JPH0644095B2 - Automatic focus adjustment device - Google Patents

Description

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

[Prior Art] One of automatic focus adjustment devices employs a system called an active system. 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. Light receiving element 4 divided into two parts installed off-axis
An image is formed by the light receiving lens 6 on a and 4b. 2 above
The difference between the outputs of the divided light receiving elements 4a and 4b is detected by, for example, an operational amplifier, and the output direction and amount of the photographing lens 5 are determined by the difference output, and the lens driving motor is rotated forward and backward. The rotation of the motor moves the taking lens 5 in the optical axis direction. The positions of the two-divided light receiving elements 4a, 4b are changed in the left-right direction in association with the movement of the photographing lens 5 so that the differential output of the light receiving elements 4a, 4b becomes zero. Move to. Then, when the difference output between the two light receiving elements 4a and 4b becomes zero, the focus state is achieved. In the in-focus state, θ = tan ⁻¹ (S / D) is satisfied. In addition, the two light receiving elements 4a,
When the difference output of 4b is obtained, not only the focusing condition but also
It is also possible to determine the directionality of defocus when out of focus, that is, the states of the front focus and the rear focus.

[Problems to be Solved by the Invention] Generally, in the above-described automatic focus adjustment device, when an attempt is made to increase the response speed of the automatic focus adjustment operation, power is supplied to the lens driving motor at the in-focus position. Even if the motor stops, the motor, the taking lens, and the like have moments of inertia, etc., so that they do not stop immediately and the focus position is overrun. Therefore, in consideration of the movement of the photographing lens due to inertia, a dead zone is provided across the focusing point where the output difference between the light receiving elements 4a and 4b is 0, and when the output difference falls within this dead zone, the motor is driven. There is a well-known device for stopping the power supply. 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. The position of the photographic lens when entering the dead band differs depending on whether the amount of light incident on the light receiving elements 4a, 4b is large or small. There are problems such as stopping without reaching the focal position. For this reason, a device has been proposed in which the dead band is set so as to be adjustable by a variable resistor (Japanese Patent Publication No. 56-41970).
However, since the dead band is manually set in this conventional device, it is impossible to accurately respond to the change in the incident light amount, and a highly accurate automatic focus adjustment operation can be performed. There wasn't.

On the other hand, there has also been 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 focusing device (Japanese Patent Publication No. 55-55-55).
13012 publication. However, in the case of such a conventional device, when the output of one of the light receiving elements is reduced when the subject is out of focus, the level of the sum output is also reduced, and the photocurrent with respect to the dark current is reduced. Since the S / N per surface is deteriorated, it is not preferable to use the above sum output as a control signal for automatic focus adjustment in order to perform an extremely accurate automatic focus adjustment operation.

The present invention has been made in view of such a problem, and detects the larger output of the two light receiving elements 4a and 4b by the priority detection circuit and outputs the output of this priority detection circuit. It is an object of the present invention to variably set the dead band in accordance with the above, so as to perform a highly accurate automatic focus adjustment operation.

[Means for Solving Problems] As shown in FIG. 1, the automatic focus adjusting device includes a light projecting means 11 for projecting a light beam onto a subject 10 and two reflected beams from the subject 10. Light receiving means 12 for receiving light by the light receiving portions 12a and 12b, and the light receiving portions 12a and 12b
Adjusting circuit 13 for obtaining an automatic focus adjustment signal based on the difference in the amount of incident light on the incident light, and a priority detecting circuit for receiving the outputs of the two light receiving portions 12a and 12b and selectively outputting the larger one of the outputs. 14 and a dead band setting circuit 15 for setting the dead band of the automatic focus adjustment signal in the adjusting circuit 13 according to the output of the priority detection circuit 14.

[Operation] In this automatic focusing apparatus, when the light beam projected by the light projecting means 11 is reflected by the subject 10 and is incident on the two light receiving portions 12a, 12b of the light receiving means 12, the two light receiving portions 12a, 12b.
The automatic focus adjustment signal is detected from the adjustment circuit 13 by the output signal based on the incident light amount difference b. This automatic focus adjustment signal is used for supplying power to the lens driving motor that drives the taking lens to the in-focus position. When the larger output signal of the output signals of the two light receiving units 12a and 12b is detected by the priority detection circuit 14 and this detection signal is guided to the dead band setting circuit 15, the dead band setting circuit 15 is detected.
Output variably sets the dead band for the automatic focus adjustment signal in the adjustment circuit 13 according to the output of the priority detection circuit 14.

[Examples] 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 24 which is the light projecting means 11 is a modulator which intermittently passes an oscillation pulse output of a constant frequency from an oscillator (hereinafter referred to as OSC) 21.
It is connected between the output end of 22 and ground, and emits infrared light intermittently to save power consumption.

Two light receiving elements 25a and 25b, which are the two light receiving portions 12a and 12b of the light receiving means 12, are respectively connected between the input terminals of the pre-stage amplifiers 26 and 27 and the ground, and are emitted from the light emitting diode 24 and reflected by the subject. When receiving external light, the amplified output signals corresponding to the respective photocurrents Ia and Ib are output to the pre-stage amplifier 2
6 and 27 respectively. Preamplifier 26 and 2
The output of 7 is guided to the differential output detector 29, and a signal corresponding to the output difference between the two front-stage amplifiers 26 and 27 is guided from the same detector 29 to the synchronous detector 30. The synchronous detector 30 samples the output of the differential output detector 29 with a pulse of a constant frequency generated by the OSC 21 and holds it to obtain an automatic focus adjustment signal. Therefore, when the relationship between the photocurrent Ia and the photocurrent Ib of the light receiving element 25a is Ia> Ib, the output level of the synchronous detector 30 is positive, and when Ia <Ib, the output of the synchronous detector 30 is The level becomes negative, and when Ia = Ib, the output level of the synchronous detector 30 becomes 0, that is, equal to the ground level.

The output of the synchronous detector 30 is connected to the non-inverting input terminals of the two comparators 31 and 32.

On the other hand, the outputs of the pre-stage amplifiers 26 and 27 are also guided to the priority detection circuit 34, and the priority detection circuit 34 selects only the output of the high level among the outputs of the pre-stage amplifiers 26 and 27. Then a bandpass filter (hereinafter,
BPF 35). The BPF 35 passes only the modulated wave component of the output of the pre-stage amplifier 26 or 27 detected by the priority detection circuit 34 and guides it to the synchronous detector 36.
The synchronous detector 36 samples and holds the output of the BPF 35 with a pulse of a constant frequency generated by the OSC 21. Therefore, the output of the synchronous detector 36 is a DC voltage signal corresponding to the output of the pre-stage amplifiers 26, 27 having a large level, and the higher the amount of light incident on the light receiving elements 25a, 25b, the higher the voltage. Conversely, if the amount of incident light decreases, the voltage drops. The DC voltage output from the synchronous detector 36 is connected to one end of the DC inverter 37 as a control signal for setting the dead band. Then, the dead band setting resistors 38, 39, 40 are provided across the DC inverter 37.
Are connected in series. The connection point between the resistors 38 and 39 is connected to the inverting input terminal of the comparator 31, and the resistor 39 and the resistor 4 are connected.
The connection point with 0 is grounded, and the negative terminal of the DC inverter 37 to which the resistor 40 is connected is connected to the inverting input terminal of the comparator 32. The anode of the diode 41 is connected to the output terminal of the comparator 31, and the diode 42 is connected to the output terminal of the comparator 32.
The cathode of the diode 41 and the anode of the diode 42 are commonly grounded via the resistor 43 and connected to the input terminal of the current amplifier 44. A lens driving motor 45 for driving the taking lens is connected between the output end of the current amplifier 44 and the ground.

The priority detection circuit 34 is constructed, for example, as shown in FIG. That is, in the priority detection circuit shown in FIG.
Capacitors 4 are provided at the output terminals of the pre-stage amplifiers 26 and 27, respectively.
The bases of the NPN transistors 51 and 52 are connected via 9 and 50, respectively, and the connection point of the voltage dividing resistors 53 and 54 connected in series between the application terminal of the power supply voltage + Vcc and the ground is connected to both the transistors 51 and 52. It is connected to the connection point of resistors 55 and 56 connected in series between the bases, the collectors of the transistors 51 and 52 are connected to the power supply voltage + Vcc application terminal, and the emitters are grounded via a common resistor 57. . The emitters of the transistors 51 and 52 are connected to the input end of the BPF 35 as the output end of the priority detection circuit 34. In the priority detection circuit 34, the influence of the variation in the DC voltage of both outputs of the pre-stage amplifiers 26 and 27 is removed by the capacitors 49 and 50, and only the modulation components of both outputs are guided to the bases of the transistors 51 and 52, respectively. A bias voltage is applied to the bases of the transistors 51 and 52 by resistors 53 to 56.

Now, in the non-focused state, the photocurrents Ia and Ib of the light receiving elements 25a and 25b become unbalanced. For example, assuming that Ia> Ib, the pre-stage amplifiers 26, 2 are led to the bases of the transistors 51, 52 through the capacitors 49, 50.
As shown in FIG. 5, the outputs S _A and S _B of 7 have modulation component voltages E _A and E _B (E _A > respectively) with reference to the voltage Eb.
Since it is a signal of E _B ), a current flows through the base emitter of the transistor 51 and the resistor 57 by the larger modulation component voltage E _A. The reference voltage Eb at the time of receiving the non-light emission of the intermittent light emission is determined by the resistors 53, 54, and by the resistors 55, 56.
Transistors 51 applied to the bases of 1, 52,
The base potential of 52 is the same. At this time, with respect to the modulation component voltage E _B , since the base-emitter of the transistor 52 is in a reverse voltage state, the transistor 52
No current flows through the emitter of the. As a result, the priority detection circuit 3 is provided on the emitter side of the transistors 51 and 52.
As fourth output Sc, signal S _A of the modulated component voltage E _A towards as large shown in Fig. 5 is preferentially detected. Similarly, when Ia <Ib, the priority detection circuit 34 detects the signal S _B of the modulation component voltage E _B.
When Ia = Ib, one of the signals S _A and S _B is detected.

As described above, in the priority detection circuit 34, the smaller output of the outputs of the two light receiving elements 25a and 25b is cut, and only the larger output is selectively detected. Light receiving element 25a,
The influence of the dark current of 25b is suppressed as low as possible, and therefore, as the output Sc of the priority detection circuit 34, a signal with a good S / N is obtained.

The signal Sc preferentially detected by the priority detection circuit 34 is then shaped into a substantially sine waveform by passing through the BPF 35, and is converted into a DC voltage signal by the synchronous detector 36 as described above. When this is inverted by the DC inverter 37, the dead band setting voltage that changes according to the amount of incident light is generated by the resistors 38 to 40. That is, the voltage at the inverting input terminals of the comparators 31 and 32 changes as the dead band setting voltage according to the change in the output of the synchronous detector 36. The dead band setting voltages at the inverting input terminals of the comparators 31 and 32 are set to V ₁ and −V ₁ , respectively, and the voltage at the non-inverting input terminal is set to V ₂ to explain the operation for setting the dead band with reference to FIG. , And the voltage V ₂ at the non-inverting input terminals of the comparators 31 and 32 is out of focus, the dead band setting voltage V ₁ , −.
When V ₁ <V ₂ or V ₂ <−V ₁ with respect to V ₁ , the motor 45 is driven by the output of the comparator 31 or 32. Then, by driving the motor 45, the voltage V ₂ is a straight line having an inclination according to the amount of incident light (for example, a straight line l ₁ ,
(eg, l ₂ etc.), it changes toward the in-focus position,
When the range of V ₁ <V ₂ <V ₁ is entered, the drive of the motor 45 is released.

That is, in the circuit shown in FIG. 3, when the output difference between the pre-stage amplifiers 26 and 27 is large and V ₁ <V ₂ , the comparators 31 and 3 are provided.
Since the output of 2 becomes a positive level, the positive output of the comparator 31 is guided to the current amplifier 44 through the diode 41, and the motor 45 makes a positive rotation toward the in-focus position of the lens.
Similarly, when V ₂ <−V ₁ , the outputs of the comparators 31 and 32 are at a negative level. Therefore, the negative output of the comparator 32 is guided to the current amplifier 44 through the diode 42 and the motor 45 focuses the lens. Reverse rotation toward the position. In addition, the output difference between the front-stage amplifiers 26 and 27 is small, and -V ₁ <V
_{When 2} <V ₁ , the output of the comparator 31 becomes negative and the output of the comparator 32 becomes positive.
The input end of is at the ground level and the motor 45 cannot be given a driving force.

By the way, when the amount of light incident on the light receiving elements 25a and 25b is large, the output difference between the light receiving elements 25a and 25b, that is, the comparator 3
The output voltage V ₂ of the synchronous detector 30 applied to the non-inverting input terminals of 1, 32 also follows the steep slope indicated by the solid line l ₁ in FIG. However, on the contrary, the light receiving elements 25a, 25
When the amount of light incident on b is small, the voltage V ₂ also changes little with respect to the amount of lens movement in accordance with the gentle slope indicated by the dotted straight line l ₂ in FIG. 6, for example. Therefore, assuming that the dead band setting voltages V ₁ and −V ₁ are fixed and do not change according to the amount of incident light, the voltage V ₂ changes according to the straight line l ₁ when the amount of incident light is large. , V ₂ = V ₁ or −V ₁ is the lens position P _A or P _A ′, but when the incident light quantity is small, the voltage V ₂ changes according to the straight line l ₂ V ₂ = V ₁ or − The lens position for V ₁ is P _B or P _B ′. In other words, since the lens position when entering the dead zone is different between when the amount of incident light is large and when the amount of incident light is small, for example, the dead zone is entered at the position P _A , power supply to the motor 45 is stopped, and then rotation due to inertia occurs. And the lens position is just the in-focus position Po.
If it is set so that the rotation of the motor 45 is stopped in the state of reaching the above condition, there is no problem when there is a large amount of incident light such that the voltage V ₂ changes according to the straight line l ₁ , but
When the amount of incident light is small and the voltage V ₂ changes according to the straight line l ₂ , the dead band is entered at the position P _B and the motor 4
Since the power supply to No. 5 is stopped, the motor 45 is stopped before the lens position reaches the in-focus position Po even if the lens is rotated by inertia after that, and a highly accurate in-focus state cannot be obtained.

Therefore, in the automatic focus adjusting device shown in FIG. 3, the dead band setting voltages V ₁ and −V ₁ are changed according to the amount of incident light in order to prevent the above-mentioned problems. That is, this will be explained with reference to FIG. 6. When the amount of incident light is large, the output level of the synchronous detector 36 rises, so that the dead band setting for the inverting input terminals of the comparators 31 and 32 is set accordingly. The voltages V ₁ and −V ₁ are set to a relatively high level as shown by the solid line in FIG. Then, at this time, the output voltage V ₂ of the synchronous detector 30 changes according to the straight line l _1, so that V ₂ = V ₁ or −V ₁
Then, the motor 45 is stopped at the lens position P _A or P _A ′ and completely stops rotating at the in-focus position Po. When the amount of incident light decreases, the output level of the synchronous detector 36 also decreases, so that the dead band setting voltages V ₁ and -V ₁ also decrease accordingly.
Then, when the output voltage V ₂ of the synchronous detector 30 has an incident light amount that changes to, for example, a straight line l ₂ , the dead band setting voltages V ₁ and −V are set according to the incident light amount.
₁ is set to a low level voltage V ₁ ′, −V ₁ ′ as shown by the dotted line in FIG. Therefore, in this case, the output voltage voltage V ₂ of the synchronous detector 30 changes according to the straight line l ₂ and enters the dead zone when V ₂ = V ₁ ′ or −V ₁ ′, and at this time the motor Similarly to the case where the amount of incident light is large, 45 is released from driving at the lens position P _A or P _A ′, and stops rotating at the in-focus position Po. In this way, the dead band setting voltage V is changed according to the change of the incident light amount.
_1, since -V ₁ is adapted to change, motor lens drive 45 can always increase the response speed will be stopped at the focus position Po.

The priority detection circuit 34 in the automatic focus adjustment device
Besides, for example, a priority detection circuit 34A configured as shown in FIG. 7 can be used. This priority detection circuit 3
4A, the contact terminals 65a and 65b of the electronic switch 65 and the input terminals of the comparator 66 are connected to the output terminals of the pre-stage amplifiers 26 and 27, respectively, and the output terminal of the comparator 66 is the drain of the FET (field effect transistor) 67. Connected to the side. The gate of this EFT 67 releases the resistor 68 and opens the OSC.
A sampling and holding capacitor 69 is connected between the output terminal of the FET 21 and the source side of the FET 67 and the ground. One end of the capacitor 69 connected to the source side of the FET 67 is connected to the control end of the electronic switch 65, and the movable contact piece of the electronic switch 65 is connected to the BPF 35 as the output end of the priority detection circuit 34A.

In the automatic focus adjusting device having the priority detection circuit 34A, the amount of light incident on the light receiving elements 25a and 25b becomes unbalanced when the subject is out of focus and, for example, the photocurrents Ia and Ib become Ia.
In the relation of> Ib, the output signals S ₁ and S _{2 of the} pre-stage amplifiers 26 and 27 also have the relation of S ₁ > S _2. Therefore, the output S ₃ of the comparator 66 is as described above as shown in FIG. The signals are in phase with the signals S ₁ and S ₂ and change to “1” and “0”. The output signal S ₃ of the comparator 66 is sampled by turning on the FET 67 at the output S ₄ of the OSC 21. The output S ₄ of the OSC 21 is the pre-stage amplifiers 26 and 27.
Since it is synchronized with the modulation waveforms of the output signals S ₁ and S ₂ of
When the signal S ₃ is sampled by the FET 67, the signal “1” is held in the capacitor 69. Therefore, at this time, the movable contact piece of the electronic switch 65 is connected to the side of the contact terminal 65a, and the output signal S _{1 of the} preamplifier 26 is B as the output signal S ₅ of the priority detection circuit 34A.
It is led to PF35.

When the photocurrent becomes Ia <Ib and the output signals S ₁ and S _{2 of the} pre-stage amplifiers 26 and 27 have the relationship of S ₁ <S ₂ ,
Since the output signal of the comparator 66 becomes a signal S _{3 'obtained} by inverting the signal S ₃ of the phase as shown in FIG. 8, the signal of "0" by the sampling at this time the capacitor 6
As a result, the electronic switch 65 switches the connection to the contact terminal 65b side.
The output signal _{S 2} of is guided to BPF35 as the output signal _{S 5} of the priority detection circuit 34A.

[Effect of the Invention] As described above, according to the present invention, since the larger output of the two light receiving portions is selectively provided with the priority detection circuit, the ratio of the photocurrent to the dark current is increased. It is possible to detect the amount of reflected light from the subject in a state where the S / N ratio is large and the S / N is good, and the dead band in the adjustment circuit that obtains the automatic focus adjustment signal is variably set using the output of this priority detection circuit. Therefore, there is an excellent effect that the automatic focusing operation with high accuracy and fast response can be performed without being affected by the fluctuation of the incident light amount.

[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 focus adjusting device showing an embodiment of the present invention, FIG. 4 is an electric circuit diagram showing an example of the priority detection circuit in FIG. 3, and FIG. FIG. 6 is a time chart showing input / output signal waveforms of the priority detection circuit shown in FIG. 6, FIG. 6 is a diagram for explaining a dead band controlled by the output of the priority detection circuit, and FIG. An electric circuit diagram showing another example, and FIG. 8 are time charts showing waveforms of input / output signals of the priority detection circuit shown in FIG. 1 ... Light emitting element (light projecting means) 3, 10 ... Object 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 ... adjusting circuit 14,34, 34A ... priority detection circuit 15 ... dead band circuit 31, 32 ... comparator (dead band setting circuit) 36 ... synchronous detection Unit (dead band setting circuit) 37 ... DC inverter (dead band setting circuit) 38-40 ... Resistor (dead band setting circuit)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenichi Oinoue 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd. (56) Reference JP-A-59-228213 (JP, A) JP-A-59-182410 (JP, A) JP-B-56-41970 (JP, B2)

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. An adjustment circuit for obtaining an automatic focus adjustment signal based on the difference between the two, a priority detection circuit for receiving the outputs of the two light receiving sections and selectively outputting the larger output of the two outputs, and the output of the priority detection circuit And a dead band setting circuit for setting a dead band of the auto focus signal in the adjusting circuit according to the above.