JPS62182729A - Range finder - Google Patents

Abstract

PURPOSE:To make a logarithmic compressor unnecessary in a light reception signal processing circuit by changing the intensity of emitted light. CONSTITUTION:A light projecting circuit 1 is provided with a means which supplies power to a light emitting element 3 so that the intensity of emitted light is raised gradually according as the time elapses. This means consists fundamentally of a capacitor 6, a constant voltage limiter 7, a transistor TR 8, and TRs 9 and 10 or TRs 11 and 12 used as a switch. Thus, the intensity of emitted light of the light emitting element 3 is raised with time in accordance with the discharge characteristic of the capacitor 6 and the constant current limiter 7. As long as the intensity of emitted light is raised according as the time elapses, another circuit can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a distance measuring device that calculates the distance from a camera to an object.

Conventional technology A light emitting circuit that causes a light emitting element installed on the front of the camera to emit light and projects it onto a subject, and a pair of light receiving elements that receive reflected light from the subject at different angles of incidence, and processes signals from the light receiving elements. A distance measuring device that includes a light reception signal processing circuit that calculates the distance to a subject and outputs a lens position signal is well known. In this device, the light-receiving signal processing circuit is provided with a logarithmic compressor after each element in order to calculate the distance by calculating the ratio of the signals from a pair of light-receiving elements. The distance was calculated by subtracting .

Problems to be Solved by the Invention As mentioned above, conventional distance measuring devices require a logarithmic compressor, which makes the circuit configuration complicated, and it is necessary to equally limit noise etc. to avoid erroneous measurements. was there.

Accordingly, an object of the present invention is to provide a distance measuring device capable of measuring distance without performing logarithmic compression.

Means for Solving the Problems The configuration of the distance measuring device of the present invention that achieves the above object includes supplying power to the light emitting circuit so that the light emission intensity gradually changes with the passage of time to the light emitting element. a first means for measuring the time when the signal from one of the light receiving elements reaches a predetermined magnitude; and a first means for measuring the time when the signal from one of the light receiving elements reaches a predetermined magnitude, and the magnitude of the signal from the other light receiving element at the measured time. and a means for determining the distance to the object based on signals from both means.

Effect When the above-described light projecting circuit is used, the intensity of the reflected light incident on the light receiving element also changes (for example, increases) over time. Therefore, the amount of light incident on a pair of light receiving elements arranged at different angles of incidence changes (for example, increases) over time (however, the slope is different). The intensity of reflected light incident on each light receiving element depends on the distance to the subject and the reflectance of the subject itself. In other words, the closer the distance, the higher the intensity of the reflected light, and the higher the reflectance (the higher the intensity of the reflected light). By the way, if you change the reflectance of objects at the same distance, Looking at the relationship between the large light intensity to the element and time, the slope changes. However, the large light intensity L1 to one light receiving element and the light intensity L2 to the other light receiving element
Looking at the relationship with , in comparison, /L2 has not changed. This is because the distance is the same and the angle of incidence does not change. This means that the intensity of light incident on one of the light receiving elements is greater than the other.

When becomes a constant value, it means that the large light intensity L2 to the other light receiving element corresponds to the distance to the subject, regardless of the reflectance of the subject.

In the present invention, the first al11 determining means of the light receiving signal processing circuit determines the time 4t11 for the large light intensity to one light receiving element to reach a constant value, and the second measuring means determines the time 4t11 for the large light intensity to one light receiving element to reach a constant value, and the second measuring means determines the time at which the large light intensity to one light receiving element reaches a constant value. The large light intensity L2 to the element is measured, and the object distance can be calculated from this measured value. Thus, it allows distance measurements to be made without the use of logarithmic compressors found in conventional devices.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 1 shows an overall circuit diagram of a first embodiment of a distance measuring device according to the present invention.

The overall distance measuring device of the first embodiment includes a light projection circuit 1 and a light reception signal processing circuit 2, and the light projection circuit 1 includes a light emitting element 3 provided on the front surface of the camera to project light onto a subject. As this light emitting element, for example, an infrared light emitting diode is used. The light-receiving signal processing circuit 2 also includes a pair of light-receiving elements 4.5 that receive reflected light from the subject. This light receiving element 4.5 is
For example, they are placed side by side in front of the camera to receive reflected light from the subject at different incident angles, so that the intensity of the incident light from the same subject is different.

In the present invention, the light projecting circuit 1 is provided with means for supplying power to the light emitting element 3 so as to gradually increase the light emission intensity over time.

This means basically includes a capacitor 6, a constant current limiter 7, a transistor 8, and transistors 9 and 10 or transistors 11 and 1 used as switches.
2, so that the light emitting intensity of the light emitting element 3 increases over time in accordance with the discharge characteristics of the capacitor 6 and the constant current limiter 7. Other circuits can be used in which the emission intensity increases over time. For example, a bootstrap circuit or a Miller integration circuit that outputs a triangular wave can be used, or other ramp voltage generation circuits can also be used. Details of the light projecting circuit 1 of this example will be described later.

The light-receiving signal processing circuit 2 includes a first circuit as a means for measuring the time when the signal from one of the light-receiving elements 4 reaches a predetermined level.
comparator 14, two second comparators 15.16 that measure the magnitude of the signal from the other light receiving element 35, and two second comparators 15.16 that receive the signals from these comparators 14.15.16 and measure the magnitude of the signal from the other light receiving element 35. A discriminator 17 for discriminating distance is provided.

Circuit 2 basically has the above configuration and does not require a logarithmic compressor. Note that the light-receiving elements 4.5 are each subjected to current-to-voltage conversion by operational amplifiers 18, 19 to facilitate subsequent signal processing. The operational amplifiers 18 and 19 can also be used as filter circuits, thereby removing stationary light components. Details of the light reception signal processing circuit of this example will be described later.

Configuration of Light Projection Circuit The detailed configuration of the distance measuring device according to this embodiment will be described in detail. First, the detailed configuration of the light projecting circuit 1 will be described. The light projection circuit 1 is provided with a pulse oscillator 20. This pulse oscillator 20 emits pulses to distinguish the light from the light emitting element 3 from stationary light, and can be set to any frequency as long as it can be distinguished from external stationary light, but in this example it is set to 30KIIz. has been done.

A frequency divider 21 is provided downstream of the pulse oscillator 20, and divides the pulse frequency of the pulse oscillator 20 to, for example, 500 Hz to produce a pulse having a pulse width of 1 millisecond and a period of 2 milliseconds. Note that this frequency divider 21 is operated by human control 2.
2 is provided, and when a low signal is input here, the counter of the frequency divider is reset and output is stopped.

The output of the frequency divider 21 is input to the terminal 25 of the switching circuit 24. The switching circuit 24 serves as a re-emission means that allows the light-emitting element 3 to emit light twice, and
According to the pulse width of, for example, the light can be emitted for 1 millisecond, then stopped for 1 millisecond, and then emitted for 1 millisecond again. This switching circuit has seven low signal input terminals 26, and when a low signal is input here, four output terminals 27
~30 outputs a low signal. The switching circuit 24 is also provided with a control input terminal 31 to which the output of the comparator 14 is input.

The switching circuit 24 is provided with the three input terminals described above, and output signals are outputted to the four output terminals 27 to 30, respectively, according to these input signals. Reset as mentioned (
When the low) signal is input to terminal 26, output terminals 27 to 3
All 0's output low signals. Next, from the frequency divider 31, the first
When the second pulse (width l milliseconds) is output and goes high, the reset (terminal 26) goes high, and the output of the first comparator 14 (terminal 31) remains high.
Output terminals 27, 28, 30 are driven high and terminal 29 is driven low. and the output of the first comparator 14 (terminal 31)
When becomes low, output terminals 27-29 become low. However, when the output of the first comparator 14 (terminal 31) remains high and the first pulse of the frequency divider 21 ends and a low level is input to the terminal 25, the output terminal 30 remains high. However, the other output terminals 27 to 29 are set to low level.

When the frequency divider 21 outputs the second pulse (1 millisecond width), the terminal 25 is set to a high level, thereby keeping the output terminal 28 low and the output terminal 30 high. , output terminals 27 and 29 are set to high level. During this second pulse period, when the output of the first comparator 14 becomes low level, a low level is input to the terminal 31, thereby causing the output terminals 27 to 29 to become low level. However, if the first comparator 14 remains high during the second pulse, terminal 25 will go low at the end of the second pulse, which will cause not only output terminals 27-29 to The output terminal 30 is also set to low level. These logics are summarized in Table 1 on the next page.

Although details of the circuit configuration of the switching circuit 24 are not shown, any configuration may be used as long as the logic shown in Table 1 can be executed. For example, D
A combination of type flip-flops or a combination of a flip-flop and a gate is also possible.

The output terminal 27 of the switching circuit 24 is connected to the base of a transistor 32 connected in parallel with the capacitor 6. This transistor 32 acts as a switch and is turned on when the terminal 27 is at a low level, discharging the charge in the capacitor 6 and turning off the transistor 8.

The output terminal 28 is connected to one input terminal of the first gate 33, and sends a high level signal to open the first gate. The other input of the first gate 33 receives a pulse from the pulse oscillator 20, and when the terminal 28 of the switching circuit 24 becomes high level, the pulse from the oscillator is sent to the transistor 9. As mentioned above, the pulse is used for pulsed light emission to distinguish it from constant light, and if it is possible to distinguish between the constant light and the light emitted from the light emitting element 3, the first gate 33 can be removed and the terminal 28 may be directly connected to transistor 9.

When the output of the first gate 33 becomes high level and a base current is supplied to the transistor 9, an emitter current flows through the transistor 9 according to the current from the transistor 8, and a base current is supplied to the transistor 10 at the subsequent stage. Receiving this base current, a collector current flows through the transistor 10, and the light emitting element 3 receives electric energy from the capacitor 34 and emits light. Note that a current limiting resistor 35 is provided between the collector of the transistor 10 and the light emitting element 3, so that the light emission intensity of the light emitting element 3 is reduced.

The output terminal 29 of the switching circuit 24 is connected to one input of the second gate 37, and like the first gate 33, the pulse from the pulse oscillator 20 is sent to the other input. The second gate 37 supplies current to the base of the transistor 11 to control the transistor 12 and cause the light emitting element 3 to emit light. Note that there is no current-limiting resistor between the collector of the transistor 2 and the light emitting element 3, and the light emitting intensity of the light emitting element 3 is not reduced.

The circuit consisting of the first gate 33, the transistor 9, the transistor 10, and the resistor 35, and the circuit consisting of the second gate 37, the transistor 11, and the transistor 12 are different from each other.
are the same, and basically either one is better, except for
These two circuits were installed for the first weak light emission and the second
This is to increase the accuracy of distance measurement during close-range shooting by emitting strong light for the second time.

Configuration of Received Light Signal Processing Circuit Next, the configuration of the received light signal processing circuit 2 will be described in detail. The light receiving elements 4 and 5 are converted into voltages by operational amplifiers 18 and 19, respectively. The common terminal of the light-receiving elements is biased with a voltage ``8'', and the output of the amplifiers 18 and 19 is made to drop from ``8'' as the intensity of light incident on the light-receiving element increases. AC amplifiers 40 and 41 are provided downstream of the amplifiers 18 and 19, respectively. This is provided in preparation for the light emitting element 3 to emit pulsed light, and thereby the steady light and the light from the light emitting element 3 can be more clearly distinguished. AC amplifier 40.41
Peak hold circuits 42 and 43 are provided at the subsequent stage, respectively, and sequentially hold the peaks of the waveforms output from the AC amplifiers 40 and 41 to remove the AC waveforms. As shown in FIG. 3, etc., the voltage obtained by this hold becomes a straight line that decreases over time from the bias voltage .

The AC amplifiers 40, 41 and peak hold circuits 42, 43 described above are provided when the light emitting element 3 emits pulsed light, and may be omitted when the light emitting element 3 does not emit pulsed light.

The output of the peak hold circuit 42 is connected to the non-inverting input of the first comparator 14, and the reference voltage VreL is input to the inverting input of the first comparator 14. Therefore, while the output voltage P1 from the peak hold circuit 42 is higher than Vref, the output of the first comparator 14 remains high. Then, when the output voltage P reaches Vref+ and drops below it, the output of the comparator 14 turns low. The output of the comparator 14 is connected to the input terminal 45 of the discriminator 17 at the subsequent stage, and also to the control input terminal 3 of the switching circuit 24 of the light projection circuit 1.
Connected to 1.

The output P2 of the peak hold circuit 43 is sent to the non-inverting inputs of two second comparators 15,16. Comparator 15.16
The basic voltages Vrefz and V are applied to the inverting input terminals of
ref 3 is given. In addition, these base voltages V
ref,, Vref2, Vref3 are V, > Vref, > Vref, > Vref in this example
+ > 0 shall be set. Comparator 15.16
The outputs of are connected to input terminals 46 and 47 of the discriminator 17, respectively.

In addition to the three input terminals 45 to 47, the discriminator 17 is provided with a terminal 18 for receiving a signal from the output terminal 30 of the switching circuit 24 of the light projection circuit 1. The discriminator 17 is
When the signal from the comparator 14 is received, and when this signal changes to low, the level of the signal from the second comparator 15.16 is checked to determine whether the subject distance is close, medium, or far. Distance. After the discrimination, from the discriminator 17,
If the distance is short, a short distance position signal is output from the output terminal 49, if the distance is medium, a medium distance position signal is output from the output terminal 50, and if the distance is long, a long distance position signal is output from the output terminal 51. A distance position signal is output. Note that light emitting elements 52 to 54 are connected to these output terminals 49 to 51, respectively.
may be connected and displayed. Further, although two second comparators are provided in the illustrated example, it may be one, or an arbitrary number of three or more may be used to improve distance measurement accuracy. Furthermore, the farthest distance position signal may be output from the output terminal 55 as shown by the broken line. These position signals are sent to a lens positioning device (not shown) to determine lens position. An example of the relationship between the input and output of the discriminator 17 is shown in Table 2 below.

The discriminator 17 may have any configuration as long as the above logic can be executed. For example, this can be done by combining a decoder and a latch.

The supply of power to the device is linked to the release button, and when the button is pressed, a reset signal (low) is output for, for example, 5 milliseconds.

motion The operation of the distance measuring device having these configurations will be explained.

When the release button is pressed, power is supplied to the device, and the light projecting circuit 1 and the light receiving signal processing circuit 2 are enabled. In the light projection circuit 1, a pulse of 301t)lz is sent from the pulse oscillator 20 to the frequency divider 21, the first gate 33, and the second gate 37. The frequency divider 21 sends a pulse with a pulse width of 1 millisecond to the switching circuit 24 at a cycle of 2 milliseconds. First, the switching circuit 24 is reset (low) for about 5 milliseconds after pressing the release button.
Receive a signal. This causes the switching circuit output terminals 27-30 to go low, as shown in Event I of Table 1. Since output terminal 27 is brought low, transistor 32 is turned on, capacitor 6 is discharged, and transistor 8 is turned off. Also, since the output terminals 28.29 are low, the gates 33.37 are also closed, and the transistors 9 and 10.
11 and 12 are also turned off. Furthermore, during this reset, capacitor 34 is also charged. When the output terminal 30 is low, the frequency divider 21 and the discriminator 17 are reset.

When the reset signal is removed and the first pulse (1 millisecond width) from the frequency divider 21 is sent to the terminal 25 of the switching circuit 24, the process moves to event H in Table 1. As a result, output terminal 2
9 remains low, but output terminals 27 and 28 go high. When the output terminal 27 is made high, the transistor 32 is turned off and the capacitor 6 is charged with a constant current. As this charging progresses, the transistor 8 gradually becomes conductive as shown in the second stage of FIG. go. Since the output terminal 28 becomes high, the output of the first gate 33 outputs a pulse for a certain period of time as shown in the third row of FIG. As a result, a pulse is input to the base of transistor 9, and on the other hand, a current that increases over time is applied to the collector from transistor 8, so that transistor 9 gradually turns on and off at a frequency of 3QKIlz and becomes conductive to a saturated state. , this waveform is amplified by transistor 10. The transistor 10 is connected to the capacitor 34
The circuit formed by the light emitting element 3 and the resistor 35 is closed, and the charge of the capacitor 34 is applied to the light emitting element 3. As mentioned above, the transistor 10 gradually becomes conductive while being modulated by a 30 KHz pulse, so the light emitting element 3 gradually increases its luminous intensity while emitting pulsed light, as shown in the bottom row of FIG. To go. Note that since the resistor 35 is provided, the current to the light emitting element 3 is limited, and the light emission intensity thereof is reduced. This restriction can prevent the light-receiving element from becoming saturated when the copy object is too close or has a high reflectance, and can improve distance measurement accuracy.

Further, the waveform in the second row from the bottom in FIG. 2 shows the light emission intensity of the light emitting element when pulsed light emission is not performed.

When the first light emission is performed as described above, in the light receiving signal processing circuit 2, reflected light from the subject enters the pair of light receiving elements 4.5. The signals from these light-receiving elements 4.5 are converted into voltage by amplifiers 18.19, noise such as stationary light is removed by AC amplifiers 40.41, and further peak hold circuits 42.43 are used to convert the signals into voltages as shown in FIG. As shown in FIG. 2, substantially linear outputs P, , P2 which decrease over time are obtained from the bias voltage (1)8.

Regarding these outputs PI and P2, a case where the subject distances are different (FIG. 3) and a case where the subject reflectances are different (FIG. 4) will be considered.

FIG. 3 shows the characteristics of the outputs P and P2 due to changes in object distance. +8) is a case where the voltage is close, and the output P reaches the reference voltage Vref+ in a short time Ta. This is because the intensity of the reflected light entering the light receiving element 4 is high. Although the slope of the output P2 is steep, it is considerably gentler than that of the output P2. This is because when the subject is close, the angle of incidence of the reflected light on the light-receiving element 5 is considerably larger than the angle of incidence on the light-receiving element 4, and as a result, the substantial light intensity on the light-receiving element is transmitted to the light-receiving element 4. This is because it is considerably smaller than that of . Therefore, the output P is the reference voltage V re
Voltage V2 of output P2 at time Ta when reaching f
becomes higher than the voltage Vrefz. This is the pattern at close range.

When the subject is far away, it takes a long time (Tc) for the output JP (as shown in C1 in FIG. 3) to reach the reference voltage VreL. That is, the slope of the output P becomes considerably gentler. On the other hand, although the output P2 has a gentler slope than the output P, the difference therebetween is small. This means that when the subject is far away, the light receiving element 4.5
This is because although the large light intensity is weak, there is not much difference in the angle of incidence, and the actual difference in received light intensity becomes small. Therefore, unlike the short distance case shown in Figure 3(a),
The voltage 2 of the output P2 at the time Tc when the output P reaches the reference voltage Vref+ becomes lower than the reference voltage Vrefi.

In the case of the middle distance shown in FIG. 3 (bl), the output P1 is the reference voltage V ref 1
The time Tb reaching the voltage is between the times Ta and Tc, and the voltage ■2 of the output P2 at the time Tb is also the reference voltage Vrefz
Although it is lower, it is higher than the reference voltage Vref3.

Incidentally, although the intensity of reflected light from a subject depends on the subject distance and the subject reflectance, it has already been stated that the influence of the subject reflectance is removed in the present invention. This point will be further explained using outputs P1 and P2. FIG. 4 shows the characteristics of outputs P1 and P2 when the reflectance of objects at the same distance is changed. Fourth
Figure (a) shows the case of high reflectance, and Figure (b) shows the case of low reflectance.

In the case of high reflectance, the slope of the output p is steep and the time (To) for reaching the reference voltage VreL is short.

The voltage of the output P2 at this time T0 is assumed to be 2. In the case of low reflectance, the time to reach the reference voltage V ref , (
T, ) becomes longer by the amount that the reflection intensity decreases.

However, the output P2 at this time T1 is the time T at high reflectance. The voltage V2 is the same as the voltage of the output P2 at. This is because, at the same distance, the angles of incidence on the light receiving elements 4 and 5 are the same, so the ratio of the output P2 to the output P1 is the same even if the reflectance is changed, and the voltage of the output P2 is This is due to the fact that the point in time when is measured is when the voltage (Vref+) of the output P becomes the same regardless of whether the reflectance is high or low.

Therefore, as in the present invention, the light emitting intensity is changed over time so that the output value of the light receiving element is changed over time, and in addition, the value of the signal from one of the light receiving elements is kept constant. By measuring the magnitude of the signal from the other light-receiving elements at the point when the distance reaches , distance information can be obtained as is, and is not affected by changes in reflectance. On the other hand, in conventional devices, in order to eliminate the influence of changes in reflectance, a large number of signals are compressed so as to take the ratio of the signals from two light receiving elements, and the two logarithmically compressed values are subtracted. was going on. That is, it will be appreciated that in the present invention there is no need for a logarithmic compressor as described above.

Based on the above-mentioned principle, the comparator 14 of the received light signal processing circuit 2
16 and the discriminator 17 calculate the object distance. The previously mentioned Table 2 was created based on the above principle. For example, when the subject distance is short, the output P is based on !, as shown in FIG. 3(a). When the $ voltage Vref+ is reached, the output of the first comparator 14 changes from high level to low level, the discriminator determines this time (T, l), and the output of the second comparator 15.16 at that time is high. When determining that it is the level, the discriminator 17 outputs a short distance position signal to the terminal 49, and causes the light emitting element 52 to emit light for display. In the case of medium distance, the comparator 15 is at low level and the comparator 16 is at low level by looking at the output of the second comparator 15. If it is determined that the level is high, a medium distance position signal is output to the terminal 50, and the light emitting element 53 is caused to emit light. In the case of a long distance, when the comparator 14 is inverted (Tc), the comparator 1
It is determined that all outputs of 5.16 are low, and a long distance position signal is output to the terminal 51, causing the light emitting element 54 to emit light. Furthermore, as is clear from Table 2, the switching circuit 24
The output terminal 30 of is outputting a high level.

When the first comparator becomes low due to the first light emission, the light emitting circuit 1
The output terminals 27 to 29 of the switching circuit 24 become low level, and the light emitting element 3 stops emitting light. More specifically, when terminal 27 goes low, transistor 32 is turned on, capacitor 6 is discharged, and transistor 8 is also turned off. Also, since the terminal 28.29 is low, the gate 33.37 is closed and the subsequent transistor 9.10.1
1.12 is never turned on. Therefore, the light emitting element 3 stops emitting light.

However, the intensity of the first light emission is set low as described above. This is to prevent the current power of the light-receiving element from being colored and to improve distance measurement accuracy when the subject has a high reflectance or is too close. Therefore, when the reflectance of the subject is low or far away, the output JP+ may not reach the reference voltage during the first light emission time (1 millisecond). In this case, proceed from event (2) to event (2) in Table 1. That is, even after the first light emission is completed, the frequency divider input terminal 25 of the switching circuit 24 is set to low without any signal being output from the discriminator. This causes the output terminals 27 to 29 of the switching circuit 24 to go low, and the light emitting element 3 stops emitting light for a certain period of time (1 millisecond) (see also FIG. 2).

After the light emission stops (event ■), the process proceeds to event V, and as shown in Table 1, the output terminals 27 and 29 of the switching circuit 24 are set to a high level, and the output terminal 28 is kept at a low level. Therefore,
Transistor 32 is turned off and as capacitor 6 is charged, transistor 8 is gradually turned on. Further, since the output terminal 29 becomes high, the gate 37 opens and outputs the pulse shown in the fourth row of FIG. 2. As a result, the transistors 11 and 12 are gradually turned on while being pulse-modulated, and the light-emitting element 3 emits pulsed light as shown in event (2) at the bottom of FIG. This second emission intensity is higher than the first emission intensity.

By the second light emission, the light reflected from the subject enters the pair of light receiving elements 4.5 of the light receiving signal processing circuit 2. The processing in this light reception signal processing circuit 2 is the same as that in the first light emission, except for the case where the output P1 does not reach the reference voltage Vref+ in the second light emission, and a description of the same parts will be omitted. . That is, when the first comparator 14 turns to low level, the distance position signal changes to the discriminator 17 according to Table 2.
After that, the process moves to event (2) in Table 1, where the light emission is stopped and distance measurement is stopped.

However, even in the second light emission, the output P may not reach the reference voltage Vref, and the first comparator 14 may remain high. In this case, as shown in the logic at the right end of Table 2, the discriminator 17 outputs a long distance position signal to the terminal 51 (note that the farthest position signal can also be output from the terminal 55). That is, as shown in event (2) in Table 1, when the second light emission is completed, its output becomes low, and the output terminal 30 of the switching circuit 24 outputs a low signal. This terminal 30 is connected to the control terminal 22 of the frequency divider 21.
The frequency divider 21 is reset, the switching circuit 24 is maintained at the event (2), and subsequent light emission is stopped. Further, the output terminal 30 of the switching circuit 24 is also input to the input terminal 48 of the discriminator 17, so that the discriminator 17 determines that the distance is long (the farthest distance may be sufficient). .

As mentioned above, the distance measuring operation takes three modes as shown in Table 3 below.

Table 3 The above explanation was given for the case where pulsed light emission was performed for each light emission, but it goes without saying that the logarithmic compressor can be removed even if pulsed light emission is not performed. In this case, the light emitting element 3 emits light in the pattern shown in the second row from the bottom in FIG.

Then, in the light reception signal processing circuit 2, an AC amplifier 40
．． 41 and peak hold circuits 42, 43 would be unnecessary. However, when pulsed light is emitted, there is an advantage that noise such as stationary light can be reliably removed.

Furthermore, although the configuration is such that light emission can be performed twice, basically it is sufficient to emit light only once. In order to improve distance measurement accuracy, the light may be emitted three or more times.

Furthermore, although the emission intensity is illustrated as increasing over time, it may be decreased over time, and it does not have to be linear as long as it increases (or decreases gradually).

Second Embodiment FIG. 5 shows a second embodiment of the distance measuring device according to the present invention. In this embodiment, the light emission intensity of the light projecting circuit 1, particularly between the first light emission and the second light emission, is changed using a configuration different from that of the first embodiment.

The other parts are the same as those in the first embodiment, so their explanation will be omitted. Further, the same reference numerals are given to the elements used in FIG. 1.

In FIG. 5, another constant current limiter 61 is connected in parallel with the constant current limiter 7, and a transistor 62 as a switch is connected in series between the constant current limiter 61 and the ground. It is connected. The gate of this transistor 62 is connected to the output terminal 29 of the switching circuit 24, and when the output terminal becomes high level, the transistor 62 becomes conductive. Further, the emitter of the transistor 9 is connected to the bases of the transistors 1 to 12.
Transistor 10 and resistor 35 in the figure have been removed.

In operation, at the first time of light emission, that is, at event (2), the output terminals 27 and 28 of the switching circuit 24 go to high level, and the output terminal 29 remains at low level.

Therefore, transistor 32 is turned off and transistor 62 remains off. Also, the base current is supplied to transistor 9, and transistor 11 is kept off.

Capacitor 6 is charged while being current limited by constant current limiter 7. As a result, transistor 8 gradually begins to conduct, and begins to supply collector current to transistor 9. This current is amplified by transistor 12,
The light emitting element 3 is energized so that its light emission intensity increases over time.

At the time of the second light emission, that is, at event V, the output terminal 27 of the switching circuit 24 becomes high level, and the output terminal 28
is at a low level, and the output terminal 29 is set at a high level. Therefore, transistor 32 is turned off and transistor 62 is turned on. Also, transistor 9 is left off and transistor 11 is supplied with base current.

As a result, the current limiter 7 and another current limiter 61 act on the capacitor 6 in parallel, and the capacitor 6 is charged at a faster rate (higher inclination angle) than during the first light emission (event ■). . That is, the transistor 8 gradually begins to conduct at a slope angle that is, for example, twice that of the first light emission (event (2)), and begins to supply collector current to the transistor 11. This current is amplified by the transistor 12, causing the light emitting element 3 to emit light gradually and at a higher light emitting intensity than the first light emitting intensity, as shown by event (2) in FIG.

According to the second embodiment, only one large and expensive transistor is required to drive the light emitting element 3, which has the advantage of keeping occupied space and cost low.

Third Embodiment FIG. 6 shows a third embodiment of the distance measuring device according to the present invention. In this embodiment, the discriminator 17 of the light-receiving signal processing circuit 2 is configured to operate effectively only during the periods when the light-emitting element 3 emits light (events (2) and (2)). The other parts are the same as those in the first embodiment, so their explanation will be omitted. Also, this sixth
In the figures, the same reference numerals are used for elements used in FIG. 1 as well.

In FIG. 6, the output of the first comparator 14 is
The input signal is not directly inputted to the input terminal 45 of the input terminal 45, but is inputted to the input terminal 45 via the inverter 71 and the NAND gate 72. An OR gate 73 is provided in front of the other inputs of the NAND gate 72, and one input of this OR gate 73 receives a signal from the output terminal 28 of the switching circuit 24, and the other input receives the signal from the output terminal 28. A signal is being sent from 29.

In operation, the output terminal 28 or 29 of the switching circuit 24
When either of these is at a high level (that is, event ■ or V), the OR gate 73 is at a high level, and N
Open the AND gate 72. That is, the signal passed through the inverter 71 from the first comparator 14 is sent to the input terminal 45 of the discriminator 17. However, when the output terminals 28 and 29 of the switching circuit 24 are at low level, the discriminator 17
The signal from the first comparator 14 is not sent to.

The output terminal 28 of the switching circuit 24 becomes high level because
As shown in Table 1, this is only the case of event H, and at this time the light emitting element 3 is emitting light for the first time. Further, as is clear from Table 1, the output terminal 29 of the switching circuit becomes high level only in the case of event (2), and at this time the light emitting element 3 emits light for the second time. Therefore, the discriminator 17 is designed to operate effectively only while the light emitting element 3 is emitting light, and is not operated at other times.

By configuring as described above, it is possible to prevent malfunctions caused by light projected from other cameras or similar light. For example, when a large number of cameras equipped with similar distance measuring devices are used at the same location, as in the case of a photo shoot, the camera may receive reflected light from other cameras.

In the distance measuring device of the first embodiment, there is a possibility that the distance measuring operation is performed using reflected light from other cameras, resulting in an out-of-focus photograph.

The device of the third embodiment prevents such malfunctions and uses only its own reflected light for distance measurement operations.

Note that in the circuit of this third embodiment, one OR gate,
Although one NAND gate and an inverter are used, any other arbitrary circuit may of course be used if the discriminator is enabled to operate only when the light emitting element emits light.

Effects of the Invention According to the present invention, by changing the emission intensity, a logarithmic compressor is not required in the received light signal processing circuit, which simplifies the circuit configuration. There is no need to be as strict about noise as in handling,
Can measure distance accurately.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a distance measuring device according to a first embodiment of the present invention, Fig. 2 is a waveform diagram of main parts in a light projecting circuit, and Fig. 3 f
a) - (C1 is a graph showing the time vs. voltage characteristics of outputs P1 and P2 when the subject distance is changed, Figure 4 (al and (b) is the output P when the subject reflectance is changed, and A graph showing the characteristics of P2, FIG. 5 is a circuit diagram of a distance measuring device according to a second embodiment of the present invention, and FIG. 6 is a circuit diagram of a distance measuring device according to a third embodiment of the present invention. ...Light emitter circuit, 2...Light receiving signal processing circuit, 3...Light emitting element, 4.5...Light receiving element, 6...Specific capacitor, 7.6f...Constant current limiter , 14... First comparator, 15.16... Second comparator, 17... Discriminator, 18.19... Operational amplifier, 20... Pulse oscillator, 21... Frequency division 24...Switching circuit, 33.37...Gate.

Claims (6)

[Claims] (1) A light projecting circuit that causes a light emitting element installed on the front of the camera to emit light and projects it onto the subject, and a pair of light receiving elements that receive reflected light from the subject at different incident angles, and processes signals from the light receiving elements. The distance measuring device includes a light receiving signal processing circuit that calculates the distance to the object by using the light emitting device, and outputs a lens position signal. The light receiving signal processing circuit is provided with a means for supplying power so that the signal from one of the light receiving elements reaches a predetermined level.
means for measuring the magnitude of the signal from the other light-receiving element at the measured time, and means for determining the distance to the subject based on the signals from both means. A distance measuring device characterized by: (2) The power supply means of the light emitting circuit includes a re-emitting means that causes the light-emitting element to emit light for a certain period of time, and then causes the light-emitting element to emit light again for a certain period after a certain period of time, and the emitted light intensity at the time of re-emission is 2. The device according to claim 1, wherein the luminescence intensity is higher than the initial emission intensity. (3) When the signal from one of the light-receiving elements does not reach a predetermined magnitude within a certain period of time, the first light-receiving signal processing circuit
3. The apparatus of claim 2, wherein the measuring means sends a signal to the re-emitting means of the illumination circuit to activate the re-emitting means. (4) The device according to claim 1, wherein the determining means of the light receiving signal processing circuit is configured to operate only when a light emitting element of the light projecting circuit is emitting light. (5) A light projecting circuit that causes a light emitting element installed on the front of the camera to emit light and projects it onto the subject, and a pair of light receiving elements that receive reflected light from the subject at different incident angles, and processes signals from the light receiving elements. The distance measuring device includes a light receiving signal processing circuit that calculates the distance to the object by using the light emitting device, and outputs a lens position signal. The light receiving signal processing circuit is provided with a means for supplying power so that the signal from one of the light receiving elements reaches a predetermined level.
means for measuring the magnitude of the signal from the other light-receiving element at the measured time, and means for determining the distance to the subject based on the signals from both means, further comprising: , the light emitting circuit is provided with means for turning on and off the light emitting element at a high frequency, and the light receiving signal processing circuit is provided with a peak hold circuit at a stage before the first measuring means and the second measuring means. A distance measuring device featuring: (6) The device according to claim 4, wherein an AC amplifier is provided at the front stage of each peak hold circuit to remove the DC component of the signal from the light receiving element.