JPH0629816A - Proximity switch - Google Patents

Abstract

PURPOSE:To detect a partial break of a coil raw wire in the proximity switch having a detection coil using Litz wires formed by twisting plural coil raw wires. CONSTITUTION:An oscillation circuit 16 is oscillated intermittently by an intermittent oscillation control circuit 14. A DC voltage applied to a detection coil L is applied to a comparator circuit 22 when the oscillation is stopped. When the level exceeds a prescribed value, it is regarded that the wire is partially broken and a broken wire diagnostic signal is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency oscillation type proximity switch having a function of detecting an abnormality due to a broken wire of a coil.

[0002]

2. Description of the Related Art In a conventional high frequency oscillation type proximity switch, for example, as shown in the sectional view of FIG. 6A, one end of a cylindrical case 1 is used as a detection surface 1a, and a ferrite core 2 is provided inside the detection surface. Mounted. The detection coil 3 is mounted in the annular groove of the ferrite core 2. An electronic circuit including an oscillation circuit that oscillates at the resonance frequency of the resonance circuit including the detection coil 3 and a detection circuit unit that detects a decrease in the oscillation level or a change in the frequency is mounted on the printed board 4. There is. Filling resin 5 is filled in the void portion of case 1. Here, the detection coil 3 is a litz wire in which a plurality of coated strands (copper wires of 0.1 mmφ or less) are twisted together.

In the proximity switch for detecting the oscillation amplitude, the admittance Y of the parallel resonance circuit in the equivalent circuit of the detection coil is shown by the following equation as shown in FIG. Y = (C · r) / L where r is approximately equal to the conductor resistance of the coil wire. When the metal object approaches, the loss r of the coil increases and the admittance Y increases, so that the approach of the metal object can be detected. Conductance g which is the real part of this admittance
The relationship between the distance to the object and the distance to the object is shown by the curve A in FIG.

A proximity switch is also known which detects the proximity of an object by changing the frequency of an oscillation circuit. Figure 8 (a)
FIG. 3 is a circuit diagram showing an example of this oscillator circuit. In the figure, a series connection body of an oscillation coil L and capacitors C11 and C12 is connected in parallel between the collector of the transistor Q1 and the power supply terminal, and the midpoint of the capacitors C11 and C12 is fed back to the emitter side of the transistor Q1.
Further, the voltage dividing circuit of the resistors R11 and R12 is connected to the base of the transistor Q1 to supply a bias current. Here, the detection coil L has an inductance L1 and a DC resistance r
Set to 1. Then, when an object comes close to the detection coil, FIG.
As shown in (b), the object can be equivalently represented by the coil L2 and the DC resistance r2. Here, if the mutual conductance is M, the impedance seen from both ends of the oscillation coil can be expressed by using Rx and Lx as shown in FIG. When a magnetic metal, such as iron, approaches the detection object, the changes in the resistance and inductance of the detection coil become Rx (iron)> Rx, Lx (iron)> Lx, which is compared to the state without the detection object. As a result, the oscillation frequency decreases and the amplitude decreases. Further, when a non-magnetic metal such as aluminum approaches, the resistance and inductance changes of the detection coil are Rx (Al) ≈Rx and Lx (Al) <Lx. As a result, the oscillation frequency rises and the oscillation amplitude does not change as compared with the case where there is no detection object.

[0005]

However, the conventional high-frequency oscillation type proximity switch is often used to detect the arrival of a metal body in an assembly and transportation line of a factory. Therefore, when the clearance between the movable area of the detection object 6 and the detection head is not sufficiently secured or the area of the detection object 6 is shaken, the detection object 6 may approach and contact the detection surface of the case. In addition, when it is attached to the aluminum cutting machine, the cut aluminum chips are accumulated on the detection surface of the proximity switch, and the chips are rubbed against the detection surface each time the detection object 6 passes. Therefore, as shown in FIG. 6B, a part of the case may be missing and the coil 3 may be disconnected. Also, the environment in which the proximity switch is used is harsh, and it is often used in a wide range, for example, at an ambient temperature of -25 ° C to 70 ° C. It may also be used in locations where hot oil directly impinges on the proximity switch. Therefore, as shown in FIG. 6, the filling resin 5 is filled in the case 1, but stress due to expansion and contraction of this resin is applied to the coil winding portion. Therefore, the litz wire of the detection coil 3 may be partially broken. In the curve of FIG. 7B, if one of the coil wires is broken, the curve A
Changes from, for example, a curve B. Further, as the number of wire breaks further increases, the conductance gradually increases as shown by the curve C. FIG. 7C is a graph showing changes in conductor resistance with respect to the number of coil strands. Therefore, eventually, even if the detected object does not approach due to the increase in the number of wire breakages, the oscillation stops and the object detection signal is continuously output.

Further, also in the frequency detection type oscillation circuit, when a part of the coil wire is broken, the resistance component Rx of the coil becomes higher than the original Rx. Therefore, the oscillation frequency increases and the amplitude decreases as compared to the case where there is no detection object. Therefore, the disconnection may increase the oscillation frequency even though there is no detection object, and a signal for detecting a metal object may be output.

The present invention has been made in view of such conventional problems, and it is a technical problem to provide a predictive signal when the coil wire is partially disconnected. And

[0008]

The invention according to claim 1 of the present application has an oscillating circuit including a coil formed by twisting a plurality of coated coil element wires, and changes in the oscillating output of the oscillating circuit. A proximity switch for detecting an object based on a feature of detecting a partial disconnection of a twisted wire based on a change in a DC resistance of a coil when an oscillation of an oscillation circuit is stopped.

According to a second aspect of the present invention, an oscillation circuit including a coil formed by twisting a plurality of coated coil wires, an intermittent oscillation control circuit for driving the oscillation circuit at a predetermined interval, and an intermittent oscillation control circuit. A proximity switch having a counting circuit that counts the number of output pulses of the oscillation circuit for each oscillation, and a disconnection wire that detects the voltage level of the detection coil when the oscillation circuit of the oscillation circuit is stopped by the control signal of the intermittent oscillation control circuit. The present invention is characterized by including a detection unit and detecting partial disconnection of the oscillation coil based on the output of the disconnection detection unit.

In the invention of claim 3 of the present application, the oscillation circuit is
A series connection body of the first resistor and the first capacitor, a detection coil connected in parallel to the first capacitor and a series connection body of the second capacitor, and a second resistance connected in parallel to the second capacitor. , A logic circuit in which an oscillation control signal is applied to one input end, a connection point between the detection coil and the second capacitor is connected to the other input end, and an output end is connected to the first resistor. The output side of is connected to the input end of the counting circuit, and one end of the detection coil is connected to the input end of the disconnection detection unit.

[0011]

According to the present invention having such a feature, the disconnection is detected based on the DC resistance of the coil when the oscillation is stopped. In the invention of claim 2 of the present application, the oscillation circuit is oscillated intermittently by the intermittent oscillation control circuit. Then, the number of pulses during the oscillation is counted to identify the presence or absence of an object. Only the DC voltage is applied to the detection coil while the oscillation is stopped, and the voltage level changes depending on the DC resistance of the detection coil. Therefore, the voltage is detected to detect the disconnection. Further, in the invention of claim 3 of the present application, the oscillator circuit oscillates according to the logic level given to the input of the logic circuit by connecting the CR element to the output side of the logic circuit and further connecting the LC element in parallel with the capacitor. Have control. In this case, since the output side of the logic circuit is at the H level when the oscillation is stopped, it is possible to determine the DC resistance group, that is, the presence / absence of disconnection, by detecting the voltage at one end of the oscillation coil.

[0012]

1 is a block diagram showing the overall configuration of a proximity switch according to an embodiment of the present invention. In the figure, a constant voltage circuit 11 is connected to the power supply terminal 10. The constant voltage circuit 11 supplies a stabilized constant voltage Vs to each unit. This voltage is applied to the reference clock generation circuit 12, the intermittent pulse oscillation circuit 13, the intermittent oscillation control circuit 1 as shown in the figure.
4, applied to the timing signal generation circuit 15. This reference voltage is also given to the oscillation circuit 16. The reference clock generation circuit 12 generates a reference clock of a constant cycle, the intermittent pulse oscillation circuit 13 generates an intermittent pulse based on this signal, and its output is given to the intermittent oscillation control circuit 14. . Intermittent oscillation control circuit 1
Reference numeral 4 controls intermittent oscillation in the oscillator circuit 16.
The oscillating circuit 16 has an oscillating coil L and oscillates intermittently based on intermittent oscillation control, and its digital output is given to a counting circuit 17. The counting circuit 17 counts the number of oscillation pulses of the oscillation circuit 16 using the intermittent oscillation control signal as a gate signal, and the frequency is measured by the number of pulses between the gate signals. The output is given to the comparison circuit 18. The comparison circuit 18 discriminates the count value by a predetermined threshold value, and when a count output exceeding the predetermined count value is obtained, the comparison circuit 18 gives an output to the latch circuit 19. The latch circuit 19 holds a signal based on the output of the timing signal generation circuit, and the held signal is output as an object detection signal via the output circuit 20.

In the present embodiment, the DC voltage applied to the oscillation coil L of the oscillation circuit 16 is given to the diagnostic detector 21.
An output obtained by inverting the intermittent oscillation control signal of the intermittent oscillation control circuit 14 is given to the diagnosis detection section 21, and the DC voltage of the oscillation coil of the comparison circuit 22 is supplied while the output is given, that is, while the oscillation is stopped. It is compared with a threshold. When a signal exceeding this threshold is obtained, it is held by the latch circuit 23. The signal held by the latch circuit 23 is output to the outside as a disconnection detection signal via the disconnection diagnosis output circuit 24.

FIG. 2 is a circuit diagram showing the configuration of the oscillator circuit 16 of this embodiment. In the figure, the NAND circuit 31 is provided with an intermittent oscillation control signal from the intermittent oscillation control circuit 14 at one input terminal. The output terminal is grounded via the series connection body of the resistor R1 and the capacitor C1, and the midpoint thereof is grounded via the oscillation coil L and the capacitor C2. A resistor R2 is connected in parallel with the capacitor C2. Here, the AND circuit 31 is an oscillation amplifier of the oscillation circuit, and if the amplification factor is set to "1" or more, the intermittent oscillation control signal a becomes H.
It oscillates with a sine wave at the level. If there is another metal body near the oscillation coil L, this oscillation frequency changes depending on the distance. Since a square wave oscillation output is obtained at the output side of the NAND circuit 31, this is given to the counting circuit 17, and the oscillation coil L and the resistor R are provided.
Since a voltage level corresponding to the DC voltage of the oscillation coil L is obtained at the common connection end of 1, the output is given to the comparison circuit 22.

Next, the operation of this embodiment will be described. FIG. 3 is a time chart showing the waveform of each part of this embodiment. When the proximity switch starts operating, the intermittent pulse oscillating circuit 13 first oscillates an intermittent pulse by the output from the reference clock generating circuit 12. Therefore, the intermittent oscillation control circuit 14 outputs an intermittent oscillation control signal as shown in FIG. This signal simultaneously serves as a reference gate signal to the counting circuit 17. If there is no object as shown in FIG. 3A, it is assumed that the oscillation circuit 16 counts a constant frequency, for example, five pulses as shown in FIG. 3C. This count output is compared by the comparison circuit 18. Here, if the threshold value is set to 7, for example, the count output is less than this value, so L is output to the latch circuit 19. This signal is held by the latch timing signal as shown in FIG. 3 (f), and then the count value of the counting circuit 17 is reset by the reset signal shown in FIG. 3 (e).

Now, at time t _1, it is assumed that the non-magnetic metal aluminum is close to the vicinity of the detection coil. Then, since the oscillation frequency rises as described above, the number of pulses input to the counting circuit 17 is, for example, 7 or more as shown in FIG. 3C. 7
A comparison signal is obtained from the comparison circuit 18 at the time when is counted. This signal is held by the latch timing signal shown in FIG. Therefore, as shown in FIGS. 3 (g) and 3 (h), the object is held by the latch circuit, and the output circuit 20 outputs an object detection signal indicating that aluminum is detected.

Now, after time t _2, the non-magnetic metal does not approach,
It is assumed that one wire of the oscillation coil L is broken at time t ₃ . In this case, as described above, for example, 6 pulses are input to the counting circuit 17 from the oscillation circuit 16 during the intermittent pulse oscillation. At this time, the object detection signal is not output because it is equal to or less than the threshold value of the comparison circuit 18, but the malfunction state is approaching. Also if the coil wires has a plurality of disconnection at time t _4, the higher the more the oscillation frequency. Therefore, during the intermittent oscillation, for example, eight pulses are counted as shown in FIG. 3C, and the comparison circuit 18 outputs an output.
In this case, as shown in the figure, an incorrect object detection signal is output from time t ₅ .

Now, FIG. 4 shows the oscillator circuit 16 and the disconnection detector 2.
3 is a time chart showing a waveform of No. 1; As shown in the figure, the intermittent oscillation control signal a and the disconnection detection control signal b which is the inverted version thereof are output from the intermittent oscillation control circuit 14. When this control signal a is applied to the NAND circuit 31 shown in FIG.
The NAND circuit 31 becomes an inverter and the oscillation circuit 16 oscillates. At this time, the output side of the NAND circuit 31 is shown in FIG.
Although the square wave output shown in FIG. 4 is obtained, at the connection point d between the oscillation coil L and the resistor R1, as shown in FIG.
A sine wave signal centered on s is obtained. The intermittent oscillation control signal a operates the counting circuit 17, and the disconnection detection control signal b operates the comparison circuit 22. The oscillation is stopped when the intermittent oscillation control signal a is at L level, and the output of the NAND circuit 31 is always at H level. This H
The level is resistance R1, the DC resistance of the oscillation coil L and the resistance R
It will be divided by 2. Therefore, when the oscillation is stopped, the voltage at the terminal d of the comparison circuit 22 is fixed to a constant value determined by these resistance values as shown in FIG. The normal voltage at this time is V _A0 . The counter circuit 17 operates as shown in FIG. 4E only during oscillation.

If it is assumed that a part of the wire of the oscillation coil L is broken at time t ₆ , its DC resistance component will increase. Thus the DC voltage level at the oscillation stop is raised, as shown in FIG. 4 (d), the V _A1. Only when this oscillation is stopped
The comparison circuit 22 operates as shown in (f) and (g), and when the voltage V _A1 exceeds the threshold level Vth, the comparison output is held by the latch circuit 23. Therefore, the disconnection can be detected based on the change in the DC resistance of the oscillation coil L.

FIG. 5 is a block diagram showing the overall construction of a proximity switch according to the second embodiment of the present invention, which is the first embodiment described above.
The same parts as those in the embodiment are designated by the same reference numerals and detailed description thereof will be omitted. In this embodiment, a direct current supply circuit 41 that supplies a constant current to the oscillation circuit 16 is provided. The DC current supply circuit 41 operates by the intermittent oscillation control signal b, and supplies the constant current from the constant voltage circuit 11 to the oscillation circuit 16 only while the output is at the H level. Then, when a constant current is supplied, a voltage output corresponding to the DC voltage of the oscillation coil L is obtained. This voltage output is the above-mentioned diagnosis detection unit 2
Given to 1. The other structure is similar to that of the first embodiment, and detailed description thereof will be omitted. Also in this case, when the wire of the oscillation coil is partially broken, the DC resistance component increases, so that the broken wire can be detected.

In each of the above-mentioned embodiments, a comparison circuit having a fixed threshold value is used as the comparison circuit for detecting the DC voltage of the detection coil of the oscillation circuit, but a plurality of threshold values may be set. This makes it possible to detect the number of breaks in the coil wire of the detection coil by selecting the threshold value.

[0022]

As described in detail above, according to the present invention, it is possible to detect the disconnection of a part of the coil wire based on the coil DC resistance group. Therefore, it is possible to issue an alarm output before the number of disconnections increases and detection becomes impossible. Therefore, the effect that the reliability of the proximity switch can be improved is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a proximity switch according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of an oscillator circuit according to an example of the present invention.

FIG. 3 is a time chart showing the operation of the proximity switch according to the first embodiment of the present invention.

FIG. 4 is a time chart showing the operation of the oscillation circuit and the disconnection detection unit of this embodiment.

FIG. 5 is a block diagram showing an overall configuration of a proximity switch according to a second embodiment of the present invention.

6A and 6B are cross-sectional views showing an example of a conventional proximity switch.

7A is an equivalent circuit of a resonance circuit of a conventional proximity switch, FIG. 7B is a graph showing a change in conductance of a coil with respect to a distance to an object, and FIG. 7C is a graph showing conductor resistance with respect to the number of twisted wires of an oscillation coil. It is a graph which shows change.

8A is a circuit diagram showing an example of an oscillation circuit of a conventional proximity switch, and FIG. 8B is a diagram showing an equivalent circuit of a detection coil.

[Explanation of symbols]

 11 Constant Voltage Circuit 12 Reference Clock Generation Circuit 13 Intermittent Pulse Oscillation Circuit 14 Intermittent Oscillation Control Circuit 16 Oscillation Circuit 18, 22 Comparison Circuit 19, 23 Latch Circuit 21 Disconnection Detection Section 24 Disconnection Diagnosis Output Circuit 41 DC Current Supply Circuit

Claims (6)

[Claims] 1. A proximity switch having an oscillation circuit including a coil configured by twisting a plurality of coated coil wires, the proximity switch detecting an object based on a change in an oscillation output of the oscillation circuit, A proximity switch characterized by detecting a partial disconnection of a twisted wire based on a change in a direct current resistance of a coil when oscillation of the oscillation circuit is stopped. 2. An oscillation circuit including a coil formed by twisting a plurality of coated coil wires, an intermittent oscillation control circuit for driving the oscillation circuit at predetermined intervals, and the oscillation for each intermittent oscillation. In a proximity switch having a counting circuit that counts the number of output pulses of the circuit, a disconnection detector that receives the control signal of the intermittent oscillation control circuit and detects the voltage level of the detection coil when the oscillation of the oscillation circuit is stopped is provided. A proximity switch, comprising: a partial disconnection of the oscillation coil detected based on an output of the disconnection detection unit. 3. The oscillation circuit includes a series connection body of a first resistor and a first capacitor, a detection coil connected in parallel to the first capacitor and a series connection body of a second capacitor, and the second connection circuit. Second resistor connected in parallel to the capacitor of the first resistor, the oscillation control signal is applied to one input end thereof, the connection point of the detection coil and the second capacitor is connected to the other input end thereof, and the output end thereof is the first A logic circuit connected to the resistor, the output side of the logic circuit is connected to the input end of the counting circuit, one end of the detection coil is connected to the input end of the disconnection detection unit, The proximity switch according to claim 2. 4. The proximity switch according to claim 2, further comprising a direct current supply circuit for supplying a direct current to the oscillation coil of the oscillation circuit when the oscillation is stopped. 5. The disconnection detection unit includes a comparison circuit that detects a voltage level applied to the detection coil, and a latch circuit that holds an output of the comparison circuit for each intermittent oscillation. The proximity switch according to any one of 2 to 4. 6. The proximity switch according to claim 5, wherein the comparison circuit has a plurality of threshold values and identifies the number of disconnection of the coil wire of the detection coil.