JP2002221408A - Optical measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of the measurement result by calculating the center of gravity on the basis of effective data as many as possible. SOLUTION: The optical measuring device includes an optical system, which projects light onto an object and receives the reflected light, and a means 23 for calculating the center of gravity, which calculates the center of gravity in a time distribution of the intensity of the received light or the center of gravity in a spatial distribution of the intensity of the received light at a photo detecting surface. The center of gravity or a result calculated based on the center of gravity using a determined method is output as measured data from the optical measuring device. Furthermore, the optical measuring device includes a range setting means 251 discriminating the change of the intensity of the received light in the time distribution or the spatial distribution and setting a range to be an object for the calculation of the center of gravity in the time distribution or the spatial distribution on the basis of the result of the discrimination.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical measuring device for measuring a distance from an object by receiving light reflected by the object.

[0002]

2. Description of the Related Art An optical scanning type three-dimensional digitizer for performing distance measurement in many directions to convert a three-dimensional shape of an object into data has been developed.
It is used for data input to G system and CAD system, body measurement, visual recognition of robots, and the like. As the distance measuring method, there are a method using a principle of triangulation represented by a light section method, and a TOF method for measuring a time (Time Of Flight) from transmission to reception of a pulse. In any of the methods, the resolution of measurement can be increased by performing the center-of-gravity calculation on the received light signal.

For example, in the measurement by the light section method, instead of simply detecting which pixel in the light receiving surface is the brightest, the following formula based on the light receiving intensity X of a plurality of pixels and the pixel position m is used. To find the maximum intensity position M '. M ′ = Σm · X _m / ΣX _m This maximum intensity position M ′ is called “spatial center of gravity” because it is the center of the spatial distribution of the received light intensity on the light receiving surface. The spatial center of gravity represents the incident position of the reflected light on the light receiving surface when the slit light is projected at a certain angle, and specifies the light receiving angle of the light from the object. The distance from the reference position of light emission / reception to the object is obtained by triangulation based on the light reception angle, the projection angle, and the distance between the reference points of light emission / reception (base line length). By obtaining the spatial center of gravity, a higher resolution than a value determined by the pixel pitch of the light receiving device can be realized.

In the measurement by the light section method, as disclosed in JP-A-10-206132,
Attention is paid to each pixel, and the maximum intensity point J 'is obtained by the following equation based on the received light intensity X of the pixel of interest and the sampling time i. J ′ = Σi · X _i / ΣX _i This maximum intensity point J ′ is called “time centroid” because it is the centroid of the temporal distribution of the received light intensity on the light receiving surface. The time barycenter represents the elapsed time from the start of the optical scanning, and specifies the projection angle of the slit light (time and angle are proportional to the constant angular velocity scanning). Since the incident angle of each pixel is known in relation to the lens, triangulation can be performed for each pixel. By obtaining the time barycenter, a higher resolution than the value determined by the sampling period can be realized. In the distance measurement by the TOF method, precise distance measurement can be performed by obtaining the time centroid as the time (reception time) corresponding to the peak of the received pulse waveform.

[0005] At both the spatial centroid and the temporal centroid, ambient light noise superimposed on the received light signal causes a calculation error. In order to reduce the influence of noise, conventionally, as shown in FIG. 7, only the data near the maximum value in the received light intensity distribution is subjected to the center of gravity calculation, or the center of gravity is obtained based on the received light data equal to or larger than a set threshold. I was FIG.
In the example of (A), the time 0 to 31
The maximum value is found among the 32 received light data sampled in the above, and the time range obtained by combining the sampling time i _peak corresponding to the maximum value with the two sampling times before and after it is set as the calculation target. The time center of gravity J 'in this case is expressed by the following equation.

[0006]

(Equation 1)

[0007] Example of FIG. 7 (B), the time 0 to 31 time range and a calculation target is for setting the threshold value X _th based on the four light-receiving data of the immediately preceding. The threshold value X _th is the sum of the maximum value Xa of the four light reception data and the fixed offset Xb. The time center of gravity J '' in this case is expressed by the following equation.

[0008]

(Equation 2)

The example shown in FIG. 7 is also applicable to the calculation of the center of gravity of space. In the case of the spatial center of gravity, the sampling time may be read as a pixel position.

[0010]

In the conventional example in which only the data near the maximum value in the received light intensity distribution is subjected to the center-of-gravity calculation as shown in FIG. 7A, the number of target data is relatively small. There was a problem that accuracy was low. In particular, when the distribution shape is a gentle mountain shape with a wide base, the error tends to increase. When the target range is expanded, an error due to noise tends to occur. Further, in the conventional example in which data equal to or larger than the threshold value is effective as shown in FIG. 7B, when a large noise suddenly occurs due to some cause including an electric shock,
There is a problem that the calculation result is far from the true center of gravity. When the threshold value is increased, the effect of sudden noise can be avoided, but the number of target data is reduced, so that the calculation accuracy is reduced as in the example of FIG. 7A.

It is an object of the present invention to perform the center of gravity calculation based on as much effective data as possible, thereby improving the accuracy of the measurement result.

[0012]

An optical measuring device according to the present invention comprises: an optical system for projecting light onto an object and receiving reflected light;
A center of gravity calculating means for calculating the center of gravity of the time distribution of the received light intensity or the center of the spatial distribution of the received light intensity on the light receiving surface, and a range setting means for setting a target range of the center of gravity calculation. The range setting means determines the aspect of the change in the received light intensity in the time distribution or the spatial distribution, and sets the target range of the center of gravity calculation in the time distribution or the spatial distribution based on the result.

In the measurement in the ideal state where the intensity of the ambient light is constant, the distribution shape of the received light intensity is a single-peak shape that rises in a time range or a space range where the reflected light is incident. However, since the ambient light intensity actually fluctuates, the distribution shape becomes a multimodal shape including a plurality of small bumps (mountains). In the present invention, a large swell corresponding to the reflected light is determined as a target range of the center-of-gravity calculation by determining the appearance of the unevenness of the distribution shape. For example, if the distribution is subdivided and the gradient of the contour of the distribution shape is determined, each range of large and small swells can be specified.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] [System Configuration] FIG. 1 is a configuration diagram of a three-dimensional input system according to the present invention.

The three-dimensional input system 100 includes a three-dimensional camera 1 for transmitting and receiving light for shape measurement by a light section method,
And a host 5 for obtaining coordinates of a plurality of points on the object 90 based on the measurement data D1 output from the three-dimensional camera 2. The three-dimensional camera 1 has an optical system 10, a signal processing circuit 20, and a drive control circuit 30,
It has a function corresponding to the optical measurement device of the present invention. Host 5
Is a computer system having a main body 51, a monitor 52, a keyboard 53, and a mouse 54. Between the three-dimensional camera 1 and the host 5, online data transfer by cable or infrared communication and offline data transfer by a portable recording medium are possible.

In the optical system 10, a laser beam emitted from a light source 11 is shaped into a slit beam by a lens group 12. The slit light travels in a direction determined by the angle of the rotating mirror of the scanner 13 and partially illuminates the object 90. Part of the slit light diffusely reflected on the surface of the object returns to the optical system 10 and enters the area sensor (two-dimensional imaging device) 15 via the lens 14. As the scanner 13 rotates, the irradiation position on the object 90 moves, and the incident position of the reflected slit light on the area sensor 15 changes. The area sensor 15 repeats the imaging operation at regular time intervals during the scanning period, and outputs a photoelectric conversion signal indicating the amount of light received by a predetermined number of pixels to the signal processing circuit 20 for each frame.

The three-dimensional input system 100 employs a measurement mode in which the resolution is improved by obtaining the time center of gravity. The reason is that it is less susceptible to the reflectance of the surface of the object as compared with the mode for obtaining the center of gravity of space.
The time barycenter is the time when the slit light irradiates the object surface in the field of view corresponding to each pixel of the area sensor 15, and is calculated based on the time distribution of the received light intensity at each pixel. If the relationship between the elapsed time from the start of scanning and the light projection direction is known, the plane equation indicating the light projection path is determined by calculating the time center of gravity. Area sensor 15 and lens 14
Since the line-of-sight equation corresponding to each pixel is determined from the positional relationship between the lens and the lens characteristics, the coordinates of the intersection of the light-projecting path and the line of sight can be obtained from the plane equation and the line-of-sight equation. The calculation of the time barycenter is performed by the signal processing circuit 20.

FIG. 2 is a functional configuration diagram of a main part of the signal processing circuit. The photoelectric conversion signal from the area sensor 15 is A / D
The data is sampled and held by the converter 21, converted into digital received light data, and temporarily stored in the memory 22 as a buffer. When the received light data for the number of frames required for the calculation of the center of gravity is stored,
By one pixel receiving data X _i is sent to. Here, i represents the frame number of imaging. The center-of-gravity calculation unit 23 performs the center-of-gravity calculation under the conditions determined by the calculation setting block 25, and sends the obtained time center of gravity j to the data output unit 24. The data output unit 24 collectively outputs the time centroid j corresponding to each of the plurality of pixels as the measurement data D1 to the host 5. The calculation setting block 25 is a component specific to the present invention, and includes a range setting unit 251 that outputs a _start end i _start and an end end i _end described later, and a threshold setting unit 252 that outputs a threshold X _TH . Note that the form of realizing the functions of the center-of-gravity calculation unit 23 and the calculation setting block 25 may be mainly hardware or software.

[Setting of Conditions for Calculation of Center of Gravity] FIG. 3 is a conceptual diagram of setting a range related to calculation of the center of gravity. The light receiving intensity at the pixel of interest is small, due to fluctuations in ambient light.
The range setting unit 251 sets the large peak M4 as a calculation target in a case where it changes so as to draw a large peak M4 due to the reception of the reflected slit light. That is, the first frame number (this is referred to as a start end i _start ) and the last frame number (this is referred to as an end end i _end ) in the frame sequence corresponding to the mountain M4 are represented by the centroid calculation unit 23.
Give to. The bottom of each of the peaks M1 to M4 is detected based on the gradient of the change in the received light intensity, and whether or not the peaks M1 to M4 are valid information corresponding to the reflected slit light is determined based on the data value (the received light intensity).

FIG. 4 is a flowchart showing the operation of the range setting unit.
It is. This routine is performed for each pixel. At first
Shows the count value of frame number i and the result of mountain determination.
The flag is reset (# 11, # 12). Frame number
Perform flag check after incrementing signal i
(# 13, # 14). Received light data of predetermined level appears
Until the flag is off. Slope if flag is off
A determination is made (# 15). X_i> X_{i + 1}Then "down"
Otherwise, it is determined to be “up”. The judgment result is
If “down”, the current frame number i is set to the starting end i
_start(# 16), and the process returns to step # 13.
If the determination result is “up”, a data value determination is performed (#
17). The sum of the data value and the fixed offset value is the reference value X
_sOtherwise, the process returns to step # 13. Fixed office
The cut value indicates that the received light intensity depends on the reflectance of the object surface.
This is a set value that is considered. When reflectance is constant, fixed
The offset value can be omitted. Data values and fixed
The sum with the offset value is the reference value X _sIf it exceeds
Is turned on (# 18), and the starting end i_st
artIs output as a formal condition (# 19), and then
Return to Step # 13. Go back to step # 13 and frame
Increment number i and check in step # 14
If the flag is on, the end is determined (# 20).
The gradient of the frame of interest at this time is “down” (X
_i-1≧ X_i) And the gradient of the next frame is “up” (X
_i≤X_{i + 1}), End the current frame number i
Edge i_end(# 21, # 22).

As a modified example of the above routine, there is a judgment of the peaks M1 to M4 based on the average gradient. In this modified example, i = 1 is set in step # 11 in order to use the data of the frames before and after the frame of interest in calculating the average gradient.
In step # 15, if the average gradient is <0, "down"
Otherwise, it is determined to be “up”. When the average gradient is obtained by the least squares method based on data of three frames, the average gradient is expressed by the following linear regression equation.

[0022]

(Equation 3)

The average gradient [(X
_{i + 1} -X _i-1 ) / 2]. Then, in step # 17, the flag is turned on when the average gradient exceeds a predetermined reference value. That is, the peak with a sharp change in the received light intensity is determined to be an effective change corresponding to the reflected slit light. Processing in steps other than steps # 11, # 15, and # 17 may be as described above.

The start end i _start and the end end i _end obtained by the operation of the range setting section are determined by the threshold setting section 252.
To the setting of the threshold value _XTH . Threshold setting unit 25
2 outputs one of the following A~I as the threshold value X _TH. A: Effective range in received light intensity distribution (i _start to
average value of data values in a range other than i _end ) B: Effective range in light reception intensity distribution (i _start to i _start )
maximum value of the data value in the range other than i _end ) C: Effective range (i _start to
i _end ) the minimum value of the data value in the range other than D: the data value in the range between the start end and the front end [X (1) to X
(I _start )] E: Data value [X (1) to X in the range between the start end and the front end thereof
(I _start )] F: Data value [X (1) to X in the range between the start end and the front end thereof
(I _start )] G: Data value in the effective range [X (i _start ) to X
(I _end )] H: Data value at start end X (i _start ) I: Data value at end end X (i _end ) Time barycenter j obtained by barycenter calculation according to the above condition setting is expressed by the following equation. You.

[0025]

(Equation 4)

[Second Embodiment] In the second embodiment, as in the first embodiment, the present invention is applied to the calculation of the center of gravity in the measurement of a three-dimensional shape. The configuration of the three-dimensional input system according to the second embodiment is almost the same as the example shown in FIG. In the second embodiment and the first embodiment,
A part of the signal processing circuit of the three-dimensional camera is different.

FIG. 5 is a functional configuration diagram of a main part of the signal processing circuit according to the second embodiment. The signal processing circuit 20b has an A /
It has a D converter 21b, a memory 22b, a center-of-gravity calculation unit 23b, a data output unit 24b, and a calculation setting block 26. The functions of the components other than the operation setting block 26 among these components are the same as those in the first embodiment.

The calculation setting block 26 includes a range setting section 261
And a threshold setting unit 262. The range setting unit 261 receives the received light data read from the memory 22b and the threshold value X _TH output by the threshold value setting unit 262. The light receiving data from the memory 22b and the start end i _start output from the range setting unit 261 are input to the threshold value setting unit 262.

The outline of the operation of the range setting unit 261 is the same as the operation of the range setting unit 251 described above, and is represented by a flowchart in FIG. However, not only when the gradient satisfies the above-described condition but also when the data value of the frame of interest is smaller than the threshold value _{XTH in} the end determination of step # 20 in FIG. _Is determined as the end i _end . That is, the starting end i
_{After the start} is determined, the gradient changes from “up” to “down”, and when the data value falls below the threshold X _TH , the end i _end is determined. As a result, the end end i _end can be determined earlier as compared with the case where the determination is made based only on the gradient, and the time required for calculating the center of gravity can be reduced.

The threshold setting unit 262 outputs one of the following A to D as the threshold X _TH when the start end i _start is input. A: Data value in the range between the start end and the front end [X (1) to X (1) to X
(I _start )] B: Data value [X (1) to X in the range between the start end and the front end
(I _start )] C: Data value [X (1) to X in the range between the start end and the front end thereof
(I _start )] D: Data value at the start end X (i _start ) [Other Embodiments] In the first and second embodiments, the case where the time barycenter is obtained has been exemplified. The present invention can be applied to such cases. In the case of the spatial center of gravity, the frame number i may be read as a pixel position in FIGS.

In the distance measurement by the TOF method for measuring the propagation time Ta of the light pulse between the object 91 and the device 2 as shown in FIG. 6, the present invention is applied to the calculation of the center of gravity for specifying the reception time t2 of the light pulse. The influence of noise can be reduced by setting the calculation target range in accordance with the following equation. When a part of the transmission light is monitored inside the device 2, the present invention can be applied to the center of gravity calculation for specifying the transmission time t1.

[0032]

According to the first to fifth aspects of the present invention,
The center of gravity calculation can be performed based on more effective data to improve the accuracy of the measurement result.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a three-dimensional input system according to the present invention.

FIG. 2 is a functional configuration diagram of a main part of a signal processing circuit.

FIG. 3 is a conceptual diagram of a range setting related to a center of gravity calculation.

FIG. 4 is a flowchart illustrating an operation of a range setting unit.

FIG. 5 is a functional configuration diagram of a main part of a signal processing circuit according to a second embodiment.

FIG. 6 is a conceptual diagram of distance measurement by the TOF method.

FIG. 7 is a diagram illustrating setting of a center of gravity calculation condition in the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Three-dimensional camera (optical measuring device) 90 Object 20 Optical system 23, 23b Center-of-gravity calculating part (centroid calculating means) j Time centroid (centroid) 251, 261 Range setting part (range setting means) X _TH threshold 252, 262 Threshold setting Unit (threshold setting means) 13 Scanner (optical scanning mechanism) D1 Measurement data (three-dimensional shape data)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA53 BB05 FF04 FF09 GG04 HH05 JJ03 LL04 LL13 LL62 QQ28 QQ31 UU05 5L096 BA08 CA02 CA08 FA14 FA35 FA60 FA66

Claims (5)

[Claims] 1. An optical system for projecting light onto an object to receive reflected light, and a center of gravity calculating means for calculating a center of gravity of a time distribution of received light intensity or a center of space of a spatial distribution of received light intensity on a light receiving surface. Or an optical measurement device that outputs a result of a predetermined calculation based on the measurement result as measurement data, and determines an aspect of a change in received light intensity in the time distribution or the spatial distribution, and based on the result, the time distribution or the spatial distribution. An optical measuring device comprising a range setting means for setting a target range of the center of gravity calculation in the above. 2. The optical measuring apparatus according to claim 1, wherein said range setting means determines said aspect based on a gradient of a temporal or spatial change in received light intensity. 3. The optical measuring apparatus according to claim 1, wherein the range setting means sets the target range based on the determination result of the aspect and a threshold value of the received light intensity. 4. An optical measuring apparatus according to claim 3, further comprising a threshold setting means for setting said threshold in accordance with a received light intensity. 5. The optical measuring apparatus according to claim 1, further comprising an optical scanning mechanism for projecting light in a plurality of directions, and outputting three-dimensional shape data as measurement data on a plurality of points on the object.