CN201463833U - Capacitive angle sensor - Google Patents

Abstract

A capacitor type angle sensor comprises a front pole plate, a shaft, a ceramic medium, a rear pole plate and a gasket, wherein the ceramic medium is fixed on the shaft, the front pole plate and the rear pole plate penetrate through the shaft and keep a gap between the pole plates fixed through the gasket and the same as the gap of the ceramic medium, the front pole plate and the rear pole plate are made of hydrocarbon ceramic materials, an excitation signal circuit is arranged on the front pole plate, an external automatic gain control circuit provides an excitation power supply for the excitation signal circuit, and a capacitor differential amplitude modulation circuit is arranged on the rear pole plate. The utility model discloses a hydrocarbon ceramic polar plate material of low linear expansion coefficient has effectively reduced capacitanc angle sensor inherent temperature drift, sets up excitation signal circuit and electric capacity difference amplitude modulation circuit respectively on the bipolar plate, has simplified the structure of sensor, and excitation signal circuit produces the excitation signal of higher frequency, has improved the sensitivity and the angle precision of sensor, utilizes outside automatic gain control circuit simultaneously, makes the sensitivity of sensor unchangeable basically under the high temperature condition.

Description

A capacitive angle sensor

technical field

The utility model relates to a capacitive angle sensor, in particular to a high-sensitivity low-temperature drift capacitive angle sensor, which can be used as a non-contact limited-angle angle measuring sensor in an industrial-grade temperature (-40°C to +85°C) environment. Angle sensor for the motor.

Background technique

At present, the capacitive angle sensors used at home and abroad are divided into variable gap, variable area, variable medium, etc. At the same time, the differential structure is also used, but there will be temperature drift phenomenon. Due to the characteristics of the capacitor itself, the polar plate under high temperature conditions The deformation of the material, the change of the gap between the plates, the change of the effective area between the plates, and the inherent temperature characteristics of the components will all bring about temperature drift. The angle sensor used on the frame scan motor is a servo system with very strict requirements on the angular position. It is required that the input control voltage and the position feedback be strictly proportional to a certain ratio within the industrial temperature range. If the angle sensor has a large temperature drift It will directly affect the scanning accuracy of the motor.

Utility model content

The technical solution of the utility model is to overcome the deficiencies of the prior art and provide a capacitive angle sensor with simple structure, low temperature drift and high sensitivity.

The technical solution of the utility model is: a capacitive angle sensor, including a front plate, a shaft, a ceramic medium, a back plate, a gasket, the ceramic medium is fixed on the shaft, and the front plate and the back plate pass through the shaft The gap between the plates is kept fixed by the spacer, and the same gap as that of the ceramic medium is maintained. The front plate is a 1/4 fan-shaped plate, and the shape of the ceramic medium is the same as that of the front plate. The front plate and the The rear pole plate is made of hydrocarbon ceramic material, and the capacitance differential amplitude modulation circuit is set on the front pole plate to convert the output capacitance of the angle sensor into a voltage value. The excitation signal circuit is set on the rear pole plate to provide the excitation signal for the angle sensor. The excitation power is provided by the external automatic gain control circuit.

The front plate and the rear plate are made of RO4350B hydrocarbon ceramic material.

The frequency of the excitation signal generated by the excitation signal circuit in the rear pole plate is 2Mhz, and the peak-to-peak value is 500V.

The gasket and the shaft are made of titanium alloy.

Compared with the prior art, the utility model has the beneficial effects that: the utility model effectively reduces the inherent temperature drift of the capacitive angle sensor by adopting the hydrocarbon ceramic plate material with a low linear expansion coefficient, and the two pole plates are respectively arranged The excitation signal circuit and the capacitor differential amplitude modulation circuit simplify the structure of the sensor. The excitation signal circuit generates a higher frequency excitation signal, which improves the sensitivity and angle accuracy of the capacitive angle sensor. At the same time, the external automatic gain control circuit is used to make the capacitive angle The sensor's sensitivity remains essentially unchanged at high temperatures, reducing the capacitive angle sensor's previous drift of 50 arc minutes to 2 arc minutes over the industrial temperature range.

Description of drawings

Fig. 1 is the structural representation of the utility model;

Fig. 2 is the plan view of the utility model front plate;

Fig. 3 is the plane view of the rear plate of the utility model;

Fig. 4 is the utility model electric capacity difference amplitude modulation circuit diagram;

Fig. 5 is the utility model excitation signal circuit diagram;

Fig. 6 is the automatic gain control circuit diagram that the utility model adopts;

Fig. 7 is a schematic diagram of the high and low temperature drift test of the utility model.

Detailed ways

As shown in Figure 1, the shaft 2 is installed on the motor in advance, and the front plate 1 shown in Figure 2 is positioned on the bottom plate shell of the motor through two pins, and then the ceramic medium 3 is set on the shaft 2, Use four gaskets 5 to fix the gap between the front plate 1 shown in Figure 2 and the rear plate 4 shown in Figure 3, and fix and tighten with screws, and connect the signal of the external circuit control board to the sensor through the DB9 connector , constitute the entire angle measurement system, and finally fix the ceramic medium 3 and the shaft 2 with a top wire, and ensure that the gaps d1 and d2 between the ceramic medium 3 and the two pole plates are the same. Wherein the shape of the front pole plate 1 shown in Figure 2 is a 1/4 fan-shaped pole plate, the shape of the ceramic medium 3 is the same as the shape and size of the front pole plate 1 shown in Figure 2, and the shaft 2 drives the ceramic medium 3 to rotate, so that The plate area of the capacitive angle sensor shown in Figure 1 changes, so that the output capacitance value can be changed to measure the angle. The capacitive angle sensor is a differential plate capacitor composed of two parallel metal plates separated by an insulating medium. The rotating ceramic medium 3 forms a medium between the two fixed plates. Its rotation causes the change of the medium, and the capacitance also changes accordingly. , and then the capacitor differential amplitude modulation circuit 6 provided on the front plate 1 performs voltage conversion of the capacitance values of the two capacitors, and then uses differential amplification to convert the rotation angle of the ceramic medium 3 into a voltage, and the two signals are amplified by the differential. The reference voltage forms an automatic gain control circuit to provide excitation power for the excitation signal circuit 7 on the rear plate 4 .

At present, domestic pole plates generally adopt ceramic materials with low temperature linear expansion coefficients, or quartz materials. Since the rear pole plate 4 of the sensor also has an excitation signal circuit 7, and the front pole plate 1 is provided with a capacitance differential amplitude modulation circuit 6, Therefore, the front and rear plate materials adopt high-frequency composite ceramic materials with low dielectric constant and low linear expansion coefficient. The utility model mainly adopts RO4350B hydrocarbon ceramic materials.

The utility model is provided with a capacitor differential amplitude modulation circuit 6 on the front plate 1, as shown in Figure 4, the circuit is composed of four diodes D1, D2, D3, D4 and capacitors C1, C2, and the differential capacitor S1 is connected to the diode D1 or D2 The rectifier circuit composed of C1 and C1 is converted into a voltage signal V1, and the differential capacitor S2 is converted into a voltage signal V2 through a rectifier circuit composed of a positive diode D3 or D4 and C2, and the capacitors C1 and C2 act as filters.

随着频率升高，容抗减小，输出电压增大，传感器灵敏度的提高依靠传感器激磁信号的频率，所以提高激磁频率也就意味着提高传感器的灵敏度，高变压比将交流信号峰峰值放大到几百伏，这样的信号在两路差分电容极板上感应出峰峰值几伏的同频率交流信号，本实用新型激磁信号电路产生的激磁信号频率为2Mhz、峰峰值为500V。The utility model is provided with an excitation signal circuit 7 on the rear pole plate 4, as shown in Figure 5, the circuit is composed of resistors R10, R11, triodes Q3, Q4 and pot-type magnetic core transformer JP2, and the circuit can pass through the pot-type magnetic core transformer JP2 outputs excitation oscillation signal, the circuit adopts self-excited push-pull type to generate high-frequency AC signal, and the excitation frequency is changed by changing the inductance of transformer JP2 magnetic core, due to capacitive reactance

As the frequency increases, the capacitive reactance decreases, the output voltage increases, and the improvement of sensor sensitivity depends on the frequency of the sensor excitation signal, so increasing the excitation frequency means improving the sensitivity of the sensor, and the high transformation ratio will amplify the peak-to-peak value of the AC signal To hundreds of volts, such a signal induces an AC signal with a peak-to-peak frequency of several volts on the two-way differential capacitance plates. The frequency of the excitation signal produced by the excitation signal circuit of the utility model is 2Mhz, and the peak-to-peak value is 500V.

The input voltage AGC of the excitation signal circuit 7 shown in Figure 5 is output by the AGC circuit shown in Figure 6, and the AGC circuit is composed of variable resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, variable resistor R6, resistor R7, resistor R8, resistor R9, an inverse proportional amplifier circuit composed of diode D5, capacitor C3 and operational amplifier LM324, and a triode Q1. Both ends of variable resistor R1 are connected to ±5 volts, and one end of resistor R7 is connected to -5 The other end is connected to the volt input terminal of the amplifier LM324, resistor R2, resistor R3, resistor R4, resistor R5, capacitor C3 and the positive pole of the diode D5, the collector of the triode is connected to a positive 15 volt voltage, and the positive input terminal of the amplifier LM324 is grounded .Improving the sensitivity of the utility model is an important means of reducing temperature drift. Only when the sensitivity is high can the capacitance be sensitive to small changes. An automatic gain control circuit (i.e. AGC) is used to correct the sensitivity of the sensor. The working principle of the circuit is: When the ambient temperature rises, due to the reduction of the expansion capacitance gap of the plate material, the capacitance increases, and the two-phase amplitude modulation signals V1 and V2 in the accompanying drawing 4 also increase, which are correspondingly amplified into the circuit in the accompanying drawing 6 after low-pass filtering. VA and VB, VA and VB and the reference voltage are summed, the error obtained is reduced, the error is integrated, and the integration result is connected to the base of the transistor Q1, the transistor amplifies the current and outputs the AGC voltage to the capacitor through the resistor R9 The angle sensor is used as the excitation power supply, and the excitation voltage becomes smaller, and the signals VA and VB after the two amplitude modulations also decrease, so the AGC circuit can always ensure that the sensitivity of the sensor remains unchanged, that is, the VA and VB remain unchanged.

The components of the utility model adopt low-temperature drift components, the detection diodes D1, D2, D3, D4, and D5 all use array diodes, the operational amplifier LM324 adopts industrial-grade four-operation amplifiers, and the remaining resistors and capacitors all use temperature coefficients of 50ppm/ Components below ℃.

Carry out the high and low temperature drift test to the utility model, the test principle is shown in Figure 7, the capacitive angle sensor described in the utility model is installed on the frame scanning motor 72 and put into the high and low temperature box 71 with the circuit control board, the frame scanning The motor 72 is powered on, and the laser beam sent by the laser 73 passes through the glass 74 of the high and low temperature box and hits the motor load lens 75, and is reflected on the opposite coordinate paper 76. After energizing at room temperature for 5 minutes, use a precision DC current regulator to adjust the given voltage value U1 (given ±5V, ±7V, ±9V in this test), and draw the corresponding values of these 6 voltage values on the coordinate paper 76. Engraved markings, turn off the machine after marking. Then first heat at +60°C, keep warm for 1 hour, and then use a precision DC current stabilizer to adjust the given voltage value U1 (given ±5V, ±7V, ±9V in this test), and record the corresponding output voltage U2′ (Table 1 middle pin 3). Observe the position of the light spot, make a mark on the coordinate paper 76, and turn off the machine after marking. At this time, there is a change between the position of the mark and the position of the mark at room temperature. After measuring the difference on the coordinate paper, divide it by the corresponding point to get The distance from the mirror is the radian value of the drift, and then converted into an angle value and recorded as a (a has a plus or minus sign, and the unit is arc minutes), a is the angle drift value corresponding to the input voltage at a temperature of +60°C. Bring in the formula |U2-U2'|×120'-a to calculate the drift position accuracy (U2 is the output voltage corresponding to the same U1 at room temperature). In the case of high temperature and heat preservation, the voltage output by the AGC circuit has been decreasing, that is, due to the influence of high temperature, the sensitivity of the capacitive angle sensor has changed, and there has been drift. The AGC circuit has been correcting the sensitivity of the sensor, and the light spot drifted before. 50 arc minutes, now the drift is within 2 arc minutes, and the temperature drift is greatly reduced, that is, the low temperature drift capacitive angle sensor is realized.

The content not described in the utility model is the well-known technology of those skilled in the art.

Claims (4)

1. A capacitive angle sensor, characterized in that: comprising front plate (1), shaft (2), ceramic medium (3), rear plate (4), gasket (5), ceramic medium (3) Fixed on the shaft (2), the front plate (1) and the rear plate (4) pass through the shaft (2) through the gasket (5) to keep the gap between the plates fixed, and maintain the contact with the ceramic medium (3) The gap is the same, the front plate (1) is a 1/4 fan-shaped plate, the shape of the ceramic medium (3) is the same as that of the front plate (1), the front plate (1) and the rear plate (4) The hydrocarbon ceramic material is used, and the capacitance differential amplitude modulation circuit (6) is set on the front plate (1) to convert the output capacitance of the angle sensor into a voltage value, and the excitation signal circuit (7) is set on the back plate (4). The angle sensor provides an excitation signal, and the excitation signal circuit (7) is provided with excitation power by an external automatic gain control circuit. 2. A capacitive angle sensor according to claim 1, characterized in that: said front plate (1) and rear plate (4) are made of RO4350B hydrocarbon ceramic material. 3. A capacitive angle sensor according to claim 1, characterized in that: the excitation signal generated by the excitation signal circuit (7) in the rear plate (4) has a frequency of 2Mhz and a peak-to-peak value of 500V. 4. A capacitive angle sensor according to claim 1, characterized in that: said gasket (5) and shaft (2) are made of titanium alloy.

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