JPH06249650A - Range finder for camera - Google Patents

Abstract

PURPOSE:To accurately measure the distance to an object with a simple inexpensive circuit by changing the gain of a light receiving circuit in stages. CONSTITUTION:A light emission circuit 10 is the drive circuit of a light emitting element 10 and the element 14 emits light upon receiving a light emitting signal from a CPU 80. The emitted light reaches an object through a projection lens 1 and the light reflected by the object is made incident to a position detecting element 3 after passing through a light receiving lens 2. The element 3 outputs currents corresponding to the intensity and incident position of the light to current-voltage conversion circuits 20 and 30. Amplifier circuits 40 and 50 are constituted so that their gains can be switched. Switches 46 and 47 or 56 and 57 are controlled by the CPU 80 and the gains of the amplifiers 41 and 52 change in stages depending upon the states of the switches. The gains of the amplifiers 41 and 51 are maintained at the highest levels at the time of starting distance measurement so as to project pulsed light upon the object by a prescribed number of times. An integration circuit 60 integrates received optical signals and lowers the gains when the integrated voltage becomes higher than a prescribed value. This operation is repeated until the integrated voltage becomes lower than the prescribed value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device such as a camera, and more particularly to an active type distance measuring device for a camera.

[0002]

2. Description of the Related Art Conventionally, various active distance measuring devices have been proposed. In these distance measuring devices, when a light signal from a subject is amplified, a light projecting circuit has a predetermined number of times (or time). ) Is operated, and the integrated voltage is A / D converted to calculate the distance to the subject.

[0003]

However, in the distance measuring device as described above, a plurality of comparators are required to convert the voltage across the terminals of the integrating capacitor into a digital signal (see, for example, Japanese Patent Laid-Open No. 3-119307). Moreover, since the resolution is proportional to the number of comparators, if the distance measurement accuracy is increased, the circuit becomes complicated, large-scaled, and expensive.

[0004]

In order to solve the above problems, in the distance measuring apparatus for a camera according to the present invention, a light projecting means for irradiating a subject with light, and the light projected from the light projecting means is reflected by the subject. Light receiving means for receiving light and converting it into two current outputs, a first current-voltage conversion circuit for converting one output current of the light receiving means into a voltage, and converting the other output current of the light receiving means into a voltage. A second current-voltage conversion circuit;
Selection circuit for selectively outputting one of the two current-voltage conversion circuits, an amplification circuit for amplifying the output signals of the first and second current-voltage conversion circuits, and a gain selection means for selecting the gain of the amplification circuit. An integrating circuit for integrating the output of the amplifying circuit, a reference voltage generating means for generating a reference voltage, and a comparing means for comparing the output of the integrating circuit with the output of the reference voltage generating means.

[0005]

Function: The gain of the light receiving circuit can be changed stepwise. At the start of distance measurement, the gain is maximized, the pulsed light is projected onto the subject a predetermined number of times, the signal light returned from the subject is integrated, and the integrated voltage exceeds the predetermined voltage. Then lower the gain. The above operation is repeated until the integrated voltage falls below the predetermined voltage.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of an embodiment of the present invention will be described with reference to FIG. The light projecting circuit 10 is a near infrared light projecting element (hereinafter, IRED).
A driving circuit for driving a transistor 14, a base resistor 12, a collector resistor 13 and an IRED 14. Arithmetic circuit (hereinafter referred to as CPU)
When the light projection signal is output from 80, the IRED 14 emits light. The emitted light passes through the light projecting lens 1, a part thereof is reflected by a subject (not shown), and a part of the reflected light passes through the light receiving lens 2 and is incident on a semiconductor position detecting element (hereinafter referred to as PSD) 3. In the present invention, the IRED 14 is pulse-driven.

Current-voltage conversion circuits 20 (far side) and 30
(Near side) constitutes a light receiving circuit together with PSD3. When an optical signal is incident on the PSD 3, the PSD 3 generates a current according to its intensity and incident position in the current-voltage conversion circuit 20.
And output to 30. The current-voltage conversion circuit 20 has an amplifier 21.
Is a circuit configured to output a voltage proportional to an input current, the current-voltage conversion circuit 30 includes an amplifier 31 and a feedback resistor 32, and has the same configuration as the current-voltage conversion circuit 20. A voltage corresponding to the current is output and guided to the switch 4.

The switch 4 has a role of transmitting the output of one of the current-voltage conversion circuits 20 and 30 to a circuit in the subsequent stage, and its state is controlled by the CPU 80. When the distance measurement on the long distance side is performed, the current-voltage conversion circuit 20 is turned on, and when the distance measurement on the short distance side is performed, the current-voltage conversion circuit 30 side is turned on.

The amplifier circuits 40 and 50 are gain switchable amplifier circuits. Since these circuits have exactly the same configuration, the amplifier circuit 40 will be described as an example. Amplifier circuit 4
A coupling capacitor 5 is connected before 0, and the DC component of the input signal is cut off here. The amplifier circuit 40 is a circuit configured of an amplifier 41 and three feedback resistors, and amplifies an input signal with a certain gain. There are two switches 46 and 47 in the circuit, and these switches can be turned on / off by the CPU 80.
Since the switch 46 turns on / off the feedback resistor 43 and the switch 47 turns on / off the feedback resistor 43 and the feedback resistor 44, respectively, the gain of the amplifier 41 changes stepwise depending on the states of these switches, and the gain depending on the changed gain. It is amplified and output to the amplifier circuit 50. The amplifier circuit 50 also operates in exactly the same manner, and the CPU 80 operates the switches 56 and 57 to set an appropriate gain, and the signal output from the amplifier circuit 40 is amplified accordingly. The output signal of the amplifier circuit 50 is output to the integrating circuit 60 in the subsequent stage via the switch 7.

The integrating circuit 60 includes an amplifier 61 and an input resistor 6
2, integrating capacitor 63, switch 64, voltage follower 6
5 is a circuit configured to integrate the input voltage with time. Prior to the integration operation, the switch 64 is turned on to discharge the electric charge remaining in the integration capacitor 63. When fully discharged, the switch 64 turns off. When the integration operation is started by turning on the switch 7, the time integration value of the input signal is stored in the integration capacitor 63 as electric charge. The value of the voltage between the terminals of the integrating capacitor 63 at this time is output to the comparator 71. When the integration operation is completed, the switch 7 is turned off.

The level determination circuit 70 is a circuit configured by a comparator 71 and reference power supplies 73 and 74 for determining the level of the input voltage. The comparator 71 compares the value of the input voltage with the voltage V1 of the reference power source 73 or the voltage V2 of the reference power source 74 selected by the switch 72, and if the input voltage is higher, it is at the “H” level, and if the input voltage is lower, The'L 'level is output to the CPU 80.

Next, the operation of the circuit according to the embodiment of the present invention will be described. When this distance measuring routine is entered, first, the power supplies of all the circuits in FIG. 1 are turned on. Next, the CPU 80 clears the contents of a readable / writable storage device (hereinafter referred to as RAM) 81 and determines the gains of the amplifier circuit 40 and the amplifier circuit 50. If it is determined in this gain determination operation that the subject is located at a position less than a certain distance, the close-up flag in the RAM 81 is set, and in that case, it is determined that the close-up is performed without performing distance measurement. After that, distance measurement is performed by the current-voltage conversion circuit 20, and the number of times N1 is stored in the RAM 81. If it is determined during the distance measurement operation by the current-voltage conversion circuit 20 that the subject is at a position equal to or greater than a certain distance, the infinity flag in the RAM 81 is set, and in that case, it is determined to be infinity. After that, distance measurement is performed by the current-voltage conversion circuit 30, and the number of times N2 is stored in the RAM 81. When the distance measuring operation is completed, the infinity flag is set to infinity, the close-up flag is set to close, and the close-up flag is set to close. A value X satisfying = N1 / (N1 + N2) is calculated.

When the value X is determined, a predetermined readable storage device (hereinafter ROM
The address to the subject is referred to (FIG. 5) to find the distance to the subject. Finally, turn off the power of the distance measuring circuit,
Exit this routine.

Next, the operation of determining the gain of the amplifier circuit 40 and the amplifier circuit 50 for the current-voltage conversion circuit 20 will be described with reference to FIGS. First, the CPU 80 turns on the switch 4 to the current-voltage conversion circuit 20 side. Switch 7
2 is turned on to the reference power source 73 side, the switch 64 is turned on,
The charge accumulated in the integrating capacitor 63 is discharged (FIG. 2a). After discharging the electric charges sufficiently, the switch 64 is turned off, and the number N1 of the counter 83 is cleared to 0 (FIG. 2b). Then, the CPU 80 operates the light projecting circuit 10 to start light projecting. In order to secure the rise time of each amplifier accompanying the start of light projection and reduce the influence of power supply fluctuation, the integration circuit is operated only during time T2 after the time T1 after light projection has elapsed. After that, the light projection and the integration are stopped, the time is waited for T3, and 1 is added to the counter.

After repeating this operation a predetermined number of times Ng (for example, 10 times) as shown in FIG.
The switch 7 is turned off and the voltage across the terminals of the integrating capacitor 63, that is, the integrated voltage Vi, is output to the comparator 71. The comparator 71 compares the voltage with the voltage V1 of the reference power source 73, converts the result into a digital signal, and the CPU 80
Output to. The output of the comparator 71 of the CPU 80 is H
If it is a level, the switch 46 is turned on. Similarly, the integration operation and the comparison operation are repeated, and if the output of the comparator 71 is H level, the switch 56, the switch 47, and the switch 57 are turned on in this order. Even if all the switches are turned on, if the output of the comparator 71 is at H level, the near flag is set. As described above, the current-voltage conversion circuit 2
The optimum gains of the amplifier circuit 40 and the amplifier circuit 50 for 0 are determined.

Also in the case of the current-voltage conversion circuit 30, first C
The PU 80 turns on the switch 4 to the current-voltage conversion circuit 30 side, and thereafter, in exactly the same manner, the current-voltage conversion circuit 30.
The optimum gains of the amplifier circuit 40 and the amplifier circuit 50 are determined.

Next, distance measurement by the current-voltage conversion circuit 20 will be described with reference to FIG. First, the switch 4 is turned on to the current-voltage conversion circuit 20 side. Next, the switch 64 is turned on to discharge the electric charge accumulated in the integrating capacitor 63. After the electric charge is sufficiently discharged, the switch 64 is turned off. Then, the number N1 of the counter 83 is cleared to 0.
The switch 72 is turned on toward the reference power supply 74.

Subsequently, the distance measuring operation is started. Figure 2 shows the distance measurement method
As shown in. While repeating the light emission, the number of times N1 is added, and the integrated voltage Vi becomes the voltage V2 of the reference power source 74.
However, if the distance to the subject is too long and the voltage V2 has not been reached even if the light is projected a predetermined number of times Nm, it is determined to be infinity and the infinity flag in the RAM 81 is set. And finish. In other cases, the number N1 remaining in the counter 83 at the end of the distance measurement is set to R.
Store in AM81.

Next, distance measurement by the current-voltage conversion circuit 30 will be described with reference to FIG. First, the switch 64 is turned on to discharge the electric charge accumulated in the integrating capacitor 63. After the electric charge is sufficiently discharged, the switch 64 is turned off. Then, the number N2 of the counter 84 is cleared to 0.
Then, the distance measurement operation starts. The distance measuring method is as shown in FIG. While repeating the light emission, 1 is added to the number N2, and the process ends when the integrated voltage Vi reaches the voltage V2. The number of times N2 remaining in the counter 84 at the end of the distance measurement is stored in the RAM 81.

The above is the operation of the circuit in this embodiment. The above operation is shown in a flow chart in FIGS.
It becomes like 1. First, the main routine will be described with reference to FIG. When this distance measuring routine is entered, the CPU 80 turns on the power supply of the entire distance measuring circuit (# 001), and the RAM 81
The contents of is cleared (# 002). Next, the optimum gain determination operation in the current-voltage conversion circuit 20 is performed, the value S1 that is uniquely determined by the gain is determined and stored in the RAM 81 (# 003), the state of the closest flag is confirmed, and if it is set. Then jump to # 014 (# 00
4). Further, the optimum gain determination operation in the current-voltage conversion circuit 30 is performed, the value S2 that is uniquely determined by the gain is determined and stored in the RAM 81 (# 005), and then the state of the infinity flag is confirmed, and if it is set. If # 0
Jump to 14 (# 006). Here, the value S1 and the value S2 in the RAM 81 are compared (# 007), and the switch 46 and the switch 4 are selected based on the larger result.
7, switch 56, switch 57 are reset (# 00
8, # 009).

Then, the current-voltage conversion circuit 20 measures the distance, stores the number N1 in the RAM 81 (# 010), and confirms the state of the infinity flag. If set, jumps to # 014 (step 014). # 011). Similarly, the current-voltage conversion circuit 30 measures the distance and RA
The number of times N1 that data is saved in M81 (# 012) and saved in RAM 81 by the operations of subroutines # 010 and # 012.
And N2 are read out to calculate the value X (# 013).
As a result, if the infinity flag is set, it is infinity. If the close flag is set, it is close. Otherwise, it is the value X.
By referring to the address of the ROM 82 uniquely determined by (FIG. 5), the distance to the subject is obtained (# 014), and the motor 85 is controlled to drive the lens barrel 86 to the in-focus position (#).
015). Finally, turn off the power to the ranging circuit (# 01
6) Exit this routine.

Next, the operation within each subroutine will be described. First, the subroutine for determining the value S1 will be described with reference to FIG. The value S1 is 1-byte data held at an appropriate address in the RAM 81. When entering the subroutine for determining the gain of the amplifier circuit in the subsequent stage, the CPU 80 turns on the switch 4 to the current-voltage conversion circuit 20 side, turns on the switch 72 to the reference power source 73 side (# 101), and clears the value S1 to 0 ( (# 102), the switch 64 is turned on to discharge the electric charge accumulated in the integrating capacitor 63 (# 10).
3), the number N1 of the counter 83 is cleared to 0 (# 1
04).

Subsequently, the CPU 80 operates the light projecting circuit 10 (# 105) and waits for the time T1 (# 10).
6), the switch 7 is turned on to perform the integral operation (# 1
07), wait for time T2. During this time, electric charge is stored in the integrating capacitor 63 (# 108). Then, the operation of the light projecting circuit 10 is stopped to end the light projecting operation, and the switch 7
Is turned off to complete the integration operation (# 109), wait for time T3 (# 110), and add 1 to the counter 83 (# 1).
11). If the number N1 of the counter 83 is less than the predetermined number Ng, the process jumps to # 105 (# 11
2). If the number of times N1 is greater than or equal to the number of times Ng, the integrated voltage Vi is output to the comparator 71, and the comparator 71 compares the voltage with the voltage V1 of the reference power supply 73, and as a result, the voltage V1.
Output o to the CPU 80 (# 113). The CPU 80 determines the level of the voltage Vo (# 114), and if it is at the H level, returns to the main routine.

When the voltage Vo is at L level, the CPU 8
For 0, add 1 to the value S1 (# 115), check whether the value S1 is equal to 1 (# 116), and if they are equal, turn on the switch 46 to reduce the gain of the amplifier 41 (# 117). ), Jump to # 103. Next, it is confirmed whether or not it is equal to 2 (# 118), and if they are equal, the switch 56 is turned on to further reduce the gain of the amplifier 51 (# 119), and the process jumps to # 103. Next, it is confirmed whether or not it is equal to 3 (# 120), and if they are equal, the switch 47 is turned on to further reduce the gain of the amplifier 41 (# 121), and the process jumps to # 103. Then 4
(# 122), and if they are equal, the switch 57 is turned on to further reduce the gain of the amplifier 51 (# 123), and the process jumps to # 103. Value S
If the value of 1 is none of 1 to 4, the close flag in the RAM 81 is set (# 124), this subroutine is exited, and the process returns to the main routine.

Next, a subroutine for determining the value S2 is shown in FIG. The operation is almost the same as the case of determining the value S1, and C
The PU 80 turns on the switch 4 to the side of the current-voltage conversion circuit 20, and determines an appropriate gain while adding 1 to the value S2 which is 1 byte of data held at an appropriate address in the RAM 81. When exiting this routine, either the value S2 that is uniquely determined by the gain is determined, or the near-field flag in the RAM 81 is set.

Next, the subroutine for determining the number of times N1 will be described with reference to FIG. When you enter this subroutine, C
The PU 80 turns on the switch 64 for a moment to turn on the integration capacitor 6
After discharging the charge accumulated in 3 (# 301), the switch 4 is turned on to the current-voltage conversion circuit 20 side, the switch 72 is turned on to the reference power source 74 side (# 302), and the number N1 of the counter 83 is set. It is cleared to 0 (# 303). Subsequently, it is determined whether or not the number N1 is the number Nm or more. If the number Nm or more, the infinity flag in the RAM 81 is set and the process returns to the main routine (# 305). If less than Nm, # 3
Jump to 06 (# 304).

Subsequently, the CPU 80 operates the light projecting circuit 10 (# 306) and waits for a time T1 (# 30).
7), switch 7 is turned on to perform integral operation (# 30
8) Wait for time T2 (# 309). During this time, the electric charge is stored in the integrating capacitor 63. Then, the operation of the light projecting circuit 10 is stopped, the light projecting operation is terminated, the switch 7 is turned off, the integrating operation is completed (# 310), and the system waits for the time T3 (# 311) and increments the counter 83 by 1 ( # 31
2) The integrated voltage Vi is output to the comparator 71. The comparator 71 compares the voltage with the voltage V2 and outputs the voltage Vo as the comparison result to the CPU 80 (# 31).
3). The CPU 80 determines the level of the voltage Vo (# 31
4) If it is H level, the number of times N1 of the counter 83 is RA
Store in M81 (# 315) and return to the main routine,
If it is L level, jump to # 304.

Next, a subroutine for determining the number of times N2 will be described with reference to FIG. When you enter this subroutine,
The CPU 80 momentarily turns on the switch 64 to discharge the electric charge accumulated in the integration capacitor 63 (# 401), then turns on the switch 4 to the current-voltage conversion circuit 30 side and turns on the switch 72 to the reference power source 74 side (# 401). 402), the number N2 of the counter 84 is cleared to 0 (# 403).

Subsequently, the CPU 80 operates the light projecting circuit 10 (# 404). Wait for time T1 (#
405), the switch 7 is turned on to perform the integration operation (# 406), and waits for the time T2 (# 407). During this time, the electric charge is stored in the integrating capacitor 63. Then, the operation of the light projecting circuit 10 is stopped to end the light projecting operation, the switch 7 is turned off, the integrating operation is completed (# 408), and the time T
It waits for 3 (# 409), adds 1 to the counter 84 (# 410), and outputs the integrated voltage Vi to the comparator 71. The comparator 71 compares the integrated voltage Vi with the voltage V2 and outputs the voltage Vo as the comparison result to the CPU 80 (# 411). The CPU 80 determines the level of the voltage Vo (# 412), and if it is at the H level, stores the number N2 of the counter 84 in the RAM 81 (# 413) and returns to the main routine. If it is L level, jump to # 404. With the above operation, the distance to the subject is measured.

As another embodiment of the present invention, it is conceivable that the gains of the amplifier circuits 40 and 50 are set to be small so as to improve the distance measuring accuracy. In that case, the switches are switched when the values S1 and S2 are determined. Align the numbers of 46, 47, 56, 57 turned on to the smaller one. The main routine is as shown in FIG. When entering this distance measurement routine, CP
U80 turns on the power of the whole ranging circuit (# 501),
The contents of AM81 are cleared (# 502). Then the value S1
Is determined (# 503), the state of the close proximity flag is confirmed, and if set, the process jumps to # 514 (# 504). Further, the value S2 is determined (# 505), the state of the infinity flag is confirmed, and if set, the process jumps to # 514 (# 506). Where R
The value S1 and the value S2 in the AM 81 are compared (# 50
7), switch 4 based on whichever is smaller
6, the switch 47, the switch 56, and the switch 57 are reset (# 508, # 509).

Then, the current-voltage conversion circuit 20 measures the distance, stores the number N1 in the RAM 81 (# 510), and then confirms the state of the infinity flag, and if set, jumps to # 514 (step 514). # 511). Similarly, the current-voltage conversion circuit 30 measures the distance and RA
Number of times N1 stored in M81 (# 512) and stored in RAM 81 by the operations of subroutines # 510 and # 512
And N2 are read out to calculate the value X (# 513).
As a result, if the infinity flag is set, it is infinity. If the close flag is set, it is close. Otherwise, it is the value X.
By referring to the address of the ROM 82 uniquely determined by (FIG. 5), the distance to the subject is obtained (# 514), and the motor 85 is controlled to drive the lens barrel 86 to the in-focus position (#).
515). Finally, turn off the power to the distance measuring circuit (# 51
6) Exit this routine. The subroutine is the same as that shown in FIGS.

In the above embodiments, a PSD having two electrodes is used as a light receiving element, but a light receiving element composed of three or more electrodes having an intermediate electrode or the like, especially an element such as a split photodiode (SPD) is used. It goes without saying that it may be used.

[0033]

According to the configuration of the present invention, the optimum gain of the light receiving circuit is determined without using the A / D conversion circuit, and the distance to the object is measured after setting the gain, and thus the simpler In addition, it is possible to perform highly accurate distance measurement with an inexpensive circuit.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is an operation diagram illustrating an integration operation according to the embodiment of this invention.

FIG. 3 is an amplifier circuit 40 and an amplifier circuit 50 according to an embodiment of the present invention.
6 is an operation diagram illustrating a method of determining the gain of FIG.

FIG. 4 is an operation diagram illustrating a series of operations during distance measurement according to the embodiment of the present invention.

FIG. 5 is a ROM for obtaining a distance from a value X according to the embodiment of the present invention.
The table on 82.

FIG. 6 is a flowchart showing the operation of the embodiment of the present invention.

7 is a flowchart showing a subroutine of a part for determining a value S1 in the flowchart of FIG.

8 is a flowchart showing a subroutine of a part for determining a value S2 in the flowchart of FIG.

9 is a flowchart showing a subroutine for determining the number of times N1 in the flowchart of FIG.

10 is a flowchart showing a subroutine of a part for determining the number of times N2 in the flowchart of FIG.

FIG. 11 is a flowchart showing the operation of another embodiment of the present invention.

[Explanation of reference numerals] 3 light receiving element (PSD) 4 switch 10 light projecting circuit 15 light projecting element (IRED) 20 current-voltage conversion circuit (far distance side) 30 current-voltage conversion circuit (short distance side) 40 amplification circuit 50 amplification circuit 60 integration circuit 70 comparison circuit 73 reference voltage source 74 reference voltage source

Claims (1)

[Claims] 1. A light projecting means for irradiating a subject with light, and a light projecting means for receiving light reflected by the subject.
Light receiving means for converting into one current output, a first current-voltage conversion circuit for converting one output current of the light receiving means into a voltage, and a second current voltage for converting the other output current of the light receiving means into a voltage A conversion circuit, and a selection circuit that selectively outputs one of the output voltages of the two current-voltage conversion circuits,
An amplification circuit for amplifying the output signals of the first and second current-voltage conversion circuits selected by the selection circuit, an integration circuit for integrating the output of the amplification circuit, and a reference voltage generation means for generating a reference voltage. Comparing the output of the integrating circuit with the output of the reference voltage generating means, and a gain selecting means for selecting the gain of the amplifying circuit based on the output result of the comparing means. Distance measuring device for cameras.