JPH0936725A - Photoelectric sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the photoelectric sensor immune to the effect of an external disturbance light. SOLUTION: A timing circuit 23 generates a projection pulse to drive a light emitting element 3. A light receiving output obtained by a light receiving element 4 is amplified and a comparator circuit 6 compares it with a threshold level. Then a leading edge detection circuit 21 detects a leading edge obtained in the timing of the projection pulse. Furthermore, a trailing edge detection circuit 22 detects a trailing edge obtained just after the projection pulse. Then the leading edge and the trailing edge are used to set RS flip-flop circuits 24, 25 and its AND output is used for an object sensing signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric sensor which eliminates the influence of disturbance.

[0002]

2. Description of the Related Art FIG. 10 is a block diagram showing an example of a conventional photoelectric sensor. As shown in the figure, in the conventional photoelectric sensor, the timing circuit 1 generates a light emission pulse signal of a constant cycle, and the light emission drive circuit 2 is generated based on this timing.
The light projecting element 3 is driven via. The light projecting element 3 irradiates the object detection area with light, and the light is incident on the light receiving element 4 through the object detection area. The signal of the light receiving element 4 is amplified by the AC amplifier 5 and transmitted to the comparison circuit 6.
A reference voltage source 7 is connected to the other input terminal of the comparison circuit 6, and if there is an input exceeding the reference voltage Vref of the reference voltage source 7, a comparison output is given to the gate circuit 8. The gate circuit 8 receives the same signal as the light projection pulse signal as a gate signal, and transmits the output RS obtained from the comparison circuit 6 to the flip-flop 9 during this gate signal. The output of the gate circuit 8 is given as a set input to the flip-flop 9, and the timing signal in the middle of the light projecting pulse is inputted as a reset signal from the timing generation circuit 1. R
The S flip-flop 9 is an RS flip-flop that operates based on these inputs, and its Q output is input to the shift register 10. The shift register 10 is shifted by the shift signal from the timing circuit 1. When the output of the shift register 10 is continuous, the control output circuit 11 outputs an output signal to the outside by the logical product.

Next, the operation of this photoelectric sensor is shown in FIG.
1, will be described based on the time chart of FIG. In these figures, (a) to (g) show the waveforms of the respective parts a to g in FIG. FIG. 11A shows the timing circuit 1.
Is also a light-emission pulse signal, and also serves as a gate signal applied to the gate circuit 8. When an object exists in the detection area, the reflected light from the light projecting element 3 enters the light receiving element 4,
The output is output through the AC amplifier 5 as shown in FIG. The reference voltage Vref of the reference voltage source 7 and this received light signal are compared by the comparison circuit 6, and an output is obtained as shown in FIG. 11C at the timing when the reference voltage is exceeded. Since this signal is applied to the gate circuit 8 together with the light projection pulse, the output shown in FIG. 11D is obtained from the gate circuit 8. The rising edge of this output becomes the set signal of the flip-flop 9 and is reset by the reset signal output between two light projecting pulses, so that the flip-flop 9 outputs the output shown in FIG. This output is sequentially given to the shift register 10, and the output is H for a predetermined number of times.
The object detection signal is output when the levels continue.

[0004]

However, in such a conventional photoelectric sensor, malfunction may occur when high-frequency light such as an inverter fluorescent lamp enters the light receiving element 4. For example, as shown in FIG. 12, the AC amplifier 5
Thus, as shown in FIG. 12B, an output independent of the light projection pulse signal is obtained. By doing so, the comparison circuit 6 shown in FIG.
The output shown in (c) is obtained. At the timing when this coincides with the light projection pulse, the gate output is obtained as shown in FIG. 12D, and the flip-flop 9 outputs the signal shown in FIG. Therefore, the same signal as the signal light is sent to the shift register, causing a malfunction.

Such a photoelectric sensor may be used, for example, for detecting a human body intrusion in an automatic assembly line using a robot arm or the like. In such an application, the robot arm must be reliably stopped when a person is entering the detection area. However, if the robot arm is in an operating state without stopping due to a malfunction of the photoelectric sensor, there is a problem that a person may be endangered.

The present invention has been made in view of such conventional problems, and the signal light is used only when the rising edge and the falling edge of the received light output are detected at a predetermined timing. It is an object to solve such a problem by improving a signal processing method.

[0007]

According to a first aspect of the present invention, a light projecting section which is driven periodically based on a light projecting pulse to irradiate an object detection area with light and the object detection area is provided with the light projecting section. A light-receiving unit that receives the light of the light-projecting unit, a comparison unit that discriminates the output of the light-receiving unit with a predetermined threshold value, and a rising edge detection circuit that detects the rising edge of the output of the comparison unit at the timing of the light-projection pulse. A trailing edge detection circuit for detecting the trailing edge of the output of the comparison means at a timing of a fixed period immediately after the light emitting pulse, and detection based on output timings of the trailing edge detection circuit and the trailing edge detection circuit. And a first discriminating means for discriminating the body.

Here, in the case of the reflection type photoelectric sensor, the first discriminating means obtains the output of the rising edge detecting circuit followed by the falling edge detecting circuit, or the state thereof is a plurality of light emitting pulses. The object is discriminated when it is obtained continuously in a cycle, and the object is discriminated when the transmission photoelectric sensor cannot obtain such a state.

According to a second aspect of the present invention, a light projecting section that is driven periodically based on a light projecting pulse and irradiates the object detection area with light, and the light of the light projecting section through the object detection area is provided. A light receiving section for receiving light, a comparing means for discriminating an output of the light receiving section with a predetermined threshold value, and a rising edge detection circuit for detecting the rising edge of the output of the comparing means at the timing of the light emitting pulse and a certain period immediately after that. A trailing edge detecting circuit for detecting the trailing edge of the output of the comparing means at the timing of the light emitting pulse and a certain period immediately after that, and one trailing edge of the trailing edge detecting circuit following the trailing edge detecting circuit. A counter circuit unit that outputs an output only when one output is obtained from each of the edge detection circuits, and a second determination unit that determines a detection object based on the output of the counter circuit unit, are provided. When Is shall.

Here, the second discriminating means detects the detection object when the output of the counter circuit portion is obtained in the reflection type photoelectric sensor or when the state continues for a plurality of cycles of the light projection pulse. The transmission photoelectric sensor discriminates the detection object when such a state cannot be obtained for several cycles.

[0011]

1 is a block diagram showing the overall structure of a photoelectric sensor according to an embodiment of the present invention. The same parts as those of the conventional example are designated by the same reference numerals and detailed description thereof will be omitted. In the present embodiment, the light projecting drive circuit 2 periodically drives the light projecting element 3 by a light projecting pulse signal, receives light through the light receiving element 4, amplifies its output, and outputs the reference voltage of the reference voltage source 7. The comparison with the voltage Vref is similar to the conventional example. In this embodiment, the output of the comparison circuit 6 is the rising edge detection circuit 21.
And falling edge detection circuit 22. The timing circuit 23 outputs the light emitting pulse signal and inputs the rising edge detection gate signal and the falling edge detection gate signal to the edge detection circuits 21 and 22, respectively. The rising edge detection gate signal is a gate signal having the same timing as the light projecting pulse signal, and the falling edge detection gate signal is a gate signal having a certain time timing immediately after the light projecting pulse. The rising edge detection circuit 21 and the falling edge detection circuit 22 generate a pulse signal for a certain period of time as a set signal to the flip-flops 24 and 25, respectively, when the comparison output rises or falls at the timing of the detection gate signal. It is what is output. These edge detection circuits 21 and 22 are composed of a monostable multivibrator or the like connected so as to be enabled by a detection gate signal from the timing circuit 23. In addition to the light emitting pulse signal and the detection gate signal, the timing circuit 23 receives the RS flip-flop 2 at the intermediate point of the light emitting pulse.
A reset signal is output to 4, 25. The RS flip-flops 24 and 25 are RS-type flip-flops set by the outputs of the rising edge detection circuit 21 and the falling edge detection circuit 22, respectively, and reset by the reset signal of the timing circuit 23, and the outputs thereof are the AND circuit 26. Given to. The AND circuit 26 outputs the logical product of these to the shift register 27. The shift register 27 shifts the logical product signal based on the shift signal from the timing circuit as in the conventional example, and its output is given to the control output circuit 28. The control output circuit 28 outputs a detection signal when the output from the shift register is continuous. Here, the shift register 27 and the control output circuit 28 constitute a first discriminating means which outputs an object detection signal when an H level output is continuously obtained from the AND circuit 26.

Next, the operation of this embodiment will be described with reference to the time charts of FIGS. Figures 2 and 3
(A)-(l) is a waveform diagram which shows the waveform of each part of a-1 of FIG. FIG. 2 is a time chart showing the operation at the time of detecting an object when the disturbance does not enter the light of this embodiment. FIG.
(A) shows the light projection pulse from the timing circuit 23, and the light projection element 3 is driven by this. The reflected light from the light projecting element 3 is received by the light receiving element 4 and amplified by the AC amplifier 5, so that a light receiving signal as shown in FIG. The reference voltage V of the reference voltage source 7
When ref is exceeded, the comparison circuit 6 obtains the comparison output shown in FIG. Then, since the rising edge detection gate signal of the timing that coincides with the light emitting pulse is given from the timing circuit 23 to the rising edge detection circuit 21, the detection circuit 21 outputs a constant signal synchronized with the rising edge as shown in FIG. The rising edge detection signal of the time width is output. This signal is flip-flop 24
2 and the Q output of the flip-flop 24 is input to FIG.
It is output as shown in (g). Further, FIG. 2H shows a falling edge detection gate signal having a time width of a fixed time after the falling edge of the light emitting pulse. Since it is considered that the falling edge of the comparison output of the received light signal is obtained during this period, if the comparison output falls within the period of the gate signal, the falling edge detection circuit 22 causes the falling edge detection circuit 22 as shown in FIG. An output with a constant pulse width will be obtained. This signal sets the flip-flop 25. Then, as shown in FIG. 2F, since the reset signal is output from the timing circuit 23 to these flip-flops 24 and 25 at the intermediate point of the light projecting pulse, the Q outputs of the flip-flops 24 and 25 are respectively shown in FIG. As shown in (g) and (j). Therefore, this logical product becomes as shown in FIG. 2 (k), and the H level signal is continuously input to the shift register by the shift pulse input to the shift register 27 during this period. Therefore, if the comparison output is obtained continuously for several cycles, the control output circuit 28 outputs the object detection signal.

On the other hand, as in the conventional example, a case will be described in which disturbance light synchronized with the light projection pulse occurs. FIG. 3A shows the timing of the light projection pulse, and it is assumed that the light reception signal is obtained so as to overlap with this timing. By doing so, the comparison circuit 6 is shown in FIG.
A comparison output is obtained as shown in (c). Similarly, the rising edge detection gate signal and the falling edge detection gate signal are applied to the gate circuits 21 and 22. In this case, the comparison output does not rise at the timing of the H level of the rising edge detection gate signal, and the comparison output does not fall at the timing of the falling edge detection gate signal. Therefore, inputs are added to the flip-flops 24 and 25. I can't. Therefore, the outputs of the flip-flops 24 and 25 are always at the L level and the object detection signal is not output. In this way, the rising and falling timings of the comparison output are defined, and the object detection signal is output only when the signal is obtained at the predetermined timing. In this way, the possibility of false detection can be greatly reduced.

Although the present embodiment describes the reflective photoelectric sensor, it can be applied to a transmissive photoelectric sensor. In this case, the output of the timing circuit 13 is extended to the light projecting portion via the signal cable, and light is emitted from the light projecting portion. Then, the time chart as shown in FIG. 2 is obtained in a state where the light is not shielded by the object, and when the light is shielded, all the outputs are at the L level, so that the output of the shift register 10 continues to be at the L level. An object can be detected from such a state. In this case as well, when the detection body is in the light-shielded state in which the optical axis is blocked, the malfunction at that time can be prevented even if there is ambient light, so that the state in which the object is present can be recognized as the state without error. Disappear.

Next, a second embodiment of the present invention will be described. FIG. 4 is a block diagram showing the overall configuration of the photoelectric sensor of the second embodiment. The same parts as those in the first embodiment described above are designated by the same reference numerals and detailed description thereof will be omitted. In this embodiment, the output of the rising edge detection circuit 21 is input to the counter circuit 31 and the output of the falling edge detection circuit 22 to the counter circuit 32. The counter circuits 31 and 32 respectively count the outputs of the rising edge detection circuit 21 and the falling edge detection circuit 22 and output the output of the first bit to the AND circuit 34. Further, the timing circuit 33 outputs to the falling edge detection circuit 21 and the falling edge detection circuit 22 a light emitting pulse and a rising / falling edge detection gate signal having a pulse width of a fixed period following the light emitting pulse in addition to the light emitting pulse. To do. At the same time, the reset signals of the counter circuits 31 and 32 and the shift signal to the shift register 35 are output at an intermediate timing between the two light projecting pulses. The clock signal of the shift register 35 is output prior to the reset signal to the counter circuits 31 and 32. The output of the counter circuit 32 is output to the rising edge detection circuit 21 as an inhibition signal. The counter circuits 31 and 32 and the AND circuit 34 output an output only when one output is obtained from each of the rising edge detection circuit and the trailing edge detection circuit for one light emission pulse. Are configured. Also, the shift register 35 and the control output circuit 3
Reference numeral 6 constitutes a second discriminating means for discriminating the presence / absence of an object based on the output of the counter circuit section when the condition of the logical product continuously becomes a predetermined logical state by the shift pulse outputted from the timing circuit. ing.

Next, a configuration example of the counter circuits 31 and 32 will be described. FIG. 5 is a diagram showing an example of the counter circuit 31, and the counter circuit 32 has a similar configuration, and therefore its description is omitted. The counter circuit 31 has a binary counter 31a as shown. The first bit Q0 output of the binary counter 31a is output to the AND circuit 26, and the Q1 output is output to the RS flip-flop 31b as a set signal. The reset input terminal of the RS flip-flop 31b is supplied with the reset signal from the timing circuit 33, and its Q output is connected so as to become the reset signal of the binary counter 31a.

Next, the operation of this embodiment will be described with reference to a time chart. (A) of FIG. 6, FIG. 7, and FIG.
(K) shows the waveform of each part of a to k of FIG. FIG.
(A) is a light projecting pulse signal output from the timing circuit 33, and light is emitted from the light projecting element 3 to the object detection region in synchronization with this pulse signal. If there is an object in the object detection area, light is received by the light receiving element 4, and the light receiving signal shown in FIG. By comparing this signal with the threshold value Vref in the comparison circuit 6, the comparison circuit 6 obtains the signal shown in FIG. The timing circuit 33 outputs a rising / falling edge detection gate signal having a pulse width almost twice that in synchronization with the rising edge of the light-emission pulse signal. ) And (h), outputs with a predetermined pulse width are obtained from the rising edge detection circuit 21 and the falling edge detection circuit 22, respectively. The output of the rising edge detection circuit 21 causes the first bit of the counter circuit 31 to become the H level as shown in FIG.
The first bit of the counter of the counter circuit 32 becomes H level as shown in FIG. The logical product of these counter circuits 31 and 32 is as shown in FIG. Then, as shown in FIGS. 6K and 6F, the clock signal of the shift register 35 is supplied to the timing circuit 33.
Since the reset signal is output to the counter circuits 31 and 32 immediately after the shift clock output, the output of the AND circuit 34 can be taken into the shift register 35. When such a state continues for several clocks, the output is transmitted from the shift register 35 to the control output circuit 36,
As a result, the object detection signal is output.

FIG. 7 is a time chart showing the operation when disturbance light of a constant cycle synchronized with the light projection pulse enters the light receiving element 4 as in the first embodiment. When the disturbance light as shown in FIG. 7 (b) enters, the output shown in FIG. 7 (c) is obtained from the comparison circuit 6, and if the timings of the rising / falling edge detection gate signals coincide with each other, FIG. The output of the signal shown in h) is obtained from the falling edge detection circuit 22. The counter circuit 32 is output by the output of the falling edge detection circuit 21.
Becomes H level as shown in FIG. Since this signal is given to the rising edge detection circuit 21 as an inhibition signal, even if the output of the comparison circuit 6 rises at the timing of the rising / falling edge detection gate thereafter, the output is output from the rising edge detection circuit 21. Not the counter circuit 31
Is never set. Therefore, the counter circuit 31
The output of is always L level as shown in FIG.
The output of the AND circuit 34 also becomes L level, and the object detection signal is not output. In this way, the two counter circuits 31,
Since the object detection signal is output based on the number and order of inputs applied to 32, the influence of ambient light can be effectively eliminated.

FIG. 8 is a time chart showing the operation when disturbance light of a higher frequency is applied. In this case, a signal having a higher frequency than that of the AC amplifier 5 and the comparison circuit 6 is obtained as shown in FIGS. 8B and 8C, and the timing of the rising / falling edge detection gate signal is shown in FIG. ，
As shown in (h), a rising edge and a falling edge are detected. Therefore, the logical condition is satisfied for a certain period after the falling edge is detected, and the output of the AND circuit 34 becomes H level. However, since this output is at the L level at the timing when the shift pulse is obtained, the shift register 35
Therefore, no output is transmitted to the control output circuit 11 and no malfunction occurs. As described above, in the present embodiment, it is possible to effectively eliminate erroneous output due to erroneous operation even when disturbance light having a relatively high frequency is applied.

This embodiment describes the transmission type photoelectric sensor. However, if the control output circuit 36 detects an object when L level is continuously input to the shift register 35, the transmission type photoelectric sensor can be detected. It can also be configured as a sensor. In this case, when the detection body is in a light-shielded state in which the optical axis is blocked, malfunctions at that time can be prevented even if there is ambient light, so that the state in which an object is present is not erroneously recognized as a non-existent state. .

FIG. 9 shows an example of a machine tool using the photoelectric sensor according to this embodiment. In this machine tool, a large number of transmissive photoelectric sensors are arranged on the front surface of the processing section, and when the optical axis of the transmissive photoelectric sensors is shielded by a person, for example, the processing in the apparatus is stopped. In this case as well, there is no detection of the power source or the like, and it is possible to reliably detect the human body by blocking the optical axis.

[0022]

As described in detail above, according to the present invention, the frequency of erroneous detection due to high-frequency ambient light is reduced, and the frequency of erroneous detection due to line output corresponding to the power supply is also reduced. Become. Therefore, it is possible to effectively prevent the malfunction of the controlled object.

[Brief description of drawings]

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

FIG. 2 is a time chart illustrating the operation of the present embodiment.

FIG. 3 is a time chart showing the operation of each part when ambient light enters in the present embodiment.

FIG. 4 is a block diagram showing an overall configuration of a photoelectric sensor according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a counter circuit of this embodiment.

FIG. 6 is a time chart showing the operation of this embodiment.

FIG. 7 is a time chart showing an operation when ambient light is incident on the present embodiment.

FIG. 8 is a time chart showing the operation when high-frequency ambient light enters the present embodiment.

FIG. 9 is a perspective view showing an example of a machine tool in which the photoelectric sensor according to the present embodiment is used.

FIG. 10 is a block diagram showing an example of a conventional photoelectric sensor.

FIG. 11 is a time chart showing the operation of a conventional photoelectric sensor.

FIG. 12 is a time chart showing an operation when ambient light is generated in the conventional photoelectric sensor.

[Explanation of symbols]

 1, 23, 33 Timing circuit 2 Light emitting drive circuit 3 Light emitting element 4 Light receiving element 5 AC amplifier 6 Comparison circuit 7 Reference voltage source 8 Gate circuit 9 Flip-flop 10, 27, 35 Shift register 11, 28, 36 Control output circuit 21 rising edge detection circuit 22 falling edge detection circuit 24, 25 RSFF 31, 32 counter circuit 26, 34 AND circuit

Claims (2)

[Claims] 1. A light projecting unit that is driven periodically based on a light projecting pulse to irradiate the object detection region with light, and a light receiving unit that receives the light of the light projecting unit through the object detection region, Comparing means for discriminating the output of the light receiving part by a predetermined threshold value, a rising edge detection circuit for detecting the rising edge of the output of the comparing means at the timing of the light emitting pulse, and projecting the falling edge of the output of the comparing means. A trailing edge detection circuit for detecting the timing at a fixed period immediately after the pulse; and a first discriminating means for discriminating the detection object based on the output timings of the trailing edge detection circuit and the leading edge detection circuit. A photoelectric sensor characterized by: 2. A light projecting unit that is driven periodically based on a light projecting pulse to irradiate the object detection region with light, and a light receiving unit that receives the light of the light projecting unit through the object detection region, Comparing means for discriminating the output of the light receiving portion by a predetermined threshold value, a rising edge detection circuit for detecting the rising edge of the output of the comparing means at the timing of the light projection pulse and a fixed period immediately thereafter, and the output of the comparing means. A falling edge detection circuit that detects a falling edge at the timing of the light emitting pulse and a fixed period immediately after that, and an output from the falling edge detection circuit following the rising edge detection circuit for one light emitting pulse, respectively. A photoelectric sensor comprising: a counter circuit unit that outputs an output only when one is obtained; and a second determination unit that determines a detection object based on the output of the counter circuit unit.