Laser Displacement Gauge Research Articles

Design and implementation of the movement gauge for rail clearance based on combination measurement method

PurposeAs the infrastructure of the railway, the rail could sink or deform to different degrees due to the impact of train operation or the geological changing force for years, which will lead to the possibility that the facilities on both sides of the rail invade the rail clearance and bring hidden dangers to the safe operation of the train. The purpose of this paper is to design the gauge to measure the clearance parameters of rail.Design/methodology/approachAiming at the problem, the gauge for clearance measurement was designed based on a combination measurement method in this paper. It consists of the measurement box and the rail measurement vehicle, which integrates a laser displacement sensor, inclination sensor, gauge sensor and mileage sensor. The measurement box was placed outside the rail vehicle. Through the design of a hardware circuit and software system, the movement measurement of the clearance parameters was realized.FindingsIn this paper, the measurement equations of horizontal distance and vertical height were established, the optimal solutions of the structural parameters in the equations were obtained by Levenberg–Marquardt method, then the parameter calibration problem was also solved.Originality/valueThe gauge has high precision; its measurement uncertainty reaches 1.27 mm. The gauge has manual and automatic working modes, which are convenient to operate and have practical popularization value.

Vibrational characteristics of a superconducting magnetic bearing employed for a prototype polarization modulator

We present the vibrational characteristics of a levitating rotor in a superconducting magnetic bearing (SMB) system operating at below 10 K. We develop a polarization modulator that requires a continuously rotating optical element, called half-wave plate (HWP), for a cosmic microwave background polarization experiment. The HWP has to operate at the temperature below 10 K, and thus an SMB provides a smooth rotation of the HWP at the cryogenic temperature of about 10 K with minimal heat dissipation. In order to understand the potential interference to the cosmological observations due to the vibration of the HWP, it is essential to characterize the vibrational properties of the levitating rotor of the SMB. We constructed a prototype model that consists of an SMB with an array of high temperature superconductors, YBCO, and a permanent magnet ring, NdFeB. The rotor position is monitored by a laser displacement gauge, and a cryogenic Hall sensor via the magnetic field. In this presentation, we present the measurement results of the vibration characteristics using our prototype SMB system. We characterize the vibrational properties as the spring constant and the damping, and discuss the projected performance of this technology toward the use in future space missions.

Development of a four-dimensional Monte Carlo dose calculation system for real-time tumor-tracking irradiation with a gimbaled X-ray head

PurposeTo develop a four-dimensional (4D) dose calculation system for real-time tumor tracking (RTTT) irradiation by the Vero4DRT. MethodsFirst, a 6-MV photon beam delivered by the Vero4DRT was simulated using EGSnrc. A moving phantom position was directly measured by a laser displacement gauge. The pan and tilt angles, monitor units, and the indexing time indicating the phantom position were also extracted from a log file. Next, phase space data at any angle were created from both the log file and particle data under the dynamic multileaf collimator. Irradiation both with and without RTTT, with the phantom moving, were simulated using several treatment field sizes. Each was compared with the corresponding measurement using films. Finally, dose calculation for each computed tomography dataset of 10 respiratory phases with the X-ray head rotated was performed to simulate the RTTT irradiation (4D plan) for lung, liver, and pancreatic cancer patients. Dose-volume histograms of the 4D plan were compared with those calculated on the single reference respiratory phase without the gimbal rotation [three-dimensional (3D) plan]. ResultsDifferences between the simulated and measured doses were less than 3% for RTTT irradiation in most areas, except the high-dose gradient. For clinical cases, the target coverage in 4D plans was almost identical to that of the 3D plans. However, the doses to organs at risk in the 4D plans varied at intermediate- and low-dose levels. ConclusionsOur proposed system has acceptable accuracy for RTTT irradiation in the Vero4DRT and is capable of simulating clinical RTTT plans.

Development of a four-axis moving phantom for patient-specific QA of surrogate signal-based tracking IMRT.

Purpose:The purposes of this study were two-fold: first, to develop a four-axis moving phantom for patient-specific quality assurance (QA) in surrogate signal-based dynamic tumor-tracking intensity-modulated radiotherapy (DTT-IMRT), and second, to evaluate the accuracy of the moving phantom and perform patient-specific dosimetric QA of the surrogate signal-based DTT-IMRT.Methods:The four-axis moving phantom comprised three orthogonal linear actuators for target motion and a fourth one for surrogate motion. The positional accuracy was verified using four laser displacement gauges under static conditions (±40 mm displacements along each axis) and moving conditions [eight regular sinusoidal and fourth-power-of-sinusoidal patterns with peak-to-peak motion ranges (H) of 10–80 mm and a breathing period (T) of 4 s, and three irregular respiratory patterns with H of 1.4–2.5 mm in the left–right, 7.7–11.6 mm in the superior-inferior, and 3.1–4.2 mm in the anterior–posterior directions for the target motion, and 4.8–14.5 mm in the anterior–posterior direction for the surrogate motion, and T of 3.9–4.9 s]. Furthermore, perpendicularity, defined as the vector angle between any two axes, was measured using an optical measurement system. The reproducibility of the uncertainties in DTT-IMRT was then evaluated. Respiratory motions from 20 patients acquired in advance were reproduced and compared three-dimensionally with the originals. Furthermore, patient-specific dosimetric QAs of DTT-IMRT were performed for ten pancreatic cancer patients. The doses delivered to Gafchromic films under tracking and moving conditions were compared with those delivered under static conditions without dose normalization.Results:Positional errors of the moving phantom under static and moving conditions were within 0.05 mm. The perpendicularity of the moving phantom was within 0.2° of 90°. The differences in prediction errors between the original and reproduced respiratory motions were −0.1 ± 0.1 mm for the lateral direction, −0.1 ± 0.2 mm for the superior-inferior direction, and −0.1 ± 0.1 mm for the anterior–posterior direction. The dosimetric accuracy showed significant improvements, of 92.9% ± 4.0% with tracking versus 69.8% ± 7.4% without tracking, in the passing rates of γ with the criterion of 3%/1 mm (p < 0.001). Although the dosimetric accuracy of IMRT without tracking showed a significant negative correlation with the 3D motion range of the target (r = − 0.59, p < 0.05), there was no significant correlation for DTT-IMRT (r = 0.03, p = 0.464).Conclusions:The developed four-axis moving phantom had sufficient accuracy to reproduce patient respiratory motions, allowing patient-specific QA of the surrogate signal-based DTT-IMRT under realistic conditions. Although IMRT without tracking decreased the dosimetric accuracy as the target motion increased, the DTT-IMRT achieved high dosimetric accuracy.

Development of a System for Measuring the Thickness of Free Curved Plates – Measurement Posture Planning Using C-Space –

Although it is important to evaluate the thickness of a product made on a press in order to evaluate the mold, there is currently no appropriate system for measuring the thickness of a free curved plate. This study details the development of an automatic measurement and evaluation system for measuring the thickness of free curved plates. The system uses laser displacement gauges and an industrial robot to measure the thickness of a plate. While the system has been capable of measuring workpieces with relatively simple shapes, there have been collisions between the laser path and workpieces with more complicated shapes, owing to geometrical limits of the gauges in terms of measuring posture. This paper proposes a new method of detecting and avoiding collisions by changing the posture on the basis of CAD data when measurements are taken. In this method, not only the geometrical characteristics of the laser path but also the measuring error characteristics of the gauges stemming from measuring posture are considered. In addition, a continuous measuring path with changes in posture to avoid collision is devised. Experimental results confirm that the proposed method does make it possible to measure the thickness of workpieces with complicated shapes.

Effect of audio instruction on tracking errors using a four‐dimensional image‐guided radiotherapy system

The Vero4DRT (MHI‐TM2000) is capable of performing X‐ray image‐based tracking (X‐ray Tracking) that directly tracks the target or fiducial markers under continuous kV X‐ray imaging. Previously, we have shown that irregular respiratory patterns increased X‐ray Tracking errors. Thus, we assumed that audio instruction, which generally improves the periodicity of respiration, should reduce tracking errors. The purpose of this study was to assess the effect of audio instruction on X‐ray Tracking errors. Anterior‐posterior abdominal skin‐surface displacements obtained from ten lung cancer patients under free breathing and simple audio instruction were used as an alternative to tumor motion in the superior‐inferior direction. First, a sequential predictive model based on the Levinson‐Durbin algorithm was created to estimate the future three‐dimensional (3D) target position under continuous kV X‐ray imaging while moving a steel ball target of 9.5 mm in diameter. After creating the predictive model, the future 3D target position was sequentially calculated from the current and past 3D target positions based on the predictive model every 70 ms under continuous kV X‐ray imaging. Simultaneously, the system controller of the Vero4DRT calculated the corresponding pan and tilt rotational angles of the gimbaled X‐ray head, which then adjusted its orientation to the target. The calculated and current rotational angles of the gimbaled X‐ray head were recorded every 5 ms. The target position measured by the laser displacement gauge was synchronously recorded every 10 msec. Total tracking system errors (ET) were compared between free breathing and audio instruction. Audio instruction significantly improved breathing regularity (p < 0.01). The mean ± standard deviation of the 95th percentile of ET (E95T) was 1.7 ± 0.5 mm (range: 1.1–2.6 mm) under free breathing (E95T,FB) and 1.9 ± 0.5 mm (range: 1.2–2.7 mm) under audio instruction (E95T,AI). E95T,AI was larger than E95T,FB for five patients; no significant difference was found between E95T,FB and ET,AI95(p = 0.21). Correlation analysis revealed that the rapid respiratory velocity significantly increased E95T. Although audio instruction improved breathing regularity, it also increased the respiratory velocity, which did not necessarily reduce tracking errors.PACS number: 87.55.ne, 87.57.N‐, 87.59.C‐,

Full-field time-series measurement for three-dimensional deformation under welding

Displacement during welding provides important information to understand the mechanisms of welding deformation and residual stress. In particular, if welding deformation can be measured sequentially and the displacement distribution over full field can be measured such as the results obtained by finite element analysis, they can be valuable information. Therefore, in this study, a 3-dimensional (3D) deformation (in-plane and out-of-plane deformation) measurement method is developed using a digital camera, which requires no special equipment. This method is a non-contact method and it can sequentially measure over the entire photographed image. Furthermore, since image analysis is based on the technique of image matching, the method is applicable even when measuring deformation is large. In addition, since it is possible to use all pixels as measuring points, the number of available measuring points at one time is the same as the number of effective pixels of the camera. This is currently more than 15 million points, and the measuring precision is expected to increase as the camera pixel resolution continues to increase. Therefore, this method is expected to have future potential. In this study, the proposed method is applied to the sequential measurement of displacement under the strong lighting levels in arc welding. By comparing the time history of transverse shrinkage, longitudinal shrinkage and angular distortion with the results of FEM thermal elastic-plastic analysis, the qualitative validity of the proposed method is verified. To investigate the measurement precision and usefulness of the method, a 3D shape measurement system (LAT-3D) using a laser displacement gauge and digital caliper are used. The distributions of residual transverse shrinkage and residual angular distortion are measured by the proposed method, LAT-3D and digital caliper. Through the comparison of the results measured by these methods, quantitative validity of the proposed method is also verified.

Development of Orthros, an Evaluation System for Free Curved Plate Thickness with a Robot - Generation of the Path Considering Collision

While it is important that evaluation of thickness of a product made with press working to evaluate a mold, currently, there is not an appropriate system which can measure thickness of a free curved plate. The study deals with a development of an automatic measurement and evaluation system for thickness of free curved plates, called Orthros. The system measures thickness of a plate with laser displacement gauges and an industrial robot. While the system has been capable for measurement of a relatively simple shaped workpiece, it had collisions between laser-path and workpiece for that of a complicated shape, owing to a geometrical limit about measuring posture of the gauges. In this article, a new method to detect collision and to avoid collision by changing measuring posture on the basis of CAD data is proposed. In the method, not only the geometrical characteristic of the laser-path but also the measuring error characteristic of the gauges depending on the measuring posture are considered and continuous measuring path having change in posture to avoid collision is devised. From the experiment result, it is confirmed that the proposed method has an ability to measure a thickness of a workpiece with complicated shape.

Positional accuracy of novel x‐ray‐image‐based dynamic tumor‐tracking irradiation using a gimbaled MV x‐ray head of a Vero4DRT (MHI‐TM2000)

To verify the positional accuracy of a novel x-ray-image-based dynamic tumor-tracking (DTT) irradiation technique using the gimbaled MV x-ray head of a Vero4DRT (MHI-TM2000). Verification of the x-ray-image-based DTT was performed using three components: a three-dimensional moving phantom with a steel ball target, a laser displacement gauge, and an orthogonal kV x-ray imaging subsystem with a gimbaled MV x-ray head and the system controller of the Vero4DRT. The moving phantom was driven based on seven periodic patterns [peak-to-peak amplitude (A): 20-40 mm, breathing period (T): 2-5 s] and 15 patients' aperiodic respiratory patterns (A: 6.5-22.9 mm, T: 1.9-5.8 s). The target position was detected in real time with the orthogonal kV x-ray imaging subsystem using the stereo vision technique. Subsequently, the Vero4DRT predicted the next position of the target, and then the gimbaled MV x-ray head tracked the corresponding orientation of the target. The displacements of the target were measured synchronously using the laser displacement gauge. The difference between the target positions predicted by the Vero4DRT and those measured by the laser displacement gauge was computed as the prediction error (E(P)), and the difference between the target positions tracked by the gimbaled MV x-ray head and predicted target positions was computed as the mechanical error (E(M)). Total tracking system error (E(T)) was defined as the difference between the tracked and measured target positions. The root mean squares (RMSs) of E(P), E(M), and E(T) were up to 0.8, 0.3, and 0.7 mm, respectively, for the periodic patterns. Regarding the aperiodic patterns, the median RMSs of E(P), E(M), and E(T) were 1.2 (range, 0.9-1.8) mm, 0.1 (range, 0.1-0.5) mm, and 1.2 (range, 0.9-1.8) mm, respectively. From the results of principal component analysis, tracking efficiency, defined as the ratio of twice the RMS of E(T) to A, was improved for patients with high respiratory function (R = 0.91; p < 0.01). The present study demonstrated that the Vero4DRT is capable of high-accuracy x-ray-image-based DTT. E(T) was caused primarily by E(P), and E(M) was negligible. Furthermore, principal component analysis showed that tracking efficiency could be improved with this system, especially for patients with high respiratory function.

Development of in situ measurement system for welding deformation using digital cameras

A three-dimensional (3D) deformation (in plane and out of plane deformations) measurement method is developed using digital cameras, which require no special equipment. This method is a non-contact method, and it can sequentially measure over the entire photographed image. Furthermore, since image analysis is based on the technique of image matching, the method is applicable even when the deformation to be measured is large. In addition, since it is possible to use all pixels as measuring points, the number of available measuring points at one time is the same as the number of effective pixels of the camera. In this study, the proposed method is applied to the sequential measurement of displacement under strong lighting levels in arc welding. Through the comparison of the results measured by a 3D shape measurement system (LAT-3D) using a laser displacement gauge and digital caliper, the quantitative validity of the proposed method is also verified.

Measurement of Mechanical Properties with Respect to Gap Healing in a Rabbit Osteotomy Model Using Echo Tracking

The most important issue in the assessment of fracture healing is to acquire information about the restoration of the mechanical integrity of bone. Echo tracking (ET) can noninvasively measure the displacement of a certain point on the bone surface under a load. Echo tracking has been used to assess the bone deformation angle of the fracture healing site. Although this method can be used to evaluate bending stiffness, previous studies have not validated the accuracy of bending stiffness. The purpose of the present study is to ensure the accuracy of bending stiffness as measured by ET. A four-point bending test of the gap-healing model in rabbit tibiae was performed to measure bending stiffness. Echo tracking probes were used to measure stiffness, and the results were compared with results of stiffness measurements performed using laser displacement gauges. The relationship between the stiffness measured by these two devices was completely linear, indicating that the ET method could precisely measure bone stiffness.

SU‐E‐J‐147: Effect of Audio Instruction on the Tracking Accuracy for a Four‐ Dimensional Image‐Guided Radiotherapy System, MHI‐TM2000 (VERO)

Purpose: To assess the effect of audio instruction on tracking accuracy for MHI‐TM2000 (VERO).Methods: Anterior‐posterior abdominal skin surface displacements for ten patients with a lung tumor were measured by a respiratory monitoring system with and without audio instruction. Based on the obtained twenty respiratory patterns, a three‐dimensional movable phantom with a steel ball target of 9.5 mm in diameter was driven along the superior‐inferior direction. The target position was measured in real time by the laser displacement gauge and the orthogonal kV x‐ray imaging subsystem. Simultaneously, the kV x‐ray imaging subsystem predicted the future target position, and then the system controller calculated the corresponding rotation angles. Thereafter, the gimbaled x‐ray head tracked the target based on the command. Total tracking system error (ET) was computed by both target prediction errors and mechanical response errors of the gimbaled x‐ray head, and then compared between with and without audio instruction.Results: By applying audio instruction, the reproducibility of respiratory pattern was significantly improved (p &lt; 0.01), although motion amplitude was increased by a factor of 2.1 on average. The root mean squares of the ET (RMSET) were up to 1.18 mm without audio instruction and 1.26 mm with audio instruction, respectively. There was no significant difference between free breathing and audio instruction in the RMSET (p = 0.26). The correlation between the RMSET and the 90th percentile of respiratory speed (v) was stronger under the conditions of audio instruction (R2 = 0.77) than under the conditions of free breathing (R2 = 0.29) Conclusions: Audio instruction improved reproducibility of respiratory pattern but increased to the v that negatively affected the tracking accuracy. The tracking errors can be deduced from the v for regular respiratory pattern, suggesting upper limit of the v to achieve high tracking accuracy.This research was in part sponsored by Mitsubishi Heavy Industries, Ltd., Japan.

SU‐E‐T‐673: Development of Monte Carlo Dose Calculation System for Tumor‐Tracking Irradiation with a Gimbaled X‐Ray Head

Purpose: To propose dose calculation model of tumor‐tracking irradiation by gimbals mechanism for MHI‐TM2000 (Vero). Methods: Our MC simulation for a 6 MV photon beam delivered by the MHI‐TM2000 system was performed using EGSnrc. First, the lateral doses (5 × 5 cm2 at 100 mm depth) with pan/tilt rotation were simulated under the SSD of 900 mm. Rotation angles along pan/tilt directions were set in the range of −2.5 to +2.5° at intervals of 0.5°. The corresponding measurements were performed using EDR2 films with water‐equivalent phantoms. Differences between simulated and measured doses were calculated. Furthermore, difference of output characteristic without setup error was estimated using the simulated lateral doses under the reference condition at the maximum and minimum rotation angles. Next, the moving phantom was driven at frequency of 0.25 Hz with amplitude of 10 mm along tilt direction. From the infrared marker positions, the corresponding pan/tilt angles were calculated. Time, phantom position by laser displacement gauge, current angle of pan/tilt, and MU were recorded in the log file. A phase space data at any angles was created from the log file and particle data under the MLC. Finally, both stationary X‐ray head and tumor‐tracking irradiation were simulated under the SSD of 950 mm (4 × 4 cm2 at 50 mm depth). Each of them was compared with the corresponding measurement using EDR2 film. Results: The lateral doses within flat region showed agreement of within 1.1% in any angles. The differences between doses at the minimum angle and at the maximum were within 0.5% and 4.5% in flat and penumbra region, respectively. The averaged differences between the simulated and the measured doses with stationary and tumor‐tracking irradiation were 1.9%. Conclusions: We have developed dose calculation model of tumor‐tracking irradiation for MHI‐TM2000. This study demonstrated our proposed model has acceptable accuracy.Research sponsored in part by Mitsubishi Heavy Industries, Ltd

SU‐E‐J‐151: Geometric Accuracy of the X‐Ray Image‐Based Dynamic Tracking for a Four‐Dimensional Image‐Guided Radiotherapy System with Gimbals Mechanism of MHI‐TM2000 (Vero)

Purpose: To verify the geometric accuracy of the X‐ray image‐based dynamic tracking for a four‐dimensional (4D) image‐guided radiotherapy system with gimbals mechanism of MHI‐TM2000 (VERO). Methods: This study was performed employing a 3D moving phantom with a steel‐ball target of 9.5‐mm‐diameter; a laser displacement gauge; orthogonal kV x‐ray imaging subsystem, a gimbaled X‐ray head, and a system controller of MHI‐TM2000. The moving phantom was driven based on the programmed motion patterns (seven periodic [Motion range: 20–40 mm, Breathing cycle: 2‐5 s] and 15 of 3D patientˈs respiratory patterns). Subsequently, the displacements of the target were measured in real time by the laser‐displacement gauge and the orthogonal kV x‐ray imaging subsystem. Meanwhile, the system predicted the future target position, and then the orthogonal gimbals were transferred to the corresponding orientation. The transferred and the current orientation of the gimbals were recorded. Predicted target positional errors (EP), mechanical errors (EM) of the gimbals, and total tracking system errors (ET) derived from EP and EM were computed. Results: Root mean square of ET (RMSET) was up to 0.68 mm for the periodic patterns. As for the entire patientˈs respiratory patterns, average RMS of EP, EM, and ET were 1.28, 0.12, and 1.24 mm, respectively. The principal component score which was computed from the patientˈs respiratory motion under the conditions of free breathing decreased with large amplitude, long breathing cycle and high breathing stability. A strong positive correlation was observed between the ratio of the RMSET to the amplitude and the principal component score of the respiratory motion (R2 = 0.76). Conclusions: This study showed that MHI‐TM2000 has the capability for high tracking accuracy. The prediction error mainly caused the total tracking system error while the mechanical error was negligible. In addition, tracking error can be predicted from the principal component analyses.This research was in part sponsored by Mitsubishi Heavy Industries, Ltd., Japan.

SU‐GG‐T‐348: Development of a Precise Position‐Controlled Moving Phantom

Purpose: Current commercially available moving phantoms are limited in their motions and accuracy of positions. The purpose of this study is to develop a moving phantom with highly accurate position control (error less than 0.2 mm) in 3 directions so that it can reproduce most of patients' tumor motions obtained by 4D‐CT. Method and Materials: The moving phantom consisted of two parts: thorax phantom and 3D‐axial control unit. The thorax phantom was made of transparent resin, which has an electron density of 1.04. The plaster bones were structured by ink‐jet printing method, and were embedded in the resin. The 3D‐axial control unit was designed to achieve any motion less than 10 cm/sec in x, y and z directions in the region of 150×350×250 mm which was a cavity in the thorax phantom. Two acryl hemispheres with a radius of 1 cm were set on the tip of the 3D‐axial control unit. The motion imitating respiratory tumor motion or sine curve was input, and the motion of the target was measured by a laser displacement gauge to evaluate the accuracy. The target motion was also captured by conventional CT and CBCT to evaluate the performance. Results: The target motion was as accurate as less than 0.1mm in the case of sine waves (1 cm, 12 bpm). In the case of patient's tumor motion (up to 7 mm, 7.5 bpm), although the motion was not modified with smoothing, the error was less than 0.2 mm. The conventional CT and CBCT images reflected the motion of the target. Conclusions: We developed a novel moving phantom with a high accuracy in position control. This moving phantom could be used for evaluation of 4DRT techniques.

溶接中における三次元変形の時系列全視野計測

Displacement during welding provides important information to understand the mechanisms of welding deformation and residual stress. In particular, if welding deformation can be measured sequentially and the displacement distribution over full-field can be measured such as the results obtained by finite element analysis, they can be valuable information. Therefore, in this study, 3-dimensional deformation (in-plane and out-of-plane deformation) measurement method is developed using a digital camera, which requires no special equipment. This method is a non-contact method and it can sequentially measure over the entire photographed image. Furthermore, since image analysis is based on the technique of image matching, the method is applicable even when measuring deformation is large. In addition, since it is possible to use all pixels as measuring points, the number of available measuring points at one time is the same as the number of effective pixels of the camera. This is currently more than 15 million points, and the measuring precision is expected to increase as the camera pixel resolution continues to increase. Therefore, this method is expected to have future potential.In this study, proposed method is applied to the sequential measurement of displacement under the strong lighting levels in arc welding. By comparing the time history of transverse shrinkage, longitudinal shrinkage and angular distortion with the results of FEM thermo-elastic plastic analysis, the qualitative validity of the proposed method is verified. To investigate the measurement precision and usefulness of the method, a 3-dimensional shape measurement system (LAT-3D) using a laser displacement gauge and digital caliper are used. The distributions of residual transverse shrinkage and residual angular distortion are measured by the proposed method, LAT-3D and digital caliper. Through the comparison of the results measured by these methods, quantitative validity of the proposed method is also verified.

Fatigue Fracture Behavior of Mg-Zn-Y Alloys

Recently, Mg-Zn-Y alloys with superior performance, which have a long period stacking order (LPSO) phase, have been developed. Therefore, it is important to understand fundamental fatigue properties in such materials. In this study, the fatigue fracture behavior of the Mg96Zn2Y2 alloy has been investigated with a plain bending testing machine, which was originally developed for thin sheet specimen at room temperature and 523K. One end of the sheet specimen is fixed at a voice coil of the loudspeaker and the other end is set free. A bending mode resonance occurs in the specimen due to forced vibration at the fixed end. To estimate stress amplitude of bending, deflections at the free end of the specimen oscillating at a frequency of about 200~500Hz was measured by a laser displacement gauge. For comparison, AZ31B alloy also has been investigated. S-N curve for the Mg96Zn2Y2 alloy was obtained using a stress ratio of R=-1, and the fatigue strengths were estimated as 200MPa at room temperature and 120MPa at 523K at 106~107 cycles. These values correspond to about 50% of 0.2% proof strengths of the Mg96Zn2Y2 alloy. Two types of fatigue surface were observed in the Mg96Zn2Y2 alloy. One was striation-like-pattern and the other was relatively flat surface. Striation-like-pattern was similar to fatigue surface of AZ31B. Therefore, these two types of fatigue surface correspond to crack passing through α-Mg phase and LPSO phase, respectively. The feature of fracture surface at 523K was almost the same as that at room temperature.

The Study about Position Sense of Human Feet

To determine the accuracy of foot position sense in the means of foot placement, young adults were asked to place either medial edge or lateral edge of their feet along the base line on the floor as close as possible, and the edge of placed feet were scanned by using laser displacement gauge. From the collected data, constant error, the distances between the edge of placed feet and the base line on the floor, and absolute error, the absolute distances between the edge of placed feet and the base line on the floor were defined and compared between the medial or lateral trials, and dominant leg or indominant leg. The statistical analysis showed significant differences of constant error between the trials only. The trials to place their medial edge tend to place their feet away from the base line, and the trials to place their lateral edge tend to place their feet in to the base line. These results indicate that we tend to expect the position of our feet more medially than actual, and these discrepancy may be one of a reasons of tripping or banging of our feet to the obstacles while walking.

Fatigue Fracture Behavior of Mg-Zn-Y Alloy

Recently, Mg-Zn-Y alloys with superior performance, which have a long period order (LPO) phase, have been developed. Therefore, it is important to understand fundamental fatigue properties in such materials. In this study, the fatigue fracture behavior of Mg-Zn2-Y2-Zr0.2 alloy has been investigated using a plain fatigue bending testing machine, which was originally developed for thin sheet specimen. One end of the sheet specimen is fixed at a voice coil of the loudspeaker and the other end is set free. A bending mode resonance occurs in the specimen due to forced vibration at the fixed end. To estimate stress amplitude of bending, deflections at the free end of the specimen oscillating at a frequency of about 250~700Hz was measured by a laser displacement gauge. For comparison, AZ31B alloy also has been investigated. S-N curve for the Mg-Zn2-Y2-Zr0.2 alloy was obtained using a stress ratio of R=-1, and the fatigue strength was estimated as about 200MPa at 106~108 cycles. The value corresponds to about 50% of 0.2% proof strength of the alloy. Two types of fatigue surface were observed in the alloy. One is striation like pattern and the other is relatively flat surface. The former is similar to fatigue surface of AZ31B. Therefore, these two types of fatigue surface correspond to crack passing through α-Mg phase and LPO phase, respectively.

Ｍｉｎｉ−ＲＴ Ｍｉｎｉ−ＲＴ装置用高温超伝導磁気浮上コイルの開発

A magnetically-levitated superconducting coil device, Mini-RT, has been constructed using a high temperature superconductor (HTS) for the purpose of examining a new magnetic confinement scheme of high-beta non-neutral plasmas. The floating coil is wound with silver-sheathed Bi-2223 tapes, and it is operated in the temperature range of 20-40 K. A number of studies and experiments were carried out in order to realize the necessary system. One of them was to demonstrate magnetic levitation using a miniature HTS floating coil having a diameter of 80 mm. The coil was fabricated using Bi-2223/Ag tapes of 12 m and excited by field cooling with liquid nitrogen. The magnetic levitation was examined using a real-time feedback control system with laser displacement gauges. Additionally, a persistent current switch (PCS) has been developed using Bi-2223/Ag tapes of 21 m, and a prototype HTS-PCS was tested in a cryostat. After construction of the floating coil and HTS-PCS for the Mini-RT device was completed, excitation tests were carried out in the cryostat and the basic properties up to the nominal operation condition were examined.