JP3122676B2 - Distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active triangular distance measuring apparatus and, more particularly, to an improvement of a double integral type distance measuring apparatus which improves distance measuring accuracy by an integrating method.

[0002]

2. Description of the Related Art An active distance detecting device which projects light toward an object and receives the reflected light to detect the distance to the object is already known from JP-A-59-9420. is there.

Conventionally, there are various types of distance measurement calculation of this kind of distance measurement apparatus, and a detailed description of the calculation is disclosed in Japanese Patent Application Laid-Open No. 1-150809 filed earlier by the present applicant. . In any of the above-mentioned types, ideally, the distance measurement calculation output is represented by one characteristic line with respect to the reciprocal of the subject distance, as shown in FIG.

However, in practice, the signal light quantity from the subject is extremely small, so that it is affected by so-called random circuit noise such as a photocurrent detection circuit and shot noise generated by stationary light, and has a certain uncertainty width. Having.
For example, the straight line shown in FIG. 8 has a band shape with the uncertainty of the hatched portion shown in FIG. Therefore, the same distance l
_The calculation output for ₀ will stochastically take any value in this band. The uncertainty width tends to increase as the distance of the subject increases and as the reflectivity of the subject decreases, since the signal light amount becomes extremely small.

[0005] One of the techniques for improving the ranging accuracy is an integration method. This is a method of obtaining an integrated value obtained by measuring the distance a number of times. One example is disclosed in Japanese Patent Application Laid-Open No. Hei 1-222461.
No. 7 has already disclosed it. According to this method, the output temporarily integrated N times has a variation of 1 / (N) ^{1/2 with} respect to the output only once. Is suppressed. That is, the ranging accuracy is N ^1/2 That is a double improvement. In this case, it can be seen that the integration should be performed about 20 times in order to increase the accuracy by 4.5 times.

[0006]

FIG. 10 shows an example in which the distance measuring accuracy is improved by the integrating means. However, the double integral type distance measuring device reads the distance measuring signal integrated by the capacitor, so that the distance measuring device shown in FIG.
As shown by the inverse integration waveform w1, a time for performing the inverse integration is required. Therefore, the count waveform 1 in FIG.
As shown in the above, there is a problem that the time required for one distance measurement becomes long. This problem is very serious especially for a camera that emphasizes a photo opportunity.

Therefore, the inverse integrated waveform w2 and FIG.
If the speed of performing the inverse integration is increased as shown by the count waveform 2, there is a problem that the resolution of the distance measurement value becomes coarse. For this reason, such a solution cannot be taken for a camera in which it is desired to focus as finely as possible.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a new integration type in which the time required for inverse integration is reduced as much as possible without reducing the resolution of distance measurement and the time required for distance measurement is shortened. An object of the present invention is to provide a distance measuring device.

[0009]

That is, the present invention provides a light projecting means for projecting a distance measuring light beam to a subject a plurality of times with pulsed light, and receiving reflected light of the distance measuring light beam from the subject. A light receiving means for outputting a signal current corresponding to the distance to the subject; an integrating means for integrating the signal current; and a light emitting time of the light emitting means until the integrated value of the integrating means exceeds a predetermined value. An integration time detecting means for detecting a total sum, wherein a distance to the subject is obtained based on a sum of the light projection times detected by the integration time detecting means.

The present invention also provides a light projecting means for projecting a light beam for distance measurement toward a subject a plurality of times with pulsed light for a predetermined time,
A light receiving unit that receives reflected light of the distance measuring light beam from the subject and outputs a signal current corresponding to the distance to the subject; an integrating unit that integrates the signal current; a light projecting frequency detecting means for detecting the light projection count by said light projecting means to over value, the integral value of the integrating means a light projecting that by the said light projecting means until it exceeds a predetermined value
Performing, after the end of the light projection, discharging the electric charge stored in the integrating means at a constant current, comprising a time measuring means for measuring the time from the start of the discharge until the integrated value returns to the predetermined value, The distance to the object is obtained based on the time measured by the time measuring means and the number of light projections by the number of light projection detecting means.

[0011]

In the distance measuring apparatus according to the present invention, the light for distance measurement is intermittently projected a plurality of times toward the object by the light projecting means, and the reflected light of the distance measurement light from the object is received by the light receiving means. And a signal current corresponding to the distance to the subject is output. This signal current is integrated by the integration means. The calculating means obtains the subject distance based on the total number of times of light emission or the light emitting time until the integration amount of the integrating means exceeds a predetermined value.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing an arrangement of a distance measuring optical system of a distance measuring apparatus according to an embodiment of the present invention. Here, two SPDs 1A and 1B are provided as light receiving elements. In the light projecting section, one IRED chip 2 is provided as a light emitting element. FIG. 2 is an arrangement diagram when these are viewed from the front direction (the direction of arrow X in FIG. 1).

In FIG. 1, the focal length f of the light projecting lens 3 is shown.
_In the light emitting element 2 having a chip size of t ₁ disposed at a position separated by _T , the light beam emitted by the element 2 is condensed by the light projecting lens 3 and projected toward the distance measuring object 4. . The light reflected by the distance measuring object 4 is transmitted from the light projecting lens 3 to the base line length L.
The light is condensed by a light receiving lens 5 that is arranged at a distance. And
The reflected light is incident from the light receiving lens 5 on SPDs 1A and 1B disposed at positions separated by a focal distance f _J. Then, each SPD1A and 1B, photocurrents I ₁ and I ₂ are respectively generated. This is supplied to the calculation unit 6 so that the distance measurement calculation is performed. FIG. 3 is an electric circuit diagram of the distance measuring device of the embodiment, and FIG.
(G) is a timing chart of a signal supplied from the control circuit unit shown in FIG.

This distance measuring device is, as shown in FIG.
A light projecting circuit section 11 for projecting an optical pulse onto a distance measuring object, and photocurrent detecting circuit sections 12A and 12B for receiving reflected light from the distance measuring object to detect and amplify a signal pulse photocurrent component.
An arithmetic output circuit unit 13 for obtaining distance information of the subject from the photocurrent superimposed on the bias current, a count circuit unit 14 for A / D converting an output of the arithmetic output circuit unit 13,
And a control circuit section 15 for sending a control signal to each of the circuit sections.

The photocurrent detection circuit sections 12A and 12B
Use the same components and have the same configuration. Therefore, only the circuit section 12A will be described here, and the reference numerals A of the same members will be replaced with B in the components of the circuit 12B. And the repeated explanation is omitted. The same applies to the drawings and each part.

In FIG. 3, the IRED of the light emitting circuit 11
The (infrared light emitting diode) 16 is driven with a constant current by a constant current drive circuit including a transistor 17, resistors 18, 19 and an operational amplifier 20. A base of a transistor 21 for controlling ON / OFF of the constant current drive circuit is connected to a terminal T ₁ of the control circuit unit 15 via a resistor 22. Infrared light-on from the IRED16 projected by the pulse waveform shown in FIG. 4 (b), the off control is performed by the output signal of the terminal T ₁ of the control circuit section 15 (see FIG. 10).

The photocurrent detection circuit section 12A includes an operational amplifier 2
3A, a preamplifier circuit section including a transistor 24A, an operational amplifier 25A, a background light removing circuit section including a transistor 26A and peripheral circuits, and a transistor 27.
A, 28A.

The signal pulse light current I ₁ obtained from the anode of the SPD 1A is supplied to an operational amplifier 23A constituting a preamplifier circuit. The operational amplifier 23A has its output terminal connected to the emitter of the transistor 24A, its inverting input terminal connected to its base, and its non-inverting input terminal connected to the reference power supply Vref. That is, the transistor 26A
As a result, the base input resistance of the transistor 24A is equivalent to several tens of K.
Ω has been lowered.

An operational amplifier 2 constituting a background light removing circuit section
5A is, "H (high)" level of the non-light-projecting time of the control circuit section 15 terminal T ₁ of the output signal of becomes is turned on and activated by applied via resistor 29A to the base of the transistor 30A. Then, a charge corresponding to the brightness of the background light is stored in the capacitor 31A connected to the output terminal. At the same time, the photocurrent component due to the background light of the SPD 1A and the bias current component of the operational amplifier 23A are converted into the transistor 26A by the feedback loop including the capacitor 31A and the transistor 26A.
Is discharged to the ground line as a collector current. As a result, the collector current of the transistor 24A has a value substantially corresponding to the pulse signal photocurrent regardless of the magnitude of the background light.

During light emission, the transistor 30A is turned off, so that the operational amplifier 25A becomes non-active. However, due to the electric charge accumulated in the capacitor 31A, the transistor 26A continues to discharge the photocurrent due to the background light to the ground line. Therefore, the pulse light component obtained by removing the photocurrent due to the background light from the photocurrent obtained from the anode of the SPD 1A is multiplied by β _N by the transistor 24A and turned back by the current mirror circuits 27A and 28A. Then, the signal pulse light current β _N and I ₁ are injected into the compression diode 37 of the operation output circuit unit 13.

The photocurrent I ₂ obtained from the anode of the other SPD 1B is also processed by the photocurrent detection circuit section 12B which operates in the same manner as the above-described circuit section 12A, and the signal pulse photocurrent β _N I ₂ Is supplied to the arithmetic output circuit unit 13 as

The operation output circuit section 13 includes the transistor 3
2, 33, 34, and 35, compression diodes 36 and 37, a constant current source 38, and buffer circuits BUF ₁ and BUF ₂ to constitute a logarithmic expansion circuit for obtaining a distance calculation output. Transistor 3 forming differential amplifier
The bases 2 and 33 are connected to the respective anodes of the compression diodes 36 and 37 via buffer amplifiers BUF ₁ and BUF _2, and the emitters are commonly connected to a constant current source 38. The collector of the transistor 33 is connected to the bases of the transistors 34 and 35 forming the current mirror circuit and the collector of the transistor 34.

By the way, the compression diodes 36, 37
The currents I _1b and I _2b are connected to each other so that the signal pulse photocurrents output from the photocurrent detection circuit units 12B and 12A flow. Therefore, in the arithmetic output circuit section 13, the current I _1b is the signal pulse light current β _N I ₂ from the photocurrent detection circuit section 12B, and similarly, the current I _2b is the signal pulse light current from the photocurrent detection circuit section 12A. Since the current becomes β _{NI 1} , I _1b = β _{NI 2} I _2b = β _{NI 1} (1).

Therefore, the collector current I of the transistor 33
_c, when the constant current of the constant current source 38 and I _E, I _c = a _{{I 2b / (I 1b +} I 2b)} · I E ... (2). Therefore, the collector current I ₁ ′ of the transistor 35, which is the output of the arithmetic output circuit section 13, is obtained by substituting the above equation (1) into the equation (2), I ₁ ′ = {I ₁ / (I ₁ + I ₂ )} I _E (3)

On the other hand, the counting circuit section 14 measures the integrated value I ₁ ′ of the collector current of the transistor 35 of the arithmetic output circuit section 13 and digitally measures it by a counter mechanism built in the control circuit section 15. Things.

The output current I ₁ ′ of the operation output circuit section 13
Is obtained as follows. Constant current synchronized with light emission
The source 38 becomes active, and the output current of the arithmetic output circuit 13 flows through the capacitor 39 every time light is projected, so that electric charges are accumulated. Operational amplifier 40 is for the reset of the capacitor 39, the base of transistor 41 for the control is connected to the terminal T ₃ of the control circuit section 15 via a resistor 42.

[0028] Thus, the output signal of the terminal T ₃ (see FIG. 4 (c)), the transistor 41 is turned on to set the potential of the capacitor 39 to the reference voltage Vref, the off immediately before the projection start op The operation of 40 is disabled. Thereafter, the potential of the capacitor 39 increases due to the current injected into the capacitor 39.

[0029] When the control circuit unit 15 to the potential of the capacitor 39 exceeds Vref ₂ at a certain number by the fall of the terminal T ₅ is detected, the control circuit section 15
Terminates light emission. That is, as shown in the timing chart of FIG. 4 (d), the the terminal T ₄ "H →
L ”, the transistor 44 is turned off via the resistor 43, and the capacitor 39 is discharged by the transistor 45.

At the same time, the counter built in the control circuit section 15 operates and continues counting until the output of the comparator 46 becomes H. Co-down comparator 46, capacitor 39
Becomes smaller than the reference voltage Vref ₂ ,
From H to H. The discharging speed of the capacitor 39 is determined by the constant current source 47 and the transistor 4 connected in series to the constant current source 47.
It is determined by a current mirror circuit composed of 5, 48.

Since the time (count value) C ₀ required for discharging from Vref ₂ to Vref ₁ is known in advance, the distance measurement output stored in the capacitor is obtained by the sum of this value and the count value C _1. be able to. When the distance measurement output count value is divided by the number of times of light projection N, a desired object distance as shown in FIG. 5 can be obtained. Next, the operation of this embodiment will be described with reference to the flowchart of FIG.

[0032] First, as shown in FIG. 4 (c), to first light is emitted, the terminal T ₃ of the control circuit section 15 is in the L (Step S1, S2). In response to this, as shown in FIG. 4 (a), the terminal T ₁ of the control circuit section 15
Becomes L (step S3), as shown in FIG. 4B, the IRED 16 of the light emitting circuit unit 11 starts emitting light. Next, after waiting for t ₁ ms (step S4), the terminal T ₁ becomes H, and the light emission of the IRED 16 is stopped (step S5). In this state, it waits for t ₂ ms (step S6).

[0033] Thereafter, as shown in FIG. 4 (e), whether the terminal T ₅ of the control circuit section 15 becomes L it is determined (step S7). Here, to the terminal T ₅ becomes L, and emission of IRED16 is repeated (step S3~
S8). Then, at some times, as shown in FIG. 4 (f), the falling (T ₅ = L) by the control circuit section 15 of the terminal T ₅ to the potential of the capacitor 39 exceeds Vref ₂ detects (Step S7), control circuit unit 15
Terminates light emission. That is, as shown in FIG. 4 (d), terminal T ₄ of the control circuit section 15 becomes L (step S9), and at the same time, work is built-in counter, the timer is started (step S10).

Thus, the terminal T ₅ of the control circuit unit 15 is set to H
The counting is continued until (S11).
When the voltage across the capacitor 39 becomes smaller than the reference voltage Vref _2, the output from the counter circuit section 14 is changed from L to H. Here, the count value while the timer is running, is a C ₁ (see FIG. 4 (g)) (step S12).

As described above, the time required for discharging from Vref ₂ to Vref ₁ (count value)
Since C ₀ is known in advance, the distance measurement output count value, which is the sum of the count value C ₀ and the count value C ₁ , is divided by the number of light projections N (step S13). Then, a distance calculation is performed (step S14), and a subject distance as shown in FIG. 5 can be obtained. Thereafter, the terminals T ₃ and T ₄ of the control circuit unit 15 are set to H, respectively (steps S15 and S16).

In the first embodiment described above, since the object distance is obtained based on the number of times of light projection, the light projection cannot be stopped even if the integral value exceeds Vref ₂ during the light projection. For that purpose, C ₁ is obtained by performing further inverse integration. Here, the circuit can be further simplified if it is obtained not from the number of times of light emission but from the light emission time until the integral value exceeds Vref ₂ (total light emission time). The circuit configuration in this case is not shown here because the transistors 44, 45, and 48, the resistor 43, and the constant current 47 are deleted from the circuit of FIG. The operation in that case will be described with reference to the flowchart in FIG.

[0037] First, put 0 into N so light is emitted (step S21), and the terminal T ₃ of the control circuit section 15 is in the L (step S22). In response to this, when the terminal T ₁ is it becomes L (step S3), IRE light projecting circuit 11
D16 starts emitting light and a timer is started (step S24).

[0038] Then, whether the terminal T ₅ of the control circuit section 15 becomes L is determined (step S25). Here, if the terminal T ₅ is not turned L, and whether t ₁ is elapsed is determined (step S26), returns to step S25 when not reached. These steps S2
In 4～S26, in which whether it is T ₅ = L during light projection time t _1, i.e. whether the host vehicle has reached the Vref ₂ is determined.

If t ₁ has elapsed in step S26, the timer is reset (step S27).
Thereafter, the terminal T ₁ goes to H, and the light emission of the IRED 16 is stopped (step S28), and the light emission OFF time t ₂ m
After waiting for s (step S29), 1 is added to the number of times of light emission N (step S30), and the process returns to step S23, where I
Light emission of the RED 16 is repeated (steps S23 to S3).
0).

At a certain number of times, when it is detected that the potential of the capacitor 39 has exceeded Vref ₂ by the fall of the terminal T ₅ (T ₅ = L) (step S 25)
The control circuit unit 15 performs step S2 to end the light projection.
The timer count value is started from 4 to C ₃ (step S31). Next, this count value C ₃ ,
The total light emitting time E is obtained from the number of times of light emission N and the light emitting time t ₁ (step S32), and the distance is calculated from the total light emitting time E (step S33). Thereby, the subject distance can be obtained. Thereafter, the terminal T ₃ of the control circuit section 15, is to H (step S34). In the above-described embodiment, the two-division SPD is used as the light receiving element.
Of course, a device using a PSD may be used. Also,
If the distance measurement output is configured to decrease as the distance increases as in the above-described embodiment, the number of integration increases as the distance increases,
The shorter the distance, the smaller the number of integrations.

As is clear from FIG. 9, the number of integrations must be increased in order to increase the distance measurement accuracy at a longer distance, and the number of integrations can be reduced at short distances since there is sufficient accuracy. Harmonious. That is, in the present invention, the number of integrations is automatically increased or decreased according to the subject distance, and a secondary effect that unnecessary light projection energy is not consumed is obtained. In addition, at short distances, several integration
Since the f2 level is reached, the effect of shortening the integration time (number of times) itself is also obtained.

[0042]

As described above, according to the present invention, the time required for the back integration can be reduced as much as possible without lowering the resolution of the distance measurement. A distance measuring device can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an arrangement of a distance measuring optical system of a distance measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a layout diagram when the SPD and the IRED chip of FIG. 1 are viewed from the front (in the direction of arrow X in FIG. 1).

FIG. 3 is an electric circuit diagram of the distance measuring apparatus according to one embodiment of the present invention.

FIGS. 4A to 4G are timing charts of signals supplied from the control circuit unit shown in FIG. 3;

5 is a diagram illustrating characteristics of a distance measurement calculation output by the distance measurement device illustrated in FIG. 3 and a reciprocal of a subject distance.

FIG. 6 is a flowchart illustrating an operation of the distance measuring apparatus in FIG. 3;

FIG. 7 is a flowchart illustrating an operation according to a second embodiment of the present invention.

FIG. 8 is a diagram illustrating characteristics of a distance measurement calculation output by a conventional distance measuring device and a reciprocal of a subject distance.

FIG. 9 is a diagram showing a partially enlarged characteristic of a distance measurement calculation output and a reciprocal of a subject distance in FIG. 8;

FIG. 10 is a diagram illustrating a characteristic of a distance measurement calculation output by a conventional distance measuring device and a reciprocal of a subject distance, and is a diagram illustrating an example in which distance measuring accuracy is improved by an integrating means.

11 (a) to 11 (c) are timing charts showing an integral waveform and a count waveform by a conventional double integral type distance measuring device.

[Explanation of symbols]

1A, 1B ... light receiving element (SPD), 2 ... light emitting element (IR
ED chip), 3 ... Projection lens, 4 ... Target object, 5 ...
Light receiving lens, 6 arithmetic unit, 11 light emitting circuit unit, 12A,
12B: photocurrent detection circuit unit, 13: operation output circuit unit, 1
4 ... Count circuit section, 15 ... Control circuit section.

Claims (2)

(57) [Claims] 1. A light projecting means for projecting a light beam for distance measurement toward a subject by pulse light a plurality of times, receiving reflected light of the light beam for distance measurement from the subject, and responding to the distance of the subject. Light receiving means for outputting a signal current; integrating means for integrating the signal current; integration time detecting means for detecting a sum of light projecting times by the light projecting means until an integrated value of the integrating means exceeds a predetermined value; A distance measuring device for calculating a distance to the subject based on a sum of light projecting times detected by the integration time detecting means. 2. A light projecting means for projecting a light beam for distance measurement toward a subject a plurality of times with pulsed light for a predetermined time, receiving reflected light of the light beam for distance measurement from the object, and detecting a distance from the object. Light-receiving means for outputting a signal current corresponding to the following; integration means for integrating the signal current; light-emission number detection for detecting the number of light-emissions by the light-emission means until the integrated value of the integration means exceeds a predetermined value and means, integral value of said integration means performs the projection that by the said light projecting means until it exceeds a predetermined value, after completion of the light projection, to discharge the charge stored in the integration unit with a constant current, the discharge Time measuring means for measuring the time from the start until the integrated value returns to the predetermined value, wherein the time measured by the time measuring means and the number of light projections by the number of light emitting number detecting means Find the distance to the subject based on Distance measuring apparatus according to claim and.