JPH0327872B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a moving object detection device, more specifically,
A so-called Doppler effect type moving object that detects the movement of an object by sending out ultrasonic waves into the monitoring space and detecting the frequency shift that occurs in the reflected waves as the object moves within the monitoring space. The present invention relates to a moving object detection device in which a single ultrasonic transducer serves as both a transmitter and a receiver.

[Background technology] Generally, ultrasonic waves are transmitted into a monitoring space and reflected waves from a detected object existing in the monitored space are received, and when the detected object moves and a frequency shift occurs due to the Doppler effect. In this type of moving object detection device that detects a moving object by detecting the difference between the transmitting frequency and the receiving frequency, it is necessary to detect the frequency deviation of the receiving frequency with respect to the transmitting frequency. Ultrasonic waves are continuously transmitted, and the transmitter and receiver are generally constructed separately so that the transmitted and received signals are not mixed. However, if the transmitter and receiver are separate, it becomes difficult to position them when setting up the monitoring space, and two ultrasonic transducers are required, which increases costs. A problem arises.

In order to solve this problem, it is possible to consider a system in which a single ultrasonic transducer serves as both a transmitter and a receiver, as shown in FIG. In this configuration, a transmission signal output from an oscillation circuit 11 that oscillates at a frequency equal to the frequency of the transmission ultrasound is amplified by an amplifier circuit 12, and then input to an ultrasound transducer 13 formed of a piezo element. Ultrasonic waves are transmitted into the monitoring space. The ultrasonic wave reflected by an object existing in the monitoring space is received by the same ultrasonic transducer 13 that sent out the ultrasonic wave and converted into a received signal, and then the received signal and the amplifier circuit 12 are combined. The signal is detected by a detection circuit 21 which receives the output as an input. Here, since the input signal to the detection circuit 21 is a mixture of the received signal and the transmitted signal, if the frequencies of the received signal and the transmitted signal are different, a beat component is generated due to the principle of superposition. It turns out. In other words, when an object existing in the monitoring space moves, a frequency shift, which is the Doppler effect, occurs in the received signal, so a beat component occurs in the input signal to the detection circuit 21. The output of the detection circuit 21 is amplified by the amplifier circuit 22 and then input to the comparison circuit 23.
When the output level is equal to or higher than a predetermined value, a detection signal is output, and a contact output is obtained from the switching circuit 24.

The above configuration operates normally when there is no noise due to disturbances such as wind or noise, but when such noise is present, a band amplification circuit is used as the amplifier circuit 22 to detect a predetermined frequency component. Even if only noise is allowed to pass through, the influence of noise cannot be completely prevented. In other words, there may be an overlap between the beat frequency caused by the frequency shift caused by the movement of the object to be detected and the beat frequency caused by noise, and this is a component that cannot be separated by the band amplification circuit. The problem with the circuit configuration is that malfunctions occur due to noise.

[Object of the Invention] The present invention has been made in view of the above points, and its main purpose is to provide a moving device in which a single vibrator serves as both a transmitter and a receiver. An object of the present invention is to provide a moving object detection device in which malfunctions due to disturbance noise do not occur in an object detection circuit.

[Disclosure of the Invention] Example 1 The configuration of the present invention will be explained based on FIG. As shown in FIG. 1, the output of an oscillation circuit 11 that continuously oscillates at a constant frequency is amplified by an amplifier circuit 12 and then input to an impedance circuit 14. The impedance circuit 14 is a circuit whose output impedance is set to be large, and is designed to reduce the looping of signals from the subsequent stage. The output of the impedance circuit 14 is input to the ultrasonic transducer 13, and the ultrasonic transducer 13 continuously emits ultrasonic waves of a constant frequency toward the monitoring space. The ultrasonic wave emitted from the ultrasonic transducer 13 is reflected by an object existing in the monitoring space, and the reflected wave is received by the ultrasonic transducer 13 again, which converts it into a received signal. The ultrasonic transducer 13 is composed of a piezo element, etc., and emits an ultrasonic wave that matches the frequency of the applied electric vibration, and also emits a received signal that matches the frequency of the received ultrasonic wave. Output. The reception signal received by the ultrasonic transducer 13 is input to the converter circuit 20 in a state where it is superimposed on the transmission signal. Here, the existence of the impedance circuit 14 prevents the received signal from going around to the circuit on the transmitting side, thereby increasing receiving sensitivity. The converter circuit 20 includes a pair of phase shift circuits 25a and 25b that respectively shift the output signals of the oscillation circuit 11 by 90 degrees;
A pair of mixer circuits 26a, 26b that mix the reference signal and the received signal, which are the output signals of each phase shift circuit 25a, 25b, and each mixer circuit 26a,
A pair of detection circuits 21a and 21b each detecting the intermediate signal output from the detection circuit 26b, and each detection circuit 2
It is composed of a pair of amplifier circuits 22a and 22b that amplify the outputs of 1a and 21b, respectively. Here, one of the phase shift circuits 25a and 25b advances the phase of the output signal of the oscillation circuit 11 by 90 degrees and outputs a reference signal.
The other outputs the reference signal with a delay of 90 degrees.

The output of the converter circuit 20 has an output level of "H" or "L" depending on whether the signal is positive or negative.
a quadrant detection circuit that detects the quadrant to which the received signal belongs in a vector plane whose reference axis is the two signals that are the output signals of the converter circuit 20;
The detected signal is input to the signal processing circuit 30, which includes a quadrant transition detection circuit that detects the quadrant transition detected by the quadrant detection circuit, and an output circuit that outputs a detection signal when a predetermined number of quadrant transitions occur in succession. When the movement of the sensing object is detected, the switching circuit 31 is closed by a detection signal obtained as an output of the signal processing circuit 30, and a display device or the like is driven. As for this signal processing circuit, a conventionally known circuit disclosed in Japanese Patent Laid-Open No. 55-63774 and the like can be used.

(Operation) The operation of the converter circuit 20 will be described below.
2a shows the output signal S ₁ of the oscillation circuit 11, and FIG. 2b shows the input signal S ₂ to the converter circuit 20. FIG. The input signal _S2 to the converter circuit 20 is a mixed signal of the output signal _S1 of the oscillation circuit 11 and the received signal which is the output signal of the ultrasonic transducer 13,
The output signal S ₁ of the oscillation circuit 11, the received signal, and the input signal S ₂ to the converter circuit 20 are each expressed as a vector.
If expressed as b ₁ , b ₂ , b, <b>=<b ₁ >+<b ₂ >
This relationship holds true. Here, each mixer circuit 26
a, 26b are input signals to the converter circuit 20;
The phase is 90 with respect to S ₂ and the output signal S ₁ of the oscillation circuit 11.
The reference signals (FIG. 2 c, d) shifted by a certain degree are mixed, and the amplitudes of both signals input to each mixer circuit 26a, 26b are Assuming that they are equal,
By the principle of superposition, each mixer circuit 26a,
As _{shown in FIG} .
The signal will be shifted by 45 degrees. Here, one phase shift circuit 2
5a indicates the phase with respect to the output signal _S1 of the oscillation circuit 11.
Advance by 90 degrees (c in Figure 3), the other phase shift circuit 25b
Since the phase is delayed by 90 degrees (d in Figure 3),
As shown in the vector relationship as shown in FIG. 3, the output e of the mixer circuit 26a is the output signal a of the oscillation circuit 11.
It can be seen that the phase of the output f of the mixer circuit 26b is delayed by 45 degrees, and the phase of the output f of the mixer circuit 26b is delayed by 45 degrees. In other words,
A phase difference of 90 degrees will occur between the output signals e and f of both mixer circuits 26a and 26b. If the detected object moves and the received signal includes a frequency shift, the received signal will be added to the transmitted signal as described above, so in the vector plane, the converter circuit The input signal b to the mixer circuit 20 is equal to the sum of the output signals e and f of the mixer circuits 26a and 26b and the received signal _b2 . That is,
The signals e and f, which serve as the reference for the intermediate signals S ₅ and S ₆ which are the outputs of the mixer circuits 26a and 26b, have a phase difference of 90 degrees, and if we consider a vector plane with these signals as the reference axis, the received wave The signal b ₂ can be thought of as a rotation vector rotating around the origin of this vector plane. In other words, the mixer circuits 26a, 26b
If the output of the vector is detected and a signal corresponding to the positive or negative sign is detected, this will represent the quadrant in which the received signal exists in the vector plane. If the signals corresponding to the positive and negative signs of the outputs detected by the mixer circuits 26a and 26b are the axis code signals X and Y, respectively, when an object that reflects ultrasonic waves approaches, the frequency of the reflected wave will be higher than the oscillation frequency. Therefore, the phase of the axis code signal It advances against Y. Therefore, in a vector plane with the axis code signals X and Y as the basic axes, when an object approaches, the rotation vector represented by the received signal rotates clockwise around the origin, and when the object moves away, it rotates counterclockwise. It rotates.
If this is detected by the signal processing circuit 30, the movement of the object to be detected and the direction of movement thereof can be detected.

As described above, by converting the received signal into a pair of intermediate signals with different phases, if the behavior of the received signal on the vector plane with both intermediate signals as the reference axis is detected, the signal processing circuit can be adjusted as appropriate. By using this, it is possible to easily separate the frequency shift component caused by the movement of the object from the noise component of the disturbance, and malfunctions due to noise can be prevented.

[Effects of the Invention] As described above, the present invention includes an oscillation circuit that continuously outputs a transmission signal of a constant frequency, and an oscillation circuit that receives the transmission signal and transmits ultrasonic waves to a monitoring space. A transmitting and receiving ultrasonic transducer that receives reflected waves from a sensing object and outputs a received signal, and a pair of reference signals and transmitting signals that have the same frequency as the transmitting signal and a 180 degree phase difference. A converter circuit that mixes the superimposed received signal and converts it into a pair of intermediate signals with a 90 degree phase difference, and a transition of the quadrant in which the received signal exists in a vector plane with both intermediate signals as the basic axes. Since it is equipped with a signal processing circuit that detects the movement of the object to be detected by detecting the movement of the object to be detected and outputs a detection signal, it is possible to detect moving objects in which a single transducer serves as both a transmitter and a receiver. In the circuit, the received signal superimposed on the transmitted signal is mixed with a pair of reference signals having a phase difference of 180 degrees and converted into a pair of intermediate signals having a phase difference of 90 degrees. By detecting the behavior of the received signal on a vector plane with the signal as the reference axis, it is possible to easily separate the frequency shift component caused by the movement of the object from the disturbance noise component by performing appropriate signal processing. This has the advantage of being able to prevent malfunctions due to disturbance noise. Moreover, the oscillation circuit continuously sends out the transmission signal, and
By using an ultrasonic transducer for both transmission and reception,
The received signal will be superimposed on the transmitted signal, but
By setting the phase difference between the pair of reference signals to 180 degrees, it is possible to obtain a pair of intermediate signals having a phase difference of 90 degrees. As a result, the movement of objects can be detected at all times, making this a particularly effective configuration when it is necessary to constantly monitor the monitoring space for purposes such as theft prevention.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is an explanatory diagram of the same operation as above, FIG. 3 is an explanatory diagram of operation of the vector representation same as above, and FIG. 4 is a block diagram showing a conventional example. 11 is an oscillation circuit, 13 is an ultrasonic transducer, 20 is a converter circuit, and 30 is a signal processing circuit.

Claims (1)

[Claims] 1 An oscillation circuit that continuously outputs a transmission signal of a constant frequency, and an oscillation circuit that receives the transmission signal and transmits ultrasonic waves to the monitoring space, and also receives reflected waves from the detected object in the monitoring space. An ultrasonic transducer that outputs wave signals for both transmitting and receiving purposes, a pair of reference signals that have the same frequency as the transmitting signal and a phase difference of 180 degrees, and a receiving signal superimposed on the transmitting signal are mixed. a converter circuit that converts into a pair of intermediate signals having a phase difference of degrees;
and a signal processing circuit that detects the movement of the object to be detected by detecting the transition of the quadrant in which the received signal exists in a vector plane with both intermediate signals as the basic axes, and outputs a detection signal. Characteristic moving object detection device.