Sensor for contactless magnetic detection of linear relative movement of a holding magnet

Abstract

Sensor (1) for contactless magnetic detection of linear relative movement of a holding magnet (2) along a measuring path (3) with at least two identical sensor elements (4), each sensor element (4) detecting 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 monotonous position signal with a value of a value range for a respective position along the measuring section (3) of the holding magnet (2), wherein the characteristics of the position signals each have a symmetry, wherein the sensor has a control and evaluation unit (6), characterized in that the control and evaluation unit (6) is designed 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 is 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) in that the position signals are static, and 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 designed to output the switching points as switching signals at a switching output (9) or an interface.

Description

[0001] The present invention relates to a sensor for the contactless magnetic detection of linear relative movement of a holding magnet according to the preamble of claim 1.

[0002] One application of the sensor concerns pneumatic grippers, specifically magnetic grippers. These magnetic grippers use a holding magnet that is moved inside the magnetic gripper. If the holding magnet is close to an active surface for holding a workpiece, the workpiece can be held. If the holding magnet is moved away from the active surface, the workpiece is released again. These grippers are used in many different applications, including welding applications. The two positions "gripper active" (holding magnet on active surface) and "gripper inactive" (holding magnet NOT on 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 a first implementation, two individual welding field-resistant sensors are used. This implementation involves two sensors that must be mounted in two different positions to detect the two switching points.

[0004] Depending on the gripper, positioning the individual sensors can be difficult or even impossible, 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, the installation and wiring work is complex. Even if all conditions are favorable for detecting both magnet positions, the sensors must be positioned carefully to achieve a good switching result. This requires a certain level of experience on the part of the user or installer.

[0005] A second known implementation uses a sensor with two switching outputs. One example of such a sensor is the MZ2Q sensor from SICK. With this sensor, the holding magnet is moved to a first position and then the current magnetic field is taught as switching point ONE. The holding magnet is then moved to a second position and taught accordingly as switching point TWO. This allows both magnet positions to be detected with one sensor.

[0006] A first problem with this second implementation is that the switching points must be taught. This process is usually not intuitive and also offers the possibility of manipulating the sensor, which is unacceptable to some users. Furthermore, the taught switching points are usually too precise for most applications, so even minor changes in the magnetic environment pose a risk of switching point loss.

[0007] One object of the invention is to reliably detect two gripper positions, "gripper active" and "gripper inactive." The two gripper positions should ideally be detected by a single sensor, which, for example, has two switching outputs. Furthermore, the sensor should be able to detect the switching positions without a teach-in process, even with different gripper types. Furthermore, the switching points should be as robust as possible against drift and other changes in the gripper, e.g., caused by ferromagnetic deposits or attachments, or the gripped object itself. Finally, the sensor should be able to suppress possible temporary, dynamic external fields, e.g., those caused by welding processes.

[0008] The object is achieved according to claim 1 with a sensor for the contactless magnetic detection of linear relative movement of a holding magnet along a measuring path 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 path, wherein the sensor elements are shorter than the measuring path, wherein the sensor elements each generate a monotonic position signal with a value of a value range for a respective position along the measuring path of the holding magnet, wherein the characteristic curves of the position signals each have a symmetry, wherein the sensor has a control and evaluation unit, wherein the control and evaluation unit is designed, 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 in that the position signals are static, and a switching point is assigned to 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 at least one switching output or an interface.

[0009] The object is further achieved according to claim 1 by a method for contactless magnetic detection of linear relative movement of a holding magnet along a measuring section with a sensor having 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 of a value range for one position along the measuring section of the holding magnet, wherein the characteristic curves of the position signals each have a 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, 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 in that the position signals are static, and a switching point is assigned to 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.

[0010] The invention is based on the idea of ​​generating 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, which are capable of calculating the magnitude of the magnetic field by measuring at least two magnetic field components. The magnitude curve is symmetrical around a maximum located at the position of closest distance to the holding magnet.

[0011] The invention has at least three significant advantages: No teaching is necessary. The switching process is triggered at the end of each movement, without any preconditions.

[0012] The switching points are precise and robust. Even if the magnetic field changes slowly over the lifetime or due to other influences, switching continues to be reliable, since only the last movement or the last static position of the holding magnet is decisive.

[0013] Temporary, dynamic external fields are suppressed. 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 is removed, the magnetic field returns to the same state as before the disturbance, and no switching occurs.

[0014] The realization according to the invention is based on two basic requirements: The magnetic field change during the movement is large enough: the larger this change, the larger the parameter Bmin can be chosen and the more robust the switching behavior becomes.

[0015] The movement of the holding magnet always ends in the end positions. The sensor or method described here does not check whether the holding magnet has moved to the correct end position. In the vast majority of applications, however, this aspect is significantly less relevant than the high availability and robustness of the sensor technology.

[0016] In a further development of the invention, the control and evaluation unit is designed to store first amounts 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 amounts 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 amounts 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 amounts 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 if a difference between the respective amounts before and after the movement exceeds a minimum threshold.

[0017] 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 and the determined values ​​of the position signals and the sensor elements before the movement are saved.

[0018] Detection of movement: As the magnetic field changes, this is detected as movement due to the changing or dynamic position signals detected by the sensor elements.

[0019] Detection of movement stop: If the magnetic field no longer changes, this is detected as a stop of movement and the values ​​of the position signals and the sensor elements after the movement are saved.

[0020] The direction of movement is then evaluated by the control and evaluation unit based on the magnitudes of the position signals of the sensor elements before and after the movement.

[0021] The basic requirement for switching the switching outputs is that the difference between the amounts 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 amount threshold.

[0022] And that at least one of the values ​​before and after the movement is above a minimum field strength. If this requirement is met, the direction in which the magnet has moved is determined. This determination can be done in various ways.

[0023] The absolute value could also be calculated using three or more field components. This would further increase robustness.

[0024] In a further development of the invention, the control and evaluation unit is designed to determine and evaluate one side starting from a center position of the holding magnet.

[0025] 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.

[0026] In a further development of the invention, the control and evaluation unit is designed to determine and evaluate a direction of movement of the holding magnet.

[0027] This is determined, for example, by the fact that the value of the position signal of a sensor element constantly increases or decreases in a direction of movement.

[0028] The invention will be explained below with reference to further advantages and features, using exemplary embodiments, with reference to the accompanying drawings. The figures of the drawing show: Fig. 1 a sensor according to the invention; Fig. 2 a schematic representation of the position signals of the sensor elements.

[0029] In the following figures, identical parts are provided with identical reference numerals.

[0030] Fig. 1 shows a pneumatic gripper, specifically a magnetic gripper 10. These magnetic grippers 10 use a holding magnet 2 that is moved inside the magnetic gripper 10. If the holding magnet 2 is close to an active surface for holding a workpiece 11, the workpiece 11 can be held. If the holding magnet 2 is removed from the active surface, the workpiece 11 is released again. These grippers are used in many different applications, including welding applications. The two positions "gripper active" (holding magnet 2 on the active surface) and "gripper inactive" (holding magnet 2 not on the active surface) can be detected by the sensor 1 or magnetic sensor, which analyzes the magnetic field 12 of the holding magnet 2.

[0031] Fig. 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 monotonic position signal, each with a value of a value range for a respective position along the measuring section of the holding magnet 2, wherein the characteristic curves of the position signals each have a symmetry, wherein the sensor 1 has a control and evaluation unit 6, wherein the control and evaluation unit 6 is designed, based on the position signals of the sensor elements 4, to determine 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 elements 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 in 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.

[0032] The switching information is not generated via absolute magnetic fields or magnetic field thresholds, but via the change or the 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.

[0033] The amount development according to Fig. 2 symmetrically around a maximum, which is located in the position of the smallest distance to the holding magnet. This is Fig. 2. The sensor elements 4 each detect a monotonic position signal with one value from a value range for one position along the measuring path of the holding magnet 2, wherein the characteristic curves of the position signals each exhibit symmetry.

[0034] The switching process is triggered at the end of each movement, without any precondition. Only the last movement or the last static position of holding magnet 2 is decisive.

[0035] The movement of the holding magnet 2 always ends in the end positions 7 or 8.

[0036] For example, the control and evaluation unit is designed to store 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 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.

[0037] The detection of the switching points works as follows: Detection of the start of movement: If the magnetic field changes, this is detected 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.

[0038] Detection of movement: As the magnetic field changes, this is detected as movement due to the changing or dynamic position signals detected by the sensor elements 4.

[0039] Detection of the movement stop: If the magnetic field no longer changes, this is detected as a movement stop and the amounts 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.

[0040] The direction of movement is then evaluated by the control and evaluation unit 6 on the basis of the magnitudes of the position signals B1v, B2v, B1n and B2n of the sensor elements 4 before and after the movement.

[0041] The basic requirement for switching the switching outputs is that the difference between the amounts before and after the movement exceeds a minimum threshold according to the equation: (abs (B1n - B1v) + abs (B2n - B2v)) > Bvnmin

[0042] 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 amount threshold.

[0043] And that at least one of the values ​​before and after the movement is above a minimum field strength Bmin. If this requirement is met, the direction in which holding magnet 2 has moved is determined. This determination can be done in various ways.

[0044] The absolute value could also be calculated using three or more field components. This would further increase robustness.

[0045] 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 center position of the holding magnet 2.

[0046] 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.

[0047] For example, the control and evaluation unit 6 is designed to determine and evaluate a direction of movement of the holding magnet 2.

[0048] This is determined, for example, by the fact that an amount 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 final 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 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), each sensor element (4) detecting 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 monotonous position signal with a value of a value range for a respective position along the measuring section (3) of the holding magnet (2), wherein the characteristics of the position signals each have a symmetry, wherein the sensor has a control and evaluation unit (6), characterized by , that the control and evaluation unit (6) is designed 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 is 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) in that the position signals are static, and 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 designed to output the switching points as switching signals at a switching output (9) or an interface. [2] Sensor (1) according to claim 1, characterized by , that the control and evaluation unit (6) is designed to store first amounts of the magnetic field signals (B1v, B2v) of the sensor elements (4) when the magnetic field (12) 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 (4) changes, to detect a stop of movement of the holding magnet (2) if the magnetic field signal of both sensor elements (4) does not change, to store second amounts 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 amounts 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) if a difference between the respective amounts before and after the movement exceeds a minimum threshold. [3] Sensor (1) according to claim 1, characterized by that the control and evaluation unit (6) is designed to determine and evaluate one side (side 1, side 2) starting from a central position of the holding magnet (2). [4] 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).

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