Position-measuring device for fluid cylinder

The invention relates to a position measuring device according to the preamble of claim 1.

In many applications of fluid cylinders, it is advantageous if the position of a piston or the piston rod of a fluid cylinder is known in order to move moving members driven by the fluid cylinder exactly into desired positions, or to determine their exact position.

A large number of position measuring devices are known from the prior art, which can detect optically detectable markings on the piston rod by means of a sensor arrangement with a light source and a light sensor that is fixed on the cylinder. Such a position measuring device for the absolute measurement of a piston rod position is for example from DE 100 14 194 A1. Another generic position measuring device is known from WO 2009/112895 A1, the sensor arrangement of which is based on a technology used in computer mice. A disadvantage of such a position measuring device is that, despite the fundamentally high measurement resolution of such a system, slight measurement inaccuracies increase in the course of use and, according to WO 2009/112895 A1, calibration positions have to be approached again and again.

The disadvantage of the first-mentioned exemplary embodiment is that, in order to determine the absolute position of the piston rod, an entire barcode of the code pattern must be recorded, although in this case this takes place sequentially. In the case of a sequence of many short movements that are shorter than the respective barcodes, measurement inaccuracies result that are only eliminated again,

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-2 if there is a movement of the piston rod that is greater than the length of a barcode and thus an exact absolute position can be recorded again.

All previously known position measuring devices of this type have in common that they have only an inadequate combination of robustness and measuring reliability as well as universally applicable compact dimensions, which is why such measuring systems based on optical measurement have only been able to gain acceptance in practice and on the market to a limited extent.

The object of the invention is to provide a position measuring device for a piston rod of a fluid cylinder which, in spite of harsh operating conditions, has a high level of reliability in terms of both mechanical and measurement technology and can nevertheless be produced economically.

The object of the invention is achieved by a generic position measuring device with the characterizing features of claim 1.

Because the lighting source and the BiEdsensor are attached to a common circuit board of the sensor arrangement and a light guide element for transmitting the luminous flux from the lighting source to the measuring cutout is arranged between the lighting source and the measuring cutout, the measuring cutout is even when using a simple, compact and inexpensive lighting source is sufficiently illuminated and reliable measurements can also be made with simple measuring optics. The light guide element is based on total reflection of a large part of the luminous flux emitted by the light source on its boundary walls and the luminous flux can be optimally distributed over the measurement section with very little losses. The light guide element uses the principle of a light guide, similar to that used in signal transmission technology, and the light guide element is formed by a coherent, in particular one-piece, light-permeable body made of light-permeable material.

The light entry surface and the light exit surface on the light guide element are translucent, while the lateral boundary walls are opaque

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7/38, Μ and, for example, can also have an internally mirrored coating, which further improves the reflection of the luminous flux on the boundary walls.

The invention can be used with all types of fluid cylinders such as single-acting cylinders, plunger or plunger cylinders, in which the piston rod is formed by the piston itself, and double-acting cylinders with a piston rod or bilateral or continuous piston rod. The position measuring device according to the invention can be provided twice on a single fluid cylinder due to its favorable manufacturing costs and its compact dimensions, whereby a redundant position measuring system is provided, as is advantageous or also prescribed for steering cylinders, for example. In the case of a fluid cylinder with piston rods on both sides, the position measuring devices can be arranged at both ends or both at one end.

Optimal utilization of the luminous flux emitted by the lighting source is achieved when the light guide element is directly connected to the lighting source or has a light entry surface that is positioned at a distance of less than 2 mm from the lighting source. The Uchtleitelement can thus contact the illumination source directly or is at least arranged in its immediate vicinity, whereby the majority of the luminous flux enters the light guide element and is available for the illumination of the measurement section.

A further advantageous embodiment variant consists in that the light guide element extends over at least 50%, preferably over at least 75%, of the smallest distance between the illumination source and the piston rod surface. This also ensures that the smallest possible proportion of the luminous flux is lost between the illumination source and the measurement section. In the event of failure, the light guide element extends from the illumination source to just before the piston rod surface, but still ends at such a distance that

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the white section can be captured by the measuring optics without being obstructed by the light guide element.

If an LED element is used as the lighting source, the sensor arrangement has a long service life and low power consumption. LED elements are available in many embodiments and can be obtained with different light frequencies, wherein the light frequency of the LED element or the lighting source can generally be adapted to the optimal sensitivity of the image sensor.

The image sensor and / or the illumination source can in particular be designed as SMD components applied to the circuit board and thereby contribute to reducing the size of the sensor arrangement.

The illumination source can advantageously have an approximately square radiation surface which, given a sufficiently high luminance, also enables a very small component size for the illumination source. The shape of the radiating surface can also differ significantly from the shape and size of the measurement section through the use of the light guide element, since the light guide element can be optimally used for guiding, shaping and directing the luminous flux.

If the light guide element has a matt light entry surface and / or a matt light exit surface, the luminous flux is distributed relatively evenly, guided inside the light guide element and / or the light exit surface itself acts like a radiating surface of a lighting source, which, however, is much closer to the white section than the actual one Lighting source. By matting the light entry surface or Light exit surface, the luminous flux emitted by the lighting source is converted into an approximately diffuse light flux, which inside the light guide element is also guided to the light exit surface for the most part by total reflection and causes very even illumination of the measurement section.

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A compact embodiment of the sensor arrangement is possible in particular if the edge length of the emitting surface is less than 2 mm and the dimensions of the measurement section are at least 10 mm by 2 mm. Through the light guide element, the intense light emitted by a small emitting surface can be transmitted to a relatively large measuring section, which means that many Koibenstangen positions can be coded even with thicker bar markings, since the measuring section covers a sufficiently large section of the code pattern

This is also facilitated if the light guide element has a rectangular cross section, a longer side of the rectangular cross section running parallel to the piston rod axis. As a result, a measurement section running in the longitudinal direction of the piston rod axis can be illuminated as evenly as possible.

If the light guide element has a cross-section that increases from the light entry surface to its light exit surface, even when using very small lighting sources with a small radiation surface, a measurement section that is large enough for measurement purposes can be uniformly illuminated.

A compact embodiment of the sensor arrangement is possible in particular when the light exit area of ​​the light guide element corresponds to at least three times the light entry area. As a result, the luminous flux of the illumination source can be spread or widened starting from a small, approximately punctiform emission surface, which results in an illumination of the measurement section which is advantageous for the optical measurement.

In contrast to pure lens systems, the light entry surface and / or light exit surface can be simply shaped by the use of the light guide element, in particular have essentially flat surfaces, whereby the production of the light guide element is particularly cost-effective and the illumination is nevertheless sufficiently strong and uniform for reliable measurements of the piston rod position.

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The light exit surface can be concave in sections and / or convex in sections, whereby the light guidance through the light guide element or the luminous flux distribution on the measuring section can be locally influenced compared to purely flat surfaces. The concave light exit surfaces cause a scattering of the exiting luminous flux, while convex sections of the light exit surface have a concentrating effect.

Another possibility for advantageously influencing the illumination of the measurement section can be that the light guide element exhibits a local disturbance in its center of the beam path in the form of a transverse bore, a cover panel or an optically refractive element. As a result, an excessively large difference in illumination between the central area of ​​the measurement section and its edge areas can be significantly reduced.

A further advantageous embodiment of the position measuring device can consist in that the light guide element and / or the measuring optics are pivotably mounted in the housing with respect to a pivot axis parallel to the Koibenstangenachse. This allows the luminous flux or the beam path of the measuring optics can be adapted to different geometric conditions, which can occur, for example, when the sensor arrangement is to be used for piston rods of different diameters or the distance between the piston rod and the circuit board of the sensor arrangement varies for structural reasons.

In order to facilitate or ensure the mutual positioning of light guide element and measuring optics, it is possible for the light guide element to be pivotably mounted on the measurement optics or for the measurement optics to be pivotably mounted on the light guide element, whereby the two components are coupled to one another in one direction and in one direction are adjustable to each other in a right-angled direction.

An embodiment with a code pattern that is easy to produce on the piston rod is given when the width of the bar markings and the unmarked code sections on the code pattern is approximately one millimeter or an integral multiple of a millimeter. The requirements for accuracy

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in the production of the code pattern are relatively low in this case, as a result of which the production costs associated therewith are also relatively low. A width of the line markings of one millimeter or a multiple thereof can be reliably scanned with simple embodiments of an image sensor in combination with simple measuring optics, whereby the measuring reliability is very high and a resolution of the position measurement is given which is sufficient for many applications of a fluid cylinder.

A measuring system that can be used advantageously for many applications is given if the code pattern is formed by a binary pseudo-random code with interlaced, mutually different code words, the length of the measurement section at least corresponding to the length of the code words and the code words having a length of at least 8 Bit, in particular 15 bits. Such a code is known from WO 66/00478 A1, for example, and it is a possibility of clearly identifying a large number of optically detectable absolute positions of the piston rod with simple line markings. With a code word length of 15 bits contained in a code pattern which corresponds to a 1000-digit binary number and which corresponds to a length of one meter with a width of the bar markings of 1 mm, more than 1000 different code words can be contained when using a code word length of 15 bits, whereby a measurement resolution of 1mm is given.

For the practice of fluid cylinder applications, it is advantageous if the measurement section on the Koibenstangen surface covers a length of at least 15 bits of the code pattern. As the length of the code words used increases, so does the number of possible different code words, which means that even very large measurement lengths can be assigned to unambiguous absolute positions of the piston rod.

An alternative embodiment of a position measuring device, which also uses a code system which is advantageous for the cases that occur in practice, consists in the code pattern being represented by a binary block code with an alternating sequence of information bits of constant number and width as well as

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Protection bits of constant number and width is formed and the measurement of the piston rod position uses a measuring method in which the position or displacement of the protection bits in the measurement section is recorded and the information bits each define unique absolute references for the piston rod position.

An inexpensive embodiment which is sufficient for position measurements is when the image sensor is formed by a line camera element or linear sensor array arranged parallel to the piston rod axis. However, the image sensor can of course also be formed by a two-dimensional CCD element, a one-dimensional sensor element also being sufficient for the one-dimensional Kotbenstangen position measurement.

The requirements for measurement accuracy that arise in practice can easily be met if the line camera element has between 32 and 2048 sensor points, in particular 128 sensor points or pixels. Such image sensors are available in many embodiments and at low cost. At the same time, such an image sensor has very compact dimensions, which enables the compactness of the entire measuring device and its universal applicability.

Sufficient measuring accuracy of the position measuring device for the applications occurring in practice is given if the line camera element has a resolution between 200 and 1200 dpi, in particular 400 dpi. Here, too, a large number of embodiments are available inexpensively on the market.

A compact embodiment of the sensor arrangement is possible in that the distance between the circuit board and the piston rod surface is selected from a range between 15 mm and 25 mm. In connection with the light guide element and the measuring optics of the position measuring device according to the invention, such a device can be provided for many different sizes of fluid cylinders without extensive structural changes being necessary.

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The image sensor is therefore relatively independent of the reflectivity of the piston rod surface and is therefore also insensitive to changes in the piston rod surface caused by wear or other environmental influences during the operation of such a fluid cylinder.

As an alternative or in addition, the main axis of the measuring optics can also be inclined to the main direction of propagation of the light beams of the illumination source, which are reflected by the piston rod surface, i.e. it can be directed eccentrically to the illumination maximum on the code pattern. This can also prevent reflections on the piston rod surface that could impair the measurement.

The sensor arrangement is very compact if the center-to-center distance between the lighting source and the image sensor on the circuit board is selected from a range between 5 mm and 12 mm Measurement section is shadowed by the measurement optics.

Another measure for miniaturizing the sensor arrangement is to arrange the evaluation unit on the circuit board. In the previously described embodiments of the image sensor and the code pattern, the computing power required for the evaluation can also be achieved with very small evaluation units and microprocessors, whereby a first image data evaluation can already be integrated in the sensor arrangement.

If the measurement results are not output directly to the sensor arrangement, but the position measurement data are processed further by an external evaluation unit, for example a control and regulating device of the device comprising the fluid cylinder, it is advantageous if an interface for power supply and data transmission is arranged on the circuit board is.

The compactness of the sensor arrangement can also be increased in that a second circuit board is connected to the circuit board in parallel or at an angle to it, to which an evaluation unit and / or a power supply unit is connected

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component and / or a data interface is arranged. The components of the sensor arrangement are divided into several circuit boards by this embodiment, whereby the individual circuit boards require a smaller area and the housing of the sensor arrangement can be kept relatively narrow and it does not protrude with respect to the outer diameter of the fluid cylinder.

A structurally advantageous embodiment of the measuring device consists in that the housing is designed in two parts and the circuit board is attached to an outer, removable housing section or housing cover. This makes the sensor arrangement easily accessible, since when the outer housing section is removed, the sensor arrangement is also separated from the fluid cylinder and an exchange of the sensor arrangement is thus made much easier.

Furthermore, it is possible for the printed circuit board to be fastened in an adjustable manner in its position within the removable housing section from the outside, in particular by means of adjusting screws. On the one hand, the measurement section on the piston rod can be offset in the circumferential direction by adjusting the printed circuit board, for example if incorrect position measurements occur due to local damage to the code pattern. Furthermore, it is possible to be able to attach the outer, removable housing section in the same size with different housing dimensions, which may be necessary for different piston rod diameters, structurally unchanged. Due to the adjustability of the circuit board within the removable housing section, an optimal adaptation to the respective piston rod diameter can take place in this case.

One possibility of reducing the manufacturing costs of such a position measuring device is furthermore that the measuring optics and / or the light guide element essentially comprise optical elements made of PMMA (Plexiglas) or polycarbonate. Since the requirements for optical quality are also met by such components, expensive optical components made of glass can be avoided.

So that the sensor arrangement or the housing does not protrude from its outer diameter even with small sizes of fluid cylinders, it is of

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Advantage if the circuit board has a rectangular basic shape with a maximum edge length of 40 mm. As a result, the housing or the removable housing section can be kept correspondingly small.

In order to permanently protect the sensor arrangement from harmful influences and to ensure a long service life with high measurement reliability, it is advantageous if the piston rod completely encompassing sealing rings or stripping elements are arranged on the housing on both sides of the measurement cutout.

Due to the cost-effective design of the position measuring device according to the invention and its compact dimensions, it is also possible to equip a fluid cylinder with at least two such position measuring devices, whereby a redundant position measurement is easily possible, which is often prescribed in safety-relevant systems. The individual sensor arrangements can each be assigned their own code pattern on the piston rod, but it is also possible for both sensor arrangements to access the same code pattern, in particular with measurement sections that are offset from one another.

In the case of fluid cylinders with piston rods on both sides, such as, for example, steering cylinders, the position measuring devices can be arranged at the two opposite ends.

For a better understanding of the invention, it is explained in more detail with reference to the following figures.

They each show in a greatly simplified representation:

1 shows a view of a fluid cylinder with a possible embodiment of a position measuring device;

2 shows a view of a sensor arrangement arranged in a removable housing section;

3 shows a cross section through a possible embodiment of a position measuring device;

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4 shows a radial section through a possible embodiment of a position measuring device in the area of ​​the light guide element;

5 shows a radial section through a possible embodiment of a position measuring device in the area of ​​the measuring optics.

As an introduction, it should be noted that in the differently described embodiments, the same parts are provided with the same reference numerals or the same component designations, whereby the disclosures contained in the entire description can be transferred accordingly to the same parts with the same reference numerals or the same component designations. The location details chosen in the description, such as above, below, to the side, etc. based on the figure immediately described and shown and are to be transferred accordingly to the new position in the event of a change in position. Furthermore, individual features or combinations of features from the different exemplary embodiments shown and described can also represent independent, inventive or inventive solutions.

All information on value ranges in the present description are to be understood to include any and all sub-areas thereof, e.g. the information 1 to 10 is to be understood in such a way that all sub-areas, starting from the lower limit 1 and the upper limit 10, are also included , ie all subranges begin with a lower limit of 1 or greater and end at an upper limit of 10 or less, for example 1 to 1.7, or 3.2 to 8.1 or 5.5 to 10.

1 shows a view of a fluid cylinder 1 with a position measuring device 2 according to the invention. The fluid cylinder 1 essentially comprises a cylinder tube 3 in which a piston (not shown) is guided, which is displaced in the cylinder tube 3 by supplying or removing fluid. The cylinder tube 3 is closed at one end with a cylinder base 4 and closed at the opposite end with a cylinder head 5 through which a piston rod 6 connected to the piston is led out. The fluid cylinder 1 can be designed as a hydraulic cylinder or a pneumatic cylinder, the execution N2009 / 06300

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- * »1 * 3&gt; · · * · ·» »is not decisive for the position measuring device 2 according to the invention. Furthermore, in the case of a single-acting plunger cylinder, the piston rod can be formed by the piston itself, and the invention is not restricted to fluid cylinders 1 with a separate piston rod 6, but can be applied to plunger cylinders.

For many applications it is advantageous if the position of the piston rod 6, with which the moving members are moved or positioned in the device, can be detected and thus such a fluid cyfinder 1 can exactly move to preprogrammed positions by means of control and regulating devices or precisely follow preprogrammed movement sequences.

The position measuring device 2 is based on the fact that a measuring standard in the form of an optically detectable code pattern 8 is arranged on the outer circumference 7 of the piston rod 6, and a sensor arrangement 9 is fixedly arranged on the fluid cylinder 1 in the area of ​​the cylinder head 5, with which a partial section of the code pattern 8 is optically detected and is evaluated. By shifting the piston rod 6 along the piston rod axis 10 when the piston moves, the code pattern 8 is moved past the sensor arrangement 9 and the position of the piston rod 6 is determined by means of an evaluation unit from the subsection of the code pattern 8 that is optically detected by it.

The code pattern 8 is composed, for example, by a binary sequence of line markings 11 oriented transversely to the piston rod axis 6, which are attached to the outer circumference 7 of the piston rod 6. The code pattern 8 or the line markings 11 can be applied, for example, by galvanic processes or metallurgical processes. One possible production method for the code pattern is that on a chrome-plated coating of the calf rod surface 6, thermal energy is introduced selectively by means of concentrated laser radiation, whereby the edge layer takes on tempering colors that differ in color from the thermally untreated sections. A code pattern applied in this way can additionally be optically throughNZ009 / 00800

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18/38 · · · * »·« · · • -14 »4 *» · · «· ··« · · 4 visible protective coating, eg an SiO2 coating, whereby the code pattern 8 has an increased wear resistance.

The subsection of the code pattern 8 optically detected by the sensor arrangement 9 corresponds to a code word to which a unique piston rod position is assigned. The sensor arrangement 9 records a specific measurement section of the code pattern 8, which extends in the direction of the piston rod axis 10, and is assigned an unambiguous piston rod position to an optically recorded code word by an evaluation unit. For example, if the measuring section in the piston rod direction 10 has a length that corresponds to eight times the line width of a line marking 11, the respective position of the piston rod 6 can be detected by an 8-bit code word.

An embodiment of the code pattern 8 which is advantageous for practical applications is that the width of the bar markings 11 and the unmarked code sections each corresponds to a millimeter or an integral multiple of a millimeter. In this case, the narrowest line marking has a board of 1mm and the narrowest unmarked code section has a width of 1mm. Code patterns 8 with this width of the line markings 11 are not very sensitive to punctual damage to the code pattern 8, for example due to wear, since the resolution here does not have to be so fine that punctual damage would also cause measurement errors. A certain minimum width of the recorded measurement section is also helpful, in that not only a narrow line is optically scanned on the code pattern 8, but an area with a width of two or more millimeters is mapped onto the image sensor.

One possible embodiment of the code pattern 8 and the evaluation method can advantageously consist in that the code pattern 8 is formed by a binary pseudo-random code with interleaved, mutually different code words, the length of the measurement section at least corresponding to the length of the code words and the Code words have a length of at least 8 bits, in particular 15 bits.

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'.45.

An alternative embodiment of the code pattern 8 can also consist in that the code pattern 8 is formed by a binary block code with an alternating sequence of information bits of constant number and width and guard bits of constant number and width, e.g. a marked or unmarked section 4 mm in length and the measurement of the piston rod position uses a measuring method in which the position or Shift of the protection bits in the measurement section is detected and the information bits each define absolute references for the piston rod position. The optically evaluated measurement section is selected so large that it contains at least one complete, coherent group of information bits.

The sensor arrangement € is arranged in a housing 12 which is fixedly arranged on the fluid cylinder 1 and contains sufficient free space in its interior for the sensor arrangement 9 and for guiding the light to and from the piston rod surface 7. The housing 12 can, as in FIG shown outside of the fluid cylinder 1 on the cylinder head 5 or integrated in the cylinder head 5 or be formed by this and protects the optically based sensor arrangement 9 from interfering light and harmful environmental influences such as mechanical loads or contamination. In order to protect against contamination, it is provided in particular that the measuring section provided on the piston rod 6 is protected on both sides by sealing rings or wiping elements encompassing the piston rod 6.

In the illustrated embodiment, the housing 12 is designed in two parts and this comprises a removable outer housing section 13 or housing cover which can be removed from the rest of the housing 12, whereby the sensor arrangement 9 is more easily accessible. Furthermore, passages for cables for the purpose of data exchange or power supply can be provided on the housing 12. This can in particular also be achieved by means of a connection socket 14.

The position measuring device 2 with the sensor arrangement 9 and its mode of operation will be described in more detail below with reference to FIGS. 2 to 5.

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FIG. 2 shows a view of the housing section 13 removed from the rest of the housing 12, the sensor arrangement 9 being fastened in the illustrated embodiment, whereby it is particularly easily accessible. The fastening of the sensor arrangement 9 in a detachable housing section 13 makes it possible to mount this structurally unchanged on housing lower parts of different sizes, so that only these have to be adapted to the respective fluid cylinder 1.

The sensor arrangement 9 essentially comprises as main components a lighting source 15 for illuminating the measurement section to be captured on the code pattern 8, as well as an image sensor 16 for optically capturing the measurement section. Illumination source 15 and image sensor 16 are arranged on a common printed circuit board 17 which, in the exemplary embodiment shown, is fastened in the removable housing section 13. An evaluation unit 18 in the form of a microprocessor 19 is also arranged on this circuit board 17, which determines the absolute position of the piston rod 6 from the image data captured by the image sensor 16 or processes the image data so that they can be evaluated by an additional external evaluation unit.

The image sensor 16 is formed, for example, by a line camera element 20 which is arranged parallel to the piston rod axis 10 and has 128 sensor points or pixels. The measurement section on the code pattern 8 is optically mapped onto the image sensor 16 by means of measuring optics 21, which optically map the measurement section illuminated by the illumination source 15 onto the image sensor 16. The measurement section has, for example, an extension of 16 mm in the direction of the piston rod axis 10 and a width of 3 mm across it, while the line camera element 20 has an effective sensor length of approximately 8 mm and an effective width of 0.1 mm.

For this purpose, the measuring optics 21 contain optical lens elements, for example made of Plexiglas (PMMA) or polycarbonate, and in particular comprise a cylinder lens adjoining the gauge camera element 20 and two lens elements on the piston rod side with non-rotationally symmetrical surfaces. The measuring optics

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13:55:19 25-08-2011 / 38 • · · · · · »· * *« »* e -« i · • ^ * 7 * · · · · ν ♦ »ό | / »» · · Ι tu * * thus has an anamorphic property and is ideally suited for imaging a rectangular measurement section on a line-shaped line camera element 20.

In the position measuring device 2 according to the invention, the luminous flux emitted by the lighting source 15 is transmitted to the measuring cutout on the outer circumference 7 of the piston rod 6 by means of a light guide element 22, which is arranged between the lighting source 15 and the measuring section, whereby the code pattern 8 is optimally illuminated for the purposes of optical detection will. The light guide element 22 has a light entry side facing the illumination source 15 and a light exit side facing the code pattern 8, and the incoming light flux is guided inside the light guide element 22, with only a very small proportion of the amount of light not reaching the light exit area due to total reflection on the lateral boundary surfaces .

The light guide element 22 preferably connects directly to the lighting source 15 or the light entry surface of the light guide element 22 is at least at a distance of less than 2mm from the illumination source, whereby the majority of the emitted light quantity enters the light guide element 22. Furthermore, the light guide element extends preferably over at least 50% of the smallest distance between the illumination source 15 and the outer circumference 7 of the piston rod 6, whereby the light exit surface is relatively close to the code pattern 8 and this is thus optimally illuminated.

The lighting source 15 is preferably formed by an LED element 23, which is characterized by a long service life and a very high light yield based on its energy consumption. The use of a surface-emitting thin-film LED has proven to be advantageous for position measurement, with the wavelength ranges white, red and infrared producing good results. Furthermore, such LED elements 23 can be used in very small dimensions. In order to keep the dimensions of the lighting source 15 small, it can in particular be provided that it has a square radiating surface 24, which also has an edge length of, for example

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I • fl »fl • 1» i »ä» has less than 2 mm. As a result of the very effective light guide element 22, such an approximately point-shaped illumination source 15 can also be used for uniformly illuminating a rectangular measurement section. The light guide element 22 makes it possible, for example, to evenly illuminate a measurement section 16 mm long and 3 mm wide with an edge length of the emitting surface 24 of, for example, 1x1 mm,

In order to further improve the uniform illumination of the measurement section, the light guide element 22 can have a matted light entry surface and / or a matted light exit surface, as a result of which the intensity differences within the luminous flux are reduced.

As FIG. 2 further shows, the light guide element 22 can have an approximately rectangular cross-section, with a longer side of the rectangular cross-section running parallel to the piston rod axis 10 and thus the light exit surface approximately having the shape of the measurement section to be illuminated. In the case of an approximately punctiform illumination source 15, it is advantageous if the cross section of the light guide element 22 increases from the light entry surface to the light exit surface, whereby the light flux can also increase in its cross section. In the example shown, the light exit area of ​​the light guide element 22 corresponds to at least three times the light entry area.

In order to be able to optimally adapt the measuring optics 21 and the light guide element 22 to one another and thereby also be able to use the sensor arrangement 9 for different piston rod dimensions, it is possible for the light guide element 22 and / or the measuring optics 21 to be pivotable in relation to a pivot axis 25 parallel to the piston rod axis 10 Housing 12 are mounted. As a result, the area on the piston rod surface wired by the illumination source 15 can be varied and / or the area detected by the measuring optics 21 can also be optimally adapted. This also makes it possible to compensate for differences in the distance between the circuit board 17 and the piston rod surface 7 with different piston rod diameters.

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19 ′ It is possible here for the light guide element 22 to be pivotably mounted on the measuring optics 21 or, conversely, for the measuring optics 21 to be pivotably mounted on the light guide element 22. As a result, these are directly coupled to one another and possible axis deviations due to assembly errors are minimized.

The measurement section on the piston rod surface 7 detected by the image sensor 16 preferably covers a length of at least 15 bits of the code pattern 8. By capturing code words with a length of 15 bits, more than 1,000 different absolute positions of the piston rod 6 can easily be clearly identified with a suitable pseudo-random code.

For the optical measurement of the code pattern 8, the line camera element 20 has a resolution between 200 and 1200 DPI, for example 400 DPI, which gives a slightly sufficient resolution for the detection of line markings 11 with a width of 1 mm.

3 shows a section transverse to the cylinder axis through the position measuring device 2, FIG. 4 shows a radial section through a position measuring device 2 in the area of ​​the light guide element 22, and FIG. 5 shows a radial section through the position measuring device 2 in the area of ​​the measuring optics.

The respective beam courses are indicated, with individual beams only being shown by way of example.

The light guide element 22 shown as an example in Fig. 4 is arranged such that its light entry surface 26 is arranged at a distance from the emitting surface 27 that is less than 2 mm, the light entry surface 26 could even directly adjoin the illumination source 15 and it is through this Arrangement ensures that the majority of the emitted light enters the light guide element 22. As a result, the light entering the light entry surface 26 is passed on to the light exit surface 28 by directly penetrating the material of the light guide element 22 or by being deflected on its side walls by total reflection in the direction of the measuring section 29.

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In the exemplary embodiment shown, the light entry surface 26 is designed as an essentially flat surface which is particularly easy to manufacture and can nevertheless meet the requirements for the light guidance to the measurement section 29. In a departure from the concave design shown in solid lines, the light exit surface 28 can also be designed as an essentially flat surface, as shown in FIG. 4th is indicated and as a result of which the production of the light guide element 22 is further simplified.

The lighting source 15 in the form of the LED element 23 is fastened to the circuit board 17, which in the illustrated embodiment is fastened in the removable, outer housing section 13. As FIG. 4 shows, it is possible to provide a second printed circuit board 30 parallel to or at an angle to the printed circuit board 17, on which components of the sensor arrangement 9 can also be arranged. This is somewhat higher for this, but can be designed with a smaller width and length in the direction of the cylinder axis 10. For example, the second printed circuit board 30 can have interfaces 31 for data transmission and / or power supply and these can be routed to the connection socket 14 via an interface cable.

As FIG. 4 shows, the light guide element 22 extends over the majority of the distance 32 between the illumination source 15 and the outer circumference 7 of the piston rod 6, but advantageously over at least 50% of the distance 32 Luminous flux is passed to the measurement section 29. Furthermore, FIG. 4 shows two further possibilities for achieving the most uniform possible illumination of the measurement section 29. The first possibility is to use a concave light exit surface 28 which, however, can also be locally flat or also convex in sections. The concave design shown causes a further dispersion of the luminous flux and a uniform illuminance is achieved as a result. As an alternative or additional measure to achieve uniform illumination, the light guide element 22 has a local disturbance 33 in its center, for example in the form of a bore 34 transversely to the direction of light propagation, which results in a maximum illumination 2009 / 06Θ00

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21 · - ··· mum is lowered in the center of the measurement section 29 and the illumination intensity is also more uniform as a result.

As an alternative to a bore 34, it is also possible to attach a local cover panel or a more concave or convex section in the central region of the light exit surface 28.

Tests have shown that it is advantageous for the manufacturing costs and the compactness of a position measuring device 2 according to the invention if the circuit board 17 has a distance from the Koibenstangen surface 7 of a range between 15 and 25 mm. Furthermore, the printed circuit board 17 can be dimensioned in such a way that it has a rectangular basic shape with a maximum edge length of 40 mm, as a result of which it protrudes only slightly from the outer circumference of common fluid cylinders 1 even after being installed in a housing.

In order to enable further adaptation to different dimensions of a fluid cylinder 1, even if the same upper housing section is used in each case, it can be provided that the printed circuit board 17 is adjustably fastened in its position within the removable housing section 13 from the outside, for example by means of adjusting screws. The sensor arrangement 9 can thus be optimally adapted in a simple manner to different mounting positions and piston rod diameters.

FIG. 3 shows a section through a position measuring device 2 along line III III in FIG. 4.

In this exemplary embodiment, the main axis of the measuring optics 21 is oriented in the direction of the piston rod axis 10, but it is also possible to provide this eccentric or skewed to the piston rod axis 10, so that the measuring optics 21 do not aim at right angles to the outer circumference 7 of the piston rod 6. As can also be seen, the illumination source 15 together with the adjoining light guide element 22 is arranged at a relatively small center-to-center distance 35 from the image sensor 16, here in the form of a line camera element 20. The center-to-center distance 35 is, for example, from a BeN2DOB / O60OO

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<img file="AT511883A1_D0005.tif" />

range between 5 mm and 12 mm, whereby the sensor arrangement 9 can be made very compact and the position measuring device 2 has few restrictions in its possible area of ​​application due to its small dimensions.

In Fig. 3 it is further indicated by dashed lines that the light guide element 22, as already described with reference to FIG can be adjusted and the illumination of the measurement section 29 can be further optimized in a simple manner or can be adapted as a function of the relative position of the illumination source 15, image sensor 16 and piston rod surface 7.

The optical detection is carried out by the image sensor 16 at a high frequency, for example with more than 1000 images per second, whereby a quasi-continuous position detection is given.

The dimensions and technical specifications mentioned on the basis of the exemplary embodiment are optimally suitable for piston rod diameters between 20 mm and 80 mm, but can be appropriately adapted for dimensions of piston rods 6 that differ therefrom. The described embodiment of the sensor arrangement 9 has sufficient tolerances with regard to component tolerances or installation tolerances, which is why there is a very wide range of application here. The components used are suitable for working temperatures of -40 ° C and +100 ° C and temperature influences on the measurement accuracy are negligible, appropriate replacement materials would have to be used for higher temperatures, such as plastics with higher softening points or replacement with metallic, ceramic or crystalline materials.

In the exemplary embodiment shown, the light guide element 22 has a light entry area 26 of 6 mm x 4 mm and a light exit area 28 of 24 mm x 4 mm, whereby on the one hand the radiation area 24 of approx. 1 mm x 1 mm on the illumination source 15 and the measurement section 29 on the Piston rod surface 2009/300

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27/38 surface 7 are adequately covered and only a small proportion of the luminous flux is lost

Fig. 5 shows in radial section the optical imaging of the measurement section 29 on the image sensor 16 in the form of the line camera element 20, the bundling in one direction directly in front of the line camera element 20 by a cylindrical lens.

The exemplary embodiments show possible design variants of the position measuring device 2, whereby it should be noted at this point that the invention is not restricted to the specifically illustrated design variants thereof. Rather, various combinations of the individual design variants with one another are also possible and this possibility of variation is within the ability of a person skilled in the art based on the teaching of technical action through the present invention. All conceivable design variants that are possible through combinations of individual details of the embodiment variants shown and described are therefore also included in the scope of protection.

For the sake of clarity, it should finally be pointed out that for a better understanding of the structure of the position measuring device 2, it or its components have been shown partially not to scale and / or enlarged and / or reduced.

The task on which the independent inventive solutions are based can be found in the description.

Above all, the individual in FIGS. 1; 2; 3; 4 and 5 form the subject of independent solutions according to the invention. The related tasks and solutions according to the invention can be found in the detailed descriptions of these figures.

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<img file="AT511883A1_D0006.tif" />

List of reference symbols

Fluid cylinder

Position measuring device

Cylinder tube

Cylinder bottom

Cylinder head

Piston rod

Outer circumference

Code pattern

Sensor arrangement

Piston rod axis

Line marking

casing

Housing section

Connection socket

Lighting source

Image sensor

Circuit board

Evaluation unit

microprocessor

Drawing camera element

Measuring optics

Light guide element

LED element

Abstraction surface

Swivel axis

Light entry surface

Light exit surface

Measurement section

Circuit board

interface

distance

disturbance

drilling

Distance between the sites

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