JP2004125651A - Optical range finder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical range finder for removing an effect of the brightness of an object. <P>SOLUTION: This optical range finder is equipped with a light projecting part including a light emitting element 1 for projecting a light beam to the object existing in an optical axis direction, a light receiving part including light receiving elements for receiving the light beam returning from the object to output a corresponding electric signal, and a computing part 11 for calculating a distance to the object based on the electric signal. The receiving part has at least two light receiving elements S1 and s2 and is switchable between a consolidation mode and a separation mode. The two light receiving elements output a single electric signal corresponding to the total amount of individually received light in the consolidation mode, while they output a plurality of electric signals corresponding to the amount of individually received light in the separation mode. The computing part 11 first finds reflectivity data expressing the surface reflectivity of the object based on an electric signal outputted in the consolidation mode, then finds distance data expressing a distance to the object based on an electric signal outputted in the separation mode, and further corrects the distance data based on the reflectivity data. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical distance measuring device for optically measuring the distance of a subject of a camera. More specifically, the present invention relates to a distance measurement method that does not depend on the reflectance of a subject.
[0002]
[Prior art]
FIG. 5 is a schematic perspective view showing an example of a camera incorporating the optical distance measuring device. As shown, the camera 5 includes a body 6 and a lens barrel 7. An optical distance measuring device including a light projecting unit 1 and a light receiving unit 2 is mounted on the front side of the body 6. This optical distance measuring device measures the distance of the subject of the camera 5 in the optical axis direction, and the measurement result is used for automatic focus adjustment and the like.
[0003]
[Patent Document 1]
Patent No. 3187621 [0004]
FIG. 6 is a schematic diagram showing an example of the optical distance measuring device. This device is based on a so-called active triangulation method. The figure shows the basic principle, wherein 1 is a light projecting unit that generates, for example, infrared light, 3 is a light projecting lens, T1 and T2 are objects, 4 is a light receiving lens, and 2 is a light receiving element S1 divided into two. , S2 are shown. The output light of the light projecting unit 1 is irradiated by the light projecting lens 3 toward the subject T1 or T2, and the light reflected by the subject T1 or T2 enters the light receiving unit 2 via the light receiving lens 4. At this time, since the incident angle with respect to the light receiving unit 2 varies in accordance with the distance to the subjects T1 and T2, the component ratio of the amount of incident light with respect to each of the light receiving elements S1 and S2 constituting the light receiving unit 2 varies. Thus, the distance to the subject T1 or T2 can be determined by comparing and calculating the amount of incident light on each of the light receiving elements S1 and S2.
[0005]
[Problems to be solved by the invention]
Devices of the active triangulation system are roughly classified into a ratio calculation method for calculating an output ratio of a pair of light receiving elements and a difference calculation method for calculating an output difference between the respective light receiving elements. In the ratio calculation method, since a factor relating to the object reflectance is offset to some extent between the numerator and the denominator in the process of the ratio calculation, it is possible to perform multi-step distance determination without being greatly affected by the object reflectance. Nevertheless, if the reflectivity of the subject is significantly different, it adversely affects the distance measurement result and causes an error, which is a problem to be solved. On the other hand, the difference operation method has a simpler circuit configuration than the ratio operation method.On the other hand, a factor relating to the object reflectance remains in the result of the difference operation, and this is a major error factor. is there. In the active triangulation method, a light beam is projected onto a subject, the reflected light is received, and distance measurement is performed. The amount of received light depends on the reflectance of the subject. Therefore, the active triangulation method has a dependency on the reflectance of the object in principle, and eliminating this is an urgent solution.
[0006]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION In view of the above-mentioned problems of the related art, an object of the present invention is to provide an optical distance measuring apparatus that can remove the influence of the reflectance of a subject with a relatively simple circuit configuration. The following measures have been taken to achieve this objective. That is, the present invention provides a light projecting unit including a light emitting element for projecting a light beam on an object in an optical axis direction, and a light receiving element for receiving a light beam returning from the object and outputting a corresponding electric signal. An optical distance measuring device comprising a light receiving unit including: a calculating unit that calculates a distance to the object based on the electric signal, wherein the light receiving unit has two or more light receiving elements. It is possible to switch between the combined mode and the separated mode. In the combined mode, the plurality of light receiving elements output a single electric signal according to the sum of the individual received light amounts, and according to the individual received light amount in the separated mode. Output a plurality of electrical signals. The calculation unit first obtains reflectance data representing the surface reflectance of the object based on the electric signal output in the coalescing mode, and then calculates the reflectance data up to the object based on the electric signal output in the separation mode. It is characterized in that distance data representing a distance is obtained, and the distance data is corrected based on the reflectance data to remove an error depending on the reflectance of the object. Specifically, the arithmetic unit stores reference reflectance data sampled from a reference object whose reflectance is known in advance, and the electric signal obtained in the uniting mode based on the reference reflectance data. To calculate reflectance data indicating the actual surface reflectance of the object. Further, the arithmetic unit obtains difference data obtained by taking a difference between at least two electric signals output in the separation mode and sum data obtained by taking a sum, and corrects the difference data and the sum data with the reflectance data. Then, the distance data is obtained by taking the ratio of the corrected difference data and the sum data.
[0007]
According to the present invention, for example, a light receiving element divided into two is connected in parallel (or in series) to a reference object whose reflectance for infrared light projection is known in advance, and the reflected light amount is apparently set as one light receiving element. Measurement is performed, and the light amount value is stored in the apparatus. This process is performed before the optical ranging device is shipped from the factory. When actually performing distance measurement on an object whose reflectance with respect to infrared light is unknown, first, the two divided light receiving elements are connected so as to be one light receiving element, and the amount of infrared reflected light is measured. The amount of reflected light of the reference object stored before the factory shipment stage is compared with the actually measured amount of received light of the object. Thereby, the actual reflectance of the object is estimated. Next, a distance measuring operation is performed with the light receiving elements divided into two, and, for example, a difference calculation of electric signals output from each light receiving element is performed to obtain distance data to the object. The distance data obtained at this stage includes the influence of the reflectance of the object. Therefore, the distance data obtained by the difference calculation is corrected based on the reflectance data of the object estimated earlier. As a result, it is possible to obtain distance data in which the influence of the reflectance of the target object has been eliminated.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of an optical distance measuring apparatus according to the present invention. This optical distance measuring device includes a light projecting unit, a light receiving unit, and a calculation unit. The light projecting unit includes a light emitting element 1 composed of an infrared light emitting diode, and emits a light beam to an object in an optical axis direction. The light receiving unit includes a light receiving element that receives a light flux returning from the object and outputs a corresponding electric signal. In the present embodiment, a pair of light receiving elements S1 and S2 composed of a silicon photodiode (SPD) divided into two parts is used. However, the present invention is not limited to this, and a multi-division type position sensitive detector (PSD) may be used instead of the SPD. The calculation unit calculates a distance to the object based on the electric signal output from the light receiving unit. The arithmetic unit includes a circuit part for performing a hardware operation and a central processing unit (CPU) for performing a software operation. The addition and subtraction necessary for calculating the distance to the object are performed on a circuit, and the correction calculation is performed by the CPU. However, the present invention is not limited to this, and all the operations may be executed on software.
[0009]
As described above, the light receiving section has two or more light receiving elements S1 and S2, and can be switched between the combined mode and the separated mode by the switch SW. In the combination mode, the pair of light receiving elements S1 and S2 output a single electric signal corresponding to the sum of the individual light reception amounts, and output a plurality of electric signals corresponding to the individual light reception amounts in the separation mode. It has become. Switching between the combination mode and the separation mode is controlled by the CPU 11 via the switch circuit SW.
[0010]
Next, the configuration and operation of the circuit portion of the optical distance measuring apparatus will be described in detail with reference to FIG. The following description is based on the separation mode for easy understanding. The light receiving element S1 is connected 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 element S1, a photocurrent I1 corresponding to the amount of incident light flows through the series circuit. . 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.
[0011]
The light receiving element S2 is connected 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 element S2, a photocurrent I2 according to the amount of incident light flows through this series circuit. . The transistor 24 forms a current mirror circuit with the transistor 25 sharing the base, and a current I2 equal to the current flowing through the transistor 24 flows through the series circuit of the transistor 25 and the transistor 26. A transistor 27 is connected between the base and the collector of the transistor 26. In the case of the PNP transistor 26, the transistor 27 has a base current that cannot be substantially ignored. Is provided for compensating for the base current. The transistor 26 forms a current mirror circuit with the transistor 28, and the same current I2 flows through the transistor 28.
[0012]
The current I1 flowing through the transistor 22 flows as a subtraction current at the negative-phase input point of the operational amplifier 29, and the current I2 flowing through the transistor 28 flows at the same negative-phase input point of the operational amplifier 29 as an addition current. Since all the current flowing to the negative-phase input point of the operational amplifier 29 flows through the feedback resistor 30 of the operational amplifier 29, when the current flowing through the feedback resistor 30 is defined as Ia, it is expressed by Ia = I2-I1. Since the reference voltage Vref is applied from the power supply 31 to the positive-phase input point of the operational amplifier 29, when the resistance value of the resistor 30 is defined as R30 and the output voltage of the operational amplifier 29 is defined as Va, The output voltage Va is
Va = Vref−R30 × Ia = Vref−R30 × (I2-I1)
Given by
[0013]
After the output voltage Va of the operational amplifier 29 is removed by the capacitor 32 for removing the steady light component (the photocurrent component flowing depending on the field light irrespective of the light emission of the light emitting diode) in the photocurrent, It is applied to the negative-phase input resistance 34 of the operational amplifier 33. The reference 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 both inputs of the operational amplifier 33. The generated voltage V34 is V34 = {Vref−R30 × (I2-I1)} − Vref
= R30 × (I1-I2),
The current I34 flowing through the resistor R34 is
I34 = R30 × (I1-I2) / R34.
[0014]
All the current I34 flows through the resistor 35, but since the reference voltage of the operational amplifier 33 is Vref, the output voltage Vb of the operational amplifier 33 is
Vb = Vref-R35 * R30 * (I1-I2) / R34
= Vref−k × (I1−I2).
However, k = R35 × R30 / R34.
[0015]
The voltage Vb output from the operational amplifier 33 in this manner is sampled and held by the sample / hold circuit (S / H) 37 and supplied to an analog-to-digital converter (A / D) built in the CPU 11. In this manner, in the separation mode, data corresponding to the difference between the amounts of light received by the pair of light receiving elements S1 and S2 is captured and sent to the CPU 11 side.
[0016]
On the other hand, in the combined mode, the photocurrents I1 and I2 flowing through the pair of light receiving elements S1 and S2 both flow as addition currents at the negative-phase input points of the operational amplifier 29. This added current is amplified by the operational amplifier 29 and the operational amplifier 33, sampled and held by the S / H 37, and sent to the A / D of the CPU 11. Therefore, in the uniting mode, the CPU 11 takes in data corresponding to the added value (total value) of the amounts of light received by the light receiving elements S1 and S2.
[0017]
With reference to FIG. 2, the distance measuring operation of the optical distance measuring apparatus shown in FIG. 1 will be described in detail. First, in step S1, the switch SW is turned on to the united mode side. Subsequently, in step S2, the light emitting element 1 is driven to emit a light beam toward the object. In step S3, the reflected light amount value is fetched from the S / H 37 and recorded in a predetermined memory. This reflected light amount value is a value proportional to the electric signal (I1 + I2) corresponding to the sum of the light receiving amounts of the light receiving elements S1 and S2. In the present embodiment, the CPU 11 stores reference reflectance data sampled from a reference object whose reflectance is known in advance, and based on the reference reflectance data, converts the electric signal obtained in the uniting mode. Then, the reflectance data representing the actual surface reflectance of the object is calculated. For example, the surface reflectance of an actual object is estimated based on an electric signal obtained in the uniting mode from a reference object placed at a distance of 1 m with a surface reflectance of 36%.
[0018]
Next, in step S4, the switch SW is turned on to the separation mode side. Subsequently, the light emitting element 1 is driven in step S5. In step S6, the distance measurement result is fetched and stored as distance data in the CPU. As described above, in the separation mode, a plurality of electric signals corresponding to the respective light receiving amounts of the light receiving elements S1 and S2 are output, and a difference between them is obtained in the circuit section. Here, when the CPU adopts the difference calculation method, the CPU stores the difference data as it is as distance data. When the ratio calculation method is adopted, addition data is also obtained in addition to the difference data, and the ratio between the two is used as distance data. Note that the addition data is obtained in the united mode. Thereafter, in step S7, the distance data is corrected using the reflectance data, and true distance data excluding the influence of the surface reflectance of the object is obtained.
[0019]
FIG. 3 is a block diagram schematically showing a data flow in the distance measurement method described with reference to FIGS. As shown, the pair of light receiving elements S1 and S2 output electric signals A and B according to the amount of received light, respectively. The switch circuit SW switches the electric signals A and B and supplies the electric signals to the difference circuit and the adder circuit (20-30). The difference circuit calculates AB, and the adder circuit calculates A + B. The difference circuit and the addition circuit correspond to the circuit elements 20 to 30 in FIG. AB and A + B are amplified by the amplifier circuits 33-35, and then sampled and held by the S / H 37. The sampled and held values of AB and A + B are taken into the CPU 11 via the A / D 11a.
[0020]
The CPU calculates the distance measurement data K = (A−B) / (A + B) by, for example, a ratio calculation method. At this time, a correction is made based on the reflectance data r of the object estimated in advance. For example,
K = (AB) / (A + B)
= R (ab) / r (a + b)
= (Ab) / (a + b)
Is obtained as distance data K. The reflectance r is canceled, and accurate distance data K independent of the reflectance of the object is obtained. In the case of the difference calculation method, the distance may be obtained from the corrected difference data ab instead of the original difference data AB.
[0021]
FIG. 4 is a schematic block diagram showing a modification of the embodiment shown in FIG. In this embodiment, a difference circuit and an addition circuit are directly connected to a pair of light receiving elements S1 and S2. A switch circuit SW is connected to a stage subsequent to these arithmetic circuits. The difference signal and the addition signal are selected by the switch circuit, and are taken into the CPU via the amplifier circuit, S / H, and A / D.
[0022]
【The invention's effect】
As described above, according to the present invention, a light-receiving element divided into two is connected in parallel or in series to an object whose reflectance for infrared light is known in advance, and the reflected light amount is measured as an apparently single sensor. Then, the light amount value is stored in the memory of the CPU. This is performed at the factory shipment stage of the optical distance measuring device. When performing distance measurement on an object having an unknown reflectance with respect to infrared light, a pair of light receiving elements are first connected so as to form one sensor, and the amount of reflected light is measured. The reflectance of the object is estimated by comparing with the value data. Next, distance data is obtained by calculating the difference between the electric signals obtained by the two divided light receiving elements. Since this includes the influence of the reflectance of the object, the distance data is corrected based on the previously estimated reflectance to remove the influence. With such a configuration, an optical distance measuring device that does not depend on the surface reflectance can be obtained without increasing the circuit scale.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of an optical distance measuring apparatus according to the present invention.
FIG. 2 is a flowchart for explaining the operation of the optical distance measuring apparatus shown in FIG. 1;
FIG. 3 is a block diagram for explaining the operation of the optical distance measuring apparatus shown in FIG. 1;
FIG. 4 is a block diagram showing a modification of the embodiment shown in FIG.
FIG. 5 is a perspective view showing an example of a camera incorporating an optical distance measuring device.
FIG. 6 is a schematic diagram showing the principle of optical distance measurement.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Light projection part, 2 ... Light receiving part, 11 ... CPU, S1 ... Light receiving element, S2 ... Light receiving element, SW ... Switch circuit

Claims (3)

A light emitting unit including a light emitting element that emits a light beam to an object in an optical axis direction,
A light receiving unit including a light receiving element for receiving a light flux returning from the object and outputting a corresponding electric signal,
An arithmetic unit that calculates a distance to the object based on the electric signal,
The light receiving unit has two or more light receiving elements, and can be switched between a combined mode and a separated mode. In the combined mode, the plurality of light receiving elements are a single electric signal corresponding to the sum of the respective received light amounts. And outputs a plurality of electric signals according to the amount of received light in the separation mode,
The calculation unit first obtains reflectance data representing the surface reflectance of the object based on the electric signal output in the combined mode, and then calculates the reflectance data up to the object based on the electric signal output in the separation mode. An optical distance measuring apparatus, wherein distance data representing a distance is obtained, and the distance data is corrected based on the reflectance data to remove an error depending on the reflectance of an object. The arithmetic unit stores reference reflectance data sampled from a reference object whose reflectance is known in advance, processes the electric signal obtained in the united mode based on the reference reflectance data, and 2. The optical distance measuring apparatus according to claim 1, wherein reflectance data representing an actual surface reflectance of the object is calculated. The arithmetic unit obtains difference data obtained by taking a difference between at least two electric signals output in the separation mode and sum data obtained by taking a sum, and corrects the difference data and the sum data with the reflectance data. 2. The optical distance measuring apparatus according to claim 1, wherein the distance data is obtained by taking a ratio of the corrected difference data and the sum data.

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