EP0229679B1 - Method of forming a shear-active area on the shaving head of a dry-shaver according to desire and application - Google Patents

Abstract

A method for making the shaving head of a dry-shaving apparatus with an effective shaving area of a desired shape, in which a shear foil is mounted in an arcuate condition in a shaving-head frame without the cutter so that the foil assumes a free clamping curvature which is not influenced by the cutter, a normal-pressure distribution is applied perpendicular to the foil curvature which simulates the pressure distribution between the cutter and the foil in conformity with a desired effective shaving area, so that the shear foil experiences in said effective shaving area a deformation relative to the free clamping curvature, the simulated pretension curvature thus obtained corresponding to the desired normal-pressure distribution on the cutter in the desired effective shaving area relative to the shear foil. The cutting edges of the cutter are curved in conformity with the pretension curvature of the shear foil thus determined and the cutter, whose shape is in conformity with said pretension curvature, is pressed into the shear foil with the force which provides the desired normal-pressure distribution.

Description

The invention relates to a method for forming a shear-active area on the shaving head of a dry shaving apparatus which is shaped as desired and intended for use, in which a shaving foil in the shaving head frame is slidably arched in the clamping points under tension and a lower knife is pressed into the prestressing arch, the cutting edges of which are also curved are, the tangents to the clamping curvature in the clamping points towards the shaving head apex enclose an acute angle with one another, and a shaving head produced with the aid of this method.

Shaving heads for dry shavers, which consist of a curved, clamped film and a lower knife, which is also pressed into the film curvature and are also curved on the cutting edges, are known (AT-PS 171 778). While in this state of the art of shear foil the shape of the circular-cylindrical lower knife is forced on with the aid of the resiliently pressed-in lower knife, it is also known to force an approximately circular clamping curvature onto a shaving foil by means of a shaping clamping, which then becomes only insignificant when a circular lower knife is pressed in Changes in shape. In the case of circularly curved shaving heads formed in this way, due to the adapted circular curvatures, it is theoretically possible to form a fairly wide-area contact between the lower knife and the film when idling. In practice, however, circular clampings tend to make contact mainly on both sides of the apex even when idling. The shaving foil is deformed by the shaving forces during the shaving operation, and a further uncontrolled lifting can take place.

Circular shaving heads with a relatively wide clamping base diameter suffer from insufficient rigidity of the shaving foil when shaving, especially when firmly clamped. Any change in shape of the shaving foil during shaving changes the surface contact between the shaving foil and the lower knife. This shortens the shaving result when shaving.

It is known from DE-OS 33 40 661 to make a shaving head slimmer by specifying both the shaving foil and the lower knife a curvature which has a cosine-hyperbolic-shaped course. Such a shaving head, which manages with lower contact forces of the lower knife, already has a greater film rigidity, as a result of which greater shaving forces are absorbed and good contact between the films and the lower knife is already improved. In this case, the shaving foil is slidably clamped, whereby the slidability is of course limited in both sliding directions.

It is an object of the invention to increase the contact pressure between the lower knife and the shaving foil in the shaving-active area in such a way that forces are formed in the idle state between the lower knife and the shaving foil, which maintain contact between the lower knife and the foil in the desired shaving-active area during shaving.

• - die Scherfolie zunächst ohne Untermesser unter einem vorgewählten Winkel, mit vorgewählter Länge und in vorgewähltem Abstand eingespannt wird und danach längs der vom Schermesser noch unbelasteten Einspannwölbung eine senkrecht zur Folienkrümmung stehende Leerlauf-Normaldruckverteilung zwischen Schermesser und Folie simuliert wird entsprechend einem gewünschten scheraktiven Bereich, wodurch die Scherfolie in diesem scheraktiven Bereich längs ihrer Wölbung nach Maßgabe dieser gewünschten Form der Normaldruckverteilung eine simulierte Verformung gegenüber der freien Einspannwölbung erleidet, wobei die so entstandene simulierte Vorspannwölbung die gewünschte Normaldruckverteilung auf das Untermesser in dem gewünschten scheraktiven Bereich gegenüber der Scherfolie wiedergibt,
• - die Schneidkanten des Untermessers entsprechend der so simulierten Vorspannwölbung der Scherfolie gewölbt werden und
• - das Untermesser mit der dieser Vorspannwölbung entsprechenden Form in die Scherfolie mit Einspannwölbung eingedrückt wird mit der Kraft, die zu der gewünschten Normaldruckverteilung führt.

The object is achieved according to the invention with the aid of a method which is characterized in that

• - The shaving foil is first clamped without a bottom knife at a preselected angle, with a preselected length and at a preselected distance, and then an idle normal pressure distribution between the shaving knife and the foil perpendicular to the curvature of the sheath is simulated according to a desired shear-active area, along the clamping curvature that is not yet loaded by the shaving knife the shaving foil in this shear-active area undergoes a simulated deformation in relation to the free clamping curvature along its curvature in accordance with this desired shape of the normal pressure distribution, the resulting simulated bias curvature representing the desired normal pressure distribution on the lower knife in the desired shear-active area compared to the shaving foil,
• - The cutting edges of the lower knife are curved in accordance with the pretension curvature of the shaving foil thus simulated and
• - The lower knife with the shape corresponding to this pre-tensioning curvature is pressed into the shaving foil with tensioning curvature with the force which leads to the desired normal pressure distribution.

Such a design of a shaving head results in a concentration of the pretensioning forces in the shear-active area. With the help of such a shaving head design, the concentration of forces between the lower knife and the shaving foil, when they work together, moves into the desired shear-active area of the shaving head. This is a force distribution that is favorable for the shaving effect. The total pressure force can be set below 4 Newtons.

The shear-active area of the shaving head can be chosen in the crown or on the side of the crown. A shear-active area in the apex area of the shaving head is preferred in the case of slim shaving heads, because the point to be shaved is easily visible to the slim tip in the mirror.

A shaving head which is produced with the aid of the method according to the invention is characterized in that the bending line of the freely clamped shaving foil on both sides of the center of the shear-active area has a larger radius of curvature than the shaving knife before the shear knife is pressed in. With such a design, the pretension can be specifically aligned to the shear-active area. Where the shear-active area is to lie, the slimmer lower knife presses against the shaving foil and tensions it or pre-tensions it more than in the other shaving foil areas.

The preselection of the clamping length, the distance between the clamping points and the clamping angle is primarily decisive for the curve shape of the shaving head. The curve shape can be wide Ren embodiment of the invention further influence that the shaving foil in the apex area, which should be the shear-active area, has a lower bending stiffness than on the flanks to the side of the apex area. The different bending stiffness can be used to bend the shaving foil in the crown more than on the flanks, so that a wedge shape can be worked out better. The change in bending stiffness can e.g. B. can be achieved by changing the cross section or perforating the film. In this way, the shaving foil can assume a more wedge-shaped shape even in the freely clamped state. The normal pressure required for shaving between the lower knife and the shaving foil in the shear-active area must be generated by shaping the lower knife appropriately using the simulation method described. A more wedge-shaped shaving head design leads to better adaptation to the shape of the face and a better view of the area just shaved.

According to a further embodiment of the invention, it is provided that the clamping height between the film clamping points and the apex is 18 to 30 mm in order to form a pointed shaving head apex with a clamping base width of the shaving foil of 12 to 20 mm. In this way, with the aid of the method according to the invention, shaving heads with shaving foils result which, with different slenderness in the shear-active area, all form forces between the lower knife and the shaving foil which are greater than the shaving forces which want to lift off the shaving foils during shaving.

• Fig. I eine frei eingespannte Scherfolie ohne Untermesser, auf die eine gewünschte Scherbelastung aufgebracht (simuliert) ist; die Scherbelastung wird durch Pfeile angedeutet,
• Fig. 2 eine Darstellung eines theoretisch in viele Einzelteile unterteilten Abschnittes der Scherfolie, im Wölbungsquerschnitt gesehen,
• Fig. 3 ein Untermesser mit der Form der Vorspannwölbung bei einer gewünschten Druckverteilung auf die Scherfolie mit einem scheraktiven Bereich im Bereich des Scherkopfscheitels,
• Fig. 4 die Einspannwölbung einer frei eingespannten Scherfolie mit einem bevorzugt scheraktiven Bereich an einer Flanke des Scherkopfes,
• Fig. 5 ein Untermesser mit der sich durch Simulation ausbildenden Vorspannwölbung der Scherfolie mit scheraktivem Bereich an einer Scherkopfflanke entsprechend Fig. 4,
• Fig. 6 eine eingespannte sehr schlanke, keilförmige Scherfolie mit geringer Biegesteifigkeit,
• Fig. 7 ein Untermesser mit einer durch Simulation ermittelten Vorspannwölbung der Scherfolie nach Fig. 6.

The invention is explained in more detail with reference to the drawing. Show it:

• I shows a freely clamped shaving foil without a bottom knife, to which a desired shear stress is applied (simulated); the shear stress is indicated by arrows,
• 2 shows an illustration of a section of the shaving foil theoretically divided into many individual parts, seen in the cross-section of the curvature,
• 3 shows a lower knife with the shape of the prestressing curvature with a desired pressure distribution on the shaving foil with a shearing-active area in the area of the shaving head apex,
• 4 shows the clamping curvature of a freely clamped shaving foil with a preferably shear-active area on one flank of the shaving head,
• 5 shows a lower knife with the pretensioning curvature of the shaving foil with a shear-active area on a shaving head flank, which is formed by simulation, in accordance with FIG. 4,
• 6 is a clamped very slim, wedge-shaped shaving foil with low bending stiffness,
• 7 shows a lower knife with a pretensioning curvature of the shaving foil according to FIG. 6 determined by simulation.

The illustration according to FIG. I shows a shaving foil I of a dry shaving apparatus, which is held in a load-free manner in clamping points 3 of a shaving head frame 4. The tangents 8 to the shaving foil enclose with the shaving head base 6 between the clamping points and to the apex acute clamping angle a. The mutual distance between the clamping points 3 is indicated by x. The clamping length of the shaving foil is I. In this way, the shaving foil gets a natural curve shape that should be as close as possible to the desired shape. In order to achieve a force distribution that prevents mutual lifting in the shear-active area SK when idling and under load, a desired normal pressure load is applied to the shaving foil, which corresponds to the desired normal pressure load by the lower knife in the idle state and which should be greater than that during shaving lifting forces occurring. This preferred load is indicated in Fig. 1 by arrows 5. The arrows 5 directly in the apex 7 should correspond to a compressive force of approximately 1.2 N and, as the flanks 9 decrease, reflect compressive forces of 0.5 N to 0 N.

2 now shows how the simulated application of the pressure load is carried out. In this case, only a section of the film or a curved film part is shown in section in FIG. 2. To simulate the film deformation resulting from the selected film loading, the film section II in FIG. 2 is divided into very small sections a, b, c, etc. using the finite element method. At each division 11.1, 11.2, 11.3, 11.4. the forces acting on the foils are applied. These forces are represented by arrows 13. The size of the arrows 13 indicates the desired pressure force distribution, as shown in Fig. I. A prestressing curvature can then be determined on the basis of this pressure force distribution. If the cutting edges 16 of the lower knife 10 are given the resulting pre-stressing shape, then the shaving foil, in cooperation with the curved lower knife 10 in the shear-active area SK, for example in FIG. I in the apex, ensures the necessary contact forces. A prerequisite for proper functioning is, of course, that the bottom knife 10 lies completely against the film in the simulated area and that the film adopts the simulated pretensioning curvature. The contact pressure of the lower knife results from the pressure distribution which acts on the cutting edges 16. In Fig. 3 the concentration of forces is placed in the shear-active area at the apex. The curvature shape A of the lower knife 10, which corresponds to the initial curvature of the film and is shown in FIG. 3, has a slimmer cutting edge contour than the film according to FIG. I in the idle state without a lower knife.

This shaving head shape, determined by simulation, can be adapted to the respective needs in accordance with the desired shaving active area. Fig. 4 shows an embodiment in which the shear active area SK is placed in a flank. According to the simulation according to FIG. 2, a corresponding distribution of forces is applied to the shaving foil 18. As a result of this force distribution simulated on the shaving foil, the shaving foil 18 experiences a prestressing curvature of shape B, which also forms the cutting edge contour of the lower knife 10 '.

FIG. 0 shows a further exemplary embodiment in which the shaving foil 31 in the apex 7 has greater flexibility. As a result, the film 31, which is clamped freely displaceably between the clamping points 3, can already form a more wedge shape when an unloaded bending line is formed. If a simulated load is now given up again in accordance with the arrows entered in FIG. 6, a simulated prestressing curvature results. The prestressing curvature is again the cutting edge contour C of the lower knife 20 according to FIG. 7.

The greater flexibility of the shaving foil 31 in the apex area 7 can be influenced by varying the thickness of the foil and the width and number of webs between the holes and also the shape and number of the holes.

The shape of the shaving head depends on the desired requirements of the device and manufacturer of the device. The curvatures of the film or lower knife can follow a cosine-hyperbolic-shaped, elliptical or parabolic course. Intermediate values are also conceivable. The basic idea of the invention can be seen in the stiffening of the shear-active area SK by the corresponding curvature of the shaving foils and the lower knife.

With the help of the method, the manufacturer or designer is given the hand to create shaving head shapes of your own choice and as desired, while maintaining contact between the shaving foil and the lower knife in the desired shaving active area and consequently achieving good shaving results. The known lifting effects, which reduce the shaving performance, are no longer present.

Claims (9)

1. A method of providing the shaving head of a dry-shaving apparatus with an effective shaving area of a desired shape in accordance with its use, in which a shear foil is mounted in an arcuate condition under pretension in a shaving head frame so as to be movable at the clamping locations, a cutter being pressed into the foil thus curved, the cutting edges of said cutter being also curved, the tangent lines to the clamping curve at the clamping locations extending at an acute angle to each other, characterized in that

- the shear foil is first clamped in without cutter at a pre-selected angle, with a pre-selected length and at a pre-selected distance and subsequently, in addition to the clamping curvature which is not yet influenced by the cutter, a no-load normal pressure distribution perpendicular to the foil curvature is simulated between the cutter and the foil in conformity with a desired effective shaving area (SK), so that in addition to its curvature depending on said desired form of the normal- pressure distribution the shear foil experiences in said effective shaving area (SK) a simulated deformation relative to the free clamping curvature, the simulated pretension curvature thus obtained being representative of the desired normal-pressure distribution on the cutter in the desired effective shaving area relative to the shear foil (1),

- the cutting edges of the cutter are curved in conformity with the pretension curvature of the shear foil thus simulated, and

- the cutter, which has a shape corresponding to said pretension curvature, is pressed into the shear foil having the clamping curvature with the force which provides the desired normal-pressure distribution.

2. A method as claimed in Claim 1, characterized in that the effective shaving area (SK) is situated at the apex area of the shaving head (Figs. 1, 2, 6 and 7).

3. A method as claimed in Claim 1, characterized in that the effective shaving area (SK) is situated at a flank of the shaving head (Figs. 4 and 5).

4. A shaving head for a dry-shaving apparatus, manufactured by means of the method as claimed in Claims 1 to 3, characterized in that before the cutter is inserted the line of curvature of the freely clamped-in shear foil (1) in the effective shaving area has a larger radius of curvature than the cutter and after insertion the cutter completely engages against the foil in the simulated area and adopts the simulated pretension curvature.

5. A shaving head for a dry-shaving apparatus, manufactured by means of the method as claimed in Claims 1 and 2, characterized in that the shear foil has a lower resistance to bending in the apex area, which is required to be the effective shaving area (SK), than at the flanks beside the apex area.

6. A shaving head as claimed in Claim 5, characterized in that in order to reduce the resistance to bending the shear foil (31) has a smaller thickness in the apex area (SK) than outside this area.

7. A shaving head as claimed in Claim 5, characterized in that the resistance to bending of the shear foil (31) in the effective apex area (SK) is influenced by varying the width and the number of connecting portions between the apertures.

8. A shaving head as claimed in Claim 5, characterized in that the resistance to bending of the shear foil (31) in the effective apex area (SK) is influenced by varying the shape and the number of apertures between the connecting portions.

9. A shaving head as claimed in any one of the Claims 4 to 8, characterized in that in order to obtain a pointed shaving-head apex the clamping height between the foil-clamping locations and the apex is approximately 18 to 30 mm when the clamping base width of the shear foil is from 12 to 20 mm.

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