JPH03220482A - Range finder - Google Patents

Abstract

PURPOSE:To measure a distance with a high accuracy regardless of the characteristics of a phase comparator by controlling such that a phase difference between the modulation signals of a modulated wave generated in a transmitter and of a modulated wave received after reflected from an object to be measured. CONSTITUTION:A transmitter 2 emits a modulated wave Sm modulated by the constant frequency modulation signal of an oscillator 1. The modulation signal is obtained by receiving 3 the modulated wave Sm reflected from an object 8 to be measured and demodulating the wave Sm. Part of the signals of the oscillator 1 are CCD-delayed 5, compared with the modulation signals by a phase comparator 4 and a signal Sp proportional to the phase difference is outputted to a voltage controlled oscillator 7 via a loop amplifier 6. A feedback control is performed by sufficiently increasing the amplification degree of the loop amplifier 6 so that the output signal of the comparator 4 is equal to zero. At this time, since the oscillation frequency of the oscillator 7 is proportional to the distance to the object 8 to be measured, by measuring the oscillation frequency of the oscillator 7 by a counter or the like, the distance to the object 8 to be measured can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a distance measuring device, and more particularly to a distance measuring device that determines a distance by measuring a phase difference between modulated signals of modulated waves.

[Conventional technology]

Conventionally, in this type of distance measuring device, as shown in a block diagram of an example of a conventional distance measuring device in FIG.
modulates a carrier wave with a modulation signal of a constant frequency outputted by a modulator to generate a modulated wave SIl, which is radiated to the object to be measured 8. The receiver 3 receives the modulated wave SIl reflected from the object under test 8 and sends the modulated signal obtained by demodulation to the phase comparator 4. The phase comparator 4 receives the modulated signal output from the oscillator 1 and the modulated signal demodulated by the receiver 3, compares the phases of both signals, and outputs an output signal Sp proportional to the phase difference. Now, when the oscillation frequency of oscillator 1 is f and the distance to the object to be measured is R, the phase difference Δφ is Δφ2yr・(2R/c)
/ (1/f)=4gfR/C (here, C is the speed of light), and the phase difference Δφ is proportional to the distance R. Therefore, since the output signal Sp of the phase comparator 6 is proportional to the distance R, the distance is measured by the output signal value.

[Problem to be solved by the invention]

In the conventional distance measuring device described above, the phases of the modulated signal outputted by the oscillator 1 and the modulated signal demodulated by the receiver 3 are compared and a voltage proportional to the phase difference is detected as an analog signal. In order to obtain distance measurement accuracy, a phase comparator with a wide dynamic range and excellent linearity is required.

Furthermore, there is a drawback that not only it is necessary to suppress fluctuations in the signal level input to the phase comparator, but also it is necessary to prevent the detection characteristics from fluctuating with respect to temperature changes.

An object of the present invention is to provide a distance measuring device capable of highly accurate distance measurement regardless of the characteristics of a phase comparator.

[Means to solve the problem]

The distance measuring device of the present invention includes a modulating signal generating means for generating and outputting a modulated signal of a constant frequency, a transmitting means for modulating a carrier wave with the modulating signal to generate a modulated wave, and radiating the modulated wave to an object to be measured; controlled oscillation means, delay means for delaying and outputting the modulated signal according to the frequency of the oscillation signal output by the voltage controlled oscillation means, and receiving and demodulating the modulated wave reflected by the object to be measured. a receiving means for outputting a modulated signal; a phase comparison means for receiving the modulated signal via the delay means and the modulated signal obtained by the demodulation, compares the phases of both signals, and outputs a signal according to the phase difference; and an amplification means for amplifying and outputting a signal according to the phase difference, and the voltage controlled oscillation means controls an oscillation frequency according to the output signal of the amplification means.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

Referring to FIG. 1 showing one embodiment of the present invention, an oscillator 1
, transmitter 2, receiver 3, phase comparator 4, CCD delay line 5
, a loop amplifier 6, and a voltage controlled oscillator 7. The transmitter 2 modulates a carrier wave with a constant frequency modulation signal output from the oscillator 1 and emits a modulated wave Sm to the object under test 8.

The receiver 3 receives 8 modulated waves reflected from the object to be measured 8 and sends the demodulated modulated signal to the phase comparator 4 . On the other hand, a part of the output signal of the oscillator 1 is delayed by the td waiting time and supplied to the phase comparator circuit 4 via the CCD delay line 5 driven by the output signal SO of the voltage controlled oscillator 7. Generally, the amount of delay caused by a CCD delay line is
The zero phase comparator 4, which is inversely proportional to the frequency of the drive signal applied to the D delay line and proportional to the number of elements, receives the modulation signal output from the oscillator 1 and the modulation signal demodulated by the receiver 3, and calculates the difference between both signals. By comparing the phases, a signal Sp proportional to the phase difference is obtained.
is output to the voltage controlled oscillator 7 via the loop amplifier 6. The amplification degree of the loop amplifier 6 is made sufficiently large and feedback control is performed so that the output signal of the phase comparator 4 becomes zero.

Now, let the oscillation frequency of the voltage controlled oscillator 7 be fO, and CC
When the number of elements of the D delay line is n, the modulated signal output from the oscillator 1 is delayed by ta=n/fo by passing through the CCD delay line 5≧. In this state, the phase difference between the two signals input to the phase comparator 4 is controlled to be O, so if the distance to the object to be measured is R, then t d = n / f a = 2 Since R/c, it becomes R-n c / 2 fo (where C is the speed of light). Therefore, since the oscillation frequency f and the distance R are proportional, the oscillation frequency f of the output signal So of the voltage controlled oscillator 7.

The distance R can be measured by measuring with a counter or the like.

Although the above embodiment uses a CCD delay line,
It is clear that any circuit other than a CCD delay line can be operated in the same manner as long as the delay time can be controlled according to the driving frequency. Further, the signal emitted to the object to be measured may be an optical signal.

〔Effect of the invention〕

As explained above, according to the present invention, a feedback loop is configured by a phase comparator, a loop amplifier, a voltage controlled oscillator, and a delay line, and the modulated wave generated by the transmitter and the modulated wave reflected by the object under test are received. Since the zero-phase method is used to control the phase difference between the modulated signal and the wave to O, the phase comparator does not require wide linearity, and furthermore, the signal level input to the phase comparator does not require a wide range of linearity. Highly accurate measurements can be made even if there are fluctuations or the detection characteristics change due to temperature changes. Further, there is an effect that it is possible to directly measure the oscillation frequency of the voltage controlled oscillator with a counter or the like, and easily perform highly accurate distance measurement.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of a conventional distance measuring device. 1... Oscillator, 2... Transmitter, 3... Receiver, 4
... Phase comparator, 5... CCD delay line, 6... Loop amplifier, 7... Voltage controlled oscillator, 8... Measured object, Sl! ...Modulated wave, SP...Phase comparator output signal, So-...Voltage controlled oscillator output signal.

Claims (1)

[Claims] a modulating signal generating means for generating and outputting a modulated signal of a constant frequency; a transmitting means for modulating a carrier wave with the modulating signal to generate a modulated wave and radiating it to the object to be measured; voltage controlled oscillation means; a delay means for delaying and outputting the modulated signal according to the frequency of the signal output by the oscillation means; a receiving means for receiving and demodulating the modulated wave reflected by the object to be measured and outputting the obtained modulated signal; a phase comparison means that receives the modulated signal via the delay means and the modulated signal obtained by the demodulation, compares the phases of both signals, and outputs a signal according to the phase difference; and amplifies the signal according to the phase difference. and an amplification means for outputting a signal, the voltage controlled oscillation means controlling an oscillation frequency according to an output signal of the amplification means.