JP3127010B2 - Distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device, more specifically, an active distance measuring device which projects pulse light such as infrared light onto a subject and detects a subject distance based on reflected light from the subject. Related to the device.

[0002]

2. Description of the Related Art An example of a conventional infrared light active type distance measuring device will be described with reference to FIG. 7. The front surface of an infrared light emitting diode (hereinafter referred to as IRED) 1 which is one of light emitting means is described. , A light projecting lens 4 is arranged, and a light receiving lens 5 is arranged away from the lens 4 by a base line length. A semiconductor position detecting element (hereinafter abbreviated as PSD) 50, which is one of the light receiving means, is provided with one end aligned with the optical axis of the light receiving lens 5.

If the base line length is s, the object distance is L, and the distance between the light receiving lens 5 and the PSD 50 is f, the PSD 50
The distance x from the optical axis of the light receiving lens 5 above to the incident position of the light beam reflected by the subject 6 is as follows: x = s · f / L ……………………………………. ............ (1) On the other hand, assuming that the length of the light receiving surface of the PSD 50 is t,
The ratio of the output currents I _a and I _b of PSD50 becomes _{I a / I b = x /} (t-x) .......................................... (2). By transforming this equation (2) and further substituting the above equation (1), I _a / (I _a + I _b ) = (s · f / t) · (1 / L) (3) become. The (3) as shown in the formula, can be uniquely determined the object distance L by calculating the ratio of the output currents I _a and I _b of PSD 50.

[0004] Now, the output light current I _a of PSD50, I _b
Are amplified by the preamplifiers 51 and 52, respectively.
Current-voltage conversion is performed by the compression diodes 53 and 54, respectively, and logarithmically compressed. These compressed voltages V _B and V _A are input to the ratio calculation circuit 60 via buffers 55 and 56, respectively.

The ratio operation circuit 60 is composed of an NPN transistor 5
7, 58 and a current source 59. Assuming that the current value of the current source 59 is I ₀ , the output current I _c is given by I _c = {I _a / (I _a + I _b )} I ₀ (4) An output proportional to _Ia / ( _Ia + _Ib ) of the above equation (3), that is, proportional to the reciprocal 1 / L of the object distance is obtained.

Next, FIG. 8 will be described as another conventional example.
In the figure, the center of the PSD 50 coincides with the optical axis of the light receiving lens 5. The same members as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted. Only different members will be described below.

The operational amplifier 65 includes external resistors 61 to 64
At the same time, the calculation of the following equation (5) is performed to output a calculation output V ₀ .

[0008]

(Equation 1)

Assuming that the length of the light receiving surface of the PSD 50 is t,
Since the ratio of the output currents I _a and I _b of PSD50 becomes _{= I a / I b (t} / 2 + x) / (t / 2-x) .................. (6), the equation (6) By substituting the above equation (1) and further substituting the result into the above equation (5), the following equation (7) is obtained.

[0010]

(Equation 2)

Then, when the operation output V ₀ is differentiated by the reciprocal 1 / L of the object distance,

[0012]

(Equation 3)

[0013] Therefore, at the object distance L, the inclination is ² sf so that (t / sf) ² > (1 / L) ^2.
/ T is equal to the straight line, and the slope becomes larger in other areas. In a normal distance measurement range, an area where (t / sf) ² > (1 / L) ² is set, so that the subject distance 1 /
L and the calculated output V ₀ have a proportional relationship, and the subject distance can be determined by calculating the calculated output V ₀ .

In the PSD 50 used in the conventional infrared active distance measuring device shown in FIGS.
The signal light current output from the signal electrodes at both ends is the same as the PSD.
It changes in proportion to the change in the amount of light radiated to 50. The amount of light applied to the PSD 50 is inversely proportional to the square of the subject distance. Therefore, in order to measure a wide ranging range from a short distance to a long distance by the PSD 50, an output current having a large dynamic range that changes in inverse proportion to the square of the distance is logarithmically compressed and processed. Thereby, it is possible to cope with a signal light current having a large dynamic range.

On the other hand, a distance measuring device for processing a signal light current output from signal electrodes on both ends of a PSD without logarithmic compression is disclosed in, for example, Japanese Patent Application Laid-Open No. 60-7317.
In this Japanese Patent Application Laid-Open No. 60-7317, as shown in FIGS. 4 and 5 in the specification, the output current of the light receiving element is linearly amplified, so that the amplified output signal has a large dynamic range.

Therefore, in order to prevent the circuit from being saturated with a high reflectance object located at a close distance where the amount of reflected light is large, as shown in FIG. AGC (auto gain control) is performed to detect and detect the light emission of the IRED.

[0017]

SUMMARY OF THE INVENTION However, PSD
In the conventional examples shown in FIGS. 7 and 8 in which the signal light current output from is subjected to logarithmic compression and then signal processing, the change in the compressed signal current value with respect to the change in the subject distance becomes smaller. There is a problem that the distance resolution is deteriorated and the distance measurement accuracy of a long-distance subject is reduced.

Further, the signal current output from the PSD is not logarithmically compressed, and the AGC is applied only to a high-reflectance object located at a close distance.
In the technical means disclosed in US Pat. No. 7,317, AGC is not used for a subject at a short distance or a medium distance, so that setting such as a circuit gain cannot be optimized for a subject at a long distance. As a result, the distance measurement accuracy for a long-distance subject is reduced.

Therefore, if the optimum circuit conditions are set for each of the distance measurement areas using AGC for short to medium distances, another problem arises that the circuit scale is increased. . Further, a general AGC in which a circuit gain is controlled by detecting the amount of reflected light from a subject has exactly the same disadvantage.

In other words, in a distance measuring device that processes the output photocurrent from the light receiving means without logarithmic compression, in order to secure a wide ranging range from a short distance to a long distance, the output photoelectric flow rate of the light receiving element is required. Accordingly, circuit means such as an AGC circuit for controlling the number of times of light emission of the IRED and the gain of the processing circuit are required, and there is a problem that the circuit scale becomes large.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a wide range from short distance to long distance without deteriorating the distance measurement accuracy on the long distance side in the active AF (auto focus) system. An object of the present invention is to provide a distance measuring device capable of measuring a distance.

[0022]

Means for Solving the Problems and action] The purpose of the
In order to achieve this, the distance measuring apparatus according to the first invention includes a light projecting unit that projects a light beam toward a subject, and a first light receiving unit that receives reflected light from the subject that is closer than a predetermined distance. A second light receiving means for receiving reflected light from the subject at a distance longer than a predetermined distance, and an output of the first light receiving means being converted by a current-voltage conversion means having a first current-voltage conversion characteristic. The first signal converting means for performing conversion processing and the output of the second light receiving means are converted by the current-voltage converting means having second current-voltage converting characteristics different from the first current-voltage converting characteristics. And second signal conversion means for processing. In addition, the measurement according to the second invention
The distance device is a light projecting unit that projects a light beam toward a subject,
Receives reflected light from the subject that is closer than a predetermined distance.
A first light receiving unit that emits light;
A second light receiving means for receiving reflected light from the subject;
Converting the output of the first light receiving means into a logarithmically compressed signal;
The output of the first signal converting means and the output of the second light receiving means are paired.
A second signal converting means for converting the signal into a signal which is not subjected to number compression.
It is characterized by having. Further, according to the third invention,
The distance measuring device is a light projecting means for projecting a light beam toward a subject.
And reflected light from the subject that is closer than a predetermined distance
And a first light receiving means for receiving the
Second light receiving means for receiving reflected light from the subject
And the output of the first light receiving means is transformed into a logarithmically compressed signal.
The first signal converting means for converting the signal and the output of the second light receiving means.
Second signal converting means for converting the force into a signal which is not logarithmically compressed
And the output of the first signal converting means and the second signal converting means.
Selecting means for selecting one of the outputs of
Based on the output selected by the selection means.
And a distance detecting means for detecting a distance.
And The distance measuring apparatus according to the fourth aspect of the present invention includes
In the distance measuring apparatus according to the third aspect, the distance detecting means
Is the first signal converting means or the second signal converting means.
A calculating means for calculating the ratio of the signal outputs of the stages;
The distance is detected based on the output of the calculating means.
It is characterized by the following.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments. Prior to describing an embodiment of the present invention, a basic concept of the present invention will be described with reference to FIGS.

Referring to FIG. 1, an IRED 1
From the subject 6 via the light projecting lens 4
Is irradiated. The reflected light from the subject 6 is incident on the first light receiving means 2 or the second light receiving means 3 via the light receiving lens 5, and the photocurrents _Ia , _Ib , I corresponding to the incident positions.
_c and _Id respectively occur.

Here, the first light receiving means 2 is arranged on the short distance side, and the second light receiving means 3 is arranged on the long distance side so as to be able to receive the reflected light from the respective objects. The light receiving unit 3 is configured such that the moving range of the incident light on the light receiving surface is narrower than the first light receiving unit 2.

FIG. 2 shows the reciprocal of the subject distance, 1 / L,
FIG. 3 is a diagram showing a relationship between the total output current due to light incident on the first light receiving means 2 or the second light receiving means 3, wherein the subject distance LN on the horizontal axis is the closest distance that can be measured, for example, 60 cm;
The subject distance LF is the longest possible distance determined by the detection limit of the distance measurement circuit, and indicates, for example, 10 m. The total output photocurrent corresponding to the reciprocal of the farthest distance LF is defined as I _M, and the vertical axis is scaled based on this.

In FIG. 2, the distance measurement range covered by the first light receiving means 2 is set to, for example, 1 / LN to 2 / LF, that is, 60 cm to 5 m in distance.
2 / LF to 1 / LF That is, the distance is set to 5 m to 10 m, respectively. Then, the dynamic range of the total photocurrent output from the first light receiving means 2 is:

[0028]

[Equation 3A]

[0029]

The dynamic range of the total photocurrent output from the second light receiving means 3 becomes a very small value as shown in the following equation.

4I _M ÷ I _M = 4 Therefore, in order to cope with these two kinds of contradictory signals, returning to FIG. 1 above, the output of the first light receiving means 2 is converted to a first signal conversion for logarithmic compression. after being logarithmically compressed is input to the means 7, Ia / by the first calculation means 9 (I _a + I _b)
Is calculated. On the other hand, the output of the second light receiving means 3 is input to the second signal conversion means 8 for linear amplification and linearly amplified, and then I _c / (I
_c + _Id ) is calculated. Note that each of the arithmetic means 9,
The calculation in 10 will be described in detail in an embodiment described later.

In this case, since the output current of the first light receiving means 2 is a relatively large value corresponding to a subject at a short distance to a medium distance, deterioration in distance measurement accuracy due to logarithmic compression hardly causes a problem. On the other hand, the output current of the second light receiving means 3 is small corresponding to a long-distance subject, but the dynamic range is small, so that it is possible to optimize circuit constants such as gain, and as a result, detection accuracy is reduced. Can be higher.

In this way, it is possible to provide a distance measuring apparatus that satisfies both distance measurement over a wide range from a short distance to a long distance and high-precision distance measurement for a long-distance object.

The selecting means 34 selects one of the first calculating means 9 and the second calculating means 10 and outputs it to the distance detecting means 11. The distance detecting means 11 detects the distance to the subject based on the output of the selecting means 34. In addition, the first,
The second calculating means 9 and 10 may be operated after the selection by the selecting means 34. The above is the description of the basic concept of the present invention. Next, an embodiment of the present invention will be described with reference to FIGS.

FIG. 3 is a block diagram of a distance measuring apparatus according to an embodiment of the present invention. A light projecting lens 4 is disposed in front of the IRED 1 and a light receiving lens 5 is provided at a distance from the light projecting lens 4 by a base line. Is arranged. Behind the light receiving lens 5, a second t _B having a length t _B centered on the optical axis of the light receiving lens 5.
PSD3 as a light receiving means is arranged.
Length t _A adjacent to the opposite side to the IRED1 respect, first
PSD2 is disposed as a light receiving means. And PSD2 is 2 / LF-1 in FIG.
/ LN and PSD3 are 1 / LF to 2 / LF
Correspond to the respective subject distances.

The reflected light from the subject 6 is PSD 2 or 3
Of the photocurrent I _a ,
I _b, I _c, I _d is output. Preamplifier 12, 1
3, 14 and 15 absorb the signal light current with low input impedance, remove the photocurrent component due to the stationary light, amplify and output only the signal light current.

The preamplifier 13 has two output terminals, and one output is input via an analog switch 17 to a light intensity integration circuit 23 comprising an operational amplifier 27 and an integration capacitor 26. After the other output is wired-ORed with the output of the preamplifier 12, the analog switch 16
Is input to the light intensity integration circuit 22 including the operational amplifier 25 and the integration capacitor 24 via The preamplifiers 12 and 13 and the light quantity integrating circuits 22 and 23 provide
Second signal converting means for converting the output of the second light receiving means into a linear signal is constituted.

The analog switches 16 and 17 are IRED
Is turned on in synchronization with the first light-emitting, the sum of the output currents of the are turned preamplifier 12 and the preamplifier 13 (I _c + I _d)
Is integrated by the integration capacitor 24. At the same time the output current I _c of the preamplifier 13 is integrated in the integrating capacitor 26.

The output currents of the preamplifiers 14 and 15 flow into compression diodes 18 and 19 and are logarithmically compressed. The preamplifiers 14 and 15 and the compression diodes 18 and 19 constitute first signal conversion means for converting the output of the first light receiving means into a logarithmically compressed signal.

The logarithmically compressed signal is supplied to a buffer 2
The signals are input to the ratio calculation circuit 33 corresponding to the first calculation means described with reference to FIG. The ratio calculation circuit 33 includes NPN transistors 29 and 30 and a current source 31.
And a current source 3 synchronized with the light emission of the IRED 1.
By turning on 1, the signal light current logarithmically compressed by the integration capacitor 28 is integrated.

The reset circuit 32 includes a light amount integration circuit 22 and
23 and a ratio calculation circuit 33, and has a function of setting the respective integration capacitors 24, 26 and 28 to an initial state.

The control circuit 35 A / D converts and reads the outputs V _B , V _A , and V _INT of the light quantity integration circuits 22 and 23 and the ratio calculation circuit 33. The amount the integrator circuit 22 of the output V _B and the light quantity output of the integration circuit 23 V _A and the basis ratio calculating V _A /
Carry out the V _B. Further, it has a function of outputting a signal T ₁ for controlling the light emission timing T of the IRED ₁ and a timing signal T ₂ for controlling the analog switches 16 and 17 and the current source 31 in synchronization with the signal T ₁ . .

Since the control circuit 35 has the functions of the second calculating means 10, the selecting means 34 and the distance detecting means 11 shown in FIG.
I _c / (I _c + I _d ) obtained by
The procedure for selecting the distance and measuring the distance of a long-distance object with high accuracy by the distance detecting means 11 will be described below.

When the analog switches 16 and 17 are turned on in synchronization with the light emission of the IRED 1, the light quantity integration circuit 2 is turned on.
2 and 23 The integration voltage V of the integration capacitors 24 and 26
_B and V _A are as follows: V _A = K · I _c · n · τ / C _p ················ (9) V _B = K · (I _c + I _d ) · n · τ / C _p ... (10) Here, n is the number of light emission times of the IRED 1 τ; integration time during one light emission C _p ; capacitance value K of the integration capacitors 24 and 26; amplification factor of the preamplifiers 12 and 13.

Then, the ratio detection V _A / V is calculated by the distance detecting means 11.
Performs _B, the ratio calculated value of _{V A / V B = I c} / (I c + I d) becomes PSD3 output current. In this case, the values of the constants n, τ, C _p , and K are, as described above, because the dynamic ranges of I _c and I _d are set relatively narrow, so that an optimal constant can be selected. With the detection sensitivity, a long distance subject can be measured with high accuracy.

Next, the reflected light from the subject at a short distance is received, and the ratio operation value I _a / (I _a + I _b ) is calculated by the ratio operation circuit 33 corresponding to the first operation means 9 (see FIG. 1). Will be described in detail.

When the current source 31 is turned on in synchronization with the light emission of the IRED 1, an integration current I _INT to the integration capacitor 28 is generated.

[0048]

(Equation 4)

Therefore, the integrating capacitor 28

[0050]

(Equation 5)

The following voltage signal is generated. Therefore, the control circuit 3
5 can obtain _a ratio operation value _Ia / ( _Ia + _Ib ) of the output current of PSD2 from the above equation (12). Here, I _{0 is} the current value of the current source 31, and C is the capacitance value of the integrating capacitor 28.

FIG. 4 shows the ratio operation values Ia / Ia + Ib,
FIG. 7 is a diagram showing a relationship between Ic / Ic + Id and a reciprocal 1 / L of a subject distance. On PSD2 or PSD3,
The distance x from the optical axis of the light receiving lens 5 to the position where the reflected light from the subject 6 enters is given by the above equation (1).
The length of the light receiving surface of PSD2 and PSD3 is because each tA · tB, the ratio calculated value Ia / Ia + I b can be expressed as the following equation. Also, the ratio operation value Ic / Ic + Id is similar.
Although it can be expressed by a similar expression, the description thereof is omitted.

[0053]

(Equation 6)

Thus, the ratio Ia / Ia + Ib and Ic
The slope of / Ic + Id is the length tA of PSD2 and PSD3 respectively.
, TB. Then, by substituting the actual subject distance, for example, LF = 10 m LN = 60 cm, the ratio between the PSD lengths tA and tB is obtained.

[0055]

(Equation 7)

And the slope of I _c / I _c + I _d is
It is about 3.7 times the gradient of _{I a / I a + I b} .

This means that the change in the specific output with respect to the change in the reciprocal 1 / L of the subject distance is large, so that the distance measurement accuracy by the PSD 3 corresponding to the long distance side is further improved. As described above, by shortening the length t _B of the PSD 3 on the long distance side to narrow the distance measurement range, the distance measurement accuracy can be improved.

The operation of the present embodiment constructed as described above will be described with reference to the flowchart shown in FIG. 5 and the timing chart shown in FIG. 6. First, as shown in FIGS. Only during the light emission period of the IRED 1 is the current source 31 and the analog switches 16 and 1 supplied from the timing signal T _2.
7 is turned on (step S1 in FIG. 5). Then, FIG.
(C), (D) and (E), as shown in FIG.
4, 26 and 28 are integrating operations 41, 42, 4 respectively.
Perform Step 3.

When the integration of the predetermined number n is completed, the control circuit 35 performs A / D conversion of the integration voltage _VINT of the integration capacitor 28 and reads out the ratio operation value 1 / LA (step S2 in FIG. 5). That is, for example, as shown in FIG. 6 (C), a reverse integration circuit (not shown) is operated to perform the reverse integration operation 44 of the integration capacitor 28, and as shown in FIG. Time 1
A / D conversion is performed by counting / LA.

Next, in the control circuit 35, the ratio operation value 1 / LA by PSD2 and 2 / LF in FIG.
Then, it is determined whether 1 / LA is valid (step S3 in FIG. 5). 1 / LA <2 / LF
In the case of, it is determined that the reflected light from the subject is incident on the PSD 3, and as shown in FIGS. 6 (G) and (H),
The integrated voltage of the integrating capacitor 24 and 26 to obtain the V _B and V _A is read in the same manner described above (step S4 in FIG. 5).

[0061] Thereafter, as shown in FIG. 6 (I), by executing the specific operation V _A / V _B obtains the 1 / LB (step S5 in FIG. 5), make this a definite distance value (Fig. 5 Step S6).

On the other hand, if 1 / LA <2 / LF is not satisfied, it is assumed that the reflected light from the object is incident on PSD2, and 1 / LA is determined as the definite distance measurement value (step S7 in FIG. 5). End the distance.

As described above, the control circuit 35 calculates the ratio operation value 1 /
When it is determined that LA is longer than the predetermined distance 2 / LF, the ratio calculation value 1 / LB is selected, and otherwise, the ratio calculation value 1 is set.
/ LA is selected to be the determined distance measurement value. The above is the description of the present embodiment.

In this embodiment, two PSDs are arranged in parallel. However, the present invention is not limited to this, and the same effect can be obtained by using a two-part SPD instead of the PSD 3. Selection of the ratio operation values 1 / LA and 1 / LB is performed by selecting PSD2 and PS
The incident light amount of D3 may be detected, and the larger one may be selected.

[0065]

As described above, according to the present invention, the predetermined
A first light receiving unit that receives reflected light from a subject that is closer than the distance, and a second light receiving unit that is disposed adjacent to the first light receiving unit and that receives reflected light from a subject that is longer than a predetermined distance . And the output of the first light receiving means is converted into a current-voltage having a first current-voltage conversion characteristic.
The conversion processing is performed by the first signal conversion means of the conversion means.
2 is output from the first current-voltage conversion characteristic.
Current-voltage having a second current-voltage conversion characteristic different from
Since the conversion process is performed by the pressure conversion means, a remarkable effect that a wide range from a short distance to a long distance can be measured without lowering the distance measurement accuracy on the long distance side is exerted.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a basic concept of the present invention.

FIG. 2 is a diagram plotting total photocurrents of first and second light receiving means with respect to a reciprocal of a subject distance.

FIG. 3 is a block diagram of a distance measuring apparatus according to an embodiment of the present invention.

FIG. 4 is a diagram plotting a photocurrent ratio with respect to a reciprocal of a subject distance in FIG. 3;

FIG. 5 is a flowchart of a distance measuring operation in the embodiment.

FIG. 6 is a timing chart of the operation of each unit in the embodiment.

FIG. 7 is a block diagram showing an example of a conventional distance measuring apparatus.

FIG. 8 is a block diagram showing another example of a conventional distance measuring apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light projection means 2 ... 1st light receiving means 3 ... 2nd light receiving means 6 ... Subject 7 ... 1st signal conversion means 8 ... 2nd signal conversion means 11 ... Distance detection means 34 … Selection means

Claims (4)

(57) [Claims] 1. A light projecting means for projecting a light beam toward an object, a first light receiving means for receiving reflected light from the object at a distance shorter than a predetermined distance, and the object at a distance longer than a predetermined distance A second light receiving means for receiving the reflected light from the first light receiving means, and a first signal converting means for converting the output of the first light receiving means by a current-voltage converting means having a first current-voltage converting characteristic. A second signal converting means for converting an output of the second light receiving means by a current-voltage converting means having a second current-voltage converting characteristic different from the first current-voltage converting characteristic; A distance measuring device comprising: 2. A light projecting means for projecting a light beam toward a subject.
And the reflected light from the subject that is closer than a predetermined distance.
A first light receiving unit that emits light, and a reflected light from the subject that is farther than a predetermined distance.
A second light receiving means for emitting light and an output of the first light receiving means are converted into a logarithmically compressed signal.
A first signal converting means for converting the output of the second light receiving means into a signal which is not logarithmically compressed.
And a second signal converting means . 3. A light projecting means for projecting a light beam toward a subject.
And the reflected light from the subject that is closer than a predetermined distance.
A first light receiving unit that emits light, and a reflected light from the subject that is farther than a predetermined distance.
A second light receiving means for emitting light and an output of the first light receiving means are converted into a logarithmically compressed signal.
A first signal converting means for converting the output of the second light receiving means into a signal which is not logarithmically compressed.
A second signal converting means, an output of the first signal converting means, and a second signal converting means.
Selecting means for selecting any one of the outputs of the stage, and a subject based on the output selected by the selecting means.
And a distance detecting means for detecting a distance to the distance measuring device. 4. The distance detecting means according to claim 1, wherein
Conversion means or the signal output ratio of the second signal conversion means.
Operation means for performing the operation of
The feature is to detect the distance based on the output.
The distance measuring device according to claim 3.