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Editorial - Since the official registration of the word “Mechatronics” as a trademark by Yaskawa Electric Corporation in 1971, explosive growth has been observed in mechatronics research and product development activities. Nowadays, mechatronics and mechatronic design methodologies play increasingly important roles in computer, communication, control, and consumer product (4C) technologies. As such, it is fair to agree that mechatronics technology has profoundly affected almost all aspects of human life, particularly, of engineering realities ranging from rehabilitation devices to ground and underwater robots, and from unmanned aerial vehicles to intelligent manufacturing facilities, constituting a rapidly progressing frontline.

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.

The interest in actuators based on dielectric elastomer films as a promising technology in robotic and mechatronic applications is increasing. The overall actuator performances are influenced by the design of both the active film and the film supporting frame. This paper presents a single-acting actuator, which is capable of supplying a constant force over a given range of motion. The actuator is obtained by coupling a rectangular film of silicone dielectric elastomer with a monolithic frame designed to suitably modify the force generated by the dielectric elastomer film. The frame is a fully compliant mechanism whose main structural parameters are calculated using a pseudo-rigid-body model and then verified by finite element analysis. Simulations show promising performance of the proposed actuator.

This article presents a finite-deformation fully-coupled thermo-electro-elastic continuum model that is suited for the analysis, design, and control of solid-state transduction devices based on electrostrictive elastomers. In the model, electrostrictive elastomers are considered as isotropic modified-entropic hyperelastic dielectrics that deform in response to a simultaneous combination of electrical, thermal, and mechanical stimuli. The model is thermodynamically consistent and comprises general balance equations, which do not require the postulation of any force or stress tensor of electrical origin, together with phenomenological invariant-based constitutive relations, which necessitate the minimum number of material parameters to be determined via experimental tests only. Comparison with existing theories and experimental results are provided that validate the proposed thermo-electro-elastic model.

In this paper, a quantitative comparison is made between straight beam and curved beam flexures for application on selectively compliant mechanisms. Following a general procedure previously described in the literature, the closed-form compliance equations for both flexural hinges are firstly derived. Then, the two morphologies are compared in terms of maximum achievable rotation and selective compliance (i.e. capability of providing low stiffness along a single desired direction). In particular, the performance of each design solution is quantified by means of purposely defined quality indexes, analytically computed on the basis of the hinges compliance matrix. Finally, the potentials of these types of flexures for the optimal design of compliant robotic fingers are critically discussed.

A continuum model is described for the study of the electro-elastic finite deformations of dielectric elastomers. The model: i) derives directly from a global energy balance; ii) does not require the postulation of any force or stresstensor of electrical origin; iii) only requires the knowledge of permittivity and shear moduli of the considered material; and iv) is presented in Lagrangian form which is suited for the implementation in multi-physic finite element simulation environments.

A continuum finite-deformation model is described for the study of the isothermal electro-elastic deformations of electrostrictive elastomers. The model comprises general balance equations of motion, electrostatics and electro-mechanical energy, along with phenomenological invariant-based constitutive relations. The model is presented in both Eulerian (spatial) and Lagrangian (material) description. Specialization of the considered model is also presented for “Dielectric Elastomers”, which are a specific class of electrostrictive elastomers having dielectric properties independent of deformation.

Constant-force actuators based on dielectric elastomers can be obtained by coupling a dielectric elastomer film with particular compliant frames whose structural properties must be carefully designed. In any case, the practical achievement of a desired force profile can be quite a challenging task owing to the time-dependent phenomena, which affect the dielectric elastomer’s electromechanical response. Within this scenario, a hyperviscoelastic model of a rectangular constant-force actuator is reported. The model, based on the bond graph formalism, can be used as an engineering tool when designing and/or controlling actuators that are expected to work under given nominal conditions. Simulations and experimental results are provided, which predict the system response to fast changes in activation voltage and actuator position as imposed by an external user.

Thanks to their large power densities, low costs and shock-insensitivity, Dielectric Elastomers (DE) seem to be a promising technology for the implementation of light and compact force-feedback devices such as, for instance, haptic interfaces. Nonetheless, the development of these kinds of DE-based systems is not trivial owing to the relevant dissipative phenomena that affect the DE when subjected to rapidly changing deformations. In this context, the present paper addresses the development of a force feedback controller for an agonist-antagonist linear actuator composed of a couple of conically-shaped DE films and a compliant mechanism behaving as a negative-rate bias spring. The actuator is firstly modeled accounting for the viscohyperelastic nature of the DE material. The model is then linearized and employed for the design of a force controller. The controller employs a position sensor, which determines the actuator configuration, and a force sensor, which measures the interaction force that the actuator exchanges with the environment. In addition, an optimum full-state observer is also implemented, which enables both accurate estimation of the time-dependent behavior of the elastomeric material and adequate suppression of the sensor measurement noise. Preliminary experimental results are provided to validate the proposed actuator-controller architecture

Massive parallel arrays of discrete actuators are forceregulated robots that undergo continuous motions despite being commanded through a large but finite number of states only. Realtime control of such systems requires fast and efficient methods for solving their inverse static analysis, which is a challenging problem. Artificial intelligence methods are investigated here for the on-line computation of the inverse static analysis of a planar parallel array featuring eight three-state force actuators and possessing one degree of revolute motion.

Monolithic Flexure-based Compliant Mechanisms (MFCM) can functionally act as nonlinear springs by providing a desired load-displacement profile at one point on their structure. Once the MFCM topology is chosen, these particular springs can be conveniently synthesized by resorting to the well-known Pseudo-Rigid-Body approximation, whose accuracy strongly depends on the modeling precision of the flexures’ principal compliance. For various types of flexures, closed-form solutions have been proposed which express the compliance factors as functions of the flexure dimensions. Nonetheless, the reliability of these analytical relations is limited to slender, beam-like, hinges undergoing small deflections. In order to overcome such limitations, this paper provides empirical equations, derived from finite element analysis, that can be used for the optimal design of circular, elliptical, and corner-filleted flexural hinges with general aspect ratios on the basis of both principal compliance and maximum bearable stress. As a case study, a nonlinear spring conceived as a four-bar linkage MFCM is synthesized and simulated by means of finite element analysis. Numerical results confirm that the aforementioned empirical equations outperform their analytical counterparts when modeling thick cross-section hinges undergoing large deflections.Copyright © 2012 by ASME

Dielectric Elastomers (DE) seem to be a promising technology for the implementation of light and compact Variable Stiffness Actuators (VSAs), thanks to their large power densities, low costs and shock-insensitivity. Nonetheless, the development of DE-based VSA is not trivial owing to the relevant dissipative phenomena that affect the DE when subjected to rapidly changing deformations. In this context, the purpose of the present paper is to investigate the practical feasibility of DE-based VSA. As a case study, two conically-shaped actuators, in agonistic-antagonistic configuration, are modeled accounting for the visco-hyperelastic nature of the DE films. The model is then linearized and employed for the design of a stiffness controller. The control algorithm requires the knowledge of the actuator configuration (via a position sensor) and of the force exchanged with the environment (via a force sensor). An optimum full-state observer is then implemented, which enables both accurate estimation of the DE time-dependent behavior and adequate suppression of sensor measurement noise. At last, experimental results are provided together with the description of an effective electronic driver that allows an independent activation of the agonistic-antagonistic DE membranes.Copyright © 2012 by ASME

This chapter addresses design issues of components realized with rubber-like PhotoPolymers (PP) recently introduced in Rapid Prototyping. In particular, the determination of accurate, hyperelastic, constitutive models which describe the PP behavior is discussed in detail. In fact, Stereolithography and Polyjet processes allow the production of highly flexible objects by using photosensitive resins whose mechanical properties are, in some cases, similar to natural rubber. These parts, being fabricated with an additive approach, eventually represent a final product instead of a mere ‘prototype’. Therefore, the term Additive Manufacturing (AM) might be used in substitution to Rapid Prototyping (Gibson et al., 2010) in order to underline a closer link to the end-use component. From a designer’s point of view, AM technologies offer the possibility, before unknown, to customize and singularly optimize each product for the end user, such that focused design methods are needed. In the case of rubber-like PP, the considered materials usually experience deviatoric (isochoric), fully reversible deformations which can be well described by hyperelastic constitutive theories capable of dealing with large (finite) strains (Holzapfel, 2001). The capability to undergo finite deformations may intrinsically solve several functional design requirements but this requires an accurate representation of the material behavior through proper constitutive models. Unfortunately, the only data which are available (e.g. data from Objet Geometries Ltd., http://www.objet.com/docs/) are limited to basicmaterial properties, namely tensile strength, tensile modulus at few reference stretch ratios, compression set, and hardness. Hence, the correct design and verification of AM rubber-like products become impossible or, at least, very difficult. For example, every shape optimization through nonlinear Finite Element Analysis (FEA) requires a constitutive material law (i.e. a relation between stress and deformation) as a key input of the numerical model. In the same way, the calculation of hardness and friction influence on the product contact behavior requires a detailed description of its deformation state for given applied loads (Shallamach, 1952). If a rough estimate of any stress-strain field based on the aforementioned data may be acceptable for the first-attempt sizing of a prototype, nonetheless the design for direct manufacturing of 6

Given the manipulator's kinematic model reported in Tab. 3, the movements of the SCC and of the patient body can be easily related to the motion of the manipulator. In particular, the dynamic model of eqs. (1) and (2) allows the study of the otoconium movements during maneuvers that can be potentially performed by the proposed serial linkage. In fact, the chosen kinematical structure allows to achieve unlimited rotations along the revolution axis of every SCC and to control the SCC planar movement in the x and y directions (Figure 5). Obviously, this kind of RM cannot be manually achieved. Note that the choice of suitable strategies for controlling the manipulator (Siciliano & Khatib, 2008) makes it possible to assume that the dynamics of the patient's body movements is described by eq. (1). Therefore, Mc can be assumed to be the identity matrix. This assumption implies that all the spurious effects that deviate the behavior of the SCC dynamics with respect to eq. (1) must be compensated by the manipulator controller. It is clear that the otoconium trajectory must be carefully selected in order to achieve a SCC motion that: 1) It is tolerable by the patient (in terms of imposed acceleration); 2) It does not overcome the manipulator limits (in terms of possible pose and velocity/acceleration). At last, it should be pointed out that eq. (1) is useful when determining the forces which are necessary to accomplish a given RM once the otoconium trajectory and the patient parameters are known.

The paper describes the effects of the presence of a viscous fluid in the internal voids of a soft pulp for robotic finger designed according to the DLD (Differentiated Layer Design) concept.

This chapter reports on advances done in the design of compliant, Dielectric Elastomer based Linear Actuators (DELA). Dielectric Elastomers (DE) are incompressible deformable dielectrics which can experience deviatoric (isochoric) finite deformations in response to applied large electric fields while, at the same time, alter the applied electric fields in response to the deformations undergone (Toupin, 1956; Pelrine et al., 1998; 2000; Kofod et al., 2003). Thanks to the strong electro-mechanical coupling, DE intrinsically offer great potentialities for conceiving novel solid-state mechatronic devices and in particular actuators. These devices can be profitably used for robotic applications (Bar-Cohen, 2004; Kim & Tadokoro, 2007; Plante & Dubowsky, 2008; Biddiss & Chaua, 2008). In fact, conventional actuation technologies (such as electric motors) leave some basic problems unaddressed or, at least, improvable, such as: - The need to increase flexibility and simplify design solutions. For an important number of applications, conventional systems are too heavy, inefficient (in terms of high power consumptions), too expensive and still relatively complex. - The need to design human-friendly machines (Bicchi & Tonietti, 2004). In order to achieve highly precise position control, many industrial mechatronic systems (especially industrial robots) are designed to be very fast and stiff and thus unsafe. A possible way to greatly increase safety, is the design of robotic structures which are less precise but more compliant when compared to traditional technologies. To this respect, it is possible to concentrate the compliance in the actuated joints by using compliant (soft) actuators. - The need for modern robots to interact with unstructured environments and to actively control force and stiffness at the contact interface. A promising approach is to rely on a mechanical system that is inherently compliant and to use active control strategies to vary this compliance (Biagiotti et al., 2004). The main advantages are less demand both on actuator and controller bandwidth and improved stability (Williamson, 1993; Paul & Shimano, 1976). -The need to develop alternative actuators to overcome design limitations which are imposed in few but very important specific applications. For instance, electromagnetic actuators cannot be used in the presence of the high magnetic fields generated by Magnetic Resonance Imaging (MRI) devices. Nevertheless, the possibility to accomplish manipulation tasks within an MRI environment would highly improve the diagnostic capabilities of this technology (Koseki et al., 2007). Thanks to their intrinsic 1) compliance, 2) lightness, 3) pliability and 4) low cost, actuators based on DE can be an explorable solution when trying to assess or improve the aforementioned issues. DELA are usually composed of one or more DE shaped as a thin membrane (film) and a flexible supporting frame. This chapter proposes a methodology that allows to modify the available thrust as a function of the actuator’s length at will of the designer and, in particular, to obtain constant force actuators. The design procedure is divided in two steps: 1) optimization of the DE electromechanical parameters 2) design of the flexible frame. The supporting frame is conceived as a compliant mechanism (Howell, 2001) and makes use of the stiffness characteristics of slider-crank mechanisms with elastic revolute pairs to be coupled (in symmetric or axis-symmetric configurations) with films of different geometries. Three actuator concepts are proposed which highlight the efficacy of the proposed method i.e. Rectangular DELA (1(a), 1(d)), Diamond DELA (1(b), 1(e)) and Conical DELA (1(c), 1(f)).

The paper describes a variable stiffness actuated joint based on two counter-acting actuators that operate on two elastic elements purposely designed in order to exhibit a non-linear elastic characteristic.

Vengono esaminati i principali aspetti relativi al dimensionamento di un giunto robotico rotativo con rigidezza variabile, focalizzando l'attenzione sugli aspetti di sintesi e di calcolo di un organo cedevole a rigidezza non lineare.

Le specifiche generali di una mano robotica di nuova generazione vengono descritte e commentate, successivamente viene proposta una rassegna delle soluzioni progettuali adottate, con particolare riferimento allo sviluppo di rivestimenti soffici secondo un concetto originale denomiantodagli autori DLD (Differentiated Layer Design).

In order to overcome the limits due to the fact that homogeneous layers of soft material placed over robotic limbs behave differently with respect to biological models, this paper suggests the adoption of soft covers (pads) with differentiated structure. In particular, it is proposed to divide the allowable pad thickness into two layers: a continuous external layer (skin) and a discontinuous internal layer, so that the overall stiffness can be adjusted by properly shaping the discontinuous layer. The methodology adopted for designing the internal layer is composed of two steps. Firstly, the cover surface is conceptually split into finite elementary triangular sub-regions. Secondly, the internal layer of each triangular element is designed in order to replicate the shape of the non-linear compression law which is typical of endoskeletal structures covered by pulpy tissues. A series of symmetrically-disposed inclined micro-beams is used for the purpose. Once the compression law of each triangular element is known, the overall pad compliance can be modulated by correctly choosing the number and size of the elements composing the pad. Equipment and results of a combined experimental and numerical analysis (FEM) are presented. The results confirm that the proposed concept can be an effective solution when designing soft covers whose behavior need to match the compliance of the biological counterpart. As an example, artificial pads which mimic the human finger behavior are presented.Copyright © 2010 by ASME

The majority of soft pads for robotic limbs studied so far were made by visco-elastic polymeric solids whose behavior is significantly influenced by the rate of application of the external loads or displacements. In particular, contact interfaces which are intrinsically visco-elastic are found, for instance, in human fingers and feet or in various robotic devices covered by a compliant surface. An outstanding instance are anthropomorphic hands where time-dependent phenomena profoundly affects the stability and sustainability of the grasp. Alternatively to homogenous solid pads, this paper proposes the use of fluid filled soft structures with differentiated layer design [1] that is the adoption of a single solid material, dividing the overall thickness of the pad into a continuous skin layer coupled with an internal layer having communicating voids. The voids are then hermetically sealed and, in case, filled with fluid. Given the allowable pad thickness, the purpose is to tailor the pad properties to the specific application by 1) selecting a skin material characterized by proper tribological features, 2) designing an inner layer geometry so as to obtain a specific static compliance, 3) filling the pad with a viscous fluid chosen so as to modify time-dependent phenomena and increase damping effects. The proposed concept is validated by designing artificial pads whose viscoelastic properties are either similar or more pronounced when compared to those of the human fingertip.

Actuators based on Dielectric Elastomers are a promising technology in robotic and mechatronic applications. The overall actuator performances are influenced by the non-linear and highly coupled electrical and mechanical behavior of the employed materials. To date, the practical electro-mechanical response and controllability of actuators based on Dielectric Elastomers are limited by the inadequacy of the employed driving circuits, which are based on voltage-regulated converters. In this paper, first a novel activation strategy is proposed for Dielectric Elastomer actuators, which is based on a custom electronic driver derived from the flyback transformer topology. Second, two closed-loop controllers employing the proposed electronic driver are presented and compared for the accurate and fast regulation of the position of Dielectric Elastomer actuators. Experimental results are reported which show that the proposed electronic driver outperforms the traditional driving circuits in terms of energy efficiency, fast open-loop actuator activation and good closed-loop actuator controllability.

Most of robotic soft pads studied so far were made with a thick layer of homogeneous material shaped around a rigid core; their behavior has been widely investigated in the literature, mainly under compressive contact load, showing typical non-linear relationship between contact deformation and applied load (the so called power law). This paper proposes differentiated layer design, that is the adoption of a single elastic material, dividing the overall thickness of the pad into layers with different structural design (e.g. a continuous skin layer coupled with an internal layer with voids). The purpose is to modify the actual pad compliance and the resulting power law; in particular, given the material and the allowable pad thickness, to increase the compliance with respect to a non structured pad. Some possible internal layer structures are described, compatible with rapid prototyping manufacturing. Their compressive behaviors are tested and comparatively evaluated showing that the concept can work and be exploited for useful application.

A conically shaped Dielectric Elastomer (DE) linear actuator is presented which is obtained by coupling a DE film with a compliant mechanism. The compliant mechanism is designed, by means of a pseudo-rigid-body model, to suitably modify the force generated by the elastomer film. The resulting actuator provides a nearly constant force along the entire actuator stroke when the DE film is activated and returns to an initial rest position when the DE film is deactivated. Experimental activity fully validates the proposed concept. Possible applications of this kind of actuator are Braille cells, light weight robots and haptic devices.

In this paper, an overall description of the design of a robotic hand is discussed, with particular attention to the required sensory subsystem, its integration within the mechanical structure of the hand and the required control architecture. Different solutions for the joint configuration and the structure of the tendon network adopted for the transmission system are present together with three types of sensors applied on the finger and on the actuators. The integrated design of the hand finger and the sensors is reported and the motivations leading to this particular implementation are thoroughly addressed, taking into account both the mechanical constraints and the control requirements.

Benign Paroxymal Positional Vertigo and variants, collectively called ”vestibular lithiasis”, designate a common disorder caused by a malfunction of the inner ear. These pathologies are connected with the presence of dense particles within the semicircular canals which interfere with the sensing capabilities of angular velocity in the patient, causing nystagmus and vertigo. Some of these conditions can be treated by repositioning maneuvers physically done by the doctor that moves the head of the patient along different poses in space. Despite the fact that the treatment shows a success rate up to 80-90%, the failure rate remains highly significant and it is proven that precision repeatability and unlimited 360 degrees manoeuvrability can improve diagnostic and treatment potential for overcoming this kind of vertigo. In this paper the kinematic design of a serial robot that will execute repositioning maneuvers automatically is performed through a simplified task based kinematic design technique. The aim of the method is to find the minimum number of degrees of freedom to carry out a set of given tasks as well as the manipulator’s topology and the Denavit-Hartenberg parameters. The proposed procedure firstly minimizes the number of degrees of freedom only and then a cost function connected to the total link length.

Nel presente lavoro viene affrontato con un approccio sistematico il progetto concettuale di un manipolatore seriale per applicazioni mediche, consistenti nella diagnosi e nel trattamento della Labirintolitiasi: si tratta di una comune forma di vertigine, attualmente curata attraverso apposite manovre liberatorie eseguite manualmente dal medico specialista che muove il capo del paziente lungo traiettorie determinate. La metodologia proposta si può applicare in generale per la sintesi topologica e dimensionale di catene cinematiche seriali. Il processo di design viene automatizzato mediante una tecnica di ottimizzazione basata su algoritmi genetici che permette di valutare in maniera oggettiva le performance di ogni possibile configurazione cinematica del manipolatore rispetto a funzioni obiettivo opportunamente definite nelle varie fasi progettuali. Una descrizione della architettura prescelta nel caso del robot per il trattamento della Labirintolitiasi esemplifica i risultati ottenuti.

the paper introduces the concept of DLD (Differentiated Layer Design) for soft pads in robotic limbs; this concept allows to obtain low thickness layers with compliance comparable with that of biological pulps even in case that elastic materials with intrinsic low compliance are adopted.