Patent Publication Number: US-9884430-B2

Title: Side shift force control

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX 
     Not applicable. 
     BACKGROUND 
     This invention relates to the web manufacturing industry. Materials like paper, films and various laminates are typically manufactured as a continuous sheet or web of material. During the processing of a continuous web, the web is handled by cylindrical rolls and cut into continuous strips. This cutting is typically required for downstream handling or for producing a final product such as a roll of tape. 
     The invention is a slitting device. The slitting device includes a circular blade with a sharp cutting edge on the periphery and a blade actuator this slitting device is referred to as a knife holder. The knife holder typically includes a means of extending and translating the circular blade into an anvil which is cylindrical in shape and has a cutting edge located on the periphery of each end. This translation develops a force between the anvil and the blade the invention pertains to this force. 
     The prior art cited in application Ser. No. 12/672,561 Chilcott teaches a translation mechanism which includes a strain gauge (Page 15 Lines 8-10). This placement of the strain gauge requires that connecting wires extend thru the side shift mechanism. Thus the mechanism cannot be removed without disconnecting these wires. Additionally, this mounting scheme requires flexure of the mechanism in a position that also requires rigid support of the circular slitting blade. This latter requirement causes a tradeoff between rigid support and force sensing accuracy. 
     Other prior art is cited which includes U.S. Pat. No. 8,707,838 Dienes. This patent teaches driving two circular blades against each other using a motor for each blade. An adaptive control assembly which includes both motors is used to maintain constant pressure against the overlap of the two blades. The specific use of strain gauges is not taught. This means that the force determination could be determined by the amount of current used to move each blade. One of the problems with this type of device is that the cutting edge (regardless of the force determination function) must be moved and in some cases both the top and bottom blade are moved. This will result in a variable width of material being cut. Most slitting applications require exacting control of the slitting location transversely along the width of the web. 
     An additional prior art example from Deines is U.S. Pat. No. 6,877,412. This patent teaches the use of a pressure sensor in conjunction with a pneumatic cylinder to determine and monitor side force. This patent however does not specifically teach a means of controlling the side force. Again in this example the pressure sensor is an integrated part of the blade support and translation mechanism and so requires removing the wires during blade maintenance. 
     Lastly, prior art U.S. Pat. No. 5,453,867 Ichikawa is considered. This patent specifically teaches the use of a strain gauge to determine side shift force. However, no method of actively controlling side shift force is provided. Additionally, an integrated translation mechanism is not contemplated. 
     Some of the embodiments of the invention include a means of determining that the blade and anvil are in contact. As can be imagined as the blade is sharpened it decreases in diameter, since the vertical extension of the blade is fixed relative to the anvil, at some point the blade and anvil will no longer touch. This causes the blade to move over the anvil edge instead of into the side. This condition results in an incorrect side force reading and the controller sets an alarm indicating maintenance is required. This is indicated in  FIG. 12  at step  3004 . 
     It is the objective of this invention to address these issues included in the above prior art by providing an improved mechanism and method of slitting materials while being processed in the form of a moving web. Additionally, each and every issue in the prior art is not addressed by each embodiment. In fact some embodiments may not address any of the prior art issues mentioned above. 
     BRIEF SUMMARY 
     In view of the previously mentioned prior art, the present invention discloses an improved mechanism and method of slitting a web of material. The present invention removes the force sensor from the side shift mechanism thus making it easy to service by eliminating the need to disconnect the force sensor wiring during maintenance. 
     In one embodiment of the invention a compliant member in the form of a spring is used to apply the side shift force. This spring is compressed by a linear actuator similar to that used in U.S. Pat. No. 8,191,451 Stolyar. As the spring is compressed the force gradually increases, this allows a load cell and force control scheme to control the side shift force. A combination of the linear actuator in the U.S. Pat. No. 8,191,451 and the instant invention is used to accurately control the amount of force applied. 
     In another embodiment of the invention the compliant member is replaced with a rigid member. This allows for tighter feedback from a force sensor and when controlled correctly provides a more accurate control of the side shift force. Additionally, this embodiment increases the rigidity of the knife holder and can be useful in some web slitting applications. 
     In another embodiment of the invention a biasing member is provided that biases the side shift mechanism it&#39;s self. In addition to contributing to the force between the blade and the anvil, this biasing member is used to translate the blade away from the anvil. 
     An embodiment includes a position controlled actuator to compress a compliant member which in turn transfers a force to a removable side shift mechanism  5  which transfers this force sideways, causing the blade to move transversally until it engages a corresponding anvil or lower knife. As the blade contacts the anvil a force between these two objects is created. This force is transferred back to the position controlled actuator thru a mechanism which includes a load cell. This load cell provides a voltage to a controller. The voltage changes as the force applied by the position controlled actuator changes. The controller is programmed to apply a predetermined amount of force to the blade by positioning the position controlled actuator. 
     The present embodiment also uses the presence of additional sensing to compensate for temperature of the load cell. This provides a more accurate indication of force as the resistance in a conventional load cell is affected by temperature. Included in the load cell are additionally configuration features which provide this compensation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of the knife holder and it&#39;s typical operation environment. 
         FIG. 2  is a side view of the knife holder with the blade cartridge separated from the blade cartridge actuator. 
         FIG. 3  is a cross sectional view of the blade cartridge actuator. 
         FIG. 4  is a front view of a knife holder illustrating the location of the section of  FIG. 3 . 
         FIG. 5  is a cross sectional view of the blade cartridge the location of this cross section is shown in  FIG. 1 . 
         FIG. 6  is a top view of the paddle and load cell. 
         FIG. 7  is a side of the paddle and load cell showing the relative locations of the plunger and pusher forces. 
         FIG. 8  is an exploded left facing isometric of the blade cartridge actuator. 
         FIG. 9  is an exploded right facing isometric of the blade cartridge actuator. 
         FIG. 10  is a front view of the dovetail gripping mechanism in the released configuration illustrating the location of  FIG. 10A  and  FIG. 10B . 
         FIG. 10A  is a cross sectional view of the dovetail gripping mechanism in the released configuration. 
         FIG. 10B  is a cross sectional view of the dovetail gripping mechanism in the released configuration. 
         FIG. 11  is a front view of the dovetail gripping mechanism in the gripping configuration illustrating the location of  FIG. 11A  and  FIG. 11B . 
         FIG. 11A  is a cross sectional view of the dovetail gripping mechanism in the gripping configuration. 
         FIG. 11B  is a cross sectional view of the dovetail gripping mechanism in the gripping configuration. 
         FIG. 12  is a flow diagram of the load cell calibration process. 
         FIG. 13  A is a first page of a force control flow chart. 
         FIG. 13  B is a final page of a force control flow chart 
         FIG. 14  is a block diagram of the controller components. 
         FIG. 15  is an electrical schematic of the load cell circuitry. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     In most applications of the invention, the invention is a component of a knife holder  100  shown in  FIG. 1 . The knife holder  100  is mounted on a transverse beam  200 . The knife holder  100  operates to slit a continuous web  300  as it travels under the knife holder  100 . An anvil  400  is positioned against the blade  134  of the knife holder  100 . The blade  134  and the anvil  400  overlap H, as shown in  FIG. 4  such that the web  300  is cut by a scissors action. The force present between the anvil  400  and the blade  134  is applied and controlled. 
     Also shown in  FIG. 1  are the blade cartridge  2  and the blade cartridge actuator  1 . This figure establishes two basic components that make up the knife holder  100 . In one embodiment of the invention the cartridge actuator  1  can be removed from the blade cartridge  2  this separation is shown in  FIG. 2 . As will be explained below these are manually separated from the left side of the knife holder  100  as seen in  FIG. 2 . This separation does not require the disconnection of wires or air lines and is one of the objectives of the invention mentioned in the Summary. 
     The cartridge actuator  1  consists of a vertical actuator  3  and a side shift actuator  4 . Both of these actuators are driven by motors.  FIG. 3  is a cross sectional view of the cartridge actuator  1 . The motor  74 B on the right in this figure is used to move the blade cartridge  2  vertically. This vertical actuator  3  is similar to the vertical actuator disclosed in the Stoylar patent. The motor  74 B is a stepper motor and is controlled to position the vertical actuator  3 , of course in other embodiments this motor could be a servo motor with an encoder for controlling position. The motor  74 B turns screw  78  which is threaded engaged with a vertical shaft  31 . This vertical shaft  31  includes internal threads  31 A and is attached to a dovetail member  19 . This dovetail member  19  is used to hold the blade cartridge  2 . For completeness the motor  74 B is attached to a housing  56  which includes a bore  56 A for guiding the vertical shaft  31 . 
     A side shift actuator  4  is also attached to the dovetail member  19 . The dovetail member  19  provides a threaded hole  19 A which receives a threaded shaft  34  using the threaded shaft threads  34 A. This combination of dovetail member  19  and threaded shaft  34  is a single embodiment of a body which can be used to provide support for other members of the side shift actuator  4 . Unlike the motor  74 B of the vertical actuator  3 , a side shift motor  74 A is attached to the opposite end of the threaded shaft  34 . This side shift motor  74 A is similar to the motor  74 B used in the vertical actuator  3 , it is used to control the position and force of the side shift actuator  4 . In this embodiment the side shift motor  74 A is a stepper motor but could be a servo motor with an encoder. This side shift motor  74 A turns a screw  69  which is threaded engaged with a follower  71 . This follower  71  includes an axial groove  71 A which is engaged by a pin or set screw  35  this prevents the follower  71  from rotating so the follower  71  is driven axially. In one embodiment the follower  71  pushes on spring  67  which in turn pushes on plunger  68 . A screw  72  is provided for establishing an initial deflection of the spring  67 . This deflection determines how hard the plunger  68  can push prior to deflecting the spring  67  and establishes a preload force between the follower  71  and the plunger  68 . In this way the combination of follower  71 , spring  67  and plunger  68  acts as a rigid member until sufficient force is applied to deflect the spring  67 . In another embodiment, not shown, the follower  71  pushes directly against the plunger  68  this embodiment and spring  67  is eliminated. This allows for more rigid blade support which can be better in some situations. 
     Also shown, is a hardened ball  70  which is not required but has been found to reduce wear on the plunger  68 . 
     Additionally, a paddle  27  is pivotally attached to the dovetail member  19  by pin  32  as shown in  FIG. 3 . The plunger  68  pushes the paddle  27  such that it rotates about the pin  32 . This paddle  27  is used to transfer force from the plunger  68  to a pusher  128  on the blade cartridge  2  see  FIG. 5 . As discussed below, this pusher  128  moves a cam  89  which in turn is pivotally mounted to the blade cartridge housing  81  by pin  84  within the blade cartridge  2  causing the blade  134  to land against the anvil  400 , of  FIG. 5 . The mechanism that moves the blade  134  against the anvil  400  is explained next. 
     Referring now, to  FIGS. 8 and 9  the side shift mechanism  5  which is a component of the blade cartridge  2  will be explained. This mechanism  5  includes a parallelogram four bar linkage.  FIG. 8  shows an exploded isometric of this mechanism  5 . The blade cartridge housing  81  acts as a fixed member within this four bar linkage, attached to this blade cartridge housing  81  are two pivot features B″ and E″ which engage corresponding features B′ on arm member  123  and E′ on guard member  94 . These engagements allow for both the arm member  123  and the guard member  94  to rotate relative to the dovetail member  81 . 
     The blade guide  88  also has two pivot features A″ and F″, these features engage corresponding features A′ on the arm member  123  and a similar feature located on the guard member  94  (this feature is not shown). This causes the blade guide  88  to translate when the arm member  123  and guard member  94  rotate.  FIG. 9  is included to illustrate a similar connection scheme on the opposite side of the blade cartridge  2 . This figure shows, an arm member  123  with engagement features C′ and D′, which pivotally engages corresponding features C″ on the blade cartridge housing  81  and D″ on the blade guide  88 . 
       FIGS. 8 and 9  shows, the pusher  127  which is vertically guided in the blade cartridge housing  81 , and cam  89  which is pivotally mounted in the blade cartridge housing  81 . The pusher  127  pushes the cam  89  vertically which in turn causes the cam  89  to pivot about pivot  84  (see  FIG. 5 ). The pivoting action of the cam  89  pushes the arm member  123 , causing the blade guide  88  to translate in direction  1001  (see  FIG. 5 ) against the anvil  400 . Notice also that springs  50  and  50 A are compressed as the blade  134  is translated toward the anvil  400 . This is best seen in  FIG. 5 . Spring  50  is shown trapped between guard member  94  and blade cartridge housing  81  as the cam  89  pivot clockwise arm member  123  rotates clockwise causing the blade guide  88  to translate to the left. 
     To retract the blade  134  from the anvil  400 , the motor  74 A reverses direction allowing springs  50  and  50 A to push the blade guide  88  to the right. This in turn pivots the cam  89  in the counterclockwise direction and pushes the pusher  127  vertically up against the paddle. 
     The blade  134  is connected to the blade guide  88  by bearings  118  A and  118  B. The bearings allow the blade  134  and supporting shaft  133  to rotate due to pressure from the anvil  400 . As the anvil  400  and the blade  134  rotate the web  300  is cut due to the overlap H. 
     So now that the actuation of the blade  134  against the anvil  400  is understood, an embodiment includes providing a load cell  73 B including strain gauges  73  and  73 A on the paddle  27 , see  FIG. 3 . Now please see  FIG. 5 , as the plunger  69  pushes the paddle  27  and pivots it against the pusher  127 , the paddle  27  is subjected to a bending stress. This stress causes the strain gauges  73 ,  73 A to provide signals to a controller not shown. This controller determines how much force is being applied to the paddle  27  by the plunger  69  and causes the side shift motor  74 A to retract or extend the plunger  69  such that a predetermined force is applied. 
     As mentioned above the blade cartridge  2  and the blade cartridge actuator  1  can be easily separated as shown in  FIG. 2 . The gripping mechanism  600  for separating these devices is explained with reference to  FIGS. 10A and 10B  and  FIGS. 11A and 11B .  FIGS. 11A and 11B  show the mechanism in the attached configuration. The lever  21  is rotated down around pin  50 , this allows the spring  603  to drive the wedge  602  to the right. As shown in  FIG. 11B  the wedge  602  has surface  602 A which presses against similar wedge like surfaces onto the dovetail member  19  at surface  19 A and gripper  604  at surface  604 A. This causes surface  604 A to press against a mating surface on the dovetail member  19 , in this manner the blade cartridge  2  is attached to the blade cartridge actuator  1 . 
     By rotating the lever  21  as shown in  FIGS. 10A and 10B , the wedge  602  is moved to the left due to the location of the pin  601  on the lever  21 . This action over comes the force of the spring  603  on the wedge  602 . As the wedge  602  moves to the left, the gripper spring  605  (shown in the loaded state) pushes the gripper  604  upward (as seen in  FIG. 11B ) and releases the blade cartridge  2 . 
     To get the maximum benefit of the use the load cell  73 B, a controller  500  is included for controlling the amount of side shift force applied to the anvil  400 . This controller  500  is shown in  FIG. 14  and includes motor driving means  501 , memory  502 , computational processing means  503  for carrying out the control scheme explained below and load cell interface means  504  for receiving voltage levels from the load cell  73 B. In one embodiment this controller  500  includes a microprocessor specifically programmed for carrying out the force control scheme described below. 
     The load cell  73 B includes the strain gauges  73  and  73 A and the separating material  73 C which separates the two strain gauges  73  and  73 A. A typical load cell interface  504  is shown in  FIG. 15 . The two load cell strain gauges are also included in this figure. This type of electrical circuit is known in the art as a full bridge device. The controller  500  determines the voltage V as shown in the figure and also provides an excitation voltage EV. Balancing resistors R 1  and R 3  provide a known resistance and complete the circuit. This particular embodiment provides a simple means of detecting the force  1003  regardless of temperature. As the temperature increases or decreases the material  73 C grows, this causes the strain gauges to stretch and increases the voltage signal from each strain gauge. Assuming the separating material  73 C has no significant temperature gradient; the difference in these voltage signals remains constant for any temperature. 
     Another advantage of this particular circuit embodiment is an increase in total signal range due to the geometry. The paddle  27  is loaded such that the strain gauge  73  is in tension while the strain gauge  73 B is in compression. This causes strain gauge  73  to increase in resistance as strain gauge  73 A decreases in resistance. The net result is a larger voltage signal V present at the controller. The voltage signal V is proportional to the amount of bending on the paddle which is directly proportional to the force  1003  being transmitted to the side shift mechanism  5 . Of course, the load cell  73 A would work just as well if the strain gauge  73  is loaded in compression and strain gauge  73 B is loaded in tension. In other words the strain gauges  73  and  73 B are loaded in opposite senses or direction. 
     The controller  500  needs to understand how to determine the side shift force given the voltage signal V. To determine this relationship a calibration scheme  3000  has been provided, refer to calibration flow chart of  FIG. 12 . The controller  500  polls the load cell  73 B, in step  3001 . Next, the controller  500 , using computational processing means  503  determines if a voltage signal V is received from the load cell  73 B as provided in step  3002  of calibration scheme  3000 . If one of the load cell voltage signal V is not provided the controller  500  sends an error message at step  3004  and the calibration scheme ends. However, if there is a voltage signal V from the load cell  73 B, then the controller  500  moves the side shift motor  74 A such that the blade  134  is half way extended. 
     In this position springs  50  and  50 A shown in  FIG. 8  are pushing against the guard member  94  which, thru the side shift mechanism  5  and applies a force against the cam  89  and the pusher  127 . This force is transferred to the paddle  27 . This force on the paddle  27  is shown as item  1003  in  FIG. 7 . As shown in  FIG. 7  the plunger  68  (of  FIG. 3 ) applies a force shown as item  1002 . These two forces  1003  and  1002  along with a reaction force at pin  32 , causes the paddle  27  to develop a bending stress. This bending stress, as understood by elementary mechanics of materials, causes the strain gauge  73  to stretch and strain gauge  73 A to compress. This stretch and compress characteristic causes the voltage across each of these strain gauges  73  and  73 A to change. 
     The calibration scheme  3000  now continues to step  3005  where the controller  500  saves the side shift motor  74 A position and the load cell  73 B signal voltage V to memory  502 . Next at step  3006 , the controller equates the signal voltage V with a known force  1003 . This force is pre-established and saved in the controller memory  502  during manufacturing of the device. At step  3007  the controller  500  stores this signal voltage V (now referred to as calibration value) and the side shift motor  74 A position. 
     During installation the knife holder  100  needs to be positioned relative to the anvil  400  such that with the side shift mechanism  5  in the half stroke extended position, the blade  134  and the anvil  400  are just touching. This allows for better control of the force between the blade  134  and the anvil  400 . 
     First the controller  500  positions the vertical actuator  3  into an extended position using the motor drive means  501  and motor  73 B. Then the controller  500  positions the side shift actuator  4  in a half extended position using the motor drive means  501  and motor  73 A. The embodiment is now ready to start the slitting force control scheme  2000  shown in  FIGS. 13A and 13B . 
     During the slitting operation, the controller uses the voltage signal V from the load cell  73 B to determine where the motor  74 A should position the paddle  27  using the force control scheme  2000  shown in  FIGS. 13A and 13B . As shown in  FIG. 13A  (step  2001 ) the controller  500  polls the load cell  73 B to determine if a voltage signal V is present at the load cell  73 B. If this voltage signal is missing the controller  500  goes to step  2005  and sends an error code and the force control scheme  2000  is terminated. Otherwise, the controller  500  proceeds to step  2003  and converts the load cell  73 B voltage signal V to a force value using the computational processing means  503  and the saved calibration value stored in memory  502 . Specifically, this is accomplished by multiplying the current voltage signal by the known half stroke force and dividing by the calibration value and obtaining a value representative of said force value. Then the controller  500  continues to step  2004  and subtracts the target force from the force determined in the previous step  2003  as shown in step  2004 , this step produces a value referred to as force error. This is done with the use of the computational processing means  503  of the controller  500 . Proceeding now to step  2006  shown in  FIG. 13B , the controller determines if the force error is positive, negative or within an acceptable absolute value. If this force error is negative the controller  500  goes to step  2008  and extends the side shift actuator  4 . If this force error is positive the controller  500  retracts the side shift actuator  4  as indicated in step  2007 . Additionally, the controller  500  proceeds to step  2009 , if the force error is within an acceptable absolute value. Also the control scheme  2000  shows that after steps  2007  and  2008  the controller  500  proceeds to step  2009 . At step  2009  the controller  500  determines if the force control scheme is still active, if not the force control is terminated, if it is the controller  500  proceeds to step  2001 . 
     To determine if the force error is within a reasonable absolute value one needs to consider the update frequency of the force control scheme  2000 . It this particular value is to large wide fluctuations in the side shift force will result. On the other hand if this value is to small the control scheme will produce small vibrations and increase power consumption. This can cause some components to overheat and fail prematurely. This absolute value is determined experimentally by simply trying various values until a good compromise has been determined. 
     The inventor submits the above embodiment of the invention with the expressed understanding that this embodiment is simply one possible way of applying the invention and is not to be used to limit the claims.