WO1996041999A1 - Displacement sensor - Google Patents

Displacement sensor Download PDF

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Publication number
WO1996041999A1
WO1996041999A1 PCT/NL1996/000240 NL9600240W WO9641999A1 WO 1996041999 A1 WO1996041999 A1 WO 1996041999A1 NL 9600240 W NL9600240 W NL 9600240W WO 9641999 A1 WO9641999 A1 WO 9641999A1
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WO
WIPO (PCT)
Prior art keywords
measuring
sensor
member
reference device
members
Prior art date
Application number
PCT/NL1996/000240
Other languages
French (fr)
Inventor
Josephus Wilhelmus Spronk
Marcus Hans Wilhelm Bonse
Original Assignee
Technische Universiteit Delft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to NL1000559 priority Critical
Priority to NL1000559A priority patent/NL1000559C2/en
Application filed by Technische Universiteit Delft filed Critical Technische Universiteit Delft
Publication of WO1996041999A1 publication Critical patent/WO1996041999A1/en

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01DMEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/24Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
    • G01D5/241Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes
    • G01D5/2412Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes by varying overlap
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00Measuring arrangements characterised by the use of electric or magnetic means
    • G01B7/34Measuring arrangements characterised by the use of electric or magnetic means for measuring roughness or irregularity of surfaces
    • G01B7/345Measuring arrangements characterised by the use of electric or magnetic means for measuring roughness or irregularity of surfaces for measuring evenness
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01DMEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/24Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
    • G01D5/241Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes
    • G01D5/2417Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes by varying separation

Abstract

There is described a measuring system for detecting a positional variation of an object (V), comprising: a reference device (10) defining an X-direction; a first group (30) of at least three sensor members (31, 32, 33) for providing measuring signals indicative of a positional variation in a Z-direction relative to the reference device; a second group (40) of at least two sensor members (41, 42; 43, 44) for providing measuring signals indicative of a positional variation in a Y-direction relative to the reference device. The sensor members can be plane plate electrodes which, together with an electrically conductive surface of reference device, form a capacitive element whose capacity is influenced by distance and/or overlap of plate electrodes with reference member. The measuring system offers a possibility for improving reproducibility and accuracy, and is, as far as design is concerned, readily adaptable to an intended use.

Description

Title: Displacement sensor

in technology, there is a need for equipment whereby it is possible to displace an object accurately according to a straight line, for instance during the manufacture of structures of that object. ithin the framework of the present invention, the position and displacement of an object will be described utilizing a rectangular coordinate system XYZ, wherein the desired direction of displacement is referred to as the X-direction. Generally, the Z-direction is chosen to be vertical and the X and Y-directions are chosen to be horizontal. Coordinates in the X, Y and Z-directions will be indicated by small letters x, y and z respectively. If the object indeed makes the desired linear movement, the value of x will change while the values of y and z remain constant; deviations from those constant (desired) values will be indicated as dy and dz respectively.

In principle, an object has six degrees of freedom. Relative to the above-mentioned rectangular coordinate system XYZ, those degrees of freedom are the three position coordinates x, y and z of one specific point of that object, usually the center of gravity M, and the three orientation coordinates φx, φy, φz, describing a rotation about the X-axis, the Y-axis and the Z-axis respectively. In a truly linear movement, those three orientation coordinates φ*, φy, φz should remain constant, deviations from those constant (desired) values will be indicated as dφx, dφy, and dφz respectively.

In general, the displacement is carried out by displacing the object along a guiding member, with bearing means being present. Examples of such bearing means are a slide bearing, roller bearing, magnetic bearing, air bearing. In a mechanical guiding, there is direct or indirect mechanical contact between the object and the guiding member. In such a guiding, deviations occur which are partly predictable, because they are caused by (supposedly constant) imperfections in the guiding (errors of form and the like) , and partly unpredictable. A problem involved is that during the processing of an object, forces are generally exerted on that object which render a slight displacement of that object unavoidable, caused by deformation of the guiding system (guides, bearings and the like) .

These performances can be improved by providing a measuring and correcting system: such a system comprises on the one hand measuring members serving to measure the deviations from the above-mentioned constant degrees of freedom desired and to provide measuring signals representative of the deviation measured, and on the other hand correcting means serving to compensate, on the basis of those measuring signals, a detected deviation by exerting a correcting displacement. In this system, those degrees of freedom, wanted to be constant, are measured relative to a reference member without requiring contact with that reference member. In principle, this enables the provision of a particularly accurate linear displacement, which can be just as accurate as the accuracy of the reference member applied. The accuracy can even be further improved through calibration, enabling possible systematic deviations of the system to be incorporated in the correction. Because the reference member only serves as reference and, accordingly, not as guiding, it will not be subject to wear, particularly so if the measurement is indeed contactless, so that it is not necessary to repeat that calibration often.

An essential component in this approach is the measuring equipment for determining those deviations dy, dz, dφx, dφy, and dφz mentioned. Different examples of such measuring equipment are already known, such as for instance a laser- interferometer and/or an autocollimator. However, conventional measuring equipment has as a drawback that it is complicated and expensive, and can measure simultaneously two degrees of freedom at the most. It is then necessary to employ several measuring systems, mostly of mutually different types, to be able to measure all five degrees of freedom to be monitored and corrected. Still more drawbacks are attached to the use of a laser- interferometer. It is necessary to use a laser source and associated optics, which requires quite some space. The reading out and processing of the light signals is fairly complicated, and the measuring accuracy is in principle limited by the wavelength of the light used. Further, the measuring result substantially depends on the refractive index integrated along the optical path, which integrated refractive index is influenced by environmental conditions such as temperature and turbulence. Further, in general, fitting such a system in already existing displacement equipment is not possible, or only with great difficulty.

The object of the invention is to remove the drawbacks mentioned. A first main object of the invention is to provide a measuring member whose manufacturing tolerances are not extremely high and which can be manufactured in a relatively cheap and simple manner, but whereby an improved measuring accuracy can nevertheless be achieved.

A second main object of the invention is to provide a measuring system for a linear displacement apparatus, wherein one single measuring device can simultaneously measure all five degrees of freedom to be monitored and corrected.

A third main object of the invention is to provide a linear displacement apparatus, wherein fewer requirements are imposed on the accuracy of the mechanical guiding members, so that they can be of cheaper design, while with this apparatus a very good accuracy can nevertheless be achieved, even to the order of l nm, if so desired.

To that end, a measuring system according to the invention has the features as described in claim l.

The above-mentioned and other aspects, characteristics and advantages of the present invention will be explained by the following description of a preferred embodiment of a linear displacement apparatus according to the invention, with reference to the accompanying drawings, wherein: Fig. 1A schematically illustrates the operation of a measuring member according to the invention for detecting a displacement;

Fig. IB schematically shows a view of an embodiment of a sensor member; Fig. 1C schematically illustrates the operation of a combination of measuring members according to the invention for detecting a displacement in two directions;

Fig. ID schematically illustrates the operation of a combination of measuring members according to the invention for detecting a rotation;

Fig. 2 schematically shows a perspective view of an embodiment of a sensor device according to the invention;

Fig. 3 schematically illustrates the operation of a variant of a measuring member for measuring a lateral displacement; Fig. 4 schematically shows a top plan view of a preferred embodiment of a sensor device according to the invention;

Fig. 5 schematically shows a cross section of a displacement apparatus;

Fig. 6 schematically illustrates the use of the present invention for calibrating a displacement apparatus;

Fig. 7 schematically illustrates the use of the present invention for controlling actuators of a displacement apparatus;

Fig. 8 illustrates a variant of the measuring member illustrated in Fig. 3;

Fig. 9 illustrates a variant of a measuring principle according to the invention; and

Fig. 10 illustrates a variant of the embodiment outlined in

Fig. 4. in the Figures, identical or comparable parts are designated by identical reference numerals.

Presently, with reference to Fig. 1A, a measuring principle used by the present invention will be discussed. By reference numeral 10, a reference device is designated, fixedly arranged relative to the environment l. The reference device 10 has a main surface 11, which is substantially plane. A sensor member 21 is provided on a support 20 and is relatively slightly spaced from the main surface 11 of the reference device 10, so that there is an electronic or electromagnetic coupling between the reference device 10 and the sensor member 21. As will be understood by a skilled person, the measure of that coupling inter alia depends on the mutual distance d between the refefence device 10 and the sensor member 21, as will be further explained.

In a preferred embodiment, the sensor member 21 is an electrically conductive plate, and at least the main surface 11 of the reference device 10 is also conductive. Accordingly, the combination of the sensor member 21 and the main surface 11 defines a capacitor, and the sensor member 21 and the main surface 11 can be regarded as plate electrodes. As is known, the thus defined capacitor has a capacity C which is inversely proportionate to distance d. Capacity C is further proportionate to the effectively overlapping surface A of the two plate electrodes; for practical purposes, if the main surface 11 is "large" enough, this overlapping surface A can initially be considered to be equal to the surface of the sensor member 21.

When the support 20 is attached to an object which is to be displaced relative to the machine frame l, this capacity C will remain constant as long as this distance d does not change. Hence, in a rectangular coordinate system of which the X-axis, parallel to the main surface 11, is perpendicular to the plane of the paper, the Y-axis is directed parallel to the main surface 11, and the Z-axis is perpendicular to the main surface 11, as indicated in Fig. 1A, this capacity C is a measure for the Z-coordinate of this object. That capacity C can be considered to be a measuring signal provided by the sensor member 21; consequently, a variation dC in that measuring signal is representative of the variation dz in the Z-coordinate of that object. It will be understood by a skilled person that it is possible to measure this capacity C. For that purpose, the sensor member 21 is connected, by means of a wire that is not shown for simplicity's sake, to a data processor, which may for instance comprise a microprocessor. In the example discussed, the electrically conductive main surface 11 is also connected to that data processor. By way of example, the measuring of C could be based on the measuring of the oscillation frequency of an RCL-network wherein the capacity C is included. Because the manner in which that capacity C is measured does not form a part of the present invention, and knowledge thereof is not required for a proper understanding of the present invention, while, further, measuring methods can be used for that measurement that are known per se, this will not be further discussed. It suffices to observe that such measuring methods can be based on the measuring of a quantity which is considered to be representative of the capacity. Hence, whenever a measuring signal C is mentioned hereinbelow, this can also be the measuring quantity representative of the capacity, rather than the capacity itself.

The combination of the sensor member 21 and the main surface 11 of the reference device 10 can also be regarded as a transmitter/receiver combination. The measure of coupling between the sensor member 21 and the main surface 11 of the reference device 10 can then be determined by, for instance, supplying a transmitted signal to the reference device 10, and processing a received signal provided by the sensor member 21 in response thereto. Such a measuring method is known per se.

Within the framework of the present invention, the combination of the sensor member 21 and the main surface 11 of the reference device 10 will be regarded as a measuring member 2111 producing a measuring signal C which is representative of the measure of electric or electromagnetic coupling between the sensor member 21 and the main surface 11, to be referred to as reference member, of the reference device 10.

On the basis of the measuring signal C produced by the measuring member 2111, it is possible to calculate the distance d in absolute magnitude. This can generally be effected with a proper accuracy. However, it is also possible to provide an actuator capable of displacing the object in Z- direction, and to control that actuator by the above-mentioned data processor so that variations in the measuring signal C are opposed. An example of a suitable actuator that can readily be operated by this data processor and that can react promptly is a piezo element.

Tt is possible to carry out such a feedback so that the measuring signal C remains constant. It will be understood that this implies that in that case, the distance d remains constant. In this manner, it is possible to keep that distance d constant with an accuracy to the order of 1 nm. This particularly high accuracy (reproducibility) is realized with a sensor member 21 which itself does not have to meet extremely high manufacturing requirements. For instance, in principle, it is not necessary to accurately determine the size of the surface A of the sensor member 21: it is more important that the size of that surface does not change during a measurement.

Further, within the framework of the inventive concept, it is not necessary to render the main surface 11 and/or the surface of the sensor member 21 extremely smooth, for instance by polishing it. Roughness and/or unevennesses of one or both of these surfaces will only slightly contribute to variations of the measuring signal C, because the influence of the distance d on that measuring signal C is as it were averaged over the surface A. An example: if the main surface 11 has an unevenness of 0.1 mm x 0.1 mm with a height of 10 μm, while the surface A is 100 mm2, then that unevenness will be able to cause an "error" in d of (0.1 x O.D/100 x 10 μm, which is about 1 nm. As a matter of fact, such relatively great unevennesses will not occur in practice.

It is further observed that in principle, the form and the dimensions of the sensor member 21 are not important. A sensor member that has proved to be suitable has a rectangular contour with dimensions 1 cm x 1 cm, with the corners being rounded. In the example discussed, the sensor member 21 cooperates with a main surface 11 of the reference device 10. As mentioned, the Y-dimension of that main surface 11 is relatively great in comparison with the Y-dimension of the sensor member 21, so that during a Y- isplacement of the sensor member 21 relative to the reference device 10, the size of the overlapping surface A mentioned does not change (i.e., it is equal to the surface of the sensor member 21) and the measuring signal C remains constant. As a variant to this, the Y-dimension of that main surface 11 can, by contrast, be chosen to be relatively small in comparison with the Y- dimension of the sensor member 21. In that case, the size of the overlapping surface A is defined by the Y-dimension of the main surface 11 multiplied by the X-dimension of the sensor member 21, which does not change during a Y-displacement of the sensor member 21 relative to the reference device 10, so that in that case, the measuring signal C remains constant as well.

In a useful exemplary embodiment, the reference device 10 comprises a wire stretched between two points of attachment. A wire forms a good straightness reference whose direction is defined by the position of these points of attachment. Possible vibrations of the wire will hardly affect the measuring result, if at all, because they will be averaged by the time-integrating action of the measurement. Deflection of the wire can be regarded as a systematic error whose magnitude is known and for which corrections can be made.

In the example discussed, the sensor member 21 can be regarded as a capacitor plate, and the main surface 11 of the reference device 10 can be regarded as a second capacitor plate cooperating with the sensor member 21. However, the invention provides different variations to this concept. In a first variation, the sensor member 21 itself consists of a measuring capacitor having two capacitor parts 22 and 23, fixedly arranged relative to each other. An example of such a configuration is outlined in Fig. IB. The capacity C defined by these capacitor parts 22 and 23 is proportionate to a dielectric constant ε, which can be influenced through the provision of a dielectric in the proximity of the sensor member 21. The reference device 10 can be regarded as such a dielectric; variation of the distance d from that dielectric 10 to the two capacitor parts 22 and 23 thus brings about a measurable variation of the capacity C. An advantage of such an embodiment is that the reference device 10 can be an electric insulator. The reference device 10 can accordingly be manufactured from a technical ceramic, which has a particularly good form retention. A further advantage is that no electric connection has to be made to the reference device 10; more in particular, no electric signal connection has to be present between the reference device 10 and a data processor.

In a second variation, the sensor member 21 is an inductive element, whose induction is influenced by the proximity of the reference device 10 in a manner comparable to that discussed hereinabove.

Hereinabove, the principle is discussed by which it is possible to keep the distance from a sensor member 21 to the reference device 10 constant, which distance is calculated in the Z-direction, perpendicular to the main surface 11 of that reference device 10. However, for accurate displacement of an object in the X-direction, it is also necessary that the Y- coordinate be kept constant. Fig. 1C illustrates a possible manner of effecting this. The reference device 10 has a second main surface 12, and the support 20 supports a second sensor member 24 which is disposed opposite that second main surface 12. The second main surface 12 acts as second reference member, and the second sensor member 24 defines, in combination with that second main surface 12, a second measuring member 2412, which, in a manner comparable with the manner described in respect of the first measuring member

2111, is adapted to provide a measuring signal indicative of the distance from the second sensor member 24 to the second main surface 12 cooperating therewith, so in this case the distance in Y-direction to the reference device 10. The second sensor member 24 can be identical to the first sensor member 21, but this is not required. The reference device 10 is for instance formed as an elongated metal (or metallized) beam whose section provides the two main surfaces 11 and 12 which are substantially perpendicular relative to each other. Examples of such sections are an L-shape, a T-shape, etc. In the schematic example of Fig. IC, the reference device 10 is represented as a beam having a substantially rectangular section, with one body surface defining the first main surface 11, and another body surface defining the second main surface 12.

These two mutually substantially perpendicular main surfaces 11 and 12 intersect according to a real or virtual line 13, which in the example of Fig. IC is a longitudinal rib 13. It will be understood that if a displacement of the object is carried out in such a manner that the measuring signals generated by the sensor members 21 and 24 always remain constant, then that displacement will be parallel to that line (rib) 13, and that hence this line (rib) 13 in fact defines the X-direction. In general, a displacement apparatus will have an X-direction of its own; consequently, during installation of the reference device 10, this line (rib) 13 should be aligned as properly as possible with the X-direction of that displacement apparatus itself.

In this connection, it is observed that the high positional accuracy mentioned hereinabove is realized without high requirements being imposed on the form accuracy of the reference device 10. For instance, it is not required that the main surfaces 11 and 12 be exactly perpendicular to each other, although this is in fact preferred. Neither is it required that as far as dimensions are concerned, the reference device 10 be absolutely stable in the longer term; for realizing the objectives of the present invention, it is sufficient if the reference device 10, during the performance of a measurement, retains its shape, i.e. the mutual proportions of its dimensions remain constant: hence, the reference device 10 must for instance not warp.

As is already observed hereinabove, it is not required that the main surfaces 11 and 12 be absolutely plane and/or that the rib 13 be absolutely straight, because unevennesses are averaged by the dimensions of the sensor members 21 and 24, so that a proper accuracy is attained all the same. Even if this involves the occurrence of deviations relative to an ideal X-displacement, those deviations will, when the same path is traversed several times, remain substantially equal, which means that the displacement imposed is reproducible in a particularly accurate manner; this is already a significant advantage of the present invention. If so desired, it is possible to increase the absolute accuracy of the system through calibration. In this connection, it is a further advantage of the present invention that the coupling of a sensor member to a reference member is contactless, so that the reference device is not subject to wear.

Hereinabove, the principle is discussed of how the Z- coordinate of the object to be displaced can be kept constant at the location of the sensor member 21 by a single measuring member 2111, and how the Y-coordinate of the object to be displaced can be kept constant at the location of the sensor member 24 by a single measuring member 2412. However, in general this is not sufficient to guarantee that the orientation of the object is maintained: hence, it is also desired that a rotation of that object about the X-axis (φx) and/or about the Y-axis (φy) and/or about the Z-axis (φz) can be measured.

For detecting a rotation, it is possible to use two measuring members, which measuring principle will be explained with reference to Fig. ID.

Fig. ID is comparable with Fig. 1A, with the understanding that instead of a single sensor member 21, two sensor members 25 and 26 are provided on the support 20. These two sensor members 25 and 26 can be identical to the sensor member 21 already discussed. The centers of the two sensor members 25 and 26 lie on an imaginary line parallel to the Y- axis. The combination of the sensor member 25 with the reference member 11 (main surface 11 of the reference device 10) defines a measuring member 2511, and the combination of the sensor member 26 with the reference member 11 defines a measuring member 2611.

With reference to the above discussion, it will be understood that each measuring member 2511 and 2611 provides a measuring signal, to be indicated by C(2511) and C(2611) respectively, which is indicative of the distance from the relevant sensor member to that main surface 11. Further, it will be understood that the measuring signals C(2511) and C(2611) remain constant in a truly linear displacement of the support 20 in the X-direction and in the Y-direction.

In a truly linear displacement of the support 20 in the Z-direction, the distances from the sensor members 25 and 26 to the main surface 11 of the reference device 10 will change to an equal extent, as a result of which the measuring signals C(2511) and C(2611) will also change to an equal extent:

ΔC(25ll) = ΔC(26ll) . For completeness1 sake, it is observed that the measuring members 2511 and 2611 may have mutually different characteristics, so that the measuring signals generated as function of the distance to the reference member 11 may differ, but it will be understood that these characteristics will be known in advance and can be discounted by a data processor, for which reason this aspect will not be further discussed.

If the support 20 is rotated about an axis of rotation directed parallel to the X-axis, the distances from the sensor members 25 and 26 to the reference member 11 will change to a non-equal extent. If that axis of rotation passes between the sensor members 25 and 26, the changes in distance will even be of opposite directions. If the support 20 is rotated about an axis of rotation directed parallel to the Z-axis, the distances from the sensor members 25 and 26 to the reference member 11 will not change. If the support 20 is rotated about an axis of rotation directed parallel to the Y-axis, the distances from the sensor members 25 and 26 to the reference member 11 will change to an equal extent.

Thus, by comparing measuring signals from two measuring members, it is possible to recognize a component of rotational movement about the X-axis. It is also possible to compensate such movement, as will be described in more detail hereinbelow.

For the complete characterization of the displacement deviation of an object, at least five independent measuring members are required. In an embodiment, the support 20 according to the present invention comprises at least five sensor members 31, 32, 33, 41, 42, as schematically illustrated in Fig. 2. In this Figure, a support 20 having an L-shaped cross section, as is also shown in Fig. IC, is represented in perspective. The five sensor members 31, 32, 33, 41, 42 are divided into two groups: a first group 30 comprises three sensor members 31, 32, 33, provided on the inside of a first leg of the L-shaped support 20, for cooperation with the first reference member 11, similarly to the measuring member 21 of Fig. IC. In combination with the reference member 11, the sensor members 31, 32, 33 define a first group 3000 of measuring members 3111, 3211, 3311. A second group 40 comprises two sensor members 41, 42, provided on the inside of a second leg of the L-shaped support 20, for cooperation with the second reference member 12 (the second main surface 12 of the reference device 10) , similarly to the sensor member 24 of Fig. IC. In combination with the reference member 12, the sensor members 41, 42 define a second group 4000 of measuring members 4112, 4212. The positions of sensor members 31, 32, 33, 41, 42 are indicated in dotted lines in Fig. 2. The measuring members of the first group 3000 are adapted to measure a local displacement (at the location of the relevant sensor member) in the Z-direction, and the measuring members of the second group 4000 are adapted to measure a local displacement in the Y-direction. Although, in principle, the precise positions of the sensor members are not essential, as long as the three sensor members of the first group 30 lie on the angular points of a triangle, it will in the following explanation be assumed that the first group 30 comprises two sensor members 31 and 32 whose centers lie on an imaginary line parallel to the Y-axis, and two sensor members 31 and 32 whose centers lie on an imaginary line parallel to the X-axis, and that the second group 40 comprises two sensor members 41 and 42 whose centers lie on an imaginary line parallel to the X-axis.

A random displacement of the support 20 can be described as a sum of six different, mutually independent displacements, which are therefore called primary displacements: 1] a true translation in the X-direction (dx) 2] a true translation in the Y-direction (dy) 3] a true translation in the Z-direction (dz) 4] a true rotation about the X-axis (dφx) ; 5] a true rotation about the Y-axis (dφy) ; 6] a true rotation about the Z-axis (dφz) . Of these displacements, the first primary displacement is a desired displacement; the other five primary displacements define an undesired deviation from the desired displacement. Any random deviation can be described as a sum of the primary displacements [2] through [6] , and can be detected by the five measuring members 3111, 3211, 3311, 4112, 4212, as will hereinafter be separately demonstrated for the five primary displacements [2] through [6] mentioned. [2] In a true translation in the Y-direction, the capacity values C(3111), C(32ll) and C(3311) will remain constant, and the capacity values C(4112) and C(4212) will change to an equal extent.

[3] In a true translation in the Z-direction, the capacity values C(4112) and C(4212) will change to an equal extent (or remain equal) , and the capacity values C(3111) , C(3211) and C(3311) will change to an equal extent. [4] In a true rotation about the X-axis, the capacity values C(4112) and C(4212) will change to an equal extent (or remain equal), the capacity values C(3lll) and C(331l) will change to an equal extent (or remain equal) , and the capacity values C(3111) and C(3211) will change in a mutually opposite sense. The XZ-plane is chosen to be halfway the centers of the sensor members 31 and 32.

[5] In a true rotation about the Y-axis, the capacity values C(4112) and C(4212) will remain equal, the capacity values C(311l) and C(321l) will change to an equal extent (or remain equal), and the capacity values C(3111) and C(3311) will change in a mutually opposite sense. The YZ-plane is chosen to be halfway the centers of the sensor members 31 and 33. [6] In a true rotation about the Z-axis, the capacity values C(3111) , C(3211) and C(3311) will remain constant, and the capacity values C(4112) and C(4212) will change in a mutually opposite sense.

Within the framework of the inventive concept, it is possible to attach the five sensor members 31, 32, 33, 41, 42 individually to the object. It is also possible that a first group 30 of three sensor members 31-33 is provided as an integrated whole, that a second group 40 of two sensor members 41-42 is provided as an integrated whole, and that the two groups are separately attached to the object. As a variant to this, it is possible that for the second group 40 a second example is used of a group 30 of three sensor members, which group is manufactured as an integrated whole, while one of those three sensor members of the second group need not be used.

However, in accordance with the present invention, it is preferred that these five sensor members 31, 32, 33, 41, 42 be formed as an integrated whole on a support 20, because then the mutual relationship between the sensor members is a constant and priorly known datum. This offers an advantage in particular in the case where the combination of the support 20 with the sensor members 31, 32, 33, 41, 42, hereinafter referred to as sensor device 50, serves to improve already existing displacement equipment, or forms part of a mobile measuring system. In the exemplary embodiment outlined in Fig. 2 of a sensor device 50 consisting of the combination of the support 20 with the sensor members 31, 32, 33, 41, 42 provided thereon, both the sensor members 31-33 of the first group 30 and the sensor members 41-42 of the second group 40 are adapted to measure a displacement in a direction perpendicular to a main surface of those sensor members themselves. That is to say: the sensor members 31-33 of the first group 30 are arranged in a plane perpendicular to the Z-axis, and measure a displacement in the Z-direction, while the sensor members 41- 42 of the second group 40 are arranged in a plane perpendicular to the Y-axis and measure a displacement in the Y-direction. Fig. 4 illustrates a variant to that embodiment, wherein the sensor members 41-42 of the second group 40 have been replaced by sensor members 43 and 44 which, like the sensor members 31-33 of the first group 30, are arranged in a plane perpendicular to the Z-axis, but are adapted to measure a displacement in the Y-direction. An advantage of such an embodiment is that all sensor members 31, 32, 33, 43, 44 can be located in the same plane, as illustrated, as a result of which the sensor device 50 can as a whole have a substantially 2-dimensional structure and can be manufactured in a simpler manner. Further, this renders it possible that the reference device 10 has a substantially 2-dimensional structure and can be manufactured in a simpler manner, as will also be described with reference to Fig. 4.

Now, referring to Fig. 3, the measuring principle on which such measuring elements 43-44 are based will be explained first. Fig. 3 is a Figure comparable with Fig. 1A, wherein like parts are designated by like reference numerals. In this illustrative example, the reference device comprises a body 10 of a non-conductive material, which body is provided, on a main surface 11 thereof, with a layer 15 of a conductive material, which layer acts as reference member. The conductive layer 15 extends over a portion of that main surface 11; in the Figure, the right portion of the main surface 11 is not covered by the conductive layer 15. The conductive layer 15 has a side edge 16 which is directed in the X-direction and which defines the transition between the portions of the main surface 11 covered and not covered by the layer 15.

In the example to be discussed, the sensor member 43 comprises an electrically conductive plate surface, which, in combination with the conductive layer 15, defines a capacity whose magnitude, indicated as C(4315), is proportionate to the surface A of the overlap between the sensor member 43 and the conductive layer 15, indicated as A(4315) . If the sensor member 43 is displaced in the Y-direction, this surface (4315) changes and, consequently, the capacity C(4315) changes, which is measurable, similarly as discussed hereinabove. In this manner, the sensor member 43 in combination with the reference member 15 defines a measuring member 4315. It is observed that the reference device 10 can as a whole be electrically conductive, with the rib 13 (see Fig. IC) acting as the side edge 16 of the conductive layer 15.

Further, it is observed that the sensor member 21 discussed with reference to Fig. IB, too, can be used for an application as sensor member 43. In that case, the reference device 10 can as a whole be manufactured from a dielectric material, with the rib 13 again acting as the side edge 16 of the conductive layer 15 of the embodiment of Fig. 3. In principle, the sensor member 43 is also sensitive to a displacement in the Z-direction. After all, in a displacement in the Z-direction, the distance between the sensor member 43 and the conductive layer 15, indicated as d(4315) , will change, and the capacity C(4315) is inversely proportionate to that distance, as observed hereinabove. This implies that the measuring signal C(4315) provided by the measuring member 4315 cannot as such discriminate between a Z-displacement and a Y- displacement. It is however possible to reduce the Y- displacement from that measuring signal C(4315) provided by the measuring member 43, because from the measuring signals from the measuring members of the first group 3000, the Z- displacement at the location of the sensor member 43 can be calculated. For a greatest possible accuracy for such a calculation, it is preferred that at least one of the sensor members of the first group 30 be arranged at a shortest possible Y-distance from the sensor member 43. However, in accordance with the invention, it is possible in a relatively simple manner, through an adjustment of the reference device 10, to provide two measuring signals by means of one sensor member 43, one signal of which is indicative of the Z-displacement at the location of the sensor member 43 and the other signal of which is indicative of the Y-displacement at the location of the sensor member 43. For that purpose, a second conductive layer 17 can be provided on the first main surface 11 next to the conductive layer 15, as is also shown in Fig. 3, with an edge 18 slightly spaced from the edge 16 of the conductive layer 15. Accordingly, the sensor member 43 defines a capacity together with that second conductive layer 17, whose magnitude, indicated as C(4317) , is proportionate to the magnitude of the overlap between the sensor member 43 and that second conductive layer 17, indicated as A(4317) , and inversely proportiate to the distance between the sensor member 43 and the second conductive layer 17, indicated as d(4317) . If the sensor member 43 is displaced in the Y- direction, these overlapping surfaces A(4317) and A(4315) will change in mutually opposite sense, while the distances d(4317) and d(4315) will remain equal. On the other hand, if the sensor member 43 is displaced in the Z-direction, these overlapping surfaces A(4317) and A(4315) will remain equal, while the distances d(4317) and d(4315) will change to an equal extent. Thus, for instance the sum signal C(4317)+C(4315) is representative of the Z-displacement, and the quotient signal C(4317) /C(4315) (or for instance the combination of sum signal and difference signal) is representative of the Y-displacement. In this manner, the second conductive layer 17 acts as second reference member, while the sensor member 43 in combination with the first reference member 15 defines a measuring member 4315 and in combination with the second reference member 17 defines a measuring member 4317, which two reference members provide two measuring signals which in combination represent the Z- displacement and the Y- isplacement. In practice, the two measuring signals C(4315) and C(4317) can be provided to a data processor, and that data processor can calculate the sum and quotient signals therefrom.

In a variant outlined in Fig. 8, the sensor member 43 is separated into two sensor elements 43ι and 432. In combination with the two reference members 15 and 17, the two sensor elements 43i and 432 define measuring members 43χl5 and 43217 for providing measuring signals C(43χl5) and C(43217), whose meaning is comparable with the measuring signals C(4315) and C(4317) discussed hereinabove. In addition, in combination with the two reference members 15 and 17, the two sensor elements 43i and 432 define "crossed" measuring members 43χl7 and 43215 for providing measuring signals C(43χl7) and C(43215) . Through the processing of these measuring signals, a signal indicative of the Y-displacement can be obtained with great sensitivity, which signal is independent of the orientation of the support 20 relative to the reference device 10.

A further advantage of the structure of the reference device 10 outlined in Fig. 3 is that the reference line for the X-direction is no longer defined by the edge 16 only. The reference line for the X-direction is now defined as a fictitious line by the edges 16 and 18 together, and will be located halfway those edges 16 and 18. Hereinabove, it is already observed that any inaccuracies in the conductive layer 15 affect the measuring signal only to a slight degree, because such inaccuracies are averaged over the surface of the sensor member 43. Likewise, any inaccuracies in the edge 16 will affect the measuring signal only to a slight degree, because such inaccuracies are averaged over the X-dimension of the sensor member 43. Moreover, if these edges 16 and 18 are manufactured as each other's mirror image, wherein any inaccuracies will be present in both edges 16 and 18 as each other's mirror image, such inaccuracies will even substantially compensate each other. Thus, it is for instance not required that the edges 16 and 18 extend exactly parallel: the fictitious X-reference line will behave as bisector of the angle defined by the two edges 16 and 18. In this manner, by the structure of the reference device 10 outlined in Fig. 3, an improvement of the measuring accuracy of the measuring system is provided. A further contribution to the improvement of the measuring sensitivity, respectively a decrease of the sensitivity to inaccuracies in the geometry of the reference members is realized by choosing the X-dimension of a sensor member to be relatively large compared with the Y-dimension thereof.

A particularly simple manner for manufacturing a reliable reference member which is highly suitable for use in the present invention starts from a flat support made of epoxy resin, of which at least one main surface 11 is entirely covered with a conductive metal layer such as copper. An example of such a starting product is a blank for manufacturing printed circuit boards. From that metal layer, a narrow, elongated strip 19 is etched away, in a manner which is in fact known, to separate that metal layer into the layers 15 and 17. For this purpose, a mask is used, as is also known per se. In accordance with the present inventive concept, a mask for the edge 16 is copied, after which the copy is arranged in mirror image next to the original mask, for the edge 18. As a variant to this, in accordance with the present inventive concept, it is possible that a mask is first exposed for the edge 16, then arranged in mirror image and exposed again for the edge 18, or vice versa.

An important advantage of the use of printed circuit board is that it can be processed in a cheap manner, and that a portion of the electronic devices for the primary processing of the measuring signals can be mounted on the same printed circuit board.

The sensor members 31, 32, 33, 43, 44 can be formed by attaching plate-shaped elements to the support 20. However, on account of the simple manufacturing possibility, it is preferred to manufacture the sensor device 50 shown in Fig. 4 starting from a metallized support 27, such as, preferably, a blank for manufacturing printed circuit boards, of which the metallization layer is etched away according to a predetermined pattern so that the plate electrodes 31, 32, 33, 43, 44 (or, for instance, sensor members having the configuration outlined in Fig. IB) are left.

It will be understood that with the sensor device 50 illustrated in Fig. 4, it is possible to detect any random displacement thereof, similarly to the sensor device discussed with reference to Fig. 2, with the two sensor members 43 and 44 being used for detecting Y-displacements, and the three sensor members 31, 32, 33 being used for detecting Z- displacements. Hereinabove, however, it is explained that the two sensor members 43 and 44 used for detecting Y- displacements are also sensitive to Z-displacements, and that through the use of a second conductive layer 17 it is possible to cause each of those sensor members 43 and 44 to provide two measuring signals, from which a first signal (sum signal) can be derived which is representative of the Z-displacement and from which a second signal (quotient signal) can be derived which is representative of the Y-displacement. On the basis of this insight, it is possible to further simplify the sensor device 50 illustrated in Fig. 4, viz. to leave out two sensor members of the three sensor members 31, 32, 33. Then, too, it is possible to provide, by means of such a sensor device, three Z-signals and two Y-signals, viz. the Z-signal originating from the remaining sensor member of the three sensor members 31, 32, 33, the two first signals (sum signals) from the two measuring members 4315 and 4317 and from the two measuring members 4415 and 4417, and the two second signals (quotient signals) from the two measuring members 4315 and 4317 and from the two measuring members 4415 and 4417. This means that within the framework of the present inventive concept, a first group 3000 of at least three measuring members for providing measuring signals indicative of a Z- displacement on the one hand, and a second group 4000 of at least two measuring members for providing measuring signals indicative of a Y-displacement on the other, can have one or several measuring elements in common. This also appears from the following example.

With reference to Fig. 3, an example is discussed of a manner in which it is possible to generate, by means of one sensor member 43, two measuring signals that are representative of Z-displacement and Y-displacement respectively. According to the concept illustrated in that Figure, the reference device 10 has for that purpose two guiding portions which can separately cooperate with the sensor member 43 so as to define two measuring members. The reverse is also possible, as illustrated in Fig. 9. In the example schematically illustrated in that Figure, two sensor members 43' and 43" are mounted in juxtaposition on the support, and provided on the reference device 10 is a conductive path 14 acting as reference member. The two sensor members 43' and 43" cooperate with that single reference member 14 to define a measuring member 43'14 and a measuring member 43"14 respectively, with the measuring member 43'14 providing a measuring signal C(43'14) which is proportionate to the overlap A(43'14) and inversely proportionate to the distance d(43'14). The same applies, mutatis mutandis, to the measuring member 43"14. In a similar manner as discussed hereinabove in respect of the measuring members 4315 and 4317, from the two measuring signals C(43'14) and C(43"14) two measuring signals can be derived representative of Z- displacement and Y-displacement respectively.

Fig. 9 further illustrates that the sensor members 43' and 43" need not have an actual overlap with the conductive path 14. In the case represented, the conductive path 14 has a Y-dimension which is smaller than the Y-distance between the sensor members 43' and 43". It will be understood by a skilled person that, although the formula which then describes the capacity value defined between a sensor member and the conductive path has become more complicated, there will nevertheless be a Y-dependent signal and a Z-dependent signal. In that respect, the actual dependence is not even very important: it can readily be understood that a feedback which undoes variations in the signals mentioned, always has the effect that positional variations are undone.

In accordance with a further elaboration of this concept, the conductive path 14 can also be provided in the form of a conductive wire attached between two suspension points. The application of this concept to the embodiment illustrated in Fig. 4 implies that the support 10 with the two conductive paths 15 and 17 can be replaced by two conductive wires suspended side by side.

Referring to Fig. 5, a linear displacement apparatus 100 will presently be discussed, wherein the measuring system illustrated in Fig. 4 is used.

The displacement apparatus 100 generally comprises a frame 101 fixed relative to the environment 102. Mounted on the frame 101 is a guiding member 105, over which guiding member a slide or carriage 103 is displaceable. The guiding member 105 can be an integrated part of the frame 101. Between the guiding member 105 and the slide or carriage 103 bearing members 104 are included. An example of a suitable guiding member 105 is a rail of a suitably selected profile. In a simple embodiment, the bearing members 104 can for instance comprise a slide bearing or roller bearing. In Fig. 5, the displacement direction of the slide or carriage 103 is directed perpendicularly to the plane of the paper, and is indicated as X-direction of the displacement apparatus 100. Displacement of the slide or carriage 103 along the guiding member 105 can be effected by elements known per se, such as for instance by means of a motor-driven screw spindle. Because the elements for effecting this displacement of the slide or carriage 103 do not constitute a subject of the present invention, and a skilled person need not have knowledge thereof for a proper understanding of the present invention, they will not be further described and are not shown in Fig. 5, for the sake of simplicity. For the same reason, the nature and construction of the guiding member 105 and of the bearing members 104 will not be further discussed. It suffices to observe that for this, guiding members and bearing members known per se can be used, and that owing to the favorable properties of the invention presently proposed, they do not have to meet requirements of extreme accuracy and can therefore be relatively cheap. Coupled to the slide or carriage 103 is a table 106 with the interposition of actuators 107. in a suitable embodiment, five actuators 107 are present, which will be individually indicated as I07ι, 107 , 1073, 107 , 1075. The table 106 comprises fastening means, not shown for the sake of simplicity, for fastening on the table 106 an object V to be dispaced. It will be understood that this fastened object v can then be displaced by displacing the table 106. The actuators 107 provide a rigid coupling between the table 106 and the slide or carriage 103, so that the table 106 accurately follows the displacement of the slide or carriage 103. In addition, through the control of the actuator 107, it is possible to set the position of the table 106 relative to the slide or carriage 103.

The actuators 107 can for instance be piezo-electric actuators known per se. Such actuators offer the advantage that they can readily be operated by supplying an electric control voltage, with a length dimension of the actuator changing in response to the changing of the control voltage, as is known per se. The construction of the actuators 107 does not constitute a subject of the present invention either, and will hence not be further described. It is sufficient to note that five actuators are present, positioned so (kinematic support) that they can cause the table 106 to perform any random displacement relative to the slide or carriage 103, which displacement is in a plane perpendicular to the X-axis. In X-direction, a coupling is present between the table 106 and the slide or carriage 103, which coupling allows such displacement. For this purpose, a sixth actuator can for instance be used. In other words: it is possible to vary the position of the table 106 relative to the slide or carriage 103 in Y-direction and in Z-direction, to be indicated as variations Δy and Δz, and to vary the orientation of the table 106 relative to the slide or carriage 103 in a rotational direction about the X-axis, the Y-axis and the Z-axis, to be indicated as variations Δφx, Δφy, and Δφz. It will be understood that the extent to which the position of the table 106 can be changed, i.e. the maximum magnitude of these variations, is determined by the range of the actuators 107 coupled between the table 106 and the slide or carriage 103.

The reference device 10 mentioned is fixedly arranged relative to the environment 102 in such a manner that the X- direction defined by the reference device 10 is substantially aligned with the X-direction defined by the guiding member 105; if the frame 101 is sufficiently rigid, the reference device 10 can be mounted thereon, as illustrated. If the displacement apparatus 100 is used for displacing the object V along a processing station or a survey station such as, for instance, a microscope, the reference device 10 can be fixed relative to such station.

The sensor device 50 is fixedly mounted on the table 106 so that the sensor device 50 is located at a short distance from the reference device 10. A distance that was found suitable during experiments lies in the range of 0.3 mm. Further, the sensor device 50 is located as closely as possible to the object V. Alternatively, the sensor device 50 can be fixedly mounted on the slide or carriage 103, but this has as a drawback that a possible displacement of the table 106 relative to the slide or carriage 103, or a displacement of the table 106 caused by a change of form (thermal expansion) of the slide or carriage 103, is not detected, so that, in view of the intended accuracy into the range of 1 nm in respect of the object to the fastened on the table 106, such a construction is not preferred. As described hereinabove, the table 106 with the object V fastened thereon can be displaced in the X-direction defined by the guiding member 105. However, it may occur that this displacement is not an exactly linear displacement, but exhibits deviations, for instance because of imperfections in the guiding member 105, as a consequence of which the position of the table 106 exhibits variations that can be indicated as dy, dz, dφx, dφy, dφz. As described hereinabove, the combination of the sensor device 50 and the reference device 10 provides five measuring signals which provide information about such positional variations. In this manner, it is possible that the combination of the sensor device 50 and the reference device 10 is used for calibrating an existing displacement apparatus. This will be explained with reference to Fig. 6, wherein these five measuring signals from the five measuring members will be indicated as Cj., C2, C3, C , and C5 respectively. These measuring signals are inputted into a data processor 200, which for instance comprises a microcomputer, calculating from these measuring signals the signal variations dCi, dC2, dC3, dC , dC5 relative to an initial value, which variations are jointly representative of the occurring positional variations dy, dz, dφj, dφy, dφz. From the calculated signal variations dCi, dC2, dC3, dC4, C5, the data processor 200 calculates the occurring positional variations dy, dz, dφx, dφy, dφz and reproduces them as a function of the location x in any desired manner, for instance in graphic form or in the form of a table, enabling the user of that displacement apparatus to carry out corrections for the observed imperfections of the guiding members 105. It will be understood that the data processor 200 may skip the intermediate step of calculating the signal variations dCi, dC2, dC3, dC4, dC5 and calculate the positional variations dy, dz, dφx, dφy, dφz directly from the measuring signals. It is also possible that the combination of the sensor device 50 and the reference device 10 is used for testing an existing displacement apparatus.

In this connection, it is observed that no stringent requirements are imposed on the attachment of the sensor device 50, only that this attachment be sufficiently rigid. The precise position of the sensor device 50 is not important: it is important that this position is maintained during the measurement. It is further observed that for such a calibration, it is not required that the X-direction of the reference device 10 be exactly aligned with the X-direction of the displacement apparatus to be examined: a possible misalignment will only result in a systematic y-deviation and/or z-deviation, and can be recognized and eliminated as such by the data processor 200.

In the displacement apparatus 100 illustrated in Fig. 5, it is possible to correct a random combination of the positional variations dy, dz, dφx, dφy, dφz by means of the actuators 107 in such a manner that these deviations dy, dz, dφx, dφy, dφz are reduced to zero. This is equivalent to reducing the deviations dCi, dC2, dC3, dC4, C5 in the measuring signals or capacity values to zero. As illustrated in Fig. 7, a control member 210 is provided for that purpose, which control member for instance comprises a microprocessor and is provided with signal inputs 211, 212, 213, 214, 215, 216 coupled to the sensor members 31, 32, 33, 43, 44 and to the reference device 10 respectively for receiving the measuring signals Cj., C2, C3, C , C5, and with control outputs 221, 222, 223, 224, 225 coupled to the actuators 107 l f 1072,

1073, 1074, 1075 respectively. In this connection, it is noted that the control member 210 in general comprises a measuring section which generates the measuring signals, and a driver section which generates the control signals required for driving the actuators. The control member 210 is adapted to set the control signals ai at the control outputs for the respective actuators 107i so that variations dCi, dC2, dC3, dC , dC5 of the measuring signals Cj., C2, C3, C , C5, or deviations in the capacity values, are substantially reduced to zero. This will be referred to by the term "feedback". A possible manner of establishing this is the dynamic determination of the required control signals ai via a closed loop method. These control signals ai are always chosen so that measured measuring signals Ci, C2, C3, C , C5 always remain equal to initial values Cι(0), C2(0), 03(0), C (0), 05(0). In this connection, it is preferred that the actuators 107 be arranged according to a pattern which corresponds to the pattern of the sensor members 31, 32, 33, 43, 44. After all, in consequence thereof, there will be a substantial correlation between in each case one measuring signal and one associated actuator. In the case of deviations from this pattern correspondence, this one-to-one correlation decreases, which can be referred to as the correction characteristic of the linear displacement apparatus 100. Here, mutual differences between the measuring members, for instance with regard to plate surface or electrode distance, also play a part. However, this always concerns apparatus constants, i.e. for a specific example of the linear displacement apparatus 100 the correlation factors can be constant and stored in a memory 230 associated with the control member 210.

In practice, it may occur that the reference device 10 is not ideal, or not ideally mounted. Possible deviations of the reference device 10 itself are, for instance: the referentie line 16 is not entirely straight throughout the range. - the surface 11 is not entirely plane throughout the range; Possible deviations of the mounting of the reference device 10 are, for instance: the reference line 16 or the edge 13 is not mounted so as to be exactly parallel to the guiding means 105.

In itself, the latter case is not such a great problem: a consequence will only be that the displacement of the object V takes place according to the actual direction of the reference line and not according to the direction determined by the guiding means 105; in principle, however, the displacement is indeed linear. The former cases have as a consequence, that a deviation is introduced into the linearity of the displacement: after all, this linearity cannot be better than the linearity of the reference. A possibility of improving the linearity of the displacement is to calibrate the system and to carry out corrections for the deviations found. In fact, what it comes down to is that during the displacement in the X-direction, the control signals ai are in always chosen so that a measured measuring signal Ci always satisfies Ci = Cι(0) + Ci (x) , for i = 1-5, wherein Cj (x) is a correction value which is dependent on the X-position and determined by calibration, and which has to correct for errors of form of the reference. These correction values can be stored in the memory 230.

It will be understood by a skilled person that it is possible to change or modify the embodiment shown of the apparatus according to the invention without departing from the inventive concept or the protective scope as described in the claims. In the embodiments described hereinabove, the three sensor members 31, 32, 33 of the first group 30 define a right-angled triangle whose legs are oriented according to the X-axis and the Y-axis. However, this is not required: in principle, it is sufficient when the three sensor members 31, 32, 33 are arbitrarily arranged according to the angular points of a triangle, as long as they are not in alignment. For a great measuring accuracy, however, it is preferred that the mutual distance of those three sensor members be chosen to be as large as possible. Further, for reasons of symmetry, it is preferred that at least one pair of those three sensor members 31, 32, 33 be aligned with the X-axis or the Y-axis. The third sensor member can then be symmetrically arranged relative tc . ,is pair to define an isosceles or even equilateral triangle. In Fig. 4, this is illustrated by the position 32' for the sensor member 32.

In the embodiments described hereinabove, the three sensor members 31, 32, 33 cooperate with the same conductive layer 15. However, this is not required. It is for instance possible that the sensor member 32 cooperates with the second conductive layer 17, and is for that purpose for instance disposed at the position 32" in Fig. 4. Because of the larger distance to the base line as defined by the two sensor members 31, 33, an increased measuring accuracy is realized. It is also possible that for each of the three sensor members 31, 32, 33, a separate conductive path is provided, substantially extending in the X-direction, to guarantee that the three measuring signals provided by these sensor members 31, 32, 33 do not influence one another. The same applies to the two sensor members 43 and 44.

Further, it is possible that the number of sensor members is greater than five.

It is also possible that the positions of the reference device and the sensor device are exchanged.

It is further possible that the three sensor members of the first group are adapted to detect a deviation in the Y- direction and that the two sensor members of the second group are adapted to detect a deviation in the Z-direction. Further, it is possible that the discussed metal or at least conductive surfaces of the sensor members and/or of the reference device are provided with an insulating covering layer.

Further, with reference to Fig. 10, it is possible that a sensor member is formed by a conductive layer 60 provided on the support 20, over which layer 60 a conductive masking member or masking layer 61 is provided, which masking member or masking layer 61 does not contact the conductive layer, for instance because an insulating layer is located therebetween. Provided in that masking member or masking layer 61 are five window-like recesses 62, 63, and for each recess a reference member 64, 65 extending in the X-direction is present, for instance in the form of a conductive path on the support 10. The communication of the conductive layer 60 provided on the support 20 with the reference device 10 takes place through the respective openings 62, 63 in that masking member or masking layer 61, and the extent of coupling between the conductive layer 60 provided on the support 20 and the reference device 10 depends on the alignment of the recesses 62, 63 with the reference paths, as will be understood. The recesses can have the same shape and are provided according to the same pattern as the sensor members described hereinabove. For the reference device 10, an existing reference for a linear displacement transducer, such as for instance an optical ruler, can be used advantageously.

It is observed that the present invention can also be efficiently used in those situations wherein it is desired to fix an object V in six degrees of freedom.

It is further observed that it is not required that the different sensor members have mutually equal configurations and dimensions.

Claims

C A I M S
1. A measuring system for detecting a positional variation of an object (V) , comprising: a reference device (10) defining an X-direction and comprising at least one reference member (11, 12) ; a sensor device (50) comprising at least one sensor member (31, 32, 33, 41, 42); wherein a combination of a sensor member (for instance 31) and a reference member (for instance 11) defines, through electric and/or electromagnetic coupling, a measuring member (for instance 3111) , wherein the number of thus defined measuring members is at least equal to five; wherein a first group (3000) of at least three measuring members (3111, 3211, 3311) is adapted to provide measuring signals indicative of a positional variation in a Z-direction relative to the reference device (10) , and wherein a second group (4000) of at least two measuring members (4112, 4212) is adapted to provide measuring signals indicative of a positional variation in a Y-direction relative to the reference device (10) .
2. A measuring system according to claim l, wherein a measuring member comprises a capacitive element of a capacity value which is influenced by the distance from the measuring member to the reference device (10) .
3. A measuring system according to claim 1, wherein a measuring member comprises an inductive element of an inductance which is influenced by the distance from the measuring member to the reference device (10) .
4. A measuring system according to claim 1, wherein a measuring member (2111) comprises a plate electrode (21) which, in cooperation with a conductive surface (11) of the reference device (10) , defines a capacitive element of which a capacity value depends on the distance (d) from said plate electrode to said conductive surface of the reference device.
5. A measuring system according to claim 1, wherein a measuring member (4315; 4317) comprises a plate electrode (43) which, in cooperation with a conductive surface (15; 17) of the reference device (10) , defines a capacitive element of which a capacity value depends on the overlap (A) of said plate electrode with said conductive surface of the reference device.
6. A measuring system according to claim 1, wherein the reference device (10) is formed by an elongated beam with an electrically conductive outer surface, with a first main surface (11) and a second main surface (12) which intersect in a longitudinal rib (13) defining the X-direction of the reference device (10) ; wherein the sensor device (50) has a substantially L-shaped cross section, wherein at least three sensor members (31, 32, 33) are mounted on a first leg of said support (20) for cooperation with the first main surface (11) of the reference device (10), and wherein at least two sensor members (41, 42; 43, 44) are mounted on a second leg of said support (20) for cooperation with the second main surface (12) of the reference device (10) .
7. A measuring system according to claim 1, wherein the reference device (10) comprises an electrically conductive plate surface (15) , of which a side edge (16) defines the X- direction of the reference device (10) ; and wherein the sensor device (50) comprises a substantially plane support (20), wherein at least three sensor members (31, 32, 33) are mounted on said support for cooperation with a central portion of said electrically conductive plate surface (15) and wherein at least two sensor members (41, 42; 43, 44) are mounted on said support for cooperation with said side edge (16) of said electrically conductive plate surface (15) .
8. A measuring system according to claim 7, wherein the reference device (10) is manufactured entirely from a conductive material, such as a metal.
9. A measuring system according to claim 7, wherein the reference device (10) comprises a non-conductive support having a surface provided with a conductive covering layer, and wherein said side edge of said electrically conductive plate surface substantially coincides with a side edge of the reference device itself.
10. A measuring system according to claim 7, wherein the reference device comprises a non-conductive support having a surface provided with a conductive covering layer, and wherein a portion is removed from said covering layer to define said side edge (16) of said electrically conductive plate surface (15) .
11. A measuring system according to claim 7, wherein the reference device comprises a non-conductive support having a surface provided with a conductive covering layer, and wherein an elongated strip (19) is removed from said covering layer for defining two mutually separate, electrically conductive plate surfaces (15) and (17).
12. A measuring system according to claim 11, wherein the at least two sensor members (43, 44) can also cooperate with the second electrically conductive plate surface (17), so that the X-direction of the reference device (10) is defined by two side edges (16, 18) of said two electrically conductive plate surfaces (15, 17) in combination.
13. A measuring system according to any one of claims 9-12, wherein the reference device is manufactured from printed circuit board or from ceramic material according to thick film-technology.
14. A measuring system according to any one of claims 6-13, wherein the at least three sensor members (31, 32, 33) are located on angular points of a triangle.
15. A measuring system according to claim 1 , wherein one side (31-33) of said triangle is directed in the X-direction.
16. A measuring system according to claim 14 or 15, wherein one side (31-32) of said triangle is directed in the Y-direction.
17. A measuring system according to any one of claims 14-16, wherein said triangle is an isosceles or equilateral triangle.
18. A measuring system according to any one of claims 6-17, wherein the sensor device (50) is manufactured from printed circuit board.
19. A sensor device (50) for use in a measuring system according to any one of the preceding claims, comprising a substantially plane support (20) supporting a first group (30) of at least three sensor members (31, 32, 33) and a second group (40) of at least two sensor members (43, 44), wherein the at least three sensor members (31, 32, 33) of the first group (30) are located on angular points of a triangle.
20. A sensor member according to claim 19, wherein the sensor members are plane plate electrodes.
21. A sensor member according to claim 19 or 20, wherein the sensor device is manufactured from a non-conductive support having a metallized surface, preferably a printed circuit board, wherein parts are removed from that metallized surface, for instance through etching, so that the structures of the sensor members are left.
22. Use of a measuring system according to any one of claims 1-18, for calibrating a displacement apparatus, wherein measuring signals originating from the measuring members (3115, 3215, 3315, 4315, 4317, 4415, 4417) are inputted into a data processor (200) which for instance comprises a micro¬ computer, and which calculates from said measuring signals the occurring positional variations dy, dz, dφx, dφy, dφz and reproduces them as function of the location x in any desired manner, for instance in graphic form or in the form of a table, for instance on a display screen or on paper, or stores them in a memory.
23. A displacement apparatus (100), comprising: a guiding member (105) ; a slide or carriage (103) displaceable over the guiding member (105) ; a table (106) coupled to the slide or carriage (103) with the interposition of actuators (I07ι, 1072, 1073, 1074, 1075) , said actuators (107ι, 1072, 1073, 1074, 1075) being adapted to retain or set the position of the table (106) relative to the slide or carriage (103) controlled by a control member (210) , which for instance comprises a microprocessor; a measuring system according to any one of claims 1-18; wherein the control member (210) is provided with signal inputs (211, 212, 213, 214, 215) for receiving the measuring signals (Ci) originating from the measuring members; wherein the control member (210) is provided with control outputs (221, 222, 223, 224, 225) coupled to said actuators (107ι, 1072, 1073, 1074, 1075) respectively; and wherein the control member (210) is adapted to set control signals (ai) for the respective actuators (107i) so that variations (dCi) of said measuring signals (Ci) relative to a predetermined target value (Ci(0); Ci(0) + Ci(x) ) are substantially reduced to zero.
PCT/NL1996/000240 1995-06-13 1996-06-13 Displacement sensor WO1996041999A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
NL1000559 1995-06-13
NL1000559A NL1000559C2 (en) 1995-06-13 1995-06-13 Displacement Sensor.

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AU60180/96A AU6018096A (en) 1995-06-13 1996-06-13 Displacement sensor

Publications (1)

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WO1996041999A1 true WO1996041999A1 (en) 1996-12-27

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AU (1) AU6018096A (en)
NL (1) NL1000559C2 (en)
WO (1) WO1996041999A1 (en)

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EP2124014A1 (en) * 2008-05-23 2009-11-25 Postech Academy-Industry Foundation Capacitive displacement sensor having a mechanical guide

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2124014A1 (en) * 2008-05-23 2009-11-25 Postech Academy-Industry Foundation Capacitive displacement sensor having a mechanical guide
US8242791B2 (en) 2008-05-23 2012-08-14 Postech Academy-Industry Foundation Area-variable type capacitive displacement sensor having mechanical guide

Also Published As

Publication number Publication date
AU6018096A (en) 1997-01-09
NL1000559C2 (en) 1996-12-13

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