Simple Compensation Research Articles

Robust flexible spacecraft attitude tracking under measurement errors, actuator nonlinearities, and faults

Reliable spacecraft attitude maneuver is one of the core research areas of the space industry due to the need for sustainable space exploration and advancements in the space technology. The paper presents an observer-based adaptive backstepping (OB-ABST) fault-tolerant control scheme for a flexible spacecraft attitude tracking under the effect of state measurement errors, inertial uncertainties, external disturbances, multiple actuator faults, and input nonlinear saturation (INS) while suppressing vibrations due to flexible modes. Initially, we design an adaptive backstepping controller to mitigate the system’s unwanted nonlinearities and observers to get estimates of the attitude dynamics in a recursive design framework. Later, the control structure incorporates a simple actuator saturation compensator to tackle input torque saturation in the system. The critical feature of the proposed OB-ABST control structure is to ensure precise attitude-tracking maneuvers and vibration suppression without intelligent materials such as shape memory alloys (SMA) and piezoelectric material (PZT). Lyapunov stability analysis proves practical finite-time convergence of the system state errors, observation errors, and actuator saturation compensators. Moreover, we provide specific conditions to tune design parameters. Finally, comparative simulation experiments validate the control performance of the proposed controller in the presence of multiple challenges.

Polarization-insensitive optical coherence tomography using polarization maintaining fiber with a simple optical configuration

Compensation of polarization-variance-related artifacts is required to steadily obtain high-quality optical coherence tomography (OCT) images at various experimental conditions. Since most OCT systems utilize optical fiber to transfer the light easily and a polarized light source, the polarization state is arbitrarily changed in every different condition. In this study, we proposed polarization-maintaining-fiber-based polarization-insensitive OCT (PM-PI-OCT) with a simple optical configuration and a simple compensation process. The proposed PM-PI-OCT is not only theoretically proved by mathematical derivations but also evaluated by quantitative analysis of various fiber twisting angles. Moreover, the applicability and robustness of the proposed PM-PI-OCT were proved by human retina imaging using the customized handheld probe. Our proposed polarization-insensitive OCT requires no pre-calibration, no post-processing procedure, and no computational load for implementation and is able to be applied to universal fiber-based OCT systems. We believe that our simple and robust polarization-insensitive OCT system is able to be applied to various existing OCT setups for polarization state variance compensation with high versatility and applicability.

Comparative Study of Methods for Robot Control with Flexible Joints

Robots with flexible joints are gaining importance in areas such as collaborative robots (cobots), exoskeletons, and prostheses. They are meant to directly interact with humans, and the emphasis in their construction is not on precision but rather on weight reduction and soft interaction with humans. Well-known rigid robot control strategies are not valid in this area, so new control methods have been proposed to deal with the complexity introduced by elasticity. Some of these methods are seldom used and are unknown to most of the academic community. After selecting the methods, we carried out a comprehensive comparative study of algorithms: simple gravity compensation (Sgc), the singular perturbation method (Spm), the passivity-based approach (Pba), backstepping control design (Bcd), and exact gravity cancellation (Egc). We modeled these algorithms using MATLAB and simulated them for different stiffness levels. Furthermore, their practical implementation was analyzed from the perspective of the magnitudes to be measured and the computational costs of their implementation. In conclusion, the Sgc method is a fast and affordable solution if joint stiffness is relatively high. If good performance is necessary, the Pba is the best option.

Ultra-Compact Pulse Charger for Lithium Polymer Battery with Simple Built-in Resistance Compensation in Biomedical Applications.

Active implantable medical devices (AIMDs) rely on batteries for uninterrupted operation and patient safety. Therefore, it is critical to ensure battery safety and longevity. To achieve this, constant current/constant voltage (CC/CV) methods have been commonly used and research has been conducted to compensate for the effects of built-in resistance (BIR) of batteries. However, conventional CC/CV methods may pose the risk of lithium plating. Furthermore, conventional compensation methods for BIR require external components, complex algorithms, or large chip sizes, which inhibit the miniaturization and integration of AIMDs. To address this issue, we have developed a pulse charger that utilizes pulse current to ensure battery safety and facilitate easy compensation for BIR. A comparison with previous research on BIR compensation shows that our approach achieves the smallest chip size of 0.0062 mm2 and the lowest system complexity using 1-bit ADC. In addition, we have demonstrated a reduction in charging time by at least 44.4% compared to conventional CC/CV methods, validating the effectiveness of our system's BIR compensation. The compact size and safety features of the proposed charging system make it promising for AIMDs, which have space-constrained environments.

Gate reliability enhancement of p-GaN gate HEMTs with oxygen compensation technique

Improved p-GaN gate reliability is achieved through a simple oxygen compensation technique (OCT), which involves oxygen plasma treatment after gate opening and subsequential wet etching. The OCT compensates for the Mg acceptors near the p-GaN surface, leading to an extended depletion region under the same gate bias and thus reducing the electric field. Furthermore, the Schottky barrier height also increases by OCT. Consequently, suppressed gate leakage current and enlarged gate breakdown voltage are achieved. Notably, the maximum applicable gate bias also increases from 4 V to 8.1 V for a 10 year lifetime at a failure rate of 1%.

A 2.41 ppm/°C bandgap voltage reference with second‐order curvature compensation

SummaryA current‐mode (CM) bandgap voltage reference (BGR) with second‐order curvature compensation is presented in this paper. The proposed CM BGR offers a simple compensation structure that requires only six additional transistors compared with traditional BGR designs, making it an attractive solution for low temperature coefficient (TC) voltage references. Proportional to absolute temperature (PTAT) current digital‐to‐analog converters (DACs) are used to suppress the effect of process variation and device mismatch on TC. The compensation signal is generated using the voltage difference of two bipolar junction transistor (BJT) emitter–bases whose currents are the sum and difference of the PTAT current and the zero to absolute temperature (ZTAT) current, respectively. The proposed CM BGR is designed with 0.18‐μm BIPOLAR CMOS DMOS process. A TC is 2.41 ppm/°C over a wide temperature range of −40°C to 150°C. The linear sensitivity of the supply voltage from 1.2 to 2 V is 0.027%/V. With an active area of 0.0721 mm2, it consumes 68 μA at room temperature. The integrated output noise from 0.1 to 10 Hz is 21.9 μV.

Frequency drift characterization of a laser stabilized to an optical fiber delay line

Lasers stabilized to optical fiber delay lines have been shown to deliver a comparable short-term (<1 s) frequency noise performance to that achieved by lasers stabilized to ultra-low expansion (ULE) cavities, once the linear frequency drift has been removed. However, for continuous stable laser operations, the drift can be removed only when it can be predicted, e.g., when it is linear over very long timescales. To date, such long-term behaviour of the frequency drift in fiber delay lines has not been, to the best of our knowledge, characterised. In this work we experimentally characterise the frequency drift of a laser stabilised to a 500 m-long optical fiber delay line over the course of several days. We show that the drift still follows the temperature variations even when the spool temperature is maintained constant with fluctuations below tens of mK. Consequently, the drift is not linear over long timescales, preventing a simple feed-forward compensation. However, here we show that the drift can be reduced by exploiting the high level of correlation between laser frequency and the fiber temperature. In our demonstration, by applying a frequency correction proportional to temperature readings, a calculated frequency drift of less than 16 Hz/s over the several days of our test was obtained, corresponding to a 23-fold improvement from uncorrected values.

An approach to solving the effect of background in fluidized bed on electromagnetic tomography

As a non-invasive measurement technique, electromagnetic tomography (EMT) system based on tunneling magneto resistance (TMR) can detect the distribution of medium in the gas–liquid–solid fluidized bed by the difference of permeability. The distribution of medium in the three-phase fluidized bed is not uniform, and the solid clusters and bubble clusters are formed in the background of the gas–liquid–solid mixture. Since the effect of the background in the pipe of the fluidized bed on the boundary measurement data of the TMR-EMT system is much greater, it is difficult to detect solid clusters and bubble clusters when the image is reconstructed directly using the boundary measurement data. In order to improve the detection of clusters by the TMR-EMT system, a method to weaken the effect of the background is proposed. The equivalent magnetic circuit model is used to estimate the background permeability. Then the magnetic dipole theory and demagnetization effect theory are utilized to establish a simple background compensation model based on the estimated background permeability. Using the compensation model, the effect of the background is weakened from the boundary measurement data and the cluster distribution information is highlighted. Simulation and experimental results demonstrate the effectiveness of the proposed method.

A Inverter Dead-time Compensation Method Based on Phase current Polarity Determination and Voltage Partitioning

The introduction of the dead time of the inverter solves the straight-arm conduction problem of the upper and lower power devices of the inverter, but also leads to the deviation of the actual output voltage of the inverter from the given voltage. Dead time increases the harmonic components of phase voltage and phase current, which is also an important factor leading to motor torque ripple. In this paper, the mechanism of the deviation of phase voltage and phase current caused by the dead time of voltage space vector modulation is analyzed, and the effect of dead time on phase voltage and phase current harmonic components is studied. A simple and effective dead time compensation method based on phase voltage division and phase current polarity determination is proposed to directly compensate the dead time. This method can suppress the current harmonic and torque ripple in the running state of the motor, and can greatly simplify the calculation process of the traditional dead time compensation method. Through the system modeling and simulation, it is verified that the method can significantly improve the current waveform distortion, and has good practical value.

Generic characterization method for nano-gratings using deep-neural-network-assisted ellipsometry

Abstract As a non-destructive and rapid technique, optical scatterometry has gained widespread use in the measurement of film thickness and optical constants. The recent advances in deep learning have presented new and powerful approaches to the resolution of inverse scattering problems. However, the application of deep-neural-network-assisted optical scatterometry for nanostructures still faces significant challenges, including poor stability, limited functionalities, and high equipment requirements. In this paper, a novel characterization method is proposed, which employs deep-neural-network-assisted ellipsometry to address these challenges. The method processes ellipsometric angles, which are measured by basic ellipsometers, as functional signals. A comprehensive model is developed to profile nano-gratings fabricated by diverse techniques, by incorporating rounded corners, residual layers, and optical constants into an existing model. The stability of the model is enhanced by implementing several measures, including multiple sets of initial values and azimuth-resolved measurements. A simple compensation algorithm is also introduced to improve accuracy without compromising efficiency. Experimental results demonstrate that the proposed method can rapidly and accurately characterize nano-gratings fabricated by various methods, with relative errors of both geometric and optical parameters well controlled under 5 %. Thus, the method holds great promise to serve as an alternative to conventional characterization techniques for in-situ measurement.

A Simple Current Measurement Scaling Error Compensation Method for PMSM Drives

A Simple Current Measurement Scaling Error Compensation Method for PMSM Drives

Single Phase Sine-Wave Inverter with High DC Bus Utilization Using Natural Compensation

Abstract- In this paper, a new fixed frequency single phase sine-wave inverter topology - having high DC bus utilization - is presented. The main inverter uses six IGBT switches operating at low frequency in over-modulation mode to create a five-level voltage waveform; thus, having low switching losses with high DC bus utilization. A series active power filter (SAPF) using power MOSFETs helps to remove the major harmonic voltages. No isolated DC power supply is required across the SAPF that works on a simple feed-forward compensation (instead of feedback), based on the principle of natural compensation. The DC bus voltage needed for the SAPF is about half of the inverter, thus the SAPF has low switching loss even at the designated switching frequency. The switching frequency components of the SAPF remain in the output as they are not compensated, necessitating the use of a small filter at the output to attenuate them, to create a low total harmonic distortion output voltage with higher fundamental compared to the conventional schemes using Sinusoidal Pulse Width Modulation. The proposed inverter is suitable for fixed frequency backup power supply or other applications like renewable energy connection to the power grid.

Accuracy estimation of low-current voltage drop method for junction temperature monitoring under DC power cycling

A thorough accuracy estimation of the well-known low-current voltage drop method is carried out in this paper. A high-performance infrared camera is utilized as the reference in a DC power-cycling test on a commercial IGBT power module. The result shows that the low-current voltage drop method produces generally a higher temperature than the actual, in particular at the bond wire's joint point. However, a simple compensation method with a linear function can be easily adopted to compensate the temperature difference. After compensation, the maximum error of temperature swing is 0.28 °C.

Inductive Compensation of an Open-Loop IPT Circuit: Analysis and Design

The main contribution of this paper is the inductive compensation of a wireless inductive power transmission circuit (IPT) with resonant open-loop inductive coupling. The variations in the coupling coefficient k due to the misalignment of the transmitter and receiver are compensated with only one auxiliary inductance in the primary of the inductive coupling. A low-power prototype was implemented with the following specifications: input voltage Vin = 27.5 V, output power Po = 10 W, switching frequency f = 500 kHz, output voltage Vo = 12 V, transmission distance d = 1.5 mm. Experimental results varying the distance “d” with several values of the compensation inductor demonstrate the feasibility of the proposal. An efficiency of 75.10% under nominal conditions was achieved. This proposal is a simple compensation topology for wireless chargers of cellular phones presenting small distances between the transmitter and receiver.

Torque-Based Control of a Bio-Inspired Modular Climbing Robot

This article presents a generalizable, low computational cost, simple, and fast gravity compensation method for legged robots with a variable number of legs. It is based on the static problem, which is a reduction in the dynamic model of the robot that takes advantage of the low velocity of climbing robots. To solve it, we propose a method that computes the torque to be applied by each actuator to compensate for the gravitational forces without using the Jacobian matrix for the forces exerted by the end-effector and without using analytical methods for the gravitational components of the model. We compare our method with the most popular method and conclude that ours is twice as fast. Using the proposed gravity compensator, we present a torque-based PD controller for the position of the leg modules, and a body velocity control without dynamic compensation. In addition, we validate the method with both hardware and a simulated version of the ROMERIN robot, a modular legged and climbing robot. Furthermore, we compare our controller with the usual kinematic inverse controllers, demonstrating that the mean angular and linear error is significantly reduced, as well as the power requirements of the actuators.

Dead-Time Effect and Compensation Technology for an Isolated Dual Active Bridge Converter

Aiming at deficiencies of output voltage distortion and circulating current generation caused by dead-time effect in the modulation process, a simple and feasible dead time compensation strategy is presented. Firstly, the influence of dead-time effect on the output voltage of bridge is analysed, and a dead time compensation strategy is added between the modulation signal and dead time procession. According to the current direction of the bridge, the rising edge or falling edge of the driving signal is selectively delayed to compensate for dead-time effect. Secondly, an Optimized Triple Phase-shift (OTPS) modulation strategy is adopted with minimizing leakage inductor current Root-Mean-Square (RMS) control, which minimizes current stress, achieves soft-switching operation, avoids phase-shift errors caused by Dead-Time Effect, and optimizes control performance of DC-DC converters. Finally, simulated and experimental results are added to verify the correctness and effectiveness of the proposed method.

Survival rates and pro-oxidant-antioxidant systems of germinated Yakutian plant seeds pretreated with super-weak constant magnetic fields of different flux densities

The aim of this study was to identify physiological and biochemical changes in seedlings of wild plants of Yakutia, grown from seeds, which have received a pre-sowing, super-weak constant magnetic field treatment of different magnetic flux densities. Review of literature sources allows us to conclude that the weak effects of low-intensity fields (nonthermal character) have not been studied sufficiently so far. The study was conducted on seeds from 14 different species of wild plants native to Yakutia. The seeds were subjected to different magnetic flux strengths of 0.2–4.0 mT for 24 hours and then were germinated on filter paper. The criterion for evaluating the effect of the super-weak constant magnetic field was the formation of a true leaf in seedlings (survival rate). The intensity of lipid peroxidation processes was recorded as a pro-oxidant reaction. The total content of low molecular weight antioxidants was determined as an example of the non-enzymatic antioxidant system. The activity of an antioxidant enzyme, superoxide dismutase, was determined. The effects of the super-weak constant magnetic fields were evaluated using regression and statistical methods. Based on the working hypothesis is that the formation of the present leaf is dependent on changes in the pro-oxidant-antioxidant equilibrium in the cells of the seedlings as a result of the action on them by the super-weak constant magnetic field as a function of the magnetic flux density. We showed that the survival rate of seedlings grown from the seeds pre-treated by super-weak constant magnetic fields of different magnetic flux density for 24 hours leads to the activation of lipid peroxidation and depends on the adaptation processes of antioxidant systems (the sum of low-molecular antioxidants and superoxide dismutase activity): simple compensation or hypercompensation. In the second case, the action of super-weak constant magnetic fields leads to an increase in the survival rate of seedlings by the criterion of the formation of the true leaf. The study is of significance for specialists in magneto-biology and researchers of plant antioxidant systems.

Experimental verification of active damping of powertrain vibrations with simple fuzzy logic compensation for time-varying control period

To ensure comfortability and lifetime of components, transient vibrations in a vehicle powertrain must be suppressed. This study proposes a novel active vibration control strategy with straightforward fuzzy inference compensation for time-fluctuations of control periods of engines used as actuators. First, a model prediction algorithm including a sampled-data controller (SDC) is applied for addressing the maximal phase lag of the control input caused by the fluctuated control period. Fluctuated renewal timings of the control input that are deviated from those of the periodical operated SDC are defined by fuzzy sets. These fuzzy sets are expressed as “Nearly past timing” and “Nearly future timing.” Using a human-intuition-like fuzzy compensation with only four inference rules, unknown control inputs at fluctuated update timings are reasonably determined from such fuzzy sets and periodical control signals given by the SDC. Experiments using an actual test device are performed to investigate the damping performance of the proposed control scheme. The experimental tests demonstrate that the novel active damping strategy significantly reduces transient vibrations despite the fluctuated control period. Moreover, several different test conditions newly reveal the robustness of the fuzzy compensation against fluctuations of variable regions in the control periods.

An overview of Methods for Simulating Sheet Metal Forming with Elastic Dies

Sheet metal forming (SMF) simulations are traditionally carried out with rigid active forming surfaces. This means that the elasticity and dynamics of presses and die structures are ignored. The only geometries of the tools included in the simulations are the active forming surfaces. One reason for this simplification is the large amount of computational power that is required to solve finite element (FE) models that incorporates elastic stamping dies. Another reason is the lack of die CAD models before the later stages of stamping projects. Research during the last couple of decades indicated potential large benefits when including elastic dies in SMF simulations. For example, for simulating die try-out or for Digital Twins of presses and dies. Even though the need and potential benefits of elastic dies in simulations are well known it is not yet implemented on a wide scale. The main obstacles have been lacking data on presses and dies, long simulation times, and no standardized implementation in SMF software. This paper presents an overview of existing methods for SMF simulations with elastic dies and discuss their respective benefits and drawbacks. The survey of methods shows that simulation models with elastic tools will be needed for detailed analyses of forming operations and also for purposes like digital twins. On the other hand, simplified and robust models can be developed for non-FEA users to carry out simple one-step compensation of tool surfaces for virtual spotting purposes. The most promising and versatile method from the literature is selected, modified, and demonstrated for industrial sized dies.

Gamma error correction algorithm for phase shift profilometry based on polar angle average

Phase errors caused by the gamma nonlinear response of the phase shift profilometry (PSP) severely affect 3D measurement accuracy. To tackle this, a simple phase error compensation technique based on polar angle average is presented in this paper to improve the accuracy. Wrapped phase values are regarded as polar angles, and a polar axis distribution map can be obtained in the polar coordinate. Practically, the polar axis distribution (PAD) of the undistorted wrapped phase is uniform. When there are nonlinear effects in an PSP, the polar axis is unevenly distributed. The difference between adjacent polar angles is computed and then rearranged with specifically labels. After that, the even PAD diagram is generated, and the smooth phase can be further recovered. Compared with conventional nonlinearity correction methods, the proposed method corrects the error without any auxiliary conditions. Its effectiveness and robustness are verified in simulations and experiments.