JPS6087576A - Automatic focus control device of video camera - Google Patents

Abstract

PURPOSE:To attain remarkable reduction of current consumption by adding respective integration values of two output current values of an optical position detector and stopping the projection of an infrared ray for range finding at a time when the added value reaches a fixed value. CONSTITUTION:Two optical current outputs outputted from an optical position detector 30 are converted into a voltage by current-voltage converters 31, 32, and converted into DC voltages at rectifiers 39, 40 via intermediate frequency band pass filters 37, 38. The integration devices 41, 42 output an integration value having a waveform increased almost linearly as time is elapsed in response to an output voltage of the rectifiers 39, 40. A voltage comparator 45 compares the sum of the said two integration values and a reference value VO, and outputs a control pulse Pc at a time when the sum is coincident with the VO. The 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] Industrial application field.

The present invention relates to an automatic focus adjustment device that correctly focuses an image of a subject to be photographed at a predetermined position when adjusting the focus of a video camera.

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 focus adjustment devices applied to video cameras is to project a distance measurement signal such as infrared rays or ultrasonic waves onto the subject to be photographed (hereinafter referred to as the subject), and then measure the distance measurement signals reflected by the subject. There is a method (hereinafter referred to as an active focusing method) in which a distance signal is received and a photographing lens is driven to an appropriate focusing position based on the distance measurement signal. Fig. 1 shows a principle diagram of an active focusing method using infrared light. In the figure, infrared light for distance measurement projected from a light projecting means 1 passes through a converging lens 2 to reach a distance measuring object 3, is reflected, passes through a converging lens 4, and enters a light receiving element 5. At this time, if the distance between the light projecting means 1 and the light receiving element 5 and the distance measuring object 3 changes,
The angle of incidence of the reflected light on the light receiving element 5 or the position of the reflected light on the surface of the light receiving element 5 changes. The calculator 6 performs a predetermined calculation based on the incident angle or position of this reflected light. The lens driving device 7 drives a photographic lens 8 (hereinafter referred to as a photographic lens) consisting of a plurality of lenses to an appropriate focusing position based on the calculation result of the arithmetic unit 6, thereby completing focus adjustment.

FIG. 2 is a conceptual diagram showing a conventional example of the actuator and f-type automatic focusing device. The infrared light emitting diode e (hereinafter referred to as an infrared LED) is caused to emit light intermittently at a constant frequency by the LED driving device 10 in order to distinguish it from surrounding infrared light. The distance measuring infrared light projected by the infrared LEDe passes through the converging lens 11 and is reflected by an object (not shown), and the reflected light passes through the converging lens 12 and
A light spot is imaged on the divided photodiode 130 surface. The photodiode divided into two has a signal current 11. on its surface having a magnitude corresponding to the position of the second light spot. Output I2. That is, Fig. 3(a)
As shown in FIG.
"The relationship between the magnitude of 2 is
1). In addition, a light beam as shown in Fig. 3(b),
) When the center of 15 is on the dividing line 16 of the photodiode divided into two, 11-12 (2) A light spot 17 as shown in FIG. 3(C) When the position of is displaced downward, Xl<I2 (3). Returning to FIG. 2 again, the explanation will be continued. Photocurrent I4 outputted from the two-divided photodiode 13. I is the photocurrent I, , I at the first signal processing device 18 and the second signal processing device 19, respectively.

A voltage proportional to the magnitude of v1. Converted to v2.

Comparator 2o detects this voltage v4. Compare the size of v2,
The determination device 21 determines whether the photographing lens 2
2 (schematically shown as one convex lens) forward or backward.
Control 3. The photodiode moving device 24 moves the two-divided photodiode 13 in the direction of the arrow in conjunction with the movement of the focus adjustment mechanism. In the automatic focus adjustment device of this conventional example, the installation position and mechanical movement amount of the photodiode 13 divided into two parts are adjusted in advance so that the extended position of the photographing lens 22 and the extended position of the two divided photodiode 13 are adjusted in advance. It is adjusted so that there is a one-to-one relationship. Therefore, the judgment device δ21 controls the moving direction of the photographing lens 22 so that the photocurrents I, I2 output from the two-divided photodiodes are always equal, stops it at an appropriate focusing position, and performs automatic focus adjustment. has been realized.

The above-mentioned conventional example is a powerful focusing method that has the features of an active focus adjustment device that its distance measurement accuracy is not affected by subject illuminance or contrast, and because it uses infrared LEDs, the beam angle can be relatively narrow. be. However, in the case of a video camera, it is necessary to shoot continuously moving subjects, and as in the case of the above embodiment, the camera continuously shoots red images while the shooting lens moves to the appropriate focusing position. It is necessary to project external light, and when the moving range is large (for example, it takes several seconds to change the photographic subject from a close object to a long distance object), a large amount of current is consumed. Normally, in an application like the above example, a current of 100 to 300 mA is consumed in the focusing center of the photographic lens, which is a serious problem for a focus adjustment device for a video camera that requires battery operation from the viewpoint of portability. .

Furthermore, the photodiode moving device must operate in conjunction with the focus adjustment device of the photographic lens, which limits the installation position of the photodiode, which poses a major constraint on the mechanical design of the photographic lens of the video camera.

Purpose of the Invention An object of the present invention is to provide a power-saving function that significantly reduces current consumption while maintaining high-precision distance measurement performance, and to provide a method for measuring distance without significantly impeding the mechanical design of the photographing lens of a video camera. An object of the present invention is to realize an automatic focus adjustment device for a video camera in which a distance projector/receiver can be installed.

Structure of the Invention The automatic focus adjustment device for a video camera of the present invention includes a projector for projecting infrared light for distance measurement, and a converging device for condensing the reflected light of the infrared light for distance measurement from a subject to be measured. a lens, an optical position detector installed at the focal position of the converging lens and outputting two photocurrents at a constant rate according to the imaging spot position of the reflected light; The first one outputs a voltage value that increases almost linearly. a second integrator;
Above 1. an adder for adding the output values of the second integrator; a subtracter that subtracts the output value of the second integrator; a lens encoder 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 the electrical signal; The adder includes a comparator that compares the output value of the subtracter and the output value of the lens encoder, and a lens drive unit that drives the position of the photographing lens forward 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 device matches a preset reference voltage value, and the output value of the lens encoder is 1) at that time.
When the value corresponding to the output value of the calculator described in u is reached, the focusing lens group of the photographing lens is driven by the lens driving section and stopped at the optimum focus position, thereby reducing the current consumption. An automatic focus adjustment device for a video camera is realized that can effectively reduce distance measurement, perform high-performance distance measurement, and relatively freely determine the installation position of a distance measurement projector/receiver.

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

FIG. 4 is a system configuration diagram of an embodiment of the present invention. Further, FIG. 5 is a diagram for explaining the geometric arrangement of the light emitting/receiving section used in this embodiment and the principle of distance measurement.

In FIG. 4, the infrared LED 26 is illuminated in a light emitting period that is repeated at regular intervals by the infrared LED driving device 27.
Infrared light for distance measurement is projected in a shape that repeats intermittent light emission at a constant frequency fc.

This infrared light for distance measurement reaches a subject (not shown) through a converging lens 28, and the reflected light is converted into a
The light is imaged as a light spot on the surface of a well-known optical position detector 3o such as a device. The position of the light spot formed on the surface of the optical position detector 3o uniquely changes in a certain direction depending on the distance to the subject. Here, the relationship between the light spot position and the distance to the subject will be explained with reference to FIG. In FIG. 5, the distance between the centers of the infrared LED 26 and the optical position detector 30 with an effective length of 2° is d.
They are placed at a distance from each other. The converging aze 29 is located at the optical position detector 3 by a distance 1η[1 which is approximately equal to its focal length f.
The light reflected from the object 62 is placed in front of the object 62 and focused on the surface of the optical position detector 30. Now, the optical position detector 30 detects reflected light 53 (infrared LE) from an infinite distance.
(considered to be parallel to the distance measuring infrared light 54 projected from D26) is received at its center point, and the electrodes 55, 5 at both ends
6 equal photocurrents 11. Device 1 that outputs I
Then, as shown in FIG. 5, the reflected light 67 from the object 62 located at a distance is downward by X (in the figure) from the center of the optical position detector 30. According to a simple geometrical consideration in FIG. 5, this amount of displacement can be expressed as shown in the following equation.

In addition, two photocurrents I output from the optical position detector 3o
, , I, are inversely proportional to the distance between each output end electrode 55, 66 and the light spot position. That is, 0 − − X l.

One + X I2-　■　・・・-・・・・・・・・・(6)l. .

(5) #10 in the formula (6) represents the total amount of current generated by the light spot. Next, (4), (5),
By transforming equation (6), we get the following equation, and according to equation (8), the reciprocal of the distance to the subject (1
/L) and dThe rotation angle of the helicoid, which is the heating point adjustment mechanism of the regular shooting lens, is approximately proportional to the reciprocal of the distance to the subject, so automatic focus adjustment is possible by detecting the rotation angle of the helicoid.

Next, returning to FIG. 4 again, we will explain the operation of the focus adjustment device 1-5, which is the gist of the present invention and is capable of highly accurate distance measurement while greatly reducing the current consumption of the infrared LED for distance measurement. . Two photocurrent outputs I, (t), output from the optical position detector 30
I2(t) is the first . Second current-voltage converter 31
．． 32, '11 current-to-voltage conversion is performed, and then the 1st current-to-voltage is converted.
The first through the second capacitor 33,34. The second amplifier 35.36g removes the noise component which is the direct current component, and only the signal light component which is the alternating current component is amplified by a predetermined magnification.

Said 1st. The output voltages of the second amplifiers 35 and 36 correspond to the driving frequency f of the infrared LED driving device. It becomes a rectangular wave-like or sinusoidal repeating waveform synchronized with the first wave. The center frequency of the second intermediate frequency pass filters (hereinafter abbreviated as B, P, and F) 37 and 38 is the drive frequency f. It is configured so as to match the above-mentioned No. 1. Noise components contained in the output of the second amplifier 36.36 are removed.

1st. The second rectifiers 39 and 40 output DC voltages 1, (t), and 2 (t) that are proportional to the AC signal amplitude values of the outputs of the first and second B, P, and F 37.38, respectively. .

1st. The second integrators 41 and 42 perform voltage-current conversion according to the rectifier output voltage value (DC), charge a capacitor (not shown) with a constant heart current, and as time passes, the voltage becomes almost linear. The integral value v1*(t
), ■Output 2*(t). The adder 43 adds the two integrator output values and calculates rv *(t)+V2*(t))
A value proportional to [Therefore, (I, (t) + I, (t)
The subtracter 44 performs subtraction between the two integrator output values v1*(t) and V2*(t).v1*(t)-'v2*(t) ) [Therefore, a value proportional to (11(t)-I2(t) l) is calculated.

The explanation will be continued below using FIG. 6 as well. Figure 6(a)
(b) shows the adder 43 when the subject is at a short distance, and (b) shows the adder 43 when the subject is at a long distance. 4 conceptually shows the output waveform of the subtracter 44. Now, for simplicity, infrared L
At the moment when the ED2e starts projecting infrared light for distance measurement at time t8, the output value of the adder 43 (Vl(ts) + V2''
(t8) ) is also the output value of the subtracter 44 (V 1(t s
) V2 (t s ) ) are both set to zero.

Also, an adder 43. It is assumed that both outputs of the subtractor 44 increase as time passes. The electric comparator 45 calculates the adder output value "1"") + V2 '7 (t))
and the reference voltage value vO output from the reference power supply 58,
After the ranging infrared LED starts emitting light at time ts, at time to when the adder output value (V1''(t)+V2*(t)>) matches the reference voltage value Vo. A control pulse Pc is output.The control pulse Pc is sent to an analog-to-digital converter (hereinafter abbreviated as A/D converter) 46 to output the subtracter output value vF-v1*(to) at time to.
-v2*(to)11161119. It provides timing for writing (9) and also acts on the infrared LED drive device 27 to forcibly stop the projection of infrared light for distance measurement. The output value vF of the subtracter at time toK is ((V1*(
t) −V2*(t) l /(V1*(t) +v2
”(t) ) ) as V1*(t) + V2*(t)=V o (t =
t o )・・・・・・・・・Value normalized as (1o)
β0] (hereinafter, vF is referred to as normalized distance voltage). Therefore, the subtractor output (V1*(t) −V2
*(t) ) to the adder output (V, *(t) +V2*(
t) ), just by subtracting the subtractor output value ■F at time to, we get [(11(t)-12(t)
)/(11(t)+I,(t) )), that is, a value proportional to the reciprocal of the distance. Further, the driving time of the infrared LED 26 can also be changed depending on the distance to the subject, and the current consumption when driving the infrared LED can be significantly reduced. This is because in this embodiment, as shown in FIG. 7, the projection time of the distance measuring infrared light is controlled using the control pulse Pc. The basic shape of the light emission in this embodiment is as shown in 0)) of the same figure, the light emission period ToN and the light emission stop period "OF
The same figure (,) is displayed during the light emitting period TON.
It is similar to the one shown in FIG. 3(c), in which intermittent light emission is repeated at a constant frequency fc. Here TON ""
TOFF ”−−・・=・(11) f c )) 1/
T ・・・−・・・・・・・・・(12) Next, within the light emission period, the infrared light for distance measurement is projected, and after a certain time, the control pulse Pc is emitted as shown in the figure (d). When the light is output, the light emission is forcibly stopped in the infrared LED moving device, so that the light emission time is limited according to the measured distance, as shown in FIG. 4(e).

Needless to say, the amount of infrared light for distance measurement that is reflected from the object and received by the optical position detector (hereinafter abbreviated as the received light amount) changes significantly depending on the distance (L) to the object. The amount of light received is large for a subject at a distance (for example, if an infrared LED with a sharp pointing property is used, the amount of light received when L = 1 m is about 100 times that when L = 10 m),
The control pulse Pa□ is generated with a short emission diameter of infrared light for distance measurement. In short, the reference voltage value Vo for generating the control pulses may be set to a value that allows sufficiently high-precision distance measurement at the farthest distance to be measured.

In addition, the reason why the value of the normalized distance voltage ■F for a close-distance object in FIG. 6 is larger than the value of vF for a far-distance object is obvious from the geometrical arrangement shown in FIG. The value of (I, (t)-I2(t)) for a subject at
) is larger than the value of

The A/D converter 46 converts the normalized distance voltage vF.

The possible voltage range (that is, the range of change in vF when the distance to the subject changes from the close distance of the photographing lens 47 to infinity) is divided into 64 equal parts, and the 6-bit digital signal A = (
Output Ot 19 as a a..., a5). Also, the focus position of the photographing lens 47 (schematically shown as one convex lens, but actually consists of multiple lenses) is detected by the lens encoder 48, and the focus position is determined from the closest photographing distance to infinity. (helicoid angle, etc.) to 6
6-bit position detection signal b divided into 4 parts: (bo, bl,
. . . b5). The lens encoder 48 maintains mechanical contact with a focus adjustment mechanism 51 such as a helicoid normally provided in the focusing lens portion of the photographic lens 47, and outputs a position detection signal in conjunction with the movement of the focus adjustment mechanism. things are used.

A digital comparator 49 compares the corresponding bits of the digital signal a output from the A/D converter 46 and the digital signal S output from the lens encoder 48. The lens drive unit 6o receives the output of the degζ sigil talco/parator 49, drives the focus adjustment mechanism 51 of the photographic lens 47 in an appropriate direction so that a = b, and stops at the optimal focus position 111. Automatic focus adjustment is completed.

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 embodiment includes many components in common with the first practical example described above, the same reference numerals used in FIG. 4 are used for common elements. This second
The biggest difference between this embodiment and the first embodiment is that in the first embodiment, the analog output value vF of the subtracter 44 is converted into a digital signal by an A/D converter 46. death,
While the digital comparator 49 compares the degree of coincidence with the digital position detection signal output from the lens encoder 48, in this second embodiment, the analog output value of the subtracter 44 and the lens encoder 60 output The point is that the comparator 69 directly compares the analog position detection signal with the analog position detection signal. Therefore, the lens encoder 60 maintains mechanical contact with the focus adjustment mechanism 51, such as a helicoid, provided in the photographic lens 47, and detects the position using a voltage value that changes in an analog manner in conjunction with movement for focus adjustment. It is configured to output a signal. Furthermore, the output voltage value range of the lens encoder 6o is the change range that the normalized distance voltage VF can take (the change range of ■F when the distance to the subject changes from the close distance of the photographing lens 47 to infinity). It is made to match. A comparator 59 compares the normalized distance voltage vF at the moment when the control pulse Pc is generated with the output value of the lens encoder 60, and sets the lens drive unit 61 so that the values match. The lens 47 is driven to the optimum focus position and then stopped, completing automatic focus adjustment. In this example, an A/D converter is used to calculate the normalized distance voltage
There is no need to digitize everything, making configuration easier.

In addition, the above @1. ．． In both of the second embodiments, neither the distance-measuring light emitter nor the light receiver has any mechanically movable parts, and there is no need for them to be linked with the photographic lens, so they can be installed independently of the photographic lens. This is very advantageous for the mechanical design of a video camera taking lens that can determine the position and has automatic focus adjustment.

Effects of the Invention As is clear from the above detailed description, the present invention provides a method for adding an integral value of each of two output current values of an optical position detector and subtracting an integral value of each of the two output current values. The projection of the distance measuring infrared light is stopped at the time when the added value reaches a certain value, and the imaging lens is focused until the subtraction value at that time matches the output value of the lens encoder. Since it is configured to drive the lens section, it is possible to significantly reduce current consumption compared to conventional active type focus adjustment devices for video cameras, and the effect is very large. Further, the light projector/receiver does not have any mechanically movable parts and does not need to come into contact with the photographic lens body, and excellent effects can be obtained in terms of mechanical design of the photographic lens.

[Brief explanation of drawings]

Figure 1 is a diagram of the principle of the active focus adjustment system, Figure 2 is a system configuration diagram showing the basic principle of a conventional active focus adjustment device, and Figure 3 is the operation of the two-divided photodiode used in the conventional example. A schematic diagram showing the principle; Fig. 4 is a system configuration diagram showing an embodiment of the present invention; Fig. 5 is a schematic diagram showing the arrangement of infrared LEDs, optical position detectors, etc. used in the embodiment and the principle of distance measurement. 6 is a schematic diagram showing the output waveforms of the adder and subtracter of the same embodiment, and FIG. 7 is a schematic diagram showing the output waveforms of the adder and subtracter of the same embodiment.
A timing chart showing the light emission control of the ED, and FIG. 8 is a system configuration diagram showing another embodiment of the present invention. 26...Infrared LED, 27...Infrared L
ED drive device, 3o...first 16 detector, 31,
32... Medium current-voltage converter, 41.42...
・Integrator, 43... Adder, 44... Subtractor, 46... Voltage comparator, 46... Analog-digital converter, 48... Lens encoder,
49...Digital comparator, 50...
・Lens drive unit, 59... Comparator, 6o...
・Lens encoder, 61...Lens drive unit. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 2 Figure 3 Figure 3

Claims (3)

[Claims] (1) A projector that emits infrared light for distance measurement, a converging lens that condenses the reflected light of the infrared light for distance measurement from the object to be measured, and a light source installed at the focal position of the converging lens. an optical device detector that outputs two photocurrents at a constant rate according to the imaging spot position of the reflected light;
The first step is to integrate the voltage value and obtain a voltage value that increases almost linearly.
a second integrator, an adder for adding output values of the first and second integrators, and a second integrator; a subtracter that subtracts the output value of the second integrator, and a lens encoder 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. The subtraction 2: includes a comparator that compares the output value of the lens encoder with the output value of +, and a lens drive unit that drives the position of the photographic lens forward 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 adder matches a preset reference voltage value, and the output value of the lens encoder becomes a value corresponding to the output value of the subtracter at that time. An automatic focus adjustment device for a video camera, characterized in that the focusing lens group of the photographing lens is driven by the lens drive unit until the optimum focus position is reached, and the focusing lens group is stopped at the optimum focus position. (2) The rotation angle corresponding to the shooting distance from close range to infinity of the helicoid of the focusing lens group is divided into a preset number of divisions,
An analog signal is output as a digital signal having the number of bits determined according to the number of divisions, and the comparator divides the signal voltage range output from the subtracter into the same number of divisions (same number of bits) as the lens encoder. A patent characterized in that the structure includes a digital converter and a digital comparator that digitally compares the output value of the analog-to-digital converter and the output value of the lens encoder for each corresponding bit. An automatic focus adjustment device for a video camera according to claim (1). (3) The lens encoder outputs an analog signal that varies linearly in accordance with the rotation angle corresponding to the shooting distance from close range to infinity of the helicoid in the focusing lens group, and the signal voltage range output by the subtracter is set to be equal to the voltage range that the lens encoder can take, and the comparator is configured to compare the output value of the subtracter and the output value of the lens encoder in an analog manner. An automatic focus adjustment device for a video camera according to claim J(1).