Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVEM_NTS RELATING TO WELI~IN~_M~SKS
Field of the Invention
This invention relates to welding masks and relates
particularly to a welding mask incorporating a filter
lens which is moveable between a position whereat the
filter lens does not obscure a user's vision of work to
be welded and an operative position in which the filter
lens shields the eyes of the user from the UV light and
other harmful radiation emitted during electric arc
welding.
The eyes of a welder must be protected against
damage from such radiation during any form of welding
operation~
Background of the Invention
It has been the practice to provide either a hand
held welding mask having a filter lens formed of a darkened
window which is moved in front of the eyes on commencement
of welding or a mask which is worn by the welder and which
is generally moveable between an operative position at
which the welder looks through the filter lens and an
inoperative position at which the mask is tilted back
on the head of the user or the filter lens moved on a
pivot allowing clear vision of the work.
Such masks, however, are unsafe due to the tendency
of the user to strike an arc before the mask is properly
in place,thus subjecting the user's eyes to the damaging
radiation. The problem is accentuated when welding is
carried out in conditions of poor light where it is
impossible for the welder to see the work through the
filter lens before the arc is struck.
The problem of eye damage caused by the radiation
emitted from a welding arc has dramatically increased
with the increasing use of hobby arc welders which are
now commonly available and used by amateur welders without
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any formal training or experience. However, the problem
also exists for trained and experienced welders who can
accidentally be exposed to the radiation.
Background Art
It has been proposed to provide welding masks
with a filter lens which becomes daxkened or opaque in
the presence of UV and other radiation but which clarifies
in the absence of such radiation. However, the time taken
for such a lens to become opaque is such that some
radiation can impinge on the eyes of a user.
Australian Patent No. 515,177 discloses a hand
held mask having a trigger which actuates a hinged filter
lens mechanism and a light switch. When the trigger is
actuated, the filter lens swings out of the line of vision
of the user to enable the work to be viewed. Greater
trigger pressure actuates the light switch to cause the
work to be illuminated by the self-contained light. On
release of the trigger, the filter lens swings back into
the shielding position.
With this construction, it is possible for the
user to strike an arc while the filter lens is out of
the line of vision so that the user is subjected to
radiation.
Australian Patent No. 419,67~ discloses another
construction of mask in which a moveable opaque filter
lens is pivoted along it's upper edge and is moveable
by a lever mechanism operable by the chin of the user
to open or close the filter lens. Again, correct operation
of this mask depends on proper actuation by the user.
Other~similar devices have been shown in Australian
Patent specification Nos. 120,050 and 261,265.
It is, therefor, desirable to provide an improved
construction of welding mask whereby the filter lens does
not obscure, or substantially obscure, vision of the work
when there is no arc but which protects the eyes of the
user against radiation when an arc is struck.
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It also deslrable to provide an improved welding
mask which is able to be used with a variety of arc welding
equipment.
It is also desirable to provide an improved welding
mask which is effective in automatically preventing
radiation reaching the eyes of a user but which enables
the user to clearly see the work and leaves one hand free
to position the work piece to be we]ded or to hold on
to a support in ha~ardous locations.
It is also desirable to provide a welding mask
which has the above features and which is also economical
to manufacture.
Summary_of the Invention
According to the invention there is provided a
welding mask comprising an opaque face shield having a
viewing opening therein, a filter lens pivoted to the
face shield adjacent the viewing opening, moving means
to move the filter lens from a closed to an open position,
said moving means including electrical transducer means
2~ to cause pivotal movement of said filter lens, restoring
means to restore the filter lens to the closed position,
and electrical control means for said transducer means,
said control means including electrode voltage sensing
means to sense electrode voltage of an arc welder and
circuit means responsive to sensed electrode voltage to
energise said transducer means when the voltage rises
above a predetermined maximum value and to de-energise
the transducer when the sensed voltage falls below a
predetermined minimum value.
Preferably, the mask is of the face shield type
adapted to be worn on the head, although it will be apprec-
iated that the invention is applicable to hand held
shields.
In a preferred form of the invention, the filter
lens is pivotally mounted on a frame forming part of or
attached to the face shield. The pivotal axis of the
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lens is generally horizontal and passes either through
the centre of gravity of the lens or adjacent thereto.
With this arrangement, the operation of the transducer
acts to pivot the lens about its axis of symmetry, thus
requiring less operational forces as compared to physically
moving the lens away from the viewing opening. In the
open position, the filter lens is substantially centrally
located in the viewing area but extends perpendicular
theretG so that the user can look past the lens to the
work.
In a preferred form of the invention, the trans-
ducer means cornprises a solenoid mounted on the face shield
and connected by a crank lever to the lens pivot shaft.
The restoring means comprises a tension spring which is
also connected by a crank lever to the lens pivot shaft
and which also constitutes part of the circuit means.
With this arrangement, if the spring fails, no current
will flow to the solenoid and the filter lens will remain
in a closed position.
The welding mask of the invention can be designed
for a standard electric arc welder which has an operating
voltage in the range of 50 to 80 volts aOc. between the
welding electrode and the work. When the arc is struck,
th~ voltage across the arc drops by approximately 50
percent.
In an alternative embodiment, the welding mask
is designed for use with a s-tandard rod arc welder, a
MIG, an a.c. TIG or a d.c. TIG. In this embodiment, a
switch is provided, preferably mounted on the face shield
or lens frame, to enable the user to switch the electrical
control means to suit the particular welder in use. Thus,
in the normal MIG and TIG type welders, direct current
is normally employed and the welder is operated by a switch
mounted on the electrode holder. For this embodiment,
3~ the control circuit must take account of both a.c. and
d.c. electrode voltages as well as the polarity differ-
en,_eJ between MIG and TIG d.c. welders.
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According to a still further broad aspect of the
present invention there is provided a welding mask which
comprises a face shield having a viewing opening therein. A
filter lens is pivotally mounted relative to the face shield
adjacent the viewing opening. Electrical transducer means
is provided and comprises a solenoid to move the filter lens
from a closed to an open position. A crank is connected to
the solenoid to pivot the filter lens about an axis which
passes either through the center of the lens or adjacent
thereto. Restoring means is provided to restore the filter
lens to the closed position. Electrical control means is
provided for controlling the transducer means. The electrical
control means includes electrode voltage sensing means to
sense the electrode voltage of an electric arc welder.
Circuit means is responsive to the sensed electrode voltage
to operate the transducer means when the vol-tage rises above
a predetermined maximum value and to deactivate the transducer
means when the sensed electrode voltage falls below a
predetermined minimum value to enable the restoring means to
move the filter lens from the open to the closed position.
The electrical control means includes voltage input terminals
to be connected to the welder electrode and the work to
receive the voltage therebetween. A reed switch is held in
a closed position when the voltage across a reed switch coil
is above the predetermined maximum value. A triac whose
gate is in the reed switch circuit and which is held on
while the reed switch is closed is provided to energize the
transducer means through a bridge rectifier. The reed switch
open-circuits the triac gate when the electrode voltage falls
below the predetermined minimum value.
The invention will be more readi]y understood
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by reference to the following description of embodiments
of the invention taken in conjunction with the accompanying
drawin~s.
Description of the ~
S ~igllre 1 is a perspective view, part cut away,
showing a weldin~ mask in accordance with one embodiment
-~ of the present invention,
Ei~ure 2 is a sectional, side elevational view
showing the filter lens frame and cover therefor,
Fi.gure 3 is a front elevational view of the filter
lens and mounting frame,
Figure 4 is one side elevational view of the filter
lens frame,
Figure 5 is a side elevational vi~w of the filter
lens frame taken from the opposite side to tha-t of Figure
4 ,
Figure 6 is a circuit diagram illustratin~ a
control circuit for a standard electric arc welder, and
Figure 7 is a circuit diagram illustrating a
control circuit for a welding mask for use with different
types of arc welders.
Description of the Preferred Embodiments
Figures 1 to 5 illustrate a welding mask 12 which
comprises a face shield 14 and a lens.frame 16 mounted
to the face shield 14 by mounting brackets 17. The face
shield 14 has an internal head band ~not shown) enabling
the face shield to be worn by a welder.
The lens frame 1S projects from the face shield
14 and includes an inner frame part 18 and a cover 19.
The cover 1g has a clear glass or glass-like protective
front 21 and upper and lower clips 22 which are adapted
to engage upstanding ribs 23 on the inner frame part 18.
Thus, the cover 19 is removeable from the inner ~rame
part 18 to provide access to the filter lens 24 which
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is mounted on the inner frame part 18.
The filter lens 24 includes a lens holder 26 which
releaseably carries the filter lens glass 27, thus per-
mitting easy replacement, if required. The lens holder
2fi is provided with opposed outwardly extending pivot
axles 28 which extend through bearings 29 on each side
of the inner frame part 18. The axis of the pivot axles
28 is substantially horizontal in normal use of the welding
mask 12 and is located slightly offset from the axis
10 through the centre of balance of the filter lens 24 so
that the lens 24 normally lies in a vertical plane.
The inner frame part 18 is provided with upper
and lower stops 31 and 32 against which the filter lens
24 en~ages when moved to the vertical, closed position.
A solenoid 33 is mounted on one side of the lens
frame 16. The solenoid plunger 34 is connected by a crank
36 to one of the pivot axles 28 so that vertical movement
of the plunger 34 causes rotational movement of the filter
lens Z4. On the opposite side of the lens frame 16, a
spring 37 engaged on a pin 38 extending from th~ lens
frame 16 is connected to a second crank 39 fixed to the
other of the pivot axles 28. The spring acts to move
the filter lens 24 about the pivot axis to the closed
position.
Z5 The solenoid 33 is actuated through a control
circuit, components of which are mounted on a printed
circuit board 41 mounted on one side of the lens frame
16. The control circuit rnay be that illustrated in Figure
6, in which case the welding mask 12 is able to be used
3~nly with a normal, a.c. arc welder. Alternatively, the
control circuit may be that illustrated in Figure 7, in
which case the welding mask 12 includes a change-over
switch 42 which enables the circuit to be switched to
suit the various types of arc welders.
Referring to Figure 6~ the control circuit illust-
rated is suited for a normal, a.c. arc welder. The circuit
includes inputs 43, one of which is connected to the weld-
ing electrode while the other of which is connected to
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the work. A reed switch coil 44 is connected across the
inputs 43 in series with a voltage dropping resistor 46.
The reed switch coil has an operating voltage of approx-
imately 10 volts and the resistor 46 is selected so that
a voltage of between 50 and 80 volts a.c. across the inputs
43, which corresponds to the open circuit electrode to
work voltage, causes operation of the reed switch 47.
The switch 47 connects the resistor 48 to the gate 49
of the triac 51 causing the triac to conduct and thus
closing the circuit to the bridge rectifier 52. The bridge
rectifier rectifies the input voltage and applies this
to the solenoid coil 53. The coil is thereforeenergised
and the plunger 34 of the solenoid 33 holds the filter
lens 24 in the open position as shown in Figure 2.
As soon as the welding electrode contacts the
work in order to strike an arc, the voltage across inputs
43 drops below a level at which the reed switch coil 44
will hold the reed switch 47 closed. The gate 49 is,
thus, open circuited and the triac 51 immediately ceases
to conduct, thereby open circuiting the solenoid coil
53. The restoring spring 37 immediately acts to rotate
the filter lens 24 about the pivot axis to the closed
position at which radiation from the welding arc is
prevented from damaging the eyes of the welder.
Immediately the arc is broken, the voltage between
the electrode and the work increases, causing the reed
switch coil 44 to close the reed switch 47,thus actuating
the solenoid coil 53 to open the filter lens 24.
The circuit illustrated in ~igure 7 includes a
change over switch 42 which enables the circuit to be
used for the various types of electric arc welders. The
change over switch 42 is a 3 pole, 3 way switch to enable
the control circuit to take account of the input voltage
being a.c. or either polarity of d.c. Referring to Figure
7, the input 54 is connected to the work while the input
55 is connected to the anode. The inputs are connected
to switch poles 56 and 57, respectively. The poles
; 56/57/58 can be switched between positions a,b and c which
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correspond to MIG, TIG d.c. and TIG a.c. respectively.
The switch is shown in Figure 7 at position a. As will
be seen, the difference between MIG and TIG d.c. positions
is simply a reversal of polarity.
The input voltage (in the case of TIG a.c., rec-
tified by the bridge rectifier 59) is applied to the
voltage regulator circuit incorporating transistor 61
and zener diode ~2. While the voltage is higher than
the zener voltage, the transistor 61 conducts, thus
energising the solenoid coil 63. As soon as the voltage
across the inputs drops due to the contact of the electrode
with the work, the transistor ceases to conduct and the
coil is open circuited causing the spring 37 to close
the filter lens 24.
In the preferred embodiment illustrated in Figure
7, the transistor is an npn type 2N3055 while the zener
diode is a 12 volt diode with the biasing resistor 64
preferably 150 ohms.
A relay coil 66 is connected across the transistor
20 61 and actuates a single pole, double throw relay switch
67. Thus, if any of the circuit components such as the
zener diode 62 or transistor 61 malfunction, the relay
actuates to open circuit the solenoid coil 63 causing
the filter lens 24 to be moved to the closed, or safe,
25 position~
In the preferred embodiments of the invention,
the spring 37 is preferably part of the electrical circuit
to solenoid 33 so that, in the event of the spring failing,
the solenoid cannot be energized to open the filter lens
30 24.
-rt has been found that with the welding mask of
the embodiments described, when the welding electrode
touches the work prior to striking the arc, the lens closes
within approximately 3 milliseconds. This time is
35 generally less than the time required to actually strike
the arc. Further, as sos:n as the arc breaks, the lens
opens at a slower rate than the closing rate, and any
subsequent contact of the electrode with the work causes
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the lens to re-close within the 3 millisecond period.
Similar times are applicable to MIG and TIG welders using
switch controls.
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