J. De Schutter

Universitair Ziekenhuis Leuven, Louvain, Flanders, Belgium

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Publications (192)217.49 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Scaled generic musculoskeletal models are commonly used to drive dynamic simulations of motions. It is however, acknowledged that not accounting for variability in musculoskeletal geometry and musculotendon parameters may confound the simulation results, even when analysing control subjects. This study documents the three-dimensional anatomical variability of musculotendon origins and insertions of 33 lower limb muscles determined based on magnetic resonance imaging in six subjects. This anatomical variability was compared to the musculotendon point location in a generic musculoskeletal model. Furthermore, the sensitivity of muscle forces during gait, calculated using static optimization, to perturbations of the musculotendon point location was analyzed with a generic model. More specific, a probabilistic approach was used: for each analyzed musculotendon point, the three-dimensional location was re-sampled with a uniform Latin hypercube method within the anatomical variability and the static optimization problem was then re-solved for all perturbations. We found that musculotendon point locations in the generic model showed only variable correspondences with the anatomical variability. The anatomical variability of musculotendon point location did affect the calculated muscle forces: muscles most sensitive to perturbations within the anatomical variability are iliacus and psoas. Perturbation of the gluteus medius anterior, iliacus and psoas induces the largest concomitant changes in muscle forces of the unperturbed muscles. Therefore, when creating subject-specific musculoskeletal models, these attachment points should be defined accurately. In addition, the size of the anatomical variability of the musculotendon point location was not related to the sensitivity of the calculated muscle forces.
    Journal of Biomechanics 03/2015; DOI:10.1016/j.jbiomech.2015.02.052 · 2.66 Impact Factor
  • Max Boegli, Tinne De Laet, Joris De Schutter, Jan Swevers
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    ABSTRACT: This paper presents a model that closely approximates the generalized Maxwell-Slip (GMS) model, a multistate friction model known to describe all essential friction characteristics in presliding and sliding motion. In contrast to the GMS model, which consists of a switching structure to accommodate for its hybrid nature, the new model, referred to as the smoothed GMS (S-GMS) model, consists of an analytic set of differential equations. Such a model is well suited for gradient-based state and parameter estimation, as in the extended Kalman filter (EKF) or in moving horizon estimation. Similar to the GMS model, the S-GMS model is a multistate model that also describes all essential friction characteristics. Moreover, the S-GMS model description includes the single-state LuGre model and Elastoplastic model as special cases. This paper also discusses the implementation of the EKF estimator for the S-GMS friction model and compares its performance to the LuGre model in joint state and parameter estimation.
    IEEE/ASME Transactions on Mechatronics 10/2014; 19(5):1593-1602. DOI:10.1109/TMECH.2013.2288944 · 3.65 Impact Factor
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    ABSTRACT: Purpose: An inherited mutation in KRAS (LCS6-variant or rs61764370) results in altered control of the KRAS oncogene. Westudied this biomarker's correlation to anti-EGFR monoclonal antibody (mAb) therapy response in patients with metastatic colorectal cancer. Experimental Design: LCS6-variant and KRAS/BRAF mutational status was determined in 512 patients with metastatic colorectal cancer treated with salvage anti-EGFR mAb therapy, and findings correlated with outcome. Reporters were tested in colon cancer cell lines to evaluate the differential response of the LCS6-variant allele to therapy exposure. Results: In this study, 21.2% (109 of 512) of patients with metastatic colorectal cancer had the LCS6-variant (TG/GG), which was found twice as frequently in the BRAF-mutated versus the wild-type (WT) group (P = 0.03). LCS6-variant patients had significantly longer progression-free survival (PFS) with anti-EGFR mAb monotherapy treatment in the whole cohort (16.85 vs. 7.85 weeks; P = 0.019) and in the double WT (KRAS and BRAF) patient population (18 vs. 10.4 weeks; P = 0.039). Combination therapy (mAbs plus chemotherapy) led to improved PFS and overall survival (OS) for nonvariant patients, and brought their outcome to levels comparable with LCS6-variant patients receiving anti-EGFR mAb monotherapy. Combination therapy did not lead to improved PFS or OS for LCS6-variant patients. Cell line studies confirmed a unique response of the LCS6-variant allele to both anti-EGFR mAb monotherapy and chemotherapy. Conclusions: LCS6-variant patients with metastatic colorectal cancer have an excellent response to anti-EGFR mAb monotherapy, without any benefit from the addition of chemotherapy. These findings further confirm the importance of thismutation as a biomarker of anti-EGFRmAbresponse in patients with metastatic colorectal cancer, and warrant further prospective confirmation. (C) 2014 AACR.
    Clinical Cancer Research 09/2014; 20(17):4499-510. DOI:10.1158/1078-0432.CCR-14-0348 · 8.19 Impact Factor
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    ABSTRACT: We aimed to better clarify the role of germline variants of the FCG2 receptor, FCGR2A-H131R and FCGR3A-V158F, on the therapeutic efficacy of cetuximab in metastatic colorectal cancer (mCRC). A large cohort with sufficient statistical power was assembled.
    Gut 07/2014; DOI:10.1136/gutjnl-2014-307234 · 13.32 Impact Factor
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    ABSTRACT: In time-optimal robot path following, a predetermined geometric trajectory is followed exactly in a time-optimal way considering system constraints, for example, actuator constraints. For a simplified robotic manipulator, this optimization problem can be reformulated into a convex optimization problem when only considering some system constraints. In this article, the convex approach is extended to account for Cartesian acceleration constraints and in turn account for inertial forces and torques acting on a load held by the robot. The focus of this article is on the reformulation of these Cartesian acceleration and inertial forces and torques to preserve the convexity of the optimization problem. We present a series of applications that result in solving a convex optimization problem, illustrating the practicality of the proposed reformulations.
    Proceedings of the Institution of Mechanical Engineers Part I Journal of Systems and Control Engineering 11/2013; 227(10):724-732. DOI:10.1177/0959651813502644 · 0.78 Impact Factor
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    ABSTRACT: Navigating an electrical wheelchair can be very challenging due to its large size and limited maneuverability. Additionally, target users often suffer from cognitive or physical disabilities, which interfere with safe navigation. Therefore, a robotic wheelchair that helps to drive can prove invaluable. Such a wheelchair shares the control with its human operator. Typically, robots excel in fine-motion control whereas users want to remain in charge. Hence, the robot should focus its help locally and let the user decide about global behavior. Further, an effective robot should understand the navigation plans of its user. It needs to consider the user's abilities to avoid frustrating the user with wrong assistance. In order to address these requirements, we propose a probabilistic framework to recognize local navigation plans in a user-specific way. The framework infers navigation plans online and provides a method to calibrate all model parameters from real driving data. It fuses past local information with a user-specific model to reason about how and where the user intends to navigate. We illustrate the validity of our approach by recognizing the local navigation plans of a spastic user driving in a daily environment.
    Robotics and Automation (ICRA), 2013 IEEE International Conference on; 01/2013
  • O. Cigdem, T. De Laet, J. De Schutter
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    ABSTRACT: In many robotic applications, the motions of a human and a robot are recognized by studying of their motion trajectories. Hence, motion trajectory recognition is important in human and robot movement analysis. In this paper, the recognition of six degrees-of-freedom rigid body motion trajectory of an object is studied. The three-dimensional measured position trajectories of LED markers attached to rigid body are transformed to the time-based invariant representation of the rigid body motion trajectories. The main objective of this paper is to evaluate the performance of classical and subsequence dynamic time warping algorithm on the recognition of the rigid body motion trajectories. The experimental results show that the use of the length of shortest warping path in the calculation of DTW distances is not significantly better than the use of only the length of model signal for the nine artificial motions used in experiments. However, the used method promises to improve recognition of more complex everyday motions. Additionally, the results indicate that the classical DTW algorithm gives more meaningful results than subsequence DTW algorithm for the available recorded motions.
    Control Conference (ASCC), 2013 9th Asian; 01/2013
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    ABSTRACT: Current state-of-the-art robot program development needs expert programmers. Moreover, most robot programs developed today are robot hardware and software specific, and therefore little reusable without modifications. This paper realizes easier robot (re-)programming, by software framework independent models that can be executed using different hard- and software platforms. First, the paper focuses on the formalization of the tasks to be fulfilled by a robot, more specifically constraint-based programming tasks using a Domain Specific Language (DSL). Second, it gives a reference implementation in Lua [1]. The presented DSL makes it easy to develop applications, yet is powerful to execute. It enables automatic model verification and code generation for different hard- and software platforms, diminishing code debugging efforts. Experimental validation shows the ease of creating an application and adapting it, the reduction of the amount of hand-written code, and the debugging aid offered through meaningful errors returned by model verification.
    Intelligent Robots and Systems (IROS), 2013 IEEE/RSJ International Conference on; 01/2013
  • W. Decre, H. Bruyninckx, J. De Schutter
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    ABSTRACT: In constraint-based programming, robot tasks are specified and solved as optimization problems with sets of constraints and one or multiple objective functions. In our previous work, we presented (i) a generic modeling approach for geometrically complex robot tasks, including the modeling of parametric uncertainty, in order to allow the robot task programmer to specify the optimization problem without explicitly writing down the different (possibly numerous and involved) constraint equations, and (ii) methods for solving these optimization problem online in the instantaneous case (reactive control), and offline in the non-instantaneous case (trajectory planning). This paper has two contributions. First, it extends our framework to include task constraints (e.g. tracking a curve) that are not given as explicit functions of time. These constraints are highly relevant in practice, for example to facilitate time-optimal path planning combined with other constraints. Second, it extends our framework to user-configurable task horizons when solving the optimization problem, to allow task programmers to make a trade-off between computational speed and (global) task optimality. Both of these novel framework extensions are illustrated by a time-optimal laser tracing experiment.
    Robotics and Automation (ICRA), 2013 IEEE International Conference on; 01/2013
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    ABSTRACT: Time-optimal path following considers the problem of moving along a predetermined geometric path in minimum time while respecting system constraints. This paper focusses on time-optimal path following problems in robotics where collision must be avoided with other robots or moving obstacles. The developed method is based on the convex reformulation of the time-optimal path following problem with simplified dynamics presented in [1]. The robot and the obstacles are modelled as unions of convex polyhedra and the collision avoidance constraints are derived using Lagrangian duality. These constraints render the optimization problem non-convex. However, numerical simulations show that the resulting non-convex optimization problem can still be solved efficiently using a non-linear solver, due to the time-optimal path following formulation [1] and the proposed formulation of the collision avoidance constraints.
    Robot Motion and Control (RoMoCo), 2013 9th Workshop on; 01/2013
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    ABSTRACT: Path following deals with the problem of following a geometric path without any preassigned timing information and constitutes an important step in solving the general motion planning problem. The current paper considers path following for differentially flat systems. In this case the dynamics of the system can be projected along the path to a single input system, resulting in a free end-time optimal control problem. We propose to rewrite the problem in terms of the velocity along the path and the path itself. This way, we arrive at a fixed end-time optimal control problem that can be solved efficiently by interior-point solvers. Two challenging examples, a truck-trailer parking simulation and a quadrotor mission, illustrate the efficiency of the problem formulation and the practicality of the developed software.
    Mechatronics (ICM), 2013 IEEE International Conference on; 01/2013
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    ABSTRACT: This paper focusses on the time-energy optimal path following for robots. This considers the problem of moving along a predetermined geometric path with a minimal trade-off between the motion time and the two major thermal energy losses in electric actuators. Theses losses consist of resistive electrical losses and mechanical friction losses. When only taking into account the electrical losses for a simplified robotic manipulator, a convex reformulation has been derived previously [1]. In this paper we include the dynamic joint friction losses into the objective. This also implies that we have to include the dynamic joint friction into the robot equations of motion, which appear in the torque constraints. Both the resulting objective and torque constraints are non-convex. The present paper proposes an efficient sequential convex programming (SCP) approach to solve the resulting optimal control problem. A key step here is to decompose the non-convex functions involved as a difference of convex functions. Numerical simulations illustrate the fast convergence of the proposed method in only a few SCP iterations, confirming the efficiency of the proposed framework. This high efficiency allows for an efficient tool to investigate the trade off between time-optimality and energy-optimality.
    Mechatronics (ICM), 2013 IEEE International Conference on; 01/2013
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    T. De Laet, H. Bruyninckx, J. De Schutter
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    ABSTRACT: This paper presents a scene graph for geometric relations between rigid bodies that keeps track of poses and twists of rigid bodies in the scene. The scene graph relies on semantic pose and twist representation, making it invariant to the actual coordinate representation at hand. This makes the scene graph more general and interoperable than most scene graphs currently available. The presented scene graph takes into account constraints imposed by particular coordinate representations, allows for constant poses, answers semantic pose and twist queries, and provides built-in semantic consistency checks. Since the scene graph also keeps track of the twist, it allows native twist calculations, as opposed to deriving the velocities from the poses in the graph. This paper comes with software released under a dual BSD/LGPLv2.1 license.
    Intelligent Robots and Systems (IROS), 2013 IEEE/RSJ International Conference on; 01/2013
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    ABSTRACT: This paper analyses an extended dynamometry setup that aims at obtaining accurate knee joint moments. The main problem of the standard setup is the misalignment of the joint and the dynamometer axes of rotation due to non-rigid fixation, and the determination of the joint axis of rotation by palpation. The proposed approach (i) combines 6D registration of the contact forces with 3D motion capturing (which is a contribution to the design of the setup), (ii) includes a functional axis of rotation in the model to describe the knee joint (which is a contribution to the modelling), and (iii) calculates joint moments by a model-based 3D inverse dynamic analysis. Through a sensitivity analysis, the influence of the accuracy of all model parameters is evaluated. Dynamics resulting from the extended setup are quantified, and are compared to those provided by the dynamometer. Maximal differences between the 3D joint moment resulting from the inverse dynamics and measured by the dynamometer were 16.4Nm (16.9%) isokinetically and 18.3Nm (21.6%) isometrically. The calculated moment is most sensitive to the orientation and location of the axis of rotation. In conclusion, more accurate experimental joint moments are obtained using a model-based 3D inverse dynamic approach that includes a good estimate of the pose of the joint axis.
    IEEE transactions on bio-medical engineering 11/2012; 60(5). DOI:10.1109/TBME.2012.2228643 · 2.15 Impact Factor
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    ABSTRACT: Rapidly growing insight into the molecular biology of colorectal cancer has led to high hopes for the identification of molecular markers to be used in optimized and tailored treatment regimens. However, many of the published data on gene-specific biomarkers are contradictory in their findings, and no tests are currently used in clinical practice, with the exception of microsatellite instability (MSI) and guanylyl cyclase C (GCC) testing in the adjuvant setting, and in Europe KRAS mutation testing is used in the setting of epidermal growth factor receptor (EGFR)-targeted therapy for metastatic disease. There are many reasons for the failure of the initial marker hypothesis-driven approach. Although supported by a good biologic rationale, single markers such as tumor protein p53 (TP53) gene mutations, when applied to a complex tumor type containing many synchronous alterations, do not perform well in predicting outcome. Many markers also suffer from technical shortcomings, resulting from the lack of quantitative techniques to capture the impact of the molecular alteration. The impact of markers obtained from microarray expression profiling needs to be further investigated in studies based on much larger cohorts, and cross-validation studies will be essential. Recently, mutations in the KRAS gene were shown to be strong negative predictors of response to EGFR inhibitors in metastatic disease. It has also been suggested that BRAF gene mutations may be predictive of EGFR inhibitor resistance, and there are some conflicting data regarding the role of the PIK3CA gene. Further studies are needed to help integrate the latest findings into clinically useful tools for personalized medicine.
    Molecular Diagnosis & Therapy 04/2012; 13(2):103-114. DOI:10.1007/BF03256319 · 2.59 Impact Factor
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    ABSTRACT: This article introduces a set of novel haptic guidance algorithms intended to provide intuitive and reliable assistance for electric wheelchair navigation through narrow or crowded spaces. The proposed schemes take hereto the non-holonomic nature and a detailed geometry of the wheelchair into consideration. The methods encode the environment as a set of collision-free circular paths and, making use of a model-free impedance controller, ‘haptically’ guide the user along collision-free paths or away from obstructed paths or paths that simply do not coincide with the motion intended by the user. The haptic feedback plays a central role as it establishes a fast bilateral communication channel between user and wheelchair controller and allows a direct negotiation about wheelchair motion. If found unsatisfactory, suggested trajectories can always be overruled by the user. Relying on inputs from user modeling and intention recognition schemes, the system can reduce forces needed to move along intended directions, thereby avoiding unnecessary fatigue of the user. A commercial powered wheelchair was upgraded and feasability tests were conducted to validate the proposed methods. The potential of the proposed approaches was hereby demonstrated.
    Proceedings - IEEE International Conference on Robotics and Automation 01/2012; DOI:10.1109/ICRA.2012.6225349
  • F De Groote, I Jonkers, J De Schutter
  • T. De Laet, H. Bruyninckx, J. De Schutter
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    ABSTRACT: This paper proposes a novel online two-level multitarget tracking and detection (MTTD) algorithm. The algorithm focuses on multitarget detection and tracking for the case of multiple measurements per target and for an unknown and varying number of targets. Information is continuously exchanged in both directions between the two levels. Using the high level target position and shape information, the low level clusters the measurements. Furthermore, the low level features automatic relevance detection (ARD), as it automatically determines the optimal number of clusters from the measurements taking into account the expected target shapes. The high level's data association allows for a varying number of targets. A joint probabilistic data association algorithm looks for associations between clusters of measurements and targets. These associations are used to update the target trackers and the target shapes with the individual measurements. No information is lost in the two-level approach since the measurement information is not summarized into features. The target trackers are based on an underlying motion model, while the high level is supplemented with a filter estimating the number of targets. The algorithm is verified using both simulations and experiments using two sensor modalities, video and laser scanner, for detection and tracking of people and ants.
    IEEE Transactions on Pattern Analysis and Machine Intelligence 01/2012; DOI:10.1109/TPAMI.2011.83 · 5.69 Impact Factor
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    ABSTRACT: In this paper, the use of a coordinate-free representation for recognizing six DOF rigid body motion trajectories is experimentally validated. In the recognition part of this approach, the three-dimensional measured position trajectories of arbitrary and uncalibrated points attached to the rigid body are transformed to an invariant, coordinate-free representation of the rigid body motion trajectory. This representation is theoretically independent of the reference frame in which the motion is observed, the chosen marker positions, the linear scale (magnitude) of the motion, the time scale, and the motion profile. During the experiments, a person manipulated an object. The camera viewpoints, time scales, motions profiles, and linear or angular scales were changed between different motion recordings. The experimental results validate that not only in similar but also in different recording conditions, through using the invariant representation, the dependency on the parameters mentioned above are eliminated, and therefore better recognition results are obtained.
    Systems, Man, and Cybernetics (SMC), 2012 IEEE International Conference on; 01/2012

Publication Stats

3k Citations
217.49 Total Impact Points

Institutions

  • 2014
    • Universitair Ziekenhuis Leuven
      Louvain, Flanders, Belgium
  • 1–2014
    • University of Leuven
      • • Department of Oncology
      • • Department of Mechanical Engineering
      • • Department of Human Genetics
      Louvain, Flanders, Belgium
  • 2009
    • Hasselt University
      Hasselt, Flemish, Belgium
  • 2008
    • Exelixis, Inc
      San Francisco, California, United States
  • 2001
    • University of North Carolina at Charlotte
      Charlotte, North Carolina, United States
    • Center for Scientific Review
      베서스다, Maryland, United States
  • 1999
    • University of British Columbia - Vancouver
      • Department of Electrical and Computer Engineering
      Vancouver, British Columbia, Canada
    • La Salle University
      Philadelphia, Pennsylvania, United States
  • 1998
    • Korea Advanced Institute of Science and Technology
      • Department of Electrical Engineering
      Seoul, Seoul, South Korea
  • 1996–1998
    • Belgian Nuclear Research Centre
      Moll, Flemish, Belgium
    • University of New South Wales
      • School of Mechanical and Manufacturing Engineering
      Kensington, New South Wales, Australia