WO2010069160A1

WO2010069160A1 - Apparatus for measuring six-dimension attitude of an object

Info

Publication number: WO2010069160A1
Application number: PCT/CN2009/070298
Authority: WO
Inventors: 罗振军; 田永利
Original assignee: 中国科学院沈阳自动化研究所
Priority date: 2008-12-19
Filing date: 2009-01-23
Publication date: 2010-06-24
Also published as: CN101750012A

Abstract

An apparatus for measuring six-dimension attitude of an object, composes of a processor (1), a receiver(2), a laser tracker(3) and at least one laser emitter (31, 32), the processor (1) and the laser tracker (3) are mounted on the stationary ground, and the receiver (2) are mounted on the object being measured (4), both of the laser tracker (3) and the receiver (2) communicate with the processor (1), the laser tracker (3) connects with the receiver (2) via a laser light path, and the laser emitter (31, 32) connects with the receiver (2) via a laser light path.

Description

Device for measuring six-dimensional pose of an object

The invention relates to a technique for measuring a six-dimensional pose of an object in a large space, in particular to a three-dimensional coordinate measurement using a laser tracker, generating a spot on a receiver by using a laser beam and measuring by parallel image processing and parallel measurement The principle realizes a device for measuring the three-dimensional posture of an object. This can be used in a wide range of applications where it is necessary to measure the six-dimensional pose of an object. It can measure both stationary and moving objects and can replace expensive six-dimensional pose measurement laser trackers. Background technique

High-precision measurement of the three-dimensional position (x, y, z) and three-dimensional pose (α, β, γ) of moving objects has a wide range of needs in the industry.

In order to measure the six-dimensional pose of an object moving over a wide range, a global positioning system is usually employed. According to the accuracy of the measurement, the global positioning system can be divided into a laser tracker, an indoor GPS, a laser navigation method based device, a laser beacon method based device, and a visual processing based device. Among them, the device based on the laser tracker has the advantages of high precision, fast measuring speed, and ability to measure moving objects, so it is the most widely used.

Both the laser tracker and the laser total station use the theodolite to measure the azimuth of the receiver (also commonly referred to as the target) (usually the horizontal and pitch angles), while the rangefinder measures the distance between the receiver and the theodolite reference point. , and convert the ball coordinates of the receiver to the three-dimensional coordinates in the Cartesian coordinate system. The static angle measurement accuracy of the theodolite can generally reach the order of 1〃 (about equivalent to the spatial comprehensive precision of 4.85ppm, of which lppm=l μ m/m), and the ranging accuracy of the range finder is different according to the ranging technology. Large difference. The laser tracker usually uses the built-in laser displacement interferometer (IFM for distance measurement). The measurement method is incremental measurement. The distance measurement accuracy can reach ±0.5ppm within 50m. It has high sampling frequency and very high measurement accuracy. Highly significant advantages, but the device is very expensive. The American Optodyne company uses the laser Doppler range finder (LDDM) for distance measurement. The measurement method is also incremental measurement, and the ranging accuracy can reach the order of ± lppm within 50m. The laser total station is equivalent to the low-end laser tracker, and most of them use the laser absolute distance measurement (ADM) instrument to measure the distance. The measurement method is usually the indirect scale frequency method (such as differential frequency phase measurement method), modulation method. Laser amplitude modulation is usually used. The accuracy of the high-end laser total station can reach ±0.2mm within 100m, the measurement range can reach lkm, and the ranging accuracy can reach ± lmm+2ppm in the full scale range; The new technology adopts the polarization angle modulation method, and the ranging accuracy is close to that of the laser Doppler range finder. The range finder can also use the time-of-flight principle ranging. For example, Leica's Disto range finder can achieve a range accuracy of less than 50mm within 50m. Epetitive-Time- proposed by Automated Precision Inc. (hereinafter referred to as API). The ranging accuracy of the of-Flight technology can even reach 2.5ppm ± 25 μm. The range finder can also be a laser structured light position sensor with triangulation ranging, which is usually used for high-precision measurement with a range of less than 1000mm. For example, Keyence's LK-G series laser displacement sensor can achieve a repeatability of 2 μ m. Take This type of range finder is usually mounted on one or more rotating shafts to form a laser scanner. In order to simplify the discussion, the theodolite, the two-degree-of-freedom turntable and other similar pointing devices are collectively referred to as the theodolite. The laser tracker, laser total station, laser scanner and other similar two-dimensional or three-dimensional coordinate measuring devices are collectively referred to as laser tracking. instrument.

The laser tracker is usually only used to measure the three-dimensional coordinates of the receiver. The receiver is usually in the form of a reflecting sphere. The reflecting sphere includes a corner cube that causes the laser to reflect back, and the fixed point of the corner cube coincides with the center of the sphere. A dedicated six-dimensional pose measurement laser tracker is required for six-dimensional pose measurements.

The United States API company's special ij "Three and five axis laser tracking systems" (US Pat. No. 4,714,339) first proposed the use of a laser tracker for five-dimensional pose measurement, using a flat type that simultaneously reflects and partially transmits the laser. The target, the target is mounted on a two-degree-of-freedom turntable, and the two-degree-of-freedom turntable is controlled according to the falling point information of the transmitted light to keep the target plane perpendicular to the incident laser, and the pitch and deflection of the target are obtained according to the rotation angle of the two-degree-of-freedom turntable. (Yaw) Two-dimensional pose, but the rolling angle of the target relative to the laser beam cannot be obtained. Although there are a variety of six-dimensional pose measurement techniques in the precision calibration of CNC machine tools and measuring machines, such as U.S. Patent Nos. 5,506,921, US 5,064,289 and 5,536,196, etc., these technologies require auxiliary devices and therefore cannot be applied to laser trackers. The API company's patent "Five-axis, six-axis laser measuring system" (US Patent No. US6049377) proposes a new target, which splits the incident laser into two beams through a beam splitter, and the beam is measured by a scheme similar to US4714339. Distance, and control the two-degree-of-freedom turntable so that the target plane is perpendicular to the incident laser, and the other beam passes through the polarization beam splitter to obtain two polarized lights, and the rolling angle is calculated according to the ratio of the intensity of the two polarized lights. The actual product of the API company SmartTRACK adopts the above scheme, and its advantage is that the attitude measurement accuracy is high, and the disadvantage is that the receiver needs to configure a two-degree-of-freedom turntable with a large volume, and the weight is large. A handheld three-dimensional measuring device proposed by the API company's patent "Multi-dimensional measuring system" (U.S. Patent No. 7,230,689) omits a two-degree-of-freedom turntable, and manually adjusts the attitude of the measuring rod to make the receiver substantially perpendicular to the laser when measuring hidden points. At this time, the accurate six-dimensional pose of the receiver can also be obtained, and the disadvantage is that the adjustment time is increased.

U.S. Patent and device for determining spatial positions and orientations (U.S. Patent No. 6,667,798) by means of opening a small hole in the tip of a pyramidal prism and placing an imaging device behind the aperture, by means of a laser in the imaging device The upper spot measures the posture, but it cannot measure the rolling angle. Leica company U "Measurement system for determining six degrees of freedom of an object" (US Patent No. US7312862) Based on the above patents, three solutions for measuring the rolling angle are proposed. The first solution is to install a camera on the laser tracker. , shooting the illuminating marker installed on the receiver; the second scheme is to install a point light source on the laser tracker and emit scattered light toward the corner cube prism, and the light passes through the small hole to obtain additional spots; the third scheme is a laser tracker A laser structured light source is mounted thereon, and a fan plane light is emitted toward the corner cube prism, and a line array vision sensor is mounted on the receiver, but these solutions have not been practically applied. The disadvantage of using a pyramidal tip to open a small hole is that it is difficult to obtain a clear spot image.

US Patent No. 5,229,828 to Geotronics, Sweden, proposes to use the dual pendulum device built into the receiver to measure the two tilt angles of the receiver and the direction of gravity. An additional laser-tracker is mounted parallel to the axis of the rangefinder. The light emitter, which emits a light beam, obtains an incident angle of the incident laser light and the receiver through an optical imaging unit on the receiver, and further calculates the attitude of the receiver according to the two inclination angles and the incident angle. This scheme is easier to obtain a clear spot image than the above-mentioned corner cube prism opening method, but since the optical imaging unit has a limited size, the attitude measurement range is small, and since the dynamic measurement accuracy of the double pendulum device angle is low, The overall pose measurement accuracy cannot be improved.

Leica's actual product, T-Probe, mainly uses photogrammetry to achieve three-dimensional attitude measurement, that is, adding a high-resolution camera above the ordinary laser tracker, and installing a corner cube and a plurality of luminescent markers on the receiver ( For example, a light-emitting diode), the three-dimensional coordinates of the receiver are obtained by a laser tracker, and the three-dimensional posture of the receiver is calculated by digital photogrammetry technology. Although photogrammetry can measure position and attitude at the same time, its position measurement accuracy is much lower than that of a laser tracker, so usually only the attitude measurement value obtained by it is taken. Norwegian Metronor has a patent for binocular photogrammetry (Patent No.: EP0880674, WO97/14015), while Swedish MEEQ has a patent for monocular photogrammetry (Swedish patent number: SE444530) and a patent for binocular photogrammetry ( US Patent No.: US6131296). In photogrammetry, the distance between the subject and the imaging device is generally very long, so the resolution of the imaging device and the accuracy of the optical system are very high, resulting in high cost of the entire system, and measurement accuracy is difficult to improve.

The solution of Oreo Products Inc.'s U "Optical coordinate measuring system for large objects" (US Patent No.: US5305091) is based on the principle of parallel platform pose measurement, that is, six built-in walls are fixed on the measurement workroom wall. The theodolite of the precision range finder, and at least two retroreflectors are mounted on the receiver. Each theodolite has a tracking function and can always point to the corresponding retroreflector, according to the ranging values of the six rangefinders. The 6-dimensional pose of the receiver is available, eliminating the need to accurately measure the angle of the theodolite. The advantage of this scheme is that it can theoretically improve the spatial accuracy of the six-dimensional pose measurement data, and the disadvantage is that the cost is too high.

High-precision six-dimensional pose measuring devices based on a single laser tracker that do not require a high-resolution camera system have not been reported yet. Summary of the invention

In order to overcome the disadvantages of high cost in the prior art, or the need for a two-degree-of-freedom turntable, or a high-resolution camera system, the present invention extends the prior art laser tracker by the close-range visual processing method proposed in the prior art. The three-dimensional pose can be obtained accurately and conveniently. The invention can replace the expensive six-dimensional pose measurement laser tracker.

The technical scheme of the present invention is as follows:

A device for measuring a six-dimensional pose of an object, comprising: a calculation processing unit (1), a receiver (2), a laser tracker (3) and at least one laser emitter; calculating the processing unit and the laser The tracker is mounted on a fixed ground; the receiver is mounted on the moving object to be tested (4); the laser tracker and receiver are in communication with the computing processing unit (1), and the laser tracker and receiver are connected by a laser beam path, the laser emitter Connected to the receiver through a laser beam path. The laser tracker has a horizontal rotation degree of freedom and a pitch rotation degree of freedom; the laser tracker includes a driving device for controlling the horizontal rotation angle and the pitch rotation angle, and further includes a rotation angle measuring device for measuring the horizontal rotation angle and the pitch rotation angle; the laser tracker At least one laser range finder is mounted thereon.

The laser range finder emits a laser beam, and the laser range finder is a laser interferometer, or a laser Doppler range finder, or a laser absolute distance measuring instrument, or a laser structured light position sensor.

The laser emitters are typically mounted on a laser tracker; each of the laser emitters emits at least one laser beam that is parallel to the laser beam emitted by the laser rangefinder.

The laser emitter may also be mounted on a two-degree-of-freedom turntable; each of the laser emitters emits at least one laser beam; the two-degree-of-freedom turntable is mounted on the laser tracker or fixedly mounted on the ground; The two-degree-of-freedom turntable has a horizontal rotation degree of freedom and a pitch rotation degree of freedom; the two-degree-of-freedom turntable includes a driving device for controlling the horizontal angle and the pitch angle thereof, and a rotation angle measuring device for measuring the horizontal angle and the pitch angle.

When the number of the laser emitters is 1, the laser emitter emits light to structure light, or emits cross-hair structured light, or emits lattice structure light.

The receiver includes a reflective target, at least one projection panel, and at least one imaging unit, and each projection panel corresponds to at least one imaging unit; wherein the reflective target is a retroreflector or a translucent reflective patch; The shape is selected from a plane, or a curved surface, or a combination of a plurality of planes, or a combination of a plurality of curved surfaces; the material of the projection panel is a diffusing light-transmitting plate, or a rough reflective reflector; the field of view of the imaging unit It is basically the same size as the projection panel.

When the material of the projection panel is a diffusing transparent plate, the imaging unit is on the back side or the inside of the projection panel, and when the material of the projection panel is a scattering reflector, the imaging unit is on the front side of the projection panel.

The imaging unit includes an imaging electronic device and an imaging lens positioned between the imaging electronic device and the projection panel; wherein the imaging electronic device is selected from the group consisting of a position sensitive detector, a charge coupled device, a charge injection device, or a complementary metal oxide semiconductor based optical Imaging device.

The imaging unit includes at least one photographic measuring device mounted directly on the surface of the projection panel, the photographic measuring device being selected from the group consisting of a position sensitive detector, a charge coupled device, a charge injection device, or a complementary metal oxide semiconductor based optical imaging device.

The method for measuring the six-dimensional pose of an object by using the device: obtaining a three-dimensional position of an object by using an existing laser tracker measurement method, and emitting a laser beam or a laser plane onto a projection panel of the receiver through a laser emitter to generate a laser spot Or laser stripe; then establish the constraint equation by close-range image capture and visual processing technology and parallel measurement principle, solve the three-dimensional pose of the object by solving the constraint equation, and obtain the six-dimensional pose of the object.

The invention has the following characteristics:

1. The three-dimensional position measurement of the device of the present invention is obtained by a laser tracker, and thus the position measurement accuracy is high.

2. The three-dimensional attitude measurement of the device of the invention has high precision and low cost. The invention is based on the principle of parallel measurement, realizes three-dimensional attitude measurement by two or more laser structured lights, and laser tracking by serial measurement using a single laser Compared with the instrument, the receiver does not need two-degree-of-freedom turntable, so the weight of the receiver is greatly reduced, and the cost is greatly reduced; the invention adopts close-range image capturing and visual processing, and the distance between the projection panel and the imaging unit has only the largest measurement range. One-hundredth or one-thousandth of a thousand, compared to photogrammetry techniques that use long-range image capture and visual processing, do not require high-resolution vision sensors, and the positioning accuracy is higher.

3. The present invention can be easily simplified to measure the three-dimensional pose of an object in a plane, that is, a two-dimensional position (x, y) and a one-dimensional rotation θ.

4. The present invention can mount a measuring rod or a three-dimensional laser scanner on the receiver, thereby measuring where the laser beam emitted by the theodolite is difficult to reach. DRAWINGS

Figure 1 is a schematic diagram of a first example of a six-dimensional pose $ device;

Figure 2 is a schematic diagram of the workflow when the device performs three-dimensional attitude measurement;

Figure 3 is a schematic diagram of a second example of a device with a dimensional pose;

Figure 4 is a schematic diagram of a third example of a dimensional pose $ device;

Figure 5 is a schematic diagram of a fourth example of a dimensional pose $ device. detailed description

The invention will be further described in detail below with reference to the accompanying drawings.

Example 1

A first example of a six-dimensional pose measurement apparatus proposed by the present invention is shown in FIG. 1, which is composed of a calculation processing unit 1, a receiver 2, and a laser tracker 3. The laser tracker 3 is usually fixedly mounted on the ground. The receiver 2 is mounted on the moving object 4 to be tested in a six-dimensional pose through a connector or directly. In the figure, the receiver coordinate system 20 is 0'-ΧΎ'Ζ', fixed on the receiver, and the global coordinate system 10 is 0-XYZ, usually fixed on the laser tracker, and the moving object coordinate system is O _m -X _m Y _m Z _m (not shown) is fixed to the moving object 4. Since the pose of the receiver coordinate system 20 with respect to the coordinate system of the moving object is always fixed and can be obtained by the calibration method, measuring the six-dimensional pose of the moving object 4 is equivalent to measuring the coordinate system of the receiver 20 with respect to the global coordinates. The six-dimensional pose of the system 10. To simplify the discussion, the six-dimensional pose measurement referred to hereinafter refers to the six-dimensional pose measurement of the receiver 2 because the six-dimensional pose of the receiver coordinate system 20 is completely equivalent to the six-dimensional pose of the receiver 2.

3 laser tracker having pitch rotation and horizontal rotation _ν _Η two rotational degrees of freedom, the horizontal angle and the pitch angle of each theodolite is controlled by the driving means and the rotation angle value can be quickly measured. The drive unit usually uses a servo motor, and can also use a higher precision piezoelectric ceramic motor and a direct drive motor. The angle measuring device is mounted on the theodolite. Usually, a high-precision encoder is used. The resolution of the encoder reaches 0.1", and the measurement is repeated. Accuracy is up to 1". The laser tracker 3 is equipped with a high-precision range finder 30, usually using a laser interferometer or an absolute distance measuring instrument. Since commercial products such as laser trackers (including laser total stations and laser scanners) are very common, they will not be described in more detail here. Two small laser emitters 31 and 32 are additionally mounted on the laser range finder 30 of the laser tracker 3. The laser range finder emits a laser beam 301, and both of the laser emitters 31 and 32 emit a laser beam, 311 and 321 respectively. The orientation of the laser emitters 31 and 32 is generally parallel to the orientation of the laser range finder 30 to achieve a larger measurement range. The distance between the laser emitters 31 and 32 and the laser range finder 30 depends on the measurement accuracy of the three-dimensional attitude, and is generally selected to be 50 to 100 mm. The laser emitters 31 and 32 generally employ a semiconductor laser, and the wavelength is usually selected in the band of red visible light or infrared light, such as 635 to 690 nm, and the output power of the laser is generally milliwatts, such as lmW. The laser light emitted from the laser emitters 31 and 32 can also be separated from the beam of the laser range finder 30 through the spectroscopic device. Generally, the diameter of the laser beam emitted by the laser range finder is large, for example, the beam diameter of the laser interferometer is on the order of 25 mm, and the small laser emitter used in the present invention has a small laser beam diameter, according to the current small semiconductor. At the laser technology level, the diameter of the laser beam is usually less than 0.5 mm at a distance of 10 m, and the diameter of the laser beam is usually less than 5 mm at a distance of 100 m. The invention requires a small laser emitter to have better directional stability. For example, when the ambient temperature rises and falls, the change of the laser beam pointing is preferably less than 1 ", so that the stability of the laser beam can be ensured by using a common temperature control device.

The receiver 2 mainly includes a retroreflector 21, a projection panel 22, and an imaging unit 23. The retroreflector 21 preferably employs a cube-corner prism or a 360-degree reflecting prism, and three vertical planes of the corner cube intersect at a sharp point P. The retroreflector 21 is mounted in the middle of the projection panel 22. The shape of the projection panel 22 in this example is a flat surface, and the material of the projection panel 22 is a material having diffuse transmission properties, such as various translucent materials. The imaging unit 23 is typically mounted behind the projection panel 22, and the imaging unit 23 includes an imaging lens 231 and an imaging electronics 232. Imaging electronics 232 can be a common optical imaging device such as CCD, CMOS, and the like. The size of the projection panel 22 and the distance between the imaging unit 23 and the projection panel 22 are typically on the order of one-hundredth to one-thousandth of the maximum measurement range of the device; assuming that the measurement range of the device of the embodiment is 10 m, the projection The panel size is not more than 100mmx lOOmm, and the distance between the imaging unit and the projection panel is within 100mm. The retroreflective mirror 21, the projection panel 22 and the imaging unit 23 are both fixed to the receiver, so that their position and attitude with respect to the receiver coordinate system 20 can be accurately obtained by calibration.

The calculation processing unit 1 is connected to the receiver 2 and the laser tracker 3 via communication means 12, 13. The communication methods 12 and 13 are wired or wireless (including laser communication by a laser beam of a range finder).

It should be noted that:

1) In the present example, the projection panel 22 is made of a material having diffuse transmission properties, but the projection panel 22 may also be a scattering reflector having a certain roughness, such as a typical Lambertian reflector, at this time, the imaging unit 23 It is usually mounted to the front side of the projection panel 22. The projection panel 22 may also be a photosensitive device capable of direct imaging, such as a common optical imaging device such as CCD, CMOS, and PSD. In this case, the imaging unit 23 can be omitted, but considering the large-area optical imaging device is expensive, this The solution is more suitable for measuring small distances (eg less than lm).

2) The shape of the projection panel 22 in this example is a flat surface, but may be a spherical surface or other curved surface. When the projection panel 22 adopts a planar shape, the imaging unit 23 recommends a layout based on the Scheimpflug principle, which can be Get clear images over a wide range. The imaging lens 23 1 usually includes a band pass filter lens, which allows only the laser light in the laser band to pass, reducing the influence of ambient light, thereby improving the image quality.

3) Two small laser emitters 3 1 and 32 are used in this example, but can be replaced by a laser structured light emitter that generates a dot matrix or laser stripe. In practical applications, in order to make the measurement results more accurate and robust, more than two laser emitters can be installed, or each laser emitter can emit two or more laser beams that are parallel to each other. .

4) In Figure 1, the global coordinate system 10 is placed on the base of the laser tracker 3 to avoid overcrowding, and the receiver coordinate system 20 is placed on the frame of the receiver. The position of the above coordinate system can be adjusted according to whether the algorithm is convenient or not. According to the basic law of the matrix transformation, the translation of the above coordinate system does not change the three-dimensional posture of the receiver coordinate system 20 with respect to the global coordinate system 10. For the sake of simplicity of discussion and ease of understanding, the origin of the global coordinate system 10 is assumed in this example. It coincides with the intersection of the vertical axis and the horizontal axis of the laser tracker 3, and it is assumed that the origin 0' of the receiver coordinate system 20 coincides with the point P of the retroreflector 21.

The method for measuring the six-dimensional pose of a moving object according to the present invention, together with the basic working process of the device, is described as follows:

The azimuth of the laser tracker is controlled by an automatic tracking control step so that the laser range finder on the laser tracker always points to the retroreflector on the receiver, and the laser light emitted by the laser emitter falls on the projection panel on the receiver. . As shown in FIG. 1, the laser range finder 30 emits a laser beam 301, which hits the retroreflector 21 and is then retroreflected to form a laser beam 302, which is essentially parallel to the laser beam 301 and enters Laser range finder 30. The laser beams 3 11, 321 respectively emitted by the laser emitters 3 1, 32 fall on the projection panel 22 on the receiver 2 to form corresponding laser spots 3 12, 322.

The three-dimensional coordinates of the origin of the receiver coordinate system in the global coordinate system are obtained by the laser tracker measurement step. After the laser range finder 30 is calculated based on the characteristics of the laser beam from the rangefinder 301 and 302, the laser tracker 30 to the sharp point P of the laser mirror 21 after further 3 _Ν and the azimuth calculated based on the reflection mirror _Η The cusp P of 21 is relative to the three-dimensional coordinates (X _P , YP, ΖΡ) of the global coordinate system 10, which is the three-dimensional coordinates of the origin 0' of the receiver coordinate system 20 in the global coordinate system 10 (x, y, z ).

Then through the matrix transformation of the laser tracker, the mathematical equations of the laser line emitted by the laser range finder and the laser emitter in the global coordinate system are obtained. Generally, the laser emitter 31, 32 relative to the laser rangefinder 30 relative position and attitude can be precisely calibrated, the measured value of the laser tracker and azimuth _Ν _Η the two laser beams can be obtained 311 Equation 321 in the global coordinate system 10, according to the basic common sense of geometric algebra, a straight line in space is determined by two ternary linear equations. Assume that the algebraic equations of the lines corresponding to the two laser beams 3 11 and 321 are: a _{3 ll} x + b _{3 ll} y + c _{3 ll} z + d _{3 ll} = 0

e _{3 ll} x + f _{3 U} y + g _{3 ll} z + h _{3 U} = 0 a32l ^X + ^321^ + ^C 32l ^Z + ^321 ~ 0

Wherein: the subscript 311 represents a linear equation corresponding to the laser beam 311, and the subscript 321 represents a linear equation corresponding to the laser beam 321. The coefficients in the above equation depend only on the azimuth measurement of the laser tracker and the fixed size of the laser tracker.

On the other hand, the laser spot or the laser stripe on the projection panel is imaged and image processed by the imaging unit to obtain the pixel coordinates of the laser spot or the image of the laser stripe in the imaging unit; the pixel on the imaging unit is obtained by calibration of the imaging unit. The position of each pixel in the coordinate with respect to the receiver coordinate system is obtained by using a one-to-one correspondence between the pixel point and the receiver coordinate system to obtain a local coordinate value of the laser spot or the laser stripe relative to the receiver coordinate system. As shown in FIG. 1, the two-dimensional coordinates of the laser spot on the imaging electronics 232 can be obtained by processing the image taken by the imaging electronics 232. According to the aperture imaging principle, the line between the laser spot and its image on the imaging electronics 232 necessarily passes through the lens center of the imaging lens 231. Since the positions of the projection panel 22, the imaging lens 23 1 and the imaging electronics 232 relative to the receiver coordinate system 20 are fixed, the laser spot is on the imaging electronics .4 '

There is a fixed one-to-one mapping between the two-dimensional coordinates on 232 and the three-dimensional coordinates of the laser spot relative to the receiver coordinate system 20, so that the three-dimensional coordinates of these laser spots relative to the receiver coordinate system 20 can be obtained by the small hole imaging mathematical model. Or directly calibrating, that is, for each pixel on the imaging electronic device 222, the three-dimensional coordinates of the corresponding point on the projection panel 22 in the receiver coordinate system 20 are directly calibrated and recorded. Assuming that the size of the projection panel 22 is 100 mm×100 mm, the pixel array of the imaging electronic device 232 is 1024 pixels×1024 pixels, and the field of view of the imaging unit 23 is substantially equal to the size of the projection panel, the visual resolution of the imaging electronic device 222 is less than 0.1 mm. .

The global three-dimensional coordinate value of the laser spot or the laser stripe obtained by the imaging unit calibration with respect to the global coordinate system is obtained by assuming that the receiver coordinate system is three-dimensionally oriented with respect to the global coordinate system. Since the three-dimensional pose of the receiver coordinate system 20 relative to the global coordinate system 10 is three unknown variables (α, β, γ), if a relative coordinate (X _A ' of a laser spot Α in the receiver coordinate system 20 is known, Y _A ', Z _A '), the three-dimensional global coordinates (X _A , Y _A , Z _A ) of the laser spot in the global coordinate system 10 can be obtained according to the following homogeneous coordinate transformation:

= Trans{x,y, z)Rot(Z, y)Rot(X, )Rot{ , a)

Where Rot(Z, r)Rot(X, β) οί(Ζ, a) means that the angle is rotated around the Z axis of the global coordinate system, and then The X-axis rotation angle, and then the Z-axis rotation angle, r _ra ^(x, _y, z) represents the translation along the vector [x, _y, z | So can get

r _n = cos ^cos a - cos β sin a sin γ

r _n = cos y sin a + cos β cos or sin γ

r ₁₃ = sin ^sin β

r _2l = - sin y cos a - cos β sin a cos γ

r ₂₂ = - sin y sin a + cos β cos or cos γ

r ₂₃ = cos ^sin β

r ₃₁ = sin β sin a

r ₃₂ =— sin cos or

r ₃₃ = cos

It can be seen that the relative coordinates (X _A ', Y _A ', Z _A ') of a laser spot in the receiver coordinate system 20 are given, and the three-dimensional coordinates of the origin of the receiver coordinate system 20 in the global coordinate system 10 have been measured. (x, y, z), then the global coordinates (X, Y, Ζ) of the laser spot in the global coordinate system 10 are three variables in the three-dimensional pose (α, β, γ) of the receiver coordinate system 20 Function expression.

Finally, the constraint relationship between the mathematical equation of the laser line in the global coordinate system and the function expression of the laser spot global coordinate is established by the synchronous trigger measurement step, and the constraint relationship is obtained to obtain the pose of the receiver coordinate system relative to the global coordinate system. Since the spots 312, 322 must be respectively located on the corresponding lines of the two laser beams 311, 312, the function expressions corresponding to the three-dimensional global coordinates of the two spots are respectively substituted into the two equations of the corresponding laser beam, and three variables can be obtained. Four equations,

^311-^312 + 3⁄411^312 + ^C 311 312 + ^311 ~ , β , Τ) ⁼ ^

E3 ^X 3 2 + ^311^312 + ^311^312 + ^311 ― S CC, β, — 0

^321-^322 + ^321^322 + ^C 321 322 + ^321 ~ TK , β , ) = 0

E32\ ^X 322 + ^321^322 + §32\ ^Ζ 322 + ^321 ~〇θί, β, — In the above four equations, assume that the global coordinates of the laser spot 312 are (x ₃₁₂ , y ₃₁₂ , _3⁄412 ), The global coordinates of the laser spot 322 are (x ₃₂₂ , y ₃₂₂ , z ₃₂₂ ), apparently they are all three-dimensional in the receiver coordinate system 20 The pose (α, β, γ) is a function expression of the variable.

A three-dimensional pose (α, β, γ) of the receiver coordinate system 20 with respect to the global coordinate system 10 can be obtained by solving the equations composed of the above four equations. The algorithms for solving the equations can be classical Newton-Raphson methods, various optimal methods, homotopy methods, and interval analysis methods.

In fact, the above-mentioned laser spot must be located on the line corresponding to the laser beam respectively. Other expression methods can be used, for example, the distance between the spot and the corresponding laser beam is equal to zero, and different mathematical equations are obtained. The three-dimensional pose of the receiver coordinate system 20 relative to the global coordinate system 10 can also be represented by other equivalent representations, such as quaternions.

Figure 2 is a schematic diagram of the workflow of the six-dimensional pose measuring device for actual measurement, including the steps of synchronous trigger measurement. This workflow is explained for the first instance, but can be generalized for other examples described later. The specific workflow is as follows:

In step 101, the laser tracker 3 is fixed to the ground. Step 102 securely mounts the receiver 2 on the moving object to be tested. Step 103, adjusting the horizontal corner and the pitch angle of the laser tracker 3 so that the laser beam 301 falls on the retroreflector 21 of the receiver 2, and the laser beams 311 and 321 fall on the projection panel 22 of the receiver 2. In step 104, the calculation processing unit 1 sends a trigger signal to the laser tracker 3 and the receiver 2, respectively. Step 105: The laser tracker 3 transmits the measured values of the three-dimensional coordinates (X, y, z) of the receiver 2 and the azimuth angles (Θ _Ν , Θ _Β ) of the receiver 2 measured at the triggering time to the calculation processing unit 1, and At the same time, the imaging unit 23 of the receiver 2 triggers the high speed shutter, captures the spot image on the projection panel 22, and transmits the calculated two-dimensional coordinate value of the laser spot in the imaging electronic device 232 to the calculation processing unit 1. Step 106, the calculation processing unit 1 calculates a local three-dimensional coordinate value of the spot relative to the receiver coordinate system 20 according to the two-dimensional coordinates of the spot and the calibrated mapping relationship; the calculation processing unit 1 according to the constraint relationship of the laser spot on the laser line, Substituting the function expression of the laser spot in the global coordinate system into the mathematical equation corresponding to the laser line, and establishing four equations with the three attitude parameters (α, β, γ) of the receiver 2 as unknown variables, solving the four equations The attitude parameter of the receiver coordinate system 20 relative to the global coordinate system 10 is obtained, and the six-dimensional pose (x, y, ζ, α, β, γ) of the receiver coordinate system 20 is obtained. In step 107, the laser tracker 3 performs an automatic tracking control algorithm. Steps 104 through 107 are then performed cyclically until the measurement is completed.

The flow of the automatic tracking control algorithm of the laser tracker is as follows. At each measurement, the current pose of the receiver 2 is calculated by the laser tracker 3, and the current pose and the receiver 2 are measured at the last time. The difference between the poses is divided by the sampling interval to obtain the motion speed of the receiver 2, and the pose that the receiver 2 will arrive at the next measurement is further estimated based on the motion speed of the receiver 2, and the new corner that the laser tracker 3 needs to reach is calculated. Position to ensure that the laser beam 301 still falls on the retroreflector 21 of the receiver 2, and. Solving the motion of the receiver 2 can also be obtained by filtering and predicting methods using the motion trajectory before the receiver 2.

The above-mentioned synchronous trigger measurement method can also be replaced by a combination of continuous measurement and measurement value interpolation, that is, the calculation processing unit 1 does not have to send a trigger signal to the laser tracker 3 and the receiver 2, and the laser tracker 3 continuously receives the receiver. 2's 3D coordinates (X, y, z) and their own azimuth ( Θ _Β ) measurements are sent to the calculation The unit 2, the receiver 2 also continuously transmits the calculated two-dimensional coordinate values of the laser spot obtained in the imaging electronics 232 to the calculation processing unit 1. The calculation processing unit 1 interpolates the data of a certain fixed time according to the received data and the time when the data arrives, further establishes a system of equations based on the interpolated data, and solves the six-dimensionality of the receiver coordinate system 20 in the global coordinate system 10. Position.

The position measurement accuracy and tracking performance of the device basically depend on the position measurement accuracy of the laser tracker. The measurement accuracy of the azimuth of the laser tracker is 1 ". When the measurement range is 10 m, the position measurement accuracy can reach the order of 0.05 mm. The horizontal tracking speed can reach 3m/s.

The attitude measurement accuracy of the device can reach the following indexes: The imaging device adopts an imaging electronic device of 1024 pixels X 1024 pixels, and a projection panel with a shooting area of 50 mm×50 mm can obtain a resolution higher than 0.05 mm, so it is assumed that the spots 312 and 322 are The position resolution is 0.05mm. With the solution of the invention, the transmission delay of the trigger signal and the shutter exposure time of the imaging unit can reach the order of 10 μ ₅ , and when the moving object speed is lm/s, the measurement deviation of the imaging unit is on the order of 0.01 mm. It is known that the equivalent radius of the projection panel of the receiver is 25mm, so the attitude measurement accuracy can reach (0.05/25) χ (180 π) = 0.114°, that is, 0.1°, if 1/10 sub-pixel image processing is used, It can reach the order of 0.01°.

Example 2

Fig. 3 shows a second example of the six-dimensional pose measuring device proposed by the present invention. The difference from the first example is that the projection panel 22 on the receiver 2 adopts a spherical shape, and the imaging unit 23 is located inside the projection panel; the projection panel 22 is provided with a magnetic support 24; the retroreflector 21 is adopted. The triangular prism reflecting ball can be reliably adsorbed on the magnetic support 24, and the operator can manually adjust the orientation of the retroreflecting mirror 21. The above two modifications can obtain a larger three-dimensional attitude measuring range. Of course, the magnetic support 24 can also be designed as a manual turntable or automatic turntable with one degree of freedom or two degrees of freedom. The rotation axes of the manual turret and the automatic turret pass through the center of the triangular prism reflecting ball, and the position of the center of the triangular prism reflecting ball relative to the receiver 2 can be maintained. The manual turntable can be equipped with an ordinary high-precision turntable. The automatic turntable is driven by installing a rotary motor on the rotating shaft of the high-precision turntable, or by directly driving the surface of the triangular prism reflecting ball by a spherical motor. Since the automatic turntable does not need to accurately control the angle between the retroreflector and the incident laser, the retroreflector can receive the incident laser only, so that the weight of the automatic turntable can be easily realized compared with the solution in US Pat. No. 6,667,798. .

Example 3

Fig. 4 shows a third example of the six-dimensional pose measurement device proposed by the present invention. This example is primarily suitable for small-scale measurements. The range finder 30 on the laser tracker 3 is a structured light position sensor measured by a triangulation method, and can be selected from the Japanese Keyence LK-G500, and the measurement range is 250 mm to 1000 mm. Since the triangulation measurement is not suitable for measuring a highly reflective surface, the retroreflector 21 is replaced with a reflective patch in this example. In the present example, the projection panel 22 is made of a scattering light-transmitting material, so that a part of the incident laser light is diffusely reflected and a part is diffusedly transmitted, so that the diffuse reflection function of the reflective patch can be realized by the projection panel 22. The projection panel 22 in this example is a spherical surface, but may be a flat surface or other curved surface. Since there is no retroreflector 21, it is assumed in the present example that the origin 0' of the receiver coordinate system 20 is located on the frame of the imaging unit 23. The laser emitter 304 on the range finder 30 emits a stimuli The beam 301 falls on the projection panel 22, forming a spot 302, part of which is scattered and returned in direction 302 to the receiving window 303 on the range finder 30, and finally imaged on the line array imaging device inside the range finder 30, thus The laser tracker 3 can accurately calculate the three-dimensional global coordinates (x ₁₂ , y ₁₂ , z ₁₂ ) of the spot 302. The laser beams 311, 321 respectively emitted by the other two laser emitters 31, 32 on the laser tracker 3 also form the spots 312, 322 on the projection panel, respectively, so that the image captured by the imaging unit 23 includes three spots 302, 312, 322.

The calculation method of this example is as follows: Assuming that the six-dimensional pose (x, y, ζ, α, β, γ) of the receiver coordinate system 20 is known, the global shape of the laser spot 302 can be calculated according to the pose transformation of the receiver 2. Coordinates (x _3Q2 , y ₃₀₂ , z ₃₀₂ ), global coordinates of laser spot 312 (x ₃₁₂ , y ₃₁₂ , _3⁄412 ), global coordinates of laser spot 322 (x ₃₂₂ , y ₃₂₂ , z ₃₂₂ ), these are obviously Both are function expressions in which the six-dimensional pose of the receiver coordinate system 20 is an unknown variable. According to the basic idea of establishing the constraint equation in Example 1, the global coordinates of the laser spot should satisfy the corresponding linear equation, and the calculated global coordinates of the spot should be consistent with the global coordinates of the spot measured by the laser tracker. It is not difficult to obtain seven constraints. Equation, solving these seven equations can obtain the six-dimensional pose (x, y, ζ, α, β, γ) of the receiver coordinate system 20.

Another calculation method of the present example is to first temporarily shift the origin 0' of the receiver coordinate system 20 to a position coincident with the laser spot 302. At this time, only four equations are obtained according to the method described in the first example. The three-dimensional pose (α, β, γ) of the receiver coordinate system 20 can be solved, and then the value of the translation vector in the global coordinate system 10 is calculated according to the three-dimensional posture of the receiver coordinate system 20, thereby obtaining the origin 0' when not yet translated. The three-dimensional position (χ, y, z).

Example 4

Fig. 5 shows a fourth example of the six-dimensional pose measurement device proposed by the present invention. In this example, the compact laser emitters 31, 32 are no longer mounted on the laser tracker 3, but are mounted on two two-degree-of-freedom turntables 5, 6. The two-degree-of-freedom turntable is usually in the form of a theodolite, that is, each two-degree-of-freedom turntable has a horizontal rotational degree of freedom and a pitching degree of freedom, including a driving device that controls its horizontal and pitching angles, and includes measuring its horizontal angle and pitch. Corner angle measuring device. The two-degree-of-freedom turntables 5, 6 are connected to the calculation processing unit 1 via communication means 15, 16 respectively, and the respective horizontal and pitch rotation angles are sent to the calculation processing unit 1.

The receptor 2 includes a retroreflector 21 and two projection panels 22a, 22b, each of which is fixed to a rigid bracket 25, and the projection panels 22a, 22b respectively correspond to an imaging unit 23a and 23b. The relative position and attitude of the retroreflector 21 and the projection panels 22a, 22b with respect to the receiver coordinate system can be obtained by a calibration method. The laser tracker 3 directs the laser beam toward the retroreflector 21, and the laser emitters 31 and 32 on the two two-degree-of-freedom stages 5, 6 respectively direct the laser beams 311, 321 toward the corresponding projection panels 22a, 22b. Laser spots 312 and 322 are formed.

The calculation method of this embodiment is basically the same as that of Embodiment 1, that is, the three-dimensional position measurement is performed by the laser tracker 3, and the three-dimensional attitude measurement is performed according to the constraint that the laser spot is located on the corresponding straight line. The only difference is that the equations of the straight line for calculating the laser beams 311, 321 are based on the azimuth angles of the two degrees of freedom turrets 5, 6 and their position and attitude with respect to the laser tracker 3, rather than the azimuth of the laser tracker 3. Two of the free turntables 5, 6 The position and attitude relative to the laser tracker 3 can be obtained by an external device direct calibration method or from a calibration procedure. A direct calibration method is to mount the two-degree-of-freedom turntables 5, 6 and the laser tracker 3 on a bracket of a known size, or to fix the two-degree-of-freedom turntables 5, 6 on the laser tracker 3. The self-calibration procedure is achieved by fixing the receiver 2 and incrementally adjusting the azimuth of the two-degree-of-freedom turntable by solving the equation.

An advantage of this embodiment is that since the distance between the projection panel and the retroreflector is relatively long, a high three-dimensional attitude measurement accuracy can be obtained.

It should be noted that although only four embodiments of the six-dimensional pose measuring device are given here, some obvious modifications can be made to the above embodiment to obtain more examples, such as the laser spot projection of the present invention. The close-up method is combined with the method of opening a small hole by a cone prism in the patent of US Pat.

Further, in the above example, the laser tracker is mounted on a fixed ground, and the receiver is mounted on the moving object to be tested, but one of the laser tracker and the receiver may be mounted on the moving object to be tested, and the other Installed on a fixed floor. In the above example, the computational processing unit and the laser tracker are two separate units, but it is obvious that the computational processing unit can also be integrated into the interior of the laser tracker.

It should also be noted that the present invention is mainly used for six-dimensional pose measurement, but can be easily simplified to measure the three-dimensional pose of an object in a plane, that is, a two-dimensional position (x, y) and a one-dimensional rotation θι. The specific solution is to remove the pitch rotation freedom of the laser tracker and only need a small laser emitter.

The scope covered by the present invention includes: realizing position measurement of an object by using a two-dimensional or three-dimensional position measuring instrument, and simultaneously generating a plurality of spots on the receiver projection panel by using a small-diameter laser beam, and performing close-range shooting and processing on the laser spot image. The local coordinates of the spot are obtained, and the equation is solved by the parallel measurement principle to obtain the relevant scheme of the object pose. It should be noted that some of the structures in the third scheme of Leica's patent US7312862 are similar to the present invention, but in this scheme, a large-diameter laser beam is passed through a small hole and then falls on the imaging electronic device to generate a spot, and the imaging device is formed. It must be on the back side of the retroreflector; whereas in the present invention the laser spot falls on the projection panel, and the projection panel and imaging electronics can be located on the side, back side or front side of the retroreflector. Furthermore, the measurement of the three-dimensional attitude in Leica's patent US Pat. No. 7,321,862 is essentially based on the principle of series measurement. Firstly, the imaging artifacts after the small holes are used to measure the two-dimensional pose (ie, the pitch angle and the deflection angle), and then the scrolling is separately calculated by the external measuring device. The corner angle is measured by the parallel measurement principle of the present invention, and the pitch angle, the deflection angle, and the rolling angle are calculated simultaneously.

Claims

Claim

What is claimed is: 1. A device for measuring a six-dimensional pose of an object, comprising: a calculation processing unit (1), a receiver (2), a laser tracker (3) and at least one laser emitter; The laser tracker is mounted on a fixed ground; the receiver is mounted on the moving object to be tested (4); the laser tracker and receiver are in communication with the computing processing unit (1), and the laser tracker and receiver are connected by a laser optical path, the laser The transmitter and receiver are connected by a laser optical path.

2. The apparatus according to claim 1, wherein: said laser tracker has a horizontal rotation degree of freedom and a pitch rotation degree of freedom; and the laser tracker includes a driving device for controlling the horizontal rotation angle and the pitch rotation angle, and further comprises A corner measuring device for measuring a horizontal corner and a pitch angle; at least one laser range finder is mounted on the laser tracker.

3. The apparatus according to claim 2, wherein: said laser range finder emits a laser beam, said laser range finder being a laser interferometer, or a laser Doppler range finder, or a laser Absolute distance measuring instrument, or laser structured light position sensor.

4. Apparatus according to claim 1 wherein: said laser emitters are mounted on a laser tracker; said each laser emitter emitting at least one laser beam, said laser beam and laser ranging The laser beam emitted by the instrument is parallel.

5. The apparatus according to claim 1, wherein: said laser emitter is mounted on a two-degree-of-freedom turntable; said each laser emitter emits at least one laser beam; said two-degree-of-freedom turntable is mounted On the laser tracker or fixedly mounted on the ground;

6. The apparatus according to claim 5, wherein: said two-degree-of-freedom turntable has a horizontal rotation degree of freedom and a pitch rotation degree of freedom; said two-degree-of-freedom turntable includes a drive for controlling a horizontal angle and a pitch angle thereof The device also includes a corner measuring device that measures its horizontal and pitch angles.

7. The device according to claim 4 or 5, wherein: when the number of the laser emitters is 1, the laser emitter emits line structured light, or emits cross-hair structured light, or emits lattice structure light. .

8. The apparatus according to claim 1, wherein: said receiver comprises a reflective target, at least one projection panel and at least one imaging unit, and each projection panel corresponds to at least one imaging unit; wherein the reflective target is backward A mirror, or a translucent reflective patch; the shape of the projection panel is selected from a plane, or a curved surface, or a combination of a plurality of planes, or a combination of a plurality of curved surfaces; the material of the projection panel is a diffusing light-transmitting plate. Or a rough reflective reflector; the field of view of the imaging unit is substantially equal to the size of the projection panel.

9. The device according to claim 8, wherein: when the material of the projection panel is a diffusing transparent plate, the imaging unit is on the back side or inside of the projection panel, when the material of the projection panel is a scattering reflector The imaging unit is on the front side of the projection panel.

10. The apparatus of claim 8 wherein: said imaging unit comprises imaging electronics and an imaging lens positioned between the imaging electronics and the projection panel; wherein the imaging electronics is selected from the group consisting of position sensitive detection , a charge coupled device, a charge injection device, or an optical imaging device based on a complementary metal oxide semiconductor.

11. Apparatus according to claim 8 wherein: said imaging unit comprises at least one photographic measuring device mounted directly on the surface of the projection panel, the photographic measuring device being selected from the group consisting of position sensitive detectors, charge coupled devices, charge injection A device, or an optical imaging device based on a complementary metal oxide semiconductor.