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

Highly Manoeuvrable Eversion Robot Based on Fusion of Function with Structure

Despite their soft and compliant bodies, most of today’s soft robots have limitations when it comes to elongation or extension of their main structure. In contrast to this, a new type of soft robot called the eversion robot can grow longitudinally, exploiting the principle of eversion. Eversion robots can squeeze through narrow openings, giving the possibility to access places that are inaccessible by conventional robots. The main drawback of these types of robots is their limited bending capability due to the tendency to move along a straight line. In this paper, we propose a novel way to fuse bending actuation with the robot’s structure. We devise an eversion robot whose body forms both the central chamber that acts as the backbone as well as the actuators that cause bending and manoeuvre the manipulator. The proposed technique shows a significantly improved bending capability compared to externally attaching actuators to an eversion robot showing a 133% improvement in bending angle. Due to the increased manoeuvrability, the proposed solution is a step towards the employment of eversion robots in remote and difficult-to-access environments

Design of Generalized Fiber-reinforced Elasto-fluidic Systems.

From nature to engineered solutions, the metrics of mechanical systems are often strength, power density, resilience, adaptability, safety, scalability, and the ability to generate the necessary forces, motions, and forms. The use of fluidic structures with fiber reinforcement to realize these metrics is seen throughout nature; however, these structures are rarely used by engineers, in part due to the absence of a generalized understanding of their kinematics and forces. Fiber-reinforced elasto-fluidic systems use fluid pressure to actuate an envelope with tuned compliance to provide desired motion, forces, flexibility, and transmission of energy. These structures combine the high strain energy utilization and flexibility of fibers, the versatility and compressive load abilities of fluids, and the continuum nature of soft materials, exploiting the best features of each. This dissertation discovered a vast array of previously unknown fiber-reinforced elasto-fluidic systems, models their mechanical behavior, experimentally verifies the models, creates methods for easy design synthesis, and applies this knowledge to multiple practical applications. Only a small subset of elasto-fluidic systems, popularly known as McKibben actuators, has been thoroughly investigated. Therefore, a vast design space of possible structures with multiple sets of fibers and different orientations yielding a rich array of functionality were yet to be investigated and applied to a wealth of applications. This dissertation develops the mechanics of generalized fiber-reinforced elasto-fluidic systems by first modeling the relationship of volume change and fiber orientation to motion kinematics and force generation. The kinematics of motions including translation, rotation, screw, bending, and helical were all modeled. Fiber configurations spanning the design space were tested to experimentally verify the predicted forces and motion. The force and kinematics were combined to form a design synthesis tool that maps the desired motions, freedoms, and constraints to fiber configurations. Synthesis methods were created for parallel combination of fiber-reinforced structures using discretized force and freedom directions. Lastly, novel applications were created using these fiber-reinforced elasto-fluidic structures, including an orthosis device for arm rotation contractures, a soft hexapod robot with an actuated flexible spine, and a structure for anchoring within pipes.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107202/1/joshbm_1.pd

Hybrid fluidic actuation for a foam-based soft actuator

Actuation means for soft robotic structures are manifold: despite actuation mechanisms such as tendon-driven manipulators or shape memory alloys, the majority of soft robotic actuators are fluidically actuated - either purely by positive or negative air pressure or by hydraulic actuation only. This paper presents the novel idea of employing hybrid fluidic - hydraulic and pneumatic - actuation for soft robotic systems. The concept and design of the hybrid actuation system as well as the fabrication of the soft actuator are presented: Polyvinyl Alcohol (PVA) foam is embedded inside a casted, reinforced silicone chamber. A hydraulic and pneumatic robotic syringe pump are connected to the base and top of the soft actuator. We found that a higher percentage of hydraulics resulted in a higher output force. Hydraulic actuation further is able to change displacements at a higher rate compared to pneumatic actuation. Changing between Hydraulic:Pneumatic (HP) ratios shows how stiffness properties of a soft actuator can be varied

Modeling, Reduction, and Control of a Helically Actuated Inertial Soft Robotic Arm via the Koopman Operator

Soft robots promise improved safety and capability over rigid robots when deployed in complex, delicate, and dynamic environments. However, the infinite degrees of freedom and highly nonlinear dynamics of these systems severely complicate their modeling and control. As a step toward addressing this open challenge, we apply the data-driven, Hankel Dynamic Mode Decomposition (HDMD) with time delay observables to the model identification of a highly inertial, helical soft robotic arm with a high number of underactuated degrees of freedom. The resulting model is linear and hence amenable to control via a Linear Quadratic Regulator (LQR). Using our test bed device, a dynamic, lightweight pneumatic fabric arm with an inertial mass at the tip, we show that the combination of HDMD and LQR allows us to command our robot to achieve arbitrary poses using only open loop control. We further show that Koopman spectral analysis gives us a dimensionally reduced basis of modes which decreases computational complexity without sacrificing predictive power.Comment: Submitted to IEEE International Conference on Robotics and Automation, 202

Utilization of Kirigami Skins as a Method of Creating Bespoke Soft Pneumatic Actuators

Soft pneumatic actuators have many applications in robotics and adaptive structures. Traditionally, these actuators have been constructed by wrapping layers of reinforcing helical fibers around an elastomeric tube. This approach is versatile and robust, but it suffers from a critical dis-advantage: cumbersome fabrication procedures. Wrapping long helical filaments around a cylindrical tube requires expensive equipment or excessive manual labor. To address this issue, we propose a new approach towards designing and constructing pneumatic actuators by exploiting the principle of kirigami, the ancient art of paper cutting. More specifically, we use “kirigami skins”—plastic sleeves with carefully arranged slit cuts—to replace the reinforcing helical fibers. This paper presents an initial investigation on a set of linear extension actuators featuring kirigami skins with a uniform array of cross-shaped, orthogonal cuts. When under internal pressurization, the rectangular-shaped facets defined by these cuts can rotate and induce the desired extension motion. Through extensive experiments, we analyze the elastic and plastic deformations of these kirigami skins alone under tension. The results show strongly nonlinear behaviors involving both in-plane facet rotation and out-of-plane buckling. Such a deformation pattern offers valuable insights into the actuator’s performance under pressure. Moreover, both the deformation characteristics and actuation performance are “programmable” by tailoring the cut geometry. A computational model was developed to predict the deformation pattern of the kirigami skins. This study lays down the foundation for constructing more capable Kirigami-skinned soft actuators that can achieve sophisticated motions. Additional design variables were implemented into the kirigami patterns to generate for rectangular and rhomboid elements. A kirigami skin defined by these parameters can produce a wide range of actuation patterns