WO2017142481A1 - High precision localizing platforms - Google Patents

High precision localizing platforms Download PDF

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Publication number
WO2017142481A1
WO2017142481A1 PCT/SG2017/050069 SG2017050069W WO2017142481A1 WO 2017142481 A1 WO2017142481 A1 WO 2017142481A1 SG 2017050069 W SG2017050069 W SG 2017050069W WO 2017142481 A1 WO2017142481 A1 WO 2017142481A1
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Prior art keywords
platform
precision
localizing
stiffness
coupling
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PCT/SG2017/050069
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French (fr)
Inventor
Tat Joo Daniel TEO
Guilin Yang
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Agency For Science, Technology And Research
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Publication of WO2017142481A1 publication Critical patent/WO2017142481A1/en

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    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02KDYNAMO-ELECTRIC MACHINES
    • H02K41/00Propulsion systems in which a rigid body is moved along a path due to dynamo-electric interaction between the body and a magnetic field travelling along the path
    • H02K41/02Linear motors; Sectional motors
    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03FPHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70Exposure apparatus for microlithography
    • G03F7/70691Handling of masks or wafers
    • G03F7/70758Drive means, e.g. actuator, motor
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02KDYNAMO-ELECTRIC MACHINES
    • H02K2201/00Specific aspects not provided for in the other groups of this subclass relating to the magnetic circuits
    • H02K2201/18Machines moving with multiple degrees of freedom

Abstract

According to various embodiments, a high precision localizing platform may be provided. The high precision localizing platform may include: a base comprising a plurality of coils, each coils configured to provide a magnetic field with at least one of a north pole or a south pole pointing at least substantially in a first direction; an outer platform comprising a plurality of magnets and configured to move along a second direction at least substantially perpendicular to the first direction when actuated by at least a first subset of the coils of the base; an inner platform comprising a plurality of magnets and configured to move along the second direction when actuated by at least a second subset of the coils of the base; and an elastic coupling configured to couple the inner platform to the outer platform, wherein the elastic coupling is configured to restrain movement of the inner platform in the first direction in accordance with a first stiffness and to provide a second stiffness along the second direction, wherein the first stiffness is higher than the second stiffness.

Description

HIGH PRECISION LOCALIZING PLATFORMS
PRIORITY CLAIM
[0001] The present application claims priority to Singapore patent application 10201601134V.
TECHNICAL FIELD
[0002] The following discloses a high precision localizing platform. BACKGROUND
[0003] Electromagnetic (EM) actuation may be used to provide automation devices with high acceleration and fast actuating speed such as the linear motors, voice-coil actuators, solenoids, brushed/brushless rotary motors, induction motors, and direct-drive rotary motors.
[0004] However, commonly used devices using EM actuation suffer from insufficient localization precision. Thus, there is a want for enhanced devices which provide high localization precision when using EM actuation.
SUMMARY OF INVENTION
[0005] According to various embodiments, a high precision localizing platform may be provided. The high precision localizing platform may include: a base comprising a plurality of coils, each coil configured to provide a magnetic field with at least one of a north pole or a south pole pointing at least substantially in a first direction; an outer platform comprising a plurality of magnets and configured to move along a second direction at least substantially perpendicular to the first direction when actuated by at least a first subset of the coils of the base; an inner platform comprising a plurality of magnets and configured to move along the second direction when actuated by at least a second subset of the coils of the base ; and an elastic coupling configured to couple the inner platform to the outer platform, wherein the elastic coupling is configured to restrain movement of the inner platform in the first direction in accordance with a first stiffness and to provide a second stiffness along the second direction, wherein the first stiffness is higher than the second stiffness. [0006] According to various embodiments, the first stiffness may be at least a factor of 5 higher than the second stiffness.
[0007] According to various embodiments, the first stiffness may be in a range between 1,000 N/m and 100,000 N/m.
[0008] According to various embodiments, the second stiffness may be in a range between 1,000 N/m and 500,000 N/m.
[0009] According to various embodiments, the inner platform may be configured to have a first resonant frequency, and the outer platform may be configured to have a second resonant frequency.
[0010] According to various embodiments, the first resonant frequency may be in a range between 10 to 500Hz.
[0011] According to various embodiments, the first resonant frequency may be at least a factor of 5 higher than the second resonant mode.
[0012] According to various embodiments, the elastic coupling may have a first dimension in the first direction and a second dimension in a direction at least substantially perpendicular to the first direction, wherein the first dimension is bigger than the second dimension.
[0013] According to various embodiments, the elastic coupling may include or may be or may be included in a flexure joint.
[0014] According to various embodiments, the first platform, the second platform, and the elastic coupling may be one of monolithically integrated or assembled from a plurality of separate parts.
[0015] According to various embodiments, the elastic coupling may include or may be or may be included in a zig-zag shape connection between the outer platform and the inner platform.
[0016] According to various embodiments, the inner platform may be configured to move along a plane at least substantially perpendicular to the first direction when actuated by at least the second subset of the coils. [0017] According to various embodiments, the elastic coupling may include a first coupling and a second coupling one of in series to the first coupling or in parallel to the first coupling.
[0018] According to various embodiments, the first coupling may provide a coupling along the second direction. According to various embodiments, the second coupling may provide a coupling along a third direction at least substantially perpendicular to the first direction and to the second direction. According to various embodiments, the first coupling may provide a coupling along the second direction (for example with the second stiffness) and may restrict (in other words: restrain) movement in the first direction (for example based on the first stiffness). According to various embodiments, the second coupling may provide a coupling along the third direction (for example with a third stiffness, which may be identical or similar to the second stiffness) and may restrict (in other words: restrain) movement in the first direction (for example based on the first stiffness).
[0019] According to various embodiments, the outer platform may include a plurality of permanent magnets with different orientations.
[0020] According to various embodiments, the outer platform may be driven based on a Halbach Moving Magnet Linear Motor.
[0021] According to various embodiments, the inner platform may include a plurality of permanent magnets with identical orientations.
[0022] According to various embodiments, the inner platform may be driven based on a Lorentz-force Motor.
[0023] According to various embodiments, the high precision localizing platform may further include a controller configured to selectively activate the coils based on a desired position of the inner platform.
[0024] According to various embodiments, a precision of positioning of the inner platform may be higher than a precision of positioning of the outer platform.
[0025] According to various embodiments, the high precision localizing platform may be configured for use in at least one of a manufacturing system, a tag reading system, or a hard disk drive head placement system. [0026] According to various embodiments, a manufacturing system may be provided. The manufacturing system may include: a tool holder; a work piece holder; and the high precision localizing platform like described above, wherein the high precision localizing platform may be configured to carry at least one of the tool holder or the work piece holder.
[0027] According to various embodiments, a hard disk drive may be provided. The hard disk drive may include: a magnetic storage medium; a reader head; and the high precision localizing platform like described above, wherein the high precision localizing platform may be configured to move the reader head relative to the magnetic storage medium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to illustrate various embodiments, by way of example only, and to explain various principles and advantages in accordance with a present embodiment.
[0029] FIG. 1 shows an illustration of stiffness in a conventional Maglev planar motor.
[0030] FIG. 2A shows a high precision localizing platform according to various embodiments.
[0031] FIG. 2B shows a manufacturing system according to various embodiments.
[0032] FIG. 2C shows a hard disk drive according to various embodiments.
[0033] FIG. 3 shows a Maglev planar positioner according to various embodiments.
[0034] FIG. 4 shows a monolithically-cut inner fine positioning stage supported by compliant joints of a flexure-based moving platen according to various embodiments.
[0035] FIG. 5 shows an illustration of a working principle of additional stiffness from compliant joint of a flexure-based moving platen according to various embodiments.
[0036] FIG. 6 shows an illustration of a working principle of a dual-stage configuration with a parallel actuation scheme according to various embodiments. [0037] FIG. 7A shows an illustration of a working principle of a dual-stage configuration with a serial actuation scheme (with a schematic of a conventional coarse-fine positioning system).
[0038] FIG. 7B shows an illustration of a working principle of a dual-stage configuration with a parallel actuation scheme (with a schematic of the dual-stage configuration with parallel actuation scheme according to various embodiments).
[0039] FIG. 8 shows an illustration of positioning stability along the X, Y and Z axes of the coarse stage according to various embodiments.
[0040] FIG. 9 shows an illustration of a 10mm circular motion with the tracking errors along the X, Y and Z according to various embodiments.
[0041] FIG. 10 shows an illustration of a motion profile according to various embodiments, wherein the outer diameter is formed by the errors of the coarse (primary) stage and the inner diameter is formed by the errors of the fine (secondary) stage.
[0042] FIG. 11A and FIG. 11B show a square coil array stator for unlimited stroke displacement and discrete coil energize according to various embodiments.
[0043] FIG. 12 shows an experimental setup of the Halbach PM array and square coil stator according to various embodiments.
[0044] FIG. 13A and FIG. 13B show illustrations of the driving force and levitation force of the Halbach PM (permanent magnet) array and square coil stator according to various embodiments.
[0045] FIG. 14A shows an illustration of the working prototype of a single-axis parallel actuated dual-stage configuration according to various embodiments.
[0046] FIG. 14B shows an illustration of the construction according to various embodiments.
[0047] FIG. 15 shows the tracking error of the coarse (primary) stage from a 1mm sinusoidal reference signal, the inner (secondary) stage and tracking error histograms of the coarse stage and the dual-stage configuration. [0048] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been depicted to scale. For example, the dimensions of some of the elements in the block diagrams or steps in the flowcharts may be exaggerated in respect to other elements to help improve understanding of the present embodiment.
DETAILED DESCRIPTION
[0049] The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description. It is the intent of the preferred embodiments to disclose a platform which is able to provide high localization precision.
[0050] Various embodiments are related to Electromagnetic (EM) actuation, magnetic levitation (Maglev) displacement motors, and a flexure -based stage. Electromagnetic (EM) actuation may be used to provide automation devices with high acceleration and fast actuating speed such as the linear motors, voice-coil actuators, solenoids, brushed/brushless rotary motors, induction motors, and direct-drive rotary motors etc. Such an actuation may be realized through various methods, for example the Lorentz-force principle and the attraction- repulsion technique. The Lorentz-force principle governs that force generation is proportional to an amount of current density within a region of static magnetic field while the attraction- repulsion technique may be force generation through attraction or repulsion of two induced magnetic poles. Unlike the pneumatic and hydraulic actuations, EM actuation offers compact and maintenance-free solution for achieving a controllable mechanical motion through a driving force, which is generated by applying current source within a magnetic field region. Most importantly, such electro-mechanical devices can deliver precision and accuracy through feedback control via high resolution encoders while the accuracy of the pneumatic and hydraulic actuators are usually limited by the compressive nature of the air and oil-fluid respectively. Consequently, electro-mechanical devices may be employed in high-precision positioning systems such as the semiconductor lithography stepper machines or scanners, pick-&-place machines, inspection machines etc.
[0051] Extreme Ultra- Violet (EUV) lithography processes may be a solution (after immerse technique) to achieve shorter wavelength of the light to fabricate the smallest possible features on the wafer chips through photo lithographic al exposure. As a result, high-resolution wafer fabrication lithography systems may be provided with an EUV light source. Within these systems, the silicon wafers need to be exposed in high vacuum environment to prevent contamination of optical elements and absorption of the EUV light by air. Hence, the magnetic bearings become the immediate solution to provide frictionless support to the moving stages in such vacuum environment without risking contamination through air, and mechanical wear, from the air-bearings, and mechanical ball-bearing guides respectively.
[0052] For conventional Maglev planar motors, the stiffness in all driving directions, i.e., in- plane and out-of-plane, may be approximately zero as shown in illustration 100 of FIG. 1. For example, interaction between the current flow inside the coil windings and the magnetic flux density emanates from the PM (permanent magnet) array generates a Lorentz-force along the X-axis represented as Fp . This force may deliver a displacement along the X-axis, δχ„ which may be expressed as
wherein Kp represents the mechanical stiffness of magnetic bearing along the X-axis.
[0053] Generally, Kp may be almost zero, Kp « 0, due to the frictionless nature. Based on Eq. (1), only a small amount of force is required to drive the platen to achieve the desired displacement, else displacement is infinitely large (in other words: with a force which is too high, the platen may move undesirably far). For Kp « 0, there is no mechanical stiffness acting as nature reaction or oppose force to create a balance point in positioning. Hence, holding at one position requires both sides of the moving platen to generate Fp with opposite magnitude to create such a balance point. Yet for nanometer positioning, control becomes extremely difficult because the current input must be of high resolution due to the low in- plane stiffness. This is because Lorentz-force generation is proportional to the input current, i, the coil length with the magnetic flux density region, L, and the magnitude of the magnetic flux density, B, which emanates from the PM:
Figure imgf000009_0001
[0001] Based on Eq. (2), assuming that L and B have constant values, the smallest achievable force is determined by the smallest controllable current from the amplifier. Due to zero mechanical stiffness, i.e., Kp « 0, such smallest achievable force may directly translate into smallest achievable displacement, e.g., δχ, based on Eq. (1). This may also be known as open-loop positioning resolution of the system. Existing Maglev planar motors are designed for large driving and levitating force due to the mass of the platen. As a result, open-loop positioning resolution may be very low, e.g., hundreds of micrometers. To increase the open- loop positioning resolution, one solution is to increase the internal resistance of the coil windings, R, with constant voltage supply, V, since V = IR. However, such an approach would increase power consumption and subsequently would lead to more heat generation, which is undesired.
[0002] Even implementing a closed-loop positioning control scheme with high resolution interferometer as feedback would be extremely challenging because of the low resonant frequency:
Figure imgf000010_0001
[0003] Based on Eq. (3), existing Maglev planar motors have very low system natural frequency due to Kp « 0, while the platen mass, m, is for example at least one kilogram, i.e., m> 1kg. The result may be low frequency and low-gain systems, which are extremely sensitive to noise. To control a moving platen with low open-loop positioning resolution but high resolution feedback requires high control frequency. In most cases, high control frequency implemented on low natural frequency systems may lead to unstable systems. This may be because a slight adjustment in control gain to reduce positioning noise of such low- gain systems may easily disturb the systems.
[0004] In addition, the stiffness of magnetic bearing in the out-of-plane workspace is also almost zero, i.e., Kpz « 0. For example, the moving platen may fluctuate along the Z-axis while it moves along the X-axis. This may be because of the force-ripple caused by the sinusoidal magnetic field distribution that interacts with a constant current flow within the coil-windings. As the stiffness along Z-axis is low, there may be insufficient oppose force to reduce or eliminate such displacement noise along the Z-axis. Consequently, nanometric positioning along the X-axis may also be coupled with displacement variation along the Z-axis. In most cases, additional control to the levitation displacement may help to minimize the variation along the Z-axis.
[0005] In summary, existing Maglev planar motors use a complex control scheme and systems to achieve both high positioning accuracy and large traveling range. Although they are lower in cost in terms of mechanical components as compared to stacked linear motors architectures, the control systems, which constitute the main cost of the system, become so much higher comparatively. Although other semiconductor system manufacturers may use alternate approaches, such as carrying another fine-motion stage, to achieve the desired accuracy, added mass and requirement of power wires for the actuators, which drive those stages, reduces the system dynamics, and introduces undesired moving power cords. With EUV lithography taking the lead in next-generation of wafer fabrication process, a cost- effective and efficient solution to develop such Maglev planar motors becomes a need.
[0006] According to various embodiments, a high precision localizing platform, which may also be referred to as parallel actuated dual-stage (PAD), may be provided.
[0007] FIG. 2A shows a high precision localizing platform 200 according to various embodiments. The high precision localizing platform 200 may include a base 202 including a plurality of coils (for example, the plurality of coils may be arranged in a regular pattern, so as to form an array of coils). Each coil may be configured to (for example, provided in a spatial orientation so that it may) provide a magnetic field with at least one of a north pole or a south pole pointing at least substantially in a first direction. The high precision localizing platform 200 may further include an outer platform 204. The outer platform 204 may include a plurality of magnets. The outer platform 204 may be configured to move along a second direction when actuated by at least a first subset of the coils of the base 202. The second direction may be at least substantially perpendicular to the first direction. The high precision localizing platform 200 may further include an inner platform 206. The inner platform 206 may include a plurality of magnets. The inner platform 206 may be configured to move along the second direction when actuated by at least a second subset of the coils of the base 202. The high precision localizing platform 200 may further include an elastic coupling 208. The elastic coupling 208 may be configured to couple the inner platform 206 to the outer platform 204. The elastic coupling 208 may be configured to restrain movement of the inner platform 206 in the first direction in accordance with a first stiffness. The elastic coupling 208 may furthermore be configured to provide a second stiffness along the second direction. The first stiffness may be higher than the second stiffness.
[0008] According to various embodiments, the magnets of the outer platform 204 and the magnets of the inner platform 206 may be permanent magnets. However, it will be understood that in an alternative arrangement, the base 202 may include permanent magnets, and the magnets of the outer platform 204 and the magnets of the inner platform 206 may be electromagnets (for example coils). [0009] In other words, according to various embodiments, a platform may be provided, which includes an inner platform 206 and an outer platform 204, which are coupled in a way that the inner platform 206 may easily move along a main movement direction of the outer platform 204, but that movement of the inner platform 206 is constraint with high stiffness in a direction perpendicular to the main movement direction of the outer platform 204.
[0010] It will be understood that although two components of the high precision localizing platform are referred to as inner platform 206 (or inner stage) and outer platform 204 (or outer stage), the outer platform 204 does not need to entirely surround that inner platform 206. According to various embodiments however, the outer platform 204 may surround the inner platform 206, for example in the second direction, and for example furthermore in a direction perpendicular to the first direction and to the second direction.
[0011] According to various embodiments, the first stiffness may be at least a factor of 5 higher than the second stiffness.
[0012] According to various embodiments, the first stiffness may be in a range between 1,000 N/m and 100,000 N/m.
[0013] According to various embodiments, the second stiffness may be in a range between 1,000 N/m and 500,000 N/m.
[0014] According to various embodiments, the inner platform may be configured to have a first resonant frequency, and the outer platform may be configured to have a second resonant frequency.
[0015] According to various embodiments, the first resonant frequency may be in a range between 10 to 500Hz.
[0016] According to various embodiments, the first resonant frequency may be at least a factor of 5 higher than the second resonant mode.
[0017] According to various embodiments, the elastic coupling 208 may have a first dimension in the first direction and a second dimension in a direction at least substantially perpendicular to the first direction, wherein the first dimension is bigger than the second dimension. [0018] According to various embodiments, the elastic coupling 208 may include or may be or may be included in a flexure joint.
[0019] According to various embodiments, the first platform, the second platform, and the elastic coupling 208 may be monolithically integrated (for example may be cut, for example laser-cut, from a single block of material) or may be assembled from a plurality of separate parts.
[0020] According to various embodiments, the elastic coupling 208 may include or may be or may be included in a zig-zag shape connection between the outer platform 204 and the inner platform 206.
[0021] According to various embodiments, the inner platform 206 may be configured to move along a plane at least substantially perpendicular to the first direction when actuated by at least the second subset of the coils.
[0022] According to various embodiments, the elastic coupling 208 may include a first coupling and a second coupling in series to the first coupling or in parallel to the first coupling.
[0023] According to various embodiments, the first coupling may provide a coupling along the second direction. According to various embodiments, the second coupling may provide a coupling along a third direction at least substantially perpendicular to the first direction and to the second direction. It will be understood that first direction refers to z direction (for example a vertical direction when the base is placed on a flat surface), the second direction refers to x direction (for example a horizontal direction), and third direction refers to y direction (for example another horizontal direction).
[0024] According to various embodiments, the outer platform 204 may include a plurality of permanent magnets with different orientations.
[0025] According to various embodiments, the outer platform 204 may be driven based on a Halbach Moving Magnet Linear Motor.
[0026] According to various embodiments, the inner platform 206 may include a plurality of permanent magnets with identical orientations. [0027] According to various embodiments, the inner platform 206 may be driven based on a Lorentz-force Motor.
[0028] According to various embodiments, the magnets of the base 202 may include or may be or may be included in coils. According to various embodiments, the high precision localizing platform 200 may further include a controller configured to selectively activate the coils based on a desired position of the inner platform 206.
[0029] According to various embodiments, a precision of positioning of the inner platform 206 may be higher than a precision of positioning of the outer platform 204.
[0030] According to various embodiments, the high precision localizing platform 200 may be configured for use in a manufacturing system.
[0031] According to various embodiments, the high precision localizing platform 200 may be configured for use in a tag reading system.
[0032] According to various embodiments, the high precision localizing platform 200 may be configured for use in a hard disk drive head placement system.
[0033] FIG. 2B shows a manufacturing system 210 according to various embodiments. The manufacturing system 210 may include a tool holder 212. The manufacturing system 210 may further include a work piece holder 214. The manufacturing system 210 may further include a high precision localizing platform (for example the high precision localizing platform 200 of FIG. 2A). The high precision localizing platform may be configured to carry at least one of the tool holder 212 or the work piece holder 214.
[0034] FIG. 2C shows a hard disk drive 216 according to various embodiments. The hard disk drive 216 may include a magnetic storage medium 218. The hard disk drive 216 may further include a reader head 220. The hard disk drive 216 may further include a high precision localizing platform (for example the high precision localizing platform 200 of FIG. 2A). The high precision localizing platform may be configured to move the reader head 220 relative to the magnetic storage medium 218.
[0035] According to various embodiments, a Maglev planar positioner may be provided that adopts compliant joints to construct a flexure-based moving platen, which consists of a monolithic-cut fine positioning stage within it, like shown in illustration 300 of FIG. 3. The Maglev planar positioner according to various embodiments may deliver both coarse motion and fine motion using one single-layer coil-winding array stator with the PM array attached underneath the flexure-based platen. Based on Lorentz-force principle and a moving magnet configuration, the flexure-based moving platen may be moving above the fixed coil array stator. Hence, this positioner may be truly contactless as there is no cable attached to the platen. Furthermore, its fine positioning capability means that there is no need to carry an additional fine-motion stage, which is usually driven by high positioning resolution actuators, e.g., piezoelectric actuators etc. Consequently, the moving platen does not even need to carry additional wirings that may cause disturbance to the positioning accuracy of the platen. Without these wirings, operating regions for the dual-stage configuration may not be limited by the moving power cables. Furthermore, the moving mass may be significantly reduced due to absent of a fine-motion stage, actuators, and encoder sensors etc.
[0036] According to various embodiments, a flexure-based moving platen (in other words: an outer platform) may be provided with an inner fine positioning stage (in other words: an inner platform), which is supported by compliant joints (in other words: with an elastic coupling) as shown in illustration 400 of FIG. 4. Based on elastic bending to overcome the limitations of the mechanical ball-bearing guides, e.g., backlash, wear-and-tear, and hysteresis etc., these compliant joints, which may also be referred to as flexure joints, may provide frictionless support with high repeatable motion for the inner stage. Such compliant joints may be monolithic -cut from one single piece of moving platen. These compliant joints may have a predictable, repeatable, and linear stiffness that may be used in the Maglev planar positioner (in other words: localizing device) according to various embodiments.
[0037] Like shown in illustration 500 of FIG. 5, the inner stage 502 of the platen may be coupled to the platen 504 through compliant joints where the stiffness, e.g., along the X-axis is represented as Kis and along the Z-axis is represented as Kis_z. For coarse motion along the X- axis, Fp, which is generated by interaction between the current flow inside the coil windings and the magnetic flux density emanating from the PM array, may be used to drive the platen. For fine positioning, the platen may first position itself through Lorentz-force, i.e., Fp + Fs, with opposite magnitude to create a balance point. Next, the adjacent coil windings underneath the inner stage, which may also be attached with the PM array, may be used to generate the necessary force to drive the inner stage. Driving this stage requires the generated force, Fs, to overcome the stiffness of those compliant joints, Kis, and this displacement may be expressed as (4)
[0038] The platen 504 is shown in two portions in FIG. 5; however, it will be understood that in a cross-sectional view like the illustration 500 of FIG. 5, even a platen which is made from only one part, may appear as having two distinct parts.
[0039] Based on Eq. (4), the displacement of the inner stage, Sinner, may be very small since the compliant joints have sufficient stiffness, Kis » 0, and the generated force may be small due to amount of coil windings and the PM array operating underneath the inner stage. Hence, a high open-loop positioning resolution (in other words: a high precision when localizing) may be achieved even with unchanged (in other words: the same) current resolution. Consequently, this may simplify the control when nanometric positioning is desired. The total displacement provided by this concept can be expressed as
Figure imgf000016_0001
[0040] In addition, the compliant joints according to various embodiments may be designed to have high aspect ratio between the thickness and width. Hence, Kis_z may be much higher than Kis. The presence of high Kis_z may passively reduce the undesired noise along the Z- axis during the fine positioning along X-axis. Consequently, various embodiments do not require additional control on the levitation displacement to address such issues and may further simplify the control strategy and systems.
[0041] The Maglev planar positioner according to various embodiments may deliver a coarse-fine motion based on a dual-stage configuration as shown in illustration 600 of FIG. 6. According to various embodiments, the entire flexure-based moving platen may be separated into a coarse positioning stage 602 and a fine positioning stage 604. Both stages may be coupled in series via compliant joints (which also provide a mechanical guide 606) to achieve fine positioning through the use of the stiffness of these compliant joints.
[0042] Like illustrated in FIG. 6, the fine positioning stage 604 may be arranged in parallel and on the same motion plane as the coarse positioning stage. Consequently, the motion of equations for the coarse and fine stages may be mcx + dcx + kcx = Fc + kf(y— x) (6) mf + dfj = Ff ~ kf(y - ) (7) [0043] Eq. (6) and Eq. (7) show that the stiffness of the flexure joints kj is the only coupling parameter between both stages. Unlike the conventional coarse-fine positioning system (like shown in illustration 700 of FIG. 7A), the damping parameter dc of the coarse positioning stage according to various embodiments may not affect the fine positioning stage. Similarly, the damping of the fine stage may have no effect on the coarse stage. In equations (6) and (7), x and y denote the position along horizontal directions, dj denotes a damping parameter of the fine stage, kc is a stiffness of the coarse stage, mc is a mass of the coarse stage, is a mass of the fine stage, Fc is a driving force of the coarse stage, and /y is a driving force of the fine stage.
[0044] According to various embodiments, like shown in illustration 702 of FIG. 7B, both positioning stages (the coarse stage 704 and the fine stage 706) may be serially connected on a same plane so that these stages can be driven concurrently or simultaneously or independently by the single-layer coil-winding array stator, which is fixed underneath the entire flexure- based moving platen. According to various embodiments, such an actuation scheme may be referred to as the parallel actuation scheme. Referring to the conventional coarse-fine positioning system (FIG. 7A), the actuation force required to position the fine stage may generate a reaction force acting on the coarse stage. As a result, this reaction force may disturb the stability of the coarse stage. On the other hand, the parallel actuation scheme may offer zero reaction force acting on the coarse stage. Referring to the dual-stage configuration according to various embodiments (FIG. 7B), the actuation of the fine stage 706 occurs only between the ground 708 and the fine stage 708 itself. Hence, the reaction force caused by the actuation force is acting on the ground 708 instead of the coarse stage 704. This may reduce the possibility of external disturbance that affects the positioning stability of the coarse stage 704.
[0045] According to various embodiments, the coarse stage (in other words: the outer platform) may employ a Halbach Moving Magnet Linear Motor (Halbach MMLM), while the fine stage (in other words: the inner stage) uses a Lorentz-force Motor (FLM). The Halbach MMLM may be driven by a 3 -phase commutation driving scheme to achieve large displacement range and the FLM, which drives the fine stage, uses a single phased non- commutation driving scheme. As the Halbach MMLM provides 2-DOF (degrees of freedom) actuation forces, i.e., an in-plane driving force and an out-of-plane levitation force, the coarse stage, which carries the fine stage, may provide the 6-DOF actuation forces. Each Halbach MMLM may provide 2 degrees -of-motion, i.e., 1 horizontal motion and 1 vertical motion. By having 4 Halbach MMLM provided (for example as shown in the configuration of FIG 11 A, 1 pair of Halbach MMLM may provide the x-axis motion, while other pair may provide the y- axis motion. All 4 Halbach MMLMs may provide orientations, i.e., θχ, θγ, θζ, and vertical motions. Using a 3 -axes laser interferometer (40nm/count resolution) system as a feedback for the coarse positioning stage, FIG. 8 shows an illustration 800 of the positioning performance of the stage. It shows that the Proportional-Integral-Derivative (PID) controller is able to levitate the prototype and position the coarse positioning stage to within +100nm along the X- and Y-axis.
[0046] For further measurements, the coarse positioning stage may be tasked to perform a 10mm diameter circular motion continuously at 0.5Hz. FIG. 9 shows an illustration 900 of the tracking error of this motion profile, which is within +25μιη along the X- and Y-axis. The coarse positioning stage may be tasked to perform a 1mm diameter motion continuously at 0.5Hz. FIG. 10 shows an illustration of 1000 of this motion profile, which is within approximately +10μιη along the X- and Y-axes. With the dual- stage configuration and parallel actuation, illustration 1000 of FIGIO shows that the tracking errors recorded from the inner (secondary) stage are +2.5μιη along the X- and Y-axes. These results show the importance/primary function of the second, inner positioning stage.
[0047] According to various embodiments, to achieve unlimited displacement stroke, a square coils array stator 1102 may be provided as shown in illustration 1000 of FIG. 11 A. The square coil array stator 1102 may be provided specifically together with the dimensions of the PM (permanent magnets) within the Halbach MMLM as shown in FIG. 11B. The permanent magnets may be provided in a plurality of arrays, for example 1104, 1106, 1108, 1110. Hence, no matter where the location of the moving platen is above the stator, there will also be two square coils interacting with three PMs within the Halbach MMLM. As there may be 12 PMs within each Halbach MMLM, eight square coils may be interacting with the Halbach MMLM at any one time. Each coil may be individually controlled, i.e., switched on or off. Depending on the location of the moving platen, only 32 coils underneath the 4 Halbach MMLMs may be energized. A similar concept may be applied to the parallel fine stage within the moving platen. Not only discrete control of coil may be achieved, it may also be an energy efficient solution of a Maglev positioner. [0048] FIG. 12 shows an illustration 1200 of the experimental setup of a single Halbach MMLM 1204 and the square coil array 1202 according to various embodiments. The Halbach MMLM may be constrained to a single degree-of-motion, i.e., the one horizontal translation motion. A force sensor 1206, an XYZ robot 1208, and an amplifier 1210 may be provided for carrying out experimental measurements.
[0049] FIG. 13A and FIG. 13B show that by energizing the square coils, the Halbach MMLM delivered a consistent driving force (illustration 1300 of FIG. 13 A) and levitation force (illustration 1302 of FIG. 13B) along the traveling range of 150mm. Experimental results prove the proposed concept works and expanding the number of square coils array may increase the displacement stroke of the Maglev positioner.
[0050] According to various embodiments, a Maglev positioner may be provided that adopts compliant joints to construct a monolithic-cut flexure-based moving platen. Various embodiments may deliver both coarse and fine motion using one single-layer coil-winding array stator with the PM arrays attached underneath the flexure-based platen.
[0051] According to various embodiments, the flexure-based moving platen may be a dual- stage configuration, which consists of a coarse positioning stage and a fine positioning stage. The fine positioning stage may be coupled in series with the coarse positioning stage via the compliant joints to achieve fine positioning through the use of the stiffness of these compliant joints.
[0052] According to various embodiments, both the coarse positioning stage and the fine positioning stage may be serially connected on a same plane so that these stages can be driven concurrently or simultaneously or independently by the single-layer coil-winding array stator, which is fixed underneath the entire flexure-based moving platen. According to various embodiments, such an actuation scheme may be termed as the parallel actuation scheme.
[0053] According to various embodiments, a monolithic flexure -based stage may be provided within the moving platen to form the fine positioning stage.
[0054] According to various embodiments, a separate flexure-based stage may be provided and mounted on the moving platen so that the separate flexure -based stage is mounted on the same plane as the moving platen, which may in turn become the coarse positioning stage. [0055] According to various embodiments, the coarse stage may be magnetically levitated to deliver at least 1 degree-of-freedom (DOF) motion and up to 6 DOF motion. According to various embodiments, the DOF may be reduced by the use of mechanical guides such as linear bearings, air bearings, compliant bearings etc.
[0056] According to various embodiments, based on Lorentz-force principle and a moving magnet configuration with a fixed array of coil windings stator, the flexure -based platen with permanent magnets mounted on it may be moving above the fixed coil-winding stator. According to various embodiments, the platen may be converted into a moving coil configuration with a fixed array of permanent magnet stator. As a result, the flexure-based platen with coils mounted on it may be moving above a fixed magnetic stator.
[0057] According to various embodiments, for large displacement stroke, an array of square- shaped coils may be provided. Each square-shaped coil may be designed specifically to the dimension of the permanent magnet within the Halbach array. However, the geometry of the coil may not be limited to square. The coil array may be formed by race-track shape coils or circular coils.
[0058] Various embodiments may be used in electronics, semi-conductor, optics, x-ray, and/or a vacuum environment.
[0059] FIG. 14A shows an illustration 1400 of the working prototype of a single-axis parallel actuated dual stage configuration according to various embodiments. FIG. 14B shows an illustration 1412 of the system according to various embodiments. The coarse stage 1402 may be kinematically supported by linear bearings. It may be tasked to perform a 1mm sinusoidal profile. Flexure 1404 may provide a coupling of the coarse stage 1402 to the fine stage 1406. Both the coarse stage 1402 and the fine stage 1406 may be actuated using a plurality of coil stators 1410. A Halbach array 1414 may be used for actuating the coarse stage 1402. A plurality of magnets 1416 may be used for actuating the fine stage 1406. An interferometer 1408 may be used for carrying out measurements of the positioning of the fine stage 1406.
[0060] FIG. 15 shows an illustration 1500 of the tracking errors of the coarse stage being approximately +10μιη and the tracking errors of the dual- stage system being less than Ιμιτι. Graph 1502 illustrates results for the coarse (primary) stage from a 1mm sinusoidal reference signal, and graph 1504 illustrates results for the inner (secondary) stage. Tracking error histograms of the coarse stage (1506) and the dual-stage configuration (1508) are shown. It will be understood that dual- stage configuration refers to a device with both the coarse stage (in other words: outer platform) and the fine stage (in other words: inner platform).
[0061] While exemplary embodiments have been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist.
[0062] It should further be appreciated that the exemplary embodiments are only examples, and are not intended to limit the scope, applicability, operation, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements and method of operation described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A high precision localizing platform comprising:
a base comprising a plurality of coils, each coil configured to provide a magnetic field with at least one of a north pole or a south pole pointing at least substantially in a first direction;
an outer platform comprising a plurality of magnets and configured to move along a second direction at least substantially perpendicular to the first direction when actuated by at least a first subset of the coils of the base;
an inner platform comprising a plurality of magnets and configured to move along the second direction when actuated by at least a second subset of the coils of the base; and
an elastic coupling configured to couple the inner platform to the outer platform, wherein the elastic coupling is configured to restrain movement of the inner platform in the first direction in accordance with a first stiffness and to provide a second stiffness along the second direction, wherein the first stiffness is higher than the second stiffness.
2. The high precision localizing platform of claim 1,
wherein the first stiffness is at least a factor of 5 higher than the second stiffness.
3. The high precision localizing platform of any one of claims 1 to 2,
wherein the first stiffness is in a range between 1,000 N/m and 100,000 N/m.
4. The high precision localizing platform of any one of claims 1 to 3,
wherein the second stiffness is in a range between 1,000 N/m and 500,000 N/m.
5. The high precision localizing platform of any one of claims 1 to 4,
wherein the inner platform is configured to have a first resonant frequency;
and wherein the outer platform is configured to have a second resonant frequency.
6. The high precision localizing platform of claim 5,
wherein the first resonant frequency may be in a range between 10 to 500Hz.
7. The high precision localizing platform of any one of claims 5 to 6, wherein the first resonant frequency may be at least a factor of 5 higher than the second resonant mode.
8. The high precision localizing platform of any one of claims 1 to 7,
wherein the elastic coupling has a first dimension in the first direction and a second dimension in a direction at least substantially perpendicular to the first direction, wherein the first dimension is bigger than the second dimension.
9. The high precision localizing platform of any one of claims 1 to 8,
wherein the elastic coupling comprises a flexure joint.
10. The high precision localizing platform of any one of claims 1 to 9,
wherein the first platform, the second platform, and the elastic coupling are one of monolithically integrated or assembled from a plurality of separate parts.
11. The high precision localizing platform of any one of claims 1 to 10,
wherein the elastic coupling comprises a zig-zag shape connection between the outer platform and the inner platform.
12. The high precision localizing platform of any one of claims 1 to 11,
wherein the inner platform is configured to move along a plane at least substantially perpendicular to the first direction when actuated by at least the second subset of the coils.
13. The high precision localizing platform of claim 12,
wherein the elastic coupling comprises a first coupling and a second coupling one of in series to the first coupling or in parallel to the first coupling.
14. The high precision localizing platform of claim 13,
wherein the first coupling provides a coupling along the second direction;
wherein the second coupling provides a coupling along a third direction at least substantially perpendicular to the first direction and to the second direction.
15. The high precision localizing platform of any one of claims 1 to 14,
wherein the outer platform is driven based on a Halbach Moving Magnet Linear Motor.
16. The high precision localizing platform of any one of claims 1 to 15,
wherein the high precision localizing platform further comprises a controller configured to selectively activate the coils based on a desired position of the inner platform.
17. The high precision localizing platform of any one of claims 1 to 16,
wherein a precision of positioning of the inner platform is higher than a precision of positioning of the outer platform.
18. The high precision localizing platform of any one of claims 1 to 17,
wherein the high precision localizing platform is configured for use in at least one of a manufacturing system, a tag reading system, or a hard disk drive head placement system.
19. A manufacturing system comprising:
a tool holder;
a work piece holder; and
the high precision localizing platform of any one of claims 1 to 18, wherein the high precision localizing platform is configured to carry at least one of the tool holder or the work piece holder.
20. A hard disk drive comprising:
a magnetic storage medium;
a reader head; and
the high precision localizing platform of any one of claims 1 to 18, wherein the high precision localizing platform is configured to move the reader head relative to the magnetic storage medium.
PCT/SG2017/050069 2016-02-16 2017-02-16 High precision localizing platforms WO2017142481A1 (en)

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