JPH07303036A - Detection switch - Google Patents

Abstract

PURPOSE:To reduce the number of comparators and to reduce current consumption in detection switchs provided with the comparator for object detection and the one for stable operation display. CONSTITUTION:An object detection signal is outputted by a first comparator 7 for object detection. An input signal can be discriminated by switching the threshold value of the comparator 21 for stable operation detection based on the output of the object detection signal. Simultaneously, such control that the output of the comparator 21 can be inverted only when the detection signal is outputted from the comparator 7 is performed. By employing such constitution, a stable or unstable state can be displayed based on the output of the comparator 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection switch, and more particularly to a detection switch characterized by a signal processing circuit.

[0002]

2. Description of the Related Art As a conventional detection switch, for example, a reflection type photoelectric switch will be described. FIG. 4 is a block diagram showing an example of the reflective photoelectric switch. In the figure, an oscillating circuit 1 periodically generates a light projecting pulse, and its output drives a light projecting element, for example, a light emitting diode 3 via a light projecting circuit 2. The projected light is applied to the object detection area via an optical system (not shown), and if there is an object, the reflected light is received by the photodiode 4, which is a light receiving element. Then, it is input to the comparators 7, 8, 9 via the preamplifier 5 and the amplifier 6. The comparators 7, 8 and 9 have threshold values Vth1, Vth2 and Vth3 (Vth2 <Vth1 <Vth3), respectively. The comparator 7 outputs an object detection signal (ON signal) to the integrating circuit 10 when a light receiving signal exceeding Vth1 is input. The integrating circuit 10 is supplied with a light projection pulse from the oscillation circuit 1, and outputs an output when the ON signal is continuously input by the comparator 7 for 8 pulses. As shown in FIG. 5, the integrator circuit 10 outputs the object detection signal when the ON signal is continuously applied for 8 pulses, and outputs the control output circuit 11
And is displayed by the operation display circuit 12.

Now, after the photoelectric switch is installed, the environment changes,
For example, the temperature, voltage, etc. may change, or dust, etc. may adhere to the optical system to lower the light reception signal level. For this reason, the output of the comparator 7 that detects an object fluctuates. On the other hand, comparators 8 and 9 are used to determine the margin of the light receiving level. The comparator 8 has a threshold value Vth2 of a stable off level lower than Vth1, and outputs a signal of H level to the gate circuit 13 when the light receiving level becomes higher than this. Further, the comparator 9 has a threshold value Vth3 having a stable ON level higher than Vth1 and outputs a signal of H level to the gate circuit 13 when a light receiving signal exceeding this is obtained. The gate circuit 13 determines an unstable state by the logical product of the H level of the comparator 7 and the inverted output of 9, and its output is an integrating circuit 14
Given to. The integrating circuit 14 outputs a signal for detecting an unstable state to the self-diagnosis output circuit 15 when the detection signal is continuously input for a plurality of light-emission pulse numbers, and lights the indicator lamp of the stable display circuit 16. Is. Therefore, FIG.
As shown in (c) to (e), when the light receiving level continues for a predetermined number of pulses between Vth2 and Vth3, a self-diagnosis signal is output to notify that the detection state is unstable. You can

[0004]

However, such a conventional photoelectric switch uses the comparator 8 for signal detection and three comparators for stable state detection. The comparator consumes a large amount of current. For example, a detection switch that requires low current consumption, such as a DC two-wire type detection switch, a battery-powered detection switch, or a detection switch that is small and needs to suppress heat generation, reduces the current consumption. It had the drawback of being difficult to do.

The present invention has been made in view of such conventional problems, and an object of the present invention is to reduce the number of comparators in a signal processing unit and reduce current consumption.

[0006]

SUMMARY OF THE INVENTION The present invention is a detection switch for determining a physical state according to the level of an input signal,
A first comparator having a first threshold level for discriminating an input signal and outputting a detection signal when the threshold level is exceeded; a second threshold level lower than the first threshold level; One of the third threshold levels higher than the threshold of is set as the threshold, and the second comparator for discriminating the input signal and the second comparator when the output of the first comparator does not output the detection signal. The threshold value is a second threshold value, and when the first comparator outputs the detection signal, the threshold value switching means that switches the threshold value of the second comparator to the third threshold value, and the first comparator detects Output inverting means for inverting the output of the second comparator when a signal is output, and a stable operation state is determined based on the output of the output inverting means. .

[0007]

According to the present invention having such features, the first
The comparator detects the input signal and outputs the detection signal. Then, if the input signal is less than or equal to the first threshold, the threshold of the second comparator is set to the second threshold based on the output of the first comparator, and when the detection signal is output from the first comparator, Two
The threshold value of the comparator is switched to the third threshold value, and the second
The comparator determines whether the threshold is exceeded. The output of the second comparator is inverted when the first comparator outputs the detection signal. In this way, the signal obtained from the second comparator via the output inverting circuit directly indicates whether the input signal is between the second threshold value and the third threshold value, and is stable or It shows an unstable condition. Therefore, a stable or unstable state can be displayed based on this output.

[0008]

1 is a block diagram of a reflection type photoelectric switch according to an embodiment of the present invention. The same parts as those in the conventional example described above are designated by the same reference numerals and detailed description thereof will be omitted. In this embodiment as well, the oscillation circuit 1 outputs light projection pulses of a constant cycle, light is applied to the object detection area through the light projection circuit 2 and the light emitting diode 3, and if there is an object, the reflected light is the photodiode. The light is received by 4 and is applied to the comparator 7 via the preamplifier 5 and the amplifier 6. The comparator 7 has a first threshold value Vth1.
Is a first comparator which discriminates the input signal level and outputs a detection signal when the input signal reaches the threshold. In the present embodiment, a second comparator 21 is provided in addition to the object detecting comparator 7. 2 at the reference input terminal of the comparator 21
Two voltage sources 22 and 23 are connected in series. Voltage source 23
Has a voltage of the threshold value Vth2, and the voltage source 23 has a voltage of the threshold value Vth3-Vth2. A transistor Q1 is connected between the connection point of these voltage sources 22 and 23 and the ground terminal. When the transistor Q1 is on, the threshold of the comparator 21 becomes the second threshold Vth2, and when the transistor Q1 is off, the threshold of the comparator 21 is the third Vth.
3

The output of the comparator 7 is given to the integrating circuit 24 in addition to the integrating circuit 10. The integrator circuit 10 outputs an object detection signal via the control output circuit 11 when the H level signal from the comparator 7 is continuously input for the number of eight light-emission pulses, and the operation display circuit 12 displays the operation. It is a thing. On the other hand, the integrator circuit 24 outputs the H level signal to the inverter 25 when the H level signal is obtained, for example, four pulses consecutively. The inverter 25 inverts the input signal and drives the transistor Q1.

On the other hand, the output of the comparator 21 is input to the integrating circuit 26. The integrating circuit 26 outputs an H level signal to the inverter 27 when the H level output of the comparator 21 is continuously input for four pulses. Inverter 2
Analog switches 28 are connected to both ends of 7. The analog switch 28 is controlled by an inverter 29 that inverts the output of the integrating circuit 10, and short-circuits the inverter 29. The output of the inverter 27 is given to the integrating circuit 30. The integrator circuit 30 determines that the H level signal is unstable when the H level signal is continuously input for 5 pulses or more,
A diagnostic signal is output to the outside through the self-diagnosis output circuit 15, and an unstable state is displayed by the stable display circuit 16. Here, the integrating circuit 24 and the inverter 25
And the transistor Q1 changes the threshold value of the second comparator to the second threshold value Vth2 when the first comparator does not output the detection signal.
And a threshold value switching means for switching the threshold value of the second comparator to the third threshold value Vth3 when the first comparator outputs the detection signal. Further, the inverters 27 and 29 and the analog switch 28 constitute output inverting means for inverting the output of the second comparator when the first comparator outputs the detection signal.

Next, the operation of this embodiment will be described with reference to the time chart of FIG. FIG. 2A shows the light emitting diode 3 in response to the light projection pulse output from the oscillation circuit 1.
3 shows the level of the light receiving signal obtained through the photodiode 4, the preamplifier 5, and the amplifier 6 when the is driven, and at the same time, shows the threshold values of the comparators 7 and 21. Immediately after the operation is started, the light receiving level is assumed to be equal to or lower than the threshold value Vth1. At this time, the threshold of the output of the comparator 21 is V
When the light receiving level is lower than th2, the outputs of the comparators 7 and 21 are both at the L level and the output of the inverter 29 is at the H level as shown in FIG. At this time, the analog switch 28 is conducting, and the output of the integrating circuit 26 is directly input to the integrating circuit 30, so that the output of the integrating circuit 30 is also at the L level. Then, when the object approaches and exceeds the threshold value Vth2, the output of the comparator 21 becomes H level, and after 4 pulses, the integrating circuit 26 causes the output of FIG.
The output is inverted to the H level as shown in (d). Therefore, the output of the inverter 27 is also inverted accordingly, and after that, the number of pulses of the integrating circuit 30, that is, after 5 pulses, is as shown in FIG.
As shown in (g), the output of the integrating circuit 30 becomes H level. At this time, since the operation is unstable, the self-diagnosis output circuit 15 outputs and the stable display circuit 16
Causes an unstable condition to be displayed.

When four pulses have passed from the time when the input level exceeded the threshold value Vth1, the output of the integrating circuit 24 is inverted to the H level as shown in FIG. 2 (b). Therefore, the output of the inverter 25 is inverted to the L level, the transistor Q1 is turned off, and the threshold value of the comparator 21 becomes Vth3 as shown in FIG. When an object is present and a light reception signal having a level exceeding the threshold value Vth1 is continuously obtained for 8 pulses or more, an H level output is obtained from the integrating circuit 10 as shown in FIG. The object detection signal is output from the control output circuit 11. At the same time, the operation display circuit 12 displays the detection of the object. Here, since the output of the integrating circuit 10 is inverted by the inverter 29 and is at the L level, the analog switch 28 is turned off.
Therefore, when the input signal is equal to or lower than the stable ON level Vth3 and exceeds the object detection threshold Vth1, the integration circuit 26
The output of is inverted by the inverter 27, and the integration circuit 3
Join 0. Therefore, the integrating circuit 30 continues to output the H level as shown in FIGS.

On the other hand, when the input level exceeds the threshold value Vth3, the object detection signal is output through the integrating circuit 10, and the analog switch 28 is also turned off at the same time, so the output of the integrating circuit 26 is inverted by the inverter 27 and integrated as the L level. Join circuit 30. Therefore, the output of the integrating circuit 30 is L
It is maintained at the level and is shown to be in a stable operating state. At this time, the self-diagnosis output circuit 15 does not output, and the stable display circuit 16 also displays the stable state.

In this embodiment, the integrating circuits 10, 24 and 26 are used to eliminate the influence of noise and to avoid sudden output fluctuations.
And 30 are provided, the number of pulses of which is 30
It can be arbitrarily set except that the number of pulses of the integrating circuit 30 is increased. Further, inverters 27 and 29 and an analog switch are provided as an output inverting circuit for inverting the output of the comparator 21 based on the object detection signal. However, the output inverting circuit is not limited to such a configuration, and it can be configured using a logic circuit including inverters 41 and 42, AND circuits 43 and 44, and an OR circuit 45 as shown in FIG. 3, for example. There is no end.
Further, the switching circuit for switching the output of the comparator 21 based on the output of the integrating circuit 24 is not limited to the configuration of this embodiment, and a voltage source having two threshold values may be directly switched by a switch.

Although the present embodiment describes the reflection type photoelectric switch, the present invention is not limited to the reflection type photoelectric switch, but other types such as a transmission type photoelectric switch and a proximity switch, etc., may be in a physical state depending on the input signal level. Can be applied to various other detection switches that output ON or OFF.

[0016]

As described above in detail, according to the present invention, the first comparator for detecting the motion and the first comparator for detecting the object are used for detecting the object, and the second comparator having the threshold values above and below the comparator. The stable state is detected by switching the threshold value using. Therefore, it can be configured with two comparators, and the effect that the current consumption of the detection switch can be significantly reduced can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a reflective photoelectric switch according to an embodiment of the present invention.

FIG. 2 is a time chart showing the operation of this embodiment.

FIG. 3 is a circuit diagram showing another example of an output inverting circuit.

FIG. 4 is a block diagram showing an example of a conventional reflective photoelectric switch.

FIG. 5 is a time chart showing the operation of a conventional reflective photoelectric switch.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 oscillation circuit 2 light emission circuit 3 light emitting diode 4 photodiodes 7-9, 21 comparators 10, 24, 26, 30 integration circuit 11 control output circuit 12 operation display circuit 15 self-diagnosis output circuit 16 stability display circuit 22, 23 voltage Source 25, 27, 29 Inverter 28 Analog switch

Claims (1)

[Claims] 1. A detection switch for discriminating a physical state according to a level of an input signal, the first switch having a first threshold level for discriminating the input signal, and outputting a detection signal when the threshold level is exceeded. And a second comparator that sets one of a second threshold level lower than the first threshold level and a third threshold level higher than the first threshold level as a threshold value and discriminates an input signal. And a threshold value of the second comparator when the output of the first comparator does not output a detection signal, and a second threshold value when the first comparator outputs a detection signal. Threshold value switching means for switching the threshold value of the second comparator to the third threshold value; output inverting means for inverting the output of the second comparator when the first comparator outputs a detection signal; Stable operation based on the output of the output inverting means Detection switch being characterized in that so as to determine the status.