JPS61251811A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To perform automatic focus adjusting operation stably with high precision by performing control on the basis of a reference signal which follows up the sum of the quantities of incident light of two photodetection parts and a signal corresponding to the difference in the quantity of incident light. CONSTITUTION:A light beam projected by a light projecting means 11 is reflected by an object 10 and enters two photodetection parts of a photodetecting means 12 and the outputs of the photodetection parts 12a and 12b are led to a reference signal generating means 13 and an adjusting circuit 14. The reference signal generating means 13 generates the reference signal which follows up the sum of both photodetection outputs and the adjusting circuit 14 generates an automatic focus adjustment signal from the reference signal and a signal corresponding to the difference between both photodetection part outputs. This automatic focus adjustment signal is used to feed a lens driving motor which moves a photographic lens to an in-focus position etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focus adjustment device, and more particularly, to an automatic focus adjustment device used in optical devices such as film cameras and TV cameras.

[Conventional technology]

One type of automatic focusing device employs a method called an active method. This active method is
It measures the distance by receiving the light that is emitted from the camera to the subject and returns after being reflected by the subject. 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 automatic focusing device using the principle of triangulation.

When a beam of light such as infrared light emitted from the light emitting element 1 is irradiated by the focusing lens 2 toward the subject 3 in parallel to the optical axis direction of the photographing lens 5, the reflected light from the subject 3 is reflected from the photographing lens 5. Two-divided light receiving element 43 installed off-axis
, 4t).

The difference in the outputs of the two divided light receiving elements 4a and 4b is detected, for example, by a differential amplifier, and the direction and amount of extension of the photographic lens 5 is determined by the difference output, and the lens drive motor is rotated in forward and reverse directions. Due to the rotation of this motor, the lens barrel of the photographing lens 5 moves in the optical axis direction while rotating around the original axis. The two-divided light-receiving elements 4a and 4b are arranged so that their inclination angles θ vary in conjunction with the movement of the photographing lens 5, and rotate in the direction in which the differential output between the light-receiving elements 4a and 4b becomes zero. Then, the two light receiving elements 4a
, 4b becomes zero, the photographing lens 5 becomes in focus. In the focused state, the light receiving elements 4a, 4
The inclination angle θ of b, the distance between the original axis of the photographing lens 5 and the two light receiving elements 4a and 4b, and the distance S from the photographing lens 5 to the subject 3 are as follows.

The expression θ=tan-' (S/D) is satisfied. In addition, the two light receiving elements 4a
, 4b, it is possible to determine not only whether the lens is in focus or out of focus, but also the directionality of the out-of-focus state at the time of out-of-focus, that is, the front focus and rear focus states.

[Problem that the invention seeks to solve]

By the way, in general, when trying to increase the response speed of the automatic focus adjustment operation in the above-mentioned automatic focus adjustment device, even if the power supply to the lens drive motor is stopped at the in-focus position, the motor, photographic lens, etc. Since it has a moment of inertia, it does not stop immediately and ends up overrunning the focus position. Therefore, anticipating that the photographic lens will move due to inertia, a dead zone is provided between the focal point where the output difference between the two light receiving elements 4a and 4b becomes 0, and when the output difference enters this dead zone, the motor is Devices that stop power supply are well known. However, when the subject distance differs or the reflectance of the subject differs, the amount of infrared light beam emitted from the light emitting element 1 and incident on the light receiving elements 4a and 4b will vary greatly. The position of the photographing lens when entering the dead zone is different depending on whether the amount of light incident on the light receiving elements 4a, 4b is large or small. Therefore, for example, the light receiving elements 4a, 4b
When the amount of light incident on the lens is small, there are problems such as the photographic lens stopping before reaching the in-focus position.
A device has also been proposed in which the dead band mentioned above can be adjusted freely using a variable resistor (Japanese Patent Publication No. 56-41
However, in this conventional device, the dead zone is manually set, and it is impossible to accurately respond to changes in the amount of incident light, and it is difficult to perform highly accurate automatic focus adjustment. could not.

On the other hand, a device has also been proposed in which the sum output of the two light-receiving elements 4a and 4b is used to perform various control operations of the automatic focus adjustment device (1996).
5-13012), but this conventional device does not disclose any specific structure in which the sum output acts on the automatic focus adjustment control system.

The present invention has been made with attention to such problems, and includes a reference signal that follows the sum of the amounts of incident light on the two light receiving sections (light receiving elements 4a and 4b), and a signal that corresponds to the difference in the amount of incident light. Based on the above, it is an object of the present invention to provide an automatic focus adjustment device in which the gain of the entire automatic focus adjustment control system does not fluctuate and a highly accurate and stable automatic focus adjustment operation is performed.

[Means for solving problems]

As shown in FIG. 1, this automatic focus adjustment device includes a light projection unit 11 that projects an original beam toward a subject 10, and two light receiving units i2a that receive the reflected beam from the subject 10.
12b, and the light receiving unit 1.
2a, 12b; a reference signal generating means 13 that generates a reference signal that follows the sum of the amounts of light incident on the two light receiving sections 12a, 12b; and an adjustment circuit 14 for obtaining an automatic focus adjustment signal.

[Effect]

In this automatic focus adjustment device, the light beam projected by the light projection means ii is reflected by the subject 1o and enters the two light receiving sections 12a and 12b of the light receiving means 12, and the outputs of the two light receiving sections 12a and 12b are as follows. When guided to the reference signal generation means 13 and the adjustment circuit 14, the reference signal generation means 13 generates a reference signal that follows the sum of the outputs of the two receiver sections, and the adjustment circuit 14 generates a reference signal that follows the sum of the outputs of the two receiver sections. An automatic focus adjustment signal is generated from a signal corresponding to the difference in output. This automatic focus adjustment signal is used, for example, to supply power to a lens drive motor that moves the photographic lens to the in-focus position.

〔Example〕

The present invention will be further explained below based on examples.

FIG. 3 is an electrical circuit of an automatic focusing device showing one embodiment of the present invention. The infrared light emitting diode 23, which is the light projection means 11, is connected between the output terminal of a current amplifier 22 that amplifies the oscillation pulse output of a constant frequency from the oscillator 21 and ground, and emits infrared light to save power consumption. The light emission is blinked and modulated.

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

Further, the outputs of the pre-stage amplifiers 26 and 27 are sent to a sum output detector 33.
A signal corresponding to the output difference between the two front-stage amplifiers 26 and 27 is guided from the detector 33 to the BPF 34. This BP
Similarly, F34 separates only the modulated wave component from the sum output signal detected from the sum output detector 33, passes it through, and guides it to the S/H circuit 35.
The output of the PF 34 is sampled with the sampling pulse from the sampling pulse generator 24, and the same sampling level is held.

In this embodiment, the modulation frequency for blinking one light emitting diode 23 is 5 KHz, so the above BPF
The center frequencies of 30 and 34 are the same as the above frequency of 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 emitted at the timing shown in FIG. 4, and the output a of the BPF 30 is modulated when in focus. A flat waveform a that contains no components. When out of focus, a waveform a1 consisting of a modulation component or a waveform a2 obtained by inverting the phase of this waveform a1 is obtained. The amplitude of the waveforms a1 and a2 is a sine waveform whose magnitude is proportional to the degree of out-of-focus. Further, the output of the BPF 34 is proportional to the amount of infrared reflected light from the subject, and the amplitude of the sine waveform changes as shown in the heptad waveform bt+b2. Waveform a of the above output a, ~
Time d when the sampling pulse C' is emitted at a3. -d2 and the time point elte2 at which the sampling pulse C is emitted in the waveforms s, , b of the above-mentioned outputs is the sampling point. Therefore, the above-mentioned point d corresponds to the focus adjustment state of the photographic lens. -d2 level is S/I (held by circuit 31 and 0.+
. As the amount of light decreases, it is converted into a lower DC voltage. 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, the photographing lens is at the focus position P. , the output voltage Va of the S/H circuit 31 becomes Ov, and the voltage Va changes as shown by straight lines 1 and 12 as it shifts to the nearer side N and farther side (1). Straight line 11 shown as a solid line
indicates the case where the detected modulation component is large, and the straight line 12 shown by a dotted line indicates the case where the detected modulation component is small. In some cases, if the S/H circuit 31
Even if a servo system is constructed by supplying the output of 2 to the motor 54 as it is to perform the automatic focus adjustment operation, the servo gain will change, making stable servo control impossible. Therefore, in order to prevent this, the output voltage Va of the S/H circuit 31 is guided to one input terminal of each of the four voltage comparators 41, 42, 43 and 44, and the output voltage Va of the S/H circuit 35 is The output voltage vb is supplied to the other input terminal of each of the four voltage comparators 41 to 44 as reference voltages (threshold voltages) at different levels. For example, the relationship between the output voltage vb of the S/H circuit 35 and the amount of infrared reflected light from the subject is as shown in FIG. It is proportional to the amount of light, and as the amount of reflected light increases, it becomes higher as shown by a solid straight line 13. S/H circuit 35
Since an inverting DC amplifier 45 is connected to the output terminal of the inverting DC amplifier 45, the output voltage of the inverting DC amplifier 45 is a voltage obtained by inverting the polarity of the voltage vb.

As the amount of reflected light increases, it decreases as shown by the dotted straight line 14.

The output voltage vh of the S/H circuit 35 is directly led to the voltage comparator 41 as the highest reference voltage (2), and the output of the S/H circuit 35 is input to the voltage comparator 42 through the resistors 37 and 38.
It is derived as a reference voltage M divided by the ratio of .

Further, the output of the S/H circuit 35 is inverted in polarity by an inverting DC amplifier 45, and is then led to the voltage comparator 43 as a reference voltage -v2, which is divided by the ratio of the resistors 39 and 40. The output of the S/H circuit 35 is inverted by the DC amplifier 4.
It is designed to be derived as the lowest reference voltage -vI with its polarity reversed at 5. Voltage comparators 41, 4
The anodes of diodes 47 and 48 are connected to the output terminals of the voltage comparators 43 and 44, respectively, and the cathodes of diodes 49 and 50 are connected to 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 a resistor 51, and the other end of this resistor 51 is connected to the cathode of the diode 47 and the anode of the diode 5o, and the connection point is , are grounded via a resistor 52 and connected to the input end of a motor drive amplifier 53. Motor drive amplifier 53
A reversible DC motor 54 for driving the photographing lens is connected between the projecting end of the lens and the ground.

Here, the reference voltage vI of the voltage comparators 41 to 44 is changed by changing the output voltage vb of the S/H circuit 35 according to the amount of reflected light incident on the light receiving elements 25a and 25b.

■, -V2. To explain that -Vl changes, these reference voltages are all 0 when there is no amount of reflected light.
(2), but its absolute value changes in proportion to the amount of reflected light, as shown in FIG. In FIG. 7, the state shown by ■ is a case where the amount of reflected light is large, and the state shown by I is a case where the amount of reflected light is small, and the reference voltages v, , 'v2. -v,.

-vl changes according to the amount of reflected light.

When the output voltage Va of the S/H circuit 31 exceeds the reference voltage V, (V+ < Va), the output voltage of the voltage comparator 41 switches from -E to +E, and when the output voltage Va exceeds the reference voltage v2. The output voltage of the voltage comparator 42 is the same <-
Switches from E to +E. Further, when the output voltage Va becomes larger in the negative direction than the reference voltage -v2, the voltage comparator 4
When the output voltage of 3 switches from +E to -E and the output voltage Va becomes larger in the negative direction than the reference voltage = ■,
The output voltage of the voltage comparator 44 switches from +E to -E. In other words, as shown in FIG. 7, the output voltage Va of the S/H circuit 31 falls within the range of Va < Vl or -Vl.
<Va, the positive output voltage terminal E of the voltage comparator 41 passes through the diode 47.

Alternatively, since the negative output voltage -E of the voltage comparator 44 is directly supplied to the motor drive amplifier 53 through the diode 50, the motor drive amplifier 53 rotationally drives the motor 54 toward the in-focus position at a relatively high speed. . Also %V
2<Va<Vl inclusive or 1■, <Va<
-V, the positive output voltage +E of the voltage comparator 42 passes through the diode 48, or the negative output voltage -E of the voltage comparator 43 passes through the diode 49 to the ratio between the resistors 51 and 52. In this case, the motor driving amplifier 53 rotates the motor 54 toward the focusing position at a relatively low speed. Furthermore, when the range equation is -V2<Va<v2, the output voltages of the voltage comparators 41 and 42 become -E, and the output voltages of the voltage comparators 43 and 44 become +E. The output voltage of diode 47~5
0, the input of the motor drive amplifier 53 is at the ground level of the resistor 52, and the driving force of the motor 54 is released.

As explained with reference to the principle diagram shown in FIG. 2, the motor 54 is mechanically linked to the two light-receiving elements 25a and 25b and also linked to the distance ring of the photographing lens. one light receiving element 25a.

Control is performed so that the reflected infrared light is uniformly irradiated onto 25b. Then, as shown in FIG. 7 above, the reference voltage V□ is set in the voltage comparators 41 to 44.

By changing V, , -V, , -V depending on the amount of reflected light, the servo gain becomes constant regardless of the amount of reflected light. That is, as mentioned above, the output voltage Va of the S/H circuit 31 is -
Entering the range formula of Vz < Va < Vl, this range formula is based on the sum output with the remaining 25b in the dead band where it is determined that the in-focus state is < proportional to the output voltage vb of the S/H circuit 35. Therefore, if the amount of reflected light is large, it will be expanded to the above range (as shown in state I in Fig. 7); if the amount of reflected light is small, it will be reduced to the above range (as shown in state I in Fig. 7).
), the servo gain will not change. In addition, since the reference voltages V, , -V, are used to speed up the response speed, the motor 5 in the above range where the photographing lens position deviates from the in-focus state, , D,'.
4 rotates at high speed, and the range near the focus Dz, D2
When reaching ', the rotational speed of the motor 54 is switched to a low speed.

Reference voltage vI.

-vl also changes depending on the amount of reflected light, and the above range Dz
, DI' and D2-D2' vary. As a result, problems such as hunting and overrun are solved.

In addition, if the amount of reflected light becomes extremely small because the subject is at an infinite distance, based on the above sum output, < S/
The output voltage vb of the H circuit 35 is extremely small and the reference voltage V1. Since the absolute value of Vz −Vt, V, is also set to be very small, in this case, these reference voltages V, ,
Instead of automatic focus adjustment control by comparing V, -V, -V with the output voltage Va of the S/H circuit 31,
Since the output voltage vb of the S/H circuit 35 is guided to another voltage comparator 55 and compared with the reference voltage VO, when the output voltage vb reaches %■<vo, the output voltage of the voltage comparator 55 is sent to the motor drive amplifier 53, and the motor drive amplifier 53 at this time receives the reference voltage V
Regardless of the automatic focus adjustment output obtained by comparing s = Vt, Vt, -■ with the output voltage Va of the S/H circuit 31, the output of the voltage comparator 55 allows the photographing lens to be positioned at infinity. The motor 54 is driven to focus.

The motor drive amplifier 53 may be configured as shown in FIG. 8, for example. In FIG. 3, one terminal of the motor 54 is grounded, but in the motor drive amplifier 53A shown in FIG. Both terminals are not grounded. That is, the input terminal of this motor drive amplifier 53A is connected to the operational amplifier 61 on the one hand.
The output terminal of the operational amplifier 61 is connected to the bases of an NPN transistor 62 and a PNP transistor 63, and the emitters of the transistors 62 and 63 are connected to one end of the motor 54. This motor 54
One end is connected to the inverting input terminal of the operational amplifier 61,
Voltage elements E and -E are applied to the collectors of the transistors 62 and 63, respectively. This operational amplifier 61 and transistors 62 and 63 constitute a first current amplifier with extremely low output impedance.

Moreover, the operational amplifier 6 is connected to the other end of the motor 54 as described above.
6 and transistors 64 and 65, and has an extremely low output impedance. 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 inverting input terminal of the operational amplifier 67 and the input terminal of the motor drive amplifier 53A via the resistor 69. The non-inverting input terminal of the operational amplifier 67 is grounded. That is, this operational amplifier 67 and resistors 68, 6
9 constitutes an inverting amplifier, and the input terminal of the motor drive amplifier 53A is connected to the inverting input terminal of the operational amplifier 66 of the second current amplifier via this inverting amplifier. When the voltage applied to the input terminal of the motor 53A is +E or -E, the voltage at one end of the motor 54 is +E by turning on the transistor 62.

Alternatively, when the transistor 63 is turned on, -E1 is applied to the other end, and when the transistor 65 is turned on, -E1 is applied, or when the transistor 64 is turned on, 10E is applied, resulting in 2
A voltage E is applied between both ends of the motor 54, and the motor 54
will rotate at high speed.

In this state, as shown in FIG.
, or when the output voltage -E is output from the voltage comparator 44, the input voltage divided by the resistors 51 and 52 is guided to the motor drive amplifier 53A to perform low speed rotation.

1. If the dead band that can be determined as the in-focus state is entered, and OV is input to the input terminal of the drive amplifier 53A,
Both terminals of the motor 54 are connected to O through current amplifiers.
Since the same potential of v is applied and these are low impedance sources, both ends of the motor 54 are equivalent to a short-circuit state and braking is applied, so that the motor 54 stably stops at the focused position. I will do it.

〔Effect of the invention〕

As described above, according to the present invention, a reference signal for determining whether the level of the output difference signal of the two light receiving sections is in an in-focus state or in an out-of-focus state is generated from the sum of the outputs of the two light receiving sections. As a result, the gain of the automatic focus adjustment control system does not vary regardless of the amount of reflected light from the object, and a highly accurate and stable automatic focus adjustment operation can be performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic circuit configuration of the automatic focus adjustment device of the present invention. FIG. 2 is a principle configuration diagram showing an example of an optical system in which the automatic focus adjustment device of the present invention is adopted. The figure is an electric circuit diagram of an automatic focus adjustment device showing one embodiment of the present invention. The figure is a diagram showing changes in the output of the S/H circuit 31 in FIG. 3 above with respect to the lens position, and FIG. FIG. 8 is an electric circuit diagram showing an example of a specific circuit configuration of the motor drive amplifier. 1......Light emitting element (light projection means) 3, 10...-...Subject 4a, 4b, 25a, 25b --- Two-split light-receiving element (two light-receiving parts) 5...
・・・・・・・・−・Photographing lens 11・・・・・・・・・・
......Light projection means 12...
...... Light receiving means 12a, 12b.
・・Song・Surroundings・・Two light-receiving areas 13・・・・・・・・・
......Reference signal generating means 14...
・・・・・・−・・・・・・Adjustment circuit h'4 Figure 5 outside the figure + Horse 6 section

Claims (1)

[Scope of Claims] A light projecting means for projecting a light beam; a light receiving means having two light receiving sections for receiving a reflected beam of the light beam from a subject; a reference signal generating means for generating a reference signal that follows the sum of the amounts of light; an adjustment circuit that obtains 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 sections; An automatic focus adjustment device comprising: