US3858316A - Shaving head having separately sprung blades - Google Patents

Abstract

A shaving head for use in a dry-shaving apparatus of the type comprising a thin circular shear foil and a rotating blade carrier which is mounted beneath the shear foil and carries a plurality of blades mounted in slots, the cutting edge of each blade which co-operates with the shear foil extending substantially in a radial direction, whilst the blades are each individually displaceable in the associated slot and also slightly tiltable, roughly in the plane of the slot. Each blade so cooperates with a part of the rotating blade carrier, which part supplies the centripetal force which compensates for the centrifugal force which acts on the blade, that when the blade is tilted from its neutral position the centrifugal force and the said centripetal force exert a restoring torque on the blade so that this will always be in a stable equilibrium. With a view to manufacturing and assembling tolerances the blade surface more remote from the axis of rotation preferably is convexly curved and cooperates with a straight wall of the associated slot, which wall extends parallel to the axis of rotation of the blade carrier.

Description

United States Patent 1 Tietjens 1 Jan. 7, 1975 SHAVING HEAD HAVING SEPARATELY SPRUNG BLADES [22] Filed: Aug. 3, 1973 [21] Appl. No.: 385,537

Related US. Application Data [63] Continuation of Ser. No. 318,011, Jan. 26, 1972,

abandoned.

[30] Foreign Application Priority Data Sept. 25, 1971 Netherlands 7113226 [52] US. Cl. 30/43.6, 30/346.51 [51] Int. Cl B26b 19/14 [58] Field of Search 30/435, 43.6, 346.51

[56] References Cited UNITED STATES PATENTS 2,245,420 6/1941 Volz 30/436 2,280,836 4/1942 Moskovics 30/436 2,289,323 7/1942 Dettle 30/416 2,618,055 11/1952 Robertson 30/436 X 3,740,843 6/1973 Tietjens 30/436 Primary ExaminerAl Lawrence Smith Assistant ExaminerGary L. Smith Attorney, Agent, or Firm-Frank R. Trifari 57 ABSTRACT A shaving head for use in a dry-shaving apparatus of the type comprising a thin circular shear foil and a totating blade carrier which is mounted beneath the shear foil and carries a plurality of blades mounted in slots, the cutting edge of each blade which co-operates with the shear foil extending substantially in a radial direction, whilst the blades are each individually displaceable in the associated slot and also slightly tiltable, roughly in the plane of the slot. Each blade so cooperates with a part of the rotating blade carrier, which part supplies the centripetal force which compensates for the centrifugal force which acts on the blade, that when the blade is tilted from its neutral position the centrifugal force and the said centripetal force exert a restoring torque on the blade so that this will always be in a stable equilibrium. With a view to manufacturing and assembling tolerances the blade surface more remote from the axis of rotation preferably is convexly curved and cooperates with a straight wall of the associated slot, which wall extends parallel to the axis of rotation of the blade carrier,

3 Claims, 9 Drawing Figures Patented Jan. 7; 1975 4 Sheets-Sheet 1 I N VEN TOR.

EDUARD W-ILLEM TIE'IJENS Patented Jan. 7, 1975 4 Sheets-Sheet 2 Patented Jan. 7, 1975 4 Sheets-Sheet 5 INVENTOR.

EDUARD WILLEM TIETJENS Patented Jan. 7, 1975 3,858,316

4 Sheets-Sheet 4 b 10b 9b IN VEN TOR.

EDUARD WILLEM TIETJENS ANT SHAVING HEAD HAVING SEPARATELY SPRUNG BLADES This is a continuation, of application Ser. No. 318,01 I, filed Jan. 26, 1972, now abandoned.

The invention relates to a shaving head for a dryshaving apparatus having a circular shear plate and a cutter member which cooperates with the shear plate and has at least one separately sprung blade the body of which is arranged to be movable in an opening in a rotatably drivable blade carrier. In operation the cutting edge of the blade, which edge extends substantially in a radial direction, resiliently engages the shear plate, which is spaced from the blade carrier.

Such a dry-shaving apparatus, described in French Pat. No. 1,188,529, is provided with separate springs for the blades, such that during use or when idling, the cutting edges of the blades are in contact wth the shear plate, ensuring that also during the cutting operation the cutting edges of the blades are in engagement with the shear plate.

To achieve a satisfactory shaving effect, dry-shaving apparatus in general requires a close engagement between the blade and the shear plate during the cutting operation, i.e., a stable equilibrium between the blade and the shear plate in this position of engagement, because the entire shaving process takes place in the plane of contact between the blade and the shear plate.

In known dry-shaving apparatus using rotatably drivable cutting members, the stable equilibrium during the cutting operation is usually achieved by maintaining the cutting path part of the shear plate (which during the shaving operation is in contact with the cutting edge of the rotating cutting member) accurately flat, and by using thrust springs urging the blades against the shear plate. Any force to be normally expected which tends to disturb this close engagement of the blades and the shear plate during the shaving operation, is neutralized by thrust forces of the springs.

Maintaining the cutting path part of the shear plate accurately flat is a factor which greatly raises the cost of manufacture. The use of strong thrust springs causes the shear plate to become inconveniently hot due to the generation of frictional heat, also use of such strong springs requires a comparatively strong source of energy for driving the cutting member in relation to the force required for cutting the hairs.

It is an object of the invention to provide a stable equilibrium, i.e., close and substantially. constant contact between the blade and the shear plate when they are in contact during operation, which state of equilibrium is to have the least possible dependence upon tolerances.

It is a further object of the invention to obviate the said disadvantages with regard to achieving the said state of stable equilibrium. The blade is mounted so as to be tiltable substantially in the radial direction; the cutting edge of the blade is resiliently held in engagement with the shear plate during idling and in the inoperative condition. The center of gravity of the blade is located so with respect to the disc-shaped blade carrier, that a centrifugal force which is produced in operation by the rotation and acts through the center of gravity will, (in the case of deviation from the initial position of engagement between the cutting edge of the blade and the shear plate,) produce a restoring force. This force increases on further deviation and tends to position the body of the blade so that the comparatively weak thrust spring, which cooperates with the blade and exerts a force which is directed towards the shear plate and is of the order of magnitude of the inertia forces exerted on the blade but exceeds them, is enabled to achieve a renewed position of engagement between the cutting edge of the blade and the shear plate.

The thrust spring for the blade, which has a comparatively small force, is required substantially only to ensure correct engagement between the blade and the shear plate in the inoperative condition. Initial deviation from this engagement in the radial direction during idling or during cutting will usually be corrected at the very beginning by a couple which results in a restoring force which increases with increase in deviation.

This means that, although a flat cutting path may be required, there is no need for extreme flatness, since even small irregularities of the cutting path will be capable of preventing significant deviation from the correct position of engagement between the blade and the shear plate. Also, the use for the blade ofa thrust spring of comparatively small force permits the use of a power source for driving the rotatable cutting member which is more in accordance with the force required for cutting the hairs than is the case in the known apparatus. Summarizing, it may be stated that according to the invention, stable equilibrium between the blade and the shear plate is obtained which is little dependent on tolerances.

The invention will now be described more fully with reference to the accompanying diagrammatic drawings which schematically show embodiments and in which:

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a schematic sectional view of a shaving head, illustrating the principle of a first embodiment of the invention,

FIG. 2 shows on an enlarged scale a detail of FIG. 1, and

FIG. 3 shows the embodiment of FIG. 1, but with the blade tilted,

FIG. 4 is a schematic sectional view illustrating the principle of a second embodiment,

FIG. 5 shows the embodiment of FIG. 4 but with the blade tilted,

FIG. 6 is a part sectional view, part elevation of the upper portion of a dry-shaving apparatus in which the principle shown in FIGS. 1 to 3 is used,

FIG. 7 is a part sectional view, part top plan view of the apparatus of FIG. 6,

FIG. 8 is similar to FIG. 6 but with the use of a modiflcation of the principle of FIGS. 4 and 5,

FIG. 9 is a top plan view of the cutting member used in the embodiment shown in FIG. 8, from which atone point a blade with an associated U-member and at an other point the U-member alone has been removed.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a shaving head 1 which comprises a rotatably drivable cutting member 2, which co-operates with a circular rigid or flexible shear plate 3, for example a shear foil supported by housing 1'.

The cutting member 2 comprises a disc-shaped blade carrier 4 which has a flat upper surface 5 and a parallel flat lower surface 6, is rotatable about an axis of rotation 7, and is formed with an opening 8 which extends in the axial direction throughout the entire thickness of the carrier 4 and in which a blade 9 having a cutting edge 10 and a body 11 is mounted movably and substantially radially tiltably. The cutting edge 10 of the blade 9 is held in engagement with the shear plate 3 by a thrust spring 12.

In the longitudinal sectional view shown in FIGS. 1 and 2, the body 11 of the blade 9 has an arcuate surface 13 remote from the axis of rotation 7 relative to the inner surface 17. The blade 9 is proportioned so that the following points of the blade lie substantially in one line: the middle 16 of the are 13, the centre of gravity l5, and the center 14 of the are 13. In the position of the blade in which it is in engagement with the shear plate, this line substantially coincides with the line of intersection of the longitudinal section shown, with the plane containing the axis of the blade carrier 4 and extending at right angles to the plane of the drawing. Preferably the centre 14 of the are 13 lies between the axis of rotation 7 and the surface 17 of the blade 9 which faces the axis of rotation 7, so that the distance R between the center 14 of the are 13 and the middle 16 of the are 13 considerably exceeds the distance Z between the center of gravity and the said middle 16. In spite of the fact that the blade 9 engages the remote wall 8a of the opening 8 relative to axis 7; and in operation the blade 9 is urged against this wall 8a by the centrifugal force produced, in a point or along a line only, this position of engagement may be regarded as a position of stable equilibrium between the shear plate and the blade. Such stability will occur, because, in the case of a departure from this engaged position, restoring forces will be produced which act on the blade 9 and tend to return it to its initial engaged position. This illustrated by FIG. 3, which shows the blade 9 in an exaggerated radially tilted position which it is assumed to have taken up in operation. In this position the arcuate surface 13 of the blade 9 engages the wall 8a of the opening 8 in a point or along a line 19, while a centrifugal force C acts through the center of gravity 15 in a horizontal direction in the plane of the drawing, and a reaction force K acts in a direction towards the center 14 of the arc at the point 19. This reaction force may be resolved into vectors V and V V extending horizontally also but in a direction opposite to that of the force C. The forces C and V form a counter-clockwise torque which tends to return the blade 9 to its initial position. The magnitude of this torque increases with increase in the vertical distance between the points 15 and 19, which means that an increasing departure of the blade 9 from its initial engaged position gives rise to an increasing restoring effect. The vector V must naturally be maintained as small as possible, and this is obtainable by keeping the deviation of the curve 13 from a straight line to a minimum, with the restriction that there must be a point or line contact between the surface 13 and the relevant wall of the opening 8. Practice has shown that with a curvature of the are 13 such that in the initial position its center lies between the axis of rotation 7 and the surface 17 of the blade 9 facing the axis of rotation 7, restoring forces of acceptable value will be produced.

Although it is far less significant than the torque produced by the centrifugal force and even is substantially negligible, it should be mentioned that, as is shown in FIG. 3, another counter-clockwise (ccw) torque is present which acts in support of the aforementioned torque. The component forces of this additional (ccw) torque are the force of gravity Zw acting at the center of gravity 15 and a normal force N acting at a pivot point 18, while the force Zw must obviously be increased by the force of the spring 12. The discrepancy between these torques will be understood by realizing that the disc-shaped blade carrier 4 may be driven at a speed of, or even exceeding, 4,000 revolutions per minute.

As has been mentioned hereinbefore, the thrust spring 12 has a comparatively small force, because it is only required to overcome the inertial forces exerted on the blade 9 and the friction between the curved surface 13 and the respective wall of the opening 8.

It will now be clear also that in the inoperative condition the center of gravity 15 need not exactly lie in a plane which contains the axis of the blade carrier and extends at right angles to the plane of the drawing. A requirement is, however, that at any deviation of the blade 9 the center of gravity 15 should remain within that part of the volume of the opening 8 which is bounded by the upper and lower surfaces of the blade carrier 4. This means that a stable equilibrium between the blade and the shear plate is obtainable even with comparatively large manufacturing tolerances, which considerably restricts the cost of manufacture.

Obviously, the invention is not restricted to the embodiment shown in the drawings. For example, the cutting edge 10 of the blade 9 may be slightly inclined with respect to the shear plate 3, and this embodiment in conjunction with the use of a shear plate in the form of a shear foil has yielded highly satisfactory shaving results, as practice has shown.

FIGS. 4 and 5 relate to an embodiment based on a slightly different principle. The blade 9'. is hingedly connected to a thin pull rod 21 oneend 20 of which passes through an opening 22 or coupling point in the blade 9' and the other end 23 of which is pivoted in an opening 24 in the cutting member 2'. The center of gravity 15 of the blade 9' and the opening 22 lie'on a straight line parallel to the cutting edge 10'. The opening 22 is located between the center of gravity l5 and the axis of rotation 7' of the cutting'member 2'.

FIG. 5 shows the blade 9 in an exaggerated tilted position. The spring 12 shown in FIGS. 1 to 3 is omitted in FIGS. 4 and 5, and only the thrust force S which is exerted by the spring 12' on the blade 9 in a direction towards the shear plate 3 is indicated symbolically by an arrow. From the foregoing discussion it will be clear that in the situation shown in FIG. 5 restoring torques act on the blade, one resulting from the centrifugal force C and the reaction force K and the other resulting from the thrust force S and the normal force N. It may be appreciated without difficulty that the construction shown in FIGS. 4 and 5 ensures a stable equilibrium of the blade 9.

FIGS. 6 and 7 show an application of the principles discussed with reference to FIGS. 1 to 3. FIG. 6 shows the upper part of a dry-shaving apparatus 25 which carries a shaving head 25 on a motor housing part 27. The shaving head 26 comprises a hood 28 at the upper end of which a substantially flat shear foil 3a is mounted by means of a tensioning member 29 pressed into the hood. The hood 28 is mounted by means of screw-thread on an insertion piece 30 which is embedded in a casing 31 of the motor housing part 27, which casing is made of a synthetic material. A blade carrier in the form of a disc 4a is mounted beneath a shear foil 3a provided with a plurality of hair passage apertures 32. The disc 4a is secured to the shaft 33 of an electric driving motor which is accommodated in the motor housing part 27 but is not shown in the drawing. The motor shaft 33 is supported for rotation in a sleeve bearing 34 pressed into the insertion piece 30. The disc 4a carries twelve blades 9a the cutting edges of which cooperate with the shear foil 3a and which are slightly tiltable with respect to this foil. To allow greater clarity in the drawing, FIG. 6 shows only two blades 9a. The cutting edges 10a of the blades 9a are elongate and extend in a direction substantially at right angles to their direction of movement. Obviously the direction of movement of each blade 9a mounted in the disc 4a is equal to the direction of rotation of the disc 4a, which direction is indicated by an arrow P in FIG. 7. Each blade 9a has antidamage portions 35 which are provided at both ends of the cutting edge 10a and have curved outlines 36 which merge into the cutting edge 10a, and each blade is mounted in an opening 8a in the disc 4a. Each blade 9a further has a convex lateral surface l3a which is urged against the outer boundary of the slot 8a, but otherwise the blade 9a has sufficient room in the slot 8a to be slightly tiltable with respect to the shear foil 3a. Thin resilient elements 12a which are rigidly secured to the lower surface of the disc 4a and pass through openings 37 in the blades 9a urge the blades with a light pressure against the lower surface of the shear foil 3a.

The shaving apparatus 25 shown in FIG. 8 is substantially equal to that shown in FIG. 6 except for the cutting member 2b. The cutting member 2b carries only four blades 9b, as the top plan view of FIG. 9 shows. The principle used in the apparatus shown in these Figures for stabilizing the blades 9b is a modification of the principle discussed hereinbefore with reference to FIGS. 4 and 5.

Each of the blades is associated with a U-member 38 which is made of metal wire that passes through the opening 22b, in the blade, ends 39 is pivotally secured in the blade carrier 4b and is freely movable in recesses 40 formed in the blade carrier 4b on either side of each blade 9b and accommodating the limbs of the U. The cross-piece of the U is freely movable in a circular central recess 41.

Each blade is freely rotatable about the cross-piece of the U-member 38 at its opening 22b. The center of gravity b and the opening 22b again are spaced from the cutting edge 10b by equal distances, but the ends 39 of the U-member are spaced therefrom by slightly greater distances. As a result, under the influence of the centrifugal force acting through the centre of gravity 15b and tending to rotate the U-member 38, a small upward force is exerted on the blade 9b so that in operation the cutting edge 10b of the blade is urged against the shear plate 3b. Thus a separate spring 12 for each blade 9 may be dispensed with.

What is claimed is:

1. For use with a dry shaver which includes a housing and a drive means for operating said shaving head, a shaving head comprising, a shear plate supported by the housing, a blade carrier within said housing and rotatably drivable about its axis of rotation by said drive means, the blade-carrier having a plurality of slots extending through it parallel to said axis, each slot having inner and outer edge surfaces respectively radially closer to and remote from said axis of rotation, a plurality of blades each positionable in one of said openings, each blade having a center of gravity (c.g.), an upper cutting edge for engagement along a line of contact with said shear plate, and inner and outer edges adjacent to corresponding edges of an associated slot, and associated with each blade a pull rod having first and second ends respectively coupled pivotally at coupling points to the inner edge of the blade and to the carrier at the inner edge of the slot, the 0g. of the blade and the blade coupling point defining a straight line which is generally parallel to the blade cutting edge when the blade is at rest and in said line contact with the shear plate, each blade being tippable within said slot the blade when rotated by said blade carrier subject to centrifugal forces which act at its center of gravity urging said c.g. generally outward of said axis, and which form part of a couple restoring force urging the blade back to its non-tipped position when it has become tipped in operation, said couple being proportionately greater when the blade tips farther and the center of gravity is moved further from its non-tipped position.

2. Apparatus according to claim 1 wherein said blade carrier in the location of said slots therethrough has thickness in the axial direction bounded by top and bottom surfaces of said carrier, said thickness being of sufficient magnitude, such that, during tipping movement of a blade within said slot during operation of the shaver, the center of gravity of the blade remains within said boundaries.

3. Apparatus according to claim 1 wherein said blade and slot inner edges each include an aperture through which one end of said pull rod extends as a pivotal coupling point.

I poqoso UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3858315 Dated January 7, 1975 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

If I

THE ASSIGNEE SHOULD BE --U.S. PHILIPS CORPORATION-- Signed and Scaled this i twenty-eight Day Of October 1975 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN A IPSIing Office (ommissiuner ufParenIs and Trademarks

Claims (3)

1. For use with a dry shaver which includes a housing and a drive means for operating said shaving head, a shaving head comprising, a shear plate supported by the housing, a blade carrier within said housing and rotatably drivable about its axis of rotation by said drive means, the blade-carrier having a plurality of slots extending through it parallel to said axis, each slot having inner and outer edge surfaces respectively radially closer to and remote from said axis of rotation, a plurality of blades each positionable in one of said openings, each blade having a center of gravity (c.g.), an upper cutting edge for engagement along a line of contact with said shear plate, and inner and outer edges adjacent to corresponding edges of an associated slot, and associated with each blade a pull rod having first and second ends respectively coupled pivotally at coupling points to the inner edge of the blade and to the carrier at the inner edge of the slot, the c.g. of the blade and the blAde coupling point defining a straight line which is generally parallel to the blade cutting edge when the blade is at rest and in said line contact with the shear plate, each blade being tippable within said slot the blade when rotated by said blade carrier subject to centrifugal forces which act at its center of gravity urging said c.g. generally outward of said axis, and which form part of a couple restoring force urging the blade back to its non-tipped position when it has become tipped in operation, said couple being proportionately greater when the blade tips farther and the center of gravity is moved further from its non-tipped position.

2. Apparatus according to claim 1 wherein said blade carrier in the location of said slots therethrough has thickness in the axial direction bounded by top and bottom surfaces of said carrier, said thickness being of sufficient magnitude, such that, during tipping movement of a blade within said slot during operation of the shaver, the center of gravity of the blade remains within said boundaries.

3. Apparatus according to claim 1 wherein said blade and slot inner edges each include an aperture through which one end of said pull rod extends as a pivotal coupling point.

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