Delay compensation for nonlinear teleoperators using predictor observers

This paper presents a delay compensation technique for nonlinear teleoperators by developing a predictor type sliding mode observer (SMO) that estimates future states of the slave operator. Predicted states are then used in control formulation. In the proposed scheme, disturbance observers (DOB) are also utilized to linearize nonlinear dynamics of the master and slave operators. It is shown that utilization of disturbance observers and predictor observer allow simple PD controllers to be used to provide stable position tracking for bilateral teleoperation. Proposed approach is verified with simulations where it is compared with two state-of-the-art methods. Successful experimental results with a bilateral teleoperation system consisting of a pair of pantograph robots also validates the proposed method

MoS2 Transistors Operating at Gigahertz Frequencies

The presence of a direct band gap and an ultrathin form factor has caused a considerable interest in two-dimensional (2D) semiconductors from the transition metal dichalcogenides (TMD) family with molybdenum disulphide (MoS2) being the most studied representative of this family of materials. While diverse electronic elements, logic circuits and optoelectronic devices have been demonstrated using ultrathin MoS2, very little is known about their performance at high frequencies where commercial devices are expected to function. Here, we report on top-gated MoS2 transistors operating in the gigahertz range of frequencies. Our devices show cutoff frequencies reaching 6 GHz. The presence of a band gap also gives rise to current saturation, allowing power and voltage gain, all in the gigahertz range. This shows that MoS2 could be an interesting material for realizing high-speed amplifiers and logic circuits with device scaling expected to result in further improvement of performance. Our work represents the first step in the realization of high-frequency analog and digital circuits based on two-dimensional semiconductors.Comment: Nano Letters (2014), Supplementary information available at http://dx.doi.org/10.1021/nl502863

Comparative study of NETmix and T-jets reactors based on pressure dynamics

Tese de mestrado integrado. Engenharia Química. Universidade do Porto. Faculdade de Engenharia. 201

Power and area efficient MOSFET-C filter for very low frequency applications

New circuit design techniques for implementing very high-valued resistors are presented, significantly improving power and area efficiency of analog front-end signal processing in ultra-low power biomedical systems. Ranging in value from few hundreds of \hbox{M}\Upomega to few hundreds of \hbox{G}\Upomega , the proposed floating resistors occupy a very small area, and produce accurately tunable characteristics. Using this approach, a low-pass MOSFET-C filter with tunable cutoff frequency (f C =20Hz-184kHz) has been implemented in a conventional 0.18μm CMOS technology. Occupying 0.045mm2/pole, the power consumption of this filter is 540 pW/Hz/pole with a measured IMFDR of 70 d

Expert designers’ perceptions about designing using Kansei engineering results

In a KE study to determine the emotional design features of a traditional product from Turkey, expert designers’ opinions were collected for the span the semantic space and span the space of properties steps of the KE methodology and an additional discussion came up. It was noted that the expert designers raised several questions about KE. They seemed to approach the potential KE results with caution because it was perceived as an intervention to their creative processes. During the interviews the following arguments came out: Design problems are irrational and wicked and do not have only one solution. What KE offers is scientific, but it may interfere with the creative process needed for designing. It can be useful for novice designers, but some experts think that they already have the intuitive knowledge of Kansei. After discussing with other KE researchers, about the similar experiences working with expert designers, there was the need to explore the issue in more detail. First, interviews were conducted with 4 expert designers. A scale was developed to assess their attitudes towards using KE results in design problems. Data was collected with an online questionnaire from 59 experts on the scale. The findings can be used in creating new strategies to introduce KE to design experts in a way that they can be convinced to use KE in their further design processes

Delay compensation in bilateral teleoperation using predictor observers

Destabilization and performance degradation problems caused by the time delay in communication channel is a serious problem in bilateral teleoperation. In particular, variability of the delay due to limited bandwidth, long distance or congestion in transmission problems has been a real challenge in bilateral teleoperation research since the internet communication has become prevalent. Many existing delay compensation techniques are designed for linear teleoperator systems. In order to implement them on real bilateral systems, the nonlinear dynamics of the robots must first be linearized. For this purpose feedback linearization is usually employed. In this thesis, the delay compensation problem is tackled in an observer framework by designing two observers. Integration of a disturbance observer to the slave side implies a linearized slave dynamics with nominal parameters. Disturbance observer estimates the total disturbance (nonlinear terms, parametric uncertainties and external disturbances) on the slave system. A second observer is designed at the master side to predict states of the slave. This observer can be designed using a variety of linear or nonlinear methods. In order to have finite-time convergence, a sliding mode observer is designed at the master side. It is shown that this observer predicts the future positions and/or velocities of the slave and use of such predictions in the computation of a simple PD control law implies stable operation for the bilateral system. Since the disturbance observer increases the robustness of the slave system, the performance of the resulting bilateral system is quite satisfactory. Force reflecting bilateral teleoperation is also considered in this thesis. Integrating the proposed observer based delay compensation technique into the well known four-channel control architecture not only stable but also transparent bilateral teleoperation is achieved. Simulations with bilateral systems consisting of 2 DOF scara robots and pantograph robots, and experiments with bilateral systems consisting of a pair of single link robots and a pair of pantograph robots validate the proposed method

OPINIONS OF TEACHER CANDIDATES ON DISTANCE EDUCATION IMPLEMENTED DURING THE COVID-19 PANDEMIC PERIOD

The learning environment, learning process and the opinions and suggestions for the problems concerning the process of students participating in distance education is thought to contribute to better planning and conducting distance education lessons. With this respect, the purpose of this study is to detect the reflections of the COVID-19 pandemic period on undergraduate education through opinions of teacher candidates. The qualitative internet research, which is one of the qualitative research models, was preferred for the study. The participant group was identified through the maximum sampling method. The participant group consisted of 27 teacher candidates studying in year 3. and year 4. The semi-structured interview form developed by the instructors was used as the data collection instrument. Content analysis was conducted through the Nvivo 11 software when analyzing the data. Positive-negative opinions of teacher candidates concerning distance education and the announcements made throughout the distance education process were collected for the study. In addition, the negative outcomes it caused on the participants, its reflections on the educational process, opinions-suggestions concerning assessment and evaluation and solution advices for the process were also identified. Article visualizations

Modeling Electrical Resistance Drift with Ultrafast Saturation of OTS Selectors

Crossbar array architecture is an essential design element for densely connected Non-Volatile Memory(NVM) applications. To overcome intrinsic sneak current problem of crossbar arrays, each memory unit is serially attached to a selector unit with highly nonlinear current-voltage (I-V) characteristics. Recently, Ovonic Threshold Switching (OTS) materials are preferred as selectors due to their fabrication compatibility with PRAM, MRAM or ReRAM technologies; however, OTS selectors suffer from the temporal drift of its threshold voltage. First, based on Poole-Frenkel conduction, we present time and temperature dependent model that predicts temporally evolving I-V characteristics,including threshold voltage of OTS selectors. Second, we report an ultrafast saturation ($\sim 10^3$ seconds) of the drift and extend the model to predict the time of drift saturation. Our model shows excellent agreement with OTS devices fabricated with 8 nm technology node at 25{\deg}C and 85{\deg}C ambient temperatures. The proposed model plays a significant role in understanding OTS device internals and the development of reliable threshold voltage jump table