Note: Descriptions are shown in the official language in which they were submitted.
CA 02578308 2011-01-25
APPARATUS FOR COATING A PIPE SURFACE
The present invention relates generally to the field of apparatus for
coating an inside surface of a pipe.
BACKGROUND OF THE INVENTION
Pipes are often used to carry fluids or abrasive slurries as part of a
treatment or disposal process. As the fluid passes through the pipe,
frictional forces
against the pipe walls can cause the pipe walls to wear. The effect of these
frictional
forces is magnified on the curved portions of the pipe as a result of complex
flow
patterns and the forces from the fluid impacting the pipe surface caused by
the fluid
io changing direction. Abrasives suspended within the fluid (e.g. solids
commonly
associated with mining slurries or sludge) can be even more detrimental to the
pipe
walls. Whatever the cause, these forces cause the pipe walls to wear even
faster,
eventually causing the pipe walls to crack or burst where the walls have worn
thin.
To minimize the effects of these frictional forces on the pipe walls, a
1s protective coating is applied (e.g., welded or sprayed) to the inner
surface of the
pipe. To provide effective protection against wear on the pipe wall, it is
important
that the entire area is completely coated with the coating material. Areas
left
unprotected will continue to be vulnerable to fracture.
A prior patent owned by the present Applicants which is US Patent No:
20 6,171,389 which corresponds to Canadian Patent Application No: 2,302,083
(Hannu) published October 12th 2000 discloses an apparatus for coating an
interior
surface of a pipe which has a support rod with a substantially square cross
section
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that extends axially along the interior surface of the pipe. An index carriage
slidably
engages the substantially square cross section of the support rod so that the
index
carriage maintains a fixed rotational orientation relative to the support rod.
An index
motor having a variable index position is carried by the index carriage. An
electric
welding head for coating the interior surface of the pipe with weld material
is
rotatably attached to the index carriage and connected to the index motor. As
such
the head has an elevation position that corresponds to the index position of
the
index motor. A drive motor carried by a drive carriage propels the drive
carriage
longitudinally along the support rod. The drive carriage and the index
carriage form
io a train with a series of intermediate carriages that slidably engage the
substantially
square cross section of the support rod to move longitudinally along the
support rod
The welding torch applies an abrasion resistant surfacing such as
tungsten carbide to the interior wear surfaces of large industrial pipe elbows
and S-
bends. The abrasion resistant surface is essentially formed through a welding
is process where layer after layer of weld beads are applied to the pipe in
the axial
direction.
A machine has been built and used extensively based on this patent
and has achieved considerable commercial success. It does however have a
number of areas where problems can arise and where improvements are desirable.
20 On this machine, the tracking bar is unsupported over the free length that
the
welding torch travels. This limits the travel distance because as the
unsupported
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length of the bar is increased oscillation and deflection problems are
encountered.
Presently the maximum travel distance is 11 feet.
Instability in the support system can create two main obstacles to fast,
efficient welding of the pipe elbows and s-bends. First is the droop of the
support
rod in the center of the pipe. This droop hinders the ability of the welder to
complete
a straight and even path through the pipe. Furthermore, the larger the bend
radius
of the pipe, the greater the effect of droop has on the quality of the welds.
A second area of concern is with respect to the unwanted oscillatory
motion that can develop in the support rod. Clearly this affects the ability
to produce
io a straight, even and acceptable weld.
The current welding set-up is in some cases not stable enough to
reliably produce fast and accurate welds in both directions of travel.
Instability can
develop into an unintended oscillating motion of the welding head that is
entirely
incompatible with the welding process used to layer the pipe. Due to the
instability
of the guiding system the operators generally can weld in one direction only.
This
combined with difficulty to rapidly return to the starting weld position can
dramatically
affect the welding cycle time.
Within a welding environment there come a number of challenges.
First is temperature, expected to range between 250 and 450 degrees
Fahrenheit.
In addition to temperature, welding smoke, ultraviolet light and weld splatter
must all
be taken into consideration.
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Another prior example of the prior art in this field is disclosed in U.S.
Patent No. 4,513,443 (Kostecki). Kostecki discloses an apparatus for coating
an
internal wall of a curved pipe with a layer of protective material. The
apparatus has
a guide means, a longitudinally flexible member, means for applying a coating,
s means for incremental rotation by the longitudinally flexible member, a
drive means
to drive the longitudinally flexible member relative to the curved pipe, and a
means
to automatically step the flexible member and consequently rotate the coating
means. However, a disadvantage of using the flexible member in Kostecki is the
associated inaccuracy in translating the rotational steps along the
longitudinally
io flexible member. Because the coating means cannot be accurately rotated,
the
protective material can be misapplied resulting in either gaps or overlap
between the
applied strips of protective material.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide a modified apparatus
is of the above general type which may overcome one or more of the above
problems
of the above machines.
According to a first aspect of the present invention there is provided an
apparatus for coating an interior surface of a pipe, the pipe having an
exterior
surface, an interior surface and a curved longitudinal axis extending between
two
20 ends and the pipe having distortions from a cylindrical shape so that a
radial
distance of the interior surface from the longitudinal axis varies at
positions along the
pipe; the apparatus comprising:
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an elongate support member extending continuously along the interior
of the pipe between the two ends and which is curved along its length to
follow the
longitudinal axis of the pipe;
a series of spacer straps each attached between the interior surface of
5 the pipe and the elongate support member at spaced positions therealong for
supporting the elongate support member within the pipe;
the spacer straps being arranged so that the elongate support member
is supported within the pipe at a position spaced from the interior surface
and
parallel to and above the longitudinal axis;
to an operating carriage mounted on the elongate support member for
movement therealong;
the elongate support member and the operating carriage having
cooperating elements which maintain the operating carriage at a fixed
rotational
orientation relative to said elongate support member;
1s the elongate support member and the operating carriage being
arranged so that the operating carriage runs along the elongate support member
and passes the spacer straps;
an electric welding head arranged to apply parallel beads of welding
material onto the interior surface of the pipe to form a coating covering the
interior
20 surface of the pipe;
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a head drive system carried by the operating carriage for moving the
electric welding head relative to the operating carriage in directions both
angularly
around and radially of the elongate support member; and
a carriage drive system for driving the operating carriage longitudinally
along said elongate support member;
wherein the head drive system comprises a multi-axis robotic arm able
to dynamically adjust the electric welding head relative to the operating
carriage in
said directions both angularly around and radially of the elongate support
member;
wherein the multi-axis robotic arm comprises a three parallel axis
to system including a shoulder axis connected to the operating carriage, an
elbow axis
and a wrist axis connected to the electric welding head with a first one of a
pair of
arms between the shoulder axis and the elbow axis and a second one of the pair
of
arms between the elbow axis and the wrist axis;
and where in the multi-axis robotic arm is arranged with the shoulder
axis at the center of the pipe on the longitudinal axis of the pipe.
Preferably the head drive system is PLC controlled.
Preferably the head is an electrical welding head although other
coating systems can be used. Where a welding head is used, the head drive
system
preferably maintains a preset electrical stick-out relative to the pipe
surface as the
distance of the surface from the carriage varies.
Preferably the head drive system maintains a preset electrical stick-out
by detecting variations in welding parameters.
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Preferably the head is an electrical welding head and wherein there is
provided a control system for controlling the head drive system and the
carriage
drive system able to program in all welding parameters including wire feed
speed,
amperage, arc voltage, torch travel speed, electrical stick-out and bead
overlap.
Preferably the support rod is carried within the pipe by at least one
connection member connected between the rod and the pipe.
Preferably the at least one connection member comprises a series of
pre-cut spacer straps.
Preferably the multi-axis robotic arm comprises a three parallel axis
io system including a shoulder axis connected to the carriage, an elbow axis
and a
wrist axis connected to the head with a pair of arms between the shoulder axis
and
the elbow axis and between the elbow axis and the wrist axis.
Preferably the shoulder pivot axis is located in the center of the pipe to
allow for smooth, easy, and accurate angular placement of the head.
Preferably the support rod is square or rectangular and the carriage
includes guide wheels supporting the carriage on the corners of the support
rod.
Preferably the guide wheels are arranged in opposed pairs at the front
and rear of the carriage.
Preferably the head is an electrical welding head and a wire feeder is
mounted just behind the head, therefore minimizing the distance over which the
wire
is pushed to the head.
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Preferably the head is an electrical welding head and a wire feeder is
pull style wire feeder located as close to the welding head as possible.
Preferably the wire feeder includes roller wire guides at the angle
transition between the head which extends radially and an axially extending
liner.
The welding cycle time; defined as the portion of time spent welding
versus time spent in set-up and adjustments to the machine may be increased
significantly in order to dramatically improve production.
It is desirable for the machine to process pipes ranging from 17 inch
inside diameter to 47 inch inside diameter and be capable of full length
welding of a
io 30" 5D90 pipe with a 24 foot center line length and welding an 18" 3D90
pipe with
54" center line radius.
In addition to welding elbow pipes and S-bends, it is desirable that the
machine be capable of welding straight pipes and concentric reducers with a
circumferential weld pattern.
is Weld parameters may provide a wire speed up to 220 inches per
minute at 29-32 volts and 600 amps. This is based off of a 7/64 wire diameter,
welding with 0.75 inch to 1.5 inch of electrical stick-out. Welding travel
speed may
be set at a maximum of 65 inches per minute. The welding head is generally
orientated at 90 degrees to the direction of travel and at an angle of attack
of 15
20 degrees with respect to the previous weld bead but this can be varied.
The ability to weld on each side of the pipe without the need to remove
and reattach the welding head is another desirable feature that will allow for
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increased cycle times and versatility. The welding head may be liquid cooled
and a
shroud to cover the support bar from weld splatter may also be provided.
The arrangement described hereinafter provides a four axis torch
positioning system with weld tracking capabilities. The carriage rides along
the
guide rod and supports a three axis manipulator arm. The arm may allow for
precise
positioning of the torch along the weld path at any position within the lower
180
degrees of the pipe. After this the system is inverted to coat the top half.
Weld tracking feedback may be provided to allow the arm to guide
itself in order to follow the path of previous weld beads.
Welding in both directions of travel is the ideal solution to increase
cycle time and the arrangement described hereinafter may have this ability.
The
arrangement described hereinafter uses a tie rod cart system which may include
the
ability to rapidly return to the starting position for improved cycle times if
two
directional welding is not feasible in general or applicable to a particular
job.
Is The carriage preferably rides on the corners of the bar and not on the
flats of the bar to produce a more stable carriage with good acceptance for
tracking
around bends.
The support rod is preferably supported on one or more straps along
its length extending from the bar to the inside surface of the pipe to help
combat the
issues associated with the droop of the bar. By supporting the support rod,
the
droop can be reduced significantly, and the moment effects created by larger
bend
radius pipes may be eliminated. The oscillatory effects may also be
significantly
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I0
reduced with the addition of the strap support as the free length of the bar
is reduced
and the system is stiffened.
The support strap or straps can simply be tack welded to the support
rod and to the top of the pipe provided that the pipe is large enough to
facilitate a
manual welder. The carriage may have a slot to incorporate clearance for this
support strap to pass as the welding assembly passes through the midpoint of
the
pipe. In situations where a manual tack joint is not possible an alternate
method
may be required if the levels of droop or oscillation are found to be
unacceptable.
One possible alternative in controlling the droop and oscillatory
Io movements of the bar is to use a pre-cambered bar, or camber a bar in the
pipe by
manipulating the end supports. An air cylinder or jack screw can then be
connected
to the center of the bar and use it to apply pressure to the top of the pipe.
This force
may act against the cambered bar to produce a more rigid and stiff support of
the
support rod.
The final point of concern with respect to the support rod stability deals
with the bars end supports. The end supports may be designed to allow for a
rigid
clamping of the support rods yet allowing ease of adjustment for alignment
purposes. In addition to the above requirement the ability to induce camber
into the
bar may provide a comfortable degree of flexibility. The connection between
the
support rod and the in-feed bar may need to be fortified to ensure a rigid
connection,
especially if a camber is to be introduced through it.
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it
A four axis manipulator arm and weld tracking system ensures that any
complications that may arise from the support rod droop or misalignment or out
of
round pipe can be easily corrected through automatic adjustment of the welding
head. The arm may be adjusted by detecting the weld parameters primarily the
current draw which indicates the distance of the torch tip from the pipe
surface.
One option is to provide a system for tracking previous weld bead by
which the manipulator arm can ensure that following welds remain straight and
in
line with the initial weld bead. This in conjunction with the above mentioned
improvements to the support rod system will produce a uniform and complete
weld
to pattern on the interior surface of the pipe.
As is well known, the pipe bending process often creates pipes with
oval diameters in the bent section of the pipe, as opposed to the true round
diameter
of the pipe outside bent sections. This creates difficulties for welding set-
ups that
incorporate fixed stick-out settings as the deviation in diameter through the
bend
section of the pipe can often be outside the acceptable variation in allowed
stick-out.
The arrangement described herein provides a four axis torch
manipulator arm able to dynamically adjust the torch position and thus
maintain
proper stick-out parameters despite variations in pipe diameter along the
direction of
travel. System stick-out will need to be monitored in real time in order to
provide
adequate feedback to the manipulator arm to allow it to adjust accordingly. A
number of options are available to monitor stick-out, including optics, laser
scanning
and weld voltage or current monitoring. The arrangement described hereinafter
may
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incorporate stick-out monitoring into the weld tracking capabilities of the
control
system.
The arrangement described herein uses push style wire feeders
mounted on the carriages outside the pipe to reduce the size and weight of the
components that the support rod must support. A pull style wire feeder can be
used
to reduce liner wear significantly by simply placing the wire in tension and
thus
reducing outward force on the liner. This requires a relatively light wire
feeder of
relatively small physical size.
In order to reduce wear on the liners at the torch the arrangement
io described herein may incorporate a water cooled torch with a robust wire
guiding
system.
The arrangement described herein uses a welding head manipulator
arm which is attached to the support carriage that is designed specifically to
ride
along the support rod. Three independent axes of control allow for precise
angular
and radial positioning anywhere within the bottom 180 degrees of the pipe.
Each
axis uses a dedicated servo-motor and gearbox sized accordingly to accommodate
anticipated payloads.
One servo-motor and gearbox is located at the "shoulder" of the arm
and used to provide course angular positioning of the welding head tip.
Another
servo-motor gearbox combination is located at the "elbow" of the arm and works
in
conjunction with the shoulder motor to provide fine angular positioning as
well as
radial positioning. At the "wrist" of the arm the final servo-motor and
gearbox
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provides precise welding head angle adjustment for the varying locations
within the
pipe.
With intelligent control of these three axes the welding head is able to
be positioned accurately anywhere within the bottom 180 degrees of the pipe
with no
mechanical adjustments required. This allows the operators to weld and switch
between either side of the pipe effortlessly.
The range of motion may be limited making it necessary to use
different upper arms lengths to incorporate the entire range of pipe diameters
that
the machine must be able to work with. Three different length arms may be
io interchangeable in a manner that will allow for a fast, accurate, and
repeatable swap
of components. One arm may be used for pipes with inside diameters between 17
and 27 inches. Another may be used for pipes with inside diameters ranging
from
27 to 37 inches and the final arm for pipes with inside diameters between 37
and 47
inches. Care may be taken to center the shoulder pivot point in the center of
the
pipe to allow for smooth, easy, and accurate angular placement of the welding
head.
The carriage case may need to be open along the top to allow the
middle support rod support to pass unobstructed. This opening may be sealed
through the use of brushes to allow the incorporation of some positive air
pressure to
help combat contamination of the rolling elements. The design may include a
support mount for the manipulator arm as well as connections for the tie rod
push
mechanism.
BRIEF DESCRIPTION OF THE DRAWINGS
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14
The present invention can be more readily understood in conjunction
with the accompanying drawings, in which:
Figure 1 is a top plan view of an apparatus showing the type of
machine with which the present invention is concerned and showing the pipe in
cross section.
Figure 2 is a side cross sectional view taken along lines 2-2 of Figure
1.
Figure 3 is an isometric view of a welding carriage of the present
invention removed from the support track.
Figure 4 is an isometric view of the base frame of the welding carriage
of the present invention removed from the support track and with the welding
and
drive components removed.
Figure 5 is a front elevational view of the frame of Figure 4.
Figure 6 is an isometric view of the welding torch and wire feed of
Figure 3.
Figure 7 is an isometric view of an intermediate carriage of the
apparatus of Figure 1.
Figure 8 is front elevational view of the intermediate carriage of the
apparatus of Figure 7.
DETAILED DESCRIPTION
An apparatus 10 is shown In Figures 1 and 2 and includes a frame 12
supports a drive carriage 13 and a support rod 14. The support rod 14 extends
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is
along the length of the frame 12 and beyond the frame 12 above the floor on
which
the frame stands so that the support rod 14 can be extended through a pipe 15
generally parallel to the axis of the pipe. In Figure 1, three intermediate
carriages 16
and an operating carriage 17 are shown for movement along the support rod 14.
s An additional support carriage 18 is provided in advance of the
operating carriage 17 to provide support for components of the system
including
control cables and other elements as required which are to be supported at a
position spaced from the operating carriage so as to keep them away from the
operating components as described hereinafter.
io The support rod 14 is shaped to provide support for the carriages as a
train of carriages so that each carriage travels longitudinally along the
support rod 14
in a fixed orientation relative to the support rod 14. For example, the
support rod 14
can have a square cross section so as to co-operate with a square receptacle
on
each of the carriages as shown in Figure 5. The intermediate carriages are
is connected to one another between the drive carriage 13 and the operating
carriage
17 with tie rods.
A coating head 20 which is preferably a welding head, but could in
other embodiments be a sprayer, nozzle, etc., or even a cleaning device such
as a
brush, is rotationally attached to the operating carriage 17 for movement
therewith.
20 Thus, when the drive carriage 13 is driven the length of the frame 12, as
described
in more detail below. The intermediate carriages and the operating carriage,
move
along the support rod 14 axially through the pipe 15. As the operating
carriage is
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16
moved along the support rod 14, the coating head 20 applies a strip of
protective
coating to the inner wall 21 of the pipe 15 along the pipe.
The coating head 20 is mounted on the operating carriage 17 by a
head drive system 22A, at the end of each longitudinal pass, the head drive
system
is activated to rotate the coating head 20 around the axis of the pipe to a
new
angular orientation, as described in more detail below, and another strip of
protective
coating is applied to the inner wall 21 of the pipe 15 as the operating
carriage is
moved along the support rod 14 by the drive carriage 13.
The frame 12 carries a rack 22 which co-operates with a gear 23A
to driven by a motor 24 on the drive carriage 13 so that operation of the
motor acts to
drive the drive carriage along the frame to force the operating carriage
through the
tie rods and the intermediate carriages to enter into and to pass through the
pipe in a
coating action. Coating can take place in one direction of movement or in both
depending on stability and dimensions of the apparatus. Each coating action is
followed by an angular adjustment of the coating head to apply another strip
of the
coating material.
The frame 12 is preferably straight and the rack 22 extends for a length
at least equal to the length of the pipe 15 that is to be coated. Thus the
entire length
of the pipe 15 that is to be coated can be coated when the drive carriage 13
travels
the length of the rack 22.
The support rod 14 is preferably securely fastened above the frame 12
to a support bracket 231 mounted on the frame 12. The support rod 14 can also
be
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17
fastened using a second support bracket 232 mounted above the floor at the
opposite end.
In operation, each of the above described components of the
apparatus 10 preferably inter-act in the following manner. Typically, the
drive
carriage 13 will alternately move between a fully retracted position and a
fully
extended position. That is, when the drive carriage is in the fully retracted
position,
the drive carriage 13 is positioned near the support bracket 231. When the
drive
carriage 13 is in the fully extended position, the drive carriage 13 is at the
end of the
frame 12 nearest the pipe 15.
30 Turning now to Figures 3, 4 and 5 there is shown more detail of the
operating carriage 17. This comprises a main frame 25 which is generally
rectangular with a front plate 27 and a rear plate 28 and includes a square
opening
26 through the frame to receive the square support rod 14. Above the opening
26 is
a slot 29 which passes though a top plate 30. This slot is narrower than the
opening
26 and is provided to allow the frame to pass by one or more straps which
support
the rod 14 and extend from that rod to the wall of the pipe.
The frame is carried on the support rod by guide wheels 31 which co-
operate with the corners of the rod. Thus the guide wheels are arranged at the
corners of the opening 26 and extend diagonally outwardly therefrom. Each
guide
wheel has a V-shaped groove to engage its respective corner. Two diagonally
opposed ones of the guide wheels are arranged at the front plate 27 and the
other
two at the rear plate 28. The guide wheels are idlers. The guide wheels are
carried
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18
in bearings 32 mounted in the end plates of the frame. One of each pair of
wheels is
spring mounted so as to be pressed inwardly toward its opposed wheel to
provide a
firm grip on the rod to accurately locate the frame on the rod. This prevents
rotation
of the frame around the rod since it is accurately located by the V-grooves.
Each tie rod 19 co-operates with a clevis 33 attached to the end plates
of the frame.
The front plate 27 includes a depending portion 34 which extends
below the frame underneath the rod 14 and which provides a circular receptacle
35
for a first servo-motor 36 carried on the frame. This motor defines an axis
parallel to
to the rod 14 and acts to drive a first arm 37 of the three axis arm system
supporting
the coating head 20. Thus the system includes the servo-motor 36 acting as a
shoulder axis, a second servo-motor 39 acting as an elbow axis and a third
servo-
motor 40 acting as a wrist axis. These co-operate with the arm 37 and a second
arm 41, with the head 20 carried on the third servo-motor to define the three
axis
system.
The welding head is a water cooled head of commercially available
type. This is supplied with electrical current through conductors defining a
positive
supply line 42 and a ground return. Welding rod supplying the coating material
44 is
carried by a feeder 45.
These supply lines are strung over the intermediate carriages to be
carried thereby. The conductors 42 and 43 are simply draped over suitable
supports. The welding rod or wire is fed through a liner which allows it to be
carried
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19
from a supply at the drive carriage on the frame at a required controlled rate
to the
feeder 45.
The feeder 45 is shown in more detail in Figure 6 and includes an
arcuate frame 46 which curves around from the torch or coating head 20 which
projects radially outwardly from the axis of the pipe to the liner 47 which
extends
axially of the pipe. The liner is attached to a swivel head 48. The torch or
coating
head 20 is carried on a phenolic isolating mount surface 50 on the frame 46.
As the
welding wire emerges from the liner 47 at the swivel head 48 it is guided
around the
arcuate frame 46 by inner guide wheels 51 and outer guide wheels 52. In this
way
io friction and wear at the arcuate guide is reduced.
A heat shield 55 is provided at the arm 41 to prevent heat and debris
from the welding action from reaching the control system and control cables on
the
carriage and extending from the carriage to the support carriage 18 in front
of the
operating carriage.
In Figures 7 and 8 is shown the basic structure of the intermediate
carriages and the drive carriage which are substantially identical to the
operating
carriage in that they include a similar rectangular frame with the opening 26
and the
slot 29 locating the guide wheels 31.
The welding head is supported symmetrically so that is provides the
ability to weld on each side of the pipe without the need to remove and
reattach the
torch that will allow for increased cycle times and versatility. The torch is
liquid
cooled and the heat shield 55 is provided to cover the support bar from weld
splatter.
CA 02578308 2011-01-25
The arrangement provides a four axis welding head positioning
system. The design includes a carriage that rides along a support rod and
supports
a three axis manipulator arm. The arm will allow for precise positioning of
the
welding head along the weld path at any position within the lower 180 degrees
of the
s pipe. After this the system is inverted to weld the top half.
As shown in Figure 2, the system is PLC controlled using a controller
and a control unit C carried on the carriage 17. The system detects the
welding
parameters from the welder and can be used to control the welder. Thus the
system
is therefore able to program in all welding parameters including wire feed
speed,
io amperage, arc voltage, torch travel speed, electrical stick-out distance
and bead
overlap. The electrical stick-out distance is controlled by operating the
servo-motors
to move the welding head relative to the frame to a required position based
upon a
detected parameter of the welding process. Thus it will maintain a preset
electrical
stick-out regardless of the base material or pipe profile. The pipes are
notorious for
15 out-of-roundness, and stick-out settings require to be continually adjusted
as the
carriage is moved along the pipe. This machine will do it automatically. The
bead
overlap is adjusted by changing the angle of rotation effected by the arms on
the
torch at the end of each stroke of the welding action.
The system can also be used to program in a number of alarm
20 conditions including loss of arc, loss of carriage travel, over travel on
all axes and
emergency stop.
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21
In addition the system can be used to program the welding head angle
of attack to the weld bead. This can be changed relative to the radial
direction of the
axis of the pipe in the radial plane of the axis by changing the angle around
the
"wrist" axis particularly as the torch approaches the 3 o'clock and 9 o'clock
positions.
The angle of attack is the angle of the torch relative to the work in the
radial
direction. At the 6 o'clock position, the angle of attack is approximately 5-8
degrees
relative to the radial direction, that is, the welding head is angled into the
toe of the
previous weld bead. As the application of further beads progresses upwards to
the
horizontal position, for example 4 o'clock, the angle of attack is increased
in order to
io build a shelf to prevent the molten puddle from dripping.
Welding in both directions of travel is the ideal solution to increase
cycle time and the system may have this ability. The system uses a tie-rod
cart
system which may include the ability to rapidly return to the starting
position for
improved cycle times if two directional welding is not feasible in general or
applicable
to a particular job.
The carriages ride on the corners of the bar and not on the flats of the
bar to produce a more stable carriage with good acceptance for tracking around
bends.
The support rod 14 is supported on one or more straps 14A along its
length extending from the bar to the inside surface of the pipe to help combat
the
issues associated with the droop of the bar. By supporting the support rod on
the
straps, the droop can be reduced significantly, and the moment effects created
by
CA 02578308 2011-01-25
22
larger bend radius pipes are eliminated. The oscillatory effects are also
significantly
reduced with the addition of the strap support as the free length of the bar
is reduced
and the system is stiffened.
The support strap or straps can simply be tack welded to the support
rod and to the top of the pipe provided that the pipe is large enough to
facilitate a
manual welder. The carriage has the slot 29 to incorporate clearance for this
support strap to pass as the welding assembly passes. In situations where a
manual tack joint is not possible an alternate method may be required.
The four axis manipulator arm ensures that any complications that may
io arise from the support rod droop or misalignment or out of round pipe can
be easily
corrected through automatic adjustment of the welding head. The arm is
adjusted
by detecting the weld parameters primarily the current draw which indicates
the
distance of the welding head tip from the pipe surface.
The arrangement described herein provides a four axis welding head
manipulator arm able to dynamically adjust the welding head position and thus
maintain proper stick-out parameters despite variations in pipe diameter along
the
direction of travel. System stick-out is monitored in real time in order to
provide
adequate feedback to the manipulator arm to allow it to adjust accordingly. A
number of options are available to monitor stick-out, including optics, laser
scanning
and weld voltage or current monitoring.
Considering the long distances that wire needs to be drawn from, the
wire feeder 45 is located as close to the welding head as possible. This
proximity
CA 02578308 2011-01-25
23
will be limited by the feeder weight and packaged size if it is to ride on the
portion of
the carriage that enters the pipe.
With this proposed design the range of motion is limited making it
necessary to use different upper arms of different lengths to accommodate the
entire
range of pipe diameters that the machine must be able to work with. Three
different
length arms are interchangeable in a manner that will allow for a fast,
accurate, and
repeatable swap of components. One arm will be used for pipes with inside
diameters between 17 and 27 inches. Another will be used for pipes with inside
diameters ranging from 27 to 37 inches and the final arm for pipes with inside
io diameters between 37 and 47 inches. The placement of the support rod within
each
varying size of pipe is arranged to center the shoulder pivot point in the
center of the
pipe to allow for smooth, easy, and accurate angular placement of the welding
head.
This is achieved by using different lengths of the straps 14A for different
pipe
diameters.
is This opening 26 and the slot 29 are sealed through the use of brushes
(not shown) along the sides to engage the rod 14 and to allow the
incorporation of
some positive air pressure to help combat contamination of the rolling
elements.
One viable method for weld tracking is the use of a vision system.
With appropriate filters the system can track and plot the weld path in real
time. If
20 multiple lines of sight are incorporated into the design, stick-out
measurement may.
be possible as well. The use of fibre optic lenses provides for a light weight
and
CA 02578308 2011-01-25
24
relatively small travelling assembly allowing for a smaller and compact
overall
design.
Another methodology is to use a laser profile scanner to track the weld.
Again this method provides adequate detail to track and plot the weld path in
real
time. A laser scanner will also easily provide stick-out measurements as well
as
allowing for full control of the manipulator arm. Scanners do tend to be
slightly more
bulky than optics but the required space and mass properties can be
accommodated
for in the design.
Real time welder control during the weld cycle is possible through
1o communication options such as ArcNet, Ethernet or equivalent. Communication
protocols are usually available in most robotic rated power sources, and
usually
come with a remote pendant for programming. This option also includes display
of
wire speed, current, voltage, and electrical stick-out on the main operator's
interface
panel.
Full robotic control of the welder can also be used to add a large
degree of flexibility to the design; with tight stick-out control, full
robotic control of
welding parameters.
Control of the automated pipe elbow welding machine with four axis
manipulator arm uses an industrial rated motion controller with Human to
Machine
Interface (HMI). The HMI allows for operator entered data to be stored and
recalled
as necessary, to include items such as: welding parameters, if a robotic
welder is
CA 02578308 2011-01-25
selected, welding speed, start and finish locations, index size, position
data, and
others as required.
Operators also have local control of the torch head by use of a pendant
station. This station can be located at the tailstock of the machine and
provide for
5 some degree of movement to enable easy and fast adjustments of the machine
while away from the actual HMI.
7ti
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