WO2015107404A1

WO2015107404A1 - Adjustable intensity constant force generator

Info

Publication number: WO2015107404A1
Application number: PCT/IB2014/067125
Authority: WO
Inventors: Dino Accoto; Nevio Luigi Tagliamonte; Giorgio CARPINO; Angelo Sudano; Alessio ALESSI
Original assignee: Meccanica Biomedica S.R.L.
Priority date: 2014-01-15
Filing date: 2014-12-19
Publication date: 2015-07-23

Abstract

The present invention relates to an adjustable intensity constant force generator (100), allowing a continuous adjustment of the force (F) outgoing from the device and minimizing the energy consumption during the force adjustment.

Description

ADJUSTABLE INTENSITY CONSTANT FORCE GENERATOR

DESCRI PTION

The present invention relates to an adjustable intensity constant force generator. It is clear that the present invention can be used in a plurality of different circumstances and applications, all having in common the need of being able to generate a constant force, for example to be transmitted to a person or to be exploited to compensate a load.

By way of example, such need appears, for example:

in the machines for fitness (multi-function platforms or for single exercises); in the machines for the physical rehabilitation and neuro-rehabilitation (both of the upper and lower limbs);

in systems for supporting the weight of patients during the physical rehabilitation and neuro-rehabilitation of lower limbs;

in industrial systems for balancing the weight of a load;

in industrial systems for lifting objects.

However, it is to be meant that still other applications could take advantage of the use and implementation of the present invention.

The technical solution usually adopted in the above-described scenarios consists in using suitable counterweights. Such solution, no matter how simple it is, involves two disadvantages. First of all the force developed by the system of counterweights is linked to the mass of the same counterweights, and then it cannot be varied unless by adding additional mass. This involves that the counterweights provide an adjustable force only in a discrete way, subject to manual intervention.

Secondly, the counterweights represent an additional mass that increases the weight of the system thereto they are connected as well as the corresponding inertial properties. Such disadvantage makes the system with counterweights a little suitable to generate constant forces in case there are stringent constraints on the maximum value of the mass or the weight of the system. To obviate these drawbacks, the development of systems alternative to the counterweights for generating constant and adjustable forces is of industrial interest.

In this optics, the implementation systems, for example of electric or fluidic type, controlled so as to supply a constant force or torque, represent a valid alternative.

However, these systems have intrinsic limitations. For example, they need a suitable power system; furthermore, in their operation they dissipate in an irreversible way a certain quantity of energy; moreover, they - generally - are not intrinsically safe, as their behaviour, in terms of developed force and torque, depends upon the control system which has to operate within determined limits to guarantee the stability of the device; at last, the developed force is substantially equal to the reference value set by the control system only due to the force- adjusting speed lower than a limited value set by the pass-band of the system in retroaction.

In order to overcome such limitations, as from the '60s of the last century several solutions of constant force generators have illustrated, mainly based upon the use of purely mechanical elements, such as elastic members and cam profiles (US2924411 , US2972264). In such patents devices are described for implementing systems for balancing the weight force of objects (functionally equivalent to counterweights) to be used, for example, to ease the displacement thereof. A system which can be compared to the previous ones is described in the patent US4914780, for balancing the weight of window sashs. In this system an adjustment is provided to compensate small variations in the force to be balanced. In the patent US8091841 the spring/cam system is used inside a telescopic system of a table.

A similar principle underlies the patents US7032870, US7506853, wherein - among other things - a system is described for simplifying the manual positioning of a monitor by balancing its weight (figure 44 and following ones in US7032870; figure 44 and following ones in US7506853). The force adjustment takes place in a continuous way, but it requests the precompression of some elastic members. This then involves the need of exerting work against said elastic members during the adjustment. This same disadvantage can be found, for example, in the patents US2972264 and US8091841 mentioned previously.

The patent US6685602B2 describes a constant force generator, based upon the use of constant force springs, for a machine to be used to carry out physical exercises in absence of gravity (spatial missions) so as to allow the astronauts to perform a training to minimize the muscular atrophy and the bone demineralization. The device is able to vary the force in a not continuous way: the adjustment takes place by the engagement, performed manually, of a different elastic members arranged parallelly.

The object of the present invention is then to overcome the above-illustrated problems and this is obtained by a force generator as defined by claim 1.

The solved technical problem consists in making available, outgoing from the generator device, an adjustable intensity constant force in a continuous and energically efficient way, that is without exerting work on the elastic members used for generating said force. The device object of the present invention, in reply to a displacement of the outgoing element, generates a constant force, that is independent from the element itself. Moreover, the width of such force can be varied: i) in a continuous way by a null value to a (theoretically) infinite value; ii) with greater sensibility for low forces; ii) with reduced use of energy during the adjustment phase.

The present invention, by overcoming the problems of known art, involves several and evident advantages.

The system is based upon the use of linear springs, that is with linear force- lengthening feature, a cam system which makes the force generated by the springs independent from the stroke of the outgoing element, and a system adjusting the transmission of the forces between the springs and the cam and allowing consequently an adjustment of the (constant) force outgoing from the device.

Such adjusting system minimizes the energy consumption during the force adjustment as work is not exerted to deform the springs during such phase.

First of all, the system generates a constant force, that is equivalent to the weight force of an object with mass m subjected to the gravity acceleration g. The motion of such body would generate inertial forces proportional to the mass m. The system object of the present invention allows generating a constant force mg in presence of inertial forces proportional to a mass m' independent from m. Ultimately, a force is obtained equivalent to the weight of a certain mass but with a different inertia, for example a lower one.

Furthermore, the system allows generating forces with not discrete variations. During the adjustment, with the still outgoing element, a reduced energy consumption by the engine is found, since no work is exerted to traction/compress the springs.

An additional advantage is given by the fact that the force adjustment does not take place by means of the precompression of the springs, all deflection available for the springs (unless an initial precompression introduced for structural reasons) is useful to the purposes of the generation of the stroke of the outgoing element.

Still an additional advantage is given by the possibility of adjusting the force with high resolution, above all for low intensities of the force. This is particularly important and useful in the applications of the rehabilitative type, when the resolution in the adjustment of low loads applied to the patient is particularly important.

Furthermore, the device according to the present invention, does not involve any energy consumption of the engine during the force generating phase. In fact, the force generation is due to the (passive) elastic members and not to the actuator performing the adjustment.

An additional advantage lies in the intrinsic safety of the device, indeed due to the fact that the force is generated by passive members.

A consequent additional advantage is that the outgoing force remains constant independently from the speed for moving the terminal element, that is the generator subject of the present invention does not have band limits.

Still an additional advantage lies in the fact that the generator according to the present invention allows a force adjustment in a continuous force range between 0 and +∞. Such range is guaranteed by the choice of the identified adjusting system. Additional advantages, together with the features and the use modes of the present invention, will result evident by the following detailed description of preferred embodiments thereof, shown by way of example and not with limitative purpose.

The figures of the enclosed drawings will be referred to, wherein:

figures 1A and 1 B illustrate the operation principle of a cam/spring system for generating a constant force;

figure 2 outlines a cam profile;

figure 3 outlines an alternative embodiment of a cam/spring system;

figures 4A to 4D illustrate the tilting principle of the springs for the variation in the equivalent stiffness of the same;

figure 5 is a graph showing the course of the force outgoing from the device in function of the adjusting angle;

figure 6 is an exemplifying scheme of a force-adjusting mechanism according to the present invention;

figures 7A and 7B illustrate am adjusting mechanism according to the present invention;

figures 8A and 8B illustrate a force-generating mechanism; e

figures 9A and 9B illustrate an adjusting mechanism according to an alternative embodiment.

The present invention will be described hereinafter by referring to the above- mentioned figures.

Hereinafter in the description an application of the present invention will be continued to be referred to, that is a machine for fitness or rehabilitation.

However, it is to be meant, as already explained, that the present invention could be find application even in other situations, therefor a problem and the needs of the same type can be present.

By firstly making reference to figures 1A and 1 B, these illustrate the operation principle of a cam/spring system for generating a constant force. This is useful to comprise well the present invention. According to such principle, a generator of constant force first of all comprises elastic components 3A and 3B, preferably springs. Advantageously such elastic components have a linear force-displacement characteristic.

The generator further comprises a cam system 1 apt to make constant the force generated by the springs independently from the stroke thereto they are subjected. Such principle will be explained in details hereinafter.

As it will be seen hereinafter, once fastened the shaped profile of the cam, springs with different elastic constant generate a different intensity constant force.

Figures 1A and 1 B, illustrate indeed the operation principle of a cam profile, so as to allow the generation of a constant force.

In particular, the device comprises a cam 1 with two guiding surfaces for the rollers 2A , 2B, each one connected to an end (free end) of the springs 3A and 3B.

The second end of such springs is connected to a frame and then it is a fixed point. The translation of the cam (for example in the passage from the configuration of figure 1A to that of figure 1 B) causes the compression of the springs. The profile of the cam is shaped so that, upon a translation of the cam itself, a constant force F is correspondingly produced.

The subsequent figure 2 shows, by way of example, a profile A(y) of the cam in function of the displacement y along the axis of the cam itself. At the level Δ,_η it is possible having an initial precompression of the springs. In order to convert the elastic spring of a linear spring with stiffness k in a constant force F it is necessary that the profile of the cam has the shape:

The subsequent figure 3 illustrates an alternative embodiment of the cam/spring system. In this case, the linear displacement cam is replaced by a rotative displacement one with profile 5 thereon the roller connected to the free end of a spring is guided. The constant force is collected by means of a cable 4 connected to a drum 6 around thereof it wraps, integral to the cam profile. The generator according to the present invention further comprises a mechanism to adjust in a continuous way the intensity of the available constant force outgoing from the device, starting from a null value to a (theoretically) infinite one.

A possible principle for adjusting the intensity of the generated force is based upon the variation in the equivalent stiffness of the springs.

By referring to figures 4A to 4D an example of such principle is illustrated.

The cam/spring system generates a constant force depending, as shown by the equation (1), upon the value of the stiffness of the springs.

A possible way to modify the equivalent stiffness of the springs consists in varying the tilting thereof.

Let's consider for example a spring with stiffness k, exerting a force on a plate 7, bound to slide along the direction 8. Such force will be proportional to the displacement along the above-mentioned direction.

By tilting the springs by an angle 9 designated with Θ, the equivalent stiffness along the direction 10 is equal to:

k

"^: OS - Θ (2)

By planning the cam profile based upon reference values F₀, k₀ and Δ_ίη,ο and by using n springs with stiffness k and precompression Δ_ίη,ο, an outgoing constant force is obtained equal to:

F = n F₀ k/ko (3)

In case two springs and two corresponding cam profiles (n=2) are used, the previous becomes:

By tilting the two springs by an angle Θ a force course in function of such angle is obtained, which becomes the adjusting parameter, equal to:

(4) That is:

Such course is graphed, by way of example, in figure 5.

It is to be noted that from the equation (3) it is possible obtaining theoretical force values equal to +∞ (for θ=90°).

From the graph of figure 5, furthermore, a high adjusting sensibility for low force intensity is to be noted. Moreover, one can see that for θ=0° there is an outgoing not null force value. The graph shows by way of example a maximum angle of 80°; upon stretching out such angle towards 90° the outgoing force tends to be infinite. However, the generator can provide a compensation mechanism, for example implemented by means of a counterweight (that is a mass balancing the force offset).

The adjustment of the elastic force acting on the cam, or seen in alternative way, the variation in the equivalent elastic constant, can be then obtained by tilting physically the springs, such as shown schematically for example in figures 4B and 4D.

However, according to the present invention, the adjustment can be advantageously obtained by means of a kinematic mechanism which varies the transmission ratio between spring and roller sliding on cam profile, by allowing to obtain substantially the same effect. Such operation principle is schematically illustrated in figure 6.

By referring to figure 4B, it is to be noted that, after the spring tilting by an angle Θ, a horizontal displacement Δχ of the plate 7 involves a variation in the spring length equal to:

ΔΙ = Ax/cos(9)

It follows that the transmission ratio between the displacement of the plate and the displacement of the spring end is x=1/cos(9). By making now reference to figure 6, any transmission T with transmission ratio x=1/cos(9), interposed between an inlet door and a spring with stiffness k, generates, at said inlet door, an equivalent stiffness equal to k_eq=k τ² = k/cos²(0). It follows that the equivalent stiffness of a linear spring with constant stiffness can be varied not only by tilting said spring, but even by having recourse to a suitable mechanical transmission.

In this sense, in the present invention, fixed springs are considered and a suitable kinematic mechanism is adopted/introduce which allows such result.

Therefore, by making now reference to figures 7 A and 7B, a generator according to the present invention will be described.

Such generator comprises a frame structure 100 and at least a cam member 13, mobile with respect to said frame structure.

The generator further comprises one or more elastic members 1 1 having an operating direction and a linear force-displacement characteristic. Such elastic members are arranged and connected so as to exert a force F on the cam member 13.

The cam member has one or more cam profiles arranged and shaped so as to cooperate with the elastic members so that the force F is constant during a displacement of the cam member 13. It is to be meant that, in this context, the term "to cooperate" is to be meant in the sense of comprising both a direct and an indirect cooperation.

According to the present invention, the generator is characterized in that it comprises a continuous adjusting mechanism of the transmission ratio between said cam member 13 and the elastic components 1 1 , this allowing a continuous adjustment of the intensity of the force F.

Such elastic components 1 1 preferably have an end bound to the frame structure 100 and a free end apt to linearly move in function of the displacement of said cam profile.

By referring to figure 7A, according an embodiment of the present invention, the adjusting mechanism comprises a kinematic mechanism implemented as described hereinafter.

By referring to figure 7A, the cam 13 is able to slide along one or more sliding rods 12 by means of prismatic joints 37. The rollers 27, integral to additional prismatic joints 26, which can slide on a guide 30 integral to the frame structure 100, slide on the profile of such cam 13.

A first crossbar 34 is connected to the prismatic joints 26 through cables 29 sliding on the idle pulleys 28. Such system makes that for a displacement y of the cam downwards (direction arrow F1 in figure), a translation A(y) upwards (direction arrow F2 in figure), of the crossbar 34 through the linear guides 35 is obtained.

The prismatic joints 24 are connected by hinges 22 to the prismatic joints 25. Cables 36 are connected by an end to the prismatic joints 24 and by the other one to the springs 11 and they are guided by the intermediate idle pulleys 15 and 17. The pulleys 15 are fixed in the space and the rotation axis thereof is at the intersection between the direction of the rods 12 and of the crossbar 34 (in the rest position thereof, in particular that shown in figure 6A).

The kinematic mechanism for adjusting the force outgoing from the generator comprises a first adjusting rod 21 connected to the first crossbar 34 and to the sliding bar 12 by correspondent prismatic joints and hinges, and a second adjusting rod 16 connected to the frame 100 by a hinge 14 arranged with its incident axis orthogonal to the axis of the sliding rod 12 and to the axis of said first crossbar 34, and connected to the first adjusting rod 21 by a hinge 18.

The hinges (or rotoidal joints) 14 and 18 are coaxial with the pulleys 15 and 17, respectively. The hinges 20 are integral to the prismatic joints 19 which can slide along the guides 12. The distance between the hinges 14, 18 is equal to the distance between the hinges 18, 20. Said distance, in the initial configuration shown in figure 7, is equal to the one between the hinges 18, 22. In other words, in the same configuration the second adjusting rod 16 is hinged to the first adjusting rod 21 at a point which is equidistant from the hinges 20, 22.

One end of said cable 36 can be connected to a terminal pulley 23 having a radius equal to said intermediate pulleys 15, 17, such terminal pulley 23 being integral to the prismatic joint 24.

According to an embodiment, the adjusting mechanism further comprises actuating means 31 , 32 apt to move said first and second adjusting rods 16, 21 , so as to change correspondent tilts α, β with respect to the sliding rod 12 and with respect to the first crossbar 34.

In particular, preferably, such said actuating means 31 , 32 comprises a linear not-reversible actuator, for example of the screw-drive type. However, it is to be meant that other solutions can be implemented for actuating the adjusting mechanism, without this involves substantial differences in the overall technical solution.

The adjustment of the force F outgoing from the generator is obtained, in fact, by lifting the crossbar 33 by means of the engine 32 through an irreversible transmission 31 (constituted for example by the screw-drive system). As shown in figure 7B, the translation of the crossbar 33 causes a tilting of the adjusting rod 21.

It is clearly preferable that the engine is suitably provided with sensors so as to be able to implement a control in the position of the crossbar 33.

The kinematic mechanism is so that, during such tilting, the position of the crossbar 34 remains unchanged and the length of the cable 36 thus remains constant.

Remaining constant such length it is obtained that, during the force adjustment, no work is exerted on the springs, which do not deform.

Also the pulley 23, integral to the prismatic joint 24, coaxial to the hinge 22 and with prevented rotation, contributes to this purpose. The role of such pulley 23 is to allow the rolling-up (that is the recovery) of the cable 36 during the adjusting phase.

Once performed the adjustment, that is once fastened the position of the crossbar 33 and the configuration of the adjusting kinematic mechanism, a constant force is generated on the cam 13 (figure 8A). The displacement in the direction of the arrow F1 in figure 7 A of the cam 13 causes the lifting of the crossbar 34 and consequently the translation of the prismatic joints 25 along the rods 21 and of the prismatic joints 24 along the crossbar 34, and the traction of the cables 36. The traction of such cables causes the lengthening of the springs 1 1 (figure 8B).

It is clear that the present invention can comprise only one of such adjusting mechanisms, but, preferably, it can comprise two thereof, symmetrical and interconnected therebetween, as in figures 7, 8 and 9. It is reminded that in the figures draft springs have been represented schematically, but it is to be meant that the present invention can be implemented even with compression springs, by introducing the due modifications. The preferred implementation is with compression springs.

An alternative embodiment is illustrated in figures 9A and 9B. This variant consists in replacing the system constituted by the members 26, 27, 28 and 29, with the system constituted by the members 38, 39, 40, 41 and 42, shown in figure 9A. The rods 40 are integral to the rods 38 (relative angle equal to 90°) and they are hinged by the hinges 39. The rollers 41 slide along the profile of the cam whereas the rollers 42 slide along the crossbar 34.

As the described system, as explained previously, allows varying the equivalent stiffness (k_eq) produced at the level of the rollers 27 of figure 7 and 8, and of the rollers 41 of figure 9, in this way changing the force F produced according to the equation 5,

apparently it does not allow generating a null force. In the present invention, however, the force offset can be compensated by means of a counterweight. Such counterweight is given by the cam 13 itself, the mass thereof can be properly selected in order to bring to 0 the minimum value of F.

The presence of the cam mass allows the additional advantage of avoiding to give excessively high accelerations on the element outgoing from the system in case thereto very high forces F are applied. In other terms, the use of the counterweight decreases the acceleration of the element outgoing from the force generator thanks to the inertial effects associated to the cam mass.

By referring to what described above it is to be meant that, as far as the members composing the generator are concerned, alternative forms and system could be chosen, on condition that they lead to the same final result.

For example:

Variants of the components can be the following ones:

For the cam

> Linear/rotative cam

> Cam with inner/outer profile > Kinematic mechanism with parabel drawing tool

> Fixed cam - mobile springs/mobile cam - fixed springs

For the springs

> Linear/torsional

> Traction/compression

> Elastic cables

> Gas springs

> Magnetic springs

For the adjusting mechanism

> Springs mounted on tiltable arms

> Fixed springs with adjustable transmission

For the prismatic joints

> Linear guides

> Telescopic guides

> Kinematic systems producing linear motion by rotoidal joints (ex.

Peaucellier - Lipkin, Watt)

For the actuating system

> Motorised

> Manual

It is further meant that the force generator could be arranged so as to cooperate with a pack of weights; furthermore several force generators could be arranged parallelly so as to generate an overall force equal to the sum of the force generated by each single generator.

The present invention has been sofar described with reference to the preferred embodiments thereof. It is to be meant that each one of the technical solutions implemented in the preferred embodiments herein described by way of example, could be advantageously combined differently therebetween, to form other embodiments, belonging to the same inventive core and however all within the protection scope of the here below reported claims.

Claims

1. An adjustable intensity constant force (F) generator comprising:

a frame structure (100);

at least one mobile cam member (13);

- one or more elastic members (11) having an operating direction and a linear force-displacement characteristic arranged so as to exert a force (F) on said cam member (13);

wherein said at least cam member has one or more cam profiles arranged and shaped so as to cooperate with said one or more elastic members so that said force(F) is constant during a displacement of the cam member;

the generator being characterized in that it comprises a continuous adjusting mechanism of the transmission ration between said at least cam member (13) and said elastic members (1 1), so allowing a continuous adjustment of the intensity of said force (F),

wherein said adjusting mechanism comprises a kinematic mechanism having a sliding rod (12), a first crossbar (34) sliding of said rod (12), a first adjusting rod (21) connected to said first crossbar (34) and to said sliding rod (12) by correspondent prismatic joints (24) and hinges (20, 22), a second adjusting rod (16) connected to the frame (100) by a hinge (14) arranged with its incident axis orthogonal to the axis of the sliding rod (12) and and to the axis of said first crossbar (34) and connected to said first adjusting rod (21) by a hinge (18),

said adjusting mechanism further comprising actuating means (31 , 32) apt to move said first and second adjusting rods (16, 21), so as to change correspondent tilts (α, β) with respect to said sliding rod (12) and to said first crossbar (34), said elastic members (11) being connected to said frame structure (100) and said first crossbar (34) by a cable (36) sliding, by pulleys (15, 17, 23), along said first and second adjusting rods (16, 21).

2. The generator according to claim 1 , wherein said elastic members (11) have one end bound to said frame structure (100) and a free end apt to linearly move in function of the displacement of said cam profile.

3. The generator according to claim 1 or 2, wherein the second adjusting rod (16) is hinged to said first adjusting rod (21) at a point which is equidistant from the hinges (20, 22).

4. The generator according to one of claims 1 to 3, wherein one end of said cable (36) is connected to a terminal pulley (23) having a radius equal to said intermediate pulleys (15, 17), said terminal pulley being integral with the prismatic joint (24).

5. The generator according to one of claims 1 to 4, wherein said actuating means (31 , 32) comprises a linear not-reversible actuator.

6. The generator according to claim 5, wherein said linear not-reversible actuator is of a screw-drive type.

7. The generator according to one of claims 1 to 6, comprising two adjusting mechanisms, symmetrical and connected therebetween.

8. A machine for the fitness, for personal assistance and/or for the rehabilitation, comprising at least an adjustable intensity constant force generator according to anyone of the preceding claims.

9. The machine for the compensation of a load, comprising at least an adjustable intensity constant force generator according to anyone of claims 1 to 7.