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Патент USA US2409398

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im i5, mß,
E_F,SHEEHAN ETA; ‘
f 2,409,397
SAFETY CUTOFF FOR POWER OPERATED' HAND TOOLS
Filed Oct. 13, 1943
. A .CSOURCE
2 Sheets-Sheet> l
Oct. 15,- 1946.
2,409,397
v E. F; sHEr-:HAN ETAL
SAFETY CUTOFF FOR POWER OPERATED HAND TOOLS
ì
Filed oci. 15, 1943
2 sheets-sheet 2
Patented Oct. 15, -1946
Í2,409,397
UNITED >s'rrxr-lïs PATENT _ ortica `Í
- sAFE'rvoUfronF‘roR POWER-,onimusha
‘
Edward
,
HAND 'rooLs
Lstechen and George-v. Hunt, n
_rmladelpma;, ra.
4
_
Application iOotoÍbcr ‘13, 19313,;Scriall No. 5106398.43
3 .oni-ms; (ol. 121-35.)
'
l
„Objects :of `the :present ;-iny_ention .are first, '.to
y-protect »workmen »and equipment-rand sub-surface
structures when 'pow-er :driven 4manually guided
tools are ~used for cutting, drilling, `:breaking or
`working «on :relatively nonaelectrically icon-ducting
stopping operation l„once ,theshutt-lng» downlactìon
of the _supervisory circuit .is initiated -by .elven
momentary occurrence of the `condition under
which tit is «desir-_ed wto Ästop the --toolg and-eleventh,
to prov-ide an :audi-ble signal ,to .indicate 1that l«the
tool has been shut downley contact with mate.
rial which is <relatively _a goed :electric .conducton
Other` objects of the invention wil-l Yappear.from
:the Y‘following description .et the rend of which-«the
material in or under orin :contact -With‘whichirell
yatively high electrically »conducting .material may
¿be embedded, for-'example when such tools 'work
Aon asphalt or other like stnee'tinavement in‘which,
.or .in the foundation of which, ¿or "under which
high tension 4metal-lic sheath :cables :irl-.pipes car
rying water; gas, steam Aor `other -fluids., :or tele
invention will `-be claimed.
Y
`
i
The invention also icomprises ,the improvements
to loe ,presently described and ,finally clair-ned»
„I-n »the ,following description ’reference will vbe
phone and »other ’conduits are usually laid orlo
cated; second, to automatically
off .the power
,and >stop ‘the opera-tion «of :the tool as soon :aait 1
-has `penetrated the "layer `of :relatively mon-’elec
made .to the accompanying draw-ings forming part
trically >conducting `zanraterial ,and
alternating Ycurrent loper-ated ,safety cut-,off em
contacted
an underlying Yor :adjoining layerv Vof :relatively
hereof :andin which,
„
l
l
‘
Figure .l is v~a „diagrammatic :View .illustrating :all
bodyinggfeatures .of vthe invention ,and ,showing
or indicating the Lposition of the lparts of .the valye
mechanism when îthe ,tool is cut oil -from the
»high «conducting material; third, Ito automatically
cutoff the power and 'therefore to stop .the :tool
immediately it «contacts >with relatively high .elec
trically :conducting material, for lexample l»the
4sour-ee of power.
-
»
i
.
‘
Figure vf2 is asimilar view yshowing ,the „position
of the jpants when the tool -isiconnected with :the
metal ,sheath of ,a :cable and before sit Acontacts
source-of power; 1and
with
and insulated
the high -from
_tension
‘fthe conductors
'metallic sheath;
¿contained
fourth,
to provide simple, reliable and efficient ,apparatus
‘ ,
«
¿Figure 3 isa view similar `to Eigure >l .and ill-us
Vtra'ting -the employment -of la fdirect- 1,cu-rnent .cir
cuit ,and omitting certain rteatures ,shown inFigS.
for :accomplishing ‘the -objects indicated :as well
as the objects tanti :results :hereinafter rseît forth
l iand‘2.
.
.
or :appearing: ,ñfth :lto `loros/tide `for 'workingìa
Referring to the drawings, ,I indicates a .han-di
power driven Vhand :guided tool on' an intended Y guided Ypovwer- operated tool, >snecíiicalvly a nnen'
material :in the
way and for automatically
mratic tool. `i'. indicates «,arsourcevof `power f_orßfop»
erating the tool. .3 is :a vsalve housing
in»
cludes a valve mechanismhav-íng a `port-A. .tor
stopping it as soon as ii-t‘contacts with and `befnre
fit penetrates another material 'which it might
damage :or which :might he highly :charged with
,admitting `air «under lprensure -to the »tool -by _way
Aa :hazardous medium~and cause injury to tele..
phone, water, _electric :power or ¿other :systems ¿or
of the hose â. - The valve .mechanismalso includes
-a port r6 `for exhausting :air under Vpressure from
the tool by
of the pipe .5 ,to the :atmosphere
at I. The valves of the -valve mechanism .are
injury to `the operator :or `¿damage ‘to fthe ätool‘;
sixth, to provide for automatically ,stopping :a
pneumatic :hand ‘tool Working l»on n :street lpave
operated ,by `the pivotal .arm ÍB which is shown
ment, building floor, -or the like, ïin the event “f in FigureZ in .position for „operating the tool under
power, .and .in Figure 1 ,it is `shown imposition .for
that fand as «soon as it contacts lwith and -betore
it ‘penetrates »an object such :as is :likely to loe
cutting .oli the supply of .fluid under _pressure
from the „source and „for exhausting :from the
buried in or under .the pavement, V«floor or "the
like, :and which might ,be damaged by the tool,
.tool «and line 5 tothe atmosphere so ,that ,thetoo'l
stops quickly. .The pi-votalhand-le 3 is connected
or itself cause injury to the _tool `.orto the 'opera
by >a link with‘the .arm S
the spring I9 op»r
tor; seventh, to _provide Àa supervisory vv.electric
.crates to normally put .and ,hold the valves the
circuit for shutting „dow-nthe ‘tool upon :occur
position shown in Figure l in whichnosition ¿the
rence of -the'conditions under <.which :it :desired
tool l `is Vat rest. ll is a -,pivotal latch normallyT
to Istop the tool; zeig-nth, kto ,provide 'for shut-down
positioned by .the spring l2, as .shown ‘in Figure
of the tool incase of .failure of «electric ,power to
the supervisory electr-ic ¿circui-t; ninth, to provid-e
1„ `in Vwhich .position it _disengagesthe handle` 9 at
>a visual Lsignal ‘to Aindicate :failure of electric
VI3 .whenthe _power is out .off from the tool„ and.
it engages the handle ..9 .at lI3 when »the ¿tool is
operating .under power, ‘The 'latch ,l .l `is ìoon'tnol-lecl
power to ëthe «supervisory electric circuit; tenth,
to `provide `a :seal-in .provision in the Vsupervisory
electric ïcircuit to cause completion of >-the tool
55
by .the solenoid ,L4 .which when energized causer»
2,409,397
3
4
the latch to hold the handle 9 in position, thereby
permitting the tool to operate under power. The
and permit the handle 9 to take up the tool
stoppìng position shown in Fig. 1. The parts are
so constructed that when the handle 9 has moved
far enough to release engagement with the lead
26, the latch Il will not be able to reengage the
handle 9 may be shifted to latched position man
ually or otherwise. The solenoid I4 is shown as
included across the leads I5 and I6 of the A. C.
source. I'I is a sensitive fast-acting two pole
double-throw relay which normally closes the line
latch pin I3.
There is also a lead 21 through the alarm 28
to the contact at the rother side of the handle 9
I6 so that the latch II is normally held against
so that when the valve is in position for stopping
the force of its spring I2 in position for en
gaging the handle 9 and permitting the tool 10 the tool the circuit is closed through the signal
28 which indicates that the power is cut off from
I to operate in the ordinary and usual manner.
the tool. Obviously, if desired, the sealing-in cir
If the position of the two pole double-throw relay
cuit may be omitted and it is, therefore, not
be changed toward the right in Figure 1, lthe
shown in Figure 3. In the latter figure there is
circuit through the solenoid will be broken, the
a D. C. source but the circuits and translating
spring I2 will release the latch and the tool will
devices are, as has been described, in connection
stop. The coil I9 serves to shift the position of
with Figures 1 and 2. In this case, however, there
the two pole double-throw relay I‘I appropriately
is a lead 29 from one side of the circuit which
for stopping the tool. There is a lead 20 from
branches to and through the coil I9' Ito ground
one side of the secondary of the transformer I8
through the coil I9 to a relatively low resistance 20 at 2 I, and through signal 28 and lead 29 through
the two-pole double-throw relay Il back to the
ground at 2I.v Two leads 22 and 23 extend from
line. The operation of the apparatus shown in
the secondary of the transformer -to the tool I
Figure 3 is as above described in connection with
where they may be regarded as connected to
Figures 1 and 2 except as indicated above. In
gether and to the tool I, and in the lead 23 there
is a signal lamp 24. At this point'in the de 25 both Figures 1 and 3, 30 is a blocking switch
which is, of course, normally closed.
scription it may be said that the tool I is for the
The operation of the apparatus of Figs. 1 and
purposes of description, assumed to be a pneu
matic tool and is intended to operate upon or
work on material a, of relatively low electrical
2 may be summarized as follows: Under normal
conditions the hand tool, driven pneumatically
conductivity, for example the asphalt pavement 30 or by other power, with the valve mechanism in
the Iposition illustrated in Fig. 2, is operated in
of a street. In the pavement there is likely to be
the usual manner to disintegrate pavement or
embedded material of relatively high electrical
other material of relatively high electric resist
conductivity, such for example as a high tension
ance a. If, however, the Pneumatic ltool in its
lead covered cable b grounded for example at c.
It must, of course, be understood that the fore 35 normal operation makes contact with under
ground water pipes, conduits or the like, b, an
going explanation is given by way of description
electric circuit is completed from one terminal of
and not by way of limitation, for example, lthe
the secondary winding of transformer I8 by Way
tool may be operated otherwise than by air, and
of conductor 22 through the tool I, conducting
-'che material b, so long as it is of relatively high
electrical conductivity, may be a telephone cable, 40 medium b, grounds c and 2|, coil I9, and con
pipe or the like. and the material a may be the
earth beneath the pavement. Riesuming the de
scription and assuming the tool to be working in
or on the material a of relatively low electrical
conductivity, any ground circuit that may exist ‘
is of too high resistance to permit the coil I9 to
be energized sufficiently to throw the relay I1.
However, if the tool contacts the material b of
relatively high conductivity, the ground circuit
between 2| and c is of relatively low resistance ‘
and is of good conductivity and permits of the
energization of the coil I9 sufficiently to throw
the relay I‘I and stop the tool.
Because the contact of the tool I with the ma
terial b, may be momentary or of chattering na- '
ture, a sealing-in circuit is provided to prevent
the fast-acting relay I'I being deenergized and
restored to its normal position before the latch
holding solenoid I4 can function to release the
latch II and permit the valve to assume the
cut-off position. This sealing-in circuit com
prises the lead 25 from one side of the secondary
circuit of the transformer to the handle 9 and
thence through the lead 26, the armature of the
relay I'I, the coil I 9, and the conductor 20, back
to the other side of the secondary circuit of the
transformer. With the valve mechanism in the
tool-operative position illustrated in Fig. 2, the
relay I‘I, when energized and thrown to the right,
will remain in that position because the coil I9 u
will remain energized through the sealing-in cir
cuit regardless of any opening or chattering of
the ground circuit through the tool I and mate
rial b. This will allow any time lag which may
be required for the solenoid I4 to release latch II
ductor 20 to the other terminal of said winding.
Flow of current in this circuit energizes coil I9,
throwing relay I1 to the right and energizing the
sealing-in circuit to hold Ithe relay in this posi
tion despite any chattering of the tool. This
energizing of the relay I‘I opens the .circuit from
the electric source Ito the solenoid I4, thereby
permitting the spring I2 to release the latch IIThe spring I0 is then free to move the arm 8 and
handle 9 to the tool-stopping position shown in
Fig. 1, moving the valve to cut off the air supply
and permit the line 5 to exhaust to the atmos
phere at 1. This movement of the handle 9 to
the position shown in Fig. 1 connects the audible
signal 28 to the secondary winding of transformer
I8 to direct attention to the occurrence of valve
operation. The visual signal 24 is connected to
the transformer I8 and when energized indicates
(1) that the supervisory electric circuit is ener
gized, and (2) that the flexible electric conductor
22 to the tool is unbroken, it being readily under
stood that this conductor is subjected to consid
erable flexure and possible abuse and is therefore
likely to break. The apparatus is reset for op
eration of the tool by merely moving the handle
9 upwardly into the position shown in Fig. 2, the
latch II automatically engaging with the pin I3.
It is obvious, of course, that should failure of the
electric source occur, solenoid I4 will be deener
gized and the tool will shut down. The super
visory electric circuit of the device shown in Fig.
3 operates in a similar manner from a direct cur
rent source, but without the sealing-in feature.
It may be remarked that as a matter of con
venience certain of the described Working parts
2,409,397
Y
may be assembled in a portable housing or case,
for example, the valve mechanism, indicated at
3, may be arranged in the case with the handle
9 projecting to theoutside, and the blocking
switch 3@ may be similarly arranged. The signal
lamp 24 may be displayed at the outside of the
case, and the relay Il may be arranged inside of
the case, and, if desirable, there may be arranged
6
i
from‘moving said cut-off means to the cut-o
position'when said detent is energized by said
electric current and to release said yieldahle
means lpermitting said cut-oiî means to assume
the cut-oil' position when the electric current .ta
said detent is interrupted, a normally closed re
lay having its contacts in said iirst circuit in
series with said detent, a second electric circuit
in the case as a D. C. source a storage battery,
connected to said source and including the oper
and the alarm 23 may also'be arranged in the 10 ating coil of said relay, and means in said second
circuit for energizing said relay operating coil
case and in that way the invention is applied to
street paving and like Work in a convenient man
responsive to the conditions under which it is de
ner.
sired tc stop the tool, whereby the .tool will be
stoppedupon operation of the means for energiz
It will be obvious to those skilled in the art
ing said relay operating coil and also upon the
that modifications may be made in details of
construction and arrangement and application in
occurrence of any other interruption of the cur
respect to the apparatus chosen for illustration
rent supply to said first circuit.
and above described without departing from the
2. The invention set forth in claim 1 char
acterized in that the relay energizing means is
spirit of the invention, which is therefore not
limited as to such matters or as to matters of 20 provided with a sealing-in circuit for holding said
mere form or otherwise than .the appended claims
relay in tool stopping position when once in that
may require.
position and until manually released.
We claim:
3. The invention set forth in claim l char
l. A safety cut-off apparatus comprising in
acterized in that said apparatus includes an elec
trically operated visual signal, said signal being
combination a power driven hand tool, power cut
off means having yieldable means normally urg
connected in series with a part of said tool .to said
ing said cut-off means to the cut-off position to
electric source, whereby the operator may be ap
prised that the circuit to the `tool is energized.
stop the tool, a source of electric current, a ñrst
electric circuit connected to said source and in
EDWARD F. SHEEHAN.
cluding an electro-mechanical detent constructed 30
and arranged to restrain said yieldable means
GEORGE V. HUNT.
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