EP3935003A1

EP3935003A1 - Method and device for tensioning a strap

Info

Publication number: EP3935003A1
Application number: EP20711019.8A
Authority: EP
Inventors: Nicolas DE LUSSY
Original assignee: Push4m
Current assignee: Push4m
Priority date: 2019-03-06
Filing date: 2020-03-06
Publication date: 2022-01-12
Also published as: FR3093510B1; FR3093510A1; WO2020178440A1; US20220177282A1; JP2022523232A

Abstract

The invention relates to a method and to a device for implementing the method for tensioning an inextensible or substantially inextensible longitudinal strap (12) comprising a distal end portion (15) and a proximal end portion (11), each end portion being respectively fixed to a corresponding attachment point (13, 16). The method is characterized in that a cycle (2) of successive transverse pressure applications is exerted on the strap (12), comprising a first transverse pressure application (23) on a first portion (20) of the strap, then a second (24) and a third (25) transverse pressure application on a second (21) and a third (22) portion of the strap, respectively.

Description

DESCRIPTION:

TENSIONING PROCESS AND DEVICE

WITH A STRAP

[0001] The present invention relates to a method of tensioning an inextensible or substantially inextensible strap allowing in particular the lifting of a load at a distance or the spatial displacement of a large mass located at a remote end of the actuating mechanism. .

[0002] It also relates to a tensioning and / or displacement device implementing such a method.

[0003] It finds a particularly important, although not exclusive, application in the construction industry, for construction machinery or for heavy load handling devices requiring a heavy lifting and / or lifting force at start-up.

[0004] But it is also applicable to the field of robotics and exoskeletons, to the field of prostheses and orthoses for humans and more generally to all fields of mechanics requiring prestressing on an elongated inextensible or substantially inextensible organ, and / or the setting in motion of a lever arm or the application of a traction force requiring a large force and / or a high speed on starting.

By substantially inextensible organ is meant an organ

25 designed to undergo an elongation of less than 5% of its length for a determined maximum tensile less than its breaking point, for example 500 MPa, for example less than 3%, advantageously less than 1%, even more advantageously 0.5%, or even 0.05%.

[0006] Devices are already known for handling large loads from a distance by means of a lever arm.

[0007] However, they have drawbacks, particularly in terms of cost and size.

[0008] These are, for example, power jacks, unwieldy, found in autonomous machines such as forklifts, excavators or backhoe loaders, or even rotary engines by

10 example used in machines on a base, of the factory robot type, whose operating torque is dependent on its weight, which will therefore tend to be oversized.

[0009] In addition, the force which will act on the axis of rotation of the lever arm is necessarily coupled to the displacement of the load, without

15 possibility of dissociation, whether the actuator is in direct engagement with the lever arm, or whether it is through a deformable quadrilateral.

[0010] Thus, the current assemblies, whether with linear cylinders or with a rotary motor, must they necessarily develop a power

20 maximum resistance torque balancing at any moment of movement. This results in a significant energy expenditure, imposes a high weight of the driving elements and causes a greater wear of the mechanical parts.

The object of the present invention is to remedy these drawbacks

25 in particular by dissociating the force exerted on the lever arm from the movement of the actuator.

To do this, the invention proceeds from an entirely different approach from that of the prior art. It starts from the careful observation of the functioning of the muscle of an arm and more particularly of the biceps which, to lift a load by hand located at the end of the forearm (lever arm) does not reduce its length but stiffens the biceps by increasing the transverse volume of the muscle fibers constituting it.

[0013] With the invention the equivalent of a transverse volume increase produces the tensioning of a not very extensible link or ligament and, in this case, the spatial displacement movement of a large mass at the end. arm, at least equivalent to a longitudinal shortening, but above all and this

10 surprisingly, produces a very large breakout force for minimal displacement, thus operating on a principle equivalent to that of an inverted hoist.

[0014] To this end, the invention proposes in particular a method of tensioning an inextensible or substantially longitudinal strap

15 inextensible comprising a distal end portion and a proximal end portion, each end portion being respectively fixed to a corresponding attachment point, characterized in that a cycle of successive transverse pressurizations is exerted on the strap including a first pressurization

20 transverse on a first portion of the strap, then a second and a third transverse pressurization respectively on a second and on a third portion of said strap without releasing the tension between successive pressurizations.

[0015] No release of the strap tension occurs between successive tensionings or, if necessary, between the various cycles of the latter.

By pressurizing or transverse thrust is meant the exercise of a force initially perpendicular and then substantially perpendicular (+ a few degrees increasing progressively with respect to 90 °) on the strap with respect to its initial longitudinal direction without displacement, "in its plane"

Advantageously the portions of straps on which are

5 exerted pressures are of small length, in comparison with the length of the strap between the end portions, for example of the order of 0.2% to 1%, for example 0.5% of the length, that is to say for example less than 5 cm, for example 1 to 2 cm for a strap 1 m long.

[0018] The strap can of course be a cable, a band, a chain, a link or more generally any elongated member, for example formed of inextensible or substantially inextensible fibers, for example of a material known under the trademark DYNE EMA of great resistance. at breakage in tension, for example greater than 500 Mpa,

15 and which nevertheless preserve sufficient flexibility to withstand a large number of flexural deformation cycles over a maximum height determined per cycle (for example 50,000 cycles over a height of a few centimeters, for example 5 cm).

[0019] Advantageously, the proximal end portion of the strap

20 being fixed to a base by a first of the attachment points and the distal end portion of the strap being fixed to a proximal part of a lever arm movable in rotation about an axis, by the second of the points attachment, said lever arm extending between said proximal portion and a distal portion arranged to support a load,

25 the successive pressurizations are arranged to actuate the lifting of said lever arm between a first rest position and a second working position.

The rest position or low position is for example a horizontal position of the arm, and the working position or position high is a position of the arm vertically, or with an angle between 30 ° and 80 °, for example 50 ° with the horizontal.

[0021] The invention thus provides a method of lifting a load fixed to a distal end of a lever arm movable in rotation around

5 of a transverse axis located on the side of a proximal part of the lever arm, by the exercise of at least one pressurization cycle, the latter taking place in the form of transverse thrusts on the inextensible strap or substantially inextensible fixed on one side to said proximal part of said arm and on the other side to a fixed point, method

10 in which the transverse pressurization takes place by successive vertical thrusts in the plane of movement on said strap at at least three locations distributed along the latter.

[0022] In advantageous embodiments, one has more and / or additionally recourse to one and / or the other of the following provisions:

[0023] - the second and third pressurizations are distributed symmetrically or substantially symmetrically on either side of the first pressurization. By substantially symmetrically is meant as symmetrically as possible, that is to say not exceeding a few centimeters from the strictly symmetrical position.

[0024] - the second and third pressurizations are exerted successively. By exerting successive thrusts on the second and third portion, the power required to increase the voltage is thus limited. The time elapsed between successive pushes is for example less than 1/10 ^th of a second or 1

25 hundredth of a second, so that the cycle exerted by the motor means is not cumulative;

- To exert the pressurization, the first, second and third strap portions are moved vertically respectively on a first, second and third determined heights then again the first part on a new determined height;

- The second and third determined heights are equal by symmetry. But in the case of asymmetric thrust the heights

5 depend on each pusher position;

- The determined heights are arranged so that the angles taken by the strap with the straight line formed between the strap portions and / or adjacent to the pressurized portions, are between 5 ° and 15 °, for example <10 °. The parts of straps and / or points

10 attachment points then become the points of support for the ends of the displaced strap part:

- We renew the pressurization cycle at least N times, with N> 2, for example N> 3 or N> 5, for example 10 times;

[0029] - at least one cycle comprises at least a fourth and a

15 fifth transverse pressurizations respectively on a fourth and on a fifth strap portion and / or an umpteenth and n + 1 th pressurements on an umpteenth and n + 1 th strap portions with, n> 6, the umpteenth and n + 1 th portions being located respectively on either side of the n-2nd and n-1 th portions of

20 strap. They can also be located inward from previous pressurizations, i.e. in the direction or side of the first thrust. Here multiple combinations can be programmed for example, if there are n thrust points, the cycles will be 1 -2 -3-4-5— ... n then again 1 -2 -3-4-5- ... not

25 etc .... But beyond n = 3, the cycles can follow another series ex: 1 -2-3-5-4-1 -2-1 -4-3, according to the needs, etc.

- The pressurization is exerted on the strap by means of rotary cams configured to allow the successive pressurization cycle (s) for determined thrust values and / or for vertical movements of the strap over determined heights.

[0031] The use of cams allows excellent continuity and flexibility in pressure build-ups, as well as a perfect

5 mechanical repetitiveness of movements.

[0032] The invention also proposes a device implementing the method or methods described above.

[0033] It also relates to a device for tensioning an inextensible or substantially inextensible strap extending

10 longitudinally between a distal end portion and a proximal end portion, each respectively fixed to a corresponding attachment point, characterized in that it comprises pushing means for placing transverse pressure on the strap comprising first pushing means pressurization

15 transverse on a first portion of strap, second and third transverse pressure pushing means respectively on a second and on a third strap portions, and control means of said pressure pushing means arranged to perform at minus one betting cycle

20 by successive pressure of the strap on said first, second and third portions of said strap in a determined manner.

Advantageously, the pushing means comprise movable rotating cams programmed and / or configured to allow the cycles of determined successive pressurization.

[0035] But they can also and for example be hydraulic or electric vertical thrust cylinders with identical or different strokes, of lengths determined in a previously programmed manner. In an advantageous embodiment, the device further comprises a lever arm extending longitudinally between a proximal portion and a distal portion for supporting a load, the proximal portion being movable in rotation about an axis set at a

5 base, the distal end portion of the strap being for its part fixed to said proximal part of the arm by one of the attachment points, directly or via a pulley and / or for example a rotary cylinder-type axis, and the portion proximal end of the strap being fixed to a fixed point forming the second of the attachment points for example

10 integral with the base.

Advantageously, the strap, the pushing means and the axis of rotation of the arm are integral with the same base.

Also advantageously the base is movable, for example mounted on a movable frame, which allows the movement of the

15 device, for example via a self-propelled vehicle.

[0039] In advantageous embodiments, the pusher means comprise a single rotary motor for actuating the cams arranged to exert one or more cycles of determined transverse pressurization on the strap.

Advantageously, the three pushing means (or systems) comprise a central means and two lateral means arranged symmetrically with respect to the central means.

Also advantageously, the number of pushing means is not limited to three, but includes n + 2 pushing means with

25 n odd greater than or equal to 3, distributed longitudinally along the strap, for example symmetrically with respect to the central pusher means located equidistant between the fixed point of attachment of the strap and a pulley or rotating cylinder for returning the strap, said pulley or said cylinder being situated in the same longitudinal plane as said fixed point.

Advantageously each pusher means comprises:

- a substantially circular disc-shaped cam

5 comprising, on one of its faces, a guide rail or groove in the form of a concentric spiral of determined length and path;

[0044] a guide roller arranged to cooperate in friction or rolling with the rail or the groove, said roller being integral with a

10 pusher system (or rod) terminated at the top by a ring or a rotating cylinder arranged to cooperate with the strap so as to transmit to it the thrust of the pusher system according to the determined pressure cycle or cycles.

We understand that the kinematics of such a device is linked to the

15 cam geometry. Indeed, it is they which impose the determined movement of the pusher system (movement of the strap in height and speed), and consequently that of the rise of the arm, as well as the torques (when pulling out and in operation) required. for setting the arm in motion.

It should be noted that the slope of the groove of the cam makes it possible to vary, for the same circular movement, the torque and the speed. Thus a low slope results in a strong torque and a reduced speed, and conversely a strong slope results in a low torque and a higher speed. Varying the slopes therefore allows you to play on the

25 speed / torque ratio at different moments of the movement. The slope of the groove is understood to mean the angle that the tangent to the curve forms with the horizontal at the location of the roller.

In an example of a set of cams with groove implemented with the invention, (groove that a person skilled in the art will therefore size in function of the desired operating parameters, depending in particular and in a known manner on the length of the lever arm between its axis of rotation and its distal attachment part of the weight to be lifted, on the value of said weight and on the height at which the arm

5 must lift said load), we observe, with three pushing means, a reduction in speed by a factor of six, for an increase in the engine torque varying between 3.7 and 6, compared to the necessary engine speed and torque to lift the load by direct action on the rotation of the axis of the lever arm. This puts

10 in relief the non-linearity of the system.

[0048] Another example of a set of cams produced has made it possible to achieve an increase in torque by a factor of more than twelve, for a reduction in speed by a factor of ten.

[0049] The invention will be better understood on reading the description which

15 follows embodiments given below by way of non-limiting examples.

[0050] The description refers to the drawings which accompany it in which:

[Fig.1] is a flowchart of the load lifting process according to a

20 embodiment of the invention, with pressurization on five portions of strap.

[Fig.2] shows the diagram of forces applied to a strap according to the embodiment of the invention more particularly described here applied to three portions of strap.

25 [Fig.3] shows a side view of a device according to one embodiment of the invention, before application of the first thrust (according to the diagram of FIG. 2), the lever arm being in its lower or lower position. rest (Figure 3A), after the first push (Figure 3B), after the 2 ^nd and 3 ^rd pushes, (Figure 3C), and after the 4 ^th push, the lever arm being in its high position (Figure 3D).

[Fig.4] is a force diagram showing a succession of push cycles on the strap of the type shown with reference to Figure 2.

5 [Fig.5] shows the curve of variation of the thrust heights produced by the central and lateral pushing means, according to the embodiment of the device of the invention more particularly described here.

[Fig.6] shows the variation curve of the angle taken by the lifting arm as a function of time, corresponding to the variations in the heights of the

10 figure 5.

[Fig.7] is a side view of the lifting device according to the embodiment of the invention more particularly described here.

[Fig.8] is an axionometric perspective view of Figure 7.

[Fig.9] is a perspective view of the three cams of the device of the

15 figure 7.

[Fig.10] shows a side view of the central and side cams in figure 9.

[0051] Figure 1 shows a flowchart 1 of a load lifting method according to an embodiment of the invention.

To do this, the load (for example a 500 kg pipeline tube portion) is fixed to a lifting device, and more precisely to a distal part of a lever arm (step 1), the part proximal part of the lever arm having been fixed at one end to the distal portion of an inextensible strap extending

25 longitudinally and horizontally, itself attached to its other end, called proximal, to a fixed point for example belonging to a carriage or to a base secured to the ground on which it rests.

To lift the load, which will for example make it possible to clear a space under the latter allowing its recovery

5 and / or its placement on a support, a first cycle 2 of transverse pressurization is then exerted, in this case vertical (that is to say transverse to the initial horizontal position of the strap) on said strap.

More specifically, cycle 2 comprises a first setting

10 pressure 3 on a first portion of the strap, for example disposed substantially centrally with respect to the strap attachment points respectively on the base and on the proximal part of the lever arm.

Then one exercises simultaneously and / or successively a 2 ^nd and a

15 ^3rd set transverse pressure on the belt (Step 4) respectively on a 2 ^nd and 3 ^rd portion of the strap, which leads, because of the inextensible character or substantially inextensible strap, the lifting arm of lever, for example a few centimeters.

[0056] Depending on the configuration of the load to be lifted, and in particular its location relative to the positioning of the lifting device comprising the strap, it is possible or not (step 5) to decide to renew the pressurizations of steps 3 and 4.

It is also possible to decide, in the event of final non-renewal or

25 simply immediate cycle 2, to carry out or not (step 6) pressurization (step 7) on a 4 ^th and 5 ^th strap portions, for example symmetrically disposed outwardly of the second and third portions, which allows to continue the movement of lifting of the arm in a more progressive manner, via a cycle 8 comprising steps 3, 4 and 7.

Cycle 8 may or may not (test 9) be repeated to continue lifting the lifting arm before ending with a last step 10,

5 for example identical to step 3 for a different height.

Thus, thanks to a successive pressurization, the first, 2 ^nd , 3 ^rd and, if necessary, 4 ^th and 5 ^th strap portions are moved vertically, respectively on the first, 2 ^nd , 3 ^rd , 4 ^e , 5 ^e etc. determined heights or distances, these displacements possibly being

10 repeated several times, then it ends for example with a displacement of the first portion to a new height carrying out the lifting of the arm between a first rest position and a last so-called working position.

There is shown in Figure 2, a block diagram illustrating

15 a simple implementation of the invention performing steps 3 and 4 and then 10, without renewing cycle 2 and without putting pressure on other portions of the strap.

The proximal end portion 1 1 of the strap 12 is fixed at 13 to a base 14, its distal end portion 15 being fixed at 16 to

20 the proximal part 17 of a lever arm, an axis 18 for maintaining the portion substantially adjacent to the distal end portion 15 of the strap allowing the maintenance of fixed points for the strap, on the one hand on the base of the device, and on the other hand on the axis or near the fixed axis 19 of rotation of the lever arm.

The centers of the strap portions 20 21, 22 on which the successive tensionings 23 24, 25 and 26 are exerted are for example distributed substantially at equal distances between them and with the fixed points 14 and 18. During successive thrusts the central parts of the strap portions are raised to height h1, h2, h3, h4 corresponding to the respective tensionings resulting in the formation of angles a, b between the direction of the strap before pressurization and management

5 of the strap after pressurization, to a value of a few degrees, for example 10 to 15 °, for example 14 °.

There is shown in Figures 3A to 3D, in side views, the device 27 according to the embodiment of the invention more particularly described here, arranged to lift a load 28

10 (represented by an arrow representing a weight) at the end or distal part of the lever arm 29. The arm 29 is movable in rotation about an axis 30 between a first horizontal position (FIG. 3A) and a last position, substantially vertical (Figure 3D).

In the remainder of the description, to the extent of the

15 possible, the same reference numbers to designate identical or similar elements.

More specifically, with the device 27 is carried out the tensioning of the strap 12, the proximal end portion 11 of which is fixed at 13 to a base 14 and the distal end portion 15 is fixed

20 at 16 to the proximal portion 17 of the arm 29, a blocking of the vertical movement of the strap by a roller 18 located vis-à-vis the axis of rotation 30 relative to the base, being provided. This fixing at 16 is for example made removably by anchoring the strap on the lever arm at a distance d from the axis 30, between 1/20 and

25 1/5, for example 1/10 of the length L of the lever arm.

The mounting of the anchor can also and for example be carried out as follows (embodiment not shown in the figure). The strap 12 in its distal end position 15 passes below or even more advantageously makes a complete turn around the axis 30 to then attach to the proximal part 17 of the arm 29 at point 16 at the distance d.

[0068] According to this embodiment of the invention, the device is therefore arranged to exert pressure for or put under tension

5 successive on the strap 12 according to the following steps.

A first tensioning 23 is first of all exerted on a central portion 20, in the center thereof, then lifting the inextensible strap, which generates to compensate for a first upward movement 31 of the lever arm (Figure 3B).

This pressurizing can for example be exerted by means of pushing means, for example vertical pistons or rotary cams as will be described below.

Then we exercise simultaneously or successively, but closely in time (for example less than a second, for

15 example, 1/10 second), a ^2nd set voltage 24 and a ^3rd set voltage 25 of the strap portions 21, 22, thereby to again move the lever arm 29 upwards (arrow 32 ) in an intermediate lifting position (figure 3).

These tensionings are carried out by vertical displacement

20 portions of inextensible strap of determined height.

[0073] Figure 3D shows the final lifting step.

Here, the central portion 20 of the strap is again moved upwards by the thrust 26 which completes the displacement by rotation of the arm (arrow 33)

FIG. 4 shows the force and / or displacement diagram 34 of the strap portions showing a succession of pushing cycles on said strap 12, of the type of that shown in FIG. 2. Only the three portions of strap 20 21, 22 are activated here, the movements in height corresponding to the respective segments in the figure, CD, EG, FH, DI, GJ, HK, etc., the angles a and b between the strap portions between the fixed points A and B and the

5 thrust being, as can be seen in the figure, a few degrees with respect to the direction taken by the strap during the previous tensioning, for example less than 10 °.

FIG. 5 shows the curves of variation of the thrust heights (on the ordinate) over time (abscissa) of the first

10 central portion (curve 35) and the second and third portions

(curves 36 and 37, respectively in phantom and dashed lines) during the implementation of the cycles of figure 4.

[0078] Figure 6 shows an example of the variation (curve 38) of the angle taken by the lifting arm during the implementation of

15 cycles of figure 4.

It is noted that the variations in the angle show a continuous lift which can therefore go up to 90 °.

[0080] Figures 7 and 8 show in side view and in perspective an exemplary embodiment of part of the device according to the invention

20 using push cams to carry out the tensioning of the strap.

As we have seen, this device acts on a lever arm 29 movable in rotation about an axis 30 integral with a base 14.

This base 14 is formed of a frame for example metal which can

25 be of significant weight (a few hundred kilos for example), to withstand the stresses during the lifting of the load by the lever arm, or which is arranged to be firmly fixed to the ground, or to a vehicle anchored in ground. The frame comprises two side cheeks 39 for example substantially rectangular to which are fixed transversely, on the one hand the axis 30 of rotation of the lever arm on one side, and on the other hand, on the other side, a bar 41 on which is fixed

5 the attachment point 42 of the portion 11 of strap 12 in a manner known per se.

The frame further comprises three modules 43, 44, 45 for supporting three cams, 46, 47, 48. Two modules (43,45) and two cams (46,48) are here identical in size and in configurations , respectively

10 arranged to activate the second and third portions of strap.

They are arranged symmetrically with respect to the central module 44 provided with the cam 47 of slightly different shape, for actuating the first portion of the strap.

Referring to Figures 9 and 10, these cams are

15 geometrically configured to exert one or more cycles of determined transverse pressure on the strap, as described above.

They are for example driven by a single rotary motor 49, axial via a single central axis 50, suitable for rotating the cams so

20 simultaneous, but allowing thrusts slightly offset in time, which considerably limits (by dividing them by three) the forces exerted on the engine, which can therefore be less powerful, which reduces costs.

More precisely the cams are in the form of discs 51, 52

25 circular or substantially circular comprising on one of their faces 53, 54 a rail 55, 56 or guide groove in the form of a concentric spiral, of determined length and trajectory to allow, when it is going to be followed, to generate a movement determined by successive pushes and supports. Each module further comprises a guide roller 57, 58 arranged to cooperate with the rail or the corresponding groove facing each other. The guide roller is integral with a pushing system 59, 60. Each pushing system is terminated at the top by a

5 ring 61, 62 arranged to cooperate with the strap so as to transmit to it the thrust of the pusher system according to the determined pressure cycle or cycles.

More precisely, each pusher system is for example constituted by a portal arm 63, 64 formed of vertical uprights

10 parallel, symmetrical with respect to a plane of geometry 65 of the base.

These arms support, at the level of the plane of symmetry 65, the rings 61, 62 therefore located centrally between the latter two.

We will now describe with reference to Figures 3A to 3D the lifting of the load 28.

[0092] In the initial state the strap is horizontal, and the cams are in the low position, no pressure was exerted on the facing portions of the strap. Then the rotary motor 49, controlled by an automatic device (not shown) in a manner known per se and programmed accordingly, actuates the cams in rotation (simultaneously),

20 the grooves being however designed to allow the first thrust 23 of the central part without allowing a thrust on the second and third portions.

As the rotation of the cams continues, it is then the turn of the grooves of the end cams 46, 48 to pressurize the

25 second, then third portions at 1/10 ^th of a second interval allowing the continuation of the ascent of the arm 29. Immediately after the end of this ascent, the central cam 47 then allows a second displacement of the first portion (FIG. 3D) bringing the lever arm in high position (according to the cycle as previously programmed).

As goes without saying and as it follows from the foregoing, the present invention is not limited to the embodiments more particularly described.

On the contrary, it embraces all variants thereof and in particular those where each cam is driven by a different motor, and / or the cams are replaced by more conventional pushing means such as electric jacks, for example.

10

Claims

[Claim 1] A method of tensioning an inextensible or substantially inextensible longitudinal strap (12) comprising a distal end portion (15) and a proximal end portion (11), each end portion being respectively fixed to a corresponding attachment point (13,16), characterized in that a cycle (2) of successive transverse pressurizations is exerted on the strap (12) comprising a first transverse pressurization (23) on a first portion (20) of the strap, then a second (24) and a third (25) placed in transverse pressure respectively on a second (21) and on a third (22) portions of said strap.

[Claim 2] A method according to claim 1, characterized in that the proximal end portion (11) of the strap (12) being fixed to a base (14) by a first of the attachment points (13) and the distal end portion (15) of the strap being fixed to a proximal part (17) of a lever arm (29) movable in rotation about an axis (19,30), by the second of the points d 'fastener (16), said lever arm extending between said proximal portion and a distal portion arranged to support a load, successive pressurizations are arranged to actuate the lifting of said lever arm between a first rest position and a second working position.

25

[Claim 3] A method according to claim 2, characterized in that a load (28) being fixed to the distal part of the lever arm (29), the transverse pressurization cycle takes place in the form of successive vertical thrusts in the plane of movement on the strap fixed on one side to said proximal part of said arm and on the other side to a fixed point, the vertical thrusts successive on said strap taking place in at least three locations distributed along the latter so as to lift the load (28).

[Claim 4] A method according to any of

5 preceding claims, characterized in that the second and third pressurizations are distributed symmetrically or substantially symmetrically on either side of the first pressurization.

[Claim 5] A method according to any of

10 preceding claims, characterized in that the second and third pressurizations are exerted successively.

[Claim 6] A method according to any one of the preceding claims, characterized in that, to exert the pressurization, the first are moved vertically,

15 second and third strap portions (20, 21, 22) respectively over a first, second and third determined height, then again the first portion (20) over a new determined height.

[Claim 7] A method according to claim 6, characterized

20 in that the second and third determined heights are equal.

[Claim 8] A method according to any one of claims 6 or 7, characterized in that the heights are arranged so that the angles (a, b) formed between the portions of

25 strap and / or the attachment points adjacent to the pressurized portion are between 5 ° and 15 °.

[Claim 9] A method according to any one of the preceding claims, characterized in that the pressurization cycle (2) is repeated at least N times, with N> 2.

30

[Claim 10] A method according to any one of the preceding claims, characterized in that each cycle comprises at least a fourth and a fifth transverse pressurizations respectively on a fourth and on a fifth strap portions and / or an umpteenth and n + 1 th pressurements on an umpteenth and n + 1 strap portions with,

5 n ³ 6, the nth and n + 1 st portions being located on either side of the n-2nd and n-1 th strap portions respectively (12).

[Claim 1 1] A method according to any one of the preceding claims, characterized in that the

10 pressurizing the strap (12) by means of cams (46, 47,

48) rotary configured to allow the successive pressurization cycle (s) for determined thrust values.

[Claim 12] Device (27) for tensioning a

15 inextensible or substantially inextensible strap (12) extending longitudinally between a distal end portion (15) and a proximal end portion (11), respectively attached to corresponding attachment points, characterized in that it comprises pushing means (43, 44, 45; 46, 47, 48; 49, 50)

20 for placing transverse pressure on the strap comprising first pushing means (44, 47) for placing transverse pressure on a first portion (20) of strap, second (43, 46) and third means (45, 48) transverse pressurizing pushers respectively on a second

25 (21) and on a third (22) strap portions, and means for controlling said pressurizing pushing means arranged to carry out at least one cycle of successive pressurizing of the strap (12) on said first, second and third portions of said strap in a determined manner.

30 [Claim 13] Device according to claim 12, characterized in that it further comprises a lever arm (29) extending longitudinally between a proximal portion and a distal load-bearing portion (28), the proximal portion being rotatable about an axis (30) attached to a pedestal (14), the distal portion of the strap being attached to said part

5 of the proximal end of the arm by one of the attachment points (16), directly or via a pulley and / or by a rotary cylinder type axis, and the proximal end portion of the strap being fixed at a fixed point

(13) forming the second of the attachment points.

[Claim 14] Device according to any of

10 claims 12 and 13, characterized in that the pushing means and the axis (30) of rotation of the arm are integral with the base (14) which is movable.

[Claim 15] Device according to any one of claims 12 to 14, characterized in that the device

15 comprises three pushing means, namely a central means (44,

47) and two lateral means (43, 46, 45, 48) arranged symmetrically or substantially symmetrical with respect to the central means.

[Claim 16] Device according to any of

20 claims 12 to 15, characterized in that the number of pushing means comprises n + 2 pushing means with odd n greater than or equal to 3, distributed longitudinally along the strap (12), symmetrically with respect to the central pushing means located equidistant between the fixed point and a

25 pulley or rotary return cylinder located in the same longitudinal plane as the fixed point.

[Claim 17] Device according to any one of claims 12 to 16, characterized in that the pushing means comprise cams (43, 44, 45) of geometry

30 configured to exert one or more cycles of transverse pressurization determined on the strap.

[Claim 18] Device according to claim 17 characterized in that the cams are activated in rotation by one and the same rotary motor (49).

[Claim 19] Device according to any of

5 claims 17 and 18, characterized in that each pushing means comprises a cam (43,44,45) in the form of a substantially circular disc comprising on one of its faces (53,54), a rail (55,56) or a guide groove in the form of a concentric spiral of determined length and path, a guide roller (57,58) arranged to cooperate with the rail or the groove facing each other, integral with a pusher system and said pusher system ( 63, 64) terminated at the top by a ring (61, 62) arranged to cooperate with the strap so as to transmit to it the thrust of the pusher system according to the determined pressure cycle (s).

20