Magnetic or inductive sensor

Abstract

Magnetic or inductive sensor (1), with at least one housing (2), with at least one sensor element (3) with which a magnet (4) of a piston (5) can be detected, whereby a piston position along a stroke (6) can be detected, with a control and evaluation unit (7) which is designed to evaluate the at least one sensor element (3) with which a piston position along a stroke (6) can be determined, characterized in that the respective first maximum piston position (8) and the first minimum piston position (9) are detected by the sensor (1) and a switching point is assigned to the respective maximum piston position (8) and the minimum piston position (9), wherein the control and evaluation unit (7) is designed to output the switching points as switching signals at a switching output (10) or an interface.

Description

[0001] The invention relates to a magnetic or inductive sensor according to the preamble of claim 1 and to a use of a magnetic or inductive sensor according to claim 10.

[0002] The invention relates in particular to magnetic or inductive sensors, which are frequently arranged on the housing of a working cylinder. Such sensors have proven effective for precise position determination through contactless detection of the position of, for example, pneumatic or hydraulic pistons within the working cylinder. For this purpose, guide grooves are provided on the outer surfaces of the housing of the working cylinder, in which the magnetic field sensors are held in an axially adjustable manner and, after adjustment, are locked in the guide groove, as is known, for example, from DE 196 43 413 A1 and DE 196 53 222 A1. A sensor adjusted and mounted in this way outputs a switching signal depending on the piston position. In most cases, the retracted end position and the extended end position of the piston are to be detected.

[0003] Such a sensor is known, for example, from DE 10 2004 046 107 A1, which describes a sensor with which two switching points can be set, for example, by setting two electronic switching thresholds. The sensor is designed in such a way that it is, in principle, capable of outputting a signal corresponding to the piston position. The switching thresholds are set once in a separate process step, either mechanically, for example, by adjusting a potentiometer, or via software.

[0004] DE102007029488A1 discloses a method for setting the switching point of a sensor, in particular a magnetic or inductive sensor, in particular for determining the position of the end positions of a piston, in which the piston position is repeatedly detected by the sensor and a frequency evaluation is carried out and, after a predetermined number of stroke movements of the piston, the switching point is assigned to the piston position at which the same measured values ​​occur frequently.

[0005] DE102017128548A1 discloses a sensor for the contactless magnetic detection of linear relative movement of a sensor magnet along a measuring path 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 path, wherein a control and evaluation unit is electronically connected to the sensor element, wherein the control and evaluation unit is designed to form a position signal, wherein the control and evaluation unit is designed to form the first time derivative of the position signal, wherein an end position signal can be output if the first time derivative of the position signal is zero.

[0006] Based on this prior art, it is the object of the invention to provide an improved method for switching point adjustment and a corresponding sensor.

[0007] The object is achieved according to claim 1 with a magnetic or inductive sensor, with at least one housing, with at least one sensor element with which a magnet of a piston can be detected, whereby a piston position along a stroke can be detected, with a control and evaluation unit which is designed to evaluate the at least one sensor element with which a piston position along the stroke can be determined, wherein the respective first maximum and first minimum piston position are detected by the sensor and a switching point is assigned to the maximum and the minimum piston position, wherein the control and evaluation unit is designed to output the switching points as switching signals at a switching output or an interface.

[0008] The first maximum and first minimum piston positions correspond to the piston's end positions. The first minimum piston position corresponds to the first end position of the piston, and the first maximum piston position corresponds to the second end position of the piston. The end positions are therefore at the respective ends of the maximum stroke of a piston-cylinder arrangement.

[0009] The first maximum piston position is determined by the control and evaluation unit, for example, by the piston changing its direction in the piston end position. For example, the maximum piston position can also be determined by the piston having a speed of zero in this end position. The two aforementioned conditions can also be ANDed, so that the first maximum piston position is determined by the control and evaluation unit, for example, by the piston changing its direction in the piston end position and the piston having a speed of zero in this end position.

[0010] The first minimum piston position is determined by the control and evaluation unit, for example, by the piston changing its direction in the piston end position. For example, the minimum piston position can also be determined by the piston having a speed of zero in this end position. The two aforementioned conditions can also be ANDed, so that the first minimum piston position is determined by the control and evaluation unit, for example, by the piston changing its direction in the piston end position and the piston having a speed of zero in this end position.

[0011] According to the invention, the first end-position signal can be output with the first stroke. It is not necessary to approach the end position multiple times and perform a frequency analysis. A further advantage is that the end-position signal is always output exactly at the end of the movement. Setting the switching points does not require a user action, such as pressing a button or a teach-in signal. The sensor does not require any input elements. According to the invention, the sensor is very easy to install. Both end positions can be detected by a single sensor.

[0012] According to the invention, the switching point in the end position is very precise and temperature-stable. Furthermore, the switching point is robust against lifetime-related remanence loss of the encoder magnet and robust against mechanical tolerances of the cylinder.

[0013] For example, pneumatic cylinders with a stroke of less than 50 mm are usually operated in two states: the piston fully retracted or fully extended. The piston position is detected by a magnet or sensor magnet located on the piston, whose magnetic field is detected in the end positions by the sensor element or a magnetic field sensor.

[0014] The sensor element is, for example, a Hall element. For example, the sensor element detects a component of a magnetic field of the sensor magnet, with the control and evaluation unit being designed, for example, to generate a continuous, monotonic measurement signal.

[0015] For example, the sensor element detects two mutually perpendicular components of a magnetic field of the sensor magnet, wherein the control and evaluation unit is designed, for example, to generate a continuous monotonic measurement signal.

[0016] The housing of the magnetic or inductive sensor is designed, for example, to be mounted in, partially in, or on a groove of the piston-cylinder assembly. For this purpose, the housing has, for example, an elongated shape with fastening means for securing the sensor housing in, partially in, or on the groove. The fastening means is, for example, a fastening screw.

[0017] In particular, the housing and especially the sensor element are shorter than the stroke of the piston.

[0018] If the sensor is moved in the groove, the respective end positions change so that the determination of the first maximum and first minimum piston position is recorded again by the sensor and a switching point is assigned again to the maximum and minimum piston position, whereby the determination of the switching points takes place again.

[0019] If the sensor is removed from the groove and / or mounted on a new drive, it detects the loss of position or a change in the end positions, allowing the process to start again. This means that the first maximum and first minimum piston positions are re-detected by the sensor, and a switching point is re-assigned to the maximum and minimum piston positions, thus determining the switching points anew.

[0020] For example, the sensor has a digital and / or analog output. The digital output can be a digital switching output, for example. However, a digital interface can also be provided for outputting the measured values ​​or switching points.

[0021] The analog output can, for example, be an interface with a current output of 4 to 20 mA.

[0022] In a further development of the invention, the control and evaluation unit has a memory for at least the switching points. The memory or switching point memory is, for example, a non-volatile memory, in particular an EEPROM or flash memory.

[0023] In a further development of the invention, the control and evaluation unit is designed to activate at least one activation range associated with the switching points, wherein the switching signal is activated by the control and evaluation unit within the activation range. The activation range extends over a partial range along the stroke and begins before the maximum or minimum piston position and ends at the maximum or minimum piston position. The activation range is set by the control and evaluation unit based on the determined piston end positions.

[0024] In a further development of the invention, the control and evaluation unit is designed to activate at least one hysteresis range associated with the switching points, wherein the switching signal is switched off by the control and evaluation unit outside the switching-on range and outside the hysteresis range.

[0025] The hysteresis range extends over a portion of the stroke and begins before the activation range of the maximum or minimum piston position. The hysteresis range is set by the control and evaluation unit based on the determined piston end positions.

[0026] In a further development of the invention, the control and evaluation unit is designed to activate at least one tolerance range associated with the switching points, wherein the switching signal is reset by the control and evaluation unit outside the tolerance range.

[0027] The tolerance range extends over a portion of the stroke and begins after the maximum or minimum piston position and is located outside the taught-in stroke of the piston. The tolerance range is set by the control and evaluation unit based on the determined piston end positions.

[0028] The maximum and minimum measured end positions are saved as the first switching point and the second switching point, for example. The control and evaluation unit then determines windows or the switching ranges, the hysteresis ranges and the tolerance ranges around these switching points. The piston normally moves within the first switching point and the second switching point. The switching output goes on within the switching ranges and off outside the hysteresis ranges. If the piston moves beyond the tolerance ranges, the opposite switching point is reset and the switching point on the side where it is exceeded is saved again. The next time the piston moves to the opposite side, the new switching point is also saved. However, the tolerance range only becomes active the next time the piston moves so that both switching points can be saved again.

[0029] If an invalid position is detected, the current state of the switching points or switching outputs or the position output can be maintained. If the position remains invalid for an extended period of time, for example, the stored switching points are reset and the teach-in process is restarted. This time delay allows the sensor to function reliably even in the presence of welding processes.

[0030] In a further development of the invention, the control and evaluation unit is configured to adjust the length of the activation range, the hysteresis range, and / or the tolerance range depending on the length of the detected stroke or piston stroke. For long strokes, the control and evaluation unit selects larger lengths of the activation ranges, the hysteresis ranges, and / or the tolerance ranges, while for short strokes, the control and evaluation unit selects smaller lengths of the activation ranges, the hysteresis ranges, and / or the tolerance ranges.

[0031] In a further development of the invention, the interface is an I / O link interface. For example, the digital interface is an I / O link interface. Furthermore, the digital output can be formed by a common bus system.

[0032] In a further development of the invention, the control and evaluation unit is designed to assign a switching point to an intermediate position between the end positions if the speed of the piston detected by the control and evaluation unit at the intermediate position is ZERO.

[0033] The intermediate position is determined by the control and evaluation unit, for example by the piston remaining in the intermediate piston position.

[0034] For example, the intermediate position can be determined by the fact that the piston has a speed of ZERO in this end position, i.e. the sensor signal of the sensor element does not change within a certain period of time.

[0035] According to the new development, the intermediate position signal can be output with the first stroke. It is not necessary to move to the intermediate position multiple times and perform a frequency analysis.

[0036] In a further development of the invention, the control and evaluation unit is implemented in a microcontroller. For very small sensors and very small housings with a volume of, for example, one cubic centimeter or less, a microcontroller has the advantage of already incorporating important peripheral components, such as A / D converters, integrated interfaces, etc.

[0037] Furthermore, the object is achieved by the use of the magnetic or inductive sensor according to one of the preceding claims for determining the piston end position on a pneumatic or hydraulic cylinder with a movable piston along the stroke path.

[0038] 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 to 3 each a magnetic or inductive sensor 1.

[0039] In the following figures, identical parts are provided with identical reference numerals.

[0040] Fig. 1 shows a magnetic or inductive sensor 1, with at least one housing 2, with at least one sensor element 3 with which a magnet 4 of a piston 5 can be detected, whereby a piston position along a stroke 6 can be detected, with a control and evaluation unit 7 which is designed to evaluate the at least one sensor element 3 with which a piston position along the stroke 6 can be determined, wherein the respective first maximum piston position 8 and first minimum piston position 9 are detected by the sensor 1 and a switching point is assigned to the maximum piston position 8 and the minimum piston position 9, wherein the control and evaluation unit 7 is designed to output the switching points as switching signals at a switching output 10 or an interface.

[0041] The first maximum piston position 8 and first minimum piston position 9 correspond to the end positions of the piston 5. The first minimum piston position 9 corresponds to a first end position of the piston 5 and the first maximum piston position 8 corresponds to the second end position of the piston 5. The end positions are therefore each at the respective ends of the maximum stroke of a piston-cylinder arrangement 16.

[0042] The first maximum piston position 8 is determined by the control and evaluation unit 7, for example, by the piston 5 changing its direction in the piston end position.

[0043] The first minimum piston position 9 is determined by the control and evaluation unit 7, for example, by the piston 5 changing its direction in the piston end position.

[0044] The piston position is detected by a magnet 4 or sensor magnet located on the piston 5, whose magnetic field is detected in the end positions by the sensor element 3 or a magnetic field sensor. The magnetic field 15 emanating from the magnet 4 is shown schematically.

[0045] The sensor element 3 is, for example, a Hall element. For example, the sensor element 3 detects a component of a magnetic field of the sensor magnet, wherein the control and evaluation unit 7 is designed, for example, to generate a continuous, monotonic measurement signal. According to Fig. 3, for example, two sensor elements 3 are provided. For example, several sensor elements 3 may also be provided.

[0046] The housing 2 of the magnetic or inductive sensor 1 is designed, for example, to be fastened in, partially in or on a groove of the piston-cylinder arrangement.

[0047] In particular, the housing 2 and in particular the sensor element 3 are, for example, shorter than the stroke 6 of the piston 5.

[0048] If the sensor 1 is moved in the groove, the respective end positions change, so that the determination of the first maximum piston position 8 and the first minimum piston position 9 is recorded again by the sensor 1 and a switching point is again assigned to the maximum piston position 8 and the minimum piston position 9, whereby the determination of the switching points takes place again.

[0049] If sensor 1 is removed from the groove and / or mounted on a new drive, it detects the loss of position or a change in the end positions, allowing the process to start again. This means that the first maximum piston position 8 and the first minimum piston position 9 are again detected by sensor 1, and a switching point is again assigned to the maximum piston position 8 and the minimum piston position 9, thus determining the switching points again.

[0050] For example, the control and evaluation unit 7 has a memory 11 for at least the switching points. The memory 11 or a switching point memory is, for example, a non-volatile memory, in particular an EEPROM or flash memory.

[0051] According to Fig. 2, the control and evaluation unit 7 is designed to activate at least one switching range 12 associated with the switching points, wherein the switching signal from the control and evaluation unit 7 is switched on within the switching range 12. The switching range 12 extends over a partial range along the stroke 6 and begins before the maximum piston position 8 or minimum piston position 9 and ends at the maximum piston position 8 or the minimum piston position 9. The switching range 12 is set by the control and evaluation unit 7 based on the determined piston end positions.

[0052] According to Fig. 2, the control and evaluation unit 7 is designed to activate at least one hysteresis range 13 associated with the switching points, wherein the switching signal from the control and evaluation unit 7 is switched off outside the activation range 12 and outside the hysteresis range 13.

[0053] The hysteresis range 13 extends over a partial range along the stroke 6 and begins before the switching range 12 of the maximum piston position 8 or the minimum piston position 9. The hysteresis range 13 is set by the control and evaluation unit 7 based on the determined piston end positions.

[0054] According to Fig. 2, the control and evaluation unit 7 is designed to activate at least one tolerance range 14 associated with the switching points, wherein the switching signal is reset by the control and evaluation unit 7 outside the tolerance range 14.

[0055] The tolerance range 14 extends over a partial range along the stroke 6 and begins after the maximum piston position 8 or the minimum piston position 9 and is located outside the taught stroke 6 of the piston. The tolerance range 14 is set by the control and evaluation unit 7 based on the determined piston end positions.

[0056] The maximum and minimum measured end positions are saved, for example, as the first switching point and the second switching point. The control and evaluation unit 7 then determines windows or the switching ranges 12, the hysteresis ranges 13 and the tolerance ranges 14 around these switching points. The piston 5 normally moves within the first switching point and the second switching point. The switching output 10, for example, goes on within the switching ranges 12 and off outside the hysteresis ranges 13. If the piston moves beyond the tolerance ranges 14, the opposite switching point is reset and the switching point on the side where it was exceeded is saved again. The next time the piston 5 moves to the opposite side, the new switching point is also saved. However, the tolerance range 14 only becomes active the next time the piston is moved so that both switching points can be saved again.

[0057] For example, the control and evaluation unit 7 is designed to adjust the length of the activation range 12, the hysteresis range 13, and / or the tolerance range 14 depending on the detected piston stroke or stroke path 6. For large stroke paths 6, the lengths of the activation ranges 12, the hysteresis ranges 13, and / or the tolerance ranges 14 are selected to be larger by the control and evaluation unit 7, and for small stroke paths 6, the lengths of the activation ranges 12, the hysteresis ranges 13, and / or the tolerance ranges 14 are selected to be smaller by the control and evaluation unit 7.

[0058] For example, the interface is an I / O link interface.

[0059] For example, the control and evaluation unit 7 is designed to assign a switching point to an intermediate position between the end positions if the speed of the piston 5 detected by the control and evaluation unit 7 at the intermediate position is ZERO.

[0060] For example, the control and evaluation unit 7 is implemented in a microcontroller. Reference symbol: 1 magnetic or inductive sensor 2 housings 3 Sensor element 4 Magnet 5 pistons 6 stroke 7 Control and evaluation unit 8 maximum piston position 9 minimum piston position 10 switching output 11 storage 12 Connection range 13 Hysteresis range 14 Tolerance range 15 magnetic field 16 piston-cylinder arrangement QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 196 43 413 A1

[0002] DE 196 53 222 A1

[0002] DE 10 2004 046 107 A1

[0003] DE 102007029488A1

[0004] DE 102017128548A1

[0005]

Claims

[1] Magnetic or inductive sensor (1), with at least one housing (2), with at least one sensor element (3) with which a magnet (4) of a piston (5) can be detected, whereby a piston position along a stroke (6) can be detected, with a control and evaluation unit (7) which is designed to evaluate the at least one sensor element (3), with which a piston position along a stroke (6) can be determined, characterized by that the respective first maximum piston position (8) and the first minimum piston position (9) are detected by the sensor (1) and a switching point is assigned to the maximum piston position (8) and the minimum piston position (9), wherein the control and evaluation unit (7) is designed to output the switching points as switching signals at a switching output (10) or an interface. [2] Magnetic or inductive sensor (1) according to claim 1, characterized bythat the control and evaluation unit (7) has a memory (11) for the switching points. [3] Magnetic or inductive sensor (1) according to one of the preceding claims, characterized by that the control and evaluation unit (7) is designed to activate at least one switching area (12) associated with the switching points, wherein the switching signal is switched on by the control and evaluation unit (7) within the switching area (12). [4] Magnetic or inductive sensor (1) according to claim 3, characterized by that the control and evaluation unit (7) is designed to activate at least one hysteresis range (13) associated with the switching points, wherein the switching signal from the control and evaluation unit (7) is switched off outside the switching-on range (12) and outside the hysteresis range (13). [5] Magnetic or inductive sensor (1) according to claim 3, characterized bythat the control and evaluation unit (7) is designed to activate at least one tolerance range (14) associated with the switching points, wherein the switching signal is reset by the control and evaluation unit (7) outside the tolerance range (14). [6] Magnetic or inductive sensor (1) according to claim 5, characterized by that the control and evaluation unit (7) is designed to set the length of the connection range (12), the hysteresis range (13) and / or the tolerance range (14) depending on the length of the detected stroke (6). [7] Magnetic or inductive sensor (1) according to one of the preceding claims, characterized by that the interface is an I / O link interface. [8] Magnetic or inductive sensor (1) according to one of the preceding claims, characterized bythat the control and evaluation unit (7) is designed to assign a switching point to an intermediate position between the end positions when the speed of the piston (5) detected by the control and evaluation unit (7) at the intermediate position is ZERO. [9] Magnetic or inductive sensor (1) according to one of the preceding claims, characterized by that the control and evaluation unit (7) is implemented in a microcontroller. [10] Use of the magnetic or inductive sensor (1) according to one of the preceding claims for determining the piston end position on a pneumatic or hydraulic cylinder.

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