Run-out Error Research Articles

Precision design of hydrostatic thrust bearing in rotary table and spindle

According to the increasing needs of rotary table and spindle to satisfy high-precision machining requirements, the accuracy of rotary table and spindle becomes an important issue due to the error averaging effect of hydrostatic thrust bearing. The objective of this study is to research a methodology to guide the precision design of hydrostatic thrust bearing in rotary table and spindle. A run-out error model based on error averaging effect is established using the Reynolds equation, pressure boundary conditions, flux continuity equations of pad and dynamic equations of shaft. The axial run-out error and angular error are calculated considering perpendicularity error and flatness error of the components. The simulation results show that the two perpendicularity errors between axis line and thrust bearing bushing surface have same direction, and the axial run-out error could reach to the maximum values. Also, the flatness error of thrust bearing bushing surface has a big influence on axial run-out error. Following the outcomes, the precision design of hydrostatic thrust bearing was conducted. The axial run-out errors of rotary table and spindle with hydrostatic thrust bearing were experimentally studied, and the results have good coherence to the simulation data. The run-out error model is demonstrated to be an effective approach to guide the precision design of hydrostatic thrust bearing in other rotary tables and spindles.

Influence of motor control characteristics on load sharing behavior of torque coupling gear set

The influence of the control characteristics of a direct torque control (DTC) motor on the load sharing behavior of a torque coupling gear set is studied by establishing a dynamic model of a multi-motor torque coupling system. The effects of run-out errors of the pinions of the torque coupling gear set on the powertrain are analyzed under steady operating conditions. The difference in rotational speed among the pinions becomes apparent, and the load sharing behavior deteriorates when there are run-out errors. The relationship between the control characteristics and load sharing behavior is studied. The difference in rotational speed decreases and the load sharing behavior improves as proportional and integral gains of the speed controller increase.

Application potential of coarse-grained diamond grinding wheels for precision grinding of optical materials

Fine-grained resin bonded diamond tools are often used for ultra-precision machining of brittle materials to achieve optical surfaces. A well-known drawback is the high tool wear. Therefore, grinding processes need to be developed exhibiting less wear and higher profitability. Consequently, the presented work focuses on conditioning a mono-layered, coarse-grained diamond grinding wheel with a spherical profile and an average grain size of 301 µm by combining a thermo-chemical and a mechanical-abrasive dressing technique. This processing leads to a run-out error of the grinding wheel in a low-micrometer range. Additionally, the thermo-chemical dressing leads to flattened grains, which supports the generation of hydrostatic pressure in the cutting zone and enables ductile-mode grinding of hard and brittle materials. After dressing, the application characteristics of coarse-grained diamond grinding wheels were examined by grinding optical glasses, fused silica and glass–ceramics in two different kinematics, plunge-cut surface grinding and cross grinding. For plunge-cut surface grinding, a critical depth of cut and surface roughness were determined and for cross-grinding experiments the subsurface damage was analyzed additionally. Finally, the identified parameters for ductile-machining with coarse-grained diamond grinding wheels were used for grinding a surface of 2000 mm2 in glass–ceramics.

High Precision Low Temperature Direct Wafer Bonding Technology for Wafer-Level 3D ICs Manufacturing

The increased microelectronic devices complexity is raising a strong demand for high wafer-to-wafer (w2w) alignment accuracy allowing for high levels of integration by wafers stacking. One of the major aspects for the alignment is the overlay alignment accuracy as this is strongly impacting on the final yield: the future generation devices will require w2w overlay alignment accuracies in the range of 100 nm or lower. The overlay alignment accuracy can be split into following errors: translation, rotation, run-out and distortion of the patterns on the wafers. In order to meet the increasing demand of overlay alignment accuracy, all those components have to be considered for optimization in the alignment technology development.This work presents different newly developed concepts for high precision aligned w2w bonding processes which are applicable for any low temperature fusion bonding or Cu/dielectric hybrid bonding processes. The new technologies enable sub-100 nm w2w overlay alignment accuracy. The components of w2w overlay accuracy and the latest developments for their optimization are introduced and different approaches of run-out compensation with and without temperature compensation are introduced. Finally, a feedback loop between SmartView®NT2 w2w alignment system with integrated run-out compensation and in-situ post bond alignment verification module (AVM) will be shown. Additionally to the w2w alignment process and the feedback-loop which is monitoring and controlling the overlay accuracy, a new technique will be presented, which allows a fully automated in-situ recycling method of bonded wafers, which are out of alignment-specification.The process development was performed using a Gemini®FB-XT fully automated wafer bonding system, equipped with a plasma activation chamber enabling low temperature bonding processes, a SmartView®NT2 optical aligner using a face-to-face alignment principle, a pre-bonding station used for bringing the substrates in contact after alignment, an alignment verification module (AVM) as well as a debonding module which allows for re-working of the wafer pairs failing the alignment criteria.For optimization of the overlay accuracy on bonded wafers, the optimization steps have to address the individual components of the overlay. A significant contributor to the overlay accuracy is the scaling or run-out error, so the main focus of this evaluation is the run-out compensation process in SmartView®NT2. A well-known run-out compensation method in lithography is a thermal compensation of the scaling, which can also be applied for bonding.Deeper investigations showed that the thermal run-out compensation has major disadvantages in terms of wafer-stress and pattern distortion, which are significant problems for BSI CIS, so this type of compensation would not be an acceptable general solution for such stress- and overlay alignment-sensitive applications.Multiple new methods for run-out compensation without using thermal compensation were successfully developed, enabling w2w overlay accuracy better than 100 nm on every point measured on the wafers stack and overlay accuracy values better than 100 nm could already be shown successfully.

Runout error correction in tomographic reconstruction by intensity summation method.

An alignment method for correction of the axial and radial runout errors of the rotation stage in X-ray phase-contrast computed tomography has been developed. Only intensity information was used, without extra hardware or complicated calculation. Notably, the method, as demonstrated herein, can utilize the halo artifact to determine displacement.

Position alignment of laser beam spots in optical disc drives using cross-correlation

Optical pickup unit (OPU) is a data read/write head in optical disc drives, and precision orientation angle adjustment of a diffraction grating (GT) is an important process in OPU manufacturing for aligning laser beam spots on the same data track of an optical disc. This paper proposes a new method for detecting alignment of laser beam spots for utilization in automation of the GT adjustment process. While a conventional method uses complicated and expensive image processing techniques to an eye diagram of a data radio frequency (RF) signal, the proposed method measures the cross-correlation of two binary signals corresponding to two of the laser beam spots in consideration of the geometric relationship between the laser beam spots and data tracks. The proposed method is not only so simple as to be implemented using a digital logic circuit but also tolerant to poor signal condition due to radial off-track run-out and disc rotational speed error. A FPGA-based implementation of the proposed method is presented, and experimental results are provided to show its validity1.

A micro-coupling for micro mechanical systems

The error motions of micro mechanical systems, such as micro-spindles, increase with the increasing of the rotational speed, which not only decreases the rotational accuracy, but also promotes instability and limits the maximum operational speed. One effective way to deal with it is to use micro-flexible couplings between the drive and driven shafts so as to reduce error motions of the driven shaft. But the conventional couplings, such as diaphragm couplings, elastomeric couplings, bellows couplings, and grooved couplings, etc, cannot be directly used because of their large and complicated structures. This study presents a novel micro-coupling that consists of a flexible coupling and a shape memory alloy (SMA)-based clamp for micro mechanical systems. It is monolithic and can be directly machined from a shaft. The study performs design optimization and provides manufacturing considerations, including thermo-mechanical training of the SMA ring for the desired Two-Way-Shape-Memory effect (TWSMe). A prototype micro-coupling and a prototype micro-spindle using the proposed coupling are fabricated and tested. The testing results show that the prototype micro-coupling can bear a torque of above 5 N • mm and an axial force of 8.5 N and be fitted with an SMA ring for clamping action at room temperature (15 °C) and unclamping action below–5 °C. At the same time, the prototype micro-coupling can work at a rotational speed of above 200 kr/min with the application to a high-speed precision micro-spindle. Moreover, the radial runout error of the artifact, as a substitute for the micro-tool, is less than 3 μm while that of turbine shaft is above 7 μm. It can be concluded that the micro-coupling successfully accommodates misalignment errors of the prototype micro-spindle. This research proposes a micro-coupling which is featured with an SMA ring, and it is designed to clamp two shafts, and has smooth transmission, simple assembly, compact structure, zero-maintenance and balanced motions.

Global sensitivity analysis of transmission accuracy for RV-type cycloid-pin drive

Global sensitivity analysis of transmission accuracy for RV-type pin-cycloid drive is studied by Sobol' method in comprehensive consideration of nonlinear factors and uncertainty factors (such as manufacturing errors, assembly errors, bearing clearances, etc.). The purpose is to study the effect of various errors on transmission accuracy, then find out main errors so as to regulate them, thus not only improve transmission accuracy, but also reduce manufacturing cost. The results show that the effect on transmission accuracy is larger of the runout error of eccentricity cam of crank shaft, the tooth groove error and accumulative pitch error of cycloid gear, the bearing clearance between cycloid gear and crank shaft, and the tooth groove error and accumulative pitch error of pin gear, large of the runout error of cycloid gear hole at crank shaft and the runout error of carrier hole at crank shaft, small of the assembly error of carrier, the bearing clearance between carrier and frame, etc. The presented method provides a basis for global sensitivity analysis of transmission accuracy for the RV-type pin-cycloid drive. It is also beneficial to global sensitivity analysis of transmission accuracy of other similar gear drives. The results of this study provide an important guideline for the design and manufacture of high accuracy and complex gear drive.

Study on methods of enhancing the quality, efficiency, and accuracy of pulsed laser profiling

A pulsed fiber laser was employed in a systematic study on the tangential profiling of a coarse-grained bronze-bond diamond grinding wheel. The goal of the present study was to improve the profile quality and enhance the efficiency and accuracy of the profiling process. Our results demonstrate that when using a long laser pulse, graphitization of the grain after profiling is unavoidable. However, by blowing argon from the side onto the surface during laser profiling, the degree of graphitization can be reduced, thereby improving the profiling quality. Higher laser peak power resulted in higher profiling efficiency. Only when the laser depth of cut was equal to the initial surface profile error of the grinding wheel, i.e., the “deep single layer cut, stepwise feeding tangential laser profiling method” was used, could the highest profiling efficiency be attained. Increasing the peak power of the laser or the overlapped rate of the laser scanning paths enhanced the profiling accuracy with no appreciable effect on the quality. After laser profiling, the initial circular runout and parallelism error of the surface of the grinding wheel were reduced from 83.1 and 324.6μm to 6.8 and 3.8μm, respectively. Because the peak power of the pulsed fiber laser was not sufficiently high, the surface profile accuracy of the grinding wheel was slightly lower than the profile accuracy using the diamond wheel.

Online, efficient and precision laser profiling of bronze-bonded diamond grinding wheels based on a single-layer deep-cutting intermittent feeding method

In this study, an online, efficient and precision laser profiling approach that is based on a single-layer deep-cutting intermittent feeding method is described. The effects of the laser cutting depth and the track-overlap ratio of the laser cutting on the efficiency, precision and quality of laser profiling were investigated. Experiments on the online profiling of bronze-bonded diamond grinding wheels were performed using a pulsed fiber laser. The results demonstrate that an increase in the laser cutting depth caused an increase in the material removal efficiency during the laser profiling process. However, the maximum laser profiling efficiency was only achieved when the laser cutting depth was equivalent to the initial surface contour error of the grinding wheel. In addition, the selection of relatively high track-overlap ratios of laser cutting for the profiling of grinding wheels was beneficial with respect to the increase in the precision of laser profiling, whereas the efficiency and quality of the laser profiling were not affected by the change in the track-overlap ratio. After optimized process parameters were employed for online laser profiling, the circular run-out error and the parallelism error of the grinding wheel surface decreased from 83.1μm and 324.6μm to 11.3μm and 3.5μm, respectively. The surface contour precision of the grinding wheel significantly improved. The highest surface contour precision for grinding wheels of the same type that can be theoretically achieved after laser profiling is completely dependent on the peak power density of the laser. The higher the laser peak power density is, the higher the surface contour precision of the grinding wheel after profiling.

Edge fabrication and process optimization of precision woodworking PCD millers with disk electrical discharge machining

Polycrystalline diamond (PCD) tools fulfil a vital role in the woodworking industry, with its ability to achieve smooth machining quality and long service life, along with excellent performance features. However, diamond tools’ fabrication is a difficult material removal process. In this study, we propose and develop an electrical discharge machining (EDM) grinding method with disk electrode. Tool profiles are captured by a measuring probe, and path curves are tracked by a peripheral disk in edge fabrication. Experiments of graphite and copper serving as electrode are carried out, respectively, in the disk discharge grinding process. In addition, with design of experiments on PCD machining, different Disk EDM parameters are obtained to evaluate the influence of dominant factors on machining speed and surface quality. Optimal gap reference voltage, wheel rotational speed and pulse width are extracted, respectively, under the conditions of two electrode materials. Results show that pulse width plays the most important role in machining, and copper electrode can effectively produce smoother surface than graphite when used as electrode in Disk EDM. Moreover, edge fabrication of spiral miller (φ125 mm) is precisely realized with circular run-out errors less than 0.050 mm.

Prediction and experimental verification of the cutting forces in gear form milling

In this paper, a mathematical model is presented by which the cutting forces in gear form milling process are predicted using the mechanistic approach. To use this approach, a detailed description of the chip geometry is needed. Eccentricity and run-out tool errors are considered, which is of great importance as the chip thickness will by these errors vary for the subsequent cuts. The chip geometry is determined by comparing the path of the cutting edge with already removed material. The boundary of the chips is determinable from the cutting edge geometry, which is here derived in parametric form so spur and helical gears are manufactured correctly. Locally on the cutting edge, the cutting forces are resolved from orthogonal cutting data and on the basis that these forces are proportional to the instantaneous chip thickness. The load each individual cutting tooth experience in operation, as well as the complete load on the tool, are resolved by summing the forces along the cutting edge. In the model, all cut chips are determined for each machined gear tooth gap, with the gear blank boundaries considered. The paper ends with experimental validation using indexable insert milling cutters. It is shown that the model predicts the force shape well and the peak force levels within 12 %.

부하를 고려한 직선운동유니트의 정밀도 시뮬레이션 기술

This paper presents the motion accuracy simulation considering loads such as workpiece weight, cutting force, cogging force of a linear motor, and force caused by misalignment and runout error of a ballscrew in linear motion units. The transfer function method is basically utilized to estimate 5-DOF motion errors, together with the equilibrium equations of force and moment on the table. The transfer function method is modified in order to consider clearance changed according to the loads in the double sided hydrostatic/aerostatic bearings. Then, the analytic model for predicting the 5-DOF motion errors is proposed with the modified transfer function method. Motion errors were simulated under different loading conditions in the linear motion units using hydrostatic, aerostatic, and linear motion bearings, respectively. And the proposed analytic model was verified by comparing the estimated and measured motion errors.

Influence of dynamic effects on surface roughness for face milling process

In face milling processes, the surface roughness of the machined part reflects the cutting performance of face milling cutter. Surface roughness depends on different factors including feed direction, axial and radial run-out errors, and cutting tool geometry. In this paper, an algorithm considering the effects of static and dynamic factors on surface roughness for predicting the surface roughness is proposed. This work is focusing on straight-edged square insert. The dynamic characteristics of the milling process are also introduced. An electronic impact hammer is used to identify the dynamic parameters of the cutting system. Milling experiments are conducted to validate the prediction model. Results show that the prediction model can estimate the surface roughness of the machined parts after face milling. This paper provides an in-depth understanding of the relationship between machined surface roughness and process conditions especially for axial and radial run-out errors induced by static deformation and Z-axial relative displacement induced by forced vibration. The outcome of this research will lead to methodologies for cost-effective monitoring and surface roughness control.

Online tangential laser profiling of coarse-grained bronze-bonded diamond wheels

A novel online tangential laser profiling method was developed in this study. The system consisted of a pulsed fiber laser, a surface grinder, a motorized three-dimensional (3D) translation stage, laser displacement sensors and a laser power meter. Online tangential laser profiling was conducted on coarse-grained (120#) bronze-bonded diamond wheels. When the laser power exceeded 40 W, the laser beam simultaneously removed the diamond grains and the bronze bond to produce a smooth wheel surface. The mean circular runout error and the axial gradient error of the grinding wheel surface decreased from 203.4 and 67.6 μm to 9.5 and 0.8 μm, respectively, indicating that the wheel contour accuracy improved significantly after profiling. The diamond grains on the grinding wheel surface were graphitized during laser profiling. However, blowing a protective argon (Ar) stream or spraying water mist from the side during profiling decreased the extent of graphitization compared to that in air.

Study on Wheel Run-Out Detection System Based on Harmonic-Analysis Principle

In order to reduce error of the wheel run-out detection system, a harmonic-analysis-based detection method was proposed to enhance the precision of online detection. The moving average filtering method was used for digital filtering between the axial and radial run-out errors so that to decrease the effect of outside noise on the measured data. Practical application shows that this system works stably and reliably on the wheel detection line and it realizes 100% online detection on the axial and radial run-out of work pieces, with the measurement error lower than 0.1mm.

Development of EDM Equipment for Machining Film Cooling Holes

To meet the requirement of precision, machining efficiency and surface quality of film cooling holes, an electrical discharge machining (EDM) equipment was developed with the function of high-accuracy rotation of tool electrode and performances of both high machining efficiency and thin recast layer. The equipment mainly consists of inchworm spindle, pulse power generator with high peak current and control system based on PMAC. Key problems were solved including precision and consistency of holes diameter, compatibility between high peak current and small pulse width and openness of the control system. Performance tests of the equipment show that runout error of the electrode is less than 25 μm, maximum peak current is 50 A while the minimum pulse width being 1μs, positioning accuracy of the control system is less than 2 μm. Machining experiments of vertical and inclined holes verified the feasibility of the designed equipment.

A high-precision instrument for mapping of rotational errors in rotary stages.

A rotational stage is a key component of every X-ray instrument capable of providing tomographic or diffraction measurements. To perform accurate three-dimensional reconstructions, runout errors due to imperfect rotation (e.g. circle of confusion) must be quantified and corrected. A dedicated instrument capable of full characterization and circle of confusion mapping in rotary stages down to the sub-10 nm level has been developed. A high-stability design, with an array of five capacitive sensors, allows simultaneous measurements of wobble, radial and axial displacements. The developed instrument has been used for characterization of two mechanical stages which are part of an X-ray microscope.

Research of On-Machine Laser Measurement Method for Cutting Tools

To successfully achieve high precision machining, process technology and on-machine measurement is essential. On-machine laser measurement will be widely used in industry because it is non-contacting, real-time and high-precision. However, proper method for tool shape monitoring and dimensional control are important to research. In this study, the measurement system consists of a laser light source and a quad photodiode array. And two different edge detection algorithms are introduced to determine the position of the tool edge accurately in order to measure the diameter of cutting tool and errors caused by tool runout. The experimental results verify the validity of measuring tool diameter and runout error.

Time efficient method for defocus error compensation in tomographic phase microscopy

We present a holographic method for defocus error compensation in tomographic phase which enables high quality reconstruction in the presence of a meaningful run-out error of the measurement system. The proposed method involves indirect determination of the sample displacement from the in-focus plane. The sought quantity is deduced from the transverse movement of the rotating sample, which can be determined with high precision using correlation-based techniques. The proposed solution features improved accuracy and reduced computation time compared to the conventional autofocusing-based approach. The validity of the concept is experimentally demonstrated by tomographic reconstruction of an optical microtip. Full Text: PDF References S. Kou, C. Sheppard, Image formation in holographic tomography, Opt. Lett. 33, 2362 (2008). CrossRef A. C. Kak and M. Slaney, Principles of Computerized Imaging (New York, SIAM 2001). CrossRef T. C. Wedberg, J. J. Stamnes, and W. Singer, Comparison of the filtered backpropagation and the filtered backprojection algorithms for quantitative tomography, Appl. Opt. 34, 6575 (1995). CrossRef J. Kostencka and T. Kozacki, Optical diffraction tomography: accuracy of an off-axis reconstruction, Proc. SPIE 9132, 91320M (2014) CrossRef A. Kuś et al., Tomographic phase microscopy of living three-dimensional cell cultures, J. Biomed. Opt. 19, 46009 (2014) CrossRef J. Kostencka, T. Kozacki, M. Dudek, and M. Kujawinska, Noise suppressed optical diffraction tomography with autofocus correction, Opt. Express 22, 5731 (2014) CrossRef W. Gorski, Tomographic imaging of photonic crystal fibers, Opt. Eng. 45, 125002 (2006) CrossRef F. Charriere et. al., Cell refractive index tomography by digital holographic microscopy, Opt. Lett. 31, 178 (2006) CrossRef Y. Jeon and C. K. Hong, Rotation error correction by numerical focus adjustment in tomographic phase microscopy, Opt. Eng. 48, 105801 (2009) CrossRef P. Langehanenberg, B. Kemper, D. Dirksen, and G. von Bally, Autofocusing in digital holographic phase contrast microscopy on pure phase objects for live cell imaging, Appl. Opt. 47, D176 (2008) CrossRef J. Kostencka, T. Kozacki, and K. Lizewski, Autofocusing method for tilted image plane detection in digital holographic microscopy, Opt. Commun. 297, 20 (2013) CrossRef K. Lizewski, S. Tomczewski, T. Kozacki, and J. Kostencka, High-precision topography measurement through accurate in-focus plane detection with hybrid digital holographic microscope and white light interferometer module, Appl. Optics 53, 2446 (2014) CrossRef T. Kozacki, M. Jozwik, and R. Jozwicki, Determination of optical field generated by a microlens using digital holographic method, Opto-Electron. Rev. 17, 58 (2009) CrossRef I. Yamaguchi and T. Zhang, Phase-shifting digital holography, Opt. Lett. 22, 1268 (1997) CrossRef M. Kujawinska et al., Interferometric and tomographic investigations of polymer microtips fabricated at the extremity of optical fibers, Proc. SPIE 8494, 849404 (2012) CrossRef T. Kozacki, K. Falaggis, and M. Kujawinska, Computation of diffracted fields for the case of high numerical aperture using the angular spectrum method, Appl. Opt. 51, 7080 (2012) CrossRef