Note: Descriptions are shown in the official language in which they were submitted.
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ROLLER TOOL AND POSITIONAL PRESSURE METHOD OF
USE FOR THE FORMING AND JOINING OF SHEET MATERIAL
Field of the Invention
[0001]The present invention relates to systems for forming and joining a first
sheet
material to a second sheet material. More particularly, the present invention
relates
to a pressure-controlled roller tool and method of use in the forming and
joining of
sheet material.
Description of the Relevant Art
[4002]One of the earliest operations required in the history of automobile
assembly
was the joining of an inner panel to an outer panel to form any of a variety
of body
parts, including doors, engine hoods, fuel tank doors and trunk lids, all
referred to
as "swing panels" which encase the vehicle frame. Known machines for the
forming and joining of sheet materials include the press-and-die set, the
tabletop
and the roller-forming tool, the latter being the most-recently introduced
device.
[0003]An unfortunate feature of forming and joining materials with the roller
forming
tool is the difficulty in controlling the variable pressures required by the
tool. A
certain approach has been undertaken to overcome this problem.
[0004] One known effort to control the variable pressures required by a roller-
forming tool to form sheet material is the employment of an air bladder for
mechanical compliance sandwiched between the faceplate of a robotic arm and
the
roller-tool in conjunction with a closed loop pneumatic pressure feedback
circuit that
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dynamically controls the pressure of the bladder. This technique was developed
during the era of on-line robotic path programming, and low speed operation.
'i
[0005]The robotic arm maneuvers the bladder and roller-tool along the variable
terrain of the sheet material while maintaining a constant distance between
the
faceplate of the robotic arm and the sheet material surface. When a change in
pressure at the roller-tool is commanded, or an imbalance is detected in the
closed
loop feedback circuit, the bladder pressure is altered to compensate.
[0006] However, the reaction time for pneumatic compressions and
decompressions required for stabilization is finite, limiting the speed of a
roller- .
forming tool equipped with a pneumatic system to 200mm/sec. This speed
limitation allows for what is known in the art as low volume production only.
[0007]Another known effort to control the variable pressures of existing
systems
has been to use servo motor amperage feed back sampling directly from the
controller of the robotic arm. However, this sampling does not allow for
mechanical
compliance of either the forming tool or the servo positioning system. This
latter
approach is clearly the least desirable.
[0008]Accordingly, prior approaches have failed to solve the speed limit
problem
associated with the control of the variable pressures required when forming
and
joining sheet materials at speeds over 200mm/sec.
SUMMARY OF THE PRESENT INVENT10N
(0009] It is thus the general object of the present invention to provide an
apparatus
and method that overcomes the problems of known techniques for forming and
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joining a fiirst sheet material to a second sheet material to form a swing
panel tar an
automobile.
j0010] ft is a particular object of the present invention to provide a
positionai
pressure roller tool for forming and joining a first sheet material to a
second sheet
material that includes an expeditious method for controlling the variable
pressures
of the tool.
j001 i ~ It is a further object of the present invention to provide such a
positional
pressure roller tool, which may include both a main roller and a touch-up
roller.
[0012]Another object of the present invention is to provide such a positional
pressure roller tool that is flexible enough to accommodate panels of various
sizes,
shapes, and contours.
j0013]A further object of the present invention is to provide such a
positional
pressure roller tool that may be used in conjunction with a robotic arm in
operation
with a variety of machine cells.
[0014]These and other objectives are achieved by the provision of a positional
pressure roller tool which is operatively associated with a programmable
positioning
apparatus in the form of a robotic arm and a machine cell which includes a
holder
for a first panel in the form of a lower nest, and a holder for a second panel
in the
form of an upper gate. The positional pressure roller toot or positional-
pressure-
variance-unit ["PPVU"] includes a cylinder head with a captured reciprocating
piston
and shaft. A biasing element in the form of a compression spring is located
inside
the cylinder and atop the piston. The biasing element urges the piston to an
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extending position. Forming steels and roller-forming tools are also attached
to the
end of the shaft.
[0015]A pair of married sheet materials, A and B, is approximated onto the
lower
nest. The first sheet material A is then precision positioned by means of
crowders.
The upper gate thereafter aligns the second sheet material B with respect to
the
first sheet material A by ~ known means. The first sheet material.A ,is then
securely
held in place either~by known means or by a vacuum system such as disclosed
and
claimed in PCT/US04/34238, incorporated by reference herein.
[0016]Thus held in place, a seaming operation executes, forming and joining
the
first sheet material A to the second sheet material B by means of the roller-
forming
tools attached to the PPVU. A positional program of the robotic arm orientates
the
PPVU in a generally perpendicular attitude with respect to the surface normal
of the
lower nest shape at the roller-forming tool contact point. The programmabiy
positioned distance between the robotic arm's faceplate and the lower nest
dictates
the pressure applied to the surface of the sheet material. The distance is
such that
the spring will compress and exert a quantitative force back through the
rolier-
forming tool.
[0017]This force exerted by the PPVU is countered by the robotic arm, which
inherently exhibits flexing of the steel structure comprising its body, and
backlash
movement within the gearing comprising its mechanical knuckles.
[0018] Robotic flexing and backlash introduces positional error. This error is
the
deviation between the physical position of the PPVU and that of the programmed
position. Thus, programmed error compensation is required.
',
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[0019]The combined errors are recorded and charted at sequential coordinates
as
the robot reaches away from itself, and at sequential pressures that would be
used
to form sheet material. The chart is built into an algorithm and used to
compensate
for deviation errors in the positional pressure programming of the PPVU.
[0020] Once the pressures are established, the positional program controls the
robotic arm such that the distance between the faceplate and the lower nest is
variably controlled while the roller-forming tool drives along the seams of
sheet
material A to be formed and joined. The roller-forming tool pressure-forms
material
A to lay over material B while being supported by the lower nest. Once all the
seams are formed, the joining operation is complete.
[0021]These and other objectives are accomplished by the provision of an
apparatus and method for the forming and joining of sheet material as set
forth
hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022]The present invention will be more fully understood by reference to the
following detailed description of the preferred embodiments when read in
conjunction with the accompanying drawings, in which like reference characters
refer to like parts throughout the views, and in which:
[0023] Figure 1 is a perspective view of a machine cell incorporating a
positional
pressure roller tool assembly according to the preferred embodiment of the
present
invention;
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(0024] Figure 2 is a sectional view of the roller tool assembly of the present
invention taken along lines 2-2, viewed from the side of the main roller and
illustrating the piston in its substantially unloaded, fully extended
position;
(0025] Figure 3 is a sectional view of the roller tool assembly of the present
invention similar to that of Figure 2 but illustrating the piston in its
substantially
loaded, partially extended position;
(0026] Figure 4 is a sectional view of the roller assembly taken along lines 4-
4,
showing the main roller and the touch-up roller, both rollers having parallel
axles
that are rotatably mounted through the piston shaft, the figure being taken
axially
along the parallel axles;
(0027] Figure 5 is a sectional view of the sheet materials taken along lines 4-
4 of
Figure 1 illustrating the materials in their positions prior to complete
forming; and
(0028] Figure 6 is a view similar to that of Figure 5 but illustrating the
materials in
their farmed positions.
DETAILED DESCRIPTION OF A PREFERRED
EMBODIMENT OF THE PRESENT INVENTION
(0029]The drawings disclose the preferred embodiment of the present invention.
While the configurations according to the illustrated embodiment are
preferred, it is
envisioned that alternate configurations of the present invention may be
adopted
without deviating from the invention as portrayed. The preferred embodiment is
discussed hereafter.
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[0030] With reference first to Figure 1, the preferred embodiment of a machine
cell,
generally referenced as 10, is illustrated in a perspective view. The machine
cell 10
includes an upper gate 20 and a lower nest 30. It should be understood that
the
configuration of the machine cell 10 as illustrated is preferred, but is not
to be
interpreted as limiting as other configurations conceivable to those skilled
in the art
may also be suited.
[0031 ]The machine cell 10 holds two portions of sheet material so that a
joining
process may be undertaken without the sheet material portions being caused to
shift or otherwise move out of position. The two portions of sheet material
include a
first sheet material A and a second sheet material B. The two sheets A and B,
in a
combination resulting from seaming, form an integrated component, of which the
first sheet material A forms the outer part or the skin and the second sheet
material
B forms the inner part or the support structure. (Sheets A and B are
illustrated in
combination in Figure 6, discussed below.) As illustrated, the first sheet
material A
and the second sheet material B have a generally square configuration
resulting in
a generally spuare-shaped integrated component. However, it is to be
understood
that other shapes may be suitable for use in the present invention.
[0032]The sheet materials A, B are captured and held between the upper gate 20
and the lower nest 30. In brief, the sheet materials A, 8 are approximated
onto the
lower nest 30. The lower nest 30 includes a nest surface 32 that is fluidly
connected to a vacuum source (not shown). The first sheet material A is then
precision positioned by means of crowders 34. Thereafter the upper gate 20 is
lowered by a robotic arm or linear slide to a precise location. The gate
aligns the
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second sheet material B with respect to the first sheet material A by way of
alignment pins from the gate engaging master locating holes in material B. The
first
sheet material A is then held in place by a vacuum applied to its under side.
[0033~Thus held in place, a seaming operation is executed for forming and
joining
the first sheet material A to the second sheet material B by means of the
roller tool.
Figure 1 illustrates the PPVU as an assembly 50 in operational association
with a
robotic arm 52. The PPVU assembly 50 mounts rigid to a robotic arm faceplate
54
that is rotatably connected to the robotic arm 52. The robotic arm 52 is
itself in
operative association with a computer 56. The computer 56 preferably effects
movement of the robotic arm 52 by a specific program as will be discussed
further
below. The PPVU assembly 50 includes a main roller tool 58 and a touch-up
roller
too! 60. Thus mounted through the PPVU assembly 50 to the rotatably attached
faceplate 54 the main roller tool 58 and the touch-up roller tool 60 may be
rotatably
selected depending upon the desired operation.
[0034]A cross-section, of the main roller tool 58 is shown in both Figure 2
and
Figure 3. A cross-section of the roller assembly 50 is shown in Figure 4 and
illustrates both the main roller tool 58 and the touch-up roller tool 60. With
respect
to these figures, the main roller tool 58 is generally and operatively mounted
to the
faceplate 54 by a reciprocating hub 62 having a piston end 64 mounted in a
cylinder 66. The cylinder 66 is fitted rigid to the faceplate 54 of the
robotic arm as is
known in the art. Biasing element or spring 68 biases the piston end 64 away
from
the end wall of the cylinder 66. As an alternative to the use of the
illustrated spring
biasing element 68 a gas-charged cylinder may be placed in the position of the
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spring 68 to execute the needed biasing. In this manner, the PPVU assembly 50
provides a positiona! pressure roller tool whereby the position of the robot
arm
faceplate 54 relative to the lower nest 30 dictates the applied pressure at
the
interface between seam S and the wear surface 78 of the roller 72.
[0035]The main roller tool 58 includes an axle 70 fixedly mounted in the hub
62. A
main roller 72 is rotatably mounted on the axle 70 by a main bearing 74. The
axle
70 includes a main roller support flange 76 that retains the main bearing 74
against
the hub 62. The outer diameter of the main roller 72 may be of a variety of
sizes
but is preferably of the 90 mm size which is known in the art as being a
standard
size.
[0036] Referring particularly to Figure 4, the main roller 72 includes a
hardened
wear surface 78. A face plate 80 is threaded to the main roller 72 thus
locking the
hardened wear surface 78 in place with respect to the main bearing 74.
[0037]The touch-up roller tool 60 includes a spindle 82 that i~ rotatably
carried by
the hub 62 by way of an array of bearings 84. The bearings 84 are disposed
within
a pocket 86 defined into the hub 62. A locking member 88 is threadably
attached
to one end of the spindle 82 thus capturing the bearings 84 there between. The
bearings 84 are themselves retained in the hub 62 by a faceplate 90 that is
screwed to the hub 62.
[0038]A tool insert 92 is slidingly positionable within an aperture 94 defined
in the
<,
end of the spindle 82 opposite the threaded end onto which the locking member
88
is attached. The tool insert 92 slip fits into the aperture 94 and is
selectively locked
in place with a bail lock interface 96. The ball lock is an industry standard
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configuration that allows the tool insert to be removed by pushing a ball
bearing 98
via an access hole 100 back into and compressing a spring 102 against a
retaining
plug 104 prior to removal. The outer diameter of the tool 92 may be of a
variety of
sizes but is preferably of the 20 mm size which is known in the art as being a
standard size. As is also known in the art the toot insert 92 may be stepped
and
may have two or more surfaces of different diameters.
[0039]The main roAer tool 58 and the touch-up roller tool 60 operate in
conjunction
with the robotic arm and the pressure system of the present invention. When no
pressure is applied to the materials to be joined the biasing element 68 of
the roller
assembly 50 urges the piston end 64 in its outwardly extended position.
Conversely, when pressure is selectively applied to the roller assembly 50 by
means ~of the robotic arm the piston end 64 may be reciprocatingly urged into
the
cylinder 66 by the opposing force of the material being formed. The biasing
element (or gas-charged cylinder) 68 acts to resist the inward movement of the
piston end 64.
[0040)The bias of element (or gas-charged cylinder} 68 is linearly
proportional to
piston end 64. Each unit of linear distance piston end 64 moves into cylinder
66
will increase the bias of element 68 in a linear proportion. In the event that
a gas-
filled cylinder is used in lieu of the spring 68 a charge is built up therein
and the
piston end 64 moves into cylinder 66. This linear relationship is the basis
for the
~~positionai pressure variance programming that the robotic arm plays.
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Operation
[0041]The operation of the machine cell 10 will now be generally described. As
the
operation begins the upper gate 20 should already be in its elevated position,
assuming that a seaming operation has already been completed and the seamed
part has been removed, thus leaving the tower nest 30 empty.
[0042] Initially a known quantity of mastic ("M" as shown in Figure 5) is
applied to
the approximate surface areas at which the first sheet material A will be
joined to
the second sheet material B. The mastic is utilized to provide a more complete
joining of the sheet materials. The mastic may be joined to one of the sheets
or to
both as may be desired. Known mastics may include glass bead-filled
compositions as are known in the art.
[0043]The machine cell 10 may then be operated by a human operator or by a
programmable logic controller as is known in the art. Regardless of the form
of the
operator, reference shall be made hereafter generically to "the operator."
[0044] Once the mastic has been selectively applied to sheets A and 8, the
operator married the first sheet material A to the second sheet material B,
then
places the combined sheets on the nest surface 32 with the first sheet
material A
face down (that is, the outer surface of the sheet material A is placed onto
the nest
surface 32). The crowder assemblies 34 (two crowders are illustrated but it
should
be understood that there is preferably one or more crowder for each side) are
then
activated by operation of a second air pressure source to advance the
alignment
fingers to their engaged and aligning positions. So engaged, the first sheet
metal A
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is in alignment relative to the nest surtace 32. This arrangement facilitates
positive
micro-positioning of the first sheet material A.
[0045]The operator then engages the robotic arm or linear slide (neither
shown) to
lower the upper gate 20 into an engaged position with material B. The robotic
control provides that movement of the upper gate 20 with a precise attitude.
j004f]Once the first sheet material A is in position, a vacuum source is
activated to
provide a vacuum between the surface of the first sheet material A and a
plurality of
vacuum channels (not shown). The first sheet material A is thus immobilized.
With
the combined assembly of the first sheet material A and the second sheet
material
B secured within the machine cell 10, an air pressure source (not shown) is
activated and the fingers of the crowder assemblies 34 are drawn away from
their
illustrated aligning positions to substantially horizontal positions. Thus
positioned,
the fingers will not interfere with the subsequent forming operation.
[0047]The forming operation then occurs by which a seam is formed around the
periphery of the combined unit of the first sheet material A and the second
sheet
material 8. With reference to Figures 5 and 6, the forming operation is
performed
in two stages. First the flange F is formed from a generally upright position
A to a
preform position A'. Next the flange F is formed from the preform position A'
to a
final form position A". The seam S is formed to capture and thus join the
first and
second sheet materials A, B. As noted above, seaming of the first sheet
material A
with the second sheet material B is accomplished by either the main roller
tool 58 or
the touch-up roller tool 60. Selection between the two of these rollers 58, 60
is
made depending upon accessibility of the material to be seamed. Specifically,
the
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touch-up roller tool 60 may be selected in the event that the main roller tool
58 is
too large for effective cornering and may thus cause undesired deformation of
the
sheet material B, or in the event that the surface terrain of the combined
sheet
materials exhibit a tight radial form that flows between inward and outward
with
respect to the frame, thus rendering use of the larger main roller toll 58
impractical.
[0048aAn advantage offered by the present invention lies in the off-line
programming of the robotic arm 52 which controls the main roller tool 58 and
the
touch-up roller tool 60. As the main roller tool 58 is engaged to undertake
the
seaming operation, it is anticipated that the. robotic arm 52 will experience
a certain
amount of structural deflection and backlash of its gearing that in turn
introduces
positional error. The present invention provides compensation for this error
during
the initial off-line programming and subsequent programming, thus resulting in
accurate seaming that is highly repeatable without loss of accuracy. The error
is
cancelled by a compensated program which is loaded into the computer 56 that
controls the positional articulation of the robotic arm 52 and the variable
pressures
of the rollers 58, 60, as they form the sheet material.
[0049] Once forming and joining of the first sheet material A and the second
sheet
material B is complete, the upper gate 20 is removed from the second sheet
material B and the vacuum source 208 is de-energized causing the first sheet
material A to be re-mobilized from the nest surface 32. The joined sheet
materials
A and B are unloaded from the top of the nest surface 32 and the next pair of
sheet
materials A and B is loaded. The joining and seaming operation is thus
repeated.
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[0050]Those skilled in the art can now appreciate from the foregoing
description
that the broad teachings of the present invention can be implemented in a
variety of
forms. Therefore, while this invention has been described in connection with
the
particular examples thereof, the true scope of the invention should not be so
limited
since other modifications will become apparent to the skilled practitioner
upon a
study of the drawings, specification and following claims.
