JPH0226728B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a distance measuring device used in a camera, etc., which projects light emitted from a light emitting element toward a distance measuring object, and transmits the reflected light to two light receivers arranged adjacently. This invention relates to an improvement of a triangular distance measuring device that receives light with an element.

Conventionally, as a distance measuring device using the method described above,
This method has been proposed in Japanese Patent Application Laid-open No. 54-39731, Japanese Patent Application Laid-Open No. 57-104809, etc.

In general, when measuring distance by receiving reflected light from the distance measurement target of light projected by the light receiving element,
The intensity of the reflected light varies by a factor of 1,000 or more depending on the reflectance of the object to be measured, the distance, etc. Therefore, the amplifier circuit that amplifies the output of the light receiving element needs to have a dynamic range of 60 dB or more.

Possible ways to widen the dynamic range include logarithmic compression of the light receiving element output and automatic gain adjustment of the amplifier circuit, but in the former case, when the amount of light received is large and the output difference between the light receiving elements is small, the S/N In the latter case, a feedback system is required, which increases unstable factors such as oscillation.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to gradually increase the output of a light-receiving element from an apparently zero or minute value by a simple means without having the drawbacks of the conventional example, and to set the comparison circuit to a certain setting that is easy to distinguish. The object of the present invention is to provide a distance measuring device that determines the distance measuring state when a value is reached.

Embodiments of the present invention will be described below based on the drawings.

First, in FIG. 1, 1 is a time forming circuit (time t = 25 ms), 2 is an inverter, 3 is a transistor, 4 is a constant current circuit, 5 is a resistor, 6 is a capacitor, 7 is an operational amplifier circuit as a buffer, 8 is a constant current circuit, 9, 10 and 11 are resistors, 13 is an operational amplifier circuit as an integrator, 14 is a capacitor, 1
5 is an operational amplifier circuit as a hysteresis comparator (the operational amplifier circuit is commonly referred to as
Describe it as OPA. ), 16 and 17 are voltage dividing resistors that divide the voltage at the end of the resistor 9, 18 and 19 are also voltage dividing resistors, 20 and 21 are transistors, respectively, and 22 is an infrared light emitting element as a light emitting element that projects a spot light to the object to be measured. is a diode (hereinafter referred to as IRD),
23 and 24 are silicon photodiodes (hereinafter referred to as SPD) as light-receiving elements arranged adjacent to each other in the baseline length direction so as to be able to receive the light projected from the IRD 22 and reflected by the distance measurement target, respectively;
5 and 26 are AC amplifier circuits, and 27 and 28 are band filter circuits (center frequency f0 =
16KHz (hereinafter referred to as BPF), 29 and 30 are detection circuits, 31 and 32 are smoothing circuits, 33 and 34 are DC amplifier circuits, respectively.
6 and 37 are comparator circuits (hereinafter referred to as CMP), respectively.
), 38 is a constant current circuit, 39, 40 and 41 are reference voltages Vr ₁ , Vr ₂ and Vr ₃ applied to the inverting input terminal (-) of CMP 35 and the non-inverting input terminal (+) of CMP 36 and 37, respectively. Partial voltage resistance to give, 42
are AND gates, 43 and 44 are D-type flip-flop circuits, and 45 is an RS-type flip-flop circuit (the flip-flop circuits are hereinafter commonly referred to as FF), which are connected as shown in the figure. .

Next, the operation shown in FIG. 1 will be explained with reference to FIG. 2.

When a power switch (not shown) is closed at the start of the operation, power is supplied to each part of the circuit, and the FFs 43, 44, and 45 are released from reset.

Further, in this initial state, that is, in a state where the transistor 3 is conductive, point a, which is formed by the constant current circuit 4 and the resistor 5, and point b, which is formed by the constant current circuit 8 and the resistor 9, are at approximately the same potential. has been set, so
The output terminal a' point of OPA7 is also at the same potential,
By extension, OPA via resistors 10, 11 and 12
Both input terminals of 13 are at the same potential, and its output terminal at point c is also at the same potential. On the other hand, assuming that the output of OPA15 is "L" level, the non-inverting input terminal (+) has a voltage divided by resistors 18 and 19 between the potential obtained by dividing the voltage at resistor 9 end and ground G. The voltage at point d is given, OPA1
The potentials of both input terminals of 5 are placed in the relationship c>d.

Then, the time forming circuit 1 operates and its output is inverted to the "H" level for a time of t=25 ms. As a result, the output of the inverter 2 similarly inverts to the "L" level and the transistor 6 is cut off, so that the capacitor 6 is charged with a constant current by the constant current circuit 4 via the resistor 5, and the constant current is transferred to I, the capacitor Assuming that the capacitance of OPA 6 is C, the voltage V at the output terminal a' of OPA 7 rises from the above-mentioned potential as shown by ◯A according to the relational expression V=(1/C)I·t.

As a result, a potential difference is generated between both input terminals of OPA 13, current Ix flows, and capacitor 14 is charged in the direction shown. Therefore, as shown in ○B,
The output terminal of OPA13, that is, the inverting input terminal (-) of OPA15, the potential at point c falls from the above-mentioned potential, and when the potential at point c reaches the potential at point d, the output terminal of OPA15 becomes "H". As shown by the dotted line, the potential at point d is increased and the transistor 20 is made conductive. Therefore,
Since the connection point between resistors 10 and 11 is lowered to the ground G level, the electrical charge of capacitor 14 is transferred to resistor 1.
1 and the transistor 20, the potential at point c rises, and when the potential at point c reaches the previously increased potential at point d, the output terminal of the OPA 15 is again inverted to the "L" level, and the potential at point c rises. The level of the point is returned to the initial state, and the transistor 20 is turned off. Then, the capacitor 14 starts to be charged again by the current Ix, and the potential at point c starts to fall again.

Repeat the above operation, IRD22 becomes OPA1
The pulse is lit only when the output terminal of 5 is inverted to the "H" level and the transistor 21 is conductive, and the current Ix increases gradually in response to the rise in the voltage V at point a', and the Since the charging time to the potential at point d becomes faster, the blinking period becomes faster, and the frequency of light emission increases from a low frequency to a high frequency toward the center frequency of BPF 27 and 28, 0=16 KHz.

The light projected by the lighting of the IRD 22 is reflected from the distance measurement target and received by the SPDs 23 and 24, and as a result, the received light output at points e and e' is superimposed on the DC component due to natural light, as shown in ○c. Occur.

Further, the outputs at points and '' after the AC amplifier circuits 25 and 26 are amplified and appear as shown in circles.

Furthermore, since the center frequency of the outputs at points g and g' after BPF 27 and 28 is set to 0=16 KHz, they appear as if the waveform at point ○2 has been amplified, as shown in ○ho.

Furthermore, h and after the detection circuits 29 and 30
The output waveform at point h' is as shown in ○F, and the DC amplifier circuits 24 and 25 pass through the smoothing circuits 31 and 32.
The latter j and j' gradually increase from the predetermined value, as shown in ◯.

As shown in FIG. 2, when the object to be measured is located at a short distance, the reflected light spot Because it is narrow,
When the output voltage Vj at the point is sufficiently higher than the output voltage Vj' at the point j' and the output voltage Vj reaches the reference voltage Vr ₁ , the output of the CMP35 is inverted to the "H" level, and the previous time The AND gate 24 to which the "H" level signal is applied during time t is opened and its output is inverted to the "H" level. On the other hand, at that point,
Since the output voltage Vj' at point j' has not reached the reference voltage Vr ₃ , both the outputs of CMP36 and CMP37 are "H".
It remains at the same level. Therefore, AND gate 42
The FFs 43 and 44, which use the "H" level rising signal of the output as a clock pulse, both read the "H" level signal and output the signals to their respective output terminals _Q1 and _Q2.
The FF45, which stores an "H" level signal at the output terminal and uses the rising signal as a set pulse, outputs the
_Q3 flips to "H" level.

In addition, when the object to be measured is located at a middle distance position, the output voltage Vj' is between Vr ₂ < Vr ₃ due to the same operation, as shown in b1 and b2.
Output Q ₁ of FF43 sends a “H” level signal, and the other
The output terminal Q ₂ of FF44 stores "L" level signals, and the output terminal Q ₃ of FF45 stores "H" level signals.
Flip to level.

Furthermore, if the object to be measured is located at a boundary position to a long distance, the reflected light spot , the output voltages Vj and Vj' are almost equal, and at the time of the determination, the output voltage Vj' is higher than the reference voltage Vr ₂ , so
The output terminals Q ₁ and Q ₂ of the FFs 43 and 44 store "L" level signals, and the output terminal Q ₃ of the FF 45 is inverted to "H" level.

Furthermore, if the object to be measured is located at a very far distance, the reflected light spot X' will be wider toward the SPD24 at c1 and c2, as shown by the chain line, but because the distance is very far away, , the output voltage Vj does not reach the reference voltage Vr ₁ within the previous time t (this may also happen when the distance measurement target has a low reflectance), and the output of the CMP35 remains at the "L" level. , and when the time t ends, the AND gate 42
closes the gate, so FF45 is not set,
Output terminal _Q3 remains at the "L" level.

Note that at this time, the output of the AND gate 42 does not invert to the "H" level, so the FF 43
and 44 do not perform a read operation.

That is, as shown in the truth value chart in Figure 3, FF
It is set to distinguish near, medium and long distance based on the signal level status of output terminals Q ₁ and Q ₂ of FF 43 and 44, and when the output terminal Q ₃ of FF 45 is at "L" level. is FF43 and 44
This is set to give priority to long-distance discrimination.

Further, the reference voltage to the CMPs 36 and 37 in FIG. 1 is a fixed bias, and the output voltage Vj' and the output voltage Vj are compared in absolute value.

In the embodiment of FIG. 4, the reference voltages to the CMPs 36 and 37 are provided in a manner that divides the varying output voltage Vj, so that the output voltage Vj' is compared as a proportion of the output voltage Vj. Note that Vb of the voltage dividing circuit is biased to, for example, the normal voltage level of the light receiving output circuit of the SPD 23 or 24 when the IRD 22 is not operating.

In addition, in the circuit operation shown in FIG. 1, when the output of the CMP 35 is inverted to the "H" level, the state of the output voltage Vj' is determined, but the AND gate 42
Due to the following accumulated operation delay time, the determination may lack accuracy.

On the other hand, the feature of the embodiment shown in FIG. 4 is that, as mentioned above, the output voltage Vj' is
Since the determination is made based on the ratio to Vj, the accuracy can be improved compared to the previous embodiment.

Note that the number of stages of the distance measurement output mentioned above can be increased or decreased, and furthermore, when determining a long distance using FF45,
It is also possible to issue an alarm accordingly.

As described above, the present invention makes it possible to determine the ranging state with stable operation using a simple configuration that changes the light emission frequency of the light emitting element without performing logarithmic compression of the light receiving element output or automatic gain adjustment of the amplifier circuit. It is possible.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the relationship between the state of the reflected light spot and the output voltage with respect to the light receiving element, and Fig. 3 shows an example of the distance measurement output. FIG. 4 is a partial circuit diagram showing another embodiment of the present invention. 1... Time forming circuit, 7, 13 and 15... Operational amplifier circuit, 22... Infrared light emitting diode, 2
3 and 24...Silicon photodiode, 25 and 26...AC amplifier circuit, 27 and 28...Band filter circuit, 29 and 30...Detection circuit, 3
1 and 32...Smoothing circuit, 33 and 34...DC amplifier circuit, 35, 36, and 37...Comparator circuit, X and X'...Reflected light spot.

Claims (1)

[Scope of Claims] 1. In a triangular distance measuring device in which light emitted from a light emitting element is projected toward a distance measuring object and the reflected light is received by two adjacently arranged light receiving elements, A band filter circuit is provided in a circuit system that pulses the light emitting element and processes the output of the light receiving element, and changes the emission frequency of the light emitting element toward the center frequency of the band filter circuit within a certain period of time, and A distance measuring device characterized in that the output state of the other light-receiving element circuit is determined when the output of one light-receiving element circuit reaches a certain set value. 2. In a triangular distance measuring device in which light emitted from a light emitting element is projected toward a distance measurement target and the reflected light is received by two adjacently arranged light receiving elements, the light emitting element is lit in pulses. At the same time, a bandpass filter circuit is provided in a circuit system that processes the output of the light receiving element, and the emission frequency of the light emitting element is changed toward the center frequency of the bandpass filter circuit within a certain period of time. The measurement is characterized in that when the output reaches a certain set value, the output of the other light-receiving element circuit is compared with a predetermined ratio of the output of the one light-receiving element circuit. range device. 3. The distance measuring device according to claim 1 or 2, wherein the output of the other light receiving element circuit is compared with a plurality of levels. 4. Claims 1 or 2, characterized in that when the output of one of the light receiving element circuits does not reach a certain set value within a certain period of time, the distance measurement output is determined as long distance. The distance measuring device described in .