Current-based Approach Research Articles

Estimating Gripping Forces During Robot- Assisted Surgery Based on Motor Current

Abstract Accurate measurement of interaction forces during robot-assisted surgery requires compact force sensing modalities in the surgical tools, thus might add considerable cost to the setup. Measuring the motor current to estimate gripping forces, is an advantageous approach since no expensive force sensor is needed. In this paper, a mechanical interface is presented, which allows actuating conventional articulated instruments for robot-assisted surgery. The interface features the estimation of static gripping forces at the instrument’s tip based on the motor current. The evaluation shows reproducible results, and the current-based approach seems to be a cost-efficient way to estimate gripping forces.

Efficient treatment of low-frequency response and decoherence in a real-time evolution scheme.

In this paper, we present an improved real-time current-based approach for calculating the frequency-dependent dielectric function of a bulk periodic system, which can achieve a unified treatment of longitudinal and transverse macroscopic geometries on the same footing, and an improvement to make the approach of calculating dielectric function more robust for the avoidance of numerical divergencies at low frequency near zero in some specific cases. The validity of the improved approach implementation is verified by calculating the dielectric function of bulk periodic system in the ground in the longitudinal geometry, enabling the improved approach to be extended to excited bulk periodic systems in the transverse geometry. Further, a phenomenological description of decoherence has been incorporated within the framework of time-dependent density-functional theory (TDDFT). It is concluded that the decoherence model can suppress the numerical divergence of low frequency and grows the excitonic feature of silicon, although it adopts the approximate time-dependent exchange-correlation potential. Thus, the use of the decoherence TDDFT model opens pathways for handling the decoherence effects within the framework of TDDFT.

Characteristic Mode Analysis of Mutual Coupling

Mutual coupling between neighboring antennas is a major concern in the array design. Using the concept of characteristic modes, this work proposes a theoretical framework for the analysis of such electromagnetic interaction and its control mechanism. The root of interelement coupling lies in the mutually induced current in the neighboring elements. Henceforth, the initial part of this work concentrates on computing the coupled current by modeling the interaction of the uncoupled modes. Closed-form formulations have been derived for quantifying the coupling impacts. The proposed formulations have been further verified with numerical examples and method of moment-based commercial solver, such as Antenna Toolbox. Later, the theory of substructure modes has been combined with the theory of coupled characteristic modes to understand the perturbation in coupling behavior in the presence of ground plane or a parasitic element. A design strategy has been suggested to optimize the shape of the intermediate parasitic structure for controlling the coupled current in the neighboring elements. This current-based approach can find applications in different coupled scenarios such as antenna arrays or in printed circuit board components.

Non-Cartesian k-space trajectory calculation based on concurrent reading of the gradient amplifiers' output currents.

Non-Cartesian imaging sequences involve sampling during rapid variation of the encoding field gradients. The quality of the reconstructed images often suffers from insufficient knowledge of the exact dynamics of the actual fields applied during sampling. We propose determination of the accurate field dynamics by measuring the currents at the gradient amplifier outputs using the amplifiers' internal sensors concurrently with imaging. The actual dynamic field evolution is then determined by convolution with the measured current-to-field impulse response function of the gradient coil. Integration of the gradient field evolution allows derivation of the k-space trajectory for reconstruction. The current-based approach is investigated in spiral and ultrashort TE phantom imaging. In comparison with the model-based product reconstruction as well as a correction approach based on the conventional input waveform-to-field impulse response function, it provides slightly improved image quality. The improvement is ascribed to a better representation of eddy current and amplifier nonlinearity effects. Trajectory calculation based on measured amplifier output currents offers a robust, purely measurement-based alternative to conventional model-based approaches. The implementation can mitigate gradient amplifier imperfections with no or little additional hardware effort.

Distributed selective harmonic mitigation and decoupled unbalance compensation by coordinated inverters in three-phase four-wire low-voltage networks

Considering the high penetration of distributed generators in low-voltage grids, establishing a coordinated operation of their grid-tied inverters has become imperative to move towards the implementation of smart grids. Yet, knowing that mitigation of power quality issues such as reactive power, current unbalance and harmonics is of importance within such a context, this work proposes a master/slave control approach, which uses a communication means of low-bandwidth, to flexibly coordinate four-leg inverters dispersed in three-phase four-wire networks. Their coordination is attained by means of a current-based approach, allowing the sharing of active, reactive, harmonic and unbalance currents drawn by loads. The control strategy also regulates the power flow at the point of common coupling of the low-voltage network, while proportionally steering inverters according to their nominal capabilities. In addition to the offering of selective harmonic mitigation, the control approach provides distributed and decoupled unbalance compensation, in partial or total portion, based on concepts from the Conservative Power Theory. Consequently, extraction of sequence components or implementation of virtual impedance control loops are not required. The proposed strategy is evaluated based on multiple simulation results, considering the CIGRE's European low-voltage distribution benchmark, including six distributed inverters, as well as linear and nonlinear loads.

A Current-Based Approach for Short-Circuit Fault Diagnosis in Closed-Loop Current Source Inverter

In this article, a method based on output currents is proposed to diagnose short-circuit faults of single or double switches in current source converter. The method only needs the feedback currents and their corresponding reference signals that can be obtained from the main control system. This diagnosis algorithm needs to calculate the average values of the feedback currents and the average absolute values of the current reference signals in one power frequency cycle. Diagnosis variables can be obtained from the ratio of the two values. Then, three detection thresholds are set to judge and locate the short-circuit power switches. The method can be implemented in the main control program directly, without additional voltage sensors and other auxiliary detection devices. Meanwhile, the method is simple and easy to implement in practice. The effectiveness of proposed algorithm is validated with experiments.

A New Consideration for Validating Battery Performance at Low Ambient Temperatures

Existing validation methods for equivalent circuit models (ECMs) do not capture the effects of operating lithium-ion cells over legislative drive cycles at low ambient temperatures. Unrealistic validation of an ECM may often lead to reduced accuracy in electric vehicle range estimation. In this study, current and power are used to illustrate the different approaches for validating ECMs when operating at low ambient temperatures (−15 °C to 25 °C). It was found that employing a current-based approach leads to under-testing of the performance of lithium-ion cells for various legislative drive cycles (NEDC; FTP75; US06; WLTP-3) compared to the actual vehicle. In terms of energy demands, this can be as much as ~21% for more aggressive drive cycles but even ~15% for more conservative drive cycles. In terms of peak power demands, this can range from ~27% for more conservative drive cycles to ~35% for more aggressive drive cycles. The research findings reported in this paper suggest that it is better to use a power-based approach (with dynamic voltage) rather than a current-based approach (with fixed voltage) to characterise and model the performance of lithium-ion cells for automotive applications, especially at low ambient temperatures. This evidence should help rationalize the approaches in a model-based design process leading to potential improvements in real-world applications for lithium-ion cells.

Optical properties of periodic systems within the current-current response framework: Pitfalls and remedies

We compare the optical absorption of extended systems using the density-density and current-current linear response functions calculated within many-body perturbation theory. The two approaches are formally equivalent for a finite momentum $\mathbf{q}$ of the external perturbation. At $\mathbf{q}=\mathbf{0}$, however, the equivalence is maintained only if a small $q$ expansion of the density-density response function is used. Moreover, in practical calculations, this equivalence can be lost if one naively extends the strategies usually employed in the density-based approach to the current-based approach. Specifically, we discuss the use of a smearing parameter or of the quasiparticle lifetimes to describe the finite width of the spectral peaks and the inclusion of electron-hole interaction. In those instances, we show that the incorrect definition of the velocity operator and the violation of the conductivity sum rule introduce unphysical features in the optical absorption spectra of three paradigmatic systems: silicon (semiconductor), copper (metal) and lithium fluoride (insulator). We then demonstrate how to correctly introduce lifetime effects and electron-hole interactions within the current-based approach.

A Novel Product-Level Human Metal Model Characterization Methodology

A new methodology for characterizing product-level failures due to the human metal model (HMM) stress is proposed and developed. This characterization framework is superior to the conventional leakage current-based approach, and it enables early wafer-level assessment of integrated circuits' HMM robustness. The new method is demonstrated in two amplifiers and is benchmarked versus the conventional leakage current method and the industry standard system-level IEC gun testing.

On the Effective Low-Grazing Reflection Coefficient of Random Terrain Roughness for Modeling Near-Earth Radiowave Propagation

An investigation on the effects of terrain roughness on near-ground radiowave propagation is featured. In spite of the fact that a variety of analytical and numerical routines have been proposed by many workers for the general treatment of the scattering properties of rough surfaces, much disagreement remains in the solution of the problem for near-grazing scenarios. In striving to analytically describe the near-grazing propagation of signals from 2D and 3D radiators, an existing volumetric polarization current-based perturbation approach is exploited in this work to formulate closed-form expressions for the coherent rough surface reflection coefficients. Although the perturbation approach was originally intended for analyzing the scattering coefficients of a ground with scale of roughness much smaller than the wavelength, it is shown through Monte Carlo simulations that the effective reflection coefficients reported herein are applicable for near-ground path-loss prediction even when the surface variation (rms height) is on the order of a wavelength or more.

Development of a displacement current-based sensor for electrical capacitance tomography applications

This paper presents the development of an Electrical Capacitance Tomography sensor, allowing for the reconstruction of the permittivity distribution in a piping system. Two suitable front-end circuit concepts for the sensor are investigated — one is based on the measurement of displacement currents and the other on electrode potential measurement. Input stage circuit models are used to analyse the robustness against stray capacitances, indicating clear advantages of the displacement current-based approach. Hence, a further examination of this concept is carried out, including the hardware design and the development of the front-ends. For the entire tomography sensor, applied image reconstruction methods, and measurement results are presented in this paper.

A Realization of a Below-1-V Operational and 30-MS/s Sample-and-Hold IC With a 56-dB Signal-to-Noise Ratio by Applying the Current-Based Circuit Approach

This paper demonstrates the low-voltage and low-power operation of a MOS sample-and-hold circuit while preserving speed and accuracy, aiming at the realization of a pipelined low-voltage and low-power analog-to-digital converter on a system large-scale integrated circuit. It was fabricated by utilizing 0.35-/spl mu/m CMOS technology. The main feature of this circuit is that all the input, signals, and output are in the current form. The circuit consists of simple current mirrors. In order to eliminate the signal-dependent current transfer ratio error, voltages at the drain terminals of mirror transistors are fixed as constant. A source degeneration resistor, which is a transistor in the triode operational region, is connected to a mirror transistor in order to alleviate the influence of the threshold and transconductance parameter variations. Control signals are boosted in voltage and applied to the gate of switch NMOS transistors in the signal path in order to reduce the on-resistance of analog switches. A differential configuration is adopted throughout the entire circuit and effectively cancels switch feedthrough errors. As a result, a 30-MS/s operation with a signal-to-noise ratio (SNR) of 56 dB from a 1-V supply has been achieved, when the input current is /spl plusmn/200 /spl mu/A. The chip even operated down to 0.85 V with a 20-MHz clock. The SNR was measured as 50 dB with an input current of /spl plusmn/100 /spl mu/A.