JPS6087577A - Automatic focus control device of video camera - Google Patents

Abstract

PURPOSE:To attain remarkable reduction of current consumption by stopping the projection of an infrared-ray for range finding when an integration value of the sum of two output current values of an optical position detector reaches a fixed value. CONSTITUTION:Two optical current outputs outputted from the optical position detector 30 are converted into a voltage by current-voltage converters 31, 32, and inputted to rectifiers 39, 40 via intermediate frequency band pass filters 37, 38. The rectifiers 39, 40 output a voltage proportional to the AC signal amplitude value of the filters 37, 38, add the two DC voltages at an adder 41 and the result is inputted to an integration device 43. On the other hand, a voltage comparator 45 compares an output voltage of the integration device 43 increased as time is elapsed with a reference voltage VO, and when they are coincident, a control pulse Pc is outputted. The control pulse Pc activates an infrared-ray LED driver 27 so as to stop forcibly the projection of the infrared-ray for range finding.

Description

DETAILED DESCRIPTION OF THE INVENTION The industrial field of application relates to an automatic focus adjustment device that adjusts the focus of a video camera to accurately focus the image of a subject to be photographed at a predetermined position.

Conventional configurations and their problems Various automatic focusing devices for cameras have been proposed and implemented to date, and are now becoming popular in the field of video cameras as well as still cameras.

One of the most popular methods for focusing devices applied to video cameras is to project distance measurement signals such as infrared rays and ultrasonic waves onto the subject to be photographed (hereinafter referred to as the subject).
There is a method (hereinafter referred to as an active focusing method) in which the distance measuring signal No. 48 reflected by the object is received and the photographing lens is adjusted to one selected focusing position based on the distance measuring signal. FIG. 1 shows a diagram of the principle of an active focus adjustment method using infrared light. In the same figure,
The distance measuring infrared light projected from the light projecting means 1 is transmitted through the converging lens 2.
After reaching the object 3 for distance measurement, the light is reflected, passes through the converging lens 4, and enters the light receiving element 6. At this time, if the distance between the light projecting means 1 and the light receiving element 6 and the distance measuring object 3 changes, the angle of incidence of the reflected light on the light receiving element 6 or the angle of incidence of the reflected light on the light receiving element 6 changes. The position 11't in "Table 5..." changes. Based on the incident angle or position 11''t of this reflected light, a predetermined calculation of ω1 KG''d is performed. The lens driving IJOJ device +"'e 7 moves a photographic lens 8 (hereinafter referred to as a photographic lens) consisting of a plurality of lenses to an MIJ based on the calculation result of the arithmetic unit 6.
Drive to J focusing position! 1ilJ L focus adjustment is completed.

FIG. 2 is a conceptual diagram showing a conventional example of the active automatic focusing device. An infrared light emitting diode 9 (hereinafter referred to as an infrared LED) is caused to emit light intermittently at a constant frequency by an LED driving device 10 in order to distinguish it from surrounding infrared light. 1] The distance measuring infrared light emitted by the infrared LED 9 has a converging lens 11 (not shown).
The reflected light is reflected by the gear body, passes through the converging lens 12, and forms a light spot on the surface 1- of the photodiode 13, which is divided into two parts. The above-mentioned two-divided photo diode has its surface −1 − light subposition ii::+”
It outputs currents I, , I2 whose magnitudes correspond to I1.

That is, as shown in FIG. 3(, ), when the light spot 14 is displaced above the two-divided photodiode 13, the signal current 11. is output from the two-divided photodiode. The larger and smaller father of I, J4, and Vmi are: I) I................................................... (1) 1 2. Moreover, when the center of the light spot 15 as shown in FIG. 3(b) is on the dividing line 16 of the photodiode divided into two parts, I = .・・・・・・・・・ (2)1
2 If the position of the spherical light spot 17 shown in Fig. 3 (C1) is displaced downward, I (I ・・・・・・・・・・・・・・・ (3) 1
It becomes 2. IIj and Figure 2 continue the theory IJIJ. I
j1 ■ Photocurrents I, , I output from the photodiode 13 divided into two. are the first signal processing device 18,
A photocurrent 11. is applied to the second signal processing device 1ff19. I.

Voltage proportional to the size of ■1. Exchanged to v2.

The ratio converter 20 compares the magnitudes of the voltages 1 and v2, and the judgment device 21 determines the focal point δ of the photographing lens 22 (schematically shown as one convex lens) based on the output of the comparator 2o. 1
The lens driving device 23 is caused to fall in order to move the four-bar mechanism 26 in the +iU direction or backward. The photodiode moving device 24 moves the divided photodiode 13 in the direction of the arrow IMJ in conjunction with the movement of the focus adjustment mechanism. In the automatic focus adjustment device of this conventional example, the two-divided photodiode 13 is installed 1 in advance.
Wa position i1? c and the amount of mechanical movement are adjusted so that the extending position of the photographing lens 22 and the extending position of the two-divided photodiode are in a one-to-one relationship. Therefore, the output from the two-divided photodiode is adjusted. Photovoltaic engineer, to be.

1. The cutting device 21 changes the moving direction of the photographing lens 22 so that 1. The system stops at a focusing position of 'J' and achieves automatic focusing, 1, ', 1 adjustment. 4. The conventional example described above has a feature of the active type focusing device, which is that it uses a distance measuring viscosity of This is a powerful focusing method that allows for a relatively narrow viewing angle because it uses infrared LEDs that are not affected by the light and contrast. In the case of the above embodiment, it is necessary to continuously project infrared light while the photographic lens is moving to the appropriate (7J) focusing position, and the range of movement is large. (for example, when changing the photographic subject from a close-distance subject to a long-distance subject), a large amount of current is consumed.Normally, for applications such as the above embodiment, it is necessary to adjust the focusing of the photographic lens. A current of 100 to 300 mA is consumed, which is a serious problem for a focus adjustment device for a video camera, which must be operated on a battery from the viewpoint of portability.In addition, the photodiode moving device is linked to the focus adjustment device of the photographic lens. This limits the installation position of the photodiode, which poses a major constraint on the mechanical design of the video camera's photographing lens.

Purpose of the present invention The purpose of the present invention is to have a power-saving function that significantly reduces current consumption while maintaining high-precision distance measurement performance, and to solve major obstacles in the mechanical design of video camera shooting lenses. An object of the present invention is to realize an automatic focusing device for a video camera in which a projector/receiver for distance measurement can be installed without giving any problems.

Structure of the Invention The automatic focus adjustment device for a video camera according to the first aspect of the invention includes a projector that emits infrared light for distance measurement, and a light projector that emits infrared light for distance measurement, and a reflector of the infrared light for distance measurement from a subject to be measured. A converging lens for condensing light, a focal image 1 for the converging lens, and a focused image 1 for the converging lens at a constant rate according to the position of the image spot of the reflected light. an optical position detector that outputs a second photocurrent; Second
The first one converts the photocurrent from current to voltage and outputs it. a second voltage converter; and the first voltage converter. an adder for adding the output values of the second photoelectric/%L; Second photoelectric fA'
, a subtracter that subtracts the output value of Oa, and a first circuit that charges the capacitor with a constant current corresponding to the amplitude value of the output of the Oa calculator and outputs a voltage value that increases almost linearly. An integrator charges a capacitor with a constant current corresponding to the amplitude value of the output of the subtracter, and a second integrator outputs a voltage value that increases in a curved manner, and a second integrator adjusts the focus of the photographic lens. a lens encoder that mechanically detects the rotation angle of the helicoid of the focusing lens group, converts it into an electrical signal, and outputs it; and a comparator that compares the output value of the second integrator with the output value of the lens encoder. and a lens drive unit that drives the position of the photographing lens +1tlf forward or backward based on the output of the comparator, and +ifJ the output value of the first integrator is equal to a preset reference voltage value. At the same time, the light emitting device stops emitting light, and +
3rJ The focusing lens group of the photographic lens is driven by the lens driving section until the output value of the lens encoder reaches a value corresponding to the output value of the second integrator at that time, and stops at the optimal focus position. This system is configured to effectively reduce current consumption, enable 10-performance distance measurement, and allow automatic focus adjustment of video cameras that allows relative freedom in determining the installation position of the distance measurement emitter and receiver. A device is realized.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be explained with reference to the drawings.

FIG. 4 is a system configuration diagram of an embodiment of Kibatsu 1''-1. Furthermore, FIG. 5 is a diagram for explaining the geometrical arrangement 11' of the light emitting/receiving sections used in this embodiment and the principle of distance measurement.

In FIG. 4, the infrared LED 26 has a shape that repeats intermittent light emission at a constant frequency fc within a light emission period that is repeated at a constant cycle by an infrared LED cutting device 27. Projects infrared light for distance.

This distance-measuring infrared light passes through a converging lens 28 and reaches an object (not shown), and the repulsed light is reflected by a converging lens 29.
S D
A well-known leading u゛′1” tester 30 such as
imaged as a spont on the surface of The light spot ii'j formed on the surface of the optical position detector 30 is
It changes uniquely in a certain direction depending on the distance in terms of weight.

Now, referring to FIG. 6, we will discuss the relationship between the light spot position and the distance to the subject. 6th
In the figure, the infrared L E D' 26 and the optical position detector 30 with a self-effective length Qo are installed with their center open distances separated by d. The converging lens 29 is arranged in front of the optical position detector 30 by a distance approximately equal to its focal length f, and focuses the reflected light from the object 52 on the surface of the optical position detector 3o. Now, the optical position detector 30 receives reflected light 53 from an infinite distance (considered to be parallel to the distance measuring infrared light 54 projected by the infrared LED 26) at its center point, and the optical position detector 30 receives the reflected light 53 from an infinite distance at its center point. 56 equal photocurrent 11
The device is designed to output ゜■2. Then, the reflected light 57 from the subject 52 located at a distance away is a distance of X
(in the figure) is displaced downward. According to a simple geometrical consideration in FIG. 6, this amount of displacement can be expressed as shown in the following equation.

In addition, two photocurrents 11 output from the optical position detector 30
．． I is inversely proportional to the distance from each output end electrode 55, 56 to the light spot position. That is, 0^ l in the above formulas (6) and (e). r1″ represents the total amount of current generated by one spot. Next, (4) and (5)
, Focus adjustment is possible by transforming equation (6).

Next, returning to IIJ and FIG. 4, we will explain the operation of the focus adjustment device that can measure distance with high precision while significantly reducing the current consumption of the infrared LED for distance measurement, which is the main point of IJj. Two photocurrent outputs 11 (t) output from the optical position detector 30
, I, (t) are the first . Current-voltage conversion is performed by the second current-voltage converters 31 and 32, and then the first current-voltage converter 31, 32 converts the current to voltage.
The first through the second capacitor 33,34. The second amplifiers 35 and 36 remove the noise component, which is a DC component, and only the signal light component, which is an AC component, is amplified by a predetermined magnification.

11a 1. The output voltage of the second intensifier 11111i 35.36 has a rectangular or sinusoidal repeating waveform which is synchronized with the J frequency fc driven by the infrared LED driving device. Second intermediate frequency pass filter (hereinafter referred to as B).

P, F) 37.38 has a center frequency of 1j
It is configured to match the driving frequency f and fc in IJ, and 1j "1, removes noise components included in the output of the 1st and 2nd amplifiers 35 and 36. 1st and 2nd rectifiers. 39
．． 40 are respectively the first. Second node B, P, F 37°38 DC voltage V1 (t
), outputs v2(t). The adder 41 includes the first
The current voltage vl(t) output from the second rectifier 39.40
, v2(t)'a=+3W L,,(Vl(tl2
(t) ) KJt example value ■ + (t) is calculated and subtracted by 1
′? 42 is the DC voltage V1(t) output from the first and second rectifiers 39 and 40.

Subtract v2(t), (V, (tl −V2(t) )
outputs a value v (t) proportional to .

V+(tl-α・(Vl(tl+−V2ft)l・・
・・・・・・・・・・・・ (9) V(jl=I・(Vlf
t)-V2(t))・・・・・・・・・・・・(10)
(α, β are constants) The first integrator 43 performs voltage-current conversion according to the DC voltage value output from the +JTF addition unit 41, and charges a capacitor (not shown) with a constant current, The integral value v of a waveform that increases almost linearly with the passage of time, -
The integrator 44 of Kon2 outputs X(t) and the subtracter 42
A voltage-current conversion is performed according to the DC voltage value outputted by the converter, an integral calculation is performed at a constant current, and v'X(t) is output.

Since the above series of arithmetic operations maintains reliable linearity, the output value v−,”(t) of the first integrator is (11(t)
+ I, (t) ), and the output value of the second integrator - t) is proportional to (11(t) - l2ft)).

Below, explanation J will be continued using Figure 6 as well. Figure 6 (-
1 is the first integrator 43.1 when the object is at a short distance, and FIG. 11(b) is the first integrator 43.1 when the object is at a long distance. The output waveform of the second integrator 44 is conceptually shown in hJ.For the sake of simplicity, the first integral Output value V- of the device 43
(t,) and the output value v'X-(t8) of the second integrator are both set to zero.

v, -X-(tll)=V-'':(tB)=o...
...(11) Also, 1st. It is assumed that both outputs of the second integrator increase as time passes. Voltage comparator 4
5 is the first integrator output value V-(t) and the base fll(
After the distance measuring infrared LED starts emitting light at time ts, the output value v-(t) of the first integrator and the reference voltage A control pulse Pc is output at time t0 when the value vO coincides with the control pulse Pc. The control pulse Pc is applied to an analog-to-digital converter (hereinafter referred to as A/
Output value of the second integrator at t0 at 46 (abbreviated as D converter) VF = Vl(to) ・・・・・・・・・・・・・・・
...The second integral is determined by the time t0 which gives the timing to write (12) and at the same time forces the infrared LED driving device 27 to stop projecting the distance measuring infrared light. The output value of the device Vpi, (V' ”(t)/V-(
t) ) (D (m woV+”(t) , == Vo
'(t-to)...A-(13) (hereinafter, VF is referred to as normalized distance m voltage). Therefore, the output value vp(t) of the second integrator is not divided by the output value V,, -X (t) of the first A sexector at time t. By simply subtracting the output value ■F of the second integrator at , [(f, (t) - f, (t) )/(I, (t
) + , l2(t)l ) A value proportional to the slope, that is, a value proportional to the reciprocal of the distance is found. It's ox, 1) a outside light distribution LE
The driving time of the D26 can also be changed according to the distance to the subject, and the current consumption when the infrared LED is moving can be significantly reduced.In this embodiment, as shown in FIG. This is because the projection time of the infrared light for distance measurement is controlled using the control pulse Pc.The basic shape of light emission in this embodiment is as shown in FIG. The light emission period ToN and the light emission stop period TOF'F'' are repeated, and within the light emission period ToN, intermittent light emission is repeated at a constant frequency fc as shown in the figure (,). It is something like (c). Here, Toh = TOFF −°−−− (14) fC) 1
/T ・・・・・・・・・・・・・・・(15) Next 1
To JF7+! When the distance measuring infrared light is projected within the light emitting period and after a certain time the 1Jif control pulse PC or the same figure (d) is output, the light emission is forced by the Orf infrared LED driving device. As shown in FIG. 2(e), the light emission time is limited according to the measured distance. Needless to say, the amount of infrared light for distance measurement that is reflected from the subject and received by the optical position detector (hereinafter abbreviated as ψ light amount 1)
becomes more friendly depending on the distance (L) to the subject, and the amount of light received is large for a close-range subject such as a rhinoceros (for example, when L==1'm when using an infrared LED with a sharp pointing property) (The amount of light received is also 10 or 1 d in the case of L-10 m), and the Lurie control pulse Pc is generated shortly after the distance measuring infrared light is emitted. In short, 1ift record 6111
The base t$ voltage value vO for pulse generation may be set to a value that allows sufficiently high accuracy distance measurement at the farthest distance to be measured. In addition, in Figure 6, the value of the normalized distance voltage ■F for the subject at a short distance is the value of ■F for the subject at a long distance (I+(i) is larger than IJ from the geometrical arrangement shown in Figure 5). Appears to be a bright object at a close distance (11
(t)-1, (t) ) or Ili<i1'l
(11(t)-I2(t)l
This is because it is larger than li+'j.

The A/Df converter 46 is connected to the voltage range that the 11-normalized distance voltage
The change range of ■F when changing from close range to infinity is divided into e4, and 6-bit digital signal 8-(aOl
"1 1 δ2..., δ5). Also, the focus position of the photographing lens 47 (schematically shown as one convex lens, but actually consists of multiple lenses) is determined by the lens encoder. Detected by 48, shooting range from near distance to infinity (helicoid angle #i;)
Position detection value Qb of 6 bits divided into 64 = (bo, b
l, . . . , δ6). Lens encoder 4slj: A device that maintains mechanical contact with the focus adjustment mechanism 51, such as a helicoid, which is normally provided in the focusing lens of the shadow lens 47, and moves the focus adjustment mechanism to output the full position detection signal. is used.

A digital comparator 49 outputs a digital signal a from the A/D converter 46 and a lens encoder 48 written as 1jO.
The bits of each corresponding digit of the output digital signal are compared. The lens driving unit 50 receives the output of the digital comparator 49 and drives the photographing lens 47 so that
The focus adjustment mechanism 61 is driven in the appropriate direction νJ and stopped at the optimal focus position, completing automatic focus adjustment.

Next, other embodiments of the present invention will be described with reference to the drawings. FIG. 8 is a system configuration diagram showing a second embodiment of the present invention. Since this second embodiment includes many co-tracing components with the first embodiment described above, the common node ■J
-C is the symbol 5 used in Figure 4 of the book +jlJ.
I duplicated it once a month. In this second embodiment, the elongated apical point with respect to the first embodiment is t''1 in the first embodiment.
．． 1] Analog output of the second integrator 44 (UVp
is converted into a digital signal by the A/D9 converter (46) and output by the lens encoder 48. Digital position detection (+'
While the digital comparator 49 compares the coincidence g of i 'j' L, in this second embodiment, the analog output value of the second integrator 44 and the analog position detection output from the lens encoder 60 are compared. The point is that the signals are directly compared using the kF59. Therefore, the lens encoder 6o maintains mechanical contact with a focus adjustment mechanism 51 such as a helicoid included in the photographic lens 47, and detects a position using a voltage value that changes in an analog manner in conjunction with movement for focus adjustment. Further, the output voltage value range of the lens encoder 60 is a variation range in which the normalized distance voltage vF can be accommodated (the distance to the subject is from the close distance of the photographing lens 47). Comparator 59F
i Normalized distance voltage VF at the moment when the control pulse Pc is generated, ! : Compare with the output value of lens encoder 6o 1
The lens driving unit 61 is actuated so that the two coincide with each other, and the photographing lens 47 is driven to the optimum focus position and stopped, thereby completing the self-help focus adjustment. In this embodiment, there is no sensor for digitizing the normalized distance voltage vF using an A/D converter, and the structure is in-cylinder.

Note that the above 1. In both of the second embodiments, both the δ111-distance projection light 19< and the light receiving section are mechanically operated. I
Since it does not have a JI no capital and does not need to be linked with the photographic lens, its installation position can be determined independently of the photographic lens.It is suitable for mechanical design of photographic lenses for video cameras equipped with automatic focusing. Very advantageous.

As explained in detail in Section 2 of ``Effects of the Invention'', the present invention is based on the integrated value of the sum of the two output current values of the optical position detector, and the two output currents of 1ji and I. The integral value of each subtracted value is calculated, and the projection of the infrared light for distance is stopped and the The structure is designed so that the focusing lens group of the photographing lens is driven at the point where the integral value obtained by the subtraction value at the time and the output value of the lens encoder match, so that the focusing lens group of the photographing lens is driven at the point where the integral value obtained by subtracting the time value matches the output value of the lens encoder.
-clause device i'? The power consumption can be reduced by 1111 J, and the effect is extremely large.

In addition, the light emitter and receiver do not have a mechanical +JJν) part, and it is inevitable that they come into contact with the photographic lens body.
The desired effect can also be achieved in terms of design.

4. Brief explanation of the drawings j) Figure 1 is a principle diagram of the active focus preparation method, and Figure 2 is a diagram of the conventional active focus *-117i1 section%'ii'
Fig. 3 is a schematic diagram showing the operating principle of the two-divided photodiode used in the conventional example, and Fig. 4 is a system configuration diagram showing an example of misfire 11. , the infrared L used in one embodiment as shown in FIG.
ED, a schematic diagram showing the arrangement of optical position detectors etc. and the principle of distance measurement;
FIG. 6 shows the first example of the same embodiment. FIG. 7 is a schematic diagram showing the output waveform of the second integrator, FIG. 7 is a timing chart showing light emission control of the infrared LED of the same embodiment, and FIG. 8 is a system configuration diagram showing another embodiment of the present invention. .

26...Infrared LED, 27...Infrared L
ED drive device, 30...; optical position detector, 31.
32... Current-voltage converter, 41...
Adder, 42...Subtractor, 43.44...
...Integrator, 45...River/voltage comparator, 46...
・Analog-digital converter, 48...lens encoder, 49...digital comparator,
6o... Lens drive unit, 59... Comparator, 6o... Lens encoder, '61...
...Lens 1. lA uJ part.

Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] (1) A projector that emits infrared light for distance measurement, a converging lens that collects the reflected light of the infrared light for distance measurement from the object to be measured, and the converging lens. is installed at the focal position of the first . Second
A photoelectric position detector that outputs the photoelectric 71', +jfi
Record 1. The first photocurrent converts the second photocurrent into voltage and outputs it. A second voltage converter and a voltage converter;
8r! an adder that adds the output values of the photocurrents of 2 and +j
7, No. 1. A subtracter subtracts the second photocurrent output n6, and a capacitor is charged with a constant current corresponding to the amplitude value of the positive output in the addition, and a voltage 1i(t The capacitor is charged with a constant current corresponding to the amplitude 6 of the output of the first integrator that outputs i and the output of the +1ft multiplier, and a voltage value that increases linearly is output. a second integrator that mechanically detects the rotation angle of the helicoid of the focusing lens group that adjusts the focus of the photographic lens, converts it into an electrical signal, and outputs it; and an output of the second integrator. and a lens drive unit that drives the position of the photographing lens in the Off direction or backward based on the output of the comparator, The light emission of the light projector is stopped at a time when the output value of the second integrator coincides with a preset reference voltage value, and the output value of the lens encoder is matched with the output value of the second integrator at that time. An automatic focus adjustment device for a video camera, characterized in that the focusing lens group of the photographic lens is driven by the lens driving section until it reaches the corresponding picture, and is stopped at the optimal focus position. (2+ Lens) The encoder divides the rotation angle corresponding to the shooting distance from close range to infinity of the helicoid of the focusing lens group into a preset number of divisions, and calculates the number of bits determined according to the division. The comparator outputs the signal voltage range output from the second integrator as an equalized digital signal, and the comparator equalizes the signal voltage range output from the second integrator by the same amount as that of the encoder:
'j' Analog divided into J number (same number of bits) -
The configuration includes a digital converter and a digital converter that digitally compares the output value of the analog-to-digital converter and the +Jfj lens encoder output value for each bit by corresponding δ. Feature J
1° A video camera automatic focus adjustment device according to claim (1). (3) The lens encoder outputs an analog signal that changes linearly in accordance with the rotation angle corresponding to the shooting distance from close range to infinity of the helicoid of the focusing lens group, and the second integrator The output reliability voltage range is jj
Voltage range IL11 of lens encoder a
And one after another? -4f1° is set, and the comparator is 1]0
The automatic focus adjustment device for a video camera according to claim 1, wherein the output 11't of the second integrator and the output value of the lens encoder are multiplied by 1+17 in an analog manner.