Linear actuator with optimized inductance, and method for winding and interconnecting coils

Abstract

The invention relates to a linear Reluctance actuator (6) comprising a stator (18) carrying at least one coil (32), and a rotor (24), the coil (32) being in the form of a double-wound winding and the linear actuator (6) having at least one return element (74) by means of which the rotor (24) can be brought into a defined initial position after a rotational movement.

Description

[0001] Linear actuator with optimized inductance and method for winding and connecting coils

[0002] Description

[0003] The invention relates to a reluctance linear actuator according to the preamble of patent claim 1 and to tools or drives designed with such a linear actuator.

[0004] Such a tool for surface peening (Machine Hammer Peening, MHP) is typically clamped into a machine tool or robot, so that the workpiece to be machined is machined by a multitude of individual, precisely sequenced impacts from a usually spherical tool tip. Contact between the tool tip and the workpiece surface can be continuous or periodic. When a commonly used carbide tip is periodically applied to a workpiece surface, a linear actuator causes the tool to oscillate with a defined impact frequency, impact amplitude, and zero crossing. This oscillating movement of the tool, also known as the ram, can be achieved using various actuator principles.

[0005] Linear actuators can basically be divided into different categories according to their mode of operation, the travel path of the slider and the design.

[0006] Linear actuators that operate predominantly mechanically are described, for example, in the documents DE 20 2015 000 360 U 1 , WO 2016 136 169 A1 , DE 10 2014 107 173 A1 , DE 10 2016 000 389 A1 , DE 202015 003 249 U1 , EP 2 851 441 A2, EP 2 851 442 A1 and US 2014 000 7 394 A1.

[0007] The tools described in publications DE 102009 041 720 A1 and DE 20 2013 002 473 U1 use a piezoelectric linear drive. Pneumatic or coolant / lubricant-operated tools are the subject of publications DE 10 2012 103 111 A1 and DE 20 2009 001 619 U1.

[0008] Direct-to-direct sonotrode controlled tools are disclosed in the documents US 6 932 876 B1, US 2007 0244 595 A, US 2015 011 4 074 A and WO 2004 028 739 A1.

[0009] In electric drives, such as those described in publications DE 10 2006 033 004 A1 and US Pat. No. 4,641,510 A, a distinction is made between the types of reaction forces depending on the operating principle. Linear actuators operating according to the electrodynamic principle (e.g., the moving coil principle) exhibit significant disadvantages in terms of dynamics and force development due to the unfavorable mass distribution of the mechanical structure. Furthermore, the highly mechanically stressed coils used in these systems and their low power density are disadvantageous for highly dynamic motion.

[0010] In addition to the linear drives described above, reluctance linear actuators are also known. These actuators have an axially adjustable rotor / actuator guided in a stator, with the stroke of the rotor / actuator being generated by the reluctance force. The mode of operation of such linear actuators is described, for example, in the publications "Identification of Some Tubular Topologies of Linear Switched Reluctance Generator for Direct Drive Applications in Oceans Wave Energy Conversion"; RPG Mendes, RMRA Calado, SJPS Mariano; Proceedings of the World Congress on Engineering 2014, Vol. 1, WCE 2014, July 2-4, 2014, London, UK and "Analysis and Modeling of Linear-Switched Reluctance for Medical Application", Jean-Francois Llibre, Nicolas Martinez, Pascal Leprinc, Bertrand Nogarede; Actuators 2013, 2, 27 - 44 (www.mdpi.com / iournal / actuators).

[0011] WO 2017 / 129 249 A1 describes a multiphase reluctance linear actuator in which a modular tubular stator has a plurality of coils arranged axially one behind the other, which are accommodated in recesses defined by radial webs. A rotor is axially displaceably guided in this stator. In this embodiment, the rotor has a plurality of annular permanent magnets on its outer circumference, each of which is inserted into an annular groove.

[0012] Corresponding reluctance linear actuators are also described in the publications DE 44 07 385 A1, DE 43 11 664 A1, and WO 85 / 05507 A1. All of these systems are designed for comparatively large strokes, so multi-phase control is provided and permanent magnets are provided on the stator or rotor.

[0013] Patent application DE 29 31 685 A1 describes reluctance linear actuators in which a stator is conical and has annular grooves along its outer circumference, the groove diameter of which changes depending on the conification. A winding made of a single wire is inserted into these grooves, with the turns of this winding oriented in opposite directions in adjacent grooves, so that an electrical current carried through this winding has an opposite current direction in two consecutive turns. This stator is surrounded by a cup-shaped, also conical rotor, with ribs formed on the inner circumference of the rotor. These ribs, together with correspondingly designed ribs separating adjacent grooves, form pairs of pole faces. Between these pairs, an air gap is formed which is minimized when the winding is energized due to the reluctance force.

[0014] DE 10 2005 017 483 A1 describes a linear actuator in which two counter-wound coils are arranged one behind the other in the stroke direction in a stator, with the winding axis of the coil running transversely to the stroke direction. The two coils are arranged within two rotor guides of the stator, on whose surfaces facing one rotor pairs are arranged pairs of teeth. The rotor, which is movable between these pairs of teeth, is U-shaped, with each U-leg consisting of a stack of permanent-magnetic bars arranged with an air gap to the pairs of teeth, so that when energized, the rotor can be adjusted in the stroke direction due to the reluctance force.DE 44 07 385 A1 describes a planar reluctance linear actuator which is designed to transport objects in a linear direction, wherein regions defining an air gap between the stator and the rotor are formed by a soft magnetic material into which grooves forming the above-described toothing are machined.

[0015] EP 2 884 637 A1 shows a reluctance linear actuator for adjusting an optical assembly, in which, similar to the solutions described above, teeth are provided on the stator and rotor sides, between which an air gap is formed, which is minimized due to the reluctance force when a stator-side coil arrangement is energized, so that the rotor performs a corresponding stroke.

[0016] WO 2019 / 096834 A1, which originates from the applicant, describes a reluctance linear actuator with a tubular stator on which a plurality of axially spaced-apart coils are arranged, each in an annular recess of an inner circumferential surface of the stator. A rotor is axially adjustably mounted in the tubular stator. The rotor has a toothed profile on its outer circumference, which forms an air gap with the radial webs delimiting the recesses of the stator. In the known reluctance linear actuator, the coils are controlled via power electronics such that the rotor performs a controlled stroke depending on the control due to the reluctance force. The current direction of adjacent coils in this known linear actuator is opposite.The geometry of the radial webs and the tooth profile is optimized with regard to the magnetic flux, allowing the stroke to be realized with high dynamics. The design of this reluctance linear actuator is further simplified because it does not use permanent magnets, as in some of the previously described solutions; the stator and rotor are made of a magnetically conductive material, preferably a soft magnetic material. With this drive design, very high force densities can be achieved in a single-phase version. The disadvantage of this solution, however, is that the design, with a large number of coils guided on a tubular stator, requires a high level of manufacturing effort and also occupies considerable space.

[0017] Further prior art is also known from DE 2602672 A1. This document discloses an electromagnetic device with a winding through which electric current can be passed, comprising two relatively movable members that move relatively in response to the magnetic field generated by the passage of electric current through the winding.It is particularly noted that one of the members is generally annular in shape and surrounds the other member at a distance, the other member having a substantially cylindrical peripheral surface, the inner surface of one member and the peripheral surface of the other member each being provided with a two-start helical groove or a helical groove having a multiple of two starts, the grooves on the surfaces forming ridges, the grooves or successive grooves on one of the members carrying the electrical winding which is arranged so that the direction of current flow in the parts of the winding in the grooves or in successive grooves is opposite, the arrangement being such that when electrical current flows through the winding the members move relative to each other in a direction such that the ridges on the two members are aligned with each other.

[0018] US 4,003,013 A also discloses an electromagnetic device comprising a pair of relatively movable magnetizable elements whose surfaces are arranged opposite each other.

[0019] US 3,353,040 A discloses a different type of electrodynamic converter, while US 2009 / 0243416 A1 discloses an electric motor. However, these devices are located in a different technical field and are outside the scope of a person skilled in the art.

[0020] A completely different type of reluctance linear actuator is further disclosed in DE 102017 127 021 A1. This describes a reluctance linear actuator with a tubular stator on which a plurality of spaced-apart coils are arranged in a circumferential recess of an inner circumferential surface of the stator, wherein the recesses are axially delimited by radial webs, comprising a rotor that is mounted for axial displacement and has a tooth profile on its magnetically active circumference facing the stator, which forms an air gap with the radial webs and is provided with power electronics for controlling the coils, so that the rotor performs a controlled / adjustable stroke depending on the control based on the reluctance force.What is particularly emphasized is that the tooth profile is designed to be complementary to the radial webs, whereby these and the tooth profile are each designed with annular grooves open towards the stator or the rotor, which are arranged approximately radially opposite one another with a minimal air gap, and that the stator and the rotor are made of magnetically conductive or soft magnetic material.

[0021] All these known solutions still have specific disadvantages that need to be eliminated or at least mitigated.

[0022] In particular, the invention is based on the object of creating a generic reluctance linear actuator that enables a highly dynamic motion sequence with a compact design. Furthermore, the invention is based on the object of creating suitable applications in which the optimized reluctance linear actuator can be used, i.e., to present an actuator that can be used effectively in various applications.

[0023] This object is achieved with regard to the reluctance linear actuator by the features of patent claim 1 and with regard to the applications by a tool according to patent claim 13 or drives according to patent claims 14 and 15, respectively.

[0024] The reluctance linear actuator according to the invention has an axially adjustable rotor and a stator arranged coaxially thereto, and at least one coil arranged in the region between the stator and the rotor. This coil is guided in a slot of the stator which is delimited by slot webs. A slot profile facing the slot webs is formed on the rotor, the slot walls of which, together with the slot webs, each form / delimit an air gap. The linear actuator is further designed with power electronics for controlling the coil such that, depending on this control, the rotor performs a controllable stroke based on the reluctance force, so that when the at least one coil is energized, the preferably axial offset between the slot webs and the slot profile is minimized. According to the invention, the stator and the rotor are made of magnetically conductive or soft magnetic material.The stroke then roughly corresponds to the axial width of a slot web or a rotor web of the slot wall. The slot and / or the slot profile, as a double helix, is designed with two threads, with the coil being guided along one helical turn from a coil inlet to a turning point and from there, returning in the opposite direction along the second helical turn to a coil outlet. The coil sections leading to and from the turning point are arranged in a bifilar configuration.

[0025] According to the invention, the linear actuator thus has at least one return element designed such that, during operation, the slider is brought into a specific, predefined starting position after a stroke movement. It thus has one or more return elements, preferably in the form of return springs, such as coil springs, preferably helical compression springs, which force the slider into a predefined starting position after a stroke movement.

[0026] This inventive design with one or more return elements enables both continuous and discrete movement (i.e., triggering one or more individual impacts) of the hammer head. Because the runner can be brought into a predefined starting position, the necessary kinetic energy, which depends on the required impact distance and the sample material, can be precisely adjusted.

[0027] Furthermore, a bifilar winding is much easier to manufacture than the complex windings according to the previously described prior art, with the internal support of the at least one coil on the stator, which is encompassed by the rotor, being particularly advantageous. Furthermore, the inventive concept is highly scalable, since the choice of the coil's wire diameter allows its axial length to be easily adapted to different requirements. In the previously described prior art, this scalability is not possible due to the complex structure of the stator. A further advantage is that the two-start double helix is ​​much easier to manufacture than the slot structure in the known solutions, which require the production of a large number of axially spaced annular slots with complex tooth profiles.

[0028] This system can be operated in both open-loop and closed-loop mode. Closed-loop control refers to the movement and thus the speed of the hammer head, and ultimately to the forming energy applied to the workpiece. The simplicity of the power electronics allows the applied energy to be precisely defined by specifying the duty cycle of the coil voltage.

[0029] Using the displacement sensor / position sensor used, this duty cycle can also be controlled with minimal inductance, so that a target speed and thus also the kinetic energy can be maintained or is maintained at a constant level.

[0030] Preferred embodiments are claimed in the subclaims and are explained in more detail below.

[0031] In a preferred embodiment, at least one return element is designed to be spring-elastic in the direction of movement of the rotor and / or a plurality of return elements are arranged distributed over the circumference of the stator. It is advantageous if the return elements, for example 3, 4 or 5, are evenly distributed over the circumference and have the same radial distance from the center. They can be designed as elastomers. All return elements can be of the same type or deliberately selected to be different. It can be provided that the linear actuator has at least one return element in the form of a return spring, preferably a plurality of return elements in the form of return springs.Particularly preferably, the linear actuator has a plurality of return elements in the form of return springs arranged distributed over the circumference of the stator, which are designed in such a way that during operation the rotor is brought into a certain predefined starting position after a stroke movement.

[0032] In a particularly preferred embodiment, the rotor is designed to be tubular on the outside, so that it encompasses the stator, wherein the groove guiding the at least one coil, designed as a double helix, is formed on the outer circumferential surface of the stator and the associated groove profile, also designed as a double helix, is formed on an inner circumferential surface of the rotor.

[0033] The dynamics of the reluctance linear actuator can be further improved if the at least one coil is designed as a stranded wire consisting of a large number of individual wires or a precisely (pre-)defined number of individual wires. The use of individual strands allows for a higher filling ratio or a higher packing density of the slot profile and thus higher currents in the winding. Alternatively, the coil is designed from a single wire with a large number of turns, for example, with 12, 13, 14, 15, or 16 turns.

[0034] The number of windings determines the total inductance, or rather, the total inductance is optimized by the (predefined) number of windings, which limits the current. Thus, there is no explicit current limit, and the system regulates itself. This ensures simple control.

[0035] In addition, the design of the tooth geometry on the rotor and stator sides, which are each formed by the slot profiles that guide the coil, is optimized to maximize the magnetic flux density. In particular, the tooth geometry and the tooth offset, which corresponds to the stroke of a single-phase coil, were designed using a FEMM (Finite Element Method Magnetics) simulation. In this design of the tooth geometry, a maximum force flow was selected as the optimization criterion to achieve high dynamics. Advantageously, the tooth geometry(s) is / are designed such that it tapers towards the web, preferably trapezoidally. The web width is greater than or equal to the tooth offset. This ensures simple manufacturing and a high force density.

[0036] In one embodiment, the coil, in particular the stranded wire, is insulated so that cooling is possible through direct coolant contact with the coil.

[0037] In order to achieve a stroke reversal or a longer stroke, several coils can be connected to form a multi-phase structure, which can be individually controlled via the power electronics.

[0038] As stated above, cooling may be associated with the coil to prevent excessive heat build-up.

[0039] This cooling can be achieved, for example, by means of a coolant, such as air or a cooling liquid, which is guided along the air gap and / or the stator.

[0040] The design of the reluctance linear actuator is particularly simple if the pitches and slot widths of the stator and rotor-side double helix are essentially the same.

[0041] The linear actuator according to the invention can be used, for example, in a tool for surface hammering, wherein a mechanical interface for a hammer head is provided on the rotor.

[0042] However, the linear actuator according to the invention can also be used in other applications, for example, in a valve train of an internal combustion engine and / or for actuating servo and / or directional valves and / or in the vibration-assisted machining of composite or monolithic materials. Preferred embodiments of the invention are explained in more detail below with reference to schematic drawings. They show:

[0043] Figure 1 is a schematic external view of a reluctance linear actuator according to the invention, which is designed to drive a surface hammer;

[0044] Figure 2 is a schematic representation of the structure of the linear actuator according to Figure 1;

[0045] Figure 3 is a schematic diagram of a coil of the linear actuator according to Figures 1 and 2;

[0046] Figure 4 shows the basic concept of a control loop of the linear actuator according to the invention;

[0047] Figure 5 shows a representation of the linear actuator corresponding to Figure 3 in a starting position and a target position with field lines that are established when the coil is energized;

[0048] Figure 6 shows a schematic diagram of the linear actuator with coolant flow paths marked;

[0049] Figure 7 Circuit symbols of a single-phase and multi-phase operated linear actuator;

[0050] Figure 8 is a schematic side sectional view of the reluctance linear actuator according to the invention, which is designed to drive a surface hammer, in a further embodiment;

[0051] Figure 9 is an isometric front view of the reluctance linear actuator according to the invention of the embodiment shown in Figure 8;

[0052] Figure 10 is an isometric rear view of the reluctance linear actuator according to the invention of the embodiment shown in Figures 8 and 9 and,

[0053] Figure 11 shows a schematic functional representation of the control unit of the linear actuator.

[0054] The invention is explained below using a forming tool for surface peening, hereinafter referred to as surface hammer 1. According to Figure 1, this tool has a hammer head 4 equipped with a striking insert 2 made of hard metal or other materials, which is set into periodic oscillations by means of a reluctance linear actuator 6 according to the invention for surface peening or can be held in continuous contact with the workpiece to be machined. The surface hammer 1 also has a mechanical interface, in this case a hollow shaft cone 8, via which the surface hammer 1 can be inserted into a corresponding tool holder of a machine tool or a robot, so that the surface hammer 1 is guided over the NC axes of the machine tool or robot during machining.

[0055] Of course, the reluctance linear actuator 6 according to the invention—hereinafter abbreviated to "linear actuator"—can also be used in other applications. For example, it is possible to operate a valve train of an internal combustion engine with such a linear actuator 6. Vibration-assisted machining of workpieces made of ceramic materials, hard metals, glass, etc., or composite materials or other monolithic materials can also be performed with a tool equipped with such a linear actuator 6. Application in valve trains is also conceivable.

[0056] A time-discrete control of the stroke of the linear actuator 6 is carried out via power electronics, the structure of which will be discussed later.

[0057] The reference numerals 10, 12 and 14 indicate radial connections for coolant and energy supply as well as for signal transmission.

[0058] Figure 2 shows the basic structure of the linear actuator 6, which is housed in a housing 16 of the surface hammer 1. Accordingly, a stator 18 arranged coaxially to the hammer head 4 is mounted in the housing 16. Bearing sections, for example, plain bearing bushes 20, 22, are formed on the two radially expanded end sections of the stator. These bushes are supported both axially and radially in the housing 16. These bushes can be made of ceramic, for example. A slider 24 is guided along these bushes so that they can be displaced in the stroke direction. In one variant, the bearing bushes are firmly pressed onto the slider and are part of the moving mass. Thus, in one variant, they are not axially supported. Radially distributed guides prevent the slider from twisting during the movement process. In the illustrated embodiment, the slider 24 is tubular and surrounds the central stator 18 at least in sections.In the illustrated embodiment, the stator 18 and the rotor 24 are made of a soft magnetic material.

[0059] A double helix, i.e., two parallel spiral grooves 28, 30, are formed on a coil holding section 26 of the stator 18 located between the two plain bearing bushes 20, 22 and radially recessed relative thereto. These grooves extend along the outer circumference of the coil holding section 26 and in which a coil 32 is guided. The two spiral grooves 28, 30 are each delimited by groove webs 34, 35, the radial extent of which is selected such that the coil winding can be fully immersed in the respective groove 28, 30 and thus does not protrude beyond the outer circumference of the stator 18.

[0060] In the illustrated embodiment, according to the detailed illustration shown at the bottom right, the coil 32 is designed as a stranded wire with a plurality of individual wires 36, which are surrounded by an insulation 38 forming the outer circumference of the stranded wire, or as a single wire 36 with several turns.

[0061] The coil 32, or more precisely the stranded wire, enters the region of the coil holding section 26 through a coil inlet 40, which extends axially parallel through the plain bearing bushing 20, and is then guided along the spiral groove 28 to a turning point 42 provided in the region of the other plain bearing bushing 22. The coil 32 (stranded wire) is then deflected via this turning point 42 and guided back along the second groove 30 to a coil outlet 44. In the illustration according to Figure 2, the coil turns leading to the turning point 42 are designed with a different shade than the coil section returning from the turning point 42 to the coil outlet 44. This creates a type of wire pair made of a robust, insulated stranded wire, which forms the wound coil. If this coil 32, which is designed in a bifilar winding manner, is now energized, the current direction is reversed in the region of the turning point 42.The inductance of the winding can be drastically reduced by the bifilar winding.

[0062] As further shown in Figure 2, a double-start groove profile with spiral rotor grooves 46, 48 is formed on the inner circumferential wall of the stator 24, the geometry of which (pitch, groove width) corresponds to that of the spiral grooves 28, 30. In principle, other configurations than those shown in the schematic diagram in Figure 2 are also conceivable. Arranged between the parallel spiral rotor grooves 46, 48 are rotor webs 50, 52, which form, so to speak, the side walls of the rotor grooves 46, 48. The geometry of these rotor webs 50, 52 corresponds to the geometry of the groove webs 34, 35.

[0063] As explained in more detail below (see Figure 5), an axial offset 58 remains between the rotor webs 50, 52 on the one hand and the slot webs 34, 35 on the other hand, which is minimized when energized by the stroke movement of the rotor due to the reluctance force.

[0064] The winding concept is explained again using the schematic diagram in Figure 3, wherein the coil 32 is shown offset by 180° from the illustration in Figure 2. Accordingly, the coil 32 enters the area of ​​the coil holding section 26 via the indicated coil inlet 40 and then runs spirally to the indicated turning point 42. This coil section follows the geometry of the spiral groove 28 not visible in Figure 3. From the turning point 42, the coil 32 then runs towards the coil outlet 44, wherein this coil section of the bifilar winding extends along the further spiral groove 30 (also not shown in Figure 3).

[0065] Indicated on the right in Figure 3 are the magnetic fields that occur in the coil section extending toward the inflection point 42 (top right in Figure 3) and in the coil section extending away from the inflection point 42 (right in Figure 3). It can be seen that, as explained above, these magnetic fields are concentrated in the area of ​​the webs due to the bifilar winding, and almost no magnetic flux occurs that flows through geometrically larger areas than the webs themselves.

[0066] The basic structure of the aforementioned power electronics 54 is shown in Figure 4. Figure 4 only shows the principle of one possible closed-loop control; Figure 11 shows the structure of the control system. It should be noted that due to the geometrically optimized design of the drive components and the rather unusual single-phase design, force density is maximized, which in turn enables high-frequency control of the coils 32 and correspondingly minimal cycle times of the system. The associated high currents and simultaneously high switching frequencies cannot be generated with conventional servo amplifiers, or can only be generated with great difficulty. Accordingly, the power electronics 54 shown in Figure 4 is optimized with regard to the control of the linear actuator according to the invention.To construct the power electronics 54, standard modules can be used in part, such as a digital signal processor for implementing the necessary computing operations, sensor components for position measurement, and converters for the voltage supply. The digital signal processor used, as an integrated logic module, processes the incoming and outgoing signals and controls the drivers of the power electronics 54. The associated software for the digital signal processor contains the complete circuit logic of the actuator unit and must send switching information to a driver stage as required by the situation. The power electronics 54, which in this example is designed for the surface peening application,... The maximum voltage in the illustrated embodiment is approximately 100 V, although the system in its current version operates between 40 and 60 V.All measured values ​​and setpoint specifications are sent to the axis control / axis regulation system based on a digital signal processor, which thus assumes the role of the central logic unit. The connected driver stage is responsible for processing the logic signals from the digital signal processor to control the power transistors in the output stage. The achievable dynamics of the switching process are important here, as the resulting switching time of the output stage has a significant impact on the expected overall performance. The output stage is designed so that the required currents can be switched by an inductive load with high dynamics. According to one embodiment, the required electrical energy is provided via an appropriately dimensioned capacitor. The energy supply can also be provided directly via the mains.This capacitor should have the lowest possible parasitic inductance to avoid negatively affecting the current rise time at the switch-on moment. The current that ultimately flows to the linear actuator is determined by the duty cycle of the coil voltage, the properties of the winding, and the total inductance of the system. The system can be operated in control mode by specifying a voltage value for a defined period of time. Furthermore, it is also possible to convert the values ​​from the displacement measurement into a vector velocity value and use this as a measured variable for control operation to regulate the velocity and thus the available kinetic energy via the system's duty cycle.

[0067] A position measuring unit transmits a signal to the power electronics 54, which uses this to determine the exact position and speed of the rotor 24.

[0068] The power electronics 54 further enables communication with a machine tool Z-robot controller so that the surface hammer 1 can be guided along the desired movement path for machining the workpiece and can be triggered at the intended positions.

[0069] The top of Figure 5 shows a highly simplified representation of the basic position of the linear actuator 6 according to the invention, more precisely the relative position of the rotor 24 with respect to the stator 18. In this basic position, which can be adjusted, for example, by preloading the rotor 24 (i.e., adjustable via the guides distributed around the circumference [serving as anti-twist protection, guiding the springs and final position of the rotor]), the helical rotor webs 50, 52 defining the rotor slots 46, 48 are offset from the slot webs 34, 35 defining the two spiral slots 28, 30, so that the offset 58 between these rotor webs 50, 52 and the slot webs 34, 35 is maximum (note the following relationship: offset < web width). In this starting position, the rotor webs 50, 52 and the slot webs 34, 35 are offset from one another by approximately one width of these webs.In the illustrated embodiment, this offset corresponds to the maximum stroke of the linear actuator 6, which can be 1 mm, for example. In this basic position, the total inductance of the entire system is at its minimum, while the magnetic resistance is at its greatest. If a voltage is now applied to the coil 32, as indicated below in Figure 5, a current flow is created in the bifilar winding, which changes direction at the turning point 42 and thus also influences the magnetic field formed. When the electrical voltage is applied, the coil 32 generates a magnetic field between the adjacent pole shoe pairs formed by the opposing slot webs 34, 35 and rotor webs 50, 52, which magnetic field is characterized by the current direction. The resulting field lines are shown in the two illustrations according to Figure 5.Furthermore, the linear actuator 6 has a position sensor (not shown here) which measures / detects the stroke of the rotor 24 over time.

[0070] When the DC voltage is applied, as explained above, the magnetic resistance is maximum at the beginning of the control process - this is shown by the comparatively widely spaced field lines in Figure 5 above. Since the system strives for minimal magnetic resistance (reluctance) when energizing the coil 32, and the greatest magnetic resistance is effective in the initial position shown (Figure 5 above), a reluctance force is generated that acts on the rotor 24 in the direction of the minimum magnetic resistance, which occurs when the rotor webs 50, 52 overlap with the slot webs 34, 35. A reluctance force is generated in the axial direction FR, as shown in Figure 5, which is comparatively large due to the reluctance-optimized web geometry.

[0071] As shown in the illustration in Figure 5 above, a deflected magnetic flux occurs in the area of ​​the magnetic flux exit surface on the stator side. This deflection depends not only on the geometric boundary conditions, such as the design of the tooth geometry on the rotor and stator sides, but also significantly on the offset 58. When current is applied to coil 32, the ideal position with regard to reluctance is established between stator 18 and rotor 24, in which the overlap of the slot webs 34, 35 and the rotor webs 50, 52 is maximum, thus resulting in an essentially homogeneous magnetic flux.

[0072] In addition, radial forces arise which act on the rotor 24 in the radial direction - these radial forces are compensated by the bearing, in particular a plain bearing.

[0073] In the illustrated embodiment, the plain bearing bushings 20, 22 are designed so that the rotor 24 can be adjusted by the reluctance force FR with high positioning accuracy. This adjustment of the rotor 24 continues until the relative position is reached in which the minimum magnetic resistance is combined with maximum total inductance. This state is shown at the bottom of Figure 5. Accordingly, this position is reached at maximum overlap of the slot webs 34, 35 with the rotor webs 50, 52, so that the maximum field line density is established, with the forces acting in the radial direction being maximum and the forces acting in the axial direction being minimum. The radial air gap AR remains constant throughout the entire movement sequence. However, the offset 58, i.e. the degree of overlap, the reluctance, the inductance, and the magnetic flux change with axial movement 18.

[0074] As explained above, power electronics 54 are required to provide the high power of coil 32. Suitable measures must be taken to protect the linear actuator 6 from overheating and thus from destruction of the drive unit. This can be achieved, on the one hand, by suitable control or regulation via the power electronics and, on the other hand, by additional cooling. Figure 6 shows possibilities for cooling the linear actuator 6 according to the invention. Accordingly, for example, the region of the linear actuator 6 in which the radial air gap AR is formed and also the internal stator can be cooled, so that coolant flow paths 62, 64 are created along the stator 18 or the air gap AR. It is particularly advantageous that, in the described embodiment, the coil 32 is formed by an insulated stranded wire, so that direct contact of the current-carrying regions of the coil with the cooling medium is excluded.Accordingly, air or a cooling liquid can be used as the coolant. In the embodiment shown in Figure 6, at least one coolant channel 60 is formed in the stator, through which the coolant flows. This coolant channel 60 can also be closed on one side, whereby a corresponding return flow of the coolant must be enabled. In principle, it is possible to use different coolants for cooling the radial air gap AR and the (internal) cooling of the stator 18.

[0075] The above-described embodiment is designed as a single-phase system—the corresponding circuit symbol for the coil is shown in Figure 7a. This means that the current is supplied via the power supply L1, with the current direction in the area of ​​the coil 32 leading to the inflection point 42 being opposite to that in the coil section extending from the inflection point 42 to the coil outlet and thus to the negative pole of the system.

[0076] Such a single-phase system is particularly well suited for short-stroke motion, with the maximum stroke—as explained above—approximately corresponding to the width of these webs 50, 52; 34, 35. Of course, the stroke can also be smaller with a smaller axial offset. According to the invention, the pole shoe pairs are each designed as a continuous helix with a predetermined pitch and a predetermined tooth geometry (tooth length and tooth width in cross-section).

[0077] Figure 7b shows an n-phase drive system, specifically a three-phase drive system, in which three coils 32a, 32b, 32c can be controlled via the power electronics 54, for example, to achieve a stroke that is greater than the width of the aforementioned webs 50, 52; 34, 35. Alternatively or additionally, bidirectional operation can also be ensured by such a multi-phase arrangement without mechanical reset (for example, via a spring).

[0078] In such an embodiment, the stator 18 would then be designed with at least two coils 32a, 32b, which can be axially offset from one another or partially overlapping, each in a bifilament winding. It should be noted that two coils appear sufficient to ensure bidirectional operation. Figure 8 shows a schematic side sectional view of the linear actuator 6 according to the invention, which has a hammer head 4 made of hard metal or other materials, which is set into periodic oscillations or discrete individual impact movements by means of a linear actuator 6 according to the invention for surface peening or can be held in continuous contact with the workpiece to be machined.The surface hammer 1 further has a mechanical interface, in this case a hollow shaft cone 8, via which the surface hammer 1 can be inserted into a corresponding tool holder of a machine tool or a robot, so that the surface hammer 1 is guided over the NC axes of the machine tool or robot during machining. The rotor 24 is arranged relative to the stator such that an air gap 66 is provided between the two elements. Furthermore, the linear actuator 6 has a temperature sensor and a displacement sensor / position sensor 70. In this view, a (combined) data and power socket 72 is arranged on the side of the linear actuator 6. Furthermore, several return elements 74, in the form of return springs, are arranged between the rotor 24 and the hollow shaft cone 8, which return the rotor 24 (after a lifting process) to a predefined starting position.Here, the return elements 74 are arranged along the circumference of the stator 18.

[0079] Figures 9 and 10 show an isometric front view and rear view, respectively, of the linear actuator 6 according to the invention of the surface hammer 1, of the embodiment shown in Figure 8. In this illustration, the linear actuator 6 has additional (coolant) connections 10, which are arranged opposite one another on the sides of the hollow shaft cone 8. Clearly visible are the multitude of return elements 74, here in the form of return springs, which are arranged between two opposite rings and are firmly connected to them. The coil 32 is arranged / wound around the stator 18. The rings are in turn firmly connected to the rotor 24. Furthermore, the rotor 24 has a rotor sleeve 76 (shown transparent here), which opens into the housing 16 of the linear actuator 6. Two plain bearings 20, 22 are arranged at the respective ends of the rotor 24.The plain bearing 22, which is arranged at the end of the hollow shaft cone 8, has an additional bearing maintenance element 78. Also shown is a measuring system 80, which detects the deflections / positions of at least one return element 74 / position changes of the rotor 24.

[0080] Figure 11 shows a schematic functional representation of the control unit 82 of the linear actuator 6. The control unit 82 has a D / A (digital-analog) input and output 84, an interface 86, a control unit 88, a power stage 90, and a power supply 92. A first communication interface of the actuator control is a serial interface, which is implemented either via an NC controller 94 or an HMI (human-machine interface) 96, for example, a PC or a tablet. Here, the processing parameters such as impact time, intensity, and / or frequency are determined and transferred to the control unit 88. The control unit 82 evaluates the values ​​recorded by the temperature sensor 68 and the position sensor 70 of the actuator 6 and outputs the electrical power 98 dependent thereon to the linear actuator 6. Thus, the hardware interface (shown here on the right) between the control unit 82 and the linear actuator 6 transmits the digital oranalog signals, such as temperature and path data as well as electrical power.

[0081] In contrast to the prior art described at the outset, in which at least two circular pole shoe pairs are formed between the stator and the rotor, according to the invention a helical pole shoe pair is formed between the stator and the rotor, to which a coil with a bifilar winding is assigned according to the invention.

[0082] The invention described above is fundamentally characterized by an extremely robust design of the coil / winding, so that shocks and vibrations can be compensated much better than with the prior art.

[0083] As mentioned, the bifilar winding design allows for scaling with regard to the achievable force or stroke more easily than with conventional solutions. Cooling of the coil is also much easier, since, for example, the stator can be hydraulically cooled and the insulated winding between the stator and rotor can also be cooled with air. This allows operation with significantly increased current densities. This results in a further increase in the force density and thus the acceleration capability. The inventive design with one or more return elements 74 enables both continuous and discrete movement (i.e., triggering one or more individual blows) of the hammer head 4.

[0084] The reduction in inductance, which is further enhanced by the bifilar winding, enables maximum dynamic response when energizing the winding. The bifilar winding also enables a further increase in packing density and thus an increase in the specific power of the drive.

[0085] List of reference symbols:

[0086] 1 surface hammer

[0087] 2 impact inserts

[0088] 4 hammer head

[0089] 6 linear actuator

[0090] 8 hollow shaft cones

[0091] 10 Connection

[0092] 12 connection

[0093] 14 Connection

[0094] 16 housings

[0095] 18 Stator

[0096] 20 plain bearings

[0097] 22 plain bearings

[0098] 24 runners

[0099] 26 Coil holding section

[0100] 28 spiral groove

[0101] 30 spiral groove

[0102] 32 coil

[0103] 34 Groove web

[0104] 35 groove web

[0105] 36 single wires

[0106] 38 Insulation

[0107] 40 coil entry

[0108] 42 Turning point

[0109] 44 Coil exit

[0110] 46 Runner groove

[0111] 48 Runner groove

[0112] 50 runners' bridge

[0113] 52 Runners' Bridge

[0114] 54 Power electronics

[0115] 56 Position measuring unit

[0116] 58 offset

[0117] 60 Coolant channel Coolant flow path

[0118] Coolant flow path

[0119] air gap

[0120] Temperature sensor

[0121] Position sensor / displacement sensor

[0122] Data and power socket

[0123] Reset element

[0124] Runner cover

[0125] Bearing maintenance element

[0126] measuring system

[0127] Control unit

[0128] D / A input / output

[0129] interface

[0130] Control unit

[0131] Performance level

[0132] power supply

[0133] NC control

[0134] Human-Machine Interface electrical power

Claims

Patent claims 1. Reluctance linear actuator (6) with an axially adjustable rotor (24) and a stator (18) arranged coaxially thereto and at least one coil (32) arranged in the area between the stator (18) and the rotor (24), which coil is guided in a groove (28, 30) of the stator (18) and which is delimited by groove webs (34, 35), wherein a groove profile facing the groove webs (34, 35) is formed on the rotor (24), the groove walls of which each form an offset (58) with the groove webs (34, 35), and with power electronics (54) for controlling the at least one coil (32) in such a way that the rotor (24) performs a controlled / regulatable stroke as a function of the control due to the reluctance force, wherein the groove profile is designed complementarily to the groove webs (34, 35) in such a way that minimal offset (58) are arranged approximately radially opposite each other,wherein the stator (18) and the rotor (24) are made of a magnetically conductive or soft magnetic material, characterized in that the linear actuator (6) has at least one return element (74) which is designed such that, during operation, the rotor (24) is brought into a certain predefined starting position after a lifting movement.

2. Linear actuator (6) according to claim 1, characterized in that the at least one return element (74) is designed to be spring-elastic in the direction of movement of the rotor (24) and / or a plurality of return elements (74) are arranged distributed over the circumference of the stator (18).

3. Linear actuator (6) according to claim 1 or 2, characterized in that the groove (28, 30) and / or the groove profile are each designed as a double helix, wherein the coil (32) is guided along one helical turn from a coil inlet (40) to a turning point (42) and from there along a second helical turn in the opposite direction to a coil outlet (44), so that the coil sections leading to the turning point (42) and away from it are arranged bifilarly.

4. Linear actuator (6) according to one of the preceding claims, wherein the rotor (24) is tubular and engages around the stator (18), wherein the grooves (28, 30) guiding the at least one coil (32) and designed as a double helix are formed on an outer circumferential surface of the stator (18) and the associated groove profile, also designed as a double helix, is formed on an inner circumferential surface of the rotor (24).

5. Linear actuator (6) according to one of the preceding claims, wherein the coil (32) is formed as a stranded wire consisting of a plurality of individual wires (36) or as a single wire (36) with several turns.

6. Linear actuator (6) according to one of the preceding claims, wherein the coil (32), in particular a stranded wire or single wire forming it, is insulated.

7. Linear actuator (6) according to one of the preceding claims, wherein a plurality of coils (32a, 32b, 32c) are connected to form a multi-phase structure and can be individually controlled via the power electronics (54), so that the stroke of the rotor (24) is increased compared to a single-phase structure or bidirectional operation is enabled.

8. Linear actuator (6) according to one of the preceding claims, with a cooling system associated with the at least one coil (32).

9. Linear actuator (6) according to claim 8, wherein the cooling is carried out by means of a coolant, for example air or a cooling liquid, which is guided along the air gap (AR) and / or the stator (18).

10. Linear actuator (6) according to one of the preceding claims, wherein the pitches and groove widths of the stator and rotor-side double helix are substantially identical.

11. Linear actuator (6) according to one of the preceding claims, wherein the linear actuator (6) has at least one return element (74) in the form of a return spring, preferably a plurality of return elements (74) in the form of return springs.

12. Linear actuator (6) according to one of the preceding claims, wherein the linear actuator (6) has a plurality of return elements (74) in the form of return springs arranged distributed over the circumference of the stator (18), which are designed such that during operation the rotor (24) is brought into a certain predefined starting position after a lifting movement.

13. Tool, in particular for surface hammering, with a linear actuator (6) according to one of the preceding claims, wherein a tool holder for a hammer head (4) is provided on the linear actuator (6) and with a machine tool interface, in particular an interface customary in machine tool construction, for example a hollow shank cone (8) for an HSK tool holder of a machine tool or a robot.

14. Valve drive for actuating servo and / or directional valves (hydraulic, pneumatic), with a linear actuator (6) according to one of claims 1 to 12.

15. Valve drive of an internal combustion engine with a linear actuator (6) according to one of claims 1 to 12.

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