Fuzzy PWM-PID control of cocontracting antagonistic shape memory alloy muscle pairs in an artificial finger

This paper presents biomimetic control of an anthropomorphic artificial finger actuated by three antagonistic shape memory alloy (SMA) muscle pairs that are each configured in a dual spring-biased configuration. This actuation system forms the basis for biomimetic tendon-driven flexion/extension of the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints of the artificial finger, as well as the abduction/adduction of its MCP joint. This work focuses on the design and experimental verification of a new fuzzy pulse-width-modulated proportional-integral-derivative (i.e. fuzzy PWM-PID) controller that is capable of realizing cocontraction of the SMA muscle pairs, as well as online tuning of the PID gains to deal with system nonlinearities and parameter uncertainties. The main contribution of this paper is the proposed biomimetic cocontraction control strategy, which co-activates the antagonistic muscle pairs as a synergistic functional unit. It emulates a similar strategy in neural control, called “common drive,” employed by the central nervous system (CNS). In order to maintain a desired position of a joint, the corresponding agonistic muscle pairs are cocontracted by the CNS and stiffen the joint. The synthesis and parametric analysis of the proposed controller are carried out via numerical simulations using a dynamic model of the system. The performance advantage of the cocontracting fuzzy PWM-PID controller over the original PWM-PID controller is shown by both numerical and experimental results. A successful application of the new controller to fingertip trajectory tracking tasks using the MCP joint’s flexion/extension and abduction/adduction is also described.     

Simple SQP approach for out-of-plane loaded homogenized brickwork panels,accounting for softening

A simple homogenized model for the non linear analysis of masonry walls out-of-plane loaded is presented.In the model, the panels are assumed to behave as Kirchhoff–Love plates. A rectangular running bond elementary cell (RVE) is subdivided into several layers along the thickness and, for each layer, a discretization where bricks are meshed with plane-stress three-noded triangular elements and joints are reduced to interfaces is assumed. Non linearity is concentrated on brick–brick and joint interfaces, which exhibit a frictional behavior with limited tensile and compressive strength with softening. Finally, macroscopic curvature bending moment diagrams are obtained integrating along the thickness in-plane micro-stresses of each layer.Homogenized masonry flexural response is then implemented at a structural level in a FE non linear code based on a discretization with three-noded elements and elasto-damaging interfaces.Three different models of increasing accuracy are presented. The first (EPP) relies in assuming an elastic-perfectly plastic behavior for the interfaces. The incremental problem is solved at a structural level through a well known quadratic-programming approach. The second (ED) accounts in an approximate way for the softening behavior and consists in a preliminary homogenized limit analysis of the structure, which allows to identify the failure mechanism and in the subsequent FE non linear analysis of the whole structure assuming that all the non linearity is concentrated on the yield line defining the failure mechanism. The last (EPD) is a sequential quadratic programming approach. Here, deteriorating bending moment curvature curves obtained through homogenization are approximated through a linear piecewise constant discontinuous function. At each load step, all interfaces are assumed to behave as an elastic-perfectly plastic material and the discretized non linear problem is solved by means of the quadratic programming algorithm used for the EPP model.The two step model proposed is validated both a cell level and at a structural level comparing results provided with both experimental data and existing macroscopic numerical approaches available in the literature.     

Creep in an electrodeposited nickel

This paper reports the experimental results on the creep behavior of electrodeposited ultrafine-grained nickel and its particle-reinforced nanocomposite. The objective of this research was to further improve the knowledge of the creep behavior of monolithic nickel and to explore the role of nano-sized SiO₂ particles in the potential creep strengthening of electrodeposited Ni nanocomposite. The creep behavior and microstructure of the pure ultrafine-grained nickel and its nanocomposite reinforced by 2 vol% nano-sized SiO₂ particles were studied at temperatures in the range from 293 to 573 K and at the applied tensile stresses between 100 and 800 MPa. The results indicate that the creep resistance of the nanocomposite may be noticeably improved compared to the monolithic nickel due to the interaction of the particles with dislocation motion. It was found that the applied stress interval can be divided into lower and higher stress intervals corresponding to dislocation (power-law) and exponential creep regions, respectively. Analysis of the creep data leads to the suggestion that the creep behavior of both electrodeposited nickel and its nanocomposite in power-law region may be grain boundary controlled. However, the mechanism responsible for the observed creep behavior at lower temperatures and the highest stresses is still not well established.     

N-methyl-p-aminophenol (metol) ozonation in aqueous solution: kinetics, mechanism and toxicological characterization of ozonized samples

The ozonation of metol, one of the main constituents of photographic developers, has been studied in aqueous solution in the pH range 2.0–7.0. Main reaction mechanisms have been assessed on the basis of observed reaction intermediates and products at varying pH of the solution. The effect of manganese addition—Mn^II ions or solid MnO₂—to the reacting system has also been evaluated.

The capability of the ozonation treatment to reduce the toxicity of metol-containing aqueous solutions, with respect to selected organisms, such as algae, has also been studied according to reported standard procedures. The results of toxicological assessments show that high levels of detoxification are achieved after 20 min of ozonation treatment and that longer treatments cause an increase in the toxicity of the solution due to the formation of secondary reaction products. The adoption of proper chemical and fluid dynamic submodels enabled the estimation of the reaction kinetics of ozone that attack to the substrate.     

Synthesis of TiO2 Thin Films: Relationship Between Preparation Conditions and Nanostructure

The influence of the synthesis conditions (pH, HF concentration, procedure of application of the voltage) during the anodization of Ti foils to produce TiO₂ thin films characterized by an ordered arrays of 1D nanostructures (nanorods, nanotubes) is discussed. Different types of 1D nanostructures could be obtained by changing the procedure of synthesis, as shown by field emission scanning electron microscopy images. The analysis of the current versus time curves during the procedure of synthesis provides indications on the sequence of processes occurring during the synthesis. It is also suggested that different growing mechanisms occur depending on the preparation, leading in turn to the different type of nanostructures observed. The relevance of this preparation method is related to the analysis of the relationship for oxide materials between nano-architecture and reactivity and gives the opportunity to prepare materials with an intermediate degree of complexity between model and applied catalysts.     

Some considerations on the polarization resistance method

A new mathematical approach aimed at giving light on the polarization resistance method is developed and its basic ideas are discussed to establish a suitable criterion to be used to compute the left bound ΔE₁ and the right bound ΔE₂ of the ΔE interval where the linear approximation works properly with reference to a prefixed degree of accuracy. Examination of the results relating to the theoretical cases, characterized by the Tafel slope values (40, 120) and (80, 100) mV, stresses that the width L() of the interval, where the linear approximation can be considered valid for a given value of , depends on B_a and B_c, their values determining the position of the inflection point ΔE_i of i(ΔE) where G(ΔE)=(αe^αΔE+βe^−βΔE)/(α+β)−1 exhibits a maximum. The maximum per cent value of the relative error μ, that is less than 10, for values ranging from 1 to 15 indicates that it is reasonable to replace i′(0) with the incremental ratio computed at ΔE₁ or ΔE₂. Furthermore, the Newton method was always successful in determining the values of ΔE₁ and ΔE₂. Applications to experimental polarization data refer to the behaviour of iron in 1 N H₂SO₄ solutions containing KCl at various concentrations. All the experimental polarization curves of the current transient type were best-fitted with a polynomial of the fourth degree over the [−50, 50] mV interval to determine the analytical expression of G(ΔE). The good agreement of the values of R_p, R_pa and R_pc, which are computed at ΔE₂ and ΔE₁ respectively for the case =10, underlines the validity of the present approach in providing accurate information on the resistance to corrosion of iron.     

About the Al–Cu–Si isothermal section at 500 °C and the stability of the ɛ-Cu15Si4 phase

The 500 °C isothermal section of the Al–Cu–Si system has been determined in the whole composition range, with special attention to the Cu-rich corner. A number of Cu–Si binary alloys equilibrated at 500–780 °C have also been investigated.A ternary point compound at 1.5 at% Al and 21 at% Si has been identified. It has the same crystal structure of the binary phase previously reported as ?-Cu₁₅Si₄. This phase however is not stable in the binary system, at least between 500 and 780 °C, and it is stabilised by small amounts of impurities. The γ₁-(Al,Cu) phase dissolves about 11.5 at% Si and ternary solubility extends in the direction of a constant valence electron concentration. The binary κ-(Cu,Si) phase is stable in a ternary solubility range close to the (Cu) terminal solid solution.