Force control of twisted and coiled polymer actuators via active control of electrical heating and forced convective liquid cooling

For decades, numerous artificial muscles have been proposed in order to implement beneficial features of biological muscles into robotics. Unfortunately, traditional artificial muscles experienced difficulties in imitating properties of the biological muscles due to mechanical and control issues. Recently, twisted and coiled polymer actuators (TCP) have been shown to produce large mechanical power via thermal stimulations and strong linearity. In this paper, a high-performance TCP thermally cycled by electrical heating and forced convective liquid cooling is designed and associated control algorithms are presented. We elaborate the model of the TCP that is simple, yet provides insight into how the electrical heating and the forced convective liquid cooling contribute to the TCP actuation. The proposed model is verified by experimental studies. Based on the proposed model, we design a feedforward–feedback controller and switching laws, which actively control the TCP in both the heating and cooling cycles. Furthermore, we extend our control methodology to agonist–antagonist TCPs. From the experimental studies, the proposed method is shown to be effective in both single TCP and antagonistic TCPs.     

Living Materials Herald a New Era in Soft Robotics

Living beings have an unsurpassed range of ways to manipulate objects and interact with them. They can make autonomous decisions and can heal themselves. So far, a conventional robot cannot mimic this complexity even remotely. Classical robots are often used to help with lifting and gripping and thus to alleviate the effects of menial tasks. Sensors can render robots responsive, and artificial intelligence aims at enabling autonomous responses. Inanimate soft robots are a step in this direction, but it will only be in combination with living systems that full complexity will be achievable. The field of biohybrid soft robotics provides entirely new concepts to address current challenges, for example the ability to self‐heal, enable a soft touch, or to show situational versatility. Therefore, “living materials” are at the heart of this review. Similarly to biological taxonomy, there is a recent effort for taxonomy of biohybrid soft robotics. Here, an expansion is proposed to take into account not only function and origin of biohybrid soft robotic components, but also the materials. This materials taxonomy key demonstrates visually that materials science will drive the development of the field of soft biohybrid robotics.     

Mechanical behavior and microstructural analysis of NiTi-40Au shape memory alloys exhibiting work output above 400 °C

Substituting Ni with Au in NiTi leads to dramatic increases in transformation temperatures, meeting one of the requirements for a viable high temperature actuator material. Consequently, four alloys containing between 49 and 51 at.% Ti, a fixed 40 at.% Au, and balance Ni, were prepared and investigated in detail using load-biased thermal cycling (LBTC), scanning electron microscopy (SEM), aberration corrected scanning transmission electron microscopy (STEM), and X-ray energy dispersive spectroscopy (XEDS). LBTC experiments demonstrated work output well above 400 °C, with full recovery up to 100 MPa. The alloys exhibit minimal variation in shape memory properties despite the relatively large composition range from Ti-lean to Ti-rich, in stark contrast to most other NiTi-based systems, which demonstrate extreme compositional sensitivity. Electron beam analysis revealed the presence of two types of secondary phases present in all compositions, which are subsequently characterized. Differences in secondary phase content as a function of alloy composition is shown to have a moderating effect on the transforming matrix composition - an important asset for this alloy system - potentially easing processing requirements and opening up shape memory alloys to new fabrication techniques. Unrecovered strain during cycling at higher loads is analyzed from a theoretical perspective to gain insight into the mechanisms of defect formation responsible for functional fatigue.     

Electron Holography Studies on Narrow Magnetic Domain Walls Observed in a Heusler Alloy Ni50Mn25Al12.5Ga12.5

Peculiar magnetic domain walls produced in Heusler alloys, which have attracted renewed interest due to their potential application to actuators and spintronic devices, are studied here using electron holography. The observations reveal unexpectedly narrow magnetic domain walls, the width of which showed perfect agreement with that of the antiphase boundaries (APB, e.g., only 3 nm). While the results can be explained by the significant depression of ferromagnetism due to the local chemical disorder, the electron phase shift indicates that ferromagnetic correlation still remains in the APB region.     

Determination of moisture content of polyamide 66 directly from combination region near‐infrared spectra

The hygroscopic nature of polyamide (PA) polymers motivates the development of analysis tools for use in assessing their moisture content. Among possible analysis techniques, near‐infrared (near‐IR) spectroscopy is non‐destructive, requires little or no sample preparation, and is compatible with sample thicknesses on the order of mm. The work reported here makes use of transmission near‐IR spectroscopy in the combination region (5000–4000 cm^?1) to develop a protocol for assessing the moisture content of PA 66 samples directly from their spectral intensities after preprocessing with the standard normal variate transform and partial least‐squares. The method is compatible with online or continuous monitoring applications and can be calibrated without the use of destructive reference measurements such as thermogravimetric analysis. The long‐term calibration performance of the technique is evaluated, and on a scale of 0–100% moisture uptake, the standard error of prediction is found to average 1.4% over 6 months. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40645.     

Sensor-less force-reflecting macro–micro telemanipulation systems by piezoelectric actuators

This paper establishes a novel control strategy for a nonlinear bilateral macro–micro teleoperation system with time delay. Besides position and velocity signals, force signals are additionally utilized in the control scheme. This modification significantly improves the poor transparency during contact with the environment. To eliminate external force measurement, a force estimation algorithm is proposed for the master and slave robots. The closed loop stability of the nonlinear micro–micro teleoperation system with the proposed control scheme is investigated employing the Lyapunov theory. Consequently, the experimental results verify the efficiency of the new control scheme in free motion and during collision between the slave robot and the environment of slave robot with environment, and the efficiency of the force estimation algorithm.     

Influence of ferroelectric domain texture on the performance of multilayer piezoelectric actuators

Lead zirconate titanate (PZT)-based multilayer piezoelectric actuators (MAs) present a maximum in their piezoelectric properties when pre-stressed with a low mechanical load (ca. 50 MPa) along the longitudinal axis of the actuator. In this work, we investigate this phenomenon by combining polarised Raman spectroscopy with a Reverse Monte Carlo (RMC) method in order to quantify the domain orientation distribution of PZT-based MAs, both in-situ and at the remanent state, under combined applied electric field and mechanical load. Our study shows that the performance maximum of MAs is the result of two competing effects: (i) an increasing reservoir for non-180° domain switching for increasing applied compressive pre-stress and (ii) a large activation energy for domain switching at high pre-stresses. Hence, our study uncovers structure-property relationships in piezoceramic components that could be used to finely tune the electromechanical response of actuators.     

Modeling and control of an airbrake electro‐hydraulic smart actuator

In this paper, an accurate model of an airbrake electro‐hydraulic smart actuator is obtained by physical considerations, and then different control strategies (variable‐gain proportional control, PT₁ control with switching integrator, and second order sub‐optimal sliding mode control) are proposed and analyzed. This application is innovative in the avionic field, and is one of the first attempts to realize a fly‐by‐wire system for airbrakes, oriented to its immediate employment and installation on current aircraft. The project was carried on with the participation of the Italian Ministry of Defense, and was commissioned to MAG, a leading provider of integrated systems and aviation services for aerospace. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Dynamic allocation for input redundant control systems

In this paper we address control systems with redundant actuators and characterize the concepts of weak and strong input redundancy. Based on this characterization, we propose a dynamic augmentation to a control scheme which performs the plant input allocation with the goal of employing each actuator in a suitable way, based on its magnitude and rate limits. The proposed theory is first developed for redundant plants without saturation and then extended to the case of magnitude saturation first and of magnitude and rate saturation next. Several simulation examples illustrate the proposed technique and show its advantages for practical application.     

Boronic acid‐based thin films that show saccharide‐responsive multicolor changes

A novel saccharide sensor that displays a distinct color change resembling a “traffic signal” was developed. By copolymerizing boronic acid and amine monomers on a glass plate, a boronic acid‐containing thin film was obtained. Anionic blue and yellow dyes were adsorbed on the thin film, and the film was immersed in aqueous saccharide solutions containing a cationic red dye. With increase in the saccharide concentration in the solution, the thin film changes color from green to red via yellow. The observed distinct changes in color were attributed to a stepwise release and binding of dyes. The sensitivity of the saccharide sensor was dependent on the monomer composition of the thin film and increased with increasing the boronic acid content. The pH of the saccharide solution was another key factor affecting the sensing behavior, and glucose‐responsive color changes were significantly enhanced at pH 7.8. By optimizing these conditions, significant color changes in response to glucose were achieved. Saccharide selectivity was found to be in the following order: fructose > glucose > galactose = mannose > sucrose. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42679.