1,720,986 research outputs found
Identifying the dynamic model used by the KUKA LWR: A reverse engineering approach
No full textAn approach is presented for the model identification of the so-called link dynamics used by the KUKA LWR-IV, a lightweight manipulator with elastic joints that is very popular in robotics research but for which a complete and reliable dynamic model is not yet publicly available. The control software interface of this robot provides numerical values of the link inertia matrix and the gravity vector at each configuration, together with link position and joint torque sensor data. Taking advantage of this information, a general procedure is set up for determining the structure and identifying the value of the relevant dynamic coefficients used by the manufacturer in the evaluation of these robot model terms. We call this a reverse engineering approach, because our main goal is to match the numerical data provided by the software interface, using a suitable symbolic model of the robot dynamics and the inertial and gravity coefficients that are being estimated. Only configuration-dependent terms are involved in this process, and thus static experiments are sufficient for this task. The main issues of dynamic model identification for robots with elastic joints are discussed in general, highlighting the pros and cons of the approach taken for this class of KUKA lightweight manipulators. The main identification results, including training and validation tests, are reported together with additional dynamic validation experiments that use the complete identified model and joint torque sensor data
A geometrical approach to the PKPD modelling of inhaled bronchodilators
No full textThe present work introduces a new method to model the pharmacokinetics and pharmacodynamics (PKPD) of an inhaled dose of bronchodilator. This method provides an alternative approach to classic compartmental representations or computational fluid dynamics.
A five compartment lung model comprising the upper airways, bronchial tree mucosa, bronchial muscles, alveoli and plasma has been modified to take into account anatomical, geometrical features such as bronchial branching and smooth muscle distribution. Many anatomical and physiological features of the bronchial tree depend, as a first approximation, on bronchial generation or on mean distance from the larynx. Among these are diameters, resistances, and receptor density, which work together in determining the local response to the inhaled dose; integrating these local responses over the whole bronchial tree allows an approximation of total broncodilator response, particularly with respect to airflow resistance.
While the PK part of the model reflects classical compartmental assumptions, the PD part substitutes a simplified geometrical and functional description of the bronchial tree for the typical PD models of effect, leading to the direct computation of the approximate FEV1.
In the present work the construction of the model is detailed, and literature data are used to derive the anatomical approximations used. Simulation of two asthmatic subjects is employed to illustrate the behaviour of the model in representing the evolution over time of the distribution and effect of an inhaled dose of bronchodilator. The relevance of formulation diffusivity on therapeutic efficacy is discussed and conclusions regarding the applicability of the model in interpreting single-subject and population experiments are drawn
Online needle-tissue interaction model identification for force feedback enhancement in robot-assisted interventional procedures
Full text linkMany interventional procedures, e.g., biopsies and tumor ablation, imply the insertion of a needle into soft tissues. The interaction force at the needle tip can convey information important for the accuracy of needle placement and the patient’s safety. This information is essential when feedback from an imaging system is missing or only available at a low rate. To isolate the force exchanged at the needle tip during the insertion, it is necessary to remove other components from the needle-tissue interaction force. In particular, the friction along the needle shaft becomes more and more relevant as the needle penetrates deeper into the tissues. In this paper, we propose a method for the identification of the friction component during needle penetration into a multi-layered target. The proposed online identification procedure allows, at the transition from one tissue layer to the next, to subtract the friction contribution from the previous layers and isolate the force relative to the layer where the needle tip is currently located. We call this an enhanced force signal because it improves the ratio of the useful information about the force at the needle tip to the total force rendered. This result can be used in teleoperated needle insertion schemes, or other robot-assisted architectures, with the aim of facilitating the user perception of variations in tissue properties. In the proposed implementation, the force at the base of the needle can either be measured or estimated by using a model-based approach. An originally developed simulation framework provides a tool for procedure planning and online monitoring
Novel patterns and methods for zooming camera calibration
No full textCamera calibration is a necessary step in order to develop applications that need to establish a relationship between image pixels and real world points. The goal of camera calibration is to estimate the extrinsic and intrinsic camera parameters. Usually, for non-zooming cameras, the calibration is carried out by using a grid pattern of known dimensions (e.g., a chessboard). However, for cameras with zoom functions, the use of a grid pattern only is not sufficient, because the calibration has to be effective at multiple zoom levels and some features (e.g., corners) could not be detectable. In this paper, a calibration method based on two novel calibration patterns, specifically designed for zooming cameras, is presented. The first pattern, called in-lab pattern, is designed for intrinsic parameter recovery, while the second one, called on-field pattern, is conceived for extrinsic parameter estimation. As an application example, on-line virtual advertising in sport events, where the objective is to insert virtual advertising images into live or pre-recorded television shows, is considered. A quantitative experimental evaluation shows an increase of performance with respect to the use of standard calibration routines considering both re-projection accuracy and calibration time
A unifying organ model of pancreatic insulin secretion
Full text linkThe secretion of insulin by the pancreas has been the object of much attention over the past several decades. Insulin is known to be secreted by pancreatic β-cells in response to hyperglycemia: its blood concentrations however exhibit both high-frequency (period approx. 10 minutes) and low-frequency oscillations (period approx. 1.5 hours). Furthermore, characteristic insulin secretory response to challenge maneuvers have been described, such as frequency entrainment upon sinusoidal glycemic stimulation; substantial insulin peaks following minimal glucose administration; progressively strengthened insulin secretion response after repeated administration of the same amount of glucose; insulin and glucose characteristic curves after Intra-Venous administration of glucose boli in healthy and prediabetic subjects as well as in Type 2 Diabetes Mellitus. Previous modeling of β-cell physiology has been mainly directed to the intracellular chain of events giving rise to single-cell or cell-cluster hormone release oscillations, but the large size, long period and complex morphology of the diverse responses to whole-body glucose stimuli has not yet been coherently explained. Starting with the seminal work of Grodsky it was hypothesized that the population of pancreatic β-cells, possibly functionally aggregated in islets of Langerhans, could be viewed as a set of independent, similar, but not identical controllers (firing units) with distributed functional parameters. The present work shows how a single model based on a population of independent islet controllers can reproduce very closely a diverse array of actually observed experimental results, with the same set of working parameters. The model's success in reproducing a diverse array of experiments implies that, in order to understand the macroscopic behaviour of the endocrine pancreas in regulating glycemia, there is no need to hypothesize intrapancreatic pacemakers, influences between different islets of Langerhans, glycolitic-induced oscillations or β-cell sensitivity to the rate of change of glycemia
Simulation of Trauma Incidents: Modelling the Evolution of Patients and Resources
No full textMathematical modeling and simulation with medical applications has gained much interest in the last few years, mainly due to the widespread availability of low-cost technology and computational power. This paper presents an integrated platform for the in-silico simulation of trauma incidents, based on a suite of interacting mathematical models. The models cover the generation of a scenario for an incident, a model of physiological evolution of the affected individuals, including the possible effect of the treatment, and a model of evolution in time of the required medical resources. The problem of optimal resource allocation is also investigated. Model parameters have been identified according to the expertise of medical doctors and by reviewing some related literature. The models have been implemented and exposed as web services, while some software clients have been built for the purpose of testing. Due to its extendability, our integrated platform highlights the potential of model-based simulation in different health-related fields, such as emergency medicine and personal health systems. Modifications of the models are already being used in the context of two funded projects, aiming at evaluating the response of health systems to major incidents with and without model-based decision support
Consistency of compact and extended models of glucose-insulin homeostasis: The role of variable pancreatic reserve
Full text linkPublished compact and extended models of the glucose-insulin physiologic control system are compared, in order to understand why a specific functional form of the compact model proved to be necessary for a satisfactory representation of acute perturbation experiments such as the Intra Venous Glucose Tolerance Test (IVGTT). A spectrum of IVGTT’s of virtual subjects ranging from normal to IFG to IGT to frank T2DM were simulated using an extended model incorporating the population-of-controllers paradigm originally hypothesized by Grodsky, and proven to be able to capture a wide array of experimental results from heterogeneous perturbation procedures. The simulated IVGTT’s were then fitted with the Single-Delay Model (SDM), a compact model with only six free parameters, previously shown to be very effective in delivering precise estimates of insulin sensitivity and secretion during an IVGTT. Comparison of the generating, extended-model parameter values with the obtained compact model estimates shows that the functional form of the nonlinear insulin-secretion term, empirically found to be necessary for the compact model to satisfactorily fit clinical observations, captures the pancreatic reserve level of the simulated virtual patients. This result supports the validity of the compact model as a meaningful analysis tool for the clinical assessment of insulin sensitivity
Detection and isolation of actuator faults and collisions for a flexible robot arm
No full textThis paper presents a unified approach to detection and isolation of both actuator faults and unexpected collisions for a two-link robot with a flexible forearm. The proposed approach is sensorless, i.e., no dedicated exteroceptive sensors are considered, and is based on the design of residuals to be used as monitoring filters. The method has been tested by extensive simulations on the Flexarm robot used as case study. The reported results show the efficacy in detecting and isolating faults in the actuators or collisions on the robot links
A model-based residual approach for human-robot collaboration during manual polishing operations
Full text linkA fully robotized polishing of metallic surfaces may be insufficient in case of parts with complex geometric shapes, where a manual intervention is still preferable. Within the EU SYMPLEXITY project, we are considering tasks where manual polishing operations are performed in strict physical Human-Robot Collaboration (HRC) between a robot holding the part and a human operator equipped with an abrasive tool. During the polishing task, the robot should firmly keep the workpiece in a prescribed sequence of poses, by monitoring and resisting to the external forces applied by the operator. However, the user may also wish to change the orientation of the part mounted on the robot, simply by pushing or pulling the robot body and changing thus its configuration. We propose a control algorithm that is able to distinguish the external torques acting at the robot joints in two components, one due to the polishing forces being applied at the end-effector level, the other due to the intentional physical interaction engaged by the human. The latter component is used to reconfigure the manipulator arm and, accordingly, its end-effector orientation. The workpiece position is kept instead fixed, by exploiting the intrinsic redundancy of this subtask. The controller uses a F/T sensor mounted at the robot wrist, together with our recently developed model-based technique (the residual method) that is able to estimate online the joint torques due to contact forces/torques applied at any place along the robot structure. In order to obtain a reliable residual, which is necessary to implement the control algorithm, an accurate robot dynamic model (including also friction effects at the joints and drive gains) needs to be identified first. The complete dynamic identification and the proposed control method for the human-robot collaborative polishing task are illustrated on a 6R UR10 lightweight manipulator mounting an ATI 6D sensor
Enhancing force feedback in teleoperated needle insertion through on-line identification of the needle-tissue interaction parameters
No full textThis paper proposes an approach for displaying
the needle-tip interaction force exchanged between the needle
tip and the tissues to the remote operator of a teleoperated
needle insertion procedure. As known, the measures of the
needle tip interaction force with tissues obtained through
F/T sensor at the robot wrist do not provide a transparent
perception of the needle-tissue interaction at the tip mainly
because of the friction between the needle shaft and the
traversed tissues. Current literature mainly proposes hardware
solutions to the problem of measuring the forces at the needle
tip. In this work we aim instead at cleaning the F/T sensor
information for rendering only the estimated force exchanged at
the needle tip. The approach is based on an online identification
of the parameters of a needle-tissue interaction force model to
isolate offset force values mainly due to friction. The approach,
validated through simulations and experiments, is expected to
increase the sensitivity of the rendered force to tissue transitions
thus improving safety and accuracy in needle placement
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