Patent Publication Number: US-6698459-B2

Title: Coil spring assembly machine

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the assembly of coil springs of the type used in bedding and upholstery and, more particularly, to an improved machine for fabricating coil spring assemblies. 
     BACKGROUND OF THE INVENTION 
     It is well known to fabricate a coil spring assembly from a plurality of coil springs organized in matrix-like fashion into columns and rows. Often the coil spring rows are interconnected in both the top and bottom planes of the assembly. The rows and columns of the matrix are held in spatial relation in the finished assembly by some type of fastener or tie, for example, a lacing wire, that interconnects adjacent springs throughout the matrix one with the other. The helical lacing wire extends from one edge to the opposite edge of the spring assembly between adjacent rows of that assembly. The lacing wire connects adjacent springs within adjacent rows simply by being wound around the juxtaposed lacing legs or end turns of the adjacent springs. After fabrication of the coil spring assembly, manufacture of a finished product is completed by placing a cushion or pad of material, e.g., woven or non-woven batting, foam rubber, or the like, over the top and/or bottom surface of the spring assembly matrix so formed, and then enclosing that structure with an upholstered fabric or cloth sheath or the like to provide a finished saleable product. One basic use of such coil spring assemblies is in the bedding industry where those assemblies find use as mattresses or box springs, but other uses are in the home finishing industry where the finished coil spring assembly may be used in a chair&#39;s seat or a chair&#39;s backrest or the like. 
     An automatic machine for assembling continuous coil spring rows is also known. Such a machine initially picks up a row of coil springs by inserting pickup blades within the spring&#39;s barrel and moving the spring through a 90° arc onto a support surface. The row of springs is then compressed against the support surface, and thereafter, the row of springs is pushed between upper and lower die boxes by upper and lower rotating transfer fingers. Assuming a row of coil springs had previously been loaded in the die boxes, upper and lower clamping dies are closed to secure lacing legs of respective top and bottom turns of the two rows of coils. A helical lacing wire is then wound around the clamped lacing legs of the two rows of coils to connect the two rows of coils together. After the two rows of coil spring rows are connected, upper and lower indexing hooks grab the connected coils and index them in a downstream direction so as to permit a next row of springs to be fed between the upper and lower die boxes and connected to the assembly. When a desired number of rows of springs have been connected, a feed-out mechanism is cycled to move the completed spring assembly away from the machine. 
     The known coil spring assembly machine has a feed conveyor for delivering coil springs to the pickup blades for each row of coils. The feed conveyor grips the coil at a location intermediate the coil ends and orients the coil horizontally so that the coil centerline is aligned with one of the pickup blades. The pickup blades are translated into the barrels of respective coils, and then, the pickup blades are pivoted 90° to a vertical position. The pivoting motion removes the coils from the feed conveyor and locates a row of coils on a support surface. While the above coil spring pickup mechanism works satisfactorily, it does have some disadvantages. First, as a pickup blade translates into a barrel of a coil, it passes across a path of the feed conveyor that moves in a direction perpendicular to the path of the pickup blade. Therefore, if, for any reason, the feed conveyor moves prior to the pickup blade initiating its pivoting motion, the feed conveyor would hit the pickup blade and potentially damage the pickup blade and supporting arm. Thus, there is a need for a device that receives a coil spring from a feed conveyor in a manner that does not cross the path of the feed conveyor. 
     The pickup blade has another disadvantage. Its length must accommodate the length of the coil as well as the length of the reciprocating stroke and the actuator that provides that stroke. Therefore, the pickup blade and supporting arm can be 24 inches or more in length. That substantial length not only increases the footprint of the machine and consumes valuable manufacturing space, but it also further separates a machine operator from a coil assembly portion of the machine. Therefore, if there is any problem or adjustment around the lacing machine in the coil assembly portion of the machine, the length of the pickup blade and supporting arm make it very difficult for the machine operator to reach in and service that area. Thus, there is a further need for a device that receives a coil spring from the feed conveyor and pivots the coil spring up to the support surface but is substantially smaller than known pickup blades. 
     Further, the known coil assembling machine has a pair of clamping dies for each coil location in the two rows of coil springs that are being laced together. Thus, there may be a dozen or more pairs of dies across a width of a platen that must be operated together. Each pair of dies is pivoted in a scissors style about a common pivot. The upstream or front dies of each pair of dies are opened or lowered, and the downstream or rear dies of each pair of dies are raised or closed as a coil is fed into the dies. Thereafter, the front dies are pivoted to a closed position to clamp the end turns of the coils in the two adjacent rows of coils between the two dies while the helical lacing wire is wrapped around lacing legs of respective coil springs. After the two rows of coils have been laced together, all of the dies are pivoted to an open position and the laced rows of coils are indexed forward without any interference between the rows of coils and the dies. The rear dies are then closed while the front dies remain open for reception of the next row of coils. 
     While the above die mechanism effectively secures the coil springs during the lacing process, it does have some disadvantages. The requirement of having the two dies in each pair of dies pivot up to a common plane places a significant demand on the die mechanisms. Thus, the die mechanisms must be constantly monitored and adjusted, if necessary, to maintain them in proper operating condition. 
     The above die mechanism has another disadvantage that relates to its pivoting motion. If any of the coil springs are not perfectly located, it may interfere with the rear die closing position. Thus, the rear die will strike the coil spring before it has finished its pivoting motion, and an upwardly angled force is applied against the end turn or loop of the coil spring. That force is reacted by the hood portion of the front die. After repeated applications of such an angled force, the hood of the front or rear dies often break. Thus, there is a need for a die mechanism that requires less maintenance and that repeatedly and reliably closes to its desired horizontal position, so that the creation of nonhorizontal forces is minimized. 
     The known coil assembly machine has a further disadvantage in not being able to automatically assemble coaxial coils. In many innerspring structures, it is desirable that some areas of the innerspring structure have a different stiffness or firmness than other areas. In one application, an increased firmness in a selected area is provided by utilizing a coil within a coil design in which a pair of coils, that is, an inner coil and an outer coil, are used to provide a coil unit having a greater stiffness. When one or more rows of such pairs of coils are laced together, they will provide an area of the innerspring structure that has an increased firmness. Thus, there is a need for a coil assembly machine that has the capability of handling and assembling rows of coils that have multiple coil springs in the row. 
     Consequently, there is a need for a coil spring assembly machine that not only is free of the disadvantages of known machines but is capable of handling and assembling coaxial coil springs. 
     SUMMARY OF THE INVENTION 
     The present invention provides a coil spring assembly machine that is capable of providing a spring structure of a matrix of coil springs that has areas of different firmness or stiffness. The coil spring assembly machine of the present invention is capable of forming one or more rows of coaxial coils along with rows of single coils. The coil spring assembly machine of the present invention is more reliable in operation and provides greater operator access in the event of a jam or other error condition. Thus, the coil spring assembly machine of the present invention is especially useful in manufacturing innerspring structures for furniture. 
     According to the principles of the present invention and in accordance with the described embodiments, the invention provides an apparatus for assembling coil springs together into a matrix of coil springs. The apparatus has workholders with respective grippers that receive and hold portions of end turns of respective coil springs, and a loader supporting the workholders for moving the workholders through a motion that transfers the respective coil springs from a conveyor to the apparatus. In one aspect of this embodiment, the portions of the end turns are resiliently secured in the grippers. By holding the end turns of the coils when moving the coils from a conveyor to the apparatus, the workholders and loader have an advantage of being substantially smaller than known devices that perform the same function. The smaller size permits better access to a lacing portion of the apparatus. 
     In another embodiment of the invention, the coil assembling apparatus has, for each coil, a die set having a fixed die and a movable die. The movable die is connected to a drive via linkage. The drive is operable to move the movable die through a motion that maintains a second planar die face of the movable die substantially parallel to a first planar die face of the stationary die. In one aspect of this embodiment, the linkage is a four-bar linkage and a toggle. This embodiment has an advantage of not requiring any adjustment by the user. In addition, the parallel motion of the die faces provides a more reliable and proper alignment of the coil springs within the dies and minimizes the likelihood of die breakage. The use of a toggle provides a further advantage of reacting the load of the closed dies instead of the toggle drive mechanism. 
     In a further embodiment of the invention, the coil assembling apparatus is operable to automatically assemble two rows of coil springs into a row of coaxial coil springs. The apparatus has a die set for each coil spring in the row of coil springs and a plurality of lifters, wherein each lifter is mounted adjacent a different one of the die sets. The lifters are movable to lift an upstream leg of an end turn of a first coil spring in the first row of coil springs that is located in a respective die set. Lifting the upstream leg of the first coil in the first row of coils permits a downstream leg of an end turn of a first coil spring in a second row of coil springs to be moved below the upstream leg of the first coil spring of the first row of coils. This interweaving of the legs of the end turns of the coil springs permits the formation of a row of coaxial coil springs from the coil springs in the first and second rows. In one aspect of this invention, the lifter is a lifter wheel with a lift cam. By lacing together rows of coaxial coils with rows of single coils, the firmness of a resulting coil spring structure can be readily varied. 
     In still further embodiments of the invention, methods associated with the above-described embodiments are also provided. 
     These and other objects and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a spring coil assembly machine in accordance with the principles of the present invention. 
     FIG. 2 is a perspective view of a row of continuous wire single coils and a row of continuous wire coaxial coils that form a spring structure that can be manufactured with the spring coil assembly machine of FIG.  1 . 
     FIG. 3 is a disassembled view of a magazine used with the spring coil assembly machine of FIG.  1 . 
     FIG. 4 is a partial perspective view of a crank arm controlling motion of a preloader of the spring coil assembly machine of FIG.  1 . 
     FIG. 5 is a partial perspective view of a crank arm for controlling a further motion of the preloader on the spring coil assembly machine of FIG.  1 . 
     FIG. 6 is a partial perspective view of preloader cars on the spring coil assembly machine of FIG.  1 . 
     FIG. 6A is a cross-sectional view taken along line  6 A— 6 A of FIG. 6  and illustrates how the cars move relative to each other. 
     FIG. 7 is a partial perspective view of a vertical transfer servomotor drive used on the spring coil assembly machine of FIG.  1 . 
     FIG. 8 is a partial cross-sectional view illustrating one set of die boxes in the spring coil assembly machine of FIG.  1 . 
     FIG. 8A is a partial cross-sectional view illustrating a lift wheel drive used within the die box of the spring coil assembly machine of FIG.  1 . 
     FIG. 9 is a perspective view of a slider mechanism used within a die box of the spring coil assembly machine of FIG.  1 . 
     FIGS. 10-14 are partial perspective views of a coil spring stacking operation on the spring coil assembly machine of FIG.  1 . 
     FIG. 15 is a perspective view of a lifter wheel used in the coil spring stacking operation on the spring coil assembly machine of FIG.  1 . 
     FIGS. 16-18 are side views illustrating the operation of a die closing mechanism used on the spring coil assembly machine of FIG.  1 . 
     FIG. 19 is a schematic block diagram of a control system of the spring coil assembly machine of FIG.  1 . 
     FIG. 20 is a partial perspective view of indexer hooks used to move laced rows of coils through the spring coil assembly machine of FIG.  1 . 
     FIGS. 21-23 are graphical representations of various cycles of operation of the spring coil assembly machine of FIG.  1 . 
     FIG. 24 is side view in elevation of an alternative embodiment of a pusher bar used on the coil spring assembly machine of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a spring coil assembly machine  20  is capable of stacking and lacing rows of continuous wire coils into a matrix of rows and columns of coils as shown in FIG.  2 . The assembly machine  20  is capable of stacking and lacing rows of single continuous wire coils as well as rows of continuous wire coaxial coils. Such coaxial coils are described in detail in U.S. Pat. No. 6,149,143 entitled “Spring Structure for a Mattress Inner Spring Having Coaxial Coil Units” and the entirety of which is hereby incorporated by reference herein. The pair of coaxial coils is comprised of a first continuous wire coil  23  and a second continuous wire coil  24 . Referring back to FIG. 1, a row of continuous wire coils indicated by a single coil  227  is indexed past a front side  27  of the assembly machine  20  on a feed conveyor  28  that orients the coil centerlines horizontally. When a row of coils is presented to the assembly machine  20 , a preloader  30  lifts the row of coils from the feed conveyor  28 , pivots the row of coils to a vertical orientation and positions the row of coils, so that it can be loaded into the assembly machine  20 . A transfer mechanism  32  drops into position, supports a compression of the row of coils and pushes it from the preloader  30  to an input of a plurality of pairs of die boxes  33 . There is a pair of die boxes  33  for each coil in the row of coils. Referring to FIG. 8, each pair of die boxes  33  is comprised of upper and lower die boxes  34 ,  36 , respectively. The first row of coil springs is represented by the coil  227 , and a second row of coil springs is represented by the coil  260 . The rows of coil springs are pushed by upper and lower slider mechanisms  38 ,  40  into respective upper and lower die sets  42 ,  44 . Each of the die sets has a stationary front die  230  and a movable rear die  238 . After two or more rows of coils are positioned within the die sets  42 ,  44 , the die sets are closed to precisely locate lacing legs of coils in the adjacent rows of coils; and a lacing machine (not shown) feeds a helical lacing wire around the lacing legs in a known manner, thereby tying or connecting the adjacent rows of coils together. The above automatic process is continuously repeated until a desired matrix of rows of coils is produced. 
     Preloader 
     Referring to FIG. 1, the preloader  30  is mounted for linear motion on a pair of vertical guides  50 . A preloader drive  51  has a pair of preloader servomotors  52 , for example, Ser. No. 10-17-478 commercially available from Baumuller LNI, Inc. of Bloomfield, Conn., which are electrically connected to a control  110  (FIG.  19 ). The control  110  is a commercially available programmable logic controller. The servomotors  52  are connected to respective crank arms  54  that, in turn, are pivotally mounted to one end of respective connecting rods  56 . The opposite end of the connecting rods  56  is pivotally mounted to the preloader  30 . Thus, as the servomotors  52  rotate the crank arms  54 , the preloader  30  is moved in a vertical direction along the guides  50 . The preloader  30  includes a spline shaft  58  that is rotatably mounted at its ends. Workholders are comprised of magazines  62  mounted on a series of cars  60  that are slidably mounted on the spline shaft  58 . Each of the magazines  62  has a pair of opposed grippers  64 . 
     Referring to FIG. 3, the grippers  64  are rigidly mounted to a base plate  66 . A compression plate  68  is interposed between the grippers  64  and the base plate  66 . The compression plate has holes  70  that slide over shoulders  72  of the fasteners  74  connecting the grippers  64  to the base plate  66 . Thus, the compression plate  68  is movable with respect to the grippers  64  and base plate  66  over the length of the shoulders  72 . Biasing elements  76 , for example, leaf springs, are mounted between the base plate  66  and the compression plate  68  and resiliently bias the compression plate  68  against the grippers  64 . Each of the grippers  64  has an inner directed cutout or notch  78 . The notch  78  has a depth less than a diameter of the coil wire and provides a lateral guide of a path for a coil end turn across the magazine  72 . The grippers  64  further have respective reliefs or chamfers  79  that guide an end turn of a coil  227  into the notches  78  and permits the magazine  72  to more readily receive an end turn of the coil. 
     To transfer a row of coil springs from the feed conveyor  28  to the preloader  30 , the servomotors  52  are activated to rotate the crank arms  54 . The crank arms  54  initially rotate toward a lowermost six o&#39;clock position and lower the preloader  30 . As the magazines  62  are lowered, the gripping fingers  64  are pushed toward and over end turns of the coil springs. Referring to FIG. 3, a portion of a coil end turn is received by the reliefs  79  and pushed into respective notches  78  of the grippers  64 . As the portion of the end turn is pushed into the notches  78 , the compression plate  68  is moved toward the base plate  66 . The portion of the end turn is now captured and secured between the grippers  64  and the compression plate  68  by biasing forces of the leaf springs  76 . Referring back to FIG. 1, as the crank arms  54  rotate past the six o&#39;clock position, the preloader  30  elevates, thereby lifting, the row of coil springs from the feed conveyor  28 . It should be noted that the preloader  30  also has counterbalance weights  57  that are connected to the preloader  30  by chains, wire or other flexible connecting links (not shown). 
     The row of coils has the same generally horizontal orientation that it had in the feed conveyor  28 ; however, before the row of coils is loaded into the die boxes  33  of the spring coil assembly machine  20 , it must be reoriented, so that the centerlines of the coils are generally vertical. Referring to FIG. 4, a preloader pivoting mechanism  81  is used to rotate the magazines  62  approximately 90°. At one end of the spring coil assembly machine, for example, the right end  80  as viewed in FIG. 1, the spline shaft  58  is connected to a crank arm  82  having a cam follower  83  that rides in a cam track  84  within the plate  86 . As the preloader  30  moves upward, the cam track  84  has an angular portion  85  that moves the crank arm  82  toward the rear of the spring coil assembly machine  20 . That action of the crank arm  82  causes the spline shaft  58 , cars  60 , magazines  62  and first row of coils to rotate approximately 90°, thereby changing the orientation of the first row of coils within the magazines  62  from horizontal to vertical. 
     Referring to FIG. 5, at an opposite end  88  of the spring coil machine  20 , the spline shaft  58  is connected to a second crank arm  90  having a cam follower  91  on its end that rides in a cam track  92  on plate  94 . When the row of coils is picked up from the feed conveyor, the cars  60  are located on the spline shaft  58  with a spacing that matches the pitch, that is, separation, of coils on the feed conveyor  28 . However, the laced rows of coil springs may have different widths depending on a desired width of a final product. Therefore, in moving the row of coil springs into the coil spring assembly machine  20 , it is necessary to adjust the pitch or spacing of the cars  60  on the spline shaft  58  so that the coils in the row of coil springs in the magazines  62  have a desired spacing or pitch to match that of the finished product. To vary the pitch of the cars  60 , the crank arm  90  is connected via a shaft (not shown) to a pivot arm  96 . A connecting rod  98  is connected at one end to the pivot arm  96  and at an opposite end to a first one of the cars  60   a . If the one end of the connecting rod  98  is connected to the pivot arm  96  at its point of rotation, then rotating the crank arm  90  will not move the connecting rod  98 . In that situation, the coils in the rows of coils will be loaded on the coil spring assembly machine  20  with the same pitch as they are received from the feed conveyor  28 . 
     Any adjustment to pitch or distance between the coils must be related to the pitch of the helical lacing wire because the coils must always be positioned so that the helical lacing wire always wraps around the lacing legs of the top and bottom turns of the coils. Therefore, any change of pitch of the coils must be in fixed increments corresponding to the pitch of the lacing operation. To achieve that adjustment, the pivot arm  96  has a plurality of holes  100  wherein each hole represents a change of coil spacing in increments of lacing pitch. For example, a first lower hole determines a first short radius and represents a car or coil spacing of one lacing pitch. A second higher hole determines a second, longer radius and represents a car or coil spacing of two lacing pitches, etc. To achieve a change in coil pitch, the one end of the connecting rod  98  is mounted at a selected one of the holes  100 . Therefore, as the crankarm  90  rotates the pivot arm  96  counterclockwise, the connecting rod  98  moves to the left, thereby pulling the cars  60  to the left. 
     Referring to FIGS. 6 and 6A, the cars  60  are connected together in a manner as illustrated by cars  60   a  and  60   b . A spacer  102  extends through an opening  104  in a tongue  106  of car  60   b  and is connected to car  60   a  via a fastener  108 . Thus, car  60   a  can be separated from car  60   b  by a displacement represented by the distance between the end  110  of the spacer  102  and the wall  112  of the opening  104 . Further, that distance provides a car and coil spacing that is equal to the lacing pitch. Therefore, as the crank arm  90  moves its cam follower through the angled portion  93  of the cam track  92 , the pivot arm  96  rotates; and connecting rod  98  pulls the first car  60   a  to the left. When the car  60   a  moves through an increment permitted by the spacer  102 , car  60   b  begins to move. When the crank arm  90  has moved to the end of the angled portion  93 , all of the cars  60  will have been moved through the displacement permitted by their respective spacers  102 . Thus, when the crank arms  54  (FIG. 1) reach a twelve o&#39;clock position, the row of coils is vertically oriented; and the coils within the row are spaced horizontally to match the desired width of the final product. 
     As will be appreciated, every time that the connecting rod  98  is connected to a different hole  100  in the pivot arm  96 , a different set of spacers  102  must be mounted on the cars  60 . It should also be noted that the spacer  102  can be removed and inverted; the cars  60   a ,  60   b  pushed together; and the spacer  102  placed in the opening  104  and fastened to the car  60   a . In this orientation, the spacer  102  fills the opening  104 ; and the cars  60   a ,  60   b  are closely locked together. 
     Transfer Mechanism 
     Referring to FIG. 1, the transfer mechanism  32  is raised and lowered by a pair of vertical transfer drives  118  that are located at the ends of the transfer mechanism  32 . Each of the drives is identical in construction, and therefore, only one of the vertical transfer drives will be described in detail. Referring to FIG. 7, each of the vertical transfer drives  118  has a vertical transfer servomotor  120 , for example, model no. 552407 commercially available from Baumuller LNI, Inc. of Bloomfield, Conn., which is electrically connected to the control  110  (FIG.  19 ). The servomotor  120  (FIG. 7) is pivotally mounted to an upper frame  122  of the coil spring assembly machine  20 . Operation of the servomotor  120  extends and retracts a drive shaft  124 . The drive shaft  124  is pivotally connected to a four bar linkage  126  that functions to raise and lower the transfer mechanism  32  in response to respective retraction and extension of the drive shaft  124 . The four bar linkage  126  is comprised of a pair of parallel links  128 ,  130  having one end pivotally connected to the upper frame  122 . Opposite ends of the parallel links  128 ,  130  are pivotally connected to end plates  132  of the transfer mechanism  32 . The drive shaft  124  is pivotally connected to the link  128 . As the drive shaft  124  extends and retracts, the pusher bar  152  is moved substantially vertically down and up. 
     Referring to FIGS. 1 and 8, a horizontal transfer drive  138  includes a horizontal transfer servomotor  140  that is the same as the servomotor  120  and is about centrally mounted within the transfer mechanism  32 . An output shaft  142  of the motor  140  is mechanically connected via gears  144  to a drive shaft  146 . The drive shaft  146  extends the full length of the transfer mechanism, and the drive shaft  146  is rotationally supported over its length within the transfer mechanism  32 . A plurality of drive links  148  are spaced along the drive shaft  146 . One end of each of the drive links  148  is rigidly connected to the drive shaft  146 , and an opposite end terminates with a clevis that is pivotally connected to one end of a connecting link  150 . The opposite end of the connecting link  150  is pivotally connected to a pusher bar  152 . Thus, rotating the servomotor  140  in one direction causes the pusher bar  152  to move along a generally horizontal path from the front toward the rear of the coil spring assembly machine  20 . Reversing the rotation of the servomotor  140  causes the pusher bar  152  to move from the rear toward the front of the coil spring assembly machine  20 . 
     As the preloader servomotors  52  raise the preloader  30 , the vertical transfer servomotors  120  lower the transfer mechanism  32  to its lower-most position. As shown in FIG. 8, as the preloader  30  moves upward, a top turn  164  of the coil  278  contacts a compression surface  162  on the lowered and stationary transfer mechanism  32 . The top turn  164  is also substantially coplanar with an upper receiving surface  166 . Continued upward motion of the preloader  30  compresses the coil  278  until its bottom turn  156  is substantially coplanar with a lower receiving surface  160 . The horizontal transfer servomotor  140  is then operated to cause the pusher bar  152  to move in a generally horizontal direction toward the rear of the coil spring assembly machine  20 , that is, to the right as viewed in FIG.  8 . The pusher bar  152  contacts the coil  278  and pushes the coil  278  through the notches  78  (FIG. 3) of the grippers  64  and across the compression plate  68 . The pusher bar  152  pushes the coil  278  out of the magazine  62 , between the surfaces  160 , 166  and into the upper and lower die boxes  34 ,  36 . As will be appreciated, while the above describes only one coil  278 , the same operation is simultaneously occurring with each coil in the row of coils. 
     Slider/Lifter 
     The pusher bar  152  pushes the coil  278  between the upper and lower die boxes  34 ,  36  into respective upper and lower slider mechanisms  38 ,  40 . Each of the slider mechanisms  38 ,  40  is identical in construction; and therefore, any of the following description that refers to one of the slider mechanisms also applies to the other slider mechanism. The servodrive for the slider mechanisms  38 ,  40  will be described with respect to the upper slider mechanism. The upper slider mechanism  38  is operated by a slide drive mechanism  200  (FIG. 1) that has a pair of slider servomotors  202 , for example, model 10-17-474 commercially available from Baumuller LNI, Inc. of Bloomfield, Conn., which are electrically connected to the control  110  of FIG.  19 . Referring to FIG. 8, each of the slider servomotors  202  has a crank arm  204  connected to its output shaft. A drive link  206  has one end pivotally connected to the crank  204  and an opposite end pivotally connected to a drive bar  208 . Thus, rotation of the servomotors  202  cause the drive bar  208  to reciprocate through a linear displacement between the front and rear sides of the coil spring assembly machine  20 . Referring to FIGS. 8 and 9, the drive bar  208  extends through all of the upper die boxes  34  across the width of the coil spring assembly machine  20 . 
     Within each of the upper die boxes  34 , a slider  210  is connected to one end of rails  212 ,  214  that extend over the length of the upper die box  34 . A slider drive bracket  216  is connected to the opposite ends of the rails  212 ,  214 . The slider drive bracket  216  has a generally U-shaped notch  218  that has a cross-sectional shape that is similar to the cross-sectional shape of the drive bar  208 . The drive bracket  216  is positioned on top of the drive bar  208 . Thus, as the slider servomotors  202  rotate in one direction that moves the slider bar  208  toward the rear of the spring coil assembly machine, the slider bar  208  pulls the slider  210  toward the rear of the spring coil assembly machine  20 . Similarly, rotation of the slider servomotors  202  in an opposite direction causes the slider bar  208  to push the slider  210  toward the front of the machine  20 . 
     Referring to FIG. 2, each coil has an upper end turn  240  and a lower end turn  242  that are interconnected by at least one intermediate turn  244 . Each of the upper and lower end turns  240 ,  242  have respective lacing legs  246 ,  248  and respective short legs  250 ,  252 . Each of the coils has a centerline  254  that is substantially perpendicular to the end turns  240 ,  242 , and the lacing legs  246 ,  248  are located at a further distance from a coil centerline  254  than the short legs  250 ,  252 . The lacing legs and short legs are alternated with successive coils along the row of coils. Thus, when upper and lower helical lacing wires  256 ,  258  are wound past the rows of coils, for example, rows of coils  21 ,  22 , the lacing wires  256 ,  258  wrap around the further extending respective lacing legs  246 ,  248  but do not wrap around the short legs  250 ,  252 . 
     Referring to FIG. 9, the slider  210  includes projecting fingers  222  that extend to a landing surface  224  of the slider  210 . The pusher bar  152  (FIG. 8) pushes the coil  278  between the upper and lower die boxes  34 ,  36 , over the top  221  of the slider  210  (FIG. 9) until the bottom turn of the coil drops onto risers  223  immediately in front of the slider  210 . The risers  223  provide a landing plane above the landing surface  224  and reduce the magnitude of the coil drop off of the surface  221 . Thereafter, simultaneous operation of the slider servomotors  202  (FIG. 8) for both the upper and lower slider mechanisms  34 ,  36  (FIG. 8) cause respective sliders  210  to push top and bottom turns of each coil in a row of coils downstream toward the respective upper and lower sets of dies  38 ,  40 . For purposes of this document, the term “upstream” refers to a direction or location that is toward, or closer to, the forward side  27  of the spring coil assembly machine  20  and away, or further, from the rear of the spring coil assembly machine  20 . Likewise, “downstream” refers to a direction or location that is toward, or closer to, the rear of the spring coil assembly machine  20  and away, or further, from the front of the spring coil assembly machine  20 . 
     An operation of a single slider  210  is illustrated and described with respect to FIGS. 9 and 10 and is illustrative of the operation of all of the sliders. The slider servomotor  202  is operated to cause the slider  210  to push a first coil  227  of the first row of coils across the landing surface  224  and onto the upstream surface  228  of a stationary front die  230 . As the first coil  227  is pushed over the surface  228 , a downstream lacing leg  229  rides up inclined surfaces  231  on the rear of the front die  230  thereby causing an upstream short leg  232  to rise. Simultaneously therewith, a downstream short leg  233  contacts and rides up inclined surfaces  234 , thereby lifting an upstream lacing leg  235 . As the upstream legs  232 ,  235  rise with the elevating downstream legs  229 ,  233 , the slider  210  is maintained in contact with the upstream legs  232 ,  235  by the slider fingers  222 . Continued downstream motion of the slider  210  pushes the coil  229  up and over the front die  230 . The slider fingers  222  then pass through the slots  236  to the end of its downstream displacement or stroke. At the end of the downstream stroke of the slider  210 , the upstream lacing leg  235  drops immediately downstream of the stationary front die  230 ; and entirety of the coils  227  of the first row of coils  21  (FIG. 2) are located downstream of the stationary front die  230  as illustrated in FIG.  10 . The rotation of the motors  202  of the upper and lower slider mechanisms  38 ,  40  continues until all of the sliders  210  have been returned to their starting upstream positions. As the sliders  210  begin to move to their respective home positions, the movable rear die  238  is moved toward the front die  230  to a partially closed position. The details of the operation of the movable rear die will be subsequently described. 
     Thereafter, the pusher bar  152  (FIG. 8) of the transfer mechanism  32  places a second row of coils on the landing surface  224  as represented by a second coil  260  in FIG.  10 . Again, the slider motors  202  (FIG. 8) are operated to move the slider  210  downstream through a second displacement or stroke. The slider  210  pushes the second coil  260  over the landing surface  224  and onto the upstream surface  228 . The upstream surface  228  is divided into two halves. A first surface  225  is substantially coplanar with the landing surface  224 . An adjacent second portion or surface  226  has an upstream edge  266  that is lower than a downstream edge  268  of the landing surface  224 . The distances between the edges  266  and  268  is slightly greater than the diameter of the wire used to form the continuous coils. Thus, an uppermost surface of the upstream lacing leg  270  is at or slightly below the plane of the landing surface  224 . The second surface  226  inclines upward as it extends downstream to the stationary die  230 . Thus, the downstream edge of the second surface  226  is substantially co-linear with a comparable downstream edge of the first surface  225 . 
     Therefore, as slider  210  pushes the second coil  260  over the upstream surface  228 , a downstream lacing leg  269  rides up the inclined surfaces  231  and over the stationary front die  230  as previously described with respect to the first coil  227 . When the slider  210  reaches the end of its second stroke, the downstream lacing leg  269  is dropped over the downstream edge of the front die  230 . The operation of the slider servomotors  202  is then reversed, and the slider returns to its starting upstream position. 
     With known coil spring assembly machines, the upper and lower dies  230 ,  238  in die sets  38 ,  40  would now be closed and lacing wires fed across the upper and lower die boxes  34 ,  36 . The lacing wires wrap around the upstream lacing legs  235  of the first coils  227  in the first row of coils and the downstream lacing legs  269  of the second coils  260  in the second row of coils, thereby lacing the first and second rows of coils together. However, with known coil spring assembly machines, it is not possible to stack and lace one or more rows of coaxial coils; however, in contrast, the spring coil assembly machine  20  is able to stack and lace rows of coaxial coils. If a coaxial row of coils is desired, referring to FIG. 11, a downstream lacing leg  302  of a third coil  278  representing a third row of coils must be fed beneath an upstream short leg  276  of the second coil  260 ; and a downstream short leg  304  of the third coil must be fed over the upstream lacing leg  270  of the second coil  260 . Referring to FIG. 8, that capability is provided by upper and lower lift wheel mechanisms  280 ,  282  associated with the respective upper and lower die boxes  34 ,  36 . 
     Referring to FIG. 8A, lift wheel drives  283  include servomotors  284 , for example, model no. 10-17-476 commercially available from Baumuller LNI, Inc. of Bloomfield, Conn., which are electrically connected to the control  110  (FIG.  19 ). The servomotors  284  are mounted to the exterior frame at one end of the coil spring assembly machine  20 . The servomotors  284  have output shafts  285  connected via respective pulleys  287 ,  288  and belts  289  to respective lift wheel drive shafts  286 . The lift wheel mechanisms  280 ,  282  are identical in construction; and therefore, the following description relating to the lower lift wheel mechanism  282  also applies to the upper lift wheel mechanism  280 . Referring to FIG. 10, the drive shaft  286  has a noncircular cross-sectional profile, for example, a hexagonal shape. The drive shaft  286  extends through hexagonally shaped centrally located holes  290  in lift wheels  292  that, in turn, are rotatably supported by bearings mounted within the drive box at each end of the lift wheel  292 . The operation of the lift wheel  292  in each of the bearing boxes  34 ,  36  is identical; and therefore, the operation of a lift wheel within a single bearing box will be described. 
     Referring to FIG. 15, the lift wheel  292  is comprised of a main body or shaft  294  on which is mounted a lift cam  296  and a stop cam  298 . Referring to FIG. 8, in a manner as previously described, a third row of coils represented by coil  278  is loaded by the transfer mechanism  32  onto the landing surface  24 ; and the slider  210  is operated to push the third row of coils toward the stationary die  230 . Referring to FIG. 11, as the third coil  278  is pushed across the landing surface  224 , the lift wheel servomotor  284  is operated to rotate the drive shaft  286  and lift wheel  292 . The lift wheel  292  starts at its home position (FIGS. 8,  10  and  15 ) and rotates in a clockwise direction as viewed in FIG.  11 . The lift wheel  292  rotates approximately 20° from its home position to move the lift cam  296  through an opening  300  of the first surface  225  of the upstream surface  228 . The lift cam  296  lifts the upstream short leg  276  of the second coil  260  above the surface  228 . However, the upstream lacing leg  270  of the second coil  260  remains flat against the second surface  226  and below the locating surface  224  because the second row of coil springs is maintained under compression between the upper and lower die boxes  34 ,  36 . 
     Referring to FIG. 12, as the third row of coils  278  is pushed onto the stationary die upstream surface  228 , the downstream lacing leg  302  of the third coil  278  moves into the lift wheel cam slot  297  that is now below the upstream short leg  276  of the second coil  260 . Referring to FIG. 13, continued rotation of the lift wheel  292  rotates the lift cam out from under the upstream short leg  276  and back below the first surface  225 . As the third coil  278  is pushed further, the downstream short leg  304  of the third coil  278  is pushed over the upstream lacing leg  270  of the second coil. Continued pushing of the third coil  278  causes the downstream lacing leg  302  to slide over the upwardly sloped inclined surfaces  231  on the rear side of the stationary die  230 . At the end of the third stroke of the slide  210 , the downstream lacing leg  302  of the third coil  278  is located immediately downstream of the front die  230  with the downstream lacing leg  269  of the second coil  260 . Further, the upstream lacing leg  312  of the third coil  278  lies over the upstream lacing leg  270  of the second coil  260 . It should be noted that pushing the downstream lacing leg  302  (FIG. 12) of coil  278  under the upstream short leg  276  of coil spring  260  and the downstream short leg  304  of coil  278  over the upstream lacing leg  270  of coil spring  260  facilitates a tight nesting of the coil springs  260 ,  278 . Further it also results in a crossover point  308  where the wire of coil  260  crosses from being under coil  278  to being over coil  278 . It should be noted that the crossover point  308  may vary from coil to coil within a row of coils. The tight nesting of the coils  260 ,  278  is facilitated by a crossover of the end turns of the coil, and it is not dependent on a particular crossover point location. 
     As shown in FIG. 13, continued rotation of the lift wheel  292  approximately 180° from its home position causes the stop cam  298  to extend above the second surface  226  and present a stop surface  310  to the upstream lacing legs  270 ,  312  of the respective second and third coils  260 ,  278 . The stop surface  310  function to align and maintain the second and third coils  260 ,  278  in a substantially parallel relationship. The parallel relationship of the second and third coils  260 ,  278  prevents misalignment of the coils within the dies that might unnecessarily stress and fracture the dies. Referring to FIG. 14, the upper and lower die sets  42 ,  44  are then closed; and the lift wheel  292  continues its rotation back to its home position, thereby rotating the stop cam  298  back below the second surface  226 . 
     Die Closing 
     The structure and operation of all the die sets within the upper and lower die boxes  34 ,  36  are identical; and therefore, an explanation of an operation of a single die set will be applicable to the other die sets. A die closing mechanism  328  (FIG. 8) for the upper die boxes  34  is operated by a die closing servomotor  330  shown in FIG. 1, for example, model no. 10-17-470 commercially available from Baumuller LNI, Inc. of Bloomfield, Conn., which is electrically connected to the control  110  of FIG.  19 . The servomotor  330  is connected to a right angle drive  332  that, in turn, rotates a drive shaft  334  extending across the full width of the spring coil assembly machine  20 . Referring to FIG. 8, the die closing mechanism  328  further includes a die closing shaft  340  connected to the drive shaft  334  via gears  336 ,  338 . A plurality of crank wheels  342  are mounted on the die closing shaft  340 . The structure and operation of all of the die sets is identical and will be described with reference to the upper and lower die boxes  34 ,  36  as is appropriate. Within the upper die box  34 , a connecting arm  344  has one end pivotally connected to the crank wheel  342  and an opposite end pivotally connected to a drive block  345 . The drive block  345  is mounted on a die slider bar  346 . The die slider bar  346  extends over a substantial length of the assembly machine  20  and is mounted on one or more linear guides  348 . Thus, the die slider bar  346  reciprocates back and forth through linear strokes in response to the operation of servomotor  330  and rotation of the crank wheel  342 . 
     FIG. 16 illustrates a lower die box  36  with the die set  44  in its open position. In the open position, the die slider bar  346  is at the downstream end of its linear stroke, and the movable rear die  238  is positioned downstream of, and below, the stationary front die  230 . The stationary front die  230  has a planar die face  237  that extends longitudinally in a direction away from the viewer that is substantially perpendicular to the coil centerlines  254 . Further, the movable rear die  238  has a planar die face  239  that is substantially parallel to the planar die face  237  of the fixed die  230 . The die closing mechanism  328  further has a toggle  350  that operates a four bar link  352 . The four bar link has a pair of parallel links  354  that have one end pivotally connected to the mounting structure of the rear die  238  and an opposite end pivotally connected to the lower die box  36 . The toggle  350  has a first link  356  pivotally connected at one end to the mounting structure of the rear die  238 , and the first link is pivotally connected at an opposite end to one end of a second toggle link  358 . The opposite end of the second toggle link  358  is pivotally connected to the lower die box  36 . A drive link  360  has one end pivotally connected to the connection between the first and second toggle links  356 ,  358  and an opposite end pivotally connected to the die slider bar  346 . 
     To close the die, the servomotor  330  (FIG. 1) is operated to rotate the first and second drive shafts  334 ,  340 , respectively, (FIG. 8) and the crank wheel  342 . The die slider bar  346  (FIG. 16) begins moving toward the left as viewed in FIG.  16 . The drive link  360  is also moved to the left and begins to rotate clockwise, thereby beginning to close the toggle  350  formed by toggle links  356 ,  358 . As shown in FIG. 17, the links  354  begin to rotate counterclockwise and function to maintain the movable rear die  238  in a substantially horizontal orientation as it moves upward and upstream toward the stationary die  230 . During the motion of the rear die  238  in closing on the front die  230 , the planar die faces  237 ,  239  remain substantially parallel. Operation of the die closing servomotor  330  continues to move the die slider bar  346  to the left, thereby continuing to close the toggle  350 . With the die closing mechanism just described, the movable rear die  238  approaches the stationary front die  230  with a nonpivoting action. Further, as the movable rear die  238  moves into a closed position with respect to the stationary front die  230 , it is moving substantially linearly toward the die as viewed in FIG.  18 . At this point, the centerlines of the toggle links  356 ,  358  are substantially collinear; the toggle  350  is locked and the operation of the servomotor  330  is stopped. The locked toggle  350  provides a very stiff mechanical support for the movable rear die  238  in its closed position. Further, substantially all of the load force imposed on the movable rear die  238  is reacted through the die box frame  362  and not the die slider bar  346 . 
     Lacing Machine 
     When the lacing dies are closed as shown in FIG. 18, one or more lacing machines  370  (FIG. 2) are operated by the control  110  of FIG.  19 . The lacing machines  370  include respective lacing wire forming apparatus of a known type. Such devices take spring wire and coil it into helical lacing coils  256 ,  258 ; and thereafter, the lacing machines  370  cause respective lacing coils to wind or lace from one edge of the rows of coil springs held in the dies  230 ,  238  to the other edge. Such a known lacing operation is described at column 17, line 61 through column 19, line 62 in U.S. Pat. No. 4,492,298 entitled Coil Spring Assembly Machine, and that cited material in its entirety is hereby incorporated herein by reference. 
     Indexer 
     Referring to FIG. 8, an indexing mechanism  380  is used to move the laced rows of coil springs through the coil spring assembly machine  20  and operates in conjunction with the upper and lower slider mechanisms  38 ,  40 . The indexing mechanism  380  uses a pair of indexing servomotors  382 , for example, Ser. No. 10-17-470 commercially available from Baumuller LNI, Inc. of Bloomfield, Conn., which are electrically connected to the control  110  of FIG.  19 . Each of the indexing servomotors  382  is mounted proximate one of the ends  27 ,  88  (FIG. 1) of the coil spring assembly machine  20 . Each of the indexing servomotors  382  is connected to a crank  384  (FIG. 8) that is pivotally connected to one end of a connecting rod  386 . The other end of the connecting rod  386  is pivotally connected to a vertical drive plate  387 . Vertical drive plates  387  at each end of the assembly machine  20  are connected to ends of upper and lower drive bars  388 ,  389 , respectively, thereby forming a generally rectangular body. The drive plates are mounted in respective linear guides  390  at each end of the assembly machine  20 . The linear guides  390  guide and support the assembly of the drive plates  387  and drive bars  388 ,  389  through a linear motion between the front and rear of the spring coil assembly machine  20 . The drive bars  388 ,  389  are mounted in respective indexing hooks  392 . 
     The operation of the upper and lower drive bars  388 ,  389  is substantially the same, and the operation of the drive bars in association with the indexing mechanism  380  will be with reference to one or the other of the drive bars. Referring to FIG. 20, a lower indexing hook  392  has a respective drive bracket  394  that is engaged with the lower drive bar  389 . The indexing hook  392  is moved by the lower drive bar  389  through a reciprocating linear motion controlled by the indexing servomotors  382  and crank  384 . Bars  396  extend from respective ends of the drive bracket  394  into slots  398  of a die plate  400 . Hook ends  402   a ,  402   b  of respective bars  396  have a sloped forward or upstream side. Therefore, as the hook ends  402  move toward the front of the machine  20 , that is, to the left as viewed in FIG. 20, the hook end  402   a  slides under a lacing leg of a coil, for example, lacing leg  229  of coil  227 . Hook end  402   b  is mounted on a shorter bar than the hook end  402   a ; and therefore, with the first row, or border row, of coils, the hook end  402   b  does not engage a coil. When the drive bar  389  moves the indexing hooks  392  and respective hook ends  402  in the opposite direction toward the rear of the machine, the hook end  402   a  of the upper and lower indexing mechanisms  380  pull the laced rows of coils toward the rear of the machine. After the coil  227  is indexed toward the rear of the machine, during subsequent coil indexing operations, the hook end  402   b  slides under a short leg  233  of coil  227 ; and both hook ends  402   b ,  402   b  function to pull laced rows of coils towards the rear of the machine. 
     In use, referring to FIG. 1, a first row  21  (FIG. 2) of coils  227  is loaded onto the coil spring assembly machine  20  in accordance with a first cycle of operation as illustrated in FIG.  21 . Prior to the operation of the assembly machine  20 , a first row of coils  227  is fed by the conveyor  28  to a location in front of the preloader  30  that is determined by a sensor  264  (FIG.  19 ), for example, a proximity switch, connected to the control  110 . Activation of the sensor  264  indicates that a full row of coils is properly located in front of the magazines  62 . Referring to FIG. 21, at  500 , the preloader servomotors  52  are operated by the control  110  to remove the row of coils from the feed conveyor  28 . The servomotors  52  move the crank arms  54  toward, through and past their bottom-dead-center positions. That crankarm motion first moves the preloader  30  down to pick up a row of coils in the magazines  62  as previously described. The preloader  30  then reverses direction and is raised to its starting position. During that operation, the coils  227  in the magazines  62  are maintained in their initial horizontal and vertical orientations by the substantially vertical linear portions  87 ,  95  of the respective cam tracks  84 ,  92  (FIGS. 4,  5 ). 
     The preloader then, at  502 , vertically orients and horizontally spaces the coils in the preloader. In this process, as the servomotors  52  and crankarms  54  continue to move the preloader  30  upward, the cam followers  83 ,  91  move through respective angular portions  85 ,  93  of the respective cam tracks  84 ,  92  (FIGS. 4,  5 ). Motion of the cam follower  83  along the angular portion  85  of cam track  84  causes the shaft  58  and magazines  62  to rotate about 90°, thereby orienting the row of coils in a substantially vertical direction. Simultaneously, the horizontal spacing of the cars  60 , that is, the pitch of the coils in the first row, is changed, if desired, by the motion of the cam follower  91  along the angular portion  93  of the cam track  92  (FIG.  5 ). 
     While the preloader  30  is being raised by the preloader servomotors  52 , the transfer drives  118  of the transfer mechanism  32  are operated by the control  110  to initiate a downward motion of the transfer mechanism  32 . The operation of the downward motion of the transfer mechanism  32  that includes the horizontal transfer mechanism  138  and compression surface  162  must be timed so that it does not mechanically interfere with the rotation of the row of coils to their vertical orientation. After the transfer mechanism  32  reaches its lowermost position, the compression surface  162  is substantially parallel with the surface  166 . Thereafter, at  504 , the control  110  continues to operate the preloader servomotors  52 ; and the first row of coils continues to move upward until the top turns  164  (FIG. 8) of the first row of coils contact the compression surface  162  on the transfer mechanism  32 . When the preloader crank arms  54  reach the top-dead-center position, the row of coils is completely compressed; and the preloader servomotors  52  are stopped. At this point, the first row of coils  227  is loaded in the coil assembly machine  20 . 
     Next, the first row of coils must be transferred into the upper and lower die boxes  34 ,  36  (FIG.  8 ), it being understood that there is a pair of upper and lower die boxes  34 ,  36  for each of the coils  227  in the row. The control, at  506 , operates the horizontal transfer motor  140 , thereby causing the pusher bar  152  to move from left to right as viewed in FIG.  8 . The pusher bar  152  simultaneously pushes all of the coils  227  in the first row over and between respective upper and lower sliders  210  of the upper and lower slider mechanisms  38 ,  40  to a position immediately downstream of the respective upper and lower sliders  210 . 
     After the first row of coils  227  is properly positioned in front of the sliders  210 , the control  110 , at  508  of FIG. 21, operates the slider servomotors  202  (FIG. 1) to move sliders  210  from left to right as viewed in FIG. 8, thereby pushing the first row of coils  227  toward the front die  230 . Upon initiating operation of the slider servomotors  202 , the control, at  506 , operates the horizontal transfer servomotor  140  to retract the pusher arm  152  to its home position. When the pusher arm  152  reaches its starting home position, the control  110  then, at  508 , operates the vertical transfer servomotors  120  to move the transfer mechanism  32  upward to its home position. While the transfer mechanism  32  that includes the horizontal transfer drive  138  and compression surface  162  are returning to their respective home positions, the control  110  operates the preloader servomotors  52  causing the preloader  30  to return to its home position. 
     While the slider servomotors  202  are moving the first row of coils  227  toward the front die  230 , the control, at  510 , operates the lift wheel servomotors  284  in each of the upper and lower die boxes  34 ,  36 , thereby causing all of the upper and lower lift wheels  292  to rotate through one revolution. The rotation of the lift wheels  292  performs no function when the first row of coils  227  is being loaded into the upper and lower die boxes  34 ,  36 . 
     The control  110 , at  512 , continues to operate the slider servomotors  202 , so that the upper and lower sliders  210  push the first row of coils  227  to a location adjacent the rear die  238 . As the first row of coils  227  is moved downstream, lateral wings  220  (FIG. 9) maintain a proper lateral orientation of each coil. The sliders  210  push the first row of coils  227  completely past respective front dies  230  to a position adjacent respective rear dies  238  as shown in FIG.  8 . After the sliders  210  have located the first row of coils  227 , the control  110 , at  514 , operates the upper and lower die closing servomotors  330  (FIG. 1) in the upper and lower die boxes  34 ,  36  to partially close the rear dies  238  to a position shown in FIG.  17 . In the partially closed position, the rear dies  238  are closed against the lower end turns of the first row of coils  227 , thereby maintaining the coils in a desired orientation. Thereafter, at  516 , the control  110  commands the slider servomotors  202  to return the upper and lower sliders  210  in the upper and lower die boxes  34 ,  36  to their starting home positions. 
     Next, a second row  23  (FIG. 2) of coils  260  is loaded onto the coil spring assembly machine  20  in accordance with a second cycle of operation as illustrated in FIG.  22 . The operation of loading and pushing the second row of coils  260  into the upper and lower slider mechanisms  38 ,  40  as indicated at  500 - 508  of FIG. 22 is identical to that described with respect to the loading of the first row of coils  227  represented in FIG.  21 . At  511 , with the second row of coils, the control  110  operates the lift wheel servomotors  284  in the upper and lower die boxes  34 ,  36  to rotate each of the lift wheels  292  through a rotation of approximately 180° rotation, thereby raising a respective stop  310  (FIG.  13 ). The control  110 , at  518 , continues to operate the slider servomotors  202  to provide a slider stroke that positions each of the upper and lower downstream lacing legs  269  of the second row of coils  260  (FIG. 10) over a respective front die  230  and each of the upper and lower upstream lacing legs  270  against a respective lift wheel stop  310  (FIG.  13 ). 
     Thereafter, at  520 , the control  110  operates the die closing servomotors  330  to fully close respective rear dies  238 , thereby locating the upstream and downstream lacing legs  235 ,  269  (FIG. 10) of the respective first and second rows of coils  227 ,  260  between respective set of front and rear dies  230 ,  238 . The control  110  also operates the indexing servomotors  382  to move the hook end  402   a  (FIG. 20) in each of the upper and lower die boxes  34 ,  36  in an upstream direction and under the downstream legs  229  of each coil in the first row of coils  227 . Then, at  522 , the control  110  operates the die closing servomotors  330  to move the upper and lower rear dies  238  back to the partially closed position of FIG.  17 . Simultaneously, the control  110  operates the slider servomotors  202  to move the upper and lower sliders  210  in each of the respective upper and lower die boxes back to their home positions. 
     Next, a third row  24  (FIG. 2) of coils  278  that is to form a row of coaxial coils with the second row  23  of coils  260  is loaded onto the coil spring assembly machine  20  in accordance with a third cycle of operation as illustrated in FIG.  23 . The operation of loading and pushing the third row  24  of coils  278  into the upper and lower slider mechanisms  38 ,  40  as indicated at  500 - 508  of FIG. 23 is identical to that described with respect to the loading of the respective first and second rows  22 ,  23  of coils  227 ,  260  described with respect to FIGS. 21 and  22 . As the sliders  210  are moving the coils  278  of the third row toward respective front dies  230 , the control  110 , at  517 , initiates operation of the lift wheel servomotors  284  in each of the upper and lower die boxes  34 ,  36 . The lift wheels  292  first rotate through an arc of about 20° to move respective lifting cams  296  (FIG. 11) through respective slots  300  in respective upstream surfaces  228 . The lifting cams  296  raise upstream short legs  276  in the top and bottom turns of the second row of coils  260 . Thus, as the coils  278  in the third row are pushed toward respective front dies  230 , respective downstream lacing legs  302  of the top and bottom turns of the coils  278  are pushed into cam slots  297  of the respective upper and lower lift wheels  292 . The lift wheels  292  continue to rotate, the upstream short legs  276  are released from respective lifting cams  296  and drop on top of respective upstream lacing legs  302  of the third row of coils  278 . Thus, the upstream lacing legs  302  of the third row of coils  278  have been located under the upstream short legs of the second row of coils  260 . 
     The control  110 , at  519 , continues to operate the slider servomotors  202  to provide a slider stroke that positions each of the upper and lower downstream lacing legs  302  of the third row of coils  278  (FIG. 13) over a respective front die  230  and each of the upper and lower upstream lacing legs  270  against a respective lift wheel stop  310 . Thereafter, at  521 , the control  110  operates the die closing servomotors  330  to fully close respective rear dies  238 , thereby locating the upstream and downstream lacing legs  235 ,  269 ,  302  of the first, second and third rows of coils  227 ,  260 ,  278 , respectively, between each set of front and rear dies  230 ,  238  in each of the upper and lower die boxes  34 ,  36 . In addition, at  521 , the control  110  commands the lift wheel servomotors  284  to rotate the lift wheels to the home position. 
     Thereafter, at  524 , the control  110  provides a cycle start signal to the lacing machines  370   a ,  370   b  (FIG. 2) that, in turn, wind, respective lacing wires  256 ,  258  around all of the adjacent lacing legs in the upper and lower die sets  42 ,  44  in a known manner. At the end of the lacing wire winding process, the lacing machines  370   a ,  370   b  proceed to cut and bend the lacing wires  256 ,  258  in a known manner. Thereafter, at  526 , when the control  110  detects cycle complete signals from the respective lacing machines  370 , the control  110 , at  528 , operates the die closing servomotors  330  in the upper and lower die boxes  34 ,  36  to open the respective rear dies  238 . 
     Next, at  530 , the control  110  proceeds to index the three rows of laced coils toward the rear of the coil assembly machine  20 . As shown in FIG. 2, the rows of laced coils are comprised of a single row  21  of coils  227  and two rows  23 ,  24  of coaxial coils  260 ,  278 . The control  110  operates the slider servomotors  202  and the indexer servomotors  382  to index the laced rows of coils downstream toward the rear of the coil spring assembly machine  20 . In this process, the control  110  again operates the slider servomotors  202  to again initiate motion of the sliders  210  toward the rear of the coil assembly machine  20 . Simultaneously, the control  110  initiates operation of the indexing servomotors  382 , and the indexing hooks  392  (FIG. 20) are moved downstream toward the rear of the assembly machine. The hook end  402   a  is effective to pull the downstream leg  229  of the first row of coils  227  toward the rear of the machine  20 . As previously noted, when the next row of laced coils is indexed, both of the hook ends  402   a ,  402   b  engage respective downstream legs  229 ,  233  to pull the next row of coils toward the rear of the machine. 
     The operation of the indexing hooks  392  and sliders  210  continues until the second and third rows of coils  260 ,  278  are moved to a location previously occupied by the first row of coils  227 . At that location, the second and third rows of coils  260 ,  278  are located completely behind the front die  230  with their upstream legs  276 ,  312  forward of the rear dies  238 . As the laced rows of coils  227 ,  260 ,  278  are moved downstream toward the rear dies  238 , the coils are maintained in lateral alignment by the wings  220  (FIG.  9 ). Thereafter, at  532 , the control  110  operates the die closing servomotors  330  to move the rear dies forward to the partially closed position, thereby locating the rear dies  238  against the upstream lacing legs  270 ,  312  of the coaxial coils  260 ,  278  to maintain the alignment of the laced rows of coaxial coils. In addition, the control  110  operates the slider servomotors  202  to return the sliders  210  to their home positions. 
     Subsequent rows of single coils and coaxial coils are stacked and laced as described with respect to FIGS. 21-23. The appropriate cycle being selected depending on the configuration of coils in a row. The last row of coils is processed substantially in accordance with the cycle shown in FIG.  23 . The only exception is at the last process step  532 . With the last row of coils, the last process step is modified in two ways. First, the control  110  does not close the rear dies  238 ; but the rear dies  238  remain in their open position in order to accept a first row of coils of the next array of coils to be laced together. Further, the control  100  operates the indexing servomotors  330  to move the indexing hooks  292  upstream toward the front of the assembly machine, so that the next first row of coils are loaded over the indexing hooks  292 . 
     The coil spring assembly machine  20  is thus capable of stacking one or more rows of coaxial coils along with rows of single coils in order to provide a spring structure of a matrix of coil springs that has areas of different firmness or stiffness. The coil spring assembly machine  20  has a preloader  30  that is smaller and more reliable than known preloaders. The smaller size of the preloader  30  provides an operator greater access to the die boxes  34 ,  36 , thereby making maintenance of the die boxes substantially easier than with known machines. Further, the die closing mechanism  328  uses a toggle mechanism  150  that consistently and reliably properly closes the dies  230 ,  238 . The toggle mechanism maintains the dies in their desired parallel relationship and does not provide or require any adjustment by the user. Improper adjustment of the die closing mechanism is a significant source of problems on known machines. Further, the generally linear approach of the rear die toward the front die upon closing provides a more reliable and proper alignment of coil springs within the dies and minimizes the likelihood of oblique forces that can stress and break a die over time. 
     While the invention has been illustrated by the description of one embodiment and while the embodiment has been described in considerable detail, there is no intention to restrict nor in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those who are skilled in the art. For example, referring to FIG. 24, in an alternative embodiment of the pusher bar  152 , pusher fingers  374  are mounted to the top and bottom of the pusher bar  152 . To move the coil  278  from left to right, outer surface  279  of the pusher bar  152  contacts on outer surface of a middle turn  373  of the coil  278 ; and the pusher fingers  374  contact inside surfaces of upper and lower turns  376 . This three-point contact reliably pushes the row of coils  278  into the upper and lower slider mechanisms  38 ,  40 . Further, as will be appreciated, the spline shaft  58  can be replaced by a shaft having a different noncircular cross-sectional profile, for example, an elliptical or square cross-sectional profile. Such profiles permit the cars  60  to slide longitudinally on the shaft, but the cars are rotated along with any rotation of the shaft 
     Therefore, the invention in its broadest aspects is not limited to the specific details shown and described. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims which follow.