Design of ultraprecision machine tools with application to manufacturing of miniature and micro components

Currently the underlying necessities for predictability, producibility and productivity remain big issues in ultraprecision machining of miniature/microproducts. The demand on rapid and economic fabrication of miniature/microproducts with complex shapes has also made new challenges for ultraprecision machine tool design. In this paper the design for an ultraprecision machine tool is introduced by describing its key machine elements and machine tool design procedures. The focus is on the review and assessment of the state-of-the-art ultraprecision machining tools. It also illustrates the application promise of miniature/microproducts. The trends on machine tool development, tooling, workpiece material and machining processes are pointed out

Design and Implementation of Position Estimator Algorithm on Voice Coil Motor

Voice Coil Motors (VCMs) have been an inevitable element in the mechanisms that have been used for precise positioning in the applications like 3D printing., micro-stereolithography., etc. These voice coil motors translate in a linear direction and require a high accuracy position sensor that amounts for a major part in the budget. In this research work., an effort has been made to design and implement an algorithm that would predict the displacement of VCM and eliminate the need of high cost sensors. VCM was integrated with dSPACE DS1104 R&D controller via linear current amplifier (LCAM) which acts as a driver circuit for VCM. Sine input was given to VCM with various amplitude and frequency and the corresponding displacement is measured by using linear variable differential transformer (LVDT). The position estimator algorithm is also implemented at the same time on VCM and its output is compared with that of LVDT. It is observed that there is 97.8 % accuracy in between algorithm output and LVDT output. Further., PID controller is used in integration with the novel algorithm to minimize the error. The estimator algorithm is tested for various amplitudes and frequencies and it is found that it has a very good agreement of 99.2% with the actual displacement measured with the help of LVDT

Hybrid Motor System for High Precision Position Control of a Heavy Load Plant

The lift up or press process with high precision position control is an important application in industries. An example of the process lift up and press is the process of a machine tool for drilling, milling, or injection. It is difficult to design the mechanism and controller to control the position of the base table accuracy because it needs to control the base position of the system with the weight varying in a large range. Also, the friction in the system would vary in a large range. This lead to low performance of the system in some range of load. Therefore, the new design system utilizes a DC motor and ball screw and pneumatic actuator to create the hybrid motor system for applying to the lift up and press system. The pneumatic actuator is designed to support the heavy load and the DC motor and ball screw is designed to control the position. Then, the developed hybrid motor can be used to improve the performance of the system. The simulation and experiment results show that the developed system can improve the rise time, setting time, and steady state error. Then, the time response of the system with heavy load look similar to the time response of the system with light load. Moreover, the developed hybrid motor technique can apply to the applications such as to control the 3D powder painter tank base position, and the silicon injection system, the 3D print head, which is a challenge system due to the high friction in tube

Dynamics and Controls of Fluidic Pressure-Fed Mechanism (FPFM) of Nanopositioning System

Flexure or compliant mechanisms are employed in many precisions engineered devices due to their compactness, linearity, resolution, etc. Yet, critical issues remain in motion errors, thermal instability, limited bandwidth, and vibration of dynamic systems. Those issues cannot be negligible to maintain high precision and accuracy for precision engineering applications. In this thesis, a novel fluidic pressure-fed mechanism (FPFM) is proposed and investigated. The proposed method is designing internal fluidic channels inside the spring structure of the flexure mechanism using the additive manufacturing (AM) process to overcome addressed challenges. By applying pneumatic/hydraulic pressure and filling media into fluidic channels, dynamic characteristics of each spring structure of the flexure mechanism can be altered or adjusted to correct motion errors, increase operating speed, and suppress vibration. Additionally, FPFM can enhance thermal stability by flowing fluids without affecting the motion quality of the dynamic system. Lastly, the motion of the nanopositioning system driven by FPFM can provide sub-nanometer resolution motion, and this enables the nanopositioning system to have two linear motion in a monolithic structure. The main objective of this thesis is to propose and validate the feasibility of FPFM that can ultimately be used for a monolithic FPFM dual-mode stage for providing high positioning performance without motion errors while reducing vibration and increasing thermal stability and bandwidth

Development of an integrated guiding and actuation element for high dynamic nanopositioning systems

In nano precision technology, actuating along the vertical axis is a special challenge because of the permanent gravitational force. In this paper, the development of an integrated guiding and actuation element for the vertical motion is presented. A pneumatic-cylinder-like setup is used with its pressure being load controlled, to compensate the gravitational force of the load. An additional electromagnetic drive creates only dynamic forces for the precision motion, keeping the ohmic heat emission to a minimum. For the vertical guiding an aerostatic bushing is used. The whole setup sits on a planar aerostatic bearing pad. Therefore, translational friction can be neglected. Initial testing results of such a unit are presented and an outlook for future research work is given

Parasitic Motion Principle (PMP) Piezoelectric Actuators: Definition and Recent Developments

Stepping piezoelectric actuators have achieved significant improvements to satisfy the urgent demands on precision positioning with the capability of long working stroke, high accuracy and micro/nano-scale resolution, coupled with the merits of fast response and high stiffness. Among them, inchworm type, friction-inertia type, and parasitic type are three main types of stepping piezoelectric actuators. This chapter is aimed to introduce the basic definition and typical features of the parasitic motion principle (PMP), followed by summarizing the recent developments and achievements of PMP piezoelectric actuators. The emphasis of this chapter includes three key points, the structural optimization, output characteristic analysis and performance enhancement. Finally, the current existing issues and some potential research topics in the future are discussed. It is expected that this chapter can assist relevant researchers to understand the basic principle and recent development of PMP piezoelectric actuators

SPARSE APERTURE SPECKLE INTERFEROMETRY TELESCOPE ACTIVE OPTICS CONTROL SYSTEM

A conventional large aperture telescope required for binary star research is typically cost prohibitive. A prototype active optics system was created and fitted to a telescope frame using relatively low cost components. The active optics system was capable of tipping, tilting, and elevating the mirrors to align reflected star light. The low cost mirror position actuators have a resolution of 31 nm, repeatable to within 16 nm. This is accurate enough to perform speckle analysis for the visible light spectrum. The mirrors used in testing were not supported with a whiffletree and produced trefoil-like aberrations which made phasing two mirrors difficult. The active optics system was able to successfully focus and align the mirrors through manual adjustment. Interference patterns could not be found due to having no method of measuring the mirror surfaces, preventing proper mirror alignment and phasing. Interference from air turbulence and trefoil-like aberrations further complicated this task. With some future project additions, this system has the potential to be completely automated. The success of the active optics actuators makes for a significant step towards a fully automated sparse aperture telescope

Mechatronic design, actuator optimization, and control of a long stroke linear nano-positioner

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.precisioneng.2018.01.007 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/In this paper, mechatronic design, actuator optimization and controls of a long-stroke (20 mm) linear nano-positioner are presented. The mechatronic design is described in terms of the stage's most prominent features regarding mechanical design, assembly, actuator configuration, and power supply. A novel air-bearing/bushing arrangement has been used in which the commonly employed double shaft arrangement is replaced with a single shaft supported by an air bearing from the bottom to constrain the roll motion. The assembly is greatly simplified by exploiting the self-aligning property of the air-bushings which are held in the housings by O-rings. Also, the footprint of the stage is reduced. Voice coil actuators (VCA) in moving magnet mode have been used in complementary double configuration for uniformity of force response. The performance objectives of previously optimized VCA's as standalone actuators are re-evaluated in this configuration. It is observed that while the performance objectives decrease a bit, the desirability of the design point is still retained. Controller design has been made for the current control and position control loops. Heydemann's method for the compensation of encoder quadrature detection errors is implemented. The positioning resolution of the stage as measured from the sensor output is experimentally determined to be +/-5 nm. Dynamic Error Budgeting (DEB) method has been used to analyze the contributing factors to the positioning error, and sensor broadband noise is determined to be the major contributor. The actual positioning accuracy of the stage is estimated by DEB to be 0.682 nm root-mean-square (RMS). The trajectory following accuracy is determined to be +/-15 nm. It is expected that trajectory following accuracy can substantially improve if more advanced compensation methods for encoder quadrature errors are implemented.Natural Sciences and Engineering Research Council of Canada [RGPIN-03879]Engage grant EGP [436910-12

Non-contact measurement machine for freeform optics

The performance of high-precision optical systems using spherical optics is limited by aberrations. By applying aspherical and freeform optics, the geometrical aberrations can be reduced or eliminated while at the same time also reducing the required number of components, the size and the weight of the system. New manufacturing techniques enable creation of high-precision freeform surfaces. Suitable metrology (high accuracy, universal, non-contact, large measurement volume and short measurement time) is key in the manufacturing and application of these surfaces, but not yet available. In this thesis, the design, realization and testing of a new metrology instrument is described. This measurement machine is capable of universal, noncontact and fast measurement of freeform optics up to Ø500 mm, with an uncertainty of 30 nm (2s). A cylindrical scanning setup with an optical distance probe has been designed. This concept is non-contact, universal and fast. With a probe with 5 mm range, circular tracks on freeform surfaces can be measured rapidly with minimal dynamics. By applying a metrology frame relative to which the position of the probe and the product are measured, most stage errors are eliminated from the metrology loop. Because the probe is oriented perpendicular to the aspherical best-fit of the surface, the sensitivity to tangential errors is reduced. This allows for the metrology system to be 2D. The machine design can be split into three parts: the motion system, the metrology system and: the non-contact probe. The motion system positions the probe relative to the product in 4 degrees of freedom. The product is mounted on an air bearing spindle (??), and the probe is positioned over it in radial (r), vertical (z) and inclination (¿) direction by the R-stage, Z-stage and ¿- axis, respectively. The motion system provides a sub-micrometer repeatable plane of motion to the probe. The Z-stage is hereto aligned to a vertical plane of the granite base using three air bearings, to obtain a parallel bearing stage configuration. To minimize distortions and hysteresis, the stages have separate position and preload frames. Direct drive motors and high resolution optical scales and encoders are used for positioning. Mechanical brakes are applied while measuring a track, to minimize power dissipation and to exclude encoder, amplifier and EMC noise. The motors, brakes and weight compensation are aligned to the centres of gravity of the R and Zstage. Stabilizing controllers have been designed based on frequency response measurements. The metrology system measures the position of the probe relative to the product in the six critical directions in the plane of motion of the probe (the measurement plane). By focussing a vertical and horizontal interferometer onto the ¿-axis rotor, the displacement of the probe is measured relative to the reference mirrors on the upper metrology frame. Due to the reduced sensitivity in tangential direction at the probe tip, the Abbe criterion is still satisfied. Silicon Carbide is the material of choice for the upper metrology frame, due to its excellent thermal and mechanical properties. Mechanical and thermal analysis of this frame shows nanometer-level stabilities under the expected thermal loads. Simulations of the multi-probe method show capabilities of in process separation of the spindle reference edge profile and the spindle error motion with sub-nanometer uncertainty. The non-contact probe measures the distance between the ¿-axis rotor and the surface under test. A dual stage design is applied, which has 5 mm range, nanometer resolution and 5° unidirectional acceptance angle. This enables the R and Z-stage and ¿-axis to be stationary during the measurement of a circular track on a freeform surface. The design consists of a compact integration of the differential confocal method with an interferometer. The focussing objective is positioned by a flexure guidance with a voice coil actuator. A motion controller finds the surface and keeps the objective focused onto it with some tens of nanometers servo error. The electronics and software are designed to safely operate the 5 axes of the machine and to acquire the signals of all measurement channels. The electronics cabinet contains a real-time processor with many in and outputs, control units for all 5 axes, a safety control unit, a probe laser unit and an interferometry interface. The software consists of three main elements: the trajectory planning, the machine control and the data processing. Emphasis has been on the machine control, in order to safely validate the machine performance and perform basic data-processing. The performance of the machine assembly has been tested by stability, single track and full surface measurements. The measurements focus on repeatability, since this is a key condition before achieving low measurement uncertainty by calibration. The measurements are performed on a Ø100 mm optical flat, which was calibrated by NMi VSL to be flat within 7 nm rms. At standstill, the noise level of the metrology loop is 0.9 nm rms over 0.1 s. When measuring a single track at 1 rev/s, 10 revolutions overlap within 10 nm PV. The repeatability of three measurements of the flat, tilted by 13 µm, is 2 nm rms. The flatness measured by the uncalibrated machine matches the NMi data well. Ten measurements of the flat tilted by 1.6 mm repeat to 3.4 nm rms. A new non-contact measurement machine prototype for freeform optics has been developed. The characteristics desired for a high-end, single piece, freeform optics production environment (high accuracy, universal, non-contact, large measurement volume and short measurement time) have been incorporated into one instrument. The validation measurement results exceed the expectations, especially since they are basically raw data. Future calibrations and development of control and dataprocessing software will certainly further improve these results

Vibration assisted machining: Modelling, simulation, optimization, control and applications

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University, 30/11/2010.Increasing demand for precision components made of hard and brittle materials such as glasses, steel alloys and advanced ceramics, is such that conventional grinding and polishing techniques can no longer meet the requirements of today's precision manufacturing engineering. Particularly, in order to undertake micro-milling of optical glasses or other hard-machining materials, vibration assisted machining techniques have been adopted. However, it is essential and much needed to undertake such processes based on a scientific approach, i.e. the process to be quantitatively controlled and optimized rather than carried out with a trial-and-error manner. In this research, theoretical modelling and instrumental implementation issues for vibration assisted micro-milling are presented and explored in depth. The modelling is focused on establishing the scientific relationship between the process variables such as vibration frequency, vibration amplitude, feedrate and spindle speed while taking into account machine dynamics effect and the outcomes such as surface roughness generated, tool wear and material removal rate in the process. The machine dynamics has been investigated including a static analysis, machine tool-loop stiffness, modal analysis, frequency response function, etc, carried out for both the machine structure and the piezo-actuator device. The instrumentation implementation mainly includes the design of the desktop vibration assisted machining system and its control system. The machining system consists of a piezo-driven XY stage, air bearing spindle, jig, workpiece holder, PI slideway, manual slideway and solid metal table to improve the system stability. The control system is developed using LabVIEW 7.1 programming. The control algorithms are developed based on theoretical models developed by the author. The process optimisation of vibration assisted micro-milling has been studied by using design and analysis of experiment (DOE) approach. Regression analysis, analysis of variance (ANOVA), Taguchi method and Response Surface Methodology (RSM) have been chosen to perform this study. The effects of cutting parameters are evaluated and the optimal cutting conditions are determined. The interaction of cutting parameters is established to illustrate the intrinsic relationship between cutting parameters and surface roughness, tool wear and material removal rate. The predicted results are confirmed by validation experimental cutting trials. This research project has led to the following contribution to knowledge: (1) Development of a prototype desktop vibration assisted micro-milling machine. (2) Development of theoretical models that can predict the surface finish, tool wear and material removal rate quantitatively. (3) Establishing in depth knowledge on the use of vibration assisted machining principles. (4) Optimisation of cutting process parameters and conditions through simulations and machining trials for through investigation of vibration assisted machining.Financial support was obtained from Brunel University