Isokinetic Approach Research Articles

Control Strategy for Boost Converter Based on Adaptive Integral Terminal Sliding-mode Control

The control system for the fixed-frequency boost converter does not consider the situation from the input voltage and the unknown load, which makes the system vulnerable to external disturbances, resulting in slow system response and large output voltage error. The state space equation of the boost converter is established by the state space averaging method, and the adaptive control rate of the load resistance and the input voltage is designed by the adaptive control, which effectively reduces the influence of the disturbance on the system output. The sliding mode surface adopts the integral terminal sliding mode surface, and the isokinetic approach law control is used to effectively reduce the influence of chattering and improve the dynamic response speed and robustness of the system. The simulation experiment proves the validity and reliability of the integral terminal adaptive sliding mode control.

Research on PMSM Sliding-mode Vector Combined Speed Controller Based on Improved Exponential Reaching Law

Abstract Sliding mode control has good robustness, but the traditional sliding mode has the problem of chattering. Aiming at the conflict between velocity and chattering in the approach stage of sliding mode control, a new reaching law is put forward. By improving the isokinetic approach term of the traditional exponential reaching law, the system’s requirements in different stages of sliding mode motion are met, and this contradiction has been effectively improved. At the same time, to better improve the control effect of permanent magnet synchronous motor (PMSM) speed regulation system, combined with the traditional PI control with no static error and no overshoot, a combined speed controller combining sliding mode control and PI control is designed to enhance the robustness of the system. By building a model in Matlab/SIMULINK for simulation, the effectiveness of the improved exponential reaching law and the improvement of the system performance brought by the combined speed controller are verified respectively.

Isokinetic approach in logarithmic mean-force dynamics for on-the-fly free energy reconstruction

Logarithmic mean-force dynamics (LogMFD) is one of free energy calculation methods that utilize fictitious dynamical variables for efficient conformational sampling. In this study, we extend the LogMFD method to incorporate the isokinetic dynamics for the fictitious dynamical variables. The isokinetic LogMFD approach requires no additional parameter for thermostatting and it obviates the issue associated with the dynamics of the thermostat variable in Nosé-Hoover type thermostats. These virtues therefore make it easier to set up and undertake LogMFD calculations. The validity of the isokinetic algorithm introduced in LogMFD is examined by a benchmark system of alanine dipeptide in explicit water.

Sensitivity Analysis of the Variable Structure Control for a Two-Wheeled Unstable Vehicle

The sensitivity function is applied to the VSC of the two-wheeled unstable vehicle in this paper. By pole placement of state feedback function we can conduct the sensitivity function of VSC. Analyzing the isokinetic approach law and quasi-sliding we can prove that compared to pole placement of state feedback control, the VSC not only has superiority in robustness for disturbance and internal perturbation, but also obtains more satisfactory dynamic performance.

Magnetic and structural characterization of Mo-Hitperm alloys with different Fe/Co ratio

The influence of the Co content on the microstructure and magnetic behaviour of a series of amorphous and nanocrystalline (FeCo) 79Mo 8Cu 1B 12 alloys is reported. Changes in the magnetic properties provoked by the microstructural evolution upon different thermal treatments of as-cast samples are analyzed as well. Kinetics of nanocrystallization process can be described by an isokinetic approach. As the Co content in the alloy increases, the Curie temperature of the amorphous as-cast samples increases while the crystallization onset temperature decreases. The crystalline volume fraction as well as the mean grain size of the nanocrystals at the end of the nanocrystallization process are slightly higher for the lowest Co content alloy but smaller than in similar Hitperm Mo-free alloys. The average magnetic field and the average isomer shift of the as-cast samples show a linear increase with two slopes with the Co content of the alloy. The same tendency is found for the saturation magnetization. Combined TEM, XRD, and MS data indicate the presence of Mo atoms in the nanocrystals. At the end of the nanocrystallization process the softest magnetic behaviour corresponds to the lowest Co content alloy. The second crystallization process provokes a magnetic hardening of these alloys.

Thermally and flow induced crystallization of polymers at low shear rate

Abstract In semi-crystalline thermoplastic products, final properties are strongly dependent on the thermo-mechanical history experienced by the polymer melt during processing. More precisely, structural heterogeneities such as rigidity gradients and shrinkage anisotropy are directly related to the crystalline microstructure. Therefore, accurate prediction of part properties by a processing computer simulation code requires the implementation of an appropriate crystallization kinetics model, including both the effects of thermally and flow induced structure development. One issue is the necessity to improve the modeling of shear/extensional experimental data by relating the crystallization accelerating factors to an easily accessible material related variable. Several authors modeled the effect of the flow on the crystallization kinetics by using the isokinetic approach of Nakamura. Often, the resulting kinetic equations of these models account only for the evolution of the crystallinity fraction α leaving the influence of crystalline morphology aside. We may quote the work of Guo and Narh [1] , which connects the flow influence on the crystallization rate to the increase in the thermodynamic melting temperature in the Nakamura model. In 2005, R.I. Tanner presented a comparison of some models describing the polymer crystallization at low shear deformation rates under isothermal conditions. Based on Tanner's study, we developed a model of crystallization at low shearing, applied to non-isothermal flows, using only macroscopic measurable parameters. The key features of the concentrated suspension theory were used to characterize the effect of crystallization on the viscosity. In addition, we assumed that the flow generates additional crystallization nuclei via a parameter which combines the deformation and the deformation rate. The concept of germination-growth is introduced using the fundamentals of the Avrami–Kolmogorov theory, coupled with a modified Schneider's approach. The model is applied to a polypropylene, in a cooled Couette flow configuration. The results show the enhancement of the crystallization kinetics due to the shearing. The definition of global parameters simplifies the type and the number of experiments needed for the model parameter identification. The use of Schneider's approach leads to a new way of discriminating the relative roles of the flow and the temperature on the crystallization phenomenon. The competition between the two driving causes is presented and discussed: at low cooling rate or at high temperature, the shearing effect predominates. Other interesting results show the size distribution of the spherulites as well as the volume proportion for each crystalline size in the polymer.

Microstructure and magnetic properties of FeMoBCu alloys: Influence of B content

Fe 91– x Mo 8Cu 1B x ( x = 12, 15, 17, 20) amorphous and nanocrystalline alloys were studied to examine the influence of B content on their microstructure and magnetic behaviour. Changes in the magnetic properties provoked by microstructural evolution upon thermal treatments of as-cast samples were also analyzed. Nanocrystallization kinetics can be described by an isokinetic approach except for the 20 at.% B content alloy. The Curie temperature of the amorphous as-cast samples increases with the alloy’s B content. Mössbauer results suggest the presence of Mo atoms in the nanocrystals. Crystalline volume fraction and mean grain size of the nanocrystals at the end of the nanocrystallization process are higher for the lowest B content alloy. The 20 at.% B content alloy develops a boride phase just after the early stages of the nanocrystallization process, which provokes a magnetic hardening in this alloy. The softest magnetic behaviour of the studied compositions corresponds to nanocrystallized 17 at.% B content alloy.

EVALUATION OF THE MAXIMAL THEORETICAL FORCE EXERTED BY THE LEGS, WITH AN ISOTONIC LEG EXTENSION MACHINE

Evaluating the maximal force exertable by a subject in a particular exercise is an important starting step in setting up rehabilitation and training programs. The current reference procedure is the isokinetic approach, which has some limitations due to poor physiological agreement and high cost of the equipment. This paper describes a method for evaluating maximal force using an isotonic approach. The maximal force value is extrapolated from the linear behavior of the relationship between the force and the maximal velocity at lower loads. The method was applied to a group of 25 students at the Sports Medicine Faculty, University of Bologna using a leg extension AirMachine (919 Tech). Loads were settled adopting a step-up protocol and the maximal velocity was calculated by measuring the instantaneous angle of the lever. The linear correlation coefficient between the settled loads and the maximal velocity ranged between 0.5679 and 0.9980 for the right leg and between 0.6791 and 0.9895 for the left leg, and the maximal estimated force ranged between 26.9 kg and 248.2 kg for the right leg and between 32.6 kg and 221.9 kg for the left leg. The method showed a good feasibility and an acceptable error level, and can be proposed as an alternative to the isokinetic approach.

Mechanisms driving primary crystallization of Al 87Ni 7Cu 3Nd 3 amorphous alloy

Al 87Ni 7Cu 3Nd 3 ribbons, prepared by melt-spinning, have been analysed by differential scanning calorimetry, and their nanostructural evolution has been studied by combining heat treatments with conventional X-ray diffraction, high-temperature X-ray diffraction, high resolution transmission electron microscopy and selected area electron diffraction. The results show that the melt-spun samples have an overall amorphous structure, though they contain quenched-in crystalline embryos. Nanocrystallization starts with the stabilization of some of the pre-existing embryos, showing parabolic growth in the first stages. Soft impingement very soon becomes the controlling mechanism, and the particle density of fcc-Al stabilizes at ∼10 17 cm −3. No clear end of nanocrystallization is observed, since secondary crystallization of intermetallic phases is promoted by continuous heating above 583 K. In this paper a new method is proposed to treat calorimetric data in the framework of the isokinetic approach. It is shown that the nanocrystallization process follows an isokinetic behaviour, with an apparent activation energy of 105 kJ/mol.

An update of neck muscle strength: From isometric to isokinetic assessment

Pain syndromes in the neck-shoulder region resulting in neck sprain after repetitive mechanical loads imposed on the neck and shoulders during car or sporting accidents do not appear to be an isolated phenomenon. These pathologies require a specific muscle assessment for the diagnosis and the management of patients. Isometric muscle assessment is classically used, involving a maximal voluntary contraction performed at specified joint position against unyielding resistance. In spite of high reliability and reproducibility, this method does not allow the investigation of the dynamic properties of muscle. For this reason, an isokinetic method has become an increasingly popular modality in rehabilitative and sport medicine. Its concept has the advantage of providing a method of measuring strength during dynamic movements in a highly standardised situation. Although trunk muscles have been widely explored by the isokinetic technique, the cervical spine has not received the benefit of isokinetic technological progress. Recently, a specific neck device has been designed and validated, permitting the first isokinetic approach of neck muscles in different healthy and sporting populations. This article examines the use of isometric neck muscle assessment and proposes the isokinetic method as a tool for assessing the cervical spine in exercise sciences, medicine, and rehabilitation.

Crystallization kinetics and solidified structure in iPP under high cooling rates

A wide set of isothermal and non-isothermal crystallization experiments were carried out in this work on an iPP resin. Several experimental techniques were adopted in order to characterize crystallization kinetics and final morphology of the material, also under cooling rates comparable to those encountered during material processing (up to several hundred K/s). The whole set of data was taken as a reference to identify a kinetic model which describes the evolution of the structural organization of iPP (α crystalline phase and mesomorphic phase) as a parallel of two non-interacting kinetic processes competing for the available amorphous volume. Kolmogoroff equation was adopted to describe the crystallization of the α form. Avrami–Evans–Nakamura isokinetic approach was adopted to describe the evolution of the mesomorphic phase. Resulting kinetic model satisfactorily describes the whole set of experimental data including those obtained on samples solidified under high cooling rates, and reveals that a correct description of the evolution of the α phase during solidification can be attained only if the evolution of the competing mesomorphic phase is kept into account. The effect of cooling rate during solidification from the melt on diameters of spherulites, observed on solidified samples, is also satisfactorily described by model predictions.

Effects of cooling rate on crystallinity of i‐polypropylene and polyethylene terephthalate crystallized in nonisothermal conditions

Crystallization of polyethylene terephthalate and i-polypropylene in nonisothermal conditions is studied by means of differential scanning calorimetry. Measurements, carried out at several constant cooling rates, are interpreted in terms of a new theory1,2 that takes into account effects related to a transient, nonsteady-state course of the process as well as athermal nucleation, which may occur under such circumstances. This article gives preliminary results based on analysis of final crystallinity reached at the end of cooling. Results indicate that the classical isokinetic approach is not adequate to describe crystallization kinetics at high cooling rates. A parameter quantizing the magnitude of deviations from isokinetic law is evaluated. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2821–2827, 1999

Effects of cooling rate on crystallinity of i-polypropylene and polyethylene terephthalate crystallized in nonisothermal conditions

Crystallization of polyethylene terephthalate and i-polypropylene in nonisothermal conditions is studied by means of differential scanning calorimetry. Measurements, carried out at several constant cooling rates, are interpreted in terms of a new theory 1,2 that takes into account effects related to a transient, nonsteady-state course of the process as well as athermal nucleation, which may occur under such circumstances. This article gives preliminary results based on analysis of final crystal- linity reached at the end of cooling. Results indicate that the classical isokinetic approach is not adequate to describe crystallization kinetics at high cooling rates. A parameter quantizing the magnitude of deviations from isokinetic law is evaluated.

Bilateral Isokinetic Knee Rehabilitation Following Bilateral Total Knee Replacement Surgery

A 67-year-old male underwent bilateral total knee replacement surgery and was subsequently placed on a bilateral isokinetic knee rehabilitation program. Isokinetic knee testing was performed on unilateral dominant (UD; right) and nondominant (UND; left) limbs as well as bilateral limbs (BLs) before and after a three-times-per-week, 8-week protocol during which the patient followed a bilateral isokinetic velocity spectrum (60 to 300°/s) rehabilitation program. The protocol was made possible by the introduction of a new bilateral isokinetic knee attachment developed by the authors. The BL extension and flexion peak torque increased 41% and 51% at 60°/s, respectively. The UD and UND extension peak torque increased 22% and 37%, respectively, while flexion peak torque increased 68% and 52%, respectively. The bilateral deficit decreased with increasing velocity for both extension and flexion. These results demonstrate that a bilateral isokinetic approach to rehabilitation may be a legitimate technique to increase knee extension and flexion peak torque both unilaterally and bilaterally following bilateral total knee replacement surgery.