Adaptive admittance tracking control for interactive robot with prescribed performance

An adaptive control approach is presented in this paper for tracking desired trajectories in interactive manipulators. The controller design incorporates prescribed performance functions (PPFs) to improve dynamic performance. Notably, the performance of the output error is confined in an envelope characterized by exponential convergence, leading to convergence to zero. This feature ensures a prompt response from admittance control and establishes a reliable safety framework for interactions. Simulation results provide practical insights,demonstrating the viability of the control scheme proposed in this paper.

Nullors, and Nullor Circuits;There Applications in Symbolic Circuit Analysis and Design

The objective in this presentation is to introduce some of the unique properties and applications of nullors in active circuit analysis and designs. The emphasis is to discuss the role nullors can play in symbolic representation of transfer functions. To show this we adopt the topological platform for the circuit analysis and use a recently developed Admittance Method (AM) to achieve the Sum of Tree Products (STP), replacing the determinant and cofactors of the Nodal Admittance Matrix (NAM) of the circuit. To construct a transfer function, we start with a given active circuit and convert all its controlled sources and I/O-ports to nullors. Now, with a solid nullor circuit (passive elements and nullors) we first eliminate the passive elements through AM operations. This produces the STPs. Second, the all-nullor circuit is then used to find the signs or the STPs. Finally, the transfer function (in symbolic, if chosen) is obtained from the ratio between the STPs.

Systematic Synthesis of Compressive VDTA-Based T-T Filter with Orthogonal Control of f_o and Q

Based on sixteen nullor-mirror models of the voltage differencing transconductance amplifier (VDTA) and port admittance matrices of the tow-Thomas (T-T) filter with orthogonal control between the characteristic frequency(f_0) and figure of merit (Q),two different categories of the voltage-mode and transconductance-mode T-T filters are synthesized by the means of the nodal admittance matrix (NAM) expansion method.The category A filter that employs two compressive VDTAs and two grounded capacitors includes four structures,and the category B filter that uses two compressive VDTAs,two grounded capacitors,and one grounded resistor,also includes four structures.These circuits are suitable for integrated circuit manufacture,and their parameters f_0 and Q can be orthogonally adjusted with varying the bias currents of VDTAs.After the paper and pencil test is completed,the computer analyses,including alternating current (AC),parameter sweep,Monte Carlo (MC),and noise analyses,are performed to support the synthesis approach.

Sound propagation in inhomogeneous waveguides with sound-speed profiles using the multimodal admittance method

The multimodal admittance method and its improvement are presented to deal with various aspects in underwater acoustics,mostly for the sound propagation in inhomogeneous waveguides with sound-speed profiles,arbitrary-shaped liquid-like scatterers,and range-dependent environments.In all cases,the propagation problem governed by the Helmholtz equation is transformed into initial value problems of two coupled first-order evolution equations with respect to the modal components of field quantities(sound pressure and its derivative),by projecting the Helmholtz equation on a constructed orthogonal and complete local basis.The admittance matrix,which is the modal representation of Direchlet-to-Neumann operator,is introduced to compute the first-order evolution equations with no numerical instability caused by evanescent modes.The fourth-order Magnus scheme is used for the numerical integration of differential equations in the numerical implementation.The numerical experiments of sound field in underwater inhomogeneous waveguides generated by point sources are performed.Besides,the numerical results computed by simulation software COMSOL Multiphysics are given to validate the correction of the multimodal admittance method.It is shown that the multimodal admittance method is an efficient and stable numerical method to solve the wave propagation problem in inhomogeneous underwater waveguides with sound-speed profiles,liquid-like scatterers,and range-dependent environments.The extension of the method to more complicated waveguides such as horizontally stratified waveguides is available.

Three-dimensional admittance analysis of lithospheric elastic thickness over the Louisville Ridge

Using bathymetry and altimetric gravity anomalies, a 1°×9 1° lithospheric effective elastic thickness（Te） model over the Louisville Ridge and its adjacent regions is calculated using the moving window admittance technique. For comparison, three bathymetry models are used： general bathymetric charts of the oceans, SIO V15.1,and BAT_VGG. The results show that BAT_VGG is more suitable for calculating T e than the other two models. T e along the Louisville Ridge was re-evaluated. The southeast of the ridge has a medium Te of 10–20 km, while Te increases dramatically seaward of the Tonga-Kermadec trench as a result of the collision of the Pacific and IndoAustralian plates.

Electric admittance analysis of quartz crystal resonator in thickness-shear mode induced by array of surface viscoelastic micro-beams

The electric admittance of a compound system composed of a thickness-shear mode （TSM） quartz crystal resonator （QCR） and an array of surface viscoelastic micro-beams （MBs） is studied. The governing equations of the MBs are derived from the Timoshenko-beam theory in consideration of shear deformation. The electrical admittance is described directly in terms of the physical properties of the surface epoxy resin （SU-8） MBs from an electrically forced vibration analysis. It is found that both the inertia effect and the constraint effect of the MBs produce competitive influence on the resonant frequency and admittance of the compound QCR system. By further comparing the numerical results calculated from the Timoshenko-beam model with those from the Euler-beam model, the shear deformation is found to lead to some deviation of an admittance spectrum. The deviations are revealed to be evident around the admittance peak（s） and reach the maximum when a natural frequency of the MBs is identical to the fundamental frequency of the QCR. Besides, a higher order vibration mode of the MBs corresponds to a larger deviation at the resonance.

Determination of interface states and their time constant for Au/SnO_2 /n-Si (MOS) capacitors using admittance measurements

The frequency dependence of admittance measurements （capacitance–voltage （C–V ） and conductance–voltage （G/ω–V ）） of Au/SnO2 /n-Si （MOS） capacitors was investigated by taking into account the effects of the interface states （N ss ） and series resistance （Rs ） at room temperature. Admittance measurements were carried out in frequency and bias voltage ranges of 1 kHz–1 MHz and （ 5V）–（＋9V）, respectively. The values of N ss and R s were determined by using a conductance method and estimating from the admittance measurements of the MOS capacitors. At low frequencies, the interface states can follow the AC signal and yield excess capacitance and conductance. In addition, the parallel conductance （G p /ω） versus log（f） curves at various voltages include a peak due to the presence of interface states. It is observed that the N ss and their time constant （τ） range from 1.23 ×10 12 eV-1 ·cm-2 to 1.47 ×10 12 eV-1 ·cm-2 and from 7.29 ×10-5 s to 1.81 ×10-5s, respectively.

Game Analysis of Rational FRS on Market Admittance

The dynamic signaling game-model is employed to study countermeasures of Q, U and C for supply-demand on financial market. As the game result, the mixed equilibrium of Q and U exists naturally without FRS. It is concluded that FRS on market admittance is objective demand of financial market, also the rational management behavior of government FRSI. And in addition to the empirical criteria, the FRS agreements between FRSI and financial-institutions should be considered as one of advanced FRS techniques. These must cover:① the regulation conformed status investigation with sufficient frequency,② corresponding punitive measures with sufficient strength. Thus the information can be delivered FRSI have ensured only qualified and regulation-conformed financial-institutions could be allowed to enter. That could safeguard the steadiness of the financial market.

Input Admittance and Current Distribution of Infinitely Long Circular Cylindrical Antenna Driven at Center

In this paper, by change of integration path in complex spectrum domain and by defining input admittance as the ratio of complex radiated power to amplitude of square of voltage across the gap, new expressions of admittance (valid for all frequencies ) of infinitely long cylindrical antenna with and without conducting ground are obtained. Meanwhile corresponding formulas of current distribution are derived in detail. Some numerical computations are also given.

A Study on a Conductor System for Investigation of Proximity Effect

The proximity effect is very significant to investigate transient peak voltages and EMC related problems of a conductor system. In this paper, effect of energized single conductor in close proximity of an Al plate when an Al plate is used as return path is investigated to find out proximity effect. The analysis involves simulation by the Finite Time Domain Method (FDTD) in comparison with field measurements. It is observed that the current distribution is uneven in pipe conductor due to the proximity effect of varying heights from ground.

Power System Harmonics Study for Unbalanced Microgrid System with PV Sources and Nonlinear Loads

Harmonics distortion is a crucial problem in microgrid. Harmonic sources can be categorized as two main factors: renewable energy integration and nonlinear loads. Both factors are investigated in this paper. For renewbale energy, photovoltaic (PV) power is one of the most effective solutions for energy crisis and it is showing great potential for serving customers in microgrid. A three- phase PV source model is establised and integrated at different locations in order to observe the impact of harmonics on a microgrid and power quality (PQ). A composite load is modeled using Crossed Frequency Admittance Matrix theory. A practicdal microgrid loacated at GA, USA is used as a study system. The microgrid, PV model and nonlinear load model are simulated in MATLAB/ Simulink environment. The results show the impact of installing PV sources at two types of locations considering linear and composite nonlinear loads. In addition, three PQ indices are discussed to show the numerical impacts with various perspectives.

Least Squares Hermitian Problem of Matrix Equation (<i>AXB</i>, <i>CXD</i>) = (<i>E</i>, <i>F</i>) Associated with Indeterminate Admittance Matrices

For A&#8712;Cm&#935;n, if the sum of the elements in each row and the sum of the elements in each column are both equal to 0, then A is called an indeterminate admittance matrix. If A is an indeterminate admittance matrix and a Hermitian matrix, then A is called a Hermitian indeterminate admittance matrix. In this paper, we provide two methods to study the least squares Hermitian indeterminate admittance problem of complex matrix equation (AXB,CXD)=(E,F), and give the explicit expressions of least squares Hermitian indeterminate admittance solution with the least norm in each method. We mainly adopt the Moore-Penrose generalized inverse and Kronecker product in Method I and a matrix-vector product in Method II, respectively.

Using an Off-the-Shelf Lock-In Detector for Admittance Spectroscopy in the Study of Plants

We report on the development of an electrical characterization admittance spectroscopy equipment and method based on an off-the-shelf lock-in detector that is cheap and yet highly sensitive. It is concluded that a contacted constant-pressure electrode configuration is preferable. It was further determined that the temperature does not have great impact in the measured values, but relative humidity of air can be important, especially in the constant-gap electrode configuration. In-situ measurements are difficult since the coupling of the plant with the environment is of high importance. Another aspect is the cables;they are important in that they have to be terminated by their characteristic impedance (50 &Omega;?in our case) to avoid reflections that introduce artificial attenuation and phase shifts in the signal. We introduce a fingerprint plot type to be able to distinguish between various plants and other specimens, and can actually detect the aqueous state of a plant.

Computing of Mutual Admittance between Two Circumferential Slots on Cylindrical Waveguide

This paper studies radiation from circumferential slots on cylindrical waveguide by Poynting’s vector method. It can help us to find mutual admittance between two circumferential slots in an antenna array. The main advantage of Poynting’s vector method is its accurate convergence to compute mutual admittance between two circumferential slots. The importance of this matter will be more salient while we want to compare it with other mutual admittances and also use it to optimize an antenna array.

On the Profiling of Air Leakage Infiltration Pattern across Chinese Vernacular Buildings

The purpose of this paper is to provide understanding of the seasonal pattern of air leakage(infiltration)in Chinese vernacular buildings across China’s five climate regions.In achieving the set purpose,a grand extensive literature survey was conducted and supported with data drawn from established Meteonorm V6.1 on sensible heat and psychrometric variables.Numerical computations for normalized and specific infiltration from stack effects followed the Gowri method in line with ASHRAE reference 2004.Solar energy admittance into building followed Bouger’s model form Angstrom properties.From the distribution of vernacular buildings across five climate regions of China,evidence from computational and numerical values showed symmetries in terms of minimums and maximums times of occurrence.Further,a reciprocal pattern exists between solar radiative admittance and region’s temperature profile.Knowing that Chinese vernacular building heritage extended to further Asia,this research became limited to only the Chinese region.It became difficult to report if the construction culture away from China has correlation with infiltration and energy admittance value.Earlier works on Chinese climate and vernacular dwellings reported a climate responsive dwelling designed by passive cooling strategy;a gap was closed by extending the previous work to specific infiltration pattern and energy admittance level.Chinese vernacular buildings by virtue of research outcomes are and should be adoptable to modern housing needs for cultural integration.

Flexible assistance strategy of lower limb rehabilitation exoskeleton based on admittance model

Exercise training based on exoskeleton is an effective rehabilitation method for stroke patients. However, some rehabilitation exoskeletons still have poor wearable performance and obvious human-robot impedance during training, which easily cause secondary injuries to the patients. In this study, a variable admittance control strategy is proposed to improve the operator's wearable comfort, which can adapt to different operators by regulating admittance parameters. The admittance controller has two feedback loops: the position inner-loop and the admittance outer-loop. Meanwhile, the exoskeleton Lagrange model is constructed with unknown friction disturbance. By using Lyapunov technique and backstepping with state observer, the joint position error of exoskeleton is convergence into a zero neighborhood. The effectiveness of the proposed admittance controller is verified by both simulation and experiment. The tracking error of hip and knee joint is less than 4 degrees while the human-robot interaction torque is constrained in a tolerable range of the operator.

An Efficient Method to Estimate Admittance of Black-boxed Inverter-based Resources for Varying Operating Points

Traditional analytical approaches for stability assessment of inverter-based resources(IBRs),often requiring detailed knowledge of IBR internals,become impractical due to IBRs’proprietary nature.Admittance measurements,relying on electromagnetic transient simulation or laboratory settings,are not only time-intensive but also operationally inflexible,since various non-linear control loops make IBRs’admittance models operating-point dependent.Therefore,such admittance measurements must be performed repeatedly when operating point changes.To avoid time-consuming and cumbersome measurements,admittance estimation for arbitrary operating points is highly desirable.However,existing admittance estimation algorithms usually face challenges in versatility,data demands,and accuracy.Addressing this challenge,this letter presents a simple and efficient admittance estimation method for blackboxed IBRs,by utilizing a minimal set of seven operating points to solve a homogeneous linear equation system.Case studies demonstrate this proposed method ensures high accuracy across various types of IBRs.Estimation accuracy is satisfying even when non-negligible measurement errors exist.

Bathymetry predicted from vertical gravity gradient anomalies and ship soundings

In this paper, the admittance function between seafloor undulations and vertical gravity gradient anomalies was derived. Based on this admittance function, the bathymetry model of 1 minute resolution was predicted from vertical gravity gradient anomalies and ship soundings in the experimental area from the northwest Pacific. The accuracy of the model is evaluated using ship soundings and existing models, including ETOPO1, GEBCO, DTU10 and V15.1 from SIO. The model＇s STD is 69. 481m, comparable with V15.1 which is generally believed to have the highest accuracy.

Control and Implementation of 2-DOF Lower Limb Exoskeleton Experiment Platform

In this study,a humanoid prototype of 2-DOF(degrees of freedom)lower limb exoskeleton is introduced to evaluate the wearable comfortable effect between person and exoskeleton.To improve the detection accuracy of the humanrobot interaction torque,a BPNN(backpropagation neural networks)is proposed to estimate this interaction force and to compensate for the measurement error of the 3D-force/torque sensor.Meanwhile,the backstepping controller is designed to realize the exoskeleton's passive position control,which means that the person passively adapts to the exoskeleton.On the other hand,a variable admittance controller is used to implement the exoskeleton's active followup control,which means that the person's motion is motivated by his/her intention and the exoskeleton control tries best to improve the human-robot wearable comfortable performance.To improve the wearable comfortable effect,serval regular gait tasks with different admittance parameters and step frequencies are statistically performed to obtain the optimal admittance control parameters.Finally,the BPNN compensation algorithm and two controllers are verified by the experimental exoskeleton prototype with human-robot cooperative motion.

Estimation of the elastic thickness over ancient Mare Moscoviense

The Moscoviense basin is an atypical lunar impact basin with concentric rings of positive and negative gravity anomalies. This basin can provide insights into the inhomogeneous thermal activities across the farside of the Moon. Based on an updated spherical harmonic thin elastic-shell loading model, we used localized admittance analyses to estimate the elastic thickness as well as other associated selenophysical parameters for the Moscoviense basin. The high precision gravity and topography data employed in our estimation were collected by the Gravity Recovery and Interior Laboratory and the Lunar Orbiter Laser Altimeter missions. Our results indicate that the crust-mantle interface is mainly compensated by the prefilling depth rather than the observed surface topography. The results constrained within two standard deviations yielded a small load ratio(~0.168), a best-fit crustal thickness of 36.2 km, and an optimized crustal density of 3159.5 kg m-3. Such large density approaches the density of olivine-rich mantle materials, implying that the excavation of the Mare Moscoviense occurred during a basin-forming impact. The inversed elastic thickness at Mare Moscoviense was around 18 km, lower than the previous results(~60 km) found over Mare basins on the lunar nearside. These results indicate that extreme thermal activity existed during the Moscoviense basin-forming period such as reheating mechanisms from a double-impact process and mare volcanism.