An integrated dynamic design system for aerostatic spindle development

In this paper an integrated dynamic design and modeling system is developed for aerostatic spindle development. This system integrates initial structural design, bearing stiffness computation and the spindle dynamic performance prediction. Modal fitting is used to transform the finite element model into a two-degree-of-freedom system model, which will make it easier to control the system and calculate the dynamic response. The design system is implemented by using commercial software, such as Pro/E, Matlab and Ansys. Consequently, the integrated dynamic design system enables the designers to cost-effectively complete structural design of an aerostatic spindle. A case study has been presented in this paper for design of an aerostatic spindle used for flycutting. The machining results demonstrate the effectiveness of the developed integrated dynamic design system for aerostatic spindles design

An integrated system for ultra-precision machine tool design in conceptual and fundamental design stage

This paper presents an integrated system used for ultra-precision machine tool (UPMT) design in conceptual and fundamental design stage. This system is based on the dynamic, thermodynamic, and error budget theories. The candidate configurations of the machine tool are first selected from the configuration library or a novel configuration designed by the user, according to the functions of the machine tool expected to realize. Then, the appropriate configuration is given by comparing the stiffness chain, dynamic performance, thermal performance, and the error budget of each candidate configuration. Consequently, the integrated design system enables the conceptual and fundamental of the UPMT to be designed efficiently with a theoretical foundation. The proposed system was used for several UPMT designs, which demonstrate the effectiveness of the integrated design system

An mechatronics coupling design approach for aerostatic bearing spindles

In this paper, a new design approach for aerostatic bearing spindles (ABS) is firstly proposed which takes into account of the interactions between the mechanical and the servo subsystems, including the integration of electromagnetic effects, static pressure characteristics, servo control and mechanical characteristics. According to the air bearing design principle, the geometry of the spindle rotor is designed. The fluid software is used to analyze the influence of the bearing capacity and stiffness on the stability of the spindle. The simulation shows when the air film thickness is 12 μm, the bearing has good load carrying capacity and rigidity. In addition, the influence of motor harmonics on the spindle shaft modes is considered to avoid the resonance of ABS, and to ensure ABS anti-interference capability, proper inertia of ABS is calculated and analyzed. Finally, ABS has a good follow-up effect on the servo control and machining performance through the experimental prototype. The electromechanical coupling design approach for ABS proposed in this paper, can achieve a peak value better than 0.8 μm (surface size: 9 mm × 9 mm) and a surface roughness better than 8 nm in end face turning experiments

Investigation of control algorithm for long-stroke fast tool servo system

Fast tool servo (FTS) is an efficient and reliable method in precision machining for fabricating freeform surfaces or microarrays with sub-micrometric form accuracy. In this paper, a Lorentz force FTS is designed where the voice coil motor is located inside the slide, and four air bearings are used as support components. Three different control algorithms, namely conventional PID control, advanced PID control with velocity/acceleration feed-forward (FF) and sliding mode control (SMC) are implemented in the system, and corresponding Simulink simulation models are built including for both mechanical and electrical systems. The results show that advanced PID and SMC can reduce phase error and overshoot, and tracking error can be controlled at 3.13% at 50 Hz. A new hybrid control algorithm (PID + SMC + FF) is developed, with system tracking error subsequently decreased to 0.871% at 50 Hz. In addition, with a suitable compensation method, the steady state tracking error is further decreased to 0.029%. Consistent results from testing with signals of different input frequency also indicate the general effectiveness of the algorithm

The molecular basis of beta-thalassemia intermedia in southern China: genotypic heterogeneity and phenotypic diversity

<p>Abstract</p> <p>Background</p> <p>The clinical syndrome of thalassemia intermedia (TI) results from the β-globin genotypes in combination with factors to produce fetal haemoglobin (HbF) and/or co-inheritance of α-thalassemia. However, very little is currently known of the molecular basis of Chinese TI patients.</p> <p>Methods</p> <p>We systematically analyzed and characterized β-globin genotypes, α-thalassemia determinants, and known primary genetic modifiers linked to the production of HbF and the aggravation of α/β imbalance in 117 Chinese TI patients. Genotype-phenotype correlations were analyzed based on retrospective clinical observations.</p> <p>Results</p> <p>A total of 117 TI patients were divided into two major groups, namely heterozygous β-thalassemia (n = 20) in which 14 were characterized as having a mild TI with the Hb levels of 68-95 g/L except for five co-inherited ααα^anti-3.7triplication and one carried a dominant mutation; and β-thalassemia homozygotes or compound heterozygotes for β-thalassemia and other β-globin defects in which the β⁺-thalassemia mutation was the most common (49/97), hemoglobin E (HbE) variants was second (27/97), and deletional hereditary persistence of fetal hemoglobin (HPFH) or δβ-thalassemia was third (11/97). Two novel mutations, Term CD+32(A→C) and Cap+39(C→T), have been detected.</p> <p>Conclusions</p> <p>Chinese TI patients showed considerable heterogeneity, both phenotypically and genotypically. The clinical outcomes of our TI patients were mostly explained by the genotypes linked to the β- and α-globin gene cluster. However, for a group of 14 patients (13 β⁰/β^Nand 1 β⁺/β^N) with known heterozygous mutations of β-thalassemia and three with homozygous β-thalassemia (β⁰/β⁰), the existence of other causative genetic determinants is remaining to be molecularly defined.</p

Comparison of cutting mechanism when machining micro and nano-particles reinforced SiC/Al metal matrix composites

Recently, metal matrix composites (MMCs) reinforced with nano-particles receive increasing attention from academia and industries. The cutting mechanism of nano MMCs is believed to be different when compared to composites reinforced with micro particles. This paper presents cutting mechanism comparison between SiC/Al metal matrix composites (MMCs) reinforced with micro and nano-particles using finite element method. The cutting mechanisms are investigated in terms of the von Mises stress distribution, tool-particles interaction, chip formation mechanism and surface morphology. It is found that the particles in nano size remained intact without fracture during the cutting process and are more likely to produce continuous chips, while the particles in micro size are easy to break and tend to form discontinues chips. Better machined surface quality with less defects can be obtained from nano size reinforced MMCs compared with their micro size counterparts. The model validation was carried out by conducting machining experiments on two types of MMCs and good agreements are found with the simulation results

An integrated dynamic design system for aerostatic spindle development

In this paper an integrated dynamic design and modeling system is developed for aerostatic spindle development. This system integrates initial structural design, bearing stiffness computation and the spindle dynamic performance prediction. Modal fitting is used to transform the finite element model into a two-degree-of-freedom system model, which will make it easier to control the system and calculate the dynamic response. The design system is implemented by using commercial software, such as Pro/E, Matlab and Ansys. Consequently, the integrated dynamic design system enables the designers to cost-effectively complete structural design of an aerostatic spindle. A case study has been presented in this paper for design of an aerostatic spindle used for flycutting. The machining results demonstrate the effectiveness of the developed integrated dynamic design system for aerostatic spindles design

Influence of unbalanced electromagnetic force and air supply pressure fluctuation in air bearing spindles on machining surface topography

Air bearing spindles (ABS) can meet high accuracy demands for the precise rotation motion, which adopt air bearings to support spindle shaft, and the spindle shaft directly connects the motor rotor. The unbalanced electromagnetic force caused by motor rotor eccentricity (MRE) and air pressure fluctuation (APF) are two important influential factors to the dynamic performance of the spindle system and machining surface quality. This paper addresses the problems of measuring the MRE and APF in an ABS through testing machining surface topography. A permanent magnet synchronous motor (PMSM) was modelled by finite element simulation (FES). Through FES it found that the MRE between the motor rotor and stator hole produced a radial magnetic force (RMF), which could cause ABS to periodically vibrate in the axial direction. Besides, the change of the air supply caused the stiffness variation of ABS and result in the tilt error motions of the spindle shaft. A theoretical model of machining surface topography considering MRE and APF was then proposed for the first time, which revealed that the MRE and APF resulted in the periodic fluctuations of the machining surface topography. The overall surface topography then became grooved surfaces. The above findings were finally validated by measurement results of ultraprecision diamond turning experiments