EP3117124A2

EP3117124A2 - Cable cylinder provided with an anti-rotation device having an elongate element which is flexible but rigid when twisted

Info

Publication number: EP3117124A2
Application number: EP15705840.5A
Authority: EP
Inventors: Philippe Garrec
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2014-03-10
Filing date: 2015-02-24
Publication date: 2017-01-18
Also published as: FR3018327A1; US20170009857A1; WO2015135747A2; WO2015135747A3; FR3018327B1

Abstract

The invention relates to a cable cylinder comprising a pin and nut device (2, 3), one of the elements of which is rotated about an axis of rotation (X) by a motor (10) and the other element is made to slide without rotating about the axis of rotation owing to an anti-rotation device, the sliding element being coupled to a cable (6) wrapped around a drive pulley (7) such that rotating the motor causes the linear movement of the sliding element, said sliding element pulling on the cable and thus rotating the drive pulley. The anti-rotation device comprises at least one elongate element (10) which is flexible but rigid when twisted, one end (11) of which is attached to the sliding element and a second end (12) of which is attached to a stationary portion of the cylinder, such that the elongate element is substantially curved in a plane parallel to the axis of rotation.

Description

Cable cylinder equipped with an anti-rotation device with an elongate element that is flexible but rigid in torsion

The invention relates to an anti-rotation device for the sliding part of a jack which is actuated by a rotary part by means of a helical connection, and a cable jack equipped with such an anti-rotation device. The invention is particularly applicable to grippers comprising phalanges equipping prostheses or prostheses.

BACKGROUND OF THE INVENTION

Cylinders are known used in particular to operate robot arms. These cylinders comprise a screw-nut assembly, one of the elements is rotated by a motor, and the other of the elements is constrained by an anti-rotation device to move slidably during a rotation of the engine. The sliding element is coupled to a cable to exert on the latter traction in one direction or another. The cable is wrapped around a drive pulley which is associated with a rotating pivot adapted to rotate an arm segment or any other element to be rotated.

The cylinder can be unilateral (open cable whose one end is connected to the sliding element, the other end being associated with a tension spring), or bilateral (the cable forms a loop between the drive pulley and a pulley of return). The motor drives the rotating element by any suitable device, such as a belt or gearbox. Moreover, the cable can be simple, or double. In the latter case, it is advantageously coupled to the sliding element by means of an anchoring member secured to the sliding member but movable relative thereto, the mobile anchoring member then serving to balance the pulls between the two cables.

These cable cylinders are used in particular to actuate finger phalanges device grippers. Indeed, these cylinders have several competitive advantages on gear reducers for the realization of force control actuators embedded in articulated structures:

longitudinal motor thus allowing the integration of an elongated motor in a segment and that the articulation of the segment is transverse or transverse;

low friction and low inertia reflected on the joint (high transparency) in particular thanks to the floating assembly described in document FR2809464

- insensitivity of performance vis-à-vis the deformations of the host structure (no jamming or variation of friction).

In the case of robotic hands, the control of multiple phalanges requires the grouping of a large number of actuators (typically 3 phalanx actuators) in the equivalent volume of the palm. The volume of the electric motors constitutes at this point a significant constraint (in thickness or in length). For example, a palm that is too long causes the knuckles to lengthen in order to preserve the possibility of palm grip and this tends to decrease the clamping force for an actuator.

It may then be desired to deport the motor in the upstream segment (forearm) by means of a transmission by means of a flexible transmission shaft, possibly in flexible sheath as shown in the document FR2990485. This offset is achievable by maintaining sufficient angulation between the forearm and the palm.

It would then remain in the palm only the device for converting the rotary movement of the motor into a linear movement of the sliding element, a linear movement that is used to drive the cable.

The invention more specifically relates to the anti-rotation device which allows this sliding by preventing the sliding element from rotating about the axis of rotation of the rotary element. Several devices are known to those skilled in the art. In particular, it is known from document FR 2 981 420 to equip the sliding element of a Holdam-shaped mount having diametrically opposed rollers constrained to slide in grooves parallel to the direction of sliding of the sliding element and preventing any rotation of the sliding element around the axis of rotation of the rotary element.

These anti-rotation devices are bulky, especially when several cylinders must be joined to each other to operate several phalanges. They are also complex to achieve, since they assume the realization of grooves to the di- precise mounts, as well as the rotational guidance of rollers on pivots.

It has furthermore been proposed to use a bellows to effect the anti-rotation of the sliding element, as shown in document FR 2 856 452. The torsional rigidity of the bellows prevents the sliding element from rotating around it. of the axis of rotation of the rotating element. However, such a bellows is unsuitable for use in a cable jack.

OBJECT OF THE INVENTION

The object of the invention is to propose a particularly simple and compact anti-rotation device which can advantageously be used in cable jacks of phalanges of gripper hands.

PRESENTATION OF THE INVENTION

In order to achieve this goal, a cable jack is proposed comprising a screw-nut device, one of the elements of which is rotated about one axis of rotation by a motor and the other of the elements is constrained to slide without rotating about the axis of rotation by means of an anti-rotation device, the sliding element being coupled to a cable wound around a drive pulley so that a rotation of the motor causes the linear displacement of the sliding element, which pulls on the cable and thus rotates the drive pulley. According to the invention, the anti-rotation device comprises at least one flexible but torsionally rigid elongated element whose first end is fixed to the sliding element and a second end is fixed on a fixed part of the vane. rin, so that the elongate element is curved substantially in a plane parallel to the axis of rotation.

The elongated member prevents rotation of the sliding member due to its torsional rigidity, but follows the longitudinal movements of the sliding member bending due to its flexibility. This anti-rotation device is very simple to implement, only the attachment of the ends of the elongate element to be expected.

Preferably, the first end and the second end of the elongate element are respectively fixed to the sliding element and the fixed part of the cylinder on either side of the axis of rotation. Thus, the curve of the elongate element is formed in front thereof, and the size of the cylinder is reduced.

According to a particular embodiment, the anti-rotation device comprises two elongate elements whose first ends are fixed diametrically opposite on the sliding element, so that the curved elongated elements extend in parallel planes.

According to a particular aspect of the invention, the elongate element is a flexible transmission shaft. Thus, the flexible transmission shaft is not used at all for its usual function which is the transmission of a torque between a motor and an actuated part. The high torsional rigidity of the flexible transmission shafts is used to ensure the anti-rotation of the sliding element of the hydraulic cylinder.

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DESCRIPTION OF THE FIGURES The invention will be better understood in the light of the following description of particular non-limiting embodiments of the invention, with reference to the figures of the accompanying drawings in which:

- Figure 1 is a schematic diagram of a cable jack according to the invention, the sliding element here being the screw;

FIGS. 2a to 2c illustrate the longitudinal displacement of the screw of the jack of FIG. 1;

FIGS. 3a to 3c are figures similar to FIGS. 2a to 2c, illustrating a jack whose sliding element is the nut;

FIGS. 4a to 4c are figures similar to FIGS. 2a to 2c, illustrating a jack with two elongate elements;

FIGS. 5 to 5c are figures similar to FIGS. 4a to 4c, illustrating a jack with two elongate elements;

FIGS. 6a and 6b are diagrammatic side and front views of a set of jacks according to FIGS. 4a to 4c;

FIGS. 7a and 7b are diagrammatic side and front views of a set of jacks according to FIGS. 4a to 4c;

FIGS. 8a and 8b are diagrammatic side and front views of a set of jacks according to FIGS. 5a to 5c;

DETAILED DESCRIPTION OF EMBODIMENTS OF

THE INVENTION

With reference to FIG. 1, and according to a first embodiment of the invention, the jack cable comprises a motor 1 adapted to drive in rotation a nut 2 which cooperates with a screw 3 which moves longitudinally along an axis X of rotation of the nut 2 in response to a rotation of the motor 1. Here, the motor 1 drives the nut 2 by means of a belt connection, the pulleys 4 and 5 of which are shown schematically. A cable 6 is stretched between a drive pulley 7 and a return pulley 8. The cable 6 passes inside the screw 3 (which is hollow) and is coupled thereto so that a displacement of the screw 3 causes a running of the cable 6 and thus a rotation of the drive pulley 7.

The foregoing is only an illustration of the technological background. The invention will now be detailed applies to this type of cylinder, but is not limited to this type of cylinder. In particular, the cylinder may have a remote motor by means of a flexible transmission shaft, the cable may be wound only around the single drive pulley, a spring now held taut. The cylinder may have two cables ...

According to the invention, the screw 7 is prevented from rotating about the axis X by means of an anti-rotation device here comprising a flexible elongated element 10 but having a high torsional stiffness, having a first end 11 fixed to the screw 3 and a second end 12 fixed to a frame of the cable jack. The elongated element 10 is curved and extends substantially in a plane parallel to the axis X.

FIGS. 2a to 2c illustrate the behavior of the elongate element 10 when the screw 3 moves under the action of the motor 1. It can be seen that the second end 12 remains of course immobile, but that the instantaneous center of curvature Ω of the curved portion of the elongate element 10 advances with the screw 3, the elongate element 10 being extending substantially in the same plane. The elongated element 10 prevents the screw 3 from rotating and therefore constitutes a device for anti-rotation of the latter. It will be noted that the plane in which the elongated element 10 extends may slightly rotate during the displacement of the screw 3, which does not interfere with the operation of the cylinder. Similarly, if the stresses of the elongate element are important, it can deform non-flat, which does not interfere with the operation of the cylinder. However, it is important to ensure that the elongated element 10 remains stable under gravity or under effort, which limits its length and therefore the stroke of the cylinder.

FIGS. 3a to 3c illustrate a variant of the jack of FIG. 1 in which the motor 1 is adapted to drive the screw 3 in rotation. It is then the nut 2 which moves longitudinally under the effect of the rotation of the motor , the cable then being coupled to the nut 2. Of course, the elongate element 10 is now coupled to the nut 2. It can be seen that the second end 12 remains of course immobile, but that the instantaneous center of curvature Ω advances with the nut 2, the elongated element extending substantially in the same plane P, small twist deformation near.

Figures 4a to 4c relate to a cable jack similar to that of Figures 2a to 2c, except that it is equipped with two elongate elements 10 and 10 ' which are fixed to the screw 3 by means of an anchoring member 13 having the form of a bar attached to the end of the screw 3. The first ends 11 and 11 'are fixed to the ends of the bar 13 diametrically opposite on either side of the X axis. It will be noted that for each of the elongate elements 10, 10 ', their ends extend on either side of the axis of rotation X. The two elongate elements 10, 10' extend in two planes parallel to each other. Ensure that the planes are sufficiently far away from the two elongated elements to avoid any interference between them in case of non-planar deformation.

The use of two elongate elements coupled diametrically opposite the sliding element of the cable jack allows to balance the parasitic forces experienced by the sliding element due to the presence of elongate elements.

FIGS. 5a to 5c show the use of two elongate elements 10 and 10 'in the context of a cable jack whose sliding element is the nut 2. The anchoring member 13 is now fixed on the nut 2.

Figures 6a and 6b show how such cylinders can be associated in a compact assembly for example to ensure 1 actuation of finger phalanges of a robotic hand. There is shown here only the screw / nut assembly of each of the cylinders. Here, it is the screws 3 which form the sliding element, the nuts 2 being rotated by their respective motor. The axes of rotation of the screw / nut devices are here all parallel to each other and extend in the same plane. All the elongated elements 10, 10 'of said cylinders extend in planes parallel to each other. The anchoring members 13 are also parallel to each other. As is more particularly visible in FIG. 6b, the planes of the elongated elements are nested inside one another, so that an elongated element of a jack is flanked by the two elongated elements of an adjacent cylinder (except of course for the end cylinders). This arrangement is very flat. It will be noted in FIG. 6a that, at least for the intermediate cylinders, the plane of one of the elongate elements converges towards the axis of the adjacent screw, so that the end 12 of an elongate element which is hitched to a fixed part of the cylinder does not extend beyond the screw of the adjacent cylinder.

Figures 7a and 7b show an arrangement even more compact in height, at the price however of increased width. Here, the arrangement still concerns cylinders whose screw is the sliding element. It can be seen that the elongated elements 10 and 10 'always extend in parallel planes. For this purpose, the anchoring members 13 which are always coupled to the screw, are now Z-shaped. The anchoring members 13 'are connected to the screw 3 by the middle of their central branch. This arrangement makes it possible to ensure that the planes of the elongate elements extend on the sides of the screws, which allows their more compact nesting.

FIGS. 8a and 8b show an arrangement similar to that of FIGS. 7a and 7b, for jacks whose sliding element is now the nut 2. Preferably, each elongated member 10 is constituted by a flexible transmission shaft of the type used in the cable jacks for driving the rotating member by means of a de-energized motor. This type of elongated element is flexible while having a high torsional rigidity.

The invention is not limited to what has just been described, but on the contrary covers any variant within the scope defined by the claims.

Claims

1. A cable jack comprising a screw-nut device (2, 3) one of whose elements is rotated about an axis of rotation (X) by a motor (10) and the other of the elements is constrained to slide without rotating about the axis of rotation by means of an anti-rotation device, the sliding element being coupled to a cable (6) wound around a drive pulley (7) so that a rotation of the motor causes the sliding element to move linearly, the latter pulling on the cable and thus rotating the drive pulley, characterized in that the anti-rotation device comprises at least one elongated element (10, 10 ') flexible but torsionally rigid, a first end (11) of which is fixed to the sliding element and a second end (12) is fixed on a fixed part of the jack, so that the elongated element is bent substantially in a plane parallel to the axis of rotation.

2. Cable cylinder according to claim 1, wherein the first end (11) and the second end (12) of the elongate element are respectively fixed to the sliding element and to the fixed part of the cylinder of part and of other of the axis of rotation. Thus, the curve of the elongate element is formed in front of it, and the clutter of the cylinder is reduced.

3. The cable jack of claim 1, wherein the anti-rotation device comprises two elongate elements (10, 10 ') whose first ends (11, 11') are fixed diametrically opposite to one another. sliding element, so that the longitudinal elements Curved lines extend in parallel planes.

4. A cable cylinder according to claim 3, in the first ends of the elongate elements are fixed to the sliding element via an anchoring member (13, 13 ') attached to the sliding element 3. nt Ô

5. A cable jack according to claim 3, wherein the first and second ends of the elongate members extend on either side of the axis of rotation.

The cable jack of claim 1, wherein the elongated member is a flexible transmission shaft.

7. Set of cable jacks according to one of the preceding claims, the jacks being juxtaposed relative to each other so that the axes of rotation of their respective screw / nut devices (2,3) are parallel to each other. and extend in the same plane, the elongate elements extending in planes parallel to each other.

8. Set of cable cylinders according to claim 6, wherein the plane of one of the elongate elements of one of the cylinders converges towards the axis of rotation of the screw / nut device of an adjacent jack.