Closed loop apparatus for cutting sheet material

Abstract

A method and apparatus for cutting sheet material utilizes a closed loop automatically controlled cutting machine having a reciprocating cutting blade as the cutting tool. Sheet material to be cut is spread in multiple plies to form a layup, and the cutting blade and the material are then moved relative to one another in cutting engagement along predefined lines of cut. During cutting, a sensor detects a cutting parameter that is affected by the interaction of the cutting blade and sheet material, and signals provided by the sensor are fed back in the closed loop automatic control mechanism to adjust or initiate further steps in the cutting operation. Such adjustment or initiation alters the cutting machine operation for cutting conditions in real time in order to improve the overall performance of the machine.

I claim: 
     
       1. An automatically controlled cutting machine for accurately cutting limp sheet material comprising: a cutting blade .Iadd.having a leading cutting edge, a trailing edge and two sides extending between the leading and trailing edges, the two sides at the leading edge meeting at an angle to form a sharp knife edge for cutting the limp sheet material.Iaddend.;   a cutting table defining a support surface on which sheet material is positioned in a spread condition for cutting by the cutting blade;   motor means for moving the cutting blade and the sheet material relative to one another in cutting engagement;   control means connected with the motor means and providing control signals to the motor means for guiding the cutting blade through the material along a predetermined cutting path;   sensing means operatively associated with the cutting blade and sheet material for detecting lateral forces applied to the .Iadd.sides of the .Iaddend.blade by the material as the .Iadd.sharp leading knife edge of the .Iaddend.blade advances through the material in cutting engagement, the sensing means also producing a signal corresponding to the detected lateral forces; and   feedback means interconnecting the sensing means and the control means for generating additional control signals to regulate the cutting of the material by the blade along the predetermined cutting path in response to the detected forces.   
     
     
       2. Apparatus for cutting limp sheet material as defined in claim 1 wherein the sensing means comprises a load sensor for sensing forces applied laterally to the blade by the material. 
     
     
       3. Apparatus for cutting as defined in claim 2 wherein the load sensor is connected with the blade to detect lateral loads applied to the blade. 
     
     
       4. Apparatus for cutting sheet material as defined in claim 1 wherein: a blade guide is provided in the cutting machine and supports the blade along an axis generally perpendicular to the sheet material spread on the cutting table; and   the sensing means comprises a load sensor interposed between the blade guide and the cutting machine to detect blade loading during cutting. .[.5. Apparatus as defined in claim 4 wherein a presser foot surrounding the cutting blade is also provided in the cutting machine and rests upon the sheet material during cutting; and the blade guide and load sensor are   
     
     
        mounted in the presser foot..]. 6. Apparatus for accurately cutting sheet material as defined in claim 1 wherein: the cutting blade extends through the sheet material along an axis generally perpendicular to the material;   the motor means includes means for rotating the blade and sheet material relative to one another about the perpendicular axis to orient the blade along the cutting path at each point; and   the feedback means is connected with the means for rotating for orienting   
     
     
        the cutting blade in accordance with the detected lateral forces. 7. Apparatus for cutting sheet material as defined in claim 6 wherein the sensing means is a sensor detecting side loads upon the cutting blade and the feedback means and the means for rotating the cutting blade are interconnected to rotate the cutting blade in a direction that reduces the 
     
     
        side loads. 8. An automatically controlled cutting machine as described in claim 1 wherein: the cutting blade is a reciprocating cutting blade; and   the cutting table has a penetrable bed defining the support surface on which the material is spread, the bed being penetrable by the cutting blade as the blade reciprocates during cutting. .[.9. An automatically controlled cutting machine as defined in claim 8 wherein the penetrable bed is comprised of bristles having free ends substantially in a common plane defining the support surface of the table whereby the blade penetrates through the support surface and between the bristles during   
     
     
        cutting..]. 10. An automatically controlled cutting machine as defined in claim 9 further including means for generating a vacuum within the bristles for rigidizing the sheet material spread on the support surface. 
     
     
         1. An automatically controlled cutting machine for cutting limp sheet material as defined in claim 1 further including means for evacuating air from a multi-ply layup of sheet material on the cutting table to compress 
     
     
        and rigidize the layup for cutting. 12. In combination in an automatically controlled cutting machine having a .Iadd.reciprocated .Iaddend.cutting blade .Iadd.in the form of a knife mounted at one end in cantilever fashion with the opposite end free and rigidly supported from said one end for penetration through limp sheet material and having a sharp, leading cutting edge .Iaddend.which translates relative to .Iadd.the .Iaddend.sheet material in a spread condition, the cutting machine including displacement means for guiding the .Iadd.sharp, leading .Iaddend.cutting .Iadd.edge of the .Iaddend.blade in cutting engagement with the material along a predefined line of cut and means for orienting the cutting blade about an axis generally perpendicular to the sheet material at each point along the line of cut, the improvement comprising: detecting means for producing information defining blade side loads generated by the interaction of the cutting blade and the sheet material as the blade is guided along the line of cut by the displacement means; and   reacting means responsive to the detected cutting information and generating blade orientation signals in accordance with the detected information, and applying the orientation signals to the orienting means   
     
     
        to reduce blade side loads. 13. The combination of claim 12 in an automatically controlled cutting machine having a cutting blade with a cutting edge and a blade sharpener for sharpening the cutting edge of the blade wherein the detecting means comprises a sensor producing an output indicative of the condition of the cutting edge of the blade; and the reacting means comprises a control regulating the operation of the blade sharpener and responsive to the output of the sensor to control initiation 
     
     
        of a sharpening operation. 14. The combination of claim 12 wherein the detecting means comprises a load sensor measuring forces generated between 
     
     
        the sheet material and the cutting blade. 15. An automatically controlled cutting machine for cutting limp sheet material with a closed loop control comprising: a reciprocated cutting blade .Iadd.having a sharp leading knife edge for cutting through and severing the material on each side of the blade.Iaddend.;   a cutting table having a bed for supporting the limp sheet material in a spread condition during cutting; .Iadd.   motor means for advancing the blade and the limp sheet material relative to one another along a line of cut with the limp sheet material severed by the sharp leading knife edge closely engaging and pressing against the sides of the blade; .Iaddend.   vacuum means associated with the sheet material spread on the bed of the cutting table for rigidizing the limp material .Iadd.pressing against the sides of the blade .Iaddend.during cutting;   sensing means cooperatively connected with the cutting blade for detecting a cutting load parameter affected by the interaction of the blade and the rigidized material during cutting; and   closed loop control means connected with the sensing means and responsive to the sensed cutting load parameter for controlling the cutting blade in accordance with cutting conditions manifested by the sensed parameter as   
     
     
        the material is cut. 16. An automatically controlled cutting machine for cutting sheet material as defined in claim 15 wherein the cutting table has a penetrable bed penetrated by the reciprocated cutting blade during 
     
     
        cutting. 17. An automatically controlled cutting machine as defined in claim 16 wherein the vacuum means is connected with the penetrable bed of the cutting table for evacuating air from the sheet material through the bed. .[.18. The combination of claim 12 wherein: the automatically controlled cutting machine includes programmed cutting control means for generating fundamental machine command signals including blade orientation signals for guiding the cutting blade tangentially along the predefined cutting path;   the detecting means provides feedback signals representative of blade side loads; and   the reacting means receives the feedback signals and produces supplemental blade orientation signals which modify the fundamental orientation signals   
     
     
        and orientation of the cutting blade..]. 19. The combination of claim .[.18.]. .Iadd.30 .Iaddend.wherein the programmed cutting control means in the automatically controlled cutting machine includes in addition to the cutting program producing fundamental command signals another program having a fixed schedule of supplemental blade orientation commands that are combined with the fundamental commands whereby the cutting blade is guided in cutting engagement with the sheet material by the combination; and the reacting means receiving the feedback signals cooperates with the program of supplemental commands and generates supplemental commands from 
     
     
        the fixed schedule in accordance with the feedback signals received. 20. An automatically controlled cutting machine for cutting limp sheet material comprising: a thin cutting blade having a sharp leading cutting edge which is advanced in cutting engagement with the sheet material and a trailing edge spaced from and generally parallel to the leading edge;   a support table defining a surface on which the limp sheet material is laid in a spread condition;   translating means for advancing the cutting blade and the sheet material relative to one another in cutting engagement with the sharp leading cutting edge of the blade extending generally perpendicular to the support surface of the table;   orientation means for rotating the cutting blade and .[.a.]. .Iadd.the .Iaddend.sheet material relative to one another about an axis generally perpendicular to the surface of the table;   sensing means operatively associated with the cutting blade for detecting unbalanced lateral blade loading and the corresponding blade deflection away from the axis perpendicular to the cutting table; and   feedback control means connected with and responsive to the sensing means and also connected in controlling relationship with the orientation means to rotate the leading cutting edge of the blade about the perpendicular axis and toward the side of the blade having the higher loading in response to detected blade deflection and thereby reduce blade deflection.   
     
     
        1. An automatically controlled cutting machine as defined in claim 20 wherein: the sensing means also detects fore-and-aft blade deflection; and the feedback control means is connected with the translating means to reduce the feed rate of the cutting blade and sheet material relative to 
     
     
        one another in response to the detected fore-and-aft deflection. 22. An automatically controlled cutting machine as defined in claim 20 wherein: 
     
     
        the cutting blade is a reciprocated cutting blade. 23. An automatically controlled cutting machine as defined in claim 20 wherein the sensing means comprises a blade position sensor. .Iadd. 24. An automatically controlled cutting machine as described in claim 1,8 or 11 wherein: the control means for guiding the cutting blade through the material includes means for establishing the rate at which the cutting blade and the sheet material are moved relative to one another along a cutting path; and   the feedback means is interconnected with the control means for adjusting the rate at which the blade and material are moved relative to one another in response to the lateral force signals from the sensing means. .Iaddend..Iadd. 25. An automatically controlled cutting machine as described in claim 24 wherein the feedback means is connected with the control means for reducing the rate at which the blade and material are moved relative to one another as the lateral force signals increase. .Iaddend..Iadd. 26. The combination of claim 12 in an automatically controlled cutting machine in which the displacement means establishes the rate of displacement of the cutting blade along the line of cut wherein the displacement means is connected with the detecting means and responsive to the detecting means to reduce the rate of displacement of the blade according to the blade side loads. .Iaddend..Iadd. 27. An automatically controlled cutting machine as defined in claim 20 or 22 wherein the feedback control means is also connected with the translating means to reduce the feed rate of the cutting blade and sheet material relative to one another in response to unbalanced lateral blade loading detected by the sensing means. .Iaddend. .Iadd. 28. An automatically controlled cutting machine for accurately cutting limp sheet material comprising:   a cutting blade having a sharp, leading cutting edge, a trailing edge and sides extending between the leading and trailing edges;   a cutting table defining a support surface on which sheet material is positioned in a spread condition for cutting by the cutting blade;   motor means for moving the cutting blade and the sheet material relative to one another in cutting engagement;   control means connected with the motor means and providing control signals to the motor means for guiding the cutting blade through the material along a predetermined cutting path;   a presser foot surrounding the cutting blade and resting on the sheet material during cutting;   a blade guide mounted in the presser foot and supporting the blade along an axis extending generally perpendicular to the sheet material spread on the cutting table;   sensing means including a load sensor mounted in the presser foot and interposed between the blade guide and the cutting machine for detecting lateral forces applied to the sides of the blade by the material as the blade advances through the material in cutting engagement, the sensing means also producing a signal corresponding to the detected lateral forces; and   feedback means interconnecting the sensing means and the control means for generating additional control signals to regulate the cutting of the material by the blade along the predetermined cutting path in response to the detected forces. .Iaddend..Iadd. 29. An automatically controlled cutting machine for accurately cutting limp sheet material comprising:   a reciprocating cutting blade having a sharp, leading cutting edge, a trailing edge and sides extending between the leading and trailing edges;   a cutting table having a penetrable bed including bristles having free ends substantially in a common plane and defining a support surface on which the sheet material is positioned in a spread condition for cutting by the cutting blade, the blade penetrating through the support surface and between the bristles during cutting;   motor means for moving the cutting blade and the sheet material relative to one another in cutting engagement;   control means connected with the motor means and providing control signals to the motor means for guiding the cutting blade through the material along a predetermined cutting path;   sensing means operatively associated with the cutting blade and sheet material for detecting lateral forces applied to the sides of the blade by the material as the blade advances through the material in cutting engagement, the sensing means also producing a signal corresponding to the detected lateral forces; and   feedback means interconnecting the sensing means and the control means for generating additional control signals to regulate the cutting of the material by the blade along the predetermined cutting path in response to the detected forces. .Iaddend..Iadd. 30. In combination in an automatically controlled cutting machine having a cutting blade in the form of a knife having a sharp, leading cutting edge which translates relative to sheet material in a spread condition, the cutting machine including displacement means for guiding the sharp, leading cutting edge of the blade in cutting engagement with the material along a predefined line of cut and means for orienting the cutting blade about an axis generally perpendicular to the sheet material at each point along the line of cut, the improvement comprising:   programmed cutting control means connected with the displacement means and the orienting means for generating fundamental machine command signals including blade orientation signals for guiding the cutting blade tangentially along the predefined line of cut;   detecting means for producing feedback signals defining blade side loads generated by the interaction of the cutting blade and the sheet material as the blade is guided tangentially along the line of cut; and   reacting means responsive to the feedback signals for generating supplemental blade orientation signals which modify the fundamental orientation signals, and for applying the modified orientation signals to the orienting means to reduce blade side loads. .Iaddend.