Equipment for stringing a tennis racket

Racket stringing equipment having movable arms, for holding the racket on the stringing cradle as the racket is strung, includes profiled gripping jaws to bring the string mesh plane of the racket into alignment with a predefined stringing plane. The string tensioner holds the string being applied to the racket in a raised position in alignment with the reference stringing plane, as the racket is being strung. The string tensioner moves to a retracted position as the stringing cradle is rotated, to allow the handle of the racket to pass over the string tensioner, and returns to the raised position when the racket handle has passed. The clips for holding tension in the strings strung on the racket are freely rotatably mounted on a rotatable satellite arm. An electromagnetic lock simultaneously locks the satellite arm and the mounting arm of the clip to prevent movement of the clip with respect to the stringing cradle.

The invention relates to equipment, a device or a machine, which allows 
stringing of a tennis racket. 
According to the French certificate of addition 43,577, equipment of this 
type has been described, comprising: 
a support; 
a stringing cradle, having the shape of a racket frame, rotationally 
mounted on the support and the angular position of which in relation to 
the support is adjustable; on the outer side, and on its periphery, this 
cradle has a plurality of braces, each provided with several adjustment 
grooves which are perpendicular, in other words directed towards the 
center of the frame; 
a rigid but movable means of fixing the frame of the racket on the 
stringing cradle, comprising a plurality of independent fixing elements 
which can be brought opposite one another movably and adjustably on the 
various braces of the cradle by virtue of threaded rods with wing-nuts 
belonging to the said elements respectively; each fixing element has a 
gripping jaw, directed and open towards the frame of the racket, having 
two parallel cheeks which can be displaced together, moving towards or 
away from each other, by virtue of a manual control mechanism with a 
pinion and screw; the gripping jaw is completed on its outer edge by a 
lateral stop which can be adjusted translationally independently of the 
cheeks. 
Such a machine has the following disadvantages. 
The positioning and removal of a same frame take place by manual control of 
the many mechanisms combined with the various fixing elements 
respectively, since each has a minimum of one adjustment of the cheeks of 
the gripping jaw and one adjustment of the lateral stop. 
In addition, for different frames, all or some of the fixing elements must 
be disassembled and reassembled differently on the same braces or 
different braces. The inner linings of the gripping cheeks must also be 
changed to match the particular racket frame to be strung. 
According to the document US-C-No. 4,706,955, stringing equipment has been 
proposed comprising: 
a rigid support; 
a stringing cradle which essentially consists of a bar, rotationally 
mounted on the support and the angular position of which in relation to 
the support is adjustable by the operator; 
a rigid but movable means of fixing the frame of the racket on the 
stringing cradle; this means, provided on the cradle, comprises two 
elements for fixing the frame, arranged opposite one another and 
translationally adjustable on the bar; each fixing element comprises a 
bracket and a horizontal pressure means mounted on the head of the 
bracket; the two pressure means face each other and enable the wedge and 
the head of the racket frame to be gripped respectively; a first pressure 
means consists of a stationary bearing surface and an adjustable stop with 
a nut; 
the lateral means or stops, on the outside, of the frame of the racket to 
be strung; these means consist in allocating to one of the fixing elements 
two arms which extend parallel to the stringing cradle, symmetrically in 
relation to the bar forming the stringing cradle; these two arms are 
articulated together on the bracket head, in an adjustable manner, between 
an averted position releasing the frame and a close position forming a 
stop against the outside of the frame, by suitably arranged movable 
rollers; 
a tensioning element for the stringing thread, integral with the support, 
located at a distance from the stringing cradle and comprising a thread 
drawing head. 
Such equipment has the following disadvantage: 
The holding of the frame of the racket appears irregular, since the only 
points or zones of firm fixing consist of the pressure means explained 
above. In this respect, the above-described lateral stops do not ensure 
any rigid fixing of the frame of the racket capable of checking localized 
deformations of the frame under the effect of the tension exerted on the 
stringing thread. These stops can only limit the outward transverse 
displacement of the frame, and nothing else . 
The two above-described pieces of equipment have in common the following 
main disadvantage: 
The shapes, geometrical designs and dimensions of the frame, which vary 
from one racket to another, result in the level or the height of the 
horizontal stringing plane, in other words of the string mesh of the 
racket when strung or to be strung, in relation to the stringing cradle or 
to the rigid support, varying from one racket to another. Consequently, 
the level of the thread drawing head, or bobbin, varies significantly in 
relation to the stringing plane from one racket to another. 
According to the French certificate of addition 43,577, this variation 
exists because of the independence of the various fixing elements which 
can move relative to the stringing cradle, and because of the 
differentiated spacings, tolerances or wears between the various fixing 
elements. 
According to the document US-C-No. 4,706,955, this variation exists because 
of the fixed nature of the support plane of the frame, determined by the 
two stationary bearing surfaces of the two pressure means respectively, 
and because of the geometrical variations in the racket frames placed on 
the support. 
As a result of the impossibility of controlling the level or height of the 
stringing plane, the tension effectively exerted on the stringing thread 
cannot be kept under control, taking into account the existence of a 
variable vertical constituent in the tension. 
The subject of the present invention is stringing equipment which affords, 
primarily, effective control of the height or level of the stringing 
plane, whatever the racket. The subject of the invention is, secondarily, 
a device which affords simultaneously an effective and relatively complete 
clamping of the frame of the racket and ease of use for the operator. 
According to the present invention, a reference plane, termed stringing 
plane, situated at a predetermined level or height, in particular relative 
to the stationary support, is first of all defined by construction. The 
specific means or those which characterize the present invention are then 
organized relative to this reference plane in the following manner: 
on the one hand, by virtue of means of control of the displacement of the 
gripping jaws, the latter are movable only in the reference plane between 
an averted position releasing the frame and a close position gripping the 
latter; 
and on the other hand, each jaw comprises means of auto-positioning the 
frame of the racket, under the effect of the displacement of at least one 
gripping jaw from the averted position to the close position, to bring the 
plane of the string mesh of the racket into the reference stringing plane. 
A preferred, but not exclusive, embodiment of the invention concerns 
equipment comprising in the conventional manner two fixing elements for 
the frame, situated opposite one another on the stringing cradle, and each 
comprising a bracket. According to this embodiment, at least two gripping 
jaws are integral with two arms respectively, forming clamping elements 
for the frame of the racket; these arms extend above the stringing cradle 
and are each mounted on the head of a bracket, being adjustable, and 
preferably concomitantly, between an averted position releasing the frame 
and a close position clamping the latter. 
The invention thus allows the frame of the racket to be fixed in space, in 
the manner of a vice, in relation to a reference plane in which the 
stringing will be carried out. 
Since the invention affords control of the level of the stringing plane, a 
preferred embodiment of the invention consists in providing a drawing head 
for the stringing thread, separate from the rest of the tensioning 
element, and height adjustable in relation to the latter, and means of 
control which allow the drawing head to be positioned on the one hand in a 
low position, retracted in relation to the handle of the racket, when the 
angular position of the cradle lies within a reference angle corresponding 
to the passage of the handle on the side of the tensioning element, and on 
the other hand in a high position, coinciding for the stringing thread to 
be drawn with the reference stringing plane, and this when the angular 
position of the cradle lies outside the aforementioned reference angle. 
This solution makes it possible to draw the stringing thread horizontally 
and to eliminate the vertical constituent in the tension exerted, over the 
major part of the angular course of the stringing cradle. Thus a major 
proportion of the pernicious constraints exerted according to the prior 
art on the mechanical components or elements supporting the racket is 
eliminated. A proportion of the friction on the thread upon being 
conducted through the frame is also eliminated, which improves precision 
with regard to the actual value of the tension of the thread. 
Lastly, according to one variant of the invention, in a manner which is 
known per se, one or several clips are used for gripping the stringing 
thread, of each of which the position is movable in the stringing plane or 
the plane of the string mesh, and each of which swivels about a swivel pin 
perpendicular to the string mesh. These clips comprise, also in known 
manner, two cheeks opposite one another with an upper edge in the form of 
a comb, and means for moving the two cheeks towards or away from one 
another. 
In a novel manner, according to the invention, each gripping clip is 
movable in the stringing plane about two hinge pins, mutually connected 
but separate, perpendicular to the stringing plane, namely: 
a first hinge pin, rotationally fixed in relation to the stringing cradle, 
and about which a satellite arm is rotationally mounted, parallel to the 
cradle, 
and a second hinge pin, rotationally fixed in relation to the satellite 
arm, and about which a clip holder arm is rotationally mounted, parallel 
to the cradle. 
Locking means are also provided to lock in position simultaneously both the 
satellite arm in relation to the cradle, and the clip holder arm in 
relation to the satellite arm. 
Such an arrangement makes it possible to move the gripping clips very 
easily into plane of the string mesh at the same time as increasing the 
range of excursion of these latter, which allows the stringing of both 
large and small string meshes.

In accordance with FIG. 1, equipment according to the invention comprises 
the following essential elements or components: 
a rigid support 1, which can be placed on any flat and horizontal surface 
or on a height adjustable base or underframe; this support has, for 
example, a rectangular shape. 
a stringing cradle 2, rotationally mounted on the support 1, and having an 
adjustable angular position in relation to the latter. 
two fixing elements 3 and 4 for the frame of the tennis racket, arranged 
and fixed on the cradle 2, opposite one another about the axis of the 
frame. 
two gripping clips 6 and 7 for the stringing thread, mounted in a movable 
manner on the stringing cradle 2. 
a tensioning element 8 for the stringing thread, integral with the support 
1, and comprising a drawing head 9 for the said thread. 
a housing 10, arranged on both sides of the tensioning element 8 for the 
stringing thread, and comprising a control keyboard facing towards the 
operator and allowing the operator to carry out the different movements 
necessary for the stringing of the racket. 
In accordance with FIGS. 2, 3 and 6, the stringing cradle 2 has a flat 
shape and is mounted rotationally about a hinge pin 12, perpendicular to 
the support 1. More specifically, the cradle 2 comprises an upper platform 
13, and a lower platform 14 arranged at a distance from the platform 13 
and connected to the latter by an angled edge 14a. The cradle 2 is 
integral with a co-axial hub 15, swivel-mounted in a cylindrical housing 
16, which is also co-axial and belongs to the support 1. 
The two fixing elements 3 and 4 ensure the horizontal clamping in position 
of the tennis racket 17 to be strung, represented in broken lines in FIGS. 
2 and 3, and comprising a frame 17a and a handle 17b. The two elements 3 
and 4 are arranged in exactly the same way so that it is sufficient to 
describe only one of them, for example fixing element 3. The elements 3 
and 4 are arranged and mounted rigidly on the cradle 2, opposite one 
another about the longitudinal axis 18 of the latter, which corresponds to 
the axis of symmetry of the racket 17. The fixing element 3 comprises a 
bracket 19, running perpendicularly to the cradle 2, two clamping arms 20 
for the frame, which extend substantially parallel to the cradle 2, 
symmetrically in relation to the alignment axis 18 of the fixing elements 
3 and 4. The general shape of these arms 20, seen from above (compare FIG. 
3) matches the rounded profile of the frame 17a. The two arms 20 are each 
articulated on the head 19a of the bracket 19, adjustably and 
concomitantly, between an averted position represented in FIG. 5, 
releasing the frame 17a of the racket, and a close position represented in 
FIG. 3, fixing and locking the said frame 17a, in the direction of the 
arrows represented by FIG. 5. 
The adjustable and concomitant articulation of the clamping arms 20 is 
achieved according to the embodiment represented in FIG. 5: 
a slide 21 is mounted in the head 19a of the bracket and is translationally 
movable in the vertical alignment plane 22 of the fixing elements 3 and 4; 
this slide 21 comprises two aligned grooves 21a and 21b, which run 
perpendicularly to the aforementioned vertical plane 22. 
two hinge pins 23 of the two arms 20 respectively, run perpendicularly to 
the stringing cradle 2 and downwards; these two hinge pins are 
swivel-mounted on the head 19a of the bracket 19, on both sides of the 
cylindrical orifice 19b which provides for the sliding travel of the slide 
21. 
two fingers 24 are arranged on the two extremities of the two arms 20 
respectively at the opposite end to the jaws 25 described below, which 
fingers are engaged respectively in the grooves 21a and 21b. 
an element 26 for adjusting the position of the slide 21 in the bracket 
head 19a comprises a knurled knob 27, which can turn freely in relation to 
the head 19a and which is situated most importantly on the outside of the 
bracket 19, and a threaded rod 28, coaxial with the slide 21 and which 
interacts with a homologous threading of an inside screw 27a provided 
along the axis of the knurled knob. 
The free extremity of each clamping arm 20 comprises a gripping jaw 25, 
directed and open towards the frame 17a of the racket, and more 
specifically represented in FIG. 4. Each of these jaws has a flattened 
shape and runs substantially perpendicularly in relation to the frame 17a 
of the racket. The opening 25a of each jaw 25 has a diverging transverse 
profile, which is V-shaped and symmetrical in relation to the reference 
plane 29 which will be described below. The internal wall of each jaw 25, 
and more specifically of the opening 25a, is covered with a molded trim 
30, made of plastic material, in order to favor the limited displacement 
of the frame 17a, without damaging it, when the clamping arms 20 are moved 
towards the racket 17, in the direction of the arrows represented in FIG. 
5. The two angled edges, or cheeks of the opening 25a of each jaw 25, end 
in a passage or slot 25b between them, which extends behind the opening 
25a and allows the passage of the stringing thread. 
As shown in FIGS. 2 and 3, the two arms 20 of the first fixing element 3 
are directed towards the two arms 20 respectively of the second fixing 
element 4, in order to contain the frame 17a of the racket. As shown in 
FIG. 4, the four matching jaws 25 extend vertically and symmetrically on 
both sides of the reference stringing plane 29. This, in association with 
the technical characteristics previously described, makes possible 
auto-positioning and clamping of the frame 17a of the racket, in the 
reference plane 29 parallel to the cradle 2, under the effect of the 
displacement of the clamping arms 20, in the direction of the arrows 
represented in FIG. 5, from the averted position to the close position 
previously described. During the movement of the jaws 25, from the outside 
towards the inside of the cradle 2, the frame 17a, whatever its geometry, 
size or thickness, is centered in the reference stringing plane 29; this 
is shown in particular by FIG. 4, in which two frames 17a of different 
thickness and dimensions have been represented. 
As shown also in FIG. 2, the reference stringing plane, which corresponds 
to what will be the string mesh of the racket 17 and is determined by the 
gripping jaws 25, is situated above the heads 19a of the fixing brackets 
19. 
To complete the description of the fixing elements 3 and 4 it is necessary 
to point out that each of them has a hook 31, or billet, which makes it 
possible to hold the frame 17a of the racket firmly in position and 
completes the fixing action of the jaws 25. 
Each billet 31 is operated and translationally adjusted, in relation to the 
bracket head 19a, independently of the clamping arms (20) for the frame. 
To this end, the embodiment according to FIG. 14 can be used, briefly 
described as follows: 
a first knurled knob 27 comprises two parts 271 and 272, rotationally 
integral with one another; the first 271 is situated on the outside of the 
head 19a, and can be manipulated by the operator; the second 272 is 
mounted freely rotationally on a ring attached to the top of the head 19a, 
and translationally stopped by a washer 71; it is this piece 272 which 
comprises the threading 27a which interacts with the hollow threaded rod 
28 which is integral with the slide; 
a second knurled knob 72 is mounted freely rotationally on the first knob 
27, and more specifically the part 271, by means of a stop ring 73 and a 
radial ball bearing 74 between the pieces 72 and 272; 
the barrel 72a of the knurled knob 72 comprises an inside thread which 
interacts with the threaded extremity 31a of the straight rod 31 of the 
billet; the latter slides freely on the inside of the tube 28 which is 
integral with the slide 21, and the rod 31 is rotationally stopped by a 
pin which is integral with the slide. 
Thus each billet can be brought firmly up against the frame by the operator 
and makes it possible to avoid any serious longitudinal displacement of 
the frame during stringing. 
In a manner known per se, the two gripping clips 6 and 7 for the stringing 
thread each comprise two opposite cheeks, of which only one 32a has been 
represented in FIG. 6, the upper edge 32a of the said cheek having the 
shape of a comb, in order to allow the passage of the transverse threads 
of the string mesh. For each gripping clip, 6 or 7, means (not shown) are 
provided for moving the two cheeks 32 together and apart. 
In accordance with FIGS. 6 and 7, the two gripping clips 6 and 7 can 
simultaneously be displaced in the stringing plane and swivelled about 
their own swivel pin 33, perpendicular to the cradle 2, or to the 
aforementioned stringing plane. To this end the two clips 6 and 7 are 
arranged in exactly the same way in relation to the cradle 2, so that the 
description of the arrangement of the clip 6 alone is sufficient, in 
accordance with FIGS. 6 and 7. 
According to this arrangement, the gripping clip 6 is movable in the 
aforementioned stringing plane, about two hinge pins 12 and 34, connected 
but separate, and both perpendicular to the said stringing plane. About 
the first hinge pin 12, fixed rotationally in relation to the stringing 
cradle 2, a satellite arm 35 is rotationally mounted, parallel to the 
cradle 2. About the second hinge pin 34, rotationally fixed in relation to 
the satellite arm 35, a clip holder arm 36 is rotationally mounted, also 
parallel to the cradle 2. This clip holder arm supports a vertical barrel 
37, in the center of which the swivel pin 33 of the clip 6 is arranged. 
The upper platform 13 of the cradle 2 comprises a circular aperture 13a, 
centered on the first hinge pin 12. The satellite arm 35 is situated below 
the platform 13, and the clip holder arm 36 above this platform, the 
second hinge pin 34 passing freely through the circular aperture 13a. 
According to the invention there are of course provided means for 
simultaneous locking in position, described below, both of the satellite 
arm 35 in relation to the cradle 2 and of clip holder arm 36 in relation 
to the satellite arm 35. 
In accordance with FIG. 11, which represents an embodiment of the schematic 
diagram explained in FIG. 6, the identical numerical references designate 
components or pieces which have the same functions as previously 
described. The means for locking in position result from the combination 
of the following means: 
the second hinge pin 34 is mounted freely rotationally in a sleeve 39 which 
is integral with the satellite arm 35. 
the clip holder arm 36 is rotationally fixed on the outer and upper 
extremity 34a of the second hinge pin 34 by means of a suitable knurling. 
an end plate 38 is rotationally fixed, by a nut 40, on the inner and lower 
extremity 34b of the hinge pin 34, parallel to the platform 13. 
an electromagnet 41 with a coil 42 on top which is centered on the second 
hinge pin 34, is integral with the satellite arm 35, between the end plate 
38 and the platform 13; the satellite arm 35 is translationally free, in a 
limited travel, in relation to the second hinge pin 34, and the 
electromagnet 41 has two opposite active faces, namely one 41a opposite 
the metallic platform 13, and the other 41b opposite the metallic end 
plate 38. 
an electric means of control for the electromagnet 41 comprises: 
1. a push button 43 translationally guided in an axial boring in the upper 
extremity 34a of the hinge pin 34, 
2. a control rod 44, arranged co-axially in the hinge pin 34a and 
translationally free in relation to this latter, 
3. a lever 45, integral with the satellite arm 35, and articulated on this 
latter, connected at one extremity with the control rod 44, 
4. a contactor 46, integral with the satellite arm 35, connected to the 
other extremity of the lever 45. 
By virtue of this arrangement and suitable electric power supply to the 
electromagnet 41, when the operator presses the button 43, the lever 45 
swings towards the contactor 46, to supply the coil 42; from this moment 
the active face 41a of the electromagnet comes into contact with the 
platform 13, and the satellite arm 35 rises slightly, whereas the active 
face 41b raises and attracts the end plate 38. 
The means previously described thus permit on the one hand the rotational 
locking of the satellite arm 35 in relation to the platform 13 and 
therefore to the cradle 2, and on the other hand the rotational locking of 
the clip holder arm 36 in relation to the satellite arm 35. 
In accordance with FIGS. 8 to 10, the drawing head 9 for the stringing 
thread is separate from the rest of the tensioning element 8, and is 
articulated on the element 8, about a horizontal hinge pin 47. This head 9 
comprises, in a manner known per se, on the one hand a roll 48, or bobbin, 
for the unrolling of the stringing thread, and on the other hand gripping 
cheeks for the said thread, which are not shown. By pivoting about the pin 
47, the drawing head 9 is height adjustable, in relation to the element 8, 
between a low position (compare FIG. 9), retracted in relation to the 
handle 17b of the racket, and a high position (compare FIG. 10) which 
coincides for the stringing thread to be drawn, or the upper tangent plane 
of the bobbin 48, with the reference stringing plane 29, described and 
defined above. By virtue of the means of control described below, the 
retracted position according to FIG. 9 is obtained when the angular 
position of the cradle 2, defined by the angular position of the handle 
17b, lies within a reference angle 49, corresponding to the passage of the 
handle 17b on the side of the tensioning element 8. The high position 
according to FIG. 10 is obtained when the angular position of the cradle 
lies outside the reference angle 49. According to the schematic diagram in 
FIG. 10 and the embodiment in FIGS. 12 and 13, the means of control of the 
drawing head 9 is arranged in the following manner. 
The tensioning element 8 comprises a column 50 on the head of which is 
articulated the drawing head 9. A control rod 51 slides in the column 50 
and at its upper extremity 51a bears against the drawing head 9. A cam 52 
is rotationally mounted on the base of the column 50, and is in contact 
with the lower extremity 51b of the rod 51. An electric motor 53 drives 
the cam 52 rotationally. The rotational travel of the cam 52 is limited to 
a halfrevolution, by means of a finger 54, rotationally integral with the 
aforementioned cam and situated outside the element 8, which interacts 
with two limit of travel contactors 55. By means of two bosses situated on 
the support, and which delimit the reference angle 49, the electric motor 
53 for control of the cam 52 is activated or deactivated according to 
whether a specific contactor on the periphery of the cradle 2 is engaged 
or disengaged by any one of the aforementioned bosses. 
The tensioning element 8 slides on a ball bearing runner 56, and is drawn 
towards the rear of the equipment by a motorized pinion and a chain, which 
are not shown. Operation of the motor 53, in order to raise the drawing 
head 9 to the level of the reference plane 29, takes place before 
tensioning of the stringing thread, by the motorized reverse movement, as 
previously described, of the element 8.