Grasp stability was studied and researched upon by various research groups, but mainly focused on robotic grippers by devising conditions for a stable grasp. Maintaining grasp stability is important so as to reduce the chances of the object slipping and dropping. But there was little focus on the grasp stability of robotic exoskeleton gloves and most of the research was focused on mechanical design. A robotic exoskeleton glove was developed as well as novel methods to improve the grasp stability. The exoskeleton glove developed is intended for patients who have suffered paralysis of the hand due to stroke or other factors. The robotic glove aids them in grasping objects as part of daily life activities. The glove is constructed with rigidly coupled 4-bar linkages attached to the finger tips. Each linkage mechanism has 1- Degree of Freedom (DOF) and is actuated by a linear Series Elastic Actuator (SEA). Two methods were developed to satisfy two of the conditions required for a stable grasp. These include deformation prevention of soft objects, and maintaining force and moment equilibrium of the objects being grasped. Simulations were performed to validate the performance of the algorithms. A battery of experiments was performed on the integrated prototype in order to validate the performance of the algorithms developed. / Master of Science / An exoskeleton glove is robotic device that can aid people who suffer from paralysis of their hands caused by a stroke or other factors with the primary goal of allowing them to regain the basic ability of grasping objects and thereby improving their quality of life. The exoskeleton glove developed in this research is focused on objects grasping assistance rather than for rehabilitation purposes. Since the exoskeleton glove lacks conscious senses like a human hand typically possesses, it may not be able to apply sufficient grasping force or may apply excessive force than required irrespective of the object being grasped. In order to ensure that the exoskeleton glove applies the proper amount of force, two novel methods were developed which help improve the overall grasping performance of the robotic glove. These methods use sensors that enable the glove to react to the force interaction changes that exists between the hand and the object being grasped through the exoskeleton glove. The first method detects any deformation that may occur while grasping a soft object and applies lesser force accordingly to prevent further damage to the object. The second method uses motion sensor to detect any movement by the user while grasping the object and applies corrective forces so that the object doesn’t slip from the hand. A prototype was designed and integrated and the two methods were tested on the prototype to validate them.

A method is presented for stably grasping 2 dimensional polygonal objects with a dextrous hand when object models are not avaiable. Basic constraints on object vertex angles are found for feasible grasping with two fingers. Local tactile information can be used to determine the finger motion that will reach feasible grasping locations. With an appropriate choice of finger stiffness, a hand can automatically grasp these objects with two fingers. The bounded slip of a part in a hand is shown to be valuable for adapting the fingers and object to a stable situation. Examples are given to show the ability of this grasping method to accomodate disturbance forces and to perform simple part reorientations and regrasping operations.

This work follows the design, prototyping and implementation of an automatic part loading and unloading system for use in thread rolling of aerospace fasteners. The thread rolling automation system is designed to function as part of a multi-process workcell, which emphasizes adaptability and ease of implementation. Design of the thread rolling automation facilitates the development of a universal gripping system, which is designed to grasp a large variety of fastener styles and sizes with a minimum of tooling changeover. A novel grasping model is developed to predict the error tolerance of the proposed gripping system design, which is validated experimentally. The proposed gripper and automation system are prototyped and tested, and shown to perform reliably with a wide range of fastener types.

No description available.

Trauma caused by grasping during laparoscopic surgery is something which will never be fully eradicated however efforts should be taken to reduce the potential to cause trauma by grasping. Tissue is often grasped with excessive forces for long periods of time during surgeries such as cholecystectomies and colectomies. This along with failed grasping actions and the occurrence of slip has been shown to damage the tissue. Design features often employed within graspers such as profiling and the occlusion mechanism of the instrument cause areas of high, uneven distribution of pressures on the tissue which can result in perforation or tissue tearing. By investigating these contributing factors, development of graspers with a low risk to cause damage this combined with actuating the grasping force should reduce the incidence of grasping trauma, currently at estimated at one incidence per procedure. These trauma events can lead to conversion to open surgery, peritonitis and even death. Development of an autonomous grasping instrument to detect and prevent slip by actuating the grasping force is reported. Piezoelectric sensors are used to detect incipient slip and slip events. A closed loop control system then reacts to these perceived slip events to prevent slip occurring by actuating the applied force by small increments to increase or decrease grasping force. This leads to a system in which only the required amount of force necessary to overcome pull force is applied to the tissue. Other areas of investigation to reduce tissue trauma are presented. In chapter 3 design features such as surface profiling and fenestrations are evaluated to determine the potential to cause damage. A variety of profiles and fenestrations are studied and each is reported by representing the applied force to retention force ratio which indicates how good the profile is at retaining tissue against a pull force. The aim of this study was to develop surface profiling which had a high retention force but a reduced number of high stress areas which can lead to tissue damage. Three new parallel action grasping designs are presented and evaluated using finite element analysis. Parallel action grasping is important in reducing tissue trauma as it distributes pressure evenly across the active grasping area as opposed to more conventional pivot style graspers which have high stress concentration areas in the proximal opening. Each area of study within the thesis addresses areas of concern which have been shown to cause tissue trauma and postulates viable solutions to reduce the incidences of tissue trauma during laparoscopic surgery with the ultimate aim of developing a deployable and autonomous grasping device which will detect and prevent slip.

La mano humana es una herramienta muy completa, capaz de adaptarse a diferentes superficies y formas, y también tocar y coger. Es una conexión directa entre el mundo exterior y el cerebro. I.Kant (filosofo alemán) definió la mano como una extensión del cerebro.En esta tesis, nosotros hemos construido una mano virtual para simular la mano humana lo más realísticamente posible. Basado en la anatomía de la mano, hemos diseñado una mano con 25 grados de libertad (DOF), con cuatro de esos grados de libertad localizados en la unión carpometacarpal, para el dedo anular y el meñique. Estos cuatro grados de libertad permiten la simulación de la mano humana cuando esta se arquea. El dedo gordo ha sido diseñado con 5 DOF, los dedos, índice y medio tienen 4 DOF, la unión metacarpofalangeal tiene dos, y las uniones interfalangeales próxima y distal tienen uno cada una. Para los dedos anular y meñique, los 4 DOF tienen las mismas uniones más los cuatro descritos arriba.El método de Denavit-Hartenberg (D-H) fue aplicado, debido a que cada dedo fue considerado como un rayo, esto es, una cadena cinemática abierta, con las uniones consideradas "revolutas". Las tablas D-H para cada dedo fueron mostradas y la aplicación de la cinemática directa e inversa permitió calcular todos los ángulos para cada unión [q1 . . . q25]T .Antes de coger cualquier objeto, nuestro sistema comprueba si el objeto esta en el espacio de la mano, mediante el análisis del espacio de trabajo.Se ha implementado un algoritmo semi-inteligente orientado a las tareas para las cuales el objeto ha sido diseñado, con el fin de tomar una decisión, una vez el usuario ha escogido el objeto y su tarea inherente. El algoritmo para coger ha sido implementado en un escenario virtual. / The human hand is the most complete tool, able to adapt to different surfaces and shapes and to touch and grasp. It is a direct connection between the exterior world and the brain. I. Kant (German philosopher) defined how the hand is an extension of the brain.In this dissertation, we built a virtual human hand to simulate the human hand as realistically as possible. Based on the anatomy of the hand, we designed a hand with 25 degrees of freedom (DOF), with four of these degrees located in the carpometacarpal joint for the ring and small fingers. These four degrees permit the simulation of the human hand when it is arched. The thumb was designed with 5 DOF, the index and middle fingers have 4 DOF, in the metacarpophalangeal joint has two, and in the proximal interphalangeal joint and in the distal interphalangeal joint each have one. For the ring and small fingers, the 4 DOF are in similar joints plus as the four described above.The Denavit-Hartenberg (D-H) method was applied because each finger was considered a ray, i.e., an open chain, with joints approximated to revolute joints. The D-H tables for each finger were shown, and the application of forward and inverse kinematics permit the calculation of all angles for each joint [q1 . . . q25]T .Before grasping any object, our system checks the reachability of the object with workspace analysis.Semi-intelligent task-oriented object grasping was implemented for making a decision once the user chooses the object and the task inherent to the object. The grasping algorithm was implemented in a virtual environment.

Although several studies have investigated the effects of aging on aspects of motor planning and control, there remains a lack of consensus about the underlying mechanisms responsible for the motor slowing associated with aging. This may, at least partially, be due to the fact that few studies have kinematically examined both the transport and grasp components in both younger and older adults, and furthermore, even fewer have examined these movements when the context of the task is changed, such as when the movement is performed in isolation compared to when it is embedded in a sequence. Therefore, the purpose of this thesis was threefold: 1) to investigate how aging affects performance on a single reach-to-grasp movement, 2) to examine how movement context affects performance on the reach-to-grasp movement when it is performed alone or as the first movement in a two-movement sequence- in other words, are older adults able to plan the first motor task movement in anticipation of performing a subsequent task, and 3) whether younger and older adults are able to plan, execute, and modify that movement in accordance with the extrinsic properties of the subsequent movement task (near versus far target for second movement). To address this, the movement profiles of both younger (N=14; mean age= 20.7 years; 4 males, 10 females) and older (N=11; mean age= 75.1 years; 3 males, 8 females) healthy right-handed adults were compared on performing a reach-to-grasp movement under 3 different movement conditions: single-movement task, two-movement sequence to near target, and two-movement sequence to far target. For the two-movement sequence conditions, participants were instructed to reach and grasp the object (like the single-movement task), but then to move and place it on either a closer (near condition) or farther (far condition) target location. Overall, the results from this study are in agreement with the literature showing older adults to have slower movements in general and consistently taking longer to both initiate and execute the reach-to-grasp movement than the younger adults for all conditions. There were no other differences between groups on the single-movement condition. For all participants, the reach-to-grasp movement took longer when it was performed in isolation than when it was embedded as the first part of a two-movement sequence. This finding can be explained by the movement termination effect and is consistent with findings from studies on aiming movements showing that when the movement plan involves stabilizing the arm at the first target (single-movement) as opposed to merely slowing it down (two-movement sequence tasks), the constraint of achieving a stabile position imposes a greater demand, thus requiring the movement iv to be made more slowly. The results obtained from the study indicate that the movement termination effect is also seen in the context of prehensile movements and furthermore, this effect on performance persists with age. Not only do the findings from this study show that this effect persists with age, but also that this effect increases with age, as revealed by a Group by Condition effect for reaction time, movement time, and relative timing of the velocity profile, indicating greater changes in reaching performance between single- and two-movement conditions for the older adults than for the younger adults. Upon further examination of the details of the movement, it is apparent this movement termination effect is reflected in the ballistic phase of the movement. This last notion is inconsistent with previous studies, which showed the increased movement time associated with the movement termination effect was the result of changes in the amount of time spent in the deceleration phase toward the end of the movement rather than the beginning of the movement. Lastly, when reach-to-grasp performance was compared between moving to a near- compared to a far-target in the two-movement conditions, no differences were found between any of the movement features for either group. This suggests that the increased proportion of time spent in deceleration for the dual-movement conditions compared to the single-movement condition in older adults is due to online feedback control for terminating the first movement rather than online planning of the second movement. Despite the changes seen in the transport component, the findings for the manipulation component indicate that the formation of the grasp and its relative coupling with the transport component remains intact with age.

<p>Primates and many other animals that move in an arboreal environment often cling, sometimes for long periods, on vertical supports. Primates, however, face a special challenge in that almost all primates bear nails on the tips of their digits rather than claws. Squirrels and other arboreal animals possess claws and/or adhesive pads on their digits in order to hold their weight on vertical substrates. Assuming the ancestral primate was arboreal and lost claws prior to the radiation of primates this paradox has important implications and raises a significant question about living primates and early primate evolution: how can primates maintain vertical postures without claws and how did early primates meet this challenge? Primate vertically clinging and grasping postures (VCG) have been studied in the wild and theoretical models of VCG postures have been described. This dissertation builds on this work, by studying the biomechanics of VCG postures in primates. Based on mechanical models, it was hypothesized VCG posture in primates will vary in three ways. </p><p>Hypothesis 1: Species with different morphological features associated with different locomotor modes will vertically cling and grasp in different ways. </p><p>Hypothesis 2: As substrate size increases, primates will place their arms to the side of the support and adjust posture and muscle recruitment in order to maintain a necessary tangential to normal force ratio to resist gravity. </p><p>Hypothesis 3: On substrates of the same relative size, larger animals should be less effective at maintaining VCG postures due to scaling relationships between muscle strength and body mass. </p><p>The sample consisted of multiple individuals from eight strepsirrhine species at the Duke Lemur Center. The sample varied in locomotor mode--habitual vertical clinging and leaping (VCL) compared to less specialized arboreal quadrupeds--and body mass--100 to 4,000 grams. Subjects were videorecorded while holding VCG postures on substrates of increasing size. Substrate preference data were calculated based on frequency and duration of VCG postures on each substrate. Qualitative kinematic data were recorded for a maximum of thirty trials per individual, per substrate. Angular data were calculated for forelimbs and hindlimbs from these videos for ten trials per individual per substrate. In addition, kinetic data from an imbedded force transducer were collected for two species that vary in locomotor mode, but not body mass. </p><p>There are several significant and relevant results from this study that address both primate functional anatomy and locomotor evolution. Hypothesis one was supported by hand and hindlimb joint postures, shown to be highly sensitive to locomotor mode. VCL primates exhibited deeply flexed limbs and more hand grasping (wrapping around the substrate) versus parallel hand postures and use of bowed finger postures compared to less specialized primates. Kinetically, species were shown to bear the majority of their weight in their hindlimbs relative to their forelimbs. The forelimb joints and foot showed little variation by habitual locomotor mode. Hypothesis two found support in that species tend to prefer smaller substrates, clinging less frequently for shorter durations as substrate size increases. Hand posture changed as size increased, as primates (except for the slow lorises) in this study grasped with their pollex on smaller substrates, but the pollex disengaged in grasping on larger substrates. Hypothesis three was not supported; body mass did not influence VCG postures. </p><p>Taken together, the finding that the forelimb held a wide range of postures on each substrate size for all species and played a limited role in weight-bearing suggests the forelimb free to move (to adjust posture and or forage). The hindlimb plays a more specific role in weight-bearing and is more sensitive to variations in primate anatomy. Additionally, these findings lead to hypotheses concerning the relatively short pollexes of primates, and that the ancestral primate was smaller than 100g and preferred small substrates as found in a fine-branch niche.</p> / Dissertation

Although several studies have investigated the effects of aging on aspects of motor planning and control, there remains a lack of consensus about the underlying mechanisms responsible for the motor slowing associated with aging. This may, at least partially, be due to the fact that few studies have kinematically examined both the transport and grasp components in both younger and older adults, and furthermore, even fewer have examined these movements when the context of the task is changed, such as when the movement is performed in isolation compared to when it is embedded in a sequence. Therefore, the purpose of this thesis was threefold: 1) to investigate how aging affects performance on a single reach-to-grasp movement, 2) to examine how movement context affects performance on the reach-to-grasp movement when it is performed alone or as the first movement in a two-movement sequence- in other words, are older adults able to plan the first motor task movement in anticipation of performing a subsequent task, and 3) whether younger and older adults are able to plan, execute, and modify that movement in accordance with the extrinsic properties of the subsequent movement task (near versus far target for second movement). To address this, the movement profiles of both younger (N=14; mean age= 20.7 years; 4 males, 10 females) and older (N=11; mean age= 75.1 years; 3 males, 8 females) healthy right-handed adults were compared on performing a reach-to-grasp movement under 3 different movement conditions: single-movement task, two-movement sequence to near target, and two-movement sequence to far target. For the two-movement sequence conditions, participants were instructed to reach and grasp the object (like the single-movement task), but then to move and place it on either a closer (near condition) or farther (far condition) target location. Overall, the results from this study are in agreement with the literature showing older adults to have slower movements in general and consistently taking longer to both initiate and execute the reach-to-grasp movement than the younger adults for all conditions. There were no other differences between groups on the single-movement condition. For all participants, the reach-to-grasp movement took longer when it was performed in isolation than when it was embedded as the first part of a two-movement sequence. This finding can be explained by the movement termination effect and is consistent with findings from studies on aiming movements showing that when the movement plan involves stabilizing the arm at the first target (single-movement) as opposed to merely slowing it down (two-movement sequence tasks), the constraint of achieving a stabile position imposes a greater demand, thus requiring the movement iv to be made more slowly. The results obtained from the study indicate that the movement termination effect is also seen in the context of prehensile movements and furthermore, this effect on performance persists with age. Not only do the findings from this study show that this effect persists with age, but also that this effect increases with age, as revealed by a Group by Condition effect for reaction time, movement time, and relative timing of the velocity profile, indicating greater changes in reaching performance between single- and two-movement conditions for the older adults than for the younger adults. Upon further examination of the details of the movement, it is apparent this movement termination effect is reflected in the ballistic phase of the movement. This last notion is inconsistent with previous studies, which showed the increased movement time associated with the movement termination effect was the result of changes in the amount of time spent in the deceleration phase toward the end of the movement rather than the beginning of the movement. Lastly, when reach-to-grasp performance was compared between moving to a near- compared to a far-target in the two-movement conditions, no differences were found between any of the movement features for either group. This suggests that the increased proportion of time spent in deceleration for the dual-movement conditions compared to the single-movement condition in older adults is due to online feedback control for terminating the first movement rather than online planning of the second movement. Despite the changes seen in the transport component, the findings for the manipulation component indicate that the formation of the grasp and its relative coupling with the transport component remains intact with age.

Magíster en Ciencias, Mención Computación / A lo largo de la historia, la humanidad se ha esforzado por desarrollar máquinas que faciliten la vida de las personas, frecuentemente concentrándose en producir máquinas autónomas que logren reemplazar a los humanos en tareas específicas. En dicho contexto, la Robótica es a menudo identificada como la disciplina que mejor simboliza el desarrollo de máquinas autónomas. En general, un robot autónomo debe exhibir al menos 3 capacidades: i) percepción de su entorno, ii) navegación y desplazamiento, e iii) interacción con su entorno. En particular, dentro de las formas interacción posibles, la manipulación de objetos es interesante, puesto que faculta al robot para modificar el ambiente de acuerdo con sus necesidades. Para que un robot pueda manipular un objeto es necesario definir una estrategia de agarre, es decir, un punto de agarre y una parametrización del efector que permita realizar el agarre según las restricciones de la tarea en ejecución. La generación de dichas estrategias es conocida como síntesis de agarres y durante la última década ha sido abordada principalmente mediante el uso de información sensorial, con el fin de identificar las características del objeto que permiten definir una estrategia de agarre adecuada. Esta tesis propone un descriptor local 3D original, denominado Directed Curvature Histograms (DCH), el cual describe la vecindad de un punto utilizando la forma en que varía la curvatura de la superficie en distintas direcciones. A diferencia de los enfoques basados en curvatura existentes en la literatura, DCH utiliza la dirección en la que varía la curvatura como un elemento significativo para la descripción de los datos. El presente trabajo también propone un método para la síntesis de agarres que utiliza DCH, combinando técnicas de aprendizaje no-supervisado y supervisado. Tal método difiere de los enfoques actuales puesto que basa sus hipótesis en el estudio del comportamiento humano en la manipulación de objetos, presentado por Feix et al. [1]. Además, el método propuesto saca provecho de la información sensorial 3D disponible, aprendiendo simultáneamente a identificar puntos de agarre adecuados, así como parametrizaciones apropiadas para manipular un objeto arbitrario. Los resultados experimentales muestran que DCH es capaz de reflejar las variaciones en la curvatura de una superficie, en diferentes direcciones. Tales resultados también muestran que la información suministrada por DCH permite que el método de síntesis de agarres propuesto pueda entrenar un clasificador (índice ROC igual a 0.961), con el objetivo de identificar los puntos de agarre y parametrizaciones adecuadas para manipular un objeto arbitrario. / Este trabajo ha sido parcialmente financiado por Proyecto FONDECYT 1140783