A dynamic tilt sensor measurement system for mobile CT

Abstract

The present invention relates to a dynamic tilt sensor measurement system for mobile CT, comprising: a posture collector: used to collect acceleration and angular velocity data of the tilted part of the mobile CT machine in real time; a compensation calibration module: connected to the posture collector, used to perform compensation calibration on the acceleration data and angular velocity data; a posture solution module: connected to the compensation calibration module, used to perform EKF posture fusion based on quaternion to obtain posture angle data; a tilt judgment module: respectively connected to the compensation calibration module and the posture solution module, used to judge whether the mobile CT machine is in a tilt state according to the real-time angular velocity; an angle filtering module: connected to the posture solution module, used to perform angle filtering on the posture angle output by the tilt judgment module according to the chi-square test value; a data communication module: respectively connected to the posture solution module and the angle filtering module, used to output the final posture angle data. Compared with the prior art, the present invention has the advantages of good real-time performance, high stability and strong vibration resistance.

Description

Technical Field

[0001] The invention relates to the field of inclination sensor measurement, and in particular to a dynamic inclination sensor measurement system for mobile CT. Background Art

[0002] When the rotating parts of the CT machine rotate, it will cause continuous vibration to the whole machine, especially when the rotating parts of the mobile CT machine are turned on and rotated on the moving guide rail, the vibration brought to the whole machine is more severe; during the EMC test of the whole machine, the CT machine will make horizontal circular motion as the test platform rotates, and motion acceleration will be introduced during the rotation process, especially during starting and stopping; in addition, when the mobile CT machine moves in a straight line along the guide rail, motion acceleration will also be introduced.

[0003] The dynamic inclination sensor for mobile CT machines is required to output angle data in real time and accurately when the tilting parts of the CT machine are tilting when the CT machine is fixed. It is also required to output angle data stably without sudden changes when the CT machine is not tilting, moving in a straight line along the guide rail, rotating horizontally with the test platform during EMC testing, and being impacted or struck.

[0004] In the current existing methods, by using the EKF algorithm to solve the gyroscope attitude, the angle of the sensor during tilt can be accurately output in real time, and it has a certain degree of vibration resistance. Motion acceleration can easily affect the accuracy of filtering. The chi-square test can identify the motion acceleration, thereby controlling or eliminating the degree to which the accelerometer participates in the measurement when the motion acceleration is too large, which can improve the impact of short-term motion acceleration on the calculation results.

[0005] However, when the mobile CT machine moves on the rail, the rotating parts continue to rotate, causing the entire CT machine to vibrate violently. In addition, the horizontal movement will make the movement acceleration even greater. In addition, the CT machine rotates horizontally for a long time on the EMC test platform, which will also be affected by the continuous movement acceleration. At this time, the EKF algorithm with the chi-square test will always limit the accelerometer from participating in the measurement, and the system will trust the gyroscope more. However, the gyroscope will also deviate in a long-term vibration environment, greatly reducing the detection accuracy. Summary of the invention

[0006] In order to solve the technical problems in the background technology, the present invention provides a dynamic tilt sensor measurement system for mobile CT, the system comprising:

[0007] Attitude collector: used to collect acceleration data and angular velocity data of the tilted part of the mobile CT machine in real time;

[0008] Compensation calibration module: connected to the attitude collector to perform compensation calibration on acceleration data and angular velocity data;

[0009] Attitude calculation module: connected with the compensation calibration module, used to perform quaternion-based EKF attitude fusion on acceleration data and angular velocity data to obtain attitude angle data;

[0010] Tilt judgment module: connected to the compensation calibration module and the attitude solution module respectively, to judge whether the mobile CT machine is in a tilted state according to the real-time angular velocity;

[0011] Angle filtering module: connected to the attitude solving module, used to perform angle filtering on the attitude angle output by the tilt judging module according to the chi-square test value;

[0012] Data communication module: connected to the attitude calculation module and the angle filtering module respectively to output the final attitude angle data.

[0013] Furthermore, the posture collector includes a three-axis accelerometer for collecting acceleration data of the tilted part of the mobile CT machine in real time and a MEMS gyroscope for collecting angular velocity data of the tilted part of the mobile CT machine in real time.

[0014] Furthermore, the attitude compensation module is used to perform power-on initial zero bias calibration and temperature compensation on the three-axis accelerometer and the MEMS gyroscope, respectively, and to perform offset error calibration and sensitivity error calibration on the three-axis accelerometer.

[0015] Furthermore, the attitude solution module uses the quaternion-based EKF attitude fusion algorithm to fuse the acceleration and angular velocity data after compensation calibration, obtains the current optimal quaternion and the three-axis zero bias data of the MEMS gyroscope, and converts the quaternion into attitude angle data output.

[0016] Furthermore, the quaternion-based EKF attitude fusion algorithm specifically includes the following steps:

[0017] 1) Construct the state equation and observation equation, then we have:

[0018] The state equation expression is:

[0019] x k+1 =f(x k )+ω k

[0020]

[0021] Among them, x k is the state vector, f(·) represents the nonlinear function, ω k is process noise, subscript k represents time k, q=[q0,q1,q2,q3] T is the attitude quaternion of the body coordinate system relative to the inertial coordinate system, and ω bias =[ω bias_x ,ω bias_y ,ω bias_z ] T is the zero bias of the gyroscope corresponding to the X-axis, Y-axis, and Z-axis;

[0022] The expression of the observation equation is:

[0023] z k =h(x k )+v k

[0024]

[0025] Among them, z k is the measurement vector, which is the acceleration data after temperature compensation and zero bias calibration, h(·) represents the nonlinear function, v k is the observation noise;

[0026] 2) Perform the Kalman filtering process and calculate the chi-square test value r at the current time k k .

[0027] Furthermore, the tilt judgment module is based on the angular velocity data collected and compensated and calibrated by the MEMS gyroscope minus the real-time zero bias data ω of the MEMS gyroscope output by the attitude solution module. bias The real-time angular velocity ω obtained after zero bias calibration is used to judge the tilt state, specifically:

[0028] If the real-time angular velocity ω shows an increasing trend and rises from 0 rad / s within the set time period Tr and exceeds the judgment threshold ω max , and continues to be greater than the judgment threshold ω max If the time exceeds the set time Tc, it is judged that the mobile CT machine enters the forward state;

[0029] If the real-time angular velocity ω shows a decreasing trend and decreases from 0 rad / s within the set time period Tr and is lower than the judgment threshold -ω max , and is continuously less than the judgment threshold -ω max If the time exceeds the set time Tc, it is judged that the mobile CT machine enters the reverse state;

[0030] The forward state and the reverse state are both determined as tilted states. When the mobile CT machine is in a tilted state, if the real-time angular velocity returns to 0 rad / s and exceeds the set time Tc, it is considered to be in a non-tilted state.

[0031] Furthermore, when the mobile CT machine is in a tilted state, the posture calculation module directly outputs the posture angle data through the data communication module. When the mobile CT machine is in a non-tilted state, the posture angle data output by the posture calculation module is subjected to first-order parameter adaptive filtering by the angle filtering module and then output through the data communication module.

[0032] Furthermore, the filtering process of the angle filtering module is specifically as follows:

[0033] 1) When the acceleration data acc collected by the three-axis accelerometer in real time is within the set time period t x The change in the value exceeds the set threshold acc x , or the chi-square test value r at the current moment k When the value exceeds the first threshold value r0, filtering is started. If the filtering parameter a<a0, a=a0 is set, where a0 is the first filtering parameter threshold value and a0>1;

[0034] 2) When the chi-square test value r k When the second threshold value r1 is exceeded, the chi-square test value r k Perform first-order parameter adaptive filtering;

[0035] 3) When the chi-square test value r k If the third threshold value r2 is exceeded, or the root mean square deviation of the three-axis acceleration from 1 exceeds the set threshold, the angle update of the first-order parameter adaptive filter is limited so that the filter output value at the current moment takes the filter output value at the previous moment.

[0036] Furthermore, in step 2), the filtering formula of the first-order parameter adaptive filtering is:

[0037]

[0038] Among them, y(k) and y(k-1) are the filter outputs at time k and k-1 respectively, and x(k) is the sampling value at time k, that is, the attitude angle output by the attitude solution module at time k.

[0039] Furthermore, in step 2), the adaptive adjustment of the filtering parameters of the first-order parameter adaptive filtering is specifically as follows:

[0040] If r k ×Gain<a0, then let a=a0;

[0041] If r k ×Gain>a max , then let a=a max ;

[0042] If a0≤r k ×Gain≤a max , then let a=rk ×Gain, where Gain is the set gain.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] The present invention divides the state of the mobile CT machine into an inclined state and a non-inclined state according to the real-time angular velocity. In the inclined state, the attitude angle data output by the attitude fusion module is directly used to ensure the real-time performance of the output angle; in the non-inclined state, parameter adaptive filtering is performed according to the motion acceleration and the chi-square test value, and the angle update is temporarily stopped when the motion acceleration exceeds the threshold, and the last angle value is directly output to ensure that the product has anti-vibration, anti-impact and anti-collision performance when it is not tilted, which meets the use requirements of the mobile CT machine under horizontal movement and horizontal rotation conditions, and has both real-time performance, stability and vibration resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a structural block diagram of the tilt sensor measurement system of the present invention;

[0046] Figure 2 A flow chart of the steps performed for the compensation calibration module;

[0047] Figure 3 A flow chart of the steps for temperature compensation using a linear interpolation method;

[0048] Figure 4 It is the principle block diagram of the EKF algorithm based on quaternion;

[0049] Figure 5 The schematic diagram of the process for dynamically adjusting the filtering parameters;

[0050] Figure 6 It is a flow chart of the dynamic tilt angle detection steps of the present invention. DETAILED DESCRIPTION

[0051] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0052] It should be noted that in this specification, similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0053] In the description of this embodiment, it should be noted that the terms "upper", "lower", "inner", "bottom", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0054] The terms “first”, “second”, etc. are only used for distinguishing descriptions and should not be understood as indicating or implying relative importance.

[0055] In the description of this embodiment, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this embodiment can be understood according to specific circumstances.

[0056] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0057] Example

[0058] The present invention provides a dynamic tilt sensor measurement system for a mobile CT, which is used to accurately measure the tilt angle of a tilted part of a mobile CT machine when the mobile CT machine is in a normal working state, moves, or moves. The mobile CT machine is generally installed on a guide rail, and includes a scanning bed and a scanning frame. The scanning frame includes a scanning part and a tilting part for tilting the scanning part. Usually, the scanning part of the mobile CT machine will not stop. When the mobile CT machine needs to be moved, it is required to move the mobile CT machine to a suitable position along the guide rail after the tilting part is kept horizontal. Therefore, it is necessary to maintain continuous, reliable, and accurate angle monitoring of the tilting part during this process.

[0059] like Figure 1 As shown, the measurement system includes a posture collector, a compensation calibration module, a posture solution module, a tilt judgment module, an angle filtering module and a data communication module.

[0060] In this example, if Figure 6As shown, the attitude collector is used to collect the acceleration and angular velocity data of the tilted part in real time. The compensation calibration module is connected to the attitude collector to realize the initial zero bias calibration, offset error offset calibration, sensitivity error calibration and temperature compensation of the three-axis accelerometer and the MEMS gyroscope, and the data after compensation calibration are sent to the attitude solution module, the tilt judgment module and the angle filtering module respectively. The attitude solution module performs EKF attitude fusion based on quaternion according to the acceleration data and angular velocity data after compensation calibration to obtain the attitude angle data, and sends it through the data communication module. The tilt judgment module is respectively connected to the compensation calibration module and the attitude solution module to determine whether the tilted part of the mobile CT machine is in a tilted state according to the real-time angular velocity. The angle filtering module is respectively connected to the compensation calibration module, the attitude solution module and the data communication module to filter the output angle of the tilted part of the mobile CT machine when it is in a non-tilted state according to the judgment result of the tilt judgment module and the acceleration data output by the compensation calibration module, so as to prevent the mobile CT machine from being unstable or causing a jump alarm due to the influence of motion acceleration brought by linear motion, impact, collision and / or horizontal rotation.

[0061] The attitude calculation module, compensation calibration module, tilt judgment module, angle filtering module and data communication module are described in detail below.

[0062] (1) Posture Collector

[0063] The attitude collector is used to collect the acceleration and angular velocity data of the tilted part in real time and send them to the compensation calibration module. In this example, the attitude collector specifically adopts a six-axis MEMS gyroscope chip including a three-axis accelerometer and a MEMS gyroscope. The real-time acceleration data collected by the three-axis accelerometer and the three-axis angular velocity data collected by the MEMS gyroscope are input into the compensation calibration module.

[0064] (2) Compensation calibration module

[0065] like Figure 2 As shown, the compensation calibration content of the compensation calibration module in the present invention includes initial zero bias calibration, offset error calibration, sensitivity calibration and temperature compensation. First, the six-axis MEMS gyroscope chip is subjected to power-on initial zero bias calibration, then the three-axis accelerometer is subjected to offset error calibration and sensitivity error calibration, and finally the six-axis MEMS gyroscope chip is subjected to temperature compensation, so that the acceleration and angular velocity data input into other modules are accurate and reliable.

[0066] The detailed introduction of this module is as follows:

[0067] 1. Initial zero bias calibration

[0068] Since the three-axis accelerometer and MEMS gyroscope of the six-axis MEMS gyroscope chip have zero bias, if they are not calibrated, it will have an adverse effect on the attitude fusion result. The initial zero bias calibration of the present invention refers to collecting a set number of data and calculating the average value as the zero bias of the gyroscope and the three-axis accelerometer when power is turned on. In subsequent measurements, the collected data will be subtracted from the initial value.

[0069] 2) Offset error and sensitivity error calibration

[0070] Since the six-axis MEMS gyroscope chip is mechanical in nature, stress and factory calibration limitations will cause offset error and sensitivity error to the three-axis accelerometer. The superposition of the two will cause greater errors. Therefore, it is necessary to calibrate the offset error and sensitivity error of the three-axis accelerometer. The specific steps are as follows.

[0071] After considering the influence of offset error and sensitivity error, the output acceleration value A of the triaxial accelerometer is out for:

[0072] A out =A offset +Sensitity*A actual

[0073] Among them, A offset is the accelerometer offset error, Sensitity is the accelerometer sensitivity, A actual True acceleration value.

[0074] Accelerometer offset error A offset The calculation method of accelerometer sensitivity is as follows:

[0075] Take the accelerometer output value in the ±1g gravity field:

[0076] Under +1g conditions:

[0077] A out +1g=A offset +1*Sensitivity

[0078] At -1g conditions:

[0079] A out -1g=A offset -1*Sensitivity

[0080] The solution of the two equations is:

[0081] A offset =0.5(A out +1g+A out -1g)

[0082] A offset =0.5(A out +1g-A out -1g)

[0083] Using the accelerometer offset error A offset The two parameters of accelerometer sensitivity can be used to calibrate the offset error and sensitivity error of the three-axis accelerometer.

[0084] 3) Temperature compensation

[0085] According to the correspondence between the output data of the six-axis MEMS gyroscope chip and the temperature, the output data is temperature compensated (in actual production, only the acceleration data output by the three-axis accelerometer can be temperature compensated, or the acceleration data output by the three-axis accelerometer and the angular velocity data output by the MEMS gyroscope can be temperature compensated separately to improve the output accuracy of the gyroscope). First, the correspondence between the acceleration and the temperature and the correspondence between the angular velocity and the temperature are saved. After reading the acceleration and / or angular velocity output by the six-axis MEMS gyroscope chip each time, temperature compensation is performed according to the corresponding temperature curve data. In the present invention, a linear interpolation method is used for temperature compensation. The specific method is as follows: Figure 3 shown.

[0086] Several temperature points are selected within the range of -40℃~85℃, and the temperature value, acceleration and angular velocity value of the product at each temperature point when it is at 0° are recorded respectively to form corresponding acceleration-temperature table and angular velocity-temperature table. The output data of the six-axis MEMS gyroscope chip is temperature compensated by table lookup combined with linear interpolation.

[0087] The calculation formula for temperature linear compensation is:

[0088]

[0089] Among them, M T∈(T[i],T[i+1]) M is the output value after difference compensation when the temperature is T. T is the output value before compensation, M0 is the compensation value, M i+1 、M i are the corresponding compensation values ​​when the temperature is T[i+1] and T[i] respectively, and T[i+1] and T[i] are adjacent step temperature values.

[0090] At this point, the calibrated and compensated acceleration and angular velocity can be put into other modules for subsequent data processing.

[0091] (3) Attitude calculation module

[0092] like Figure 4As shown in the figure, the attitude solution module uses the quaternion-based EKF attitude fusion algorithm to fuse the three-axis acceleration and angular velocity data output by the compensation calibration module to obtain the current optimal quaternion and the three-axis zero bias data of the MEMS gyroscope, and convert the quaternion into attitude angle data output. First, the state equation and observation equation are constructed respectively, specifically:

[0093] Define the quaternion-based state vector x k :

[0094]

[0095] Where q=[q0,q1,q2,q3] T is the attitude quaternion of the body coordinate system (b system) relative to the inertial coordinate system (n system), which is obtained by converting the three-axis angular velocity data, and ω bias =[ω bias_x ,ω bias_y ,ω bias_z ] T is the zero bias of the MEMS gyroscope corresponding to the X-axis, Y-axis, and Z-axis. Since the Z-axis of the body coordinate system is perpendicular to the ground and upward, it is difficult to estimate its zero bias by gravity acceleration. Therefore, in the present invention, ω is always considered bias_z =0;

[0096] The constructed state equation is:

[0097] x k+1 =f(x k )+ω k

[0098] Among them, x k is the state vector, f(·) represents the nonlinear function, ω k is process noise, subscript k represents time k;

[0099] The constructed observation equation is:

[0100] z k =h(x k )+v k

[0101]

[0102] Among them, z k is the measurement vector, which is the three-axis acceleration data output by the three-axis accelerometer after temperature compensation and zero bias calibration. h(·) represents the nonlinear function, and v k is the observation noise;

[0103] Then the Kalman filter process is performed. The prediction stage of the Kalman filter process includes state estimation, calculation of error covariance matrix, calculation of estimation error, and calculation of chi-square test value, which are as follows:

[0104] State Estimation:

[0105]

[0106] in, are the estimated state vectors at time k and k-1 respectively;

[0107] Compute the error covariance matrix:

[0108]

[0109] in, is the error covariance matrix estimated at time k, F k is the Jacobian matrix of the nonlinear function f(·), is the Jacobian matrix estimated at time k;

[0110] Calculate the estimated error:

[0111]

[0112] Among them, e k is the estimation error;

[0113] Calculate the chi-square test value:

[0114]

[0115] Among them, r k is the chi-square test value, H k is the Jacobian matrix of the nonlinear function h(·).

[0116] The update phase of the Kalman filter process includes calculating the Kalman filter gain, state update, error covariance update, and chi-square test, then:

[0117] Calculate the Kalman filter gain:

[0118]

[0119] Among them, K k is the Kalman filter gain;

[0120] Status Update:

[0121]

[0122] Error covariance update:

[0123]

[0124] Finally, the system estimates the optimal attitude quaternion and gyroscope zero bias value based on the Kalman filter, and finally converts the optimal attitude quaternion into attitude angle output.

[0125] (4) Tilt determination module

[0126] In this example, the tilt judgment module is based on the angular velocity data collected by the MEMS gyroscope and subjected to temperature compensation and error calibration, minus the real-time zero bias data ω of the MEMS gyroscope output by the attitude solution module. bias The real-time angular velocity ω obtained after zero bias calibration is used to judge the tilt state. The specific judgment steps are as follows:

[0127] If the real-time angular velocity ω shows an increasing trend and rises from near 0 rad / s within the set time period Tr and exceeds the judgment threshold ω max , and continues to be greater than the judgment threshold ω max If the time exceeds the set time Tc, it is judged that the mobile CT machine enters the forward state;

[0128] If the real-time angular velocity ω shows a decreasing trend and decreases from near 0 rad / s within the set time period Tr and is lower than the judgment threshold -ω max , and is continuously less than the judgment threshold -ω max If the time exceeds the set time Tc, it is judged that the mobile CT machine enters the reverse state;

[0129] In this example, the forward and reverse states of the mobile CT machine are both judged as tilted states. When the mobile CT machine is in a tilted state, if the real-time angular velocity returns to near 0 rad / s and exceeds the set time Tc, it is considered to have exited the tilted state.

[0130] In this example, the set time period Tr, the set time Tc and the judgment threshold ω max All are determined according to needs and actual working conditions.

[0131] (5) Angle filtering module

[0132] In actual testing conditions, the chi-square test value r k The larger the value, the greater the current environmental motion acceleration. At this time, the error of the accelerometer will become larger, and the attitude angle obtained by attitude fusion will also be affected. For a mobile CT machine, it will introduce a large motion acceleration during horizontal movement, impact, collision, and horizontal rotation, requiring additional angle filtering; when the mobile CT machine is in a tilted state, the environmental motion acceleration is small and no additional angle filtering is required. Therefore, when the mobile CT machine is in a non-tilted state, this system uses the current chi-square test value r k The attitude angle obtained by attitude fusion is then subjected to parameter adaptive filtering.

[0133] In this example, the angle filtering module processes the attitude angle obtained by the attitude settlement module according to the judgment result of the tilt judgment module. If the mobile CT machine is in a tilted state, the angle filtering process is not performed, and the data communication module directly outputs the attitude angle calculated by the attitude solution module; if the mobile CT machine is in a non-tilted state, the attitude angle calculated by the attitude solution module is filtered according to the size of the motion acceleration and then output through the data communication module.

[0134] The filtering process of the angle filtering module is as follows:

[0135] (1) If the acceleration data acc collected by the three-axis accelerometer in real time is within the set time period t x The change in the value exceeds the set threshold acc x , or the chi-square test value r at the current moment k If the acceleration exceeds the first threshold r0, it is determined that a sudden change has occurred in the acceleration and the filtering process needs to be started;

[0136] At this time, if the filter parameter a<a0, then let a=a0, and a0>1 to prevent the angle data from changing suddenly (in the initial state, the filter parameter a=1), where the first threshold r0, the set time period t x , threshold acc x , the filtering parameter threshold a0 are set as needed;

[0137] (2) When the chi-square test value r k When the second threshold value r1 is exceeded, it is determined that a large environmental motion acceleration of the mobile CT machine has occurred. At this time, the chi-square test value r k The first stage of adjustment of the first-order parameter filter is performed, specifically:

[0138] If r k ×Gain<a0, then let a=a0; if r k ×Gain>a max , then let a=a max ; if a0≤r k ×Gain≤a max , then let a=r k ×Gain, where Gain, the second threshold r1, the maximum value a max The value of is set according to actual needs;

[0139] For (1) and (2), the filter parameters are substituted into the following formula for first-order parameter filtering, and we have:

[0140]

[0141] Among them, y(k) and y(k-1) are the filter outputs at time k and k-1 respectively, and x(k) is the sampling value at time k, that is, the attitude angle output by the attitude solution module;

[0142] (3) Root mean square of three-axis acceleration Under normal circumstances, its value should be 1. n The deviation from 1 exceeds the set threshold g0, or the chi-square test value r k If the third threshold value r2 is exceeded, it is considered that the current motion acceleration of the mobile CT machine is too large, and there may be impact, collision or starting. In order to prevent the angle from changing suddenly in the non-tilted state, the angle update of the first-order parameter filter is limited at this time, and the filter output value at the current moment is the filter output value at the previous moment, then:

[0143] y(k)=y(k-1)

[0144] (4) If none of the above situations (1), (2) and (3) exist, the filtering parameter is slowly reduced within the set time until filtering stops, and a=1 at this time.

[0145] In summary, the present invention divides the state of the mobile CT machine into a tilted state and a non-tilted state according to the real-time angular velocity. In the tilted state, the attitude angle data output by the attitude fusion module is directly used to ensure the real-time performance of the output angle; in the non-tilted state, parameter adaptive filtering is performed according to the motion acceleration and the chi-square test value, and the angle update is temporarily stopped when the motion acceleration exceeds the threshold, and the last angle value is directly output to ensure that the product has anti-vibration, anti-impact, and anti-collision performance when it is not tilted, meeting the use requirements of the mobile CT machine under horizontal movement and horizontal rotation conditions, and having both real-time performance, stability, and vibration resistance.

[0146] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A dynamic tilt sensor measurement system for mobile CT, characterized in that: include: Attitude collector: used to collect acceleration data and angular velocity data of the tilted part of the mobile CT machine in real time; Compensation calibration module: connected to the attitude collector to perform compensation calibration on acceleration data and angular velocity data; Attitude calculation module: connected with the compensation calibration module, used to perform quaternion-based EKF attitude fusion on acceleration data and angular velocity data to obtain attitude angle data; Tilt judgment module: connected to the compensation calibration module and the attitude solution module respectively, to judge whether the mobile CT machine is in a tilted state according to the real-time angular velocity; Angle filtering module: connected to the attitude solving module, used to perform angle filtering on the attitude angle output by the tilt judging module according to the chi-square test value; Data communication module: connected to the attitude calculation module and the angle filtering module respectively to output the final attitude angle data.

2. A dynamic tilt sensor measurement system for mobile CT according to claim 1, characterized in that: The posture collector comprises a three-axis accelerometer for collecting acceleration data of the tilted part of the mobile CT machine in real time and a MEMS gyroscope for collecting angular velocity data of the tilted part of the mobile CT machine in real time.

3. A dynamic tilt sensor measurement system for mobile CT according to claim 2, characterized in that: The attitude compensation module is used to perform power-on initial zero bias calibration and temperature compensation on the three-axis accelerometer and the MEMS gyroscope, and to perform offset error calibration and sensitivity error calibration on the three-axis accelerometer.

4. The dynamic tilt sensor measurement system for mobile CT according to claim 1, characterized in that: The attitude solution module adopts the quaternion-based EKF attitude fusion algorithm to fuse the acceleration and angular velocity data after compensation calibration, obtains the current optimal quaternion and the three-axis zero bias data of the MEMS gyroscope, and converts the quaternion into attitude angle data output.

5. A dynamic tilt sensor measurement system for mobile CT according to claim 4, characterized in that: The quaternion-based EKF attitude fusion algorithm specifically includes the following steps: 1) Construct the state equation and observation equation, then we have: The state equation expression is: x k+1 =f(x k )+ω k Among them, x k is the state vector, f(·) represents the nonlinear function, ω k is process noise, subscript k represents time k, q=[q0,q1,q2,q3] T is the attitude quaternion of the body coordinate system relative to the inertial coordinate system, and ω bias =[ω bias_x ,ω bias_y ,ω bias_z ] T is the zero bias of the gyroscope corresponding to the X-axis, Y-axis, and Z-axis; The expression of the observation equation is: z k =h(x k )+v k Among them, z k is the measurement vector, which is the acceleration data after temperature compensation and zero bias calibration, h(·) represents the nonlinear function, v k is the observation noise; 2) Perform the Kalman filtering process and calculate the chi-square test value r at the current time k k .

6. The dynamic tilt sensor measurement system for mobile CT according to claim 1, characterized in that: The tilt judgment module is based on the angular velocity data collected and compensated by the MEMS gyroscope minus the real-time zero bias data ω output by the attitude solution module. bias The real-time angular velocity ω obtained after zero bias calibration is used to judge the tilt state, specifically: If the real-time angular velocity ω shows an increasing trend and rises from 0 rad / s within the set time period Tr and exceeds the judgment threshold ω max , and continues to be greater than the judgment threshold ω max If the time exceeds the set time Tc, it is judged that the mobile CT machine enters the forward state; If the real-time angular velocity ω shows a decreasing trend and decreases from 0 rad / s within the set time period Tr and is lower than the judgment threshold -ω max , and is continuously less than the judgment threshold -ω max If the time exceeds the set time Tc, it is judged that the mobile CT machine enters the reverse state; The forward state and the reverse state are both determined as tilted states. When the mobile CT machine is in a tilted state, if the real-time angular velocity returns to 0 rad / s and exceeds the set time Tc, it is considered to be in a non-tilted state.

7. The dynamic tilt sensor measurement system for mobile CT according to claim 1, characterized in that: When the mobile CT machine is in a tilted state, the posture calculation module directly outputs the posture angle data through the data communication module. When the mobile CT machine is in a non-tilted state, the posture angle data output by the posture calculation module is subjected to first-order parameter adaptive filtering by the angle filtering module and then output through the data communication module.

8. The dynamic tilt sensor measurement system for mobile CT according to claim 7, characterized in that: The specific process of filtering by the angle filtering module is as follows: 1) When the acceleration data acc collected by the three-axis accelerometer in real time is within the set time period t x The change in the value exceeds the set threshold acc x , or the chi-square test value r at the current moment k When the value exceeds the first threshold value r0, filtering is started. If the filtering parameter a<a0, a=a0 is set, where a0 is the first filtering parameter threshold value and a0>1; 2) When the chi-square test value r k When the second threshold value r1 is exceeded, the chi-square test value r k Perform first-order parameter adaptive filtering; 3) When the chi-square test value r k If the third threshold value r2 is exceeded, or the root mean square deviation of the three-axis acceleration from 1 exceeds the set threshold, the angle update of the first-order parameter adaptive filter is limited so that the filter output value at the current moment takes the filter output value at the previous moment.

9. A dynamic tilt sensor measurement system for mobile CT according to claim 8, characterized in that: In the step 2), the filtering formula of the first-order parameter adaptive filtering is: Among them, y(k) and y(k-1) are the filter outputs at time k and k-1 respectively, and x(k) is the sampling value at time k, that is, the attitude angle output by the attitude solution module at time k.

10. The dynamic tilt sensor measurement system for mobile CT according to claim 9, characterized in that: In the step 2), the adaptive adjustment of the filtering parameters of the first-order parameter adaptive filtering is specifically as follows: If r k ×Gain<a0, then let a=a0; If r k ×Gain>a max , then let a=a max ; If a0≤r k ×Gain≤a max , then let a=r k ×Gain, where Gain is the set gain.

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