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Integrated Planar 6-DOF Nanopositioning System
8th IFAC Symposium on Mechatronic Systems 8th IFAC Symposium on Mechatronic Systems Vienna, Sept. on 4-6,Mechatronic 2019 8th IFAC IFACAustria, Symposium on Mechatronic Systems online at www.sciencedirect.com 8th Symposium Systems Available Vienna, Sept. on 4-6,Mechatronic 2019 8th IFACAustria, Symposium Systems Vienna, Austria, Sept. Vienna, Austria, Sept. 4-6, 4-6, 2019 2019 Vienna, Austria, Sept. 4-6, 2019
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IFAC PapersOnLine 52-15 (2019) 313–318
Integrated Integrated Integrated Integrated
Planar 6-DOF Nanopositioning Planar 6-DOF PlanarSystem 6-DOF Nanopositioning Nanopositioning PlanarSystem 6-DOF Nanopositioning System System ∗ ∗ ∗∗ S. Gorges ∗ S. Hesse ∗ C. Schäffel ∗∗ I. Ortlepp ∗∗ ∗∗ E. Manske ∗∗
∗ ∗∗ ∗∗ Gorges ∗∗∗ S. Hesse ∗∗∗ C. Schäffel S. ∗ I. Ortlepp ∗∗ E. Manske ∗∗ ∗∗∗ ∗∗∗ ∗∗ ∗ S. Gorges Gorges ∗ S. Hesse C. Schäffel I. Ortlepp Ortlepp E. Manske Manske ∗∗ E. Langlotz S. S. Hesse I. ∗∗∗ D. ∗Dontsov ∗∗∗ ∗∗ E. ∗ C. Schäffel E. Langlotz D. Dontsov ∗∗∗ ∗∗∗ S. Gorges S. Hesse C. Schäffel I. Ortlepp E. Manske ∗∗ ∗∗∗ D. Dontsov ∗∗∗ E. E. Langlotz Langlotz ∗∗∗ D. Dontsov ∗∗∗ E. Langlotz D. Dontsov ∗ ∗ IMMS Institut für Mikroelektronik- und Mechatronik-Systeme Institut für Mikroelektronikund Mechatronik-Systeme ∗ ∗ IMMS IMMS Institut für Mikroelektronikund Mechatronik-Systeme gemeinnützige GmbH (IMMS GmbH), 98693 Ilmenau, für MikroelektronikMechatronik-Systeme ∗ IMMS Institut gemeinnützige GmbH (IMMS GmbH),und 98693 Ilmenau, Germany Germany IMMS Institut für Mikroelektronikund Mechatronik-Systeme gemeinnützige GmbH GmbH (IMMS GmbH), 98693 98693 Ilmenau, Germany Germany (e-mail:(IMMS [email protected]) gemeinnützige GmbH), Ilmenau, (e-mail: [email protected]) ∗∗ gemeinnützige GmbH GmbH), 98693 Ilmenau, Germany (e-mail:(IMMS [email protected]) Ilmenau, 98693 Ilmenau, Germany (e-mail: [email protected]) ∗∗ Technische Universität Universität Ilmenau, 98693 Ilmenau, Germany ∗∗ (e-mail: [email protected]) ∗∗ Technische Technische Universität Ilmenau, 98693 Ilmenau, Germany (e-mail: [email protected]) Technische (e-mail: Universität Ilmenau, 98693 Ilmenau, Germany ∗∗ ∗∗∗ [email protected]) Technische (e-mail: Universität Ilmenau, 98693 Ilmenau, Germany [email protected]) GmbH, 98693 ∗∗∗ SIOS Meßtechnik (e-mail: [email protected]) SIOS Meßtechnik GmbH, 98693 Ilmenau, Ilmenau, Germany Germany ∗∗∗ (e-mail: [email protected]) ∗∗∗ SIOS Meßtechnik GmbH, 98693 Ilmenau, Ilmenau, Germany Germany (e-mail: [email protected]) GmbH, 98693 ∗∗∗ SIOS Meßtechnik (e-mail: [email protected]) SIOS Meßtechnik GmbH, 98693 Ilmenau, Germany (e-mail: [email protected]) (e-mail: [email protected]) (e-mail: [email protected]) Abstract: The integrated planar 6-DOF drive system evolves from the combination of a 3D Abstract: The integrated planar 6-DOF drive system evolves from the combination of a 3D Abstract: integrated drive system evolves from combination of planar motorThe to actuate x, y,planar and ϕz6-DOF and three individual allow actuation Abstract: The integrated planar 6-DOF drive system vertical evolves actuators from the the which combination of a a 3D 3D planar motor to actuate x, y, and ϕ and three individual vertical actuators which allow actuation z Abstract: The integrated planar 6-DOF drive system evolves from the combination of a 3D planar motor to actuate x, y, and ϕ and three individual vertical actuators which allow actuation in z, ϕ and ϕ . In all axes aerostatic guiding is applied while the vertical actuators additionally z and three individual vertical actuators which allow actuation xmotor to y actuate x, y, and ϕz planar in z, and In guiding is while the vertical actuators additionally y ..actuate planar x,weight y,aerostatic and compensation ϕz and three individual vertical which actuation in z, ϕ ϕxxxmotor anda ϕ ϕto In all all axes axes aerostatic guiding istoapplied applied while theactuators vertical actuators additionally implement pneumatic carry while the static weight actuators of the allow slider which is y in z, ϕ and ϕ aerostatic guiding is applied the vertical additionally y . In all axes implement a pneumatic weight compensation to carry the static weight of the slider which is in z, ϕ and ϕ . In all axes aerostatic guiding is applied while the vertical actuators additionally x y implement a pneumatic pneumatic weight compensation toand carry the static static weight of the the slider which is why these elements are also referred to as liftingto actuation units (LAU). For slider 6D closed loop implement a weight compensation carry the weight of which is why these elements are also referred to as lifting and actuation units (LAU). For 6D closed loop implement adisplacements pneumatic weight compensation toand carry the with static of the slider which is why these are also referred to as lifting actuation units (LAU). For 6D closed loop control theelements and tilting angles are measured a weight high precision multichannel why these elements are also referred to as lifting and actuation units (LAU). For 6D closed loop control the displacements and tilting angles are measured with a high precision multichannel why these elements are also referred to as lifting and actuation units (LAU). For 6D closed loop control the displacements and tilting angles are measured with a high precision multichannel plane mirror interferometer system. The paper introduces the concept of the integrated planar 6control the displacements and tilting angles are measured with a high precision multichannel plane mirror interferometer system. The paper introduces the concept of integrated planar 6control thesystem displacements and tilting angles are measured a ahigh precision plane drive mirror interferometer system. The paper introduces thewith concept of the the integrated planar 6DOF and explains the design of the realized system for travel range ofmultichannel 100 mm in plane mirror interferometer system. The paper introduces the concept of the integrated planar 6DOF drive system and explains the design of the realized system for a travel range of 100 mm in plane mirror interferometer system. The paper introduces the concept of the integrated planar 6DOF drive system and explains the components: design of of the the realized realized system for aa travel travel range ofplanar 100 mm mm in x, y and 10 system mm in z. The three key the lifting and actuation units, theof direct DOF drive and explains the design system for range 100 in x, yy and 10 mm in z. The three key components: the lifting and actuation units, the planar direct DOF drive system and explains the design of the realized system for a travel range of 100 mm in x, and 10 mm in z. The three key components: the lifting and actuation units, the planar direct drive system and the multichannel interferometer system are explained in more detail including x, y and 10 mm inthe z. The three key components: the liftingare andexplained actuationinunits, the planar direct drive system and multichannel interferometer system more detail including x, y and 10 mm z. The three key components: the lifting andexplained actuation the planar direct drive system and multichannel interferometer system are in more detail including preliminary investigations of these individual systems which were carried out to evaluate and drive system andinthe the multichannel interferometer system are explained inunits, more detail including preliminary investigations of these individual systems which were carried out to evaluate and drive system and the multichannel interferometer system are explained in more detail including preliminary investigations of these these individual systems which weresystem. carried out to to evaluate and improve the investigations performance prior to the integration into the overall preliminary of individual systems which were carried out evaluate and improve the performance prior to the integration into the overall system. preliminary of these individual systems which weresystem. carried out to evaluate and improve the the investigations performance prior prior to the the integration into the the overall system. improve performance to integration into overall © 2019, IFAC (International prior Federation of integration Automatic Control) Hosting bysystem. Elsevier Ltd. All rights reserved. improve the performance to the into the overall Keywords: Keywords: nanopositioning nanopositioning and and -measuring -measuring machines, machines, nanofabrication, nanofabrication, integrated integrated direct direct drives, drives, Keywords: and -measuring machines, direct air bearingnanopositioning stage, multi-coordinate drive, plane mirrornanofabrication, interferometer integrated Keywords: nanopositioning and -measuring machines, nanofabrication, integrated direct drives, drives, air bearing stage, multi-coordinate drive, plane mirror interferometer Keywords: and -measuring machines, air stage, drive, mirror interferometer air bearing bearingnanopositioning stage, multi-coordinate multi-coordinate drive, plane plane mirrornanofabrication, interferometer integrated direct drives, air bearing stage, multi-coordinate drive, plane mirror interferometer 1. common 1. INTRODUCTION INTRODUCTION common approach approach of of a a passive passive mechanical mechanical guiding, guiding, this this 1. common approach of a aheight passive mechanical guiding, this guiding will introduce deviations and guiding, tilting errors 1. INTRODUCTION INTRODUCTION common approach of passive mechanical this guiding will introduce height deviations and tilting errors 1. INTRODUCTION approach of passive mechanical this Our modern society is characterized by countless appli- common guiding movement. will introduce height deviations and guiding, tilting errors during In aheight addition, the thickness or height guiding will introduce deviations and tilting errors Our modern society is characterized by countless appliduring movement. In addition, the thickness or height guiding will introduce height deviations and tilting errors Our modern society is characterized by countless applications resulting from the advances in the semiconductor during movement. In addition, the thickness or height of the objects is not constant for example varying wafer Our modern society characterized appli- during movement. addition, the thickness or height cations resulting fromis advances in by thecountless semiconductor of the objects is notIn for example varying wafer Our modern isthe characterized by appli- during movement. Inconstant addition, the thickness or height cations resulting from the advances inand thecountless semiconductor technology andsociety in from other fields of micronanotechnology of the is constant for example varying wafer thickness or wafer bow. Besides certain application cations resulting the advances in the semiconductor of the objects objects is not not constant forthat, example varying wafer technology and in other fields of microand nanotechnology thickness or wafer bow. Besides that, certain application cations resulting from the advances in the semiconductor of the objects is not constant for example varying wafer technology and in inlithographic other fields fields of of micro- and and nanotechnology as well. Thereby, methods are the most import thickness thickness or or wafer bow. Besides that, that, certain lenses, application scenarios, like the manipulation of optical may technology and other micronanotechnology wafer bow. Besides certain application as well. Thereby, lithographic methods are the most import scenarios, like the manipulation of optical lenses, technology and in other fields of microand nanotechnology thickness or wafer bow. Besides that, certain application as well. Thereby, lithographic methods are the most import part. But moving down to sub-10 nm nodes the production scenarios, like the the manipulation manipulation of at optical lenses, may may require a measurement or structuring large macroscopic as well. Thereby, lithographic methods are the most import scenarios, like of optical lenses, may part. But moving down to sub-10 nm nodes the production aa measurement or structuring large macroscopic as well. Thereby, methods are the import require scenarios, likeInthe manipulation of at optical lenses, may part. But moving down nm the production facilities become increasingly complex and very expensive. require measurement or structuring at large macroscopic height levels. view of these aspects, the observance of part. But movinglithographic down to to sub-10 sub-10 nm nodes nodes themost production require a measurement or structuring at large macroscopic facilities become increasingly complex and very expensive. height levels. In view of these aspects, the observance of part. Butbecome moving down to sub-10 nm nodes the production require a measurement or structuring at large macroscopic facilities become increasingly complex and investigated very expensive. Therefore, new fabrication methods are to Abbe’s height levels. In view of these aspects, the observance of principle requires a dynamic raising or lowering facilities increasingly complex and very expensive. height levels. In view of these aspects,raising the observance of Therefore, new fabrication methods are investigated to Abbe’s principle requires a dynamic or lowering facilities become increasingly complex and very expensive. height levels. In view of these aspects, the observance of Therefore, new fabrication methods are investigated investigated to Abbe’s allow for a new morefabrication flexible and still profitable production Abbe’s principle requires a dynamic dynamic raising or lowering of the mirror corner and the sample, in order to keep the Therefore, methods are to principle requires a raising or lowering allow for a more flexible and still profitable production of the mirror corner and the sample, in order to keep the Therefore, new fabrication methods are investigated to Abbe’s principle requires a dynamic raising or lowering allow for a more flexible and still profitable production of microand nanodevices, see Kühnel et al. (2018); Tseng of the mirror corner and the sample, in order to keep the touch each case Abbe point. Realizing allow for and a more flexible and still profitable production of the point mirrorin corner and in thethe sample, in order to keep this the of micronanodevices, see Kühnel et al. (2018); Tseng touch in each case in Abbe point. Realizing allow for a more flexible and still profitable production of the point mirror corner and thethe sample, in order to keep this the of microand nanodevices, see et Tseng (2011); Vorbringer-Doroshovets et al. (2013). The authors touch point in each case in the Abbe point. Realizing this vertical motion within a long-range nanopositioning of microand nanodevices, see Kühnel Kühnel et al. al. (2018); (2018); Tseng precise touch point in each case in the Abbe point. Realizing this (2011); Vorbringer-Doroshovets et al. (2013). The authors precise vertical motion within aa long-range nanopositioning of microand Kühnel etdevelopment al. (2018); Tseng in each case in the Abbe point. Realizing this (2011); Vorbringer-Doroshovets et al. al. (2013). The authors authors contribute in nanodevices, this researchseewith the(2013). of a touch precisepoint vertical motion within long-range nanopositioning system (NPS) is a demanding challenge since it needs to (2011); Vorbringer-Doroshovets et The precise vertical motion within a long-range nanopositioning contribute in this research with the development of a system (NPS) a challenge it (2011); Vorbringer-Doroshovets et al. (2013). The authors precise motion within a long-range nanopositioning contribute in this research with the development of a novel multicoordinate nanopositioning system which can system vertical (NPS) is is a demanding demanding challenge since since it needs needs to to contribute in this research with the development of a system (NPS) is a demanding challenge since it needs to novel multicoordinate nanopositioning system which contribute in with the sample development ofcan a system (NPS) is a demanding challenge since it needs to novel multicoordinate nanopositioning system which can be applied for this the research movement of the during the novel multicoordinate nanopositioning system which can be for the movement of the novel multicoordinate nanopositioning system during which can be applied applied forand thefabrication movement of the the sample sample during the measurement process. be applied for the movement of the sample during the measurement and fabrication process. be applied for the movement of the sample during the measurement and and fabrication fabrication process. process. measurement Usually the measuring and structuring systems for these measurement and fabrication process. Usually the measuring and systems for Usually the measuringrequire and structuring structuring systems for these these kinds of the technologies an xy-stage that moves the Usually measuring and structuring systems for these kinds of technologies require an xy-stage that moves the Usually the measuring and structuring systems for plane. these kinds ofwith technologies require an xy-stage xy-stage that moves moves the sampleof very highrequire precision in the horizontal kinds technologies an that the sample with very high precision in the horizontal plane. kinds ofwith technologies require an xy-stage thatamoves the sample precision in the horizontal plane. To avoid firstvery orderhigh measurement errors, such system is sample with very high precision in the horizontal plane. To avoid first order measurement errors, such a system is sample with very high precision in the horizontal plane. To avoid first order measurement errors, such a system is designed so that the measuring axes meet at one point, To avoid first order measurement errors, such aone system is designed so that the measuring axes meet at point, To avoid first order measurement errors, such a system is designed so that which the measuring measuring axes meet at one one point, the Abbe so point, is also theaxes point where the probe designed that the meet at point, the Abbe point, which is also the point where the probe designed so that the measuring axes meet at one point, thethe Abbe point, which which is also also the thewith point where thesurface. probe or processing tool interacts thewhere sample the Abbe point, is point the probe or the processing tool interacts the sample surface. the Abbe point, which is also when thewith point where the probe or the tool interacts with the sample surface. This is processing achieved, for example, the object is located or the processing tool interacts with the sample surface. This is achieved, for example, when the object is located or the processing tool interacts with the sample surface. This is achieved, for example, when the object is located within a mirror corner and all virtually extended measuring This for example, when the object measuring is located withinis aachieved, mirror corner and all virtually extended This for example, when is located within mirror corner and all all virtually virtually extended measuring beamsisaaachieved, of the corner interferometers meetthe at object the probing or within mirror and extended measuring beams of the interferometers meet at the probing or within a mirror corner and all virtually extended measuring beams of of point the interferometers interferometers meetprinciple, at the the probing probing or processing (Abbe’s comparator see Manske beams the meet at or processing point (Abbe’s comparator principle, see Manske beams of point the interferometers meet at the probing or Fig. 1. Abbe’s comparator principle processing (Abbe’s see Manske et al. (2012)), as showncomparator in Fig. 1.principle, However, with the processing point (Abbe’s comparator principle, see Manske Fig. et al. (2012)), as shown in Fig. 1. However, with the processing point (Abbe’s comparator principle, see Manske Fig. 1. 1. Abbe’s Abbe’s comparator comparator principle principle et al. (2012)), as shown in Fig. 1. However, with the 1. Abbe’s comparator principle et al. (2012)), as shown in Fig. 1. However, with the Fig. 1. Abbe’s comparator principle et al. (2012)), as shown in Fig.Federation 1. However, with Control) the Fig. 2405-8963 © 2019, IFAC (International of Automatic Hosting by Elsevier Ltd. All rights reserved.
Copyright © 2019 IFAC 838 Copyright © under 2019 IFAC 838 Control. Peer review responsibility of International Federation of Automatic Copyright © 838 Copyright © 2019 2019 IFAC IFAC 838 10.1016/j.ifacol.2019.11.693 Copyright © 2019 IFAC 838
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permanently counteract the gravitational force and the vertical drive system needs to be designed in a way that it induces only a minimum of disturbances into the overall system while it is still enabling nanometer precision in the other axes of motion. Different design approaches for zdrives in NPS’s can be found in Hackel (2010); Donker et al. (2009) and Manske et al. (2017). The paper at hand presents the idea of an integrated planar 6-DOF drive which evolves from the combination of a 3D planar direct drive to actuate x, y, and ϕz and three individual vertical actuators which allow actuation in z, ϕx and ϕy . 2. BASIC CONCEPT OF THE 6D NPS A common approach is the serial arrangement of x-, y- and z-stage, found in Hausotte (2002); Manske et al. (2017). Here single axis translational stages are stacked on top of each other, locking the rotating motions by design but also increasing the mechanical complexity. Furthermore, the upper stages need to be moved by the lower stages, increasing the load on these.Our development of a 6-DOF NPS presented in this paper is based on the Nanometer Planar Positioning System NPPS100. This mechanically simple planar direct drive system (details see sec. 3) should be used and expanded to allow a 6D manipulation. The term planar direct drive refers to a drive system which positions an object within the horizontal xy-plane and where the driving forces act directly on the moving mass without any force transmission system. In recent research work IMMS together with TU Ilmenau and SIOS realized the NPPS100 as a demonstrator setup for a planar nanopositioning system with 100 mm travel range based on the planar direct drive approach, see Hesse et al. (2008, 2012). Our concept works with an integration of the z-drives into the parallel drive structure, thereby maintaining the benefits of the direct drive principle for all actuated degrees of freedom. This parallel kinematic approach is shown in Fig. 2.
(LAU, see sec. 4). These LAUs are integrated between the slider body and the planar air bearing. For a projected nanometer precision the additional degrees of freedom (vertical coordinate z, two tilting angles ϕx , ϕy ) need to be measured extremely precise. Therefore, the measurement system needs to be expanded (details in sec. 5). In the following sections, these three main subsystems of the NPPS100-6D are described. 3. PLANAR DIRECT DRIVE SYSTEM The design of this NPS follows the basic idea to move a zerodur reflector very precisely while its position is measured with high resolution laserinterferometers and in accordance with the Abbe principle as mentioned above. Following this idea the approach here was to apply a planar direct drive system with aerostatic guiding for the lateral positioning of the zerodur corner mirror in a large travel range. Fig. 3 shows a photo of the assembled NPPS100 integrated planar drive system. The moving zerodur slider has an aerostatic guiding consisting of three air bearing pads and providing virtually frictionless planar support with respect to the granite base plate. Thus, the slider is free to move in x, y and ϕz . In regulated operation however, the movement in x, y and ϕz is actively controlled while the movement in z, ϕx and ϕy is mainly determined by the flatness of the granite base. The direct drive system is created by the superposition of three linear actuators each consisting of a pair of frame fixed flat coils and a corresponding magnet array on the sliders underside. The three individual driving forces act simultaneously on the slider and combine to an arbitrarily directed horizontal driving force that moves the slider in x and y and a torque around the z-axis to control the rotation ϕz . Interferometers on the base measure the distance to plane mirrors on top of the slider and deliver the feedback signal for the x, y and ϕz control loop. At this point it becomes important that for the interferometers a reflector is necessary in at least the same size as the intended travel range. For this reason the slider itself is made of zerodur and has the reflectors directly bonded to it on the upper side so that the slider of the drive system and the reflector
Fig. 2. Comparison of different kinematics for a 6-DOF 1 : planar drive system, based on a planar drive. 2 3 4 : parallel with 3-DOF; , : serial kinematics; kinematics This concept has already been realized as Mag6D, but with reduced precision and a very small lifting range of just 100 µm, see Schäffel et al. (2016). To use the concept where a vertical travel in the millimeter range is needed, new drives and guidings need to be integrated. Therefore, the slider will sit on three Lifting and Actuating Units 839
1 : air bearing; Fig. 3. Components of the NPPS100: 2 : x-reflector; 3 : x-interferometer; 4 : drive coils; 5 : granite base; 6 : zerodur slider; 7 : object table; 8 : y, ϕz -reflector; 9 : y, ϕz -interferometer; 10 : capac itive probes
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for the interferometers are incorporated in one and the same rigid body. This leads to a simple and stiff kinematic structure and together with the frictionless guiding allows for nanometer positioning. From Fig. 3 can be seen that the granite base serves as a basis for the setup. It delivers the reference for the movement of the slider in z-direction as well as for its tilting around the horizontal axes ϕx and ϕy . This reference however, is not perfectly flat as a surface flatness of about 0.5 up to 1 µm is the economic limit. In this way, a vertical position error is introduced into the sliders movement. As this error is different for all three pads the slider performs an error motion in z but also shows two tilting angle errors in ϕx and ϕy . These errors change as a function of the sliders xy-position but they may also change with time so that height compensation at the base points of the slider support is necessary to keep up the exact horizontal position. Having the NPPS100 as a test setup with subnanometer positioning performance regarding the closed loop control in x, y and ϕz (see Hesse et al. (2012); Zschäck et al. (2014)) in a first step we used this setup to determine the actual extent of the parasitic error motions in z, ϕx and ϕy . Therefore, we added another plane mirror interferometer and a two-axes autocollimator (see Schmidt (2008)) both looking at the z-mirror on the sliders underside, see Fig. 4. With these measurement capabilities we analyzed the error motions when the slider is positioned within its travel range. At a number of commanded positions within the travel range the actual z-position, as well as ϕx and ϕy were traced with 10 kHz for 1 second and from that time series the mean value was calculated as a measure for the static position of the slider in the respective degree of freedom. The results presented in Fig. 5 (top) reveal an overall ±8 µm inclination of the slider with respect to the guiding reference. This error has its origin in the height adjustment of the air bearings. The remaining z-variation after the linear trend is removed is in the range of ±60 nm (see Fig. 5 bottom) with the corresponding angular error motions in the range of ±1 . These curves result most likely from shape deviations of the mirror and granite surface. To generate the horizontal drive forces, the magnets are preferably arranged at a low height above the coils in order to make efficient use of the strong magnetic field of the permanent magnets. Fig. 6 shows a field distribution of a drive element with a schematically indicated pair of coils. FEM analysis of such arrangements also shows that horizontal forces can still be generated even when the
Fig. 4. Measurement setup for z, ϕx and ϕy .
Fig. 5. Measured z-variation of the NPPS100 (top: zposition; bottom: z-position, removed trend). distance between coils and magnets is increased (dotted coil cross-sections), i.e. when the slider is lifted considerably by a z-drive system. For the same force higher currents are needed as the distance increases due to the lower flux density. Consequently, to a certain extend no dynamic compromises need to be made. For an exemplary magnet arrangement, it was estimated that even with an enlargement of the magnetic air gap from 1 mm to 7 mm, 50 % of the original motor power is still available with the same current supplied to the coils. With the aid of a heightdependent commutation of the coils, however, the drop in motor power can be counteracted. The achieved performance of the NPPS100 and the described investigations of its error motions and the height characteristics of the motor force led us to the conclusion that if the aerostatic bearing pads were replaced by active height-adjustable z-drive elements, the result is a 6-DOF direct drive system with the prospect of excellent positioning properties.
Fig. 6. FEM analysis of the drive units. 840
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4. LIFTING AND ACTUATING UNIT Three identical Lifting and Actuating Units (LAU), each mounted at one corner of the slider body, were developed to lift the slider and to compensate its tilt. By closed loop controlling the 3 cornerpoints of the slider body, the additional degrees of freedom z, ϕx and ϕy can be controlled. To allow a relative vertical motion between the base (planar air bearing contacting the granite base) and the slider each LAU has an internal vertical aerostatic guiding. A voice coil drive was designed and integrated, to generate a contactless vertical driving force. To avoid permanent power loss and heating in the voice coil, a pneumatic pressure chamber is added as a weight force compensation system (WFC). Therefore, the static component of the load is taken off the voice coil. Additionally, a linear encoder is included to measure the vertical position of the LAU. This is necessary since the 6D measurement system is not available for the initialization process. The whole setup sits on a very compact planar aerostatic bearing, which allows the slider to move along x, y and rotate around the z-axis. All the components are shown in Fig. 7. A special focus during the design was set onto the two actuators in each LAU: the voice coil dynamic drive and the pneumatic WFC. Since the slider sits on three LAUs, the pressure chamber of one LAU was dimensioned in a way that a pressure of 1 bar cancels one third of the sliders gravitational force. The constant pressure is maintained via a precision pressure controller. The assembled LAUs (see Fig.8) were tested with a separate measurement setup where they act against a dummy weight. The cooperation of the two actuators can be seen in Fig. 9. The upper graphic shows the step response for a 1 µm step in closed loop operation. An overshoot as well as a convergence towards the setpoint is clearly visible. Subsequently, the setpoint is reached with a positional deviation of about 1 nm RMS for the steady state. The second graphic shows the power loss in the coil of the voice coil. Clearly visible is the acceleration spike in the beginning of the motion. Hereafter, the power drops dramatically as the pressure controller feeds air into the chamber to reach the equilibrium pressure. For holding the drive at a constant position less than 1 µW is needed.
Fig. 8. Photo of the assembled LAU
Fig. 9. Step response of a 1 µm step and corresponding electrical power loss of the voice coil 5. 6D LASERINTERFEROMETRIC MEASUREMENT SYSTEM In order to meet the high demands on position-accuracy and reproducibility, special differential interferometer systems (SIOS GmbH) are to be used for the position measurement, see Schott et al. (2009). These measuring systems are based on the measuring principle of the Michelson interferometer. The complete interferometer optics are placed in a compact sensor head from which measurement and reference beams are guided out to the target mirrors. Both beams pass through identical paths and are influenced equally by environmental changes such as temperature fluctuations. Thus, a temperature stability of < 20 nm K−1 is achieved by the sensor head.
Fig. 7. LAU main components from left to right: WFC, vertical guiding, vertical measurement, voice coil 841
Its strictly symmetrical optical design results in an extremely high long-term stability of the length measurement. With the environmentally corrected wavelength of a stabilized He-Ne laser as a highly stable measuring standard, these sensors have nanometer accuracy. Two parallel beams record the relative movement between
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a reference mirror and the measuring point on the moved mirror with highest resolution and precision. The measuring range is 5 m with a resolution of 20 pm. The Plane mirror concept is distinguished by the fact that only one measuring beam, which is reflected by the measuring mirror back into itself, is used for the interferometric length measurement. This results in a well-defined sensing point which, in turn, enables the design of Abbe error free measurement arrangements. A planar 2D arrangement is shown in Fig. 10.
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related between measurement and reference beam, are fully compensated. Noise values below 10 pm can be achieved. The usage of differential interferometer systems for positioning measurements allows high precision measurements as several disturbing influences can be compensated by the differential setup. 6. REALIZATION OF THE 6D NPS After these preliminary investigations we refined and completed the constructive implementation of the machine concept as described in section 2. The set up system is shown in Fig. 12. For the first time the existing setup of the NPPS100 is brought together with the three novel lifting and actuation units and the new configuration of the 6D measurement system with differential interferometers at its core. During the design special focus had to be put on the electrical and pneumatic supply of the LAU. It has been possible to accommodate the system of hoses on the underside of the slider. However, the number of tube bends from the fixed frame to the moving slider increased significantly. For that reason we realized a second feeding point to distribute the disturbing forces of the tubes and wires more evenly.
Fig. 10. Interferometer concept In order to verify the suitability of the measuring system, the differential interferometer was compared with a plane mirror interferometer. Both systems were mounted on an optical table of stainless steel and aligned to a common measuring reflector. The measuring distance was about 1 m. The length signals of the interferometer channels were recorded over several hours and subsequently evaluated. The measurements were made under measurement room conditions without climate control. The differential interferometer is characterized by a considerably lower drift, because this type of interferometer setup is compensating the influences of the measurement setup like thermal expansion of the optical table. As can be seen from Fig. 11, the signal-to-noise ratio can also be significantly improved due to the optical difference formation. The decisive influencing factor for the noise are refractive index fluctuations in the beam path caused by air turbulences. All portions of this effect, that are cor-
Also worth mentioning are the three measuring laser beams in the y-direction. This is due to the application of the differential interferometers. The x and y-translation are measured with a single measuring beam on each reflector while the corresponding reference beam paths are led out of the interferometer housing and run right above the measurement paths. Conversely, the sliders rotation around the z-axis is measured with both laser beams of the differential interferometer. Thus, the rotation ϕz is not calculated from two interferometric length measurements but it is directly measured as difference in the optical path length of the two measuring beams. For data acquisition and control the existing and proven modular dSpace real-time system of the NPPS100 remains in use in combination with Matlab/Simulink for programming. The position values are retrieved from the interferometer electronics as 32-bit digital signal representing the actual counter value. Within the control algorithm the interferometer and angular sensor readings are used
Fig. 12. Foto of the NPPS100-6D with the 6D differential interferometric measurement system and the 3 LAUs
Fig. 11. Comparison of interferometer setups 842
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to calculate the six coordinates in x, y, z and ϕx , ϕy , ϕz (input transformation). The individual controllers (SISO) for these coordinates are each set up as a cascade of a velocity- and a position controller with PID characteristics. The required machine states are reconstructed from the measured values and the controller outputs with the help of an observer. The observer is based on the rather simple system model of a double integrator for the moving mass. However this proved to be sufficient, as there are only marginal disturbances and disturbing forces and as the system can be considered as a rigid body in the relevant frequency range (see Hesse et al. (2011)). Output values of the axis controllers are the commanded accelerations in all 6 DOF, which are then transformed into the required phase currents for the six drive coils, the currents for the 3 LAUs and the control voltage for the WFC (output transformation). After putting the NPPS100-6D into operation the first measurements were quite successful. With minimal adjustments of the controllers it was already possible to levitate the slider at z = 1 mm in full 6D closed loop control. Resting at this position RMS-errors (root-mean-square) of 2.3 nm for x and 1.6 nm for y were achieved. For ϕz the measurement resulted in an RMS-error of 26 nrad. 7. OUTLOOK In the future more advanced control strategies will be investigated. Additionally, the positioning accuracy of the NPPS100-6D for every point in the available volume will be evaluated, as well as the 6D deviation from a given trajectory. Further, a redesign of the LAU will be carried out before in a final step the performance of the NPPS1006D in a fabrication environment will be evaluated. ACKNOWLEDGEMENTS This work has been developed in the INPOS project which is funded by the Federal Ministry of Economics and Energy on the basis of a resolution of the German Bundestag under the reference ZF4085707LT7. Furthermore, the authors gratefully acknowledge the support by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the Research Training Group “Tip- and laser-based 3D-Nanofabrication in extended macroscopic working areas” (GRK 2182) at the Technische Universität Ilmenau, Germany. REFERENCES Donker, R., Widdershoven, I., Brouns, D., and Spaan, H.A.M. (2009). Realization of isara 400: A large measurement volume ultra-precision cmm. Proc. of the 24th Annual Meeting of The American Society for Precision Engineering ASPE. Hackel, T. (2010). Grundlegende Untersuchungen zu vertikalen Positioniersystemen für Nanopräzisionsmaschinen. Phd thesis, Technische Universität Ilmenau. Hausotte, T. (2002). Nanopositionier- und Nanomessmaschine. Phd thesis, Technische Universität Ilmenau. Hesse, S., Schäffel, C., Katzschmann, M., and Büchner, H.J. (2011). Interferometric controlled planar nanopositioning system with 100mm circular travel range. Proc. of 26th ASPE Annual Meeting. 843
Hesse, S., Schäffel, C., Katzschmann, M., Maass, T., and Mohr, H.U. (2008). Planar motor concept for positioning with nanometer positioning uncertainty. Proc. of the 8th Int. Conf. of the European Society for Precision Engineering and Nanotechnology, 1, 150–154. Hesse, S., Schäffel, C., Mohr, H.U., Katzschmann, M., and Büchner, H.J. (2012). Design and performance evaluation of an interferometric controlled planar nanopositioning system. Meas. Sci. Technol., 23. Kühnel, M., Fröhlich, F., Füßl, R., Hoffmann, M., Manske, E., Rangelow, I., Reger, J., Schäffel, C., Sinzinger, S., and Zöllner, J.P. (2018). Towards alternative 3d nanofabrication in macroscopic working volumes. Meas. Sci. Technol., 29, 19pp. Manske, E., Jäger, G., Hausotte, T., and Füßl, R. (2012). Recent developments and challenges of nanopositioning and nanomeasuring technology. Measurement Science and Technology, 23(7), 10pp. Manske, E., Jäger, G., Hausotte, T., Müller, A., and Balzer, F. (2017). Nanopositioning and nanomeasuring machine npmm-200 — sub-nanometer resolution and highest accuracy in extended macroscopic working areas. Proc. of the 17th Int. Conf. of the European Society for Precision Engineering and Nanotechnology, 17, 81pp. Schmidt, I. (2008). Beiträge zur Verringerung der Positionierunsicherheit in der Nanopositionier- und Nanomessmaschine. Phd thesis, Technische Universität Ilmenau. Schott, W., Dontsov, D., and Pöschel, W. (2009). Developments in homodyne interferometry. tm - Technisches Messen Plattform für Methoden, Systeme und Anwendungen der Messtechnik, 76/5, 239–244. Schäffel, C., Katzschmann, M., Mohr, H.U., Glöss, R., Rudolf, C., Mock, C., and Walenda, C. (2016). 6d planar magnetic levitation system - pimag 6d. Bulletin of the JSME Mechanical Engineering Journal, 3. Tseng, A. (2011). Advancements and challenges in development of atomic force microscopy for nanofabrication. Nano Today, 6, 493–509. Vorbringer-Doroshovets, N., Balzer, F., Füßl, R., Manske, E., Kästner, M., Schuh, A., Zöllner, J., Hofer, M., Guliyev, E., Ahmad, A., Ivanov, T., and Rangelow, I. (2013). 0.1nanometer resolution positioning stage for sub-10 nm scanning probe lithography. Proceedings of SPIE The International Society for Optical Engineering, 8680, 18pp. Zschäck, S., Hesse, S., Amthor, A., Katzschmann, M., Schäffel, C., and Ament, C. (2014). Vergleich der ScanPerformance bei Nanopositioniersystemen mit großem Bewegungsbereich. tm - Technisches Messen, 81, 335– 342.
ScienceDirect
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Integrated Integrated Integrated Integrated
Planar 6-DOF Nanopositioning Planar 6-DOF PlanarSystem 6-DOF Nanopositioning Nanopositioning PlanarSystem 6-DOF Nanopositioning System System ∗ ∗ ∗∗ S. Gorges ∗ S. Hesse ∗ C. Schäffel ∗∗ I. Ortlepp ∗∗ ∗∗ E. Manske ∗∗
∗ ∗∗ ∗∗ Gorges ∗∗∗ S. Hesse ∗∗∗ C. Schäffel S. ∗ I. Ortlepp ∗∗ E. Manske ∗∗ ∗∗∗ ∗∗∗ ∗∗ ∗ S. Gorges Gorges ∗ S. Hesse C. Schäffel I. Ortlepp Ortlepp E. Manske Manske ∗∗ E. Langlotz S. S. Hesse I. ∗∗∗ D. ∗Dontsov ∗∗∗ ∗∗ E. ∗ C. Schäffel E. Langlotz D. Dontsov ∗∗∗ ∗∗∗ S. Gorges S. Hesse C. Schäffel I. Ortlepp E. Manske ∗∗ ∗∗∗ D. Dontsov ∗∗∗ E. E. Langlotz Langlotz ∗∗∗ D. Dontsov ∗∗∗ E. Langlotz D. Dontsov ∗ ∗ IMMS Institut für Mikroelektronik- und Mechatronik-Systeme Institut für Mikroelektronikund Mechatronik-Systeme ∗ ∗ IMMS IMMS Institut für Mikroelektronikund Mechatronik-Systeme gemeinnützige GmbH (IMMS GmbH), 98693 Ilmenau, für MikroelektronikMechatronik-Systeme ∗ IMMS Institut gemeinnützige GmbH (IMMS GmbH),und 98693 Ilmenau, Germany Germany IMMS Institut für Mikroelektronikund Mechatronik-Systeme gemeinnützige GmbH GmbH (IMMS GmbH), 98693 98693 Ilmenau, Germany Germany (e-mail:(IMMS [email protected]) gemeinnützige GmbH), Ilmenau, (e-mail: [email protected]) ∗∗ gemeinnützige GmbH GmbH), 98693 Ilmenau, Germany (e-mail:(IMMS [email protected]) Ilmenau, 98693 Ilmenau, Germany (e-mail: [email protected]) ∗∗ Technische Universität Universität Ilmenau, 98693 Ilmenau, Germany ∗∗ (e-mail: [email protected]) ∗∗ Technische Technische Universität Ilmenau, 98693 Ilmenau, Germany (e-mail: [email protected]) Technische (e-mail: Universität Ilmenau, 98693 Ilmenau, Germany ∗∗ ∗∗∗ [email protected]) Technische (e-mail: Universität Ilmenau, 98693 Ilmenau, Germany [email protected]) GmbH, 98693 ∗∗∗ SIOS Meßtechnik (e-mail: [email protected]) SIOS Meßtechnik GmbH, 98693 Ilmenau, Ilmenau, Germany Germany ∗∗∗ (e-mail: [email protected]) ∗∗∗ SIOS Meßtechnik GmbH, 98693 Ilmenau, Ilmenau, Germany Germany (e-mail: [email protected]) GmbH, 98693 ∗∗∗ SIOS Meßtechnik (e-mail: [email protected]) SIOS Meßtechnik GmbH, 98693 Ilmenau, Germany (e-mail: [email protected]) (e-mail: [email protected]) (e-mail: [email protected]) Abstract: The integrated planar 6-DOF drive system evolves from the combination of a 3D Abstract: The integrated planar 6-DOF drive system evolves from the combination of a 3D Abstract: integrated drive system evolves from combination of planar motorThe to actuate x, y,planar and ϕz6-DOF and three individual allow actuation Abstract: The integrated planar 6-DOF drive system vertical evolves actuators from the the which combination of a a 3D 3D planar motor to actuate x, y, and ϕ and three individual vertical actuators which allow actuation z Abstract: The integrated planar 6-DOF drive system evolves from the combination of a 3D planar motor to actuate x, y, and ϕ and three individual vertical actuators which allow actuation in z, ϕ and ϕ . In all axes aerostatic guiding is applied while the vertical actuators additionally z and three individual vertical actuators which allow actuation xmotor to y actuate x, y, and ϕz planar in z, and In guiding is while the vertical actuators additionally y ..actuate planar x,weight y,aerostatic and compensation ϕz and three individual vertical which actuation in z, ϕ ϕxxxmotor anda ϕ ϕto In all all axes axes aerostatic guiding istoapplied applied while theactuators vertical actuators additionally implement pneumatic carry while the static weight actuators of the allow slider which is y in z, ϕ and ϕ aerostatic guiding is applied the vertical additionally y . In all axes implement a pneumatic weight compensation to carry the static weight of the slider which is in z, ϕ and ϕ . In all axes aerostatic guiding is applied while the vertical actuators additionally x y implement a pneumatic pneumatic weight compensation toand carry the static static weight of the the slider which is why these elements are also referred to as liftingto actuation units (LAU). For slider 6D closed loop implement a weight compensation carry the weight of which is why these elements are also referred to as lifting and actuation units (LAU). For 6D closed loop implement adisplacements pneumatic weight compensation toand carry the with static of the slider which is why these are also referred to as lifting actuation units (LAU). For 6D closed loop control theelements and tilting angles are measured a weight high precision multichannel why these elements are also referred to as lifting and actuation units (LAU). For 6D closed loop control the displacements and tilting angles are measured with a high precision multichannel why these elements are also referred to as lifting and actuation units (LAU). For 6D closed loop control the displacements and tilting angles are measured with a high precision multichannel plane mirror interferometer system. The paper introduces the concept of the integrated planar 6control the displacements and tilting angles are measured with a high precision multichannel plane mirror interferometer system. The paper introduces the concept of integrated planar 6control thesystem displacements and tilting angles are measured a ahigh precision plane drive mirror interferometer system. The paper introduces thewith concept of the the integrated planar 6DOF and explains the design of the realized system for travel range ofmultichannel 100 mm in plane mirror interferometer system. The paper introduces the concept of the integrated planar 6DOF drive system and explains the design of the realized system for a travel range of 100 mm in plane mirror interferometer system. The paper introduces the concept of the integrated planar 6DOF drive system and explains the components: design of of the the realized realized system for aa travel travel range ofplanar 100 mm mm in x, y and 10 system mm in z. The three key the lifting and actuation units, theof direct DOF drive and explains the design system for range 100 in x, yy and 10 mm in z. The three key components: the lifting and actuation units, the planar direct DOF drive system and explains the design of the realized system for a travel range of 100 mm in x, and 10 mm in z. The three key components: the lifting and actuation units, the planar direct drive system and the multichannel interferometer system are explained in more detail including x, y and 10 mm inthe z. The three key components: the liftingare andexplained actuationinunits, the planar direct drive system and multichannel interferometer system more detail including x, y and 10 mm z. The three key components: the lifting andexplained actuation the planar direct drive system and multichannel interferometer system are in more detail including preliminary investigations of these individual systems which were carried out to evaluate and drive system andinthe the multichannel interferometer system are explained inunits, more detail including preliminary investigations of these individual systems which were carried out to evaluate and drive system and the multichannel interferometer system are explained in more detail including preliminary investigations of these these individual systems which weresystem. carried out to to evaluate and improve the investigations performance prior to the integration into the overall preliminary of individual systems which were carried out evaluate and improve the performance prior to the integration into the overall system. preliminary of these individual systems which weresystem. carried out to evaluate and improve the the investigations performance prior prior to the the integration into the the overall system. improve performance to integration into overall © 2019, IFAC (International prior Federation of integration Automatic Control) Hosting bysystem. Elsevier Ltd. All rights reserved. improve the performance to the into the overall Keywords: Keywords: nanopositioning nanopositioning and and -measuring -measuring machines, machines, nanofabrication, nanofabrication, integrated integrated direct direct drives, drives, Keywords: and -measuring machines, direct air bearingnanopositioning stage, multi-coordinate drive, plane mirrornanofabrication, interferometer integrated Keywords: nanopositioning and -measuring machines, nanofabrication, integrated direct drives, drives, air bearing stage, multi-coordinate drive, plane mirror interferometer Keywords: and -measuring machines, air stage, drive, mirror interferometer air bearing bearingnanopositioning stage, multi-coordinate multi-coordinate drive, plane plane mirrornanofabrication, interferometer integrated direct drives, air bearing stage, multi-coordinate drive, plane mirror interferometer 1. common 1. INTRODUCTION INTRODUCTION common approach approach of of a a passive passive mechanical mechanical guiding, guiding, this this 1. common approach of a aheight passive mechanical guiding, this guiding will introduce deviations and guiding, tilting errors 1. INTRODUCTION INTRODUCTION common approach of passive mechanical this guiding will introduce height deviations and tilting errors 1. INTRODUCTION approach of passive mechanical this Our modern society is characterized by countless appli- common guiding movement. will introduce height deviations and guiding, tilting errors during In aheight addition, the thickness or height guiding will introduce deviations and tilting errors Our modern society is characterized by countless appliduring movement. In addition, the thickness or height guiding will introduce height deviations and tilting errors Our modern society is characterized by countless applications resulting from the advances in the semiconductor during movement. In addition, the thickness or height of the objects is not constant for example varying wafer Our modern society characterized appli- during movement. addition, the thickness or height cations resulting fromis advances in by thecountless semiconductor of the objects is notIn for example varying wafer Our modern isthe characterized by appli- during movement. Inconstant addition, the thickness or height cations resulting from the advances inand thecountless semiconductor technology andsociety in from other fields of micronanotechnology of the is constant for example varying wafer thickness or wafer bow. Besides certain application cations resulting the advances in the semiconductor of the objects objects is not not constant forthat, example varying wafer technology and in other fields of microand nanotechnology thickness or wafer bow. Besides that, certain application cations resulting from the advances in the semiconductor of the objects is not constant for example varying wafer technology and in inlithographic other fields fields of of micro- and and nanotechnology as well. Thereby, methods are the most import thickness thickness or or wafer bow. Besides that, that, certain lenses, application scenarios, like the manipulation of optical may technology and other micronanotechnology wafer bow. Besides certain application as well. Thereby, lithographic methods are the most import scenarios, like the manipulation of optical lenses, technology and in other fields of microand nanotechnology thickness or wafer bow. Besides that, certain application as well. Thereby, lithographic methods are the most import part. But moving down to sub-10 nm nodes the production scenarios, like the the manipulation manipulation of at optical lenses, may may require a measurement or structuring large macroscopic as well. Thereby, lithographic methods are the most import scenarios, like of optical lenses, may part. But moving down to sub-10 nm nodes the production aa measurement or structuring large macroscopic as well. Thereby, methods are the import require scenarios, likeInthe manipulation of at optical lenses, may part. But moving down nm the production facilities become increasingly complex and very expensive. require measurement or structuring at large macroscopic height levels. view of these aspects, the observance of part. But movinglithographic down to to sub-10 sub-10 nm nodes nodes themost production require a measurement or structuring at large macroscopic facilities become increasingly complex and very expensive. height levels. In view of these aspects, the observance of part. Butbecome moving down to sub-10 nm nodes the production require a measurement or structuring at large macroscopic facilities become increasingly complex and investigated very expensive. Therefore, new fabrication methods are to Abbe’s height levels. In view of these aspects, the observance of principle requires a dynamic raising or lowering facilities increasingly complex and very expensive. height levels. In view of these aspects,raising the observance of Therefore, new fabrication methods are investigated to Abbe’s principle requires a dynamic or lowering facilities become increasingly complex and very expensive. height levels. In view of these aspects, the observance of Therefore, new fabrication methods are investigated investigated to Abbe’s allow for a new morefabrication flexible and still profitable production Abbe’s principle requires a dynamic dynamic raising or lowering of the mirror corner and the sample, in order to keep the Therefore, methods are to principle requires a raising or lowering allow for a more flexible and still profitable production of the mirror corner and the sample, in order to keep the Therefore, new fabrication methods are investigated to Abbe’s principle requires a dynamic raising or lowering allow for a more flexible and still profitable production of microand nanodevices, see Kühnel et al. (2018); Tseng of the mirror corner and the sample, in order to keep the touch each case Abbe point. Realizing allow for and a more flexible and still profitable production of the point mirrorin corner and in thethe sample, in order to keep this the of micronanodevices, see Kühnel et al. (2018); Tseng touch in each case in Abbe point. Realizing allow for a more flexible and still profitable production of the point mirror corner and thethe sample, in order to keep this the of microand nanodevices, see et Tseng (2011); Vorbringer-Doroshovets et al. (2013). The authors touch point in each case in the Abbe point. Realizing this vertical motion within a long-range nanopositioning of microand nanodevices, see Kühnel Kühnel et al. al. (2018); (2018); Tseng precise touch point in each case in the Abbe point. Realizing this (2011); Vorbringer-Doroshovets et al. (2013). The authors precise vertical motion within aa long-range nanopositioning of microand Kühnel etdevelopment al. (2018); Tseng in each case in the Abbe point. Realizing this (2011); Vorbringer-Doroshovets et al. al. (2013). The authors authors contribute in nanodevices, this researchseewith the(2013). of a touch precisepoint vertical motion within long-range nanopositioning system (NPS) is a demanding challenge since it needs to (2011); Vorbringer-Doroshovets et The precise vertical motion within a long-range nanopositioning contribute in this research with the development of a system (NPS) a challenge it (2011); Vorbringer-Doroshovets et al. (2013). The authors precise motion within a long-range nanopositioning contribute in this research with the development of a novel multicoordinate nanopositioning system which can system vertical (NPS) is is a demanding demanding challenge since since it needs needs to to contribute in this research with the development of a system (NPS) is a demanding challenge since it needs to novel multicoordinate nanopositioning system which contribute in with the sample development ofcan a system (NPS) is a demanding challenge since it needs to novel multicoordinate nanopositioning system which can be applied for this the research movement of the during the novel multicoordinate nanopositioning system which can be for the movement of the novel multicoordinate nanopositioning system during which can be applied applied forand thefabrication movement of the the sample sample during the measurement process. be applied for the movement of the sample during the measurement and fabrication process. be applied for the movement of the sample during the measurement and and fabrication fabrication process. process. measurement Usually the measuring and structuring systems for these measurement and fabrication process. Usually the measuring and systems for Usually the measuringrequire and structuring structuring systems for these these kinds of the technologies an xy-stage that moves the Usually measuring and structuring systems for these kinds of technologies require an xy-stage that moves the Usually the measuring and structuring systems for plane. these kinds ofwith technologies require an xy-stage xy-stage that moves moves the sampleof very highrequire precision in the horizontal kinds technologies an that the sample with very high precision in the horizontal plane. kinds ofwith technologies require an xy-stage thatamoves the sample precision in the horizontal plane. To avoid firstvery orderhigh measurement errors, such system is sample with very high precision in the horizontal plane. To avoid first order measurement errors, such a system is sample with very high precision in the horizontal plane. To avoid first order measurement errors, such a system is designed so that the measuring axes meet at one point, To avoid first order measurement errors, such aone system is designed so that the measuring axes meet at point, To avoid first order measurement errors, such a system is designed so that which the measuring measuring axes meet at one one point, the Abbe so point, is also theaxes point where the probe designed that the meet at point, the Abbe point, which is also the point where the probe designed so that the measuring axes meet at one point, thethe Abbe point, which which is also also the thewith point where thesurface. probe or processing tool interacts thewhere sample the Abbe point, is point the probe or the processing tool interacts the sample surface. the Abbe point, which is also when thewith point where the probe or the tool interacts with the sample surface. This is processing achieved, for example, the object is located or the processing tool interacts with the sample surface. This is achieved, for example, when the object is located or the processing tool interacts with the sample surface. This is achieved, for example, when the object is located within a mirror corner and all virtually extended measuring This for example, when the object measuring is located withinis aachieved, mirror corner and all virtually extended This for example, when is located within mirror corner and all all virtually virtually extended measuring beamsisaaachieved, of the corner interferometers meetthe at object the probing or within mirror and extended measuring beams of the interferometers meet at the probing or within a mirror corner and all virtually extended measuring beams of of point the interferometers interferometers meetprinciple, at the the probing probing or processing (Abbe’s comparator see Manske beams the meet at or processing point (Abbe’s comparator principle, see Manske beams of point the interferometers meet at the probing or Fig. 1. Abbe’s comparator principle processing (Abbe’s see Manske et al. (2012)), as showncomparator in Fig. 1.principle, However, with the processing point (Abbe’s comparator principle, see Manske Fig. et al. (2012)), as shown in Fig. 1. However, with the processing point (Abbe’s comparator principle, see Manske Fig. 1. 1. Abbe’s Abbe’s comparator comparator principle principle et al. (2012)), as shown in Fig. 1. However, with the 1. Abbe’s comparator principle et al. (2012)), as shown in Fig. 1. However, with the Fig. 1. Abbe’s comparator principle et al. (2012)), as shown in Fig.Federation 1. However, with Control) the Fig. 2405-8963 © 2019, IFAC (International of Automatic Hosting by Elsevier Ltd. All rights reserved.
Copyright © 2019 IFAC 838 Copyright © under 2019 IFAC 838 Control. Peer review responsibility of International Federation of Automatic Copyright © 838 Copyright © 2019 2019 IFAC IFAC 838 10.1016/j.ifacol.2019.11.693 Copyright © 2019 IFAC 838
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permanently counteract the gravitational force and the vertical drive system needs to be designed in a way that it induces only a minimum of disturbances into the overall system while it is still enabling nanometer precision in the other axes of motion. Different design approaches for zdrives in NPS’s can be found in Hackel (2010); Donker et al. (2009) and Manske et al. (2017). The paper at hand presents the idea of an integrated planar 6-DOF drive which evolves from the combination of a 3D planar direct drive to actuate x, y, and ϕz and three individual vertical actuators which allow actuation in z, ϕx and ϕy . 2. BASIC CONCEPT OF THE 6D NPS A common approach is the serial arrangement of x-, y- and z-stage, found in Hausotte (2002); Manske et al. (2017). Here single axis translational stages are stacked on top of each other, locking the rotating motions by design but also increasing the mechanical complexity. Furthermore, the upper stages need to be moved by the lower stages, increasing the load on these.Our development of a 6-DOF NPS presented in this paper is based on the Nanometer Planar Positioning System NPPS100. This mechanically simple planar direct drive system (details see sec. 3) should be used and expanded to allow a 6D manipulation. The term planar direct drive refers to a drive system which positions an object within the horizontal xy-plane and where the driving forces act directly on the moving mass without any force transmission system. In recent research work IMMS together with TU Ilmenau and SIOS realized the NPPS100 as a demonstrator setup for a planar nanopositioning system with 100 mm travel range based on the planar direct drive approach, see Hesse et al. (2008, 2012). Our concept works with an integration of the z-drives into the parallel drive structure, thereby maintaining the benefits of the direct drive principle for all actuated degrees of freedom. This parallel kinematic approach is shown in Fig. 2.
(LAU, see sec. 4). These LAUs are integrated between the slider body and the planar air bearing. For a projected nanometer precision the additional degrees of freedom (vertical coordinate z, two tilting angles ϕx , ϕy ) need to be measured extremely precise. Therefore, the measurement system needs to be expanded (details in sec. 5). In the following sections, these three main subsystems of the NPPS100-6D are described. 3. PLANAR DIRECT DRIVE SYSTEM The design of this NPS follows the basic idea to move a zerodur reflector very precisely while its position is measured with high resolution laserinterferometers and in accordance with the Abbe principle as mentioned above. Following this idea the approach here was to apply a planar direct drive system with aerostatic guiding for the lateral positioning of the zerodur corner mirror in a large travel range. Fig. 3 shows a photo of the assembled NPPS100 integrated planar drive system. The moving zerodur slider has an aerostatic guiding consisting of three air bearing pads and providing virtually frictionless planar support with respect to the granite base plate. Thus, the slider is free to move in x, y and ϕz . In regulated operation however, the movement in x, y and ϕz is actively controlled while the movement in z, ϕx and ϕy is mainly determined by the flatness of the granite base. The direct drive system is created by the superposition of three linear actuators each consisting of a pair of frame fixed flat coils and a corresponding magnet array on the sliders underside. The three individual driving forces act simultaneously on the slider and combine to an arbitrarily directed horizontal driving force that moves the slider in x and y and a torque around the z-axis to control the rotation ϕz . Interferometers on the base measure the distance to plane mirrors on top of the slider and deliver the feedback signal for the x, y and ϕz control loop. At this point it becomes important that for the interferometers a reflector is necessary in at least the same size as the intended travel range. For this reason the slider itself is made of zerodur and has the reflectors directly bonded to it on the upper side so that the slider of the drive system and the reflector
Fig. 2. Comparison of different kinematics for a 6-DOF 1 : planar drive system, based on a planar drive. 2 3 4 : parallel with 3-DOF; , : serial kinematics; kinematics This concept has already been realized as Mag6D, but with reduced precision and a very small lifting range of just 100 µm, see Schäffel et al. (2016). To use the concept where a vertical travel in the millimeter range is needed, new drives and guidings need to be integrated. Therefore, the slider will sit on three Lifting and Actuating Units 839
1 : air bearing; Fig. 3. Components of the NPPS100: 2 : x-reflector; 3 : x-interferometer; 4 : drive coils; 5 : granite base; 6 : zerodur slider; 7 : object table; 8 : y, ϕz -reflector; 9 : y, ϕz -interferometer; 10 : capac itive probes
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for the interferometers are incorporated in one and the same rigid body. This leads to a simple and stiff kinematic structure and together with the frictionless guiding allows for nanometer positioning. From Fig. 3 can be seen that the granite base serves as a basis for the setup. It delivers the reference for the movement of the slider in z-direction as well as for its tilting around the horizontal axes ϕx and ϕy . This reference however, is not perfectly flat as a surface flatness of about 0.5 up to 1 µm is the economic limit. In this way, a vertical position error is introduced into the sliders movement. As this error is different for all three pads the slider performs an error motion in z but also shows two tilting angle errors in ϕx and ϕy . These errors change as a function of the sliders xy-position but they may also change with time so that height compensation at the base points of the slider support is necessary to keep up the exact horizontal position. Having the NPPS100 as a test setup with subnanometer positioning performance regarding the closed loop control in x, y and ϕz (see Hesse et al. (2012); Zschäck et al. (2014)) in a first step we used this setup to determine the actual extent of the parasitic error motions in z, ϕx and ϕy . Therefore, we added another plane mirror interferometer and a two-axes autocollimator (see Schmidt (2008)) both looking at the z-mirror on the sliders underside, see Fig. 4. With these measurement capabilities we analyzed the error motions when the slider is positioned within its travel range. At a number of commanded positions within the travel range the actual z-position, as well as ϕx and ϕy were traced with 10 kHz for 1 second and from that time series the mean value was calculated as a measure for the static position of the slider in the respective degree of freedom. The results presented in Fig. 5 (top) reveal an overall ±8 µm inclination of the slider with respect to the guiding reference. This error has its origin in the height adjustment of the air bearings. The remaining z-variation after the linear trend is removed is in the range of ±60 nm (see Fig. 5 bottom) with the corresponding angular error motions in the range of ±1 . These curves result most likely from shape deviations of the mirror and granite surface. To generate the horizontal drive forces, the magnets are preferably arranged at a low height above the coils in order to make efficient use of the strong magnetic field of the permanent magnets. Fig. 6 shows a field distribution of a drive element with a schematically indicated pair of coils. FEM analysis of such arrangements also shows that horizontal forces can still be generated even when the
Fig. 4. Measurement setup for z, ϕx and ϕy .
Fig. 5. Measured z-variation of the NPPS100 (top: zposition; bottom: z-position, removed trend). distance between coils and magnets is increased (dotted coil cross-sections), i.e. when the slider is lifted considerably by a z-drive system. For the same force higher currents are needed as the distance increases due to the lower flux density. Consequently, to a certain extend no dynamic compromises need to be made. For an exemplary magnet arrangement, it was estimated that even with an enlargement of the magnetic air gap from 1 mm to 7 mm, 50 % of the original motor power is still available with the same current supplied to the coils. With the aid of a heightdependent commutation of the coils, however, the drop in motor power can be counteracted. The achieved performance of the NPPS100 and the described investigations of its error motions and the height characteristics of the motor force led us to the conclusion that if the aerostatic bearing pads were replaced by active height-adjustable z-drive elements, the result is a 6-DOF direct drive system with the prospect of excellent positioning properties.
Fig. 6. FEM analysis of the drive units. 840
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4. LIFTING AND ACTUATING UNIT Three identical Lifting and Actuating Units (LAU), each mounted at one corner of the slider body, were developed to lift the slider and to compensate its tilt. By closed loop controlling the 3 cornerpoints of the slider body, the additional degrees of freedom z, ϕx and ϕy can be controlled. To allow a relative vertical motion between the base (planar air bearing contacting the granite base) and the slider each LAU has an internal vertical aerostatic guiding. A voice coil drive was designed and integrated, to generate a contactless vertical driving force. To avoid permanent power loss and heating in the voice coil, a pneumatic pressure chamber is added as a weight force compensation system (WFC). Therefore, the static component of the load is taken off the voice coil. Additionally, a linear encoder is included to measure the vertical position of the LAU. This is necessary since the 6D measurement system is not available for the initialization process. The whole setup sits on a very compact planar aerostatic bearing, which allows the slider to move along x, y and rotate around the z-axis. All the components are shown in Fig. 7. A special focus during the design was set onto the two actuators in each LAU: the voice coil dynamic drive and the pneumatic WFC. Since the slider sits on three LAUs, the pressure chamber of one LAU was dimensioned in a way that a pressure of 1 bar cancels one third of the sliders gravitational force. The constant pressure is maintained via a precision pressure controller. The assembled LAUs (see Fig.8) were tested with a separate measurement setup where they act against a dummy weight. The cooperation of the two actuators can be seen in Fig. 9. The upper graphic shows the step response for a 1 µm step in closed loop operation. An overshoot as well as a convergence towards the setpoint is clearly visible. Subsequently, the setpoint is reached with a positional deviation of about 1 nm RMS for the steady state. The second graphic shows the power loss in the coil of the voice coil. Clearly visible is the acceleration spike in the beginning of the motion. Hereafter, the power drops dramatically as the pressure controller feeds air into the chamber to reach the equilibrium pressure. For holding the drive at a constant position less than 1 µW is needed.
Fig. 8. Photo of the assembled LAU
Fig. 9. Step response of a 1 µm step and corresponding electrical power loss of the voice coil 5. 6D LASERINTERFEROMETRIC MEASUREMENT SYSTEM In order to meet the high demands on position-accuracy and reproducibility, special differential interferometer systems (SIOS GmbH) are to be used for the position measurement, see Schott et al. (2009). These measuring systems are based on the measuring principle of the Michelson interferometer. The complete interferometer optics are placed in a compact sensor head from which measurement and reference beams are guided out to the target mirrors. Both beams pass through identical paths and are influenced equally by environmental changes such as temperature fluctuations. Thus, a temperature stability of < 20 nm K−1 is achieved by the sensor head.
Fig. 7. LAU main components from left to right: WFC, vertical guiding, vertical measurement, voice coil 841
Its strictly symmetrical optical design results in an extremely high long-term stability of the length measurement. With the environmentally corrected wavelength of a stabilized He-Ne laser as a highly stable measuring standard, these sensors have nanometer accuracy. Two parallel beams record the relative movement between
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a reference mirror and the measuring point on the moved mirror with highest resolution and precision. The measuring range is 5 m with a resolution of 20 pm. The Plane mirror concept is distinguished by the fact that only one measuring beam, which is reflected by the measuring mirror back into itself, is used for the interferometric length measurement. This results in a well-defined sensing point which, in turn, enables the design of Abbe error free measurement arrangements. A planar 2D arrangement is shown in Fig. 10.
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related between measurement and reference beam, are fully compensated. Noise values below 10 pm can be achieved. The usage of differential interferometer systems for positioning measurements allows high precision measurements as several disturbing influences can be compensated by the differential setup. 6. REALIZATION OF THE 6D NPS After these preliminary investigations we refined and completed the constructive implementation of the machine concept as described in section 2. The set up system is shown in Fig. 12. For the first time the existing setup of the NPPS100 is brought together with the three novel lifting and actuation units and the new configuration of the 6D measurement system with differential interferometers at its core. During the design special focus had to be put on the electrical and pneumatic supply of the LAU. It has been possible to accommodate the system of hoses on the underside of the slider. However, the number of tube bends from the fixed frame to the moving slider increased significantly. For that reason we realized a second feeding point to distribute the disturbing forces of the tubes and wires more evenly.
Fig. 10. Interferometer concept In order to verify the suitability of the measuring system, the differential interferometer was compared with a plane mirror interferometer. Both systems were mounted on an optical table of stainless steel and aligned to a common measuring reflector. The measuring distance was about 1 m. The length signals of the interferometer channels were recorded over several hours and subsequently evaluated. The measurements were made under measurement room conditions without climate control. The differential interferometer is characterized by a considerably lower drift, because this type of interferometer setup is compensating the influences of the measurement setup like thermal expansion of the optical table. As can be seen from Fig. 11, the signal-to-noise ratio can also be significantly improved due to the optical difference formation. The decisive influencing factor for the noise are refractive index fluctuations in the beam path caused by air turbulences. All portions of this effect, that are cor-
Also worth mentioning are the three measuring laser beams in the y-direction. This is due to the application of the differential interferometers. The x and y-translation are measured with a single measuring beam on each reflector while the corresponding reference beam paths are led out of the interferometer housing and run right above the measurement paths. Conversely, the sliders rotation around the z-axis is measured with both laser beams of the differential interferometer. Thus, the rotation ϕz is not calculated from two interferometric length measurements but it is directly measured as difference in the optical path length of the two measuring beams. For data acquisition and control the existing and proven modular dSpace real-time system of the NPPS100 remains in use in combination with Matlab/Simulink for programming. The position values are retrieved from the interferometer electronics as 32-bit digital signal representing the actual counter value. Within the control algorithm the interferometer and angular sensor readings are used
Fig. 12. Foto of the NPPS100-6D with the 6D differential interferometric measurement system and the 3 LAUs
Fig. 11. Comparison of interferometer setups 842
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to calculate the six coordinates in x, y, z and ϕx , ϕy , ϕz (input transformation). The individual controllers (SISO) for these coordinates are each set up as a cascade of a velocity- and a position controller with PID characteristics. The required machine states are reconstructed from the measured values and the controller outputs with the help of an observer. The observer is based on the rather simple system model of a double integrator for the moving mass. However this proved to be sufficient, as there are only marginal disturbances and disturbing forces and as the system can be considered as a rigid body in the relevant frequency range (see Hesse et al. (2011)). Output values of the axis controllers are the commanded accelerations in all 6 DOF, which are then transformed into the required phase currents for the six drive coils, the currents for the 3 LAUs and the control voltage for the WFC (output transformation). After putting the NPPS100-6D into operation the first measurements were quite successful. With minimal adjustments of the controllers it was already possible to levitate the slider at z = 1 mm in full 6D closed loop control. Resting at this position RMS-errors (root-mean-square) of 2.3 nm for x and 1.6 nm for y were achieved. For ϕz the measurement resulted in an RMS-error of 26 nrad. 7. OUTLOOK In the future more advanced control strategies will be investigated. Additionally, the positioning accuracy of the NPPS100-6D for every point in the available volume will be evaluated, as well as the 6D deviation from a given trajectory. Further, a redesign of the LAU will be carried out before in a final step the performance of the NPPS1006D in a fabrication environment will be evaluated. ACKNOWLEDGEMENTS This work has been developed in the INPOS project which is funded by the Federal Ministry of Economics and Energy on the basis of a resolution of the German Bundestag under the reference ZF4085707LT7. Furthermore, the authors gratefully acknowledge the support by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the Research Training Group “Tip- and laser-based 3D-Nanofabrication in extended macroscopic working areas” (GRK 2182) at the Technische Universität Ilmenau, Germany. REFERENCES Donker, R., Widdershoven, I., Brouns, D., and Spaan, H.A.M. (2009). Realization of isara 400: A large measurement volume ultra-precision cmm. Proc. of the 24th Annual Meeting of The American Society for Precision Engineering ASPE. Hackel, T. (2010). Grundlegende Untersuchungen zu vertikalen Positioniersystemen für Nanopräzisionsmaschinen. Phd thesis, Technische Universität Ilmenau. Hausotte, T. (2002). Nanopositionier- und Nanomessmaschine. Phd thesis, Technische Universität Ilmenau. Hesse, S., Schäffel, C., Katzschmann, M., and Büchner, H.J. (2011). Interferometric controlled planar nanopositioning system with 100mm circular travel range. Proc. of 26th ASPE Annual Meeting. 843
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