JPS6320914A - Proximity switch - Google Patents

Abstract

PURPOSE:To increase the response speed by providing a resonance circuit, a current mirror circuit outputting a feedback current to the resonance circuit and a switching element increasing/decreasing the feedback current intermittently to a current feedback oscillation circuit. CONSTITUTION:A transistor (TR) 5 is turned off for this period only in providing a negative pulse (p) with a small duty ratio to a base of the TR 5 via terminal 5. Thus, the feedback current being a current I1 at the on-state goes into I1+I2, then the oscillating state of a resonance circuit 5 is increased. When an object to be detected, however, is being parted and the resonance circuit 3 is going to start the oscillation. a slope (s) in the increased oscillation amplitude, shown C in figure is made steep while the TR 5 is turned off. Thus, the time from the oscillation start till the saturated oscillation is much shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a proximity switch, and more particularly to a high-frequency oscillation type proximity switch with a fast response speed for detecting an object to be detected.

(Prior art) A high-frequency oscillation type proximity switch houses a detection coil in a detection head, uses this detection coil as an oscillation coil to configure an oscillation circuit, and detects an object by reducing the output of this circuit. At this time, the response speed, which is the time required for detection, changes depending on the shape of the detection coil, the number of turns per turn, etc.
It can be regarded as the sum of the time required to start oscillation and the time required to stop oscillation of the oscillation circuit. Usually, the time required to start oscillation is extremely long compared to the time required to stop oscillation. Furthermore, if the shape of the detection coil is made larger in order to extend the detection distance, the response speed will become slower in proportion. Therefore, there is a problem in that if the object to be detected is moving at high speed, it cannot be detected. Therefore, the i! l! It was said to be a topic.

There have been proposals to solve this problem.Firstly, there is a first technique disclosed in Japanese Utility Model Application Publication No. 145742/1983.This technique uses a Schmitt circuit in the oscillation circuit to detect a decrease in the oscillation output. The output of this circuit changes the resistance value of the oscillation state adjustment resistor provided in the oscillation circuit, and after the oscillation output decreases due to the proximity of the detection target and a detection signal is output, the detection target is further detected. Even when the proximity switch approaches, oscillation continues with a small amplitude from the proximity switch to a predetermined position.

Next, JP-A-61-35619.32620,3562
There is a second technique disclosed in Japanese Patent No. 1,35622.35623. In this technique, a comparator circuit is operated by a drop in the output of an oscillator circuit, and a current mirror circuit is operated by the output of this circuit. Then, after the oscillation output is reduced due to the proximity of the detection target and a detection signal is output, even if the detection target continues to approach, the oscillation does not stop and oscillation is continued at a low level 41c.

[Problem that the invention seeks to solve]

However, these two techniques have the following problems. Both of the above two techniques work to continue oscillation with a smaller amplitude when the object to be detected approaches and the oscillation amplitude becomes smaller.

Therefore, the operation is opposite to the hysteresis that is performed for the purpose of stable operation and noise resistance. That is, hysteresis is a difference between the operating levels at the start and end of an operation, which is provided to stabilize the operating points at the start and end of the operation. Therefore, it starts working.

If the end levels are the same, the operation will become unstable at that level. Since the above two techniques operate in a direction to eliminate this hysteresis, there is a problem in that the operation stability is poor and they are easily affected by noise.

The present invention has been made in view of the above problems, and an object thereof is to provide a high frequency oscillation type proximity switch that has a fast response speed, excellent operational stability, and is less susceptible to noise.

[Means for solving problems]

A specific means for solving the above problems and achieving this objective is to provide a proximity switch that detects an object by reducing the output of a current feedback type oscillator circuit that feeds back a part of the oscillation current. type oscillation circuit, resonant circuit,
The present invention includes a current mirror circuit that outputs a feedback current to the resonant circuit, and a switching element that intermittently increases or decreases the feedback current.

[For production]

Since this invention employs the above-mentioned means, the following effects are brought about. When the object to be detected approaches, the oscillation output by the resonant circuit of the current feedback oscillation circuit decreases. In response to this decrease, the feedback current output from the current mirror circuit also decreases. When the object to be detected gradually approaches and the oscillation output falls below the detection level, a detection signal is output. Further, as the object to be detected approaches, the oscillation output gradually decreases, and finally the oscillation is stopped. The switching element intermittently increases or decreases the feedback current.

A case will be described in which the feedback current decreases while the switching element is in the operating state. During periods other than this operating state, the total feedback current to the resonant circuit increases. Therefore, even if the oscillation output is stopped, the feedback current intermittently flows into the resonant circuit, causing the resonant circuit to start oscillating.

At this time, if the object to be detected is still close and the oscillation of the resonant circuit has stopped, the oscillation will quickly attenuate. Furthermore, when the object to be detected is moving away, the oscillation speed of the resonant circuit increases in response to the rise of this oscillation, and the time required to start oscillation is shortened.

Next, a case will be described in which the feedback current increases while the switching element is in the operating state. Contrary to the above, the total feedback current to the resonant circuit decreases during periods other than this operating state. Therefore, when the object to be detected approaches and the resonant circuit is about to stop oscillating, the oscillation quickly attenuates.

〔Example〕

This invention will be explained in detail below based on one embodiment.

As shown in FIG. 1, the oscillation circuit of the proximity switch according to this embodiment connects a coil L to a constant current source 1 via a DC power source 2.
A resonant circuit 3 consisting of a capacitor C and a capacitor C is connected.

Further, the base of the transistor Tr is also connected to the constant current source I.

The emitter of this transistor Tr is grounded via a resistor R, which determines the collector current, and is also connected to an 0LIT terminal that transmits a detection signal.

In addition, the collector is a transistor Tr, , Tra,
It is connected to a current mirror circuit 4 consisting of Tra.

A diode D is connected between the collectors of the transistors Tr3 and Tr4, and the collector of the transistor Trs, which is a switching element, is connected to the collector of the transistor Tr#. The emitter of this transistor TrS is grounded, and the base is connected to the terminal 5.

The operation of this oscillation circuit will be explained. Current is supplied from the constant current source 1 to the resonant circuit 3 via the DC type -rA2. The current value obtained by the resonant circuit 3 is amplified by the transistor Tr, and a feedback current 11.12 whose sum of the respective current values is the same as the collector current I0 of the transistor Tr is amplified by the current mirror circuit 4. The current is fed back to the resonant circuit 3 via the Tr. Therefore, since positive current feedback is applied, oscillation is started at the resonant frequency of the resonant circuit 3.

Note that the resistor R0 is provided to set the detection distance,
When the resistance value is set to a small value, the collector current 1G, that is, the total feedback current (1+ +lz) becomes large. Therefore, the oscillation amplitude increases, and detection becomes impossible unless the object to be detected is closer. Naturally, if the resistance value of the resistor R8 is set to a large value, the detection distance will become longer. Feedback current 11
．． The ratio of the current values of I2 is the transistor Tr: +, T
It can be set to a desired value depending on the area ratio of ra. When the transistor TrS is in the on state, the feedback current is only I1, and when the transistor TrS is in the off state, the feedback current is 1. +1. becomes.

In this oscillation circuit, the transistor T
When a negative pulse p with a small duty ratio is applied to the base of rs, as shown in FIG. Feedback current is 1+
12, and the oscillation amplitude of the resonant circuit 3 increases. In this way, the oscillation amplitude of the resonant circuit 3 is increased periodically. As shown in fbl of the figure, in case A when the oscillation of the resonant circuit 3 is saturated, no effect occurs even if the oscillation amplitude is increased periodically. In state B where oscillation is stopped, oscillation starts to rise periodically due to the pulse p, but quickly attenuates. The output signal caused by this rising edge is integrated in an integrating circuit (not shown) connected to the OUT terminal, and its influence is removed, so that it does not affect the equivalence detection operation.

However, in case C (see FIG. 2(b)) when the object to be detected is moving away and the resonant circuit 3 is about to start oscillating, the oscillation amplitude increases at an increasing rate during the off-state period of the transistor Trs. S becomes steep.

Therefore, the time from the start of oscillation to oscillation saturation (the time required to start oscillation) is extremely shortened. On the other hand, in case D (see Tb in the same figure) when the object to be detected is approaching and the resonant circuit 3 is about to stop oscillating, the transistor Tr
During the off state of s, it acts to prevent the oscillation from stopping. Therefore, the time from oscillation saturation to oscillation stop (oscillation stop time) is slightly extended, but the reduction in the oscillation start time is much longer than the extension of the oscillation stop time. Overall, the response speed of the proximity switch using the oscillation circuit according to this embodiment is faster.

In this embodiment, the response speed of the proximity switch is increased by periodically changing the magnitude of the feedback current of the current mirror circuit 4, but the following may be made. As shown in FIG. 3, the current mirror circuit 4a is connected to a transistor Tr.
2. Trx, and the resistor R0 for setting the detection distance is divided into resistors R, l and resistor Ra2, and the transistor Tr5, which is a switching element, is connected in parallel to both ends of the resistor Ra2. With such a configuration, when the transistor Tr5 is turned on, the resistor R8
The resistance value of the resonant circuit 3 becomes smaller, and the oscillation amplitude of the resonant circuit 3 becomes larger as described above. Conversely, when it is in the off state, the oscillation amplitude becomes smaller. Therefore, the same effect as in the above embodiment is brought about.

As another example, as shown in FIG. 4, the emitter of the transistor Tr, which is a switching element, is
C terminal, and its collector is connected to the resonant circuit 3 via a resistor R1. Then, when the transistor Trs is turned on, a current shock is periodically applied to the resonant circuit 3. That is, since the feedback current increases periodically, the same effect as in the above embodiment is brought about.

Contrary to the above embodiments, a positive pulse with a small duty ratio may be applied to the terminal 5 connected to the transistor Tr5, which is a switching element in these three embodiments. This brings about the effect of periodically reducing the feedback current of the current mirror circuit and speeding up the stopping of oscillation. Therefore, if the object to be detected approaches and the oscillation of the resonance circuit 3 is about to stop, the oscillation will quickly attenuate and the response speed to the proximity of the object to be detected will become faster.

By configuring an oscillation circuit that combines this embodiment and the above three embodiments, it is possible to further speed up the response speed of the proximity switch by dumping when the oscillation is saturated and excitation when the oscillation is stopped. . When adopting such a circuit configuration, it is important to prevent the circuit from operating during a period when the oscillation state is changing in order to prevent chattering.

〔Effect of the invention〕

As is clear from the above description, the present invention provides a proximity switch that detects an object by reducing the output of a current feedback oscillation circuit that feeds back a part of the oscillation current. circuit, a current mirror circuit that outputs a feedback current to this resonant circuit, and a switching element that intermittently increases or decreases the feedback current, so even if the detection coil is increased in size to extend the detection distance. Response speed can be increased. When converting the proximity switch into an IC, it is not necessary to use a high-speed response PNP) transistor, so the IC can be formed using normal bipolar C-MO3 technology. It also has good temperature characteristics and is resistant to temperature changes. Furthermore, since hysteresis is added to the operating level, it is not affected by noise and has good operating stability.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment of a proximity switch according to the present invention, FIG. 2 is an explanatory diagram of the operation of this embodiment, and FIGS. 3 and 4 are circuit diagrams of other embodiments. 3... Resonance circuit, 4, 4a... Current mirror circuit, L
...Detection coil, C...Capacitor, R,,R,,
, R, +・+resistance, Trz, Try, Tra
・= ) Transistor, Tr, . . . Transistor (switching element), I. ■2...Feedback current. Patent applicant: Reed Electric Co., Ltd. Figure 1> Figure 3> -/4a@flow mirror circuit <Figure 4> Resonant circuit

Claims (2)

[Claims] (1) In a proximity switch that detects an object to be detected by reducing the output of a current feedback oscillation circuit that feeds back a part of the oscillation current, the current feedback oscillation circuit has a resonant circuit and a feedback current to the resonant circuit. A proximity switch comprising: a current mirror circuit that outputs the feedback current; and a switching element that intermittently increases or decreases the feedback current. (2) The proximity switch according to claim 1, wherein a negative pulse with a small duty ratio is applied to the switching element at regular intervals.