JPH04339208A - Distance detector - Google Patents

Abstract

PURPOSE:To enable highly accurate measurement in a wide range by projecting two distance measuring lights with different spot diameters in the direction of a base line length and a distance is computed based on a photoelectric conversion signal as obtained by receiving the reflection light from an object desired to measure a distance. CONSTITUTION:Luminous flux emitted from light emitting elements 20 and 20A of chip sizes t1 and t2 which are provided at the positions separated by a focal length fr of a projection lens 26 is condensed with the lens 26 to be projected to an object 28 desired to measure a distance. Then, the light reflected on the object 28 is condensed with a photodetecting lens 27 disposed at a distance of base length line L from the lens 26 and impinged into silicon photo diodes 1A and 1B provided at the position separated by a focal distance f1 from the lens 27. Then. photocurrents I1 and I2 generated in the diodes 1A and 1B are supplied to an arithmetic means 29 to compute a distance to be measured thereby enabling highly accurate measurement in a wide range.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a distance detection device used in a camera or the like, in particular, a light projecting section emits light toward an object to be measured, and the reflected light is emitted from the projecting section over a predetermined baseline length. The present invention relates to a light irradiation type triangulation type distance detection device that performs detection by receiving light with a light receiving section placed at a distance.

0002

2. Description of the Related Art The above-mentioned light irradiation type triangulation type distance detection apparatus is already well known, and various types have been provided in the past. For example, as shown in FIG. 12(A), the distance measuring device described in Japanese Patent Application Laid-Open No. 57-104809 projects a light emitting pattern 85 from a light emitting element 80 toward a distance measuring object 86 via a light projecting lens 83. The light reflected from the distance measuring object 86 is made incident on the light receiving elements 81 and 82 by the light receiving lens 84, and the distance is measured based on the output state of the light receiving elements 81 and 82. Then, the light emitting element 80 and the light receiving element 8
1 and 82 are respectively arranged at predetermined positions on a single substrate 87, as shown in FIG. 12(B). That is, the light emitting element 80 is located near one edge of the substrate 87, and the two light receiving elements 81 and 82 are located near the other edge, with the boundary line between the light receiving elements being perpendicular to the base line length direction 88. They are fixed in close proximity to each other.

[0003] In the distance measuring device configured in this way,
The position of the reflected light image 89 formed on the baseline length direction 88 of the light receiving surface changes according to the distance to the object to be measured based on the principle of triangulation, and the position of the reflected light image 89 causes the light receiving element 81 to Since there is a difference between the light-receiving area and the light-receiving area of the light-receiving element 82, the distance to the distance-measuring object can be detected based on the difference in output between both the light-receiving elements 81 and 82.

FIG. 13 shows the arrangement of the distance measuring optical system in the distance measuring apparatus shown in FIGS.
The focal length fT is located at a distance from the focal length fT. Photocurrents I1 and I output from the light receiving elements 81 and 82, which are arranged at a focal length fJ of the light receiving lens 84, which is arranged at a baseline length L from the light projecting lens 83.
2 to find the subject distance a to the distance measurement target 86. 14(A) to (D) show how the reflected light image moves according to the distance to the distance measuring object, and the reflected light image 89 with the outer diameter tJ reaches the distance measuring object. When moving on the light receiving elements 81, 82 according to the distance, the photocurrents I1, I output from the light receiving elements 81, 82
The distance measurement calculation output I2/(I
1 + I2 ) changes from 1 to 0 depending on the subject distance, as shown in FIG. 14(E). This one
The range from 0 to 0 is exactly the diameter tJ of the reflected light image 89.
It is between.

[0005]

However, in the conventional distance detecting device configured as described above, there arise fundamentally contradictory problems of improving the distance measurement accuracy and expanding the distance measurement range. This will be explained below.

In the distance detection device as described above, the reciprocal of the distance a to the object and the distance measurement calculation output I2/(I1
+I2), there is a relationship as shown in FIG. 15(A). That is, the solid lines l1 and l2 in FIG. 15(A)
, the light emitting chip size is t1 and t2 (t1
<t2), and represents the relationship between the distance measurement calculation output I2/(I1 +I2) with respect to the reciprocal of the subject distance a.

Generally, the amount of signal light incident on the photodetector from the subject is very weak, so the signal current ratio I2/(I
1 +I2) is affected by circuit noise and the like. The variation in the output signal caused by circuit noise, that is, the noise width, is expressed by the characteristic line l, as shown in FIG. 15(B).
3 and l4, the noise widths Δl3 and Δl4 are the same at the same distance a1, and the distance measurement calculation output I2/(I1 +I2) to which the noise component is added is shown by the diagonal line.

Therefore, in order to judge the object distance a1, the characteristic line l3 uses the judgment level Va, and the characteristic line l4
Then, the determination level Vb will be used.

[0009] Then, due to the noise component, the range of uncertainty in distance determination is α for the characteristic line l3 and β for the characteristic line l4. In other words, when the distance is measured using the characteristic line l4, the range of uncertainty in distance determination becomes wider than in the case of the characteristic line l3, resulting in poorer distance measurement accuracy.

Therefore, as an index representing the distance measurement accuracy of the distance detection device, (noise width)/(slope of distance measurement calculation output)
can be evaluated. That is, the ranging range S is S=∞~fT·L/t, where fT is the distance between the projection lens and the light emitting element, L is the base line length, and t is the chip size of the light emitting element. In addition, the distance measurement accuracy R is determined by the distance measurement calculation output noise N
Then, R=N・fT・L/t. As can be seen from the above equation, the distance measurement range S becomes larger as the focal length fT of the projection lens and the base line length L become smaller, and when the chip size t of the light emitting element becomes larger as t2, the range S becomes larger as shown in FIG. 15(A). As shown in the characteristic line l2, the distance measurement range S increases because the closest side extends to fT·L/t2, but the distance measurement accuracy R deteriorates. Conversely, as fT and L become larger, and as t becomes smaller, the distance measurement accuracy R improves, but the distance measurement range S becomes smaller. In other words, in such a distance measuring device, improving the distance measuring accuracy and expanding the distance measuring range are contradictory to each other.

[0011]Also, in order to both improve distance measurement accuracy and expand the distance measurement range, there is a method of increasing the amount of projected light to reduce the noise width of the distance measurement calculation output, but this method is difficult for small devices such as cameras. If it is built in, the space for the power supply and the emitter/receiver is limited, and the power that can be supplied to the distance measuring device is also limited, so the solution to this problem by increasing the amount of projected light is costly and space-efficient. Due to some problems, it cannot be adopted.

Furthermore, in order to expand the range of distance measurement, if means are adopted such as increasing the chip size t of the light projecting element or decreasing the focal length fT of the light projecting lens, usually the object to be measured is a person. Since it is a limited size item such as
The projected light pattern may be larger than the object to be measured, making it difficult to accurately measure the distance.

The distance detecting device of the present invention has been made with attention to such problems, and its purpose is to:
It is an object of the present invention to provide a distance detection device that can expand the distance measurement range while improving the distance measurement accuracy.

[0014]

[Means for Solving the Problems] In order to solve the above problems, the distance detecting device of the present invention projects at least two distance measuring lights having different spot diameters in the base line length direction toward an object to be measured. a light projecting means for emitting light, and at least two light receiving elements disposed at a distance from the light projecting means by a baseline length, each of the light receiving elements receiving the reflected light from the distance measuring object. A light receiving means outputs a photoelectric conversion signal from the light receiving means, and a calculation means calculates the distance to the object to be measured based on the photoelectric conversion signal of the light receiving means.

[0015]

[Operation] That is, in the present invention, at least two distance measuring lights having different spot diameters in the base line length direction are projected toward the object to be measured, and the distance measuring light is emitted from the object to be measured. The distance of the object to be measured is calculated based on photoelectric conversion signals obtained by receiving reflected light and photoelectrically converting the respective reflected lights.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings.

FIG. 1 is a diagram showing the arrangement of a distance measuring optical system of a distance detecting device according to an embodiment of the present invention. Here, two SPDs (silicon photo diodes) are used as light receiving elements.
1A and 1B are provided. Further, the light projecting section is provided with two light projecting chips (IRED chips). FIG. 3 is a layout diagram when this is viewed from the front direction Y. In this embodiment, the lengths of the light emitting surfaces of the light projecting chips differ in the baseline length direction, and t1 > t2.

In FIG. 1, the chip size is t, which is disposed at a distance from the projection lens 26 by the focal length fT.
1, t2, the light emitting elements 20, 20A are the same elements 20, t2.
The luminous flux emitted at 20A is condensed by the projection lens 26 and projected toward the object 28 to be measured. Same distance measurement target 28
The light reflected at
S located at a distance of its focal length fJ from
It enters PD1A, 1B. Then, each SPD1A,1
Photocurrents I1 and I2 are generated in B, respectively, and these are supplied to calculation means 29, where distance measurement calculations are performed.

5, 6, and 7 are electrical circuit diagrams of the distance detecting device of this embodiment, and FIG. 8 is a timing chart of signals supplied from the control circuit section 25 in FIG.

As shown in the figure, this distance detecting device includes light projection circuit sections 21 and 21A that project light pulses onto an object to be measured, and a signal pulse photocurrent component that receives reflected light from the object to be measured. Photocurrent detection circuit sections 22, 22A that detect and amplify
, an arithmetic output circuit section 23 that obtains object distance information from the photocurrent superimposed on the bias current, and a count circuit section 24 that A/D converts the output of the arithmetic output circuit section 23.
It is composed of a control circuit section 25 that sends control signals to each of the above-mentioned circuit sections.

Since the photocurrent detection circuit sections 22 and 22A each use the same components and have the same configuration, only the circuit section 22 will be explained, and the components of the circuit 22A will be explained using the same components. I will just add A and omit the repeated explanation.

In FIG. 5, the IRED of the light projection circuit section 21
(Infrared light emitting diode) 68 is driven at a constant current by a constant current driving circuit including a transistor 67, resistors 66 and 69, and an operational amplifier 65. The base of a transistor 70 that controls on/off of this constant current drive circuit is connected to the terminal T1 of the control circuit section 25 via a resistor 71, and the red light is projected from this IRED 68 in the pulse waveform shown in FIG. T7 for external light on/off control
=L, the output signal from the terminal T1 of the control circuit section 25 (see FIG. 8) is used. T6 also in 21A
=L, it is controlled in the same way.

The photocurrent detection circuit section 22 in FIG. It consists of a mirror circuit.

A signal pulse photocurrent I1 obtained from the anode of the SPD 1A is supplied to an operational amplifier 3 constituting a preamplifier circuit section. This operational amplifier 3 has its output terminal connected to the emitter of transistor 2 and its inverting input terminal connected to its base so that feedback is applied by transistor 2.
Since the non-inverting input terminals are connected to the reference power source Vref, the base input resistance of the transistor 2 is equivalently reduced to about several tens of kilohms.

Operational amplifier 5 constituting the background light removal circuit section
becomes active when turned on by applying the "H" level of the output signal from the terminal T1 of the control circuit section 25 to the base of the transistor 6 through the resistor 73 when no light is being emitted. In addition to accumulating charges according to the brightness of this background light, a feedback loop composed of the same capacitor 7 and transistor 4 transfers the photocurrent component due to the background light of the SPD 1A and the bias current component of the operational amplifier 3 to the collector of the transistor 4. Discharged to the ground line as current. As a result, the collector current of the transistor 2 has a value that substantially corresponds to the pulse signal photocurrent, regardless of the magnitude of the background light. When light is emitted, the operational amplifier 5 becomes non-active because the transistor 6 is turned off, but due to the charge accumulated in the capacitor 7, the transistor 4 continues to discharge the photocurrent due to the background light to the ground line, so that the photocurrent is obtained from the anode of the SPD1A. The pulsed light component obtained by subtracting the photocurrent due to the background light from the photocurrent is multiplied by βN in the transistor 2 and reflected by the current mirror circuits 8 and 9, and the signal pulsed photocurrent βN is sent to the compression diode 47 of the calculation output circuit section 23.
Injected as I1.

Further, the photocurrent I2 obtained from the anode of the other SPD 1B is also processed by the photocurrent detection circuit section 22A which operates in the same manner as the circuit section 22 described above, and is outputted as a signal pulse photocurrent βN I2 by the calculation output circuit. It is supplied to the compression diode 46 of section 23.

The arithmetic output circuit section 23 in FIG. 6 includes transistors 41, 42, 44, 45 and compression diodes 46, 47.
, constant current source 43, and buffer circuits BUF1 and BUF2
This constitutes a logarithmic expansion circuit for obtaining the distance measurement calculation output.

Transistor 4 forming a differential amplifier
1 and 42 are connected to the compression diodes 46 and 47.
are connected to respective anodes of , via buffer circuits BUF1 and BUF2, and each emitter is commonly connected to a constant current source 43. The collector of transistor 42 is connected to the bases of transistors 44 and 45 forming a current mirror circuit and to the collector of transistor 44.

By the way, the currents I1b and I2b flowing through the diodes 46 and 47, respectively, are circuit-connected so that the signal pulse photocurrent output from the photocurrent detection circuit section 22 flows. Therefore, in the calculation output circuit section 23, the above-mentioned current I1b is the signal pulse photocurrent βN I2 from the photocurrent detection circuit section 22A, and the current I2b is the signal pulse photocurrent βN I1 from the photocurrent detection circuit section 22. , I1b=βN I2

...(1) I2b=βN
I1
...(1)
′.

Therefore, the collector current IC of the transistor 42 is expressed as follows, assuming that the constant current of the constant current source 43 is IE.
IC = I2b・IE / (I1b+I2b)
…(
2). Therefore, the collector current I1' of the transistor 45, which is the output of the arithmetic output circuit section 23, is expressed as (1) above.
, Substitute equation (1)' into equation (2) and get I1'=I1 ・IE /(I1 +I2
) …(
3).

Output current I1 of the arithmetic output circuit section 23
' is the subject distance a as shown in FIGS. 10(A) and (B)
The distance measurement range from infinity to the closest distance is divided and measured according to the reciprocal of .

In the present invention, the distance measurement range from infinity to the closest distance is divided and measured according to the reciprocal of the object distance a. In other words, on the long distance side, as shown in FIG. 10(B)
As shown in FIG. 2, the output current I1 is
Find ′. Similarly, on the short distance side, as shown in FIG. 10(A), the output current I1' is determined using a light emitting element 20 with a chip size t1 that can provide a large diameter light emitting spot.

[0033] In both of the obtained measured values, the distance is normally measured using the light emitting element 20A, which has good distance measurement accuracy, and at this time, the distance measurement value using 20 is used only when it is outside the short range interlocking range. It would be better to adopt it.

Furthermore, it is not necessary to find I1' for both the light emitting elements 20 and 20A, and if it is found that they are within the interlocking range in the distance measurement of FIG. 10(A) or FIG. The distance can be omitted.

Furthermore, for tilt correction, shift correction, etc. of the distance measurement output with respect to 1/a, correction values are written in the E2-PROM, and each correction calculation is performed using the correction values.

On the other hand, the count circuit section 24 in FIG.
The integrated value of the collector current I1' of the transistor 45 of the arithmetic output circuit section 23 is measured and digitally measured by a counter mechanism (not shown) built in the control circuit section 25.

Output current I1 of the arithmetic output circuit section 23
′ can be found as follows. That is, the capacitor 43 becomes active in synchronization with the projection of light, and the output current of the arithmetic output circuit section 23 flows through the capacitor 52 every time the light is projected, and charges are accumulated in the capacitor 52. The operational amplifier 53 is for resetting the capacitor 52, and the base of the control transistor 54 is connected to the terminal T3 of the control circuit section 25 via a resistor 76. Therefore, the output signal of this terminal T3 (see FIG. 8) turns on the transistor 54 and changes the potential of the capacitor 52 to the reference potential Vre.
f and is turned off immediately before the start of light emission to make the operational amplifier 53 inoperable. Thereafter, the potential of the capacitor 52 increases due to the current injected into the capacitor 52.

When the predetermined number of light projections is completed, as shown in the timing chart of FIG. 8, the terminal T4 changes from H to L, so the transistor 63 is turned off via the resistor 77, and the transistor 55 discharges the capacitor 52. I will do it. At the same time, a counter built in the control circuit section 25 operates and continues counting until the output of the comparator 62 becomes H. The comparator 62 changes from L to H when the voltage across the capacitor 52 becomes lower than the reference voltage Vref. The discharge rate of the capacitor 52 is determined by a current mirror circuit consisting of a constant current source 61 and transistors 56 and 55 connected in series thereto. In this way, an output corresponding to the object distance can be obtained as the count value of the counter in the control circuit 25.

The arithmetic output circuit section 23 is not limited to the above-mentioned configuration, and other circuit configurations and detailed explanations of their operations are disclosed in, for example, Japanese Patent Application Laid-open No. 1-150809 by the present applicant, and will therefore be omitted. do.

FIG. 2 shows another method of obtaining different projected spot diameters. Here, different spot diameters are obtained by setting the two focal lengths of the light projection lens in the relationship fT1>fT2, but in any case, the present invention is valid as long as the projection spot diameters are different. .

In addition, as shown in FIG. 4(A), a small beam spot diameter is obtained with 1A, and 1A, 1B
A large light spot may be obtained by lighting both at the same time. In addition, as shown in FIG. 4(B), 1
In addition to obtaining a small projection spot with A, 1A,
A large light projection spot may be obtained by illuminating 1B and 1C at the same time. Furthermore, the number of light projection spots is not limited to two either.

FIG. 9 shows a sequence in which inverse integration is performed once to shorten the time required for distance measurement. In this case, the calculation outputs in FIG. 10 are combined and the result is as shown in FIG. 11. . The nonlinearity of the distance measurement output can be resolved by calculating the distance by applying shift and tilt correction to the data written in the E2-PROM. Note that since the details are well known, their explanation will be omitted.

[0043]

Effects of the Invention As described above, in the present invention, a plurality of light projection spots with different diameters are projected in time series toward an object to be measured in the base line length direction, and a large light projection spot is Accuracy is low, but wide ranging distance measurement is possible.
The accuracy is good, but it measures the distance in a narrow range, and on the short distance side,
On the long distance side, by using the later distance measurement calculation results,
This enables accurate and wide-range measurement. With this configuration, not only is the structure simple, but it is also compact and can be used in small devices such as cameras without using large power batteries to increase the light emitting energy of the light emitting element. Suitable for integration, it can improve the distance measurement accuracy of the camera without reducing it and expand the distance measurement range.

[Brief explanation of the drawing]

FIG. 1 is a layout diagram of a distance measuring optical system in a distance detecting device showing an embodiment of the present invention.

FIG. 2 is a layout diagram of a distance measuring optical system for obtaining different projection spot diameters using other methods.

3 is a layout diagram of the light projecting chip shown in FIG. 1 when viewed from the front direction Y; FIG.

FIGS. 4(A) and 4(B) are diagrams showing other embodiments in which different projected spot diameters are obtained.

FIG. 5 is a part of an electrical circuit diagram of the distance detection device of the present invention.

FIG. 6 is a part of an electrical circuit diagram of the distance detection device of the present invention.

FIG. 7 is a part of an electrical circuit diagram of the distance detection device of the present invention.

FIG. 8 is a timing chart of signals in the control circuit diagram in FIG. 7;

FIG. 9 is a timing chart showing a sequence for shortening the time required for distance measurement.

10A and 10B are diagrams showing the relationship between the distance measurement range from infinity to the closest distance and the output current based on the reciprocal of the subject distance a.

FIG. 11 is a characteristic diagram obtained by combining the calculation outputs of FIGS. 10(A) and 10(B).

12A and 12B are a perspective view and a front view, respectively, showing the arrangement of a distance measuring optical system of a conventional distance detecting device.

FIG. 13 is a plan view showing the arrangement of a distance measuring optical system of a conventional distance detecting device.

[Figure 14] Figures 14 (A), (B), (C), and (D) are
FIG. 14 is an explanatory diagram showing how the reflected image from the object to be measured is formed on the light-receiving element group in accordance with the object distance;
In E), the center position of the light reception and reflection image is shown in Figs. 14(A), (B),
Calculation output I when located at the position corresponding to (C) and (D)
2/(I1 + I2) characteristic diagram.

FIG. 15(A) shows the distance measurement calculation output I2/(I1
+I2) is a characteristic line diagram showing the relationship between
) is a characteristic diagram when noise is superimposed on the diagram shown in FIG. 15(A).

[Explanation of symbols]

1A, 1B... SPD (light receiving element), 20, 20A... Light emitting element, 26... Light projecting lens (light projecting means), 27... Light receiving lens (light receiving means), 28... Distance measuring object, 29... Calculating means.

Claims (1)

[Claims] 1. Light projecting means for projecting at least two distance measuring lights having different spot diameters in the direction of the baseline length toward an object to be measured; a light-receiving means having two light-receiving elements, receiving the reflected light of the distance-measuring light from the distance-measuring object, and outputting a photoelectric conversion signal for each of the light-receiving elements; A distance detection device comprising: calculation means for calculating the distance of the object to be measured based on the distance measurement object.