JP2012042374A - Distance measurement apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a distance measuring precision from being lowered even if the distance to a target object is long.SOLUTION: A distance measurement apparatus is configured by installing an infrared LED and an image sensor 12 on a substrate. The image sensor 12 incorporates: a pixel array 20; a DSP circuit 21 for processing light receiving signals from pixels of the pixel array 20; a memory 22 for storing information or the like to be used for processing by the DSP circuit 21; and a driver circuit 23 for driving the infrared LED. The DSP circuit 21 determines a diameter of a light quantity distribution 24 diffused and reflected by a target object and formed on the pixel array 20, and compares the diameter with a comparison value stored in the memory 22 to determine a distance to the target object. Therefore, even if a reflectance of the target object is non-uniform, the influences can be minimized and the distance to the target object can be more accurately determined.

Description

  The present invention relates to a distance measuring device that measures a distance from a target object by an optical method.

  A distance measuring device (hereinafter also referred to as a distance measuring sensor) that measures a distance from a target object by a non-contact method is used in various applications. For example, it is installed in a toilet to detect the entry / exit of a user, or is installed in a projector to measure the distance between the screen and the lens when the projection screen is focused, or is installed in a robot such as an automatic vacuum cleaner. It is used to detect obstacles in advance and perform avoidance actions.

In general, the following principle is used for a method of measuring a distance without contact.
(1) Ultrasonic method
(2) Capacitance method
(3) Optical system

  In the ultrasonic method of (1) above, the ultrasonic wave is emitted from the transmitter built in the distance measuring sensor, and the time required for the round trip of the ultrasonic wave is received after receiving the reflected wave that is reflected and hits the target object. The distance to the target object is measured using a known sound velocity value. This method has the disadvantage that the size of the distance measuring sensor increases.

  The capacitance method (2) measures the distance to the target object by measuring the amount of charge induced when the target object approaches the surface of the distance measuring sensor. This method has a drawback that the measurement range is limited to a close region of about several centimeters.

  In addition, products using the ultrasonic sensor of the above (1) or the capacitive sensor of the above (2) have a large system and are relatively expensive. For this reason, it is rarely installed in general home appliances, and is mainly used for FA (Factory Automation).

  On the other hand, the optical method (3) is easy to mount on a small device because the size of the distance measuring sensor is relatively small. For this reason, this method is widely used in the projectors, automatic vacuum cleaners, human body sensors and the like described above.

  Currently, the following two methods (principles) are used for optical distance measuring sensors that are mainly used. Hereinafter, the principle and problems of each method will be described in detail.

(A) “Triangulation + PSD (Position Sensitive Detector)” Method FIG. 7 shows an outline of an optical distance measuring sensor based on the “triangulation + PSD” method. As shown in FIG. 7, a light emitting unit 1 composed of an LED (Light Emitting Diode) provided with an optical system and a light receiving unit 2 composed of a PSD composed of a photodiode have a certain interval. This optical distance measuring sensor is arranged side by side. Then, the reflected light from the target object 3, 3 ′ of the light beam from the LED 1 irradiated to the target object 3, 3 ′ is received by the PSD 2, and the light receiving position on the light receiving region of the PSD 2 is changed from the LED 1 to the target object 3, 3 ′. The distance is calculated by using the movement on the light receiving area as the distance changes. The light receiving position on the light receiving region of PSD2 is determined by the ratio of output currents from two output terminals provided on PSD2.

  As shown in FIG. 7, the light receiving position of the reflected light on the PSD (photodiode) 2 emits light near the light emitting unit 1 when the distance to the target object 3 is long, and light when the distance to the target object 3 ′ is short. Move far from part 1. At this time, the distance from the light emitting unit 1 to the target objects 3 and 3 ′ and the light receiving position on the PSD 2 (output value of PSD 2) have a one-to-one correspondence as shown in FIG. Therefore, the distance to the target objects 3 and 3 ′ can be calculated based on the light receiving position using the relationship shown in FIG.

(B) Time detection method The light detection unit includes a light emitting unit and a light receiving unit, and the light receiving unit detects the reflected light from the target object of the light beam emitted from the light emitting unit. This is the same as the case of the “triangulation + PSD” method. However, this time detection method calculates the distance to the target object based on the speed of light by measuring the time from the light emission time to the light reception time of the reflected light (that is, the light round trip time).

  In this time detection method, since the time required for the round trip of light is measured and the distance to the target object is calculated, there is no drawback in terms of accuracy as in the case of the “triangulation + PSD” method. .

  As another method of the optical distance measuring sensor, there is a method using a size measuring device that measures the actual size of a measurement object using a camera disclosed in Japanese Patent Laying-Open No. 2005-164513 (Patent Document 1). Conceivable.

  In the method using the size measuring device disclosed in Patent Document 1 above, for a plurality of objects whose actual sizes are known, the ratio value between the actual size and the image size (size on the display screen) The relationship with the distance to the object is prepared in advance as a database. And from the picked-up image image | photographed by the said camera imaging | photography part, any of the objects registered into the said database are designated as a measuring object. Then, the image size is calculated for each of the designated measurement objects by analyzing the captured image by a CPU (central processing unit). Further, a ratio value between the actual size and the image size is calculated based on the specified actual size of the measurement target (registered in the database), and the camera is referred to based on the ratio value. The distance from the imaging unit to the measurement target is calculated.

  As another method of the optical distance measuring sensor, a distance measuring apparatus that measures the distance to a target object using a CCD (Charge Coupled Device) camera is disclosed in Japanese Patent Laid-Open No. 04-249711 (Patent Document). 2).

  In the distance measuring device disclosed in Patent Document 2, a laser parallel beam having a ring-shaped cross section is formed by a lens, a collimator lens, and a light-shielding plate disposed therebetween based on a laser beam from a laser tube, and a half mirror Thus, a ring-shaped laser parallel beam centered on the optical axis of the two-dimensional CCD camera is obtained. Then, the measurement plane illuminated by the laser parallel beam is imaged by the two-dimensional CCD camera, and the distance from the two-dimensional CCD camera to the measurement plane is calculated based on the ring radius of the laser parallel beam in the image. I have to.

  The distance measuring apparatus has a complicated structure for producing the laser parallel beam. However, when the sizes of the optical systems of the light emitting unit and the light receiving unit are not exactly the same, it is not necessary to be parallel light.

  As another method of the optical distance measuring sensor, an electronic camera system in which the target object is limited to a light emitting object such as a remote controller is disclosed in order to compensate for the drawbacks of the distance measuring device disclosed in Patent Document 2. This is disclosed in Japanese Patent Laid-Open No. 2001-346090 (Patent Document 3).

  In the electronic camera system disclosed in Patent Document 3, when the first LED and the second LED of the remote controller emit light, the image is picked up by the image sensor of the electronic camera, and the emission color of the first and second LEDs is detected, and the emission color is detected. The position of the selected pixel is stored. Then, the distance from the electronic camera to the remote controller is calculated based on the interval between the first and second LEDs on the imaging screen and the actual interval.

  As described above, in the electronic camera system, the target object is limited to a light emitting object such as the remote controller, and the distance is measured using a known light emission interval.

  However, each of the conventional optical distance measuring sensors has the following problems.

(a) “Triangulation + PSD” method This method uses a geometric principle called triangulation, and can easily measure distances in principle. However, in practice, as shown in FIG. 8, as the distance from the target object 3 increases, the amount of movement of the light receiving position (that is, the amount of fluctuation in the output current value from the output terminal) suddenly increases. Since it becomes smaller, the accuracy decreases. In order to avoid this, it is effective to widen the distance between the light emitting unit 1 and the light receiving unit 2. However, in that case, the optical distance measuring sensor and the equipment on which the optical distance measuring sensor is mounted are increased in size, and it is very difficult to produce a small optical distance measuring sensor.

  For example, a distance sensor of several centimeters in size cannot measure a distance of 100 cm or more with high accuracy, and the accuracy is 20% or more.

  Furthermore, the calculation of the distance requires the light receiving position on the light receiving area of PSD 2 as an accurate absolute position, not as a relative position. For this reason, the performance of the optical distance measuring sensor greatly depends on the assembly accuracy, and there is a problem that accurate distance measurement cannot be performed unless the initial position correction is performed on the side of the device on which the optical distance measuring sensor is mounted.

  The light receiving position of the PSD 2 on the light receiving region can be obtained by obtaining the light intensity centroid of the light receiving spot. As a result, the reflectance of the irradiated light is non-uniform depending on the target object, so that the light receiving position on the light receiving region of PSD 2 becomes inaccurate, and the distance to the target object cannot be measured accurately. .

(b) Time detection method Since this method measures the time required for the reciprocation of the emitted light and calculates the distance to the target object, there is no accuracy drawback as in the "triangulation + PSD" method. However, since the speed of light is very high, the time required for the outgoing light to reciprocate is very short, and a high-performance light-receiving unit (light-receiving element) and a high-speed arithmetic circuit are required. Since this requires an expensive semiconductor process, there is a problem that the optical distance measuring sensor itself becomes expensive.

(c) Method using the size measuring device disclosed in Patent Document 1 In this method using the size measuring device, the value of the ratio between the actual size and the image size for a plurality of objects whose actual sizes are known, There is a problem that it is necessary to register the relationship with the distance in advance, which places a heavy burden on the registrant. Furthermore, there are a huge database for registering the relationship between the ratio of the actual size to the image size and the distance to the object, and a high-performance computer for analyzing the captured image and calculating the distance. I need it. Therefore, there is a problem that a small optical distance measuring sensor cannot be realized.

(d) Ranging device disclosed in Patent Document 2 In this ranging device, based on the laser beam from the laser tube, the optical axis of the two-dimensional CCD camera is centered by a lens, a collimator lens, a light shielding plate and a half mirror. In order to produce the ring-shaped laser parallel beam, a complicated optical system is required. And in such a large-scale optical system, there exists a problem that it is impossible to mount in a household appliance.

(e) Electronic camera system disclosed in Patent Document 3 In this electronic camera system, a target object is limited to a light emitting object such as a remote controller. For this reason, the target object has a fatal defect that it is necessary to always mount a light emitting object, and there is a problem that there is no versatility.

  In any of the above optical distance measuring sensors, the target object is irradiated with light from one light emitting unit, and the distance to the target object is calculated based on the reflected light from the target object. ing. However, in that case, it is impossible to determine whether the light from the light emitting unit is correctly tracking the target object that is located almost in front of it, and thus it is possible to accurately obtain the distance to the target object. There is a problem that you can not.

Japanese Patent Laid-Open No. 2005-164513 Japanese Patent Laid-Open No. 04-249711 JP 2001-346090 A

  Accordingly, an object of the present invention is to provide a small and inexpensive optical distance measuring device that can more accurately determine the distance to the target object, and whose performance does not greatly depend on assembly accuracy. .

In order to solve the above problems, the distance measuring device of the present invention is:
A light projecting unit including a light source that emits light toward the target object;
A light receiving unit including an image sensor that detects light from the light source reflected by the target object,
The above image sensor
A pixel array that receives reflected light from the target object and outputs image data corresponding to the light amount distribution;
A digital signal processing device that obtains a specific dimension related to an image formed by reflected light from the target object based on image data from the pixel array and obtains a distance to the target object based on the obtained dimension When,
A drive circuit for driving the light source of the light projecting unit to emit light is mounted.

  According to the said structure, the distance to the said target object is calculated | required based on the specific dimension regarding the image of the said light quantity distribution. Therefore, compared with the case where the light receiving position on the light receiving area is obtained as in the “triangulation + PSD” method, the influence can be minimized even if the reflectance of the target object is not uniform. Therefore, the distance to the target object can be obtained more accurately.

  Furthermore, the calculation of the distance does not require detection of the position of the light quantity distribution on the pixel array as an accurate absolute position, and the performance of the distance measuring apparatus does not depend greatly on assembly accuracy.

In the distance measuring device of one embodiment,
The digital signal processing device obtains the size of an image formed by the reflected light from the target object as a specific dimension related to the image.

  According to this embodiment, since the size of the image is obtained as a specific dimension relating to the image, the specific dimension relating to the image can be easily obtained.

In the distance measuring device of one embodiment,
The light emitted from the light source of the light projecting unit toward the target object has a light beam whose vertical section of the optical axis is substantially circular,
The digital signal processing apparatus obtains a circle having a minimum diameter including an image formed by reflected light from the target object, and obtains the diameter of the circle as the size of the image.

  According to this embodiment, the vertical section of the optical axis of the light emitted from the light source of the light projecting unit is substantially circular, and the digital signal processing device of the light receiving unit displays an image of reflected light from the target object. The diameter of the circle having the smallest diameter that is included is obtained as the size of the image. Therefore, it is not necessary to use an object whose actual size is known as the target object, and the image can be easily and stably obtained even when the image formed on the pixel array of the light receiving unit is not a correct circle. Can be obtained.

In the distance measuring device of one embodiment,
The light projecting unit includes two light projecting units, a first light projecting unit located on one side of the light receiving unit and a second light projecting unit located on the other side of the light receiving unit,
The drive circuit drives the light sources so that the light source of the first light projecting unit and the light source of the second light projecting unit emit light alternately,
Based on the image data from the pixel array, the digital signal processing device obtains a distance between two images alternately formed by reflected light from the target object as a specific dimension related to the image.

  According to this embodiment, two spots are formed on the target object by the light emitted from the light sources of the two light projecting units. Therefore, it is possible to determine whether or not the target object that exists substantially in front is correctly tracked based on the received light amounts of the two images formed by the reflected light from the two spots. As a result, the distance to the target object can be measured more accurately.

  Further, the light sources of the first and second light projecting units emit light alternately, and two images are alternately formed on the pixel array by two reflected lights from the target object. Therefore, the position of each image can be specified independently, and it is possible to cope with the case where the two images on the pixel array overlap and cannot be separated.

In the distance measuring device of one embodiment,
In the digital signal processing apparatus, the reference point of each image when the interval between two images formed by the reflected light from the target object is obtained is set as the light intensity centroid of each image.

  According to this embodiment, the interval between two images formed on the pixel array can be obtained more accurately.

In the distance measuring device of one embodiment,
In the digital signal processing apparatus, the reference point of each image when obtaining the interval between two images formed by the reflected light from the target object is set as the area center of gravity of each image.

  According to this embodiment, the interval between two images formed on the pixel array can be obtained more accurately.

In the distance measuring device of one embodiment,
Based on the image data from the pixel array, the digital signal processing device compares the integrated values of the received light amounts for two images formed by the reflected light from the target object, and the difference between the two integrated values is 20%. If it is above, it is determined that the reflected light forming one image and the reflected light forming the other image are not reflected light from the same target object, and the calculation of the interval between the two images is stopped. .

  According to this embodiment, it is possible to reliably prevent erroneous measurement when the reflected light that forms two images on the pixel array is not reflected light from the same target object.

In the distance measuring device of one embodiment,
The digital signal processing device obtains a first distance to the target object based on a size of a first image formed by reflected light from the target object related to light emitted from the first light projecting unit. The second distance to the target object is obtained based on the size of the second image formed by the reflected light from the target object with respect to the light emitted from the second light projecting unit, and the first distance The distance to the target object is obtained using the value, the second distance value, and the third distance value based on the interval between the first image and the second image.

  According to this embodiment, the value of the third distance to the target object based on the interval between the first image and the second image, and the size based on the size of the first image and the second image. By using a total of three distance values including the two first and second distance values to the target object, the distance to the target object can be determined more accurately.

In the distance measuring device of one embodiment,
The digital signal processing apparatus sets an arithmetic average value of the first distance value, the second distance value, and the third distance value as a distance to the target object.

  According to this embodiment, based on the values of the two first and second distances based on the sizes of the first image and the second image, and the interval between the first image and the second image. By calculating the arithmetic average value with the value of the third distance, a more accurate distance to the target object can be easily obtained.

In the distance measuring device of one embodiment,
The digital signal processing device sets a median value of the first distance value, the second distance value, and the third distance value as a distance to the target object.

  According to this embodiment, based on the values of the two first and second distances based on the sizes of the first image and the second image, and the interval between the first image and the second image. By obtaining the median with the value of the third distance, a more accurate distance to the target object can be easily obtained.

In the distance measuring device of one embodiment,
The light source is an infrared light emitting diode.

  According to this embodiment, since an infrared light emitting diode is used as the light source, the light emitted from the light source and the reflected light from the target object are not visible to human eyes. Therefore, it is possible to eliminate the influence of the surroundings due to the visible appearance of the emitted light and the reflected light.

In the distance measuring device of one embodiment,
The image sensor is manufactured by a complementary metal oxide semiconductor process.

  According to this embodiment, since the image sensor is manufactured by a complementary metal oxide semiconductor process, it is possible to easily incorporate the digital signal processing device, the drive circuit, the memory element, and the like.

In the distance measuring device of one embodiment,
The image sensor includes a memory element in which a correction value obtained as a result of calibration of the distance to the target object is recorded.

  According to this embodiment, when the distance to the target object is actually measured, the more accurate distance can be obtained by correcting the measurement result with the correction value recorded in the memory element. .

  As is clear from the above, the distance measuring device according to the present invention is based on the specific dimensions relating to the image of the light amount distribution formed on the pixel array of the light receiving unit by the light from the light source reflected by the target object. Since the distance to the target object is obtained, even if the reflectance of the target object is not uniform as compared with the case of obtaining the light receiving position on the light receiving area as in the “triangulation + PSD” method, the influence is extremely small. Can be small. Therefore, the distance to the target object can be obtained more accurately.

  Furthermore, the calculation of the distance does not require detection of the position of the light quantity distribution on the pixel array as an accurate absolute position, and the performance of the distance measuring device does not depend greatly on assembly accuracy.

It is a longitudinal cross-sectional view in the distance measuring device of this invention. It is the schematic which shows the locus | trajectory of the infrared rays which permeate | transmitted the light emission side lens in FIG. It is a figure which shows schematic structure of the image sensor in FIG. It is a longitudinal cross-sectional view in the distance measuring device different from FIG. It is the schematic which shows the locus | trajectory of the infrared rays which permeate | transmitted the 1st, 2nd light emission side lens in FIG. It is a figure which shows schematic structure of the image sensor in FIG. It is a figure which shows the outline of the optical ranging sensor by a "triangulation survey + PSD" system. It is a figure which shows the correspondence of the distance from the light emission part in FIG. 7, and a target object, and the output value of PSD.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

First Embodiment FIG. 1 is a longitudinal sectional view of a distance measuring device according to the present embodiment. As shown in FIG. 1, in this distance measuring apparatus, an infrared LED 11 and an image sensor 12 incorporating a DSP (Digital Signal Processor) circuit and a driver circuit are installed on a substrate 13. In order to prevent the infrared light emitted from the infrared LED 11 from entering the image sensor 12 as stray light between the infrared LED 11 and the image sensor 12 on the surface of the substrate 13, An infrared shielding plate 14 for preventing stray light is disposed.

  The infrared LED 11 and the image sensor 12 are electrically connected by a wiring pattern (not shown) provided on the substrate 13. Further, the image sensor 12 is connected to an external terminal 15, and the image sensor 12 is connected to a power source and an external circuit via the external terminal 15, and this distance measuring device is used.

  The entire infrared LED 11, image sensor 12, substrate 13 and infrared light shielding plate 14 are sealed with an infrared transmissive black resin 16 by molding. Further, the upper surface of the infrared transmissive black resin 16 is molded into a lens shape, and the light-emitting side lens 17 that collects the infrared rays emitted from the infrared LED 11 toward the target object and the reflected light from the target object are imaged. A light receiving side lens 18 that collects light toward the light receiving region of the sensor 12 is formed. The focal lengths of the light emitting side lens 17 and the light receiving side lens 18 can be individually set. With such a configuration, the distance measuring device can be configured with a minimum number of components.

  Furthermore, when it is desired to increase the accuracy of the optical system, a plurality of lenses may be separately prepared and incorporated in the infrared transparent black resin 16 or outside.

  FIG. 2 is a schematic diagram showing the locus of infrared rays transmitted through the light-emitting side lens 17. In FIG. 2, the infrared LED 11 is driven by the electric power supplied from the driver circuit built in the image sensor 12. The infrared light emitted from the infrared LED 11 is converged on the target object 19 through the light-emitting side lens 17, and a substantially circular spot is formed on the target object 19. Further, a part of the infrared light emitted to the surroundings by the diffuse reflection from the spot area on the target object 19 forms an image on the light receiving area of the image sensor 12 through the light receiving side lens 18.

  FIG. 3 shows a schematic configuration of the image sensor 12. The image sensor 12 stores a rectangular pixel array 20 serving as the light receiving area, a DSP circuit 21 that processes a light reception signal from each pixel of the pixel array 20, and information used in processing by the DSP circuit 21. And a driver circuit 23 for driving the infrared LED 11 are incorporated.

  In the configuration of the image sensor 12, when a part of infrared light diffusely reflected by the target object 19 forms an image on the pixel array 20 on the image sensor 12 through the light receiving side lens 18, a circular shape is formed on the pixel array 20. A light quantity distribution 24 is formed. Here, the pixel array 20 is composed of, for example, 400 pixels × 400 pixels. Then, photoelectric conversion is performed for each pixel, and a received light signal representing the obtained image data is sent to the DSP circuit 21 and calculated, and the number of pixels corresponding to the diameter of the circular light amount distribution 24 is obtained.

  Note that the pixel is composed of a plurality of sub-pixels, and sub-pixel processing is performed, so that the diameter of the light quantity distribution 24 can be accurately determined with a resolution smaller than that of the pixel.

  The value of the diameter of the light quantity distribution 24 obtained in this way changes according to the distance from the distance measuring device to the target object 19. Therefore, information indicating the correspondence between the diameter value of the light quantity distribution 24 and the distance from the distance measuring device to the target object 19 is stored in the memory 22 in advance as a reference value. Then, the DSP circuit 21 calculates the distance from the distance measuring device to the target object 19 by comparing the diameter value of the obtained light quantity distribution 24 with a reference value stored in the memory 22 in advance. Can do it. At that time, by interpolating using the reference value stored in the memory 22, the value of the distance from the distance measuring device to the target object 19 can be obtained in more detail.

  Hereinafter, the principle of calculating the distance to the target object 19 by the distance measuring apparatus having the above configuration will be described.

  The principle of distance calculation in the present embodiment utilizes the fact that the size of the object on the image sensor depends on the distance to the subject when the object is photographed by the camera. For example, when shooting a human face, the size of the face in the screen (that is, the proportion of the face in the screen) changes as the person moves away from the camera. That is, since the size of the face on the screen decreases as the distance to the person increases, the distance to the person is calculated from the relationship based on the face size on the screen and the actual face size. It can be done.

  In this case, the actual size of a known general human face can be used as the actual face size. However, in the case of the present embodiment, since the target object 19 is not specified, the distance from the actual size of the target object 19 to the target object 19 cannot be calculated.

  Therefore, in the present embodiment, the target object 19 is irradiated with a light beam having a circular cross-sectional shape. At this time, the size of the circular spot that can be formed on the target object 19 can be determined in advance by the optical system (lens diameter and radiation angle) of the light emitting unit. The distance to the target object 19 can be calculated by measuring the size on the pixel array 20).

For example, when the lens diameter of the light emitting side lens 17 constituting the light emitting unit is 1 cm and the irradiation angle is 3 degrees, the light emitting side lens 17 is formed on the target object 19 located at a distance of Lcm from the light emitting side lens 17. The spot diameter R is
R = 1 + 2 * L * tan (1.5 °)
It becomes. Further, when the lens diameter of the light receiving side lens 18 is 1 cm and the angle of view is 20 degrees, the captured image width W at a position away from the light receiving side lens 18 by Lcm is:
W = 1 + 2 * L * tan (10 °)
It becomes.

  Here, if W> R, the light amount distribution 24 is formed on the pixel array 20 based on the reflected light from the spot on the target object 19. The diameter of the light quantity distribution 24 is approximately inversely proportional to the distance L. Therefore, if a relational expression between the diameter of the light quantity distribution 24 and the distance L is obtained, by using this relational expression, if the diameter of the light quantity distribution 24 is known, the distance from the light emitting side lens 17 or the light receiving side lens 18 to the target object 19 is obtained. L will be understood.

  Therefore, based on the above relational expression, some corresponding values between the diameter of the circular light amount distribution 24 formed on the pixel array 20 and the distance L from the light emitting side lens 17 or the light receiving side lens 18 to the target object 19 are calculated. If stored in the memory 22, the diameter of the light quantity distribution 24 actually formed on the pixel array 20 is measured by the DSP circuit 21, and the measured value 2 is stored in the memory 22. The distance L from the light-emitting side lens 17 or the light-receiving side lens 18 to the target object 19 when the diameter of the light quantity distribution 24 is obtained can be obtained by linearly complementing the corresponding values.

For example, assuming that the resolution of the pixel array 20 in the image sensor 12 is 400 pixels in the horizontal direction, the target object 19 on the pixel array 20 when the target object 19 is separated from the light-emitting side lens 17 or the light-receiving side lens 18 by 50 cm or 100 cm. The diameter of the light quantity distribution 24 is respectively
77.7 pixels at 50cm
At 100 cm, it becomes 68.8 pixels. Therefore, (77.7, 50) and (68.8, 100) are stored in the memory 22 as the corresponding values (the diameter x of the light quantity distribution 24 and the distance L of the target object 19). When the diameter x of the light quantity distribution 24 measured by the DSP circuit 21 is between 77.7 pixels and 68.8 pixels,
(L-50) / (100-50) = (x-68.8) / (77.7-68.8)
Thus, the distance L can be obtained by substituting the diameter x (pixel value) measured by the DSP circuit 21 into this equation.

  Here, the number of pixels of the corresponding value stored in the memory 22 is not an integer value, but the above calculation can be performed by using a general pixel sub-pixel technique of an image sensor. .

  In the present embodiment, infrared light from the infrared LED 11 is used as light to be irradiated to the target object 19. Thus, it is desirable to use infrared rays that are invisible to human eyes without affecting the surroundings.

  The light received by the light receiving side lens 18 is imaged in a substantially circular shape on the pixel array 20 of the image sensor 12 to form a light quantity distribution 24. However, depending on the situation of the target object 19, for example, the target object 19 does not have a uniform reflectance, a part of the light quantity distribution 24 may be missing or an unclear area may be formed. In that case, since it is known that the shape of the light amount distribution 24 originally formed on the pixel array 20 is circular, the diameter of the minimum circle including the entire region of the formed light amount distribution 24 is determined by the least square method. The image of the original light quantity distribution 24 can be obtained by calculating with the above. Therefore, the distance can be obtained from the diameter of the original light quantity distribution 24.

  In the case of the conventional “triangulation + PSD” method, only the position of the center of gravity of the light receiving spot formed on the light receiving region of the PSD can be detected. Therefore, the method using the image sensor 12 as in the present embodiment is efficient. Is not possible.

  As described above, in the present embodiment, a substantially circular spot is formed on the target object 19 by the infrared rays emitted from the infrared LED 11, and the pixel array 20 of the image sensor 12 is diffused and reflected from the spot area. A substantially circular light amount distribution 24 is formed. The diameter of the light quantity distribution 24 is obtained by the DSP circuit 21 of the image sensor 12, and the distance to the target object 19 is obtained based on the diameter of the light quantity distribution 24.

  Therefore, compared with the case of obtaining the position of the light quantity distribution 24 on the pixel array 20 as in the “triangulation + PSD” method, the influence is minimized even if the reflectance of the target object is not uniform. Thus, the distance to the target object 19 can be obtained more accurately.

  Furthermore, for the calculation of the distance, it is not necessary to detect the position of the light quantity distribution 24 on the pixel array 20 as an accurate absolute position. Therefore, the measurement performance of the distance measuring device does not depend greatly on the assembly accuracy.

Second Embodiment FIG. 4 is a longitudinal sectional view of the distance measuring device according to the present embodiment. As shown in FIG. 4, in the distance measuring apparatus, the first infrared LED 31 and the second infrared LED 32 are positioned on both sides of the image sensor 33 incorporating the DSP circuit and the driver circuit, and the image sensor 33 At the same time, it is installed on the substrate 34. And between the 1st infrared LED31 and the image sensor 33 in the surface of the board | substrate 34, and between the 2nd infrared LED32 and the image sensor 33, the infrared light radiate | emitted from infrared LED31 and 32 is. In order to prevent stray light from entering the image sensor 33 directly, infrared light shielding plates 35 and 36 for preventing stray light are arranged.

  As in the case of the first embodiment, the first infrared LED 31 and the image sensor 33 and the second infrared LED 32 and the image sensor 33 are formed by a wiring pattern (not shown) provided on the substrate 34. Electrically connected. Further, the image sensor 33 is connected to an external terminal 37. The image sensor 33 is connected to a power source and an external circuit via the external terminal 37, and the distance measuring device is used.

  Then, the first infrared LED 31, the second infrared LED 32, the image sensor 33, the substrate 34, the infrared light shielding plate 35 and the infrared light shielding plate 36 are entirely sealed with an infrared transmitting black resin 38 by molding. It has been stopped. Further, the upper surface of the infrared transmissive black resin 38 is molded into a lens shape, and a first light-emitting side lens 39 that collects infrared rays emitted from the first infrared LED 31 toward the target object, and a second infrared ray. A second light emitting side lens 40 that condenses the infrared light emitted from the LED 32 toward the target object, and a light receiving side lens 41 that condenses the reflected light from the target object toward the light receiving region of the image sensor 32. Is formed. The focal lengths of the first light emitting side lens 39, the second light emitting side lens 40, and the light receiving side lens 41 can be set individually. With such a configuration, the distance measuring device can be configured with a minimum number of components.

  Furthermore, when it is desired to increase the accuracy of the optical system, a plurality of lenses may be separately prepared and incorporated in the infrared transparent black resin 38 or outside.

  FIG. 5 is a schematic diagram showing the locus of infrared rays transmitted through the first light-emitting side lens 39 and the second light-emitting side lens 40. In FIG. 5, the first infrared LED 31 and the second infrared LED 32 are driven by the power supplied from the driver circuit built in the image sensor 33, and infrared rays are emitted alternately. The infrared light emitted from the first infrared LED 31 is converged on the target object 42 through the first light-emitting side lens 39, while the infrared light emitted from the second infrared LED 32 passes through the second light-emitting side lens 40. On the target object 42, two substantially circular spots are formed by being converged on the target object 42. Furthermore, a part of each infrared light radiated by the diffuse reflection from the two spot areas on the target object 42 has a time difference on the light receiving area of the image sensor 33 through the light receiving side lens 41. Form an image.

  FIG. 6 shows a schematic configuration of the image sensor 33. The image sensor 33 stores a rectangular pixel array 43 as the light receiving region, a DSP circuit 44 that processes a light reception signal from each pixel of the pixel array 43, information used in processing by the DSP circuit 44, and the like. A memory 45 and a driver circuit 46 for driving the first infrared LED 31 and the second infrared LED 32 are incorporated.

  In the configuration of the image sensor 33, when part of the two infrared lights diffusely reflected by the target object 42 forms an image on the pixel array 43 of the image sensor 33 through the light receiving side lens 41, Two circular light quantity distributions 47 and 48 are formed. Here, the pixel array 43 is composed of, for example, 400 pixels × 400 pixels. Then, photoelectric conversion is performed for each pixel, and the obtained light reception signal is sent to the DSP circuit 44 and calculated, and the light intensity centroids (hereinafter simply referred to as the centroids) of the two circular light intensity distributions 47 and 48 are calculated. Two corresponding pixel coordinates are obtained, and the number of pixels corresponding to the distance between the two pixel coordinates is obtained.

  The pixel is composed of a plurality of sub-pixels, and sub-pixel processing is performed to accurately determine the distance between the two pixel coordinates from pixel coordinates that are originally integers with a resolution smaller than that of the pixel. Is possible.

  The value of the distance between the centroids of the two light quantity distributions 47 and 48 obtained in this way changes according to the distance from the distance measuring device to the target object 42. Therefore, by storing in advance in the memory 45 information indicating the correspondence between the value of the distance between the centers of gravity of the two light quantity distributions 47 and 48 and the distance from the distance measuring device to the target object 42 as a reference value. The distance between the centroids of the two obtained light quantity distributions 47 and 48 is compared with a reference value stored in the memory 45 in advance by the DSP circuit 44, so that the distance measurement device to the target object 42 is compared. The distance can be obtained. At this time, by interpolating using the reference value stored in the memory 45, the value of the distance from the distance measuring device to the target object 42 can be obtained in more detail.

  Hereinafter, the principle of calculating the distance to the target object 42 by the distance measuring apparatus having the above configuration will be described.

  Although only one light emitting unit is used in the first embodiment, the light emitting units are arranged on both sides of the image sensor 33 in the present embodiment. Also in the present embodiment, the distance to the target object 42 can be calculated based on the same principle as in the first embodiment.

  That is, infrared rays emitted from the two LEDs 31 and 32 form two spots on the object 42. Reflected light obtained from them forms two light quantity distributions 47 and 48 on the pixel array 43 of the image sensor 33. The distance between the two light quantity distributions 47 and 48 in the pixel array 43 becomes smaller as the distance from the light emitting side lenses 39 and 40 and the light receiving side lens 41 to the target object 42 increases. Therefore, the distance can be measured by calculating the interval between the two light quantity distributions 47 and 48.

  In this case, the distance between the two light quantity distributions 47 and 48 at a specific distance can be set in advance when the distance measuring device is optically designed. Further, in order to obtain the interval between the actual two light quantity distributions 47 and 48 formed on the pixel array 43, the light quantity centroid and the area centroid of each light quantity distribution can be used.

For example, when the distance between the two LEDs 31 and 32 is 2 cm and the infrared light is set to be emitted in a direction perpendicular to the upper surface of the substrate 34, the first and second light emitting side lenses 39, The distance between two spots formed on the target object 42 at a distance of Lcm from 40 is:
D = 2cm
It becomes. In addition, when the lens diameter of the light receiving side lens 41 is 1 cm and the angle of view is 15 degrees, the interval W between two captured images at a position separated by Lcm from the light receiving side lens 41 is
W = 1 + 2 * L * tan (7.5 °)
It becomes.

  Here, if W> D, light amount distributions 47 and 48 are formed on the pixel array 43 based on the reflected light from the two spots on the target object 42. The distance between the two light quantity distributions 47 and 48 is approximately inversely proportional to the distance L. Therefore, if a relational expression between the distance between the two light quantity distributions 47 and 48 and the distance L is obtained, by using this relational expression, if the distance between the two light quantity distributions 47 and 48 is known, the light-emitting side lenses 39 and 40 or the light reception are received. The distance L from the side lens 41 to the target object 42 is known.

  Therefore, based on the above relational expression, a correspondence value between the distance between the two light quantity distributions 47 and 48 formed on the pixel array 43 and the distance L from the light-emitting side lenses 39 and 40 or the light-receiving side lens 41 to the target object 42. Are calculated and stored in the memory 45, the distance between the two light quantity distributions 47 and 48 actually formed on the pixel array 43 is measured by the DSP circuit 44, and this measured value is used. The distance L from the light-emitting side lenses 39 and 40 or the light-receiving side lens 41 to the target object 42 in the case where the two corresponding values stored in the memory 45 are linearly complemented to provide an interval between the two light quantity distributions 47 and 48. Can be sought.

For example, assuming that the resolution of the pixel array 43 in the image sensor 33 is 400 pixels in the horizontal direction, the pixel array 43 when the target object 42 is 50 cm or 100 cm away from the light-emitting side lenses 39, 40 or the light-receiving side lens 41. The interval between the above two light quantity distributions 47 and 48 is respectively
56.5 pixels at 50cm
At 100 cm, it becomes 29.3 pixels. Therefore, (56.5, 50) and (29.3, 100) are stored in the memory 45 as the corresponding values (interval x between the light quantity distributions 47, 48, distance L of the target object 42). When the distance x between the two light quantity distributions 47 and 48 measured by the DSP circuit 44 is between 56.5 pixels and 29.3 pixels,
(L-50) / (100-50) = (x-29.3) / (56.5-29.3) (10)
Thus, the distance L can be obtained by substituting the interval x (pixel value) measured by the DSP circuit 44 into the equation (10).

  In order to cope with the case where the two light quantity distributions 47 and 48 on the pixel array 43 in the image sensor 33 overlap and cannot be separated, the first infrared LED 31 and the second infrared LED 32 are alternately arranged as described above. By emitting light, the center of gravity of the light quantity distribution 47 and the center of gravity of the light quantity distribution 48 are measured independently.

  Further, the distance measurement method in the first embodiment can be applied to each of the two light quantity distributions 47 and 48 formed on the pixel array 43 in the image sensor 33. Therefore, the distance measurement method in the first embodiment is applied to the light quantity distributions 47 and 48 to obtain the distance information obtained from the diameter of the light quantity distribution 47 and the distance information obtained from the diameter of the light quantity distribution 48. A more accurate distance value can be obtained by performing arithmetic average using three distance information together with the distance information obtained from the distance between the light quantity distribution 47 and the light quantity distribution 48 depending on the form. Alternatively, the median value between the maximum value and the minimum value may be a more accurate distance value.

  The size of the distance measuring device itself in the present embodiment is larger than that of the distance measuring device in the first embodiment. However, according to the distance measuring apparatus in the present embodiment, the infrared rays emitted from the two LEDs 31 and 32 accurately capture the target object 42 by comparing the light amounts of the two light amount distributions 47 and 48. It can be determined whether or not. Therefore, when the light amounts of the two light amount distributions 47 and 48 are different, it is possible to determine that the same target object 42 is not irradiated with light and to output an error signal.

  For example, if there is a difference of 20% or more between the integrated values of the light amounts in the two light amount distributions 47 and 48, the target object 42 does not exist in front of the first light emitting side lens 39 and the second light emitting side lens 40. In other words, the reflected light forming the two light quantity distributions 47 and 48 on the pixel array 43 is determined not to be reflected light from the same target object 42, and the calculation is stopped and an error signal is output.

  As described above, in the present embodiment, two substantially circular shapes are formed on the target object 42 by the infrared rays alternately emitted from the first infrared LED 31 and the second infrared LED 32 located on both sides of the image sensor 33. Spots are formed, and two circular light quantity distributions 47 and 48 are formed with a time difference on the pixel array 43 of the image sensor 33 by diffuse reflection from both spot areas. The distance between the light intensity centroids (area centroids) of the light intensity distributions 47 and 48 is obtained by the DSP circuit 44 of the image sensor 33, and the distance to the target object 42 is obtained based on the distance between the light intensity distributions 47 and 48. I am doing so.

  Therefore, compared with the case of the “triangulation + PSD” method, the influence of the non-uniformity of the reflectance on the target object can be minimized, and the distance to the target object 42 can be obtained more accurately. is there.

  Furthermore, two substantially circular spots are formed on the target object 42 by the light emitted from the two LEDs 31 and 32. Therefore, it is possible to determine whether or not the target object 42 that exists substantially in front is correctly tracked based on the light amounts of the light amount distributions 47 and 48 formed by the reflected light from the two spots. .

  Further, for calculating the distance, it is not necessary to detect the positions of the light quantity distributions 47 and 48 on the pixel array 43 as accurate absolute positions. Therefore, the measurement performance of the distance measuring device does not depend greatly on the assembly accuracy.

  In order to incorporate a DSP circuit and a driver circuit in the image sensor, it is optimal to use a CMOS (Complementary Metal Oxide Semiconductor) image sensor because of the consistency of the semiconductor process.

  Further, as described above, in the distance measuring device in each of the above embodiments, the measurement accuracy does not depend on the assembly accuracy between the light emitting unit and the light receiving unit.

  However, due to variations in the optical system, variations in the light amount distribution (spot) size and variations in the distance between the two light amount distributions (spots) occur. Therefore, it is desirable to perform calibration after manufacturing. In that case, when a CMOS process is used, it is easy to incorporate a memory element, so that correction data can be written into the memory element for use. That is, when the distance to the target objects 19 and 42 is actually measured, the more accurate distance can be obtained by correcting the measurement result with the correction data recorded in the memory element.

  In each of the above embodiments, two corresponding values are stored in the memories 22 and 45 in order to illustrate the case where one specific distance is calculated. However, it goes without saying that three or more corresponding values are actually stored so that various distances can be calculated.

  Further, in each of the above embodiments, the light projecting unit is configured to include the infrared LEDs 11, 31, 32 as the light source and the light emitting side lenses 17, 39, 40. Further, the light receiving unit is configured including the image sensors 12 and 33 and the light receiving side lenses 18 and 41. However, the light source of the present invention is not limited to the infrared LED, and may be an LED other than the infrared LED, and a laser element may be used.

11, 31, 32 ... Infrared LED,
12, 33 ... Image sensor,
13, 34 ... substrate
14, 35, 36 ... Infrared shading plate,
15, 37 ... external terminals,
16, 38 ... Infrared transparent black resin,
17, 39, 40 ... light emitting side lens,
18, 41 ... light-receiving side lens,
19, 42 ... target object,
20, 43 ... Pixel array,
21, 44 ... DSP circuit,
22, 45 ... Memory,
23, 46 ... driver circuit,
24, 47, 48 ... Light intensity distribution.

Claims (13)

A light projecting unit including a light source that emits light toward the target object;
A light receiving unit including an image sensor that detects light from the light source reflected by the target object,
The above image sensor
A pixel array that receives reflected light from the target object and outputs image data corresponding to the light amount distribution;
A digital signal processing device that obtains a specific dimension related to an image formed by reflected light from the target object based on image data from the pixel array and obtains a distance to the target object based on the obtained dimension When,
A distance measuring device comprising: a driving circuit that drives the light source of the light projecting unit to emit light. The distance measuring device according to claim 1,
The digital signal processing device obtains the size of an image formed by reflected light from the target object as a specific dimension related to the image. The distance measuring device according to claim 2,
The light emitted from the light source of the light projecting unit toward the target object has a light beam whose vertical section of the optical axis is substantially circular,
The distance measuring device according to claim 1, wherein the digital signal processing device obtains a circle having a minimum diameter including an image formed by reflected light from the target object, and obtains the diameter of the circle as the size of the image. The distance measuring device according to claim 1,
The light projecting unit includes two light projecting units, a first light projecting unit located on one side of the light receiving unit and a second light projecting unit located on the other side of the light receiving unit,
The drive circuit drives the light sources so that the light source of the first light projecting unit and the light source of the second light projecting unit emit light alternately,
The digital signal processing device is characterized in that, based on image data from the pixel array, obtains an interval between two images alternately formed by reflected light from the target object as a specific dimension related to the image. Distance measuring device. The distance measuring device according to claim 4,
The digital signal processing apparatus is characterized in that a distance between two images formed by reflected light from the target object is used as a reference point of each image as a light intensity centroid of each image. apparatus. The distance measuring device according to claim 4,
The digital signal processing apparatus is characterized in that the reference point of each image when obtaining the interval between two images formed by reflected light from the target object is the center of gravity of the area of each image. apparatus. In the distance measuring device according to any one of claims 4 to 6,
Based on the image data from the pixel array, the digital signal processing device compares the integrated values of the received light amounts for two images formed by the reflected light from the target object, and the difference between the two integrated values is 20%. If it is above, it is determined that the reflected light forming one image and the reflected light forming the other image are not reflected light from the same target object, and the calculation of the interval between the two images is stopped. A distance measuring device characterized by that. In the distance measuring device according to any one of claims 4 to 7,
The digital signal processing device obtains a first distance to the target object based on a size of a first image formed by reflected light from the target object related to light emitted from the first light projecting unit. The second distance to the target object is obtained based on the size of the second image formed by the reflected light from the target object with respect to the light emitted from the second light projecting unit, and the first distance A distance measurement characterized in that a distance to the target object is obtained using a value, a value of the second distance, and a value of a third distance based on a distance between the first image and the second image. apparatus. The distance measuring device according to claim 8, wherein
The digital signal processing apparatus uses an arithmetic average value of the first distance value, the second distance value, and the third distance value as a distance to the target object. Distance measuring device. The distance measuring device according to claim 8, wherein
The digital signal processing apparatus uses a median value of the first distance value, the second distance value, and the third distance value as a distance to the target object. measuring device. In the distance measuring device according to any one of claims 1 to 10,
The distance measuring device, wherein the light source is an infrared light emitting diode. In the distance measuring device according to any one of claims 1 to 11,
The distance measuring device, wherein the image sensor is manufactured by a complementary metal oxide semiconductor process. In the distance measuring device according to any one of claims 1 to 12,
The image sensor includes a memory element in which a correction value obtained as a result of calibration of the distance to the target object is incorporated.

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