Electromagnetic actuators and their uses

Abstract

The electromagnetic actuator includes a housing (1), two ferromagnetic pole pieces (4, 5), and a movable structure (3). The two ferromagnetic pole pieces (4, 5) are arranged at a distance from each other and are rigidly connected to the housing. The movable structure (3) can be moved along an axis within the housing (1) between two end positions and includes at least one magnet system arranged between the pole pieces (4, 5). The movable structure (3) is connected to a shaft (2) that is axially displaceable within the housing (1). The magnet system includes at least one array of one or more permanent magnets (9, 10) polarized radially relative to the axis and an annular coil (8) that can be connected to a current source, and together with the pole pieces (4, 5), forms an air gap system with axially variable air gaps (L1, L2). The movable structure (3) can be fixed in each of the two extreme positions without energizing the coil (8) and can be moved from one of the occupied extreme positions to the opposite extreme position by energizing the coil (8).

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic actuator comprising a housing, two ferromagnetic pole pieces arranged at a distance from each other and rigidly connected to the housing, and a movable structure arranged between the pole pieces and including at least one magnet system, which can be moved along an axis within the housing between two end positions. The present invention also relates to the use of the electromagnetic actuator with a motor spindle. [Background technology]

[0002] DE 19712293 A1 discloses an electromagnetically operated actuator including two magnet systems arranged at a distance from each other, each with an excitation coil. Between these two magnet systems is an armature disk rigidly connected to an adjustment shaft. The armature disk is located between two opposing springs and can be moved to two switching positions by the magnet systems. One of the magnet systems is assigned a permanent magnet polarized in the direction of armature movement, which stabilizes the armature in one switching position in the de-energized state. To hold the armature in the other switching position, permanent energization is required.

[0003] Furthermore, EP0568028A1 discloses an electromagnetic linear motor consisting of an armature, two inner pole pieces, two outer pole pieces, two permanent magnets, and one coil. The armature, together with the inner and outer pole pieces, forms an air gap system consisting of four magnetic air gaps that are variable in the axial direction and have the same size at the center. The permanent magnets stabilize the armature when the coil is de-energized at the center. The pole pieces are split and, together with the permanent magnets, which are also split, form two fixed-polarization magnet systems.

[0004] An electromagnetic solenoid for achieving high holding forces in stable end positions is known from DE 10207828 B4. It comprises a stator with two axially spaced magnet systems, each including an excitation winding for generating electromagnetic flux. An armature is guided between the two magnet systems and holds a permanent magnet arrangement polarized perpendicular to its direction of movement to permanently hold the armature in place even without energizing the excitation winding. In this case, the permanent magnet arrangement is located between the two excitation windings, which results in its effectiveness being impaired by leakage flux. Furthermore, the typically brittle material of the permanent magnet arrangement can suffer from impulsive movement of the armature.

[0005] US2016 / 0293310A1 discloses an electromagnetic actuator capable of generating symmetric bidirectional forces. The device includes 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 disposed on opposing inner end walls of the housing, and an electromagnetic coil is disposed on the center of the shaft.

[0006] US5257014A1 discloses an electric actuator having a core and a cylindrical shell disposed around the core to define an annular space therebetween. A coil is disposed within the annular space. 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 relative movement of either the coil or the core relative to the other.

[0007] DE 102013102400 A1 discloses an electromagnetic actuator including a housing and an armature, the armature having two armature disks arranged at a distance from each other and movable within the housing between two end positions, and an armature shaft. Two annular arrays of permanent magnets polarized in the same direction radially relative to the axis are arranged within the housing between the armature disks, and an annular coil connectable to a current source is arranged between the two permanent magnets. The armature can be fixed in two end positions without excitation of the coil, and can be moved from one end position occupied in each case to the opposite end position by excitation of the coil. Summary of the Invention

[0008] The object of the present invention is to provide an electromagnetic actuator of the type mentioned at the outset, which is stable in both extreme positions without current excitation and is capable of absorbing a high holding force in at least one extreme position, and which preferably can be manufactured simply and inexpensively.

[0009] This object is achieved by an electromagnetic actuator having the features defined in claim 1. Advantageous embodiments of the actuator are defined in the dependent claims.

[0010] According to the present invention, an electromagnetic actuator comprises a housing, two ferromagnetic pole pieces arranged at a distance from each other and rigidly connected to the housing, and a movable structure movable along an axis within the housing between two end positions, the movable structure being arranged between the pole pieces and including at least one magnet system. The movable structure is connected to a shaft axially displaceable within the housing, the magnet system including radially inner and radially outer pole pieces made of a magnetic flux conducting material, at least one arrangement of one or more permanent magnets radially polarized with respect to the axis, and an annular coil that can be connected to a current source, forming together with the pole pieces an air gap system with an axially variable air gap. The movable structure can be fixed in each of the two end positions without excitation of the coil, and can be moved from the end position occupied in each case to the opposite end position by excitation of the coil.

[0011] The present invention has the advantage over the prior art that the movable structure can be fixed in both extreme positions without energizing the coil. When the movable structure is to be moved to the opposite extreme position, the coil is energized. As a result, simple and fast switching of the actuator is possible. Furthermore, the use of only one coil results in low manufacturing costs and a small overall size. Furthermore, the movable structure, together with the magnetic components, is securely embedded in the housing, thereby protecting it from dynamic stresses.

[0012] In one embodiment of the actuator, the permanent magnet may consist of individual magnets arranged in a ring or may be designed in the form of a ring magnet. The shape of the one or more permanent magnets may be freely designed, for example, annular, angular, etc. Furthermore, magnets made of highly sensitive magnetic materials, such as composite materials, may be used, allowing for high polarization values and magnetic field strengths.

[0013] It may be advantageous if the magnet system has an annular arrangement of radially polarized permanent magnets arranged on either side of the coil. In a preferred embodiment of the invention, the magnet system and the coil are rotationally symmetric, although other designs are also possible.

[0014] The magnet system has a radially inner pole body and a radially outer pole body made of a magnetic flux-conducting material. The advantage of arranging a permanent magnet between the pole bodies and directly adjacent to the pole piece is that it allows for a high holding force when the coil is not energized with current. According to a further proposal of the invention, one or more magnets and coils are arranged between pole bodies made of a soft magnetic material, which pole bodies can be, for example, ring-shaped. The axial thickness of the pole pieces is preferably the same, but may be different to achieve different holding forces at the two end positions.

[0015] In an advantageous embodiment, the shaft can be guided in a plain bearing present in the pole piece.

[0016] In the present invention, the housing of the actuator forms a cavity in which the components of the actuator are present, and is preferably made of a non-magnetic material to prevent scattering of magnetic flux and concentrate the magnetic flux in the movable structure.

[0017] Preferably, there is an air gap between the housing and the outer pole piece, which may prevent friction between the movable structure and the housing, although it may also be proposed that there be sliding bushings or other means to assist movement of the movable structure within the housing.

[0018] A particularly advantageous use of the actuator according to the invention is a motor spindle with such an actuator, comprising a spindle housing, in which the spindle can be rotated by an electric motor and a spindle including a tool holder for a tool for machining a workpiece, the spindle being designed as a hollow shaft and including a clamping device in its longitudinal bore for firmly clamping the tool or tool holder, the actuator housing being directly or indirectly attached to the spindle housing, the movable structure being capable of being brought into force-transmitting and movement-transmitting operative connection with elements of the clamping device, the clamping device being axially displaceable within the spindle longitudinal bore, and the clamping device being capable of being moved to an open position, which in an advantageous embodiment can be achieved by cooperation with a spring arranged around the shaft of the movable structure or its tappet. The present disclosure therefore also encompasses a combination of the disclosed electric actuator with a motor spindle. The described advantages of the electric actuator equally apply to the use and the combination.

[0019] The use of such an actuator in the motor spindle makes it possible to dispense with complex actuators, which are often considered disadvantageous and are driven by pneumatic or hydraulic energy as is customary for actuating tool clamping devices in motor spindles. With the aid of the actuator according to the invention, a sufficiently high actuation force can be achieved with a suitable size and acceptable weight to press together the spring clamp sets of such a tool clamping device and release the clamping device. With the device according to the invention, the holding force required to hold the tool clamping device in the release position can be generated using a permanent magnet, and only a short actuation of the coil is required to release the tool clamping device and return it to the clamped position. As a result, fast switching times can be achieved.

[0020] A spring may be arranged around the tappet so that the movable structure can be moved to one of the extreme positions against the spring force. In some embodiments, the spring may assist the actuator when the clamping device is released or when it is returned to the clamping position, thereby reducing switching times.

[0021] The use according to the invention is possible in particular in motor spindles which require only one drive energy, e.g. current, for clamping and releasing the tool and for driving the tool to perform the machining operation.

[0022] The actuator can advantageously be mounted directly on the motor spindle. For this purpose, the actuator may in particular comprise means such as a bore or screw connection that allow a quick and reversible connection to the motor spindle. However, the invention also includes embodiments in which the actuation movements and forces are transmitted to the motor spindle by means of a mechanical transmission system, for example a push-pull cable, or a hydraulic transmission system, so that the weight of the motor spindle can be kept low.

[0023] In addition to use in motor spindles, actuators according to the present invention may be used in a variety of applications, such as clamping a workpiece, rapidly switching electrical contacts, or generating compressed air, etc. Further applications, such as but not limited to clamping a workpiece or locking a table, are also possible. In the following, the invention will be explained in more detail with reference to embodiments shown in the drawings. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a cross-sectional view of a preferred electromagnetic actuator. [Figure 2] FIG. 2 is a schematic diagram of a motor spindle with an electric actuator. [Figure 3] FIG. 3 is a diagram of magnetic field lines when the coil is energized to generate an actuation force in a first direction. [Figure 4] FIG. 4 shows the magnetic field lines when the coil is de-energized and maintained in position by a permanent magnet. [Figure 5] FIG. 5 is a magnetic field diagram when the coil is energized in the opposite direction to generate an actuation force in a second direction. DETAILED DESCRIPTION OF THE INVENTION

[0025] The electromagnetic actuator shown in FIG. 1 comprises a pot-shaped housing 1. The housing 1 may be formed in one piece or in multiple pieces, for example, it may have a cover and a base that can be connected to the main body. An armature is arranged in the housing 1. The armature is mounted axially movably and comprises a shaft 2 and a movable structure 3 fixedly connected to the shaft 2. The movable structure 3 is arranged between two rotationally symmetrical pole pieces 4, 5 fixedly connected to the housing 1. The pole pieces 4, 5 have parallel sides and a hole that accommodates a plain bearing for linear guidance of the shaft 2. The front pole piece 4 can be fixed to the housing base, for example, by a screw connection. The rear pole piece 5 can be fixed in the housing 1, for example, between the shoulder and the periphery of the housing 1.

[0026] The movable structure 3 is disposed in the intermediate space between the pole pieces 4, 5. In one embodiment, the movable structure 3 may have an inner annular pole piece 6 and an outer annular pole piece 7 radially spaced therefrom. The pole pieces 6, 7 may also be multi-component. A coil 8 having at least one winding is disposed in the space between the two pole pieces 6, 7, and permanent magnets 9, 10 are disposed on either side of the coil 8. The two permanent magnets 9, 10 are polarized in the same radial direction, i.e., transverse to the direction of armature movement, 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 disposed annularly around the pole piece 6 and may be designed as a ring magnet or as an array of individual magnets polarized in the same direction. Other designs of the permanent magnets 9, 10, such as prismatic permanent magnets, are also possible. The pole pieces 6, 7 and permanent magnets 9, 10 may be rigidly connected to one another.

[0027] Instead of being arranged symmetrically with respect to the coil 8, the permanent magnets 9, 10 may be arranged side by side adjacent to one side of the coil 8, or may be formed by a single permanent magnet of corresponding thickness, for example a ring magnet.

[0028] The axially variable air gaps L1, L2 of the air gap system are located between the movable structure 3 and the pole pieces 4, 5 respectively.

[0029] The two pole bodies 6, 7 and the pole pieces 4, 5 are made of a material with good electrical conductivity, in particular a soft magnetic material. The shaft 2 may also be made of a magnetic flux-conducting material, but is preferably made of a non-magnetic material that counteracts the scattering of magnetic flux. The housing 1 is also made of a non-magnetic material.

[0030] In this electromagnetic actuator, the movable structure 3 can be held at its extreme positions with a relatively large force by the magnetic forces of the permanent magnets 9, 10. The central position of the movable structure 3, which is the position with the same size air gaps L1, L2, is unstable. To move the movable structure 3 to one or the other extreme position, the coil 8 is energized with a current for a short time, the direction of which determines the direction of movement of the movable structure 3.

[0031] 1 shows a preferred embodiment of an electric actuator in which a shaft 2 in the form of a tappet 11 protrudes through a cover 12 which is connected to a housing 1. The cover 12 can be connected to the housing 1 via a threaded connection 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 pieces. The same applies to the shaft 2, which can also be made in one piece or in multiple pieces.

[0032] Movement of the movable structure 3 causes the tappet 11 to move in a corresponding direction. A spring 13 may be arranged around the tappet 11, supported by a shoulder 14 in the cover 12 and a rim 15 on the tappet 11. Depending on the design of the spring, the movable structure 3 is moved to one side or the other, i.e., to one end position or the other, against the spring force of the spring 13, which assists the movement of the movable structure 3 to the opposite end position. The spring 13 may be designed as a tension spring or a compression spring.

[0033] A hole 16 may be provided in the housing 1 to ensure power supply to the coil 8 .

[0034] The electric actuator can be used, for example, when changing a tool in a motor spindle 17, as shown diagrammatically in FIG. 2. This is merely an exemplary use of the device, shown by way of example. In this case, the actuator can be fixed with the aid of a cover 12 to the end of the spindle housing 19 opposite (facing away from) the conical bore 18 for receiving the tool holder. The end of the shaft 2 protruding from the cover, in the form of a tappet 11, can be engaged in a longitudinal bore of the spindle 20 and, in the position of the movable structure 3 retracted into the housing 1, can be arranged opposite and at a short distance from the end faces of the elements of the clamping device 22, in particular the 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 a disc spring. The movable structure 3 is held in the retracted position by a magnet system consisting of a permanent magnet 9 and a pole piece 4, without energizing the coil 8.

[0035] When the tool holder with the attached tool needs to be replaced, the coil 8 is energized with a current after the spindle 20 has stopped. This current moves the movable structure 3 to a position where it extends further outward from the housing 1, as shown in FIG. 3. In this case, the shaft 2 together with the tappet 11 is moved downwards against the force of the disc spring, so that, for example, the clamping pin of the tool cone of the tool holder, which engages in the conical hole 18, is released from the clamping device 22, allowing the tool cone to be released. This allows the tool holder and the tool fixed thereto to be removed manually or automatically. The tool cone may be attached directly to the machining tool or to the tool holder.

[0036] After the clamping device 22 is released, the coil 8 is de-energized, but the released position of the clamping device 22 is maintained as shown in FIG. 3 by the permanent magnets 9, 10 alone, without the coil 8 being energized, against the force of the disc spring.

[0037] After inserting a new tool into the receptacle of the spindle 20, the coil 8 is energized in the opposite direction to clamp the new tool, and the movable structure 3 moves back together with the tappet 11, as shown in FIG. 4 . In this case, with the help of the disc spring, 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, the spring 13 can assist the movement of the movable structure 3. That is, if the spring 13 is designed as a compression spring, the movable structure 3 can be moved toward the rear pole piece 5 against the spring force of the spring 13, or can be moved toward the front pole piece 4 with the help of the spring force. On the other hand, the spring 13 can also be designed as a tension spring (not shown) so that the movement of the movable structure 3 is assisted in the opposite direction.

[0038] Figures 3 to 5 show the magnetic flux lines in different operating states of the actuator, where an axial section (at the centre) of half of the part carrying the magnetic flux is shown.

[0039] 3, coil 8 is energized with a current oriented to generate a coil magnetic field in the same direction as the magnetic field of permanent magnets 9 and 10. These two magnetic fields complement each other to generate a strong electromagnetic flux, which is deflected by permanent magnet 9 and conducted through pole piece 4. The magnetic field of permanent magnets 9 and 10 is weakened in the direction of pole piece 5. As a result, a strong force acts on movable structure 3 in the direction of arrow F, which moves movable structure 3 to its leftmost position.

[0040] Figure 4 shows the leftmost position of the movable structure 3 after de-energisation of the coil 8. The permanent magnet 9 generates a strong magnetic field which grips the pole piece 4, holding the movable structure 3 in the end position with a force F. The magnetic field of the permanent magnet 9 is further strengthened by a portion of the magnetic field of the permanent magnet 10. The magnetic flux of the permanent magnet 10 conducted through the right-hand pole piece 5 is now strongly weakened by the wide air gap L2 and has little effect.

[0041] 5 shows the course of the magnetic flux when coil 8 is excited with a current in the opposite direction to move movable structure 3 in the opposite direction. The magnetic field of the coil now strengthens the magnetic field of permanent magnet 9 and weakens the magnetic field of permanent magnet 10, which then directs the common magnetic flux of coil 8 and the magnetic flux of permanent magnet 9 toward pole piece 5, and movable structure 3 is moved to the rightmost position.

Claims

1. A housing (1), two ferromagnetic pole pieces (4, 5) spaced apart from each other and rigidly connected to said housing; a movable structure (3) that can be moved along an axis between two end positions within the housing (1) and that is arranged between the pole pieces (4, 5) and includes at least one magnet system; Equipped with The movable structure (3) is connected to a shaft (2) that is axially displaceable within the housing (1); The magnet system comprises: radially inner and outer pole bodies (6, 7) made of a magnetic flux conducting material; at least one arrangement of one or more permanent magnets (9, 10) polarized radially relative to said axis; a toroidal coil (8) that can be connected to a current source; and together with said pole pieces (4, 5) form an air gap system having an axially variable air gap (L1, L2), the movable structure (3) can be fixed in each of the two extreme positions without energizing the coil (8) and can be moved from the end position occupied in each case to the opposite end position by energizing the coil (8), The magnet system comprises an annular arrangement of a plurality of permanent magnets (9, 10) polarized in the same radial direction; The plurality of permanent magnets (9, 10) are arranged on both sides of the coil (8). Electromagnetic actuator.

2. The magnet system and the coil (8) are rotationally symmetric 2. The electromagnetic actuator according to claim 1.

3. The radially inner pole piece (6) is ring-shaped and extends inside the one or more permanent magnets (9, 10) and the coil (8).

3. The electromagnetic actuator according to claim 1 or 2.

4. The radially outer pole piece (7) annularly surrounds the one or more permanent magnets (9, 10) and the coil (8).

4. The electromagnetic actuator according to claim 1, wherein the first and second electrodes are electrically connected to each other.

5. The axial thicknesses of the pole pieces (4, 5) are different 5. The electromagnetic actuator according to claim 1, wherein the first and second electrodes are electrically connected to each other.

6. The shaft (2) is guided in plain bearings present in the pole pieces (4, 5).

6. The electromagnetic actuator according to claim 1, wherein the first and second electrodes are electrically connected to each other.

7. The housing (1) is made of a non-magnetic material.

7. The electromagnetic actuator according to claim 1, wherein the first and second electrodes are electrically connected to each other.

8. An air gap exists between the housing (1) and the radially outer pole piece (7).

8. The electromagnetic actuator according to claim 1, wherein the first and second electrodes are electrically connected to each other.

9. A spring (13) acts directly or indirectly on said shaft (2), The movement of the movable structure (3) to one of the end positions is performed against the spring force of the spring.

9. The electromagnetic actuator according to claim 1, wherein the first and second electrodes are electrically connected to each other.

10. A motor spindle (17) comprising, in a spindle housing (19), an electric motor and a spindle (20) which can be driven in rotation by the electric motor and which includes a tool holder for a tool for machining a workpiece, The spindle (20) is designed as a hollow shaft and includes a clamping device (22) for firmly clamping a tool or tool holder in its internal longitudinal bore.

10. A method for using an electromagnetic actuator according to any one of claims 1 to 9 in a motor spindle (17) comprising: The housing (1) of the actuator is fixed directly or indirectly to the spindle housing (19), the movable structure (3) can be brought into force-transmitting and movement-transmitting operative connection with the element (21) of the clamping device (22), The clamping device (22) is axially displaceable within the longitudinal bore of the spindle (20); The clamping device (22) is movable to an open position A method characterized by:

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