Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2 I O
SAFETY MOUNTING DEVICE
Background of the Invention
This invention relates to a safety mounting device
that may be used for mounting a member that is subject
to various external forces, the safety mounting device
functioning to prevent the member from being damaged if
the forces should become excessive. The safety
mounting device of the present invention was designed
for use in robotic welding applications to mount a
welding torch and will be described herein in such an
lo environment. Those skilled in the art will appreciate,
however, that this is only one of many applications to
which the safety mounting device of the present
invention may be put.
When a robot is used for arc welding applications,
it is almost inevitable that, occasionally, the welding
torch will strike some obstruction. This can be due to
a variety of reasons, chief among them being operator
error and equipment malfunction. Should such a
collision occur, it is imperative that the robot be
stopped immediately to prevent damage. Most robots can
be fitted with torch contact circuits which trip the
robot control in the event of the torch contacting any
grounded metallic object However, if the robot is
moving at a reasonable speed, damage will occur before
the robot can be stopped. Furthermore, such torch
contact circuits are subject to frequent nuisance
tripping as a result of weld spatter buildup, the
presence of ionized gases, etc.
Even a minor collision of the torch usually
results in a certain amount of displacement, requiring
time-consuming reprogramming of the robot. More
violent collisions can result in serious damage, not
only to the welding torch, but also to the mechanical
elements of the robot itself.
Various desirable characteristics of a safety
mounting device for use in robotic welding applications
are as follows:
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1. The safety mounting device should be
flexible, having compliance in as many planes as
possible.
2. The force required to displace the safety
mounting device should be less than that which would
cause damage to the robot.
3. The safety mounting device should return to
its preset position (home position) with repeatable
accuracy upon removal of the obstruction or external
force.
The force required to displace the safety
mounting device should be greater than that imposed on
the welding torch by the constraints of the attached
welding cables, hoses, etc. during normal operation of
the robot.
lo 5. The safety mounting device should be fitted
with some means of indicating abnormal displacement to
the robot control so that the robot can be stopped
before the safety mounting device has reached the limit
of its displacement.
6. The safety mounting device should be capable
of withstanding the ambient conditions existing near an
arc welding operation, such as high temperature, smote
weld spatter, ozone and high levels of ultra violet and
beta radiation.
7. The safety mounting device should be of
rugged construction.
8. The safety mounting device should be of
minimal weight so as not to compromise the dynamic
performance of the robot.
In accordance with a preferred embodiment of this
invention there is provided a safety mounting device
having all of the desirable characteristics noted
above.
Summary of the Invention
An aspect of this invention is as follows:
A safety mounting device comprising a housing
having a longitudinal axis; a first movable member
mounted within said housing for sliding movement along
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said longitudinal axis; a second movable member mounted
within said housing between said first movable member
and a stop member, said second movable member being
mounted within said housing for sliding movement along
said longitudinal axis, for rotation about said
longitudinal axis and for tilting movement with respect
to said longitudinal axis; biasing means for biasing
said first movable member against said second movable
member to sandwich said second movable member between
said first movable member and a stop member; and switch
lo means having an on position and an off position and
operable by said first movable member, in one position
of said first movable member along said longitudinal
axis said switch means being in one of its two
positions, in other positions of said first movable
member along said longitudinal axis said switch means
being in the other of its two positions; said first and
second movable members contacting each other by means
of a cam surface and a cam follower surface such that
rotation of said second movable member about said
- 20 longitudinal axis from a home position wherein said
first movable member is in its said one position
displaces said first movable member by cam surface-cam
follower action to said other poSitiolls thereof, said
first movable member also being movable from said one
position thereof to said other positions thereon by
virtue of movement of said second movable member along
said longitudinal axis toward said first movable member
and by virtue of tilting of said second movable member
relative to said longitudinal axis.
Brief Description of the Drawings
This invention will become more apparent from the
following detailed description, taken in conjunction
with the appended drawings, in which:
Figure 1 is a front elevation, partly broken away,
showing a safety mounting device embodying the present
invention, a part of a robot to which the safety
mounting device is secured, a welding torch bracket
mounted on the safety mounting device and a welding
torch supported by the aforementioned bracket;
Figures 2, 3 and are front elevation Al views,
partly broken away, of a safety mounting device of the
type shown in Figure 1 and showing various positions of
the components thereof, these figures being useful in
describing the operation of the safety mounting device;
and
Figure 5 is a perspective view of several of the
components of a safety mounting device embodying the
present invention.
Detailed Description of the Invention Including the
Preferred Embodiment
A safety mounting device 10 constituting a
preferred embodiment of the invention is shown in the
drawings. It is secured to a robot 11, only a part of
which is shown, since the robot forms no part of the
instant invention, and carries or mounts a mounting
bracket 12 on which, in turn, is mounted a welding
torch 13.
Safety mounting device 10 includes a housing 14
having a longitudinal axis 15. Housing 14 may be
fabricated from aluminum, for example, and, in the
illustrated embodiment, simply is a hollow cylinder. A
straight slot or channel 16 running parallel to
longitudinal axis 15 is provided in the inner side wall
of housing 14 for a purpose which will become more
apparent hereinafter.
Mounted within housing 14 is a movable member 17
that functions like a piston within housing 14. It is
cylindrical in configuration, bears against the inner
side wall of housing 14 and is movable along
longitudinal axis 15. The upper end surface 18 of
movable member 17 is provided with a cylindrical recess
19. The lower end surface 20 of movable member 17 is
provided with a cam follower surface 21 which, in the
illustrated embodiment, is of V-shaped configuration.
A second movable member 22 is mounted within
housing 14, a part 23 thereof being sandwiched between
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movable member 17 and a stop member 24. Stop member or
retaining plate 24 simply is of annular configuration,
preferably is fabricated of aluminum and is secured to
housing 14 in any suitable way, e.g., by threaded
fasteners. It has an enlarged opening 25 to
accommodate a stem 26 of movable member 22 formed
integral with part 23 and which extends out of housing
14 through opening 25. Movable member 22 is mounted
within housing 14 for movement along longitudinal axis
15, for rotation about longitudinal axis 15 and for
tilting movement with respect to longitudinal axis 15
as shown in Figures 2, 4 and 3 respectively.
Secured to the opposite end of housing 14 from
stop member 24 is a cover plate 27 that is generally
disc-shaped. Cover plate 27 preferably is constructed
of aluminum and may be secured to robot 11 and to
housing 14 by any suitable means, e.g., threaded
fasteners. The lower end surface of cover plate 27 is
recessed at 50 in the same way that upper surface 18 of
movable member 17 is recessed at 19.
- 20 Cover plate 27, housing 14 and retaining plate 24
may be held together by bolts 52 whose heads are
recessed within cover plate 27 and which extend through
channels bored in housing 14 and thread ably engage
retaining plate 24.
Movable member 17 is biased against movable member
22 by means of a spring 28 which sandwiches part 23 of
movable member 22 between lower end surface 20 of
movable member 17 and stop member 24. Spring 28 is
compressed between cover plate 27 and movable member
and has its free ends mounted in recesses 19 and 50.
A switch 29 is mounted on housing 14 and has an on
position and an off position. A protective cover 51 is
secured in position over switch 29. Generally
speaking, switch 29 is operable by movable member 17
such that in one position (the home position) of
movable member 17 along longitudinal axis 15, switch 29
will be in one of its two positions, i.e., either on or
off, while in other positions of movable member 17
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along longitudinal axis 15, switch 29 will be in tune
other of its two positions, i.e., either off or on
respectively. In the illustrated embodiment this
operation of switch 29 is achieved by means of a switch
operator 30 extending part way through housing 1~1 and
engaging a ball 31 which, in the home position of
movable member 17, is located in a detent 32 in the
side wall of movable member 17. Any displacement of
movable member 17 along longitudinal axis 15 from its
home position shown in Figure 1 results in ball 31
being moved into engagement with switch operator 30 to
change the position of switch 29, all as is clearly
shown in Figures 2, 3 and JO Of course, the
illustrated technique for operating switch 29 is merely
one of many different techniques that may be used
without departing from this invention.
Mounted within an opening in movable member 17 is
a pin 34 that protrudes into slot 16. Pin 34 and slot
I merely cooperate with one another to ensure that, in
the home position of the components, ball 31 will rest
in detent 32. This also could be achieved by making
detent 32 of annular configuration so that in the home
position of movable member 17, ball 31 would rest in
detent 32 regardless of any rotation of member 17 that
might take place about longitudinal axis 15.
As previously noted, lower end surface 20 of
movable member 17 is constituted, in part, by a cam
follower surface 21. The upper surface of part 23 of
movable member 22 is a cam surface 33. Cam surface 33
is of generally conical configuration but with two
flats that incline toward each other making a generally
V-shaped configuration that nests within cam follower
surface 21 in the home position of movable member 17.
Thus, in the home position of the various
components cam surface 33 nests within cam hollower
surface 21, and switch 29 is in one of its two
positions, switch operator 30 not having been activated
by ball 31.
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When a force tending to laterally displace welding
torch 13 is applied to welding torch 13, movable member
22 tilts with respect to longitudinal axis 15, as shown
in Figure 3, resulting in movable member 22 displacing
movable member 17 upwardly along longitudinal axis 15,
as shown in Figure 3 and causing switch 29 to be
tripped to its other position.
If a direct upward force should be applied to
welding torch 13, as shown by the arrow in Figure 2,
movable member 22 will move along longitudinal axis 15
causing upward displacement of movable member 17 and
again tripping switch 29.
When a rotary (with respect to longitudinal axis
15) force is applied to welding torch 13, the
engagement of cam surface 33 with cam follower surface
21 results in upward displacement of movable member 17
along longitudinal axis 15, as shown in Figure 4, again
resulting in tripping of switch 29.
It will be seen from the foregoing that when
movable member 22 is deflected in any lateral
- 20 direction, is displaced upwardly along longitudinal
axis 15 or is rotated relative to longitudinal axis 15,
the result is that movable member 17 is displaced from
its home position (Figure 1) and switch 29 is moved
from its on or off position when movable member 17 is
in s home position to an off or on position
respectively when movable member 17 is displaced away
from its home position. Switch 29 is connected, of
course, to the control (not shown) for robot 11 and
causes the robot to trip before any damage can occur to
it resulting from the unnatural displacement of welding
torch 13.
Upon removal of the external forces acting on
welding torch 13, the pressure of spring 28 returns all
components to the home position shown in Figure 1.
If desired a gauge (not shown) may be removably
mounted on stem 26 of movable member 22 to facilitate
mounting of welding torch 13 so that its electrode just
reaches longitudinal axis 15.
g Lo
While a preferred embodiment of the invention has
been disclosed herein, those skilled in the art will
appreciate that changes and modifications may be made
therein without departing from the spirit and scope of
this invention as defined in the appended claims.
