Information
-
Patent Grant
-
6698459
-
Patent Number
6,698,459
-
Date Filed
Thursday, April 4, 200222 years ago
-
Date Issued
Tuesday, March 2, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Wood, Herron & Evans, L.L.P.
-
CPC
-
US Classifications
Field of Search
US
- 140 3 CA
- 140 928
- 140 9294
-
International Classifications
-
Abstract
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. 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 planar die face of the movable die substantially parallel to a planar die face of the stationary die. The coil assembling apparatus is also operable to automatically assemble two rows of coil springs into a row of coaxial coil springs.
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's seat or a chair'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'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'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'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'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.
Claims
- 1. An apparatus for assembling coil springs together into a matrix of coil springs, each of the coil springs having a centerline and a pair of end turns substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, the coil springs being supplied by a conveyor, the apparatus comprising:workholders having respective grippers adapted to receive and hold end turns of respective coil springs; a loader supporting the workholders and being operable to move the workholders through a motion adapted to transfer the respective coil springs from the conveyor to the apparatus.
- 2. The apparatus of claim 1 further comprising a plurality of die sets, and the loader further comprises a pusher bar operable to push the coil springs in the workholders to a location adjacent respective die sets.
- 3. The apparatus of claim 1 wherein the loader comprises:a first mechanism being operable to rotate the workholders about 90° with respect to an axis of rotation; and a second mechanism being operable to separate the workholders.
- 4. The apparatus of claim 3 wherein the second mechanism being operable to separate the workholders in a direction substantially parallel to the axis of rotation and substantially simultaneously with the first mechanism rotating the workholders.
- 5. The apparatus of claim 4 wherein the loader further comprises a shaft for supporting the workholders, the workholders being mounted on the shaft to permit relative motion longitudinally on the shaft, but the shaft engaging the workholders for simultaneous rotational motion.
- 6. The apparatus of claim 5 wherein the shaft is a spline shaft.
- 7. The apparatus of claim 5 wherein the workholders are mechanically coupled together on the shaft to permit each of the workholders to separate from adjacent workholders by substantially equal increments.
- 8. The apparatus of claim 1 wherein the workholder further comprises a plurality of magazines mounted on the loader, each of the plurality of magazines adapted to receive and hold a turn of a coil spring.
- 9. The apparatus of claim 8 wherein the plurality of magazines are movable in a first motion pushing the plurality of magazines over turns of first coil springs on the conveyor, thereby securing a first coil spring in a respective magazine.
- 10. The apparatus of claim 9 wherein the loader and the coil springs held in the plurality of magazines are movable through a second motion substantially opposite the first motion and adapted to remove the first coil springs in the magazines from the conveyor.
- 11. The apparatus of claim 10 wherein the first coil springs held in the plurality of magazines are movable through a pivoting motion adapted to rotate centerlines of the first coil springs to a substantially vertical direction.
- 12. The apparatus of claim 8 wherein each of the magazines captures and holds a portion of a turn of the coil spring.
- 13. The apparatus of claim 12 wherein each of the magazines comprises fixed and resilient members that capture the portion of the turn of the coil spring therebetween.
- 14. A workholder of a coil spring assembly machine that assembles successive groups of coil springs into a matrix of coil springs, each of the coil springs having a centerline and end bottom turns substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, the workholder comprising:a base plate; a gripper mounted on the base plate; and a compression plate interposed between the base plate and the gripper, the compression plate being resiliently mounted relative to the base plate and adapted to receive a turn of a coil spring between the gripper and the compression plate.
- 15. The workholder of claim 14 further comprising a pair of grippers.
- 16. The workholder of claim 14 further comprising a leaf spring between the base plate and the compression plate.
- 17. The workholder of claim 14 wherein the gripper has a relief adapted to receive and guide a turn of the coil spring between the gripper and the compression plate.
- 18. An apparatus for assembling coil springs together into a matrix of coil springs, each of the coil springs having a centerline and a pair of end turns substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, the apparatus comprising:a stationary die adapted to receive an end turn of a first coil spring, the stationary die having a planar die face substantially perpendicular to the centerline of the first coil spring; a movable die adapted to receive an end turn of a second coil spring, the movable die having a planar die face substantially parallel to the planar die face of the stationary die; a drive; and a four bar linkage connected between the movable die and the drive and operable to move the movable die through a motion that maintains the planar die face of the movable die substantially parallel to the planar die face of the stationary die.
- 19. The apparatus of claim 18 wherein the movable die is one link of the four bar linkage.
- 20. The apparatus of claim 19 wherein the linkage further comprises a toggle pivotally connected to the four bar linkage.
- 21. The apparatus of claim 20 wherein the drive further comprises a linear drive connected to the toggle.
- 22. An apparatus for assembling coil springs together into a matrix of coil springs, each of the coil springs having a centerline and a pair of end turns substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, the apparatus comprising:a stationary die adapted to receive a turn of a first coil spring; a movable die adapted to receive a turn of a second coil spring; a pair of parallel guide links having first ends adapted to be pivotally connected to the machine and second ends pivotally connected to the movable die; a toggle having a first toggle link having one end pivotally connected to a second end of one of the guide links, and a second toggle link having one end pivotally connected to an opposite end of the first toggle link, the second toggle link having an opposite end adapted to be pivotally connected to the machine; a drive link having one end pivotally connected to the toggle; and a drive operable to move an opposite end of the drive link through a first motion that moves the movable die to an open position at which the moving die is separated from the stationary die, and a second motion that moves the movable die to a closed position at which the movable die is in juxtaposition with the stationary die.
- 23. An apparatus for assembling coil springs together into a matrix of coil springs, each of the coil springs having a centerline and a pair of end turns substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, and each of the end turns having a short leg and an opposed lacing leg, coil springs being connectable with each other by a lacing wire wound around lacing legs of respective coil springs, the apparatus comprising:a die set having first and second dies movable with respect to each other; and a lifter mounted adjacent the die set and being movable to lift an upstream leg of an end turn on a first coil spring located in the die set to permit a downstream leg of an end turn of a second coil spring to be moved below the upstream leg of the first coil spring, thereby forming a pair of coaxial coils.
- 24. An apparatus for assembling rows of coil springs together into a matrix of coil springs, each of the coil springs having a centerline and a pair of end turns substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, each of the end turns having a short leg and an opposed lacing leg, and the coil springs being connectable with each other by a lacing wire wound around lacing legs of respective coil springs, the apparatus comprising:a plurality of die sets, each of the die sets having first and second dies movable with respect to each other; and a plurality of lifters, each lifter being mounted adjacent a different one of the die sets and being movable to lift a short 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 to permit a lacing leg of an end turn of a first coil spring in a second row of coil springs to be moved below the short leg of the first coil spring of the first row of coils, thereby forming a row of coaxial coil springs from the coil springs in the first and second rows.
- 25. The magazine of claim 24 wherein the plurality of lifters further comprises a plurality of lifter wheels, each lifter wheel being located adjacent a different one of the plurality of die sets and comprising a lift cam.
- 26. The magazine of claim 25 further comprising a drive shaft, the plurality of lifter wheels being mounted on, and rotatable by, the drive shaft, each of the lift cams of respective lifter wheels adapted to contact and lift the short leg of the coil spring in the first row of coils in response to rotation of the lifter wheel.
- 27. The magazine of claim 26 wherein each of the plurality of lifter wheels further comprising a stop cam having a stop surface for locating a lacing leg of an end turn of a coil spring in the first row of coil springs that is adjacent the first coil spring in the first row of coil springs.
- 28. The magazine of claim 27 wherein each stop surface locates a lacing leg of an end turn of a coil spring that is adjacent the first coil spring in the second row of coil springs.
- 29. An apparatus for assembling coil springs together into a matrix of coil springs, each of the coil springs having a centerline and a pair of end turns substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, the apparatus comprising:a plurality of pairs of upper and lower die sets, each die set having a stationary forward die and a movable rear die; a plurality of pairs of upper and lower sliders, each pair of upper and lower sliders being located upstream of the respective pair of upper and lower die sets and being movable along respective linear paths toward and away from the respective pair of upper and lower die sets, the plurality of pairs of sliders being operable to successively position a first row of coils springs and a second row of coil springs immediately adjacent each other to form a row of coaxial coil springs; and a loader adapted to successively locate the first and second rows of coil springs downstream of the plurality of pairs of upper and lower sliders and upstream of the plurality of pairs of upper and lower die sets.
- 30. The spring coil assembly machine of claim 29 wherein each end turn of each coil spring has a short leg and an opposed lacing leg, and the apparatus further comprises a plurality of pairs of upper and lower lifters located upstream of respective pairs of upper and lower die sets, each of the lifters operating substantially simultaneously to lift a short leg of an end turn of a coil spring in the first row of coil springs located in a respective die set to permit a lacing leg of an end turn of a coil in the second row of coil springs to be moved under the short leg of the coil in the first row of coil springs, thereby forming a row of coaxial coil springs.
- 31. An apparatus for assembling rows of coils together into a matrix of coil springs, each of the coil springs having a centerline and a pair of end turns substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, the coil springs being supplied by a conveyor and the apparatus comprising:a preloader adapted to transfer a first row of coil springs from the conveyor to the apparatus; a plurality of pairs of upper and lower die sets; a plurality of pairs of upper and lower sliders, each pair of upper and lower sliders being located upstream of a different one of the upper and lower die sets; a transfer device moving along a linear path and adapted to push the first row of coils from the preloader to a location downstream of the plurality of sliders and upstream of the plurality of die sets, the plurality of sliders being operable to move the first row of coils into the plurality of die sets.
- 32. The apparatus of each claim 31 wherein end turn of each coil spring has a short leg and an opposed lacing leg, and the apparatus further comprises pairs of upper and lower lifters, each pair of upper and lower lifters being positioned between a pair of upper and lower forward dies and a respective pair of upper and lower sliders, each pair of upper and lower lifters adapted to raise short legs of respective end turns of a second row of coils as the pairs of upper and lower sliders push short legs of respective end turns of a second rows of coils under the short legs of respective end turns of the first row of coils.
- 33. The spring coil assembly machine of claim 32 wherein the sliders are adapted to push lacing legs of respective end turns of the second row of coils over lacing legs of respective end turns of the first row of coils.
- 34. A method of positioning coil springs with respect to a die set on a coil spring assembly machine, each of the coil springs having a centerline and end turns that are substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, and each of the end turns having one short leg and an opposed lacing leg, the coil springs being supplied by a conveyor, the method comprising:securing an end turn of a coil spring on the conveyor with a gripper; transferring the coil spring with the end turn from the conveyor to the coil spring assembly machine; and transferring the coil spring from the gripper to a location adjacent the die set.
- 35. The method of claim 34 further comprising securing the end turn of a coil spring on the conveyor with a resiliently biased gripper.
- 36. The method of claim 35 further comprising pushing the coil spring from the gripper to a location adjacent the die set with a pusher bar moving along a linear path.
- 37. A method of positioning coil springs with respect to a die set having fixed and movable dies on a coil spring assembly machine, each of the coil springs having a centerline and end turns that are substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, and each of the end turns having one short leg and an opposed lacing leg, the method comprising:automatically moving a first coil spring to a location where an upstream leg of an end turn of the first coil spring is located between the fixed and movable dies; automatically moving a second coil spring to a location where a downstream leg of an end turn of a second coil spring is located between the fixed and movable dies; automatically moving the movable die with a four bar linkage mechanism and a toggle toward the fixed die while maintaining a planar die face of the movable die substantially parallel to a planar die face of the fixed die to secure the upstream leg of the first coil spring against the downstream leg of the second coil spring.
- 38. A method of positioning coil springs with respect to a die set on a coil spring assembly machine, each of the coil springs having a centerline and end turns that are substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, and each of the end turns having one short leg and an opposed lacing leg, the method comprising:automatically moving a first coil spring to a location where a lacing leg of an end turn of the first coil spring is located in the die set; automatically moving a second coil spring toward the first coil spring; and automatically locating one leg of an end turn of the second coil spring beneath a leg of an end turn of the first coil spring to provide coaxial coil springs from the first and second coil springs.
- 39. The method of claim 38 comprising automatically locating a short leg of an end turn of the second coil spring beneath a short leg of the end turn of the first coil spring.
- 40. A The method of claim 39 further comprising:automatically raising the short leg of the end turn of the first coil spring; and automatically moving a lacing leg of the end turn of the second coil beneath a raised short leg of the first coil.
- 41. The method of claim 40 further comprising automatically locating a lacing leg of the end turn of the second coil spring in the die set over the lacing leg of the end turn of the first coil spring.
- 42. A method of positioning rows of coil springs with respect to die sets on a coil spring assembly machine, each of the coil springs having a centerline and end turns that are substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, and each of the end turns having one short leg and an opposed lacing leg, the method comprising:automatically moving a first row of coil springs to a location where lacing legs of first coil springs of the first row of coils are located in respective die sets; automatically moving a second row coil springs toward the die sets; automatically locating short legs of first coil springs of the second row of coil springs beneath short legs of the first coil springs of the first row of coil springs to provide a row of coaxial coil springs from the first and second rows of coil springs.
- 43. The method of claim 42 further comprising automatically locating lacing legs of the first coil springs of the second row of coil springs beneath short legs of the first coil springs of the first row of coil springs as the second row of coil springs is moved toward the die sets.
- 44. The method of claim 43 futher comprising automatically raising the short legs of the first coils of the first row of coil springs as the second row of coils is moved toward the die sets.
- 45. The method of claim 42 further comprising automatically locating lacing legs of the first coil springs of the second row of coil springs in the respective die sets with the lacing legs of the first coils of the first row of coil springs.
- 46. The method of claim 42 further comprising automatically locating lacing legs of second coil springs of the first row of coil springs lower than lacing legs of second coil springs of the second row of coil springs to facilitate locating the lacing legs of the second coil springs of the second row of coil springs over the lacing legs of the second coil springs of the first row of coil springs.
- 47. The method of claim 46 further comprising automatically locating short legs of the second coil springs of the second row of coil springs over short legs of the second coil springs of the first row of coil springs.
- 48. A method of positioning rows of coil springs on a coil assembly machine, each of the coil springs having a centerline and end turns that are substantially perpendicular to the centerline, the end turns being interconnected by at least one intermediate turn, and each of the end turns having one short leg and an opposed lacing leg, the method comprising:automatically moving a first row of coil springs to a location where upstream lacing legs of first coils of the first row of coil springs are located between a fixed die and a movable die; automatically moving a second row of coil springs to a location where downstream lacing legs of first coil springs in the second row of coil springs are located between the fixed die and the movable die; and automatically moving a third row of coil springs to a location where downstream lacing legs of first coils in the third row of coils are located between the fixed die and the movable die and upstream short legs of the first coils of the third row of coils are located below upstream short legs of the first coils of the second row of coils, the second and third rows of coils forming a coaxial row of coils.
- 49. The method of claim 48 further comprising:automatically closing the movable die against the fixed die to secure the lacing legs of the first coils of the first, second and third rows of coils therein; and automatically lacing the lacing legs of the first coils of the first, second and third rows of coils together.
US Referenced Citations (13)