Publications (21)11.88 Total impact
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Article: Locomotor adaptation and retention to gradual and sudden dynamic perturbations.
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ABSTRACT: Motor learning principles are increasingly used in robotic rehabilitation. These principles are mainly derived from reaching studies and it is currently unknown whether the same principles apply in locomotion. The aim of this study was to determine the effect of a gradually and suddenly introduced dynamic perturbation on locomotor adaptation and on recalling the adaptation when being re-exposed to the same perturbation. Subjects walked on a treadmill and adapted to a viscous force field that was applied during the swing phase. In one group the strength of the force field was gradually increased over different steps whereas in a second group it was introduced suddenly at full strength. The gradual group showed less adaptation and a faster decay of the adaptation during the washout than the sudden group. Strikingly, when both groups were being re-exposed to the perturbation at full strength, the gradual group showed no adaptation whereas the sudden group showed a faster occurring adaptation than during the first exposure. In conclusion, in contrast to the reported beneficial effects of a gradual introduction of a perturbation on adaptation in reaching, it seems to have a detrimental effect on locomotor adaptation. These results indicate that caution should be taken when applying motor learning principles solely derived from reaching studies to improve robotic gait rehabilitation.IEEE ... International Conference on Rehabilitation Robotics : [proceedings]. 06/2011; 2011:5975379. -
Article: Velocity-dependent reference trajectory generation for the LOPES gait training robot.
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ABSTRACT: The aim of this study is to assess the feasibility of an approach for generating velocity-dependent trajectories to train neurologically injured patients. The reference trajectories are constructed based on the gait patterns of subjects walking on a treadmill. By extracting key events (parameters) from these trajectories, the velocity dependency of the parameters is determined by regression analysis. Then, splines are fitted through these points to obtain gait patterns (position, velocity and acceleration) for specific walking velocities. Considering the severely injured patients, a feedforward controller is used in addition to the impedance controller. The approach is implemented on the LOPES gait rehabilitation robot and evaluated on healthy subjects. Results indicate that the subjects can walk naturally in the robot with the constructed reference trajectories. Further improvements to the technical design and additional testing of healthy and impaired subjects are required to show whether this approach can be transferred to clinical domain.IEEE ... International Conference on Rehabilitation Robotics : [proceedings]. 06/2011; 2011:5975414. -
Article: Effect of added inertia on the pelvis on gait.
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ABSTRACT: Gait-training robots must display a low inertia in order to allow normal-looking walking. We studied the effect of inertia added to the pelvis during walking. We attached subjects to a mechanism that displays inertia to the pelvis in the anterior/posterior (AP) direction and the lateral direction independently. During walking we measured EMG, metabolic rate and kinematics of nine subjects. We found that inertias up to 5.3 kg added in lateral direction had no significant effect on gait. We found that 4.3 kg added in the AP direction had a significant but not relevant effect on the range of motion (RoM) of pelvis AP displacement and acceleration, and on hip flexion. 10.3 kg caused a significant and relevant difference in pelvis acceleration RoM. 6 kg is estimated as the maximum inertia that gait-training robots can add to the pelvis, without affecting the gait.IEEE ... International Conference on Rehabilitation Robotics : [proceedings]. 06/2011; 2011:5975493. -
Article: Model Predictive Control-based gait pattern generation for wearable exoskeletons.
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ABSTRACT: This paper introduces a new method for controlling wearable exoskeletons that do not need predefined joint trajectories. Instead, it only needs basic gait descriptors such as step length, swing duration, and walking speed. End point Model Predictive Control (MPC) is used to generate the online joint trajectories based on these gait parameters. Real-time ability and control performance of the method during the swing phase of gait cycle is studied in this paper. Experiments are performed by helping a human subject swing his leg with different patterns in the LOPES gait trainer. Results show that the method is able to assist subjects to make steps with different step length and step duration without predefined joint trajectories and is fast enough for real-time implementation. Future study of the method will focus on controlling the exoskeletons in the entire gait cycle.IEEE ... International Conference on Rehabilitation Robotics : [proceedings]. 06/2011; 2011:5975442. -
Conference Proceeding: Flexible Assistive Robots Through AFO-Based Intention Detection
Procedia Computer ScienceProcedia Computer Science; 01/2011 -
Conference Proceeding: In vivo measurement of human knee and hip dynamics using MIMO system identification
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ABSTRACT: This study presents a new method for the estimation of the dynamic impedance of multi-joint leg movements. The method is based on Multi Input Multi Output (MIMO) system identification techniques and is designed for continuous torque perturbations at the hip and knee joint. Preliminary results from this study indicate that MIMO system identification can successfully be used to estimate the hip and knee impedance and the interaction dynamics between both joints. It is also concluded that, in order to create a good model representation of the leg impedance, the effect of biarticular muscles needs to be taken into account. The obtained measures for joint impedance might be used for clinical assessment and follow up of patients, as well as for the development of supportive devices.Engineering in Medicine and Biology Society (EMBC), 2010 Annual International Conference of the IEEE; 10/2010 -
Chapter: Feasibility of selective robotic support of foot clearance with continuously adapting impedance levels
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ABSTRACT: Encouraging stroke survivors to actively participate in robot aided gait training is critical for optimizing the outcome of this intervention. In this respect, it is of crucial importance that the timing of the provided assistance and the amount of assistance is in accordance with the subjects needs. We tested the feasibility of a control algorithm for a powered exoskeleton that selectively supports foot clearance and adapts its support to the performance of the subject. This was done in five chronic stroke survivors with stiff knee gait. Foot clearance was selectively supported through a virtual spring between the desired and actual ankle height of the paretic leg. The virtual spring stiffness was automatically adapted based on the experienced movement error in the previous step and a forgetting factor. The results showed that the virtual spring stiffness profile converged to a steady state pattern in about 20 steps. The pattern was subject specific and was roughly shaped to the deviation of the actual ankle trajectory from the reference trajectory before the assistance was turned on. The assistance resulted in an increased foot clearance through increased knee flexion, whereas it left other aspects of gait unaffected. The presented algorithm turned out to be effective in providing appropriately timed assistance according to the subjects needs. KeywordsAdaptive control-stroke-rehabilitation robots-gait training01/2010: pages 92-95; -
Conference Proceeding: Selective and adaptive robotic support of foot clearance for training stroke survivors with stiff knee gait
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ABSTRACT: Interactive control schemes are rapidly gaining popularity in the control of robotic gait trainers. Interactive control allows for the modification of the support level based on the patient's performance. However, only few algorithms exist that adapt the support to the patient's needs. The aim of this study was to assess the feasibility of an adaptive and selective method to support a specific subtask of walking. In this study we focused on providing assistance during foot clearance and analyzed the effects in four chronic stroke survivors whose gait is characterized as stiff knee gait. We recently introduced a method to selectively support the foot clearance by defining a virtual spring between the desired and the actual ankle height. Here, this method was extended with an algorithm that automatically adapts the stiffness of the virtual spring, and consequently, adapts the amount of support to the experienced movement error in the previous steps. The results showed that the stiffness profile converged to a subject specific pattern that varied over the gait cycle and was according to the subject's requirements. The proposed algorithm was used in a training study that specifically aimed at increasing the foot clearance. Preliminary results demonstrated that the training resulted in improved foot clearance, which was accompanied by an increased walking speed. This proposed algorithm reduces the need for the therapist/operator to set the amount of support on a trial and error basis and decreases the chances of reliance on the robotic support.Rehabilitation Robotics, 2009. ICORR 2009. IEEE International Conference on; 07/2009 -
Article: Reference Trajectory Generation for Rehabilitation Robots: Complementary Limb Motion Estimation
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ABSTRACT: For gait rehabilitation robots, an important question is how to ensure stable gait, while avoiding any interaction forces between robot and human in case the patient walks correctly. To achieve this, the definition of ldquocorrectrdquo gait needs to adapted both to the individual patient and to the situation. Recently, we proposed a method for online trajectory generation that can be applied for hemiparetic subjects. Desired states for one (disabled) leg are generated online based on the movements of the other (sound) leg. An instantaneous mapping between legs is performed by exploiting physiological interjoint couplings. This way, the patient generates the reference motion for the affected leg autonomously. The approach, called Complementary Limb Motion Estimation (CLME), is implemented on the LOPES gait rehabilitation robot and evaluated with healthy subjects in two different experiments. In a previously described study, subjects walk only with one leg, while the robot's other leg acts as a fake prosthesis, to simulate complete loss of function in one leg. This study showed that CLME ensures stable gait. In a second study, to be presented in this paper, healthy subjects walk with both their own legs to assess the interference with self-determined walking. Evaluation criteria are: Power delivered to the joints by the robot, electromyography (EMG) distortions, and kinematic distortions, all compared to zero torque control, which is the baseline of minimum achievable interference. Results indicate that interference of the robot is lower with CLME than with a fixed reference trajectory, mainly in terms of lowered exchanged power and less alteration of EMG. This implies that subjects can walk more naturally with CLME, and they are assisted less by the robot when it is not needed. Future studies with patients are yet to show whether these properties of CLME transfer to the clinical domain.IEEE Transactions on Neural Systems and Rehabilitation Engineering 03/2009; · 3.44 Impact Factor -
Conference Proceeding: Ambulatory assessment of balance
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ABSTRACT: Gait analysis is commonly done in gait laboratories, where several gait variables are estimated using measurement systems installed in the laboratory. Two important variables to characterize human gait are the Center of Mass (CoM) and the Center of Pressure (CoP). The major drawback of existing measurement systems is their restriction to the laboratory. This study demonstrates the possibilities of an ambulatory measurement system: the forceshoe. It consists of an orthopaedic sandal with six-degrees-of-freedom force/moment sensors beneath the heel and the forefoot and an inertial sensor rigidly attached to each force/moment sensor. For validation, the measurement system has been compared to a reference system consisting of an optical position measurement system and two force plates. The root-mean-square (rms) difference between the CoP trajectories was (0.0051 plusmn 0.0007) m, corresponding to (1.7 plusmn 0.3)% of the length of the shoe. The rms difference between the CoM trajectories estimated by both measurement systems was (0.025 plusmn 0.007) m. Based on the results presented in this study, it is concluded that the instrumented shoe allows accurate and continuous estimation of gait variables that can be used to assess balance.Biomedical Robotics and Biomechatronics, 2008. BioRob 2008. 2nd IEEE RAS & EMBS International Conference on; 11/2008 -
Article: Use of Induced Acceleration to Quantify the (De)stabilization Effect of External and Internal Forces on Postural Responses
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ABSTRACT: Due to the mechanical coupling between the body segments, it is impossible to see with the naked eye the causes of body movements and understand the interaction between movements of different body parts. The goal of this paper is to investigate the use of induced acceleration analysis to reveal the causes of body movements. We derive the analytical equations to calculate induced accelerations and evaluate its potential to study human postural responses to support-surface translations. We measured the kinematic and kinetic responses of a subject to sudden forward and backward translations of a moving platform. The kinematic and kinetics served as input to the induced acceleration analyses. The induced accelerations showed explicitly that the platform acceleration and deceleration contributed to the destabilization and restabilization of standing balance, respectively. Furthermore, the joint torques, coriolis and centrifugal forces caused by swinging of the arms, contributed positively to stabilization of the center of mass. It is concluded that induced acceleration analyses is a valuable tool in understanding balance responses to different kinds of perturbations and may help to identify the causes of movement in different pathologies.IEEE Transactions on Biomedical Engineering 01/2008; · 2.28 Impact Factor -
Article: Design and Evaluation of the LOPES Exoskeleton Robot for Interactive Gait Rehabilitation
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ABSTRACT: This paper introduces a newly developed gait rehabilitation device. The device, called LOPES, combines a freely translatable and 2-D-actuated pelvis segment with a leg exoskeleton containing three actuated rotational joints: two at the hip and one at the knee. The joints are impedance controlled to allow bidirectional mechanical interaction between the robot and the training subject. Evaluation measurements show that the device allows both a "pa- tient-in-charge" and "robot-in-charge" mode, in which the robot is controlled either to follow or to guide a patient, respectively. Electromyography (EMG) measurements (one subject) on eight important leg muscles, show that free walking in the device strongly resembles free treadmill walking; an indication that the device can offer task-specific gait training. The possibilities and limitations to using the device as gait measurement tool are also shown at the moment position measurements are not accurate enough for inverse-dynamical gait analysis.IEEE Transactions on Neural Systems and Rehabilitation Engineering 10/2007; · 3.44 Impact Factor -
Conference Proceeding: Detecting asymmetries in balance control with system identification: first experimental results from above knee amputees
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ABSTRACT: A prosthetic leg can influence balance in various ways, but not all changes in postural performance can easily be identified with the naked clinical eye. Various studies have shown that dynamic posturography is able to detect more subtle changes in balance control. Here, we describe a modification of a new posturography technique we previously developed, which combines dynamic platform perturbations with (non) parametric system identification techniques to detect asymmetries in balance control of four subjects with an above knee prosthesis. The method also estimates the mechanical impedance of the prosthetic ankle joint. The time needed for the experiment and data analysis is less than 3 minutes. Results were compared to those of six healthy controls. Our pilot data show clear asymmetries in dynamic balance control. We also found asymmetries in weight bearing and centre of pressure movements, but the asymmetries in dynamic balance contribution were larger. Finally, asymmetries in weight bearing and dynamic balance in patients were not tightly coupled as in healthy controls. The relative contribution to dynamic balance control of the prosthetic leg was positively related with the stiffness of the prosthetic ankle joint. More transfemoral amputees have to be tested to more extensively evaluate the results of this pilot study.Rehabilitation Robotics, 2007. ICORR 2007. IEEE 10th International Conference on; 07/2007 -
Conference Proceeding: Selective control of a subtask of walking in a robotic gait trainer(LOPES)
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ABSTRACT: Robotic gait trainers are used all over the world for the rehabilitation of stroke patients, despite relatively little is known about how the robots should be controlled to achieve the optimal improvement. Most devices control complete joint trajectories and assume symmetry between both legs by either a position or an impedance control. However we believe that the control should not be on a joint level but on a subtask level (i.e. foot clearance, balance control). To this end we have chosen for virtual model control(VMC) to define a set of controllers that can assist in each of these tasks. Thus enabling the exoskeleton to offer selective support and evaluation of each substask during rehabilitation training. The aim of this explorative pilot study was to assess the performance of a VMC of the step height and to assess if selective control of the step height left the remaining of the walking pattern unaffected. Four young healthy subjects walked on a treadmill with their legs and pelvis attached to the lopes exoskeleton in 3 different conditions: (1) providing minimal resistance, (2) control of the left step height with a low stiffness (3) control of the step height with a large stiffness. We have shown that it is possible to exert a vertical forces for the support of foot clearance during the swing phase. The higher stiffness of the VMC resulted in a greater change of the step height, which was achieved by a larger increase of the maximal hip and knee flexion compared to the low stiffness condition. The control of the step height resulted in minor changes in the cycle time and swing time. The joint angles also showed only minor changes. The preliminary results suggest that we were able to control a subtask of walking, while leaving the remaining walking trajectory largely unaffected. In the near future, control of other subtask will be implemented and evaluated in isolation and in conjunction with each other.Rehabilitation Robotics, 2007. ICORR 2007. IEEE 10th International Conference on; 07/2007 -
Article: Detecting asymmetries in balance control with system identification: first experimental results from Parkinson patients.
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ABSTRACT: Cognitive processes can influence balance in various ways, but not all changes in postural performance can easily be identified with the naked clinical eye. Various studies have shown that dynamic posturography is able to detect more subtle changes in balance control. For patients with Parkinson's disease (which is typically an asymmetric disease), changes in the symmetry of balance control might provide a sensitive measure of cognitive influences on balance. Here, we describe a new posturography technique that combines dynamic platform perturbations with system identification techniques to detect such asymmetries in balance control of two patients with Parkinson's disease. Results were compared to those of six healthy controls. Our pilot data show clear asymmetries in dynamic balance control, even though patients themselves were not aware of this and had no subjective problems with stability or standing. We also found asymmetries in weight bearing, but the asymmetries in dynamic balance contribution were larger. Finally, asymmetries in weight bearing and dynamic balance in patients were not tightly coupled as in healthy controls. Future studies could incorporate this approach when examining the influence of mental decline on postural regulation.Acta Neurovegetativa 02/2007; 114(10):1333-7. · 2.73 Impact Factor -
Article: Ambulatory estimation of foot placement during walking using inertial sensors
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ABSTRACT: This study proposes a method to assess foot placement during walking using an ambulatory measurement system consisting of orthopaedic sandals equipped with force/moment sensors and inertial sensors (accelerometers and gyroscopes). Two parameters, lateral foot placement (LFP) and stride length (SL), were estimated for each foot separately during walking with eyes open (EO), and with eyes closed (EC) to analyze if the ambulatory system was able to discriminate between different walking conditions. For validation, the ambulatory measurement system was compared to a reference optical position measurement system (Optotrak). LFP and SL were obtained by integration of inertial sensor signals. To reduce the drift caused by integration, LFP and SL were defined with respect to an average walking path using a predefined number of strides. By varying this number of strides, it was shown that LFP and SL could be best estimated using three consecutive strides. LFP and SL estimated from the instrumented shoe signals and with the reference system showed good correspondence as indicated by the RMS difference between both measurement systems being 6.5±1.0 mm (mean ±standard deviation) for LFP, and 34.1±2.7 mm for SL. Additionally, a statistical analysis revealed that the ambulatory system was able to discriminate between the EO and EC condition, like the reference system. It is concluded that the ambulatory measurement system was able to reliably estimate foot placement during walking. -
Article: First clinical results with the new innovative robotic gait trainer LOPES
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ABSTRACT: The results of five chronic stroke patients in a first explorative training study using the new robotic device LOPES are presented. Conclusions Positive effects of gait training in LOPES were found in four out of five subjects. Future study will focus on including larger sample sizes and introducing LOPES in rehabilitation care of acute stroke patients. Introduction Robotic devices for gait rehabilitation enable task specific and intensive training, without placing high physical demands on physiotherapists. Previous devices like Lokomat [1] and Gait Trainer [2] are generally characterised as position controlled: enforcing gait by moving the legs through prescribed patterns. An active contribution of the patient is not necessary, and movement errors are not experienced. Both are crucial in motor learning. Recently, a new gait trainer (LOPES) was developed, which can selectively and partially support different aspects of gait at specified gait cycle phases. In a first study LOPES was used in chronic stroke patients with stiff knee gait. Patients/materials and methods The prototype of LOPES was used (Fig. 1). The exoskeleton has eight actuated degrees of freedom [3]. The robot is impedance controlled, i.e. it applies assistive forces proportional to the deviation of the actual movement to a reference movement. This study focussed on supporting step height (foot clearance) using virtual model control [4]. An adaptive impedance controller was used that adapted the amount of support based on the experienced “movement error” in the previous step, increasing it when errors were large, decreasing it when errors were small. Five chronic stroke patients (age 50–61 y, time since stroke 6–72 m) received the support during a 6-week training program (3 times per week, max 45 min per session) as part of a larger study. Besides improving foot clearance, the training aimed at increasing walking speed and endurance. Gait analysis and clinical tests (3 min and 10 m walking test) were performed pre and post training. Patient satisfaction was assessed using a custom-made questionnaire. Results Four subjects improved after the training program: mean paretic knee flex/ext range improved with 4.3° (range 0.2–9.6°) and mean paretic knee angular velocity increased with 36.3°/s (range 24.1–58.4°/s). Mean walking distance improved with 19 m (range 14.0–21.8 m), walking speed increased with 0.04 m/s (range 0.03–0.05 m/s). One subject showed a different pattern: mean paretic knee flex/ext range and angular velocity decreased (5.9° and 48.2°/s, respectively). Walking distance and walking speed decreased with 6 m and 0.02 m/s, respectively. All subjects enjoyed the LOPES training and reported positive effects on gait pattern and endurance. Discussion A small sample size was included as this is a first explorative study using LOPES in stroke patients. Results of gait analysis and clinical tests show positive effects of training in four out of five subjects. The subject showing negative effects experienced a fall in the home situation, thereby interrupting the training program with 1 week. All subjects reported positive on using LOPES as a gait training device. -
Article: Ankle-foot orthoses in stroke: Effects on functional balance, weight-bearing asymmetry and the contribution of each lower limb to balance control
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ABSTRACT: Background Ankle-foot orthoses are often provided to improve walking in stroke patients, although the evidence of effects on walking and balance control is still inconsistent. This could be caused by a lack of insight into the influence of orthoses on the underlying impairments. These impairments can be assessed with dual plate posturography to determine the relative contribution of each lower limb to balance control and weight-bearing. This study examined the effects of ankle-foot orthoses on functional balance, static and dynamic weight-bearing asymmetry and dynamic balance control of the paretic and non-paretic lower limbs. Methods Twenty stroke subjects (time since stroke 5–127 months) completed the study. Subjects were assessed with and without ankle-foot orthosis. Functional balance was assessed using the Berg Balance Scale, Timed Up & Go test, Timed Balance Test, 10-m walking test and Functional Ambulation Categories. Weight-bearing asymmetry and dynamic balance control were assessed with force plates on a movable platform. Findings No significant effects of ankle-foot orthoses were found for weight-bearing asymmetry and dynamic balance control, but significant differences in favour of ankle-foot orthosis use were found for most functional tests. Interpretation Although ankle-foot orthoses had no effect on weight-bearing asymmetry or dynamic balance contribution of the paretic lower limb, functional tests were performed significantly better with orthoses. Apparently, improvements at functional level cannot be readily attributed to a greater contribution of the paretic lower limb to weight-bearing or balance control. This finding suggests that ankle-foot orthoses influence compensatory mechanisms. -
Article: Ambulatory Assessment of Balance
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ABSTRACT: Gait analysis is commonly done in gait laboratories, where several gait variables are estimated using measurement systems installed in the laboratory. Two important variables to characterize human gait are the center of mass and the center of pressure. The major drawback of existing measurement systems is their restriction to the laboratory. This study demonstrates the possibilities of an ambulatory measurement system: the forceshoe. It consists of an orthopaedic sandal with six-degrees-of-freedom force/moment sensors beneath the heel and the forefoot and an inertial sensor rigidly attached to each force/moment sensor. For validation, the measurement system has been compared to a reference system consisting of an optical position measurement system and two force plates. The root-mean-square (rms) difference between the center of pressure trajectories was (5.1±0.7) mm, corresponding to (1.7±0.3)% of the length of the shoe. The rms differences between the center of mass trajectories estimated by both measurement systems was (0.025 ± 0.007) m. Based on the results presented in this study, it is concluded that the instrumented shoe allows accurate and continuous estimation of gait variables that can be used to assess balance. -
Article: Complementary Limb Motion Estimation (CLME): Experimental Results
Top co-authors
Top Journals
Institutions
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2007–2010
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Universiteit Twente
- Department of Biomechanical Engineering
Enschede, Provincie Overijssel, Netherlands
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2009
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ETH Zurich
- Power Systems Laboratory
Zürich, ZH, Switzerland
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