Diamagnetically levitated nano positioners with large-range and multiple degrees of freedom

Abstract

Precision positioning stages are indispensable in many branches of science and engineering, where they are employed for imaging, manipulation, fabrication, and material characterization. Compact, multi-degree-of-freedom stages with a large dynamic range are especially desirable since they improve the throughput, versatility in manipulation, and ease of integration with other instruments. However, most positioning technologies demand large compromises be made on one or more of these fronts. This work describes compact diamagnetically levitated nano-positioners to achieve large-range and high precision six-degrees-of-freedom (DOF) positioning. The first part of the thesis describes the design and modeling of a diamagnetically levitated multi-DOF actuator. The actuator comprises a levitating magnetic stage sandwiched between two current-carrying traces. The levitation height of the magnetic stage above the pyrolytic graphite plate was derived by modeling the diamagnetic force. Next, an analytical model was devised to evaluate the electromagnetic forces, torques, and trap stiffness. Subsequently, the developed model was used to demonstrate that dual-sided actuation enables trapping a magnetic stage in 3-dimensions (3D), with independent control of the trap stiffness about two axes and independent application of forces in 3D and torques about two axes. Next, the maximum loads that can be generated using the dual-sided actuation were evaluated. Finally, the maximum possible trap stiffness along all the 3-axis was determined. Although the proposed actuator has multiple degrees of freedom, it cannot be rotated about the Z-axis, and further, it has a limited out-of-plane motion range. The second part of the thesis discusses the design of two novel six-axis positioners based on dual sided-actuation that addresses the limitations of the actuator proposed in the first part. The first design employs four independent actuating zones to apply a couple on a symmetrical X-shaped magnetic stage and thus rotate it about the Z-axis. The second design employs compliant mechanisms integrated with two actuators to convert large range in-plane motion to large range out-of-plane motion. Next, the dynamic model of the positioner was obtained and used to determine its natural frequency. Finally, an analysis was performed to determine the minimum volume of the diamagnetically levitated nano positioners based on the desired travel range and the desired load applying capacity. The third part of the thesis presents the development of the positioning system, which includes the measurement system, the control system, and the positioners. The position measurement system employed high resolution and high-speed cameras integrated with microscopes to acquire the motion of the positioner. The images acquired from the measurement system are digitally processed to make sub-pixel measurements of positioners’ motion. The resolution and range of the developed position measurement system are 1.85 nm and 5.4 mm respectively. The developed positioners demonstrate in-plane translational motion with a range of 5 mm and with positioning precision better than 1.88 nm and an angular motion range of 1.1 radians with a resolution of 50 micro-radian. The out-of-plane translational range has been shown to be 900 μm. In the fourth part of the work, the applications of the developed diamagnetically levitated nano positioners are showcased. Due to the large positioning range and unprecedented positioning resolution of the compact flexure-mechanism-based positioner, it was employed to perform in-situ automated replacement of the tip of Atomic Force Microscope (AFM) probe. It is worthwhile to note that because of the small volume of the nano-positioner (10-20 〖cm〗^3) and the compatibility of the developed tip-replacement module with the available commercial AFM cantilevers, the developed system can be retrofitted in an existing AFM set-up.