DE4341810A1 - Sensor device for position detection of a piston - Google Patents

Abstract

A sensor device for a cylinder 12 containing a moving piston 11 comprises a permanent magnet 13 or 13a on the piston 11 or on an element connected with the piston, and at least one magnetic field responsive device 15 or 15a, having a preferential direction, arranged on the cylinder 12 and responsive to the approach of the permanent magnet The permanent magnet 13 or 13a and the at least one device 15 or 15a are so aligned that on mutual passage the magnetic field 14 or 14a of the permanent magnet at spatially consecutive points acts substantially parallel to the preferential direction of the sensor 15 or 15a but in opposite directions and thus causes different sensor reactions, means being provided for the storage of such sensor reactions. Accordingly it is possible not only to ascertain the exact current position of the piston 11 on passing the device 15 or 15a but furthermore information is always available as to whether the piston is to the left or to the right of the field responsive device. <IMAGE>

Description

The invention relates to a sensor device for a a movable piston containing cylinder for posi tion detection of the piston, with one on the piston or one arranged permanently with the piston connected element magnets, with at least one arranged on the cylinder more sensitive to magnetic fields, having a preferred direction Sensor responds when the permanent magnet approaches.

Such a sensor device for position detection a piston is for example from DE-C 37 08 989 known. There should be such sensor devices in particular by reaching the end position ranges the pistons are monitored. With the well-known sensor facilities can recognize and indicate the time shows to which the piston just the sensor device tion happens, but beyond that it behaves pas siv and cannot provide any information about the stay give the location of the sensor. However, for many applications it is  desirable to receive such information in order to for example to be able to determine whether the piston located in one or the other end area.

It is therefore an object of the present invention in, a sensor device of the type mentioned to create that not only reaching the sensor posi tion can be detected by the piston, but by the it can also be determined whether the Piston on one side or the other of the sensor device tung is located.

This object is achieved in that the Permanent magnet and the at least one sensor so out are directed that the magnetic field of the permanent magnet when passing each other at local successive the places essentially parallel to the preferred direction of the sensor directed in opposite directions acts and thereby two different sensor reaction triggers, using means to store this sensor reactions are provided.

Every time the piston passes the sensor device and the permanent magnets are therefore two different Liche sensor reactions, such as sensor signals  solved, with the last being saved so that the means for storing a different memory content depending on whether the piston is on the left or to the right of the sensor position. The users The possible uses of the sensor device are therefore through simple and inexpensive measures significantly expanded, the original function of Position detection when passing the sensor device in is maintained unchanged. Such a sen In certain cases, the sensor device can therefore have two sensors sor devices or complex detection logic put.

By the measures listed in the subclaims are advantageous developments and improvements of possible in the sensor device specified in claim 1.

To achieve the magnetic field of the permanent magnet two times when passing the sensor device focuses on these acts to those of the below triggering different sensor reactions will either the north-south axis of the permanent magnet radial and the Preferred direction of the sensor parallel to the direction of movement of the piston, or the north-south axis of the Per manentmagneten is parallel to the direction of movement of the  Piston and the preferred direction of the sensor radially out judges. An advantageous solution for electrical storage Sure of the sensor reactions is that the sensor has a magnetic field sensitive electrical element, the different electrical Si as sensor reactions gnale generated, this magnetic field sensitive Ele an electrical signal memory is connected downstream. This electrical signal memory is expedient trained as a comparator or as a bistable multivibrator det, for example as a Schmitt trigger. Especially at a comparator with hysteresis, such as a Schmitt Trigger is a particularly safe switching behavior because there is a higher positive Threshold switched on and when falling below a low rigorous negative threshold is turned off. The two Signal states as sensor reactions remain saves. The sensor device according to the invention can therefore in a simple and inexpensive way from two Manufacture commercially available components.

To prevent the arrangement from being switched on again a random memory signal is present, either the Signal store constantly with an operating voltage strikes, or an error signal stage is provided, after switching on the supply voltage until  the first time the sensor responds, an error signal generated. This error signal indicates that the ge stored sensor signal not correct at the moment have to be.

Another advantageous way of magnetic Storage of the sensor response is that the Sensor as a signal store a magnetizable and around has a magnetizable element with a magnet field-sensitive electrical element in operative connection stands, which different sensor reactions as sensor trical signals generated.

The means for reproducing the different electri signals can be optical, acoustic or electrical To be means.

The magnetic field sensitive electrical element can be used as Hall element, as a field plate or as an induction coil be trained.

Finally, there is also an advantageous possibility ability to save the sensor reactions mechanically. Here the sensor has a movable signal storage magnetic or magnetizable, from permanent magnet  element that can be changed in its position. Preferably the element is arranged pivotable about an axis, wherein Means for setting the two swivel end positions seen and the passing permanent magnet these Means overcomes. At the respective swivel end position or generally at the position of this movable element can then be read on which side the sensor the piston is located.

Embodiments of the invention are in the drawing shown and in the following description explained. Show it

Fig. 1 is a schematic representation of a magnet piston-cylinder unit with two possibilities for the arrangement of permanent arranged on the piston and arranged on the cylinder Sen sors,

Fig. 2 shows a signal diagram for explaining the field trials run in the sensor as it passes the permanent magnet,

Fig. 3 shows a first embodiment of a electrical-specific signal storage,

Fig. 4 shows a second embodiment of a magnetic signal storage and

Fig. 5 shows a third embodiment of a mechanical signal storage African.

Referring to FIG. 1 a connected to a piston rod 10 piston 11 is slidably disposed in a cylinder 12. In the piston 11 in the upper part of FIG. 1, a permanent magnet 13 is inserted so that its north-south axis is radially aligned. This creates the magnetic field 14 acting in the outside space. On the outside of the cylinder 12 , a sensor 15 is arranged for position detection, the preferred direction indicated by a double arrow is arranged parallel to the direction of movement of the piston 11 , that is to say in the axial direction. In principle, this sensor 15 can also be inserted into the wall of the cylinder 12 .

As can be seen from FIG. 1, the sensor 15 is first penetrated by a magnetic field which is directed to the right and then by a magnetic field which is opposite when the piston 11 or the permanent magnet 13 passes in the course of a movement directed to the right. is directed to the left. The field lines penetrating the sensor 15 at locally successive locations of the piston 11 each run essentially parallel to the preferred direction of this sensor 15 .

In the lower part of FIG. 1, an alternative arrangement is shown. A permanent magnet 13 a is inserted into the piston 11 so that its north-south axis runs parallel to the direction of movement of the piston 11 , that is to say axially. A magnetic field 14 a is formed. A sensor 15 a is arranged on the outside of the cylinder 12 with a radially aligned preferred direction.

When passing the piston 11 or the permanent magnet 13 in the course of a movement to the right, the sensor 15 a is therefore first penetrated by radially inward field lines of the magnetic field and then by radially outward field lines of the magnetic field of the permanent magnet 13 a.

In FIG. 2, the field distribution H in the sensor 15 or 15 a as it passes the permanent magnet is shown 13 and 13 a. When approaching, the magnetic field initially rises to a maximum, which is reached when the field lines reach their greatest field strength parallel to the preferred direction of the sensor. The field strength then drops sharply until shortly thereafter the oppositely directed field lines reach an oppositely directed maximum, which is shown in FIG. 2 as a minimum. Then the magnetic field decreases with increasing distance of the permanent magnet from the sensor and goes to zero.

In Fig. 3, a first embodiment of such a sensor 16 is shown with electrical signal storage, and an evaluation device. This sensor 16 can take the place of the sensor 15 or sensor 15 a, with a corresponding orientation of the preferred direction.

The sensor 16 consists of a Hall element 17 , the signal of which is fed to a Schmitt trigger 18 . The two complementary outputs of the Schmitt trigger 18 are connected to indicator lights 19 , 20 . Furthermore, these two outputs are fed via an OR gate 21 to a bistable switching stage 22 , the second input of which is acted upon by a switch-on signal S when the supply voltage is switched on. An output of the bistable switching stage 22 is connected to an error detection lamp 23 .

When passing the permanent magnet 13 , an electrical signal is generated in the Hall element 17 which is in essence proportional to the magnetic field strength from which the Hall element is acted upon. The elec trical signal when passing the permanent magnet 13 thus has a profile that corresponds essentially to that of the curve shown in FIG. 2. The Schmitt trigger 18 be sits an upper positive switching threshold Sp and a lower negative switching threshold Sn. In the position of the piston 11 shown in FIG. 1, the output signal of the Schmitt trigger 18 for controlling the indicator lamp 19 is initially designed as a 1 signal, so that the indicator lamp 19 burns and the indicator lamp 20 is not switched on. At point X1, the lower switching threshold Sn is undershot, so that the Schmitt trigger switches, that is, the indicator lamp 19 goes out, and the indicator lamp 20 is switched on. The lighting of the indicator light 20 then indicates that the piston is now to the right of the sensor with respect to FIG. 1. When the piston moves backwards in the opposite direction, the Schmitt trigger is switched again when the upper switching threshold Sp is exceeded. This means that one of the two indicator lights 19 , 20 always lights up and thus indicates on which side of the sensor the piston is located. At the same time, the position of the piston 11 on the sensor is recognized by the changeover time.

Instead of the display device given as a simple example by two indicator lights 19 , 20, it is of course also possible to use an indicator, a computer, a printer or the like in an appropriate manner.

When the operating voltage is switched on, the Schmitt trigger 18 is either in a random state or in a defined state, which, however, does not reflect the position of the piston 11 . In order to make this state known, the bistable switching stage 22 is actuated by the signal S when the operating voltage is switched on, so that the error detection lamp 23 lights up. Only when the Schmitt trigger 18 switches for the first time due to the permanent magnet 13 passing through is the bi-stable switching stage 22 reset via the OR gate 21 , so that the error detection lamp 23 goes out. Only after the error detection lamp 23 has gone out is the position of the piston 11 correctly represented by the indicator lamps 19 , 20 .

Instead of the Hall element 17 , of course, in principle, another magnet-sensitive element can occur, for example a field plate or an induction coil. Furthermore, another comparator with or without hysteresis or a bistable multivibrator can be used instead of the Schmitt trigger 18 .

In the second embodiment shown in FIG. 4, a soft magnetic core 24 is provided as a means for storing the position, which is magnetized or magnetized when passing through the permanent magnet 13 or 13 a. The magnetization state of this soft magnetic core 24 is detected by a Hall element 25 or another magnetic field sensitive element. Whose output signal is fed to an evaluation and display device 26 , which represents the two positions of the piston to the left and right of the sensor depending on the detected magnetization state. Since the magnetization state is retained in the soft magnetic core 24 , a correct position is immediately available when the supply voltage is switched on.

In the third embodiment shown in FIG. 5, a bar magnet 27 is pivotally arranged on a joint 28 . In the two pivot end positions, the bar magnet 27 is in electrical contact with one of the two end stops 29 , 30 . These end stops 29 , 30 are each connected to the indicator lights 19 and 20 , the second connection of which is electrically connected to the joint 28 via a voltage source 31 . A spring not shown Darge holds the bar magnet 27 each resiliently at one of the two end stops 29 , 30 , the spring force being such that it is overcome when passing the permanent magnet 13 or 13 a.

Assumes the arrangement shown in FIG. 5, the position of the sensor 15 a in Fig. 1 so when passing the piston 11 and the permanent magnet 13 a of the bar magnet 27 is initially deflected to the stop 29 and then to the end stop 30th There he then takes up his position. When moving back and when passing the piston 11 , it is then moved again to the end stop 29 . So there is the rod magnet 27 at the end stop 30 , which is indicated by a switched on indicator light 20 , the piston 11 is shown in FIG. 1 to the right of the sensor 15 a, and when the bar magnet 27 is at the end stop 29 , so that the Indicator lamp 19 burns, then it is located on the left of sensor 15 a.

Instead of the pivotable bar magnet 27 can in principle also be provided on a permanent magnet which can be moved into different positions when passing the piston 11 be, for example a piston-like parallel or perpendicular to the piston movement movable permanent magnet magnet. The identification of the respective position of the permanent magnet or bar magnet 20 can take place in various ways, as has already been explained in connection with FIG. 3.

Instead of the permanent magnet 13 a, two radially aligned permanent magnets arranged in a juxtaposition, which have radially outward different magnetic poles, can of course also occur in principle.

Claims (14)

1. Sensor device for a cylinder containing a movable piston for position detection of the piston, with a permanent magnet arranged on the piston or an element connected to the piston, at least one magnetic field sensitive arranged on the cylinder having a preferred direction when the sensor approaches the permanent magnet, thereby responding indicates that the permanent magnet ( 13 , 13 a) and the at least one sensor ( 15 , 15 a; 16 ; 24 , 25 ; 27-30 ) are aligned so that the magnetic field ( 14 , 14 a) of the permanent magnet ( 13 , 13 a) when passing each other at locally successive points substantially parallel to the preferred direction of the sensor ( 15 , 15 a; 16 ; 24 , 25 ; 27-30 ) each acting in opposite directions and thereby triggering two different sensor reactions, whereby means to store these sensor reactions are provided. 2. Sensor device according to claim 1, characterized in that the north-south axis of the permanent magnet ( 13 ) is aligned radially and the preferred direction of the sensor ( 15 ) par allel to the direction of movement of the piston ( 11 ). 3. Sensor device according to claim 1, characterized in that the north-south axis of the permanent magnet ( 13 a) parallel to the direction of movement of the piston ( 11 ) and the preferred direction of the sensor ( 15 a) is radially aligned. 4. Sensor device according to one of the preceding claims, characterized in that the sensor ( 16 ) has a magnetic field-sensitive electrical element ( 17 ) which generates different electrical signals as sensor reactions and which is followed by an electrical signal memory ( 18 ). 5. Sensor device according to claim 4, characterized in that the electrical signal memory ( 18 ) is designed as a comparator or as a bistable multivibrator. 6. Sensor device according to claim 5, characterized in that the electrical signal memory ( 18 ) is designed as a Schmitt trigger. 7. Sensor device according to one of claims 4 to 6, characterized in that the electrical signal memory ( 18 ) is constantly supplied with an operating voltage. 8. Sensor device according to one of claims 4 to 6, characterized in that an error signal stage ( 22 ) is provided which generates an error signal after switching on the supply voltage until the first response of the sensor ( 16 ). 9. Sensor device according to one of claims 1 to 3, characterized in that the sensor as a signal memory has a magnetizable and reversible element ( 24 ) which is in operative connection with a magnetic field-sensitive electrical element's ( 25 ), which as sensor reactions different electrical signals testifies. 10. Sensor device according to claim 9, characterized in that the magnetizable and magnetically reversible element ( 24 ) is designed as a soft magnetic core. 11. Sensor device according to one of claims 4 to 10, characterized in that means ( 19 , 20 ) are provided for reproducing the different electrical signals. 12. Sensor device according to one of claims 4 to 11, characterized in that the magnetic field-sensitive electrical element ( 17 ; 25 ) is designed as a Hall element, as a field plate or as an induction coil. 13. Sensor device according to one of claims 1 to 3, characterized in that the sensor as a signal memory has a movable magnetic or magnetizable, by the permanent magnet ( 13 , 13 a) in its position changing element ( 27 ). 14. Sensor device according to claim 13, characterized in that the element ( 27 ) is arranged pivotably about an axis, means for fixing the two pivoting end positions being provided and the passing permanent magnet ( 13 , 13 a) overcoming these means.