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, thereby enabling the detection of a piston position along a stroke (6), with a control and evaluation unit (7) which is configured to evaluate the at least one sensor element (3) with which the piston position along the stroke (6) can be determined, wherein the first maximum piston position (8) and the first minimum piston position (9) are detected by the sensor (1) and a first switching point is assigned to each of the maximum piston position (8) and the minimum piston position (9), wherein the control and evaluation unit (7) is configured to output the first switching points as switching signals at a switching output (10) or an interface, characterized in that the control and evaluation unit (7) is configured to provide a further switching point for an intermediate position between the end positions (8,9) of the piston (5) if the speed of the piston (5) detected by the control and evaluation unit (7) at the intermediate position is zero.

Description

[0001] The invention relates to a magnetic or inductive sensor according to the preamble of claim 1, as well as a method with a magnetic or inductive sensor according to the preamble of claim 10, and a use of a magnetic or inductive sensor according to claim 9.

[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 by non-contact 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 working cylinder housing, in which the magnetic field sensors are axially adjustable 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 secured in this way outputs a switching signal depending on the piston position. In most cases, the retracted and extended end positions of the piston must 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, wherein 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 by software.

[0004] DE 10 2007 029 488 A1 discloses a method for setting the switching point of a sensor, in particular a magnetic or inductive sensor, especially 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 most frequently.

[0005] 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.

[0006] DE 10 2020 128 600 A1 discloses a valve device, in particular a thermostatic valve, for shutting off and / or controlling the flow of a fluid. This device comprises a housing assembly with a valve opening that, in one flow direction, has at least one approximately cylindrical passage section and a sealing passage section, wherein the sealing passage section has a larger diameter than the passage section, and a closing element for closing the valve opening, comprising at least one approximately cylindrical closing passage section that can be arranged in the region of the cylindrical passage section, and a closing sealing passage that can be arranged in the region of the sealing passage section, wherein the closing sealing passage section has a larger diameter than that of the cylindrical passage section.and wherein an annular gap with an approximately constant opening cross-section is provided between the passage section and the closure section, wherein the annular gap is designed such that the opening cross-section is constant when the valve device is opened over a predetermined valve stroke of the closure element.

[0007] DE 10 2010 034 994 A1 relates to a measuring device with a measuring housing and a measuring element movably mounted in the measuring housing, as well as with a sensor device for detecting a position of the measuring element relative to the measuring housing, wherein the sensor device comprises at least one for providing an analog sensor signal depending on the position of the measuring element, as well as switching means for analog-to-digital conversion of the sensor signal, processing means for processing the sensor signal, and bus communication means for bidirectional digital data transmission between the sensor device and a control device.It is provided that the processing means for a programmable logical combination of at least two amounts of sensor signals, as well as for providing a combination result and the analog sensor signal in digitized encoding, in particular with an encoding comprising at least 2 bits, are provided to the bus communication means.

[0008] 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.

[0009] Based on this state of the art, the object of the invention is to provide an improved method for setting the switching point and a corresponding sensor.

[0010] The problem is solved 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 configured to evaluate the at least one sensor element with which a piston position along the stroke can be determined, wherein the first maximum and first minimum piston position are detected by the sensor and a switching point is assigned to each of the maximum and minimum piston positions, wherein the control and evaluation unit is configured to output the switching points as switching signals at a switching output or an interface.

[0011] The problem is further solved according to claim 10 by a method for determining the position of a magnet of a piston with a magnetic or inductive sensor, with at least one housing, with at least one sensor element with which the magnet of a piston can be detected, whereby a piston position along a stroke can be detected, with a control and evaluation unit which evaluates the at least one sensor element with which a piston position along the stroke is determined, wherein the first maximum and first minimum piston position are detected by the sensor and a switching point is assigned to each of the maximum and minimum piston positions, wherein the control and evaluation unit outputs the switching points as switching signals at a switching output or an interface.

[0012] 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 located at the respective ends of the maximum stroke of a piston-cylinder assembly.

[0013] The first maximum piston position is determined by the control and evaluation unit, for example, by the piston changing its direction at its end position. Alternatively, the maximum piston position can also be determined by the piston having a speed of zero at this end position. These two conditions can also be combined using an AND operation, so that the first maximum piston position is determined by the control and evaluation unit, for example, by the piston changing its direction at its end position and the piston having a speed of zero at this end position.

[0014] The first minimum piston position is determined by the control and evaluation unit, for example, by the piston changing its direction at its end position. Alternatively, the minimum piston position can also be determined by the piston having a speed of zero at this end position. These two conditions can also be combined using an AND operation, so that the first minimum piston position is determined by the control and evaluation unit, for example, by the piston changing its direction at its end position and the piston having a speed of zero at this end position.

[0015] According to the invention, the first end-position signal can be output with the very 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 precisely at the end of the movement. Setting the switching points does not require a user action, such as pressing a button or sending a learning signal. The sensor requires no input elements. According to the invention, the sensor is very easy to install. Both end positions can be detected by a single sensor.

[0016] 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.

[0017] For example, pneumatic cylinders with a stroke of less than 50 mm are usually operated in two states: fully retracted or fully extended. The piston position is detected by a magnet or encoder magnet located on the piston, whose magnetic field is detected by the sensor element or magnetic field sensor at the end positions.

[0018] The sensor element is, for example, a Hall effect sensor. For instance, the sensor element detects a component of the magnetic field of the sensor magnet, with the control and evaluation unit being designed, for example, to generate a continuous monotonous measurement signal.

[0019] For example, the sensor element detects two components of a magnetic field of the sensor magnet that are perpendicular to each other, with the control and evaluation unit being designed, for example, to generate a continuous monotonic measurement signal.

[0020] 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.

[0021] In particular, the housing and especially the sensor element are, for example, shorter than the stroke of the piston.

[0022] 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 again recorded by the sensor and a switching point of the maximum and minimum piston position is assigned again, whereby the determination of the switching points takes place anew.

[0023] 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 restart. This means the sensor again detects the first maximum and minimum piston positions and assigns a new switching point to each, thus re-determining the switching points.

[0024] For example, the sensor has a digital and / or analog output. The digital output could be, for instance, a digital switching output. However, a digital interface for outputting measured values ​​or switching points could also be provided.

[0025] The analog output could, for example, be an interface with a current output of 4 to 20 mA.

[0026] 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.

[0027] In a further development of the invention, the control and evaluation unit is configured 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 area along the stroke and begins before 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.

[0028] 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 activation range and outside the hysteresis range.

[0029] The hysteresis range extends over a portion of the stroke and begins before the activation point 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.

[0030] In a further development of the invention, the control and evaluation unit is configured 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.

[0031] The tolerance range extends over a portion of the stroke and begins after the maximum or minimum piston position, lying outside the piston's learned stroke. The tolerance range is set by the control and evaluation unit based on the determined piston end positions.

[0032] The maximum and minimum measured end positions are stored, for example, as the first and second switching points. The control and evaluation unit then defines windows (or activation ranges), hysteresis ranges, and tolerance ranges around these switching points. The piston normally moves within the first and second switching points. The switching output is activated within the activation ranges and deactivated outside the hysteresis ranges. If the piston moves beyond the tolerance ranges, the opposite switching point is reset, and a new switching point is stored on the side where the limit was exceeded. The next time the piston moves to the opposite side, the new switching point is also stored. However, the tolerance range only becomes active during the next start-up in order to store both switching points again.

[0033] If an invalid position is detected, the current state of the switching points, switching outputs, or position output can be maintained. If the position remains invalid for an extended period, the stored switching points are reset, and the learning process is restarted. This time delay ensures that the sensor can function reliably even in the vicinity of welding processes.

[0034] 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 large strokes, the control and evaluation unit selects larger lengths for the activation ranges, the hysteresis ranges, and / or the tolerance ranges, and for small strokes, the control and evaluation unit selects smaller lengths for the activation ranges, the hysteresis ranges, and / or the tolerance ranges.

[0035] 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.

[0036] According to the invention, the control and evaluation unit is designed to assign a switching point to an intermediate position between the end positions when the speed of the piston detected by the control and evaluation unit at the intermediate position is zero.

[0037] The intermediate position is determined by the control and evaluation unit, for example, by the piston remaining stationary in the intermediate position. The intermediate position can also be determined by the piston having a speed of zero in this end position, meaning the sensor signal from the sensor element does not change within a specific time period.

[0038] This allows the intermediate position signal to be output with the very first stroke. It is not necessary to repeatedly approach the intermediate position and perform a frequency analysis.

[0039] 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 that it already incorporates important peripheral components such as A / D converters, integrated interfaces, etc.

[0040] Furthermore, the problem is solved by using 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.

[0041] The invention is further explained below with regard to its advantages and features, with reference to the accompanying drawing and by means of exemplary embodiments. The figures in the drawing show: Fig. 1 to 3 each a magnetic or inductive sensor 1.

[0042] In the following figures, identical parts are labelled with identical reference symbols.

[0043] Fig. Figure 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 configured to evaluate the at least one sensor element 3 with which a piston position along the stroke 6 can be determined, wherein the 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 respectively, wherein the control and evaluation unit 7 is configured to output the switching points as switching signals at a switching output 10 or an interface.

[0044] The first maximum piston position 8 and the 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 at the respective ends of the maximum stroke of a piston-cylinder arrangement 16.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] Sensor element 3 is, for example, a Hall effect sensor. Sensor element 3 detects, for example, a component of the magnetic field of the sensor magnet, and the control and evaluation unit 7 is configured, for example, to generate a continuous monotonic measurement signal. According to Fig. For example, two sensor elements 3 are provided. It is also possible, for example, to provide more than one sensor element 3.

[0049] The housing 2 of the magnetic or inductive sensor 1 is, for example, designed to be attached in, partially in or on a groove of the piston-cylinder assembly.

[0050] In particular, the housing 2 and especially the sensor element 3 are, for example, shorter than the stroke 6 of the piston 5.

[0051] 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 again detected 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 is carried out again.

[0052] 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 restart. This means that the first maximum piston position 8 and the first minimum piston position 9 are detected again by sensor 1, and a switching point is assigned to each of the maximum piston position 8 and the minimum piston position 9, thus re-determining the switching points.

[0053] For example, the control and evaluation unit 7 has a memory 11 for at least the switching points. The memory 11, or switching point memory, is, for example, a non-volatile memory, in particular an EEPROM or flash memory.

[0054] According to Fig. 2 The control and evaluation unit 7 is configured to activate at least one activation range 12 associated with the switching points, whereby the switching signal is activated by the control and evaluation unit 7 within the activation range 12. The activation range 12 extends over a partial area 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 activation range 12 is set by the control and evaluation unit 7 based on the determined piston end positions.

[0055] 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 is switched off by the control and evaluation unit 7 outside the switch-on range 12 and outside the hysteresis range 13.

[0056] The hysteresis range 13 extends over a partial area along the stroke 6 and begins before the activation area 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.

[0057] 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, whereby the switching signal is reset by the control and evaluation unit 7 outside the tolerance range 14.

[0058] The tolerance range 14 extends over a partial area along the stroke 6 and begins after the maximum piston position 8 or the minimum piston position 9 and is located outside the learned 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.

[0059] The maximum and minimum measured end positions are stored, for example, as the first and second switching points. The control and evaluation unit then defines windows (or activation ranges 12), hysteresis ranges 13, and tolerance ranges 14 around these switching points. The piston 5 normally moves within the first and second switching points. The switching output 10, for example, is activated within the activation ranges 12 and deactivated 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 the limit 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 during the next start-up in order to save both switching points again.

[0060] For example, the control and evaluation unit 7 is configured 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 control and evaluation unit 7 selects larger lengths for the activation ranges 12, the hysteresis ranges 13, and / or the tolerance ranges 14, and for small stroke paths 6, the control and evaluation unit 7 selects smaller lengths for the activation ranges 12, the hysteresis ranges 13, and / or the tolerance ranges 14.

[0061] For example, the interface is an I / O-Link interface.

[0062] 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.

[0063] For example, the control and evaluation unit 7 is implemented in a microcontroller. Reference symbol: 1 magnetic or inductive sensor 2 cases 3 Sensor element 4 Magnet 5 pistons 6 stroke 7 Control and evaluation unit 8 maximum piston position 9 minimum piston position 10 switching outputs 11 storage 12 Switching range 13 Hysteresis range 14 Tolerance range 15 magnetic field 16 piston-cylinder arrangement

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