JPH03135714A - Range finder - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution and to enable high-SN-ratio range finding arithmetic by converting an analog signal outputted by a photodetecting element into a digital signal and calculating a new gain value from the correlation between its digital value and a current gain value. CONSTITUTION:A PSD(semiconductor position detector) 9 as the photodetecting element converts range finding light reflected by a subject photoelectrically and outputs a photoelectric signal of level corresponding to the quantity of the incident light. The output signal of the photodetecting element is amplified by gain control amplifiers 18a and 18b with specific gains and then converted 25 into a digital value. When this digital value is inputted to the microcomputer 14 of an arithmetic means, a CPU 24 performs digital arithmetic based upon the digital value to decide whether the gain values of the amplifiers 18a and 18b at this time are proper or not, and controls the amplifiers 18a and 18b through a logic circuit 15 and a gain controller 16 so that the gain values are re-set when the gain values are not proper.

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 position of light incidence, and the position of light incidence is calculated based on each current value. can do.

In an active type distance measuring device, the intensity of reflected light from a subject changes depending on the subject distance, so the absolute value of the output signal from the light receiving element changes depending on whether the subject distance is close or far. In this case, by calculating the distance by taking the ratio of the two output signals from the light receiving element,
Although the influence of the intensity of incident light on the PSD can be removed, if the absolute value of the signal for performing these calculations is too small or too large, it becomes impossible to keep the distance measurement accuracy constant.

For this reason, conventional active type ranging devices use gain control amplifiers, and are devised to adjust the gain by applying feedback to the gain control amplifier in response to the magnitude of the output signal from the light receiving element. There is.

[Problem to be solved by the invention]

However, in the conventional method described above, in addition to a logarithmic amplifier, a differential amplifier, a logarithmic expansion amplifier, etc. are required to determine the intensity of light incident on the light receiving element based on the output signal from the light receiving element, and a distance measurement IC is required. The circuit configuration becomes complicated. Moreover, logarithmic amplifiers have a higher S/
The N ratio is poor, which is disadvantageous in improving distance measurement accuracy.

[Object of the Invention] The present invention has been made in order to solve the problems of the prior art as described above. An object of the present invention is to provide a distance measuring device with a simplified circuit configuration.

(Means for Solving the Problems) In order to achieve the above object, the present invention digitally converts the output signal from the light receiving element obtained through the gain control amplifier, and calculates the correlation between this digital value and the gain value at that time. A calculation means for calculating a new gain value from the above, and a gain setting means for resetting the calculated gain value to the gain control amplifier are used.

[Effect]

The light receiving element photoelectrically converts the ranging light reflected from the subject and outputs a photoelectric signal of a level corresponding to the amount of incident light. The output signal from the light receiving element is amplified by a predetermined gain by a gain control amplifier and then converted into a digital value. When this digital value is input to the calculation means, the calculation means uses digital calculation to determine whether the gain value of the gain control amplifier at that time is appropriate based on this digital value, and if it is inappropriate, the calculation means Control the gain control amplifier to reset the value.

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, 3c are arranged horizontally, the central LED 3a is on the optical axis 4a, and the LEDs 3b, 3c are arranged horizontally.
are located on the left and right sides, respectively, and each sequentially projects a beam-shaped ranging light toward three locations within 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 incident light and the incident position from each output terminal 9a, 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 based on the ratio of the output signals from the output terminals 9a and 9b, 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, and if the incident height in the vertical direction is the same, the ratio of the output signals from the output terminals 9a and 9b is equivalent even if the incident position in the horizontal direction is different. Become something.

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 ranging sequence according to commands from the microcomputer 14, operates the LED driver 11, and also amplifies and samples and holds the respective signals from the output terminals 9a and 9b of the PSD 9. It is processed and output to the microcomputer 14. The microcomputer 14 uses the first. Calculations are performed based on the output signal of the second channel to calculate a distance measurement signal that has a correlation with the subject distance. Then, 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 photometric data, drives the stepping motor 54 via the exposure control circuit 53, and operates the program shutter 55 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.

The autofocus IC 12 and microcomputer 14 are schematically constructed as 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, the first. a preamplifier 17a that converts the signal current of the second channel into voltage;
17b1 gain control amplifier 18a, 18b.

It consists of sample hold circuits 20a, 20b, buffer amplifiers 21a, 21b, etc.

The gain control amplifiers 18a and 18b are designed 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 provided by the gain control processing described later. The sample and hold circuits 20a and 20b receive the sampling pulse from the logic circuit 15, sample and hold the signals amplified by the gain control amplifiers 18a and 18b, and send these signals to the microcomputer 14 via the buffer amplifiers 21a and 21b. Output. The logic circuit 15 basically consists of a serial-in/parallel-out shift register, and the gain controller 16 reads gain control data set at a predetermined bit position of the shift register, and based on this, the gain controller 16 reads out the gain control data set in a predetermined bit position of the shift register. .

The gain of 18b is varied.

The microcomputer 14 has a CPU 24, a 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. cereal boat 2
5 converts the command from the CPU 24 into a serial data pulse (AFSD) and supplies it to the logic circuit 15.
K), Serial data latch and LEDs 3a to 3c
Control pulse (APLCK) that determines the light emission timing of
Output. Further, the A/D converter 26 receives an analog signal supplied from the autofocus IC 12.
A 7-bit digital value (
(expressing 0 to 127 in decimal).

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-04 contain gain control data (GA IN), and D5 to D6
The 2 bits contain the LED light emission data (LED), and the D
LED light emission/reset switching data (SET) is set in 1 bit of 7. The 5-bit gain control data can represent gain levels from "0" level to "31" level. In addition, 2-bit LED light emitting data H'OJ,'IJ.

It can represent four states: "2J, r3", when "0" all LEDs 3a to 3c are turned off, when "1" only LED 3a lights up, and when "2" and "3" respectively, LED 3b and LED 3C are turned off. Indicates to turn on the light.

FIG. 4 is a flowchart showing the steps of the basic distance measurement sequence, including the process of detecting the offset value of the amplifier system of the autofocus IC 12, and measuring the output signal obtained at that time while lighting the LEDs 3a to 3c in order. Distance measurement processing that is taken in as distance data, and processing that calculates the set position of the photographic lens 5 by performing calculations based on the obtained distance measurement data are sequentially executed. Note that before the distance measurement process is performed, a gain setting process is performed to set the gains of the gain control amplifiers 18a and 18b to optimal values.

The effects of the above configuration will be explained below.

For example, when a distance measurement sequence is started by a shutter button half-press signal, the offset value detection process shown in FIG. 5 is first executed. When offset value detection processing is performed, "01000000J (binary number) is set in each bit position of rDO-D7J of the shift register 30. This is grinning, rGAIN=8", rLED
= 0".

Each command data of rsE'r=oJ is set.

This command data setting is performed at the time point Pl shown in the timing chart of FIG. 6, that is, when the transfer pulse AFSC
After K sends 8 pulses, the control pulse APLCK
is latched when becomes low level. Note that the serial data pulses are sequentially transferred to the shift register 30 at the rising edge of the transfer pulse AFSCK. Furthermore, after transferring the above command data, CPU2
"rcOUNT=8" is set in a predetermined register in 4.

Among the command data set in the shift register 30, the data of rGAIN=8J is sent to the gain controller 16.
The signal is supplied to the gain control amplifiers 18a and 18b via the gain control amplifiers 18a and 18b, and the gains of the gain control amplifiers 18a and 18b are each set to "8". Note that rC,AIN=
31'' corresponds to the maximum amplification factor, and rGAIN=o corresponds to the minimum amplification factor.

After this serial data transfer, the first. The output signal from the second channel is sampled and held, and digital values AFDI and AFD2 obtained by A/D conversion are read into the microcomputer 14.

The procedure for this reading process is as shown in the flowchart of FIG. 7, in which the control pulse APLCK is first set to a low level during a period of ΔT1. If the serial data pulse AFSD changes during this period, the LED
3a to 3c, sample and hold circuits 20a, 20b, etc. are controlled.

First, at the time of P2 when AFSD becomes low level, LE
It is used for the lighting timing of D3a to 3C. however,
During offset value detection processing, since the command is rLED=OJ, any of LED3 a to 3
c is not lit either.

When ΔT2 has elapsed from the time of P2, AFSD becomes high level, and at this timing, the sample and hold cycle 120a
, 20b hold the output signals from each of the gain control amplifiers 18a and 18b. Note that these output signals are converted to 'C, AlN3. The value is amplified by Furthermore, after ΔT3 has elapsed, AFSD becomes low level and is used as a light emission stop signal for LEDs 3a to 3c.
After T4, it returns to high level. AFLCK is ΔT
After 1 low level period, it becomes high level again,
One cycle is completed after this high level period ΔT5 has elapsed.

When ΔT6 has elapsed from the time point P3 when AFSD became low level, the sample hold circuit 20a.

The output signal held in the first . Second channel distance measurement data AFDI.

It is taken into the CPU 24 as AFD2, and then the RAM
28 at a predetermined address location.

The above distance measurement data AFDI, AFD2 import process is 8
repeated times. Then, these eight ranging data are averaged for each channel, and these average values are determined as offset values OFI and OF2. Since this offset value detection process is executed with the LEDs 3a to 3c turned off, these average values are subject to noise due to ambient light incident on the PSD 9 and preamplifiers 17a and 17.
It means the value due to noise etc. generated by the amplifier and signal processing system after b.

After offset value detection, gain determination processing and distance measurement processing are performed. These processes are individually executed for the LEDs 3a to 3C. The gain determination process is executed according to the flowchart in FIG. When the gain determination process is started, rGFLA set in RAM2B
Each flag of GJ and rOVFLAGJ is in the initial state "0"
is set to After that, 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 r.
o 1000011. The binary data of is set. As a result, rC;AIN=84°'LED=1'','5
ET=1'' (7) code v7. Therefore, the LED
Only 3a is in a state where it can be lit.

After setting the above command, the reading process of distance measurement data AFDI and AFD2 is executed in the same way as the offset value detection process, but in this case, as is clear from the time chart of FIG. It will be lit. Therefore, in the state shown in FIG. 1, the distance measuring light from the LED 3a is irradiated onto the main subject S1, and the reflected light passes through the light receiving lens 8 and enters the PSD 9. At this time, the signals outputted from both terminals 9a and 9b of the PSD 9 include information on the intensity and position of the light incident on the PSD 9.

After each of these signals is digitally converted and taken in as ranging data AFDI and AFD2, it is determined whether any of them reaches r127J in decimal notation. The fact that the values of AFDI and AFD2 have reached r127J means that one of them has overflowed, and the amount of light incident on PSD9 is quite large, making the distance measurement data extremely reliable. It is considered thin. Therefore, in this case, after confirming that rGAIN=8, rAFREsULTa4-1
27'' (rAFRESULTaJ will be described later). In this state, the subject at the center of the screen is located quite close to the subject, and the reflected light is too strong even at a fairly low gain of rGAIN=8J. In addition, rG
Although it is possible to reset the value of AI NJ to "8" or less, a gain of "7" or less tends to cause problems such as the amplification characteristics of the gain control amplifiers 18a and 18b becoming nonlinear. In this embodiment, such gain settings are avoided.

If no overflow is recognized in the distance measurement data AFDI, AFD2, each distance measurement data AFDI, AFD
2, calculation processing of the addition distance measurement data AFADD and the subtraction distance measurement data AFDIF shown in FIG. 9 is performed. In this process, distance measurement data AFDI,
Offset values OFI and OF2 are subtracted from AFD2. Then, the calculated additional distance measurement data AFAD
For D, the value is r136. It is determined whether the above is true or not. 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 executing subsequent distance measurement calculations, and the gains of the gain control amplifiers 18a and 18b are set to the rGA IN at that time. ” and continues to be determined as the value of LE
Distance measurement processing by D3a will be executed.

On the other hand, if the value of the additional distance measurement data AFADD is less than "136", check that "rGFLAG", which indicates that the value of "rGAIN" at that time was inappropriate, is not "1". , ranging data AFDI, AFD
In order to increase the absolute value of 2, the value of rGAI NJ is
” is added.

The value of “N” added in this way is the added distance measurement data AF.
It is set as shown in the following table according to the size of ADD.

In the process of changing the values of rGA and INJ, the commands are reset, but the commands from "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 gains of the gain control amplifiers 18a and 18b in accordance with the new value of rGAINJ, and continues to repeat the same process. During this repeated processing, rGAIN>8. + may overflow; in this case, rGFLAGJ is set to "1" and then the rGAINJO value is reset to "1" lower.

If the value of rGAI NJ reaches the maximum gain of "31" but the addition distance measurement data AFADD with an appropriate absolute value cannot be obtained, the reflected light from the subject is extremely weak or is not returning to PSD9. In this case, the subject distance is extremely long. In this case, the process "rAFREsULTa=o" is performed.

When the value of rC;AINJ is determined by the above-described processing, distance measurement processing using the LED 3a is subsequently performed with the gains of the gain control amplifiers 18a and 18b set to that value. FIGS. 10 and 11 show this distance measurement processing procedure. This distance measurement process is performed using the LED3a
Light up 18 times and read AFDI and AFD2 each time.

And when reading AFDI and AFD2 every time,
It is determined whether any of them is overflowing, or whether the value is less than "15" and is insufficient as an absolute value of distance measurement data, and if this is the case, "0VCOUNTJ" indicating inappropriate distance measurement is determined. Count up by "1".

When rOVcOUNTJ reaches "4", it is determined that the gain value determined in the gain determination process is inappropriate, and rOVFLAG is set to "1" and rGA
Reset INJ lower by "1" and restart the distance measurement process from the beginning. In addition, in order to prevent the distance measurement process from being repeated many times, when rOVFLAG is set to "1" and rOVcOUNT reaches "4" again, the value of rGAINJ at that time is In response, “AFR
The value of ESULTaJ is determined as "M".

When making this determination, the following table is referred to.

In the process of importing the distance measurement data AFDI and AFD2 18 times, after identifying the minimum value and maximum value among them,
AFDI and ADF2 are rsuMIJ and 'SUM2J, respectively.
It is summed up as . And these total value rsU
M1", rsUM2", the maximum value of each of AFDI and AFD2.

After subtracting the minimum value, the average value is calculated.

Note that the maximum value is set to increase the reliability of the average value.

Although the minimum value is subtracted, these subtractions may be omitted.

The average values obtained for each channel in this way are updated as new average distance measurement data AFDI and AFD2,
After correcting the offset value according to the process shown in FIG.
Additive ranging data ADADD.

It is converted to subtraction distance measurement data AFDIF. Then, the value of these ratios is r128. Multiply by rAFRESULTa
J is calculated, and the distance measuring process using the LED 3a is completed.

Subsequently, the gain determination process-distance measurement process while lighting the LED 3b and the gain determination process-distance measurement process while lighting the LED 3c are repeated in exactly the same manner. and,
rAFRESULTbJ respectively.

The value of rAFRESULTcJ is determined.

These rAFREsULTj values are
The value corresponds to the subject distance obtained for each distance measurement at c. In the subject arrangement shown in Figure 1, rAFRE
SULTaJ is the distance to the main subject S1, rAFRE
SULTtz indicates a value corresponding to the distance to the background object S2, and rAFREsULTcJ is "0" (see FIG. 8) because the ranging light is not reflected. In such a case, the microcomputer 14 operates the rAF according to a program stored in the ROM 27.
REsULTa”, “AFRESULTbJ, r
The value corresponding to the closest subject distance among AFRESULTcJ is determined as the final distance measurement signal, and the distance measurement sequence is completed. Note that when the ranging data AFDI and AFD2 overflow, the value of rAFRESULTJ becomes "127", which corresponds to the closest subject distance, but this singular value is ignored when determining the final ranging signal. be done. After the distance measurement signal is determined in this way, the stepping motor 60 is driven via the lens moving circuit 58, and the photographing lens 5 is moved to the focusing position corresponding to the distance measurement signal.

As described above, the three LEDs 3a, 3b, and 3c are used to sequentially measure the distance at three locations within the photographic screen.
The same can be applied to a device in which distance measuring light is projected onto a subject using more than one lens. Furthermore, in carrying out the present invention, it is possible to omit the offset value detection process, or to partially change the gain determination process procedure and distance measurement process procedure, and the light receiving element may be a PSD, such as a COD image sensor, etc. You can also use something else.

〔Effect of the invention〕

As described above, according to the distance measuring device of the present invention, in adjusting the output signal from the distance measuring light receiving element to an appropriate gain corresponding to the incident light intensity, the analog signal output from the light receiving element is converted into a digital signal. Since the new gain value is calculated from the correlation between this digital value and the gain value at that time, the amount of light incident on the light receiving element is detected through a logarithmic amplifier at 4° as in the conventional method. This not only simplifies the circuit configuration compared to a system in which the gain is adjusted based on this method, but also enables distance measurement calculations with a high S/N ratio to be performed without being affected by noise.

[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 the processing procedure for offset value detection. FIG. 6 is a time chart illustrating the reading timing of distance measurement data. FIG. 7 is a flowchart showing the procedure for reading distance measurement data. FIG. 8 is a flowchart showing the processing procedure for determining the gain. FIG. 9 is a flowchart illustrating the calculation processing procedure for addition distance measurement data and subtraction distance measurement data. FIG. 10 and FIG. 11 are flowcharts showing the distance measurement processing procedure. 2 ・ ・ ・ 7 ・ ・ ・ 9 ・ ・ 12 ・ ・ 14 ・ ・ 15 ・ ・ 16 ・ ・ 18, 1 20a. 26 ・・ Light emitter light receiver SD Autofocus IC Microcomputer logic circuit Gain controller 8b...Gain control amplifier 20b...Sample hold circuit A/D converter. Figure 4 Figure 5 σD

Claims (1)

[Claims] (1) In a distance measuring device that receives distance measuring light reflected from a subject with a light receiving element and obtains a ranging signal corresponding to the distance to the subject based on an output signal from the light receiving element, the output from the light receiving element a gain control amplifier that amplifies a signal; a calculation means that digitally converts the output from the gain control amplifier; and calculates a new gain value from the correlation between the digital value and the gain value of the gain control amplifier; and the gain control amplifier. and gain setting means for resetting the gain value of 1 to the new gain value.