Shobhit Verma

Six-axis nanopositioning device with precision magnetic levitation technology

In this paper, we present the design, control, and testing of a 6 degrees-of-freedom magnetically-levitated system with nanometer-precision positioning capability and several-hundred-micrometer travel range. This system levitates a triangular single-moving-part platen, and produces the six-axis motion with six single-axis linear actuators. One of the prominent advantages of this magnetic levitation (maglev) system is that there is no physical contact between the moving part and the stator, which eliminates friction, wear, backlash, and hysteresis. As compared to other traditional devices, the present system is very compact with the minimum number of actuators for six-axis motion generation. The maglev device presented herein shows the position resolution better than 5 nm with 2-nm rms position noise, and is capable of a velocity of 0.5 m/s and an acceleration of 30 m/s/sup 2/. The nominal power consumption is only 15 mW by each horizontal actuator, and 320 mW by each vertical actuator. The actuators are sized to be able to orient and position a maximum payload of 1 kg. The key application of this maglev device is the manipulation at nanoscale for microassemblies and manufacture of their parts. Other potential applications are stereolithography, vibration-free delicate instrumentation, and microscale rapid prototyping.

Multi-axis maglev nanopositioner for precision manufacturing and manipulation applications

We present a six-axis magnetic-levitation (maglev) stage capable of precision positioning down to several nanometers. This stage has a simple and compact mechanical structure advantageous to meet the performance requirements in the next-generation nanomanufacturing. It uses the minimum number of linear actuators required to generate all six axis motions. In this paper, we describe the electromechanical design, modeling, and control, and the electronic instrumentation to control this maglev system. The stage has a light moving-part mass of 0.2126 kg. It is capable of generating translation of 300 /spl mu/m in the x, y, and z axes, and rotation of 3 mrad about the three orthogonal axes. The stage demonstrates position resolution better than 5 nm rms and position noise less than 2 nm rms. Experimental results presented in this paper show that the stage can carry, orient, and precisely position a payload as heavy as 0.4 kg. The pull-out force was found to be 8.08 N in the vertical direction. Furthermore, under a load variation of 0.14 N, the nanopositioner recovers its regulated position within 0.6 s. All these experimental results match quite closely with the calculated values because of the accurate plant model and robust controller design. This device can be used as a positioning stage for numerous applications, including photolithography for semiconductor manufacturing, microscopic scanning, fabrication and assembly of nanostructures, and microscale rapid prototyping.

Novel electromagnetic actuation scheme for multiaxis nanopositioning

In this paper, we present a novel electromagnetic actuation scheme for nanoscale positioning with a six-axis magnetic-levitation (Maglev) stage, whose position resolution is 3 nm over an extended travel range of 5x5 mm in the x-y plane. We describe the conceptualization of the actuation scheme, calculation of forces, and their experimental verification in detail. This actuation scheme enables the application of forces in two perpendicular directions on a moving permanent magnet using two stationary current-carrying coils. The magnetic flux generated by the magnet is shared by the two coils, one right below and another on one side of the magnet. The magnitudes and directions of the currents in the coils govern the forces acting on the magnet, following the Lorentz-force law. We analyzed and calculated the electromagnetic forces on the moving magnet over a large travel range. We used feedback linearization to eliminate the force-gap nonlinearity in actuation. The new actuation scheme makes the Maglev stage very simple to manufacture and assemble. Also, there is no mechanical constraint on the single moving platen to remove it from the assembly. There are only three NdFeB magnets used to generate the actuation forces in all six axes. This reduces the moving-part mass significantly, which leads to less power consumption and heat generation in the entire Maglev stage. We present experimental results to demonstrate the payload and precision-positioning capabilities of the Maglev nanopositioner under abruptly and continuously varying loads. The potential applications of this Maglev nanopositioner include microfabrication and assembly, semiconductor manufacturing, nanoscale profiling, and nanoindentation.

Multiaxis Maglev Positioner With Nanometer Resolution Over Extended Travel Range

This paper presents a novel multiaxis positioner that operates on the magnetic-levitation (maglev) principle. This maglev stage is capable of positioning at the resolution of a few nanometers over a planar travel range of several millimeters. A novel actuation scheme was developed for the compact design of this stage that enables six-axis force generation with just three permanent magnets. We calculated the forces with electromagnetic analysis over the whole travel range and experimentally verified them with a unit actuator. The single-moving part, namely, the platen, is modeled as a pure mass due to the negligible effect of magnetic spring and damping. There are three laser interferometers and three capacitance sensors to sense the six-axis position/rotation of the platen. A lead-lag compensator was designed and implemented to control each axis. A nonlinear model of the force was developed by electromagnetic analysis, and input current linearization was applied to cancel the nonlinearity of the actuators over the extended travel range. Various experiments were conducted to test positioning and loading capabilities. The 0.267 kg single-moving platen can carry and precisely position an additional payload of 2k g. Its potential applications include semiconductor manufacturing, microfabrication and assembly, nanoscale profiling, and nanoindentation. DOI: 10.1115/1.2789468

Nanoscale Motion Control With a Compact Minimum-Actuator Magnetic Levitator

This paper presents a novel magnetically levitated (maglev) stage developed to meet the ever-increasing precise positioning requirements in nanotechnology. This magnetic levitator has 6 independent linear actuators necessary and sufficient to generate all 6-degree-of-freedom (6-DOF) motions. This minimum-actuator design concept led to a compact, 200 g lightweight moving part and the power consumption less than of a Watt, thereby reducing the thermal-expansion error drastically. The analysis and sizing of the magnetic linear actuators and the working principle of the maglev stage are presented. We designed and implemented stabilizing controllers for 6-DOF motion control with the dynamic model based on the actuator analysis. Test results showed nanoscale step responses in all six axes with 2 nm rms horizontal position noise. A noise propagation model and analysis identified the capacitance sensor noise and the floor vibration as the dominant noise sources in the vertical and horizontal dynamics, respectively. A comparison of noise performances with controllers closed at 25, 65, and 90 Hz crossover frequencies illustrated how the selection of the control bandwidth should be made for nanopositioning. Experimental results including a 250 μm step response, sinusoidal and square-wave trajectories, and spherical motion generation demonstrated the three-dimensional (3D) nanoscale motion-control capability of this minimum-actuator magnetic levitator. Potential applications of this maglev stage include manufacture of nanoscale structures, atomic-level manipulation, assembly and packaging of microparts, vibration isolation for delicate instruments, and seismic motion detection.

System Identification and Optimal Control of a 6-DOF Magnetic Levitation Stage With Nanopositioning Capabilities

A systematic procedure for modeling and optimal control of a multivariable 6-DOF (degree-of-freedom) magnetically levitated (maglev) stage has been described in this paper. In our previous publications, we have presented the design, SISO (single-input single-output) control, and testing of the maglev stage with nanometer-precision positioning capability and several-hundred-micrometer travel range. In the present work, we extended the current model to a more rigorous LQR (linear quadratic regulation) controller for the lateral control to reduce the coupling between axes. Independent lead-lag controllers have been used for the vertical control. The system equations have been derived using the Euler angle methodology and linearized about an operating point. The performance of this multivariable control has been analyzed and compared with all the six decoupled SISO controllers. The effect of adding the integrators to eliminate the steady-state error has also been discussed and the performance of the LQR controller with different weight matrices has been compared. In this paper, we also address the issues related to the stochastic modeling of the stage to analyze the coupling between different axes and transfer function identification.Copyright

Multi-Axis Maglev Positioner With High Resolution Over Large Travel Range

This paper presents a novel multi-axis positioner that operates on the magnetic-levitation (maglev) principle. This maglev stage is capable of positioning at the resolution of a few nanometers over a planar travel range of several millimeters. A novel actuation scheme was developed for the compact design of this stage that enables 6-axis force generation with just 3 permanent magnets. We calculated the forces with electromagnetic analysis over the whole travel range and experimentally verified them with a unit actuator. The single moving part, namely the platen, is modeled as a pure mass due to the negligible effect of magnetic spring and damping. There are 3 laser interferometers and 3 capacitance sensors to sense the 6-axis position/rotation of the platen. A lead-lag compensator was designed and implemented to control each axis. A nonlinear model of the force was developed by electromagnetic analysis, and feedback linearization was applied to cancel the nonlinearity of the actuators over the large travel range. Various experiments were conducted to test positioning, loading, and vibration-isolation capabilities. This maglev stage has a moving mass of 0.267 kg. Its position resolution is 4 nm over a travel range of 5 × 5 mm in the x-y plane. It can carry and precisely position an additional payload of 2 kg. Its potential applications include semiconductor manufacturing, micro-fabrication and assembly, nanoscale profiling, and nano-indentation.Copyright

Maglev 6-DOF Stage for Nanopositioning

This paper presents a novel magnetically levitated (maglev) stage with nanoscale positioning capability in all six degrees of freedom (DOFs). The key aspect of this device is that its single moving part has no mechanical contact with its stationary base, which leads to no mechanical friction and stiction, and no wear particle generation. We present herein the mechanical design, instrumentation, and test results of this maglev stage. Currently it shows position resolution of 4 nm, position noise of 2 nm rms, hundreds-of-micrometer translational travel range, a-few-milliradian rotational travel range, and power consumption less than a fraction of a Watt per axis. This maglev stage can be used in numerous applications such as manufacture of nanoscale structures, assembly and packaging on micro-size parts, vibration isolation for delicate instrumentation, and telepresence microsurgery.Copyright