JP5350331B2 - Distance sensor - Google Patents

Description

  The present invention relates to a distance sensor that calculates a measurement distance to a measurement object based on a phase difference between a transmitted wave and a reflected wave.

  In the phase-type distance sensor, the distance to the measurement object is calculated from the phase difference between the transmission wave and the reflected wave reflected by the measurement object (see, for example, Patent Document 1).

JP-A-8-88672

  In a phase-type distance sensor, the maximum distance (so-called “distance range”) that can be measured is determined by the frequency of the transmission wave. Specifically, the lower the frequency, the longer the wavelength, and the greater the distance range. On the other hand, in order to measure the distance with high accuracy, it is necessary to set the frequency of the transmission wave to a high frequency. That is, depending on the actual distance to the object to be measured, the distance can be measured, and the distance range considered to have the best measurement accuracy differs. Therefore, how to switch the distance range and how to detect an appropriate distance range are problems.

  Further, in the phase type distance sensor, it is necessary to detect the phase difference between the transmitted wave and the reflected wave with higher accuracy in order to measure the distance with high accuracy. However, noise (noise) is often superimposed on the reflected wave propagating in space, and noise removal is necessary.

  The present invention has been made in view of the above circumstances, and an object thereof is to realize switching to an appropriate distance range in a phase-type distance sensor. The second purpose is to enable detection of an appropriate distance range. A third object is to enable accurate detection of the phase difference between the transmitted wave and the reflected wave.

The first form for solving the above problem is
A frequency divider (for example, frequency divider 4 in FIG. 3) capable of changing a frequency division ratio for dividing a clock signal having a predetermined reference frequency is provided, and is transmitted from the frequency-divided signal divided by the frequency divider. A transmission unit (for example, the light emitting unit 6 in FIG. 3) that generates and transmits a wave;
A receiving unit (for example, the light receiving unit 8 in FIG. 3) that receives a reflected wave of the transmission wave;
A synchronous detector (for example, the delay circuit 22 and mixers 24 and 26 in FIG. 3) that synchronously detects the reflected wave received by the receiver using the divided signal;
A DC component extraction unit (for example, LPFs 28 and 30 in FIG. 3) that extracts a DC component from the signal synchronously detected by the synchronous detection unit;
A phase difference detection unit (for example, the control unit 40 in FIG. 3) that detects a phase difference between the transmission wave and the reflected wave based on the DC component extracted by the DC component extraction unit;
A frequency division ratio control unit (for example, the control unit 40 in FIG. 3) that changes the wavelength of the transmission wave by changing and controlling the frequency division ratio of the frequency divider;
A distance calculation unit (for example, the control unit 40 in FIG. 3) that calculates a measurement distance to the measurement object based on the phase difference detected by the phase difference detection unit;
Is a distance sensor (for example, the distance sensor 100 of FIG. 3).

  According to the first embodiment, in the distance sensor that calculates the measurement distance to the measurement object based on the phase difference between the transmitted wave and the reflected wave, the divided signal obtained by dividing the clock signal having the predetermined reference frequency. From this, a transmission wave is generated, and the frequency division ratio of the frequency divider that divides the clock signal is controlled to be changed. Thus, the frequency of the transmission wave, that is, the distance range can be easily changed by simply changing the frequency dividing ratio of the frequency divider. Further, since only the frequency division ratio of the frequency divider needs to be changed and controlled, only one oscillator having a fixed oscillation frequency is sufficient as an oscillator for generating a transmission wave.

Further, as a second form, the distance sensor of the first form,
The synchronous detection unit and the DC component extraction unit constitute a two-phase lock-in amplifier circuit (for example, the two-phase lock-in amplifier 20 in FIG. 3),
The phase difference detection unit detects the phase difference using a positive / negative combination of two DC components extracted by the DC component extraction unit and the DC component.
A distance sensor may be configured.

  According to the second embodiment, the synchronous detection of the reflected wave using the frequency-divided signal and the extraction of the DC component from the synchronously detected signal are realized using the two-phase lock-in amplifier circuit. Thus, accurate phase difference detection that is resistant to noise is realized.

Further, as a third form, the distance sensor of the first or second form,
A phase shift unit (for example, the phase shift circuit 12 in FIG. 5) for correcting the phase of the reflected wave received by the reception unit;
The synchronous detection unit synchronously detects the reflected wave phase-shifted by the phase shift unit,
When performing a predetermined calibration process, the distance measurement is calibrated by adjusting the phase shift amount of the phase shift unit so that the phase difference detected by the phase difference detection unit satisfies a predetermined calibration phase difference condition. A configuration control unit,
With
A distance sensor may be configured.

  According to the third embodiment, the distance measurement is calibrated by executing the calibration process, thereby realizing more accurate distance measurement.

Further, as a fourth form, the distance sensor according to any one of the first to third forms,
A suitable distance range suitable for measurement when the division ratio is used for each division ratio is determined in advance (for example, the division ratio switching table 44 in FIG. 7).
The division ratio control unit repeatedly performs the division ratio change control and the distance calculation so that the division ratio becomes a division ratio corresponding to the preferred distance range including the measurement distance. ,
A distance sensor may be configured.

  According to this 4th form, the suitable distance range suitable for the measurement at the time of setting the said frequency division ratio for each frequency division ratio of the frequency divider is determined in advance, and the frequency division ratio preferably includes the measurement distance. The division ratio change control and the distance calculation are repeatedly performed so that the division ratio corresponds to the distance range. That is, the distance range is changed to a suitable distance range according to the calculated measurement distance.

Further, as a fifth form, the distance sensor of the fourth form,
The control unit temporarily calculates the measurement distance by changing the division ratio to a changeable maximum value, and changes the division ratio to a suitable division range including the provisionally calculated measurement distance. Calculate the measurement distance,
A distance sensor may be configured.

  According to the fifth aspect, the measurement distance is provisionally calculated by changing the frequency division ratio of the frequency divider to the maximum changeable value, and the frequency division ratio corresponding to the preferred distance range including the provisionally calculated measurement distance The measurement distance is calculated again. That is, first, provisional measurement is performed in the maximum distance range, and then the measurement distance in the provisional measurement is changed to the optimum distance range to perform the main measurement. Thereby, an appropriate distance range can be detected efficiently and can be measured.

The schematic diagram of distance measurement by a distance sensor. Explanatory drawing of the difference in the measurement precision by a transmission frequency. The principle block diagram of a distance sensor. Correspondence between calculated phase difference and actual phase difference. The block diagram of a distance sensor. The data structural example of a phase difference correction table. The data structural example of a division ratio switching table. An example of the correspondence of a frequency division ratio and a suitable distance range. The flowchart of a distance measurement process. The flowchart of another distance measurement process. Explanatory drawing of the measurement of the distance exceeding the half wavelength of a transmission signal. Explanatory drawing of correction | amendment of measurement distance when an actual distance exceeds the half wavelength of a transmission signal. The flowchart of another distance measurement process.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following, a lightwave distance sensor to which the present invention is applied will be described, but embodiments to which the present invention can be applied are not limited thereto.

[Overview]
FIG. 1 is a schematic diagram of distance measurement by the distance sensor 100 in the present embodiment. This distance sensor 100 is a light wave distance sensor using light waves such as infrared rays and laser light, and measures the distance L to the measuring object 200 by a phase method.

That is, as shown in FIG. 1A, a transmission wave that is a light wave is emitted toward the measurement object 200, and the reflected wave reflected by the measurement object 200 is received. Then, as shown in FIG. 1B, the distance L to the measurement object 200 is calculated from the phase difference φ between the transmitted wave and the received reflected wave. The distance L to the measuring object 200 is calculated as L = (C · φ / 2πf) / 2. Here, “C” is the speed of light, and C≈3 × 10 ⁸ m / s.

  Further, since the distance L is calculated from the phase difference φ between the transmission wave and the reflected wave, the phase difference φ is within one cycle of the transmission frequency when the distance L is calculated using only one transmission frequency. For this reason, the maximum measurable distance Lm (so-called “distance range”) is theoretically determined by the frequency f of the transmission wave and is Lm = λ / 2 = C / (2 · f). For example, when the frequency of the transmission wave is “50 MHz”, the wavelength λ is “6 m” and the maximum measurable distance Lm is “3 m”.

  The calculation accuracy of the measurement distance L by the phase-type distance sensor differs depending on the frequency of the transmission wave. Specifically, the calculation accuracy is better as the frequency of the transmission wave is higher.

  FIG. 2 is a diagram for explaining the difference in calculation accuracy of the measurement distance L due to the difference in the frequency of the transmission wave. In the drawing, the upper side shows a transmission wave and a reception wave having a frequency fa, and the lower side shows a transmission wave and a reception wave having a frequency fb (= 3 · fa) higher than the frequency fa.

  When the same distance L is measured, the phase difference φ between the transmitted wave and the reflected wave differs depending on the wavelength λ when the frequency f is different. Specifically, the higher the frequency, the larger the phase difference φ. In FIG. 2, the phase difference φb at the frequency fb is larger than the phase difference φa at the frequency fa, and φb = 3 · φa.

  When detecting the phase difference φ between two signals, the smaller the phase difference φ, the easier the detection error. That is, as the frequency f of the transmission wave is lower, a detection error of the phase difference φ is more likely to occur, and the calculation accuracy of the measurement distance L is reduced. In other words, as the frequency f of the transmission wave is higher, the detection error of the phase difference φ is less likely to occur and the calculation accuracy of the measurement distance L is improved.

[principle]
FIG. 3 is a principle configuration diagram of the distance sensor 100 in the present embodiment. As shown in FIG. 3, the distance sensor 100 according to the present embodiment detects a phase difference φ between a transmission wave and a reception wave using a two-phase lock-in amplifier. A frequency divider 4, a light emitting unit 6, a light receiving unit 8, a BPF 10, a two-phase lock-in amplifier 20, and a control unit 40 are configured.

  For example, the oscillator 2 includes a crystal resonator and generates a reference signal F1 having a reference frequency f.

The frequency divider 4 divides the frequency f of the reference signal F1 output from the oscillator 2 by 1 / N and outputs it as a transmission signal V _T. The frequency division ratio N of the frequency divider 4 is “N = 2 ⁿ (n is a positive number)”, and is changed and controlled by the control unit 40.

Emitting unit 6 is composed of, for example, a light-emitting element such as a laser diode, an optical signal whose intensity is modulated at a frequency of the transmitted signal V _T output from the frequency divider 4, and emits a transmission wave. That is, a transmission wave having a frequency “f / N” is emitted.

The light receiving unit 8 is composed of, for example, a light receiving element such as a photodiode converts the light waves received into an electrical signal, and outputs as a reception signal V _R.

BPF10 is the received signal V _R, is passed through a signal of a predetermined band, for blocking an out-of-band frequency components. The center frequency fo of this BPF10 from the received signal _{V R,} for extracting only the signal of the reflected wave at the same frequency as the transmission wave, the control unit 40, fo = f / N, is set to.

2 phase lock-in amplifier 20, a transmission signal V _T which is output from the frequency divider 4 as "reference signal", the received signal V _R as "measurement signal", the synchronous detection in the transmit signal V _T the received signal V _R (Phase detection) and two orthogonal DC signals X and Y are output. In principle, the two-phase lock-in amplifier 20 includes a delay circuit 22, mixers 24 and 26, and LPFs 28 and 30.

The delay circuit 22 delays the phase of the transmission signal V _T (reference signal) by “π / 2 (90 °)”.

The mixer 24 multiplies (synthesizes) the signal output from the BPF 10 and the transmission signal V _T (reference signal) and outputs the result. The mixer 26 multiplies the signal output from the BPF 10 and the signal output from the delay circuit 22.

  The LPF 28 passes a predetermined low-band signal with respect to the output signal of the mixer 24, and blocks out-of-band frequency components. The cutoff frequency fc of the LPF 28 is set by the control unit 40 to fc = f / 2N.

  The LPF 30 passes a predetermined low-band signal with respect to the output signal of the mixer 26 and blocks out-of-band frequency components. The cutoff frequency fc of the LPF 30 is set to fc = f / 2N by the control unit 40.

In this distance sensor 100, if the reference signal F1 generated by the oscillator 2 is F1 = sin (ωt), the output signal of the frequency divider 4, that is, the transmission signal V _T (reference signal) is V _T = sin ( ωt / N). The output signal D of the delay circuit 22 is D = sin (ωt / N−π / 2) = cos (ωt / N).

Further, when the phase difference between the transmitted signal _{V T} and the received signal _{V R} and "phi", the received signal _{V R is, V R = sin (ωt /} N-φ), and becomes. The received signal _{V R} is directly passed through the BPF 10.

The output signal MIX1 of the mixer 24 is expressed by the following equation (1).
MIX1 = sin (ωt / N) × sin (ωt / N−φ)
= − (Cos (2ωt−φ) −cosφ) / 2 (1)
The signal MIX1 is blocked from high frequency components by passing through the LPF 28. The output signal X of the LPF 28 is X = (cosφ) / 2.

Further, the output signal MIX2 of the mixer 26 is expressed by the following equation (2).
MIX2 = cos (ωt / N) × sin (ωt / N−φ)
= (Sin (2ωt−φ) + sinφ) / 2 (2)
The high frequency component of the signal MIX2 is blocked by passing through the LPF 30. The output signal Y of the LPF 30 is Y = (sin φ) / 2.

Thus, these signals X, the Y, the phase difference φ between the transmitted signal _{V T} and the received signal _{V R,} the equation (3).
φ = tan ⁻¹ (Y / X) (3)

However, the actual phase difference [phi] r of the transmission signal _{V T} and the received signal _{V R} is "0 ≦ φr <2π (360 ° ) ". However, the phase difference φ calculated by the above equation (3) is a value of “−π / 2 (−90 °) ≦ φ ≦ π / 2 (90 °)”. For this reason, it is necessary to correct the calculated phase difference φ so as to be the actual phase difference φr. Specifically, the calculated phase difference φ is corrected by a positive / negative combination of the signals X and Y.

FIG. 4 is a diagram showing the relationship between the actual phase difference φr and the positive and negative of the signals X and Y. In Figure 4, the actual phase difference φr of the horizontal axis and the transmission signal V _T and the received signal V _R, the signal X, and Y, respectively, the signal X, a phase difference φ being calculated from the Y, the actual phase difference φr.

  As shown in FIG. 4, when “0 ≦ φr <π / 2 (90 °)”, φ = φr, but when “π / 2 (90 °) ≦ φr <2π (360 °)”, φ ≠ φr. Specifically, in “π / 2 (90 °) ≦ φr <3π / 2 (270 °)”, φ = φr−π (180 °), and in “3π / 2 ≦ φr <2π”, φ = φr−2π. For this reason, it is necessary to correct the calculated phase difference φ so that the actual phase difference φr is obtained. Since the positive and negative combinations of the values of the signals X and Y differ for each quadrant, the necessary correction amount Δφ is determined from the positive and negative combinations of the values of the signals X and Y.

[Constitution]
FIG. 5 is a configuration diagram of the distance sensor 100 that realizes the above-described principle configuration. According to FIG. 5, the distance sensor 100 includes the oscillator 2, the frequency divider 4, the light emitting unit 6, the light receiving unit 8, the BPF 10, the phase shift circuit 12, the two-phase lock-in amplifier 20, the A / A D conversion unit 14 and a control unit 40 are provided.

  The oscillator 2 generates a square wave having a frequency f as the reference signal F1.

The phase shift circuit 12 changes the phase of the signal (reception signal V _R ) output from the BPF 10. This phase shift θ due to the phase shift circuit 12 can be changed, it is determined by the calibration processing of distance measurement for adjusting a phase shift between the transmission signal V _T and the received signal V _R.

  In the calibration process, for example, the control unit 40 gradually changes the phase shift amount θ of the phase shift circuit 12 while measuring the distance to the measurement object whose distance L is clear, and the calculated distance L is the actual distance L. Is a process of searching for the phase shift amount θ when the same. This calibration process may be performed by the manufacturer before shipping the product, or may be performed regularly / irregularly at the facility where calibration is performed after the sale, or may be performed by the user. Anyway. In any case, the control unit 40 changes and sets the phase shift amount θ of the phase shift circuit 12 so that the calculated distance L is the correct distance.

Further, the calibration process may be performed as follows as long as the delay time of both transmission and reception of light waves is compensated. That is, a transmission signal V _T which is input to the light emitting portion 6, providing a possible short short circuit immediately after the output of the light receiving portion 8. Then, the control unit 40, upon execution of the calibration process, to short-circuit the received signal V _R and the transmission signal V _T by the short circuit, the measurement distance L is calculated so as to be zero, the phase shift circuit 12 Adjust and set the phase shift amount θ.

  The two-phase lock-in amplifier 20 includes a delay circuit 22, an inverting amplifier 32, PSDs (Phase Sensitive Detectors) 34 and 36, and LPFs 28 and 30.

  The inverting amplifier 32 inverts the polarity (positive / negative level) of the signal output from the phase shift circuit 12.

The PSD 34 has a switch element that switches contacts according to the polarity of the transmission signal V _T (reference signal), and switches and outputs a non-inverted signal / inverted signal of the output signal of the phase shift circuit 12. The LPF 28 passes a predetermined low-band frequency component to the output signal of the PSD 34 and blocks out-of-band frequency components.

  The PSD 36 has a switch element that switches contacts according to the polarity of the output signal of the delay circuit 22, and switches and outputs the non-inverted signal / inverted signal of the output signal of the phase shift circuit 12. The LPF 30 allows a predetermined low-band frequency component to pass through the output signal of the PSD 36 and blocks out-of-band frequency components.

  The A / D converter 14 converts the signals X and Y output from the LPFs 28 and 30, respectively, into digital signals.

  The control unit 40 includes an arithmetic device such as a CPU, and executes a distance measurement process for measuring the distance L to the measurement object. In this distance measurement process, first, the frequency division ratio N of the frequency divider 4 is set to the maximum value Nmax. Further, the center frequency fo of the BPF 10 is set in accordance with the set frequency dividing ratio N, and the cut-off frequency fc of the LPFs 28 and 30 is set. The center frequency fo is given by fo = f / N, and the cutoff frequency fc is given by fc = f / 2N.

Next, the distance L to the measurement object is measured. That, A / D converter 14 signals output from the X, based on the Y, according to the above equation (3), calculates the phase difference φ between the transmitted signal V _T and the received signal V _R. Subsequently, the calculated phase difference φ is corrected according to the phase difference correction table 42 based on the positive / negative combination of the signals X and Y.

  FIG. 6 is a diagram illustrating an example of a data configuration of the phase difference correction table 42. According to FIG. 6, the phase difference correction table 42 stores the correction amount 42c of the phase difference φ in association with each combination of the positive / negative 42a of the value of the signal X and the positive / negative 42b of the value of the signal Y. . The phase difference correction table 42 is stored in the control unit 40.

  Then, the measurement distance L is calculated from the phase difference φ and is set as the initial measurement distance Lx. The measurement distance L is given by L = (C · φ · N) / (2 · ω). When the initial measurement distance Lx is calculated, the optimum frequency division ratio N corresponding to the initial measurement distance Lx is subsequently determined according to the frequency division ratio switching table 44.

  FIG. 7 is a diagram illustrating an example of a data configuration of the frequency division ratio switching table 44. As shown in FIG. 7, the frequency division ratio switching table 44 stores a frequency division ratio 44a that can be set in the distance sensor 100 and a suitable distance range 44b in association with each other. “E” defining the preferred distance range 44b is an error margin representing an error expected for the measurement distance L, and is a value of “0.0 <e ≦ 1.0”, which is arbitrarily set by the user of the distance sensor 100, for example. Given to. For example, the error margin e = 0.9 represents that an error of “10% (= 0.1 = 1.0−0.9)” with respect to the measurement distance L is included. This frequency division ratio switching table 44 is stored in the control unit 40.

  The control unit 40 determines that the frequency division ratio N corresponding to the preferred distance range including the initial measurement distance Lx is the optimum frequency division ratio N. Then, the frequency division ratio N of the frequency divider 4 is changed to the frequency division ratio N determined to be optimal, and the cutoff frequency fc of the LPFs 28 and 30 is changed in accordance with the frequency division ratio N after the change. Thereafter, the distance L to the measurement object is recalculated and output as a measurement result.

  Here, the correspondence relationship between the “frequency division ratio N” and the “suitable distance range” determined in the frequency division ratio switching table 44 is determined as follows. FIG. 8 is a diagram illustrating an example of a correspondence relationship between the frequency division ratio N and the preferred distance range. FIG. 8 shows, in order from the top, cases of error margin e = 1.0, error margin e = 0.9, and error margin e = 0.5. However, the settable division ratio N is “N = 1, 2, 4, 8, 16”, and the reference frequency f is “f1 = 50 MHz”.

  As shown in FIG. 8, a suitable distance range that does not overlap each other is associated with each settable division ratio N. This preferred distance range is determined according to the distance range of the frequency division ratio N and the error expected for the distance measured by the distance sensor 100.

  That is, when an error is not expected (error margin e = 1.0), the preferred distance range corresponding to a certain frequency division ratio N has a maximum distance range at the frequency division ratio N, and is one level lower than that. It is determined as a range in which the distance range at the circumferential ratio N (= N / 2) is the minimum value.

  For example, the distance range of the frequency division ratio N = 16 is “48 m”, and the distance range of the frequency division ratio N = 8 is “24 m”. Accordingly, “24 to 48 m” is associated with the frequency division ratio N = 16 as the preferred distance range.

  Similarly, “12 to 24 m” is associated with the frequency division ratio N = 8 as a suitable distance range, and “6 to 12 m” is associated with the frequency division ratio N = 4 as the suitable distance range. “3 to 6 m” is associated with the circumferential ratio N = 2 as a preferred distance range, and “0 to 3 m” is associated with the circumferential ratio N = 1 as the preferred distance range.

  When the error is expected, the minimum value and the maximum value of the preferable distance range in the case where the error is not expected (error margin e = 1.0) are changed to values that allow the error.

  For example, when an error of “50%” is expected with respect to the measurement distance L (error margin e = 0.5), the frequency division ratio N = 16 (maximum value Nmax) is preferable when no error is expected. “12 m (= 24−24 × 0.5)” that allows for an error of “50%” with respect to “24 m” that is the minimum value of the distance range is set as the minimum value. That is, “12 to 48 m” is associated with the frequency division ratio N = 16 as a preferable distance range.

  For the next largest division ratio N = 8 (= 16/2), the maximum value of the preferred distance range is set to the division ratio N = 16 so as not to overlap with the preferred distance range of the division ratio N = 16. The minimum value is “12 m”, and the minimum value is “6 m (= 12−12 × 0.5)” with an error of “50%” compared to the minimum value “12 m” when no error is expected. To do. That is, “6 to 12 m” is associated with the frequency division ratio N = 8 as the preferred distance range.

  Similarly, the frequency division ratio N = 4 is associated with “3 to 6 m” as the preferred distance range, and the frequency division ratio N = 2 is associated with “1.5 to 3 m” as the suitable distance range. The frequency division ratio N = 1 is associated with “0 to 1.5 m” as a preferred distance range.

  Here, as a processing procedure in the present embodiment, the priority distance range of the maximum value Nmax of the frequency division ratio N is given priority over the correspondence between the frequency division ratio N and the suitable distance range in which an error is expected. This is because the optimum frequency division ratio N is determined and changed after setting the frequency division ratio N of the frequency divider 4 to the maximum value Nmax.

[Process flow]
FIG. 9 is a flowchart for explaining the flow of the distance measurement process executed by the control unit 40. According to FIG. 9, the control unit 40 first sets the frequency division ratio N of the frequency divider 4 to the maximum value Nmax (step A1). Further, the center frequency fo of the BPF 10 is set in accordance with the set frequency division ratio N, and the cutoff frequencies fc of the LPFs 28 and 30 are set (step A3).

Then, the signal X, Y to the original, calculates the phase difference φ between the transmitted signal V _T and the received signal V _R (step A5), with reference to the phase difference correction table 42, the signal X, the values of Y The calculated phase difference φ is corrected according to the positive / negative combination (step A7). Based on this phase difference φ, the initial measurement distance Lx is calculated (temporary calculation) (step A9).

  Subsequently, the optimal frequency division ratio N corresponding to the calculated initial measurement distance Lx is determined with reference to the frequency division ratio switching table 44 (step A11). Then, the frequency division ratio N of the frequency divider 4 is updated to the frequency division ratio N determined to be optimal (step A13), and the center frequency fo of the BPF 10 and the LPF 28 are adjusted in accordance with the frequency division ratio N after the change. , 30 is updated (step A15).

Thereafter, similarly, signals X, to re-calculate the phase difference phi between the transmission signal V _T and the received signal V _R from Y (step A17), calculated by correcting the phase difference phi (step A19), the corrected phase difference Based on φ, the measurement distance L is recalculated (step A21).

[Action / Effect]
Thus, the distance sensor 100 of the present embodiment, sends a signal V _T and the "reference signal", the received signal V _R is configured to have a second phase lock-in amplifier 20 to "measurement signal", the 2 the phase lock-in amplifier 20, the phase difference φ is calculated from the transmitted signal V _T and the received signal V _R. When measuring the distance, first, the frequency division ratio N of the frequency divider 4 is set to the maximum value Nmax, and the frequency division ratio N of the frequency divider 4 is set according to the measurement distance Lx calculated at this time. After changing to the optimum frequency division ratio N, the measurement distance is calculated again. Thereby, automatic switching of an appropriate distance range according to the actual distance to the measuring object 200 is realized. Further, the phase difference φ is accurately detected by the two-phase lock-in amplifier 20, and a highly accurate distance measurement is realized.

[Modification]
It is to be noted that the present invention is not limited to the applicable embodiments and the above-described embodiments, and can of course be changed as appropriate without departing from the spirit of the present invention.

(A) Switching of frequency dividing ratio For example, switching of the frequency dividing ratio N of each frequency divider 4 in the distance sensor 100 may be changed so as to decrease the distance range one step at a time.

  FIG. 10 is a flowchart of the distance measurement process when the frequency division ratio N is changed so as to lower the distance range step by step. As shown in FIG. 10, first, the frequency division ratio N of the frequency divider 4 is set to the maximum value Nmax (step B1), and the center frequency fo of the BPF 10 and the LPF 28 are matched to the frequency division ratio N. , 30 is set (step B3).

  Next, the phase difference φ is calculated from the signals X and Y at this time (step B5), and the calculated φ is corrected according to the phase difference correction table 42 based on the positive / negative combination of the values of the signals X and Y. (Step B7). Based on the corrected phase difference φ, the measurement distance Lx to the measurement object is calculated (step B9).

  The current division ratio N is “2” or more (step B11: YES), and the calculated measurement distance Lx is the minimum value “(N / 2) · Lmin · e ”or less (step B13: YES), the frequency division ratio N is changed to be decreased by one step (step B15). Thereafter, the process returns to step B3, and similarly, the measurement distance to the measurement object is recalculated.

  On the other hand, when the current frequency division ratio N is “1” (step B11: NO), or the calculated measurement distance Lx is the minimum value “(N / 2) · Lmin · e ”(step B13: NO), it is determined that the current division ratio N is a suitable division ratio N (step B17), and the measurement distance Lx calculated at the end is determined. Is output as a measurement result.

  For example, when measuring a short distance L, it is expected that the calculation error of the measurement distance L at the maximum frequency division ratio Nmax is large, and there is a possibility that the optimum frequency division ratio N is erroneously detected. Therefore, by changing the division ratio N so that the distance range is lowered step by step in this way, the optimum division ratio N can be detected more accurately and the calculation error of the measurement distance L can be reduced. .

Furthermore, the distance in this case, the distance range by calculating the measured distance L in all distance range while changing the frequency division ratio N to decrease by one step, more than half wavelength lambda / 2 of the transmission signal V _T L can also be measured, and more accurate distance measurement is realized.

Figure 11 is a diagram for explaining the measurement of the distance L exceeding the half-wavelength lambda / 2 of the transmission signal V _T. In the figure, upper, a frequency f1 / N of the transmission signal _{V T} shows the case of the "frequency fa (wavelength [lambda] a)", the lower side, the frequency f1 / N of the transmission signal _{V T,} higher than the frequency fa " The frequency fb (wavelength λb) ”is shown.

  As described above, since the distance L from the phase difference φ between the transmission signal and the reception signal to the measurement object is measured, the calculated distance L is L <λ / 2. That is, when the actual distance Ls is measured, as shown in the upper side, when Ls <(λa / 2), the calculated distance L is “Ls”, but as shown in the lower side, Ls> The distance L calculated at (λb / 2) is “Ls−λb / 2”, which is not correct.

However, if the lower limit of the frequency division ratio N (the limit frequency division ratio N _L at which the cycle of the transmission signal V _T is not inverted) can be determined so that the actual distance Ls does not exceed the half wavelength λ / 2 of the transmission signal Vt. , the measurement distance L in the frequency division ratio N below this lower limit, it is corrected by adding the wavelength lambda / 2 minutes distance of the transmitted signal V _T at that time is calculated more accurately measured distance L It becomes possible.

FIG. 12 is a diagram for describing correction of the measurement distance L when the actual distance Ls exceeds the half wavelength λ / 2 of the transmission signal Vt. In the figure, upper, transmit signal V _T indicates the case of frequency fb, the lower shows the case where the transmission signal V _T is the frequency fc (> fb), both half-wavelength λ of the transmitted signal V _T / 2 is shorter than the actual distance Ls. As shown on the upper side, in the case of the frequency fb, the calculated distance L is “Ls−λb / 2”, and correction is performed by adding the half wavelength “λb / 2”. As shown on the lower side, in the case of the frequency fc, the calculated distance L is “Ls−3 · λc / 2”, which is three times the half wavelength λc / 2, “3 · λc / Add 2 ”to correct.

At this time, whether or not the calculated distance L needs to be corrected depends on whether the measured distance Lx at a certain frequency division ratio N is a process of changing the frequency division ratio N so as to lower the distance range step by step. The determination can be made based on whether the distance is within a preferable distance range corresponding to the frequency division ratio N. That is, it can be realized by determining the lower limit (limit frequency dividing ratio N _L ) of the frequency dividing ratio N that the actual distance Ls does not exceed the half wavelength λ / 2 of the transmission signal V _T. Then, when the frequency division ratio N is lower than the limit frequency division ratio N _L , that is, when the calculated measurement distance L needs to be corrected, how many times the half wavelength λ / 2 of the transmission signal V _T is added. This can be determined from the approximate distance calculated so far.

  FIG. 13 is a flowchart for explaining measurement processing for calculating measurement distances in all distance ranges. As shown in the figure, first, the frequency division ratio N of the frequency divider 4 is set to the maximum value Nmax (step C1), and the center frequency fo of the BPF 10 and the LPF 28, LPF 28, The cutoff frequency fc of each 30 is set (step C3).

  Next, the phase difference φ is calculated from the signals X and Y at this time (step C5), and the calculated φ is corrected according to the phase difference correction table 42 based on the positive / negative combination of the values of the signals X and Y. (Step C7). Subsequently, the measurement distance Lx to the measurement object is calculated based on the corrected phase difference φ (step C9). The calculated measurement distance Lx is stored in association with the current frequency division ratio N (step C11).

The current division ratio N is “2” or more (step C13: YES), and the calculated measurement distance Lx is the minimum value “(N / 2) · Lmin · e ”or more (step C15: YES), the current frequency division ratio N is updated as the limit frequency division ratio N _L for period inversion (step C17). Then, the frequency division ratio N is changed so that the distance range is reduced by one step (step C19). Thereafter, the process returns to step C3, and similarly, the measurement distance Lx to the measurement object is calculated.

  If the current frequency division ratio N becomes “1” (step C13: NO), the stored measurement distance L and the limit frequency division ratio NL at each frequency division ratio N are stored. The final measurement distance L is determined and output (step C21).

(B) Distance sensor In the above-described embodiment, the distance sensor 100 is a light wave distance sensor. However, for example, if the distance sensor is a phase type distance sensor such as a distance sensor using electromagnetic waves or ultrasonic waves, the present invention is similarly applied. Is applicable.

DESCRIPTION OF SYMBOLS 100 Distance sensor 2 Oscillator, 4 frequency divider, 6 Light emission part 8 Light reception part, 10 BPF, 12 Phase shift circuit 20 2 phase lock-in amplifier 22 Delay circuit, 24, 26 Mixer, 28, 30 LPF
32 inverting amplifier, 34, 36 PSD
14 A / D converter, 40 Control unit 200 Measurement object

Claims (5)

A transmitter having a frequency divider capable of changing a frequency dividing ratio for dividing a clock signal having a predetermined reference frequency, and a transmitter that generates and transmits a transmission wave from the frequency-divided signal divided by the frequency divider;
A receiver for receiving a reflected wave of the transmission wave;
A two-phase lock-in amplifier circuit unit that synchronously detects the reflected wave received by the receiving unit using the divided signal and extracts two orthogonal DC components;
A phase difference detection unit that detects a phase difference between the transmitted wave and the reflected wave by correcting a phase indicated by the two DC components with a phase correction amount based on a positive / negative combination of the two DC components ;
Based on the phase difference detected by the phase difference detection unit, a control unit that calculates a measurement distance to the measurement object;
Distance sensor equipped with. Further comprising a phase shifter for a given amount of phase shift phase shift the received the reflected wave of the phase at the receiving unit,
The two-phase lock-in amplifier circuit unit synchronously detects the reflected wave phase-shifted by the phase-shift unit,
The control unit adjusts the phase shift amount of the phase shift unit so that the phase difference detected by the phase difference detection unit satisfies a predetermined calibration phase difference condition when executing a predetermined calibration process. A means for performing control to calibrate the distance measurement,
The distance sensor according to claim 1 . A suitable distance range suitable for measurement when the division ratio is used for each division ratio is determined in advance.
The control unit repeatedly performs the change control of the division ratio and the calculation of the distance so that the division ratio becomes a division ratio corresponding to the suitable distance range including the measurement distance.
The distance sensor according to claim 1 or 2 . The control unit temporarily calculates the measurement distance by changing the division ratio to a changeable maximum value, and changes the division ratio to a suitable division range including the provisionally calculated measurement distance. Calculate the measurement distance,
The distance sensor according to claim 3 . The control unit repeatedly performs the control for gradually decreasing the frequency division ratio and the calculation of the measurement distance, and when the measurement distance exceeds the half wavelength of the transmission wave, the previously calculated measurement distance and the measurement distance Based on the half wavelength, the addition distance of the integral multiple of the half wavelength included in the length of the portion exceeding the half wavelength is determined, and the measurement distance is corrected by adding the addition distance to the measurement distance. Having means,
  The distance sensor as described in any one of Claims 1-4.

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