Nonlinear Static and Dynamic Stiffness Characteristics of Support Hydraulic System of TBM

Full-face hard rock tunnel boring machines(TBM)are essential equipment in highway and railway tunnel engineering construction.During the tunneling process,TBM have serious vibrations,which can damage some of its key components.The support system,an important part of TBM,is one path through which vibrational energy from the cutter head is transmitted.To reduce the vibration of support systems of TBM during the excavation process,based on the structural features of the support hydraulic system,a nonlinear dynamical model of support hydraulic systems of TBM is established.The influences of the component structure parameters and operating conditions parameters on the stiffness characteristics of the support hydraulic system are analyzed.The analysis results indicate that the static stiffness of the support hydraulic system consists of an increase stage,stable stage and decrease stage.The static stiffness value increases with an increase in the clearances.The pre-compression length of the spring in the relief valve a ects the range of the stable stage of the static stiffness,and it does not a ect the static stiffness value.The dynamic stiffness of the support hydraulic system consists of a U-shape and reverse U-shape.The bottom value of the U-shape increases with the amplitude and frequency of the external force acting on the cylinder body,however,the top value of the reverse U-shape remains constant.This study instructs how to design the support hydraulic system of TBM.

Effect of Manufacturing Errors on Static Characteristics of Externally Pressurized Spherical Air Bearings

Externally pressurized spherical air bearings are the key component of the three-axis air bearing table, and the manufacturing errors of the bearing affects the performance of the air bearing table. However, the manufacturing errors are unavoidable, and the pursuit to enhance the manufacturing accuracy will increase the cost greatly. In order to provide some theoretical guideline for the tolerance choice in the design of the externally pressurized spherical air bearings with inherent compensation, the effects of several manufacturing errors on the static characteristics of the air bearing are studied. Due to the complex geometry of the computational domain, an unstructured meshing technology is used for mesh generation. A finite-volume method is adopted to discretize the three-dimensional steady-state compressible Navier-Stokes equations. A modified SIMPLE algorithm which is suitable for compressible flows is applied to solve the discretized governing equations. The effects of the dimension error and the roundness error of the ball head and the ball socket on the static characteristics are investigated. The investigation result shows that the positive dimension error and the oblate spheroid-type roundness error of the ball head as well as the negative dimension error and the prolate spheroid-type roundness error of the ball socket can improve the bearing capacity and static stiffness of the air bearings by reducing the mass flow. The calculation method proposed in this paper fits well for the general principle, which can be extended to the characteristics analysis of other air bearings.

Stiffness Analysis of Spherical Parallel Mechanism U_(P+R) with 2-DOF

As one of the typical less-mobility parallel mechanisms,the spherical parallel mechanism U_(P + R) with two degrees of freedom(2-DOF)possess high order overconstraints,and the calculation of its stiffness is partly different with general parallel mechanisms owing to the bars in each branch are assumed to be arc-shaped.By means of small deformation superposition principle,the relationship between the angle displacement and line displacement of moving platform and the forces acted on the branches were derived out.Based on the results of static analysis,the relationship between the applied force,the line displacement and the angle displacement of the mechanism was set up.And then the stiffness matrix was obtained.The six principal stiffness of the mechanism and the corresponding directions were achieved by the orthogonal transformation.The numerical calculation was performed and the results showed that the principal stiffness and directions are varied with the pose-position of the mechanism,and the principal stiffness is gradually enlarged when it is far away from the origin.In addition,the torsion stiffness is much greater and the line deformation stiffness is smaller,the difference between the two parts is huge.The research content of this paper supplies the theoretical foundation for the further engineering design and application of the spherical parallel mechanism.

Development and testing of a wireless smart toolholder with multi-sensor fusion

The smart toolholder is the core component in the development of intelligent and precise manufacturing.It enables in situ monitoring of cutting data and machining accuracy evolution and has become a focal point in academic research and industrial applications.However,current table and rotational dynamometers for milling force,vibration,and temperature testing suffer from cumbersome installation and provide only a single acquisition signal,which limits their use in laboratory settings.In this study,we propose a wireless smart toolholder with multi-sensor fusion for simultaneous sensing of milling force,vibration,and temperature signals.We select force,vibration,and temperature sensors suitable for smart toolholder fusion to adapt to the cutting environment.Thereafter,structural design,circular runout,dynamic balancing,static stiffness,and dynamic inherent frequency tests are conducted to assess its dynamic and static performance.Finally,the smart toolholder is tested for accuracy and repeatability in terms of force,vibration,and temperature.Experimental results demonstrate that the smart toolholder accurately captures machining data with a relative deviation of less than 1.5%compared with existing force gauges and provides high repeatability of milling temperature and vibration signals.Therefore,it is a smart solution for machining condition monitoring.