Note: Descriptions are shown in the official language in which they were submitted.
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WO 96!29183 PCTIUS96/03758
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&afetv Razors
This iaventioa relates to safety razors and
is particularly concerned with safety razors having
blade units with a plurality of blades defining
parallel sharpened edges arranged to pass in succession
over a skin surface being shaved. The invention is
applicable to safety razors having their blade units
permanently attached to the razor handle, and to safety
razors having their blade units detachably mounted on
the handle for replacement~when the blade edges have
become dulled, and is either case the iaveation can be
incorporated whether the blade unit is immovably
mounted to the haadla or mouatad to move, e.g., to
pivot about as axis parallel to the blade edges,
relative to the handle under the iaflueace of forces
imparted on the blade unit during shaving.
Tha present invention has specific reference
to safety razor blade units incorporating three blades,
and the relative positioning of the blade edges. Our
prior patent application No. PCT/VS94/10717 teaches
that with such blade units an improved overall shaving
performance can be achieved when the blade edges are
set according to a particular geometrical patters,
namely with the first blade, which has its edge nearest
the guard, having an exposure not greater than zero,
and the third blade, which defines the edge nearest the
cap, having as exposure sot less than zero. In the
most efficacious geometrical arrangement, the first or
primary blade has a negative exposure with as absolute
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value in the range of 0 to 0.2amn, preferably equal to
about -0.04mm for a primary blade span of around 0.7mm,
the third blade has an exposure with a positive value
not greater than about +0.3atm (preferably
less than +0.2mm), for example around +0.06ami or
+0.09mm, and the second blade has an exposure of about
zero, the second and third blade spans each being 1.0
to 2.Omm, preferably about l.5mm. For convenience the
geometrical arrangements described and claimed in the
aforementioned prior application are referred to herein
as "the target geometry for the blades". For further
information and details of the blade geometry reference
may be made to the earlier application the contents of
which are incorporated herein by this reference.
The blade exposure is defined to be the
perpendicular distance or height of the blade edge
measured with respect of a plane tangential to the skin
contacting surfaces of the blade unit elements next in
front of and next behind the blade edge. This can be a
positive number if the blade edge is a~SQve this plane
i.e., closer to the akin surface to be shaved than the
tangential plane, or a negative cumber if the blade
edge is below this tangent place, i.e., further away
from the skin than the tangent plane. The spas of- a
blade is the-distance from the blade edge to the skin
contacting element immediately in front of that edge as
measured along a tangent line extending between..said
element and the blade edge.
The three-blade geometry specified above, is
applicable to a blade wait in which the blades-are "
ia~ovably mounted relative to the guard and cap. It
also applies to the initial or at rest geometry in the
case of a blade unit in which the blades are spring
mounted and capable of being deflected under the forces
applied to the.blades during shaving.
V
The present invention, recognizes that it may
be desirable for some parts of a blade unit to be
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movable relative to other parts and that this may be
accommodated without forfeiting the advantages of the blade
geometry discussed above. Thus, according to a preferred
embodiment of the present invention there is provided a safety
razor blade unit comprising a guard, a cap, and first, second
and third blades with parallel sharpened edges located in
sequence between the guard and cap, at least one element
selected from the blades, guard and cap being movable from a
non-shaving position (i.e., at a rest position not loaded by
shaving forces) to modify a blade exposure dimension of the
blade unit and to attain a modified blade geometry (also
referred to as the target geometry) wherein the exposure of the
first blade is not greater than zero and the exposure of the
third blade is not less than zero, at least one of the first and
third blades having a different exposure when the at least one
movable element is in the non-shaving position.
The at least one element can be lightly biased, such
as by means of a spring, to an initial, non-shaving (at rest)
position at which the target geometry of the blades does not
apply, but when the blade unit is applied to the skin during
shaving the at least one element can be displaced to a position
in which the target geometry of the blades is attained.
The at least one element can comprise the guard and/or
the cap and/or one or more of the blades.
In accordance with another aspect the present
invention provides a safety razor blade unit comprising a guard,
a cap and a plurality of blades with parallel sharpened edges
located in succession between the guard and cap, at least one of
the guard and cap being movable against a spring force from a
non-shaving (at rest) position to a predetermined operable
position in which a modified blade geometry (target geometry) is
obtained, in the non-shaving position the blade edges being
disposed below a plane tangential to the skin contacting
surfaces of the guard and cap.
A full understanding of the invention will be
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gained from the following detailed description in which
reference is made to the accompanying drawings,
wherein:
Figure l illustrates a preferred blade
geometry during shaving and corresponds tci Figure 2 of
earlier application No. PCT/US94/10717;
Figure 2 is a transverse cross-section
through a first embodiment of the present invention
when not in use;
Figure 3 shows the blade wait of Figure 2
with the parts occupying different relative positions;
Figures 4 and 5 are views corresponding to
Figures 2 and 3. respectively and showing a second
embodiment of the invention; and
Figures 6 and 7 are views corresponding to
Figures 2 and 3 and illustrating a third embodiment of
the invention.
Figures 8-10 are illustrations of different
orientations of a cartridge with respect to a shaver's
skin.
Figure 11 is a cross-section through a
further embodiment showing the use of cantilever arms
for spring mounting of blades.
Figure l illustrates schematically a safety
razor blade unit having a frame 1 defining a guard 2
and a cap 3 and mounting a lubricating strip 4.
Supported by the frame and carried by respective
support members are a primary blade 11, a secondary
blade-12 and a tertiary blade 13, the blades having
their edges lying in a common plane P. The target
geometry .of the blade unit is as follows:
a) The span S1 of the primary blade 11 is 0.5
to l.5mm, and is preferably 0.7am1;
b) The span S2 of the secondary blade 12 and
the span S3 of the tertiary blade 13 are in the range
of 1.0 to 2.Omm, and each is preferably l.5mm;
c) The distance S4 from the edge of the
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tertiary blade to the cap is about 1.80mm;
d) The exposure of the primary blade is -0.04mm;
e) The exposure of the secondary blade 12 is not less
than the exposure of the primary blade 11 and not greater than
the exposure of the tertiary blade 13 and, as shown, is equal to
zero;
f) The exposure of the tertiary blade is about
+0.09mm.
Except as otherwise noted, the embodiments of the
present invention described below are so arranged that a
substantially similar blade target geometry can be achieved
although such geometry does not apply when the blade unit is at
rest and not in use (i.e., a non-shaving position not loaded by
shaving forces).
In the blade unit shown in Figures 2 and 3, the guard
2 is mounted to the frame for up and down sliding movement
between upper and lower end positions defined by stop surfaces
provided on the frame. The guard is urged lightly to the upper
end position by a spring 20. The cap 3 is similarly slidably
mounted by the frame for up and down movement between end
positions defined by stops, and a spring 21 lightly biases the
cap to its upper end position. In the upper end position of the
guard an upwardly facing shoulder 30 on the guard abuts a stop
surface 31 defined by a flange 32 integral with the frame, as
seen in Fig. 2. Similarly, in the upper end position of the cap
an upwardly facing shoulder 34 on the cap abuts a stop surface
defined by a flange 36 integral with the frame. In the lower
end positions of the guard and cap, the guard and cap
respectively abut stop surfaces 37 and 38 defined by a bottom
30 wall portion of the frame, as shown in Fig. 3. The three blades
11, 12, 13, can be stationarily mounted in the frame or can be
biased by respective springs against a stop surface 18 defined
by inturned flanges on the end walls of the frame. In the out
of use condition, the blade geometry is outside the target
35 geometry for the blades. The negative exposure of the primary
blade has an absolute value significantly greater than 0.2mm and
the tertiary blade has a negative exposure. In use, the guard
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and cap can be depressed against the springs 20, 21 which act
respectively thereon and occupy their lower end positions, as
shown in Figure 3, when in the start-shaving disposition a
modified geometry (i.e., the target geometry) substantially
corresponding to that of Figure 1 is obtained. From this target
geometry the blades may be deflected downwardly against their
individual springs 19, but the enhanced shaving performance due
to the target geometry need not be lost. Furthermore, it is not
essential that the guard and cap remain in their lower end
positions when they are in contact with the skin in use of the
blade unit and they can be permitted to move under the influence
of their respective springs 20,21.
In the embodiment of Figures 4 and 5, the cap 3 and
guard 2 are fixed to the frame as in Figure 1, but the blades in
this case are movable and influenced by respective springs 24.
The springs could press the blades lightly upwardly against a
stop surface (as mentioned in relation to Figures 2 and 3) but
as shown the springs are unstressed when the blade unit is at
rest and not in use so there is no preload on the blades. In
this condition of the blade unit the target geometry for the
blades is not satisfied, e.g., because the primary blade has a
positive exposure, and the exposure of the tertiary blade is
greater than the preferred maximum of +0.2mm. In use, however,
the blades are depressed gainst the force of the springs so that
a modified geometry is obtained, as shown in Figure 5, and
substantially the target geometry of Figure 1 can be obtained.
If required the blades could be provided with stops to
predetermine the positions to which they need to be deflected to
reach the target geometry. Alternatively, the spring rates can
be chosen so that deflection from positions according to the
target geometry will not be excessive.
The embodiment of Figures 6 and 7 also has a
stationary guard 2 and cap 3. The three blades il, 12, 13 are
mounted on a rocker unit 26 supported in the frame 1, such as by
a shell bearing, for pivotal movement of the blades in unison
about a pivot axis A located above the blade edges. A leaf
spring 28 carried by the frame acts on the rocker urging it
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lightly to the non-shaving (i.e., at rest) position shown in
Figure 6, at which the blades are outside the target geometry
for the blades, the primary blade having a positive exposure and
the tertiary blade having a negative exposure. In use, forces
applied will cause the rocker unit 26 to pivot against the
action of the spring 28 and to take up the position which is
shown in Figure 7 and which may be predetermined by a stop f fixed
on the frame such as stop 40 or stop 41 indicated schematically
in the drawings. In this condition of the blade unit the
geometry is substantially as specified above in relation to
Figure 1, and hence the target geometry for the blades applies.
As illustrated, the blades are fixedly mounted on the rocker but
the blades may be mounted on the rocker by springs so that
during shaving the blades may become deflected from the target
geometry, as mentioned above in relation to Figures 2 and 3.
It will be understood that although in the at rest
position they do not initially satisfy the geometrical
parameters to obtain the best shaving performance, all of the
embodiments are adapted so that these geometrical parameters
will be obtained in use. While some embodiments have been
described it will be appreciated that others are also possible
within the scope of the claims. For example, just one of the
guard and cap could be movable, or the blades and the guard/or
cap could be movable, or just one or two of the blades
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could be movable. Other combinations of movable
elements are also possible. Futhermore, the elements
could be adapted to move in a different manner, such as
by the guard being arranged to flex or tilt and/or to
move to vary the span of the primary blade as well as
modify the blade exposure.
A feature of the guard and/or cap being
movabl~v and sprung as in the embodiment of Figures 2
and 3 is that when not in use the blade edges are all
disposed below a plane tangential to the skis
contacting surfaces of the guard~and cap. However, the
guard and/or cap can be readily displaced to the
retracted position defined by a stop so that a desired
target blade geometry is obtained.
It is believed that beneficial shaving
results are achieved when cartridges with three
resiliently mounted blades exhibit, during shaving, a
"progressive force" pattern. i.e. the force on the
tertiary blade is greater than the force on the primary
blade and the force on the secondary blade is
intermediate to the forces on the primary and tertiary
blades or equal to the force on either the tertiary or
the primary blade. The force pattern oa the blades can
be influenced by the cartridge orientation bias effect,
blade geometry, and blade spring arrangement, as is
discussed in detail below.
The cartridge orientation bias effect relates
to how the angular orientation of the cartridge with
respedt to the skin surface influences the forces on
the individual blades. Figs. 8;=10 illustrate three
cartridge orientations, a neutral orientation, a cap-
heavy orientation, and a guard-heavy orientation. In
these figures. cartridge 130 is illustrated
schematically to include a guard 132, cap 134 and
blades 136, 138. 140 and is shown with a cartridge
orientation relative to the skin surface 142 before the
skin surface has been deflected. During actual
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shaving, the cartridges would in general be pushed into
the skin surface, deflecting it so that the entire top
part of the cartridge will contact the skin. If it is
assumed that the exposures at rest (non-shaving
condition), spring preloads and spring rates are equal
for each of the blades, then the cartridge orientation
will control the force pattern on the blades during
shaving.
. In Figure 8, the cartridge 130 is oriented in
the neutral condition. In this case, as the cartridge
130 is pressed against the skin surface 142 by the user
to bring all of the blades into shaving contact, the
forces are-applied uniformly to the three blades. To
produce a progressive force pattern, the blade geometry
and/or the blade spring arrangement can be modified, as
discussed in detail below.
Ia Figure 9, the cartridge 130 has a cap-
heavy orientation. Ia this case, the cap 132 contacts
the skin surface initially. As the remainder of the
top part of the cartridge is pushed aga3ast the skin,
more force is applied to the blades sear the cap.
Accordingly, the force oa the tertiary blade is greater
than the force oa the secondary blade, which is greater
than the force on the primary blade, which is a
progressive force pattern.
In Figure 10, the cartridge 130 has a guard-
heavy orientation. In this case; the guard 134
contacts the skin surface initially. As the remainder
of the top part of the cartridge is pushed against the
skin, more force is applied to the blades near the
guard. Accordingly, the force on the primary blade is
greater than the force on the secondary blade, which is
greater than the force on the tertiary blade. The
guard-heavy condition thus promotes the opposite of
"progressive force." To produce a progressive force
pattern, the blade geometry and/or the blade spring
arrangement can be modified to counteract the force
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2 ~ ~ Q 2 G 9 PCT~S96103758
WO 96129183
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pattern that would otherwise be caused by the guard
heavy condition, ae discussed in detail below.
For cartridges that are sot pivotally
connected to the handle, the cartridge orientation with
respect to the skis, and thus the cartridge orientation
bias affect, is generally determined by the orientation
of the cartridge with respect to the handle. For .
cartridges attached to the handle through a pivot, is
addition to the at rest orientation of the cartridge,
the pivot location sad return spring force will affect
the cartridge orientation bias affect. For example, if
the at rest cartridge orientation is as shown in Figure
9, the cap will initially contact the skin; however, if
the pivot is in the region of the guard, and there is
light return spring force, the cartridge will become
guard heavy during shaving.
As noted above, the force pattern on the
blades can also be influenced by the blade geometry and
blade spring arrangement. The blade geometry refers to
the exposure at rest. The blade spring arrangement
refers to the spring rate and praload.
Figure 11 111ustrates one way of providing
resilient mounting for the blades and how at rest
exposure of a blade can be adjusted. (Other spring
mounting approaches can also be used.) Referring to
Figure 11, cantilevered plastic arm 144 extends in from
housing aide wall 146 and provides resilient support
for the bent upper portion 146 at one end of the blade.
The cutting edge 150 of the blade is prevented from
further upward movement by metal clip 152, which is
secured to the housing. A similar arm extends in from
the other side of the cartridge and provides resilient
support. for the other end of the blade under a similar
retaining clip. The pair of arms 144 corresponds to
springs 19, 24 shown is Figures 2-5. The upward force '
F that arm 144, acting as a cantilevered beam, exerts
on blade portion 148 is a linear function of its
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downward displacement, y, from its unbiased position:
F = k * y, where k is a spring constant that depends
upon the length of the arm, L, the moment of inertia of
the arm, I, and the modulus of elasticity, E
(k = L3/ (3EI)). If arm 144 is deflected a distance yp
by clip 152 in manufacture (i.e., providing arm 144
with a preload force Fp of k * yp), then y in the-
formula equals yp + yd, where yd equals the movement
downward from the at rest position shown in Figure 11.
The forces oa the blades can be controlled in
a variety of ways to cause a progressive force patters
during shaving: E.g., arm 144 can be provided with a
different spring constant by changing the length of arm
144 or the moment of inertia (e.g.. by providing a
thicker cross-section for arm 144). Arm 144 can also
be provided with a different preload force Fp by
keeping the same arm section and length, but moving the
location at which the arm 144 is attached to housing
side wall 146 upward (to increase preload force) or
downward (to decrease preload force). :The position or
shape of clip 152 could also be adjusted relative to
the arms to adjust preload force Fp; e.g., clip 152
could be.mouated so that the portion contacting one
blade is lower or higher than the portion contacting a
different blade.
One way to achieve a progressive force
patters during shaving is to have an initial .
progressive exposure and the same preload force and
spring constant for all blades. Another way to achieve
a progressive force pattern during shaving is to have
the same initial exposure (e. g.. all zero) and to have
progressive preload. A progressive preload can be
provided by having the spring constant for the tertiary
blade be higher than the spring constant for the second
blade, and by having the spring constant for the
primary blade be less than the spring constant for the
second blade. A progressive preload can also be
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achieved by using the same arms (i.e., same spring
constants) for all blades, but having the second arm
mounted higher than the primary blade and the third arm
mounted higher than the second.
The springs, preloads and initial exposures
can be used in combination with the cartridge
orientation bias affect to produce progressive exposure
and/or a progressive force pattern. For example, if
the cartridge has a guard-heavy orientation (e.g., a
cap first orientation though with a pivot in the
proximity of the guard and a light return spring, as
noted above), progressive geometry in use can be
effected with higher preloads, spring constants, and
at-rest exposures on the tertiary and secondary blades
than on the primary blade. Other combinations that
can be used to promote a progressive force during
shaving include a higher preload, spring constant, or
at rest exposure on the third blade than on the first
blade or combinations of these parameters having higher
values on the third blade as compared ~o the first
blade. Preferably the second blade would have
intermediate values or values that are the same as the
third blade in order to promote the progressive force
patters.
The spring preloads are typically in the
range of about 25g or less. The force on the
individual blades would be expected to be is the range
of about 0-40g, with between zero and 20 gms on the
first blade, and between greater than zero aad.less
than 40 gms oa the third blade. Typically the forces
on the individual blades would be greater than 5gm. At
rest exposures and exposures during shaving.typically
are in the ranges noted earlier.
