JP2010223913A - Non-contact position sensor - Google Patents

Abstract

An object of the present invention is to suppress position information detection errors caused by temperature fluctuations of a detector.
A non-contact position sensor penetrates a core made of a magnetic material into a detection coil and utilizes the fact that the impedance of a detection unit having the detection unit changes depending on the penetration amount. 1 penetration amount is detected. However, since the impedance of the detection unit A varies depending on the temperature variation of the detection unit A, an error due to the temperature variation may occur between the actual penetration amount of the core 1 and the detected penetration amount of the core 1. There is. In the present invention, a serial connection circuit of the detection coil 2 having a positive temperature characteristic and the negative thermistor 3 having a negative temperature characteristic is used for the detection unit A. As a result, the variation range of the resistance value variation of the detection unit A with respect to the temperature variation of the detection unit A is smaller than the conventional non-contact position sensor using only the detection coil 2 as the detection unit A. Can be reduced.
[Selection] Figure 1

Description

  The present invention relates to a non-contact position sensor that detects a relative positional relationship between a detection coil and a core.

  Conventionally, for example, as described in Patent Document 1, it is used that a voltage generated between both ends of a detection coil changes when a predetermined alternating current is applied to the detection coil in accordance with the magnetic flux inside the detection coil. A non-contact position sensor is provided. This non-contact position sensor includes a detection unit composed of a detection coil, a core formed of a magnetic material, penetrated into the detection coil, and the amount of penetration changes according to an external input, and a voltage across the detection unit. A measuring circuit for detecting, an alternating current circuit for supplying a predetermined alternating current to the detection unit, a detection circuit for detecting the penetration amount of the core from the voltage across the detection unit, and a detection coil and a core based on the detected penetration amount An output circuit for outputting the relative position information as a position signal to the outside.

The detection unit of the conventional example is always supplied with an alternating current having a constant amplitude and frequency from an alternating current circuit. At this time, the absolute value | Z | of the impedance of the detection unit is obtained from the amplitude I _{0 of the} alternating current input from the alternating current circuit and the amplitude V _{0 of} the voltage generated between both ends of the detection unit. Calculated as V ₀ / I ₀ . The detection circuit calculates the impedance of the impedance based on the correspondence between the absolute value of the impedance of the detection unit calculated based on the relational expression and the absolute value of the impedance of the detection unit determined in advance one-to-one and the penetration amount of the core. The core penetration corresponding to the absolute value is detected. In the conventional example, the penetration amount of the core is detected by the above-described operation, and a position signal based on the detected penetration amount is output to the outside.

Japanese Patent No. 4135551

  By the way, the detection coil is generally formed of a conductive wire made of a metal material such as copper, and the resistance component of the impedance has a positive temperature characteristic that increases as the temperature rises. Further, the temperature of the detection unit varies due to the influence of heat generated from the detection coil and the conductive wire and the outside air temperature. Therefore, in the position sensor as described above, even if the penetration amount of the core is the same, the impedance of the detection unit varies due to the variation of the temperature of the detection unit due to the influence of the generated heat and the outside air temperature.

  Usually, the correspondence between the predetermined absolute value of the impedance of the detection unit and the penetration amount of the core is determined at a specific temperature as a reference. However, as described above, since the impedance of the detection unit varies depending on the temperature, an error occurs between the actual penetration amount and the detected penetration amount when the detection unit is at a temperature other than the reference temperature. .

  In order to overcome the above problem, for example, the temperature of the detection unit is measured, and the correspondence between the absolute value of the impedance of the detection unit to be referred to and the penetration amount of the core is properly used according to the temperature. It is conceivable to use a temperature compensation circuit as described in. However, even with these methods, it is difficult to completely reproduce the temperature characteristic of the impedance of the detection unit, and therefore there may be an error between the penetration amount after calibration and the actual penetration amount.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a non-contact position sensor that can improve the detection accuracy of position information with a simple configuration.

  In order to achieve the above object, the present invention provides a detection unit including a detection coil and a magnetic material, penetrates into the winding of the detection coil, and moves to the detection coil in the winding direction of the detection coil. An impedance of the detection coil based on a voltage between the both ends of the detection unit generated by the AC current, an AC current circuit that outputs an AC current having a predetermined frequency and amplitude to the detection unit A detection circuit for detecting the penetration amount of the core penetrating into the detection coil based on the absolute value of the impedance, and a relative position between the detection coil and the core based on the penetration amount An output circuit that outputs information as a position signal to the outside, and the detection unit includes a series of the detection coil having a positive temperature characteristic and a thermistor having a negative resistance characteristic. And characterized by being connected.

  In the present invention, a detection coil uses a series connection circuit of a detection coil whose resistance value increases as the temperature rises and a negative thermistor whose resistance value decreases as the temperature rises. As a result, since the fluctuation range of the resistance component of the impedance of the detection unit due to the temperature variation of the detection unit is smaller than when only the detection coil is used as the detection unit, the detection accuracy of the position information of the sensor can be improved. .

  The present invention can improve the detection accuracy of position information with a simple configuration.

It is a figure which shows the circuit structure of embodiment of this invention. It is a top view of the embodiment of the present invention. It is sectional drawing of the AA 'cross section of embodiment of this invention. It is sectional drawing of the detection coil based on embodiment of this invention. It is a figure which shows the relative resistance value in each temperature when the resistance value in 25 degreeC is set to 1 of the negative thermistor which concerns on embodiment of this invention. It is a figure which shows the relative resistance value in each temperature of the detection coil which concerns on embodiment of this invention, a negative thermistor, and the series connection circuit of both.

(Embodiment)
As shown in FIG. 1, this embodiment includes a detection unit A and an ASIC 4.

  As shown in FIGS. 1 to 4, the detection unit A has a U-shaped cross section and is formed by bending an insulating material with a certain curvature, and a detection coil 2 wound around the bobbin 10. A curvature correcting member 11 made of an insulating material for correcting the curvature change of the detection coil 2, and a cylindrical body 12 a and a cylindrical body centering on the center of the arc of the detection coil 2 curved in an arc shape A movable block 12 formed of a protrusion 12b formed on the outer side of 12a, one end of which is fixed to the protrusion 12b, penetrates into the hollow portion of the detection coil 2, and has the same curvature as the hollow portion of the detection coil 2 from a magnetic material. A curved core 1, a housing 13 for placing and fixing each member on the surface, and a negative thermistor 3 having one end connected in series to the detection coil 2 and the other end grounded. I have. The movable block 12 rotates about the rotation axis C, and the penetration amount of the core 1 penetrating the detection coil 2 decreases as the angle θ shown in FIG. 2 increases.

  The negative thermistor 3 is disposed in spatial proximity to the detection coil 2. Further, as shown in FIG. 5, the resistance value of the negative thermistor 3 in the present embodiment has a negative temperature characteristic that decreases as the temperature rises at 180 ° C. or lower.

  The ASIC 4 includes an alternating current circuit that supplies an alternating current having a predetermined amplitude and frequency to the detection unit A, a measurement circuit that detects a voltage across the detection unit A, an amplitude of the alternating current, and a detection detected by the measurement circuit. Based on the amplitude of the voltage across the part A, the absolute value of the impedance of the detection part A is calculated, and from this absolute value of the impedance, a predetermined absolute value of the impedance of the detection part A and the amount of penetration of the core 1 Based on the relationship, a detection circuit for detecting the penetration amount of the core 1 penetrating into the detection coil 2 and a position signal indicating the penetration amount are output to the outside as relative position information of the detection coil 2 and the core 1. An output circuit is integrated.

  In the present embodiment, the operation of each component for deriving the penetration amount of the core 1 is the same as in the case of the above-described conventional example, so that description thereof is omitted.

  The resistance value of the detection unit A of the present embodiment is represented by the sum of the resistance value of the detection coil 2 and the resistance value of the negative thermistor 3. Here, since the detection coil 2 and the negative thermistor 3 are disposed spatially close to each other, the temperatures of the detection coil 2 and the negative thermistor 3 are substantially the same. Therefore, the resistance value of the detection unit A is represented by the sum of the resistance value at each temperature of the detection coil 2 and the resistance value at each temperature of the negative thermistor 3. As shown in FIG. 6, this combined resistance has a smaller fluctuation range with respect to temperature fluctuation than the resistance value of the detection coil 2. Therefore, in the present embodiment, the impedance of the detection unit A is stabilized against temperature fluctuations of the detection unit A as compared with a non-contact position sensor using only the detection coil 2 as the detection unit A as in the prior art. Therefore, the error between the actual penetration amount of the core 1 and the detected penetration amount is reduced, and the detection accuracy of the position information can be improved with respect to the temperature fluctuation of the detection unit A.

  In the present embodiment, the rotary position sensor has been described, but the detection coil 2 and the core 1 are linearly formed, and the core 1 moves relative to the detection coil 2 in the central axis direction of the detection coil 2. A linear non-contact position sensor may be used. In the present embodiment, one negative thermistor 3 is used. Instead, a plurality of negative thermistors and thermistors having a positive temperature characteristic are connected in series or in parallel to detect the temperature of the detection coil 2. A circuit configured to compensate for a change in resistance value due to the change may be used.

  Further, by combining the present embodiment and a conventional temperature compensation circuit and compensating the absolute value of the impedance of the detection unit A, which has been reduced by a negative thermistor due to temperature fluctuation, with the temperature compensation circuit, further detection accuracy can be achieved. It can also be improved.

2 Detection coil 3 Negative thermistor 4 ASIC
A detector

Claims (1)

A detection unit including a detection coil;
A core made of a magnetic material, penetrating into the winding of the detection coil, and relatively displaced with respect to the detection coil in the winding axis direction of the detection coil;
Based on an alternating current circuit that outputs an alternating current having a predetermined frequency and amplitude to the detection unit, and a voltage across the detection unit that is generated by the alternating current, an absolute value of the impedance of the detection coil is calculated, A detection circuit for detecting the amount of penetration of the core penetrating into the coil based on the absolute value of impedance, and outputting relative position information of the coil and the core based on the penetration amount to the outside as a position signal. Output circuit,
The non-contact position sensor, wherein the detection unit is formed by connecting the detection coil having a positive temperature characteristic and a thermistor having a negative resistance temperature characteristic in series.

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