JP2013104784A - Optical three-dimensional camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high precision in distance measurement over the range from short distance to long distance.SOLUTION: An optical three-dimensional camera includes; a light source 3 for outputting transmission light to a target 20; a diffuser plate 4 for diffusing the transmission light into a predetermined irradiation intensity pattern; a photo-detector array 7 for receiving light scattered by the target 20, in response to the transmission light in the predetermined irradiation intensity pattern, using a plurality of photo-detector elements and converting the light received by each element into an electrical signal; a phase detector array 8 for detecting phase from each electrical signal; an intensity detector 101 for detecting intensity from each electrical signal; distance detector 102 for measuring the distance from each element to a corresponding point of the target 20 by triangulation method based on the detected intensity; a distance detector 103 for measuring the distance from each element to a corresponding point of the target 20 by TOF method based on the detected phase; a determination unit 104 for selecting one of the measurement results produced by the distance detectors 102, 103 for each element based on the detected intensity; and a three-dimensional image output unit 105 for measuring three-dimensional shape of the target 20 based on the selected measurement results.

Description

  The present invention relates to an optical three-dimensional camera that measures the three-dimensional shape of a target by measuring the distance from the own device to a plurality of points on the target.

  Conventionally, as an optical three-dimensional camera that measures the three-dimensional shape of the target by measuring the distance from the own device to a plurality of points on the target, for example, the triangulation method disclosed in Patent Document 1 is used. And those using the TOF (Time Of Flight) method disclosed in Patent Document 2.

In the triangulation method disclosed in Patent Document 1, a target is irradiated with random pattern light from a transmission optical system, and this pattern is imaged by a light receiving element of a two-dimensional array. Then, the three-dimensional shape of the target is obtained by using the principle of triangulation from the way the pattern changes due to the movement of the target.
This triangulation method is generally said to be advantageous in that the distance measurement accuracy at a short distance is high, although the imaging distance is limited to a short distance.

In the TOF method disclosed in Patent Document 2, uniform pattern light is irradiated onto a target, and scattered light from each point on the target is received by a light receiving element of a two-dimensional array. Then, at each element in the array corresponding to each point on the target, the three-dimensional shape of the target is obtained by measuring the distance from the round trip time to the target of the optical signal to the target.
Unlike the triangulation method, the TOF method directly determines the distance, so that a complicated calculation is not required for obtaining the three-dimensional shape. On the other hand, a high reception signal-to-noise ratio is required to increase the accuracy of distance measurement using the TOF method. However, as long as the reception signal-to-noise ratio is maintained, high-precision distance measurement at a long distance, which is difficult with the triangulation method, is possible.

JP-T 2009-511897 Japanese translation of PCT publication No. 2003-510561

  As described above, the conventional optical three-dimensional cameras disclosed in Patent Documents 1 and 2 have merits but also disadvantages in each of the triangulation method and the TOF method. That is, it is difficult to measure a long distance with the triangulation method, and a required reception SN ratio becomes high with the TOF method. There is nothing that can overcome these disadvantages, and there is a problem that three-dimensional measurement cannot be performed with high accuracy both at a short distance and a long distance.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical three-dimensional camera that can ensure high ranging accuracy from a short distance to a long distance.

  An optical three-dimensional camera according to the present invention includes a light source that outputs transmission light to a target, a pattern generation unit that uses the transmission light output from the light source as a predetermined irradiation intensity pattern, and a predetermined irradiation intensity pattern that is generated by the pattern generation unit. The received light scattered from the target for the transmitted light is received by a plurality of elements, and the phase is detected for each element from the light receiving element array that converts the light into an electric signal and the electric signal converted by each element of the light receiving element array. A phase detector array, an intensity detector for detecting the intensity of each element from the electric signal converted by each element of the light receiving element array, and a triangulation method based on the intensity detected by the intensity detector , Based on the first distance detector for measuring the distance to the corresponding point of the target for each element and the phase detected by the phase detector array, Based on the second distance detector that measures the distance to the corresponding point of the target for each element and the intensity detected by the intensity detector, the measurement result by the first and second distance detectors for each element And a three-dimensional shape measurement unit that measures the three-dimensional shape of the target based on the measurement result selected for each element by the determination unit.

  According to this invention, since it comprised as mentioned above, high ranging accuracy can be implement | achieved from a short distance to a long distance.

It is a schematic diagram which shows the structure of the optical three-dimensional camera which concerns on Embodiment 1 of this invention. It is a block diagram which shows the internal structure of the signal processing part in Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the optical three-dimensional camera which concerns on Embodiment 1 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing a configuration of an optical three-dimensional camera according to Embodiment 1 of the present invention.
As shown in FIG. 1, the optical three-dimensional camera includes an oscillator 1, a distributor 2, a light source 3, a diffusion plate (pattern generation unit) 4, a transmission optical system 5, a reception optical system 6, a light receiving element array 7, and a phase detector. An array 8, a multiplexer 9, and a signal processing unit 10 are included.

  The oscillator 1 oscillates a predetermined sine wave signal (modulation signal). The sine wave signal oscillated by the oscillator 1 is output to the distributor 2.

  The distributor 2 distributes the sine wave signal from the oscillator 1 into two. One sine wave signal distributed by the distributor 2 is output to the light source 3, and the other sine wave signal is output to the phase detector array 8.

The light source 3 outputs transmission light (optical signal) to the target (person in the example of FIG. 1) 20. At this time, the light source 3 applies a sine wave modulation to the intensity of the optical signal by the sine wave signal from the distributor 2.
The diffusion plate 4 diffuses the optical signal output from the light source 3 so as to have a predetermined irradiation intensity pattern (for example, randomization).

The transmission optical system 5 irradiates the optical signal diffused by the diffusion plate 4 toward the target 20 with a predetermined beam divergence angle. At this time, the transmission optical system 5 roughly matches the irradiation area of the optical signal with the instantaneous visual field of the entire light receiving element array 7.
The reception optical system 6 converges scattered light from each point on the target 20 with respect to the transmission light irradiated by the transmission optical system 5.

  The light receiving element array 7 is a two-dimensional array having a plurality of elements, and receives the scattered light converged by the receiving optical system 6 by each element and converts it into a received signal composed of an electrical signal. Received signals received and converted by each element of the light receiving element array 7 are output to the phase detector array 8.

  The phase detector array 8 is a two-dimensional array having a plurality of elements, receives reception signals from the respective elements of the light receiving element array 7 by the corresponding elements, and uses the sine wave signal from the distributor 2 as a local signal. Phase detection is performed. An IQ signal (complex amplitude signal) obtained as a result of reception and phase detection by each element of the phase detector array 8 is output to the multiplexer 9.

  The multiplexer 9 arranges IQ signals from the respective elements of the phase detector array 8 in series and collects them into one output. The IQ signals collected as one output by the multiplexer 9 are output to the signal processing unit 10.

  The signal processing unit 10 processes the IQ signals that are combined into one output by the multiplexer 9 and output in series, and measures the three-dimensional shape of the target 20. As shown in FIG. 2, the signal processing unit 10 includes an intensity detection unit 101, a triangulation method distance detection unit (first distance detection unit) 102, and a TOF method distance detection unit (second distance detection unit). 103, a determination unit 104, and a three-dimensional image output unit (three-dimensional shape measurement unit) 105.

  The intensity detection unit 101 detects the intensity of each IQ signal (IQ signals from each element of the arrays 7 and 8) collected as one output from the multiplexer 9. Information (reception intensity information) indicating the intensity of each IQ signal detected by the intensity detection unit 101 is output to the distance detection unit 102 and the determination unit 104.

  The distance detection unit 102 measures the change in the received intensity pattern for each element of the arrays 7 and 8 using the triangulation method based on the intensity of each IQ signal detected by the intensity detection unit 101. The distance to the corresponding point of the target 20 is measured. Then, three-dimensional shape information can be obtained from this distance information. Information indicating the three-dimensional shape of the target 20 measured by the distance detection unit 102 (three-dimensional shape information) is sent to the determination unit 104.

  The distance detecting unit 103 measures the distance to the corresponding point of the target 20 for each element of the arrays 7 and 8 using the TOF method based on each IQ signal collected as one output from the multiplexer 9. Is. Then, three-dimensional shape information can be obtained from this distance information. Information (three-dimensional shape information) indicating the three-dimensional shape of the target 20 measured by the distance detection unit 103 is sent to the determination unit 104.

  Based on the intensity of each IQ signal detected by the intensity detection unit 101, the determination unit 104 determines the measurement result by the triangulation method of the distance detection unit 102 or the TOF method of the distance detection unit 103 for each element of the arrays 7 and 8. One of the measurement results by is selected. Information indicating the selection result by the determination unit 104 is output to the three-dimensional image output unit 105.

  The three-dimensional image output unit 105 calculates the final three-dimensional shape of the target 20 based on the measurement result (three-dimensional shape information) by the method selected by the determination unit 104 for each element of the arrays 7 and 8. The result is output.

Next, the operation of the optical three-dimensional camera configured as described above will be described. FIG. 3 is a flowchart showing the operation of the optical three-dimensional camera according to Embodiment 1 of the present invention.
In the operation of the optical three-dimensional camera, as shown in FIG. 3, first, the oscillator 1 oscillates a predetermined sine wave signal (modulation signal) (step ST1). The sine wave signal oscillated by the oscillator 1 is output to the distributor 2.

  Next, the distributor 2 distributes the sine wave signal from the oscillator 1 into two (step ST2). One sine wave signal distributed by the distributor 2 is output to the light source 3, and the other sine wave signal is output to the phase detector array 8.

  Next, the light source 3 outputs transmission light (optical signal) to the target 20. At this time, the light source 3 modulates the intensity of the optical signal with the sine wave signal from the distributor 2 (step ST3).

  Next, after passing the modulated optical signal through the diffusion plate 4, the transmission optical system 5 adjusts to a predetermined beam divergence angle and irradiates the target 20 (step ST4). At this time, the irradiation area is roughly matched to the instantaneous visual field of the entire light receiving element array 7. Further, by passing the diffuser plate 4, the pattern of the irradiation intensity of the transmission light is randomized as described in Patent Document 1, for example.

Next, each element of the light receiving element array 7 receives the scattered light from each point on the target 20 with respect to the transmission light irradiated by the transmission optical system 5 via the reception optical system 6, and receives a reception signal composed of an electrical signal. (Step ST5). Received signals received and converted by each element of the light receiving element array 7 are output to the phase detector array 8.
Here, since the transmission light is subjected to sinusoidal intensity modulation, the same intensity is applied to the intensity of the reception light. Further, the phase of modulation at the time of reception is delayed by the round trip time of the optical signal from the optical three-dimensional camera to the target 20 with respect to the phase of modulation at the time of transmission.

  Next, each element of the phase detector array 8 performs phase detection on the received signal from each element of the light receiving element array 7 using the sine wave signal from the distributor 2 as a local signal (step ST6). An IQ signal (complex amplitude signal) obtained as a result of reception and phase detection by each element of the phase detector array 8 is output to the signal processing unit 10 via the multiplexer 9.

  Next, the intensity detecting unit 101 of the signal processing unit 10 detects the intensity of the IQ signal from each element of the array 8 (step ST7). Specifically, the intensity is detected by calculating the square sum of the amplitude of the I signal and the amplitude of the Q signal. Information (reception intensity information) indicating the intensity of each IQ signal detected by the intensity detection unit 101 is output to the distance detection unit 102 and the determination unit 104.

  Next, the distance detection unit 102 measures the three-dimensional shape of the target 20 using the triangulation method based on the intensity of each IQ signal detected by the intensity detection unit 101 (step ST8). That is, in the triangulation method, specifically, by the method described in Patent Document 1, for each element of the arrays 7 and 8, up to the corresponding point of the target 20 based on the change in the received intensity pattern of the IQ signal. By measuring the distance, the three-dimensional shape of the target 20 can be measured. The three-dimensional shape information of the target 20 by the distance detection unit 102 is sent to the determination unit 104.

  Next, the distance detection unit 103 measures the three-dimensional shape of the target 20 using the TOF method based on the IQ signals from the elements of the arrays 7 and 8 (step ST9). Specifically, using the fact that the phase of the IQ signal is the phase difference of the sine wave signal between transmission and reception, the distance to the target 20 is measured for each element by the TOF method from this phase, the modulation frequency, and the speed of light. . Then, the three-dimensional shape of the target 20 can be measured from the obtained distance value and information on the viewing direction corresponding to each element. The three-dimensional shape information of the target 20 by the distance detection unit 103 is sent to the determination unit 104.

ここで、ｗは受光素子アレイ７中心と光源３の間隔（ｍ）であり、Ｌは距離（ｍ）であり、ＳＮＲはＴＯＦ方式での受信ＳＮ比であり、ｃは光速（ｍ／ｓ）であり、ｆ_mは変調周波数（Ｈｚ）である。 Next, based on the intensity of each IQ signal detected by the intensity detection unit 101, the determination unit 104 uses the three-dimensional shape information by the triangulation method of the distance detection unit 102 or the TOF method of the distance detection unit 103 for each element. One of the three-dimensional shape information is selected (step ST10). That is, the determination unit 104 first calculates a reception SN ratio for each element from the reception intensity information of the IQ signal from each element and the reception noise level that is known in advance. Then, it is determined from this received S / N ratio whether the value obtained by the triangulation method or the TOF method is selected from the distance measurement values corresponding to each element. Qualitatively, if the received signal-to-noise ratio is less than a certain threshold under a certain target distance condition, the distance measurement accuracy by the triangulation method is superior. Specifically, the distance measurement accuracy by the triangulation method is superior under the condition of the following expression (1).

Here, w is the distance (m) between the center of the light receiving element array 7 and the light source 3, L is the distance (m), SNR is the reception SN ratio in the TOF system, and c is the speed of light (m / s). F _m is the modulation frequency (Hz).

  When the determination is made using equation (1), a distance measurement value (symbol L in equation (1)) is required in determining which method to select. The distance result is used as a temporary true value. Although the value of the TOF method itself has an error, the determination formula can be applied approximately if the reception SN ratio is sufficiently high.

  As described above, the determination unit 104 determines which of the two ranging methods is to be selected by obtaining the reception S / N ratio from the reception intensity of each element and confirming whether the expression (1) is satisfied. This is done for each element. Information indicating the selection result by the determination unit 104 is output to the three-dimensional image output unit 105.

  Next, the three-dimensional image output unit 105 calculates the final three-dimensional shape of the target 20 based on the three-dimensional shape information according to the method selected by the determination unit 104 for each element of the array 8 and outputs the result. (Step ST11).

  As described above, according to the first embodiment, since the three-dimensional distance measurement for the target 20 is performed by the two methods of the triangulation method and the TOF method, the demerits of the triangulation method and the TOF method can be obtained. It can be supplemented, and high-precision ranging is possible from a short distance to a long distance. As a result, a highly accurate three-dimensional shape can be acquired.

  In addition, in the optical three-dimensional camera according to Embodiment 1, after combining the two methods, one of the two ranging values having high accuracy is further calculated based on the reception SN ratio for each element. Since it is configured to automatically select according to the situation, it is possible to realize an optimal combination of the two methods, and to measure a three-dimensional shape with higher accuracy.

  In the optical three-dimensional camera according to the first embodiment, a method of modulating with a sine wave signal is shown with respect to the modulation of light necessary for the TOF method. However, the present invention is not limited to this. For example, the modulation method may be a pulse method, and distance measurement and reception intensity detection may be performed using this method.

In the optical three-dimensional camera according to Embodiment 1, the irradiation pattern is randomized by the diffusion plate 4. However, the present invention is not limited to this, and the diffuser plate 4 may be a liquid crystal type so that randomization ON / OFF can be controlled.
Here, when the pattern is randomized, a dark pixel, that is, a pixel with a poor reception S / N ratio is always generated. Therefore, when the TOF method is selected for the first imaging, turning off the pattern randomization can avoid the occurrence of pixels with a poor reception S / N ratio and further improve the imaging performance in the TOF. .

  In the present invention, any constituent element of the embodiment can be modified or any constituent element of the embodiment can be omitted within the scope of the invention.

  DESCRIPTION OF SYMBOLS 1 Oscillator, 2 Distributor, 3 Light source, 4 Diffusing plate (pattern production | generation part), 5 Transmission optical system, 6 Reception optical system, 7 Light receiving element array, 8 Phase detector array, 9 Multiplexer, 10 Signal processing part, 20 Target , 101 intensity detection unit, 102 distance detection unit, 103 distance detection unit, 104 determination unit, 105 three-dimensional image output unit (three-dimensional shape measurement unit).

Claims (3)

A light source that outputs transmission light to the target;
A pattern generator that uses the transmission light output by the light source as a predetermined irradiation intensity pattern;
A light receiving element array that receives scattered light from the target with respect to transmission light that has been set to a predetermined irradiation intensity pattern by the pattern generation unit, and converts the light into an electrical signal;
A phase detector array for detecting a phase for each of the elements from an electrical signal converted by each element of the light receiving element array;
An intensity detector that detects the intensity of each element from the electrical signal converted by each element of the light receiving element array;
A first distance detection unit that measures a distance to a corresponding point of the target for each element by a triangulation method based on the intensity detected by the intensity detection unit;
A second distance detector for measuring a distance to a corresponding point of the target for each element by the TOF method based on the phase detected by the phase detector array;
Based on the intensity detected by the intensity detection unit, for each element, a determination unit that selects one of the measurement results by the first and second distance detection units;
An optical three-dimensional camera comprising: a three-dimensional shape measurement unit that measures a three-dimensional shape of the target based on a measurement result selected for each of the elements by the determination unit. The determination unit calculates a reception S / N ratio for each element from the intensity, and when the reception S / N ratio is equal to or less than a predetermined threshold, selects a measurement result by the first distance detection unit, and The optical three-dimensional camera according to claim 1, wherein when the ratio is larger than the threshold value, a measurement result by the second distance detection unit is selected. 3. The optical three-dimensional camera according to claim 1, wherein the pattern generation unit randomizes the transmission light, and can switch ON / OFF of the randomization.

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