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The present invention concerns a system for fabricating a lead wire for a
Ceramic Metal Halide Lamp constructed of three constituent wire
components.
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Figure 1 is a depiction of a prior art Ceramic Metal Halide Lamp 10. A metal
base 11 defines circumferentially extending threads for connecting the lamp
10 to a socket which supplies an energizing voltage to the lamp. The lamp
includes a clear outer jacket 12 coupled to the base and having an interior
that has been evacuated to a specified pressure and may optionally include
nitrogen gas as an added component. Mounted to the base in a generally
central position is an arc tube 13 filled with an ionizable metal halide material.
In order to initiate and sustain light emission from the arc tube 13 a voltage
difference is applied between two electrodes or leads 14, 16 which extend
into the arc tube. The arc tube 13 is a ceramic material and for example may
be molded from an aluminum oxide so that necked down regions 13a, 13b of
the tube form a seal about the leads 14, 16.
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Each of the leads 14, 16 (Figure 3) includes a tungsten tip T having an
encircling coil end T' (Figure 3). The tungsten tip T is attached at one end to
a molybdenum wire segment M having an outer coiled winding, which in turn
is attached to a Niobium wire segment N. The three segments or
components T, M, N together make up a wire lead which when energized with
an appropriate signal ignites and maintains light emission from the ionizable
material inside the arc tube 13. Figure 3 is a depiction on an enlarged scale
of such a lead 16. The diameter of the niobium wire component having
uniform cross section is about 0.025 inches but can be varied depending on
the lamp into which it is mounted.
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Currently Ceramic Metal Halide Lamp lead wires are manufactured on a turret
style machine that has twelve fixtures. The machine loads three wire
components T,M,N axially into the fixtures and attaches them at two weld
junctions between the lead wire components. Due to variations from fixture to
fixture, component length tolerance stack up and lack of controlled
displacement means, a percentage of the molybdenum and niobium welds
exceed a maximum allowable width. Since all three wire components T, M, N
are welded in a single fixture, the relatively expensive tungsten tip of this
defectively formed lead must be discarded along with the molybdenum and
niobium components.
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The present invention includes apparatus for manufacturing a wire lead
having at least two wire components which are welded at facing ends of the
wire components. The apparatus includes a first support for supporting a first
wire component and a second support for supporting a second component.
The supports are positioned to axially align the two wire components for
welding.
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A drive moves the first support with its first wire component along a travel
path until facing ends of the first and second axially aligned wire components
contact each other. In the exemplary embodiment of the invention the drive
maintains a force of engagement between the facing ends of the first and
second wire components as the two wire components are welded together to
form a two component wire lead.
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Practice of the invention negates component length variation due to the way
the components are accurately positioned when they are loaded into their
respective alignment fixtures. In accordance with the exemplary process, the
less expensive molybdenum-niobium weld is first made and inspected prior to
welding the more expensive tungsten tip. The fixture provides a means to
limit axial displacement or follow through during welding which helps control
the diameter of a weld knot formed during welding.
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These and other advantages and features of the invention are explained in
further detail in the accompanying detailed description of a preferred
embodiment of the invention which is described in conjunction with the
accompanying drawings, in which:
- Figure 1 is a perspective view of a metal halide lamp;
- Figure 2 is section view of a ceramic metal halide arc tube having electrodes
or leads that extend into an interior of the arc tube;
- Figure 3 is a plan view of a electrode or lead wire constructed in accordance
with the present invention;
- Figures 4A - 4G are a sequence of depictions showing the fabrication of part
of a lead wire;
- Figures 5A - 5G are an alternative sequence of depictions showing the
fabrication of part of a lead wire;
- Figures 6A - 6G are a sequence of depictions showing a completion of the
lead wire that is partially formed by the steps depicted in Figures 4A - 4G and
5A - 5G;
- Figures 7A - 7G are a further alternative sequence of depictions showing the
fabrication of part of a lead wire; and
- Figure 8 is a schematic depiction of lead wire components as they are fed to
a welding station.
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Figures 4A - 4G, 5A - 5G and 6A - 6G depict a system for forming a lead wire
having at least two wire components which are welded together. In
accordance with the presently preferred embodiment of the invention there
are two workstations 110, 111 for manufacturing a three component lead wire
such as the lead depicted in Figure 3. Alternate embodiments of the first
station 110 are depicted in the workstation 110a of Figures 5A - 5G.
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As illustrated in Figure 4A the workstation 110 includes two supports or
fixtures 112, 114. One fixture 112 supports a first wire component N and a
second, stationary fixture 114 that supports a second wire component M in an
axially aligned arrangement with respect to the first wire component. A drive
120 moves the first fixture with its first wire component N in a direction
indicated by an arrow 121 in Figure 4D of the common axis until facing ends
of the first and second axially aligned wire components contact each other.
The drive 120 maintains a force of engagement between the facing ends of
the first and second wire components M, N as the facing ends are welded
together to form a wire lead from the first and second wire components. A
cam actuated lever or a pneumatic cylinder can be used to secure the fixture
112 while the wire is moved into place. Such a mechanism would release the
fixture 112 and allow the drive 120 to provide follow through during welding.
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In accordance with the exemplary embodiment of the invention, the fixtures
112, 114 have V grooves 115 extending along the length of each fixture to
align the centerlines of their respective components N, M loaded into the
supports 112, 114 concentric to one another within an accuracy of 0.0005
inch. One 'V' fixture 112 is attached to a linear slide 122 having low inertia
that allows it to move toward and away from the stationary 'V' fixture 114 with
low friction. A niobium wire component N is fed onto the left hand 'V' fixture
while the molybdenum component is fed onto the right hand 'V' fixture. The
two wire components are fed via vibratory linear inline feeders, which are
schematically depicted by two arrows 128, 129 having tracks leading to the
fixtures so that an endmost wire component is pushed into a fixture by a next
succeeding wire component in the feeder. It should be apparent to those
skilled in the art that alternate structure for feeding the wire components into
the fixtures can be used.
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The vibratory in line feeders 128, 129 move the wire components into the 'V'
shaped support until the wire components contact a moveable stop 130 so
that facing ends of the wire components engage opposite sides 130a, 130b of
the moveable stop. While the back pressure from the respective linear
feeders pushes the two components against the vertical stop, two sets of hold
down fingers 132, 134 are activated to hold the wire components in place
within their respective 'V' shaped supports. The hold down fingers 132, 134
(Figure 4B) engage a top surface of the wire components to create a three
point contact. The hold down fingers are most preferably either knurled or
serrated on their contact surfaces to prevent axial movement of the
components N, M relative to the 'V' shaped fixtures. Alternate wire component
hold down means may utilize a clamp that extends the length of the fixture
instead of spaced apart fingers. A second alternate embodiment of the
invention may have a clam shell pivoting type hold down structure.
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To allow facing ends of the wire components to be brought into engagement
for welding, the vertical stop 130 is retracted out of the way (Figure 4C). The
left hand fixture 112 and the niobium wire component N that is secured to the
left hand fixture are moved to the right until an overhanging right end of the
niobium wire component contacts the exposed end of the molybdenum wire
component. In an alternate embodiment of the invention the fixture to the
right that supports the molybdenum moves to the left so that the two wire
components abut each other at ends that face each other.
In the exemplary embodiment wherein the left hand fixture moves, the fixture
112 is held in such a manner that sufficient contact force is applied between
the abutting ends of the wire components. The interface between the
molybdenum and niobium wire components melts during welding but a
consistent force is applied to the fixture to avoid neckdown of the weld region
formed as the ends melt. In the exemplary embodiment of the invention, this
force to the fixture is applied by a compression spring that constitutes the
drive 120 interposed between a fixed stop 140 and the left hand side of the 'V'
support 112. In an alternate embodiment of the invention the force is applied
by a linear motor. In another alternate embodiment of the invention the
contact force is applied by a moving coil actuator or voice coil actuator. One
suitable source for a moving coil actuator is SMAC of Carlsbad, California. In
another alternate embodiment of the invention the force is applied to the "V"
support is by a pneumatic drive. In the embodiment that uses a spring, the
force of engagement can be adjusted by means of a manual spring
compression control.
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The welding of the molybdenum wire component M to the niobium wire
component N is preferably performed by two ND:YAG lasers beams 142 (only
one of which is shown in the Figure 4E depiction) spaced from the fixtures so
that laser beams emanating from the lasers merge at the weld region "X"
where the wire components abut each other. The laser beams form an angle
of from about 135 degrees to 170 degrees to each other and are normal to
the axial axis of the wire components. In an alternate embodiment of the
invention, there are three laser beams and they are equally spaced about the
region of wire component abutment so that their included angle is 120
degrees. A relatively short pulse (approx 7 milliseconds) of laser energy is
concentrated in the region where the wires abut one another to weld the wires
together. The laser beams 142 are aligned to the Molybdenum side 130b of
the reference stop 130.
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A cover gas is applied to the weld junction region by a conduit 144 positioned
between the angled laser beams 142 to prevent oxidation of the weld region
and resulting embrittlement of that junction. A ¼" ID stainless steel tube/pipe
with an exit end held about 3/8 -1/2" above weld junction is suitable. The
cover gas can be either pure argon or a forming gas that is a mixture of
nitrogen and hydrogen. The cover gas flows long enough after welding to
cool the weld junction to prevent oxidation, typically between 1 and 2
seconds. As the weld junction melts during application of energy from the
lasers, the left "V" fixture continues to be pushed by the drive 120 toward the
right (molybdenum) fixture to produce a good weld that does not neck down in
the weld region. A hard stop 150 limits the overall travel of the fixture 112 to a
displacement gap of between 0.001 inch and 0.002 inch from the point the
two wire components first contact each other. In another embodiment of the
present invention, a linear motor can be used to limit travel to no more than
0.001- 0.002 inches past the region of wire components first come into
contact. In an alternate embodiment of the invention, a moving coil actuator
would be programmed not to exceed specified (0.001-0.002 inch)
displacement limits once melting occurs during welding. In another alternate
embodiment a dial indicator with a sufficiently adequate spring is preset to the
displacement desired, with the niobium and molybdenum wire components in
contact end to end. During welding, the moveable fixture can only move to
the preset tension (or less), as no more linear force can be applied (spring
fully relaxed or limited). There may be other embodiments of limiting the
follow through or displacement, which are based on the aforementioned
examples.
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After the weld is made the hold down fingers are moved out of contact with
their respective leads (See Figure 4F). Next, the two fixtures 112, 114
simultaneously rotate about an axis of rotation and drop the completed two-part
lead onto a transfer device (Figure 4G).
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Figures 5A - 5G illustrate a work station 110a constructed with an alternate
embodiment of the invention. In Figures 5A - 5G like reference characters
are used for components also depicted above with reference to Figures 4A -
4G. In this alternate embodiment the fixtures 112,114 define 'V' shaped
grooves to accommodate the wire components M, N. In this embodiment the
fixtures 112, 114 move vertically down in the direction indicated by the arrows
160, 161 such that the completed welded wire component (N-M) is placed
upon a pair of transfer wheels 170, 171, having spaced notches around its
periphery. The wheels rotate the lead (N-M) out of the work area and drop it
onto a separate conveyor. In an alternate embodiment of the invention, the
completed lead is transferred out of the fixtures via a walking beam transfer
system. A walking beam has a box pattern motion. For example, two vertical
fingers would move up (vertical) to pick the lead wire out of the fixtures, then it
would move horizontally, away from the fixture, a set distance and then move
down. (vertically to the starting level) Then it would move horizontally back to
the starting position. The two part lead wire can now be inspected prior to
delivery to a second weld station 111 depicted in Figures 6A - 6G.
The steps in forming the weld between the tungsten tip T and the
molybdenum portion of the already completed two part lead (N-M) are
depicted in Figures 6A - 6G. This second weld step takes place after the first
weld joint between the wire components N, M has been inspected and two
part components having malformed weld joints are discarded.
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The exemplary embodiment of the invention has a third V groove fixture 212
for the two part component (N-M) and a clam shell support fixture 214 for the
tungsten tip T. The clamshell has two internally nesting "V"s that accurately
hold/align the tip T. The two fixtures 212, 214 are aligned such that the
centerlines of the respective components loaded into the support fixtures 212,
214 are held concentric to one other within an accuracy of 0.0005 inch. The
two component wire (N-M) is fed via vibratory linear inline feeders having
tracks leading to the fixture 212. Alternate structure for feeding the wire
components into the fixtures can be used.
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The vibratory feeder moves the wire component into the 'V' shaped support
until the wire component contact a moveable stop 230. The support fixture
214 moves the tip T so that an exposed end of the tip T engages an opposite
side of the moveable stop 230. While the back pressure from the respective
linear feeder pushes the two component wire (N-M) against the vertical
stop230, hold down fingers 232 are activated to hold the component (N-M) in
place within the V groove 215 of its support fixture 212. The hold down
fingers (Figure 6B) engage a top surface of the wire components to create a
three point contact. The hold down fingers are most preferably either knurled
or seriated on their contact surfaces to prevent the components axial
movement relative to the 'V' shaped fixtures. Alternate wire component hold
down means may utilize a clamp that extends the length of the fixture instead
of spaced apart fingers. The second support fixture 214 includes a clamshell
pivoting type hold down structure.
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To allow facing ends of the wire components to be brought into engagement
for welding, the vertical stop 230 is retracted out of the way (Figure 6C). The
tungsten tip T that is secured to the right hand fixture 214 is moved to the left
until its exposed end contacts the overhanging molybdenum wire of the two
part lead component N-M.
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In the exemplary embodiment wherein the right hand fixture 214 moves, this
fixture is held in such a manner that sufficient contact force is applied
between the abutting ends of the wire components T, N-M. The interface
between the molybdenum and tungsten wire melts during welding by two or
more laser beams 242 but a consistent force is applied to the fixture to avoid
neckdown of the weld region formed as the ends melt. In the exemplary
embodiment of the invention, this force to the moveable fixture 214 is applied
by a spring, or linear motor (not shown). A hard stop 250 limits the overall
travel of the fixture 214 to between 0.001 inch and 0.002 inch from the point
the two wire components T, N-M first contact each other. The motion of the
clamshell fixture 214 to make contact with the molybdenum can be cam lever,
pneumatic cylinder or linear motor/voice coil. A spring with hard stop and
helper spring dial indicator can also be used to limit movement.
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The tip T is welded to the Molybdenum part of the two part component N-M
and the displacement during this process is limited in a similar manner to the
movement depicted in Figures 4A - 4G. After the weld is made the hold down
fingers 232 are opened and the fixture 214 is opened by pivoting one half
214a of the clam shell open to release the tip T. The completed three part
electrode 16 is removed via a pair of notched rollers 270, 271 that are moved
up to engage the electrode 16. Once a completed electrode has been
contacted the rollers are rotated so that the completed electrode 16 is moved
to a separate conveyor. In alternate embodiments the completed electrode is
removed with a walking beam mechanism. In either embodiment a visual
inspection of the now completed lead is performed so that faulty welds of the
tip to the molybdenum can be performed.
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Figures 7A - 7G depict an alternative system for forming a lead wire having at
least two wire components which are welded together. In this embodiment as
illustrated in Figure 7A a workstation 310 includes two supports or fixtures
312, 314. One fixture 312 supports a first wire component N and a second,
stationary fixture 314 that supports a second wire component M in an axially
aligned arrangement with respect to the first wire component. A first drive
moves the first fixture with its first wire component N in a direction indicated
by a first arrow 321 in Figure 7A and a second drive moves the second
fixture 314 in the direction of an arrow 322 along the common axis until facing
ends of the first and second axially aligned wire components contact each
other.
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In accordance with the exemplary embodiment of the invention, the fixtures
312, 314 have V grooves extending along the length of each fixture to align
the centerlines of their respective components N, M loaded into the supports
312, 314 concentric to one another within an accuracy of 0.0005 inch. Both
fixtures are attached to linear slides having low inertia that allows it to move
toward a weld zone between the fixtures with low friction.
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In line feeders move the wire components into the 'V' shaped support until the
wire components contact moveable stops 330, 331 so that facing ends of the
wire components engage opposite sides of the moveable stops 330, 331.
While the back pressure from the respective linear feeders pushes the two
components against the vertical stop, two sets of hold down fingers 332, 334
are activated to hold the wire components in place within their respective 'V'
shaped supports. The hold down fingers 332, 334 (Figure 7B) engage a top
surface of the wire components to create a three point contact. The hold
down fingers are most preferably either knurled or serrated on their contact
surfaces to prevent axial movement of the components N, M relative to the 'V'
shaped fixtures. Alternate wire component hold down means may utilize a
clamp that extends the length of the fixture instead of spaced apart fingers. A
second alternate embodiment of the invention may have a clam shell pivoting
type hold down structure.
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To allow facing ends of the wire components to be brought into engagement
for welding, the vertical stops 330, 331 are retracted out of the way (Figure
4C). The left hand fixture 312 and the niobium wire component N that is
secured to the left hand fixture are moved to the right. The molybdenum
fixture 314 is moved to the left toward the fixture 312 and is held in place with
a hard stop 315 positioned such that the molybdenum wire end facing the
niobium wire is aligned to the laser beam or laser beams. The interface
between the molybdenum and niobium wire components melts during welding
but a consistent force is applied to the two fixtures to avoid neckdown of the
weld region formed as the ends melt.
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Several methods of displacement control can be used. In one embodiment of
the invention the force is applied by a linear motor. In another alternate
embodiment of the invention the contact force is applied by a moving coil
actuator or voice coil actuator. One suitable source for a moving coil actuator
is SMAC of Carlsbad, California. Another means would be to employ a spring
and hard stop mechanism. The molybdenum fixture 314 is held fast against
its hard stop 315 by a cam lever, pneumatic cylinder or linear motor.
As shown in Figure 7E the parts are then laser welded as a cover gas is sent
to the region prior to and after welding for two seconds. Once the weld is
complete the gripper jaws 332, 334 open and the fixtures 312, 314 rotate 180
degrees to unload the two part lead wire onto a conveyor.
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Figure 8 discloses delivery stations for moving the wire to a weld station 110
such as the weld station of Figure 4A - 4G. A niobium wire feeder bowl 350
and a molybdenum wire feeder bowl 352 are supported to deliver lengths of
wire to respective in line vibrabory feeders 360, 362 which push an endmost
portion of their respective wires against a stop 354, 356. The niobium wire is
placed on a first conveyor 370 and the molybdenum wire is placed on a
second conveyor 372. These conveyors deliver the wire components to the
work station 110 for welding. In the embodiment shown in figure 8 a pusher
assembly (rather than a vibratory feeder) delivers the wire components N, M
to the work station 110 by pushing individual wires onto their respective
fixtures 112, 114. Walking beams 410, 411 deliver welded two component
leads N-M to a single conveyor 420 for inspection.
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The disclosed process of forming a lead wire can be modified to use resistive
welding to join the components provided that sufficient insulation is provided
to insulate the fixtures and bearing for supporting the moveable fixture from
welding flux needed at the weld region between wire components. Plasma
welding and ultrasonic welding are other alternative welding processes that
can be used in conjunction with the invention.
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For completeness, various aspects of the invention are set out in the following
numbered clauses:
- 1. A method of forming a wire lead having at least two wire components
which are welded together to form the lead comprising the steps of:
- a) supporting first and second wire components (N, M) in first and
second wire supports (112, 114) that axially align the wire components along
a common axis;
- b) moving a moveable wire support (112) of at least one of the first and
second wire supports in a direction of the common axis until facing ends of
the first and second wire components (N, M) contact each other;
- c) maintaining a force of engagement between the facing ends of the
first and second wire components (N, M) ; and
- d) welding the facing ends together to form a wire lead from the first
and second wire components.
- 2. The method of clause 1 wherein energy is provided to a weld region
(X) where the first and second wire components are maintained in contact.
- 3. The method of clause 1 wherein the moveable wire support (112) is
coupled to a bearing (122) and wherein the step of maintaining the force of
engagement between facing ends of said wire components is performed by
biasing the moveable wire support.
- 4. The method of clause 1 additionally comprising the step of feeding at
least one of the wire components to the first and second wire supports by an
automated feeder (128) and wherein movement of the at least one wire
component within a travel path through its support is limited by an end of
travel stop (130).
- 5. The method of clause 4 wherein the automated feeder is a vibratory
feeder.
- 6. The method of clause 4 additionally comprising the step of clamping
the wire components in place within a concave region (115) of the supports
once the wire components have engaged the end of travel stop.
- 7. The method of clause 6 wherein one side of the end of travel stop
(130) precisely positions one end of a stationary wire component to define a
weld region (X) once the second wire component moves into engagement
with the first.
- 8. The method of clause 7 wherein one side of the travel stop (130)
defines a position for directing a laser beam (142) for forming the weld.
- 9. The method of clause 1 additionally comprising the step of forming a
junction between a third wire component (T) and the combination (N-M) of
said first and second wire components.
- 10. The method of clause 9 wherein before forming the junction with the
third wire component, a weld junction between the first and second wire
components is inspected.
- 11. The method of clause 9 wherein the first wire component (N)
comprises niobium, the second wire component comprises molybdenum (M),
and the third wire component comprises tungsten (T).
- 12. The method of clause 1 wherein during the step of maintaining the
force of engagement an extent of movement of the moveable wire support is
limited to help maintain the weld junction.
- 13. Apparatus for forming a wire lead having at least two wire components
which are welded together comprising:
- a) two supports (112, 114), one support for supporting a first wire
component (N) and a second support for supporting a second wire
component (M) in an axially aligned arrangement with respect to the first wire
component;
- b) a drive (120) for moving the first support with its first wire component
in a direction of the common axis until facing ends of the first and second
axially aligned wire components contact each other wherein said drive
maintains a force of engagement between the facing ends of the first and
second wire components; and
- c) structure (142) for welding the facing ends together to form a wire
lead from the first and second wire components.
- 14. The apparatus of clause 13 additionally comprising a conduit (144) for
routing a gas into a region of a weld.
- 15. The apparatus of clause 13 wherein the drive comprises a drive motor
for moving the first support relative to a stationary support.
- 16. The apparatus of clause 13 additionally comprising a hold down clamp
(132, 134) for holding the first and second wire components in place within
the first and second supports (112, 114).
- 17. The apparatus of clause 13 wherein the drive (120) comprises a spring
for moving the first support relative to the stationary support.
- 18. The apparatus of clause 13 additionally comprising a transfer device
(170, 171) for moving the wire lead away from the workstation.
- 19. The apparatus of clause 13 wherein the structure for welding
comprises one or more lasers.
- 20. The apparatus of clause 13 wherein one of said two supports
comprises a pivotal member (214) for holding an associated wire component
during welding and for then releasing the wire component after welding.
- 21. The apparatus of clause 13 comprising a component delivery structure
for moving the first and second wire components into the respective supports
and a spacer stop (130) for limiting movement of the wire components by the
component delivery structure.
- 22. The apparatus of clause 21 wherein one side of the spacer stop
defines a weld junction (X).
- 23. The apparatus of clause 13 further comprising a limit stop (150) for
limiting movement of the wire component during a process of welding.
- 24. The apparatus of clause 13 wherein both supports (312, 314) are
mounted for movement along respective travel paths and further including
first and second drives for moving the supports toward each other along their
respective travel paths for welding two wire components carried by the
supports.
- 25. The apparatus of clause 24 further including first and second reference
stops (330, 331) for positioning the wire components within the supports.
- 26. The apparatus of clause 25 further including a hard stop (315) for
positioning one of the first and second supports with respect to the laser
beams to define a laser weld position.
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