EP1070856B1 - Piston position indicator - Google Patents

Abstract

The detection device includes a sensor device which has a fixed sensor element outside the region of the fluid and a movable sensor element inside this region. The movement of the measuring rod (13), which has a thread (14) in its longitudinal direction, is turned forcibly through an angle which is detected without contact by the fixed sensor element.

Description

The invention relates to a device for detecting the position of a piston in a cylinder, in particular a pressure medium cylinder, with a bore having a piston rod, in which a measuring rod is arranged, wherein in dependence on the longitudinal movement the piston rod, the measuring rod forced by a rotation angle and the Rotation angle converted by means of a sensor device into an electrical sensor signal becomes.

It is known for non-contact measurement of paths and angles inductive pickups use. For example, the axial displacement of a shaft can be measured inductively become. The inductive pickup can be installed in a cylinder chamber be within which the shaft is slidably guided. A disadvantage of this method of measurement However, that connections of the transducer via special feedthroughs from the cylinder chamber must be led to the outside. Especially in pressurized rooms the use of this known device is relatively expensive.

Furthermore, it is for detecting the position of a piston in a cylinder under pressure known to attach a sensor device to an outer circumferential surface of the cylinder tube. This sensor device acts with a within the cylinder on a peripheral surface the piston mounted permanent magnet together. Due to the fact that the cylinder tube or the cylinder wall is made of a magnetic material, is a switching signal on a fixed magnetic field sensitive attached to the outside of the cylinder tube Sensor element generated as soon as the piston with the permanent magnet in the area of the sensor element is moved. The thus obtained switching signal can in one Downstream electronic evaluation unit for detecting the position of the piston in evaluated the cylinder. A disadvantage of the known device is that of Cylinder due to the attachment of the sensor element on the outside of the cylinder tube Has unwanted projections, the cylinder to an asymmetric Surface contour gives and on the other hand requires a larger radial space. The electrical leads connected to the sensor device must be in the environment be led to a central evaluation unit. To avoid these disadvantages it is already known from DE 197 03 903 A1, a sensor device with magnetic field sensitive Sensors in axial extension to a its location to be detected cylindrical part to arrange. In the known part to be detected is However, it is a steering shaft of a steering wheel for motor vehicles, in which the Rotation angle of the same should be detected. However, this known sensor device is only suitable for detecting the rotation of an elongate member. The capture the axial position of a particular piston is known from this known device not removable.

From DE 195 45 923 A1 discloses a device for detecting the position of a piston in a cylinder with a piston rod known, which is provided with a bore, in the a measuring rod is arranged. Furthermore, a fixed sensor element is provided, which includes the measuring rod within the bore of the piston rod. By relative displacement the measuring rod to the stationary sensor element is inductive way generates a sensor signal in response to the displacement of the piston rod. The well-known Device is relatively expensive and requires a relatively large amount of space because on the one hand, the measuring rod to be firmly connected within the bore with the piston rod must and must be provided on the other means, the low-friction displacement the stationary sensor element relative to the measuring rod and the piston rod guarantee. Furthermore, a sufficient seal of the stationary sensor element be provided to the interior of the cylinder.

From US 4,386,552 it is also known, a twisted measuring rod forcibly guided in to arrange a pick piston rod. For a straight-line movement of the piston rod this is converted into a rotational movement of the measuring rod. A sensor element within the pressure medium detects this rotational movement and converts it into a corresponding sensor signal, which indicates the relative position of the piston rod to the cylinder tube. adversely in this arrangement, the installation position of the sensor element within the pressure chamber. The electrical signals must be through elaborately sealed electrical feedthroughs out of the printing area out. Also the control of the sensor device, the retrofitting of a lifting cylinder with the sensor device or a repair of the sensor device can be difficult to perform, since the lifting cylinder for it must be disassembled.

Object of the present invention is therefore to provide a device for detecting the position of a piston in a cylinder in such a way that the position of the piston to simple Way and can be reliably detected, where possible, the known deficiencies resolved should be.

To achieve this object, the invention in conjunction with the preamble of the claim 1 characterized in that the sensor device at least one fixed Sensor element outside the pressure medium range and a movable, of the Measuring rod driven, sensor element has within the pressure medium range and the movement of the driven sensor element contactless from the fixed Sensor element is detected.

The particular advantage of the invention is that a simple measuring system is formed by the formation of the sensor device, which determines the relative position of the piston rod to the cylinder housing. Particularly advantageous is the non-contact determination of the rotational movement of the measuring rod. This eliminates complex rotary feedthroughs, which lead to a reduction of costs and at the same time to new fields of application for the measuring system according to the invention. By attaching the stationary sensor element outside the pressure medium range, this can be made particularly simple by no special requirements related to the pressure medium and the pressure in the pressure medium must be made to the execution. Only the environmental conditions, such as moisture and dust protection outside of the lifting cylinder must be taken into account in the design of the sensor element.
To arrange the sensor device in an edge region of a pressurized space, has the advantage that the required space of the lifting cylinder is not increased. Furthermore, a sensor device can easily be introduced into the lifting cylinder bottom.
There is usually, for holding the cylinder, structurally unnecessary housing material into which the sensor device can be easily integrated without changing the function or the size of the lift cylinder. Also, this installation position prevents damage to the sensor device from the outside. Due to this mounting position on the cylinder bottom side, the accessibility to the sensor device is also made easy by not having to dismantle the lifting cylinder for mounting or checking the device.
For the non-contact transmission of the rotational movement of the measuring rod to the stationary sensor element, known as operating, for example, according to the magnetic, inductive or capacitive measuring principle sensor devices are available. Thus, the movable sensor element can be designed according to the measuring principle used and the movement of the measuring rod can be converted depending on the measuring principle used in a correspondingly recognizable signal. This may be a change in distance between the two sensor elements, a rotation of the elements to each other or even by constructive configurations of the elements with a corresponding movement thereof.

In a particularly advantageous embodiment of the invention, located in the cylinder bottom a removable sensor housing, which is circumferentially equipped with a seal and on the one hand the fixed sensor element separates from the pressure medium and on the other hand has a recess on the side in communication with the pressure medium side, which for receiving a connected to the front end of the measuring rod connecting element, wherein the connecting element is rotatably mounted about the longitudinal axis of the measuring rod in the recess.
This embodiment represents a particularly simple embodiment, which is easy and inexpensive to produce. The sensor housing is a simple rotary part with a circumferential groove for receiving a seal and provided at both end faces, each with a recess. In the recess, on the pressure medium remote side of the sensor housing, can easily attach the fixed sensor element. For this purpose, the sensor element itself can in turn be directly connected to an evaluation electronics and be secured in the recess of the sensor housing directly by means of a potting compound, clamping, pressing or screwing. The sensor housing itself is fixed in a central bore to the measuring rod assembly in the cylinder bottom bore and closes the cylinder bottom against the pressure medium range. On the pressure medium side of the sensor housing a further stepped recess is attached. This serves to fix or support a connecting element, which has a congruent to the recess shape, and is in communication with the measuring rod. Due to the position of the sensor housing in the lifting cylinder bottom, and the measuring rod is fixed in the recess with respect to the piston rod. The congruent shape of the Anschlußelemendes to the recess in the sensor housing, causes an almost backlash-free mounting of the connecting element in the recess. This is particularly advantageous since the movements made possible by play of the connecting element in this storage lead to a change in the accuracy of measurement. This storage also allows a free rotational movement of the connecting element in connection of the measuring rod in the sensor housing.

The connecting element according to the invention can be further configured by the connecting element is designed for fixing and storage with a ring element, which on the one hand on a shoulder of the cylinder bottom and on the other hand in the recess supported. By this embodiment of the invention the connection element is achieved a simple storage and disassembly of the sensor device. Front side becomes the cylinder bottom with a through hole that extends into the pressure medium range, Mistake. Central to this is provided with a larger diameter hole in introduced the cylinder bottom, but not reaching into the pressure medium range. Thereby creates a paragraph in the hole, which serves as a stop for the sensor housing and the Ring element is used. The ring element thereby limits the movement of the connecting element in the direction of the pressure medium range. A movement in the opposite Direction is effected by the adjoining sensor housing.

In a further embodiment of the invention, the connecting element has a central bore for receiving the front end of the measuring rod and the measuring rod is connected by means of a transversely to the longitudinal axis of the same extending bolt releasably and hingedly in the bore with the connecting element.
This embodiment has the advantage that the measuring rod is decoupled in the axial direction of the connecting element at least in a certain area. As a result, different orientations of the axes of piston rod and measuring rod are compensated and thus reduces wear on the bearing of the measuring rod and on the guide element. Furthermore, different materials can be coupled together by this connection point. Thus, the connection element can advantageously be made of a metallic material and the measuring rod made of a non-metal and connect. Also, thus differently worn components can be renewed and replaced independently, and the standardized sensor elements are adapted to a use case of the pressure medium cylinder adapted Meßstangelänge or twisting embodiment.

The sensor housing is in a particular embodiment of the invention, on one of Measuring rod remote from the back by means of a holding element releasably connected to the cylinder bottom attached. As a result, the sensor element securely fixed in the cylinder bottom but also be removed from there easily. The introduction into the cylinder bottom also allows a reduction in the manufacturing cost of the Hubzylindem used, optionally at the same location, for example, a pressure measuring system or a closure element can be used and fixed by means of the retaining element. Also, the possibility of retrofitting the prepared lifting cylinder with a pressure or Distance measuring system is thereby given at any time. The retaining element is advantageously a Seeger ring, which engages in a groove located in the bore of the cylinder base.

According to a preferred embodiment of the invention, the movable sensor element as a permanent magnet and the stationary sensor element as magnetic field sensitive Sensor element formed. The movable sensor element is fixed in the with the Measuring rod connected connection element bordered. In cooperation with the established Sensor element of the sensor device, this can be a non-contact measurement achieve the way of the piston rod. A movement of the piston rod is in a rotation of the measuring rod and a corresponding rotational movement of the connecting element transferred. Depending on the arrangement of the permanent magnet in the connection element, this leads Rotational movement at least to a changed orientation of the magnetic field to the fixed Sensor element or at a different distance of the sensor elements to each other. Advantageously, the sensor housing and / or the connecting element made of a non-magnetizable material, such as brass, whereby an improved effect of the measuring principle is achieved. For detecting a magnetic field are various sensors such as magnetoresistive sensors, Hall sensors and so-called field plates known. Particularly cost-effective prove for the mass use the Hall sensors. These can be easily on a small space requirement integrate an electronic circuit and then with additional evaluation circuits and equip interfaces.

According to a preferred embodiment of the sensor device is at least one permanent magnet aligned in the end portion such that the magnetic axis of the permanent magnet is perpendicular to the longitudinal axis of the measuring rod, and that at least one sensor element in Radial distance is arranged to the permanent magnet within the sensor housing. In the end portion of the connecting element becomes a permanent magnet with the magnetic axis arranged perpendicular to the axis of rotation of the connecting element. Advantageously, the extends Permanent magnet over the full diameter of the end section. This can be a flat or Bar magnet introduced into a groove or bore. The magnetic field is approaching vertically out of the pole faces and then penetrates directly through the sensor housing the magnetic field sensitive sensor elements arranged therein. At least one magnetic field sensitive Sensor is on the circumference of the connecting element facing side the recess arranged in the sensor housing and is, at least in the position with the smallest distance to one of the pole faces, approximately perpendicular to the magnetic field flows through. Advantageously, two or more magnetic field-sensitive sensors arranged distributed around the circumference of the recess, resulting in a more accurate evaluation the position of the connecting element in the recess is made possible. The decrease of Strength of the magnetic field by a sensor element is simultaneously by an increase in the Strength of the magnetic field detected in the other sensor element. An evaluation electronics then evaluates the measured values of the magnetic field-sensitive sensors according to direction and strength of the magnetic field and determines the angle of rotation of the connecting element in the recess. By appropriate learning process, the transmitter, the position of the piston in the zero position and the corresponding angle of rotation. Furthermore, the Evaluation the angle of rotation of the measuring rod directly into the position of the piston relative to convert the cylinder tube as a direct path signal. The evaluation electronics may be provided with a microprocessor and memory means and also have an interface that communicates with, for example, a CAN bus system.

In a further embodiment of the invention, at least one permanent magnet is so on the Oriented end portion is that the magnetic axis of the permanent magnet radially offset in Direction to the longitudinal axis of the measuring rod, and that at least one sensor element approximately arranged centrally to the longitudinal axis of the measuring rod within the sensor housing are. By this arrangement of the sensor elements to each other can be achieved that only the direction but not the strength of the magnetic field in a rotation of the connecting element changed by the magnetic field sensitive sensor element. The permanent magnet can be designed as a bar magnet and directly in a frontal bore on the connection element be arranged. Due to the decentralized arrangement, the direction of the Magnetic field through the centrally arranged, fixed sensor element in a rotation of the connection element in the recess on the sensor housing. For reinforcement of the magnetic field, the magnetic field can also be generated by a plurality of permanent magnets. Advantageously, the arrangement of two permanent magnets coaxial with the direction of rotation in the same radial distance from the axis of rotation in a complementary orientation. The magnetic field sensitive Sensor element is centrally located in the sensor housing and so executed that it can detect the magnetic field direction. This is special cost-effective, as the magnetic field-sensitive sensor easily executed and directly in one Electronic module integrated and so easily connected to other evaluation circuits can be.

The design of the measuring rod determines the rotational movement of the connecting element in the recess of the sensor housing. Alone by this design of the measuring rod, the measuring range or the Meßauflösung can be specified. The object causing the rotation, such as a piston in a cylinder, merely needs to have a bore with an opening cross-section which corresponds to the contour of the measuring rod in cross-section.
Particularly advantageous is the execution of the measuring rod with a pitch-large twist of at least 70 °. As a result, long strokes of a piston with a simple and provided with a few twisting measuring rod can be seen. In addition, the friction between the elements is kept low due to the large pitch.
An increase in the slope, up to greater than the angle of repose of 76 °, is a particular embodiment of the invention. Incline angles in this area prevent the elements guided against one another from being suitable for transmitting a rotational movement and thus can not stimulate mutual rotational movement. As a result, wear on the guide and bearings are reduced and kept the game between the elements low.

In a further embodiment of the invention, the twisting of the measuring rod extends evenly over the entire length of the measuring rod. Through this design, the Evaluation of the rotational angle signal easily done, since the rotation over the entire Measuring range linear to the stroke movement of the piston behaves.

In a preferred embodiment, the twist extends helically essentially along a circumferential angle of 360 °. This makes it easy on Make a clear dependence of the angle of rotation of the measuring rod of the longitudinal movement achieve the piston rod, since the connecting element over the entire stroke the piston experiences only a maximum of one full turn. On a special evaluation and determination of the executed number of revolutions of the measuring rod can according to the invention be waived.

According to a further embodiment of the invention, the measuring rod can only partially identify a twist. As a result, the distance measuring system according to the invention can be limited to the Kolbenhubbereich in which a special evaluation or only there a distance measurement is necessary. The measuring rod is provided for example only in the middle with a twist and designed in the other Meßstangenbereich so that no change in pitch occurs and thus in these Hubbereichen the piston, no rotation of the measuring rod is caused. This embodiment is particularly suitable for executable by the lifting cylinder movements that have a different position from the end stops of the piston, in which the position of the piston must be particularly controlled or regulated or detected. Especially for from a transport in a working position pivoting implements, this embodiment is suitable. Thus, for this purpose, the measuring rod has a twist only in the stroke position corresponding to the working position in order, for example, to enable detection there and optionally also a control of the working position.
In a further development of the measuring rod, this is provided at least two points with a twist. As a result, individual positions of the piston and optionally layers of actuated elements can be detected and controlled. Thus, can be saved in a cost effective manner, individual, located outside the lifting cylinder position detection means and it is also then no additional space required more.

In a further embodiment of the invention, the measuring rod has areas with different Gradients of twisting. The Meßstange twisting can be to the respective Requirement adapted, be designed differently. This is a special one Advantage of the sensor device according to the invention over the known position and Distance measuring systems. By the shaping or the different gradients the twisting of the measuring rod results in special fields of application and forms, in which otherwise resorted to outside of the cylinder position detection means had to become. These can be relocated according to the invention in the lifting cylinder and thus require no additional space and are also available then Damage protected arranged. Have different slopes of twist the advantage that the measuring rod to the specific requirements along the piston stroke can be adapted. So there are Stellbereiche, in which only must be recognized whether the Lifting cylinder has passed through this or reached and continue to areas in which a piston position exactly maintained or closely monitored along a certain stroke range must become. For this purpose, then the measuring rod with different slopes of twisting Mistake. In the areas, which only one position must be recognized, is the measuring rod equipped with a large pitch of twist, so that the measuring rod is only slightly rotated at these piston positions. In the areas with a finer Detecting the measuring rod is provided with a smaller pitch, so that in This piston stroke area a stronger rotation of the connecting element occurs.

In a further embodiment of the invention, have only the opposite ends the measuring rod on a twist. The measuring rod is designed so that the measuring rod only at the ends have a twist of the rod and in the intervening No distortion of the measuring rod is located. This then makes a special one Advantage, if the task of the lifting cylinder is an object or element from one position or position to another. For the control of the Lifting cylinders are the individual end positions of particular importance to There, for example, implement a so-called end position damping control technology can. Also, the inventive sensor device can only act as a position indicator the end positions of the piston can be used.

In a further embodiment of the invention, the length of the measuring rod does not extend over the entire stroke of the piston rod. This simplifies the sensor device considerably, since then the bore in the piston rod does not have to be performed over the entire piston stroke. Such embodiments are particularly appropriate when only in the lower, retracted piston position, the position of the piston must be detected. When the measuring rod length exceeds piston stroke, this is then no longer guided by the guide member in the piston head and then stands freely in the cylinder. Advantageously, the Meßstangenende is then provided with a taper in order to ensure the recovery and safe insertion of the measuring rod in the piston bore, the renewed immersion of the piston in the measuring range.
It is particularly advantageous if the measuring rod corresponds at least to the full stroke length of the piston rod. A secure guidance of the measuring rod is guaranteed at any time.

In a further embodiment of the invention, the guide element at a free end on a radially inwardly oriented resilient nose, which abuts at least partially on the peripheral surface of the measuring rod. This embodiment of the guide element enables a particularly precise guidance of the measuring rod in the bore of the piston rod. The nose is slightly springy on the measuring rod and thus ensures a play-free guidance of the measuring rod. Also wear on the measuring rod or on the guide element are compensated by the guide element itself in a certain range.
In a further embodiment of the invention, the nose of the guide element is hook-shaped and equipped with a in the direction of the measuring rod to the peripheral surface thereof the same sealing lip. This hook-shaped embodiment provides a special leadership property of the measuring rod in the bore of the piston rod by also compensating by the snug sealing lip and small distortion of the peripheral surfaces of the measuring rod. Also, it is achieved by the light acting in the axial direction of the measuring rod surface guidance of the hook-shaped nose, a good leadership property at the passages between different slopes of the torsion of the measuring rod.

The measuring rod according to the invention can also be further developed by the measuring rod has at least one hook-shaped support member, which the measuring rod partially against the central bore on the peripheral surface of the same fitting supports. This embodiment is suitable according to the invention especially for longer Measuring rod to this in the retracted areas and positions of the piston rod before to protect radial movements. For this purpose, opposite to the connecting element Side of the measuring rod annularly attached a hook-shaped support element. The Measuring rod is carried out a little longer than necessary for the maximum piston stroke, Thus, the guide element and the support member in the extended position of Piston rod does not interfere with each other. The measuring rod is generally of the connecting element held in axiler direction and by the guide element respectively guided in the radial direction of the support element, wherein the support element is designed so that that it has no guide properties based on the measuring rod. This is the support element on the one hand to the outer contour of the measuring rod and the other to the contour designed adapted to the bore in the piston rod.

Figur 1

eine schematische Seitenansicht eines Ackerschleppers mit hydraulisch betätigter Frontschaufel in einer oberen und in einer unteren Stellung der Frontladerschwinge,

Figur 2

einen Längsschnitt eines Hubzylinders gemäß Figur 1 in einer Einfahrposition,

Figur 3

einen Hubzylinder gemäß Figur 1 in einer Ausfahrposition,

Figur 4

einen Teilschnitt X aus Figur 2 in vergrößerter Darstellung,

Figur 5

eine schematische Darstellung einer Meßstange nach einer ersten Ausführungsform,

Figur 6

eine schematische Darstellung einer Meßstange nach einer zweiten Ausführungsform,

Figur 7

eine schematische Darstellung einer Meßstange nach einer dritten Ausführungsform und

Figur 8

eine alternative Ausführungsform einer federnden, hakenförmigen Nase eines Führungselementes gemäß Figur 4,

An embodiment of the invention will be explained in more detail with reference to the drawings. Show it:

FIG. 1

a schematic side view of an agricultural tractor with hydraulically operated front blade in an upper and in a lower position of the front loader rocker,

FIG. 2

3 a longitudinal section of a lifting cylinder according to FIG. 1 in a retracted position;

FIG. 3

a lifting cylinder according to FIG. 1 in an extended position,

FIG. 4

a partial section X of Figure 2 in an enlarged view,

FIG. 5

a schematic representation of a measuring rod according to a first embodiment,

FIG. 6

a schematic representation of a measuring rod according to a second embodiment,

FIG. 7

a schematic representation of a measuring rod according to a third embodiment and

FIG. 8

an alternative embodiment of a resilient, hook-shaped nose of a guide element according to Figure 4,

An agricultural tractor 1 shown schematically in FIG. 1 has a front bucket 2 for lifting, transporting and loading goods which can be actuated by means of paired first lifting cylinders 3 and second lifting cylinders 4. The first lifting cylinder 3 serve to raise and lower the Frondladerwing 5 and in conjunction with the blade 2. The second lifting cylinder 4 are used for pivoting the front blade 2 relative to the front loader swing 5. The lifting cylinder 3, 4 are designed as a hydraulic cylinder and substantially similar.
For example, the operation of the second lifting cylinder 4 in connection with Figures 2 and 3 will be described in more detail below.
The second lifting cylinder 4 are used to adjust the hinged on a front loader swing 5 front bucket 2. At this front loader swing 5 joins to the body of the tractor 1 toward a console 6 for receiving the front loader rocker 5.

In the figure 1 are each in the upper and lower positions of the front loader rocker fifth different positions of the front blade 2 relative to the front loader rocker 5 shown. The position of the front loader rocker 5 itself to the console 6 and the position of the front bucket 2 relative to the Frondladerschwinge 5, can be in a simpler, inventive Way by a determination of the relative piston positions to the respective cylinder tube. 7 determine.

In a retraction position of the lifting cylinder 4 according to FIG. 2, the front blade 2 is located in a transport position while in a deployed position of the lift cylinder 4 is located in a Auskippositon according to FIG. Own the controls of front loaders usually also an automatic parallel guidance of the front bucket 2 to the footprint of the Agricultural tractors 1. This is done by a controller, depending on the position of the lifting cylinder 3, electrohydraulic automatic one piston position on the two two stroke cylinders 4 set so that the bottom of the front bucket 2 over the entire pivoting the front loader swing 5, from the lower to the upper position, parallel to the base the Acherschleppers 1 is held. The position of the piston in at least one of Lifting cylinder 3 is determined by means of the measuring system according to the invention and to a controller to hand over. This then accesses a stored table on the basis of the measured value and this takes a necessary Hubzylinderlänge for the lifting cylinder 4, which a Parallel position of the bottom of the front bucket 2 according to the position of the front loader swing 5 and the stand areas of the tractor 1 corresponds. A subsequent one Control or a control command then causes, based on the determined length signal for the lifting cylinder 4, a corresponding adjustment of the Hubzylinderlänge the Lifting cylinder 4. The length of at least one lifting cylinder 4 is in turn with an inventive Detected measuring system and reported back to the controller.

The lifting cylinder 3 or 4 itself has a cylinder tube 7, in which a piston 8 is longitudinally displaceable is stored. The piston 8 is fixedly connected to a piston rod 9. The piston rod 9 has at a first end face on a hinge eye 10, for example hingedly connected to a blade joint part 11 on the front loader rocker 5. The piston rod 9 has a central bore 12 and on a hinge eye 10 facing away from End of a guide member 45, so that a measuring rod 13 as a measuring element is longitudinally movably guided relative to the piston rod 9. The piston rod 9 is hollow drilled formed and lies with the guide member 45 at least partially peripherally the measuring rod 13 at.

The measuring rod 13 has in the illustrated example over the entire length of a slope-sized Torsion 14, which extends along a circumferential angle of 360 ° over the entire length of the measuring rod extends. Preferably, the measuring rod 13 in cross section rectangular shaped, wherein the edges of the rectangle of each one of the Piston rod 9 facing away from end face 15 to one of the piston rod 9 facing end side 16 continuous and helical (helical) a circumferential angle of Sweep 360 °.

Towards the end face 15 of the measuring rod 13, a permanent magnet is shown schematically in FIG. 4 19 in a fixedly connected to the measuring rod 13 connecting element 20 bordered. This connecting element 20 is rotatably in a radial recess 21 of a rotationally fixed stored in the cylinder bottom 18 mounted sensor housing 22.

The sensor housing 22 has at least one bore for receiving a sensor element 24, which is at a radial distance from the permanent magnet 19 within the sensor housing 22 is arranged. This supplies depending on the magnetic field of the permanent magnet 19, a sensor signal, which is evaluated in an evaluation and as Wegmeßsignal can be transmitted to a central control unit. The evaluation electronics preferably directly associated with the sensor element 24 and with this together in one Assembly arranged within the sensor housing 22. The sensor housing 22 itself can made of a non-magnetizable material in which the sensor elements 24 is enclosed, exist. Preferably, the sensor element 24 is operating as a Hall-effect Hall sensor element formed.

The cylinder bottom 18 has for articulated mounting of the lifting cylinder 3.4 a joint eye 25 on. For actuating the lifting cylinder 4, this has a first hydraulic connection 27 in the cylinder bottom 18 and a second hydraulic connection 28 in a fixed with the cylinder tube 7 connected cylinder head 29. Through these connections 27, 28 is a hydraulic fluid in the cylinder interior or removed. When pressurized of the cylinder 4, the piston rod 9 is moved in the longitudinal direction, wherein the Measuring rod 13 according to the orientation of the twist 14 in a predetermined Direction of rotation 32 is rotated.

According to a further embodiment of the sensor device can in the sensor housing also a plurality of uniformly arranged in the circumferential direction sensor elements in an outer ring be arranged of the sensor housing 22. By the simultaneous provision of a plurality of sensor signals, a unique determination of the position of the piston 8 is realized. Due to the fact that the distortion 14 only over a twist angle of Extends 360 °, more intermediate positions of the piston 8 - not only the end positions according to Figures 2 and 3 - are detected.

As better seen in Figure 4, the measuring rod 13 by means of a transverse pin 17 with connected to the connection element 20. The bolt 17 is in a transverse bore of the measuring rod 13 stored. The connecting element 20 is plate-shaped and has a ring element 34, which is supported on a shoulder 35 of the cylinder bottom 18. The connection element 20 has on a measuring rod 13 side facing a recess 36, in the front end 15 of the measuring rod 13 can engage. On one of the measuring rod 13 opposite side joins to the ring member 34, an end portion 37 which together is positioned with the ring member 34 in the cylinder bottom 18. In the end section 37, at least one movable sensor element is designed as a permanent magnet 19 arranged.

On the measuring rod 13 facing away from the back of the sensor housing 22, is a holding element 38 is provided, by means of which the sensor housing 22 is pressed against the shoulder 35 and the ring member 34 of the connecting element 20 is guided correspondingly low backlash. The holding element 38 is preferably designed as a retaining ring and serves for releasable attachment the sensor housing 22 or the connecting element 20 and the measuring rod 13 inside the cylinder tube 7. The sensor housing 22 is in a groove of a seal 39 which seals the pressure area of the lifting cylinder relative to the environment and between the wall 40 of the cylinder bottom 18 and the sensor housing 22 is pressed is.

The sensor housing 22 and the connecting element 20 are preferably made of a metallic Material, in particular brass, within which the sensor element 24 or the permanent magnet 19 are enclosed.

On a sensor housing 22 side facing the piston rod 9 with a Damping pin 41 is formed. The damping pin 41 extends in accordance with 2 end position shown in a constriction portion 42 of the cylinder tube. 7 and allows a hydraulic cushioning of the piston 8 in the retracted position thereof.

At the end of the damping pin 41, the guide member 45 frictionally or non-positively used and has a resilient nose 43 which radially inwardly against the measuring rod 13 presses. The nose 43 may be made of a rigid plastic material. The Contour of the guide element 45 corresponds at least in regions to the contour of the It can be polygonal, preferably square, be formed. The guide element 45 is also aligned coaxially with the piston rod 9.

Figure 5 shows a measuring rod 13 which is provided over the entire Meßstangenlänge with a twist. It is shown here in a developed form and can at the ends, depending on the design and application of the measuring rod 13, in addition to guide or holding elements, such as a hole, be equipped.
Characterized in that the measuring rod 13 is arranged stationary and a corresponding figure 5 formed distortion 14, the measuring rod 13 is rotated at an axial displacement of the piston 8 and the piston rod 9 about the longitudinal axis of the piston rod 9 by a rotational angle φ, so that a corresponding angle-dependent signal is detected by the sensor device. This is evaluated in the evaluation unit, wherein the relationship between the translational path of the piston 8 and the piston rod 9 and the rotation angle φ of the measuring rod 13 can be determined by a characteristic curve. It is thus formed a positioning of the piston rod 9 and the path change thereof representative measurement signal.

The twist 14 of the measuring rod 13 has a direction to the longitudinal direction of the measuring rod thirteenth forming pitch angle α of at least 70 °, preferably 76 °. Preferably the pitch angle α should not fall below a drag angle β of 76 °. hereby is a smooth movement in the relative movement between the measuring rod 13 and the Piston rod 9 ensures, the translational movement of the piston rod 9 friction is converted into a rotational movement of the measuring rod 13, without the To hinder movement of the piston 8.

Characterized in that the measuring rod 13 is locked by the transverse bolt 17 in the longitudinal direction, In addition, a decoupling between the connecting element 20 on the one hand and the Measuring rod 13 on the other hand done. In non-parallel orientation of the measuring rod 13 and the connection element 20 can automatically compensate by pivoting about the Bolt axis of the bolt 17 are brought about.

According to a second embodiment of the measuring rod 13 according to Figure 6, a measuring rod 45 is provided, each having a twist 46 in the region of the front ends. The twists 46 each sweep over a circumferential angle of 180 °, so that over the entire length of the measuring rod 45 there is a twist of 360 ° and thus an unambiguous assignment is given. This measuring rod 45 serves to position the piston rod in an end region thereof. Preferably, the measuring rod 45 can be used for cushioning.
According to the embodiment shown in FIG. 7, the twisting can also be arranged in any area of the measuring rod 13. The arrangement may be dependent on the use of the piston rod 9 and the piston 8, respectively. The measuring range is therefore determined solely by the shape of the measuring rod.

Preferably, once before the start of the measurement to compensate for hysteresis errors due to the tolerances in the axial direction of the connecting element 20, the measuring rod 13 and the piston rod 9 carried out a calibration of the transmitter. These hysteresis errors would be negative especially in direction reversal of the piston rod 9 on the Affect measurement result. Therefore, a reference measurement is performed, in which the piston rod 9 over the entire length in one direction and then in the other direction becomes. A rotation angle characteristic is recorded depending on the path and in the Evaluation electronics stored. After recording this characteristic, the hysteresis error can and the measured sensor value as a function of the direction of movement the piston rod 9 corrected according to the determined hysteresis error become. This calibration process becomes unique after assembly of the sensor device or the measuring rod 13 made in the lifting cylinder 3.4.

The measuring rod 13 and the piston rod 9 can each be made of a metallic Material or be formed from a plastic.

According to an embodiment according to FIG. 8, the guide element 45 can also be made in one piece be connected to a damping pin 41 and has an inwardly deflected Sealing lip 44, which conforms as shown on the guide surfaces of the measuring rod 13.

Claims (20)

1. Apparatus for detecting the position of a piston in a cylinder, in particular a pressure fluid cylinder, comprising a piston rod (9) which has a bore and in which a measuring bar is arranged, wherein the measuring bar (13) is positively displaced through a rotary angle (ϕ) in dependence on the longitudinal movement of the piston rod (9) and the rotary angle (ϕ) is converted into an electrical sensor signal by means of a sensor device,
      characterised in that
      the sensor device has at least one fixed sensor element (24) outside the pressure fluid region and a movable sensor element (19) driven by the measuring bar (13) within the pressure fluid region and the movement of the driven sensor element (19) is contact-lessly detected by the fixed sensor element (24).
2. Apparatus according to claim 1 characterised in that disposed in the end (18) of the cylinder is a removable sensor housing (22) which is provided at the periphery with a seal (39) and which on the one hand accommodates the fixed sensor element (24) in separate relationship from the pressure fluid and on the other hand on the side communicating with the pressure medium has an opening (21) which serves to accommodate a connection element (20) connected to the front end of the measuring bar, wherein the connection element (20) is mounted in the opening (21) rotatably about the longitudinal axis of the measuring bar (13).
3. Apparatus according to one of claims 1 and 2 characterised in that the connection element (20) is provided for fixing or mounting with a ring element (34) which is supported on the one hand against a step (35) of the end (18) of the cylinder and on the other hand in the opening (21).
4. Apparatus according to one of claims 1 to 3 characterised in that the connection element (20) has a central bore (36) for accommodating the front end (15) of the measuring bar (13) and the measuring bar (13) is connected to the connection element (20) releasably and pivotably in the bore (36) by means of a pin (17) extending transversely with respect to the longitudinal axis of the measuring bar.
5. Apparatus according to one of claims 1 to 4 characterised in that a holding element (38) is provided on a rear side of the sensor housing (22), which is remote from the measuring bar (13), for releasably fixing the sensor housing (22) in the end (18) of the cylinder.
6. Apparatus according to one of claims 1 to 5 characterised in that the movable sensor element (19) is in the form of a permanent magnet (19) and the fixed sensor element (24) is in the form of a magnetic field-sensitive sensor element.
7. Apparatus according to one of claims 1 to 6 characterised in that the sensor element (24) is in the form of a Hall sensor element.
8. Apparatus according to one of claims 1 to 7 characterised in that at least one permanent magnet (19) is oriented in the end portion (37) in such a way that the magnet axis of the permanent magnet (19) is perpendicular to the longitudinal axis of the measuring bar (13) and that at least one sensor element (24) are arranged at a radial spacing relative to the permanent magnet (19) within the sensor housing (22).
9. Apparatus according to one of claims 1 to 8 characterised in that at least one permanent magnet (19) is oriented in the end portion (37) in such a way that the magnet axis of the permanent magnet (19) is radially displaced in a direction with respect to the longitudinal axis of the measuring bar (13) and that at least one sensor element (24) is arranged approximately centrally relative to the longitudinal axis of the measuring bar (13) within the sensor housing (22).
10. Apparatus according to one of claims 1 to 9 characterised in that the measuring bar (13) has a large-pitch twist (14) with a pitch angle (α) in a region of at least 70°.
11. Apparatus according to one of claims 1 to 10 characterised in that the pitch angle (α) is greater than a locking angle (β) of 76°.
12. Apparatus according to one of claims 1 to 11 characterised in that the large-pitch twist (14) extends uniformly over the entire length of the measuring bar (13).
13. Apparatus according to one of claims 1 to 12 characterised in that the twist of the measuring bar (13) extends at a maximum over a peripheral angle of 360°.
14. Apparatus according to one of claims 1 to 12 characterised in that the measuring bar (13) has a twist only in region-wise manner.
15. Apparatus according to one of claims 1 to 14 characterised in that the measuring bar (13) has regions with different pitches in its twist.
16. Apparatus according to one of claims 1 to 15 characterised in that the measuring bar (13) has a twist (14) only in the region of respective opposite ends (15, 16).
17. Apparatus according to one of claims 1 to 16 characterised in that the length of the measuring bar (13) does not extend over the entire stroke movement of the piston rod (9).
18. Apparatus according to one of claims 1 to 17 characterised in that at a free end the guide element (45) has a resilient nose (43) which is oriented radially inwardly and which bears at least region-wise against the peripheral surface of the measuring bar (13).
19. Apparatus according to one of claims 1 to 18 characterised in that the nose (43) is of a hooked configuration with a sealing lip (44) which in the direction of the measuring bar (13) bears snugly against the peripheral surface thereof.
20. Apparatus according to one of claims 1 to 19 characterised in that the measuring bar (13) has at least one support element which is of a hooked configuration and which supports the measuring bar (13) in region-wise manner with respect to the central bore (12) in a condition of bearing snugly against the peripheral surface thereof.

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