The scope of this work is to show the applicability of the Twisted String Actuators (TSAs) for lightweight, wear- able and assistive robotic applications. To this aim, we have developed a novel surface electromyography (sEMG)-driven soft ExoSuit using the TSAs to perform both single and dual- arm elbow assistive applications. The proposed ExoSuit, with an overall weight of 1650g, uses a pair of TSAs mounted in the back of the user, connected via tendons to the user's forearms to actuate each arm independently for supporting external loads. We confirm this new light-weight and customizable wearable solution via multiple user studies based on the biceps and tricep’ sEMG measurements. We demonstrate that user muscles can automatically activate and regulate the TSAs and compensate for the user's effort: by using our controller based on a Double Threshold Strategy (DTS) with a standard PID regulator, we report that the system was able to limit the biceps’ sEMG activity under an arbitrary target threshold, compensating a muscular activity equal to 220% (related to a single arm 3kg load) and 110% (related to a dual arm 4kg load) of the threshold value itself. Moreover, the triceps’ sEMG signal detects the external load and, depending on the threshold, returns the system to the initial state where it requires no assistance from the ExoSuit. The experimental results show the proposed ExoSuit's capabilities in both single and dual- arm load compensation tasks. Therefore, the applicability of the TSAs is experimentally demonstrated for a real-case assistive device, fostering future studies and developments of this kind of actuation strategy for wearable robotic systems.

This paper presents a controller design to compensate the effects of time delay in a flexure-based piezoelectric stack driven nanopositioner. The effects of the time delay in flexure nanopositioners is illustrated and identified by means of experimentally obtaining the frequency response of the system. Moreover, a theoretical model which takes into account the dependence between the sampling time and the delay introduced is proposed. The proposed control design methodology not only accommodates for time delay but also ensures the robust stability and allows its application to systems with a larger delay than other schemes proposed previously. Limitations and future work are discussed.

We propose a new control approach for the twisted string actuation (TSA) system; a hybrid control scheme consisting of two nested loops, considering the motor angle and the axial force at the clamping point of the actuator as the system outputs. We show that measuring the axial force at the base of the actuator, we can effectively estimate and compensate the coupling torque between the motor and the external load. Then, compensation of the coupling torque allows formulating a linear control law to control the angular position of the actuator and, at the same time, implement an external control loop to regulate the force applied by the actuator. Simulated and experimental results validate the proposed original control scheme. Furthermore we highlight the contributions of this work in the broader context of control of twisted string actuators.

This paper presents a climbing robot with wheeled locomotion which uses permanent magnets as adhesion mechanism. The robot designed is intended for the inspection of various types of ferromagnetic structures, such as ship hulls, wind turbine towers, bridges, and fuel tanks, in order to detect surface faults or cracks caused by, for example aging or atmospheric corrosion. The proposed robotic system consists of a cordless teleoperated mobile platform which can move on vertical ferromagnetic walls. The robot can be equipped with the various testing probes and cameras that are necessary for different inspection tasks. First, different prototypes of magnetic wall climbing robots are analyzed in order to establish the current state-of-the-art, and to provide the background required to analyse the main advantages and drawbacks of the prototypes presented. The design of the proposed robotic system is then explained, and details are provided of the new approach for the design of the permanent magnetic adhesion mechanism. Finally the mechanical and electrical construction, the control architecture implemented, and the human-machine interface for its control and teleoperation are presented too.

Vibrations are present in many mechanical structures and machines, and are often associated with their elastic parts. Characterizing these vibrations, i.e., obtaining their frequencies, amplitudes and phases, is of most interest in many applications ranging from the maintenance of civil structures to motion control. This paper presents a method for the online and reliable identification of the defining parameters of two unknown sinusoidal signals through the use of their measured sum in the presence of noise and an offset. It is based on the algebraic derivative approach, defined in the frequency domain, which yields exact calculation formulae for the unknown parameters of the signal, i.e., the amplitudes, phases, and frequencies of the two sinusoids and the value of the constant term. The online estimation is performed in a time interval which is only a fraction of the first full cycle of the slower component of the measured signal. This feature allows the algorithm to be used to monitor time-varying parameters in these vibration signals. This algorithm has been used in experiments with a flexible beam, which is a representative platform of a vibrating mechatronic system. It estimated all the vibration signal parameters quickly and accurately, proved to be insensitive to high-frequency noises, and accurately tracked the time variations of the signal parameters.