JPH0949727A - Optical distance-measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a measuring error that a distance of an object outside a measuring range is output as a value within the measuring range in an optical distance-measuring method based on the principle of triangulation. SOLUTION: A light is cast on an object to be measured, and a scattering light by the object is condensed onto a light receiving element by a photodetecting lens, whereby a distance to the object from the condensed point is measured in the apparatus. A plurality of position sensors of different resolutions are used for the light receiving element 22, for example, a position sensor 22a of a good positional resolution having a photodetecting face corresponding in size to a measuring range and a position sensor 22b which does not have a so good positional resolution, but is inexpensive or easy to use. Accordingly, the generation of an error to judge the distance as indefinitely far is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical distance measuring device.

[0002]

2. Description of the Related Art Conventionally, various optical distance sensors have been developed as distance measuring sensors for autofocus of cameras and obstacle sensors of vehicles. Since the optical distance measuring method using such a sensor can measure the distance to the object to be measured without contact, it is used in various other fields. There are various optical distance measuring methods, such as one that measures the propagation time of light and one that uses the principle of triangulation.

Among the methods utilizing the principle of triangulation, there is a method of irradiating the object to be measured with light from a distance measuring device and obtaining the distance from the information of the scattered light, which is generally called the active method. It is widely used as an auto focus for compact cameras and a distance measurement method for automatic doors. The principle of distance measurement by this method will be described with reference to FIG. First, the light emitting element 12
And a light beam from the light beam projecting unit 1 equipped with a condenser lens 11.
The object 4 is irradiated with the beam 4 as spot light. The light beam is scattered by this, and a part of the light 5 is incident on the light detector 2 having the light receiving lens 21 and the light receiving element 22,
It is condensed on the light receiving element 22 to form a point image. The focal point position x, which is a numerical value required to calculate the distance, is obtained from the output of the light receiving element, but the photocurrent generated in the case of PSD (Position-Sensitive Detector) which is often used as this active type light receiving element. From I1 and I2, x = L × I2 / (I1 + I
2) x can be obtained, and the maximum output is obtained in the case of a light receiving element in which pixels are separated from each other such as a CCD or a photodiode array, in other words, a digital light receiving element for positioning. X can be obtained from the pixel position. The distance D from this x to the object to be measured can be obtained from D = B × f / x. Note that these expressions and f in FIG. 3 represent the focal length of the light receiving lens.

[0004]

However, for example, when obtaining the distance from the focus point position x on the light receiving surface detected by PSD to the object, the position resolution (on the light receiving surface of the PSD) is changed from infinity to a short distance. (The minimum displacement of the condensing point that can be detected by) is good, but if you try to measure using a PSD with a short light-receiving surface, the range of position change of the condensing point is PSD.
Is longer than the length of the light receiving surface of, and part of the scattered light from the measurement target range is not collected on the light receiving surface of the PSD.
For example, scattered light 5 and 5a from the object to be measured located at 3a in FIG. 3 and the object to be measured located farther than that are incident on the light receiving element (length L). The condensing point of the scattered light from the DUT located closer than the
It comes off from the light receiving surface of D. In such a case, there is a problem that the distance measurement becomes erroneous. In order to prevent this erroneous distance measurement, a PSD having a long light receiving surface may be used, or the focal length of the light receiving lens may be shortened. In the former case, the position resolution of PSD increases with the length of the light receiving surface. Another problem is that the distance resolution is lowered, and as a result, the distance resolution is lowered. In the latter case, the position resolution is good, but the position resolution is actually reduced because the condensed image is reduced. Another problem was that the range resolution was reduced.

The problem of erroneous distance measurement occurs not only when the PSD of the short light receiving surface is used as a position sensor, but also when a digital element (for example, CCD) is used for positioning, in order to avoid the problem. If a long element (for example, a CCD) having the same total number of pixels is used, the resolution is similarly deteriorated, and a long element having the same pixel density (for example, C
The use of (CD) does not lower the resolution but causes another significant increase in cost.

The present invention has been made in order to solve such a problem, and it is possible to measure from a long distance to a short distance without erroneous distance measurement, and also has high resolution for distance measurement in a predetermined distance range and low cost. The purpose of the present invention is to provide a distance measuring device.

[0007]

Therefore, according to the present invention, firstly, a light beam projecting unit for irradiating a light beam to an object to be measured, and a scattered light of the irradiated light beam from the object to be measured are condensed. A light receiving lens and a light detecting unit having a light receiving element for detecting the position of the condensing point of scattered light by the light receiving lens, and a signal processing unit for calculating the distance to the object to be measured by the signal from the light detecting unit. In the optical distance measuring device, there is provided an optical distance measuring device characterized in that the light receiving element has a plurality of position sensors having different resolutions. Further, the present invention secondly provides an optical distance measuring device characterized in that the plurality of position sensors are arranged adjacent to each other. Furthermore, the present invention thirdly provides a light beam projector for irradiating an object to be measured with a light beam, a light receiving lens for collecting and condensing scattered light of the irradiated light beam by the object to be measured, and scattering by the light receiving lens. In the optical distance measuring device including a plurality of light detectors having a light receiving element for detecting the light condensing point position, and a signal processor for calculating the distance to the object to be measured by signals from the light detectors. The light receiving element of each photodetector has a different resolution.
There is provided an optical distance measuring device characterized in that it has either one of position sensors of different types, and that the plurality of photodetection sections are arranged separately from each other.

[0008]

When the distance to the object is measured by using the distance measuring device as shown in FIG. 3, the light collection point of the light from the object at the long distance and the light collection point of the light from the object at the short distance are As shown in FIG. 4, it is located on both ends of the light receiving element 22.
Therefore, when trying to measure from infinity to a short distance using one light receiving element, a long light receiving element is inevitably required. However, in the actual distance measurement, a high distance resolution is required only in a predetermined distance range, and in most other distance ranges, the distance resolution is not so much required to the left. Therefore, in consideration of this, a position sensor having high resolution is used for a distance range that requires high resolution, and one position sensor that prioritizes cost and ease of use for other distance ranges is used. Alternatively, by using a plurality of them, it is possible to perform distance measurement from a long distance to a short distance at a low cost without lowering the accuracy in practical use.
That is, according to the present invention, for example, by arranging at least two position sensors having different resolutions so as to be adjacent to each other as an arrangement of the position sensors, the same effect as in the case of using one light receiving element which is actually long is obtained. I can do things. Also,
For example, the same effect can be obtained by arranging at least two position sensors having different resolutions and light receiving lens groups (at least two light detecting portions) corresponding to the respective position sensors at different positions. That is,
According to the present invention, it is possible to perform distance measurement from a long distance to a short distance without erroneous distance measurement, and it is possible to perform distance measurement with high resolution in a predetermined distance range.

[0009]

【Example】

-Embodiment 1- Fig. 1 is a schematic configuration diagram showing a light detection unit 2 of an optical distance measuring apparatus of the present embodiment. In this implementation, it is possible to measure a wide range of distance by using two position sensors having different position resolutions. That is, the light receiving element 22 has a position sensor 22a having a high position resolution and a position sensor 22a having a low resolution but excellent characteristics in other respects (cost and ease of use).
It consists of b. In the present embodiment, as the former, P having a length of 3 mm is used.
For the SD, the latter is a silicon photodiode array (hereinafter referred to as SPD) having a length of 3 mm and a number of pixels of 4.
When the light receiving element is composed of only the position sensor 22a, only the scattered light which is incident in the range of 5b to 5a in the figure is condensed on the light receiving element, whereas the two position sensors 22a and 22b. In the light receiving element 22 of the present embodiment consisting of, the scattered light entering from 5a to 5c is also received.

A distance measuring experiment was conducted by incorporating the light receiving element 22 into the apparatus shown in FIG. As main parameters of the device configuration, the distance B between the condenser lens and the light receiving lens was 50 mm, and the focal length f of the light receiving lens was 20 mm. When the distance between an object located at a position of 10 m from the measuring device was measured accurately by using the device configured as described above, the PSD 22a was activated and a measurement result of exactly 10 m was obtained. Next 22.5
When the distance of the object at the position of cm is measured, SPD22b
Was activated and a measurement result of 24.5 cm was obtained.

On the other hand, the conventional light receiving element (one P
When measured with a device using SD), the same measured value as that of the device of this example was obtained for an object at a distance of 10 m, but infinite for an object at a distance of 22.5 cm. The measurement result of distance was output, resulting in incorrect distance measurement. Therefore,
Consider the phenomenon that causes an erroneous distance measurement when an object is in a short distance and the device's response to the phenomenon. When the object is at a short distance as described above, the condensing point of scattered light is PSD
, The photocurrent becomes zero, the outputs I1 and I2 consist only of noise components, and I1 = I2
Becomes If I1 = I2, x = L / 2 from the above calculation formula
, The distance becomes D = 2 × B × f / L, but in the conventional apparatus, when I1 + I2 is small, it is general to judge the distance to be infinity by the logical operation processing in the signal processing unit. Therefore, the above-mentioned erroneous distance measurement erroneously determined that the photocurrent was zero because the condensing point was not located on the light receiving surface, and that the photocurrent was zero because the scatterer was at infinity. It is due to things. On the other hand, according to the apparatus of this embodiment, such an erroneous determination can be prevented.

In FIG. 1, the SPD is located on the near side of the PSD.
However, the SPD may be arranged on the far side of the PSD (on the left side of the PSD in FIG. 1). In this case, the distance of an object at a short distance can be measured more accurately, which is preferable. Further, when the intermediate distance is emphasized, it is preferable that the PSD is sandwiched by a plurality of SPDs because accurate measurement can be performed.

Second Embodiment FIG. 2 is an explanatory diagram showing a schematic structure and a positional relationship of a photodetector of the optical distance measuring apparatus of the present embodiment. In this embodiment, a wide range of distances can be measured by using a plurality of photodetectors each having a light receiving element and a light receiving lens having one of two types of position sensors having different position resolutions. Light receiving lens 2
1a21b and photodetectors 2a and 2b having position sensors (light receiving elements) 22a and 22b are arranged separately from each other. In the figure, the position sensor 22a has a high position resolution, one end of its light receiving surface is on the optical axis of the light receiving lens 21a, and the light receiving surface can receive scattered light such as 5. On the other hand, the position sensor 22b is a position sensor having a low position resolution but excellent characteristics in other respects (cost and ease of use), and one end of its light receiving surface is located from the optical axis of the light receiving lens 21b to the position sensor 22a. It is arranged so as to be displaced by the length of the light receiving surface, and can receive scattered light such as 5d. By arranging such a set of the light receiving lenses 21a and 21b and the position sensors 22a and 22b (that is, the respective photodetecting sections 2a and 2b) at equal distances around the optical axis of the condenser lens 11, the scattered light 5 is generated. The scattered light from a distant object is received by the position sensor 22a, and the scattered light from a nearby object such as the scattered light 5d is received by the position sensor 22b. Here, a PSD having a length of 3 mm is used as the position sensor-22a, and an SPD having a length of 3 mm and a pixel number of 4 is used as the position sensor-22b.
The distance between the optical axes of the condenser lens 11 and the light receiving lenses 21a and 21b is 50 mm, and the focal length of the light receiving lenses 21a and 21 is 20 mm.
When the apparatus was constructed in mm and the distance measurement experiment similar to that in Example 1 was performed, the same satisfactory result was obtained. According to the distance measuring device of the present embodiment, it is possible to measure a distance from a long distance to a short distance, and it is possible to measure a high resolution in a predetermined distance section, which can be practically used without any problem. In the above two embodiments, PSD is used as an element (position sensor) having high resolution, and SPD is used as an element (position sensor) which is not as high in resolution as the left but is excellent in other points (cost and ease of use). However, the present invention is not limited to these. A CCD or phototransistor may be used as the photodetector. Further, in the above embodiment, PSD
Although only one set of position sensor (light receiving element) and light receiving lens (light detecting unit) other than the above is arranged, a plurality of such light detectors, for example, are arranged concentrically with respect to the projected light beam. By doing so, it is possible to further increase the ranging accuracy over a wide range. Further, in order to improve the S / N ratio in distance measurement, the light projecting element may be modulated to emit light, and the photocurrent generated in the light receiving element may be demodulated to measure the signal.

[0014]

As described above, according to the present invention, the distance measuring device can detect the signal of the object to be measured from a long distance to a short distance. That is, the light beam dead zone is eliminated. Furthermore, since a high-resolution position sensor (PSD) having a short length is used, it is possible to perform distance measurement with high resolution in a predetermined distance range. Further, a plurality of light detecting portions as shown in FIG. 2 are arranged on a concentric circle centered on the optical axis of the light projecting portion,
A high-resolution position sensor with a short length as its photodetector
By using (for example, PSD), the measurement range can be expanded with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a light receiving element of a first embodiment according to the present invention.

FIG. 2 is a schematic configuration diagram of a second embodiment according to the present invention.

FIG. 3 is a schematic configuration diagram of a general distance measuring device using the principle of triangulation.

FIG. 4 is a diagram illustrating a difference in angle of incident light when distance measurement is performed on an object at a long distance and an object at a short distance.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light beam projector 11 ... Condensing lens 12 ... Light emitting element 2, 2a, 2b ... Photodetector 21, 21a, 21b ... Light receiving lens 22 ... Light receiving element 22a , 22b ... Position sensor 3, 3a, 3b ... DUT 4 ... Irradiated light beam 5, 5a, 5b, 5c, 5d ... Scattered light

Claims (3)

[Claims] 1. A light beam projecting unit for irradiating an object to be measured with a light beam, a light receiving lens for collecting and condensing scattered light of the irradiated light beam by the object to be measured, and a collection of scattered light by the light receiving lens. In an optical distance measuring device including a photodetector having a light receiving element for detecting a light spot position, and a signal processor for calculating a distance to an object to be measured by a signal from the photodetector,
The optical distance measuring device, wherein the light receiving element has a plurality of position sensors having different resolutions. 2. The optical distance measuring apparatus according to claim 1, wherein the plurality of position sensors are arranged adjacent to each other. 3. A light beam projector for irradiating an object to be measured with a light beam, a light receiving lens for collecting and condensing scattered light of the irradiated light beam by the object to be measured, and a collection of scattered light by the light receiving lens. In the optical distance measuring device including a plurality of photodetector units each having a light receiving element for detecting a light spot position and a signal processing unit for calculating a distance to an object to be measured based on signals from the photodetector units, The optical distance measuring device, wherein the light receiving element of the detection unit has one of two types of position sensors having different resolutions, and the light detection units are arranged separately from each other.