JPH0875854A - Distance measuring device - Google Patents

Abstract

PURPOSE: To correct an error generated accompanying judgment on the receiving time of a distance measuring signal so as to enhance the measuring accuracy. CONSTITUTION: At the time of measuring distance to an object 8 from the reciprocessing time T of a distance measuring signal going to and returning from the distance-measured object and the proceeding speed of the distance measuring signal, the distance measuring signal reflected by the object 8 and received is time-differentiated, and the peak value is held. The influence of the rising waveform of an input signal on the clocking of the reciprocating time T is corrected on the basis of this differential peak value Dp. The distance to the object showing difference in received waveform in spite of being the same distance can thereby be measured correctly by correcting a distance measuring time error ΔT caused by the difference of received waveform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device which corrects an error associated with a reception time determination of a distance measuring signal to improve measurement accuracy.

[0002]

2. Description of the Related Art When measuring the distance to an object, that is, the object distance, the time until the light emitted toward the distance measurement target is reflected back by the distance measurement target is measured, and this time is multiplied by the speed of light. Optical rangefinders are often used to determine the round trip distance.

In an optical distance measuring apparatus 1 shown in FIG. 4, a laser diode 2 which is a light source is made to intermittently emit light by a driving circuit 3 at a predetermined cycle, and laser light is irradiated forward through a light transmitting lens 4 and at the same time. A light emitting timing, that is, a light sending time is detected by a monitoring photodiode 5 arranged opposite to the laser diode 2. Monitor photodiode 5
The received light output of is detected by the comparator 6 as a threshold value, and the counter 7 for counting the distance measurement time starts counting with the threshold value determination output of the comparator 6. Laser diode 2
The laser beam emitted from is reflected by the surface of an object 8 such as a vehicle in front of which the distance is to be measured and returns to the receiving lens 9
The light is received by the photodiode 10 through. The received light output of the photodiode 10 is amplified by the receiving amplifier circuit 11 and then sent to the comparator 12 for threshold value determination. When the light receiving output of the photo diode 10, strictly speaking, the output of the receiving amplifier circuit 11 exceeds the threshold value Rf set in the comparator 12 by the threshold value setting circuit 13, the light receiving time of the laser beam is matched with the comparator. A count stop signal is supplied from 12 to the counter 7, whereby a count value N counted by the counter 7 is obtained while the laser beam, which is a distance measurement signal, travels back and forth to the object 8. The counter 7 performs a counting operation based on a clock signal that oscillates at a highly accurate clock cycle τ, and a laser beam reciprocates between the distance measuring device 1 and the object 8 by multiplying the count value N by the clock cycle τ. Round-trip time T (= N
τ) is obtained. In the case of this example, this multiplication is performed by the CPU 14, but the CPU 14 also returns the round trip time N obtained by the multiplication.
In τ, the traveling speed of the laser light which is the distance measurement signal, that is, the speed of light c
The obtained round trip distance Nτc is multiplied by 1/2 to obtain the distance Nτc / 2 to the object 8.

[0004]

DISCLOSURE OF THE INVENTION The above conventional distance measuring device 1
Can always accurately grasp the emission time of the laser beam based on the output of the monitor photodiode 5.
Regarding the light receiving time, because the received signal obtained by amplifying the light receiving output of the photodiode 10 by the receiving amplifier circuit 11 is determined by the threshold value judgment by the comparator 12,
Even for the reflected waves from the object 8 at the same distance, the entire irradiation area of the irradiated laser beam is all included in the object 8 as shown by the solid line in FIG. 4, or is shown by the dotted line in FIG. As described above, the received light waveform differs depending on whether only a part of the irradiation area of the laser beam is applied to the object 8, and the difference in the received light waveform damages the light reception time, and an error cannot be avoided.
For example, as is clear from the light-transmitting waveform and the light-receiving waveform which are compared with FIG. When the irradiation area of the irradiated laser beam is different, the influence of the object shape appears on the received light waveform. That is, the received light waveforms having the three types of peak values shown in the figure are the same object 8 at the same distance.
The received light waveform having a maximum peak value is the received light waveform when all the laser beams are incident on the object 8 and reflected, that is, when the irradiation area of the laser beam is entirely included in the object 8. Yes, it corresponds to the reference waveform. Therefore, when it is assumed that the point where this reference waveform crosses the threshold value set in the comparator 12 provides the reference point To for the distance measurement time error correction, the received light waveform of the intermediate peak value and the received light waveform of the minimum peak value are Between the point crossing the threshold value Rf of the comparator 12 and the above-mentioned reference point To, there are obvious time differences ΔTa and ΔTb based on the difference in the rising waveform, and this difference is an error in the determination of the light reception time and thus in the distance measurement error. It was the cause.

On the other hand, there is disclosed a distance measuring device in which the count value N of the counter 7 is corrected according to the intensity of the received light waveform, that is, the crest value, and the correction content based on the crest value of the received light waveform can be corrected in a timely manner. -266382 "Laser range finder". Since this one holds the relationship between the intensity of the reflected signal and the count value of the counter 7 in a rewritable characteristic map at any time, the characteristic map can be rewritten and accuracy can be compensated when a drift or the like occurs. However, for example, when the photodiode 10 is saturated because the intensity of the reflected signal is excessive,
Since the intensity of the reflected signal cannot be accurately grasped, no effective clue can be obtained for the distance correction, and therefore the ranging accuracy cannot be improved.

Further, a distance measuring device having a structure in which the light receiving time is determined at the apex of a light receiving waveform close to a sawtooth wave is disclosed in Japanese Patent Laid-Open No. 3-73.
No. 880, "Laser Range Finder". This discriminates the apex of the received light waveform, so that the point where the power of the reflected light is maximum is determined as the apex of the received light waveform. However, it is assumed that the received light waveform is a sawtooth wave. However, when the sawtooth wave becomes dull or becomes a trapezoidal wave due to saturation, there is a problem that accurate distance correction is difficult. Also, as a prerequisite technology that triggered the introduction of the maximum power point detection, a method of detecting the peak of the received light waveform at the time when the time derivative of the received light waveform is inverted from positive to negative is described, and the distance to the distance measurement target is described. It has been pointed out that the output of the differentiating circuit is reduced when it becomes long and it is easy to interrupt the practical accuracy. However, it is natural that the method of detecting the output inversion of such a differentiating circuit is weak against the slump of the input level where the differential output itself does not change so much. On the contrary, the output is saturated and the differential value continues to take zero. In such a case, it is difficult to capture the polarity reversal point of the differential value, so that the apex of the received light waveform cannot be accurately detected, and there is a drawback that the distance measurement accuracy decreases.

[0007]

DISCLOSURE OF THE INVENTION The present invention has solved the above-mentioned problems and provides a round-trip time until a distance-measuring signal transmitted to a distance-measuring object is reflected and received by the distance-measuring object. In a distance measuring device for measuring and calculating the distance to the distance measurement object from the round trip time and the traveling speed of the distance measuring signal, a differential circuit for time differentiating the received distance measuring signal, and an output of the differentiating circuit. A peak hold circuit for peak-holding, and a distance measurement time error correction means for correcting the influence of the rising waveform of the received signal on the round trip time measurement based on the output of the peak hold circuit. To do.

Further, according to the present invention, the distance measuring time error correcting means corrects the influence of the rising waveform of the received signal on the basis of an arithmetic expression defined as a function of the output of the peak hold circuit and the round trip time. Or a memory for storing correction data for correcting the influence of the rising waveform of the received signal by using the output of the peak hold circuit and the round trip time as an address, and a distance measuring unit. Another feature is that it includes a CPU that controls the reading of the memory each time.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit configuration diagram showing an embodiment of a distance measuring device of the present invention, and FIG. 2 is a CP shown in FIG.
It is a figure which shows in a graph the arithmetic expression which U uses for calculation of a ranging time error.

In the distance measuring device 21 shown in FIG. 1, a differentiating circuit 22, a peak hold circuit 23 and an AD converter 24 are cascade-connected between the receiving amplifier circuit 11 and the CPU 14, and a CPU 25 is provided.
The rising information of the received light waveform is taken in to correct the distance measurement time error ΔT based on the relationship with the irradiation area of the laser beam. The CPU 25 constitutes a distance measurement time error correction means for correcting the influence of the rising waveform of the received signal on the measurement of the round trip time T, and is a function of the output of the peak hold circuit 23, that is, the differential peak value Dp and the round trip time T. Is defined as ΔT = f (T, D
Based on p), the distance measurement time error ΔT associated with the rising waveform of the received signal is calculated, and this is used as correction data.

The differentiating circuit 22 differentiates the output of the receiving amplifier circuit 11 with respect to time, and grounds the non-inverting input terminal of the operational amplifier 22a whose output terminal and inverting input terminal are connected via the feedback resistor R0. The configuration is such that the output of the reception amplifier circuit 11 is input to the inverting input terminal via the differential capacitor C0. The differentiating circuit 22 has an inversion frequency at 1 / 2πR0C0, and performs an inversion-type time differentiation in which the polarity of the input signal is inverted and differentially output. The peak hold circuit 23 is
The output of an inverting amplifier (amplification factor R2 / R1) configured by connecting an input resistor R1 and a feedback resistor R2 to the inverting input terminal of an operational amplifier 23a whose non-inverting input terminal is grounded is held via a rectifying diode D. The hold capacitor C1 is held by the capacitor C1, and the hold capacitor C1 is discharged by the reset switch S that is closed later by the CPU 25 each time the distance is measured. The hold capacitor C1 holds the differential peak value Dp. The AD converter 24 is
It has a resolution corresponding to the number of bits of the CPU 25,
The differential peak value Dp held by the hold capacitor C1 is converted into digital data and sent to the CPU 25. C
The PU 25 shifts the differential peak value Dp sent from the AD converter 24 from the point where the leading edge of the received light waveform, that is, the rising waveform, crosses the threshold value Rf of the comparator 12 and the reference point To related to the reference waveform. The distance measuring time error ΔT is calculated according to a predetermined arithmetic expression ΔT = f (T, Dp), and the distance measuring value Nτc / 2 is calculated as (Nτ−ΔT) c / 2 using this distance measuring time error ΔT as correction data. to correct.

As shown in FIG. 2, the relationship between the distance measurement time error ΔT and the differential peak value Dp is the round trip time T (T1 <T
2. ． ． <Tn) can be graphed as a parameter, and from the graph of FIG. 2 created based on the measured values, ΔT = f (T, T, f) between the distance measurement time error ΔT, the round trip time T and the differential peak value Dp. Dp) can be extracted. As is clear from the graph of FIG. 2, the relationship defined by this arithmetic expression is such that the larger the differential peak value Dp is, that is, the steeper the rising edge of the received light waveform, the smaller the distance measurement time error ΔT with respect to the reference waveform. Value, and the same differential peak value Dp
Even when the distance is obtained, as the distance from the distance measuring device 21 to the object 8 increases (that is, as the round trip time T increases), the distance measurement time error ΔT increases because the light attenuation due to the round trip is more strongly influenced. Can be kept small.

Here, when the same object 8 located at the same distance from the distance measuring device has a different irradiation area of the laser beam, as shown by the solid line in FIG. In this case, since the received light waveform having the maximum peak value shown in FIG. 5, that is, the reference waveform, is obtained, the distance measurement time error ΔT is zero, and the distance measurement value Nτc / 2 is directly used as the distance data. On the other hand, as shown by the dotted line in FIG. 1, when the object 8 is irradiated with only 1/4 or 1/2 of the irradiation area of the laser beam, only the light receiving waveforms in the middle and below shown in FIG. 5 are obtained. , The distance measurement time error corresponding to the time difference ΔTa, ΔTb between the point where this light receiving waveform intersects the threshold value Rf of the comparator 12 and the reference point To is obtained from the arithmetic expression ΔT = f (T, Dp). . The distance measurement time errors ΔTa and ΔTb thus obtained are used as correction data for the round trip time T, and when the irradiation area of the laser beam is ½, the CPU 25 (Nτ−ΔTa) c /
Distance correction is performed as shown in 2, and the irradiation area of the laser beam is 1
In the case of / 4, distance measurement correction is performed as in (Nτ-ΔTb) c / 2.

As described above, according to the distance measuring device 21,
When measuring the distance by multiplying the round-trip time T of the distance measurement signal that reciprocates the object 8 by the traveling speed c of the distance measurement signal, the distance measurement signal reflected and received by the distance measurement target is time differentiated to obtain the peak value. Hold, and based on this differential peak value Dp, round trip time T
Since the influence of the rising waveform of the received light signal on the measurement of is received is corrected, the distance to the object 8 that shows the difference in the received light waveform due to the different irradiation area of the laser beam at the same distance is the difference in the received light waveform. Distance measurement error due to Δ
It is possible to correct T and perform accurate measurement, and for a distance measurement target that is as close as the received light waveform is saturated, the differential peak value Dp obtained during the process until the received light waveform rises and becomes saturated is used for distance correction. Since the necessary data can be reliably obtained, the distance measurement time error can be corrected regardless of saturation, and even if the peak value of the received light waveform is low and the differential value does not change so much, the differential peak value Dp can be used for distance correction. Since the necessary data can be obtained, it is possible to perform appropriate distance correction.

Further, a CPU which is a distance measuring time error correcting means.
25 is an arithmetic expression ΔT = f (T, D defined as a function of the output Dp of the peak hold circuit 23 and the round trip time T.
Since the correction data for correcting the influence of the rising waveform of the received light signal is calculated based on p), the function f
(T, Dp) is calculated from the empirical value based on the actual measurement,
By preparing the calculation formula from the beginning, it is possible to perform accurate correction in a short time by the formulated correction method and the numerical calculation function of the CPU 25.

In the above embodiment, the differential peak value Dp
The CPU 25 calculates the distance measurement time error ΔT in accordance with the predetermined calculation formula ΔT = f (T, Dp). However, as in the distance measurement device 31 shown in FIG.
The distance measurement time error ΔT corresponding to p is written in the memory 32 such as a ROM by using the time differential value Dp and the round trip time T as addresses, and the memory 32 is read out and controlled by a command from the CPU 14 each time the distance measurement is performed. You can also In this case, no special arithmetic expression is required, and the correction data can be obtained by mechanically reading the distance measurement time error ΔT from the memory 32. Therefore, the calculation load on the CPU 25 can be reduced, and quick and reliable distance correction can be performed. Becomes

Furthermore, in both of the above embodiments, the differentiating circuit 22 and the peak hold circuit 23 are analog circuits, but the functions of these analog circuits can be replaced by the CPU 25 by software processing.

[0018]

As described above, according to the present invention,
When measuring the distance from the round-trip time of the distance measurement signal that travels back and forth to the distance measurement target and the traveling speed of the distance measurement signal, the distance measurement signal reflected and received by the distance measurement target is time-differentiated to hold the peak value, Based on this differential peak value, the influence of the rising waveform of the received signal on the measurement of the round-trip time is corrected, so that the received waveform shows a difference because the irradiation area of the laser beam is different even at the same distance. The distance to the object can be measured accurately by correcting the distance measurement time error due to the difference in the received waveform, and the received waveform rises and saturates even for distance measurement targets that are as close as the received waveform is saturated. Since the data required for distance correction can be reliably obtained from the differential peak value obtained in the process up to
It is possible to correct the distance measurement time error regardless of saturation, and even if the peak value of the received waveform is low and the differential value does not change so much, the data required for distance correction can be obtained from the differential peak value. An excellent effect such as correction is possible.

Further, according to the present invention, the distance measurement time error correction means uses the correction data for correcting the influence of the rising waveform of the received signal based on the arithmetic expression defined as a function of the output of the peak hold circuit and the round trip time. Since it is composed of a CPU for calculation, the peak of the time-differential value of the received waveform, that is, the function of the differential peak value and the round-trip time is calculated from the empirical value based on the actual measurement, and is prepared from the beginning as a calculation formula. The correction method and the numerical operation function of the CPU provide an effect that accurate correction can be performed in a short time.

Further, according to the present invention, the distance measurement time error correction means has a memory in which correction data for correcting the influence of the rising waveform of the received signal is stored, with the output of the peak hold circuit and the round trip time as addresses. Each time the distance is measured, the memory is configured to read and control the CPU. Therefore, the peak of the time-differential value of the received waveform, that is, the differential peak value and the round-trip time is used as an address and is calculated from the empirical value obtained based on the actual measurement. By preparing the memory in which the correction data is written, the correction data can be mechanically read from the specified address without using a special calculation formula, thereby reducing the calculation load on the CPU and speedily. In addition, it is possible to perform a reliable distance correction.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a distance measuring device of the present invention.

FIG. 2 is a graph showing an arithmetic expression used by a CPU shown in FIG. 1 for calculating a distance measurement time error.

FIG. 3 is a circuit configuration diagram showing a modified example of the distance measuring device of the present invention.

FIG. 4 is a circuit configuration diagram showing an example of a conventional distance measuring device.

FIG. 5 is a waveform diagram showing a light transmitting waveform and a light receiving waveform of a distance measurement signal.

[Explanation of symbols]

 2 laser diode 3 drive circuit 4 light transmitting lens 5 photo diode 6 comparator 7 counter 8 object 9 light receiving lens 10 photo diode 11 receiving amplifier circuit 12 comparator 13 threshold value setting circuit 21, 31 range finder 22 differentiating circuit 23 peak hold circuit 24 AD converter 25 Distance measuring time error correcting means (CPU) 32 Distance measuring time error correcting means (memory)

Claims (3)

[Claims] 1. A round trip time until a distance measurement signal transmitted to a distance measurement target is reflected and received by the distance measurement target is measured, and the round trip time and the traveling speed of the distance measurement signal are used to calculate the round trip time. In a distance measuring device that calculates a distance to a distance measurement target, a differentiating circuit that time-differentiates the received distance measuring signal,
A peak hold circuit for peak-holding the output of the differentiating circuit, and a distance-measuring time error correction means for correcting the influence of the rising waveform of the received signal on the measurement of the round-trip time based on the output of the peak-hold circuit. A distance measuring device characterized by: 2. The distance measurement time error correction means calculates correction data for correcting the influence of the rising waveform of the received signal based on an arithmetic expression defined as a function of the output of the peak hold circuit and the round trip time. The distance measuring apparatus according to claim 1, further comprising a CPU that operates. 3. The distance measurement time error correction means uses the output of the peak hold circuit and the round trip time as an address, and a memory that stores correction data for correcting the influence of the rising waveform of the received signal, The distance measuring device according to claim 1, further comprising a CPU that controls reading of the memory each time the distance is increased.