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Showing papers in "Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology in 2009"


Journal ArticleDOI
TL;DR: In this paper, the effect of the texture shape on the machinability of an aluminum alloy was investigated with a turning experiment applying the minimum quantity lubrication method, and the texture decreased the cutting force due to the corresponding reduction in the friction on the rake face.
Abstract: We developed novel cutting tools that had either microscale or nanoscale textures on their surfaces. Texturing microscale or nanoscale features on a solid surface allowed us to control the tribological characteristics of the tool. The textures, which had pitches and depths ranging from several hundreds of nanometers to several tens of micrometers, were fabricated utilizing the ablation and interference phenomena of a femtosecond laser. The effect of the texture shape on the machinability of an aluminum alloy was investigated with a turning experiment applying the minimum quantity lubrication method. The texture decreased the cutting force due to the corresponding reduction in the friction on the rake face. This effect strongly depended on the direction of the texture; lower cutting forces were achieved when the texture was perpendicular to the chip flow direction rather than parallel. This effect was only observed at high cutting speeds over 420 m/min. These results indicate that the developed tools effectively improved the machinability of the alloy.

360 citations


Journal ArticleDOI
TL;DR: In this paper, the size effect in micromilling hardened tool steel was observed by studying the effect of the ratio of undeformed chip thickness to the cutting edge radius on process performance, and how this ratio drove the specific cutting force, surface finish and burr formation in micro-scale machining.
Abstract: The market for freeform and high quality microdies and moulds made of steel is predicted to experience a phenomenal growth in line with the demand for microsystems. However, micromachining of hardened steel is a challenge due to unpredictable tool life and likely differences in process mechanism compared to macro-scale machining. This paper presents an investigation of the size effect in micromilling of H13 hardened tool steel. In this case, the size effect in micromilling hardened tool steel was observed by studying the effect of the ratio of undeformed chip thickness to the cutting edge radius on process performance. The paper explores how this ratio drives the specific cutting force, surface finish and burr formation in micro-scale machining. In addition, the effect of different microend mill geometry on product quality was explored. The paper provides a valuable insight into optimum micro-scale machining conditions for obtaining the best surface finish and minimizing burr size.

306 citations


Journal ArticleDOI
TL;DR: In this paper, a single crystalline silicon was plunge-cut using diamond tools at a low speed, and cross-sectional transmission electron microscopy and laser micro-Raman spectroscopy were used to examine the subsurface structure of the machined sample.
Abstract: Single crystalline silicon was plunge-cut using diamond tools at a low speed. Cross-sectional transmission electron microscopy and laser micro-Raman spectroscopy were used to examine the subsurface structure of the machined sample. The results showed that the thickness of the machining-induced amorphous layer strongly depends on the tool rake angle and depth of cut, and fluctuates synchronously with surface waviness. Dislocation activity was observed below the amorphous layers in all instances, where the dislocation density depended on the cutting conditions. The machining pressure was estimated from the micro-cutting forces, and a subsurface damage model was proposed by considering the phase transformation and dislocation behavior of silicon under high-pressure conditions.

198 citations


Journal ArticleDOI
TL;DR: In this article, a literature review of the existing flexible fluidic actuators is established, which can serve as basis to develop flexible instruments based on these actuators, and the advantages and drawbacks linked to the use of flexible actuators are listed.
Abstract: Flexible instruments, i.e. instruments presenting a great number of degrees of freedom and able to perform snake-like movements when avoiding obstacles, can find a lot of applications in the medical field. On the other hand, flexible fluidic actuators, i.e. actuators having a flexible inflatable structure and actuated by fluid, present interesting features regarding medical applications. Therefore, this paper proposes to use these actuators to develop medical flexible instruments. Firstly, the advantages and drawbacks linked to the use of flexible fluidic actuators are listed and a discussion about the miniaturization of fluidic actuators peripherics (such as valves) is led. Next, a literature review of the existing flexible fluidic actuators is established. It can serve as basis to develop flexible instruments based on these actuators.

182 citations


Journal ArticleDOI
TL;DR: In this article, a cutting tool with a nano/micro-textured surface utilizing femto-second laser technology was proposed in order to improve the anti-adhesive effect of aluminum alloys.
Abstract: Demand for lightweight aluminum-based composites is rapidly increasing in the transport industry. Generally it is considered that aluminum alloys are easy-to-cut materials due to their low hardness. However, it is noted that some serious problems exist. Because of low lubricity against the cutting tool surface during deep-hole drilling, milling, and tapping, aluminum chips may adhere strongly to the cutting edge of the tool, leading to tool breakage. To solve this problem, a cutting tool with a nano/micro-textured surface utilizing femto-second laser technology was proposed in our previous research. A series of face-milling experiments for aluminum alloy showed that a nano/micro-textured surface promoted anti-adhesive effects at the tool–chip interface, although adhesion remained a problem. In this study, the ways to improve the anti-adhesive effect with nano/micro-textures were studied. Based on this, a cutting tool with a banded nano/micro-textured surface was newly developed and it was revealed that the surface significantly improved the anti-adhesiveness and lubricity.

176 citations


Journal ArticleDOI
TL;DR: In this article, a high performance piezoelectric actuator is used to drive a flexure-based mechanism for ultra-precision turning operation, where a parallel flexure hinge mechanism is utilized to guide the moving platform and to preload the piezel actuator.
Abstract: This paper presents the methodology for modeling and control of a high precision flexure-based mechanism for ultra-precision turning operation. A high performance piezoelectric actuator is used to driven the flexure-based mechanism. A parallel flexure hinge mechanism is utilized to guide the moving platform and to preload the piezoelectric actuator. A high resolution capacitive sensor is used to measure the displacement of the flexure-based mechanism for closed-loop control. With consideration of the driving circuit, the dynamic model of the flexure-based mechanism has been established. The effect of the driving circuit on the dynamic response of the precision mechanism is investigated. Experimental tests have been carried out to verify the established model and the performance of the flexure-based mechanism.

164 citations


Journal ArticleDOI
TL;DR: In this article, the effects of the electrolyte, the pulse on/off-time ratio, the voltage, the feedrate, the rotational speed, and the electrolytes concentration in the drilling and milling processes were studied to minimize structures and obtain good surface microstructures.
Abstract: Micro-electrochemical discharge machining (ECDM) was studied in order to improve the machining of 3D micro-structures of glass. To minimize structures and obtain good surface microstructures, the effects of the electrolyte, the pulse on/off-time ratio, the voltage, the feedrate, the rotational speed, and the electrolyte concentration in the drilling and milling processes were studied.In ECDM, voltage is applied to generate a gas film and sparks on a tool electrode; however, high voltage produces poor machining resolution. To obtain a stable gas film over the whole surface of the tool at a low voltage, a new mechanical contact detector, based on a loadcell, was used; the immersion depth of the tool electrode in the electrolyte was reduced as much as possible. In this study, various micro-structures less than 100 μm in size, such as O 60 μm micro-holes, a 10 μm-thin wall, and a 3D micro-structure were fabricated to demonstrate the potential for micro-machining of glass by ECDM.

152 citations


Journal ArticleDOI
TL;DR: In this article, a simulator of machining geometric errors in five-axis machining by considering the effect of kinematic errors on the three-dimensional interference of the tool and the workpiece is presented.
Abstract: Kinematic errors due to geometric inaccuracies in five-axis machining centers cause deviations in tool positions and orientation from commanded values, which consequently affect geometric accuracy of the machined surface. As is well known in the machine tool industry, machining of a cone frustum as specified in NAS979 standard is a widely accepted final performance test for five-axis machining centers. A critical issue with this machining test is, however, that the influence of the machine's error sources on the geometric accuracy of the machined cone frustum is not fully understood by machine tool builders and thus it is difficult to find causes of machining errors. To address this issue, this paper presents a simulator of machining geometric errors in five-axis machining by considering the effect of kinematic errors on the three-dimensional interference of the tool and the workpiece. Kinematic errors of a five-axis machining center with tilting rotary table type are first identified by a DBB method. Using an error model of the machining center with identified kinematic errors and considering location and geometry of the workpiece, machining geometric error with respect to the nominal geometry of the workpiece is predicted and evaluated. In an aim to improve geometric accuracy of the machined surface, an error compensation for tool position and orientation is also presented. Finally, as an example, the machining of a cone frustum by using a straight end mill, as described in the standard NAS979, is considered in case studies to experimentally verify the prediction and the compensation of machining geometric errors in five-axis machining.

152 citations


Journal ArticleDOI
TL;DR: In this article, the design and development of a high precision microgripper for micromanipulation is presented, which is based on a hybrid flexure-based compliant mechanism and a bias spring structure which render high fidelity and inherent mechanical advantages.
Abstract: This paper presents the design and development of a high precision microgripper for micromanipulation. The design is based on a hybrid flexure-based compliant mechanism and a bias spring structure which render high fidelity and inherent mechanical advantages. Finite element analysis (FEA) was conducted to evaluate responses of the model under specified load and displacement to investigate optimum design of the model. The prototype of the proposed microgripper was fabricated using electro-discharge machining (EDM) process. An experimental study of the performance was carried out and the results are presented. The experimental results are also compared with the computational analysis results. The results show that a high level of displacement amplification and a maximum stroke of 100 μm can be achieved.

118 citations


Journal ArticleDOI
B. Bringmann1, Wolfgang Knapp1
TL;DR: In this paper, the problem of error interdependencies leading to a worse test uncertainty is explained, and a method for estimating the overall test uncertainty even for complex measurements is introduced.
Abstract: In order to show a sufficient geometric performance, every machine tool has to be calibrated geometrically before it may come into operation. The geometric machine errors have to be identified. They can afterwards be compensated either mechanically or numerically in the machine control. Machine tools are usually calibrated geometrically by performing a sequence of different measurements to identify single errors such as squareness errors between linear axes, straightness errors, positioning errors etc. The uncertainty of such measurements is of course affected by the uncertainty of the measuring device under the given environmental conditions. Methods to describe such influences are widely known and applied. Other effects having an impact on the error parameters to be determined (e.g. squareness errors) are dependent on the performance of the machine tool under test. Neglected geometric errors, hysteresis and thermal drift affect the measurement result. Such effects may be much more important contributors to the overall test uncertainty than the measurement uncertainty of the measuring device. In this paper the problem of error interdependencies leading to a worse test uncertainty is explained. The occurrence of such effects is shown with exemplary measuring results. A method for estimating the overall test uncertainty even for complex measurements is introduced. The dependence of the test uncertainty on the geometric machine performance is explained.

92 citations


Journal ArticleDOI
TL;DR: In this article, a two-step pressing process is proposed according to the non-linear thermal expansion characteristics of glass, where the temperature dependence of specific heat and thermal conductivity of glass is considered.
Abstract: Glass molding is as an effective approach to produce precision micro optical elements with complex shapes at high production efficiency. Since glass is deformed at a high temperature where the mechanical and optical properties depend strongly on temperature, modeling the heat transfer and high-temperature deformation behavior of glass is an important issue. In this paper, a two-step pressing process is proposed according to the non-linear thermal expansion characteristics of glass. Heat transfer phenomenon was modeled by considering the temperature dependence of specific heat and thermal conductivity of glass. Viscosity of glass near the softening point was measured by uniaxially pressing cylindrical glass preforms between a pair of flat molds using an ultraprecision glass molding machine. Based on the numerical models and experimentally measured glass property, thermo-mechanical finite element method simulation of temperature rise during heating and material flow during pressing was carried out. The minimum heating time and pressing load changes were successfully predicted.

Journal ArticleDOI
TL;DR: In this paper, a long-range, precision fast tool servo (FTS) system was developed that is capable of accurately translating the cutting tool on a diamond turning machine (DTM) with maximum accelerations of 260m−s−2 and bandwidths of up to 140Hz.
Abstract: A long-range, precision fast tool servo (FTS) system was developed that is capable of accurately translating the cutting tool on a diamond turning machine (DTM) with maximum accelerations of 260 m s−2 and bandwidths of up to 140 Hz. The maximum displacement range of the cutting tool is 2 mm. The FTS utilizes a flexure mechanism driven by a voice coil actuator, a custom linear current amplifier and a laser interferometer feedback system. This paper describes the design of the electromechanical system, controller configuration and cutting tests to evaluate the system. Initially, low disturbance rejection and poor command following degraded the surface finish of machined test parts. Several techniques to add damping to the dynamic system were investigated to improve the generated surface finishes. Electromotive damping was applied inside the voice coil actuator, and two different viscoelastic damping materials were applied to the flexure mechanism. A control strategy consisting of linear and non-linear feedforward controllers and a proportional, integral and derivative (PID) feedback controller was implemented to accommodate the changed system dynamics. The workpieces were analyzed using form and surface inspection instruments to evaluate the overall system performance. A cylindrical part with five lobes cut across the face had a surface finish value between 20 and 30 nm Ra.

Journal ArticleDOI
TL;DR: In this paper, an overview of the methods used to model the dynamic characteristics of aerostatic films, deducing that the method of harmonic perturbation is often sufficient in providing a good estimate of the dynamic stiffness.
Abstract: Determination of the static characteristics of air bearings constitutes the necessary first phase in a design problem, which determines general feasibility. In order to realize a successful application, a good knowledge and assessment of the dynamic behaviour is needed to complement the previous step. In a conventional, passive bearing application, dynamically stable behaviour should be ensured by overcoming the occurrence of self-excited vibrations; the so-called “pneumatic hammering”. In active bearing applications, on the other hand, the dynamic bearing force, induced by actuation of the gap geometry or supply pressure, provides for a means of enhancing bearing static and dynamic performance, when integrated in a mechatronics system context. This paper presents on the one hand an overview of the methods used to model the dynamic characteristics of aerostatic films, deducing that the method of harmonic perturbation is often sufficient in providing a good estimate of the dynamic stiffness. This is confirmed by comparing theoretical results with dynamic response experiments. On the other hand, the general problem of active dynamic compensation is outlined and an application example is provided to show the high levels of performance achievable by employing this method.

Journal ArticleDOI
TL;DR: In this article, the forward kinematics of a five-bar compliant micro-manipulator with piezoelectric actuators are presented. And the velocity of the end-effector is obtained by differentiating the forward position kinematic equation, and the local mobility index of the five bar compliant mechanism is determined and analyzed.
Abstract: This paper presents the forward kinematics of a five-bar compliant micro-manipulator. To overcome the limited displacement of such a flexure-based mechanism driven by piezoelectric actuators, lever mechanisms are utilized to enlarge the working range. The mechanical design of the micro-manipulator is firstly described. Mathematical formulations for the five-bar mechanism are described and the solutions are developed to decide the end-effector position in Cartesian space. The amplification factor of the lever mechanism is also derived based on the analytical solution of the four-bar linkages. The velocity of the end-effector is obtained by differentiating the forward position kinematic equation, and the local mobility index of the five-bar compliant mechanism is determined and analysed. Based on linearization of trigonometric functions and constant Jacobian matrix, numerical simulations are carried out to investigate the performance of the five-bar compliant manipulator and to determine the optimal geometric parameters for the configuration. The comparisons between the exact solution and simplified methodologies are conducted. Experiments are carried out to validate the established model and the performance of the developed micro-manipulator.

Journal ArticleDOI
TL;DR: In this article, a two-dimensional finite element method (FEM) was used to analyze the electromagnetic field taking into account electromagnetic induction, assuming that trapezoidal pulse current is supplied to the wire, distributions of the current density and magnetic flux density were analyzed.
Abstract: This paper clarifies the mechanism of how electromagnetic force applied to the wire electrode in wire electrical discharge machining (wire-EDM) is generated. This electromagnetic force is caused not only by DC component but also by AC components of the discharge current supplied to the wire. We therefore developed and used a two-dimensional finite element method (FEM) program to analyze the electromagnetic field taking into account electromagnetic induction. Assuming that trapezoidal pulse current is supplied to the wire, distributions of the current density and magnetic flux density were analyzed and changes in the electromagnetic force applied to the wire were calculated. Wire movement when the electromagnetic force alone was applied to the wire was also calculated. The calculated wire movement agreed with the measured wire movement when pulse current actually used in WEDM was supplied to the wire, clarifying the mechanism of electromagnetic force generation.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the mechanism of UHMWPE wear and proved that scratch marks caused by a sliding motion against the metal surface are the prime cause of wear.
Abstract: The effective life of artificial joints is approximately 15 years. A smooth metal sliding surface is presumably the most suitable when manufacturing artificial joints; however, the relationship between the characteristics of metal sliding surface and ultra high molecular polyethylene (UHMWPE) wear has not been confirmed. Further, there is no apparent proof that a smooth surface is the optimal option for the improvement in the wear resistance of artificial joints. In this study, we investigated the mechanism of UHMWPE wear and proved that scratch marks caused by a sliding motion against the metal surface are the prime cause of UHMWPE wear. Furthermore, we used a micro-dimpled surface as an effective sliding surface to reduce the UHMWPE wear. A 2-axes pin-on-plate sliding test proved that the life of artificial joints can be extended to approximately 35 years by using a micro-dimpled surface with 1-μm deep dimples.

Journal ArticleDOI
TL;DR: In this article, two new equations for torsional compliance of rectangular cross-section beams are proposed, which are thickness-to-width ratio independent, and suitable for variable cross-sections beams and optimization design of compliant mechanisms.
Abstract: Several approaches exist for calculating the torsional compliance of rectangular cross-section beams, but most depend on the relative magnitude of the cross-section thickness and width, which might be changing during the design phase (especially for design optimization) or is variant for variable cross-section beams such as circular flexure hinges and tapered bars. After summarizing current equations and analyzing their computational accuracy, two new equations are proposed, which are thickness-to-width ratio independent, and suitable for variable cross-section beams and optimization design of torsional elements in compliant mechanisms. The closed-form equations for the torsional compliance of elliptical and circular flexure hinges are derived by using the new equations.

Journal ArticleDOI
TL;DR: In this article, a dual-stage XY table driven by the permanent magnet synchronous motor (PMSM) and the piezoelectric actuator (PA) is identified.
Abstract: The purpose of this study is to develop a micro/nano-meter XY precision positioning table, in which the coarse and fine positionings are performed by the permanent magnet synchronous motor (PMSM) and piezoelectric actuator (PA), respectively. The main contribution is to identify the XY table driven by the PM and PA, where the Bouc-Wen hysteresis phenomenon of the PA and cross-coupling effects between the X and Y axes are included. In system identification, the real-coded genetic algorithm (RGA) method is employed to find the optimized parameters, where the parameter identification is divided into the individual and integral identifications, and their numerical simulations and experimental results are compared. In conclusion, the dual-stage XY precision positioning table driven by the PM and the PA including the cross-coupling and hysteresis phenomenon can be successfully identified, and it is found that the identified parameters by the integral identification are better.

Journal ArticleDOI
TL;DR: In this paper, an empirical correction model for thermal errors is presented, which is based on the empirical arm positioning error characterization of several temperatures inside its measuring range and by posterior corrections implemented using an average error approximation.
Abstract: The influence of thermal changes in the accuracy of articulated arm coordinate measuring machines (AACMMs) is one of their main error sources. Usually, the effects of this problem are minimized by using low thermal-expansion materials in the arm design or by implementing an empirical error correction model based on the outputs of several temperature sensors placed inside the arm. These models, inherited from temperature correction models for robot arms, are based on the empirical arm positioning error characterization of several temperatures inside its measuring range and by posterior corrections implemented using an average error approximation. Considering this approximation as a correction valid for all the temperature range violates the AACMM calibration conditions, which are defined by a kinematic parameter identification procedure at 20 °C. This implies that, by applying these models, the AACMM will work outside of calibration conditions and will not meet the nominal accuracy values obtained from the identification procedure. In this work a new empirical correction model for thermal errors is presented. This model keeps the calibration conditions established in the parameters identification procedure unaltered. This fact makes it possible to apply other correction models for geometric and non-geometric errors obtained at the calibration temperature after having applied the temperature correction. The algorithm and objective functions used, which are based on a new approach including terms regarding measurement accuracy and repeatability and using the measurements of a ball-beam gauge artifact are shown. The empirical correction model and the arm accuracy and repeatability results before and after correction are also explained, showing an important accuracy improvement in the arm performance for typical arm operation at temperatures different from 20 °C.

Journal ArticleDOI
TL;DR: In this article, a spectral-Tchebychev model of the Timoshenko beam equation was used to obtain a completely parameterized solution of the tool-tip dynamics for arbitrary tool-and-holder combinations.
Abstract: In addition to the precise kinematic motions of the machine tools and spindles, machining accurate parts necessitates controlling the dynamic behavior of the tool tip with respect to the workpiece. High-fidelity models of tool-tip dynamics can be used to select operating parameters that improve the accuracy by reducing the effect of vibrations. To effectively model the tool-tip dynamics for arbitrary tool-and-holder combinations using the receptance coupling substructure analysis (RCSA) technique, highly accurate and numerically efficient models of the tool–holder dynamics are needed. In this paper, we present a tool–holder model that incorporates a spectral-Tchebychev technique with the Timoshenko beam equation to obtain a completely parameterized solution. Comparison of the tool–holder model to a three-dimensional finite elements solution shows that the dynamic behavior is captured with sufficient accuracy. The tool–holder model is then coupled with the experimentally determined spindle–machine dynamics through RCSA to realize a model of the tool-tip dynamics. The coupled model is validated through experiments for three different tool overhang lengths. The presented technique can be used to predict the tool-tip dynamics for different tool-and-holder combinations and for optimization studies without the need for extensive experimentation.

Journal ArticleDOI
TL;DR: A unified localization technique is developed for sculptured surface machining to satisfy a user-defined set of constraints for some specific surfaces where the machining allowance is preferentially guaranteed and results show that the proposed method is appropriate and feasible to distribute the stock allowance.
Abstract: The goal of workpiece localization is of interest to find the optimal Euclidean transformation that aligns the sampled points to the nominal CAD model to ensure sufficient stock allowance during the machining process. In this paper, a unified localization technique is developed for sculptured surface machining. This technique concerns an alignment process to satisfy a user-defined set of constraints for some specific surfaces where the machining allowance is preferentially guaranteed. The mathematical model of the constrained optimization alignment is firstly established, and is efficiently solved by a combination of the multipliers method and the BFGS algorithm to handle the large number of constraints in allowance optimization. To efficiently calculate the Euclidean oriented distance, a novel approach, which combines the robust arithmetic for multivariate Bernstein-form polynomials and Bezier surface segmentation algorithm, is presented based on recursive quadtree decomposition. Two typical sculptured surfaces are used to test the developed algorithm and comparisons between the proposed algorithm and the existing algorithms are given. Experiment results show that the proposed method is appropriate and feasible to distribute the stock allowance for proper sculptured surface machining.

Journal ArticleDOI
TL;DR: Chemo-mechanical grinding (CMG) is potentially emerging defect-free machining process which combines the advantages of fixed abrasive machining and chemical mechanical polishing (CMP) is often utilized.
Abstract: Finishing process of quartz glass substrate is meeting great challenges to fulfill the requirements of photomask for photolithography applications. For the final finishing of the substrate surface, chemical mechanical polishing (CMP) is often utilized. Those free abrasive processes are able to offer a great surface roughness, but sacrifice profile accuracy. On the other hand, the fixed abrasive process or grinding is known as a promising solution to improve accuracy of profile geometry, but always introduces damaged layer. Chemo-mechanical grinding (CMG) is potentially emerging defect-free machining process which combines the advantages of fixed abrasive machining and CMP. In order to simultaneously achieve high surface quality and high profile accuracy, CMG process has been applied into machining of large size quartz glass substrates for photomask use. Reported in this paper are CMG performances in finishing of quartz glass substrates including material removal rate (MRR), surface roughness, flatness and optical characteristics.

Journal ArticleDOI
TL;DR: In this article, a high-resolution digital angle encoder served as the transfer standard for this comparison, and the results proved to be consistent with the measurement uncertainties that the participants attributed to their calibration.
Abstract: Germany's National Metrology Institute the Physikalisch-Technische Bundesanstalt (PTB) and the DR. JOHANNES HEIDENHAIN GmbH (HEIDENHAIN) have conducted and compared measurements using their primary angle standards, which are realized as angle comparators of similar design. A high-resolution digital angle encoder served as the transfer standard for this comparison. Calibrations of the transfer standard by the two angle comparators resulted in an agreement of ±0.002″. The result proved to be consistent with the measurement uncertainties that the participants attributed to their calibration. PTB succeeded, using an additional comparison with a self-calibration method, in improving the measurement uncertainty of its comparator by a factor of 2.5 to 0.002″ ( k = 2). The results of both participants demonstrated the suitability of the digital angle encoder as transfer standard for angle measurement comparisons aimed at uncertainties of a few thousandths of an arcsecond.

Journal ArticleDOI
TL;DR: The MIT-SS-1 as mentioned in this paper is a hybrid 5-axis CNC milling machine that combines serial and parallel mechanisms, which can tolerate over-constraint through a novel layout of axes.
Abstract: 5-Axis CNC milling machines are important in a number of industries ranging from aerospace to consumer-die-mold machining because they can deliver high machining accuracy with a spindle tilting capacity. Most of these machines have serial mechanisms so that modest static and dynamic stiffness become very critical design issues when high speed machining capability is required. Parallel mechanisms have recently received attention from machine tool designers because of their inherent potential for stiffness and because of their compactness. However, much of the promised advantages of parallel machines only occur within a very small region of their workspace. We discuss some of the kinematic and structural challenges to extract machining performance from serial and parallel machines. We compare a hybrid machine, which combines serial and parallel mechanisms, with typical serial and parallel machines such as Euler angle machines and a hexapod. In particular, we consider singularities, reversal characteristics, and manufacturability. We show that hybrid machines can benefit from the advantages of serial and parallel mechanisms while avoiding most potential pitfalls. However, hybrid structures can suffer from the manufacturing problem of over-constraint. We show that the degree of over-constraint depends on machine size. We have designed a small hybrid 5-axis motion platform, the MIT-SS-1, which can tolerate this over-constraint through a novel layout of axes. We show that this structure has potential as a small 5-axis CNC milling machine.

Journal ArticleDOI
TL;DR: In this article, a calibration method for the pseudo-3D-artefact on a coordinate measuring machine (CMM) is presented, with the aim to minimise the influence of geometric CMM errors.
Abstract: The presented 3D-ball plate is used for testing machine tools with a workspace of 500 mm × 500 mm × 320 mm. The artefact consists of a 2D-ball plate which is either located by a kinematic correct coupling on a base plate or on a spacer. The spacers are placed between the base plate and the ball plate and are also kinematic coupled to the other elements of the artefact. The kinematic couplings provide a high repeatability of the measurement setup. Because of the specific application the known calibration procedures for 2D-ball plates are not applicable. A calibration method for the pseudo-3D-artefact on a coordinate measuring machine (CMM) is presented, with the aim to minimise the influence of geometric CMM errors. Therefore a computer simulation is used to analyse the effects of these disturbing errors on the calibration of the ball plate and the spacers. Using a reversal method, the plate is measured at four different horizontal positions after rotating the ball plate around its vertical axis. A couple of the CMM errors, e.g., a squareness error C0Y between the X - and Y -axis of the CMM, can be eliminated by that method—others have to be determined with additional measurements, e.g., the positioning errors EXX or EYY of the X - and Y -axis, respectively. The paper also contains a measurement uncertainty estimation for the calibration by use of experiments, tolerances and Monte Carlo-simulations. The achieved uncertainty for ball positions in the working volume is less than 2.1 μm (coverage factor k = 2).

Journal ArticleDOI
TL;DR: In this paper, the authors show that the conventional step-diagonal measurement is valid only when implicit assumptions related to the configuration of laser and mirror setups are met, and that its inherent problem is that it is generally not possible to guarantee these conditions when volumetric errors of the machine is unknown.
Abstract: The laser step-diagonal measurement modifies the diagonal displacement measurement by executing a diagonal as a sequence of single-axis motions. It has been claimed that the step-diagonal test enables the identification of all the volumetric error components, including linear errors, straightness and squareness errors, in three-dimensional space. In this paper, we show that the conventional formulation of the step-diagonal measurement is valid only when implicit assumptions related to the configuration of laser and mirror setups are met, and that its inherent problem is that it is generally not possible to guarantee these conditions when volumetric errors of the machine is unknown. To address these issues, we propose a new formulation of the step-diagonal measurement, in order to accurately identify volumetric errors even under the existence of setup errors. To simplify the discussion, this paper only considers the two-dimensional version of laser step-diagonal measurement to estimate volumetric errors on the XY plane. The effectiveness of the proposed modified identification scheme is experimentally investigated by an application example of two-dimensional laser step diagonal measurement to a high-precision machine tool.

Journal ArticleDOI
TL;DR: In this paper, the authors formulated the evaluation of roundness error as a non-differentiable unconstrained optimization problem and proposed a relationship between the minimum zone circle and maximum inscribed circle, minimum circumscribed circle.
Abstract: Following the minimum zone criterion set forth in the current ANSI and ISO standards, evaluation of roundness error is formulated as a non-differentiable unconstrained optimization problem and hard to handle. The maximum inscribed circle and minimum circumscribed circle are all easily solved by iterative comparisons, so the relationship between the minimum zone circle and maximum inscribed circle, minimum circumscribed circle is proposed to solve efficiently the minimum zone problem. Based on the known minimum zone circle, the maximum inscribed circle and minimum circumscribed circle can be easily determined. The relationship is implemented and validated with the data available in the literature.

Journal ArticleDOI
TL;DR: In this paper, the authors propose a micro gripper system where actuators and the end-effectors of the gripper are fabricated separately, which can be adapted to the manipulated micro-objects without new design and/or fabrication of the actuator.
Abstract: Micromanipulation is a key task to perform serial assembly of MEMS. The two-fingered microgrippers are usable but require specific studies to be able to work in the microworld. In this paper, we propose a new microgripping system where actuators and the end-effectors of the gripper are fabricated separately. End-effectors can thus be adapted to the manipulated micro-objects without new design and/or fabrication of the actuator. The assembly of the end-effectors on our piezoelectric actuators guarantee a great modularity for the system. This paper focuses on the original design, development and experimentation of new silicon end-effectors, compatible with our piezoelectric actuator. These innovative end-effectors are realized with the well known DRIE process and are able to perform micromanipulation tasks of objects whose typical size is between 5 μm and 1 mm.

Journal ArticleDOI
TL;DR: In this article, a nominal characteristic trajectory following control (NCTF) controller is proposed to realize high performance and ease of application of point-to-point (PTP) positioning.
Abstract: The present paper describes a practical control method for a precision motion system and the performance thereof. For practical use, high motion control performance and ease of design and controller adjustment are desired. A nominal characteristic trajectory following control (NCTF control) has been investigated to realize high performance and ease of application of point-to-point (PTP) positioning. The controller comprising a nominal characteristic trajectory (NCT) and a PI compensator is free from exact modeling and parameter identification. In the present paper, the NCTF control is modified in order to improve the control performance of continuous motions such as tracking and contouring motions. The NCTF controller for continuous motion (referred to as Continuous Motion NCTF controller) has a structure that is almost identical to the conventional NCTF controller and is designed using the same design procedure. The Continuous Motion NCTF controller is applied to ball screw mechanisms, and its motion control performance is evaluated from the experimental tracking, contouring, and positioning control results. The experimental results prove that the Continuous Motion NCTF controller achieves the same positioning performance as the conventional NCTF controller, and generally achieves better continuous motion control performances than PI-D or conventional NCTF controllers. In 0.25 Hz and 100-nm radius circular motion, the experimental tracking errors for Continuous Motion NCTF were smaller than 10 nm.

Journal ArticleDOI
TL;DR: A prototype atomic force microscope (AFM) uses a piezoelectric tube to scan a probe tip over a sample surface, while a PC-based digital controller maintains a constant tip-sample separation based on feedback from a quartz tuning fork proximity sensor.
Abstract: Our prototype atomic force microscope (AFM) uses a piezoelectric tube to scan a probe tip over a sample surface, while a PC-based digital controller maintains a constant tip–sample separation based on feedback from a quartz tuning fork proximity sensor. We have successfully run the AFM in both the shear and tapping modes, using optical fibers as probe tips. The AFM utilizes a set of capacitance sensors with a spherical target for direct measurement of probe tip displacements. We have used this system to image localized surface topography of a square wave silicon calibration grating with localized step height accuracy of 1 nm in the vertical direction and vertical RMS noise less than 4 nm. The lateral accuracy is on the order of 100 nm, and our largest lateral measurement scans have been performed on 20 μ m × 20 μ m regions with step heights of 26.5 nm and a modest scan speed of 0.8 μ m / s .