JPH05280973A - Range finder - Google Patents

Abstract

PURPOSE:To perform range finding with a wide dynamic range with an A/D- converter having low resolution used. CONSTITUTION:A timing signal generator 5 is used first to turn ASa1, ASa2 ON and turn ASb1, ASb2 OFF, and steady photo current is bypassed to Q1, Q2. Then ASa1, ASa2 are turned OFF and ASb1, ASb2 are turned ON so that IRED 1 is illuminated and signal current i1, i2 is integrated in integral capacitors C3, C4. At this time the number and time of integrations, etc., are controlled so that the current is within a dynamic range of the A/D-converter 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device, and more particularly to an active distance measuring device which projects pulsed light such as infrared light onto a subject and detects the subject distance based on the reflected light from the subject. Regarding

[0002]

2. Description of the Related Art Autofocus by an active triangulation method applied to compact cameras (hereinafter referred to as
The apparatus (abbreviated as AF) is constructed based on the principle of distance measurement as shown in FIG. That is, the light projecting lens 11 and the light receiving lens 13 having optical axes parallel to each other are located apart from each other by the base line length S, and the near-infrared light emitting LED is on the optical axis of the light projecting lens.
2 (hereinafter referred to as IRED), and a position detecting element (hereinafter referred to as PSD) 1 having a length b and having an end face at a position shifted by a on the optical axis of the light receiving lens. ..

The light energy projected from the IRED 2 is reflected by the subject 12 at a distance L, and the light receiving lens 1
It is imaged on PSD1 through 3. This PSD1 has two output terminals, 1ch and 2ch. When the stationary photocurrent component such as sunlight is removed, the output currents i ₁ and i ₂
Between the incident position x of the reflected spot light and

[Equation 1] The relational expression of is established. Set the focal length of the light receiving lens 13 to f _j
Then, x can be obtained by x = S · f _j / L ………………………………………… (2), so from equations (1) and (2) above

[Equation 2] Is obtained. Therefore, the reciprocal of the subject distance L can be obtained by obtaining i ₂ / i ₁ + i ₂ .

FIG. 12 is a circuit diagram of a main part of a conventional distance measuring device based on the active triangulation method. IR not shown
Before the ED emits light, the operational amplifier A is controlled by the control signal 1.
Analog switch A arranged on the output side of 11, A12
S11 and AS12 are on. Therefore, this amplifier A
All the stationary photocurrents flowing through the PSD1 due to the negative feedback of 11, A12 flow through the transistors Q11, Q12, and the base potential necessary for that is charged in the capacitors C11, C12. Immediately before the IRED emits light, the analog switch A on the output side of the operational amplifiers A11 and A12
When S11 and AS12 are turned off, the potentials required to pass the stationary light are stored in the capacitors C11 and C12.

Next, the increments i ₁ and i ₂ of the photocurrent due to the reflected light from the subject of the IRED projection flow into the bases of the amplification transistors Q13 and Q14. Now transistor Q
Assuming that the DC current amplification factor of 13 and Q14 is β, βi ₁ and βi ₂ flow into the logarithmic compression diodes Q15 and Q16.
The cathodes of the logarithmic compression diodes Q15 and Q16 are
The constant current I ₀ is input to the bases of the differential amplifier circuits Q19 and Q20.

The collector currents of the transistors Q19 and Q20 are i ₁ ′ and i ₂ ′, and the transistors Q15 and Q1 are
When the reverse saturation currents of Q6, Q19 and Q20 are I _s and the thermal voltage is V _T , the following relational expressions are established for these transistor diodes.

[0007]

[Equation 3] ∴i ₁ × i ₁ ′ = i ₂ × i ₂ ′ ……………………………… (5) Substituting equation (5) into i ₁ ′ + i ₂ ′ ＝ I ₀ … (6) Then the following formula is established.

[0008]

[Equation 4] On the other hand, the current I _INT that integrates the integrating capacitor C13 is i
Is equal to ₁ '. Therefore, as shown in FIG. 13, the capacitor C13 is used for a predetermined time t ₁ by I _{INT in the} double integration method.
Is charged, then discharged in the reverse direction with a constant current I _G , and the time t ₂ required to return to the original voltage is measured. As a result, t ₁ × I _INT = t ₂ × I _G …………………… ………………… (8) is obtained. From the above equations (7) and (8)

[Equation 5] Is obtained. Therefore, from equations (3) and (9)

[Equation 6] Therefore, the subject distance L can be obtained by measuring t ₂ .

[0009]

By the way, the above-mentioned FIG.
The distance measurement circuit shown in (1) is composed of a bipolar process IC. In addition to this, control and calculation of the entire camera require a microcomputer, which is usually constructed by a CMOS process. Needing two types of ICs in this way naturally increases the cost. Bipolar and CMOS
Bi-CMO that creates processes on one IC chip
If the S process technology is used, the system can be constructed with one chip, but the cost of the process is high and the cost is high.

On the other hand, if the AF circuit is constructed using the CMOS process of the microcomputer, the cost can be kept low. But bipolar transistors and MOS
Transistors have a large difference in their basic characteristic formulas. That is, between the collector current I _C of the bipolar transistor and the base-emitter voltage V _BE

[Equation 7] Therefore, if the signal current is logarithmically compressed and the “difference” is taken and then exponential expansion is performed, the above (4),
Division will be executed as shown in the equation (7). However, since the MOS transistor does not have this property, the signal currents i ₁ and i ₂ are divided by a microcomputer after A / D conversion of i ₁ and i ₂ respectively.

Here, in order to obtain the 1ch and 2ch signal currents i ₁ and i ₂ of the PSD, first, the overall signal current i _S = i
_By obtaining ₁ + i ₂ , the following equation (12) is obtained.

[0012]

[Equation 8] However, each variable in the above equation (12) is defined as follows.

P _t : Light output of projected LED [W] (radi
ant power) ρ: subject reflectance (a function of wavelength λ, but here considered to be constant) d _t , d _j : effective aperture of light emitting / receiving lens τ _t , τ _j : transmittance of light emitting / receiving lens R _p : PSD radiation sensitivity [a / W] Omega: solid angle [sr] f _t: the focal length above the projection lens (1), (2), (12) from the equation (when a = 0)

[Equation 9] become that way. That is, i ₂ is inversely proportional to the cube of the distance, so when trying to measure a distance from 1 m to 10 m, i ₂ becomes 10
It will have a dynamic range of 00 times. Therefore, the A / D converter requires a performance of 10 bits or more, which is expensive.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a distance measuring device capable of performing distance measurement with a wide dynamic range even if an A / D converter having a low resolution is used.

[0015]

SUMMARY OF THE INVENTION A distance measuring device of the present invention includes a light projecting unit for projecting a light beam toward an object a plurality of times, and a reflected light of the light beam from the object for photoelectric conversion. ,
At the initial stage of a plurality of light projecting operations by the light receiving means for outputting a current signal, a capacitor for integrating the current signal, an A / D converting means for A / D converting the output of the capacitor, and the light projecting means. The output of the capacitor is A /
The number of times the output current is integrated, the integration time per time, so that the output current falls within the dynamic range of the D conversion means,
The distance to the subject is calculated based on the output of the A / D conversion means and the control means for controlling the elements that change the dynamic range such as the capacitance of the integration capacitor, the integration interval, or the projection intensity of the projection means. Computing means to
Is provided.

[0016]

By using a microcomputer or logic circuit having a CMOS process and an inexpensive A / D converter or comparator (having a small number of bits of 4 to 6 bits), a signal for obtaining a dynamic range of an AF light receiving element current is obtained. Current integration time, number of integrations, A / D
The voltage to be converted, the capacitance value of the integrating capacitor, the integration interval, etc. are made variable according to the situation. And, all of these are constructed by CMOS process, and bipolar and B
No i-CMOS is used.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a distance measuring device showing a first embodiment of the present invention. One channel 1ch of the PSD1 is connected to the drain of an N-channel MOS transistor Q1 that stores and bypasses a stationary photocurrent, and is also connected to the inverting input terminal of the operational amplifier A1. The reference voltage V _ref is connected to the non-inverting input terminal of the operational amplifier A1, and the output terminal is connected to the storage capacitor C1 for stationary photocurrent and the gate of the transistor Q1 through the analog switch Asa1.

One channel 1ch of the PSD1 is
Operational amplifier A3 via another analog switch ASb1
Of which is also connected to the inverting input, the non-inverting input is connected to V _{re f.} A capacitor C3 for integrating the current signal i ₁ is connected between the output terminal and the inverting input terminal of the operational amplifier A3, and the analog switch AS is further provided.
It is input to the A / D converter 3 via c1. Above P
The other channel 2ch side of SD1 has the same configuration. The capacitor C5 is a noise absorbing capacitor.

The output of the A / D converter 3 is input to the control device 4. The control device 4 controls the operation sequence of the entire system. The timing signal generator 5 controls the light emission of the IRED2 via the transistors Q3 and Q4, and controls the ON / OFF of each of the analog switches Asa1 to ASc2. Then, the control device is formed by the control device 4 and the timing signal generation device 5, and
The control device 4 also serves as a calculation means.

FIG. 2 is a circuit diagram showing the internal structure of the analog switches Asa1 to ASc2 in FIG. 1, in which an N-channel MOS transistor Q8 and a P-channel MOS transistor Q9 are connected in parallel with each other. The control voltage is supplied to the gate of the transistor Q9 directly and to the gate of the transistor Q8 via the inverter INV1. The operation of the first embodiment thus constructed will be described with reference to the time chart of FIG. 3 and the flowcharts of FIGS. Figure 3
In the time chart of the operation of each part in FIG.
In the stage before 1, as shown in FIGS. 3A, 3B, and 3C, the projection control transistor Q3 is turned off,
The timing signal generator 5 outputs a control signal such that the analog switches ASa1 and ASa2 are turned on and the analog switches ASb1 and ASb2 are turned off. Then, one channel 1ch of PSD1 is by the operational amplifier A1 and the other channel 2
For ch, each feedback loop by the operational amplifier A2 operates. Therefore, all the stationary photocurrent flowing through PSD1 is bypassed to the transistors Q1 and Q2, and the gate potential required for this purpose is set to the capacitors C1 and C2.
2 is charged by the operational amplifiers A1 and A2.

At time t1, in the timing signal generator 5, the light emission controlling transistor Q3 is turned on, the analog switches Asa1 and Asa2 are turned off, and ASb1 and AS are turned on.
b2 is turned on, and the signals as set are output. In this case, even if the analog switches Asa1 and Asa2 are turned off, the gate voltage necessary for bypassing the stationary photocurrent continues to be stored in the capacitors C1 and C2. Continue to apply the corresponding current. Therefore, only the signal currents i ₁ and i ₂ based on the reflected light from the subject due to the IRED emission flow into the integrating capacitors C3 and C4.

Now, the output voltage V ₀₁ of the operational amplifier A3 is
If n times integration is performed and the m-th integration time is tm,

[Equation 10] become. Similarly, the output voltage V ₀₂ of the operational amplifier A4 is

[Equation 11] Given in. Each of these voltages is (D), (E),
Straight lines LD1 and LD in respective descending directions shown in (F)
2, LE1, LE2, LF1, LF2. Note that FIG. 3 (D) is when the subject is located at a short distance, FIG. 3 (E) is at a short distance but the reflectance of the subject is small, and FIG. 3 (F) is at a long distance. V in each
₀₁ and V ₀₂ are shown.

At time t2, when the state before the time t1 is restored, the IRED emission is stopped and the integration operation is finished. Then, according to the control signal from the timing signal generator 5, the analog switch ASc1 or A
Since Sc2 is turned on, the output voltages V ₀₁ and V _{02 of the} operational amplifiers A3 and A4 are taken into the A / D converter 3.
Then, the same converter 3 performs A / D conversion on this, and i ₁ , i
By obtaining ₂ , it is possible to obtain the subject distance L from the equation (3). As a result, the factors that change the dynamic range of the A / D converter 3 in a plurality of subsequent light projecting operations, in this case, the number of times the signal current is integrated and the integration time per time are determined as described below. To do.

Next, the operation for increasing the dynamic range during A / D conversion will be described. In the case of the short distance shown in FIG. 3D, the integration operation is performed a predetermined number of times, once in this case, A / D conversion is performed, and when it is determined that the absolute values of the signal currents i ₁ and i ₂ are large, Then a small number of integrations,
In this case, the integration operation is performed twice to execute the final A / D conversion. Since i ₁ and i ₂ include random noise components, it is desirable to increase the number of integrations. However, when the signal currents i ₁ and i ₂ are large at a short distance, the output of the operational amplifier A3A4 reaches the ground level. It reaches the limit and cannot perform correct A / D conversion. Therefore, the absolute value of the signal currents i ₁ and i ₂ is predicted by the first predetermined number of integrations to determine the remaining number of integrations. ₁ ,
Perform A / D conversion of i ₂ .

Next, when the reflectance of the object is small even at a short distance, as shown in FIG. 3 (E), the signal currents i ₁ , i
_{Since 2} becomes smaller, this is recognized by the first predetermined number of A / D conversions, and the remaining number of integrations is increased before the final A / D conversion.
Perform D conversion.

In the case of a long distance, the incident position of the reflected light spot is very close to 1ch, so that the signal current i _{2 of} 2ch is smaller than the signal current i _{1 of} 1ch. In this case 1ch and 2
The level of ch is recognized by the first A / D conversion, and as shown in FIG. 3 (F), 1ch is A / D converted with a small number of remaining integrations, and 2ch is A / D converted by further increasing the number of integrations. I have to. Also, in FIG. 3, the integration time is shortened for the first three times. This is to prevent the output currents of the operational amplifiers A3 and A4 from overflowing because the signal currents i ₁ and i ₂ are too large at a short distance. Further, a method of setting the subsequent integration time based on the value of the first A / D conversion may be used.

FIG. 4 is a flow chart of the distance measuring operation in the first embodiment, and FIG. 5 is a flow chart showing the details of the subroutines "S-AF60" and "S-AF120" in FIG. In step # 1 of FIG. 4, the subroutine "S-AF60" is executed. As shown in FIG. 5, this subroutine is a flow in which light is emitted once. First, in steps # 31 and # 32, the stationary photocurrent is stored in the capacitors C1 and C2, and in step # 33, the time for storing the stationary light is stored. Is passed, step # 34,
At # 35, the stationary light storage is terminated.

Next, the transistor Q3 is turned on to emit light (step # 36), and 60 μsec in step # 37.
Wait until elapses. Only step # 37 is different between the subroutines "S-AF60" and "S-AF120".
It is c. When the above waiting time elapses, step #
At 38, the transistor Q3 is turned off, and step # 3
The process returns to the main routine of FIG. 4 through 9, # 40.

Next, in step # 2, the analog switch AS
When c1 is turned on, the electric charge accumulated in the capacitor C3 is transferred to the capacitor C5, and A / D conversion is performed in step # 3. In this embodiment, the stronger the signal, the lower the value.
In step # 4, the calculation of the number of integrations is performed using the result of the A / D conversion. Next, in steps # 5 to # 9, the PSD
Similarly, the prediction calculation of the number of integrations is performed for the other channel 2ch.

After initializing the number of integration times N (step #
10), the light emission time is set to 60 μsec until the number of integration times N becomes 4 in step # 11 (step # 1
2) On the other hand, when the number of integration times N exceeds 4, the light emission time is set to 120 μsec by the subroutine “S-AF120” (step # 14), and the distance measuring operation is repeated. When the number of times of light emission predicted and calculated in step # 25 ends during this repetition, the subject distance is calculated in step # 26 and the flow ends.

According to the first embodiment, since the number of subsequent integrations and the integration time per one time are set based on the first A / D conversion result, an A / D converter having a low resolution is used. It is possible to perform distance measurement operation with a wide dynamic range while using it.

FIG. 6 is a circuit diagram of a distance measuring device showing a second embodiment of the present invention. The second embodiment is greatly different from the first embodiment in that two comparators COMPA6 and COMB7 are used in place of the A / D converter 3, so that the comparators COMA6 and COMPB7 have a reference voltage V
_It has two different comparator levels obtained by dividing _ref by the voltage dividing resistors R1, R2, and R3. From the number of integrations until the respective comparators are inverted, the signal current i ₁ ,
It is to obtain the i _2. The voltage division ratios p and q in the comparators COMPA6 and COMPB7 are given by the following equations.

P = R1 / (R1 + R2 + R3) q = (R1 + R2) / (R1 + R2 + R3) Except for this point, there is no difference from the first embodiment. Therefore, the same components as in the first embodiment are designated by the same reference numerals. The description of the configuration is omitted, and only the distance measuring operation is shown in FIG.
This will be described below with reference to the flowchart of FIG.

In FIG. 7, when this flow starts, variables N, j1 and j2 are initialized respectively (step # 51). Then, after light emission is performed by the subroutine "S-AF60" described in FIG. 5 (step # 52), the variable N is incremented by +1 (step #
53), the analog switch ASc1 is turned on (step # 54), and the process proceeds to step # 55.

At step # 55, it is checked whether or not the comparator COMPA6 is inverted by the voltage obtained by integrating the signal current i ₁ from one channel 1ch of the PSD 1. When this COMPA is not inverted, the analog switch ASc1 is turned off and the ASc2 is turned on (steps # 62, # 63), and the COMPA6 is applied to the voltage obtained by integrating the signal current i ₂ from the other channel 2ch of the PSD1. It is checked whether or not is reversed (step # 64).

Returning to step # 55, when the comparator COMPA is inverted, it is checked whether the number of integration times N has reached the predetermined number of times m (step # 56).
If m has not been reached, it is next checked whether or not the comparator COMPB7 has been inverted. In this case, the predetermined number of times m
The calculation at the time of calculating the subject distance in step # 73, which will be described later, differs depending on whether COMPB 7 is inverted or not before reaching. Therefore, the number of integration times N until COMPA or COMPB is inverted is stored in n1, and the voltage division ratio p or q is stored in j1, respectively (steps # 58 to # 61).

In steps # 64 to # 71, PS
The same processing as above is performed for the integrated voltage of the signal current i ₂ from the other channel 2ch of D1. However, in this case, the number of integration times N is stored in n2, and the voltage division ratio p or q is stored in j2.

When the reversing operation of COMPA and COMPB is completed (step # 72), the process proceeds to step # 73, the subject distance is calculated, and this flow is ended.

According to the second embodiment, since no A / D converter is required, cost reduction can be expected.

FIG. 8 is a circuit diagram of essential parts of a distance measuring apparatus showing a third embodiment of the present invention. The third embodiment is different from each of the above embodiments in that when the subject distance is too close and the A / D conversion result overflows, the light emission power from the IRED 2, that is, the light emission intensity of the light emitting means is gradually reduced. Is provided. That is, normally, the timing signal generator 5 operates the transistors Q3 and Q4 to emit light.
When the control device 4 receives the first A / D conversion signal or the COMP signal and determines that it is an overflow, it controls the timing signal generation device 5 to turn on the transistor Q5 instead of the transistor Q3. Therefore, the current flowing through IRED2 is limited to V _BE (about 0.7 V) / R4 of the transistor Q6, and the emission power can be gradually reduced.

According to the third embodiment described above, the light projection intensity of the subsequent light projecting means is changed based on the first A / D conversion result, so that the dynamic resolution is achieved while using the A / D converter having a low resolution. It is possible to perform a range-finding operation with a wide range.

FIG. 9 is a circuit diagram of a distance measuring device showing a fourth embodiment of the present invention. The difference between the fourth embodiment and the above-mentioned embodiments is that the capacitance of the integrating capacitor is changed by providing two kinds of integrating capacitors. By changing the value, the dynamic range of the A / D converter 3 can be widened. That is, the integrating capacitor C3 in the first and second embodiments is
In addition to C4, capacitors C6 and C7 and operational amplifier A5
A6 is provided and the analog switches ASb1 to ASb4 and AS are controlled by the control signal from the timing signal generator 5.
c1 to ASc4 are turned on and off. Except for this point, there is no difference from each of the above-described embodiments, and therefore, the same components are designated by the same reference numerals and the description thereof will be omitted.

According to the fourth embodiment, by varying the capacitance value of the integrating capacitor, it is possible to perform a distance measuring operation with a wide dynamic range while using an A / D converter with low resolution.

FIG. 10 is a time chart of the distance measuring apparatus according to the fifth embodiment of the present invention, in which the light emission interval of the IRED is shortened from the middle so that the dynamic range can be widened. According to the fifth embodiment, it is particularly effective in measuring a long distance subject. Normally, if the light emission interval of the IRED is too short, the IRED will be damaged, but there is no problem if it is only for a long distance.

According to each of the above-described embodiments, the number of times the reflected light current of the object is integrated, the integration time per time, the integration voltage, the capacitance value of the integration capacitor, the integration interval, or the light projection intensity from the light projecting means is variable. To lower the resolution A /
While using the D converter, the dynamic range can be expanded to realize inexpensive and highly accurate AF.

[0046]

As described above, according to the present invention, at the initial stage of a plurality of light projecting operations by the light projecting means, the signal current from the light receiving means for receiving the reflected light of the light projecting signal from the object is changed. The number of integrations of the output current, the integration time per one time, the capacity of the integration capacitor, the integration interval, or the light projecting means of the light projecting means so that the output of the capacitor to be integrated falls within the range of the dynamic range of the A / D conversion means. Since the elements that change the dynamic range, such as the intensity of light projection, are controlled, the remarkable effect that distance measurement with a wide dynamic range can be performed even with an A / D converter having a low resolution is exhibited. It

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing an internal configuration of an analog switch shown in FIG.

FIG. 3 is a time chart of the operation of each part in FIG.

FIG. 4 is a flowchart of a distance measuring operation in the first embodiment.

5 is a subroutine "S-AF6" shown in FIG.
The flowchart which shows the detail of 0 ".

FIG. 6 is a circuit diagram of a distance measuring device showing a second embodiment of the present invention.

FIG. 7 is a flowchart of a distance measuring operation in the second embodiment.

FIG. 8 is a circuit diagram of a main part of a distance measuring device showing a third embodiment of the present invention.

FIG. 9 is a circuit diagram of a distance measuring device showing a fourth embodiment of the present invention.

FIG. 10 is a time chart of a distance measuring device showing a fifth embodiment of the present invention.

FIG. 11 is an optical path diagram of an active triangulation method.

FIG. 12 is a circuit diagram of a main part of a conventional distance measuring device.

13 is a diagram for explaining the double integration operation in FIG.

[Explanation of symbols]

1 ………………………… PSD (light receiving means) 2 ………………………… IRED (projecting means) 3 ………………………… A / D converter ( A / D conversion means) 4 ... Control device (control means, calculation means) 5 ... Timing signal generator (control means) C3, C4, C6 , C7 ... Capacitor

Claims (1)

[Claims] 1. A light projecting means for projecting a light flux toward an object a plurality of times, a light receiving means for receiving reflected light of the light flux from the object, photoelectrically converting the light, and outputting a current signal, and the current. A capacitor for integrating a signal, an A / D conversion means for A / D converting the output of the capacitor, and an initial stage of a plurality of light projecting operations by the light projecting means,
The number of integrations of the output current, the integration time per time, the capacity of the integration capacitor, the integration interval or the projection of the light projecting means so that the output of the capacitor falls within the range of the dynamic range of the A / D converting means. A measuring unit comprising: a control unit that controls an element that changes the dynamic range such as light intensity; and a calculating unit that calculates the distance to the subject based on the output of the A / D converting unit. Distance device.