Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Description
Apparatus_and Method for Fabricatin~ Wood Trusses
Technical Field
The present invention relates generally to wood trusses
used in building construction and in particular to an
apparatus and method for fabricating wood trusses.
Back~round Art
According to prior practice, wood trusses msy be
10 fabricated by placing the top and bottom chords in position
on a movable support surface, such as a truss assembly ~ig,
and by attaching the vertical connector members and web
members between the chords with corrugated fasteners or nails
to hold the vertical connector members and web members in
15 position. Stop members are typically positioned in contact
with the top and bottom chords along the respectlve outer
surfaces thereof to hold the truss members securely in
position on the moveable surface of the jig.
A first set of connector plates is placed over the
20 joints at which the verticsl connector members and web
members intersect the top and bottom chord~ on the upwardly
facing ~urface of the truss and tapped so that the teeth of
the connector plates are slightly imbedded into the wood to
hold them in place. A lifting device is then used to raise
25 the truss from the support surface sufficiently to place a
second set of connector plates under the truss on the ~oints
on the downwardly facing surface of the truss at
substantially the same locstions as on the upwardly facing
surface thereof. At this stage, connector plates are
30 positioned on the trus3 joints on both the upwardly and
downwardly facing surfaces thereof, with the second set of
connector plates positioned between the downwardly facing
surface of the truss and the moveable support surf2ce.
The truss is then carried by the support surface into
35 one or more pressing stations, which are compris-ed of one or
more pairs of pressing rollers, whereby the connector plates
are embedded into the wooden members at the truss joints as
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the truss is passed between each pair of rollers. Camber is
typically imparted to the truss by a plurality of camber
rollers positioned downstream of the first pressing station.
Apparatus and methods known in the art for fabricating
5 wood trusses have several disadvantages and limitations. One
problem associated with such prior art apparatus and methods
i9 that the first pair of pre~sing rollers typically has a
substantially smaller diameter than the sets of pressing
rollers located downstream. The first pair of pressing
10 rollers is used to partially embed the teeth of the connector
plates into the wood members of the truss. The relatively
abrupt curvature of the roller surface, as compared to the
larger diameter rollers located downstream, may impart a
rocking motion to the connector plates, which prevents the
15 teeth from being pressed straight into the wood members.
Another problem associated with such prior art truss
assembly apparatus and methods is the problem of controlling
the amount of camber applied to the truss. It is often
difficult to produce a consistent, predetermined camber
20 because of the difficulty in properly positioning the camber
rollers and in maintaining the camber rollers in position.
The mechanism used to position the camber rollers is
subjected to large mechanical stresses when the truss is
being cambered, which msy result in slippage and free play
; 25 in the camber roller positioning mechanism. S t i 1 1
another problem associated with prior srt apparatus and
methods of fabricating trusses is the problem of maintaining
the truss in proper alignment as the truss passes through the
various stages of pres~ing rollers and through the camber
30 rollers. In order to securely attach the connector plates,
the truss must be moved from the support surface of the jig
before the trus~ enters the final pressing station.
Misalignment of the truss as it passes through the final
pressing station causes critical errors in the fabrication
35 of the truss.
Disclosure of Invention
It is therefore the principal object of the present
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invention to provide sn approved apparatus and method for
~ fabricating wood trusses.
It is another object of the invention to provide an
improved apparatus and method for imparting camber to a wood
5 truss.
It is still another object of the invention to provide
an apparatu3 and method for enhancing the precision and
consistency of the camber imparted to a wood truss.
It i9 yet another object of the invention to provide an
10 improved apparatus and method for attaching metal connector
plates to the joints of a wooden truss.
A further object of the invention is to provide an
improved apparatus for maintaining the truss sub~tantially
in proper alignment during the fabrication of the truss.
These and other objects are accomplished in accordance
with the present invention wherein an apparatus and method
for fabricating truss members into a completed truss is
provided. The truss members are comprised of a plurality of
wood members and a plurality of metal connector plates for
20 ~oining the wood members. The apparatus includes a
relatively flat conveyor surface for supporting the tru~s
members with the connector plates positioned below and on
top of the wood member; means for moving the conveyor surface
with the truss members supported thereon in a predetermined
25 direction; a first pressing station having at least one pair
of pressing rollers disposed substantially in registration
for receiving the truss members therebetween to partially
embed the connector plates into the wood members; and a
second pressing station spaced from the firqt pressing
30 station and beyond the conveyor surface. The second pressing
station has a pair of pressing rollers disposed substantially
in registration for receiving the truss members therebetween
to substantially fully embed the connector plates into the
wood members to complete fabrication of the truss.
In accordance with one aspect of the invention, the
pressing rollers of the second pressing station have
substantially the same size as the pressing rollers of the
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first pres~ing station. In one embodiment 811 of the
pressing rollers have a substantially cylindrical shape and
the diameter of all of the pressing rollers is as large as
practicable in accordance with the spatial constraints of
5 the apparatus. In the preferred embodiment esch of the
pressing rollers has a diameter of at least ten inches. The
use of relatively large diameter pressing rollers in both the
first and second pressing stations has the advantage of
pressing the connector plates into the wood members
10 straighter than when smaller diameter rollers are used
because larger diameter roller~ impart substantially less
rocking action on the front and back ends of the connector
plates than do the smaller diameter rollers.
In accordance with another aspect of the invention, the
15 apparatus includes a plurality of elongated guide rails
extending along the predetermlned direction of movement of
the truss beneath the conveyor surface for supporting the
conveyor surface and the tru~s members. At least one of the
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guide rails extends beyond the first pressing station to
20 maintain the alignment of the conveyor surface. In one
embodiment the plurality of guide rails is comprised of a
central guide rail and two outer guide rails. The two outer
guide rails extend beyond the first pressing station to
maintain conveyor surface alignment. The conveyor surface
25 preferably includes a plurality of cooperating pairs of guide
rollers positioned on an underside thereof for contacting
respective opposite side~ of one of the outer guide rails to
maintain conveyor surface alignment. In another embodiment
the plurality of guide rails is comprised of two outer guide
30 rails positioned adjacent to respective opposite edges of the
conveyor surface and two inside guide rails disposed between
the two outer guide rails. The two outer guide rails extend
beyond the first pressing station to maintain the conveyor
surface alignment. When four guide rails are used, the
35 conveyor surface has a plurality of cooperating palrs of
guide rollers disposed on an underside thereof. The guide
rollers of each cooperating pair contact the respective outer
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surfaces of the two outside guide rails to maintain the
conveyor surface in alignment.
In yet another aspect of the invention, a lifting roller
is disposed between the first and second pressing stations
5 for engaging an underside of a leading portion of the truss
for maintaining the vertical position of the truss as the
truss is moved between the first and second pressing
stations.
In accordance with a further aspect of the invention,
10 the apparatus includes means for selectively imparting camber
to the truss. Switch means i5 positioned between the first
pressing station and the camber means for disabling the
operation of the apparatus when the switch means is activated
by contact with the truss. The switch means is positioned
15 90 that the truss will only contact the switch means when the
truss is improperly aligned with respect to the camber means.
In one embodiment the switch means includes a projection
member which is positioned to contact the truss when the
truss i9 out of alignment. In another embodiment the
20 position of the switch means is adjustable along an axis
which is transverse with respect to the predetermined
direction of movement of the truss to conform to the width
of the truss as measured along the transverse axis. In yet
another embodiment the camber means is comprised of first,
25 second, third and fourth camber rollers. The first and
second camber rollers contact the top chord and the third and
fourth camber rollers contact the bottom chord of the trus~
to apply a bending moment thereto. The third and fourth
camber rollers are adjustable along the transverse axi~ to
30 conform to the width of the truss. The switch means is
mechanically coupled to the third camber roller so that the
position of the switch means is adjustable along the
transverse axis together with the third camber roller.
In accordance with yet another aspect of the invention,
35 the first and second camber rollers are mounted on a first
surface of an arm member, which is pivotally mounted adjacent
to a first side of the apparatus and beyond the conveyor
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surface and the third and fourth camber rollers are
positioned adjacent to a second side of the apparatus,
opposite from the first side thereof. The first and second
camber rollers are out of alignment with respect to an axis
S which is parallel to the predetermined direction of movement
of the truss when the arm member i9 pivoted from a first
position at which the arm member is substantially parallel
to the predetermined direction. The amount of displacement
of the arm member from the first position determines the
10 amount of camber imparted to the truss. Ad~ustment means i9
provided for ~electively pivoting the arm member to position
the arm membe~ to impart the predetermined amount of camber
and engagement means is provided for preventing the arm
member from pivoting back toward the first position after the
15 arm member has been pivoted away from the first position,
thereby counteracting torque exerted on the arm member by
the truss tending to bend the arm member back toward the
first position. In the preferred embodiment, the engagement
mean~ is comprised of a threadedimember, one end of which
20 engages a second surface of the arm member, which is opposite
from the first ~urface thereof on which the fir~t and second
camber rollers are mounted. The rotation of the threaded
member in a first direction moves the threaded member toward
the second surface of the arm member to engage the arm member
25 and prevent it from being moved back toward the first
position. The rotation of the threaded member in a second
direction, opposite from the first direction, moves the
threaded member away from the second surface of the arm
member to allow the arm member to be moved back toward the
30 first position.
In accordance with still another aspect of the invention
the third and fourth camber rollers are maintained
substantially in alignment along an axis which i~ parallel
to the predetermined direction of movement of the truss.
35 Means for adJusting the position of the third and fourth
camber rollers laterally with respect to the predetermined
direction of the truss i~ provided so that the thlrd and
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fourth camber rollers are movable substantially in unison in
~ each direction alGng the lateral axis. In one embodiment the
adjustment means i3 comprised of first and second spaced
apart vertical arms, each of which has a threaded sleeve at
5 each end thereof. The third camber roller i9 mounted on the
first verticsl arm and the second camber roller is mounted
on the second vertical arm. First and second cooperating
pairs of threaded shaft~ extend laterally with respect to the
predetermined direction of movement of the truss. The
10 individual shafts in the first cooperating pair extend
through corresponding sleeves on the first vertical arm so
that the ~haft threads en8age complementary threads in the
corresponding sleeves. The individual shafts in the second
cooperating pair extend through corresponding sleeves on the
15 second vertical arm 90 that the shaft threads engage
complementary threads in the corresponding sleeves. Means
for rotating the first and second cooperating pairs of shafts
in unison is provided ~o that the engagement between the
shaft threads and the sleeve threads results in movement of
20 the first and second vertical arms and the corresponding
third and fourth camber rollers laterall~ along the
corresponding shafts.
In accordance with a further sspect of the invention,
the apparatus includes drive means for moving the conveyor
25 surface with the truss members supported thereon in a
predetermined direction. The drive means is comprised of
first and second chain and sprocket drives in ~paced parallel
relationship. Each of the chain and sprocket drives has
first and second end sprockets with a drive chain disposed
30 on the end sprockets to define a continuous loop drive. The
first end sprocket of the ~irst chain and sprocket drive is
substantially aligned with the corresponding first end
sprocket of the second chain and sprocket drive along a first
axis extending laterally with respect to the predetermined
35 direction and the second end sprocket of the first chain and
sprocket drive is substantially aligned with the
corresponding second end sprocket of the second chain and
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sprocket drive along a second axis extending laterally with
respect to the predetermined direction. A first plurality
of elongated members extends laterally with respect to the
predetermined direction for connecting the corresponding
5 first end sprockets and a second plurality of elongated
members extends laterally with respect to the predetermined
direction for connecting the corresponding ~econd end
sprockets. The elongated members are substantislly rigid
for maintaining the corresponding first end sprockets in
lO substantially parallel relationship and the corresponding
second end sprockets in substantially parallel relationship.
In yet another aspect of the invention camber is
imparted to the truss by providing a relatively flat surface
for supporting the wood members of the truss; mounting first
15 and second sets of restraining members at selected fixed
positions on the support surface 90 that the restraining
members define a boundary corresponding to the desired
configuration of the truss to be cambered; and placing the
wood members on the support surface within the boundary
20 defined by the restraining members 90 that the connector
plate~ are disposed below and on top of the wood members.
Web members are connected to the top and bottom chords to
urge the chords into contact with corre~ponding ones of the
restraining members 90 that an outwardly facing surface of
25 the top chord contacts respective inwardly facing surfaces
of the first set of restraining members and an outwardly
facing surface of the bottom chord contacts respective
lnwardly facing surfaces of the second set of restraining
members, so that the restraining members exert a bending
30 moment on the top and bottom chords to impart camber to the
truss.
In the preferred embodiment the support surface is
comprised of a plurality of elongated slats oriented
trsnsversely with respect to the major axis of the support
35 ~urface. Selected ones of the slats have a plurality of
openings spaced at predetermined intervals along the
respective major axes of the corresponding slats.
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Corresponding openings of ad~acent ones of the slats are
offset relative to one another along the respective major
axes of the corresponding slats 80 that imaginary line
segments connecting the corresponding openings define a curve
5 representing the desired amount of camber to be imparted to
the truss. The restraining members have respective base
portions with a plurality of holes extending therethrough.
Selected ones of the holes are positioned in regi~tration
with ~elected ones of the openings in the corresponding slats
10 for mounting the restraining members thereon. In accordance
with the present invention camber is imparted to the truss
prior to the attachment of the metal connector plates, which
facilitates the cambering operating, particularly when heavy
duty trusses are bein8 fabricated for commercial
15 applications.
Brief Descri~tion of the DrawinRs
Further ob~ect3 and advantages of the invention will be
apparent from the detailed description and claims when read
in conjunction with the accompanying drawings wherein:
FIGURE 1 is a perspective view of an apparatus for
fabricating a wood truss in accordance with the present
invention;
FIGURE 2 is a top plan view of the apparatus of FIGURE
1, emphasizing selected portions of the Apparatus;
FIGURE 3A is a side elevation view of a first embodiment
of the apparatus according to the present invention;
FIGURE 3B is a side elevation view of a portion of a
second embodiment of the apparatus;
FIGURE 4 is an end elevation view of the apparatus
30 according to the present invention, viewed from the discharge
or downstream end of the apparatus;
FIGURE 5 is a side elevation view of a portion of the
apparatus, illustrating means for lifting the truss as it
passes through the pressing ststion~ in the apparatu~;
FIGURE 6 is a top plan, partial cu~away view,
illustrating the mechanism by which selected ones of the
camber rollers are positioned to impart predetermined camber
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to the truss;
FIGURE 7 is a side elevation view, illustrating the
positioning of a cut-off switch for stopping the operation
of the apparatus when the truss is out of alignment; ~ ~ -
FIGURE 8 is an end elevation view, illustrating three
guide rails beneath the movable support surPace of the
apparatus;
FIGURE 9 is a top plan view of the table sectlon of the
apparatus on which the truss members are disposed,
10 illustrating the means by which camber is imparted to the
truss prior to the attachment of the metal connector plates;
~ IGURE 10 is a top plan view detailing a portion of the
apparatus and truss depicted in FIGURE 9;
FIGURE 11 is a perspective view of a portion of a chain
15 and sprocket drive system for the apparatus; and
FIGURE 12 is a circuit diagram illustrating means for
selectively enabling and disabling the apparatus; and
FIGU~E 13 is an end elevation view, illustrating three
chain drives and four guide rails beneath the moveable
20 support surface of the apparatus.
Best Mode for CarrYin~ Out the Invention
In the description which follows like parts are marked
throughout the specification and drawings, re~pectively.
The drawings are not necessarily to scale and in some
25 instances proportionq have been exaggerated in order to ~ore
clearly depict certain features of the invention.
Referring to FIGURES 1, 2, 3A and 4, an apparatus 10 for -~
fabricating wood trusses in accordance with the present
invention is comprised of a table section 12 and a head
30 section 14. Table section 12 includes a motor-driven -` i
conveyor, which is preferably comprised of a pair of
parallel, continuous loop chain and sprocket drives 16A and
16B, which are attached to the respective undersurfaces of
a plurality of parallel steel slats 18, which define conveyor
35 surface 19 of table section 12. Selected ones of slats 18
have a plurality of pre-drilled threaded holes (not shown)
therein for positioning a plurality of tooling blocks (as
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will be described in greater detail hereinafter with
reference to FIGURE 9) on the corre9ponding top surface5
thereof for anchoring the chord9 of the truss while the web
members and vertical connector members are placed
5 therebetween. The actual placement of the tooling blocks is
adjusted to fit the dimensions of the truss being assembled.
Head section 14 has a first pressing station with first
and second pairs of press rollers 20 and 22, respectively,
for partially embedding the connector plates into the truss
lO members as the truss passes between each pair of rollers 20
and 22. Roller pairs 20 and 22 are comprised of respective
top roll,ers 20A and 22A and bottom rollers 20B and 22B for
exerting a pressing force in a direction which is
substantially perpendicular to the plane of movable conveyor
15 surface 19. Top rollers 20A and 22A are independently
adjustable along a vertical axis to adjust the spacing
between each top roller 20A and 22A and its corresponding
bottom roller 20B and 22B to conform to the thickness of the
truss being fabricated. The vertical adjustment of top
20 rollers 20A and 22A is accomplished in a conventional manner,
such as by means of a screw-operated adjustment mechanism,
as described in U. S. Patent No. 3,667,379.
A second pressing station, located downstream of the
first pressing station, includes a third pair of rollers 24,
which is comprised of a corresponding top roller 24A and
bottom roller 24B for completing the attachment of the
connector plates to the truss members after the predetermined
camber has been applied to the truss. The connector plates
must be embedded into the truss by first and second sets of
rollers 20 and 22 sufficiently to ensure that the plates are
not dislodged during the cambering operation and yet not so
much as to prevent the camber rollers from imparting the
desired amount of camber to the truss. Camber is applied to
the truss by means of four camber rollers 26, 28, 30 and 32.
Camber rollers 26 and 28 engage the top chord of the truss
and camber rollers 30 and 32 engage the bottom chord of the
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truss. The operation of the camber rollers will be described
in greater detail hereinafter.
In one aspect of the invention, rollers 20A and 20B, 22A
and 22B, and 24A and 24B all have substantially the same
5 diameter. The sequential action by which the plates are
embedded into the truss members is controlled by the vertical
adjustment of the three top roller~ 20A, 22A and 24A with
respect to their corresponding bottom rollers 20B, 22B and
24B, as previously described. The diameter of each of these
10 rollers is preferably as large as possible within the spatial
constraints of head section 14. The larger diameter rollers
tend to press the connector plates into the truss members
much straighter than when smaller diameter rollers are used
because of the more gradual curvature of the surface of the
15 larger diameter rollers, which reduces the rocking action
on the upstream and downstream ends of the connector plates.
A roller diameter on the order of 10 inches is usually
sdequate.
Referrin8 to FIGURE 3B, an alternate embodiment of an
20 apparatus 11 for fabricating wood trusses has three pairs of
rollers 21, 23 and 25 in the flrst pressing station instead
of two pairs. A fourth pair of rollers 27 is positioned in
the second pressing station. All of the rollers comprising
first, second, third and fourth pairs of rollers preferably
25 have substantially the same diameter. The use of three pairs
of rollers instead of two in the fir~t pressing station is
advantageous when large, heavy duty trusses for commercial
buildings are being fabricated because of the larger truss
members and connector plates used, which reguire 8reater
30 pressing forces to embed the connector plates.
Referring again to FIGURES 1, 2, 3A and 4, all three
pairs of press rollers 20, 22 and 24 are driven by means of
a common chain and sprocket drive arrangement 29, as best
seen in FIGURE 1, which is slaved to chain and sprocket
35 drives 16A and 16B 90 that the press rollers are
synchronously driven in connection with movable conveyor
surface 19. The motive apparatus for the chain and sprocket
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drives assoclated with movable conveyor surface 19 and roller
sets 20, 22 and 24 is provided by an electric motor 34, which
turns the aforementioned chain and ~procket drives through
a reduction gear 36. An air clutch 38 i8 interposed between
5 motor 34 and reduction gear 36 to provide a smooth startup
for apparatus 10 so the connector plates positioned between
the truss and the top surface of slats 18 do not 91ip during
start up.
Referring also to FIGURE 8, each slat 18 i9 attached to
10 drive chains 40A and 40B compri~ing chain and sprocket drives
16A and 16B at respective opposite ends of each slat. Three
elongated guide rails 42A, 42B and 42C are disposed beneath
slats 18 for maintainin8 the alignment of slats 18 along a
predetermined downstream direction when appsratus 10 is being
15 operated so as to move the truss members along table section
12 and into head section 14 in proper position. Selected
ones of slats 18 have a pair of guide rollers 44 positioned
on an undersurface thereof for contacting respective opposite
sides of outer guide rail 42A to keep each slat 18 in proper
alignment. Each guide rail 42A, 42B and 42C has a low
friction material 43 disposed thereon to facilitate the
sliding actlon of slats 18 along guide rail~ 42A, 42B and
42C. Low friction material 43 is preferably comprised of
UHMW (ultra-high molecular weight) polyethylene material.
In another aspect of the invention center guide rail 42C
is added to outside rails 42A and 42B to better support slats
18 and the truss members being carried thereon. The addition
of center guide rail 42C prevents sagging at the center of
movable conveyor surface 19, which can lead to deformation
30 of the truss and improper positioning thereof as the truss
enters head section 14. In another embodiment, as shown in
FIGURE 13, four guide rails 42D, 42E, 42F and 42G are
provided for supporting conveyor surface 19, ~uch that there
are two outside rails and two inside rails. A guide roller
35 44 i9 positioned in contact with the outside surface of each
- of the two outside rails to guide the slats along the rails.
Three chaln and drive mechani~m~ 16C, 16D and 16E are
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posltioned as shown in FIGURE 13, with guide rails 42D and
42E positioned between chain and drive mechanisms 16C and 16D
and guide rails 42F and 42G positioned between chain and
drive mechanisms 16D and 16E, to increase the driving force
5 imparted to the conveyor. This configuration i9 well-suited
for the fabrication of hea~y duty trusses for commercial
application.
In yet another aspect of the invention, as best seen in
FIGURES 2 and 5, outer guide rails 42A and 42B are extended
10 beyond the first pressing station in head 3ection 14 in order
to maintain con~eyor surface l9 in proper alignment as the
connector plates are being partially embedded into the truss
members in head section 14. As best seen in FIGURE 5, outer
guide rails 42A and 42B extend to a posltion which is
15 substantially coterminous with drive shaft 48 at the
downstream end of chain and sprocket drives 16A and 16B,
although only guide rail 42A and chain and sprocket drive 16A
are depicted in FIGURE 5. It i8 at this location that chain
and sprocket drive 16A and, of course, chain and sprocket
~0 drive 16B on the opposite side, make a U-turn at the
downstresm end of the continuous loop chain and sprocket
drives. An elongated roller 50 is positioned at the inlet to
the second pressing station and beneath camber roller~ 26 and ~ -~
30 for lifting truss 52 upwardly 90 that the truss 52 clears
25 lower press roller 24B as truss 52 continues its downstream 1
movement. Lifting roller 50 preferably spans substantially
the entire width of apparatus 10. -~
Referring to FIGURES 2 and 7, an electrical cut-off
switch 54 is posltioned downstream of chain and ~procket
30 drives 16A and 16B at the inlet to the second pressing
station. Switch 54 is mounted on an elongated bar 56, which
is in turn attached to an arm 58 on which camber roller 30
is mounted. Arm 58 has a pair of threaded sleeves 60
disposed at respective opposite ends thereof for engaging
35 complementary threads on a pair of parallel shafts 62, which
extend laterally with respect to the direction of movement
of truss 52. Camber roller 32 i8 mounted in substantlally
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the same manner on arm 64, which engages a corresponding pair
of parallel shafts 66.
Camber rollers 30 and 32 are positioned in contact with
the bottom chord of tru~s 52. The position of camber rollers
5 30 and 32 is ad~usted laterally with respect to the axis of
movement of truqs 52 to conform to the width dimensions of
the truss being fabricated. As camber roller 30 i~ moved
laterally, cu~-off switch 54 i9 also moved laterally ~o that
the position of cut-off switch 54 is adjusted in accordance
10 with the width of truss 52. If truss 52 is out of alignment
as it moves pa~t the down~tream end of conveyor surface 19,
truss 52 will contact switch 54, which automatically disables
motor 34 and air clutch 38 and stops the operation of
apparatus 10, as shown in FIGURE 12. Motor 34 must be
15 restarted and then air clutch 38 before apparatus 10 can be
reactivated. An emergency stop cable extends around the
perimeter of the entire apparatus 10 and associated machinery
to disable motor 34 and air clutch 38 when the cable is
pulled. Apparatus lO cannot be reactivated until motor 34
20 is fir~t restarted and then air clutch 38.
Referring also to FIGURE 3A, a limit switch 55 is
mounted on frame 57 for engaging a projection 59 mounted on
a particular slat 18 to temporarily disable apparatus 10 when
switch 55 is open. Switch 55 is normally in a closed
25 position, but is open when pro~ection 59 engages switch 55.
Pro~ection 59 includes a cam member, which engages a cam
roller attached to switch 55 to open switch 55. As shown in
FIGURE 12, air clutch 38, but not motor 34, is disabled when
switch 55 is open. In this manner apparatus 10 is
30 temporarily disabled after each truss fabrication cycle to
allow the operators to position the truss components on
conveyor surface 19 for the next fabrication cycle. Thus,
apparatus 10 will be started from and stopped at
substantially the same position for each cycle. Keeping
35 motor 34 running decreases the time required be~tween cycles
by eliminating the delays assoc~ated with motor ~tart-up.
Referring specifically to FIGURES 2, 3A and 4, camber
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rollers 30 and 32 are movable laterally with respect with the
axis of movement of truss 52 by means of a common adjustment
device. Each pair of threaded shafts 62 and 66 i8
mechanically slaved together by means of a common chain and
5 sprocket mechanism 61, as best qeen in FIGURES 2 and 3A.
Chain and sprocket mechanism 61 is operated by means of a
handle 68. The direction in which handle 68 is turned
determines the direction of rotation of chain and sprocket
mechanism 61, which in turn determines the direction of
lO rotation of threaded shafts 62 and 66, thereby causing arms
58 and 64 and their respective camber rollers 30 and 32 to
move in the desired direction laterally with respect to the
axis of movement of truss 52. In this manner camber rollers
30 and 32, which contact the bottom chord of truss 52, are
15 ad~usted together in a single step operation, which
facilitates the adjustment process and enhances the
positioning accuracy of camber rollers 30 and 32.
Referring to FIGURES 2 and 6, camber rollers 26 and 28,
which contact the top chord of truss 52, are mounted on a
20 pi~ot arm 70 which pivots about a vertical axis passing
through a position indicated at 72. A crank handle 74 i9
turned to ad~ust the position of pivot arm 70. The more that
camber roller 28 is moved out of alignment with camber roller
26, the greater will be the camber imparted to truss 52. To
25 prevent slippage of pivot arm 70, which can result in errors
in the truss camber, and to mechanically strengthen pivot arm
70 and hold it in a fixed position, a stabilizer bolt 76 is
positioned in contact with back surface 70A of pivot arm 70,
which is opposite from front surface 70B of pivot arm 70 on
30 which camber rollers 26 and 28 are mounted. Bolt 76 is
adjusted snug again~t back surface 70A of pivot arm 70 to
counteract the torque which tends to bend pivot arm 70 away
from truss 52 when camber is being imparted thereto. A nut
77 holds bolt 76 in position in housing 79, which has aligned
35 threaded openings for receiving bolt 76 and engaging
complementary threads on bolt 76.
Referring to FIGURE 9, an alternate embodiment for
Zf Z'~
1 33~559
-17-
imparting camber to truss 52 i9 depicted. As previously
mentioned, selected one of slats 18 have a plurallty of pre-
drilled threaded holes 75 at selected positions along
corresponding ~lats 18 for receiving corre~ponding tooling
5 blocks 78, which are used to hold the truss members in
position during the fabrication process. Holes 75 are
po~itioned at intervals of approximately one and one-half
inches along the corresponding slats 18. Individual slats
18 having holes 75 are arranged at approximately two foot
10 intervals along the axis of movement of conveyor surface 19.
Each tooling block 78 has a series of holes on the base
portion thereof at intervals of approximately three-fourths
of an inch. Each block 78 is affixed to a corresponding slat
18 by positioning two of the holes in block 78 in
15 registration with a selected pair of holes 75 on the
corresponding slat 18 and by bolting block 78 to the
corresponding slat 18. The positions of blocks 78 may be
ad~usted in increments of approximately one-half inch.
Tooling blocks 78 are positioned to define the desired lines
20 along which truss 52 is to be cambered. Top chord 52A,
bottom chord 52B, web members 52C and vertical members 52D
are forced into position between fixed blocks 78 to form the
outline of truss 52. Connector plates 80 are positioned over
the truss ~oints both above and below truss 52, as previously
25 described. At this ~uncture, connector plates 80 have not
yet been embedded into the truss joints 90 that less force
is required to impart camber to trus~ 52 than when camber
rollers are used in the second pressing station after
connector plates 80 have been partially embedded into truss
30 52. Tooling blocks 78 hold the truss members in position to
maintain the desired amount of camber as truss 52 is moved
through the first and second pressing stations in which
connector plates 80 are fully embedded into trusg 52, thereby
eliminating the need for camber rollers in the second
35 pressing station.
Referring to FIGURE 10, holes 75 on each slat 18 are
preferably offset slightly, along an axis which i9 trangver9e
1 33~55~
-18-
relative to the movement of conveyor surface 19, with respect
to the corresponding holes 75 on ad~acent slats 18 so that
imaginary line segments connecting corresponding holes 18 on
adjacent Qlats 18 approximate a curve representing the
5 desired amount of camber of truss 52. Holes 75 are pre-
drilled to specifications depending upon the desired camber.
For example, if the desired amount of camber is such that the
center of each trus~ chord i9 displaced approximately three-
fourths of an inch from an axis connecting the ends of the
10 truss for each 40 foot span of truss (a radius of curvature
of approximately 3,200 feet), holes 75 are predrilled 90 that
the top and bottom chords will be bent to define that
approximate arc when the chords are positioned between
tooling blocks 78. FIGURE 10 illustrates the central portion
15 of bottom chord 52B, which is bent by tooling blocks 78 to
impart the desired amount of camber. Although not shown in
FIGURE 10, the top chord is also cambered the same amount as
bottom chord 52B by corresponding tooling blocks positioned
to define the desired camber arc. It is easier to impart the
20 camber before the connector plates are embedded, particularly
when heavy duty trusses, which may be comprised of 4x4 or
even larger chords, are being fabricated. Blocks 78 are
mounted in the corresponding holes 75 in accordance with the
width of the truss (i.e., the distance between the respective
25 outer surfaces of the top and bottom chords).
Referring to FIGURE 11, four elongated rigid bars 82 are
attached at their respective opposite ends to the facing
ma~or surfaces of sprockets 84A and 84B at both ends of chain
and sprocket drives 16A and 16B in order to stabilize
30 sprockets 84A and 84B and prevent the sprockets from wobbling
during operation. Although only the downstream ends of chain
and sprocket drives 16A and 16B are shown, one skilled in the
art will appreciate that the two sprockets at the upstream
ends of drives 16A and 16B also have four stabilizer bars 82
35 extending therebetween. Bars 82 are disposed at
substantially equal angular intervals around central drive
shaft 48 connecting sprockets 84A and 84B.
1 332559
-19-
. Various embodiments of the invention have now been
described in detail. Since it iq obvious that changeq in and
sdditions to the above-described preferred embodiment msy be
made without departing from the nature, spirit and scope of .
5 the invention, the invention is not to be limited to said
details, except as ~et forth in the sppended claims.
, . ,. :.. , , .s.,. - .... ,. :: . . : ::,,:: , : .: .: . , . - . : . .. . ~ .
