这篇文章非常详尽地介绍了用于磁驱动的各种方法和系统，总体分为四大类，单永磁，多永磁，线圈组，分布式电磁铁组合。
用于微型机器人的磁驱动系统：回顾
Magnetic Actuation Systems for Miniature Robots: A Review [1]
Paper Link
Authors: Yang, Zhengxin, et al.
2020, Advanced Intelligent Systems
目录 outline
0. Abstract 摘要
对用于微型机器人的最新磁驱动系统的回顾被展示，目的是提供给读者对磁驱动的更好的理解以及对未来系统设计的指导。
a review on the state-of-the-art magnetic actuation systems for miniature robots is presented with the goal of providing readers with a better understanding of magnetic actuation and guidance for future system design.
1. Introduction 介绍
这篇系统回顾主要聚焦在当前的磁驱动系统的配置和它们的磁场生成能力。
The system review mainly focuses on the configurations of the current magnetic actuation systems and their capability of magnetic field generation
2. Magnetic Actuation and Magnetic Fields 磁驱动和磁场
2.1 Magnetic Actuation Principle
2.2 Magnetic Field Generation
2.2.1 Permanent magnets
2.2.2 Electromagnets
2.3 Magnetic Field Safety 磁场安全
据报道，当暴露在低于2T的磁场中时没有一致的生物学影响。文献表明没有严重的不利健康影响当健康人暴露在8T以下的磁场中。然而，对于有导电性植入物的人来说，安全值下降到25mT，对于有心脏起搏器和电激活植入物的工人来说则为0.5mT。
It is reported that no consistent biological effect exerts on humans when exposed to magnetic fields below 2 T. The literature indicates no serious adverse health effects from the exposure of healthy people up to 8 T. However, the safety value reduces to 25 mT for people with conductive implants, and 0.5 mT for workers with cardiac pacemakers and electrically active implants.
感应电场正比于磁场变化率和一个依赖于场分布，身体几何形状和组织特征的常数。磁场变化率的一个推荐的限制为：
The induced electric field is proportional to the magnetic field variation rate and a constant that depends on field distribution, body geometry, and tissue characteristics. A recommended restriction of magnetic field variation rate is expressed as
∣ d B d t ∣ = 20 ( 1 + 0.36 τ ) |\frac{d \mathbf{B}}{d t}|=20(1+\frac{0.36}{\tau}) ∣dtdB∣=20(1+τ0.36)
这里的 τ \tau τ是刺激持续时间。
where τ \tau τ is the stimulus duration (in ms).
3. Magnetic Actuation Systems 磁驱动系统
这些系统整体按照它们的磁源和配置特性被分为四类。受控磁小型机器人，它们被视为驱动系统的远程末端执行器，为了简化被缩写为设备。
the overview of such systems is divided into four categories according to their magnetic sources and configurational characteristics. The controlled magnetic miniature robots, which can be viewed as the remote end effectors of the actuation systems, are abbreviated as devices for simplicity.
3.1 Systems with permanent magnets 使用永磁体的系统
3.1.1 Single magnet 单磁体
一个单个的外部永磁体能够控制磁设备的移动和旋转运动，通过改变它的位姿来施加一个动态的力和/或力矩，这种方案便宜且有较高的紧凑性。
A single external permanent magnet can control the translational and rotational motions of the magnetic device by applying a dynamic force and/or torque via changing its pose, which is inexpensive and has high compactness.
商用设备，Ankon Technologies实现胶囊在胃部的5D自由度运动。
3.1.2 Multiple magnets 多磁体
多磁体被用于多种目的，其中之一是为了产生一个有高均匀化的磁场用于力矩驱动，因为使用对称分布的磁场导数可以部分受损。
Multiple magnets are introduced for various purposes, one of which is to produce a magnetic field with high uniformity for torque actuation because the field gradient can be partly impaired using symmetric distribution.
商用设备，Niobe system实现导航磁导管。 Genesis system是Niobe system的升级版。
还介绍了很多组的多磁体驱动装置，总结来说，各有以下好处：与使用单个磁体相比能产生更高的均匀性；恒定强度的旋转磁场；任意变化强度的全向磁场；产生局部最大磁场（磁力陷阱）；强均匀偶极场。
3.2 Systems with electromagnets 使用电磁体的系统
3.2.1 paired coils 线圈对
最常见的配置为多轴 Helmholtz线圈组；多轴square Helmholtz线圈组；Helmholtz线圈组用来产生均匀磁场来对齐磁设备，Maxwell线圈组用来产生均匀磁场梯度来产生推进力； Helmholtz线圈组和Maxwell线圈组可以结合起来使用；但是以上两个组合都无法实5D自由度的运动，因为这两个组合产生的磁场和磁场导数根本不解耦。Helmholtz线圈组和Maxwell线圈组以及它们的组合所配置的磁驱动系统只有很低的有效空间率，存在尺度问题。
为了增加紧凑型和减少能量消耗，鞍马型线圈被包含，这些系统通常有管状结构，它适合安放人体。
For the sake of increasing compactness and decreasing energy consumption, saddle coils have been included, and these systems usually have tubular constructions that suitably accommodate the human body.
商用设备，magnetically guided capsule endoscopy (MGCE) system (Olympus Corporation (Tokyo, Japan)和Siemens Healthineers AG (Erlangen, Germany)联合开发) 和 magnetic resonance imaging (MRI) scanner
3.2.2 distributed electromagnets 分布式电磁体
磁驱动系统的另一个分支是利用分布式电磁体，它们被开发用来提高能量效率和减轻排布限制。
Another branch of magnetic actuation systems utilizing distributed electromagnets has been developed to improve energy efficiency and mitigate layout restrictions.
这是可取的把软铁芯插入到线圈中来聚焦和增强磁场和磁场导数，它们能被施加的外部磁场简单地磁化，并且磁场消失时快速失磁。
It is preferable to insert soft-iron cores into coils to concentrate and enhance the magnetic field and field gradient, which can be easily magnetized with the applied external magnetic field and rapidly demagnetized when the magnetic field disappears.
OctoMag是最具代表性的分布式磁驱动系统，利用了8个电磁铁；
MiniMag是为了最高紧凑型的目标将OctoMag重新设计；
含有8个不一样的电磁铁的系统被提出从而最大化生成磁场和磁场导数；
9电磁铁的系统也被提出，优化了驱动和定位，而且增加了一维输入作为冗余；
另外还将电磁铁均匀地在工作空间周围排布以获得更好的各向一致性；
各个系统的力生成，力矩生成，工作空间各向一致性，工作空间可到达性等属性被比较和研究；
一个含有6个正交和相同的电磁铁的系统被提出，它能获得较大工作空间。
商用设备， Catheter Guidance Control and Imaging (CGCI) system developed by Magnetecs Corporation (California, USA) consists of eight electromagnets；Aeon Scientific AG (Zurich, Switzerland) released the Aeon Phocus system with seven electromagnets. These two systems are primarily targeted for magnetic catheter steering.
除了有固定电磁铁的系统，可移动的电磁体也被开发了。有不同配置的驱动系统展现多种考虑的磁驱动操纵性和灵活性：一些在力控制上更优异，其他在力矩控制上有更好的表现。更进一步，奇异点可能存在对于一些系统来说，这意味这系统在奇异点将失去产生确切力/力矩的能力或者在奇异点附近花费很大代价，但是驱动应该是全面的。
Apart from the systems with stationary electromagnets, transformable ones have also been developed. The actuation systems with different configurations perform diversely considering magnetic actuation manipulability and dexterity: some are superior in force control, and others have better performance at torque control. Moreover, singularities may exist for some systems, which means that the systems will lose the ability to generate certain force/torque at the singularity or cost a lot near the singularity, but the actuation should be comprehensive.
BigMag包含放置在两个固定装置中的六个电磁体，避免奇异点和最小化总电流；
含有四个固定和四个可移动电磁铁的设备被提出，这导致在均匀磁场和均匀磁场梯度之间优先排序的问题；
将圆柱形电磁铁与机械臂结合，来扩大工作空间而没有增加电磁铁体积；
DeltaMag将电磁体放入并行结构中，增加工作空间而减少总体体积；
含有9个电磁铁的BatMag可以独立控制3D空间中的两个设备；一个模块化且可重新配置的磁致动系统，该系统包含多个Omnimagnets，可以在致动过程中立即重新布置，每个Omnimagnet都包括一个球形磁芯和三个正交环绕的嵌套螺线管；
一个具有四个电磁体的系统被开发，每个电磁体都具有带锥状探头和磁盘的阶梯状磁芯，这种优化的磁芯形状用于进一步增强磁场强度和磁场梯度。
5. 结论 Conclusions
控制磁场的原始想法包括一个永磁体的空间变换和电磁电流的不同组合。
The initial concept of controlling the magnetic field involves spatial variations of a permanent magnet and different combinations of electromagnetic currents.
有一个球形驱动器和八个独立旋转磁体的永磁系统能够实现场生成的灵巧性，减轻复杂性和运动危险性，而且没有热量产生。对于部分电磁系统来说，减少热量产生，扩大工作空间，开闭磁场操纵性，与图像设备的合适安装。
the permanent magnetic system with a spherical actuator and with eight independent rotary magnets can realize high dexterity of field generation, mitigated complexity and perilousness of motion, and no heat generation. With regard to the electromagnetic system, the ARMM system and the DeltaMag system possess enlarged workspaces with reduced heat generation, on/off manipulability of the magnetic field, and suitable accommodation with imaging devices.
在磁驱动系统上未来的焦点可能在四个部分，它们中的大部分主要关注医疗应用。
第一个是尺度问题，这对于电磁系统来说很突出。磁场和磁场导数随着距离快速衰减；因此，一个更大的工作空间通常需要更膨胀/臃肿的电磁铁和更高的电流。
第二个是在系统集成图像设备的问题。在体外应用中，图像设备大多数安装在驱动系统的空隙处，这个安排通常是可接受的。考虑到体内应用，图像拍摄还是一个挑战。
第三个是安全考虑。医疗设备冒险可能威胁病人和医务人员；因此，确保安全是关键问题之一。
第四个是提高施加磁场的性能。高频磁场在一些场景下是需要的，它是难以产生的因为带宽限制。对于永磁系统来说，惯性局限了机构的物理运动。对于电磁驱动系统来说，多股铜线导致很强的感应，并且软铁芯的磁滞现象也有一个必然的影响，它们两者在低频时都忽略，但是需要在高频时被补偿。另一个问题是磁场精度被发热影响。
The future focus on magnetic actuation systems may be fourfold, most of which mainly concentrate on medical applications.
First is the scaling issue, which is prominent for electromagnetic systems. The magnetic field and field gradient attenuate rapidly with the distance; therefore, a larger workspace usually requires bulkier electromagnets and higher currents.
Second is the integration with imaging devices at the system level. Imaging devices are mostly positioned at the interspace of the actuation system for in vitro applications, and this arrangement is generally accepted. Concerning in vivo applications, imaging remains a challenge.
Third is safety considerations. Medical equipment hazards may threaten both patients and medical staff; therefore, ensuring safety is one of the critical issues.
Fourth is improving the performance of the applied magnetic field. The high-frequency magnetic field, which is necessary for some situations (usually less than 150 Hz), is hard to be produced due to bandwidth limitation. For the permanent magnetic system, the inertia confines the physical motion of the mechanism. Regarding the electromagnetic actuation system, multiturn copper wire results in strong induction, and the hysteresis of the soft-iron core also has an inevitable effect, both of which are ignored at low frequency but need to be compensated at high frequency. Another issue is magnetic field inaccuracy caused by heat effect, which needs to be addressed for the generation of highly precise magnetic fields.
[1]: Yang, Zhengxin, and Li Zhang. “Magnetic Actuation Systems for Miniature Robots: A Review.” Advanced Intelligent Systems 2.9 (2020): 2000082.