JP2675671B2 - Active distance measuring method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an active type distance measuring method in which distance measuring light is projected onto a subject and reflected light from the subject is received to perform distance measurement. .

[Conventional technology]

Active type distance measuring devices are used in recent compact cameras. An active type distance measuring device projects near-infrared light toward a subject and reflects light from the subject on a semiconductor position detector (PSD: Position Sensitive Det
The light is received by a light receiving element such as an ector). The incident position of the reflected light on the light receiving element corresponds to the subject distance, and the light receiving element outputs an electric signal corresponding to the light incident position. Therefore, the subject distance can be obtained by analyzing the electric signal. .

When the PSD is used as the light receiving element, its output signal becomes an analog value, but this analog value is digitized in order to process the subsequent distance measurement operation at high speed.
It is converted into, for example, 8-bit measurement data by binary coding.

On the other hand, ambient light is incident on the PSD in addition to the distance measuring light reflected by the subject, and noise is superimposed from the circuit system such as the amplifier after PSD. It often contains unnecessary signal components. In order to remove such unnecessary signal components, the signal from the PSD is obtained in the state where the ranging light is not projected, this is digitized and used as an offset value, and the
It is effective to subtract the offset value from the measurement data obtained from D and use the measurement data thus obtained for the subsequent distance measurement calculation.

[Problems to be solved by the invention]

However, when the abnormal light is incident, the offset value is detected, and when the measured data obtained by projecting the distance measuring light is at a low level, the offset value is subtracted from the measured data. And the measured data may be negative. Generally, when processing binary coded data, it is possible to represent a negative number by setting the most significant bit to "1", but it is not necessary to consider a negative value for measurement data used for distance measurement calculation. For example, 8-bit data often represents measurement data of "0" to "255". When the distance measurement calculation is performed after sampling the measurement data on such a premise, if the measurement data having a negative value is obtained and is directly subjected to the binary encoding process, it is meaningless in the distance measurement calculation thereafter. Calculations may be performed, and in extreme cases even program runaway may occur.

[Object of the invention]

The present invention has been made in view of such circumstances,
An object of the present invention is to provide an active distance measuring method in which even if negative measurement data is calculated by the offset correction process, a runaway program or the like does not adversely affect the subsequent distance calculation.

[Means for solving the problem]

In order to achieve the above object, the present invention, when obtaining measurement data by subtracting an offset value from a measurement value represented by a binary number of a predetermined number of bits obtained by projecting distance measuring light,
When the value becomes negative, the measurement data is set to zero and the subsequent distance measurement calculation is performed.

[Action]

In most cases, the measured value obtained from the PSD when projecting the ranging light is larger than the offset value, and the measured data becomes a positive value, but in a unique ambient environment, the measured data becomes a negative value. It can happen. Even in such a case, by substituting zero for the measured data, the distance signal can be calculated by a calculation targeting a positive value range without requiring special processing for the subsequent distance measurement calculation.

Hereinafter, the present invention will be described with reference to the illustrated embodiments.

〔Example〕

In FIG. 1 schematically showing the configuration of a distance measuring device used in the present invention, a light projecting section 2 is composed of a light source section 3 and a light projecting lens 4, and an optical axis 4a of the light projecting lens 4 is a taking lens. It is almost parallel to the optical axis 5a of No. 5. The light source unit 3 includes three LEDs (light emitting diodes) 3a, 3b, 3 each emitting near infrared light.
Consists of c. These LEDs 3a, 3b, 3c are arranged horizontally, the center LED 3a is located on the optical axis 4a, and the LEDs 3b, 3c are located on the left and right sides, respectively, and each of the LEDs 3a, 3c has a beam shape toward three places in the shooting screen. The ranging light is sequentially emitted.

The light receiving section 7 includes a light receiving lens 8 and a PSD 9, and the optical axis 8a of the light receiving lens 8 is also substantially parallel to the optical axis 5a of the photographing lens. The PSD 9 outputs a signal corresponding to the amount of incident light and the incident position from each of the output terminals 9a and 9b. As is clear from Fig. 1, the closer the subject is, the more the reflected light from the subject is incident on the output terminal 9b side of the PSD9, but the ratio of the sum and difference of the output signals from the output terminals 9a and 9b. By calculating, it is possible to obtain a signal corresponding to the incident position. Note that PSD9 does not have a discriminating action in the horizontal direction, and if the incident height in the vertical direction is the same, the ratio of the output signals from output terminals 9a, 9b is equivalent even if the incident position in the horizontal direction is different. It will be

The light emission of the LEDs 3 a to 3 c is controlled via the LED driver 11 by 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 and activates the LED driver 11, and also outputs the output terminal 9 of the PSD 9.
The signals from a and 9b are amplified or sampled and held and output to the microcomputer 14. The microcomputer 14 calculates based on the output signals of the first and second channels obtained as described above, and calculates a distance signal having a correlation with the object distance. Then, the set position of the taking lens 5 is determined according to the distance signal calculated by the microcomputer 14.

A general-purpose microcomputer is used for the microcomputer 14, and photometric data detected by the photometric circuit 51 and digitally converted by the A / D converter 52 is also input. The microcomputer 14 calculates an optimal exposure condition based on the photometric data, drives a stepping motor 54 via an exposure control circuit 53, and sets the program shutter 55 to a program shutter with an aperture value and a shutter speed satisfying the optimal exposure condition. Open and close 55. Further, after photographing, the film feeding circuit 57 drives the film feeding motor 57 to feed the film one frame. Before the program shutter 55 is opened or closed, the lens moving circuit 58 drives the stepping motor 60 at a rotation angle corresponding to the distance signal, and the photographing lens 5 is controlled to be extended to the in-focus position.

The autofocus IC 12 and the microcomputer 14 are configured as schematically shown in FIG. The autofocus IC 12 is composed of a one-chip IC and has a logic circuit 1
5. In addition to the gain controller 16, preamplifiers 17a and 17b for converting signal currents of the first and second channels output from the output terminals 9a and 9b of the PSD 9 into voltages, gain control amplifiers 18a and 18b, and a sample and hold circuit 20a , 20b and buffer amplifiers 21a, 21b.

The gain control amplifiers 18a and 18b consider that when the subject distance is long, the amount of reflected light entering 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 a gain control process described later. The sample and hold circuits 20a and 20b receive a sampling pulse from the logic circuit 15 and
The signals amplified by the amplifiers 18a and 18b are sampled and held, and these signals are output to the microcomputer 14 via the buffer amplifiers 21a and 21b. The logic circuit 15 basically includes a serial-in / parallel-out shift register, and the gain controller 16 reads the gain control data set at a predetermined bit position of the shift register, and based on the read data, sets the gain control amplifier 18a. , 18b.

The microcomputer 14 has a CPU 24 and a serial port 2
5, In addition to the A / D converter 26, a ROM 27 storing a program for executing the distance measuring sequence and a RAM 2 for temporarily storing data and various flags obtained at the time of executing the distance measuring sequence.
Consists of eight. The serial port 25 converts the command from the CPU 24 into a serial data pulse (AFSD) and supplies it to the logic circuit 15. The serial port 25 also converts the serial data transfer pulse (AFSCK), the serial data latch, and the light emission timing of the LEDs 3a to 3c. Outputs control pulse (AFLCK) to be determined. Also, the A / D converter 26 is an autofocus IC1.
The analog signal supplied from 2 is converted into a 7-bit digital value (0 to 12 in decimal) corresponding to the signal voltage level.
(Representing 7).

FIG. 3 conceptually shows an 8-bit serial-in-parallel shift register 30 used in the logic circuit 15. Gain control data (GAIN) is set in 5 bits of D0 to D4, and LED is set in 2 bits of D5 to D6.
Light emission data (LED) is set, and in one bit of D7, 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. The 2-bit LED emission data is "0",
It can represent 4 states of "1", "2", "3",
"0" indicates that all of the LEDs 3a to 3c are off, "1" indicates that only the LED 3a is lit, and "2" and "3" indicate that the LEDs 3b and 3c are lit, respectively.

FIG. 4 is a flowchart showing the procedure of the basic distance measurement sequence. The process of detecting the offset value of the amplifier system of the autofocus IC 12, the LEDs 3a to 3c are sequentially turned on, and the output signal obtained at that time is measured. Distance measurement processing taken in as data, processing for obtaining distance measurement data by performing offset correction processing on the obtained measurement data, and processing for calculating distance signals by performing calculation based on the distance measurement data,
The process of moving the taking lens 5 to the position corresponding to the distance signal is sequentially executed. Before the distance measuring process is performed, a gain setting process for setting the gain of the gain control amplifiers 18a and 18b to an optimum value is performed.

 Hereinafter, the operation of the above configuration will be described.

For example, when the distance measurement sequence is started by a half-press signal of the shutter button, first, an offset value detection process shown in FIG. 5 is executed. When the offset value detection processing is performed, “01000000” (binary number) is set in each bit position of “D0 to D7” of the shift register 30. Thereby, each command data of “GAIN = 8”, “LED = 0”, and “SET = 0” is set. This command data is set at the time of P1 shown in the timing chart of FIG.
That is, when the control pulse AFLCK goes low after the transfer pulse AFSCK has sent out eight pulses, it is latched. The transfer of the serial data pulse is sequentially transferred to the shift register 30 at the rise of the transfer pulse AFSCK. Further, after the command data is transferred, "COUT = 8" is set in a predetermined register in the CPU 24.

Among the command data set in the shift register 30, the data of "GAIN = 8" is supplied to the gain control amplifiers 18a and 18b via the gain controller 16, and the gains of the gain control amplifiers 18a and 18b are each "8".
Is set to Note that “GAIN = 31” is the maximum amplification rate, and “GA
“IN = 0” corresponds to the minimum amplification factor.

After the transfer of this serial data, the output signals from the first and second channels are sampled and held, and the digital value obtained by A / D converting this is converted into measurement data AFD1 and AFD2 represented by a 7-bit binary number. Read in. In the procedure of this reading process, as shown in the flowchart of FIG. 7, first, the control pulse AFLCK is set to the low level during the period of ΔT1. If the serial data pulse AFSD changes during this period, LEDs 3a-3
Control of the c and sample hold circuits 20a and 20b is performed.
First, at the time of P2 when AFSD became low level, LEDs 3a to 3c
It is used for the lighting timing of. However, during the offset value detection processing, none of the LEDs 3a to 3c are lit because the command is “LED = 0”.

When ΔT2 elapses from the time point of P2, AFSD becomes high level, and at this timing, the sample and hold circuits 20a and 20b hold the output signals from the respective gain control amplifiers 18a and 18b. Note that these output signals have values amplified by “GAIN8” by the gain control amplifiers 18a and 18b, respectively. Further, after ΔT3, AFSD becomes low level and is used as a light emission stop signal of LEDs 3a to 3c, and after ΔT4, returns to high level. AFLCK is ΔT
After the lapse of the low level period of 1, the level becomes high again, and this high level period ΔT5 elapses, thus completing one cycle.

When ΔT6 elapses from the time point P3 when AFSD becomes low level, the output signal held in the sample hold circuits 20a, 20b is converted into a 7-bit digital value by the A / D converter 26 via the buffer amplifiers 21a, 21b. Converted and these are the CPU24 as measurement data AFD1 and AFD2 of the 1st and 2nd channels.
And stored at a predetermined address position in the RAM 28.

The process of capturing the measurement data AFD1 and AFD2 is repeated eight times. Then, these eight pieces of measurement data are averaged for each channel, and the average value is used as an offset value OF.
Determined as 1, OF2. Since this offset value detection process is executed with the LEDs 3a to 3c turned off, the average value of these values is the peculiar noise due to the ambient light incident on the PSD9, the amplifiers after the preamplifiers 17a and 17b, and the signal processing system. It means a value due to noise or the like caused by.

After the detection of the offset value, a gain determination process and a distance measurement process are performed. These processes are individually executed for the LEDs 3a to 3c. The gain determination process is executed according to the flowchart of FIG. When the gain determination process is started, “GFLAG” and “OVFLA” set in the RAM 28
Each flag of "G" is set to the initial state "0". Thereafter, serial data representing a new command is transferred from the serial port 25 to the logic circuit 15, and binary data “01000011” is set in each bit position of the shift register 30. As a result, “GAIN = 8”, “LED =
1 "and" SET = 1 ". Therefore, the LED
Only 3a is turned on.

After setting the above command, measurement data AFD1, AFD2 represented by 7-bit binary number is used as in the offset value detection process.
The reading process is executed, but in this case, as is clear from the time chart of FIG. 6, LED3a displays "ΔT2 +
It is lit for a period of ΔT3 ”. Therefore, in the state shown in FIG. 1, the distance measuring light from the LED 3a is applied to the main subject S1, and the reflected light enters the PSD 9 through the light receiving lens 8. Then, at this time, the signals output from both terminals 9a and 9b of the PSD 9 include information on the intensity of the light incident on the PSD 9 and the incident position.

When these signals are digitally converted and then taken in as measurement data AFD1 and AFD2, it is determined whether or not either of them reaches "127" in decimal. AFD1,
The fact that the value of AFD2 reaches "127" means that either of them has overflowed, the light quantity of the incident light to PSD9 is quite large, and it is extremely unreliable as measurement data. Is judged. Therefore, in this case, after confirming that "GAIN = 8",
RESULTa ← 127 "(" AFRESULTa "will be described later)
Is performed. In this state, the subject in the center of the screen is located very close to each other, and the reflected light is too strong even with a fairly low gain of "GAIN = 8". It is also possible to reset the value of "GAIN" to "8" or less, and this minimum gain value "8" can be appropriately changed according to the camera specifications and the light amounts of the LEDs 3a to 3c. .

When no overflow is found in the measurement data AFD1 and AFD2, the addition distance measurement data AFADD and the subtraction distance measurement data AFDIF shown in FIG. 9 are calculated from the respective measurement data AFD1 and AFD2. In this process, the offset value OF is added to the measurement data AFD1 and AFD2 to remove the noise component.
1, OF2 is subtracted, and the calculation result is the distance measurement data AFD1,
Subsequent addition distance measurement data AFADD, subtraction distance measurement data as AFD2
Used to calculate AFDIF.

If "AFD1 <OF1" or "AFD2 <OF2" in the process of calculating the distance measurement data AFD1 and AFD2 by the offset correction, the distance measurement data AFD1 and AFD2 may have negative values. In this case, after adding "0" to the values of the distance measurement data AFD1 and AFD2, the additional distance measurement data AFAD represented by an 8-bit binary number
D, Calculation of subtraction distance measurement data AFDIF is executed. In addition, PSD
Since the setting of the reference position of 9 does not result in "AFD1 <AFD2", the value of the subtraction distance measurement data AFDIF does not become negative, but the subtraction distance measurement data AFDIF becomes a negative value due to the influence of noise etc. When it becomes, "0" is determined as the value of the subtraction distance measurement data AFDIF, as in the calculation of the distance measurement data AFD1 and AFD2 by the offset correction processing.

Regarding the added ranging data AFADD calculated in this way,
It is determined whether the value is “136” or more. When this value is "136" or more, the distance measurement data AFD1, AFD2
It is determined that each value of is within the range suitable for executing the distance measurement calculation thereafter, and the gain control amplifiers 18a, 18b
The gain of is determined as the value of "GAIN" at that time, and the distance measurement process by the LED 3a is subsequently executed.

On the other hand, when the value of the addition distance measurement data AFADD is less than "136", it was confirmed that "GFLAG" indicating that the value of "GAIN" at that time was inappropriate was not "1". Above, "N" is added to the value of "GAIN" in order to increase the absolute values of the measurement data AFD1 and AFD2. The value of "N" added in this way is set as shown in the following table according to the size of the added distance measurement data AFADD.

In the process of changing the value of “GAIN”, the command is reset, but only the data at the bit positions “D0” to “D4” of the shift register 30 changes, and the data at the other bit positions remains unchanged. I have. And the gain controller 16
Adjusts the gains of the gain control amplifiers 18a and 18b according to the new value of "GAIN", and subsequently repeats the same processing. At the time of this repetition processing, “GAIN> 8”
May overflow, but in this case, "GF
After setting “LAG” to “1”, the value of “GAIN” becomes “1”
It is reset lower.

Even if the value of “GAIN” reaches the maximum gain of “31”, if the added distance measurement data AFADD with an appropriate absolute value cannot be obtained, the reflected light from the subject is extremely weak, or
This is a state where it has not returned to PSD9, and in this case, it corresponds to the fact that the subject distance is extremely long. In this case, the processing of “AFRESULTa ← 0” is performed.

When the value of “GAIN” is determined by the above-described processing, the distance measurement processing by the LED 3a is continuously performed with the gain of the gain control amplifiers 18a and 18b set to the value. FIG. 10 and FIG. 11 show this distance measurement processing procedure. In this distance measuring process, the LED 3a is turned on 18 times and the measurement data AFD1 and AFD2 are read each time. And every time A
At the time of reading FD1 and AFD2, it is determined whether either of them has overflowed or the value is less than "15", which is insufficient as the absolute value of the measured data.
"OVCOUN", which indicates inappropriate distance measurement when applicable
Count up "T" by "1".

When “OVCOUNT” reaches “4”, it is determined that the gain value determined in the gain determination process is inappropriate,
Set "OVFLAG" to "1" and set "GAIN" to "1"
Set it low again and restart the ranging process from the beginning. Also, in order to prevent the ranging process from being repeated many times, once "OVFLAG" is set to "1", "OVCO
When "UNT" reaches "4", "GAIN" at that time
The value of “AFRESULTa” is determined as “M” corresponding to the value of “. At the time of this determination, the following table is referred to.

In the process of importing the measurement data AFD1 and AFD2 18 times, the minimum value and the maximum value among them are identified, and then AFD1 and AFD2
DF2 is added up as "SUM1" and "SUM2", respectively.
Then, from these sums “SUM1” and “SUM2”, the AFD
After subtracting the maximum value and the minimum value of 1, AFD2, the average value is calculated. Although the maximum value and the minimum value are subtracted in order to improve the reliability of the average value, the subtraction may be omitted.

The average value thus obtained for each channel is newly updated as the averaged measurement data AFD1, AFD2, and after the offset value is corrected according to the processing of FIG. 9, the addition distance measurement data ADADD, the subtraction distance measurement data Converted to AFDIF. Also in the offset correction processing at this time, when the values of the distance measurement data AFD1 and AFD2 after the offset correction become negative, "0" is substituted as the distance measurement data, and the subtraction distance measurement data AFDIF has a negative value. When it becomes, "0" is similarly substituted. After the addition distance measurement data ADADD and the subtraction distance measurement data AFDIF are obtained, the value of these ratios is multiplied by "128" to obtain "A
"FRESULTa" is calculated, and the distance measuring process using the LED 3a is completed.

Continuing, gain determination processing while lighting LFD3b −
Distance measurement processing, gain determination processing while lighting LED3c-
The ranging process is repeated in exactly the same way. And each "AF
RESULTb "and" AFRESULTc ".

These "AFRESULT" values are values corresponding to the subject distance obtained for each distance measurement by the LEDs 3a to 3c. In the subject arrangement shown in FIG. 1, “AFRESULTa” indicates a value corresponding to the distance to the main subject S1, “AFRESULTb” indicates a value corresponding to the distance to the background subject S2, and “AFRESULTc” reflects the distance measuring light. It is "0" (see FIG. 8) because it has not been performed. In such a case, the microcomputer 14 executes the “AFR
The value corresponding to the closest object distance among “ESULTa”, “AFRESULTb”, and “AFRESULTc” is determined as the final distance signal, and the distance measurement sequence is completed. The measurement data AF
When D1 and AFD2 overflow, the value of "AFRESULT" becomes "127", which corresponds to the closest object distance, but this singular value is ignored when determining the final distance signal. After the distance signal is thus determined, the stepping motor 60 is driven via the lens moving circuit 58, and the photographing lens 5 is moved to the in-focus position corresponding to the distance signal.

As described above, the embodiment in which the three LEDs 3a, 3b, and 3c are used to sequentially measure the distance at three locations in the shooting screen has been described. However, the present invention employs one or two LEDs, and more than four LEDs. The present invention can be similarly applied to an apparatus that projects distance measuring light to a subject using the method. Further, in carrying out the present invention, it is possible to use a logic circuit instead of the microcomputer 14 for calculation, and to use a light receiving element other than PSD such as a CCD image sensor.

〔The invention's effect〕

As described above, according to the distance measuring method of the present invention, when the distance measuring operation is performed based on the measured data represented by the binary number of the predetermined number of bits, when the measured data has a negative value, Since zero is substituted and processed, all binary numbers with a predetermined number of bits can be treated as values in the positive range,
It is possible to reduce the capacity of the distance measurement calculation program and improve the processing efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the structure of a distance measuring device used in 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 entire ranging sequence. FIG. 5 is a flowchart showing a processing procedure for detecting an offset value. FIG. 6 is a time chart explaining the reading timing of the measurement data. FIG. 7 is a flowchart showing the procedure for reading measurement data. FIG. 8 is a flowchart showing a procedure for determining a gain. FIG. 9 is a flowchart showing a procedure for calculating the added distance measurement data and the subtraction distance measurement data. FIG. 10 and FIG. 11 are flowcharts showing the distance measurement processing procedure. 2 …… Emitter 7 …… Receiver 9 …… PSD 12 …… Autofocus IC 14 …… Microcomputer 15 …… Logic circuit 16 …… Gain controller 18a, 18b …… Gain control amplifier 20a, 20b …… Sample Hold circuit 26 …… A / D converter.

Front page continuation (72) Inventor Tatsuo Saito 1-324, Uetake-cho, Omiya-shi, Saitama Fuji Photonics Co., Ltd. (56) Reference JP-A-1-202614 (JP, A)

Claims (1)

(57) [Claims] 1. A distance measuring light is projected to a subject, a reflected light from the subject is received by a light receiving element, an output signal from the light receiving element is converted into a digital value, and then a distance measuring operation is performed to obtain a distance signal. In the active distance measuring method for calculating, the value of the output signal obtained from the light receiving element is digitized by converting the value of the output signal obtained from the light receiving element into a binary offset value having a predetermined number of bits. After digitizing, the value of the output signal obtained from the light receiving element is converted into binary measurement data of the number of bits, and the offset value is subtracted from the measurement data to be used for distance measurement calculation. An active distance measuring method characterized in that distance measuring data is obtained, and when the value of the distance measuring data becomes negative, zero is substituted for the distance measuring data to perform distance measuring calculation. .