JP2003075106A - Position detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position detection device having a highly-accurate, small- sized and simple structure, excellent in compensation performance of a temperature characteristic. SOLUTION: This device includes first and second detection coils A, B excited by an alternating-current signal, and a magnetic response member 12 arranged so as to bring about different impedance changes to each detection coil corresponding to the position which is a detection object. A position detection signal corresponding to the position which is the detection object is generated by operating the ratio of a detection signal level corresponding to the impedance of each detection coil.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device for detecting a position by utilizing a change in impedance of a detecting coil excited by an AC signal, and more particularly, it has excellent temperature characteristic compensation performance and is relatively long. The present invention relates to a linear position detecting device having a compact structure in which the arrangement and size of detection coils can be made considerably smaller than the linear position detectable range.

[0002]

2. Description of the Related Art A conventionally known inductive linear position detecting device is a differential transformer. The differential transformer excites one primary winding in one phase and differentially operates according to the linear position of the iron core that interlocks with the detection target position at each position of the two differentially connected secondary windings. The reluctance that changes with time is generated, and the voltage amplitude level of the resulting one-phase inductive output AC signal indicates the linear position of the iron core. In this differential transformer, in the range in which the two secondary windings are provided so that the induced voltage changes differentially, the induced voltage value is only in a range showing linearity with respect to the linear position. Since the linear position cannot be detected, the length of the detectable range is usually shorter than the total length of the arranged coil. Therefore, it is completely unsuitable for long length detection. That is,
To extend the detectable range, there is no choice but to lengthen the winding length and the core length, which naturally has a limit and causes an increase in the size of the device. In addition, the voltage amplitude level of the induction output signal is susceptible to not only the linear position of the iron core but also the surrounding environment such as temperature change, so that there is a problem in accuracy. In particular, the temperature characteristics of the magnetic characteristics of the metal such as iron existing in the detection device such as the iron loss of the movable iron core and the iron loss of the coil winding core are not considered, and these iron losses are not compensated. Due to this, the detection accuracy was lowered.

On the other hand, there is also known a phase shift type inductive linear position detecting device which outputs an AC signal having an electrical phase angle which correlates with a linear position to be detected. For example, JP-A-49-107758 and JP-A-53.
-106065, JP-A-55-13891, JP-B-1-25286, and the like. In this type of conventionally known phase type inductive linear position detecting device, for example, two primary windings that are displaced from each other in the linear displacement direction of the movable iron core that interlocks with the detection target position are electrically connected to each other. Two-phase AC signals with different phases (for example, sin ωt and cos ωt) are excited respectively, and each is
The secondary side induction signal from the secondary winding is combined to generate one secondary output signal. The electrical phase shift in this secondary output signal with respect to the excitation AC signal indicates the linear position of the core core that is interlocked with the detection target position.
Further, in Japanese Utility Model Publication No. 1-25286, a plurality of iron cores are intermittently and repeatedly provided at a predetermined pitch to detect a linear position over a range wider than a range in which primary and secondary windings are provided. Is possible. However, even with these types, a plurality of coils must be dispersed and arranged in correspondence with the length of one cycle of the predetermined detection range, so the arrangement length, that is, the size of the coil is one cycle of the detection range. The length must be equal to the length, and a compact structure cannot be achieved. Also in this case,
The temperature characteristics of the magnetic characteristics of the metal such as iron existing in the detector, such as the iron loss of the movable iron core and the iron loss of the coil winding core, are not taken into consideration, and these iron losses are not compensated. The detection accuracy was declining.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention to provide a highly accurate position detection device having excellent temperature characteristic compensation performance.
Another object of the present invention is to provide a highly accurate linear position detecting device having a small size and a simple structure, capable of detecting a linear position over a wide range, and having excellent temperature characteristic compensation performance.

[0005]

A position detecting device according to the present invention includes first and second detection coils excited by an AC signal, and different impedances for the respective detection coils depending on a position to be detected. A position detection signal corresponding to the linear position as the detection target by calculating a ratio of a detection unit including a magnetically responsive member arranged so as to cause a change and a detection signal level according to the impedance of each detection coil. And a calculation means for generating.

In the impedance of the detecting coil, the error due to the temperature characteristic of the magnetic characteristic of the metal such as iron existing in the detecting device, such as the iron loss of the movable iron core and the iron loss of the coil winding core, is a component as a coefficient. have. Therefore, the output level of the first detection coil is set to A (x) and the output level of the second detection coil is set to B (x) according to the position x to be detected, and the iron loss of the movable iron core and further the coil core are set. When the error coefficient based on the temperature characteristic of the magnetic characteristic of the metal such as iron existing in the detection device such as iron loss of the core is γ, the actual output level of the first detection coil is γA (x), and the second detection coil is The output level of the coil can be expressed as γB (x). The ratio of the detection signal level according to the impedance of each detection coil is
"ΓA (x) / γB (x)" or "γB (x) / γA
(X) ”, the error coefficient e is canceled by taking the ratio, and“ A (x) / B (x) ”or“ B (x) / A
A position detection signal "(x)" is generated. A (x) ≠
Since it is B (x), "A (x) / B (x)" or "B
“(X) / A (x)” indicates a value corresponding to the linear position x that is the detection target. Since the arrangement of the first detection coil and the second detection coil is not limited to a specific arrangement with respect to the entire length of the detection target range, the first detection coil and the second detection coil are arranged relatively close to each other. It doesn't matter. Therefore, the coil assembly including the first and second detection coils can be compactly arranged as compared with the length of the detection target range, and linear position detection over a long range is possible with a small and simple structure. .

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is an axial sectional view of a linear position detecting device according to an embodiment of the present invention.
The detection head 10 includes a first detection coil A and a second detection coil B, and further includes auxiliary coils C and D as a preferred but not essential embodiment. In the detection head 10, a rod 11 is provided so as to penetrate through the cylindrical space of each coil. The detection head 10 is linearly displaced relative to the rod 11. For example, when it is used for the purpose of detecting the slide amount of a seat (not shown), the rod 11 is fixed in a predetermined arrangement, and the detection head 10 is linearly displaced within a predetermined range as the seat is slid.

The rod 11 is provided with a magnetic responsive member 12 which is arranged so as to cause different impedance changes to the respective detection coils A and B according to the linear position to be detected. The magnetically responsive member 12 is made of a magnetic material such as iron or a diamagnetic material such as copper, and has a shape such as an elongated cone whose radial cross section gradually changes in the longitudinal direction, that is, the axial direction ( The axial cross section has a triangular shape as shown). The outer circumference of the rod 11 is composed of a magnetic non-responsive (non-magnetic and non-diamagnetic) pipe 11a such as plastic, and an elongated conical magnetic responsive member 12 is inserted into the pipe 11a and appropriate means are used. It is fixed.

Assuming that the magnetically responsive member 12 is made of a magnetic material such as iron, the impedances of the detection coils A and B are the same when the location having the largest radial cross-sectional area corresponds to the detection coils A and B. When the location where the radial cross-sectional area is maximum and the radial cross-sectional area is minimum corresponds to the detection coils A and B, the impedance of the detection coils A and B is minimum. As shown in the figure, since the arrangement of the detection coils A and B is slightly shifted in the axial direction, that is, the linear displacement direction, the correspondence relationship between the detection coils A and B and the magnetic response member 12 is the detection target linear position x. To produce a somewhat different impedance change. FIG. 2 shows an example of impedance changes of the detection coils A and B according to the detection target linear position x. In the present embodiment, the detection coils A and B are assumed to have the same physical and electrical characteristics (the number of turns and the like), but the present invention is not limited to this, and it depends on the configuration of the magnetically responsive member 12. The design may be changed accordingly.

The auxiliary coils C and D compensate the temperature drift characteristics (temperature drift characteristics of pure resistance) of the detection coils A and B, and respond to the detection target linear position x, that is, the displacement of the magnetic response member 12. In order not to do so, it is magnetically shielded by the shield material 13 made of a magnetic material or a diamagnetic material. As a result, as shown in FIG. 2, the impedances of the auxiliary coils C and D do not change according to the detection target linear position x, that is, the displacement of the magnetic response member 12, and are kept constant. In the present embodiment, the physical and electrical characteristics (number of turns and the like) of the auxiliary coils C and D are the same as those of the detection coils A and B, but the present invention is not limited to this.

FIG. 3A is a diagram showing an example of connection between the detection coils A and B and the auxiliary coils C and D. The auxiliary coil C is connected to the detection coil A in anti-phase series connection (differential connection), the auxiliary coil D is connected to the detection coil B in anti-phase series connection (differential connection), and an appropriate AC source 14 is applied. It Since the impedance change of the coil due to the temperature drift appears in the detection coils A and B and the auxiliary coils C and D in the same manner, an undesired impedance change (detection coils A and B caused by the temperature drift due to the temperature drift ( The change in impedance of the pure resistance component is canceled or reduced.

The detection coil A according to the linear position x to be detected
Is represented by Va (x), and the output voltage obtained from the detection coil B is represented by Vb (x). Figure 3
(B) is the output voltage Va (x), V of the detection coils A, B
The structural example of the circuit which processes b (x) is shown. The output voltages Va (x) and Vb (x) of the detection coils A and B are the rectifier circuit 1
It is converted into a DC voltage in 5, and further converted into a digital value in the analog / digital converter 16. The calculation means 17 calculates the ratio of the digital values a (x) and b (x) corresponding to the output voltages Va (x) and Vb (x) of the detection coils A and B.

The magnetic circuits of the detection coils A and B are mainly composed of
The magnetic responsive member 12 and the iron core 10a of the detection head 10 are present, and the magnetic characteristics of these magnetically responsive metals have temperature drift characteristics (iron loss or copper loss), which are undesired according to temperature changes. It causes impedance change. The change in impedance due to these iron loss or copper loss appears as a coefficient component γ in the output voltages Va (x) and Vb (x) of the detection coils A and B. That is, regarding the digital values a (x) and b (x) corresponding to the output voltages Va (x) and Vb (x) of the detection coils A and B, considering the coefficient component γ of the impedance change due to iron loss or copper loss. It can be expressed as follows. Note that A (x) and B (x) are values corresponding to the impedance corresponding to the detection target position x from which the impedance change due to the iron loss or the copper loss is removed. a (x) = γA (x) b (x) = γB (x)

Therefore, the calculating means 17 detects both detected values a.
By calculating the ratio of (x) and b (x), a (x) / b (x) = γA (x) / γB (x) = A
(X) / B (x), and the impedance change component γ due to iron loss or copper loss can be removed. Numerator in ratio calculation
The denominator may be the opposite of the above, as follows. b (x) / a (x) = γB (x) / γA (x) = B
(X) / A (x) Ratio calculation result “A (x) / B (x)” (or B (x) /
Since A (x) is correlated with the detection target position x, it may be used as it is as position detection data. That is, A (x) ≠ B (x) because the magnetic response member 12 is arranged so as to cause different impedance changes for the respective detection coils A and B according to the detection target linear position x.
The calculation result of the ratio can be used as data indicating the position x. In this way, the temperature drift characteristic (iron loss or copper loss) of the magnetically responsive metal present in the magnetic circuit of the detection coils A and B can be compensated, and the detection accuracy can be improved.

Structure of the detection head 10 and the magnetic response member 1
The configuration of No. 2 is not limited to the above embodiment, but may be variously modified. FIG. 4 shows an example thereof, and as shown in the schematic side view of FIG. 4A, one end of each coil A, B, C, D in the detection head 10 is provided on the side surface of the rod 11 with a gap of a predetermined interval. Facing each other. As shown in the schematic plan view of FIG. 4B, the side surface of the rod 11 has an elongated shape in which the area facing one end of each coil of the detection head 10 gradually changes in the longitudinal direction, that is, the axial direction. A magnetically responsive member 12 having a triangular shape is arranged. It is preferable that at least the surface of the rod 11 on which the magnetically responsive member 12 is arranged is flat, but the rod 11 is not limited to this and may have a cylindrical shape or the like. In the case of FIG. 4, each detection coil A,
The area of the magnetically responsive member 12 on the surface of the rod 11 facing one end of B changes according to the detection target position x, and the impedance change according to the detection target position x causes the detection coils A,
B occurs.

FIG. 5 shows another example. One end of each coil A, B, C, D in the detection head 10 faces the side surface of the rod 11 with a gap, and the distance of this gap is detected. It changes according to the target position x. For example, on the surface of the rod 11, the height of the magnetically responsive member 12 arranged facing one end of each of the detection coils A and B of the detection head 10 is configured to change according to the detection target position x. There is. As a result, the gap distance between one end of each of the detection coils A and B and the magnetically responsive member 12 on the surface of the rod 11 facing it changes according to the detection target position x, and the impedance change according to the detection target position x. Occurs in each of the detection coils A and B.

Temperature drift characteristics (iron loss or copper loss) of the magnetically responsive metal present in the magnetic circuit of the detection coils A and B.
The auxiliary coils C and D may be omitted in each of the above embodiments from the viewpoint of compensating for the above. Further, in the above embodiment, there is only one magnetic response member 12 arranged so as to cause different impedance changes to the respective detection coils A and B according to the linear position x to be detected. However, the magnetic response member 12 may be separately provided for each of the detection coils A and B. For example, the magnetic response member 12 may be provided on each of the two rods 11, and the detection coils A and B and the auxiliary coils C and D, respectively, may be provided corresponding to each rod. Further, in the above embodiment,
Although the ratio is calculated with respect to the digital values a (x) and b (x), the invention is not limited to this, and the ratio with respect to the analog value may be calculated by the analog calculating means.
Further, the calculation means 17 is not limited to a single calculation circuit, but a CP
It is also possible to use a computing function of a microcomputer such as U. Further, the present invention is applicable not only to the linear position detecting device but also to the rotational position detecting device.

[0018]

As described above, according to the present invention, the temperature drift characteristic (iron loss or copper loss) of the magnetically responsive metal present in the magnetic circuit of the detection coil can be compensated, and the detection accuracy can be improved. It is possible to provide a position detecting device. Further, it is possible to provide a highly accurate linear position detection device which is capable of linear position detection over a wide (long) range even though the arrangement and configuration of the detection coil is small and simple, and which has excellent temperature characteristic compensation performance. it can.

[Brief description of drawings]

FIG. 1 is an axial sectional view of a linear position detecting device according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of impedance change of each coil in the example.

FIG. 3 is a diagram showing an example of connection of each coil in the embodiment and a block diagram showing an example of a circuit for processing a coil output.

FIG. 4 is a schematic side view and a plan view showing another embodiment of the linear position detecting device according to the present invention.

FIG. 5 is a schematic side view showing still another embodiment of the linear position detecting device according to the present invention.

[Explanation of symbols]

10 Detection head 11 rod 12 Magnetic response member A, B detection coil C, D auxiliary coil 17 Computing means

Claims (3)

[Claims] 1. A first and second detection coil excited by an AC signal, and a magnetic responsive member arranged so as to cause different impedance changes to each detection coil depending on a position to be detected. A position detection device comprising: a detection unit that includes the detection unit; and a calculation unit that calculates a ratio of detection signal levels according to the impedance of each of the detection coils to generate a position detection signal according to the position to be detected. 2. The magnetically responsive member is such that the area or gap facing the first and second detection coils changes according to the position to be detected, and has a length of one cycle within a predetermined detection range. The position according to claim 1, wherein the area or the gap has a shape corresponding to a temporary change, and the displacement of the arrangement of the first and second detection coils is shorter than the length of the one cycle. Detection device. 3. The detection unit includes a first auxiliary coil differentially connected to the first detection coil and a second auxiliary coil differentially connected to the second detection coil. Further comprising: outputting a first detection signal corresponding to a differential value of the impedance of the front first detection coil and the impedance of the first auxiliary coil, and outputting the impedance of the second detection coil and the second detection coil. A second detection signal corresponding to the differential value of the impedance of the auxiliary coil is output, and the calculation means calculates the ratio of the levels of the first detection signal and the second detection signal. The position detection device according to claim 1.