Abstract:
A positioning actuator with three axes includes a base having a movable supporting member and a device for moving the member up and down, and a shaft connecting the movable head of the actuator to the base. The connecting shaft forms a swivel-type double linkage enabling sideways movement of the head relative to the base, and the lower end of the connecting shaft engages a part made of elastomeric material and is provided within the movable supporting member.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to three-axis positioning jacks, capable of supporting objects whose weights can be as high as several hundred metric tons whilst allowing their positioning with an accuracy of the order of one micrometer. 
     At present, when a structure has to be positioned or shaped with respect to a foundation, jacks are used which are disposed between that foundation and the structure. These jacks are adjusted manually or electrically by agents who will carry out iterative adjustment operations until the desired position is reached. It is however extremely difficult in practice, if not impossible, to obtain high accuracy in such a context. 
     For the positioning of these structures, the actuators normally used are jacks, the two best known types of which are: 
     mechanical jacks, 
     hydraulic jacks. 
     The mechanical solution, which is the most conventional one, uses a micrometric ball screw driven by a stepper motor. A compensation system often relieves the screw for heavy load applications. The principle of the hydraulic jack is itself so well known and its use is so widespread that a description of this type of jack would be superfluous if our new jack did not exhibit similarities with this technology. 
     In a hydraulic jack, a piston, provided with a fluid-tight seal, is free to move in the base of the jack, whose chamber is filled completely with a liquid which is only very slightly compressible. The piston moves, either because the volume of liquid in the chamber is modified by the injection or evacuation of the liquid via a pipe, a pump, a stop valve and a reservoir, or because an actuating piston, which is also provided with a fluid-tight seal, driven for example by a screw/nut assembly, modifies the shape of the chamber. As the liquid is virtually incompressible, the piston moves such that the volume of the chamber remains practically constant. 
     However, this type of jack which makes it possible to apply very high forces has three disadvantages: 
     the equipment is often dirty, the fluid-tightness of the hydraulic chambers becoming relative because of the wear and ageing of the seals; 
     micrometric positioning is impossible, the slight leakages and the high coefficient of expansion of the liquids used give rise to this positioning inability; 
     the manufacturing cost is generally high, the friction surfaces necessitating precise and high-quality practices. 
     From the French patent FR 2179572 there is known a force multiplier device comprising a first hydraulic jack, whose piston rod is mounted slidingly in an enclosure integral with the base of that jack and constituting the chamber of a second jack also equipped with a sliding piston subjected to the action of an elastomer confined in that chamber and transmitting pressures in a hydrostatic manner. 
     There is also known, from the German patent DE 3916539, a transmission and/or pressure device comprising a principal piston driven by a rod subjected to a pressure. This piston acts on an elastomer mass confined in a chamber and which provides transmission of pressure to two actuating pistons. These actuating pistons are controlled in displacement by piezoelectric actuators. 
     These force multiplier devices use an elastomer mass as a working fluid. They cannot however provide the function of a positioning jack offering the accuracy required here. In fact, in the device described in the document FR 2179572, the first jack or actuating jack is a hydraulic jack, which makes it difficult to attempt to achieve high accuracy. Furthermore, the transmission device divulged in the document DE 3916539 is not a force multiplier and cannot be used as a positioning jack since its principal piston has a cross-section less than that of the actuating pistons controlled by the piezoelectric actuators and small travels are therefore obtained at the level of the actuating pistons and a large travel of the principal piston is obtained, which would not make it possible to obtain the required level of accuracy. 
     The purpose of the present invention is to overcome these disadvantages by proposing a three-axis positioning jack which procures a high positioning accuracy whilst being of less expensive and more reliable construction than those of jacks of the prior art. 
     This purpose is reached with a three-axis positioning jack with at least one motorised axis, comprising: 
     a base comprising movable supporting means and means for vertically displaying said movable supporting means, and 
     a rod providing a link between the movable head of said jack and said base. 
     According to the invention, the linking rod is designed to form a double connection of the ball joint type providing with a lateral displacement of the head with respect to the base, and the movable supporting means comprise an elastomer mass on which the lower end of the linking rod is supported. 
     Such a jack allows, by means of the double link of the ball joint type, a more accurate tridimensional positioning than what can be expected from present jack techniques. Implementing a piece made with an elastomer material procures effort transmission and damping functions that are particularly appreciated in position controls for heavy structures. 
     Moreover, in a first embodiment of jacks according to the invention, the piece made from an elastomer material can be advantageously used as a working fluid. 
     Thus, there is proposed a three-axis positioning jack having at least one motorised axis, comprising: 
     a base comprising a bore containing a chamber in which there is confined a working fluid and a rod providing a link between the head of the jack and the base, 
     and means for modifying the shape of the confinement chamber for the purpose of obtaining a vertical displacement of the head, these means comprising at least one motorised actuating piston, characterized in that the working fluid is constituted by the elastomer mass. 
     In this first embodiment, the solid elastomer mass, which behaves like a quasi-fluid when under load, is deformed by an actuating piston which is motorised. This deformation has the effect of displacing the working piston in order that the volume of the chamber remains constant. The servo-control of a one-axis motorised jack according to the invention with respect to an absolute reference allows easy use of the latter in installations requiring an alignment of deformable structures. Furthermore, one-axis jacks according to the invention can be designed such that they are extra-flat. 
     The condition for correct operation of this new type of jack is that the pressure generated by the load applied to the piston which compresses the elastomer must be sufficient for the latter to behave like a quasi-fluid without, however, its viscosity lowering to such an extent that the polymer can be extruded through the construction clearance between the piston and the bore made in the base of the jack. This jack has minimum and maximum loads proportional to the cross-section of the bore-piston pair and to the Shore hardness of the elastomer used. 
     In a second embodiment of the present invention, there is proposed a three-axis positioning jack, characterised in that the movable supporting means comprise a movable piece for receiving the elastomer piece acting as a ball joint, said movable piece being slidingly mounted with respect to the base and being actuated by micrometric ball screw means. 
     This jack further comprises preferably a second elastomer piece acting as a ball joint between the higher end of the connecting rod and the movable head. 
     A bone-shaped connecting rod with complex-shaped ends can be provided, with said elastomer pieces preferably having housings or hollows fitted for receiving the respective ends of the connecting rod. Cylinder-shaped elastomer pellets can also be used with plane supporting faces against which plane or substantially plane ends of a connecting rod are supported. 
     Jacks according to the invention are compact and of small size. Furthermore, they are easy to produce and are therefore economical. Their functioning is reliable since there is no longer any risk of a sealing breakdown. Furthermore, coupled with servo-control means, jacks according to the invention allow very accurate positioning because of a high positioning resolution. 
     In this way there are available, with three-axis positioning jacks according to the invention, particularly effective actuators for carrying out positioning of a heavy structure with respect to an absolute reference or of several structures with respect to each other, with a high level of accuracy, since by combining several three-axis jacks according to the invention (for example three three-axis jacks of which two axes are motorised), it is possible to control the six degrees of freedom of an object. 
     Within the framework of the present invention, it is possible to provide: 
     a three-axis positioning jack, two of the axes being motorised, one of them being vertical and the other planimetric, the remaining axis being free or guided; 
     a three-axis positioning jack having a vertical motorised axis, the other two planimetric axes being free or guided. 
     A three-axis positioning jack of which two axes are motorised can furthermore comprise a motorised stop to procure a lateral displacement of the head of the jack along a first horizontal axis. This motorised stop comprises for example an actuating screw driven by a motor reduction gear. 
     Furthermore, in order to achieve manual guidance or displacement of the head of the jack along the non-motorised horizontal axis, it is possible to provide a screw and its thrust ring for this purpose. 
     Three-axis positioning jacks according to the invention can advantageously be servo-controlled in position with respect to an absolute reference, along at least one of the said motorised axes. 
     According to particular embodiments of one or three-axis jacks according to the invention, 
     additional actuating pistons can be distributed over the periphery of the chamber in order to increase or pre-adjust the travel of the jack; these actuating pistons are then driven by a screw-nut system which can be motorised or hand-driven; 
     a mechanical system for pre-loading (by springs) the elastomer can be provided for use under very light loads; 
     a displacement sensor can be associated with the jack for the servo-controlled versions. 
     Displacement sensors can be associated with all of these embodiments, allowing a relative servo-control of these jacks. 
     According to yet another aspect of the invention, there is proposed a method for the servo-control of the position of a structure supported by positioning jacks according to the invention, comprising measurements of the position of this structure and with each jack being servo-controlled on the basis of these measurements and of position commands. 
     Advantageously, it is possible to use a set of N jacks with one servo-controlled axis, to act on a deformable solid and to define its geometry, for example for the servo-levelling or servo-alignment of large machines or of long tubes, or for correcting the shape of a deformable solid of large size, or for achieving the flatness of a frame of a large machine tool or the straightness of the movement of translation of a large mass. 
     Servo-controls of N jacks according to the invention using the appropriate number of sensors measuring with respect to one or more absolute references are also included within the scope of the present invention. 
     Other features and advantages of the invention will furthermore appear in the following description. In the accompanying drawings given by way of non-limitative examples: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross-section of an embodiment of a three axis jack, according to the invention, of which two axes are motorised; 
     FIG. 2 is a cross-sectional plan view of the jack shown is FIG. 1; 
     FIG. 3 is a cross-sectional view of an embodiment of a three-axis jack, according to the invention, of which one axis is motorised; 
     FIG. 4 is a cross-sectional plan view of the top part of the jack shown in FIG. 3; 
     FIG. 5 is a cross-sectional view of a first example of another embodiment of a three-axis jack according to the invention; 
     FIG. 6 is a cross-sectional view of a second example of said other embodiment of a three-axis jack according to the invention; 
     FIG. 7 shows an example of the use of three jacks according to the invention in order to control the six degrees of freedom of a structure; 
     FIG. 8 shows a first combination of sensors used for providing a spatial position with respect to absolute references of a non-deformable structure; 
     FIG. 9 shows a second combination of sensors used for providing a spatial position of a structure in the servo-control method; 
     FIG. 10 shows a third combination of sensors used for providing a spatial position of a structure in the servo-control method according to the invention; and 
     FIG. 11 shows an example of the use of a set of one-axis jacks according to the invention for the alignment of long tubes. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Several embodiments of jacks according to the invention, with three axes of displacement, with one or two motorised axes, will now be described with reference to FIGS. 1 to  6 . 
     These jacks are particularly appropriate when an object has to be positioned and servo-controlled in space. In fact, in order to position and maintain an object in space, it is necessary to manage its six axes of freedom. These axes are generally controlled by three actuators which manage the different axes and support the weight of the object to be positioned. The solution traditionally employed uses three jacks oriented along the vertical axis Z which manage and control that vertical axis by simultaneous movements, and the rotations in the horizontal plane Ox, Oy by differential movement. A cross-movements table placed under one of the jacks manages the horizontal displacements of the X and Y axes. A third means of simple translation is disposed under one of the other two jacks and oriented along the Y axis is also necessary in order to manage the last axis Oz. 
     The use of three three-axis jacks therefore has the advantage of combining the two movements, vertical and planimetric respectively, whilst taking up very little volume. The six degrees of freedom of an object can be controlled by supporting it with three three-axis jacks. The positional servo-control of the object to be supported is then controlled by sensors which measure the displacements of the structure directly. The measurements are made either with respect to the ground (relative servo-control), or with respect to absolute references such as a taut line, a light beam, a liquid surface or any other equivalent means. This therefore makes it possible to position two or more blocks with respect to each other. 
     According to particular variant embodiments of the invention, it is possible to devise: 
     a jack  40  allowing motorised displacements along two axes, the vertical axis Z and the lateral axis X (FIGS.  1  and  2 ); 
     a jack  60  allowing motorised displacement along the vertical axis and displacements by manually adjustable stops along its horizontal axes X and Y (FIGS.  3  and  4 ). 
     With reference to FIG. 1, the base  41  of the jack  40  according to the invention comprises a bore  410  which receives a first elastomer pellet  2  and a bone-shaped piston  43  of the double ball joint type whose lower end bears against the pellet  2 . The jack furthermore comprises a movable head  45  comprising a bore  456  containing a second elastomer pellet  455  against which the upper end of the piston  43  bears, and a peripheral cylindrical section  450 . 
     The vertical movement Z is obtained by the action of actuating pistons  44 ,  4  on the elastomer  2 , manually adjustable actuating pistons  44  providing the initial adjustment of the positioning, and at least one actuating piston  4  being motorised for the positional servo-control. Besides the vertical movement, the geometry of the piston allows the rotations about the X and Y axes which then generate movements of translation along the X axis and the Y axis respectively of the head of the jack  40 . The elastomer pellet  455  is confined in the second chamber whose shape is modified by the displacement of two actuating pistons  451 ,  452  controlled manually by adjusting screws  453 ,  454 . 
     This makes it possible to increase the vertical travel and to tolerate non-parallelism of the base of the jack with respect to its head. 
     The motorisation on the horizontal axis X is achieved by means of a motorised stop bearing against the external periphery  42  of the base  41  and driven by a motor reduction unit  48  for the driving along the axis in question and comprising: 
     a thrust ring  461  which provides the guidance on the axis in question X and adjustment of the operational play, and 
     a drive screw  46 . 
     The motor reduction unit  48  is attached to the head  45  of the jack  40  by attachment means  49 . The drive screw  46  is displaced in translation by a motorised yoke  47  driven by the shaft of the motor reduction unit  48 . The second horizontal axis Y is simply blocked by the intermediary of unlockable stop screws  50 ,  51 , as shown in FIG.  2 . 
     In a variant of this embodiment, shown in FIGS. 3 and 6 wherein identical references have been used for identical elements already shown in FIGS. 1 and 2, the two horizontal axes X, Y are acted upon by non-motorised manual stops  610 ,  620 ;  660 ,  670  which can be adjusted by screws  61 ,  62 ;  66 ,  67  traversing the top part  65  of the jack  60 . This jack  60  comprises a bore  410  receiving an elastomer pellet  2  and a piston  63  whose ball-joint shaped base rests on the elastomer pellet  2  and whose upper end comprises a housing  433  designed for receiving a ball  431  providing the second ball joint function, the top part  65  also comprising an appropriate housing  432  for receiving this ball. 
     In another embodiment of a three-axis according to the invention, the ball joints are made in elastomer material and the following displacement of the connecting rod is achieved by a micrometric ball-screw device, with reference to the examples of embodiment illustrated by FIGS. 5 and 6 wherein common elements feature common references. 
     Thus, the jack  50  comprises a base  51  provided with a higher cylindrical part  52  comprising a bore  521  wherein a movable piece  550  slides whose positioning is controlled by a micrometric screw-ball device  510 . The movable piece  550  is designed for receiving a first piece  554  made in elastomer material wherein a lower end  532  of a bone-shaped piston  53  of the double ball-joint type. The higher end  531  of the piston  53  is housed in a second piece  555  in elastomer material fitted into a bore  556  of a movable head  55  of the jack  50 . 
     The vertical movement along Z of the movable head  55  is obtained by acting on the micrometric ball-screw device  510  which can be actuated by a stepper motor. The two elastomer pieces  554 ,  555  achieve both a function of ball-joint link and a function of damping. 
     In addition to the vertical movement, the geometry of the piston  53  allows rotations around the axes X and Y which therefore generate translations respectively on the axis X and the axis Y of the head of the jack  50 . Motorisation on the horizontal is achieved by means of a motorised stop supported on the external periphery of the higher part  52  of the base  51  and actuated by a motoreductor  58  for control on the considered axis, and comprising: 
     a thrust stop  561  which ensures guiding on the considered axis X and adjusting of the working looseness; and 
     an action screw  56 . 
     The motoreductor  58  is mounted on the peripheric cylindrical part  551  of the head  55  of the jack  50  by mounting means  59 . The action screw  56  is displaced in translation by means of a motorised nut  57  driven by the shaft of the motoreductor  58 . The second horizontal axis Y is merely blocked by means of stop screws. 
     In a second example of this embodiment with a micrometric ball-screw illustrated by FIG. 5, the piston  33  of the jack  30  comprises respectively lower and higher substantially plane ends  332 ,  331  which bear against respectively a first and a second pieces  354 ,  355  in elastomer material. Said first and second pieces  354 ,  355 , which for example are shaped as cylindrical pellets, are respectively housed inside the sliding movable piece  550  and into the bore  556  provided inside the movable head  55 . 
     There will now be described an example of the use of the positioning servo-control method using jacks according to the invention and combinations of sensors used for measuring the position of a structure, with reference to FIGS. 7 to  11 . 
     The servo-control method according to the invention can for example be used for maintaining the geometry of a deformable structure. The use of N jacks with one motorized axis servo-controlled with respect to external absolute references therefore makes it possible to compensate for ground movements, mechanical stresses, etc., for example for the alignment of a long tube or the levelling of a machine tool. 
     In a first configuration shown in FIG. 11 which represents a system for the alignment of a long tube, the absolute reference is defined by a taut wire F. A long tube  111  rests on a first set of one-axis jacks V 1 -V 6  according to the invention disposed in the axis Z to be corrected, whilst a second set of one-axis jacks V′ 1 -V′ 6  according to the invention is disposed along the tube  111  and in the horizontal axis X. A set of biaxial deviation measuring devices E 1 -E 6  makes it possible to take biaxial deviation measurements with respect to this line in order to correct the alignment of the tube  111 . 
     In a second configuration, the reference can be defined by a stretch of water defining horizontality. 
     In a third configuration, the reference can be defined by one-axis or two-axis inclinometers. 
     Three-axis jacks according to the invention can for example be used for the spatial position servo-control of two or of N non-deformable structures  80 . There is carried out, using the servo-control method according to the invention, a control of the six degrees of freedom of non-deformable structures  80  each supported by three three-axis positioning jacks  81 ,  82 ,  83  according to the invention disposed on the ground  84 , each of these positioning jacks  81 ,  82 ,  83  being allocated to one vertical displacement axis A 1 , A 2 , A 3  and one lateral displacement axis A 5 , A 4 , A 6 . Each positioning jack  81 ,  82 ,  83  according to the invention is provided with a first motor reduction unit  812 ,  822 ,  832  for driving an actuating piston controlling the vertical displacement Z and the tilts Θx, Θy of the structure. Two positioning jacks  81 ,  82  are furthermore provided with a second motor reduction unit  818 ,  828  for driving a motorized stop controlling the displacement Y and Θz of the structure. The third positioning jack  83  is provided with a manually adjustable stop controlling the displacement along the horizontal axis X. 
     This servo-control method comprises a detection of the spatial position of each structure  80  with respect to an absolute reference R, and a closed loop servo-control of three positioning jacks  81 ,  82 ,  83  with respect to this reference. 
     In a first configuration, shown in FIG. 8, the absolute reference is defined by two taut wires and the position measurements comprise: 
     a uniaxial measurement of deviation ECZ from a wire made at a first point in the structure  80  along a vertical axis Z, with respect to a first taut wire F 1  along a first horizontal axis X, and 
     two bi-axial measurements of deviation ECD 1 , ECD 2  each made along the vertical axis Z and along the second horizontal axis Y at two other different points, with respect to a second taut line F 2  along a second horizontal axis X. 
     In a second configuration, shown in FIG. 9, the absolute reference is defined by two taut wires and the position measurements comprise: 
     a uniaxial measurement of deviation ECZ along a vertical axis Z, with respect to a first taut wire F 1  along a first horizontal axis X, 
     two uniaxial measurements of deviation ECY 1 , ECY 2  made at two different points along a second horizontal axis Y related to a second taut wire F 2  along a second horizontal axis, and 
     two clinometric measurements IN to provide two measurements Dx, Dy of the inclination of the structure  80  with respect to the vertical axis Z, about the first horizontal axis X and about the second horizontal axis Y respectively. 
     In a third configuration shown in FIG. 10, the position measurements comprise: 
     an altitude measurement AL made at a first point in the structure  80  along a vertical axis Z, 
     two uniaxial measurements of deviation ECY 1 , ECY 2  made at two different points along a second horizontal axis Y, with respect to a taut wire F 2  along a first horizontal axis X, and 
     two biaxial clinometric measurements IN to provide two measurements Dx, Dy of the inclination of the structure  80  with respect to the vertical axis Z about the first horizontal axis X and about the second horizontal axis Y respectively. 
     The position measurements are for example made at the locations of the jacks, but can very well be made at other points in the structure. With each positioning jack  81 ,  82 ,  83  there is associated a measurement along the vertical axis Z, and with two of the said positioning jacks  81 ,  82  there are associated the two measurements along the second horizontal axis Y. 
     The invention is not of course limited to the examples which have just been described and many developments can be applied to these examples without departing from the scope of the invention. It is possible, for example, to design other embodiments of the positioning jacks. Other combinations of position sensors can also be envisaged. It is possible to use polyurethane or natural rubber for producing the elastomer mass. This mass can consist of a multitude of elastomer balls.