JP3187621B2 - Active triangulation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an active triangulation device, and more particularly, to a method of comparing an output difference signal of at least two divided light receiving means with a reference voltage.
Assuming a difference calculation type active triangulation device that determines whether the subject is closer or farther than the reference distance,
The present invention relates to a triangulation device that eliminates the need to separately provide a circuit for determining infinity.

[0002]

2. Description of the Related Art First, FIG. 3 shows the basic principle of the active triangulation method, wherein 1 is a light projecting means for generating, for example, near-infrared light, 2 is a light projecting lens, 3 is a subject, and 4 is a subject. The light receiving lens 5 is light receiving means having light receiving cells S1 and S2 divided into two. The output light of the light projecting means 1 is irradiated to the subject 3 by the light projecting lens 2, and the light reflected by the subject 3 enters the light receiving means 5 via the light receiving lens 4. At this time, since the incident angle with respect to the light receiving means 5 varies according to the distance to the subject 3, the component ratio of the amount of incident light to each of the light receiving cells S1 and S1 constituting the light receiving means 5 varies. Therefore, the distance to the subject 3 can be determined by comparing and calculating the amount of incident light with respect to each of the light receiving cells S1 and S1. The active triangulation devices are broadly classified into a ratio calculation method for calculating the output ratio of the light receiving cells and a difference calculation method for calculating the output difference of the light receiving cells, and both methods have advantages and disadvantages. The ratio calculation method has an advantage that a multi-step distance discrimination can be performed without being affected by the subject reflectance because a factor relating to the subject reflectance is canceled between the numerator and the denominator in the process of the ratio calculation. In order to perform the ratio operation, a combination circuit of a logarithmic amplifier and a differential amplifier is required, and the circuit configuration is complicated and expensive. On the other hand, the difference calculation method has the advantage that the circuit configuration is simple and inexpensive because a logarithmic amplifier is not required, but the difference calculation result has a factor related to the object reflectance in the difference calculation result. Depending on whether the subject is positive or negative, only a two-step distance determination of whether the subject is closer or farther than a predetermined reference distance can be performed. For this reason, the ratio calculation method is generally used for a relatively expensive camera, and the difference calculation method is generally used for a relatively low-cost camera. It is premised on a triangulation distance measuring device of the ratio calculation method used for various cameras.

FIG. 4 is a block diagram showing the basic principle of a difference calculation type triangulation distance measuring apparatus.
1. S2 denotes each of the light receiving cells described above, and the light emitted by the light projecting means 1 passes through the light receiving cells S1. S
2 is incident. Therefore, at this time, the light receiving cells S1. The incident light amount for each of S2 has a difference corresponding to the subject distance. Light receiving cell S1. In S2, a photocurrent corresponding to the amount of received light flows, is shaped by current shaping circuits 6 and 7, and is input to the subtraction circuit 8, which generates a voltage signal corresponding to the input current difference. The output voltage of the subtraction circuit 8 is compared with a reference voltage 10 indicating a reference subject distance by a comparison circuit 9 to determine whether the subject is closer or farther than the reference distance, and the determination result is given to the control unit 11. Then, the control unit 11 performs, for example, control of a focus adjustment mechanism (not shown) or tuning timing of a strobe device (not shown) based on the determination result of the distance.

FIG. 5 shows an example of a circuit configuration in which the conventional difference calculation method is more concretely described. Reference numeral 1 denotes the above-described light emitting unit using an infrared light emitting diode, 11 denotes the above-described control unit, and S1 denotes a control unit.・
S2 indicates each of the light receiving cells using the photodiode. The light receiving cell S1 is connected in series to a series circuit of a resistor 20 and a transistor 21 whose base and collector are short-circuited. When light enters the light receiving cell S1, a photocurrent I1 corresponding to the amount of incident light is applied to this series circuit. Flows. The transistor 21 forms a current mirror circuit with the transistor 22 sharing the base, and a current I1 equal to the current flowing through the transistor 21 flows through the transistor 22.

The light receiving cell S2 is connected in series to a series circuit of a resistor 23 and a transistor 24 whose base and collector are short-circuited. When light enters the light receiving cell S2, the light corresponding to the amount of incident light is applied to this series circuit. The current I2 flows.
Transistor 24 is a transistor 25 sharing a base
And a current mirror circuit.
5 and the transistor 26 in the series circuit
A current I2, which is equal to the current flowing in The transistor 27 is connected between the base and the collector of the transistor 26. In the case of the transistor 26 having a PNP configuration, the transistor 27 has a base current that cannot be substantially ignored. Are provided for compensating for the base current component. The transistor 26 forms a current mirror circuit with the transistor 28, and the same current I2 flows through the transistor 28.

The current I1 flowing to the transistor 22 flows as a subtraction current to the negative-phase input point of the operational amplifier 29, and the current I2 flowing to the transistor 28 flows as an addition current to the negative-phase input point of the operational amplifier 29. All the current flowing to the negative-phase input point of the operational amplifier 29 is the feedback resistor 30 of the operational amplifier 29.
Therefore, if the current flowing through the feedback resistor 30 is defined as Ia, the current Ia is expressed by (Equation 1). Since the reference operating point voltage Vref is applied from the power supply 31 to the positive-phase input point of the operational amplifier 29, the resistance value of the resistor 30 is set to R3.
When it is defined as 0 and the output voltage of the operational amplifier 29 is defined as Va, the output voltage Va of the operational amplifier 29 is expressed by (Equation 2). Ia = I2-I1 (Equation 1) Va = Vref-R30.times.Ia = Vref-R30.times. (I2-I1) (Equation 2)

The output voltage of the operational amplifier 29 is removed by a capacitor 32 for removing a stationary light component (a photocurrent component flowing depending on the object field light irrespective of the light emission of the light emitting diode 1) in the photocurrent. After that, the voltage is applied to the negative-phase input resistance 34 of the operational amplifier 33. The reference operating point voltage Vref is applied from the power supply 31 to the positive-phase input point of the operational amplifier 33, and the negative-phase input level of the operational amplifier 33 is also considered to be Vref due to an imaginary short between the two inputs of the operational amplifier 33. Voltage V34 generated at both ends
Is expressed by (Equation 3), and the current I34 flowing through the resistor R34 is expressed by (Equation 4). V34 = {Vref−R30 × (I2-I1)} − Vref = R30 × (I1-I2) (Expression 3) I34 = R30 × (I1-I2) / R34 (Expression 4)

The current I34 shown in the above equation (4) all flows through the resistor 35, and the reference operating point voltage of the operational amplifier 33 is Vref.
Becomes a value represented by (Equation 5). Vb = Vref−R35 × R30 × (I1-I2) / R34 = Vref−k × (I1-I2) (5) where k is R35 × R30 / R34.

The output Vb of the operational amplifier 33 is applied to the positive-phase input of the comparator 36, and the reference voltage Vref is applied to the negative-phase input of the comparator 36 from the power supply 31. The comparator 36 is an operational amplifier 33
Is low when the output voltage Vb of the
Generate a pulse. Therefore, the condition under which the comparator 36 generates an L pulse is expressed by (Equation 6). When Vref and the constant k on the right and left sides in (Equation 6) are arranged, the condition under which the comparator 36 generates an L pulse is expressed by (Equation 7). Is shown. Vref> Vb = Vref-k * (I1-I2) (Equation 6) I1> I2 (Equation 7)

As is clear from FIG. 3, as the subject distance increases, the amount of light incident on the light receiving cell S1 relatively increases, and when the subject distance becomes longer than a predetermined distance (for example, 3 m) (Equation 7). Is satisfied, the comparator 36 generates an L pulse. When the comparator 36 generates an L-pulse when the light emitting unit 1 generates a near-infrared pulse, the control unit 11 determines that the subject is in a long-distance region of 3 m or more, and when the comparator 36 does not generate an L-pulse, the subject is 3 m. It is determined that it is within the short distance area within.

[0011]

As described above, in the conventional circuit of this type, a common reference power supply 31 is used for a subtraction circuit centered on operational amplifiers 29 and 33 and a comparison circuit using a comparator 36. Therefore, it is necessary to separately provide a circuit element for performing infinity discrimination, and the processing time for performing infinity discrimination is added, so that the time required for the distance measurement operation becomes longer as a whole. There was a problem.

More specifically, FIG. 6 shows the output voltage Vb of the operational amplifier 33 when the light projecting unit 1 generates a near-infrared pulse. As is clear from FIG. The photocurrent I2 of the light receiving cell S2 becomes relatively large, and accordingly, the output voltage Vb of the operational amplifier 33 shown in (Equation 5) also becomes large. Accordingly, when the subject is sufficiently close, the output voltage Vb of the operational amplifier 33 as shown by the curve a in FIG. 6 is obtained. Then, as the subject distance increases, the output voltage Vb of the operational amplifier 33 decreases as curves b and c in FIG. When the output voltage Vb of the operational amplifier 33 falls below the reference voltage Vref, the comparator 3
6 generates an L pulse. Then, the control unit 11
It is determined whether the subject is in a long distance area or a close area based on the presence or absence of the pulse. Now, the output voltage Vb of the operational amplifier 33 changes to the curve d ・ ef as the subject distance further increases, but the absolute values of the photocurrents I1 ・ I2 decrease as the distance increases. The absolute value of (I1−I2) decreases, and the value of the output voltage Vb of the operational amplifier 33 eventually converges to Vref in the infinity region. Therefore,
In the vicinity of the branch point between the short distance area and the long distance area, whether the subject distance is near the branch point between the short distance area and the long distance area, or whether the subject distance is substantially infinite is determined. Therefore, the conventional circuit example shown in FIG.
It is necessary to perform infinity determination before determining the distance of the subject.

Therefore, in the conventional circuit shown in FIG. 5, a transistor 37 and a diode 38 are used to determine infinity.
Is incorporated. That is, if the transistor 37 is turned on prior to the determination of the distance, the photocurrent I2 flowing through the transistor 28 flows into the ground via the transistor 37, and one photocurrent I1 is supplied to the output after the operational amplifier 29.
Only reflected. When the absolute value of the one photocurrent I2 falls below a certain level, it can be determined that the subject is at infinity. However, in such a method, infinity determination must be performed prior to distance determination, and not only a circuit element for this infinity determination is required, but also the time required for infinity determination. Therefore, there is a problem that the distance measurement time becomes longer as a whole. In addition, since the photocurrent flowing through the light receiving cells S1 and S2 is affected by the fluctuation of the power supply voltage and the ambient temperature, there is a problem that the discrimination accuracy is apt to be reduced due to this.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and it is possible to immediately determine a long-distance region and a short-distance region without performing infinity determination. It is a first object of the present invention to provide an active triangular distance measuring apparatus having a reduced configuration, and a second object of the present invention is to provide an active triangular distance measuring apparatus capable of preventing a decrease in determination accuracy due to a fluctuation in a power supply voltage or a fluctuation in an ambient temperature. The purpose of. In summary, the active triangulation device of the present invention comprises: a light projecting means for irradiating light toward a subject; and at least two divided light receiving means for receiving light reflected by the subject irradiated by the light projecting means. Subtracting means for calculating, as a voltage signal, a difference between the output signals of the light receiving means, which changes according to the amount of light incident on the light receiving means, and generating a reference voltage corresponding to a predetermined reference distance from the light receiving means to the subject. Active triangulation comprising: a reference value generating means; and a comparing means for determining whether the subject is closer or farther than the reference distance by comparing the voltage signal calculated by the subtracting means with the reference voltage generated by the reference value generating means. In the distance measuring device, the reference value generating means, when the subject is in an infinite distance region with respect to the light receiving means, sets a reference operating point voltage, which is a convergence point of the voltage signal calculated by the subtracting means, as a reference voltage. The reference voltage is offset with respect to the reference operating point voltage to the side corresponding to the direction in which the subject is closer to the light receiving means, so that infinity determination prior to distance determination is unnecessary, and The reference value generation means includes:
The configuration is such that the reference voltage and the reference operating point voltage are changed depending on the temperature and the power supply voltage, so that the influence of the power supply voltage fluctuation and the temperature fluctuation is removed.

[0015]

In other words, in the active triangulation device of the present invention,
When the distance from the light receiving unit to the subject (subject distance) becomes infinity, the voltage signal calculated by the subtracting unit (output voltage of the subtracting unit) converges to the reference operating point voltage. However, the reference voltage has a value offset from the reference operating point voltage, and the output voltage of the subtraction means does not converge on the reference voltage. At this time, since the reference voltage is offset with respect to the reference operating point voltage to a side corresponding to a direction in which the subject becomes closer, if the output voltage of the subtraction means is near the reference operating point voltage, Is determined to be farther than the reference distance. Therefore, it is not necessary to perform infinity determination prior to determination of a long-distance region and a short-distance region.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram of an active triangulation device according to one embodiment of the present invention. The same circuit elements as those of the conventional circuit shown in FIG. Although the description is omitted, in the present invention, the resistor 40,
The terminal voltage of the resistor 41 when a current flows in the series circuit of the diode 41 and the diode 42 is added to the positive phase inputs of the operational amplifiers 29 and 33 as the reference operating point voltage Vref1, and the terminal voltage of the resistor 40 is set as the reference voltage Vref2. By adding to the negative phase input, the reference voltage of the comparator 36 is offset with respect to the reference operating point voltages of the operational amplifiers 29 and 33, and the transistor 43 acting as a power source-dependent current source and the temperature-dependent current source A current is supplied from the transistor 44 acting as a resistor to a series circuit of the resistors 40 and 41 and the diode 42 so that the reference operating point voltage Vref1 and the reference voltage Vref2 have power supply dependency and temperature dependency.

First, VB is a power source directly obtained from a battery for a camera, and naturally has a power source dependency. Power supply V
A current is supplied from B to the series circuit of the resistors 45 and 46, and the level of the voltage dividing point of the resistors 45 and 46 fluctuates depending on the power supply voltage VB. The voltage dividing points of the resistors 45 and 46 are connected to the base input of the transistor 47, and the base level of the transistor 47 varies depending on the power supply voltage VB. A current depending on the power supply voltage VB flows.

The transistor 48 forms a current mirror circuit with the transistor 43 sharing the base. Since a current equal to (or proportional to, depending on the base-emitter junction area) flows through the transistor 48, a current flows through the transistor 43. , The transistor 43 is a resistor 4
It acts as a current source having a dependency on the power supply voltage VB with respect to the series circuit composed of 0, 41 and the diode 42.

Reference numeral 50 denotes a constant voltage source which does not depend on the power supply voltage. The constant voltage source 50 is connected to the base input of the transistor 51. The collector of the transistor 51 is connected to the transistor 52, and the emitter of the transistor 51 is connected to a resistor 53 having a high temperature dependency (a large change in resistance due to a temperature change). Accordingly, when a base current is supplied from the constant voltage source 50 to the transistor 51 and a current flows through the series circuit of the transistors 52, 51 and the resistor 53, the transistor 51 corresponds to the resistance value of the resistor 53 which changes depending on the temperature. The base-emitter voltage fluctuates, so that the current value flowing through this series circuit fluctuates with temperature dependence.

The transistor 52 forms a current mirror circuit with the transistor 44 sharing the base. Since a current equal to (or proportional to) the current flowing through the transistor 52 flows through the transistor 44, the transistor 44 is connected to the resistor 40. , 41 and a diode 42 act as a temperature-dependent current source.

Next, the operation of the above embodiment will be described with reference to the above items. First, when the distance measuring operation is started, the control unit 11 supplies a pulse current to the light projecting unit 1, and the light projecting unit 11 generates a near-infrared pulse. The near-infrared pulse is applied to the subject 3 by the light projecting lens 2, and the reflected light from the subject 3 enters the light receiving cells S 1 and S 2 via the light receiving lens 4. At this time, the amount of light incident on the light receiving cells S1 and S2 is determined depending on the subject distance, and a photocurrent I1 corresponding to the amount of light incident on the light receiving cell S1 flows through the transistor 22 in the same manner as in the conventional circuit shown in FIG. The photocurrent I2 corresponding to the amount of light incident on the cell S2 is
Therefore, the current Ia shown in (Equation 1) flows through the resistor 30.

In this embodiment, the operational amplifiers 29, 3
Since the reference operating point voltage Vref1 depending on the power supply voltage and the temperature is applied to the positive-phase input of the resistor 3 from the voltage dividing points of the resistors 40 and 41, the output voltage Vc of the operational amplifier 29 becomes a value represented by (Equation 8). , And the output voltage Vd of the operational amplifier 33 becomes a value represented by (Equation 9). Vc = Vref1-R30 × (I2-I1) (Equation 8) Vd = Vref1-k × (I1-I2) (Equation 9) where k is R35 × R30 / R34.

The output Vd of the operational amplifier 33 is applied to the positive-phase input of the comparator 36, and the reference voltage Vref2 depending on the power supply voltage and temperature is applied to the negative-phase input of the comparator 36 from the connection point of the resistor 40 and the transistor 43. Therefore, the condition under which the comparator 36 generates an L pulse is represented by (Equation 10). Vref2> Vd = Vref1-k * (I1-I2) (Equation 10)

FIG. 2 shows the output voltage Vd of the operational amplifier 33 when the light projecting unit 1 generates a near-infrared pulse. As is apparent from FIG. Of the photocurrent I2 of
The output voltage Vd of the operational amplifier 33 shown in FIG. Therefore, when the subject 3 is sufficiently close, the output voltage Vd of the operational amplifier 33 as shown by the curve a in FIG. 2 is obtained. The operational amplifier 33 increases as the subject distance increases.
The output voltage Vd of the curve b · c · d · e · in FIG.
f, the output voltage Vd of the operational amplifier 33 becomes equal to the reference voltage Vref2 applied to the negative-phase input of the comparator 36.
, The comparator 36 generates an L pulse. Then, the control unit 11 determines whether the subject 3 is in a long distance area or a close area based on the presence or absence of the L pulse. Now,
When the object distance further increases, the absolute values of the photocurrents I1 and I2 decrease as the distance increases. Therefore, the absolute value of (I1−I2) in Expression (10) decreases. The value of the output voltage Vd eventually converges to Vref1, which is the reference operating point voltage of the operational amplifier 33. However, in the present invention, the comparator 3
6 is offset with respect to the reference operating point voltage Vref1 which is the convergence point of the output voltage Vd of the operational amplifier 33, and the reference operating point voltage Vref1 is the convergence point of the output voltage Vd of the operational amplifier 33 at infinity. As shown in FIG. 2, since the level is lower than the reference voltage Vref2 of the comparator 36 (that is, the long-distance shooting area), it is necessary to perform infinity determination before determining whether the area is the long-distance area or the short-distance area. Completely disappears. The reference voltage V of the comparator 36
It goes without saying that the direction of the offset of ref2 and the amount of the offset are appropriately determined according to the positive and negative polarities and various characteristics of the circuit element.

[0025]

As described above, according to the present invention, the reference voltage of the comparing means is offset from the reference operating point voltage of the subtracting means to the side corresponding to the direction in which the subject is closer to the light receiving means. Therefore, the convergence point of the voltage signal calculated by the subtraction means in the infinity area becomes different from the reference voltage of the comparison means, and the infinity determination is performed prior to the determination of the long distance area and the short distance area. There is no need at all. Furthermore, since the temperature dependency and the power supply voltage dependency are given to the reference operating point voltage of the subtraction means and the reference voltage of the comparison means,
Characteristic fluctuations of the light receiving means due to power supply voltage fluctuations and temperature fluctuations are canceled out, and a decrease in determination accuracy due to temperature fluctuations and power supply voltage fluctuations is effectively prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing a change in an output voltage of a subtracting unit when the light emitting unit emits a pulse in the embodiment shown in FIG. 1;

FIG. 3 is an explanatory diagram showing a basic principle of an active triangulation device.

FIG. 4 is a block diagram illustrating the principle of an active triangulation device using a difference calculation method.

FIG. 5 is a circuit diagram of a conventional active triangulation device.

FIG. 6 is a diagram showing a change in an output voltage of a subtracting unit when the light emitting unit emits a pulse in the conventional example shown in FIG. 5;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light projecting means 5 light receiving means S 1, S 2 light receiving cell 29, 33 operational amplifier 36 comparator Vref 1 reference operating point voltage Vref 2 reference voltage 43 transistor as voltage-dependent current source 44 transistor as temperature-dependent current source

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 7/32 G01C 3/00 G03B 13/36

Claims (2)

(57) [Claims] 1. A light projecting means for irradiating light to a subject; a light receiving means divided into at least two portions into which light irradiated by the light projecting means and reflected by the subject is incident; and an incidence on the light receiving means. Subtraction means for calculating, as a voltage signal, a difference between the output signals of the light receiving means, which changes in accordance with the amount of light, and reference value generation for generating a reference voltage corresponding to a predetermined reference distance from the light receiving means to the subject Means for comparing the voltage signal calculated by the subtraction means with the reference voltage generated by the reference value generation means, thereby determining whether the subject is closer or farther than the reference distance. In the distance measuring device, the reference value generation unit is a convergence point of the voltage signal calculated by the subtraction unit when the subject is in an infinite distance region with respect to the light receiving unit. Generating a quasi-operation point voltage together with the reference voltage, wherein the reference voltage is offset with respect to the reference operation point voltage to a side corresponding to a direction in which the subject is closer to the light receiving unit. Active triangulation device. 2. The active triangulation apparatus according to claim 1, wherein said reference value generating means is configured to vary said reference voltage and said reference operating point voltage depending on temperature and power supply voltage. An active triangulation device, characterized in that: