JPH01285883A - Microwave proximity switch - Google Patents

Abstract

PURPOSE:To certainly detect a stationary body even when said body is present at any position, by a method wherein a proximity switch is driven by a drive signal having two or more different voltage levels to transmit two or more difference frequencies and different phase differences are subject to level discrimination. CONSTITUTION:A drive signal having a waveform wherein different voltage levels V1, V2 appear alternately at a definite cycle is inputted to a microwayve oscillator 12 and also inputted to the input terminal of a differential amplifying circuit 16 as a reference signal. The oscillator 12 generates a microwave of frequency f1 at the time of voltage V1 and a microwave of frequency f2 at the time of voltage V2. Each of the microwaves is transmitted toward the detection region of a body 30 through a transmitter-receiver 14 and a mixer 13 mixes the microwave, which is returned from the body 30 and received by the transmitter-receiver 14, with the oscillation output of the oscillator 12. An amplifying circuit 15 amplifies the output of the mixer 13 to a reference signal. The differential amplifying circuit 16 amplifies the difference between the mixer signal inputted through the circuit 15 and the reference signal. A comparator 17 compares the output signal of the circuit 16 with voltage of a definite threshold value level and applies an H-level signal to an integrating circuit 18 when said output signal exceeds the threshold value level.

Description

[Detailed Description of the Invention] Summary of the Invention A voltage waveform having at least two or more different levels and in which these levels are switched at a constant cycle is used to
By driving a microwave oscillation element r having O characteristics, one or more microwaves of two or more different frequencies are generated and transmitted toward an object. The presence or absence of an object is determined by mixing the received microwave signal and the oscillation signal (transmission signal) and detecting their phase difference. Even if the phases of the transmitted and received signals of one frequency match, the phases of the transmitted and received signals of the other frequency do not match, so even if the object is stationary, can be detected.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective microwave proximity switch that uses microwaves to detect whether there is an object nearby that reflects microwaves.

Conventional technology and its problems Proximity switches use magnetism, electromagnetic induction, ultra-blind waves, light, etc. to detect the presence or absence of products in factories.

- With the progress of automation such as factory automation and CIM (combicoater integrated manufacturing), its importance as the most basic sensor is increasing.

However, proximity switches that use magnetism and electromagnetic induction have shorter detection distances than proximity switches that use ultrasonic waves, light, etc., and the detection object is magnetic.

The drawback is that it is limited to metals, etc. On the other hand, with proximity switches that use ultrasonic waves, it is difficult to detect objects near the sensor due to the reverberations of the mechanical vibrations of the ultrasonic transducer, and objects within a distance range of 10 cm to 20 cttl from the sensor are difficult to detect. The disadvantage is that it cannot be detected. In addition, proximity switches that use light (photoelectric switches) have a longer detection distance than other types of proximity switches, but due to the nature of light, they cannot detect objects that are transparent like glass or have a matte black surface. On the other hand, the reflected light is particularly difficult to detect.

Furthermore, conventional proximity switches using microwaves have an i+J ability to detect moving objects, but there is a problem in that they cannot reliably detect stationary objects.

A conventional microwave proximity switch transmits a continuous oscillation microwave signal with a single frequency and receives the reflected wave from an object.The transmitted signal and the received signal are combined lr1' to determine the phase. The presence or absence of an object is determined by homodicy detection. If the object is moving, the frequency of the reflected microwave changes due to the Doppler effect, so a detection output can be obtained. On the other hand, if the object is stationary, the frequencies of the transmitting signal and receiving signal are the same, so for an object located at a position where the phases of the transmitting signal and receiving signal match, the detection output will be zero. Put it away.

SUMMARY OF THE INVENTION OBJECTS OF THE INVENTION An object of the present invention is to provide a microwave proximity switch that can reliably detect stationary objects.

Arrangement 1 of the Invention Functions and Effects The microwave proximity switch according to the present invention has a microwave transmitting means including a microwave oscillating means whose oscillation frequency is variable depending on the voltage, and has at least two or more different voltage levels. A drive means which generates a drive signal whose level changes periodically at a constant cycle and gives it to the oscillation means; The output signal of the microwave receiving means including the mixing means for outputting and the mixing means described in -1- is compared with the reference signal corresponding to the output of the mixing means in the case where there is no microwave reflecting object, and the presence or absence of the object is determined. The present invention is characterized in that it includes object detection means that outputs a signal representing .

According to the microwave proximity switch of this invention.

By driving the microwave oscillation means with at least two or more different voltage levels using a drive signal, microwaves of at least two or more different frequencies are periodically transmitted in a time-division manner. Therefore, even if the transmitted microwave signal of one frequency and the received signal (microwaves reflected from an object) are in a position where the phases match, the transmitted microwave signal and the received microwave signal of the other frequency There is a phase difference in the signal.

It becomes possible to detect objects based on this phase difference. This makes it possible to reliably detect a stationary object no matter where it is located.

It is also possible to detect objects with transparent glass or black surfaces that do not reflect light.

Furthermore, there is no dead zone near the switch and the distance Oa
It is possible to detect objects from a distance of m, and the detectable distance can be relatively long.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 shows the electrical configuration of a microwave proximity switch.

The drive circuit 11 generates a drive signal having a waveform having a positive offset voltage and in which 12 different voltage levels V 1 and 2 appear alternately at a constant period. This drive signal is applied to the VCO (
The signal is applied to a microwave oscillator 12 having voltage controlled oscillation characteristics, and is also input to one input terminal of a differential amplifier circuit 16 as a reference signal. An example of the waveform of this drive signal (reference signal) is shown on the left side of FIG.

The microwave oscillator 12 has a drive signal of voltage ■1;
When the voltage is V2, a microwave with a frequency f2 different from f is emitted! This oscillated microwave is transmitted through a transducer (antenna, L-:, Z, etc.) 14 toward the detection area of the object 30. The microwave oscillator includes a Gunn diode.

A mixer (mixing circuit) 13 mixes the microwave (received signal) reflected from the object 30 and received by the transducer 14 with the oscillation output (transmitted signal) of the oscillator 12. It includes a Gunn diode and a square-law detection diode connected to the anode.The high frequency component obtained by this mixer 3 is attenuated because it has an extremely high frequency (for example, several tens of G11z), and the mixer 3 outputs only the signal component representing the phase difference between the transmitted signal and the received signal.

The amplifier circuit 15 amplifies the output of the mixer 3 to the level of the reference signal, and can independently adjust the offset amplification factor and amplitude amplification factor. The mixer output when no object is present within the detection area is depicted in the center of Figure 2. The amplifier circuit 15 converts such mixer output into a second
As shown on the right side of the figure, the signal is amplified to have exactly the same waveform as the reference signal mentioned above. If an object exists, the phase difference component mentioned above appears in the mixer output, and the waveform becomes different from that shown in the center of FIG. 2, so the output of the amplifier circuit 15 also differs from the reference signal as described later. It becomes a waveform. The output of the amplifier circuit 15 is input to the other input terminal of the differential amplifier circuit 16.

The differential amplifier circuit 6 functions to amplify the difference between the mixer output inputted through the amplifier circuit 15 and the reference signal (equal to the mixer output when no object exists, such as in a double series). Includes an absolute value circuit that converts the difference into an absolute value. The output signal of the differential amplifier circuit 16 is input to a comparator 17.

Comparator 17 compares the output signal of differential amplifier circuit 16 with a voltage at a certain threshold level, and generates an H level signal when the output signal level exceeds this threshold level. The output of the comparator 17 is given to an integrating circuit 18.

The integrating circuit 18 is a circuit that rapidly charges when the output of the comparator 17 is at H level, and slowly discharges when it is at L level. The output circuit 19 generates a sufficiently large output current or output voltage from the output of the one integrating circuit 18, and includes a comparator that compares the output of the integrating circuit 18 with a predetermined threshold value.

In the circuit of FIG. 1, the output signal of the mixer 13 when no object is present is made to match the output signal of the drive circuit 11 by the amplifier circuit 15, but the output signal of the drive circuit 11 is added to the output signal of the mixer 13. (or its amplified signal). Alternatively, the output of the differential amplifier circuit 16 may be integrated and compared with a predetermined threshold value in a comparator to generate an on/off signal.

FIG. 3 shows the principle of detecting a stationary object using microwaves alternately oscillated at two frequencies f 1 and f 2 . FIG. 3(A) shows a microwave transmission signal of frequency f1 (shown by a solid line) and a received signal (shown by a broken line) from an object 30.
This shows that the phase of the reflected wave from the Regarding this frequency fl, as shown in FIG. 3(C), the mixer output (in FIGS. 3 and 4 and their explanations, the mixer output refers to the output after being amplified by the amplifier circuit 15) is the standard. It matched the signal.

These differential outputs become zero. However, one frequency f
Even if the phases of the transmitted signal and the received signal of 1 match, for a different frequency f2.

As shown in Figure 3 (B), the transmitted signal (solid line) and the object 3
The phases of the received signal (broken line), which is a reflected wave from 0, are never the same, and as shown in FIG. 3(C), a mixer output having a level difference from the reference signal is obtained.

In this way, even if the transmitting and receiving waves are in the same phase for microwaves of one frequency.

For microwaves of the other frequency, we can expect a mixer output that is different from the mixer output when there is no object.
The mixer output will never match the reference signal as a whole.

No matter what position the stationary detection object 30 is in, the mixer output will be as shown in FIG. 4 (A), (
B), (C), and (D), and as long as the object 30 is within the detection range, it will never completely match the reference signal.

As mentioned above, the difference between the reference signal and the mixer output is amplified by the differential amplifier circuit 16 and then sent to the comparator 17. However, since the differential amplifier circuit 16 includes an absolute value circuit, the difference between the reference signal and the mixer output is
) and (D) and (B) and (C) each have the same differential output, and this output always has a positive voltage value. Regarding the mixer outputs in Figures 4(A) and (D), the comparator 17 output is always at the H level (object detected), but as shown in Figures 4(B) and (C). As for the mixer output, as shown in FIG. 5, 1H level and L level are alternately repeated. (, or [, from] - As described above, the output waveform of the integrating circuit 18 is always above a certain level due to the integrating circuit 18 having different charging and discharging time constants.

It becomes possible to obtain the output of the detection a by the comparator included in the output circuit 19.

In this way, this microwave proximity switch is of the single-reflection type and is capable of detecting stationary objects. Of course, it is also possible to detect moving objects.

Microwaves do not become transparent even on glass, which is transparent to light, and reflect almost no light, and sufficient reflected waves can be obtained even on metals, resins, etc. that have matte surfaces. Both are detectable. Therefore, these objects, which are difficult to detect with conventional reflective photoelectric switches, can be detected only by 1-iJ.

Furthermore, as is clear from the detection principle described in -1-1,
Unlike ultrasonic proximity switches, there is no dead zone in proximity, and objects can be detected from a distance of 0 button. The detection distance varies depending on the capability of the device, but is up to 24Gtl.
When using microwaves with a drive frequency of 50011z and an output of 5IIIW, the detection distance of foci culm is sufficiently possible and is sufficiently longer than the normal maximum detection distance of about 2 cm for magnetic type and electromagnetic induction type proximity switches. .

Microwave proximity switches can detect objects without being affected by the color or slight unevenness of the surface, and since microwaves pass through cardboard boxes, it is possible to detect whether or not there is an object inside the cardboard box. It can also be applied to destructive fluoroscopic inspection.

In the second embodiment, the mixer output is signal-processed by an analog circuit, but after A/D conversion of the mixer output,
By a digital signal processing processor or CPU,
Needless to say, it is also possible to perform digital signal processing equivalent to analog signal processing circuits.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the electrical configuration of a microwave proximity switch according to an embodiment of the present invention. FIG. 2 is a waveform diagram showing how the reference signal and mixer output are amplified. 3(A) and 3(B) show the phase relationship between microwave transmission and reception, and FIG. 3(C) is a waveform diagram showing the mixer output obtained. Figures 4 (A), (B), (C), and (D> are waveform diagrams of various mixer outputs. Figure 5 is a waveform diagram showing an example of the output waveforms of the comparator and the integrating circuit. 10... Microwave proximity switch. ii... Drive circuit. 12... Oscillation circuit. 13... Mixer. 16... Differential amplifier circuit 2 17... Comparator. 18... Integral circuit. Patent applicant Tateishi Electric Co., Ltd. Agent Patent attorney Kenji Ushiku (and one other person) Figure 3 (A) (B) (C) Time - Figure 4 (A) (C)

Claims (1)

[Claims] Microwave transmission means including microwave oscillation means whose oscillation frequency is variable depending on voltage, and a drive having at least two or more different voltage levels, in which these voltage levels are periodically switched at a constant cycle. A microwave receiving means including a driving means for generating a signal and applying it to the oscillating means, a mixing means for mixing the oscillated signal by the oscillating means and a received signal and outputting a signal representing a phase difference thereof, and the mixing means. A microwave proximity switch comprising: object detection means for comparing the output signal of the means with a reference signal corresponding to the output of the mixing means when there is no microwave reflecting object, and outputting a signal indicating the presence or absence of the object.