Magnetic Actuation System Research Articles

Dynamic modeling and simulation of a new conceptual design of a magnetic capsule robot by application of endoscopic capsule

This paper investigates design, modeling, simulation, and dynamic issues related to self-propelled endoscopic capsule navigated inside the human body through external magnetic fields. A novel magnetic propulsion system is proposed and fabricated, which has great potential of being used in the field of noninvasive gastrointestinal endoscopy. The endoscopic capsule dynamic is studied on a medical silicone plate as the closest available material for the stomach tissue. First, the mechanical characteristics of the medical silicone plate is measured. Next, the forces acted on the endoscopic capsule which are friction, hydrodynamic and magnetic forces are determined by means of test and numerical techniques such as finite element method. Having known the magnitude of forces and torques on the endoscopic capsule, the dynamics of capsule are calculated under different initial conditions and external magnetic fields.

Strong magnetic actuation system with enhanced field articulation through stacks of individually addressed coils

Miniaturization of medical tools promises to revolutionize surgery by reducing tissue trauma and accelerating recovery. Magnetic untethered devices, with their ability to access hard-to-reach areas without physical connections, emerge as potential candidates for such miniaturization. Despite the benefits, these miniature devices face challenges regarding force and torque outputs, restricting their ability to perform tasks requiring mechanical interactions such as tissue penetration and manipulation. To overcome magnetic actuation system-based force and torque limitations, this study proposes Variable Outer Radius Individually Addressable Coil Stacks (VORIACS), a novel magnetic actuation system optimized for high force output generation to magnetic devices within its workspace. The VORIACS marks significant improvements and breakthroughs in magnetic actuation within decimeter-scale workspace. The VORIACS is comprised of 12 coils that are optimized for 2D magnetic field generation under maximized power consumption of up to 12 kW. We implement six two-channel motor controllers, powered by six separate power supplies. Each of the twelve coils in the system is operated on its own motor-controller channel. This arrangement allows the system to exceed the magnetic forces and torques possible for single-coil versions of the same geometry. This study elaborates on optimizing, manufacturing, integrating, and demonstrating this system. Comparative analysis reveals that while a suboptimal, single-coil version of this system generates 0.31 N force (710 mT/m magnetic gradient magnitude), the VORIACS produces 1.673 N force (3834 mT/m magnetic gradient magnitude) on the same magnetic object placed 5 cm away from the coils. Moreover, the strong penetration force generated by VORIACS enables needle penetration to a mock gel that has the rigidity of liver tissue. In addition, we demonstrate the advantage of stacked coils with variable radii for magnetic field manipulability while maintaining the optimized force delivery property of the system, which improves control and could facilitate multi-tool manipulation. By enabling a fivefold increase in magnetic pulling force compared to its single-coil counterpart, VORICAS raises the potential penetration capabilities of untethered magnetic robotics in surgical procedures.

Improving the steering performance of microrobots by using a magnetically actuated technique

Mobile microrobots show the significance of potential medical procedures and challenge areas within the human body. An applied electromagnetic field is used as a precise magnetic actuation system for controllable steering mobility, and positioning is used. In this work, an adaptable microrobot is developed with an effective technique to enhance steering. An electromagnetic system is employed to produce an external magnetic field that guides a microrobot to improve its steerability. In particular, a driving system of eight coils creates a magnetic field that actuates the microrobot and enables upward and downward motion. Accordingly, three types of microrobot designs are proposed. Consequently, an efficient variation of steering in terms of deformation angle is achieved. The corresponding performance is determined mathematically in terms of the main system parameters, such as external magnetic field and microrobot geometry. In addition, finite element model is used for comparison and validation. Simulation results show that for a relatively high value of magnet field, namely, 15 mT and 90°, the deformation angles were 36.98° for the first design, 39.11° for the second design, and 34.48° for the third design in upward deformation. By contrast, the downward deformation ranges were –40.42°, –39.46°, and –37.04° for the first, second, and third designs, respectively, at –90° The error between the upward and downward steering of the second design had the lowest value of 0.35° The second design of the microrobots has the least error between the upward and downward deformation ratio at 0.89 %. In comparison, the first design has a 9.3 % error, and the third design has a 7.42 % error, with a relatively high value of magnetic field density (15 mT). Simulations have shown that the proposed second design is suitable for navigating narrow artery branches with the least error ratio and more precise control. This work verifies that the model could accurately control the steering of microrobots.

Magnetically actuated cisplatin-loaded nanoparticle collectives enhance drug penetration for potentiated ovarian cancer chemotherapy

Chemotherapy is the main clinical treatment for ovarian cancer, but still faces challenges of low drug targeting efficiency and insufficient drug permeability. Drug-loaded nanoparticle collectives, which are actuated by magnetic field, could be targeted to a designated location and achieve targeted drug delivery. In this work, we report a strategy that utilizes magnetic mesoporous silica nanoparticles loaded with cis-diaminodichloroplatinum (Fe3O4@SiO2-CDDP) for targeted delivery of chemotherapeutic drugs and enhances penetration into deep tumors. The Fe3O4@SiO2-CDDP collectives actively moved to the target tumor site, and this movement was regulated by a magnetic actuation system. Under the action of a torque-force hybrid magnetic field (TFMF), Fe3O4@SiO2-CDDP could further penetrate into the interior of tumors and achieve pH-responsive drug release in the tumor environment. The feasibility of this strategy was verified in three-dimensional cell spheres in vitro and in a tumor-bearing mouse model in vivo. This magnetically actuated nanoparticle collectives enhanced drug penetration strategy provides a new paradigm for targeted drug delivery and potentiated tumor therapy.

A magnetically driven symmetrical leech-inspired soft robot for various applications

In this study, we present a symmetrical leech-inspired soft robot that employs a magnetic actuation system for precise movement control. The robot weighs only 1.17 g and has a symmetrical micro-concave structure that maintains a stable kinematic posture during high-frequency motion. The gravity generated by the magnets is used to simulate the attraction of the two suckers of the leech. The experimental results show that the micro-concave structure is designed to achieve a robot velocity of up to 22.66 mm/s under 45 Gauss conditions, which is a better kinematic performance compared to the single symmetric structure (with a velocity of 13.2 mm/s). According to our experiments testing the robot in different motion modes, it has shown the ability to stably climb over obstacles, transport objects, and detect solutions, demonstrating its potential for diverse applications in healthcare, emergency rescue, and environmental monitoring.

Low-cost force-driven modular magnetic actuation system for microswimmer maneuvering

Low-cost force-driven modular magnetic actuation system for microswimmer maneuvering

Optimal Parameter Design and Microrobotic Navigation Control of Parallel-Mobile-Coil Systems

In this work, we study the optimal parameter design and microrobotic navigation control of the parallel-mobile-coil system (PMCS) that consists of three mobile electromagnetic coils. With motion driven by a parallel mechanism, the three coils can move in 3D large space and keep as close as possible to the controlled microrobot for magnetic actuation. Although promising for microrobotic applications, how to design such a type of system for a specific workspace requirement is untackled. Regarding this issue, we propose a computational design method, by which one can calculate the structural parameters of a PMCS starting from a required cylindrical workspace. With the derived performance metrics for motion actuation and magnetic actuation of the PMCS, the system actuation performance (composed of motion and magnetic actuation) is optimized. Utilizing the design method, we optimally construct a prototype PMCS for microrobotic navigation. We then conduct experiments to validate the demanding field/force generation capability of the PMCS and demonstrate the navigation control of different types of magnetic microrobots. In particular, we design closed-loop motion controllers for both torque and force-driven microrobots, using which automated large-workspace and high-accuracy trajectory tracking is realized. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This work is motivated by the recent wide interest in magnetic microrobots. Driven by external magnetic fields, magnetic microrobots can navigate in a wireless manner for targeted delivery/therapy. To promote microrobot applications to the human body, a magnetic actuation system with large workspace is desirable. However, due to the fast decay of magnetic field, the commonly used stationary coil-based magnetic actuation systems have the workspace scalability problem. Thus, several mobile-coil-based systems have been designed. In this work, we propose an optimal design method for the PMCS, using which one can design a PMCS starting from a cylindrical workspace with performance being optimized. We construct a PMCS prototype with a workspace of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi 230 \times 100$</tex-math> </inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^3$</tex-math> </inline-formula> , and we then study the automated microrobotic navigation control methods for the PMCS. Controllers are designed for different types of magnetic microrobots, and experiments show that, using the controllers, the PMCS can perform automated large-workspace microrobotic navigation control with high accuracy.

Dual-Functional Laser-Guided Magnetic Nanorobot Collectives against Gravity for On-Demand Thermo-Chemotherapy of Peritoneal Metastasis.

Combining hyperthermic intraperitoneal chemotherapy with cytoreductive surgery is the main treatment modality for peritoneal metastatic (PM) carcinoma despite the off-target effects of chemotherapy drugs and the ineluctable side effects of total abdominal heating. Herein, a laser-integrated magnetic actuation system that actively delivers doxorubicin (DOX)-grafted magnetic nanorobot collectives to the tumor site in model mice for local hyperthermia and chemotherapy is reported. With intraluminal movements controlled by a torque-force hybrid magnetic field, these magnetic nanorobots gather at a fixed point coinciding with the position of the localization laser, moving upward against gravity over a long distance and targeting tumor sites under ultrasound imaging guidance. Because aggregation enhances the photothermal effect, controlled local DOX release is achieved under near-infrared laser irradiation. The targeted on-demand photothermal therapy of multiple PM carcinomas while minimizing off-target tissue damage is demonstrated. Additionally, a localization/treatment dual-functional laser-integrated magnetic actuation system is developed and validated in vivo, offering a potentially clinically feasible drug delivery strategy for targeting PM and other intraluminal tumors.

Multimodal Motion Control of Soft Ferrofluid Robot With Environment and Task Adaptability

Soft microrobotics has recently been an active field that advances new microrobot design, adaptive motion, and biomedical applications. In this work, we study the ferrofluid robot (FR), which has soft nature and exhibits paramagnetism. Currently, motion of the FR is usually realized by magnetic force, and the task execution requires relatively complex systems for simultaneous field and gradient control. To enable the FR with more motion modes for environment and task adaptability, we program three dynamic field forms and realize three corresponding torque-actuated motion modes: <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Rolling</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Wobbling</i> , and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Oscillating</i> . Together with the force-based <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Dragging</i> mode, we provide a complete motion control scheme for the FR. As this scheme only requires 3-D dynamic fields or gradients for actuation, the complexity of the magnetic actuation system is reduced. We formulate the motion and deformation actuation principles of the FR, and the four motion modes are demonstrated and characterized. With the implementation of automated tracking and control algorithms, controllability of the new torque-based modes is testified. We then fabricate different kinds of environments and cargoes to validate the environment and task adaptability of the FR by using the proposed scheme. Especially, we implement the scheme on a self-constructed system consisting of three mobile coils, and experiments realize the long-distance navigation of the FR via <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Rolling</i> or <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Dragging</i> modes. The ultrasound-guided navigation in a 3-D tissue-mimicking endovascular environment shows the potential for delivery applications.

Inverse kinematic analysis and agile control of a magnetically actuated catheter

In recent years, there has been a growing application of robotic-assisted magnetic actuation systems in the treatment of cardiovascular diseases because of the fast response and the miniaturization of medical tools. However, inverse kinematic (IK) modeling in permanent magnet systems is still a challenging task due to the complexity of the magneto-solid strong coupling field. In this paper, we present a magnetic actuation system that uses the rotation of a single permanent magnet to steer the intravascular catheter. The main contribution is the proposal of an IK modeling method that establishes a relationship between the catheter's deflection angle and the rotation angle of the driving magnet (DM). Our proposed method uses the constant curvature model (CCM) to decouple the catheter's deformation and the magnetic loads, thus enabling the efficient estimation of the position of the catheter's tip based on the desired deflection angle. After establishing the equilibrium equation, we employ a numerical computation method to optimize the rotation angle of the DM. To facilitate fast convergence, we propose an analytical solution to determine the optimal initial value. Our proposed IK modeling method has been proven to be effective in the model validation experiment, which achieves a good balance between accuracy and efficiency. The difference between the planned and actual deflection angle is 4.55±3.44° and the distal position error is 1.26±0.74 mm. The completion time of our IK method is 1–4 ms. The performance of our magnetic actuation system has been evaluated in the phantom experiment, in which the catheter can pass sequentially through the planned bifurcations and finally reach all the goals under the magnetic guidance.

A programmable ferrofluidic droplet robot.

Soft miniature robots have wide potential applications in lab-on-a-chip and biomedical sciences due to their deformability, safety, and remarkable controllability. However, current ferrofluidic droplet robots have some problems, such as easy broken, limited motion range and high energy consumption. Therefore, the objective of this study is to propose a programmable ferrofluidic flexible droplet robot (PFDR) with control strategies for elongation, splitting and merging behaviors by designing an actuation system consisting of a row of electromagnets and a robotic arm or a coordinate robot. The PFDR can not only deform actively to prevent itself from breaking, but also deform passively to fit the profile of channels or tubes to move efficiently. The actuation system can make PFDR have larger motion range as well as lower energy consumption. The design concept and the operating principle of PFDR are presented. The magnetic actuation system is developed. The lag of PFDR is analyzed in theoretical and experimental ways. The splitting and merging behaviors are investigated and other functionalities are studied as well.

A Model Predictive Control Based Magnetorquer-only Attitude Control Approach for a Small Satellite

Magnetic attitude control is an essential topic in attitude determination and control (ADC) studies as it can be used as the main or backup attitude control method in different scenarios. The magnetic actuation system is advantageous for its low cost, reliability, and ease of implementation when the pointing accuracy requirement is not high. The major issue in using magnetorques for attitude control is that it provides controllability over a period. In this study, a magnetic attitude control algorithm is designed for a low Earth orbit sun-synchronous small satellite by using a model predictive control approach which is an advanced control technique that generates control input using the system model to predict the future behavior of the system. The control algorithm is integrated into the overall ADC algorithm and the complete algorithm is tested via simulations. The simulation results show that the three-axis attitude control can be achieved with an accuracy of below 10 deg in around 10 orbits from the tumbling status of the satellite.

Magnetic Levitation Actuation and Motion Control System with Active Levitation Mode Based on Force Imbalance

Accurate large-displacement magnetic levitation actuation and its stability remain difficult in non-liquid environments. A magnetic levitation actuation and motion control system with active levitation mode is proposed in this paper. The actuating force of the system is generated by the external magnetic field. A neural network proportion-integration-differentiation (PID) controller is designed for active actuation, and a force imbalance principle is built for the step motion mode. Dual electromagnetic actuators are configured to generate a superimposed magnetic field, ensuring that the electromagnetic force on the ball is more uniform and stable than single actuators. Dual-hall-structure sensors are used to measure displacement, thereby reducing overshoot and ensuring stability whilst motivating the ball. Due to the high adaptability of the neural network to complex systems with nonlinear and ambiguous models, the PID controller composed of neurons has stronger adaptability through tuning the PID controller parameters automatically. Furthermore, the proposed controller can solve the shortcoming that the deviation between the controlled object and the steady-state operating point increases and the tracking performance deteriorates rapidly. The strong robustness and stability in active levitation and motion control is achieved during both ascending and descending processes.

A 5-D Large-Workspace Magnetic Localization and Actuation System Based on an Eye-in-Hand Magnetic Sensor Array and Mobile Coils

Simultaneous magnetic localization and actuation in a human-scale workspace are challenging but essential for medical applications such as whole gastrointestinal (GI) tract monitoring and blood clot clearance in the leg. In this article, we propose a 5-D magnetic localization and actuation system that can track and actuate magnetic robots in a cylindrical workspace with a diameter of 500 mm. Based on the eye-in-hand configuration of the sensor array and the flexibility of the mobile electromagnetic manipulation system (mEMS), we realize a high localization accuracy in a large workspace with only 25 sensors. Moreover, we design an accurate magnetic field modeling method that can attenuate the electromagnets’ hysteresis and provide a precise actuation field estimation. Taking advantage of the mobile sensor array, we developed a signal-quality-based tracking strategy (STS) that could improve the localization performance by adjusting the movement of the sensor array. The effectiveness and advantages of the proposed methods are verified by simulations and experiments. Results show that the STS could decrease 25% position root-mean-square error (RMSE). The resulting position RMSE and orientation RMSE are 2.02 mm and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {8.24}}^{\circ} $ </tex-math></inline-formula> , respectively. We experimentally prove the viability of the proposed strategy by propelling a magnetic helical robot through a 400-mm long 3-D twisted silicone phantom.

Detachable electromagnetic actuation system for inverted microscope and its function in motion control of microrobots

In recent years, magnetic microrobots have shown unique advantages and exciting prospects in many application fields. However, the motion mechanism, driving force and imaging effect of magnetic microrobots still need to be further studied and improved. These factors are related to the design of magnetic actuation systems and the manufacturing of microrobots. This paper presents a new structural design involving detachable electromagnetic coils for developing a combinable magnetic actuation system that can be integrated with inverted microscopes for microrobot research. A maximum magnetic field intensity of 20 mT and uniform working space of 10 mm × 10 mm are achieved by applying coil parameter optimization and the yoke design. Furthermore, a dumbbell microrobot, which is symmetrical along its length axis, and a moon microrobot, which is asymmetric along its length axis, are fabricated and their motion characteristics are compared. The dumbbell microrobot exhibits reversible switching of three motion modes, whereas the motion of the moon microrobot exhibits the obvious drift. These dumbbell and moon microrobots are successfully controlled to move along a square path and a labyrinth path respectively, thus verifying the control performance of the magnetic actuation system.

Planar Magnetic Actuation for Soft and Rigid Robots Using a Scalable Electromagnet Array

Magnetic actuation system manipulates micro soft or rigid robots by a controllable magnetic field to move them freely in the narrow or enclosed space, which has demonstrated its huge potential in medical interventional surgery and drug delivery. However, the limited working space of paired or area-centered electromagnets restricts its practical applications. In this paper, we propose a convenient coils drive scheme for the scalable electromagnet array, and present an efficient planar magnetic actuation system with a spacious workspace. During the actuation process, our system activates selectively the effective electromagnets neighboring to the magnetic robot by coil selectors, and generates an alternating magnetic field with sufficient gradients to guide the robot's orientation and position. For the soft magnetic pipe, our system can push it to perform the continuous deflections around the stand columns on the plane. For the rigid magnetic cube, the designed magnetic-quadrupole structure allows it to receive various forces from different directions, and achieve a stable displacement in the heterogeneous magnetic field.

Scale-reconfigurable miniature ferrofluidic robots for negotiating sharply variable spaces.

Magnetic miniature soft robots have shown great potential for facilitating biomedical applications by minimizing invasiveness and possible physical damage. However, researchers have mainly focused on fixed-size robots, with their active locomotion accessible only when the cross-sectional dimension of these confined spaces is comparable to that of the robot. Here, we realize the scale-reconfigurable miniature ferrofluidic robots (SMFRs) based on ferrofluid droplets and propose a series of control strategies for reconfiguring SMFR’s scale and deformation to achieve trans-scale motion control by designing a multiscale magnetic miniature robot actuation (M3RA) system. The results showed that SMFRs, varying from centimeters to a few micrometers, leveraged diverse capabilities, such as locomotion in structured environments, deformation to squeeze through gaps, and even reversible scale reconfiguration for navigating sharply variable spaces. A miniature robot system with these capabilities combined is promising to be applied in future wireless medical robots inside confined regions of the human body.

Multiphysical Analytical Modeling and Design of A Magnetically Steerable Robotic Catheter for Treatment of Peripheral Artery Disease.

This article presents a unique multiphysical analytical modeling framework and solution algorithm to provide an effective tool for design of magnetically steerable robotic catheters (MSRCs) experiencing external interaction loads. Particularly, in this study, we are interested in design and fabrication of a MSRC with flexural patterns for treatment of peripheral artery disease (PAD). Aside from the parameters involved in the magnetic actuation system and the external interaction loads acting on the MSRC, the considered flexural patterns have a critical role on the deformation behavior and steerability of the proposed MSRC. Therefore, to optimally design such MSRC, we utilized the proposed multiphysical modeling approach and thoroughly evaluated the influence of involved parameters on the performance of the MSRC via two simulations studies. We also conducted experimental studies in a free bending condition and in the presence of different external interaction loads on two custom-designed MSRCs to thoroughly evaluate the efficacy of the proposed multiphysical model and solution algorithm. Our analysis demonstrates the accuracy of the proposed approach and necessity of utilizing such models to optimally design a MSRC before fabrication procedure.

A composite electro-permanent magnetic actuator for microrobot manipulation

The properties of conventionally utilized magnetic cores limit the generation of a strong controllable magnetic force for the manipulation of micro-/nanorobots. This study proposes a novel electro-permanent magnetic actuator having a composite core structure that can significantly improve the magnetic field and field gradient. The core structure, called the composite electro-permanent magnetic actuator (CEPMA), consists of a hybrid permanent magnet sandwiched between an iron core and iron disk with a copper wire wound around it. . The CEPMA creates a strong magnetic field and enables the switching on/off of the magnetic field. A prototype of a magnetic actuator system using six CEPMAs was built with optimal parameters and was capable of 3-dimensional (3D) position control with a maximum achievable field and gradient field of 124 mT and 1.9 T/m, respectively, by utilizing a lower power consumption. We derived a mathematical model and control approach to address its hysteresis property and obtain a current input for the desired magnetic force for precise control of a microrobot. The theoretical analysis and experimental validation of CEPMA indicated that the proposed structure could enhance the controllable magnetic field and gradient field by up to 30% compared to the conventional iron core electromagnet. The system was also tested for 3D manipulating different microrobots in an in vitro environment with high accuracy. The experimental results demonstrate the potential of this newly developed platform for manipulating microrobots with high throughput.

Magnetic Micro-Driller System for Nasolacrimal Duct Recanalization

Primary acquired nasolacrimal duct obstruction (PANDO) is the commonest cause of obstructive tearing and can lead to infections including dacryocystitis, cellulitis and postoperative endophthalmitis. External or endoscopic dacryocystorhinostomy (DCR) is the current standard treatment of PANDO. However, DCR is technically challenging, invasive, and not without risks, especially epistaxis and recurrent obstruction. We designed and constructed a magnetic micro-driller system for nasolacrimal duct (NLD) recanalization as a minimally invasive alternative to conventional treatment. The drilling microrobot consists of a 3D printed helical tip and a permanent magnet. A magnetic actuation system with three electromagnets is developed to well accommodate the human anatomy and generate three-dimensional dynamic magnetic fields along the NLD. To navigate the microrobot safely inside the NLD, the micro-driller is integrated with a guidewire and a feed drive system to control its motion. Furthermore, a force sensor is installed on the proximal end of the guidewire to report the force signal, through which the state of the micro-driller can be detected and the control input can be decided. Our results show that the guide-wired microrobot can navigate through the NLD phantom and remove the blockage automatically. The proposed strategy provides a microrobot-assisted endoluminal solution for NLD recanalization with improved safety by introducing the magnetic manipulation and force control method.