Implements or apparatus for applying pushing or pulling force – Traversing jack
Reexamination Certificate
1998-06-08
2001-02-13
Scherbel, David A. (Department: 3723)
Implements or apparatus for applying pushing or pulling force
Traversing jack
C254S00200C
Reexamination Certificate
active
06186480
ABSTRACT:
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
ut 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
Nanotec Solution
Scherbel David A.
Shanley Daniel
Young & Thompson
LandOfFree
Triaxial positioning actuator and control methods using same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Triaxial positioning actuator and control methods using same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Triaxial positioning actuator and control methods using same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2593387