Abstract:
A method for minimizing contact between a needle point and a needle thread in a computer controlled embroidery machine, to prevent breakage of the needle thread by the needle point upon penetration of a workpiece during stitching. The method includes the steps of: determining a first straight path between a current needle penetration location and a next needle penetration location; and, moving to the next needle penetration location along a second non-straight path so that the needle thread is pulled away from the needle point.

Description:
This application claims priority from Canadian Patent Application No. 2,411,955, filed Nov. 15, 2002, the disclosure of which is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The invention relates to the field of embroidery machines, and more specifically, to a system and method for reducing thread breakage due to needle puncture during the embroidery process. 
   BACKGROUND OF THE INVENTION 
   Industrial high-speed embroidery machines generally have a workpiece support table which is mounted for movement along several axes relative to a needle carrying sewing head. The support table is driven by stepper motors which are responsive to signals from a computer control system. The signals are generated according to a digitized pattern. The workpiece is then moved under the sewing instruments through a desired path. 
   Typically, the sewing head includes a drive shaft to vertically reciprocate a swingable needle to penetrate a fabric to be embroidered and also to reciprocate a thread take-up lever to supply an upper thread from a supply and to tighten a stitch to be formed. 
   Thread breakage is a significant problem in high speed embroidering systems. It is estimated that thread breakage occurs once every few minutes in a 1000 stitch per minute machine. Effective upper thread tension control is considered important to achieving accurate stitching. If the upper thread tension is not properly controlled prior to needle penetration, thread breakage can occur. In particular, if there is too much slack in the upper thread, thread can wrap around the point of the needle, prevent loop seizure, break the thread, or interfere with correct stitch formation. 
   Several devices are known for controlling upper thread tension and hence for preventing thread breakage, as for example U.S. Pat. Nos. 4,320,712, 4,590,879 and 4,616,583. 
   Other systems for reducing thread breakage function by controlling the position of the needle thread relative to the descending needle to avoid contact between the two. For example in U.S. Pat. No. 4,706,589 to Tsukioka, a needle thread guide is disclosed for a button holing sewing machine. The needle thread guide is provided at the needle bar frame and located adjacent to the needle entry protects the needle thread from being struck by the needle when the workpiece is fed during button holing. The guide guides the needle thread outwardly when the needle descends, thus the needle thread positioned lower than the needle eye is protected from being struck by the needle. The guide is associated with the oscillating motion of the needle, but its direction of oscillation is opposite to the direction of needle oscillation, and its amplitude is almost twice the amplitude of the needle. A similar thread deflection device for zigzag stitching is disclosed in U.S. Pat. No. 4,949,657 to Hanyu, et al. 
   One shortcoming of these devices is that their mechanics limit their ability to effectively adapt to varying stitch and workpiece characteristics prevalent in modem high speed automated embroidery machine applications. 
   A need therefore exists for an improved method and system for reducing thread breakage due to the needle contacting the needle thread as it penetrates the fabric and that allows for the effective adaptation to varying stitch and workpiece characteristics and that is not limited by sewing machine mechanics. 
   SUMMARY OF THE INVENTION 
   The invention provides a method of preventing needle thread breakage between the needle and workpiece of an automated embroidery machine system by introducing an indirect path between a first needle penetration point and a next needle penetration point in the workpiece. The characteristics of the indirect path are determined by a sequence of instructions stored in the data processing system associated with the automated embroidery machine system. An advantage of the present invention is that it requires minimal or no modification of existing automated embroidery machine mechanics. 
   According to one aspect of the invention, a method is provided for minimizing contact between a needle point and a needle thread in a computer controlled embroidery machine, to prevent breakage of the needle thread by the needle point upon penetration of a workpiece by the needle during stitching. The method includes the steps of: determining a first straight path between a current needle penetration location and a next needle penetration location; and, moving to the next needle penetration location along a second non-straight path so that the needle thread is pulled away from the needle point. 
   Preferably, the method further includes the steps of: determining a probability of needle thread breakage for the first straight line path; and, selecting said second non-straight path if the probability is within a predetermined range. 
   Preferably, the shape of the second non-straight path is variable. Preferably, the shape of the second non-straight path includes sinusoids, curves, arcs, and straight lines. Preferably, the shape is modified in response to variables including thread tension, thread strength, thread diameter, stitch length, workpiece thickness, workpiece material, sewing speed, acceleration, speed of movement, and the distance between the needle point and the workpiece. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may best be understood by referring to the following description and accompanying drawings which illustrate the invention. In the drawings: 
       FIG. 1A  is a perspective view illustrating a first automated embroidery machine system in accordance with the prior art; 
       FIG. 1B  is a perspective view illustrating a second automated embroidery machine system in accordance with the prior art; 
       FIG. 1C  is a perspective detail view illustrating the stitching instruments and bobbin assembly of the automated embroidery machine system of  FIG. 1B ; 
       FIG. 1D  is a perspective detail view illustrating the stitching instruments of the automated embroidery machine system of  FIG. 1B ; 
       FIG. 2  is a block diagram of an exemplary data processing system for implementing the invention according to one embodiment; 
       FIGS. 3A and 3B  are top views illustrating the positional relationship between needle thread, needle eye, direction of threading into the needle eye, and the position of an operator in accordance with the prior art; 
       FIGS. 3C and 3D  are side views corresponding to  FIGS. 3A and 3B , respectively; 
       FIG. 4  is a top view illustrating an embroidery machine needle and areas about the needle of differing thread breakage probability in accordance with one embodiment of the invention; 
       FIG. 5  is a graph illustrating direct and indirect paths for workpiece movement between needle penetration locations in accordance with one embodiment of the invention; and, 
       FIG. 6  is a flow chart illustrating a general method for guiding a needle thread for an automated embroidery machine to prevent breakage of the needle thread by the point of the needle according to one embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following description, numerous specific details are set forth to provide a thorough understanding of the invention. However, it is understood that the invention may be practiced without these specific details. In other instances, well-known software, circuits, structures and techniques have not been described or shown in detail in order not to obscure the invention. The term data processing system is used herein to refer to any machine for processing data, including the computer and control systems described herein. In the drawings, like numerals refer to like structures or processes. 
   Referring to  FIG. 1A , there is shown a perspective view illustrating a first automated embroidery machine system in accordance with the prior art. In  FIG. 1A , the automated embroidery machine system is shown generally by the numeral  100 . The automated embroidery machine system  100  includes an embroidery machine  1  mounted on a plateform  2  in operative association with a movable workpiece support table  3 . The workpiece support table  3  is moved under the stitching instruments  4  along tracks  5  and  6  by stepping motors  7  and  8 . Data processing system  200  generates signals to activate motors  7  and  8  to move workpiece support table  3  through a path determined by a digitized embroidery pattern which is input to data processing system  200 . The stitching instruments  4  generally consist of needle  10 , presser foot  11 , thread feed  14 , and a bobbin assembly (not shown) located underneath the workpiece support table  3 . Presser foot  11  is reciprocated by a cam in timed relation with needle  10  and may be retracted at the end of the sewing operation by air cylinder  12 . Generally, presser foot  11  has an opening  13  through which needle  10  passes during the stitching operation. Thread feed  14  consists of a variety of eyes and pulleys and generally guides thread  15  from a supply spool (not shown) through a variable tension device  16  to the needle  10 . 
   Referring to  FIG. 1B , there is shown a perspective view illustrating a second automated embroidery machine system  1100  in accordance with the prior art. In addition,  FIGS. 1C and 1D  are perspective detail views illustrating the stitching instruments  4  and bobbin assembly  1009  and the stitching instruments  4 , respectively, of the automated embroidery machine system  1100  of FIG.  1 B. Rather than using tracks  4 ,  6  and stepping motors  7 ,  8 , the second automated embroidery machine system  1100  may use more modern linear or servo motors. In addition, the second automated embroidery machine system  1100  may use multiple stitching instrument heads  1101 ,  1102 , each containing multiple stitching instruments  4 , along with tensioners including eyes, pulleys, and guides. 
   Referring to  FIG. 2 , there is shown a block diagram of an exemplary data processing system for implementing the invention according to one embodiment. In  FIG. 2 , the exemplary data processing system is shown generally by the numeral  200 . The data processing system  200  includes an input device  210 , a central processing unit or CPU  220 , memory  230 , a display  240 , and an embroidery machine interface  250 . The input device  210  may be a keyboard, mouse, trackball, or similar device. The CPU  220  may include dedicated coprocessors and memory devices. The memory  230  may include RAM, ROM, databases, or disk devices. The display  240  may include a computer screen or terminal device. And, the embroidery machine interface  250  may include inputs and outputs for receiving and sending data and commands to and from the embroidery machine  1  and its stepping motors  7  and  8 . The data processing system  200  has stored therein data representing sequences of instructions which when executed cause the method described herein to be performed. Of course, the data processing system  200  may contain additional software and hardware a description of which is not necessary for understanding the invention. 
   Referring to  FIGS. 3A and 3B , there are shown top views illustrating the positional relationship between needle thread  24 , needle eye  2   a , direction of threading into the needle eye  2   a , and the position of an operator M in accordance with the prior art. Referring to  FIGS. 3C and 3D , there are shown side views corresponding to  FIGS. 3A and 3B , respectively. The needle eye  2   a  of needle  10  is threaded by a needle thread  24  which has a portion of the needle thread  24   a  which is positioned above the needle eye  2   a , and a portion of needle thread  24   b  which is positioned below the needle eye  2   a . Under such a positional relationship, when a workpiece  22  is fed in the direction of D, the needle thread portion  24   b  positioned below the needle eye  2   a  is positioned toward the operator&#39;s side M in relation to the needle&#39;s position as shown in  FIGS. 3A and 3C . By contrast, when the workpiece  22  is fed in the direction of C, the needle thread portion  24   b  positioned below the needle eye  2   a  is positioned partly toward the rear side of the needle and away from the operator&#39;s side as shown in  FIGS. 3B and 3D . Therefore, it is possible that the needle  10  sticks the needle thread portion  24   b  when the needle  10  descends, thereby cutting the needle thread  24 . 
   Referring to  FIG. 4 , there is shown a top view illustrating an embroidery machine needle  10  and areas about the needle of differing thread breakage probability in accordance with one embodiment of the invention. As a workpiece  22  mounted on workpiece support table  3  is moved under the control of data processing system  200  in direction C, from a first needle penetration location A to a next needle penetration location B along a path  460 , the probability of breakage of the needle thread  24  varies. The probability of needle thread breakage decreases as the location of the next needle penetration location B shifts to the left right side  410  or left side  420  of the operator M with respect to direction C and the needle eye  2   a . The highest probability of breakage area  430  is aligned with direction C and the needle eye  2   a . Areas of decreasing probability of thread breakage  440 ,  450  are found to the left and right of direction C and the needle eye  2   a.    
   Referring to  FIGS. 1A through 4 , according to the present invention, sequences of instructions are stored in the memory  230  of data processing system  200  to control stepping motors  7  and  8  through interface  250  to move workpiece  22  mounted on workpiece support table  3  from the first needle penetration location A to the next needle penetration location B along an indirect path  470 . By moving the workpiece  22  along an indirect path  470  between needle penetration locations A, B, the needle thread portion  24   b  positioned below the needle eye  2   a  is guided away from the needle point thus preventing breakage by the needle point upon penetration of the workpiece  22  by the needle  10  during stitching. 
   Referring to  FIG. 5 , there is shown a graph illustrating direct and indirect paths  460 ,  470  for workpiece movement between needle penetration locations A, B in accordance with one embodiment of the invention. In  FIG. 5 , first needle penetration location A is shown at the origin of the x and y axes in the plane of the workpiece  22 . Next needle penetration location B is shown at a point along the y-axis. In effect, the selection of an indirect path  470  introducing a component of movement to the path from A to B along the x-axis. This movement along the x-axis allows needle thread portion  24   b  to slide along the needle below the needle eye  2   a  away from the needle point. In this way, the needle thread portion  24   b  positioned below the needle eye  2   a  is guided away from the needle point thus preventing breakage by the needle point upon penetration of the workpiece  22  by the needle  10  during stitching. 
   Selection of an indirect path  470  is optional. In addition, the shape of the indirect path  470  is variable. The data processing system  200  determines the need for an indirect path based on factors including the location of needle penetration locations A, B relative to the direction of threading through the needle eye  2   a . Typically, an indirect path  470  would be selected by the data processing system  200  for next needle penetration locations B lying in areas of high probability of needle thread breakage  430  as illustrated in FIG.  4 . The data processing system  200  may determine the shape of the indirect path  470  based on factors including the probability of needle thread breakage. Thus, for next needle penetration locations B lying in a high probability of needle thread breakage area  430  the degree of distortion of the indirect path  470  may be greater than the degree of distortion of the indirect path for next needle penetration locations B located in areas of decreasing probability of needle thread breakage  440 ,  450 . The shape of the indirect path  470  is variable and may include sinusoids, curves, arcs, and straight lines. Other factors in determining the need for an indirect path and the shape of the indirect path include thread tension, thread strength, thread diameter, stitch length, workpiece thickness, workpiece material, sewing speed, acceleration, speed of movement, and the distance between the needle point and the workpiece. Note that it is important to keep the needle thread straight. 
   Referring to  FIG. 6 , there is shown a flow chart illustrating a general method for guiding a needle thread  24  for an automated embroidery machine  1 , the needle thread  24  extending between the eye of a needle  2   a  and a workpiece  22  being stitched when the needle  10  is above the workpiece  22 , to prevent breakage of the needle thread  24  by the point of the needle upon penetration of the workpiece  22  by the needle  10  during stitching, according to one embodiment of the invention. In  FIG. 6 , the flow chart is shown generally by numeral  600 . At step  601 , the method starts. At step  602 , a first needle penetration location and a next needle penetration location are read. At step  603 , a path for movement of the workpiece  22  between the first needle penetration location A and the next needle penetration location B is determined, wherein the path is selectively indirect. This step of determining a path can include the following: determining a probability of needle thread breakage for a direct path  460  between the first needle penetration location A and the next needle penetration location B; and, selecting an indirect path  470  if the probability is within a predetermined range. At step  604 , the workpiece  22  is moved along the path  460 ,  470  from the first needle penetration location A to the next needle penetration location B, thereby guiding the needle thread  24  away from the needle point. At step  605 , the method ends. 
   Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.