JPS63107315A - Proximity switch - Google Patents

Abstract

PURPOSE:To improve the response speed of an abject detection by detecting the proximity of an object through the decrease in the oscillation output of an oscillation circuit, increasing the gain of the oscillation circuit for a prescribed time by the use of a timer and holding the detection output during that time. CONSTITUTION:The oscillation circuit 1 having a detection coil and to which oscillation gain is varied based on an external signal, a holding circuit 8 holding a comparison output, the timer 5 triggered based on the detection output and increasing the gain of the oscillating circuit 1 for a 1st operating time and a timer 7 triggered by the detection output of the holding circuit 8 for a longer operating time than the operating time above are provided. The oscillation circuit 1 keeps the oscillation at a fine level while the object approaches. The signal is held by the holding circuit 8 during that time and after the oscillating level is increased or the oscillation is stopped depending on the presence of the proximity of the object, the operation of the timer 7 is stopped to stop the output holding. Thus, immediately after the operation of the timer 7 is finished, an object detection signal is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a high frequency oscillation type proximity switch with improved response speed for object detection.

[Summary of the invention]

The proximity switch according to the present invention detects the proximity of an object by reducing the oscillation output of the oscillation circuit, increases the gain of the oscillation circuit for a predetermined period of time using a timer, and maintains the detection output of the detected object during that time. be. In this way, when it is known in advance that objects will arrive at predetermined intervals, the response speed of object detection can be improved.

[Prior art and its problems]

(Prior Art) A high-frequency oscillation type proximity switch has a detection coil provided in a detection head portion, an oscillation circuit is configured with the detection coil as an oscillation coil, and an object is detected based on a decrease in oscillation output. The speed of the oscillation circuit when the oscillation is stopped is changed by adjusting the shape of the detection coil, the winding value, and other circuit constants. Therefore, the response speed of the proximity switch can be considered to be the total time of the oscillation start speed and oscillation stop speed. Generally, oscillation circuits have a problem in that the rise (start) speed of oscillation is very slow, and when the oscillation stops when an object approaches, the response speed decreases. Therefore, JP-A-61-35
As shown in No. 622, the first comparison circuit detects the proximity of an object by reducing the oscillation amplitude, and when the oscillation falls below a predetermined level, the gain is increased to continue oscillation at a minute level. A proximity switch has been proposed in which a second comparison circuit is provided to improve object detection response speed.

(Problem to be solved by the invention) However, in such a conventional proximity switch having two comparison circuits, in order to perform stable operation, the first
Hysteresis is provided in the dark value level of the comparator circuit, and the levels at which the output is turned on and off are different. Hysteresis is also provided in the dark level of the second comparator circuit for improving the gain, and the on/off levels are different. Therefore, four levels must be set for the oscillation amplitude value. Therefore, it is preferable to set the power supply voltage to a sufficiently high level in order to set a level at which each comparison circuit operates stably.

However, for example, in a two-wire proximity switch, it is necessary to make the output residual voltage as low as possible during the ON operation, and the power supply voltage of the proximity switch cannot be made very high. Therefore, a two-wire proximity switch with a low electric voltage has a problem in that it is difficult to increase the response speed by continuously oscillating at a low level for m when an object is detected.

[Technical issues]

The present invention has been made in view of the problems of the conventional proximity switch, and the present invention is designed to improve the gain of the oscillation circuit by using a timer without setting a dark value for the oscillation amplitude. This is a technical issue.

[Structure and effects of the invention]

(Means for Solving the Problems) The present invention is a high-frequency oscillation type proximity switch with improved response speed for object detection, and as shown in FIGS. 1 and 2, it has a detection coil and an external an oscillation circuit that changes the oscillation gain based on a signal from the oscillation circuit, a comparison circuit that detects the proximity of an object by a decrease in the oscillation output of the oscillation circuit, a holding circuit that holds the comparison output of the comparison circuit, and a comparison circuit that detects the proximity of an object by the comparison circuit. a first timer means that is triggered based on the detection output and increases the gain of the first operating time oscillation circuit; and a first timer means that is triggered based on the detection output of the object by the comparison circuit and increases the gain of the first operating time oscillation circuit; The device is characterized in that it has a long second operation time and a second timer means for holding the output of the holding circuit.

(Function) According to the present invention having such characteristics, when an object approaches and the oscillation amplitude decreases, the comparison circuit outputs a comparison signal, and based on the signal, the first timer means outputs the first signal.
The gain of the oscillation circuit is increased for a predetermined period of time. Then, while the object is close, the oscillation circuit continues to oscillate at a minute level.

During that time, the signal is held by a holding circuit, and after the first timer means is activated, the oscillation amplitude is increased or the oscillation is stopped depending on whether an object approaches, and then the second timer means is stopped and output. has stopped holding.

(Effects of the Invention) Therefore, according to the present invention, during the operation of the first timer means, the oscillation continues at a minute level, and if the object moves and leaves the proximity switch during that time, the oscillation amplitude decreases. rises again and exceeds the darkness value level set in the comparison circuit. Therefore, the object detection signal can be output immediately after the operation of the second timer means is completed, and the responsiveness of object detection can be improved. Continuation of oscillation at such a minute amplitude level is performed regardless of the dark value level of the oscillation amplitude. Therefore, there is no need to set a large number of dark values.
m can be continued. Furthermore, since oscillation is not continued after the first timer means stops operating, it is possible to reduce current consumption when the detection object is stopped.

[Explanation of Examples]

FIG. 1 is a block diagram showing the overall configuration of a proximity switch according to an embodiment of the present invention. In the figure, an oscillation circuit 1 has a detection coil 2 in its detection head, and its oscillation output is given to a comparison circuit 4 via a detection circuit 3. The detection circuit 3 converts the oscillation output into a DC level signal corresponding to its amplitude level, and the output is sent to the comparison circuit 4.
give to The comparison circuit 4 has a darkness value level Vref that detects a decrease in the oscillation output when an object approaches, and a threshold level Vrefz higher than Vref+ that detects an increase in the oscillation output when the object moves away. is given to a timer 7 and a holding circuit 8 via a timer 5 and a delay circuit 6. The delay circuit 6 delays the operation start signal given to the timer 7 by a small amount of time. Timers 5 and 7 are triggered by the human-powered rising signal to the first . This is a one-shot timer that opens for a second operating time T1°T2, and the operating time T2 of the timer 7 is slightly longer than the operating time T1 of the timer 5. The output of the timer 5 is given to the oscillation circuit 1 as a gain control signal, and the oscillation gain is increased while the timer 5 is operating. Since the oscillation circuit 1 is oscillating at a level different from normal while the timer 5 is operating, the timer 7 holds the comparison signal of the comparison circuit 4 for a predetermined time and detects the object detection signal based on the change in the amplitude. The output of the holding circuit 8 is outputted to the outside via the output circuit 9.

Next, FIG. 2 shows the oscillation circuit 1 of the proximity switch according to this embodiment.
It is a circuit diagram showing an example. In this figure, a capacitor C is connected in parallel with a detection coil 2 provided on the front side of the proximity switch to form a resonant circuit. A current is supplied to this resonant circuit from a constant current source 11 via a power supply 12, and its common connection terminal is applied to a transistor 13 to amplify the current. The collector of the current amplifying transistor 13 is connected to the collector of the PNP transistor 14, and the transistors 14 and 15 form a current mirror circuit CMI. Further, the emitter of the transistor 13 is grounded via a variable resistor 16 that determines the collector current. The collector of transistor 15 is connected to the emitter of transistor 17. As shown in the figure, the transistor 17 is a multi-collector transistor having two collectors, and its collector terminal 17a is connected to the LC resonance circuit for feedback. The other collector terminal 17b is connected to the collector-base common terminal of the NPN transistor 18. transistor 1
8 constitutes a current mirror circuit CM2 together with a transistor 19. The collector of the transistor 19 is connected to the base-collector common connection terminal of the multi-collector transistor 20. Multi-collector transistor 2
The other collector terminal of 0 is connected to the LC resonant circuit. Further, the base and collector of the transistor 18 are connected to the collector terminal of a switching transistor 21. The transistor 21 operates so as to be turned on when no output is transmitted from the timer 5 and turned off when the output is transmitted.

When the transistor 21 is off, the collector current of the collector 17a of the transistor 17 flows through the current mirror circuit CM2.
And it is fed back to the LC resonance circuit via the transistor 20 to increase the oscillation gain.

(Operation of this embodiment) FIGS. 3 and 4 are time charts showing the operation of this embodiment. Figure 3 shows, for example, a case in which detection objects arranged at predetermined intervals on a belt conveyor approach a proximity switch continuously at approximately constant intervals, and Figure 4 shows a case in which a detection object that does not move for a long time is detected by a proximity switch. 3 is a time chart showing the operation of FIG. When the detected object approaches the proximity switch at predetermined time intervals as shown in FIG. 3(al), the oscillation circuit 1
oscillation amplitude changes. And time 1. If the object to be detected approaches V ref , the amplitude level will drop sharply, so the comparator circuit 4 provides a comparison output at time t2 when the threshold level V ref is reached. Then, the comparison output is shown in Figure 3 (
As shown in C), an object detection signal is output from the output circuit 9 via the holding circuit 8. At the same time, the timer 5 and the delay circuit 6 are triggered, and the timer 5 operates for a predetermined time T to turn off the transistor 21 of the oscillation circuit 1. Therefore, while the timer 5 is operating, if the object to be detected is close, the
As shown in the figure, the oscillation continues at a minute level. Then, the timer 7 is activated via the delay circuit 6 in FIG.
The holding circuit 8 operates as shown in FIG. 3(C).
The object detection signal shown in is held. When the detected object leaves the proximity switch at time t while the timer 5 is operating, the third
As shown in FIG. At the time t4 when the operation is stopped, the holding circuit 8 stops holding the output, and the comparison output is directly outputted to the outside via the output circuit 9. In this way, the operating time T of the timer 5.

If the objects to be detected successively arrive within the same range, the proximity switch can detect the objects with an extremely fast response speed.

In addition, when the detection object is stopped for a predetermined time in the vicinity of the time point as shown in FIG. 4(b),
, As shown in (C), a detection object detection signal is output at time t6. Then, the timer 5 and the timer 7 start operating after a small time delay, and the oscillation continues at a small level for the operating time T1 of the timer 5 until the time t7 when the timer 5 stops operating. Because the object is approaching, the oscillation is completely stopped as shown in Fig. 4 (bl).Then, no output is output even at time t8 when timer 7 ends its operation.Now, at time t, the object to be detected is approaching. After leaving the switch, the oscillation gradually rises as shown in FIG. 4(b), so the time t is slightly delayed as shown in FIG. 4(C).
An object detection signal will be output at 10.

As described above, the present invention can be highly effective when applied to a proximity switch placed at a location where it is known in advance that objects will arrive at predetermined intervals.

The oscillation circuit according to this embodiment uses a current mirror circuit to vary the feedback voltage to the resonant circuit to change the gain of the oscillation circuit, but the emitter resistance of the current amplification transistor is changed by the timer 5, etc. It goes without saying that various types of oscillator circuits can be used.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of a proximity switch according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an oscillation circuit of the proximity switch according to this embodiment, and FIGS. 3 and 4 are according to this embodiment. 3 is a time chart showing the operation of FIG. 1-...-Oscillation circuit 3-...-Detection circuit 4-
−−−−1・Comparison circuit 5,7・−・−・−Timer
8--Holding circuit 9--Output circuit Patent applicant Tateishi Electric Co., Ltd. Agent Patent attorney Yoshiki Okamoto (and one other person) Fig. 1 Fig. 2 Fig. 1 -----1 2nd photo shoot of camellia 3rd picture

Claims (2)

[Claims] (1) An oscillation circuit that has a detection coil and changes its oscillation gain based on an external signal; a comparison circuit that detects the proximity of an object by a decrease in the oscillation output of the oscillation circuit; and a comparison output of the comparison circuit. A holding circuit that holds the first object is triggered based on the detection output of the object by the comparison circuit.
a first timer means for increasing the gain of the oscillation circuit; a second timer means triggered based on the object detection output by the comparison circuit and longer than the first operation time of the first timer circuit;
1. A high frequency oscillation type proximity switch, comprising second timer means for holding the operating time of the holding circuit and the output of the holding circuit. (2) The proximity switch according to claim 1, wherein the comparison circuit is a circuit having hysteresis.