KR20050087174A - Laser range finder - Google Patents

Abstract

According to the present invention, the control circuit unit adjusts the operating current of the transmitting circuit unit to adjust the intensity of the laser light signal received in the receiving circuit unit so that the phase difference caused by the characteristics of the APD can be corrected. It is possible to provide a laser range finder which minimizes the error by making the intensity of the laser light received and the intensity of the laser light received in the receiving circuit part the same, thereby enabling accurate distance measurement, and does not use an expensive optical attenuator. It is a very useful invention that can provide a laser range finder capable of localization of parts.

Description

Laser range finder {Laser range finder}

The present invention relates to a laser range finder, and in particular, by adjusting the operating current of the transmitting circuit portion to adjust the intensity of the laser light signal received in the receiving circuit portion to correct the phase difference of the frequency generated by the characteristics of the APD accurate distance The present invention relates to a laser range finder that enables measurement.

In general, a laser range finder is a device that shoots a laser on a target to measure a distance, measures the time when the emitted laser is reflected by the target, and then converts the time into a distance so that the measurer can visually determine the distance. .

The conventional laser range finder is a transmission circuit part including a transmitting lens and a transmitting laser diode, and a receiving circuit part including a receiving lens and a receiving laser diode, as shown in FIG. 1, and comparing with the transmitting circuit part and the receiving circuit part. And a control circuit unit for controlling a display device, etc., wherein an optical attenuator is provided between the receiving lens and the receiving laser diode to adjust the intensity of the received optical signal. The optical attenuator generates a large phase difference as the difference between the intensity of the laser beam shot from the transmitting circuit unit, that is, the APD and the intensity of the laser signal received by the receiving circuit unit, increases. The larger the accuracy, the lower the accuracy is necessary to control this, but it is too expensive to have the disadvantage that is the main reason for the price increase of the laser range finder.

Therefore, the present invention has been made to solve the disadvantages of the conventional laser range finder as described above, the laser is received by the receiving circuit portion by adjusting the operating current of the transmitting circuit portion by the control circuit portion without using an expensive optical attenuator By adjusting the intensity of the optical signal, it is possible to correct the phase difference caused by the characteristics of the APD, and eventually minimize the error by making the intensity of the laser light transmitted from the transmitting circuit part equal to the intensity of the laser light received from the receiving circuit part. This is to provide a laser range finder that enables accurate distance measurement.

The distance measuring method of the present invention using beam modulation is described in more detail. First, beam transmitting beams are modulated at a constant modulation frequency to emit radiation to a measuring point, and the light returned from the measuring point is sent to a laser receiving diode. It is a method of demodulating the received modulated signal, making it a frequency signal (1 / N frequency at modulated frequency) which is easy to measure phase electronically, and then measuring the phase of these two frequencies to find the distance.

The modulation frequency and mixing frequency generation circuit requires high frequency stability, so the frequency must be locked by a PLL (Phase Locked Loop) circuit. The measurement error can be corrected by classifying and measuring for small distance measurement.

However, the distance measuring method using the beam modulation requires a very difficult technique, and it is difficult to directly compare the wavelength signals of the laser light. Therefore, when the laser light is amplitude-modulated at the frequency of f1 and transmitted and demodulated again by the light receiving unit, Frequency can be obtained. Here, the higher the frequency of f1 used for modulation, the more accurate the distance measurement is possible. However, when using a high frequency modulated wave, a number of technical problems arise. Therefore, it is important to select the modulation frequency that is the easiest to operate electronically while ensuring accuracy, and to use the two- or three-frequency method to remove the measurement error that occurs when the distance is measured by one modulation frequency. Two frequencies were used.

If f1 = 30Mhz, wavelength of f1 (λ) = 3 x 10m / s / 30 x 10hz = 10m

f2 = 234.375Khz, the wavelength of f2 (λ) = 3 x 10m / s / 234.375 x 10hz = 1280m, where the frequency of f2 has a wavelength value of the maximum measurement distance x 2, and has a frequency of f1 / n By selecting, it is efficient to simply find f2 by one oscillation frequency of f1. N must be an integer.

When described in detail by the accompanying drawings the technical configuration of the present invention as follows. 1 is a block diagram of the laser range finder of the present invention, Figure 2 is a block diagram of the laser range finder of the present invention.

In FIG. 1 and FIG. 2, the laser range finder 1 of this invention is comprised including the transmission circuit part 10, the reception circuit part 20, and the control circuit part 30. As shown in FIG.

The transmission circuit unit 10 includes a crystal oscillator 100 for generating a reference frequency, a frequency divider 200 for generating an existing frequency as a new frequency, and inputs f1 and f2 frequencies of the microprocessor 1900. The difference is determined by comparing the frequency selector (300,400) for selecting by the switching signal, the laser transmitting diode (500) for transmitting the laser light of the selected frequency, and the transmitted and received signal and the reference signal again. A detector 600, a delay filter 700 for correcting the phase difference of the frequency, and an oscillator 800 for generating a mixing frequency having a deviation from the f1 frequency and simultaneously generating a frequency whose phase is synchronized with the f1 frequency. And a band pass filter 900 for obtaining a reception signal of 15.625 KHz when using the f1 or f2 frequency, and a microprocessor for the corresponding mixing signal when using the f1 or f2 frequency. It consists of a frequency selector 1000 for selecting the fm1 or fm2 frequency by the switching signal of the signal (1900).

In this case, the crystal oscillator 100 oscillates a frequency of 10m wavelength and has a temperature compensation function, and the frequency divider 200 divides 234.375KHz: 30.00MHz by 1/128 times (λ: 1,289m), and 250.000 KHz: divides 30.00MHz (mixing frequency when using f2) by 1/120 times, 15.625KHz: divides 30.00MHz (reference frequency for phase comparison between Ref and Tx signals) by 1/1920 times, and divides f1 and VCO. It has the function to find the deviation frequency of the output frequency. Thus, 31.015625-30.000 MHz = 15.625 KHz.

The f1 and f2 frequencies input to the frequency selector 300 are λ: 10m and λ: 1,280m, respectively, and the f1 and f2 frequencies input to the frequency selector 400 measure delay times of optical and electrical signals of the range finder. The Ref (reference signal) and the target for distance measurement are converted to a Tx laser diode that emits laser light.

The oscillator (VCO, 800) generates a mixing frequency having a deviation of f1 and 15.625 KHz, and simultaneously extracts a phase deviation from the detector 600 to oscillate a frequency synchronized with f1 and then through a delay filter 700. The DC voltage proportional to the phase deviation causes 31.015625 MHz to be synchronized with f1.

The band pass filter 900 has a band pass filter of 30.015625 MHz for the mixing signal to obtain a 15.625 KHz reception signal using the f1 frequency and 250.000 KHz of the mixing signal for the reception signal of 15.625 KHz using the f2 frequency. It is divided into a band pass filter.

Therefore, when the frequency selector 1000 uses f1 (λ: 10m) and f2 (λ: 1,280m), the mixing signal is converted to fm1 and fm2 by the switching signal of the microprocessor 1900 of the control circuit unit 30. It is a choice.

The reception circuit unit 20 includes a laser reception diode (APD) 1100 for receiving laser light emitted from the laser transmission diode 500, and a signal other than the laser light emitted from the measuring instrument is removed. A tuning circuit 1200, an amplifier 1300 for amplifying the weak output signal of the tuning circuit to a predetermined signal level, a frequency mixer 1400 for obtaining an intermediate frequency 15.625KHz as a frequency mixing circuit, and an intermediate A band pass filter 1500 for passing only the frequency (15.625 KHz) and removing the other frequency is formed.

At this time, the tuning circuit 1200 is configured in the stagger method of the circuit tuning to the frequency of f1 and f2, the band pass filter 1500 is configured so that the intermediate frequency due to noise and other signals in the front end receiving circuit is not received. .

The control circuit unit 30 converts an intermediate frequency (15.625 KHz, a received signal) output as a sin wave into a square wave, and simultaneously synchronizes only an intermediate frequency within a preset frequency range to accurately synchronize the phase difference. A phase difference counter 1700 for comparing, calculating, and converting a demodulator (PLL Demodulator 1600) and a phase difference of 15.625 KHz of the transmitting circuit section 10 and 15.625 KHz of the receiving circuit section 20 to convert it into time; An oscillator 1800 for outputting a pulse to obtain a phase difference of 1700, and an 8-bit MCU, a microprocessor for controlling a display module 2100 for distance calculation, control and communication of each part, and item display. 1900, an oscillator 2000 for generating a clock, an indicator 2100 for visually displaying a distance value, and the like, an interface 2200 for communicating with an external computer and equipment, It comprises a power supply unit 2300 for supplying electricity to all the circuit groups.

At this time, the clock of the microprocessor 1900 uses 12.288 MHz (810 ns), the phase difference counter 1700 uses a high speed 32 bit counter, and the resolution of the phase difference is 1/2000.

In addition, the oscillator 2000 for generating a clock uses 12.288 MHz as a clock, in order to ensure an accurate baud rate in RS-232 communication.

In addition, the interface 2200 performs RS-232 communication, and a baud rate of 1200 to 38400 bps is possible, and the power supply unit 2300 uses DC 12V to obtain a reverse bias voltage of the receiver APD. Use it by boosting to DC 150V.

The operating method of the laser range finder 1 of the present invention having the above configuration is as follows.

First, a light having a specific wavelength is generated by applying a rated voltage to the anode of the laser diode of the measuring device 1 of the present invention, and the wavelength is used as a carrier frequency.

When the modulation frequency is amplitude modulated, the modulation frequency is transmitted as a signal. The modulation frequency should have a very stable frequency stability, so it is necessary to lock the frequency using a high-definition X-Tal oscillator or a PLL circuit. At this time, if you want to use the two-frequency method, f1 / n can be easily obtained by using the frequency divider circuit. The f1 and f2 frequencies shall be chosen to have the precision of the measurement by selecting the most appropriate frequency as described above.

It is very difficult to directly phase compare the frequency of the amplitude modulated beam, so the received frequency must be converted back to a frequency for easy phase comparison. This frequency should be obtained from the frequency f1 / n₁ for modulation and f2 / n₂ at the same time, and the frequency best suited for separation from the output frequency through LPF in the mixer circuit of the receiver. It should be a frequency.

If the reference frequency for phase comparison is Tx_f3

   Tx_f3 = f1 / 1920 (n₁ = 1920)

           = 30 x 10hz / 1920

           = 15.625Khz

    Tx_f3 = f2 / 15 (n₂ = 15)

           = 234.375 x 10hz / 15

           = 15.625Khz.

When the laser receiving diode 1100 receives the amplitude-modulated light of the laser, f1 or f2 can be obtained. A down converter circuit is required to lower the frequency to Rx_f3 for easy phase comparison.

The down converter circuit immediately becomes a frequency mixer 1400. When f1 and the local oscillation frequency f0 are applied to the frequency mixer 1400, Rx_f3 = f0 ± f1 = f0 ± f2 is output. Where f0 = f1 + Tx_f3 or f0 = f2 + Tx_f3. In order to obtain such f0, a local oscillation frequency f0 = f1 + Tx_f3 must be obtained through a modulation frequency generator circuit and a separate oscillator circuit.

f0 is obtained by the X-Tal oscillator and applied to the mixer circuit of the receiver through the PLL circuit whose phase is locked by the phase comparison frequency Tx_f3 to obtain an accurate phase comparison Rx_f3. In the two-frequency method, the frequency is different when f0 is f1 and f2, so there must be a frequency switching circuit and a respective BPF.

In practice, in order to obtain a highly accurate phase difference, the delay time of light from a light emitting source to a light receiving unit needs to be measured.As a result of the signal propagation delay characteristics of various electronic devices, the overall delay time is added to the actual delay time of the light and the phase delay is added. This can cause errors in the measurement.

Therefore, the phase delay must be corrected by obtaining the circuit delay time. When the laser beam is directly sent to the laser receiving diode 1100 at the same position as the laser beam transmitting diode 500 for distance measurement, the resulting phase difference θ is obtained, and θref is subtracted from the phase difference θdis obtained from the distance measurement. The actual phase difference θstd can be obtained.

θstd = θdis- θref

The intensity of light emitted from the laser transmitting diode 500 is changed when the current is changed by a voltage applied to the anode within the rated current range. By using this property, a transistor for controlling the current of the laser diode is added to control the transistor at a modulation frequency so that the laser light can be amplitude modulated. At this time, the modulation frequency is to use a method of modulating a square wave (Square Wave).

And, it should be designed to operate by the control signal for switching the phase correction light emitting circuit and the distance measuring light emitting circuit and the control signal for switching the modulation frequency to f1 and f2.

The amplification characteristics of f1 and f2 are flattened using a wideband amplification circuit. In the process of incidence of the laser light, since other lights in the surrounding area are incident together, the lights become noise sources, which are converted into electrical signals in the light receiving diodes, and have a significant adverse effect on signal processing. Therefore, an optical filter is required and an electronic circuit filter circuit is required. LPF (f1 = 30Mhz) should be added immediately after the laser receiving diode and BPF (f3 = 15.625Khz) should be used after the mixer circuit to cut off the noise.

Finally, the received signal Rx_f3 should be extracted only by the signal returned by the light emitted from the light emitting diode to prevent an error from occurring during distance measurement. The comparison becomes difficult. Therefore, only accurate demodulation signals should be extracted.

Therefore, in the present invention, the demodulation signal is extracted by using the demodulation method using the PLL circuit. Since the signal frequency to be demodulated is already known in the design, the demodulation signal is applied to the reference frequency input of the PLL circuit and the PLL locking frequency is set. As a result, noise frequencies that do not match the phase of the input frequency and the locking frequency are not output.

Since the demodulated signal frequency Rx_f3 and the phase comparison reference frequency Tx_f3 are the same frequency and have a duty ratio of 50%, the distance can be measured by phase comparison. However, in order to have a 5mm resolution in comparing the phase difference between the frequencies of the two signals, it is necessary to measure the phase at 15.625Khz (T = 64us) at 1/1000 (64ns). However, it is very difficult for the microprocessor 1900 to directly measure the phase difference between the two signals in units of 64 ns. The reason is that the clock of the microprocessor 1900 should be about 64ns / 4 max. There is no microprocessor 1900 capable of using this high speed clock (62.5Mhz). Therefore, the phase difference comparator must use a high speed counter.

As described above, the present invention provides an optical signal delay compensation method using an electronic circuit of a rangefinder, that is, directly irradiates a laser light to the front surface of the receiver APD, measures the phase difference of f1 and f2 at that time, and then corrects the phase difference of the signal measuring the actual distance. The actual distance could be calculated by measuring the phase difference of each signal.

That is, the actual distance value of f1 = (Tx phase difference-Ref phase difference) * 0.64m

Actual distance value of f2 = (Tx phase difference-Ref phase difference) * 5.0mm

In addition, the laser receiving diode 1100 has a characteristic that there is an electrical signal delay phenomenon according to the intensity of the incident light, and the stronger the intensity of the light has the disadvantage that more signal delay occurs, the light is reflected at the same distance When the incident intensity is different, the phase difference between the two signals is so great that it is difficult to measure the accurate distance. Therefore, it is necessary to process the intensity of the incident light evenly, in order to solve this problem, it is possible to control the intensity of the light reflected from the front end of the laser receiving diode 1100 evenly, the laser transmitting diode ( This is made possible by controlling the output so that the light intensity of 500) is at a constant received signal level.

At this time, the distance calculation algorithm by the combination method of the distance value of f1 and the distance value of f2 is as follows.

The maximum distance that can be measured using f1 is 640m and the resolution is 0.64m. The maximum distance that can be measured using f2 is 5.0 m and the resolution is 0.5 mm.

The ref phase of f1 and the reflected light incident at a distance within 640m are 180 degrees, and the phase relationship of f2 has a 180 degree phase difference equal to f1 within a distance of 5m, and a phase at a distance of 5m or more and within 10m. Only the phase difference proportional to the distance that is not reversed is obtained. The distance measurement of f1 determines the distance in m, and the measurement of f2 is used to measure the distance in mm. The maximum distance value that can be measured using f2 is 5m. The distance between 5m and 10m is determined by reversal of the phase, and as mentioned above, the distance is not reversed and the measured distance is 5m + 10m. Can be measured.

As described above, the present invention enables the manufacture of a laser range finder without using an optical attenuator, which enables the supply of a laser range finder which is inexpensive, and enables localization of parts. By adjusting the intensity of the laser light signal received in the circuit part, it is possible to correct the phase difference caused by the characteristics of the APD, and eventually the same intensity of the laser light transmitted from the transmitting circuit part and the laser light received in the receiving circuit part. It is a very useful invention that can provide a laser range finder that can minimize the error by making accurate distance measurement.

1-a block diagram of the inventive laser range finder.

2-a schematic diagram of the inventive laser range finder.

* Explanation of symbols for main parts of the drawings

1: the present invention laser range finder

10: transmitting circuit unit 11: transmitting lens

12: laser transmission diode

20: receiving circuit unit 21: receiving lens

22: diode for laser reception (hereinafter referred to as APD)

30: control circuit 40: optical attenuator

50: reference photodiode

Claims (1)

In the laser range finder comprising a transmitting circuit portion, a receiving circuit portion, and a control circuit portion for measuring the distance of the target using a laser, The transmission circuit unit 10 includes a crystal oscillator 100 for generating a reference frequency, a frequency divider 200 for generating an existing frequency as a new frequency, and inputs f1 and f2 frequencies of the microprocessor 1900. The difference is determined by comparing the frequency selector (300,400) for selecting by the switching signal, the laser transmitting diode (500) for transmitting the laser light of the selected frequency, and the transmitted and received signal and the reference signal again. A detector 600, a delay filter 700 for correcting the phase difference of the frequency, and an oscillator 800 for generating a mixing frequency having a deviation from the f1 frequency and simultaneously generating a frequency whose phase is synchronized with the f1 frequency. And a band pass filter 900 for obtaining a reception signal of 15.625 KHz when using the f1 or f2 frequency, and a microprocessor for the corresponding mixing signal when using the f1 or f2 frequency. And a frequency selector 1000 for selecting the fm1 or fm2 frequency by the switching signal of the processor 1900, The reception circuit unit 20 includes a laser reception diode 1100 for receiving laser light emitted from the laser transmission diode 500, and a tuning circuit 1200 for removing signals other than the laser light emitted from the measuring device. ), An amplifier 1300 for amplifying the output signal of the weak tuning circuit to a constant signal level, a frequency mixer 1400 for obtaining an intermediate frequency of 15.625 KHz, passing only the intermediate frequency, and removing other frequencies. It is made of a band pass filter 1500 for, The control circuit unit 30 converts an intermediate frequency output as a sine wave into a square wave and simultaneously synchronizes only the intermediate frequency within a preset frequency range so that the phase difference is accurately pixelated. Phase difference counter 1700 for comparing, calculating and converting the phase difference of 15.625 KHz and 15.625 KHz of the receiving circuit unit 20 into time, and an oscillator 1800 for outputting a pulse for calculating the phase difference of the phase difference counter 1700. A microprocessor (1900) for controlling an indicator (2100) module for distance calculation, control and communication of each part, and an item display, an oscillator (2000) for generating a clock, and a distance. An indicator 2100 for visually displaying a value, an interface 2200 for communicating with an external computer and equipment, and a power supply unit 23 for supplying electricity to all the circuits. 00) Laser range finder characterized in that consisting of.