Run-out Error Research Articles

Process Feedback Control of the Noncircular Turning Process for Camshaft Machining

This paper presents a frequency domain learning control scheme for a class of nonlinear systems and its application to the process feedback control of the noncircular turning process for camshaft machining. In frequency domain, periodic signals are represented by the Fourier expansions that are nonzero only at discrete frequency points. An input dependent system matrix can be used to describe the input-output relationship of a class of nonlinear systems with periodic input and output signals. A learning controller is designed based on the system matrix and the bound of unmodeled dynamics. Conditions to achieve asymptotic stability and tracking performance are derived. To further improve system robustness, a low pass filter is used to turn off the learning scheme at high frequencies. The learning control scheme is then applied to the process feedback control of camshaft machining using the noncircular turning process. A two level control structure is adopted. The first level is servo control that ensures precise tool slide motion. The second level is frequency domain learning control that compensates machined profile errors due to the effects of tool/workpiece geometry, tool wears, machine deformations, and spindle runout errors. Relationship between the servo control and learning control is discussed. Implementation of the process feedback control on a steel camshaft turning demonstrates improvement of the maximum cam profile errors from 80μm to within 20μm in five iterations.

Submicron Radial Runout Error Compensation Method for the Turntable in a Wafer Prealigner

In order to eliminate the influence of the radial runout error of the turntable on the prealignment precision of a wafer pre- aligner,an on-line detection and compensation method for the error is proposed.The mandrel above and rotating along with the turn- table is taken as the detecting component of the radial runout,and the radial distance of the mandrel is detected by a vortex sensor. The sensor's measurement value consists of fixed error and radial runout error,the former is solved off-line by means of ensemble average method or radial runout features of the turntable,based on which the radial runout error is separated from the data of the vortex sensor when working on-line.The radial runout error is used to compensate the peripheral data of the wafer detected by a laser displacement sensor with the compensation method simplified according to the error features.The experimentation has proved that the use of the radial runout compensation method has improved the prealignment precision of the system and made it meet the re- quirement of micron positioning precision.

ELID Assisted Precision Conditioning of Coarse-Grained Diamond Grinding Wheel

In order to realize ductile machining of optical glasses using mono-layer nickel electroplated coarse-grained diamond grinding wheel, a novel conditioning technique features using a copper bonded diamond grinding wheels of 15m grain size dressed by ELID (electrolytic inprocess dressing) to condition the 46m grain sized diamond wheel has been developed. During the conditioning process, a force transducer was used to monitor the conditioning force, a coaxial optical distance measurement system was used to in-situ monitor the modified wheel surface status. White-light interferometry (WLI), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the conditioned wheel surface status as well as the ground optical glass surface topography correspondingly. The experimental result indicates that a minimized wheel radial run-out error of less than 2μm as well as the top-flattened diamond grains of constant wheel peripheral envelop profile were generated on a 5-axis ultra-precision machine tool. The grinding experiment proved that the well conditioned 46μm coarse-grained diamond wheel can be used in realizing the ductile grinding of optical glass BK7, which indicates that the newly developed conditioning technique is feasible and applicable to introduce the coarse-grained diamond wheels into precision machining of brittle and hard-to-machine materials.

Ultra-precision ductile grinding of BK7 using super abrasive diamond wheel

In this paper, a novel conditioning technique using copper bonded diamond grinding wheels of 91 μm grain size and electrolytic in-process dressing (ELID) is first developed to precisely and effectively condition a nickel-electroplated monolayer coarse-grained diamond grinding wheel of 151 μm grain size. Under optimised conditioning parameters, the super abrasive diamond wheel was well conditioned in terms of a minimized run-out error and flattened diamond grain surfaces of constant peripheral envelope. The conditioning force was monitored by a force transducer, while the modified wheel surface status was in-situ monitored by a coaxial optical distance measurement system. Finally, the grinding experiment on BK7 was conducted using the well-conditioned wheel with the corresponding surface morphology and subsurface damage measured by atomic force microscope (AFM) and scanning electric microscope (SEM), respectively. The experimental result shows that the newly developed conditioning technique is applicable and feasible to ductile grinding optical glass featuring nano scale surface roughness, indicating the potential of super abrasive diamond wheels in ductile machining brittle materials.

Fabrication of Diamond Micro Tool Array (DMTA) for Ultra-Precision Machining of Brittle Materials

A novel conditioning technique to precisely and effectively condition the nickel electroplated mono-layer coarse-grained diamond grinding wheel of 91m grain size was developed to fabricate a Diamond Micro Tool Array (DMTA) in ductile machining of brittle materials. During the fabricating process, a copper bonded diamond grinding wheels (91m grain size) dressed by ELID (electrolytic in-process dressing) was applied as a conditioner, a force transducer was used to monitor the conditioning force, and a coaxial optical distance measurement system was used to insitu monitor the modified wheel surface status. The experimental result indicates that the newly developed conditioning technique is applicable and feasible to generate required wheel topography of less than 2μm run-out error and grain geometries. The taper cutting test on BK7 proves the fabricated DMTA is capable of realizing ductile machining of brittle materials.

Analysis and Validation of Cutting Forces Prediction Models in Micromachining

Many investigations have been developed related to precision machining with features in the millimetre scale. In this paper different cutting force models for micromilling are analyzed and compared. A new model based on specific cutting force that also considers run-out errors has been developed. The estimated cutting forces obtained with this model had good agreement with the experimental data. Also, the proposed model allows to be implemented within the machine control for the on-line optimization of the micromilling process.

Runout effects in milling: Surface finish, surface location error, and stability

This paper investigates the effect of milling cutter teeth runout on surface topography, surface location error, and stability in end milling. Runout remains an important issue in machining because commercially-available cutter bodies often exhibit significant variation in the teeth/insert radial locations; therefore, the chip load on the individual cutting teeth varies periodically. This varying chip load influences the machining process and can lead to premature failure of the cutting edges. The effect of runout on cutting force and surface finish for proportional and non-proportional tooth spacing is isolated here by completing experiments on a precision milling machine with 0.1 μm positioning repeatability and 0.02 μm spindle error motion. Experimental tests are completed with different amounts of radial runout and the results are compared with a comprehensive time-domain simulation. After verification, the simulation is used to explore the relationships between runout, surface finish, stability, and surface location error. A new instability that occurs when harmonics of the runout frequency coincide with the dominant system natural frequency is identified.

ULTRA-PRECISION GRINDING OF BK7 OPTICAL GLASS USING COARSE-GRAINED ELECTROPLATED DIAMOND WHEEL

A novel conditioning technique is developed to precisely and effectively condition the 151μm grain-sized nickel electroplated monolayer coarse- grained diamond grinding wheel in aiming to realize ductile grinding of brittle materials. During the conditioning process, a copper bonded diamond grinding wheel (91μm grain size) dressed by ELID (electrolytic in-process dressing) is applied as a conditioner, a force transducer was used to monitor the conditioning force, and a coaxial optical distance measurement system are used to in-situ monitor the modified wheel surface status. Ultimately the coarse-grained diamond wheel is conditioned to achieve an ideal state in terms of less than 2μm run-out error, top-flattened diamond grains and constant wheel envelop profile. Then the well- conditioned 151μm wheel is applied to conduct taper grinding and contour grinding tests, the ground surface and sub-surface integrity are measured by WLI (white light interferometer), AFM (atomic force microscope) and SEM (scanning electrical microscope) respectively. The experimental results indicate that the well-conditioned 151μm grain-sized diamond wheel is able to realize ductile grinding of BK7 with nano-scale surface roughness, as well as the almost damage free sub-surface integrity. The results also show the promising prospect of the conditioning technique and coarse-grained diamond wheels to be applied in machining the hard-machine-materials and the other brittle materials such as ceramic and silicon carbide, etc.

Investigation of Cutting Characteristics in Side-milling a Multi-thread Worm Shaft on Automatic Lathe

This paper investigates the cutting characteristics of side-milling which is proposed as a more efficient way to manufacture worms of higher accuracy than form-threading and planetary milling. A tool-tip trajectory based on the tool-workpiece interaction is modelled in terms of matrix transformation. Chip thickness, cutting force and surface roughness are simulated using the calculated tool-tip trajectories. The effects of various errors in the real cutting such as run-out errors of a tool axis, tool setup errors and workpiece deflection due to cutting forces are investigated. The simulation results are verified through numerous experiments on an automatic lathe.

Roughness and texture generation on end milled surfaces

Plane surface generation mechanism in flat end milling is studied in this research. The bottom of a flat end mill has an end cutting edge angle that plays an important role in surface texture. Surface texture is produced by superposition of conical surfaces generated by the end cutting edge rotation. The machined surface is cut once again by the trailing cutting edge. This back cutting phenomenon is frequently observed on surfaces after finishing. Tool run-out and tool setting error including tool tilting and eccentricity between tool center and spindle rotation center are considered together with tool deflection caused by cutting forces. Tool deflection affects magnitude of back cutting and the surface form accuracy. As a result, the finished surface possesses peaks and valleys with form waviness. Surface topography parameters such as RMS deviation, skewness and kurtosis are used for evaluating the generated surface texture characteristics. Through a set of cutting tests, it is confirmed that the presented model predicts the surface texture and roughness parameters precisely including back cutting effect.

Prediction of the cutting tool edge position and orientation accuracy through error synthesis of spindle elements

Achieving workpiece high accuracy at low cost is one of the greatest challenges in the machining industry. The runout of the cutting tool is prejudicial to precision machining, causing errors in the machined part, variation in the tool life, and premature tool breakage. This paper focuses on modelling the cutting tool edge position and orientation variations of a spindle system. This is a static approach based on the errors of the spindle elements. A kinematic model of the spindle/toolholder/cutting tool using homogeneous transformation matrices is first present. The model takes into account the runout and tilt errors of the spindle, the parts tolerances of the toolholder interfaces (spindle nose-toolholder and toolholder-cutting tool shank), as well as the cutting tool edge tolerance. The paper concludes with a simulation based on common values of the spindle elements. The proposed model is expected to provide insights into the advanced tolerance analysis of the spindle system.

Influence of manufacturing errors on the dynamic characteristics of planetary gear systems

A dynamic analysis using a hybrid finite element method was performed to characterize the effects of a number of manufacturing errors on bearing forces and critical tooth stress in the elements of a planetary gear system. Some tolerance control guidelines for managing bearing forces and critical stress are deduced from the results. The carrier indexing error for the planet assembly and planet runout error are the most critical factors in reducing the planet bearing force and maximizing load sharing, as well as in reducing the critical stress.

돔 유리를 이용한 위치이동 다중화 홀로그램 정보저장장치용 서보 컨트롤

위치이동 다중화 홀로그램 정보저장장치에서, 돔 형태(dome-type)유리를 이용한 서보 컨트롤 방법을 제안하였다. 5개의 2차원 데이터를 재생효율 균일도 5% 이내로 위치이동 다중화 기록을 한 후, 직경이 25.4 mm 이고 두께가 1 mm 인 돔 유리를 사용하여, 재생 시에 발생하는 홀로그램 디스크의 기울어짐 각도오차가 <TEX>$\pm$</TEX>0.2<TEX>$^{\circ}$</TEX>,위치오차 <TEX>$\pm$</TEX>50<TEX>$\mu\textrm{m}$</TEX>인 경우에 대해서도 정확한 오차보정이 가능함을 실험적으로 검증하였다. 돔 유리를 이용하는 방식은 기존에 제안된 평판유리를 이용하는 방식［김성필 외, 한국광학회지, Vol. 14, No.1, pp. 58-64, 2003］에 비해 구동이 간편하기 때문에, 서보 컨트롤을 위한 광 픽업 장치를 간단하고 작은 규모로 모듈화 하는데 매우 유용하다. We propose a servo control method using a dome-type glass in shift-multiplexed holographic data storage. We frist store live 2-D data by shift-multiplexing in a holographic disk with 5％ variation in their. diffraction efficiencies. During read-out of the stored data, the servo control using the dome glass correctly compensates mechanical errors of the disk; the error of <TEX>$\pm$</TEX>0.2<TEX>$^{\circ}$</TEX>and run-out error of <TEX>$\pm$</TEX>50 <TEX>${\mu}{\textrm}{m}$</TEX>. Use of the dome-type glass in servo control makes a pickup module more compact in size and easier to control than the previous method using parallel glass plate ［Sungphil Kim, et al., Hankook Kwanghak Hoeji, Vol. 14, No. 1, pp.58-64, 2003］.

312 光学式仮想Vブロック方式によるスピンドル回転誤差測定(OS10 加工計測・評価)

A run-out measuring instrument with capacitance displacement probe is widely used in industry. However, this measurement method has the defect that measurement result depend on a feature of measured object. Furthermore, attachment error between measured object and spindle is never detected in measurement at are section. In this paper, we compare the optical measurement by virtual V-block method which does not depend on a feature of a measured subject to 2-point method with capacitance displacement probe in view of measurement principle. And we show how to separate the attachment error from the run-out error of a spindle.

Influence of Carrier and Gear Manufacturing Errors on the Static Load Sharing Behavior of Planetary Gear Sets

In this paper, a state-of-the-art contact mechanics model of a planetary gear set is employed to study the effect of a number of manufacturing and assembly related carrier and gear errors on the load sharing amongst the planets. Three different groups of errors are considered: (i) time-invariant, assembly-independent errors such as carrier planet pinhole position errors, (ii) time-invariant, assembly-dependent errors such as planet tooth thickness errors, and (iii) time-varying, assembly-dependent errors such as gear run-out errors. With such errors present, planet load sharing characteristics of an n-planet system (n=3 to 6) is investigated for different piloting configurations under quasi-static conditions. Load sharing behavior as a function of key manufacturing errors is quantified and design guidelines are proposed for better planet load sharing behavior.

가공오차 및 조립오차가 유성기어열의 정특성에 미치는 영향

Static analysis using hybrid finite element(FE) method has been applied to characterize the influence of position, runout and thickness errors of the sun, ring and planet on the bearing forces and critical tooth stress. Some guidelines for tolerance control to manage critical stress and bearing forces are deduced from the results. Carrier indexing error planet assembly and planet tooth thickness error are most critical to reduce planet bearing force and maximize load sharing as well as to reduce critical stresses. Sun and carrier bearing forces due to errors increase several times more than those of normal condition.

Reduction of flow-induced suspension vibrations in a hard disk drive by dual-stage suspension control

A control design methodology is proposed to control an active dual-stage suspension for the reduction of flow-induced vibrations (windage) in a hard disk drive. The design of the controller uses dynamical models of both the suspension and the stochastic behavior of the windage to design a low third-order discrete-time feedback controller to reduce windage-induced track misregistration. Experimental results show that nonrepeatable runout errors due to windage are reduced by an order of a magnitude.

Focus on Sensors

Focus on Sensors

Modelling and control of a disk file head-positioning system

This paper overviews servo control technology in the field of motion control for disk file systems. In the hard disk drive (HDD) system, the head must be positioned on the desired track quickly and precisely, and this performance must be robust. Recent required positioning accuracy is about 50 nm (±3σ). To meet these requirements, many servo control methods have been proposed and applied to the system. Major research subjects for fast movement are a reference trajectory design and a track-seeking servo design. In particular, a two-degree-of-freedom (2 DOF) servo control with a multirate sampling period has been developed for the track-seeking servo. Two design methods of 2 DOF feedforward controller are proposed here. While reading/writing data, very precise positioning on a target data track is required. One of the most effective methods for precise positioning under various disturbances is to increase the servo bandwidth. This paper examines the use of loop shaping, state feedback and a dual-stage actuator servo to increase the servo bandwidth with sufficiently robust stability. Feedforward methods to cancel disturbances are also applied under the condition that the disturbances are either detectable or can be estimated, such as repeatable runout error, which is synchronous to disk rotation.

Optimization of feedrate in a face milling operation using a surface roughness model

Optimization of feedrate is valuable in terms of providing high precision and efficient machining. The surface roughness is particularly sensitive to the feedrate and the runout errors of the inserts in a face-milling operation. This paper analyzes the effects of the insert runout errors and the variation of the feedrate on the surface roughness and the dimensional accuracy in a face-milling operation using a surface roughness model. The validity of the developed model was proved through cutting experiments, and the model was used to predict the machined surface roughness from the information of the insert runouts and the cutting parameters. From the estimated surface roughness value, the optimal feedrate that gave a maximum material removal rate under the given surface roughness constraint could be selected by a bisection method.