Mechatronic Design, Dynamics, Controls, and Metrology of a Long-Stroke Linear Nano-Positioner

Precision motion systems find a broad range of application in various fields such as micro/nano machining tools, lithography scanners, testing and metrology machines, micro-assembly, biotechnology, optics manufacturing, magnetic data-storage, and optical disk drives. In this thesis, an ultraprecision motion stage (nano-positioner) is designed and built based on the concept of a low-cost desktop precision micro machine tool. Linear positioning performance requirements of such a machine tool are used as design objectives. The nano-positioner’s mechatronic design is carried out in such a way to integrate different components towards high performance in terms of high dynamic range, high feedrate, servo accuracy, and geometric accuracy. A self-aligning air-bearing/bushing arrangement is employed for frictionless motion with infinite theoretical resolution, as well as reduced assembly costs and footprint. The air discharge from the air bearings/bushings are also utilized for assistance in the removal of heat dissipated from actuator coils. A voice coil actuator (VCA) is chosen for continuous, non-contact operation, and designed from scratch. A number of dimensional variables of the cylindrical VCA are set according to required forces, motion range, production/assembly tolerances, magnet availability, leakage flux, etc. The remainder of variables is determined according to two novel optimization objectives defined independent of the coil wire gauge, which separately aim for maximum stage acceleration capacity and minimum heat generation per generated force. The actuators are operated in a complementary double configuration for control simplicity which allows for a straightforward and robust design for controller stability. Controller design is carried out at current control and position control levels. Current frequency response of the voice coil actuators is obtained, and they are observed to possess additional high frequency dynamics on top of the expected first order lumped resistance and inductance model. These are attributed to the eddy currents in the stator structure. A closed loop bandwidth of better than 907 [Hz] is achieved using the integrator plus lead current controller. The position controller is designed using the identified overall plant which includes the moving body, current dynamics and the force response. The lead-lag position controller is tuned at 450 [Hz] cross-over frequency and 40 [deg] phase margin. The control error during the tracking of a step trajectory filtered at 40 [Hz] is found to vary between ±5 [nm], indicating a 4 million dynamic range over the 20 [mm] stroke length. Dynamic Error Budgeting (DEB) method has been used to resolve the components of the error, and the largest contributor is found to be the sensor noise. The actual positioning error, which is an ideal signal excluding sensor noise is estimated using the same methodology and disturbance models, and it is found to be 0.680 [nm] root-mean-square (RMS). For the trajectory following case, experiments are carried out with and without a compensation scheme for encoder quadrature detection errors. The compensation is observed to reduce the ±45 [nm] control error to ±15 [nm]. For the assessment of stage performance and the verification of design choices, modal testing and laser interferometric metrology have been applied to the linear nano-positioner. For modal testing, two independent methods are used and their predictions are compared. In the first method, a graphical approach, namely the peak-picking method, is employed to identify modal parameters (natural frequency and damping ratio) and mode shapes. In the second method, a modal testing software package is used to identify the same using automated algorithms. The first mode, which is the most critical one for controller design, is identified at 65 [Hz] as a roll mode, followed by horizontal, vertical, and pitch modes at 450, 484, and 960 [Hz], respectively. The geometric errors of the system are identified using laser interferometric measurements, using various optical setups for linear and angular components. An error budget is formed using these results, together with the estimated thermal errors and servo errors. The accuracy of the stage is determined to be ±5.0 [μm], which had a ±1.1 [μm] non-repeatable component. In the future, the controller structure can be enhanced with an additional pole beyond the crossover frequency, in order to suppress unnecessary oscillations of the control effort signal around the set point due to the encoder noise transmitted to the controller input. Using an estimation of air bearing pitch stiffness from the catalogue values for normal stiffness, the roll mode was predicted at 672 [Hz]. The much lower natural frequency for that mode identified in modal testing (65 [Hz]) can be attributed to the shortcomings of the estimation method, primarily the neglect of the distortion of the supporting air cushion at the bearing interface due to out of plane rotations. In the future, experimental data can be obtained to characterize the air bearing pitch stiffness more accurately. It was observed that the preferred compensation scheme for the encoder quadrature detection errors is unable to match third and fourth harmonics of the encoder measurement error sufficiently. In the future, better compensation methods can be investigated for an improved match. During laser interferometric measurements, measurement uncertainty due to laser beam misalignment and air turbulence were inferred to be high. In the future, better ways to align the laser with the optics, as well as methods for improved assessment and compensation of environmental effects can be investigated

Development of a Traceable Atomic Force Microscope with Interferometer and Compensation Flexure Stage

Entwicklung eines ruckfuhrbaren Rasterkraftmikroskops auf der Basis von Interferometern und einer geregelten Einkorperfuhrung Abstrakt Rastersondenmikroskope, zu denen unter anderem Rastertunnelmikroskope (STM) und Rasterkraftmikroskope (AFM) gezahlt werden, werden an vielen Stellen in der Material- und Oberflachenforschung, der Halbleitertechnologie sowie der Biotechnologie angewendet. Sie sind zudem denkbare Werkzeuge der Nanotechnologien, so beispielsweise der Nanolithographie. Zudem konnen sie der Manipulation von Atomen und zur Nanometrologie dienen. Kommerzielle AFM bestehen unter anderem aus einem Laser, Photoempfanger, Regler, Piezoantriebssystem sowie einem Tastsystem. Dabei kommt den Piezoelementen des Antriebssystems besondere Bedeutung zu. Die von Piezoelementen bekannten Nachteile, wie Nichtlinearitat, Hysterese, Alterung, thermische Drift, Kriechen und Ubersprechen, konnen durchaus 20% der Messabweichungen bei Vorwartssteuerung verursachen. Daher sollten AFM, Metrologiestandards entsprechend, zur Reduzierung der Mesunsicherheit regelmasig ruckfuhrbar kalibriert werden. Das Ziel der vorliegenden Arbeit bestand in der Entwicklung eines ruckfuhrbaren Rasterkraftmikroskops (Traceable Atomic Force Microscope, TAFM) zum Einsatz als staatliches Normal zur ruckfuhrbaren Vermessung von Normalen im Nanometer- Bereich fur die taiwanesische Industrie. Das TAFM wurde als Kombination eines kommerziellen AFM, zwei Laserinterferometern, einer aktiv geregelten dreiachsigen Prazisionsfuhrung, einem Metrologierahmen aus Super-Invar, einer Schwingungsdampfung sowie einer temperaturgeregelten Umhausung konzipiert und aufgebaut. Zur Reduzierung des Abbe-Offsets wurden die Interferometer derart angeordnet, dass sich ihre virtuell verlangerten Messstrahlen im Antastpunkt des Cantilevers und damit direkt auf der Probenoberflache im Messpunkt schneiden. Eine einwandfreie Referenzbewegung des Systems wurde durch die eingesetzten Prazisionsfuhrungen sichergestellt, wahrend die direkte Ruckfuhrbarkeit auf die Definition der Langeneinheit ?Meter" durch den Einsatz von zwei Laser- Interferometern erreicht wurde. Die ermittelte erweiterte Messunsicherheit des TAFM fur die laterale Messung einer Lange von 292 nm betrugt bei einer statistischen Sicherheit von 95% unter Berucksichtigung von 29 Freiheitsgraden 2,5 nm. Da die ermittelte erweiterte Messunsicherheit fur laterale Langenmessungen noch nicht zufriedenstellend und die Ruckfuhrbarkeit in Richtung der Z-Achse nicht gewahrleistet ist, soll das TAFM verbessert werden, um perspektivisch eine Messunsicherheit von 0,5 nm in allen drei Messachsen zu erreichen. Dieses Ziel kann zunachst durch den Einbau eines weiteren Laserinterferometers zur Kalibrierung des Messystems der Z-Achse erreicht werden. Zusatzlich sollte die Umhausung statt auf einem Tisch auf dem schwingungsarmeren Boden platziert werden, was das Rauschen der Interferometer auf weniger als 5 nm reduzieren sollte. Ein verstarkter Metrologierahmen, die Verlagerung der Referenzspiegel vom AFM auf die Prazisionsfuhrung und verkurzte Messkreise, die Konstruktion aller Teile aus dem gleichen Material, ein symmetrischer mechanischer Aufbau und der Einsatz einer aktiven Temperaturregelung mit einer Temperaturstabilitat von 20¡Ó0.1 ¢XC sind weitere wichtige Schritte.Scanning Probe Microscopes (SPMs), generally including such instruments as Scanning Tunneling Microscopes (STMs) and Atomic Force Microscopes (AFMs), have been widely applied to measure engineering surfaces in a variety of fields, such as material sciences, semiconductor industry, and biotechnology. SPMs will also be a potential tool in nanotechnology, for example nanolithography, atom manipulation, and nanometrology. Normally, a commercial AFM consists of a laser, a photo-detector, a controller, a piezo-scanner, and a cantilever tip. The piezo-scanner is critical to the performance of AFMs. The intrinsic properties of piezo-scanners, for instance non-linearity, hysteresis, aging, thermal drift, creep, and coupling effect will result in measurement errors that may reach up to 20 % of the reading. To reduce major measurement errors mentioned above, an AFM should be periodically calibrated with a traceable standard. The goal of my research study was to design a state-of-the-art Traceable Atomic Force Microscope (TAFM) to be used as a primary realization of nanometer scale standards for Taiwan industry. The TAFM was composed of a commercial AFM, two laser interferometers, a 3-axis active compensation flexure stage, a super-Invar metrology frame, a vibration isolator, and a temperature-controlled enclosed box with circulating water. To eliminate the Abbe-offset, the surface-plane of specimens was arranged on the same plane-level to the laser beams emitted by interferometers. The compensation flexure stage was aimed to provide a perfect reference motion mechanism. To achieve the direct traceability to the definition of meter, two interferometers were added to the flexure stage. The TAFM was evaluated to have an expanded uncertainty of 2.5 nm at a confidence level of 95 % and 29 degrees of freedom for a nominal pitch value of 292 nm. Since the expanded uncertainty of pitch measurement is not satisfactory and there is no traceability in the Z direction. The TAFM needs to be improved to meet the requirement of an expanded uncertainty of no more than 0.5 nm at 95 % confidence level at all three axes. The requirement can be achieved by the following improvements: A laser interferometer is added to the flexure stage for Z-height calibration. To reduce the noise of laser interferometer to about 5 nm, the support of the enclosed box is moved from tabletop to the floor. The metrology frame is improved by changing the reference mirrors from AFM to flexure stage, thickening the super-Invar frame, shortening the structure loop and metrology loop, using one material, and realizing a symmetrical mechanism design. The passive temperature control is changed to active temperature control, which will approach an anticipative temperature stability of (20¡Ó0.1) ¢XC in the measuring volume

Three-Dimensional Shape Measurements of Specular Objects Using Phase-Measuring Deflectometry

The fast development in the fields of integrated circuits, photovoltaics, the automobile industry, advanced manufacturing, and astronomy have led to the importance and necessity of quickly and accurately obtaining three-dimensional (3D) shape data of specular surfaces for quality control and function evaluation. Owing to the advantages of a large dynamic range, non-contact operation, full-field and fast acquisition, high accuracy, and automatic data processing, phase-measuring deflectometry (PMD, also called fringe reflection profilometry) has been widely studied and applied in many fields. Phase information coded in the reflected fringe patterns relates to the local slope and height of the measured specular objects. The 3D shape is obtained by integrating the local gradient data or directly calculating the depth data from the phase information. We present a review of the relevant techniques regarding classical PMD. The improved PMD technique is then used to measure specular objects having discontinuous and/or isolated surfaces. Some influential factors on the measured results are presented. The challenges and future research directions are discussed to further advance PMD techniques. Finally, the application fields of PMD are briefly introduce

Design and Applications of Coordinate Measuring Machines

Coordinate measuring machines (CMMs) have been conventionally used in industry for 3-dimensional and form-error measurements of macro parts for many years. Ever since the first CMM, developed by Ferranti Co. in the late 1950s, they have been regarded as versatile measuring equipment, yet many CMMs on the market still have inherent systematic errors due to the violation of the Abbe Principle in its design. Current CMMs are only suitable for part tolerance above 10 μm. With the rapid advent of ultraprecision technology, multi-axis machining, and micro/nanotechnology over the past twenty years, new types of ultraprecision and micro/nao-CMMs are urgently needed in all aspects of society. This Special Issue accepted papers revealing novel designs and applications of CMMs, including structures, probes, miniaturization, measuring paths, accuracy enhancement, error compensation, etc. Detailed design principles in sciences, and technological applications in high-tech industries, were required for submission. Topics covered, but were not limited to, the following areas: 1. New types of CMMs, such as Abbe-free, multi-axis, cylindrical, parallel, etc. 2. New types of probes, such as touch-trigger, scanning, hybrid, non-contact, microscopic, etc. 3. New types of Micro/nano-CMMs. 4. New types of measuring path strategy, such as collision avoidance, free-form surface, aspheric surface, etc. 5. New types of error compensation strategy

High precision angle calibration for spherical measurement systems

The European Synchrotron Radiation Facility (ESRF) located in Grenoble, France is a joint facility supported and shared by 19 European countries. It operates the most powerful synchrotron radiation source in Europe. Synchrotron radiation sources address many important questions in modern science and technology. They can be compared to “super microscopes”, revealing invaluable information in numerous fields of diverse research such as physics, medicine, biology, geophysics and archaeology. For the ESRF accelerators and beam lines to work correctly, alignment is of critical importance. Alignment tolerances are typically much less than one millimetre and often in the order of several micrometers over the 844 m ESRF storage ring circumference. To help maintain these tolerances, the ESRF has, and continues to develop calibration techniques for high precision spherical measurement system (SMS) instruments. SMSs are a family of instruments comprising automated total stations (theodolites equipped with distance meters), referred to here as robotic total stations (RTSs); and laser trackers (LTs). The ESRF has a modern distance meter calibration bench (DCB) used for the calibration of SMS electronic distance meters. At the limit of distance meter precision, the only way to improve positional uncertainty in the ESRF alignment is to improve the angle measuring capacity of these instruments. To this end, the horizontal circle comparator (HCC) and the vertical circle comparator (VCC) have been developed. Specifically, the HCC and VCC are used to calibrate the horizontal and vertical circle readings of SMS instruments under their natural working conditions. Combined with the DCB, the HCC and VCC provide a full calibration suite for SMS instruments. This thesis presents their development, functionality and in depth uncertainty evaluation. Several unique challenges are addressed in this work. The first is the development and characterization of the linked encoders configuration (LEC). This system, based on two continuously rotating angle encoders, is designed improve performance by eliminating residual encoder errors. The LEC can measure angle displacements with an estimated uncertainty of at least 0.044 arc seconds. Its uncertainty is presently limited by the instrumentation used to evaluate it. Secondly, in depth investigation has lead to the discovery of previously undocumented error-motion effects in ultra-precision angle calibration. Finally, methods for rigorous characterisation and extraction of rotary table error motions and their uncertainty evaluation using techniques not previously discussed in the literature have been developed

An in-process, non-contact surface finish sensor for high quality components generated using diamond turning

The object of this Ph.D. project was to design and construct an in-process, non contact surface finish sensor for high quality components generated using diamond turning. For this application the instrument must have the following properties: i rapid acquisition of data. ii capability of measuring translating and or rotating surfaces. iii ruggedness for in-process use. iv insensitivity to moderate vibrations. v remoteness from the surfaces to be measured. The remoteness requirement virtually excludes the otherwise ubiquitous stylus instrument, while the rapid gathering of data from rotating surfaces excludes other profiling techniques. The above mentioned properties strongly suggest an optical method. An optical diffraction technique has been chosen, since it produces an optical Fourier Transform of the surface. This transform is produced at the speed of light, since the optical system has the property of parallel data processing, unlike a typical electronic computer. With the aid of a microprocessor various surface finish parameters can be extracted from the optical transform. These parameters are respectively the rms surface roughness, slope and wavelength. The actual sensor consists of a measuring head and a minicomputer. It fulfils the above mentioned requirements. Its only limitations are: i limited to surface finishes up to 100nm ii presence of cutting fluids has to be avoided, although certain modern lubricating fluids can be tolerated. The algorithms devised to extract the surface finish parameters from the optical transforms have initially been tested on optical spectra produced by Thwaite. Comparison of the optical roughness values and the values quoted by Thwaite show close agreement. Thwaite's values are obtained by a stylus instrument. Rqopt (um) Rqstylus (um) 0.16 0.156 0.38 0.37 0.44 0.40 In addition a computer program has been devised which simulates the optical sensor head. The input data can be obtained by a profiling instrument, or generated by a computer program. This last option enables the creation of surface profiles with "controllable" machining errors. This program can be utilised to create an atlas, which maps optical diffraction patterns versus machine-tool errors

Research on profile compensation, on-machine metrology and precision monitoring of ultrahigh precision machining process using real-time position capture system

東京電機大学202

Manufacturing Metrology

Metrology is the science of measurement, which can be divided into three overlapping activities: (1) the definition of units of measurement, (2) the realization of units of measurement, and (3) the traceability of measurement units. Manufacturing metrology originally implicates the measurement of components and inputs for a manufacturing process to assure they are within specification requirements. It can also be extended to indicate the performance measurement of manufacturing equipment. This Special Issue covers papers revealing novel measurement methodologies and instrumentations for manufacturing metrology from the conventional industry to the frontier of the advanced hi-tech industry. Twenty-five papers are included in this Special Issue. These published papers can be categorized into four main groups, as follows: Length measurement: covering new designs, from micro/nanogap measurement with laser triangulation sensors and laser interferometers to very-long-distance, newly developed mode-locked femtosecond lasers. Surface profile and form measurements: covering technologies with new confocal sensors and imagine sensors: in situ and on-machine measurements. Angle measurements: these include a new 2D precision level design, a review of angle measurement with mode-locked femtosecond lasers, and multi-axis machine tool squareness measurement. Other laboratory systems: these include a water cooling temperature control system and a computer-aided inspection framework for CMM performance evaluation