JP3142731B2 - 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 an active distance measuring apparatus (hereinafter abbreviated as active AF) for obtaining distance information by, for example, projecting light from a camera and measuring light reflected from an object to be measured. is there.

[0002]

2. Description of the Related Art Conventionally, an infrared light emitting device (IRED) and a PS
I emitted from the camera in combination with D or SPC
2. Description of the Related Art A distance measuring apparatus that obtains a distance by receiving light reflected by an object of an RED by a light receiving unit such as a PSD is well known.

In a distance measuring device using a PSD, P
The difference signal (F−N) between the two outputs F and N of SD is normalized with respect to the sum signal (F + N) by the double integration method, and the accuracy is high regardless of the subject reflectance or the intensity of light from the subject. Distance measuring devices that enable distance measurement are also well known. At this time, when F ≒ N (when the subject is located at a middle distance),
Since the integration at the predetermined integration time becomes almost zero (FN ≒ 0), it is necessary to distinguish it from infinity without exceeding the reference value. Therefore, a distance measuring device disclosed in Japanese Patent Application Laid-Open No. 61-90006 discloses a sum signal (F +
The integration of N) is continued for a predetermined period of time, and whether the distance is infinity or a medium distance is distinguished based on whether or not the integration value is larger than a reference value.

At present, most of the distance measuring devices of cameras use a microcomputer, and in this case, the only signals sent to the microcomputer are a comparator signal of a reference voltage and an integrated voltage and a signal obtained by A / D conversion of the integrated voltage. . Then, the microcomputer latches the comparator signal at the time when the integration of the difference signal (F−N) is completed, measures the time until the comparator signal is inverted by integration of the sum signal (F + N), and obtains the distance based on this time. ing.

[0005]

However, just F
When = N, the integration of the difference signal (F-N) also becomes zero, and the signal of the comparator that compares the reference voltage and the integrated voltage becomes indeterminate within a range of several mV. Then, the comparator signal latched by the AF control circuit may be different from the comparator signal latched by the microcomputer. Since the integration of the time difference signal (F−N) is small and the sum signal (F + N) is large, it is determined that the distance is a finite distance. However, the microcomputer cannot detect the inversion (zero cross) of the comparator.
This is because the comparator signal must be integrated in the opposite direction to the comparator signal.
If the comparator signal latched by the F control circuit is the opposite, the signal will be integrated in the same direction as the signal when viewed from the microcomputer. As a result, the inversion of the comparator cannot be detected, so the integration time of the sum signal (F + N) will be Depending on the direction of the comparator, the distance may be maximum and the distance may be erroneously measured if the distance is closest or infinite. SUMMARY OF THE INVENTION It is an object of the present invention to provide a distance measuring apparatus that can always accurately measure a distance with a microcomputer without changing an AF control circuit even when a comparator becomes unstable at a medium distance.

[0006]

According to a first aspect of the present invention, there is provided a configuration for receiving light reflected from a measuring object to change the distance depending on the distance of the measuring object. A light receiving means for outputting a first signal and a second signal, and a difference integration operation for integrating a difference between the first and second signals of the light receiving means for a predetermined time, and after completion of the difference integration operation. Integrating means for performing an inverse integration operation for performing an inverse integration of the sum of the first signal and the second signal; and distance information for obtaining a distance information by detecting a reverse integration time until an output level of the integration means returns to an initial value. In a distance measuring device having a detecting means, an infinity determining means for performing an infinity determination according to an output level of the integrating means after a lapse of a certain infinity determining time from a start point of the back integration, Not determined, incorrect back integration time Inverse integration time to a minimum when knowledge is the minimum time to the distance measuring apparatus characterized by having a false positive determination means and inverse integration time in said distance information detecting means.

In this configuration, even if the first signal and the second signal are determined to be finite by the infinity determination means in the middle distance where they are substantially the same, if an erroneous detection of the inverse integration time occurs, the inverse integration is performed. Since the time is set to the minimum time, the closest distance or the farthest distance at which the inverse integration time becomes the maximum is not determined, and the middle distance can be accurately determined.

The erroneous detection determining means includes an output level of the integrating means after integrating the signal difference for a predetermined time, and an output level of the integrating means after integrating the sum of the signals for a fixed infinite determination time. Erroneous detection of the inverse integration time can be determined from the inverse integration time, so that the control device on the side of the distance information detecting means composed of a microcomputer or the like does not need to change the conventional AF control circuit. Such a configuration can be realized by programming.

[0009]

1 to 8 show an embodiment of the present invention.

FIG. 1A is a block diagram showing the concept of active AF.

1 is a PSD (Position Sens).
2) an IRED, 3 an AF control circuit, 4 an A / D conversion circuit for A / D conversion of the INT output, 5 a timer for measuring the integration time, 6 a microcomputer, 7 a subject It is. The spot projected from the camera by the IRED is reflected by the subject 7 and returns to the PSD 1. At this time, the distance to the subject can be determined from where on the PSD 1 the reflected light (spot) of the IRED 2 is formed. By the way, when the subject is near, PSD1
Spot is imaged from Near, Far when far
More spots are imaged. PSD1
After integrating the two signal outputs F and N with the difference signal (F−N) for a predetermined time, the inverse integration time until the sum signal (F + N) is inversely integrated and returned to the reference voltage is obtained by the timer circuit 5. From the microcomputer 6 to obtain the distance to the subject. Also,
In order to determine infinity or the like, the A / D conversion circuit 4 uses the integral
T is A / D converted and the microcomputer 6 makes a judgment.

FIG. 1B shows a part of the AF control circuit 3 for performing particularly integration.

Reference numeral 8 denotes an amplifier for the sum signal (F + N), and reference numeral 9 denotes an amplifier for the difference signal (F−N). When integrating the difference signal (FN), the analog SW 11 is turned on and the integrator 1 is turned on.
Integrate with 2. When integrating the sum signal (F + N),
The analog SW 10 is turned on, and the integrator 12 performs integration.
The integrated output INT is subjected to A / D conversion by the A / D conversion circuit 4 and input to the microcomputer 6. The comparator 13 determines whether the integration is an upward integration or a downward integration, and also inputs a comparator signal COMP to the microcomputer 6.

FIGS. 3 to 7 show differences in time charts depending on the distance of the comparator signal COMP between the integrated voltage INT, the reference voltage KVC, and the integrated voltage INT at the time of distance measurement. FIG. N), FIG. 4 shows a case of long distance (F> N), FIG. 5 shows a case of short distance (F <N), FIG. 6 shows a case of medium distance (F ≒ N), and FIG. ≒ 0, N
≒ 0).

In the period, the integral voltage INT is changed to the reference voltage KVC.
Adjust the voltage to the same as above. At this time, it is undefined which of the comparator signal COMP of the comparator 13 is Low or Hi. In addition, the gain of the amplifier is adjusted to keep the output of PSD1 constant irrespective of the subject distance and the reflectance. This is called AGC, and when the gain decreases, AGC is applied.

In the period, the difference signal (F
-N). When the integration is started, the comparator signal COMP is stabilized.

During the period, the microcomputer 6 latches the comparator signal COMP to determine whether or not to perform infinite determination. The infinity determination is to determine whether the subject is at an intermediate distance or infinitely by continuing integration for a predetermined time even after the comparator signal COMP is inverted by integration of the sum signal (F + N). AGC is not applied, and the integral value Vsm of the difference signal (FN) in the period is not used.
When all is smaller than a predetermined reference value Vsmm, a flag for performing the infinite determination is set. Where V
"small" is obtained by subjecting the integrated voltage INT to A / D conversion by a microcomputer.

In the period, the sum signal (F + N) is integrated,
Time Tin until the comparator signal COMP is inverted
Measure t.

When the infinite decision is made in the period, the integration of the Tref time is continued even after the comparator signal COMP is inverted.

In the period, the distance is obtained from the time Tint and the comparator signal COMP.

FIG. 8 is a model diagram of the relationship between time Tint.COMP and distance. Comparator signal COMP = Lo
At w, when the time Tint is large, the subject is far, and the time Tint decreases as the subject gets closer. When the distance is medium, the time Tint is the shortest, and when the distance is short, the comparator signal COMP becomes Hi.
int increases. As described above, the subject distance can be temporarily obtained by calculation from the time Tint and the comparator signal COMP according to the characteristic diagram of FIG.

When the subject shown in FIG. 4 is at a long distance (F> N), the integrated output INT is integrated below the reference voltage KVC in a period. The integration is suspended during the period, and C
The microcomputer latches the OMP signal. Since the voltage is integrated below the reference voltage KVC, the microcomputer 6 latches the CO
The MP signal becomes Low. The integration of the sum signal (F + N) is performed during the period, and when the COMP signal is inverted (becomes Hi), the integration is stopped, and the Tint time at this time and the latched CO
The distance is obtained according to the characteristic diagram when the MP signal is low.
When the subject shown in FIG. 5 is at a short distance (F <N), the signal is integrated above the reference voltage KVC during the period, and the COMP signal becomes H
The distance is obtained according to a characteristic diagram of the time Tint until the COMP signal is inverted in the period and the COMP signal Hi.

By the way, the object shown in FIG.
In the case of (≒ N), the integral value of the difference signal (F-N) in the period becomes small. Further, the subject shown in FIG. 7 is infinite (F ≒ 0,
Also when N ≒ 0), the integral value of the difference signal (F−N) in the period is small, so whether the integral value is small at a medium distance or infinite and no signal is output and the integral value is small ends the period. Cannot be determined at that point.

Therefore, when the integrated value of the difference signal (FN) does not exceed Vsmm in the period, the sum signal (F + N) is integrated in the period, and the time Tint until the COMP signal is inverted is obtained. The integration is continued thereafter, and the integrated value Vsma obtained when the integration is performed for Tref of the same time as the period
It is determined whether the distance is infinity or middle distance based on the size of ll. This is referred to as “infinite judgment”. At this time, although not shown, a predetermined reference value Vinf is compared with Vsmall to obtain Vsm.
If all is large (in the case of FIG. 6), it is determined that the distance is medium,
Time Tint and COMP until the COMP signal is inverted
The distance is obtained from the characteristic diagram according to the signal Hi. Further, when the predetermined reference value Vinf is larger (in the case of FIG. 7).
Makes the distance infinite regardless of the time of Tint. In the case of infinity, the signal of PSD1 hardly appears and the noise becomes larger. For this reason, in the example of FIG. 7, the COMP signal is inverted, but depending on the situation, the distance measurement may end without being inverted, and the Tint becomes less reliable (S / N becomes worse). Therefore, when the integral value is small, the distance is forcibly set to infinity.

When the object is at a middle distance and especially when F = N as shown in FIG. 3, the difference signal (FN) in the period is obtained.
Becomes zero, and the COMP signal becomes indefinite in the range of several mV. During this period, the microcomputer 6 latches at either Hi or Low even if the COMP signal is undefined. At this time, the AF control circuit 3 also latches the COMP signal, and performs inverse integration with the latched direction during the period. Therefore, when COMP is undefined, the microcomputer 6 latches C
The OMP signal and the COMP signal latched by the AF control circuit 3 are opposite, and the microcomputer 6 sees that the AF control circuit 3 integrates in the same direction as the period.
The microcomputer 6 finishes the integration of the predetermined Tref time without detecting the inversion of the COMP signal, and Tint is the maximum Tr.
ef. Also, since the integral value Vsmall becomes larger than a reference value Vinf (not shown), the C
Depending on the direction of the OMP signal, it is determined that the distance is the closest or farthest even though the distance is actually a middle distance. The above operation for preventing such erroneous distance measurement will be described with reference to a flowchart shown in FIG.

When the distance measuring operation is started (100), 10
1 = constant signal regardless of subject distance or reflectance
Adjust the amplifier gain to get out of D1. At this time, the gain is gradually reduced in descending order of gain so that an appropriate signal amount is obtained by the PSD1 signal when the IRED2 is turned on. Note that the case where the gain has decreased is referred to as “AG
It took C "(period).

The integration of the difference signal (F-N) is started at 102, the integration of Tref time is performed at 103, the integration is temporarily stopped at 104 (period), and the integration INT is higher or lower than 105 at 105. Is latched as a COMP signal.

At 106 and 107, the AGC is not applied and the integrated value Vsmall of the period is equal to the predetermined reference value Vsm.
If it is smaller than m, a flag is set (period) to perform "infinite determination" to continue integration even when the integration period of the sum signal (F + N) crosses zero at 108 (period). 109 at C
A timer for measuring the time until the OMP signal is inverted is started, integration of the sum signal (F + N) is started at 110, and it is checked at 111 whether or not the COMP signal latched at 105 is inverted.

In step 111, when the COMP signal is not inverted, it is checked whether the integration time exceeds Tref, and the integration time is set to Tref time at the maximum. This is because the signal obtained by integrating the difference signal (F−N) during the period Tref during the period is integrated with the sum signal (F + N) during the period.
This is because the sum signal naturally becomes larger and does not take longer than the Tref time until the COMP signal is inverted. Also,
When the COMP signal is inverted at 111, the timer is stopped at 113 and the time at that time is set as Tint.

If the flag at 108 is set at 114, the integration is continued, and at 115, the integration time of the sum signal (F + N) is set to Tref. If the flag at 108 is not set at 116, the Tint at 113 at 120 and the latching of the COMP signal at 105 from FIG.
Find the distance as indicated by.

If the flag is set at 116, the integrated value Vsmall of the sum signal (F + N) from the period is compared with a predetermined integrated value Vinf at 117, and Vs
When mall is small, it is assumed that the distance is infinite at 121. Also, when Vsmall is large, Tint at 118
Is smaller than the maximum integration time Tref (Tint does not become larger than Tref), the distance is obtained at 120. Then, when Tint becomes equal to Tref at 118, the COMP signal is indefinite in the period and COMP
Means that the microcomputer could not detect the reversal of Tint.
Find the distance with.

[0032]

According to the first aspect of the present invention, even if the first signal and the second signal are determined to be finite by the infinity determination means in the case of a middle distance where they are substantially the same, the inverse integration time is reduced. When the false detection is made, the inverse integration time is set to the minimum time, so that the intermediate distance can be accurately determined without determining the closest or farthest distance where the inverse integration time is the maximum.

According to the invention described in claim 2, the conventional A
Such a configuration can be realized by programming on the side of the distance information detecting means constituted by a microcomputer or the like without changing the F control circuit.

[Brief description of the drawings]

1A and 1B show an embodiment of the present invention, in which FIG. 1A is a block diagram, and FIG. 1B is a circuit diagram showing a part of an AF control circuit.

FIG. 2 is a flowchart showing the operation of one embodiment of the present invention.

FIG. 3 is a time chart of an integration output INT and a COMP signal, showing a case of a medium distance (F = N).

FIG. 4 is a time chart of the integration output INT and the COMP signal, showing a case of a long distance (F> N).

FIG. 5 is a time chart of the integration output INT and the COMP signal, showing a case of a short distance (F <N).

FIG. 6 is a time chart of the integration output INT and the COMP signal, showing a case of a medium distance (F ≒ N).

FIG. 7 is a time chart of the integration output INT and the COMP signal, showing the case of infinity (F ≒ 0, N ≒ 0).

FIG. 8 is a diagram showing a relational model between Tint · COMP and a distance.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... PSD sensor 2 ... IRED 3 ... AF control circuit 4 ... A / D conversion circuit 5 ... Timer circuit 6 ... Microcomputer 7 ... Subject

Claims (2)

(57) [Claims] 1. A light receiving means for outputting a first signal and a second signal which change depending on the distance of a measurement object by receiving reflected light from the measurement object, and a first light receiving means of the light receiving means.
Integrating means for performing a difference integration operation for integrating a difference between the second signal and the second signal for a predetermined time, and performing an inverse integration operation for performing an inverse integration of a sum of the first signal and the second signal after the end of the difference integration operation. A distance information detecting means for detecting a reverse integration time until the output level of the integrating means returns to the initial value to obtain distance information, wherein a certain infinite determination time has elapsed since the start of the back integration. Infinity determination means for performing infinity determination in accordance with the output level of the integration means later; and when the infinity determination means does not determine infinity and the reverse integration time is erroneously detected, the inverse integration time is minimized. And an erroneous detection determining means for setting an inverse integration time in the distance information detecting means. 2. The erroneous detection determining means according to claim 1,
From the output level of the integration means after integrating the signal difference for a predetermined time, the output level of the integration means after integrating the sum of the signals for a certain infinite determination time, and the inverse integration time, the error of the inverse integration time is determined. A distance measuring device for determining detection.