the knife are possible, such as, but not limited to, a mass spring system that is excited by an electromagnetic actuator. 
     Shown in  FIG. 2  is a cutting table generally designated by the reference number  100 . The table includes a frame  101  and a work material support surface  102  adapted to carry at least one layer of sheet-type work material  105 . The work material includes, but is not limited to, leather or vinyl thereon. A beam  103  is coupled to the frame for movement back-and-forth in a first direction as indicated by the arrows labeled “X.” A carriage  104  is mounted to the beam  103  and is movable back-and-forth along a second direction as indicated by the arrows labeled “Y.” A tool head  51  is mounted to the carriage and moves in the directions “X” and “Y” in response to commands issued from a controller  106 . 
       FIG. 3  illustrates one embodiment of the tool head  51 , which includes a main support bracket  25 , a power tool generally designated  50 , and a guided pneumatic cylinder designated by reference numerals  20 ,  21 ,  22 ,  23 , and  24 , which in response to commands issued by the controller  106 , engages and disengages the power tool  50  with the work material  105 . A bushing block  26  guides and supports the knife end of the power tool  50 . 
     Illustrated in  FIGS. 4 and 5  are the internals of one embodiment of the power tool  50 . A knife I is held in a tool holder  2 . A rod  4  connects the tool holder  2  to a spool  5 . A bushing  3  permits rotary and linear motion and supports the knife end of the rod  4 . A servomotor  13  orients the heading of the knife  1  in response to commands issued from the controller. 
     As shown in  FIG. 5 , a crankshaft  15  has an eccentric end  8  onto which the ball bearing  6  is press fit. A motor  12  is attached to a second coupling  11  that drives the first bearing  6  in an orbit between the flanges of the spool  5 . The second coupling has a head  10  to assist in connection. The orbit motions cause the spool  5  to reciprocate in a linear motion. In turn the knife  1  reciprocates. 
     Further shown in  FIG. 5 , the servomotor  13  and the motor  12  can be attached to a housing  16 . The outer race of the double row ball bearing  9  fits into a round pocket in the housing  16 , and is secured by an internal retaining ring. A tube  17  leads away from the housing  16 . The remote end of the housing tube has external thread onto which is screwed a presser foot  19 . The threads provide a means of adjusting the maximum cutting depth. A spring-loaded catch  18  prevents the presser foot from rotating during cutting operation. It is apparent that other means known by those skilled in the art can be utilized to adjust the height of the cutting knife and secure the adjustment. The above are examples and are not mentioned to limit the invention to these particular embodiments. 
       FIG. 6  illustrates ball bearing  6  being constrained between the flanges of the spool  5 . Shown in  FIG. 7 , a pressure distributor  7  may be attached to the outer race of the ball bearing  6 . This reduces the contact stresses on the flanges of the spool  5 . 
     Shown in  FIG. 8 , the servomotor  13  has an output shaft  28  that is attached a first coupling  14 . The output shaft passes through a slot  27  in the first coupling  14 . The spool  5  has a hole feature  29 , a first flat  30 , a second flat  31  that mate with the slot  27  of the first coupling  14 . Depending on the embodiment, the spool  5  is fabricated from, but not limited to, Teflon® (tetrafluroethyene) filled acetal. The first coupling  14  depending on the embodiment is made from, but not limited to, stainless steel. 
     As shown in  FIG. 9  the second coupling  11  has a slot, through which passes the shaft  33  of the motor  12 . The crankshaft  15  has a hole feature  35  and a plurality of flats  36 ,  37 ,  38  and  39 . These flats mate with the slot  32  of the second coupling  11  and the shaft  33 . The crankshaft  15  is supported by a double row ball bearing  9  shown in  FIG. 5  that is retained by an external retaining ring that is placed in a groove feature  34  of the crankshaft  15 . 
       FIG. 10  shows an embodiment of the power tool  50  where a mass-spring system is utilized and powered by an electromagnetic actuator. In this embodiment, the electromagnetic actuator replaces the reciprocating drive motor. Similar to the embodiment of  FIG. 4 , a servomotor  2101  orients a knife  2013  tangent to the cut path. Attached to the servomotor  2101  is an encoder  2102  or other means of angular shaft position feedback. Rod  2106  is slidably coupled to move relative to housing  2001 . A first linear bearing  2008  and a second linear bearing  2009  are included to provide a means of sliding contact for rod  2106 . A transducer  2053  provides feedback of the motion of knife  2013 . Depending on the implementation, the knife  2013  is secured to a knife holder  2012  that is coupled to rod  2106 . A voice coil actuator that comprises of a coil  2002  and a magnetic field assembly  2003  provides excitation or actuation of the mass spring system. The first linear bearing  2008  is disposed in a bearing support  2010  that is attached to magnetic field assembly  2003 . A first spring  2005  and a second spring  2006  provide elastic elements of the dynamic system. 
       FIG. 11  is an enlarged partial view showing portions of the embodiment of  FIG. 10 . The servomotor has an output shaft  2103  to which is attached a first hub  2104 . The first hub  2104  has a slot  2115 , and into the space formed by the slot  2115  the output shaft passes. The first hub  2104  mates with a second hub  2105 , that has a first flat surface  2113 , a second flat surface  2114 , and a hole  2112  whose diameter is a location-clearance fit to the output shaft  2103 . A rod  2106  is attached to the second hub  2105 . The first hub  2104  and the second hub  2105  form a coupling that allows translation while stopping rotation of the rod  2106  relative to the output shaft  2103 . Material choices for the hubs, include but are not limited to, materials that accommodate the relative sliding motion. For example, the first hub  2104  may be fabricated of stainless steel, and the second hub  2105  of tetrafluroethylene filled acetal. Those skilled in the art will recognize other ways to make couplings that allow translation while stopping rotation, as well as other material from which to fabricate them. 
     A cupped spool  2004  has a cup feature  2112  that radially captures a flange feature  2107  of the rod  2106 . A first thrust bearing  2108 , a second thrust bearing  2109 , a third spring  2110 , and a cup washer  2111  capture the flange feature  2107  axially. With this arrangement, the rod  2106  is free to rotate, but cannot translate relative to the cupped spool  2004 . The first thrust bearing  2108 , a second thrust bearing  2109  may be fabricated from, for example, plastic suitable for bearing applications. Thrust washers of sintered bronze impregnated with oil are another example of a substitute. As with the other embodiment described in  FIG. 4 , the servomotor  2101  orients the knife  2013 . 
     It should be understood that the above description is only representative of illustrative examples of embodiments. For the reader&#39;s convenience, the above description has focused on a representative sample of possible embodiments, a sample that teaches the principles of the invention. The description has not attempted to exhaustively enumerate all possible variations. 
     Therefore, the embodiments described herein are examples only, as other variations are within the scope of the invention as defined by the appended claims.