JP2002040352A - Scanner and three-dimensional measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of triangulation by reducing the influence of non-linear errors of a galvano scanner. SOLUTION: Set target angle is made coincident with a real mirror angle by previously measuring the non-linear error of the galvano scanner 14, and correcting the angle setting signal S2 while anticipating the error. Or calculation of triangulation is performed by applying a corrected projection angle according to the error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvano scanner and an optical scanning type three-dimensional measuring device for deflecting a reference beam by the galvano scanner.

[0002]

2. Description of the Related Art A non-contact three-dimensional measuring device for obtaining shape information by optically scanning an object is used for data input to a CG system or a CAD system, body measurement, visual recognition of a robot, and the like. .

[0003] For example, a light cutting method (also called a slit light projection method), which is a kind of active measurement method of irradiating a reference light, is used.
In the three-dimensional measurement, optical scanning is performed to project slit light as reference light onto an object, deflect the slit light with a mirror, and move the irradiation position on the object in one direction. And
An object is imaged at a position distant from the projection start point (generally, the rotation center of the mirror). At some point during the scan, the slit light illuminates only a portion of the object. Although the beam cross section of the slit light is linear, there is a parallax between the projection and the imaging, so that the illuminated portion on the object is reflected on the imaging surface as a bright line curved according to the undulation of the surface of the object. If the object is planar, the bright line becomes a straight line. If the positional relationship between the imaging surface and the light receiving lens is known, the incident angle of light incident on each pixel on the imaging surface can be known. Therefore, by detecting the pixel position of the portion where the bright line is reflected in the imaging plane, the direction of the irradiated portion on the object viewed from the imaging plane (hereinafter, this is referred to as a light receiving angle) can be determined. On the other hand, from the relationship between the elapsed time from the start of scanning and the scanning speed, the projection direction of the slit light at the time when the above-mentioned bright line is imaged, that is, the direction of the irradiated portion on the object viewed from the starting point of projection (hereinafter referred to as the projection Angle).
In the light sectioning method, a distance from a base line to an object is calculated by triangulation based on a light receiving angle, a projection angle, and a length of a base line connecting a projection start point and a light receiving reference point (generally, a principal point of a lens). Method. The light sectioning method is more efficient than the spot light projection method because the undulation of a linear irradiation portion on an object can be measured by one imaging. By performing periodic imaging in synchronization with scanning, a group of data (three-dimensional data) indicating the distance to each of a number of positions on the object surface can be obtained.

A galvano scanner used as a scanning means for deflecting the reference light has an optical or capacitance type angle sensor. Servo control is performed on the galvano scanner to make the output of the angle sensor follow an angle setting signal (target value), and the galvanomirror is rotated by changing the target value every moment.

[0005]

Heretofore, there has been a problem that the accuracy of triangulation for calculating the distance to an object depends on the error of the angle sensor. In the mirror rotation range, there is an error of about 0.1 to several percent even in a region of high linearity, and the relationship between the output of the angle sensor and the actual mirror angle is slightly different for each individual. Galvano scanners with smaller errors are desirable, but the higher the accuracy, the more expensive.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the influence of a non-linearity error, which is an error between the output of an angle sensor of a galvano scanner and an actual mirror angle, and to improve the accuracy of triangulation.

[0007]

According to the present invention, a non-linearity error of a galvano scanner is measured in advance, and an angle setting signal is corrected in consideration of the error, so that a set target angle and an actual mirror angle are corrected. To match. Alternatively, the accuracy of the triangulation is improved by applying the projection angle corrected according to the error and performing the calculation.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is a configuration diagram of a three-dimensional measuring apparatus according to a first embodiment.

The three-dimensional measuring device 1 projects slit light as reference light for triangulation. The light source is a semiconductor laser 12, which receives a power supply from the light emitting driver 41 and emits laser light of a predetermined wavelength. Laser light is in lens group 1
The beam is shaped into slit light by 3 and travels to the target object Q via the galvano scanner 14. The laser light reflected back from the target object Q enters the area sensor 22 via the light receiving lens 21. The area sensor 22 outputs a photoelectric conversion signal according to the amount of light received by each pixel in synchronization with a clock from the light receiving driver 45. The photoelectric conversion signal is converted into light reception data by the A / D converter 46 and stored by the memory circuit 47. Such light emission and light reception control is performed by a CPU.
31 performs. The CPU 31 has a data processing function element 33 including a center-of-gravity calculation unit 331 and a distance calculation unit 332, in addition to a control function element (controller) 32.

The center-of-gravity calculating section 331 calculates a “time center of gravity” indicating the time at which the received light intensity at each pixel of the area sensor 22 is maximum, or a “spatial center of gravity” indicating the pixel position at which the received light intensity is maximum at each sampling time. Ask. By obtaining the time barycenter, the time can be specified in smaller steps than the imaging cycle (sampling interval). If the relationship between the elapsed time from the start of scanning (sampling time) and the projection angle is known, the time barycenter indicates the projection angle when the slit light passes through the position on the object that each pixel looks at. Since the light receiving angle of each pixel is known in relation to the optical characteristics of the light receiving lens such as the principal point of the lens, the distance to the position on the object can be calculated by applying the time centroid to triangulation. Also, by finding the center of gravity of space,
Pixel positions can be specified in smaller steps than the pixel pitch. The spatial center of gravity indicates the light receiving angle of the light reflected back from the object at a certain sampling time. If the relationship between the sampling time and the projection angle is known, the distance can be calculated based on the center of gravity of space. In any case,
Performing the center of gravity calculation increases the resolution of the measurement. The calculated distance is sent to an external device (for example, a computer) 5 in response to the data output instruction. The calculation for obtaining three-dimensional coordinates from the angle information of the projection (or light reception) and the measured distance is performed by the external device 5. However, the system may be configured such that the coordinate calculation is performed by the three-dimensional measuring device 1 or the distance calculation is performed by the external device 5.

When performing active triangulation for projecting light as in the three-dimensional measuring apparatus 1, it is necessary to grasp the relationship between the sampling time at which an object is imaged and the projection angle. In particular, in a configuration in which the resolution is increased by calculating the center of gravity, it is necessary to precisely control the projection angle. In order to realize this precise control, the three-dimensional measuring apparatus 1 includes an error data table T1.
Is provided. Hereinafter, the control of the galvano scanner 14 will be described in detail.

FIG. 2 is a graph showing an example of a measured value of a mirror angle error, FIG. 3 is a diagram showing the contents of an error data table,
FIG. 4 is a diagram showing a relationship between a mirror and a projection angle. In the scanning, the galvano scanner 14 is controlled to rotate at a constant angular velocity. The scanner driver 43 receives an angle setting signal S1 from the angle setting unit 322 of the controller 32 via the D / A converter 42, and receives a detection signal S3 from an angle sensor built in the galvano scanner 14. You. The scanner driver 43 uses PI
D control means, and a drive signal S2 corresponding to the input so that the detection signal S3 and the angle setting signal S1 have a fixed relationship.
To the galvano scanner 14. The angle setting unit 322 updates the set angle data D1 (the resolution is about 16 bits) at regular intervals. The galvano scanner 1 is controlled so that the detection signal S3 follows a change in the angle setting signal S1 accompanying the change.
4 rotates.

If the relationship between the detection signal S3 and the mirror angle is completely linear, the constant angular speed rotation is realized by increasing or decreasing the set angle data D1 by a constant angle. However, there is actually a subtle mirror angle error as shown in FIG. In the error data table T1, an error actually measured using a rotary encoder in advance is associated with the set angle. For example, if a high-resolution encoder that outputs 1.8 million pulses in one rotation (360 degrees) is used, a true angle can be substantially detected. The shaft of the rotary encoder and the shaft of the galvano scanner 14 are directly connected, and the shaft is forcibly rotated.
An error data table T1 is created by examining the relationship between No. 3 (strictly, a signal after predetermined signal processing) and the number of encode pulses.

In the error data table T1, as the number of association sets increases, more precise control becomes possible. However, the actual measurement is troublesome and the required capacity of the memory 51 is increased. In the example of FIG. 3, a table is created at intervals of 0.1 degrees. Projection angle correction unit 321 in controller 32
Refers to the error data table T1 and corrects the angle control command value according to the mirror angle error. For the set projection angle for which there is no corresponding value in the error data table T1, an error is obtained by interpolation to correct the command value. The set angle data D1 output by the angle setting unit | 22 is data indicating a command value that has been corrected by the projection angle correction unit 321.

In this embodiment, the projection angle θ is defined as
Is an inclination angle with respect to the horizontal line H as shown in FIG. It is assumed that slit light is incident on the galvanometer mirror 141 from a light source immediately below the same, and the inclination angle of the mirror surface with respect to the horizontal line H when the set angle data D1 = 0 is β. The projection angle θ when the set angle data D1 = 0 is 90−2β,
The projection angle θ when the set angle data D1 = Δ is 90-2.
(Β−Δ).

[Second Embodiment] FIG. 5 is a block diagram of a three-dimensional measuring apparatus according to a second embodiment, FIG. 6 is a schematic diagram showing a relationship between a projection angle and received light data, and FIG. 7 shows the contents of an error data table. FIG.

The structures of the light projecting system and the light receiving system of the three-dimensional measuring device 2 are the same as those of the three-dimensional measuring device 1 described above. The light emission and light reception are controlled by the CPU 61. Angle setting unit 6 constituting control function element (controller) 62 of CPU 61
Reference numeral 22 outputs set angle data D1 'representing the control target of the projection angle when the relationship between the mirror angle and its detection signal S3 is regarded as linear. The scanner driver 43 provides the galvano scanner 14 with a drive signal S2 'corresponding to the angle setting signal S1' obtained by D / A conversion of the set angle data D1 'and the detection signal S3.

The three-dimensional measuring device 2 corrects an error between the mirror angle and the detection signal S3 in the process of processing the received light data. The data processing function element 63 of the CPU 61 includes a center-of-gravity calculation unit 631, a distance calculation unit 632, and a data correction unit 633. In the memory 51, an error data table T2 that associates the set projection angle indicated by the set angle data D1 'with the true projection angle is written. The error data table T2 is created based on the actual measurement by the rotary encoder, similarly to the above-described error data table T1. Hereinafter, the operation of the three-dimensional measuring device 2 will be described in more detail.

The three-dimensional measuring device 2 deflects the slit light at a constant angular velocity α [rad / sec] to measure the three-dimensional coordinates of a point on the object Q by using the triangulation method. Scan.

Upon receiving the measurement start signal from the external device 5 or the operation panel, the CPU 61 calculates the scanning angle range (start angle, end angle) and rotation speed α ′ (= α / 2), or from the external device 5. The information is fetched and scanning is started.

A fixed time t ₀ synchronized with the projection of the slit light
The object Q is imaged N times in total by the area sensor 22 every time. If the projection angle of the first image pickup time of the theta _1, the projection angle theta _k imaging time of the k-th (1 ≦ k ≦ N) is alpha (k-
1) It is t ₀ + θ ₁ .

The output of all pixels in the i-th row and the j-th column of the area sensor 22 is stored for each image pickup. For example, when a VGA CCD sensor is used, 640 × 4
Light reception data of 80 pixels is obtained. The received light data is stored in the memory circuit 47. After the N times of imaging, the galvanomirror is returned to the initial position.

After the N times of imaging, a projection angle (time center of gravity θ _G ) at which the received light intensity is considered to be the maximum is calculated based on the received light data of N times for each pixel. that time,
The data correction unit 633 calculates the set projection angle θ ′ corresponding to each image pickup from the order of imaging (1 to N) and the cycle t _0, and refers to the error data table T2 to correspond to the set projection angle θ ′. Is transmitted to the center-of-gravity calculation unit 631. If there is no corresponding projection angle θ ′ in the error data table T2, the true projection angle θ is obtained by interpolation. The time center of gravity θ _G is represented by the following equation. θ _G = (θ ₁ p ₁ + θ ₂ p ₂ +... + θ _{N PN} ) / (p
₁ + p ₂ + ... + p _N ) θ ₁ , θ ₂ … θ _N : true projection angles at each imaging p ₁ , p ₂ … p _N : light receiving data values at each imaging The calculated time centroids θ _G are all Are temporarily stored in the memory circuit 47 until the calculation for the pixel is completed, and then sent to the distance calculation unit 632.

In the above operation, the true projection angle θ is obtained for all of the N times of imaging, and the center of gravity is calculated, but the operation is not limited to this. The slit width of the slit light on the light receiving surface is about several times the pixel pitch, and the range where the reflected light is incident in each imaging is only a part of the light receiving surface.
Therefore, when focusing on one image, of the N times of imaging, effective light receiving data relating to the center of gravity can be obtained only in several times of imaging with similar projection angles. It can be considered that the detection error of the angle sensor is almost the same in a narrow angle range. As a result, the center of gravity is calculated first based on the set projection angle θ ′, and the error data table T
2, a simple process of performing correction with reference to FIG.

In order to reduce the required capacity of the memory circuit 47, a form in which the true projection angle θ is obtained in parallel with scanning without waiting for the end of the N times of imaging may be adopted. The received light data obtained in each imaging is sequentially sent to the center-of-gravity calculating unit 631,
The true projection angle θ obtained with reference to the error data table T2 is substituted into the center of gravity calculation formula. This gives N
It is not necessary to store the data of the batch, and the memory capacity can be reduced. Further, the time from when the measurement is started to when the result of the center of gravity calculation is obtained can be shortened.

As described above, the embodiment in which the non-linearity of the galvano scanner is compensated at the data processing stage is applicable not only to calculating the time center of gravity but also calculating the space center of gravity.

[0027]

According to the first to fifth aspects of the present invention,
The accuracy of triangulation can be improved by reducing the effect of the non-linearity error, which is the error between the output of the angle sensor of the galvano scanner and the actual mirror angle. Three-dimensional input can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a three-dimensional measurement device according to a first embodiment.

FIG. 2 is a graph showing an example of an actual measurement value of a mirror angle error.

FIG. 3 is a diagram showing the contents of an error data table.

FIG. 4 is a diagram showing a relationship between a mirror and a projection angle.

FIG. 5 is a configuration diagram of a three-dimensional measurement device according to a second embodiment.

FIG. 6 is a schematic diagram illustrating a relationship between a projection angle and received light data.

FIG. 7 is a diagram showing the contents of an error data table.

[Explanation of symbols]

 14 Galvano scanner 43 Scanner driver (drive circuit) S2, S2 'Angle setting signal S3 Detection signal (output of angle sensor) 1 3D measuring device (scanner device) 2 3D measuring device T1, T2 Error data table 51 Memory D1 setting Angle data (correction signal value) 2 3D measuring device θ Projection angle θ 'Set projection angle (set angle) 322,622 Angle setting unit (optical scanning control means) 12 Semiconductor laser Q object 22 Area sensor (imaging device) 332 632 Distance calculation unit (distance calculation means)

Continued on the front page F term (reference) 2F065 AA04 AA06 AA53 DD03 EE05 FF09 FF25 FF65 GG06 GG16 HH05 JJ03 JJ26 LL62 MM16 QQ03 QQ17 QQ21 QQ24 QQ28 QQ32 2F112 AA01 BA06 CA08 CA12 DA09 FA25 FA03 FA21

Claims (5)

[Claims] 1. A scanner device comprising: a galvano scanner having a sensor for detecting a mirror angle; and a drive circuit for driving the galvano scanner so that an output of the sensor follows an angle setting signal. A memory storing an error data table indicating a correspondence relationship between the set angle indicated by the angle setting signal and the actual mirror angle, and referring to the error data table so that the actual mirror angle matches the set target angle. A scanner device for correcting the angle setting signal and supplying the corrected angle setting signal to the drive circuit. 2. The error data table is a data set indicating a correction signal value corresponding to a representative signal value which is a part of a plurality of signal values that the angle setting signal can take. 2. The scanner device according to claim 1, wherein the correction signal value is supplied to the drive circuit, and a signal value other than the representative signal value is calculated by interpolation to be supplied to the drive circuit. 3. An angle setting signal is output as a reference light projection angle control signal for performing three-dimensional measurement by projecting reference light so as to scan an object and receiving reflected light from the object. 3. The scanner device according to claim 1, further comprising an optical scanning control unit. 4. A light source for projecting reference light onto an object to be measured, a galvano scanner for deflecting the reference light to change a projection angle, a drive circuit for driving the galvano scanner, and a reference light. Optical scanning control means for outputting an angle setting signal that is a projection angle control signal, an imaging device for receiving reflected reference light reflected by the object, and a distance to the object based on light reception data obtained by the imaging device. The galvano scanner has a sensor that detects a mirror angle, and the drive circuit drives the galvano scanner so that the output of the sensor follows the angle setting signal. The three-dimensional measuring device according to claim 1, wherein an error data table indicating a correspondence relationship between a set angle indicated by the angle setting signal and an actual projection angle is stored. The distance calculation means has a distance to the object by triangulation based on the projection angle of the reference light, the light receiving angle of the reflected reference light, and the distance from the reference position of the projection to the reference position of the light reception. A three-dimensional measuring apparatus, wherein a result obtained by calculating and correcting a set angle indicated by the angle setting signal based on the error data table is used as the projection angle. 5. The three-dimensional measuring apparatus according to claim 4, wherein the projection angle is calculated by a center-of-gravity calculation based on the respective light reception data at a plurality of time points having different set angle values.