Dynamic Characteristics Of Mechanism Research Articles

Dynamic characteristics analysis of multi-link mechanism with clearances considering uncertain parameters

As a typical multi-body system, multi-link mechanisms are widely used in industry. Inevitably, there are joint clearances in multi-link mechanisms. Besides under the conditions of manufacturing, assembly and wear, the parameters of the multi-link mechanism can create uncertainty, and joint clearances and uncertain parameters of the multi-link mechanisms deteriorate the dynamic characteristics, this directly leads to a reduction in working accuracy of the mechanisms. At present, the research focus on multi-link mechanism with clearance considering certain parameters, and relatively few research on the multi-link mechanism with clearance considering uncertain parameters, the existing research on uncertain parameters mainly focus on the uncertainty of single parameter, while the research on the dynamic response of the mechanism with multi-clearances considering the uncertainty of multiple parameters is very less. The main purpose of this article is to provide a novel feasible method for studying the dynamic characteristics of multi-link mechanisms with joint clearances under the consideration of interval uncertain parameters and random parameters. Therefore, the dynamic characteristics of mechanism with multiple clearances considering uncertain parameters, which includes interval parameters and random parameters, are investigated in this article. Taking the 6-bar mechanism as the research object, considering clearances, Poisson’s ratios, stiffness coefficients, and driving speed as the uncertain parameters, the dynamic models of 6-link mechanism with multiple clearances considering interval parameters and random parameters are developed respectively. Using Chebyshev polynomial to solve interval parameters and polynomial chaos to solve random parameters, the effects of uncertain parameters such as clearances, Poisson’s ratios, stiffness coefficients, and driving speed on the dynamic response of the mechanism are analyzed, respectively. This research can not only provide a basis for studying the essential dynamic characteristics of multi-link mechanism with uncertain parameters, but also lay the foundation for dynamic optimization design of the real mechanisms.

Analysis of the Synchronized Locking Dynamic Characteristics of a Dual-Sidestay Main Landing Gear Retraction Mechanism

As an advanced design technology for large wide-body airliners, the three-dimensional (3D) dual-sidestay (DSS) landing gear retraction mechanism can share the ground loads transferred by the landing gear, reducing the load on the wings. However, the addition of a strut system may significantly impact the synchronous locking performance of the landing gear with extremely high sensitivity. To study this impact pattern, both a rigid–flexible-coupling dynamic model of DSS landing gear considering joint clearance and node deviation and a synchronous locking test platform are established in this paper, and the simulation model is validated through the experimental results. Based on the simulation model, this paper conducts a detailed study on the influence of different node deviations and joint clearance on the synchronous locking dynamic characteristics of the DSS landing gear. The results show that, as the node deviation increases, the locking of the lock link gradually lags until one side cannot be fully locked; the structural clearance has a smaller impact on the synchronous locking of the landing gear. The feasible region of parameters satisfying the synchronous locking condition is given, which provides a basis and support for the parameter design of dual-sidestay retraction mechanisms.

Research on the dynamic characteristics of the electromagnetic repulsion mechanism of a self-driving fault current limiter

A fault self-driven current limiter is proposed in the paper, which uses a special fault current direct-driven electromagnetic repulsion mechanism to realize the first half-wave of the fault current over the zero point into the current-limiting reactance. The paper analyzes the working principle of the self-driven electromagnetic repulsion mechanism, establishes the equivalent model of the mechanism, and simulates the dynamic characteristics of the electromagnetic repulsion mechanism through the calculation of the double-layer iterative algorithm in time and space. The LC oscillation loop test platform is built, and the stroke–time curve of the prototype is measured. In the test, the prototype is driven by a 3 kA current, and the first half-wave stroke (FHWS) is 3.55 mm past the zero point, which is consistent with the simulation and test results. The effects of structural parameters such as the radius, thickness, and number of turns of the self-driven electromagnetic repulsion mechanism on the dynamic characteristics of the electromagnetic repulsion mechanism are investigated, and it is found that the first half-wave stroke can be significantly improved by increasing the number of turns and outer diameter of the coil. The optimum height of the dynamic repulsion coil is approximately 3 mm.

Designing a Model Predictive Controller for Displacement Control of Axial Piston Pump

Variable displacement hydraulic pumps are widely used for energy efficiency, and they often have a mechanical feedback mechanism to ensure target tracking control performance and stability of tilt angle control. Furthermore, there are many examples which add electronic control to realize higher tracking control performance. However, in such cases, the control performance is significantly affected by the dynamic characteristics of the mechanical feedback mechanism, and this problem prevent its widespread use. Additionally, tilt angle control is susceptible to changes in dynamic characteristics and load pressure depending on the operating point, and there are constraints on the tilt angle. Hence, high control performance cannot be obtained without considering these nonlinearities. In this study, the variable displacement pump without mechanical feedback mechanism is focused on, and the objective of this study is to design a displacement control system for a hydraulic pump based on a model predictive control (MPC) that can consider various constraints on the design step. An adaptive system, which handles changes in dynamic characteristics and the effects of load pressure, is introduced. Additionally, the control performance of adaptive MPC is compared to adaptive model matching-based MPC with inverse optimization that can optimally design the weight matrices of the evaluation function without trial and error. Furthermore, in order to improve the transient response, a variable control input constraints are added in these two control systems. Experimental results of control performance have shown that the proposed method achieved a high tracking performance and short settling time, which confirmed the effectiveness of the variable control input constraints.

Mechanism of pH Effect on Mass Transfer During Bubble Evolution on Photoelectrode Surfaces

This study conducted in-depth research on the limitation problem of mass transfer of gas molecules on the surface of the photoelectrode to the efficiency of photoelectrochemical water splitting. Experimental results reveal significant differences in the dynamic characteristics of bubbles and mass transfer mechanisms during bubble growth under different pH conditions. As the pH deviates from 7.0 (vs RHE), the reaction rate increases, the bubble nucleation voltage decreases, and the terminal rising velocity increases significantly. During the rapid growth phase of bubbles, the mass transfer coefficient reaches its peak, accounting for only 1% of the entire evolution cycle. In a neutral environment (pH = 7.0), the transient mass transfer coefficient reaches a maximum at approximately 1 s of bubble growth, while in an alkaline environment (pH = 12.0), it reaches a maximum at around 0.1 s. In strongly alkaline environments (pH = 13.0), the PEC reaction rate and mass transfer rate increase, resulting in the highest gas production efficiency. The mass transfer coefficients were improved by about 72.4% and 42.8% (vs Ag/AgCl) and by about 22.2% and 33.3% (vs RHE) in the strong alkaline environment relative to the strong acid environment (pH = 1.0) and the neutral environment, respectively.

Theoretical and experimental studies on effect of impact load on dynamic characteristics of multi-link press mechanisms with clearances

Theoretical and experimental studies on effect of impact load on dynamic characteristics of multi-link press mechanisms with clearances

Design and analysis of a novel flexible variable stiffness damping mechanism for grinding electric spindle

The purpose of this research is to design a flexible variable stiffness damping mechanism to solve the load impact problem in the grinding process of permanent magnet electric spindle. Firstly, combined with the structure and usage scene of the grinding permanent magnet electric spindle, according to the design principles and technical indicators, a novel flexible variable stiffness vibration damping joint is proposed. Then the stiffness and energy storage model of the flexible variable stiffness damping mechanism is established, and the stiffness and energy storage characteristics of the mechanism are analyzed. The strength and dynamic characteristics of the flexible variable stiffness mechanism are analyzed by Ansys and Adams, respectively. Finally, an experimental platform for the comprehensive performance verification of the flexible variable stiffness damping mechanism is built to verify the dynamic characteristics and damping effect of the mechanism. The research results show that the designed flexible variable stiffness structure has better vibration damping effect and can improve the grinding performance of the permanent magnet electric spindle.

THE USAGE OF COMPUTER-AIDED ENGINEERING SYSTEM “SOLIDWORKS MOTION” TO SOLVE THE PROBLEMS OF KINEMATICS AND DYNAMICS OF TECHNICAL SYSTEMS

The paper is dedicated to the problems of engineering analysis of technical systems by means of computer modeling, in particular the calculation of kinematic and dynamic characteristics of mechanisms and machines using the Computer-Aided Engineering system – SOLIDWORKS Motion, that allows to conduct numerical experiments to check the working capacity of mechanisms and machines, determine their main kinematical and dynamical characteristics, including for the purpose of further optimization according to various criteria. The paper shows results of the performed calculations of various types of mechanisms using examples used in the academic process within the course “Theory of Mechanisms and Machines”, which can be also successfully used within the design process, and includes examples of kinematic and dynamic analysis of linkage mechanisms, cam mechanisms, gear trains. In particular, the paper includes the simulation of the work process of the robot-manipulator using SOLIDWORKS Motion. It is shown that the usage of modern Computer-Aided Engineering systems (like SOLIDWORKS Motion or similar) enables to simplify the design process, shorten the design time and give an ability to carry out multi-parametric optimization procedures using different criteria, such as displacement values, velocities, accelerations, the values of reaction forces, overall dimensions etc. Besides, the usage of CAE-technologies enables to transform the academic process and makes it much more interesting or the students, who can use such technologies in their professional work in the future and become more competitive in the job market.

Analysis and Optimization of Dynamic and Static Characteristics of the Compliant-Amplifying Mechanisms.

Compliant amplifying mechanisms are used widely in high-precision instruments driven by piezoelectric actuators, and the dynamic and static characteristics of these mechanisms are closely related to instrument performance. Although the majority of existing research has focused on analysis of their static characteristics, the dynamic characteristics of the mechanisms affect their response speeds directly. Therefore, this paper proposes a comprehensive theoretical model of compliant-amplifying mechanisms based on the multi-body system transfer matrix method to analyze the dynamic and static characteristics of these mechanisms. The effects of the main amplifying mechanism parameters on the displacement amplification ratio and the resonance frequency are analyzed comprehensively using the control variable method. An iterative optimization algorithm is also used to obtain specific parameters that meet the design requirements. Finally, simulation analyses and experimental verification tests are performed. The results indicate the feasibility of using the proposed theoretical compliant-amplifying mechanism model to describe the mechanism's dynamic and static characteristics, which represents a significant contribution to the design and optimization of compliant-amplifying mechanisms.

Dynamic characteristics of the rack and pinion lift mechanism of the combined command cabin

This paper presents a novel approach to accurately simulate the dynamic characteristics of a rack and pinion lifting mechanism while accounting for the coupling effect of meshing tooth pair stiffness and grease characteristics in real-world environments. A structure-grease coupling meshing stiffness model is established based on the deformation coordination conditions of the tooth pair meshing. The model incorporates the effect of the grease stiffness term on the time-varying meshing stiffness of the rack and pinion. By analyzing the dynamic characteristics of the combined command cabin lifting mechanism using this model, we find that the total meshing stiffness of the gear teeth is lower when the transient thermoelastic flow effect of the grease is considered. Furthermore, the total stiffness value decreases as the normal meshing force at the meshing point decreases. This research reveals that the worst lubrication conditions are typically found on the gear wheel teeth near the base circle, where the grease film temperature rise is highest, the grease film pressure is highest, and the grease film thickness is thinnest.

Dynamic response and nonlinear characteristics of multi-link mechanism with clearance joints

Dynamic response and nonlinear characteristics of multi-link mechanism with clearance joints

OPTIMIZATION OF TOWER CRANE SLEWING MECHANISM CONTROL

The article considers the optimal speed-optimal control of the tower crane turning mechanism. A calculation scheme has been compiled according to which a mathematical model has been obtained that describes the operation of the boom rotary crane - cargo system. Solutions of the system of equations are obtained and phase coordinates are chosen, according to which the motion of the considered mechanical system is studied. Using the maximum principle, the laws of change of the control parameter are substantiated, taking into account the engine torque and the speed-optimal law of motion of the turning mechanism, which is the main scientific novelty of this article. On the example of a crane on a column with a lifting capacity of 5 tons, phase trajectories are calculated and graphs are plotted for changing the dynamic characteristics of the rotation mechanism that is optimal in terms of speed.

Dynamic Features of Non-Return Mechanism in Hatch Door of Amphibious Aircraft

The non-return mechanism is the key device that plays the role of braking in the opening-and-closing electric actuator of an amphibious aircraft hatch door. The ball-and-socket contact pair, providing the pressing force, and the multi-disc friction pair, supplying the braking torque, are two core components in the non-return mechanism. In this paper, the dynamic model of the non-return mechanism is established considering the freedom of rotation-translation. Based on MATLAB/Simulink, the solution framework of the overall dynamic model is built. The dynamic response characteristics of the non-return mechanism in the process of reverse load braking, forward load braking, and continuous closing are analyzed. The braking time and the angular displacement of the output shaft in the braking phase have been presented. Compared with forward load braking, reverse load braking has a longer braking time and smaller angular displacement of the output shaft. In addition, the compaction function of the ball-and-socket contact pair is verified by experiment, and the influence of the cone angle, distribution radius of the ball socket, and the steel ball diameter on the pressing force has been discussed. This study provides a theoretical basis and parametric design platform for the design and optimization of non-return mechanisms, which can shorten the product development time.

Nonlinear dynamics of 1D meta-structure with inertia amplification

Considering the low-frequency vibration isolation properties of the inertial amplification mechanism (IAM) and the band gap of the periodic structure, this paper is concerned with the dynamic characteristics of the nonlinear inertial amplification mechanism (NIAM), theoretically. This study focused on the influence of nonlinearity on vibration isolation characteristics. Both analytical and numerical methods are adopted. Through the analysis of a basic NIAM element, nonlinear modes and complex phase motions are observed. The bifurcation property shows that complex motions (periodic, quasi-periodic, and chaotic) can be obtained by altering the exciting frequency for some intended goals, especially for vibration reduction. Analysis of the dispersion relation and the vibration transmissibility of the 1D periodic meta-structure composed of multiple NIAMS (NIAMMS) demonstrates its superiority with a decrease of 18.4% in the lower bound of the band gap, compared with a common 1D nonlinear periodic meta-structures. Furthermore, it is possible to obtain an ultra-low and ultra-wide nonlinear band gap by properly adjusting the parameters such as nonlinear stiffness, mass ratio, assembly angle, and damping.

Dynamic Characteristics and Frequency Reliability Analysis of an Optimized Compliant Stroke Amplification Mechanism

Abstract To rapidly analyze the dynamic characteristics of a compliant stroke amplification mechanism (CSAM) with completely distributed compliance, an analytical model based on the dynamic stiffness matrix with consideration of the damping effect is proposed. The natural frequency of the CSAM is optimized without attenuation of the amplification ratio based on this model. The optimized CSAM exhibits an approximately 112% higher natural frequency than the original mechanism along the main motion direction. The optimization result is verified through finite element simulation, with less than a 7% difference being observed. Moreover, the effects of frequency on the amplification ratio and input stiffness of the optimized CSAM are also discussed. The structural resonance is defined as the failure criterion of the optimized CSAM, and the sensitivity of the failure probability to manufacturing errors at different positions is analyzed. The findings show that the failure probability of the CSAM is more sensitive to parameters associated with the coordinates of the output stage and vertex.

Identification of the self-oscillating mode in metal-cutting machines in the production of agricultural machinery

The production of modern agricultural machinery includes various technological chains machining workshops, consisting mostly of turning and milling machining centers. The influence of self-oscillations on the dynamic characteristics of mechanisms for various purposes is due to the increased requirements for the quality and reliability of products of modern machines and units. Timely detection and reduction of the impact of oscillatory processes makes it possible to qualitatively optimize the design of mechanisms. A special role in the process of operation is exerted by self-oscillations on metal-cutting machines in the processing of materials. The consequence of the self-oscillatory process is a violation of the performance of a metal-cutting machine, expressed in a parametric (accuracy) failure. In this paper, the possibility of using parametric spectral analysis for the early identification of a self-oscillating process in hexapod machine tools was evaluated, for which the objective function was determined, i.e. the value of the damping coefficient of the dynamic system.

Fine-scale analysis of edge effect of shrub patch in different grassland types

Boundaries may have important effects on landscape patterns, landscape change mechanisms, and dynamic processes. However, little is known about the dynamic mechanism of patch boundary changes at a fine scale. To elucidate the characteristics of grassland patches at fine scales and to provide a reference for the mechanism of change and development direction of patchy landscapes. In this paper, the patch of different grassland types in Xilingol League was studied by NMDS, RDA, and SEM methods, to analyze the vegetation community and soil characteristics of surface soil and the relationship between them: The changes in soil vegetation community and soil characteristics were completely different among the three grassland types, and the abrupt changes of vegetation index and soil properties were different. Vegetation index mostly ranged from −1 m to 0 m, and soil index mostly ranged from −0.5 m to 1 m. Fine-scale vegetation and soil boundaries are well defined, vegetation boundaries are mostly between −1 and 0 m and soil boundaries are mostly between −0.5–1 m, and soil properties have a clear influence on plant characteristics. The difference in organic matter, nitrogen, and phosphorus content is an important factor affecting the change of patch boundary, the distribution of the RDA results showed that the organic matter, nitrogen and phosphorus contents in all three grasslands explained >70% of the environmental factors. The emergence of annual vegetation involves a process of succession, specifically, the nature of the underlying soil determines the type of plants at the boundary. The dynamic characteristics of the soil-plant mutual-feed mechanism determine the location and variation of patch boundaries to adapt to disturbance states. The results of this study provide insight into how boundaries respond to changes in environmental conditions and drive dynamic changes at the landscape level.

Optimization design method of upper limb exoskeleton cam mechanism’s motion trajectory model

In order to solve the problem caused by the coupling clearance of the upper-limb cam mechanism, based on cam entity structure’s data and motion trajectory characteristics, with the cam axle acceleration αc and the output torque accuracy σT as the optimization targets, a mathematical model of cam mechanism is established in the study. Cam mechanisms was established with the radial basis function (RBF) method to restore the physical model of upper-limb exoskeleton’s motion trajectory model accurately. Then, global optimization was performed with adaptive non-dominated sorting genetic algorithm-II (NSGA-II) to get αc and σT s’ Pareto solution sets and form a data mapping cam mechanism with the dynamic feedback between the motion trajectory model and the entity model. In the verification experiments, the motion trajectory model established with only 37 response points only required a low amount of computation, and the response point verification error was within 3%, indicating the high restoration accuracy. After physical parameters were optimized with NSGA-II, the optimal pareto solution sets of dynamic characteristic parameters of the cam mechanism were obtained. αc and σT were respectively decreased by 52% and 81%. The deviation of αc between the entity model test data and simulation data was 3.84°/s2 and σT was 30.23 N·mm, indicating that cam motion deviation could be adjusted by dynamic data feedback. This study verifies that the dynamic characteristics of the cam mechanism can be optimized by optimizing the material parameters of the rollers, thereby improving the performance of the upper limb exoskeleton.

Effects of nonlinearity of restoring springs on propulsion performance of wave glider

Wave glider is an unmanned surface vehicle that can directly convert wave energy into forward propulsion and fulfill long-term marine monitoring. A previous study suggested that the wave motion and stiffness of restoring springs mounted on the hydrofoil are the main factors affecting the propulsion performance of the wave glider. In this paper, the dynamic responses and nonlinear characteristics of the underwater propulsion mechanism considering the nonlinear stiffness of restoring springs are investigated based on a fluid–rigid body coupled model. Firstly, models of propulsion mechanism with different kinds of restoring springs are proposed, and the linear and nonlinear characteristics of the restoring spring are considered. Then, a fluid–rigid body coupled model of a wave glider is developed by coupling the rigid body dynamics model and hydrodynamic model. Dynamic responses are simulated by the numerical analysis method, and the nonlinear characteristics with different restoring springs are illustrated by the time/frequency domain motion response and phase diagram analysis. The effects of the wave excitation frequency, wave heights and the location of the connection point of springs on the propulsion performance of the wave glider are analyzed. The results show that multi-frequency responses occurred in the propulsion system, and the nonlinear restoring spring on the hydrofoil can provide a larger restoring moment to avoid excessive pitch angle and is more suitable for different sea conditions, which provides a reference for developing propulsion mechanisms with high performance in complex marine environments.

Dynamic Analysis of Rudder Transmission Mechanism Considering Clearance Joint and Friction

Based on the theory of multi-body dynamics, this paper proposes typical impact model and friction model to research the dynamic characteristics of the transmission mechanism with clearance joints in ADAMS softwear environment; On this basis, considering the hinge gap and friction factors under the rigid condition of the mechanism, a multi-body model is developed. Dynamic simulation analysis has studied the influence of five hinge gaps and three friction coefficients on the speed and output displacement of the rudder transmission mechanism. The research results lay an important foundation for the further development of the rigid-flexible coupling and thermal-mechanical coupling dynamic characteristics of the rudder transmission mechanism base.