JPH0697300B2 - Automatic focus adjustment device - Google Patents

Description

The present invention relates to an automatic focusing device, and more particularly to an automatic focusing device used for optical devices such as film cameras and TV cameras.

[Conventional technology]

One of the automatic focus adjustment devices employs a method called an active method. With this active method,
Of the light emitted from the camera to the subject, the light reflected by the subject and returning is received, and distance measurement is performed. In this case, the principle of triangulation is generally used as the distance measuring means.

FIG. 2 is a principle diagram showing an example of the configuration of an optical system of an active type automatic focus adjusting device using the principle of triangulation.

When a light flux such as infrared light emitted from the light emitting element 1 is irradiated by the focusing lens 2 toward the subject 3 in parallel with the optical axis direction of the taking lens 5, for example, the reflected light from the subject 3 is the light of the taking lens 5. Two-divided photo detectors 4a, 4 installed off-axis
Imaged on b. The difference between the outputs of the two-divided light receiving elements 4a and 4b is detected by, for example, a differential amplifier, and the output direction and amount of the taking lens 5 are determined by the difference output, and the lens driving motor is rotated forward and backward. By the rotation of this motor, the lens barrel of the taking lens 5 moves in the optical axis direction while rotating around the optical axis. The two-divided light receiving elements 4a, 4b are designed so that the inclination angle θ changes in conjunction with the movement of the taking lens 5, and rotate in the direction in which the difference output of the light receiving elements 4a, 4b becomes zero. Then, when the difference output between the two light receiving elements 4a and 4b becomes zero, the taking lens 5 is brought into the in-focus state. In the focused state, between the tilt angle θ of the light receiving elements 4a and 4b, the distance D between the optical axis of the taking lens 5 and the two light receiving elements 4a and 4b, and the distance S from the taking lens 5 to the subject 3. , The equation θ = tan ^-1 (S / D) is satisfied. In addition, the above two light receiving elements 4a, 4b
When the differential output of is obtained, it is possible to determine not only the in-focus state but also the defocusing directionality at the time of out-of-focus, that is, the front focus state and the rear focus state.

[Problems to be solved by the invention]

By the way, generally, in the above-described automatic focus adjusting device, when trying to increase the response speed of the automatic focus adjusting operation, even if the power supply to the lens driving motor is stopped at the in-focus position, the motor, the photographing lens, etc. are not affected. Since it has a moment of inertia, it does not stop immediately and the focus position is overrun. Therefore, in anticipation of the movement of the taking lens due to inertia, a dead zone is provided by sandwiching the focusing point where the output difference between the light receiving elements 4a and 4b becomes 0, and when the output difference enters this dead zone, the motor A device for stopping power supply is well known. However, when the subject distance is different or the reflectance of the subject is different, the light amount of the infrared light beam emitted from the light emitting element 1 and incident on the light receiving elements 4a and 4b greatly changes. Light receiving element
The position of the photographing lens when entering the dead band differs depending on whether the amount of incident light on 4a, 4b is large or small, and therefore, for example, when the amount of incident light on the light-receiving elements 4a, 4b is small, the photographing lens is in focus. There is a problem such as stopping without reaching. For this reason, there has been proposed a device in which the dead band is set so as to be adjustable by a variable resistance (Japanese Patent Publication No. 56-41970). However, in this conventional device, the dead band is manually set. It is impossible to accurately respond to the change in the amount of incident light, and it is not possible to perform a highly accurate automatic focus adjustment operation.

On the other hand, there is also proposed a device which uses the sum output of the two light receiving elements 4a and 4b in order to perform various control operations of the automatic focus adjusting device (Japanese Patent Publication No. 55-13012).
However, this prior art device does not disclose any specific configuration in which the sum output acts on the control system for automatic focus adjustment.

The present invention has been made in view of such a problem, and a reference signal that follows the sum of the incident light amounts of the two light receiving portions (light receiving elements 4a and 4b) and a signal that corresponds to the difference between the incident light amounts. Based on the above, there is provided an automatic focus adjusting device of this type, which does not change the gain of the entire control system for automatic focus adjustment, performs highly accurate and stable automatic focus adjusting operation, and is simple and inexpensive in configuration. With the goal.

[Means for solving problems]

This automatic focusing device, as shown in FIG.
A light projecting means 11 for projecting a light beam toward 10 and a subject
Light receiving means 12 for receiving the reflected beam from 10 by two light receiving portions 12a and 12b, and reference signal generating means 13 for generating a reference signal that follows the sum of the amounts of light incident on these light receiving portions 12a and 12b.
And adjusting means 14 for obtaining an automatic focus adjustment signal based on the reference signal and a signal corresponding to the difference in the amount of light incident on the two light receiving portions 12a, 12b, and the reference signal generating means 13
Is a DC signal level for each sampling period obtained by sampling and holding the value of the sum of the incident light quantities that can change over time at a predetermined sampling period, or a DC signal level in which the polarity is inverted. , A DC signal level generated by directly dividing the DC signal level, and a plurality of DC signal levels are generated as the reference signals, and the adjusting means 14 causes the reference signal generating means 13 A plurality of reference signals corresponding to each of the plurality of reference signals are included, and each of the comparison means has a signal corresponding to the difference between the level value of the reference signal corresponding to itself and the incident light amount. A DC drive signal of each corresponding predetermined polarity and level corresponding to the comparison result is generated, and the photographing lens is driven based on this DC drive signal. It is characterized by being made as follows.

[Action]

In this automatic focusing device, the light beam projected by the light projecting means 11 is reflected by the subject 10 and the two light receiving parts of the light receiving means 12 are provided.
When the outputs of the two light receiving portions 12a, 12b are guided to the reference signal generating means 13 and the adjusting means 14 after entering the light receiving portions 12a, 12b, the reference signal generating means 13 follows the sum of the outputs of both the light receiving portions. Then, the adjusting means 14 generates an automatic focus adjustment signal from the reference signal and a signal corresponding to the difference between the outputs of the both light receiving portions. This automatic focus adjustment signal is used for supplying power to the lens driving motor that moves the taking lens to the in-focus position.

〔Example〕

 Hereinafter, the present invention will be described based on Examples.

FIG. 3 is an electric circuit of the automatic focusing apparatus showing an embodiment of the present invention. The infrared light emitting diode 23 which is the light projecting means 11 is connected between the output end of the current amplifier 22 for amplifying the oscillation pulse output of the constant frequency from the oscillator 21 and the ground, and the infrared light is used for saving power consumption. The light emission of is blinking and modulated.

Two light receiving elements 25a and 25b of the light receiving means 12, which are two light receiving portions 12a and 12b divided into two on the same plane, receive the modulated infrared light emitted from the light emitting diode 23 and reflected by the subject. At this time, photoelectric conversion outputs corresponding to the respective amounts of incident light are input to the pre-stage amplifiers 26 and 27 and voltage-amplified. The outputs of the pre-stage amplifiers 26 and 27 are guided to the difference output detector 29, so that a signal corresponding to the output difference between the pre-stage amplifiers 26 and 27 is sent to the band pass filter (hereinafter referred to as BPF) 30 from the detector 29. Be guided. The BPF 30 separates only the modulated wave component of the difference output signal detected by the difference output detector 29, extracts it, and passes it through to the sampling and holding circuit (hereinafter referred to as S / H circuit) 31. The S / H circuit 31 samples the output of the BPS 30 with a sampling pulse from the sampling pulse generator 24 that is generated based on the oscillation frequency signal of the oscillator 21, and holds the same sampling level.

Further, the outputs of the pre-stage amplifiers 26 and 27 are guided to the sum output detector 33, and a signal corresponding to the output difference between the pre-stage amplifiers 26 and 27 is guided from the detector 33 to the BPF 34. Similarly, this BPF 34 also separates and extracts only the modulated wave component of the sum output signal detected from the sum output detector 33 and passes it through to the S / H circuit 35, where the S / H circuit 35 outputs the output of the BPF 34. Is sampled with the sampling pulse from the sampling pulse generator 24, and the same sampling level is held. In this example,
The modulation frequency for blinking the light emitting diode 23 is 5 KHz, and therefore the center frequency of the BPFs 30 and 34 is the same as the frequency 5 KHz.

The outputs a and b of the BPFs 30 and 34 and the sampling pulse c which is the output of the sampling pulse generator 24 are designed to be emitted at the timing shown in FIG.
Output a has a flat waveform a ₀ that does not include a modulation component when in focus, and has a waveform a ₁ that includes a modulation component or a waveform a _{2 that} is a phase inversion of this waveform a ₁ when out of focus. The magnitude of the amplitude of the waveforms a ₁ and a ₂ is a sine waveform having a magnitude proportional to the degree of out-of-focus. Further, the output b of the BPF 34 has the amplitude of the sine waveform changed like the waveforms b ₁ and b ₂ in proportion to the amount of infrared reflected light from the subject. The time points d ₀ to d ₂ at which the sampling pulse c is emitted in the waveforms a _{1 to} a ₃ of the output a and the time points e ₁ and e ₂ at which the sampling pulse c is emitted in the waveforms b ₁ and b ₂ of the output b are sampling points. Is. Therefore, the level of any of the sampling points d _{0 to} d ₂ depending on the focus adjustment state of the taking lens is S / H.
The signal is held by the circuit 31 and converted into a DC voltage of either 0, +, or −, and the level of any of the sampling points e ₁ and e ₂ depending on the magnitude of the infrared reflected light amount is S / H circuit 35. The DC voltage is converted into a higher DC voltage as it is held more and the light amount increases, and becomes lower as the light amount decreases. That is, since the output voltage Va of the S / H circuit 31 and the focus adjustment state have the relationship shown in FIG. 5, when the photographing lens is at the in-focus position P _0.
The output voltage Va of the S / H circuit 31 becomes 0V, and as it deviates to the short distance side N and the long distance side ∞, the voltage Va becomes a straight line l ₁
Or l ₂ . The straight line l ₁ shown by the solid line is the case where the detected modulation component is large, and the straight line l ₂ shown by the dotted line is the case where the detected modulation component is small. In this way, if the detection sensitivity of the reflected infrared light may change depending on the condition of the subject, etc., the output of the S / H circuit 31 is temporarily output to the motor 54 to cause the automatic focus adjustment operation. Even if it is supplied and the servo system is configured, the servo gain will change,
Stable servo control becomes impossible. Therefore, in order to prevent this, the output voltage Va of the S / H circuit 31 has four voltage comparators 4
Led to one of the input ends of 1, 42, 43 and 44,
The output voltage Vb of the S / H circuit 35 is supplied to the other input terminal of each of the four voltage comparators 41 to 44 as a reference voltage (threshold voltage) of a different level. The relationship between the output voltage Vb of the S / H circuit 35 and the amount of infrared reflected light from the subject is, for example, as shown in FIG. 6, so the voltage Vb becomes 0 V when there is no reflected light amount, but A solid straight line as the amount of reflected light increases in proportion to the amount of light
It becomes higher as shown by l ₃ . Since the inverting DC amplifier 45 is connected to the output terminal of the S / H circuit 35, this inverting DC amplifier 45
The output voltage of 45 is a voltage obtained by inverting the polarity of the above voltage Vb,
As the reflected light amount increases, it decreases as shown by the dotted straight line l ₄ .

Then, the output voltage Vb of the S / H circuit 35 is directly led to the voltage comparator 41 as the highest reference voltage V ₁ , and the voltage comparator 42
Is output as a reference voltage V _{2 obtained by} dividing the output of the S / H circuit 35 by the ratio of the resistors 37 and 38, and the voltage comparator 43 receives the S / H circuit 3
The output of 5 is inverted by the inverting DC amplifier 45, and then the resistance 39
It is introduced as a reference voltage -V ₂ divided by the ratio of 40 and 40, and the output of the S / H circuit 35 is fed to the voltage comparator 44 and the inverting DC amplifier 45
It is designed to be guided as the lowest reference voltage -V ₁ with the polarity reversed as it is. The anodes of diodes 47 and 48 are connected to the output terminals of the voltage comparators 41 and 42, respectively.
Diodes 49 and 50 are provided at the output terminals of the voltage comparators 43 and 44, respectively.
The cathode of the diode 48 and the anode of the diode 49 are commonly connected to one end of the resistor 51, and the cathode of the diode 47 and the anode of the diode 50 are connected to the other end of the resistor 51. The connection point is grounded via the resistor 52 and is also connected to the input end of the motor drive amplifier 53. A reversible DC motor 54 for driving the taking lens is connected between the output end of the motor drive amplifier 53 and the ground.

Here, depending on the amount of reflected light incident on the light receiving elements 25a and 25b, S
Explaining that the output voltage Vb of the / H circuit 35 changes, the reference voltages V ₁ , V ₂ , -V ₂ , -V ₁ of the voltage comparators 41 to 44 change. When there is no light quantity, all are 0V, but the absolute value changes in proportion to the magnitude of the reflected light quantity, as shown in FIG. I in FIG.
If the state is the amount of reflected light is often indicated by the state shown by II is a case where a small amount of reflected light, the reference voltage V _1, V ₂ is set to the voltage comparator 41 to 44, -V _2, -V ₁ Changes according to the amount of reflected light. The output voltage Va of the S / H circuit 31 is the reference voltage V
_When it exceeds ₁ (V ₁ <Va), the output voltage of the voltage comparator 41 is −
The output voltage Va changes from E to + E, and the output voltage Va becomes the reference voltage V ₂
Output voltage of the voltage comparator 42 from -E to +
Switch to E. When the output voltage Va becomes larger than the reference voltage −V _{2 in the} negative direction, the output voltage of the voltage comparator 43 switches from + E to −E, and the output voltage Va becomes the negative direction from the reference voltage −V _1. When it becomes larger, the output voltage of the voltage comparator 44 switches from + E to -E. That is, as shown in FIG. 7, the output voltage Va of the S / H circuit 31 is in the range of Va <V ₁
When D ₁ or −V ₁ <Va in the range D ₁ ′, the voltage comparator 41
The positive output voltage + E of the motor is supplied to the motor drive amplifier 53 as it is through the diode 47 or the negative output voltage -E of the voltage comparator 44 through the diode 50. 54 is rotated toward the in-focus position. Further, when in the range D _{2 of} V ₂ <Va <V ₁ or the range D ₂ ′ of −V ₁ <Va <−V ₂ , the voltage comparator 42
Since the positive output voltage + E of the above is output through the diode 48, or the negative output voltage -E of the voltage comparator 43 is divided through the diode 49 into the ratio of the resistor 51 and the resistor 52 and supplied to the motor drive amplifier 53, In this case, the motor drive amplifier 53 rotationally drives the motor 54 toward the in-focus position at a relatively low speed.
Further, when in the range D ₀ of −V ₂ <Va <V ₂ , the output voltage of the voltage comparators 41, 42 becomes −E, and the output voltage of the voltage comparators 43, 44 becomes + E. When these output voltages are blocked by the diodes 47-50, the motor drive amplifier
The input of 53 becomes the ground level of 0V by the resistor 52 and the motor 54
Is released from the driving force.

As described with reference to the principle diagram shown in FIG. 2, the motor 54 is mechanically interlocked with the two light receiving elements 25a and 25b, and is also interlocked with the distance ring of the photographing lens, so that it is The infrared light reflected by the two light receiving elements 25a and 25b is controlled to be uniformly irradiated. Then, as shown in FIG. 7, the reference voltage set in the voltage comparators 41-44.
_{V 1, V 2, -V 2} , the servo gain is constant regardless of the amount of reflected light by -V ₁ is changed by the amount of reflected light. That is,
As described above, the output voltage Va of the S / H circuit 31 is −V ₂ <Va <V ₂
When the range D ₀ is entered, the range D ₀ is a dead zone in which it is determined that the focus state is in effect. Therefore, the motor 54 is stopped and the focus state is maintained. The focus determination reference voltage V _2, since -V ₂ will vary in proportion to the output voltage Vb of the S / H circuit 35 based on the sum output of the light receiving elements 25a and 25b, when the reflected light amount is large the The range D _{0 is} also expanded (in the case of state I in FIG. 7), and the range D ₀ is also decreased in the case of a small amount of reflected light (in the case of state II in FIG. 7), and the servo gain does not change. Become. Further, since the reference voltages V ₁ and −V ₁ are for increasing the response speed, in the above range D ₁ and D ₁ ′ where the photographing lens position deviates more than the in-focus state, the motor 54
Rotates at high speed, and when it reaches the range D ₂ and D ₂ ′ near the focus, the rotation speed of the motor 54 switches to low speed. Reference voltage
V ₁ and −V ₁ also change depending on the magnitude of the reflected light amount, and the above range D ₁ and
D ₁ ′ and D ₂ , D ₂ ′ fluctuate. As a result, problems such as hunting and overrun are solved.

If the amount of reflected light becomes extremely small because the subject is at infinity, the output voltage Vb of the S / H circuit 35 based on the sum output is extremely small and the reference voltages V ₁ , V ₂ , −
Since the absolute values of V ₂ and −V ₁ are also set to be extremely small, in this case, these reference voltages V ₁ , V ₂ , −V ₂ and −V ₁ and the S / H circuit
Instead of the automatic focusing control by comparing with the output voltage Va of 31, the output voltage Vb of the S / H circuit 35 is different from that of another voltage comparator 55.
Since so as to be compared with the reference voltage V ₀ is guided to, when it becomes Vb <V _0, the output of the voltage comparator 55 is not adapted to be sent to the motor driving amplifier 53, a motor drive amplifier 53, this time, the reference voltage _{V 1, V 2, -V 2} , -V 1
The output of the voltage comparator 55 drives the motor 54 so that the taking lens is focused on the infinite position, regardless of the output for automatic focus adjustment by comparing the output voltage Va of the S / H circuit 31 with the output voltage Va.

The motor drive amplifier 53 may be configured, for example, as shown in FIG. In FIG. 3, one terminal of the motor 54 is grounded, but in the motor drive amplifier 53A shown in FIG. 8, the speed of the motor 54 is rotated to the maximum speed under the limited power supply voltage condition. Both terminals are not grounded. That is, the input end of the motor drive amplifier 53A is connected to the non-inverting input end of the operational amplifier 61, and the output end of the operational amplifier 61 is the emitters of the transistors 62 and 63 connected to the bases of the NPN transistor 62 and the PNP transistor 63. Is connected to one end of the motor 54. One end of the motor 54 is connected to the inverting input end of the operational amplifier 61, and the voltages + E and -E are applied to the collectors of the transistors 62 and 63, respectively. This operational amplifier 61
And the transistors 62 and 63 form a first current amplifier having an extremely low output impedance. Also the motor
At the other end of 54, operational amplifier 66 and transistor
The output terminal of a second current amplifier having an extremely low output impedance composed of 64 and 65 is connected. The non-inverting input terminal of the operational amplifier 66 is connected to the output terminal of the operational amplifier 67 and one end of the resistor 68, and the other end of the resistor 68 is connected to the input terminal of this motor drive amplifier 53A via the inverting input terminal of the operational amplifier 67 and the resistor 69. It is connected and the non-inverting input terminal of the operational amplifier 67 is grounded. That is, the inverting amplifier is composed of the operational amplifier 67 and the resistors 68 and 69, and the input end of the motor drive amplifier 53A is also connected to the inverting input end of the operational amplifier 66 of the second current amplifier via the inverting amplifier on the other hand. It is connected.

When the voltage applied to the input terminal of the motor drive amplifier 53A is + E or -E, the transistor 62 is turned on at one end of the motor 54 by turning on the transistor 62.
-E when the transistor is turned on, and -E when the transistor 65 is turned on at the other end, or + E when the transistor 64 is turned on.
Is applied, and as a result, a voltage of 2E is applied across the motor 54, and the motor 54 rotates at high speed. This state corresponds to the case where the voltage comparator 41 supplies + E or the voltage comparator 44 outputs -E in FIG. Voltage comparator 42 to + E, or voltage comparator
When −E output voltage is supplied from 43,
The input divided by 52 is the motor drive amplifier 53A.
Is guided to and rotates at low speed. In addition, it enters the dead zone where it can be determined that it is in focus, and 0 is input to the input end of the motor drive amplifier 53A.
When V is input, the same potential of 0 V is applied to both terminals of the motor 54 via the current amplifiers respectively, and since these are low impedance sources, both ends of the motor 54 are equivalent to a short circuit condition. Then, the braking is applied, and at this time, the motor 54 stably stops at the in-focus position.

〔The invention's effect〕

As described above, according to the present invention, a reference signal for determining whether the levels of the output difference signals of the two light receiving units are in the in-focus state or the out-of-focus state is generated from the output sum of the two light receiving units. As a result, regardless of the amount of light reflected from the subject of the projected light, the gain of the control system for automatic focus adjustment does not fluctuate, stable and highly accurate automatic focus adjustment operation is performed, and the configuration is simple and inexpensive. It has an excellent effect such that an automatic focusing device of this kind can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic circuit configuration of an automatic focus adjusting device of the present invention, and FIG. 2 is a principle configuration diagram showing an example of an optical system in which the automatic focus adjusting device of the present invention is adopted. FIG. 4 is an electric circuit diagram of an automatic focusing device showing an embodiment of the present invention, FIG. 4 is a time chart of output waveforms of the BPFs 30 and 34 and the sampling pulse generator 24 in FIG. 3, and FIG. FIG. 6 is a diagram showing a change in output with respect to the lens position of the S / H circuit 31 in FIG. 3, and FIG. 6 shows a change in output with respect to the reflected light amount of the S / H circuit 35 in FIG. Diagram, FIG. 7 is a diagram showing a reference voltage that changes according to the output change of the S / H circuit 35, and FIG. 8 is an electric circuit diagram showing an example of a specific circuit configuration of the motor drive amplifier. is there. 1 ... Light emitting element (light projecting means) 3,10 ... Subject 4a, 4b, 25a, 25b ... Two-divided light receiving element (two light receiving parts) 5 ... Photographing lens 11 ... Light projecting means 12 ... Light receiving means 12a, 12b ...... Two light receiving parts 13 ...... Reference signal generating means 14 ...... Adjusting circuit 35 ...... S / H circuit (reference signal generating means) 37 to 40 ...... Resistance (reference signal generating means) 45 ... Inverting DC amplifier (reference signal generating means) 41 to 44 ... voltage comparator (adjusting circuit) 47 to 50 ... diode (adjusting circuit) 51,52 ... resistance (adjusting circuit) 53,53A ... motor drive amplifier (Adjustment circuit) 54 ... Lens drive motor (Adjustment circuit)

Claims (1)

[Claims] 1. A light projecting unit for projecting a light beam, a light receiving unit having two light receiving units for receiving a reflected beam of the light beam by a subject, and an amount of light incident on the two light receiving units. A reference signal generating means for generating a reference signal that follows the sum of the two, and an adjusting means for obtaining an automatic focus adjustment signal based on the reference signal and a signal corresponding to the difference in the amount of light incident on the two light receiving portions. In the automatic focus adjusting device, the reference signal generating means obtains a DC signal level for each sampling period obtained by sampling and holding the value of the sum of the incident light quantities that can change over time at a predetermined sampling period. A plurality of DC signal levels, which are a DC signal level in which the polarity is inverted and a DC signal level generated by directly dividing this DC signal level, are used as the reference signal. The adjusting means is configured to include a plurality of comparing means provided corresponding to each of the plurality of reference signals generated by the reference signal generating means. The level value of the corresponding reference signal is compared with the signal level value corresponding to the difference in the amount of incident light to generate a DC drive signal of each corresponding predetermined polarity and level according to the comparison result, and this DC drive An automatic focusing device, characterized in that it is configured to drive a taking lens based on a signal.