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Title: Brushed permanent magnet DC MLC motor operation in an external magnetic field

Abstract

Purpose: Linac-MR systems for real-time image-guided radiotherapy will utilize the multileaf collimators (MLCs) to perform conformal radiotherapy and tumor tracking. The MLCs would be exposed to the external fringe magnetic fields of the linac-MR hybrid systems. Therefore, an experimental investigation of the effect of an external magnetic field on the brushed permanent magnet DC motors used in some MLC systems was performed. Methods: The changes in motor speed and current were measured for varying external magnetic field strengths up to 2000 G generated by an EEV electromagnet. These changes in motor characteristics were measured for three orientations of the motor in the external magnetic field, mimicking changes in motor orientations due to installation and/or collimator rotations. In addition, the functionality of the associated magnetic motor encoder was tested. The tested motors are used with the Varian 120 leaf Millennium MLC (Maxon Motor half leaf and full leaf motors) and the Varian 52 leaf MKII MLC (MicroMo Electronics leaf motor) including a carriage motor (MicroMo Electronics). Results: In most cases, the magnetic encoder of the motors failed prior to any damage to the gearbox or the permanent magnet motor itself. This sets an upper limit of the external magnetic field strengthmore » on the motor function. The measured limits of the external magnetic fields were found to vary by the motor type. The leaf motor used with a Varian 52 leaf MKII MLC system tolerated up to 450{+-}10 G. The carriage motor tolerated up to 2000{+-}10 G field. The motors used with the Varian 120 leaf Millennium MLC system were found to tolerate a maximum of 600{+-}10 G. Conclusions: The current Varian MLC system motors can be used for real-time image-guided radiotherapy coupled to a linac-MR system, provided the fringe magnetic fields at their locations are below the determined tolerance levels. With the fringe magnetic fields of linac-MR systems expected to be larger than the tolerance levels determined, some form of magnetic shielding would be required.« less

Authors:
; ; ;  [1];  [2];  [3];  [2]
  1. Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7 (Canada) and Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2 (Canada)
  2. (Canada) and Department of Oncology, Medical Physics Division, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2 (Canada)
  3. (Canada)
Publication Date:
OSTI Identifier:
22096692
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 37; Journal Issue: 5; Other Information: (c) 2010 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; COLLIMATORS; ELECTROMAGNETS; IMAGES; LINEAR ACCELERATORS; MAGNETIC FIELDS; MAGNETIC SHIELDING; MOTORS; NEOPLASMS; NMR IMAGING; PERMANENT MAGNETS; RADIOTHERAPY

Citation Formats

Yun, J., St Aubin, J., Rathee, S., Fallone, B. G., Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7, and Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2. Brushed permanent magnet DC MLC motor operation in an external magnetic field. United States: N. p., 2010. Web. doi:10.1118/1.3392165.
Yun, J., St Aubin, J., Rathee, S., Fallone, B. G., Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7, & Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2. Brushed permanent magnet DC MLC motor operation in an external magnetic field. United States. doi:10.1118/1.3392165.
Yun, J., St Aubin, J., Rathee, S., Fallone, B. G., Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7, and Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2. 2010. "Brushed permanent magnet DC MLC motor operation in an external magnetic field". United States. doi:10.1118/1.3392165.
@article{osti_22096692,
title = {Brushed permanent magnet DC MLC motor operation in an external magnetic field},
author = {Yun, J. and St Aubin, J. and Rathee, S. and Fallone, B. G. and Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2 and Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7 and Department of Medical Physics, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2},
abstractNote = {Purpose: Linac-MR systems for real-time image-guided radiotherapy will utilize the multileaf collimators (MLCs) to perform conformal radiotherapy and tumor tracking. The MLCs would be exposed to the external fringe magnetic fields of the linac-MR hybrid systems. Therefore, an experimental investigation of the effect of an external magnetic field on the brushed permanent magnet DC motors used in some MLC systems was performed. Methods: The changes in motor speed and current were measured for varying external magnetic field strengths up to 2000 G generated by an EEV electromagnet. These changes in motor characteristics were measured for three orientations of the motor in the external magnetic field, mimicking changes in motor orientations due to installation and/or collimator rotations. In addition, the functionality of the associated magnetic motor encoder was tested. The tested motors are used with the Varian 120 leaf Millennium MLC (Maxon Motor half leaf and full leaf motors) and the Varian 52 leaf MKII MLC (MicroMo Electronics leaf motor) including a carriage motor (MicroMo Electronics). Results: In most cases, the magnetic encoder of the motors failed prior to any damage to the gearbox or the permanent magnet motor itself. This sets an upper limit of the external magnetic field strength on the motor function. The measured limits of the external magnetic fields were found to vary by the motor type. The leaf motor used with a Varian 52 leaf MKII MLC system tolerated up to 450{+-}10 G. The carriage motor tolerated up to 2000{+-}10 G field. The motors used with the Varian 120 leaf Millennium MLC system were found to tolerate a maximum of 600{+-}10 G. Conclusions: The current Varian MLC system motors can be used for real-time image-guided radiotherapy coupled to a linac-MR system, provided the fringe magnetic fields at their locations are below the determined tolerance levels. With the fringe magnetic fields of linac-MR systems expected to be larger than the tolerance levels determined, some form of magnetic shielding would be required.},
doi = {10.1118/1.3392165},
journal = {Medical Physics},
number = 5,
volume = 37,
place = {United States},
year = 2010,
month = 5
}
  • Permanent magnet linear synchronous motors (PMLSM's) are proposed for many applications ranging from ground transportation to servo system and conveyance system. In this paper, the fields and forces of permanent magnet linear synchronous motor (PMLSM) with segmented or skewed magnet arrangement are analyzed according to length of segment or skew. And, the effects according to the lateral overhang of magnet are investigated. For the analysis, 3-dimensional equivalent magnetic circuit network (3-D EMCN) method is used. The analysis results are compared with the experimental ones and shown a reasonable agreement.
  • The accurate computation of the external magnetic field from a permanent magnet motor is accomplished by first computing its magnetic scalar potential. In order to find a solution which is valid for any arbitrary point external to the motor, a number of proven methods have been employed. Firstly, A finite element model is developed which helps generate magnetic scalar potential values valid for points close to and outside the motor. Secondly, charge simulation is employed which generates an equivalent magnetic charge matrix. Finally, an equivalent multipole expansion is developed through the application of a toroidal harmonic expansion. This expansion yieldsmore » the harmonic components of the external magnetic scalar potential which can be used to compute the magnetic field at any point outside the motor.« less
  • The pulsed nuclear magnetic resonance (NMR) method has enjoyed liberal practical application in the physics of petroleum traps. A standard sample in the form of a cylinder having a diameter and height of 30 mm is used to determine the properties of traps by classical methods (capillarometry, centrifuging, etc.). Pulsed spectrometers used in the past had a gap not greater than 20 mm between the pole pieces, which made it impossible to record spectra for standard samples. It is quite obvious that the magnetic field in a 40-mm gap will be highly nonuniform. It is therefore essential to investigate themore » configuration of the magnetic field in the gas in order to find an optimal position of a proton-containing sample where reproducible values of the measured signal and relaxation time will be obtained in a certain interval of the gap. An optimal interval of constant, reproducible relaxation parameters has thus been found and corresponds to distances of 4.5-6.5 cm from the bottom of the sensor to the bottom of the vial. The corresponding pulse durations are 11-12 {mu}sec. Subsequent measurements of the relaxation parameters of various objects have demonstrated high stability and reproducibility of the data under the conditions determined here.« less
  • We have developed a new type of microwave ion source which has an axial magnetic field generated by a permanent magnet. By the combination of the permanent magnet and ferromagnetic materials, a closed magnetic circuit is formed through an ion extraction electrode. This axial magnetic field is utilized both for the high-density plasma production by the electron- cyclotron resonance process and for the high efficient ion extraction by transporting the generated ions along the magnetic force lines. The continuous ion beams of 2--3 mA are delivered from the extraction aperture (2 mm in diameter) when various gases (Ar, N/sub 2/,more » CO/sub 2/), metal vapors (Cs, Rb), and reactive gas (O/sub 2/) are used. Extremely low impurities are present in the extracted ion beam. An ion beam with low emittance of 10/sup -8/ m rad order and high brightness of 10/sup 11/ A m/sup -2/ rad/sup -2/ order is obtained. The size of this ion source is 50 mm in diameter and 65 mm in height. The discharge power of the microwave with the frequency of 2.45 GHz is 7 to 30 W. Thus, a high-current microwave ion source with compact structure and low power consumption is realized.« less