Sensor for magnetically detecting linear relative motion of holding magnets without contact and method for magnetically detecting linear relative motion of holding magnets without contact

Abstract

To provide a method for reliably recognizing two states of a gripper, namely, a "gripper activated" state and a "gripper deactivated" state.SOLUTION: At least two identical sensor elements (4) detect at least two components of a magnetic field of a holding magnet (2). The sensor elements (4) are arranged along a measurement section (3) at a constant spacing (A), the sensor elements (4) being shorter than the measurement section (3). Each of the sensor elements (4) generates a monotonic position signal having one value within a defined range for each position of the holding magnet (2) along the measurement section (3). The characteristic curves of the position signals each exhibit symmetry. The sensor includes a control and evaluation unit (6). The control and evaluation unit (6) is configured to evaluate, on the basis of the position signals of the sensor elements (4), a first end position (7) of the holding magnet (2) and a second end position (7) of the holding magnet (2) captured by the sensor elements (4).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sensor for contactless magnetically detecting the linear relative movement of holding magnets according to the preamble of claim 1 and to a method for contactless magnetically detecting the linear relative movement of holding magnets according to the preamble of claim 5. [Background technology]

[0002] An application of the sensor is a pneumatic gripper, particularly a magnetic gripper. This magnetic gripper utilizes a holding magnet that moves inside the magnetic gripper. When the holding magnet is near the working surface for holding the workpiece, it can hold the workpiece. When the holding magnet is moved away from the working surface, the workpiece is released again. This gripper is used in many different applications, notably welding. Both positions, "gripping machine active" (holding magnet on working surface) and "gripping machine inactive" (holding magnet not on working surface), can be captured by a magnetic sensor that analyzes the magnetic field of the holding magnet.

[0003] Currently, there are at least two implementations available, but they only address some aspects of the requirements outlined above. For example, a first implementation uses two separate sensors that are robust to the welding field, and in this implementation the two sensors must be mounted in different locations to detect the two switch points.

[0004] The placement of the individual sensors can be difficult or even impossible depending on the gripper, either because there is not enough space available in the groove for two sensors or because the magnetic field is so specific that the sensors cannot detect one of the magnet positions. Furthermore, the installation and wiring costs are high. Even if all given conditions are favorable for detecting both magnet positions, the sensors must be carefully positioned to achieve good switching results, which requires a certain level of experience on the part of the user or assembler.

[0005] A second known implementation uses one sensor with two switch outputs. An example of such a sensor is the SICK MZ2Q sensor. With this sensor, the holding magnet is moved to a first position and the resulting magnetic field is learned as "switch point 1." Then, the holding magnet is moved to a second position and "switch point 2" is learned in the same way. This allows both magnet positions to be recognized with one sensor.

[0006] The first problem with this second implementation is that the switch points must be learned. This process is often counterintuitive and introduces the possibility of sensor tampering, which some users find unacceptable. Additionally, the learned switch points are often too precise for most applications, and even slight changes in the magnetic field environment can cause the switch points to be lost. Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to reliably recognize the two gripper states: "gripping machine active" and "gripping machine inactive." The two gripper states should preferably be recognized by a single sensor, e.g., a sensor with two switch outputs. Furthermore, the sensor should be able to recognize each switch position without a teaching process, and this should be true for various gripper types. Furthermore, each switch point should be as robust as possible to changes, such as drift caused by ferromagnetic deposits or attachments or the gripped object itself. Finally, the sensor should be able to filter out temporary, dynamic external magnetic fields that may be caused by, for example, a welding process. [Means for solving the problem]

[0008] This problem is solved by a sensor for contactless magnetic detection of the linear relative movement of a holding magnet along a measuring section by means of at least two identical sensor elements. wherein each sensor element captures at least two components of the magnetic field of the holding magnet, the sensor elements are arranged at regular intervals along the measurement section, the sensor elements are shorter than the measurement section, the sensor elements each generate a monotonic position signal having one value within a certain value range for each position of the holding magnet along the measurement section, the characteristic curves of the position signals each exhibit symmetry, the sensor comprises a control and evaluation unit configured to evaluate a first end position of the holding magnet captured by the sensor element based on the position signals of the sensor elements, the first end position of the holding magnet and the second end position of the holding magnet being determined by the control and evaluation unit when the position signals are in a static state, and the control and evaluation unit is configured to assign switch points to the first end position and the second end position, respectively, and to output the switch points as switch signals to at least one switch output or interface.

[0009] The object is further achieved by a method for contactless magnetic detection of the linear relative movement of a holding magnet along a measuring section by means of a sensor having at least two identical sensor elements. wherein each sensor element captures at least two components of the magnetic field of the holding magnet, the sensor elements are arranged at regular intervals along the measurement section, the sensor elements are shorter than the measurement section, the sensor elements each generate a monotonic position signal having one value within a certain value range for each position of the holding magnet along the measurement section, the characteristic curves of the position signals each exhibit symmetry, the sensor is equipped with a control and evaluation unit, which uses the position signals of the sensor elements to evaluate a first end position of the holding magnet and a second end position of the holding magnet captured by the sensor elements, the first end position of the holding magnet and the second end position of the holding magnet being determined by the control and evaluation unit when the position signals are in a static state, and switch points are assigned to the first end position and the second end position, and the control and evaluation unit is configured to output the switch points as switch signals to a switch output or an interface.

[0010] The invention is based on the idea that the switching information is generated not through an absolute magnetic field or a magnetic field threshold, but through the change in the magnetic field when the magnet is moved or in a static state. To this end, two sensor elements are used that are suitable for determining the magnitude of the magnetic field through the measurement of at least two magnetic field components. The progression of the magnitude is symmetrical around a maximum at the position where the distance to the holding magnet is minimum.

[0011] The present invention has at least three distinct advantages. No learning or "teach" is required: the switch process is triggered at the end of every move with no preconditions.

[0012] The switch point is accurate and robust: even if the magnetic field gradually changes due to age or other influences, switching remains reliable, since only the most recent movement or most recent static state of the holding magnet is always the determining factor.

[0013] Temporary and dynamic external magnetic fields are excluded. Such temporary or dynamic fields are perceived as movement, so the sensor will not switch while the external magnetic field is applied. When the external magnetic field gradually disappears again, the magnetic field returns to the same state as before the disturbance, so the switching process will not be performed.

[0014] The implementation according to the present invention is based on two basic assumptions. The change in the magnetic field during the transfer is sufficiently large, i.e. the larger this change is, 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 up in an end position. The sensors described herein or the methods described herein do not check whether the holding magnet has reached the correct end position. However, this is far less important than the availability and robustness of the sensor system in most applications.

[0016] In a further development of the invention, the control and evaluation unit is configured to store a first magnitude of the magnetic field signal of each sensor element when the magnetic fields of both sensor elements are unchanged and at least one magnitude of the magnetic field signals exceeds a predetermined minimum magnetic field strength, recognize the start of movement of the holding magnet when the magnetic field signals of both sensor elements change, recognize the stop of movement of the holding magnet when the magnetic field signals of both sensor elements are unchanged, store a second magnitude of the magnetic field signal of each sensor element when the magnetic fields of both sensor elements are unchanged and at least one magnitude of the magnetic field signals exceeds a predetermined minimum magnetic field strength, and assign the switch point to the first and second end positions, respectively, when the difference between the magnitudes before and after the movement exceeds a minimum threshold value.

[0017] The switch point is recognized by the following operation. Recognition of the start of movement: When the magnetic field changes, this is recognized as the start of movement of the holding magnet, and the calculated magnitude of the position signal of each sensor element before the movement is stored.

[0018] Movement recognition: During a changing magnetic field, movement is recognized based on the fluctuating or dynamic position signals captured by the sensor elements.

[0019] Recognition of movement stop: When the magnetic field stops changing, it is recognized as movement stop, and the magnitude of the position signal of each sensor element after movement is stored.

[0020] The direction of movement is then evaluated by the control and evaluation unit on the basis of the magnitude of the position signal of each sensor element before and after the movement.

[0021] The basic premise for switching the switch output is that the difference between the magnitude before and after the shift exceeds a minimum threshold according to the following equation: (|B1n-B1v|+|B2n-B2v|)>Bvnmin where B1v and B2v are the position signals of each sensor element before movement, B1n and B2n are the position signals of each sensor element after movement, and Bvnmin is a predetermined minimum magnitude threshold.

[0022] Then, at least one of the magnitudes must exceed the minimum magnetic field strength before and after the movement. If this condition is met, determine in which direction the magnet moved. This determination can be done in a variety of ways.

[0023] The magnitude can also consist of three or more magnetic field components, which provides even greater robustness.

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

[0025] This can be determined, for example, by the fact that on one side of the intermediate position the magnitude of the position signal of one sensor element is greater 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 the direction of movement of the holding magnet.

[0027] This can be determined, for example, from the fact that the magnitude of the position signal of one of the sensor elements always increases or decreases in the direction of movement.

[0028] The invention, together with further features and advantages thereof, will now be described in more detail on the basis of exemplary embodiments with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0029] [Figure 1] A sensor according to the present invention. [Figure 2] 5 is a schematic diagram of a position signal of each sensor element. DETAILED DESCRIPTION OF THE INVENTION

[0030] In the following drawings, the same parts are designated by the same reference numerals.

[0031] FIG. 1 shows a pneumatic gripper, specifically a magnetic gripper 10. This magnetic gripper 10 utilizes a holding magnet 2 that moves within the magnetic gripper 10. When the holding magnet 2 is near an operating surface for holding the workpiece 11, it can hold the workpiece 11. When the holding magnet 2 is moved away from the operating surface, the workpiece 11 is released again. This gripper is used in many different applications, notably welding. Both positions, "gripping machine active" (holding magnet 2 on the operating surface) and "gripping machine inactive" (holding magnet 2 not on the operating surface), can be detected by a sensor 1, i.e., a magnetic sensor, which analyzes the magnetic field 12 of the holding magnet 2.

[0032] 1 shows a sensor 1 for contactless magnetic detection of the linear relative movement of a holding magnet 2 along a measuring section 3 using at least two identical sensor elements 4, each capturing at least two components of the magnetic field 12 of the holding magnet 2, the sensor elements 4 being spaced apart at a fixed distance A along the measuring section 3 and being shorter than the measuring section 3, the sensor elements 4 each generating a monotonic position signal having one value within a fixed value range for each position along the measuring section of the holding magnet 2, the characteristic curves of the position signals each exhibiting symmetry, and the sensor 1 comprising a control and evaluation unit 6 which, based on the position signals of the sensor elements 4, determines the relative movement of the sensor elements 4. The control and evaluation unit 6 is configured to evaluate a first end position 7 of the holding magnet 2 captured by the magnet 2 sensor 4 and a second end position 8 of the holding magnet 2, the first end position 7 of the holding magnet 2 and the second end position 8 of the holding magnet 2 being determined by the control and evaluation unit 6 through the position signal being in a static state, and is configured to assign switch points to the first end position 7 and the second end position 8, respectively, and the control and evaluation unit 6 is configured to output the switch points as switch signals to at least one switch output 9 or interface, for example one switch output 9 for each switch signal.

[0033] The switching information is generated not through an absolute magnetic field or a magnetic field threshold, but through the change or static state of the magnetic field 12 when the holding magnet 2 moves, for which two sensor elements 4 are used, which are suitable for determining the magnitude of the magnetic field 12 through the measurement of at least two magnetic field components.

[0034] The magnitude profile shown in Figure 2 is symmetrical about a maximum at the minimum distance to the holding magnet, as shown diagrammatically in Figure 2. Each sensor element 4 captures a monotonic position signal that has a value within a certain range for each position along the measuring path of the holding magnet 2, and the characteristic curves of these position signals each exhibit symmetry.

[0035] The switching process is triggered at the end of each movement without preconditions. The only decisive factor is always the most recent movement or the most recent static state of the holding magnet 2.

[0036] The movement of the holding magnet 2 always ends in the end position 7 or 8 .

[0037] For example, the control and evaluation unit is configured to store first magnitudes B1v, B2v of the magnetic field signals of each sensor element 4 when the magnetic fields of both sensor elements 4 are not changing and at least one of the magnitudes B1v, B2v of the magnetic field signals exceeds a predetermined minimum magnetic field strength Bmin, recognize the start of movement of the holding magnet 2 when the magnetic field signals of both sensor elements 4 change, recognize the stop of movement of the holding magnet 2 when the magnetic field signals of both sensor elements 4 are not changing, store second magnitudes B1n, B2n of the magnetic field signals of each sensor element 4 when the magnetic fields of both sensor elements 4 are not changing and at least one of the magnitudes B1v, B2v of the magnetic field signals exceeds a predetermined minimum magnetic field strength Bmin, and assign the switch points to the first end position 7 and the second end position 8, respectively, when the difference between the magnitudes before and after the movement exceeds a minimum threshold value.

[0038] The switch point is recognized by the following operation. Recognition of the start of movement: That is, when the magnetic field changes, this is recognized as the start of movement of the holding magnet 2, and the calculated magnitudes B1v and B2v of the position signals of each sensor element before the movement are stored.

[0039] Movement recognition: During a changing magnetic field, this is recognized as movement based on the fluctuating or dynamic position signal captured by the sensor element 4.

[0040] Recognition of movement stoppage, i.e. when the magnetic field no longer changes, this is recognized as movement stoppage and the magnitudes B1n and B2n of the position signals of each sensor element 4 after the movement are saved in a memory located in the sensor 1 by the control and evaluation unit 6.

[0041] The direction of movement is then evaluated by the control and evaluation unit 6 on the basis of the magnitudes B1v, B2v, B1n and B2n of the position signals of each sensor element 4 before and after the movement.

[0042] The basic premise for switching the switch output is that the difference between the magnitude before and after the shift exceeds a minimum threshold according to the following equation: (|B1n-B1v|+|B2n-B2v|)>Bvnmin Here, B1v and B2v are the position signals of each sensor element 4 before movement, B1n and B2n are the position signals of each sensor element 4 after movement, and Bvnmin is a predetermined minimum magnitude threshold.

[0043] Then, at least one of the magnitudes before and after the movement must exceed the minimum magnetic field strength Bmin. If this condition is met, it is determined in which direction the holding magnet 2 has moved. This determination can be made in various ways.

[0044] The magnitude can also consist of three or more magnetic field components, which provides even greater robustness.

[0045] In one example, the control and evaluation unit 6 is configured to calculate and evaluate one side, for example "Seite1" or "Seite2", starting from an intermediate position of the holding magnet 2.

[0046] This is determined, for example, by the fact that on one side of the intermediate position the magnitude of the position signal of one sensor element 4 is greater than the magnitude of the position signal of the other sensor element 4 .

[0047] In one example, the control and evaluation unit 6 is configured to calculate and evaluate the direction of movement of the holding magnet 2 .

[0048] This can be determined, for example, from the fact that the magnitude of the position signal of one of the sensor elements 4 always increases or decreases in the direction of movement. [Explanation of symbols]

[0049] 1...Sensor 2...Holding magnet 3...Measurement section 4...Sensor element 6...Control and evaluation unit 7...First end position 8...Second end position 9...Switch output 10...Magnetic gripping machine 11...Workpiece 12...Magnetic field Seite1...side Seite2...side B1v, B2v...First magnitude of the magnetic field signal B1n, B2n...second magnitude of the magnetic field signal Bmin: Minimum magnetic field strength A…Spacing

Claims

1. A sensor (1) for magnetically detecting the linear relative movement of a holding magnet (2) along a measuring section (3) without contact, using at least two identical sensor elements (4), each sensor element (4) detecting at least two components of the magnetic field (12) of said holding magnet (2), The sensor elements (4) are arranged at regular intervals (A) along the measurement section (3), The sensor element (4) is shorter than the measurement section (3), each of the sensor elements (4) generates a monotonic position signal having a value within a certain range of values ​​for each position along the measuring section (3) of the holding magnet (2); the characteristic curves of the position signals each exhibit symmetry; The sensor is equipped with a control and evaluation unit (6). In the sensor (1), The control and evaluation unit (6) Based on the position signal of the sensor element (4), It is configured to evaluate a first end position (7) of the holding magnet (2) captured by the sensor element (4) and a second end position (7) of the holding magnet (2), a first end position (7) of the holding magnet (2) and a second end position (8) of the holding magnet (2) are determined by the control and evaluation unit (6) through the static state of the position signal, The control and evaluation unit (6) is configured to assign a switching point to each of the first end position (7) and the second end position (8), and to output the switching point as a switching signal to a switching output (9) or an interface. A sensor (1) characterized in that

2. The control and evaluation unit (6) storing a first magnitude (B1v, B2v) of the magnetic field signal of each sensor element (4) when the magnetic fields (12) of both sensor elements (4) are not changing and at least one of the magnitudes (B1v, B2v) of the magnetic field signals of both sensor elements (4) exceeds a predetermined minimum magnetic field strength (Bmin); The start of the movement of the holding magnet (2) is recognized when the magnetic field signals of both sensor elements (4) change; When the magnetic field signals of both sensor elements (4) are unchanged, the stopping of the movement of the holding magnet (2) is recognized; When the magnetic fields of both sensor elements (4) are not changing and at least one of the magnitudes (B1v, B2v) of the magnetic field signals of both sensor elements (4) exceeds a predetermined minimum magnetic field strength (Bmin), storing second magnitudes (B1n, B2n) of the magnetic field signals of each sensor element (4); assigning the switch point to the first terminal position (7) and the second terminal position (8) when the difference between the magnitudes before and after the movement exceeds a minimum threshold value; It is configured as follows: Sensor (1) according to claim 1 .

3. 2. The sensor (1) according to claim 1, characterized in that the control and evaluation unit (6) is configured to calculate and evaluate one side (Side 1, Side 2) starting from an intermediate position of the holding magnet (2).

4. 2. The sensor (1) according to claim 1, characterized in that the control and evaluation unit (6) is configured to determine and evaluate the direction of movement of the holding magnet (2).

5. A method for contactless magnetically detecting the linear relative movement of a holding magnet (2) along a measuring section (3) using a sensor (1) with at least two identical sensor elements (4), each of which detects at least two components of the magnetic field (12) of the holding magnet (2), The sensor elements (4) are arranged at regular intervals (A) along the measurement section (3), The sensor element (4) is shorter than the measurement section (3), each of the sensor elements (4) generates a monotonic position signal having a value within a certain range of values ​​for each position along the measuring section (3) of the holding magnet (2); the characteristic curves of the position signals each exhibit symmetry; The sensor is equipped with a control and evaluation unit (6). In the method, Using a control and evaluation unit (6), Based on the position signal of the sensor element (4), A first end position (7) of the holding magnet (2) and a second end position (8) of the holding magnet (2) captured by the sensor element (4) are evaluated, a first end position (7) of the holding magnet (2) and a second end position (8) of the holding magnet (2) are determined by the control and evaluation unit (6) through the static state of the position signal, A switching point is assigned to each of the first end position (7) and the second end position (8), and the control and evaluation unit (6) is configured to output the switching point as a switching signal to a switching output (9) or an interface. A method characterized by:

6. Using said control and evaluation unit (6), When the magnetic fields (12) of both sensor elements (4) are not changing and at least one of the magnitudes (B1v, B2v) of the magnetic field signals of both sensor elements (4) exceeds a predetermined minimum magnetic field strength (Bmin), a first magnitude (B1v, B2v) of the magnetic field signals of each sensor element (4) is stored; The start of movement of the holding magnet (2) is recognized when the magnetic field signals of both sensor elements (4) change; The stopping of the movement of the holding magnet (2) is recognized when the magnetic field signals of both sensor elements (4) are unchanged; When the magnetic fields of both sensor elements (4) are not changing and at least one of the magnitudes (B1v, B2v) of the magnetic field signals of both sensor elements (4) exceeds a predetermined minimum magnetic field strength (Bmin), a second magnitude (B1n, B2n) of the magnetic field signal of each sensor element (4) is stored; assigning the switch point to the first terminal position (7) and the second terminal position (8) when the difference between the magnitudes before and after the movement exceeds a minimum threshold value; 6. The method of claim 5.

7. 6. The method according to claim 5, characterized in that, using the control and evaluation unit (6), one side (first side, second side) of the holding magnet (2) is calculated and evaluated starting from an intermediate position.

8. 6. The method according to claim 5, wherein the control and evaluation unit (6) is used to determine and evaluate the direction of movement of the holding magnet (2).

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