scholarly journals Rigid-Flexible Modal Analysis of the Hydraulic 6-DOF Parallel Mechanism

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1604
Author(s):  
Chenyang Zhang ◽  
Hongzhou Jiang
Keyword(s):  
Dynamic Model ◽  
Parallel Mechanism ◽  
Degrees Of Freedom ◽  
Natural Frequencies ◽  
Hydraulic Cylinder ◽  
Flexible Structure ◽  
Actual Performance ◽  
Experimental Platform ◽  
Response Characteristics ◽  
Dynamic Response Characteristics

In view of the problems encountered in previous hydraulic 6-DOF parallel mechanism projects, flexible modes appear that the actual natural frequencies of x and y degrees of freedom of the parallel mechanism are lower than those obtained through calculation. The phenomenon above not only decreases the dynamic response characteristics of the mechanism, but also leads to doubts about the actual performance of the mechanism. The real reason for the phenomenon above is solved in this paper. First the flexible structure of the hydraulic cylinder is analyzed and simplified, and then the dynamic model of the rigid-flexible 6-DOF parallel mechanism is established with the extended Hamilton’s principle. Finally the rigid-flexible modes are calculated with the dynamic model obtained, further analysis and verification with a simulation model and an experimental platform are also conducted. Results show that the phenomenon of the flexible modes is mainly caused by the O-rings of the step-seals of the guide sleeve and those with less elasticity should be adopted to keep the dynamic characteristics of the parallel mechanism.

Static and Vibration Analyses of a Three-Dimensional Snake-Like Micropositioning Stage

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Nicola Scuor ◽  
Paolo Gallina ◽  
Marco Giovagnoni
Keyword(s):  
Dynamic Model ◽  
Degrees Of Freedom ◽  
Dynamic Models ◽  
Natural Frequencies ◽  
Three Dimensional ◽  
Dynamic Tests ◽  
Lumped Mass ◽  
Simulation Data ◽  
End Effector ◽  
Three Degrees Of Freedom

This paper presets three degrees of freedom (DOF) piezoelectric micropositioning stage. The stage is composed of a stack of piezodisk bender actuators actuated in such a way to prevent the end-effector from rotating; this way the end-effector can only translate along the x, y, and z axes. Thanks to its snake-like configuration, the system is capable of large displacements (of the order of 50 μm) with low driving voltages (of the order of 100 V). Several lumped-mass static and dynamic models of the device have been implemented. Static experimental results, which are in agreement with simulation data, confirmed the performances of the device. A dynamic model showed the natural frequencies of the mechanism. Also dynamic tests have been conducted in order to validate the dynamic model.

Locally Linearized Dynamic Analysis of Parallel Manipulators and Application of Input Shaping to Reduce Vibrations

2004 ◽  
Vol 126 (1) ◽  
pp. 156-168 ◽  
Author(s):  
Kris Kozak ◽  
Imme Ebert-Uphoff ◽  
William Singhose
Keyword(s):  
Dynamic Model ◽  
Degrees Of Freedom ◽  
Natural Frequencies ◽  
Model Simulation ◽  
Parallel Architecture ◽  
Robotic Manipulators ◽  
Parallel Manipulators ◽  
Dynamic Equations ◽  
Input Shaping ◽  
Multiple Degrees Of Freedom

Input Shaping is a technique that seeks to reduce residual vibrations through modification of the reference command given to a system. Namely the reference command is convolved with a suitable train of impulses. Input shaping has proven to be successful in reducing the vibrations of a great variety of linear systems. This article seeks to apply input shaping to robotic manipulators of parallel architecture. Such systems have multiple degrees-of-freedom and non-linear dynamics and therefore standard input shaping techniques cannot be readily applied. In order to apply standard input shaping techniques to such systems, this article linearizes the dynamic equations of the system locally and determines the configuration-dependent natural frequencies and damping ratios throughout its workspace. Techniques are developed to derive the dynamic equations directly in linearized form. The method is demonstrated for a sample manipulator with two degrees-of-freedom. A linearized dynamic model is derived and input shaping is locally tuned according to the linearized dynamic model. Simulation results are provided and discussed.

Modeling and Stability Analysis of Turboprop Engine Installations

2001 ◽  
Author(s):  
Rabih Alkhatib ◽  
Farid Golnaraghi
Keyword(s):  
Dynamic Model ◽  
Degrees Of Freedom ◽  
Vibration Isolation ◽  
Natural Frequencies ◽  
Aerodynamic Forces ◽  
Simple Formulation ◽  
Turboprop Engine ◽  
Reaction Forces ◽  
Engine Mount ◽  
The Stability

Abstract In this paper a simple formulation of dynamic model of a turboprop installations has been presented incorporating aerodynamic forces. A four-bladed propeller-engine is simplified to have six rigid-body degrees of freedom. The engine is connected to the nacelle through resilient elements in order to reduce vibration transmission from the engine to the airplane structure. The aerodynamic forces acting on the propeller are modeled utilizing quasi-steady airfoil theory by considering their effect as reaction forces. Using the formulated dynamic model, an analysis of the stability of the engine-mount is conducted by deriving a second order eigenvalue problem. The system natural frequencies are found to be dependent on the rotational speed. At lower speeds, the aerodynamic forces have a stabilizing effect on the system. At higher rotational frequencies, the engine reaches a speed after which the system becomes unstable. The use of soft resilient mounts maximizes the vibration isolation but lowers instability threshold speed.

scholarly journals Dynamic model analysis of hydraulic support

2019 ◽  
Vol 11 (1) ◽  
pp. 168781401882014 ◽  
Author(s):  
Enguang Guan ◽  
Huihua Miao ◽  
Peibo Li ◽  
Jihao Liu ◽  
Yanzheng Zhao
Keyword(s):  
Support System ◽  
Natural Frequencies ◽  
Hydraulic Cylinder ◽  
Limited Range ◽  
Loop Modeling ◽  
Analysis Model ◽  
Hydraulic Support ◽  
Response Characteristics ◽  
Kinematic Diagram ◽  
The Relationship

In view of the shortcomings of traditional hydraulic support system, such as poor mobility and limited range of adjustment, a new configuration with double parallelogram structure is proposed. Combining the kinematic diagram of the mechanism of the new support system and the relevant parameters of the balance moment, using the kinematic vector closed-loop modeling method and D’Alembert’s principle, the relationship equation between the generalized coordinates of the hydraulic support and the geometric position parameters is obtained, and the analysis model with plural-freedom is established. Dynamic response characteristics and natural frequencies of column hydraulic cylinder and balance hydraulic cylinder are analyzed. The results demonstrate that the natural frequencies of the improved balance hydraulic cylinder and column hydraulic cylinder have been greatly improved, and the safety performance of the hydraulic support has been greatly increased.

Modeling and Control Design for an Inlet Metering Valve-Controlled Pump Used to Control Actuator Velocity Via H-Infinity and Two-Degrees-of-Freedom Methods

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Hasan H. Ali ◽  
Roger C. Fales ◽  
Noah D. Manring
Keyword(s):  
Fluid Flow ◽  
Control System ◽  
Dynamic Model ◽  
Degrees Of Freedom ◽  
Closed Loop ◽  
High Efficiency ◽  
Hydraulic Cylinder ◽  
Velocity Control ◽  
Hydraulic Actuator ◽  
Two Degrees Of Freedom

Using a unique inlet metering pump with fixed displacement and speed, this work introduces a new way to control a linear hydraulic actuator velocity. The inlet metering system consists of an inlet metering valve that adjusts the hydraulic fluid flow that enters the pump and a fixed displacement pump. Fluid is supplied to the inlet metering valve at a fixed pressure. Energy losses associated with flow metering in the system are reduced because the pressure drop across the inlet metering valve can be small compared to a traditional valve-controlled system. A velocity control system is designed using the inlet metering pump to control the fluid flow into a hydraulic cylinder. First, the valve dynamic model is ignored, the open-loop response is studied, and closed-loop proportional and proportional derivative controllers are designed. Next, the valve dynamic model is included and closed-loop proportional integral derivative, H∞, and two-degrees-of-freedom controllers are designed. Designs with the goals of stability and performance of the system are considered so that a precise velocity control system for the hydraulic cylinder is achieved. In addition to the potentially high efficiency of this system, there is potential for low-cost, fast-response, and less complicated dynamics compared to other systems. The results show that the velocity control system can be designed so that the system is stable for all cases and with 0% overshoot and no oscillation depending on valve dynamics using the two-degrees-of-freedom controller for tracking the desired velocity.

Dynamic model for high-speed rotors based on their experimental characterization

2017 ◽  
Vol 2 (4) ◽  
pp. 25
Author(s):  
L. A. Montoya ◽  
E. E. Rodríguez ◽  
H. J. Zúñiga ◽  
I. Mejía
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Experimental Characterization ◽  
Rotating Systems ◽  
Computing Performance ◽  
The Impact ◽  
Stiffness Distribution ◽  
Good Agreement

Rotating systems components such as rotors, have dynamic characteristics that are of great importance to understand because they may cause failure of turbomachinery. Therefore, it is required to study a dynamic model to predict some vibration characteristics, in this case, the natural frequencies and mode shapes (both of free vibration) of a centrifugal compressor shaft. The peculiarity of the dynamic model proposed is that using frequency and displacements values obtained experimentally, it is possible to calculate the mass and stiffness distribution of the shaft, and then use these values to estimate the theoretical modal parameters. The natural frequencies and mode shapes of the shaft were obtained with experimental modal analysis by using the impact test. The results predicted by the model are in good agreement with the experimental test. The model is also flexible with other geometries and has a great time and computing performance, which can be evaluated with respect to other commercial software in the future.

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