Ultra Precision Research Articles

Discrete-time sliding mode control and observation via an adjustable accuracy disturbance estimation

Across the industrial sector, precision engineering represents a set of technologies that are the key to successful international competitive development. Ultra precision machine tools demand to control the point of contact of tool and workpiece within the range 100 nm to 0.1 nm. This work presents the novel Adjustable Accuracy (AA) approximation of a DT function based on user-defined previous steps values. Three control and observation problems are addressed with this novel AA Disturbance Estimation that allows to achieve an adjustable accuracy boundary layer of order O(Tβ) of the corresponding sliding manifold of the closed loop system in the presence of disturbances while avoiding the undesired chattering phenomenon with an ultimate bound that decay exponentially w.r.t. the used number of previous steps for the disturbance approximation. The corresponding simulations show the effectiveness of each scheme.

Polishing of Silicon Nitride Ceramic Balls by Clustered Magnetorheological Finish.

In this study, a novel finishing method, entitled clustered magnetorheological finish (CMRF), was proposed to improve surface finish of the silicon nitride () balls with ultra fine precision. The effects of different polishing parameters including rotation speeds, eccentricities and the machining gaps on surface finish of balls were investigated by analyzing the roughness, sphericity and the micro morphology of the machined surface. The experimental results showed that the polishing parameters significantly influenced the surface finish. The best surface finish was obtained by using the polishing parameters: the machining gap of 0.8 mm, the eccentricity of 10 mm and the rotation ratio of 3/4. To further investigate the influence of the polishing parameters on the surface finish, an analytical model was also developed to analyze the kinematics of the ceramic ball during CMRF process. The resulting surface finish, as a function of different polishing parameters employed, was evaluated by analyzing the visualized finishing trace and the distribution of the contact points. The simulative results showed that the distribution and trace of the contact points changed with different polishing parameters, which was in accordance with the results of experiments.

Temperature Dependence of The Growth Process of Grain Boundary Steps Formed on Ultra–Precision Finished Polycrystalline Copper Surface

Temperature Dependence of The Growth Process of Grain Boundary Steps Formed on Ultra–Precision Finished Polycrystalline Copper Surface

MPC Inspired Dynamical Output Feedback and Adaptive Feedforward Control Applied to Piezo-Actuated Positioning Systems

It has been shown that the closed-loop transfer function representation of the unconstrained model predictive control (MPC) for single input single output systems is similar to a two-degree-of-freedom controller, which is capable of improving the tracking performance of positioning systems. Conventionally, the optimal parameters of the above-mentioned transfer function are result of a quite complicated MPC tuning. This paper proposes a new approach to obtain the parameters directly instead, where the input/output constraints are not considered. The method combines conventional feedback and adaptive feedforward techniques to minimize the tracking error as well as mitigate the influence of the load disturbance. Experiments on an ultra precision positioning system actuated by piezoelectric actuator show that the proposed method achieves much better tracking performance over a well-tuned conventional MPC.

High Precision Characterization of Li-Ion Batteries during Extreme Fast Charging

With current lithium ion batteries optimized for performance under relatively low charge rate conditions, implementation of Extreme Fast Charging (XFC, 6C charging and above) has been hindered by drawbacks including Li plating, kinetic polarization, and heat dissipation. Novel electrode designs, including anodes optimized for rapid lithium diffusion, show promise in alleviating these drawbacks.[1] However, in order to assess potential anode improvements, materials must be characterized in relevant settings, with tools that can discern critical metrics. This submission will detail efforts at Sandia National Lab to assess battery performance under XFC conditions using ultra high precision coulometry to track cycle-to-cycle efficiency and in-cycle dQdV. Efficiency deviations can reveal lithium plating or cathode breakdown, while dQdV measurements can reveal unintended side processes like lithium stripping during discharge. This submission will also describe the need for quick-response temperature control during XFC testing to minimize the effect of cell heating on characterization. Figure 1 shows dQdV vs V on a 5Ah NMC/graphite COTS pouch cell, for charge rates of 0.5C (cycle 3), 1C (cycle 6), and 6C (cycle 24) during a rate capability test. It also shows subsequent 1C discharge cycles, and a 1C/1C cycle after the rate capability (cycle 25). Of note is the particular clarity of the dQdV curves, enabled by high precision coulometry performed on a high precision Arbin battery cycler. Charge curves shift right and peaks become more spread out, which is a consequence of cell polarization at higher charge rates. Discharge curves, however, remain nearly identical throughout cycling, indicating that no lithium stripping processes are seen after increasing charge rates. Figure 2 shows cycling and temperature data for 6C charging / 2C discharge, on the same 5Ah pouch cell type. In this case, rapid response cooling plates are fitted around the cell to reduce cell heating during the high charge rate. The temperature data shows a worst-case temperature rise of only 3oC at the peak of charging along the cell’s edge, which minimizes heating artifacts during cell characterization. [1] S. Ahmed et al, J. Power Sources, 367, 250-262 (2017). Figure 1

A study on the ultra precision machining of free-form molds for advanced head-up display device

A study on the ultra precision machining of free-form molds for advanced head-up display device

Influence of diamond tool chamfer angle on surface integrity in ultra-precision turning of singe crystal silicon

Ultra precision diamond machining enables the economical production of freeform optics on infrared materials such as silicon. To produce optics with acceptable surface integrity, it is important to have a good understanding of process-work material interaction between diamond tool and brittle and hard single crystal IR materials. Chamfered cutting edges are known to have high strength, which makes them suitable for machining difficult-to-cut materials. This study investigates the influence of chamfer angle on the surface integrity of silicon. Diamond tool chamfer angles of − 20°, − 30°, and − 45° are considered under practical diamond turning conditions of single crystal silicon. State-of-the-art techniques were used to investigate the surface integrity of the machined silicon surfaces. The results show that chamfer angle of 30° yields more favorable results compared to 20° and 45° under the conditions tested. The results indicate the complex interplay between tool geometry and process parameters in reaching an acceptable level of surface integrity. A machinability map indicating ductile and brittle machining conditions for 30° chamfered diamond tool has been presented which includes directly transferable knowledge to the precision machining industry.

A study of highly conductive ester co-solvents in Li[Ni0.5Mn0.3Co0.2]O2/Graphite pouch cells

The effect of low viscosity esters on rate capability and lifetime of Li[Ni0.5Mn0.3Co0.2]O2/graphite pouch cells was studied using a variety of methods including ultra high precision coulometry, isothermal calorimetry and long term cycle testing. Methyl acetate (MA) and methyl propionate (MP) were selected as the ester co-solvents in ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) (25:5:70 vol%) blended solvent along with 2% vinylene carbonate (VC) or 2% fluoroethylene carbonate (FEC) additives. Cells containing electrolytes with 20% or 40% MA or MP could support higher charging rates without unwanted lithium plating than those without esters. All electrolytes with 2% FEC could support higher charging rates without unwanted lithium plating compared to corresponding electrolytes with 2% VC. However, UHPC and microcalorimetry measurements indicate that both the use of esters and the use of FEC over VC lead to lifetime penalties which were confirmed by long term cycling tests. Useful electrolytes, detailed in this report, that yield a good compromise between high charging rates and long lifetime are those that contain 20% MA by weight.

Optimal Whole Blood Storage Conditions for Measuring BCR-ABL1 Accurately for Xpert® BCR-ABL Ultra

Abstract Reliably quantifying BCR-ABL1 and ABL1 transcripts in whole blood for patients on TKI therapy is essential, but it can be challenging because intracellular RNA may rapidly degrade during storage. The purpose of the studies is to evaluate the effect of blood storage conditions with increased time interval on BCR-ABL1 and ABL1 gene expression, and demonstrate the validity of results in %BCR-ABL/ABL (IS) generated from Xpert® BCR-ABL Ultra. The whole blood stability was evaluated in contrived and CML patient samples. Contrived samples were prepared by spiking CML+ cells into normal EDTA or PAXgene blood at ~0.1% (IS). In EDTA, it was stable for 48 hours at room temperature (RT) and up to 3 days at 2-8°C. In PAXgene, it was stable for 5 days at RT or 2-8°C, and up to 25 months at -80°C. The CML EDTA specimens evaluated at ~10%, ~1%, ~0.1% and 0.01% (IS) were stable at RT for 48 hours and up to 4 days at 2-8°C. To evaluate long term storage for whole blood, contrived samples at ~0.1% (IS) and CML EDTA specimens at various % IS were spotted onto a Dried Blood Spot (DBS) paper template. The DBS stability at RT was demonstrated for more than 40 days from the CML clinical specimens and up to 12 months on the contrived samples. In addition, the long term stability was evaluated on frozen lysates prepared from contrived and CML EDTA specimens using Xpert® BCR-ABL Ultra lysis buffer containing Guanidine Hydrochloride. The frozen contrived blood lysates were stable for 48 hours at RT and 2-8°C and up to 3.5 months at -20°C with ≤2-fold difference from the original testing time-point. The frozen CML blood lysates were stable up to 4 years at -80°C with ≤2-fold difference at ≥ 0.01% (IS) and ≤2.5-fold below 0.01% (IS). In summary, the presented studies demonstrated that the fresh blood can be stored at RT for 48 hours and at refrigerated temperature for more 3 days without compromising the Xpert® BCR-ABL Ultra assay sensitive, precision and accuracy. The long term storage can be achieved on DBS at RT for up to 1 year and in PAXgene and frozen lysate at -80oC for more than 2 years and 4 years, respectively. DBS, the spotted blood method, can potentially benefit the CML patients in resource-poor areas, who can be monitored more frequently during TKI therapy by reducing the sample transport cost significantly. Disclosures Day: Cepheid: Employment. Levitas: Cepheid: Employment. Shridhar: Cepheid: Employment. Huang: Cepheid: Employment. Rhees: Cepheid: Employment. Bates: Cepheid: Employment. Wong: Cepheid: Employment. Radich: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees; ARIAD: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Giliad: Membership on an entity's Board of Directors or advisory committees; AMGEN: Membership on an entity's Board of Directors or advisory committees.

Numerical simulation analysis of four-step variable-diameter pipe by solid-liquid two-phase grinding

In order to investigate the effect of abrasive flow on the polishing effect of variable diameter pipe parts, taking the fourth-order variable-diameter pipe part as the research object, the solid-liquid two-phase abrasive grains are used as the processing method of the fourth-order variable-diameter pipe, the numerical simulation of the machining process of the four-order variable-diameter pipe parts were carried out. Analysis of different inlet speed conditions, the dynamic pressure and the distribution of turbulence intensity of the flow field of the fourth order variable diameter pipe. Through comparative analysis, the effects of the four-stage variable-diameter pipe flow field are studied, which can provide the theoretical basis for the continuous improvement of the abrasive flow precision and ultra precision machining technology, which can improve the efficiency of abrasive flow processing, so that the workpiece fatigue strength is improved, enhance the reliability of the workpiece, extend the service life of the workpiece.

Understanding the high-point formation mechanism on large optical surface during ultra precision fly cutting process

It was found that there always exists high points during cutting in and cutting out in the fly cutting of potassium dihydrogen phosphate (KDP) crystals. This results in poor surface flatness of KDP devices and degrades their optical performance. It is believed that the high-point formation are related to the cutting heat; however, the manner in which the cutting heat produces the high points and its control are still unclear. A thermomechanical model of the tool system in the fly cutting process is established to reveal the high-point formation mechanism on a large optical surface during the ultra-precision fly cutting process. The temperature field distribution of the tool system and axial displacement variation due to thermal deformation are solved and analyzed. The results indicate that the slow cutting heat accumulation caused by the discontinuous fly cutting process leads to moving of the cutting point in the axial direction, which is the main reason for the height difference during the process. Further analysis demonstrates that moving of the cutting point is primarily caused by the thermal deformation of the tool holder, not the tool or tool handle. Therefore, reducing the tool holder thermal deformation is the key to further improving the surface flatness of the workpiece. This study is of great significance for the improvement of the surface quality of large aperture optical devices in fly cutting.

Numerical analysis for viscosity temperature characteristics of abrasive flow finishing on micro-bore nozzle

Abrasive flow machining has become an efficient and economical ultra precision process for machining micro-bore parts. In this paper, aiming at viscosity temperature characteristics of abrasive flow finishing on micro-bore nozzle, under the guidance of the three governing equations of fluid mechanics theory, mixed phase model and discrete phase model were conducted, FLUENT software was resorted to simulate the discrete and fluid phase numerical characteristics of the solid-liquid two-phase flow field in the nozzle orifice with various field temperature and viscosity of slurry, the mechanism of erosion and wear of particles and effect of different processing parameters on particle erosion rate were uncovered, which provides a theoretical basis for the nozzle structure of abrasive flow machining.

Simulation Research on Micro Contact Based on Force in Silicon Wafer Rotation Grinding

Silicon wafer rotation grinding with cup type diamond wheel is a typical ultra precision grinding process. In this paper, a simulation model based on force for micro contact between wheel micro unit and silicon wafer is established from the stable ductile grinding process. Micro contact process in grinding is simulated using the nonlinear explicit finite element analysis software LS-DYNA. The stress-strain results on silicon wafer and wheel micro unit are analyzed by finite element method. The results show that the critical displacement and load corresponding elastic to plastic - plastic to brittle exist on silicon wafer. In silicon plastic zone tangential sliding can produce plastic groove and uplift. Wear of wheel micro unit can be based on the simulation data to judge. The research provides support for wafer grinding and wheel wear mechanism.

Reduction of material swelling and recovery of titanium alloys in diamond cutting by magnetic field assistance

Ultra precision machining (UPM) is extensively used to fabricate high accuracy products. However, the problematic material swelling/recovery effect due to the elastic recovery of materials in UPM remains unresolved. It causes a ragged surface and extra engineering tolerances which are unadoptable in extremely precise components. In particular to high elastic recovery rate with low thermal conductivity materials like titanium alloys, the swelling effect is intensified during machining processes. In this study, a magnetic field was superimposed on titanium alloys during the single point diamond cutting which aimed to minimize the material swelling effect on the machined surface using the magnetic field influence. In the experiments, titanium alloys were located at the center of two permanent magnets with intensity 0.02T and undergone a diamond groove cutting. The experimental results showed the material swelling/recovery on the machined surface was significantly reduced in presence of magnetic field in comparison to that of diamond cutting without a magnetic assistance; the accuracy of depth of cut, width and radius of cutting groove in a magnetic field reached satisfactorily over 98%. The proposed machining technology solves the problem of material swelling/spingback of low thermal conductivity materials by a cost-efficient way which is needless of complicated equipment.

Magnetostrictive and Kinematic Model Considering the Dynamic Hysteresis and Energy Loss for GMA

Due to the influence of magnetic hysteresis and energy loss inherent in giant magnetostrictive materials (GMM), output displacement accuracy of giant magnetostrictive actuator (GMA) can not meet the precision and ultra precision machining. Using a GMM rod as the core driving element, a GMA which may be used in the field of precision and ultra precision drive engineering is designed through modular design method. Based on the Armstrong theory and elastic Gibbs free energy theory, a nonlinear magnetostriction model which considers magnetic hysteresis and energy loss characteristics is established. Moreover, the mechanical system differential equation model for GMA is established by utilizing D’Alembert’s principle. Experimental results show that the model can preferably predict magnetization property, magnetic potential orientation, energy loss for GMM. It is also able to describe magnetostrictive elongation and output displacement of GMA. Research results will provide a theoretical basis for solving the dynamic magnetic hysteresis, energy loss and working precision for GMA fundamentally.

Analysis on the Action of Oxidant in Chemical Mechanical Polishing of 304 Ultra-Thin Stainless Steel

The ultra-thin stainless steel sheet will be used in flexible displays for substrate material. The application of the substrate requires its surface very smooth, no defects and damage free. Chemical mechanical polishing (CMP) has been considered as a practical and irreplaceable planarization technology in the ultra precision machining of the flexible display substrate. In chemical mechanical polishing of ultra-thin stainless steel, the oxidant of polishing slurry has an important influence on the material removal rate (MRR). In this paper, the influences of oxidant in slurry on MRR and surface roughness had been studied in CMP of ultra-thin 304 stainless steel based on alumina (Al2O3) abrasive. The research results show that the oxidant of the hydrogen peroxide and the oxalic acid have the interaction in CMP 304 stainless steel and when using the only one oxidant in polishing slurry, the hydrogen peroxide or oxalic acid, the MRR is less than the maximum. The oxalic acid can provide a strong acidic environment to ensure the stability of the hydrogen peroxide in polishing slurry and to improve the MRR in CMP 304 stainless steel. The research results can provide the reference for studying the slurry in CMP of ultra-thin stainless steel.

Thermal effects in single point diamond turning: Analysis, modeling and experimental study

Single Point Diamond Turning is one of the ultra precision methods to generate surface finish with highest possible dimensional accuracies. It involves material removal by shearing mechanism using a diamond tool tip, shearing of material results in generation of thermal energy which causes adverse impact on the tool wear, dimensional accuracy, and surface quality of work piece and on the cost of production. Thermal issues are generally taken care of by the application of coolant. Even after use of coolant, heat is transferred to workpiece while machining, which contributes to the residue of heat for next machining cycle. It deteriorates the surface quality of machined work piece to some extent. In this work, a mathematical model is proposed to compute the net residual heat transferred in the workpiece in terms of machining parameters. The equations describing temperature distribution inside cylindrical work piece, rate of heat transfer, net residual heat for a constant depth of cut are also computed and presented. The mathematical model is followed by the simulation model and the resultant parametric values through well designed sets of precision machining experiments using proper optimization technique to predict optimum machining combination that result in less distortion of surface quality.

Minimizing the effects of unmodulated light and uneven intensity profile on the holographic images reconstructed by pixelated spatial light modulators

UK Engineering and Physical Sciences Research Council (EPSRC) through the EPSRC Centre for Innovative Manufacturing in Ultra Precision (EP/I033491/1)

超精密位置決めステージ向け微小振動除去機構に関する研究

超精密位置決めステージ向け微小振動除去機構に関する研究

Design of the Aerostatic Linear Guideway with Micro-structured Surfaces for Ultra Precision Machine Tools

Design of the Aerostatic Linear Guideway with Micro-structured Surfaces for Ultra Precision Machine Tools