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Author

Lijie Zhang

Bio: Lijie Zhang is an academic researcher from Yanshan University. The author has contributed to research in topics: Stewart platform & Natural frequency. The author has co-authored 3 publications.

Papers
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Journal ArticleDOI
Lijie Zhang1, Zong Xuemei1, Yue Tang1, Xinchun Chen1, Junxue Feng, Xiaoming Yuan1 
TL;DR: This study can provide theoretical support for dynamic optimization of the electrohydraulic Stewart platform by calculating the natural frequency and sensitivity of the platform under typical conditions.
Abstract: Electrohydraulic Stewart platform is a multi-input and multi-output mechanical-hydraulic coupling system, which has the advantages of large power-to-weight ratio and high accuracy. It has been widely used in construction machinery, aerospace, and other fields. In the actual working process, especially in the high-speed motion, the Stewart platform movement process will produce a large impact and vibration and then affect the stability, accuracy, and service life of the platform. When the frequency of the external excitation coincides with the natural frequency of the electrohydraulic Stewart platform, it may cause the failure of the platform. Therefore, based on the relationship between the volumetric elastic modulus of the gas-bearing oil and the hydraulic stiffness of the leg, a mechanical-hydraulic coupling dynamic model of the electrohydraulic Stewart platform was established, and the natural frequencies and modal shapes of the platform were analyzed under typical conditions. The sensitivity calculation formula of the natural frequency of the system on the upper platform mass and the hydraulic stiffness of the outer leg is given by an analytical method, and the influence law of the upper platform mass and the outer leg stiffness on the natural frequency and the sensitivity of the electrohydraulic Stewart platform under typical conditions is discussed. This study can provide theoretical support for dynamic optimization of the electrohydraulic Stewart platform.

2 citations

Journal ArticleDOI
TL;DR: Through the parameter vibration analysis of two different positions of the electro-hydraulic Stewart platform, it is concluded that when the platform is in an asymmetric position, each leg of the system is more involved in vibration.
Abstract: Electro-hydraulic Stewart 6-DOF platform is a 6-DOF parallel mechanism combined with the electro-hydraulic servo control system, which is widely used in the field of construction machinery. In actual working conditions, the flow and pressure pulsation of the hydraulic oil output from the hydraulic leg of the electro-hydraulic Stewart platform are inevitable, so the equivalent stiffness of the platform leg will change, and the stiffness parameters of the transmission system will change, resulting in vibration, which will affect the accuracy of the platform. This paper considering the fluid unit equivalent stiffness cyclical fluctuations and leg, on the basis of the relationship between hydraulic stiffness, constructs the electric hydraulic Stewart platform machine vibration dynamics equation, fluid coupling parameters of vibration parameters using the method of the multiscale approximate analytic formula of the main resonance and combination resonance are derived, and the system parameters vibration time-domain response and frequency response under two different poses are discussed. Results show that the system first to six order natural frequency and the first to the sixth order natural frequency and frequency of hydraulic oil equivalent stiffness of the combination of frequency will have an effect on the parameters of the system vibration. In the main resonance, the dominant frequency is mainly the first to sixth order natural frequency of the system; in the combined resonance, the dominant frequency is the combined frequency. Through the parameter vibration analysis of two different positions of the platform, it is concluded that when the platform is in an asymmetric position, each leg of the system is more involved in vibration. This study can provide the reference for the subsequent dynamic optimization and reliability analysis of the electro-hydraulic Stewart platform.
Patent
04 Dec 2020
TL;DR: In this paper, an adjustable steel pier is described, which consists of a top cover, a top seat, a guide seat, guide rod, an adjustable supporting assembly, a base and a support, the base and the adjustable support assembly sequentially sleeve the support from bottom to top.
Abstract: The invention relates to the technical field of ship building and discloses an adjustable steel pier which comprises a top cover, a top seat, a guide seat, a guide rod, an adjustable supporting assembly, a base and a support, the base and the adjustable supporting assembly sequentially sleeve the support from bottom to top, the lower end of the base is connected with the support, and the upper endof the base is connected with the lower end of the adjustable supporting assembly. The upper end of the adjustable supporting assembly is connected with the guide rod, the guide seat is horizontallyinstalled on the guide rod in a sliding mode, the top seat is installed above the guide seat, and the top cover is in threaded connection above the top seat. According to the adjustable steel pier, the small-range adjustment of the height of the steel pier can be achieved, the large-range rapid adjustment of the height of the steel pier can also be achieved, the operation is easy, and the cost issaved; the guide seat can drive the top seat and the top cover to freely move in a large range in the horizontal direction, the multi-directional adjustment is achieved, the construction time is saved, and the construction efficiency is improved. The base and the adjustable supporting assembly are arranged on the support in a sleeving mode, so that the strength and the stability of the adjustablesupporting assembly are improved.

Cited by
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TL;DR: In this article , a modified MFS calculation method is proposed by solving the critical variable expression with non-homogeneous formula, which avoids the influence of frequency resolution and the accuracy is significantly improved.
Journal ArticleDOI
TL;DR: In this article , a modal analysis based on finite element analysis (FEA) is introduced as a fundamental linear dynamics analysis to provide insight into how a pipeline sectionalized gate valve structure may respond to different types of dynamic loading.
Abstract: Sectionalized gate valves can reduce the volume of product released in the event of a buried pipeline failure or rupture. The risk of pipeline failure is a constant and common occurrence, and many factors can lead to pipeline incidents. In this paper, the free undamped vibration of the pipeline, sectionalized gate valve structure, and the dynamics of the fluid passing through the system are investigated. First and foremost, a modal analysis based on finite element analysis (FEA) is introduced as a fundamental linear dynamics analysis to provide insight into how a pipeline sectionalized gate valve structure may respond to different types of dynamic loading. Secondly, an implicit numerical analysis using computational fluid dynamics (CFD) is employed to describe physical quantities such as the flow velocity profiles at different stream positions and pressure fields at different points in a control volume. Through modal analysis, the effective mass factor shows the mass involved in each mode and helps identify modes with high potential to cause damage and prioritize efforts to address them. The CFD suggests that the sectionalized design of the gate valve leads to a strong vorticity of the fluid in the transversal direction of the flow and a decrease in efficiency due to pressure drop.