GB2286049A - A sensor device responsive to the position of a piston - Google Patents

A sensor device responsive to the position of a piston Download PDF

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Publication number
GB2286049A
GB2286049A GB9423992A GB9423992A GB2286049A GB 2286049 A GB2286049 A GB 2286049A GB 9423992 A GB9423992 A GB 9423992A GB 9423992 A GB9423992 A GB 9423992A GB 2286049 A GB2286049 A GB 2286049A
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United Kingdom
Prior art keywords
sensor
sensor device
piston
permanent magnet
magnetic field
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Granted
Application number
GB9423992A
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GB9423992D0 (en
GB2286049B (en
Inventor
Kurt Stoll
Hans Gerlach-Erhardt
Ralf Medow
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Festo SE and Co KG
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Festo SE and Co KG
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Publication date
Application filed by Festo SE and Co KG filed Critical Festo SE and Co KG
Publication of GB9423992D0 publication Critical patent/GB9423992D0/en
Publication of GB2286049A publication Critical patent/GB2286049A/en
Application granted granted Critical
Publication of GB2286049B publication Critical patent/GB2286049B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/20—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature
    • G01D5/2006—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils
    • G01D5/2033—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils controlling the saturation of a magnetic circuit by means of a movable element, e.g. a magnet
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B15/00—Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
    • F15B15/20—Other details, e.g. assembly with regulating devices
    • F15B15/28—Means for indicating the position, e.g. end of stroke
    • F15B15/2807—Position switches, i.e. means for sensing of discrete positions only, e.g. limit switches
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/142—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage using Hall-effect devices
    • G01D5/145—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage using Hall-effect devices influenced by the relative movement between the Hall device and magnetic fields

Description

1 2286049 A Sensor Device responsive to the Position of a Piston
The invention relates to a sensor device for a cylinder, containing a movable piston, responsive to the position of the piston, comprising a permanent magnet placed on the piston or an element connected therewith and a sensor having a preferential direction, is arranged on the cylinder, is sensitive to a magnetic field and is adapted to respond on approach of the permanent magnet.
Such a sensor device responsive to the position of a piston is for example disclosed in the German patent publication 3,708,989 C. Such sensor devices are more particularly intended to detect the end of stroke position of the piston. While known sensor devices can recognize and indicate the time at which the piston is just moving past the sensor device, they are in other respects passive and do not provide any information about the position in which the sensor is located. For many applications it is however desirable to provide such information in order, for instance, to ascertain whether the piston is at the one or the other end part.
One object of the present invention is consequently to provide a sensor device of the type initially mentioned which is not only able to detect when the piston reaches the sensor position, but furthermore provides an indication whether the piston is on the one or the other side of the sensor device.
In order to achieve this and/or other aims appearing herein, in the context of a sensor device for a cylinder, containing a movable piston, responsive to the position of the piston, comprising a permanent magnet placed on the piston or an element connected therewith and a sensor having a preferential direction is arranged on the cylinder, is sensitive to a magnetic field and is adapted to respond on approach of the permanent mag net, the invention provides that the permanent magnet and the at least one sensor are so aligned that, when the magnet moves past the sensor, the magnetic field of the permanent magnet at spatially consecutive points, aligned to be substantially parallel to the preferential direction of the sensor, acts respectively oppositely on the sensor to accordingly cause two different reactions of the sensor, said device furthermore comprising means for storage of such sensor reactions.
Each time the piston or, respectively, the permanent magnet moves past the sensor device two different sensor reactions are elicited, for example sensor signals, of which respectively the last one is stored so that the 1 storage means or memories have a different stored item of information dependent on whether the piston is located on the left or on the right of the sensor position. The possible applications for the sensor device are therefore substantially increased by adopting simple, low-cost measures, and the original function of recognition of position on moving past the device sensor device is adhered to without change. Such a sensor device may hence in certain cases possess two sensor devices or an elaborate iogic system for recognition.
Further advantageous developments and features of the sensor device in accordance with claim 1 are recited in the dependent claims.
In order to ensure that when the magnetic field moves past the sensor device twice the field of the permanent magnet acts on it oppositely in order to cause the two different sensor reactions, either the north-south axis of the permanent magnet is arranged radially and the preferential direction of the sensor is arranged parallel to the direction of movement of the piston, or the north-south axis of the permanent magnet is arranged parallel to the direction of movement of the piston and the preferential direction of the sensor is arranged radially. An advantageous way of electrically storing the sensor reactions is such that the sensor possesses an electrical element sensitive to a magnetic field and adapted to produce different electrical signals as sensor reactions and having an output thereof connected with an electrical signal memory. This electrical signal memory is preferably designed in the form of a comparator or as a bivibrator, for instance in the form of a Schmitt trigger. It is more especially in the case of a comparator subject to hysteresis, as for example a Schmitt trigger, that a particularly regular switching behavior is provided, since it is only on exceeding a higher positive level that switching on takes place and on going below a lower negative that switching off takes place. The two signal states as sensor reactions remain stored in this case. The sensor device in accordance with the invention is consequently able to be produced in a simple and low-price manner using two commercially available components.
In order to ensure that no random signal is present in the memory on switching on the device after it has been switched off, either the signal memory is constantly supplied with an operating voltage or an error stage is provided, which after switching the supply voltage on produces an error signal until the sensor responds. This error signal indicates that the stored sensor signal does not currently have to be a true signal.
A further advantageous possibility for magnetic storage of the sensor reaction is such that the sensor as a signal memory possesses a magnetizable and remagnetizable element, which is operatively connected with an electrical element, sensitive to a magnetic field, and as sensor reactions produces different electrical signals.
2 The means for the reproduction or display of the different electrical signal may be optical, acoustic or electrical means.
The electrical element sensitive to magnetic fields may take the form of a Hall element, a field plate or a coil detecting induction.
Finally there is also one advantageous method for mechanically storing the sensor reactions by fitting the sensor with a moving magnetic or magnetizable element able to be changed in position by the permanent magnet. Preferably the element is arranged for pivoting about an axis, means being provided for setting the two positions of pivoting, the permanent magnet overcoming such means as it moves past. It is then possible to see from the respective position of pivoting or from the position of such movable element generally on which side of the sensor device the piston is presently located.
Embodiments of the invention are represented in the accompanying drawings and elucidated in the following particular description.
Figure 1 is a diagrammatic representation of a piston and cylinder unit with two possibilities for the arrangement of the permanent magnet arranged on the piston and for the sensor arranged on the cylinder.
Figure 2 is graph of signal level against time to explain the variations at the sensor on passage, or sweeping past, of the permanent magnet.
Figure 3 shows a first working embodiment for electrical signal storage.
Figure 4 shows a second embodiment of the invention involving magnetic signal storage.
Figure 5 illustrates a third working embodiment for mechanical signal storage.
In accordance with figure 1 a piston 11 connected with a piston rod 10 runs in a cylinder 12. As shown in the upper part of figure 1 a permanent magnet 13 is so set in the piston 11 that its north-south axis is aligned radially. This means that a magnetic field 14 is produced acting in the external space. On the outside of the cylinder 12 a position detecting sensor 15 is placed, whose preferential direction, indicated by a double arrow, runs parallel to the direction of movement of the piston 11, that is to say in the axial direction. This sensor 15 may in principle also be arranged in the wall of the cylinder 12.
As shown in figure 1, when the piston 11 or, respectively, the permanent magnet moves past it, the sensor 15 is firstly pervaded by a magnetic field, which is directed to the right, and then by a magnetic field, which
3 is oppositely directed, that is to say to the left. The field lines pervading the sensor 15 at spatially consecutive points on the piston 11 then each extend substantially in parallelism to the preferential direction of the sensor of such sensor 15.
In the lower part of figure 1 an alternative arrangement is depicted. A permanent magnet 13a is so set in the piston 11 that its north-south axis runs parallel to the direction of movement of the piston 11, i. e. axially. A magnetic field 14a is produced. A sensor 15a is arranged externally on the cylinder 12, its preferential direction being radial.
As the piston 11 or, respectively, the permanent magnet 13, moves during motion to the right the sensor 15a is hence firstly pervaded by radial, inwardly directed lines of the magnetic field and then by outwardly extending lines of the magnetic field of the permanent magnet 13a.
Figure 2 shows changes in the field H in the sensor 15 or, respectively, 15a on passage, i. e. on mutual sweeping movement past, of the permanent magnet 13 and 13a. As the magnet approaches the magnetic field firstly increases up to a maximum, which is then reached, when the field lines are parallel to the preferential direction of the sensor. Afterwards the field strength will steeply diminish until the oppositely directed field line reach an oppositely directed maximum shortly after this, such maximum constituting a minimum in figure 2. After this the magnetic field will decrease again with an increase in the distance of the permanent magnet from the sensor and approaches zero.
In figure 3 a first embodiment of such a sensor 16 is represented with electrical signal memory and a signal processing device. This sensor may take the place of the sensor 15 or, respectively, of the sensor 15a, given suitable alignment of the preferential direction.
The sensor 16 consists of a Hall element 17, whose signal is supplied to a Schmitt trigger 18. The two complementary outputs of the Schmitt trigger 18 are connected with control lights 19 and 20. Furthermore such two outputs are connected via an OR gate 21 to a bistable switching stage 22, whose second input receives a switch-on signal S when the power supply is turned on. An output of the bistable switching stage 22 is connected with an error detect light 23.
Upon passage of the permanent magnet 13 an electrical signal is produced in the Hall element 17 and is essentially proportional to the magnetic field strength respectively pervading the Hall element. The electrical signal on passage of the permanent magnet 13 therefore has a characteristic which is essentially the curve represented in figure 2. The Schmitt trigger 18 possesses an upper positive switching threshold Sp and a lower negative switching threshold Sn. In the position represented in figure 1 of the piston 11 the output signal of the north-south axis 18 is firstly formed for the operation of the control light 19 as a 1 signal so that the control
4 A, i light 19 will be on and the control 20 will not be on. At the point X1 the lower switching threshold Sn will be gone below so that the Schmitt trigger is kicked over, i. e. the control light 19 will be extinguished and the control light 20 turned on. Operation of the control light 20 indicates that the piston is now to the right of the sensor in terms of figure 1. During the opposite backward movement of the piston the Schmitt trigger is switched over again, when the upper switching threshold Sp is exceeded. This means that one of the two control lights 19 and 20 will always be turned on and consequently indicates on which side of the sensor the piston is located. Simultaneously the position of the piston 11 in relation to the sensor is recognized by the point in time of switching over.
Instead of the indicating device represented as a simple example using two control lights 19 and 20 it is naturally possible to perform evaluation with a computer, a printer or the like in a corresponding fashion.
At power-up the Schmitt trigger 18 will either be in a random state or in a state set by something but not indicating the actual position of the piston 11. In order to indicate this state, on switching the power on the signal S operates the bistable switching stage 22 so that the error detect light 23 is turned on. It is only when the Schmitt trigger 18 switches for the first time because of the passage of the permanent magnet 13 that the bistable switching stage 22 is reset via the OR gate 21 so that the error detect light 23 goes out. It is only after the extinction of the error detect light 23 that thus by means of the control lights 19 and 20 the position of the piston 11 is indicated.
Instead of the Hall element 17 it is naturally possible in principle to use another type of magnetic field responsive element, as for example a field plate or a coil responsive to induction. Furthermore instead of the Schmitt trigger 18 it is possible to employ another comparator with or without hysteresis or a bistable multivibrator.
In the case of the second embodiment depicted in figure 4 the means for storage of the position is constituted by a soft magnetic core 24, which on passage of the permanent magnet 13 or, respectively, 13a is magnetized or demagnetized. The magnetization state of this soft magnetic core 24 is detected by a Hall element 25 or another element sensitive to magnetic fields. Its output signal is supplied to an evaluating and indicating device 26, which in a manner dependent on the detected state of magnetization of the piston represents the two positions of the piston to the left and to the right of the sensor. Since the magnetization state of the soft magnetic core 24 is maintained, on power-up there is immediately a correct indication of the position.
With the third embodiment illustrated in figure 5 a rod magnet 27 is pivotally arranged on a joint 28. In the two positions of pivoting the rod magnet 27 is respectively in electrical contact with one of the two terminal abutments 29. These terminal abutments 29 and 30 are electrically connected with the control lights 29, whose second connection is connected via a power supply 31 with the joint 28. A spring (not illustrated) keeps the rod magnet 27 respectively resiliently against one of the two terminal abutments 29 and 30, the resilient force being so selected that on passage of the permanent magnet 13 and, respectively, 13a it is overcome.
If the arrangement in accordance with figure 5 assumes the position of the sensor 15a in figure 1, then on passage of the piston 11 or, respectively, of the permanent magnet 13a the rod magnet 27 will firstly be moved as far as the terminal abutment 29 and then to the terminal abutment 30. It assumes its position here. On return movement and on passage of the Piston 11 it is then moved as far as the terminal abutment again. Therefore if the rod magnet 27 is at the terminal abutment 30, something indicated by the control light's 20 being switched, the piston 11 will be to the right of the sensor 15a in terms of figure 1, and when the rod magnet 27 is at the terminal abutment 29, so that the control light 19 is turned on, it will be to the left of the sensor 15a.
Instead of the pivotal rod magnet 27 it is possible in principle to provide some other form of permanent magnet, which may be moved into different positions on passage of the piston 11, for example a permanent magnet able to be shifted like a piston parallel or perpendicular to the piston's movement. Furthermore the indicating of the respective position of the permanent magnet or, respectively, rod magnet 20 may take place in different manners, as described in connection with figure 3 supra.
Instead of the permanent magnet 13a it would be obviously be possible to employ two adjacently placed, radially aligned permanent magnets, which radially outward possess different magnet poles.
6

Claims (18)

1. A sensor device for a cylinder which contains a movable piston, the device being responsive to the position of the piston, and comprising a permanent magnet placed on the piston or an element connected therewith, and a sensor having a preferential direction, which is arranged on the cylinder, is sensitive to a magnetic field and is adapted to respond on approach of the permanent magnet, the permanent magnet and the sensor being aligned that, when the magnet moves past the sensor, the magnetic field of the permanent magnet at spatially consecutive points, is aligned to be substantially parallel to the preferential direction of the sensor, and acts respectively oppositely on the sensor to accordingly cause two different reactions of the sensor, said device furthermore comprising means for storage of such sensor reactions.
2. A sensor device as claimed in claim 1, wherein the north-south axis of the permanent magnet is arranged radially t the direction of movement of the piston and the preferential direction of the sensor is arranged parallel to said direction.
3. A sensor device as claimed in claim 1, wherein the north-south axis of the permanent magnet is arranged in parallel to the direction of movement of the piston and the preferential direction of the sensor is radial in relation to said direction.
4. A sensor device as claimed in any one of the preceding claims, wherein the sensor possesses a magnetic field sensitive electrical element, which as sensor reactions produces different electrical signals and whose output is connected with and electrical signal memory.
5. A sensor device as claimed in claim 4, wherein the electrical signal memory is designed in the form of a comparator or as bistable multivibrator.
6. A sensor device as claimed in claim 5, wherein the electrical signal memory is designed in the form of a Schmitt trigger.
7. A sensor device as claimed in any of claims 4 to 6, wherein the electrical signal memory is constantly supplied with an operating voltage.
8. A sensor device as claimed in any of claims 4 to 6, wherein an error signal stage is provided which after the switching on of the power supply produces an error signal until the sensor responds for the first time.
9. A sensor device as claimed in any of claims 1 to 3, wherein as a signal memory the sensor comprises a magnetizable and remagnetizable element, which is operationally connected with a magnetic field responsive electrical element adapted to produce different electrical signals as sensor reaction.
10. A sensor device as claimed in claim 9, wherein the magnetizable and remagnetizable element is designed in the form of a soft magnetic core.
11. A sensor device as claimed in any of claims 4 to 10, wherein means for the reproduction of different electrical signals is provided.
12. A sensor device as claimed in any of claims 4 to 11, 8 - J wherein the magnetic field responsive electrical element is designed in the form of a Hall element, as a field plate or as an induction responsive coil.
13. A sensor device as claimed in any of claims 1 to 3, wherein as a signal memory the sensor comprises a moving magnetic or magnetizable element able to be changed in position by the permanent magnet.
14. A sensor device as claimed in claim 13, wherein said element is arranged for pivoting about an axis, means being provided for setting two positions of pivot, said permanent magnet being arranged to overcome such means.
15. A sensor device substantially as hereinbefore described with reference to Figs. 1, 2 and 3 of the accompanying drawings.
16. A sensor device substantially as hereinbefore described with reference to Figs. 1, 2 and 4 of the accompanying drawings.
17. A sensor device substantially as hereinbefore described with reference to Figs. 1, 2 and 5 of the accompanying drawings.
18. Any novel subject matter or combination including novel subject matter disclosed in the foregoing specification or claims and/or shown in the drawings, whether or not within the scope of or relating to the same invention as any of the preceding claims.
- Q - --I
GB9423992A 1993-12-08 1994-11-28 A sensor device responsive to the position of a piston Expired - Fee Related GB2286049B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE4341810A DE4341810B4 (en) 1993-12-08 1993-12-08 Sensor device for position detection of a piston

Publications (3)

Publication Number Publication Date
GB9423992D0 GB9423992D0 (en) 1995-01-11
GB2286049A true GB2286049A (en) 1995-08-02
GB2286049B GB2286049B (en) 1997-10-08

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GB9423992A Expired - Fee Related GB2286049B (en) 1993-12-08 1994-11-28 A sensor device responsive to the position of a piston

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DE (1) DE4341810B4 (en)
FR (1) FR2713757B1 (en)
GB (1) GB2286049B (en)
IT (1) IT1271109B (en)

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US8203331B2 (en) 2009-02-17 2012-06-19 Goodrich Corporation Non-contact sensor system and method for selection determination
US8207729B2 (en) 2009-02-17 2012-06-26 Goodrich Corporation Non-contact sensor system and method for displacement determination
US8405386B2 (en) 2009-02-17 2013-03-26 Goodrich Corporation Non-contact sensor system and method for position determination
US8988069B2 (en) 2009-02-17 2015-03-24 Goodrich Corporation Non-contact sensor system and method for displacement determination
GB2467823B (en) * 2009-02-17 2015-04-01 Goodrich Corp Non-contact sensor system and method for position determination
US9086301B2 (en) 2009-02-17 2015-07-21 Goodrich Corporation Non-contact sensor system and method for displacement determination

Also Published As

Publication number Publication date
DE4341810A1 (en) 1995-06-14
ITMI942415A1 (en) 1996-05-29
FR2713757B1 (en) 1997-01-31
FR2713757A1 (en) 1995-06-16
IT1271109B (en) 1997-05-26
DE4341810B4 (en) 2004-01-29
GB9423992D0 (en) 1995-01-11
GB2286049B (en) 1997-10-08
ITMI942415A0 (en) 1994-11-29

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