JPH0644094B2 - Automatic focus adjustment device - Google Patents

Description

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.

[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 applied to the subject 3 by the focusing lens 2 in parallel to the optical axis direction of the taking lens 5, reflected light from the subject 3 is reflected by the taking lens 5. Two-divided photo detectors 4a, 4b installed outside the optical axis
An image is formed on the upper surface by the light receiving lens 6. 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 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 and 4b are changed in the left-right direction in association with the movement of the taking lens 5, so that the differential output of the light receiving elements 4a and 4b becomes zero. Moving. Then, when the difference output between the light receiving elements 4a and 4b becomes zero, the taking lens 5 is brought into the in-focus state. In the focused state, the tilt angle θ of the incident light on the light receiving elements 4a and 4b is
And the distance S from the baseline length taking lens 5 to the subject 3 satisfies the equation θ = tan ⁻¹ (S / D). In addition, the 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 adjustment device, the light receiving element 4 is used when the subject is far and near, or when the reflectance differs depending on the subject.
The outputs a and 4b have large fluctuations due to fluctuations in the amount of incident light, which causes the inconvenience that the operation of the automatic focusing device becomes very unstable.
Therefore, the outputs of the two light-receiving elements 4a and 4b are added, and the added outputs of the light-receiving elements 4a and 4b are used to control the gain of the adjusting circuit that is the control system of the lens driving motor. A device has also been proposed (Japanese Patent Publication No. 55-130).
In the case of this conventional device, when the output level of one of the light receiving elements is lowered in the out-of-focus state, the output level of the added light receiving element is also reduced, and the light level against the dark current is reduced. Since the current is low and the S / N ratio per unit area is deteriorated, even if the automatic focus adjustment circuit is controlled using this addition output, there are problems such as very low focusing accuracy. there were. The present invention has been made in view of such a problem, and selectively outputs the larger output of the two light receiving elements 4a and 4b, and the same output is used to drive the lens drive motor. The purpose is to control the gain in a control circuit that is a control system.

[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, 12b, an adjusting circuit 13 for obtaining an automatic focus adjustment signal based on the difference in the amount of light incident on these light receiving portions 12a, 12b, and the above two A priority detection circuit 14 that receives the outputs of the light receiving sections 12a and 12b and selectively outputs the larger output of the two outputs, and a gain that adjusts the gain in the adjustment circuit 13 according to the output of the priority detection circuit 14. The adjusting circuit 15 is provided.

[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 light is incident on 12a and 12b, the automatic focusing signal is detected from the adjusting circuit 13 by the output signals of the two light receiving units 12a and 12b based on the difference in the incident light amount. 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. Then, of the output signals of the two light receiving units 12a and 12b, the larger output signal is the priority detection circuit 14
When the detection signal is detected and guided to the gain adjustment circuit 15, the output of the gain adjustment circuit 15 causes the adjustment circuit 13
The gain at is adjusted. In other words, even if the subject 10 is far away or the reflectance of the subject 10 is low and the incident light amount of the reflected beam is weak, the priority detection circuit 14 detects
Only the larger output signal of the outputs of the two light receiving sections 12a and 12b is selected, and the gain is adjusted based on the good output signal of this S / N, whereby a stable automatic focus adjustment operation is performed.

〔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. Infrared light emitting diode which is the light projection means 11
24 is connected between the output end of the LED drive circuit 23 provided at the output end of the modulator 22 for intermittently energizing the oscillation pulse output of the constant frequency from the oscillator (hereinafter referred to as OSC) 21 and the ground, and the power consumption. To save energy, it emits infrared light intermittently.

The two light receiving elements 25a and 25b, which are the two light receiving portions 12a and 12b of the light receiving means 12, are connected between the grounds of the input ends of the pre-stage amplifiers 26 and 27, respectively, and are emitted from the light emitting diode 24 and reflected by the subject. When receiving external light, the preamplifiers 26 and 27 output amplified output signals corresponding to the photocurrents Ia and Ib, respectively. The outputs of the pre-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 guided to the synchronous detector 30 from the detector 29. The synchronous detector 30 samples the output of the differential output detector 29 with a pulse of a constant frequency emitted by the OSC 21 and holds it to obtain an automatic focus adjustment signal. Therefore, when the relation between the photocurrent Ia of the light receiving element 25a and the photocurrent Ib is Ia> Ib, the output level of the synchronous detector 30 becomes positive, and Ia
When <Ib, the output level of the synchronous detector 30 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 guided to the current amplifier 32 through the gain switching circuit 31 and current-amplified. Since the lens driving motor 33 for driving the photographing lens is connected between the output end of the current amplifier 32 and the ground, the photocurrent Ia is decreased when the output level of the synchronous detector 30 is positive, and the photocurrent Ia is decreased. The motor 33 rotates forward in the direction of increasing Ib, and the synchronous detector
When the output level of 30 is negative, the motor 33 reversely rotates in the direction of increasing the photocurrent Ia and decreasing the photocurrent Ib. When the output level of the synchronous detector 30 is 0, the potentials of both terminals of the motor 33 become equal and the motor 33 stops rotating. At this time, the photocurrent Ia = Ib.

In the gain switching circuit 31, the contacts of the electronic switch 34
34a is connected to the output end of the synchronous detector 30, and the contact 34a is connected to the connection point of the voltage dividing resistors 35 and 36 connected in series between the output end of the synchronous detector 30 and the ground. The movable contact of the electronic switch 34 is contacted based on the output of the priority detection circuit 38 described later.
Connect to 34a side or contact 34b side. Electronic switch 34 is a contact
When connected to the 34a side, the output of the synchronous detector 30 is guided to the current amplifier 32 without being attenuated, and also the electronic switch
When 34 is connected to the contact 34b side, the output of the synchronous detector 30 is divided by the resistance ratio of the resistors 35 and 36 and guided to the current amplifier 32 at a level attenuated.

In addition, the outputs of the preceding stage amplifiers 26 and 27 are the priority detection circuit 38.
Be led to. The priority detection circuit 38 includes the pre-stage amplifiers 26 and 27.
The bases of the NPN transistors 41 and 42 are connected to the output terminals of the capacitors via capacitors 39 and 40, respectively, and the connection point of the voltage dividing resistors 43 and 44 connected in series between the power supply voltage + Vcc application terminal and ground is Connected to the connection point of resistors 45 and 46 connected in series between both bases of the transistors 41 and 42, the collectors of the transistors 41 and 42 are connected to the power supply voltage + Vcc application terminal, and the emitter is grounded via a common resistor 47. Has been configured. The emitters of the transistors 41 and 42 are connected to the input end of a bandpass filter (hereinafter referred to as BPF) 48 as the output end of the priority detection circuit 38. In the priority detection circuit 38, the effects of variations in the DC voltage of both outputs of the pre-stage amplifiers 26 and 27 are removed by the capacitors 39 and 40, and only the modulation components of both outputs are guided to the bases of the transistors 41 and 42, respectively. A bias voltage is applied to the bases of the transistors 41 and 42 by resistors 43 to 46.

If it is out of focus, the photocurrent of the light receiving elements 25a, 25b 1
a and Ib are unbalanced. For example, if Ia> Ib, the transistors 41 and 42 are passed through the capacitors 39 and 40.
As shown in FIG. 4, the outputs S _A and S _B of the pre-stage amplifiers 26 and 27, which are guided to the bases of the two, are such that the modulation component voltages are E _A and E _B (E _A > E _B ), respectively, based on the voltage E _b . Since it is a signal, the larger modulation component voltage E _A causes a current to flow through the base-emitter of the transistor 41 and the resistor 47. The reference voltage Eb at the time of non-light emission in intermittent light emission is determined by the resistors 43 and 44, and by the resistors 45 and 46, a transistor
The base potentials of the transistors 41 and 42 applied to the bases of 41 and 42 are the same. At this time, with respect to the modulation component voltage E _B, the base of the transistor 42 - between the emitter current does not flow through the emitter of the transistor 42 since the reverse voltage condition. As a result, on the emitter side of the transistors 41 and 42, the signal S _A of the larger modulation component voltage E _A is preferentially detected as the output Sc of the priority detection circuit 38 as shown in FIG. Similarly, when Ia <Ib, the priority detection circuit 38 detects the signal S _B of the modulation component voltage E _B. When Ia = Ib, either one of the signals S _A and S _B is detected.

As described above, in the priority detection circuit 38, 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. The influence of the dark current of the light receiving elements 25a and 25b is suppressed as low as possible, and as a result, the output Sc of the priority detection circuit 38 is a signal with a good S / N.

The signal Sc preferentially detected by the priority detection circuit 38 is then shaped into an almost sine waveform by passing through the BPF 48, and is sampled and held by the synchronization detector 49 at the timing of pulse output of a constant frequency from the OSC 21. To be done. The output of the DC voltage from the synchronous detector 49 is guided to one input end of a comparator 50 that forms a circuit corresponding to the gain adjusting circuit 15 together with the gain switching circuit 31. At 50, the level of the one input terminal is compared with the level of the other input terminal connected to the connection point of the resistors 51 and 52 connected in series between the terminal of the power supply voltage + Vcc and the ground. The comparator 50 generates a high level output when the output level of the synchronous detector 49 exceeds a reference level determined by the voltage division ratio of the resistors 51 and 52, and outputs a low level output when the output level falls below the reference level. Generate output. The electronic switch 34 of the gain switching circuit 31 is switch-controlled according to the output level of the comparator 50, and the electronic switch 34 is connected to the contact 34b side when the output of the comparator 50 is at a high level. When the output of the comparator 50 is low level, it is connected to the contact 34b side. In other words, when the amount of light incident on the light receiving elements 25a and 25b increases when the subject is close to the subject or the reflectance of the subject is high, the output of the comparator 50 causes the electronic switch 34 to contact the contact 34b.
The output of the synchronous detector 30 is connected to the resistor 35,
Since the value attenuated by 36 is guided to the current amplifier 32, at this time, the lens drive control operation of the motor 33 described above is performed with low sensitivity. On the contrary, when the amount of light incident on the light receiving elements 25a, 25b decreases when the subject is far away or the reflectance of the subject is low, the output of the comparator 50 causes the electronic switch 34 to move to the contact 34a side. Connected to the current detector without damaging the output of the synchronous detector 30.
Since it is guided to 32, the lens drive control operation of the motor 33 is performed with high sensitivity at this time. Further, by providing the priority detection circuit 38, as described above, even when the amount of light incident on the light receiving elements 25a, 25b is reduced,
Since only the larger output of the two outputs of the light receiving elements 25a, 25b is detected by the priority detection circuit 38, the comparator 50 is reliably operated by this detection output, and the gain switching circuit 31 responds to the automatic focus adjustment signal. The gain switching operation is performed stably.

Further, since the output of the synchronous detector 49 is guided to the LED drive circuit 23 as a signal for controlling the light emission amount of the light emitting diode 24, for example, the subject is close or the reflectance of the subject is high. When the incident light amount increases and the DC output voltage of the synchronous detector 49 increases, the LED drive circuit 23 is controlled to reduce the light emission amount of the light emitting diode 24. Conversely, the subject is far and the reflectance of the subject is high. When the incident light amount is low or the DC output voltage of the synchronous detector 49 is low, the LED drive circuit 23 is controlled to increase the light emission amount of the light emitting diode 24.

Instead of the priority detecting circuit 38, a priority detecting circuit 54 configured as shown in FIG. 5 can be used. In this priority detection circuit 54, the contact terminals 55a and 55b of the electronic switch 55 and the input terminals of the comparator 56 are connected to the output terminals of the pre-stage amplifiers 26 and 27, respectively, and the output terminal of the comparator 56 is an FET (field effect transistor). ) Connected to the drain side of 57. The gate of the FET 57 is connected to the output end of the OSC 21 via the resistor 58, and the sampling hold capacitor 59 is connected between the source side of the FET 57 and the ground. One end of the capacitor 59 connected to the source side of the FET 57 is connected to the control end of the electronic switch 55, and the movable contact piece of the electronic switch 55 serves as an output end of the priority detection circuit 54 as a BPF 48.
Connected to.

In the automatic focus adjustment device having the priority detection circuit 54, when the light is not focused, the amounts of light incident on the light receiving elements 25a and 25b become unbalanced, and for example, the photocurrents Ia and Ib have a relationship of Ia> Ib. , The output signals S ₁ and S _{2 of} the pre-stage amplifiers 26 and 27 are also S
₁ > S ₂ and therefore the output S _{3 of the} comparator 56
, As shown in FIG. 6, the signal changes to "1", "0" by the signal _S 1, _{S 2} in phase. The output signal S ₃ of the comparator 56 is sampled by turning on the FET 57 at the output S ₄ of the OSC 21. Since the output S _{4 of the} OSC ₂₁ is synchronized with the modulation waveforms of the output signals S ₁ and S ₂ of the pre-stage amplifiers 26 and 27, when the signal S ₃ is sampled by the FET 57, the signal of “1” becomes a capacitor. Hold on to 59. Therefore, at this time, the electronic switch
The movable contact piece of 55 is connected to the contact terminal 55a side,
The output signal S ₁ of the above is guided to the BPF 48 as the output signal S ₅ of the priority detection circuit 54.

When the photocurrent becomes Ia <Ib and the output signals S ₁ and S _{2 of the} pre-stage amplifiers 26 and 27 have a relationship of S ₁ <S ₂ , the output signal of the comparator 56 is as shown in FIG. Signal S
_Since the signal S ₃ ′ is obtained by inverting the phase of ₃ , the signal of “0” is held in the capacitor 59 by sampling at this time, and the electronic switch 55 is connected to the contact terminal 55b.
Switch the connection to the side, and thus the output signal S of the preamplifier 27
₂ is led to the BPF 48 as the output signal S ₅ of the priority detection circuit 54.

〔The invention's effect〕

As described above, according to the present invention, since the priority detection circuit that selectively detects the larger output of the two light receiving units is included, the ratio of the photocurrent to the dark current becomes large. Therefore, the level of reflected light from the subject can be detected with a good S / N ratio. Therefore, the output of this priority detection circuit is used to control the adjustment circuit that obtains the automatic focus adjustment signal. It has an excellent effect that the focusing accuracy of the operation is significantly improved.

[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 a time chart showing input / output signal waveforms of the priority detection circuit in FIG. 3, and FIG. FIG. 6 is an electric circuit diagram showing another example of the priority detection circuit used in the present invention, and FIG. 6 is a time chart showing input / output signal waveforms of the priority detection circuit of FIG. 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 …… Adjusting circuit 14,38,54 …… Priority detection circuit 15 …… Gain adjusting circuit 31 …… Gain switching circuit (gain adjusting circuit) 50 …… Comparator (gain Adjustment circuit)

Front page continuation (72) Inventor Kenichi Oinoue 2-43-2 Hatagaya, Shibuya-ku, Tokyo Within Olympus Optical Co., Ltd. (56) Reference JP-A-59-228213 (JP, A) JP-A-SHO 59-182410 (JP, A)

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 an output of the priority detection circuit A gain adjusting circuit for adjusting the gain in the adjusting circuit according to the above, and an automatic focus adjusting device.