In this paper the authors presented a methodology to study the viscoelastic behavior of the human finger tissue by using the indentation process with a steel ball and indentation speed between 0.02 mm/s to 4 mm/s. Considering that at very low speeds the viscoelastic effects can be neglected, an effective Young’s modulus of the human finger as function of the indentation force was determinate based on the Hertzian equation and validated with experimental data. The influence of the indentation speed on both, the indentation force and depth, was studied and a mathematical model was proposed. The authors observed that the normal force resulting from the indentation process increase with speed due to an important damping effect in the finger tissue. Also, based on the Hertzian contact model the contact pressure during the indentation process has been calculated.

On the context of industry 4.0 there are still huge gaps, in several areas, and some scientific and technological challenges are addressed in the domains of sensing, communication, computing, cognition and autonomous control. In this paper there are discussed some issues on modelling cyber-physical systems, as well as possible directions to follow, in this aspect, for obtaining correct specifications for distributed controllers’ systems. This work is focused on the main issues considering plant modelling approaches.

In this paper, the authors present a new methodology to study the viscoelastic behaviour of the human finger. The methodology is based on experimental research consisting of a finger's indentation with a small steel cylindrical object for various indentation speeds. The tests were realized on a CETR UMT-2 Tribometer for indentation speed between 0.02 mm/s and 4 mm/s with a normal load of up to 22 N. Using the force-deformation diagrams recorded at the smallest indentation speed determined the elastic modulus of the human finger according to an adapted Hertzian model. By considering the increasing of the indentation force with indentation speed, the viscous component of the human finger was evidenced. The power dissipated in the finger tissue as a result of the prehension process has been obtained as a function of indentation speed and indentation depth. In addition, a general equation for the prehension force as a function of indentation speed and indentation depth has been obtained. The results of this study will be relevant for selection of the specific elastomers used in biomimetic hands.

This paper presents an experimental technique to investigate the electromechanical properties of silicone dielectric elastomers actuated with high DC electric fields. A non-contact measurement technique is used to capture and monitor the thickness strain (contraction) of a circular film placed between two metallic disks electrodes. Two active fillers such as silica (10, 15 and 30 wt%) and barium titanate (5 and 15 wt%) were incorporated in order to increase the actuation performance. Thickness strain was measured at HV stimuli up to 4.5 kV and showed a quadratic dependence against applied electric field indicating that the induced strain is triggered by the Maxwell effect and/or electrostriction phenomenon as reported in literature. The actuation process evidences a rapid contraction upon HV activation and a slowly relaxation when the electrodes are short-circuit due to visco-elastic nature of elastomers. A maximum of 1.22 % thickness strain was obtained at low actuating field intensity (1.5 V/mu m) comparable with those reported in literature for similar dielectric elastomer materials.

The design of mechatronic systems is a multidisciplinary task that involves skills from mechanic, electronic and informatics areas. Recently, the expertise from such different fields is able to communicate and exchange the necessary contribution to successful design solutions, through a myriad of internet tools available. The introduction of internet of services on the design of mechatronic systems, mainly when teams, with different skills, operate in different geographic places, has contributed to flawlessly integrate better and interoperable final solutions. The design of mechatronic systems without errors that operate without failures - is an important contribution to such goal. Safe behavior of mechatronic systems is crucial, mainly, in what concerns human safety. The correct behavior of those systems can be improved by the development of safe software for their controllers using some analysis techniques. Among them, Formal Verification (FV) is able to guarantee the best results. One of the main gaps using this technique is the difficulty of obtaining adequate plant models, in a systematic way, because this task is, usually, related with high level of expertise of designers and, in industry, this fact causes some difficulties for using those methods and tools. The work presented in this paper is a part of a larger project developed in the context of Software as a Service (SaaS) platform. It is intended to develop a systematized approach in order to obtain meaningful plant models out of existing CAD data, from Autodesk Inventor (or CATIA), and translate those models to formatted files according to input data of the UPPAAL model checker (because it allows dealing with time variable).The main idea is to obtain, systematically, plant models for Formal Verification purposes, considering that nowadays companies with different CAD systems are using increasingly often STEP-File format. A solution for this specific problem is explored and presented in this paper.

To use the elastomers as a interfacial surface in the prehension systems, the authors experimentally determined the elastic deformation and sliding friction of a plane elastomer sample in contact with small steel roller for normal loads up to maximum 9 N and linear speed of 0.1 mm/s. The experiments were realized on a Tribometer CETR UMT 2, by using two procedures: firstly was determined the Young’s modulus of the elastomer by indentation with a steel roller with normal loads between 1 and 9 N and secondly was determined the friction forces in sliding of the steel roller on elastomer sample with normal loads between 1 and 5 N. On contact surfaces was experimentally determined the total friction force including both elastic deformation force and sliding force. Also, an analytical model for friction force has been developed.

The development of dependable software for mechatronic systems can be a very complex and hard task. For facilitating the obtaining of dependable software for industrial controllers, some powerful software tools and analysis techniques can be used. Mainly, when using simulation and formal verification analysis techniques, it is necessary to develop plant models, in order to describe the plant behavior of those systems. However, developing a plant model implies that designer takes his (or her) decisions concerning granularity and level of abstraction of models; approach to consider for modeling (global or modular); and definition of strategies for simulation and formal verification tasks. This paper intends to highlight some aspects that can be considered for taking into account those decisions. For this purpose, it is presented a case study and there are illustrated and discussed very important aspects concerning above exposed issues.

Dielectric elastomers (DEs) are being developed as artificial muscles for diverse applications, including soft machines, adaptive optics, haptic surfaces, micro air vehicles, strain sensors, fluidic micro-pumps and energy harvesting (Carpi et al., 2008; Carpi et al., 2010; Brochu & Pei, 2010; Kornbluh et al., 2012). They are superior to piezoelectric, shape memory alloys and electrostrictive materials in terms of large voltage-induced deformation, high energy density, fast response, quiet operation, light weight, and low cost. To increase the electromechanical performance, the elastomers are pre-stretched with an in-plane area stretch up to 36. These large deformations may lead to rupture and thus impair the mechanical integrity of the devices. Further development of dielectric elastomer transducers demands accurate and efficient computational methods (Wissler, 2007; Lochmatter, 2007). The transducers involve nonlinear electromechanical coupling, and are often hybrid structures of soft membranes in tension and hard materials in compression. This work reports about a systematic investigation of mechanical characteristics of elastomer films used as dielectric layer in actuation systems. Uniaxial tensile and compression tests were performed in order to investigate the elastic properties of some poly(dimethylsiloxane)-based elastomers. The results ∗Corresponding author; e-mail: carlescu.vlad@yahoo.com 88 Vlad Cârlescu et al. obtained in uniaxial tension and compression stress states were compared in terms of nonlinear elastic behavior and found to lead in similar values of elastic modulus. Various hyperelastic constitutive models were used to fit the experimental stress-strain data. Finite element method (FEM) was used to simulate the large strain deformation in tension and compression. The simulation results were compared with experimental data in terms of true stress-strain and showed good correspondence, especially for tensile tests. Some discrepancies were observed between experimental and simulations in the case of compression tests. However, to determine the compressive modulus it is necessary to carry out experimental test according to the test standards to verify the characteristics of elastomers.

The human prehension systems realized by two ore more fingers are important inspiration sources for development of the performed actuators, especially for prehension of the small objects. In the contact between the fingers and the small objects the adhesion and skin deformation are essentially for a good and precision prehension. Based on the human finger configuration was realized from elastomer artificial fingers to be used in the prehension systems of the robots. In the present paper authors included the methodology to determine the friction forces and friction coefficient between cylindrical objects and an artificial finger. Also, some friction forces and friction coefficients obtained by experiments between elastomer fingers and cylindrical objects have been presented.

The authors developed an experimental methodology to determine the friction forces and friction coefficient in dry and lubricated conditions between steel cylinder and some types of polyurethanes. The method consists in sliding of a steel cylinder on a polymer flat sample in the direction of the cylinder axis. The experiments were realized using the TRIBOMETER UMT-2 (CETR) at normal loads between 1 N and 15 N and with cyclic linear speeds of 1mm/s, 5mm/s and 10 mm/s. A lot of 8 different types of polyurethane were experimentally tested and the friction forces and friction coefficients have been determined according to normal load, sliding velocity and dry and lubricated conditions.

Modeling large nonlinear elastic deformation of elastomers is an important issue for developing new materials. Particularly, this is very promising for design and performance analysis of dielectric elastomers (DEs). These “smart materials” are capable of responding to an external electric field by displaying significant change in shape and size. In this paper, finite element method (FEM) was used to simulate the mechanical behavior of soft elastomers on uniaxial tension. Experimental data from uniaxial tensile tests were used in order to calibrate hyperelastic constitutive models of the material behavior. The constitutive model parameters were evaluated in ABAQUS/CAE. The 3D-model simulation results of a dumbbell shaped specimen at uniaxial tension shows very good correspondence with experimental data.

The use of analysis techniques for industrial controller's analysis, such as Simulation and Formal Verification, is complex on industrial context. This complexity is due to the fact that such techniques require sometimes high investment in specific skilled human resources that have sufficient theoretical knowledge in those domains. This paper aims, mainly, to show that it is possible to obtain a timed automata model for formal verification purposes, considering the CAD model of a mechanical component. This systematic approach can be used, by companies, for the analysis of industrial controllers programs. For this purpose, it is discussed, in the paper, the best way to systematize these procedures, and this paper describes, only, the first step of a complex process and promotes a discussion of the main difficulties that can be found and a possibility for handle those difficulties. A library for formal verification purposes is obtained from original 3D CAD models using Software as a Service platform (SaaS) that, nowadays, has become a common deliverable model for many applications, because SaaS is typically accessed by users via internet access.

This paper refers to the electromechanical strain response of PDMS/TiO2/SiO2 composites as an electroactive polymer actuator. Lightweight electro-active polymers (EAPs) are ideal for control surface since they offer high strain rate, fast response, high elastic energy density and ease of manufacture [1,2]. We investigate the frequency response and vibrational modes of rectangular films with aluminum electrodes using Scanning Laser Doppler Vibrometry (SLDV) technique described elsewhere [3,4]. The results showed a similar behaviour with those of acrylic and silicone films coated with carbon-based compliant electrodes from literature. Field-induced vibrational strains decrease with frequency due to the increase in stiffness of sample and change of dielectric permittivity. These materials are possible candidates in polymer actuators for micro-pump and micro-valve applications in MEMS.

Modeling and numerical simulation of electroactive polymers is considered in this work using finite element method (FEM). In this paper are presented some preliminary results regarding the simulation of the thickness compressions of some dielectric elastomers subjected to electrical stimulations. A simple planar configuration is used for actuator model consisting of an elastomer film sandwiched between two circular rigid electrodes. The expressions of the electrostatic pressures exerted by the electrodes in response to an applied voltage were calculated and inserted into the expressions of the actuator mechanical deformations, obtained by assuming linearly stress-strain constitutive equations of the material for small strains. The strain responses of elastomers was observed to increase with decrease of Young's modulus. Finite element simulation was performed using an elastic model for elastomer film and strains up to 20.5% were obtained. These strains are quite high considering that we used rigid electrodes.

This paper investigates the transverse strain response of some elastomeric dielectric materials as a means of actuation. When a voltage is applied to the electrodes, the elastomeric films expand in area and compresses in thickness. The static transverse strain response was measured using a non-contant displacement sensor and rigid electrodes. A quadratic dependence of strain response on applied electric filed was obtained, that is specific to electrostrictive materials. The results obtained allow us to propose these materials for actuator and sensor applications in mechatronic systems.

To determine the rolling friction resistance in the micro rolling systems we developed a new micro tribometer consisting in a driving rotational disc in contact with 3 microballs which sustain an inertial driven rotational disc. The driving disc has a constant rotational speed and his rotational motion is transmitted to the inertial driven disc by rolling friction forces, developed in the rolling contacts between the microballs and the inertial disc. When the rotational speed of the inertial driven disc becomes constant, the driven disc is stopped and the inertial driven disc starts a deceleration process until it completely stops due to friction. A camera monitors the angular position of the inertial driven disc, from the start of the deceleration process to his completely stop (the spin-down method). An analytical model based on the integration of the inertial disc motion equation, including both rolling frictions in the rolling contacts and the friction between the inertial disc and air has been developed. The equation of the inertial disc angular position, as function of the time was obtained considering two hypothesis: (i) in the first hypothesis it was considered that rolling friction torque does not depend on rotational speed in dry contacts; (ii) in the second hypothesis it was considered a linear dependence between rolling friction torque and rotational speed for dry contacts. Experimental investigations using the new microtribometer with three 1.588mm diameter stainless steel microballs, for a range of rotational speed between 30rpm and 210rpm and for normal contact loads between 8mN and 33mN confirm the validity of the hypothesis of constant friction torque in dry conditions. Based on the hypothesis of constant friction torque, the rolling friction torque in the contacts between the microballs and the two discs having values between 1.8μNmm and 7.2μNmm have been obtained with the new microtribometer. Also, rolling friction coefficients having values between 0.0002 and 0.0004 have been obtained.

The water existing in the atmosphere condenses on the surfaces of elements in contacts in some molecular layers and water acts by capillary effect and lead to increases of the normal forces and of the rolling/sliding resistance. Authors consider important to determine the dimensional limits in micro rolling and sliding systems for what water condensed on surfaces increases the friction. Both rolling and sliding friction experiments was realized and some results regarding the limits for influence of the condensed water to the friction coefficient has been determined.

There is a strong demand on soft actuators based on electro-active polymers ( EAPs). In particular, dielectric elastomers are well studied for actuators applications. Thus, measurement of static and dynamic strain response is important. A technique for static strain response measurement using a displacement sensor has been already presented in a previous paper [1]. In this paper we present a strain measurement system based on laser vibrometry to study the dynamic transverse strain response of some elastomeric polymer films that are subject to high electric fields. The films were coated on both sides with compliant electrode material. When voltage was applied, the film compressed in thickness and expanded in area. Laser vibrometry offer a good accuracy and can measure displacements in order of pm. A variety of actuators, including electrooptical devices, diaphragm pumps, and muscle-like linear actuators, have been demonstrated with dielectric elastomer materials, suggesting that this technology is well suited to small-scale electromechanical devices and robots [2].