DE29620915U1 - Actuator with adhesive device - Google Patents

Description

Actuator with holding device

The invention relates to an actuator or a tool, handling or measuring machine according to the preambles of claims 1, 2, 4 or 5.

Linear or rotary drives with stators or rotors with flat running surfaces are known in many different forms. The rotor moves relative to the stator.

Air bearings are usually used in such drives, with an air cushion being formed between the stator and the rotor. In order to ensure mechanically rigid guidance, this air cushion is usually pre-tensioned by ensuring a magnetic pre-tension between the stator and the rotor.

In machining stations, a controlled relative movement must be carried out between the tool and the workpiece in order to be able to machine the workpiece at the desired points, for example by cutting or simply measuring or handling it. Depending on the workpiece and the production process, only the workpiece or the tool is moved on machine tools, or a combination of both movements takes place. Especially with large and heavy workpieces, it is advantageous to essentially only move the tool while the workpiece remains stationary.

From the previously unpublished German patent application with the official file number P 19641879.8, a 3-coordinate actuator is known which works in overhead operation, whereby the adjustment in the X and Y directions is carried out by a so-called planar drive, while another linear drive is provided for the Z direction. The stator of the planar drive provided for the X and Y directions has the shape of a large, flat plate with a correspondingly flat running surface, which the running surface of the rotor forms the aforementioned thin air gap.

is assigned. The stator is arranged above the rotor and the tool "hangs" downwards and is attached to the rotor. Such a design has the advantage of replacing a gantry machine in its function, but in doing so it has to move smaller masses and can achieve greater rigidity and thus machining accuracy, since the gantry is saved. However, a relatively large distance must be provided between the running surfaces and a base area of the machine tool so that workpieces that have a relatively large extension in the vertical direction can also be machined. This means that large moments must be absorbed by the running surfaces or, more precisely, by the air cushion, which is pre-tensioned by the magnetic force between the stator and the rotor. Although it is in the nature of the linear drive to provide high attractive forces and thus ensure a magnetic preload acting on the air cushion, this is sometimes not enough to prevent the rotor from lifting off the stator because the long lever arm causes forces acting on the tool in the X and Y directions to result in significant moments, especially in the case of shock loads. These moments must be absorbed by the running surfaces.

Even greater problems with detachment arise with inclined and especially with vertically arranged running surfaces. In this case, moments with a detachment effect arise due to the dead weight. In addition to the dead weight-related moments, the aforementioned moments arise due to external forces acting on the tool and due to the moments of inertia that occur when the runner accelerates or decelerates.

To make matters worse, the magnetic preload can also be impaired if the running surfaces become dirty/ and even medium forces can cause the rotor to lift off due to the long lever arm.

The same applies to rotary drives with a

disc-shaped runner and rotor. These problems also occur

not only in overhead operation, but also in

normal machines where the stator is below the

rotor and thus on the stator
rests instead of hanging on to it.

The invention is based on the object of creating an actuator or a tool, handling or measuring machine of the type mentioned at the beginning, whereby a secure adhesion of the

rotor on the stator is guaranteed in all operating conditions.

This is achieved according to the invention by the actuators with the

Features in the characterizing part of claim 1 or 4 and by the tool, handling or measuring machine with the
Features in the characterizing part of claim 2 or 5
achieved. Advantageous further training is available in the
Described in the subclaims.

Advantageously, the linear motor drive system is designed as a planar drive, which allows a 2-coordinate adjustment
Alternatively, only one adjustment direction may be sufficient, for example in the X-direction or Y-direction.

Advantageously, the runner is essentially rectangular
and provided with magnetic strips along all four edges, which surround the runner, so to speak. However, it is also possible to use several discrete individual magnets instead of magnetic strips, which are arranged at a distance from one another along at least one edge.

Advantageously, a scraper is arranged along at least one edge of the runner, which further advantageously consists essentially of felt and can, for example, have the shape of a strip with a cross-sectional area of approximately 20 x 3 mm. However, any other materials such as plastic, brushes, foam or rubber are also possible.

To keep the running surfaces of the rotor and stator clean, cleaning grooves are advantageously provided around the rotor, in which dirt and abrasion can collect. These cleaning grooves can be provided independently of the holding magnet arrangements, i.e. even if the rotor is not provided with holding magnet arrangements at all. The cleaning grooves can be integrated into the housing of the rotor or alternatively be provided on the outside of an edge of the rotor. These cleaning grooves can be provided with various devices for cleaning the running surfaces, advantageously with a scraper and/or an electrostatic element and/or a filter magnet. Dirt particles can be attracted by the electrostatic element and the filter magnet. The cleaning grooves are particularly advantageously connected to a suction channel through which dirt can be sucked out. However, it is also possible to do without such a suction channel and to clean the electrostatic element and/or the filter magnet from time to time.

A particularly advantageous combination arrangement can be provided by combining the magnetic strips and scrapers to form a sandwich package and pressing them against the edge of the runner using an L-profile strip with screws. This makes it possible to create a combination of scraper and magnet using simple means. Instead of the L-profile strip, the scraper and magnet can also be screwed together as a sandwich to the peripheral edge of the runner using a plurality of screws arranged at a distance from one another.

Since in rotary drives of the aforementioned type there is often congruence between the rotor and stator and no edge is provided surrounding the effective rotor or stator surfaces, it is advantageous to either provide an iron ring enclosing the outer circumference of the rotor or stator, or to provide a central, so to speak hub-like, iron plate on the rotor or stator, and as

A corresponding counterpart, magnetic strips or discrete magnets, or a large central magnet, can be provided. However, it is also possible to make the rotor or stator larger in diameter than the effective running surfaces, which means that a separate iron ring can be omitted, for example.

If magnetic strips are used, a particularly advantageous embodiment is a magnet designed as a sandwich magnet, with a magnet arranged between two return plates. This has the advantage of enabling a large force of attraction using a relatively small magnet. The magnet is also advantageously set back slightly compared to the return plates. This prevents the magnet from coming into direct contact with the stator and thus contributing to damage to the stator or the magnet. In addition, the set-back magnet between the return plates creates a groove, the side walls of which are formed by the return plates themselves and the bottom by the magnet. Dirt can collect in this groove, and metal chips in particular can collect in it, which are then attracted and held by the magnet or the return plates. The entire lamella magnet arrangement does not lose any of its force of attraction because most of this runs over the return plates.

The magnet is advantageously designed as a NdFeB magnet in order to ensure a high attractive force in a small installation space. Several magnets and more than two return plates can also be provided in order to ensure a stronger attractive force without having to use larger and therefore more expensive magnets.

In addition to the magnet, an aluminum spacer bar is advantageously arranged between the return plates, which can be used for fastening. The dimensions of such a magnet arrangement can be such that the magnet itself has a cross-section of '5x7 mm, the two return plates

a cross-section of 25 x 3 mm and the spacer bar made of aluminium a cross-section of 5 x 12 mm. Such a sandwich magnetic bar develops an attractive force of 40 N per cm compared to an iron stator, even with a gap height of 0.1 mm.

It has also proven advantageous to coat the magnet on its free side facing the stator with a protective layer of varnish. This protects the magnet against corrosion and brittle fracture, while the attractive force does not diminish, as this is mainly transmitted via the return plates. An air gap of 0.1 mm to 0.2 mm is advantageous between the running surfaces of the stator and the end faces of the iron return plates facing the stator.

The air gap between the running surfaces of the stator or rotor is advantageously only 10-20μπα.

A brief summary of the main points of the invention is given below:

Rotors of hybrid stepper motors are magnetically preloaded with respect to the stator due to the permanent magnets installed between the motor coils. This makes it possible to mount linear, planar and rotating direct drives using aerostatic air cushions between the rotor and the stator surface (= running surface). These air bearings can be subjected to both compression and tension. This makes it possible to use the rotors in any spatial position, i.e. even overhead, provided that the static and dynamic forces perpendicular to the running surface do not exceed the net attractive force between the rotor and the stator. The net attractive force is the force of the magnetic attractive force (= preload) minus the force that the air cushion generates in the gap between the rotor and the running surface (= stator) against the magnetic attraction. Due to the usually small air gap of 10-20 μηη the attractive forces are very large, since a high magnetic flux density (induction) is created between the

permanent magnet and current-excited motor coils of the rotor on the one hand and the stator made of soft iron on the other. The housing of the rotor is made of a non-magnetic material, e.g. aluminum, in order to avoid magnetic influences. In order to achieve the highest possible power output, it is packed as densely as possible with motor coils, so that the running surface is filled as far as possible by the end surfaces of these motor coils. In order to make rotors, which are subjected to such stresses due to their spatial position by their own weight, by dynamic or external forces that tensile forces also occur which tend to lift the rotor from the running surface, more resistant to tensile stress, it is proposed to provide additional permanent holding magnets which increase the attractive force but do not act against the direction of movement of the rotor or only act to an insignificant extent. The adhesive effect must also be maintained when the rotor is de-energized, which is why permanent magnets are primarily suitable for this. By adjusting the air pressure, the air bearing can be adapted to the increased magnetic preload.

Such holding or clamping magnets must also be arranged in such a way that they do not affect the operation of the actual drive motor coils and increase the dimensions and weight of the rotors as little as possible. If the dimensions of the clamping surfaces of the magnet and the return plates are integer multiples of the stator pole pitch (in one direction for linear drives, in two directions for surface or planar drives), the resulting force effect in the stator plane, i.e. in the direction of movement (perpendicular to the pole structure), is constant to a first approximation. In principle, all types of clamping magnets that are usually used are suitable: clamping magnet disks, gripper rods, pot magnets and U-magnets. The best types, however, are sandwich clamping magnet strips. These are simply constructed, have a small width, develop large forces per unit length and are easy to attach to the side of existing rotors. Depending on the forces acting on the rotor, the clamping magnet strips can be attached to one or more sides without the rotor having to be fundamentally changed.

Simple threaded holes are usually sufficient to attach magnetic strips as required. The outer layer is, due to the leverage effect, particularly good against tipping moments that act on the rotor. A sandwich magnet consists of one or more permanent magnet strips lined up next to one another, on which two iron return plates are attached (preferably by gluing) on the sides (on the pole faces). The magnetization direction therefore runs perpendicular to these. The return plates can be made higher to make them easier to attach. At the free point protruding above the magnets, they are connected by a strip of non-magnetic material, e.g. aluminum. In this area, they can be screwed to the rotor. It is also possible to leave gaps between the magnets and to attach fastening screws through the return plates. The strongest permanent magnet materials, especially NdFeB, are known to be difficult to work with.

The magnet can be slightly recessed from the holding surface. In this gap, it can be protected by a protective coating, e.g. paint. This air gap does not reduce the attractive force, as the magnetic flux runs through the return plates into the stator. These return plates are mounted so that they are only 0.1-0.2 mm away from the running surface (= holding surface). This does reduce the holding force somewhat, but it does protect the running surface of the stator against scratching and allows air to escape unhindered from the air bearing gap. In addition, any metallic dust that may be present on the running surface collects there. This therefore causes the holding magnet to have a cleaning effect.

A wiper made of felt, for example, can also be attached to the outside, which is held to the return plate by an angle or a band made of non-metallic material. The other types of holding magnets mentioned can also, in principle, be attached to the outside of the rotor.

All types of magnets can also be inserted into the housing

of the runner so that their adhesive surface protrudes from the running surface. However, this is less advantageous because a high level of flatness is required in the area of the running surface, so the return plates must be ground together with the runner, unless they are set back far enough. However, depressions in the running surface would in turn impair the effectiveness of the air bearing. Holding magnets can also be designed so that they can be switched off or amplified electrically, or can be switched on and off using suitable mechanisms to make it easier to remove the runner. To keep the running surfaces clean, grooves can also be made in the housing of the runner in which scrapers and/or electrostatic and/or magnetic dust compartments are installed. These cleaning grooves can also be combined with the holding magnets.

Dust can also be extracted from the cleaning grooves, whereby the suction effect of the compressed air-operated Venturi tube can be utilized, since compressed air is always supplied for the air bearings. This avoids the need for a separate suction pump.

The invention is explained below using preferred embodiments with reference to the drawing. The drawing shows:

Figure 1 is a schematic side view of the machine operating in overhead mode; Figure 2 is a partial section showing the magnetic strip;

Figure 3 shows a partial section similar to Figure 2, with a scraper additionally provided; Figures 3a to 3b show sections or partial sections of the magnetic strip;

Figure 4 is a side view of the runner edge along which a plurality of magnetic strips are arranged; Figure 5 is a perspective view of the magnetic strip in sandwich construction;

Figure 6 shows schematically a first construction of a cleaning groove;

Figure 7 schematically shows a second construction of a

cleaning groove;

Figure 8 shows schematically a third construction of a cleaning groove;

Figure 9 is a schematic bottom view of the rotor, showing a circumferential cleaning groove;

Figure 10 schematic bottom views of the rotor with different magnet arrangements;

Figure 11 is a cross-sectional view of a conventional hybrid stepper motor linear drive structure;

Figure 12 is a side view of a conventional design of a linear actuator with air bearings;

Figure 13 is a bottom view of a conventional planar drive with air bearings;

Figure 14 is a perspective, schematic arrangement 15 of a rotor-stator arrangement of a planar drive;

Figure 15 is another schematic bottom view of a conventional planar drive rotor;

Figure 16 shows a rotary drive in a bottom view of the rotor and a sectional view through the rotor and stator; Figure 17 shows a schematic, perspective view of another embodiment of the actuator in a vertical arrangement.

As Figure 12 shows schematically, a conventional planar drive or linear drive with air bearings has a rotor 1, which is movable relative to a stator 2. An air gap 3 is formed between the rotor 1 and the stator 2. Figure 11 shows such an arrangement in somewhat more detail, from which a permanent magnet 4, windings 5, a nozzle 6 for an air bearing, and lines 7, which illustrate the magnetic flux, can be seen. Figure 14 shows such an arrangement in perspective, from which the pole pitch of the stator can also be clearly seen. Figure 13 shows a bottom view of a rotor with air nozzles 8, whereby this rotor is suitable for a planar drive, i.e. can be moved in the X and Y directions. Another arrangement with somewhat more details, also in a bottom view of the rotor, is shown in Figure 15. Such drives basically function as

Stepper motors that allow very precise positioning depending on the input pulses.

Figure 1 shows a machine which has several runners 1 which carry different tools 9. The various runners can be moved on a stator 2 in the X and Y directions. The machine can be used for machining, as a handling machine or as a measuring machine. The workpiece can be clamped onto a base plate 10, for example. The machine stands on the floor 11.

Around the edges of the rotor 1, which in this embodiment has a rectangular base, holding magnet arrangements 12 are provided, which have return plates 14 in addition to a holding magnet 13. In addition, a spacer bar 15 is provided. The holding magnet arrangement 12 consisting of spacer bar 15, magnet 13 and return plates 14 is attached to the outer edge 17 of the rotor 1 by means of a countersunk screw that can be screwed into a threaded hole 16. In the return plates

14 or the spacer bar 15 are provided with corresponding through holes for receiving the countersunk head screw.

A corresponding embodiment is shown in Figure 3, wherein a stripper 18 is additionally provided, whereby the unit consisting of magnet 13, return plates 14, spacer bar

15 and scraper 18 formed holding magnet arrangement 12 by means of an L-profile-shaped strip 19 on the outer edge of the

30. Runner 1 is attached.

According to the embodiment according to Figure 3a, the magnet is set back by a dimension M relative to the return plates 14, which results in a groove 20 between the side walls of the return plates 14 and the magnet 13, which forms the bottom of the groove, so to speak. On the one hand, dirt particles can collect in this groove, in particular metal dust, which can be attracted by the magnet 13, and

On the other hand, the groove prevents the magnet from coming into contact with the stator 2, which could damage both the stator and the magnet.

In the embodiment shown schematically in Figure 3b, the magnet 13 is additionally coated with a layer of lacquer 21. This does not reduce the attractive force because the magnetic flux flows over the return plates 14, which define only a narrow gap, for example 0.1 to 0.2 mm wide, relative to the stator 2. Figure 3c again shows the structure of the holding magnet arrangement 12, essentially consisting of return plates 14, magnet 13 and spacer strip 15.

Figure 4a shows a side view of the rotor, from which it can be seen that several holding magnet arrangements in strip form, in this case 4 pieces, are arranged next to each other along the edge of the rotor. Figure 4b shows a schematic section through one of the holding magnet arrangements for explanatory purposes only.

Another embodiment of the holding magnet arrangement is shown in Figure 5, where two magnets 13 are arranged between three return plates 14 in a so-called sandwich construction. This arrangement enables a particularly high magnetic attraction force to be achieved without having to use permanent magnets with large dimensions, which would be significantly more expensive.

Figure 9 shows a circumferential cleaning groove 22, whereby the runner, in this embodiment, has a square running surface. According to the embodiment shown in Figure 6, a scraper 18 is mounted in the cleaning groove 22 by means of an L-shaped profile 23. In addition, an electrostatic attraction element 24 and a filter magnet 25 are arranged in the cleaning groove, which serves to hold metal dust, while the electrostatic attraction element 24 serves to hold other dusts. A suction channel 26 is also provided. The scraper is on the outside of the runner 1 in this embodiment.

13 ·· ·

in the cleaning groove 22. Figure 7 shows an inverse arrangement, so to speak, whereby the scraper is attached to the inside of the rotor or the cleaning groove and, in contrast to the embodiment shown in Figure 6, the filter magnet 25 and the electrostatic attraction element 24 are on the outside. A suction channel was omitted in this embodiment. Figure 8 shows an embodiment similar to Figure 7, but with an additional suction channel 26 and the electrostatic attraction element 24 in the form of a wire. Unlike the other embodiments, the filter magnet 25 is not embedded in the groove wall, but is attached to a groove shoulder. The holding magnets can be used independently of the cleaning grooves.

Figure 10 shows various arrangements and shapes for holding magnets, whereby in the embodiment shown top left and bottom right, holding magnet strips were used which are integrated into the housings of the rotors, while in the other two embodiments, different arrangements of discrete magnets 13 were chosen.

An embodiment with a rotary drive is shown in Figure 16, where the stator is surrounded by an iron ring 27 and the rotor 1 by a holding magnet arrangement in the form of a concentric circle, where the cross section of this holding magnet arrangement can be, for example, the cross section shown in Figure 3c, but is curved in the longitudinal direction in order to be mounted on the circular rotor.

Alternatively, discrete magnets 13 can be provided around the rotor or the stator, as shown in the bottom view of the rotor in Figure 16. A holding magnet arrangement 12 or an iron element 28 can also be arranged centrally, like a hub, in the core of the rotor 1 or stator 2.

Figure 17 shows another possible embodiment in which the stator 2 and, accordingly, the rotor 1 are vertical. The holding magnet arrangements 12 run around the outer edges of the stator 1 and are shown schematically. Figure 17 also shows a side view in which identical elements are designated with identical reference numerals. It can be seen that a force 29 acting on the tool transmits a moment to the rotor 1 with a relatively long lever arm, which moment is largely absorbed by the holding magnet arrangements 12.

Claims (25)

Expectations 1. Actuator, in particular for a tool, handling or measuring machine, with a linear motor drive system, which has a rotor with edges and a stator, which can perform a linear relative movement to each other, for which purpose the rotor is air-mounted on the stator, characterized in that at least along one edge of the rotor (1) holding magnet arrangements (12) are arranged, which increase the already prevailing force of attraction between the rotor (1) and stator (2) by several times, which is attributable to the nature of the linear motor drive system. 2. Tool, handling or measuring machine with a Actuator in the form of a linear motor drive system, which has a rotor with edges and a stator, which can perform a linear relative movement to one another, for which purpose the rotor is air-mounted on the stator, the rotor being arranged below the stator when viewed in the vertical direction or the running surfaces of the rotor and stator being inclined or vertical and being secured against detachment from the stator due to gravity or external force due to an attractive force attributable to the nature of the linear motor drive system between the rotor and stator, characterized in that holding magnet arrangements (12) are arranged at least along one edge of the rotor (1), which increase the attractive force that already prevails between the rotor (1) and stator (2) by several times, attributable to the nature of the linear motor drive system. 3. Actuator according to claim 1 or tool, handling or measuring machine according to claim 2, characterized in that the linear motor drive system is designed as a planar drive which allows a 2-coordinate adjustment. 4. Actuator, in particular for a machine tool, handling or measuring machine, with a linear motor-like rotary drive which has a rotor and a stator with a flat, circular disk-shaped rotor or stator surface, which can perform a rotary relative movement to one another, for which purpose the rotor is air-mounted on the stator, characterized in that holding magnet arrangements (12) are arranged around the circumference of the rotor (1) or stator (2) or centrally in the middle thereof, which increase the already prevailing force of attraction between the rotor (1) and stator (-2) attributable to the circular disk-shaped rotor or stator surface by a multiple. 5. Tool, handling or measuring machine with an actuator in the form of a linear motor-like rotary drive, which has a rotor and a stator with a flat, circular disk-shaped rotor or stator surface, which can perform a rotary relative movement to one another, for which purpose the rotor is air-mounted on the stator, the rotor being arranged below the stator when viewed in the vertical direction or the running surfaces of the rotor and stator being inclined or vertical and being secured against detachment from the stator due to gravity or external force due to an attractive force attributable to the nature of the linear motor drive system between the rotor and stator, characterized in that holding magnet arrangements (12) are arranged around the circumference of the rotor (1) or stator (2) or centrally in the middle thereof, which increase the attractive force between the rotor (1) and stator (2) that already prevails and is attributable to the nature of the circular disk-shaped rotor or stator surface by a multiple of increase. 6. Actuator according to claim 1 or 3 or tool, handling or measuring machine according to claim 2 or 3, characterized in that the rotor (1) is essentially rectangular and holding magnet arrangements (12) are arranged along all 4 edges. 7. Actuator according to claim 1 or 3 or 5 or tool, handling or measuring machine according to claim 2 or 3 or 5, characterized in that along at least one edge of the A wiper (18) is arranged on the rotor (1). 8. Actuator according to claim 7 or tool, handling or measuring machine according to claim 7, characterized in that the scraper (18) consists essentially of felt. 9. Actuator according to claim 7 or 8 or tool, handling or measuring machine according to claim 7 or 8, characterized in that the stripper (18) has the shape of a strip with a cross-sectional area of approximately 20 x 3 mm. 10. Actuator according to claim 1, 3 or 5 to 9 or tool, handling or measuring machine according to claim 2, 3 or 5 to 9, characterized in that in order to keep the running surfaces of the rotor (1) and stator (2) clean, cleaning grooves (22) are provided around the rotor (1), in which dirt and abrasion can collect. 11. Actuator according to claim 10 or tool, handling or measuring machine according to claim 10, characterized in that the cleaning grooves (22) are equipped with a scraper (18) and/or an electrostatic element (24) and/or a filter magnet (25). 12. Actuator according to claim 11 or tool, handling or measuring machine according to claim 11, characterized in that the cleaning grooves (22) are connected to a suction channel (26) through which dirt can be sucked off. 13. Actuator according to claim 7 or tool, handling or measuring machine according to claim 7, characterized in that the holding magnet arrangements (12) and strippers (18) are assembled to form a sandwich package and are pressed against the edge of the rotor (1) by means of an L-profile-shaped strip with screws. 14..Actuator according to claim 4 or tool, handling or measuring machine according to claim 5, characterized in that a concentric iron ring (27) is arranged around the outer circumference of the stator (2) or rotor (1), while a concentric holding magnet strip is arranged on the rotor (1) or stator (2) facing the iron ring (27), which is approximately congruent with the iron ring (27). 15. Actuator according to claim 4 or tool, handling or measuring machine according to claim 5, characterized in that a concentric iron ring (27) is arranged around the outer circumference of the stator (2) or rotor (1), while on the rotor (1) or stator (2) facing the iron ring (27) a plurality of holding magnets (13) are arranged opposite the iron ring (27) in the circumferential direction at a distance from one another. 16. Actuator according to claim 4 or tool, handling or measuring machine according to claim 5, characterized in that a round iron element (28) is arranged centrally in the core of the stator (2) or rotor (1), while a holding magnet (13) is arranged on the rotor or stator (2) facing the iron element (28) and is essentially congruent with the iron element (28). 17. Actuator according to claim 1 or 4 or tool, Handling or measuring machine according to claim 2 or 5, characterized in that the holding magnet device (12) is designed as a sandwich magnet, with a magnet (13) being arranged between two return plates (14). 18. Actuator according to claim 17 or tool, handling or measuring machine according to claim 17, characterized in that the magnet (13) is slightly set back from the return plates (14). 19. Actuator according to claim 17 or 18 or tool, handling or measuring machine according to claim 17 or 18, characterized in that the magnet (13) is a NdFeB magnet. 20. Actuator according to one of claims 17 to 19 or tool, handling or measuring machine according to one of claims 17 to 19, characterized in that in addition to the magnet (13) between the return plates (14) a 5. Spacer bar (15) made of aluminum is arranged. 21. Actuator according to one of claims 17 to 20 or tool, handling or measuring machine according to one of claims 17 to 20, characterized in that the magnet (13) has a cross-section of 5x7 mm, the two return plates (14) have a cross-section of 25 x 3 mm, and the spacer bar (15) made of aluminum has a cross-section of 5 x mm. 22. Actuator according to one of claims 17 to 21 or tool, handling or measuring machine according to one of claims 17 to 21, characterized in that the magnet (13) is coated on its free side facing the stator (2) with a protective layer (21) of varnish. 23. Actuator according to one of claims 17 to 22 or tool, handling or measuring machine according to one of claims 17 to 22, characterized in that an air gap of 0.1 mm to 0.2 mm exists between the running surfaces of the stator and the end faces of the iron return plates facing the stator. 24. Actuator according to claim 1 or 4 or tool, handling or measuring machine according to claim 2 or 5, characterized in that the air gap (3) between the running surfaces of the stator (2) or rotor (1) is 10 to 20 μιη. 25. Actuator according to claim 1 or 4 or tool, handling or measuring machine according to claim 2 or 5, characterized in that the actuator or the machine works in overhead operation.