EP0876239A1

EP0876239A1 - Precision translation guiding system

Info

Publication number: EP0876239A1
Application number: EP97901670A
Authority: EP
Inventors: Michel Demesy; Eric Collard
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1996-01-26
Filing date: 1997-01-24
Publication date: 1998-11-11
Also published as: FR2744050A1; FR2744050B1; WO1997027025A1; JP2000503910A

Abstract

A device for achieving a translational movement over several hundred millimetres that is accurate to the nearest micrometre during relative movement between a moving part and a stationary part in a mechanical machine. The device mainly uses two separate continuous parallel rails that each consist of eight continuous tracks arranged in facing pairs and defining a sideways-facing V shape on either side of a rail (10) of the stationary part (11). Needles are placed between the eight continuous tracks to enable movement of the moving part (12) relative to the stationary part (11). The spacing between the rails is maximised in order to optimise the accuracy of the assembly. The device may be used in machine tools and control and assembly machines.

Description

HIGH PRECISION TRANSLATION GUIDANCE DEVICE

DESCRIPTION

Field of the invention

The invention relates to machines comprising parts that are movable relative to a frame, such as machining, assembly, control, etc. machines. It relates, in particular, to guiding carriages, laggards, tool holders, fixing tables or spindle heads of milling machines, boring machines or machining centers, that is to say of all the movable parts d '' a machine tool which must move slowly with great precision, while having to possibly endure significant mechanical stresses.

Prior art and problem posed

In the context of the construction of modern machining, assembly and control machines, it becomes necessary to use more and more high precision guidance systems for the mobile structures of these machines. In the field of translational or linear guides, several technologies are known which are summarized as follows:

- The friction bearings ^' whose phenomenon of "stick-slip", that is to say, grazing, encountered at low speeds of movement, limits the positioning accuracy;

- very efficient aerostatic and hydrostatic bearings, but which prove to be costly solutions, difficult to implement and relatively fragile, in particular with regard to aerostatic bearings;

- Bearings on bearings which are means which do not have the drawbacks mentioned above. In the latter category, we consider, in particular, cage systems of rolling elements between two rails integral with the fixed and movable parts of the guide. The term "rolling elements" means balls, rollers or needles. Also known in this category, short length skid systems operating with a recirculation of balls or rollers between the skate and the guide rail.

In the latter two cases, and especially for skid systems, which their short length disadvantages, the performances obtained with the assemblies used in a standard manner by the bearing manufacturers, are limited, for strokes of approximately 200 mm, to defects parasites of the guides, which are of the order of 1 to 2 μm in horizontal or vertical straightness and 1 to 2 seconds of arc in yaw, roll or pitch. This materializes, for example, in the field of turning, on a conventional lathe, by a theoretical manufacturing tolerance of plus or minus 5 μm, which can be obtained on a series of several parts, when the machining operations take place normally and without taking into account the settings and wear of the tool. Taking into account these last two parameters, the range of plus or minus 5 μm is very often exceeded. As a result, the manufacturing tolerances are found to be greater. The object of the invention is therefore to remedy these drawbacks by presenting a high-precision translational guidance system of different design by avoiding the use of a shoe system. Summary of the invention

The main object of the invention is a device for guiding in high precision translation of a part of a machine, the device using rolling elements between continuous tracks of bearings arranged laterally in a V and, facing each other, both on the mobile part and on the fixed part of the machine, to form bearings in translation. According to the invention, the device comprises two parallel continuous slides spaced from one another and each comprising:

- A rail integral with one of the parts and having two lateral faces each consisting of two continuous rolling tracks arranged in a V; two bearing parts integral with the other part, each having an internal double side face consisting of two continuous rolling tracks arranged in a V and parallel to the continuous rolling tracks of the rail which face them; and the rolling elements which consist of cylindrical needles placed in large numbers in protruding needle cages between the eight continuous tracks of each of the two continuous slides. Preferably, the two branches of each V are oriented symmetrically with respect to a horizontal plane.

The device is advantageously completed by a clamping system for continuous slides to pre-load the needles in a controlled manner.

In its preferred embodiment, the bearing parts are concave and each placed against an internal side wall of a cavity of the moving part. Likewise, the two lateral faces of each rail preferably consist of a convex rolling part placed against an internal surface of the rail.

List of Figures

The invention and its various technical characteristics will be better understood on reading the following description, accompanied by three figures representing respectively:

- Figure 1, in section, the diagram of a structure of a device according to the prior art;

- Figure 2, in section, the diagram of a device according to one invention; and - Figure 3, in a perspective view, the device according to the invention.

Detailed description of an embodiment

In Figure 1 is shown in section, a fixed part 1 of the device according to the prior art. This fixed part can be a horizontal or vertical part of the frame of the machine equipped with this device. Similarly, there is shown in section, a movable part 2 of the device according to the invention, in this case the table of a machine tool on which is fixed a workpiece, the base of a carriage or a lap stroller, etc.

These two parts are each equipped with two respective rolling parts, convex rolling parts 3 for the fixed part and concave rolling parts 4 for the moving part, the latter constituting a kind of rolling sheath. These parts are associated in pairs so as to face one relative to the other. Thus, on the side faces 5 of a top part 10 constituting a rail of the fixed part 1 is placed a convex piece of bearings 3. This piece has two continuous rolling tracks inclined relative to each other to form a V. It is noted that, preferably, the V is often symmetrical with respect to a median horizontal plane . In correspondence, each of the two concave rolling parts 4 is fixed against an internal lateral surface 6 of the moving part 2 and opening out inside a cavity 7 of the latter. Each concave rolling part 4 has two continuous rolling tracks inclined in a V, corresponding to the two continuous rolling tracks of the two convex rolling parts 3. Each continuous rolling track is therefore parallel to a continuous rolling track which makes it face. By placing rollers or needles inside the space defined by two continuous rolling tracks facing each other, a continuous slide is thus created allowing the movable part 2 to move relative to the fixed part without apparent friction .

With reference to FIG. 2, the device according to the invention also comprises a fixed part 11 and a movable part 12. The movement is carried out using two sets of technology similar to that used for the device in FIG. 1. By cons , two sets of slides are used, that is to say two continuous slides placed parallel to one another in a relatively spaced apart position. Therefore, each continuous slide each comprises two convex rolling parts 13 fixed laterally on a rail 16 of the fixed part 11. Each continuous slide also has a rolling sheath consisting of two concave rolling parts 14 placed laterally at the inside a cavity 17 of the moving part 12. Continuous rolling tracks are provided on the faces located opposite, in V, on each of these bearing parts.

It is understood that the minute parasitic movements of the moving part 2 of FIG. 1 relative to its fixed part 1, in particular in yaw, are amplified by the dimension of the moving part 2 relative to the spacing of the two pairs of tracks. V-shaped bearings on one side and on the other of the rail 6. This amplification cannot take place with a device according to the invention, which has two continuous parallel bearing slides. Indeed, this theoretical yaw rotation movement due to minute play of a continuous slide is prevented by the presence of the second continuous slide prohibiting this type of movement. The spacing of the two continuous slides must therefore be relatively large, that is to say occupy part of the width of the sliding or guide assembly that constitutes the assembly of the part 11 and the moving part 12 On this occasion, a guiding ratio is defined which is the ratio of the length L of the continuous slide to the spacing 1 of the two continuous slides.

Figure 3 shows, in a perspective view, the device according to the invention. The rails 16 of the fixed part 11 have been shown protruding in length to show the rollers 18 mounted in sheaths of needle bearings. The sheaths 19 are inclined in a V with the same inclination as the continuous tracks of bearings marked 20. It is preferable to use assemblies with protruding needle cages, that is to say having a number of needles such that these needle cages have a greater length than the length of the movable part 12, in the direction of sliding. In this way, the mobile part 12 always rests, over its entire length and whatever its position, on a maximum number of needles 18.

There have been set adjustment screws 21 on the outer side wall 22 of the movable part 12, the purpose of which is to symbolize a clamping device intended to preload each continuous slide and, more particularly, to preload the needles 18. Thus, we catch up by tightening the possible lateral clearance existing in the assembly of each continuous slide, and the clearances between the various mobile elements are optimally minimized with respect to each other. As a result, the accuracy of the guide device is improved.

In fact, the device according to the invention has a very high degree of precision by the multiplicity of continuous rolling tracks 20, that is to say eight pairs of continuous rolling tracks arranged in V. This also makes it possible to average d '' possible faults.

By using an electronic calculation program, it is possible to dimension or model by finite elements, each part. Thus, for a stroke of 150 mm obtained, thanks to a prototype, it was possible to detect, by means of a laser interferometer, parasitic defects smaller than the micrometer (smaller than 0.4 μm in straightness and smaller than 0.3 seconds from bow to yaw and pitch). These tolerances perfectly meet the specifications expected in the design of this type of guide device for the intended applications, in particular for very high precision machining.

The movement obtained is a relatively slow movement of the mobile part, free of jerks, compatible with very low movement speeds and positioning accuracies of a few hundredths of a micrometer, as we are entitled to expect in the context of high precision machining of mechanical parts. Continuous slides or slide elements used in the device according to the invention are known and marketed. Consequently, the production of such a device is not very expensive.

It can be specified that this type of device can be used for traditional machining by machine tool or in the context of very high level precision techniques.

Claims

1. A device for guiding in translation of a high precision part of a machine, using rolling elements (18) between continuous rolling tracks (20) arranged laterally in V and facing each other two by two, at the times on a movable part (12) and a fixed part (11) of the machine, to form bearings in translation, characterized in that it comprises two continuous parallel slides spaced from one another and each comprising:

- A rail (16) secured to one of the parts (11) having two lateral faces each consisting of two continuous rolling tracks (20) arranged in a V;

- two pieces of bearings (14), integral with the other part (12) each having an internal double side face consisting of two tracks of continuous bearings (20) arranged in V and parallel each to a track of continuous bearings (20) rail facing them; and

- The rolling elements (18) which consist of cylindrical needles placed in large numbers in protruding needle cages between the eight continuous rolling tracks (20) of the two continuous slides.

2. Device according to claim 1, characterized in that the inclinations of the continuous tracks (20) in V are symmetrical with respect to a horizontal plane.

3. Device according to claim 1, characterized in that it comprises a clamping system (21) of the continuous slides for preloading the needles (18) in a controlled manner.

4. Device according to claim 1, characterized in that the bearing parts (14) are concave and each placed against an internal side wall (16) of a cavity (17) of the movable part.

5. Device according to claim 1, characterized in that the two lateral faces of each rail (10) consist of a convex rolling part (13) placed against an internal surface (15) of the rail (10).