JPS62237411A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To obtain exact distance measuring information by repeating light emission and non-light emission in a light emitting part, and interposing a circuit, for correcting an integrated value of an integrating part at the time of the light emission by an integrated value of an integrating part at the time of the non-light emission, between the integral part and an arithmetic part. CONSTITUTION:After the number of light emitting pulses, namely, an integral time has been determined, a light emitting part LED is set to a non-light emission, and by its integration time, an output from a PSD is integrated by integration circuits 3, 3', integrated values VAoff, VBoff by an offset variation, etc., caused by an offset shift, noise light, etc., are obtained, and these values are held in holding condensers 6, 6' by turning off analog switches 5, 5' and turning on analog switches 4, 4'. Subsequently, said integration is executed by making the light emitting part LED emit a light beam by the same integration time as the previous time, by turning off the analog switches 4, 4', and turning on the analog switches 5, 5'. In this way, distance measuring information is obtained from a difference of its integrated values VA, VB and the integrated values VAoff, VBoff which have been held in the holding condensers 6, 6'.

Description

DETAILED DESCRIPTION OF THE INVENTION (If not for industrial use) The present invention relates to, for example, an active type automatic focusing device for a camera, and particularly to a method for eliminating errors in distance measurement information.

(Prior Art) In the so-called active type automatic focusing device that determines the distance to the subject by projecting light onto the subject and receiving the reflected light, there has been a conventional method disclosed in Japanese Patent Laid-Open No. 57-44.
As in No. 809 and JP-A No. 59-201007, an integrating circuit is provided on the output side of the light receiving element that divides the amount of received light into nine parts until it reaches a predetermined level. However, since the distance measurement results are affected by the offset deviation of the integrating circuit itself and the amount of noise, highly accurate offset adjustment is required to avoid erroneous distance measurements. In addition, it is difficult to avoid offset changes due to changes in the physical properties of resistors, etc. due to a 1 degree change in the environment, so the distance measurement accuracy only takes these changes into consideration, and conventional systems cannot achieve this level of accuracy. An example of such a system that had no choice but to be satisfied with is the Japanese Unexamined Patent Publication No. 59-2010.
The synchronous detection method used in No. 07 will be briefly explained. Figure 3 is a system diagram of this synchronous detection method.
The light emitted by the light emitting unit LED modulated at a specific frequency is reflected by the subject.''!The light is received by the 4:2 split element, and the output current from both ends is converted into voltage by the current-voltage converter 1.1'. The direct current component of this signal is cut by the coupling capacitor marked 20 and 20'.
0.30' is an AC amplifier, which sufficiently amplifies the components near the modulation frequency, and then transmits them to the next stage synchronous detection circuit 2.
2'. In the synchronous liquid injection circuit 2.2', the analog switch 50.6 is activated in synchronization with the modulation of the light emitting part LED.
By alternately switching between 0.50' and 60',
Negative components of the signal are inverted by inverters 40 and 40' to perform synchronous detection.

For those who want to explain the problems of such a system, to explain this further, in conventional active automatic focusing devices that project infrared light, the amount of reflected light received on the light receiving side is used as the output of the light receiving element. The amount of reflected light was integrated to a measurable level by integrating using an integrating circuit provided on the side and changing the integration time according to the amount of reflected light.

A system diagram of such a conventional integral method is shown in FIG.

In Figure 4, the reflected light of the light modulated at a specific frequency emitted by the light emitting system via the light projecting lens is received by the light receiving element through the light receiving lens, and converted into voltage by the I-V conversion circuit 1.1'. Then, the detection circuit with reference numeral 2.2 performs synchronous detection in synchronization with the above-mentioned specific frequency, and detects only the signal component with reference numeral 3゜3.
′ is integrated using the integrator circuit. The integrated value vA%vB is added by an adder circuit 40 to produce vA-)-vB. The integral time control circuit 50 monitors this time, determines the integral time so that it reaches a predetermined level that allows distance measurement, and controls the integral circuit 3.3' accordingly. Then let East do the next integration. By repeating this, distance measurement is always performed with v and +vB at predetermined levels. Note that the distance measurement information is based on the voltages vA and V obtained from both ends of the light receiving element.
Obtained by Bt-treatment (for details, see
For example, JP-A-57-44809, JP-A-59-201
(See No. 007).

FIG. 5 shows the waveforms of each part. In the fitted system shown in Figure 4, 14! When there is no signal, the offset of the integral waveform is adjusted using a relatively long integration time, and distance measurement is performed so that the output waveform becomes zero when there is no signal, as shown in the output waveform shown in (■) in FIG.

However, this system has the following problems (
(See Figure 5■).

0 High precision adjustment is required during adjustment.

- If the offset deviates after the adjustment, the system will be biased by the amount of deviation on the distance measurement t[, and accurate distance measurement information will not be obtained.

0 If the noise light cannot be removed by the detection circuit alone, such as when there is a lot of infrared light in the outside light, the noise light may bias the integral output and the distance measurement information will be lost. If the time is long, even a small offset shift will result in a large shift charge, and if the amount of reflected light is small, the distance measurement information will be inaccurate.

0 Offsets due to changes in the physical properties of constituent elements due to changes in environmental temperature are unavoidable, which limits the usable width range and results in insufficient accuracy. In addition, to expand this range, it is necessary to use expensive parts that are not dependent on Fi temperature.
It is necessary to provide a warm correction circuit separately from the distance measurement circuit.

(Problems to be Solved by the Invention) An object of the present invention is to solve the above-mentioned problems of the conventional automatic focusing device. Therefore, we have developed a low-cost system that eliminates errors in distance measurement information caused by offset shifts due to insufficient adjustment, noise light, or offset changes that are unavoidable due to environmental temperature changes, etc. in active type automatic focusing devices. (Means for solving the problem) The automatic focusing device of the present invention includes a light-emitting section that emits light modulated at a specific frequency, and a light-emitting section that emits light modulated at a specific frequency, and uses the light as a spot light to focus on a subject. a light projecting optical system that projects light upward; a light receiving optical system that makes reflected light from the subject of the spot light enter a light spot position detection element; and an output signal of the light spot position detection element that is synchronized with the specific frequency. a detection section that detects the detected signal; an integration section that integrates the output of the detection section; a calculation section that calculates the output of the integration section and outputs ranging information corresponding to the distance to the subject; and this calculation section. and a control section that controls the driving of the focusing optical system based on distance measurement information from the light emitting section, the light emitting section repeats light emission and non-emission at a specific period, and the integrating section when no light is emitted. A circuit for correcting the integral value of the integrating section during light emission using the integral value of is interposed between the integrating section and the calculating section, and distance measurement information is obtained based on the corrected integral value.

When using a device that outputs two output signals as the light spot position detection element, it is provided with a detection section and an integration section for each output signal, and the integration of each integration section when no light is emitted [by direct] It is preferable to correct each integral valueO.In addition, the circuit for correcting the integral direct is a circuit that maintains the integral direct when no light is emitted, and the integral value obtained from the integrated value of the integral section when light is emitted. It is preferable to include a circuit for subtracting .

(Example) Next, the present invention will be explained in detail. Figure 1 is a system diagram showing the main parts of this automatic focusing device.The light emitting unit LED emits light through a projecting lens, and a large area of light such as infrared light modulated at a constant frequency is spotted on the subject. The reflected light is emitted as light, and the reflected light is received by the light spot position detection element PSD through the light receiving lens. PSDHl A typical example is one in which the current output from the electric currents at both ends changes depending on the position of the light spot incident on the PSD in the longitudinal direction of the PSD, and the position of the light spot on the PSD can be determined from the relationship between these two currents. It is possible to detect the object and measure the distance to the object using the principle of triangulation. The two outputs of the PSD are converted into current and voltage by an l-V converter 1.1', and signal voltages vA and VB are obtained through an acting circuit 2.2' and an integrating circuit 3.3'. Correction circuit 4-8.4'
~8' analog switch 4.4' is turned OFF, analog switch 5.5' is turned ON, and these seven signals, VB, are passed through analog switch 5.5' and subtractor 8.8', and then offset The signal 7, vB, which has not been corrected for deviations, etc., is obtained from the output terminal of the correction circuit. After converting these signals directly from analog to digital through an A/D converter (IW not shown), a logic circuit module microcomputer (not shown) calculates VA + VB corresponding to the amount of light received on the PSD. , monitors the value of v people - 4 - vB and controls the integration time and the light emitting interval of the light projection system.
do.

That is, in one light emission, light modulated at a specific frequency is emitted by pulse control through a light emission and light amount control circuit (not shown) for a time corresponding to the integration time. The number of pulses for controlling the integration time and the light emission time is controlled by a microcomputer or the like. For example, if the amount of light received by the PSD decreases, the rfi of VA+VB becomes smaller. At this time, increase the integration time and the number of light emitting pulses (extend the light emitting time) until the cough of vA + VB is within the range where accurate distance measurement can be performed (until it exceeds the predetermined first reference value), and then increase the value of VA + VB. Try to make it bigger. On the contrary, P
When the amount of light received by the SD increases and the value of vA+VB becomes larger, the integration time and emission pulse are similarly adjusted until the value of VA+VB falls within the range that allows accurate distance measurement (until it falls below a predetermined second standard). Reduce the number (reduce the light emission time 1)
2) Try to reduce the noise of vA+vB.

In this way, the normal integration time schedule and light emission amount control are performed. The above points are similar to the conventional technology.

In the present invention, after the number of light emitting pulses, that is, the integral time is determined in this way, the 1f5h light part LED is set to non-emitting light, and after the integral time is determined, as shown in the waveform of each part in FIG. The output is integrated by the integrating circuit 3.3, and there is an offset shift due to insufficient adjustment of the circuit at that time, noise light: or an offset change due to environmental temperature changes, etc. ff vBoff is obtained, the analog switch 5.5'1 is turned OFF, and the analog switch 4.4' is turned ON to hold the hold capacitor 6.6'1C1fi.

Next, turn off the analog switch 4.4', turn on the analog switch 5.5', and make the light emitting part LED emit light for the same integration time as the previous time to perform integration.
Difference between A, VB and the integral held in the hold capacitor 6.6' (m vAOf f - "Bof f vA = vA VAoff, VB = VB - V
Boll f reduction 'pi device 8.8' is obtained. These corrections are made by processing No. 4, ■- in the same way as the conventional ones, and adjusting the distance measurement f.
By controlling the drive of the p focusing lens based on the distance measurement information such as il, it is possible to always accurately correct the offset t that affects the distance measurement information.

The concept of performing the integration during no light emission in the present invention in parallel with the integration during normal light emission is not limited to the above embodiments, and can be modified in various ways. Listing the length F51r corresponding to the conventional method of the invention: 〇 - Even if the offset deviates after the adjustment, accurate distance measurement information can be obtained because the offset deviation is automatically corrected. .

0 In cases where there is a lot of infrared light in the outside light, it is also possible to correct noise caused by outside light that the performance circuit cannot take advantage of.

0 It is possible to configure a system that is resistant to environmental temperature changes.

Offset adjustment can be made in a wider range than in a method in which OA/D conversion is performed and then corrected.

In the manner described above, a highly accurate automatic focusing device with a wide temperature range can be realized without using expensive parts or high-level adjustments.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing the main parts of an embodiment of the present invention, FIG. 2 is a waveform diagram of each part of the automatic focusing device shown in FIG. 1, and FIG.
The fourth factor is a system diagram of the main parts of a conventional active type automatic focusing device, and FIG. 5 is a waveform diagram of the trough of the automatic focusing device shown in FIG. 1, l/:]-V converter 2.2': l* wave circuit 3.3
': Integrating circuit 4.4', 5.5': Analog switch 6.6': Hold capacitor 7.7': Buffer
8, 8': Subtractor patent applicant Roku Konishi Photo Industry Co., Ltd. Applicant's agent Fumi Sato (and 2 others) No. 3 (121 Light projection lens leather 4 Figure Preliminary light emission Figure 5

Claims (3)

[Claims] (1) A light emitting unit that emits light modulated at a specific frequency, a light projection optical system that projects the light onto a subject as a spot light, and a light spot position detection element that emits light reflected from the subject of the spot light. a detection unit that detects the output signal of the light spot position detection element in synchronization with the specific frequency; an integration unit that integrates the output of the detection unit; and a calculation of the output of the integration unit. an automatic focusing device comprising: a calculation section that outputs distance measurement information corresponding to the distance to the subject; and a control section that controls driving of a focusing optical system based on the distance measurement information from the calculation section. In the above, the integrating section and the calculating section include a circuit that repeats light emission and non-emission in the light emitting section at a specific period and corrects the integral value of the integrating section when the light is emitted by the integral value of the integrating section when the light is not emitted. What is claimed is: 1. An automatic focusing device that obtains ranging information based on a corrected integral value. (2) In claim 1, the light spot position detection element has two output signals, and includes the detection section and the integration section for each output signal, and for each output signal when no light is emitted. An automatic focusing device characterized in that the integral value of each integral part at the time of light emission is corrected by the integral value of the integral part. (3) In claim 1 or 2, the circuit for correcting the integral value includes a circuit for holding the integral value of the integrating section when no light is emitted, and a circuit that holds the integral value of the integrating section when no light is emitted. An automatic focusing device comprising: a circuit for subtracting a held integral value.