Note: Descriptions are shown in the official language in which they were submitted.
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RAZOR
This invention relates to safety razors, and in particular it is concerned
with a blade unit for a safety razor. The blade units of the invention may be either
cartridges which are mounted replaceably on a handle for use, or the shaving heads of
5 disposable razors having blade carrying parts permanently attached to a handle. A
safety razor cartridge as currently marketed comprises a generally rectangular moulded
plastics frame with guard and cap surfaces on the lengthwise extending frame parts.
Within the opening of the frame are a pair of blades arranged in tandem with their
cutting edges parallel to each other and directed towards the guard surface. The blades
are carried on respective supports to which they are fixedly attached, and the ends of
the blade supports are slidably guided in grooves in the end walls of the frame to
enable the blades to retract, under forces exerted on the blades during shaving. Springs
act on the blades to urge them to a normal rest position.
It is well known that the so-called shaving geometry of a blade unit is
important in determining the shaving performance of the blade unit. The shaving
geometry defines the position and orientation of the ~lades in relation to other skin
contacting parts, in particular the guard and cap, of the blade unit. One parameter of
the shaving geometry is the blade exposure, which is the perpendicular distance by
which the edge of a blade protrudes above a shaving plane tangential to the surfaces of
the skin contacting parts imme~ tely in front of and behind the blade edge. The
known blade unit described above has the blades mounted so that the exposure is
reduced when loads of sufficient magnitude to overcome the force of the springs are
exerted on the blades. Anotner important factor in the shaving geometry is the blade
tangent angle, which is the angle at which the central plane of the blade intersects the
tangent plane, the tangent plane being the plane which is tangent to the edge of the
blade and to the surface of the skin contacting part next in front of the blade. For
example, in a twin blade cartridge, the blade tangent angle of the first or primary blade
is the angle of the blade to the tangent plane tangential to the guard surface and the
edge of the primary blade.
During shaving the blades of a blade unit are subjected to a combination
of drag forces and load forces. Drag forces are those forces directed essentially parallel
to the shaving plane, and load forces are those forces directed against the blade by the
.
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skin in the direction substantially perpendicular to the shaving plane.
It has been proposed for example in U.S. 4,709,477 and U.S. 4,774,765,
to mount the blades so that the blades can move to increase both exposure and blade
tangent angle in response to increasing drag forces. Strain gauge measurements have
5 shown that drag forces do not vary subst~nti~lly during shaving. Hairs do not usually
grow perpendicular to the skin surface and for the majority of men beard hair isinclined downwardly with respect to the face. It is believed that, when shaving, men
apply the razor against the face with less pressure during upstrokes, when the blades
are moving es~entiS~lly against the grain, than during downstrokes, and the net result is
10 that drag forces are not substantially different during upstrokes and downstrokes. On
the basis that by applying the razor against the skin surface under greater load pressure
a person is seeking greater closeness of shave, a more aggressive blade geometry would
be desirable under such conditions. The prior art razors with movable blades are not
capable of responding to load forces in this way.
Accordingly, the present invention seeks to fill this gap left by the prior
art and in accordance with the invention there is provided a safety razor blade unit
having at least one blade mounted for independent movement relative to other skin
contacting parts of the blade unit under forces exerted at the blade edge during shaving,
wherein the or each blade is mounted to move to increase the blade tangent angle in
20 response to load forces exerted on the blade during shaving.
In the preferred embodiments of this invention the blade unit includes a
frame, and the or each blade is fixedly carried on a blade support, and the blade
support is connected to the frame by means defining a fulcrum, the movement of the
blade under load fulcrum being located closer to the blade edge than is the point where
25 the tangent plane meets the skin contacting surface next in front of the blade. Also, the
fulcrum lies in or closely adjacent to the tangent plane. This arrangement minimi7.~s
the changes in blade exposure as the blade tangent angle increases, and to the extent
that the exposure of the blade does change it reduces as the blade tangent angleincreases. Also, the angular displacement of the blade is largely insensitive to the drag
30 forces on the blade, and the blade span, i.e. the distance between the blade edge and the
skin contacting surface in front of the blade edge measured in the tangent plane, does
not change significantly as the blade tangent angle increases. It is expedient for the
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fulcrum to be spaced from the blade edge at a distance in the range of 0.2 mm to0.6 mm.
With a blade unit embodying the invention the blade or blades are
initially set with a minimllm blade tangent angle, and this angle increases under
increasing load forces. As a consequence there is greater comfort as compared with
other arrangements which provide the blade tangent angle to be initially set at a
m:~ximllm .
The blade supports can conveniently be coupled to the frame so that the
fulcrum is fixed with respect to the frame, but this is not essential and it is also
possible to allow a degree of controlled movement of the fulcrum.
A better underst~nrling of the invention will be gained from the detailed
description which follows reference being made to the accompanying drawings in
which:
Figure l is a cross-section through a razor cartridge in accordance with
the invention, the blades being shown in a normal rest position;
Figure 2 shows the cartridge of Figure 1 with the blades in the position
of maximum angular displacement;
Figure 3 is an exploded perspective view of the cartridge shown in
Figure l;
Figure 4 is an enlarged detail showing part of a blade unit and its
support;
Figure ~ is a perspective view showing a modified blade mounting
arrangement;
Figures 6A and 6B are perspective and end views showing an alternative
blade mounting arrangement with a hinge;
Figures 7A and 7B are perspective and end views showing another
alternative blade mounting arrangement with a shell bearing;
~ Figures 8A and 8B are perspective and end views showing a further
alternative blade mounting arrangement with a moving fulcrum;
Figures 9A and 9B show in perspective and end view a blade mounting
arrangement including a four bar linkage, and
Figure 9C shows this embodiment in a maximum blade displacement
-- , ..... .
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condition.
The safety razor blade unit shown in Figures 1-4 is a shaving cartridge.
The handle to which the cartridge is attached is not shown and may be of conventional
form. The cartridge comprises a moulded plastics frame 1 of generally rectangular
S shape. The front rail of the frame includes a guard bar 2 and carries a guard strip 3 of
elastomeric material having upst~n(ling fins extending along the strip. The rear rail of
the frame defines a cap surface 5 and carries a strip 6 of lubricating material. Three
blades 7 with parallel edges are mounted in the frame between the guard bar 2 and cap
surface 5 so that the blades pass in turn over the skin during shaving. Each blade is
10 fixedly attached to a blade support 8, and as best seen in Figure 4, integral with each
end of the blade support is a forwardly and upwardly inclined suspension arm 9 having
a journal 10 at its free end. The journal axis is parallel to the edge of the blade and
spaced forwardly thel~fivlll at a distance of 0.2 to 0.6 mm. The journals are received
in bearings defined by spring blocks 12 and the end walls of the cartridge frame. The
15 spring blocks have connection elements 13 which engage with a snap fit in sockets
formed in the frame walls, and integral with the spring blocks are spring fingers 14
which act on the undersides of the respective blades for urging the blades to their rest
positions shown in Figure 1. Upwardly directed key elements 15 on the spring blocks
are arranged to extend into slots formed in the end walls of the frame to retain the
20 journals 10 in their bearings defined at the upper ends of these slots, as may be seen in
Figures 1 and 2. By this arrangement each blade 7 is mounted in the cartridge frame 1
for pivotal movement about the axis defined by the journals 10, this axis being located
between the blade edge, and the skin contacting member next in front of the blade, this
axis being in or closely adjacent the tangent plane of the blade. The spring fingers 14
25 bias the blades to the rest position of Figure 1 in which the blades, or their support,
abut against shoulders 18 formed on the frame end walls. When a blade 7 is subjected
to a load force, applied at the blade edge and directed substantially perpendicular to the
shaving plane, and the load force is of sufficient magnitude to overcome the prestress
in the spring fingers 14, the blade is caused to pivot so that the blade tangent angle
30 gradually increases as the load force increases further. As may be seen from Figure 2,
the blade exposure reduces, but only slightly if desired, the reduction in exposure could
be compensated by arranging for the guard bar 2 to be itself spring mounted or to be
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elastically deformable so that it will be gradually depressed under the corresponding
load force applied on the guard bar as the blades pivot under the load forces imparted
on the blades. It will be understood that the cartridge construction is such that the
blade tangent angles will increase with increasing force used by the razor user to press
the razor against the skin being shaved.
Instead of being formed integrally with the blade support, as shown in
Figure 5, the suspension arms 9 and journals 10 can be formed as a separate moulded
members 20 which can be formed with slots to receive the ends of the blade support 8.
Figures 6A and 6B illustrate an arrangement in which a fulcrum about
which a blade 7 is pivotable is formed by a living hinge 22 incorporated in a member
23 including the suspension arm 9. The member may be integral with the cartridgeframe 1 or can be moulded separately and attached to it.
In the alternative construction of Figures 7A and 7B the blade support is
arcuate and end extensions 24 on the support are arranged to fit into correspondingly
curved slots in the frame end walls to form a shell bearing defining the centre of
pivotal movement of the blade 7.
It is not essential for each of the blades to be constrained to move about
a fixed fulcrum or pivot axis. In the modified construction of Figures 8A and 8B, the
suspension arms 9 showing integral with the blade support although they could bemoulded separately and attached to the blade support as in Figure 5, have hooks 26 at
their free forward ends. The hooks rest on cantilever support bars 27 fixed to the
frame end walls and having substantially ~lat surfaces with opposite edges defining
respective pivot axes. During initial pivotal displacement of the blade, the suspension
arms 9 and blade 7 pivot about the axis defined by the forward edges of the support
bars 27, and during subsequent angular movement the pivoting takes place about the
pivot axis defined by the rear edges of support bars.
~n the modified embodiment of Figures 9A, 9B and 9C, the blades 7 are
~ supported by integrally moulded four bar linkage assemblies. A first link 30 forms the
suspension arm 9, a second L-shaped link 31, is fixed to the cartridge frame, a third
link 32 is connected to the suspension arm 9 by one living hinge 33 defining a fulcrum
for movement of the blade 7, and to one end of the second link 31 by another living
hinge 34, and a fourth link 35 of short length is connected by respective living hinges
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36, 37 to the other end of the second link and to the first link. I~nder load forces
applied at the blade edge the link 30 moves about the fulcrum defined by the hinge 33.
There is some downward movement of the fulcrum due to the hinge 34, but this
displacement which will result in reduction of the blade exposure, is only small due to
5 the short length of the fourth link 35. In all the described embodiments the fulcrums
will be located substantially as described in relation to the embodiment of Figures 1-4
and as a conse~uence the desired effect of the blade tangent angels increasing as the
load forces increase is obtained, while the blade spans do not change substantially, and
the changes to the blade exposures are kept small.
