CN103411624A - Calibration method and calibration system, based on micro-motion stage, for magnetic field source of magnetic tracking system - Google Patents

Calibration method and calibration system, based on micro-motion stage, for magnetic field source of magnetic tracking system Download PDF

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CN103411624A
CN103411624A CN2013103080520A CN201310308052A CN103411624A CN 103411624 A CN103411624 A CN 103411624A CN 2013103080520 A CN2013103080520 A CN 2013103080520A CN 201310308052 A CN201310308052 A CN 201310308052A CN 103411624 A CN103411624 A CN 103411624A
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magnetic
source
coordinate
axle
sensor
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CN103411624B (en
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邬小玫
丁宁
王一枫
沙敏
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复旦大学
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Abstract

The invention belongs to the technical field of electromagnetic measurement, and particularly relates to a calibration method and a calibration system which are based on a triaxial micro-motion stage and used for the origin and the initial attitude of a magnetic field source of a magnetic tracking system. The calibration system comprises the triaxial micro-motion stage, a triaxial magnetic sensor, two rotatable magnetic field sources capable of achieving any spatial direction, and a controlling, processing and displaying device. The calibration system can achieve calibration of relative positions and attitudes between the magnetic field resources. The calibration method in specific comprises steps of controlling the magnetic sensor to move to five selected coordinate-known points by the triaxial micro-motion stage, locating spatial positions of the five points by utilization of the electromagnetic tracking system to obtain spatial position information between the magnetic field sources and the points, and calculating the initial relative position and attitude between the magnetic field sources. A magnetic tracking algorithm based on a rotatable magnetic field is calibrated according to the calibration results, thereby improving the locating precision significantly.

Description

Magnetic Field Source scaling method and system based on the electromagnetic tracking system of micromotion platform
Technical field
The invention belongs to the Techniques in Electromagnetic Measurement field, be specifically related to scaling method and the system of Magnetic Field Source relative position and initial attitude in electromagnetic tracking system.
Background technology
Electromagnetism is followed the tracks of (Electromagnetic Tracking), or claims the electromagnetic field location, is that a kind of magnetic field or electromagnetic field of utilizing detects the method with real-time follow-up to the locus of object and attitude.The method can be applicable to the navigation of Minimally Invasive Surgery, also can apply to the fields such as virtual reality, 3-D supersonic imaging.In the electromagnetic tracking system that contains 2 or 2 above Magnetic Field Source, location/track algorithm will be used the spatial relation between Magnetic Field Source usually, and whether position relationship accurately directly affects tracking accuracy, therefore need to demarcate the locus of electromagnetic tracking system Magnetic Field Source.
Scaling method commonly used is optical calibrating at present.Because the precision of optical positioning system is high, can obtain higher stated accuracy.But when between light source and spotting, barrier being arranged, or spotting just can not be used optical positioning system to demarcate while being hidden in black box.For electromagnetic tracking system, use optical positioning system to be difficult to the initial point of three quadrature coils is demarcated.Therefore the practical application of optical positioning system demarcation has certain limitation.
Summary of the invention
The object of the invention is to propose a kind of based on the Magnetic Field Source relative space position of three axle micromotion platforms and scaling method and the system of initial attitude, be used to the demarcation of the electromagnetic tracking system that contains an above Magnetic Field Source.
The calibration system that the present invention proposes is comprised of following four parts: Magnetic Field Source, magnetic sensor device, control processes and displays device and three axle micromotion platforms; Wherein:
Described Magnetic Field Source is 2, forms by quadrature three axial coils and three corresponding control driving circuits; Three magnet coil geometric centers of quadrature three axial coils overlap; The initial point of Magnetic Field Source 2 is on the X-axis of Magnetic Field Source 1, and the distance between two Magnetic Field Source initial points is d, and Y-axis and the Z axis of two Magnetic Field Source are parallel to each other; The electromagnet that forms Magnetic Field Source adopts constant current exciting mode, controls every group of exciting current intensity by controlling the processes and displays device; The bar magnet that quadrature three axial coils point to arbitrarily in order to virtual space;
Described magnet sensor arrangement is fixed in three axle micromotion platforms, by three axle micromotion platforms, controls it and accurately moves in space, measures the magnetic induction density of three orthogonal directionss; Described triaxial magnetic field sensor device comprises: three axle component sensors, signal condition and analog to digital (AD) modular converter, three axle component sensors are used for respectively detecting the magnetic induction density of three orthogonal directions X ', Y ' and Z ', its output is sent into control processes and displays device through follow-up signal condition and analog to digital (AD) modular converter, and the sampling processing module samples in controlling the processes and displays device is processed;
Described control processes and displays device is comprised of control module, algorithm unit, demonstration output unit and three axle micromotion platform control modules, wherein:
Described control module comprises three parts: sampling processing module, exciting current strength control module and micromotion platform control module; Described sampling processing module is the I/O mouth that microprocessor carries, for the signal of sampling processing from signal condition and analog-digital conversion module; Described exciting current strength control module is the exciting current of microprocessor according to three quadrature coils of the corresponding Magnetic Field Source of the simulation bar magnet anglec of rotation that calculate, control driving circuit by I/O mouth controlling magnetic field source, provide the excitation of three axle quadrature coils is controlled, the simulation bar magnet of synthetic required sensing; Described micromotion platform control module is that microprocessor passes through I/O mouth output signal, control as requested the movement of three axles of micromotion platform, and drive thus the Magnetic Sensor be fixed on micromotion platform and move to selected coordinate points (for example hereinafter n1, n2, n3(overlap with m1), m2, five points of m3) on;
Described algorithm unit, at microprocessor internal, can, according to the rotation angle information obtained in simulation magnetic bar rotation searching final orientation sensor process, be used the origin calibration algorithm, the origin of calculating magnetic field source 1, Magnetic Field Source 2; Use the initial attitude calibration algorithm, the initial directional of each coordinate axis of calculating magnetic field source 1, Magnetic Field Source 2;
Described demonstration output unit is liquid crystal display and the I/O mouth be connected with microprocessor, for being exported and be shown on display by the calibration result that algorithm unit calculates;
Described three axle micromotion platform control modules, at microprocessor internal, are accurately controlled the movement of three axles of micromotion platform by the instruction of I/O mouth output as requested;
Described three axle micromotion platforms by three mutually orthogonal tracks and can be in orbit accurately mobile stationary installation form, be used to controlling magnetic sensor, accurately move in space.
In the present invention, described sensor can be selected magnetoresistive transducer, hall effect sensor or fluxgate sensor etc., for the magnetic induction density of three orthogonal directionss of measurement space.
In order to describe better the present invention, according to right-hand rule, defined seven coordinate systems as shown in table 1, wherein CS1 is global coordinate system, CS6 is the micromotion platform coordinate system, the reference coordinate system while being also calibration.
Table 1 Coordinate system definition
The coordinate system title Abbreviation Describe
Coordinate system 1 CS1 The original coordinate system of Magnetic Field Source 1
Coordinate system 2 CS2 The desirable original coordinate system of Magnetic Field Source 2
Coordinate system 3 CS3 When the x of Magnetic Field Source 1 axle (bar magnet axis direction) orientation sensor, the actual coordinates of Magnetic Field Source 1
Coordinate system 4 CS4 When the x of Magnetic Field Source 2 axle (bar magnet axis direction) orientation sensor, the actual coordinates of Magnetic Field Source 2
Coordinate system 5 CS5 The magnetic sensor coordinate system
Coordinate system 6 CS6 The micromotion platform coordinate system
Coordinate system 7 CS7 The actual original coordinate system of Magnetic Field Source 2
The scaling method of the above-mentioned Magnetic Field Source relative space position based on three axle micromotion platforms of use that the present invention proposes and the calibration system of initial attitude, concrete steps are as follows:
Step 1, by the calibration system initialization;
Step 2, by three axle micromotion platforms, control the magnetic sensor devices and shift to space known coordinate point;
Step 3, with Magnetic Field Source 1 and the corresponding simulation bar magnet of Magnetic Field Source 2, search for and point to described magnetic sensor device;
The bar magnet that step 4, recording magnetic field source 1, Magnetic Field Source 2 are simulated is from initial position to the horizontal and vertical rotation angle of pointing to magnetic sensor device process;
Step 5, judge whether three axle micromotion platforms have moved to the magnetic sensor device the selected known coordinate point in five, space, if be no, repeating step three, four; If be yes, go to step six;
Step 6, in step 5, be under the condition of positive result, use Magnetic Field Source origin calibration algorithm, the origin of calculating magnetic field source 1, Magnetic Field Source 2;
Step 7, utilization Magnetic Field Source initial attitude calibration algorithm, the initial directional of each coordinate axis of calculating magnetic field source 1, Magnetic Field Source 2.
The first step of the inventive method, be after start, moves/turn to initial position separately by controlling processes and displays device control micromotion platform, Magnetic Field Source 1 and Magnetic Field Source 2; Three axles that are specially micromotion platform all move to true origin, the X-axis that Magnetic Field Source 1 and Magnetic Field Source 2 turn to both is parallel to each other, and Y-axis is parallel to each other, and Z axis is parallel to each other, and (this is ideal situation, actual capabilities have error, and this is also the purpose that attitude of the present invention is demarcated).
The second step of the inventive method is by micromotion platform, to control sensor to shift to space known coordinate point.Described numerical control triaxial micromotion platform comprises mutually orthogonal x, y, and tri-tracks of z, positioning precision reaches 0.1mm.Utilize this micromotion platform, by Magnetic Sensor be placed on respectively n1, n2, n3(overlaps with m1), on m2, five points of m3, and, by subsequent step, by Magnetic Field Source 1, Magnetic Field Source 2, these five points are positioned.In the CS6 coordinate system, to these five points require as follows:
N3 and m1 overlap;
N1, n2, n3 point-blank, and between n1, n2 the distance with n2, n3 between the distance equate;
M1, m2, m3 are on another not parallel with n1, n2, n3 straight line, and the distance between m1, m2 equates with the distance between m2, m3.
The 3rd step of the inventive method is when sensor arrives n1, n2, n3(overlaps with m1), certain in m2, m3 is when a bit, by Magnetic Field Source 1, Magnetic Field Source 2, it is positioned.Specific practice encourages in the mode of constant current alternative excitation quadrature three axial coils that form Magnetic Field Source respectively by controlling the processes and displays device; The geometric center that described quadrature three axial coils need meet three coils overlaps, and the mutually orthogonal condition of the axis of three coils; Described constant current drive alternative excitation mode, be that each Energizing cycle is divided into at least two time periods, and in first time period in constant current drive cycle, the amplitude that gives on x axle transmitting coil is A Sin (φ)The exciting current of ampere, give amplitude A on y axle transmitting coil Cos (φ)The exciting current of ampere, take and synthesize size and be the A ampere, at the x-y Plane Rotation φThe bar magnet of degree, control φAt 0-2 π, change, when simulating the bar magnet orientation sensor in x-y plane projection direction, sensor can detect maximum magnetic induction, and the anglec of rotation of now simulating bar magnet is φ Ij (wherein I=1-2,Corresponding Magnetic Field Source 1 and Magnetic Field Source 2; J=1-5Corresponding n1, n2, n3 (or m1), m2, five coordinate known points of m3); Afterwards, on x axle transmitting coil, giving amplitude is A Sin (φ Ij )* Sin (θ)The exciting current of ampere, the amplitude that gives on y axle transmitting coil is A Cos (φ Ij )* Sin (θ)The exciting current of ampere, now on z axle transmitting coil, giving amplitude is A Cos (θ)The exciting current of ampere, can synthesize at the simulation bar magnet hung down as for the x-y Plane Rotation; Control θIn 0-π scope, change, when simulation bar magnet orientation sensor, sensor can detect maximum magnetic induction, now simulates bar magnet in the anglec of rotation of vertical plane to be θ Ij .The record anglec of rotation now θ Ij .
The 4th step of the inventive method is the feathering angle of recording magnetic field source 1,2 bar magnet of simulating from initial position to the orientation sensor process φ Ij (namely simulate bar magnet and by initial position, rotate the anglec of rotation when this plane projection to orientation sensor on the x-y plane) and vertical rotary angle θ Ij (namely simulating the anglec of rotation of bar magnet while rotating to orientation sensor by initial position on the plane perpendicular to x-y).
The 5th step of the inventive method, complete Magnetic Field Source to being positioned at n1, n2, n3(overlaps with m1), the sensor of m2, five points of m3 locates respectively.
The 6th step of the inventive method is to use Magnetic Field Source origin calibration algorithm, the origin (x in calculating magnetic field source 1,2 i, y i, z i); , Magnetic Sensor can be placed on three points of known spatial coordinate for this reason, can set up the system of equations of three equations compositions of geometric relationship between reflection simulation bar magnet and Magnetic Sensor, and then solve bar magnet rotation center coordinate.But three equation system of equations not necessarily have solution, and the present invention has designed the scheme of setting up 5 system of equations, in the situation that exceed increase method complexity, improve the stability of algorithm.The scaling scheme of different number Magnetic Field Source can be analogized and be obtained by the present invention.
With reference to accompanying drawing 4(, only drawn Magnetic Field Source 1, can draw Magnetic Field Source 2 by same procedure) by system of equations (1), can calculate coordinate (x1, y1, z1), (x2, y2, the z2) of initial point in CS6 of Magnetic Field Source 1,2:
????(1)
Wherein (n1x, n1y, n1z) is the coordinate of n1 point in CS6, and the rest may be inferred for all the other.R I1, r I2, r I3, r I5, r I6Can be calculated by formula (2)~(6).
????(2)
????(3)
????(4)
???(5)
???(6)
α in formula (2)~(6) I1, α I2, α I3, α I4Can be calculated by formula (7):
(7)
In formula (7) P Ij , q Ij With k Ij Can be calculated by system of equations (8):
????(8)
The 7th step of the inventive method is the demarcation that realizes the Magnetic Field Source initial attitude.CSr is expressed as to R to the rotation relationship between CSs Rs, r=1-7, s=1-7(mean defined seven coordinate systems of table 1).In the coordinate system of table 1 definition, CS1 is the original coordinate system of Magnetic Field Source 1, is also system coordinate system.CS2 is the desirable original coordinate system of Magnetic Field Source 2, and its y, z axle are parallel with y, the z axle of CS1, and the x axle overlaps with the x axle of CS1, and namely the coordinate origin of CS2, on the x of CS1 axle, but does not overlap with the coordinate origin of CS1; But when the actual placement Magnetic Field Source, relation between two Magnetic Field Source may can not reach above-mentioned ideal situation, therefore defined again the actual original coordinate system CS7 of Magnetic Field Source 2, the demarcation of Magnetic Field Source initial attitude changed into to the rotation relationship of finding between the desirable original coordinate system CS2 of Magnetic Field Source 2 and its current coordinate system CS4, namely obtain R 24.
CS1 can utilize and measure to the rotation matrix of CS3 φ 11 With θ 11 By formula (9), calculated:
????(9)
Can calculate the rotation matrix of CS7 to CS4 by formula (10) equally:
?????( 0)
Suppose the initial point of CS6 is moved to the initial point of CS1, and make the x axle orientation sensor of CS6, can try to achieve CS6 to the CS3 rotation matrix by formula (11) :
?????(11)
In formula (11), ω 0 ', θ 0' and φ 0' for the hypothesis CS6 x axle orientation sensor the time required rotation Eulerian angle.In order to solve ω 0 ', movable sensor, obtain another one mapping point, so that simultaneous becomes equation.Keep CS6 to overlap with the true origin of CS1, and make the x axle of CS6 point to the sensor after moving, can try to achieve CS6 to the CS3 rotation matrix by formula (12) :
????(12)
Because the rotation matrix of CS1 and CS6 is constant, that is:
????(13)
Formula (11) and (12) substitution (13) can be obtained: (14)
Solving equation group (14), can obtain With , the substitution formula can obtain in (13) R 61.
In like manner, suppose the initial point of CS6 is moved to the initial point of CS7, and make the x axle orientation sensor of CS6, can obtain the rotation matrix of CS6 to CS4 by formula (15), wherein ω 6 ', θ 6' and φ 6' for the hypothesis CS6 x axle orientation sensor the time required rotation Eulerian angle:
????(15)
????(16)
According to formula (17) and (18), can obtain formula (19) again:
????(17)
????(18)
????(19)
Can push type (20) by formula (10) and formula (19):
????( )
Now obtained the rotation relationship between CS2 and CS4, by the R in breakdown (20) 24, i.e. the anglec of rotation of through type (21) after can being proofreaied and correct , , :
????( )。
According to calibration result, the magnetic track algorithm based on rotating magnetic field is proofreaied and correct, thereby improved positioning precision.
The present invention, by three axle micromotion platforms, utilizes the positioning function of electromagnetic tracking system itself to realize demarcating simultaneously, not limited by the spotting locus, significantly improves the electromagnetic tracking system positioning precision.
The accompanying drawing explanation
Fig. 1 is that the system of the embodiment of the present invention forms.
Fig. 2 is the details block diagram of the device in Fig. 1.
Fig. 3 is the working-flow block diagram of embodiments of the invention.
Fig. 4 is calibration principle of the present invention.
Embodiment
The present embodiment to be to comprise two Magnetic Field Source (Magnetic Field Source 1 and Magnetic Field Source 2), the situation of more Magnetic Field Source can analogize obtain), and the electromagnetic tracking system that Magnetic Field Source adopts the DC pulse mode to encourage is that example describes.Figure 1 shows that the Magnetic Field Source relative tertiary location based on three axle micromotion platforms of the design according to the present invention and the calibration system of initial attitude, comprise five parts: Magnetic Field Source 1, Magnetic Field Source 2, triaxial magnetic field sensor device 3, control processes and displays device 4 and three axle micromotion platforms 5.Sensor device 3 is fixed on three axle micromotion platforms 5, by micromotion platform 5, controls it and accurately moves.The locus of Magnetic Field Source 1, Magnetic Field Source 2 is fixed, and the distance between both initial points is d, and initial attitude ideally is: the initial point of Magnetic Field Source 2 is on the x of Magnetic Field Source 1 axle, and each coordinate axis of two Magnetic Field Source is parallel to each other.Control processes and displays device 4 output DC pulse currents, three axial coils of excitation field source 1, Magnetic Field Source 2, the bar magnet that virtual space points to arbitrarily, by changing and output to the DC-pulse intensity of flow on Magnetic Field Source 1, Magnetic Field Source 2 three axles simultaneously, realize the rotation of bar magnet.
The exploded block diagram of system each several part as shown in Figure 2.Sensor device 3 is selected three axle magnetoresistive transducers, comprises three axle component sensors 6,7 and 8, is used for respectively detecting the magnetic induction density of three orthogonal directions X ', Y ' and Z '.Sensor output is sent into control processes and displays device 4 through follow-up signal condition and analog to digital (AD) modular converter 9.
Magnetic Field Source 1,2 is by quadrature three axial coil installation compositions, and the Magnetic Field Source 1 of below take describes (situation of Magnetic Field Source 2 roughly the same, repeats no more) as example.Magnetic Field Source 1 is comprised of three groups of magnet coils 10,11 and 12, and coil is controlled and driven by circuit 13,14 and 15 respectively.Require three groups of coil geometric centers to overlap, and will make the synthetic magnetic induction density of three axial coils in same distance situation lower axis place maximum, and should locate magnetic direction along axis.In the present embodiment, three axial coils are on the cube of 2.5cm around the length of side, and the number of turn of each coil is 1000 circles.In addition, electromagnet is by the pulse direct current excitation of controlling 4 outputs of processes and displays device.
Controlling processes and displays device 4 is comprised of control module 18, algorithm unit 19, demonstration output unit 20.Wherein:
Control module 18 comprises three parts: sampling processing module 16, exciting current strength control module 17 and micromotion platform control module 29; Wherein:
Exciting current strength control module 17 adopts DC pulse to control, to control driving circuit 13,14,15 to realize three axle quadrature coils 10,11 of formation Magnetic Field Source 1 and 12 excitation, in the present embodiment, the pulse direct current mode is adopted in the bar magnet excitation, per cycle is divided three time periods, first time period excitation three axle quadrature coils 10,11 and 12 synthetic simulation bar magnets 1; Second time period excitation forms the synthetic simulation of three the quadrature coil (not shown)s bar magnet 2 of Magnetic Field Source 2; The 3rd time period do not encourage, and the magnetic induction density that the magnetic induction density that during using the excitation of simulation bar magnet, Magnetic Sensor records and the 3rd time period record subtracts each other the magnetic induction density produced at sensing station as the simulation bar magnet.The energisation mode of this pulse direct current is conducive to eliminate the eddy current interference that the environment metallics causes, and offsets the background magnetic field interference of terrestrial magnetic field and the generation of environment ferromagnetic material.For Magnetic Field Source 1 (situation of Magnetic Field Source 2 is identical, repeats no more) in first time period of pulse direct current Energizing cycle, the amplitude that gives on x axle transmitting coil 10 is A Sin (φ)The exciting current of ampere, the amplitude that gives on y axle transmitting coil 11 is A Cos (φ)The exciting current of ampere, give the exciting current of 0 ampere on z axle transmitting coil 12, take and synthesize size and be the A ampere, at the x-y Plane Rotation φThe bar magnet of degree, control φAt 0-2 π, change, when simulating the bar magnet orientation sensor in x-y plane projection direction, sensor can detect maximum magnetic induction, the record anglec of rotation now φ 1j .Afterwards, on x axle transmitting coil 10, giving amplitude is A Sin (φ 1j )* Sin (θ)The exciting current of ampere, the amplitude that gives on y axle transmitting coil 11 is A Cos (φ 1j )* Sin (θ)The exciting current of ampere ( φ 1j Namely simulate the anglec of rotation of bar magnet when the orientation sensor of x-y plane), on z axle transmitting coil 12, giving amplitude simultaneously is A Cos (θ)The exciting current of ampere, can synthesize at the simulation bar magnet hung down as for the x-y Plane Rotation; Control θIn 0-π (0-pi/2) scope, change, when simulation bar magnet orientation sensor, sensor can detect maximum magnetic induction, and vertical rotary angle now is designated as θ 1j .In said method, by changing φ, θCan realize simulating any sensing of bar magnet in space, and make its final Magnetic Sensor that points to;
Micromotion platform control module 29, be the movement of controlling micromotion platform X-axis 23, Y-axis 24 and Z axis 15, and drive thus that the Magnetic Sensor 26 be fixed on micromotion platform 5 moves to selected n1, n2, n3(overlaps with m1), on m2, five points of m3;
Sampling processing module 16 is that collection is detected from Magnetic Sensor 26 3 axles 6,7,8, through signal condition and AD conversion 9 digitizings the magnetic induction density signal, and by the mode of vector summing, these signals are synthesized to a magnetic flux density vector with size and Orientation.
The Magnetic Field Source 1 that algorithm unit 19 is recorded to according to above-mentioned steps, Magnetic Field Source 2 are from the anglec of rotation of initial position rotary search orientation sensor φ Ij , θ Ij ,Formula in summary of the invention (1)-(8), calculate the coordinate of initial point in the CS6 coordinate system of Magnetic Field Source 1 and Magnetic Field Source 2, realizes the demarcation to the Magnetic Field Source initial point; According to the formula in summary of the invention (9)-(21), obtain the rotation relationship between Magnetic Field Source 1 and Magnetic Field Source 2 initial position coordinates, realize the demarcation to the Magnetic Field Source initial attitude.
20 calibration results that algorithm unit 19 is obtained of demonstration output unit are exported and show.
Fig. 3 is the working-flow block diagram, illustrated and realized the links of demarcating and order, and by step 30-36, the final demarcation realized Magnetic Field Source initial point and initial attitude.
Figure 4 shows that the schematic diagram of realizing Magnetic Field Source origin position calibration algorithm 32.The present invention be take to the origin calibration of Magnetic Field Source 1 as the example explanation, can demarcate the initial point of more Magnetic Field Source (comprising Magnetic Field Source 2) by same procedure.The initial point of Magnetic Field Source 1 is positioned at the common center of three quadrature coils that form Magnetic Field Source 1, i.e. O1 point shown in Figure 4.According to what in measuring process 37, be recorded to φ Ij , θ Ij , can try to achieve the coordinate (x1, y1, z1) of Magnetic Field Source 1 in the CS6 coordinate system according to formula (1)-(8); In like manner can try to achieve the coordinate (x2, y2, z2) of Magnetic Field Source 2 in the CS6 coordinate system.
The purpose of Magnetic Field Source initial attitude calibration algorithm module 36, be in the situation that system comprises a plurality of Magnetic Field Source, obtains the rotation relationship between each Magnetic Field Source initial attitude.In the present embodiment, be the rotation relationship obtained between the initial attitude of Magnetic Field Source 1 and Magnetic Field Source 2.For this reason, defined 7 coordinate systems shown in table 1, the problem of calibrating of initial attitude has been converted into to the rotation relationship solved between coordinate system.The present invention, according to the rotary course of formula (9)-(21), finally obtains CS4 to the rotation relationship R between CS2 24.
So far, namely completed the electromagnetic tracking system Magnetic Field Source origin that formed by a plurality of Magnetic Field Source and the demarcation of initial attitude.Calibration result can be used for revising the location algorithm of electromagnetic tracking system, significantly improves the positioning precision of system.

Claims (2)

1. the calibration system of the Magnetic Field Source based on the electromagnetic tracking system of micromotion platform and rotating magnetic field, is characterized in that being comprised of following four parts: Magnetic Field Source, magnetic sensor device, control processes and displays device and three axle micromotion platforms; Wherein:
Described Magnetic Field Source has 2, forms by quadrature three axial coils and three corresponding control driving circuits; Three magnet coil geometric centers of quadrature three axial coils overlap; The initial point of the second Magnetic Field Source is on the X-axis of the first Magnetic Field Source, and the distance between two Magnetic Field Source initial points is d, and Y-axis and the Z axis of two Magnetic Field Source are parallel to each other; The electromagnet that forms Magnetic Field Source adopts constant current exciting mode, controls the exciting current intensity of every group by controlling the processes and displays device; The bar magnet that quadrature three axial coils point to arbitrarily in order to virtual space;
Described magnet sensor arrangement is fixed in three axle micromotion platforms, by three axle micromotion platforms, controls it and accurately moves in space, measures the magnetic induction density of three orthogonal directionss; Described triaxial magnetic field sensor device comprises: three axle component sensors, signal condition and analog-digital conversion module, three axle component sensors are used for respectively detecting the magnetic induction density of three orthogonal directions X ', Y ' and Z ', its output is sent into control processes and displays device through follow-up signal condition and analog-digital conversion module, and the sampling processing module samples in controlling the processes and displays device is processed;
Described control processes and displays device is comprised of control module, algorithm unit, demonstration output unit and three axle micromotion platform control modules, described control module comprises three parts: sampling processing module, exciting current strength control module and micromotion platform control module, the sampling processing module is the I/O mouth that microprocessor carries, for the signal of sampling processing from signal condition and analog-digital conversion module; Exciting current strength control module is the exciting current of microprocessor according to three quadrature coils of the corresponding Magnetic Field Source of the simulation bar magnet anglec of rotation that calculate, control driving circuit by I/O mouth controlling magnetic field source, provide the excitation of three axle quadrature coils is controlled, the simulation bar magnet of synthetic required sensing; The micromotion platform control module is that microprocessor passes through I/O mouth output signal, controls as requested the movement of three axles of micromotion platform, and drives thus the magnetic sensor device be fixed on micromotion platform and move on selected coordinate points;
Described algorithm unit, at microprocessor internal, according to the rotation angle information obtained in simulation magnetic bar rotation searching final orientation sensor process, is used the origin calibration algorithm, calculates the origin of the first Magnetic Field Source, the second Magnetic Field Source; Use the initial attitude calibration algorithm, the initial directional of each coordinate axis of the first calculating magnetic field source, the second Magnetic Field Source;
Described demonstration output unit is liquid crystal display and the I/O mouth be connected with microprocessor, for being exported and be shown on display by the calibration result that algorithm unit calculates;
Described three axle micromotion platform control modules, at microprocessor internal, are accurately controlled the movement of three axles of micromotion platform by the instruction of I/O mouth output as requested;
Described three axle micromotion platforms by three mutually orthogonal tracks and can be in orbit accurately mobile stationary installation form, be used to controlling magnetic sensor, accurately move in space.
2. one kind based on electromagnetic tracking system Magnetic Field Source initial point claimed in claim 1 and initial attitude scaling method, it is characterized in that, at first according to right-hand rule definition seven coordinate systems as shown in table 1, wherein CS1 is global coordinate system, CS6 is the micromotion platform coordinate system, the reference coordinate system while being also calibration;
Table 1 Coordinate system definition
The coordinate system title Abbreviation Describe Coordinate system 1 CS1 The original coordinate system of Magnetic Field Source 1 Coordinate system 2 CS2 The desirable original coordinate system of Magnetic Field Source 2 Coordinate system 3 CS3 When the x of Magnetic Field Source 1 axle is bar magnet axis direction orientation sensor, the actual coordinates of Magnetic Field Source 1 Coordinate system 4 CS4 When the x of Magnetic Field Source 2 axle is bar magnet axis direction orientation sensor, the actual coordinates of Magnetic Field Source 2 Coordinate system 5 CS5 The magnetic sensor coordinate system Coordinate system 6 CS6 The micromotion platform coordinate system Coordinate system 7 CS7 The actual original coordinate system of Magnetic Field Source 2
Concrete steps are as follows:
Step 1, by the calibration system initialization;
Step 2, by three axle micromotion platforms, control the magnetic sensor devices and shift to space known coordinate point;
Step 3, with the first Magnetic Field Source and the corresponding simulation bar magnet of the second Magnetic Field Source, search for and point to described magnetic sensor device;
The bar magnet that step 4, record the first Magnetic Field Source, the second Magnetic Field Source are simulated is from initial position to the horizontal and vertical rotation angle of pointing to magnetic sensor device process;
Step 5, judge whether three axle micromotion platforms have moved to the magnetic sensor device the selected known coordinate point in five, space, if be no, repeating step three, step 4; If be yes, go to step six;
Step 6, utilization Magnetic Field Source origin calibration algorithm, the origin of calculating the first Magnetic Field Source, the second Magnetic Field Source;
Step 7, utilization Magnetic Field Source initial attitude calibration algorithm, the initial directional of each coordinate axis of calculating the first Magnetic Field Source, the second Magnetic Field Source;
The described calibration system initialization of step 1, after referring to start, move/turn to initial position separately by controlling processes and displays device control three axle micromotion platforms, the first Magnetic Field Source and the second Magnetic Field Source;
Step 2 is described shifts to space known coordinate point by three axle micromotion platforms control magnetic sensor devices, is by three axle micromotion platform control modules, to control respectively three axles of micromotion platform to move, and the magnetic sensor device is placed in to selected known coordinate point; If selected known coordinate point is 5: n1, n2, n3, m2, m3, to establish m1 and overlap with n3, these coordinate points meet following condition:
Point-blank, and the spacing between n1, n2 equates with the spacing between n2, n3 for n1, n2, n3; M1, m2, m3 are on another straight line of the straight line parallel do not formed with n1, n2, n3, and the spacing between m1, m2 equates with the spacing between m2, m3;
Step 3 is described with the first Magnetic Field Source and the corresponding simulation bar magnet of the second Magnetic Field Source, search for and point to described magnetic sensor device, by the first Magnetic Field Source and the second Magnetic Field Source that exciting current strength control module alternative excitation is comprised of quadrature three axial coils, simulate two rotatable bar magnets; Concrete energisation mode is: the circle core shaft of crossing of establishing three quadrature coils that form Magnetic Field Source is respectively the x axle, the y axle, and the z axle, in first time period of Energizing cycle, the amplitude that gives on x axle transmitting coil is A Sin (φ)The exciting current of ampere, the amplitude that gives on y axle transmitting coil is A Cos (φ)The exciting current of ampere, take and synthesize size and be the A ampere, at the x-y Plane Rotation φThe bar magnet of degree, control φAt 0-2 π, change, when simulating the bar magnet orientation sensor in x-y plane projection direction, sensor can detect the maximum magnetic induction on the x-y plane; Afterwards, on x axle transmitting coil, giving amplitude is A Sin (φ Ij )* Sin (θ)The exciting current of ampere, the amplitude that gives on y axle transmitting coil is A Cos (φ Ij )* Sin (θ)The exciting current of ampere, φ Ij Namely simulate the anglec of rotation of bar magnet when the orientation sensor projection of x-y plane; Now on z axle transmitting coil, giving amplitude is A Cos (θ)The exciting current of ampere, namely synthesize at the simulation bar magnet hung down as for the x-y Plane Rotation; Control θIn 0-π scope, change, when simulation bar magnet orientation sensor, sensor detects maximum magnetic induction, and note is now simulated bar magnet and in the anglec of rotation of vertical plane is θ Ij
The bar magnet that described record the first Magnetic Field Source of step 4, the second Magnetic Field Source are simulated, from initial position to the horizontal and vertical rotation angle of pointing to magnetic sensor device process, namely horizontally rotates angle φ Ij With the vertical rotary angle θ Ij , wherein I=1-2Corresponding to two Magnetic Field Source, J=1-5Corresponding to the known point of five, space coordinate, lower same;
The described Magnetic Field Source origin of step 6 calibration algorithm, be recorded to according to step 4 φ Ij With θ Ij , calculating the first Magnetic Field Source, origin (x1, y1, z1), (x2, y2, the z2) of the second Magnetic Field Source in the micromotion platform coordinate system, its formula is:
Wherein (n1x, n1y, n1z) is the coordinate of n1 point in CS6, and the rest may be inferred for all the other, (x i, y i, z i) be the Magnetic Field Source origin; r I1, r I2, r I3, r I5, r I6By following one group of formula, calculated:
Wherein α Ij By following formula, obtained:
?,
i=1、2,? j=1、2、3、4;
The described Magnetic Field Source initial attitude of step 7 calibration algorithm, according to table 1, be expressed as R by CSr to the rotation relationship between CSs Rs, r=1-7, s=1-7, change into the rotation relationship of finding between the desirable original coordinate system CS2 of the second Magnetic Field Source and its current coordinate system CS4 to the demarcation of Magnetic Field Source initial attitude, namely obtain R 24:
, , For the anglec of rotation after being proofreaied and correct.
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