Abstract:
A quilting machine is provided having at least one set of single needle stitch forming elements for forming chain stitched patterns on a thick multilayered material such as a mattress cover. The machine is preferably web-fed, with a panel of the continuous web being clamped and held stationary on a frame. The stitch forming elements include a needle and a looper mounted on separate heads that are independently moveable on a bridge transversely relative to the panel, which is moveable longitudinally relative to the frame. The bridge is longitudinally moved by a servo and the heads are transversely moved on the bridge by separate servos. The stitching elements on each head are driven by separate servos. A controller drives the servos to chain stitch patterns and differentially move the heads transversely to account for transverse needle deflection. The drives of the needle and looper are phased to compensate for longitudinal needle deflection. The controller determines or predicts needle deflection. It may store empirically determined data and respond to control signals and/or sensors to determine or predict deflection and to calculate the needle deflection compensation, in response to which it generates deflection compensation signals to drive the servos. Infrared, LED or magnetic deflection sensors are preferred, but many other types are or will become available that will be suitable.

Description:
This is a continuation-in-part of the and commonly assigned U.S. application Ser. No. 08/831,060 filed on Apr. 01, 1997 now U.S. Pat. No. 5,832,849, hereby expressly incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the quilting of patterns on multiple layer materials, and particularly to the stitching of 360° patterns on thick multilayer materials such as mattress covers. 
     BACKGROUND OF THE INVENTION 
     Quilting is a special art in the general field of sewing in which patterns are stitched through a plurality of layers of material over a two-dimensional area of the material. The multiple layers of material normally include at least three layers, one a woven primary or facing sheet having a decorative finished quality, one a usually woven backing sheet that may or may not be of a finished quality, and one or more internal layers of thick filler material, usually of randomly oriented fibers. The stitched patterns maintain the physical relationship of the layers of material to each other as well as provide ornamental qualities. Quilting is performed on the customary quilts or comforters and on the covers of mattresses, for example. In the stitching of quilts for these two applications, two different approaches are typically used. Both approaches use stitches that employ both a top and a bottom thread. 
     Single needle quilters of the type illustrated and described in U.S. Pat. Nos. 5,640,916 and 5,685,250, hereby expressly incorporated by reference herein, and those patents cited and otherwise referred to therein are customarily used or the stitching of comforters and other preformed rectangular panels. Such single needle quilters typically use a pair of cooperating a lock stitch sewing heads, one carrying a needle drive that is typically positioned above the fabric and one carrying a bobbin that is opposite the fabric from the needle, with both heads being mechanically linked to move together in two dimensions, relative to the panel, parallel to the plane of the panel. A common arrangement of this type of quilting apparatus is to support the panel of fabric on a longitudinally moveable shuttle with the sewing heads moveable transversely of the panel to provide two-dimensional stitching capability of the pattern on the panel. 
     Multiple needle quilters of the type illustrated in U.S. Pat. No. 5,154,130 are customarily used for the stitching of mattress covers, which are commonly formed from multilayered web-fed material. Such multi-needle quilters typically use an array of cooperating a double chain stitch sewing elements, one element being a needle that is typically positioned above the material and one element being a looper that is opposite the material from the needle, with the entire arrays of both elements being mechanically linked together to move in unison in two dimensions, relative to the material, parallel to the plane of the material in paths that corresponds to identical patterns of a pattern array. The needles and loopers also operate in unison so that the sets of elements simultaneously form identical series of stitches. A common arrangement of this type of quilting apparatus is to support the panel of multilayered material and feed the material from a web longitudinally relative to the sewing element array and in coordination with the motion and operation of the sewing elements. The sewing element array may be shiftable transversely of the web to provide two-dimensional stitching capability of the pattern on a panel length of the web. Alternatively, the array is stationary and rollers that support the web shift transversely relative to the array. Some multi-needle quilters of this type have longitudinally bi-directional web feeding capability which, when synchronized with the transverse shifting of the web or the sewing elements, provides for 360° pattern sewing capability. 
     The single needle quilters are regarded as preferable for the sewing of a wider range of patterns and particularly more highly decorative patterns. In addition, in single needle quilters, the lock stitch is commonly used. Lock stitch machines, with their needle and bobbin arrangement, have been made somewhat able to tolerate or avoid needle deflection problems that can result in a missing of stitches when a needle is deflected. Needle deflection is more of a problem when quilting thick materials and complex patterns that involve many directional changes in the sewing path, particularly where higher sewing speeds are used. The lock stitch also provides equally aesthetically acceptable stitching on both sides of the fabric. 
     The multi-needle quilters are regarded as preferable for sewing mattress covers. With mattress covers, the less attractive looper side stitch may be confined to the inside of the mattress cover on the backing layer of material that is not visible to the observer. Further, the double chain stitch heads of the multi-needle quilters apply a looper side thread from an external spool, which can accommodate a substantially larger thread supply than can the bobbin of a lock stitch machine. As a result, the lock stitch machine can be run longer before the need arises to replenish the bottom thread supplies. The bobbins of the lock stitch machines require frequent changing, particularly with thick multilayered materials such as mattress covers which require more thread per stitch. A drawback to the use of double chain stitch machines has been the greater likelihood for stitches to be missed as a result of needle deflection. This is in part because a double chain stitch requires the looper on one side of the material to enter a thread loop in close proximity to the needle that has passed through the material from the other side, which needle itself must pass through a thread loop presented by the looper. Misalignment of the needle and looper due to deflection of the needle can result in the missing of stitches which, in the formation of more highly decorative patterns, is undesirable for not only aesthetic reasons but because it can result in an unraveling of the stitched pattern. Attempts at high speed sewing on mattress covers, where the material is generally very thick and the outer or ticking layer of fabric may be heavy and even of an upholstery-like nature, produce unavoidable needle deflection. 
     With the increased use of computerized pattern control and the resulting ability to provide a wider variety of quilted patterns, particularly patterns of a high ornamental quality, there has been an increasing demand for an ability to sew more, more complex and larger patterns onto the covers of mattresses. To this end, equipment of the prior art such as discussed above has had limitations. Accordingly, there remains a need for a capability to stitch more highly ornamental and complex patterns onto mattress covers at high speed. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a computer controlled pattern quilting method and apparatus that will provide wide variety of quilted patterns, particularly patterns of a high ornamental quality. A particular objective of the present invention is to provide a quilting method and apparatus employing a single needle quilting head and having the capability of quilting at high speed, particularly on thick materials such as those used for mattress covers. 
     A further objective of the present invention is to provide a quilting method and apparatus having one or more independently moveable sets of single needle chain stitch quilting heads that will stitch at high speeds, particularly on thick materials. A particular objective of the present invention is to provide such a quilting apparatus and method that does not suffer adversely from needle deflection. 
     According to the principles of the present invention, a quilting machine is provided with at least one a set of chain stitch quilting heads that are independently moveable relative to each other and relative to the material being quilted. The machine is preferably web-fed and its method of use preferably includes 360° stitching onto material webs of thicknesses typical of those used for mattress covers. In accordance with the preferred embodiment of the invention, a single-needle double chain stitch quilting method and apparatus are provided with independently operable servo driven quilting heads that are each independently moveable relative to the material being quilted. The heads are preferably also independently movable relative to each other in at least one direction, preferably the transverse direction, and the operation of each of the heads is preferably also independent to allow for effective control of the cooperating positions of the needle and looper relative to each other. In the preferred and illustrated embodiment, the needle and looper heads are independently moved transversely to permit adjustment of the cooperating positions of the needle and looper in the transverse direction and the cycles of the needle and looper heads are relatively phased to allow adjustment of the cooperating positions of the needle and looper in the longitudinal direction. 
     The relative movements and operation of the heads are brought about by computer controlled servos that move and drive the heads so as to maintain the proper cooperative relationship between the needle and looper in accordance with whatever needle deflection takes place. 
     According to one embodiment, needle deflection is determined in advance by empirical measurements and data is stored in memory in a programmable microprocessor-based controller of the quilting machine. The stored measurements may be in the form of a look-up table or sets of formula, constants and/or parameters from which needle deflection compensation signals can be supplied to affect the operation of servo motors driving and moving the heads relative to each other and to the material being quilted. Preferably also, the stored empirical data include alternative data that will provide needle deflection compensation for different conditions, such as different materials and fabrics, needles that differ in size or stiffness, varying stitch speeds and stitch sizes, and or other variables that can have an effect on the amount and direction of needle deflection that is expected to occur or does occur. 
     In accordance with the preferred embodiment of the invention, a quilting machine is provided with web supplies of the various layers of a mattress cover, which webs are brought together in the form of a multiple layered web and fed onto a machine frame, preferably in a horizontal plane. The frame preferably includes a plural belt conveyor that supports the web and aids in the advancement of the web onto the frame. A pair of side edge grippers, which may be in the form of opposed belt grippers, pin chains, clamping finger sets or other side securements, engage the opposite side edges of the web and move the web onto the frame in synchronism with the operation of the belt conveyor. The machine may optionally be provided with a pair of edge stitching heads to at least temporarily stitch together the layers of material of the portion of the web that is advanced onto the frame. Once on the frame, the edge clamps as well as tension rolls at the front and back of the frame tension a portion of the web for quilting. 
     The quilting is performed by a pair of heads that are each mounted to a bridge structure that is moveable longitudinally on the frame. The bridge is moveable on the frame by a computer controlled servo motor that positions the set of heads in accordance with the pattern to be stitched. Each of the heads is mounted on the bridge so as to be independently transversely moveable. Each head, including an upper needle head and a lower looper head, is provided with a servo motor drive that drives the respective head through its stitching cycle. The two head drive servo motors are operated in synchronism under computer control to sew series of double chain stitches in the fabric. Each head is mounted to the bridge on a linear servo motor that independently positions the head transversely on the frame under the control of the programmed controller of the machine in accordance with the pattern to be stitched. 
     Needle deflection is accommodated in one of, and preferably both of, two ways. First, needle deflection is accommodated by providing either a table of correction values, or preferably a correction formula based on several empirical constants, and a program in a memory accessible by a microprocessor of the controller in response to which the controller may vary control signals to the servos to control the positions of the heads relative to each other and the relative operational phases of the heads in a way that will compensate for whatever needle deflection is likely to occur. Second, needle deflection is accommodated by sensing certain conditions or parameters. The sensing can be a sensing of those machine conditions, such as speed, load or power demand or torque angle of servo motors, needle or looper position, or some other relevant machine condition that have a relation to needle deflection, or can be achieved by directly sensing the deflection of a needle. The sensing may be provided by reading data already present in the controller, by reading control signals being sent to machine servos and other drive elements or by monitoring various sensors separately provided on the machine to sense machine element status or the properties or states or the material or of the thread. 
     The method used for determining or predicting needle deflection can use any of the above described methods or combinations of the above described methods. For example, the first order of predicting needle deflection can be by the use of lookup tables, based on empirical or experimental data or theoretical data, from which tables corrective actions may be selected in response to, for example, measurements of sewing speed or input parameters such as fabric thickness. This estimate can provide for substantial corrective action being taken before actual deflection of the needle occurs. Further, actual needle deflection can be measured by sensors, such as magnetic or induction sensors, LED array sensors that may be infrared sensors, pictorial vision systems, ultrasonic detection systems, strain gage sensors, accelerometer sensors, or other techniques. A detected error can be used to adjust the lookup table produced response to anticipate and correct the error as the quilting proceeds. 
     Preferably, transverse deflection of the needle is provided by differently driving the heads transversely so that the looper and needle align whether or not the needle is deflected transversely. Preferably also, longitudinal deflection of the needle is provided by controlling the relative phases of the head drive servos so that the needle and looper engage at the proper time in the cycle whether or not the needle is deflected longitudinally. 
     The present invention provides for the high speed quilting of patterns on a web of thick fabric of the type of which mattress covers are made. A double chain stitch is sewn without the stitch quality being adversely affected by needle deflection, because servos drive the heads to provide for precise relative positioning. As a result, large spools of lower thread may be provided, eliminating the need to replenish bobbin thread supplies as would be the case with lock stitch machines. Overall higher operating speed and throughput is obtained. 
     These and other objects of the present invention will be more readily apparent from the following detailed description of the drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a web-fed mattress cover quilting machine embodying principles of the present invention. 
     FIG. 2 is a side elevational view of the machine of FIG.  1 . 
     FIG. 3 is a diagrammatic perspective view of the sewing heads of the machine of FIG.  1 . 
     FIG. 4 is a diagrammatic representation of the control system of the machine FIG.  1 . 
     FIGS. 5-5C are sequences of diagrams representing needle deflection problems that can occur in the high speed chain stitch quilting of thick fabrics. 
     FIGS. 6-6C are sequences of diagrams representing needle deflection compensation in accordance with principles of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 illustrate a quilting machine  10  having a stationary frame  11  with a longitudinal extent represented by arrow  12  and a transverse extent represented by arrow  13 . The machine  10  has a front end  14  into which is advanced a web  15  of multi-layered material that includes a facing material layer  16 , a backing material layer  17  and a filler layer  18 . The machine  10  also has a back end from which quilted multilayered material is advanced to a take-up or panel cutting section (not shown). 
     On the frame  11  is mounted a conveyor table  20  that includes a set of longitudinally extending belts  22  supported on a set of transverse rollers  23  journaled to the frame  11  to rotate thereon under the power of a drive motor  24 . The motor  24  drives the belts  22  to advance the unquilted web  15  onto the frame  11  at the front end  14  thereof and to advance a quilted portion of the web  15  from the frame  11  to the take-up section at the back end  19  of the machine  10 . The belts  22  support a panel of the web  15  in a horizontal quilting plane during quilting. The machine  10  also has a right side  25  and a left side  26 , along each of which is mounted a side securement  27  in the form of a pair of opposed conveyor clamp belt or chain loops  28  that operate as a set of edge clamps to grip the edges of the web  15  to assist the feed of the web  15  onto and off of the frame  11  and to apply transverse tension to the web  15  in the quilting plane while a panel of the web  15  is being quilted. The securements  27  may be in the form of a series of gripping finger sets that are spaced along one of the loops  28  of the securements  27 . Preferably, however, the securements  27  are preferably each in the form of a pin chain having a plurality of pins on one of the clamp loops  28  that penetrate the web  15  and extend into holes in the other of the clamp loops  28  of the respective pair. A pair of edge stitching heads  29  is also provided, one forward of each of the side securements  27  to temporarily stitch the layers  16 - 18  of the web  15  together for quilting. Immediately upstream of each of the stitching heads  29  is an edge slitter for trimming excess material to the outside of the edge stitch formed by the stitching heads  29 . The loops  28  are linked to move in unison with the belts  22 , which are driven by the drive motor  24  on the frame  11 . 
     The machine  10  has a sewing head bridge  30  mounted thereon that extends transversely across the frame  11  and is supported at each side of the frame  11  on a carriage  41 . The bridge  30  carriages  41  are each mounted to move longitudinally on the frame  11  on a pair of tracks  31  on each side of the frame  11 . The bridge is driven longitudinally on the tracks  31  by a bridge drive servo motor  32 , mounted on the frame  11 , which is responsive to signals from a machine controller  60  (FIG.  4 ). 
     The bridge  30  has a pair of transverse rails extending from one side of the frame  11  to the other, including an upper rail  33  and a lower rail  34 . On the upper rail  33  is mounted an upper quilting head  35  that includes a needle  36  and a needle drive servo motor  37  (FIG.  3 ), which reciprocally drives the needle in a sewing cycle in response to signals from the machine controller  60 . On the lower rail  34  is mounted a lower quilting head  38  that includes a looper  39  and a looper drive servo motor  40  (FIG.  3 ), which rocks the looper  39  in an arc in a sewing cycle, in synchronism with the motion of the needle  36  in a relationship responsive to separate signals from the machine controller  60 . 
     The upper quilting head  35  is moveable transversely on the upper rail  33  by a linear servo motor  43  in response to signals from the controller  60 , while the lower quilting head  38  is also moveable transversely on the lower rail  34  by a linear servo motor  44  in response to signals from the controller  60  independently of the upper head  35 . Both of the linear servo motors  43  and  44  are preferably of the iron core type, such as the Ironcore Series of motors manufactured by Koll Morgen Motion Technologies Group of Commack, N.Y. 
     The bridge  30  carries a set of three idler rollers  46  that move longitudinally on the frame  11  with the bridge  30 . The rollers  46  direct the belts  22  downwardly in a loop  47  below the lower rail  34  and lower quilting head  38  to permit the lower quilting head  38  to pass between the belts  22  and the web  15 . The loop  47  moves with the bridge  30  and remains aligned with the bridge  30  directly below the lower quilting head  38 . 
     in a preferred embodiment of the machine  10 , a needle deflection sensor  80  is provided to measure the actual deflection of the needle  36 . As illustrated in FIG. 3, the sensor  80  may take the form of an LED array mounted beneath needle plate  85  on which the fabric  15  that is being quilted rests. The LED array sensor  80  may, for example, include a transverse deflection portion  81  and a longitudinal deflection portion  82 , to provide orthogonal coordinate information to the controller  60  of the actual deflection of the needle  36  in the transverse and longitudinal directions. Each of the portions  81 ,  82  of the needle deflection sensor  80  include arrays of emitting and receiving LEDs positioned on opposite sides of the needle opening in the needle plate  85 , with those of the transverse portion being situated along the sides of a rectangular arrangement of LEDs and those of the longitudinal portion being situated do along the front and back sides thereof. This device generates two outputs, one for transverse deflection and one for horizontal deflection, to the controller  60 . These outputs can easily be zeroed by setting them to zero on the control interface when the needle  36  is stationary and extending through the needle opening in the needle plate  85 , without horizontal deflection forces on the needle  36 . This set of conditions results in the centerline of the needle  36  being in the longitudinal plane  72  and transverse plane  76  in FIGS. 5-5C and FIGS. 6-6C. The density of the individual detectors of the array is determined by the deflection measurement resolution required to insure accurate deflection compensation to the degree necessary to avoid missing stitches due to the looper or needle missing loops. Such a deflection sensor  80  can produce either analog or digital signals to the controller  60  representative of the amount of the deflection of the needle  36  from its zeroed position. 
     Alternative forms of sensors can be provided. Magnetic detectors, for example, are available suitable for the purpose. Whatever the form of the sensor  80 , the outputs from the sensor provide the controller  60  with the ability to compensate for needle deflection by closed loop feedback, which may be carried out as a second order correction to predicted needle deflection based on the consideration of other parameters. 
     The interconnection of controller  60  with the servos  32 ,  37 ,  38 ,  43  and  44  is diagrammatically illustrated in FIG.  4 . The controller  60  includes a CPU or microprocessor  61  and a servo driver module  62 . The servo driver module  62  has outputs on which signals are communicated for driving the servos  32 ,  37 ,  38 ,  43  and  44  and has inputs for receiving feedback signals from the servos  32 ,  37 ,  38 ,  43  and  44  to maintain the servos  32 ,  37 ,  38 ,  43  and  44  at positions calculated by CPU  61 . Inputs are provided the controller  60  to receive sewing speed setting or measurement information, to receive data of material properties that could affect needle deflection and inputs from the needle deflection sensor  80  with information of the actual needle deflection in the transverse and longitudinal directions. 
     The controller  60  also includes a non-volatile memory module  64  that includes a pattern implementation program  65 , a needle deflection compensation program  66  and deflection compensation data  67 , that may include lookup tables or stored constants or coefficients for use by a compensation formula in the compensation program  66 . The controller  60  also has outputs to other components of the machine  10 , including the web feed motors  24 , the edge stitch units  29  and other machine motors and actuators not relevant to the present invention. 
     The controller  60  moves the bridge  30  by driving the bridge drive servo  32 , and moves the linear servos  43  and  44  to move the quilting heads  35  and  38  in unison in accordance with the stitching pattern provided by the pattern program  65 . These movements are carried out in coordination with the driving of the needle drive servo  37  and looper drive servo  40  to stitch patterns with stitches of controlled lengths. 
     In addition to the programed stitching of the patterns in accordance with the program  65 , the CPU  61  modifies signals sent to the drivers  62  by differentially driving the transverse linear servos  43  and  44  to offset the needle  36  and the looper  39  transversely by a distance of preferably plus or minus approximately 0.1 inches, to an accuracy of preferably approximately 0.001 inches. The offset is determined, preferably at least partially, by the CPU  61  in response to a deflection compensation program  66  and empirical data in deflection tables  67  in an amount necessary to precisely compensate for the transverse deflection of the needle  36  that is expected to occur. The offset is also determined, preferably at least partially, by the measurements of actual needle deflection from the output of the sensor  80 . 
     Further, in accordance with the program  65 , the CPU  61  also modifies signals sent to the drivers  62  by differentially driving the looper drive servo  40  so as to advance or retard the phase of the looper  39  relative to the needle  36  to longitudinally offset the loop take positions of the needle  36  and the looper  39  a phase angle of preferably plus or minus approximately 2.5° to a minimum accuracy of preferably approximately 0.25°. The offset is determined by the CPU  61  in response to a deflection compensation program  66  and empirical data in deflection tables  67  in an amount necessary to precisely compensate for the longitudinal deflection of the needle  36  that is expected to occur. 
     FIGS. 5-5C diagrammatically illustrates in front view a series showing how the needle  36  might deflect in transverse direction. In FIG. 5, the needle  36  is shown as it begins to pierce the web  15  in the downward part of its cycle in a portion of a pattern at which the web  15  is moving transversely relative to the needle  36 , as represented by the arrows  71 . At this point in the cycle, the centerline of the needle  36  lies on a vertical centerline of the upper head  35  that lies in longitudinal plane  72 , which centerlines are the line of normal alignment of the needle  36  at which the looper  39  would, if the needle  36  were to remain in the longitudinal plane  72 , bring the needle  36  into a loop engaging relationship with the looper  39  below the web  15 . At this point, the transverse deflection determining portion  81  of the needle deflection sensor  80  should be outputting a signal indicating that the transverse deflection is essentially zero. By the time the needle  36  has reached the bottom extent in its cycle, as illustrated in FIG. 5A, the relative motion of the needle  36  relative to web  15  results in a bending of the needle  36  to the right in the figure, which moves the tip of the needle  36  away from the plane  72  and out of alignment with the path of the looper  39 . At this point, the transverse deflection determining portion  81  of the needle deflection sensor  80  should be outputting a signal indicating the magnitude of the transverse deflection of the needle  36  at the point it crosses the horizontal plane in which the sensor  80  is mounted. The controller  60  calculates from this the actual configuration of the needle  36  in its bent or deflected state. In this position, the looper  39  is in a retracted position moving forward in a path that is supposed to pass between the needle  36  and top thread  74  that runs through the eye  70  of the needle  36 . As the needle  36  ascends, as is illustrated in FIG. 5B, the needle  36  moves to a plane through which the looper  39  is moving forwardly and at which the looper  39  is supposed to pass between the needle  36  and top thread  74 . However, due to the deflection of the needle  36  to the right caused by the continued motion of the web  15  relative to the centerline  72  of the upper head  35 , the looper  39  misses the thread  74 . 
     In accordance with certain embodiments of the present invention, under the conditions illustrated, the CPU  61  recognizes the needle deflection condition and determines the direction and amount of transverse deflection of the needle  36 , then retrieves information  67  stored in the memory  64  and calculates the amount of compensation necessary to position the looper  39  so as to insure that the looper  39  passes between the needle  36  and the top thread  74 . This amount of transverse compensation is represented by the dimension t in FIG.  5 C. Movement of the lower head  38  relative to the normal position of the upper head  35  places the looper  39  in position  39   a  in a vertical longitudinal plane  72   a , displaced a distance t from the plane  72  that passes through the proper point for the looper  39  to pass between the needle  36  and the top thread  74 . 
     Preferably, the CPU makes corrections by generating the main component of the signal to the servos  43  and  44  in accordance with the pattern program  65 . Then, this signal is modified by the substantially smaller deflection compensation signal read by the program  66  from the table  67  that modifies one or both of the signals to the servos  43  and  44 . The CPU further uses the output from the needle deflection sensor  80  to determine if the predicted deflection derived from the lookup tables is correct and that the correction has been adequate. If not, an adjustment to the correction is calculated and stored for use in calculating further corrections. Preferably, transverse needle deflection compensation is made to the looper head positioning servo  44 . 
     The longitudinal correction for needle compensation works in a somewhat different manner. In FIGS. 6-6C there is diagrammatically illustrated a series of side views showing how the needle  36  can deflect in the longitudinal direction. In FIG. 6, the needle  36  is shown as it begins to pierce the web  15  in the downward part of its cycle in a portion of a pattern at which the needle  36  is moving longitudinally relative to the web  15 , as represented by the arrows  75 . As in the case of transverse needle deflection, the deflection sensor  80  should output a signal indicating that there is no deflection of the needle  36  occurring in this position. At this point in the cycle, the needle  36  lies in a vertical transverse plane  76  that contains the vertical centerline of the upper head  35 , which is the line of normal alignment of the needle  36  with the looper  39  and the line that contains the position at which the looper  39  would, if the needle  36  were to remain in the plane  76 , bring the needle  36  into contact with the looper  39  below the web  15  and pass between the needle  36  and the top thread  74 . By the time the needle  36  has reached the lowest point in its cycle, as illustrated in FIG. 6A, the relative motion of the needle  36  relative to the web  15  results in a bending of the needle  36  forward (to the right in FIG.  6 A), which moves the needle  36  away from the plane  76  of the normal intercept point of the needle  36  with the looper  39 . At this time, the looper  39  is in a retracted position moving forward in a path that is supposed to pass between the needle  36  and top thread  74  that runs through the eye  70  of the needle  36 . As the needle  36  ascends, as is illustrated in FIG. 6B, the needle  36  moves to adjacent the point through which the looper  39  is moving forwardly and at which the looper  39  is intended to pass between the needle  36  and top thread  74 . However, due to the deflection of the needle  36  to the right (forward) caused by the continued motion of the upper head  35  relative to the web  15 , the looper  39  misses the thread  74 . 
     In accordance with certain embodiments of the present invention, under the conditions illustrated, the CPU  61  recognizes the condition and determines the longitudinal deflection of the needle  36 , then retrieves information  67  stored in the memory  64  and calculates of the amount of compensation necessary to position of the looper  39  so as to insure that the looper  39  passes between the needle  36  and the top thread  74 . Preferably, actual needle deflection is measured by the longitudinal portion  82  of the sensor  80  which is used to make adjustments to the calculated correction that is necessary. The amount of longitudinal compensation is in the form of an angular adjustment or relative phase angle in the drive cycles of the heads  35  and  38  as controlled by the operation of the servos  37  and  40 . The phase difference is represented by the angle φ in FIG.  6 C. Phasing of the looper drive  40  relative to the normal looper angle places the looper  39  in position  39   c  in transverse vertical plane  76   a  that passes through the proper point for the looper  39  to pass between the needle  36  and the top thread  74 . 
     According to alternative embodiments of the invention, data from sensors can supply the controller  60  with information of the actual deflection of the needle  36 . in FIGS. 3,  5 - 5 C and  6 - 6 C, for example, an infrared sensor  80  in the form of an LED array is fixed to the bottom of conventional needle plate  85  which supports the fabric  15  being quilted. The sensor  80  has a rectangular arrangement surrounding the hole in the plate  85  through which the needle  36  passes. The sensor  80  may include, for example, a row of light sources on one transverse side and one longitudinal side of the needle  36  opposite a row of infrared LED detectors on each of the transverse and longitudinal sides opposite the sources. The sources and detectors can be connected by fiber optic conductors to the sensor array. 
     A longitudinal deflection detector portion  81  has elements on the sides of the needle  36  to detect longitudinal needle position at its point of intersection with the plane of sensor  80 , while the transverse deflection sensor  82  has elements on the longitudinal sides of the needle  36  which detect the transverse position of the needle at its point of intersection of the plane of the sensor  80 . Both sensor portions  81 , 82  are zeroed at the controller  60  when no horizontal forces are on the needle. This is accomplished by cycling the machine  10  slowly with no fabric  15  on the needle plate  85 . Sensors available to perform the function of sensors  80  include laser through-beam photoelectric sensor, LX series, such as LX-130, cat. no. KA-SW-31, manufactured by Keyance Corporation of America, Woodcliff Lake, N.J., or glass fiber optic sensor series BMM-442P, manufactured by Banner Engineering Corporation of Minneapolis, Minn. 
     The sensors  81 , 82  are connected to inputs of the CPU  61 , as illustrated in FIG.  4 . The CPU  61  may be programmed to compensate for the detected deflection of the needle  36  by straight forward closed loop feedback logic. Signals from the sensors  81 ,  82  may also be used by the controller  60  to supplement or adjust deflection compensation predictions, or to refine predictions, that are based on data from the lookup table  67 , either by updating the data in the table  67 , by updating the program  66 , or by providing a temporary correction to the output of the program  66  that is based on data from the lookup table  67 . 
     Preferably, the CPU makes corrections by generating the main component of the signal to the servos  37  and  40  in accordance with the pattern program  65 . Then, this signal is modified by the substantially smaller deflection compensation signal read by the program  66  from the table  67  that modifies one or both of the signals from the controller  60  to the servos  37  and  40 . Preferably, the compensation is made to the looper drive servo  40 . 
     Concepts of the invention may also be applied to alter the transverse motion of the upper head  35  by operation of the servo  43  or to alter the longitudinal motion of both heads  35  and  38  by affecting movement of the bridge  30  by servo  32  so as to decrease, at least in part, the amount of needle deflection. This, in effect, produces an indexing motion to the quilting heads  35  and  38  relative to the web  15 , which is not fully practical in high speed quilting processes. 
     Details of machines  10  of the above described embodiment that are known in the art can be found in U.S. patent application Ser. No. 08/497,727, filed Jun. 30, 1995 entitled Quilting Method and Apparatus, which relates to single needle quilters but of the lock stitch type, and in U.S. Pat. No. 5,154,130, which relates to web-fed chain stitch quilters but of ganged multi-needle type, both of which are assigned to the assignee of the present invention and are hereby expressly incorporated by reference herein. 
     More than one set of independently driven heads may be supported on the frame  11 . For example, two sets of heads  35 , 38  may be supported for transverse movement on the bridge  30 , each separately controllable in the transverse direction and each separately driveable to stitch patterns on the web  15 , with separate control thereof to compensate separately for the needle deflection that would occur at each head. 
     Those skilled in the art will appreciate that various changes and additions may be made to the embodiments described above without departing from the principles of the present invention. Therefore, the following is claimed: