A gradient force driving control method and system for multi-modal motion of a micro robot
By using coil combination and gradient force drive control methods, the problems of passage and field of vision expansion of microrobots in highly confined spaces were solved, achieving stable translation and local operation, and improving the robot's spatial passage and operation capabilities.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGNAN UNIV
- Filing Date
- 2026-03-24
- Publication Date
- 2026-06-23
AI Technical Summary
Existing magnetically controlled microrobots cannot perform a complete crawling gait in highly confined spaces, resulting in passage failure, and they struggle to achieve effective field of vision expansion and localized manipulation in complex intestinal environments.
A coil combination consisting of three pairs of Helmholtz coils and one pair of Maxwell coils is used. The magnetic field model is compactly represented by the Jacobian matrix, the magnetic field gradient expression is obtained by the central difference method, a linear homogeneous control equation is constructed, and the optimal coil input current is obtained by singular value decomposition to drive a micro-robot to achieve multimodal motion.
It enables quasi-static stable translation and local manipulation capabilities of microrobots in highly confined spaces, improving spatial mobility and field of view expansion capabilities, and avoiding posture instability and tissue damage.
Smart Images
Figure CN122250902A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of magnetically controlled microrobot technology, and in particular to a gradient force-driven control method and system for multimodal motion of a microrobot. Background Technology
[0002] Intestinal diseases have a high incidence and wide range of harm, making endoscopy and minimally invasive instruments important tools for diagnosis and treatment. However, the intestine, as a typical tubular organ, has a narrow, tortuous, flexible, deformable, moist surface with unstable frictional properties. In recent years, microrobots have shown significant promise for biomedical manipulation due to their small size. Among them, magnetic actuation is considered particularly suitable for in vivo cavity scenarios due to its advantages such as strong tissue penetration, no need for onboard power supply, and the ability to achieve non-contact remote control. Most current magnetically controlled microrobots rely on uniform magnetic fields to generate magnetic torque and move using a single crawling, rolling, or helical gait. These studies have, to some extent, expanded the range of movement of microrobots within the body.
[0003] However, existing magnetically driven microrobots generally suffer from limited adaptability to local environments and insufficient interactive operation capabilities. On the one hand, when faced with low passages with severely limited height, the single crawling or rolling drive mechanism often fails directly due to insufficient space to support the robot in completing a full gait cycle. On the other hand, in current endoscopic procedures, intestinal wall folds, mucus, or thin membrane tissues easily obstruct the field of vision of the target area, and robots currently driven by gradient magnetic field torque often lack effective spatial magnetic field gradients and local interactive forces in the vertical direction, making it difficult to perform operations such as expanding the field of vision (e.g., lifting the mucosa by tilting the head).
[0004] Furthermore, at the control level, existing magnetic control methods are mostly designed for single gradient magnetic field torque drives, making them difficult to directly apply to gradient magnetic field force control, which is highly sensitive to non-uniform magnetic fields in space. Since the magnitude and direction of the gradient magnetic field force change significantly with the robot's spatial position, existing systems lack an optimization mechanism that combines real-time pose feedback with multiple physical constraints (such as power limiting and magnetic field safety thresholds) when facing local operations under complex contact conditions. This can easily lead to undesirable slippage, bouncing, or attitude instability in the robot, making it difficult to guarantee the smoothness and repeatability of multimodal movements such as translation and lifting.
[0005] Therefore, there is an urgent need to propose a control method and system that can adapt to the complex confined intestinal environment, combine an effective pose perception and force control solution model, and achieve multimodal motions such as pulse translation and vertical head lifting of microrobots in confined space through precise gradient magnetic field force control, so as to expand its application potential in intestinal examination and surgical assistance. Summary of the Invention
[0006] Therefore, the technical problem to be solved by the present invention is to overcome the problem in the prior art that magnetically controlled microrobots fail to pass through highly confined spaces because they cannot execute a complete crawling gait.
[0007] To address the aforementioned technical problems, this invention provides a gradient force-driven control method for multimodal motion of a microrobot, comprising: The robot to be controlled is placed in the magnetic field of a coil combination consisting of three pairs of Helmholtz coils orthogonally arranged along the X, Y, and Z axes, and one pair of Maxwell coils arranged along the Z axis. The magnetic field model under non-uniform magnetic field is compactly represented based on the Jacobian matrix, and the magnetic field gradient at each position coordinate under the compact representation is numerically approximated using the central difference method to obtain the magnetic field gradient expression. Based on the contribution of the unit current of each coil in the coil combination to the magnetic field and the gradient magnetic field force, the magnetic field mapping matrix and the gradient magnetic field force mapping matrix are obtained. Then, the magnitude scalars of the magnetic field vector and the gradient magnetic field force vector in the direction of the desired gradient magnetic field force are introduced to construct a linear homogeneous control equation that makes the magnetic field direction collinear with the direction of the desired gradient magnetic field force. Singular value decomposition is performed on the coefficient matrix of the linear homogeneous control equation to extract the null space basis vector as the general solution. Under preset constraints, the optimal coil input current corresponding to each coil is obtained by maximizing the magnitude scalar of the gradient magnetic field force vector in the desired gradient magnetic field force direction. The optimal coil input current corresponding to each coil is used to drive the coil combination to generate a target uniform magnetic field and a target gradient magnetic field, which are applied to the microrobot to be controlled, thereby driving the microrobot to achieve multimodal motion.
[0008] Preferably, the Maxwell coils arranged along the Z-axis have zero magnetic induction at the center point, with only the first-order gradient term being non-zero, which is used to generate a highly linear uniform gradient magnetic field in the neighborhood of the center of the workspace; the Helmholtz coils generate a uniform magnetic field when they are in the ideal same direction and have the same current, and an adjustable first-order gradient component is introduced by independently applying a pair of differential currents to the same pair of horizontal Helmholtz coils.
[0009] Preferably, when the magnetic field model under a non-uniform magnetic field is compactly represented based on the Jacobian matrix, the Jacobian matrix satisfies symmetry and its trace is zero.
[0010] Preferably, the magnetic field gradient expression is: ; ; ; in, Represents position coordinates Magnetic field strength at that location , and These represent minute increments along the X-axis, Y-axis, and Z-axis, respectively. , This indicates the partial derivative.
[0011] Preferably, a linear homogeneous governing equation is constructed that makes the direction of the magnetic field collinear with the direction of the desired gradient magnetic force, expressed as: ; in, Represents the magnetic field mapping matrix. Represents the gradient magnetic field force mapping matrix. This represents the unit vector indicating the direction of the desired gradient magnetic field force. This represents the current vector composed of the input currents of each coil in the coil assembly. To achieve what is desired; , and The input currents for the left and right coils of the X-axis Helmholtz coil are given. and Input current to the corresponding coils of the front and rear coils of the Y-axis Helmholtz coil. The input current of the Z-axis Helmholtz coil is the coil whose two coils are connected in series. The input current to the coil after the two coils of the Maxwell coil are connected in reverse series; This represents the magnitude scalar of the magnetic field vector in the direction of the desired gradient magnetic force. It represents the magnitude scalar of the gradient magnetic field force vector in the direction of the desired gradient magnetic field force.
[0012] Preferably, singular value decomposition is performed on the coefficient matrix of the linear homogeneous control equations to extract the null space basis vectors as the general solution. Under preset constraints, the optimal coil input current for each coil is obtained by maximizing the magnitude scalar of the gradient magnetic field force vector in the desired gradient magnetic field force direction, including: The singular value decomposition of the coefficient matrix of the linear homogeneous governing equations is expressed as: ; Extracting the null space basis vectors, we can represent them as follows: ; Obtain the general solution , is represented as: ; The current limiting constraint is constructed as follows: ; The lower limit constraint of the magnetic field amplitude is constructed as follows: ; The upper limit constraint on the amplitude of the gradient magnetic field force is constructed as follows: ; The objective, maximizing the magnitude scalar of the gradient magnetic field force vector along the desired gradient magnetic field force direction, is expressed as: ; Find the optimal coefficients in the coil combination using linear programming. Calculate the optimal coil input current; in, , represents the set of indices corresponding to all null space bases in the coil combination. express The i-th number on the diagonal, It is an equation The solution set The vectors in the vectors are linearly independent; express The first of the matrix List, express The first of the matrix Line 1 List, , ; for The 7th row of the matrix The column represents the magnitude scalar of the magnetic field vector in the direction of the desired gradient magnetic force. , Indicates the lower limit of the magnetic field amplitude; for The 8th row of the matrix The column represents the magnitude scalar of the gradient magnetic field force vector in the direction of the desired gradient magnetic field force. ; This indicates the upper limit of the gradient magnetic field force amplitude.
[0013] Preferably, driving the microrobot to achieve multimodal motion includes putting the microrobot into a pulse translation mode, including: Two optimal coil input currents are applied to Helmholtz coils in the same horizontal direction to construct a three-dimensional magnetic field gradient in the horizontal direction; the horizontal direction is the direction parallel to the XoY plane. Based on the pulse gradient magnetic field force driving strategy, the gradient magnetic field force is output during the excitation period to overcome the maximum static friction force and cause the microrobot under control to generate displacement. During the non-excitation period, the applied gradient magnetic field force is reduced so that the microrobot under control decelerates and stops due to frictional resistance. Quasi-static stable translation of the microrobot under control is achieved by displacement during the excitation period and deceleration and stopping during the non-excitation period.
[0014] Preferably, driving the microrobot to achieve multimodal motion includes putting the microrobot into a head-up mode, including: With the desired gradient magnetic field force pointing vertically upward, the corresponding optimal coil input current is input to the Maxwell coil and each Helmholtz coil in the coil combination to generate a vertically upward gradient magnetic field force. A continuous loading strategy with a duty cycle of 100% and a slowly increasing upper limit of the gradient magnetic field force amplitude was adopted to smoothly raise the head of the micro-robot to be controlled and perform the lifting operation. After the lifting operation is completed, a gradual unloading strategy is adopted, in which the upper limit of the gradient magnetic field force amplitude is slowly reduced, symmetrical to the continuous loading strategy, so that the microrobot to be controlled falls back to its original position.
[0015] This embodiment provides a gradient force drive control system for multimodal motion of a microrobot, including: A dual-view camera is used to capture images of the micro-robot to be controlled and obtain its coordinates. The coil assembly includes three pairs of Helmholtz coils orthogonally arranged along the X, Y, and Z axes, and one pair of Maxwell coils arranged along the Z axis. The host computer is connected to the dual-view camera so as to obtain the optimal coil input current corresponding to each coil based on the gradient force drive control method for multimodal motion of microrobots as described above. The current-driven module has its input end connected to the host computer and its output end supplying power to the coil combination, so as to drive the coil combination to generate the target uniform magnetic field and the target gradient magnetic field based on the input current of each optimal coil.
[0016] Preferably, the current drive module includes: The first independent constant voltage DC power supply has its input end connected to the host computer, and its output end connected to the left coil of the X-axis Helmholtz coil through the first bidirectional full-bridge PWM current drive board. The second independent constant voltage DC power supply has its input end connected to the host computer, and its output end connected to the right coil of the X-axis Helmholtz coil through the second bidirectional full-bridge PWM current drive board. The third independent constant voltage DC power supply has its input end connected to the host computer, and its output end is connected to the front coil of the Y-axis Helmholtz coil through the third bidirectional full-bridge PWM current drive board. The fourth independent constant voltage DC power supply has its input end connected to the host computer, and its output end connected to the rear coil of the Y-axis Helmholtz coil through the fourth bidirectional full-bridge PWM current drive board. The fifth independent constant voltage DC power supply has its input end connected to the host computer, and its output end is connected to the coil of the Z-axis Helmholtz coil after the two coils are connected in series through the fifth bidirectional full-bridge PWM current drive board. The sixth independent constant voltage DC power supply has its input end connected to the host computer, and its output end is connected to the coil of the Maxwell coil after the two coils are connected in reverse series through the sixth bidirectional full-bridge PWM current drive board. Each bidirectional full-bridge PWM current drive board is used to adjust the PWM duty cycle of the current in its branch according to the instructions of the host computer and switch the conduction direction of the bridge, so as to realize the continuous and fine adjustment of the amplitude of the coil input current, the rapid switching of the current direction, and the microsecond-level high-frequency dynamic refresh of the gradient magnetic field force.
[0017] Compared with the prior art, the above-described technical solution of the present invention has the following advantages: The gradient force-driven control method for multimodal motion of microrobots described in this invention is based on the contribution of the unit current of each coil in the coil assembly to the magnetic field and gradient magnetic force. It obtains the magnetic field mapping matrix and the gradient magnetic force mapping matrix, and introduces the magnitude scalars of the magnetic field vector and the gradient magnetic force vector in the desired gradient magnetic force direction to construct a linear homogeneous control equation that makes the magnetic field direction collinear with the desired gradient magnetic force direction. Based on this, singular value decomposition is performed on the coefficient matrix of the linear homogeneous control equation to extract the null basis vector as the general solution. Under preset constraints, the method maximizes the gradient magnetic force vector in the desired gradient magnetic force direction. Using the amplitude scalar as the objective, the optimal coil input current corresponding to each coil is obtained by solving the problem. This invention uses the optimal coil input current corresponding to each coil to drive a coil combination consisting of three pairs of Helmholtz coils and one pair of Maxwell coils, generating a target uniform magnetic field and a target gradient magnetic field, which act on the microrobot to be controlled, driving it to achieve multimodal motion. This ensures that the magnetic field strength is sufficient to lock the direction of the magnetic moment, and also ensures that the output gradient magnetic field force reaches its maximum within the range allowed by the system hardware and task safety, thus achieving a unity of control accuracy and driving efficiency, and breaking through the limitation of a single crawling gait in the confined space of the microrobot.
[0018] This invention constructs a three-dimensional magnetic field gradient in the horizontal direction by independently applying the corresponding optimal coil input current to a pair of Helmholtz coils in the same horizontal direction. Combined with a pulsed gradient magnetic field force driving strategy, the output gradient magnetic field force overcomes the maximum static friction during the excitation period, causing the microrobot to move. During the non-excitation period, the applied gradient magnetic field force is reduced, causing the robot to decelerate and stop due to frictional resistance, maintaining a static friction state. This achieves quasi-static stable translation of the microrobot in highly confined spaces. This pulsed driving method effectively avoids the velocity accumulation and attitude instability problems caused by traditional continuous sliding, enabling the robot to achieve controllable movement even in extremely confined environments where a complete crawling gait cannot be completed, significantly improving the microrobot's spatial maneuverability.
[0019] This invention uses a vertically upward direction as the desired gradient magnetic field force. Optimal coil input currents are input to the Maxwell coil and each Helmholtz coil to generate a vertically upward gradient magnetic field force. A continuous loading strategy with a 100% duty cycle and a slowly increasing upper limit of the gradient magnetic field force amplitude is employed to smoothly raise the head of the microrobot for a lifting operation. After the operation is completed, a gradual unloading strategy with a symmetrically decreasing upper limit of the gradient magnetic field force amplitude is used to safely lower the robot back to its original position. This gradual loading and unloading strategy effectively avoids posture instability or tissue damage caused by sudden impacts, significantly improving the robot's spatial maneuverability and its ability to expand its field of vision through local interactions. It provides a reliable technical means for microrobots to perform field-of-view expansion operations in intestinal examinations and surgical assistance. Attached Figure Description
[0020] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein: Figure 1 This is a flowchart of the gradient force-driven control method for multimodal motion of a microrobot according to the present invention; Figure 2 This is a schematic diagram of the gradient magnetic field simulation results of the Z-axis Maxwell coil; Figure 2 (a) is a simulated thermal diagram of the magnetic field of a Maxwell coil. Figure 2 (b) is a simulation diagram of the magnetic field components of the Maxwell coil along the Z-axis. Figure 2 (c) is a simulation diagram of the magnetic field components of the Maxwell coil along the X-axis. Figure 2 (d) is a simulation diagram of the magnetic field gradient in the Z-axis direction of the Maxwell coil; Figure 3 These are two typical toroidal coil model diagrams; Figure 3 (a) is a model diagram of a Helmholtz coil. Figure 3 (b) is the Maxwell coil model; Figure 4 This is a schematic diagram of the gradient force drive control system for multimodal motion of a microrobot; Figure 5 This is a schematic diagram of the tunnel structure; Figure 5 (a) is a schematic diagram of a type I tunnel. Figure 5 (b) is a schematic diagram of an L-shaped tunnel. Figure 5 (c) is a schematic diagram of an S-shaped tunnel; Figure 6 This is a schematic diagram of a micro-robot moving through a Type I tunnel; Figure 7 This is a schematic diagram of a micro-robot moving through an L-shaped tunnel; Figure 8 This is a schematic diagram of a micro-robot navigating an S-shaped tunnel; Figure 9 This is a demonstration diagram of a microrobot's membrane lifting verification experiment. Detailed Implementation
[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.
[0022] Reference Figure 1 The flowchart shown is a step diagram of the gradient force drive control method for multimodal motion of microrobots of the present invention, and the specific steps include S101 to S105.
[0023] S101: Place the robot to be controlled within the magnetic field of a coil combination consisting of three pairs of Helmholtz coils orthogonally arranged along the X, Y, and Z axes, and one pair of Maxwell coils arranged along the Z axis.
[0024] The external magnetic field drive system of this embodiment includes three pairs of orthogonally arranged Helmholtz coils and one pair of Maxwell coils arranged along the Z-axis, used to generate a controllable uniform magnetic field and a gradient magnetic field within the workspace. The Maxwell coils arranged along the Z-axis have zero magnetic induction at their center point, with only the first-order gradient term being non-zero, used to generate a highly linear uniform gradient magnetic field in the central neighborhood of the workspace. The Helmholtz coils generate a uniform magnetic field under ideally unidirectional and uniform current conditions. An adjustable first-order gradient component is introduced by independently applying a pair of differential currents to the corresponding pair of horizontally oriented Helmholtz coils.
[0025] S102: Based on the Jacobian matrix, a compact representation of the magnetic field model under a non-uniform magnetic field is constructed. The central difference method is then used to numerically approximate the magnetic field gradient at various coordinates under the compact representation, yielding the magnetic field gradient expression, which is: ; ; ; in, Represents position coordinates Magnetic field strength at that location , and These represent minute increments along the X-axis, Y-axis, and Z-axis, respectively. , This indicates the partial derivative.
[0026] In this embodiment, when the magnetic microrobot is placed in a non-uniform magnetic field, it will be subjected to a gradient magnetic force, the basic expression of which is: Expanding the Hamiltonian operator, we get: Therefore, the components of the gradient magnetic force can be expressed as a linear combination of the partial derivatives in each coordinate direction, by introducing the Jacobian matrix. The gradient magnetic force can be compactly expressed as In the region of approximately no free current, the magnetic field gradient matrix at the operating point Simultaneously satisfying symmetry, that is and zero-trace structure characteristics, i.e. Therefore, this embodiment uses central difference to numerically approximate the gradient in the calculation to obtain the magnetic field gradient expression.
[0027] S103: Based on the contribution of the unit current of each coil in the coil combination to the magnetic field and the gradient magnetic force, the magnetic field mapping matrix and the gradient magnetic force mapping matrix are obtained. Then, the magnitude scalars of the magnetic field vector and the gradient magnetic force vector in the direction of the desired gradient magnetic force are introduced to construct a linear homogeneous governing equation that makes the magnetic field direction collinear with the direction of the desired gradient magnetic force, expressed as: ; in, Represents the magnetic field mapping matrix. Represents the gradient magnetic field force mapping matrix. This represents the unit vector indicating the direction of the desired gradient magnetic field force. This represents the current vector composed of the input currents of each coil in the coil assembly. To achieve what is desired; , and The input currents for the left and right coils of the X-axis Helmholtz coil are given. and Input current to the corresponding coils of the front and rear coils of the Y-axis Helmholtz coil. The input current of the Z-axis Helmholtz coil is the coil whose two coils are connected in series. The input current to the coil after the two coils of the Maxwell coil are connected in reverse series; This represents the magnitude scalar of the magnetic field vector in the direction of the desired gradient magnetic force. It represents the magnitude scalar of the gradient magnetic field force vector in the direction of the desired gradient magnetic field force.
[0028] Specifically, the magnetic field force control method in this embodiment defines the contribution of the unit current of each channel power supply and defines a magnetic field mapping matrix by concatenating columns. Mapping matrix with gradient magnetic field force This allows the total magnetic field and the total gradient magnetic force to be written as... and In practical motion control, the robot's equivalent magnetic moment Under the influence of an external magnetic field torque, it will always tend to resonate with the local magnetic field. The direction remains consistent, that is Simultaneously, in order to obtain the largest possible effective magnetic field force in the desired direction of motion for the target task (such as translation or lifting), the equivalent magnetic moment must be... Align the direction to the desired gradient magnetic field force In the direction of the magnetic moment attitude, since the magnetic moment attitude is simultaneously constrained by the direction of the magnetic field and guided by the goal of maximizing the force, the direction of the actually generated magnetic field must be parallel and collinear with the direction of the desired gradient magnetic field force, that is... .
[0029] Based on this prior physical constraint, we define a unit vector for the known desired magnetic field and gradient magnetic field force direction. Introducing scalars and To represent the magnitude under collinear conditions, construct a linear homogeneous equation, which is abbreviated as: .
[0030] S104: Perform singular value decomposition on the coefficient matrix of the linear homogeneous control equations, extract the null space basis vectors as the general solution, and under preset constraints, solve for the optimal coil input current corresponding to each coil by maximizing the magnitude scalar of the gradient magnetic field force vector in the desired gradient magnetic field force direction, including: The singular value decomposition of the coefficient matrix of the linear homogeneous governing equations is expressed as: ; Extracting the null space basis vectors, we can represent them as follows: ; Obtain the general solution , is represented as: ; The current limiting constraint is constructed as follows: ; The lower limit constraint of the magnetic field amplitude is constructed as follows: ; The upper limit constraint on the amplitude of the gradient magnetic field force is constructed as follows: ; The objective, maximizing the magnitude scalar of the gradient magnetic field force vector along the desired gradient magnetic field force direction, is expressed as: ; Find the optimal coefficients in the coil combination using linear programming. Calculate the optimal coil input current; in, , represents the set of indices corresponding to all null space bases in the coil combination. express The i-th number on the diagonal, It is an equation The solution set The vectors in the vectors are linearly independent; express The first of the matrix List, express The first of the matrix Line 1 List, , ; for The 7th row of the matrix The column represents the magnitude scalar of the magnetic field vector in the direction of the desired gradient magnetic force. , Indicates the lower limit of the magnetic field amplitude; for The 8th row of the matrix The column represents the magnitude scalar of the gradient magnetic field force vector in the direction of the desired gradient magnetic field force. ; This indicates the upper limit of the gradient magnetic field force amplitude.
[0031] Specifically, in this embodiment, the force-controlled solution model defined in step S104 is applied to the coefficient matrix. Perform singular value decomposition, extract its null space basis tensor to form a general solution, and maximize the gradient magnetic field force amplitude term. The objective function is defined as follows: physical constraints of the system are introduced, including current limiting, lower limit of magnetic field amplitude, and upper limit of gradient magnetic field force amplitude; the optimal coefficients are solved using linear programming. The optimal combination of coil input currents is obtained.
[0032] S105: The optimal coil input current corresponding to each coil drives the coil combination to generate the target uniform magnetic field and the target gradient magnetic field, which are applied to the microrobot to be controlled, thereby driving the microrobot to achieve multimodal motion.
[0033] The gradient force-driven control method for multimodal motion of microrobots described in this invention is based on the contribution of the unit current of each coil in the coil assembly to the magnetic field and gradient magnetic force. It obtains the magnetic field mapping matrix and the gradient magnetic force mapping matrix, and introduces the magnitude scalars of the magnetic field vector and the gradient magnetic force vector in the desired gradient magnetic force direction to construct a linear homogeneous control equation that makes the magnetic field direction collinear with the desired gradient magnetic force direction. Based on this, singular value decomposition is performed on the coefficient matrix of the linear homogeneous control equation to extract the null basis vector as the general solution. Under preset constraints, the method maximizes the gradient magnetic force vector in the desired gradient magnetic force direction. Using the amplitude scalar as the objective, the optimal coil input current corresponding to each coil is obtained by solving the problem. This invention uses the optimal coil input current corresponding to each coil to drive a coil combination consisting of three pairs of Helmholtz coils and one pair of Maxwell coils, generating a target uniform magnetic field and a target gradient magnetic field, which act on the microrobot to be controlled, driving it to achieve multimodal motion. This ensures that the magnetic field strength is sufficient to lock the direction of the magnetic moment, and also ensures that the output gradient magnetic field force reaches its maximum within the range allowed by the system hardware and task safety, thus achieving a unity of control accuracy and driving efficiency, and breaking through the limitation of a single crawling gait in the confined space of the microrobot.
[0034] Based on the above embodiments, the theoretical modeling and gradient construction of the magnetically controlled coil system are described in this embodiment of the invention. (Refer to...) Figure 2 The figure shows the simulation results of the gradient magnetic field of the Maxwell coil along the Z-axis. Figure 2 (a) is a simulated thermal diagram of the magnetic field of a Maxwell coil. Figure 2 (b) is a simulation diagram of the magnetic field components of the Maxwell coil along the Z-axis. Figure 2 (c) is a simulation diagram of the magnetic field components of the Maxwell coil along the X-axis. Figure 2 (d) is a simulation diagram of the magnetic field gradient in the Z-axis direction of the Maxwell coil. In this system, the magnetic field generating module based on multiple coil combinations is surrounded by three pairs of Helmholtz coils and one pair of Z-axis Maxwell coils. Theoretical modeling shows that the magnetic induction intensity of the Maxwell coil at the center point is strictly zero, and only the first-order gradient term is non-zero, which can be approximated as a uniform gradient magnetic field, providing an accurate gradient magnetic field force for the vertical lifting of the robot. For the Helmholtz coil, although it generates an approximately uniform magnetic field when the current is ideally in the same direction, in the gradient magnetic field force translational control of this invention, the system applies a differential current to the same pair of Helmholtz coils, and uses the current difference to introduce an adjustable first-order gradient component, thereby constructing the magnetic field gradient required to drive the robot's translation in the horizontal direction.
[0035] Reference Figure 3 The diagram shows two typical toroidal coil models. Figure 3 (a) is a model diagram of a Helmholtz coil. Figure 3(b) is the Maxwell coil model. The finite element magnetic field gradient simulation verification of the single-axis coil is as follows: To verify the influence of actual finite-sized conductors and coil windings on the magnetic field gradient distribution characteristics, the system was numerically simulated based on the finite element method. The simulation results of the Z-axis Maxwell coil show that the magnetic field amplitude at its geometric center is close to zero, while the axial magnetic field gradient exhibits a highly linear variation characteristic in the central neighborhood, and the radial gradient maintains a strict proportional distribution relationship with the axial gradient, verifying its ability to provide a highly linear uniform gradient magnetic field to support vertical lifting action.
[0036] Based on the above description, in this embodiment, driving the microrobot to achieve multimodal motion includes putting the microrobot into a pulse translation mode, including: applying the corresponding two optimal coil input currents to the Helmholtz coils in the same horizontal direction to construct a three-dimensional magnetic field gradient in the horizontal direction; the horizontal direction is the direction parallel to the XoY plane; based on the pulse gradient magnetic field force driving strategy, during the excitation period, the gradient magnetic field force is output to overcome the maximum static friction force and cause the microrobot to move; during the non-excitation period, the applied gradient magnetic field force is reduced, causing the microrobot to decelerate and stop due to frictional resistance and maintain a static friction state; based on the displacement during the excitation period and the deceleration and stopping during the non-excitation period, the quasi-static stable translation of the microrobot is achieved.
[0037] This invention constructs a three-dimensional magnetic field gradient in the horizontal direction by independently applying the corresponding optimal coil input current to a pair of Helmholtz coils in the same horizontal direction. Combined with a pulsed gradient magnetic field force driving strategy, the output gradient magnetic field force overcomes the maximum static friction during the excitation period, causing the microrobot to move. During the non-excitation period, the applied gradient magnetic field force is reduced, causing the robot to decelerate and stop due to frictional resistance, maintaining a static friction state. This achieves quasi-static stable translation of the microrobot in highly confined spaces. This pulsed driving method effectively avoids the velocity accumulation and attitude instability problems caused by traditional continuous sliding, enabling the robot to achieve controllable movement even in extremely confined environments where a complete crawling gait cannot be completed, significantly improving the microrobot's spatial maneuverability.
[0038] Based on the above description, in this embodiment, driving the microrobot to achieve multimodal motion includes putting the microrobot into a head-raising mode, including: inputting the corresponding optimal coil input current to the Maxwell coil and each Helmholtz coil in the coil assembly with the desired gradient magnetic field force direction of vertically upward, generating a vertically upward gradient magnetic field force; using a continuous loading strategy with a duty cycle of 100% and a slowly increasing upper limit of the gradient magnetic field force amplitude to smoothly raise the head of the microrobot to perform the lifting operation; after the lifting operation is completed, using a gradual unloading strategy with a slowly decreasing upper limit of the gradient magnetic field force amplitude, symmetrical to the continuous loading strategy, to slowly reduce the gradient magnetic field force, causing the microrobot to fall back to its original position.
[0039] This invention uses a vertically upward direction as the desired gradient magnetic field force. Optimal coil input currents are input to the Maxwell coil and each Helmholtz coil to generate a vertically upward gradient magnetic field force. A continuous loading strategy with a 100% duty cycle and a slowly increasing upper limit of the gradient magnetic field force amplitude is employed to smoothly raise the head of the microrobot for a lifting operation. After the operation is completed, a gradual unloading strategy with a symmetrically decreasing upper limit of the gradient magnetic field force amplitude is used to safely lower the robot back to its original position. This gradual loading and unloading strategy effectively avoids posture instability or tissue damage caused by sudden impacts, significantly improving the robot's spatial maneuverability and its ability to expand its field of vision through local interactions. It provides a reliable technical means for microrobots to perform field-of-view expansion operations in intestinal examinations and surgical assistance.
[0040] Based on the above embodiments, this embodiment also provides a gradient force drive control system for multimodal motion of a microrobot, referring to... Figure 4 The diagram shown is a schematic representation of the gradient force drive control system for multimodal motion of a microrobot in this embodiment, including: A dual-view camera is used to capture images of the micro-robot to be controlled and obtain its coordinates. The coil assembly includes three pairs of Helmholtz coils orthogonally arranged along the X, Y, and Z axes, and one pair of Maxwell coils arranged along the Z axis. The host computer is connected to the dual-view camera so as to obtain the optimal coil input current corresponding to each coil based on the gradient force drive control method for multimodal motion of microrobots as described above. The current-driven module has its input end connected to the host computer and its output end supplying power to the coil combination, so as to drive the coil combination to generate the target uniform magnetic field and the target gradient magnetic field based on the input current of each optimal coil.
[0041] Among them, the Z-axis Maxwell coil in the coil combination has a strictly zero magnetic induction intensity at the center point, with only the first-order gradient term in the axial direction being non-zero. It is used to generate a highly linear uniform gradient magnetic field in the neighborhood of the center of the workspace, providing a precise vertically upward gradient magnetic field force for the vertical lifting action of the microrobot. The Helmholtz coil is used to generate an approximately uniform spatial magnetic field when the current is ideally in the same direction. In the gradient force translational control mode of the present invention, the system independently applies differential current to the same pair of Helmholtz single coils in the horizontal direction (X-axis or Y-axis), and uses the current difference to introduce an adjustable first-order gradient component, thereby constructing the three-dimensional magnetic field gradient required to drive the robot's translation in the horizontal direction.
[0042] Specifically, the dual-view camera includes an upper camera and a front camera to achieve more comprehensive position coordinate acquisition.
[0043] Specifically, the current driving module in this embodiment includes: The first independent constant voltage DC power supply has its input end connected to the host computer, and its output end connected to the left coil of the X-axis Helmholtz coil through the first bidirectional full-bridge PWM current drive board. The second independent constant voltage DC power supply has its input end connected to the host computer, and its output end connected to the right coil of the X-axis Helmholtz coil through the second bidirectional full-bridge PWM current drive board. The third independent constant voltage DC power supply has its input end connected to the host computer, and its output end is connected to the front coil of the Y-axis Helmholtz coil through the third bidirectional full-bridge PWM current drive board. The fourth independent constant voltage DC power supply has its input end connected to the host computer, and its output end connected to the rear coil of the Y-axis Helmholtz coil through the fourth bidirectional full-bridge PWM current drive board. The fifth independent constant voltage DC power supply has its input end connected to the host computer, and its output end is connected to the coil of the Z-axis Helmholtz coil after the two coils are connected in series through the fifth bidirectional full-bridge PWM current drive board. The sixth independent constant voltage DC power supply has its input end connected to the host computer, and its output end is connected to the coil of the Maxwell coil after the two coils are connected in reverse series through the sixth bidirectional full-bridge PWM current drive board. Each bidirectional full-bridge PWM current drive board is used to adjust the PWM duty cycle of the current in its branch according to the instructions of the host computer and switch the conduction direction of the bridge, so as to realize the continuous and fine adjustment of the amplitude of the coil input current, the rapid switching of the current direction, and the microsecond-level high-frequency dynamic refresh of the gradient magnetic field force.
[0044] In this embodiment, the current drive module uses six independent constant voltage DC power supplies as energy sources, and each power supply is connected to an independent bidirectional full-bridge PWM current drive board between itself and its corresponding single coil or series coil group. By issuing commands from the host computer to adjust the PWM duty cycle and switch the conduction direction of the bridge in real time, the system overcomes the limitation of the constant voltage DC power supply being difficult to adjust quickly, and realizes continuous and fine adjustment of the input current amplitude of each coil and rapid switching of the current direction. This satisfies the microsecond-level high-frequency dynamic refresh and precise control of the gradient magnetic field force required for the pulse translation and continuous lifting of the microrobot.
[0045] Guided by the aforementioned simulation and modeling theories, this embodiment employs six constant-voltage DC power supplies. To overcome the limitation of constant-voltage DC power supplies in rapidly adjusting amplitude and direction, bidirectional full-bridge PWM driver boards are configured between the power supplies and the coil array. During system operation, the host computer first receives images from dual-view cameras via a data acquisition card and extracts the robot's spatial coordinates. Due to the non-uniformity of the spatial magnetic field gradient, the system utilizes the central difference method to construct the Jacobian gradient matrix at the working point in real time. By combining linear programming algorithms online, the optimal current distribution of each channel that maximizes the gradient magnetic field force in the desired direction under the current pose is obtained. Finally, the PWM duty cycle and direction signal are sent to the corresponding driver board via the 485 bus to achieve microsecond-level high-frequency refresh of the gradient magnetic field force.
[0046] Based on the above embodiments, this invention describes the pulsed magnetic field force-driven translational control process for a microrobot navigating in a confined space. For example... Figure 5 The diagram shown is a schematic of the tunnel structure. Figure 5 (a) is a schematic diagram of a type I tunnel. Figure 5 (b) is a schematic diagram of an L-shaped tunnel. Figure 5 (c) is a schematic diagram of an S-shaped tunnel. Figure 6 The diagram shown illustrates the movement of a micro-robot within a type I tunnel; Figure 7 The diagram shown illustrates the movement of a micro-robot within an L-shaped tunnel. Figure 8 The diagram shows a microrobot navigating an S-shaped tunnel.
[0047] This embodiment describes a robot in, for example Figure 5 This illustrates translational control in a confined tunnel where the height is insufficient to support a crawling gait. First, the robot's foot magnetic moment is adjusted to a horizontal sliding posture opposite to the direction of movement. Then, a pulsed gradient magnetic field is generated using the method of this invention: during the excitation period (ON), the gradient magnetic field force output by the system overcomes the maximum static friction force, causing the robot to produce an effective small displacement; during the non-excitation period (OFF), the applied gradient magnetic field force is removed or significantly reduced, and the robot gradually decelerates due to contact friction resistance until it stops and returns to a static friction holding state. This quasi-static pulse control, with its short-term drive and full-stop cycle, effectively avoids velocity accumulation and posture instability caused by continuous sliding.
[0048] Based on the above embodiments, this embodiment simulates the vertical gradient magnetic field film lifting control for intestinal mucosal dissection. For example... Figure 9 The diagram shown illustrates a verification experiment of a microrobot's membrane-lifting mechanism. Specifically, to address situations where intestinal wall folds or a membrane obstructs the view, this embodiment employs a vertically upward gradient magnetic field force for the head-lifting operation. The system sets the desired gradient magnetic field force direction vertically upward, causing the robot's feet to stand upright, and the magnetic moment... The current should be directed as far as possible in the positive Z-axis direction. The force-controlled solution model primarily outputs current to the Maxwell and Helmholtz coils along the Z-axis. This embodiment employs a continuous loading strategy with a 100% duty cycle and sets the upper limit parameter of the target gradient magnetic field force in the solution model. The loading strategy gradually increases the magnetic field force from small to large, allowing the robot's head to rise smoothly and eventually stabilize, lifting the membrane above. After the operation is complete, the gradient magnetic field force is gradually reduced through a symmetrical, gradual unloading method, allowing the robot to safely fall back to its original position.
[0049] At the hardware level, this invention employs six independent constant-voltage DC power supplies paired with six bidirectional full-bridge PWM current drive boards. Through coil series optimization, precise control of eight coils is achieved, preserving the three-dimensional magnetic field gradient control capability while reducing hardware cost and control complexity. Simultaneously, the drive boards enable continuous and fine adjustment of coil current amplitude and rapid direction switching, providing hardware assurance for microsecond-level high-frequency dynamic refresh of the gradient magnetic field force. At the control level, this invention introduces a Jacobian matrix to construct a compact expression model of the gradient magnetic field force. By extracting the null space basis vector through singular value decomposition, and under constraints such as current limiting, lower limit of magnetic field amplitude, and upper limit of gradient magnetic field force amplitude, linear programming is used to solve for the optimal coil input current, achieving precise control where the magnetic field and the desired gradient magnetic field force direction are collinear. By combining a pulse gradient magnetic field force-driven strategy, the robot can complete quasi-static stepping translation without inertial drift in low and confined tunnels. At the same time, it can achieve stable vertical head-raising and lifting actions by relying on the Z-axis gradient magnetic field, effectively removing local obstructions, greatly improving the ability to operate in confined spaces and the accuracy of local interaction. This allows the system to be adapted to complex biomedical environments such as the intestines, avoiding tissue damage while achieving real-time posture feedback and dynamic adjustment, and has good versatility and scalability.
[0050] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.
[0051] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.
[0052] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.
[0053] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.
[0054] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. A gradient force-driven control method for multimodal motion of a microrobot, characterized in that, include: The robot to be controlled is placed in the magnetic field of a coil combination consisting of three pairs of Helmholtz coils orthogonally arranged along the X, Y, and Z axes, and one pair of Maxwell coils arranged along the Z axis. The magnetic field model under non-uniform magnetic field is compactly represented based on the Jacobian matrix, and the magnetic field gradient at each position coordinate under the compact representation is numerically approximated using the central difference method to obtain the magnetic field gradient expression. Based on the contribution of the unit current of each coil in the coil combination to the magnetic field and the gradient magnetic field force, the magnetic field mapping matrix and the gradient magnetic field force mapping matrix are obtained. Then, the magnitude scalars of the magnetic field vector and the gradient magnetic field force vector in the direction of the desired gradient magnetic field force are introduced to construct a linear homogeneous control equation that makes the magnetic field direction collinear with the direction of the desired gradient magnetic field force. Singular value decomposition is performed on the coefficient matrix of the linear homogeneous control equation to extract the null space basis vector as the general solution. Under preset constraints, the optimal coil input current corresponding to each coil is obtained by maximizing the magnitude scalar of the gradient magnetic field force vector in the desired gradient magnetic field force direction. The optimal coil input current corresponding to each coil is used to drive the coil combination to generate a target uniform magnetic field and a target gradient magnetic field, which are applied to the microrobot to be controlled, thereby driving the microrobot to achieve multimodal motion.
2. The gradient force-driven control method for multimodal motion of a microrobot according to claim 1, characterized in that, The Maxwell coils arranged along the Z-axis have zero magnetic induction at the center point, with only the first-order gradient term being non-zero. They are used to generate a uniform gradient magnetic field with high linearity in the neighborhood of the center of the workspace. The Helmholtz coils generate a uniform magnetic field when they are in the ideal same direction and have the same current. An adjustable first-order gradient component is introduced by independently applying a pair of differential currents to the same pair of horizontally oriented Helmholtz coils.
3. The gradient force-driven control method for multimodal motion of a microrobot according to claim 1, characterized in that, When using the Jacobian matrix to compactly represent the magnetic field model under non-uniform magnetic fields, the Jacobian matrix satisfies symmetry and its trace is zero.
4. The gradient force-driven control method for multimodal motion of a microrobot according to claim 1, characterized in that, The expression for the magnetic field gradient is: ； ； ； in, Represents position coordinates Magnetic field strength at that location , and These represent minute increments along the X-axis, Y-axis, and Z-axis, respectively. , This indicates the partial derivative.
5. The gradient force-driven control method for multimodal motion of a microrobot according to claim 1, characterized in that, A linear homogeneous governing equation is constructed that makes the direction of the magnetic field collinear with the direction of the desired gradient magnetic force, expressed as: ； in, Represents the magnetic field mapping matrix. Represents the gradient magnetic field force mapping matrix. This represents the unit vector indicating the direction of the desired gradient magnetic field force. This represents the current vector composed of the input currents of each coil in the coil assembly. To achieve what is desired; , and The input currents for the left and right coils of the X-axis Helmholtz coil are given. and Input current to the corresponding coils of the front and rear coils of the Y-axis Helmholtz coil. The input current of the Z-axis Helmholtz coil is the coil whose two coils are connected in series. The input current to the coil after the two coils of the Maxwell coil are connected in reverse series; This represents the magnitude scalar of the magnetic field vector in the direction of the desired gradient magnetic force. It represents the magnitude scalar of the gradient magnetic field force vector in the direction of the desired gradient magnetic field force.
6. The gradient force-driven control method for multimodal motion of a microrobot according to claim 5, characterized in that, Singular value decomposition is performed on the coefficient matrix of the linear homogeneous control equations to extract the null space basis vectors as the general solution. Under preset constraints, the optimal coil input current for each coil is obtained by maximizing the magnitude scalar of the gradient magnetic field force vector in the desired gradient magnetic field force direction, including: The singular value decomposition of the coefficient matrix of the linear homogeneous governing equations is expressed as: ; Extracting the null space basis vectors, we can represent them as follows: ; Obtain the general solution , is represented as: ; The current limiting constraint is constructed as follows: ; The lower limit constraint of the magnetic field amplitude is constructed as follows: ; The upper limit constraint on the amplitude of the gradient magnetic field force is constructed as follows: ; The objective, maximizing the magnitude scalar of the gradient magnetic field force vector along the desired gradient magnetic field force direction, is expressed as: ; Find the optimal coefficients in the coil combination using linear programming. Calculate the optimal coil input current; in, , represents the set of indices corresponding to all null space bases in the coil combination. express The i-th number on the diagonal, It is an equation The solution set The vectors in the vectors are linearly independent; express The first of the matrix List, express The first of the matrix Line 1 List, , ; for The 7th row of the matrix The column represents the magnitude scalar of the magnetic field vector in the direction of the desired gradient magnetic force. , Indicates the lower limit of the magnetic field amplitude; for The 8th row of the matrix The column represents the magnitude scalar of the gradient magnetic field force vector in the direction of the desired gradient magnetic field force. ; This indicates the upper limit of the gradient magnetic field force amplitude.
7. The gradient force-driven control method for multimodal motion of a microrobot according to claim 1, characterized in that, Driving a microrobot to achieve multimodal motion involves putting the microrobot into a pulse translation mode, including: Two optimal coil input currents are applied to Helmholtz coils in the same horizontal direction to construct a three-dimensional magnetic field gradient in the horizontal direction; the horizontal direction is the direction parallel to the XoY plane. Based on the pulse gradient magnetic field force driving strategy, the gradient magnetic field force is output during the excitation period to overcome the maximum static friction force and cause the microrobot under control to generate displacement. During the non-excitation period, the applied gradient magnetic field force is reduced so that the microrobot under control decelerates and stops due to frictional resistance. Quasi-static stable translation of the microrobot under control is achieved by displacement during the excitation period and deceleration and stopping during the non-excitation period.
8. The gradient force-driven control method for multimodal motion of a microrobot according to claim 1, characterized in that, Driving the microrobot to achieve multimodal motion includes putting the microrobot into a head-up mode, including: With the desired gradient magnetic field force pointing vertically upward, the corresponding optimal coil input current is input to the Maxwell coil and each Helmholtz coil in the coil combination to generate a vertically upward gradient magnetic field force. A continuous loading strategy with a duty cycle of 100% and a slowly increasing upper limit of the gradient magnetic field force amplitude was adopted to smoothly raise the head of the micro-robot to be controlled and perform the lifting operation. After the lifting operation is completed, a gradual unloading strategy is adopted, in which the upper limit of the gradient magnetic field force amplitude is slowly reduced, symmetrical to the continuous loading strategy, so that the microrobot to be controlled falls back to its original position.
9. A gradient force drive control system for multimodal motion of a microrobot, characterized in that, include: A dual-view camera is used to capture images of the micro-robot to be controlled and obtain its coordinates. The coil assembly includes three pairs of Helmholtz coils orthogonally arranged along the X, Y, and Z axes, and one pair of Maxwell coils arranged along the Z axis. The host computer is connected to the dual-view camera so as to obtain the optimal coil input current corresponding to each coil based on the gradient force drive control method for multimodal motion of microrobots as described in any one of claims 1 to 8. The current-driven module has its input end connected to the host computer and its output end supplying power to the coil combination, so as to drive the coil combination to generate the target uniform magnetic field and the target gradient magnetic field based on the input current of each optimal coil.
10. The gradient force drive control system for multimodal motion of a microrobot according to claim 9, characterized in that, The current drive module includes: The first independent constant voltage DC power supply has its input end connected to the host computer, and its output end connected to the left coil of the X-axis Helmholtz coil through the first bidirectional full-bridge PWM current drive board. The second independent constant voltage DC power supply has its input end connected to the host computer, and its output end connected to the right coil of the X-axis Helmholtz coil through the second bidirectional full-bridge PWM current drive board. The third independent constant voltage DC power supply has its input end connected to the host computer, and its output end is connected to the front coil of the Y-axis Helmholtz coil through the third bidirectional full-bridge PWM current drive board. The fourth independent constant voltage DC power supply has its input end connected to the host computer, and its output end connected to the rear coil of the Y-axis Helmholtz coil through the fourth bidirectional full-bridge PWM current drive board. The fifth independent constant voltage DC power supply has its input end connected to the host computer, and its output end is connected to the coil of the Z-axis Helmholtz coil after the two coils are connected in series through the fifth bidirectional full-bridge PWM current drive board. The sixth independent constant voltage DC power supply has its input end connected to the host computer, and its output end is connected to the coil of the Maxwell coil after the two coils are connected in reverse series through the sixth bidirectional full-bridge PWM current drive board. Each bidirectional full-bridge PWM current drive board is used to adjust the PWM duty cycle of the current in its branch according to the instructions of the host computer and switch the conduction direction of the bridge, so as to realize the continuous and fine adjustment of the amplitude of the coil input current, the rapid switching of the current direction, and the microsecond-level high-frequency dynamic refresh of the gradient magnetic field force.