JP2016180724A - Distance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measuring device capable of improving distance detection accuracy when a light flying time range finding method is used.SOLUTION: A distance measuring device 1 comprises: a light source 10 which irradiates an object with modulation light; a sensor which detects reflected light from the object (human) 2 by the modulation light; a distance detecting unit 15 which detects the distance between the object and a prescribed position on the basis of the phase difference between the modulation light and the reflected light detected by the sensor; an object detecting unit 16 which detects a relative size of the object on the basis of the reflected light detected by the sensor; and a distance correcting unit 17 which corrects the distance detected by the distance detecting unit when the relative size of the object is smaller than a prescribed reference value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a distance measurement technique using an optical time-of-flight ranging method.

  An optical time-of-flight ranging method is known as one of the techniques for measuring the distance from a target object at a predetermined position (see, for example, JP 2011-122913 A). In this optical time-of-flight ranging method, the target object is irradiated with modulated light from a predetermined position, the reflected light is detected, and the relative distance from the target object is measured by obtaining the phase difference between the modulated light and the reflected light. Is done.

  By the way, in the distance measurement using the optical time-of-flight ranging method, there is a case where a false detection of the distance occurs when the distance from the object is relatively long. Such erroneous detection can occur when the delay of the reflected light increases due to the distance from the target object and the phase difference between the modulated light and the reflected light exceeds one period of the modulated light. For example, even if the phase difference between the modulated light and the reflected light is 1.2 cycles, it is difficult on the detection side to distinguish between the case where the phase difference is 0.2 cycles and the case where the phase difference is 1.2 cycles. Is determined to have the same phase difference.

JP 2011-122913 A

  A specific aspect according to the present invention is to provide a technique for improving the accuracy of distance detection when the optical time-of-flight ranging method is used.

  A distance measuring device according to one aspect of the present invention includes (a) a light source that irradiates a target with modulated light, (b) a sensor that detects reflected light from the target by the modulated light, and (c) the above A distance detector for detecting a distance between the object and a predetermined position based on a phase difference between the modulated light and the reflected light detected by the sensor; and (d) the reflected light detected by the sensor. And (e) a detection by the distance detection unit when the relative size of the target object is smaller than a predetermined reference value. A distance measuring device including a distance correcting unit that corrects the measured distance.

  According to the above configuration, it is possible to eliminate the phase difference repetition problem in the case of using the optical time-of-flight ranging method, and to improve the detection accuracy of the relative distance to the object.

  In the distance measurement device, the distance correction unit may calculate the distance when the light intensity of the reflected light is smaller than a predetermined threshold and the relative size of the object is smaller than a predetermined reference value. It is also preferable to correct.

  In the distance measuring apparatus, it is also preferable that the distance correcting unit corrects the distance by adding a correction value obtained based on a value of light speed and a modulation frequency of the modulated light to the distance.

  In the distance measuring apparatus, the sensor detects the reflected light as an image including a plurality of pixels, and the object detection unit is based on the number of pixels in a region corresponding to the object in the image. It is also preferable to detect the relative size of the object.

  An electronic device according to an aspect of the present invention is an electronic device including the above-described distance measuring device. Here, “electronic device” means that some kind of control is executed based on the detection result of the relative distance of the target object. For example, the number of target objects (humans, etc.) passing through a certain place is measured. And a security system that detects an approach or approach of an object (such as a person) to a certain place.

  According to the above configuration, it is possible to improve the distance detection accuracy in the electronic device that performs control using the relative distance to the object.

FIG. 1 is a block diagram illustrating a configuration of a distance measuring device according to an embodiment. FIG. 2 is a diagram for explaining the principle of distance measurement. FIG. 3A is a diagram conceptually showing a detection result of a human being at a relatively far position, and FIG. 3B conceptually shows a detection result of a human being at a relatively close position. FIG. FIG. 4 is a flowchart showing the operation of the distance measuring device.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram illustrating a configuration of a distance measuring device according to an embodiment. The illustrated distance measuring apparatus 1 is incorporated in various electronic devices (for example, a human flow counter, a security system, etc.), for example, to detect a person 2 as a target and detect the relative distance (position). And includes a light source 10, a light receiving unit (sensor) 11, and a control unit 14.

  The light source 10 irradiates the person 2 as the object with modulated light. The modulated light emitted from the light source 10 is, for example, light (infrared light, visible light, etc.) modulated at high speed with a sine wave, a rectangular wave or the like. As the light source 10, for example, a light emitting element capable of high-speed modulation such as an LED can be used.

  The light receiving unit 11 detects reflected light by the modulated light irradiated to the person 2 by the light source 10, and includes a photoelectric conversion unit 12 and a charge storage unit 13. The photoelectric conversion unit 12 includes a plurality of photoelectric conversion elements, and converts the amount of light incident on each photoelectric conversion element into a charge amount. Each photoelectric conversion element is arranged in a matrix along two directions, for example. The charge storage unit 13 stores the charge obtained by each photoelectric conversion element of the photoelectric conversion unit 12.

  The control unit 14 controls the operations of the light source 10 and the light receiving unit 11 and performs information processing for measuring a relative distance between a predetermined position (for example, the installation position of the distance measuring device 1) and the human 2. This is performed and includes a distance detection unit 15, a target object detection unit 16, a distance correction unit 17, and a distance image generation unit 18 as functional blocks. For example, the control unit 14 is realized by executing a predetermined operation program in a computer system including a CPU, a ROM, a RAM, and the like.

  The distance detector 15 is based on the phase difference between the modulated light emitted from the light source 10 and the reflected light detected by the light receiver 11, and the person 2 and a predetermined position (for example, the installation position of the distance measuring device 1). Detect the distance between. An optical time-of-flight ranging method is used to calculate the distance based on the phase difference.

  The target object detection unit 16 is a target object by performing predetermined image processing (pattern matching processing) based on an array of reflected light intensity in each of the plurality of photoelectric conversion elements obtained by the light receiving unit 11, that is, an image. The relative size of the human 2 is detected. In the present embodiment, the relative size of the person 2 is detected based on the number of pixels in an area corresponding to the person 2 in the image.

  The distance correction unit 17 corrects the distance detected by the distance detection unit 15 when the relative size of the person 2 detected by the object detection unit 16 is smaller than a predetermined reference value. In the present embodiment, the distance correction unit 17 further determines whether or not the light intensity of the reflected light detected by the light receiving unit 11 is smaller than a predetermined threshold value. The distance is corrected when the relative size of 2 is smaller than a predetermined reference value.

  The distance image generation unit 18 calculates a distance value for each pixel by performing a predetermined calculation on the amount of charge accumulated in each charge accumulation unit 13 of the light receiving unit 11, and is an image representing these distance values. A certain distance image is generated. The distance image here is, for example, an image to which different colors are assigned according to the size of each distance value. By outputting the distance image to a display device (not shown), the distance image that can be visually recognized by the user is displayed. As a method for calculating the distance value, for example, the method disclosed in Japanese Unexamined Patent Application Publication No. 2011-122913 described above can be used, and detailed description thereof is omitted here.

FIG. 2 is a diagram for explaining the principle of distance measurement. In FIG. 2, the positional relationship between the light receiving unit 11 and the object P is shown in a plan view. The light intensity of the reflected light from the object P due to the irradiation light from the light source 10 changes according to the distance to the object P. Specifically, when the distance is doubled, The light intensity is 1/4 (1/2 ² ). As shown in the figure, the distance when the target P is relatively close to the light receiving unit 11 is L1, and the distance when the object P is far is L2. In this case, for example, compared with the light intensity of the reflected light when L1 = 1 meter, the light intensity of the reflected light when L2 = 16 meter is very small, 1/65536 times. Here, the light intensity of the reflected light can be obtained by the following equation, for example, assuming that the charge amount accumulated in each period obtained by dividing one period of the modulated light into four equal parts is C1, C2, C3, and C4. .

  Therefore, the distance of the target P can be determined by comparing the light intensity of the reflected light detected by the light receiving unit 11 with a preset threshold value. However, when the light reflectivity of the target object P is extremely low, the light intensity of the reflected light is reduced even when the distance of the target object P is relatively small. Therefore, it is erroneously determined that the target object P is far away. there's a possibility that.

  For example, if the modulation frequency is 15 MHz, a problem (repetition problem) that the phase difference appears to be the same every 10 meters occurs. For example, in FIG. 2, when L1 = 1 meter and L2 = 11 meters, the values detected as the phase difference between the modulated light and the reflected light are equal, making it difficult to identify the two. For this reason, in this embodiment, as will be described below, the relative size of the object P is detected by image processing and the result is used.

  In FIG. 2, it is assumed that the number of pixels in the horizontal direction included in the range of the angle of view θ (for example, 90 °) of the light receiving unit 11 is, for example, 200 pixels. Further, it is assumed that a human is detected as the object P. FIG. 3A is a diagram conceptually showing a detection result of a human being at a relatively far position, and FIG. 3B conceptually shows a detection result of a human being at a relatively close position. FIG. For example, if the width X1 of the object P existing at the position of L2 = 11 meters is 5 pixels, the width X2 of the object P existing at the position of L1 = 1 meter is 55 pixels. Alternatively, if the width X1 of the object P existing at the position of L2 = 11 meters is 10 pixels, the width X2 of the object P existing at the position of L1 = 1 meter is 110 pixels. The same applies to the vertical heights Y1 and Y2 of the object P. In consideration of the current image processing technology, it is considered that at least 5 pixels in the width direction and 10 pixels in the height direction are necessary to detect a person as the object P by pattern matching processing.

  When a human being as the target object P is detected as described above, the relative size thereof can be detected based on the number of pixels in the region corresponding to the target object P. Specifically, even if the relative size of the object P is detected by the number of pixels of any one of the widths X1 and X2 and the heights Y1 and Y2 shown in FIGS. 3 (A) and 3 (B). Alternatively, the relative size of the object P may be detected based on the number of pixels included in the region defined by the width and height.

  Next, the operation of the distance measuring device 1 will be described in detail. FIG. 4 is a flowchart showing the operation of the distance measuring apparatus 1.

  The distance detector 15 detects the relative distance of the person 2 based on the modulated light from the light source 10 and the reflected light thereby (step S11).

  Further, the distance correction unit 17 acquires the light intensity of the reflected light detected by the light receiving unit 11 (step S12), and determines whether or not the light intensity has exceeded a predetermined threshold (step S13).

  If the light intensity exceeds the threshold value (step S13; YES), the distance correction unit 17 does not correct the distance, and the distance detected by the distance detection unit 15 is output to an external device or the like (step S14). ). This is because the position of the person 2 is relatively close and the reflectance of the clothes is high, so that the distance can be detected with necessary and sufficient accuracy without causing the phase difference repetition problem.

  On the other hand, when the light intensity is equal to or less than the threshold value (step S13; NO), the distance correction unit 17 causes the image size (number of pixels) of the person 2 detected by the object detection unit 16 to exceed a predetermined specified value. It is determined whether or not (step S14).

  Here, the specified value may be set based on the pixel size corresponding to the distance at which the phase difference repetition problem occurs. If the modulation frequency in the above example is 15 MHz, the phase difference becomes equal when the difference between the distance L1 and the distance L2 is 10 [m]. For example, the human 2 when L2 = 11 [m] When the pixel size is exceeded (for example, the width of 5 pixels), it is considered that the human 2 is at a short distance to the extent that the phase difference repetition problem does not occur, and it can be determined that distance correction is not necessary. On the other hand, if the pixel size is equal to or smaller than the above-described pixel size, it is considered that the phase difference is equal, so it can be determined that distance correction is necessary. Note that when the difference between the distance L1 and the distance L2 is 20 [m], 30 [m]..., It is difficult to detect the human 2 by the pattern matching process. Is not considered.

  When the pixel size of the human 2 exceeds the specified value (step S15; YES), the distance correction unit 17 does not correct the distance, and the distance detected by the distance detection unit 15 is output to an external device or the like. (Step S14). This is because the position of the human 2 is a short distance because the pixel size is relatively large, and the low light intensity of the reflected light is considered to be simply due to the low reflectance of the clothes, which causes a phase difference repetition problem. This is because it can be determined that the situation does not occur.

  When the pixel size of the human 2 is equal to or smaller than the specified value (step S15; NO), the distance correction unit 17 corrects the distance detected by the distance detection unit 15 and outputs the corrected distance to an external device or the like (step S16). For example, the distance is corrected by adding the value of light speed / (modulation frequency × 2) to the distance detected by the distance detector 15. The “light speed” here is the speed of light in a vacuum, and specifically, 29792458 [m / s]. If the modulation frequency is 15 MHz, about 9.99 [m] is added to the distance detected by the distance detection unit 15 as a correction value.

  According to the embodiment as described above, it is possible to solve the phase difference repetition problem in the case of using the optical time-of-flight ranging method, and to improve the detection accuracy of the relative distance to the object.

  In addition, this invention is not limited to the content of embodiment mentioned above, In the range of the summary of this invention, it can change and implement variously. For example, the numerical conditions and the like shown in the above-described embodiments are examples, and are not limited to them. Moreover, the target object for which the distance is to be detected is not limited to a human being.

1: Distance measuring device 10: Light source 11: Light receiving unit (sensor)
12: Photoelectric conversion unit 13: Charge storage unit 14: Control unit 15: Distance detection unit 16: Object detection unit 17: Distance correction unit 18: Distance image generation unit

Claims (5)

A light source for irradiating the subject with modulated light;
A sensor for detecting reflected light from the object by the modulated light;
A distance detector that detects a distance between the object and a predetermined position based on a phase difference between the modulated light and the reflected light detected by the sensor;
An object detection unit that detects a relative size of the object based on the reflected light detected by the sensor;
A distance correction unit that corrects the distance detected by the distance detection unit when the relative size of the object is smaller than a predetermined reference value;
Including a distance measuring device. The distance correction unit corrects the distance when the light intensity of the reflected light is smaller than a predetermined threshold and the relative size of the object is smaller than a predetermined reference value.
The distance measuring device according to claim 1. The distance correction unit corrects the distance by adding a correction value obtained based on a value of light speed and a modulation frequency of the modulated light to the distance.
The distance measuring device according to claim 1 or 2. The sensor detects the reflected light as an image including a plurality of pixels,
The target object detection unit detects a relative size of the target object based on the number of pixels in a region corresponding to the target object in the image.
The distance measuring device according to claim 1.   An electronic device comprising the distance measuring device according to claim 1.

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