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This paper aims to address robot/environment interacting problems by designing an adaptive finite-time impedance controller. To deal with crucial issues regarding these sorts of problems, namely interacting with unknown environments and the system's uncertain nonlinearity, a backstepping control structure accompanied by an adaptive Taylor series system is developed. By designing a sliding surface term, two new variables are defined to form the backstepping controller to guarantee that the sliding surface converges to zero in a finite time. Also, impedance parameters are tuned adaptively using the gradient-descent algorithm inspired by a well-designed control literature. The designed controller has several useful features, such as being capable of implementing on n-DOF (degree-of-freedom) industrial manipulators, a guaranteed finite-time stability analysis, a regressor-free design, and dealing with uncertainties. Finally, a numerical simulation applied on a six-DOF manipulator and also a comparison with an impedance control are provided to show the efficiency of the designed controller. [ABSTRACT FROM AUTHOR]

In the present study, halloysite nanotubes (HNTs) were firstly functionalized using N‐β‐(aminoethyl)‐γ‐aminopropyltrimethoxy silane and then employed as nanofillers to fabricate mixed‐matrix membranes including poly (ether‐block‐amide) polymer as the primary material. To characterize the HNTs, as well as the obtained membranes, thermal gravimetric analysis, Fourier‐transform infrared spectroscopy, X‐ray powder diffraction, and Field emission scanning electron microscopy analyses were employed. Effects of the modified and pure HNTs loadings, as well as feed pressure on CH4 and CO2 permeabilities and ideal CO2/CH4 selectivity of the prepared membranes, were surveyed. The experimental permeation results indicated that incorporation of 1.5 wt% of amine‐functionalized HNTs into the polymer matrix improves CO2 permeability and the ideal selectivity by nearly 37 and 24%, respectively, due to the higher CO2 adsorption capacity of the amine‐functionalized HNTs. [ABSTRACT FROM AUTHOR]

The present paper aims to design an integrated kinematic/dynamic-based tracking controller for wheeled mobile robots (WMRs) considering motors' dynamics. By defining a reference WMR, the role of kinematic controller is to not only minimize the posture error which indicates the difference between the reference and actual WMRs, but also to generate a desired path for the actual WMR. The kinematic tracking control problem of WMRs is so challenging if motors' dynamics, parametric and nonparametric uncertainties and external disturbances are considered. Thus, proposing a dynamic control law alongside a kinematic control is unavoidable. In this study, we propose a new dynamic controller, namely, a state augmented adaptive backstepping such that the desired path is asymptotically tracked. Several numerical results accompanied by 3D simulations of trajectory tracking control of a WMR in 'Simscape Multibody' environment and comparisons with two well-designed controllers in the literature are reported to show the high performance of proposed control structure. [ABSTRACT FROM AUTHOR]

An uncertainty estimation and compensation can improve the performance of control systems due to structured and unstructured uncertainty. This paper presents a robust task-space control approach using an adaptive Taylor series uncertainty estimator for electrically driven robot manipulators. It is worth noting that not only the lumped uncertainty is estimated and employed in the indirect form of robust controller, but also the upper bound of approximation error is estimated to form a robustifying term and the asymptotic convergence of tracking error and its time derivative are proven based on stability analysis. Finally, the effectiveness of the proposed controller is shown through simulation and comparison with two valuable control schemes applied on the Selective Compliance Assembly Robot Arm (SCARA) robot manipulator. [ABSTRACT FROM AUTHOR]

SUMMARY: Achieving the asymptotic tracking control of electrically driven robot manipulators is a challenging problem due to approximation/modelling error arising from parametric and non-parametric uncertainty. Thanks to the specific property of Taylor series systems as they are universal approximators, this research outlines two robust control schemes using an adaptive Taylor series system for robot manipulators, including actuators' dynamics. First, an indirect adaptive controller is designed such as to approximate an uncertain continuous function by using a Taylor series system in the proposed control law. Second, a direct adaptive scheme is established to employ the Taylor series system as a controller. In both controllers, not only a robustifying term is constructed using the estimation of the upper bound of approximation/modelling error, but the closed-loop stability, as well as the asymptotic convergence of joint-space tracking error and its time derivative, is ensured. Due to the design of the Taylor series system in the tracking error space, our technique clearly has an advantage over fuzzy and neural network-based control methods in terms of the small number of tuning parameters and inputs. The proposed methods are simple, model free in decentralized forms, no need for uncertainty bounding functions and perfectly capable of dealing with parametric and non-parametric uncertainty and measurement noise. Finally, simulation results are introduced to confirm the efficiency of the proposed control methods. [ABSTRACT FROM AUTHOR]

It is known that the mechanical properties of bone-mimicking porous biomaterials are a function of the morphological properties of the porous structure, including the configuration and size of the repeating unit cell from which they are made. However, the literature on this topic is limited, primarily because of the challenge in fabricating porous biomaterials with arbitrarily complex morphological designs. In the present work, we studied the relationship between relative density (RD) of porous Ti6Al4V EFI alloy and five compressive properties of the material, namely elastic gradient or modulus (Es20-70), first maximum stress, plateau stress, yield stress, and energy absorption. Porous structures with different RD and six different unit cell configurations (cubic (C), diamond (D), truncated cube (TC), truncated cuboctahedron (TCO), rhombic dodecahedron (RD), and rhombicuboctahedron (RCO)) were fabricated using selective laser melting. Each of the compressive properties increased with increase in RD, the relationship being of a power law type. Clear trends were seen in the influence of unit cell configuration and porosity on each of the compressive properties. For example, in terms of Es20-70, the structures may be divided into two groups: those that are stiff (comprising those made using C, TC, TCO, and RCO unit cell) and those that are compliant (comprising those made using D and RD unit cell). [ABSTRACT FROM AUTHOR]

This study aimed to investigate the biocompatibility and osseointegration of novel titanium (Ti) implants with a perforated part with high surface roughness (Ra >4 μm) and a smooth solid part (test group), as compared to smooth solid Ti implants (control group; Ra < 0.8 μm). Test and control implants were implanted in rabbit femurs. After 4 and 15 weeks, host tissue reaction and quality of tissue formed were evaluated with histopathology, while micro‐CT scans were used to quantitatively assess bone–implant contact (BIC), surrounding bone formation, and bone ingrowth.After 4 and 15 weeks, minimal host reaction was found in the test group. Histopathological analysis showed new bone formation around the implants in both the test and control groups after 4 weeks. Furthermore, additional bone growth was often observed within the holes of the test implants. After 15 weeks, the test implants showed high bone ingrowth and the presence of mature bone in direct contact with the implant surface, whereas, bone ingrowth was poorer for the control group with 30% of the control implants, showing larger gaps at the bone–implant interface. Quantitative micro‐CT analysis revealed comparable BIC and bone formation in both groups at 4 weeks, but higher BIC and more bone formation in the test group than in the control group after 15 weeks. No significant differences were observed in any of the analyses. In conclusion, partially perforated, high‐roughness Ti implants showed excellent osseointegration and minimal host reaction, indicating their potential for orthopedic applications in bone repair and regeneration. [ABSTRACT FROM AUTHOR]

Background: Bioactive glasses with different compositions have been extensively used as bone tissue engineering. Preparation, development and characterization of alginate pastes containing bioglass for bone repair applications were the purposes of this study., Objective: The injectable bone pastes were produced from sol-gel derived bioactive glass nanoparticles with various CaO/P 2 O 5 ratios of 19, 9.5 and 4.75 and sodium alginate solutions with different concentrations of 1, 2 and 4 wt.%. The effect of CaO/P 2 O 5 and powder to liquid (P/L) ratios and alginate concentration on injectability, biodegradation, rheological properties, bioactivity and cellular behavior of the pastes have been studied. The behavior of human mesenchymal stem cells (hMSCs) in the presence of the pastes was assessed by MTT assay, biomineralization assay, ALP activity, Acridine orange staining and Alizarin red staining tests., Results: By adding sodium alginate, the pastes exhibited a thixotropy behavior. The storage modulus of all pastes was larger than the loss modulus in the frequency range of 0.1-100 s-1. Cytotoxicity evaluation results revealed that there was a critical amount of bioactive glass in pastes which are above the limit; the viability of hMSCs will be at risk. The pastes made of bioactive glass nanoparticles with CaO/P 2 O 5 = 9.5 and sodium alginate 1% with P/L ratio of 0.8 showed optimum behavior in terms of mineral carrying capacity, injectability characteristics, accellular bioactivity in SBF, loss weight and wash out behavior, proliferation and differentiation of hMSCs., Conclusion: According to the results, the pastes prepared with sodium alginate solution and bioactive glass nanoparticles can be beneficial in bone tissue engineering., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)