Chris May

Modeling and Control of the Twisted String Actuation System

The innovative actuation concept presented in this paper allows the implementation of powerful, simple, compact, and light-weight tendon-based driving systems, using as actuators small-size dc motors characterized by high speed and low torque. Due to its properties, this actuation system is very well suited for implementation in highly integrated robotic devices. The basic working principle of this novel actuation system is introduced, and the constitutive equations of the system are given, together with their experimental validation. Driven by the necessity of controlling the actuation force in the robotic hand, the problem of tracking a desired force profile is tackled. With the aim of guaranteeing a high level of robustness against disturbances, a control algorithm based on a second-order sliding manifold has first been evaluated by means of simulations and then validated by experiments. The results obtained with this simple and compact actuation system demonstrate its suitability for use in robotic devices such as robotic hands.

The twisted string actuation system: Modeling and control

This paper describes a novel actuation system for very compact and light-weight robotic devices, like artificial hands. The actuation concept presented here allows the implementation of powerful tendon-based driving systems, using as actuators small-size DC motors characterized by high speed and low torque. After the presentation of the basic concept of this novel actuation system, the constitutive equations of the system are given, validated by means of laboratory tests. Moreover, the problem of tracking a desired actuation force profile is taken into account, considering as load a mass-spring-damper system. A control algorithm based on a second-order sliding manifold has been firstly evaluated by means of simulations, and then validated by experiments. This output-feedback controller has been chosen to guarantee a high level of robustness against disturbances, parameter variations and uncertainties while maintaining a low computational burden.

The DEXMART hand: Mechatronic design and experimental evaluation of synergy-based control for human-like grasping

This paper summarizes recent activities carried out for the development of an innovative anthropomorphic robotic hand called the DEXMART Hand. The main goal of this research is to face the problems that affect current robotic hands by introducing suitable design solutions aimed at achieving simplification and cost reduction while possibly enhancing robustness and performance. While certain aspects of the DEXMART Hand development have been presented in previous papers, this paper is the first to give a comprehensive description of the final hand version and its use to replicate human-like grasping. In this paper, particular emphasis is placed on the kinematics of the fingers and of the thumb, the wrist architecture, the dimensioning of the actuation system, and the final implementation of the position, force and tactile sensors. The paper focuses also on how these solutions have been integrated into the mechanical structure of this innovative robotic hand to enable precise force and displacement control of the whole system. Another important aspect is the lack of suitable control tools that severely limits the development of robotic hand applications. To address this issue, a new method for the observation of human hand behavior during interaction with common day-to-day objects by means of a 3D computer vision system is presented in this work together with a strategy for mapping human hand postures to the robotic hand. A simple control strategy based on postural synergies has been used to reduce the complexity of the grasp planning problem. As a preliminary evaluation of the DEXMART Hand’s capabilities, this approach has been adopted in this paper to simplify and speed up the transfer of human actions to the robotic hand, showing its effectiveness in reproducing human-like grasping.

Innovative Technologies for the Next Generation of Robotic Hands

With the aim of reproducing the grasping and manipulation capabilities of humans, many robotic devices have been developed all over the world in more than 50 years of research, starting from very simple grippers, normally used in industrial activities, to very complex anthropomorphic robotic hands. Unfortunately, the reduced functionality and/or reliability of the devices developed so far prevent, together with the cost, their usability in unstructured environments, and in particular in human everyday activities. The adoption of design solutions inherited from conventional mechanics and the lack of purposely developed sensors and actuators are among the main causes of the partial fail in achieving the final goal of reproducing human manipulation capabilities. Our research activity aims at developing innovative solutions concerning the mechanical design, the sensory equipment and the actuation system for the implementation of anthropomorphic robotic hands with improved reliability, functionality and reduced complexity and cost, considering also aspects related to safety during human–robot interaction, paving the way toward the next generation of robotic hands.

Modelling and control of a smart auxiliary mass damper equipped with a bragg grating

This paper presents the results of a key activity of a large research project in the aeronautics field, funded by the European Community under the Sixth Framework Programme, namely the modelling and control of a magnetostrictive actuator to be used for broadband vibration and noise control. The developed auxiliary mass damper is designed in order to meet the demanding requirements of the application at hand, especially in terms of weight reduction and force capability. The specifications are successfully satisfied using an inertial resonant actuator concept based on a nonlinear amplification mechanism of the seismic mass displacement. The nonlinearities of the actuator highly affect the problem of its adoption within the active feedback control system devoted to vibration and noise reduction of the controlled structure. In order to overcome the limitation and negative effects of these nonlinearities within the main control system, the actuator is equipped with an optical sensor based on a Bragg grating used for a low-level control loop aimed at imposing a desired linear behaviour to the actuator itself. A preliminary modelling and characterization of the dynamic behaviour of the actuator is performed taking into account also the hysteretic nonlinearity exhibited by the active material as well as the nonlinear dynamics of the mechanical actuator structure. A model-following control algorithm, designed on the basis of an experimentally identified dynamic model, is adopted as the low-level control algorithm. Experimental results show the effectiveness of the approach and its validity as the first step to be taken during the design phase of the complete noise and vibration control system.

Modeling, identification and control of a force generator for vibration attenuation

This paper presents a smart force generator for vibration attenuation based on magnetostrictive material. After introducing the basic concepts, the paper develops a detailed mathematical model, and discusses its main properties. Then, a simplified linear model is identified for control design purposes. Finally, a gain scheduling control algorithm for the suppression of tonal disturbance is presented and experimental results are discussed.

A Pendulum Actuator and Its Force Generation Capabilities

This paper presents the construction and properties of a so-called pendulum actuator used for generating dynamic forces. The discussion illustrates that this type of actuator can potentially cover a wide field of applications. Generating harmonic force signals, however, demands special provisions due to the inherent non-linear kinematics of the actuator device. The paper explains the selected measures and presents the achieved results.© 2009 ASME

Generating periodic forces with the pendulum actuator

This paper presents the construction, modeling and properties of a compact, efficient electro-mechanical device called a ‘pendulum actuator’, used for generating periodic dynamic forces. Essentially, the device is composed of a transducer based on a smart material (e.g., a piezoelectric stack or a magnetostrictive rod), placed in a mechanical structure dedicated to hosting the electric or magnetic circuit for transducer excitation, and the mechanical displacement amplifier. This type of actuator can potentially cover a wide range of applications, but it also presents some fundamental challenges. In particular, generating periodic force signals demands special provisions due to the inherent nonlinear kinematics of the actuator device. This paper illustrates the potential and the limits of the device by developing an accurate mathematical model and presenting an extensive experimental investigation.

Adaptronischer Schwingungsabsorber für einen weiten Einsatzbereich Adaptronic Vibration Absorber for a Wide Field of Applications

Abstract In vielen mechanischen Strukturen unserer technisierten Umwelt kommen unerwünschte, fremd- oder selbsterregte Schwingungen vor, die im Hinblick auf geringere Umweltbelastung und höhere Lebensdauer reduziert werden müssen. Dieses Ziel lässt sich häufig mit Hilfe von Schwingungsabsorbern erreichen, die dem schwingenden Hauptsystem entweder kinetische Energie entziehen oder gegenphasige Kompensationskräfte in die Struktur einleiten; dem entsprechend unterscheidet man passive und aktive Absorber. Der vorliegende Beitrag zeigt am Beispiel eines Hilfsmassedämpfers, wie beide Absorberklassen unter Anwendung des adaptronischen Konzepts und durch Einsatz aktiver Werkstoffe in einer einzigen kompakten Baueinheit realisiert werden können. An einer konkreten Anwendung wird abschließend demonstriert, dass sich hiermit auch zeitlich veränderliche Frequenzkomponenten von Strukturschwingungen breitbandig dämpfen lassen.