Frequency Response Experiments Research Articles

An optimum structural design method for a torque sensor measuring the control moment of the micro flapping-wing robot

Abstract This paper presents an optimum structural design method for a sensor capable of measuring the control torque of the micro flapping-wing robot. Torque measurement in flapping-wing robots has special demands on the sensor bandwidth. The method in this paper focuses on the development of a multi-objective optimization method based on the surrogate model to solve the sensor indicator design issues, for example, increasing sensitivity while meeting bandwidth requirements. Initially, Latin hypercube sampling was applied to the choice of the characteristic parameters of the sensor. Based on finite element techniques, the surrogate models describing displacement and eigenfrequency were established to characterize the sensor indicators, and a multi-objective optimization was conducted. According to the optimization results, the sensor structure was manufactured, and a torque measurement platform was set up. Calibration experiments and frequency response experiments demonstrated a high level of consistency between the surrogate model and the experimental data. With the assistance of the eddy current displacement sensor, the actual displacement sensitivity coefficient of the torque sensor is determined to be 0.4325 mm mNm−1, consistent with the calculation of the surrogate model. The characteristic frequency is 488.5 Hz, with a relative error of 7.47% compared to the surrogate model. This indicates that the optimum structural design method can be utilized for the rapid design of torque sensors for special requirements, thus laying the foundation for the control torque measurement of micro flapping-wing robots.

Vibration reduction of cables with pendulum-type elastic metamaterials

Elastic metamaterials (EMMs) have been used to reduce the vibration of various mechanical structures. Recent studies have proposed methods to reduce the vibration of cables and space tethers by introducing pendulum-type EMMs. However, the vibration absorption characteristics in the bandgaps of pendulum-type EMMs need to be investigated in relation to the local resonances of the unit cell structure because only beams among the unit cell structure were considered. Furthermore, it is necessary to improve the vibration reduction performance of the pendulum-type EMMs by allocating as many bandgaps as possible in the frequency range of interest. In this study, the effect of the dynamic characteristics of the coupled structure with the same configuration as the unit cell structure including the ring or annular plate as well as the beam were investigated in depth. Further, based on these results, an improved pendulum-type EMM with multiple bandgaps in the frequency range of interest was developed, which is well suited for most practical applications in mechanical systems where the influence of low vibration modes is dominant. The vibration reduction performance and the effect of the bandgaps of the pendulum-type EMM with an annular plate were verified through comparison between the experimental and simulation results. The frequency response experiments and simulation results were consistent in terms of the resonant peak frequencies outside the bandgaps and the low response amplitude within the bandgaps. Moreover, the experimentally visualized and simulated operational deflection shapes showed that the cable hardly vibrates at the frequency within the bandgap; at this frequency, the operational deflection shape of the annular plate is very similar to the mode shape of the vibration mode of the coupled structure.

Predicting diffusion barriers and diffusivities of C6–C12 methylbenzenes in MFI zeolites

Mass transport plays an important role in zeolite catalyzed reactions and catalyst deactivation, yet experimental measurement of mass transport, particularly ultra-slow diffusion processes (e.g., of bulky aromatics), is limited because of time scale restraints. Here, we use density functional theory to overcome these limitations and calculate diffusion barriers of benzene and all twelve C 7 –C 12 methylbenzenes through the straight and sinusoidal channels of silicalite-1 (MFI framework). Straight and sinusoidal diffusion barriers are well-predicted by a critical diameter describing the minimum width of the molecule, where benzene, toluene, and para -xylene (all 6.6 Å) diffuse through both channels with barriers 200 kJ mol −1 lower than those of pentamethylbenzene (8.2 Å). The MFI framework distorts to accommodate species with larger critical diameters and this distortion correlates to activation barriers where smaller molecules, such as benzene, distort the framework to smaller extents compared to larger species, such as pentamethylbenzene. Diffusing through the straight channel of MFI is always more facile than via the sinusoidal channel, by an average of 39 kJ mol −1 because the tortuosity of the sinusoidal channels forces larger framework distortions than straight channel diffusion. We show that DFT-calculated straight channel diffusion activation barriers agree well with those reported by frequency response experiments and can be used to calculate self-diffusivities of molecules, with appropriate entropy corrections. Examining all aromatics provides insights to the role of molecule size, channel tortuosity, and entropy during intracrystalline diffusion to provide a reference point for the species that can reasonably diffuse through both channels (e.g., benzene, toluene, xylenes, durene), through straight channels only (e.g., 1,2,3-trimethylbenzene), or simply are ‘stuck’ within intersections (e.g., pentamethylbenzene) in MFI. • Diffusion barriers trend with critical diameter where aromatics with smaller critical diameters diffuse with lower barriers. • MFI distorts to accommodate aromatic diffusion and the extent of this distortion is predicted by critical diameter. • Diffusing through the straight channel occurs with barriers, on average, 39 kJ mol −1 lower than sinusoidal diffusion.

Module coordination control of multi-modular lead-based reactor systems

The multi-modular reactor, which connects multiple reactor units to drive a single turbine, is considered to be an innovation in the nuclear energy system. Since multiple reactor units are coupled together by the common secondary loop, the load change of any reactor will affect its own coolant temperature, and also the power of other reactor units. It is obviously that module coordinated control is significant for the safe and stable operation of the multi-modular reactor, which induces the necessity of the study in module coordination. Motivated by this, this paper proposes the method of decoupling between each module to realize the coordinated control of the multi-modular reactor. An operation and control simulation of the multi-modular lead-based reactor based on the China lead-based research reactor (CLEAR-I) is performed. The frequency domain identification method combined with the multivariable frequency response method is proposed to realize the effective decoupling of the system. The purpose of this method is to reduce the complexity of the control system design and make full use of the computer aided design technology. The transfer function matrix of the system is identified through the frequency response experiments. The pseudo diagonal dominance method is adopted to develop the constant diagonal dominant compensation matrix for the inverse transfer function, and then the inverse Nyquist array (INA) method is adopted to design controller for the compensated system. The design of the multiple-input multiple-output system is simplified to a series of single-variable system designs. The numerical results show the feasibility and satisfactory control performance.

State Switched Discrete-Time Model and Digital Predictive Voltage Programmed Control for Buck Converters

Switched mode power converters are nonlinear systems, and it is a constant challenge to improve their modeling accuracy and control performance. In this paper, a State Switched Discrete-time Model (SSDM) is proposed, which achieves a higher accuracy at a high frequency than that of conventional state averaged models. Instead of averaging the converter states for approximation, the states within each switching cycle are considered in the modeling. Based on total differential equations of switching-ON and switching-OFF durations, the inductor current and output voltage within a cycle are accurately calculated, which derives the SSDM. Furthermore, a Digital Predictive Voltage Programmed (DPVP) control strategy is derived through the SSDM. Through voltage prediction, a suitable duty ratio is calculated that regulates the output voltage to its reference value in the minimum switching cycles. In this way, the converter achieves a very fast load/line transient response and reference tracking speed, and it exhibits a high stability under deviated inductance. Finally, the accuracy of SSDM and the system stability are proved by frequency response analyses and experiments.

Acoustic radiation from an infrasonic ball-valve siren.

The concept of a ball-valve siren is developed through experimentation and theoretical modeling. The ball-valve siren is a source transducer developed for the purpose of establishing the concept of infrasound generation through the modulation of compressed air flowing through a rotating ball valve and released into the atmosphere, in the context of a siren. Directivity, frequency response, and propagation experiments were performed for the fundamental frequency component, and the results compare favorably to an empirical model based on monopole and dipole radiation. The results show that a small ball-valve siren can generate useful infrasound radiation with nominal directivity at frequencies in the range 1 to 8 Hz.

Modeling, online identification, and compensation control of single tendon sheath system with time-varying configuration

• The transmission models of single TSS with arbitrary route configurations are developed. • A tendon-sheath-based bending sensor is proposed for online parameter identification. • Two compensation strategies are developed to enhance the control accuracy of TSS without distal feedback. • The effectiveness is validated by trajectory tracking and frequency response experiments. Tendon sheath system (TSS) has been widely used in many applications with strict spatial limitations due to its flexibility, dexterity, and remote transmission ability. However, the inherent configuration-dependent nonlinearities between tendon and sheath seriously degrade the transmission performance and result in inaccurate force and position control. In this paper, the force and position transmission models of single TSS with arbitrary route configurations and terminal loads are developed based on the analysis of system friction and deformation. A tendon-sheath-based bending sensor is proposed for the online identification of accumulated bending angle. To enhance the accuracies of force control and position control with time-varying configuration, two control strategies are developed for the friction and deformation compensation without sensory feedback from distal end. An experimental setup of tendon sheath actuation is established to gain insights into the force and position transmission processes and evaluate the effectiveness of the developed transmission models and compensation controllers. The results of model validation experiments with sinusoidal force input show that the modeling errors of force and position transmission are less than 5% and 2.5%, respectively. Moreover, the trajectory tracking experiments and frequency response experiments are carried out, and the results demonstrate the feasibility of the proposed identification strategy and compensation controllers in improving control accuracy and ensuring control bandwidth of single TSS with time-varying bending angle.

Motion characteristics and non-ideal dynamics of a stereoscopic symmetrical quadruple hair gyroscope (SSQHG)

In this paper, the motion characteristics and non-ideal dynamics of a stereoscopic symmetrical quadruple hair gyroscope (SSQHG) are explored. The device description and operating principle of SSQHG are briefly interpreted. Based on a simplified mass-spring-damping model, the motion characteristics of SSQHG under different excitation methods (anti-phase drive, in-phase drive and single mass drive) are deduced, and the angular velocity mechanical sensitivity of SSQHG is subsequently calculated. The effects of electrostatic force error, mass error and stiffness error on structural dynamics are analyzed in detail. Finite element method (FEM) simulations are implemented to verify the correctness of proposed dynamic model. The simulation results show a highly consistency with theoretical analysis. Finally, the frequency response and angular velocity sensitivity experiments are performed on two fabricated prototypes. The experimental results confirm that the inevitably non-ideal errors of prototypes lead to distinct performance difference. The kinematic analysis methodology of SSQHG presented in this paper is suitable for other quadruple mass gyroscopes (QMG).

Research of a novel stereoscopic symmetrical quadruple hair gyroscope

This paper presents a novel stereoscopic symmetrical quadruple hair gyroscope (SSQHG) which is distinguished from the conventional flat structures to achieve better angular rate measurement performance. A symmetrical device architecture is designed to realize the differential detection of Coriolis force, thereby effectively eliminate the common mode interference. Four stereoscopic hair posts are adopted to increase the quality of the lumped inertia masses, so as to enhance the measurement sensitivity. A simplified mass-spring-damper model of idealized SSQHG is established and verified by a modal simulation to synthetic analysis the motion modal. A set of finite element method simulations including modal distribution simulation and harmonic response simulation are implemented to acquire accurate vibration information and to identify the structure parameters quantitatively. A micromachining procedure based on the standard deep dry silicon on glass is adopted to fabricate the proposed micro-gyroscope. The frequency response experiments indicate that the vacuum packaged prototype has a drive mode frequency of 536.2 Hz with a quality factor of 1319.7 and a sense mode frequency of 535.7 Hz with a quality factor of 1334.5. An analog closed-loop driving circuit is designed to realize the self-excited oscillation of SSQHG and an open-loop sensing circuit is designed to extract the Coriolis force signal. The preliminary experimental results demonstrate that the fabricated SSQHG prototype exhibits an angular rate sensitivity of 16.03 mV/°/s and a bias instability of 16.26°/h at room temperature.

A Novel Inertia Identification Method and Its Application in PI Controllers of PMSM Drives

A novel method for inertia determination of a permanent magnet synchronous machine (PMSM) drive is proposed and analyzed, which employs a sinusoidal perturbation torque with a dc offset to drive the PMSM, and the amplitudes of reference sinusoidal torque and sinusoidal speed response are used to compute the system inertia. Compared with other methods, it is robust and fast to obtain the accurate quantity of the inertia. First, the inverter measures the resistances and inductances of a PMSM through a static voltage vector and stand-still frequency response experiments. The parameters are adopted to design the current proportion and integral controller and make both dq-axes currents to perform the first-order response. Second, the results of constant torque experiment employing the current controller are applied to get the friction coefficient and no-load torque. Third, a sinusoidal torque with a dc offset is applied and the response performs a sinusoidal speed with a constant offset. All the above experimental results and other preinstalled parameters are employed to get the system inertia, and the accuracy is verified by another experiment. As compensation for a position signal from a hall sensor, a corresponding method is also proposed to compute the sinusoidal speed response amplitude, which is the key in the procedure.

A chatter mitigation technique in milling based on H∞-ADDPMS and piezoelectric stack actuators

Chatter is a kind of self-excited vibration which may occur in the milling process and has several negative effects such as poor surface quality and severe tool wear. This paper presents an active chatter control method based on H∞ almost disturbance decoupling problem with measurement feedback and with internal stability (H∞-ADDPMS) and piezoelectric stack actuators. First, a milling process model considering regenerative effect is constructed to find out the milling conditions when chatter occurs. Then, the whole active control system and constructing procedure of an active controller based on H∞-ADDPMS is proposed. Next, the milling process is simulated and the H∞-ADDPMS controller is calculated based on cutting force coefficient identification, frequency response experiments, and modal analysis technique. Finally, the active control experiment is carried out on a computer numerical control (CNC) milling machine to verify the feasibility and effectiveness of the proposed active control strategy.

Construction and validation of a high resolution finite element model of the Japanese koto

The Japanese koto is recognized for its complex resonances, but few studies have been conducted to understand its acoustic properties. This paper presents a COMSOL Multiphysics finite element model of a hand-crafted, professional-grade Japanese koto. To do this, the complex internal and external geometry was captured on 2400 CAT scan cross-sections and imported into Comsol. The model was validated by reference to literature data, Chladni patterns, frequency response experiments, acoustic camera and laser scanning vibrometer studies. These results were then compared to the sound as played on the actual instrument. Challenges in the model’s development arising from the materials and construction of the instrument are discussed, most notably the anisotropic nature of the paulownia wood including multiple grain orientations used in its construction and the added complexity of modeling the organic shape of the real, hand-crafted 1.83 m long instrument with its major internal variations. These developments were guided by parallel studies in less intractable geometry such as simpler box models or models with idealized geometrical shapes lofted along a spline. The CAT scan derived model is used as a quasi-experimental tool to investigate the effect of internal components of the koto on its resonances and results presented.The Japanese koto is recognized for its complex resonances, but few studies have been conducted to understand its acoustic properties. This paper presents a COMSOL Multiphysics finite element model of a hand-crafted, professional-grade Japanese koto. To do this, the complex internal and external geometry was captured on 2400 CAT scan cross-sections and imported into Comsol. The model was validated by reference to literature data, Chladni patterns, frequency response experiments, acoustic camera and laser scanning vibrometer studies. These results were then compared to the sound as played on the actual instrument. Challenges in the model’s development arising from the materials and construction of the instrument are discussed, most notably the anisotropic nature of the paulownia wood including multiple grain orientations used in its construction and the added complexity of modeling the organic shape of the real, hand-crafted 1.83 m long instrument with its major internal variations. These developments were...

Distributed Partial Discharge Detection in a Power Transformer Based on Phase-Shifted FBG

To overcome the low sensitivity of power transformer partial discharge (PD) detection by a lead zirconate titanate (PZT) sensor, we propose a novel PD detection system based on phase-shifted fiber Bragg gratings (PS-FBG). Compared with the conventional method, the proposed sensor can be installed inside the power transformer, which takes the advantage of the optical fiber status as an insulator. Distributed PD detection is achieved using wavelength and time-division multiplexing. Frequency response experiments indicate that the sensitivity of the PS-FBG is 8.46 dB higher than that of the conventional ultrasonic sensor. Moreover, a PD detection experiment shows that the PD sensitivity of the PS-FBG immersed in oil is 17.5 times higher than that of the PZT sensor. Furthermore, the multiplexing and the feasibility of defect localization of the proposed distributed PD detection system are demonstrated.

Model-based feedforward and cascade control of hydraulic McKibben muscles

McKibben artificial muscle actuators are predominantly pneumatically powered. Recently, hydraulic operation has gained interest due to its higher rigidity and efficiency. While there has been extensive control system development for pneumatic artificial muscles, little has been conducted hydraulically. This paper investigates three different controllers developed for a loaded robotic arm actuated with oil-hydraulic McKibben muscles. The goal was to achieve good angular position tracking over a range of frequencies up to 1 Hz. The first scheme, serving as the baseline, is a proportional-integral controller. The second architecture adds a nonlinear model-based feedforward term to the baseline controller; the feedforward includes the expected flowrate demands based on the actuator kinematics as well as the valve flow gain. The last scheme adds an inner pressure feedback loop to the second architecture. All controllers were evaluated with frequency and step response experiments. The results show that a simple proportional-integral controller has significant phase lag and attenuation at the higher frequencies tested; including the feedforward term almost completely eliminates these. The cascaded loop improves rise and settling times.

Design and Fuzzy Sliding Mode Admittance Control of a Soft Wearable Exoskeleton for Elbow Rehabilitation

Exoskeletons composed of rigid frames and joints have been widely implemented in rehabilitation application. However, the rigid mechanical structure introduces many problems, such as heavy weight, large inertia, and joint misalignment. To overcome these undesirable inherent disadvantages of rigid exoskeletons, the innovative contributions of this paper are to investigate the design and fuzzy sliding mode admittance (FSMCA) control of a soft wearable exoskeleton with compliance tendon-sheath actuation (CTSA) for multi-mode elbow rehabilitation training. The CTSA system is developed on the base of the Hill-based muscle model to imitate the working characteristics of human muscle and improve the compliance and coordination of human–robot cooperation. The FSMCA controller is capable of providing patient-passive and patient-active therapies under different training intensities and encouraging the active participation of the patients with various weakness levels. Further experimental investigations, including the trajectory tracking experiments with/without admittance regulation, the step response experiments with disturbance, the frequency response experiments, and the patient-active training experiments, are carried out by three healthy volunteers. Experimental results demonstrate the effectiveness of the proposed FSMCA control scheme in achieving high control accuracy and favorable frequency response characteristic. Besides, the training intensity can be qualitatively adjusted via appropriate admittance parameters.

Merohedral icosahedral M48 (M = CoII, NiII) cage clusters supported by thiacalix[4]arene.

Cage clusters are a discrete chemically and topologically diverse family of molecule-based functional materials. Presented here are two isostructural M48 (M = CoII for LSHU01, NiII for LSHU02) cage clusters with a merohedral icosahedral cage structure featuring 12 M4-TC4A (H4TC4A, p-tert-butylthiacalix[4]arene) second building units as vertices and 18 asymmetric 5-(1H-tetrazol-1-yl)isophthalate ligands as faces. They are the highest-nuclearity cage compounds of CoII and NiII. The activated Co48 cage exhibited high selectivity in the sorption of C3H8 over CH4 under ambient conditions. Frequency response experiments indicated that the extrinsic voids and matrix interface of the activated crystalline samples are primarily responsible for the observed gas adsorption performance.

Stabilization of pilot valve system using linear flow resistance

In a pilot valve system, the pressure in the control chamber of the main valve is straightforwardly affected by pressure oscillation in the downstream pipeline or the pilot tube. To solve this problem, an orifice is generally installed in the pilot tube to restrain the oscillation. However, the orifice is a nonlinear flow resistance; the amplitude of the oscillation alters the gain curve of the control pressure response. In this study, a linear flow resistance such as a porous material is employed to stabilize the pilot valve system. A test pilot valve was manufactured, and a pilot valve system was developed in the laboratory of the authors of this article. A mathematical model of the pilot valve system using linear and nonlinear flow resistances was simulated in MATLAB. The linearity of the P–Q characteristics of the linear flow resistance was confirmed, and a series of frequency response experiments were performed to examine the dynamic characteristics of the pilot valve system with various flow resistances. The experimental results were in accord with the simulation results. This implied that when porous materials were used in the pilot valve system, the gain of the pressure response did not vary regardless of the varying pressure vibration amplitude. Therefore, porous materials are suitable to be used in the pilot valve system instead of an orifice to enhance its stability.

Frequency response experiments of eye-vergence visual servoing in lateral motion with 3D evolutionary pose tracking

Visual servoing towards moving target with hand-eye cameras fixed at hand is inevitably affected by hand dynamical oscillations. Therefore, it is difficult to make target position keep always at the center of camera's view, as nonlinear dynamical effects of whole manipulator stand against tracking ability. To overcome this defect of the hand-eye fixed camera system, an eye-vergence system has been put forward, where the cameras could rotate to observe the target object. The visual servoing controllers of hand and eye-vergence are installed independently, so that it can observe the target object at the center of camera images through eye-vergence function. The dynamical superiorities of eye-vergence system are verified through frequency response experiments, comparing with hand tracking performances and the proposed eye-vergence tracking performances. This paper analyzes the performance of 3D-object position and orientation tracking, in which orientation representation method is based on quaternion, and the orientation tracking results are shown with more comprehensive analysis of system performance.

실린더를 이용한 서보 밸브 대역폭 주파수의 측정에 관한 연구

In this study, a metering cylinder was constructed, and the velocity obtained from the linear velocity transducer (LVT) of the cylinder piston was used to evaluate the dynamic performance of an electro-hydraulic servovalve. Frequency response experiments involving the spool displacement and piston velocity (LVT signal) were conducted with different input signal amplitudes, hydraulic pipe diameters, and supply pressures. The spool displacement signal accurately reflected the performance of the servovalve. Meanwhile, the -3 dB bandwidth frequency of the LVT signal was similar to the spool displacement signal, except for a small-amplitude input signal, and the <TEX>$-90^{\circ}$</TEX> phase lag bandwidth frequency showed some differences.

Analyses about Trackability of Hand-Eye-Vergence Visual Servoing in Lateral Direction

Visual Servoing to Moving Target with Fixed Hand-Eye Cameras Mounted at Hand of Robot is Inevitably Be Affected by Hand Dynamical Oscillations, then it is Hard to Keep Target at the Centre of Camera’s Image, since Nonlinear Dynamical Effects of Whole Manipulator Stand against Tracking Ability. in Order to Solve this Problem, an Eye-Vergence System, where the Visual Servoing Controller of Hand and Eye-Vergence is Controlled Independently, so that the Cameras can Observe the Target Object at the Center of the Camera Images through Eye-Vergence Functions. the Eyes with Light Mass Make the Cameras’ Eye-Sight Direction Rotate Quickly, so the Track Ability of the Eye-Vergence Motion is Superior to the One of Fixed Hand-Eye Configuration. in this Report Merits of Eye-Vengence Visual Servoing for Pose Tracking Have been Confirmed through Frequency Response Experiments.