Model-free robust adaptive integral sliding mode impedance control of knee-ankle-toe active transfemoral prosthesis.

BACKGROUND: Wearing appropriate active prosthesis is the guarantee of daily life for amputees. Normally the controller of the traditional active transfemoral prosthesis is designed based on the mathematical model. The modelling error and the external interference will reduce the control accuracy of the system and make the prosthesis unable to operate in the desired trajectory. METHODS: Firstly, combined with time delay estimation (TDE), a model-free robust integral sliding mode impedance controller is designed. This method not only suppress the impedance error, but also eliminate the nonlinear relationship and disturbance in the dynamic model. Secondly, an adaptive law is proposed to update the controller gain, which provide stable control effect. Thirdly, the stability of prosthesis closed-loop system is proved by Lyapunov stability theory. Finally, the motor torque is used to drive each joint, and Matlab/Simscape is used to verify the prosthesis control system. RESULTS: From the result of the simulation experiment, the control method has a good tracking effect on each joint. The root mean square error and mean absolute errors of each joint's angle tracking error are 0.6123°, 1.9976°, 0.5574° and 0.2635°, 1.8175°, 0.4796°. Compared with the controller without adaptive gain and impedance control, the control effect is improved, and the plantar pressure of amputees is closer to the sound side. CONCLUSIONS: Comparing the results of different controllers, the adaptive integral sliding mode impedance controller with TDE can better track the expected angles of each joint. The gait is more normal. The walking performance of the prosthesis wearers is improved.

Selective Ensemble Based on Extreme Learning Machine for Sensor-Based Human Activity Recognition.

Sensor-based human activity recognition (HAR) has attracted interest both in academic and applied fields, and can be utilized in health-related areas, fitness, sports training, etc. With a view to improving the performance of sensor-based HAR and optimizing the generalizability and diversity of the base classifier of the ensemble system, a novel HAR approach (pairwise diversity measure and glowworm swarm optimization-based selective ensemble learning, DMGSOSEN) that utilizes ensemble learning with differentiated extreme learning machines (ELMs) is proposed in this paper. Firstly, the bootstrap sampling method is utilized to independently train multiple base ELMs which make up the initial base classifier pool. Secondly, the initial pool is pre-pruned by calculating the pairwise diversity measure of each base ELM, which can eliminate similar base ELMs and enhance the performance of HAR system by balancing diversity and accuracy. Then, glowworm swarm optimization (GSO) is utilized to search for the optimal sub-ensemble from the base ELMs after pre-pruning. Finally, majority voting is utilized to combine the results of the selected base ELMs. For the evaluation of our proposed method, we collected a dataset from different locations on the body, including chest, waist, left wrist, left ankle and right arm. The experimental results show that, compared with traditional ensemble algorithms such as Bagging, Adaboost, and other state-of-the-art pruning algorithms, the proposed approach is able to achieve better performance (96.7% accuracy and F1 from wrist) with fewer base classifiers.

[Recognition of walking stance phase and swing phase based on moving window].

Wearing transfemoral prosthesis is the only way to complete daily physical activity for amputees. Motion pattern recognition is important for the control of prosthesis, especially in the recognizing swing phase and stance phase. In this paper, it is reported that surface electromyography (sEMG) signal is used in swing and stance phase recognition. sEMG signal of related muscles was sampled by Infiniti of a Canadian company. The sEMG signal was then filtered by weighted filtering window and analyzed by height permitted window. The starting time of stance phase and swing phase is determined through analyzing special muscles. The sEMG signal of rectus femoris was used in stance phase recognition and sEMG signal of tibialis anterior is used in swing phase recognition. In a certain tolerating range, the double windows theory, including weighted filtering window and height permitted window, can reach a high accuracy rate. Through experiments, the real walking consciousness of the people was reflected by sEMG signal of related muscles. Using related muscles to recognize swing and stance phase is reachable. The theory used in this paper is useful for analyzing sEMG signal and actual prosthesis control.

Site-specific metallization of multiple metals on a single DNA origami template.

This work examines the selective deposition of two different metals on a single DNA origami template that was designed and assembled to direct the deposition. As a result, we were able to direct copper and gold to predesignated locations on the template, as verified by both compositional and morphological data, to form a heterogeneous Cu-Au junction. Seeding and deposition were performed in sequential steps. An enabling aspect of this work was the use of an organic layer or "chemical mask" to prevent unwanted deposition during the deposition of the second metal. In light of recent efforts in the field, the ability to localize components of different composition and structure to specific sections of a DNA template represents an important step forward in the fabrication of nanostructures based on DNA templates.

Electrically conductive gold- and copper-metallized DNA origami nanostructures.

This work demonstrates the use of a circuit-like DNA origami structure as a template to fabricate conductive gold and copper nanostructures on Si surfaces. We improved over previous results by using multiple Pd seeding steps to increase seed uniformity and density. Our process has also been characterized through atomic force microscopy, particle size distribution analysis, and scanning electron microscopy. We found that four successive Pd seeding steps yielded the best results for electroless metal plating on DNA origami. Electrical resistance measurements were done on both Au- and Cu-metallized nanostructures, with each showing ohmic behavior. Gold-plated DNA origami structures made under optimal conditions had an average resistivity of 7.0 × 10(-5) Ω·m, whereas copper-metallized structures had a resistivity as low as 3.6 × 10(-4) Ω·m. Importantly, this is the first demonstration of electrically conductive Cu nanostructures fabricated on either DNA or DNA origami templates. Although resistivities for both gold and copper samples were larger than those of the bulk metal, these metal nanostructures have the potential for use in electrically connecting small structures. In addition, these metallized objects might find use in surface-enhanced Raman scattering experiments.

Metallization of branched DNA origami for nanoelectronic circuit fabrication.

This work examines the metallization of folded DNA, known as DNA origami, as an enabling step toward the use of such DNA as templates for nanoelectronic circuits. DNA origami, a simple and robust method for creating a wide variety of shapes and patterns, makes possible the increased complexity and flexibility needed for both the design and assembly of useful circuit templates. In addition, selective metallization of the DNA template is essential for circuit fabrication. Metallization of DNA origami presents several challenges over and above those associated with the metallization of other DNA templates such as λ-DNA. These challenges include (1) the stability of the origami in the processes used for metallization, (2) the enhanced selectivity required to metallize small origami structures, (3) the increased difficulty of adhering small structures to the surface so that they will not be removed when subject to multiple metallization steps, and (4) the influence of excess staple strands present with the origami. This paper describes our efforts to understand and address these challenges. Specifically, the influence of experimental conditions on template stability and on the selectivity of metal deposition was investigated for small DNA origami templates. These templates were seeded with Ag and then plated with Au via an electroless deposition process. Both staple strand concentration and the concentration of ions in solution were found to have a significant impact. Selective continuous metal deposition was achieved, with an average metallized height as small as 32 nm. The shape of branched origami was also retained after metallization. These results represent important progress toward the realization of DNA-templated nanocircuits.

A general microchip surface modification approach using a spin-coated polymer resist film doped with hydroxypropyl cellulose.

We have developed a simple and effective method for surface modification of polymer microchips by entrapping hydroxypropyl cellulose (HPC) in a spin-coated thin film on the surface. Poly(methyl methacrylate-8.5-methacrylic acid), a widely available commercial resist formulation, was utilized as a matrix for dissolving HPC and providing adherence to native polymer surfaces. Various amounts of HPC (0.1-2.0%) dissolved in the copolymer and spun on polymer surfaces were evaluated. The modified surfaces were characterized by contact angle measurement, X-ray photoelectron spectroscopy and atomic force microscopy. The developed method was applied on both poly(methyl methacrylate) and cyclic olefin copolymer microchips. A fluorescently labeled myoglobin digest, binary protein mixture, and human serum sample were all separated in these surface-modified polymer microdevices. Our work exhibits an easy and reliable way to achieve favorable biomolecular separation performance in polymer microchips.