JP2763828B2 - Apparatus and method for automatically adjusting video camera focus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device for a video camera and a method thereof, and more particularly to an automatic focusing device for a video camera capable of automatically adjusting the focus of a video camera on a moving subject. It is about the method.

[0002]

2. Description of the Related Art In general, an automatic focusing (AF) system of a video camera is roughly classified into an active system such as an infrared distance measuring system and an ultrasonic system, and a passive system such as an image sensing system and an image detecting system. You.

[0003] In particular, the principle of an active method using an infrared distance measuring method in which an infrared ray is projected onto a subject to be photographed and a reflected distance measurement signal reflected by the subject is obtained is as shown in FIG.

In FIG. 1, infrared light emitted from an infrared light source (not shown) such as an infrared light emitting diode (hereinafter referred to as an infrared LED) is transmitted through a light projecting lens 201 to a subject 2.
The light is reflected at 04, and the reflected light forms an image on the light receiving element 203 through the light receiving lens 202. At this time, L is the distance from the light projecting lens 201 to the subject 204, R is the distance from the light projecting lens 201 to the light receiving lens 202, F is the focal length of the light receiving lens 202, and X is the distance from the center of the light receiving element 203 to the light receiving lens 202. If the distance to the infrared beam that has passed through and entered the light receiving element 203 is L = L
A relationship such as R · (F / X) holds. Accordingly, since the distance L from the light projecting lens 201 to the subject 204 is inversely proportional to the distance X from the light receiving element 203 to the reflected light incident point, the distance can be measured.

Here, the light receiving element 203 is divided into two channels, A and B, and its electrical equivalent circuit is as shown in FIG. In the drawing, when the P-side electrodes are A and B and the N-side electrode is C in the structure of the light receiving element, I ₀ is the total current generated by the light spot irradiation position, V ₀ is the driving voltage, and D ₁ is the ideal diode. , C _i is the coupling capacity, R _sh
Is a shunt resistance, R ₁ and R ₂ are resistances from the incident point of the reflected light to the electrodes A and B, S is a current source,
₁ indicates a load resistance. At this time, the photocurrents I ₁ and I ₂ output from the light receiving element can be represented by the following equations.

(I ₂ −I ₁ ) / (I ₂ + I ₁ ) = {R _p / (R _p + R ₁ )} (2 / L) · X (where R _p = R ₁ + R ₂ ) According to the above equation, the ratio of the output current difference to the sum (I ₂ −I
₁ ) / (I ₂ + I ₁ ) is proportional to the distance X from the midpoint of the electrodes A and B, that is, the midpoint of the light receiving element to the incident point of the reflected light. The incident angle or the incident point of the reflected infrared beam, which is the distance measurement signal, on the light receiving element changes due to a variation in the distance between the subject and the light projecting device.

Here, when the object is focused, the reflected light is incident on the center of the light receiving element and I ₁ and I ₂ are converted into current signals of the same magnitude, so that the value of the equation becomes 0. If the light is out of focus, the incident position of the reflected light is imaged by one of the light receiving elements, so that the current magnitudes I ₁ and I _{2 of} both channels are different, and the value of the equation becomes a non-zero value. . Therefore, the ratio (I ₂ −I ₁ ) / (I ₂ + I) of the difference and the sum of the distance X from the middle point of the electrodes A and B to the incident point of the reflected light and the output current.
Unless the AF motor is controlled so that the relationship between ₁ ) and ₂ ) maintains linearity, accurate focusing cannot be achieved.

In FIG. 3, the infrared light generated by the infrared LED 1 of the light emitting section is projected onto an object (not shown), reflected and incident on the light receiving element 2, and the two-channel electrodes A and B of the light receiving element 2. Is converted to a photocurrent and output as a minute current signal.
After converting this minute current signal into a voltage signal by the first and second preamplifiers 3 configured for each channel,
And a second synchronous detection / amplification unit 4 detects and amplifies the output signals of the first and second preamplifiers 3 so as to be synchronized with a synchronization signal for turning on / off the infrared LED.

In the first and second buffer amplifiers 5, the first
After integrating the output signal of the second synchronous detection amplification section 4, the noise component is removed and the signal level is increased to output. At this time, if the outputs of the first and second buffer amplifiers 5 are A signal and B signal, respectively, the A / D converter 6 composed of an operational amplifier receives the A and B signals and
(| A−B | ≧ V _d , A ≧ B, A + B ≧ V _h ,
A + B ≧ V ₁ ) and outputs this to the microcomputer 7. Here, V _d , V _h , and V ₁ are reference voltages for determining the width of the reaction range, the need for focus adjustment, and the speed control range, respectively. The microcomputer 7 determines the traveling direction, the speed, or the stop of the motor M that moves the imaging lens according to the combination of the four signals in the A / D converter 6, and then sends the speed signal V and the direction signals F, B to the motor drive unit 10. Output, the motor M drives the imaging lens of the video camera to the optimum focus position to complete the automatic focusing.

The microcomputer 7 turns on / off the infrared LED 1.
Clock signal CL for synchronous detection of off and received light signals
K is supplied to the first and second synchronous detection amplifying sections 4 and the infrared LED driving section 9, and the charge of the integration capacitor is used as a signal for determining the integration period of the signal output from the first and second synchronous detection amplifying sections 4. Close-up prevention unit 8 for clearing the image and for preventing focus adjustment on a subject at a short distance within 1 m, for example.
To generate a clear signal CLR to be input to the.

[0011]

However, until the position detection signals of the A and B channels output according to the incident position of the reflected light from the light receiving element are combined with the control signal by the A / D converter to drive the AF motor. Problems such as a large amount of hardware such as a preamplifier, a synchronous detection amplifying unit, and a buffer amplifying unit composed of two channels, and a low bias current and a low There is a problem in that the device needs to be driven with a small offset voltage, and there is a problem that the amount of hardware is further increased in order to improve the problem.

[0012] Further, only the level of both channel signals output from the light receiving element is detected, and the signal obtained by the combination in the A / D conversion unit constituted by the operational amplification unit is used as the motor M.
Therefore, if the difference between the two channel signals is small, accurate focus adjustment of the video camera cannot be performed.

On the other hand, for a subject at a close distance or an infinite distance where focus adjustment is not required, a separate close-in prevention unit 8 is provided.
Or a stopper must be provided in the drive mechanism of the imaging lens, so that the configuration of the video camera becomes complicated.

The present invention has been made to solve the above problems, and has as its object to provide an automatic focusing apparatus for a video camera having a simple and highly reliable structure. .

[0015]

In order to achieve the above-mentioned object, an automatic focusing apparatus for a video camera according to the present invention comprises a light emitting section for emitting a light beam for distance measurement, and a driving section for driving the light emitting section. And a light receiving unit configured with two channels and outputting photocurrent signals corresponding to the two channels in accordance with the incident point of the reflected light projected from the light emitting unit and reflected by the subject. First to convert to an amplified voltage signal and output
And a second current-to-voltage conversion unit, a selection unit that selects the output signals of the first and second current-to-voltage conversion units in a time-division manner, a detection unit that detects the selected output signal, Amplifying and integrating section for amplifying and integrating the output signal to output an integrated voltage signal, a comparing section for comparing the integrated voltage signal with a set voltage and outputting a level signal based on the comparison value, and driving a focus adjustment motor And the level difference of the comparison unit corresponding to both channels is sequentially received, and the difference is compared. The difference between the two level signals drives the motor drive unit until the two level signals match. A non-inverting amplifier circuit for non-inverting amplifying the signal filtered by the detection unit, and a signal output from the non-inverting amplifier circuit having a predetermined setting. And an integrator that integrates the input signal when the output voltage is higher than the voltage and holds the output signal at a predetermined voltage when the output signal of the non-inverting amplifier circuit is lower than the predetermined set voltage. It is characterized by.

Further, the automatic focusing method for a video camera according to the present invention is directed to a video camera using a light emitting unit for emitting a measuring light beam and a two-channel light receiving unit for detecting reflected light of the light beam to a subject. A first channel set determining step of selecting one of the two channels and determining whether a detection signal of the selected channel is set at a predetermined voltage; A second channel determining step of selecting one channel and determining whether a detection signal of this channel is set at the predetermined voltage; and a count amount of the detection signal of the two channels being equal to or longer than a predetermined lower limit period, and After the upper limit period, the focus adjustment is stopped, and when the focus period is equal to or less than the upper limit period, the focus is adjusted to infinity. A long-distance focusing step of feeding back to the first channel set determining step; and a count of the two channels being less than the predetermined lower limit period, and a clock quantity in which the count amounts of the two channels do not match is equal to or greater than the predetermined upper limit period. If so, the closest focus adjustment step in which the motor is rotated in the closest direction and then fed back to the first channel set determination step;
The channel count is less than the predetermined lower limit period,
When the count amounts of the two channels are substantially the same, a light emitting unit and a focus adjustment control step for controlling the light emission intensity, the focus adjusting direction and the speed of the light emitting unit are included.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 4 is a block diagram showing the overall configuration of an embodiment of a video camera according to the present invention.

In FIG. 4, the light emitting section 10 generates infrared rays using, for example, an infrared LED, and emits the infrared rays to a subject to be photographed through a light projecting lens. The reflected infrared light reflected by the subject is focused on the light receiving surface of the light receiving unit 20 at the light incident position through the light receiving lens. This light receiving unit 20
It is composed of a two-divided light receiving element having two channels A and B, and converts incident light into minute current signals I ₁ and I ₂ . First
The second current / voltage converters 30 and 40 amplify the minute current signals I ₁ and I ₂ output from the light receiving unit 20 and output the amplified current signals as voltage signals. The selection unit 50 is formed of an analog switch, and the first and second current-voltage conversion units 30 and 4
At 0, the output signals transmitted to the two channels A and B are sequentially changed in time division and output to the detection unit 60.

The detection section 60 allows only a narrow band frequency component including the driving frequency of the infrared LED among the output signals of the channel selected by the selection section 50 to pass, thereby providing a signal-to-noise ratio (S / N). ) And outputs an amplified signal. The amplification and integration unit 70 amplifies the signal amplified and detected by the detection unit 60 again, converts it into a corresponding current signal, integrates this with a voltage signal that increases linearly with time, and outputs the resulting signal.

In the comparison section 80, the amplification and integration section 70
Is compared with the set voltage, and a level signal based on the comparison value is output. The microcomputer 90 transmits the discharge signal to the capacitor of the integration unit 70 when the output signal of the comparison unit 80 is at a low level, and outputs the voltage output by the amplification and integration unit 70 from the time when the driving signal of the infrared LED starts. The reference clock is counted until the signal reaches the reference voltage, and the infrared LED driving unit 100 and the motor driving unit 110 are controlled.

The infrared LED driving unit 100 receives a burst signal of a predetermined frequency from the microcomputer 90 and adjusts the intensity of the light of the infrared LED, that is, the power in a plurality of stages under the control of the microcomputer 90 to operate the infrared LED. Flash. The motor drive unit 110 receives the speed control signal V and the direction control signals F and B based on the signal counted by the counter of the microcomputer 90, and drives the motor M.

FIG. 5 is a detailed circuit diagram of the automatic focusing apparatus of the video camera according to FIG.

In FIG. 5, the two-part light receiving element 20 has A, B
The first and second current-voltage converters 30 and 4 generate a minute current proportional to the amount of light incident on the two channels, respectively.
Supply 0. By the way, when shooting in a place where the external light is bright, a DC current due to the disturbance light is generated in the light receiving element 20, whereby the first and second current-voltage converters 3 are output.
Both the DC signals supplied to 0 and 40 increase, the level of the output voltage of the operational amplifier OP1 gradually decreases, and a phenomenon occurs that the operational amplifier OP1 is negatively saturated. Therefore, when a DC current flows, a disturbance light elimination circuit 31 for minimizing the feedback impedance and selectively amplifying only the current based on the burst signal from the microcomputer 90, for example, a 10 kHz AC signal is provided. The disturbance light removing circuit 31 increases the DC current due to the disturbance light, the output voltage level of the operational amplifier OP1 gradually decreases, and the output voltage V
_{When a} becomes -0.7 V or less, the transistor TR1 is in a conductive state, and the transient current is removed by the resistors R3, R4 and the capacitor C2. If the DC current due to the disturbance light is removed by the first disturbance light removal circuit 31, at the output terminal of the operational amplifier OP1 of the first I / V converter 32, for example,
In a high-pass filter that outputs an amplified voltage signal having a gain of 50 dB, a capacitor C5 and a resistor R
9 removes low frequency noise of 60 Hz or less from the output signal from the output terminal of the operational amplifier OP1 to output a signal with an improved signal-to-noise ratio (S / N).

Since the structure and operation of the second current / voltage converter 40 are the same as those of the first current / voltage converter 30, the corresponding members are indicated by numbers obtained by adding 10 to the member numbers of the first current / voltage converter 30. The overlapping description is omitted.

The switch 50 selectively changes the output signals of the first and second current-voltage converters 30 and 40 by time division under the control of the microcomputer 90. Switch 5
The output signal of the current-to-voltage converters 30, 40 selected by “0” is detected by the detector 60 including the operational amplifier OP3, capacitors C7, C8, and resistors R11, R12.
The filter is filtered so as to have a driving frequency of 0, that is, a frequency band having only a signal component of 10 KHz, and is amplified and output to have a gain of, for example, 33 dB. The frequency response characteristic of the detection unit 60 has a peak value near 2π × 10 ⁴ rad / sec as shown in FIG. In the drawing, the infrared LED driving frequency, that is, a burst signal of 10 KHz
/ Sec corresponds to 2π × 10 ⁴ rad / sec.
The magnitude of the gain at this time is about 33 dB. The non-inverting amplifier OP of the non-inverting amplifier circuit 71 of the amplifying and integrating section 70
4, the output signal of the detection unit 60 is set to, for example, 13d.
Amplify to have B gain.

The non-inverting amplifier circuit a voltage signal output from the output terminal 71 when the V _p, the integrator 72 in the non-inverting amplifier circuit reference voltage, for example 2 V _p the output voltage signal 71.
If 5V larger applies a current value of V _p / R16 to the inverting terminal of the operational amplifier OP5 Thereby the operational amplifier OP
The output of 5 goes low, turning on transistor TR3. Therefore, the first switch SW1 is connected to the first terminal, and the capacitor C is charged with the current value V _p / R16. When the voltage V output from the output terminal of the non-inverting amplifier circuit 71 is 2.5
If it is less than V, the output of the operational amplifier OP5 goes high, thereby turning off the transistor TR3 and clamping the output of the operational amplifier OP5 through the diode D1, that is, maintaining the output at a predetermined voltage.
At this time, the subject is at a distance farther than the closest distance, for example, 7
m, the non-inverting amplifier circuit 7
The signal amplified and output at 1 has a waveform as shown in FIG. 7A, and the output signal of the non-inverting amplifier circuit 71 is charged in the capacitor C of the integrator 72 and the integrated signal is shown in FIG. 7B. It has such a waveform. At this time, if the amplitude of the waveform of the output signal of the non-inverting amplifier circuit 71 is large, the integrator 7
A large current flows through the capacitor No. 2 and reaches the set voltage quickly. Therefore, the voltage difference between the two channels A and B changed in a time-division manner by the switch 50 can be converted into a time difference between the integrated signals. That is, a proportional relationship is established between the two, and (V _a −V _b ) ∝ (t _b −t _a ). Therefore, the necessity and the degree of the focus adjustment are determined by counting the reference clock of the microcomputer 90 and calculating the difference between the integration times t _a and t _b .

On the other hand, the integrated voltage charged in the capacitor C of the integrator 72 and integrated by the comparing section 80 is applied to the differential amplifier OP6.
When the voltage is equal to or higher than the reference voltage Vcc set at the + terminal of the differential amplifier OP6, the output level of the differential amplifier OP6 is set low and applied to the microcomputer 90. Accordingly, the microcomputer 90 clears the integrator 72 by transmitting the discharge signal and discharging the charge charged in the capacitor C through the discharge resistor R.

FIG. 7 shows the infrared LE output from the microcomputer 90.
FIG. 7 is a waveform diagram of a 10 KHz burst signal which is a driving frequency of D. For example, the period of the burst signal is 100 μsec.
And the infrared LED is illuminated for 40 msec.
If the motor is controlled during c, the sampling cycle of the apparatus of the present invention is 70 msec.

FIG. 8 shows the infrared LED driving unit 10 shown in FIG.
0 is a detailed circuit diagram of FIG. According to FIG. 8, the drive signal supplied from the microcomputer 90, that is, the 10 KHz burst signal 1R is applied to the transistor TR4 of the infrared LED on / off circuit 101. On the other hand, the microcomputer 90 is
, The amplitudes of the output signals of the two channels A and B set at the low level are counted, and the light amount adjustment signals P1 and P in four stages are calculated.
The light is supplied to the infrared LED driving unit 100 separately at 2, P3 and P4. In the infrared LED light intensity control circuit 102, when a high signal is applied to the terminal P1 from the microcomputer 90, the transistors TR9 and TR10 connected by Darlington connection are turned on, and the infrared LED1 has an intensity corresponding to the current (i1 + i2).
Light is emitted by adjusting the light amount of 0. From microcomputer 90 to P3
When a high signal is applied to the end, the transistors TR11 and TR12 connected by Darlington connection become conductive, and the intensity of the light of the infrared LED 10 is adjusted by the current (i1 + i2 + i3) to emit light. When a high signal is applied to the terminal P4 from the microcomputer 90, the transistors TR13 and TR14 connected by the Darlington connection become conductive and currents i1, i2 and
The light intensity of the infrared LED 10 is adjusted by i3 and i4 to emit light.

FIG. 10A shows the driving circuit of FIG.
4 is a diagram illustrating the relationship between the intensity of light emission for driving the number and the count amount calculated by the microcomputer. In the drawing, the count amount of the microcomputer and the light intensity control signal are displayed in terms of dimensionless quantities. As described above, the reason for adjusting the light emission intensity in multiple stages is that the intensity of the reflected light input to the light receiving element differs depending on the type and distance of the subject. It is for obtaining. That is, if the count value of the microcomputer indicating the integration time difference between the two channel signals is large, the infrared LED is driven with a large light emission intensity, and if the reflectance of the subject is low, the infrared LED is driven with a large light amount. At this time, since the overall gain of the automatic focusing apparatus of the above-described embodiment is about 100 dB, the intensity of the light emitted from the infrared LED is set so as to always have a dynamic range regardless of the type and distance of the subject, that is, about 100 dB. In other words, the driving voltage is controlled from four stages.

FIG. 9 is a detailed circuit diagram of the motor drive unit 110 shown in FIG.

In FIG. 9, the motor driving section 110 includes a motor direction control circuit 111 and a motor speed control circuit 112. At this time, the motor direction control circuit 111
The rotation direction of the motor is determined by the signal counted at 0. For example, if the microcomputer 90 applies a positive control signal to the positive end (P direction) as a high signal, this control signal is applied to the transistors TR20, TR22, The motor is rotated in the forward direction via TR19.

On the other hand, if the microcomputer 90 applies a reverse control signal as a "high" signal to the reverse end (N direction), the control signal is applied to the transistors TR21, TR23, TR18.
, The motor is rotated in the reverse direction.

If the signal difference between the channels A and B, that is, the difference between the count values is large, the motor should be controlled at a high speed. On the other hand, if the motor has inertia, hunting is likely to occur. Therefore, when the signal difference between the two channels A and B is small, the motor should be controlled at a low speed.

Therefore, if the signal difference between the two channels A and B becomes small, the microcomputer 90 will operate the motor speed control circuit 112.
A high-speed signal is supplied to the low-speed end of the transistor TR1 by a low-speed control signal, whereby the transistor TR15 is turned on to cause the motor to rotate at a low speed, thereby preventing hunting. At the time of motor direction and speed control, a constant voltage is supplied according to a signal counted by the microcomputer 90 as shown in FIG. 10B, and control is performed by a pulse-width modulated PWM signal. In the drawing, the pulse width of the control signal represented by the vertical dotted line increases toward the right side, and the driving speed of the motor increases.

FIGS. 11 to 13 are flow charts showing the steps from the control of each unit by the microcomputer shown in FIG. 4 to the driving of the infrared LED and the AF motor, which are linked to FIGS. 4 to 9. Will be explained.

In step S1, the microcomputer 90 is initialized to select and clear the memory and counter modes, and then the capacitor C of the integrator 72 is discharged for 1 msec in order to prevent noise, and the light amount corresponding to the maximum power is temporarily set. The adjustment signal P4 is selected. S2 or S3
In the step, the minute current signal 1
After the signals 1 and 12 are converted into voltage signals by the first and second current-to-voltage converters 30 and 40, a control signal is output to the switch 50 to select the A channel (step S2) and transmitted to the A channel. The signal is charged and integrated by the amplification and integrator 70 through the detection unit 60 (S3 step). S4
Or 10K to drive the infrared LED in step S5
Hz burst signal is turned on, for example, for 50 μsec, and the counter is turned on (S4 step).
By turning off the burst signal for 50 μsec, a drive signal for the infrared LED having a period of 100 μsec is output (step S5). In steps S6 to S8, it is determined whether the A-channel integration signal transmitted to the comparison unit 80 has been set at the set voltage (S6 step). The number of burst signals up to the completion is stored in a counter (Step S7), and a clear signal for discharging the capacitor C of the integrator 72 is output (S8).
Steps). In step S9, it is determined whether the number of burst signals counted that the A channel signal is not set from step S6 is 200 or more, for example, and if it is 200 or more, step S7 is performed. This is fed back to step S4. Here, the burst signal count number 200 is a value corresponding to 20 msec, which is a value set as a lower limit value in a case where the subject is at the closest distance or the integration is interrupted by noise or the like.

In steps S10 to S11, a control signal is sent to the switch to select the B channel (step S10), and the signal transmitted to the B channel is charged into the capacitor C of the integrator 72 to perform integration (step S11). . In steps S12 and S13, a 10 KHz burst signal for driving the infrared LED is turned on and the counter is turned on for 50 μsec (step S12), and then the burst signal is turned off for 50 μsec. An LED drive signal is output (S13 step). S14 to S16
In step S14, it is determined whether the B-channel integration signal transmitted to the comparison unit 80 is set at the set voltage (step S14). The number of signals is stored in the counter (step S15), and a clear signal for discharging the capacitor C of the integrator 72 is output (step S16). In step S17, if the B-channel integrated signal transmitted to the comparing section in step S14 is not set, it is determined whether the number of burst signals is 200 or more. If it is 200 or more, step S15 is performed. If not, it is fed back to step S12. In steps S18 to S21, A and B
It is determined whether the count amount of each channel is equal to or less than the above-described lower limit period, that is, 20 msec (step S18).
It is determined whether it is 0 second or more (step S19), and if it is 10 seconds or more, it is determined that the taking lens moves to the infinity position, and the motor is stopped (step S20).
Otherwise, the motor is rotated in the infinite direction, and the feedback is made to step S2 (step S21).

In steps S22 to S24, the above-described S
If the counts of the A and B channels are each less than 20 msec in step 18, it is compared whether the counts of the A channel and the B channel match (step S22).
If they do not match, it is determined again whether the counted amount is 10 seconds or more (step S23), and if it is 10 seconds or more, the taking lens is regarded as moving to the closest position and the motor is stopped (step S24). If it is less than 10 seconds, the motor is rotated in the closest direction and then fed back to step S2 (step S24). In steps S25 to S28, when the counts A 'and B' of the A channel and the B channel substantially coincide with each other in step S22, that is, when the amplitudes of the position detection signals of the A channel and the B channel substantially coincide with each other, each channel is The amplitude of the transmitted signal is proportional to the reciprocals of the counts A 'and B'. Therefore, the difference between the amplitudes is the ratio of the difference between the count amount and the product (B ').
-A ') / (A'B'), so this value is stored in the register R5 (step S25), and the sum of the amplitudes is calculated as the ratio of the sum of the counts to the product (B '+ A') / (A ' B '), this value is stored in the register R4 (step S26). The ratio between the value stored in the register R5 and the value stored in the register R4, that is, the ratio of the difference between the counts and the sum (B'-
After storing the value of (A ') / (B' + A ') in the register R3 (step S27), the power of the infrared LED is selected according to the value stored in the register R4 (step S27).

By the way, as shown in FIG. 10A, the count amount increases as the distance of the subject to be measured increases, thereby increasing the required light emission intensity of the infrared LED, that is, the power. Therefore, in the present invention, the infrared L
The emission intensity of the ED is controlled in four stages, and when the stages are changed for system stability, the front and rear ends of each stage are overlapped with each other. This superimposed portion corresponds to the hysteresis band.

In steps S29 to S31, it is determined whether a change in sign, that is, a carry has occurred in the value stored in the register R5 (step S29).
If carry has occurred, move the motor in the reverse direction (S3
(Step 0), otherwise move the motor in the forward direction (Step S31). In steps S32 to S33, the ratio (B'-A ') / (B' + A ') of the difference between the count amount and the sum stored in the register R3 is compared with a predetermined error value ε indicating the hysteresis band ( S32 step),
If the difference is less than the error value, the motor is stopped to complete the automatic focus adjustment, and then the feedback is made to step S2 (S33).
Steps). At this time, the error value ε is set, for example, when the value stored in R3 is 5% or less. S34 to S37
In the step, the register R3
If the value stored in the register R3 is equal to or larger than the error value ε, it is determined whether the value stored in the register R3 is equal to or larger than the set value K for low-speed driving (step S34). The motor M is controlled at a high speed by modulation (PWM) (steps S35 and S37). If the motor M is smaller than the set value K, the motor is driven at a low speed to focus, and then fed back to the step S2 (steps S36 and S37). . At this time, the set value K is set, for example, when the value stored in the register R3 is 20% or less.

[0043]

According to the present invention as described above, the configuration can be simplified by processing the two-channel minute current output from the light-receiving unit in one channel. In addition, by processing the control signals for driving the infrared LED and the AF motor in a software manner by a microcomputer, it is possible to overcome the difficulty of maintaining a low bias current and a small offset voltage characteristic required in a hardware configuration. This has the effect of increasing the reliability and stability of the system.

[Brief description of the drawings]

FIG. 1 is a view illustrating a principle of an active system in a general automatic focusing apparatus.

FIG. 2 is an electrical equivalent circuit diagram of a general light receiving element.

FIG. 3 is an overall configuration block diagram of a conventional automatic focus adjustment device for a video camera.

FIG. 4 is a block diagram showing the overall configuration of an automatic focusing apparatus for a video camera according to the present invention.

FIG. 5 is a circuit diagram of an embodiment embodying the automatic focusing apparatus of the video camera shown in FIG. 4;

FIG. 6 is a diagram illustrating a frequency response characteristic of the band pass filter illustrated in FIG. 5;

7A is a waveform diagram of a signal output from the non-inverting amplifier circuit of the amplifying and integrating unit shown in FIG. 4, and FIG. B is an integrator of the amplifying and integrating unit shown in FIG. It is a waveform diagram of a signal to be output, and FIG. C is a waveform diagram of a drive signal for driving the infrared LED by the microcomputer shown in FIG.

8 is a detailed circuit diagram of the infrared LED driving unit shown in FIG.

FIG. 9 is a detailed circuit diagram of the motor driver shown in FIG. 4;

10 is a diagram illustrating the relationship between the power of an infrared LED drive unit and the count amount of a microcomputer, and FIG. 10B is a diagram illustrating the relationship between a motor control signal and a voltage in the motor drive unit illustrated in FIG. 9; FIG.

11 is a first flowchart illustrating a process of controlling each unit by the microcomputer illustrated in FIG. 4 to drive the infrared LED and the AF motor.

FIG. 12 is a second part of the flowchart.

FIG. 13 is a third part of the flowchart.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Light-emitting part 20 Light-receiving part 30, 40 Current-voltage conversion part 50 Selection part 60 Detection part 70 Amplification and integration part 80 Comparison part 90 Microcomputer 100 Infrared LED drive part 110 Motor drive part M Motor

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 7/11

Claims (19)

(57) [Claims] 1. A light emitting unit that emits a light beam for distance measurement, a driving unit that drives the light emitting unit, and two channels. The light emitting unit emits light at a point of incidence of reflected light projected from the light emitting unit and reflected by a subject. A light-receiving unit that outputs a photocurrent signal corresponding to each of the two channels, a first and a second current-voltage converter that converts the photocurrent signals of both the channels into amplified voltage signals, and outputs the amplified voltage signals. A selection unit that selects the output signals of the first and second current-voltage conversion units in a time-division manner, a detection unit that detects the selected output signals,
An amplification and integration unit that amplifies and integrates the output signal of the detection unit and outputs an integrated voltage signal, a comparison unit that compares the integrated voltage signal with a predetermined set voltage and outputs a level signal based on the comparison value, A motor drive unit for driving a focus adjustment motor, and a level signal of the comparison unit corresponding to each of the two channels are sequentially received, and the difference is compared. The difference between the two level signals is compared until the two level signals match. A microcomputer that drives the motor driving unit in response to the signal, wherein the amplification and integration unit outputs a signal from the non-inverting amplifier circuit, and a non-inverting amplifier circuit that non-inverts and amplifies the signal filtered by the detection unit. When the signal is higher than a predetermined voltage, the input signal is integrated. When the output signal of the non-inverting amplifier is lower than the predetermined voltage, the output signal is maintained at a predetermined voltage. Autofocus system of a video camera to an integrator to the said comprise be configured to. 2. The first and second current-to-voltage converters respectively include first and second disturbance light current elimination circuits for eliminating the influence of disturbance light, and a photocurrent signal output from the light receiving unit as a voltage signal. 2. The video camera according to claim 1, further comprising first and second I / V converters for converting, and a high-pass filter for removing noise of signals output from the first and second I / V converters. Automatic focusing device. 3. The first and second disturbance light current elimination circuits respectively include a transistor that is turned on when a DC current due to the disturbance light is applied to each collector terminal, and an excessive current when the transistor is turned on. 3. The automatic focusing apparatus for a video camera according to claim 2, further comprising a resistor and a capacitor to be removed. 4. The video camera according to claim 1, wherein the selection unit receives the control signal from the microcomputer and sequentially selects and time-divides the output signals of both channels for a predetermined sampling period. Automatic focusing device. 5. The automatic focusing apparatus for a video camera according to claim 4, wherein said selection unit is constituted by an analog switch. 6. An operational amplifier for filtering and amplifying only a signal component of a predetermined frequency among signals filtered by the high-pass filters of the first and second current-voltage converters, 3. An automatic focusing apparatus for a video camera according to claim 2, comprising a band-pass filter including a capacitor. 7. The video as claimed in claim 1, wherein the comparing section includes a comparator which is set at a predetermined level when the amplification and integration section performs integration of a predetermined voltage or more. Automatic focusing device for camera. 8. The microcomputer includes a burst signal for driving the light emitting unit, a control signal for the amplifying and integrating unit according to a level signal output from the comparing unit, and a reflection signal incident on both channels of the light emitting unit. 2. A control signal for the drive unit and the motor drive unit, which is calculated by converting a magnitude of the position detection signals of both channels outputted according to a position of light into a count amount and generating a control signal. Video camera automatic focusing device. 9. The infrared LED on / off circuit for turning on / off the light emitting unit in response to a burst signal of a predetermined frequency output from the microcomputer, and the light emitting unit receiving a control signal from the microcomputer. 2. The automatic focus adjusting device for a video camera according to claim 1, further comprising an infrared LED light intensity adjusting circuit for determining the light intensity of the unit. 10. A control signal of the microcomputer is the infrared signal L.
10. The automatic focusing apparatus for a video camera according to claim 9, wherein the ED light intensity adjusting circuit is controlled at four power levels. 11. The video camera automatic focusing apparatus according to claim 1, wherein the driving unit receives the control signal from the microcomputer and adjusts the light emitting unit at a predetermined level. 12. The motor control device according to claim 1, wherein the motor driving section includes a motor direction control circuit for controlling a direction of the motor, and a motor speed control circuit for controlling a speed of the motor. Automatic focusing device for video cameras. 13. The motor direction control circuit includes a plurality of transistors having an H-bridge structure and a resistor,
13. The automatic focus adjusting device for a video camera according to claim 12, wherein the direction of the motor is controlled according to a control signal output from the microcomputer. 14. The motor speed control circuit includes a plurality of transistors, elements, resistors, and diodes, and controls the speed of the motor at a low speed when a low speed control signal of the microcomputer is input to a low speed end. Claim 12
An automatic focusing device for a video camera as described in the above. 15. The automatic focus adjusting device for a video camera according to claim 13, wherein the control signal output from the microcomputer is a pulse width modulated signal. 16. A light emitting unit that emits a measurement light beam;
In the automatic focus adjustment method for a video camera using a two-channel light receiving unit for detecting the reflected light of the light beam with respect to a subject, any one of the two channels is selected, and a detection signal of this channel is set to a predetermined value. A first channel set determining step of determining whether the voltage has been set, and a second channel determining step of selecting the remaining one of the two channels and determining whether a detection signal of this channel has been set at the predetermined voltage. When the count of the detection signals of the two channels is equal to or longer than a predetermined lower limit period and equal to or longer than a predetermined upper limit period, the focus adjustment is stopped, and if the count amount is equal to or shorter than the upper limit period, the focus is adjusted to infinity. A long-distance focusing step of feeding back to the first channel set determining step; If the amount is less than the predetermined lower limit period and the clock quantity in which the count amounts of the two channels do not match is equal to or greater than the predetermined upper limit period, the motor is rotated in the closest direction and then fed back to the first channel set determination step. And controlling the light emission intensity of the light emitting unit, the focus adjustment direction, and the speed when the counts of the two channels are less than the predetermined lower limit period and the counts of the two channels are substantially the same. An automatic focus adjustment method for a video camera, comprising a light emitting unit and a focus adjustment control step. 17. A light projecting step of projecting infrared light to a subject to be measured by an infrared LED, and receiving reflected light reflected by the subject on two channels and outputting the received light current signals. A light-receiving step, a current-voltage conversion step of converting the photocurrent signal into an amplified voltage signal and outputting the amplified voltage signal, a selection step of sequentially selecting a signal output from the current-voltage conversion step, A detection step of detecting the selected signal; an amplification and integration step of amplifying the signal output from the detection step and outputting an integrated voltage signal corresponding to the amplified signal; and an output of the amplification and integration step. Comparing the output signal with a predetermined set voltage and outputting a level signal by the comparison inner shield; and A control signal for converting the signal integrated in the amplifying and integrating steps into a counting amount in accordance with the level signal to be output, and outputting a control signal for driving the infrared LED and the focus adjustment motor; and Infrared LED of the light emitting step according to the control signal
And a motor driving step of driving the motor in response to a control signal output from the control step. 18. The infrared LED driving step, wherein the emission intensity of the infrared LED is driven in a predetermined stage according to the count amount in the control step.
8. The video camera automatic focusing method according to 7. 19. The video according to claim 17, wherein the motor driving step controls the direction and speed of the motor in accordance with a pulse width modulated signal according to the count output from the control step. Camera automatic focus adjustment method.