WO2003066288A1

WO2003066288A1 - Device for the spherical displacement of an element

Info

Publication number: WO2003066288A1
Application number: PCT/FR2003/000298
Authority: WO
Inventors: Jean-Pierre Friconneau; Mourad Karouia
Original assignee: Commissariat A L'energie Atomique
Priority date: 2002-02-04
Filing date: 2003-01-31
Publication date: 2003-08-14
Also published as: FR2835579B1; EP1476282A1; FR2835579A1

Abstract

The invention relates to a device (1) that is used to displace at least one element (2) in a space. The inventive device comprises the element to be displaced (2) and a fixed element (4) which is connected to the element to be displaced (2) by means of three arms (6a, 6b, 6c). Each of said arms comprises numerous segments (8, 14, 18, 22) that are interconnected by means of three linking elements (10, 16, 20) which each authorise at least one degree of rotation freedom along an axis. The axes (10a, 16a, 20a) of the aforementioned linking elements (10, 16, 20) of each arm (6a, 6b, 6c) meet at a fixed point (P) around which the element to be displaced (2) can rotate in a spherical manner with three degrees of freedom. According to the invention, for each arm (6a, 6b, 6c) of the device (1), the sum of the degrees of freedom authorised by the linking elements (10, 16, 20) is greater than or equal to five. The inventive device can be used for robotic surgical wrists in the field of endoscopy.

Description

DEVICE FOR SPHERICAL DISPLACEMENT OF AN ELEMENT

DESCRIPTION

TECHNICAL AREA

The invention relates to the field of devices for moving an element, comprising the element to be moved as well as a fixed element connected to the element to be moved by means of three arms, the element to be moved being suitable to describe a spherical rotational movement with three degrees of freedom around a fixed point.

The invention further relates to the application of this type of device, also called "parallel mechanism orientable to three degrees of freedom", in the field of robots used in endoscopy, intended to recreate the movements of the hand of a surgeon.

STATE OF THE PRIOR ART

Parallel mechanisms usually consist of an element to be moved and a fixed element, linked together by as many arms as there are degrees of freedom associated with the element to be moved.

In the particular case of the field of the invention where the device comprises an element to be displaced capable of describing a spherical rotational movement with three degrees of freedom around a fixed point, the device generally comprises three arms of complex structure, connecting separately the element to be moved to the fixed element. In this specific area, several achievements have already been proposed.

Firstly, devices are known which use ball-joint connections between the element to be moved and the fixed element, this type of connection in fact making it possible to generate a spherical rotation movement with three degrees of freedom.

However, the major problem relating to the use of ball joint connections in such devices is characterized by the absence of satisfactory means capable of motorizing this type of link.

From the prior art, there is also known a parallel mechanism orientable with three degrees of freedom, used for moving and positioning means of the video camera type.

In this mechanism, a mobile platform and a fixed platform are interconnected by means of three identical arms. Each of these arms is made up of a plurality of structural members connected to one another by means of three similar connections of the pivot connection type, also known as “rotoid kinematic couple”.

The mechanism therefore comprises nine pivot links, each allowing a degree of freedom, and whose axes are concurrent at a fictitious fixed point, corresponding to the center of the spherical rotation of the mobile platform.

However, it turns out that to ensure the proper functioning of such a mechanism, geometric constraints, notably concerning the positioning connections with each other must necessarily be strictly satisfied. Thus, to avoid a malfunction of the mechanism, it is imperative to respect very low tolerances for all of the constituent elements of the mechanism, which consequently generates significant costs and assembly difficulties.

During a movement of the mobile platform, it was indeed noticed that in the event of non-compliance with strict convergence of the axes of the connections at a fixed point, the mechanism was liable to jam, a such blockage can cause damage or even total deterioration.

PRESENTATION OF THE INVENTION The object of the invention is therefore to present a device for moving at least one element in space, the device comprising the element to be moved as well as a fixed element connected to the element to move by means of three arms, the element to be moved being able to perform a spherical rotational movement with three degrees of freedom around a fixed point, this device at least partially overcoming the drawbacks mentioned above relating to the embodiments of the prior art. To do this, the invention relates to a device for moving at least one element in space, the device comprising the element to be moved as well as a fixed element connected to the element to be moved via of three arms each comprising a plurality of segments connected together by means of three links each authorizing at least one degree of freedom of rotation along an axis, the axes of the connections of each of the arms being concurrent at a fixed point around which the element to be moved is able to describe a spherical rotation movement with three degrees of freedom. According to the invention, for each arm of the device, the sum of the degrees of freedom authorized by the links is greater than or equal to five.

Advantageously, unlike the mechanism of the prior art in which the mobile platform is connected to the fixed platform by means of three arms each comprising three pivot connections, the arms of the device according to the invention each comprise three connections, the sum of the degrees of freedom authorized by these connections is greater than or equal to five. This specific characteristic of the invention has the beneficial effect of making the device isostatic, and not hyperstatic, as is the case for the mechanism of the prior art. Thus, due to the isostatic mechanical state in which it is located, the device according to the invention is no longer subject to strict geometrical constraints, in particular as regards the relative positioning of the axes of the links present on each of the arms of the device. This observation can be verified using the mobility formula, known as the Tchebychev or Grûbler-Kutzbbach formula, this formula having also been generalized by Hervé.

(1): F ≈ d (nl) - Σ ± (df) with: F: overall degree of freedom of the device; d: dimension of the subgroup of the group of displacements associated with the device; n: number of rigid bodies of the device; f _± : degree of freedom of a connection i between two rigid bodies.

In the general case, that is to say when we consider the whole group of displacements, d ≈ 6. In addition, the device according to the invention as well as the mechanism of the prior art both comprising an element mobile as well as a fixed element, it is also possible to simplify this formula by setting n = 2. Finally, fi corresponds in this case to the degree of freedom of an arm i. The simplified general formula can then be written as follows: (2): F = 6 - ∑i (6-fi)

With regard to the device according to the invention, when we take the case in which the three arms are identical and each include three connections whose sum of the authorized degrees of freedom is 5, the formula can then be written:

(3): F = 6 - 3. (6-5) = +3

It can therefore be seen that the device according to the invention is indeed isostatic, with three degrees of freedom. On the other hand, as regards the mechanism according to the prior art, the arms all being identical and authorizing three degrees of freedom (three pivot connections), the formula can then be written: (4): F = 6 - 3. (6-3) = -3 As we can see with the result of formula (4), the parallel mechanism of art anterior is well hyperstatic. It is in fact by respecting a strict geometrical position of the axes of the pivot links, that the parallel mechanism of the prior art is capable of operating. In contrast, due to its isostatic nature, the device according to the invention is more tolerant in terms of specific geometric constraints, which gives rise to simplifications in the manufacture as well as in the mounting of the constituent elements of such a device.

Preferably, each arm successively comprises, from the fixed element towards the element to be moved, a pivot connection, a first sliding pivot connection, as well as a second sliding pivot connection. In addition, provision can be made for the device to comprise three - primary actuation means rigidly mounted on the fixed element, the three primary actuation means being capable of respectively driving the pivot connections of each of the three arms of the device. Advantageously, in this specific configuration, the orientation of the element to be moved is effected by piloting simple pivot links.

According to a preferred embodiment, the axes of the second sliding pivot links of each of the three arms of the device are combined.

Advantageously, when the device includes this specific characteristic, the element to be moved has a fourth possible degree of freedom, corresponding to a translation along the common axis of the second sliding pivot connections. It is then desirable to provide the device with a secondary actuating means, capable of generating a linear displacement of the element to be displaced, along the common axis of the sliding pivot connections. Advantageously, the device can be used as an endoscopic wrist.

Other characteristics and advantages of the invention will appear in the detailed, non-limiting description, below.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be made with reference to the attached drawings, in which:

- Figure 1 shows a device for moving at least one element in space, according to a first preferred embodiment of the invention; and

- Figure 2 shows a device for moving at least one element in space, according to a second preferred embodiment of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to Figure 1, there is shown a device 1 for moving at least one element in space, according to a first preferred embodiment of the invention. The device 1 comprises an element to be moved 2, a fixed element 4, as well as three arms 6a, 6b, 6c connecting the element to be moved 2 to the fixed element 4, the elements 2 and 4 preferably being platforms . Each arm 6a, 6b, 6c of the device 1 comprises a plurality of segments, connected to each other by means of links each allowing at least one degree of freedom of rotation. In this configuration, the three arms

6a, 6b, 6c are identical and arranged at 120 °, but could also be of different design. Thus, only the arm 6a will be described in detail below. The arm 6a first of all comprises a segment

8 connecting the fixed element 4 to a pivot link 10, able to be controlled by a primary actuation means 12 of the motor type, also integral with the fixed element 4. Via the pivot link 10 to a degree of freedom, a segment 14 of the arm 6a. is capable of being rotated relative to the fixed element 4 about an axis 10a of the pivot link 10, this segment 14 also being connected to a first sliding pivot link 16, with two degrees of freedom.

A segment 18 establishes the junction between the first sliding pivot link 16, and a second sliding pivot link 20, also having two degrees of freedom. The segment 18 is therefore capable of being driven, relative to the segment 14, by a rotational movement combined with a translational movement, along an axis 16a of the first sliding pivot link 16.

In the same way, a segment 22 establishes the junction between the second sliding pivot liarson 20, and the element to be moved 2. The segment 22 is therefore capable of being animated, with respect to the segment, 18, of a rotational movement combined with a translational movement, along an axis 20a of the second sliding pivot link 20. Furthermore, the respective axes

10a, 16a, 20a of the connections 10, 16, 20 of the arm 6a, are concurrent at a fixed point P, this point also being the point of intersection of all the axes of the connections of the two other arms 6b, 6c. Consequently, the point P is the point of intersection of all the axes of the nine links present in the device 1.

Note that in this preferred embodiment, each of the arms 6a, 6b, 6c is set in motion using a primary actuating means 12 capable of controlling the single pivot link 10 of each of the arms 6a, 6b , 6c, this pivot link 10 being located near the fixed element 4 of the device 1. However, it is also possible to provide that the primary actuating means 12 are located on a link other than the pivot link 10, whatever that is the positioning of this link on the arm concerned.

It is however specified that the choice of having the primary actuating means 12 coupled to the pivot links 10 corresponding to the closest links to the fixed element 4, has been made to limit the problems of space requirement of the device 1. The primary actuating means 12 being of relatively large dimensions compared to the dimensions of the connections 10, 16, 20 and of the segments 8, 14, 18, 22, it is therefore preferable, to avoid any interference between the different elements, to move these means 12 as far as possible from an area in which the links 10, 16, 20 and the segments 8, 14, 18, 22 are caused to be in motion. The various alternatives described above, concerning different possible designs for the realization of the arms 6a, 6b, 6c, must however meet a necessary condition. Indeed, each arm 6a, 6b, 6c must be such that the sum of the degrees of freedom authorized by the links of the arm is greater than or equal to five. As mentioned and demonstrated above, compliance with this condition makes it possible to obtain an isostatic device 1, for which the geometric constraints are less restrictive than for a hyperstatic mechanism.

The device 1 is able to operate in the following manner.

The primary actuation means 12 are connected to computer means (not shown), capable of communicating information to each of the primary actuation means 12. This information is of the control law type, and makes it possible, when applied by the primary actuating means 12, to put the arms 6a, 6b, 6c in movement in a controlled manner, so that the element to be moved 2 is oriented in a determined position.

Note that the control laws communicated to the primary actuation means 12 are predetermined, and in particular established as a function congestion problems encountered within the device 1.

In this way it is then possible to put the element to be moved 2 in movement according to a spherical rotation with three degrees of freedom, around the fixed point P. It should be noted that the term "spherical rotation" can be assimilated to a motion of a ball joint , so that the points located on the element to be moved 2 describe localized trajectories on concentric spheres in P.

Referring to Figure 2, there is shown a device 1 for moving at least one element in space, according to a second preferred embodiment of the invention. In this preferred embodiment, the arms 6a, 6b, 6c of the device 100 each comprise a second sliding pivot link 120a, 120b, 120c, the axes of which coincide in a common axis 2.

Similarly, the element to be moved 102, in the form of a rod capable of moving linearly with respect to the sliding pivot connections 120a, 120b, 120c, can here be likened to a support, on which it is for example possible to mount an instrument Surgical 28. All the other components of the device 100 being similar to the components of the device 1 relating to the first preferred embodiment of the invention described above, it will not be described further.

Nevertheless, it remains to be specified that the operation of such a device 100 is substantially identical to the operation of the device 1, at the difference that the specific characteristic of a common axis 24 for the sliding pivot connections 120a, 120b and 120c, makes it possible to obtain a fourth degree of freedom for the element to be moved 102. In fact, in addition to the three possible rotations around the point P, the element to be moved 102 can now be brought into translation, along the common axis 24 and relative to the sliding pivot connections 120a, 120b, 120c, using a secondary actuating means (not shown ). The devices 1 and 100 which have just been described can have various applications, such as that of an endoscopic wrist of a surgical robot. Indeed, devices 1 and 100 are capable of reproducing the movement of a surgeon's wrist, with three degrees of rotation around a fixed intra-corporeal point. In addition, the design of the devices 1 and 100 being that of a parallel mechanism, the primary actuating means 12 employed can be deported outside the patient, which has non-negligible advantages in terms of sterilization of the equipment. used.

Other applications are also possible. As examples, one can cite the orientation supports for camera, for parabolic antenna, for tank turret, or for projectile battery. In addition, the device also finds an application in the field of micromanipulation, as a micromanipulator wrist, or for carrying out the orientation of a laser beam with a memory system. Of course, various modifications can be made by those skilled in the art to the devices 1 and 100 which have just been described, only by way of nonlimiting examples.

Claims

1. Device (1,100) for moving at least one element (2,102) in space, the device comprising the element to be moved (2,102) as well as a fixed element (4) connected to the element to be moved ( 2) by means of three arms (6a, 6b, 6c) each comprising a plurality of segments (8,14,18,22) interconnected by means of three connections (10, 16, 20, 120a, 120b, 120c) each authorizing at least one degree of freedom of rotation along an axis, the axes

(10a, 16a, 20a) of the connections (10, 16, 20, 120a, 120b, 120c) of each of the arms (6a, 6b, 6c) being concurrent at a fixed point (P) around which the element to be moved ( 2) is capable of describing a spherical rotational movement with three degrees of freedom, characterized in that for each arm (6a, 6b, 6c) of the device (1), the sum of the degrees of freedom authorized by the links (10, 16, 20, 120a, 120b, 120c), is greater than or equal to five.

2. Device (1,100) according to claim 1, characterized in that each arm

(6a, 6b, 6c) comprises a pivot connection (10), a first sliding pivot connection (16), as well as a second sliding pivot connection (20, 120a, 120b, 120c).

3. Device (1,100) according to claim 1 or claim 2, characterized in that each arm (6a, 6b, 6c) successively comprises, from the fixed element (4) towards said element to be moved

(2,102), a pivot link (10), a first sliding pivot link (16), as well as a second sliding pivot link (20, 120a, 120b, 120c).

4. Device (1,100) according to claim 3, characterized in that it comprises three primary actuation means (12) rigidly mounted on the fixed element (4), the three primary actuation means (12) being suitable piloting respectively the pivot connections (10) of each of the three arms (6a, 6b, 6c) of the device (1,100).

5. Device (1) according to any one of the preceding claims, characterized in that the element to be moved (2) and the fixed element (4) are platforms.

6. Device (100) according to any one of claims 2 to 4, characterized in that the axes of the second sliding pivot connections (120a, 120b, 120c) of each of the three arms (6a, 6b, 6c) of the device ( 100) are merged into a common axis (24).

7. Device (100) according to claim 6, characterized in that it further comprises a secondary actuation means able to move linearly, along the common axis (24) of the second sliding pivot connections (120a, 120b, 120c ), the element to be moved (102) of the device (100).

8. Device (100) according to claim 6 or claim 7, characterized in that the element to be moved (102) is a support for a surgical instrument (28).

9. Device (1,100) according to any one of the preceding claims, characterized in that it is capable of being used as an endoscopic wrist.