Electromagnetic lifting and / or holding actuator

Abstract

Actuator designed as a lifting and / or holding magnet for an armature, with at least one outer magnetically conductive housing (2) and an inner core (3), wherein at least a part (5) of the inner core (3) is movably designed along an axis of movement (6) perpendicular to a front boundary plane (7) which is spanned by end faces of the outer housing (2) which are directed towards the armature (4) to be attracted during the use of the actuator, and magnetic flux guidance through the outer magnetically conductive housing (2) and the inner core (3) is such that that the movable part (5) can be moved into a forward end position solely by energizing the actuator due to an electromagnetic reluctance force (11), in which it extends beyond the forward boundary plane (7) and is closer to the anchor than in a rest position in which no reluctance force acts on the movable part.

Description

Technical application area

[0001] The present invention relates to an electromagnetic actuator configured as a lifting and / or holding magnet. The structural elements of such an actuator are the movable armature, an outer magnetically conductive housing, an inner core / pole, and a coil.

[0002] Due to their simple and highly efficient design, these actuators, based on electromagnets, represent one of the oldest drive elements and are used in many application areas such as mechanical engineering, automotive engineering, and automation technology. As a drive element for limited rotary and linear movements, usually with low power consumption, an electromagnetic actuator first converts the input electrical energy into magnetic energy via the coil before this is converted into mechanical kinetic energy in the form of force or torque at interfaces. Depending on the application and task, these actuators can be categorized according to the type of force applied, including traction, impact, rotary, oscillating, and holding / holding magnets, which can perform linear / pivoting or rotary movements. A traction or impact magnet is generally understood to be a lifting magnet that performs linear movements.

[0003] A solenoid has a larger travel range (up to a few millimeters) with a characteristic force-displacement curve that can be adjusted. Depending on the application, for example, when using the solenoid to actuate a valve, adjusting / optimizing the magnetic circuit and / or implementing control or regulation is often necessary to influence the force-displacement curve. The solenoid can be energized either in an analog or pulsed manner.

[0004] The primary function of a holding magnet, however, is to hold or fix magnetizable workpieces or objects, which in this case serve as anchors. The generated magnetic holding force magnetizes ferromagnetic material and holds it with high force by the generated magnetic field. The force is limited to a very short distance and is characterized by a highly nonlinear force-displacement curve. For this task, it is not necessary for the electromagnet to cover a large travel distance. Attraction from a short distance with a holding force that increases strongly nonlinearly with decreasing air gap up to the point of contact is sufficient. State of the art

[0005] When a holding magnet is subjected to current and an armature (with a magnetizable component) is attracted by the generated magnetic field, this process is often accompanied by an unwanted closing noise. Fig. Figure 1 shows a schematic representation of an electromagnetic holding magnet system comprising an outer housing 2 and an inner core 3, which form the outer and inner poles of the electromagnet. When a component to be held, in the form of an armature plate 4, is attracted by this electromagnet through the application of a current and the resulting force to the coil 1, an undesired closing noise occurs when the armature plate 4 strikes the poles of the electromagnet, as described in Fig. As indicated in Figure 1, a similarly problematic noise characteristic is exhibited by lifting magnets in which the armature or armature plate is part of the moving electromagnet system. Undesirable noise also occurs when the armature switches / moves from the initial stroke position to the final stroke position. These closing noises are problematic because they are often perceived as disturbing and violate the customer's specifications, and ideally should be avoided or optimized to minimize noise.

[0006] To minimize noise when switching an electromagnet, it is known to insert additional components into the air gap, such as damping elements designed as damping rings or similar devices, to reduce the switching noise, as proposed, for example, in DE 36 32 475 A1. This shortens the magnet's stroke and reduces the kinetic energy towards the end of the stroke. Other common technical solutions are implemented in the form of non-magnetic anti-adhesive discs, which also lead to a shorter stroke and a reduced increase in the pull-in force at the end wall.

[0007] For each switching or holding operation, the user typically has to decide whether the characteristics of a lifting or holding magnet are required or suitable. A lifting magnet allows the design or adjustment of the force-displacement characteristic with respect to the stroke distance. Linearization and current-proportional force or stroke behavior are possible and can be achieved through appropriate design of the magnetic circuit and control of the magnet. The initial stroke position is critical here, as the force level must be above a minimum sufficient for the drive task to enable starting or switching in every application. This is achieved by influencing the characteristic curve, in which the available stroke work is optimized to provide a sufficiently high force level at the beginning of the stroke.However, it is not yet possible to generate or maintain a large force over a large stroke with reasonable electrical energy input. Therefore, development efforts have often focused solely on providing a large force or achieving a large stroke. This involves using holding magnets for high forces with small strokes and lifting magnets for lower forces with large strokes.

[0008] German patent DE 10 2016 203 063 A1 describes a reluctance actuator for active bearings, such as active motor bearings, comprising a ferromagnetic stator, an excitation coil, and an active element that is movably mounted relative to the stator. The stator has a gap into which a ferromagnetic section of the active element can be inserted. The active bearing is intended to at least partially compensate for an applied bearing force by exerting a counterforce through the reluctance actuator.

[0009] DE 20 2014 010 132 U1 deals with a drawing jaw control with a permanently polarized reversing stroke magnet. This magnet has two stroke end positions and a stroke center position between the stroke end positions, as well as an armature. A spring system exerts a force on the armature in the direction of the stroke center position in each of the two stroke end positions, whereby the spring system and the reversing stroke magnet are coordinated such that the armature can be held permanently magnetically in both stroke end positions against the spring force.

[0010] The object of the present invention is therefore to provide an electromagnetic actuator with which a large force can be applied or maintained over a larger travel distance when an armature is pulled. Description of the invention

[0011] The problem is solved with the electromagnetic actuator according to claim 1. Advantageous embodiments of the actuator are the subject of the dependent claims or can be found in the following description and the exemplary embodiments.

[0012] The proposed electromagnetic actuator is designed as a lifting and / or holding magnet for an armature, which, depending on the configuration of the magnetic system, can be implemented as part of this actuator or as an external component that is to be held by the actuator. The proposed actuator has at least one outer magnetically conductive housing and an inner core or pole, and is thus, for example, designed as a solenoid, pot, or shackle magnet with an inner core. A (virtual) front boundary plane is defined by the end face(s) of the outer housing, which are oriented towards the armature to be attracted during operation of the actuator. The proposed actuator is characterized by the fact that at least a part of the inner core or pole isThe pole is designed to be movable along an axis perpendicular to the front boundary plane, also referred to as the axis of movement in the present patent application, and the magnetic flux guidance in the actuator is such that the movable part can be moved into a forward end position, in which it projects beyond the front boundary plane, solely by energizing the actuator, i.e., the actuator's electrical coil(s), due to the electromagnetic reluctance force. In the forward end position, the movable part is closer to the armature than in a rest position, in which no reluctance force acts on the movable part. Thus, in this actuator, an internal positioning movement of the movable part of the inner core is enabled during operation, i.e., when the actuator's electrical coil(s) are energized.This positioning movement is performed electromagnetically based on the reluctance force and thus relies on the tendency to achieve the most electromagnetically favorable state with the lowest magnetic resistance. This state corresponds to a position of the moving part in its forward end position, in which it extends beyond the front boundary plane and has approached the armature. The movable part tends to assume this position because it seeks to improve the magnetic flux, which previously existed solely via the air above the front boundary plane, in the more magnetically conductive return material.

[0013] In the proposed armature, the outer housing and inner core with its movable part are designed such that the movement of the movable part into its forward end position is caused by an energizing current applied to the actuator, as occurs during normal operation to attract the armature. A suitable design can be determined, for example, by simulating the forces at different geometries and corresponding currents applied to the actuator's electrical coil(s). During normal operation, i.e., when the current is applied to attract the armature, the movable part of the inner core initially moves into its forward end position, thus shortening the distance to the armature being attracted. This advantageously influences the force-displacement characteristic of the actuator or electromagnet, as will be explained in more detail in the following exemplary embodiments.

[0014] With an actuator designed in this way, the movable part of the inner core or pole is brought closer to the armature than the outer housing or the outer pole(s) when the actuator is energized and thus the pulling process begins. This results in a greater force being exerted on the armature at the start of the pulling process compared to a conventional actuator with an outer housing and inner core. As soon as the armature touches the movable part of the inner core during the pulling movement, it moves it towards a rear end position against the reluctance force acting on the movable part until the lifting or pulling movement of the armature is terminated by a corresponding stop. This stop can occur when the armature reaches the rear end position of the movable part, which corresponds to its rest position, by striking the outer housing or pole(s).The impact may be caused by the outer pole(s) or by the armature striking an additional stop element on the actuator. The actuator can preferably be designed as an electromagnet or a hybrid magnetic assembly consisting of a coil and permanent magnets.

[0015] The proposed actuator thus combines the positive properties of a lifting magnet and a holding magnet to obtain an optimal force-displacement characteristic suitable for the respective application, with an adapted force level. Previous concepts reach their limits in terms of design and control technology. Any increase in the armature's attracting force at the beginning of the stroke by influencing the characteristic curve in a conventional lifting magnet is associated with a decrease in magnetic force as the air gap narrows. With holding magnets, on the other hand, a significant non-linear decrease in force with an increasing air gap is unavoidable, and attracting force is no longer possible at longer strokes. By combining the characteristic properties of a lifting magnet and a holding magnet according to the present invention, it is possible to achieve a traversing or lifting motion with a correspondingly high force level at the beginning of the stroke and also a correspondingly high force level at the end of the stroke.This enables a high force with reasonable electrical energy input over a larger stroke than previously possible with such actuators / magnets. Since the armature's attraction or lifting motion, upon contact with the moving part, acts against the reluctance force that moved the moving part to its forward end position, the armature's movement is slightly decelerated or magnetically damped, thus also reducing noise during electromagnet operation. Additional mechanical damping elements can be added as required to achieve the permissible noise level. The proposed electromagnet design therefore provides a noise-dampened actuator that allows for adjustment or linearization of the force-displacement characteristic with considerable design flexibility in the travel range, while simultaneously providing high holding force and reduced electrical energy input.

[0016] Preferably, the actuator is designed, i.e., the outer magnetically conductive housing and the inner core with the movable part are dimensioned such that the front end position corresponds to at least one equilibrium position in which, during intended operation of the actuator, a weight force acting on the movable part and the electromagnetic reluctance force acting on the movable part, which opposes the weight force, are in balance. The actuator is arranged such that the armature is located above the actuator, meaning that the weight force on the movable part is directed in the same direction as the attractive force of the electromagnet on the armature.

[0017] To reduce the magnetic attraction force acting on the moving part in the opposite direction to the electromagnetic reluctance force, the movable part, in its rest position, preferably does not rest directly against the magnetic material of the inner core or a rear part of the outer housing with its rear end face (i.e., the end face not facing the armature). This is preferably achieved by a spacer made of a non-ferromagnetic material between the rear end face of the moving part and the static part of the inner core or the rear part of the outer housing, which locally weakens the magnetic field at this point. This spacer can, for example, be applied as a layer to the rear end face of the moving part or to the opposite surface of the static part of the inner core or outer housing.The spacer can be made of materials such as aluminum or plastic. Its thickness can be minimal, for example, only 100 to 500 µm. Alternatively, an air gap can be incorporated in this area. In this case, the movement of the moving part into its rear end position must be mechanically limited. Using this spacer or air gap ensures that the magnetic flux enters the moving part laterally at this point, rather than through the rear end face. This reduces the magnetic attraction to the moving part along its axis of movement in this area.

[0018] The movable part preferably represents an outer circumferential portion of the inner core with respect to a cross-section perpendicular to the axis of movement. Thus, for example, in the case of a cylindrical inner core, it is shaped like a cylindrical shell and encloses the static part of the inner core. However, the present actuator is not limited to such a geometric configuration.

[0019] It is also possible to extend the area of ​​the actuator where the armature, the moving part, and the magnetic return meet by means of a cone control through appropriate geometric design. This allows for additional influence on the characteristic curve control. Alternatively, suitable established control concepts, such as pseudoforce control, make it possible to adjust the magnetic force-stroke characteristic of the actuator without altering the characteristic curve itself, thus making it more technically usable. Brief description of the drawings

[0020] The proposed actuator is explained in more detail below using exemplary embodiments in conjunction with the drawings. These show: Fig. 1 a schematic representation of the structure and operation of a holding magnet according to the state of the art; Fig. 2 a schematic representation of an embodiment of the proposed actuator in cross-section and top view; Fig. 3. A schematic representation of the intermediate positions and magnetic flux path during a complete switching operation of the actuator; and Fig. 4. A representation of the forces acting on the moving part of the proposed actuator in the equilibrium state. Ways to implement the invention

[0021] The function and construction of a holding magnet with an outer housing and inner core according to the state of the art was described in conjunction with Fig. 1 already explained in the introductory description.

[0022] An exemplary embodiment of the actuator according to the invention is shown in Fig. Figure 2 shows a schematic cross-section and a top view. In this example, the actuator is pot-shaped and accordingly has an outer magnetically conductive housing 2 and an inner core 3. The inner core 3 has a movable part 5, hereinafter also referred to as a plunger, which, when the coil 1 of the actuator is energized, moves along the axis of movement 6 towards the armature plate 4 due to an electromagnetic reluctance force, i.e., beyond the front boundary plane 7 of the actuator, which is formed by the end faces of the outer housing 2 facing the armature. This is, for example, in the Fig. 4 indicated in cross-section. Top view of this actuator (lower part of the illustration). Fig. (2 without the armature plate) the outer housing 2, the inner core 3, the movable part 5 of the inner core and the coil 1 can be seen.

[0023] The actuator shortens the air gap to the armature plate 4 in the air through the internal positioning movement of the ferromagnetic plunger 5, thus reducing the overall magnetic resistance of the system. Without the positioning movement of the plunger 5, the overall magnetic resistance of the system is therefore higher.

[0024] For the intended positioning movement of the plunger 5, the magnetic force pulling the plunger 5 downwards must not be greater than the opposing electromagnetic reluctance force. This can be achieved by a suitable design of the actuator via the magnetic flux guidance. Preferably, the magnetic force pulling the plunger 5 downwards is reduced or eliminated by preventing a direct attraction between the plunger / return interfaces at the rear or lower end face of the plunger 5. In the present example, this is achieved by a spacer ring 8, which is not ferromagnetic. In the rear end position of the plunger 5, the spacer ring 8 prevents a magnetic flux from the outer housing 2 through the rear end faces of the plunger 5 into the plunger. Instead, the magnetic flux can only enter the plunger 5 laterally, as shown by the magnetic field lines 9 in Fig. 3 is indicated.

[0025] This Fig. Figure 3 shows four different intermediate positions AD during the switching process of the actuator. In the initial position (position A), the armature plate 4 is not within range of the electromagnetic attraction force (see the depicted magnetic field lines 9, which result from energizing the coil 1). Only a significant increase in the current through the coil and a consequent increase in the area of ​​attraction of the magnetic field strength could attract the armature plate 4 at all. However, this would lead to various problems, such as excessive heating of the coil and a considerable force when the armature plate 4 strikes the iron core, i.e., the outer housing 2 and the inner core 3, resulting in a pronounced closing noise.If, in the actuator proposed here, the plunger 5 moves upwards due to the electromagnetic reluctance force (position B), the total magnetic flux of the actuator increases due to the reduction of the air gap to the armature plate 4. In the present example, at least one force equilibrium position of the plunger 5 is reached (see also ). Fig. 4), in which the plunger remains in this position with the coil continuously energized at an unchanged current. Due to the new position of the plunger 5, the armature plate 4 enters the area of ​​attraction of the magnetic pull force without an increase in the coil current and thus experiences an attractive force towards the plunger 5 (position C), since the air gap between the armature plate 4 and plunger 5 is reduced, thereby maximizing the Maxwell pull force. The magnetic flux now increases due to the reduced overall magnetic resistance of the smaller air gap, and the armature plate 4 moves towards the iron return. In the final step, the armature plate 4 and plunger 5 move together into the end position of the stroke, thus completing the switching process (position D).

[0026] When the armature plate 4 strikes the plunger 5 during a switching operation, it is magnetically damped by the reluctance force that moved the plunger 5 into this position, thus slightly slowing its movement. However, since the force acting on the armature plate 4 is significantly greater than the force attempting to hold the plunger 5 in its forward position, a complete switching operation can be carried out, and the armature plate 4 ultimately contacts the iron return of the actuator's outer housing. Due to the described relationship, this occurs with reduced speed and consequently reduced switching noise, and this can be adjusted within certain limits through further measures.Additional damping elements on the plunger or on the fixed pole, i.e. between the rear end face of the plunger and the rear area of ​​the outer magnetically conductive housing or the inner core against which the plunger moves during its return movement to the rear end position, are of course also possible.

[0027] The actuator can also be equipped with an additional anti-stick disc between armature plate 4 and plunger 5 and / or a damping insert between armature plate 4 and magnetic return, which also contributes to reduced noise generation.

[0028] Fig. Figure 4 shows a schematic cross-sectional representation of an embodiment of the proposed actuator, in which the plunger 5 has moved beyond the actuator's front boundary plane 7 into its forward end position due to energizing the actuator. This end position corresponds to at least one equilibrium state in which the weight force 10 acting on the plunger 5 and the electromagnetic reluctance force 11 are in balance. In principle, the reluctance force 11 can still be greater than the weight force 10 even in this end position. The plunger 5 can then, for example, be held in the forward end position by a mechanical limit.

[0029] The cross-sections and spacing of the actuator's components and the electrical excitation (current) are coordinated accordingly to achieve the intended functionality of the actuator, as described in Fig.Figure 3 is shown schematically. For example, a first prototype of the actuator was made of steel (9SMn28K) with a diameter of 77 mm and a height of 49 mm. The inner core had a total diameter of 54 mm, of which the static part had a diameter of 48 mm. The spacer ring, which locally attenuated the magnetic field, was made of aluminum and was only 0.5 mm thick. Reference symbol list 1 coil 2 Outer casing 3 Inner core 4 Anchor plate 5. Movable part or plunger 6. Axis of movement 7 Front boundary plane 8 spacer ring 9 magnetic field lines 10 Weight force 11 Electromagnetic reluctance force

Claims

[1] Actuator designed as a lifting and / or holding magnet for an armature, comprising at least one outer magnetically conductive housing (2) and an inner core (3), wherein at least a part (5) of the inner core (3) is movably designed along an axis of movement (6) perpendicular to a front boundary plane (7) which is spanned by end faces of the outer housing (2) which are directed towards the armature (4) to be attracted during the use of the actuator, and magnetic flux guidance through the outer magnetically conductive housing (2) and the inner core (3) is such that that the movable part (5) can be moved into a forward end position solely by energizing the actuator due to an electromagnetic reluctance force (11), in which it extends beyond the forward boundary plane (7) and is closer to the anchor than in a rest position in which no reluctance force acts on the movable part. [2] Actuator according to claim 1, characterized by , that between a rear end face of the movable part (5), which is directed away from the armature (4), and a rear section of the outer magnetically conductive housing (2) or the inner core (3) a spacer (8) made of a non-ferromagnetic material is arranged, which opposes a magnetic attraction of the movable part (5). [3] Actuator according to claim 2, characterized by , that the spacer (8) has a thickness between 100 µm and 1 mm. [4] Actuator according to claim 2 or 3, characterized by , that the spacer (8) is made of a material that achieves noise damping of a switching operation of the actuator. [5] Actuator according to claim 2 or 3, characterized by, that a damping element is arranged between the rear end face of the movable part (5) and the rear section of the outer magnetically conductive housing (2) or the inner core (3) which achieves noise damping of a switching operation of the actuator. [6] Actuator according to claim 1, characterized by , that a damping element is arranged between a rear end face of the movable part (5), which is directed away from the armature (4), and a rear section of the outer magnetically conductive housing (2) or the inner core (3), which achieves noise damping of a switching operation of the actuator. [7] Actuator according to any one of claims 1 to 6, characterized by, that the outer magnetically conductive housing (2) and the inner core (3) with the movable part (5) are dimensioned and arranged such that the front end position is an equilibrium position in which, when the actuator is energized as intended, a weight force (10) acting on the movable part (5) and the electromagnetic reluctance force (11) acting on the movable part (5) due to the energization are in equilibrium. [8] Actuator according to any one of claims 1 to 7, characterized by , that the movable part (5) extends in a cross-section perpendicular to the axis of movement (6) over the circumference of the inner core (3).

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