Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED KNIFE
BACKGROUND TO THE INVENTION
This invention concerns a knife of the kind
(hereinafter termed 'of the kind referred to')
comprising a blade and handle.
In industry many accidents are caused by hand
~nives. Tne most serious injuries occur when the blade,
forcibly applied to the work-piece, slips and strlkes
the lim~s or body of the user. In textile mills such
accidents happen most frequen~ly where residual thread
is being stripped Erom bobblns or where entangled
threads are being cut away from rollers on spinning
' machines.
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In such accidents the worker may be applying a
force of such magnitude ~c 150 N) that the knife, at the
moment of slipping, can move with an acceleration l0
times that of gravity.
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It is an object of the present invention ~o
j provide a knife of the kind referred to which prevents
`, 25 or al least reduces the incidence of the kinds of
, accident men~ioned above.
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SUMMARY OF TI~E INVENTLON
~ ccordlng to the present invention there is
provided a knife of the kind referred to incorporating
accelera~ion detection means adapted ~o cause automatic
retraction of the blade into the handle upon detection
of violent movement of she knife at least with the
cutting edge of the blade in a leading at~itude.
BRIEF DESCRIPTION OF THE ORAWINS~S
The inven~ion will be further apparent from the
following description, with reference to the flgures of
~' ~he accompanying drawing, which show, by way of example
', 15 only, ~o forms of knife of the kind referred to and
embodying the invention.
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~ Of the drawings:-
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Figures 1 and 2 are longi~udinal cross-sections
through the first form of knife
with ~he blade thereof in its
extended and retracted
positions respectively.
Figure 3 is a longitudinal cross-section
through the second form of
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knife with the blade thereof in
an extended operative position;
- and Figure 4 is an end view of the knife
seen in the direction of arrow
IV on Figure 3.
DETAIL~.D DESCRIPTION OF T~E PREFERRED EMBODIMENTS
Referring first tO Figures 1 and 2 it will be
seen that the first form of knife comprises a handle 10
of hollo~ box-llke construction and a ~lade 11 on the
forward end of a tang 12. The blade 11 and tang 12 are
slidable axially within the handle 10 to enable the
blade 11 tO be moved from an operative position wherein
its cu~ting edge lla extends out~ardly from the forward
. end of ~he handle (Figure 1) to an inoperative or safe
position ~herein the ~lade 11 is fully retracted into
he handle 10 (Figure 2).
A tension spring 13 has its opposite ends
'~ anchored to the blade 11 and the rear of the handle 10
~e~ respec~ively and acts to urge the blade 10 in~o its
j inoperative or safe posltion.
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The blade 11 may ~e slid into its operative
position by pushing on the end of the tang 12 which
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pro]ec~s rear~ardly from the handle 10 and there locked
in posi~ion by engagemen~ of a latch 14 projecting from
~he tang 12 ~l~h a detent 15 ln a heavy arm 16 pivotally
connected with the handle 10 at 17 and extending
generally parallel with the tang 12.
In use if the body of the knife accelerates
violently in the plane of movemen~ of the arm 16 with
the cutting edge of the blade in a leading attitude, the
arm, o~ing to its inertia, moves relative to the tang 12
thus releasing the lalch and retracting the blade.
~qually cne latch may be released tO retract the blade
11 for safe storage simply by a sharp rap on the handle
10 of the knlfe.
; Tne sensitiv1ty of the system may ~e engineered
~y appropriate geomecry but day to day adjustments may
made ~y adjusting the force exerted on the arm 16 by a
compression spring 18 ~y means of a grub screw 19.
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Referring now to Figures 3 and 4, it will be
seen that the second form of knife comprises a handle
110 formed from two shell-like halves 111 and 112 which
can ~e joined by screws at 113 and 114 on a longltudinal
25 central plane of the handle 110 to form a box-like
enclosure which houses the working par~s of the knife.
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The knife includes a blade 115, which is a
replaceable item, and which is clamped bet~een support
plates 116 by means of a screw 1.17. To gain access tO
screw 117 for blade replacement purposes it is necessary
~o separate the handle halves 111 and 112
One of the support plates 116 is connected to or
integrally formed wi~h a rearwardly projecting tang-like
member 118 ~hich has a longltudinally extending lateral
recess 119 which houses a tension spring 120 ~hose
forward end is anchored tO tne member 118 adjacent the
I plates 116 and whose rearward end is anchored tO a
s transverse pin 121 extending between the halves 111 and
. 15 112 and through a longitudinally extending slot 122 in
~ the mem~er 118.
i The assembly including mernber 118 is slidable
between a forward positi.on wherein the blacle 115
pro~rudes operatively from ~he handle 110 and a rearward
position wherein the blade 115 is retracted to lie
within ~he body of the handle 110. The spring 120 acts
- to urge the assembly including member 118 into the
rearward position.
'~ A cranked lever 125 is pivotally mounted at the
rear oi the handle such that one of its arms 126 is
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accessl~le from wltnout tne handle foL movement (in the
dlrectlon of arLo~ X) agalnst the action o a return
torslon spring 127 tO move the other of its arms 128
in~o engagement with an abutment surface at the rear end
of member .L18 tO slide the assem~ly including member 118
forwardly to lock blade 115 protruding outwardly from
handle 110 by a desired extent by engagement of one of a
series of longitudinally spaced teeth 130 alony the
upper face of member 118 with a tooth 131 on the
underside of a pivotally mounted weighted arm 132
mounted ~ith1n tne nandle 110 above member 118. A
spring 133 urges arm 132 towards member 118 and its
Strength lS selected to ensure retrac~ion of the
assembly lncluding member 118 and hence blade 115 when
tne handle 110 of the knife accelerates in the plane of
movemen~ of arm 132 wi~h the cuttlng edge oE the blade
~ in a leading at~itude at or above a predetermined rate
because of relative movement between arm 132 and member
118 to dlsenyage the tooth 131 from ~he tooth 130
; 20 Again the blade 115 may be moved to its retracted
position by delivery of a sharp rap to the handle 110.
I~ will be appreciated that it is not intended
to limi~ the lnvention to the above example only, many
variations, such as might readily occur to one skilled
in the art, belng possible, wi~hout departing from the
scope thereof as defined by the appended claimsO
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For example, a longitudlnal thumb slide
protruding from t~e underside of ~he Kinfe nandle may be
provided for movement of the blade carrylng assembly to
i~s forward or operaclve position.
Other means for detectlng acceleration tnan that
descri~ed may ~e used such as electronic transducer
means, but a simple mechanical system is preferred on
the grounds of reliability and cos~.
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