CN103746616B - Mobile CT synchronous scannings control system and method - Google Patents

Abstract

The present invention relates to a mobile CT synchronous scanning control system, wherein the main controller is used to send operation command information to the synchronous control module; the synchronous control module is used to convert the command information into the control amount of each driver, and The control quantity is sent to the driver of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame respectively; the drivers of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame are used to control the drive the respective motors; the encoders of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame are used to feed back the actual position and speed information to the synchronous control module; the synchronous control module is also used to The actual position and speed information of each of the above-mentioned motors is used to calculate the synchronization error and compensation amount of the above-mentioned dual motors. The invention also relates to a method for controlling the synchronous scanning of the mobile CT.

Description

Mobile CT synchronous scanning control system and method

【Technical field】

The invention relates to a mobile CT synchronous scanning control system and method.

【Background technique】

In the current CT helical scanning synchronous control system, the mechanical transmission chain is mostly used. The increase in the number of internal parts not only increases the cost pressure, but also violates the original intention of the portable design of the mobile CT. The inherent step loss problem of the motor reduces the precision of the screw synchronization.

Mobile CT scanners have multiple imaging modes, one of which is helical scanning. In this mode, the rotating frame equipped with the main components of the image chain such as X-ray tubes, detectors, and data acquisition systems is driven by a direct drive motor to continuously rotate, while the rotating frame moves horizontally. These two movements have a certain positional correspondence to achieve uniform projection data acquisition. In fact, whether it is the above-mentioned direct drive motor or an AC motor, it is difficult to ensure absolute uniform motion during the motion process, and fluctuations in speed are unavoidable. Therefore, a synchronous control technology needs to be adopted in the implementation process to achieve the purpose of uniform sampling. The patent application with the application number 201110273871.7 proposes a master-slave synchronous control strategy to realize the synchronous control of dual motors, but the inherent defect of the master-slave synchronous control method is that when the slave motor is affected by interference, the master motor cannot perceive and follow the movement of the slave motor. Changes, poor synchronization accuracy, and certain limitations.

At present, in the mechanical structure of large fixed CT scanners, the rotating frame and the horizontal moving bed are two separate and independent components, and the loads of the rotating frame and the scanning bed are very different. When the slave motor is disturbed, the master motor cannot track the change of the slave motor in time, and the synchronization accuracy is poor, which has great limitations.

【Content of invention】

In view of this, the present invention provides a mobile CT synchronous scanning control system, including a main controller, a rotating frame rotating motor control module, a rotating frame horizontal motor control module and a synchronous control module, wherein the rotating frame rotating motor Both the control module and the horizontal motor control module of the rotary frame include respective drivers, motors and encoders. The main controller is used to send running command information to the synchronous control module; the synchronous control module is used to receive the running command information sent by the main controller, and convert the command information into the rotating rack rotating motor control module, the rotating rack level The control amount of each driver in the motor control module at the current moment, and the control amount is sent to the respective drivers of the rotating frame rotating motor control module and the rotating frame horizontal motor control module; the rotating frame rotating motor control module and the rotating frame The driver of the horizontal motor control module of the rack is used to drive the respective motors according to the control amount respectively; Position and speed information, and feed back the actual position and speed information to the synchronous control module; the synchronous control module is also used to calculate the synchronization of the above-mentioned dual motors according to the actual position and speed information of the above-mentioned motors and the synchronization error transfer function Error, and then calculate the compensation amount according to the synchronization error, and compensate in real time to the rotary motor control module of the rotating frame and the horizontal motor control module of the rotating frame, so as to realize the precise synchronization of the double motors.

The control quantity includes: the position and speed information of each motor of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame.

The synchronization error transfer function is defined as:

Among them, Gc is the synchronization error transfer function:

α＝(1+G _py G _y )(1+G _px G _x )

The synchronous control module includes an ARM synchronous control board.

The ARM synchronous control board includes an MCU unit, a rotating frame rotating motor driver interface, a rotating frame horizontal motor driver interface, a digital-to-analog conversion unit, a serial port interface, a JTAG interface and a CAN interface.

The CAN interface is used to realize the communication between the ARM synchronization control board and the main controller.

The digital-to-analog conversion unit is used to convert the command information into an analog signal.

In view of this, the present invention also provides a method for synchronous scanning control of mobile CT, including: the synchronous control module receives the running command information sent by the main controller; the synchronous control module converts the received running command information into a rotating frame The current control amount of each driver in the rotating motor control module and the rotating rack horizontal motor control module, and send the controlled amount to the respective drivers of the rotating rack rotating motor control module and the rotating rack horizontal motor control module; The drivers of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame drive their respective motors according to the control quantities; the encoders of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame are respectively Collect the actual position and speed information of the above-mentioned motors, and feed back the actual position and speed information to the synchronous control module; the synchronous control module calculates the above-mentioned dual The synchronous error of the motor, and then calculate the compensation amount according to the synchronous error, and compensate in real time to the rotary motor control module of the rotating frame and the horizontal motor control module of the rotating frame, so as to realize the precise synchronization of the double motors.

The control quantity includes: the position and speed information of each motor of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame.

The synchronization error transfer function is defined as:

Among them, Gc is the synchronization error transfer function:

α＝(1+G _py G _y )(1+G _px G _x )

The synchronous control module includes an ARM synchronous control board.

The mobile CT synchronous scanning control system and method of the present invention can realize the precise synchronization of the double motors in the mobile CT helical synchronous scanning mode, and improve the imaging quality in the CT helical scanning mode.

【Description of drawings】

Fig. 1 is a schematic diagram of the scanning trajectory in space of the rotary motor (motor 1) of the rotary frame and the horizontal motor (motor 2) of the rotary frame.

FIG. 2 is a schematic diagram of a straight line profile after motor 1 and motor 2 are coupled.

Fig. 3 is a structural block diagram of the non-cross-coupling control system of the dual-motor synchronous control system.

Figure 4 is a structural block diagram of the cross-coupling control system of the dual-motor synchronous control system.

Fig. 5 is a hardware architecture diagram of the mobile CT helical synchronous scanning control system.

Fig. 6 is a schematic diagram of the hardware circuit of the ARM synchronous control board.

Fig. 7 is a flow chart of the operation of the mobile CT synchronous scanning control system and method of the present invention.

【detailed description】

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

In order to better explain the present invention, firstly, the synchronization error and cross-coupling synchronization error transfer functions are defined.

Synchronization error:

In the mobile CT dual-motor helical motion synchronous control system, the rotary motor (motor 1) of the rotating frame performs continuous uniform rotational motion along the vertical plane, and the horizontal motor (motor 2) of the rotating frame moves synchronously and uniformly in a straight line on the horizontal plane, so that the two motors The scanning trajectory in space advances in a spiral shape. As shown in Figure 1. The two motors move continuously at a constant speed in their respective planes, and the synchronous relationship between the two can be expressed by the following formula:

In the formula:

L _r1 (t)—the length of the arc of rotation on the surface of the circumference;

L _r2 (t)—the advance distance of linear motion in the horizontal plane;

r—the radius of rotation of the helix;

τ—the pitch of the helix.

According to the synchronous relationship (1), in the synchronous control of dual-motor helical motion, the essence of the helical trajectory can be regarded as a straight line that couples the rotational motion of motor 1 and the linear motion of motor 2 in the XY plane. The synchronous error is defined through this coupling relationship, and the straight line profile after the coupling of motor 1 and motor 2 is shown in Figure 2.

In Figure 2, P* is the expected position of any reference input, P is the actual position of the system at this moment, θ is the angle between the straight line at the reference point and the horizontal left axis, Ey is the tracking error of the continuous rotation motion of the vertical plane at a constant speed, Ex is the tracking error of horizontal synchronous linear motion, ε is the system profile error, which is defined as the shortest distance between the expected position and the actual position, the advantage of this definition is: the goal of cross-coupling synchronous control and compensation is to make the expected position consistent with the actual position , the synchronous error model constructed from this is a real-time error model, which has practical significance. According to the geometric relationship of each variable shown in Figure 3, the synchronization error can be expressed as:

Cross-coupled synchronization error transfer function:

The cross-coupled synchronization error transfer function is used to describe the dynamic relationship of the synchronization error between the non-cross-coupled control system and the cross-coupled control system. The design of cross-coupled compensators through this function can be simply regarded as a feedback control problem.

The structural block diagram of the non-cross-coupling control system of the dual-motor synchronous control system is shown in Figure 3, and ε ₀ is defined as the synchronous scan synchronization error in the non-cross-coupling control. The structural block diagram of the cross-coupling control system of the dual-motor synchronous control system is shown in Figure 4, and _εc is defined as the synchronous scan synchronization error during the cross-coupling control.

In order to simplify the analysis, let the speed loop and integral loop of motor 1 and motor 2 be equivalent to Gy and Gx respectively, then ε ₀ and ε _c are respectively:

Combine formula (3) and formula (4) to get the synchronization error transfer function:

in:

α＝(1+G _py G _y )(1+G _px G _x )

In the formula: Gc is defined as the synchronization error transfer function between the non-cross-coupling control system and the cross-coupling control system, and C _C is the synchronization error compensation allocation controller. It can be seen from formula (5) that by designing a suitable compensator C _C and assigning additional synchronization error compensation to the speed loops of the respective control loops, the precise synchronization of motor 1 and motor 2 can be achieved.

Figure 5 shows the hardware architecture diagram of the mobile CT helical synchronous scanning control system. The system is mainly composed of four parts: main controller, motor 1 control module, motor 2 control module and synchronous control module. Wherein, the motor 1 control module and the motor 2 control module adopt the same control structure, the motor 1 control module includes a driver 1, a motor 1 and an encoder 1; the motor 2 control module includes a driver 2, a motor 2 and an encoder 2 ; The synchronous control module includes an ARM (Advanced RISCMachine, Advanced Reduced Instruction Set Machine) synchronous control board.

The main controller is used to send running command information to the synchronous control module.

The synchronous control module is used to receive the operation command information sent by the main controller, convert the command information into the current control quantities of the motor 1 and the motor 2, and send the control quantities to the driver 1 and the driver 2 respectively.

The driver 1 and the driver 2 are used to drive the motor 1 and the motor 2 according to the control amount.

The encoder 1 and the encoder 2 are used to collect the actual position and speed information of the motor 1 and the motor 2, and feed back the actual position and speed information to the synchronous control module through the driver 1 and the driver 2 respectively.

The synchronous control module is used to calculate the synchronous error of the motor 1 and the motor 2 in real time according to the actual position and speed information of the motor 1 and the motor 2 fed back, and the definition of the synchronous error transfer function, and then pass the synchronous error through the compensator C _C compensation, the compensation amount is finally calculated, and the real-time compensator is given to the motor 1 control module and the motor 2 control module to achieve precise synchronization of the two motors.

Figure 6 is a schematic diagram of the hardware circuit of the ARM synchronous control board. The ARM synchronous control board includes an MCU unit, a driver 1 interface, a driver 2 interface, a digital-to-analog conversion unit, a serial interface, a JTAG interface and a CAN interface. Among them, the driver 1 interface and the driver 2 interface are electrically connected to the MCU unit through the drive circuit, the ARM synchronous control board communicates with the main controller through the CAN interface, the serial interface mainly realizes communication and debugging with the host computer, and the JTAG interface mainly uses To realize the programming of the program.

The working process of the ARM synchronous control board in Fig. 6 will be described below in conjunction with Fig. 5 .

The MCU unit receives the running command information sent by the main controller, and sends the command information to the digital-to-analog conversion unit.

The digital-to-analog conversion unit converts the command information into an analog signal, that is, into the control quantity of the motor 1 and the motor 2 at the current moment, and the control quantity includes the position and speed information of the motor 1 and the position and speed information of the motor 2 .

The interface of the driver 1 sends the control quantity of the motor 1 to the driver 1 , and the interface of the driver 2 sends the control quantity of the motor 2 to the driver 2 .

The driver 1 and the driver 2 perform double closed-loop control of position and speed loops according to the transmitted control amount, that is, the driver 1 drives the motor 1 to move according to the corresponding speed and position, and the driver 2 drives the motor 2 according to the corresponding speed. speed and position for movement. The encoder 1 collects the actual position and speed information of the motor 1 at this time, and feeds back the actual position and speed information of the motor 1 to the ARM synchronous control board through the driver 1; the encoder 2 collects the actual position and speed of the motor 2 at this time information, and feed back the actual position and speed information of the motor 2 to the ARM synchronous control board through the driver 2.

The MCU unit makes the difference between the actual position and speed information of motor 1 fed back by encoder 1 and the actual position and speed information of motor 2 fed back by encoder 2, and the control amount converted by the digital-to-analog conversion unit to obtain the motor 1 and motor 2 values. Tracking error, and then the tracking error of motor 1 and motor 2 is sent to the synchronization error transfer function in real time.

The synchronization error transfer function calculates the synchronization error of the motor 1 and the motor 2 according to the tracking errors of the motor 1 and the motor 2, and then compensates the synchronization error through the compensator _CC , and finally calculates the compensation amount as the motor 1 and the motor 2. The control amount of the next sampling period of motor 2. The MCU unit sends the control quantity of the next sampling period to the main controller through the CAN interface.

Fig. 7 is a flow chart of the operation of the mobile CT synchronous scanning control method of the present invention.

This flowchart takes a sampling cycle as an example for illustration:

Step S401: The ARM synchronous control board receives the running command information sent by the main controller.

Step S402: The ARM synchronous control board converts the command information received from the main controller into an analog signal through the digital-to-analog conversion unit, that is, into the control quantity of the motor 1 and the motor 2 at the current moment, and the control quantity includes the position of the motor 1 , speed information and the position and speed information of motor 2. Then the ARM synchronous control board sends the control quantity of the motor 1 to the driver 1 through the driver 1 interface, and sends the control quantity of the motor 2 to the driver 2 through the driver 2 interface.

Step S403: Driver 1 and driver 2 perform position and speed loop double closed-loop control according to the control amount sent by the ARM synchronous control board, that is, driver 1 drives motor 1 to move according to the corresponding speed and position, and driver 2 drives motor 2 according to corresponding speed and position for movement. At the same time, the encoder 1 collects the actual position and speed information of the motor 1 at this time, and feeds back the actual position and speed information of the motor 1 to the ARM synchronous control board through the driver 1; the encoder 2 collects the actual position of the motor 2 at this time , speed information, and feed back the actual position and speed information of the motor 2 to the ARM synchronous control board through the driver 2.

Step S404: The ARM synchronous control board makes the difference between the actual position and speed information of motor 1 fed back by encoder 1 and the actual position and speed information of motor 2 fed back by encoder 2, and the control amount obtained after conversion in step S402 to obtain the motor 1. The tracking error of motor 2, and then send the tracking errors of motor 1 and motor 2 to the synchronization error transfer function in real time.

Step S405: The synchronous error transfer function calculates the synchronous error of motor 1 and motor 2 according to the tracking error of motor 1 and motor 2, and then compensates the synchronous error through the compensator compensator, and finally calculates the compensation amount as motor 1 and the control amount of the next sampling period of motor 2. The ARM synchronous control board sends the control quantity of the next sampling period to the main controller through the CAN interface.

According to this cycle, the timer interrupt unit in the ARM synchronous control board performs timer interrupt processing at every sampling time T _S , that is, steps S401 to S405 are performed to calculate the synchronization error between motor 1 and motor 2 in real time, and then Calculate the control quantities of motor 1 and motor 2 in the next sampling period, and finally realize the precise synchronization of the two motors.

The invention proposes a cross-coupling synchronization control scheme based on the synchronization error transfer function with the mobile CT scanner as the controlled object, and designs the hardware and software system for realizing the synchronization strategy, and realizes dual The precise synchronization of the motors improves the imaging quality in CT helical scan mode.

The specific embodiments of the present invention described above do not constitute a limitation to the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (9)

1. A mobile CT synchronous scanning control system is characterized in that the system includes a main controller, a rotating frame rotating motor control module, a rotating frame horizontal motor control module and a synchronous control module, and the rotating frame rotating motor controls The module and the horizontal motor control module of the rotating frame all include respective drivers, motors and encoders, wherein: The main controller is used to send operation command information to the synchronous control module; The synchronous control module is used to receive the operation command information sent by the main controller, convert the command information into the control amount of each driver in the rotary motor control module of the rotating rack and the horizontal motor control module of the rotating rack at the current moment, and convert the command information The control quantity is sent to the respective drivers of the rotary motor control module of the rotary rack and the horizontal motor control module of the rotary rack; The drivers of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame are used to drive the respective motors according to the control quantities; The encoders of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame are used to respectively collect the actual position and speed information of the rotary motor of the rotary frame and the horizontal motor of the rotary frame, and store the actual position and speed The information is fed back to the synchronous control module; The synchronous control module is also used to calculate the synchronous error of the rotary motor of the rotating frame and the horizontal motor of the rotating frame according to the actual position and speed information of the above-mentioned motors and the synchronous error transfer function, and then calculate the compensation amount according to the synchronous error, Real-time compensation to the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame to achieve precise synchronization of the two motors; The synchronization error transfer function is defined as: ${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; GC</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}$ Among them, Gc is the synchronization error transfer function: Among them, ε ₀ is the synchronization error of synchronous scanning under non-cross-coupling control, ε _c is the synchronization error of synchronous scanning under cross-coupling control, Gx is the integral loop, Gy is the speed loop, and _CC is the allocation controller for synchronization error compensation. 2 . The system according to claim 1 , wherein the control quantity includes: the position and speed information of the motors of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame. 3 . 3. The system of claim 1, wherein the synchronization control module comprises an ARM synchronization control board. 4. The system according to claim 3, wherein the ARM synchronous control board comprises an MCU unit, a rotating frame rotating motor driver interface, a rotating frame level motor driver interface, a digital-to-analog conversion unit, a serial port interface, a JTAG interface and CAN interface. 5. The system according to claim 4, wherein the CAN interface is used to realize the communication between the ARM synchronization control board and the main controller. 6. The system according to claim 4, wherein the digital-to-analog conversion unit is used to convert the command information into an analog signal. 7. A method for mobile CT synchronous scanning control, comprising: The synchronous control module receives the running command information sent by the main controller; The synchronous control module converts the received operation command information into the control quantity of each driver in the rotary motor control module of the rotary rack and the horizontal motor control module of the rotary rack at the current moment, and sends the control amount to the rotary rack respectively. Drivers for the motor control module and the horizontal motor control module of the rotating rack; The drivers of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame respectively drive their respective motors according to the control amount; The encoders of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame respectively collect the actual position and speed information of the rotary motor of the rotary frame and the horizontal motor of the rotary frame, and store the actual position and speed information Feedback to the synchronous control module; The synchronous control module calculates the synchronous error of the rotary motor of the rotating frame and the horizontal motor of the rotating frame according to the actual position and speed information of the above-mentioned motors and the synchronous error transfer function, and then calculates the compensation amount according to the synchronous error, and compensates in real time for Rotary frame rotary motor control module and rotary frame horizontal motor control module to achieve precise synchronization of dual motors; The synchronization error transfer function is defined as: ${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; GC</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}$ Among them, Gc is the synchronization error transfer function: Among them, ε ₀ is the synchronization error of synchronous scanning under non-cross-coupling control, ε _c is the synchronization error of synchronous scanning under cross-coupling control, Gx is the integral loop, Gy is the speed loop, and _CC is the allocation controller for synchronization error compensation. 8 . The method according to claim 7 , wherein the control quantity includes: position and speed information of each motor of the rotary motor control module of the rotary frame and the horizontal motor control module of the rotary frame. 9. The method of claim 7, wherein the synchronization control module comprises an ARM synchronization control board.