JP3041998B2 - Proximity switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a proximity switch having a function of detecting an abnormality due to disconnection of a coil.

[0002]

2. Description of the Related Art A conventional high-frequency oscillation type proximity switch has a detection surface 1a at one end of a cylindrical case 1 as shown in a sectional view of FIG. Mounted. The 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 coil 3 and a detection circuit that detects a decrease in the oscillation level is mounted on the printed circuit board 4. FIG. 5 shows a detection circuit for detecting and integrating the oscillation circuit 11 and its output.
FIG. 3 is a circuit diagram showing a configuration of an integration circuit 12; As shown in the figure, a constant current source 1 is
3. Power is supplied through the diode D1, and voltage / current conversion is performed by the transistor Q1. This current value is positively fed back to the resonance circuit via the current mirror circuit 14, and oscillation continues. In the detection / integration circuit 12, the anode terminal voltage of the diode D1 is received by the emitter follower type transistor Q2, converted into a current, and converted into a current.
, A current corresponding to the collector current of the transistor Q2 is supplied to the resistor R3, converted into a voltage value and smoothed to obtain a DC level signal Vi corresponding to the amplitude. This voltage Vi
Is compared with a threshold value Vref by the comparator 16 to output an object detection signal. Now the integrated voltage V
The relationship between i and the distance L to the object is, for example, shown by a curve A in FIG.

[0003]

However, the conventional high-frequency oscillation type proximity switch is often used for detecting the arrival of a metal body in a factory assembly transfer line or the like. For this reason, if the clearance between the movable area of the detection object 5 and the detection head is not sufficiently ensured or the area of the detection object 5 is shaken, the detection object 5 may approach the detection surface of the case and come into contact therewith. When the chip is mounted on an aluminum cutting machine, the cut aluminum chips are accumulated on the detection surface of the proximity switch, and the chips are rubbed on the detection surface every time the detection object 5 passes. Therefore, FIG.
As shown in the figure, the coil 3 may be disconnected due to a part of the case missing.

As shown in FIG. 3B, the coil 3 is formed by winding a plurality of coated wires, for example, a wire in which seven wires are twisted, around a coil spool several tens of times. When the twisted wire is completely broken by the collision of the object, a constant integrated voltage is obtained irrespective of the distance to the object as shown by a broken line B in FIG. When one or two of the wires of the coil 2 are broken, the Q of the coil decreases, and the integrated voltage Vi with respect to the detection distance changes as shown by the broken line C1 or C2 in FIG. Therefore, the normal detection distance L0 changes to L1,
Further, the output is always turned on and malfunctions. In the conventional proximity switch, a complete disconnection can be detected by another comparator having the threshold value Vref2 at a level higher than the threshold value Vref, but such a partial disconnection state cannot be detected.

The present invention has been made in view of such a problem of the conventional proximity switch, and it is a technical object of the present invention to enable an abnormal state to be identified even when one of the twisted wires is broken. And

[0006]

According to the present invention, there is provided a coil formed by twisting a plurality of covered coil wires, a resonance circuit including the coil, and an oscillation circuit oscillating at a resonance frequency of the resonance circuit. A proximity switch, comprising: a proximity switch for outputting an output based on a change in an output state of an oscillation circuit, wherein at least one coil element of the coil is disconnected.
And the output level of the monitoring circuit
An abnormality detection circuit for detecting disconnection of the coil element wire based on the
It is characterized by having.

[0007]

According to the present invention having such features, at least one coil wire of a coil composed of a plurality of coil wires is used as a part of a disconnection monitoring circuit to detect the disconnection. Then, the disconnection of the coil element wire is detected by the abnormality detection circuit 22. If this coil wire breaks, there is a high possibility that other wires used in a part of the oscillation circuit are also broken, so that a wire break detection signal is output regardless of the output state at that time.

[0008]

FIG. 1 is a block diagram showing a configuration of a high-frequency oscillation type proximity switch according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a detailed configuration of a main part thereof. In these figures, the same parts as those in the conventional example described above are denoted by the same reference numerals, and detailed description is omitted. Also in this embodiment, the coil 20 is connected to the oscillation circuit 11, and a detection / integration circuit 12 for detecting / integrating the oscillation output is connected. A comparator for discriminating the output with a predetermined threshold value Vref is connected similarly to the above-described conventional example. The comparator 16 is included in the signal processing circuit 17, and supplies an object detection signal to the output circuit 18 when the comparator 16 outputs continuously for a predetermined period. The output circuit 18 outputs a detection signal to the outside of the proximity switch.

In this embodiment, a monitoring circuit 21 is connected to one end of the detection coil 20. The monitoring circuit 21 is a circuit used for detecting disconnection of the coil, and the output voltage of the monitoring circuit is detected by the abnormality detection circuit 22.
When the abnormality of the coil is detected by the abnormality detection circuit 22, an abnormality detection signal is output from the output circuit 23 to the outside.

Next, the configuration of the detection coil used in this embodiment will be described. As shown in the enlarged view of FIG. 3A and the enlarged sectional view of the coil wire in the detection coil 20, the coil wire of the coil has a plurality of wires, for example, seven coil wires 24a to 24g. Are twisted with each other. The coil wire is a thin copper wire covered with each of 24a to 24g, which is twisted and wound several tens times around the coil spool 25 to form the coil 20.
In this embodiment, one of the coil wires of the coil 20 is used.
For this purpose, for example, the coil wire 24a is used for disconnection detection, and the ends of the other coil wires 24b to 24g are collected to form the oscillation circuit 11
Connected to As shown in detail in FIG. 3C, the coil of FIG. 2 uses one coil wire 24a of the coil 20 and the other coil wires 24b to 24g separately.

One end of the coil wire 24a is grounded together with the other coil wires, and the other end is connected to a resistor R4 as shown in FIG.
And a common connection point with the resistor R4 is connected to the abnormality detection circuit 22. Abnormality detection circuit 22
The comparator 26 has an input terminal connected to the common connection terminal,
A constant reference voltage V2 is supplied from the voltage source 27 to the other input terminal. The comparator 26 determines the terminal voltage of the coil wire using this voltage as a reference value. This comparator 26
May be output directly from the diagnostic output circuit 23 to the outside, or the output of the signal processing circuit 17 may be prohibited by the output.

Next, the operation of this embodiment will be described. When power is supplied to the high-frequency oscillation type proximity switch, a DC current flows through the coil wire 24a. This DC resistance is R0
Then, the terminal voltage V1 is a voltage Vcc · R0 / (R4 + R) determined by the voltage division of the resistors R0 and R4.
0). At this time, the threshold value V2 is determined so that V1 <V2. In this case, the comparator 26 becomes H level and is diagnosed as normal. Therefore, the signal processing circuit 17
An object detection signal corresponding to the presence or absence of the object is output.

As shown in FIG. 4B, when the detection object 5 or the like collides with the tip of the case and a part of the coil 20 is disconnected, the coil 20 is wound around the coil spool 25 many times. Therefore, there is a high possibility that the coil wire 24a for disconnection detection will be disconnected at the same time. In the case of disconnection, the voltage V1 at the connection point of the coil wires becomes a level V1 'almost equal to the power supply voltage Vcc. Accordingly, the comparator 26 outputs an L-level output, and the disconnection state is detected. In this way, the disconnection can be detected with a high probability including the disconnection of a part of the wires. When disconnection is detected, the object detection signal obtained from the signal processing circuit 17 may be prohibited, or an abnormality detection signal may be output in parallel with the detection. In this case, even when some of the coil wires are disconnected, the Q of the coil is reduced and the output characteristics of the object and the detection / integration circuit 12 change as shown by the broken line C1 or C2 in FIG. You can know for sure.

[0014]

As described in detail above, according to the present invention, since a part of the coil composed of the stranded wire is used for disconnection detection, a wire dedicated to disconnection detection is provided around the coil. The wire for disconnection detection can be connected at the same time during the coil manufacturing process. Since this wire is wound around the coil spool integrally with the coil, it is possible to detect a broken state of the coil wire with a high probability. Further, since it is possible to recognize an abnormality when the coil is not completely disconnected, it is possible to improve the reliability of the object detection distance.

[Brief description of the drawings]

FIG. 1 is a block diagram of a high frequency oscillation type proximity switch according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing configurations of an oscillation circuit, a detection / integration circuit, a monitoring circuit, and an abnormality detection circuit according to the present embodiment.

3A is an enlarged view of a coil, FIG. 3B is an enlarged sectional view of a coil wire, and FIG. 3C is an enlarged view showing a connection state of the coil.

FIG. 4A is a cross-sectional view of a general high-frequency oscillation proximity switch, and FIG. 4B is a cross-sectional view showing a state in which a metal body collides with a tip of the switch and is broken.

FIG. 5 is a circuit diagram showing an example of an oscillation circuit and a detection / integration circuit of a conventional high-frequency oscillation type proximity switch.

FIG. 6 is a graph showing a relationship between an integrated output of a high-frequency oscillation type proximity switch and a distance to an object.

[Explanation of symbols]

 Reference Signs List 1 case 2 ferrite core 3, 20 coil 11 oscillation circuit 12 detection / integration circuit 14, 15 current mirror circuit 16, 26 comparator 17 signal processing circuit 18, 23 output circuit 21 monitoring circuit 22 abnormality detection circuit 24a to 24g coil element wire 27 Voltage source

Claims (1)

(57) [Claims] A coil configured by twisting a plurality of covered coil wires; a resonance circuit including the coil; and an oscillation circuit oscillating at a resonance frequency of the resonance circuit. in proximity switch out an output based on the change in the oscillation state of the circuit, the using at least one coil wire of the coil
Proximity switch, characterized by comprising a monitoring circuit for disconnection of the coil wire and the voltage change, an abnormality detection circuit for detecting the disconnection of the coil wires on the basis of the output level of the monitoring circuit.