JPH02259523A - Electrostatic capacity type stroke detecting device - Google Patents

Abstract

PURPOSE:To easily adjust an output DC voltage for an electrostatic capacity value due to a manufacture error by providing a differential amplifier whose amplification degree is adjustable by varying a negative feedback quantity. CONSTITUTION:A C/V converting means 7 is provided with an oscillator 9 which outputs a signal of constant frequency (f), a Schmitt trigger circuit 10 which receives the output signal of the oscillator 9, and a charge pump circuit 11 as a charging and discharging means which charges and discharges a capacitor C repeatedly at a set period in synchronism with the output signal of the Schmitt trigger circuit 10. Further, this means is provided with a resistance R which is connected to the charge pump circuit 11 and generates a DC voltage V1 corresponding to the capacity value of the capacitor C and the differential amplifier 12 which adjusts the offset of the DC voltage V1 generated in the resistance R and performs amplification with the set amplification degree. Consequently, the output DC voltage is easily adjusted for the electrostatic capacity value due to the manufacture error.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a C
The present invention relates to a capacitive stroke detection device provided with /V conversion means.

[Conventional technology]

To explain the case in which this type of capacitive stroke detection device is used as a means for detecting the stroke of a cylinder such as a hydraulic cylinder or a pneumatic cylinder, for example, the cylinder case side and the piston rod that are displaced relative to each other. If electrodes are formed on each side, the capacitance 1 (a) of the capacitor formed between the pair of electrodes will change according to the stroke change of the piston rond with respect to the cylinder case. By converting the capacitance value of a capacitor formed between a pair of electrodes formed on the and piston rod sides into a DC voltage using a C/V conversion means, a DC voltage corresponding to the cylinder stroke can be obtained. (See, for example, Japanese Patent Application No. 19374/1983, which was previously proposed by the present applicant).

[Challenges to be solved by the invention] However, the dimensions of each pair of electrodes and the capacitance of the insulating layer of dielectric material used to insulate between the pair of electrodes may vary due to manufacturing errors. become. As a result, C
The value of the DC voltage output from the /V conversion means will have errors due to manufacturing errors of the above-mentioned parts.

Therefore, for example, it is necessary to set the value of the DC voltage at the reference point where the stroke is minimum or the rate of change of the DC voltage with respect to a unit change in the stroke for each detection device.

The offset voltage at the reference point of the stroke and the rate of change of the DC voltage with respect to the stroke change, that is, the amplification degree, can be adjusted separately and independently so that adjustment of one does not affect the other. It is hoped that

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to easily adjust the output DC voltage to the capacitance value caused by manufacturing errors.

[Means to solve the problem]

The capacitive stroke detection device according to the present invention is provided with a C/V conversion means that outputs a DC voltage according to the capacitance value of a capacitor formed between a pair of relatively displaced electrodes. Its characteristic structure is as follows.

That is, a differential amplifier is provided that can freely change and adjust the degree of amplification by varying the amount of negative feedback, and one input terminal of the differential amplifier receives the DC voltage output from the C/V conversion means. , and a DC voltage having the same value as the DC voltage output by the C/V conversion means when the capacitance value of the capacitor is at a maximum or minimum is input to the other input terminal of the differential amplifier. At the point.

[For production]

As shown in FIG. 4, the amplification degree of the differential amplifier (12) is
The amount of negative feedback can be adjusted by varying the value of a negative feedback resistor (Rf).

However, as shown in the above formula, in the differential amplifier (12),
The difference between the DC voltage (ε) input to the non-inverting input terminal (i1) and the input voltage (Vi) input to the inverting input terminal (i-) is set to the value of the negative feedback resistor (Rf). It will be amplified with a correspondingly set amplification factor.

2f Vo=−·(ε−Vi)+ε i In the above equation, ν0 is the output voltage of the differential amplifier (12).

Therefore, the output offset voltage of the differential amplifier (12) is the DC voltage (
This can be adjusted by varying ε), but if the negative feedback amount is changed, the offset voltage adjusted by the non-inverting DC voltage (ε) will also change.

However, as is clear from the above equation, when the input voltage (Vi) on the inverting side and the input voltage (ε) on the non-inverting side are equal, the output voltage of the differential amplifier (12) It will be in a state where it is not affected by the amount.

Therefore, the same voltage as the DC voltage (Vl) output from the C/V conversion means at the cylinder stroke where the capacitance value of the capacitor (C) is maximum or minimum is applied to the non-inverting side input terminal (ε). This allows the amplification degree and offset voltage of the differential amplifier (12) to be adjusted separately.

〔Effect of the invention〕

Therefore, by simple modification of the device, it has become possible to easily adjust errors in the capacitance value of the capacitor caused by manufacturing errors, errors in the rate of change of the capacitance value with respect to stroke changes, etc.

〔Example〕

Embodiments in which the present invention is applied to a stroke detection device for a hydraulic cylinder will be described below with reference to the drawings.

As shown in FIG. 2, a metal piston rod (1) is telescopically fitted along the longitudinal direction of a metal cylinder case (2), and a recess is formed on the inner surface of the piston rod (1). An entry portion (3) is formed along its longitudinal direction.

A resin insulator (5) press-fitted inside the end (2A) of the cylinder case (2) is provided, and a cylindrical metal sensor rod (4) is inserted into the recess (3).
) is movably inserted into the sensor rod (
One end of 4) is press-fitted and fixed to the insulator (5). In the figure, (6) is an insulating layer of dielectric material provided so as to cover the outer surface of the sensor rod (4),
It is formed using a so-called heat shrink tube or the like.

That is, the recess (3) formed on the inner surface of the piston rod (1) and the sensor rod (4) act as a pair of electrodes that are relatively displaced, so that the piston rod (1) As the case (2) expands and contracts along the longitudinal direction, the capacitance value of the capacitor (C) formed between the inner surface of the recess (3) and the outer surface of the sensor rod (4) increases. , is configured to increase or decrease in inverse proportion to the cylinder stroke.

However, since the piston rod throat (1) expands and contracts while in contact with the cylinder case (2), when the cylinder case (2) is grounded, the sensor rod (1) and the capacitor (C) A capacitance value of the capacitor (C) is connected to a C/V conversion circuit (7) as a C/V conversion means for converting the capacitance value of the capacitor (C) to a DC voltage (Vl) through an output line (8). is detected as a value relative to ground.

The C/V conversion circuit (7) is integrally assembled into the end (2A) of the cylinder case (2) in a state where it is potted with resin or the like.

As shown in FIG. 1, the C/V conversion means (7) includes an oscillator (9) that outputs a signal of a constant frequency (f), and a Schmitt trigger circuit (10) that receives the output signal of the oscillator (9). ), a charge pump circuit (11) as a charging/discharging means for repeatedly charging and discharging the capacitor (C) at a set cycle in synchronization with the output signal of the Schmitt trigger circuit (10), and the charge pump circuit (11). is connected to the DC voltage (C) according to the capacitance value of the capacitor (C).
The differential amplifier (12) adjusts the offset of the DC voltage (vl) generated across the resistor (R) and amplifies it at a set amplification degree. (, E, L) The resistor (l?) is provided with a temperature characteristic that is opposite to that of the capacitor (C), so that it can prevent fluctuations in the capacitance value of the capacitor (C) due to temperature fluctuations. It is designed to cancel out.

To explain, the DC voltage (Vl) output from the C/V conversion circuit (7) is as shown in equation (i) below.
Input frequency to the Schmitt trigger circuit (10)<f
”), the capacitance value of the capacitor (C), and the resistance (R)
The structure is such that the value is proportional to the product of

v, = to -f-C-R... (i) However, in the above formula, K is a proportionality constant.

In other words, the temperature characteristics of the resistor (R) are
If the temperature characteristics of the capacitor (C) are reversed, the temperature characteristics of the capacitor (C)
) can accurately cancel out variations in capacitance due to temperature.

By the way, the capacitance value of the capacitor (C) is maximum when the piston rod (1) is most compressed, and the state where the capacitance value is maximum is the reference position of the cylinder stroke. Therefore, the DC voltage (V) is inversely proportional to the cylinder stroke. or,
Since the capacitance value does not become zero even in the state where the cylinder stroke is maximum, the DC voltage (Vl
) does not become zero. In addition, the capacitance value will not be the same for the same stroke due to manufacturing errors, etc.
The C/V is adjusted such that the DC voltage (Vl) is zero at the reference position where the cylinder stroke is zero, and the same voltage is at the position where the cylinder stroke is maximum.
It becomes necessary to adjust the DC voltage (Vl) output by the conversion circuit (7). The adjustment is performed using the differential amplifier (12).

To explain, the output voltage (
Vo) is a variable variable that adjusts the amount of negative feedback by the difference between the voltage (ε) of the non-inverting input terminal (i1) and the voltage (Vi) of the inverting input terminal (i-), as shown in equation (ii) below. Resistance (Ilf
) is amplified with an amplification degree set based on the value of .

Note that each resistor in the above formula (ii) corresponds to the symbol attached to each resistor shown in FIG. 1, and a description thereof will be omitted.

Therefore, when the voltage (ε) of the non-inverting input terminal (i1) and the voltage (Vi) of the inverting input terminal (i-) are the same value, the output voltage (Vo) is larger than the variable resistor CRf>
Regardless of the value of , that is, the degree of amplification, the state can be uniquely determined by the voltage (ε) of the non-inverting input terminal (i1).

Therefore, the input voltage (Vi
) is connected so that it becomes the DC voltage (vl) output from the C/V conversion circuit (7), and the voltage (ε) of the non-inverting side input terminal (i1) becomes the voltage for offset adjustment, When the voltage (ε) of the non-inverting side input terminal (i1) is adjusted so that the input voltages (ε) and (Vi) to both the input terminals (i1) and (i-) are equal, the differential amplifier The value of the output voltage (Vo) in the state where the offset, that is, the cylinder stroke is zero, can be adjusted independently without being affected by the change in the degree of amplification (12) (see FIG. 3).

In Fig. 1, (Cs) is a smoothing capacitor for the DC voltage (Vl), and (Rx) and (Ry) are capacitors for adjusting the input voltage (ε) to the non-inverting input terminal (i1). It is a resistor that divides the power supply voltage.

[Another example]

In the above embodiment, the output (Vl) of the C/V converter (7) is input to the inverting input side of the differential amplifier (12), and the voltage (ε) for offset voltage adjustment is input to the non-inverting input side. Although the case where this is done is illustrated, the input voltage to the differential amplifier (12) may be reversed between the inverting input side and the non-inverting input side. Further, the negative feedback circuit of the differential amplifier (12) may be simplified as shown in FIG.

Further, in the above embodiment, the stroke and the capacitance value of the capacitor (C) are configured to be inversely proportional to each other, and the differential amplifier (1
Although the case where the offset voltage in 2) is adjusted in the state where the capacitance value of the capacitor (C) is the maximum is illustrated, it is configured so that the cylinder stroke and the capacitance value of the capacitor (C) are directly proportional. , the capacitance value may be adjusted in a state where the capacitance value is the lowest.

Further, in the above embodiment, the case where the insulation N (6) made of dielectric material is provided on the outer surface of the sensor iron (4) is exemplified, but the recess (3) formed inside the piston iron (1) is
It may be provided on the inner surface of the.

Further, in the above embodiment, the present invention is applied to a cylinder stroke detection device, but the present invention can be applied to various stroke detection devices, and includes a pair of electrodes (3) that are relatively displaced.

The specific structure of (4), its mounting structure, etc., and the specific structure of each part necessary for carrying out the present invention can be changed in various ways.

Incidentally, although reference numerals are written in the claims section for convenient comparison with the drawings, the present invention is not limited to the structure shown in the accompanying drawings.

[Brief explanation of drawings]

The drawings show an embodiment of the capacitive stroke detection device according to the present invention, FIG. 1 is a circuit diagram showing the configuration of the C/V conversion means, FIG. 2 is a longitudinal sectional view of the cylinder, and FIG. A characteristic diagram of the output voltage of the C/V conversion circuit with respect to the capacitance value of the capacitor, and FIG. 4 is an explanatory diagram of the differential amplifier. (3), (4)... a pair of electrodes, (7).
...C/V conversion means, (12)...Differential amplifier, (i1), (i-)...Input terminal, (C)... Capacitor, (V,), (ε)・
...DC voltage.

Claims (1)

[Claims] A DC voltage (
This is a capacitance type stroke detection device equipped with a C/V conversion means (7) that outputs a C/V conversion means (7) that outputs a differential amplifier (12 ) is provided, and one input terminal (i-) of the differential amplifier (12) is provided with the C/V conversion means (7).
The DC voltage (V_1) outputted by the capacitor (C) is input to the other input terminal (i+) of the differential amplifier (12) in a state where the capacitance value of the capacitor (C) is maximum or minimum. A capacitive stroke detection device to which a DC voltage (ε) having the same value as the DC voltage (V_1) outputted by the /V conversion means (7) is input.