JPS6379010A - Distance measuring apparatus - Google Patents

Abstract

PURPOSE:To enable accurate measurement of distance regardless of pulse-like noise received, by a method wherein the measurement of distance by the emission of light beam is repeated twice continuously and the third distance measurement is performed at a timing avoiding the incidence of noise light when the results of the measurement differ. CONSTITUTION:When a shutter release of a camera is depressed, a clock pulse is supplied from a terminal 7 and a decoder 4 generates an emission driving pulse 8 at a specified timing to emit light with a driving circuit 2 from a light emitting element 1. Then, the decoder 4 generates a driving pulse 9 at a timing after the passage of a specified time to emit second pulse light from the element 1. On the other hand, a light receiving element 11 receives reflected light of the emission light from an object to compute 13 distance and the results of the measurement is latched by latch circuits 14 and 15 respectively. Outputs of the circuits 14 and 15 are applied to a coincidence judging circuit 16 and outputs an H level to make an AND gate 6 for passage when non-coincidence is judged and a driving pulse 10 is generated from the decoder 4 at a specified timing avoiding the incidence of noise light. The results of the third distance measurement are latched by the circuit 14 to be a distance measurement output 17.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a distance measuring device used for autofocus of a camera and the like.

(Prior Art) Conventionally, distance measuring devices used in cameras, etc., use a triangular distance measuring method to emit pulsed light from a light-emitting element to a subject, and then direct the reflected light from the subject to the light-emitting element by a baseline length. Light is received by a light-receiving element placed at a distant position, and the distance to the subject is measured based on the receiving position of the reflected light.

(Problems to be solved by the invention) However, such conventional distance measuring devices always have the following problems:
When the subject is illuminated with a fluorescent lamp, etc., the illumination light also enters the light receiving element, and in the case of fluorescent lamps, the illumination light also becomes a kind of pulsed light, so the pulsed light for distance measurement and the pulsed light from the illumination are separated. If the timings of the two overlap, it is impossible to separate the light reception signal for distance measurement from the noise signal caused by the illumination light, and a problem arises in that the illumination light causes erroneous distance measurement results.

(Means for Solving the Problems) The present invention has been made in view of such conventional problems, and it is possible to accurately measure the distance to an object even when pulsed noise light is incident from illumination or the like. The object of the present invention is to provide a distance measuring device that can perform measurements.

To achieve this objective, the present invention provides a distance measuring device that emits a light beam from a light emitting element, receives reflected light from a subject with a light receiving element, and calculates the distance to the subject from the received light signal. Continuous distance measurement by beam firing 2 times
If the first and second distance measurement results are different, it is determined that the distance measurement was incorrect due to noise light, and the third distance measurement is performed without receiving the noise light. This is done at a predetermined timing.

(Function) According to the configuration of the present invention, if the first and second distance measurement results are different, an error due to reception of noise light due to illumination light such as a fluorescent lamp may be detected in one of the distance measurements. In this case, for example, since the pulse width and period of the noise light are known in advance for the illumination light of a fluorescent lamp, a predetermined distance measurement that is not subject to the incidence of noise light can be determined. It was decided to conduct the third distance measurement at the timing, and the third distance measurement was carried out.
Correct distance measurement results that are not affected by noise light can be obtained by the second distance measurement.

Of course, if the first and second distance measurement results match, both distance measurement results will be determined to be correct and the third distance measurement will not be performed.

(Example) FIG. 1 is a block diagram showing one embodiment of the present invention.

First, the configuration will be described. Reference numeral 1 denotes a light emitting element, which emits pulsed light having a predetermined pulse width TW toward a subject based on a light emission drive pulse sent to a drive circuit 2. This drive circuit 2
The light emission drive of the light emitting element 1 is performed by a counter 3 and a decoder 4.
, an OR gate 5 and an AND gate 6.

That is, when the shutter release button of the camera is pressed, distance measurement control is started, and a clock pulse is supplied to the counter 3 from the terminal 7, and the counter 3 counts this clock pulse. The count value of the counter 3 is decoded by a decoder 4, and the decoder 4 generates a light emission drive pulse 8 with a pulse width Tw at a predetermined timing to, and causes the light emitting element 1 to emit light by the drive circuit 2 via an OR gate 5. Then, the first light emission drive is performed. Further, the decoder 4 generates a drive pulse 9 having the same pulse width TW at the timing t1, which is a predetermined time T1 after the first light emission drive at the time to, and activates the drive circuit 2 via the OR gate 5. By doing so, the light emitting element 1 emits the second pulsed light to the subject.

Further, the decoder 4 records the elapsed time T2, which is preset based on the emission pulse width and repetition period of the fluorescent lamp, from the second pulse emission at time t1, for example, in the case of a fluorescent lamp as noise light caused by illumination. At the later timing t2, the third light emission drive pulse 10 having the pulse width Tw is outputted, and 'this third light emission drive pulse 1
0 is OR on the condition that AND gate 6 is in the allowable state.
The light is supplied to the drive circuit 2 through the gate 5, and the drive circuit 2 drives the light emitting element 1 to perform the third light emission drive.

On the other hand, a light-receiving element 11 is arranged at a position separated from the light-emitting element 1 by a baseline length, and receives the light reflected by the object of the light pulse emitted from the light-emitting element 1. After signal amplification is performed by an amplifier 12, calculation is performed. An amplified signal is given to the circuit 13 to calculate the distance to the subject. The distance measurement results calculated by the calculation circuit 13 are latched by the latch circuit 14 for the distance measurement results obtained by the first light emission drive. Latch driving of the latch circuit 14 is performed by an OR gate 20 and a monostable multivibrator 21, and a latch pulse obtained by delaying the first light emission driving pulse outputted from the decoder 4 by a predetermined time is given to the latch circuit 14, and the arithmetic circuit 13 The first distance measurement result obtained from the first distance measurement is latched. In addition, the arithmetic circuit 1
The output of No. 3 is also given to the latch circuit 15, and the latch circuit 15 latches the distance measurement result obtained in the second light emission drive. Therefore, for the latch circuit 15, the decoder 4
The second light emission driving pulse 9 obtained from the above is given as a latch pulse after being delayed by a predetermined time in the monostable multivibrator 22. The outputs of the latch circuits 14 and 15 are given to a coincidence judgment circuit 16, and when the first and second ranging results latched by the latch circuits 14 and 15 match, the coincidence judgment circuit 6 goes to L level. The output of the match judgment circuit 16 is outputted to the AND gate 6.
, the AND gate 6 becomes inhibited, and the third light emission drive pulse 1 from the decoder 4
Output to the drive circuit 2 of 0 is prohibited. On the other hand, when the coincidence determination circuit 16 determines that there is a discrepancy between the first and second distance measurement results, the output of the coincidence determination circuit 16 becomes H level, and the AND gate 6 is set to the permissible state and the second distance measurement result is output from the decoder 4. The output of the third light emission drive pulse is allowed, and the light emitting element 1 is caused to perform the third light emission drive. In this way, when the coincidence determination circuit 16 determines the discrepancy between the first and second distance measurement results and performs the third light emission drive, the third distance measurement obtained from the calculation circuit 13 The result is latched into latch circuit 14. In order to latch the third distance measurement result to the Q latch circuit 14, the output of the AND gate 6 is output to the OR gate 2.
0, and when the third light emission drive pulse 10 is output, a latch pulse is given to the latch circuit 14 from the monostable multivibrator 21, and the third distance measurement result obtained by the arithmetic circuit 13 is It will latch.

Furthermore, the output 17 of the latch circuit 14 and the output 18 of the coincidence determination circuit are given to an autofocus control circuit of a camera (not shown), and when the first and second distance measurement results match, the output 17 is sent to the latch circuit 14. The first latched
The distance measurement result of the first time is used as the distance measurement output, while the first and second
If the second distance measurement result is different, latch circuit 1
The third distance measurement result latched at 4 is taken as the distance measurement output.

Next, the distance measuring principle of the present invention will be explained along with its operation, taking as an example a case where the subject is illuminated by a fluorescent lamp.

FIG. 2 is a time chart showing the light emitting pulse P, the light reception signal VO, and the timing T of the distance measurement operation during the distance measurement operation when there is no noise or human incident from a fluorescent lamp or the like.

That is, the first light emission is performed with the pulse width TW at time to, and the second light emission is performed with the same pulse width TW after a predetermined time T1. This consecutive first and second
By emitting the second light emitting pulse P, a light receiving signal Vo is obtained by amplifying the light receiving signal of the light receiving element 11 with the amplifier 12 at each light emitting timing, and distance measurement calculation is executed after TS has elapsed from the start of each light emission at times to and tl. to calculate the distance to the subject. The method of calculating the distance to the object is determined according to the calculation principle of, for example, Japanese Patent Publication No. 1983-29112@.

The distance measurement results obtained by such distance measurement calculations using the first and second light emission drives are similar to those of the first time because in the case of Fig. 2, there is no reception of noise light such as fluorescent lamps. The second distance measurement results are equal, and it is determined that accurate distance measurement has been performed.

FIG. 3 shows signal waveforms when the object is illuminated with a fluorescent lamp or when light from a fluorescent lamp directly enters the light receiving element when performing a distance measuring operation.

For example, if the light reception noise component VN from the fluorescent lamp overlaps at the timing of the second light emission drive at time ↑1,
By superimposing the received light signal VS with the received light signal VS when there is no noise light VN, the actually obtained received light signal becomes as shown in VO. Therefore, the first distance measurement result and the second distance measurement result are different. Therefore, in the present invention, the first and second
If the distance measurement results are different, the third distance measurement is performed at a timing free of noise light to obtain accurate distance measurement results.

Here, even if the fluorescent lamp is lit at 50H2 or 60T IZ, the temporal change in the light display is not sinusoidal, and the repetition period is a pulse waveform twice the commercial AC period, and during this period, the noise is small. There is a rough period. That is, as shown in the noise signal VN of FIG. 3, a pulse waveform of pulse width TN is generated with a repetition period Tc, and 11! of TM within the repetition period Tc! ] There is no noise during this time. Therefore, the third distance measurement may be performed during this noise-free TH period.

Although Fig. 3 shows a case where a distance measurement error occurs due to noise during the second distance measurement, in reality, if a distance measurement error occurs only during the first distance measurement, the second distance measurement When a distance error occurs, there are three cases in which a distance measurement error occurs both in the first measurement and in the second measurement.

As shown in Fig. 3, when a distance measurement error occurs for the second time, the period from the end of the light emission pulse P to the third light emission pulse (T2-Tw>) should be made larger than the noise period Tn of the noise light. If you do this, the third distance measurement will be performed during noise-free period 1.
'-m can be used correctly.

On the other hand, when an error occurs due to noise light during the first distance measurement, the sum of the periods of the first and second and second and third pulses P (T1+T2> is the noise of the noise light). If the third light emission is performed in a period smaller than the short period Tm, the third distance measurement can be performed before receiving the next noise. That is, T2-Tw>Tn -- (1) T1+T2< If the period T1, T2 and pulse width Tw of the light emitting pulse P are selected so that Tm ---(2> holds true), noise will not occur during the third distance measurement.

Specifically, in the case of a fluorescent pair, 7-n=2m5. Tc=8
．． 3ms (at 60Hz), or 10m5 (50
In the case of H2>. Regarding T1-1-T2,
Just consider the shorter 3.3ms, so Tw=0.5
Substituting msST1=2ms into equations (1) and (2> above, T2-0.5ms>2ms =13>TI+T2<
(8,3-2>ms---(4), and the (3rd)
From the formula, T2 > 2.5 mS, and from formula (4), T2 < 6.3-2 = 4.3 ms.
2, if you set T2=3mS2=3, even if an incorrect distance measurement result is obtained due to noise light in the first or second measurement, or in both the first and second measurements, the third
For the second time, it is possible to obtain a correct distance measurement result that avoids noise light.

Therefore, if noise light from a fluorescent pair is applied to the decoder 4 shown in the embodiment of FIG.
The circuit conditions are set so that a light emission drive pulse of pulse width Tw=Q, 5 ms is generated at each timing of 3.
The period T1 of the first and second light emission pulses is T1=2mS.
By setting the emission period T2 of the second and third times to T2=3mS, noise light can be eliminated in the first or second time, or in both the first and second time. Even if an incorrect distance measurement result is obtained, a correct distance measurement result can always be obtained the third time.

Although the above embodiment takes noise light caused by a fluorescent pair as an example, the present invention is not limited to this, and the noise light during distance measurement is not continuous noise light, but noise light. Regarding the noise light that periodically generates low periods, as in the case of the fluorescent pair, the emission pulse width TW is based on the repetition period of the noise light, the noise period, and the no-noise period, and the first and second emission periods T1. And by setting the second and third light emitting periods T2 to meet the conditions shown in formula ('I) and (2>), either one of the first and second light emitting times, or Even if erroneous distance measurement results occur in both cases due to noise light, accurate distance measurement results can be obtained in the third distance measurement without receiving noise light.

(Effects of the Invention) As explained above, according to the present invention, distance measurement by emitting a light beam is performed twice in succession, and when the first and second distance measurement results are different, noise light is Because it was determined that an erroneous distance measurement had been performed and the third distance measurement was performed at a predetermined timing when no noise light was incident, the subject may have been illuminated by a disturbance light source such as a fluorescent pair. Even when light from a disturbance light source directly enters the light receiving element, the distance to the object can always be accurately measured, and the reliability of distance measurement can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a signal/waveform diagram when there is no noise light, and FIG. 3 is a signal waveform diagram when noise light is received. 1: Light emitting element 2: Drive circuit 3: Counter 4: Decoder 5.20: OR gate 6: AND gate 7: Terminal (clock input) 8.9, 10: Light emission drive pulse 11: Light receiving element 12: Amplifier 13: Operation Circuit 14.15: Latch circuit 16: Match determination circuit

Claims (1)

[Claims] A distance measuring device comprising a light emitting means for emitting a light beam toward a subject, a light receiving means for receiving reflected light from the subject, and a calculation means for calculating a distance to the subject based on a light reception signal of the light receiving means. Distance measurement control means that measures the distance of the subject twice in succession by emitting the light beam, and performs the third distance measurement when the results of the first and second distance measurements are different. A distance measuring device characterized by being provided with.