Extended PKM Fixturing System for Micro-Positioning and Vibration Rejection in Machining Application

The paper aims to present a mechatronic device able to micro-position the workpiece and to reject disturbances due to machining operation. A decoupling method is proposed for a parallel kinematic machine (PKM) fixturing platform composed by a 3-DoF flexure-based piezo-actuated mechanism. The parallel platform, with a vertical motion and two rotations, is described and its kinematics and dynamics are studied. The coupling undesirable effect is investigated based on a set of poses. To improve the quasi-static regulator model for a set-point following system, a bump less switching controller and a fine-tuning procedure, to estimate the parameter uncertainty and enable the external disturbance containment in an extended broadband frequency range, are presented. The platform and the piezo-actuator controllers are modelled based on a gain scheduling, standard ISA form method, to guarantee the stability. The accuracy is demonstrated through a set of simulations and experimental comparisons. A sensitivity analysis that evaluates the tracking performance and the disturbance rejection based on the number of signal amplitudes, frequencies, and phases is discussed. A validation phase has shown that the developed architecture presents a steady state error lower than 1.2 µm, a vibration reduction of 96% at 1130 Hz with a maximum resolving time of 6.60 ms.

Research of the Piezo Actuator Information-Measuring System for Studying the Strength Characteristics of Filling Materials

В статье рассмотрена пьезоактюаторная информационно-измерительная система с телекоммуникационной сетью для изучения композитных пломбировочных материалов, реализующая тензометрический, акустический, оптический и электрометрический способы контроля образцов. Изложена возможность анализа прочностных характеристик образца по его диаграммам сжатия в статическом режиме и при циклических нагрузках с заданными частотой колебаний и законом воздействия в цифровом виде. Получены рекомендации, что для изучения твердых тканей зубов лучше применять последовательное расположение двух пьезоактюаторов, а не параллельное. Это связано с тем, что твердые ткани зубов имеют относительно малый модуль Юнга (в частности, у дентина 14,7 МПа). При этом максимальная генерируемая сила от двух последовательных пьезоактюаторов будет больше, чем от параллельных. Разработана электромеханическая модель процесса нагружения образца в силовой пьезоактюаторной установке, исследованы вопросы повышения точности измерения прочностных характеристик с применением пакета Micro-Сap. Создана трехмерная модель напряженно-деформируемого состояния образца в программе Ansys Mechanical, дающая возможность проводить теоретические исследования надежности соединения пломбировочных материалов с твердыми тканями зуба. Разработана методика сравнительной оценки погрешностей моделирования работы силовой установки в пакете Micro-Cap с результатами, полученными в программе Ansys Mechanical (принятыми в качестве эталона). Для реализации методики оценки в приведенных моделях одновременно менялся модуль Юнга образца от 10 до 330 ГПа.

Model-Based FDI Applied to a Piezoelectric Active Vibration Suppression System for Smart Flexible Spacecraft

Fault Detection and Isolation (FDI) techniques have captured extensive interest and attention in modern autonomous systems; in particular, they are of foremost importance in space applications, due to their scientific relevance, cost and current inability of doing on-orbit maintenance of space systems. In this scenario, FDI strategies are required to counteract possible failure events that, if not properly handled, can reduce system performance or compromise the realization of the mission objectives. In this paper, a model-based FDI strategy is implemented onboard a satellite equipped with a very large mesh reflector on which a distributed network of smart actuators/sensors is mounted to actively counteract undesired elastic vibrations. In particular, the detection and isolation of a possible piezo-actuator failure occurring in the Active Vibration Control (AVC) system of the antenna is addressed by a bank of Unknown Input Observers (UIOs). The design of the proposed UIOs is derived by solving a Linear Matrix Inequality (LMI) problem, which provides the conditions for their existence, and it is based on the linearized 3D state-space model of the controlled spacecraft, under the assumption that all the uncertainties, exogenous disturbances and measurement noises are neglected. Furthermore, pole assignment in the sense of D-stability is integrated in the standard formulation of the UIO to guarantee an adequate transient behaviour of the observers. Finally, an extensive Monte Carlo simulation campaign is conducted to assess the effectiveness of the proposed FDI architecture and its robustness against modelling uncertainties and measurement noise.

The design of a lumped parameter model considering the stimulus path of round window

BACKGROUND: Sound normally enters the ear canal, passes through the middle ear, and stimulates the cochlea through the oval window. Alternatively, the cochlea can be stimulated in a reverse manner, namely round window stimulation. The reverse stimulation is not well understood, partly because in classic lumped-parameter models the path of reverse drive during the round window stimulation is usually not considered. OBJECTIVE: The study goal is to gain a better understanding of the hearing mechanism during round window stimulation. METHODS: A piezo actuator was coupled to the oval and round window of the guinea pigs. The auditory brainstem response produced by the forward and reverse stimulation at four frequencies was recorded. RESULTS: The results show that the input voltage of the actuator required at the hearing threshold in the round window drive was higher than that in the oval window drive. In order to understand the data, we designed a lumped-parameter cochlear model that can simulate both forward and reverse drive. The model-predicted results were consistent with the experimental results. CONCLUSIONS: The response of the auditory system to stimulus of oval window and round window was quantified through animal experimentation, and guinea pigs were used as experimental animals. When the same stimulus was applied to the oval window and round window of the cochlea, the ABR signals were compared. A lumped parameter model was designed to incorporate the sound transmission paths in both oval and round window stimulation. The simulated results are consistent with those of animal experiments. This model will be useful in understanding the inner-ear response in round window.