METHOD AND DEVICE FOR TENSIONING A STRAP

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 die 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.

Claims

1. A 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 anchor point (13, 16), characterized in that a cycle (2) of successive applications of transverse pressure to the strap (12) is applied, this cycle comprising a first application (23) of transverse pressure to a first portion (20) of the strap, followed by a second (24) and a third (25) application of transverse pressure to a second (21) and to a third (22) portion of said strap respectively.

2. The method as claimed in claim 1, characterized in that, with the proximal end portion (11) of the strap (12) fixed to a base (14) by a first of the anchor points (13) and the distal end portion (15) of the strap fixed to a proximal part (17) of a lever arm (29) rotationally mobile about an axle (19, 30) by the second of the anchor points (16), said lever arm extending between said proximal part and a distal part designed to support a load, the successive applications of pressure are designed to actuate the lifting of said lever arm between a first, rest, position and a second, working, position.

3. The method as claimed in claim 2, characterized in that, with a load (28) being fixed to the distal part of the lever arm (29), the cycle of applications of transverse pressure is performed in the form of successive vertical thrusts in the plane of movement to the strap fixed on one side to said proximal part of said arm and, on the other side, to a fixed point, the successive vertical thrusts on said strap being performed at least at three locations distributed along this strap so as to lift the load (28).

4. The method as claimed in claim 1, characterized in that the second and third applications of pressure are distributed symmetrically or substantially symmetrically on either side of the first application of pressure.

5. The method as claimed in claim 1, characterized in that the second and third applications of pressure are applied successively.

6. The method as claimed in claim 1, characterized in that, in order to perform the applications of pressure, the first, second and third portions of strap (20, 21, 22) are moved vertically over, respectively, a first, second and third determined height, then the first portion (20) is moved once again over a new determined height.

7. The method as claimed in claim 6, characterized in that the second and third determined heights are equal.

8. The method as claimed in claim 6, characterized in that the heights are arranged so that the angles (α, β) formed between the portions of strap and/or the anchor points adjacent to the portion to which pressure is applied are comprised between 5° and 15°.

9. The method as claimed in claim 1, characterized in that the pressure application cycle (2) is repeated at least N times, where N≥2.

10. The method as claimed in claim 1, characterized in that each cycle comprises at least a fourth and a fifth application of transverse pressure to a fourth and a fifth portion of strap respectively and/or an nth and an n+1.sup.th application of pressure to an nth and an n+1.sup.th portion of strap where n≥6, the nth and n+1.sup.th portions being situated respectively on either side of the n−2.sup.th and n−1.sup.th portions of strap (12).

11. The method as claimed in claim 1, characterized in that the applications of pressure to the strap (12) are performed via rotary cams (46, 47, 48) configured to permit the successive pressure-application cycle or cycles for determined values of thrust.

12. A device (27) for tensioning an inextensible or substantially inextensible strap (12) extending longitudinally between a distal end portion (15) and a proximal end portion (11) which are respectively fixed to corresponding anchor points, characterized in that it comprises thruster means (43, 44, 45; 46, 47, 48; 49, 50) for applying transverse pressure to the strap, comprising first thruster means (44, 47) for applying transverse pressure to a first portion (20) of strap, second (43, 46) and third (45, 48) thruster means for applying transverse pressure to a second (21) and to a third (22) portion of strap respectively, and control means controlling said pressure-application thruster means and designed to perform at least one cycle of successive applications of pressure to the strap (12) on said first, second and third portions of said strap in a determined manner.

13. The device as claimed in claim 12, characterized in that it additionally comprises a lever arm (29) extending longitudinally between a proximal part and a distal part for supporting a load (28), the proximal part being rotationally mobile about an axle (30) fixed to a base (14), the distal portion of the strap being for its part fixed to said proximal end part of the arm by one of the anchor points (16), directly or via a pulley and/or via an axle of the rotary cylinder type, and the proximal end portion of the strap being fixed to a fixed point (13) forming the second of the anchor points.

14. The device as claimed in claim 12, characterized in that the thruster means and the rotation axle (30) of the arm are secured to the base (14) which is mobile.

15. The device as claimed in claim 12, characterized in that the device comprises three thruster means, namely a central means (44, 47) and two lateral means (43, 46, 45, 48) positioned symmetrically or substantially symmetrically with respect to the central means.

16. The device as claimed in claim 12, characterized in that the number of thruster means comprises n+2 thruster means where n is an uneven number greater than or equal to 3, distributed longitudinally along the strap (12), symmetrically with respect to the central thruster means situated equidistant between the fixed point and a return pulley or rotary cylinder situated in the same longitudinal plane as the fixed point.

17. The device as claimed in claim 12, characterized in that the thruster means comprise cams (43, 44, 45) of a geometry configured to perform one or more determined cycles of applications of transverse pressure to the strap.

18. The device as claimed in claim 17, characterized in that the cams are activated in rotation by one and the same single rotary motor (49).

19. The device as claimed in claim 17, characterized in that each thruster means comprises a cam (43, 44, 45) in the form of a substantially circular disk comprising, on one of its faces (53, 54), a guide groove or rail (55, 56) in the form of a concentric spiral of determined length and trajectory, a guide roller (57, 58) designed to collaborate with the groove or rail opposite, secured to a thruster system, and said thruster system (63, 64) ending at the top in a ring (61, 62) designed to collaborate with the strap in such a way as to transmit the thrust of the thruster system to it according to the determined pressure cycle or cycles.

Description

[0050] The description refers to the accompanying drawings, in which:

[0051] FIG. 1 is a flow diagram of a method for lifting a load according to one embodiment of the invention, with the application of pressure to five portions of strap.

[0052] 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.

[0053] FIG. 3 shows, in side view, a device according to one embodiment of the invention, prior to the application of the first thrust (according to the diagram of FIG. 2), the lever arm being in its lowered or rest position (FIG. 3A), after the first thrust (FIG. 3B), after the 2.sup.nd and 3.sup.rd thrusts (FIG. 3C), and after the 4.sup.th thrust, the lever arm being in its raised position (FIG. 3D).

[0054] FIG. 4 is a diagram of forces showing a succession of cycles of thrust on the strap of the type shown with reference to FIG. 2.

[0055] FIG. 5 shows the curve of the variation in thrust heights achieved by the central and lateral thrusting means according to the embodiment of the device of the invention more particularly described here.

[0056] FIG. 6 shows the curve of the variation in the angle adopted by the lifting arm as a function of time, corresponding to the variations in height of FIG. 5.

[0057] FIG. 7 is a side view of the lifting device according to the embodiment of the invention more particularly described here.

[0058] FIG. 8 is a view in axionometric perspective of FIG. 7.

[0059] FIG. 9 is a perspective view of the three cams of the device of FIG. 7.

[0060] FIG. 10 shows, in side view, the central and lateral cams of FIG. 9.

[0061] FIG. 1 shows a flow diagram 1 of a method of lifting a load according to an embodiment of the invention.

[0062] To do this, the load (for example a 500 kg portion of pipeline tube) is fixed to a lifting device and, more particularly, to a distal part of a lever arm (step 1), the proximal part of the lever arm having itself been fixed at one of its ends to the distal portion of an inextensible strap extending longitudinally and horizontally, itself fixed at its other end, referred to as the proximal end, to a fixed point, for example belonging to a truck or to a base secured to the ground on which it rests.

[0063] In order to raise the load, which will for example allow space to be cleared beneath it, so that it can be recovered and/or set down on a support, a first cycle 2 of applications of transverse pressure, in this instance vertical (namely transverse with respect to the horizontal initial position of the strap) is applied to said strap.

[0064] More specifically, the cycle 2 comprises a first application of pressure 3 to a first portion of the strap, for example arranged substantially centrally with respect to the points of attachment of the strap to the base and to the proximal part of the lever arm respectively.

[0065] Next, a 2.sup.nd and a 3.sup.rd application of transverse pressure are applied simultaneously and/or successively to the strap (step 4) on a 2.sup.nd and on a 3.sup.rd portion of the strap respectively, this, because of the inextensible or substantially inextensible nature of the strap, causing the lever arm to lift, for example by a few centimeters.

[0066] Depending on the configuration of the load that is to be lifted, and notably its location with respect to the positioning of the lifting device comprising the strap, the decision may or may not (step 5) be taken to repeat the applications of pressure of steps 3 and 4.

[0067] It is also possible to decide, if the cycle 2 is not to be repeated definitively or simply immediately, whether or not (step 6) to apply pressure (step 7) to a 4.sup.th and a 5.sup.th portion of strap, these for example being positioned symmetrically towards the outside of the second and third portions, this being something that allows the lifting movement of the arm to continue more progressively, via a cycle 8 comprising steps 3, 4 and 7.

[0068] The cycle 8 may or may not (test 9) be repeated in order to continue to lift the lifting arm before the cycle is ended with a final step 10, for example identical to the step 3, for a different height.

[0069] Thus, through successive applications of pressure the first, 2.sup.nd, 3.sup.rd and, where applicable, 4.sup.th and 5.sup.th portions of strap are moved vertically over first, 2.sup.nd, 3.sup.rd, 4.sup.th, 5.sup.th etc. determined heights or distances respectively, these movements potentially being repeated several times, before ending for example with a movement of the first portion over a new height causing the arm to lift between a first, rest, position and a final, so-called working, position.

[0070] FIG. 2 depicts an outline diagram illustrating one simple embodiment of the invention performing steps 3 and 4 and then 10 without repeating the cycle 2 and without applying pressure to other portions of strap.

[0071] The proximal end portion 11 of the strap 12 is fixed at 13 to a base 14, its distal end portion 15 being fixed at 16 to the proximal part 17 of a lever arm, an axle 18 for holding the portion substantially adjacent to the distal end portion 15 of the strap making it possible to maintain the fixed points for the strap, on the one hand on the base of the device and, on the other hand, on or close to the fixed axle 19 of rotation of the lever arm.

[0072] The centers of the portions of strap 20, 21, 22 to which the successive applications of tension 23, 24, 25 and 26 are applied, are, for example, distributed at substantially equal distances from each other and from the fixed points 14 and 18.

[0073] Upon successive thrusts, the central parts of the portions of strap are lifted by heights h1, h2, h3, h4 corresponding to the respective applications of tension leading to the formation of angles α, β between the direction of the strap before the application of pressure and the direction of the strap after the application of pressure, with a magnitude of a few degrees, for example 10 to 15°, for example 14°.

[0074] FIGS. 3A to 3D depict, in side views, the device 27 according to the embodiment of the invention more particularly described here, designed to lift a load 28 (represented by an arrow indicating a weight) at the end or distal part of the lever arm 29. The arm 29 is rotationally mobile about an axle 30 between a horizontal first position (FIG. 3A) and a substantially vertical final position (FIG. 3D).

[0075] In the remainder of the description, as far as possible, the same reference numerals will be used to denote elements that are identical or similar.

[0076] More specifically, using the device 27, tension is applied to the strap 12 of which the proximal end portion 11 is fixed at 13 to a base 14 and the distal end portion 15 is fixed at 16 to the proximal part 17 of the arm 29, there being provision to block the vertical movement of the strap using a roller 18 situated facing the rotation axle 30 with respect to the base. This fixing at 16 is performed for example removably by anchoring the strap on the lever arm at a distance d from the axle 30 of between 1/20 and ⅕, for example 1/10 of the length L of the lever arm.

[0077] The anchor point may also and for example be mounted as follows (an embodiment not depicted in the figures). The strap 12 in its distal end position 15 passes under or, more advantageously still, makes a complete turn around the axle 30 before then being fixed to the proximal part 17 of the arm 29 at the point 16 at the distance d.

[0078] According to this embodiment of the invention the device is therefore designed to apply successive pressures or tensions to the strap 12 according to the following steps.

[0079] A first application of tension 23 is first of all applied to a central portion 20, at the center thereof, thus lifting the inextensible strap, which to compensate brings about a first upward movement 31 of the lever arm (FIG. 3B).

[0080] This application of pressure tension may for example be achieved via thruster means, for example vertical pistons or rotary cams as will be described later on.

[0081] Next, a 2.sup.nd application of tension 24 and a 3.sup.rd application of tension 25 are applied simultaneously or successively, but in a manner that is closely spaced in time (for example less than one second, for example 1/10 of a second apart) to the strap portions 21, 22, and this once again allows the lever arm 29 to be moved upwards (arrow 32) into an intermediate raised position (FIG. 3).

[0082] These applications of tension are performed by moving the portions of inextensible strap vertically over a determined height.

[0083] FIG. 3D shows the final lifting step.

[0084] Here, the central portion 20 of the strap is once again moved upward by the thrust 26 thereby completing the rotational movement of the arm (arrow 33).

[0085] FIG. 4 shows the diagram 34 of forces and/or movements of the portions of strap showing a succession of cycles of thrusts on said strap 12, of the type of that shown in FIG. 2.

[0086] Only the three portions of strap 20, 21, 22 are activated here, the heightwise movements corresponding to the respective segments in the figure, CD, EG, FH, DI, GJ, HK, etc., the angles α and β between the portions of strap between the fixed points A and B and the thrust points being, as can be seen in the figure, by a few degrees with respect to the direction adopted by the strap in the previous application of tension, for example less than 10°.

[0087] FIG. 5 shows the curves of the variation in the thrusting heights (on the ordinate axis) with respect to time (abscissa axis) for the central first portion (curve 35) and for the second and third portions (curves 36 and 37 respectively drawn in chain line and in broken line) during the implementation of the cycles of FIG. 4.

[0088] FIG. 6 for its part shows an example of the variation (curve 38) in the angle adopted by the lifting arm during the implementation of the cycles of FIG. 4.

[0089] It may be noted that the variations in the angle show a continuous lift which may therefore extend as far as 90°.

[0090] FIGS. 7 and 8 show in side view and in perspective an exemplary embodiment of part of the device according to the invention using thrusting cams to achieve the application of tension to the strap.

[0091] As has been seen, this device acts on a lever arm 29 which is rotationally mobile about an axle 30 secured to a base 14.

[0092] This base 14 is formed of a framework, for example a metal framework, which may be of substantial weight (several hundreds of kilos for example) so as to absorb the stress loadings as the load is raised by the lever arm, or which is designed to be fixed solidly to the ground, or to a vehicle anchored in the ground.

[0093] The framework comprises two for example substantially rectangular side plates 39 to which there are fixed transversely, on the one hand, the rotation axle 30 of the lever arm on one side, and, on the other hand, on the other side, a bar 41 to which the point of attachment 42 of the portion 11 of strap 12 is fixed in a way known per se.

[0094] The framework additionally comprises three modules 43, 44, 45 supporting three cams 46, 47, 48. In this instance, two modules (43, 45) and two cams (46, 48) are identical in terms of size and configuration and designed respectively to activate the second and third portions of strap. They are positioned symmetrically with respect to the central module 44 provided with the cam 47 which is slightly different in form, for actuating the first portion of strap.

[0095] With reference to FIGS. 9 and 10, these cams are geometrically configured to carry out one or more cycles of application of determined transverse pressure to the strap, as described above.

[0096] They are for example driven by a single rotary motor 49, which is axial, via a single central axle 50 capable of causing the cams to rotate simultaneously, but allowing thrusts that are offset slightly in time, thereby considerably limiting (by dividing by a factor of three) the forces applied to the motor, which can therefore be less powerful, thereby reducing costs.

[0097] More specifically, the cams are in the form of circular or substantially circular disks 51, 52 comprising, on one of their faces 53, 54, a guide groove or rail 55, 56 in the form of a concentric spiral of determined length and trajectory so that, when followed, it generates a determined movement of successive thrusts and presses.

[0098] Each module additionally comprises a guide roller 57, 58 designed to collaborate with the corresponding groove or rail opposite. The guide roller is secured to a system of thrusters 59, 60. Each thruster system ends at the top in a ring 61, 62 designed to collaborate with the strap in such a way as to transmit to it the thrust from the thrusters system according to the determined cycle or cycles of pressure.

[0099] More specifically, each thruster system consists for example of a portal frame arm 63, 64 formed of parallel vertical uprights which is symmetric with respect to a geometric plane 65 of the base.

[0100] These arms support, at the plane of symmetry 65, the rings 61, 62 which are therefore situated centrally between these two arms.

[0101] The lifting of the load 28 will now be described with reference to FIGS. 3A to 3D.

[0102] In the initial state, the strap is horizontal and the cams are in the lowered position, no pressure being applied to the portions of strap opposite. Next, the rotary motor 49, controlled by a controller (not depicted) in a way known per se, and programmed accordingly, actuates the (simultaneous) rotation of the cams, although the grooves are designed to allow the first thrust 23 on the central part without allowing thrust on the second and third portions.

[0103] As the cams continue to rotate, it is then the turn of the grooves of the end cams 46, 48 to cause pressure to be applied to the second and then third portions at 1/10th of a second intervals to allow the continued raising of the arm 29. Immediately after the end of this raising, the central cam 47 then allows a second movement of the first portion (FIG. 3D) bringing the lever arm into the raised position (according to the cycle as programmed beforehand).

[0104] As goes without saying and as is evident from the foregoing, the present invention is not restricted to the embodiments more particularly described.

[0105] On the contrary, it encompasses all variants and notably those in which each cam is driven by a different motor and/or the cams are replaced by more conventional thruster means such as rams, for example electric rams.