This method demonstrates an approach to determine the best grasping location on an unknown object using Weighted Random Forest Algorithm. It used RGB-D value of an object as input to find a suitable rectangular grasping region as the output. To accomplish this task, it uses a subspace of most important features from a very high dimensional extensive feature space that contains both image and point cloud features. Usage of most important features in the grasping algorithm has enabled the system to be computationally very fast while preserving maximum information gain. In this approach, the Random Forest operates using optimum parameters e.g. Number of Trees, Number of Features at each node, Information Gain Criteria etc. ensures optimization in learning, with highest possible accuracy in minimum time in an advanced practical setting. The Weighted Random Forest chosen over Support Vector Machine (SVM), Decision Tree and Adaboost for implementation of the grasping system outperforms the stated machine learning algorithms both in training and testing accuracy and other performance estimates. The Grasping System utilizing learning from a score function detects the rectangular grasping region after selecting the top rectangle that has the largest score. The system is implemented and tested in a Baxter Research Robot with Parallel Plate Gripper in action.

Object deformation is an essential factor for the robot to manipulate the object, as the deformation impacts the grasping of the deformable object either positively or negatively. One of the most challenging problems with deformable objects is estimating the stiffness parameters such as Young’s modulus and Poisson’s ratio. This thesis presents a learning-based approach to predicting the stiffness parameters of a 3D (volumetric) deformable object based on vision and haptic feedback. A deep learning network is designed to predict Young’s modulus of homogeneous isotropic deformable objects from the forces of squeezing the object and the depth images of the deformed part of the object. The results show that the developed method can estimate Young’s modulus of the selected synthetic objects in the validation samples dataset with 3.017% error upper bound on the 95% confidence interval. The conclusion is that this method contributes to predicting Young’s modulus of the homogeneous isotropic objects in the simulation environments. In future work, the diversity of the object shape samples can be expanded for broader application in predicting Young’s modulus. Besides, the method can also be extended to real-world objects after validating real-world experiments. / Objekt är en väsentlig faktor för roboten att manipulera objektet, eftersom det påverkar greppet om det deformerbara objektets deformation antingen positivt eller negativt. Ett av de mest utmanande problemen med deformerbara objekt är att uppskatta styvhetsparametrarna som Youngs modul och Poissons förhållande . Denna avhandling presenterar en inlärningsbaserad metod för att förutsäga styvhetsparametrarna för ett 3D (volumetriskt) deformerbart objekt baserat på syn och haptisk feedback. Ett nätverk för djupinlärning är utformat för att förutsäga Youngs modul av homogena isotropa deformerbara objekt från krafterna från att klämma ihop objektet och djupbilderna av den deformerade delen av objektet Resultaten visar att den utvecklade metoden kan uppskatta Youngs modul för de utvalda syntetiska objekten i valideringsexempeldatauppsättningen med 3.017% fel övre gräns på 95% konfidensintervall. Slutsatsen är att denna metod bidrar till att förutsäga Youngs modul för de homogena isotropa objekten i simuleringsmiljöerna. I framtida bredare arbete kan mångfalden av objektformproverna utökas för tillämpning vid förutsägelse av Youngs modul. Dessutom kan metoden också utvidgas till verkliga objekt efter validering av verkliga experiment.

Visual cues have previously been classified as visual exproprioceptive, when defining the relative position of the body within the environment and are continuously updated while moving (online), and visual exteroceptive when describing static features of the environment which are typically elaborated offline (feedforward). However peripheral visual cues involved in the control of movement have not previously been clearly defined using this classification. Hence the role played by peripheral visual cues in the planning and/or online control of movement remains unclear. The aim of this thesis was to provide a systematic understanding of the importance of peripheral visual cues in several types of movement, namely overground locomotion, adaptive gait, postural stability and reaching and grasping. 3D motion capture techniques were used to collect limb and whole body kinematics during such movements. Visual peripheral cues were manipulated by visual field occlusion conditions or by the employment of point-lights in a dark room. Results showed that the visual cues provided by different parts of the peripheral visual field are mainly used for online fine tuning of limb trajectory towards a target (either a floor-based obstacle or an object to grasp). The absence of peripheral visual cues while moving disrupted the spatio-temporal dynamic relationship between subject and target and resulted in increased margins of safety between body and target and increased time and variability of several dependent measures. These findings argue in favour of the classification of peripheral visual cues as visual exproprioceptive.

The integration of robotic modules is common both in industry and in academia, especially when it comes to robotic grasping and object tracking. However, there are usually two challenges in the integration process. Firstly, the respective fields are extensive, making it challenging to select a method in each field for integration according to specific needs. Secondly, because the integrated system is rarely discussed in academia, there is no set of metrics to evaluate it. Aiming at the first challenge, this thesis reviews and categorizes popular methods in the fields of robotic grasping and object tracking, summarizing their advantages and disadvantages. This categorization provides the basis for selecting methods according to the specific needs of application scenarios. For evaluation, two well-established methods for grasp pose detection and object tracking are integrated for a common application scenario. Furthermore, the technical, as well as the task-related challenges of the integration process are discussed. Finally, in response to the second challenge, a set of metrics is proposed to evaluate the integrated system. / Integration av robotmoduler är vanligt förekommande både inom industrin och i den akademiska världen, särskilt när det gäller robotgrepp och objektspårning. Det finns dock vanligtvis två utmaningar i integrationsprocessen. För det första är både respektive fält omfattande, vilket gör det svårt att välja en metod inom varje fält för integration enligt relevanta behov. För det andra, eftersom det integrerade systemet sällan diskuteras i den akademiska världen, finns det inga etablerade mätvärden för att utvärdera det. För att fokusera på den första utmaningen, granskar och kategoriserar denna avhandling populära metoder inom robotgreppning och spårning av objekt, samt sammanfattar deras fördelar och nackdelar. Denna kategorisering utgör grunden för att välja metoder enligt de specifika behoven i olika applikationsscenarion. Som utvärdering, integreras samt jämförs två väletablerade metoder för posdetektion och objektspårning för ett vanligt applikationsscenario. Vidare diskuteras de tekniska och uppgiftsrelaterade utmaningarna i integrationsprocessen. Slutligen, som svar på den andra utmaningen, föreslås en uppsättning mätvärden för att utvärdera det integrerade systemet.

Hand exoskeletons are wearable robotic devices which are used to compensate for impaired handmovements in patientswith impaired upper-limbs. These devices can either help patients to grasp objects for a therapeutic purpose or to performactivities of daily living. This Thesis describes the development of a novel hand exoskeleton, with a focus on the user, based on the product development methodology "the V-Model". Therefore, user needs are identified through interviews and a thorough literature review. Three potential concepts are developed and sub-sequential a concept is selected based on a logical decision process. A mathematical model of the selected concept is generated and then used for dimensioning the hand exoskeleton. Moreover, three variants of the hand exoskeleton are built as prototypes. Finally, the variants of the device are tested on a bench top. The result of the development process is a novel hand exoskeleton for the rehabilitation of upper motor neuron syndrome patients. Force and range of motion tests revealed, that a design with a higher level of underactuation is favourable. The design presented in this thesis does not reach the defined range of motion and force augmentation. However, the defined target values are the results of a conservative approach, thus are a challenge to reach. The augmented closing force and range of motion surpass other state of the art hand exoskeletons. Nevertheless, the augmented opening force under-performs in comparison with other designs. Decisively, a validation with users is needed for a usability assessment. / Exoskelett för händer är robotiska hjälpmedel som kan användas för att kompensera nedsatt muskelstyrka och rörlighet hos patienter med nedsatt muskelfunktion i armarna. Dessa hjälpmedel kan hjälpa patienter att greppa föremål i ett terapeutiskt syfte eller för att utföra vardagliga sysslor. Examensarbetet beskriver utvecklingsarbetet av ett nytt exoskelett med fokus på användaren genom att tillämpa produktutvecklingsmotodikens V-modell. Användarens krav och behov identifieras genom intervjuer och en gedigen litteraturstudie. Tre koncept utvecklas och ett vidareutvecklat koncept väljs slutligen baserat på en logisk beslutsprocess. En matematisk modell genereras och används för att dimensionera exoskelettet. Dessutom tillverkas tre prototyper av exoskelettet i olika utföranden för att slutligen utvärderas i en testrigg. Resultatet av utvecklingsprocessen är ett nytt handexoskelett ämnat för rehabilitering av patienter med övre motorneuronsjukdom. Tester som genomfördes för att mäta Kraft och rörlighet visade att en design med en högre grad av underaktuering är gynnsamt. Designen som presenteras här når inte upp till de krav som ställs på kraft och rörlighet, de målvärden som definieras är dock baserade på ett konservativt synsätt och är därmed svåra att uppnå. Exoskelettet producerar en högre stängningskraft och uppvisar bättre rörlighet än andra toppmoderna exoskelett. Exoskelettet underpresterar dock vad gäller den producerade öppningskraften jämfört med andra modeller och designen behöver valideras hos användarna för att användarbarheten ska kunna bestämmas.

<p dir="ltr">To ensure safety, traditional industrial robots must operate within cages to separate them from human workers. This requirement has led to the rapid development of collaborative robots (cobots) designed to work closely to humans. However, existing cobots often prioritize <a href="" target="_blank">performance </a>aspects, such as precision, speed, and payload capacity, or prioritize safety, leading to a challenging balance between them. To address this issue, this dissertation introduces innovative concepts and methodologies for variable stiffness mechanisms. These mechanisms are applied to create easily fabricated cobot components to allow for controllable trade-offs between safety and performance in human-robot collaboration intrinsically. Additionally, the end-effectors developed based on these mechanisms enable the flexible and adaptive gripping of objects, enhancing the utility and efficiency of cobots in various applications.</p><p dir="ltr">This article-based dissertation comprises five peer-reviewed articles. The first essay introduces a reconfigurable variable stiffness parallel-guided beam (VSPB), whose stiffness can be adjusted discretely. An accurate stiffness model is also established, capable of leveraging a simple and reliable mechanical structure to achieve broad stiffness variation. The second essay discusses several discrete variable stiffness actuators (DVSAs) suitable for robotic joints. These DVSAs offer high stiffness ratios, rapid shifting speeds, low energy consumption, and compact structures compared to most existing variable stiffness actuators. The third essay introduces a discrete variable stiffness link (DVSL), applied to the robotic arm of a collaborative robot. Comprising three serially connected VSPBs, it offers eight different stiffness modes to accommodate diverse application scenarios, representing the first DVSL in the world. The fourth essay presents a variable stiffness gripper (VSG) with two fingers, each capable of continuous stiffness adjustment. The VSG is a low-cost, customizable universal robotic hand capable of successfully grasping objects of different types, shapes, weights, fragility, and hardness. The fifth essay introduces another robotic hand, the world's first discrete variable stiffness gripper (DVSG). It features four different stiffness modes for discrete stiffness adjustment in various gripper positions by on or off the ribs. Therefore, unlike the VSG, the DVSG focuses more on adaptability to object shapes during grasping.</p><p dir="ltr">These research achievements have the potential to facilitate the construction and popularize of next-generation collaborative robots, thereby enhancing productivity in industry and possibly leading to the integration of personal robotic assistants into countless households.</p>

L'objectif du travail proposé est de concevoir et commander un groupe des robots mobiles similaires et d'architecture simple appelés m-bots (mono-robots). Plusieurs m-bots ont la capacité de saisir ensemble un objet afin d'assurer sa co-manipulation et son transport quelle que soit sa forme et sa masse. Le robot résultant est appelé p-bot (poly-robot) et est capable d'effectuer des tâches de déménageur pour le transport d'objets génériques. La reconfigurabilité du p-bot par l'ajustement du nombre des m-bots utilisés permet de manipuler des objets lourds et des objets de formes quelconques (particulièrement s'ils sont plus larges qu'un seul m-bot). Sont considérés dans ce travail l'évitement d'obstacle ainsi que la stabilité du p-bot incluant la charge à transporter. Une cinématique pour un mécanisme de manipulation a été proposée et étudiée. Ce dernier assure le levage de la charge et son dépôt sur le corps des robots pour la transporter. Plusieurs variantes d'actionnement ont été étudiées : passif, avec compliance et actionné. Un algorithme de positionnement optimal des m-bots autour de l'objet à manipuler a été proposé afin d'assurer la réussite de la tâche à effectuer par les robots. Cet algorithme respecte le critère de "Force Closure Grasping" qui assure la stabilité de la charge durant la phase de manipulation. Il maintient aussi une marge de stabilité statique qui assure la stabilité de l'objet durant la phase de transport. Enfin, l'algorithme respecte le critère des zones inaccessibles qui ne peuvent pas être atteintes par les m-bots. Une loi de commande a été utilisée afin d'atteindre les positions désirées pour les m-bots et d'assurer la navigation en formation, durant la phase du transport, durant laquelle chaque robot élémentaire doit maintenir une position désirée par rapport à l'objet transporté. Des résultats de simulation pour un objet de forme quelconque, décrite par une courbe paramétrique, sont présentés. Des simulations 3D en dynamique multi-corps ainsi que des expériences menées sur les prototypes réalisés ont permis de valider nos propositions. / Our goal in the proposed work is to design and control a group of similar mobile robots with a simple architecture, called m-bot. Several m-bots can grip a payload, in order to co-manipulate and transport it, whatever its shape and mass. The resulting robot is called a p-bot andis capable to solve the so-called "removal-man task" to transport a payload. Reconfiguring the p-bot by adjusting the number of m-bots allows to manipulate heavy objects and to manage objects with anyshape, particularly if they are larger than a single m-bot. Obstacle avoidance is addressed and mechanical stability of the p-bot and its payload is permanently guaranteed. A proposed kinematic architecture for a manipulation mechanism is studied. This mechanism allows to lift a payload and put it on them-bot body in order to be transported. The mobile platform has a free steering motion allowing the system maneuver in any direction. An optimal positioning of the m-bots around the payload ensures a successful task achievement without loss of stability for the overall system. The positioning algorithm respects the Force Closure Grasping (FCG) criterion which ensures the payload stability during the manipulation phase. It respects also the Static Stability Margin (SSM) criterion which guarantees the payload stability during the transport. Finally, it considers also the Restricted Areas (RA) that could not be reached by the robots to grab the payload. A predefined control law is then used to ensure the Target Reaching (TR) phase of each m-bot to its desired position around the payload and to track a Virtual Structure (VS), during the transportation phase, in which each elementary robot has to keep the desired position relative to the payload. Simulation results for an object of any shape, described by aparametric curve, are presented. Additional 3D simulation results with a multi-body dynamic software and experiments by manufactured prototypes validate our proposal.

The aim of the thesis is to design, create and evaluate a user interface for control of service robot. I will focus on controlling of robotic arm, to be able to accomplish pick and place tasks. Specifically I will work with robotic platform PR2. The thesis describes different devices for sensing and perception of a user and usage of information from these devices to control robotic arm. Moreover, different methods for controlling of robotic arm are described there. Application design and implementation is presented further in this thesis together with description of the experiments used for evaluation of application.

Le cortex moteur primaire (M1) est souvent endommagé lors des lésions cérébrales telles que les accidents vasculaires cérébraux. Ceci entraîne des déficits moteurs tels qu'une perte de contrôle des membres controlatéraux. La récupération des lésions M1 s'accompagne d'une réorganisation hémodynamique dans les zones motrices intactes des deux hémisphères. Cette réorganisation est plus prononcée dans les premiers jours et semaines qui suivent la lésion. Toutefois, nous avons une compréhension limitée de la réorganisation neuronale rapide qui se produit dans ce réseau moteur cortical complexe. Ces changements neuronaux nous informent sur l’évolution possible de la plasticité subaiguë impliquée dans la récupération motrice. Par conséquent il était grand temps qu’une caractérisation de la réorganisation rapide de l'activité neuronale dans les régions motrices des deux hémisphères soit entreprise. Dans cette thèse nous avons exploré l'impact d'une lésion corticale localisée, unilatérale et réversible dans M1 sur l'activité neuronale des zones motrices des hémisphères ipsi et contralésionnel lorsque des primates non humains ont effectués des mouvements d’atteinte et de saisie. Notre modèle d'inactivation nous a permis d'enregistrer en continu des neurones isolés avant et après l'apparition des déficits moteurs. Dans une première étude, la réorganisation rapide qui se produit dans le cortex prémoteur ventral (PMv) des deux hémisphères a été étudiée (Chapitre 2). Le PMv est une zone connue pour être impliquée dans le contrôle moteur de la main et la récupération des lésions M1. Dans une seconde étude, la réorganisation rapide du M1 contralésionnel (cM1) a été étudiée et comparée à celles se produisant dans les PMv bilatérales (Chapitre 3). Le cM1 joue un rôle complexe dans la récupération des mouvements de précision de la main suite à une blessure à son homologue. Nous révélons une réorganisation neuronale importante et beaucoup plus complexe que prévu dans les deux hémisphères lors de l’apparition initiale des déficiences motrices. Nos données démontrent que les changements neuronaux survenant quelques minutes après une lésion cérébrale sont hétérogènes à la fois dans et entre les zones du réseau moteur cortical. Ils se produisent dans les deux hémisphères lors des mouvements des bras parétiques et non parétiques, et ils varient au cours des différentes phases du mouvement. Ces découvertes constituent une première étape nécessaire pour démêler les corrélats neuronaux complexes de la réorganisation au travers du réseau moteur des deux hémisphères à la suite d’une lésion cérébrale. / After brain injuries such as stroke, the primary motor cortex (M1) is often damaged leading to motor deficits that include a loss of fine motor skills of the contralateral limbs. Recovery from M1 lesions is accompanied by hemodynamic reorganization in motor areas distal to the site of injury in both hemispheres that are most pronounced early after injury. However, we have limited understanding of the rapid neuronal reorganization that occurs in this complex and distributed cortical motor network. As these neural changes reflect the landscape on which subacute plasticity involved in motor recovery will take place, an exploration of the rapid reorganization in neural activity that occurs in motor regions of both hemispheres is long overdue. In the current thesis, we set out to explore the impact of a localized, unilateral and reversible cortical injury to the M1 hand area on neuronal activity in motor-related areas of both the ipsi and contralesional hemispheres as non-human primates performed a reach and grasp task. Our inactivation model allowed us to continuously record isolated neurons before and after the onset of motor deficits. In a first study, the rapid reorganization taking place in the ventral premotor cortex (PMv) of both hemispheres was investigated (Chapter 2). The PMv is an area well-known to be critically involved in hand motor control and recovery from M1 lesions. In a second study, the rapid reorganization taking place in the contralesional M1 (cM1) was studied and compared to those occurring in bilateral PMv (Chapter 3). The cM1 has a complex role in recovery of dexterous hand movements following injury to its homologue. We reveal extensive, and much more complex than expected, neuronal reorganization in both hemispheres at the very onset of motor impairments. Our data demonstrate that neuronal changes occurring within minutes after brain injury are heterogenous both within and across areas of the cortical motor network. They occur in the two hemispheres during movements of both the paretic and non-paretic arms, and they vary during different phases of movement. These findings constitute a first step in a much needed and timely effort to unravel the complex neuronal correlates of the reorganization that takes place across the distributed motor network after brain injury.

Cette recherche a pour but d’évaluer le rôle de la vision et de la proprioception pour la perception et le contrôle de l’orientation spatiale de la main chez l’humain. L’orientation spatiale de la main est une composante importante des mouvements d’atteinte et de saisie. Toutefois, peu d’attention a été portée à l’étude de l’orientation spatiale de la main dans la littérature. À notre connaissance, cette étude est la première à évaluer spécifiquement l’influence des informations sensorielles et de l’expérience visuelle pour la perception et le contrôle en temps réel de l'orientation spatiale de la main pendant le mouvement d’atteinte naturel vers une cible stationnaire. Le premier objectif était d’étudier la contribution de la vision et de la proprioception dans des tâches de perception et de mouvement d’orientation de la main. Dans la tâche de perception (orientation-matching task), les sujets devaient passivement ou activement aligner une poignée de forme rectangulaire avec une cible fixée dans différentes orientations. Les rotations de l’avant-bras et du poignet étaient soit imposées par l’expérimentateur, soit effectuées par les sujets. Dans la tâche de mouvement d’orientation et d’atteinte simultanées (letter posting task 1), les sujets ont réalisé des mouvements d’atteinte et de rotation simultanées de la main afin d’insérer la poignée rectangulaire dans une fente fixée dans les mêmes orientations. Les tâches ont été réalisées dans différentes conditions sensorielles où l’information visuelle de la cible et de la main était manipulée. Dans la tâche perceptive, une augmentation des erreurs d’orientation de la main a été observée avec le retrait des informations visuelles concernant la cible et/ou ou la main. Lorsque la vision de la main n’était pas permise, il a généralement été observé que les erreurs d’orientation de la main augmentaient avec le degré de rotation nécessaire pour aligner la main et la cible. Dans la tâche de mouvement d’orientation et d’atteinte simultanées, les erreurs ont également augmenté avec le retrait des informations visuelles. Toutefois, les patrons d’erreurs étaient différents de ceux observés dans la tâche de perception, et les erreurs d’orientation n’ont pas augmenté avec le degré de rotation nécessaire pour insérer la poignée dans la fente. En absence de vision de la main, il a été observé que les erreurs d’orientation étaient plus petites dans la tâche de mouvement que de perception, suggérant l’implication de la proprioception pour le contrôle de l’orientation spatiale de la main lors des mouvements d’orientation et d’atteinte simultanées. Le deuxième objectif de cette recherche était d’étudier l’influence de la vision et de la proprioception dans le contrôle en temps réel de l’orientation spatiale de la main. Dans une tâche d’orientation de la main suivie d’une atteinte manuelle (letter posting task 2), les sujets devaient d’abord aligner l’orientation de la même poignée avec la fente fixée dans les mêmes orientations, puis réaliser un mouvement d’atteinte sans modifier l’orientation initiale de la main. Une augmentation des erreurs initiales et finales a été observée avec le retrait des informations visuelles. Malgré la consigne de ne pas changer l’orientation initiale de la main, une diminution des erreurs d’orientation a généralement été observée suite au mouvement d’atteinte, dans toutes les conditions sensorielles testées. Cette tendance n’a pas été observée lorsqu’aucune cible explicite n’était présentée et que les sujets devaient conserver l’orientation de départ de la main pendant le mouvement d’atteinte (mouvement intransitif; letter-posting task 3). La diminution des erreurs pendant l’atteinte manuelle transitive vers une cible explicite (letter-posting task 2), malgré la consigne de ne pas changer l’orientation de la main pendant le mouvement, suggère un mécanisme de corrections automatiques pour le contrôle en temps réel de l’orientation spatiale de la main pendant le mouvement d’atteinte naturel vers une cible stationnaire. Le troisième objectif de cette recherche était d’évaluer la contribution de l’expérience visuelle pour la perception et le contrôle de l’orientation spatiale de la main. Des sujets aveugles ont été testés dans les mêmes tâches de perception et de mouvement. De manière générale, les sujets aveugles ont présenté les mêmes tendances que les sujets voyants testés dans la condition proprioceptive (sans vision), suggérant que l’expérience visuelle n’est pas nécessaire pour le développement d’un mécanisme de correction en temps réel de l’orientation spatiale de la main basé sur la proprioception. / The goal of this research was to study the contribution of vision and proprioception to the perception and control of hand orientation in human subjects. Spatial orientation of the hand is an important component of reaching and grasping movements. However, not much attention has been given to spatial hand orientation in the literature. To our knowledge, this study is the first to specifically investigate the influence of sensory information for the perception and on-line control of hand orientation during natural reaching movement to stationary targets. The first objective of this research was to study the contribution of vision and proprioception in perceptual orientation-matching and motor letter posting tasks. In the perceptual orientation-matching task, subjects attempted to passively or actively align a match handle, to a target that was fixed in different orientations. In the passive perceptual task, passive rotations of the forearm and wrist were imposed by the experimenter; whereas in the active perceptual task, the rotations were actively executed by the subjects. In letter posting task 1, subjects simultaneously reached and rotated the right hand to insert a match handle into a target slot fixed in the same orientations. The tasks were performed in different sensory conditions where the visual information about the target and the hand was manipulated. In the perceptual orientation-matching task, augmentation of hand orientation errors was observed with the withdrawal of visual information related to either the target and/or the hand. When full vision was not allowed, hand orientation errors were larger overall when larger rotations of the wrist were required to match the target, whether the rotations were made actively by the subject or were imposed passively by the experimenter. In letter posting task 1, augmentation of hand orientation errors was also observed with the withdrawal of visual information related to either the target and/or the hand. However, errors patterns were different from those observed in the perceptual task, and hand orientation errors were not larger for larger target orientations. Without vision of the hand, final hand orientation errors were smaller overall in letter-posting task 1 than in the orientation-matching task. This suggests the implication of the proprioceptive information for the control of spatial hand orientation during reach-and-orient movements. The second objective of this research was to study the influence of vision and proprioception in on-line control of spatial hand orientation. In letter posting task 2, subjects first aligned their hand to the angle of the target and then reached to it with the instruction not to change their initial hand orientation. The augmentation of initial and final errors was observed with the withdrawal of vision. Although subjects were instructed to not change their hand orientation, in all sensory condition tested, hand orientation changed overall during reaching in a way that reduced the initial orientation errors. This trend did not occur when there was no explicitly defined target toward which the subjects reached (letter-posting task 3; intransitive movement). The reduction in hand orientation errors during transitive reach in letter-posting task 2, even when told not to change it, suggests the engagement of an automatic error correction mechanism for hand orientation during natural reaching movements toward stationary targets. The third objective of this research was to investigate the contribution of visual experience to the perception and control of spatial orientation of the hand. Blind subjects were tested in the same perceptual and motor tasks. Overall, no differences were observed between performance of blind subjects and normally-sighted subjects tested without vision (proprioceptive condition), suggesting that prior visual experience is not necessary for the development of an on-line error correction mechanism for hand orientation guided by proprioceptive inputs.