Dynamic Unbalance Research Articles

Mild Cognitive Impairment Subtypes Are Associated With Peculiar Gait Patterns in Parkinson's Disease.

BackgroundMild cognitive impairment (MCI) is frequent in Parkinson’s disease (PD) and represents a risk factor for the development of dementia associated with PD (PDD). Since PDD has been associated with disability, caregiver burden, and an increase in health-related costs, early detection of MCI associated with PD (PD-MCI) and its biomarkers is crucial.ObjectiveGiven that gait is considered a surrogate marker for cognitive decline in PD, the aim of this study was to compare gait patterns in PD-MCI subtypes in order to verify the existence of an association between specific gait features and particular MCI subtypes.MethodsA total of 67 patients with PD were consecutively enrolled and assessed by an extensive clinical and cognitive examination. Based on the neuropsychological examination, patients were diagnosed as patients with MCI (PD-MCI) and without MCI (no-PD-MCI) and categorized in MCI subtypes. All patients were evaluated using a motion capture system of a BTS Bioengineering equipped with six IR digital cameras. Gait of the patients was assessed in the ON-state under three different tasks (a single task and two dual tasks). Statistical analysis included the t-test, the Kruskal–Wallis test with post hoc analysis, and the exploratory correlation analysis.ResultsGait pattern was poorer in PD-MCI vs. no-PD-MCI in all tasks. Among PD-MCI subtypes, multiple-domain PD-MCI and amnestic PD-MCI were coupled with worse gait patterns, notably in the dual task.ConclusionBoth the magnitude of cognitive impairment and the presence of memory dysfunction are associated with increased measures of dynamic unbalance, especially in dual-task conditions, likely mirroring the progressive involvement of posterior cortical networks.

ВЛИЯНИЕ ПОГРЕШНОСТЕЙ ИЗГОТОВЛЕНИЯ ДЕТАЛЕЙ НА ДИСБАЛАНСЫ РОТОРА ГАЗОТУРБИННОГО ДВИГАТЕЛЯ ПРИ ЕГО СБОРКЕ

Increased vibrations of a gas turbine engine reduce the reliability and overall service life of the engine. The main reason for the appearance of increased vibrations is the dynamic imbalance (dynamic imbalance) of one or more engine rotors. Dynamic un-balance in its turn is a cumulative manifestation of static and moment unbalance of the rotor. One of the reasons for the appearance of unacceptable values of rotor imbalances is the imperfection of the geometric pa-rameters of the parts, that is, the manufacturing errors of these parts. Despite the fact that at present there are strict requirements for the accuracy of manufacturing parts of a gas turbine engine, it is impossible to manufacture a part without errors. When joining several rotors, the summing errors in the manufacture of parts may lead to a shift in the center of mass of the rotors, as well as to a misalignment of their axes, which in turn leads to an increase in the imbalances of the assembled rotor. As a result of the vibration of the assembled engine significantly exceed the permissible. The problem of the influence of errors in the manufacture of parts on the unbalances of the gas turbine engine rotor during its assembly is analyzed. A review analysis of the methods for solving this problem, presented in modern scientific papers, is car-ried out. A technique for 3D modeling of the GTE rotor assembly is given, taking into account the beat vectors to predict the static and moment imbalances of the assembled rotor. Based on the simulation results, the displacements of the center of mass of the analyzed rotor and the distortions of its axis are calculated for different positions of the beat vectors. The conclusion is made about the expediency of applying the considered methodology in the design of modern gas turbine engine.

Vibration Design of CT Scanner with Transfer Function

This paper provides a new vibration evaluation method of CT scanner with a non-axisymmetric rigid rotor. Vibration at the fundamental frequency under unbalanced load is expressed by the product of unbalance load and its transfer function obtained either by calculation of frequency responses function (FRF) or experimental measurement. Additionally, we provide a formulation of dynamic unbalance load for non-axisymmetric rigid rotor. Although applying correction weights is general way to eliminating residual vibration, but arbitrary weight set can be designed by satisfying the same unbalance load. Furthermore, optimization of the machine structure and the layout of units mounted in the rotor can also be made by evaluating transfer function of the machine with FEM and unbalance load, respectively.

Optimization and Design of Hammerheads and Fenders on Scrap Metal Shredders Based on Improved Genetic Algorithm

Dynamic unbalance force is an important factor affecting the service life of scrap metal shredders (SMSs) as the product of mass error. Due to the complexity of hammerheads arrangement, it is difficult to take all the parts of the hammerhead into account in the traditional methods. A novel optimization algorithm combining genetic algorithm and simulated annealing algorithm is proposed to improve the dynamic balance of scrap metal shredders. The optimization of hammerheads and fenders on SMS in this paper is considered as a multiple traveling salesman problem (MTSP), which is a kind of NP-hard problem. To solve this problem, an improved genetic algorithm (IGA) combined with the global optimization characteristics of genetic algorithm (GA) and the local optimal solution of simulated annealing algorithm (SA) is proposed in this paper, which adopts SA in the process of selecting subpopulations. The optimization results show that the resultant force of the shredder central shaft by using IGA is less than the traditional metaheuristic algorithm, which greatly improves the dynamic balance of the SMS. Validated via ADAMS simulation, the results are in good agreement with the theoretical optimization analysis.

Dynamic modeling and open-loop analysis of a control moment gyroscope considering the influence of a flexible vibration isolator

The microvibrations that affect the output performance of control moment gyroscopes (CMGs) are important in spacecraft attitude control systems. To reduce the influence of vibrations, researchers have done much work to isolate the vibrations between the CMG and the satellite. However, the deformation of the flexibility isolator affects the direction of the angular momentum, which affects the dynamic performance of the CMG inverse. In this research, using the Lagrange’s equation, the dynamic model of the CMG-isolator coupling system with the exciting force of the dynamic unbalance torque, the CMG’s gyro torque and the gimbal motor torque is developed. Based on this model, the coupling relationship between the gimbal rotation and the isolator deformation is established. For this CMG-isolator coupling system, we conduct the simulations to study the influence of the flywheel speed and the isolator stiffness on the CMG’s output performance and its gimbal’s rotation. Finally, the experiments on a CMG prototype are conducted, which verify the dynamic model and the simulation results of the CMG-isolator coupling system.

A numerical study of rotor eccentricity and dynamic load in induction machines for motor current analysis based diagnostics

The asymmetry in the manufacturing and assembling is the common issue of rotor systems. Different degrees of errors are inevitable in alternating current (AC) motors, which causes degraded performances. Furthermore, around 80 % of mechanical faults link to rotor eccentricity. The eccentricity faults (EFs) generate excessive mechanical stress and then lead to fatigue in the other parts of the motor. Motor current signal analysis (MCSA) can be used to diagnose induction machine (IM) faults. As the EF leads to an unequal air gap when the rotor rotates, the inductance of IM also responds to the EF. Moreover, the dynamic load is a typical situation due to residual dynamic unbalance and misalignment. To study how EFs and dynamic load affect the stator current. The current model of symmetrical motor, asymmetrical motors with three-level EFs and with dynamic load are investigated numerically. The correctness of models is verified through experimental study. The results show the level of EF affects the sideband peak values significantly in the stator current spectrum. These findings will provide a foundation for the accurate diagnosis of motor health conditions.

Abnormal Wear Mechanism and Improvement of High-Speed Cylindrical Roller Bearing

This paper presents the dynamic differential equations of cylindrical roller bearing, considering the dynamic unbalance mass of roller and the contact between the roller end face and the inner ring rib. The influence of bearing working condition and structural parameters on the P V value of roller end face and the slip speed of roller working surface were analysed. The theoretical analysis and experimental results both show that the large amount of roller’s dynamic unbalance mass due to the difference in chamfering size on both sides of the roller and the deviation of the bearing axial clearance are the main causes of abnormal wear on the roller working surface and end face.

Research on Over-temperature Online Rapid Early Warning Methods of Oil-immersed Transformer under the Condition of Three-Phase Unbalance

The number of oil-immersed transformers in the distribution network is huge, and the real-time electrical quantity information of a single device is little in number and longer in period in comparison with the main network device. Owing to the randomness of the load, the transformer has long been dynamic three-phase unbalance. The short-term emergency load formed by the rapid rise of residents’ load in summer and winter causes the hotspot temperature of the single-phase winding to rise, the insulation quickly ages, the operating life suffer serious losses, and even cause the transformers in the area to be burned out in large areas. On the basis of the existing data resources, the feasible judgment methods is made from the overall interests, which can avoid damage of the equipment and inform the operating personnel of the residual margin simultaneously. This paper fully proposes the over-temperature online early warning method of oil-immersed transformers under three-phase unbalance, analyzes the compatibility of various commonly used three-phase unbalance algorithms and the hotspot temperature of winding, establishes the logic model of transformer over-line and abnormal warning, and assesses the life loss during the extreme operation of the equipment for reliability. The results of the calculation examples show that the research on the over-temperature online early warning method of oil-immersed transformer under the condition of three-phase unbalance has the capacity to prevent extensive burning of equipment and predict the extreme residue of the transformer.

Design of Laboratory Dynamic Balancing Device and Investigation of Vibrations of Rotating Bodies

The rotor part to be balanced is mounted on the balancing device using a suitably designed fixture. When the rotor is rotated around its own axis, static and dynamic unbalance in the rotor, static and dynamic bending, which are simple harmonic movements in nature, cause oscillating motion. This harmonic motion of the static and dynamic elasticities is detected by the respective sensors and converts the mechanical input of the harmonic motion proportionally to the electrical voltage output. These readings are used to calculate the current static and dynamic unbalance in the rotor using the calibration constants. In this study, we designed a new balancing machine by using Arduino and MATLAB program and gave analysis results.

Model based estimation of inertial parameters of a rigid rotor having dynamic unbalance on Active Magnetic Bearings in presence of noise

Unbalance in rotors is known as the primary source of excitation, the state of unbalance changes over time and, therefore, industrial rotors require online or smart identification and attenuation of unbalance for smooth operation. To begin with, this paper proposes the use of Active Magnetic Bearings (AMBs) to identify the unbalance. Unbalance is defined as the location of centre of mass of the rotor and orientation of the axes of principal mass moments of inertia, both with respect to the spin-axis, assumed as the geometric axis of symmetry of rotor. Non-uniform distribution of mass makes a rotor dynamically unbalanced. The centre of mass shifts from the spin-axis and none of the principal axes of inertia is aligned with it. Dynamic behaviour of such a rotor is modelled by a set of differential equations with time varying coefficients. A rigid rotor is assumed to be supported on two AMBs with all known characteristics. A methodology based on modelling and simulation is proposed to determine the eccentricity and the orientation of the principal axes of inertia (angles of its skewness) by utilizing the force and response of the rotor recorded by each AMB. The median of simulated inertial properties are shown to be in close agreement with their actual values. The proposed methodology is also found robust enough in the presence of different types of simulated noise used to pollute signals from the bearings. Therefore, the methodology is suitable for online identification of inertial properties of a rotor.

Containment of blade shedding in gas turbine engines: part I—design and development of a scaled down test rig

Part I of this complementary article is concerned with the design, development and commissioning of a novel instrumented scaled down test rig to examine the dynamics and containment of a released blade during blade shedding (blade out) incidents in aviation gas turbine engines. The scaled down fully bladed disk is designed using non-dimensional parameters derived using Buckingham’s dimensional analysis technique. These parameters are enforced to ensure dynamic equivalency of the scaled down model and a realistic full size gas turbine engine. The rotor with drive system is encapsulated in a thick protective casing to contain all fragments within the confines of test rig and ensure safety of operation. The test rig is equipped with a high speed camera and numerous sensors interconnected via data acquisition system to two processors for data collection and data management. The purpose is to measure the released blade trajectory, its multiple interactions with the trailing blades, containment within the ring, the stresses resulting from dynamic unbalance and blade impingement, and their effect on engine mount. The successful operation of the newly commissioned test rig is tested under steady state conditions and we were able to demonstrate the applicability of the rig to blade shedding and containment tests in an efficient and cost effective manner.

Исследование динамической неуравновешенности вращающейся механической системы

The paper presents the results of development of an automated laboratory complex for the study of dynamic reactions of bearings of a rotating mechanical system. This complex includes an electromechanical model unit equipped with sensors for measuring reactions and angular speed of the system rotation, a power supply and control unit and a PC for processing the results of measurements and calculations of dynamic reactions. The theoretical basis for calculating the dynamic reactions of the unbalanced rotating mechanical system bearings is given, and a description of the research laboratory complex is provided. The results of experimental determination of these reactions as well as the corresponding calculated dependences of the latter on the angular speed of rotation and the degree of system unbalance are presented. The presence of a region of mechanical system insensitivity to its dynamic unbalance caused by the effects of friction in the bearings is confirmed. There is a good agreement between the proposed method for calculating dynamic reactions of rotating mechanical system bearings and experimental data on their measurement. The effectiveness of the developed laboratory complex in the training process at higher school when teaching the appropriate section of theoretical mechanics is noted.

Dynamic Balance Method for Grading the Chain Drive Double Threshing Drum of a Combine Harvester

Although the individual threshing drum of a combine harvester was balanced on a dynamic balancing machine before it is assembled, there were still unbalances after multiple drums were assembled with the chain drive. In this paper, the double drums with a chain drive of a crawler combined harvester were selected as the research subject. The aim of this study was to develop a dynamic unbalance mode for grading chain drive double drums. Based on the dynamic unbalance characteristics of the main driven drum, the experimental research on the radial balance of the driven drum end face was carried out. It was known that the chain drive had a direct and obvious influence on the unbalanced phase of the drum. The unbalance of the drive load had an obvious effect on unbalanced amplitude of an active drum through the transfer characteristics of the chain drive. For the multi-stage transmission characteristics of a combine harvester, a step-by-step balanced grading chain drive double drum dynamic balancing method was practiced. Results showed that the unbalanced amplitude after balancing threshing drum I chain transmission mode of the combine harvester can be reduced by a maximum of 91%. Simultaneously, the unbalanced amplitude of threshing drum II can reduced by a maximum of 69.2%. The size and position of the wrap angle of the chain drive would directly affect the phase of the two equivalent unbalanced masses.

Exploring Risk of Falls and Dynamic Unbalance in Cerebellar Ataxia by Inertial Sensor Assessment.

Background. Patients suffering from cerebellar ataxia have extremely variable gait kinematic features. We investigated whether and how wearable inertial sensors can describe the gait kinematic features among ataxic patients. Methods. We enrolled 17 patients and 16 matched control subjects. We acquired data by means of an inertial sensor attached to an ergonomic belt around pelvis, which was connected to a portable computer via Bluetooth. Recordings of all the patients were obtained during overground walking. From the accelerometric data, we obtained the harmonic ratio (HR), i.e., a measure of the acceleration patterns, smoothness and rhythm, and the step length coefficient of variation (CV), which evaluates the variability of the gait cycle. Results. Compared to controls, patients had a lower HR, meaning a less harmonic and rhythmic acceleration pattern of the trunk, and a higher step length CV, indicating a more variable step length. Both HR and step length CV showed a high effect size in distinguishing patients and controls (p < 0.001 and p = 0.011, respectively). A positive correlation was found between the step length CV and both the number of falls (R = 0.672; p = 0.003) and the clinical severity (ICARS: R = 0.494; p = 0.044; SARA: R = 0.680; p = 0.003). Conclusion. These findings demonstrate that the use of inertial sensors is effective in evaluating gait and balance impairment among ataxic patients.

Effect of cage dynamic unbalance on the cage’s dynamic characteristics in high-speed cylindrical roller bearings

Purpose The purpose of this paper is to study the influence of the cage dynamic unbalance on the dynamic performances in cylindrical roller bearings. Design/methodology/approach The dynamic analysis model which considering cage dynamic unbalance is presented, and the relationship between the cage dynamic unbalance and the cage stability, the cage slip ratio and the cage skew angle is investigated. Findings Cage dynamic unbalance has a great effect on the cage stability. The cage dynamic unbalance which in an axial excursion affects the cage characteristics is greater than that only in the radial direction. The cage slip ratio and the cage skew increases with the cage dynamic unbalance, especially with the axial excursion. The non-metal cage is more sensitive to the cage dynamic unbalance than that of the metal cage. Originality/value The analytical method and model can be applied by the bearing engineering designers.

Gradient Descent-Based Optimization Method of a Four-Bar Mechanism Using Fully Cartesian Coordinates

Machine vibrations often occur due to dynamic unbalance inducing wear, fatigue, and noise that limit the potential of many machines. Dynamic balancing is a main concern in mechanism and machine theory as it allows designers to limit the transmission of vibrations to the frames and base of machines. This work introduces a novel method for representing a four-bar mechanism with the use of Fully Cartesian coordinates and a simple definition of the shaking force (ShF) and the shaking moment (ShM) equations. A simplified version of Projected Gradient Descent is used to minimize the ShF and ShM functions with the aim of balancing the system. The multi-objective optimization problem was solved using a linear combination of the objectives. A comprehensive analysis of the partial derivatives, volumes, and relations between area and thickness of the counterweights is used to define whether the allowed optimization boundaries should be changed in case the mechanical conditions of the mechanism permit it. A comparison between Pareto fronts is used to determine the impact that each counterweight has on the mechanism’s balancing. In this way, it is possible to determine which counterweights can be eliminated according to the importance of the static balance (ShF), dynamic balance (ShM), or both. The results of this methodology when using three counterweights reduces the ShF and ShM by 99.70% and 28.69%, respectively when importance is given to the static balancing and by 83.99% and 8.47%, respectively, when importance is focused on dynamic balancing. Even when further reducing the number of counterweights, the ShF and ShM can be decreased satisfactorily.

High-precision control method for the satellite with large rotating components

Satellites with large rotating components may accomplish some specific scientific missions and have attracted a great deal of research interests. This paper investigates the control problem of such satellites. The model of the rotating component is carefully studied and both the static and dynamic unbalance are analyzed and demonstrated. To achieve a high precision control with unbalance rejection, a sliding mode control strategy is proposed. Practical simulations are conducted to verify the effectiveness of the proposed controller and simulation results illustrate that both the static and dynamic unbalance are perfectly compensated and a high-precision control is achieved.

A new real-time multi-agent system for under frequency load shedding in a smart grid context

Automatic under frequency load shedding schemes need to be carefully designed in order to reduce the risk of widespread system collapse. This paper proposes a centralized hierarchical multi-agent system that coordinates various stages of monitoring and decision making processes. The main contribution is to improve traditional contingency response algorithms such as load shedding schemes, taking advantage of the future smart grid infrastructure. The multi-agent system seeks for a minimum amount of load disconnection in a short period of time, causing the least possible disturbance in the system frequency. A hardware-in-the-loop simulation of a full electric power system using a real time digital simulator was utilized. The solution was embedded in a real time system, consisting of hardware and software, to test and validate the proposed methodology. In addition, the studied methodology was compared with two other load shedding philosophies through a load shedding metric score. Shedding was carried out in a single step and the amount of disconnected load was close to the dynamic power unbalance. The results show that it is possible to improve the traditional load shedding philosophy schemes and use advanced communication infrastructure, monitoring and embedded processing capabilities to provide better stability and reduce unnecessary load disconnections from the system.

Multiple-degree-of-freedom rotor model with total unbalance and possible contact on stator

Mathematical model for the flexible rotor which has static and dynamic unbalance and enabled slip rolling on the compliant stator is developed. Also, rotation inertia, gyroscopic effect, bearings characteristics, internal hysteresis, and external viscous friction are included. The matrix approaches are used. The proposed model allows investigating the dynamic effect of total unbalance and stator displacements as an elastic and solid body on basis of the ordinary differential equations.

Research on the Device Design for Calculation Distribution Line Loss Based on Dynamic Three-phase Unbalance Degree

For the power distribution network line loss calculation, there are some problems, such as backward method, long calculation period, large workload and poor real-time performance. To this end, this paper proposes a real-time calculation method for distribution line loss based on dynamic three-phase unbalance, and a hardware device system with unbalanced phase sequence identification function, three-phase unbalance detection function and line loss real-time calculation function has been developed. The system uses a master-slave design based on the principle of wireless transmission. The slave collects standard three-phase current signals and transmits them to the host through wireless transmission. The host is installed on the low voltage side of the transformer in the transformer region, and the current signal of the transformer region is collected in real time. Unbalanced phase sequence identification, unbalance calculation, and line loss calculation based on dynamic unbalance are performed by comparing the current signals collected by the master and the slave. The above algorithm implementation process can be displayed online in real time. In addition to the core data processing and waveform display functions, the device also includes a battery power supply and management system, a signal storage and transmission system, and temperature measurement, and overcurrent and overvoltage protection. The test results of the device show that the device has the characteristics of convenient carrying, fast detection of three-phase unbalance, and accurate calculation of line loss. The device can monitor the running status of the distribution network transformer region in real time.