JPS5931012B2 - AC bridge type displacement detection device that can detect abnormalities - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC bridge type displacement detection device that detects the displacement of the core by measuring the unbalance of the AC bridge circuit based on the impedance change of the detection coil due to the displacement of the core. The purpose of this is to enable the detection of disconnections in bridge circuits, abnormalities in applied voltage, etc.

Conventionally, in order to measure the diameter of a workpiece, first and second cores connected to ten contactors are inserted into the workpiece.
detection coil, and a first detection coil connected to both of these detection coils.
, and a second fixed coil to form an AC bridge circuit, and an AC voltage is applied between the connection part of both detection coils and the connection part of both fixed coils, and the voltage between both detection coils is By measuring the voltage, the displacement of the core and thus the diameter of the workpiece is determined.

However, according to this, for example, if the voltage between both detection coils is zero, is this because the displacement of the core is zero?
It is unclear whether this is due to a disconnection in the AC voltage application section 20,
It was not possible to detect a defect in the AC bridge circuit. The present invention has been made to solve such conventional problems, and embodiments thereof will be described below with reference to the drawings.

251, 2 are the first and second with the same shape and electromagnetic characteristics.
The detection coils are arranged in series with each other.

Reference numeral 3 denotes a core inserted into the inner holes of the first and second detection coils, and is connected to a contact that comes into contact with the outer diameter of the workpiece, for example, so as to be variable by about 30 degrees depending on the diameter of the workpiece. It's summery.

One end of each of the first and second detection coils 1 and 2 is connected to one end of each of first and second fixed coils 4 and 5 having the same impedance, thereby forming an AC bridge circuit. The other ends of both detection coils 1 and 2 are connected to each other and
It is connected to one terminal of the AC applying power source 6, and the other ends of both fixed coils 4, 5 are connected to each other and connected to the other terminal of the AC applying power source 6. Therefore, if the voltage applied by the AC power supply 6 is 2E, then the first
, the voltage at each end of the second detection coils 1 and 2 is (
E+ΔE), (E−ΔE), and one end of each is connected to the + side terminal and one side terminal of the differential amplifier 7, respectively, so the output terminal of the differential amplifier 7 is connected to the core 3. Therefore, the voltage 2ΔE corresponding to the diameter of the workpiece is detected. One end of each of the first and second detection coils 1 and 2 is connected to the input terminal of a voltage follower operational amplifier 8 and 9, which detects an output voltage equal to the input voltage and has an extremely large input impedance. The respective output terminals of the amplifiers 8 and 9 are connected in parallel to the input terminal of a voltage follower operational amplifier 12 via mutually equal resistors 10 and 11.

Therefore, the voltage at the output terminal of this operational amplifier 12 is half the sum of the voltages at each end of both detection coils 1 and 2 {(E+△E)+
(E-△E)}×Z=E, which is constant regardless of the displacement of the core 3. Arithmetic amplifier 8 for these voltage followers
, 9, 12 and resistors 10, 11, an adding circuit 1 that adds the voltages at each end of the first and second detection coils 1 and 2.
3 are made up. Reference numeral 14 denotes a field effect transistor constituting an analog switch, whose source is connected to the output terminal of the voltage follower operational amplifier 12, and whose gate is connected via a diode 15 to the single-power terminal of the AC applying power source 6. are connected, and a constant voltage v is connected in parallel via a resistor 16, and a capacitor 18 is connected to the drain via a resistor 17.

These transistor 14, diode 15, resistor 16,
17 and the capacitor 18 constitute a rectification and smoothing circuit 19 that rectifies and smoothes the output voltage of the adder circuit 13. The output terminal of the rectifying and smoothing circuit 19, that is, one end of the resistor 17, is connected to the ten side terminal and the one side terminal of operational amplifiers 20 and 21 constituting the first and second comparators, respectively. Arithmetic amplifier 2 that constitutes a comparator
The upper limit value (E+
A divided voltage is applied to δ), and a voltage divided to the lower limit value (E-δ) by resistors 24 and 25 is applied to the positive terminal of the operational amplifier 21 constituting the second comparator. is applied.

The output terminals of the operational amplifiers 20 and 21 are connected to diodes 26 and 2.
An abnormality detection relay 29 is connected between the collector of the transistor 28 and the constant voltage v. These operational amplifiers 20 and 21, resistors 22 to 25, and diodes 26 and 27
, transistor 28, and relay 29 constitute a determination circuit 30 that sends out an abnormality signal when the output voltage from the rectification and smoothing circuit 19 exceeds an upper limit value or a lower limit value. Next, the operation of the above embodiment will be explained.

When the core 3 is displaced according to the diameter of the workpiece, the impedance of the first and second detection coils 1 and 2 changes, and their output voltages become (E + △E) and (E - △E), respectively, and both voltages is subtracted in the differential amplifier 7, and a voltage 2ΔE corresponding to the diameter of the workpiece is output from its output terminal. On the other hand, each output voltage of the first and second detection coils 1 and 2 is applied to the voltage follower operational amplifiers 8, 9, 12 of the adder circuit 13.
and is arithmetic averaged by resistors 10 and 11, and a constant voltage E is output from the output terminal of the operational amplifier 12 regardless of the displacement of the core 3.

The output voltage E from the operational amplifier 12 is transmitted to the rectifying and smoothing circuit 19.
is synchronously rectified by the transistor 14 of the capacitor 18vr. The signal is thus smoothed and applied to the operational amplifiers 20 and 21 of the determination circuit 30. Disconnection of AC bridge circuit,
If there is no abnormality in the applied lightning pressure, the output E from the rectifier and smoothing circuit 19 is the upper limit value (E + δ) or the lower limit value (E - δ).
is not exceeded, no output is sent from the operational amplifiers 20 and 21, and the transistor 28 is not conductive.
The relay 29 is not energized and the determination circuit 30 does not send out an abnormality signal. In this case, the rectifier smoothing circuit 1
Even if the output voltage E from 9 changes slightly due to temperature change, etc., if it is within the range between the upper limit value and the lower limit value, the judgment circuit 30
No abnormal signal is sent. On the other hand, for example, if the detection coil 1 connected to the non-grounded side of the AC applying power source 6 is disconnected, the output voltage of the detection coil 1 becomes O, and the output voltage of the detection coil 2 (E - △E) Therefore, the output from the adder circuit 13 becomes (E-ΔE)/2, and the output from the rectifying and smoothing circuit 19 becomes less than or equal to the lower limit value (E-δ).

As a result, an output is sent from the operational amplifier 21, the transistor 28 is made conductive, the relay 29 is energized, and the determination circuit 30 sends out an abnormality signal. On the other hand, if the fixed coil 4 connected to the ground side of the AC applying power source 6 is disconnected, the output voltage of the detection coil 1 will be 2E, so the output from the adder circuit 13 will be (3E-△E)~ Therefore, the output from the rectifying and smoothing circuit 19 becomes equal to or higher than the upper limit value (E+δ).

As a result, in this case, an output is sent from the operational amplifier 20, the transistor 28 is made conductive, and an abnormality signal is sent out in the same manner as described above. In the above embodiment, a fixed coil is connected to the detection coil to form an AC bridge circuit, but a bridge circuit may be formed by connecting a resistor to the detection coil.

As detailed above, in the present invention, the output voltages output from a pair of opposing terminals of a bridge circuit are added together and rectified and smoothed, and when this rectified and smoothed voltage exceeds an upper limit value or a lower limit value, Since an abnormality signal is sent out, a disconnection in the AC bridge circuit or an abnormality in the applied voltage can be detected regardless of the displacement of the core. In addition, since the AC signal output from the adder circuit is rectified by an analog switch that is opened and closed by the AC voltage applied to the bridge circuit, there is almost no voltage drop in the rectifier circuit, and the The amount of voltage drop does not change due to changes in temperature.

Therefore, even if the output of the adder circuit is below the forward voltage drop of the diode, it is possible to detect a disconnection in the detection coil, etc., and the output of the smoothing circuit does not fluctuate due to changes in ambient temperature, so There is an advantage that the width between values can be set narrowly, and it is possible to detect at an early stage that a detection coil or the like is about to break. Furthermore, a first comparator outputs a signal with a specific polarity when the smoothed voltage exceeds the upper limit, and a signal with the same polarity as the first comparator when the smoothed voltage falls below the lower limit. Since a second comparator is provided, there is an advantage that the circuit that outputs the abnormal signal in response to the signal output from the comparator only needs to be a circuit that responds to a single polarity signal. .

[Brief explanation of drawings]

The drawing is a circuit diagram showing an AC bridge type displacement detection device capable of detecting an abnormality according to the present invention. 1, 2...first and second detection coils, 3...core,
4, 5... First and second fixed coils, 6... AC applied power source, 7... Differential amplifier, 13... Adder circuit, 1
9... Rectification smoothing circuit, 30... Judgment circuit.

Claims (1)

[Claims] 1 A pair of detection coils with substantially equal electromagnetic characteristics and whose impedance changes depending on the displacement of the internal core are arranged on two sides of a bridge circuit, and an alternating current is applied between a pair of opposing connection points on one side of the bridge circuit. In the AC bridge type displacement detection device, the displacement of the core is detected by applying a voltage, one of which is grounded, and the other of which is measured between a pair of opposing connection points to detect displacement of the core. An adder circuit that adds the voltages at the other pair of connection points, a rectifier circuit connected to the output of this adder circuit, a smoothing circuit connected to the output of this rectifier circuit, and an adder circuit that adds the voltages of the other pair of connection points. a first comparator that determines that the grounding side of the bridge circuit is disconnected due to exceeding the lower limit value and outputs a signal; a second comparator that outputs a signal upon determining that the side edge is disconnected; and an output circuit that outputs an abnormal signal when a signal is output from either the first comparator or the second comparator. An AC bridge type displacement detection device capable of detecting an abnormality, characterized in that it is provided with: