Papers by Pierre-Olivier Lemieux
Digital Human Modeling and Applied Optimization
ObjectiveGrasp planning is a popular topic in the fields of robotic and Digital Human Model (DHM)... more ObjectiveGrasp planning is a popular topic in the fields of robotic and Digital Human Model (DHM) (4, 6, 7, 9, 10, 11). So far, the proposed planners do not consider the final posture of the DHM has a criteria when determining potential grasps. In (4), a grasping algorithm has been developed to automatically grasp known tools. The present work introduces a grasp planner for single-hand grasp on an unknown object, further referred as “part”.MethodThe grasp planner gives has a result a grasp pose (position + orientation) for the posture solver (Smart Posturing Engine) to reach. The input necessary to the grasp planner are the 3D model of the object to grasp and of the surrounding environment, and an initial manikin position that is automatically determines by the posture solver algorithm.First the part is approximated by its oriented bounding box (OBB), limiting the grasp poses to 6 (one for each face of the OBB). Then precise grasp types (5) and apertures are chosen based on the face...
(Lauranne) Sins , (Pierre-Olivier) Lemieux , (Patrice) Tetreault , (Natalia) Nuno 1, , (Fabien) B... more (Lauranne) Sins , (Pierre-Olivier) Lemieux , (Patrice) Tetreault , (Natalia) Nuno 1, , (Fabien) Billuart , (Nicola) Hagemeister 1, 2, 3 1 Ecole de technologie superieure (ETS), Montreal (QC), Canada 2 Laboratoire de recherche en imagerie et orthopedie (LIO), Montreal (QC), Canada 3 Centre de recherche du centre hospitalier de l’Universite de Montreal (CRCHUM), Hopital Notre-Dame, Montreal (QC), Canada 4 Ceraver, Roissy, France
Human tasks involve variable degrees of vision requirements that can influence the posture. Some ... more Human tasks involve variable degrees of vision requirements that can influence the posture. Some digital human models (DHM) have proposed constraints based on vision, but did not account for 3 important aspects: (1) target size, (2) target orientation and (3) level of precision/focus of the task. The present study proposes a novel vision constraint that simultaneously accounts for these 3 aspects. This constraint was used to predict the "head-target" distance of a DHM, using 2 precision levels (PL) obtained experimentally (HPL = 1.18 (± 0.06) and LPL = 0.78 (± 0.01)). A similar distance was obtained with no vision constraint (56.3 cm) and LPL constraint (52.3 cm), respectively. However, this distance was less than half (23.8 cm) with the HPL constraint. The proposed LogVA vision constraint needs further development but already seems promising in helping DHM users to posture the manikin while considering the PL of the task.
Introduction: Visual acuity is the capacity to discriminate fine details in the field of view. Cu... more Introduction: Visual acuity is the capacity to discriminate fine details in the field of view. Currently, digital human models (DHM) such as Delmia do not acccount for that aspect during the process of posture prediction. Some studies have proposed visual acuity constraints for DHM applications. However, they did not clearly show how visual acuity may influence the posture of the DHM. This study proposes a new visual acuity constraint for DHM allowing different acuity requirements. The Delmia DHM is used as an example to show how this constraint can adjust the head-target (HT) distance of the DHM, given a prescribed requirement of visual acuity. Methods: A measure called “LogVA” was created, inspired from the LogMAR used in optometry. Using a geometrical approach, the LogVA computed the visual angle (VA) as the angle subtended by the target size, but with an additional consideration of the incidence angle (δ) between the target face normal and HT vector. Visual angles for high and low acuity requirements were first estimated with a preliminary experiment conducted on one subject. The task of high visual acuity involved inserting resistors in a breadboard. The task of low visual acuity involved identifying shapes on a computer screen. Head and target positions were measured. Thereafter, both tasks were reproduced in a virtual environment. The visual acuity constraint was applied on the DHM and the experimental visual angles were used as prescribed acuity requirements for posturing the DHM. The 3D visual space representing the spectrum of allowed HT distances for the required acuity was also simulated. Results: The results showed a good agreement between simulated and experimental parameters (HT, β, δ). During the simulation, the high and low requirements limited the head position inside visual spaces of different dimensions. From an initial head position outside that space, the IK solver equipped with the visual acuity constraint was further able to adapt the posture of the DHM so that the final head position was lying on the outer surface of that space. Discussion: The integration of the LogVA constraint in the posture prediction engine of the Delmia DHM was successful. This further allowed automatic adjustment of the head and the whole position of the DHM to meet a prescribed requirement of visual acuity. One of the next steps is to elaborate a rigorous experimental protocol, with more subjects and further differentiation between the levels of visual acuity.
Multibody System Dynamics, 2016
The present study introduced a new method to simultaneously optimize the path, magnitude and orie... more The present study introduced a new method to simultaneously optimize the path, magnitude and orientation of medial and lateral femorotibial contact forces using bone geometry constraints. The new method will be numerically compared to the known contact point method while estimating the muscle and contact forces for the stance phase of a single gait trial.A single generic lower extremity model was modified to allow knee flexion with an instantaneous rotation center. The contact point method simulated medial and lateral contact forces with no limited magnitude and with predefined one-dimensional paths and orientations. The new contact zone method simulated contact forces with a limited magnitude and with two-dimensional paths and orientations constrained by the geometry of the bones. A high and low limit was used to study the effect of limiting the contact force magnitude on the predicted forces.The paths of the contact forces for the contact zone method showed a difference up to 25.5 mm with respect to the contact point model. The contact zone method also allowed for more shear contact forces and for some modulation of the external frontal moment. Further limiting the contact force magnitude induced noticeable differences of muscle forces.The contact zone method allows the path, magnitude and orientation of the femorotibial contact forces to be sensitive to knee bone geometries and to the amount of allowable joint contact force. Such a method is promising in characterizing the contact forces with modified gait, bone geometries and knee strength associated with pathological conditions such as osteoarthritic and ACL-deficiency.
Cuff tear arthropathy (CTA) is a shoulder pathology characterized by a massive and irreparable ro... more Cuff tear arthropathy (CTA) is a shoulder pathology characterized by a massive and irreparable rotator cuff tear and an abnormal contact between the humeral head and the acromion. CTA is often associated with shoulder pseudo-paralysis. However, the fact that some patients still maintain a functional shoulder remains unexplained. The goal of the present work was to numerically assess the biomechanical parameters that influence the function of the shoulder with CTA. The specific objectives were to show the influence of: (1) a variation of the medial offset of the proximal humerus on the destabilizing forces at the intact (healthy) shoulder; (2) the elevation plane and the friction coefficient on the “mechanics of CTA” and; (3) the geometrical parameters of the humeral head on the “mechanics of CTA” in the context of an hemiarthroplasty. Study #1 assessed the influence of a minimum (0 mm), average (7 mm) and maximum (14 mm) medial offset on the destabilizing glenohumeral forces (transv...
Computer Methods in Biomechanics and Biomedical Engineering, 2013
This study assessed the influence of the medial offset of the proximal humerus on the glenohumera... more This study assessed the influence of the medial offset of the proximal humerus on the glenohumeral destabilising forces during arm elevation in the plane of the scapula, using the AnyBody Modeling System. The variability of the medial offset was covered using literature data (minimum, 0 mm; average, 7 mm and maximum, 14 mm). The following parameters were studied: moment arm (MA; middle deltoid), muscle activity and stability ratios. The minimum offset decreased the MA of the middle deltoid ( -11%), increased its activation (+18%) and its superior destabilising action (+40%). The maximum offset had an opposite effect (+9%, -30% and -30%). The stabilising action of the rotator cuff was not affected. Varying the medial offset seems to have an influence on the destabilising action of the middle deltoid. The AnyBody simulation tool appears to be promising in establishing links between shoulder morphology and stability.
Clinical Biomechanics, 2012
International Journal of Human Factors Modelling and Simulation, 2017
The upper limbs of digital human models have many degrees of freedom. Moreover, their range of mo... more The upper limbs of digital human models have many degrees of freedom. Moreover, their range of motion tends to be overestimated. In some conditions, the resulting kinematic chain may predict unrealistic postures. Many kinematic correlations or 'couplings' have been measured at the upper limb (ex. shoulder rhythm, sinus cone limits). So far, a few of them were adapted to digital human models. These models often use a simplified 'claviscapular' segment, which simplifies the shoulder girdle, (i.e., clavicle and scapula) as a single segment. This paper presents the development of a set of upper limb degree of freedom couplings for digital human models, adapted from experimental kinematic data that comes from different published studies. It is shown how these couplings improve the upper limb model by reducing its overestimated ranges of motion and reachable workspace and by improving its kinematic behaviour. The use of experimental data from a single group of subjects is ...
L’arthropathie de rupture de coiffe (ARC) est une pathologie de l’epaule caracterisee par une rup... more L’arthropathie de rupture de coiffe (ARC) est une pathologie de l’epaule caracterisee par une rupture massive et irreparable de la coiffe des rotateurs et un contact anormal entre la tete humerale et l’acromion. L’ARC est souvent associee a une pseudo-paralysie de l’epaule. Or, le fait que certains patients conservent malgre tout une epaule fonctionnelle reste inexplique. L’objectif de ce travail etait d’analyser numeriquement les parametres biomecaniques influencant la fonction de l’epaule atteinte d’ARC. Les objectifs specifiques etaient de montrer l’influence : (1) de la variation du deport medial de l’humerus proximal sur les forces destabilisatrices a l’epaule intacte ; (2) du plan d’elevation et du coefficient de friction sur la « mecanique de l’ARC » et (3) des parametres geometriques de la tete humerale sur la « mecanique de l’ARC » dans le contexte d’une hemiarthroplastie. L’etude #1 a evalue l’influence d’un deport medial minimum (0 mm), moyen (7 mm) et maximum (14 mm) sur...
This numerical study assesses the influence of an oversized humeral hemiprosthesis with a larger ... more This numerical study assesses the influence of an oversized humeral hemiprosthesis with a larger medial offset on the mechanics of the shoulder with cuff tear arthropathy (CTA). Shoulder elevation in the scapular plane is performed, and a Seebauer Type IIa CTA is simulated: a massive rotator cuff tear, a proximal and static migration of the humeral head, and two contacts with friction (glenohumeral and acromiohumeral). The CTA model without a prosthesis (friction coefficient 0.3) is evaluated first as a reference model. Then, three humeral head prosthetic geometries (friction coefficient 0.15) are evaluated: anatomical head, oversized head, and oversized head with a large medial offset. The function of the middle deltoid (i.e. moment arm, applied force, and strength), the contact forces, and the range of motion are studied. The anatomical head, which reduces friction by half, decreases the middle deltoid force (25%) and the contact forces (glenoid 7%; acromion 25%), and increases the range of motion from 41 to 54°. The oversized head increases the moment arm (15%) and the middle deltoid strength (13%), which further decreases the deltoid force (7%) and the contact forces (glenoid 7%; acromion 17%), and increases the range of motion from 54° to 69°. The oversized head with a large medial offset enhances these effects: the moment arm increases by another 3.1%, the deltoid force decreases by another 5% and the acromiohumeral contact force by another 12%, and the range of motion increases from 69° to 84°. These results suggest that increasing the medial offset and oversizing the hemiprosthetic head improve the function of the deltoid, reduce acromial solicitation, and restore elevation to almost 90°.
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Papers by Pierre-Olivier Lemieux
Methods: First, degree of freedom couplings were estimated for the claviscapular configuration. These couplings were then applied on the DHM of Delmia. The joint range of motion and reachable workspace were estimated for the model with and without DoF coupling. Moreover, the kinematic behavior of both models was analysed through a “bottom-top-bottom” vertical trajectory task.
Results: The application of degree of freedom coupling reduced the range of motion of the sternum-claviscapular, claviscapular-humerus and wrist joints by 72, 29 and 39%, respectively. This reduction of range of motion further induced a 33% reduction of the reachable workspace volume. A major portion of that reduction occurred behind the body. Finally, the model with degree of freedom coupling showed more similar patterns of angles between the “bottom-to-top” and “top-to-bottom” phases of the vertical trajectory task.
Conclusions: Degree of freedom coupling was successfully adapted to the upper limb of the digital human model of Delmia and its claviscapular segment. Other digital human models that use this simplified segment may also benefit from the present findings. Deeper investigations on experimental subjects may help verifying the correctness of the proposed couplings.
Methods: A measure called “LogVA” was created, inspired from the LogMAR used in optometry. Using a geometrical approach, the LogVA computed the visual angle (VA) as the angle subtended by the target size, but with an additional consideration of the incidence angle (δ) between the target face normal and HT vector. Visual angles for high and low acuity requirements were first estimated with a preliminary experiment conducted on one subject. The task of high visual acuity involved inserting resistors in a breadboard. The task of low visual acuity involved identifying shapes on a computer screen. Head and target positions were measured. Thereafter, both tasks were reproduced in a virtual environment. The visual acuity constraint was applied on the DHM and the experimental visual angles were used as prescribed acuity requirements for posturing the DHM. The 3D visual space representing the spectrum of allowed HT distances for the required acuity was also simulated.
Results: The results showed a good agreement between simulated and experimental parameters (HT, β, δ). During the simulation, the high and low requirements limited the head position inside visual spaces of different dimensions. From an initial head position outside that space, the IK solver equipped with the visual acuity constraint was further able to adapt the posture of the DHM so that the final head position was lying on the outer surface of that space.
Discussion: The integration of the LogVA constraint in the posture prediction engine of the Delmia DHM was successful. This further allowed automatic adjustment of the head and the whole position of the DHM to meet a prescribed requirement of visual acuity. One of the next steps is to elaborate a rigorous experimental protocol, with more subjects and further differentiation between the levels of visual acuity.