JPH095428A - Ultrasonic range finder - Google Patents

Abstract

PURPOSE: To accurately measure the distance by passing a very weak transmission signal received by a receiver through a digital filter, full-wave-rectifying the signal wave, increasing the size of the signal every elapsed time from the transmission time, and obtaining the time-differentiated value of the wave-form passing through a low-pass filter. CONSTITUTION: The wave-form (a) from a transmitter A is continuously transmitted to a receiver B located at the location of distance L, the wave-form (b) mixed with noises is received, and it is amplified by an amplifier C as the wave-form (c). The wave-form (c) is digitally processed via an anti-aliasing filter D1 and a FIR type band-pass filter D2 , noises are removed, and the wave- form (d) is selectively extracted. The wave-form (d) is processed by a full-wave rectifier E into the wave-form (e), the wave-form (e) is added 100 times from the transmission time by an adder F into the wave-form (f), and it is processed by a FIR type low-pass filter D3 into the wave-form (g). The wave-form (g) is differentiated with time by a computer G, the propagation time between the transmitter A and the receiver B is measured from the wave-form (h), and the distance L is displayed H.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic distance meter.

[0002]

2. Description of the Related Art In addition to noise generated by a transmitter / receiver and an internal circuit, many received signals of ultrasonic waves intrude from the outside. In the past, in order to increase the SN ratio, it was necessary to output a large transmission signal that was not inferior to noise, so an ultrasonic range finder equipped with a transmitter that is relatively large in output and size and high in cost was used. . Further, in the case of using an analog circuit type filter in which electronic parts are combined in the ultrasonic wave receiving means for removing the noise,
There are problems such as an increase in the number of parts and changes in characteristics, and once the parts are set, the filter characteristics are fixed and the variability disappears.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide predetermined information from a received signal containing noise without providing a transmitter having a relatively large output, a relatively large size and a high cost. It is an object of the present invention to provide a small-sized, highly reliable and low-cost ultrasonic distance measuring device, which is provided with a receiving means for selectively and accurately extracting a transmitted signal.

[0004]

In order to achieve the above object, a digital filter functioning by hardware such as CPU, memory, converter, amplifier, low-pass filter and software for digital signal processing is provided. Prepare

[0005]

By passing the weak transmission signal captured by the receiver through the digital filter, the transmission signal having the predetermined information can be selectively extracted from the reception signal in which noise is mixed relatively easily. become able to. Further, the signal wave after passing through the digital filter is full-wave rectified, and the magnitude of the signal is added at each time elapsed from the time of transmission, so that the variation in data can be averaged and a weak signal can be revealed. . Furthermore, the time taken for the ultrasonic signal to propagate between the transmitter and the receiver can be accurately measured by observing the time differential value of the waveform that has passed through the low-pass filter by digital signal processing. To be able to measure.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a concrete example for explaining the present invention.
It is a conceptual diagram of the process which the ultrasonic waveform for distance measurement is processed. Waveform a with a frequency of 40 KHz from transmitter A is distance L
Are being transmitted to the receiver B located at the position of 1 above. The receiver B receives the waveform b in which noise is mixed, and the amplifier of C amplifies the transmission signal and the noise together to form the waveform c. D ₁ is an anti-aliasing filter with an analog active filter having a cutoff frequency of 60 KHz, and D ₂ is a 40 KHz ± ₂ KHz FIR type bandpass filter which digitally processes the data sampled at 160 KHz. The removed waveform and the transmitted waveform like the waveform d can be selectively taken out. The waveform e processed by the full-wave rectifier E becomes a waveform f by adding 100 times including the elapsed time from the transmission time point using the adder F, and thus becomes a waveform f, so that the FIR low-pass filter D ₃ of 5 KHz is used. When processed, a smooth waveform g is obtained. G is the rising point s from the waveform h obtained by differentiating the waveform g with time by a computer
Then, the time required for the ultrasonic signal to propagate between the transmitter and the receiver is measured, and the calculated distance L between the transmitter and the receiver is displayed on the display H. Here, D ₂ , E, F, D ₃ , and G are made to function by digital signal processing using a small computer board equipped with a high-speed CPU such as DSP, memory, converter, amplifier, and timer. be able to.

FIG. 2 shows an embodiment of a conventional ultrasonic distance meter.
The waveform a ₀ having a frequency of 40 KHz from the transmitter A ₀ is the distance L
The waveform b ₀ in which noise is mixed at the receiver B ₀ , which is transmitted intermittently toward the receiver B _{0 at} the position
Is received and the transmission signal and noise are amplified together by the C ₀ amplifier, a waveform c ₀ is obtained. When this waveform is passed through an analog type bandpass filter D ₂₀ , it becomes a waveform d ₀ , but it is difficult to obtain a stable waveform with a high SN ratio due to variations in electronic components forming the filter. E ₀ is an analog diode whose rectified waveform is e ₀ . The waveform processed by the analog low-pass filter D ₃₀ becomes g ₀ , and in the analog comparison circuit G ₀ , it is necessary to propagate the ultrasonic signal between the transmitter and the receiver from the intersection s ₀ with the threshold m _0. The time is measured and the distance L is displayed on the display H. In order to improve the measurement accuracy, it is necessary to prevent the threshold m _{0 from} being affected by the change in noise level, and the output of the transmitter A ₀ must be increased.

FIG. 3 shows an example in which the present invention is applied to a snow depth measuring device. By fixing ultrasonic wave transmitters / receivers S and R to a support pillar K and analyzing reflected signals of snow surfaces P ₁ , P _{2 and the} like. ,
The snow depths n ₁ and n ₂ are measured. The waveform g ₁ is
Although obtained in the same manner as in the specific example of FIG. 1, since there is reflection of ultrasonic waves from the snow surfaces P ₁ and P ₂ , p ₁ and p ₂
, The waveform h ₁ has rising points of s ₁ and s ₂ . m ₁ is a value that is set to 1/10 of the size of p ₁ , and is a threshold value that is provided to specify the snow depth n ₁ .

[0009]

According to the present invention, the noise mixed in the ultrasonic signal can be easily removed by the digital signal processing by the operation of software, and the ultrasonic wave of small size, light weight, low cost and high reliability can be obtained. Type range finder is provided.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the present invention, which is a conceptual diagram of a process in which an ultrasonic waveform is processed.

FIG. 2 is an explanatory diagram of an embodiment that does not use the present invention.

FIG. 3 is an explanatory diagram of an example applied to a snow depth meter.

[Explanation of symbols]

A transmitter a waveform L distance B receiver b waveform C amplifier c waveform D ₁ anti-aliasing filter D ₂ bandpass filter d waveform E full-wave rectifier e waveform F adder f waveform D ₃ low-pass filter G computer g waveform h waveform s rising point H display A ₀ transmitter a ₀ waveform B ₀ receiver b ₀ waveform C ₀ amplifier c ₀ waveform D ₂₀ band pass filter d ₀ waveform E ₀ diode e ₀ waveform D ₃₀ low pass filter g ₀ waveform G ₀ comparison circuit m ₀ threshold s ₀ intersection H indicator K support column S transmitter R receiver P ₁ snow surface P ₂ snow surface n ₁ snow depth n ₂ snow depth g ₁ waveform p ₁ peak p ₂ peak h ₁ waveform m ₁ threshold s ₁ rising point s ₂ rising point

Claims (2)

[Claims] 1. In an ultrasonic wave receiving means of a range finder for measuring a distance between a transmitter and a receiver based on a result of measuring a time required for an ultrasonic wave signal to propagate between the transmitter and the receiver, noise is mixed. Ultrasonic range finder having a digital filter capable of selectively extracting a transmission signal having predetermined information from the received signals 2. A received signal of the ultrasonic signal, which is intermittently and repeatedly received a predetermined number of times, is passed through a digital filter, then full-wave rectified, and a signal is sent every time the ultrasonic signal is transmitted. 2. The ultrasonic wave according to claim 1, further comprising means for adding a predetermined number of times to a predetermined number of times and measuring the required time by observing the time differential value of the waveform passed through the low-pass filter by digital signal processing. Type rangefinder