JP2000028719A - Range finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize highly precise ranging which is independent of the reflectivity of an object. SOLUTION: This device is provided with a light projecting means for irradiating a pulse light to the outside part and a light receiving means for receiving the pulse light reflected at the outside part, and operating photoelectric conversion so that inter-object distance data can be outputted by measuring a time from the irradiating point of time of the pulse light until a light receiving point of time. In this case, an electric signal obtained by photoelectric conversion by the light receiving means is periodically sampled for storing instantaneous values at plural point of times, and a point of time (ip) at the point of infection of received light quantity change is calculated based on the plural stored instantaneous values so that inter-object distance data can be generated by using the calculated point of time (ip) as the light receiving point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring apparatus for measuring the round trip propagation time of light to an object reflecting light as distance information.

[0002]

2. Description of the Related Art By measuring the time from transmission of a light pulse to reception of a pulse reflected back from an object, the distance between objects can be obtained by applying a known light propagation speed. This ranging method is applied in various fields such as civil engineering and astronomy. In principle, the closer the pulse width is to zero, the higher the measurement accuracy is. However, in practice, the pulse width is equal to or larger than a value determined by constraints such as light source response and reception sensitivity. In a general distance measuring device, the pulse width is set to a value of about 50 to 100 ns at which a resolution of about several cm can be obtained, and the waveform is a single-peak mountain-like shape.

[0003] Conventionally, a pulse receiving time (light receiving time)
Is the time when the amount of received light increases from zero and reaches a predetermined threshold. Although it is easiest to simply detect a light receiving point by simply comparing one threshold value with the amount of received light, in such a configuration, the level of the reflectance of the object remarkably appears as a measurement error.
This is because when the reflectance is low and the amplitude of the received light amount is small, the timing at which the received light amount reaches the threshold value is later than when the amplitude is large. Therefore, a configuration has been proposed in which a plurality of thresholds are set at predetermined intervals, and a point in time when the amount of received light reaches the highest threshold is detected (Japanese Patent Application Laid-Open No. H5-100026). According to this, a time point within a range close to the apex (peak) of the received waveform can be set as a light receiving time point, and a measurement error can be reduced.

[0004]

However, in the conventional example,
Since the threshold value does not always coincide with the maximum amount of received light, there has been a problem that the deviation of the light receiving point due to the magnitude of the amplitude of the amount of received light is not completely eliminated. In order to reduce the measurement error, the threshold interval must be made small, and a light receiving circuit having a large number of comparators is required. In addition, if the vicinity of the top of the received waveform is flat or bimodal, it is difficult to secure desired accuracy.

An object of the present invention is to realize a highly accurate distance measurement that does not depend on the reflectance of an object.

[0006]

According to a first aspect of the present invention, there is provided an apparatus comprising: a light projecting means for emitting pulse light to the outside; and a light receiving means for receiving the pulse light reflected outside and performing photoelectric conversion. A distance measuring device that measures the time from the point of emission of the pulsed light to the point of light reception and outputs data on the distance between objects, and periodically samples an electric signal obtained by photoelectric conversion by the light receiving means. The instantaneous values at a plurality of time points are stored, and the time point of the inflection point of the change in the amount of received light is calculated based on the plurality of stored instantaneous values. Things.

The inter-object distance data generally means numerical information having a value corresponding to the inter-object distance, and includes data indicating the round-trip propagation time of the pulsed light or the one-way propagation time obtained from the round-trip propagation time. Output means sending information to another device, displaying on a display or a numeric display, and providing information including audio notification.

In the distance measuring apparatus according to the present invention, the electric signal is an analog signal obtained by integrating a photoelectric conversion signal of the received pulse light. 4. The distance measuring apparatus according to claim 3, wherein the light projecting means emits pulse light to the light receiving means simultaneously with emission of the pulse light to the outside, and the light receiving means emits the pulse light from the light projecting means and from the outside. Receiving the pulsed light and performing photoelectric conversion, periodically sampling the electrical signal obtained by the photoelectric conversion by the light receiving means, storing instantaneous values at a plurality of points in time, based on the stored plurality of instantaneous values. The inflection point of the change in the amount of received light is calculated using the calculated first time as the emission time and the second time as the light reception time to generate the inter-object distance data.

In the distance measuring apparatus according to a fourth aspect of the present invention, the light receiving means includes a first photoelectric conversion means for receiving the pulse light from the light projecting means, and a second photoelectric conversion means for receiving the pulse light from the outside. Photoelectric conversion means, wherein the first time point is calculated based on the electric signal obtained by the first photoelectric conversion means, and the first time is calculated based on the electric signal obtained by the second photoelectric conversion means. A second time point is calculated.

A distance measuring apparatus according to a fifth aspect of the present invention calculates a time point of the inflection point by a center of gravity calculation based on a plurality of the instantaneous values. An apparatus according to a sixth aspect of the present invention is a three-dimensional input device that emits the pulsed light a plurality of times while changing the direction or position of the optical axis thereof, and generates the inter-object distance data each time.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is an overall configuration diagram of a distance measuring apparatus 1 according to a first embodiment.

The distance measuring device 1 includes a transmitting unit 1 as a light projecting unit.
0, a reception unit 20 as a light receiving unit, a reception processing circuit 30,
It comprises a controller 40 and a clock generator 50. The transmitting unit 10 includes a light emitting element (semiconductor laser) 11, a light emitting driver 12, a pulse circuit 13 for defining a light emitting time, a light projecting lens 14, and a light amount distributor 15, and responds to an instruction from the controller 40. Then 1
The pulse light P having a pulse width of about 00 ns is emitted to the outside and the receiving unit 20. The amount of light emitted to the receiving unit 20 may be very small.
The pulse light P is distributed at a light amount ratio of about 1000: 1.
The receiving unit 20 includes a light receiving element (for example, a photodiode) 2
1, a light receiving driver 22, an amplifier 23 for converting a photocurrent into a voltage, a light receiving lens 24, and a mirror 25 for guiding the pulse light from the transmitting unit 10 to the light receiving element 21; (Photoelectric conversion signal) S20 is output to the reception processing circuit 30. The reception processing circuit 30
20, data D30 having a value corresponding to the distance L to the external object Q is generated. Data D30 is the light receiving unit 2
At 0, a time centroid ip0 of the light quantity distribution of the pulse light P directly incident from the transmission unit 10 and a time centroid ip1 of the light quantity distribution of the pulse light P reflected and incident on the object Q are shown. The time centroids ip0 and ip1 correspond to peak times at which the amount of received light becomes maximum (details will be described later). The time from the time centroid ip0 to the time centroid ip1 is determined as the light propagation time (the time required for the round trip of the distance L) Ta, and the distance L is calculated by applying a known light propagation velocity (3 × 10 ⁸ m / s). The calculation performed is performed by the controller 40. The calculated distance L is output as measurement data DL to another device (display, computer, etc.). Note that a clock that defines a sampling cycle is input from the clock generator 50 to the reception processing circuit 30 via the controller 40.

In the distance measuring apparatus 1, as described above, the transmission point in time of the light propagation time Ta is set to the time centroid ip0, and the reception point is set to the time centroid ip1. Measurement becomes possible. This is because the amount of received light is indeterminate depending on the reflectance, but the position on the time axis of the peak, which is the inflection point of the pulse waveform, does not change. Further, the transmission time can be set based on the output time of the light emission control signal. However, as in this example, the actual light emission amount is monitored to detect the time centroid ip0, so that the characteristic change of the light emitting element can be performed. And the effects of delay of the control signal and the like can be eliminated.

FIG. 2 is a diagram showing the concept of the time center of gravity. The time barycenter ip is the barycenter on the time axis in the distribution of a predetermined number n (n = 30 in the figure) of received light data obtained by periodically sampling the amount of received light of pulsed light. Correspond to a certain peak time. The light receiving data at each sampling time is assigned a sampling number of 1 to n. The i-th light reception data is represented by Xi. i is an integer of 1 to n and corresponds to an address of a memory for storing the received light data. The time centroid ip for the 1st to nth light reception data X1 to Xn can be obtained by dividing the sum of i · XiΣi · Xi by the sum of XiΣXi for n light reception data. That is,

[0015]

(Equation 1)

## EQU1 ## The reception processing circuit 30 performs the operation of this equation. FIG. 3 is a diagram showing the principle of calculating the light propagation time, and FIG.
3 is a block diagram of the reception processing circuit 30. FIG.

As described above, the light receiving element 21 has the transmitting section 10
Since the pulse light P is sequentially incident from the outside, the received signal S20 has two peaks during the measurement as shown in FIG. Time T from an appropriate time before and after the start of emission of pulsed light P to the time barycenter ip0 of the transmission (first) peak
10 and the time T11 to the time barycenter ip1 of the reception (second) peak, the light propagation time Ta (= T11
−T10) can be calculated.

The reception processing circuit 30 includes an integrator 31, an A / D
Converter 32, delay circuit 33, subtractor 33, memory 35,
And a center-of-gravity calculation unit 36. The received signal S20 from the receiving unit 20 is input to the integrator 31. Here, assuming that the value of the received signal S20 is Vs, the output signal S3 of the integrator 31
The value Vo of 1 is represented by the following equation.

[0019]

(Equation 2)

The A / D converter 32 periodically samples and holds the output signal S31 of the integrator 31 in synchronization with the clock CLK and digitizes the output signal S31. The clock cycle is sufficiently shorter than the pulse width of the pulse light P, specifically, 10n
s. In the figure, the output signal S31 is sampled at time points t1 to t7. The sampling data D32 output by the A / D converter 32 corresponds to the accumulation of the amount of received light from the start of integration to the time of sampling. For example, the value of the sampling data D32 (t4) at the time point t4 is obtained by digitizing Vo (t4) represented by the following equation.

[0021]

(Equation 3)

[0022] The subtracter 34, and the latest sampling data D32 (t _i) and via the delay circuit 33 by one clock cycle delayed by sampling data D32 (t _i-1) is input in synchronization with the clock CLK . By the difference operation in the subtractor 34, the light receiving data D34 corresponding to the integration result for one clock cycle of the reception signal S20 is obtained. The light reception data D34 is represented by the following equation.

D34 = D32 (t _i ) −D32 (t _i−1 ) For example, the light receiving data D34 (t4) at the time t4 is the time t
It corresponds to the integral value Vo ′ (t4) from 3 to time t4.

[0024]

(Equation 4)

The light receiving data D34 is written in the memory 35 in synchronization with the clock CLK. At this time, the address is specified by the address signal Add from the controller 40. The address is incremented in the clock cycle. That is, one address is assigned to each sampling time point of the received signal S20, and time-series light receiving data D34 corresponding to each sampling time point is sequentially stored. The memory 35 has a data capacity necessary for storing data for the light propagation time at the longest measurable distance.

When a predetermined time corresponding to the longest measurable distance has elapsed from the start of the measurement, the reading of the received light data D34 from the memory 35 is started. The address range to be read is set individually for the calculation of the transmission time point and the calculation of the reception time point, and addresses are specified n by n. The read light receiving data D34 is sent to the center-of-gravity calculating unit 36. The center-of-gravity calculating unit 36 outputs data D30 indicating the time centers of gravity ip0 and ip1 corresponding to the peak times of transmission and reception to the controller 40.

FIG. 5 is a block diagram of the center-of-gravity calculating unit 36. In the present embodiment, the light receiving data D34 from the memory 35 is not used for the center of gravity calculation as it is, but a value obtained by subtracting the steady light data from each light receiving data D34 (when the value becomes negative, zero) is used. The stationary light data is data calculated in advance based on the received light data when the pulse light P is not incident. That is, an offset is given to the amount of received light.

The center-of-gravity calculator 36 includes a subtractor 361, a stationary light data memory 362, a first adder 363, and a second adder 3.
64, and a divider 365. These are configured by hardware circuits, but all or some of them may be configured by software.

The steady light data memory 362 stores the steady light data D362. The subtractor 361 calculates the received light data D34
Is subtracted from the constant light data D362. Here, the data output from the subtractor 361 is referred to as light reception data Xi again. The first adding unit 363 adds i · Xi for i = 1 to n and outputs the total value. The second adding unit 364 adds Xi for i = 1 to n,
Output the total value. The divider 365 includes the first adder 3
The output value of 63 is divided by the output value of the second adder 364 to calculate the time centroids ip0 and ip1.

According to the reception processing circuit 30 having the above configuration,
Since the integrator 31 is provided, the received light data Xi used for the center-of-gravity calculation is obtained by interpolating a change in the amount of received light within one clock cycle. Therefore, more waveform information of the pulsed light P is obtained than in the case where the received signal S20 is sampled as it is, and the accuracy of the center of gravity calculation is improved.

FIG. 6 is a block diagram showing a modification of the configuration of the transmitting section. The transmitting unit 10c includes a light emitting element (semiconductor laser) 11c, a light emitting driver 12c, a pulse circuit 13c for defining a light emitting time, a light projecting lens 14c, an optical path switching mechanism 16, and a switching circuit 17. The pulse circuit 13c and the switching circuit 17 are connected to the controller 50c.
Is controlled by

The transmitting section 10c selectively emits the pulse light Pc to either the receiving section or the outside. As a result, the pulse light Pc enters the receiving unit. For example, by emitting the light only to the receiving unit at the time of inspection or adjustment, it is possible to observe a pulse waveform that is not affected by external light. According to this modification, it is possible to measure the time from when the irradiation timing signal is irradiated to when the amount of emitted light reaches a peak. If this time is stored, the actual light emission timing can be obtained from the light emission timing signal and this time. Therefore, it is not necessary to guide the irradiation light to the light receiving unit when measuring the distance, and the entire amount of light can be irradiated to the outside.

FIG. 7 is a block diagram showing a modification of the configuration of the receiving section. The receiving unit 20d includes light receiving elements 21d and 21
d ', light-receiving drivers 22d, 22d', amplifiers 23d, 23d 'for converting a photocurrent into a voltage, a light-receiving lens 24d, and a pulse light Pd from a transmission unit.
A mirror 25d for guiding the light to d 'is provided, and the photoelectric conversion is individually performed on the pulse light Pd incident from the outside and the pulse light Pd incident directly from the transmission unit. Each amplifier 23d, 23
The reception signals S20d and S20d 'output from d' are individually binarized by comparators 33d and 33d 'in the reception processing circuit 30d.

According to such a two-system configuration, even when the distance to be measured is relatively short and the transmission pulse waveform and the reception pulse waveform overlap, the time centroids ip0, i
p1 can be calculated correctly. However, unlike the configuration of one system in which one light receiving element receives transmission / reception pulse light, there is a possibility that a measurement error may occur due to a slight shift in circuit characteristics between the systems. [Second Embodiment] In the above-described embodiment, both the transmission time and the reception time are specified by the center of gravity calculation based on the photoelectric conversion signal of the pulsed light. However, for the transmission, it is not always necessary to perform the photoelectric conversion, and the peak time at which the light amount becomes maximum may be specified based on the timing of the light emission control, and may be set as the transmission time. This is suitable for simplifying the device configuration. If the emission timing is stable,
A sufficiently high measurement accuracy can be obtained.

FIG. 8 is an overall configuration diagram of the distance measuring apparatus 2 of the second embodiment. The distance measuring device 2 includes a transmitting unit 6 as a light projecting unit.
0, a reception unit 70 as a light receiving unit, a reception processing circuit 80,
It comprises a controller 90 and a clock generator 100. The transmitting unit 60 includes a light emitting element (semiconductor laser) 61, a light emitting driver 62, a pulse circuit 63 for defining a light emitting time, and a light emitting lens 64, and responds to an instruction from the controller 40 for about 100 ns. A pulse light PP having a pulse width is emitted to the outside. The pulse waveform has a bilaterally symmetric mountain shape. The receiving unit 70 includes a light receiving element (for example, a photodiode) 71, a light receiving driver 72,
It includes an amplifier 73 for converting a photocurrent into a voltage, and a lens 74 for receiving light, and outputs a reception signal (photoelectric conversion signal) S70 corresponding to the amount of received light to a reception processing circuit 80. The reception processing circuit 80 generates data D80 of a value corresponding to the distance L to the external object Q based on the reception signal S70. The data D80 is the pulse light P reflected and incident on the external object Q.
Is the time center of gravity ip1 of the amount of received light. Calculation for calculating the light propagation time Ta from the transmission time point tp0 based on the light emission control timing to the time center of gravity ip1, and further calculating the distance L from the light propagation time Ta and a known light propagation speed (3 × 10 ⁸ m / s). Is assigned to the controller 90. A clock for clocking is input to the reception processing circuit 80 from the clock generator 100 via the controller 90.

FIG. 9 is a block diagram of the reception processing circuit 80 of the second embodiment, and FIG. 10 is a time chart of signals related to the reception processing. The reception processing circuit 80 includes the A / D converter 8
2, a memory 85, and a center of gravity calculation unit 86. The reception processing circuit 80 receives the clock CL from the controller 90.
K, an address signal Add, and a memory control signal R / W. The clock cycle is sufficiently shorter than the pulse width of the pulse light P. The address signal Add is an output of an address counter for counting the clock CLK,
Input in synchronization with LK. Therefore, the address specified for the memory 85 is incremented in synchronization with the clock CLK. The address counter is reset in synchronization with turning on of the transmission timing signal generated in the controller 90 and switching from the write mode level to the read mode level in the memory control signal R / W.

At the start of the measurement, the memory 85 is set to the write mode by the memory control signal R / W in synchronization with the transmission timing signal. After that, the reception signal S
70 is input. The A / D converter 82 receives the clock CL
The reception signal S70 is periodically sampled and held and digitized in synchronization with K. The received light data D82 obtained by the A / D converter 82 is input to the memory 85 in synchronization with the clock CLK, and is sequentially written to the designated addresses. That is, one address is assigned to each sampling time point of the received signal S70, and time-series light receiving data D82 corresponding to each sampling time point is sequentially stored. The memory 85 has a capacity necessary for storing data for the light propagation time corresponding to the longest measurable distance.

When a predetermined time corresponding to the longest measurable distance has elapsed from the start of the measurement, the memory control signal R / W switches from the write mode level to the read mode level,
The light receiving data D82 is sequentially read from the head address of the memory 85. The read light receiving data D82 is sent to the center-of-gravity calculating unit 86. The center-of-gravity calculating unit 86 calculates the time center-of-gravity ip1 corresponding to the peak time of reception, and outputs data D80 indicating the same to the controller 40. Note that the configuration of the center-of-gravity calculation unit 86 is the same as that of the example of FIG.

According to the distance measuring apparatus 1 of the above embodiment, the transmission time is calculated by monitoring the pulse light, so that high-precision measurement with little influence of signal delay in the circuit can be performed. Further, if the distance measuring devices 1 and 2 change the emission direction of the pulse light so as to scan the object Q and measure the distance between the objects in each emission direction, it can be used as a three-dimensional input device. Can be.

In the above embodiment, instead of calculating the peak time of transmission and reception by calculating the center of gravity, the memory 3
The maximum value of the light receiving data Xi and D82 stored in the storage units 5 and 85 may be detected, and the address storing the maximum value may be set as the peak time. Further, the peak time may be calculated by an interpolation operation based on data of addresses before and after the address storing the maximum value.

[0041]

According to the first to sixth aspects of the present invention,
Thus, highly accurate distance measurement independent of the reflectance of the object can be realized.

According to the second aspect of the invention, the measurement accuracy can be further improved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a distance measuring apparatus according to a first embodiment.

FIG. 2 is a diagram illustrating a concept of a time center of gravity.

FIG. 3 is a principle diagram of calculation of a light propagation time.

FIG. 4 is a block diagram of a reception processing circuit.

FIG. 5 is a block diagram of a center-of-gravity calculation unit 36;

FIG. 6 is a block diagram showing a modification of the configuration of the transmitting unit.

FIG. 7 is a block diagram illustrating a modification of the configuration of the receiving unit.

FIG. 8 is an overall configuration diagram of a distance measuring device 2 according to a second embodiment.

FIG. 9 is a block diagram of a reception processing circuit 80 according to the second embodiment.

FIG. 10 is a time chart of signals related to a reception process.

[Explanation of symbols]

 1, 2 distance measuring device P, Pc, Pd pulsed light 10, 60 transmitter (light emitting means) S20, S70 photoelectric conversion signal (electric signal) 20, 70 receiver (light receiving means) ip0 time center of gravity (injection time) ip1 Time center of gravity (light receiving time) Ta Light propagation time (time) DL Distance data (distance data between objects)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F112 AD01 BA06 BA07 CA12 DA04 DA26 DA28 EA03 EA11 FA01 FA03 FA05 FA07 FA14 FA21 FA29 FA41 FA43 FA50 5J084 AA05 AB06 AB08 AB17 AD01 BA04 BA11 BA14 BA36 BA52 BB02 BB35 CA03 CA10 CA12 CA23 CA44 CA49 CA52 CA53 CA57 CA64 CA70 CA76 EA01 EA02 EA04

Claims (6)

[Claims] A light projecting means for emitting a pulse light to the outside, and a light receiving means for receiving the pulse light reflected outside and performing photoelectric conversion, wherein the light is emitted from a point in time when the pulse light is emitted to a point in time when the pulse light is received. A distance measuring apparatus for measuring time and outputting inter-object distance data, wherein an electrical signal obtained by photoelectric conversion by the light receiving means is periodically sampled and instantaneous values at a plurality of time points are stored and stored. A distance measuring apparatus which calculates a time point of an inflection point of a change in received light amount based on the plurality of instantaneous values, and generates the inter-object distance data using the calculated time point as the light receiving time point. 2. The distance measuring apparatus according to claim 1, wherein the electric signal is an analog signal obtained by integrating a photoelectric conversion signal of the received pulse light. 3. A light projecting means for emitting a pulse light to the outside, and a light receiving means for receiving the pulse light reflected outside to perform photoelectric conversion, wherein the light is emitted from a point in time when the pulse light is emitted to a point in time when the pulse light is received. A distance measuring apparatus that outputs time-to-object distance data by measuring time, wherein the light projecting means emits pulse light to the light receiving means simultaneously with emission of pulse light to the outside; The pulse light from the light projecting means and the pulse light from the outside are received and subjected to photoelectric conversion, and the electric signal obtained by the photoelectric conversion by the light receiving means is periodically sampled to store instantaneous values at a plurality of time points. Calculating the time point of the inflection point of the change in the amount of received light based on the plurality of stored instantaneous values, setting the calculated first time point as the emission time point and setting the second time point as the light receiving time point between the objectives. Characteristic of generating distance data Distance measuring device to be. 4. The light receiving means includes: first photoelectric conversion means for receiving pulse light from the light projecting means; and second photoelectric conversion means for receiving pulse light from the outside, The first time point is calculated based on the electric signal obtained by the photoelectric conversion means, and the second time point is calculated based on the electric signal obtained by the second photoelectric conversion means. 3. The distance measuring device according to 3. 5. The distance measuring apparatus according to claim 1, wherein a time point of said inflection point is calculated by a center-of-gravity calculation based on a plurality of said instantaneous values. 6. A distance measuring device according to claim 1, wherein said pulse light is emitted a plurality of times by changing the direction or position of an optical axis thereof, and said pulse light is emitted between said objects each time. A three-dimensional input device for generating distance data.