U.S. patent application number 10/618906 was filed with the patent office on 2004-06-03 for method for immobilizing a frame structure in its free state to establish a net datum position.
Invention is credited to Kline, John.
Application Number | 20040103529 10/618906 |
Document ID | / |
Family ID | 24858929 |
Filed Date | 2004-06-03 |
United States Patent
Application |
20040103529 |
Kind Code |
A1 |
Kline, John |
June 3, 2004 |
METHOD FOR IMMOBILIZING A FRAME STRUCTURE IN ITS FREE STATE TO
ESTABLISH A NET DATUM POSITION
Abstract
An apparatus and method for immobilizing a vehicle chassis frame
in its free state atop a frame fixture so as to establish a net
datum position of the chassis frame for enabling a net datum
feature to be fabricated in a location net to the fixture and in
design-intent position on the chassis frame. The apparatus does not
compressingly clamp any portion of the chassis frame in order to
avoid deforming or displacing the chassis frame and to avoid
building stress into the chassis frame or incurring springback of
the chassis frame. The chassis frame is interposed between a pair
of opposed pads used for contacting opposite portions of the
chassis frame. A work support connects to each of the opposed pads
for advancing the opposed pads from a retracted position to an
advanced position to find opposite portions of the chassis frame.
The advancing device advances the pair of opposed pads into contact
with the chassis frame without measurably displacing the chassis
frame despite the tolerance variations. Once the opposed pads find
their respective opposite reference contact surfaces on the chassis
frame, a locking mechanism is provided for locking the pair of
opposed pads in place in the advanced position so as to immobilize
the chassis frame therebetween. Subsequently, a forming and
piercing mechanism may be used to fabricate locating features net
to the frame fixture and in design-intent position on the chassis
frame.
Inventors: |
Kline, John; (Rochester,
MI) |
Correspondence
Address: |
VAN OPHEM & VANOPHEM, PC
51543 VAN DYKE
SUITE 103
SHELBY TOWNSHIP
MI
48317-4447
US
|
Family ID: |
24858929 |
Appl. No.: |
10/618906 |
Filed: |
July 14, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10618906 |
Jul 14, 2003 |
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09711644 |
Nov 13, 2000 |
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6629354 |
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Current U.S.
Class: |
29/822 |
Current CPC
Class: |
Y10T 29/53091 20150115;
B62D 65/02 20130101; Y10T 29/53961 20150115; Y10T 29/49998
20150115; Y10T 29/53539 20150115 |
Class at
Publication: |
029/822 |
International
Class: |
B23P 019/00 |
Claims
What is claimed is:
1. An apparatus for finding and immobilizing a workpiece in its
free state so as to establish a net datum position of said
workpiece, said apparatus comprising: at least one pair of opposed
pads; means for advancing said at least one pair of opposed pads
from a retracted position to an advanced position in contact with
opposite portions of said workpiece so as to find said workpiece
without measurably displacing said workpiece; and means for locking
said at least one pair of opposed pads in said advanced position,
whereby said at least one pair of opposed pads lock in place so as
to immobilize said workpiece in its free state.
2. The apparatus as claimed in claim 1, further comprising:
unlocking means for unlocking said at least one pair of opposed
pads so as to release said workpiece; and retracting means for
retracting said at least one pair of opposed pads from said
advanced position to said retracted position clear of said
workpiece.
3. The apparatus as claimed in claim 2, wherein said advancing
means and said retracting means comprises: a spring for biasing
each pad of said at least one pair of opposed pads toward said
retracted position; and means for pneumatically actuating each pad
of said at least one pair of opposed pads toward said advanced
position.
4. The apparatus as claimed in claim 3, wherein said locking means
and said unlocking means comprises a hydraulic locking device
associated with each pad of said at least one pair of opposed pads
to lock each pad of said at least one pair of opposed pads in said
advanced position.
5. The apparatus as claimed in claim 4, wherein said advancing
means, said retracting means, said locking means, and said
unlocking means comprise a work support device of the
pneumatic-advance, hydraulic-lock, and spring-retract type.
6. The apparatus as claimed in claim 5, wherein: each pad of said
at least one pair of opposed pads comprises a workpiece contact
side and a locking side opposite said workpiece contact side; and
said advancing means and said retracting means comprise a pair of
fluidic cylinder devices mounted between said at least one pair of
opposed pads in contact with said workpiece contact sides of said
at least one pair of opposed pads, and said locking and unlocking
means comprise a pair of locking fluidic cylinder devices in
contact with said locking sides of said at least one pair of said
opposed pads.
7. An apparatus for finding and immobilizing a chassis frame in its
free state, despite within-tolerance variations in size or location
of said chassis frame, so as to establish a net datum position of
said chassis frame to enable net datum features to be fabricated
net to a fixture and in design-intent position on said chassis
frame, said apparatus comprising: a pair of opposed hydraulic
units, each hydraulic unit of said pair of opposed hydraulic units
being disposed on opposite sides of a portion of said chassis frame
such that said portion of said chassis frame is between said pair
of opposed hydraulic units, each hydraulic unit of said pair of
opposed hydraulic units comprising: a plunger mounted displaceably
therein and terminating in a pad, said plunger being normally
biased toward a retracted position clear of said chassis frame;
means for advancing said plunger from said retracted position to an
advanced position, such that said pad contacts said chassis frame
without measurably displacing said chassis frame; and means for
locking said pad in said advanced position, so as to immobilize
said chassis frame in its free state between said pair of opposed
hydraulic units.
8. The apparatus as claimed in claim 7, further comprising: a
stationary support positioned on one side of said chassis frame,
one hydraulic unit of said pair of opposed hydraulic units being
mounted to said stationary support; and a movable support
positioned opposite said stationary support on an other side of
said chassis frame, the other hydraulic unit of said pair of
opposed hydraulic units being mounted to said movable support.
9. The apparatus as claimed in claim 8, wherein said movable
support moves between a home position and a work position, said
home position being distal said chassis frame to permit said
chassis frame to be loaded in position with respect to said
apparatus, said work position being proximate said chassis frame to
permit said pair of opposed hydraulic units to find and immobilize
said chassis frame.
10. The apparatus as claimed in claim 9, wherein each hydraulic
unit of said pair of opposed hydraulic units further includes a
spring therein biased against said pad to retract said pad toward
said retracted position.
11. An apparatus for finding and immobilizing a chassis frame in
its free state, despite tolerance variations in size or location of
said chassis frame, so as to establish a net datum position of said
chassis frame to enable net datum features to be fabricated net to
a fixture and in design-intent position on said chassis frame, said
apparatus comprising: a pair of fixed platens comprising one platen
and an opposite platen mounted opposite said one platen, said
opposite platen being spaced a predetermined distance apart from
and substantially parallel to said one platen; a plurality of guide
bars extending between said pair of fixed platens; a pair of
displaceable pads mounted about said guide bars between said pair
of fixed platens, said pair of displaceable pads comprising one pad
and an opposite pad mounted opposite said one pad, said opposite
pad being mounted about said guide bars a spaced predetermined
distance apart from and substantially parallel to said one pad,
said pair of displaceable pads being displaceable from a retracted
position distal from said chassis frame to an advanced position in
contact with said chassis frame; displacing means, positioned
between said pair of displaceable pads, for displacing said pair of
displaceable pads between said retracted position and said advanced
position into contact with opposite reference surfaces on said
chassis frame without measurably displacing said chassis frame so
as to find said chassis frame; and locking means, positioned
between said pair of fixed platens and said displaceable pads, for
locking said pair of displaceable pads in said advanced position so
as to immobilize said chassis frame in said free state.
12. An apparatus as claimed in claim 11, further comprising: a base
structure; and a support displaceably mounted to said base
structure and being displaceable between a home position distal
said chassis frame and a work position proximate said chassis
frame, said pair of fixed platens mounting to and extending from
said support.
13. An apparatus as claimed in claim 12, wherein said locking means
comprises a pair of locking cylinders positioned between said pair
of fixed platens and said pair of displaceable pads, said
displacing means comprising a pair of finding cylinders positioned
between said pair of displaceable pads.
14. An apparatus as claimed in claim 13, wherein said pair of
locking cylinders comprises hydraulic work supports and said pair
of finding cylinders comprise hydraulic cylinders.
15. An apparatus as claimed in claim 13, wherein said pair of
locking cylinders comprises hydraulic work supports and said pair
of finding cylinders comprise pneumatic cylinders.
16. A method of finding and immobilizing a workpiece in its free
state despite within-tolerance variations in size or location of
said workpiece so as to establish a net datum position of said
workpiece to enable net datum features to be fabricated net to a
fixture and in design-intent position on said workpiece, said
method comprising the steps of: mounting said workpiece in its free
state atop said fixture; advancing an opposed pair of pads from a
retracted position to an advanced position in contact with opposite
portions of said workpiece without measurably displacing said
workpiece despite said tolerance variations, such that said
opposite portions of said workpiece are between said opposed pair
of pads; and locking said opposed pair of pads in said advanced
position against said opposite portions of said workpiece so as to
immobilize said workpiece in said free state.
17. The method as claimed in claim 16, further comprising the steps
of: unlocking said opposed pair of pads; and retracting said
opposed pair of pads from said advanced position to said retracted
position such that said workpiece may be withdrawn from said
fixture.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to a method and
apparatus for establishing a net datum position of a framing
structure. More specifically, this invention relates to a method
and apparatus that finds reference surfaces of an automotive
vehicle frame that has been assembled within an acceptable
tolerance range, and despite the within-tolerance variation of the
reference surfaces on the frame, the frame is immobilized in its
free state so that work can be subsequently performed on the frame
to fabricate a net datum locating feature in its original
design-intent location on the frame.
[0003] 2. Description of the Prior Art
[0004] In the manufacturing of automobiles and trucks, a chassis
frame typically includes an underbody, a pair of side frames, and
front and rear headers wherein such chassis frame usually undergoes
a progressive series of positioning and welding steps before a
rigid chassis frame is produced. Though vehicle bodies are still
manually assembled and welded, emphasis on automated assembly and
welding operations has generated numerous automated and
semi-automated framing systems.
[0005] Generally, in such prior art processes it is a common object
of a framing system to accurately locate the body components
relative to each other and maintain such location throughout later
welding operations, until the structural rigidity of the body is
sufficient to preserve the desired geometric configuration
throughout the assembly line. A further object for most framing
systems is to provide sufficient flexibility to accommodate more
than one body style, so as to enhance the versatility of the
assembly line and reduce the tooling cost per assembly unit.
[0006] Chassis frames, however, have not received as much attention
as vehicle bodies with respect to automated assembly techniques and
accordingly, are currently still being assembled on fixtures built
to design-intent, wherein a pair of rail members are clamped in
place with a series of cross members therebetween and subsequently
welded together to permanently fasten the rails and cross
members.
[0007] Unfortunately, the heat generated from welding operations
causes the chassis frame to warp or twist out of its design-intent
geometry and position. Such warping is problematic because the
individual components of the chassis frame include locating
surfaces or holes that are relied upon for locating other features
produced in subsequent operations. Unfortunately, due to warpage of
the chassis frame from the welding operation, such locating
surfaces or holes are intolerably displaced from their
design-intent position, and thereby negatively effect the location
of the other features produced during subsequent operations.
[0008] There are at least two well-known attempts to solving this
problem. First, many manufacturers use a frame straightening
process in an attempt to correct the warping. The frame
straightening process, however, tends to be an exercise in futility
since the process introduces additional built-in stress to the
chassis frame and can lead to further displacement of the rails and
cross member structure. Such frame straightening processes are
rarely, if ever, capable of reliably straightening the entire
chassis frame back into its exact design-intent geometry.
[0009] A second solution involves welding the components of the
chassis frame together, then forcibly clamping the chassis frame
from its free state back into its exact design-intent geometry,
then producing holes and other features, and finally unclamping the
chassis frame. This solution is performed with the expectation that
the holes and other features will remain positioned within a
certain tolerance relative to the design-intent geometry of the
chassis frame when the part is unclamped. Unfortunately, however,
the chassis frame tends to spring back to its warped free state
when unclamped and thus, the holes and other features of the
chassis frame are carried away from their design-intent position,
in some cases out of the acceptable tolerance range.
[0010] In addition to the above-mentioned general approaches,
several other locating or positioning devices associated with
processing vehicle chassis frames have been proposed in the prior
art. For example, U.S. Pat. No. 4,976,026 to Dacey, Jr. addresses
the problems associated with locating a datum reference on a
partially assembled structural object such as an automobile chassis
frame. As a solution, Dacey, Jr. teaches an apparatus having a
probe portion thereof for detecting pre-established surfaces and
features on the vehicle body to establish a datum position. Tooling
attached to the apparatus subsequently references the datum
position established by the probe portion, and performs work on the
vehicle body in relation thereto.
[0011] Dacey, Jr. discloses the apparatus as having a base rigidly
mounted to a floor, and having a transfer platform attached to the
base with guideposts to ensure freedom of movement of the transfer
platform in a first horizontal direction toward the vehicle body. A
support platform is attached to the transfer platform using
guideposts to ensure freedom of movement relative thereto in a
second horizontal direction that is perpendicular to the first
horizontal direction. A vertical platform is attached to the
support structure and is moveable therewith along guideposts in a
vertical direction. A form and pierce device is attached to a lower
portion of the vertical platform for performing work on the vehicle
body. A pair of hydraulic work supports interpose each of the
platforms, at clamping plate locations, for locking horizontal and
vertical movement of the apparatus. A series of probes are attached
to an upper end of the vertical platform for detecting the
pre-established surfaces and features of the vehicle body from
which the datum position is established. For example, one of the
probes includes a tapered surface to permit the probe to climb
vertically onto a fender rail, and another probe is tapered to
guide it into a preformed orifice in the vehicle body. Once the
probes locate the pre-established surfaces and features of the
vehicle body, fluid pressure is introduced to the work supports so
that push rods of the work supports exert an equal clamping force
on either side of the positioning plates for locking the transfer,
support, and vertical platforms in place. The datum position of the
pre-established surfaces and features is thereby established to
permit the form and pierce tool to perform work upon the chassis
frame in relation to the datum position.
[0012] As discussed above, Dacey, Jr. provides an apparatus having
a sub-assembly for forming and piercing a vehicle body panel or
sub-frame in direct relation to a datum position established by
detecting pre-established surfaces and features of the vehicle body
by another sub-assembly of the same apparatus. Unfortunately,
however, Dacey, Jr. requires that a preformed orifice and specific
body panels be located on the vehicle body prior to immobilizing
the tooling device for subsequent forming and/or piercing
operations. Additionally, Dacey, Jr. does not teach or disclose
that the apparatus is capable of rigidly immobilizing the entire
vehicle body by itself, not just proximate the datum location,
thereby enabling work to be performed anywhere on the vehicle body.
Finally, the piercing operation disclosed in Dacey, Jr. is
performed by a tooling device, relative to a datum location
established by probing various predefined features that have
pre-existing tolerance variation. The positions of the various
predefined features on the vehicle body, such as the top of the
fender rail and the preformed orifice, have size and locational
tolerance variations. Further, the apparatus including the probes,
platforms, and piercing tooling have size and locational tolerance
variations also. Therefore, the piercing operation is performed
relative to specific features of the vehicle body that have
tolerance variation, rather than performed directly relative to a
net datum position of the entire vehicle body frame.
[0013] U.S. Pat. No. 5,987,726 to Akeel identifies a general
problem with assembling body panels, wherein internal stresses are
built into body assemblies. Therefore, Akeel teaches use of
programmable body panel positioners for compliant positioning of
body panels or tooling during assembly operations to achieve a
stress-free vehicle body assembly. Akeel discloses a parallel link
mechanism having a base plate, a locator plate spaced above the
base plate, and three pairs of linear actuator links attached
between the base and locator plates by universal joints. Either a
tool or a body panel member is clamped to the locator plate for
processing the body panel member. The actuators are screw drives
for changing the length of each link in a corrective manner in
response to variation in processing forces. A feedback control
system, including force sensors and encoders, is communicated with
the links so that the actuators react to processing forces for
increasing the holding force on the body panel member for higher
support rigidity, or to decrease the holding force for controlled
compliance and a stress free assembly.
[0014] Unfortunately, Akeel involves use of very complex apparatus
used to avoid building stresses into the body assembly.
Additionally, clamping forces are nonetheless imparted to the body
panels, albeit in an adjustable manner.
[0015] From the above, it can be appreciated that the general
solutions of the prior art relative to frame warpage and out of
position holes and features are not fully optimized, and no
specific viable solutions have been identified in the prior art.
Therefore, what is needed is a simple apparatus and method for
finding a chassis frame despite within-tolerance variation in size,
position, or geometry of the chassis frame, and immobilizing the
chassis frame in its free state without imparting forces sufficient
to displace the chassis frame, whereby a net datum position of the
chassis frame is established so that net datum locating features
can be subsequently produced in precise design-intent locations on
the frame.
SUMMARY OF THE INVENTION
[0016] According to the present invention, there is provided an
apparatus and method for finding and immobilizing a workpiece in
its free state, within an acceptable tolerance range, to establish
a net datum position of the workpiece without compressingly
clamping any portion of the workpiece so as to avoid deforming or
displacing the workpiece to avoid building stress into the
workpiece or incurring springback of the workpiece. The apparatus
includes a pair of opposed pads for "finding" the workpiece by
independently coming into contact with opposite reference surfaces
of the workpiece. An advancing device, such as a work support,
connects to each of the opposed pads for advancing the opposed pads
from a retracted position to find an advanced position in contact
with the opposite portions of the workpiece. The advancing device
advances the pair of opposed pads into contact with the workpiece,
regardless of the exact location of the reference surfaces on the
workpiece, without measurably displacing the workpiece. A locking
mechanism is provided for locking the pair of opposed pads in their
advanced position, whereby the pair of opposed pads lock in place
without imparting any force on the workpiece, so as to immobilize
the workpiece therebetween so that a net datum position is
established for the workpiece.
[0017] It is an object of the present invention to provide an
apparatus and method that is capable of immobilizing a chassis
frame or carriage and establishing a net datum position of such
carriage for subsequent processing.
[0018] It is still another object to provide an apparatus and
method that is adapted to immobilize a chassis frame or carriage in
its free state as it rests upon a chassis frame fixture.
[0019] It is yet another object to provide an apparatus and method
for finding the position of a chassis frame and immobilizing the
chassis frame in its free state as it rests upon a fixture, that
can be used in conjunction with a tool such as a form and pierce
device, to produce features in precise locations on the chassis
frame that are net to the fixture, and thus to design-intent,
despite tolerance variations within preselected acceptable limits
in size or location of the chassis frame.
[0020] It is a further object to provide an apparatus and method
that finds the position of and immobilizes a chassis frame in its
free state without imposing on the chassis frame external forces
sufficient to measurably deform or displace the chassis frame from
its free state, in order to establish a net datum position
according to design-intent so that this net datum position can be
used as a reference to perform subsequent work on the chassis frame
after engagement of the apparatus.
[0021] It is yet a further object to provide an apparatus and
method for finding and immobilizing a chassis frame in its free
state at a series of different workstations to perform work on the
chassis frame so as to establish a net datum position or location
and use the net datum position throughout using common fixtures, to
perform subsequent work on the chassis frame without subjecting the
chassis frame to clamping forces that not only deform and distort
the chassis frame, but that also vary from workstation to
workstation. Thus, the different tools produce different features
in precise locations on the chassis frame that are net to the
common fixtures, and thus to design-intent, despite tolerance
variations in size or location of the chassis frame, and that are
not influenced by varying clamping forces.
[0022] These objects and other features, aspects, and advantages of
this invention will be more apparent after a reading of the
following detailed description, appended claims, and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a perspective view of a schematic of a chassis
frame or carriage in a workstation;
[0024] FIG. 2 is a perspective view of a portion of one rail of a
chassis frame that is located within an acceptable tolerance range,
and is found by an immobilizer apparatus according to a preferred
embodiment of the present invention;
[0025] FIG. 3 is a plan view of the portion of the chassis frame
and the locator and immobilizer apparatus shown in FIG. 2;
[0026] FIG. 4 is a side view of the portion of the chassis frame
and locator and immobilizer apparatus shown in FIG. 2; and
[0027] FIG. 5 is a side view of the chassis frame and a locator and
immobilizer apparatus according to an alternative embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] Referring now in detail to the Figures, FIG. 1 schematically
illustrates a perspective view of a workpiece or chassis frame 10.
The chassis frame 10 is shown positioned, symbolically, within a
workstation according to an apparatus and method of the present
invention. As illustrated in FIG. 1, the chassis frame 10 is a
welded structure composed of a right and left rail 12 and 14, and
front and rear cross-members 16 and 18 welded therebetween. The
chassis frame 10 is shown resting upon a chassis frame fixture
symbolized by four rest buttons R, a two-way pin 2, and a four-way
pin 4, as is commonly known in the art. As is well known, the pins
2 and 4 necessitate use of corresponding holes or slots in each of
the cross-members 16 and 18, for cooperation therewith. One skilled
in the art will recognize that alternative fixturing arrangements
could be substituted for that described herein without affecting
the novelty of the present invention. The rest buttons R and pins 2
and 4 serve to establish the chassis frame 10 in position freely
upon the fixture.
[0029] As is also well known in the art, the chassis frame 10 may
enter the workstation using any of a number of material handling
systems including an automatically guided vehicle (AGV), a
dedicated sled, or preferably an overhead gantry. Therefore,
identical individual chassis frame fixtures composed of rest
buttons R and pins 2 and 4 can be positioned at each of several
separate workstations along an assembly line, such as is used with
an overhead gantry. Alternatively, one chassis frame fixture can be
positioned on a sled or AGV such that the exact same rest buttons R
and pins 2 and 4 are used from workstation to workstation, for any
given chassis frame 10.
[0030] In the workstation, the chassis frame 10 is positioned on
the rest buttons R and pins 2 and 4 of the chassis frame fixture in
its free state, in other words, its unstressed or relaxed
condition. Since the chassis frame 10 is a welded construction, its
free state is usually a slightly warped or twisted condition due to
the heat effects of preceding welding operations. Typically,
however, any given point of the chassis frame 10 is tolerated to be
out of dimension within a certain acceptable limit, for example
plus or minus 8 mm along any axis, from a nominal design-intent
size or position and with respect to the chassis frame fixture.
[0031] The chassis frame 10 is immobilized in two planes by four
pairs of immobilizing devices I. As will be discussed in structural
detail below, this is accomplished by activating the immobilizing
devices I and allowing plungers or push rods to float in towards
the chassis frame 10 under very low pressure so as to come into
contact with the chassis frame 10 to locate, or "find", the chassis
frame 10 in its free state position. Each of the immobilizing
devices I is actuated accordingly, and function so as to find
reference surfaces on the chassis frame 10. During this finding
phase, the immobilizing devices I come into contact with the
chassis frame 10 at the various reference surfaces and produce a
slight force, approximately 8 psi of effort, on the frame so as to
firmly establish contact with the various portions of the chassis
frame 10. Upon all of the immobilizing devices I establishing
contact and finding the chassis frame 10, each immobilizing device
I locks up under hydraulic force sufficient to render the chassis
frame 10 immovable from its free state so that work can be
performed on the chassis frame 10 in the form of establishing net
datum locating features on the chassis frame 10. The net datum
locating features to be established may be similar to that as
taught in commonly owned U.S. Pat. No. 4,760,633 to Dacey et al. or
any other convenient net locating scheme.
[0032] Alternatively, the chassis frame 10 could be located in
three planes, or only one plane if desired, by using immobilizing
devices I specifically located to accomplish the desired result. As
such, the immobilizing devices I of the present invention may be
configured in any manner to accommodate any material handling
system for the chassis frame 10, and are not limited to the exact
configurations disclosed herein.
[0033] Therefore, as long as the chassis frame 10 is within the
acceptable variation limit, it is preferable to find or locate the
chassis frame 10 wherever it is in its free state and rather than
forcibly clamp the chassis frame 10 back toward its nominal or
design-intent position. In this manner, the chassis frame 10 is not
distorted or displaced by the immobilizing devices I, as would be
the case using a prior art clamping method. According to the
present invention, the immobilizing devices I simply find and then
confine, restrict, or restrain the chassis frame 10 from moving
from its free state, such that the chassis frame 10 is immobilized
in its free state during operations that are performed thereupon,
such as forming, drilling, or fastening operations. In this way,
formed pads, holes, fasteners, and other features are fabricated in
net datum position on the chassis frame 10, at their design-intent
location, with respect to the position of the chassis frame 10 that
is established by the rest buttons R and pins 2 and 4. More
importantly, these welds, holes, fasteners, and other features
remain at design-intent location even after the chassis frame 10 is
released from the immobilizing devices I since the force of the
immobilizing devices I is equalized from both sides of the chassis
frame and cancels itself out so that no external load is applied to
the frame in its free state location. The present invention is not
limited to only the above-mentioned operations on vehicle chassis
frames, but is also applicable to any other carriage or frame
structure. The immobilizing devices I will now be described in
structural detail below.
[0034] FIGS. 2 through 4 specifically illustrate the preferred
embodiment of the present invention, showing front and rear
dual-axis immobilizing devices 22A and 22B that are represented by
the symbols I in FIG. 1. As shown in FIG. 2, the front and rear
dual-axis immobilizing devices 22A and 22B are mounted to a floor
or a workstation platen 20 within a workstation of an assembly
line. A portion of the right-hand rail 12 of the chassis frame 10
spans the front and rear dual-axis immobilizing devices 22A and
22B. The rear dual-axis immobilizing device 22B is shown in a
completely retracted or home position, whereas the front dual-axis
immobilizing device 22A is shown in a completely advanced or work
position in contact with the chassis frame 10. Pairs of guide posts
24 are mounted to the workstation platen 20, that are used to
prevent the chassis frame 10 from crashing into the immobilizing
devices 22A and 22B upon being loaded thereto, and establish outer
tolerance limits of an acceptable chassis frame 10. One skilled in
the art of manufacturing chassis frames will readily recognize that
the chassis frame 10 may be lowered to its position as shown when
the immobilizing devices 22A and 22B and associated components are
fully retracted out of the way. The chassis frame 10 is preferably
lowered into position by an overhead gantry (not shown), but may
also be lowered using a lift deck on an AGV (not shown), as is well
known in the art.
[0035] With regard to each of the front and rear dual-axis
immobilizing devices 22A and 22B, there is shown an hydraulic unit,
or lower work support 26, bolted to the workstation platen 20,
directly underneath the chassis frame 10. Positioned just inboard
of the right-hand rail 12 of the chassis frame 10, is an inboard
stanchion 28 bolted to the workstation platen 20. In turn, an
inboard work support 30 is bolted to the top of the inboard
stanchion 28. Opposite the inboard work support 30, a transfer
assembly 32 is shown bolted to the workstation platen 20. The
transfer assembly 32 includes a riser plate 34 bolted to the
workstation platen 20 and supporting a pair of guide rails 36
bolted thereto. In turn, the guide rails 36 support pillow blocks
38 bolted to the bottom of a transfer plate 40. The transfer plate
40 supports a transfer stanchion 42 extending upwardly therefrom,
the transfer stanchion 42 supports an upper mounting block 44 that
is bolted thereto, and the upper mounting block 44 supports an
upper work support 46 with a bolting arrangement, directly opposite
the lower work support 26. The upper work support 46 is aligned
with respect to the lower work support 26 such that the operational
axes of the work supports 26 and 46 are coaxial. Similarly, the
transfer stanchion 42 supports an outboard mounting block 48 that
is bolted to the side thereof and that has an outboard work support
50 bolted thereto. The outboard work support 50 is aligned with
respect to the inboard work support 30 such that the operational
axes of the outboard and inboard work supports 50 and 30 are
coaxial.
[0036] Each of the work supports 26, 30, 46, and 50 is a standard
work support unit including pneumatic advance, hydraulic lock, and
spring return functions. Preferably, the work support is a Hytec
model number 100847 available from SPX Corporation. Such work
supports are typically proposed for hydraulic clamping applications
with precisely controlled high clamping forces. Nevertheless, each
support 26, 30, 46, and 50 includes a plunger 52 or piston rod
displaceably mounted therein that terminates in a pad 52A. Each
plunger 52 is normally biased to a home or retracted position by a
spring (not shown) within its respective work support. As will
later be described in greater detail, each plunger 52 individually
advances under pneumatic pressure necessary only to overcome the
retracting bias force of its spring and to overcome friction to
extend the plunger 52 to an advanced position against the chassis
frame 10 in the process of finding the reference surfaces on the
chassis frame 10. Pneumatic pressure can be precisely adjusted and
controlled to vary plunger contact force with the chassis frame 10,
and should be balanced between opposed plungers 52 so that a zero
net force is applied to the chassis frame 10. It is important to
note that the plunger force of the present invention is not to be
confused with clamping forces typically employed with prior art
clamping arrangements. The plunger force is only that which is
necessary to make contact with the chassis frame, and is not at all
sufficient to reposition, or displace the chassis frame, as with
prior art clamping arrangements.
[0037] Upon finding the reference surfaces on the chassis frame 10,
the plungers 52 are locked in place using hydraulic pressure to
immobilize the plungers by contracting a sleeve or collet (not
shown) within their respective work support that circumscribes each
plunger 52 and lockingly grips each plunger 52 in its advanced
position. Once the plungers 52 are locked in place they remain
rigid and limit elastic deflection. The work supports 26, 30, 46,
and 50 are supplied and controlled with hydraulic and pneumatic
fluid systems as is very well known in the art, and exemplified by
the 1998 SPX Hytec catalog. It is considered to be well within the
knowledge of one of ordinary skill in the art to select and apply
any of a multitude of such fluid power and control systems and
variations thereof to communicate and operate the work supports, as
specified herein.
[0038] In accordance with the present invention, the preferred
operation and method first involves loading the chassis frame 10 to
the dual-axis immobilizing devices 22A and 22B by an overhead
gantry (not shown). As illustrated by the rear dual-axis
immobilizing device 22B in FIG. 2, the transfer assembly 32 and
work supports 26, 30, 46, and 50 must be fully retracted to their
home positions, to provide clearance for the chassis frame 10 to
enter the workstation. The chassis frame 10 is loaded to the front
and rear dual-axis immobilizing devices 22A and 22B such that it
rests on a chassis frame fixture having pins and rest buttons, not
shown here, but as described previously with respect to FIG. 1.
Still referring to FIG. 2, the guide posts 24 mounted to the
workstation platen 20 help guide the chassis frame 10 into the
correct position with respect to the front and rear dual-axis
immobilizing devices 22A and 22B and thereby help avoid collision
of the chassis frame 10 with the work supports 26, 30, 46, and
50.
[0039] Once the chassis frame 10 is loaded to the front and rear
dual-axis immobilizing devices 22A and 22B, each transfer assembly
32 of each of the front and rear dual-axis immobilizing devices 22A
and 22B advances from its home or retracted position, as shown by
the rear dual-axis immobilizing device 22B, to its advanced
position, as shown by the front dual-axis immobilizing device 22A.
For illustrative purposes, only the front dual-axis immobilizing
device 22A is shown in its advanced position. Each transfer
assembly 32 is preferably advanced using a hydraulic cylinder (not
shown) that advances the transfer plate 40 toward the chassis frame
10 to a positive stop, and each transfer assembly 32 is retracted
by the hydraulic cylinder by pulling the transfer plate 40 back to
another positive stop. The positive stops are integrated into a
positive stop detail 37, as is well known in the art.
Alternatively, a ball screw device (not shown) could be used to
advance and retract the transfer assemblies 32. Such advancing and
retracting devices and applications thereof are well known to
persons of ordinary skill in the art. Also well known in the art
are pneumatic and hydraulic systems for actuating the work supports
26, 30, 46, and 50 of the present invention. Such systems include
computer controls, power sources, control valves, and fluid and
electrical circuits that connect to the work supports and that are
all well within the realm of knowledge of one skilled in the
art.
[0040] Once each transfer assembly 32 is advanced to an advanced
position, each plunger 52 is then individually pneumatically
advanced from a retracted position in order to find respective
opposite portions of the chassis frame 10 wherever it may be
located within its tolerance range and thereby establish an
advanced position for each plunger 52, as best shown in FIG. 4.
Referring again to FIG. 2, and as mentioned above, the work
supports 26, 30, 46, and 50 are oriented such that the plungers 52
are coaxially aligned in opposed orientation. Each plunger 52
continues to advance individually until the respective pad 52A
finds the surface of the chassis frame. Upon finding the chassis
frame 10, the plungers 52 cease any further advancement so as not
to deflect or displace the chassis frame 10.
[0041] Preferably, the pneumatic pressure advance of the plungers
52 is set to a predetermined minimal value to prevent deflection or
displacement of the chassis frame 10. The pneumatic pressure is
selected so that it is only slightly greater than that required to
overcome static friction and the spring force associated with each
plunger 52, in order to displace each plunger 52 from its retracted
position with the work support 26, 30, 46, or 50 toward the chassis
frame 10. In any case, since the plungers 52 are in opposed
orientation, the plunger forces are cancelled out to a net
effective zero force imparted to the chassis frame. Preferably,
however, the preset pneumatic pressure must be determined through
experimentation, by choosing a pressure setting that does not yield
any deflection or displacement of the chassis frame 10 upon contact
of the plunger 52 with the chassis frame 10. With regard to a test
model, the pneumatic pressure was set to a value less than
approximately 8 psi. It is reasonable to expect, however, that
other predetermined minimum values will need to be experimentally
determined on a case-by-case basis for different workpieces used in
different workstations. In summary, each plunger 52 finds
respective opposing portions of the chassis frame 10 without
measurably displacing the chassis frame 10, despite where the
chassis frame 10 is relative to its design-intent position within a
specified tolerance band.
[0042] After each plunger 52 has found the chassis frame 10 and is
in contact therewith, the sleeves (not shown) within the work
supports 26, 30, 46, and 50 hydraulically lock the plungers 52 in
place in their advanced position, and the pneumatic pressure is
relieved. As such, the work supports 26, 30, 46, and 50 do not
hydraulically 5 advance the plunger. Rather, the work supports 26,
30, 46, and 50, via the sleeves therein, constrain the plungers 52
from any axial movement. Likewise, the plungers 52 do not impart
any force along their respective axes to the chassis frame 10. In
this way, the chassis frame 10 is passively immobilized, trapped,
constrained, restricted, or restrained by the plungers 52 so that
there is no gap or slack between the plungers 52 and the surface of
the chassis frame 10. In contrast, the chassis frame 10 is not
forcibly or actively clamped, clenched, or gripped by the plungers
52.
[0043] Once the chassis frame 10 is immobilized as described above,
desired manufacturing operations, such as forming, piercing, or
fastening, are then performed upon the chassis frame 10 to produce
net datum features as more fully described in U.S. Pat. No.
4,760,633 to Dacey, Jr., owned by the common assignee hereof and
incorporated herein by reference. The desired features are produced
in the chassis frame 10 in its free state and net with respect to
the rest buttons and pins of its chassis frame fixture. In other
words, in the absence of any clamping forces upon the chassis frame
10, the desired features are manufactured net to the chassis frame
fixture, and thereby net to design-intent and the theoretical
centerline of the chassis frame 10. Accordingly, the desired
features will remain in position, as manufactured, with respect to
the theoretical centerline of the chassis frame 10, from
workstation to workstation, without being deflected or displaced by
the work immobilizing apparatus. Alternatively, a piercing
apparatus similar to that disclosed in the '026 Dacey, Jr. device,
as described in above, can be used in addition to the present
invention in order to pierce a hole relative to a specific net
datum feature on the chassis frame 10.
[0044] When such manufacturing operations have been completed, the
work supports, and hence the plungers 52, are unlocked by releasing
the hydraulic pressure applied thereto. The plungers 52 then
automatically retract from their advanced positions to their
retracted positions by virtue of the return spring force acting
upon the plungers 52. The transfer assemblies 32 are also retracted
so that the chassis frame 10 can be lifted out of the
workstation.
[0045] FIG. 5 illustrates an alternative embodiment of the present
invention wherein a single-axis immobilizing device 60 is mounted
atop a workstation platen 62.. It is contemplated that several such
single axis immobilizing devices 60 can be used and oriented
horizontally or otherwise with respect to any axis of the chassis
frame 10, instead of vertically as shown. The single-axis
immobilizing device 60 includes a riser block 64 bolted to the
workstation platen 62 that supports a pair of guide rails 66 bolted
thereto. In turn, the guide rails 66 support pillow blocks 68
bolted to the bottom of a tombstone weldment 70.
[0046] The tombstone weldment 70 includes a base 72, a vertical
platen 74, and a gusset 76 welded therebetween. The vertical platen
74 supports an upper platen 78 and an opposed lower platen 80
spaced a distance apart from and substantially parallel to the
upper platen 78. The upper and lower platens 78 and 80 extend
horizontally outwardly from the vertical platen 74 and are welded
thereto, using gussets 82 for support. Guide bars 84 extend
between, and are fastened to, the fixed upper and lower platens 78
and 80. Upper and lower bars or pads 86 and 88 are mounted loosely
about the guide bars 84 between the upper and lower platens 78 and
80. The upper pad 86 is spaced parallel with respect to the lower
pad 88 a predetermined distance above the lower pad 88. The upper
and lower pads 86 and 88 are moveably mounted about the guide bars
84 such that they are displaceable between a home or retracted
position, and an advanced position as shown.
[0047] Work supports 90 are fixed to the upper and lower platens 78
and 80 respectively such that plungers 92 of the work supports
contact locking surfaces 86A and 88A of the upper and lower pads 86
and 88. Similarly, a pair of opposed threaded body cylinders 94 are
disposed between the upper and lower pads 86 and 88 such that they
are oppositely fastened, one into the upper pad 86 and one into the
lower pad 88, and have plungers 96 that find workpiece contact
surfaces 86B and 88B of the respective opposite upper and lower
pads 86 and 88. Preferably, the work supports 90 are a Hytec model
100998 spring advance type, and the threaded body cylinders 94 are
a Hytec model 11AA spring return type, or equivalent.
[0048] In accordance with the alternative embodiment of the present
invention, the associated operation and method involves loading the
chassis frame 10 to the single-axis immobilizing device 60 via an
AGV (not shown). Accordingly, the immobilizing device 60 must be
fully retracted to a home position, to provide clearance for the
chassis frame 10 to enter the workstation. Additionally, the
threaded body cylinders 94 are in their fully extended position.
The chassis frame 10 is loaded to the workstation such that it
rests on an AGV chassis frame fixture having pins and rest buttons,
as described above.
[0049] Once the chassis frame 10 is loaded to the workstations, the
immobilizing device 60 advances from its home position to its
advanced position, as described above in the preferred embodiment.
Accordingly, the upper and lower pads 86 and 88 respectively extend
over and under the chassis frame 10 such that the chassis frame 10
is in position therebetween. The distance between the upper and
lower pads 86 and 88 in the extended position is such that each pad
86 and 88 is nominally spaced from the respective surface of the
chassis frame 10. The spacing is equal to the chassis frame 10
positional tolerance, for example 8 mm as stated previously, from a
nominally sized and positioned chassis frame 10. Due to the spring
advance, each of the work supports 90 is in constant contact with
its respective upper and lower pad 86 and 88. Pressure is then
slowly relieved from each of the threaded body cylinders 94, until
the spring force of the work supports 90 advances the plungers 92,
and thereby the upper and lower pads 86 and 88 into contact with
the chassis frame 10 in order to find respective opposite portions
of the chassis frame 10 and thereby establish an advanced position
for each upper and lower pad 86 and 88. As with the pneumatic
pressure described in the preferred embodiment, the spring force of
the work supports 90 is selected such that the spring force is
sufficient to displace the pads 86 and 88 but is insufficient to
deflect or displace the chassis frame 10 upon contact therewith. In
other words, upon finding the chassis frame 10, the upper and lower
pads 86 and 88 cease any further advancement so as not to deflect
or displace the chassis frame 10. In summary, each pad 86 and 88
finds respective opposite portions of the chassis frame 10 without
measurably displacing the chassis frame 10 despite where the
chassis frame 10 is relative to the chassis frame fixture, within
acceptable tolerance limits.
[0050] Once the upper and lower pads 86 and 88 have found the
chassis frame 10 and are in contact therewith, sleeves (not shown)
within the work supports 90 hydraulically lock the plungers 92 in
place in their advanced position. As such, the work supports 90 do
not hydraulically advance the plunger 92. Rather, the work supports
constrain the plungers 92 from any axial movement. Likewise, the
plungers 92 do not impart any force along their respective axes to
the pads or the chassis frame 10. In this way, the chassis frame 10
is gently or passively immobilized, trapped, constrained,
restricted, or restrained by the upper and lower pads 86 and 88 so
that there is no gap or slack between the pads 86 and 88 and the
chassis frame 10. In contrast, the chassis frame 10 is not forcibly
or actively clamped, clenched, or gripped by the upper and lower
pads 86 and 88.
[0051] After the chassis frame 10 is immobilized as described
above, desired manufacturing operations, such as forming, piercing,
or fastening, are then performed upon the chassis frame 10 to
produce desired features, as described in the preferred embodiment.
Once such operations have been completed, the work supports 90, and
hence plungers 92, are unlocked by releasing the hydraulic pressure
applied thereto. The threaded body cylinders 94 are actuated to
advance their plungers 96 and thereby overcome the spring force of
the work supports 90 and hence spread the upper and lower pads 86
and 88 apart. The immobilizing device 60 is then retracted so that
the chassis frame 10 can be advanced out of the workstation.
[0052] While the present invention has been described in terms of a
preferred embodiment, it is apparent that other forms could be
adopted by one skilled in the art. Additionally, the verb "to
locate" as used in describing the present invention is used in the
passive sense. That is to say, it is used in the sense of finding
or discovering the workpiece, and is not used in the sense of
displacing the workpiece against a fixture. Accordingly, the-scope
of the present invention is to be limited only by the following
claims.
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