JPH0414755B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pulse radar that measures distance using pulse waves.

[Conventional technology]

Measurement using a pulse radar emits a pulse modulated wave with a rectangular envelope, and measures the distance from the reception time until the reflected wave from the target object is received. As a method of detecting received waves, either envelope detection or synchronous detection was used. Note that the pulse radar may use not only radio waves but also ultrasonic waves, but the principles are the same.

[Problem that the invention seeks to solve]

In a pulse radar, a transmitted wave repeatedly emits a waveform including several waves of constant amplitude, as shown in FIG. The received wave is received with a delay of the time it takes to propagate twice the distance to the target object. The waveform at this time is not rectangular as shown in the diagram, but has a rising edge.
The waveform becomes a mountain-shaped waveform with a gentle fall.

Conventionally, distance measurement using a detection method using envelope detection measures the time difference between the rise time t ₀ of the transmitted wave and the rise time of the signal wave after detection, but in order to distinguish between the received signal wave and noise, A certain threshold was set, and it was assumed that a received wave had arrived when the threshold was exceeded. However, since the rise of the received wave after detection is not sharp, the point at which it is assumed to have arrived depends on the size of the threshold level, for example, as shown in the figure.
t ₁ and t ₁ ' will be different. If the level value is set low, m, t ₁ will be close to the leading edge of the received wave, but if the level value is set high, m', t ₁ ' will be delayed from the leading edge, and the time point of distance measurement will be shifted. Accuracy decreases. The measurement accuracy improves as the level value is lowered, but as shown in the figure, at a low level m, noise is detected and _t0 is mistakenly recognized as the time point of distance measurement, resulting in a large measurement error.

On the other hand, in distance measurement using a detection method using synchronous detection, a detection output that is not affected by noise is obtained by taking the product of the received wave and the carrier wave, but in order to remove the second harmonic generated by the product, a low-pass Pass through the filter. Therefore, there is a time delay due to the filter,
The disadvantage is that a time measurement value for accurate distance measurement cannot be obtained. In addition, when using envelope detection,
There is no such time delay.

The purpose of the present invention is to make use of the difference in the detection characteristics of the two detection methods described above, and to use both together to measure reception time without large errors due to noise and without time delay, thereby enabling accurate distance measurement. The purpose is to provide pulse radar.

[Means for solving problems]

In order to achieve such an object, the present invention includes a transmitter that emits a transmitted wave to an object to be measured, and a receiver that receives reflected waves from the object to be measured. In a pulse radar that measures the distance to an object from the time it takes to receive a reflected wave from the radar, a counter is connected to the transmitter and starts counting a time measurement clock each time the transmitter emits a transmitted wave; An envelope detection circuit that inputs the reflected wave received by the receiver, a synchronous detection circuit that inputs the reflected wave and synchronously detects the reflected wave and the carrier wave, and a low frequency component that removes high frequency components from the detection output of this synchronous detection circuit. a first latch circuit that latches the count value of the counter using the detection output of the pass filter and the envelope detection circuit;
A second latch circuit that latches the counted value held in the first latch circuit by the output of the low-pass filter, and calculates the distance to the object to be measured from the counted value held in this second latch circuit. This is a pulse radar characterized by comprising a calculation section.

[Effect]

The present invention has both an envelope detection circuit and a synchronous detection circuit, and each is assigned a different function. The count value of the distance measuring clock is latched by the output of the envelope detection circuit, and the time at that point is determined. At this time, the threshold level is lowered to improve measurement accuracy, but if there is noise, its output is also detected and the current count value of the counter is latched. Therefore, the latched count value may be a received signal or may be noise.

On the other hand, the synchronous detection circuit outputs the detection output with a slight delay from the received signal due to its low-pass filter. This detection output is not affected by noise, so
Accurately indicates that the received signal has arrived slightly before the detection output is generated. Therefore, the count value latched by the output of the envelope detection circuit just before the time of occurrence is due to the received signal and corresponds to the reception time. This latched count value is output to the outside by the output of the synchronous detection circuit.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a pulse radar using radio waves.

Radio waves are emitted from the transmitter 10 via the antenna 9, and the antenna 1 receives reflected waves from the object to be measured. The antennas 1 and 9 may be a common antenna. The tank circuit 2 removes noise having a frequency far from the radio wave frequency from the received signal. However, noise at the radio wave frequency or nearby frequencies will be mixed in as is. Next, after being amplified by the amplifier 3, the signal is input to both the envelope detection circuit 4 and the synchronous detection circuit 6.

The signal detected by the envelope detection circuit 4 is detected by the comparison circuit 5, and at that point the signal is detected by the latch circuit 13.
receives the latch signal 5a. The comparator circuit 5 keeps the potential E at a low level (m in FIG. 2), and when this level is exceeded, the output changes suddenly and generates a latch signal 5a. On the other hand, the counter 11 counts the time measurement clock of the clock oscillator 12, and each time the transmitter 10 generates a pulse,
It is cleared by a signal from , and time is measured again from that point onwards. A latch circuit 13 connected to the counter 11 latches the count value of the counter 11 every time it receives the latch signal 5a. In this case, as shown in FIG. 2, if there is a large-amplitude noise that is not removed by the tank circuit 2, the latch signal 5a may be generated due to the noise.

In the present invention, the received radio waves are simultaneously input to the synchronous detection circuit 6, the high frequency component of the detection output is removed by the low pass filter 7, the waveform is shaped by the waveform shaping circuit 8, and the latch signal 8a is sent to the latch circuit 14. . Since it is synchronous detection, it is not affected by noise contained in the received radio waves, but due to the delay characteristics of the low-pass filter 7, the latch signal 8a is delayed a little from the arrival time of the received radio waves. Therefore, the count value corresponding to the arrival time of the received radio wave, which has been previously latched in the latch circuit 13 by the latch signal 5a, is transferred to the latch circuit 14 by the latch signal 8a, and the calculation display section 15 , calculates the distance to the object to be measured from the counted number of clocks, and displays the distance.

As long as the received radio waves are received by the antenna 1, the latch signal 8a due to the synchronization signal is always generated immediately after the latch signal 5a due to envelope detection. Therefore, even if noise is mixed into the antenna 1 after the transmission pulse is generated, and the latch signal 5a is generated and the count value is latched in the latch circuit 13, the latch signal 8a due to the received radio wave will not be generated immediately thereafter. Therefore, latch circuit 14 does not receive the count value of latch circuit 13. In this way, the distance measurement count value is input to the calculation display unit 15 only when the antenna 1 receives a true reflected received wave instead of noise.

The time difference between the envelope detection output and the synchronous detection output is due to the delay time of the low-pass filter and is extremely small, so there is no need to consider noise occurring during this time.

The above embodiments are cases where radio waves are used, but in the case of ultrasonic waves, a similar circuit configuration may be used if a resonant vibrator is used instead of the antenna.

〔Effect of the invention〕

As explained in detail above, the envelope detection method can obtain a detected signal without time delay, but if you try to improve the measurement accuracy when identifying the arrival of a received wave, large errors may occur due to noise. Garu. On the other hand, the synchronous detection method is not affected by noise at all, but there is a time delay in the detection output. Therefore, in the present invention, time measurement is performed using the detection output of the envelope detection method, and the detection output of the synchronous detection method is used to measure the time.
The time measurement is taken as the true value and transferred to the distance calculation section. Therefore, it is possible to measure distances with high measurement accuracy without being affected by noise.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram of an embodiment of the present invention, and FIG. 2 is a diagram for explaining reception time measurement of reflected radio waves by envelope detection. 1, 9...Antenna, 4...Envelope detection circuit,
5... Comparator, 6... Synchronous detection circuit, 7... Low pass filter, 10... Transmitter section, 11... Counter, 13, 14... Latch circuit.

Claims (1)

[Claims] 1. A transmitter that emits a transmitted wave to an object to be measured, and a receiver that receives a reflected wave from the object to be measured, and emits the transmitted wave and then receives the reflected wave. A pulse radar that measures the distance from the time to the object to be measured includes a counter connected to the transmitter and starts counting a time measurement clock every time the transmitter emits a transmission wave; An envelope detection circuit that inputs the received reflected wave, a synchronous detection circuit that inputs the reflected wave and synchronously detects the reflected wave and the carrier wave, and a low-pass filter that removes high frequency components of the detection output of this synchronous detection circuit. a first latch circuit that latches the count value of the counter by the detection output of the envelope detection circuit; and a first latch circuit that latches the count value held in the first latch circuit by the output of the low-pass filter. 1. A pulse radar comprising: a second latch circuit; and a calculation unit that calculates a distance to an object from the count value held in the second latch circuit.