Passive Impedance Research Articles

Adaptive impedance control of a variable stiffness actuator

This paper proposes an optimal impedance control method for a variable stiffness actuator (VSA), in which a variable stiffness mechanism and an actuator are aligned in series. First, we introduce a circuit expression of the robotic system and provide a unified framework to determine an optimal index of robots driven by VSAs, irrespective of the presence or absence of the environment. Next, we design a torque controller for a one-degree-of-freedom (DOF) robot and find the optimal condition of the stiffness in the VSA for a given task. Then, we design a stiffness control law for the VSA exploiting the intrinsic indivisible property between motion and passive impedance. This stiffness control law adaptively tunes the passive stiffness to minimize the energy consumption without defining any explicit desired impedance, which is usually required in impedance controllers. The stability of the closed loop system is proved using Lyapunov’s analysis. Simulations and experimental results validate the effectiveness of the proposed method and the robustness in response to parameter changes.

Wideband Impedance Measurements and Modeling of DC Motors for EMI Predictions

In electromagnetic interference prediction, dc motors are usually modeled as a source and a series impedance. Previous researches only include the impedance of the armature, while neglecting the effect of the motor's rotation. This paper aims at measuring and modeling the wideband impedance of a dc motor under operating conditions. These measurements are performed by injecting a small signal, using a method based on conducted susceptibility measurement setups as described in military standards. Different setups are developed to cover a wideband, from 0 Hz up to 200 MHz. The measurements provide satisfying results for the wideband impedance of the rotating dc motor, and the setups’ validation is discussed. Finally, the resulting impedance is modeled as a passive impedance network.

Broadband Bent Triangular Omnidirectional Antenna for RF Energy Harvesting

In this letter, a broadband bent triangular omnidirectional antenna is presented for RF energy harvesting. The antenna has a bandwidth for ${\hbox {VSWR}}\leq2$ from 850 MHz to 1.94 GHz. The antenna is designed to receive both horizontal and vertical polarized waves and has a stable radiation pattern over the entire bandwidth. Antenna has also been optimized for energy harvesting application and it is designed for $100~\Omega $ input impedance to provide a passive voltage amplification and impedance matching to the rectifier. A peak efficiency of 60% and 17% is obtained for a load of $500~\Omega $ at 980 and 1800 MHz, respectively. At a cell site while harvesting all bands simultaneously a voltage of 3.76 V for open circuit and 1.38 V across a load of $4.3~\hbox{k} \Omega $ is obtained at a distance of 25 m using an array of two elements of the rectenna.

Design of Mechanical Structure & Control System of a Lower Limb Rehabilitative Robot

The rehabilitation robot which consists of two mechanical legs and an automatic seat was produced according to ergonomics. Each mechanical leg has three DOF. It can train patients combined with sEMG signal and FES. The rehabilitation robot has three train modes: passive mode, assistant mode and impedance mode, and it suits patients with different rehabilitation phases.

A two-axis cable-driven ankle-foot mechanism

Abstract This paper describes a novel cable-driven ankle-foot mechanism with two controllable degrees of freedom (DOF) in dorsiflexion-plantarflexion (DP) and inversion-eversion (IE). The presented mechanism is a proof of concept to demonstrate feasibility. Ankle kinematic measurements demonstrate that ankle IE rotations during a step turn are significantly different from walking on a straight path. This suggests that the ankle-foot mechanisms used in prostheses, exoskeletons, and bipedal robots can be improved by controlling a second degree of freedom in the frontal plane. The proposed prototype mechanism is described in detail, and its design considerations and parameters are presented. The mechanism is capable of producing trajectories similar to the human ankle during a step turn. The device shows passive mechanical impedance close to the human ankle mechanical impedance, allowing its mechanical impedance to be controlled using an impedance controller. The presented mechanism is capable of providing key mechanical characteristics similar to the human ankle, including power, range of motion, and weight, suggesting the feasibility of this design concept.

Sensorless Implementation of a PPF Controller for Active <inline-formula> <tex-math notation="TeX">$Q$ </tex-math></inline-formula> Control of an AFM Microcantilever

Reducing the cantilever quality (Q) factor in the atomic force microscope (AFM), when operating in tapping mode, allows for an increase in imaging speed. Passive piezoelectric shunt control has several advantages over alternative methods of cantilever Q factor reduction. However, this technique uses a passive electrical impedance to modify the mechanical dynamics of the cantilever, which limits the amount of Q factor reduction achievable. This paper demonstrates that further reductions in the cantilever Q factor may be obtained with the use of an active impedance in the piezoelectric shunt control framework. The active impedance parameters are designed in such a way that the piezoelectric shunt controller emulates a positive position feedback controller in a displacement feedback control loop. A significant reduction in cantilever Q factor is obtained using an active impedance compared with that achieved with a passive impedance. The improvement in scan speed using this control technique is demonstrated with AFM images of a test sample.

Performance Improvement of Isolated High Voltage Full Bridge Converter Using Voltage Doubler

The performance of an isolated high voltage full bridge converter is improved using a voltage doubler. In a conventional high voltage full bridge converter, the diode of the transformer secondary voltage undergoes a voltage spike due to the leakage inductance of the transformer and the resonance occurring with the parasitic capacitance of the diode. In addition, in the phase shift control, conduction loss largely increases from the freewheeling mode because of the circulating current. The efficiency of the converter is thus reduced. However, in the proposed converter, the high voltage dual converter consists of a voltage doubler because the circulating current of the converter is reduced to increase efficiency. On the other hand, in the proposed converter, an input current is distributed when using parallel input / serial output and the output voltage can be doubled. However, the voltages in the 2 serial DC links might be unbalanced due to line impedance, passive and active components impedance, and sensor error. Considering these problems, DC injection is performed due to the complementary operations of half bridge inverters as well as the disadvantage of the unbalance in the DC link. Therefore, the serial output of the converter needs to control the balance of the algorithm. In this paper, the performance of the conventional converter is improved and a balance control algorithm is proposed for the proposed converter. Also, the system of the 1.5[kW] PCS is verified through an experiment examining the operation and stability.

Multi-state and Interleaved Converters With Passive Impedances for Current Sharing

This paper presents multilevel switching cells that allow the generation of high-power nonisolated dc-dc, ac-dc, dc-ac, and ac- ac converters. The cells are classified in two groups: multi-state switching cells (MSSC) based on autotransformer and interleaved switching cells (ISC) based on inductors. Each switching cell has an impedance based on a small inductor Lsh connected between the legs, which is named current sharing circuit (CSC) and guarantees zero average voltage across the involved magnetic components, therefore compensating eventual differences between the PWM (pulse width modulation) duty cycles. The small inductor causes the duty cycle to be reduced, and consequently its inductance is typically very small. In order to verify the current sharing between the magnetic components, two dc-dc buck converters operating at 25 kHz and rated at 1 kW, where the input voltage is 200 V and the output voltage is 60 V , are implemented and evaluated in laboratory.

A Passive Impedance Matching Interface Using a PC Permalloy Coil for Practically Enhanced Piezoelectric Energy Harvester Performance at Low Frequency

This paper presents an analytical and experimental study of a passive impedance matching interface based on a large inductive reactance but with a centimeter-scaled size for practically enhanced piezoelectric energy harvester performance at low frequency. Low frequency vibration normally leads to a large capacitive reactance value for small-sized piezoelectric energy harvesters and it is impractical to achieve the maximum power transfer condition by use of a conventional inductor as its volume would be of a few cubic meters. In this paper, PC permalloy material was used to implement a passive impedance matching interface in order to reduce the size of the inductor to a few cubic centimeters as it has a very high initial magnetic permeability of 6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> H/m. The implemented interface is capable to practically perform the complex conjugate load matching of a macrofiber composite energy harvester at a frequency ≤10 Hz. The effects of the interface on the voltage, current, and power transferred to resistive loads were examined through comparisons of the results between configurations with and without the interface for applied strain levels and frequencies in the range between 480-1170-με peak-to-peak and 2.5-10 Hz, respectively. An increment of the power around 94.6% was obtained under an excitation of 480 με at 10 Hz in correspondence to an optimal resistive load reduced by over 70%. Compared with the state-of-the-art active impedance matching techniques, which use additional power sources to control the signal generated by piezoelectric energy harvesters, the developed interface is totally passive, easier to be implemented, and can be potentially used for the enhancement of vibration energy harvesting performance.

Properties of passive nano films on zircaloy-4 affected by defects induced by hydrogen permeation

In this work, hydrogen absorption and the permeation behavior of the passive layer formed on zircaloy-4 are investigated. Potentiodynamic polarization, Mott—Schottky analysis, electrochemical impedance spectroscopy, and Raman scattering spectroscopy are employed to characterize the passive defects before and after hydrogen permeation. It is found that the nanoscale passive ZrO2 films play an important role in the resistance against corrosion; hydrogen impingement, however, reduces the passive impedance towards hydrothermal oxidation. The increase of defects (vacancies) in passive film is probably attributed to the degradation. We believe that this finding will provide valuable insight into the understanding of the corrosion mechanism of zircaloys used in light water reactors.

Analysis of Coupled Stability in Multilateral Dual-User Teleoperation Systems

In this paper, we set out a framework for the analysis of coupled stability in dual-user linear teleoperation systems. An extension of the Zeheb–Walach (ZW) criteria for absolute stability of an $n$ -port network will be stated and proven. While the original theorem states conditions for asymptotic stability of a network terminated by passive impedances, the extended version allows for poles on the imaginary axis, which makes it applicable to a larger class of systems, such as robotic applications with position feedback. The extended theorem includes conditions on the Laurent expansion of the elements and the principal minors of the network immittance matrix. A novel dual-user shared control paradigm, realizing a three-way gearbox mechanism, is presented. A numerical analysis of absolute stability of the three-port network, representing the shared control architecture, demonstrates the effectiveness of the extended Zeheb–Walach method.

Equivalent Circuit of Single-Core Cable Lines Suitable for Grounding Systems Analysis Under Line-to-Ground Faults

This paper presents two approaches where the single-core cable line and an additional conductor laid in parallel can be reduced to a simple equivalent π-circuit containing an active element beside the usual passive impedances. The parameters of the equivalent circuit are calculated using a numerical approach where the distributed parameter line was discretized and an analytical approach is based on the wave propagation theory. A series of tests has been performed to determine error levels in both cases showing that they are less than 1%. With numerical examples, we show that the cable equivalent circuit offers a simple way to calculate voltages in complex grounding systems. The results are in good agreement with the previously published calculated and/or measured values. Both approaches offer the possibility of calculating voltage and current distribution along the cable line which gives insight into the significance of each cable component in the complex grounding system.

Sensorless Damping Control of a High Speed Flexure Guided Nanopositioner

The scan speed of the Atomic Force Microscope (AFM) is limited by the highly resonant nature of the nanopositioner which scans the sample relative to the probe tip. Feedback control may be used to dampen the resonance; however this requires external displacement sensors which may introduce high frequency noise into the feedback loop. In this work an active piezoelectric shunt control system, which requires no external feedback sensors, is designed to damp the resonance of a high speed flexure guided nanopositioner. The shunt impedance is designed in such a way that the closed loop transfer function from applied voltage to actuator displacement is equivalent to that of a displacement feedback system using a Positive Position Feedback (PPF) controller. This impedance design is an improvement over a passive impedance in that higher damping of the resonance is achievable. AFM images of a test sample were obtained to demonstrate the reduction of image artifacts when this control technique is applied.

Active Impedance Matching

Electrically small antenna suffer from the high Q impedance such as narrow bandwidth and poor gain. To improve them, passive impedance matching is often used but it is restricted to a Bode-Fano limit. To skip it, active matching incorporating non-Foster circuits can provide a good solution. Using non-Foster theory, in this paper an active reactance circuit (ARC) design is proposed for application to electrically small antenna prototypes.

Development of Lean Duplex Stainless Steels (LDSS) with Superior Mechanical and Corrosion Properties on Laboratory Scale

Low-Ni and Ni-free varieties of duplex stainless steels (DSSs) have been successfully developed for the first time on laboratory scale in SAIL. The alloy compositions for Ni-free and low-Ni (&lt;1.5 wt%) DSSs were evolved through formulation of appropriate chromium and nickel equivalents to achieve an optimum phase balance of 55 vol% austenite and 45 vol% ferrite in stainless steel microstructures. Laboratory heats were made achieving target chemistries and cast into 100 mm square cross-sectioned ingots. The ingots were subsequently soaked at 1150 °C for 3 hrs for thermal/ compositional homogenization and hot rolled in number of passes to 6 and 16 mm strips in Hillé experimental rolling mill with finish rolling temperatures of 950-980 °C. The hot rolled strips were eventually conferred solution annealing treatment by soaking them at 1060 °C for 2 hours followed by rapid quenching in water to prevent precipitation of deleterious intermetallic compounds (IMCs) and secondary phases. The new steels revealed an exceptional combination of properties: higher yield strength (488 MPa for low-Ni DSS and 501 MPa for Ni-free DSS), higher tensile strength (664 MPa for low-Ni DSS and 677 MPa for Ni-free DSS) and superior Charpy V-notch impact toughness (230 and 129 Joules at room temperature and -20°C, respectively, for low-Ni DSS as against 80 and 52 Joules at similar temperatures for Ni-free DSS). The yield strength of the steels was assessed to be about 1.6-1.8 times that of conventional austenitic grades AISI 304 L and AISI 316 L in annealed condition. The low-Ni and Ni-free DSS showed remarkable corrosion resistance and have been found to exhibit passivity, corrosion rates as low as 0.08-0.11 mpy, pitting potentials in the range of 482-596 mV and charge transfer resistances of the order of 106 W.cm2 in highly corrosive environment of 3.5% NaCl. The steels have been thus found to be superior in pitting/ localized corrosion resistance to AISI 304 L with pitting potential of 437 mV and comparable in performance with AISI 316 L with its high pitting potential of 602 mV. Even in the strongly reducing environment of 0.1 N H2SO4, the new steels have revealed tendency to passive film formation, breakdown potentials of 1127-1153 mV and passive film impedances of 104 W.cm2, comparable to the standard austenitic grades AISI 304 L and AISI 316 L. In boiling MgCl2 solutions, the low Ni DSS has been found to resist stress corrosion cracking (SCC) up to 24 h; the time for crack initiation being intermediate to that for AISI 304 L (3 h) and AISI 316 L (32 h). The Ni-free DSS, on the other hand, was found to exhibit no signs of SCC failure even after 72 h of exposure to the test solution. The degree of sensitization (DoS) for both low Ni and Ni-free DSSs has been quantified to be £ 0.05 in 0.5 M H2SO4 + 0.01 M KSCN, which has revealed their insusceptibility to intergranular corrosion (IGC). The steels have been found to be free from deleterious intermetallic phases such as sigma (s), chi (c), etc. and this has been ascertained from corrosion rates of &lt;10 mdd in ferric chloride corrosion testing as per ASTM A 923 Method C.

An Exposition on the Choice of the Proper S Parameters in Characterizing Devices Including Transmission Lines with Complex Reference Impedances and a General Methodology for Computing Them

The purpose of this paper is to demonstrate that the recently published paper [1] dealing with little known facts and some new results on transmission lines is due to an incomplete interpretation of the nonphysical artifacts resulting from a particular mathematical model for the S parameters. These artifacts are not real and do not exist when a different form of the S parameters is used.The first objective of this paper is thus to introduce the two different types of S parameters generally used to characterize microwave circuits with lossy characteristic impedance. The first type is called the pseudo wave, an extension of the conventional traveling-wave concepts, and is useful when it is necessary to discuss the properties of a microwave network junction, irrespective of the impedances connected to the terminals. However, one has to be extremely careful in providing a physical interpretation of the mathematical expressions, as in this case the reflection coefficient can be greater than one, even for a passive load impedance with a conjugately matched transmission line. The power balance also cannot be simply obtained from the powers associated with the incident and reflected waves. Hence, this cannot be applied for broadband characterization of antennas. The second type of S parameter is called the power-wave scattering parameter. This is useful when one is interested in the power relationship between microwave circuits connected through a junction. In this case, the magnitude of the reflection coefficient cannot exceed unity, and the power delivered to the load is directly given by the difference between the powers associated with the incident and the reflected waves. Since this methodology deals with the reciprocal relationships between powers from various devices, this may be quite suitable for dealing with a pair of transmitting and receiving antennas where power reciprocity holds. This methodology is also applicable in network theory, where the scattering matrix of a two-port (or a multi-port) can be defined using complex reference impedances at each of the ports without any transmission line being present, so that the concept of characteristic impedances becomes irrelevant. Such a situation is typical in small-signal microwave transistor amplifiers, where the analysis necessitates the use of complex reference impedances in order to study simultaneous matching and stability. However, for both definitions for the S parameters, when the characteristic impedance or the reference impedance is complex, the scattering matrix does not need to be symmetric, even if the network in question is reciprocal.The second objective is to illustrate that when the characteristic impedance of the line or the reference impedances in question is real and positive, then both of the pseudo-wave and the power-wave scattering parameters provide the same results. Finally, a general methodology is presented with examples to illustrate how the S parameters can be computed for an arbitrary network without any a priori knowledge of its characteristic impedance.

Service Robot Passive Safety Impedance Mechanism Design and Dynamics Analysis

The wide application of service robot caused security problems between humans and robots. Through the theoretical analysis and mathematical formula based on the calculation. Designing a novel safe impedance joint mechanism consisting of an inclined link, a slider with rollers, and linear springs is proposed. Analysis the institutions of different friction between rollers and tilt links in the form of organization function at the same time. Using solidworks software to mechanism of 3D modeling, the design of two different partial CAM model, importing ADAMS software and analysis the function, Comparison between simulation data and experimental data consistency, for later used in robot mechanical arm to provide a theoretical basis.

Automatic impedance matching and antenna tuning using quantum genetic algorithms for wireless and mobile communications

In this study an adaptive impedance tuning scheme based on the quantum genetic algorithm (QGA) is proposed. A low-pass passive LC impedance matching network is used and tuned by a QGA controller. The tuning algorithm iterates until the matching point is reached. Simulations and results of the QGA tuning method are presented for 1.8 and 2.4 GHz of mobile and wireless communications with different antenna impedances. Comparison of the proposed QGA tuning method with conventional genetic algorithm-based tuning method is also given, which shows that the QGA tuning algorithm is much faster. The proposed QGA method can also be used for tuning a radiofrequency band by tuning the impedance matching network to the band centre frequency. Simulation results for the universal mobile telecommunications system band of 60 MHz width and Industrial, Scientific and Medical band of 200 MHz width all show good performances.

Series-Parallel Six-Element Synthesis of Biquadratic Impedances

The object of this paper is to give a complete treatment of the realizability of positive-real biquadratic impedance functions by six-element series-parallel networks comprising resistors, capacitors, and inductors. This question was studied but not fully resolved in the classical electrical circuit literature. Renewed interest in this question arises in the synthesis of passive mechanical impedances. Recent work by the authors has introduced the concept of a regular positive-real functions. It was shown that five-element networks are capable of realizing all regular and some (but not all) nonregular biquadratic positive-real functions. Accordingly, the focus of this paper is on the realizability of nonregular biquadratics. It will be shown that the only six-element series-parallel networks which are capable of realizing nonregular biquadratic impedances are those with three reactive elements or four reactive elements. We identify a set of networks that can realize all the nonregular biquadratic functions for each of the two cases. The realizability conditions for the networks are expressed in terms of a canonical form for biquadratics. The nonregular realizable region for each of the networks is explicitly characterized.

Broadband Omnidirectional and Miniature Fold-up Discone Antenna in VHF/UHF Band

In this article, a novel miniature broadband omnidirectional antenna is proposed. This antenna is suitable to use in vehicles, especially in unmanned aerial vehicles, since it will be folded in order to reduce its size when the unmanned aerial vehicle lands. A special kind of wire discone antenna is chosen to achieve all desired goals. Passive broadband impedance matching at the input of the antenna improves the voltage standing-wave ratio. A telescopic fiberglass axis is used in the antenna structure in order to reduce size and increase wind resistance. The assessment of the novel structure in implementing the antenna is confirmed by experimental measurements. The measurement results reveal the preference of the new techniques over the existing approaches, showing voltage standing-wave ratio better than 2.1 and gain between −5.9 and 2 dBi in a total band of 30–500 MHz.