The present invention relates to a method for tensioning an inextensible or substantially inextensible strap notably for lifting a load from a distance or else for moving in space a significant mass situated at an end remote from the actuating mechanism.
It also relates to a tensioning and/or movement device employing such a method.
It finds a particularly important, although not exclusive, application in the field of building and public works, for site equipment or for devices for handling heavy loads requiring a significant force for lifting-off and/or detaching the load at the outset.
However, it is also applicable to the field of robotics and exoskeletons, to the field of prosthetics and orthotics for man and more generally to all fields of mechanics requiring a preload on an inextensible or substantially inextensible longilinear member and/or the application of movement to a lever arm or the application of a tensile force that requires a significant force and/or a significant speed at the outset.
What is meant by a substantially inextensible member is a member designed to experience elongation of less than 5% of its length for a determined maximum tensile force below its breaking point of, for example, 500 MPa, for example less than 3%, advantageously less than 1%, more advantageously still, less than 0.5% or even 0.05%.
Devices that allow heavy loads to be handled from a distance using a lever arm are already known.
However, these have disadvantages, particularly in terms of cost and bulk.
These are, for example, power rams which are not easy to handle and that are found in autonomous vehicles of the lift truck, excavator or mechanical shovel type, or else rotary motors used for example in vehicles mounted on a base, of the factory robot type, the operating torque of which is dependent on their weight, and which will therefore have a tendency to be oversized.
In addition, the force that will act on the lever arm rotation axle is necessarily coupled to the movement of the load, without the possibility of dissociation, whether the actuator engages directly with the lever arm or whether it does so via a deformable quadrilateral.
Thus, the current setups, whether these involve linear actuators or rotary motors, necessarily have to deliver a maximum power for equalizing the resistive torque at each instant of the movement. This leads to a significant expenditure in terms of energy, imposes a high weight on the drive elements and leads to greater wearing of the mechanical parts.
It is an object of the present invention to overcome these disadvantages notably by dissociating the force exerted on the lever arm from the movement of the actuator.
In order to do this, the invention takes an entirely different approach from that of the prior art. It is derived from careful observation of the working of an arm muscle, and more particularly of the biceps which, in order to lift a load in the hand situated at the end of the forearm (lever arm), does not decrease in length but stiffens the biceps by increasing the transverse volume of the muscle fibers of which it is made.
With the invention, the equivalent of a catch of transverse volume causes the tensioning of a somewhat inextensible tie or ligament and, in this instance, the movement in space of a significant mass at the end of the arm, in a way that is at the very least equivalent to a longitudinal shortening but which, above all and surprisingly, produces a very high lift-off force for a minimum movement, thus operating on a principle equivalent to that of a reverse block and tackle.
To this end, the invention notably proposes a method for tensioning an inextensible or substantially inextensible longitudinal strap comprising a distal end portion and a proximal end portion, each end portion being respectively fixed to a corresponding anchor point, characterized in that a cycle of successive applications of transverse pressure to the strap is applied, this cycle comprising a first application of transverse pressure to a first portion of the strap, followed by a second and a third application of transverse pressure to a second and to a third portion of said strap respectively without relaxing the tension between the two successive applications of pressure.
No relaxing of the tension of the strap occurs between the successive applications of tension or, where applicable, between the various tension application cycles.
What is meant by the application of transverse pressure or thrust is the application of a force initially perpendicular and then substantially perpendicular (+a few degrees increasing progressively with respect to 90°) to the strap with respect to its initial longitudinal direction without movement “in its plane”.
Advantageously, the portions of strap to which the pressures are applied are short in length by 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, namely for example less than 5 cm, for example than 1 to 2 cm, for a strap 1 m long.
The strap may of course be a cable, a belt, a chain, a tie or more generally any longilinear member for example formed of inextensible or substantially inextensible fibers, for example a material known by the brand name DYNEEMA which has a very high tensile strength, for example in excess of 500 MPa, and which nevertheless maintains sufficient flexibility to be able to absorb a great many cycles of deformation in bending over a determined maximum height per cycle (for example 50.000 cycles over a height of a few centimeters, for example 5 cm).
Advantageously, with the proximal end portion of the strap fixed to a base by a first of the anchor points and the distal end portion of the strap fixed to a proximal part of a lever arm rotationally mobile about an axle by the second of the anchor points, 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.
The rest position or low position is, for example, a position in which the arm is horizontal, and the working position or raised position is a position in which the arm is vertical, or at an angle of between 30° and 80°, for example 50°, to the horizontal.
The invention thus proposes a method for lifting a load fixed at a distal end of a lever arm rotationally mobile about a transverse axle situated on the side of a proximal part of the lever arm, by applying at least one pressure application cycle, this cycle being performed in the form of transverse thrusts on the inextensible or substantially inextensible strap fixed on one side to said proximal part of said arm and on the other side to a fixed point, in which method the applications of transverse pressure are performed in successive vertical thrusts in the plane of movement to said strap at least at three locations distributed along this strap.
In advantageous embodiments, recourse is further had to one and/or another of the following arrangements:
The use of cams allows excellent continuity and a high level of flexibility in the increases in pressure, as well as perfect mechanical repeatability of the movements.
The invention also proposes a device implementing the method or methods described above.
It also relates to a device for tensioning an inextensible or substantially inextensible strap extending longitudinally between a distal end portion and a proximal end portion, each of which are respectively fixed to corresponding anchor points, characterized in that it comprises thruster means for applying transverse pressure to the strap, comprising first thruster means for applying transverse pressure to a first portion of strap, second and third thruster means for applying transverse pressure to a second and to a third 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 on said first, second and third portions of said strap in a determined manner.
Advantageously, the thruster means comprise rotationally mobile cams programmed and/or configured to allow the determined successive pressure application cycles.
However, it is also possible, for example, to use vertically thrusting hydraulic or electric actuators with identical or different strokes, of lengths determined in a preprogrammed manner.
In one advantageous embodiment, the device additionally comprises a lever arm extending longitudinally between a proximal part and a distal part for supporting a load, the proximal part being rotationally mobile about an axle fixed to a base, the distal end portion of the strap being for its part fixed to said proximal part of the arm by one of the anchor points, directly or via a pulley and/or for example an axle of the rotary cylinder type, and the proximal end portion of the strap being fixed to a fixed point forming the second of the anchor points for example secured to the base.
Advantageously, the strap, the thruster means and the arm rotation axle are secured to the one same base.
Advantageously also, the base is mobile, for example mounted on a mobile chassis, thereby allowing the device to be moved around, for example by a self-propelled vehicle.
In advantageous embodiments, the thruster means comprise a single rotary motor for actuating cams designed to perform one or more cycles of determined applications of transverse pressure to the strap.
Advantageously, the three thruster means (or systems) comprise a central means and two lateral means positioned symmetrically with respect to the central means.
Also advantageously, the number of thruster means is not limited to three, but comprises n+2 thruster means where n is an uneven number greater than or equal to 3, distributed longitudinally along the strap, for example, symmetrically with respect to the central thruster means situated equidistant between the fixed strap fixing point and a rotary cylinder or pulley for returning the strap, said pulley or said cylinder being situated in the same longitudinal plane as said fixed point.
Advantageously, each thruster means comprises:
It will be appreciated that the dynamics of such a device are connected to the geometry of the cams. Indeed it is these that dictate the determined movement of the thruster system (the movement of the strap in terms of height and in terms of speed) and therefore the upward movement of the arm, as well as the torques (lift-off and operating torques) needed for setting the arm in motion.
Note that the slope of the groove of the cam allows the torque and the speed to be varied, for the one same circular movement. Thus, a shallow slope results in a high torque and a low speed, and conversely a steep slope results in a low torque and a higher speed. Varying the slopes therefore makes it possible to alter the speed/torque ratio at various moments in the movement. What is meant by the slope of the groove is the angle that the tangent to the curve makes with the horizontal at the location of the roller.
In an example of a set of grooved cams implemented with the invention (which groove a person skilled in the art will therefore dimension according to the desired operating parameters, dependent notably and in a known way on the length of the lever arm between its rotation axle and its distal end for attachment to the weight that is to be lifted, the value of said weight and the height to which the arm is to lift said load) there is found, with three thruster means, a reduction in speed by a factor of six, for an increase in drive torque varying between 3.7 and 6 with respect to the motor speed and torque required to lift the load through direct action on the rotation of the lever arm axle. This sharply highlights the non-linearity of the system.
Another example of a set of cams produced made it possible to achieve a torque increase by a factor in excess of twelve, for a speed reduction by a factor of ten.
The invention will be better understood from reading the following description of embodiments given hereinafter by way of nonlimiting examples.
The description refers to the accompanying drawings, in which:
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.
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.
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.
Next, a 2nd and a 3rd application of transverse pressure are applied simultaneously and/or successively to the strap (step 4) on a 2nd and on a 3rd 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.
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.
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 4th and a 5th 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.
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.
Thus, through successive applications of pressure the first, 2nd, 3rd and, where applicable, 4th and 5th portions of strap are moved vertically over first, 2nd, 3rd, 4th, 5th 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.
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.
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.
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°.
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.
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.
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.
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.
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 (
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.
Next, a 2nd application of tension 24 and a 3rd 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 (
These applications of tension are performed by moving the portions of inextensible strap vertically over a determined height.
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).
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°.
It may be noted that the variations in the angle show a continuous lift which may therefore extend as far as 90°.
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.
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.
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.
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.
With reference to
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.
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.
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.
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.
These arms support, at the plane of symmetry 65, the rings 61, 62 which are therefore situated centrally between these two arms.
The lifting of the load 28 will now be described with reference to
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.
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 (
As goes without saying and as is evident from the foregoing, the present invention is not restricted to the embodiments more particularly described.
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.
Number | Date | Country | Kind |
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1902282 | Mar 2019 | FR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2020/056074 | 3/6/2020 | WO | 00 |