Design of a Magnetic Bearing

A popular approach to nano-positioning requirements in precision engineering in general and micro-lithography in particular is to subdivide the stage positioning architecture into a coarse positioning module with micrometer accuracy (Long Stroke), onto which a fine positioning module (Short Stroke) is cascaded. The latter is responsible for correcting the residual error of the coarse positioning module to the last nanometers. High accuracy positioning in 6 Degrees Of Freedom put severe constraints on the actuators and/or bearing systems. Actuators are used for generating a varying force being part of a control loop. Bearing systems should generate a force as constant as possible in the bearing direction, but the force perpendicular to that direction should be as low as possible. Actuators could serve as a bearing system, but on the one hand this would require the actuators to be large and thus heavy and on the other hand a substantial amount of heat is continuously dissipated in order to generate the static forces. Such heat generation does not contribute to the positioning performance of the actuators, but significantly affects the thermal stability of the application. The latter implication will be overcome if the bearing system is established by a system with permanent magnets

Common zeros in synchronization of high-precision stage systems

In synchronization of high-precision motion systems, in particular the synchronization between a wafer stage system and a reticle stage system of a wafer scanner, a novel feedforward structure is studied. In this structure, the numerator of each plant model is described by an input shaping filter capturing the zeros of said model. The denominator is described by a feedforward filter capturing the poles. Ideally, this gives zero error tracking of both the reticle and wafer stage systems without the need for plant inversion. But in view of the different input shaping filter operations, appropriate synchronization behavior is not guaranteed. To obtain both appropriate tracking and synchronization behavior, we propose to augment the reticle stage filters with the zeros from the wafer stage plant model. Reversely, the wafer stage filters are augmented with the zeros from the reticle stage plant model. The feasibility of such an approach is confirmed by simulation results and, to some extend, by measurement results obtained from an industrial wafer scanner

Heterodyne displacement interferometer, insensitive for input polarization

Periodic nonlinearity (PNL) in displacement interferometers is a systematic error source that limits measurement accuracy. The PNL of coaxial heterodyne interferometers is highly influenced by the polarization state and orientation of the source frequencies. In this Letter, we investigate this error source and discuss two interferometer designs, designed at TU Delft, that showed very low levels of PNL when subjected to any polarization state and/or polarization orientation. In the experiments, quarter-wave plates (qwps) and half-wave plates (hwps) were used to manipulate the polarization state and polarization orientation, respectively. Results from a commercial coaxial system showed first-order PNL exceeding 10 nm (together with higher order PNL) when the system ceased operation at around ±15°??hwp rotation or ±20°??qwp rotation. The two “Delft interferometers,” however, continued operation beyond these maxima and obtained first-order PNLs in the order of several picometers, without showing higher order PNLs. The major advantage of these interferometers, beside their high linearity, is that they can be fully fiber coupled and thus allow for a modular system buildup.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin

Fast response thermal linear motor with reduced power consumption

AbstractThis paper presents the principle, fabrication and characterization of a fast response Thermal Linear Motor (TLM) havingreduced heat loss (and thus power consumption) without reduction in mechanical output power. Our double wedge shaped, aluminum TLM is 12 μm and 6 μm wide at the edges respectively center and 400 μm long. Theory and measurements show that this TLM has up to 20% more mechanical output power for the same electrical input power compared to a simple rectangular beam TLM. The TLM is the crucial driving element for our Hard Disk Drive (HDD) thermal micro actuator. The actuator uses two of the here presented TLMs to accurately move the HDD head up to several micrometers

Validation of separated source frequency delivery for a fiber-coupled heterodyne displacement interferometer

The use of optical fibers presents several advantages with respect to free-space optical transport regarding sourcefrequency delivery to individual heterodyne interferometers. Unfortunately, fiber delivery to individual coaxial heterodyne interferometers leads to an increase of (periodic) nonlinearity in the measurement, because transporting coaxial frequencies through one optical fiber leads to frequency mixing. Coaxial beams thus require delivery via free-space transportation methods. In contrast, the heterodyne interferometer concept discussed in this Letter is based on separated source frequencies, which allow for fiber delivery without additional nonlinearity. This investigation analyzes the influence of external disturbances acting on the two fibers during delivery, causing asymmetry in phase between the two fibers (first-order effect), and irradiance fluctuations (second-order effect). Experiments using electro-optic phase modulation and acousto-optic irradiance modulation confirmed that the interferometerconcept can measure with sub-nanometer uncertainty using fiber delivered source frequencies, enabling fully fiber-coupled heterodyne displacement interferometers.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin

An apparatus for carrying and transporting a product

An apparatus for carrying and transporting a product, comprising a conveyor having a surface, which surface is during use directed towards the product and is provided with inlet openings and outlet openings for a medium for supporting and providing the product with traction, wherein the surface is divided into adjacent surface parts, and wherein the inlet openings and outlet openings are provided in the vicinity of the surface parts, and said adjacent surface parts are adjustable in height and/or form and/or shape so as to control the flow of the medium from the inlet openings to the outlet openings.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin

Fiber-coupled displacement interferometry without periodic nonlinearity

Displacement interferometry is widely used for accurately characterizing nanometer and subnanometer displacements in many applications. In many modern systems, fiber delivery is desired to limit optical alignment and remove heat sources from the system, but fiber delivery can exacerbate common interferometric measurement problems, such as periodic nonlinearity, and account for fiber-induced drift. In this Letter, we describe a novel, general Joo-type interferometer that inherently has an optical reference after any fiber delivery that eliminates fiber-induced drift. This interferometer demonstrated no detectable periodic nonlinearity in both free-space and fiber-delivered variants.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin

Design of a folded, multi-pass Fabry–Perot cavity for displacement metrology

We present a folded, multi-pass cavity design for displacement measuring Fabry–Perot interferometry. The cavity length is designed to be one-quarter of the physical length needed for a typical Fabry–Perot interferometer by using a quarter-wave plate and a retroreflector. This enhances the displacement sensitivity by a factor of four, allowing for higher resolution in viewing the effects caused by mechanical motions, refractive index changes and frequency fluctuations from the laser source. Furthermore, the geometrical error motions are minimized by using a retroreflector due to its tip–tilt insensitivity. In this note, a theoretical analysis of the folded, multi-pass Fabry–Perot cavity is described and analyzed with Jones matrices in ideal and non-ideal designs.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin