JPS6173117A - Automatic focusing device of video camera - Google Patents

Abstract

PURPOSE:To execute an automatic focusing by driving a focusing lens groups until an output value of a lens becomes a value corresponding to an output signal of the second integrator at the time when an output signal of the first integrator has coincided with a reference voltage signal, and stopping it at an optimum focused position. CONSTITUTION:A sum and difference operation of I1, I2 is executed in an initial stage, and a signal processing constitution which is advantageous to a dispersion of the gain of an I1 system and an I2 system is set. A margin to an offset voltage quantity in an input stage is improved by compressing a dynamic range of a signal inputted to the first and the second integrators. A margin to an offset of the integrator is improved by using not only an automatic gain adjusting function but also a light emitting quantity automatic adjusting function of an infrared light emitting diode, and compressing a signal range. When executing a range measurement of the N + 1-th time, in case when the N-th time is a long distance, the infrared light emitting diode is made to emit a light by a prescribed light quantity value so that the automatic gain adjustment works mainly. In this way, the reliability of an integral value is improved, and a focusing function of a high accuracy can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic focusing device for a video camera that projects infrared light and is based on the principle of triangulation.

Conventional Structure and Its Problems FIG. 1 shows the principle of an automatic focus adjustment device for a video camera (hereinafter referred to as an active focus adjustment device) based on the principle of triangulation using infrared light.

In the figure, infrared light for distance measurement projected from a light projection means 1 passes through a projection lens 2 and reaches a distance measurement object 3, and then is reflected and enters a light receiving element 6 through a converging lens 4. . At this time, if the distance between the light projecting means 1 and the light receiving element 6 and the distance measurement object 3 changes, the angle of incidence of the reflected light on the light receiving element 5 or the position of incidence of the reflected light on the surface of the light receiving element changes.

The gap calculating unit 6 performs a predetermined calculation based on the incident angle of this reflected light or the above-mentioned incident position. The lens driving device 7 drives the photographing lens made up of a plurality of lenses to an appropriate focusing position based on the calculation result of the calculator 6, and completes the focus adjustment.

Next, as a conventional example, the light receiving element 5 is PSD.
(Position 5
A signal corresponding to the distance between the subject and the light projecting means is obtained by calculating the ratio of two photocurrents taken out from the optical position detector using a well-known optical position detector such as A method for adjusting the focus of a video camera based on a signal will be explained.

FIG. 2 shows the geometrical arrangement of the light emitting/receiving section and the principle of distance measurement in the conventional example. FIG. 3 is a block diagram showing components such as an arithmetic unit in the conventional example.

Infrared light emitted from an infrared light emitting diode 9 (hereinafter referred to as an infrared LED) is focused by a projection lens 10 and projected onto a subject 11 . The reflected light from the object is converged by a converging lens 12 and forms a spot image on the light receiving surface of the original position detector 13.

The effective length of the light receiving surface of the optical position detector is t. , the optical axes of the emitter lens and receiver lens are arranged parallel to each other,
The distance between the optical axes is d, the focal length of the light-receiving lens is f, and the distance between the subject and the light-emitting lens is assumed to be d.

When L is infinitely far away, a spot image forms at the center of the PSD and is extracted by the optical position detector.

(2) The center position of the optical position detector is adjusted so that 2 is equal. Let X be the positional amount of the spot image formation position at a distance from the center position of the optical position detector. At this time,
The displacement amount X is expressed by the following formula.

d″f...(1)=!ta,
Two photocurrents 11 output from the optical position detector 13. I
2 is inversely proportional to the distance between each output end electrode 14, 15 and the spot image formation position.

In other words, ! 1° in the above equation represents the total amount of current generated by the amount of light of the spot image. Next, transforming equations (1), (2), and (3) gives the following. (→According to the formula, it is the reciprocal of the distance to the subject. Since the rotation angle of the helicoid, which is the focus adjustment mechanism of a normal photographic lens, and the reciprocal of the distance to the subject are almost proportional, the rotation angle and Then, automatic focus adjustment is possible.Next, a conventionally known arithmetic processing method will be explained using FIG.

Infrared light generated by an infrared LED 17 driven by an LED drive circuit 16 is projected onto a subject by a projection lens 18. The reflected light from the object is converged by the converging lens 19 to form a spot image on the light receiving surface of the optical position detector 2Q. Generally, the output signal from the optical position detector 20 includes a component caused by the infrared LED 17 and a component in response to background light such as sunlight or fluorescent light. is pulse-driven at a certain predetermined frequency f0, and the above-mentioned predetermined frequency f is detected by the optical position detector 20.
A method is used to detect a desired signal component by extracting an AC component corresponding to c. Output current 11 from optical position detector 2o. I2 are respectively current-voltage converted by the first and second current-voltage converters 21.22, and then the first
．． The signal is supplied to the first and second amplifiers 25, 26 via the second capacitors 23, 24, and only the signal components that are tributary components are amplified at a predetermined magnification. Next, the output signals of the first and second amplifiers 25 and 26 are supplied to first and second intermediate frequency pass filters 27 and 28 (hereinafter referred to as BPF), respectively. The BPF is configured such that its center frequency matches the drive frequency fc of the infrared LED 17, and has a function of greatly improving the ratio of noise components to signal components. The output signal of the first 28 PF27.28 is
After passing through two second rectifiers 30, a DC voltage v1. Output v2. The adder 31 performs the above v1. Add v2 and [V1
+V2), and the subtracter 32 outputs a signal V+ proportional to v1.+V2). By subtracting v2, a value V- proportional to vl-v2) is output.

■+=α・(v1+v2) ・・・・・・
...(5)v=β・(v1+v2)・
(6) α and β are constants The first integrator 33 performs voltage-to-current conversion according to the DC voltage value output from the adder 31, charges the capacitor with a constant current, and charges the capacitor with a constant current. It is configured to output an integral value v+* of a waveform that increases almost linearly as time progresses.

The second integrator 34 performs voltage-to-current conversion according to the DC voltage value output from the subtracter 32, charges the capacitor with a constant current, and generates a waveform that increases almost linearly as time passes. It is configured to output an integral value of 7 years.

Since the series of arithmetic operations described above is a process that maintains linearity, the output value v+* of the first integrator 33 is proportional to (11 + engineering,), and the output value v! of the second integrator 34 is proportional to (11 + engineering). is (I, -I2
) will be proportional to The explanation will be continued below with reference to FIG. Waveform a in FIG. 4 is a waveform diagram showing light emission from an infrared LED. Light is emitted intermittently at a certain fixed period, and pulses are generated at a driving frequency f0 during the light emitting period.

Waveforms S and C show examples of output waveforms of the adder 31 and the subtracter 32, respectively. The waveforms d and e are respectively connected to the first integrator 33. An example of the output of the second integrator 34 is shown. The output v+* of the first integrator is supplied to a comparator 36 and compared with a reference voltage VR36.

As shown in FIG. 4d, the polarity of the output of the comparator 36 is reversed at the intersection of the reference voltage value vR and the v+* waveform to generate a pulse signal. Waveform V, *d・V±・both start integration at the same time, and ■+*.

A 7-year-old has the following relationship with I, , I, and I.

v+*=A, (I, +I21, t
・---<7'>V *=B, (11-I2)-t
, -, -(@t; Integration time, A and B are constants. Therefore, if the output level vF of the second integrator at the time when v4*=vR is detected, this value is essentially the same as already explained. The signal is proportional to the reciprocal (T-) of the distance to the subject.The second integrator output signal VF is supplied to the analog-to-digital converter 37 and converted into a digital signal.On the other hand, The focus position of the photographing lens 38 is detected by the lens encoder 39, and ranges from close photographing distance to infinity (helicoid angle).
', etc.) is divided into 64 and output as a 6-bit position signal. The lens encoder is one that maintains mechanical contact with a focus adjustment mechanism such as a helicoid that is normally provided in the focusing lens section of a photographic lens, moves to adjust the focus, and outputs a position detection signal. Ru.

A digital comparator 4o compares bits of corresponding digits between the output signal a of the analog-to-digital converter 37 and the output signal S of the lens encoder 39. The lens drive unit 41 receives the output of the digital comparator 40. The focus of the photographing lens 38 is adjusted so that a=b, and the automatic adjustment is completed by stopping at the optimum focus position.

If we consider the performance required for an autofocus device for a video camera, we can see that home video cameras are generally equipped with a 6x zoom lens as standard equipment, and
Sufficient focusing accuracy is required over the range from about m to 20 m.

Next, consider the dynamic range of signals that should be handled in the active focus adjustment device. In general, the amount of light incident on the light receiving element is proportional to the amount of light emitted by the infrared LED, proportional to the infrared reflectance of the subject, and inversely proportional to the square of the distance to the subject. If the reflectance is 10% to 100%. ,
If you want to measure a distance of 1m to 20m, use 1:4o.
We will be dealing with oO, a signal with a very wide dynamic range. Therefore, the factors that determine the performance of an active focus adjustment device are the signal-to-noise ratio (S/N) of the photodetector and first-stage amplifier, the wide dynamic range mentioned above, variations in circuit elements, temperature changes, DC The question becomes whether signal arithmetic processing with sufficiently good linearity is possible with respect to factors such as offset.

When considering the conventional example shown in FIG. 3 from the above viewpoint, it has the following problems. First, the output signals I, I2 from the optical position detector 2° are passed through a current-voltage converter, an amplifier, a BPF, and a rectifier to obtain signals vl and v2. At this time, Assuming that the gain q of the I, -V1 system and the gain q2 of the 2-v2 system, the ranging signal vF
(shown in Figure 4) becomes substantially te. Therefore, if q1=q2, I corresponding to the change in distance measurement,
Since the original linearity is maintained with respect to relative changes in ,I, no errors occur in distance measurement accuracy. However, with the conventional configuration as it is, it is very difficult to ensure consistency between ql and q2. For example, it is nearly impossible to compensate for variations in BPF and temperature characteristics.

The second problem is that it is very difficult to accurately generate vF for a required signal dynamic range. A circuit configuration for realizing the functions required of the first integrator 33 and the second integrator 34 is shown in FIG. The output signal V+ of the adder 31 is input from the input terminal 42,
The inverting amplifier 43 inverts the polarity of the signal. The switch 44 is closed except during the light emission period of the infrared LED 1a, and the reference voltage 47 applied to the non-inverting input terminal of the operational amplifier 46 is output as is to the output terminal 45. Next, during the light emission period, the switch 44 is opened, and the capacitor 49 is charged with a constant current value determined by the value obtained by dividing the potential difference between the output voltage of the inverting amplifier 43 and the reference voltage 47 by the resistor 48, and the output is output. A triangular voltage waveform that increases linearly with time is output to the terminal 45. With the above configuration, when the amount of light received by the light receiving element is zero, no signal component appears at the input terminal 42 and a constant DC voltage value is obtained. Make initial adjustments to prevent this from occurring. However, due to temperature changes and power supply fluctuations, an integral waveform may be generated at the output terminal 45 even though there is originally no signal. This is because there are fluctuations in the DC voltage value at the input terminal, offset voltage of the inverting amplifier 43, offset voltage of the operational amplifier, etc. Since the integrated output value for this off-set voltage becomes a direct distance measurement error, it is necessary to limit the amount of offset fluctuation due to the power supply fluctuation and temperature change to within a certain tolerance value.

In general, there is a strong demand for low power consumption in video cameras, and the circuit shown in FIG. 6 also needs to be operated with a power supply voltage of about 6V. Assuming that the required signal dynamic range is limited to 1:400 (distance 1 m to 20 m2 with 100% reflectance), the maximum signal level at the output of the inverting amplifier 43 is designed to be approximately 1 V, and the minimum signal level is 2.6
The most appropriate design is mV. Integral time constant (5th
The product of the resistor value and the capacitance value of the capacitor shown in the figure) and the maximum integration time Tmax are set to values that allow distance measurement to be performed at the required minimum signal level. The fact that distance measurement is executed here means that the first integrator output v+* reaches the reference voltage value vR within the maximum integration time Tmax, the polarity of the comparator output is reversed, and the value of analog-digital conversion +v1- Therefore, if the integration time constant and maximum integration time Tmax are set so that ranging is performed at a minimum signal level of 2-5 mV, then for a maximum signal level of 1v, Tmax / 400. Distance measurement will be performed in time. The above is a case in which the circuit configurations shown in FIGS. 3 and 5 work ideally, but the occurrence of an offset voltage of about several mV due to power supply voltage fluctuations, temperature fluctuations, etc. is unavoidable. Therefore, when the signal level is small, it is impossible to distinguish between the signal and the offset amount, making it impossible to guarantee accurate ranging operation.

As is clear from the above explanation, i
t, it is practically impossible to achieve the required performance required for the automatic focus adjustment function of a video camera.

Object of the Invention The object of the present invention is to provide an automatic focus adjustment for a video camera that has highly accurate distance measurement performance and that allows a distance measurement projector/receiver to be installed without causing any major obstacles to the mechanical design of the video camera's photographing lens. The goal is to realize the device.

Structure of the Invention The automatic focus adjustment device for a video camera of the present invention includes a light emitting source that emits infrared light for distance measurement, a light source driving section that drives the light source, and a light source that emits infrared light for distance measurement. a converging lens that condenses reflected light from an object to be photographed, and a light position that is installed at a fish gathering position of the converging lens and outputs a first and second photocurrent at a constant rate according to the imaging spot position of the reflected light. a detector; a first and second current-voltage converter that converts the first and second photocurrents into current-voltage; and an adder that adds output signals of the first and second current-voltage converters. , also the above first
a subtracter that performs subtraction of each output signal of the second current-voltage converter; a first variable gain amplifier to which the output signal of the adder and the first control signal are supplied; and an output signal of the subtracter; and a second variable gain amplifier to which the first control signal is supplied, an output signal of each of the first and second variable gain amplifiers, a first second detector, and the first and second detector. a first and second integrator that is supplied with each output signal of the detector, charges a capacitor with a constant current having a magnitude responsive to the output signal of the detector, and outputs a voltage value that increases or decreases approximately linearly; and a level determiner which is supplied with the output signal of the first integrator and the reference voltage signal and compares the levels of both signals, and which mechanically detects the rotation angle of the helicoid of the focusing lens group that adjusts the focus of the photographic lens. a lens encoder that converts the signal into an electrical signal and outputs it; a comparator that compares the output signal of the second integrator with the lens encoder output signal; and a focusing lens of the photographic lens in response to the output signal of the comparator. a lens drive section that drives the position of the group forward or backward; a second control signal that is supplied with the lens encoder output signal and the first detector output signal and that controls the light emitting source drive section; an error detector that generates the first control signal that controls the gain of the second variable gain amplifier, and the output value of the lens encoder matches the output signal of the first integrator and the reference voltage signal. The focusing lens group of the photographing lens is driven by the lens driving section until it reaches a value corresponding to the output signal of the second integrator at the time when the focusing lens group of the photographing lens is driven, and the focusing lens group is stopped at the optimum focus position, which is highly accurate. The present invention is intended to realize an automatic focus adjustment device for a video camera having 11 distance performance.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The basic configuration of the present invention is based on the principle of infrared projection triangulation and is exactly the same as the configuration shown in FIG. Furthermore, the geometrical arrangement of the light emitting and receiving parts and the principle of distance measurement are also exactly the same as those shown in FIG. Therefore, the configuration of the arithmetic unit, which is the main point of the present invention, will be explained below with reference to FIG.

The light projector 60 is composed of a light source 51 and a light source driver 52, which emit light intermittently at a certain period and are pulse-driven at a certain frequency fs during the light emission period. The case where an infrared LED is used as the light emitting source 61 will be described below. Infrared light from the infrared LEDs1 is projected onto the subject by a projection lens 53. The reflected light from the subject passes through the converging lens 54 to the optical position detector 6.
A spot image is formed on the light receiving surface of 5. Here, it is assumed that the optical position detector uses the same element as that used in the description of the conventional example. The first signal from the optical position detector 5i
Second output current 11. I, are respectively supplied to first and second current-voltage converters 56, 67 and converted into voltage signals.

In addition, the output current 11゜■ is divided into two parts: 60H2,12
It contains low frequency components such as 0 Hz, etc., and is configured so that the above-mentioned unnecessary components are not outputted to the output of the first and second current-voltage converters. First and second current-voltage converter 56.6
The output signals of 7 are provided to an adder 58 and a subtracter 59, respectively, 11+I,.

Outputs a signal corresponding to 1l-I2. The output signals of the adder 58 and the subtracter 59 are respectively supplied to first and second variable gain amplifiers 60 and 61, and the gains are adjusted by the first control signal 62. The output signals of the first and second variable gain amplifiers are respectively supplied to first and second wave detectors 65 and 66 via first and second band amplifiers 63 and 64. The band amplifier is configured to amplify and pass only a frequency component in a narrow band centered around one driving frequency fs of the infrared LED, and has a function of improving the signal-to-noise ratio.

The first and second wave detectors 65 and 66 respectively receive DC signals v+ and v- in response to the output signal amplitude values of the first and second band amplifiers.
Output. The output signal V+ of the first detector 65 is supplied to an error detector 67, which outputs a first control signal 62 for varying the gain of the first and second variable gain amplifiers, and a second control signal 62 for controlling the light source driving section 52. A control signal 68 is output. Infrared LE
The amount of light emitted by D51 is substantially adjusted by the second control signal 68. The first integrator 69 is the first detector 6
5 output signal V+ is supplied, ■ voltage-current conversion is performed according to the DC voltage value of It is configured to output an integral value v+*. The second integrator To is supplied with the output signal V- of the second detector 66, performs voltage-to-current conversion according to the DC voltage of V-, charges the capacitor with a constant current, and charges the capacitor almost linearly over time. It is configured to output an integral value v4 of a waveform that increases or decreases in a straight line. FIG. 7 shows an example of signal waveforms at each part. Waveform & is
The driving waveforms, waveforms S and c of the infrared LEDs1 are the first waveforms, respectively.
Waveforms d and e, which are output signal waveform examples of the second current-voltage converter 56 and 67, respectively show waveform examples of the output signals v+ and v- of the first and second wave detectors 65 and 66. First integrator 6
The output signal v+* of 9 is supplied to a level determiner 71, where it is compared with a reference voltage signal Vp 72, and a pulse signal is generated at a time when v+*=vP. The waveform q in Figure 7 is
This shows the pulse signal mentioned above.

In the above signal processing, v++=01. (Work, + Work,) −t −=−−−
--(1o)C1C2 is a constant v-*=C1・(engineering, -12)・t・・・・・・(11
) over the integral time holds, so if we always detect the value of v-* (hereinafter referred to as Vy) at the time when v+*=vP, due to the nature of the hanging device, the reciprocal of the distance Since it is proportional to vFOc
r, and the focus of the video camera can be adjusted using the value of VF. The waveform in Figure 7 is v! This shows the waveform of VF is the amplitude value of v-* at the rising edge of the output pulse waveform q of the level determiner 71. FIG. 8 shows a specific circuit configuration of the first and second integrators 69 and 70, and the output signal V+ of the first detector 65 is supplied from the input terminal 73. The switch 74 is closed during the period when the infrared LED does not emit light, and the reference voltage 75 applied to the non-inverting input terminal of the operational amplifier 76 appears as it is at the output terminal 77. Conversely, during the light emission period, the switch 74 is open, and the capacitor 79 is charged with a constant current value obtained by dividing the potential difference between the voltage applied to the input terminal 73 and the reference voltage 75 by the resistor 78.

Here, the timing of switching the switch 74 from closed to open needs to be delayed by a certain period of time (τ), as shown in the waveform f in FIG. This is to avoid the transient response time of the rising portion of v+ and v-. The output signal of the second integrator 7o (MF) is supplied to a comparator 80.

On the other hand, the focus position of the photographing lens is determined by the lens encoder 81.
The range from close shooting distance to infinity (
Actually, it is output as a 6-bit position signal b' obtained by dividing the helicoid angle, etc. into 64 parts, and is supplied to the comparator 80.

The comparator 8o is composed of an analog-digital converter 82 and a digital comparator 83, and the signal VF is converted by the analog-digital converter 82 into a 6-bit digital signal a'.

The digital comparator 83 compares the digital signal a' and the position signal b'. Lens drive unit 8
4 receives the output of the digital comparator 83, and a'=
The focus of the photographic lens 85 is adjusted so that the image becomes b', and the automatic adjustment is completed by stopping at the optimum focus position.

FIG. 9 shows the detailed configuration of the error detector 67. The error detector includes first and second switching circuits 86 and 87 and a differential amplifier 88. First switching circuit 8
6 outputs a first reference voltage signal 90 according to the output 89 of the lens encoder 81, or outputs the first reference voltage signal 90 according to the output 89 of the lens encoder 81,
Switching is performed to output the output signal V+91. The output signal of the first switching circuit is the first control signal 62.

When the first control signal 62 is a constant reference voltage signal, the first and second variable gain amplifiers 60 and 61 operate with a constant gain. Further, when the first control signal 62 outputs the output signal V+ of the first detector 66, the first variable gain amplifier 60. First band amplifier 63. The first detector 66 and the error detector 67 form a closed loop so that even if the input signal of the first variable gain amplifier 6Q changes, the value of the output signal V+ of the first detector 65 always remains constant. A negative feedback loop configuration is provided to automatically adjust the gain of the first variable gain amplifier 6o. At this time,
Since the gain of the second variable gain amplifier 61 is similarly adjusted by the first control signal, the gain of the second variable gain amplifier 61 is adjusted by following the imaging width value of V+.
The level of the output signal V- of the detector 66 is also adjusted. On the other hand, the second switching circuit 87 switches between outputting the second reference voltage signal 92 and outputting the output signal of the differential amplifier 88 based on the output signal 89 of the lens encoder.

The differential amplifier 88 receives the output signal v+91 of the first detector 65.
and the third reference voltage signal 93.

The output signal of the second switching circuit 87 becomes the second control signal. When the output of the differential amplifier 88 appears as the second control signal 68, the light source driver 62. Infrared LED51,
Optical position detector 55, first and second current-voltage converter 66.5γ
, adder 68. First variable gain amplifier 60, first band amplifier 63. A closed loop is formed by the first detector 66 and the error detector 67, and the amount of light emitted by the infrared LED 51 is varied according to the output signal V+ of the first detector 65, so that the automatic light amount always keeps the value of V+ constant. A negative feedback loop configuration is used so that the adjustment function works. When the second control signal 68 is a constant voltage value, the infrared LED s1 is configured to always emit light at a preset maximum amount.

The configuration method of one embodiment of the present invention has been described in detail above. Next, key points for obtaining highly accurate ranging performance, which is a feature of the present invention, will be explained.

The first point is that the sum-difference calculation of I, . . . I2 is performed at an early stage, resulting in a signal processing configuration that is advantageous against variations in gain of the system, I2 system, and I2 system. In other words, in the conventional configuration,
Before performing the sum-difference calculation, the AC signal valve amplifier, BPF
, a rectifier, etc., so the gain variations in each block are superimposed, and overall, the engineering, system, and engineering are affected. The gain ratio of the system increases, which is a factor that greatly deteriorates the ranging accuracy, but in the configuration according to the present invention, the cause of the mismatch in the gain ratio of the 11th system and the 12th system is limited to the first stage current-voltage converter. Therefore, the above problems can be greatly improved.

In addition, in the conventional example, since the sum-difference calculation is performed at the DC signal level after rectification, the DC operating point inevitably fluctuates due to the weight of the offset voltage component, which deteriorates direct distance measurement accuracy. However, in the present invention, since the sum-difference calculation is performed at the AC signal stage, the above problem does not occur at all.

The second point is that by compressing the dynamic range of the signal entering the first and second integrators, the margin for the amount of offset voltage at the input stage of the integrator is greatly improved. In the explanation of the conventional example, when the signal dynamic range is assumed to be 1=400 (distance 1 m to 20 m, object reflectance 100%), the integrator input has a practical circuit configuration of approximately 2. While it is necessary to integrate a signal of smV to 1V, it is necessary to integrate a signal of several meters due to power supply voltage fluctuations and temperature changes.
It has been explained that when a DC offset voltage of V or more is expected to occur and the signal level at the integrator input is small, it is difficult to distinguish between the offset voltage amount and the signal voltage amount, resulting in malfunction. Therefore, compressing the signal level to 25mV
~1v, the margin for offset can be improved by a factor of 10. Similarly, if the signal level is compressed by 4 degrees to 250 mV to 1 V, the margin against offset will be improved by a factor of 100, and the influence of the DC offset voltage will become almost negligible. As a method of signal level compression, a variable gain amplifier 60.
A possible method is to change the gain of 61. Check the signal level. . A variable gain amplifier 60.6
1, it is necessary to have a gain change of 4 odB, but in this case, both the variable gain amplifiers 60 and 61 are connected to the first
Since it is controlled by the control signal 62, two variable gain amplifiers 60 and 61 are required to prevent the ranging accuracy from deteriorating.
It is necessary to ensure sufficient consistency of the gain characteristics with respect to the zero first control signal. If the above consistency is not achieved, for example, the output current 11 of the optical position detector 65. I2
As, depending on the magnitude of the quantity value (absolute quantity of 11 + I 2),
11-■2 system and 11+ after variable gain amplifier 60.61
I.

An imbalance occurs in the gain ratio of the system, and the final ranging signal V
The value of F will be different. In a practical circuit configuration, it is extremely difficult to realize a variable gain amplifier 60, 61 with good gain matching with respect to the control voltage in a range of 4 odB. Therefore, it is practically necessary to limit the gain variation width of the variable gain amplifiers 60 and 61 to about 20 dB.

In view of the above problems, in the present invention, the signal range is compressed by not only using an automatic gain adjustment function using a variable gain amplifier but also an automatic light emission adjustment function of an infrared light emitting diode. We are trying to improve the margin against offset. Automatically adjusting the amount of light emitted generally has a large amount of light received at short distances (the S/N is also considered to be sufficient), so even if the amount of light is reduced, virtually no problems will occur in terms of distance measurement performance. In other words, as a method of signal dynamic range compression, the output signal V+ of the detector 66 is
As a way to automatically adjust the value so that it is always constant,
The above automatic gain adjustment and automatic light emission amount adjustment are used together, but the above two automatic adjustment functions are used under conditions that do not cause any unnaturalness in consideration of the actual operation of the video camera, and under conditions that do not cause unstable circuit operation. It is necessary to operate under conditions such that this does not occur.

With this method, distance measurement can be completed and the focus of the photographing lens can be adjusted with -1 flash of light. Therefore, the basic repetition period of light emission can be freely designed. If distance measurement is performed at a repetition frequency of several Hz from the viewpoint of operability, it is rare for the subject to move significantly between the Nth and N+1th distance measurement periods. Therefore, it is considered that there will be no major contradiction even if the N-th distance measurement data is referred to during Ne's first distance measurement. From the above point of view, in the present invention, when the N+1th distance measurement is performed, if the Nth time is a short distance measurement, the automatic light emission amount adjustment is mainly operated, and the error detector 67 is set so that the automatic gain adjustment does not work. Switch.

On the other hand, if the Nth time is at a long distance, the infrared light emitting diode is made to emit light at a constant light intensity value, and the automatic light emission adjustment does not work, and the error detector 6 is set so that the automatic gain adjustment mainly works. The configuration is such that the (N+1)th distance measurement is performed by switching the completed state. Whether or not the Nth distance measurement data is a short distance can be easily determined by using the output value of the lens encoder, and the state switching of the error detector 67 is configured to be performed using the lens encoder output. . As explained above, by using the two automatic adjustment functions together, it is possible to easily compress the signal dynamic range by about 40 clB in practice, and therefore, the margin for the allowable offset amount of the integrator can be greatly improved. becomes possible.

In the embodiment of the present invention shown in FIG. 6, even if the positions of the variable gain amplifiers 60, 61 and the band amplifiers 63, 64 are switched back and forth, the same functionality can be realized in practice. Furthermore, in the above description, the lens encoder 81. Analog-
Although the case where the digital converter 82 or the like handles a 6-bit digital signal has been described, the present invention is not limited to this, and the number of bits may be increased or decreased as necessary. Furthermore, in the above description, the case where infrared light for distance measurement is projected using the projection lens 53 has been explained, but the photographing lens or a part of the lens group constituting the photographing lens and the optical system that reflects or refracts the infrared light. Similar automatic focus adjustment can be achieved even when projection is performed using a system.

Effects of the Invention As explained in detail above, the present invention has two advantages of the optical position detector.
An integral value based on the added value of two output currents and an integral value based on the subtracted value of the two output currents are calculated, and the value of the integrated value based on the subtracted value at the time when the integrated value based on the added value reaches a certain constant value, In a device that adjusts the focus of the photographic lens by driving the focusing lens group of the photographic lens so that the output values of the lens encoder match, the actual distance measurement error is increased by calculating the sum and difference of the two output currents at an early stage. In addition to improving the reliability of the integral value mentioned above, by compressing the dynamic range of the signal through automatic light emission amount adjustment and automatic gain adjustment,
It is possible to obtain a highly accurate ranging signal and to use this to realize a highly accurate focusing function of a video camera.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram of an automatic focus adjustment device based on the infrared projection triangulation principle, Fig. 2 is a schematic diagram showing the operating principle of the optical position detector used in the conventional example and the present invention, and Fig. 3 is FIG. 4 is a block diagram showing the system configuration of the conventional example. FIG. 4 is a signal waveform diagram showing the response of each part in the conventional example. FIG. 5 is a block diagram showing the configuration of the integrator. FIG. 6 is the system configuration of the present invention. , FIG. 7 is a signal waveform diagram showing the response of each part in the present invention, FIG. 8 is a circuit diagram showing the configuration of the integrator, and FIG. 9 is a block diagram showing the configuration of the error detector. It is. . 61... Infrared LED, 52... Light source drive section, 64... Converging lens, 56...
・Optical position detector, 66.5...Current voltage converter, 58...Mark adder, 69...Subtractor, 6
0,61...Variable gain amplifier, 63.64...
... Bandwidth amplifier, 65.66・Old...Detector, 67・
...Error detector, 69.70...River integrator, 7
1... Level judger, 81. Mark/lens encoder, 82... Analog digital converter, 83
・Mountain: Digital comparator, 84: River: Lens drive section, 86: --- Photographing lens, 86.87...
...Switching circuit, 88...Differential amplifier.

Claims (3)

[Claims] (1) A light source that emits infrared light for distance measurement, a light source drive unit that drives the light source, and a condenser that collects the reflected light of the infrared light for distance measurement from the object to be measured. a lens; an optical position detector installed at the focal position of the converging lens and outputting first and second photocurrents at a constant rate according to the imaging spot position of the reflected light; and the first and second photocurrents. first and second current-voltage converters that convert photocurrent into current-voltage;
an adder that adds the output signals of the second current-voltage converters; a subtracter that also subtracts the output signals of the first and second current-voltage converters; and an output of the adder. a first variable gain amplifier to which the signal and the first control signal are supplied, a second variable gain amplifier to which the output signal of the subtracter and the first control signal are supplied; a first, a second, and a
a first and second detector to which output signals of each of the first and second band amplifiers are supplied; and an output signal of each of the first and second detectors to which the first and second detectors are supplied; A first and second integrator that charges a capacitor with a constant current of a magnitude responsive to the output signal of the detector and outputs a voltage value that increases or decreases approximately linearly, and an output of the first integrator. A level determiner that is supplied with a signal and a reference voltage signal and compares the levels of both signals, and a lens that mechanically detects the rotation angle of the helicoid in the focusing lens group that adjusts the focus of the photographic lens, converts it into an electrical signal, and outputs it. - an encoder, a comparator that compares the output signal of the second integrator and the lens encoder output signal, and a position of the focusing lens group of the photographic lens in response to the output signal of the comparator; a lens drive section that drives forward or backward; a second lens drive section that is supplied with the lens encoder output signal and the first detector output signal and that controls the light emitting source drive section;
and an error detector that generates the first control signal that controls the gain of the first and second variable gain amplifier, and the output value of the lens encoder is the output signal of the first integrator. The focusing lens group of the photographing lens is driven by the lens driving section until it reaches a value corresponding to the output signal of the second integrator at the time when and the reference voltage signal coincide with each other, and the focusing lens group is stopped at the optimum focus position. An automatic focus adjustment device for a video camera, comprising: (2) The lens encoder equally divides the rotation angle of the helicoid in the focusing lens group corresponding to the shooting distance from close range to infinity into a preset number of divisions, and the bit is determined according to the division. an analog-to-digital converter that outputs a digital signal having a number, and the comparator divides the signal voltage range output from the second integrator into the same number of divisions (the same number of bits) as the lens encoder; Claim (1) characterized in that it is configured to include a digital comparator that digitally compares the output value of the analog-digital converter and the output value of the lens encoder for each corresponding bit. Automatic focus adjustment device for a video camera as described in Section 2. (3) The output signal of the first detector and the first reference voltage signal were supplied, the lens encoder output signal was used to switch between the two signals, and one or both signals were added at a certain ratio. a first switching circuit that outputs a signal as a first control signal; a differential amplifier that is supplied with the output signal of the first detector and a second reference voltage signal and amplifies the difference between the two signals; Using a second switching circuit that is supplied with the output signal of the amplifier and the third reference voltage signal, switches between both signals using the lens encoder output signal, and outputs one of the signals as a second control signal. Claim No. (1) is characterized in that an error detector is configured.
Automatic focus adjustment device for a video camera as described in Section 2.