Flexible Multi-body Dynamic Model Research Articles

Dynamic optimization of robot arm based on flexible multi-body model

This paper examines the effect mechanism of torsional stiffness on flexible joints and the dynamic optimization of a six Degree-of-freedom industrial robot arm. The design optimization of the robot arm is investigated based on the rotor-torsional spring model and finite element method. The flexible multi-body dynamic model of the robot arm are established by considering the flexible characteristics of arms and joints, and the natural frequencies of a robot arm are calculated to obtain the torsional stiffness of the flexible joints. Natural frequency results gradually increased with joint stiffness improvement. Using the established dynamic model, the topology optimization on the robot arm is carried out by regarding lightweight as design goal and total displacement as constraints. The tare-load ratio and dynamic performance of the optimized robot arm are significantly enhanced compared with the original design model. This research can provide the theoretical basis for the dynamic optimization and upgrade of lightweight robot arm.

Dynamic Modelling of Hoisting Steel Wire Rope

Aiming at the steel wire rope and its connecting mechanism, the modeling method and dynamic behavior analysis was carried out. The flexible multibody dynamics model of the rope was established by using cable element basing on the absolute nodal coordinate formation, while, other parts in the connecting mechanism were simplified as rigid bodies. The contact impact force between the flexible rope and other rigid bodies was incorporated into the dynamic model through the Hertz contact theory. Finally the rigid-flexible coupled dynamic model which can describe the large rotation and large displacement of the whole steel rope system was established. The simulation of the steel rope’s dynamic model was presented. The results show that the developed model can be used in the analysis of dynamic behavior and the accurate control of the motion.

Dynamic analysis of the deployment for mesh reflector deployable antennas with the cable-net structure

This paper presents a dynamic analysis approach for the composite structure of a deployable truss and cable-net system. An Elastic Catenary Element is adopted to model the slack/tensioned cables. Then, from the energy standpoint, the kinetic energy, elasticity-potential energy and geopotential energy of the cable-net structure and deployable truss are derived. Thus, the flexible multi-body dynamic model of the deployable antenna is built based on the Lagrange equation. The effect of the cable-net tension on the antenna truss is discussed and compared with previous publications and a dynamic deployment analysis is performed. Both the simulation and experimental results verify the validity of the method presented.

The coupling effects of the missile launcher and the ground in vehicle-mounted missile erecting

In order to study the coupling effect of the equipment and the launching site during the erecting process of the vehicle missile system, the lumped parameter model of the multi-stage hydraulic cylinder is deduced, the flexible multi-body dynamic model is established in ADAMS, and the normal and tangential coupling forces in the coupling relationship are derived. The coupling calculation model of the weapon system and the launching site is established in the co-simulation of the ADAMS and MATLAB/Simulink. The results show that the vertical slip of the launching platform is much greater than longitudinal and lateral ones. The erection angles of the cylinders at all levels when they begin to extend are 0°, 22.16°, 43°, and 65.52°, respectively, of which the speeds are 50 mm/s or so, and there are little limit impacts between the cylinders. The thickness of the surface layer has greatest influence on the stability and security of the launching platform, followed by the thickness of the base layer as well as the elastic moduli of the surface layer and the base layer. The conclusion provides important theoretical basis for the selection of the unsupported launching site.

Multibody modeling of varying complexity for dynamic analysis of large-scale wind turbines

Guaranteeing a robust and reliable wind turbine design under increasingly demanding conditions requires an expert insight into dynamic loading effects of the complete turbine and its subsystems. Traditionally, aeroelastic codes are used to model the wind turbine, where the gearbox is reduced to a few or only one degree of freedom, as bring limitations to describe the dynamic behavior in detail. In this paper, the gearbox dynamic behavior is assessed by means of three multibody models of varying complexity, which are assessed based on modal and dynamic behaviors. This work shows that the fully flexible multibody dynamic model can better reflect the operating condition of the wind turbine. However, due to high calculation precision, the fully flexible multibody dynamic model consumes much times. Therefore, an artificial neural network method is proposed for the prediction of wind turbine dynamic behaviors. The results show that combination of the multibody method and the artificial neural network can reduce the simulation runtime, guaranteeing the accuracy meantime. Therefore, it is of great significance in engineering practice.

Analyzing Vibration Suppression of Nuclear Power Crane with Model Coupling Mechanism and Structure

The nuclear power crane possesses strict safety requirements. Based on the special structure of its hoisting mechanism, it has two sets of independent lifting ropes to drive a hook synchronously and two pressure buffer devices on both ends of winding system’s balancing lever, in order to play protective roles and increase its working reliability. The flexible multi-body dynamics model which coupled mechanism and structure of the nuclear power crane is constructed when broken accident of rope occurs in the lifting process from the ground or smooth lifting. The importance of a buffer damping device installed in crane hoist mechanism has been proved through the vibration simulation about wire rope at the failure state. And the vibration of mechanism and the main girder structure is remitted and controlled at the time of failure in operation. The most important advantage is that has improved the safety of nuclear power crane.

Active control scheme for vibration suppression of flexible forks on a solar cell glass manipulator

An active control scheme is used for vibration suppression of a flexible multi-body dynamics model of a solar cell manipulator. The solar cell manipulator has large rotational or translational operation. The fork has a relatively small deformation on its tip. The floating frame of reference frame method (FFRF) is used to represent the flexible body. The result is compared to a commercial flexible multibo-dy dynamics analysis program to verify the developed program. While the manipulator is operating, the flexible fork shows vibration due to its high flexibility. The vibration influences the productivity, as it takes a few seconds for the tip to converge and a very small space is allowed for the fork to put the solar cell glass on a cassette. A state-space equation of the flexible fork model is derived and the control force equation is defined using gains. The control force is applied to the numerical model in order to suppress vibration of manipulator fork.

Flexible Multibody Dynamics Modeling and Simulation Analysis of Large-scale Wind Turbine Drivetrain

In order to prevent resonance dangerous and damage in the operation process of large wind turbines, a time / frequency domain integrated resonance screening method is presented. A flexible multibody dynamics simulation model of MW grade wind turbine drivetrain according to the "Guideline for the Certification of Wind Turbines Edition 2010" is established. Three levels of complexity modeling program are comprised and determined optimum modeling program according to the frequency coverage. Accurate flexible multibody dynamics model of drivetrain is achieved by flexible components, bearing stiffness and mesh flexibility, by which Campbell diagram, energy distribution diagram and fast Fourier transform(FFT) diagram are drawn and analyzed for dangerous resonance screening. Theoretical calculations and third-party software are applied for model validation. The results show that the flexible multibody modeling program can describe the dynamics characteristics of complex systems more deeply and comprehensively, avoid frequency limit caused by simplified simulation model, there are dangerous resonance points on natural frequency 9.86 Hz and 206.27 Hz, response components are gearbox housing and stage 2 wheel gear shaft and worthy of attention, the simulation calculation results are in agreement with the theoretical results and third-party software calculation results.

대형 패널 이송 로봇에 사용되는 타이밍벨트 구동계의 모델링

Most of large scale solar panel handling robots adopt the timing-belt drive system for its driveline because of the simplicity and the easiness of implementation. The vibration caused by the flexure of the timing belt would increase as the size and the weight of the panel that the robot handles increase and the vibration would deteriorate the precision and/or productivity of the whole robot system. For the development of a proper control system and for the improvement of the design of the robot it is important to estimate the oscillatory response of the robot system including the flexible drive system properly. In this paper a flexible multi-body dynamics model of a large-scale solar-panel-handling robot with the flexible timing-belt drive system is developed using a generic multi-body dynamics analysis program, RecurDyn.

Modeling of large scale solar cell handling robot with belt-driven flexible arms

To increase the competition of the solar energy collection system, the size of the solar panel module during the manufacturing process is being increased continuously. As the size of the solar panel increases, the size of the robot to handle the panel increased also. The change in scale of the robot inevitably results in the amplification of the adverse effect of the flexure. The main source of the flexure in the large scale solar cell panel handling system is the long and thin fork fingers of the hand and the solar cell panel. In addition, the belt-driven actuator system used by most of the large scale panel handling robot is another significant source of the vibration. In this paper, the flexible multi body dynamic model of a large scale solar cell panel handling robot, which is being designed and constructed with the help of Kyung Hee University, is developed. The belt-driven system in the robot is also modeled as flexible system and included in the robot to represent the actual vibration characteristics of the actuator system.

A controlled deployment method for flexible deployable space antennas

A decoupling control method is presented for the controlled deployment of flexible deployable space antennas. The deformable antenna bodies are discretized with a hypothesized displacement field structured according to the Rayleigh–Ritz method. Combined with the Lagrange method, the deployable antenna's flexible multi-body dynamic model is established. Based on the result of a dynamic analysis and an Fast Fourier Transform (FFT) spectrum analysis of the deployment trajectory, a filter is used to decouple the movement feedback signal into two separate parts: the rigid movement and the vibration caused by flex factors. Based on the instantaneous structure modal analysis of the mechanism, the eigenfrequency affiliation between the mechanism and the structure is discussed, thus the cut-off frequency of the low-pass filter is determined. The rigid and flex controllers are designed according to the characteristics of the decoupled feedback respectively. The rigid controller ensures that the antenna deploys along a specified trajectory and the flex controller restrains the flex vibration. The coupling relationship of the gain parameters between the two controllers is discussed and a guideline for the proper parameter selection is proposed based on an energy correlation analysis. Numerical simulations of a practical application for an Astromesh-type antenna are carried out below, and these simulations demonstrate the rationality and feasibility of the proposed methodology.

Sound quality improvement for a four-cylinder diesel engine by the block structure optimization

High sound quality and low radiated noise are two dominant demands for the vibro-acoustic performance of internal combustion engines. Such engines with high acoustic quality will greatly improve the acoustic environment both inside and outside of the passenger compartment of an automobile. In this paper, this performance of the block of a four-cylinder diesel engine was simulated and bench-tested. Then the vibro-acoustic problems were diagnosed and optimized. The finite element analysis method was adopted to numerically analyze the natural modes of the block. The finite-element model of the block was verified by the experimental modal analysis utilizing the single-input and multiple-output technology. The results indicate that the modal frequency errors from the simulation and experiment are permissible in respect of engineering and the accuracy of the finite-element model highly matching the real one is validated. Then, the flexible multi-body dynamics model of the diesel engine was constructed and excited by the boundary conditions comprised of in-cylinder gas pressures, cylinder liner-piston contact induced lateral forces and valve system motion induced impact forces. The simulated vibration velocity levels from the block surface were obtained under the rated condition (75kW/3600rpm) and well verified by the bench test. Boundary element analysis method was employed to acquire the radiated acoustic pressures from the block surface in the frequency range of interest. Optimized schemes are implemented to the block surface in order to reduce the radiated noise and enhance the sound quality of the diesel engine. Finally, the optimal block was cast. And the bench-test results indicate that the sound quality of the new-block engine is substantially improved. The research achievements validate the feasibility and reliability of the optimal design for the block.

Computational model for analyzing the kinematics and compliance characteristics of a commercial vehicle’s front suspension system

This paper develops a computational model that can analyze the kinematics and compliance characteristics of the front suspension of a commercial vehicle. This computational model is called the flexible multi-body dynamic model because it is developed by interfacing the finite element model of the multi-leaf spring with the dynamic model of the front suspension. In this paper, the bump mode and roll mode tests are performed with a suspension parameter measuring device (SPMD). An excitation load for creating the bump mode and roll mode motion is applied on the left and right tires slowly in in-phase and out-of-phase modes. In the test, wheel rate, toe angle change, caster angle change, and camber angle change, which together represent the wheel alignment, are measured along with the longitudinal and lateral wheel center loci which together represent the wheel center trajectory change. The reliability of the developed computational model is verified by comparing the simulation results with the SPMD test results. The developed flexible multi-body computational model will provide useful information on kinematics and compliance characteristics in the earliest stages of the commercial vehicle design process.

유연체 동역학 모델과 전력전자 회로의 연동해석을 통한 단기통 왕복 압축기 거동해석에 관한 연구

The characteristics of vibration and noise of a compressor used for electric appliances have significant influence on the quality of the products. For improvement on the quality of electric appliances, investigations for understanding the dynamic behaviour of the compressor are essential. Since Virtual Lab for the dynamics model and MAXWELL for the electromagnetics model are separate software programs with no interface, the joint simulation of the models could not be performed. This study suggests a way to develop the compressor model capable of the joint simulation with MATLAB/SIMULINK linking a flexible multi-body dynamics model, a torque model, and an electricity control model. The compressor model is found to be able to perform I/O data transfer among the sub-models and joint simulation. The simulation results of the flexible body and rigid body dynamics models were compared to check availability of the joint simulation system. In addition, the simulated vibration and driving torque of the compressor mechanisms were compared with measurements. Through the simulations, the influence of springs and LDT on the dynamic behaviour of the compressor was examined. This study examines the influence of the dynamic behaviour of the compressor mechanisms through joint simulation of the flexible multi-body dynamics model and electromagnetic circuit allows analysis.

Fatigue analysis of the main frame of over head transportation vehicles using flexible multibody dynamics

The industrial over head transportation vehicle is a guided railway vehicle that is attached overhead and transports cargo, hoisting it up and down from the factory ceiling. The vehicle is widely used in many industries, such as automobile and liquid crystal display (LCD), because it can carry freight very safely and quickly to destinations. This kind of freight transportation usually operates for several months to a few years, carrying large amounts of products. Accidently, the vehicle often fails during operation because of a part’s plastic deformation from large loads. Furthermore, periodic dynamic loads cause fatigue accumulation, which leads to OHT failure. This failure is directly connected to significant economic loss during mass production processes. Therefore, the prediction of fatigue life for the important parts becomes an important task. In this study, the fatigue life of an OHT main frame was calculated and predicted by using a flexible multibody dynamic model. The development of a flexible multibody dynamic model and the procedure of fatigue life prediction were presented. To predict the fatigue lives of parts of interest, the prediction procedure required three kinds of data: Dynamic stress time history from a dynamic analysis, material properties of the parts, and stress-life curves of the parts. Using a finite element model and a multibody model, a flexible multibody model was developed. To ensure the reliability of the model, displacement and strain measurement tests were conducted. After verification of the reliability, the fatigue life of the main frame was predicted.

자동차 와이퍼 시스템의 유연 다물체 동역학 해석

This paper presents the dynamic analysis method for estimating the performance of flat-type blades in wiper systems. The blade has nonlinear characteristics since the rubber is a hyper-elastic material. Thus, modal coordinate and absolute nodal coordinate formulations were used to describe the dynamic characteristic of the blade. The blade was structurally analyzed to find the bending characteristics of the cross section of the blade. According to the analysis results, the blade section is divided into three deformation bodies: rigid, small, and large. For the small deformation body, the modal coordinate formulation is used, while the absolute nodal coordinate formulation is used for the large deformation body. To verify the dynamic analysis result, an experiment was performed. The simulation and experiment results were compared to verify the flexible multi-body dynamic model.

Model and Control of Flexible Multibody Satellite

In order to estimate total disturbances including parametric uncertainties, unmodeled dynamics, and external disturbances, and achieve the dynamic feedback compensation of the estimated total disturbances, we design a double closed loop attitude active disturbance rejection controller (ADRC). By taking flexible vibrations of solar panels and a flexible antenna as an external disturbance, and using only the estimated transformation matrix of control input, a simplified dynamic model has been used to replace the accurate dynamic model of a rigid body in a flexible multibody satellite dynamics model. Simulation results indicate that the attitude ADRC designed still has the original dynamic response when large external disturbance acts on the system. Therefore, we come to the conclusion that the ADRC designed can be used to solve the problem of control systems with uncertainties in the process of modeling different flexible multibody systems.

Dynamic load analysis and design methodology of LCD transfer robot

The objective of the present study is to develop a design methodology for the large scale heavy duty robot to meet the design requirements of vibration and stress levels in structural components resulting from exposure of system modules to LCD (Liquid Crystal Display) processing environments. Vibrations of the component structures significantly influence the motion accuracy and fatigue damage. To analyze and design a heavy duty robot for LCD transfer, FE and multi-body dynamic simulation techniques have been used. The links of a robot are modeled as flexible bodies using modal coordinates. Nonlinear mechanical properties such as friction, compliance of reducers and bearings were considered in the flexible multi-body dynamics model. Various design proposals are investigated to improve structural design performances by using the dynamic simulation model. Design sensitivity analyses with respect to vibration and stresses are carried out to search an optimal design. An example of an 8G (8th-Generation) LTR (LCD Transfer Robot) is illustrated to demonstrate the proposed methodology. Finally, the results are verified by real experiments including vibration testing.

A flexible multi-body dynamic model for analyzing the hysteretic characteristics and the dynamic stress of a taper leaf spring

This paper proposes a modeling technique which is able to not only reliably and easily represent the hysteretic characteristics but also analyze the dynamic stress of a taper leaf spring. The flexible multi-body dynamic model of the taper leaf spring is developed by interfacing the finite element model and computation model of the taper leaf spring. Rigid dummy parts are attached at the places where a finite element leaf model is in contact with an adjacent one in order to apply contact model. Friction is defined in the contact model to represent the hysteretic phenomenon of the taper leaf spring. The test of the taper leaf spring is conducted for the validation of the reliability of the flexible multi-body dynamic model of the taper leaf spring developed in this paper. The test is started at an unloaded state with the excitation amplitude of 1–2 mm/sec and frequency of 132 mm. First, the simulation is conducted with the same condition as the test. Then, the simulations are conducted with various amplitudes in a loaded state. The hysteretic diagram from the test is compared with the ones from the simulation for the validation of the reliability of the model. The dynamic stress analysis of the taper leaf spring is also conducted with the developed flexible multi-body dynamic model under a dynamic loading condition.

Flexible multibody dynamics based fixture-workpiece analysis model for fixturing stability

The machining force and torque exerted on a workpiece vary as the cutter moves along the tool path, therefore a dynamic approach is essential for fixturing stability analysis. This paper presents a technique to dynamically model and analyze the fixture-workpiece system subjected to time-varying machining loads. Combining the advantages of FEA (Finite Element Analysis) and nonlinear rigid body dynamics, a flexible multibody dynamic model is formulated to incorporate the overall interaction (clamping forces, machining loads, and contact friction) between flexible workpiece and compliant fixture elements. Three major parameters affecting the fixturing stability, namely the magnitude, application sequence, and placement of fixturing clamps, are analyzed. Additionally, the time dependent deformation of a flexible workpiece under clamping and machining loads is estimated. A scaled engine block with the 3–2–1 fixturing scheme subjected to face milling operation is given as an example. Comparison between the simulation result and experimental data shows a reasonable agreement.