Electromagnetic Position Sensor Research Articles

Soft Robots: Computational Design, Fabrication, and Position Control of a Novel 3-DOF Soft Robot

This paper presents the computational design, fabrication, and control of a novel 3-degrees-of-freedom (DOF) soft parallel robot. The design is inspired by a delta robot structure. It is engineered to overcome the limitations of traditional soft serial robot arms, which are typically low in structural stiffness and blocking force. Soft robotic systems are becoming increasingly popular due to their inherent compliance match to that of human body, making them an efficient solution for applications requiring direct contact with humans. The proposed soft robot consists of three soft closed-loop kinematic chains, each of which includes a soft actuator and a compliant four-bar arm. The complex nonlinear dynamics of the soft robot are numerically modeled, and the model is validated experimentally using a 6-DOF electromagnetic position sensor. This research contributes to the growing body of literature in the field of soft robotics, providing insights into the computational design, fabrication, and control of soft parallel robots for use in a variety of complex applications.

Development of a Hybrid Reference Model for Performance Evaluation of Resolvers

Resolver is an electromagnetic position sensor typically used in the closed-loop control of permanent magnet synchronous motors (PMSMs). In terms of structure and principle of operation, resolvers are very similar to electrical machines. In this regard, different numerical and analytical models have been developed for the performance prediction of a resolver, with a compromise between computational burden and accuracy. Therefore, a fast and accurate hybrid model of the resolver is presented in this article, which can be used for resolvers with different structures. Additionally, this model can easily be implemented in software such as MATLAB/SIMULINK. The performance of different variable reluctance (VR) and wound rotor (WR) resolvers calculated from the model and finite element analysis (FEA) is compared to show the value of the proposed model. The model is also used to improve the position determination accuracy of a VR resolver. Finally, a prototype of the optimized resolver is used for experimental tests to confirm the validity of the analysis.

Electromagnetic Induction Position Sensor Applied to Anti-Misalignment Wireless Charging for UAVs

Misalignment of wireless power transfer (WPT) system's transmitting and receiving ends can cause severe efficiency degradation and electromagnetic radiation. In this paper, a novel parallel transmission (TX) coil matrix structure was proposed to improve the performance of the WPT in the misalignment condition. The receiving (RX) coil's position measurement method was innovated by investigating the magnetic field and the mutual inductance change caused by the relative position change between RX and TX coils. Both theory and experiments confirmed that the phase difference between signal coil and detector coil can be featured as the parameter to represent the magnetic field's change. Based on this principle, a 4×4 TX coil matrix was made which verified the proposal and the sensitivity of the sensor. It was found that the position measurement result was sufficient to decide which TX coil to gate to facilitate the wireless charging in misalignment conditions. The structure and the size of the TX coil matrix could be further optimized to enhance the sensor's reliability and sensitivity.

Position error calculation of linear resolver under mechanical fault conditions

Position sensors are inseparable part of motion control systems. Linear resolvers (LRs) are electromagnetic position sensors that are suitable for high vibration, polluted environments. The accuracy of their detected position can be affected by different mechanical faults. In this study, variety of possible mechanical faults along with their mathematical index in LRs is introduced. Static eccentricity, dynamic eccentricity, inclined mover and run out error are the presented mechanical faults that are discussed independently and simultaneously. Then, three-dimensional non-linear, time-stepping finite element method is employed to investigate the performance of the studied resolver under different mechanical faults. Finally, the prototype of the studied sensor is built. An experimental test setup is designed and built in order to measure the output characteristic of the LR under studied mechanical faults. Good correlation between the experimental and simulation results is obtained.

Ultrasound-Guided Radiofrequency Ablation Using a New Electrode with an Electromagnetic Position Sensor for Hepatic Tumors Difficult to Place an Electrode: A Preliminary Clinical Study.

To evaluate whether a new electrode embedded with an electromagnetic position sensor (EMPS) improves the technical feasibility of percutaneous radiofrequency ablation (RFA) in patients with hepatic tumors difficult to place an electrode under ultrasonography (US) guidance and to assess short-term therapeutic efficacy and safety. This prospective study was approved by the institutional review board, and written informed consent was obtained from all patients. Between January 2015 and December 2016, 10 patients (7 men and 3 women; age range 52-75years) with a single hepatic tumor (median 1.4cm; range 1.1-1.8cm) difficult to place an electrode under US guidance were enrolled. The technical feasibility of targeting and overlapping ablation during the RFA procedure was graded using a four-point scale and analyzed using the Wilcoxon signed rank test according to the use of EMPS. In addition, the rates of technical success, local tumor progression (LTP), and major complications were assessed. The use of the new RF electrode with EMPS significantly improved the technical feasibility of targeting and overlapping ablation (p=0.002 and p=0.003, respectively). After treatment, the technical success rate was 100%. LTP was not found in any patient during the follow-up period (median 8months; range 4-22months). No major procedure-related complications occurred. The technical feasibility of percutaneous RFA improves with the use of this RF electrode embedded with an EMPS. Short-term therapeutic efficacy and safety after RFA using the electrode were promising in patients with hepatic tumors difficult to place an electrode under US guidance.

Design, Analysis, and Prototyping of a New Wound-Rotor Axial Flux Brushless Resolver

Resolvers are electromagnetic position sensors that are widely used in industrial applications. In this study, a new axial flux brushless resolver (AFBR) with a wound rotor is introduced. In the proposed resolver, the core of the rotary transformer (RT) is omitted, and an innovative design is used to supply the excitation winding of the resolver. The proposed resolver can be built with smaller dimensions, and its thermal stability and mechanical strength are increased compared with conventional AFBRs. The performance of the proposed structure is simulated and optimized by using a three-dimensional time-stepping finite element method. The effect of the leakage flux of the RT on the excitation and signal windings is also discussed for both the proposed and conventional structures. A prototype based on the optimized topology is constructed and tested. Good agreement is obtained between the simulation and experimental results, validating the success of the proposed resolver.

Design, Performance, and Testing of a Brushless Axial Flux Resolver Without Rotor Windings

Resolvers are electromagnetic position sensors that are widely used in industrial applications. In this paper, a novel axial flux resolver with a simple solid rotor is introduced for the first time. The stator of the proposed resolver has a disk type structure with two-phase distributed windings as signal windings and a concentric winding as an excitation winding. The rotor is a disc with a simple structure. Its width is 20° without any winding, and thus, the proposed resolver has the advantages of variable reluctance resolvers for having no winding on rotor and also its manufacturing process is much simpler than that of variable reluctance resolvers. The performance analysis of the proposed structure is simulated and optimized using a 3D time stepping finite element method. Then, a prototype is constructed based on the optimized dimensions and tested. Good agreement between the simulation and the experimental results validates the success of the proposed resolver.

<i>In Vivo</i> Dosimetry of an Anthropomorphic Phantom Using the RADPOS for Proton Beam Therapy

The radiation positioning system (RADPOS) combines an electromagnetic positioning sensor with metal oxide semiconductor field-effect transistor (MOSFET) dosimetry, enabling simultaneous online measurement of dose and spatial position. Evaluation points can be determined with the RADPOS. The accuracy of in-vivo proton dosimetry was evaluated using the RADPOS and an anthropomorphic head and neck phantom. MOSFET doses measured at 3D positions obtained with the RADPOS were compared with treatment plan values calculated using a simplified Monte Carlo (SMC) method. MOSFET responses, which depend strongly on the linear energy transfer of the proton beam, were corrected using the SMC method. The SMC method was used to calculate only dose deposition determined by the experimental depth-dose distribution and lateral displacement of protons due to the multiple scattering effect in materials and incident angle. This method thus enabled rapid calculation of accurate doses in even heterogeneities. In vivo dosimetry using the RADPOS, as well as MOSFET doses, agreed with SMC calculations in the range of ?3.0% to 8.3%. Most measurement errors occurred because of uncertainties in dose calculations due to the 1-mm position error. The results indicate that uncertainties in measurement position can be controlled successfully within 1 mm when using the RADPOS with in-vivo proton dosimetry.

SU‐E‐T‐482: In Vivo Dosimetry of An Anthropomorphic Phantom by Using the RADPOS System for Proton Beam Therapy

Purpose:Delivered doses in an anthropomorphic phantom were evaluated by using the RADPOS system for proton beam therapy.Methods:The RADPOS in vivo dosimetry system combines an electromagnetic positioning sensor with MOSFET dosimetry, allowing simultaneous online measurements of dose and spatial position. Through the RADPOS system, dose evaluation points can be determined. In vivo proton dosimetry was evaluated by using the RADPOS system and anthropomorphic head and neck phantom. MOSFET doses measured at 3D positions obtained with the RADPOS were compared to the treatment plan values that were calculated by a simplified Monte Carlo (SMC) method. Although the MOSFET response depends strongly on the linear energy transfer (LET) of proton beam, the MOSFET responses to proton beams were corrected with the SMC. Here, the SMC calculated only dose deposition determined by the experimental depth–dose distribution and lateral displacement of protons due to both multiple scattering effect in materials and incident angle. As a Result, the SMC could quickly calculate accurate doses in even heterogeneities.Results:In vivo dosimetry by using the RADPOS, as well as the MOSFET doses agreed in comparison with calculations by the SMC in the range of −3.0% to 8.3%. Most measurement errors occurred because of the uncertainties of dose calculations due to the position error of 1 mm.Conclusion:We evaluated the delivered doses in the anthropomorphic phantom by using the RADPOS system for proton beam therapy. The MOSFET doses agreed in comparison with calculations by the SMC within the measurement error. Therefore, we could successfully control the uncertainties of the measurement positions by using the RADPOS system within 1 mm in in vivo proton dosimetry. We aim for the clinical application of in vivo proton dosimetry with this RADPOS system.

A Novel Electrode With Electromagnetic Tip Tracking in Ultrasonography-Guided Radiofrequency Ablation

The objective of this study was to compare the targeting and ablation performance between a newly developed radiofrequency (RF) electrode embedded with an electromagnetic position sensor (EMPS) at the electrode tip and a conventional RF electrode. The institutional animal care and use committee approved this study. The targeting of paint balls within phantoms was performed under ultrasonography guidance by 2 radiologists (beginner vs expert) with an "in-plane" and "out-of-plane" approaches using the new RF electrode and a conventional RF electrode (n = 20 for each method). To evaluate the targeting performance, the electrode placement time and the number of electrode pullbacks for redirection were compared between the 2 electrodes. The ablation performance was also compared by analyzing the ablation volumes in ex vivo bovine and in vivo porcine livers (n = 30 and n = 24, respectively) and the cellular viability of the ablation zone in in vivo specimens. In the phantom study, the RF electrode embedded with an EMPS showed a significantly shorter electrode placement time compared with the conventional RF electrode in both the in-plane and out-of-plane approaches by both radiologists (P < 0.05). The electrode pullback rate for both radiologists was lower in the new RF electrode than in the conventional RF electrode, but it did not reach statistical significance in the in-plane approach by the expert (P = 0.059). The ablation volumes analyzed with and without cellular viability in the ex vivo and in vivo studies were not significantly different between the 2 electrodes (P > 0.05). The RF electrode embedded with an EMPS is faster than the conventional electrode in the electrode placement into the target lesions. The ablation performance is not significantly different between the 2 electrodes.

Design and Analysis of Dual Hall Position Sensor with Automatic Direction Recognizing and Pre-Positioning Function

As an electromagnetic position sensor, Hall position sensor is widely used in various fields. In this paper, we discussed the working principle of the Hall sensor, and proposed a new method on direction recognizing technology. The dual Hall sensor structure has automatical direction recognizing and pre-positioning function, which can improve the adaptability of the sensor. Meanwhile, this new design can be used for other position sensor applications.

Poster — Thur Eve — 23: Dose and Position Quality Assurance using the RADPOS System for 4D Radiotherapy with CyberKnife

Introduction:RADPOS 4D dosimetry system consists of a microMOSFET dosimeter combined with an electromagnetic positioning sensor, which allows for performing real‐time dose and position measurements simultaneously. In this report the use of RADPOS as an independent quality assurance (QA) tool during CyberKnife 4D radiotherapy treatment is described. In addition to RADPOS, GAFCHROMIC® films were used for simultaneous dose measurement.Methods:RADPOS and films were calibrated in a Solid Water® phantom at 1.5 cm depth, SAD= 80 cm, using 60 mm cone. CT based treatment plan was created for a Solid Water® breast phantom containing metal fiducials and RADPOS probe. Dose calculations were performed using iPlan pencil beam algorithm. Before the treatment delivery, GAFCHROMIC® film was inserted inside the breast phantom, next to the RADPOS probe. Then the phantom was positioned on the chest platform of the QUASAR, to which Synchrony LED optical markers were also attached. Position logging began for RADPOS and the Synchrony tracking system, the QUASAR motion was initiated and the treatment was delivered.Results:RADPOS position measurements very closely matched the LED marker positions recorded by the Synchrony camera tracking system. The RADPOS measured dose was 2.5% higher than the average film measured dose, which is within the experimental uncertainties. Treatment plan calculated dose was 4.1 and 1.6% lower than measured by RADPOS and film, respectively. This is most likely due to the inferior nature of the dose calculation algorithm.Conclusions:Our study demonstrates that RADPOS system is a useful tool for independent QA of CyberKnife treatments.

Subject-specific real-time respiratory liver motion compensation method for ultrasound-MRI/CT fusion imaging.

Ultrasound-MRI/CT fusion imaging is widely used in minimal invasive surgeries, such as liver biopsy and tumor ablation. However, respiration-induced quasi-periodic liver motion and deformation cause unacceptable misalignment of the fusion images (i.e., fusion error). A subject-specific liver motion model based on skin-mounted position sensor and corresponding ultrasound liver image sequence was developed to compensate for liver motion. External surrogate respiratory motion signal is used to predict internal liver motion. An electromagnetic position sensor fixed on abdominal skin is introduced to track the respiratory motion, and 2D ultrasound images are used to track the liver motion synchronously. Based on these measurements, a subject-specific model describing the relationship of respiratory skin motion and internal liver motion is built and applied in real time (ultrasound-MRI/CT fusion imaging system) to predict and to compensate for the liver motion due to respiratory movement. Feasibility experiments and clinical trials were carried out on a phantom and eight volunteers. Qualitative and quantitative analyses and visual inspections performed by experienced clinicians show that the proposed model could effectively compensate for the liver motion, and the ratio of motion-compensated fusion error to the original varied from 10 % (0.96/9.40 mm) to 28 % (2.90/10.22 mm). An online liver motion modeling and compensation method was developed that provides surgeons with stable and accurate multimodality fusion images in real time.

Automatic registration of CT images to patient during the initial phase of bronchoscopy: A clinical pilot study

Electromagnetic based navigated bronchoscopy using preoperative CT images has reached the clinic during the last decade. One of the challenges is the "CT to patient anatomy alignment" of the CT images acquired days or even weeks ahead of bronchoscopy. An automatic registration method, without manual registration of anatomical landmarks, was developed, implemented, and evaluated in the current study. The registration method aligns automatically the preoperative CT images to the patient's anatomy during the initial part of the bronchoscopy. The algorithm is a modified version of an iterative closest point algorithm, which in addition to the positions also utilizes the orientation of the bronchoscope and the running direction of the CT centerline. The method was evaluated both by model-based simulated bronchoscopies and by clinical data from six real bronchoscopies. In the clinical evaluation, an electromagnetic position sensor was placed temporarily in the working channel close to the tip of a conventional bronchoscope. Position data, which were acquired while the bronchoscope was moving inside the airways, were registered to the centerline extracted from the airways in the CT image. A mean registration accuracy of 3.0 ± 1.4 mm was found when simulating bronchoscopies. In the clinical part of the study, the registration method was successfully applied to the data from all six patients. The positions of the bronchoscope tip aligned to the CT centerline with a mean distance range 4.7-6.5 mm. The authors have developed and evaluated an automatic registration algorithm for electromagnetic navigated bronchoscopy. It functioned to its purpose and did not affect the workflow for the bronchoscopic investigation of the six patients included in the study.

Real-time measurement of urethral dose and position during permanent seed implantation for prostate brachytherapy

The invivo dosimetry tool, RADPOS, has been modified to include a metal oxide-silicon semiconductor field effect transistor (MOSFET) array with an electromagnetic positioning sensor. This allows dose monitoring at five points rather than just at single dose point as in the other versions of the device. The detector has been used in a clinical trial, which is the first to measure both urethral dose and internal motion concurrently during permanent seed implantation for prostate brachytherapy using a single probe. The RADPOS detector was secured inside a Foley catheter inside the patient's urethra. Spatial coordinates of the RADPOS detector were read every 0.5s, and the timing of events such as needle insertion was noted. The MOSFET readings were taken over two 10-min periods; once all seeds had been implanted both before and after the transrectal ultrasound (TRUS), the probe was removed. Measurements were completed for 16 patients. Maximum integral dose in the prostatic urethral ranged from 89 to 195Gy, and dose varied from -66% to 36% depending on the rectal probe position. The change in position of the RADPOS sensor owing to the removal of the TRUS probe ranged from 1.4 to 9.7mm. The modified RADPOS detector with MOSFET array is able to provide real-time dose information, which can be used to monitor dose rates while implantation is performed and to estimate the total integrated dose. Changes in position including those owing to the TRUS probe can be significant and should be quantified to evaluate the influence on dose distributions.

Anterior tibiofemoral intersegmental forces during landing are predicted by passive restraint measures in women

BackgroundPassive restraint capabilities may influence sagittal plane knee joint mechanics during activity. This study aimed to determine if measures associated with passive restraint of anterior translation of the tibia are predictive of peak anterior knee shear force during landing. MethodsPassive restraint measures were assessed via joint arthrometry and during 40% body weight simulated weight acceptance using recreationally active students (73F, 42M; 21.8±2.9yr, 1.69±0.1m, 68.9±14.1kg). Anterior knee laxity (mm) at 133N and initial (0–20N) and terminal (100–130N) anterior stiffnesses (N/mm) were calculated from arthrometer data. Peak anterior tibial acceleration (m∙s−2) relative to the femur was assessed via electromagnetic position sensors during 40% body weight acceptance trials. Peak knee shear force was assessed during double-leg drop jumps. ResultsSex specific linear stepwise regressions revealed that in females, increasing peak tibial acceleration (5.1±1.8m·s−2) (R2∆=7.3%, P∆=0.021), increasing initial anterior stiffness (31.0±14.0N/mm) (R2∆=5.9%, P∆=0.032), and decreasing terminal anterior stiffness (43.4±17.4N/mm) (R2∆=4.9%, P∆=0.046) collectively predicted greater peak knee shear forces (66.6±12.03% BW) (multiple R2=18.1%). No male regressions were significant. ConclusionsSagittal laxity measures are associated with anterior knee shear loads during landing in females. Greater tibial acceleration during early axial load along with greater initial and lesser terminal anterior stiffnesses predicted increasing anterior knee shear forces. Future work should investigate the combined contribution of passive and active restraints to high-risk ACL biomechanics.

Vibrations of a Non Jeffcott Rotor with One Non Linear Bearing

Magnetic bearings support a body by mechanical pulling forces without any mechanical contact. They consist of an electromagnetic actuator, position sensors, power amplifiers and feedback controller. All of these components are characterized by nonlinear behavior and hence the entire system is inherently nonlinear. This paper presents a mathematical model for the vibrations of a non-Jeffcott type rotor supported on a non-linear bearing. The model can be used as a reference for systems supported on nonlinear bearings like magnetic bearings.

Poster - Thur Eve - 03: LDR to HDR: RADPOS applications in brachytherapy.

The RADPOS in vivo dosimetry system combines an electromagnetic positioning sensor and either one or five MOSFET dosimeters. The feasibility of using the system for quality control has been explored for a range of radiotherapy treatment techniques including most recently transperineal interstitial permanent prostate brachytherapy and high dose rate (HDR) treatments. Dose and position information was collected by a RADPOS array detector inside a Foley catheter within patients' urethra during permanent seed implantation. Ten patients were studied, and average displacement during implantation was Δr = (1.4-5.1) mm, with movements up to 9.7 mm due to the removal of the transrectal ultrasound probe. Maximum integral dose in the prostatic urethra ranged from 110-195 Gy, and it was found that the dose can change up to 63 cGy (62.0%) depending on whether the rectal probe is in place. For HDR, a RADPOS detector was first calibrated with an Ir-192 source. A treatment was then simulated using a total of 50 dwell positions in 5 catheters in an acrylic phantom. Dwell positions ranged from 1 to 10 cm away from the RADPOS detector and dose was measured for each source position. An average calibration coefficient of 0.74±0.11 cGy/mV was calculated for the detector and the average absolute difference between measured values and expected dose was 0.7±5.4 cGy (5±20%). The demonstrated accuracy of RADPOS dose measurements along with its ability to simultaneously measure displacement makes it a powerful tool for brachytherapy treatments, where high dose gradients can present unique in vivo dosimetry challenges.

WE-G-BRB-07: Application of RADPOS in Vivo Dosimetry for QA of High Dose Rate Brachytherapy.

The RADPOS in vivo dosimetry system combines an electromagnetic positioning sensor with MOSFET dosimetry, allowing for simultaneous online measurements of dose and spatial position. In this work, we assess the potential use of RADPOS for measurements of motion and dose during prostate HDR brachytherapy. The RADPOS was positioned in the centre of a thin plastic tube supported by two parallel acrylic plates submerged in water. The detector was calibrated by sending an Ir-192 source into an adjacent tube, to positions ranging from 8.0 to -8.0 cm along the vertical axis in increments of 0.5 cm. The dwell time at each position was 20 s and the change in threshold voltage of the RADPOS dosimeter was recorded for each position. The expected dose for each source position was calculated and compared to RADPOS measurements to obtain a detector calibration coefficient (cGy/mV). The procedure was then repeated sending the Ir-192 source into 5 other tubes, located 1 to 10 cm away from the RADPOS. Source positions, dwell times, and position of the RADPOS detector were the same as for the calibration. The dose for each source position was determined by RADPOS measurements and calibration coefficient and compared to the expected dose. An average calibration coefficient of 0.74±0.11 cGy/mV was calculated for RADPOS measurements of Ir-192 irradiations. The absolute difference between RADPOS values and expected dose for subsequent measurements averaged over all source positions was 0.7±5.4 cGy. In vivo dosimetry can potentially signal errors in catheter placement or numbering before entire dose is delivered. The demonstrated accuracy of RADPOS dose measurements and its ability to simultaneously measure displacement makes it a powerful tool for HDR brachytherapy treatments for prostate cancer, where high dose gradients and movement of the prostate gland can present unique in vivo dosimetry challenges. Financial and technical support has been received from Best Medical Canada and Ascension Technology Corporation.

Closed-Loop Planar Motion Control of a Steerable Probe With a “Programmable Bevel” Inspired by Nature

Percutaneous intervention has attracted significant interest in recent years, but many of today's needles and catheters can only provide limited control of the trajectory between an entry site and soft tissue target. In order to address this fundamental shortcoming in minimally invasive surgery, we describe the first prototype of a bioinspired multipart probe that can steer along planar trajectories within a compliant medium by means of a novel “programmable bevel,” where the steering angle becomes a function of the offset between interlocked probe segments. A kinematic model of the flexible probe and programmable bevel arrangement is derived. Several parameters of the kinematic model are then calibrated experimentally with a fully functional scaled-up prototype, which is 12 mm in diameter. A closed-loop control strategy with feed-forward and feedback components is then derived and implemented in vitro using an approximate linearization strategy that was first developed for car-like robots. Experimental results demonstrate satisfactory 2-D trajectory following of the prototype (0.68 mm tracking error, with 1.45 mm standard deviation) using an electromagnetic position sensor that is embedded at the tip of the probe.