DE102005055045A1 - Displacement sensor with temperature compensation, e.g. for coordinate measurement, has additional reference measuring surfaces, thermally coupled to main measuring surfaces, and evaluation circuit deriving compensated displacement signal - Google Patents

Abstract

The sensor is constructed with inductive elements formed on a PCB (10), their actual inductance depending on the position of two metallic plates (44, 46) that are rigidly connected with one another. Movement of the plates alters the inductance of a conductive track (12), but scarcely affects that of an additional track (28) which is perpendicular to the first. Since the inductance of the additional track is however, affected similarly by temperature, this may be used to provide a compensation for such ambient changes.

Description

The The invention relates to a position sensor according to the generic term of claim 1.

Similar position sensors are z. B. in the form of differential transformers, in which an electrically conductive coil with respect to a core movable is.

occasionally become such Wegfühler used in conditions in which the temperature changes greatly. Around corresponding distortions of the measurement result concerns, can you get the way sensor thermally couple with a temperature sensor, the z. B. may be a thermistor, and the output of the position sensor below Using a addressed by the output of the thermistor Correct the correction table.

These However, the nature of the procedure in many cases does not allow a satisfactory one Compensation of temperature drifts, as the displacement sensor and thermistor differ interact physically with the environment. So z. B. temperature-related at a Wegfühler dimensional changes play an important role while the temperature measurement of the thermistor because of its small size without appreciable dimensional changes he follows.

By the present invention is a Wegfühler according to the preamble of claim 1 be further developed so that a good temperature Compensation of the path signal is obtained.

These The object is achieved by a way sensor with the features specified in claim 1.

at the Wegfühler invention has one in addition to the actual Wegmeßflächen whose overlap is measured, additional Reference measuring surfaces, constructed similarly are like the measuring surfaces and in which temperature effects are thus largely similar as in the measuring surfaces themselves.

Of the the only difference between the displacement measuring surfaces and the reference measuring surfaces is ideally in that the Reference measuring surfaces not are movable against each other, or, more generally speaking, that with the reference paths connected reference signal generator no path dependence of its output signal shows.

The latter let yourself not just to ensure that he excludes a relative movement between the Referenzmeßflächen, but also by the fact that one the geometric position of Referenzmeßflächen against each other so chooses that on the interaction between the Referenzmeßflächen a Relative movement between these two surfaces no or only one has very little influence.

The Interaction between the Wegmeßflächen and the Referenzmeßflächen, the ultimately used to overlap these surfaces in To convert an electrical signal can be an inductive, a capacitive or some other interaction, such as B. the absorption of light or the reflection of light (in partially translucent Wegmeßflächen and Reference measuring surfaces or at absorbing or reflective Wegmeßflächen and Referenzmeßflächen).

advantageous Further developments of the invention are specified in subclaims.

The Further development of the invention as claimed 2 has the advantage that the temperature-related changes in the output of the cooperating with the Referenzmeßflächen reference signal generator no longer reflect any other disturbing influences.

With the development of the invention according to claim 3 is achieved that the Overall arrangement of Wegmeßflächen and Reference measuring surfaces especially compact builds.

there is according to claim 4 ensures that the interaction the Referenzmeßfläche with their formed by the second Wegmeßfläche Against reference reference surface not travel-dependent is.

Also The development of the invention according to claim 5 is in view on compact dimensions of the position sensor advantageous.

used one the Wegmeßflächen and the Referenzmeßflächen according to claim 6 as frequency-determining elements of an oscillator, it can be the distance measurement in a particularly simple way digitally by frequency measurement transact.

For some applications, it is desirable that the size of the position sensor is not appreciably increased by the Referenzmeßflächen. Thus, one chooses the dimensions of the reference measuring surfaces in one of their directions of extension (usually the dimension parallel to the direction of the relative movement between the Wegmeßflächen) significantly smaller than the corresponding dimensions of the Wegmeßflächen. With unchanged specification of the other frequency-determining element of the LC circuit results from the reduction of the dimension of the Referenzmeßfläche an increase in the oscillation frequency of LC circuit. This frequency increase can be compensated according to claim 7 by frequency division of the output signal of the reference signal generator, so that the LC resonant circuits formed with the participation of Wegmeßflächen or Referenzmeßflächen result in the result signals of the same frequency.

According to claim 9, the frequency differences between the two oscillating circuits, which is a measure of the shift the Wegmeßflächen against each other are from the vibration frequencies of the displacement LC circuit and the reference LC circuit determine.

This let yourself according to claim 10 particularly easy to accomplish, since the low-frequency Sideband of the mixing frequency is used for their frequency measurement simple and inexpensive frequency meter is sufficient.

The Development of the invention according to claim 11 allows easy calculation of corrected path signals.

One position sensors according to claim 12 has the advantage that itself Location disorders the first path measuring surface in direction perpendicular to the direction of motion is not strong on the measurement result impact.

below The invention will be described with reference to embodiments with reference explained in detail on the drawing. In show this:

1 a perspective view of a Wegmeßleiterbahn supported by a printed circuit board and a reference Meßleiterbahn perpendicular thereto and of two metallic Wegmeßplatten, which are arranged on both sides of the Wegmeß interconnect and the reference Meßleiterbahn;

2 a block diagram of a measuring circuit, which together with a conductor arrangement according to 1 forms a path sensor;

3 the transmission behavior of a low-pass filter of the measuring circuit after 3 ; and

4 a side view of a modified arrangement of Wegmeßflächen and Referenzmeßflächen. which instead of the track arrangement after 1 in the way sensor after 2 is usable.

In figure is with 10 denotes a printed circuit board, which is arranged in the xy plane of a coordinate system x, y, z. The circuit board 10 carries on its top a Wegmeß conductor track 12 which has substantially the shape of a rectangular frame with the same frame width.

The conductor track 12 comprises two parallel to the x-axis extending conductor track sections 14 . 16 , a conductor track section parallel to the y-axis 18 who the in 1 right-hand ends of the conductor track sections 14 and 16 connects, as well as two short trace sections 20 . 22 that of the in 1 left-hand ends of the conductor track sections 14 . 16 run back in the direction of the x-axis and with further short to the x-axis parallel track sections 24 . 26 are connected.

The conductor track sections 14 to 26 thus forming a flat coil having a turn, at the free ends of the conductor track sections 24 . 26 will be contacted.

The circuit board 10 also carries a trace 28 , which lies in the xz-plane and parallel to the x-axis extending conductor track sections 30 . 32 , a conductor track section which connects to the z-axis and has its right ends connected 34 , from the left ends of the track sections 30 . 32 to the x-axis returning trace sections 36 . 38 and again to the x-axis parallel track sections 40 . 42 having. The latter serve again contacting the coil having a turn.

The geometry of the conductor track 28 is thus similar to that of the track 12 , only the conductor track plane is tilted by 90 °, the width of the conductor track sections is smaller, and the extension of the conductor track 28 in the z-direction is significantly smaller than the extension of the conductor in the y-direction.

Preferably, the ratio between the y-extension of the conductor track corresponds 10 and the z-extension of the conductor track 28 an integer number 2 ²ⁿ (n = 0, 1, 2, ...) such that resonant circuits passing through the track 12 and 28 and equal capacitors are formed, have natural oscillations which are in the ratio of integers 2 ⁿ (n = 0, 1, 2, 3).

Symmetric to the conductor track arrangement described above and symmetrical to the xy plane of FIG 1 are two electrically conductive position measuring plates 44 . 46 intended.

By one only schematically by an arrow 48 indicated guide device ensures that a relative movement between the two measuring plates 44 . 46 and the circuit board 10 in the x direction is enabled.

The arrangement is made in detail so that the Leiteberbahn 12 exactly between the distance measuring plates 44 . 46 lies.

For the purpose of explanation, let it be Taken that the two Wegmeßplatten 44 . 46 are rigidly interconnected, as by a dashed line 47 indicated, and are movable in the x direction, while the circuit board 10 and the tracks she carries 12 . 28 are provided fixed space.

If you move the distance measuring plates 44 . 46 from the in 1 show position in which they the trace 12 fully overlap, then the inductance L12 of the conductor track 12 increasingly smaller. The inductance of the conductor track 28 On the other hand, it is practically unaffected since this trace is perpendicular to the measuring plates 44 . 46 stands.

The conductor track 28 but is otherwise subject to the same environmental conditions as the track 12 , Their inductance changes according to the ambient temperature.

This can be using the inductor L28 of the conductor 28 the temperature-related component in the change in the inductance of the conductor track 12 determine, and by subtracting this temperature-related portion of the inductance of the conductor 12 of the total inductance can be a temperature-compensated inductance of the conductor 12 determine which is an accurate measure of the relative motion between the circuit board 10 and the distance measuring plates 44 . 46 is.

How this can be done in detail, is now based on 2 described.

There are the tracks 12 and 28 shown as inductors L12 and L28.

The through the conductor track 12 formed inductance L12 is as frquezbestimmendes element to an oscillator 50 connected, whose output with the one input of a mixing circuit 52 connected is. This can be formed for example by an AND gate or by an OR gate.

The through the conductor track 28 Inductance L28 formed as a frequency-determining element to an oscillator 54 whose output is when the trace 28 same geoetry has as the track 12 , directly to the second input of the mixing circuit 52 connected is.

The oscillators 50 . 54 can contain as other frequency-determining elements in the individual capacitors, not shown, each forming an LC circuit together with the inductance L12 and L28. A likewise in the oscillator 50 respectively. 54 contained feedback amplifier ensures that the entire arrangements oscillate in natural frequency.

In the event that the conductor track 28 significantly smaller than the track 12 and that the oscillator 54 same structure as the oscillator 50 (which also includes a same capacitor to complete an LC circuit) is between the output of the oscillator 54 and the second input of the mixing circuit 52 a frequency divider 56 inserted, the dividing ratio is set so that by the reduction of the conductor 28 obtained increase in the natural frequency of the conductor track 28 formed LC circuit is just compensated.

In one end position of Wegmeßplatten 44 . 46 , in the 1 is shown, are thus both inputs of the mixing circuit 52 acted upon by signals of the same frequency, so that one from the output of the mixing circuit 52 receives a signal with twice the frequency and a signal with a frequency near zero.

At the exit of the mixing circuit 52 is a low pass 58 connected, whose cutoff frequency is about 600 kHz. This low-pass filter thus allows the low-frequency sideband of the mixed signal to pass, which at completely from the conductor track 12 weggefahrenen odometer plates 44 . 46 a signal at about 50 kHz, while at full overlap of Wegmeßplatten 44 . 46 and trace 12 receives a signal of about 550 kHz.

The whole circuit design is such that the cut-off frequency of the low-pass filter is approximately one-hundredth of the natural oscillation of the LC circuit, its inductance through the track 12 is formed.

The output signal of the low-pass filter 58 is via an amplifier 60 amplified with a high amplification factor, at whose output one thus contains a square wave whose frequency of the difference between the oscillation frequency of the measuring oscillator 50 and the oscillation frequency of the reference oscillator 54 equivalent.

The output signal of the amplifier 60 one can do using a digital frequency meter 62 convert to a digital signal representing a path raw signal and to address a correction memory 64 is used, which contains a correction table for non-linearities of the path sensor. That at the output of the correction memory 64 obtained final digital path signal can be applied to a D / A converter 66 which may be connected to a display and / or a controller.

The circuit after 2 thus provides path signals in the form of pulse trains, digital signals and analog signals ready, which are suitable for further processing in controls or the like.

A reference inductance having the same temperature response as that through the trace 12 formed Meßinduktivität L12 can also be realized by one of the conductor track 12 completely corresponding further conductor track 28 ' provides, in turn, as well as the conductor track 12 between two distance measuring plates 44 ' and 46 ' is arranged and from a printed circuit board 10 ' is worn as in 4 shown.

For the track 28 ' carrying circuit board 10 ' but no guide means is provided, so that changes in the inductance of the conductor 28 ' solely due to temperature effects.

The tracks 12 and 28 ' according to the embodiment 4 are connected to an evaluation circuit as well as to the tracks 12 and 28 in 2 shown. As the conductor track 28 ' the same geometry as the track 12 ' , eliminates the frequency divider.

The through the Wegmeßplatten 44 and 46 sandwiched conductor track 12 and those through the displacement measuring plates 44 ' . 46 ' sandwiched conductor track 28 ' are spatially close to each other. Through an intervening medium 68 , which may be a gas or a liquid, both become conductive tracks 12 and 28 ' and their environment kept at the same temperature.

When using the track arrangement according to 4 in the circuit after 2 Thus one also obtains a position sensor with temperature-compensated output signal.

In the embodiment described above, the path signal was inductively from the overlap between the conductor track 12 and the distance measuring plates 44 . 46 derived. It is understood that one can make such a derivation on a capacitive path, in which case the conductor track 12 is formed as a capacitor plate whose edge contour of the edge contour of the conductor track 12 equivalent. This capacitor plate then forms together with the Wegmeßplatten 44 . 46 a capacitor whose capacity clearly reflects the displacement of the displacement measuring plates 44 . 46 is assigned in the x direction.

The evaluation can be made similar to this, as with reference to 2 described, with the only difference that the oscillators 50 . 54 then instead of a capacitor include an inductance, which together with the connected external capacitors form an LC circuit with the desired own frequency.

In a further modification, one can see the implementation of the overlap between the conductor track 12 and the distance measuring plates 44 . 46 also optically determine, for. B. by increasing limiting a light curtain. Also you could see the displacement of the track 12 also measure by forming these as a contact strip, which cooperates with a sheet-like resistance layer, by one of the Wegmeßplatten 44 . 46 worn. Such pickups could also be interconnected again as frequency-determining elements of a resonant circuit whose natural frequency then again as in 2 shown and measured above.

A modified position sensor is characterized in that two second displacement measuring surfaces are connected by a perpendicular thereto surface to a Wegmeßschlitz, as in 4 shown.

One further modified non-illustrated position sensor is characterized in that that two second Through measuring surfaces two perpendicular surfaces to a rectangular Wegmeßkanal are connected.

In a further modification, the second displacement measuring surface can be considered as the first displacement measuring surface 12 surrounding cylinder or pipe formed.

at the embodiments described above were the path measuring surfaces and the reference surfaces just. It goes without saying that one the surfaces also as cylinder surfaces or partial cylinder surfaces can train, whose transactions then those shown in the figures Correspond to measuring surfaces. Of the entire way sensor then has cylindrical or tubular External geometry.

you can also mix cylindrical and planar geometries and e.g. level first measuring surfaces inside use of cylindrical second measuring surfaces. The important thing is that the different relative positions of the measuring surfaces and reference surfaces reproducible are adjustable.

Claims (15)

Position sensor, with a first electrically conductive measuring surface ( 12 ) and at least one second electrically conductive measuring surface ( 44 . 46 ), with a management facility ( 48 ), through which first measuring surface ( 12 ) and second measuring surfaces ( 44 . 46 ) are displaceable relative to each other in a predetermined plane of movement so that the overlap of the first measuring surface and second measuring surfaces ( 44 . 46 ) Seen in the direction perpendicular to the direction direction, and with a path signal generator (L12), which a the overlap of the first Meßflä che ( 12 ) and second measuring surfaces ( 44 . 46 ) generates corresponding signal, characterized in that a first electrically conductive Referenzmeßfläche ( 28 ) and at least one second electrically conductive Referenzmeßfläche ( 44 . 46 ) is provided and with the Referenzmeßflächen a reference signal generator (L28) cooperates, the Referenzmeßflächen ( 28 . 44 . 46 ) and the measuring surfaces ( 12 . 44 . 46 ) are thermally coupled, and that an evaluation circuit ( 50 to 62 ) is provided, which generates a temperature-compensated path signal from the output signals of path signal generator (L12) and reference signal generator (L28). Path filter according to claim 1, characterized in that the first and second reference measuring surfaces ( 28 . 44 . 46 ) are adjacent to each other and not movable against each other. Position sensor according to claim 1, characterized in that the first reference measuring surface ( 28 ) with the first path measuring surface ( 12 ) is connected so that it has a different inclination to the second path measuring surface ( 44 . 36 ) and the second Referenzmeßfläche by the second Wegmeßfläche ( 44 . 46 ) is formed. Position sensor according to claim 3, characterized in that the first reference measuring surface ( 28 ) perpendicular to the second path measuring surface ( 44 . 46 ) stands. Position sensor according to one of Claims 1 to 4, characterized in that the first reference measuring surface ( 28 ) at least in one direction compared to the first path measuring surface ( 12 ) has low Abmeßung. Position sensor according to claim 5, characterized in that the displacement measuring surfaces ( 12 . 44 . 46 ) and the reference measuring surfaces ( 28 . 44 . 46 ) in each case a frequency-determining element (L12, L28) of an LC circuit (L12, 50 ; L28, 54 ) form. Position sensor according to claim 6, characterized in that the two LC circuits (L12, 50 ; L28, 54 ) Have vibration frequencies whose ratio is 1: 2 ⁿ (n = 0, 1, 2, 3 ...). Position sensor according to Claim 7, characterized in that the output of the higher-frequency oscillating LC circuit ( 28 . 54 ) a frequency divider ( 56 ) whose part ratio is 2 ^m (m = 0, 1, 2). Position sensor according to one of Claims 1 to 8, characterized in that the displacement measuring surfaces ( 12 . 44 . 46 ) and the reference measuring surfaces ( 28 . 44 . 46 ) each have a frequency-determining element of a resonant circuit (L12, 50 ; L28, 54 ) and the evaluation circuit ( 50 to 62 ) a mixing circuit ( 52 ) connected to the output signals of the two oscillating circuits (L12, 50 ; L28, 54 ) is acted upon. Position sensor according to claim 9, characterized by a to the output of the mixing circuit ( 52 ) connected lowpass ( 58 ) and one with the output signal of the low pass ( 58 ) acted upon frequency meter ( 62 ). Position sensor according to one of claims 1 to 10, characterized by a correction memory ( 64 ), which is supplied with path raw signals and provides corrected correction signals from a correction table or according to a predetermined algorithm. Position sensor according to one of claims 1 to 11, characterized in that the first path measuring surface ( 12 ) symmetrically between two second displacement measuring surfaces ( 44 . 46 ) lies. Position sensor according to one of Claims 1 to 12, characterized in that two second displacement measuring surfaces ( 44 . 46 ) are connected by a perpendicular thereto surface to a Wegmeßschlitz. Position sensor according to one of Claims 1 to 12, characterized in that two second displacement measuring surfaces ( 44 . 46 ) are connected by two perpendicular thereto surfaces to a Wegmeßkanal. Position sensor according to one of claims 1 to 12, characterized in that the second displacement measuring surface as the first displacement measuring surface ( 12 ) surrounding cylinder is formed.