WO2005026773A1

WO2005026773A1 - Optical distance measurement device and vehicle optical radar device

Info

Publication number: WO2005026773A1
Application number: PCT/JP2004/012568
Authority: WO
Inventors: Tetsuo Nishidai
Original assignee: Omron Corporation
Priority date: 2003-09-11
Filing date: 2004-08-31
Publication date: 2005-03-24

Abstract

Upon detection of pulse present intervals (t1 to t2) where a reception pulse (22) exists from a reception signal (21), inclination of a delay time control signal (23) in the intervals is decreased. When a sampling pulse generated according to the delay time control signal (23) is used, the number of samplings in the pulse present intervals is increased. Accordingly, it is possible to obtain a time axis-expanded wave in which the reception pulse (25) of the reception signal (24) has a waveform greatly enlarged and improve the resolution of the periphery of the reception pulse (25). On the other hand, inclination of the delay time control signal (23) out of the pulse present intervals is increased. Thus, it is possible to improve the distance measurement accuracy without lowering the response.

Description

Specification

Optical ranging device, optical ranging method, and in-vehicle optical radar device

Technical field

The present invention relates to a technique for measuring a distance to an object using a light pulse.

Background art

[0002] An optical distance measuring device that irradiates an object with a light pulse and receives the light pulse reflected by the object to measure the distance to the object is known. There are two major methods for measuring the distance of this optical distance measuring device: a triangular distance measuring method using a position detection device (PSD) and a pulse flight time method that measures the round trip time of an optical pulse. (See, for example, Non-Patent Document 1).

[0003] The triangulation method, as shown in Fig. 12, measures the distance d to an object 103 by using the ratio of two sides of two similar right triangles 100 and 101 to each other. The feature is that relatively high-accuracy distance measurement can be realized with a simple configuration.

[0004] However, in this method, the change amount X measured by the PSD 104 becomes large at a short distance and becomes small at a long distance. Therefore, in order to obtain high resolution in long-distance measurement, it is necessary to increase the distance L between transmission and reception and the focal length f, and there is a problem that the casing becomes large. Similarly, in order to guarantee a certain resolution, the measurement range becomes narrower, so that multiple types of products are required according to the distance range, and the cost of designing and manufacturing increases.

[0005] On the other hand, in the pulse time-of-flight method, the distance is measured by multiplying the time required for a light pulse to reciprocate with an object by the speed of light. In this way, the pulse time-of-flight method has a feature that it is suitable for miniaturization of the housing because it is not necessary to secure a large distance between transmission and reception and a focal length in principle. In addition, since a single optical system can measure short distance force and long distance with the same resolution, a single model can cover a wide range of distances.

[0006] In the pulse time-of-flight method, since the pulse reciprocation time is extremely short, on the order of nanoseconds, and direct measurement is difficult, a time axis expansion process by equivalent time sampling is usually used. The time axis expansion means that a sampling noise that gradually delays with respect to the irradiation light pulse is generated, and the light reception signal is sampled at the timing of this pulse to form a waveform on the time axis. This is to increase the geometric ratio. As a result, highly accurate distance calculation can be performed even when a relatively low-speed timing device such as a microcontroller is used.

[0007] With respect to force radio sensors in different technical fields, a technique has been proposed to improve the SZN ratio by sampling the peak position of the reflected wave a plurality of times and accumulatively adding the peak position in the time axis expansion process ( Patent Document 1).

Non-patent document 1: Seiji Iguchi, Kosuke Sato, "Three-dimensional image measurement", Shokodo, 1990 Patent document 1: Japanese Patent Application Laid-Open No. 2001-264419

Disclosure of the invention

Problems to be solved by the invention

[0008] In a conventional optical distance measuring device, in order to obtain good measurement accuracy by increasing the distance resolution, the delay time change of the sampling pulse is reduced (the number of times of sampling is increased), and the time axis expansion rate is increased. Generally, an increasing approach is taken. However, when the time axis expansion rate is increased, the measurement cycle is extended and the response performance is degraded. That is, in the pulse-time-of-flight optical distance measuring device, there is a trade-off relationship between "response" and "distance measurement accuracy", and it has been difficult to achieve both.

[0009] Therefore, the present inventor has diverted the technique of Patent Document 1 to an optical distance measuring device, and could not suppress a decrease in responsiveness by sampling only the peak position of the received light pulse a plurality of times. Study was carried out. However, in the case of a force photometric device, it was found that this method could increase the distance measurement error. This is because a radio sensor uses a pulse with a steep pulse width on the order of picoseconds to detect the peak position with high accuracy, whereas the pulse width of an optical pulse is on the order of nanoseconds. It is considered that the accuracy of peak position detection is about 1000 times lower than that of simple calculation.

[0010] Furthermore, since the light pulse has a shorter wavelength than the radio wave, the light pulse is susceptible to disturbances such as the inclination of the object to be reflected, the unevenness of the surface of the object to be reflected, and the unevenness of the propagation space due to the fluctuation of the atmosphere. Therefore, a waveform in which a plurality of optical pulses that have undergone different time delays via different optical paths are synthesized is observed, and the received light pulse waveform is distorted. Fig. 13 shows an example of the received light pulse waveform. The broken line shows the waveform obtained in an ideal measurement environment, and the solid line shows the waveform when disturbance is intentionally applied. In the latter, pulse swelling and peak bimodality were confirmed (Particularly, the section after the peak position tends to expand). If such a received pulse waveform distortion occurs, it becomes difficult to specify the peak position, and the distance measurement accuracy is deteriorated.

Regarding the problem of waveform distortion, a countermeasure to collectively store the received pulse waveform in a memory using an A / D converter and a microcomputer and perform waveform shaping by digital signal processing is also conceivable. In this case, another problem such as an increase in the complexity of the circuit and an increase in the size of the housing and an increase in cost arises, and the size advantage of the pulse-time-of-flight optical distance measuring device is impaired.

[0012] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technology capable of achieving both responsiveness and distance measurement accuracy with a simple and compact configuration. To do so.

Means for solving the problem

[0013] In order to achieve the above object, the optical distance measuring apparatus of the present invention variably controls the increase rate of the delay time of the sampling pulse according to the section, so that the time axis of the section required for distance measurement is controlled. Increase the magnification only and / or adjust the time axis magnification of the received light pulse to correct the received light pulse waveform distortion. Then, the pulse flight time is obtained from the adjusted time-axis extension wave, and the distance to the object is calculated. As a result, the distance measurement accuracy can be improved without lowering the responsiveness.

More specifically, the optical distance measuring device of the present invention includes at least a light emitting unit, a light receiving unit, a sampling unit, a pulse detecting unit, and a delay time varying unit. The light pulse reflected by the object is received by the sampling means, and the sampling means expands the time axis of the received light signal based on the sampling pulse having a cycle such that the delay time for the irradiation light pulse gradually increases, and the time axis is expanded by the pulse detection means The pulse existence section where the received pulse is present is detected from the wave, the delay time variable means adjusts the increase rate of the delay time of the sampling pulse, and the object is extracted from the time axis extension wave that is extended on the time axis based on the adjusted sampling pulse. Calculate the distance to.

[0015] Here, it is preferable that the delay time varying means makes the rate of increase of the delay time of the sampling pulse in the noise existence section smaller than the rate of increase of the delay time outside the section. If the time axis is extended by the sampling pulse adjusted in this way, the sample in the noise existence section can be obtained. Since the number of times of reception increases and the reception noise waveform is greatly expanded, it becomes easy to analyze the waveform and specify the peak position with high accuracy, and the distance measurement accuracy can be improved. In addition, by increasing the enlargement ratio only for the part (pulse existence section) necessary for distance measurement, it is possible to suppress a decrease in responsiveness. The method of specifying the peak position includes a method of detecting by simple comparison of the sampled values and a method of detecting a value at which the differential value becomes 0 from the waveform.

[0016] At this time, the delay time variable means increases the rate of increase of the delay time outside the section according to the degree of decrease in the rate of increase of the delay time of the sampling pulse in the pulse existence section. As a result, the number of times of sampling of a portion unnecessary for distance measurement (outside the section where the pulse exists) is reduced, and the response is improved.

[0017] Further, the delay time variable means may adjust the rate of increase of the delay time in each of the pulse existence section and the delay time outside the section so that the number of samplings for generating one time base extension wave is constant. Is also preferred. As a result, a constant responsiveness is always guaranteed regardless of how the increase rate of the delay time changes.

[0018] The delay time varying means S adjusts the rate of increase of the delay time of the sampling noise in the pulse existence section so that the time-axis elongation wave in the pulse existence section has a substantially symmetrical waveform around the peak position. It is also preferable to do so. Thereby, the distortion of the received light pulse waveform due to the influence of the disturbance is corrected, so that the waveform analysis and the peak position can be easily specified with high accuracy, and the distance measurement accuracy can be improved. Moreover, since the distortion of the received light pulse waveform is corrected only by adjusting the delay time of the sampling noise, the configuration is simple, and the circuit becomes complicated, the casing becomes large, and the cost does not increase.

[0019] As a detailed configuration for distortion correction, an integrating means for integrating the time-axis expanded wave is provided, and a pulse change rate minimum point at which the pulse change rate becomes minimum is detected from the time-axis expanded wave by the pulse detecting means. Then, the integration means calculates the integral value of the first section in the first section from the start point of the pulse existence section to the minimum point of the pulse change rate, and the second section in the second section from the minimum point of the pulse change rate to the end point of the pulse existence section. Calculate the integral value of the two sections, and use the delay time variable means to increase the delay time of at least one of the first and second sections so that the integral value of the first section and the integral value of the second section are substantially equal. Can be preferably adopted. In such a configuration, for example, a section integration circuit is used as the integration means, and a pulse detection means is used as the pulse detection means. It can be realized with a simple configuration by simply adding a differentiating circuit for detecting the minimum change rate point and a zero-crossing detecting circuit.

[0020] The pulse detection means may set a pulse existence section from the time when the crest value of the time-axis extended wave exceeds a predetermined threshold (start point) to the time when the peak value falls below the threshold (end point). . With such a configuration, for example, a simple circuit that only outputs a comparison result between the peak value voltage and the threshold voltage can be realized, and the configuration can be simplified. Further, since the pulse existence section is determined irrespective of the peak position, the pulse existence section can be correctly detected even when the received light pulse waveform is distorted. In addition, the midpoint of the pulse existence section can be regarded as the peak position, and when the distortion of the noise waveform is known in advance, the distance is set to a predetermined position in the section in consideration of the distortion. Can measure force s.

[0021] Alternatively, the pulse detection means may detect a peak position from the time-axis expanded wave, and set a predetermined time before and after the peak position as a pulse existence section. A powerful configuration can be realized by a simple circuit that only detects the minimum point of the panel change rate, for example, and the configuration is simplified. Note that the peak position detected here is not used directly for distance measurement, but is used only for delay time adjustment processing, which is the pre-processing of distance measurement. If the true peak position is included in the existing section, it is good.)

[0022] The present invention can be considered as an optical distance measuring device having at least a part of the above means. Further, the present invention can be considered as an optical distance measuring method including at least a part of the above processing. The above means and processes can be combined with each other as much as possible to constitute the present invention.

The invention's effect

According to the present invention, it is possible to achieve both responsiveness and distance measurement accuracy with a simple and small configuration.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. (First Embodiment)

First, a basic configuration of an optical distance measuring apparatus according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing the configuration of the optical distance measuring device, and FIG. 2 is a waveform diagram for explaining the operation of the optical distance measuring device.

[0026] The optical ranging device 1 irradiates a light pulse to the detection target object 2, receives the light pulse reflected by the detection target object 2, and measures the flight time (round trip time) of the light pulse. Then, the distance to the detection target object 2 is calculated. In the present embodiment, it is assumed that the distance between the device and the object is within a few meters.

[0027] The optical ranging device 1 includes an oscillator 3, a pulse generator 4, a light-emitting element 5, a light-receiving element 6, a waveform amplifier.

7. It has a sampling threshold unit 8, a sampling pulse generator 9, an A / D converter 10, a threshold detector 11, a microcontroller 12, a DZA converter 13, and a voltage-delay time converter 14.

[0028] The oscillator 3 is a circuit that generates the transmission clock signal (a). The transmission clock signal (a) is input to the pulse generator 4 after being inverted, and is used as a reference clock signal for generating irradiation light pulses. The transmission clock signal (a) is also input to the voltage-to-delay time converter 14, and is also used as a reference clock signal for generating a sampling pulse. The oscillator 3 can be composed of, for example, a CR circuit and an inverter. In this case, the CR time constant should be set so that the clock frequency (= 1 / (2.2CR)) is less than or equal to the round trip time of the optical pulse (maximum detection distance X2 / light speed).

[0029] The pulse generator 4 is a circuit that converts the inverted clock signal (b) into a pulse signal (c) having a minimum time width. The noise signal (c) is input to the light emitting element 5. The noise generator 4 can be composed of, for example, a differentiating circuit. The pulse width of the pulse signal (c) is determined by the time constant set in this circuit.

[0030] The light emitting element 5 is an element that converts the electric energy of the pulse signal (c) into light energy and emits the light pulse (d) into space. That is, the light emitting element 5 is a light emitting unit that irradiates the detection target object 2 with the light pulse (d) at a fixed time interval synchronized with the transmission clock (a). As the light emitting element 5, a device having a short pulse response such as an LED or a laser diode can be used. The pulse width of the optical pulse (d) is on the order of nanoseconds. This is due to the photoelectric conversion characteristics of the light emitting element 5.

[0031] The light receiving element 6 is an element that converts light energy into electric energy, and can be configured by a device such as a photodiode. In the present embodiment, a reverse voltage is applied to the photodiode to reduce the capacitance, thereby responding to high-speed pulse light reception. The change in current of the photodiode is converted and amplified into a voltage waveform by a waveform amplifier 7 composed of a ΔP amplifier, and output to the sample-and-hold device 8 as a light receiving signal (i). That is, the light receiving element 6 and the waveform amplifier 7 are light receiving means for receiving the light pulse reflected by the detection target object 2.

The sample hold unit 8 is a sampling unit that performs sampling (sampling) / hold (hold) of the light receiving signal (i) based on the sampling pulse (h) input from the sampling pulse generator 9. In the sampling pulse (h), the sampling period S and the hold period H are repeated in a cycle such that the delay time with respect to the irradiation light pulse (d) gradually increases. Therefore, the light receiving signal (i) can be extended in time axis by repeating the sampling-holding process in the sampler holder 8. The time axis expansion wave (j) is converted into a digital signal by the A / D converter 10 and then input to the microcontroller 12. Further, the time-base expanded wave (j) is also input to the value detector 11.

[0033] The threshold detector 11 is a pulse detection unit that detects a pulse existence section in which a light receiving pulse exists from the time-axis extended wave (j). The threshold detector 11 includes a comparator, a voltage setting unit, and a level conversion unit, and outputs an H level when the crest value voltage of the time-base expanded wave (j) exceeds a predetermined threshold voltage, and outputs a signal. This is a simple configuration that outputs an L level when the voltage falls below the threshold voltage. The output signal of the threshold detector 11 is input to the microcontroller 12.

[0034] The microcontroller 12 is an IC that performs digital signal processing according to a program.

The microcontroller 12 mainly executes a distance measurement process for calculating a distance to the detection target object 2 based on the time-axis stretched wave (j) and a delay time control process for generating a delay time control pattern. . The details of each process will be described later.

The delay time control pattern generated by the microcontroller 12 is converted by the D / A converter 13 into a delay time control signal (e) that is a voltage signal. Delay time control signal (e) Is a signal that repeats monotonically increasing in synchronization with one measurement cycle, and its slope is larger than 0. FIG. 2 shows a ramp signal as an example of the delay time control signal (e).

The voltage-delay time converter 14 is a circuit that generates a sampling clock signal (g) having a delay time proportional to the voltage of the delay time control signal (e) based on the transmission clock signal (a). is there. Specifically, the voltage-delay time converter 14 generates the superimposed signal (f) by adding the transmission clock signal (a) and the delay time control signal (e), and inputs the superimposed signal (f) to the inverter. Power. When the signal passes through the inverter, the falling input is output as a rising edge with a small delay proportional to the voltage of the superimposed signal (f). The sampling pulse generator 9 uses the rising edge of the sampling clock signal (g) as a delay clock to generate a sampling pulse (h).

Next, the processing of the microcontroller 12 will be described with reference to FIGS. FIG. 3 is a flowchart showing the flow of the process of the microcontroller 12. FIG. 4 is a diagram for explaining the variable control of the delay time. The upper part shows the waveform of the delay time control signal, and the lower part shows the time-base extended wave.

[0038] In an initial state at power-on, the microcontroller 12 sets a delay time control pattern to a ramp waveform (step Sl). The ramp waveform is represented by the following equation.

[0039] [Equation 1] y-ax (0≤x <t _c )

[0040] Here, a is the slope of the ramp waveform set in advance, and tc is the end time of one measurement cycle when tO = 0 is set to the start time IJ.

This delay time control pattern is converted into a voltage signal by the D / A converter 13 and output as a delay time control signal 20 shown by the thin line in the upper part of FIG. In this state, since the slope of the delay time control signal 20 is constant, the rate of increase in the delay time of the sampling pulse is constant throughout the measurement period. Therefore, the light receiving signal 21 is expanded in a proportional manner as shown by the thin line in the lower part of FIG.

Here, it is assumed that the detection target object 2 appears in the detection area of the optical distance measuring device 1 and the light receiving pulse 22 appears in the light receiving signal 21. This light receiving pulse 22 is detected by the value detector 11, (Rise / fall) when crossing the threshold voltage Vth which has been previously set (step S2).

In the microcontroller 12, an interrupt is activated by the detection signal. The microcontroller 12 records the ON time tl and the OFF time t2 of the light receiving pulse 22 with reference to the start point of the delay time control pattern (0 at the start of one measurement cycle), and records the 〇N time tl The center time of the OF time t2 is recorded as a temporary peak time ta (step S3). The pulse ON time tl is the start point of the pulse existence section, and the pulse OFF time t2 is the end point of the pulse existence section.

Next, the microcontroller 12 generates a new delay time control pattern to expand the pulse existence section (Step S4). In this embodiment, the rate of increase of the delay time of the sampling pulse in the pulse existence section (tl-t2) is set to be smaller than the increase rate of the delay time outside the section (tO-tl, t2-tc). The length of the measurement period, that is, one time-axis extension wave, is generated by appropriately increasing the delay time increase rate outside the section according to the degree of decrease in the delay time increase rate in the pulse existence section. So that the number of times of sampling is constant.

The algorithm for generating the delay time control pattern will be described in detail by taking as an example a case where the pulse existence section (tl-t2) is multiplied by n (t−Χ ′).

First, the microcontroller 12 calculates the ON time tl ′ and the OFF time Ijt2 ′ after the pulse existence section is expanded using the following equation, with the temporary peak time ta as the center.

[0047] [Number 2]

7 '= ^ — —) '"= +

2 {("ー (" one} t2 '= ta + {-t _a ) -n = ^ ¹ {{n + l) -t _2- {ni t ₁ }

[0048] Then, the microcontroller 12 determines the section before the pulse existence section (tO-tl '), the panelless section (t-t2'), and the section after the pulse existence section (ΐ2'-tc). The control waveform of each delay time control pattern is set as follows.

[0049] [Equation 3]

a, x

y―— x + n-tj-t ₁ ) (t ₁ '<x <t ₂ ')

[0050] This delay time control pattern is converted into a voltage signal by the DZA converter 13, and is output as a delay time control signal 23 indicated by a bold line in the upper part of FIG.

[0051] The slope of the delay time control signal 23 in the pulse existence section becomes gentler as 1 / n times as compared with the initial state (ramp waveform), and the increase rate of the delay time in this section becomes relatively small. When the sampling pulse generated based on the delay time control signal 23 is used, the number of times of sampling in the pulse existence section increases. Therefore, as shown by the bold line in the lower part of FIG. 4, a time-axis extended wave in which the waveform of the light receiving pulse 25 of the light receiving signal 24 is greatly enlarged is obtained, and the resolution around the light receiving pulse 25 can be increased.

On the other hand, the slope of the delay time control signal 23 outside the pulse existence section becomes larger than in the initial state, and the rate of increase of the delay time in this section becomes relatively large. Therefore, the number of times of sampling of a portion unnecessary for distance measurement is reduced, and a decrease in responsiveness is suppressed. Note that, here, the voltage value of the delay time control signal 23 at time tc is set to be the same value as in the case of the ramp waveform condition, so that the constant value is always constant regardless of the change rate of the delay time. Responsiveness (length of measurement period) is guaranteed.

In the present embodiment, the distance measurement process is performed using the time-base stretched wave after the pulse existence section is expanded (step S5).

The light receiving pulse 25 in the time-axis expanded wave is detected by the threshold detector 11. In the microphone port controller 12, an interrupt is activated by the detection signal. The microcontroller 12 sequentially captures and records the peak value of the received light pulse 25 from the A / D converter 10 during the time tl'-t2 ', and then specifies the peak time tp of the enlarged waveform. Since the waveform of the light receiving pulse 25 is magnified n times, it is possible to analyze the waveform and specify the peak position with high accuracy. Then, the microcontroller 12 converts the peak time tp of the enlarged waveform into the actual peak time tr by the following equation.

[0056] [Equation 4]

n

Here, since the tO force coincides with the S pulse transmission time, the peak time tr is the flight time (after time expansion) of the light pulse. Therefore, the distance d to the detection target object 2 is calculated by the following equation. In the following equation, c is the speed of light, and α is the waveform expansion rate (= ramp signal period / maximum delay time). This calculation result is output to an external device or the like.

[0058] [Equation 5]

_Α 1 _t

a = — t _r -c

2a

[0059] Here, when the detection target object 2 goes out of the detection area and the light reception noise disappears, the microcontroller 12 sets the delay time control pattern to the initial ramp waveform, and the light reception noise appears again. Wait until the operation is completed (step S6). Alternatively, if multiple light-receiving panels appear due to another object, etc., and the result of comparison of the peak value and the detection mask area, etc., changes the noticeable light-receiving pulse, the delay time control pattern is once set to the ramp waveform. Then, the same pattern generation algorithm as described above is applied to the received light pulse.

As described above, according to the present embodiment, the distance measurement accuracy can be improved with a simple and small circuit configuration without lowering the response.

(Second Embodiment)

FIG. 5 shows a configuration of an optical distance measuring apparatus according to a second embodiment of the present invention.

The optical distance measuring device 30 of the present embodiment is provided with a peak detector 31 instead of the threshold value detector 11 of the optical distance measuring device 1 of the first embodiment. Since other circuit configurations are the same as those of the first embodiment, the same reference numerals are given and the detailed description is omitted.

[0063] The peak detector 31 detects a pulse existence section in which the received light pulse exists from the time-axis extended wave. It is a pulse detecting means for detecting. The peak detector 31 is composed of a differentiating circuit and a zero-cross detection circuit, and when the rate of change of the crest value of the time base extension wave becomes the minimum (when it is estimated that the peak is reached), the microcontroller 12 detects the peak value. Send a signal.

In the microcontroller 12, an interrupt is activated by the detection signal. The microcontroller 12 records the time as a temporary peak time ta, and sets [peak time ta—predetermined time width] to the start time tl of the pulse existence section and [peak time ta + predetermined time width]. Record as the end time t2 of the pulse existence section. Subsequent processing is the same as that of the first embodiment.

[0065] Also in the case of the present embodiment, the same operation and effect as those of the first embodiment can be obtained.

(Third Embodiment)

FIG. 6 shows a configuration of an optical distance measuring apparatus according to a third embodiment of the present invention.

The optical distance measuring apparatus 40 of the present embodiment is provided with a threshold / peak detector 41 instead of the threshold detector 11 of the optical distance measuring apparatus 1 of the first embodiment. Is added. Since other circuit configurations are the same as those of the first embodiment, the same reference numerals are given and detailed description is omitted.

The threshold / peak detector 41 is a pulse detection unit having a circuit configuration in which the threshold detector 11 of the first embodiment and the peak detector 31 of the second embodiment are combined, The start point and end point of the pulse existence section and the pulse change rate minimum point at which the pulse change rate is minimum are detected. The section integration circuit 42 is an integration means for integrating the time-base extended wave. Each output signal is input to the microcontroller 12.

The processing of the microcontroller 12 will be described. Since the general flow of the process is the same as that of the first embodiment, the flowchart of FIG. 3 is referred to for convenience.

In steps S 1 and S 2, a process of generating a ramp waveform delay time control pattern and a process of detecting a received light pulse are performed in the same manner as in the first embodiment.

When the threshold / peak detector 41 detects a light receiving pulse, the microcontroller 12 starts an interrupt by the detection signal. As shown in FIG. 7, the microcontroller 12 records the start time tl and the end time t2 of the pulse existence section of the light receiving pulse 43 based on the detection signal from the threshold Z peak detector 41, The minimum point And record the time as tp (step S3).

Next, the microcontroller 12 generates a new delay time control pattern to correct the distortion of the received light pulse waveform (Step S4). In the present embodiment, the time-axis extended wave in the pulse existence section is made to have a substantially symmetrical waveform around the peak time tp.

First, the microcontroller 12 uses the section integration circuit 42 to calculate the first section integration value (area Sip) in the first section from the start time tl to the peak time tp, and the first section integrated value (area Sip) from the peak time tp to the end time t2. Obtain the second section integral value (area Sp2) in the second section. The areas Sip and Sp2 are expressed by the following equations.

[0074] [Number 6]

Here, v (t) is the peak value (voltage value) of the received light pulse at time t.

Next, the area Sip and the area Sp2 are compared, and the rate of increase of the delay time of at least one of the first section and the second section is adjusted so that both values are substantially equal. This is based on the fact that increasing the rate of increase in the delay time increases the number of samplings and increases the area, and conversely, decreasing the rate of increase decreases the area.

[0077] The delay time control pattern generated by the microcontroller 12 is converted into a voltage signal by the D / A converter 13, and output as a delay time control signal.

[0078] Various methods of adjusting the increase rate are conceivable.

For example, in the method of FIG. 8, the slope of the delay time control signal in the second section is increased in the case of Sip and Sp2, and is reduced in the case of Slp> Sp2. This method is the simplest because the value of the area Sip does not change.

In the method of FIG. 9, the timing of the first section is reduced in the case of Sip × Sp2, and the slope of the first section is increased in the case of Slp> Sp2. At the same time, the slope of the second section also changes.

The method of FIG. 10 combines “correction processing of waveform distortion” and “enlargement processing of pulse existence sections” described in the first embodiment. That is, at the start of the pulse existence section From the time tl and the end time t2, find the expanded times tl 'and X2'.If Slp <Sp2, make the slope of the section tp—12' larger than the slope of the section t1 '1 tp, and set Slp> Sp2 Reverse if you want. According to this method, since the received light pulse is enlarged, it is possible to accurately correct waveform distortion.

When the received signal was sampled with a sampling pulse whose delay time increase rate was adjusted by any of the above methods, the received pulse force was expanded backward as shown by the broken line in FIG. It was shaped like a waveform without distortion.

In the present embodiment, the distance measurement process is performed using the time-base expanded wave after the distortion correction. Subsequent processing (steps S5 and S6) is the same as in the first embodiment.

As described above, according to the present embodiment, since the distortion of the received light pulse waveform due to the influence of disturbance is corrected, it is easy to analyze the waveform and specify the peak position with high accuracy, and to measure the distance. Accuracy can be improved. Since the distortion of the received pulse waveform is corrected only by adjusting the delay time of the sampling pulse, the configuration is simple, the circuit is complicated, and the size of the housing is not increased and the cost is not increased. Also, as is clear from FIGS. 8 to 10, the length of one measurement period is constant, and the response does not decrease.

[0085] The above embodiment is merely an example of one specific example of the present invention. The scope of the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the technical idea.

[0086] For example, in the above-described embodiment, the force S that adjusts the rate of increase of the delay time by changing the slope of an arbitrary section of the delay time control signal, the peak position and the waveform that cannot be controlled by such linear control The delay time control may be performed by a curve function according to a distortion pattern or the like.

In the above embodiment, the peak position is used for calculating the distance, but it is also preferable to use the barycentric position of the time-axis stretched wave instead of the peak position. Even when the peak position is difficult to identify due to waveform distortion due to the influence of disturbance, the distance measurement error can be reduced by using the center of gravity position.

Industrial applicability

[0088] The present invention can be used for a general-purpose photoelectric sensor, and more preferably a distance for short-distance measurement. The present invention can be used for a detachable photoelectric sensor. This type of photoelectric sensor is used, for example, for a manufacturing device or an industrial robot for controlling a positioning sensor, a detection sensor for detecting an intruder or an intruder, an inter-vehicle sensor (on-vehicle optical radar device), a vehicle sensor. It can be applied to various uses.

FIG. 14 shows a configuration example of an inter-vehicle sensor to which the present invention is applied. Fig. 14 shows the road viewed from above. The inter-vehicle sensor 50 is an on-vehicle optical radar device mounted on the vehicle 51. The inter-vehicle sensor 50 measures the distance (inter-vehicle distance) between a preceding vehicle (vehicle in front) 52 and a following vehicle (vehicle in rear) 53 using light pulses. At this time, by performing the above-described correction of the received light pulse waveform distortion, it is possible to achieve both responsiveness and inter-vehicle distance measurement accuracy with a simple and compact configuration. Further, the inter-vehicle sensor 50 may be provided with a function (relative speed calculating means) for calculating a relative speed with respect to the preceding vehicle 52 or the following vehicle 53 based on a plurality of distance measurement results. For example, if the distance measurement is performed continuously at a fixed time interval, the relative speed between the preceding vehicle 52 or the following vehicle 53 and the own vehicle can be easily calculated from the temporal change of the inter-vehicle distance. The calculated relative speed information can be used for speed control of vehicle 51, collision prevention control, and the like. Furthermore, as shown in FIG. 14, if a function (direction switching means) for switching the irradiation direction of the light pulse is provided, it is possible to detect the direction in which the preceding vehicle 52 or the following vehicle 53 exists. In addition, the inter-vehicle sensor 50 (on-vehicle optical radar device) can also detect an obstacle other than a vehicle and measure the distance to the obstacle other than the inter-vehicle distance.

Brief Description of Drawings

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

FIG. 2 is a waveform chart for explaining the operation of the optical distance measuring apparatus in FIG. 1.

FIG. 3 is a flowchart showing a processing flow of a microcontroller in FIG. 1.

FIG. 4 is a diagram for explaining variable control of a delay time according to the first embodiment.

FIG. 5 is a block diagram showing a configuration of an optical distance measuring apparatus according to a second embodiment.

FIG. 6 is a block diagram showing a configuration of an optical distance measuring apparatus according to a third embodiment.

FIG. 7 is a view for explaining variable control of a delay time in a third embodiment.

FIG. 8 is a diagram for explaining a method 1 for adjusting a delay time increase rate. FIG. 9 is a diagram for explaining a delay time increase rate adjustment method 2.

FIG. 10 is a diagram for explaining a delay time increase rate adjustment method 3.

FIG. 11 is a diagram illustrating the effect of distortion correction of a received light pulse waveform.

FIG. 12 is a diagram for explaining the principle of the triangulation method.

FIG. 13 is a diagram for explaining distortion of a received light pulse waveform.

FIG. 14 is a diagram showing a configuration example of an inter-vehicle sensor.

Explanation of symbols

1 Optical distance measuring device

2 Object to be detected

3 Oscillator

4 Pulse generator

5 Light emitting device

6 Light receiving element

7 Waveform amplifier

8 Sample hold device

9 Sampling pulse generator

10 AZD converter

11 Threshold detector

12 Microcontroller

13 D / A converter

14 Voltage-delay time converter

20 Delay time control signal

21 Light reception signal

22 Received pulse

23 Delay time control signal

24 Received signal

25 received pulse

30 Optical ranging device Peak detector Optical distance measuring device

Threshold / peak detector Section integration circuit Light receiving pulse

Inter-vehicle sensor

Vehicle

Leading vehicle

Subsequent car

Claims

The scope of the claims

[1] An optical distance measuring device that measures a distance to an object using an optical pulse,

Light emitting means for irradiating an object with a light pulse,

Light receiving means for receiving the light pulse reflected by the object,

Sampling means for extending the time axis of the received light signal based on a sampling pulse having a cycle such that the delay time for the irradiation light pulse gradually increases,

Pulse detection means for detecting a pulse existence section in which a light receiving pulse exists from a time axis extension wave,

Delay time varying means for making the rate of increase of the delay time of the sampling pulse in the pulse existence section smaller than the rate of increase of the delay time outside the section;

An optical distance measuring device comprising:

2. The optical distance measuring device according to claim 1, wherein the delay time varying means increases a delay time increase rate outside the section in accordance with the degree of decrease in the delay time increase rate of the sampling pulse in the pulse existence section.

[3] The delay time varying means adjusts an increasing rate of the delay time in each of the pulse existence section and the delay time outside the section so that the number of times of sampling for generating one time-base stretched wave is constant. Light ranging device.

[4] The optical ranging according to claim 1, wherein the pulse detection means sets a pulse existence section from a time when the crest value of the time-base extended wave exceeds a predetermined threshold value to a time when the crest value falls below the predetermined threshold value. Equipment

[5] The optical ranging device according to claim 1, wherein the pulse detection means detects a peak position from the time-axis extended wave, and a predetermined time before and after the peak position is defined as a pulse existence section.

[6] The delay time varying means further adjusts the rate of increase of the delay time of the sampling pulse in the pulse existence section so that the time axis extension wave in the pulse existence section has a substantially symmetrical waveform around the peak position. The optical distance measuring device according to claim 1.

[7] An optical distance measuring device that measures a distance to an object using an optical pulse,

Light emitting means for irradiating an object with a light pulse,

Light receiving means for receiving the light reflected by the object, Sampling means for extending the time axis of the received light signal based on the pulse; and

Delay time varying means for adjusting the rate of increase of the delay time of the sampling pulse in the pulse existence section so that the time axis extension wave in the pulse existence section has a substantially symmetrical waveform around the peak position;

An optical distance measuring device comprising:

[8] Further comprising an integration means for integrating the time-axis stretched wave,

The pulse detecting means detects a pulse change rate minimum point at which the pulse change rate is minimum from the time-base stretched wave,

The integration means includes a first section integral value in a first section from a start point of the pulse existence section to a pulse change rate minimum point, and a second section integral value in a second section from the pulse change rate minimum point to the end point of the pulse existence section. Calculate the two-section integral value,

The delay time varying means adjusts an increasing rate of delay time of at least one of the first section and the second section so that the first section integral value and the second section integral value are substantially equal. Light ranging device.

[9] Further comprising an integrating means for integrating the time-axis stretched wave,

The delay time varying means adjusts an increase rate of at least one of the delay time of the first section and the second section so that the first section integral value and the second section integral value become substantially equal. Light ranging device.

[10] Irradiate the object with a light pulse,

Receives the light pulse reflected by the object, There is a cycle such that the delay time for the irradiation light pulse gradually increases.

Detects the pulse existence section where the received light pulse exists from the time axis extension wave,

Adjust the rate of increase of the delay time of the sampling pulse in the pulse existence section so as to be smaller than the rate of increase of the delay time outside the section,

Calculate the distance to the object from the time-base stretched wave based on the adjusted sampling pulse

Light ranging method.

[11] Irradiate the object with a light pulse,

Receives the light pulse reflected by the object,

Extending the time axis of the received light signal based on the sampling pulse having a period such that the delay time for the irradiation light pulse gradually increases,

The rate of increase of the sampling pulse delay time in the pulse existence section was adjusted so that the time axis extension wave in the pulse existence section became a substantially symmetrical waveform around the peak position, and the time axis was extended based on the adjusted sampling pulse. Calculate the distance to the object from the time axis stretching wave

Light ranging method.

[12] irradiate the object with a light pulse,

Receives the light reflected by the object,

The increase rate of the delay time of the sampling pulse in the pulse existence section is smaller than the increase rate of the delay time outside the section, and the time-axis elongation wave in the pulse existence section is substantially symmetrical about the peak position. Adjust so that it has a waveform,

Calculate the distance to the object from the time-base stretched wave based on the adjusted sampling pulse Light ranging method.

[13] An on-vehicle optical radar device that measures the distance to a preceding or following vehicle using optical pulses.

Light emitting means for irradiating a preceding vehicle or a following vehicle with a light pulse,

Light receiving means for receiving a light pulse reflected by a preceding or following vehicle,

An in-vehicle optical radar device comprising:

[14] An on-vehicle optical radar device that measures the distance to a preceding vehicle or a following vehicle using optical pulses.

An in-vehicle optical radar device comprising:

[15] Further comprising a relative speed calculating means for calculating a relative speed with respect to a preceding vehicle or a following vehicle based on a plurality of distance measurement results.

14. The on-vehicle optical radar device according to claim 13.

[16] Relative speed to calculate relative speed with preceding or following vehicle based on multiple ranging results Further comprising a degree calculating means

15. The on-vehicle optical radar device according to claim 14.