JPH0774854B2 - Automatic focus adjustment device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjustment control device used in an automatic focus adjustment device that projects a light flux onto a subject and uses the reflected light to perform focus adjustment.

2. Description of the Related Art Conventionally, a light flux is projected toward a subject, the reflected light is photoelectrically detected, a signal corresponding to the distance to the subject (hereinafter referred to as a distance signal) is calculated, and focus adjustment of an optical system is performed. A so-called active type automatic focus adjusting device has been proposed. In the active type automatic focusing device,
When the subject is at a short distance, or when the amount of incident light on the light receiving element is very large, such as when the subject has a high reflectance, Since the reflected light from a subject having a very wide dynamic range must be processed up to a state in which the amount of incident light on the light receiving element is extremely weak, various measures have been taken.

For example, in Japanese Patent Laid-Open No. 61-73117 already proposed by the applicant, infrared light is projected toward a subject, and the reflected light is guided to a light position detection element (PSD) via a light receiving lens,
The ratio of the sum and difference of the _two photocurrents I ₁ and I ₂ output according to the spot position of the infrared light is calculated to obtain the distance signal to the subject, and the distance signal and the focusing lens of the photographing lens The focus adjustment amount and direction are obtained using the lens encoder output signal indicating the position, and the focusing lens is driven to perform focus adjustment.

At this time, in order to compress the dynamic range of the signal intensity handled by the arithmetic circuit that calculates the light-receiving element output signal, the signal corresponding to the sum of the light-receiving element output signals is used to adjust the gain and adjust the light emission amount. The function to perform is provided, and both adjustment functions are used together to perform highly accurate distance.

In the conventional example, in order to properly operate both the automatic gain adjustment function and the automatic light emission amount adjustment function, the lens encoder output indicating the position of the focusing lens of the imaging lens is used.
If the lens encoder output at the time of the distance measurement for the first time indicates a short distance, the automatic light emission amount adjustment is mainly activated and the automatic gain adjustment is not operated. Conversely, the lens encoder output at the time of the Nth distance measurement is If it is a long distance, the amount of light emission is constant, and the automatic gain adjustment is mainly operated to set N + 1.
The second distance measurement is being performed.

Problems to be Solved by the Invention In the above-mentioned conventional example, the position of the subject is determined using the lens encoder output. However, the lens encoder output supplies an output corresponding to the subject position only after the focusing lens is driven based on the obtained distance signal and stopped at the in-focus point. Therefore, the lens encoder output has a time delay from the end of the distance measurement until the output corresponding to the subject position is supplied. Usually, in the case of a video camera lens, it takes several seconds for the focusing lens to be driven to change from the infinity shooting state to the close-up shooting state. On the other hand, the distance measurement interval is selected to be several Hz because it corresponds to the movement of the subject. As a result, the time until the focusing lens is driven and stopped may be longer than the distance at which distance measurement is performed, and the lens encoder output indicating the position of the focusing lens when performing the (N + 1) th distance measurement. May not correctly indicate the subject position. Therefore, a subject located at a long distance may be operated by the automatic light emission adjustment function to measure the distance, or a short-distance subject may be operated by the automatic gain adjustment function to measure the distance. The dynamic range becomes severe, and the desired accuracy cannot be obtained.

Means for Solving the Problems In order to solve the above-described problems, the present invention provides a light projecting unit that projects a light beam toward a subject, and after the light is projected by the light projecting unit, is reflected by the subject. A light-receiving lens that collects the reflected light coming in, a light-receiving element that outputs two photocurrents at a ratio according to the position of the image-forming spot formed by the light-receiving lens for the reflected light, and an output signal of the light-receiving element is calculated to calculate the object To a distance signal corresponding to the distance to, the arithmetic unit uses an output signal from the adder and an adder that outputs a signal corresponding to the sum of the output signals from the light receiving elements. And an automatic gain adjusting unit for adjusting the gain of the signal, and an automatic light emitting amount adjusting unit for adjusting the light emitting amount of the luminous flux projected from the light projecting unit using the output signal from the adder, Output signal of the arithmetic unit A focus adjusting device for driving a photographic lens to perform focus adjustment based on the signal, and when the distance signal output from the calculation unit indicates a short distance, the gain applied to the signal is kept constant next time. , Mainly by operating the automatic light emission amount adjustment unit, to secure the signal output level by changing the light emission amount based on the output signal from the adder, if the distance signal indicates a long distance, next time The amount of light emitted from the light projecting unit is kept constant, the automatic gain adjusting unit is mainly operated, and the signal output level is secured by changing the gain based on the output signal from the adder to measure the distance. Is configured to do.

With the above-described configuration, the present invention switches the operation of the automatic light emission amount adjustment unit and the automatic gain adjustment unit using the distance signal of the operation unit that responds quickly to changes in subject conditions, so that it is more accurate. In addition, the dynamic range can be compressed according to the subject condition, and highly accurate distance measurement can be realized.

Embodiment FIG. 1 is a block diagram showing an embodiment of an automatic focus adjustment device including a controller for automatic focus adjustment according to the present invention.

The basic configuration of the present invention is based on the trigonometric distance measurement principle. The light projecting means including the light projecting lens 1 and the light emitting element 3 and the light receiving means including the light receiving lens 2 and the light receiving element 4 are arranged at a predetermined interval. Has been done. The light emitting device intermittently emits light at a certain fixed period, and within the light emission period, the light flux output from the light emitting element 3 pulse-driven at a certain frequency s is directed toward a subject (not shown). Is projected. The reflected light from the subject forms a spot image on the light receiving surface of the light receiving element 4 via the light receiving lens 2. Here, it is assumed that a light position detector (PSD) that outputs two output currents I ₁ and I ₂ according to the position of the spot image on the light receiving surface is used as the light receiving element. Output current I ₁ , I from the light receiving element 4
₂ is input to the calculation unit 5, supplied to the first and second current-voltage converters 7 and 8, respectively, and converted into a voltage signal. The output signals of the first and second current-voltage converters 7 and 8 are supplied to the adder 9 and the subtractor 10, and output signals corresponding to I ₁ + I ₂ and I ₁ -I ₂ , respectively. The output signals of the adder 9 and the subtractor 10 are input to the first and second variable gain amplifiers 11 and 12, respectively, and the output signals of the adder 9 and the subtractor 10 are passed through the first and second band amplifiers 14 and 15 to the first Then, it is supplied to the second detectors 16 and 17. Here, the first and second band amplifiers 14 and 15 are configured to amplify and pass only a narrow band frequency component having the drive frequency s center frequency of the light emitting element 3 and improve the signal-to-noise ratio. It has a function. Further, the first and second detectors 16 and 17 are respectively the first and second detectors.
DC signal V corresponding to the output signal amplitude value of band amplifiers 14 and 15
_+, V _- to output.

Here, the output signal of the first detector, that is, the signal corresponding to the sum of the output signals of the light receiving elements 4 is the error detector 13
The error detector 13 outputs the first control signal 30 for adjusting the gain of the variable gain amplifier, and constitutes an automatic gain adjusting unit together with the variable gain amplifier.

The output signal of the first detector is the error detector 13
The second control signal 29 for controlling the light emission amount of the light emitting element 3 via
To the light emission drive unit 6, and the light emission drive unit 6 drives the light emitting element 3 in accordance with the second control signal to configure an automatic light emission amount adjustment unit.

The automatic gain adjustment unit and the automatic light emission amount adjustment unit are configured to be switched by the error detector 13 according to an output signal from the control device 28 described later.

On the other hand, the output signals V ₊ and V ₋ of the first and second detectors 16 and 17 are respectively
It is input to the first and second integrators 18 and 19. Integrator detector output voltage V _+, V _- according to the DC voltage value to charge the capacitor at substantially constant current performs voltage-current conversion so as to increase or decrease substantially linearly over time the integrated value V ₊ ^* of the waveform, V _- ^* a configured to output, respectively.
The output signal V ₊ ^* of the first integrator 18 is supplied to the level determiner 20 and compared with the reference voltage signal V _P 21 to generate a pulse signal at the time when V ₊ ^* = V _P , The output of the second integrator 19 which receives the pulse signal is sampled and held at that time.

^{_{Here, V + * = C 1 ×}} {I 1 + I 2} × t ......... (1) V - * = C 2 × {I 1 -I 2} × t ......... (2) provided that C _1, since C ₂ is a constant t is satisfied the relationship of the integration time equation, V ₊ ^* = V _P to become time V _- (hereinafter referred to as V _F) ^* values _{(I 1 -I 2) / (} I 1 It is a value proportional to + I ₂ ).

Since (I ₁ −I ₂ ) / (I ₁ + I ₂ ) is proportional to the reciprocal of the distance L to the subject, focus adjustment can be performed using this value of V _F.

The control device 28 includes an analog-digital converter 26 and a digital comparator 25, and outputs the output V of the second integrator 19.
_F is input to the analog-digital converter 26 and converted into a 6-bit digital signal. Further, the lens encoder output for outputting a digital signal indicating the position of the focusing lens of the photographing lens is input to the digital comparator 25 and compared with the output of the analog-digital converter 26, and the lenses are matched so that the two coincide. The lens is driven by the driving unit 24, and the focus adjustment is completed.

On the other hand, the analog-digital converted V _F signal is input to the perspective discriminating unit 27 in the control device 28 to discriminate between long-distance data and short-distance data, and the error detector 13 in the arithmetic unit 5 outputs the result. Is supplied.

The error detector 13 sets the second control signal 29 to a constant voltage value when the output of the distance determination unit 27 is long distance data, and the light emitting element 3 is configured to emit light with a preset maximum light emission amount. , The first control signal 30 is configured to output the output signal V ₊ of the first detector 16. At this time, the first variable gain amplifier 1
1, the first band amplifier 14, the first detector 16, the error detector 13 constitutes a closed loop, even if the input signal of the first variable gain amplifier 11 changes, the output signal V ₊ of the first detector 16 A negative feedback loop configuration is adopted so that the gain of the first variable gain amplifier 11 is automatically adjusted so that the value becomes substantially constant. Second variable gain amplifier 12
Similarly, since the gain is adjusted by the first control signal 30, the output signal V ₋ of the second detector 17 is changed according to the amplitude value of the V ₊ signal.
Is also adjusted.

When the output of the perspective determination unit 27 is short range data, the first
The control signal 30 is a constant reference voltage signal, and the first and second variable gain amplifiers 11 and 12 work with a constant gain. The second control signal 29 is
A signal corresponding to the output signal V ₊ of the first detector 16 is used. At this time, the light emission drive unit 6, the light emitting element 3, the light receiving element 4, the first and second current / voltage converters 7, 8, the adder 9, the 1 variable gain amplifier 11, first band amplifier 14, first detector 16, error detector 13 forms a closed loop, and the light emission amount of light emitting element 3 becomes variable according to the output signal V ₊ of first detector 16. , V ₊ value is almost constant, a negative feedback loop is constructed so that the automatic light emission adjustment function works.

With the above configuration, the output of the second integrator 19 in the calculation unit 5 is used to determine the long distance and the short distance of the subject, and when the subject is located at the long distance, the automatic gain adjustment is mainly performed. When the unit is operated and is located at a short distance, the automatic light emission amount adjusting unit is mainly operated.

When the subject is in a short distance, the amount of light on the light receiving element is large and the signal-to-noise ratio is good, so the amount of light emission is adjusted and the signal amount is compressed, and the subject is in a long distance. Since the gain is adjusted, the dynamic range can be significantly compressed, and high-precision distance measurement can be realized.

Further, since both the adjusting units are switched by using the output signal of the arithmetic unit instead of using the lens encoder output, it is possible to quickly respond to the change in the subject condition.

As described above, the automatic focus adjustment device of the present invention includes the automatic gain adjustment unit and the automatic light emission amount adjustment unit, and responds to the distance signal corresponding to the distance to the subject, which is output from the calculator. Then, when the distance signal indicates a short distance, the automatic light emission adjustment unit is mainly operated next time, and when the distance signal indicates a long distance, the automatic gain adjustment unit is mainly operated next time. Since the distance is adjusted, it is possible to accurately and quickly respond to the reflected light from a subject having a wide dynamic range to compress the dynamic range of the signal to be handled, and realize highly accurate focus adjustment.

[Brief description of drawings]

FIG. 1 is a block diagram showing the system configuration of the present invention. 1 ... Emitting lens, 2 ... Receiving lens, 3 ... Light emitting element, 4 ... Light receiving element, 5 ... Calculation unit, 23 ... Lens encoder, 28 ... Control device.

Front page continuation (72) Inventor Hiroyuki Asakura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Reference JP-A-60-59313 (JP, A) JP-A-59-160108 (JP, A)

Claims (1)

[Claims] 1. A light projecting means for projecting a light beam toward a subject, a light receiving lens for collecting reflected light reflected by the subject after being projected by the light projecting means, and a light receiving device for receiving the reflected light. A light receiving element that outputs two photocurrents at a ratio according to the image forming spot position by the lens, and a calculation unit that calculates an output signal of the light receiving element and outputs a distance signal corresponding to the distance to the subject, The arithmetic unit outputs an signal corresponding to the sum of the output signals from the light receiving elements, an automatic gain adjustment unit that adjusts the gain of the signal using the output signal from the adder, and the addition unit. An automatic light emission amount adjusting unit for adjusting the light emission amount of the luminous flux projected from the light projecting unit by using an output signal from the projector, and based on the output signal of the arithmetic unit, drives the photographing lens to focus. Focus to make adjustments In the node device, when the distance signal output from the calculation unit indicates a short distance, next time the gain applied to the signal is kept constant, and mainly the automatic light emission amount adjustment unit is operated, The signal output level is secured by changing the light emission amount based on the output signal from the adder, and when the distance signal indicates a long distance, the light emission amount emitted from the light emitting means is kept constant next time, An automatic focusing apparatus configured to mainly operate the automatic gain adjusting section and change a gain based on an output signal from the adder to secure a signal output level and perform distance measurement.