CN106983487B - Three-dimensional position and three-dimensional attitude positioning system and positioning method of wireless capsule endoscope - Google Patents

Abstract

The invention provides a three-dimensional position and three-dimensional attitude positioning system of a wireless capsule endoscope and a positioning method thereof, including a transmitting coil arranged outside the human body and having three axes orthogonal, an external wireless receiving module, an external position and attitude calculation module, and an internal The wireless capsule endoscope adopts a three-axis orthogonal transmitting coil arranged outside the human body, and only a two-axis orthogonal induction coil is arranged in the wireless capsule endoscope. The transmitting coil is placed near the human body, and the coil I of the transmitting coil is , Coil II and Coil III sequentially transmit signals of their respective fixed frequencies. After the three-axis transmitting coil transmits a signal once, it is called a cycle. For the calculation of the three-dimensional position and the three-dimensional attitude, the method is easy to integrate, the two-axis induction coil occupies a small space of the wireless capsule endoscope, and can continuously position the wireless capsule endoscope in real time, which is convenient for subsequent operations, safe, reliable, and low-cost.

Description

Positioning system and positioning of three-dimensional position and three-dimensional attitude of wireless capsule endoscope method

【Technical field】

The invention relates to a three-dimensional positioning technology, in particular to a positioning system and a positioning method for the three-dimensional position and three-dimensional attitude of a wireless capsule endoscope.

【Background technique】

At present, one of the shortcomings of the clinical wireless capsule endoscope is that it cannot be actively controlled. To achieve this actively controlled function and facilitate clinical use, the three-dimensional position and three-dimensional attitude information of the wireless capsule endoscope must be fed back to the control system in real time; At the same time, the visual navigation of the wireless capsule endoscope in the reconstructed digestive tract also requires three-dimensional position and three-dimensional attitude information, so that the doctor can easily control the wireless capsule endoscope.

In view of the above problems, in the prior art, X-ray imaging, CT (computed tomography) and MRI (magnetic resonance) imaging technologies are generally used for three-dimensional reconstruction to locate wireless capsule endoscopes. are affected, and there is damage to the rays, so it is not suitable for long-term positioning.

Given Imaging Company of Israel first proposed a wireless radio frequency (RF) signal positioning technology for wireless capsule endoscope positioning. It uses 8 wireless radio frequency antennas outside the human body to receive the radio frequency signals emitted by the wireless capsule endoscope in the body, and uses an algorithm to obtain the position of the wireless capsule endoscope. The method directly utilizes the radio frequency signal of the image transmitted by the wireless capsule endoscope, but has the disadvantage of low positioning accuracy, with an average positioning accuracy of 37.7 mm, and the clinical application effect is not good.

It has also been proposed to use permanent magnet positioning technology to locate wireless capsule endoscopes. A permanent magnet is placed inside the wireless capsule endoscope as a magnetic marker, multiple magnetic field sensors are arranged around the human body to measure the magnetic field at different points, and an algorithm is used to calculate the three-dimensional position and lens alignment (two-dimensional) direction of the wireless capsule endoscope. This technology has the advantages of high accuracy and fast positioning speed, but it cannot determine the direction change information of the wireless capsule endoscope rotating around the main axis. If this dimensional information is missing, the image captured by the wireless capsule endoscope cannot be used for 3D reconstruction of the digestive tract; In addition, since the magnetic field strength of the permanent magnet decays rapidly with the increase of the distance, the effective distance between the magnetic field sensor and the magnetic marker is difficult to meet the requirements of the size of the human body.

Some people have also proposed a positioning method based on permanent magnets and induction coils, that is, using a robotic arm to control the position and direction of the permanent magnets, allowing the permanent magnets to reciprocate under the action of the vibration module to generate a changing magnetic field, and the three-axis induction coil in the capsule outputs the output. Induced electromotive force. This method needs to arrange two three-axis induction coils in the wireless capsule endoscope for positioning, which increases the volume of the wireless capsule endoscope.

[Content of the invention]

In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a wireless capsule endoscope that uses only one two-axis induction coil, is easy to integrate, occupies a small space for the wireless capsule endoscope, can continuously position the wireless capsule endoscope in real time, and is convenient for subsequent operations. A positioning system and a positioning method for the three-dimensional position and three-dimensional attitude of a wireless capsule endoscope.

In order to realize the above-mentioned purpose of the invention, the technical scheme adopted in the present invention is:

The first purpose of the invention is to provide a positioning system for the three-dimensional position and three-dimensional attitude of a wireless capsule endoscope, including a transmitting coil disposed outside the human body and having three axes orthogonal, an external wireless receiving module, an external posture calculation module, and an internal The wireless capsule endoscope, the transmitting coil is composed of three-axis orthogonal coil I, coil II and coil III, the coil I, coil II and coil III sequentially transmit signals of their respective fixed frequencies, coil I, coil II , Coil III transmits a signal to form a cycle; the wireless capsule endoscope is provided with a two-axis orthogonal induction coil, and the two-axis orthogonal induction coil outputs three groups of different frequencies in one cycle corresponding to the transmitting coil The number of voltage signals of each group of different frequencies output by the two-axis orthogonal induction coil is two; a magnetic circuit is formed between the transmitting coil and the wireless capsule endoscope through an alternating magnetic field, and the wireless The capsule endoscope and the external wireless receiving module are connected by wireless signals, and the pose calculation module and the external wireless receiving module are directly connected.

Preferably, the wireless capsule endoscope further includes a signal amplification module, an AD conversion module and a wireless transmission module, the two-axis orthogonal induction coil is directly connected to the signal amplification module, and the signal amplification module is directly connected to the AD conversion module connected, the AD conversion module is directly connected with the wireless transmission module.

The second purpose of the present invention is to provide a method for locating the three-dimensional position and three-dimensional attitude of a wireless capsule endoscope, including the following steps:

Step 1. A three-axis orthogonal transmitting coil is set outside the human body, and a two-axis orthogonal induction coil is set in the wireless capsule endoscope, and the transmitting coil is composed of three-axis orthogonal coil I, coil II and coil III;

Step 2. The coordinate system OXYZ established by the three axes where the transmitting coil is located is used as the reference coordinate system, and the intersection of the two axes of the induction coil is set at the center point of the wireless capsule endoscope as the position of the wireless capsule endoscope, which is in the reference coordinate system The coordinate system O'u _x u _y u _z established by the two axes where the induction coil is located is used as the object coordinate system, and the unit vectors u _x and u _y are used to indicate the position of the wireless capsule endoscope. attitude;

Step 3. After the power is turned on, the coil I, the coil II and the coil III of the transmitting coil sequentially transmit signals of their respective fixed frequencies in each cycle;

Step 4. The amplification module in the wireless capsule endoscope amplifies the output voltage of the induction coil;

Step 5. The AD conversion module in the wireless capsule endoscope samples the amplified output voltage;

Step 6. The wireless sending module in the wireless capsule endoscope sends the sampling signal;

Step 7. The external wireless receiving module receives the sampling signal and sends it to the pose calculation module;

Step 8. The positioning process of the pose calculation module is as follows:

Solve for 9 parameters (x,y,z,u _xx ,u _xy ,u _xz ,u _yx ,u _yy ,u _yz ), where (u _xx ,u _xy ,u _xz ) and (u _yx ,u _yy ,u _yz ) respectively represent the projection components of u _x and u _y on the X, Y, and Z axes of the reference coordinate system;

The transmitting coil of each axis is equivalent to a magnetic dipole. According to Biosafal's law, the magnetic flux density generated by the magnetic dipole at the position of the wireless capsule endoscope is along the X, Y, Z of the reference coordinate system. The three orthogonal components of the axis are shown in equations (1), (2), (3):

Among them, (m, n, p) is the direction vector of the transmitting coil of each axis, (x, y, z) is the position of the induction coil, (a, b, c) is the position of the transmitting coil, and B _T is the position of the transmitting coil. A related constant, L is the distance from the induction coil to the transmitter coil, L is shown in formula (4):

Due to the deflection of the object coordinate system, the coordinate axis of the object coordinate system does not coincide with the coordinate axis of the reference coordinate system, the magnetic flux density generated by the transmitting coil at the position of the wireless capsule endoscope in the object coordinate system is the value given by formula (5). Show:

Among them, R is the azimuth matrix, as shown in formula (6), since there are only two induction coils, B' _z does not excite the coil output voltage;

in

(u _xx , u _xy , u _xz )＝u _x (7)

(u _yx , u _yy , u _yz )=u _y (8)

The output of the induction coil is an induced voltage signal. According to Faraday's law of electromagnetic induction, the induced electromotive force generated by the induction coil is shown in formula (9):

Among them, N is the number of turns of the induction coil, and φ is the magnetic flux passing through the curved surface S;

In the u _x and u _y directions, the relationship between the voltage signal output by the induction coil and the magnetic flux density is as follows:

Since the inductor coil is very small, its volume is ignored, and the magnetic flux density is considered to be equal everywhere in the inductor coil, so formulas (10) and (11) become the following formulas (12) and (13),

Because the direction of the induction coil is the same as the direction of the coordinate axis of the object coordinate system, the following formulas (14) and (15) are obtained,

If a sinusoidal signal of known frequency is emitted, the magnetic flux density in the object coordinate system can be described as the following formula (16):

So far, the relationship between the u _x and u _y axis output voltage values of the induction coil and the magnetic flux density on each axis of the object coordinate system can be obtained, as shown in formulas (17) and (18):

The output voltage signal of the induction coil is a cosine signal with the same frequency as the transmitted signal, and the amplitude of the signal is taken to establish a system of equations. Let E _Tx =-ω _x N _x ·S _x , E _Ty =-ω _y N _y ·S _y , E _Tz =-ω _z N _z ·S _z , the equations (19) and (20) are obtained as follows:

ε _{x max} = -ωN _x · B' _{x max} · S _x =E _Tx · B' _{x max} (19)

ε _{y max} =-ωN _y ·B' _{y max} ·S _y =E _Ty ·B' _{y max} (20)

The methods of extracting the amplitude and phase of the cosine signal include fast Fourier transform or function fitting methods;

If the transmitting coils of the three axes excite the sinusoidal signals of their respective fixed frequencies in turn, the induction coils of the two axes induce a total of 6 groups of alternating signals, so that 6 equations can be established. Since 9 unknown parameters need to be solved, 3 more Equation; since u _x and u _y take unit vectors and are perpendicular to each other, the following three constraint equations are added, and the three equations (21), (22), (23) are as follows:

u _xx .u _yx +u _xy .u _yy +u _xz .u _yz =0 (23)

The three axes of the transmitting coil are analyzed as follows:

Coil I corresponds to the X-axis of the reference coordinate system, and its position and orientation parameters are

(a, b, c) = (0, 0, 0)

(m,n,p)=(1,0,0)

Bringing it into equations (1), (2) and (3), we get equations (24), (25) and (26) as follows:

Coil II corresponds to the Y-axis of the reference coordinate system, and its position and orientation parameters are

(a, b, c) = (0, 0, 0)

(m,n,p)=(0,1,0)

Bringing this into equations (1), (2) and (3), we get equations (27), (28) and (29) as follows:

Coil III corresponds to the Z axis of the reference frame, and its position and orientation parameters are

(a, b, c) = (0, 0, 0)

(m,n,p)=(0,0,1)

Bringing it into equations (1), (2) and (3), we get equations (30), (31) and (32) as follows:

According to formulas (5), (19) and (20), formula (33) is redefined as follows:

Among them, B _{ix max} , B _{iy max} and B _{iz max} are respectively the magnetic flux density generated at the induction coil along the X, Y and Z axes of the reference coordinate system when the coil I, coil II and coil III of the three-axis transmitting coil transmit. The amplitudes of the three components are the amplitudes of B _ix , B _iy and B _iz ; ε _{ix max} and ε _{iy max} are respectively the coil I, coil II and coil III of the three-axis transmitting coil. The theoretical amplitude of the u _x and u _y -axis induced voltages of the two-axis induction coil in the mirror, ε _{iz max} has no induction coil output, so it does not participate in the calculation;

Let ε′ _{ix max} and ε′ _{iy max} be the actual output values of the u _x and u _y -axis induced voltages of the two-axis induction coil in the wireless capsule endoscope when the coil I, coil II and coil III of the transmitting coil transmit, respectively, That is, the measured value, the formula (34) that defines the error E is as follows:

Using optimization algorithms such as Levenberg-Marquardt or Gauss-Newton algorithm to minimize E, the pose parameters (x, y, z, u _xx , u _xy , u _xz , u _yx , u ) of the wireless capsule endoscope can be solved _yy , u _yz );

Step 9: The pose calculation module sends the pose information of the wireless capsule endoscope to the display terminal, and reflects the current pose of the wireless capsule endoscope in real time, which is convenient for the operator to observe or follow-up application.

The beneficial effects of the present invention are:

In the present invention, a three-axis orthogonal transmitting coil is arranged outside the human body, and only one two-axis orthogonal induction coil is arranged in the wireless capsule endoscope. The transmitting coil is placed near the human body, and the coil I, coil II and Coil III transmits signals of their respective fixed frequencies in sequence. After the three-axis transmitting coil transmits a signal once, it is called a cycle. The two-axis induction coil induces and outputs three sets of voltage signals of different frequencies in one cycle, thereby establishing a system of equations for wireless capsule endoscopy. The calculation of the three-dimensional position and three-dimensional attitude of the mirror is convenient for integration, and the two-axis induction coil occupies a small space of the wireless capsule endoscope.

【Description of drawings】

Fig. 1 is the enlarged structural schematic diagram of the external three-axis transmitting coil of the present invention and the corresponding internal two-axis coil of the wireless capsule endoscope;

Fig. 2 is a positioning flow chart of the present invention.

【Detailed ways】

In order to make the above objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The positioning system of the three-dimensional position and three-dimensional attitude of the wireless capsule endoscope, as shown in Figure 1, includes a transmitting coil set outside the human body and three-axis orthogonal, an external wireless receiving module, an external posture calculation module and a wireless capsule located in the body. In the endoscope, the transmitting coil is composed of three-axis orthogonal coil I, coil II and coil III. The coil I, coil II and coil III transmit signals of respective fixed frequencies in sequence. Coil I, coil II and coil III One cycle is formed after one signal is transmitted; the wireless capsule endoscope is provided with a two-axis orthogonal induction coil, and the two-axis orthogonal induction coil outputs three groups of voltage signals with different frequencies in one cycle corresponding to the transmitting coil , and the number of voltage signals of each group of different frequencies output by the two-axis orthogonal induction coil is two; a magnetic circuit is formed between the transmitting coil and the wireless capsule endoscope through an alternating magnetic field, and the wireless capsule endoscope forms a magnetic circuit. The mirror and the external wireless receiving module are connected by wireless signals, and the pose calculation module and the external wireless receiving module are directly connected.

The wireless capsule endoscope further includes a signal amplification module, an AD conversion module and a wireless transmission module. The two-axis orthogonal induction coil is directly connected to the signal amplification module, and the signal amplification module is directly connected to the AD conversion module. The AD conversion module is directly connected with the wireless transmission module.

The method for locating the three-dimensional position and three-dimensional attitude of the wireless capsule endoscope in this embodiment, as shown in FIG. 2 , includes the following steps:

Step 1. A three-axis orthogonal transmitting coil is set outside the human body, and a two-axis orthogonal induction coil is set in the wireless capsule endoscope, and the transmitting coil is composed of three-axis orthogonal coil I, coil II and coil III;

Step 2. The coordinate system OXYZ established by the three axes where the transmitting coil is located is used as the reference coordinate system, and the intersection of the two axes of the induction coil is set at the center point of the wireless capsule endoscope as the position of the wireless capsule endoscope, which is in the reference coordinate system The coordinate system O'u _x u _y u _z established by the two axes where the induction coil is located is used as the object coordinate system, and the unit vectors u _x and u _y are used to indicate the position of the wireless capsule endoscope. attitude;

Step 3. After the power is turned on, the coil I, the coil II and the coil III of the transmitting coil sequentially transmit signals of their respective fixed frequencies in each cycle;

Step 4. The amplification module in the wireless capsule endoscope amplifies the output voltage of the induction coil;

Step 5. The AD conversion module in the wireless capsule endoscope samples the amplified output voltage;

Step 6. The wireless sending module in the wireless capsule endoscope sends the sampling signal;

Step 7. The external wireless receiving module receives the sampling signal and sends it to the pose calculation module;

Step 8. The positioning process of the pose calculation module is as follows:

Solve for 9 parameters (x,y,z,u _xx ,u _xy ,u _xz ,u _yx ,u _yy ,u _yz ), where (u _xx ,u _xy ,u _xz ) and (u _yx ,u _yy ,u _yz ) respectively represent the projection components of u _x and u _y on the X, Y, and Z axes of the reference coordinate system;

The transmitting coil of each axis is equivalent to a magnetic dipole. According to Biosafar's law, the magnetic flux density generated by the magnetic dipole at the position of the wireless capsule endoscope is along the X, Y, and Z axes of the reference coordinate system. The three orthogonal components of are shown in formulas (1), (2), (3):

Among them, (m, n, p) is the direction vector of the transmitting coil of each axis, (x, y, z) is the position of the induction coil, (a, b, c) is the position of the transmitting coil, and B _T is the position of the transmitting coil. A related constant, L is the distance from the induction coil to the transmitter coil, L is shown in formula (4):

Due to the deflection of the object coordinate system, the coordinate axis of the object coordinate system does not coincide with the coordinate axis of the reference coordinate system, the magnetic flux density generated by the transmitting coil at the position of the wireless capsule endoscope in the object coordinate system is the value given by formula (5). Show:

Among them, R is the azimuth matrix, as shown in formula (6), since there are only two induction coils, B' _z does not excite the coil output voltage;

in

(u _xx , u _xy , u _xz )＝u _x (7)

(u _yx , u _yy , u _yz )=u _y (8)

The output of the induction coil is an induced voltage signal. According to Faraday's law of electromagnetic induction, the induced electromotive force generated by the induction coil is shown in formula (9):

Among them, N is the number of turns of the induction coil, and φ is the magnetic flux passing through the curved surface S;

In the u _x and u _y directions, the relationship between the voltage signal output by the induction coil and the magnetic flux density is as follows:

Since the inductor coil is very small, its volume is ignored, and the magnetic flux density is considered to be equal everywhere in the inductor coil, so formulas (10) and (11) become the following formulas (12) and (13),

Because the direction of the induction coil is the same as the direction of the coordinate axis of the object coordinate system, the following formulas (14) and (15) are obtained,

If a sinusoidal signal with a known frequency is emitted, other signals can also be used. The present invention is not limited to this. The magnetic flux density in the object coordinate system can be described as the following formula (16):

So far, the relationship between the output voltage values of the u _x and u _y axes of the induction coil and the magnetic flux density on each axis of the object coordinate system can be obtained, as shown in formulas (17) and (18):

The output voltage signal of the induction coil is a cosine signal with the same frequency as the transmitted signal, and the amplitude of the signal is taken to establish a system of equations. Let E _Tx =-ω _x N _x ·S _x , E _Ty =-ω _y N _y ·S _y , E _Tz =-ω _z N _z ·S _z , the equations (19) and (20) are obtained as follows:

ε _{x max} = -ωN _x · B' _{x max} · S _x =E _Tx · B' _{x max} (19)

ε _{y max} =-ωN _y ·B' _{y max} ·S _y =E _Ty ·B' _{y max} (20)

The method for extracting the amplitude and phase of the cosine signal includes fast Fourier transform or function fitting method, and other methods can also be used, the present invention is not limited to this,

The transmitting coils of the three axes excite sinusoidal signals of different frequencies in turn, and the two-axis induction coils induce a total of 6 groups of alternating signals, so that 6 equations can be established. Since 9 unknown parameters are required to be solved, 3 equations are required; Since u _x and u _y take unit vectors and are perpendicular to each other, the following three constraint equations are added. The three equations (21), (22), (23) are as follows:

u _xx .u _yx +u _xy .u _yy +u _xz .u _yz =0 (23)

The three axes of the transmitting coil are analyzed as follows:

Coil I corresponds to the X-axis of the reference coordinate system, and its position and orientation parameters are

(a, b, c) = (0, 0, 0)

(m,n,p)=(1,0,0)

Bringing it into equations (1), (2) and (3), we get equations (24), (25) and (26) as follows:

Coil II corresponds to the Y-axis of the reference coordinate system, and its position and orientation parameters are

(a, b, c) = (0, 0, 0)

(m,n,p)=(0,1,0)

Bringing this into equations (1), (2) and (3), we get equations (27), (28) and (29) as follows:

Coil III corresponds to the Z axis of the reference frame, and its position and orientation parameters are

(a, b, c) = (0, 0, 0)

(m,n,p)=(0,0,1)

Bringing it into equations (1), (2) and (3), we get equations (30), (31) and (32) as follows:

According to formulas (5), (19) and (20), formula (33) is redefined as follows:

Among them, B _{ix max} , B _{iy max} and B _{iz max} are respectively the magnetic flux density generated at the induction coil along the X, Y and Z axes of the reference coordinate system when the coil I, the coil II and the coil III of the three-axis transmitting coil transmit. The amplitudes of the three components are the amplitudes of B _ix , B _iy and B _iz ; ε _{ix max} and ε _{iy max} are respectively the coil I, coil II and coil III of the three-axis transmitting coil. The theoretical amplitude of the u _x and u _y -axis induced voltages of the two-axis induction coil in the mirror, ε _{iz max} has no induction coil output, so it does not participate in the calculation;

Let ε′ _{ix max} and ε′ _{iy max} be the actual output values of the u _x and u _y -axis induced voltages of the two-axis induction coil in the wireless capsule endoscope when the coil I, coil II and coil III of the transmitting coil transmit, respectively, That is, the measured value, the formula (34) that defines the error E is as follows:

Using an optimization algorithm such as Levenberg-Marquardt or Gauss-Newton algorithm, other methods can also be used, the present invention is not limited to this, and the pose parameters of the wireless capsule endoscope (x, y, z, u _xx , u _xy ,u _xz ,u _yx ,u _yy ,u _yz );

Step 9: The pose calculation module sends the pose information of the wireless capsule endoscope to the display terminal, and reflects the current pose of the wireless capsule endoscope in real time, which is convenient for the operator to observe or follow-up application.

The above-mentioned embodiments are only preferred embodiments of the present invention, and are not intended to limit the scope of implementation of the present invention. Except for the cases listed in the specific embodiments, all equivalent changes made according to the principles of the present invention shall be covered in within the protection scope of the present invention.

Claims (3)

1. A positioning system for the three-dimensional position and three-dimensional attitude of a wireless capsule endoscope, including a transmitting coil arranged outside the human body and having three axes orthogonal, an external wireless receiving module, an external posture calculation module and a wireless capsule endoscope located in the body, It is characterized by: The transmitting coil is composed of three-axis orthogonal coil I, coil II and coil III. The coil I, coil II and coil III transmit signals of their respective fixed frequencies in sequence, and the coil I, coil II and coil III transmit the signal once. form a cycle; The wireless capsule endoscope is provided with two-axis orthogonal induction coils, and the two-axis orthogonal induction coils output three groups of voltage signals of different frequencies in one cycle corresponding to the transmitting coil, and the two-axis orthogonal induction coils. The number of voltage signals of each group of different frequencies output by the coil is two; A magnetic circuit is formed between the transmitting coil and the wireless capsule endoscope through an alternating magnetic field, the wireless capsule endoscope and the external wireless receiving module are connected by wireless signals, and the pose calculation module is connected to the external wireless receiving module. direct connection between. 2 . The three-dimensional position and three-dimensional attitude positioning system of the wireless capsule endoscope according to claim 1 , wherein the wireless capsule endoscope further comprises a signal amplification module, an AD conversion module and a wireless transmission module, and the The two-axis orthogonal induction coil is directly connected to the signal amplification module, the signal amplification module is directly connected to the AD conversion module, and the AD conversion module is directly connected to the wireless transmission module. 3. A method for locating a three-dimensional position and a three-dimensional attitude of a wireless capsule endoscope, wherein the wireless capsule endoscope is provided with two-axis orthogonal induction coils, characterized in that it comprises the following steps: Step 1. Set up a three-axis orthogonal transmitting coil outside the human body, and the transmitting coil is composed of three-axis orthogonal coil I, coil II and coil III; Step 2. The coordinate system OXYZ established by the three axes where the transmitting coil is located is used as the reference coordinate system, and the intersection of the two axes of the induction coil is set at the center point of the wireless capsule endoscope as the position of the wireless capsule endoscope, which is in the reference coordinate system The coordinate system O'u _x u _y u _z established by the two axes where the induction coil is located is used as the object coordinate system, and the unit vectors u _x and u _y are used to indicate the position of the wireless capsule endoscope. attitude; Step 3. After the power is turned on, the coil I, the coil II and the coil III of the transmitting coil sequentially transmit signals of their respective fixed frequencies in each cycle; Step 4. The amplification module in the wireless capsule endoscope amplifies the output voltage of the induction coil; Step 5. The AD conversion module in the wireless capsule endoscope samples the amplified output voltage; Step 6. The wireless sending module in the wireless capsule endoscope sends the sampling signal; Step 7. The external wireless receiving module receives the sampling signal and sends it to the pose calculation module; Step 8. The positioning process of the pose calculation module is as follows: Solve for 9 parameters (x,y,z,u _xx ,u _xy ,u _xz ,u _yx ,u _yy ,u _yz ), where (u _xx ,u _xy ,u _xz ) and (u _yx ,u _yy ,u _yz ) respectively represent the projection components of u _x and u _y on the X, Y, and Z axes of the reference coordinate system; The transmitting coil of each axis is equivalent to a magnetic dipole. According to Biosafal's law, the magnetic flux density generated by the magnetic dipole at the position of the wireless capsule endoscope is along the X, Y, Z of the reference coordinate system. The three orthogonal components of the axis are shown in equations (1), (2), (3): Among them, (m, n, p) is the direction vector of the transmitting coil of each axis, (x, y, z) is the position of the induction coil, (a, b, c) is the position of the transmitting coil, and B _T is the position of the transmitting coil. A related constant, L is the distance from the induction coil to the transmitter coil, L is shown in formula (4): Since the object coordinate system is deflected, the coordinate axis of the object coordinate system does not coincide with the coordinate axis of the reference coordinate system, and the magnetic flux density generated by the transmitting coil at the position of the wireless capsule endoscope in the object coordinate system is the value given by formula (5). Show: Among them, R is the azimuth matrix, as shown in formula (6), since there are only two induction coils, B' _z does not excite the coil output voltage; in (u _xx , u _xy , u _xz )＝u _x (7) (u _yx , u _yy , u _yz )=u _y (8) The output of the induction coil is an induced voltage signal. According to Faraday's law of electromagnetic induction, the induced electromotive force generated by the induction coil is shown in formula (9): Among them, N is the number of turns of the induction coil, and φ is the magnetic flux passing through the curved surface S; In the u _x and u _y directions, the relationship between the voltage signal output by the induction coil and the magnetic flux density is as follows: Since the inductor coil is small, its volume is ignored, and the magnetic flux density is considered equal everywhere in the inductor coil, so formulas (10) and (11) become the following formulas (12) and (13), Because the direction of the induction coil is the same as the direction of the coordinate axis of the object coordinate system, the following formulas (14) and (15) are obtained, If a sinusoidal signal of known frequency is emitted, the magnetic flux density in the object coordinate system can be described as the following formula (16): So far, the relationship between the output voltage value of the induction coil u _x , u _y axis and the magnetic flux density on each axis of the object coordinate system can be obtained, as shown in formulas (17) and (18): The output voltage signal of the induction coil is a cosine signal with the same frequency as the transmitted signal, and the amplitude of the signal is taken to establish a system of equations. Let E _Tx =-ω _x N _x ·S _x , E _Ty =-ω _y N _y ·S _y , E _Tz =-ω _z N _z ·S _z , equations (19) and (20) are obtained as follows: ε _xmax = -ωN _x · B' _xmax · S _x =E _Tx · B' _xmax (19) ε _ymax =-ωN _y ·B' _ymax ·S _y =E _Ty ·B' _ymax (20) The methods of extracting the amplitude and phase of the cosine signal include fast Fourier transform or function fitting; If the transmitting coils of the three axes excite the sinusoidal signals of their respective fixed frequencies in turn, the two-axis induction coils induce a total of 6 groups of alternating signals, so that 6 equations can be established. Since 9 unknown parameters need to be solved, 3 equations are needed. ; Since u _x and u _y take unit vectors and are perpendicular to each other, the following three constraint equations are added, and the three equations (21), (22), (23) are as follows: u _xx .u _yx +u _xy .u _yy +u _xz .u _yz =0 (23) The three axes of the transmitting coil are analyzed as follows: Coil I corresponds to the X-axis of the reference coordinate system, and its position and orientation parameters are (a, b, c) = (0, 0, 0) (m,n,p)=(1,0,0) Bringing this into equations (1), (2) and (3), we get equations (24), (25) and (26) as follows: Coil II corresponds to the Y-axis of the reference coordinate system, and its position and orientation parameters are (a, b, c) = (0, 0, 0) (m,n,p)=(0,1,0) Bringing it into equations (1), (2) and (3), we get equations (27), (28) and (29) as follows: Coil III corresponds to the Z axis of the reference frame, and its position and orientation parameters are (a, b, c) = (0, 0, 0) (m,n,p)=(0,0,1) Bringing it into equations (1), (2) and (3), we get equations (30), (31) and (32) as follows: According to formulas (5), (19) and (20), formula (33) is redefined as follows: Among them, B _ixmax , B _iymax and B _izmax are the three components of the magnetic flux density generated at the induction coil along the X, Y and Z axes of the reference coordinate system when the coil I, the coil II and the coil III of the three-axis transmitting coil are respectively transmitted. is the amplitude of B _ix , B _iy and B _iz ; ε _ixmax and ε _iymax are the two-axis induction in the wireless capsule endoscope when coil I, coil II and coil III of the three-axis transmitting coil transmit, respectively. The theoretical amplitude of the induced voltage of the u _x and u _y axes of the coil, ε _izmax has no corresponding induction coil output, so it does not participate in the calculation; Let ε' _ixmax and ε' _iymax be the actual output values of the induced voltages of the u _x and u _y axes of the two-axis induction coil in the wireless capsule endoscope when the coil I, coil II and coil III of the transmitting coil are respectively transmitting, that is, the measurement value, the formula (34) that defines the error E is as follows: Using the optimization algorithm Levenberg-Marquardt or Gauss-Newton algorithm to minimize E, the pose parameters of the wireless capsule endoscope (x, y, z, u _xx , u _xy , u _xz , u _yx , u _yy , u _yz ); Step 9: The pose calculation module sends the pose information of the wireless capsule endoscope to the display terminal, so as to reflect the current pose of the wireless capsule endoscope in real time, which is convenient for the operator to observe or follow-up application.