Advancing the Underactuated Grasping Capabilities of Single Actuator Prosthetic Hands

The last decade has seen significant advancements in upper limb prosthetics, specifically in the myoelectric control and powered prosthetic hand fields, leading to more active and social lifestyles for the upper limb amputee community. Notwithstanding the improvements in complexity and control of myoelectric prosthetic hands, grasping still remains one of the greatest challenges in robotics. Upper-limb amputees continue to prefer more antiquated body-powered or powered hook terminal devices that are favored for their control simplicity, lightweight and low cost; however, these devices are nominally unsightly and lack in grasp variety. The varying drawbacks of both complex myoelectric and simple body-powered devices have led to low adoption rates for all upper limb prostheses by amputees, which includes 35% pediatric and 23% adult rejection for complex devices and 45% pediatric and 26% adult rejection for body-powered devices [1]. My research focuses on progressing the grasping capabilities of prosthetic hands driven by simple control and a single motor, to combine the dexterous functionality of the more complex hands with the intuitive control of the more simplistic body-powered devices with the goal of helping upper limb amputees return to more active and social lifestyles. Optimization of a prosthetic hand driven by a single actuator requires the optimization of many facets of the hand. This includes optimization of the finger kinematics, underactuated mechanisms, geometry, materials and performance when completing activities of daily living. In my dissertation, I will present chapters dedicated to improving these subsystems of single actuator prosthetic hands to better replicate human hand function from simple control. First, I will present a framework created to optimize precision grasping – which is nominally unstable in underactuated configurations – from a single actuator. I will then present several novel mechanisms that allow a single actuator to map to higher degree of freedom motion and multiple commonly used grasp types. I will then discuss how fingerpad geometry and materials can better grasp acquisition and frictional properties within the hand while also providing a method of fabricating lightweight custom prostheses. Last, I will analyze the results of several human subject testing studies to evaluate the optimized hands performance on activities of daily living and compared to other commercially available prosthesis

Tribology of Skin: Review and Analysis of Experimental Results for the Friction Coefficient of Human Skin

In this review, we discuss the current knowledge on the tribology of human skin and present an analysis of the available experimental results for skin friction coefficients. Starting with an overview on the factors influencing the friction behaviour of skin, we discuss the up-to-date existing experimental data and compare the results for different anatomical skin areas and friction measurement techniques. For this purpose, we also estimated and analysed skin contact pressures applied during the various friction measurements. The detailed analyses show that substantial variations are a characteristic feature of friction coefficients measured for skin and that differences in skin hydration are the main cause thereof, followed by the influences of surface and material properties of the contacting materials. When the friction coefficients of skin are plotted as a function of the contact pressure, the majority of the literature data scatter over a wide range that can be explained by the adhesion friction model. The case of dry skin is reflected by relatively low and pressure-independent friction coefficients (greater than 0.2 and typically around 0.5), comparable to the dry friction of solids with rough surfaces. In contrast, the case of moist or wet skin is characterised by significantly higher (typically >1) friction coefficients that increase strongly with decreasing contact pressure and are essentially determined by the mechanical shear properties of wet skin. In several studies, effects of skin deformation mechanisms contributing to the total friction are evident from friction coefficients increasing with contact pressure. However, the corresponding friction coefficients still lie within the range delimited by the adhesion friction model. Further research effort towards the analysis of the microscopic contact area and mechanical properties of the upper skin layers is needed to improve our so far limited understanding of the complex tribological behaviour of human ski

Innovative robot hand designs of reduced complexity for dexterous manipulation

This thesis investigates the mechanical design of robot hands to sensibly reduce the system complexity in terms of the number of actuators and sensors, and control needs for performing grasping and in-hand manipulations of unknown objects. Human hands are known to be the most complex, versatile, dexterous manipulators in nature, from being able to operate sophisticated surgery to carry out a wide variety of daily activity tasks (e.g. preparing food, changing cloths, playing instruments, to name some). However, the understanding of why human hands can perform such fascinating tasks still eludes complete comprehension. Since at least the end of the sixteenth century, scientists and engineers have tried to match the sensory and motor functions of the human hand. As a result, many contemporary humanoid and anthropomorphic robot hands have been developed to closely replicate the appearance and dexterity of human hands, in many cases using sophisticated designs that integrate multiple sensors and actuators---which make them prone to error and difficult to operate and control, particularly under uncertainty. In recent years, several simplification approaches and solutions have been proposed to develop more effective and reliable dexterous robot hands. These techniques, which have been based on using underactuated mechanical designs, kinematic synergies, or compliant materials, to name some, have opened up new ways to integrate hardware enhancements to facilitate grasping and dexterous manipulation control and improve reliability and robustness. Following this line of thought, this thesis studies four robot hand hardware aspects for enhancing grasping and manipulation, with a particular focus on dexterous in-hand manipulation. Namely: i) the use of passive soft fingertips; ii) the use of rigid and soft active surfaces in robot fingers; iii) the use of robot hand topologies to create particular in-hand manipulation trajectories; and iv) the decoupling of grasping and in-hand manipulation by introducing a reconfigurable palm. In summary, the findings from this thesis provide important notions for understanding the significance of mechanical and hardware elements in the performance and control of human manipulation. These findings show great potential in developing robust, easily programmable, and economically viable robot hands capable of performing dexterous manipulations under uncertainty, while exhibiting a valuable subset of functions of the human hand.Open Acces

Understanding the effect of skin mechanical properties on the friction of human finger-pads

The aim of this work is to achieve an understanding of the effect of skin mechanical properties on the friction of human finger-pads. This project primarily concentrates on gaining a more fundamental understanding of the frictional properties of skin. To achieve this, various parameters (epidermis thickness, sweat-gland counts, etc.) affecting skin friction were evaluated using an in-vivo technique, Optical Coherence Tomography (OCT) and a friction testing device. This project is also interested in investigating how those parameters alter the friction for different ages, genders, ethnicities and different contact conditions, such as moisture, temperature, loads, etc. Experimental studies were conducted to investigate the skin frictional behaviour. The findings showed that the skin friction obeys a two-term relationship. The skin friction was found to be strongly associated with its Young’s modulus. Tests on the skin structural properties showed the moisture level of the skin, skin thickness and skin morphological properties play important roles in determining the skin friction. The findings gained can be applied to explain how the skin friction varies among different participants. Further tests showed that physico-chemical properties of the skin can have a significant effect on the skin friction. The OCT system was combined with a multi-axis force plate to measure the contact area between fingers and smooth surfaces. Static measurement showed both apparent and real contact area increase with normal load following a power-law relationship. This is associated with the skin mechanical properties. The dynamic contact area was investigated using a Digital Image Correlation (DIC) method. As a finger was sliding along a flat surface, the dynamic apparent contact area was found to decrease with time

Methods and Sensors for Slip Detection in Robotics: A Survey

The perception of slip is one of the distinctive abilities of human tactile sensing. The sense of touch allows recognizing a wide set of properties of a grasped object, such as shape, weight and dimension. Based on such properties, the applied force can be accordingly regulated avoiding slip of the grasped object. Despite the great importance of tactile sensing for humans, mechatronic hands (robotic manipulators, prosthetic hands etc.) are rarely endowed with tactile feedback. The necessity to grasp objects relying on robust slip prevention algorithms is not yet corresponded in existing artificial manipulators, which are relegated to structured environments then. Numerous approaches regarding the problem of slip detection and correction have been developed especially in the last decade, resorting to a number of sensor typologies. However, no impact on the industrial market has been achieved. This paper reviews the sensors and methods so far proposed for slip prevention in artificial tactile perception, starting from more classical techniques until the latest solutions tested on robotic systems. The strengths and weaknesses of each described technique are discussed, also in relation to the sensing technologies employed. The result is a summary exploring the whole state of art and providing a perspective towards the future research directions in the sector

Role of Sensation in Altered Phalanx Grip Force in Persons with Stroke

Many individuals experience hand impairment after stroke leading to decreased ability to perform daily living activities. Previous research studies have investigated how stroke survivors\u27 pinch grip control differs from healthy individuals, even though many individuals can only grasp with power grip after stroke. Furthermore, many stroke survivors experience tactile sensory deficit in their paretic limb in addition to motor deficit. It is currently unknown how stroke induced tactile sensory deficit affects power grip force directional control, which is important in terms of preventing object slippage and power grip normal force generation. Additionally it is unknown if power grip could be improved through tactile sensory enhancement. This dissertation investigated how stroke survivors\u27 power grip force control is different from healthy individuals. Also, the effect of stroke induced tactile sensory deficit on power grip force control and the benefits of a sensory enhancement method using remote subsensory vibrotactile noise on power grip phalanx force deviation was assessed. In addition, the effect of noise on the tactile sensation for stroke survivors with tactile sensory deficit and their performance on two dynamic gripping tasks, the Box and Block Test (`BBT\u27, number of blocks moved in 60 seconds) and the Nine Hole Peg Test (`NHPT\u27, time to pick up, place, and remove 9 pegs from 9 holes), were investigated. The theoretical framework of this dissertation is that tactile sensation is critical for grip control and impairment or enhancement of tactile sensation impacts power grip force control post stroke. Results showed that stroke survivors, especially those with tactile sensory deficit, gripped with increased phalanx force deviation compared to healthy individuals, showing reduced directional force control and increasing their chances of dropping objects. Remote subsensory vibrotactile noise improved fingertip and upper palm tactile sensation for stroke survivors with tactile sensory deficit. The noise also improved phalanx force directional control during power grip (reducing phalanx force deviation) for stroke survivors with and without tactile sensory deficit and age-matched healthy controls and improved the BBT score and time to complete the NHPT for stroke survivors with tactile sensory deficit. Overall, stroke survivors, particularly those with tactile sensory deficit, appear to have reduced phalanx force control during power grip, which may biomechanically result from a muscle activation pattern. Remote subsensory vibrotactile noise may have enhanced tactile sensation and hand motor control via stochastic resonance and interneuronal connections and could have potential as a wearable rehabilitation device for stroke survivors. This dissertation contributes to the long term goal of increasing stroke survivors\u27 independence in completing daily living activities