ELECTROMAGNETIC ACTUATOR AND USE THEREOF

Abstract

In an electromagnetic actuator having a housing, two ferromagnetic pole shoes are distanced from each other and are rigidly connected to the housing. A mobile structure, which can be moved in the housing along an axis between two end positions, is arranged between the pole shoes, includes at least one magnet system, and is connected to a shaft that is axially displaceable in the housing. The magnet system includes at least one arrangement of at least one permanent magnet polarized radially with respect to the axis, and an annular coil connectable to a current source. The magnet system forms, together with the pole shoes, an air gap system having axially variable air gaps. The mobile structure is securable in each end position without excitation of the coil and is movable from one assumed end position into the opposite end position by excitation of the coil.

Claims

1. An electromagnetic actuator comprising a housing (1), two ferromagnetic pole shoes (4, 5) which are arranged at a distance from one another and are rigidly connected to the housing, a mobile structure (3) which can be moved in the housing (1) along an axis between two end positions and is arranged between the pole shoes (4, 5) and comprises at least one magnet system, which structure is connected to a shaft (2) which is axially displaceable in the housing (1), wherein the magnet system comprises radially inner and radially outer pole bodies (6, 7) comprising a magnetic flux-conducting material, at least one arrangement of one or more permanent magnets (9, 10) which are polarized radially with respect to the axis, and an annular coil (8) which can be connected to a current source, and forms, together with the pole shoes (4, 5), an air gap system having axially variable air gaps (L1, L2), wherein the mobile structure (3) can be secured in each of the two end positions without excitation of the coil (8), and can be moved out of the end position, taken up in each case, and into the opposite end position, by excitation of the coil (8).

2. The electromagnetic actuator according to claim 1, wherein the magnet system has an annular arrangement of permanent magnets (9, 10), radially polarized in the same direction, which are arranged on both sides of the coil (8).

3. The electromagnetic actuator according to claim 1, wherein the magnet system and the coil (8) are rotationally symmetrical.

4. The electromagnetic actuator according to claim 1, wherein a radially inner pole body (6) in the form of a ring extends inside the permanent magnet or the permanent magnets (9, 10) and the coil (8).

5. The electromagnetic actuator according to claim 1, wherein a radially outer pole body (7) annularly surrounds the permanent magnet or the permanent magnets (9, 10) and the coil (8).

6. The electromagnetic actuator according to claim 1, wherein the axial thickness of the pole shoes (4, 5) is different.

7. The electromagnetic actuator according to claim 1, wherein the shaft (2) is guided in plain bearings which are present in the pole shoes (4, 5).

8. The electromagnetic actuator according to claim 1, wherein the housing (1) comprises non-magnetic material.

9. The electromagnetic actuator according to claim 1, wherein an air gap is present between the housing (1) and the outer pole body (7).

10. The electromagnetic actuator according to claim 1, wherein a spring (13) acts directly or indirectly on the shaft (2) in such a way that the movement of the mobile structure (3) into one of the end positions takes place counter to the spring force of the spring.

11. An assembly comprising the actuator according to claim 1 and a motor spindle (17), which comprises, in a spindle housing (19), an electric motor and a spindle (20) which can be rotatably driven by the electric motor, and comprising a tool holder for a tool for workpiece machining, wherein the spindle (20) is designed as a hollow shaft and comprises, in the longitudinal hole therein, a clamping device (22) for firmly clamping a tool or a tool holder, wherein the housing (1) of the actuator is fastened directly or indirectly to the spindle housing (19), and wherein the mobile structure (3) can be brought into operative connection, in a force-transmitting and movement-transmitting manner, with an element (21) of the clamping device (22) which is axially displaceable in a longitudinal hole in the spindle (20), and the clamping device (22) can move into a release position.

Description

[0025] FIG. 1 is a cross-section through a preferred electromagnetic actuator,

[0026] FIG. 2 is a schematic representation of a motor spindle with an electrical actuator,

[0027] FIG. 3 is a representation of the field lines when the coil is energised for generating an actuating force in a first direction,

[0028] FIG. 4 is a representation of the field lines in the case of a deenergised coil and a position maintained by permanent magnet, according to FIG. 3, and

[0029] FIG. 5 is a representation of the field lines in the case of a coil energised in a reverse direction for generating an actuating force in a second direction.

[0030] The electromagnetic actuator shown in FIG. 1 comprises a pot-shaped housing 1. The housing 1 can be formed in one piece or in multiple parts and can comprise, for example, a cover and a base that can be connected to a main body. An armature, which is mounted so as to be movable in the direction of the axis and which is composed of a shaft 2 and a mobile structure 3 fixedly connected thereto, which are arranged between two rotationally symmetrical pole shoes 4, 5 fixedly connected to the housing 1, is located in the housing 1. The pole shoes 4, 5 have parallel side faces and have holes which accommodate a plain bearing for linear guidance of the shaft 2. The front pole shoe 4 can, for example, be fastened to the housing base by means of screw connections. The rear pole shoe 5 can, for example, be fixed in the housing 1 between a shoulder and a peripheral edge of the housing 1.

[0031] The mobile structure 3 is arranged in the intermediate space between the pole shoes 4, 5. In one embodiment, the mobile structure 3 can have an inner annular pole body 6 and, at a radial distance therefrom, an outer annular pole body 7. The pole bodies 6, 7 can also be constructed in multiple parts. A coil 8 having at least one winding is located in the space between the two pole bodies 6, 7, and a permanent magnet 9, 10 is located, in each case, on either side of the coil 8. The two permanent magnets 9, 10 are polarised radially in the same direction and thus transversely to the direction of movement of the armature, and, in one embodiment, form a magnet system, in particular together with the pole bodies 6, 7 and the pole shoes 4, 5. The permanent magnets 9, 10 are arranged annularly around the pole body 6 and can be designed as ring magnets or also as an arrangement of individual magnets polarised in the same direction. Other designs of the permanent magnets 9, 10, such as angular permanent magnets, are also possible. The pole bodies 6, 7 and the permanent magnets 9, 10 can be rigidly connected to one another.

[0032] Instead of the permanent magnets 9, 10 being arranged symmetrically with respect to the coil 8, these can also be arranged adjacently side-by-side on one side of the coil 8, or formed by a single permanent magnet of corresponding thickness, for example a ring magnet.

[0033] An axially variable air gap L1, L2 of an air gap system is located, in each case, between the mobile structure 3 and the pole shoes 4, 5.

[0034] The two pole bodies 6, 7 and the pole shoes 4, 5 consist of a material of good conductivity, in particular soft-magnetic material. The shaft 2 can also consist of a magnetic flux-conducting material, but preferably consists of non-magnetic material in order to counteract a scattering of the flux. The housing 1 also consists of non-magnetic material.

[0035] In the case of the described electromagnetic actuator, the mobile structure 3 can be held by a comparatively high force in its two end positions by the magnetic force of the permanent magnets 9, 10. The central position of the mobile structure 3 having air gaps L1, L2 of the same size is unstable. In order to move the mobile structure 3 into one or the other end position, the coil 8 is briefly excited with a current, the current direction determining the direction of movement of the mobile structure 3.

[0036] FIG. 1 shows a preferred embodiment of the electrical actuator in which the shaft 2 in the form of a tappet 11 projects through a cover 12 which is connected to the housing 1. The cover 12 can be connected to the housing 1 via screw connections or via an internal thread present in the housing. The shaft 2 and the tappet 11 can be designed in one piece or in multiple parts. The same applies to the shaft 2, which can also be formed in one piece or in multiple parts.

[0037] A movement of the mobile structure 3 causes the tappet 11 to move in the corresponding direction. A spring 13, which is supported on a shoulder 14 in the cover 12 and on a peripheral edge 15 on the tappet 11, can be arranged around the tappet 11. Depending on the design of the spring, the mobile structure 3 is moved in one or the other direction or into one or other end position, counter to the spring force of the spring 13, the spring 13 supporting the movement of the mobile structure 3 into the opposite end position. The spring 13 can be designed as a tension or compression spring.

[0038] In order to ensure a power supply to the coil 8, a hole 16 can be provided in the housing 1.

[0039] The electrical actuator can be used, for example, when changing a tool in a motor spindle 17, as shown schematically in FIG. 2. This is only one exemplary use of the device, which is shown by way of example. In this case, the actuator can be fastened with the aid of the cover 12 to an end of a spindle housing 19 facing away from a conical hole 18 for receiving a tool holder. The end of the shaft 2 projecting from the cover can engage, in the form of the tappet 11, in a longitudinal hole in a spindle 20 and, in the position of the mobile structure 3 in which it is retracted into the housing 1, can be located opposite and at a short distance from an end face of an element of a clamping device 22, in particular a tappet 21 of the clamping device 22. In this described position of the actuator, the tool holder can be clamped by the clamping device 22, for example with the aid of the force of disc springs. The mobile structure 3 is held in the retracted position without excitation of the coil 8, by the magnet system consisting of the permanent magnet 9 and pole shoe 4.

[0040] If the tool holder with a tool attached thereto is to be changed, the coil 8 is excited by a current after the spindle 20 has been stopped, by means of which current, as shown in FIG. 3, the mobile structure 3 is moved into the position extended further out of the housing 1. In this case, the shaft 2, together with the tappet 11, is moved downwards, counter to the force of the disc springs, such that, for example, a clamping pin of a tool cone of the tool holder engaging in the conical bore 18 is released from the clamping device 22 and the tool cone can be released. The tool holder and the tool fastened thereto can thereby be removed by hand or automatically. The tool cone can be attached either directly to a machining tool or to the tool holder.

[0041] After the release of the clamping device 22, the coil 8 is deenergised and the release position of the clamping device 22 is held, counter to the force of the disc springs, without excitation of the coil 8, solely by the permanent magnets 9, 10, as shown in FIG. 3.

[0042] After the insertion of the new tool into the receptacle of the spindle 20, the coil 8 is, conversely, energised in order to clamp a new tool and, as shown in FIG. 4, the mobile structure 3 moves back, with the tappet 11. In this case, with the aid of the disc springs, the clamping pin of the new tool is gripped by the clamping device 22 and clamped in the receptacle of the spindle 20. Depending on the design of the spring 13, it can support the movement of the mobile structure 3. That is to say if the spring 13 is designed as a compression spring, the mobile structure 3 will be moved in the direction of the rear pole shoe 5, counter to the spring force of the spring 13, and in the direction of the front pole shoe 4 with the assistance of the spring force. However, the spring 13 can also be designed as a tension spring (not shown), such that the movement of the mobile structure 3 will be assisted in the opposite direction.

[0043] FIGS. 3 to 5 show the field lines of the magnetic flux in different operating states of the actuator. A half axial cross-section of the parts conducting the magnetic flux is shown here.

[0044] In the example shown in FIG. 3, the coil 8 is excited by a current of such a direction that it generates a coil field which is in the same direction as the field of the permanent magnets 9, 10. The two fields supplement each other and produce a strong electromagnetic flux which is deflected by the permanent magnet 9 and conducted via the pole shoe 4. The field of the permanent magnets 9, 10 is weakened in the direction of the pole shoes 5. As a result, a strong force acts on the mobile structure 3 in the direction of the arrow F, by means of which the mobile structure 3 is moved into the left-hand end position.

[0045] FIG. 4 shows the left-hand end position of the mobile structure 3 after de-excitation of the coil 8. The permanent magnet 9 generates a strong field that grips the pole shoe 4 and with a force F holds the mobile structure 3 in the end position. The field of the permanent magnet 9 is additionally strengthened by a portion of the field of the permanent magnet 10. The flux of the permanent magnet 10 conducted through the right-hand pole shoe 5 is greatly weakened by the air gap L2, which is wide here, and is therefore barely effective.

[0046] FIG. 5 shows the course of the magnetic flux upon excitation of the coil 8 by a current of the reverse direction, in order to move the mobile structure in the opposite direction. The coil field now strengthens the field of the permanent magnet 9 and weakens the field of the permanent magnet 10, and the permanent magnet 10 deflects the common flux of the coil 8 and flux of the permanent magnet 9 to the pole shoe 5, such that the mobile structure 3 is moved into the right-hand end position.