JPH05172564A - Active range finder - Google Patents

Abstract

PURPOSE:To enable the changing of projection time according to a stationary light AC component detected by improving errors in the measurement of distances because of change in background light under an AC light source in an active AF apparatus having a stationary light removing circuit. CONSTITUTION:AC component of a stationary light of an AF sensor (PSD) is detected with an AF sensor stationary light AC component detector 26 while the distance to an object desired to measure distances is detected by a focal point distance detector 27. Two detection outputs are supplied to an arithmetic device 28 for an IRED emission pulse width and the frequency of emission. Then, with the IRED emission pulse width/frequency of emission arithmetic device 28, the emission pulse width of an IRED is determined by computation to control an IRED drive circuit 29 based on the pulse width obtained thereby obtaining a value to satisfy a specified AF performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active distance measuring device, and more particularly to an active distance measuring device using an active autofocus (AF) stationary optical storage device.

[0002]

2. Description of the Related Art Active AF which has been conventionally used
The optical arrangement of is shown in FIG.
A light projecting lens 1 and a light receiving lens 2 whose optical axes are parallel to each other,
It has an IRED 3 for projecting infrared rays and a PSD 5 for receiving reflected light from the subject 4 which is the projected infrared rays. The position where the reflected light from the subject 4 is incident on the PSD 5 depends on the subject distance L. In addition, since the ratio of the output currents I ₁ and I ₂ of the PSD 5 changes depending on the incident position of the reflected light, the calculation of I ₂ / (I ₁ + I ₂ ) results in 1/1 as shown in FIG. A relationship proportional to L is obtained.

However, the light incident on the PSD 5 is IR
Not only the reflected light of the ED 3 but also so-called stationary light (hereinafter, referred to as I _{0 in} the symbol) such as sunlight or room illumination light is included. Therefore, the stationary photocurrents I ₀₁ and I ₀₂ are usually flowing out from the electrodes 1ch and 2ch of the PSD5.
When D is caused to emit light, the signal currents I ₁ and I ₂ are superimposed. What is proportional to the reciprocal of the subject distance, 1 / L,
It is just I ₂ / (I ₁ + I ₂ ). Therefore, usually I
A work of extracting only the signal current from the output currents of ₀₁ + I ₁ and I ₀₂ + I ₂ , that is, so-called stationary optical memory is required.

FIG. 15 is a circuit diagram of conventional stationary optical storage and signal light processing. In the figure, 3 is IRED, 5 is P
SD, 6 is an IRED control transistor, 7 is a preamplifier that determines the bias level of PSD 5, 8 is a transistor that amplifies the signal current of PSD 5, 9 is a diode that compresses the signal current, and 10 is a constant that determines the bias point of preamplifier 7. It is a current source. Further, 11 is a diode for balancing with the compression diode 9, 12 is a differential amplifier for storing stationary photocurrent, 13 is a transistor for supplying stationary photocurrent, and 14 is a capacitor for storing stationary photocurrent. Further, 15 is a differential amplifier for calculating the signal current of 1ch and 2ch of PSD5, 16 is an amplifier for initializing the integration capacitor, 17 is a feedback buffer, 18 is a comparator, 19 is an integration capacitor, and 20 is a constant current source. Is. SW1 to SW4
Represents a switch.

Before the IRED3 emits light, the feedback circuit indicated by C operates, and the steady photocurrent I of the PSD5 is generated.
_{All 01} (I ₀₂ ) flows to the transistor 13. Also, I ₀₂
A charge equal to the base voltage of the transistor 13 necessary to secure the capacitor is stored in the capacitor 14.

FIG. 16 shows a time chart of the circuit of FIG. 15, and as shown in FIG.
D3 emits light for 100 μs at intervals of about 2 ms. In conjunction with this, as shown in FIG.
1 turns off. When the switch SW1 is turned off, the amplifier 12 is turned off, so that the feedback loop shown by C in the figure is cut off, and the transistor 13 is connected to the capacitor 14
It continues to operate with the electric charge stored in. That is, the switch S
The steady-state DC photocurrent that turns off W1
13 keeps flowing. Therefore, the signal photocurrent I ₁ is amplified by the transistor 13. The switch SW2 is turned on when the switch SW1 is turned off, and charges the capacitor 19 with a slope proportional to I ₂ / (I ₁ + I ₂ ) of the signal currents I ₁ and I ₂ , and then the switch SW2 is turned on (c) in FIG. The potential drops as indicated by the integrated voltage of.

In this way, after the IRED 3 is made to emit light a predetermined number of times, the constant current source 20 is connected to the capacitor 19 by the switch SW4. As a result, the capacitor 19 is discharged and the potential rises as shown in FIG.
The output of the comparator 18 is inverted when _ref is reached (see (e) in the figure). Then, the value of I ₂ / (I ₁ + I ₂ ) can be obtained by measuring the time t ₁ in FIG.

[0008]

The long range performance of AF is I
It depends on the projected energy of the RED. Therefore,
When illuminating the IRED, it is desirable to illuminate it with the highest possible accuracy for a long time. The brightness of the IRED is determined by the process, chip size, etc. Further, the light emission time is limited to about 100 μs in the conventional stationary light storage system, as shown in FIG.

The reason for this will be described with reference to FIG.
There is no problem if the ambient light is a direct current light source such as sunlight,
In case of AC light source, steady photocurrent is 100Hz or 120
The wave is oscillating at a frequency of Hz (see (a) in the figure). Under such circumstances, the circuit shown in FIG.
When light is emitted for μs or more, as shown in FIG. 17B, a difference occurs between the time when the steady light is stored in the capacitor 18 and the actual light when the light emission ends (this value is Δ
I ₀₁ and ΔI ₀₂ ). Then, originally I ₂ / (I ₁ + I
₂ ) should be calculated, but when the light emission of the IRED3 ends, (I ₂ + ΔI ₀₂ ) / [(I ₁ + ΔI ₀₁ ) + (I
₂ + ΔI ₀₂ )] and an error occurs. The level at which this error can be ignored is 100 μs.

The present invention has been made in view of the above problems, and in an alliative AF apparatus having a stationary light removing circuit, an error between the time when the stationary light is stored and the actual stationary light at the time when the light emission ends. It is an object of the present invention to provide an active distance measuring device that improves the AF accuracy and improves the AF accuracy.

[0011]

That is, as shown in FIG. 1, an active distance measuring apparatus according to the present invention is a distance measuring object.
Projecting means 22 for projecting a light beam toward 21 and the distance measurement target
Light-receiving means 23 that receives the reflected light of the light flux from 21 and outputs a position signal according to the light-receiving position and a stationary light signal according to the stationary light, and to the distance measurement target 21 based on the position signal. The distance detecting means 24 for detecting the distance, and the light emitting time control signal for detecting the fluctuation component of the stationary light signal and controlling the light emitting time of the light flux based on the fluctuation component
By including the projection control means 25 for outputting to, the error between the time when the stationary light is stored and the actual stationary light at the time when the light emission ends is improved and the AF accuracy can be improved.

[0012]

In the active distance measuring apparatus according to the present invention, the luminous flux is projected from the light projecting means 22 toward the distance measuring object 21, and the reflected light of the luminous flux from the distance measuring object 21 is received by the light receiving means 23. The light receiving means 23 outputs a position signal corresponding to the light receiving position and a stationary light signal corresponding to the stationary light. Then, based on the position signal output from the light receiving means 23, the distance detecting means 24 detects the distance to the distance measuring object 21. In addition, the fluctuation component of the stationary light signal is detected by the light projecting control means 25, and the light emission time control signal for controlling the light emitting time of the light flux based on the detected fluctuation component is the light projecting means. It is output to 22. This allows
It is possible to improve the AF accuracy by suppressing the error of the stationary light AC component to be a predetermined value or less.

[0013]

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

First, the concept of the present invention will be described as a first embodiment with reference to FIGS. In FIG.
The vertical axis represents the current flowing through the PSD, and the horizontal axis represents time.
In the figure, the stationary photocurrent is shown by a triangular wave for simplification of description. When the constant light level is BV10 and the IRED emits 100 μs, the signal light of 100 μs is superimposed on the constant light level. IRE
If the stationary light is stored when D starts to emit light, the current ΔI ₀ becomes an error at the end of light emission. By the way, this Δ
When I ₀ is the allowable limit, all the currents of the stationary light at BV9 are 1/2 of BV10. Therefore, the light emission time of IRED reaching the allowable limit ΔI ₀ is 200 μs.
That is, if the steady light level flowing through the PSD becomes small, the AF accuracy due to the steady light storage error does not deteriorate even if the light emission time of the IRED is increased.

Accordingly, as shown in FIG. 2, the AF sensor stationary light AC component detecting device 26 detects the AC component of the stationary light of the AF sensor (PSD), while the distance to the object to be measured is detected by the focal length. Detected by the device 27, each detection output is supplied to the IRED light emission pulse width and light emission number calculation device 28. Then, in the IRED light emission pulse width light emission number calculation device 28, the light emission pulse width of the IRED is made variable.
By controlling the drive circuit 29, it is intended to satisfy a predetermined AF performance.

FIG. 3 is a second embodiment and is an explanatory view to which the concept of FIG. 1 is applied. In FIG. 3, in addition to the AF sensor stationary light AC component detecting device 26 and the focal length detecting device 27 of FIG.
Photometric device (BV) 30, film sensitivity detection device (SV) 3
1. Then, from the outputs of the photometry device (BV) 30 and the film sensitivity detection device (SV) 31, the AV (aperture value) at the time of actual shooting is predicted from BV and SV and calculated by the AV calculation device 32. This is reflected in the light emission pulse width and the number of times of light emission.

Here, the relational expression of the AF performance will be clarified with reference to FIGS.

The base length is S, the focal length of the light receiving lens 2 of the PSD 5 is f _j , the length of the PSD 5 is t, and the AFIC output when the reflected light of the IRED 3 is incident on the left end of the PSD 5 is D
Assuming that M (maximum value), as shown in FIG.
The relationship between (AFIC output) and the horizontal axis 1 / L is as shown in Equation 1.

[0019]

[Equation 1] Since the AFIC output fluctuates with each distance measurement, if the standard deviation is σ and its 3σ value is Δy, the above equation 1 is
Expressions 2 and 3 are obtained and can be transformed into an expression for obtaining the sensor error Δ (1 / L).

[0020]

[Equation 2]

[0021]

[Equation 3] Further, the standard deviation σ of the AFIC output has the relationship shown in the following Expressions 4 and 5.

[0022]

[Equation 4]

[0023]

[Equation 5] Taking the above relationship into consideration, Δ (1 / L) becomes as shown in Formula 5.

[0024]

[Equation 6] Here, L, I _V , t _P , and other than Equation 7 are constants determined at the time of design.

[0025]

[Equation 7] Therefore, if these are put together and set to A, it will become like Formula 8.

[0026]

[Equation 8] Further, the relationship between the subject distance L, the focal length f _TL of the photographing lens, and the lens extension amount is as shown in FIG.
Therefore, the equations 9 and 10 are obtained.

[0027]

[Equation 9]

[0028]

[Equation 10] Therefore, the error Δk given to the image plane by the sensor error Δ (1 / L)
(Defocus) is as shown in Expression 11.

[0029]

[Equation 11] Generally, the open F number is F ₀ , and the target permissible circle of confusion diameter is δ _0.
Then, the target permissible defocus amount Δk on the image plane in the open state is given by Expression 12.

[0030]

[Equation 12] Now, in order to satisfy the target permissible defocus amount at the distance of the image magnification of 1/50 (L = 50 f _TL ) and the aperture open, Δk
It is only necessary to satisfy the relation of> ΔK. Therefore, Equations 13 and 14 are obtained from Equations 11 and 12 described above.

[0031]

[Equation 13]

[0032]

[Equation 14] That is, the light emission pulse width per IRED or the number of times of light emission may be set according to the focal length of the taking lens and the open F number.

The above is the case of satisfying the predetermined circle of confusion diameter with the open F number, but in the actual shooting situation, the aperture value changes according to the subject brightness (BV) and the film sensitivity (SV). The number 15 does not necessarily have to satisfy the number 14.

[0034]

[Equation 15] For example, in the case of a camera having a program diagram as shown in FIG. 8, when the brightness of the subject is high, the relationship of AV = TV is established. By applying this to the relational expression of Apex, Equations 16 and 17 are obtained.

[0035]

[Equation 16]

[0036]

[Equation 17] Here, when substituting Formula 17 for F ₀ in Formula 14,
Equation 18 is obtained.

[0037]

[Equation 18] Therefore, when the subject brightness BV becomes brighter, it is possible to reduce the value of Expression 15 described above.

FIG. 9 shows a third embodiment of the present invention and is a block diagram schematically showing a main part of an active distance measuring apparatus. The signal light processing circuit is the same as the conventional example shown in FIG.

In the above-mentioned conventional example, the COM terminal of the PSD 5 was connected to V _DD , but in the present embodiment, it is connected to V _DD via the PNP transistor 33 which is diode-connected. The transistor 34 is the same as the transistor 33 described above.
It is a current mirror with the base and emitter connected together. The collector output of the transistor 34 is connected to the diode 35. The anode of the diode 35 is connected to the A / D converter 36. The result of A / D conversion by the A / D converter 36 is input to the stationary optical AC component detection device 37. Further, an A / D conversion command is output from the stationary light AC component detection device 37 to the A / D converter 36 at a predetermined timing. The detection result of the stationary light AC component detection device 37 is the IRED light emission pulse width / light emission number calculation device 28.
Is input to.

The output of the focal length detection device 27 such as a zoom encoder is also input to the IRED light emission pulse width / light emission number calculation device 28. The output of the IRED light emission pulse width / light emission number calculation device 28 is input to the IRED drive circuit 29, and the output of the IRED drive circuit 29 is connected to the IRED control transistor 6. The focal length detecting device 27 is used for a camera having a variable focal length.

Next, the operation of the embodiment will be described.

Before the distance measuring operation is started, the PSD 5 has
Steady light such as sunlight or AC light source is incident,
Transistor 33 in which the steady photocurrent I ₀ is flowing
Flows the same current as I ₀ flowing through the PSD 5. Since the transistors 33 and 34 have a current mirror configuration, I ₀ flows through the collector of the transistor 34. Then, this current I ₀ flows into the compression diode 35.
The voltage V _F between the anode and the cathode of the compression diode 35 is given by the _equation 19 and V _F is increased every time I ₀ is doubled at room temperature.
_T ln2 = 18 mV change.

[0043]

[Formula 19] The A / D converter 36 uses the A from the stationary light AC component detection device 37.
As shown in FIG. 10, the / D conversion instruction causes 100
A / D conversion is executed in a short cycle of μs, and the result is transmitted to the stationary optical AC component detecting device 37. In the stationary optical AC component detector 37, the maximum (MAX) value and the minimum (MI)
N) The value is stored and the AC component of the stationary light is recognized based on the difference. That is, when B is a constant of proportionality, the following equation 20 is obtained.

[0044]

[Equation 20] Allowable emission pulse width t ₀ of IRED3 under AC light source
Is calculated as in Expression 21 from FIGS. 4 and 17.

[0045]

[Equation 21] That is, the light emission time must be halved each time the amplitude of the AC light source is doubled.

IRED light emission pulse width and light emission frequency calculation device
In the case of 28, the value of equation 22 is transmitted from the stationary optical AC component detecting device 37, while the focal length detecting device 27 transmits the focal length f.
_TL is transmitted.

[0047]

[Equation 22] IRED light emission pulse width and light emission number calculation device 28
_TL, and the highest t _p and n from _Equations 14, 21 and 22
Ask for. First, according to Equation 21, under the current AC light source,
It is calculated to what extent the emission pulse width t _P per one time can be widened, and then t _P is used to obtain the required number of emission times n by the equation (14).

In general, when the number 22 is large, the visible light brightness BV is also high, so it is predicted that the diaphragm will be narrowed,
The number of times of light emission n may be fixed and only t _P may be calculated. The IRED drive circuit 29 is controlled on the basis of the obtained values of t _P and n. In addition, each switch SW1 in FIG.
.. to SW4 perform photometric operation by controlling at timings in the conventional example.

Next, referring to FIG. 11, the fourth embodiment of the present invention will be described.
An example will be described.

The above-described second embodiment satisfies the predetermined performance even when the diaphragm is open, but the fourth embodiment is based on the equation (18) and the diaphragm can be narrowed under high brightness. In the circuit of FIG. 9, a photometering device 30 for AE, a film sensitivity detecting device 31, and an AV computing device are newly added.
It is configured to add 32. Film sensitivity detector 31
From the output of F
The number is calculated to obtain Equation 15.

Then, the operation is based on the equation (18).
_{Find P p} . Next, _Equation 7 is obtained from f _TL , BV, SV, and t _P based on Equation 18.

Further, FIG. 12 shows a fifth embodiment. In this embodiment, in the circuit configuration of FIG.
Detection, the base potential of the transistor 13 is A / D converter
It is configured to be obtained by A / D conversion at 36.

As described above, when the influence of the AC light source is small (when the value of Expression 22 is small), the number of light emission times n can be decreased by increasing the light emission pulse width t _P per IRED. Therefore, the distance measurement can be completed in a short time.

[0054]

As described above, according to the present invention, the error between the actual stationary light at the time when the stationary light is stored and the actual stationary light at the time when the stationary light is stored is eliminated in the aliative AF apparatus having the stationary light removing circuit. It is possible to provide an active distance measuring device that improves the AF accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an active distance measuring apparatus of the present invention.

FIG. 2 is a block diagram for explaining the concept in the first embodiment of the present invention.

FIG. 3 is a block diagram for explaining the concept in the second embodiment of the present invention.

FIG. 4 is a characteristic diagram of a current flowing through a PSD of the active distance measuring device of the present invention.

FIG. 5 is a diagram showing an optical arrangement of active AF for explaining a relational expression of AF performance.

FIG. 6 is a characteristic diagram showing a relationship between AFIC output and 1 / L for explaining a relational expression of AF performance.

FIG. 7 is a diagram showing a relationship between a subject distance L, a focal length f _TL of a photographing lens, and a lens extension amount.

FIG. 8 is a program diagram showing an F value characteristic.

FIG. 9 shows a third embodiment of the present invention and is a block diagram schematically showing a main part of an active distance measuring device.

FIG. 10 is a diagram showing changes in stationary light and an A / D conversion command in the stationary light AC component detection device and the A / D converter.

FIG. 11 shows a fourth embodiment of the present invention and is a block diagram schematically showing a main part of an active distance measuring device.

FIG. 12 shows a fifth embodiment of the present invention and is a diagram schematically showing a main part of an active distance measuring device.

FIG. 13 is a diagram showing an optical arrangement of a conventional active AF.

FIG. 14: PSD output current I ₂ / (I ₁ + I ₂ ) and 1
It is a characteristic view showing the relationship with / L.

FIG. 15 is a circuit diagram of conventional stationary light storage and signal light processing.

16 is a time chart of the circuit of FIG.

FIG. 17 is a waveform diagram illustrating IRED light emission when the stationary light is an AC power source.

[Explanation of symbols]

3 ... IRED, 5 ... PSD, 6 ... IRED control transistor, 7 ... Preamplifier, 8, 13, 33, 34 ... Transistor, 11, 35 ... Diode, 12, 15 ... Differential amplifier, 16 ... Amplifier, 17 ... For feedback Buffer, 18 ... Comparator, 19 ... Integrating capacitor, 21 ... Distance measurement object, 22 ... Light emitting means, 23 ... Light receiving means, 24 ... Distance detecting means, 25 ... Projection controlling means, 26 ... AF
Sensor stationary light AC component detector, 27 ... Focal length detector, 28 ... IRED light emission pulse width, light emission number calculation device, 29
... IRED drive circuit, 30 ... Photometric device, 31 ... Film sensitivity detection device, 32 ... AV computing device, 36 ... A / D converter, 37 ...
Stationary optical AC component detector.

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[Procedure amendment]

[Submission date] July 31, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

[0022]

[Equation 4]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

[0023]

[Equation 5] Taking the above relationship into consideration, Δ (1 / L) becomes as shown in Formula 5.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction content]

[0024]

[Equation 6] Here, L, I _V , t _P , and other than Equation 7 are constants determined at the time of design.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

[0026]

[Equation 8] Further, the relationship between the image distance L, the focal length f _TL of the photographing lens, and the lens extension amount is as shown in FIG. Therefore, the equations 9 and 10 are obtained.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

[0029]

[Equation 11] Generally, the open F number is F ₀ and the target permissible circle of confusion is δ _0.
Then, the target permissible defocus amount Δk on the image plane in the open state is given by Expression 12.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

[0031]

[Equation 13]

[Procedure Amendment 7]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction content]

[0032]

[Equation 14] That is, the light emission pulse width per IRED or the number of times of light emission may be set according to the focal length of the taking lens and the open F number.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction content]

[0034]

[Equation 15] For example, in the case of a camera having a program diagram as shown in FIG. 8, when the brightness of the subject is high, the relationship of AV = TV is established. By applying this to the relational expression of Apex, Equations 16 and 17 are obtained.

[Procedure Amendment 9]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Change

[Correction content]

[0037]

[Equation 18] Therefore, when the subject brightness BV becomes brighter, it is possible to reduce the value of Expression 15 described above.

[Procedure Amendment 10]

[Document name to be amended] Statement

[Name of item to be corrected] 0045

[Correction method] Change

[Correction content]

[0045]

[Equation 21] That is, each time the amplitude of the AC light source is doubled, the light emission time must be ¼ .

Claims (1)

[Claims] 1. A light projecting means for projecting a light beam toward an object for distance measurement, and a reflected light of the light beam from the object for distance measurement, which receives a position signal corresponding to the light receiving position and a stationary light. A light receiving means for outputting a stationary light signal, a distance detecting means for detecting a distance to the distance measuring object based on the position signal, a fluctuation component of the stationary light signal is detected, and the luminous flux is based on the fluctuation component. And a projection control means for outputting a light emission time control signal for controlling the light emission time to the light projecting means.