WO2002014012A1

WO2002014012A1 - Mechanical stage for effecting displacements in a two-dimensional coordinate system

Info

Publication number: WO2002014012A1
Application number: PCT/EP2001/009342
Authority: WO
Inventors: Dirk Schmidt; Klaus Martin
Original assignee: Lat Suhl Ag
Priority date: 2000-08-14
Filing date: 2001-08-13
Publication date: 2002-02-21
Also published as: AU8401101A; DE10040277A1; DE10040277C2

Abstract

The invention relates to a mechanical stage for effecting displacements in a two-dimensional coordinate system, comprising a stationary base (1), a lower mobile body (2) that is mounted on the base so that it can be displaced in a first direction (x), an upper mobile body (3) that is mounted on the lower mobile body so that it can be displaced in a second direction (y), and at least one drive system (9, 13) that effects the displacement of the two mobile bodies. Both the base (1) and the two mobile bodies (2, 3) consist of the same hard rock material.

Description

Cross table for the provision of movements in a two-dimensional coordinate system

The present invention relates to a cross table for providing movements in a two-dimensional coordinate system with a fixed base body, a lower barrel body, which is slidably mounted on the base body in a first direction, an upper barrel body, which is slidably supported on the lower barrel body in a second direction is, and with at least one drive system, which causes the displacement of the two barrel bodies.

In automated processes, in measuring systems, in precision applications and in connection with other modern technologies, drive and positioning systems are often required which enable very fast and / or very precise movements. In general, various principles of implementing the drive system are used. a lot of

Applications, however, have in common that with increased demands on speed and accuracy there are a number of problems in the realization of the bearing of the moving parts. The bearings required should have as little play as possible in order to keep the resulting errors in positioning and repetition accuracy small. In addition, the bearings must run as smoothly as possible so that the friction forces that occur are small.

Particularly when positioning accuracies in the micrometer range are to be achieved, particular problems arise due to the different temperature-dependent expansion coefficients of the materials used. At tempera- Fluctuations in the fluctuations in the play in the bearing can change so much that either excessive frictional forces occur or, in the other case, there is too much play so that the required positioning accuracy can no longer be achieved.

In order to keep the temperature-related expansion low, attempts have been made in some cases to produce at least the load-bearing element of the base body from materials which have a small expansion coefficient. In some cases, a simple base support was made from rock material. However, since the barrel bodies have more complicated shapes, they are generally made from materials that are easier to machine, but this again resulted in difficulties in changing the ambient temperature.

The difficulties already mentioned increase if a so-called cross table is to be used to implement a two-dimensional movement. Such cross tables usually have two running bodies which move in mutually perpendicular directions. It is also known to support the running bodies with air bearings in order to keep the friction losses low. If a barrel slides on an air bearing, lateral guidance in the direction of movement is also required. In order to avoid undesirable torques, which can occur in particular at high acceleration values, the running bodies are usually supported on both sides. However, a fixed bearing can only be used on one side, while a spring-loaded bearing is required on the other side to compensate for temperature-related material expansion. A particular problem with previous applications of air bearings is that these air bearings increase the construction height of the running body, so that the center of gravity of the running body is not in the plane of the attacking driving force. At higher acceleration values, tilting moments and vibrations then occur, which lead to positioning inaccuracies and increased loads on the bearings used.

From DE 68 08 097 U, a cross table bearing is known, which has a base body and two movable running bodies that are movable in different directions. The use of parallel roller rails results in a relatively precise mounting, but also a complicated structure with a large overall height and the resulting tilting moments.

DE 33 47 282 AI shows an aerostatic bearing device that enables movement in one direction. The main body and the barrel body are made of granite. In order to keep the center of gravity low, the barrel is composed of several solid blocks, which greatly increase the overall mass and cancel the homogeneity of the barrel. The temperature-dependent length differences increase again and the dynamic properties are no longer suitable for fast movements.

It is therefore an object of the present invention to provide a cross table which enables movements in a two-dimensional coordinate system, but overcomes the disadvantages of the prior art, in particular enables more precise and faster movements, the

Positioning accuracy should be maintained even when temperature fluctuations occur. Another development of a cross table, in which the amounts of undesirable moments are kept as small as possible by a flat construction of the running body.

These and other objects are achieved according to the invention by a cross table in which both the base body and the two barrel bodies consist of the same hard rock material and are each formed in one piece, in which the bearing between the base body and the first barrel body and between the first and the second barrel body is formed by air bearings, the air bearings comprising air nozzles which are integrated in the sliding surfaces of the base body and / or the running body.

In this way, all difficulties which result from the use of different materials with different expansion coefficients and which significantly improve the dynamic properties of the cross table compared to the prior art are avoided.

Hard rock has a relatively small coefficient of expansion (eg granite: α «10 ^{" 6} K ^"1 ). However, even those linear expansions that can occur in spite of the low expansion coefficient with larger temperature fluctuations do not lead to those known from the prior art.

ten disadvantages, since both the base body and the two barrel bodies will expand evenly.

With this solution according to the invention existing prejudices of the professional world have been overcome. So far, it has often been assumed that the barrel bodies cannot be produced from hard rock material due to their complexity.

The advantages already mentioned are particularly important in a preferred embodiment if the base body and the two barrel bodies are each formed in one piece from the hard rock material. In this way, inhomogeneities are avoided and no connecting sections between individual rock blocks are necessary. In other embodiments, however, it is also conceivable that individual rock sections are glued together.

In an advantageous embodiment, the two running bodies are table-shaped and are mounted on both sides in fixed bearings along the direction of movement. It is particularly expedient if air bearings are used which are integrated directly into the base body and / or the running body. For example, this is done by arranging air nozzles in the sliding surfaces of the running bodies, which are arranged on the side surfaces and undersides. The latter measure keeps the height of the respective running body low, since, in contrast to solutions known from the prior art, the air bearings are not attached to the running body as independent elements and protrude beyond its surface. The tilting moments that occur during acceleration can thus be kept very small. An advantageous embodiment is characterized in that each of the two running bodies is assigned an independent drive system. In addition, measuring systems are preferably arranged with which the positions and / or the speeds and / or the accelerations of the running bodies can be determined. The drive and measuring systems are expediently coupled to a control unit which evaluates the corresponding data and supplies the required signals to the drive systems.

Further advantages, details and further developments result from the following description of a preferred embodiment of the invention, with reference to the drawing. Show it:

Figure 1 is a simplified top view of a cross table according to the invention.

Figure 2 shows the cross table in a simplified sectional view from the front.

3 shows the cross table in a simplified sectional view from the side;

4 shows the cross table in a view from the front with a first measuring system; 5 shows the cross table in a view from the side with a second measuring system;

Fig. 6 is a sectional detailed view of an integrated air bearing.

Fig. 1 shows a cross table in a simplified view from above. This cross table is used to provide whose position is defined by the xy coordinates shown in FIG. 1. The cross table has a fixed base body 1, a lower barrel body 2 and an upper barrel body 3. The base body 1, the lower barrel body 2 and the upper barrel body 3 consist of the same hard rock material. These elements are preferably formed in one piece from this material. The lower barrel body 2 is movable in the x direction, a lateral longitudinal guide being formed by a guide section 4 of the base body 1. Shock absorbers 5 are also arranged on the lower barrel body 2, which allow a damped end stop when the end position is reached in the positive or negative x-direction.

The upper barrel body 3 is seated on the lower barrel body 2 and is movable thereon in the y direction. The upper running body 3 is also guided laterally in the direction of movement, the corresponding guide sections being provided by the lower running body 2. Likewise, further shock absorbers 6 are provided which dampen the end stop when the upper running body 3 moves.

Fig. 2 shows the cross table in a sectional view from the front. The sectional view clearly shows the monolithic structure of the base body 1, the lower barrel body 2 and the upper barrel body 3. The lower barrel body 2 has a table-shaped design, on the one hand to provide a sufficiently large usable area on the top and on the other hand to have the necessary stability. The under barrel 2 is in the guide sections 4 of the

Base body 1 supported by air bearings. There are several in the lower and side sliding surfaces of the lower barrel 2 first lower air bearings 7 and first lateral air bearings 8 are formed on the respective side of the lower running body 2.

Means are preferably also provided with which a vacuum preload of the air bearings can be generated. Such a vacuum preload stiffens the vertically acting air bearings in addition to the effect of gravity.

The two sides of the lower barrel body 2, which extend in the direction of movement, can be stored in fixed bearings in this way, since due to the hard rock materials used, different lengths of the base body and the lower barrel body must not be expected.

An x drive system 9, which is designed here as a linear drive, is also shown schematically in FIG. 2. However, the special shape of the drive is not important. The drive is adapted to the respective application in terms of the desired speeds and acceleration values, as well as the forces to be applied.

Fig. 3 shows the cross table in a sectional view from the side. It can be clearly seen in this illustration that the upper barrel 3 is mounted in the lower barrel 2 in a manner which corresponds to the mounting of the lower barrel 2 in the base body 1. With respect to the direction of movement of the upper running body 3 (y direction), second lower air bearings 11 and second lateral air bearings 12 are arranged on the longitudinal sides. Here too, storage can take place in fixed bearings, since the upper running body 3 is made of the same material The upper barrel 3 is also table-shaped in order to provide a usable surface on its upper side and to meet the static requirements. For example, a workpiece can be positioned on the top of the upper barrel 3, which is to be moved into different positions during machining. In the embodiment shown, an independent y-drive system 13 serves to drive the upper barrel body 3.

When determining the possible (maximum) travel of the two running bodies, the use of the vacuum preload in conjunction with the air bearings has a positive effect. This allows the center of gravity to be moved out of the bearing, since the tilting moments that occur in such a case are compensated for by the vacuum preload.

Fig. 4 shows the cross table again in a view from the front. It is expedient to arrange a first measuring system 15 with which the movement or the position of the lower running body 2 can be monitored. The measuring system must be arranged as close as possible to the drive system in order to avoid control problems.

Fig. 5 shows the cross table in a view from the side. In this illustration, a second measuring system 16 can be seen, which monitors the movement or the position of the upper barrel. Furthermore, it is shown schematically how energy can be supplied to the lower barrel 2 and the upper barrel 3. For example, a flexible supply line 17 is provided, which both provides electrical energy and serves to supply the compressed air to the air bearings. 6 shows a sectional detailed view of the lower barrel body 2, the integrated air bearings being clearly visible. The first lower air bearing 7 is formed by a nozzle insert 18 and a screw-in nozzle 19 screwed into it. At the back, the screw-in nozzle is connected to a compressed air supply unit (e.g. with a hose). Additional structures are no longer required. The air bearing then forms directly between the lower barrel body and the base body. The side air bearing 8 is constructed in the same way.

Other shapes can be selected for the base body and the two barrel bodies. It is always crucial that these three basic elements are made of the same hard rock material in order to ensure high precision and insensitivity to temperature fluctuations. In the case of modified embodiments, other bearings could also be used.

The flat design explained, which is only made possible by the integration of the air bearings, reduces the undesired tilting moments during acceleration of the barrel body. The flat arrangement of the bearings used in the illustrated embodiment, which extends over the entire length of the guide, increases the guide accuracy compared to point-shaped bearings. In addition, the integration of the air bearings in the running body eliminates the need for other components that would otherwise reduce the rigidity. As a result, vibrations typical of air bearings are largely avoided. LIST OF REFERENCE NUMBERS

Claims

New claims

1. Cross table for the provision of movements in a two-dimensional coordinate system (xy) with a fixed base body (1), a lower barrel body (2), which is slidably mounted on the base body in a first direction (x), an upper barrel body ( 3), which is mounted displaceably on the lower barrel body in a second direction (y), and with at least one drive system (9, 13) which causes the displacement of the two barrel bodies, characterized in that

• Both the base body (1) and the two running bodies (2, 3) consist of the same hard rock material;

• the base body (1) and the two barrel bodies (2, 3) are each formed in one piece;

• the bearing between the base body (1) and the first barrel (2) and between the first and the second barrel (2, 3) is formed by air bearings (7, 8, 11, 12); and • the air bearings (7, 8, 11, 12) comprise air nozzles (18, 19) from which compressed air emerges for the construction of the air bearing, these air nozzles being integrated in sliding surfaces of the base body and / or the running body.

2. Cross table according to claim 1, characterized in that the two running bodies (2, 3) are table-shaped and are mounted on two sides in fixed bearings. Cross table according to claim 2, characterized in that the sliding surfaces are arranged in sections of the undersides ^" and the side surfaces of the running bodies, and that the side surfaces continue to have air extraction areas, a vacuum being generated with the air extraction areas, which serves to preload the air bearings.

Cross table according to one of claims 1 to 3, characterized in that each of the two running bodies (2, 3) is assigned an independent drive system (9, 13).

Cross table according to one of claims 1 to 4, characterized in that one or more measuring systems (15, 16) are provided with which the positions of the running bodies (2, 3) can be determined.

Cross table according to one of claims 1 to 5, characterized in that a control unit is provided which controls the drive systems (9, 13) and optionally evaluates data supplied by the measuring systems (15, 16).