Portable Low-Cost MRI System Based on Permanent Magnets/Magnet Arrays

Shaoying Huang,Zhi Hua Ren,Sergei Obruchkov,JIa Gong,Robin Dykstra,Wenwei Yu 대한자기공명의과학회 2019 Investigative Magnetic Resonance Imaging Vol.23 No.3

Portable low-cost magnetic resonance imaging (MRI) systems have the potential to enable “point-of-care” and timely MRI diagnosis, and to make this imaging modality available to routine scans and to people in underdeveloped countries and areas. With simplicity, no maintenance, no power consumption, and low cost, permanent magnets/magnet arrays/magnet assemblies are attractive to be used as a source of static magnetic field to realize the portability and to lower the cost for an MRI scanner. However, when taking the canonical Fourier imaging approach and using linear gradient fields, homogeneous fields are required in a scanner, resulting in the facts that either a bulky magnet/magnet array is needed, or the imaging volume is too small to image an organ if the magnet/magnet array is scaled down to a portable size. Recently, with the progress on image reconstruction based on nonlinear gradient field, static field patterns without spatial linearity can be used as spatial encoding magnetic fields (SEMs) to encode MRI signals for imaging. As a result, the requirements for the homogeneity of the static field can be relaxed, which allows permanent magnets/magnet arrays with reduced sizes, reduced weight to image a bigger volume covering organs such as a head. It offers opportunities of constructing a truly portable low-cost MRI scanner. For this exciting potential application, permanent magnets/magnet arrays have attracted increased attention recently. A magnet/magnet array is strongly associated with the imaging volume of an MRI scanner, image reconstruction methods, and RF excitation and RF coils, etc. through field patterns and field homogeneity. This paper offers a review of permanent magnets and magnet arrays of different kinds, especially those that can be used for spatial encoding towards the development of a portable and low-cost MRI system. It is aimed to familiarize the readers with relevant knowledge, literature, and the latest updates of the development on permanent magnets and magnet arrays for MRI. Perspectives on and challenges of using a permanent magnet/magnet array to supply a patterned static magnetic field, which does not have spatial linearity nor high field homogeneity, for image reconstruction in a portable setup are discussed.

Portable Low-Cost MRI System Based on Permanent Magnets/Magnet Arrays

Huang, Shaoying,Ren, Zhi Hua,Obruchkov, Sergei,Gong, JIa,Dykstra, Robin,Yu, Wenwei Korean Society of Magnetic Resonance in Medicine 2019 Investigative Magnetic Resonance Imaging Vol.23 No.3

Portable low-cost magnetic resonance imaging (MRI) systems have the potential to enable "point-of-care" and timely MRI diagnosis, and to make this imaging modality available to routine scans and to people in underdeveloped countries and areas. With simplicity, no maintenance, no power consumption, and low cost, permanent magnets/magnet arrays/magnet assemblies are attractive to be used as a source of static magnetic field to realize the portability and to lower the cost for an MRI scanner. However, when taking the canonical Fourier imaging approach and using linear gradient fields, homogeneous fields are required in a scanner, resulting in the facts that either a bulky magnet/magnet array is needed, or the imaging volume is too small to image an organ if the magnet/magnet array is scaled down to a portable size. Recently, with the progress on image reconstruction based on non-linear gradient field, static field patterns without spatial linearity can be used as spatial encoding magnetic fields (SEMs) to encode MRI signals for imaging. As a result, the requirements for the homogeneity of the static field can be relaxed, which allows permanent magnets/magnet arrays with reduced sizes, reduced weight to image a bigger volume covering organs such as a head. It offers opportunities of constructing a truly portable low-cost MRI scanner. For this exciting potential application, permanent magnets/magnet arrays have attracted increased attention recently. A magnet/magnet array is strongly associated with the imaging volume of an MRI scanner, image reconstruction methods, and RF excitation and RF coils, etc. through field patterns and field homogeneity. This paper offers a review of permanent magnets and magnet arrays of different kinds, especially those that can be used for spatial encoding towards the development of a portable and low-cost MRI system. It is aimed to familiarize the readers with relevant knowledge, literature, and the latest updates of the development on permanent magnets and magnet arrays for MRI. Perspectives on and challenges of using a permanent magnet/magnet array to supply a patterned static magnetic field, which does not have spatial linearity nor high field homogeneity, for image reconstruction in a portable setup are discussed.

엔코더리스 마그넷 모션을 이용한 위치제어에 대한 리니어모터 실험적 연구

김홍윤(Kim Hong-youn),윤영민(Yun Young-Min),심호근(Shim Ho-Keun),권영목(Kwon Young-Mok),허훈(Heo Hoon) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.1

영구자석 선형 동기전동기(PMLSM : Permanent Magnet Linear Synchronous Motor)의 구조에서, 영구자석이 레일에 고정되고 코일이 움직이는 기존 영구자석 선형 동기전동기와 달리(영구자석 = 고정자, 코일 = 이동자), 코일이 고정되고, 영구자석을 움직이는(영구자석 = 이동자, 코일 = 고정자) 구조의 위치제어시스템을 제안하고자 한다. 위치 측정은 2개의 홀센서를 사용한다. 이 방식은 엔코더 출력 펄스 신호 대신에 2개의 홀센서에서 발생되는 구형파 신호를 4체배하여 이동자의 속도와 위치를 추정한다. 구형파를 발생시키는 2개의 홀센서로 PMLSM의 벡터제어를 구현하였을 때 정격속도 범위 내에서 안정적이고 효율적으로 제어되는 것을 시뮬레이션을 통하여 입증하였다. 또 하드웨어 실험으로 시스템의 위치제어성능은 30~50㎛의 측정범위 내에서 10~20㎛의 정밀도로 기존시스템보다 2배나 개선되며, 경제적 효율성과 제안된 위치제어 개념의 실용적인 유용성도 확인하였다. 2개의 홀센서를 이용한 벡터제어는 협소한 공간에도 취부 할 수 있으므로 엔코더나 레졸버의 장착이 어려운 시스템에 적용될 수 있다. A position control system composed of the PMLSM(Permanent Magnet Linear Synchronous Motor), unlike conventional linear permanent magnet synchronous motor is fixed to the permanent magnet moving coil rails (permanent magnet = stator, coil = mover), the coil is fixed, moving the permanent magnet, we propose a position control system (permanent magnet = mover, coil = stator) structure. Position is measured not using conventional encoder or resolver but by adopting vector control method using 2 hall sensors generating rectangular signal. This method estimate the velocity and position of mover by using the quadruple of two hall sensor signal instead of encoder signal. Vector control of PMLSM using 2 hall sensor generating rectangular wave is proved to control the system stable and efficiently through simulation. Also hardware experiment reveals that the position control performance is measured within the range of 30~50㎛ in the accuracy of 10~20㎛, which is improved twice to the conventional method. The proposed method exhibits its economical efficiency and practical usefulness. The vector control technique using two hall sensors can be installed in narrow place, accordingly it can be implemented on the system where the conventional encoder or resolver cannot operate.

홀센서가 내장된 고분해능 마그네틱 엔코더에 관한 연구

김성락(S. R. Kim),박철수(C. S. Park),김현희(H. H. Kim),김성훈(S. H. Kim),이경창(K. C. Lee) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월

인력을 대체할 수단인 산업용 로봇의 생산이 증가하면서 로봇 제어에 필요한 엔코더에 수요도 높아지고 있다. 엔코더는 분해능이 높을수록 정밀 제어가 가능해 산업현장에서는 정밀도가 높은 광학식 엔코더를 주로 사용하였다. 그러나 현장에서 발생되는 먼지 및 오염 물질과 같은 요소들이 디스크와 슬롯에 방해가 되어 내구성 및 출력에 영향을 주어 고장이 발생하였다. 이러한 문제를 해결하기 위한 방안으로 마그네틱 엔코더에 관심이 높아졌다. 마그네틱 엔코더는 자기 저항 센서의 배열 위에서 회전하는 자기화된 디스크를 사용해 내구성이 높고 소형화 설계가 가능해 활용도가 많다는 장점이 있다. 하지만 마그네틱 엔코더의 경우 자계가 존재하는 장소에서 위치정보에 대한 오류가 발생하였다. 따라서 본 논문에서는 위와 같은 오류에 대해 고장을 진단이 가능한 마그네틱 엔코더에 대해 연구하고자 한다. 본 연구에서는 데이터 취득 과정에서 어려움을 겪어 이를 해결하기 위해 사용환경을 모사한 테스트베드를 구성하여 오류 데이터를 획득하였다. 그리고 기존 환경의 구동장치를 DC 모터에서 서보 모터로 교체하여 회전과 각도의 정확도를 높였고 평가 보드와 엔코더의 연결을 간소화하였다. 이를 통해 기존 엔코더 파형 및 고장 파형 데이터 파형을 분석하여 위치 이동과 공극 및 틸팅 오류에 대한 데이터를 취득하여 각 오류에 대해 판단할 수 있는 고장진단 GUI 를 설계하였다. 그 결과 엔코더의 고장유무 및 고장 데이터에 대한 상세한 정보를 획득할 수 있었다. 하지만 현재 실험에서는 소량의 정보만 취득하여 소량의 결과만 확보하였다. 향후 추가적인 실험을 통해 각 오류별로 많은 데이터를 확보할 계획이다.

Improve Efficiency Multi-Turn Magnetic Encoder that uses Gear System

Jae Wan Park,Ha Xuan Nguyen,Thuong Ngoc-Cong Tran,Jae Wook Jeon 제어로봇시스템학회 2017 제어로봇시스템학회 국제학술대회 논문집 Vol.2017 No.10

This paper presents a method for the improvement of the performance of a gear-system-based battery-less multiturn absolute magnetic encoder (BLMA-ME). these encoders, the magnetic absolute encoder requires several subshafts and gear systems for the detection of multiple rotations. This paper describes some of the problems of the encoder for which a gear system is used, and a method to increase the resolution and accuracy.

차량용 엔코더씰에 대한 성형성 및 실험적 연구

이지호(JiHo Lee),김권태(Gwontae Kim),안희섭(Huiseop Ahn),양동욱(DongUk Yang) 한국자동차공학회 2019 한국자동차공학회 부문종합 학술대회 Vol.2019 No.5

The encoder seal corresponds to the speed sensor in the wheel bearing and is assembled between the hub and the knuckle to transmit the rotation and steering of the hub. In addition, it is mounted on the car wheel drive bearing and detects the change of the output signal when the rotation and stop between each wheel is detected. It is an important part to drive the ABS and it operates according to the magnetic N / S output signal. , A high-power encoder seal with a MAG flux density of 1.3mT or more, a single pitch error of within ± 1.8%, and a total pitch error of 3.0% or less at an air gap of 3.0 mm is required. In this paper, the quality and test evaluation of encoder seal using ferrite compounding and spinning process optimization method were performed. First, the error measurement of the encoder seal was verified by comparing the 3D modeling with the SCAN DATA. The mechanical properties of the rubber compound were evaluated and it was verified that the corrosion and distortion of the seal occurred. Evaluation was performed to confirm the physical properties.

Analysis of Direction and area of Magnetic Susceptibility Artifact according to Frequency-encoding Changes in 3.0 Tesla MRI

Ji-Won Kim,Wan-Sik Park,Hyun-Sung Kim,Soo-Chul Kim,Yoon-Heui Kang,Tae-Kun Kim,Dong-Kyoon Han,Yeong-Cheol Heo Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4

In this study, the length and area of t he artifact were quantitatively evaluated according to the direction of the magnetic susceptibility artifact. Using a self-made magnetic susceptibility artifact phantom the frequencyencoding direction in the 3.0T MRI system was changed in axial, coronal, and sagittal planes using T2 fast spin echo (FSE). The results showed a difference in length when the frequency encoding was changed from anteroposterior (AP) to right-to-left (RL) in the axial, RL to superior-inferior (SI) in coronal and AP to SI in sagittal planes (p < 0.05). In addition, the difference occurred when the magnetic susceptibility artifact area was measured according to the frequency-encoding direction conversion (p < 0.05). However, additional studies of magnetic susceptibility artifacts using various types of screws and plates are needed. This study provides basic data to prevent magnetic susceptibility artifact due to screw fixation.

Detection of Absolute Position for Magneto-Optical Encoder Using Linear Table Compensation

김슬기(Seul Ki Kim),김형준(Hyeong Jun Kim),이석(Suk Lee),박성현(Sung Hyun Park),이경창(Kyung Chang Lee) Korean Society for Precision Engineering 2016 한국정밀공학회지 Vol.33 No.12

This paper presents the development of a magneto-optical encoder for higher precision and smaller size. In general, optical encoders can have very high precision based on the position information of the slate, while their sizes tend to be larger due to the presence of complex and large components, such as an optical module. In contrast, magnetic encoders have exactly the opposite characteristics, i.e., small size and low precision. In order to achieve encoder features encompassing the advantages of both optical and magnetic encoders, i.e., high precision and small size, we designed a magneto-optical encoder and developed a method to detect absolute position, by compensating for the error of the hall sensor using the linear table compensation method. The performance of the magneto-optical encoder was evaluated through an experimental testbed.

자동차 자기장 제어씰의 고장분석을 통한 가속수명설계에 관한 연구

구남규(Nam-Kyu Koo),김성옥(Sung-Ok Kim),김종갑(Jong-Gap Kim) 한국자동차공학회 2017 한국자동차공학회 학술대회 및 전시회 Vol.2017 No.11

In order to assess the reliability of the magnetic encoder seal for the vehicle, accelerated life test model and procedure are developed. By using this method, failure mechanism and life distribution are analyzed. The main results are as follows; 1) the main failure mechanism is thermal fatigue failure that is, thermal stress due to the difference in thermal expansion coefficient between different materials. 2) the life distribution of the magnetic encoder seal is fitted well to Weibull life distribution and the accelerated life model of that is fitted well to Coffien-Manson model. At the above results of the failure analysis, the enviromnents influence was verified and the accelerated life test was designed, so the service life of the product was predicted from the life distribution results.

마그네틱 엔코더씰 자기특성 예측 프로그램 활용

최현진(H. J. CHoi),우종서(J. S. Woo),김종갑(J. G. Kim) 한국기계가공학회 2020 한국기계가공학회 춘추계학술대회 논문집 Vol.2020 No.6