In this paper we present a methodology for optimising the design of a metamaterial structure with one degree of freedom that is able to simultaneously bend and stretch. The structure is intended for assisting flexion-extension of the wrist joint. The metamaterial is comprised of serially connected, individually designed cells. The design parameters can be chosen to optimally fit a desired planar curve such as the curvature of the skin on a plane normal to the flexion/extension axis of the wrist joint. A tool for the optimised design is described and the experimental validation of the output is conducted, to show the ability of the mechanism to conform to a 2D curve, also exhibiting a change in length, which is desirable for reducing sliding and shear on the skin. The design tool allows the generation of metamaterials optimised for a multitude of other applications where actuated mechanisms must be worn by a user for rehabilitation or assistance purposes.

Rotary Series Elastic Actuators (SEAs) are largely adopted to safely and accurately modulate interaction torques when robots operate in close contact with humans. Torque control is often based on a cascade scheme including PI regulators for a velocity controller nested in a torque controller. This solution is simple, robust and can potentially guarantee coupled stability. A high-level impedance control loop is also commonly added to regulate the behavior of the interaction port as a desired virtual viscoelastic body. In the present work, passivity is analyzed when a cascade controlled SEA is employed to display a virtual parallel spring-damper system. The case of a null desired impedance and of a pure spring are also tackled. The range of renderable mechanical impedance and guidelines for the selection of the control gains are derived.

In cyclic motions, e.g. during locomotion, part of total kinetic energy, which otherwise would be wasted during direction inversion, can be conveniently stored in elastic elements in order to be later reused. Such energy recovery strategy, which can be adopted in robotic systems to improve energetic autonomy, mimics biological solutions, where muscles, tendons and ligaments are exploited also as elastic energy buffers. The addition of compliant elements, in parallel or in series to conventional actuators, may result in complex assemblies. Conversely, compact solutions can be obtained if elasticity is embedded in the structure of the actuator. In this paper an electric rotary compliant actuator, integrating a magnetic non-linear torsion spring, is presented. The system is a parallel elastic actuator and it allows to efficiently produce oscillating motions, as needed in several biorobotic applications. The stator comprises mono-phase windings while the rotor includes permanent magnets in axial Halbach configuration. Additional magnets are advantageously located in the stator to embody the intrinsic parallel elasticity. A proof-of-concept prototype was developed, whose winding coils were designed based on magneto-static FEM simulations. The actuator was experimentally characterized and the present dynamic behavior was compared to the theoretical one calculated by considering a non-linear electro-mechanical model.

In complex dynamical tasks human motor control notably exploits the possibility of regulating joints mechanical impedance, both for stability and for energetic optimization purposes. These biomechanical findings should translate in design requirements for wearable robotics joints, which are required to produce adaptable intrinsic viscoelastic behaviors.

This paper describes the optimization of a planar wearable active orthosis for hip and knee assistance during overground walking. A non-anthropomorphic design is pursued in order to improve ergonomics and to reduce torque requirements. Based on a previously-developed systematic search algorithm of the admissible generalized solutions for the selected problem, a solution is selected and optimized by means of genetic algorithms and constrained non-linear optimization. The optimized design allows to conveniently redistribute mechanical power through different actuators, i.e. peak torque and velocity requirements for each actuator can be modulated, thus promoting a lighter design. A detailed analysis of the resulting mechanism workspace is carried out, including the evaluation of kinematic singularities, in order to verify the adequateness of the design in real-world scenarios. The developed model and optimization results are validated through a numerical analysis and experiments in a mock-up system.

This paper reports on an autonomous mobile robot embodying a simple instantiation of theDouble Hybrid Control Architecture, with a living animal in the control loop for improving robot navigational capabilities. In particular, a Carassius auratus (common Goldfish) receives a natural visual feedback from the environment, while its motor reactions, acquired by a digital camera and adequately processed, are mapped into motor commands, which are fed as inputs to the robot controller. Both the hardware and the software required for robot control is presented, as well as preliminary experimental data demonstrating the viability of the proposed approach.

The need for novel, high performance actuators felt in several fields of robotics, such as assistive or rehabilitative robotics, is not fully satisfied by current actuation means. This fosters an intense research on novel energy transduction methods. In particular, propellant-based chemical actuators, able to directly convert chemical energy into mechanical energy, appear very promising, although their potential in robotics has not yet been deeply investigated. This work focuses on H2O2, used as propellant for actuators. This chemical was first used in robotics, with excellent results, by Goldfarb and collaborators, in 2003. H2O2dissociation is strongly exothermic, which generates important design issues when the actuated machine operates in close proximity to the human body. In this paper it is shown that: 1) is possible to operate the decomposition process at acceptable temperature, by means of basic solutions of hydrogen peroxide; 2) for basic pH solutions, tin becomes an effective catalyst for H2O2dissociation. A kinetic model of H2O2dissociation in basic solutions is provided, that is in good agreement with experimental data. We show how the model can be used to gather the necessary information for the dimensioning of H2O2-based actuators.

In the design of wearable robots, the possibility of dynamically regulating the mechanical output impedance is crucial to achieve an efficient and safe human-robot interaction and to produce useful emergent dynamical behaviors. In this paper we propose a Variable Impedance Differential Actuator (VIDA) for wearable robotics applications. The system comprises two actuators (one being an impedance-controlled rotary Series Elastic Actuator) connected through a Harmonic Drive in a differential configuration used to separately control output position and mechanical impedance. Design choices regarding the overall architecture and the single components are presented and discussed. The mechanical structure also comprises a custom-made torsion spring designed after a CAD/FEM optimization. An electromechanical model of the system has been developed and a control strategy, based on the equilibrium point approach, is simulated to validate the performances of the system against system requirements. The actuation architecture allows to implement a control strategy where an equilibrium position and impedance field are simultaneously and independently regulated. This is possible still adopting very simple control laws: two controls for position and impedance regulation of the two input shafts.

Ideally, robots used for motor rehabilitation, in particular, during assessment, should minimally perturb the voluntary movements of a subject. In this paper, we show how a state-of-the-art back-drivable robot, i.e., a robot that can be moved by the user with a low perceived mechanical impedance, when used for assessment can still perturb the voluntary movements of a subject. In particular, we show that, despite its low mechanical impedance, a robot may still not comply with the intrinsic kinematic constraints, which are of neural origin and are adopted by the human brain to solve redundancy in motor tasks. Specifically, the redundant task under consideration is the 2-D pointing task, which is performed by a subject with the sole use of the wrist [3 degree of freedom (DOF) kinematics]. Wrist orientations during pointing tasks are assessed in two different scenarios. In the first experiment, a lightweight handheld device is used, which introduces no loading effect. In the second experiment, similar pointing tasks are performed with the subject interacting with a state-of-the-art robot for wrist rehabilitation. In the first case, intrinsic kinematic constraints arise as 2-D surfaces embedded in the 3-D space of wrist configuration. Such surfaces are typically subject-dependent and reveal personal motor strategies. In the second case, a strong influence of the robot is remarked. In particular, 2-D surfaces still arise but are similar for all subjects and are referable to a mechanical origin (excessive loading by the robot). The assessment approach described in this paper, including both the experimental apparatus and data-analysis method, can be used as a test for the degree of back-drivability of mechanisms and robots in relation to constraints of neural origin, thus allowing the design of robots that can actually cope with such constraints. The clinical potential impact is also discussed.

In this work, the kinematics of the human wrist during pointing tasks is assessed and discussed, especially in relation to the use of wrist robots. First, the existence of intrinsic kinematics constraints (or Donders' law, similarly to oculomotor system) for the human wrist during pointing tasks is verified. To this end, a novel approach based on a hand-held device is presented which allow assessing wrist movements without any mechanical loading. Second, similar pointing tasks are assessed by means of a state-of-the-art wrist robot, typically used in robot-mediated therapy as well as assessment tool. By comparing experimental results relative to the pointing task performed by healthy subjects with the hand-held device and with the robot, a loading effect on the performance due to the mechanisms of the robot is remarked. A functional requirement for the next generation of rehabilitation robots is thus provided.

This paper presents the design criteria of a robot manipulator for the rehabilitation of the upper limb. The machine is conceived to optimize the dynamic behavior in the interaction with the patient, basically in terms of low impedance when back-driven and low and isotropic inertial properties. Robot kinematics and dynamics are mathematically modeled and its dynamic properties are measured in the workspace in terms of inertia and acceleration capabilities. A method is used that is borrowed from the literature and is based on inertia and acceleration graphical representation through ellipsoids.

This paper presents the design of a novel sensor for slip detection. It consists of an easily fabricated miniaturized thermal probe that senses the additional convective heat transfer associated with the occurrence of mechanical slip. The fabrication procedures and the operating principle for the device are described in detail. A simple experimental setup was used to test the effectiveness of the proposed device. Tests were performed with varying velocities on four materials of differing thermal properties and surface roughnesses. The results show that slip can be effectively detected by the proposed sensor with a response times which can be as low as 6.3 ms. The performance of the device can be further improved when used in conjunction with a separate pressure sensor and by using more accurate methods of electrical resistance measurement.

This paper presents a new biphasic electrofluidic rotary actuator relying on electrochemical mechanisms. Gas (H2and O2) is generated at two platinum (Pt) electrodes, immersed in an electrolytic solution, when a low voltage, V, is applied to them. The generated gas pressurizes a closed elastomeric chamber, that deforms under the action of the applied pressure. The chamber is shaped so that no structural failure occurs and the desired output motion is produced, without any need for additional mechanical means such as motion converters. Simple thermodynamic considerations allow estimating the electromechanical coupling factors for the most common external loads.

Movement and behavior analysis is a key research area in the domain of biomedical engineering and in many other medical research domains aiming at the understanding of physiological motor and cognitive basic mechanisms. The systematic application of robotic and mechatronic technologies to realize new tools and measurement methods for quantitatively assessing motor and cognitive functions in humans as well as in animal models is gaining an increasing popularity. This work represents a first step towards the development of a sensorised environment for behavioral phenotyping of animal models. In particular, this paper focuses on tremor analysis in reeler mice, an emerging potential animal model for anatomical and behavioral traits observed in autism. Ground reaction force (GRF) sensing is indeed the most direct means of measuring tremor. Although force platforms have extensively been used for large size animals, only few attempts have been made to measure GRF at a single paw for animals as small as mice or rats. Under the hypothesis that in-plane GRF components are directly connected to tremor, a small size, low-cost, 2-axis force sensor for measuring the in-plane components of GRF was designed and developed. Special care was paid to design a structure that would allow self-aligned assembly, for repeatability, and modularity for combining multiple platforms for a sensorised floor. Preliminarily testing was performed with both reeler and wildtype mice. Fourier analysis was deployed to extract information due to tremor, validating the hypothesis of a direct connection between tremor and in-plane GRFs.