JPH04319683A - Apparatus for detecting object - Google Patents

Abstract

PURPOSE:To use an antenna small-sized lightweight and inexpensive like a plane antenna in this apparatus by preventing the effect due to the direct wave emitted from a transmission antenna and directly received by a receiving antenna. CONSTITUTION:The output signal 21a from an oscillator 1 is distributed into two signals by a distributor 2. One distributed output signal 21b is emitted to space from a transmission antenna 3. The other output signal 21c distributed by the distributor 2 is inputted to a synthesizer 6 as a signal 21h of a state equal to a receiving signal 21f due to a direct wave in amplitude but different therefrom in phase by 180 deg.. Therefore, when the signal 21h and the receiving signal 21f are synthesized by the synthesizer 6, a direct wave component 21df is cancelled and only a reflected wave component 21ef is outputted from the synthesizer 6.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an object detection device. Specifically, the present invention relates to an object detection device that detects an object by emitting radio waves and detecting radio waves reflected by an object.

0002

2. Description of the Related Art FIG. 4 is a block diagram showing the configuration of a conventional object detection device 50, and FIGS. 5(a) to 5(d) are time charts showing signal waveforms at various parts in FIG. In addition, the area on the left side of FIG. 5 is the object detection device 5.
0, the area on the right side shows the signal waveform when there is a detected object 53 in front of the object detection device 50.
3 is not present.

The operation of the conventional object detection device 50 when a detection object 53 is present in front will be explained with reference to FIGS. 4 and 5. The oscillator output signal 61a (FIG. 5(a)) output from the oscillator 51 is transmitted to the transmitting antenna 5.
2 is radiated into space as radio waves 61b. The radio wave 61b radiated into space is reflected by the surface of the detection object 53,
The signal is received by the receiving antenna 54. Receiving antenna 54
The radio wave 61b received by
c, and further amplified by the amplifier 55 to a signal 61d (FIG. 5(b)) at a level that is easy to process. The amplified signal 61d is envelope-detected by the detection circuit 56, converted into a low frequency signal 61e (FIG. 5(c)), and then sent to the comparator 58.
is input. On the other hand, a reference voltage 61f is inputted to the comparator 58 from the reference power supply 57, and the low frequency signal 61e inputted to the comparator 58 is compared with the reference voltage 61f. This reference voltage 61f is set to be lower than the level of the low frequency signal 61e when the detection object 53 is present, as shown in FIG. 5(c).
As shown in (d), the comparator 58 outputs a high (H) level detection signal 61g representing object detection.

On the other hand, when there is no detection object 53 in front of the object detection device 50, the transmitting antenna 52
Since the radio wave 61b radiated from the receiving antenna 54 is not received by the receiving antenna 54, the received signal 61c obtained from the receiving antenna 54 and the amplified signal 61d output from the amplifier 55
becomes zero level, as shown in FIG. 5(b). Therefore, the low frequency signal 6 whose envelope has been detected by the detection circuit 56
1e also becomes zero level as shown in FIG. 5(c) and becomes lower than the reference voltage 61f of the reference power source 57, so the comparator 58 outputs a low (L) level indicating that no object is detected as shown in FIG. 5(d). A detection signal 61g is output. Therefore, the presence or absence of the detection object 53 can be determined based on the level (H, L) of the detection signal 61g.

FIG. 6 shows the structure of a conventional object detection device 50. This object detection device 50 incorporates a transmitting circuit board 72 in which an oscillator and the like are mounted in a waveguide 71 on the transmitting side, and widens the opening of the waveguide 71 in a tapered shape to form a transmitting antenna (horn antenna). )52. Similarly, a receiving circuit board 74 on which an amplifier, a detection circuit, etc. are mounted is built into the waveguide 73 on the receiving side, and the receiving antenna (
(horn antenna) 54.

[0006] As described above, the conventional object detection device was of the horn antenna type, which had the drawbacks of being large in size, heavy, and expensive.

On the other hand, planar antennas are attracting attention as small, lightweight, and low-cost antennas. The planar antenna is 1
A microstrip line is constructed on a printed circuit board and can be used as an antenna.For example, a batch type planar antenna 81 as shown in FIG. Slot type planar antenna 82, coplanar type planar antenna 8 as shown in FIG. 7(c)
3. There is a line type planar antenna 84 as shown in FIG. 7(d).

However, there are problems when using such a planar antenna in an object detection device. Planar antennas have weaker directivity than horn antennas, and radiated radio waves tend to spread out and wrap around. ), the radio waves radiated from the transmitting flat antenna are
Even if there is no object to be detected, it will be received by the receiving antenna due to wraparound, making it impossible to correctly determine the presence or absence of an object. In other words, the strength of the received signal (reflected signal) due to the radio waves reflected by the sensing object and received by the receiving flat antenna is the same as the strength of the radio wave that directly enters the receiving flat antenna from the transmitting flat antenna due to wraparound (hereinafter referred to as direct wave). ), the received signal is a weak reflected signal superimposed on a large loop signal, and even if an object is present, the reflected signal / loop signal is very small. The ratio was small, and even when an object was not present, the receiving planar antenna received a wraparound signal, resulting in low accuracy in determining the presence or absence of an object, making it impossible to put it into practical use.

The present invention has been made in view of the drawbacks of the conventional examples described above, and its purpose is to prevent the influence of received signals radiated from a transmitting antenna and directly received by a receiving antenna. By doing so, it is possible to use a small, lightweight, and inexpensive antenna such as a planar antenna in the object detection device.

0010

[Means for Solving the Problems] The object detection device of the present invention includes an oscillator, a distributor that distributes the output of the oscillator, and converts one of the oscillator output signals distributed by the distributor into radio waves and radiates them into space. a transmitting antenna for receiving radio waves radiated from the transmitting antenna and converting them into received signals; and a receiving antenna for receiving the radio waves radiated from the transmitting antenna and converting them into received signals, and the received signal of the receiving antenna and the output of the other oscillator distributed by the distributor. It is characterized by consisting of a synthesizer that synthesizes the signals.

Particularly, the object detection device of the present invention is effective when the amplitudes of the oscillator output signal synthesized by the synthesizer and the received signal due to the direct wave are made equal, and the phases of both signals are made to differ by 180 degrees. be.

0012

[Operation] In the present invention, since a part of the oscillator output signal is transmitted from the transmitting side distributor to the receiving side combiner,
A synthesizer combines the direct wave received signal that is radiated from the transmitting antenna and goes directly to the receiving antenna without being reflected by an object, and the oscillator output signal that is input to the receiving side through the distributor and combiner. It can be synthesized. At this time, by appropriately adjusting the amplitude and phase of the oscillator output signal transmitted from the distributor to the combiner, the combined signal with the received signal due to the direct wave can be made smaller than the received signal due to the radio waves reflected by the detection object. It can be reduced to the level In particular, if the amplitudes of the oscillator output signal and the received signal to be combined by a combiner are made equal, and the phases of the two signals are made to differ by 180 degrees, the combined signal can be made zero.

As a result, the influence of direct waves can be reduced or eliminated, and antennas with low directivity, such as planar antennas, can be used as transmitting antennas and receiving antennas.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the configuration of an object detection device 31 according to an embodiment of the present invention. 1 is an oscillator provided on the transmitting side, and an oscillator output signal 21a output from the oscillator 1 is distributed by a distributor 2 into two oscillator output signals 21b and 21c. One of the distributed oscillator output signals 21b is sent to the transmitting antenna 3, and is radiated into space from the transmitting antenna 3 as radio waves 21d and 21e.

Part of radio waves radiated into space (direct waves) 2
1d goes around to the receiving antenna 4 and is directly received. In addition, part 2 of the radio waves radiated from the transmitting antenna 3
If the detection object 5 exists, the signal 1e is reflected by the surface of the detection object 5 and received by the reception antenna 4. The radio waves 21d and 21e received by the receiving antenna 4 are again converted into an electrical received signal 21f and input to the combiner 6. Therefore, when the detection object 5 does not exist, the reception signal 21f is only a reception signal due to the direct wave 21d, and when the detection object 5 exists, the reception signal 21f includes the reception signal due to the direct wave 21d reflected by the object 5. This is a form in which weak received signals from the radio waves 21e are superimposed (see FIG. 2(c)).

The other oscillator output signal 21c distributed by the divider 2 is input to the combiner 6 through a phase shifter 7 and an attenuator 8. The phase shifter 7 is adjusted so that the phase of the oscillator output signal 21h input to the synthesizer 6 differs by 180 degrees from the phase of the received signal 21f due to the direct wave. The amplitude of the input oscillator output signal 21h is adjusted to be equal to the amplitude of the direct wave reception signal 21f. The synthesizer 6 outputs a composite signal 21i obtained by superimposing the oscillator output signal 21h and the received signal 21f. The composite signal 21i is amplified by the amplifier 9 to a signal 21j at a level that is easy to process. This amplified signal 21j is envelope-detected by the detection circuit 10, converted into a low frequency signal 21k, and then sent to the comparator 1.
1 is input. On the other hand, a reference voltage 21m is inputted to the comparator 11 from the reference power source 12, and the low frequency signal 21k inputted to the comparator 11 is compared with the reference voltage 21m. This reference voltage 21m is set to be lower than the level of the low frequency signal 21k when the detection object 5 is present (see FIG. 2(g)), and the comparator 11 detects the presence or absence of the object. A detection signal 21n for discrimination is output.

FIG. 3 is a schematic perspective view showing the configuration of the object detection device 31 mentioned above. The transmitting antenna 3 and the receiving antenna 4 are planar antennas, and the transmitting antenna 3 is a planar antenna.
The receiving planar antenna 4 is constructed on the same printed circuit board 32. Also, behind the transmitting antenna 3 and the receiving antenna 4, an oscillator 1, a distributor 2, a combiner 6,
A circuit board 33 on which the amplifier 9 and other circuits are mounted is disposed, and both antennas 3 and 4 and the circuit board 33 are housed in a casing 34.

FIGS. 2A to 2H are time charts showing signal waveforms at various parts in the block diagram of FIG. In FIG. 2, the left region shows the signal waveform when the detection object 5 does not exist in front of the object detection device 31, and the right region shows the signal waveform when the detection object 5 exists in front of the object detection device 31. It shows.

First, the operation when the object 5 does not exist in front of the object detection device 31 will be explained. From the oscillator 1, a sinusoidal oscillator output signal 2 is output as shown in FIG. 2(a).
1a is output. This oscillator output signal 21a is
The signal is divided into two by the distributor 2, and in-phase oscillator output signals 21b and 21c as shown in FIG. 2(b) are obtained. The oscillator output signal 21b is converted into a radio wave and radiated from the transmitting antenna, but since there is no detection object 5, the radio wave received by the receiving antenna 4 is a radio wave (direct wave) 21d that is directly received by looping around. It is. A received signal 21f converted from this direct wave 21d is shown in FIG. 2(c). On the other hand, the oscillator output signal 21c distributed by the distributor 2
By passing through the phase shifter 7, the phase is shifted so that it becomes a signal 21g whose phase is 180 degrees different from the received signal 21f as shown in FIG. 2(d), and further by passing through the attenuator 8. , as shown in FIG. 2(e), the received signal 21f
The signal 21h is attenuated to have the same amplitude as the signal 21h. Therefore, since the received signal 21f and the signal 21h input to the combiner 6 have the same amplitude and a 180 degree difference in phase, when the two signals 21f and 21h are added together,
As shown in FIG. 2(f), the combined output 21 from the combiner 6
i becomes zero. As a result, the amplified signal 21j input to the wave detector 10 is also zero, and the low frequency signal 21k whose envelope has been detected by the wave detector 10 is also zero. Therefore, Fig. 2 (g
), when the low frequency signal 21k and the reference voltage 21m are compared, the comparator 11 outputs a low (L) level detection signal 2 indicating that no object is detected, as shown in FIG. 2(h).
1n is output.

Next, the operation when the detection object 5 is present in front of the object detection device 31 will be explained. In this case, the radio waves radiated from the transmitting antenna 3 include a direct wave 21d due to wraparound and a radio wave 21e reflected by the object 5.
are received by the receiving antenna 4 in a mixed state,
It is converted into a received signal 21f. This received signal 21f is
As shown in FIG. 2C, a signal component (direct wave component) 21df due to the direct wave 21d and a signal component (reflected wave component) 21ef due to the reflected wave 21e overlap. This direct wave component 21df has the same amplitude as the signal 21h which is distributed by the distributor 2, passes through the phase shifter 7 and the attenuator 8, and is input to the combiner 6, and has a phase difference of 180 degrees, so the combiner When the signal 21h and the received signal 21f are added in step 6, the direct wave component 21df is canceled, and the result is shown in FIG. 2(f).
As shown in , only the reflected wave component 21ef is the combined output 21
It is output from the synthesizer 6 as i. This reflected wave component 21
ef is amplified by an amplifier 9. At this time, since the signal to be amplified does not include the direct wave component 21df, only the reflected wave component 21ef can be amplified to the required voltage level. Thereafter, the amplified signal 21j is envelope-detected by the detection circuit 10, and becomes a low-frequency signal 21k larger than the reference voltage 21m as shown in FIG. 2(g).
When k and the reference voltage 21m are compared by the comparator 11, FIG.
As shown in (h), the comparator 11 outputs a high (H) level detection signal 21n representing object detection.

In the above embodiment, the phase and amplitude of the oscillator output signals distributed by the distributor are adjusted using a phase shifter and an attenuator, respectively, but the phase shifter and attenuator may be omitted. It is possible. Since the transport device changes the phase of the signal, it is sufficient if it includes some kind of signal delay means. The simplest means of delay is to change the length of the connection lines that constitute each circuit block. Therefore, it is sufficient to adjust the length of the signal line connecting the divider and combiner, and adjust the impedance of the line so that the phase differs by 180 degrees from the phase of the direct wave component input to the combiner. Furthermore, if the distribution ratio of the distributor is adjusted so that the amplitude of the signal input from the distributor to the combiner and the direct wave component are equal, an attenuator is also not necessary.

[0022] With the above configuration, it is possible to prevent the influence of radio waves (direct wave components) and to configure an object detection device using a planar antenna.

[0023]

According to the present invention, the oscillator output signal transmitted from the transmitting-side distributor to the receiving-side combiner and the received signal as a direct wave received by the receiving antenna are partially (
Alternatively, the influence of direct waves can be prevented by canceling them out (completely). As a result, it becomes possible to use an antenna with low directivity, such as a planar antenna, as a transmitting antenna or a receiving antenna, and it becomes possible to manufacture a small, lightweight, and inexpensive object detection device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an object detection device according to an embodiment of the present invention.

2(a) to (h) are time charts showing signal waveforms at each part in FIG. 1; FIG.

FIG. 3 is a schematic perspective view showing the structure of an object detection device using a planar antenna.

FIG. 4 is a block diagram showing the configuration of a conventional object detection device.

5A to 5D are time charts showing signal waveforms at each part in FIG. 4;

FIG. 6 is a schematic perspective view showing the structure of an object detection device using a horn antenna.

FIGS. 7(a), (b), (c), and (d) are perspective views showing various planar antennas.

[Explanation of symbols]

1 Oscillator 2　Distributor 3 Transmission antenna 4 Receiving antenna 6 Synthesizer

Claims (2)

[Claims] [Claim 1] An oscillator, a distributor that distributes the output of the oscillator, a transmitting antenna that converts one of the oscillator output signals distributed by the distributor into a radio wave and radiates it into space, and An object consisting of a receiving antenna for receiving radiated radio waves and converting them into a received signal, and a combiner for combining the received signal of the receiving antenna and the output signal of the other oscillator distributed by the distributor. Detection device. 2. The oscillator output signal synthesized by a synthesizer and the received signal as a direct wave have the same amplitude, and the phases of the two signals are made to differ by 180 degrees. The object detection device described.