JP3232421B2 - Distance measuring device - Google Patents

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 for a camera or the like .

[0002]

2. Description of the Related Art A known active type distance measuring device emits near-infrared light toward a subject, and receives light reflected from the subject by a light receiving element. Since the incident position of the reflected light on the light receiving element changes according to the subject distance, the distance to the subject can be measured by electrically examining the incident position of the reflected light.

As the light receiving element, a semiconductor position detecting element (Position Sensitive Device) is used.
e, hereafter referred to as PSD). PSD
Has two output terminals, and outputs a current corresponding to the intensity and position of incident light from each output terminal. By calculating the value of the two output currents or the ratio of the two voltages corresponding to the two output currents, it is possible to obtain a signal that depends only on the light incident position.

In such a distance measuring apparatus, a near-infrared emitting element (hereinafter, referred to as IRED) is pulse-driven, and a signal from the PSD is extracted by an AC coupling to a signal component and is appropriately amplified. The amplified signal is integrated for the latter half of the light emission time, and the integration is repeated until the integrated voltage reaches a predetermined voltage, and the number of times until the integration is taken as the magnitude of the signal from the PSD. Assuming that the number of integrations up to a predetermined voltage for the two outputs from the PSD is N1 and N2, the distance to the subject is calculated from the value X of Expression (1). X = N1 / (N1 + N2) (1)

[0005]

As described above, the magnitude of the AC-coupled signal differs depending on the distance to the subject and the reflectance of the subject. If the values N1 and N2 are set to be large, the accuracy of the value X can be increased. However, for that purpose, it is necessary to have many gains that can be set in the amplifier circuit, and the circuit scale increases.

[0006]

In order to solve the above problems, the present invention provides a light projecting means for irradiating a subject with a plurality of pulsed lights, a light receiving means for receiving light reflected from the subject , An integrating circuit for integrating the output signal of the means , and the pulse until the output signal of the integrating circuit reaches a predetermined value.
Counting means for counting the number of light beams;
Calculating means for calculating the distance to the subject based on the count value of the means , wherein the integrating circuit projects the pulsed light.
A configuration that performs an integration operation with an operation time that can be set within the light time
are doing.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described with reference to FIG. The light projecting circuit 10 is a light projecting circuit that projects projection light for distance measurement to a subject. The PSD 3 receives the reflected light from the subject and outputs a signal corresponding to the light receiving position to the current / voltage conversion circuits 20 and 30. Current-voltage conversion circuits 20 and 3
Numeral 0 denotes a circuit for converting the output current of the PSD 3 into a voltage, and one of these output signals is selected by the switch 4. The selected signal is supplied to the following amplifying circuit 40.
, And is further integrated by the integrating circuit 50, compared with the reference voltage by the level determination circuit 60, and the comparison result is output to the CPU 70. CPU7
0 transmits / receives data to / from the RAM 71, the ROM 72, the counter 73, the counter 74, and outputs a drive signal to the light emitting circuit 10 and the motor 75. The motor 75 is the lens barrel 7
6 is driven. The outline of the operation is that the subject
And the gain of the amplifier circuit according to the level of the reflected light.
To determine. As a result, when the reflected light level is very high,
If the gain is minimized, shorten the integration time of the integrator.
Comb, maintaining ranging accuracy without saturating the amplifier circuit
You.

Next, the operation of each circuit will be described in detail. When a known release switch (not shown) is pressed, the power of all the circuits in FIG. 1 including the CPU 70 is turned on prior to the distance measuring operation. Next, the CPU 70 clears the contents of the RAM 71 and determines the gain of the amplifier circuit 40. The light projecting circuit 10 is a driving circuit for driving the IRED 14, and includes a base resistor 11, a transistor 12, a current limiting resistor 13, and the IRED 14. When a pulsed light emission signal is output from the CPU 70, the base resistor 11 outputs the IRED 14 under the condition that the signal becomes high ("H") level.
And the IRED 14 emits light. The emitted light is condensed by the light projecting lens 1 and projected toward a subject (not shown). Part of the light reflected by the subject is collected again by the light receiving lens 2 and enters the PSD 3.

The current-voltage conversion circuit 20 and the current-voltage conversion circuit 30 constitute a light receiving circuit integrally with the PSD 3. When an optical signal is incident on the PSD 3, the PSD 3 outputs a current corresponding to the intensity and the incident position to the current-voltage conversion circuit 20 and the current-voltage conversion circuit 30. Current-voltage conversion circuit 20
Is a circuit comprising an amplifier 21 and a feedback resistor 22 and outputting a voltage proportional to the input current.
Has an amplifier 31 and a feedback resistor 32, has exactly the same configuration as the current-voltage conversion circuit 20, and outputs a voltage corresponding to the input current.

The switch 4 has a role of transmitting the output of one of the current-voltage conversion circuit 20 and the current-voltage conversion circuit 30 to a subsequent circuit, and its state is controlled by the CPU 70. It turns on the current-voltage conversion circuit 20 when measuring the distance of the long-distance signal of the PSD 3, and turns on the current-voltage conversion circuit 30 when measuring the distance of the short-distance signal.

The amplifying circuit 40 is an amplifying circuit capable of switching a gain. The coupling capacitor 5 is connected before the amplifier circuit 40, and the DC component of the input signal is cut off here. The amplification circuit 40 is a circuit composed of an amplifier 41 and two feedback resistors, and amplifies an input signal with a certain gain. The switch 46 and the switch 47 in the circuit
Has two switches, these switches are CPU
ON / OFF can be controlled by 70. Since the switch 46 turns on / off the feedback resistor 43 and the switch 47 turns on / off the feedback resistor 44, the gain of the amplifier 41 changes stepwise according to the state of these switches. Therefore, signal amplification is also performed in accordance with the stepwise changed gain, and is output to the integration circuit 50 in the subsequent stage. Since the amplifier circuit 40 performs inverting amplification, the polarity of the output voltage is opposite to the power supply voltage.

An integrating circuit 50 includes an amplifier 51 and an input resistor 5.
2, integrating capacitor 53, switch 54, voltage follower 5
5 is a circuit for integrating the input voltage with time. Prior to the integration operation, the switch 54 is turned on to discharge the charge remaining in the integration capacitor 53. When the discharge is sufficient, the switch 54 turns off. When the integration operation is started by turning on the switch 6, the integration capacitor 53
Stores the time integrated value of the input signal as electric charge. At this time, the voltage between the terminals of the integrating capacitor 53 is output to the comparator 61. When the integration operation is completed, the switch 6 turns off.

The level determining circuit 60 is a circuit for determining the level of the input voltage composed of the comparator 61, the reference power supply 63, and the reference power supply 64. Comparator 61
Is a digital signal such that the integrated voltage Vi is sequentially compared with the voltage V1 of the reference power supply 63 or the voltage V2 of the reference power supply 64 selected by the switch 62. If the integrated voltage Vi is higher, the digital signal becomes H level; The output voltage Vo is output to the CPU 70.

Next, the operation of the circuit according to the embodiment of the present invention will be described. When entering this distance measurement routine, first, the power supplies of all the circuits in FIG. 1 are turned on. Next, the CPU 70
The contents of 71 are cleared, and the gain of the amplifier circuit 40 is determined by a method described later. If the reflected light from the subject is very large during the operation of determining the gain, the close flag in the RAM 71 is set. In this case, it is determined that the distance is not measured and the close distance is determined. Then, the distance is measured by the current-voltage conversion circuit 20, and the value N1 is stored in the RAM 71. If the reflected light from the subject is very small during the distance measuring operation on the far side, the infinity flag in the RAM 71 is set.
In that case, it is determined to be infinity. Then, the distance is measured by the current-voltage conversion circuit 30, and the value N2 is stored in the RAM 71. When the distance measuring operation is completed as described above, it is determined that the infinity flag is set to infinity, and if the close flag is set, it is determined to be close. Otherwise, the values N1 and N2 stored in the RAM 71 are used. To calculate a value X. Value X
Is determined, the distance to the subject is determined by referring to the address of the ROM 72 uniquely determined by the value X as shown in FIG. 5, and the lens barrel 76 is driven by controlling the motor 75. Finally, the CPU 70 turns off the power of all the circuits in FIG. 1 and exits this routine. FIG. 4 shows a change of each part in FIG. 1 during the distance measuring operation.

Next, the operation of determining the gain of the amplifier circuit 40 will be described with reference to FIGS. First, the switch 4 is turned on by the CPU 70 to the current-voltage conversion circuit 20 side. The switch 62 is turned on to the reference power supply 63 side, and the switch 54 is turned on. This is the condition of FIG. 3a. The charge stored in the integrating capacitor 53 is discharged (FIG. 2a), and after sufficiently discharging, the switch 54 is turned off and the value N1 in the counter 73 is cleared to 0 (FIG. 2b). Then, the CPU 70 operates the light emitting circuit 10 to start emitting light. In order to secure the rise time of each amplifier at the start of light emission and to reduce the influence of power supply fluctuation, the integration circuit is activated after the time T1 (for example, 36 microseconds) has elapsed after light emission.
2 (for example, 64 microseconds). After that, the light emission / integration is stopped, and the apparatus stands by only for the time T5, and adds 1 to the counter.

As shown in FIG. 2, after repeating this operation a predetermined number of times Ng (for example, 10 times),
The switch 6 is turned off to output the voltage between the terminals of the integration capacitor 53, that is, the integration voltage Vi, to the comparator 61. The comparator 61 compares the voltage with the voltage V1 of the reference power supply 63, converts the result to a digital signal, and converts the result into a digital signal.
Output to The output of the comparator 61 is H
If the level is the level, the switch 46 is turned on. This is the condition of FIG. 3B, and the gain at this time is half that of the previous light projection as shown in FIG. Hereinafter, similarly, the integration operation and the comparison operation are repeated, and the output of the comparator 61 becomes H
If the level is the level, the switch 47 is turned on. This is the condition shown in FIG. 3C, and the gain at this time is one quarter that of the previous light projection, as shown in FIG. Even if all the switches are turned on, if the output of the comparator 61 is at the H level, a smaller gain cannot be set with this integration time.
The switch T4 is set to a time T3 (8 microseconds in this case), which is 1 / min and the equivalent gain is reduced to 1/8.
6 and 47 are opened, and the same processing is performed. This is Figure 3d
Is the condition.

At this time, the gain can be set to 1/8, 1/16, or 1/32 of the first light projecting operation, which correspond to the conditions of FIGS. 3d, 3e, and 3f, respectively. The operation of the switch 6 is indicated by a broken line in FIG. Still comparator 61
Becomes H level, the integration time during one light projection time is set to time T4 (1 microsecond in this case), which is 1/64 of time T2, and the equivalent gain is set to 64 minutes. 1
Then, the switches 46 and 47 are opened, and the same processing is performed. At this time, the gain can be set to 1/64, 1/128, and 256/1, which correspond to the conditions of FIGS. 3g, h, and i, respectively. Switch 6
Is indicated by the dotted line in FIG. If the integration time during one light emission period is time T4 and the output of the comparator 61 is still at the H level even when both the switches 46 and 47 are turned on, the reflected light from the subject is very large, and the subject is at a close distance. Since it can be considered that there is, the close flag is set and the process exits this routine. Otherwise, finally FIG.
Since any one of the gains i is selected, this condition is stored in an appropriate address in the RAM 71.

The same operation as described above is performed by the current-voltage conversion circuit 30.
Is performed, and any of the finally obtained gains a to i is compared with the gain obtained by the gain determination operation of the current-voltage conversion circuit 20.
47 and the integration time are set to the condition with the smaller gain.

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 54 is turned on, and the electric charge accumulated in the integration capacitor 53 is discharged. After sufficiently discharging the charge, the switch 54 is turned off. Then, the value N1 in the counter 73 is cleared to zero.
The switch 62 is turned on toward the reference power supply 64, and starts the distance measuring operation in the current / voltage conversion circuit 20. The method of distance measurement is as shown in FIG. While repeating the light emission, the value N1 is added, and when the integrated voltage Vi reaches the voltage V2 of the reference power supply 64, the light emission ends. However, if the distance to the subject is long and the predetermined number of times Nc is reached. V
If it does not reach 2, the reflected light from the subject is very small, so it is determined that the subject is at the infinity position.
Set the infinity flag in 1. Otherwise, the value N1 remaining in the counter 73 at the end of the distance measurement is stored in the RAM 7
1 is stored and the routine exits.

The distance measurement by the current-voltage conversion circuit 30 is almost the same. First, the switch 54 is turned on and the integrating capacitor 5 is turned on.
The charge accumulated in 3 is discharged. After sufficiently discharging the charge, the switch 54 is turned off. And the counter 74
The middle value N2 is cleared to 0. Subsequently, the operation proceeds to the distance measuring operation.
The method of distance measurement is as shown in FIG. The value N2 is added while repeating the light emission, and the light emission ends when the integrated voltage Vi reaches V2. Counter 74 at the end of ranging
Is stored in the appropriate address of the RAM 71, and the process exits from this routine.

The above is the operation of the circuit in this embodiment. The above operations are represented by flowcharts in FIGS.
become that way. First, the main routine will be described with reference to FIG. When entering the distance measurement routine, the CPU 70 turns on the power of the entire distance measurement circuit (S001), and the CPU 70 clears the contents of the RAM 71 (S002). Next, the final gain of the amplifier circuit 40 is determined by the current / voltage conversion circuit 20, and the gain is stored in an appropriate address of the RAM 71 (S003). At this time, if the close flag is set, the process jumps to S012 (S004). Further, the final gain of the amplifier circuit 40 is determined by the current / voltage conversion circuit 30, and the gain is stored at an appropriate address of the RAM 71 (S005). At this time, if the closest flag is set, the process jumps to S012 (S00).
6) Then, the gains obtained in S003 and S005 are read from the RAM 71 and compared, and the switches 46 and 47 of the amplifier circuit and the integration time are set to the condition of the smaller gain (S007).

Then, the distance is measured by the current / voltage conversion circuit 30, the value N1 is stored in an appropriate address of the RAM 71 (S008), the state of the infinity flag is checked, and if it is set, the process jumps to S012 (S012). S009). Similarly, distance measurement is performed by the current-voltage conversion circuit 30, and the value N2 is set to RA
It is stored in an appropriate address of M71 (S010). The values N1 and N2 stored in the RAM 71 are read out by the operations of the subroutines S008 and S010 to calculate the value X (S011). As a result, if the infinity flag is set, the distance to the object is determined by referring to the address of the ROM 72 (FIG. 5) uniquely determined by the value X. Ask (S
012), controlling the motor 75 to position the lens barrel 76 at an appropriate position.
Is driven (S013). Finally, the power supply of the distance measuring circuit is turned off (S014), and the process exits from this routine.

Next, the operation in each subroutine will be described. First, a subroutine for determining the gain of the amplifier circuit 40 will be described with reference to FIG. When the CPU 70 enters a subroutine for determining the gain of the amplifier circuit 40, the CPU 70 turns on the switch 4 on the current / voltage conversion circuit 20 side and switches the switch 62 on the reference power source 6
3 is turned on (S101), the switch 54 is momentarily turned on, and the electric charge accumulated in the integration capacitor 53 is discharged (S1).
02), the integration time is set to time T2, and the value N1 in the counter 73 is cleared to 0 (S103).

Subsequently, light emission is started by the CPU 70 (S104), and after waiting for a time T1 (S105),
While the switch 6 is turned on, the integration operation is performed for a predetermined time while performing the integration operation (S106). During this time, charge is stored in the integration capacitor 53 (S107). Then, the operation of the light projecting circuit 10 is stopped to end the light projecting operation, the switch 6 is turned off, the integration operation is finished (S108), the process waits for a time T5 (S109), and 1 is added to the counter 73 (S108).
110). If the value N1 in the counter 73 is less than the predetermined number Ng, the process jumps to S104 (S1).
11). If the value N1 is equal to or greater than the number Ng, the integrated voltage Vi is output to the comparator 61, and the comparator 61 compares the voltage with V1, and as a result outputs the output voltage Vo to the CPU 70.
(S112). The CPU 70 determines the level of the output voltage Vo (S113), and if it is at the H level, stores the states of the switches 46 and 47 and the integration time at that time (S114), and returns to the main routine. The conditions determined here are not changed until this distance measurement routine is exited.

When output voltage Vo is at L level, CP
U70 first checks the state of the switch 46 (S11).
5) If it is off, switch 46 is turned on and amplifier 41 is turned on.
After decreasing the gain of (S116), S102
Is jumped to (S117). If the switch 46 is on, the state of the switch 47 is checked. If the switch 46 is off, the switch 47 is turned on to reduce the gain of the amplifier 41 (S118), and then jump to S102 (S11).
9). If the switch 47 is on, the integration time is set to time T
3 (S120), and if it is longer than the time T3, the time is set to the time T3, the switches 46 and 47 are turned off, and the process jumps to S102 (S121). If the integration time is longer than the time T3, it is further compared with the time T4,
If the time is longer than the time T4, the time is set to the time T4, the switches 46 and 47 are turned off, and the process jumps to S102 (S122). If it is time T4, the closest flag in the RAM 71 is set (S123), and the process exits this subroutine and returns to the main routine. Since the gain determination operation by the current-voltage conversion circuit 30 is the same as that from S101 to S123 except that the switch 4 is first turned on to the current-voltage conversion circuit 30, the flowchart is omitted.

Next, a subroutine for distance measurement by the current / voltage conversion circuit 20 will be described with reference to FIG. When a subroutine for distance measurement by the current / voltage conversion circuit 20 is entered, the CPU 7
0 turns on the switch 4 on the current / voltage conversion circuit 20 side, turns on the switch 62 on the V2 side, further reproduces the switches 46 and 47 and the integration time stored in S114 (S201), and turns on the switch 54 for a moment. After discharging the charge accumulated in the integration capacitor 53 (S202),
The value N1 in the counter 73 is cleared to 0 (S20)
3). Subsequently, it is determined whether or not the value N1 is equal to or greater than the number of times Nc,
If the number is equal to or greater than the number Nc, the infinity flag in the RAM 71 is set and the process returns to the main routine (S205). If the number is less than Nc, the process jumps to S206 (S204).

Subsequently, light emission is started by the CPU 70 (S206), and after waiting for a time T1 (S207),
The switch 6 is turned on to start the integration operation (S208), and S
The integration operation is performed under the conditions stored in step 114 (S20).
9). During this time, charges are stored in the integration capacitor 53. Then, the operation of the light emitting circuit 10 is stopped to end the light emitting operation, the switch 6 is turned off, and the integration operation is completed (S21).
0), and waits for a time T5 (S211);
(S212), and outputs the integrated voltage Vi to the comparator 61. The comparator 61 calculates the voltage as V2
And outputs the output voltage Vo to the CPU 70 as a result (S213). The CPU 70 determines the level of the output voltage Vo (S214), and if it is at the H level, stores the value N1 in the counter 73 in the RAM 71 (S215) and returns to the main routine. If it is at the L level, the process jumps to S204.

Next, a subroutine for distance measurement by the current / voltage conversion circuit 30 will be described with reference to FIG. When the subroutine of the distance measurement by the current / voltage conversion circuit 30 is started, the CPU 7
0 turns on the switch 4 on the current-voltage conversion circuit 30 side, turns on the switch 62 on the V2 side, further reproduces the switches 46 and 47 and the integration time stored in S114 (S301), and turns on the switch 54 for a moment. After discharging the charges accumulated in the integration capacitor 53 (S302),
The value N2 in the counter 74 is cleared to 0 (S30)
3).

Subsequently, light emission is started by the CPU 70 (S304), and after waiting for a time T1 (S305),
While the switch 6 is turned on to perform the integration operation (S306), S
The integration operation is performed under the conditions stored in 114 (S30).
7). During this time, charges are stored in the integration capacitor 53. Then, the operation of the light emitting circuit 10 is stopped to end the light emitting operation, the switch 6 is turned off, and the integration operation is completed (S30).
8) Wait for time T5 (S309),
(S310), and outputs the integrated voltage Vi to the comparator 61. The comparator 61 calculates the voltage as V2
And outputs the output voltage Vo to the CPU 70 as a result (S311). The CPU 70 determines the level of the output voltage Vo (S312), and if it is at the H level, stores the value N2 in the counter 74 in the RAM 71 (S313) and returns to the main routine. If it is at the L level, the process jumps to S304. With the above operation, the distance to the subject is measured.

In this embodiment, the integration time during one light projection is set to three stages of 64, 8, and 1 microsecond, but it goes without saying that any value may be set. Also, the gain of the amplifier is 32 times, 16 times, and 8 times.
However, any number of switches and resistors can be used.

[0031]

According to the configuration of the present invention, the voltage between the terminals of the integrating capacitor is not converted into a digital signal, and the voltage of the integrating circuit is reduced .
Since the distance to the subject is calculated based on the number of pulse lights until the output signal reaches a predetermined value, highly accurate distance measurement can be performed with a simpler and less expensive circuit.

Since the integration time for obtaining the same effect as the gain setting can be made variable, the gain
Control is simpler than when only a variable gain amplifier circuit is used
The count value of the counting section is larger than the specified number
And the output signal of the integrator circuit becomes a predetermined value.
The distance to the subject based on the number of pulsed light
In the distance measuring device to be calculated, the distance measurement accuracy is low with a simple configuration.
The bottom can be prevented .

[Brief description of the 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 an embodiment of the present invention.

FIG. 3 is a diagram illustrating gains that can be set in an embodiment of the present invention.

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 calculating a distance from a value X according to the embodiment of the present invention;
Table on 72

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

7 is a flowchart showing a subroutine of a part for determining a gain of the amplifier circuit 40 in the flowchart of FIG. 6;

8 is a current-voltage conversion circuit 20 in the flowchart of FIG.
Flowchart showing the subroutine of the distance measurement part by using

9 is a current-voltage conversion circuit 30 in the flowchart of FIG.
Flowchart showing the subroutine of the distance measurement part by using

[Explanation of symbols]

Reference Signs List 10 light emitting circuit 3 semiconductor position detecting element (PSD) 20, 30 current / voltage conversion circuit 40 amplification circuit 50 integration circuit 60 level determination circuit 70 arithmetic circuit (CPU) 71 counting section

Continuation of the front page (56) References JP-A-62-260009 (JP, A) JP-A-5-5621 (JP, A) JP-A-61-240113 (JP, A) JP-A 64-105210 (JP) JP-A-1-205679 (JP, A) JP-A-1-288178 (JP, A) JP-A-4-351074 (JP, A) JP-A-5-280973 (JP, A) 6-67087 (JP, A) JP-A-5-306931 (JP, A) JP-A-2-12215 (JP, A) JP-A-62-165613 (JP, A) (58) Fields investigated (Int. G02B ^7/ 28-7/40 G01C 3/06

Claims (1)

(57) [Claims] 1. A light projecting means for irradiating a subject with a plurality of pulsed lights, a light receiving means for receiving reflected light from the subject, an integrating circuit for integrating an output signal of the light receiving means , and an output of the integrating circuit. The pulse until the signal reaches the predetermined value
Counting means for counting the number of light beams;
An arithmetic means for calculating a distance to the object based on the count value means, said integrating circuit measuring you and performing integral action of the operating time freely set within the light projecting time of the pulsed light Distance device.