Variable Inertia Research Articles

Variable inertia training: Optimization of explosive-power exercises with robotic-resistance strength machines

Strength training machines with computer-adjustable resistance mechanisms can simulate external resistance of different kinds (i.e. gravitational, elastic, and viscous) and magnitude R, and different levels of inertial force (the product of the resistance mass m and its acceleration). Notably, the simulated levels of R and m can be freely adjusted, during movement, independently of each other. In this study, the authors have performed a numerical simulation of exercises for explosive power to analyze the kinematic and kinetic effects of resistances that combine different levels of R and m (i.e. different levels of external resistance and inertial force). A progressive increase in m gradually enhances the peak user’s force and reduces the peak acceleration at all resistances R, enhances and shifts later in time the peak power at low resistances, and reduces the mean power at high resistances. The mass m also induces a rate of force development at the beginning of movement in a time frame which becomes progressively longer with higher values of m. Complete lack of mass m would be needed in the final phase of the movement to attain an effective training stimulus for high-velocity strength. In light of this evidence, the authors have devised a new training modality for explosive power (the “Variable Inertia Training”) with strength machines that use a motor and an electronic management system to simulate mass m variations in response to the kinematic parameters (position, velocity, and acceleration) of movement. This training modality can be designed to closely reproduce the kinematic and kinetic patterns occurring during ballistic or explosive sport movements, such as those occurring during throwing, hitting, rowing, and pushing activities. In addition, it may potentially enable the integrated development of the main neuromuscular components (force, rate of force development, and high-velocity strength) that contribute to the expression of explosive power for sports performance.

Cluster analysis of acoustic emission activity within wood material: Towards a real-time monitoring of crack tip propagation

Non-destructive monitoring of crack growth within material becomes an essential tool to better understand cracking mechanisms of materials, and therefore to reduce failure risks. This paper presents results from laboratory static tests that were conducted to investigate the monitoring of crack tip growth within wood material. Double Cantilever Beam specimens with variable inertia were tested in opening mode configuration. Acoustic emission (AE) technique was used to monitor the acoustic activity within wood material. In a first step, the reliability of the crack tip monitoring is evaluated in terms of Probability of Detection (PoD). Results show that for all specimens the PoD is larger than 70% for a detection threshold of 1mm. In a second step, a K-means++ algorithm was used to perform a cluster analysis of AE data, and to allow the AE events that were generated by the crack tip growth to be identified. Evolutions of both strain energy and AE energy are compared, and the experimental results show that the first AE events appear when the wood material reaches its limit to store strain energy, so at the vicinity of the end of its linear elastic behaviour.

Evaluation of aggregate gradation and distributing homogeneity based on the images of asphalt mixture

In order to quantitatively evaluate aggregate gradation and distributing homogeneity in asphalt mixture, digital image processing techniques were used to obtain the two-dimensional gradation characteristics in several cross-sections of the coring specimen, and the stereoscopy theory was applied to reconstruct the three-dimensional gradation characteristics, which was compared with the actual gradation, and a correction factor was deduced. It is found that the relative error between corrected and actual aggregate gradation is less than 5%. Then, the aggregated distributing information in horizontal and vertical sections were analysed to establish the horizontal and vertical distributing homogeneity indexes, respectively. The horizontal distributing homogeneity can be evaluated by the variation of inertia of the X-axis, Ix, during rotating, and the vertical distributing homogeneity can be evaluated by the statistical index of the aggregate centroids, Sa. The smaller the Ix variation, the better the horizontal distributing homogeneity. The larger the Sa, the better the vertical distributing homogeneity.

Research on No Load Shifting Process of AMT in Pure Electric Vehicles

This paper aims at increasing the robustness of shifting with the PMSM with the inertia variation. According to the characteristics of the structure of the dynamical system in PEV, inertia variation can cause control instability when AMT is in shifting process. The control method of PMSM is studied. MATLAB/Simulink software is used to build simulation model, combined with fuzzy sliding mode vector control algorithm for simulation. The results show that the control algorithm can effectively reduce the wear of the synchronous device and realize the rapid shift.

Influence of hygrothermal effects in the fracture process in wood under creep loading

The knowledge of crack driving forces such as energy release rate is very important in the assessment of the reliability of timber structures. This work deals with both static and creep fracture tests in opening mode crack growth under hygro-thermal and mechanical loadings. The experimental tests combining creep and hygro-thermal loadings are performed in a climatic chamber. The Double Cantilever Beam specimen with variable inertia machined in Douglas Fir and White Fir species is used to investigate the effects of these loadings on fracture processes. Two experimental protocols are presented. First, instantaneous tests are carried out in order to identify the moisture content effects on fracture properties. R-curves are studied using a finite element approach. Secondly, creep tests are performed by imposing high speed humidity variations in a climatic chamber. During these tests, the evolutions of the crack length are recorded.

Characteristic model–based adaptive controller with discrete extended state observer for servo systems

Inertia variations and torque disturbances, most often considered as two of the major uncertainties in servo systems, highly affect the control performance. This article presents a characteristic model–based adaptive controller in the presence of large-range load inertia variations. A discrete-time characteristic model of the servo system, which has more advantages in describing time-varying dynamics, is established. The parameters of characteristic model are identified by a recursive least squares algorithm. To restrain the identification error and load torque disturbances, a discrete extended state observer is newly designed for the discrete-time system. Both the convergence of discrete extended state observer and the stability of closed-loop system are verified by the Lyapunov theory. Finally, simulation and experimental results demonstrate that the proposed controller provides better performance than the fuzzy proportional integral controller in terms of adaptability and robustness.

Basic Consideration on Variable Inertia and Damping Control of Micro-Wind Turbine

Basic Consideration on Variable Inertia and Damping Control of Micro-Wind Turbine

Thermal Imaging Performance of TIR Onboard the Hayabusa2 Spacecraft

The thermal infrared imager (TIR) is a thermal infrared camera onboard the Hayabusa2 spacecraft. TIR will perform thermography of a C-type asteroid, 162173 Ryugu (1999 JU3), and estimate its surface physical properties, such as surface thermal emissivity \(\epsilon \), surface roughness, and thermal inertia \(\varGamma \), through remote in-situ observations in 2018 and 2019. In prelaunch tests of TIR, detector calibrations and evaluations, along with imaging demonstrations, were performed. The present paper introduces the experimental results of a prelaunch test conducted using a large-aperture collimator in conjunction with TIR under atmospheric conditions. A blackbody source, controlled at constant temperature, was measured using TIR in order to construct a calibration curve for obtaining temperatures from observed digital data. As a known thermal emissivity target, a sandblasted black almite plate warmed from the back using a flexible heater was measured by TIR in order to evaluate the accuracy of the calibration curve. As an analog target of a C-type asteroid, carbonaceous chondrites (\(50~\mbox{mm} \times 2~\mbox{mm}\) in thickness) were also warmed from the back and measured using TIR in order to clarify the imaging performance of TIR. The calibration curve, which was fitted by a specific model of the Planck function, allowed for conversion to the target temperature within an error of 1 ∘C (\(3\sigma \) standard deviation) for the temperature range of 30 to 100 ∘C. The observed temperature of the black almite plate was consistent with the temperature measured using K-type thermocouples, within the accuracy of temperature conversion using the calibration curve when the temperature variation exhibited a random error of 0.3 ∘C (\(1\sigma \)) for each pixel at a target temperature of 50 ∘C. TIR can resolve the fine surface structure of meteorites, including cracks and pits with the specified field of view of 0.051∘ (\(328 \times 248~\mbox{pixels}\)). There were spatial distributions with a temperature variation of 3 ∘C at the setting temperature of 50 ∘C in the thermal images obtained by TIR. If the spatial distribution of the temperature is caused by the variation of the thermal emissivity, including the effects of the surface roughness, the difference of the thermal emissivity \(\Delta \epsilon \) is estimated to be approximately 0.08, as calculated by the Stefan-Boltzmann raw. Otherwise, if the distribution of temperature is caused by the variation of the thermal inertia, the difference of the thermal inertia \(\Delta \varGamma \) is calculated to be approximately \(150~\mbox{J}\,\mbox{m}^{-2}\,\mbox{s}^{0.5}\,\mbox{K}^{-1}\), based on a simulation using a 20-layer model of the heat balance equation. The imaging performance of TIR based on the results of the meteorite experiments indicates that TIR can resolve the spatial distribution of thermal emissivity and thermal inertia of the asteroid surface within accuracies of \(\Delta \epsilon \cong 0.02\) and \(\Delta \varGamma \cong 20~\mbox{J}\,\mbox{m}^{-2}\,\mbox{s}^{0.5}\,\mbox{K}^{-1}\), respectively. However, the effects of the thermal emissivity and thermal inertia will degenerate in thermal images of TIR. Therefore, TIR will observe the same areas of the asteroid surface numerous times (\({>}10\) times, in order to ensure statistical significance), which allows us to determine both the parameters of the surface thermal emissivity and the thermal inertia by least-squares fitting to a thermal model of Ryugu.

Effects of two‐area variable inertia on transient stabilisation in interconnected power system with DFIG‐based wind turbines

This study investigates a novel operating method of the interconnected power grid to improve dynamic stability using variable inertia control of large wind farms. In this scheme, the system inertia is considered as an adjustable operating parameter which can be regulated for inter-area power oscillation control and frequency support. Based on the linear state equations derived from a two-area interconnected power system, the effect of the controlled inertia on power oscillation damping is evaluated theoretically considering the different cases of power feeding and receiving networks. The respective wind turbine variable inertia control strategies for the feeding and receiving regional networks are proposed to enhance both inter-area power oscillation damping and frequency stability. A typical two-area interconnected power system with a high 30% wind penetration is simulated, which consists of four conventional power plants and two doubly fed induction generator (DFIG)-based wind farms. The results demonstrate that by using the proposed control scheme, the frequency stability and the inter-area oscillation damping are both significantly improved for the more effective inertia support in the interconnected power system.

The Reaction Mass Biped: Geometric Mechanics and Control

Inverted Pendulum based reduced order models offer many valuable insights into the much harder problem of bipedal locomotion. While they help in understanding leg behavior during walking, they fail to capture the natural balancing ability of humans that stems from the variable rotational inertia on the torso. In an attempt to overcome this limitation, the proposed work introduces a Reaction Mass Biped (RMB). It is a generalization of the previously introduced Reaction Mass Pendulum (RMP), which is a multi-body inverted pendulum model with an extensible leg and a variable rotational inertia torso. The dynamical model for the RMB is hybrid in nature, with the roles of stance leg and swing leg switching after each cycle. It is derived using a variational mechanics approach, and is therefore coordinate-free. The RMB model has thirteen degrees of freedom, all of which are considered to be actuated. A set of desired state trajectories that can enable bipedal walking in straight and curved paths are generated. A control scheme is then designed for asymptotically tracking this set of trajectories with an almost global domain-of-attraction. Numerical simulation results confirm the stability of this tracking control scheme for different walking paths of the RMB. Additionally, a discrete dynamical model is also provided along-with an appropriate Geometric Variational Integrator (GVI). In contrast to non-variational integrators, GVIs can better preserve energy terms for conservative mechanical systems and stability properties (achieved through energy-like lyapunov functions) for actuated systems.

Exact solutions for axisymmetric flexural free vibrations of inhomogeneous circular Mindlin plates with variable thickness

Circular plates with radially varying thickness, stiffness, and density are widely used for the structural optimization in engineering. The axisymmetric flexural free vibration of such plates, governed by coupled differential equations with variable coefficients by use of the Mindlin plate theory, is very difficult to be studied analytically. In this paper, a novel analytical method is proposed to reduce such governing equations for circular plates to a pair of uncoupled and easily solvable differential equations of the Sturm-Liouville type. There are two important parameters in the reduced equations. One describes the radial variations of the translational inertia and flexural rigidity with the consideration of the effect of Poisson’s ratio. The other reflects the comprehensive effect of the rotatory inertia and shear deformation. The Heun-type equations, recently well-known in physics, are introduced here to solve the flexural free vibration of circular plates analytically, and two basic differential formulae for the local Heun-type functions are discovered for the first time, which will be of great value in enriching the theory of Heun-type differential equations.

無段変速機を用いた可変慣性質量をもつ振動抑制装置

In this paper author proposed a unique vibration suppression device that has variable inertia mass using continuously variable transmission (CVT) in order to obtain vibration isolation when a harmonic frequency was coincided with an anti-resonance frequency of 1DOF system. The device complies a ball screw mechanism, a flywheel, servo motors and CVT. The CVT is composed of toroidal wheels and power transmission wheels. The device has a small inertia force when an attitude angle of the power transmission is low by the servo motor as depending on a contact radius between two half toroidal wheels, on the other hand the large inertia force under high angle, so variable inertia force which acts as series inertia mass can be controlled continuously. The trial device was manufactured and the resisting force characteristics were measured. Theory of the variable inertia force was introduced, and compared with the experimental results. In order to confirm vibration control, an optimized inertia mass which always adjusts to anti-resonance frequency was determined in case of 1DOF system with the device, frequency response tests were carried out by using a shaking table, and experimental results were compared with calculated ones. Finally, the theory of resisting force and effects of vibration suppression were confirmed.

Enhancing of nominal characteristic trajectory following control for motion systems

The goal of this paper is to enhance a practical nominal characteristic trajectory following (NCTF) controller that is specifically designed for two-mass point-to-point positioning systems. A nominal characteristics trajectory contained in the NCTF controller acts as movement/motion reference and a compensator is utilized to force the object to detect and follow the reference/desired trajectory. The object must follow and track closely and should be as fast as possible. The NCTF controller is designed with two different intelligent based compensator approaches which are fuzzy logic and extended minimal resource allocation network. The proposed controller which is NCTF are compared with the conventional proportional integral compensator. Then the results of simulation are discussed for the positioning performances. The inertia variations due to the effect of the design parameters are also assessed to see the robustness of controllers. The results show that the NCTF control method designed from an intelligent based compensator has a better positioning performance in terms of percentage of overshoot, settling time, and steady state error than the classical based compensator.

Dynamic performance analysis of the X4 high-speed pick-and-place parallel robot

With the closed-loop structure, parallel manipulators possess some inherent advantages, such as high stiffness, enhanced dynamics, and compact structure. As a result, parallel manipulators gradually gain wide application. In the great variety of parallel manipulators, a kind of high-speed parallel robot, the limb of which is composed of active pendulum and passive parallelogram, gets popular and has realized industrial application firstly. Dynamic performance is the core of the high-speed parallel manipulator, which is usually illustrated through dynamic performance analysis with the aid of the index. Thus, developing reasonable dynamic performance indices is of great theoretical and practical significance for the high-speed parallel manipulator. In this paper, the Coefficient of Variation of joint-space Inertia (CVI) index is proposed to illustrate the acceleration consistency of each limb of the parallel manipulator. By taking the X4 high-speed pick-and-place parallel manipulator as object, the dynamic model and joint-space inertia matrix is established, and the dynamic performance analysis is carried out with the proposed CVI index and the existing Joint-Reflected Inertia (JRI) index. Simulation results illustrate changes of the dynamic performance of the X4 parallel manipulator, and reveal that the JRI index is well complemented with the CVI index. Finally, the workspace with good dynamic performance is discussed. This paper provides a new approach for dynamic analysis and optimal design of high-speed parallel manipulator. Limb Jacobian matrices of the X4 manipulator are given.Dynamic model and inertia matrix of the X4 manipulator are deduced.The CVI index is proposed to evaluate the dynamic performance.Dynamic performance of the X4 mahipulator is analyzed with indices.The workspace with good dynamic performance is disscussed.

Synthesis, optimization and experimental validation of reactionless two-DOF parallel mechanisms using counter-mechanisms

The synthesis of reactionless mechanisms generally involves the force balancing of a mechanism using countermasses followed by the dynamic balancing of the inertia using counter-rotations. This approach requires that the force balanced mechanism have a constant equivalent moment of inertia for any configuration. Two of the main drawbacks of reactionless mechanisms are a significant increase in mass and actuation inertia. In this paper, a counter-mechanism is introduced in order to dynamically balance a force balanced two-DOF mechanism with variable inertia, which is expected to reduce the aforementioned drawbacks. The conditions for which the counter-mechanism matches the moment of inertia of the main mechanism for any configuration are derived. Then, in order to fairly compare the use of a counter-mechanism instead of counter-rotations, the balancing strategies are optimized regarding the addition of mass and actuation inertia using Lagrange multipliers. The results are optimal rules for the design of reactionless mechanisms and optimal mass-inertia curves which are akin to Pareto curves. These results allow to demonstrate the advantages of counter-mechanisms over counter-rotations, especially regarding added actuation inertia and compactness. Also, the significant influence of the radius of gyration of the counter-inertias on the optimal mass-inertia curves is revealed. Finally, examples of reactionless mechanisms are presented and prototypes are tested in order to validate the concepts.

Epidemic spreading on adaptively weighted scale-free networks.

We introduce three modified SIS models on scale-free networks that take into account variable population size, nonlinear infectivity, adaptive weights, behavior inertia and time delay, so as to better characterize the actual spread of epidemics. We develop new mathematical methods and techniques to study the dynamics of the models, including the basic reproduction number, and the global asymptotic stability of the disease-free and endemic equilibria. We show the disease-free equilibrium cannot undergo a Hopf bifurcation. We further analyze the effects of local information of diseases and various immunization schemes on epidemic dynamics. We also perform some stochastic network simulations which yield quantitative agreement with the deterministic mean-field approach.

Coordinated Microgrid Frequency Regulation Based on DFIG Variable Coefficient Using Virtual Inertia and Primary Frequency Control

This paper proposes a variable coefficient combined virtual inertia and primary frequency control strategy for doubly fed induction generators (DFIG) in coordination with diesel generator to participate in wind/photovoltaic/diesel microgrid frequency regulation. The frequency response characteristic is analyzed under different wind speeds with corresponding inertia control parameters different. A 10% wind power margin is preserved through overspeed control and pitch angle control to offset the decrease of wind output power after temporary extra power surge, and provide a permanent frequency support for microgrids. The influence of droop control gain setting is also illustrated under different wind velocities. By continuously adjusting the control parameters according to wind speed variation, a variable coefficient method is realized. The method can guarantee an efficient implementation of this strategy in time-varying conditions. Finally, this coordinated control strategy is tested in a storage-independent microgrid with solar, wind, and diesel generators.

Performance optimization of dielectric electro active polymers in wave energy converter application

This paper presents a design, modeling and control of a novel wave energy converter (WEC) using Dielectric electro active polymer (DEAP). Application of DEAP in WEC has attracted a lot of works due to development of renewable energy and increasing of human energy demand. However, various challenges of the WEC using DEAP must be overcome before going to realistic application. Firstly, stretch ratio has significant influence on energy conversion efficiency of DEAP. It cannot exceed the limitation value due to mechanical or electrical breakdown, whereas small stretch ratio reduces the energy conversion efficiency significant. Secondly, WEC has to be controlled to maximize the absorbed energy. Therefore, this study employs an innovative device which can adjust the inertia of the floating buoy. A variable inertia hydraulic flywheel is attached on the main thrust shaft to control stretch ratio based on change in the hydrodynamic behavior of the system. A proportional–integral–derivative (PID) controller is designed to optimize stretch ratio under different regular waves. Consequently, the overall energy conversion efficiency of the proposed WEC can reach up to 25%.

Application of second order sliding mode algorithms for output feedback control in hydraulic cylinder drives with profound valve dynamics

The application of second order sliding mode algorithms for output feedback control in hydraulic valve-cylinder drives appear attractive due to their simple realization and parametrization, and strong robustness toward bounded parameter variations and uncertainties. However, intrinsic nonlinear dynamic effects of hydraulic valves such as slew rate limitations and time delays arising in the electrical and mechanical amplification stages limits the applicability of such methods, and may lead to partial losses of robustness and limit cycles/oscillations in the outputs, internal states and the valve input signals. The application of some popular second order sliding mode controllers and their smooth counterparts are analyzed and experimentally verified. The controllers are considered for output feedback control and compared with a conventional PI control approach. The controllers under consideration are applied for position tracking control of a hydraulic valve-cylinder drive exhibiting strong variations in inertia- and gravitational loads, and furthermore suffer from profound valve dynamics. Results demonstrate that both the twisting- and super twisting algorithms may be successfully applied for this purpose, when continuous approximations of discontinuous are utilized, and furthermore that excellent performance may be achieved when applying their smooth counterparts directly.

Design, Modeling and Testing of a Two-Terminal Mass Device With a Variable Inertia Flywheel

In this paper, we present a flywheel that can adaptively generate variable equivalent mass in response to application requirements. The motivation for the design comes from the need to achieve passive inertial mass, which eventually will lead to passive vibration isolation. This flywheel features a “host” flywheel frame with four sliders, each in a separate track. As the rotational speed of the variable inertia flywheel changes, the distance between sliders and rotation center changes, leading to a variable equivalent mass. The mathematical model of the flywheel is developed to examine its performance. The flywheel is mounted on a two-terminal hydraulic device to test its behavior. Experimental work has also been carried out to identify the parameters of the system (hydraulic device plus flywheel). The mathematical model with the identified parameters is then validated experimentally. During the experiments, the variable inertial force generated by the variable inertia flywheel in response to the changes in the excitation inputs is in good agreement with the prediction of the mathematical model, with the exception of spikes due to backlash of the two-terminal hydraulic system. The proposed design and experimental approach could inspire other passive variable inertial mass control of vibration systems.