A review of magnetic actuation systems and magnetically actuated guidewire- and catheter-based microrobots for vascular interventions

Magnetic actuation techniques and microrobots have attracted considerable interest due to their potential applications in biomedicine. Interventional techniques have emerged as a minimally invasive approach to treat a wide range of vascular diseases. The current practice of interventional procedures is, however, limited by manual control of interventional devices and time-consuming procedures. Moreover, fluoroscopy is considered as an essential part of the procedure today despite posing many limitations for patients and physicians. Recently, various microrobotic solutions have been proposed for vascular interventions, including advances in magnetic navigation systems and magnetically steerable catheters and guidewires, which have shown potential benefits such as reduced radiation doses, improved access to difficult-to-reach and tortuous anatomy. This paper reviews the commercial magnetic actuation systems and magnetically actuated interventional microrobots that have been developed by academic research groups and medical companies worldwide, outlining their capability, applicability as well as limitations. We further address the challenges and future prospects of the research toward clinical acceptance of magnetic interventional technologies.

     

Rotationally controlled magneto-hydrodynamic particle handling for bead-based microfluidic assays

This work presents a novel magnetic actuation scheme for advanced particle handling on our previously introduced, centrifugal microfluidic platform for array-based analysis of individual cells and beads. The conceptually simple actuation is based on the reciprocating motion of an elastomeric membrane featuring an integrated permanent magnet and a stationary magnet aligned along the orbit of a disc-based chamber. This compression chamber is placed at the downstream end of the particle capture chamber to induce centripetally directed, hydrodynamic lift forces on particles trapped in V-shaped geometrical barriers. Towards high frequencies of rotation, the on-disc magnet ceases to follow the rapidly oscillating magnetic field, so that the magnetic actuator is disabled during the initial, sedimentation-based filling of the trap array. At reduced spin speeds, the residence time of the magnetic actuator is sufficient to displace the magnetic actuator, resulting in a flow through the V-cup array that re-distributes, and eventually fully depletes, the previously trapped beads from the array. The same magnetic deflection scheme is also demonstrated to accelerate mixing, e.g. for upstream sample preparation.     

Three-dimensional swimming tadpole mini-robot using three-axis Helmholtz coils

Electromagnetic-actuated robotic systems have been studied recently for special purposes. Because these systems use external magnetic fields to control their robots, the robots can have simple structures and move with much freedom. In particular, these electromagnetic actuation (EMA) systems are being widely adopted for the actuation of biomedical mini-robots and microrobots for minimally invasive surgery (MIS) and diagnosis. We previously reported, as a feasible biomedical robot, the biomimetic swimming tadpole mini-robot, which can only swim above water. Indeed, the two-dimensional (D) plane swimming tadpole mini-robot is limited in its use because of its motility in the 2D plane. Therefore, this paper proposes a 3D swimming tadpole mini-robot that can move freely in water. First, in the proposed 3D swimming tadpole mini-robot, the buoyancy force was regulated for subaqueous swimming, and the permanent magnet was rearranged for precise movement. Second, to attain a 3D swimming motion, the actuation mechanism of the robot was developed using an EMA system. Finally, various experiments verified that the proposed 3D swimming tadpole mini-robot can swim freely in a 3D water environment.     

A rapid magnetic particle driven micromixer

Performances of a magnetic particle driven micromixer are predicted numerically. This micromixer takes advantages of mixing enhancements induced by alternating actuation of magnetic particles suspended in the fluid. Effects of magnetic actuation force, switching frequency and channel’s lateral dimension have been investigated. Numerical results show that the magnetic particle actuation at an appropriate frequency causes effective mixing and the optimum switching frequency depends on the channel’s lateral dimension and the applied magnetic force. The maximum efficiency is obtained at a relatively high operating frequency for large magnetic actuation forces and narrow microchannels. If the magnetic particles are actuated with a much higher or lower frequency than the optimum switching frequency, they tend to add limited agitation to the fluid flow and do not enhance the mixing significantly. The optimum switching frequency obtained from the present numerical prediction is in good agreement with the theoretical analysis. The proposed mixing scheme not only provides an excellent mixing, even in simple microchannel, but also can be easily applied to lab-on-a-chip applications with a pair of external electromagnets.     

An overview of magnetic micro-robot systems for biomedical applications

Untethered and wirelessly-controlled micro-robots have been catching substantial attention for a long time due to their great potentials in biomedical areas. Their small sizes and property of wireless magnetic actuation and control make them fit in tiny and closed environments both in vitro and in vivo such as lab-on-a-chip and human blood vessels for micromanipulations, minimum/non-invasive theoretical and diagnostic applications, respectively. In recent years, micro-robots driven by magnetic fields become a hotspot due to their good controllability and motion performance they have shown in both wet and dry environments. And they hardly bring harm under magnetic actuation and control, which qualify them especially for biomedical applications. This paper reviews the state of the art of hjbvmagnetic-micro-robot systems, including the related knowledge and theories, design works of magnetic micro-robots and magnetic navigation systems. For a straightforward understanding, several types of magnetic micro-robot systems are presented. And some applications of magnetic micro-robot systems are introduced at the end to show their great potentials. However, for further developments, many obstacles still need to be solved.     

Nonlinear controller design for a magnetic levitation device

Various applications of micro-robotic technology suggest the use of new actuator systems which allow motions to be realized with micrometer accuracy. Conventional actuation techniques such as hydraulic or pneumatic systems are no longer capable of fulfilling the demands of hi-tech micro-scale areas such as miniaturized biomedical devices and MEMS production equipment. These applications pose significantly different problems from actuation on a large scale. In particular, large scale manipulation systems typically deal with sizable friction, whereas micro manipulation systems must minimize friction to achieve submicron precision and avoid generation of static electric fields. Recently, the magnetic levitation technique has been shown to be a feasible actuation method for micro-scale applications. In this paper, a magnetic levitation device is recalled from the authors’ previous work and a control approach is presented to achieve precise motion control of a magnetically levitated object with sub-micron positioning accuracy. The stability of the controller is discussed through the Lyapunov method. Experiments are conducted and showed that the proposed control technique is capable of performing a positioning operation with rms accuracy of 16 μm over a travel range of 30 mm. The nonlinear control strategy proposed in this paper showed a significant improvement in comparison with the conventional control strategies for large gap magnetic levitation systems.     

Path guidance and control of a guided wheeled mobile robot

A practical mobile-robot-based automatic transport service system is presented and discussed in this paper. A wheeled mobile robot, capable of two-directional movement, is developed to transport and feed materials to an industrial production line. For path guidance, an electromagnetic approach is investigated in detail. A conductor line laid on or under the ground defines the path, through which runs a square-wave current signal of a certain frequency, to produce an alternating magnetic field. Specific sensors are designed to measure this field and provide a path guidance signal for the robot. For path control, the proportional plus derivative (PD) algorithm is adopted to control the robot's movement along the path line. Multi-mode control strategies are developed to cover different path cases. The active turn control scheme is used for turning path modes. Finally, some practical testing results are presented.     

A compact electromagnetic micro-actuator using the meander springs partially exposed to magnetic field

We present the design, fabrication, and testing of a compact electromagnetic micro-actuator using meander springs that are partially exposed to the magnetic field. The previous electromagnetic micro-actuators using cantilever springs require large electromagnetic force for large displacement actuation and therefore require high-current input and a large magnet. The previous electromagnetic actuators using low-stiffness meander springs are limited in large displacement actuation because actuation forces cancelled each other due to changes in the current path under the magnetic field. In this paper, we compare two prototypes: a conventional prototype F with the meander springs exposed fully to the magnetic field and the present prototype P with the meander springs partially exposed to the magnetic field. In the experimental study, the amplitude of prototype P is measured as 30.49 ± 0.36 µm at the 40 mA square input current, while the amplitude of prototype F is measured as 26.02 ± 0.65 µm. The amplitude of prototype P is 17.2 % larger than that of prototype F, verifying the effect of partial exposure of the meander springs to the magnetic field. Therefore, we experimentally demonstrate the large-displacement actuation performance of the present actuator using the partial exposure of the meander springs to the magnetic field.     

Magnetic particle dosing and size separation in a microfluidic channel

Separation of functional magnetic particles or magnetically labeled entities is a key feature for bioanalytical or biomedical applications and therefore also an important component of lab-on-a-chip devices for biological applications. We present a novel integrated microfluidic magnetic bead manipulation device, comprising dosing of magnetic particles, controlled release and subsequent magnetophoretic size separation with high resolution. The system is designed to meet the requirements of specific bioassays, in particular of on-chip agglutination assays for the detection of rare analytes by particle coupling as doublets. Integrated soft-magnetic microtips with different shapes provide the magnetic driving force of the bead manipulation protocol. The magnetic tips that serve as field concentrators of an external electromagnetic field, are positioned in close contact to a microfluidic channel in order to generate high magnetic actuation forces. Mixtures of 1.0 μm and 2.8 μm superparamagnetic beads have been used to characterize the system. Magnetophoretic size separation with high resolution was performed in static conditions and in continuous flow mode. In particular, we could demonstrate the separation of 1.0 μm single beads and doublets in a sample flow.     

Development of a novel type of microrobot for biomedical application

This paper proposes a new type of microrobot that can move along a narrow area such as blood vessels which has great potential for application in microsurgery. Also, the development of a wireless microrobot that can be manipulated inside a pipe by adjusting an external magnetic field has been discussed. The model microrobot utilizes an electromagnetic actuator as the servo actuator to realize movement in biomedical applications. The structure, motion mechanism, and evaluation characteristic of motion of the microrobot have been discussed, and the directional control can be realized via the frequency of the input current. The moving experiments have been carried out in branching points in the horizontal direction, and the moving speed of the robot has been measured in vertical direction by changing frequency. Based on the results, the microrobot has a rapid response, and it can clear out dirt which is adhering to the inner wall of pipe. This microrobot will play an important role in both industrial and medical applications such as microsurgery.     

An efficient and robust method for Lagrangian magnetic particle tracking in fluid flow simulations on unstructured grids

In this paper we report on a newly developed particle tracking scheme for fluid flow simulations on 3D unstructured grids, aiming to provide detailed insights in the particle behaviour in complex geometries. A possible field of applications is the magnetic drug targeting (MDT) technique, on which this paper will be focused. MDT is a promising medical technique that uses locally applied magnetic fields to capture magnetic drug carriers at the desired locations in the human body, strongly increasing the efficiency of medical drugs. The new particle tracking scheme combines the advantages of existing methods and is easy for implementation in a generic numerical code. The scheme is tested and validated for simple MDT cases that include effects of a non-homogeneous magnetic field on deposition of magnetic particles in laminar flow. The first test case is a validation study of the magnetic particle trajectories released in a horizontal circular pipe flow with a current-carrying wire parallel to the flow, for which analytical solutions are reported in literature. The second test case involves particle capture efficiencies in a 90° bent tube for different configurations of the imposed magnetic field. This configuration corresponds more closely to the conditions inside blood vessels, because of the presence of secondary motions. These results are compared with numerical studies from literature too. The obtained results demonstrate that the developed particle tracking scheme is a very robust, efficient and accurate method, which can give detailed insights in particle behaviour in complex geometries. As such it is a good candidate for future applications and optimisations of MDT technique for loco-regional cancer treatment or treatment of cardiovascular diseases.     

Electromagnetic Two-Dimensional Scanner Using Radial Magnetic Field

In this paper, we present the design, fabrication, and measurement results of a two-dimensional electromagnetic scanning micromirror actuated by radial magnetic field. The scanner is realized by combining a gimbaled single-crystal-silicon micromirror with a single turn electroplated metal coil, with a concentric permanent magnet assembly composed of two concentric permanent magnets and an iron yoke. The proposed scanner utilizes the radial magnetic field rather than using a lateral magnetic field oriented 45deg to the horizontal and vertical scan axes to achieve a biaxial magnetic actuation. The single turn coil fabricated with electroplated copper achieves a nominal resistance of 1.2 Omega. A two-dimensional scanner with mirror size of 1.5 mm in diameter was fabricated. Maximum optical scan angle of 8.8deg in horizontal direction and 8.3deg in vertical direction were achieved. Forced actuation of the gimbal at 60 Hz and resonant actuation of the micromirror at 19.1-19.7 kHz provide slow vertical scan and fast horizontal scan, respectively. The proposed scanner can be used in raster scanning laser display systems and other scanner applications.     

Enhanced‐image‐quality raster‐scanning chipset using feedback‐control actuation

Abstract— A new raster‐scanning chipset which provides enhanced projection performance is presented. The design is novel in that it combines electrostatic and electromagnetic actuation methods, along with a unique feedback‐control scheme to produce SVGA and WVGA projected images. A micromirror, the actuators, and drive electronics are integrated into a small, power‐efficient system, a scanning chipset, to increase its reliability and manufacturability.     

Resource-aware MPC for constrained linear systems: Two rollout approaches

In systems with resource constraints, such as actuation limitations in sparse control applications or limited bandwidth in networked control systems, it is desirable to use control signals that are either sparse or sporadically changing in time. Motivated by these applications, in this paper we propose two resource-aware MPC schemes for discrete-time linear systems subject to state and input constraints. The two MPC schemes exploit ideas from rollout strategies to determine simultaneously the new (continuous) control inputs and the (discrete) time instants at which the control actions are updated. The first scheme provides performance guarantees by design, in the sense that it allows the user to select a desired suboptimal level of performance, where the degree of suboptimality provides a trade-off between the guaranteed closed-loop control performance on the one hand and the utilization of (communication/actuation) resources on the other hand. The second scheme provides a guaranteed (average) resource utilization, while cleverly allocating these resources in order to maximize the control performance. By means of numerical examples, we demonstrate the effectiveness of the proposed strategies.     

电磁导航智能车检测和控制系统的研究

对电磁导航智能车的信号检测、控制系统的设计和实现做了介绍。通过Matlab对不同路径进行了磁场分析,确立了传感器的排布方案,并针对采集的信号进行了后续信号处理电路的设计,完成了信号的采样,确定了控制策略,单片机根据传感器采集的跑道信号通过A/D转换进行分析,通过增量式PID来控制智能车的速度,并通过脉宽控制舵机转角来实现智能车的拐弯,最终实现了能够针对不同路径稳定快速运行的电磁导航智能车的制作。     

Application of a multilayered magnetostrictive film to a micromachined 2-D optical scanner

A novel two-dimensional (2-D) optical scanner has been designed, manufactured and characterized. This scanner features a large mirror (8/spl times/6 mm) and is therefore suitable for industrial applications where cheap optical sources and lenses are requested. This scanner uses a multilayer film for its actuation. This film is well known for its high magnetostriction. The mechanical design has been optimized using conventional mechanical considerations as well as finite-element simulations. The device has been characterized in two configurations. Depending on the direction of the applied magnetic field, the magnetostrictive properties of the active film or the electromagnetic force are selectively used. Using this last, total optical deflection angles of 32/spl deg/ and 11/spl deg/ for an applied magnetic field of 0.3 mT are obtained. The ratio of the corresponding resonant frequencies is around 4.5, allowing a nice scanning pattern. Compared to our previous prototype on the same project , the mechanical-magnetic sensitivity has been improved by about a factor 24 when the magnetostriction is used, and by about a factor 75 when the electromagnetic force is used.     

Soft medical robotics: clinical and biomedical applications,challenges, and future directions

Bioinspired soft robotics allow for safer clinical interactions with human patients but conventional, hard robots, which are often built with rigid materials and complex control systems, compromise tissue integrity, freedom of movement, conformability, and overall human bio-compatibility. Soft, compliant materials intrinsically reduce mechanical complexity, accommodate their usage environment, and provide great practical potential for medical device developments. Previous review papers have generally covered the topics of materials, manufacturing processes, actuator modeling and control, and current trends. Here, we focus on recent developments in soft robotic applications for the medical field including advances in cardiac devices, surgical robots, and soft rehabilitation and assistance devices. In medical applications, soft robotic devices not only expedite the evolution of minimally invasive surgery but also improve the bio-compatibility of rehabilitation and assistance devices. Here, we evaluate design requirements, mechanisms, achievements and challenges in these key areas. Of particular note, this paper concludes with a discussion on advances in 3D printing and adapting neural networks for modeling and control frameworks that have facilitated the development of faster and less expensive soft medical devices.     

A novel levitation control strategy for a class of redundant actuation maglev system

In most maglev (magnetic levitation) systems, redundant electromagnetic actuators are usually used to increase the stability and robustness of the levitation motion. However, the obvious interactions generate between the redundant actuators and other general electromagnetic actuators. In this paper, a new and efficient redundant levitation control strategy is developed to overcome the interactions in this maglev system. In the strategy, some separate general controllers are designed for all general actuators, and then some special controllers are used to real-time track the electromagnetic forces of all general actuators, and accordingly they create control signal for the redundant actuators to counteract the interactions among general actuators and redundant actuators. To further illustrate the strategy, a novel redundant actuation maglev system is then demonstrated, and a simplified expression of the redundant control strategy is investigated for the maglev system. The experimental results show that the redundant levitation controller successfully removes the interactions between redundant actuator and general actuators, and the redundant levitation controller maintains good robustness under disturbance.     

宽幅度摩擦力控制触觉再现系统

触觉再现能够表达虚拟物体的表面特征,提高虚拟现实系统的真实感,因而成为人机交互领域内的研究重点。本文将空气压膜效应与电磁激励相结合,提出一种新颖的摩擦力控制触觉再现方法,并研制一种宽幅度摩擦力控制触觉再现系统,其中电磁激励用于增加摩擦力控制范围。经过一系列触觉感知实验验证了本系统的有效性,实验结果表明本文提出的方法相对于传统的摩擦力控制方法可以实现更宽泛的摩擦力系数控制。     

Design and characterization of a multi-stable magnetic shape memory alloy hybrid actuator

This paper describes the design and the characterization of a multi-stable hybrid actuator composed of a single magnetic shape memory alloy element and an electromagnetic actuator. The series arrangement of the active material and the electromagnetic actuator allows a new shape of hysteresis curve and a precise positioning can be obtained. The design of the different magnetic circuits has been done by analytic and numeric simulations in MatLab and FEMM 4.2. This study gives results of the elongation, the blocking force, and the holding force that can be obtained with such an actuator. Strokes up to 0.35 mm and a blocking force of 2.6 N have been measured for the hybrid actuator using a magnetic shape memory alloy with a cross section of 2.5 mm². Such an actuator can find application in precise positioning and medium frequency actuation systems. Nevertheless, there is much design space for improvements in terms of energy consumption, heat transfer, and overall cost of the device.