JPH0713066A - Range finder for camera - Google Patents

Abstract

PURPOSE:To shorten the distance measurement time without lowering the distance measurement precision by integrating and comparing the output signal of a photodetecting element with a specific voltage and switching input registers of an integration circuit corresponding to the level. CONSTITUTION:A level decision circuit 60 compares the output of the integration circuit 50. i.e., an integrated voltage Vi with the reference V1 selected with a switch 62 and outputs the comparison result, i.e., an output voltage Vo to a CPU 70. While light projection is repeated. the switch 62 is turned ON to a reference voltage source 63 at the moment the integrated voltage Vi reaches V2 of a reference voltage source 64, and while similar operation is repeated. the operation is ended once the integrated voltage Vi reaches the reference V1. Further, while the light projection is repeated, the switch 6 is connected to the side of an input resistance 53 and the switch 62 is connected to the side of the reference voltage source 63 once the integrated voltage Vi reaches V2 of the reference voltage source 64 to attenuate the input signal to the integration circuit 50 to 1/10. Consequently, higher resolution than before is obtained.

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 which emits distance measuring light to a subject and receives reflected light from the subject to measure the distance.

[0002]

2. Description of the Related Art A conventional known active type distance measuring device projects 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 subject distance can be measured by electrically checking the incident position of the reflected light.

A semiconductor position detecting element (PSD) is often used as the light receiving element. The PSD has two output terminals, and each output terminal generates a current according to the intensity and position of incident light. By obtaining the ratio of the currents of the two channels or the two voltages corresponding thereto, a signal that depends only on the incident position of light can be obtained.

In such a distance measuring apparatus, a near infrared light projecting element (hereinafter referred to as IRED) is pulse-driven, and a signal from the PSD is AC-coupled to extract only a signal component and appropriately amplify it.
The amplified signal is integrated within the light emission time, the integration is repeated until the integrated voltage reaches a predetermined voltage, and the number of times up to that point is PS.
The magnitude of the signal from D is used.

When the number of integrations up to a predetermined voltage for the two outputs from the PSD is N1 and N2, it is possible to maintain stable ranging accuracy regardless of the reflectance of the object by obtaining the value X of the equation 1. Becomes

X = N1 / (N1 + N2) (1)

[0007]

In the method of obtaining the value X from the number of integration times N1 and N2 as described above, if N1 and N2 are increased in order to improve the distance measurement accuracy, the count error near the predetermined voltage becomes smaller. Although the distance measurement accuracy is improved, the distance measurement time becomes longer. On the other hand, if N1 and N2 are reduced, the count error near the predetermined voltage is reduced and the distance measurement time is shortened, but the resolution is reduced and the distance measurement accuracy is reduced.

[0008]

In order to solve the above problems, in the distance measuring apparatus for a camera of the present invention, a light projecting means for projecting pulsed light to a subject and a light reflected from the subject are received. Light receiving means, a current-voltage conversion circuit for converting the output signal of the light receiving means into a voltage corresponding thereto, an amplifier circuit for amplifying the output signal of the current-voltage conversion circuit, and an integration circuit for integrating the output signal of the amplifier circuit. A first reference voltage source for generating a predetermined voltage, a second reference voltage source for generating a predetermined voltage lower than the first reference voltage, and a voltage level of an output signal of the integrating circuit, First or the second
Comparing means for comparing with the output voltage of the reference voltage source, and computing means for computing the distance to the object from the output signal of the comparing means.

[0009]

The output signal of the light receiving element is integrated with normal accuracy until the integrated voltage reaches the second predetermined value which is lower than the first predetermined value, and the integration circuit operates from the second predetermined value to the first predetermined value. Switch the input resistance to and integrate with higher accuracy.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure 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 onto a subject. The light projecting circuit 10 is a drive circuit for driving the IRED 14, and includes a base resistor 11, a transistor 12, a current limiting resistor 13 and an IRED 14.
The PSD 3 receives the reflected light from the subject and outputs a signal according to the light receiving position to the current-voltage conversion circuits 20 and 30.

The current-voltage conversion circuit 20 and the current-voltage conversion circuit 30 are integrated with the PSD 3 to form a light receiving circuit. When an optical signal is incident on the PSD 3, the PSD 3 outputs a current according 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 which is composed of an amplifier 21 and a feedback resistor 22 and outputs a voltage proportional to an input current.
Has an amplifier 31 and a feedback resistor 32, and has exactly the same configuration as the current-voltage conversion circuit 20, and outputs a voltage according to the input current.

The switch 4 has a role of transmitting the output of either the current-voltage conversion circuit 20 or the current-voltage conversion circuit 30 to a circuit in the subsequent stage, and the state thereof is controlled by the CPU 70. When the distance is measured using the long distance side signal of the PSD 3, it is turned on to the current-voltage conversion circuit 20 side, and when the distance is measured using the short distance side signal, it is turned on to the current voltage conversion circuit 30 side.

The subsequent amplifier circuit 40 amplifies the signal selected by the switch 4. Due to inverting amplification, the polarity of the output signal is opposite to the power supply voltage.

The switch 6 includes an amplifying circuit 40 and an integrating circuit 50.
, And the input resistance of the amplifier 51 in the integration circuit 50 is determined to be either the input resistance 52 or the input resistance 53. The input resistor 52 has a resistance value that is one tenth of that of the input resistor 53. Therefore, the amplifier 51 when the input resistor 53 is selected.
The gain is 1/10 of that when the input resistor 52 is selected. Further, it is possible to select neither circuit, and in this case, the output of the amplification circuit 40 is not transmitted to the integration circuit 50.

The integrating circuit 50 includes an amplifier 51 and an input resistor 5
2, input resistor 53, integrating capacitor 54, switch 5
5. A circuit for integrating the input voltage with time, which is composed of a voltage follower 56. A switch 55 is provided to discharge the electric charge remaining in the integration capacitor 54 prior to the integration operation.
Turns on. When discharged sufficiently, the switch 55 is turned off. When the integration operation is started by turning on the switch 6,
The integrating capacitor 54 stores the time integrated value of the input signal in the form of electric charge. The value of the voltage between the terminals of the integrating capacitor 54 at this time is output to the comparator 61. When the integration operation is completed, the switch 6 is turned off.

The level judging circuit 60 is a circuit for judging the level of the input voltage which is composed of a comparator 61, a reference voltage source 63 and a reference voltage source 64. The comparator 61 compares the integrated voltage Vi with the voltage V1 of the reference voltage source 63 or the voltage V2 of the reference voltage source 64 selected by the switch 62, converts the result into a digital signal output voltage Vo, and outputs it to the CPU 70. The level determination circuit 60 switches the output of the integration circuit 50, that is, the integrated voltage Vi, to the switch 6
It is compared with the reference V1 selected by 2 or the comparison result, that is, the output voltage Vo is output to the CPU 70.
The CPU 70 includes a RAM 71, a ROM 72, a counter 73,
Data is transmitted to and received from the counter 74, and the light projecting circuit 1
0 and a drive signal are output to the motor 75. Motor 75
Drives the lens barrel 76.

Next, the operation of the circuit according to the embodiment of the present invention will be described. When a known release switch (not shown) is pressed, the CPU 70 enters a distance measuring routine and first turns on the power supplies of all the circuits in FIG. Next, the CPU 70 is a RAM
The contents of 71 are cleared and a pulsed light emitting signal is output to the light emitting circuit 10. The signal of the base resistor 11 is high ("
Drive the IRED 14 under the condition that the H ") level is reached.
The ED 14 emits light. The emitted light is condensed by the light projecting lens 1, part of it is reflected by a subject (not shown), and part of the reflected light is condensed again by the light receiving lens 2 and enters the PSD 3.

First, 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, the switch 62 is turned to the reference voltage source 64 side, and the switch 6 is turned to the input resistor 52 side.
Next, the switch 55 is turned on to discharge the electric charge accumulated in the integrating capacitor 54. After discharging the electric charge sufficiently, the switch 55 is turned off. And the value N1 in the counter 73
Is cleared to 0. Next, the distance measuring operation in the current-voltage conversion circuit 20 is started, and the distance measuring method is as shown in FIG. While repeatedly projecting light, 10 is added to the value N1, and when the integrated voltage Vi reaches V2 of the reference voltage source 64, the switch 62 is turned on toward the reference voltage source 63, and the same operation is repeated again. Add 1 to the value N1,
The process ends when the integrated voltage Vi reaches V1. If the distance to the subject is too long, a predetermined number of times Nc
If it does not reach V2 even if only the light is projected, it is determined to be infinity,
The infinity flag in the RAM 71 is set and the process ends. In other cases, the value N1 remaining in the counter 73 at the end of the distance measurement is stored in the RAM 71 at an appropriate address.

Subsequently, the CPU 70 controls the current-voltage conversion circuit 30.
Distance measurement by. First, the switch 4 is turned on to the current-voltage conversion circuit 30 side, the switch 62 is turned to the reference voltage source 64 side, and the switch 6 is turned to the input resistor 52 side. Next, the switch 55 is turned on to discharge the electric charge accumulated in the integrating capacitor 54. After fully discharging the charge, switch 5
5 turns off. Then, the value N2 in the counter 74 is cleared to 0. Next, the distance measuring operation in the current-voltage conversion circuit 30 is started, and the distance measuring method is as shown in FIG. While repeatedly projecting light, 10 is added to the value N2, and when the integrated voltage Vi reaches V2 of the reference voltage source 64, the switch 6
To the input resistor 53 side, and the switch 62 to the reference voltage source 63
, And turn on the input signal to the integrating circuit 50 to 1
Attenuate to 1/0. Therefore, higher resolution can be obtained. While repeating the same operation again, the value N
One is added to 1, and the process ends when the integrated voltage Vi reaches V1. The value N2 remaining in the counter 74 at the end of the distance measurement is stored in an appropriate address of the RAM 71.

When the above distance measuring operation is completed, the CPU 70
Calculates the value X using the values N1 and N2 stored in the RAM 71 if the infinity flag is set to infinity, and if not set. When the value X is determined, the distance to the object is obtained by referring to the address of the ROM 72 that is uniquely determined by the value X as shown in FIG. 4, and the motor 75 is controlled to drive the lens barrel 76 according to the result. Finally, the CPU 70 turns off the power of all the circuits in FIG. 1 and exits this routine. FIG. 3 shows changes in each part of FIG. 1 during the distance measuring operation.

The above is the operation of the circuit in this embodiment. The above operation is shown in a flow chart in FIGS.
become that way. First, the main routine will be described with reference to FIG. When this distance measuring routine is entered, the CPU 70 turns on the power supply of the entire distance measuring circuit (S001), and the CPU 70 clears the contents of the RAM 71 (S002). Then, the distance is measured by the current-voltage conversion circuit 20, and the value N1 is set in the RAM 7
1 is stored (S003), the state of the infinity flag is checked at the same time, and if set, the process jumps to S009 (S004). Similarly, the current-voltage conversion circuit 30 measures the distance, stores the value N2 in the RAM 71 (S005), and reads the values N1 and N2 stored in the RAM 71 by the operations of the subroutines S003 and S005 to calculate the value X. Yes (S006). As a result, if the infinity flag is set, it is at infinity, otherwise, as shown in FIG. 4, a predetermined ROM 72 that uses the value of X as an offset value.
The distance to the subject is obtained by referring to the address (S
007). Finally, turn off the power of the distance measuring circuit (S00
8) Exit this routine.

Next, the operation within each subroutine will be described. First, a subroutine for distance measurement by the current-voltage conversion circuit 20 will be described with reference to FIG. When entering the distance measurement subroutine by the current-voltage conversion circuit 20, the CPU 70 turns on the switch 4 to the current-voltage conversion circuit 20 side (S101),
After turning on the switch 55 for a moment to discharge the electric charge accumulated in the integrating capacitor 54 (S102), 0 is assigned to the value N1 and 10 is assigned to the value n in the counter 73, the switch 62 is turned on to the V1 side, and the switch is turned on. The input resistor 52 is selected at 6 (S103). Subsequently, it is determined whether or not the value N1 is the number Nc or more. If the number Nc or more, the infinity flag in the RAM 71 is set and the process returns to the main routine (S10).
5). If it is less than the number of times Nc, jump to S106 (S
104).

Subsequently, the CPU 70 starts light emission (S106) and waits for a time T1 (S107).
The switch 6 is turned on (S108), and the integration operation is performed for the time T2 (S109). During this time, the charge is stored in the integrating capacitor 54. Then, the operation of the light projecting circuit 10 is stopped to end the light projecting operation, the switch 6 is turned off to complete the integrating operation (S110), and waits for a time T3 (S111).
The value n is added to the counter 73 (S112). CPU7
0 determines the level of the output voltage Vo (S113), and if it is at L level, jumps to S104. If it is at the H level, it is next determined whether or not the switch 62 is selecting V2. If V2 is selected, the value N1 in the counter 73 is stored in the RAM 71 (S114) and the process returns to the main routine. If V1 is selected, 1 is substituted for the value n, the reference voltage is set to V2, the input resistor 53 is selected, and the process jumps to S104.

Next, a subroutine for distance measurement by the current-voltage conversion circuit 30 will be described with reference to FIG. When the subroutine for distance measurement by the current-voltage conversion circuit 30 is entered, the CPU 7
0 turns on the switch 4 to the current-voltage conversion circuit 30 side, turns on the switch 62 to the V2 side (S201), and switches 5
After turning on 5 for a moment to discharge the electric charge accumulated in the integrating capacitor 54 (S202), 0 is assigned to the value N2 and 10 is assigned to the value n in the counter 73, and the switch 62 is set to V1.
And the switch 6 selects the input resistor 52 (S
203).

Subsequently, the CPU 70 starts light emission (S204) and waits for a time T1 (S205).
The switch 6 is turned on (S206), and the integration operation is performed for the time T2 (S207). During this time, the charge is stored in the integrating capacitor 54. Then, the operation of the light projecting circuit 10 is stopped to end the light projecting operation, the switch 6 is turned off, the integrating operation is completed (S208), and the process waits for time T3 (S20).
9), the value n is added to the counter 74 (S210). C
The PU 70 determines the level of the output voltage Vo (S21
1) If it is H level, the value N2 in the counter 74 is RA
Store in M71 (S212) and return to the main routine.
If V1 is selected, substitute 1 for the value n and set the reference voltage to V
Set to 2, select the input resistor 53, and jump to S204. With the above operation, the distance to the subject is measured.

As another embodiment of the present invention, the integration time is set to 2
Until the second predetermined value, which has a kind and an integration voltage lower than the first predetermined value, repeats the integration with the longer integration time, and from the second predetermined value to the first predetermined value with the shorter integration time. The same effect as that of the first embodiment of the present invention can be obtained by repeating the integration and adding N1 and N2 respectively according to the ratio of the integration time.

According to another embodiment of the present invention, a plurality of gains of the amplifier circuit are provided, and integration is repeated at the higher gain until the second predetermined value where the integrated voltage is lower than the first predetermined value. From the predetermined value of 1 to the first predetermined value, the integration is repeated at the lower gain side, and N1 and N2 are similar to those of the first embodiment of the present invention as long as values corresponding to the gain ratios are added. The effect is obtained.

[0028]

According to the structure of the present invention, the output signal of the light receiving element is integrated and compared with a specific voltage, and the input resistance of the integrating circuit is switched according to the level thereof, so that the ranging accuracy is not lowered. , Distance measurement time can be shortened.

[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 an embodiment of the present invention.

FIG. 3 is an operation diagram illustrating a series of operations during distance measurement according to the embodiment of the present invention.

FIG. 4 is a ROM for obtaining a distance from a value X according to the embodiment of the present invention.
Table on 72

FIG. 5 is a main flow chart showing the operation of the embodiment of the present invention.

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

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

[Explanation of symbols]

 10 Light emitting circuit 3 Semiconductor position detecting element (PSD) 20, 30 Current-voltage conversion circuit 40 Amplifying circuit 50 Integrating circuit 63, 64 Reference voltage source 60 Level determination circuit 70 Operation circuit (CPU)

Claims (4)

[Claims] 1. A light projecting means for projecting pulsed light onto a subject, a light receiving means for receiving reflected light from the subject, and a current-voltage conversion circuit for converting an output signal of the light receiving means into a voltage corresponding thereto. An amplification circuit for amplifying the output signal of the current-voltage conversion circuit, an integration circuit for integrating the output signal of the amplification circuit, a first reference voltage source for generating a predetermined voltage, and a first reference voltage A second reference voltage source for generating a predetermined voltage that is lower than the above, a comparing means for comparing the voltage level of the output signal of the integrating circuit with the output voltage of the first or the second reference voltage source, and the comparing means. In the distance measuring device, which has distance calculating means for calculating the distance from the output signal of the above-mentioned object to the subject, and which uses the number of integrations until the integrated voltage reaches a predetermined first voltage as the distance data. It is a predetermined value of 1 A range finder for a camera, characterized in that the level of the integral input is switched after reaching a second lower predetermined value. 2. The range finder for a camera according to claim 1, wherein the level of the integration input switches the input resistance value of the integration circuit. 3. The range finder for a camera according to claim 1, wherein the level of the integration input switches integration time. 4. The range finder for a camera according to claim 1, wherein the level of the integral input switches the gain of the amplifier circuit.