DE29812827U1 - Pallet changing system - Google Patents

Description

Track & Large

Patent Attorneys Munich Stuttgart

Dr. jur. Alf-Olav Gleiss, Oipl.-Ing. Rainer Große, Dipl.-Ing.
Dr. Frhr. v. Uexküll, Dipl.-Chem. Dr. Andreas Schrell, Dipl.-Biol. Dr. Wilhelm Heuer, Dipl.-Phys.

European Patent Attorneys
European Trademark Attorneys

Torsten Krüger Attorney at Law D-70469 STUTTGART
MAYBACHSTRASSE 6A
Telephone: +49(0)711 8145 55 Fax: +49(0)711 8130 32 Telex: 72 27 72 jurad

e-mail: jurapat@aol.com

D-80469 MUNICH
MORASSISTRASSE 20
Telephone: +49(0)89 21578080 Fax: +49(0)89 21578090 e-mail: GGpat@aol.com

Utility model application Paiette changing system

Dr. Suhr & Partner GmbH Pforzheimer Strasse 377

70499 STUTTGART

14 578GR-to-bf July 18, 1998

Tracks & Large

Patent attorneys
Munich Stuttgart

Description

The invention relates to a pallet changing system, in particular for machine tools, according to claim 1.

In metal machining, the workpieces to be machined are usually clamped directly onto a T-slot machine table or appropriate devices for the workpiece to be clamped are attached to the machine table. In order to achieve short set-up times, universally usable perforated grid plates are often used as a base module on which the workpiece is clamped. The perforated grid plate is mounted on an interchangeable pallet, which in turn can be positioned and clamped precisely on the machine table using an appropriate clamping mechanism. This makes it possible for the actual clamping process of the workpiece and the alignment of the perforated grid plate to also take place outside the machine tool. Such interchangeable pallets are standardized according to DIN 55201. It is also known that the interchangeable mechanism can sometimes be coupled directly to the perforated grid plate, which makes it possible to achieve a compact and cost-effective design.

14 578GH-to-bf July 16, 1998

Practice shows that this method, which is now widely used in companies, has various disadvantages. When a perforated grid plate is combined with an interchangeable pallet with a T-slot holder, the perforated grid plate must be realigned and measured each time the device is changed. If the perforated grid plate and interchangeable pallet are left connected, this results in a considerable amount of capital being tied up. Furthermore, the flexibility of the interchangeable plate system standardized in accordance with DIN 55201 is low. Square formats are predominantly used, even though most machine tools have rectangular formats for the clamping surfaces and machining paths. One reason for this is the possible need for multi-sided machining.

Due to their heavy weight and poor handling, the known interchangeable pallets are generally only used in so-called pallet stations that are permanently coupled to one or more machine tools. It is practically not possible to remove the interchangeable pallets from the pallet station, for example to check clamped and machined workpieces on a measuring machine or to carry out further processing on machines that are not integrated into the machining cell without re-clamping. Furthermore, the interchangeable pallets are not readily removed from the pallet station because they do not have a smooth bottom surface and therefore offer poor storage and stacking options.

Furthermore, due to their very high weight and the lack of transport facilities, the interchangeable pallets can currently only be moved outside the processing cells using a crane as a pendulum load.

For small workpieces and weights, there are still non-standardized interchangeable pallet systems known, which, however, only cover the range up to approx. 300 mm x 300 mm. The associated interchangeable pallet holders are designed as a unit that can be mounted on the machine table, in a measuring machine or at other processing locations. The interchangeable pallet with the workpiece can thus be easily transported through various machine stations, even manually. In order to circumvent the restriction on the size range, modular systems have been developed based on the same principle. In general, these are clamping pins that are screwed to the underside of the interchangeable pallet. Individual chucks serve as the clamping device, which are mounted on the machine table at the distance from the clamping pins attached to the interchangeable pallet. The movement for clamping and releasing is pneumatic, hydraulic or mechanical. Since the arrangement of the clamping pins on the interchangeable pallet is arbitrary, any base plate format for the interchangeable pallet can be realized. The disadvantage of the known change pallet is that the clamping pins protruding from the underside represent a disturbing edge on the one hand and are also constantly at risk of being damaged by impact. Since the clamping pins simultaneously define the accuracy of the change system,

-A-

There is a weak point inherent in the system here. Furthermore, the chucks that have to be mounted on the machine table with the associated connecting lines for the medium by means of which the clamping device can be tightened and released cause problems with the disposal of chips from the machine table of the machine tool. A further disadvantage is that the interchangeable pallets have to be brought into the machine tool from above and positioned on the machine table. For this it is necessary to use a hoist for the loads. Because the interchangeable pallet holders have a small catch area of around 1 mm, in many cases the interchangeable pallet is hung on the hoist and then lowered into the machine in a pendulum motion. Due to the pendulum load, collisions between the interchangeable pallet and injuries to people cannot be ruled out. In addition, a quick pallet change causes considerable problems on machines that are not accessible from above (fully enclosed).

In summary, the main disadvantages of the known systems are as follows:

low flexibility in the size of the change pallet,

very heavy weights for interchangeable pallets for larger workpieces,

large construction height when combining perforated grid plate and interchangeable pallet,

- Problems with changing the pallet and positioning the change pallet on the machine table, especially when the weight of the change pallet and workpiece exceeds 25 kg,

- or when using interchangeable pallets according to DIN, there is only limited flexibility for the removal of interchangeable pallets from the fixed machine-pallet station arrangement.

Various approaches are known to remedy the disadvantages described above, but always only in partial aspects.

It is therefore an object of the invention to provide a pallet changing system which does not have the disadvantages mentioned above.

To solve this problem, a pallet changing system with the features of claim 1 is proposed. This comprises at least one mineral cast plate that can be attached to a walking table by means of at least one clamping device. The clamping device comprises a clamping pin and a counter element that interacts with the clamping pin when coupled. The clamping pin and the counter element are designed in such a way that, when not coupled, they do not protrude beyond the contact surface of the mineral cast plate with which it rests on a support surface of the counter table, or the support surface of the counter table. Due to the arrangement that can be retracted into the support surface of the counter table and the contact surface of the mineral cast plate

of the clamping pin or the counter element, it is possible for the mineral cast plate to be moved on the counter table during assembly, which improves the handling of the mineral cast plate. A further advantage of the parts of the clamping device integrated into the flat contact surface or support surface is that dirt on these surfaces, for example chips, coolant and the like, can be easily removed. Another advantage is the relatively low weight of the pallet changing system, especially that of the mineral cast plate.

In an advantageous embodiment of the pallet changing system, the counter table is mounted on a machine table, for example a machine tool. The mineral cast plate, on which at least one workpiece is clamped, can therefore be positioned outside the machine on another counter table and the workpiece to be clamped can be precisely aligned and secured there. The modular unit formed from the mineral cast plate with the mounted workpiece can be brought into the machine in a short time, so that short downtimes can be achieved when changing workpieces. In another embodiment, the counter table is formed by the machine table itself. The mineral cast plate is therefore fixed within the machine when the clamping device is operated and at the same time moved to an exact position. Since the adjustment in this embodiment is un-

takes place indirectly on the machine table, short preparation times are possible.

A particularly preferred embodiment of the pallet changing system is one in which the counter element is guided in a bore in a housing of the clamping device and is subjected to a force directed towards the clamping pin by means of at least one spring element, for example a compression spring. This makes it possible for the elastically mounted counter element to protrude beyond the support surface of the counter table or the contact surface of the mineral cast plate in the pressure-free state of the clamping device, which can be actuated by means of a liquid and/or gaseous medium. This means that the counter element, which is integrated either in the counter table or in the mineral cast plate, protrudes by a small amount, for example 1 mm, beyond the support surface or the contact surface. When the mineral cast plate is moved onto the counter table, the counter element is pushed back into the bore by the weight of the mineral cast plate. After the mineral cast plate has been moved to the position provided on the counter table, in which the counter element and the clamping pin are arranged essentially opposite each other, the counter element automatically moves out of the hole again, which secures the mineral cast plate against displacement. The mineral cast plate can now be fixed to the counter table by operating the clamping device.

Further advantageous embodiments emerge from the remaining subclaims.

The invention is explained in more detail below with reference to the drawing.

Figure 1 is a plan view and a sectional view of a first embodiment of a mineral cast plate;

Figure 2 is a sectional view of a first embodiment of a counter table;

Figure 3 a sectional view of a part

an embodiment of the pallet

ten changing system in the area of a clamping device;

Figure 4 is a side view and a plan view of part of another embodiment of a pallet changing system in the region of a transport device;

Figures 5A and 5B show a top view and a side view of an embodiment of the counter table and

Figures each show a plan view of a part 6A and 6B of an embodiment of the pallet changing system.

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The upper illustration in Figure 1 shows a top view of an embodiment of a mineral cast plate I which is part of a pallet changing system, for example for machine tools. The lower illustration in Figure 1 shows a cross section of the mineral cast plate according to the section line A-A shown in the upper illustration. The structure of the mineral cast plate, which is rectangular here, is generally known, so it will only be discussed briefly. The mineral cast plate comprises cover plates 3 and 5 which form the top and bottom. Between the cover plates 3, 5, a spacer 7 is inserted for each threaded and fitting hole for fastening a holder for the workpiece, for example. The front sides of the cover plates 3, 5 are covered with strips 9 which are preferably also made of sheet metal. The space enclosed by the cover plates 3, 5 and the strips 9 is cast with mineral cast II, thereby forming a solid unit. As an alternative to the cover plates 3, 5, preferably thin-walled cast plates can also be used. The mineral cast plate 1 has comparable damping properties to a solid cast plate, but the weight of the mineral cast plate is, depending on the design, only about half as much as that of a plate made of gray cast iron. The durability and precision of the cover plates 3, 5 are comparable to a solid gray cast iron plate. Using higher-alloyed sheets for the top and bottom of the mineral cast plate 1 can even make the surfaces of the cover plates 3, 5 more scratch-resistant.

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The cover plates 3, 5 and strips 9 as well as the mineral casting 11 are therefore firmly glued together due to the manufacturing process. The mineral casting plate 1 is given additional stability by the metal spacers 7. As mentioned, threaded holes or dowel pin holes can be made in these as required in order to obtain conventional perforated grid plates. In this embodiment, a total of two housing bells 13 are inserted into the mineral casting plate 1, each of which accommodates a movable clamping pin 14. The clamping pins, which each interact with a counter element integrated in a counter table (not shown in Figure 1), are part of a clamping device 15 or 15 ·. The structure of such clamping devices is basically known, so that it will only be discussed briefly below. The mineral casting plate 1 is manufactured in such a way that the finished, ground underside 17 of the mineral casting plate 1, which forms a contact surface, is flush with the edge of the housing bells 13. The lower end of the clamping pin 14 is set back slightly from the underside 17 of the mineral cast plate; it therefore does not protrude beyond the underside 17. This arrangement of the clamping pin 14 ensures a high level of security against damage to the clamping pin.

It has been shown that at least two clamping pins 14 are necessary for the clear positioning of the mineral cast plate on a counter table (not shown in Figure 1). For larger mineral cast plates, for reasons of stability and

The number of clamping pins can be increased accordingly for better force introduction. The centering rings 19 in the housing bells 13 are designed differently in order to avoid mechanical overdetermination. Only one clamping pin per mineral cast plate is therefore position-determining. The other clamping pins only determine the rotational position of the mineral cast plate and are preferably designed in such a way that they allow a change in the length of the mineral cast plate due to a change in temperature. The position-determining clamping pin is expediently marked with a marking.

The housing bell 13 is glued directly into a recess or opening in the mineral cast plate or cast into the mineral cast plate. A housing for screwing in the housing bell 13 that accommodates the clamping pin 14 is dispensed with here in order to achieve greater accuracy in positioning the housing bell and to achieve a low overall height of the mineral cast plate. In order to ensure that the clamping pin 14 of the housing bell 13 remains movable, the top of the clamping pin must be protected by a cover 21 that is firmly connected to the housing bell 13 before it is glued or cast into the mineral cast. The cover 21 is only provided for the clamping device 15 shown on the left side in Figure 1. In this embodiment of the clamping device, the clamping pin is no longer replaceable when cast in. In the clamping device 15', even when installed, the clamping pin is

In the locked state, the clamping pin 14 can be replaced by providing a bore 23, here a through-bore, which can be closed with a removable plug 25 on the top side of the mineral cast plate 1. The plug 25 shown in Figure 1 is connected to the housing bell 13 by means of fastening means 27, here screws.

For special applications for the assembly of defined clamping devices, it is not necessary to produce complete perforated grid plates, i.e. mineral cast plates. In these cases, it is sufficient to insert spacers 7 into the mineral cast plate only at the desired locations, for example for fastening screws and locking dowel pins. The fewer spacers 7 that are installed in the mineral cast plate, the greater the weight advantage compared to a solid metal cast plate. With perforated grid sections of 50 mm, a weight advantage of almost 50% is achieved compared to a normal perforated grid plate made of gray cast iron. With hole grid spacings of 40 mm, the weight reduction is approximately 40%. The arrangement of the clamping pin with the housing bell is expediently carried out in the mineral cast plate in such a way that as few grid positions as possible of a standard perforated grid plate are lost. Individual adaptation can be made here by appropriately adjusting the bell size. It is important to ensure that the size of the housing bell is sufficient to withstand the clamping forces that are transmitted via the clamping pin into the mine.

· · ■

ral cast plate to be safely transferred over the bonding point.

Figure 2 shows a sectional view of an embodiment of a counter table 29 to which the mineral cast plate 1 described with reference to Figure 1 can be fastened by means of the clamping pins 14. The counter table can be attached to a machine table, for example a machine tool. In another embodiment, the counter table 29 is formed by the machine table itself. In order to fix the mineral cast plate to the counter table 29, several counter elements 31 are integrated into the counter table 29. These each comprise a housing 33 into which a bore is made. A locking means 35 is slidably guided in this bore, which is subjected to a force by means of a spring element (not shown in Figure 2), which acts in the direction of the support surface 37 on which the mineral cast plate rests with its underside when the pallet changing system is assembled. Connecting lines are connected to the housings 33 of the counter elements 31, which are inserted/cast into the counter table 29 made of mineral cast. A first connecting line 39 is used for clamping and a second connecting line 41 is used for releasing the clamping devices 15, 15 ¹ . A third connecting line 43 is used for relief. In total, only three hydraulic and/or pneumatic connections are provided on the counter table 29.

-14-

When using multiple clamping devices or counter elements, the positioning of the housings 3 3 in the counter table 29 must of course be carried out with the corresponding position tolerance. For this purpose, suitable gauges are required when inserting the housings 3 3 into the counter table 29 during the manufacturing process. If desired, a cover plate 45, preferably made of steel, glued to the mineral casting can be provided on the top of the counter table - as shown in Figure 2. High-alloy steel or even a hardened plate can be used here too. These materials have advantages over a known T-slot table made of gray cast iron.

In another embodiment, not shown in the figures, the counter table is made of metal, so that the counter elements of the clamping devices and the connecting lines have to be incorporated into the counter table.

Figure 3 shows part of an embodiment of a pallet changing system, namely a mineral cast plate 1, which rests with its underside 17 forming a contact surface on a support surface 37 of a counter table 29 (not shown in detail). A clamping pin 14 is integrated into the mineral cast plate 1 and a counter element 31 is integrated into the counter table 29, which are part of a further embodiment of the clamping device 15 described with reference to Figures 1 and 2. Figure 3 shows a spring element 47 which the locking means 35

-15-

with a force directed towards the clamping pin 14. In the functional position of the clamping device 15 shown in Figure 3, it is in a pressureless state, i.e. the connecting lines 39 and 41 are pressureless. As a result, the locking means 35 is raised by the spring element 47 with a small force, so that the locking means protrudes from the support surface 37 by approximately 1 mm to 2 mm.

The catch area of the clamping device 15, i.e. the play between the locking means 35 and a recess 49 in the housing bell 13, is approximately 1 mm. The mineral cast plate must therefore be aligned relatively precisely on the counter table 29 before the clamping process can be initiated. If the counter table is loaded manually, this can be done using stops. However, these should be retractable or foldable so that the advantage of the smooth support surface of the counter table for chip disposal is retained. In another embodiment, not shown in the figures, the stops can be automatically and/or manually retracted and extended into the counter table or folded in or out using pneumatically, hydraulically and/or mechanically actuated means. Furthermore, if the counter table is loaded manually, appropriate markings on the support surface 37 can provide assistance for positioning the mineral cast plate.

The positioning of the mineral cast plate on the counter table is carried out using the tools shown in Figures 1

I · · ■

· I

-16-

to 3, which comprises the locking means 35 raised by the spring element 47, which protrudes from the support surface 37 when the clamping device is not under pressure (neither clamping nor relaxing). The mineral cast plate 1 is pushed over the counter table in the relaxed position of the clamping device and positioned approximately in the correct position (assisted by the markings on the counter table). The relaxed position is then released and the spring element 47 attempts to push the locking means 35 into the recess 49 in the housing bell, preferably formed by a pre-centering cone. If the mineral cast plate is not positioned precisely enough, this will not succeed, but the mineral cast plate can still be moved manually until the locking means 35 has engaged in the pre-centering cone. This means that further displacement of the mineral cast plate on the counter table is no longer possible. If the first connecting line 39 is now subjected to a pressurized medium in order to couple the counter element to the clamping pin, the locking means 35 is completely pushed into the housing bell 13 and thereby precisely positions the mineral cast plate, namely before the clamping pin 14 is finally clamped via balls 51 of the counter element 31.

Another possibility to carry out pre-centering without using a spring element interacting with the locking means is to apply a relatively low pressure to the first connecting line 39, which leads to

the locking means is only raised by a small amount if it is positioned in the centering cone. With this centering method, when using several counter elements that can each be coupled with a clamping pin, their first connecting lines 39, which are pressurized with a medium to couple the counter elements to the clamping pins, must be hydraulically decoupled from one another, since otherwise, when one of the locking means is centered in a centering cone, the locking means is completely extended due to the pressure, while the other locking means would remain in their basic position.

The arrangement described above offers considerable advantages for both manual and automatic assembly of mineral cast plates. In order to place a mineral cast plate 1 on the counter table 29, all that is needed is a plate storage unit, a conveyor belt or the like, which is at the same height as the counter table 29, over which the mineral cast plate 1 can then be pushed onto the counter table 29. This can be done manually, but also using handling machines for unmanned operation. Since the mineral cast plate 1 does not have to be lifted in this embodiment, it can be moved from the plate storage unit to the counter table by sliding it using push/pull rods of the handling device. In the simplest case, handles or eyelets on the mineral cast plate are not even required for this, since the sliding movement is carried out by pressure on an end face of the mineral cast plate 1. If the same

-18

If a mineral cast plate 1 arranged on the counter table is to be removed with the same push/pull rod from the side on which the plate storage is arranged, a corresponding docking device (eyelet, locking hook or the like) must be provided on the front surface of the mineral cast plate 1. For larger workpieces and pallet weights, it is advantageous if the transfer section between the plate storage and the counter table 29 has corresponding roller conveyors so that the displacement movement is facilitated.

Figure 4 shows a side view and a top view of part of an embodiment of a pallet changing system in the area of a plate storage 53, which is arranged at a distance from a base 54 on which the counter table 29 is located. In order to realize automatic loading of mineral cast plates on the counter table 29, a transport device 55 is provided, which comprises a slider 59 that can be displaced in the direction of a double arrow 57 and is designed as a push/pull rod in this embodiment. The slider 59 has a docking device 61 at its end, by means of which it can be coupled to the mineral cast plate 1. In the space between the plate storage 53 and the base 54, a transfer table 63 is provided, which is attached to the base 54 purely as an example. As can be seen from Figure 4, the support surface of the counter table 29, that of the transfer table 63 and that of the plate storage 53 are at the same height, so that the mineral cast plate 1 can be moved by means of the slide

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59 can be pushed from the disk storage 53 onto the counter table 29 and pulled down again.

In a further embodiment not shown in the figures, the transfer table 63 is formed by only two narrow rails or roller conveyors, which can ensure that any chips that are carried away are safely and specifically disposed of from the machine table. To ensure that no chips that remain there get jammed between the mineral cast plate and the machine table when the mineral cast plate is pushed onto the machine table, the rails of the transfer table are inclined at a preferably small angle to the support surface of the machine table, such that when the mineral cast plate is pushed from the rails onto the support surface of the machine table, the lower front edge of the mineral cast plate safely pushes the chips on it in front of it as it slides onto the machine table.

If no pallet stops are provided, appropriate markings are made on the counter table, with the help of which mineral cast plates that are manually placed or pushed onto the counter table can be positioned quickly and precisely. The markings 65 shown in Figures 6A and 6B, for example color-contrasting elements, such as stripes, can be cast into the mineral cast. If there is a steel cover on the top of the counter table, the markings 65 can be made by etching reference lines.

lines that indicate the outer edges of the mineral cast panels used.

Since mineral cast plates are usually equipped with more than one clamping pin 14 and thus the counter table usually also has four or more counter elements, different pallet formats can be used as desired. For example, it is possible to place either a large mineral cast plate with four clamping pins (Figure 6A) or two small mineral cast plates, each with two clamping pins (Figure 6B) on a counter table with four elements. This flexibility allows pallet sizes to be used as required and, in the case of smaller workpieces, multiple clamping on the machine. This combination option is not provided for in known pallet systems and offers a further advantage of the pallet changing system according to the invention. The advantage of the underside of the mineral cast plate resting flat on the support surface of the counter table leads to increased stability compared to other known pallet changing systems with regard to the introduction of force into the counter table or into the base of the machine and thus also to significantly improved damping properties. If the lifting becomes too difficult due to the high adhesive forces between the mineral cast plate and the counter table, for example due to moisture, the underside of the mineral cast plate can be partially exposed by grinding in channels crosswise. The penetration of cooling liquid into these

-21 -

Channels during workpiece machining do not cause any problems as the clamping devices or counter elements are self-sealing. This means that the mineral cast plates can also be used in the bath without the need for additional seals. This is particularly important when machining workpieces using sinking erosion.

Although, if the underside of the mineral cast plate and the support surface of the counter table are sufficiently flat, the flat contact between the counter table and the mineral cast plate brings advantages in terms of force application and vibration damping, even with larger mineral cast plates, only sliding tracks in the counter table can be used. This means that in the area of the counter elements 31 there is a continuous web 67 on which the mineral cast plate is moved on the counter table. The counter table is recessed accordingly between the webs 67, as shown in Figure 5A. The counter table shown in Figure 5B has a flat support surface.

To ensure that the counter table is really free of chips, a scraper rubber, a scraper brush or something similar can be moved over the counter table before the mineral cast plate is placed on the counter table.

If the counter elements are installed in a movable machine table, it is advisable to place the

-22-

The guides and spindle drive must be designed accordingly. This design has significant advantages, particularly for movable machine tables, due to the relatively low mass to be moved. Furthermore, by integrating the counter element into the machine table, i.e. when the counter table is formed by the machine table itself, it is possible to achieve a low overall height for the plate changing system, which can also improve the rigidity of the machine itself.

What all embodiments described with reference to the figures have in common is that the counter element can also be integrated into the mineral cast plate and the clamping pin can be integrated into the counter table.

Claims (24)

1. Pallet changing system, in particular for machine tools, which comprises at least one mineral cast plate ( 1 ) which can be fastened to a counter table ( 29 ) by means of at least one hydraulically and/or pneumatically actuated clamping device ( 15 ; 15 '), wherein the clamping device ( 15 ; 15 ') comprises a clamping pin ( 14 ) and a counter element ( 31 ) which interacts with the clamping pin ( 14 ) in the coupled state, and wherein the clamping pin ( 14 ) and the counter element ( 31 ) in the uncoupled state do not protrude beyond the contact surface (underside ( 17 )) of the mineral cast plate ( 1 ), with which the plate rests on a support surface ( 37 ) of the counter table ( 29 ), or the support surface ( 37 ) of the counter table ( 29 ). 2. Pallet changing system according to claim 1, characterized in that the counter table ( 29 ) is mounted on a machine table or is formed by the machine table itself. 3. Pallet changing system according to claim 1 or 2, characterized in that the counter element ( 31 ) comprises a locking means ( 35 ) which is displaceably guided in a bore made in a housing ( 33 ) of the clamping device ( 15 ; 15 ') and which is subjected to a force directed towards the clamping pin by means of at least one spring element ( 47 ). 4. Pallet changing system according to claim 3, characterized in that in the pressureless state of the clamping device ( 15 ; 15 ') the elastically mounted locking means ( 35 ) projects beyond the support surface ( 37 ) of the counter table ( 29 ) or the contact surface (underside ( 17 )) of the mineral cast plate ( 1 ). 5. Pallet changing system according to one of the preceding claims, characterized in that the locking means ( 35 ) is a centering sleeve. 6. Pallet changing system according to one of the preceding claims, characterized in that the clamping pin ( 14 ) is arranged on the mineral cast plate ( 1 ) and the counter element ( 31 ) is arranged on the counter table ( 29 ). 7. Pallet changing system according to one of the preceding claims, characterized in that the clamping device ( 15 ; 15 ') is self-sealing, so that no additional seals are required between the mineral cast plate ( 1 ) and the counter table ( 29 ) or the clamping device ( 15 ; 15 '). 8. Pallet changing system according to one of the preceding claims, characterized in that the counter table ( 29 ) is a mineral cast plate into which the housing ( 33 ) receiving the locking means ( 35 ) and hydraulic, pneumatic and/or other connecting lines connected to the housing ( 33 ) are cast. 9. Pallet changing system according to claim 8, characterized in that on the side of the counter table ( 29 ) facing the mineral cast plate ( 1 ), a cover plate ( 45 ) preferably made of steel is attached to the counter table, preferably by means of a material connection. 10. Pallet changing system according to one of the preceding claims, characterized in that auxiliary markings are provided for positioning the mineral cast plate ( 1 ) on the support surface of the counter table ( 29 ). 11. Pallet changing system according to claim 10, characterized in that the auxiliary markings in a counter table formed by a mineral cast plate are formed by preferably colored stripes cast into the mineral cast plate. 12. Pallet changing system according to claims 9 and 10, characterized in that the auxiliary markings are formed by markings etched into the steel cover plate. 13. Pallet changing system according to one of the preceding claims, characterized in that several clamping devices are provided and that only the clamping pin of a clamping device determines the position for the mineral cast plate. 14. Pallet changing system according to claim 13, characterized in that the side and/or corner of the mineral cast plate ( 1 ) on/at which the position-determining clamping pin ( 14 ) is located is marked by a marking. 15. Pallet changing system according to one of the preceding claims, characterized in that a plurality of mineral cast plates can be fastened to the counter table with the aid of at least one clamping device ( 15 ), wherein the size and/or the shape of the contact surfaces of the mineral cast plates ( 1 ) are the same or different. 16. Pallet changing system according to one of the preceding claims, characterized in that at least one transport device is provided for feeding the counter table, which comprises a displaceable slider, with the aid of which the mineral cast plate can be pushed from a plate storage device, conveyor belt or the like onto and over the counter table. 17. Pallet changing system according to claim 16, characterized in that the slider can be coupled to the mineral cast plate ( 1 ) in such a way that the latter can be pulled down from the counter table. 18. Pallet changing system according to one of the preceding claims, characterized by a housing bell ( 13 ) which receives the clamping pin ( 14 ) of the clamping device ( 15 ; 15 ') and which is cast into the mineral cast plate ( 1 ) or glued into an opening in the mineral cast plate ( 1 ). 19. Pallet changing system according to claim 18, characterized in that the opening is a through hole whose diameter is larger than the clamping pin diameter, and that the through opening is closed with a plug ( 25 ) on the side facing away from the counter table. 20. Pallet changing system according to claim 19, characterized in that the plug ( 25 ) can be detachably fastened to the mineral cast plate ( 1 ). 21. Pallet changing system according to one of the preceding claims, characterized in that the upper and lower sides of the mineral cast plate ( 1 ) are formed by cover plates ( 3 , 5 ) which consist of a high-alloy and/or hardened steel. 22. Pallet changing system according to one of the preceding claims, characterized in that the cover plate ( 45 ) consists of a high-alloy or hardened steel. 23. Pallet changing system according to one of the preceding claims, characterized in that stops for the mineral cast plate ( 1 ) are integrated in the counter table ( 29 ), which stops can be automatically and/or manually moved in and/or extended/folded in and/or out into the counter table by means of pneumatically, hydraulically and/or mechanically actuated means. 24. Pallet changing system according to one of the preceding claims, characterized in that the support surface ( 37 ) of the counter table ( 29 ) is provided with recesses, wherein a preferably continuous web ( 67 ) is formed between two recesses, in the region of which the counter element ( 31 ) is arranged.