JPH03135713A - Range finder - Google Patents

Abstract

PURPOSE:To suppress the generation of a range finding error and to simplify the circuit constitution by selecting and supplying a couple of output signals from a photodetecting element alternately to a common signal processing means through the switching of a switching means. CONSTITUTION:A 1st output signal which is selected by an analog switch 18 between the two output signals from a PSD(semiconductor position detector) 9 as the photodetecting element is processed by a signal processing means consisting of a gain control amplifier 20, etc., first and outputted at 1st range finding data AFD1. This range finding data AFD1 is stored and held in a RAM 28 temporarily by a microcomputer 14 as an arithmetic means. Then the 2nd output signal which is selected by the analog switch 18 is processed similarly by the common signal processing means and inputted as 2nd range finding data AFD2 to the arithmetic means. The arithmetic means performs arithmetic according to those obtained range finding data AFD1 and AFD2 and outputs a range finding signal correlative to a subject distance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an active type distance measuring device that projects distance measuring light onto a subject and measures distance by receiving reflected light from the subject. .

[Conventional technology]

Recent compact cameras use active type distance measuring devices. Active type ranging device is
Near-infrared light is projected toward the subject, and a light receiving element receives the reflected light from the subject. Since the incident position of the reflected light on the light receiving element corresponds to the subject distance, it is possible to obtain a distance measurement signal corresponding to the subject distance by electrically detecting the incident position of the reflected light.

As the light receiving element, a semiconductor device detector (PSD:
Po5ition 5intensive Detect
or ) has been widely used. The PSD has two output terminals, and each terminal outputs a current with a different value depending on the light incident position, and the light incident position can be calculated based on each current value. , can be issued.

Conventionally, when using this PSD, a preamplifier and a gain control amplifier were installed at each terminal of the PSD.

Various types of amplifiers such as logarithmic amplifiers and differential amplifiers were connected, and distance measurement signals were obtained based on the ratio of the output signals from these amplifiers.

(Problem to be Solved by the Invention) However, according to the conventional method described above, the output current from both terminals of the PSD is processed through current-voltage conversion, amplification, etc. through separate amplifier systems, although they have the same configuration. Therefore, if there is a difference in the input-output characteristics of each amplifier system, it will cause an error in the ranging signal. In addition, when performing offset adjustment or gain control for each amplifier system to improve distance measurement accuracy, these [ff] are required for each amplifier system individually.
Another disadvantage is that the circuit configuration becomes complicated.

[Purpose of the invention]

The present invention has been made in order to solve the problems of the prior art as described above, and is applicable to a distance measuring device that obtains a distance measuring signal based on two outputs from a light receiving element, such as a distance measuring device using a PSD. The purpose of this invention is to suppress the occurrence of ranging errors and to simplify the circuit configuration of a ranging device.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a switching means that alternately selects either one of the first and second output signals from the light receiving element, and a switching means that alternately inputs the selected output signal, 1. one system of signal processing means for converting into second distance measurement data, and one of the distance measurement data outputted from the signal processing means is temporarily stored and held;
A distance measuring device is constituted by a calculation means that starts calculation using both of the distance measurement data after the other distance measurement data is output.

[Effect]

Of the two output signals from the light receiving element, the first output signal selected by the switching means is first processed by the signal processing means and output as first distance measurement data, and this first distance measurement data is processed by the calculation means. Once stored in memory. The second output signal selected by the switching means is then
Similar signal processing is applied by a common signal processing means, and the resultant data is inputted to the calculation means as second ranging data. The calculation means is the first . Calculation is performed based on the second distance measurement data to calculate a distance measurement signal that has a correlation with the subject distance.

An embodiment of the present invention will be described below with reference to the drawings.

〔Example〕

In FIG. 1, which schematically shows the configuration of the distance measuring device of the present invention, the light projecting section 2 is composed of a light source section 3 and a projecting lens 4, and the optical axis 4a of the projecting lens 4 is parallel to that of the photographing lens 5. It is parallel to the optical axis 5a. The light source section 3 includes three LEDs (light emitting diodes) 3a, 3b, and 3c that each emit near-infrared light.
Consisting of

These LEDs 3a, 3b, and 3c are arranged horizontally, and each sequentially projects distance measuring light toward three locations on the photographic screen.

The light receiving section 7 is composed of a light receiving lens 8 and a PSD 9, and the optical axis 8a of the light receiving lens 8 is also parallel to the photographing lens optical axis 5a. The PSD 9 outputs a signal corresponding to the amount of light passing through the light receiving lens 8 and the incident position to each output terminal 9a,
Output from 9b.

As is clear from FIG. 1, the closer the object is, the more the reflected light from the object will be incident on the lower side of the PSD 9, but the ratio or magnitude relationship (sum, Based on the difference), a signal corresponding to the position of incidence of the incident light can be obtained without depending on the amount of the incident light. Note that the PSD 9 does not have a discrimination function in the horizontal direction; if the incident height in the vertical direction is the same, equivalent output signals will be output from the output terminals 9a and 9b even if the incident positions in the horizontal direction are different. It will be done.

The light emission of the LEDs 3 a to 3 c is controlled via the LED driver 11 in response to a signal from the autofocus IC 12 . The autofocus IC 12 executes a predetermined distance measurement sequence according to a command from the microcomputer 14, operates the LED driver 11, and converts each signal from the output terminals 9a and 9b of the PSD 9 into distance measurement data. It is converted and output to the microcomputer 14. The microcomputer 14 performs calculations based on the two types of distance measurement data obtained as described above, and calculates a distance measurement signal that has a correlation with the subject distance. and,
The set position of the photographic lens 5 is determined in accordance with the distance measurement signal calculated by the microcomputer 14.

A general-purpose microcomputer is used as the microcomputer 14, and photometric data detected by a photometric circuit 51 and digitally converted by an A/D converter 52 is also input. The microcomputer 14 calculates optimal exposure conditions based on the photometry data, drives the stepping motor 54 via the exposure control circuit 53, and sets the program shutter 55 to the programmed shank at an aperture value and shutter speed that satisfy the optimal exposure conditions. 55 is opened and closed. After photographing, the film transport circuit 56 drives the film feed motor 57 to advance the film one frame. Note that, before the program shutter 55 is opened or closed, the stepping motor 6 is rotated by the lens moving circuit 58 at a rotation angle corresponding to the distance measurement signal.
0 is driven, and the photographing lens 5 is controlled to move out to the in-focus position.

Autofocus IC12, microcomputer 14
is constructed as schematically shown in FIG. The autofocus IC 12 consists of a one-chip IC, and includes a logic circuit 15. In addition to the gain controller 16, PSD9
Preamplifiers 17a and 17b that convert signal currents outputted from output terminals 9a and 9b into voltages, an analog switch 18, and a gain control amplifier 20. Sample and hold circuit 21. It consists of a buffer amplifier 22, etc. The analog switch 18 performs a switching operation in response to a switching signal from the logic circuit 15, and the preamplifier 17
Either one of the signals a and 17b is selected and supplied to the gain control amplifier 20.

The gain control amplifier 20 is provided in consideration of the fact that when the object distance is long, the amount of reflected light incident on the PSD 9 decreases, and the absolute value of the signal current from the output terminals 9a and 9b decreases. An appropriate amplification factor is given by gain control processing, which will be described later.

The sample and hold circuit 21 receives the sampling pulse from the logic circuit 15, samples and holds the signal amplified by the gain control amplifier 20, and outputs this as ranging data to the microcomputer 14 via the buffer amplifier 22. Note that the logic circuit 1
5 basically consists of a serial-in-parallel-out shift register, and a gain controller 16 reads out a gain control command set in a predetermined bit position of the shift register, and varies the gain of the gain control amplifier 20 based on this.

The microcomputer 14 includes a CPU 24. Serial port 25. In addition to the A/D converter 26, it includes a ROM 27 that stores a program for executing a distance measurement sequence, and a RAM 28 that temporarily stores data and various flags obtained when executing the distance measurement sequence. The serial port 25 converts a command from the CPU 24 into a serial data pulse (AFSD) and supplies it to the logic circuit 15.
CK), and outputs a control pulse (APLCK) that determines the latch of serial data and the light emission timing of the LEDs 3a to 3c. Further, the A/D converter 26 converts the input analog signal into a 7-bit digital value (0 to 1 in decimal).
27).

FIG. 3 shows an 8-bit serial-in/parallel-out shift register 30 used in the logic circuit 15.
is shown conceptually. The 5 bits of DO-D4 contain gain control data (GAIN), and the 2 bits of D5 to D6 contain the gain control data (GAIN).
The bit contains LED light emission data (LED), and the 1 bit of D7 contains LED light emission/reset switching data (
SET) is set. The 5-bit gain control data can represent gain levels from "0" level to "31" level. Also, 2-bit L
ED luminescence data are r□'', rl''.

r2”, “3.”, and “0”.
When , all of the LEDs 38 to 3c are turned off, when the value is "1", only the LED 3a is turned on, and when the value is "2" and "3", the LEDs 3b and 3C are turned on, respectively.

FIG. 4 is a flowchart showing the basic distance measurement sequence processing, which includes the process of detecting the offset value of the amplifier system of the autofocus IC 12, lighting up LEDs 3a to 3C in order, and collecting distance measurement data for each of LEDs 3a to 3C. A distance measurement process for importing and a process for calculating a final distance measurement signal from a plurality of obtained distance measurement data are performed. Note that before distance measurement processing is performed, the gain control amplifier 2
Gain setting processing is performed to set the gain of 0 to the optimum value.

The effects of the above configuration will be explained below.

When the distance measurement sequence is started, first, the offset value detection process shown in FIG. 5 is executed. When offset value detection processing is performed, rDo of the shift register 30
-rolooooooo” (2
decimal number) is transferred.

As a result, rGAIN=8'', rLED=o''.

Each data of rsET=or is set. At the same time, C.P.
rcOUNT=8J is set in a predetermined register in U24.

Of the data set in the shift register 30, rGA
The data of IN=84 is supplied to the gain control amplifier 20 via the gain controller 16, and the gain of the gain control amplifier 20 is set to "8". Note that rGA I N = 31'' is the maximum gain, rGAI
N=04 corresponds to the minimum gain.

After transferring this serial data, the logic circuit 15 outputs a serial data pulse (AFSD), a transfer pulse (AFSC), and a transfer pulse (AFSC).
K), a sampling pulse is output to the sample hold circuit 21 based on the control pulse (AFL, CK), and the output signal output from the gain control amplifier 20 at that time is held. Note that during normal distance measurement, a light emitting pulse for lighting the LED is output just before the sampling pulse is output, but since rLED=OJ, the generation of the light emitting pulse is prohibited, and LED3a~
3C does not emit light. Further, in the initial state, the analog switch 18 is in the solid line position shown in FIG. Therefore, with LEDs 3a to 3C turned off, first turn on the PS
After the signal from the output terminal 9a side of D9 is amplified by the gain control amplifier 20, it is sampled and held.

The signal thus sampled and held is sent to the A/D of the microcomputer 14 via the 7Nl software amplifier 22.
The data is digitally converted by the converter 26 and stored in the RAM 2B as the first channel distance measurement data AFDI.

Subsequently, a switching signal is output from the logic circuit 15 to the analog switch 18. As a result, the analog switch 18 is switched to input the signal on the broken line side, that is, on the output terminal 9b side of the PSD 9, to the gain control amplifier 20. Thereafter, the second sampling pulse is output from the logic circuit 15 to the sample and hold circuit 21, the signal obtained from the output terminal 9b side is sampled and held, and after digital conversion by the A/D converter 26, the second RAM2 as channel distance measurement data AFD2
It is stored in 8.

In this way, the first and second
Eight channel distance measurement data AFDI and AFD2 are each sampled. However, since these distance measurement data are data with the LEDs 3a to 3C turned off, they depend mainly on the signal components caused by the ambient light at that time and the characteristics of the circuit system. Microcomputer 1
4 is 8 distance measurement data AFDI, AF of each channel
Based on D2, the average value is calculated for each channel and stored in a predetermined register as offset values OFI and OF2.

After the offset value detection process described above, a gain determination process and a distance measurement process are successively executed. When the gain determination process is started, serial data representing a new command is transferred from the serial port 25 to the logic circuit 15, and each bit position of the shift register 30 is filled with ro 1.
Binary data of 000011J is set. As a result, "GAIN=8J,""LED=1", rs
ET=1'', and immediately before a sampling pulse is output from the logic circuit 15, a light emitting pulse is supplied only to the LED 3a.

As shown in the flowchart of FIG. 6, the gain determination process first involves repeatedly causing the LED 3a to emit light and using the distance measurement data AFDI obtained at that time.

This is done while monitoring the value of AFD2. Of course, when taking in the ranging data AFDI and AFD2, the analog switch 18 is switched, the LED 3a emits light twice, and a pair of ranging data AFDI is obtained.

AFD2 is obtained. And these distance measurement data AF
DI and AFD2 each have a gain control amplifier 20. The signal is output through a signal processing system consisting of a sample and hold circuit 21 and a buffer amplifier 22.

When a pair of ranging data AFDI and AFD2 are obtained, it is determined whether any of them has reached "r127" in decimal notation. If the value of AFDI or AFD2 reaches r127, it means that one of them has overflowed, and the amount of reflected light that entered PSD9 is quite large, making it extremely reliable as distance measurement data. is judged to be thin. Therefore, in this case, “G
After confirming that AIN=84, close-up processing is performed assuming that the subject is quite close.

With this close-up processing, the distance measurement data AFDI and AFD2 when the LED 3a is lit is invalidated, and a flag indicating that the distance to the subject located in the center of the shooting screen is even closer than the close-up shooting distance is set to a predetermined value in the RAN28. Set to address location.

Note that it is possible to reset the value of rGAI NJ to "8" or less, but this tends to cause problems such as the amplification characteristics becoming nonlinear, and it is desirable to avoid this.

If no overflow is recognized in the distance measurement data AFDI, AFD2, the offset values OFI, OF2 obtained by the above-described offset processing are subtracted from the values of the distance measurement data AFDI, AFD2. Thereby, ambient light and DC noise components generated in the signal processing system can be removed. Then, the corrected ranging data AFD1 and AFD2 are added to add data AFADD.
It is determined whether the value is equal to or greater than r136J. This value is r136. When the above is the case, it is determined that the absolute value of each of the distance measurement data AFDI and AFD2 is within an appropriate range for subsequent distance measurement calculations, and the gain of the gain control amplifier 20 is determined as the value of rGAI NJ at that time. It turns out.

On the other hand, when the value of the addition data AFADD is less than "r136", the absolute value of the ranging data AFDI, AFD2 is increased (preferably, "N" is added to the value of rGATNJ at that time. The values are set according to the size of the addition data AFADD as shown in the following table.

In the process of changing the value of rGAINJ, the command is reset, but "DO" to "D4" of the shift register 30
Only the data in the bit position changes, and the data in the other bit positions remains unchanged. Then, the gain controller 16 adjusts the gain of the gain control amplifier 20 according to the new value of rGAINj.

Note that even if the value of rGAINJ reaches "31", if the addition data AFADD with an appropriate absolute value cannot be obtained, the reflected light from the subject is extremely weak, or the PSD
9, and in this case, the subject distance is extremely long. Therefore, in such a case, infinity processing is performed. Through this infinity process, a flag indicating that the distance measurement result by the LED 3a is infinite is set at a predetermined address position of the RAN 28.

Once the value of rGAI NJ is determined by the above-described process, the distance measurement process using the LED 3a is subsequently executed with the gain of the gain control amplifier 2o set to that value. The distance measurement process is carried out by alternately switching the analog switch 18 as shown in the flowchart of FIG.
1st. Second channel distance measurement data AFDI, AFD2
Take in 18 pieces at a time. At this time, the LED 3a emits pulse light 18 times for each channel, a total of 36 times. Note that the sampled distance measurement data AFDI,A
For each FD2, correction is performed using the offset values OFI and OF2 determined by the offset value detection process described above.

In this way, the distance measurement data AFDI is captured in 18 pieces at a time.
The AFD2 is averaged by the microcomputer 14, and the average value is the average ranging data AFAVI, AFAV2.
It is calculated as Furthermore, this average distance measurement data AFAV
I and AFAV2 are added and subtracted from each other to obtain distance measurement sum data AFADD.

It is calculated as distance measurement difference data AFDIF. Then, r128. The value multiplied by 'AFRESULTaJ' is obtained as 'AFRESULTaJ, and this is stored in RAM2B as the final distance measurement result by
will be saved in

When distance measurement by the LED 3a is completed as described above, gain determination processing and distance measurement processing by the LED 3b are then executed. These processes are performed using LED3 instead of LED3a.
The same process is performed except that b is emitted in pulses, and finally rAFRESULTb is obtained. Further, similar processing is performed while causing the LED 3 C to emit pulsed light, and rAFRESULTcJ is calculated.

As shown in FIG. 1, distance measurement using the LED 3a is performed with respect to the main subject S1, and the value of "rAFRESULTa" indicates a value corresponding to the distance to the main subject S1. Furthermore, distance measurement using the LED 3b is performed with respect to the background subject S2, and the value of rAFRESULTb indicates a value corresponding to the distance to the background subject s2. Furthermore, L
In distance measurement using the ED3c, since there is no object in the optical path, the reflected light does not enter the PSD9. Therefore, a flag indicating that the distance measurement result by LED 3 c is infinite is set in the RAM 28, and in this case, the correct value for rAFREsULTCJ is "
0”.

In this way, the LEDs 3a, 3b, and 3c are made to emit pulses in sequence, and the three data rAFREsULTa'', rAFRE
sULTb'', rAFRESULTCJ is obtained,
The microcomputer 14 determines the data corresponding to the closest distance among these as the final distance measurement data. After the final distance measurement data is thus determined, the stamping motor 60 is driven via the lens moving circuit 58, and the photographing lens 5 is moved to the focusing position corresponding to the final distance measurement data. However, when determining the final distance measurement data, RA
Flag data at a predetermined address position of M28 is referenced,
If the data corresponding to the closest distance at that time is even closer than the closest shooting distance, that data becomes invalid. In this case, a short distance warning may be provided on the finder or the like.

Above, an embodiment has been described in which a plurality of LBDs 3a, 3b, and 3c are used to measure distances at a plurality of locations.
The present invention can be similarly applied to a device that projects distance measuring light onto a subject using individual LEDs. Also, offset value detection processing and gain determination processing are omitted,
A device that obtains a pair of ranging data simply based on two signal outputs output from a light-receiving element such as a PSD9, or a device that causes an LED to emit pulse light once at a time to obtain a pair of ranging data. The present invention can also be applied to

〔Effect of the invention〕

As described above, according to the distance measuring device of the present invention, a pair of output signals are extracted from a light receiving element, and each of these output signals is input to a signal processing means for amplification and signal processing. , the signal processing means are arranged in one system, and the outputs are alternately selected by switching the switching means and supplied to the common signal processing means, so that each signal is passed through a different signal processing means. Not only is the circuit configuration simpler than that of a conventional method, but even if the signal processing means has unique input-output characteristics, the influence on each output signal does not differ between them. By performing a distance measurement calculation based on the output signal, it becomes possible to calculate a distance measurement signal with almost no errors.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a distance measuring device according to the present invention. FIG. 2 is a block diagram showing the configuration of the autofocus IC. FIG. 3 is a conceptual diagram of a shift register used in a logic circuit. FIG. 4 is a flowchart showing the overall distance measurement sequence. FIG. 5 is a flowchart showing offset value detection processing. FIG. 6 is a flowchart showing gain determination processing. FIG. 7 is a flowchart showing distance measurement processing. 2... gain control amplifier.

Claims (1)

[Claims] (1) The distance measuring light reflected from the subject is received by the light receiving element, and calculation is performed based on the first output signal and the second output signal output from the light receiving element to determine the incident position of the ranging light on the light receiving element. The distance measuring device for detection includes a switching means for alternately selecting either one of the first and second output signals, and a signal processing of the output signal selected by the switching means to generate the first or second distance measurement data. a system of signal processing means for outputting a signal, and storing and holding at least one of the first and second distance measurement data from the signal processing means, and after the other distance measurement data is output, the first and second distance measurement data are A distance measuring device comprising: calculation means for performing calculations based on data.