Magnetic or inductive sensor

Abstract

To provide a better method for setting switch points, and a corresponding magnetic or inductive sensor.SOLUTION: The invention provides a method for determining the position of a magnet 4 of a piston 5 using a magnetic or inductive sensor 1. The sensor comprises: a sensor element 3 by which the magnet 4 of the piston 5 can be captured to allow a piston position along a stroke length 6 to be captured; and a control and evaluation unit 7 which evaluates the sensor element 3. The magnetic or inductive sensor 1 captures an initial maximum piston position 8 and an initial minimum piston position 9 each time, and a switch point is assigned to each of the maximum piston position 8 and the minimum piston position 9. The control and evaluation unit 7 outputs each switch point as a switch signal to a switch output 10 or interface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The invention relates to a magnetic or inductive sensor according to the preamble of claim 1, to a method using a magnetic or inductive sensor according to the preamble of claim 11 and to the use of a magnetic or inductive sensor according to claim 10. [Background technology]

[0002] The invention particularly relates to magnetic or inductive sensors, which are often arranged on the casing of the actuating cylinder. Such sensors have proven effective for contactlessly detecting the position of, for example, a pneumatic or hydraulic piston in the actuating cylinder, thereby determining its exact position. For this purpose, a guide groove is provided on the outer surface of the actuating cylinder casing, in which a magnetic field sensor is held so that its position can be adjusted axially and, after adjustment, is locked in the guide groove. This is known, for example, from US Pat. No. 5,629,491 and US Pat. No. 5,629,491. The sensor, adjusted and fixed in this way, outputs a switch signal depending on the position of the piston. The piston's end positions, which are usually detected, are pushed in and pulled out.

[0003] Such a sensor is known, for example, from US Pat. No. 5,629,499, which describes a sensor in which two switching points can be set, for example by setting two electronic switching thresholds, which are in principle designed to output a signal corresponding to the piston position. The switching thresholds are set mechanically (e.g., by the position of a potentiometer) in a separate process step or set once by software.

[0004] Patent document 4 discloses a method for setting a switch point of a sensor (especially 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 captured by the sensor, a frequency evaluation is performed, and after a predetermined number of piston stroke movements, a switch point is assigned to the piston position at which the same measurement value frequently occurs.

[0005] Patent document 5 discloses a sensor for contactlessly magnetically detecting the linear relative movement of a transmitting magnet along a measurement section using at least one sensor element, wherein the sensor element detects at least one component of the magnetic field of the transmitting magnet, the sensor element is shorter than the measurement section, a control and evaluation unit is electronically connected to the sensor element, the control and evaluation unit is configured to generate a position signal, the control and evaluation unit is configured to determine the first time derivative of the position signal, and an end position signal can be output when the first time derivative of the position signal is zero. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] DE 196 43 413 A1 [Patent Document 2] DE 196 53 222 A1 [Patent Document 3] DE 10 2004 046 107 A1 [Patent Document 4] DE 10 2007 029 488 A1 [Patent Document 5] DE 10 2017 128 548 A1 Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE INVENTION Starting from this prior art, the object of the present invention is to provide a better method for setting the switch point and a corresponding sensor. [Means for solving the problem]

[0008] This problem is solved by means of a magnetic or inductive sensor according to claim 1, which comprises at least one casing, at least one sensor element by means of which the magnet of the piston can be detected and thereby the piston position along its stroke length can be detected, and a control and evaluation unit which is configured to evaluate the at least one sensor element and by means of which the piston position along the stroke length can be determined, wherein a first maximum piston position and a first minimum piston position are detected by the sensor, and a switching point is respectively assigned to the maximum piston position and the minimum piston position, and the control and evaluation unit is configured to output each switching point as a switching signal at a switching output or an interface.

[0009] The object is further achieved by a method for determining the position of a magnet of a piston by means of a magnetic or inductive sensor as claimed in claim 11. The sensor comprises at least one casing, at least one sensor element by means of which the magnet of the piston can be detected and thereby the piston position along its stroke length can be determined, and a control and evaluation unit for evaluating the at least one sensor element, by means of which the piston position along the stroke length is determined, a first maximum piston position and a first minimum piston position are respectively detected by the sensor, a switching point is assigned to each of the maximum and minimum piston positions, and the control and evaluation unit outputs each switching point as a switching signal at a switching output or an interface.

[0010] The first maximum piston position and the first minimum piston position correspond to the piston's end positions. The first minimum piston position corresponds to the piston's first end position, and the first maximum piston position corresponds to the piston's second end position. That is, each end position is at each end of the maximum stroke of the piston-cylinder device.

[0011] The first maximum piston position is determined by the control and evaluation unit, for example, by the piston changing its direction at the piston end position. The maximum piston position can also be determined, for example, by the piston showing zero velocity at this end position. The two conditions mentioned above 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 at the piston end position and the piston showing zero velocity at this end position.

[0012] The first minimum piston position is determined by the control and evaluation unit, for example, by the piston changing its direction at the piston end position. The minimum piston position can also be determined, for example, by the piston showing zero velocity at this end position. The two conditions mentioned above 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 at the piston end position and the piston showing zero velocity at this end position.

[0013] According to the invention, the first end position signal can be output already on the first stroke. There is no need to go to the end positions multiple times and perform a frequency analysis. Another advantage is that the end position signal is always output right from the start, exactly at the end of the movement. The determination of the switch point does not have to be initiated by a user action (e.g. key operation or learning signal). The sensor does not require an input element. The sensor can be mounted very simply according to the invention. Both end positions can be detected with a single sensor.

[0014] The present invention provides very accurate and temperature stable switch points at the end positions, and is also robust to residual magnetism loss of the transmitter magnet over its lifespan and to mechanical tolerances of the cylinder.

[0015] For example, pneumatic cylinders with a stroke of, say, less than 50 mm are often operated in two states: with the piston fully pushed in or fully extended. The piston position is recognized via a magnet or transmitting magnet located on the piston, whose magnetic field in the end position is detected by a sensor element or magnetic field sensor.

[0016] The sensor element is, for example, a Hall element. In one example, the sensor element captures a component of the magnetic field of a transmitting magnet, and the control and evaluation unit is configured to generate, for example, a continuous, monotonic measurement signal.

[0017] In one example, the sensor element captures two mutually orthogonal magnetic field components of a transmitting magnet, and the control and evaluation unit is configured to generate, for example, a continuous, monotonic measurement signal.

[0018] The housing of the magnetic or inductive sensor is designed, for example, to be fixed in, partially in or on the groove of the piston-cylinder arrangement. For this purpose, the housing may, for example, be elongated and have fixing means for fixing the sensor housing in, partially in or on the groove. The fixing means may, for example, be a fixing screw.

[0019] Furthermore, the housing in particular, and in particular the sensor element, is shorter than the stroke length of the piston, for example.

[0020] When the sensor is shifted in the groove, the end positions change, so the first maximum piston position and the first minimum piston position are newly determined by the sensor, and new switch points are assigned to the maximum piston position and the minimum piston position, respectively, thereby determining the switch points again.

[0021] If the sensor is removed from the groove and / or attached to a new drive, it will recognize the loss of position or the change of end position and can therefore start the process anew, whereby the respective initial maximum and minimum piston positions are captured anew by the sensor, and new switch points are assigned to the maximum and minimum piston positions, respectively, whereby the determination of the switch points is carried out again.

[0022] In one example, the sensor has a digital and / or analog output. The digital output can be, for example, a digital switch output. However, a digital interface can also be provided for outputting a measurement value or a switch point.

[0023] The analog output can be, for example, an interface with a current output of, for example, 4 to 20 mA.

[0024] In a further development of the invention, the control and evaluation unit comprises a memory for at least the switch points, the memory or switch point memory being, for example, a non-volatile memory, in particular an EEPROM or flash memory.

[0025] In a further development of the invention, the control and evaluation unit is configured to activate at least one switching region associated with the switching point, within which the control and evaluation unit switches on the switching signal. The switching region extends over a region along the stroke length, starting before or ending at the maximum or minimum piston position. The switching region is set by the control and evaluation unit on the basis of the calculated piston end position.

[0026] In a further development of the invention, the control and evaluation unit is configured to activate at least one hysteresis region associated with the switch point, and the switch signal is switched off by the control and evaluation unit outside the switch-on region and outside the hysteresis region.

[0027] The hysteresis region extends over a portion of the stroke length and begins before the switch-on region of the maximum or minimum piston position, and is set by the control and evaluation unit based on the calculated piston end position.

[0028] In a further development of the invention, the control and evaluation unit is configured to activate at least one tolerance range associated with the switch point, the switch signal being reset by the control and evaluation unit outside the tolerance range.

[0029] The tolerance range extends over a portion of the stroke length, starts behind the maximum or minimum piston position, and is outside the learned piston stroke length. The tolerance range is set by the control and evaluation unit based on the calculated piston end position.

[0030] The measured maximum and minimum end positions are saved, for example, as a first and second switch point. The control and evaluation unit then determines windows around these switch points, i.e., a switching region, a hysteresis region, and a tolerance region. The piston typically moves between the first and second switch points. The switch output is on inside the switching region and off outside the hysteresis region. When the piston moves out of the tolerance region, the opposite switch point is reset and a new switch point is saved. The next time the piston moves in the opposite direction, this new switch point is saved as well. However, to ensure that both switch points can be saved anew, the tolerance region is not activated until the next time it moves in that direction.

[0031] If an invalid position is recognized, the current state of the switch point or switch output or position output can be maintained. If the position remains invalid for a longer period of time, for example, the stored switch point is reset and the learning process begins anew. This time delay allows the sensor to function reliably in the welding process environment.

[0032] In a further development of the invention, the control and evaluation unit is configured to set the lengths of the switching-on region, the hysteresis region and / or the tolerance region as a function of the captured stroke length or the length of the piston stroke, such that in the case of a long stroke length, the control and evaluation unit selects longer lengths of the switching-on region, the hysteresis region and / or the tolerance region, and in the case of a short stroke length, the control and evaluation unit selects shorter lengths of the switching-on region, the hysteresis region and / or the tolerance region.

[0033] 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, and the digital output can be configured via a commercially available bus system.

[0034] In a further development of the invention, the control and evaluation unit is configured to assign a switch point to an intermediate position between the end positions if the velocity of the piston captured by the control and evaluation unit becomes zero at this intermediate position.

[0035] The intermediate position is determined by the control and evaluation unit, for example, by the piston remaining stationary in an intermediate piston position, for example, by the piston exhibiting zero velocity in this end position, i.e., the sensor signal of the sensor element not changing within a certain time range.

[0036] According to this further development, an intermediate position signal is output as soon as the first stroke, so that frequent visits to the intermediate positions for frequency analysis are not necessary.

[0037] In a further development of the invention, the control and evaluation unit is implemented in a microcontroller. If the sensor is very small and the housing has a very small housing volume, for example of the order of one cubic centimeter or less, the microcontroller has the advantage that it already includes important peripheral components such as an A / D converter and an integrated interface.

[0038] Furthermore, the problem is solved by the use of a magnetic or inductive sensor according to one of the preceding claims for determining a piston end position in a pneumatic or hydraulic cylinder with a movable piston along its stroke length.

[0039] The invention, together with further advantages and features thereof, will now be described in more detail by way of example with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0040] [Figure 1] Magnetic or inductive sensor 1. [Figure 2] Magnetic or inductive sensor 1. [Figure 3] Magnetic or inductive sensor 1. DETAILED DESCRIPTION OF THE INVENTION

[0041] In the following drawings, the same parts are designated by the same reference numerals.

[0042] 1 shows a magnetic or inductive sensor 1. The sensor comprises at least one casing 2, at least one sensor element 3 by means of which a magnet 4 of a piston 5 can be detected and thereby the piston position along a stroke length 6 can be detected, and a control and evaluation unit 7 which is configured to evaluate the at least one sensor element 3 and by means of which the piston position along the stroke length 6 can be determined, a respective first maximum piston position 8 and a respective first minimum piston position 9 being detected by the sensor 1, each of which is assigned a switch point, and the control and evaluation unit 7 is configured to output each switch point as a switch signal at a switch output 10 or an interface.

[0043] The first maximum piston position 8 and the first minimum piston position 9 correspond to 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 a second end position of the piston 5. That is, each end position is at each end of the maximum stroke of the piston-cylinder arrangement 16.

[0044] The initial 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.

[0045] The initial 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.

[0046] The piston position is known through a magnet 4 or transmitting magnet on the piston 5, whose magnetic field in the end positions is detected by a sensor element 3 or magnetic field sensor. A magnetic field 15 emanating from the magnet 4 is depicted diagrammatically.

[0047] The sensor element 3 is, for example, a Hall element. In one example, the sensor element 3 captures a component of the magnetic field of a transmitting magnet, and the control and evaluation unit 7 is configured to generate, for example, a continuous, monotonic measurement signal. In Figure 3, two sensor elements 3 are provided by way of example. For example, more sensor elements 3 can also be provided.

[0048] The casing 2 of the magnetic or inductive sensor 1 is configured, for example, to be fixed in, partially in or on a groove of a piston-cylinder arrangement.

[0049] Furthermore, the casing 2 in particular, and in particular the sensor element 3 , is shorter than the stroke length 6 of the piston 5 for example.

[0050] When the sensor 1 is shifted in the groove, the end positions change, and the first maximum piston position 8 and the first minimum piston position 9 are newly identified by the sensor 1, and new switch points are assigned to the maximum piston position 8 and the minimum piston position 9, respectively, thereby re-identifying the switch points.

[0051] If the sensor 1 is removed from the groove and / or attached to a new drive, it will recognize the loss of position or the change of end position and can therefore start the process anew, whereby the respective first maximum piston position 8 and first minimum piston position 9 are captured anew by the sensor 1 and new switch points are assigned to the respective maximum piston position 8 and minimum piston position 9, whereby the determination of the switch points is carried out again.

[0052] In one example, the control and evaluation unit 7 comprises a memory 11 for at least the switch points. This memory 11 or switch point memory is, for example, a non-volatile memory, in particular an EEPROM or a flash memory.

[0053] 2, the control and evaluation unit 7 is configured to activate at least one switching region 12 associated with the switching point, within which a switching signal is switched on by the control and evaluation unit 7. The switching region 12 extends over a portion of the stroke length 6, starting before the maximum piston position 8 or the minimum piston position 9 and ending at the maximum piston position 8 or the minimum piston position 9. The switching region 12 is set by the control and evaluation unit 7 on the basis of the calculated piston end positions.

[0054] In FIG. 2, the control and evaluation unit 7 is configured to activate at least one hysteresis region 13 associated with the switch point, and the switch signal is switched off by the control and evaluation unit 7 outside the switch-on region 12 and outside the hysteresis region 13.

[0055] The hysteresis region 13 extends over a portion of the stroke length 6 and begins before the switch-on region 12 of the maximum piston position 8 or the minimum piston position 9. The hysteresis region 13 is set by the control and evaluation unit 7 on the basis of the calculated piston end positions.

[0056] In FIG. 2, the control and evaluation unit 7 is configured to activate at least one tolerance range 14 associated with the switch point, and the switch signal is reset by the control and evaluation unit 7 outside the tolerance range 14.

[0057] The tolerance region 14 extends over a portion of the stroke length 6, starting behind the maximum piston position 8 or the minimum piston position 9 and extending beyond the learned piston stroke length 6. The tolerance region 14 is set by the control and evaluation unit 7 on the basis of the calculated piston end positions.

[0058] The measured maximum and minimum end positions are stored, for example, as a first switch point and a second switch point. The control and evaluation unit 7 then determines windows around these switch points, namely a switch-on region 12, a hysteresis region 13, and a tolerance region 14. The piston 5 normally moves within the first and second switch points. The switch output 10 is on within the switch-on region 12 and off outside the hysteresis region 13. When the piston moves out of the tolerance region 14, the opposite switch point is reset and a new switch point is saved. The next time the piston 5 moves in the opposite direction, this new switch point is saved as well. However, to allow both switch points to be saved anew, the tolerance region 14 is not activated until the next time it moves in that direction.

[0059] In one example, the control and evaluation unit 7 is configured to set the lengths of the switching region 12, the hysteresis region 13 and / or the tolerance region 14 depending on the captured piston stroke or stroke length 6. If the stroke length 6 is long, the control and evaluation unit 7 selects longer lengths of the switching region 12, the hysteresis region 13 and / or the tolerance region 14, and if the stroke length 6 is short, the control and evaluation unit 7 selects shorter lengths of the switching region 12, the hysteresis region 13 and / or the tolerance region 14.

[0060] In one example, the interface is an I / O-Link type interface.

[0061] In one example, the control and evaluation unit 7 is configured to assign a switch point to an intermediate position between the end positions when the velocity of the piston 5 captured by the control and evaluation unit 7 becomes zero at this intermediate position.

[0062] In one example, the control and evaluation unit 7 is implemented in a microcontroller. [Explanation of symbols]

[0063] 1...Magnetic or inductive sensor 2...Casing 3...Sensor element 4...Magnet 5...Piston 6...Stroke length 7...Control and evaluation unit 8...Maximum piston position 9...Minimum piston position 10...Switch output 11...Storage section 12...Switch-on area 13...Hysteresis region 14...Acceptable range 15...Magnetic field 16...Piston-cylinder device

Claims

1. 1. A magnetic or inductive sensor (1) comprising at least one casing (2), at least one sensor element (3) by means of which a magnet (4) of a piston (5) can be detected and thereby the piston position along a stroke length (6) can be detected, and a control and evaluation unit (7) configured to evaluate the at least one sensor element (3) and by means of which the piston position along the stroke length (6) can be determined, characterized in that a first maximum piston position (8) and a first minimum piston position (9) are detected by the sensor (1), and switching points are assigned to the respective maximum piston position (8) and the respective minimum piston position (9), and the control and evaluation unit (7) is configured to output each switching point as a switching signal to a switching output (10) or an interface.

2. 2. Magnetic or inductive sensor (1) according to claim 1, characterized in that the control and evaluation unit (7) comprises a memory (11) for the switch points.

3. 2. The magnetic or inductive sensor (1) according to claim 1, characterized in that the control and evaluation unit (7) is configured to activate at least one switching area (12) associated with the switching point, and the switching signal is switched on by the control and evaluation unit (7) inside the switching area (12).

4. 4. The magnetic or inductive sensor (1) according to claim 3, characterized in that the control and evaluation unit (7) is configured to activate at least one hysteresis region (13) associated with the switch point, and the switch signal is switched off by the control and evaluation unit (7) outside the switch-on region (12) and outside the hysteresis region (13).

5. 4. The magnetic or inductive sensor (1) according to claim 3, characterized in that the control and evaluation unit (7) is configured to activate at least one tolerance range (14) associated with the switch point, and the switch signal is reset by the control and evaluation unit (7) outside the tolerance range (14).

6. 6. The magnetic or inductive sensor (1) according to claim 5, characterized in that the control and evaluation unit (7) is configured to set the length of the switching-on region (12), the hysteresis region (13) and / or the tolerance region (14) depending on the length of the captured stroke length (6).

7. A magnetic or inductive sensor (1) according to claim 1, characterized in that the interface is an I / O-Link type interface.

8. 2. The magnetic or inductive sensor (1) according to claim 1, wherein the control and evaluation unit (7) is configured to assign a switch point to an intermediate position between the end positions when the velocity of the piston (5) captured by the control and evaluation unit (7) becomes zero at the intermediate position.

9. 2. Magnetic or inductive sensor (1) according to claim 1, characterized in that the control and evaluation unit (7) is implemented in a microcontroller.

10. 10. Use of a magnetic or inductive sensor (1) according to claim 1 for determining piston end positions in pneumatic or hydraulic cylinders.

11. 1. A method for determining the position of a magnet (4) of a piston (5) by means of a magnetic or inductive sensor (1), the sensor comprising at least one casing (2), at least one sensor element (3) by means of which the magnet (5) of the piston can be detected and thereby the piston position along a stroke length (6) can be determined, and a control and evaluation unit (7) for evaluating the at least one sensor element (3), wherein a first maximum piston position (8) and a first minimum piston position (9) are respectively detected by the sensor (1), a switching point is assigned to each of the maximum piston position (8) and the minimum piston position (9), and the control and evaluation unit (7) outputs each switching point as a switching signal at a switching output (10) or an interface.

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