Shen Dong

An Ultra-Low Frequency Parallel Connection Nonlinear Isolator for Precision Instruments

In order to improve the working performance of precision instruments, it is desirable to isolate ambience wideband vibrations. Nonlinear isolator is superior to linear isolator. In this paper, a novel combined positive and negative stiffness isolator is developed based on the analysis of the mechanism of negative stiffness, whose negative stiffness cancels much of the positive stiffness of the elastic element in the vicinity of the balance point. The stiffness at the balance point has a nonlinear characteristic and the net stiffness tends to be zero. This type of isolator has high support stiffness as well as low vibration stiffness. Its inherent frequency can be adjusted to zero by adjusting the initial deformation of the elastic elements of the negative stiffness mechanism. Experimental results show that the inherent frequency of the isolator can be adjusted from 10 Hz to 1 Hz. The isolation bandwidth of the isolator is widened and the performance of isolation is distinctly enhanced. Introduction Low frequency micro-vibration isolation technology is becoming more and more important in high-tech fields such as ultra-precision manufacturing, ultra-high-precision measuring system and space micro-gravity research experiments [1]. The partx92s surface quality in ultra-precision machining is not only related to the amplitude of the vibrations but also to the frequency of the vibrations. The frequencies, which affect the performance of most precision engineering, are from 0.5Hz to 70Hz [2]. At present, air-spring type isolators provide the top vibration isolation performance in these high precision engineering fields. The inherent frequency of air spring isolator is about 2 -3 Hz [3-4]. But they are usually much more complex and expensive. In order to further decrease the isolatorx92s inherent frequency, we have to add active vibration control systems to the air spring isolator [5], which further makes the vibration isolation system more expensive. Therefore, the air spring isolator has some limitations in practical application. In conventional passive linear vibration isolation systems, the isolator has constant stiffness characteristic. There are two methods to enhance the isolation performance of the isolator: one is to reduce the stiffness K of the isolation system; the other is to increase the isolated mass M. However, reducing the stiffness of the spring can cause the system instability and deformation space to increase, and the mass cannot be too heavy because of the restriction of construction and space. Therefore, the conventional passive linear isolators have good performance in isolating the middle and high frequencies vibration and poor ability to isolate low or ultra-low frequencies vibration. This paper introduces a newly developed passive vibration isolation system adopting negative-stiffness element [6] in parallel with the positive spring. It has variable stiffness characteristic in the vicinity of the balance point which has high supporting stiffness as well as low vibration stiffness. In addition, it makes the inherent frequency of the vibration isolation system very low and therefore provides good isolation performance with respect to floor vibrations. Definition of the Negative and Positive Stiffness The general definition of stiffness is the derivative of the elastic element supported load G with respect to its deformation, given by [7] Key Engineering Materials Online: 2004-02-15 ISSN: 1662-9795, Vols. 257-258, pp 231-238 doi:10.4028/www.scientific.net/KEM.257-258.231

Research on Micro Machining Using AFM Diamond Tip

In this paper, micro machining is performed using AFM diamond tip, which is similar to a single abrasive particle, and a high precision stage. Using mechanical scratching, microstructures are machined on the surface of single crystal copper. Based on the system, some experiments are carried out: Parameters such as velocity of machining, applied force and amount of feed, which will influence process of micro machining, are analyzed. The diamond tip statex92s influence on micro machining is also studied. And using the optimum parameters and proper machining technique, the microstructures are machined. This approach is a novel unconventional micro machining technology. It can be applied in some micro machining fields such as: MEMS micro devicesx92 fabrication, mask fabrication of lithography, micro-partsx92 micro machining, and machining or dressing on the micro-parts fabricated by other ways. Introduction Since 1986, STM has been used as an important apparatus for surface observation. But with the development of Scanning Probe Microscope (SPM) research, SPM (including AFM and STM) has been applied in surface modification on a very localized region. Particularly, AFM is studied by many researchers because of its ability of controlling the force between the tip and the sample surface. Recently micro machining using AFM ordinary measuring tips has two main methods: oxidation and mechanical scratching. Won Bane Lee and H. Dai machined nano lines by oxidation [1-2]. Hideki, S. Tegen, and H. F. Chen machined two-dimensional figures using mechanical scratching [3-5]. Using diamond tip, most researchers investigated micro wear. Ti Miyamoto, G. J. Zhao and R. Kaneko investigated micro wear characteristics of different materials using this method [6-8]. Only simple figures such as square holes are machined in these experiments to find out the influence of material and scratching parameters on wear process. As a novel machining way, AFM diamond tip has been used as a cutting tool and it has been applied in the fields of nano cutting mechanism and microstructures fabrication. T. Sumomogi and his coworkers carried out the micro machining experiments using the diamond tip on surface of Ni, Au and Cu. They found out several factors influencing micro machining of metal materials on nano meter scale [9]. Jae-Mo Lee and his coworkers developed a system which is similar to AFM. Based on this system, they performed micro machining using diamond tip. And they thought that this way may be used as the procedure before etching or as a new method to machine moulds of micro parts [10]. Similar studies are also conducted by Q. L. Zhao of our team. The diamond tipx92s theoretical model was established. And experiment results showed that the surface alterative layer using this method was less than that of surface machined by conventional polish and grinding [11-12]. In this paper, micro machining is performed using an AFM diamond tip and precision stage. Some experiments are carried out: Parameters such as velocity of machining, applied force and amount of feed, which will influence process of micro machining, are analyzed. Two fabrication methods of two-dimensional microstructures are investigated. The diamond tip statex92s influence on micro machining is studied. Finally using the optimum parameters and proper machining technique, microstructures are machined. Experimental Setup Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 577-581 doi:10.4028/www.scientific.net/KEM.259-260.577

Magnetorheological Finishing of Glass Ceramic

Glass ceramic is a kind of important material, which has been widely used in modern optics industry. Magnetorheological Finishing (MRF) is a newly developed technology, which eliminates subsurface damage, reduces micro roughness, and corrects surface errors. In the present study, glass ceramic was polished using Magnetorheological Finishing (MRF). The finished surface was tested with an AFM. The result shows that the workpiece has good surface quality. The flexibility of MRF makes it effective for ultra-precision machining of glass ceramic.

Factors Influencing the Surface Quality during Ultra-Precision Grinding of Brittle Materials in Ductile Mode

The factors influencing surface quality for brittle materials is theoretically analyzed during ultra-precision grinding. Grinding experiments of brittle materials are carried out. The results show that the average abrasive grain size of the diamond wheel has a main influence on the surface quality, and the influence of the wheel speed and feed rate is secondary. In the case of s=1200m/min, f=0-20 μm/rev, and ap=0.1-10μm, only when the average abrasive grain size of the diamond wheel is less than 10μm, the super-smooth surface, for which Ra is 6.200nm and rms is 8.201 nm, can be obtained under grinding in the ductile mode. Introduction With the development of science and technology, high quality products of brittle materials play more and more important roles in many key instruments, such as various optical glasses, single crystal silicon, microcrystalline glass and ceramic bearing are very widely applied in space-flight and military equipment, and the requirement for surface quality of the workpiece is very high. In ultra-precision grinding, in order to obtain a super smooth surface of brittle materials, how to improve the surface roughness is hot theoretic direction of many countries [1-2]. But there are very few relative literatures on analysis and experimental study of effecting factors to surface roughness for brittle material. During grinding brittle material, the removal mode of the material at the workpiece surface affects the surface quality obviously [3-5]. In the paper, firstly the main influence factors of the surface quality are studied by dynamic grinding theoretically in the ductile mode. Afterwards some grinding experiments of brittle materials are carried out, and an Atomic Force Microscope (AFM) is used to characterize the machined surface. Experimental results show that theoretic analysis in this paper is correct. Critical Condition of the BrittleDuctile Transition of the Brittle Materials The critical condition of the brittle-ductile transition (the critical cutting of brittle materials) can be obtained by [6] 2 0 0 0 2 ) 2 cot( = H K a K a ld gc , (1) where H is the micro-hardness of the material, is the geometry factor of the indenter, =1.8854, 0 is the integrative factor, 0=(1.0 1.6)×10, Kld is the dynamic fracture toughness of the material and K0 is the affecting coefficient to brittle-ductile transition of the coolant. From theoretic analysis and experimental study, such a conclusion can be drawn concluded whether the grinding of brittle materials is in the ductile mode depends on the maximum cutting depth of single abrasive grain. The maximum cutting depth (agmax) of single abrasive grain is obtained by Key Engineering Materials Online: 2004-02-15 ISSN: 1662-9795, Vols. 257-258, pp 201-206 doi:10.4028/www.scientific.net/KEM.257-258.201

Geometric Models of the Ultra-Precision Grinding for Large Non-Axisymmetric Optical Aspheric Surfaces

Traditionally 2-axis Numerical Controlled (NC) machine is used to manufacture axisymmetric aspheric surface. If a coding disc offering accurate readings of the rotation angle is installed on the spindle, large non-axisymmetric aspheric surfaces can be manufactured on an ultra-precision 2-axis NC grinding machine by employing a diamond wheel. Geometric models for machining non-axisymmetric aspheric surfaces are presented based on a curvature analysis to solve the problems of high production cost and low efficiency in machining. The machining approach is verified to be simple and reliable by computer simulation. According to the geometric models, 3-D machining can be achieved by reforming a 2-axis machine. This will allow equipment investment be decreased. Introduction The aspheric surfaces used in optical systems can control the aberrations and reduce the number of elements while maintaining equivalent image quality. Especially asymmetrical and eccentric surfaces have the advantage of eliminate obscurations to improve image quality. Whereas nonrotational symmetry causes the manufacture of such optical elements made of brittle materials considerably more difficulty, so these elements are expensive and rare. With development of space optics, remote sensing, high power high energy laser system, and others, great demands for such optical elements, especially for accurate large non-axisymmetric optical elements present the challenge of the processing technique being efficient at the lowest possible cost. Small production may be hand polished by continuous test till the desired surface is obtained. Large volume production of not too large size aspheric elements is often achieved through replication processes [1,2]. However for large size elements NC machines may make it economical to directly manufacture. An example of this is the production of off-set aspheric for large telescope. The fabrication of non-axisymmetric optical surfaces needs new generation of ultra-precision machine. Diamond turning method employing fast tool servo system to produce the nonrotationally symmetric surfaces is investigated in [3-5]. The authors of [6-10] introduce method of grinding non-axisymmetric surface with diamond wheel by providing the correct rectilinear motion between the tool and the workpiece to form the desired surface. Computer Controlled Optical Surface (CCOS) and Stressed-lap polishing process have been used for fabricating large off-axis aspheric surfaces [11-13]. They all produced high accurate non-axisymmetric optical surfaces efficiently. At least a 3-axis NC machine is needed to process a free-form surface and a 2-axis NC machine is commonly used to create axisymmetric aspheric surface. In this work we shall concern ourselves with fabrication of non-axisymmetric aspheric by remodelling a 2-axis NC machine. This proposition has the advantage that we can produce non-axisymmetric aspheric surface with lower equipment input. The corresponding geometric models are presented which are based upon the theory of differential geometry. Specifically, we apply these models on off-set aspheric surface. Ultra-Precision Grinding System Key Engineering Materials Online: 2004-02-15 ISSN: 1662-9795, Vols. 257-258, pp 57-62 doi:10.4028/www.scientific.net/KEM.257-258.57

Effects of the Substrate on the Determination of SEBS Thin Film Mechanical Properties by Nanoindentation

In order to investigate nanoindentation data of polymer film-substrate systems and to learn more about the mechanical properties of polymer film-substrate systems, SEBS (styreneethylene/ butylene-styrene) triblock copolymer thin film on different substrate systems have been tested with a systematic variation in penetration depth and substrate characteristics. Nanoindentation experiments were performed using a Hysitron TriboIndenter with a Berkvoich tip. The resulting data were analyzed in terms of load-displacement curves and various comparative parameters, such as hardness and Young’s modulus. The results obtained by the Oliver and Pharr method show how the composite hardness and Young’s modulus are different for different substrates and different penetration depth.

Research on the Influence of the Diamond Wheel Wears on Machining Accuracy during Large Depth-to-Diameter Ratio Ultra-Precision Aspheric Grinding Process

During grinding large depth-to-diameter ratio aspheric surface part of high precision and high quality, the wearing of the diamond wheel would affect the machining accuracy of the aspheric surface part greatly. The influences of the wearing of the diamond wheel on machining accuracy of large depth-to-diameter ratio aspheric surface part are analyzed theoretically in this paper. The ultra-precision aspheric grinding system is researched out. In this system, the shape of the diamond wheel is ball-headed, and on-position dressing mechanism of the discharge principle is designed. After dressing, the profile accuracy of the ball-headed diamond wheel is very high, its diameter error is less than 0.1 μm, and the micro-blade group on the same height of the ball-headed diamond wheel is very well, it could be dressed directly without tearing down the workpiece when the diamond wheel is blunt. After dressing, this ball-headed diamond wheel could machine the aspheric workpiece directly. It resolved the problem that the assembling and wearing of the ball-headed diamond wheel affected the machining accuracy greatly. Finally, lots of grinding experiments are carried out on the grinding system. Grinding results show that profiles accuracy was 0.3 μm and the surface roughness is less than 0.01 μm. Introduction With the development of science and technology, the optical aspheric surface parts play more and more important roles in key instruments. Especially these parts are used in spaceflight and military equipments in evidence, such as imaging head of the reconnaissance satellite, the telescope of the heavenly body observation, reflector and medical microscope etc which need high accuracy aspheric parts [1-3]. However, it is still very difficult to machine aspheric parts with high accuracy, especially those concave parts with large depth-to-diameter ratio. Therefore many countries are paying attention to the study of optical aspheric parts machining. For aspheric surface partx92s machining of large depth-to-diameter ratio, the wearing influence of the diamond wheel on the machining accuracy of aspheric surface parts is obvious. In order to improve the profile accuracy of the aspheric surface part and reduce its surface roughness, it is a hot study direction of many countries studies how to solve wearing and dressing question of the diamond wheels during grinding [4-6]. In this paper, grinding the large depth-to-diameter ratio aspheric surface part at the machine, the influence of the diamond wheel wearing on the profile accuracy of the aspheric surface part is firstly analyzed theoretically. Afterwards the on-position dressing mechanism of discharge principle are designed and manufactured. The dressing system solves the wearing question of the ball-headed diamond wheel bonded by cast-iron during the large depth-to-diameter ratio optical aspheric parts machining. Finally grinding experiments of the aspheric surfaces are carried out on the grinding system and experiments results show that the expected results are obtained. Ultra-precision Aspheric Surface Grinding System Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 312-317 doi:10.4028/www.scientific.net/KEM.259-260.312

Subatomic Imaging of Si (001) Surface by Molecular Dynamic Simulation

In this study we predict the frequency modulation atomic force microscopy (FM-AFM) subatomic frequency shift images of a Si (001) surface using empirical potential molecular dynamic methods. We model carbon single-wall nanotube caped tip and Si (001) surface to investigate the tip-surface interaction. The simulation shows that the FM-AFM imaging force mainly comes from C-Si/C-C chemical covalent bonding forces; the long range nonbond van der Waals forces are slight and can be ignored

Research on Periodic Structures Aroused by Femtosecond Laser Irradiation on Single-Crystalline Silicon Wafer

Ripples in the area of femtosecond laser irradiated discrete points and continuous lines were studied. The characteristics of interference-induced ripples (LSFL) in the area irradiated by single shot were investigated by AFM. During single point irradiation, morphology of the irradiated area changed with energy deposition. Morphologies of the irradiated continuous lines with and without ablated groove inside were both investigated. The intensity of interfered light waves varied in different positions of each energy stripes. Thus the characteristics of ripples in the irradiated area varied with different positions. Ripples much larger than LSFL were found perpendicular to laser polarization.

Surface Quality Improvement of Aspheric Pressing Mould Using Parallel Grinding Method

It is a cost-effective technology to obtain aspheric optics made from optical glass and other brittle materials using pressing mould. The optical quality of molded optics is determined mostly by the surface quality of the mould, which means poor mould surface with lots of cutter marks will result in adhesion phenomena and error replication between the optics and mould. [1] In this article, a chatter model about parallel grinding system was presented, and the reasons of chatter induced by velocity feed back was analyzed and simulated. By using parallel grinding system integrated ELID technology, and wheel with greater cross-section radius in rough grinding and constant grinding velocity in fine grinding, the amplitude of cutter marks in the surface of mould was minimized and the quality of the mould surface was improved.