Abstract:
A hinge includes a first rigid element enclosing elastic elements that have at least one elastic end oriented so that the elastic elements extend into a plane perpendicular to the axis of rotation of the hinge. One end of the first rigid element is formed by a knuckle-piece, which is inserted between a pair of knuckles that together constitute the rigid second element. A pin passes through all the knuckles. A bush, disposed between a female hinge of the second rigid element and the pin, defines a peripheral surface which serves as a cam surface, against which at least one portion of the elastic elements is adjusted.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an extendable hinge, and more particularly a hinge for spectacles. 
     Known extendable or spring hinges usually incorporate two rigid parts whose adjoining ends have a matching configuration and may include an external surface producing a cam action on the bearing faces, which parts are hinged to each other about a point of pivoting and connected to each other by a helical compression spring whose function is to return the rigid parts towards each other and keep these parts in one or more stable positions. When fitted to, say, a spectacle frame, hinges of the abovementioned type sometimes allow extended opening of the sidepieces beyond the stable open position (in which the sidepieces form an angle of approximately 93° with the front face of the frame) in such a way as to facilitate the placing of the frame on the wearer&#39;s face. 
     In recent years much research on hinges of this type has been targeted at reducing their size as far as possible, particularly in terms of their height, in order to enable them to be built into the increasingly lightweight frames now found on the market. This research has led to the springs being miniaturized, which, although giving satisfactory results, has by now reached a limit, the reduction in the size of the turns being limited by the diameter of the spindle around which they must sit. 
     Recent developments in spring hinges have therefore led to helical springs being replaced by a leaf of an elastic material such as polyurethane, or by a leaf spring. Progress in terms of size has however been insignificant because the reduction in size of these hinges is necessarily accompanied by a decrease in the height of the bearing faces of the rigid parts, thus resulting in enormous wear which makes it impossible to guarantee reliable operation of the hinge. 
     For example, patent application EP-A-0,115,826 discloses a spring hinge for a spectacle sidepiece in which the sidepiece is connected to a socket that pivots, about a screw, on a head forming a cam which is itself integral with the front face of the frame. The socket contains a leaf spring consisting of a stack of three diamond-shaped leaves held in place by fixing one of its ends in the socket while its other end is intended to press against either of two perpendicular surfaces of the said cam in order to define two stable positions, namely open and closed, of the sidepiece. The hinge disclosed also allows slightly extended opening of the sidepiece which is limited by stop means. A device working on the same principle is disclosed in EP-A-0,235,780. This device additionally incorporates a screw for adjusting the initial tension of the spring, which in this patent application has a circular cross section with frustoconical ends. 
     In these two known devices, the cam head has such small bearing surfaces that the device cannot, without deformation, take stresses very slightly greater than those which it undergoes normally in the course of use, particularly stresses applied at right angles to the normal plane of articulation of the hinge, unless the height of the cam part is increased—the very opposite of what is intended. Also, these devices require adjustment screws and/or fastening screws. Consequently the known spring hinges which use leaf springs are unsuited to the stresses currently imposed in the spectacles market both by manufacturers, as regards the minimum load the frames must be able to withstand without deforming, and by users concerned about the aesthetic appearance of the frames. 
     French Patent No. 1,593,112 in the name of Mari discloses a click-action hinge for a spectacle frame that comprises a square-section spindle about which can pivot a sharp-edged seat mounted in a spectacle sidepiece. The sidepiece has two stable positions. In addition, the seat has a longitudinal slot which gives it a certain elasticity and allows elastic return of the sidepiece to the normal open position after it has been opened slightly past the perpendicular to the face. 
     The known hinge does not have the disadvantages of the devices mentioned earlier. However, it requires, by its very design, a gap between the sidepiece and the front face of the frame, and dirt can settle in this gap. The gap is also aesthetically unattractive, as is the visible seat. In addition, a slight tug on the sidepiece in the direction of the wearer&#39;s ear is sufficient to pull the hinge apart. Lastly, the elastic return to the open position has to overcome friction forces—which themselves cause hinge wear—exerted by the seat on the square-section spindle and, because of the configuration of the spindle, this action can, beyond a certain angle of pivoting of the sidepiece, take the sidepiece as far as a position lying in the continuation of the face of the frame. 
     SUMMARY OF THE INVENTION 
     The Object of the invention is therefore to overcome the disadvantages of the prior art. 
     More specifically, it is an object of the invention to provide a novel extendable hinge that is extremely small, particularly in terms of height, but nonetheless does not impair the ability of the said hinge to withstand breakage, particularly during the application of stresses perpendicular to its normal plane of articulation or under the action of a tensile force acting along the sidepiece. 
     Another object of the invention is to provide an extendable hinge that has no visible screws or connecting and/or return parts. 
     Another object of the invention is to provide an extendable hinge whose manufacturing costs are less than those of hinges of the prior art. 
     These objects are achieved by the present invention in that it provides a hinge comprising, in a manner known per se, a first rigid part mounted so as to pivot about a pin on a second rigid part, which first part contains spring means that consist of at least one leaf spring and are such as to engage with a part having a cam surface fixed to the said second part, or made in one piece with it, in order to define stable relative angular positions of the said rigid parts. 
     The hinge according to the invention differs from the known hinges, however, in that one end of the said first rigid part is connected to, or consists of, a portion forming a knuckle which is inserted between a pair of knuckles that form the end of the said second rigid part, with the said pin being inserted through all these knuckles, while a bush is interposed between one knuckle of the said second rigid part and the said pin, which bush defines both a cylindrical passage in which to accommodate the said pin and an external peripheral surface constituting the said cam surface and against which at least a portion, termed the “clamping portion”, of the said spring means is designed to fit. 
     The clamping portion of the spring means may be, for example, in the general shape of a Y or in the general shape of a flat hook. Furthermore, the spring means may be composed of a single leaf spring or several leaf springs that are superimposed and/or arranged side by side and oriented in such a way that their smallest dimension, in cross section, extends in a plane perpendicular to the normal plane of articulation of the two rigid parts. In order to reduce the size of the hinge to a minimum, the smallest dimension of the spring means will be, for example, approximately 0.4 mm, so as to give a hinge having a total height of no more than approximately 2 mm. 
     The stable relative angular positions of the rigid parts will preferably be obtained by engagement of at least one recess provided on the said cam surface with at least one matching protuberance provided on one end of the said clamping portion of the spring means. The number of protuberances and matching recesses, by which one rigid part is held in a stable position relative to the other, is not restrictive and will depend on the intended use of the hinge according to the invention. As a variant and/or in addition, the holding of the sidepiece in the open and closed positions could be produced instead by the bush being “squeezed” by the clamping portion of the spring means. If so, the recesses and protuberances would not necessarily match each other exactly. 
     In a first embodiment of the invention, the knuckle portion is formed by one end of the said first rigid part, in which case the spring means are preferably in the general shape of a Y whose two arms form the said clamping portion of the said spring means. Advantageously, the spring means also include a return part composed of a third arm, made in one piece with the said two arms and adjacent to these in the said normal plane of articulation, which third arm is such as to abut elastically against the said second rigid part. 
     In a second embodiment of the invention, the said knuckle portion of the first rigid part is formed by another portion, termed the “encircling portion”, of the spring means. 
     In this case the spring means advantageously also include a return part shaped like a flat hook having an outwardly curved tip that is such as to abut elastically against the said second rigid part. The return part may be a separate part which is placed on top of the said encircling portion of the said spring means. As a variant, it may be formed by a portion surrounding the encircling portion of the spring means, in the normal plane of articulation. 
     It will be understood that the special structure of the hinge according to the invention, particularly the engagement of the knuckles and the close fit of the clamping portion of the spring means around the bush, gives the hinge good resistance to the stresses which may be applied to it in several planes. It is obvious too that, because of the elimination of the bearing faces on the external surface of the second rigid part, the latter may advantageously be made from a commonly used material, such as nickel-silver or titanium, whereas more expensive materials capable of withstanding a large shearing force, such as treated steel, may be reserved for the bush described earlier. 
     The invention also relates to applications of the hinge described above. The hinge finds its most useful application as a spectacle frame hinge, in which one of the rigid parts is mounted on, or consists of, a spectacle sidepiece and the other part is a rigid component integral with the front face of the said spectacle frame, often known as a “corner piece”. The hinge according to the invention may be used, in a variant, in the hinging of a door, such as a refrigerator door or a vehicle door, with respect to a door frame. However, these applications are not of course restrictive, and other types of articulation familiar to those skilled in the art can be fitted with the abovementioned hinge. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail with reference to the following description, taken in combination with the appended drawings in which: 
     FIG. 1 is a schematic view from beneath, in exploded perspective, of a hinge in a first embodiment of the invention; 
     FIGS. 2 to  4  are schematic views from beneath, in partial section, of parts of a hinge in a variant of the first embodiment of the invention, applied to a spectacle frame, and illustrating the closed, open and extended open positions, respectively, of the sidepieces of the spectacles; 
     FIG. 5 is an exploded schematic view, seen in perspective from above and in partial section, of a hinge in a second embodiment of the invention; 
     FIG. 6 is an exploded schematic view, seen in perspective from above, of a hinge in a variant of the embodiment in FIG. 5; 
     FIG. 7 is an exploded schematic view, seen in perspective from above, of a hinge in another variant of the embodiment seen in FIG. 5; and 
     FIGS. 8A to  8 C are schematic views, seen from above, illustrating the operation of the hinge shown in FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In this description the term “height” refers to a dimension measured in the direction of the height of the sidepieces of the spectacles, considered in their normal use by a wearer. Also the expression “angle of extended opening” refers to the difference between the obtuse angle formed by the sidepiece with the front face of the spectacle frame in the maximum stretched open position and the angle (about 93°) formed by the sidepiece with the front face of the frame in the normal open position. 
     Referring initially to FIG. 1, this shows a hinge according to the invention fitted to a spectacle frame comprising, in a manner known per se, rigid part  1 , generally termed the corner piece, which is designed to be fixed to the front face of the frame by a first end (not shown). The corner piece  1  may be screwed and/or joined by some fusion-based process to the front face of the frame, optionally after first being bent to adjust its curvature to that of the front face. In the embodiment illustrated, the end  2  of the corner piece  1  remote from its first end possesses two flat lobes  2   a ,  2   b  situated in planes parallel to each other and to the normal plane of articulation P of the hinge. An approximately circular through hole  3 , whose periphery defines two projections such as  3   a , is formed in lobe  2   a , while a circular through hole  4  of smaller diameter is formed in lobe  2   b . The lobes  2   a  and  2   b  form the knuckles of the rigid part  1 . 
     The other rigid part of the hinge consists of one of the sidepieces  5  of the spectacles. As seen in FIG. 1, the end  5   a  of the sidepiece  5  has a through hole  7  of the same diameter as the hole  4 , so that the said end  5   a  forms the knuckle of the sidepiece  5 . More specifically, the hole  7  is made in the bottom of a recess  6  in the shape of a curvilinear isosceles triangle formed in the thickness of the sidepiece  5 . 
     The knuckle  5   a  of the sidepiece  5  fits between the two knuckles  2   a  and  2   b  of the corner piece  1 , the corner piece  1  and the sidepiece  5  being hinged to each other about a crimped pin  9  which is inserted in the direction of the arrow F 1  through the aligned holes  4  and  7  and fits into a bush  10  which is inserted in the direction of the arrow F 2  through the through hole  3 . 
     Movement of the bush  10  perpendicularly to the plane P is prevented by engagement of the pin  9  with the bush  10 . Specifically, the pin  9  is pushed in and then crimped or adhesively bonded or fixed in some other way inside the bush  10 . Clearly, however, some form of locking part could, as a variant, be inserted into the pin  9 , as illustrated for example at  29  in FIG.  5 . Either way, the person skilled in the art will note that the resulting assembly can easily be taken apart with a hammer and a pin drift, e.g. in order to replace a damaged sidepiece. 
     Rotary movement of the bush  10  in the plane P is prevented by the engagement of the two projections, such as  3   a , with two recesses  16  and  17  formed in the periphery of the bush  10 . The number of paired recesses and projections is however not a limitation. Another function of the recesses  16  and  17  will be seen below. It will be realized that the pin  9  and locking part  29  turn freely as an assembly in the bush  10 . 
     Still referring to FIG. 1, it can be seen that the hinge according to the invention also comprises spring means  8  which in this embodiment form an approximate Y shape, the arms  8   a  and  8   b  of the Y having an approximately rectangular cross section and having respective protuberances  14   a  and  14   b  towards their free end. The spring means  8  are designed to sit in the recess  6  whose periphery is of a similar shape, but with slightly greater dimensions than those of the said spring means. 
     The hinge illustrated also includes a protective cap  11  in the form of a plate designed to cover the spring means  8  completely and containing an opening  12  of larger dimensions than the periphery of the bush  10 . The cap  11  is designed to fit on top of the spring means  8 , on a shoulder  13  formed in the recess  6  so as to conceal the spring means  8  from sight and protect it from dust. 
     It will be appreciated that, in view of the very flat configuration of the spring means  8 , whose height may be of the order of 0.4 mm, the sidepiece  5 , and hence also the corner piece  1 , can also be of minimal height. It will be appreciated too that the fitting together of the knuckle  5   a  and the knuckles  2   a  and  2   b  with the pin  9  ensures that the hinge cannot come apart if subjected to unusual stresses. 
     FIGS. 2 to  4  illustrate a variant of the hinge shown in FIG.  1 . In these figures, structural parts identical to parts shown in FIG. 1 will be given the same reference numbers. Similar parts will be denoted by the same reference numbers followed by the prime sign. 
     As FIG. 2 shows, this embodiment differs from that described with reference to FIG. 1 essentially in that the spring means  8 ′ include an extra portion  8   c  which is made in one piece with the common end  8   ab  of portions  8   a  and  8   b . The parts of this hinge which are not shown, such as the sidepiece, the second knuckle of the corner piece, and the pin, are the same as illustrated in FIG.  1 . It will be understood therefore that, in reality, portions  8   a  and  8   b  of the spring means are not placed against the hinge  2   a  as depicted, but that the knuckle  5   a  is interposed between these parts. 
     The portions  8   a  and  8   b  are adjusted tightly around the bush  10 , possibly with an initial stress if it is wished to reduce to a minimum the play between the corner piece  1  and the sidepiece (which is not shown). As can be seen in these figures, another difference between this and the variant illustrated in FIG. 1 is that the spring means  8 ′ are formed by two stacked leaf springs, such as  15   a ,  15   b , although this number is not restrictive. Actually, the number of stacked leaf springs will depend on how much resistance to stress it is wished to give the frame. 
     In FIG. 2 the hinge according to the invention is fitted to a spectacle frame in which the sidepieces are in the closed or folded position. In this position the protuberance  14   b  extending from the free end of the portion  8   b  engages in the recess  16  defined in the periphery of the bush  10  so as to keep the sidepiece still, while the protuberance  14   a  on portion  8   a  is simply resting against the outer periphery of the bush  10 . It will be observed also that portion  8   c  of the spring means  8 ′ is under no stress. 
     FIG. 3 shows the same parts as before, but with the sidepiece in the normal open position, that is to say a position in which the sidepiece of the spectacles (not shown) forms an angle of about 93° with the front face of the frame (not shown). The stability of this position of the sidepiece is ensured here by the respective engagement of protuberances  14   a  and  14   b , on portions  8   a  and  8   b  respectively, in the recesses  16  and  17 , while the free end  19  of portion  8   c  of the spring means  8 ′ has come into contact with the inner wall  18  of the corner piece  1 , although this portion  8   c  is under no bending force. 
     At this stage the operation of this hinge is no different than that of the hinge shown in FIG.  1 . 
     FIG. 4 illustrates a subsequent stage in the opening of the sidepiece, corresponding to a so-called extended open position, in which the sidepiece can form an angle of as much as 120° with the front face of the frame. In this extended open position, the protuberances  14   a ,  14   b  and the recesses  16 ,  17  are no longer in mutual engagement. In addition, since the end  19  of portion  8   c  of the spring means  8 ′ is still in contact with the wall  18 , because of the continued rotation of the sidepiece relative to the position illustrated in FIG. 3, portion  8   c  now comes under a bending force in the direction of the arrow F which presses it at  34  against portion  8   b . It will be seen therefore that the size of the angle of the extended opening will depend on the flexibility of the spring means  8 ′. It is obvious too that the configuration shown in FIG. 4 corresponds to an unstable position of the spectacle sidepiece, which will have a tendency to spring back, under the return force exerted by the spring means  8 ′, to a position shown in FIG.  3 . 
     Turning now to FIG. 5, this shows a hinge in a second embodiment of the invention, prior to assembly. Identical reference numbers increased by the value  100  will be given to parts similar to those described with reference to FIGS. 1 to  4 . 
     The hinge shown in FIG. 5 thus comprises a corner piece  101  and a spectacle sidepiece  105 . These are designed to be hinged to each other about a pin  109  which fits into a bush  110 . In this embodiment the knuckle  36  of the sidepiece  105  is formed in one end of a connecting spring part  20  which is in the general form of a thin leaf spring. The other end  21  of the connecting part  20  is barbed so that it can be inserted into and blocked inside the sidepiece  105 . The end  21  of the connecting part  20  and the sidepiece  105  can therefore be overmoulded, that is, the part  20  is positioned inside the mould in which the sidepiece is made before the plastic material is injected into the mould to produce the sidepiece. Alternatively the part  20  can be pushed into the sidepiece  105  while the material of the sidepiece is raised to a temperature above its softening point. The hinge also possesses, as its spring means  108 , two leaf springs  108   a  and  108   b , which are each roughly the shape of a thin, flat hook whose curved end terminates with a protuberance  114   a  and  114   b , respectively, turned towards the inside of the hook, and includes a projection  24   a  and  24   b , respectively, on the outside curve of the hook. The connecting part  20  and the leaf springs  108   a ,  108   b  are stacked so that the opening  23  of the connecting part  20  is lined up with the area inscribed inside the hooked curved end of the leaf springs  108   a ,  108   b  and also so that the respective bodies  37 ,  38   a  and  38   b  of the said part and of the said leaf springs are superimposed on each other. In the variant illustrated, the hooks of the leaf springs  108   a  and  108   b  face in the same direction; however, they could face in opposite directions. The connecting part  20  and the leaf springs  108   a  and  108   b  together form the spring means of the hinge. 
     In this embodiment, the bush  110  is integral with a supporting plate  27  on which there also stands a cylindrical dowel  25 . The knuckle part of the corner piece  101  contains an opening  28  matching the shape of the bush and a through hole  26  of a diameter slightly greater than that of the dowel  25 , so that the bush  110  and the dowel  25  fit into the opening  28  and the hole  26 , respectively. 
     When the sidepiece of the spectacles is in the open position, the protuberances  24   a  and  24   b  abut against the dowel  25  which forms a stop. In this position the protuberances  114   a  and  114   b  are sitting in the recess  117  formed in the periphery of the bush  110 . The stable closed, or folded, position of the sidepiece is arrived at by engaging the same protuberances  114   a  and  114   b  in the recess  116  formed in the periphery of the bush  110 . In this second embodiment of the invention the connecting part  20  and the leaf springs  108   a  and  108   b  preferably have more or less identical characteristics of elasticity which, as will be seen from FIG. 5, will determine the maximum amplitude of the extended open angle of the spectacle sidepiece, which can be as much as 90°. 
     Mechanical tests carried out on a spectacle frame fitted with the hinge described with reference to FIG. 5 have shown that the frame fulfils the strength requirements imposed by manufacturers of spectacles for children, in the sense that they withstood, without breaking, the application of a 4.535 kg load on each sidepiece at a distance of 50.8 mm from the axis of rotation of the hinge so that the sidepiece was pivoted through 180° in the normal plane of articulation, relative to its folded position. 
     Two variants of the hinge illustrated in FIG. 5 are shown in FIGS. 6 and 7. In FIG. 6, parts similar to those described with reference to FIG. 5 will be given the same reference numerals followed by the prime sign. Some of these parts will therefore not be described again. 
     The variant seen in FIG. 6 differs from that of FIG. 5 essentially in that in the first place a single leaf spring  108 ′ replaces the leaf springs  108   a  and  108   b , and in the second place it incorporates a separate return part. 
     More precisely, the spring means shown in FIG. 6 include a return leaf spring  30  on top of both a connecting piece  20 ′ and a leaf spring  108 ′ and all three of these have a barbed end  21   a-c  similar to the end  21  of the connecting part  20  shown in FIG. 5, by means of which ends they are held firmly in the sidepiece  105 ′ of the spectacles. 
     At the opposite end from the end  21   c  of the leaf spring  108 ′ is a Y-shaped free end comprising two arms  108   a ′ and  108   b ′, in a similar way to the spring means  8  of FIG.  1 . Parts  108   a ′ and  108   b ′ of the leaf spring  108 ′ are designed to fit around the periphery of a bush  110 ′ and engage in the recesses  116 ′ and  117 ′, respectively, formed in the bush in the same way as will be described with reference to FIGS. 8A to  8 C. 
     At the opposite end from the end  21   a , the return leaf spring  30  is formed into a hook, the curved tip of which is bent out, as indicated at  31 . 
     The knuckles  102   a ′ and  102   b ′ of the corner piece  101 ′ are integral with a curved wall  22  of which one end  35  comes into alignment with the front face of the frame and of which the tapering other end  32  is approximately perpendicular to the end  35 . With the sidepiece  105 ′ in the stretched open or extended open position, the bent-out tip  31  of the return leaf spring  30  abuts against the wall  32  of the corner piece  101 ′, in a similar way to that illustrated in FIG.  8 B. 
     It will be observed that the embodiment illustrated includes a locking part  29  which engages with the opposing hollow end of the pin  109 ′. To be specific, in order to prevent any movement of the bush  110 ′ perpendicular to the plane P, the part  29  is inserted and then crimped or adhesively bonded or fixed in some other way inside the pin  109 ′. 
     FIG. 7 illustrates a variant of the hinge shown in FIG.  6 . In this figure, parts identical to those of FIG. 6 are identified by the same reference numbers and will not be described again, and parts that are similar will be identified by the same reference numbers increased by 100. 
     The hinge shown in FIG. 7 differs from that in FIG. 6 essentially by the fact that the connecting part  20 ′ and the return leaf spring  30  of FIG. 6 are replaced by a single connecting and return leaf spring  33  which is designed to sit on top of the leaf spring  108 ′ and is forced into a spectacle sidepiece  105 ′. The free end of the connecting and return leaf spring  33  comprises two distinct parts made in one piece, one forming the connecting part  120 ′ and the other the return leaf spring  130 . Much as in FIG. 6, the portion that forms the connecting part  120 ′ contains a circular opening  123 ′ while the portion that forms the return leaf spring  130  is in the shape of a hook whose curved tip  131  is bent out. 
     FIGS. 8A to  8 C illustrate the operation of the hinge shown in FIG.  7 . Down the left-hand side are views taken in a plane which is both parallel to the plane of articulation and intermediate between the leaf spring  108 ′ and the connecting and return leaf spring  33 , while in parallel, down the right-hand side, are views taken in a plane which is parallel to the plane of articulation and which contains the said connecting and return leaf spring  33  viewed in section. 
     FIG. 8A shows that in the closed position of the sidepiece (not shown) of the spectacles, the protuberance  114   b ′ of the leaf spring  108 ′ is received in the recess  116 ′ formed in the periphery of the bush  110 ′ and the connecting and return leaf spring  33  is not under any stress. 
     As the sidepiece is moved into the normal open position, the protuberance  114   b ′ drops into the other recess  117 ′ formed in the bush  110 ′ and, at the same time, the portion forming the connecting part  120 ′ of the connecting and return leaf spring  33  rotates about the pin  109 ′ until the bent-out tip  131  of the portion forming the return leaf spring  130  of the connecting and return leaf spring  33  abuts against the end  32  of the corner piece, as illustrated in FIG.  8 B. 
     It will be understood therefore that the positions shown in these figures correspond to stable positions of the sidepiece of the spectacles relative to the corner piece. 
     If the sidepiece opens further as far as the extended open position illustrated in FIG. 8C, the protuberance  114   b ′ will come out of the recess  117 ′, with the result that the ends of the leaf spring  108 ′ will simply rest against the periphery of the bush  110 ′: the position thus defined is unstable. Simultaneously, because the rotation of the portion forming the connecting part  120 ′ about the pin  109 ′ has been continued while the portion forming the return leaf spring  130  is in abutment against the corner piece  101 ′, the two portions of the connecting and return leaf spring  33  have met and have been deformed to the limit of their elasticity. It will thus be understood that the position illustrated in FIG. 8C is a position of maximum stretched opening, corresponding to an angle of extended opening of about 45° or more, in which the connecting and return leaf spring  33  has a tendency to return to its undeformed condition as in FIG.  8 B and thus has a tendency to exert a return action on the sidepiece of the spectacles. 
     The embodiment illustrated in FIGS. 5 to  7  has the advantage over that illustrated in FIGS. 1 to  4  that the sidepiece of the spectacles may be made of plastic because it does not define a passage for the pin, this function being provided by the connecting part. 
     Clearly, the above description is given purely by way of example, and various modifications could be made to it without departing from the scope of the invention. For example, the hinges illustrated in FIGS. 5 to  7  could, much as in FIGS. 2 to  4 , include elastic parts that each consist of a stack of two leaf springs or more. 
     As is apparent from the above description, the spring hinge according to the invention, when fitted to a spectacle frame, is therefore extremely small, particularly in terms of its height, and yet exhibits good resistance to the stresses which may be applied to it in several planes. It will be seen too that, in all the embodiments of the invention, the special shaping of the spring means makes the use of fixing and adjusting screws superfluous. However, a screw could if wished be used in the place of the locking part  29  of FIGS. 6 and 7. 
     The above remarks are of course also valid for the other applications of the hinge according to the invention, in which the sidepiece and the corner piece described above are replaced by other portions of rigid parts that have to be hinged, such as a door and door frame.