Safe and effective physical human-robot interaction: Approaches to variable compliance via soft joints and soft grippers

The work described in this thesis focusses on designing and building two novel physical devices in a robotic arm structure. The arm is intended for human-robot interaction in the domestic assistive robotics area. The first device aims at helping to ensure the safety of the human user. It acts as a mechanical fuse and disconnects the robotic arm link from its motor in case of collision. The device behaves in a rigid manner in normal operational times and in a compliant manner in case of potentially harmful collisions: it relies on a variable compliance. The second device is the end-effector of the robotic arm. It is a novel grasping device that aims at accommodating varying object shapes. This is achieved by the structure of the grasping device that is a soft structure with a compliant and a rigid phase. Its completely soft structure is able to mould to the object's shape in the compliant phase, while the rigid phase allows holding the object in a stable way.In this study, variable compliance is defined as a physical structure's change from a compliant to a rigid behaviour and vice versa. Due to its versatility and effectiveness, variable compliance has become the founding block of the design of the two devices in the robot arm physical structure. The novelty of the employment of variable compliance in this thesis resides in its use in both rigid and soft devices in order to help ensure both safety and adaptable grasping in one integrated physical structure, the robot arm.The safety device has been designed, modelled, produced, tested and physically embedded in the robot arm system. Compared to previous work in this field, the feature described in this thesis' work has a major advantage: its torque threshold can be actively regulated depending on the operational situation. The threshold torque is best described by an exponential curve in the mathematical model while it is best fit by a second order equation in the experimental data. The mismatch is more considerable for high values of threshold torque. However, both curves reflect that threshold torque magnitude increases by increasing the setting of the device. Testing of both the passive decoupling and active threshold torque regulation show that both are successfully obtained. The second novel feature of the robot arm is the soft grasping device inspired by hydrostatic skeletons. Its ability to passively adapts to complex shapes objects, reduces the complexity of the grasping action control. This gripper is low-cost, soft, cable-driven and it features no stiff sections. Its versatility, variable compliance and stable grasp are shown in several experiments. A model of the forward kinematics of the system is derived from observation of its bending behaviour.Variable compliance has shown to be a very relevant principle for the design and implementation of a robotic arm aimed at safely interacting with human users and that can reduce grasp control complexity by passively adapting to the object's shape

Active soft end effectors for efficient grasping and safe handling

The end effector is a major part of a robot system and it defines the task the robot can perform. However, typically, a gripper is suited to grasping only a single or relatively small number of different objects. Dexterous grippers offer greater grasping ability but they are often very expensive, difficult to control and are insufficiently robust for industrial operation. This paper explores the principles of soft robotics and the design of low-cost grippers able to grasp a broad range of objects without the need for complex control schemes. Two different soft end effectors have been designed and built and their physical structure, characteristics and operational performances have been analysed. The soft grippers deform and conform to the object being grasped, meaning they are simple to control and minimal grasp planning is required. The soft nature of the grippers also makes them better suited to handling fragile and delicate objects than a traditional rigid gripper

Autistic traits affect interpersonal motor coordination by modulating strategic use of role-based behavior

Background: Despite the fact that deficits in social communication and interaction are at the core of Autism Spectrum Conditions (ASC), no study has yet tested individuals on a continuum from neurotypical development to autism in an on-line, cooperative, joint action task. In our study, we aimed to assess whether the degree of autistic traits affects participants' ability to modulate their motor behavior while interacting in a Joint Grasping task and according to their given role. Methods: Sixteen pairs of adult participants played a cooperative social interactive game in which they had to synchronize their reach-to-grasp movements. Pairs were comprised of one ASC and one neurotypical with no cognitive disability. In alternate experimental blocks, one participant knew what action to perform (instructed role) while the other had to infer it from his/her partner’s action (adaptive role). When in the adaptive condition, participants were told to respond with an action that was either opposite or similar to their partner. Participants also played a non-social control game in which they had to synchronize with a non-biological stimulus. Results: In the social interactive task, higher degree of autistic trait s predicted less ability to mod ulate joint action according to one’s interactive role. In the non-social task, autistic traits did not predict differences in movement preparation and planning, thus ruling out the possibility that social interact ive task results were due to basic motor or executive function difficulties. Furthermore, when participants played the non-social game, the higher their autistic traits, the more they were interfered by the non-biological stimulus. Conclusions: Our study shows for the first time that high autistic traits predict a stereotypical interaction style when individuals are required to modulate their movements in order to coordinate with their partner according to their role in a joint action task. Specifically, the infrequent emergence of role-based motor behavior modulation during on-line motor cooperation in participants with high autistic traits sheds light on the numerous difficulties ASC have in nonverbal social interaction

Optimal Navigation Functions for Nonlinear Stochastic Systems

This paper presents a new methodology to craft navigation functions for nonlinear systems with stochastic uncertainty. The method relies on the transformation of the Hamilton-Jacobi-Bellman (HJB) equation into a linear partial differential equation. This approach allows for optimality criteria to be incorporated into the navigation function, and generalizes several existing results in navigation functions. It is shown that the HJB and that existing navigation functions in the literature sit on ends of a spectrum of optimization problems, upon which tradeoffs may be made in problem complexity. In particular, it is shown that under certain criteria the optimal navigation function is related to Laplace's equation, previously used in the literature, through an exponential transform. Further, analytical solutions to the HJB are available in simplified domains, yielding guidance towards optimality for approximation schemes. Examples are used to illustrate the role that noise, and optimality can potentially play in navigation system design.Comment: Accepted to IROS 2014. 8 Page

On Neuromechanical Approaches for the Study of Biological Grasp and Manipulation

Biological and robotic grasp and manipulation are undeniably similar at the level of mechanical task performance. However, their underlying fundamental biological vs. engineering mechanisms are, by definition, dramatically different and can even be antithetical. Even our approach to each is diametrically opposite: inductive science for the study of biological systems vs. engineering synthesis for the design and construction of robotic systems. The past 20 years have seen several conceptual advances in both fields and the quest to unify them. Chief among them is the reluctant recognition that their underlying fundamental mechanisms may actually share limited common ground, while exhibiting many fundamental differences. This recognition is particularly liberating because it allows us to resolve and move beyond multiple paradoxes and contradictions that arose from the initial reasonable assumption of a large common ground. Here, we begin by introducing the perspective of neuromechanics, which emphasizes that real-world behavior emerges from the intimate interactions among the physical structure of the system, the mechanical requirements of a task, the feasible neural control actions to produce it, and the ability of the neuromuscular system to adapt through interactions with the environment. This allows us to articulate a succinct overview of a few salient conceptual paradoxes and contradictions regarding under-determined vs. over-determined mechanics, under- vs. over-actuated control, prescribed vs. emergent function, learning vs. implementation vs. adaptation, prescriptive vs. descriptive synergies, and optimal vs. habitual performance. We conclude by presenting open questions and suggesting directions for future research. We hope this frank assessment of the state-of-the-art will encourage and guide these communities to continue to interact and make progress in these important areas

Analysis and Experiments for Tendril-Type Robots

New models for the Tendril continuous backbone robot, and other similarly constructed robots, are introduced and expanded upon in this thesis. The ability of the application of geometric models to result in more precise control of the Tendril manipulator is evaluated on a Tendril prototype. We examine key issues underlying the design and operation of \u27soft\u27 robots featuring continuous body (\u27continuum\u27) elements. Inspiration from nature is used to develop new methods of operation for continuum robots. These new methods of operation are tested in experiments to evaluate their effectiveness and potential

A New Approach to Dynamic Modeling of Continuum Robots

ABSTRACT In this thesis, a new approach for developing practically realizable dynamic models for continuum robots is proposed. Based on the new dynamic models developed, a novel technique for analyzing the capabilities of continuum manipulators to be employed in various real world applications has also been proposed and developed. A section of a continuum arm is modeled using lumped model elements (masses, springs and dampers). It is shown that this model, although an approximation to a continuum structure, can be used to conveniently analyze the dynamics of the arm with suitable tradeoff in accuracy of modeling. This relatively simple model is more plausible to implement in an actual real-time controller when compared to other techniques of modeling continuum arms. Principles of Lagrangian dynamics are used to derive the expressions for the generalized forces in the system. The force exerted by McKibben actuators at different pressure level - length pairs is characterized and is incorporated into this dynamic model. The constraints introduced in the analytical model conform to the physical and operational limitations of the Octarm VI continuum robot manipulator. The model is validated by comparing the results of numerical simulation with the physical measurements of a continuum arm prototype built using McKibben actuators. Based on the new lumped parameter dynamic model developed for continuum robots, a technique for deducing measures of manipulability, forces and impacts that can be sustained or imparted by the tip of a continuum robot has been developed. These measures are represented in the form of ellipsoids whose volume and orientation gives information about the various functional capabilities (end effector velocities, forces and impacts) of the arm at a particular configuration. The above mentioned ellipsoids are exemplified for different configurations of the continuum section arm and their physical significances are analyzed. The new techniques proposed and methodologies adopted in this thesis supported by experimental results represent a significant contribution to the field of continuum robots

The Hydra Hand: A Mode-Switching Underactuated Gripper with Precision and Power Grasping Modes

Human hands are able to grasp a wide range of object sizes, shapes, and weights, achieved via reshaping and altering their apparent grasping stiffness between compliant power and rigid precision. Achieving similar versatility in robotic hands remains a challenge, which has often been addressed by adding extra controllable degrees of freedom, tactile sensors, or specialised extra grasping hardware, at the cost of control complexity and robustness. We introduce a novel reconfigurable four-fingered two-actuator underactuated gripper -- the Hydra Hand -- that switches between compliant power and rigid precision grasps using a single motor, while generating grasps via a single hydraulic actuator -- exhibiting adaptive grasping between finger pairs, enabling the power grasping of two objects simultaneously. The mode switching mechanism and the hand's kinematics are presented and analysed, and performance is tested on two grasping benchmarks: one focused on rigid objects, and the other on items of clothing. The Hydra Hand is shown to excel at grasping large and irregular objects, and small objects with its respective compliant power and rigid precision configurations. The hand's versatility is then showcased by executing the challenging manipulation task of safely grasping and placing a bunch of grapes, and then plucking a single grape from the bunch.Comment: This paper has been accepted for publication in IEEE Robotics and Automation Letters. For the purpose of open access, the author(s) has applied a Creative Commons Attribution (CC BY) license to any Accepted Manuscript version arising. 8 pages, 11 figure