Sensor for non-contact magnetic detection of linear relative movement of a holding magnet and method for non-contact magnetic detection of linear relative movement of a holding magnet

Abstract

Sensor (1) for non-contact magnetic detection of linear relative motion of a holding magnet (2) along a measuring section (3) with at least two identical sensor elements (4), wherein each sensor element (4) detects at least two components of a magnetic field (12) of the holding magnet (2), wherein the sensor elements (4) are arranged at a distance (A) along the measuring section (3), wherein the sensor elements (4) are shorter than the measuring section (3), wherein the sensor elements (4) each generate a monotone position signal as a magnetic field signal, with each value having a value within a range of values ​​for each position of the holding magnet (2) along the measuring section (3), wherein the characteristic curves of the position signals each have a symmetry, wherein the sensor (1) has a control and evaluation unit (6), characterized by the fact that the control and evaluation unit (6) is formed, based on the position signals of the sensor elements (4), to evaluate a first end position (7) of the holding magnet (2) and a second end position (8) of the holding magnet (2), which are detected by the sensor elements (4), wherein the first end position (7) of the holding magnet (2) and the second end position (8) of the holding magnet (2) are determined by the control and evaluation unit (6) by the fact that the position signals are statically available, and each to assign a switching point to the first end position (7) and the second end position (8), wherein the control and evaluation unit (6) is configured to output the switching points as switching signals at a switching output (9) or an interface, wherein the control and evaluation unit (6) is configured to store the first values ​​of the magnetic field signals (B1v, B2v) of the sensor elements (4) when the magnetic field signal of both sensor elements (4) does not change, where at least one of the first magnitudes of the magnetic field signals (B1v, B2v) is above a defined minimum field strength (Bmin), to detect a movement start of the holding magnet (2) when the magnetic field signal of both sensor elements (4) changes, to detect a movement stop of the holding magnet (2) when the magnetic field signal of both sensor elements (4) does not change, to store second magnitudes of the magnetic field signals (B1n, B2n) of the sensor elements (4) when the magnetic field signal of both sensor elements (4) does not change, wherein at least one of the second magnitudes of the magnetic field signals (B1n, B2n) is above the defined minimum field strength (Bmin), and to assign the respective switching point to the first end position (7) and the second end position (8) if a difference between the respective amounts before and after the movement exceeds a minimum threshold (Bvnmin).

Description

[0001] The present invention relates to a sensor for the non-contact magnetic detection of linear relative movement of a holding magnet according to the preamble of claim 1 and a method for the non-contact magnetic detection of linear relative movement of a holding magnet according to the preamble of claim 4.

[0002] One application of the sensor involves pneumatic grippers, specifically magnetic grippers. These magnetic grippers utilize a holding magnet that moves inside the gripper. When the holding magnet is near an active surface for holding a workpiece, the workpiece can be held. When the holding magnet is moved away from the active surface, the workpiece is released. These grippers are used in many different applications, including welding. The two positions, "gripper active" (holding magnet at active surface) and "gripper inactive" (holding magnet NOT at active surface), can be detected by a magnetic sensor that analyzes the magnetic field of the holding magnet.

[0003] Currently, there are at least two implementations, but they only solve partial aspects of the tasks required above: For example, in an initial implementation, two weld-field-resistant individual sensors are used. This implementation involves two sensors that must be mounted in two different positions to detect the two switching points.

[0004] Positioning individual sensors is difficult or even impossible depending on the gripper, as either the available space in the groove is insufficient for two sensors, or the magnetic field is so strong that one of the magnet positions cannot be detected by the sensors. Furthermore, this involves considerable assembly and wiring effort. Even when all conditions are favorable for detecting both magnet positions, the sensors must be carefully positioned to achieve reliable switching. This requires a certain level of experience from the user or installer.

[0005] In a known second implementation, a sensor with two switching outputs is used. An example of such a sensor is the MZ2Q from SICK. With this sensor, the holding magnet is moved into a first position, and the current magnetic field is then learned as switching point ONE. Subsequently, the holding magnet is moved into a second position, and switching point TWO is learned accordingly. In this way, both magnet positions can be detected with a single sensor.

[0006] One initial problem with this second implementation is that the switching points need to be learned. This process is usually not intuitive and also offers the possibility of sensor manipulation, which is unacceptable to some users. Furthermore, the learned switching points are often too precise for most applications, meaning that even slight changes in the magnetic environment can lead to a loss of switching points.

[0007] DE 10 2017 128 548 A1 discloses a sensor for the non-contact magnetic detection of linear relative movement of a sensor magnet along a measuring section with at least one sensor element, wherein the sensor element detects at least one component of a magnetic field of the sensor magnet, wherein the sensor element is shorter than the measuring section, wherein a control and evaluation unit is electronically connected to the sensor element, wherein the control and evaluation unit is configured to generate a position signal, wherein the control and evaluation unit is configured to generate the first time derivative of the position signal, wherein an end position position signal can be output when the first time derivative of the position signal is zero.

[0008] DE 10 2019 120 538 A1 discloses a sensor for the non-contact magnetic detection of linear relative movement of an encoder magnet along a measuring section, comprising at least two identical sensor elements, wherein each sensor element detects at least one component of a magnetic field of the encoder magnet, wherein the sensor elements are arranged at a distance along the measuring section, the sensor element being shorter than the measuring section, wherein the sensor elements each generate a monotonic position signal with one value from a range for each position along the measuring section of the encoder magnet, wherein the characteristic curves of the position signals each exhibit point symmetry, wherein an evaluation unit is provided, wherein the evaluation unit is configured to calculate a linearized position signal according to a formula.if the absolute value of the position signal of the first sensor element is less than the absolute value of the position signal of the second sensor element, or to be calculated according to another formula if the absolute value of the position signal of the first sensor element is greater than the absolute value of the position signal of the second sensor element, so that a linearized position signal with a linearized value range is formed over the entire measuring section.

[0009] DE 10 2016 110 968 A1 discloses a sensor for the non-contact magnetic detection of the linear relative movement of an encoder magnet along a measuring section, comprising at least one sensor element. The sensor element detects two components of a magnetic field of the encoder magnet that are perpendicular to each other. The sensor element and the sensor are shorter than the measuring section. A first component is an axial component, and a second component is a radial component. An evaluation unit is provided, wherein the axial component and the radial component can be evaluated in the evaluation unit according to a mathematical function. The mathematical function is ARCTAN (radial component / axial component) or ARCTAN (axial component / radial component), whereby a sectionally monotonic position signal is formed, with each value from a range of values ​​representing a position along the measuring section of the encoder magnet.wherein the evaluation unit is configured to correct the position signal in at least one area of ​​the measuring section with a constant correction value, so that a monotonic position signal with a monotonic value range is formed over the entire measuring section.

[0010] One object of the invention is to reliably detect two gripper positions, "gripper active" and "gripper inactive." Ideally, these two gripper positions should be detected by a single sensor, which, for example, has two switching outputs. Furthermore, the sensor should be able to recognize the switching positions without a teach-in process, even with different gripper types. Additionally, the switching points should be as robust as possible against drift and other changes to the gripper, e.g., due to ferromagnetic deposits or attachments, as well as the workpiece itself. Finally, the sensor should be able to filter out any temporary, dynamic external fields, e.g., from welding processes.

[0011] The problem is solved according to claim 4 by a sensor for the non-contact magnetic detection of the linear relative movement of a holding magnet along a measuring section, comprising at least two identical sensor elements, wherein each sensor element detects at least two components of a magnetic field of the holding magnet, wherein the sensor elements are arranged at a distance along the measuring section, wherein the sensor elements are shorter than the measuring section, wherein the sensor elements each generate a monotone position signal with one value from a range of values ​​for each position along the measuring section of the holding magnet, wherein the characteristic curves of the position signals each exhibit symmetry, wherein the sensor comprises a control and evaluation unit, wherein the control and evaluation unit is configured, based on the position signals of the sensor elements, to determine a first end position of the holding magnet and a second end position of the holding magnet.which is detected by the sensor elements, wherein the first end position of the holding magnet and a second end position of the holding magnet are determined by the control and evaluation unit by the fact that the position signals are static, and a switching point is assigned to each of the first end position and the second end position, wherein the control and evaluation unit is configured to output the switching points as switching signals at at least one switching output or interface.

[0012] The problem is further solved by a method for the non-contact magnetic detection of the linear relative movement of a holding magnet along a measuring section using a sensor with at least two identical sensor elements, wherein each sensor element detects at least two components of a magnetic field of the holding magnet, wherein the sensor elements are arranged at a distance along the measuring section, wherein the sensor elements are shorter than the measuring section, wherein the sensor elements each generate a monotonic position signal with one value from a range of values ​​for each position along the measuring section of the holding magnet, wherein the characteristic curves of the position signals each exhibit symmetry, wherein the sensor has a control and evaluation unit, wherein, by means of a control and evaluation unit, based on the position signals of the sensor elements, a first end position of the holding magnet and a second end position of the holding magnet are determined.which is detected by the sensor elements, is evaluated, wherein the first end position of the holding magnet and a second end position of the holding magnet are determined by the control and evaluation unit by the fact that the position signals are static, and a switching point is assigned to each of the first end position and the second end position, wherein the control and evaluation unit is designed to output the switching points as switching signals at a switching output or an interface.

[0013] The invention is based on the idea of ​​generating the switching information not via absolute magnetic fields or magnetic field thresholds, but via the change or static presence of the magnetic field during the movement of the magnet. For this purpose, two sensor elements are used that are suitable for calculating the magnitude of the magnetic field by measuring at least two magnetic field components. The magnitude profile is symmetrical around a maximum located at the position of the shortest distance to the holding magnet.

[0014] The invention has at least three significant advantages: No learning or "teaching" is necessary. The switching process is triggered at the end of each movement, without any preconditions.

[0015] The switching points are precise and robust. Even if the magnetic field changes slowly over its lifespan or due to other influences, switching continues reliably, as only the last movement or the last static position of the holding magnet is decisive.

[0016] Temporary, dynamic external fields are ignored. Such a temporary or dynamic field is detected as movement, and the sensor does not switch while the external field is present. Once the external field has dissipated, the magnetic field returns to its state before the disturbance; no switching occurs.

[0017] The implementation according to the invention is based on two basic requirements: The change in the magnetic field during movement is large enough: the larger this change, the larger the parameter Bmin can be chosen and the more robust the switching behavior becomes.

[0018] The movement of the holding magnet always ends in the end positions. The sensor and method described here do not check whether the holding magnet has moved into the correct end position. However, in the vast majority of applications, this aspect is far less important than high availability and robustness of the sensor.

[0019] According to the invention, the control and evaluation unit is configured to store first values ​​of the magnetic field signals of the sensor elements when the magnetic field of both sensor elements does not change, wherein at least one of the values ​​of the magnetic field signals is above a defined minimum field strength; to detect a start of movement of the holding magnet when the magnetic field signal of both sensor elements changes; to detect a stop of movement of the holding magnet when the magnetic field signal of both sensor elements does not change; to store second values ​​of the magnetic field signals of the sensor elements when the magnetic field of both sensor elements does not change, wherein at least one of the values ​​of the magnetic field signals is above a defined minimum field strength; and to assign the switching point to the first end position and the second end position, respectively, when a difference between the respective values ​​before and after the movement exceeds a minimum threshold.

[0020] The detection of the switching points works as follows: Detection of movement start: If the magnetic field changes, this is recognized as the start of movement of the holding magnet and the determined values ​​of the position signals and the sensor elements before the movement are stored.

[0021] Detection of movement: As the magnetic field changes, this is recognized as movement due to the changing or dynamic position signals detected by the sensor elements.

[0022] Detection of movement stop: If the magnetic field no longer changes, this is recognized as a movement stop and the values ​​of the position signals and the sensor elements after the movement are stored.

[0023] The control and evaluation unit then evaluates the direction of movement based on the magnitudes of the position signals from the sensor elements before and after the movement.

[0024] The basic requirement for switching the switching outputs is that the difference in magnitudes before and after the movement exceeds a minimum threshold according to the equation: (abs (B1n - B1v) + abs (B2n - B2v)) > Bvnmin Where B1v and B2v are position signals of the sensor elements before a movement, B1n and B2n are position signals of the sensor elements after a movement, and Bvnmin is a defined minimum magnitude threshold.

[0025] And that at least one of the values ​​before and after the movement exceeds a minimum field strength. If this condition is met, the direction in which the magnet moved is determined. This determination can be carried out in various ways.

[0026] The value could also be calculated using three or more field components. This would further increase its robustness.

[0027] In a further development of the invention, the control and evaluation unit is designed to determine and evaluate one side starting from a central position of the holding magnet.

[0028] This is determined, for example, by the fact that on one side of the center position, the magnitude of the position signal of one sensor element is higher than the magnitude of the position signal of the other sensor element.

[0029] In a further development of the invention, the control and evaluation unit is designed to determine and evaluate the direction of movement of the holding magnet.

[0030] This is determined, for example, by observing that the magnitude of the position signal from a sensor element constantly increases or decreases in a direction of movement.

[0031] The invention is further explained below with regard to its advantages and features, using exemplary embodiments and the accompanying drawing. The figures in the drawing show: Fig. 1 a sensor according to the invention; Fig. 2 a schematic representation of the position signals of the sensor elements.

[0032] In the following figures, identical parts are labelled with identical reference symbols.

[0033] Fig. Figure 1 shows a pneumatic gripper, specifically a magnetic gripper 10. This magnetic gripper 10 uses a holding magnet 2, which moves inside the gripper 10. When the holding magnet 2 is near an active surface for holding a workpiece 11, the workpiece 11 can be held. When the holding magnet 2 is moved away from the active surface, the workpiece 11 is released. These grippers are used in many different applications, including welding. The two positions "gripper active" (holding magnet 2 at active surface) and "gripper inactive" (holding magnet 2 not at active surface) can be detected by the sensor 1, or magnetic sensor, which analyzes the magnetic field 12 of the holding magnet 2.

[0034] Fig. Figure 1 shows the sensor 1 for the contactless magnetic detection of linear relative movement of a holding magnet 2 along a measuring section 3 with at least two identical sensor elements 4, wherein each sensor element 4 detects at least two components of a magnetic field 12 of the holding magnet 2, wherein the sensor elements 4 are arranged at a distance A along the measuring section 3, wherein the sensor elements 4 are shorter than the measuring section 3, wherein the sensor elements 4 each generate a monotone position signal with one value from a range of values ​​for each position along the measuring section of the holding magnet 2, wherein the characteristic curves of the position signals each have symmetry, wherein the sensor 1 has a control and evaluation unit 6, wherein the control and evaluation unit 6 is configured, based on the position signals of the sensor elements 4, to define a first end position 7 of the holding magnet 2 and a second end position 8 of the holding magnet 2.which is detected by the sensor element 4, wherein the first end position 7 of the holding magnet and a second end position 8 of the holding magnet 2 are determined by the control and evaluation unit 6 by the fact that the position signals are static, and a switching point is assigned to each of the first end position 7 and the second end position 8, wherein the control and evaluation unit 6 is configured to output the switching points as switching signals at at least one switching output 9 or an interface. For example, one switching output 9 is provided for each switching signal.

[0035] The switching information is not generated via absolute magnetic fields or magnetic field thresholds, but via the change or static presence of the magnetic field 12 during the movement of the holding magnet 2. For this purpose, the two sensor elements 4 are used, which are suitable for calculating the magnitude of the magnetic field 12 by measuring at least two magnetic field components.

[0036] The amount history according to Fig. 2 symmetrically around a maximum located at the position of least distance to the holding magnet. This is in Fig. 2 schematically represented. The sensor elements 4 each detect a monotonous position signal with one value from a range of values ​​for one position along the measuring path of the holding magnet 2, wherein the characteristic curves of the position signals each exhibit symmetry.

[0037] The switching process is triggered at the end of each movement, without any preconditions. Only the last movement or the last static position of the holding magnet 2 is decisive.

[0038] The movement of the holding magnet 2 always ends in the end positions 7 or 8.

[0039] For example, the control and evaluation unit is configured to store the first magnitudes of the magnetic field signals B1v, B2v of the sensor elements 4 when the magnetic field of both sensor elements 4 does not change, wherein at least one of the magnitudes of the magnetic field signals B1v, B2v is above a defined minimum field strength Bmin; to detect a start of movement of the holding magnet 2 when the magnetic field signal of both sensor elements changes; to detect a stop of movement of the holding magnet 2 when the magnetic field signal of both sensor elements 4 does not change; to store the second magnitudes of the magnetic field signals B1n, B2n of the sensor elements 4 when the magnetic field of both sensor elements 4 does not change, wherein at least one of the magnitudes of the magnetic field signals B1v, B2v is above a defined minimum field strength Bmin; and to assign the switching point to the first end position 7 and the second end position 8, respectively.if the difference between the respective amounts before and after the movement exceeds a minimum threshold.

[0040] The detection of the switching points works as follows: Detection of the start of movement: If the magnetic field changes, this is recognized as the start of movement of the holding magnet 2 and the determined values ​​of the position signals B1v and B2v of the sensor elements before the movement are stored.

[0041] Detection of movement: As the magnetic field changes, this is recognized as movement due to the changing or dynamic position signals detected by the sensor elements 4.

[0042] Detection of the movement stop: If the magnetic field no longer changes, this is recognized as a movement stop and the magnitudes of the position signals B1n and B2n of the sensor elements 4 after the movement are stored in the sensor 1 by the control and evaluation unit 6 in an arranged memory.

[0043] The direction of movement is then evaluated by the control and evaluation unit 6 based on the magnitudes of the position signals B1v, B2v, B1n and B2n of the sensor elements 4 before and after the movement.

[0044] The basic requirement for switching the outputs is that the difference between the magnitudes before and after the movement exceeds a minimum threshold according to the equation: (abs (B1n - B1v) + abs (B2n - B2v)) > Bvnmin

[0045] Where B1v and B2v are position signals of the sensor elements 4 before a movement, B1n and B2n are position signals of the sensor elements 4 after a movement, and Bvnmin is a defined minimum value threshold.

[0046] And that before and after the movement, at least one of the values ​​exceeds a minimum field strength Bmin. If this condition is met, the direction in which the holding magnet 2 moved is determined. This determination can be carried out in various ways.

[0047] The value could also be calculated using three or more field components. This would further increase its robustness.

[0048] For example, the control and evaluation unit 6 is designed to determine and evaluate a side, e.g., side 1 or side 2, starting from a central position of the holding magnet 2.

[0049] This is determined, for example, by the fact that on one side of the center position, the magnitude of the position signal of one sensor element 4 is higher than the magnitude of the position signal of the other sensor element 4.

[0050] For example, the control and evaluation unit 6 is designed to determine and evaluate the direction of movement of the holding magnet 2.

[0051] This is determined, for example, by observing that the magnitude of the position signal of a sensor element 4 constantly increases or decreases in a direction of movement. Reference symbol: 1 sensor 2 holding magnets 3 Measuring section 4 sensor elements 6 Control and evaluation unit 7 first end position 8 second end position 9 switching output 10 magnetic grippers 11 Workpiece 12 Magnetic field Page 1 Page Page 2 Page B1v, B2v first magnitudes of the magnetic field signals B1n, B2n second magnitudes of the magnetic field signals Bmin minimum field strength A distance

Claims

[1] Sensor (1) for non-contact magnetic detection of linear relative motion of a holding magnet (2) along a measuring distance (3) with at least two identical sensor elements (4), wherein each sensor element (4) detects at least two components of a magnetic field (12) of the holding magnet (2), wherein the sensor elements (4) are arranged at a distance (A) along the measuring section (3), wherein the sensor elements (4) are shorter than the measuring section (3), wherein the sensor elements (4) each generate a monotone position signal as a magnetic field signal, with each value having a value within a range of values ​​for each position of the holding magnet (2) along the measuring section (3), wherein the characteristic curves of the position signals each have a symmetry, wherein the sensor (1) has a control and evaluation unit (6), characterized by , that the control and evaluation unit (6) is formed, based on the position signals of the sensor elements (4), to evaluate a first end position (7) of the holding magnet (2) and a second end position (8) of the holding magnet (2), which are detected by the sensor elements (4), wherein the first end position (7) of the holding magnet (2) and the second end position (8) of the holding magnet (2) are determined by the control and evaluation unit (6) by the fact that the position signals are statically available, and each to assign a switching point to the first end position (7) and the second end position (8), wherein the control and evaluation unit (6) is configured to output the switching points as switching signals at a switching output (9) or an interface, wherein the control and evaluation unit (6) is configured to store the first values ​​of the magnetic field signals (B1v, B2v) of the sensor elements (4) when the magnetic field signal of both sensor elements (4) does not change, where at least one of the first magnitudes of the magnetic field signals (B1v, B2v) is above a defined minimum field strength (Bmin), to detect a movement start of the holding magnet (2) when the magnetic field signal of both sensor elements (4) changes, to detect a movement stop of the holding magnet (2) when the magnetic field signal of both sensor elements (4) does not change, to store second magnitudes of the magnetic field signals (B1n, B2n) of the sensor elements (4) when the magnetic field signal of both sensor elements (4) does not change, wherein at least one of the second magnitudes of the magnetic field signals (B1n, B2n) is above the defined minimum field strength (Bmin), and to assign the respective switching point to the first end position (7) and the second end position (8) if a difference between the respective amounts before and after the movement exceeds a minimum threshold (Bvnmin). [2] Sensor (1) according to claim 1, characterized by, that the control and evaluation unit (6) is designed to determine and evaluate a side (side 1, side 2) starting from a central position of the holding magnet (2). [3] Sensor (1) according to claim 1, characterized by , that the control and evaluation unit (6) is designed to determine and evaluate a direction of movement of the holding magnet (2). [4] Method for non-contact magnetic detection of linear relative motion of a holding magnet (2) along a measuring distance (3) with a sensor (1) having at least two identical sensor elements (4), wherein each sensor element (4) detects at least two components of a magnetic field (12) of the holding magnet (2), wherein the sensor elements (4) are arranged at a distance (A) along the measuring section (3), wherein the sensor elements (4) are shorter than the measuring section (3), wherein the sensor elements (4) each generate a monotone position signal as a magnetic field signal, with each value having a value within a range of values ​​for each position of the holding magnet (2) along the measuring section (3), wherein the characteristic curves of the position signals each have a symmetry, wherein the sensor (1) has a control and evaluation unit (6), characterized by , that by means of the control and evaluation unit (6), based on the position signals of the sensor elements (4), a first end position (7) of the holding magnet (2) and a second end position (8) of the holding magnet (2), which are detected by the sensor elements (4), are evaluated, wherein the first end position (7) of the holding magnet (2) and the second end position (8) of the holding magnet (2) are determined by the control and evaluation unit (6) by the fact that the position signals are statically available, and each switching point is assigned to the first end position (7) and the second end position (8), wherein the control and evaluation unit (6) is designed to output the switching points as switching signals at a switching output (9) or an interface, wherein with the Control and evaluation unit (6), The first values ​​of the magnetic field signals (B1v, B2v) of the sensor elements (4) are stored when the magnetic field signal of both sensor elements (4) does not change. where at least one of the first magnitudes of the magnetic field signals (B1v, B2v) is above a defined minimum field strength (Bmin), A movement start of the holding magnet (2) is detected when the magnetic field signal of both sensor elements (4) changes, A movement stop of the holding magnet (2) is detected when the magnetic field signal of both sensor elements (4) does not change, The second values ​​of the magnetic field signals (B1n, B2n) of the sensor elements (4) are stored when the magnetic field signal of both sensor elements (4) does not change. where at least one of the second values ​​of the magnetic field signals (B1n, B2n) is above the defined minimum field strength (Bmin), and the respective switching point is assigned to the first end position (7) and the second end position (8) if a difference between the respective amounts before and after the movement exceeds a minimum threshold (Bvnmin). [5] Method according to claim 4, characterized by , that by means of the control and evaluation unit (6) a side (side 1, side 2) is determined and evaluated starting from a central position of the holding magnet (2). [6] Method according to claim 4, characterized by , that the direction of movement of the holding magnet (2) is determined and evaluated by means of the control and evaluation unit (6).

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