Abstract:
A hair clipper, particularly for incorporation in a battery powered electric dry shaver, comprising first and second mutually slidingly reciprocable and inherently slightly resilient toothed cutters resiliently urged to assume a similar curvature to one another along the direction of reciprocation to tend to render uniform the pressure distribution therebetween.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to hair clippers. Hair clippers may be incorporated in other appliances such as ac or battery powered electric dry shavers, where they are sometimes referred to as long hair trimmers, or may be separate appliances. 
     FIELD OF THE INVENTION 
     In certain presently available electric dry shavers a long hair trimmer is provided comprising first and second mutually slidingly reciprocable toothed cutters. Both cutters are rectilinear, one being fixed and the other movable, and the movable cutter is urged against the fixed cutter by means of a number of coil springs. Both cutters are substantially rigid but there is a size, weight and power consumption limit to the rigidity that can be given to the cutters. Consequently it has been found that the cutters can bow to some extent, and thus to achieve an effective cutting action at points between the springs, the force of the springs has to be increased such that the cutters are pressed together to a greater extent than necessary in the neighbourhood of the springs. The efficiency is thereby reduced and the power consumption increased. 
     An object of the invention is to provide a hair clipper of improved efficiency consistent with an effective clipping action. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a hair clipper comprising first and second mutually slidingly reciprocable and inherently slightly resilient toothed cutters resiliently urged to assume a similar curvature to one another along the direction of reciprocation to tend to render uniform the pressure distribution therebetween. 
     More particularly, the invention provides a hair clipper comprising first and second toothed cutters adapted to be driven in relative sliding reciprocation to effect a cutting action, wherein both cutters are inherently slightly resilient, wherein resilient means acts on the first cutter to urge it against the second cutter, wherein reaction means acts on the second cutter to oppose the force due to said resilient means, and wherein said resilient means and said reaction means provide a force couple that imparts a similar curvature to both cutters along the direction of reciprocation, whereby to tend to render uniform the pressure distribution between the two urged together cutters. 
     The resilient means may comprise at least one spring acting on the first cutter intermediate its ends, and the reaction means may include substantially non-resilient reaction structure acting on each end portion of the second cutter. 
     In one embodiment the first cutter is adapted to be driven in sliding reciprocation, and means is provided to locate the second cutter in position longitudinally and laterally while permitting it to curve resiliently to assume a similar curvature to the first cutter. Said locating means may include at least one piston working in a bore in the shaver body and urged into engagement with the second cutter to act thereon away from the first cutter and against said reaction means. Said piston may pass through a slot in the first cutter and thus also serve to locate the first cutter laterally and to guide the first cutter in its longitudinal reciprocation. 
     In another embodiment, the substantially non-resilient reaction structure comprises a pair of pins near opposite ends of the second cutter, the pins also serving to locate the second cutter longitudinally and laterally, and furthermore to locate the first cutter laterally and to guide it in its longitudinal reciprocation. 
     The result of tending to render uniform the pressure distribution between the cutters is to provide an effective or improved cutting action with greater efficiency and thus at reduced power consumption. With an effective cutting action the comfort of the user is enhanced and hair pulling during clipping is minimized. In a battery powered electric dry shaver it is important that the power consumption of the clipper is as low as possible consistent with an effective cutting action. When a clipper is driven by an AC reluctance motor the amplitude of clipper reciprocation decreases if the mechanical power consumed by the clipping action increases, thus decreasing the effectiveness of the cutting action, and therefore again it is important to increase the clipper efficiency. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a longitudinal section, partly broken away, through a hair clipper according to the invention; 
     FIG. 2 is a scrap section on an enlarged scale on line 2--2 of FIG. 1; 
     FIGS. 3A and 3B are a top plan and an end view respectively of the movable cutter of the clipper; 
     FIGS. 4A and 4B are a top plan and an end view respectively of the fixed cutter of the clipper; 
     FIG. 5 is a longitudinal section, partially broken away, through a second embodiment of a hair clipper according to the invention; and 
     FIG. 6 is a section on line A--A of FIG. 5. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to the drawings there is shown a hair clipper, sometimes referred to as a long hair trimmer, incorporated in a AC or battery powered electric dry shaver, a portion of the body of the shaver being shown at 10. The clipper comprises a first elongate movable toothed cutter 11 and a second substantially fixed elongate toothed cutter 12. The first cutter 11 is adapted to be driven in sliding longitudinal reciprocation relative to the second cutter 12 to effect a cutting action. To this end the rear edge of the cutter 11 is provided with an obliquely bent tab 13 provided with a notch 14. In use a reciprocating element of the shaver drive mechanism is engaged in the notch 14 to reciprocate the cutter 11. Such drive mechanism is not shown but a number of suitable mechanisms are currently available in the dry shaver art. The drive mechanism would normally be under control of a switch for selective operation of the clipper when required. 
     The area of mutual sliding contact between the two cutters in use is shown on cutter blade 11 as the longitudinal forward toothed strip portion 18 and the two longitudinally spaced strip portions 19, 20 at the rear edge of cutter 11, as shown in FIGS. 3A and 3B. 
     The cutters are each inherently slightly resilient along their length. A number of metals are suitable for forming cutter teeth and most of such metals would also exhibit sufficient inherent resilience for the purpose of this invention, thereby permitting the teeth to be integrally formed along the forward edges of the respective cutters. A preferred material is a stainless tempered steel. 
     The first, movable cutter 11 is resiliently urged against the second cutter by resilient means in the form of two spaced coil springs 15 received in frusto-conical recesses 16 in the body 10 of the shaver. During reciprocation the springs 15 can tilt from side to side in their recesses 16 to follow the cutter reciprocation. The springs 15 act on cutter 11 substantially midway between the centre of the length of the cutter 11 and its end. The cutter 11 is located laterally and guided in its longitudinal reciprocation by means of two pistons 28, to be described below, extending through slots 17 formed near the end portions of the cutter 11. 
     The second, fixed cutter 12 has set-back end portions 22 trapped beneath flanges 23 formed on the body 10 of the shaver. Two spaced coil springs 24 are received in respective bores 25 in the body 10. The springs 24 act on the respective pistons 28 which work in and extend partially from the bores 25. The outward ends of the pistons 28 are provided with studs 26 fitted into bores 27 through the second cutter 12. The pistons 28 and springs 24 are located between the springs 15 and the end portions 22 of the second cutter 12. The pistons 28 thus urge the end portions 22 against the flanges 23, to locate the second fixed cutter 12 in position longitudinally and laterally, while permitting the cutter 12 to curve between its ends to assume a similar curvature to the first cutter 11, as imposed by the first cutter 11 under the action of the springs 15. 
     It will be appreciated that the flanges 23 serve as substantially non-resilient reaction structure opposing the major action of the two springs 15 and the minor action of the two springs 24. In FIG. 1, the left-hand structure 23 and spring 15 form a first force couple and the right-hand structure 23 and spring 15 form a second force couple, both couples acting similarly to resiliently urge the cutters to assume a similar upward curvature to one another along the direction of reciprocation. 
     It is found that the action of the couples in causing the cutters to assume a similar curvature to one another together with the inherent slight resilience of the cutters themselves tends to render uniform the pressure distribution between the two urged together cutters. The pressure distribution is found to be more nearly uniform than in the case of two substantially rigid rectilinear cutters. In consequence the total force between the cutters can be reduced, the cutting action efficiency is improved, and the power consumption considerably reduced. For example in one embodiment the total force between the cutters was 300 grams. 
     The clipper in the embodiment of FIGS. 1 to 4 may also be readily and quickly assembled. The springs and pistons are dropped in their recesses, the movable blade 11 located over the pistons, and the end portions 22 of the fixed blade 12 are then slid beneath the flanges 23, perpendicular to the plane of FIG. 1, until the studs 26 enter into the bores 27. 
     Referring now to FIGS. 5 and 6 there is shown a second embodiment of the invention. The following structure is similar to correspondingly referenced structure in FIGS. 1 to 4: the shaver body 10, the first movable cutter 11, the second fixed cutter 12, drive tap 13, coil springs 15, frusto-conical recesses 16, slots 17 in cutter 11, and strip portions 18 and 20 of cutter 11 that slide in engagement with cutter 12. As shown in FIG. 5, three spaced coil springs in three recesses 16 are provided resiliently to urge the first movable cutter 11 against the second fixed cutter 12, in place of the two coil springs of FIG. 1. 
     In this embodiment the reaction structure opposing the action of the three springs 15 comprises a pair of pins 29 and flat spring clips 40, the pins 29 also serving to locate the second fixed cutter longitudinally and laterally, and to guide the first cutter in its longitudinal reciprocation. The pins 29 are disposed near opposite ends of the cutter 12. Each pin has a shank having a central portion 30 ground to be a press fit in a bore 31 in the shaver body 10. The shank has an enlarged diameter upper portion 32 providing a shoulder 33 seated against the shaver body 10. Each pin has a head 34 and a neck 35 between the head and the portion 32. The spring clips 40 clip on the neck 35. The clips 40 are shaped part-rings and, being inherently resilient, can accommodate the blade curvature as seen in FIG. 5. 
     The pin portions 32 extend through the slots 17 of the first blade, to locate the first blade laterally and to guide it in its longitudinal reciprocation, and also extend through apertures through the end portions of the second blade 12. The left-hand aperture 36 in FIG. 5 is circular and locates the blade 12 longitudinally and laterally on the portion 32 of the pin 29. The right-hand aperture 37 in FIG. 5 is slightly elongate in the direction of the blade 12 to accommodate the upward resilient curvature of the blades. The aperture 37 also locates the blade 12 laterally on portion 32 of the pin 29. 
     Referring again to FIGS. 4 and 5, it will be appreciated that there is inevitably a small increase of pressure between the two cutters in the neighbourhood of the springs 15. This pressure increase is relatively very small as compared with the prior art case of two rectilinear cutters, as explained above. In a further modification even this very small pressure increase can be reduced by appropriate shaping of the cutters.