Controlled electromagnet with end position determination

Abstract

A linear actuator (1) in the form of an electric reversing solenoid, comprising a cylindrical metal housing (2) in which two magnetic coils (3, 3') are housed and which metal housing (2) guides an armature element (4) axially displaceable along its central axis (A), wherein the armature element (4) is movable between a first end position (push) and a second end position (pull) by a stroke length (H). The cylindrical metal housing (2) is covered at its end faces by a first (7) and a second (7') shunt element. The electronic controls are housed in an additional enclosure (12) to which a connector element (13) is provided for supplying power to the magnetic coils (3, 3') and the electronic control, as well as for transmitting control signals and communication data.Two Hall sensors (15, 15') are integrated in the center of the metal housing (2), arranged in the transverse plane T and in different radial directions (R1, R2). These Hall sensors are located adjacent to the first and second permanent magnet elements (16) fitted into the armature element (4) at the respective end positions of the armature element (4). Together with these magnet elements (16), they form a detector pair to generate a switching signal at these positions. To increase the positioning accuracy (g) of the armature element, the position of the individual elements (15, 16) of the respective detector pairs is individually adjusted relative to each other such that the signal steepness of the signal step in the output signal is maximized in the region of the respective end position. For further precision in switching accuracy, a switching point for controlling the magnetic coils is defined in the steepest part of this signal step.

Description

[0001] The present invention relates to a linear actuator in the form of a reversing solenoid according to the preamble of claim 1.

[0002] Industrial robots are used in the production of industrial products. Their manipulators are typically actuated by pneumatic actuators (pneumatic cylinders) and are used in numerous pneumatic processes, particularly in conveying, handling, and drive technology, or in injection molding tools, as described, for example, in EP-0264682. These pneumatic actuators typically have contactless limit switches, especially magnetic switches, to control the reciprocating actuation.

[0003] To accelerate the sequence of piston movements, EP-0417024 proposed using two magnetic switches arranged in series to control the piston movement. The first magnetic switch initiates the reversal of the piston movement, and the second magnetic switch starts the reverse movement. Hall sensors can also be used instead of the usual magnetic switches.

[0004] Unfortunately, pneumatic cylinders generally exhibit undesirably high mechanical wear (abrasion of the seals) and energy consumption (high heat losses) and, in light of the current energy crisis, are to be replaced by more efficient drives. Therefore, today's industry aims to achieve significant energy savings in manufacturing through the use of electric drives, particularly electric cylinders.

[0005] Electrically driven devices for generating reciprocating motion have therefore become known in the field. For example, EP-2075656 describes an electric actuator as a replacement for a pneumatic cylinder, whose piston rod is moved by means of an electrically driven spindle. The position of the piston rod is controlled by a motor control circuit.

[0006] EP-0671070 describes a rotary cylinder designed in the form of an electric motor, which moves a drive rod back and forth inside it via a thread. The respective position of this drive rod is determined using an optical rotary position detection device.

[0007] Unfortunately, these linear actuators prove to be undesirably slow for industrial use. Furthermore, optical detectors require additional space, which contradicts the desired miniaturization of these actuators.

[0008] It is therefore an object of the present invention to create a linear actuator which overcomes the disadvantages of known actuators and in particular to create an electrically driven actuator which enables fast and, above all, precise stroke movements, has low energy and heat losses and no significant wear, is in particular maintenance-free and allows a robust, i.e., compact design using standard components.

[0009] This problem is solved according to the invention with a linear actuator according to claim 1 and in particular with the aid of an electric reversing solenoid of a known type, which has a cylindrical metal housing in which two magnetic coils are inserted. An axially displaceable armature element is mounted in these magnetic coils, which is movable between a first end position (extended) and a second end position (retracted).

[0010] At its end face, this metal housing is terminated by a metallic, typically ferromagnetic, first and second shunt element. A drive pin, centrally located and thus rigidly connected to this armature element, projects through the first shunt element and out of the metal housing on the working side to move a coupled working element. A central guide element is provided for the mechanical stabilization of the armature element. This guide element engages the armature element in a way that allows axial displacement, while simultaneously being rigidly anchored to the second shunt element located at the base. A circuit board for the electronic control is housed in an additional enclosure mounted on the metal housing and preferably features an 8-pin connector, common in the machine industry, for supplying power to the magnetic coils and transmitting control signals for the electronic controls.In particular, this circuit board includes a microprocessor that processes and forwards all operationally relevant signals, such as those for end-position detection, coil control, LED activation and deactivation, and the supply of other digital inputs and outputs, including those for external controllers. For example, the controllers on this circuit board allow the magnetic coils to be digitally controlled, thus enabling energy-efficient operation instead of switching them directly via their supply voltage. This electronic control of the coil current allows the user to easily implement customer-specific special functions (holding force or time), reducing energy consumption and heat generation from the coils during operation.

[0011] To achieve a compact design for this actuator, two Hall sensors are integrated into the center of the metal housing, i.e., in the area between the magnetic coils. These sensors are arranged in the transverse plane and in opposite radial directions, positioned in close proximity to the movable armature element. Two LEDs mounted on the circuit board are electronically connected to these Hall sensors and visualize the first and second end positions of the armature element as detected by the sensors. Finally, the housing incorporates two light elements, which, in the form of light guides, direct the light from the LEDs outwards for visibility.

[0012] When this actuator is in operation, in the first end position (push) of the armature element, a first permanent magnet element, fitted into the armature element in a first radial direction, is adjacent to a first of these two Hall sensors arranged in this first radial direction, thus forming a first detector pair for generating a first switching signal and activating a first LED. In the second end position (pull) of the armature element, a second permanent magnet element, magnetically insulated within the armature element and fitted in a second radial direction, is adjacent to a second of these two Hall sensors arranged in this second radial direction, thus forming a second detector pair for generating a second switching signal and activating a second LED.

[0013] It is understood that these permanent magnet elements are integrated into the armature element within a non-magnetic holder, specifically embedded, to prevent short-circuiting the magnetic field of these permanent magnets. To prevent the armature element from twisting, a threaded pin guided in the metal housing engages in a longitudinal groove of this armature element.

[0014] Standard components are preferably used for the construction of the present actuator, such as an 8-pin connector for power supply and control signal transmission, or a robust housing commonly used in the manufacturing industry. A preferred stroke length between the first and second end positions of the armature element is 20 mm, but can also be 40 mm, 60 mm, or more depending on the application. In a preferred embodiment of the actuator according to the invention, this reversing solenoid is designed for a nominal DC voltage of 24 VDC, and the radial directions in which the Hall sensors are arranged are each inclined at an angle of α = 24° to the sagittal plane of the solenoid housing.

[0015] In a first further development of this actuator, the second shunt element has an adapter piece on the outside, with which the actuator according to the invention can be connected to existing robots in order to replace their pneumatic drive in a simple manner.

[0016] In a particular embodiment of the present invention, the positioning accuracy of the armature element's end positions is maximized. For this purpose, the position of the corresponding elements of the respective detector pairs—that is, the positioning and orientation of the respective magnetic elements and Hall sensors—is individually adjusted relative to each other, in order to minimize field line scattering in the area of ​​the Hall sensors, i.e., to optimize the distribution of the field line density of the useful field and the interfering field in this area. In a preferred configuration of the present device, the intrinsic polarization direction of the magnetic element and the orthogonality of the associated Hall sensor are each aligned with one another in order to eliminate their geometric and orthogonality errors (including manufacturing tolerances).This error elimination leads to a significant increase in the steepness (signal steepness) of the Hall sensor's output signal in the region of its signal discontinuity, thus allowing for a substantial increase in switching accuracy and consequently in the positioning accuracy of the respective end positions of the armature element. In this contactless, Hall effect-based end-position determination system, the invention, for the sake of particular precision, considers not only the Cartesian (x, y, z) positioning (Cartesian coordinates), i.e., the distances between the magnetic element and the Hall sensor as well as their lateral arrangement in their respective mountings, but also their spatial orientation (spherical coordinates) in the magnetic field.

[0017] In another embodiment of the actuator according to the invention, the permanent magnetic elements are made of a plastic, e.g. PANiCNQ.

[0018] In the following, the term "sagittal plane," as it is well known in medicine, is used in the same sense, i.e., it defines a plane that encompasses the main axis and, in the sense of a longitudinal section, runs through the front and back, or top and bottom, of the actuator. Likewise, the term "transverse plane" is used here in a manner well known in medicine, i.e., it defines a plane that, in the sense of a cross-section, is perpendicular to the sagittal plane and runs through the area of ​​the housing's center.

[0019] The term "integrated" used here refers to an arrangement inside the housing material.

[0020] The term "magnetically isolated" is used here to describe a magnetically non-short-circuited magnetic element. To prevent a magnetic short circuit, the two magnetic poles of a permanent magnet are embedded in non-magnetizable materials (e.g., brass, aluminum, etc.), i.e., separated from magnetizable materials (e.g., iron). Furthermore, the term "signal transconductance" should be used in the same sense as the term "edge transconductance" known from digital signals, i.e., it refers to the transconductance [V / mm] of the Hall sensor's output signal, where V denotes the voltage difference of the output signal for a specific stroke of the armature element.

[0021] The invention will now be explained in more detail using an exemplary embodiment and the figures. These show: Fig. 1: Schematic longitudinal section (in the sagittal plane) through a preferred embodiment of an actuator according to the invention in its first end position; Fig. 2: Schematic cross-section (in the transverse plane) through a preferred embodiment of an actuator according to the invention in its first end position; Fig. 3: The course of a typical output signal of a Hall sensor along the axis of movement.

[0022] The in Fig. 1 The longitudinal section shown through a preferred embodiment of a reversing solenoid (1) according to the invention clearly illustrates its basic structure. This reversing solenoid (1) comprises, in a known manner, a cylindrical metal housing (2) in which two magnetic coils (3, 3') are housed and which guides an armature element (4) that is displaceable along its central axis (A). Depending on which of the two coils (3, 3') is energized, the armature element (4) moves to one or the other end position, i.e., extended or retracted. At its end faces, this cylindrical metal housing (2) is covered by a metallic first (7) and a second (7') shunt element. These metallic shunt elements (7, 7') are typically made of a ferromagnetic material. A centrally arranged drive pin (5) is rigidly connected to this armature element (4), e.g.,by means of a spring pin (6), wherein the drive pin (5) extends through the first shunt element (7) and out of the metal housing (2) on the working side to move a working element coupled to it. The operating principle of this type of reversing solenoid is well known and will not be explained further here. A central guide element (8) is provided for the mechanical stabilization of the armature element (4), which engages slidably with its first end in the armature element (4) and is firmly anchored with its other end in the second base-side shunt element (7'). To prevent rotation of the armature element (4), a threaded pin (10) located on the underside in the area of ​​the center of the housing engages in a longitudinal groove (9) of this armature element (4). It is understood that the sliding components (drive pin (5), guide element (8), etc.) are each guided in a maintenance-free bearing, e.g., made of polytetrafluoroethylene (PTFE).

[0023] An electronic control unit arranged on a printed circuit board (11) is housed in an additional enclosure (12) attached to the metal housing (2). This additional enclosure (12) has a connector element (13) for supplying power to the magnetic coils (3, 3'), preferably operated at a voltage of 24 V, and for transmitting control signals for the electronic control unit, in particular for controlling the holding power of the coils and / or for transmitting communication data, e.g., to a machine or a robot. This electronic control unit includes a microprocessor, which allows the magnetic coils (3, 3') to be controlled as desired.

[0024] The magnetic coils are therefore not switched directly (on / off) via the applied supply voltage (e.g., 24 V), but rather controlled by the electronic control unit. This control unit also electronically reduces the power dissipation of the magnetic coils, meaning that the energy loss of the magnetic coils can be electronically reduced, which simultaneously reduces the heat losses from the magnetic coils. Two LEDs (14) are connected on this circuit board (11), by means of which – as will be shown later with the help of the Fig. 2 As explained in more detail below, the two end positions of the armature element (4) detected by Hall sensors (15, 15') can be visualized. For this purpose, this additional housing (12) has two light guide elements (18) which make the light from these two LEDs (14, 14') arranged on the circuit board (11) visible on the outside of the additional housing (12). In the preferred embodiment, one of the LEDs illuminates when the first end position (stroke = 20 mm) of the ejected (move-out) armature element (4) is reached, and a second LED illuminates when the second end position (stroke = 0 mm) of the retracted (move-in) armature element (4) is reached. It is understood that neither of the magnetic coils needs to be energized at these end positions, even though the corresponding LEDs are illuminated.

[0025] Fig. 2 The inventive detection of the end positions of the armature element (4) is illustrated by means of two Hall sensors (15) arranged radially to the central axis (A) in the area of ​​the housing center in the transverse plane T and two magnetic elements (16) interacting with these. Fig. 2 Figure 1 shows the inventive reversing solenoid in its first (move-out) end position. In this position, a first magnetic element (16) radially fitted in the armature element (4) is adjacent to a Hall sensor (15) also radially arranged in the center of the housing. In this position, the Hall sensor (15) generates an electrical switching signal due to the magnetic field of the permanent magnet element (16). This signal is fed via a conductor element (17) to an electronic control unit and its microprocessor mounted on the circuit board (11) for further processing, in order to activate a first (14) of the two LEDs. This permanent magnet is magnetically insulated in the armature element (4), for example, embedded in a brass or aluminum holder.

[0026] Similarly, a second LED is activated when the armature element (4) is in its second (move-in) end position, and at the same time a second permanent magnet element (permanent magnet) radially fitted in the armature element (4) is adjacent to a second radially arranged Hall sensor at this second end position.

[0027] The two Hall sensors (15, 15') arranged in the transverse plane T in the area of ​​the housing center in different radial directions (R1, R2) and their respective adjacent magnetic elements (16) are positioned at an angle to each other that is adapted to the available space for the required components, in particular the armature radius, the metal housing radius, and the dimensions of the holders for the Hall sensors and permanent magnets. Preferably, the radial directions (R1, R2) in which the Hall sensors (15) and their respective adjacent magnetic elements (16) are aligned are inclined at an angle α = 24° to the sagittal plane S of the magnet housing (2).It is understood that the respective conductor elements (17) preferably lead directly from the respective Hall sensor (15) into the interior of the additional housing (12) and are connected there to the respective LED (14) arranged on the circuit board (11).

[0028] According to the present invention, the positioning accuracy of the armature element's end positions is also maximized. To this end, the position, i.e., the Cartesian positioning (in the Cartesian coordinate system), as well as the angle-specific orientation of the magnetic elements (16) and Hall sensors (15) of a detector pair relative to each other and within their respective embedding (shielding), are individually adjusted in order to minimize, in particular, the field line scattering in the area of ​​the respective Hall sensors (15), i.e., to optimize the field line density of the useful field and the interfering field in this area. In a preferred configuration of the present device, the intrinsic polarization direction of the magnetic element (16) and the orthogonality of the associated Hall sensor (15) are aligned with each other in order to eliminate, in particular, their geometric and orthogonality errors (including manufacturing defects).This error elimination leads to a surprisingly significant increase in the steepness of the output signal of the Hall sensors in the area of ​​their signal discontinuities, thus allowing a substantial increase in the switching accuracy and therefore the positioning accuracy of the respective end positions of the armature element (4).

[0029] The course of a typical output signal (AS) of the Hall sensor of an adjusted detector pair along the movement path is from Fig. 3 As can be seen, in this exemplary signal waveform (AS), the actuator according to the invention is balanced in its first end position (push, extended position), i.e., at 0.0 mm stroke and a field strength of 0.0 T. With increasing displacement of the armature element (4) towards the second end position (pull, retracted position), the stray field of the magnetic element (16) running through the armature element (4), also referred to here as the interference field (f(S)), becomes noticeable and initially leads to a negative output signal of, for example, -1.7 VDC at a field strength of -0.03 T during the pull-in phase. In the region of the second end position of the armature element (4), the output signal (AS) exhibits a signal discontinuity due to the close proximity of the detector pair, before remaining at a signal value of 4.9 VDC.In this second end position, the direct magnetic field of the magnetic element (4), also referred to here as the useful field (f(N)), is essentially the determining factor and amounts to 4.9 VDC at a field strength of +0.2 T. In this position-dependent output signal, this signal exhibits a signal transconductance of at least 2.4 VDC [ΔU HALL ] per 2.5 mm [displacement of the armature element] in the region of this signal discontinuity. The switching point (SP) for controlling the magnetic coils (3) is located at this signal discontinuity. In a preferred embodiment of the present invention, the transconductance of this signal discontinuity is maximized, particularly to improve the switching accuracy for controlling the magnetic coils. This precision is achieved, as described in more detail above, by adjusting the position of the individual and interacting elements of each detector pair within their respective embedding.This allows the positioning accuracy (g) of the anchor element to be specified in such a way that it is less than 1 mm (g < 1 mm), in particular less than 0.5 mm (g < 0.5 mm) and preferably less than 0.25 mm (g < 0.25 mm).

[0030] It is understood that the output signal of the second or subsequent detector pair shows an analogous curve.

[0031] In a further embodiment of the actuator (1) according to the invention, the permanent magnetic elements (16) are made of a plastic, e.g. PANiCNQ.

[0032] The advantages are immediately apparent to the expert and are primarily evident in the maintenance-free and compact design, for which essentially all standard components can be used, such as reversing solenoids, Hall sensors, and common connector elements. The electronic control not only allows for fast and precise end-position determination but also for electronic minimization of the power loss of the magnetic coils, thus significantly reducing heat losses from these coils at high holding forces. This results in energy-saving and efficient operation. Furthermore, the radial arrangement of the Hall sensors (15, 15') and their associated magnetic elements (16, 16') allows for a particularly space-saving design. With the use of coated sliding surfaces, especially polytetrafluoroethylene (PTFE)-coated bearings, the actuator can also be operated maintenance-free in the long term.For the astonishingly high precision of the positioning accuracy (g) of the armature element, compared to known actuators, the position of the individual elements (15, 16) of the respective detector pairs is individually adjusted to each other in such a way that the signal steepness at the signal step point of the output signal in the area of ​​the respective end position is maximized, whereby a switching point for the control of the magnetic coils is defined in the steepest area of ​​this signal step point to further refine the switching accuracy. Referenzzeichenliste

[0033] 1 Linear actuator 2 Metal housing 3, 3' Magnetic coils 4 Armature element 5 Drive pin 6 Tension pin 7 First shunt element (working side) 7' Second shunt element (base side) 8 Guide element 9 Longitudinal groove 10 Threaded pin 11 Circuit board 12 Auxiliary housing 13 Connector element 14 LED 15, 15' Hall sensors 16 Magnetic element 17 Conductor element 18 Light elements A Central axis H Stroke length S Sagittal plane T Transverse plane R 1 , R 2 Radial directions AS Output signal f(S) Output signal in the area of ​​the disturbance field f(N) Output signal in the area of ​​the useful field SP Switching point in the area of ​​the signal jump point

Claims

1. Linear actuator (1) in the form of an electric reversing solenoid, with a cylindrical metal housing (2) in which two magnetic coils (3, 3') are inserted and which metal housing (2) guides an armature element (4) axially displaceable along its central axis (A), wherein the armature element (4) is movable between a first end position (move-out) and a second end position (move-in) by a stroke length (H), wherein the cylindrical metal housing (2) is covered at its end faces by a first (7) and a second (7') shunt element and a centrally arranged drive pin (5) is rigidly connected to this armature element (4), wherein this drive pin (5) projects out of the metal housing (2) through the first working-side arranged shunt element (7), characterized by the fact thatFor the mechanical stabilization of the armature element (4), a central guide element (8) is provided, which on the one hand engages axially displaceably in the armature element (4) and on the other hand is firmly anchored in the second shunt element (7') arranged on the base side, and wherein electronic controls for the operation of the magnetic coils arranged on a circuit board (11) are housed in an additional housing (12) mounted on the metal housing (2), on which a connector element (13) is provided for the power supply of the magnetic coils (3, 3') and the electronic control as well as for the transmission of control signals, and in the area of ​​the center of the metal housing (2) two Hall sensors (15, 15') arranged in the transverse plane T and in different radial directions (R1, R2) are integrated,wherein a threaded pin (10) attached to the underside of the metal housing (2) engages in a longitudinal groove (9) of this armature element (4) to prevent rotation of the armature element (4), and wherein in the first end position (push) of the armature element (4) a first permanent magnet element (16), magnetically insulated in the armature element (4) and fitted in a first radial direction (R1), is adjacent to a first (15) of these two Hall sensors (15, 15') arranged in this first radial direction (R1) in order to form a first detector pair for generating a first switching signal, and wherein in the second end position (pull) of the armature element (4) a second permanent magnet element (16'), magnetically insulated in the armature element (4) and fitted in a second radial direction (R2), is adjacent to a second (15') of these two Hall sensors (15, 15') arranged in this second radial direction (R2). Hall sensors (15, 15') are adjacent,in order to form a second detector pair for generating a second switching signal.

2. Actuator according to claim 1, characterized by the fact that the permanent magnetic elements (16, 16') are made of a magnetic plastic.

3. Linear actuator (1) according to claim 1, characterized by the fact that the additional housing (12) has a first (14) and second (14') LED (14, 14') which can be activated by means of the first and second switching signals, with which the first and second end positions of the armature element (4) can be visualized.

4. Actuator (1) according to claim 1, characterized by the fact that the electronic control arranged on the circuit board (11) for the operation of the magnetic coils (3, 3') is programmable by means of a microprocessor.

5. Actuator (1) according to claim 1, characterized by the fact that the connector element (13) is an 8-pin connector element.

6. Actuator according to claim 1, characterized by the fact thatThis is designed for a nominal DC voltage of 24 V.

7. Actuator according to claim 1 of any of the preceding claims 1 to 6, characterized by the fact that the drive pin (5) which is firmly connected to the anchor element (4) and is centrally arranged, is firmly connected to the anchor element (4) by means of a tension pin (6).

8. Actuator according to claim 7, characterized by the fact that the stroke length (H) between the first (push) and the second (pull) end position of the anchor element (4) is 20 mm or more, i.e. H ≤ 20 mm.

9. Actuator according to one of claims 7 or 8, characterized by the fact that the two Hall sensors (15, 15') arranged in the transverse plane (T) in different radial directions (R1, R2) in the area of ​​the center of the housing are arranged such that their conductor elements (17) lead directly into the interior of the additional housing (12).

10. Actuator according to claim 9, characterized by the fact thatthe radial directions (R1, R2) in which the Hall sensors (15, 15') are arranged are each inclined at an angle α = 24° to the sagittal plane (S) of the metal housing (2).

11. Actuator according to any one of the preceding claims 1 to 10, characterized by the fact that the position of the elements of at least one of the first and second detector pairs for determining the respective end position of the anchor element (4) is adjusted such that the end position of the anchor element has a positioning accuracy (g) of less than 1 mm (g < 1 mm), in particular less than 0.5 mm (g < 0.5 mm) and preferably less than 0.25 mm (g < 0.25 mm).

12. Actuator according to claim 11, characterized by the fact thatthat at least one detector pair is adjusted such that the curve [V / mm] of the output signal of the at least one Hall sensor (R1, R2) of this at least one detector pair in the region of the respective second end position of the armature element (4) has a signal discontinuity with a signal steepness of at least 2.4 VDC [ΔU HALL ] per 2.5 mm [displacement path of the anchor element].

13. Actuator according to claim 12, characterized by the fact that For determining the respective second end position of the armature element (4) in the area of ​​the signal jump point, a switching point (SP) is defined for generating the switching signal intended for controlling the armature element.

14. Actuator according to claim 13, characterized by the fact that The switching point (SP) is defined to refine the switching accuracy in the steepest part of the signal jump point.

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