JP2011112542A - Electro-optical distance meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a cyclic error from occurring in an electro-optical distance meter. <P>SOLUTION: In the electro-optical distance meter including a light emitting part (d) for emitting a ranging light (L), a modulator (14) for modulating the ranging light, a reference signal generator (12) for sending a reference signal (K) to the modulator, a light receiving part (e) for converting the received ranging light into ranging signals (P), and a distance calculation part (26) for finding a distance to a measuring point by the ranging signals, the modulator is composed of a switch element (28) connected with the light emitting part and two-stage XOR circuits (30A and 30B) interposed between the switch element and the reference signal generator, and phase inversion signals (T<SB>A</SB>and T<SB>B</SB>) from the distance calculation part are input to the XOR circuit on the respective stage, respectively. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention transmits distance measuring light toward the target, receives the distance measuring light reflected by the target, and determines the distance to the target from the phase difference between the transmitted distance measuring light and the received distance measuring light. The present invention relates to a light wave distance meter to be measured.

  FIG. 7 shows a conventional optical distance meter described in Patent Document 1 below. The light wave distance meter includes a light emitting unit d that emits distance measuring light L, an oscillation unit a that generates a plurality of reference signals having different frequencies, a frequency selection unit b that selects one reference signal from the plurality of reference signals, The modulation unit c that modulates the distance measuring light L emitted from the light emitting unit d by the selected reference signal K, and the distance measuring light L emitted from the light emitting unit d is reflected and returned by a target (not shown) installed at the measuring point. A light receiving portion e that receives the distance measuring light L when it comes and converts it into a distance measuring signal M, and a counter f that measures the phase difference between the reference signal K and the distance measuring signal M to calculate the distance to the target. With. At this time, the distance to the target is calculated by combining the measured values obtained from the reference signals K having different frequencies.

  Further, the distance measuring light L from the light emitting part d is reflected by the distance measuring light L toward the target by the optical path switch g and the reference light path h which is reflected by the mirrors i1 and i2 inside the lightwave distance meter and reaches the light receiving part e. It is switched to the reference light R that advances. The reference signal S converted from the reference light R incident on the light receiving unit e through the reference light path h is also measured by the counter f with respect to the reference signal K, and the distance is also calculated from this phase difference. Thus, the distance calculated from the distance measurement signal M is corrected.

  Usually, in order to increase the stability of the measured value, the optical path switch g emits the reference light R, the distance measuring light L, the reference light R, and the distance measuring light L in order, and performs a number of distance measurements. The average value was obtained.

  In a conventional lightwave distance meter, a frequency of several tens of MHz or less was used as the reference signal K. However, in recent lightwave distance meters, a higher frequency than the conventional frequency is used as the reference signal K in order to increase measurement accuracy. Have come to use until. When the frequency of the reference signal K output from the frequency selection unit b is increased, the reference signal K enters the circuit between the light receiving unit e and the counter f as noise due to electrostatic coupling, electromagnetic coupling, electromagnetic wave radiation, or the like. The distance to the target is input to the counter f without going back and forth, and this causes a problem of causing an error called a cyclic error.

  The following Patent Document 1 also discloses an optical distance meter that prevents such a cyclic error. Below, this light wave distance meter is demonstrated.

  FIG. 8 is a block diagram of this light wave distance meter. The lightwave distance meter 10 includes a light emitting unit (light emitting diode) d that emits distance measuring light L toward the target 8, a reference signal generator 12 that generates a reference signal K, and a light emitted from the light emitting unit d by the reference signal K. A modulator 14 for modulating the ranging light L to be received, and when the ranging light L is reflected by the target (prism) 8 and returns, the ranging light L is received and the ranging signals P and Pr are generated. A light receiving unit (photodiode) e, an amplifier 16 that amplifies the ranging signals P and Pr, and a distance calculating unit 18 that calculates a distance using the ranging signals P and Pr are provided. However, P is each ranging signal when the reference signal K is rotated forward, and Pr is each ranging signal when the reference signal K is inverted.

  The reference signal generator 12 includes a crystal oscillator 20 that generates a basic signal having a stable frequency, and a frequency selector 22 that selects a reference signal K having an appropriate frequency from a plurality of frequencies obtained by multiplying or dividing the basic signal. Consists of.

  When the phase inversion signal T is not sent from the CPU 26 (T = 0), the modulator 14 modulates the distance measuring light L with the reference signal K, and the phase inversion signal T (T = 1) is sent from the CPU 26. In this case, the ranging light L is modulated by the reference signal -K whose phase is inverted. For this reason, the modulator 14 includes a modulation transistor (switch element) 28 and an XOR circuit (exclusive OR circuit) 30 for controlling energization of the modulation transistor 28. Specifically, the modulator 14 has a base. Is connected to the output terminal of the XOR circuit 30. The light emitting section d is connected to the collector of the modulation transistor 28, and the XOR circuit 30 receives the reference signal K from the frequency selector 22 and the phase inversion signal T from the CPU 26.

  When the CPU 26 sends the phase inversion signal T (T = 1) to the XOR circuit 30, the high level signal (1) from the frequency selector 22 is phase inverted to the low level (0) and output from the XOR circuit 30, The low level signal (0) from the frequency selection 22 is phase-inverted to the high level (1) and output from the XOR circuit 30.

  If the phase inversion signal T is not sent from the CPU 26 to the XOR circuit 30 (T = 0), the high level signal (1) from the frequency selector 22 is output from the XOR circuit 30 with the high level (1), and the frequency is selected. The low level signal (0) from the device 22 is output from the XOR circuit 30 with the low level (0). Thus, depending on the presence or absence of the phase inversion signal T, the light emitted from the light emitting unit d is modulated by either the reference signal K that is not phase-inverted or the reference signal -K that is phase-inverted.

  The distance measuring light L emitted from the light emitting part d is sent to the light receiving part e through the distance measuring light L traveling on the distance measuring optical path j toward the target 8 and the reference optical path h inside the optical distance meter 10 by the optical path switch g. It is switched to the guided reference light R. The reference optical path h is composed of mirrors i1 and i2 guided from the light emitting part d to the light receiving part e. The reference signal S converted from the reference light R by the light receiving unit e is used for correcting the phase difference between the standard signal K and the distance measurement signals P and Pr.

  The distance calculation unit 18 includes a phase comparator 24 that measures the phase difference between the reference signals K and −K sent from the modulator 14 and the distance measurement signals P and Pr sent from the amplifier 16. A CPU 26 for calculating the distance from the phase difference to the target 8 is provided.

  In this optical distance meter 10, reference light R modulated by the reference signal K, distance measuring light L modulated by the reference signal K, phase-reversed reference signal by the switching by the optical path switch g and the phase inversion signal T from the CPU 26. The ranging light R modulated with -K and the reference light L modulated with the phase-inverted reference signal -K are repeatedly emitted in this order from the light emitting part d, and the distance measurement is performed many times to obtain a large number of measured values. The distance is calculated by averaging.

  Now, the principle that distance can be measured by removing noise with this optical distance meter 10 will be described with reference to FIG. First, the reference light R modulated by the standard signal K is emitted, and then the distance measuring light L modulated by the standard signal K is emitted. At this time, the distance measurement signal P obtained by the light receiving unit e is obtained by adding noise N to the true distance measurement signal M. The phase difference θp between the distance measurement signal P and the reference signal K is measured by the phase comparator 24 and stored in the CPU 26. This phase difference θp is corrected by the CPU 26 using the phase difference between the reference signal S obtained from the reference light R and the standard signal K.

  Next, the ranging light L modulated by the phase-inverted reference signal -K is emitted, and then the reference light R modulated by the phase-inverted reference signal -K is emitted.

  At this time, the ranging signal Pr obtained by the light receiving unit e is obtained by adding noise N to the inverted ranging signal Mr obtained by inverting the phase of the true ranging signal M. A phase difference .theta.r between the distance measurement signal Pr and the phase-inverted reference signal -K is obtained by the phase comparator 24 and stored in the CPU. This phase difference θr is also corrected by the phase difference between the reference signal S obtained from the reference light R and the phase-inverted reference signal -K.

  The CPU 26 calculates an average value θt between the two phase differences θp and θr, and calculates a distance to the target 8 from the average value θt.

  As can be seen from FIG. 9, the phase difference θr between the distance measurement signal Pr and the reference signal −K whose phase is inverted is equal to the phase difference between the signal −Pr whose phase is inverted and the reference signal. When the ranging signal P and the signal -Pr obtained by inverting the phase of the ranging signal Pr are averaged, the noise N component disappears, and the average ranging signal Pt of both of them almost coincides with the true ranging signal M. To do. Therefore, since the phase error of the average value θt of the two phase differences θp and θr becomes extremely small, the cyclic error can be greatly reduced.

JP 2004-264112 A

  By the way, in the optical distance meter disclosed in Patent Document 1, in recent years, the reference signal K has been increased in frequency, and even if the phase of the reference signal K is inverted due to the phase delay of the XOR circuit 30, the phase is completely 180 °. Is not reversed, and actually the phase angle is smaller than 180 °, and usually only about 170 °, there is a problem that the cyclic error cannot be completely removed.

  This problem will be described in more detail. FIG. 10 shows respective vectors of the true reference signal S at the time of normal rotation of the reference signal K, the actual reference signal U to which noise N is added, the true ranging signal M, and the actual ranging signal P to which noise N is added. Show. FIG. 11 shows vectors of the true reference signal Sr, the actual reference signal Ur, the true ranging signal Mr, and the actual ranging signal Pr when the reference signal K is inverted. FIG. 12 shows the vectors U, P, S, M, and N when the reference signal K is rotated forward, and the vectors Ur, Pr, Sr, Mr, and N when the reference signal K is inverted, as Sr and S, Mr and M. FIG. 8 shows a diagram in which vectors Ur ′, Pr ′, and N ′ rotated so as to coincide with each other are superimposed.

However, the reference signals U and Ur and the ranging signals P and Pr correspond to the ranging value Dr by the reference light R and the ranging value Dl by the ranging light L, respectively. The phase difference between the average of the reference signals U and Ur ′ and the average of the distance measurement signals P and Pr ′ corresponds to the distance value to be displayed. This displayed distance value is
{(P + Pr ′) / 2} − {(U + Ur ′) / 2}
= {(P−U) + (Pr′−Ur ′)} / 2
Therefore, the same result can be obtained by averaging the distance measurement value at the time of normal rotation of the reference signal K and the distance measurement value at the time of inversion. This method is used in the present invention described later.

Now, the distance measurement value Dr by the reference light R and the distance measurement value Dl by the distance measurement light L are obtained from the following equations, respectively. Where λ is the ranging wavelength, As is the amplitude of the reference signal S, ψs is the phase of the reference signal S, An is the amplitude of the noise N, ψn is the phase of the noise N, Ap is the amplitude of the ranging signal P, and ψp is the measurement This is the phase of the distance signal P.
Dr = {λ / (2π)} tan ⁻¹ {(As · sinψs + An · sinψn) / (As · cosψs + An · cosψn)} (1)
Dl = {λ / (2π)} tan ⁻¹ {(Ap · sinφs + An · sinφn) / (Ap · cosφs + An · cosφn)} (2)

  Here, a distance measurement value is obtained from D1-Dr. Therefore, the wavelength λ is 2 m, the amplitude of the reference signal S is 1, the amplitude of the ranging signal P is 0.01, the amplitude of the noise is 0.001, the phase of the reference signal S is 0 °, and the phase of the ranging signal P is At 180 °, each distance measurement value at the time of forward rotation of the reference signal K and at the time of reversal of the reference signal K is calculated, and a distance measurement error compared with the distance measurement value when there is no noise N is calculated. Shown in The reason why the phase difference between the reference signal S and the distance measurement signal P is set to 180 ° is that the distance measurement error can be maximized. From this, when the distance measurement values at the time of the reference signal K forward rotation and the reference signal K inversion are averaged, the distance measurement errors at the time of the reference signal K forward rotation and the reference signal K inversion cancel each other, and the distance measurement error is greatly increased. You can see that it decreases.

  However, in actuality, the XOR circuit 30 cannot completely invert the phase of the reference signal K by 180 °, and the phase is changed by a phase angle somewhat smaller than 180 °. Hereinafter, such a case is also referred to as phase inversion. Therefore, the reference signal K has a phase angle (180−φ) ° (where 0 ° <φ <180 ° and the actual φ is about 10 °. However, if the reference signal K is further increased in frequency in the future, φ FIG. 14 shows respective vectors of the reference signal Sr, ranging signal Pr, noise N, and inverted reference signal K ′. Similarly to FIG. 12, the vectors U, P, S, M, and N at the time of normal rotation of the reference signal K and the vectors at the time of inversion of the reference signal K match S and Sr, and M and Mr. FIG. 15 shows a diagram in which the vectors Ur ′, Pr ′, N ′ rotated in this manner are superimposed. Further, the distance measurement value is calculated under the same conditions as those for obtaining the distance measurement error shown in FIG. 13 to obtain the distance measurement error, and the result is shown in FIG. FIG. 16 shows that the distance measurement error is extremely small when φ = 0 °, but the distance measurement error increases as φ increases. That is, the conventional lightwave distance meter has a problem that the cyclic error cannot be completely removed.

  This invention is made | formed in view of the said problem, and makes it a subject to make cyclic error still smaller in a light wave rangefinder.

  In order to solve the above-mentioned problems, an invention according to claim 1 includes a light emitting unit that emits distance measuring light, a modulator that modulates the distance measuring light, a reference signal generator that transmits a reference signal to the modulator, In the lightwave distance meter comprising: a light receiving unit that converts received ranging light into a ranging signal; and a distance calculation unit that calculates a distance to a measuring point using the ranging signal, the modulator includes the light emitting unit And a two-stage phase inverter interposed between the switch element and the reference signal generator, and the phase-inverted signal from the distance calculation unit is provided in each phase inverter of each stage. It is input.

  In the invention according to claim 2, in the invention according to claim 1, the phase inverter is an XOR circuit, and a second-stage XOR circuit that outputs a signal for controlling the switch element, and the second-stage XOR circuit An initial stage XOR circuit is provided that outputs a signal to be input and receives the reference signal.

  In the invention according to claim 1, the modulator includes a switch element connected to the light emitting unit and a two-stage phase inverter interposed between the switch element and the reference signal generator. A phase inversion signal from the distance calculation unit is input to each device. As a result, both the first-stage phase inverter and the second-stage phase inverter are normally rotated, one of the first-stage phase inverter and the second-stage phase inverter is rotated forward and the other is inverted, and the first-stage phase inverter and the second-stage phase inverter are reversed. The instrument can be inverted together to make three measurements. Then, in the second measurement, the reference signal has a predetermined angle phase change between 90 ° and 180 ° with respect to the first measurement, and in the third measurement, the predetermined angle is changed with respect to the first measurement. 2 times the phase changes. By taking the average of the first and second measurements, the average of the second and third measurements, and the average of both averages, the noise components cancel each other out and the cyclic error can be reduced. Further, a modulator can be manufactured more easily than a modulator that can modulate with a reference signal whose phase is almost completely inverted, and the lightwave distance meter of the present invention can be manufactured at a low cost.

  According to the invention of claim 2, the phase inverter is an XOR circuit, and a second-stage XOR circuit that outputs a signal for controlling the switch element, and a signal that is input to the second-stage XOR circuit Since the first stage XOR circuit for outputting the reference signal and outputting the reference signal is provided, the modulator has a particularly simple configuration, and the lightwave distance meter of the present invention can be manufactured at a lower cost.

It is a block diagram explaining the 1st Example of the lightwave distance meter of the present invention. It is a figure explaining the distance measuring method with the said light wave distance meter. It is a figure which shows the ranging error of the said light wave rangefinder. It is a figure which shows the ranging error of the said light wave rangefinder. It is a block diagram explaining 2nd Example of the lightwave distance meter of this invention. It is a block diagram explaining another Example of the lightwave distance meter of this invention. It is a block diagram of a general conventional lightwave distance meter. It is a block diagram of the conventional lightwave distance meter which reduced the cyclic error. It is a figure explaining the principle which reduces a cyclic error with the conventional lightwave distance meter which reduced the said cyclic error. It is a figure which shows the relationship between the reference signal at the time of normal rotation of a standard signal, a ranging signal, and noise in the conventional optical wave rangefinder which reduced the said cyclic error. It is a figure which shows the relationship between the reference signal at the time of standard signal inversion in the conventional lightwave distance meter which reduced the said cyclic error, a ranging signal, and noise. It is the figure which reversed FIG. 11 and overlapped on FIG. It is a figure which shows the theoretical ranging error of the conventional lightwave rangefinder which reduced the said cyclic error. It is a figure which shows the relationship between a reference signal, a ranging signal, and noise when a standard signal changes phase by (180-φ) ° in the conventional optical wave rangefinder in which the cyclic error is reduced. FIG. 11 is a diagram in which FIG. 14 is rotated to the right by (180−φ) ° and superimposed on FIG. 10. It is a figure which shows the realistic ranging error of the conventional lightwave rangefinder which reduced the said cyclic error.

  Hereinafter, preferred embodiments of the lightwave distance meter of the present invention will be described in detail with reference to the drawings.

  First, based on FIGS. 1-4, the 1st Example of the light wave distance meter of this invention is described. As shown in the block diagram of FIG. 1, in this optical distance meter, two stages of XOR circuits 30A and 30B, which are phase inverters, are provided between the reference signal generator 12 and the modulation transistor 28. Except for this, it is the same as the conventional one shown in FIG. Therefore, the same parts as those in the prior art are designated by the same reference numerals in the drawings, and description thereof is omitted. Of course, the XOR circuits 30A and 30B cannot completely invert the phase by 180 ° in one stage, but change the phase by slightly smaller than 180 ° (180−φ) °. However, 0 ° <φ <90 °.

The first stage of the XOR circuit 30A, the phase inversion signal _{T A} from the CPU 26, can be switched to the normal rotation reversal and. Similarly, the second stage XOR circuit 30B also, by the phase inversion signal _{T B,} Dekiru switched to the normal rotation reversal and.

  In the device disclosed in Patent Document 1, the XOR circuit 30 is measured twice by normal rotation and inversion, and the average is used as the distance measurement value. In this embodiment, the first-stage XOR circuit 30A and the two-stage circuit are used. Both the first XOR circuit 30B is normal, the first XOR circuit 30A is inverted (or normal), the second XOR circuit 30B is normal (or inverted), and both the first XOR circuit 30A and the second XOR circuit 30B are inverted. A distance measurement value is obtained by measuring three times and taking the average of the first and second measurements, the average of the second and third measurements, and the average of both averages.

  In the present embodiment, in the second measurement, the phase of the reference signal K changes by (180−φ) ° with respect to the first measurement (see K ′ in FIG. 14), and in the third measurement, the reference signal K However, the 2 * (180-φ) ° phase changes with respect to the first measurement. For the third measurement, a vector diagram similar to FIG. 15 is drawn as shown in FIG. However, in FIG. 2, only the noise N, the inverted noise N ′, and the inverted noise N ″ are displayed to prevent the drawing from becoming complicated. In the third measurement, the noise N ″ is The position is rotated 2φ from the original noise N.

  Therefore, for the second measurement and the third measurement, distance measurement values are calculated under the same conditions as when the distance measurement error shown in FIG. 13 is obtained. Then, the average of the two distance measurement values is taken, and the distance measurement error when there is no noise of the average is shown in FIG. For the first measurement and the second measurement, the distance measurement error when there is no average noise of the distance measurement values is as shown in FIG. Therefore, the average of the first and second measurements, the average of the second and third measurements, and the average value of both averages are calculated, and the distance measurement error when there is no noise of the average value is shown in FIG. Shown in From FIG. 4, the distance measurement error when φ = 0 ° is extremely small, and the distance measurement error is still small even when φ = 45 °, and the distance measurement error increases as φ increases, but even when φ <90 °, It can be seen that the distance measurement error can be made smaller than that of the above.

  Thus, according to this embodiment, even if the reference signal K is increased in frequency and φ increases in the future, the average of the first and second measurements, the average of the second and third measurements, Further, by taking the average of both averages, the noises N cancel each other, and the cyclic error can be reduced. Further, the modulator 14 can be manufactured more easily than the modulator that can modulate with the reference signal K whose phase is almost completely inverted, and the optical distance meter of the present invention can be manufactured at a low cost.

  Next, a second embodiment of the lightwave distance meter of this embodiment will be described in detail. FIG. 5 shows a block diagram of this light wave distance meter.

First, a reference signal having a frequency F ₁ is generated by the oscillator 51. The reference signal having the frequency F ₁ is input to the frequency divider 52 and is also input to the oscillator 56 via the PLL 55. The frequency divider 52 divides the reference signal having the frequency F ₁ to generate the reference signals having the frequencies F ₂ and F ₃ . The reference signals of the frequencies F ₂ and F _{3 and} the reference signal of the frequency F ₁ pass through the frequency superimposing circuit 53 and then through the first stage XOR circuit (phase inverter) 30A and the second stage XOR circuit (phase inverter) 30B. This is input to a drive circuit (switching element such as a modulation transistor) 54. The output of the drive circuit 54 is supplied to a light emitting element (light emitting unit) 61 through a load resistor 58. The light emitting element 61 emits light modulated at frequencies F ₁ , F ₂ and F ₃ . The first-stage XOR circuit 30A and the second-stage XOR circuit 30B are phase-inverted by phase inversion signals T _A and T _B from a CPU (distance calculation unit) (not shown).

Oscillator 56 generates a somewhat different local oscillation signal of frequency _{F 1} + _{Δf 1} and frequency _{F 1.} From the local oscillation signal of frequency F ₁ + Δf ₁ , the frequency generation circuit 57 divides the frequency to generate local oscillation signals of frequencies F ₂ + Δf ₂ and F ₃ + Δf ₃ that are somewhat different from the frequencies F ₂ and F ₃ , respectively. The The local oscillation signals of these frequencies F ₁ + Δf ₁ , F ₂ + Δf ₂ and F ₃ + Δf ₃ are input to frequency converters 82, 85 and 88, respectively, as will be described later.

  The light emitted from the light emitting element 61 is divided into two by the beam splitter 70, and by switching the shutter 78, one of the light is emitted as distance measuring light from a light transmission optical system (not shown) and is installed at a target point. The light enters the light receiving element (light receiving unit) 80 through a distance measuring optical path 73 that reciprocates up to the reflecting object (target) 72, and the other enters the light receiving element 80 through the reference light path 76 inside the lightwave distance meter as reference light. In the distance measuring optical path 73, a light receiving optical system 74 and a variable density filter 75 for adjusting the amount of light are disposed in front of the light receiving element 80. Also in the reference light path 76, a density filter 77 for attenuating the light amount is disposed in front of the light receiving element 80.

  The ranging signal output from the light receiving element 80 is divided into three through an amplifier 81, the first being input to the first frequency converter 82, and the second being input to the second frequency converter 85. The third is input to the third frequency converter 88.

The first frequency converter 82 uses a frequency F ₁ component of the ranging signal obtained from the ranging light that has passed through the ranging optical path 73 or the reference light that has passed through the reference optical path 76 to a frequency F that is somewhat different from the frequency F ₁ described above. Multiply the ₁ + Δf ₁ local oscillator signal to generate an intermediate frequency signal of frequency Δf ₁ . The second frequency converter 85 uses a frequency F ₂ component of the ranging signal obtained from the ranging light that has passed through the ranging optical path 73 or the reference light that has passed through the reference optical path 76 to a frequency F that is somewhat different from the frequency F ₂ described above. Multiply the ₂ + Δf ₂ local oscillation signal to generate an intermediate frequency signal of frequency Δf ₂ . The frequency F ₃ component of the ranging signal obtained from the third frequency converter 88, ranging light that has passed through the ranging optical path 73 or reference light that has passed through the reference optical path 76, has a frequency F _{3 that} is somewhat different from the frequency F ₃ described above. Multiply the + Δf ₃ local oscillation signal to generate an intermediate frequency signal of frequency Δf ₃ .

The intermediate frequency signals output from the frequency converters 82, 85, and 88 are respectively removed from the high frequency components by the low-pass filters 83, 86, and 89.
The intermediate frequency signals that have passed through the low-pass filters 83, 86, and 89 are input to A / D converters 84, 87, and 90, respectively. These intermediate frequency signals are sent to a CPU (distance calculation unit) (not shown), where the initial phase and amplitude are obtained. When the initial phase of each intermediate frequency signal is obtained, the distance value to the target reflector 72 is corrected with the distance value obtained from the reference light that has passed through the reference light path 76. Further, when the amplitudes of the intermediate frequency signals are obtained, these amplitudes are used for light amount adjustment by the variable density filter 75.

Also in this embodiment, since the modulator 14 is configured in the same manner as the modulator 14 of the first embodiment, the same effect as that of the first embodiment can be obtained. Further, in the present embodiment, since the ranging light L is simultaneously modulated with the _three frequencies F ₁ , F ₂ and F ₃ , the measurement time can be shortened compared with the case where the modulation is performed by switching the three frequencies.

  By the way, the present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the present invention can be applied to all surveying instruments including a light wave distance meter, such as a total station including a light wave distance meter, in addition to the light wave distance meter. Further, when the distance measurement error can be reduced by further increasing the number of XOR circuits and averaging the measured values, the number of XOR circuits may be increased. Further, the phase inverter does not need to use the XOR circuits 30A and 30B as in the above-described embodiment, and an appropriate phase inverter that can change the phase from 90 ° to 180 ° with respect to the reference signal is used. For example, as shown in FIG. 6, it can be configured by NOT circuits (NOT circuits) 31B and 32B and switches 31A and 32A.

8 Target 10 Lightwave Distance Meter 12 Reference Signal Generator 14 Modulator 26 CPU (Distance Calculation Unit)
28 Modulation transistor (switch element)
30A, 30B XOR circuit (phase inverter)
d emitting portion e light receiving portion K reference signals _{T, T A, T B} phase inversion signal

Claims (2)

A light emitting unit that emits distance measuring light; a modulator that modulates the distance measuring light; a reference signal generator that transmits a reference signal to the modulator; and a light receiving unit that converts the received distance measuring light into a distance measuring signal; In a lightwave distance meter comprising a distance calculation unit that calculates a distance to a measurement point using the distance measurement signal,
The modulator includes a switching element connected to the light emitting unit, and a two-stage phase inverter interposed between the switching element and the reference signal generator, and each of the phase inverters in each stage has the distance. A light wave distance meter, to which a phase inversion signal from a calculation unit is input. The phase inverter is an XOR circuit, a second-stage XOR circuit that outputs a signal for controlling the switch element, and a first-stage XOR that outputs a signal input to the second-stage XOR circuit and receives the reference signal The lightwave distance meter according to claim 1, further comprising a circuit.

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