JP3236095B2 - 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 a distance measuring apparatus for detecting a subject distance, and more particularly, to projecting a pulse light such as an infrared light to the subject and detecting the subject distance based on the reflected light from the subject. The present invention relates to an active distance measuring device for detecting the distance.

[0002]

2. Description of the Related Art Generally, an autofocus (AF) device applied to a still camera, a video camera, and the like generally includes two types.

[0003] One is a passive system using luminance distribution information of a subject, and the other is a so-called active system in which a signal is projected by itself and a distance is measured by a reflected signal.

[0004] Of these, the active system has a simple configuration and is inexpensive, so its penetration rate is high. However, the biggest disadvantage is that the reflected signal becomes smaller as the distance increases.
At long distances, it is very difficult to separate this signal from noise and perform distance measurement calculation.

The method of projecting infrared rays is disclosed in
As disclosed in Japanese Unexamined Patent Publication No. 19116 and Japanese Unexamined Patent Publication No. 63-132110, by repeating a synchronous integration operation, noise generated at random is canceled out, and a signal component is separated to thereby achieve a high-precision distance. Suggestions have been made to achieve it.

Here, a configuration of a generally known active AF device will be described with reference to FIG. Referring to FIG. 1, light emitted from an infrared light emitting diode (hereinafter abbreviated as IRED) 1 is condensed by a light projecting lens 2 and irradiated toward a subject 3. The reflected light is imaged by a light receiving lens 4 on a well-known position detecting element (hereinafter, abbreviated as PSD) 5 made of a semiconductor element. This P
In SD5, the photocurrents I ₁ and I ₂ according to the imaging position
Are split, and the split photocurrents I ₁ and I ₂ are supplied to the AF IC 6. The AF IC 6 drives the IRED 1 via the IRED driving transistor 7 in a pulsed manner, and supplies the CPU 8 with distance measurement data based on the photocurrents I ₁ and I ₂ from the PSD 5.

On the other hand, a light receiving element 9 for exposure control (hereinafter abbreviated as EE) for converting the brightness of a subject into an electric signal is
In combination with the E IC 10, the proper exposure is controlled. The CPU 8 controls the sequence of the entire camera, and also performs calculations for driving the shutter opening time, the focus adjustment lens, and the like. The output of the CPU 8 drives a motor 12 which is a power source for performing shutter and film winding and lens extension by a driver 11.

Here, the operation principle of the infrared light projection type triangulation which measures the object distance by the PSD 5 will be described. When the optical axis of the light receiving lens 4 is made coincident with the center line of the PSD 5 and this is set as the origin, the incident position of the reflected light is x, and the distance between the principal points between the light projecting lens 2 and the light receiving lens 4, that is, the base line length is S. If the focal length of the light receiving lens 4 is f ₀ , the subject distance L is given by the following equation (1).

[0009]

(Equation 1)

[0010] By the reflected light of the subject by the IRED1,
The photocurrents I ₁ and I ₂ generated in the PSD ₅ are both proportional to the intensity of the reflected light, but the photocurrent ratio I ₁ / I ₂ does not depend on the intensity of the reflected light but is determined only by the incident light position x. Assuming that the total length of the PSD 5 is t, the photocurrent ratio I ₁ / I ₂ is represented by the following equation (2).

[0011]

(Equation 2) By substituting equation (1) into equation (2), equation (3) is obtained.

[0012]

(Equation 3) Therefore, if the photocurrent I ₁ / I ₂ of the PSD ₅ is determined, the subject distance L is uniquely determined. By transforming the above equation (3), the equation (4) is obtained.

[0013]

(Equation 4) At a short distance where the photocurrents I ₁ and I ₂ are sufficiently large, the distance information L can be obtained with high accuracy from the equation (4). That is, it is expressed as in equation (5).

[0014]

(Equation 5)

By calculating I ₁ / (I ₁ + I ₂ ) (ratio calculation) in this way, the subject distance can be obtained. To improve the accuracy of the distance detection, simply calculate the distance. Circuits that perform operations many times to obtain the average value are widely known.

[0016]

However, as the distance increases, the circuit noise components I _N1 and I _{N2 which} cannot be ignored become smaller than I ₁ / (I ₁ + I ₂ ) in the above equation (5). _They are superimposed in the form of (I ₁ + I _N1 ) / (I ₁ + I ₂ + I _N1 + I _N2 ). No matter how much the average value is obtained in a form in which the error is superimposed, it is difficult to obtain a correct value.

In the circuits disclosed in the above-mentioned Japanese Patent Application Laid-Open Nos. 60-19116 and 63-132110, the direction of integration of the photocurrent is switched so that the noise canceling effect by the integration and the operation of the ratio operation are obtained. Is also aiming. However, in such a method, since the number of integrations becomes the resolution of the distance measurement as it is, a long distance measurement time is required to obtain a predetermined resolution, which greatly affects the shutter time lag when applied to a camera. Met.

In the former case, in particular, a power control, a gain control, or a circuit similar thereto is required for the application of the double integration type A / D converter. This is because the dynamic range of the signal light current reaches 300 times.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a simple configuration of a distance measuring apparatus which is not affected by an error due to a circuit noise component even at a long distance, and has measures against time lag and dynamic range. The purpose is to provide.

[0020]

That is, the present invention comprises a light projecting means for projecting a light beam toward a subject, and a first light receiving means for receiving the reflected light of the light beam from the subject, at a rate corresponding to the subject distance. Light receiving means for outputting a photocurrent and a second photocurrent ;
Adding means for adding the first and second photocurrents;
First integrating means for integrating the output of the means, second integrating means for integrating the first photocurrent , the first photocurrent and the second
Calculate the distance to the subject based on the ratio of photocurrent
First calculating means, an output of the first integrating means and the second product
Calculates the distance to the subject based on the output of the minute means
Based on the output of the second calculating means and the output of the adding means.
A third calculating means for calculating a distance to the subject;
The first arithmetic means and the second arithmetic means are based on the first and second photocurrents.
Selection of selecting one of the two arithmetic means and the third arithmetic means
Means . The present invention includes a light projecting means for projecting a light beam toward an object, receiving the reflected light of the light flux from the subject, light receiving means for outputting a photocurrent corresponding to an object distance, of the light receiving means output
Integrating means for integrating the obtained photocurrent signal;
Using the output photocurrent signal and the integration result of the integration means,
The subject distance using three different types of ranging methods.
Calculating means for calculating, based on the output of the light receiving means,
Whether the subject is in the long range, medium range, or short range
Determining means for determining whether the area is within the range.
A distance measuring method based on the calculation means based on the determination result of the means
Is switched . Further, according to the present invention, there is provided a light receiving means for receiving an optical signal from a subject, and a first light receiving means for integrating an output of the light receiving means at a first timing.
A second integrating means for integrating the output of the light receiving means at a second timing different from the first timing.
, First calculating means for calculating the distance to the subject based on the output of the first integrating means, output of the first integrating means, and output of the second integrating means. And a second calculating means for calculating the distance to the subject based on the above, and after the operation of the first integrating means,
Whether to operate the second integration means according to the amount of integration
Is determined .

[0021]

According to the distance measuring apparatus of the present invention, a light beam is projected from the light projecting means toward the subject, and the reflected light of the light beam from the subject by the light projecting means is received by the light receiving means. The first photocurrent and the second photocurrent are output at a ratio according to the following. Then, the first and second photocurrents are added by adding means.
The output of the adding means is integrated by the first integrating means.
Then, the first photocurrent is integrated by the second integrating means.
Based on the ratio of the first photocurrent and the second photocurrent,
The distance to the object is calculated by the first calculation means, and the first product
Based on the output of the dividing means and the output of the second integrating means,
The distance to the subject is calculated by the second calculation means. Change
Then, based on the output of the adding means, the distance to the subject is calculated.
The separation is calculated by a third calculating means, and the first and second photocurrents are calculated.
Based on the first computing means, the second computing means,
One of the third calculation means is selected by the selection means. Also, in the distance measuring apparatus of the present invention, a light beam is projected from the light projecting means toward the subject, reflected light of the light beam is received from the subject by the light receiving means, and a photocurrent corresponding to the subject distance is output. Is done. The photocurrent signal output from the light receiving means is the product
Photocurrent signal integrated by the minute means and output from the light receiving means
And the integration result of the integration means are used to calculate
The subject distance can be measured using three different distance measurement methods.
Is calculated. Further, based on the output of the light receiving means,
Whether the object is in the long range, medium range, or short range
Is determined by the determining means. And the above
Based on the result of determination by the
The formula is switched. Further, in the distance measuring apparatus of the present invention, the light signal from the subject is received by the light receiving means, and the first
The integrating means integrates the output of the light receiving means at the first timing. Further, the output of the light receiving means is integrated at a second timing different from the first timing by the second integrating means. Further, the distance to the subject is calculated by the first calculating means based on the output of the first integrating means, and the output of the first integrating means and the second
The distance to the subject is calculated by the second calculating means based on the output of the integrating means. And the first integration
After the operation of the means, the second integrating means is operated in accordance with the amount of integration.
Is determined.

[0022]

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

FIG. 1 is a block diagram of the configuration of a subject distance detecting device showing the basic concept of the distance measuring device of the present invention. In the figure, IRED1, IRED driver 11, PSD
The arithmetic control circuit 7 including the light projecting lens 2, the light receiving lens 4, and the CPU has the same configuration as that of the conventional example shown in FIG.

The photocurrent outputs I ₁ and I ₂ of the PSD ₅ are
Preamplifiers 13 and 1 with low input impedance, respectively
The DC current component due to the steady light is separated by 4, and the respective outputs are input to the addition circuit 15 and the ratio calculation circuit 16, respectively. Then, the switch (SW) 17a is turned off, and S
W17b is during on, the first current I ₁ and the second current I ₂ of the summing current integrator circuit 18 that is summed by summing circuit 15
Is input to Here, a predetermined number of integration operations are performed in synchronization with the emission of the IRED1. Also, the ratio calculation circuit 16
Performs a ratio operation of the two currents I ₁ and I ₂ .

The outputs of the ratio calculation circuit 16 and the integration circuit 18 are input to the CPU 8. In addition, the integration circuit 18
W1 7 a on, SW1 7 b Off is capable of integrating only the signal current I _1. Further, the timing circuit 1
Reference numeral 9 causes the IRED 1 to emit light via the IRED driver 11 and performs integration timing, control of the SWs 17a and 17b, and the like.

In the distance measuring apparatus thus configured,
The operation will be described with reference to the flowchart of FIG. still,
It is the CPU 8 that controls the operation in the flowchart of FIG. 2 and the calculation of the distance measurement.

First, in step S1, I ₁ / (I ₁ + I
_The CPU 8 inputs the output of the ratio calculation circuit 16 for performing the calculation of ₂ ). The subject distance is obtained from the result according to the above equation (5). In step S2, the result L is changed to L _1.
(For example, 5 m). Here, L is if closer than L _1, the distance measurement result can be considered as a result a reliable obtained under sufficient S / N. Therefore, the process proceeds to step S7 to adopt this result, and focus is performed in step S8. On the other hand, in step S2,
L is farther than L _1, if further than L ₂ (e.g. 10 m), and calculates the distance from the output of the integrating circuit 18 proceeds to step S6.

At a long distance, it is difficult to detect not only the ratio calculation but also the signal. Therefore, the total signal light amount is used to determine whether or not the subject is a scene of infinity.
As described later, assuming that the reflectance of the subject is constant, I ₁
The distance may be calculated based on the principle that + I ₂ is inversely proportional to the square of the distance.

In steps S2 and S3, L becomes L ₁
If between the the L _2, the process proceeds to step S4, SW17a
Is turned on, the SW 17b is turned off, and the light emission and integration operation of the IRED 1 is repeated again. Thereby, since the integrated value of I ₁ is obtained from the integrating circuit 18, at step S5, with the integral value of I ₁ + I ₂ obtained above, I ₁ / (I ₁ +
The calculation of I ₂ ) is performed. In this calculation, since the ratio calculation is performed after the noise is smoothed by the numerator and the denominator and by the integration, the output is less scattered and more accurate than the ratio calculation circuit 16. Based on this result, focusing is performed in step S8 based on the distance L obtained by using equation (5). Then, shooting the sequence is completed. As described above, since the ratio calculation by integration is performed only at the distance of L ₁ ≦ L ≦ L ₂ , the distance measuring apparatus can be configured without worrying about the dynamic range. In addition, when the distance is not within the distance range, the time lag is shortened because the step does not pass through the step S4.

By the way, in the flowchart of FIG. 2, the adoption of the ratio operation after integration is determined from the result of the ratio operation. However, as shown in the flowchart of FIG. 3, the determination may be made by I ₁ + I ₂ .

That is, at step S11, I ₁ + I ₂
Is read out, and at steps S12 and S13, I ₁ + I
₂ and I _R1 and I _R2 are compared. Here, I _R1 and I _R2 are predetermined photoelectric flow rates. In this case, steps S2 and S3
The inequality sign is opposite to that shown in FIG. 2 because I ₁ + I ₂ decreases as the distance increases. The other steps S14 to S19 are the same as steps S4 to S9 in the flowchart of FIG. 2 described above, and a description thereof will be omitted.

FIG. 4 shows a second embodiment of the distance measuring apparatus more specifically constructed according to the basic concept of the present invention shown in FIG. However, in this embodiment, the portion of the ratio calculation circuit 16 in FIG. 1 is improved to have higher performance by integrating the output of the ratio calculation circuit a plurality of times. Further, the addition circuit 15 of FIG.
b is simply replaced as SW17.

[0033] That is, when turning on the SW 17, the collector current of the transistor 22a and 22b, that is I ₁ and the signal current depending on the I ₂ is integrated. And SW1
When turning off the 7, the collector current of the transistor 22b will not be integrated, so that the integral that depends only on I ₁ is performed.

In the same embodiment, the PSD 5, the amplifier 13,
Reference numeral 14 and the like have the same functions as those in FIG. 1 described above, and also amplify two signals of the photocurrents I ₁ and I ₂ generated by the PSD 5 and lead them to the adder 15 and the ratio calculator 16 for comparison. Since the systems are formed in exactly the same manner, only the circuit system for _one photocurrent I ₁ will be described here.
Circuit system of the optical current I ₂ is assumed to represent by replacing a reference number b.

When the camera is pointed at the subject, the subject is generally constantly illuminated by sunlight or artificial illumination light. The PSD ₅ outputs the steady photocurrent I ₀ due to these. In the AF calculation, it is necessary to remove the steady-state light current I ₀ and discriminate and extract only the signal light currents I ₁ and I ₂ by the IRED 1 (see FIG. 1).

Therefore, the operation of removing the stationary photocurrent will be described first. The distinction between the steady light current I ₀ and the signal light currents I ₁ and I ₂ is basically based on the fact that the component of the steady light current I ₀ does not change between the state in which the IRED 1 does not emit light and the state in which the IRED 1 emits light. Is determined by determining that the signal light currents are I ₁ and I ₂ .

Before the light emission of the IRED 1, the steady-state photocurrent I ₀ is sucked into the amplifier 13 (14) by a low input impedance and is amplified by the transistor 20a (20b). This amplified current is supplied to the current mirror circuits 21a and 23a (2
1b and 23b), the compression diode 26a (26
b). At this time, the compression diode 26a (2
When the potential of 6b) becomes high due to the inflow of the current I ₀ , the hold amplifier 28a (28b) operates to control the base potential of the transistor 30a (30b), so as to discard the steady light current I ₀ to GND. I do.

A constant current source 25a (25b) is connected to the input terminal on the plus (+) side of the hold amplifier 28a (28b).
Diode 26a biased by the constant current I _DB of
The voltage of the compression diode 33, which is also biased by the constant current source _DB by the constant current source 28a (28b), is supplied to the buffers 27a (27b) and 31 at the negative (-) side input terminal. Respectively. Therefore, the hold amplifier 28a (28
As long as b) is functioning, the compression diode 26a (26
In b), a current due to the steady photocurrent I ₀ does not flow. In other words, this circuit is stable with no current flowing between the lines indicated by the arrow X in the figure.

Next, when the IRED 1 emits light, it is input to the preamplifier 13 (14) with the signal light current I ₁ (I ₂ ) added to the steady light current I ₀ . At this time, the hold amplifier 28a is synchronized with the light emission of the IRED1.
Since (28b) is turned off, the steady-state photocurrent I ₀ is supplied through the transistor 30a (30b) based on the potential stored by the hold capacitor 29a (29b).
Discarded by ND. Here, only the signal light current I ₁ (I ₂ ) is amplified by the transistor 20a (20b),
Current mirror circuits 21a and 23a (21b and 23b)
Through the compression diode 26a (26b).
At this time, similarly to the constant current source 25a (25b) hold amplifier 28a is (28b), because it is turned off by a bias cut signal B outputted from the timing circuit 19 to the line indicated by reference numeral B _0, compression diodes 26a compression voltage by only the signal light current I ₁ is generated in the. Similarly, the signal light current I ₂ flows into the compression diode 26b after the stationary light current I ₀ is removed.

The compressed voltages V _A and V _B are supplied to the transistor 3 via the buffers 27a and 27b, respectively.
4, 35, a constant current source 36, and an integration capacitor 37 . Also, this ratio operation circuit 16
Constitutes a second integration circuit 39 together with the reset circuit 38.

The ratio calculation circuit 16, when turning on the constant current source 36 in synchronization with the emission of IRED1, integration current I _INT
Satisfies the relationship of equation (6), so that the integration capacitor 37
Generates a voltage signal of the formula (7).

[0042]

(Equation 6)

[0043]

(Equation 7) Here, n is the number of times of light emission of the IRED ₁ and I ₀ is the constant current source 3
6, τ is one integration time, and C is the capacity of the integration capacitor 37. The reset circuit 38 includes an IRED
Prior to the light emission of 1, the potential of the integration capacitor 37 is set to an initial state, and serves to set the integration voltage V _INT = 0.

The arithmetic control circuit (CPU) 8 _reads the V _{INT in the} above equation (7) by A / D conversion. Since the equation (8) holds from the above equations (5) and (7), V _INT is obtained.
Distance information 1 / L is obtained from _INT .

[0045]

(Equation 8)

The above is the description of the ratio calculation circuit 16 in the embodiment.
Operation. Since the ratio operation signal is averaged over n times, the signal is guided to the light amount integration circuit by the above-described Lerr circuits 21a and 22a. Similarly, the amplified signal light current I
_{2. When} the SW 17b is on, the current mirror circuit 21
b, it is added to the above signal photocurrent I ₁ by 22b.

Here, the signal light current I is applied to the transistors 22a and 22b constituting the current mirror circuit.
_1, in addition to I ₂ is the bias current constantly flowing.
This is because the transistors 20a, 21a, 22a, 23
This is because a (20b, 21b, 22b, 23b) deteriorates the response of the IRED 1 to the signal current unless it is biased. Accordingly, in the state where the current of the line X becomes 0 by the above-described steady light removing operation, the current is biased by the constant current sources I _PB flowing from the constant current sources 24a (24b).

Therefore, the light quantity integration circuit is a circuit that removes the bias by the constant current source I _PB and integrates only the signal light currents I ₁ and I ₂ or I ₁ depending on the state of SW 17. In other words, the current flowing from the transistors 22a and 22b is removed before the light emission of the IRED _1, and the subtracted current I ₁ + I ₂ or I ₁ alone is integrated. The same operation is performed.

The switching circuit connected to the addition circuit 15 has a switch SW4 before the light emission of the IRED1.
2 and 43 are on and SWs 40 and 41 are off, so that 2I
_PB is discarded to GND by the operation of the hold amplifier 46. This is because, when a current flows through the resistor 45, the voltage drop is detected by the hold amplifier 46 and the transistor 48 is controlled. That is, in this case, when a current flows in the direction of arrow C in the figure, the potential of the + input terminal of the hold amplifier 46 increases. Then, the transistor 48 tries to increase the collector current to suppress the flow in the arrow C direction. Conversely, when a current is to flow in the direction indicated by arrow D, the potential of the negative input terminal of the hold amplifier 46 rises, and the transistor 48 reduces the collector current to suppress the flow in the direction indicated by arrow D. .

As described above, no matter which direction the current flows through the resistor 45 due to the noise component included in the bias current 2I _PB , this circuit removes the current sensitively.

Next, when the IRED 1 emits light, the SW 42
And 43 are turned off by the integration signal INT from the timing circuit 19, and SWs 40 and 41 are turned on. Based on the charge stored in the hold capacitor 47, the bias current is discarded by the transistor 48 while the signal light current I ₁ , Only the current based on I ₂ is introduced into the first integration circuit 18 along the path in the direction of arrow E in the figure. The first integration circuit 18 is configured by a light quantity integration circuit including an integration amplifier 49 and an integration capacitor 50, and integrates the signal light currents I ₁ and I ₂ .

This integration is based on the amplification transistor 20
Assuming that the current amplification factors of the a and 20b are β, the integrating amplifier 49
The output voltage V _pINT is expressed by the equation (9) when the switch SW17 is turned on.

[0053]

(Equation 9)

[0054] Here, the C _p is the capacitance of the integrating capacitor 50. Similarly to the above ratio operation, the reset circuit 5
1 serves to reset the output voltage _VpINT of the integrating amplifier 49 to an initial state before the light emission of the IRED1. And
The CPU 8 _{reads the VpINT} by A / D conversion, and _obtains distance information 1 / L according to the expression (13) described later. Here, assuming that the reflectivity of the subject is constant and that the projected spot of the IRED 1 hits the subject entirely, Expression (10) is obtained based on the principle of light diffusion.

[0055]

(Equation 10) Here, assuming a noise current I _N, it is shown in equation (11).

[0056]

[Equation 11] Before performing the square root operation, the equation (12) is obtained.

[0057]

(Equation 12)

Here, the above equation (12) will be considered. The In this equation, if the moment of short distance measurement, a large difference is not in error △ 1 / L noise components I _N gives a long time the distance measuring operation, the difference in performing a number of times Occurs. That is, since the noise component _IN is random noise, the closer to integration, the closer to zero. Therefore, the above equation (12) approaches 0 as the integration is made, and the error becomes smaller. Therefore, the above (10)
Equation (13) is obtained from the equation (9) and the distance information 1
/ L can be obtained.

[0059]

(Equation 13)

FIG. 5 is a timing chart showing the operation of the AF circuit described above. As shown in the timing chart, the integration of the ratio operation and the light amount integration are performed simultaneously, and the respective results are obtained by a known double integration type A / D conversion method, the time of the second integration by a predetermined current, t. _1, t _2,
The data is input to the CPU 8 at t ₃ and t ₄ . That is, C
The PU 8 may count this time with a built-in clock. There is also a method in which the integrated voltage itself is directly read by the built-in A / D converter at the timings a, b, c, and d in the drawing.

Further, as described in the flowcharts of FIGS. 2 and 3 above, when the subject is not within the predetermined distance range, these integration operations need to be performed only once. In this case, after the SW 17 is turned off, integration is performed again as shown in FIG. That is, if n is constant, the relationship as shown in Expression (14) is established.

[0062]

[Equation 14] Therefore, the CPU 8 can perform the post-integration ratio calculation, which is the object of the present invention, by calculating t ₃ / t ₁ .

As described above, in this embodiment, t ₁ at a long distance.
The distance calculation is performed using t ₃ / t ₁ for the medium distance and t ₂ for the short distance. Therefore, it can be said that there are three distance measurement methods. However, only two distance measuring means, the above-mentioned calculating means and light quantity integrating means, are required.

The above-mentioned constant K is the light amount of IRED 1, P
It varies greatly depending on the photoelectric conversion efficiency of the SD5, the amplification factor of the preamplifiers 13 and 14, and the dispersion of the AF projecting / receiving lenses 2 and 4. However, here, by using the storage circuit 52, correction data for correcting these variations for each product is stored, and the distance measurement calculation by the above equation (10) is realized with higher accuracy. Making it possible.

Next, referring to the flowchart of FIG.
The calculation of the actual distance by the subject distance detecting device having the two distance measuring means will be described. In this flowchart, the above equation (13) is simplified to a form like the equation (15), but I _p DATA is a digital value _obtained by the CPU 8 reading the SW 17 and the signal V _pINT at the time of ON.

[0066]

(Equation 15) In the above equation (8), a digital value obtained by reading the ratio operation signal V _INT by the CPU 8 is expressed as AD, which is simplified to a form as shown in the equation (16).

[0067]

(Equation 16) In addition, SW17, the light intensity integration signal _VpINT1 at the time of OFF is _set to A /
Assuming that the D-converted value is I _p DATA1, the relationship as shown in equation (17) holds.

[0068]

[Equation 17] Here, K, A, B, A ₁ , and B ₁ are constants.

In the flowchart of FIG. 6, first, in step S21, the SW 17 is turned on, and the count value n of the number of times of light emission is initialized to "0". Next, in step S22, the light emission of the IRED 1 and the integration operation are performed. Step S
At 23, n is incremented by the number of times of light emission of the IRED1, and then the light emission / integration operation is repeated until the light emission end is determined 16 times at step S24. Also,
Step S25 is the reading of I _p DATA by double integration. This start point corresponds to the point a in the timing chart of FIG.

Next, in step S26, a distance calculation is performed according to equation (15). Based on this result, the embodiment determines which of the three distance measurement methods is to be adopted. This determination is performed in steps S27 and S30. Here, if it is determined that the distance is less than 5 m (1 / L> １ ／),
In step S28, the CPU 8 inputs the result of the ratio calculation. Then, in step S29, a distance measurement operation is performed by the equation (16).

If it is determined in steps S27 and S30 that the distance is more than 10 m (1 / L ≦ 1/10), the process branches in step S30 to determine whether the distance is equal to the distance obtained in step S26. Focusing is performed. Further, when the distance is between 5 m and 10 m, the process proceeds to step S31, and the count value n of the number of integrations is initialized again. Here, SW17 is turned off and IRED is again
The light emission of 1 and the arithmetic integration are performed (Steps S32 to S
34).

Then, c in the timing chart of FIG.
At this point, the CPU 8 reads I _p DATA ₁ (step S35), and in step S36, performs the distance measurement calculation according to the above equation (17).

In the example of FIG. 6, there is a slight difference from the timing chart of FIG. 5. When the light emission of the IRED 1 is performed in step S32, the ratio calculation reading of b to b 'of FIG. We are trying to reduce time. FIG. 7 (a)
FIGS. 7A to 7C are graphs showing distance measurement results obtained by the subject distance detection device of the present invention.

In FIG. 7A, the solid line shows the result of the ratio calculation, and the broken line shows the distance measurement result of the ratio calculation after integration. As shown in the figure, S / N is degraded enough to become far, it is understood that variations W ₁ increases. This variation before exceeding the permissible amount (L _CH2以近), so as to adopt the results of the integration after the ratio calculation.

However, if the ratio calculation after integration is performed more than necessary to a short distance, a power control and gain control circuit is required in consideration of the dynamic range of the integration circuit as described above. The time lag is long as shown in FIG. With these ratio calculation methods, distance measurement that does not depend on the reflectance of the subject is possible. Next, it will be described that the influence of the reflectance is reduced in a farther distance range.

FIG. 7B shows the result of light quantity integration. Variation due to noise is small due to the canceling effect due to integration. Rather, variation due to the reflectance of the subject is the main factor of the variation W ₂ . However, considering that the reflectivity of the general subject to the signal light of the IRED 1 is 30% to 70%, when the above equation (15) is satisfied for the intermediate 50% reflectivity, the infrared reflection The I _p DATA for a subject with a rate of 30% is given by equation (18), and the I _p DATA for a subject with an infrared reflectance of 70% is (1)
Equation 9) is obtained.

[0077]

(Equation 18)

[0078]

[Equation 19] Since the difference in the variation is represented by Expression (20), the greater the subject distance L, the smaller the difference.

[0079]

(Equation 20)

This is just the opposite of the variation due to the ratio calculation. By combining this light amount integration method with the above-described ratio calculation or the ratio calculation after integration, as shown in FIG. In addition, it is possible to provide a high-accuracy distance detecting device with little variation from a long distance to a short distance. However,
In a camera that does not need far distance measurement, the distance measurement based on the light amount integration may be omitted.

In order to further reduce the time lag, an embodiment as shown in FIG. 8 can be considered. In the embodiments described below, the same parts as those in the above-described embodiments are denoted by the same reference numerals, and description thereof will be omitted.

In the third embodiment shown in FIG. 8, two light quantity integrating circuits are prepared so that signals depending on the photocurrents I ₁ and I ₁ + I ₂ can be simultaneously integrated. First
The output of the integration circuit 18 is I _p DATA, the second integration circuit 39
Is I _p DATA1.

The short distance range is covered by the output of the ratio calculation circuit 16, and the long distance range is subjected to the ratio calculation after integration from these integrated outputs. The timing circuit 19 of FIG. 1 is shared by the CPU 8 in the third embodiment. Next, FIG.
The operation of this circuit will be described with reference to the flowchart of FIG.

In this embodiment, first, at step S41, I
The RED1 emits light, and is received at both ends of the PSD5, integrated, and a ratio operation is performed to obtain 1 / L. Then, step S
At 42, it is determined whether or not L is greater than 5 m. If L is greater than 5 m, the same processing as in steps S31 to S36 in the flowchart of FIG. 6 is performed in steps S43 to S48.

In the third embodiment, since the result of the integration operation is adopted only at a distance of 5 m or more, the dynamic range of the integration circuit need not be so large. Therefore, power control, gain control, etc. are not required.

FIG. 10 shows, as a fourth embodiment of the present invention, an example of high precision using a multi-electrode PSD 5a having an intermediate electrode. This is different from the example of FIG. 8 in that the second integration circuit 39 is connected to the amplifier 13a that amplifies the output of the intermediate electrode of the PSD 5a.

The multi-electrode PSD 5a is a PSD capable of changing t in the above equation (4). For example, when the intermediate electrode is provided at a half of t, the equation (4) 'is obtained from the equation (4). Can be

[0088]

(Equation 21)

Thus, the output I ₁ / (I ₁ + I ₂ )
Changes with a slope twice that of the equation (4). In other words, for a small change in L, I ₁ and I ₂ are extracted at a minute portion sandwiching the portion where the reflected signal light enters, and I ₁ / (I ₁ +
It is clear from this equation that the calculation of I ₂ ) is more accurate.

However, when t is used with a small value, the distance range in which the distance can be measured becomes short. Therefore, in the case of the multi-electrode PSD, the distance measurement must be divided into two times. First, PS
The distance is measured using the total length t of D, and only when the result is within a predetermined distance range in which the distance can be measured within the range of t / 2, the distance is again measured using the t / 2 portion. .

The post-integration calculation of the present invention also requires two distance measurements as in steps S41 and S44 in FIG.
The fourth embodiment shown in FIG. 10 realizes more accurate ranging within the same time by combining these.

The fourth embodiment has the characteristic that, when both ends of the PSD are used and when the intermediate electrode is used, I ₁ + I ₂ is the same because of the total amount of light incident on the PSD. We are using. In the fourth embodiment, FIG.
By adopting the flowchart of (a), highly accurate ranging can be performed in a shorter time.

In FIG. 11A, first, at step S
At 51, the preamplifiers 13 and 14 for amplifying the signals at both ends of the PSD 5 a are enabled, the IRED 1 emits light, and 1 / L is calculated from the output of the ratio calculation circuit 16. At this time, the input of the intermediate electrode preamplifier 13a is open. The CPU 8 can detect the integrated value of I ₁ + I ₂ by inputting the output of the adding circuit 15 to the first integrating circuit 18 and performing the integrating operation by the light emission of the IRED ₁ .

Next, in step S52, it is determined whether or not L is greater than 5 m. If L is more than 5 m, the process proceeds to step S53, where the integration and detection of I ₂ + I ₃ is omitted, and the integration and detection of I ₃ are performed. At this time,
The light spot consists of the intermediate electrode and the PS near the IRED1.
The position of the PSD is determined so as to be incident between the D end electrodes. Thus, the preamplifier 13 is an open state input, and only the pre-amplifier 13a and 14 in the enabled state, IRED emission at the output of the second integrating circuit 39, CPU 8 detects the integrated value of I _3.

Thereafter, at step S54, the integrated value of I ₁ + I ₂ obtained earlier and the integrated value of I ₃ are used.
By performing the same calculation as the expression (16), it is possible to perform a highly accurate distance measurement calculation in a shorter distance measurement time. A ₂ ,
B ₂ are constants.

FIG. 11B is a flowchart simply showing an example in which the present invention is used in combination with the multi-electrode PSD. However, in this case, the integration operation and the like are omitted and simplified.

First, in step S55, FIG.
As in step S51, the IRED 1 emits light and the PSD
The light is received at both ends of 5a, integrated, ratio operation is performed, and 1 / L is obtained. In step S56, the same operation as in step S52 in FIG. 11A is performed. When the result is less than 5 m, focusing is performed based on the result as in the flowchart in FIG. If it is far, the process branches to step S57,
This time, with the intermediate electrode of the PSD 5a and one end electrode of the PSD 5a being used, the IRED 1 emits light and the first integration circuit 18 integrates I ₃ + I ₂ .

Next, at step S58, the IRED
The first light emission and the second integration circuit 39 integrate I ₃ . Then, these are calculated in step S59 to obtain focusing information.

Here, I ₂ + obtained in step S57
I ₃ is equal to I ₁ + I ₂ when measured using the entire length of the PSD, regardless of the length of the PSD, if the reflected signal light spot is correctly incident.

FIG. 12 shows a fifth embodiment in which the calculation of I ₁ / (I ₁ + I ₂ ) is not performed. This basic configuration is the same as that of FIG. 1 except that a comparator 54 is connected to the output of the first integration circuit 18. The comparator 54 is connected to a constant voltage source 53, which compares the integration result with a constant voltage V _COM and inputs to the CPU 8 whether or not the integration result has reached a predetermined level.

FIG. 13 is a flowchart showing the distance measurement using such a circuit without performing the calculation of I ₁ / (I ₁ + I ₂ ) in the CPU 8 as described above.

In step S61, as in FIG.
This is a step in which the CPU 8 emits 1 and the CPU 8 inputs the distance measurement result of the ratio calculation. Then, likewise, with a predetermined distance L ₁ at step S62. In the case of a short distance, the distance according to the equation (5) is adopted via step S63.

Then, the process branches off from step S62, and in steps S64 and S66, the switch 17a is turned off, the switch 17b is turned on, and the integration of I ₁ + I ₂ is performed by the voltage source 53.
Is repeated until a predetermined voltage _VCOM is reached. Then, the number of integrations n until reaching the predetermined voltage is counted in step S65. Then, equation (9) 'is obtained from equation (9).

[0104]

(Equation 22) Therefore, the number of integrations n is as shown in equation (21).

[0105]

(Equation 23)

Next, with OFF ON, the SW17b the SW17a in step S67, the only I ₁ integrating n times.
Since V _PINT = A · I ₁ · n as in the above equation (9) ′, equation (22) is obtained from equation (21).

[0107]

(Equation 24)

Next, in step S68, the CPU 8 inputs the integration result V _PINT of this I ₁ . As is apparent from the above equation (22), V _PINT itself is output as a result of the calculation even when the CPU 8 does not calculate I ₁ / (I ₁ + I ₂ ). Since V _COM is a constant, the CPU 8 proceeds to step S
At 69, I ₁ / (I ₁ + I ₂ ) is obtained from V _PINT / V _COM , and the distance measurement can be performed based on the above equation (5). In this embodiment, since only once the process of CPU8 to input data by converting A / D, smaller quantization error compared to the embodiment described above enables more accurate distance measurement.

As in the flow chart shown in FIG. 14A, an embodiment in which the step of step S61 in FIG. 13 is omitted and the distance is determined from the number of integrations n in steps S64 to S66 is also possible. In this embodiment, FIG.
Step S7 instead of step S62 for determining the perspective
At 0, the branch to step S63 is determined. That is, I
₁ + integrated amount per time integral of I ₂ is the distance increases nearer, integration count up to a predetermined voltage V _COM is considered as decreases when the distance measuring a short distance. Therefore, it is only necessary to branch to step S63 when the number of integrations n is smaller than the predetermined number of integrations n _CON .

Further, using the circuit shown in FIG. 12, an embodiment as shown in the flowchart of FIG. 14B is also possible. In this case, steps S64 to S66, S7
0, S63 is similar to FIG. 14 (a), the not performed n times the integral of I ₁ in this embodiment, similar to the integral of I ₁ + I _2, the process of step S71, S72, S73 , Integrates I ₁ until a predetermined voltage V _CON is reached,
The integration number n is counted. At this time, the above (2)
Equation (21) 'is obtained in the same manner as equation (1).

[0111]

(Equation 25) That is, if n / n ₁ is calculated, equation (23) is obtained.

[0112]

(Equation 26)

Therefore, in step S74, this n
_{From 1} / n, if the distance measurement calculation is performed using the above equation (5),
The distance can be calculated. In this embodiment, since it is not necessary to read out the integrated voltage, A /
The need for a D converter is eliminated.

[0114] Also, even if V _COM varies with temperature, etc., as is clear in (23), since the offset if constant in the process of obtaining the n ₁ and n, the temperature characteristic in the configuration of the V _COM There is an advantage that it is not necessary to consider. In the above-described embodiment, the first and second integrating circuits may be switched by a switch so as to be shared by one integrating circuit.

[0115]

As described above, according to the present invention, there is provided a distance measuring apparatus having a simple structure which is not affected by errors due to the circuit noise component even at a long distance, and measures against time lag and dynamic range. can do.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of a subject distance detection device showing a basic concept of a distance measurement device of the present invention.

FIG. 2 is a flowchart illustrating an operation of the distance measuring apparatus in FIG. 1;

FIG. 3 is a flowchart illustrating another operation of the distance measuring apparatus in FIG. 1;

FIG. 4 is a circuit diagram specifically configured in a second embodiment of the distance measuring apparatus of the present invention.

FIG. 5 is a timing chart showing an operation of the AF system.

FIG. 6 is a flowchart illustrating an actual distance determination of a subject distance detection device having two distance measuring means.

FIG. 7 is a graph showing a result of distance measurement by the subject distance detection device of the present invention.

FIG. 8 is a circuit diagram showing a third embodiment of the present invention,
One prepared a block diagram of a distance measuring apparatus which can integrate the signal depending on the photocurrent I ₁ and I ₁ + I ₂ simultaneously.

FIG. 9 is a flowchart for explaining the operation of the distance measuring apparatus in FIG. 8;

FIG. 10 is a block diagram of a distance measuring apparatus using a multi-electrode PSD having an intermediate electrode as a fourth embodiment of the present invention.

FIG. 11 is a flowchart illustrating an operation of the distance measuring apparatus in FIG. 10;

FIG. 12 shows a fifth embodiment of the present invention,
FIG. 2 is a block diagram of a distance measuring apparatus that does not perform the calculation of ₁ / (I ₁ + I ₂ ).

FIG. 13 is a flowchart illustrating an operation of the distance measuring apparatus in FIG. 12;

FIG. 14 is a flowchart illustrating another operation example of the distance measuring apparatus in FIG. 12;

FIG. 15 is a block diagram showing a configuration of a conventional active AF device.

[Explanation of symbols]

1. Infrared light emitting diode (IRED) 2. Projection lens,
3 subject, 4 light receiving lens, 5 position detecting element (PS
D), 6: AF IC, 7: IRED driving transistor 7, 8: Operation control circuit (CPU), 9: Exposure control (E
E) light receiving element, 10 ... EE IC, 11 ... driver,
12 ... motor, 13, 13a, 14 ... preamplifier, 15
... Addition circuit, 16 ... Ratio operation circuit, 17, 17a, 17b
... switch (SW), 18 ... integration circuit, 19 ... timing circuit.

Claims (3)

(57) [Claims] 1. A light projecting means for projecting a light beam toward a subject, receiving a reflected light of the light beam from the subject, and outputting a first light current and a second light current at a ratio corresponding to the subject distance. Light- receiving means, an adding means for adding the first and second photocurrents, a first integrating means for integrating the output of the adding means, a second integrating means for integrating the first photocurrent, based on 1 photocurrent and the ratio of the second photocurrent, a first calculating means for calculating a distance to the subject, and the output of the output and the second integration means of the first integration means
Second calculating means for calculating the distance to the subject based on the second calculating means
And the distance to the subject based on the output of the adding means.
A third calculating means for calculating , the first calculating means based on the first and second photocurrents,
Select either the second operation means or the third operation means
Distance measuring apparatus characterized by comprising a selection means, the that. A light projecting means for projecting a light beam 2. A toward a subject, receives the reflected light of the light flux from the subject, light receiving means for outputting a photocurrent corresponding to an object distance, of the light receiving means Integrating means for integrating the output photocurrent signal
And the product of the photocurrent signal output by the light receiving means and the integrating means
By using the minute result and three types of ranging methods with different methods
Calculating means for calculating a subject distance; and, based on an output of the light receiving means, the subject is positioned in a long distance range.
Is in the middle, medium or short range
Comprising a that judging means, and based on the determination result of the determination means, by the calculating means
A distance measuring device characterized by switching a distance measuring method . 3. A light receiving means for receiving an optical signal from an object, a first integrating means for integrating an output of the light receiving means at a first timing, and a first timing for outputting an output of the light receiving means. A second integration means for integrating at a second timing different from the first integration means; a first calculation means for calculating a distance to the subject based on an output of the first integration means; the output of the integrating means, based on an output of said second integrating means, comprising second calculating means for calculating a distance to the subject, and after operation of the first integrating means, the integrating Above according to the quantity
It is determined whether or not to operate the second integrating means.
A distance measuring device characterized by the above-mentioned.