WO2019224586A1

WO2019224586A1 - Linear position sensor

Info

Publication number: WO2019224586A1
Application number: PCT/IB2018/053752
Authority: WO
Inventors: Andreas Kurz; Sina FELLA; José João CUNHAL FONTAÍNHAS; Jorge Miguel NUNES DOS SANTOS CABRAL; Luís Alexandre MACHADO DA ROCHA; José António AZEVEDO GONÇALVES; Ângelo Rafael GOMES DE ARAÚJO
Original assignee: Bosch Car Multimedia Portugal, S.A.; Universidade Do Minho
Priority date: 2018-05-24
Filing date: 2018-05-25
Publication date: 2019-11-28

Abstract

The present application discloses a linear position sensor (1), comprising an element (3) where sensor coils (6), (7), (8), (9) are disposed, and a partly electrically conductive element (2), both elements are moved relative to each other in a direction along a measurement path S0 to S1. The partly electrically conductive element (2) comprises two measurement tracks (4), (5) with a sinusoidal-type shape, which differ on the number of revolutions. The inductance of the sensor coils or the coupling between the sensor coils (6), (7), (8), (9), changes due to the overlap of the respective measuring tracks (4), (5); this generates a sine and cosine type of response which are used to calculate the position, within the measuring tracks.

Description

DESCRIPTION

"LINEAR POSITION SENSOR"

Technical field

This application relates to a linear position sensor.

Background art

There are known sensors based on the Eddy current principle. One detection principle, as described in document DE 102004033083, is that the measuring signal is a frequency change of a resonant circuit, whose measuring coil is disposed over an electrically conductive track. The electrically conductive track changes its width along a measuring path in such a way that the area covering the measuring coil with respect to the electrically conductive track along the measuring path changes. The measuring coil induces Eddy currents in the conductive track, which leads to an inductance change of the measuring coil.

Another possibility is that the coupling between two coils is changed by an electrically conductive track such as described in W02017/102137 and WO2017/198468. All these measurement principles are based on fixed geometric shapes that are elongated if a longer linear position sensor is desired. Therefore, there is a strong degradation of the resolution of the sensor as the dynamic range increases.

Summary

The present application discloses a linear position sensor, comprising an element where sensor coils are disposed, and a partly electrically conductive element, both elements are moved relative to each other in a direction along a measurement path; the partly electrically conductive element comprising two measuring tracks of a sinusoidal-type shape, wherein the measuring tracks differ in the number of revolutions .

In one embodiment of the linear position sensor, the sinusoidal-type shape of one measuring track has at least one more revolution than the sinusoidal-type shape of the other measuring track.

In another embodiment of the linear position sensor, the functional relation between the element with the sensor coils and the partly electrically conductive element implies that the sensor inductive coils are arranged above the measuring tracks, and wherein an overlap between the sensor coils and the measuring tracks changes along the measurement path in such a manner that the inductance of the sensor coils or the coupling between the sensor coils is dependent on the position of the measurement path.

Yet in another embodiment of the linear position sensor, two sensor coils are used for each measuring track.

In another embodiment of the linear position sensor, the sensor coils are inserted in an oscillating circuit.

In another embodiment of the linear position sensor, the measuring tracks and the sensor coils are printed directly on a plastic component or a printed circuit board.

Finally, in another embodiment of the linear position sensor, the partly electrically conductive element is inserted in a closed radial shape and the element with the sensor coils is placed in such an arrangement that the sensor coils area is covered by the measuring tracks according to the measurement path rotation.

General Description

The technology now developed intends to solve the problem of achieving long linear position sensors with improved resolution and absolute positioning, i.e. to have high- dynamic range linear position sensors with high signal-to- noise ratio.

According to principles described herein, the linear position sensor now developed is based on a sensor target including two measuring tracks of a sinusoidal-type shape, which differ on the number of revolutions, rather than using only one fixed geometric shape, as the state of the art techniques suggest. This pattern configuration implies that one sinusoidal shape of a measuring track has always at least one more revolution than the other. For each measuring track two sensor coils are used, and are inserted in an oscillating circuit that detects the change of their inductance or coupling as the electrically conductive tracks move relatively to the coils, enabling position measurement. For different lengths of the target shapes, the number of revolutions of the measuring tracks can be increased, keeping the predefined pattern configuration of one measuring track with a sinusoidal-type shape with at least one more revolution than the other track, which enables to keep resolution while increasing dynamic range.

In keeping with these objects and with others which will become apparent hereinafter, one feature of the technology developed resides, briefly stated, on a linear position sensor comprised by an element where sensor coils are disposed and a partly electrically conductive element, where both elements are moved relative to each other in a direction along a measurement path. The sensors inductive coils are arranged above the measuring tracks, and wherein an overlap between the sensor coils and the measuring tracks changes along the measurement path in such a manner that the inductance of the sensor coils or the coupling between the sensor coils is dependent on the position of the measurement path .

The partly electrically conductive element comprises the two measurement tracks with a sinusoidal-type shape, according to the predefined pattern configuration. The inductance or the coupling changes on the pairs of sensor coils, and due to the overlap of the measuring tracks, generates a sine and cosine type of response, which are used to calculate the position within the measuring tracks. The linear position of the partly electrically conductive element, which represents the sensor output, is calculated by using the difference between the responses of inductive coils over the measuring tracks, according to the Vernier Principle. This position calculation method enables to have high resolutions for long measurement paths, since it is possible to increase the measuring tracks (extra revolutions), without loss of resolution .

Both the sensor target - measuring tracks - and the sensor coils can be printed directly on a plastic peace or on a printed circuit board. As another approach, the sensor target can be implemented on a fully-metallic conductive component, i.e. the tracks are obtained by openings with the metallic material, or by placing the metallic tracks within a non- metallic holder.

In the view of what is disclosed in the present application, the technology now developed represents an improvement when compared to state of the art Eddy current sensors as its geometry allows to minimize the degradation of the resolution of the sensor as the dynamic range of the sensor increases.

Thus, concept now disclosed is prepared to face situations where an improved resolution is required.

Brief description of drawings

For easier understanding of this application, figures are attached in the annex that represent forms of implementation which nevertheless are not intended to limit the technique disclosed herein.

Figure l.a illustrates on embodiment of the linear sensor position developed, used along a measurement path SO to SI, in which reference numbers represent:

1 - linear sensor position;

2 - partly electrically conductive element;

3 - element with sensor coils;

4 - measuring track with a sinusoidal-type shape;

5 - measuring track with a sinusoidal-type shape;

6 - sensor coil of measuring track (4);

7 - sensor coil of measuring track (4);

8 - sensor coil of measuring track (5);

9 - sensor coil of measuring track (5); Figures l.b and l.c illustrate the sine and cosine type response generated due to inductance changes on the pairs of sensor coils, (6), (7) and (8), (9), resulting from the overlap with the respective measuring tracks (4) and (5), along the measurement path SO to SI.

Figure 2 illustrates the graphic for determining the position within the measuring tracks (4) and (5), representing the relation between the cosine and sine type responses along the measurement path SO to SI.

Figure 3 illustrates an embodiment of the linear sensor position developed, adapted to measure the radial position of a rotating element, in which reference numbers represent:

2 - partly electrically conductive element;

3 - element with sensor coils;

4 - measuring track with a sinusoidal-type shape;

5 - measuring track with a sinusoidal-type shape;

10 - rotating element.

Description of embodiments

Now, embodiments of the present application will be described with reference to the annexed drawings. However, they are not intended to limit the scope of this application.

In one embodiment of the linear position sensor (1), as illustrated on Figure l.a, the sensor (1) comprises an element (3) with sensor coils (6), (7), (8), (9) and a partly electrically conductive element (2), where both elements are moved relative to each other in a direction along a measurement path SO to SI. The partly electrically conductive element comprises two measuring tracks (4) and (5) with a sinusoidal-type shape, with track (5) containing at least one more revolution than track (4) . In the example sketched in Figure l.a measuring track (4) has one revolution and measuring track (5) has two revolutions. For each measuring track, two sensor coils are used - (6), (7) for track (4) and (8), (9) for track (5) . The inductance changes on the pairs of sensor coils, pair (6), (7) and pair (8), (9), and due to the overlap of the respective measuring tracks (4) and (5), it is generated a sine and cosine type response, as can be seen in Figure lb and Figure lc, that is used to calculate the position within the measuring tracks (4) and (5), as illustrated in Figure 2. The linear position of the partly electrically conductive element, which represents the sensor output, is calculated by using the difference between the responses of inductive coils over measuring tracks (4) and (5), according to the Vernier Principle.

For different lengths of the target shapes - longer distances SO to SI - the number of revolutions can be increased, keeping the same pattern configuration between both measuring tracks - a measuring track has a sinusoidal-type shape that has at least one more revolution than the other.

In another embodiment, according to Figure 3, the partly electrically conductive element is inserted in a closed radial shape, and the element (3) with the sensor coils (6), (7), (8), (9), is placed in such an arrangement that the sensor coils area is covered by the measuring tracks (4) and (5) according to the measurement path rotation. This configuration enables the measurement of the radial position of a rotating element (10) . This description is of course not in any way restricted to the forms of implementation presented herein and any person with an average knowledge of the area can provide many possibilities for modification thereof without departing from the general idea as defined by the claims. The embodiments described above can obviously be combined with each other. The following claims further define forms of implementation .

Claims

1. Linear position sensor comprising an element where sensor coils are disposed, and a partly electrically conductive element, both elements are moved relative to each other in a direction along a measurement path; the partly electrically conductive element comprising two measuring tracks of a sinusoidal-type shape, wherein the measuring tracks differ in the number of revolutions.

2. Linear position sensor according to claim 1, wherein the sinusoidal-type shape of one measuring track has at least one more revolution than the sinusoidal-type shape of the other measuring track.

3. Linear position sensor according to any of the previous claims, wherein the functional relation between the element with the sensor coils and the partly electrically conductive element implies that the sensor inductive coils are arranged above the measuring tracks, and wherein an overlap between the sensor coils and the measuring tracks changes along the measurement path in such a manner that the inductance of the sensor coils or the coupling between the sensor coils is dependent on the position of the measurement path.

4. Linear positon sensor according to any of the previous claims, wherein two sensor coils are used for each measuring track .

5. Linear position sensor according to claim 3, wherein the sensor coils are inserted in an oscillating circuit.

6. Linear position sensor according to any of the previous claims, wherein the partly electrically conductive element is a metallic conductive component.

7 . Linear position sensor according to claim 6, wherein the measuring tracks are opened on the partly electrically conductive element.

8. Linear position sensor according to any of the previous claims 1 to 5, wherein the measuring tracks and the sensor coils are printed directly on a plastic component or a printed circuit board.

9 . Linear position sensor according to any of the previous claims, wherein the partly electrically conductive element is inserted in a closed radial shape and the element with the sensor coils is placed in such an arrangement that the sensor coils area is covered by the measuring tracks according to the measurement path rotation.