Showing papers in "Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology in 2013"

Crater and flank wear resistance of cutting tools having micro textured surfaces

Abstract: We have proposed cutting tools with various textured surfaces to increase cutting tool life. Our previous studies have developed cutting tools having periodical stripe-grooved surfaces on their rake face formed using femtosecond laser technology, which displayed high crater wear resistance in cutting of steel materials. In this study, the mechanism for suppressing the crater wear on the tool surface and the relationship between texture dimensions and wear resistance were investigated to provide a guideline for developing tools with textured surfaces. Furthermore, we newly introduced the textured surfaces into a flank face of cutting tools to improve flank wear resistance. Face milling experiments on steel materials exhibited that the newly developed tool having the textured flank face significantly reduced the flank wear. Moreover, the influences of texture dimensions and cutting conditions on the flank wear resistance were also discussed.

Development of a tertiary motion generator for elliptical vibration texturing

Abstract: The elliptical vibration texturing process is an innovative machining method for the fast generation of textured surfaces. It adds a tertiary motion component to the tool tip, which introduces deliberate elliptical vibrations between the cutting tool and the workpiece. The elliptical locus lies in the plane that is defined by the cutting direction and the radial direction in the turning operation. This paper proposes a new design for a resonant mode 2D tertiary motion generator (TMG) that can deliver the required elliptical trajectory at an ultrasonic frequency. The device works in the resonant mode, with tangential and normal vibrations at a nearly identical resonant frequency. Simulation and experiments were carried out to perform a modal analysis of the system. Different design parameters were adjusted to achieve large vibration amplitudes in both tangential and normal directions. The elliptical vibration texturing process was implemented by integrating the newly developed TMG into a turning operation. Preliminary test results of dimple array patterns are presented that validate the performance and principle of the proposed design.

A six-degree-of-freedom surface encoder for precision positioning of a planar motion stage

Abstract: This paper presents a multi-axis surface encoder that can measure six-degree-of-freedom (six-DOF) translational displacement motions and angular motions of a planar motion stage. The six-DOF surface encoder is composed of a planar scale grating and an optical sensor head. A blue laser diode with a wavelength of 405 nm and an output power of 25 mW was employed as the light source of the sensor head. The light rays from the laser diode were collimated to a parallel beam with a diameter of 1.8 mm. The collimated beam was divided by a beam splitter into two beams, which were projected onto the scale grating and a reference grating with an identical grating period of 0.57 μm, respectively. The three-DOF translational displacement motions of the scale grating with respect to the sensor head along the X -, Y - and Z -directions were detected from the interference signals generated by superimposition of the first-order diffraction beams from the two gratings. A part of the zeroth-order and the negative first-order diffraction beams from the scale grating were employed for detection of the three-DOF angular motions about the X -, Y - and Z -axes. The sensor head was designed to have a dimension of 95 mm ( X ) × 90 mm ( Y ) × 25 mm ( Z ) so that it can be mounted on a previously developed planar motion stage. The grating area of the scale grating was designed to be 60 mm ( X ) × 60 mm ( Y ), which was larger than the stage moving ranges of 40 mm ( X ) × 40 mm ( Y ). Experiments were carried out to test the basic performances of the surface encoder.

Investigation of different grain shapes and dressing to predict surface roughness in grinding using kinematic simulations

Abstract: This paper presents a comprehensive study of a computationally efficient kinematic simulation to predict workpiece surface roughness in grinding using three different abrasive grain shapes (sphere, truncated cone, and cone) and a single-point diamond dressing model having both a ductile cutting and brittle fracture component. The resulting predicted workpiece surface roughness was experimentally validated for three different workpiece speeds, three different dressing depths of cut and three different dressing overlap ratios. For the surface grinding and single-point dressing conditions used in this research, the results showed that the dressing parameters used in the simulations supersede the assumed abrasive grain shape in their ability to influence the predicted workpiece surface finish. Furthermore, the corresponding average measured and predicted workpiece surface roughness agreed within approximately 7–11%.

Efficient estimation by FEA of machine tool distortion due to environmental temperature perturbations

Abstract: Machine tools are susceptible to exogenous influences, which mainly derive from varying environmental conditions such as the day and night or seasonal transitions during which large temperature swings can occur. Thermal gradients cause heat to flow through the machine structure and results in non-linear structural deformation whether the machine is in operation or in a static mode. These environmentally stimulated deformations combine with the effects of any internally generated heat and can result in significant error increase if a machine tool is operated for long term regimes. In most engineering industries, environmental testing is often avoided due to the associated extensive machine downtime required to map empirically the thermal relationship and the associated cost to production. This paper presents a novel offline thermal error modelling methodology using finite element analysis (FEA) which significantly reduces the machine downtime required to establish the thermal response. It also describes the strategies required to calibrate the model using efficient on-machine measurement strategies. The technique is to create an FEA model of the machine followed by the application of the proposed methodology in which initial thermal states of the real machine and the simulated machine model are matched. An added benefit is that the method determines the minimum experimental testing time required on a machine; production management is then fully informed of the cost-to-production of establishing this important accuracy parameter. The most significant contribution of this work is presented in a typical case study; thermal model calibration is reduced from a fortnight to a few hours. The validation work has been carried out over a period of over a year to establish robustness to overall seasonal changes and the distinctly different daily changes at varying times of year. Samples of this data are presented that show that the FEA-based method correlated well with the experimental results resulting in the residual errors of less than 12 μm.

Non-contact R-test with laser displacement sensors for error calibration of five-axis machine tools

Abstract: The R-test is an instrument to measure three-dimensional displacement of a precision sphere attached to a spindle relative to a work table by using three displacement sensors. Its application to error calibration for five-axis machine tools has been studied in both academia and industry. For the simplicity in calculating the sphere center displacement, all conventional R-test devices use contact-type displacement sensors with a flat-ended probe. Conventional contact-type R-test may be potentially subject to the influence of the friction or the dynamics of supporting spring in displacement sensors particularly in dynamic measurement. This paper proposes a non-contact R-test with laser displacement sensors. First, a new algorithm is proposed to calculate the three-dimensional displacement of sphere center by using non-contact displacement sensors. The compensation of measurement error of a laser displacement sensor due to the curvature of target sphere is incorporated. Then, the measurement uncertainty of four laser displacement sensors with different measuring principles is experimentally investigated in measuring the geometry of a sphere in order to select the laser displacement sensor most suitable for the application to a non-contact R-test. A prototype non-contact R-test device is developed for the verification of the proposed algorithm for non-contact R-test. Experimental case studies of error calibration of (1) static and (2) dynamic error motions of rotary axes in a five-axis machine tool with the developed non-contact R-test prototype are presented. Its measurement performance is compared to the conventional contact-type R-test device.

Semi-empirical material removal rate distribution model for SiO2 chemical mechanical polishing (CMP) processes

Abstract: Precision Engineering 37 (2013) 483– 490 Contents lists available at SciVerse ScienceDirect Precision Engineering jou rnal h om epage: www.elsevier.com/locate/precision Semi-empirical material removal rate distribution model for SiO 2 chemical mechanical polishing (CMP) processes H.S. Lee a,∗ , H.D. Jeong a , D.A. Dornfeld b a b School of Mechanical Engineering, Pusan National University 30, Jangjeon-dong, Geumjeong-gu, Busan 609-735, Republic of Korea Department of Mechanical Engineering, University of California, Berkeley, CA 94720-1740, USA a r t i c l e i n f o Article history: Received 24 August 2012 Received in revised form 20 December 2012 Accepted 28 December 2012 Available online 10 January 2013 Keywords: Chemical mechanical polishing (CMP) Material removal rate (MRR) MRR distribution Modeling a b s t r a c t A novel semi-empirical model was developed for predicting the material removal rate (MRR) dur- ing chemical mechanical polishing (CMP) based on the following assumptions: plastic contact at the wafer–particle interface, elastic contact at the pad–particle interface, a particle size distribution, and a randomly distributed surface roughness of the polishing pad. The proposed model incorporates the effects of particle size, concentration, and distribution, as well as the slurry flow rate, pad surface topog- raphy, material properties, and chemical reactions during the silicon dioxide (SiO 2 ) CMP. To obtain the unknown parameters and ensure the validity of the model, a SiO 2 CMP experiment was conducted by using various-sized CMP slurries. The spatial distribution of the MRRs is expressed with respect to the normal contact stress distribution and the relative velocity distribution. The proposed MRR model can be used for the development of a CMP simulator, the optimization of CMP process parameters, and the design of next-generation CMP machines. © 2013 Elsevier Inc. All rights reserved. 1. Introduction Chemical mechanical polishing (CMP) is a process of smoothing and planarizing wafer surfaces by using a combination of chemi- cal reactions and mechanical forces [1]. Numerous parameters are involved in the material removal process, such as the type of abra- sive, pressure on the wafer, relative velocity between the polishing pad and the wafer, slurry chemistry, polishing pad, and substrate characteristics [2–5]. The modeling of the material removal rate (MRR) is crucial to understand the complexity of the CMP process, and considerable research efforts have been concentrated on this topic. The fundamentals of silicon dioxide (SiO 2 ) CMP are under- stood via studies of glass polishing. The predominant mechanism responsible for SiO 2 removal is the mechanical abrasion followed by the hydration of the SiO 2 surface in the presence of an alkaline slurry [6,7]. The hydrated layer is rapidly formed on the SiO 2 sur- face by the indentation of the silica particles against the SiO 2 film in the slurry [8]. Early models of CMP were based on glass polishing technol- ogy and the MRR was described by Preston’s equation [9], which indicates that the product of the pressure and the relative velocity between the wafer and the polishing pad contributes significantly toward the MRR. Alternatively, Runnels and Eyman [10] replaced ∗ Corresponding author. Tel.: +82 51 510 3210; fax: +82 51 518 8442. E-mail address: hyunseop.lee@pusan.ac.kr (H.S. Lee). 0141-6359/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.precisioneng.2012.12.006 the applied pressure and the relative velocity with normal and tan- gential stresses at the wafer–pad interface in Preston’s equation. In addition, Liu et al. [11] developed a CMP model based on elas- tic theory and the kinematics of an abrasive particle moving in the gap of a pair of surfaces in rolling contact. Fu et al. [12] assumed that perfect plastic deformation occurred when particles abraded the softer hydrated layer on the SiO 2 surface. Luo and Dornfeld [13] investigated the material removal model under the follow- ing assumptions: plastic contact between the wafer–abrasive and the pad–abrasive interfaces, a periodic roughness of the polishing pad, and a normal distribution of particle size. The synergetic effect of chemical and mechanical forces was represented by a dynamic hardness of the wafer surface. Zhao and Chang [14] proposed a CMP model for silicon wafer based on contact mechanics. In their model, plastic contact at the wafer–particle interface and elastic contact at the particle–pad interface were assumed for calculating the inden- tation depth of the particle in the wafer surface. The line density of uniformly dispersed particles in the slurry and the real contact area between the wafer and the polishing pad were used to calcu- late the number of active particles. Qin et al. [15] took into account the chemical and mechanical interactions involved in a typical CMP process, using the thickness of the thin chemically modified layer and the indentation depth of the particle into the wafer surface to understand the nonlinear behavior of the MRR. Lin [16] described the relationship between the polishing parameters and the MRR with an analytical model on the basis of elastic and elastic–plastic deformations during a polishing process. Jiang et al. [17] modified

Mechanics of the burnishing process

Abstract: Burnishing is a low-cost surface treatment process. However, scientific studies on this process have so far failed to describe how the process leads to surface hardening and improvement in the geometric quality of the material. Indeed, in spite of its apparent simplicity the process is rather complicated to reproduce by numerical simulation. This paper proposes a finite element modelling of the ball burnishing process. Thanks to this model, the effect of the burnishing process on the material is analysed. A ridge phenomenon that affects the mechanics of the process is demonstrated, allowing for improved modelling of the burnishing process.

Spatial statistical analysis and compensation of machining errors for complex surfaces

Abstract: In order to obtain high machining accuracy for free-form surface components, an on-line inspection system with error compensation is proposed in this paper. Once the component is machined, it can be measured by the probe inspection system. Based on these measurement data, a deterministic surface can be established based on a bicubic B-spline surface. Through the spatial statistical analysis of the residual errors of a regression model, the machining errors are decomposed into systematic errors and random errors. For the systematic errors, the numeric control program is modified and the compensation for the machining errors calculated can be conducted without altering the machining benchmarks. Therefore, the combination of the on-line inspection and the compensation of the machining errors is achieved successfully. Experiments were conducted to verify the effectiveness of the proposed methodology.

Mechanism design and process control of micro EDM for drilling spray holes of diesel injector nozzles

Abstract: Machining quality of spray holes directly affects injection performance and combustion efficiency of diesel engines. With the high standards of less emission and fuel economy, the spray holes used in the case of high injection pressure require the characters of small diameter 1 mm, multi-holes >4, micro-taper shape with K-factor 0–2 and multidimensional space position. Mechanical drilling is difficult to meet the machining requirements of the spray holes. Micro electro discharge machining (EDM) has the advantages of less cutting force, without burrs, and even finish machining after heat treatment, so it fits for machining micro holes on metal alloy materials. In this study, a micro EDM equipment was developed for drilling the spray holes. Key technologies were discussed including an electrode feed head, a workpiece positioning mechanism and process control methods. In order to machine micro-taper holes and improve processing efficiency, the electrode feed head was designed with the special multifunction modules of a novel taper-swinging mechanism (TSM), a piezoelectric (PZT) actuator for assisting high-frequency vibration, and a dual-clamps inchworm mechanism for wear compensation of wire tool electrode. The equipment can achieve the spatial positions of pitch angle, roll angle, focal distance, and reference points of nozzles. The particular attention was also given to the proposed process control methods to ensure high consistency accuracy in machining multi-nozzles. In addition, performance tests and applied experiments were carried out. The study results show that the equipment can meet the machining requirements of the spray holes with diameters Φ140–300 μm, taper-angles 0–1.3° (K-factor 0–2.3) with adjustment error

Development of a three-dimensional vibrating tactile probe for miniature CMMs

Abstract: This paper presents the development and characterisation of a vibrating tactile probe for miniature co-ordinate measuring machines. Current probing technology is limited by several factors including the reduced size of the parts to be measured, the use of novel and delicate materials for manufacturing and the need for lower uncertainties of measurement. The solution developed at the National Physical Laboratory (NPL) is a novel, silicon-free triskelion (three-legged) MEMS flexure structure assembled with a sphere-tipped micro-stylus. The mechanical design and modelling of the probe are reported along with a description of the manufacturing routes, assembly solutions developed, operation and metrological characterisation methods. Results from the experimental testing demonstrate that the probe is not affected by snap-in when probing in vertical and lateral directions. Preliminary results from experimental testing also demonstrate that the probe is capable of detecting the effect of the surface interaction forces within 150 nm of the physical surface, suggesting that the probe is capable of operating in a non-contact mode. The performance of the probe has been tested in both the vertical and lateral directions.

Observer-based adaptive sliding mode control for pneumatic servo system

Abstract: In this paper, an extended state observer (ESO) being incorporated with the adaptive sliding mode control theory is proposed to deal with a nonlinear pneumatic servo system characterized with input dead-zone, unknown system function, and external disturbance. The ESO is used to estimate system state variables of the unknown nonlinear system; the adaptive law is employed to compensate for dead-zone system behavior. Positioning experiments based on the derived control strategy were performed. As one example of positioning results, the positioning accuracy with sub-micrometers range was verified for both forward and backward actuations with step commands of 3 mm. The control scheme provided in this paper that can significantly improve the positioning performance of a traditional pneumatic servo system is demonstrated.

Accurate control of ball screw drives using pole-placement vibration damping and a novel trajectory prefilter

Abstract: This paper presents a pole-placement technique to achieve active vibration damping, as well as high bandwidth disturbance rejection and positioning, in ball screw drives. The pole-placement approach is simple and effective, with an intuitive physical interpretation, which makes the tuning process straightforward in comparison to existing controllers which actively compensate for structural vibrations. The tracking performance of the drive is improved through feedforward control using inverted plant dynamics and a novel trajectory prefilter. The prefilter is designed to remove tracking error artifacts correlated to the velocity, acceleration, jerk and snap (fourth derivative) of the commanded trajectory. By applying the least-squares method to the data from a single tracking experiment, the prefilter can be tuned quickly and reliably. The proposed controller has been compared to the P-PI position–velocity cascade controller commonly used in industry. The controller design, stability analysis and experimental results are discussed in the paper.

Microstructuring of carbide metals applying Jet Electrochemical Machining

Abstract: Electrochemical machining (ECM) is a potential procedure for high precision micromanufacturing. Especially the machining of work pieces without any thermal or mechanical impact is a significant feature. Additionally, the electrochemical dissolution behavior of the work piece material is only defined by its electrochemical attributes. Hence, mechanical characteristics such as the material's hardness and the ductility have no influence. This makes ECM an alternative process for mechanically hard to machine materials. In this study, a special procedure for machining microgeometries in carbide metal alloys is investigated, whereat a continuous electrolytic free jet (Jet Electrochemical Machining – Jet-ECM) is applied. The special characteristic of this technology is the restriction of the electric current to a confined area by the jet, which leads to a high localization of the removals. Even complex structures can be machined by the help of continuous direct current. Hence, higher dissolution rates compared to pulsed electrochemical processes can be achieved. In the experiments the machining of step holes and grooves in tungsten carbide alloys is performed. Therefore, point erosions without nozzle movement and linear erosions by single- and multi-axis motions of the tool are conducted. In addition, three-dimensional shaping of the investigated materials is presented by overlapping linear erosions.

Freeform surface filtering using the lifting wavelet transform

Abstract: Texture measurement for simple geometric surfaces is well established. Many surface filtration techniques using Fourier, Gaussian, wavelets, etc., have been proposed over the past decades. These filtration techniques cannot be applied to today's complex freeform surfaces, which have non-Euclidean geometries in nature, without distortion of the results. Introducing the lifting scheme opens the opportunity to extend the wavelet analysis to include irregular complex surface geometries. In this paper, a method of filtering those complex freeform surfaces presented by triangular meshes based on the lifting wavelet has been proposed. The proposed algorithm generalises the traditional lifting scheme to any freeform surface represented by any type of triangular mesh; regular, semi-regular or irregular mesh. This technique consists of five major stages; split, predict, update, simplify (down-sampling) and merge (up-sampling). All of these techniques are discussed and explained in the paper. Results and discussion of the application of this method to simulated and measured data are presented.

Large deflection stiffness analysis of parallel prismatic leaf-spring flexures taking into account shearing, constrained warping and anticlastic curving effects

Abstract: The support stiffness of a parallel leaf-spring flexure should ideally be high, but deteriorates with increasing displacement. This significant characteristic needs to be quantified precisely, because it limits the use of parallel leaf-spring flexures in precision mechanisms. We present new and refined analytic formulas for the stiffness in three dimensions taking into account shear compliance, constrained warping and limited parallel external drive stiffness. The formulas are supplemented by a finite element analysis using shell elements to include anticlastic curving effects. Several approximation equations are presented for determining the drive force precisely. Even at relatively large deflections the derived formulas are in good agreement with the finite element results

Influences of vibration on surface formation in rotary ultrasonic machining of glass BK7

Abstract: This paper presented a fundamental investigation of the surface formation mechanisms involved in rotary ultrasonic machining (RUM) of glass BK7 process. Comparative observations of the scratches, generated in the scratching tests with and without ultrasonic, were performed using optical microscopy, white-light interferometer, and scanning electron microscopy (SEM). Giving consideration to the scratch morphologies and the abrasive process kinematics, the mechanisms of surface formation provoked by the ultrasonic superposition were investigated. Additionally, the formal machining tests with and without ultrasonic were also conducted to validate these surface formation mechanisms. As a result, a nondimensional parameter K was proposed to quantitatively describe the ultrasonic effects of the abrasives as well as to correlate these effects with the machining conditions. Due to the periodic variation in the effective work angle of the abrasive, the material accumulated slightly at the RUM groove entrance, whereas serious material accumulation appeared at the exit. The stress imbalance on the specimen surface induced by the dramatic fluctuation of the abrasive inertia load caused plenty of tortuous cracks in 0.2 μm-sized length emerge on the RUM grooves generated in the ductile material removal stage. A novel theoretical model of the surface formation mechanisms involved in formal RUM process was established by incorporating the ultrasonic effects, such as the lower dynamic fracture toughness of material, cyclical variation in the effective work angle of the abrasive, and the larger abrasive inertia force. Experimental results obtained in formal machining tests revealed that superimposing an ultrasonic vibration could distinctly reduce the cutting force of the diamond tool without seriously worsening the surface quality of the specimens.

Adaptive inspection in coordinate metrology based on kriging models

Abstract: The paper describes a model-based statistical methodology to design adaptive inspection plans for the geometric control of mechanical parts with Coordinate Measuring Machines (CMM). The inspection is adaptive because the design and measurement phases are not separate in time, as they usually are. Rather, they are carried out in a combined way: first designing the next measurement location, then measuring at that location and so on. This strategy is most informative as it allows for the exploitation of all of the currently available measurements. The next measurement point is selected by using predictions and prediction uncertainty of geometric deviations provided by non-parametric statistical models, known as kriging models. Based on stationary Gaussian stochastic processes, their merit is the ability to vary flexibly at each added point. The methodology is demonstrated in an illustrative case study, then its performance is compared to that of two statistical non adaptive plans, and two deterministic adaptive plans proposed in the literature. In each comparison kriging-based plans have proved to be superior in terms of the accuracy of the predicted geometric error and the inspection cost. The method is sufficiently general to enable technology transfer to different metrological sectors.

Surface finishing of intricate metal mould structures by large-area electron beam irradiation

Abstract: The advancement of polymer moulding tools is increasingly focused on imparting not only form but also surface texture for functionality to the surfaces of parts that are created. Furthermore, the increasing demand for inexpensive and higher quality micro-components means that tools for replication processes must take advantage of advanced manufacturing techniques. Tools created by processes such as micro-investment casting, as in this case, may often suffer from excessive surface roughness, malformed edges and general deformation. This results in higher de-moulding forces and a reduction in fidelity of moulded parts to design intent. In this study, large-area electron beam irradiation (EB) is shown to be an effective technique for improving these metrics. For the first time, large population, high aspect ratio micro-features are subject to this process and the mechanisms of smoothing and key enhancement phenomena are demonstrated. The possibility of including EB irradiation in an integrated process chain for arriving at net shape is also discussed. Surfaces of protruding features are shown to have surface roughness reduced significantly from 126 to 22 nm Ra value, with bottom substrate also similarly improving from 150 to 27 nm Ra. Bottoms of recessed features are also observed to have much improved surface finishes. ‘Doming’ of tops of column features is also demonstrated, further enhancing form. These features would be far too fragile to be polished by any other mechanical method.

Analysis and design of a cartwheel-type flexure hinge

Abstract: This paper presents an analytic model of cartwheel flexure. 6-DOF (degrees of freedom) stiffness equations for cartwheel flexure are derived and verified by comparing the model's predictions with FEM (finite element method) simulations and experiments. The model prediction accuracy relative to FEM simulations is found to be satisfactory, with errors of less than 10%. The deviation of the model's prediction from the experiments’ results is slightly higher because of body deformations and manufacturing errors. The effects of manufacturing errors on the model accuracy are analyzed, with the results indicating that the first mode is greatly affected by the manufacturing errors, while the thickness variation of the cartwheel flexure hinge has the largest effect on the model prediction accuracy. The cartwheel flexure hinge is evaluated in terms of the motion range, stiffness and stiffness ratio and compared with the conventional right circular hinge to confirm the appropriateness of the cartwheel flexure hinge as a large displacement flexure joint. Finally, an example of cartwheel flexure design is presented to show that the analytic stiffness model can provide a set of optimized design parameters in less time than FEM simulations.

Closed-form compliance equations for power-function-shaped flexure hinge based on unit-load method

Abstract: A new type of flexure hinge, called power-function-shaped flexure hinge, is presented in this paper. Based on the unit-load method, the closed-form compliance equations of the flexure hinge are derived, and the motion accuracy is investigated. These equations are verified through finite element analysis, which shows that the maximum error is less than 15%. Based on the compliance equations, numerical simulations are conducted to discuss the performance of the flexure hinge. The results indicate that, the stiffness of the power-function-shaped flexure hinge decreases as r increases, increases as β increases, and increases as t increases; the displacement along axis y is the dominant parasitic motion; and based on the same l , h and b , the power-function-shaped flexure hinge can rotate more accurately than circular flexure hinge with the same β and V-shaped flexure hinge with the same β and r . The equations obtained can be utilized to design the power-function-shaped flexure hinges, and can achieve higher motion accuracy than the commonly used circular flexure hinge and V-shaped flexure hinge.

A new method for measuring a large set of poses with a single telescoping ballbar

Abstract: This paper presents a novel method of measuring a set of more than fifty poses under static conditions, using a single telescoping ballbar and two fixtures, each bearing three equally spaced magnetic cups. The position accuracy of the device is in the ±0.003 mm range, making it suitable for measuring the pose accuracy and repeatability of industrial robots and even calibrating them. The proposed method is an extension of a known approach using a hexapod (a Stewart-Gough platform) comprising telescoping ballbar legs and provides an original solution to the constraint imposed by the limited measurement range of current telescoping ballbars, namely an innovative hexapod geometry capable of assembly in 144 different configurations. An additional advantage of the method is that the pose of one fixture with respect to the other can be obtained for each of these configurations by solving a cascade of three quadratic equations using the six hexapod leg lengths as input. The application of the device and method to measuring numerous poses of an ABB IRB 120 industrial robot is presented.

The response of the high strength Ti-10V-2Fe-3Al beta titanium alloy to laser assisted cutting

Abstract: Metal cutting is a process that uses tools to create new surfaces by imparting intense shear stresses and high strain rates on the work material. Consequently, the mechanical properties of the work material directly influence its machinability, and high strength materials such as titanium are notoriously difficult to cut. Laser assisted machining (LAM) is a promising solution to reduce the cutting pressures when machining difficult-to-cut materials. The method involves using a laser beam to locally heat and reduce the flow stress of the material ahead of an advancing cutting tool, making the metal shearing process easier. To date there is limited, if any, published literature on using the technology to improve the machinability of metastable β-titanium alloys. It remains unclear whether these materials will respond to laser assisted machining since many are specifically designed to exhibit high temperature strength. This paper compares the conventional and laser assisted machining method for the high strength Ti–10V–2Fe–3Al β-titanium alloy over a wide range of cutting parameters. The effect of the laser beam on the cutting force, cutting temperature and chip formation is discussed. The effectiveness of the LAM process in reducing the cutting pressure of Ti–10V–2Fe–3Al alloy is also compared against other alloys including commercial-purity titanium and Ti–6Al–4V.

Development of micro polishing system using a magnetostrictive vibrating polisher

Abstract: Recently, micro-optical lenses are highly required in new fields such as Fresnel lenses for solar panels and Wafer Level Cameras (WLC). The lenses are generally molded by micro ceramic molds. In this paper, a novel vibration-assisted polishing (VAP) method by using a magnetostrictive vibrating polisher is proposed to improve the efficiency and stability of micro-optical mold polishing. The magnetostrictive vibrating polisher is composed of a vibrator and a small polishing tool. The small polishing tool is screwed into the head of the vibrator. The vibrating polisher is fixed on a 5-axis ( X , Y , Z , B , C ) controlled table via a balancing adjustment mechanism. The vibration characteristics are evaluated and the polisher vibrates in a lateral motion at frequency of 9.2 kHz with amplitude of 30 μm. The polishing force is controllable within a range of 2–200 mN with a resolution of 2 mN by the balancing adjustment mechanism. Some fundamental polishing experiments are conducted by using molds made of binderless tungsten carbide; the shape of removal function is acquired and surface roughness is improved from 30 nm Rz (4 nm Ra) to 10 nm Rz (2 nm Ra).

Influence of measurement noise and laser arrangement on measurement uncertainty of laser tracker multilateration in machine tool volumetric verification

Abstract: This paper aims to present different techniques and factors that affect the measurement accuracy of a commercial laser tracker responsible for capturing checkpoints used in machine tool volumetric verification. This study was conducted to uncover various sources of error affecting the measurement uncertainty of the laser tracker, additional sources of error that further contributed to the uncertainty, and the factors influencing these techniques. We also define several noise reduction techniques for the measurements. The improvement in the accuracy of captured points focuses on a multilateration technique and its various resolution methods both analytically and geometrically. Similarly, we present trilateration and least squares techniques that can be used for laser tracker self-calibration, which is an essential parameter in multilateration. This paper presents the influence of the spatial distribution of laser trackers (LTs) in measurement noise reduction by multilateration, which produces an improvement in volumetric error machine tool reduction. A study of the spatial angle between LTs, the distance and the visibility of the point to be measured are presented using a synthetic test. All of these factors limit the scope of multilateration. Similarly, a comparison of self-calibration techniques using the least squares and trilateration methods with which to determine the relative position of the laser tracker employees is presented. We also present the influence of the relationship between the radial and angular measurement noise self-calibration processes as it relates to the volumetric error reduction achieved by the machine tool with multilateration. All studies were performed using synthetic tests generated using a synthetic data parametric generator.

Sensitivity analysis of nanoparticles pushing manipulation by AFM in a robust controlled process

Abstract: This paper investigates the sensitivity of nanoparticle parameters in a robust controlled process, by a compatible nanomanipulation model consisting of all effective phenomena in nanoscale. The dynamic model of nanoparticle displacement utilizes the Lund–Grenoble (LuGre) friction model, since it demonstrates pre-slip displacement, friction delay, various forces of failure and the stick-slip movement, with respect to other presented models. Also, the interaction force between nanoparticle and AFM cantilever tip are modeled by using the Derjaguin model. Sliding mode control (SMC) approach is used to provide the desired substrate motion trajectory, despite the challenges in the piezoelectric substrate motion control, consisting of thermal drift, hysteresis, and other uncertainties. In this paper, the dynamic model of nanoparticle manipulation is expressed to determine the nanoparticle behavior for substrate movement with desired trajectory and the effect of pre-process selections of the result of the manipulation. Depending on obtained diagrams for parameters sensitivity, the prediction of manipulation result is more precise, and also this is effective on choosing of proper initial condition and parameter selection in pushing purposes. Finally, it can be used to adjust proper pushing time and input for an accurate and successful pushing and assembly. It also provides a real-time visualization during micro/nanomanipulation and increases complexity of the resulting created structures.

Minimization of the residual vibrations of ultra-precision manufacturing machines via optimal placement of vibration isolators

Abstract: Ultra-precision manufacturing (UPM) machines are used to fabricate and measure complex parts having micrometer-level features and nanometer-level tolerances/surface finishes. Consequently, low-frequency residual vibrations that occur during the motion of the machines’ axes must be mitigated. A long-standing rule of thumb in vibration isolation system design is to locate the isolators in such a way that all vibration modes are decoupled. This paper uses the 2D dynamics of a passively isolated system to show that coupling the vibration modes of the isolated system by altering the location of the isolators provides conditions which allow for the drastic reduction of residual vibrations. An objective function which minimizes residual vibration energy is defined. Perturbation analyses of the objective function reveal that the recommended practice of decoupling the vibration modes more often than not leads to sub-optimal results in terms of residual vibration reduction. The analyses also provide guidelines for correctly locating the isolators so as to reduce residual vibrations. Simulations and experiments conducted on a passively isolated ultra-precision machine tool are used to validate the findings of the paper; a 5-fold reduction of the dominant residual vibrations of the machine tool is achieved without sacrificing vibration isolation quality (i.e., transmissibility).

Kinematic modeling and calibration of a flexure based hexapod nanopositioner

Abstract: This paper covers the kinematic modeling of a flexure-based, hexapod nanopositioner and a new method of calibration for this type of nanopositioner. This six degrees of freedom tri-stage nanopositioner can generate small displacement, high-resolution motions with high accuracy by actuating three inexpensive, high quality planar stages. Each stage is equipped with linear actuators. In this paper, we discuss the calibration of the nanopositioner and methods to improve its accuracy. First, we derive the kinematic model of the nanopositioner that is a Stewart platform with spherical joints. Based on this kinematic model, we then calculate the actuation data for a set of commands for decoupled and coupled motions. We use an interferometer and an autocollimator to measure the actual displacement and rotation of the platform. Finally, we obtain the Jacobian matrix of the moving platform for the controller. Experiments showed that with the calibration-corrected parameters, the maximum error is approximately 0.002° in rotations and 3.3 μm in translation for a workspace of ± 0.2° and ±200 μm in x, y and z direction.

Fabrication of large-size SiC mirror with precision aspheric profile for artificial satellite

Abstract: This paper presents an on-machine surface profile measurement system for a large mirror to be used on artificial satellites. The measurement system is constructed by mounting a long-stroke length gauge on a commercial rotary grinder for fabrications of mirror profiles. Mounting the length gauge on slides of the rotary grinder enables evaluations of the mirror profiles, which results would be used to compensate profile errors of the mirrors. In the developed system, both positioning errors and tilt misalignments of the length gauge would induce significant measurement errors. In this study, a quantitative alignment method and a compensation method are therefore developed to reduce the measurement errors related to both the positioning errors and tilt misalignments of the length gauge. In addition, a measurement uncertainty of the developed system has been systematically investigated to confirm its feasibility on the mirror profile measurements. The measured results were finally fed back to the mirror profile fabrication so that the profile error could be reduced to less than 5 μm. Mirror profiles measured on machine before and after compensation machining are also reported.

Customized cutting edge preparation by means of grinding

Abstract: Due to their low load resistance, sharp ground cutting edges are generally considered disadvantageous to high performance cutting processes. Consequently, providing additional cutting edge preparation in order to enhance tool-lifetime and – performance has become increasingly important. In this context, the following paper presents a novel method for generating customized cutting edges by means of grinding. An approximation of general round edges by applying several chamfers has been proposed and a geometric model for designing these special edges has been suggested. Grinding tests have been carried out to verify the reliability of the new method. The relative errors caused by the limited precision of the machine tool have also been taken into account. Furthermore, an improvement of the edge quality based on the implementation of the micro geometry has been demonstrated.