A magnetic levitating stage system comprising one or more magnets and a floating stage

Abstract

A magnetic levitating stage system (100) comprising one or more magnets (601, 602) and a floating stage (300), wherein the stage (300) floats above a base, and the base comprises a magnet system (600) and an actuation board (101) comprising multiple electrically conducting electrodes (400-403) for positioning and control of the stage (300).

Description

[0001] A magnetic levitating stage system comprising one or more magnets and a floating stage

[0002] The invention relates to a magnetic levitating stage system comprising one or more magnets and a floating stage.

[0003] Such a magnetic levitating stage is known from JP4590846B2. US2006 / 0162452 discloses a diamagnetic levitation system with features according to the preamble of claim 1.

[0004] It is an object of the invention to provide a low cost yet precise nano positioning stage which operates at low levels of energy.

[0005] The magnetic levitating stage system of the invention is therefore provided with features according to one or more of the appended claims.

[0006] Essential to the invention is that the stage floats opposite to a base, i.e. the larger part of the stage being at all times substantially above the base, wherein the base comprises a magnet system and an actuation board, said actuation board comprising multiple electrically conducting electrodes for positioning and control of the stage and that one of the electrodes in the actuation board is a central ground electrode centered on a rest position of the stage and fully covered by the stage.

[0007] Advantageously the stage substantially comprises one of diamagnetic material and superconducting material so as to provide that the stage is subjected to a repelling force. The repelling force causes the stage to float so that contact of the stage with the magnet system and the actuation board is avoided In practice this means that the stage must be sufficiently near to the base, for instance at a distance of less than 5 mm without contacting the base, so that a sufficiently strong repelling force will be generated acting on the stage.

[0008] Suitably the actuation board comprises a controller and interface unit equipped with a communications channel for exchange of position and orientation information with an operator .

[0009] Preferably the controller drives the electrodes in the actuation board.

[0010] To improve accuracy it is beneficial that the actuation board comprises one or more sensors for determining a distance of the stage to the electrodes in the actuation board.

[0011] Suitably the sensors are of a type selected from the group comprising capacitive sensors, interferometric sensors, laser deflection sensors with four-quadrant detection, optical gratings, Hall sensors, interferometric microscopy sensors, vibrometer sensors. Sensors that operate contactless are preferred .

[0012] It is further preferred that the magnet system holds one or more magnets in a nonmagnetic support material.

[0013] In certain embodiments it may be preferable that the magnet system comprises magnets on opposite sides of the stage. The magnetic levitating stage system of the invention may then be employed not only with the stage horizontally with the stage above the base, but also upside down.

[0014] Although use can be made of different types of magnets such as electromagnets or superconducting electromagnets, it has preference that the magnets are permanent magnets. Such permanent magnets do not require an external power source. Known permanent magnets comprise ferromagnetic material.

[0015] One of the aspects of the invention is that the stage is arranged to act as an electrode of a capacitor, wherein one or more of the electrodes in the actuation board act as a counter electrode of the capacitor.

[0016] There are many possible arrangements of the electrodes in the actuation board, but the following arrangements are preferable :

[0017] - at opposing sides of the central ground electrode there are off-centered electrodes to provide translation forces to the stage along x, y and / or z-axis, and / or to provide rotation forces around x, y and z-axis, wherein the z-axis is perpendicular to the plane of the electrodes;

[0018] - the x-y translational electrodes and the z-rotational electrodes are partly covered by an edge or by an extension of the stage;

[0019] - the z-translat ional and x-y rotational electrodes that are fully covered by the stage, or by an extension of the stage .

[0020] One of the favorable aspects that the magnetic levitating stage system of the invention thus provides is that it enables controlling 6 degrees of freedom simultaneously. And further that it provides precise position control with sub-pm or even sub-nm precision and precise angle control with sub milliradian precision.

[0021] It is further preferred that the electrodes in the actuation board are covered with an insulating dielectric layer. This avoids that charge transfer can take place between the electrodes and the stage which might affect the generated forces and the power / voltage generation. It also protects people from getting in contact with potential dangerous high voltages.

[0022] There are numerous lucrative application possibilities of the magnetic levitating states system of the invention.

[0023] In several applications it is useful that the stage is provided with a reflective mirror coating. The mirror coating can act as a rotating mirror in laser scanners, deformable imaging systems or as a moving mirror in a spectrometer.

[0024] In other applications it is useful that the stage is provided with a measurement and control unit that comprises a temperature controller with heater. The levitating nature of the stage then provides for a high thermal isolation, which allows heating of the stage to high temperatures without melting of the surrounding materials.

[0025] Heating can be done in several ways, for instance by using an optical system for heating with a laser, and / or by arranging that the actuation board comprises a coil for heating. The heating may be inductive heating.

[0026] Another application is the use of the stage for vibration isolation, where the acceleration of the stage is measured and the forces on the stage are controlled to minimize those accelerations. In other applications, providing a vibration may be desirable.

[0027] One of the strengths of the magnetic levitating stage system of the invention is its high position accuracy and / or precision in the nanometer range. When extended ranges need to be covered, it may be preferable that the system is mounted atop of a second stage which forms part of an external stage system.

[0028] The accompanying drawing, which is incorporated into and forms a part of the specification, illustrates one or more embodiments of the present invention and, together with the description, serves to explain the principles of the invention. The drawing is only for the purpose of illustrating one or more embodiments of the invention and is not to be construed as limiting the invention.

[0029] In the drawing:

[0030] -figure 1 provides a top view at the magnetic levitating stage system of the invention;

[0031] -figure 2 provides a side view of the magnetic levitating stage system of the invention;

[0032] -figure 3 provides a top view of the stage and the magnet configuration to illustrate pushing of the stage laterally to a center position;

[0033] -figure 4 provides different views to illustrate the electrostatic actuation of the stage in six degrees of freedom; and

[0034] -figure 5 shows at the left-hand side of the figure an alternative electrode arrangement together with on the righthand side of the figure a coil for heating in the actuation board . Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

[0035] According to the invention a magnetic levitating positioning stage system 100 is proposed with a stage 300, whose position and orientation can be controlled and set along 6 degrees of freedom (6DOF) . A schematic top view drawing of the system is shown in Fig. 1. The stage 300 comprises an actuator board 101 that contains multiple electrostatic electrodes 400-403 to exert attractive electrostatic forces and force moments on the levitating stage 300 along different axes. Reference 400 depicts a central ground electrode that is centered on the rest position of the stage 300 and is fully covered by it. The stage 300 is preferably constructed out of diamagnetic (e.g. highly oriented pyrolytic graphite HOPG) or superconducting material, such that a repelling force is generated when the stage 300 is close to a magnet. This repelling force is used to counteract the gravitational and other forces on the stage 300, thus enabling it to levitate above a magnet system 600.

[0036] The stage also needs to be electrically conducting or have electrically conducting electrodes incorporated, to enable a contactless electrostatic actuation of the stage 300.

[0037] Figure 1 further shows that the actuator board 101 comprises electronic devices 210, actuation and sensing electrodes 400-403 and wires for interconnecting these elements. A controller and interface unit 201 obtains and communicates information on the actual and desired position and orientation of the stage 300 with a human or machine operator via a communication channel 208 and is powered by a power source 204. Based on the desired position and orientation, the controller and interface unit 201 will calculate and control the voltages on the electrostatic electrodes via a multi-terminal voltage controller 203 that uses a voltage source 202 to generate these voltages and apply them on the electrodes 400-403 via electronic leads that are integrated in the actuator board 101. The actuator board can for instance be a printed circuit board (PCB) , silicon IC CMOS chip or co-fired ceramic circuit.

[0038] For more accurate and precise feedback control, the controller and interface unit 201 can use input from various sensors 205 that are connected by separate wires 206. As shown in Fig. 1, these sensors can be capacitive sensors that determine the distance of the stage 300 to the electrode 400-403 by measuring the capacitance of the capacitors formed by the stage 300 and the electrodes 400-403.

[0039] Instead of a capacitive sensing, other types of sensors might be used, like interferometric sensors, laser deflection with 4-quadrant detection, optical gratings, Hall-sensors or other optical and electrical sensors. Also an interferometric microscope, vibrometer or other optical or microscopic system 700 may be used to accurately determine the position and orientation of the stage 300. Methods that sense position contactless (like capacitive, magnetic or optical) are preferred .

[0040] The actuator board 101 is placed on top of a magnet assembly 600 that holds one or more permanent magnets 601 in a non-magnetic support material. The magnets 601 are arranged in such a way that they provide a repelling force on the stage 300 that counteracts gravity and other forces acting on the stage, such that the stage 300 remains in a levitating state. If the assembly is always kept horizontal as shown in Fig. 2 with gravity pointing downward, it is sufficient to have only magnets 601 below the stage 300. If the stage 300 needs to operate under a variety of angles, at least one additional set of magnets 602 is needed above the stage 300 to counteract gravity if the assembly is held upside-down and the assembly support structure needs to be designed such that the relative positions between the magnets are held nominally fixed.

[0041] Besides a vertical force, the magnets 601 are arranged to also generate a lateral force on the stage 300, such as to generate a potential minimum in the center to which the stage 300 is pushed if all other forces except gravity are zero. A possible arrangement that achieves this is a N-S-N-S alternating permanent magnet 601 configuration as shown in the lower part of Fig . 2.

[0042] Although multiple electrostatic electrode configurations are possible, preference has a specific arrangement of electrostatic electrodes 400-403 as shown in Figs. 1 and 2 that allows controlling the translation and rotation of the stage 300 along all 6 DOFs as shown in Figs. 3 and 4. Since the stage 300 is levitating, it acts as a capacitively floating electrode between two or more electrodes 400-403 in the actuation board 101. Reference 400 depicts a central ground electrode that is centered on the rest position of the stage 300 and is fully covered by it. The electrodes 401- 403 beneath the stage 300 are preferably arranged as follows: reference 401 depicts x-y rotational electrodes, that are off- centered and also fully covered by the stage 300 to generate a couple vector along the x or y direction. Reference 402 depicts x-y translational electrodes, that are off-centered and partly covered by the edge of the stage 300. Reference 403 depict z rotational electrodes that are partly covered by the edge of the stage 300 or a special extension 301 of the stage which is configured to provide a couple vector along the z-axis on the plate if two electrodes are actuated simultaneously.

[0043] An electrostatic force is generated by applying a voltage between at least two electrodes. This can be the ground electrode 400 and one of the other electrodes 401-403, but may also be another combination of electrodes. Since the stage 300 is a floating electrode, it will acquire a voltage that depends on a capacitive voltage division between the different electrodes 400-403 at which voltages are applied.

[0044] The electrostatic force F between the stage 300 and the electrodes 400-403 is determined by the voltage difference

[0045] AV and the gap g between the electrodes and stage. In a parallel plate approximation, the force component perpendicular to the electrodes is given by F=As AV2 / (2g2) , where A is the overlap area between stage 300 and the respective electrodes 400-403 and s is the effective dielectric constant of the material and / or gas in the gap between the stage 300 and the concerning electrode 400-403. More generally, the electrostatic forces on the stage 300 can be calculated by the method of virtual work, determining the gradient of the electrostatic potential energy. E.g. the magnitude of the force component in the x direction is Fx= d / dx (p2 C AV2) wherein C is the capacitance between the stage 300 and the concerning electrode 400-403. Similarly, moments can be calculated via derivatives towards the rotational angles.

[0046] In figs. 1 and 2 all of the electrodes 400-403 also generate a translational attractive force along the z-axis, since electrostatic force is always attractive. The electrodes 400-403 are conductors, that are preferably covered by a thin insulating dielectric layer. This layer is advantageous to prevent charge transfer between the electrodes 400-403 and the stage 300 which might affect the generated forces. It is also advantageous because it protects people against potentially high voltages (nominal operation voltages can be up to or above 200V) . The levitation height of HOPG above permanent magnets, like those made from FeNdB, is about 1.4 mm [see lit. 1-3] . It may be noted from Fig. 2, that the actuation board 101 needs to be substantially thinner than this distance, the actuation board 101 has a typical thickness of 0.6 mm. This leaves a gap between the actuation board 101 and the stage 300 of less than 0.8 mm.

[0047] Since any voltage on an electrode will pull the stage 300 downward, in a proposed way of operation, a voltage on all electrodes is applied to pull the stage 300 downward by -100 micron in the static position. Then relative variations of the electrode voltages will be used to rotate and translate the stage 300 while keeping the static height at, for example, 100 micron below the unactuated position. The translation and rotation of the stage 300 for any combination of electrode voltages can be calculated and implemented in the controller and interface unit 201 to facilitate position control of the stage 300. In the case sensors 205 are integrated in the actuation board 101, a feedback approach can also be used to position the stage 300 up to a condition where the position and orientation of the stage 300 correspond to the desired values, even without an accurate model .

[0048] The range of rotation and translation of the stage 300 is limited by several factors. For the lateral translation and z-axis rotation, using electrodes 402, 403 it is required that the edge of the stage 300 partly overlaps with these electrodes, and the range is therefore limited by the size of the electrodes. Other configuration of stage edge and electrodes may increase the range. An example is shown in Fig. 5 with electrodes 404 arranged such that always a few of the electrodes are partly covered by the stage 300, allowing them to be used to translate the stage 300 in the x and y direction.

[0049] For out-of-plane translation and rotation, the gap 303 between the stage 300 and the actuation board 101 limits the motion range of the stage 300 until contact is made.

[0050] Other translation and rotation limits are given by the maximum voltage provided to the electrodes, and the pull-in voltage, which is the voltage at which the electrostatic force is so large that an instability occurs by which the stage 300 will collapse on the actuation board 101. This instability roughly occurs when the average z-displacement of the stage 300 is more than 1 / 3 of the initial gap 303. The load carrying capacity of the stage 300 is also limited by the levitation force provided by the magnets.

[0051] The magnetic levitation stage system of the invention excels in its high position precision (the inventors expect that the system can potentially reach sub-nm position accuracy with good feedback control) , its 6 DOF control, its miniaturization capability (it can be scaled down to <1 cmA3 especially if part of electronics 210 is made external of the actuation board 101) , and low fabrication cost.

[0052] Since the stage 300 is levitating, another major advantage is that the stage has virtually no mechanical wear and friction, thus enabling extreme good longevity and very low hysteresis. Also operation in vacuum and at low or (very) high temperatures is possible.

[0053] Depending on the application the stage can be functionalized with specialized layers and structures. For application as rotating mirror in laser scanners, deformable imaging systems, and as moving mirror in e.g. spectrometers, a highly reflective mirror coating 302 can be applied. In other experiments, one might want to use the stage as a temperature- controlled sample holder. For these applications the levitating nature of the stage 300 is very beneficial, because it provides very high thermal isolation, and allows heating of the stage to high temperatures without melting of the surrounding materials.

[0054] A measurement and control unit 500, comprising a temperature controller with heater and power source and wireless communication unit 501 can be integrated on the levitating stage 300. The measurement and control unit 500 can also comprise a measurement circuit for performing electrical and magnetic measurements on samples that are placed on the stage 300. Laser controlled heating from an optical system 700 is also a possibility. An alternative method for heating from a distance is using a coil 800 (see fig. 5) that is embedded in the actuation board 101. The coil 800 may generate eddy currents in the stage 300 that causes heating of the stage 300. The coil 800 might also be used for wireless communication or for powering and charging the electronics of the measurement and control unit 500.

[0055] By adding accelerometers and gyroscopes in the measurement and control unit 500 and or controller and interface unit 201 vibration isolation of the stage 300 is possible. Alternatively, the mass of the stage 300 can be used as a 6DOF gyroscope and accelerometer, where the output from the sensors 205 provides a measure of the accelerations and rotations.

[0056] The low cost of the stage 300, that can be less than 10 or even 1 euro, allows it to be a disposable.

[0057] Although the discussed embodiments focus on a magnetic configuration where the stage 300 has a stable minimum in the center and moves with respect to that, other magnet and actuation electrode configurations can be designed, where the stage 300 can be moved over larger lateral distances. It may be beneficial to mount the stage on top of another (less-precise) stage with larger range.

[0058] An attractive embodiment of the invention is the realization of an array of mirrors, each of which is individually controllable. The magnetically levitating stage system 100 of the invention may be miniaturized down to mirror element sizes of 1 mmA2 or less, and many mirrors may be placed near each other to enable an optical tunable surface.

[0059] Although the invention has been discussed in the foregoing with reference to exemplary embodiments of the invention, the invention is not restricted to these particular embodiments which can be varied in many ways without departing from the invention. The discussed exemplary embodiments shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiments are merely intended to explain the wording of the appended claims without intent to limit the claim to these exemplary embodiments. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using these exemplary embodiments.

[0060] Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference. Unless specifically stated as being "essential" above, none of the various components or the interrelationship thereof are essential to the operation of the invention. Rather, desirable results can be achieved by substituting various components and / or reconfiguration of their relationships with one another. Literature

[0061] 1] Chen, X. , Ke§kekler, A. , Alijani, F. , & Steeneken, P. G.

[0062] (2020) . Rigid body dynamics of diamagnet ically levitating graphite resonators. Applied Physics Letters, 116 (24) .

[0063] [2] Chen, X. , Kothari, N. , Ke§kekler, A. , Steeneken, P. G. , & Alijani, F. (2021) . Diamagnet ically levitating resonant weighing scale. Sensors and Actuators A: Physical, 330, 112842.

[0064] [3] Chen, X. , Ammu, S. K. , Masania, K. , Steeneken, P. G. , & Alijani, F. (2022) . Diamagnetic Composites for High-Q Levitating Resonators. Advanced Science, 9 (32) , 2203619.

Claims

CLAIMS1. A magnetic levitating stage system (100) comprising one or more magnets (601, 602) and a floating stage (300) , wherein the stage (300) floats opposite to a base, wherein the base comprises a magnet system (600) and an actuation board (101) comprising multiple electrically conducting electrodes (400-403) for positioning and control of the stage (300) , characterized in that one of the electrodes in the actuation board is a central ground electrode (400) centered on a rest position of the stage (300) and fully covered by the stage.

2. The magnetic levitating stage system of claim 1, characterized in that the stage (300) substantially comprises one of diamagnetic material and superconducting material so as to provide that the stage (300) levitates opposite to the magnet system (600) .

3. The magnetic levitating stage system of claim 1 or 2, characterized in that the actuation board (101) comprises a controller and interface unit (201) equipped with a communications channel (208) for exchange of position and orientation information with an operator.

4. The magnetic levitating stage system of any one of claims 1 - 3, characterized in that the controller and interface unit (201) drives the electrodes (400-403) in the actuation board (101) to generate an electrostatic force or moment on the stage (300) .

5. The magnetic levitating stage system of any one of claims 1 - 4, characterized in that the actuation board (101) comprises one or more sensors (205) for determining a distance of the stage (300) to the electrodes (400-403) in the actuation board (101) .

6. The magnetic levitating stage system of claim 5, characterized in that the sensors (205) are of a type selected from the group comprising capacitive sensors, interferometricsensors laser deflection sensors with four-quadrant detection, optical gratings, Hall sensors, interferometric microscopy sensors, vibrometer sensors.

7. The magnetic levitating stage system of any one of claims 1 - 6, characterized in that the magnet system (600) holds one or more magnets (601) in a nonmagnetic support material .

8. The magnetic levitating stage system according to any one of claims 1 - 7, characterized in that the magnet system comprises magnets (601, 602) on opposite sides of the stage (300) .

9. The magnetic levitating stage system according to any one of claims 1 - 8, characterized in that the magnets (601, 602) are permanent magnets.

10. The magnetic levitating stage system according to any one of claims 1 - 9, characterized in that the stage (300) is arranged to act as an electrode of a capacitor, wherein one or more of the electrodes (400-403) in the actuation board (1) act as a counter electrode of the capacitor.

11. The magnetic levitating stage system according to any one of claims 1 - 10, characterized in that at opposing sides of the central ground electrode (400) there are off- centered x-y rotational electrodes (401) and / or off-centered translational electrodes (402) .

12. The magnetic levitating stage system according to claim 11, characterized in that the x-y translational electrodes (402) are partly covered by an edge of the stage (300) , and / or the x-y rotational electrodes (401) are fully covered by the stage (300) .

13. The magnetic levitating stage system according to any one of claims 1 - 12, characterized in that there are z rotational electrodes (403) that are partly covered by an edge of the stage (300) , or by an extension (301) of the stage.

14. The magnetic levitating stage system according to any one of claims 1 - 13, characterized in that the electrodes(400-403) in the actuation board (101) are covered with an insulating dielectric layer.

15. The magnetic levitating stage system according to any one of claims 1 - 14, characterized in that the stage (300) is provided with a reflective mirror coating (302) .

16. The magnetic levitating stage system according to any one of claims 1 - 15, characterized in that the stage (300) is provided with a measurement and control unit (500) that comprises a temperature controller with heater.

17. The magnetic levitating stage system according to any one of claims 1 - 16, characterized in that the system comprises an optical system (700) for heating with a laser.

18. The magnetic levitating stage system according to any one of claims 1 - 17, characterized in that the actuation board (101) comprises a coil (800) for heating and / or actuation .

19. The magnetic levitating stage system according to any one of claims 1 - 18, characterized in that the system is mounted atop of a second stage which forms part of an external stage system.

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