ELECTROMAGNETIC ACTUATORS AND THEIR USE

Description

[0001] The invention relates to an electromagnetic actuating device according to claim 1 with a

[0002] Housing, two ferromagnetic pole pieces arranged at a distance from one another and firmly connected to the housing, and a mobile structure arranged between the pole pieces and comprising at least one magnet system, movable along an axis in the housing between two end positions. The invention also relates to the use of an electromagnetic actuator with a motor spindle.

[0003] DE 197 12 293 A1 discloses an electromagnetically operating actuating device with two spaced-apart magnet systems, each with an excitation coil, between which an armature disk is rigidly connected to an actuating shaft. The armature disk is located between two opposing springs and can be moved into two switching positions by the magnet systems. A permanent magnet polarized in the direction of movement of the armature is assigned to one of the magnet systems, which stabilizes the armature in one switching position when de-energized. If the armature is to be held in the other switching position, a continuous current supply is required.

[0004] Furthermore, EP 0 568 028 A1 discloses an electromagnetic linear motor consisting of an armature, two inner pole pieces, two outer pole pieces, two permanent magnets, and a coil. The armature, together with the inner and outer pole pieces, forms an air gap system consisting of four axially variable magnetic air gaps that are equal in size in the center position. The permanent magnets stabilize the armature in the center position when the coil is de-energized. The pole pieces are half-shell-shaped and, together with the half-shell-shaped permanent magnets, form two fixed-pole magnetic systems.

[0005] An electromagnetic solenoid for achieving high holding forces in the stable end positions is known from DE 102 07 828 B4. It consists of a stator with two axially spaced magnet systems, each with an excitation winding for generating an electromagnetic flux. An armature is guided between the two magnet systems, which carries a permanent magnet arrangement polarized perpendicular to its direction of movement to permanently hold the armature without energizing the excitation winding. The permanent magnet arrangement is located between the two excitation windings, which impairs its effectiveness due to stray flux. Furthermore, the usually brittle material of the permanent magnet arrangement can suffer from jerky movement of the armature.

[0006] US 2016 / 0 293 310 A1 describes an electromagnetic actuator capable of generating a symmetrical bidirectional force. The device comprises a housing made of a ferromagnetic material and a shaft made of a magnetically inert material that is movable along an axis within the housing. In one type of actuator, permanent magnets are arranged on opposite inner end walls of the housing, and an electromagnetic coil is arranged at a central portion of the shaft.

[0007] US Pat. No. 5,257,014 A1 discloses an electric actuator comprising a core and a cylindrical shell arranged around the core, defining an annular space therebetween, in which a coil is located. A DC amplifier transmits an excitation signal in response to a desired position signal. The coil is designed to receive the excitation signal and, in response, generate a magnetic field proportional to the magnitude of the excitation signal, causing movement of one of the coil and the core relative to the other.

[0008] DE 10 2013 102 400 A1 discloses an electromagnetic actuating device comprising a housing and an armature movable within the housing between two end positions. The armature comprises two spaced-apart armature disks and an armature shaft. Two annular arrangements of permanent magnets, polarized radially in the same direction relative to the axis, are arranged between the armature disks in the housing. An annular coil, connectable to a power source, is arranged between the two permanent magnets. The armature can be held in two end positions without energizing a coil and can be moved from one end position to the opposite end position by energizing the coil.

[0009] US 2017 / 175919 A1 discloses an electric coaxial valve with double magnetic locking, comprising an electrically pulsed permanent magnet with an armature with three active poles. The coaxial valve is equipped with a spring that, together with the armature, increases the internal force and travel of a pipe while reducing the energy required to operate the valve. This provides a coaxial valve capable of handling increased pressure or flow ranges. A similar coaxial valve is known from US 2012 / 175974 A1.

[0010] The invention is based on the object of creating an electromagnetic actuating device of the type mentioned above that is stable in both end positions without electrical excitation and can absorb high holding forces in at least one end position. Furthermore, the actuating device should be simple and cost-effective to manufacture.

[0011] This object is achieved by an electromagnetic actuating device having the features specified in claim 1. Advantageous embodiments of the actuating device are specified in the dependent claims.

[0012] According to the invention, the electromagnetic actuating device according to claim 1 comprises a housing, two ferromagnetic pole pieces arranged at a distance from one another and firmly connected to the housing, a mobile structure movable along an axis in the housing between two end positions, arranged between the pole pieces and comprising at least one magnet system, which is connected to a shaft axially displaceable in the housing, wherein the magnet system comprises radially inner and radially outer pole bodies made of a material that conducts the magnetic flux, at least one arrangement of several permanent magnets polarized radially to the axis and an annular coil connectable to a power source and forms an air gap system with axially variable air gaps with the pole pieces,wherein the mobile structure can be held in each of the two end positions without excitation of the coil and can be moved from a respective end position to the opposite end position by excitation of the coil, and wherein the magnet system comprises an annular arrangement of permanent magnets radially polarized in the same direction, which are arranged on both sides of the coil.

[0013] The invention has the advantage over the prior art that the mobile structure can be held in both end positions without energizing the coil. If the mobile structure is to be moved to the opposite end position, the coil is energized. This enables simple and quick switching of the actuating device. Furthermore, the use of only one coil contributes to low manufacturing costs and compact size. Furthermore, the mobile structure with its magnetic components is securely embedded in the housing and thus protected from dynamic stress.

[0014] In one embodiment of the actuator, the permanent magnet can consist of individual magnets arranged in a ring or can be designed as a single ring magnet. The shape of the permanent magnets or the permanent magnet is freely selectable—shapes such as ring-shaped, square, or similar are possible. Furthermore, magnets made of sensitive magnetic materials, such as composite materials, can be used, which allow for high polarization values ​​and field strengths.

[0015] According to the invention, the magnet system comprises an annular arrangement of permanent magnets with the same radial polarity, arranged on both sides of the coil. In a preferred embodiment of the invention, the magnet system and the coil are rotationally symmetrical. However, other designs are also possible.

[0016] The magnet system has radially inner and radially outer pole bodies made of a material that conducts magnetic flux. The advantageous arrangement of the permanent magnets between the pole bodies and immediately adjacent to the pole shoes enables high holding forces when the coil is not energized. According to a further proposal of the invention, the magnets and the coil are arranged between pole bodies made of soft magnetic material, which can, for example, be in the shape of rings. The axial thickness of the pole shoes is preferably the same, but can also be different to achieve different holding forces in the two end positions.

[0017] In an advantageous embodiment, it can be provided that the shaft is guided in plain bearings which are present in the pole shoes.

[0018] According to the invention, the housing of the actuator, which also forms the chamber in which the components of the actuators are located, is preferably made of a non-magnetic material in order to avoid scattering of the magnetic flux and to concentrate the flux on the mobile structure.

[0019] It is preferred that there be an air gap between the housing and the outer pole body. This prevents friction between the mobile structure and the housing. However, it can also be provided that sliding bushings or other means are provided to support the movement of the mobile structure within the housing.

[0020] A particularly advantageous use of the adjusting device according to the invention comprises a motor spindle with a previously explained adjusting device, which contains an electric motor in a spindle housing and a spindle which can be driven in rotation by the motor and has a tool holder for a tool for machining a workpiece, wherein the spindle is designed as a hollow shaft and has a clamping device for clamping a tool or a tool holder in its longitudinal bore, wherein the housing of the adjusting device is fastened directly or indirectly to the spindle housing, and wherein the mobile structure can be brought into operative connection with an element of the clamping device which can be axially displaced in a longitudinal bore of the spindle, so as to transmit a force and a movement, and can move the clamping device into a release position, which in an advantageous embodiment can take place with the assistance of a spring arranged around the shaft of the mobile structure or its plunger.The present disclosure thus also encompasses the combination of a disclosed electrical actuator with a motor spindle. The described advantages of the electrical actuator apply analogously to the use or combination.

[0021] By using the actuating device in a motor spindle, complex and often considered disadvantageous pneumatic or hydraulic actuating devices, which have been commonly used to operate tool clamping devices in motor spindles, can be eliminated. With the actuating device according to the invention, with a suitable size and acceptable weight, sufficiently high actuating forces can be achieved to compress the spring clamping sets of such tool clamping devices and release the clamping device. Furthermore, with the device according to the invention, the holding forces required to hold the tool clamping device in the release position can be generated with the help of permanent magnets, so that the coil only needs to be actuated briefly to release the tool clamping device and return it to the clamped position. This also enables fast changeover times.

[0022] A spring can be arranged around the plunger so that the mobile structure can be moved into an end position against the spring force. Depending on the design, the spring can assist the adjusting device when releasing the clamping device or when returning to the clamped position. This allows for shorter changeover times.

[0023] The use according to the invention enables, in particular, motor spindles which require only one drive energy, namely electrical current, for clamping and unclamping the tool and for driving the tool to carry out machining operations.

[0024] The actuating device can advantageously be mounted directly on the motor spindle. For this purpose, the actuating device can, in particular, comprise means such as bores or screw connections that enable a quick and reversible connection to a motor spindle. However, the invention also includes embodiments in which the actuating movement and force are transmitted to the motor spindle via a mechanical transmission system, e.g., a pull-push cable, or via a hydraulic transmission system, thereby keeping the weight of the motor spindle low.

[0025] In addition to use with a motor spindle, the actuator according to the invention can be used for various applications, such as clamping workpieces, quickly switching electrical contacts, or generating compressed air. Applications such as, but not limited to, workpiece clamps or table locks are also possible.

[0026] The invention will be explained in more detail below with reference to exemplary embodiments shown in the drawings. Figure 1 shows a cross section through a preferred electromagnetic actuating device, Figure 2 shows a schematic representation of a motor spindle with an electrical actuating device, Figure 3 shows a representation of the field lines when the coil is energized to generate an actuating force in a first direction, Figure 4 shows a representation of the field lines when the coil is de-energized and in a permanently magnetically held position according to Figure 3 and Figure 5 shows the field lines when the coil is energized in reverse to generate an actuating force in a second direction.

[0027] The Figure 1The electromagnetic actuating device shown comprises a pot-shaped housing 1. The housing 1 can be designed in one part or in several parts and, for example, comprise a cover and base that can be connected to a base body. In the housing 1 there is an armature that is movably mounted in the direction of the axis and is composed of a shaft 2 and a mobile structure 3 that is firmly connected to the shaft and is arranged between two rotationally symmetrical pole shoes 4, 5 that are firmly connected to the housing 1. The pole shoes 4, 5 have parallel side surfaces and have bores that accommodate a plain bearing for the 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.

[0028] The mobile structure 3 is arranged in the space between the pole pieces 4, 5. In one embodiment, the mobile structure 3 can have an inner, annular pole body 6 and, at a radial distance from this, an outer, annular pole body 7. The pole pieces 6, 7 can also be constructed in several parts. In the space between the two pole pieces 6, 7 there is a coil 8 having at least one winding and a permanent magnet 9, 10 on each side of the coil 8. The two permanent magnets 9, 10 are polarized radially in the same direction and thus transversely to the direction of movement of the armature and, in one embodiment, form a magnet system, particularly with the pole pieces 6, 7 and the pole pieces 4, 5. The permanent magnets 9, 10 are arranged in a ring around the pole body 6 and can be designed as ring magnets or as an arrangement of individual magnets polarized in the same direction.Other designs of the permanent magnets 9, 10, such as square permanent magnets, are also possible. The pole bodies 6, 7 and the permanent magnets 9, 10 can be firmly connected to each other.

[0029] Between the mobile structure 3 and the pole pieces 4, 5 there is an axially variable air gap L1, L2 of an air gap system.

[0030] The two pole bodies 6, 7 and the pole shoes 4, 5 are made of a material that conducts magnetic flux well, particularly a soft magnetic material. The shaft 2 can also be made of a material that conducts magnetic flux, but is preferably made of a non-magnetic material to counteract flux dispersion. The housing 1 is also made of a non-magnetic material.

[0031] With the described electromagnetic actuator, the mobile structure 3 can be held in its two end positions with comparatively high force by the magnetic force of the permanent magnets 9, 10. The center position of the mobile structure 3, with equally sized air gaps L1, L2, is unstable. To move the mobile structure 3 to one or the other end position, the coil 8 is briefly energized with a current, whereby the direction of the current determines the direction of movement of the mobile structure 3.

[0032] In Figure 1A preferred embodiment of the electrical actuating device is shown, in which the shaft 2, in the form of a plunger 11, extends through a cover 12 that is connected to the housing 1. The cover 12 can be connected to the housing 1 via screw connections or via an internal thread in the housing. The shaft 2 and plunger 11 can be designed as one or more parts. The same applies to the shaft 2, which can also be designed as one or more parts.

[0033] A movement of the mobile structure 3 causes the plunger 11 to move in the corresponding direction. A spring 13 can be arranged around the plunger 11, which is supported on a shoulder 14 in the cover 12 and on a peripheral edge 15 on the plunger 11. Depending on the design of the spring, the mobile structure 3 is moved in one direction or the other, or to one or the other end position, against the spring force of the spring 13, with the spring 13 supporting the movement of the mobile structure 3 to the opposite end position. The spring 13 can be designed as a tension or compression spring.

[0034] To ensure a power supply to the coil 8, a bore 16 can be provided in the housing 1.

[0035] The electrical actuating device can be used, for example, when changing a tool on a motor spindle 17, as shown schematically in Figure 2shown. This is only an exemplary use of the device, which is shown by way of example. The adjusting device can be fastened to an end of a spindle housing 19 facing away from a conical bore 18 for receiving a tool holder, by means of the cover 12. The end of the shaft 2 protruding from the cover, in the form of the plunger 11, can engage in a longitudinal bore in a spindle 20 and, when the mobile structure 3 is retracted into the housing 1, can be located at a short distance from an end face of an element of a clamping device 22, in particular a plunger 21 of the clamping device 22. In this described position of the adjusting device, the tool holder can be clamped by the clamping device 22, for example with the help of disc springs. The mobile structure 3 is held in the retracted position by the magnetic system comprising the permanent magnet 9 and the pole piece 4, without excitation of the coil 8.

[0036] If the tool holder with a tool attached to it is to be changed, after the spindle 20 has been stopped, the coil 8 is excited with a current through which, as shown in Figure 3 As shown, the mobile structure 3 is moved into the position further extended from the housing 1. In this case, the shaft 2 with the plunger 11 is moved downwards against the force of the disc springs to such an extent that, for example, a clamping pin of a tool taper of the tool holder engaging in the taper bore 18 is released from the clamping device 22 and the tool taper can be released. The tool holder and the tool attached to it can be removed manually or automatically in this way. The tool taper can be attached either directly to a machining tool or to the tool holder.

[0037] After releasing the clamping device 22, the coil 8 is de-energized and the release position of the clamping device 22 without excitation of the coil 8 solely by the permanent magnets 9, 10 as in Figure 3 shown, held against the force of the disc springs.

[0038] After inserting the new tool into the spindle 20 holder, the coil 8 is reversely excited to clamp a new tool and, as shown in Figure 4shown, the mobile structure 3 is moved back with the plunger 11. With the help of the disc springs, the clamping pin of the new tool is gripped by the clamping device 22 and clamped firmly in the receptacle of the spindle 20. Depending on the design of the spring 13, this can support the movement of the mobile structure 3. This means that if the spring 13 is designed as a compression spring, the mobile structure 3 is moved against the spring force of the spring 13 in the direction of the rear pole piece 5 and with the support of the spring force in the direction of the front pole piece 4. However, the spring 13 can also be designed as a tension spring (not shown), so that the movement of the mobile structure 3 is supported in the opposite direction.

[0039] The Figures 3 to 5 show the field lines of the magnetic flux under various operating conditions of the actuator. Each shows half of the axial section of the parts conducting the magnetic flux.

[0040] In the Figure 3 In the example shown, coil 8 is energized with a current of such a direction that it generates a coil field in the same direction as the field of permanent magnets 9, 10. Both fields complement each other and produce a strong electromagnetic flux, which is deflected by permanent magnet 9 and directed over pole piece 4. The field of permanent magnets 9, 10 is weakened in the direction of pole pieces 5. This exerts a strong force on mobile structure 3 in the direction of arrow F, moving mobile structure 3 to the left end position.

[0041] Figure 4shows the left end position of the mobile structure 3 after de-energization of the coil 8. The permanent magnet 9 generates a strong field that captures the pole piece 4 and holds the mobile structure 3 in the end position with a force F. The field of the permanent magnet 9 is additionally amplified by part of the field of the permanent magnet 10. The flux of the permanent magnet 10, guided through the right pole piece 5, is greatly weakened by the large air gap L2 and is therefore hardly effective.

[0042] Figure 5 shows the magnetic flux path when coil 8 is energized with a current of the opposite direction to move the mobile structure in the opposite direction. The coil field now strengthens the field of permanent magnet 9 and weakens the field of permanent magnet 10. Permanent magnet 10 directs the combined flux of coil 8 and the flux of permanent magnet 9 to pole piece 5, so that mobile structure 3 is moved to the right end position.

Claims

1. Electromagnetic actuating device 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) consisting of a magnetic flux-conducting material, at least one arrangement of 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); characterized in that the magnet system has an annular arrangement of permanent magnets (9, 10) polarized in the same direction and arranged radially, which are arranged on both sides of the coil (8).

2. Actuating device according to claim 1, characterized in that the magnet system and the coil (8) are rotationally symmetrical.

3. Actuating device according to one of the preceding claims, characterized in that the radially inner pole piece (6) in the form of a ring extends within the permanent magnet or magnets (9, 10) and the coil (8).

4. Actuating device according to any one of the preceding claims, characterized in that a radially outer pole body (7) annularly surrounds the permanent magnet or the permanent magnets (9, 10) and the coil (8).

5. Actuating device according to one of the preceding claims, characterized in that an axial thickness of the pole pieces (4, 5) is different.

6. Actuating device according to any one of the preceding claims, characterized in that the shaft (2) is guided in plain bearings, which are present in the pole shoes (4, 5).

7. Actuating device according to any one of the preceding claims, characterized in that the housing (1) consists of non-magnetic material.

8. Actuating device according to any one of the preceding claims, characterized in that an air gap is present between the housing (1) and the outer pole body (7).

9. Actuating device according to any one of the preceding claims, characterized in that 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.

10. Use of an actuating device according to any one of the preceding claims in a motor spindle (17), which comprises in a spindle housing (19) an electric motor and a spindle (20) which can be rotatably driven thereby, 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 bore therein, a clamping device (22) for firmly clamping a tool or a tool holder, wherein the housing (1) of the actuating device is fastened directly or indirectly to the spindle housing (19), and wherein the mobile structure (3) can be brought into a force- and movement-transmitting operative connection with an element (21) of the clamping device (22), which element is axially displaceable in a longitudinal bore of the spindle (20), and can move the clamping device (22) into a release position.