Shaving apparatus

A shaving apparatus has a head assembly (2) which houses rotary cutters (8), and guards (4) which are provided with an annular series of hair-entry apertures (6). A fixed supporting surface is provided inside and outside the ring of apertures, to provide support when shaving with large applied pressure.

BACKGROUND OF THE INVENTION 
This invention relates to a shaving apparatus of the type having a shaving 
head with at least one rotary cutting assembly which comprises a rotary 
cutter housed within a guard. 
In a conventional shaving apparatus of the type described above, the rotary 
cutter is housed within a substantially cylindrical guard having a closed 
end face for contact with the skin. Hair-entry apertures are provided 
around the outer edge of this face, and the blades of the rotary cutter 
rotate within the guard adjacent these apertures. The cutter assembly has 
a spring mounting within the shaving head, so that the guard projects 
beyond a peripheral face of the shaving head. 
When pressure is applied to the shaving head against the operator's face 
during use, the cutter assemblies may retract until they reach a stop, and 
any further pressure increase is distributed over the guards and the 
peripheral face of the shaving head. An assembly of this type is described 
in EP-0-231 966, which corresponds substantially to U.S. Pat. No. 
4,711,028. 
SUMMARY OF THE INVENTION 
It is an object of the invention to improve the shaving characteristics of 
a rotary head shaving apparatus over the wide range of forces which may be 
applied to the shaver during use. 
According to the invention, there is provided a shaving apparatus 
comprising a head assembly which houses at least one cutter assembly, the 
cutter assembly comprising a rotary cutter having cutter blades housed 
within a guard, the guard being provided with hair-entry apertures 
arranged in an annular ring, wherein a peripheral surface of the head 
assembly comprises, for the or each cutter assembly, a first portion 
inside the annular ring and a second portion outside the annular ring, the 
first and second portions being fixed with respect to each other (when the 
shaving apparatus is assembled, if supplied as a kit of parts). 
In the shaving apparatus of the invention, the area within the ring of 
hair-entry apertures comprises a fixed surface which defines part of the 
force-absorbing peripheral surface of the head assembly. Thus, an 
increased force absorbing surface is provided which is found to improve 
the shaving characteristics over a wide range of applied forces, as will 
be explained in the following description. 
Preferably, the rotary cutter and the first portion of the peripheral 
surface are fixed to the body of the shaving apparatus, and the guard is 
fixed to a removable cover portion of the housing. In this way, the 
removal of the cover portion simultaneously exposes the guard and the 
rotary cutter or cutters for subsequent cleaning. Preferably, a cut-off 
switch is provided so that the rotary cutters may not be operated when the 
removable cover has been removed. 
The guard is preferably slidably received within the removable cover, and 
the rotary cutter is resiliently biased towards the guard. The shaving 
apparatus preferably comprises two or three cutter assemblies.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The shaving apparatus shown in FIG. 1 comprises a body 1 and a shaving head 
2, the head 2 housing three cutter assemblies 3. Each cutter assembly 3 
comprises an external guard 4 provided with hair-entry apertures 6 
arranged in an annular ring, and an internal rotary cutter 8 (shown in 
FIGS. 2 and 3) which is rotatable relative to the guard 4. The rotary 
cutters 8 are driven by means of an electric motor which is accommodated 
in the body 1 of the shaving apparatus. 
The features described so far are present in both a conventional rotary 
shaving apparatus and in the shaving apparatus of the invention. 
FIG. 2 shows in greater detail one example of a conventional cutter 
assembly 3. The shaving head 2 comprises a shaving head housing 10 having 
apertures for receiving the cutter assemblies 3. Each cutter assembly 3, 
comprising the guard 4 and the rotary cutter 8, is retained in the shaving 
head 2 by a retaining plate 12 which releasably engages the housing 10. 
The guard 4 is detachably secured to the retaining plate 12, and the 
retaining plate 12 is secured to the housing 10 by a fixing screw 14. A 
resilient element in the form of a helical spring 16 is compressed between 
the retaining plate 12 and the head of the fixing screw 14, which enables 
the retaining plate 12 to move to a limited extent relatively to the 
housing 10. As a result, the guard 4 is moveable relatively to the housing 
10 substantially perpendicularly to the peripheral face 18 of the housing 
10. The fixing of the retaining plate 12 within the housing 10 is arranged 
such that the closed end face of each guard 4 projects beyond the 
peripheral face 18 of the housing 10. 
The rotary cutters 8 are each engaged by an associated drive shaft 20 which 
centers the respective rotary cutter 8. The shaft itself is retractable 
along the direction of its axis, to enable the retraction of cutter 
assembly while it is being driven. The guard 4 has hair-entry apertures 6 
disposed in a ring at the outer edge of the end face of guard 4, and has a 
sunk portion 7, within the ring defined by the hair-entry apertures 6. 
The cutter assembly 3 of the invention is shown in detail in FIG. 3, in 
which the same reference numerals have been used as in FIG. 2 for similar 
components. The guard 4 used in the cutter assembly 3 of the invention 
again has an annular series of hair-entry apertures 6, but the guard 4 has 
a central opening 32 within the ring defined by the apertures 6. A fixed 
supporting disc 22 is provided in this central opening 32, and may be 
considered to define a portion of the peripheral face 18 of the shaving 
head. Thus, a first portion of the peripheral face 18 of the head 2 is 
defined by the disc 22, and a second portion is defined by the housing 10. 
The supporting disc 22 may have a raised portion around its circumference, 
which may be arranged to be level with the second portion of the face 18 
outside the ring of hair-entry apertures 6. Thus, the outer edge of the 
disc 22 provides a skin-contact surface. 
The disc 22 is fixed to the body 1 of the shaving apparatus through a 
spindle 24, which also acts as a central support for the drive mechanism 
of the rotary cutter 8. This drive mechanism comprises a gear wheel 26 
which is coupled to the drive motor of the shaving apparatus by a 
mechanism which is not shown in the drawings. The gear wheel 26 has a 
series of internal teeth 27 which engage external teeth 29 on a coupling 
member 28 which transmits rotational torque from the gear wheel 26 to the 
rotary cutter 8. The engagement between the coupling member 28 and the 
gear wheel 26 enables limited movement of the coupling member 28 along the 
axis of the spindle 24, and the coupling member 28 is biased towards the 
peripheral face 18 by a spring 30. 
The rotary cutter 8 is coupled to the end of the coupling member 28 by any 
appropriate bearing, which should enable some movement of the rotary 
cutter 8 in a plane perpendicular to the axis of the spindle 24. The 
rotary cutter 8 is centered through the engagement of the cutter blades in 
the channel defined by the annular guard 4. 
The improved shaving response of the shaving apparatus of the invention 
will now be described. The overall pressing force applied to a shaving 
apparatus in use is distributed over the cutter assemblies and over the 
peripheral surface of the shaving head. In a conventional shaving head, a 
raised rim may surround each cutter assembly which acts as a 
skin-tautening rim, and this rim also acts as a force-absorbing surface. 
The force on the skin at the location of the hair-entry apertures 
determines the level of bulging of the skin into the hair-entry apertures. 
This is an important parameter to control, since some skin bulging is 
desirable for a close shave, whereas excessive bulging will result in 
discomfort or irritation to the skin. Preferably, the level of bulging 
should be independent of variations in the pressing force applied by the 
user (hereinafter referred to as "shaving force"). 
In FIG. 4, curve 40 shows the ideal bulging B of the skin as a function of 
the shaving force F applied to the shaving apparatus, and which should be 
approximated to by a practical apparatus. For low shaving forces, the 
degree of bulging should increase rapidly, after which it should remain as 
constant as possible for higher shaving forces. To approximate to this 
curve, the cutter assemblies (of both FIGS. 2 and 3) are arranged to 
absorb all of the shaving force in the case of low shaving forces, and the 
shaving head housing absorbs a proportion of the shaving force in the case 
of high shaving forces, when the cutter assemblies have retracted. 
This optimum response can not be achieved totally in practice. For example, 
a conventional shaving apparatus, such as shown in FIG. 2, has the 
response shown by curve 44. The suspension of the cutter assemblies within 
the shaving head does ensure that only the cutter assemblies are in 
contact with the skin for low shaving forces, and this gives rise to the 
relatively rapid initial rise in bulging. However, the central portion of 
each cutter assembly absorbs some of the shaving force even for low 
shaving forces, which limits the initial rise in bulging. For higher 
overall shaving forces, the fixed peripheral surface of the housing then 
absorbs a further proportion of the force increase, in such a manner that 
the bulging increases less rapidly. However, the flat ideal response of 
curve 40 cannot be approached, particularly because of the small area of 
the skin-tautening rims in the conventional apparatus. 
The apparatus according to the invention has the response shown as curve 46 
which approximates much more closely to the desired ideal response. For 
low shaving forces, the annular ring of hair entry apertures absorbs the 
total shaving force, so that the bulging rises rapidly to the selected 
optimal value for shaving. For higher shaving forces, the provision of a 
force absorbing surface within the rim of hair-entry apertures provides a 
greater surface for distributing the additional shaving force, and 
provides support for the skin both inside and outside the ring of 
apertures. Consequently, the additional applied shaving force is 
distributed over the fixed peripheral face (face 18 and disc 22), and the 
pressing force on the annular ring of hair entry apertures remains 
substantially constant. 
The shaving apparatus of the invention, as shown in FIG. 3, also simplifies 
the cleaning operation of the shaving head assembly. In particular, the 
rotary cutter 8 and the coupling member 28 are secured to the body 1 of 
the shaving apparatus and thereby remain in place when the head 2 is 
removed. The guard 4 is secured to the head 2 to allow limited movement of 
the guard with respect to the head 2 by a suitable coupling (not shown in 
the drawings). Thus, removal of the head 2 exposes the rotary cutter 8 
which remains connected to the body 1 of the shaving apparatus, and also 
exposes the hair-entry apertures 6 which are coupled to the removed head 
2. The supporting disc 22 remains secured to the body 1 of the shaving 
apparatus. A cut-off switch 34 is required to ensure that the rotary 
cutter 8 cannot be operated when the head assembly 2 has been removed, and 
an appropriate form of cutoff switch will be apparent to those skilled in 
the art. 
The cutter assemblies in the shaving apparatus of the invention are 
independently sprung, and the suspension of the cutter assemblies will be 
designed to achieve the best shaving characteristics, by appropriate 
selection of the spring stiffness and pre-tension. For example, the ring 
of hair-entry apertures may have an inner diameter of 14 mm and an outer 
diameter of 20 mm. For this size of cutter assembly, a spring pre-tension 
of approximately 0.5N is appropriate, so that for shaving forces of less 
than 0.5N, the entire shaving force is absorbed by the ring of hair-entry 
apertures. A shaving force of approximately 0.5N is required to obtain the 
ideal level of bulging into the hair-entry apertures. A low spring 
stiffness is desired so that the cutter assembly retracts quickly once the 
ideal level of bulging has been obtained. Consequently, the peripheral 
face of the shaving head housing absorbs any further increase in the 
shaving force, and the force on the ring of hair-entry apertures remains 
substantially constant. For example, a spring stiffness of 0.1 to 0.2 N/mm 
is appropriate. 
Manipulation of the spring characteristics will influence the response of 
FIG. 4. Furthermore, the design of the inner supporting disc 22 also 
influences the shaving response. For example, the amount of projection of 
the guard 4 beyond the face 18 may be different from the projection of the 
guard beyond the disc 22. Typically, the projection of the ring of 
hair-entry apertures 6 when the guard is fully extended is 0.5 to 1.0 mm. 
The supporting disc 22 may project slightly beyond the face 18, for 
example with the ring of hair-entry apertures 6 of the guard 4 projecting 
0.9 mm beyond the face 18 and 0.7 mm beyond the rim of the supporting disc 
22. 
The shape of the central supporting disc may also influence the response of 
FIG. 4, and may be designed to optimize the skin-tautening effect of the 
disc during shaving.