Cross country ski linkage apparatus including pre-stressed blade

A linkage apparatus between the end of a boot and a cross-country ski, includes a flexion blade adapted to be affixed to a ski by its anterior end and to receive the end of a ski boot or shoe at its posterior end has a lower surface which is fitted against an upper surface of a support plate attached to the ski or the ski itself. The lower surface of the blade and the upper side of the ski lie in planes which are non-complementary with respect to each other in a manner which creates during assembly of the boot to the ski a pre-stressed moment in the blade which tends to counteract the tendency of the rear portion of the blade to lift-off the ski when the material making up the blade becomes fatigued by maintaining the rear portion of the flexion blade pressed against the ski when the boot has been detached.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to linkage apparatus provided on 
cross country skis for the attachment of ski boots to the skis. More 
particularly, the present invention is directed to an improvement of 
linkage apparatus in which the linkage element is an elongate elastic 
element in the shape of a blade positioned to interconnect the ski and the 
boot which is provided with a pre-stressed moment when attached to the ski 
which counteracts the tendency of the elastic elongate element to lift off 
the ski in the absence of externally applied force. 
2. Description of Background and Material Information 
French Patent No. 2,447,731, commonly owned with the present application, 
describes a linkage apparatus in which the ski, or other support element, 
is provided with an upper horizontal surface adapted to receive an elastic 
blade, known as a flexion blade, which forms a connection between the ski 
and the tip of the boot. The anterior section of the flexion blade is 
fitted in a housing attached to the upper surface of the ski in a manner 
so as to be pressed against the upper surface of the support element. The 
posterior section of the flexion blade is free or otherwise unattached to 
the upper surface of the ski. The rear end of the flexion blade is adapted 
to receive, in a removable fashion, the front end of a boot or shoe by 
means of an appropriate boot insertion mechanism. Typical boot insertion 
mechanisms include an attachment ring, a pivotable lever and a support 
plate. In the course of use, the movements applied by the skier 
principally involve pivoting the boot with respect to the ski in a 
longitudinal vertical plane. Such action results with a corresponding 
flexing of the flexion blade generally around an axis extending 
transversely through a region of reduced thickness of the flexion blade in 
which the flexing preferably occurs. After a certain amount of use, 
however, it appears that the flexion blade exhibits a permanent 
deformation in its pivot or flexing zone of reduced thickness, due to the 
fatigue of the material from which it is formed, such that the posterior 
region of the blade, when the blade is at rest, rises away from the upper 
surface of the ski in a substantially lifted-off position. 
This phenomenon is disadvantageous in that a space results between the 
flexion blade and the upper surface of the ski. This gap allows snow to 
become lodged between the upper surface of the ski and the lower surface 
of the flexion blade in this important region of the binding. The presence 
of snow or ice in this region of the binding can prevent the blade, and 
consequently the boot, from flattening against the ski to the discomfort 
and inconvenience of the skier during skiing. 
Another disadvantage which stems from the deformation of the blade is more 
of a psychological concern than a practical problem. When a skier observes 
the permanent deformation of the flexion blade, as discussed above, the 
skier tends to associate the deformation of the blade with a deterioration 
of the linkage apparatus. Although the disadvantages relating to snow pose 
real problems from the standpoint of performance, the deformation of the 
blade does not adversely affect the durability of the binding apparatus 
nor is it indicative of deterioration of the flexion blade. 
It has been observed that the previously discussed disadvantages occur with 
linkage apparatus in which the toe of the boot is fixed in a removable 
fashion at the posterior end of the flexion blade, as well as with linkage 
apparatus in which the flexion blade is integral with the toe area of the 
boot. In this latter case, however, the permanent deformation by fatigue 
of the flexion blade is less perceptible and problems caused by snow 
becoming packed between the blade and the upper surface of the support 
element while the boot and its integral flexion blade are disengaged from 
the ski do not occur. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a linkage apparatus for 
connecting the end of a boot with a cross-country ski including a 
generally elongate elastic element for associating the upper side of a ski 
with an end of a boot to allow for a pivoting movement of the boot around 
a substantially horizontal axis which is transverse to the ski, adapted to 
have a pre-stressed moment when the elastic elongate element is associated 
with the ski whereby the tendency of the elastic element to lift off the 
the ski in the absence of force being applied to the elastic elongate 
element is counteracted by the pre-stressed moment. 
Another object of the present invention is to provide a linkage apparatus, 
as described above, wherein the elongate elastic element includes an 
anterior portion having a front end and a forward lower surface area 
adapted to be connected to an upper surface associated with the ski, and a 
posterior portion having a rear end adapted to be attached to the boot and 
a rearward lower surface area adapted to contact the upper surface, with 
the forward lower surface area extending rearwardly from the front end, 
and the rearward lower surface area extending forwardly from the rear end 
to meet and form a lower surface of the elastic elongate element. 
A further object of the present invention is the provision of a linkage 
apparatus, as described above, wherein the elastic elongate element has an 
upper surface and predetermined thickness between the upper surface and 
the lower surface, and is provided with a flexion zone intermediate the 
front end and the rear end of the elastic elongate element. The forward 
lower surface area and the rearward lower surface area preferably slope 
with respect to each other to meet within an area of intersection below 
the flexion zone, preferably wherein the slope is towards the upper 
surface so that the area of intersection defines a region of reduced 
thickness with the upper surface. The area of intersection is preferably 
V-shaped, and at least one of the forward lower surface area and the 
rearward lower surface area is planar. The area of intersection may 
include a curved section, and the lower surface of the elastic member may 
be generally concave, preferably wherein at least one of the forward lower 
surface area and the rearward lower surface area is planar, and the upper 
surface includes a transverse groove above the region of reduced 
thickness. The elongate elastic element is preferably in the form of a 
blade. 
A still further object of the present invention is the provision of a 
linkage apparatus, as described above, which also includes means for 
securing the anterior portion of the elastic elongate element in position 
with respect to an upper surface associated with a ski which attached to 
the ski, preferably wherein the means for connecting includes means for 
compressing the anterior portion of the elongate elastic element, such as 
a housing having a dimension less than a corresponding dimension of the 
anterior portion, a screw passing through the anterior portion and 
anchored in the ski, or wherein the means for securing includes a support 
having lateral sides attached to the ski and means for pressing the 
anterior portion towards the ski pivotably connected to the support by a 
journal extending transversely between the lateral sides, in addition to 
means for pivoting the means for pressing pivotably connected to the 
support by a second journal extending transversely between the lateral 
sides, wherein the means for pivoting is a lever, and the means for 
pressing is a hook. 
A yet still further object of the present invention is a linkage apparatus, 
as described above, which also includes a base plate including the upper 
side associated with the ski, and a bottom side adapted to be attached to 
the ski, wherein the lower surface of the elastic element has a 
longitudinal profile and the upper surface of the base plate has a 
longitudinal profile which are non-complimentary. The base plate 
preferably includes an anterior region having a front end and an anterior 
upper surface area adapted to be connected to the forward lower surface 
area of the elongate elastic element, and a posterior region having a rear 
end and a posterior upper surface area adapted to contact the rearward 
lower surface area of the elongate elastic means wherein the anterior 
upper surface area extends rearwardly from the front end and the posterior 
upper surface area extends forwardly from the rear end so as to meet and 
form the upper surface of the base plate. The anterior region is 
preferably wedge-shaped and the anterior upper surface area slopes 
downwardly from the front end to meet the posterior upper surface area at 
an intersection, which is generally V-shaped. At least one of the anterior 
upper surface area and the posterior upper surface area is planar, and the 
intersection preferably includes a curved section. 
Another further object of the present invention is the provision of a 
linkage apparatus, as described above, wherein the forward lower surface 
area and the rearward lower surface area meet at a predetermined angle of 
intersection prior to the elastic elongate element being secured in 
position on the ski, and wherein the angle of intersection subsequent to 
the elastic elongate element being secured in position differs from the 
predetermined angle of intersection by an angle of deformation within the 
range of 5.degree. and 45.degree., and preferably 20.degree.. The force 
required to overcome the pre-stressed moment of the elastic elongate 
element when it is associated with the ski is on the order of 11 kgf. 
Another still further object of the present invention is the provision of a 
linkage apparatus, as described above, wherein the elastic elongate 
element is integral with the boot having a front end, preferably in the 
form of an extension of the front end of the boot, which includes an 
anterior portion having a forward lower surface area adapted to be secured 
to the ski, and a posterior portion having a rearward lower surface area 
integral with the boot, preferably wherein the forward lower surface area 
and the rearward lower surface area slope with respect to each other to 
meet at an intersection, and preferably the forward lower surface area 
slants downwardly away from the front end of the boot, and the 
intersection defines a flexion zone of the elastic elongate element. 
Another yet still further object of the present invention is the provision 
of a ski boot including an upper portion for receiving a foot having a 
front end and a sole, and an elastic elongate element extending from the 
front end of the boot adapted to connect the ski boot to a ski; the 
elastic elongate element includes a forward lower surface area and a 
rearward surface area which slope with respect to each other to meet at an 
intersection below a flexion zone of the elastic elongate element, 
preferably wherein the rearward lower surface area is planar with the sole 
and the forward lower surface area slants downwardly away from the 
rearward lower surface.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention is directed to a linkage apparatus including a 
flexible generally elongate, elastic element adapted to be mounted to a 
ski and attached to a boot for interconnecting the ski and the boot in a 
manner which overcomes the previously discussed disadvantages associated 
with prior art binding systems. To accomplish this, linkage apparatus has 
been developed wherein the flexion blade of the linkage apparatus 
experiences substantially no, and in any event imperceptible, deformation 
manifested by virtually no lifting of the free posterior portion of the 
blade with respect to the ski, base plate or other support element in the 
absence of external force being applied to bend the blade. 
In accordance with to the present invention, the respective longitudinal 
associated surface areas of the lower surface of the flexion blade of the 
linkage apparatus and of the upper surface of the ski, base plate or 
support element, before mounting of the flexion blade on the ski, are 
substantially noncomplementary. The unique, combination of 
noncomplementary profiles of the lower surface of the flexion blade with 
respect to the upper surface of the ski, base plate or support element are 
such that the assembly of the flexion blade on the ski causes a 
pre-stressed moment in the flexion zone of the flexion blade which 
counteracts the tendency of the posterior portion of the flexion blade to 
rise or be lifted off the upper surface of the ski. 
According to a particular embodiment of the invention, before assembly, the 
longitudinal surface configuration of the lower surface of the flexion 
blade is generally concave, and preferably V-shaped In another embodiment 
of the present invention, the upper surface of the base plate is generally 
concave, and may also be V-shaped. 
FIG. 1 schematically and partially illustrates a side view in partial cross 
section of a prior art apparatus for linking a cross country ski with the 
front of a cross country ski boot. The prior art apparatus typically 
includes a base plate 10 attached to the upper surface 12 of the ski. The 
base plate 10 is provided with a longitudinal guide rail 14 on its upper 
surface which is conventional and adapted to firmly seat the boot on the 
ski to enhance guidance of the ski by the foot when the sole of the boot 
is placed flat against the ski. 
As shown more clearly in the left of FIG. 1, the anterior region of the 
base plate is provided with a horizontal surface adapted to receive a 
blade 16, referred to herein as a flexion blade. This blade, of 
appropriate elasticity, is adapted to form the junction between the ski 
and the front of boot 19. To this end, the anterior portion of the flexion 
blade is pressed firmly against the horizontal surface of the plate 10. 
For this purpose, a maintenance cap 11, adapted to receive the front end 
of the flexion blade, is attached to the ski. Thus, maintenance cap 11 
houses the front end of the flexion blade 10 in a cavity or chamber 17 
formed between the base plate 10 and the maintenance cap 11. The rigid 
binding together of the assembly of cap 11, anterior portion of blade 16 
and plate 10 is assured by a screw 18 which passes through the previously 
mentioned elements into the ski. This assembly nevertheless permits blade 
16 to remain free over its entire posterior portion. 
In one embodiment, the end of boot or shoe 19 is adapted to be fixed to the 
rear end of the flexion blade 16 by means of a conventional attachment 
mechanism, for example of the binding ring type, which includes a pivoting 
lever for insertion of the boot and support plate, which are conventional 
and need not be further described at this point. The drawings show only 
the base plate or metallic insert 15 of this mechanism. Further details of 
this apparatus are discussed in French Patent No. 2 447 731, and its 
corresponding U.S. Pat. No. 4,562,653, commonly owned with the present 
application, which is explicitly incorporated herein by reference, 
particularly with respect to the details of such a mechanism. 
In the course of use, the movements imparted by the skier involve lifting 
the rear portion of the boot 19 with respect to ski 12 in a longitudinal 
vertical plane, in substantially the same manner as natural walking 
movements flex the sole of a shoe. In this regard, the sole of the boot 
flexes in the area of the ball of the foot and the portion of the sole 
toward the rear of the boot rises vertically while the portion of the sole 
in front of the ball of the foot remains in contact with the surface of 
the ski. 
As shown in FIG. 1, blade 16 of the prior art has a region of reduced 
thickness 16a with respect to the thickness of the anterior portion of the 
blade and the posterior portion of the blade. The narrow region of the 
blade, i.e., the flexion zone is provided in the area of the blade which 
is intended to flex to allow for the previously described walking or 
skating movement when the boot is attached to the ski during cross country 
skiing. Thus, blade 16 deforms elastically, as illustrated in FIG. 2, 
around an axis situated in the pivot region of reduced thickness 16a of 
the blade, which defines a preferred flexion zone, between a horizontal 
position A and a maximum inclination position B. 
As previously mentioned, after a certain amount of use and as a result of 
fatigue of the material making up the blade, blade 16 exhibits a certain 
permanent deformation in its pivot region or flexion zone such that the 
posterior portion of the blade tends to rise off the surface of the ski 
and forms a residual angle alpha with respect to the upper surface of base 
plate 10, shown as position C, in the absence of pressure being applied by 
the boot. The angle of deformation, i.e., alpha, can reach 
15-20.degree.degrees. It has been observed that after the initial fatigue, 
the angle of deformation does not increase but remains substantially 
within this range for the remainder of the useful life of the linkage 
apparatus such that the angle of permanent deformation appears to be 
maintained at a substantially constant value with time. 
The preferred embodiments of the invention will now be described with 
reference to FIGS. 3a, 3b; 4a, 4b; and 5. 
In these Figures, identical or analogous elements to those of FIGS. 1 and 2 
are designated by the same reference numerals. Furthermore, only the 
region of the ski 12, on which the base plate 10 of the linkage apparatus 
is attached, is shown in the figure. Although the figures illustrate the 
linkage apparatus of the present invention mounted to an intermediate base 
plate 10 attached to ski 12, it should be pointed out that the linkage 
apparatus of the present invention functions equally well when the base 
plate 10 is omitted and the linkage apparatus is mounted directly to the 
upper surface of the ski, and the linkage apparatus are appropriately 
adapted to function as such. Thus, either the ski or the base plate can 
provide an upper contact surface to which the elongate element, or blade, 
of the linkage apparatus is attached. 
With the foregoing in mind, reference is made to FIG. 3a, wherein base 
plate 10 is shown as being attached to ski 12 in a conventional manner. In 
particular, the anterior region 10a of the base plate 10 has a horizontal 
surface 20a on which the flexion blade 16' is positioned. As shown in FIG. 
3a, flexion blade 16' is constructed in a manner so that the lower surface 
22' of the blade lies in at least one plane which is not parallel with the 
plane through which the horizontal longitudinal axis of the flexion blade 
passes in the absence of external force applied to the blade. In this 
regard, the lower surface of the blade is generally concave, and 
preferably V-shaped with the arms of the "V" forming an obtuse angle with 
respect to each other. The lower surface of the blade angled in the 
previously described manner allows the blade to assume the longitudinal 
profile or configuration, such as is illustrated in FIG. 3a, when the 
blade is at rest. More precisely, it will be observed that the rearward 
lower surface area 22'b of the posterior portion of the blade, shown 
towards the right in the Figures, is generally inclined downwardly towards 
the ski by an angle beta on the order of 5.degree.-45.degree., preferably 
of 20.degree., with respect to the forward lower surface area 22'c of the 
anterior portion of the blade, which is intended to be fixed to the ski. 
As shown, the lower surface 22' of the flexion blade has a profile in the 
form of an inverted "V" with an obtuse apex angle 22a' provided in the 
region of reduced thickness 16a', or flexion zone, of the blade. 
When the flexion blade 16' is positioned and fixed by its anterior portion 
16b', in an otherwise conventional fashion, on the associated anterior 
upper surface area 20a of upper surface 20 of base plate 10, as shown in 
FIG. 3b, the blade 16' is deformed elastically by the forces exerted 
thereon to cause the forward lower surface area 22'c and rearward lower 
surface area 22'b of the lower surface 22 of the blade to lie in 
substantially the same plane essentially parallel to the upper surface 20 
of base plate 10 or the ski. Thus, the lower surface 22 of the blade 
assumes a horizontal position against the associated upper surface 20 of 
the base plate. 
The angular configuration of the lower surface areas of the anterior and 
posterior portions of the blade causes the creation of a return or 
pre-stressed moment in the flexion zone of the blade which tends to force 
the blade into its original shape. Consequently, the posterior portion of 
the blade is urged towards the base plate when the anterior portion of the 
blade is associated with the base plate in a manner which firmly presses 
the lower surface area of the anterior portion of the blade against the 
base plate. 
The behavior of the linkage apparatus of the present invention is as 
follows. During skiing, the repeated flections of the blade cause the 
material of the flexion blade to fatigue, as described above. The fatigue 
of the blade tends to cause a permanent angular deformation of the flexion 
blade. The pre-stressed moment created in the blade according to the 
present invention as described above, however, acts in the opposite 
direction of this tendency of deformation thereby minimizing it. In other 
words the permanent deformation due to fatigue of the material of the 
blade is manifest when the blade is in a relaxed condition, i.e., the 
position which the blade occupies when no force is exerted against it 
which would cause the blade to bend. By forming the blade to have the 
longitudinal profile as shown in FIG. 3a wherein the posterior portion of 
the blade is angularly displaced downwardly, the tendency of the posterior 
portion to lift off the ski after fatigue is counterbalanced. Thus, the 
initial pre-stressed moment imparted to a flexion blade having a 
configuration in accordance with the present invention during assembly 
makes it possible to substantially attenuate the tendency of the the 
posterior portion of the blade to rise from the upper surface of the ski 
due to fatigue of the material. Accordingly, it is possible to prevent 
lift-off of the posterior portion of the flexion blade from the upper 
surface of the ski so that essentially no gap or space will exist between 
the blade and the ski during those times when no external force is applied 
which would otherwise cause the blade to bend. Thus, one of the main 
disadvantages of flexion blades of prior art devices is effectively 
eliminated. 
In FIGS. 4a and 4b a second embodiment to the invention is shown. In this 
embodiment, however, the flexion blade 16 is formed in a conventional 
manner, i.e., its lower surface 22 is substantially planar. In contrast, 
the upper surface 20' of the base plate 10' in the anterior region for 
receiving the anterior portion of blade 16 is provided with a 
protuberance, preferably in the form of a wedge 40. The anterior upper 
surface area 40a of the wedge-shaped protuberance 40 inclines downwardly 
from the front end of the wedge in a rearward direction to meet with the 
posterior upper surface area 20'b of plate 10' so as to impart a generally 
concave configuration to the upper surface 20' of the base plate or 
support element to which blade 16 is mounted. The concave upper surface of 
the support element is preferably V-shaped having an obtuse apex angle. 
Thus, an area of intersection or bend 20a' is provided in the region of 
the base plate which will correspond, after assembly, to the preferred 
flexion region 16a of the blade. The anterior upper surface area 40a of 
the wedge-shaped anterior region of the base plate is inclined upwardly by 
an angle gamma on the order of 5.degree.-45.degree., preferably 
20.degree., with respect to a horizontal posterior region of the base 
plate. 
In a manner similar to the embodiment of FIGS. 3a and 3b, the act of 
pressing the anterior portion of the flexion blade 16 in place against 
protuberance 40 causes an elastic deformation of an angle gamma in the 
narrow region 16a of the blade which causes the posterior portion of the 
blade, shown towards in the right in the figures, to press against the 
associated region of posterior upper surface area 20'b, thus creating a 
similar pre-stressed moment in the flexion blade. Although in the 
embodiment shown in FIGS. 4a and 4b, the blade is angled in a direction 
opposite to the angle of the blade shown in FIGS. 3a and 3b, the 
pre-stressed moment loaded in the blade has substantially the same effects 
as those explained above in the description of the apparatus of the first 
embodiment shown in FIGS. 3a and 3b. In this embodiment, however, the 
pre-stressed moment is caused by the anterior upper surface area 40a of 
the protuberance which bends the anterior portion of the blade upwardly 
away from horizontal plane in which the posterior region of the base plate 
is located. This has the effect of urging the nonstressed position of the 
posterior portion of the blade angularly downwardly with respect to the 
position which it occupies after assembly to seek its natural 
configuration. The previously discussed disadvantages of prior art devices 
are here again substantially attenuated by the linkage apparatus of the 
present invention. 
A third embodiment, whose configuration is intermediate between that of the 
previously discussed first and second embodiments, is illustrated in FIG. 
5. More specifically, the anterior upper surface area 40a of the anterior 
region of base plate 10' inclines by an angle delta with respect to the 
posterior upper surface area 20'b of a substantially planar posterior 
region 20'. Similarly, the lower surface 22' of the flexion blade 16 has a 
generally bent longitudinal profile such that the lower surface area 22'b 
of the posterior portion of the blade is generally inclined downwardly by 
an angle theta with respect to the forward lower surface area 22'c of the 
anterior portion of the blade. In this example, the values of delta and 
theta are selected such that their sum is between 5.degree. and 
45.degree., and preferably equal to 20.degree.. In the embodiment 
illustrated, delta is equal to theta which is equal to 10.degree.. Here 
again, it will be understood that the assembly of the blade 16' on base 
plate 10 consequently creates a pre-stressed moment in the blade due to 
the forced angular deformation of the posterior region of the blade by an 
angle equal to the sum of the angles delta and theta. This pre-stressed 
moment will have the same effects as discussed with respect to the two 
first embodiments, i.e., to substantially reduce and even eliminate the 
upward displacement of the posterior portion of the blade from the 
associated region of the base plate, after permanent deformation due to 
fatigue of the material making up the blade occurs. In the previously 
discussed embodiments of the present invention, the anterior and posterior 
portions and regions, respectively, of the blade and base plate have been 
separated by an obtuse angle. 
Turning now to FIG. 6, a linkage apparatus in accordance with the present 
invention is shown which is generally similar in certain respects to that 
of FIG. 3. In this regard, the upper surface 20 of the base plate 10 is 
planar. However, the lower surface 22" of the flexion blade 16" has a 
generally rounded section 22a" in the region of reduced thickness 16a" of 
the blade. In effect the obtuse angle at the apex of the V-shaped profile 
of FIG. 3a has been substantially blunted in this embodiment wherein the 
lower surface of the blade has a curved, preferably concave configuration. 
The angle beta at the intersection of the planes of the forward and 
rearward lower surface areas (22c" and 22b") of the lower surface 22" of 
the flexion blade is here again between 5.degree. and 45.degree., and 
preferably on the order of 20.degree.. It will be understood that the 
general effect of the use of such a flexion blade will be essentially the 
same as that which has been described with reference to FIGS. 3a and 3b. 
In this embodiment, however, the progressiveness of the angle between the 
forward and rearward lower surface areas due to the rounded section at 
their intersection makes it possible to redistribute the stresses which 
consequently are substantially less concentrated at the intermediate 
flexion zone 16a" of the blade. 
FIG. 7 illustrates an embodiment of the linkage apparatus of the invention 
which is generally similar to that of FIG. 4. In this embodiment, however, 
the profile of the upper surface 20" of base plate 10" is generally 
rounded, with the obtuse angle of the base of the "V" of the embodiment 
shown in FIG. 4 having been substantially blunted in a manner similar to 
that described above with respect to the differences between the 
embodiments shown in FIGS. 3a and 3b, and FIG. 6. Thus, the ramp formed by 
the anterior upper surface area 40a of the generally wedge-shaped 
protuberance or anterior region 40 slopes upwardly from a curved section 
located between the planar upper surface area 20"b of the posterior region 
of the base plate and the anterior upper surface area 40a of the anterior 
region of the base plate. As in the embodiment shown in FIG. 4, the 
flexion blade 16 in the embodiment shown in FIG. 7 assumes its 
conventional form, i.e., its lower surface 22 is planar, before assembly. 
The advantages obtained as a result of curving a section of the upper 
surface of the base plate in the vicinity of the region of reduced 
thickness of the blade are substantially the same as in the embodiment of 
FIG. 6 wherein the lower surface area below the region of reduced 
thickness of the blade is curved and the upper surface of the base plate 
is substantially planar and horizontal. 
Along the same idea, one can modify the linkage apparatus of FIG. 5 such 
that the respective profiles of the upper surface 20a' of the base plate 
10' and of the lower surface 22' of the flexion blade 16' are 
substantially rounded, in contrast to being sharply V-shaped, to have the 
previously mentioned angular values. 
In general, the advantages and characteristics of the present invention 
will take effect as soon as one provides the lower surface of the flexion 
blade and/or the upper surface of the base plate with a generally hollow 
or concave configuration. 
FIGS. 8a and 8b show a sixth embodiment of the invention wherein the 
linkage apparatus is shown respectively, before and after attachment of 
the boot 119 to the ski by means of a flexion blade 116". Although flexion 
blade 116' is shown as being integral with the sole of boot 119, the 
invention further described herein with respect to this embodiment may 
also be used in the instance wherein the boot is attached to the flexion 
blade by conventional means for attachment, such as the one previously 
mentioned herein. This embodiment, however, will be described with respect 
to a flexion blade which is integral with the end of the boot. The linkage 
apparatus of this embodiment includes a base plate 110 mounted on the 
upper surface of a ski 120. A mechanism for receiving the flexion blade 
116' of the boot is mounted on a support 30 The mechanism is somewhat 
conventional in that it includes a hook 32 which pivots around an axis 34, 
and a lever 36 which pivots around an axis 38. Axes 34 and 38 are 
transverse to the longitudinal axis of the ski. The end of the boot 119 
includes a projection in the form of a flexion blade 116' as a forward 
extension of the sole whose free end is constituted by an attached or 
integral protuberance or region of increased thickness 116b' extending 
upwardly from the top or upper surface of blade 116'. Thus, there exists a 
region of reduced thickness 116a' located between the region of increased 
thickness 116b' and the toe of boot 119 defining the flexion region of the 
blade. The upper surface 120 of the base plate 110 is planar and 
horizontal in the region of the mechanism for receiving the flexion blade 
of the boot. As shown, the anterior portion of the flexion blade 116' is 
bent downwardly at 116a' by an angle beta. Accordingly, when the mechanism 
for receiving the flexion blade of the boot is utilized to attach the end 
of the boot 119 to the ski 12, as illustrated in FIG. 8b, the anterior 
portion 116b' of the flexion blade 116' is pressed against the upper 
surface 120 of the base plate 110 by an appropriate pivoting of lever 36 
which in turn biases the hook 32 to secure the anterior portion or region 
of increased thickness 116b' of the blade. As shown, hook 32 extends 
generally longitudinally from pivot 34 rearwardly towards the boot. The 
hook includes a generally elongate narrow intermediate portion and an 
end-portion having increased thickness with respect to the narrow 
intermediate portion extending downwardly towards the upper surface 120 of 
base plate 110 for firmly securing the anterior portion of increased 
thickness 116b' of the flexion blade 116' within the narrow intermediate 
portion of the hook. 
This action of insertion of the flexion blade of the boot is similar in 
effect to the assembly of the flexion blade in the preceding embodiments 
in creating a pre-stressed moment in the flexion blade. As previously 
explained in detail above, this causes an off-setting of the angular 
position of the flexion blade, to counteract the angle of permanent 
deformation, due to the fatigue of the material constituting the flexion 
blade so as to attenuate the bending of the blade after this fatigue 
occurs. 
FIGS. 9a and 9b illustrate a linkage apparatus of the same general type as 
shown in FIGS. 8a and 8b. In these figures, identical or similar elements 
or parts are designated by the same reference numerals. As shown, the 
flexion blade 116 which extends from the front of the sole of the boot 119 
in this embodiment is generally planar and coextensive with the sole of 
the boot. The upper surface 120' of the base plate 110' has an angled 
section 120a' in the region situated immediatelY to the rear of the 
immobilization position of the mechanism for receiving the anterior end of 
the flexion blade of the boot. More precisely, the anterior upper surface 
area 40a of the anterior portion of upper surface 120' is inclined 
generally upwardly, by an angle gamma of preferably between 5.degree. and 
45.degree., and more preferably equal to approximately 20.degree.. 
When the anterior portion 116b of flexion blade is positioned and 
immobilized by hook 32 of the mechanism for receiving the boot in a manner 
similar to that previously discussed with respect to FIGS. 8a and 8b, the 
angular deformation of the flexion blade in the angled section 120a' of 
the base plate 110' causes the blade, which assumes a corresponding 
elastic deformation, to have a pre-stressed moment with the attendant 
effects consistent with those previously discussed in detail herein with 
respect to the other embodiments of the present invention. 
Of course, even though it has not been shown in the drawings, it is also 
envisioned that any intermediate embodiment, in which either the flexion 
blade and/or the associated reception surface of the base plate are 
provided with an angled surface, could be used, in a manner consistent 
with the embodiment shown in and discussed with respect to FIG. 5. 
Related to this, although FIGS. 8a and 9a illustrate a flexion blade having 
an anterior lower surface areas 116c (FIG. 8a) and a base plate having a 
wedge-shaped anterior region 40 with an anterior upper surface area 40a 
(FIG. 9a) which are offset at acute angles with respect to the horizontal 
plane in which the longitudinal axis of the ski is disposed, these angles 
may be blunted, so that the intersection of the surface areas of the 
flexion blade and/or of the base plate assume a more rounded 
configuration, in a manner consistent with the embodiments shown in FIGS. 
6 and 7, respectively, and previously discussed in detail herein. 
Moreover, it should be understood that the present invention is in no way 
limited to the specific embodiments described herein. In particular, one 
can design the flexion blade and/or the associated reception surface of 
the base plate with any appropriate profile such as is obtained during 
assembly or during insertion of the boot so as to result with an elastic 
deformation of the preferred flexion zone of the blade to create a 
pre-stressed moment opposing the permanent deformation which the blade 
tends to assume due to material fatigue after a certain amount of use. 
Furthermore, although the description herein often refers to a linkage 
apparatus for a cross-country ski in which a base plate of the apparatus 
includes a surface which receives the flexion blade substantially over its 
entire length, the invention applies equally well to apparatus in which 
the flexion blade is at least partially in contact directly with the ski 
in which case the lower surface of the flexion blade is designed and 
adapted in an appropriate fashion to fit flush against the upper surfaces 
of the ski and its associated support plate. 
Finally, it may be noted that one can select for the flexion blade any 
elastically deformable material which is suitable for flexing in the 
required manner, such as the material commercially known as "HYTREL". 
Although the invention has been described with reference to a particular 
means, materials and embodiments, from the foregoing description, one 
skilled in the art can easily ascertain the essential characteristics of 
the present invention, and without departing from the spirit and scope 
thereof, may make changes and modifications of the invention to adapt it 
to various usages and conditions.