Performance Evaluation of a Parallel Cantilever Biaxial Micropositioning Stage | NIST

1. System Overview The phenomenal growth of opto-electronic manufacturing and future applications in micro and nano manufacturing has raised the need for lowcost high performance micro-positioners. The National Institute of Standards and Technology (NIST) Advanced Technology Program (ATP) funded a team of NIST scientists and engineers to address the performance, testing and calibration needs of micropositioners. As a result of this effort various performance testing and calibration techniques are being developed on a new generation of micro-positioners with low crosstalk, good lateral resolution and strong load capabilities for delicate sub-micron automated assembly and positioning applications. The Parallel Cantilever Biaxial Micropositioning Stage (Figure 1.) is composed of two piezo-electric translators (PZTs) with internal capacitance sensors, two flexure joint couplings, a monolithic mechanical flexure baseplate, two capacitance sensors measuring the inner stage motions, control software and supporting commercial electronics. Inspired from the PiezoFlex Stage [1] which has only one cantilever flexure mechanism on each axis, this new micropositioning stage has a novel configuration and design in that it has two parallel sets of cantilever beam flexures. This design reduces crosstalk in the X and Y translations and creates motions that are more linear and independent from each other in the X and Y directions. The other improvement includes the addition of sensors on axis with the actuator of the system. This is designed to reduce Abbe offset errors for precision measurement and control of the stage. Our new design has the potential to reduce the error caused by the rotation of the cantilever and also provide room for on-axis sensing of the moving x-y stage. It has two micro actuators and two sensors to directly monitor the actuator and stage motions respectively. One of the more important performance characteristics of any planar micro-positioner is its angular cross talk error. All other errors can be compensated with the use of sensors and closed-loop feedback control. Correcting angular error cross talk can often require the use of expensive sensors and additional micro-positioners, which would then have to be connected in series with the planar micro-positioner to induce equal and opposite sign angular displacements. Our first generation micro-positioner has an unqualified (uncertainties yet to be determined) angular error of 0.3” to 0.4” ((1/12000)o to (1/9000)o). 2. Micro-positioner Controller A simple motion controller of the micro-positioner has been developed. Figure 2 shows a schematic block diagram of the controller. The controller is running on a PC and issues motion commands to the controller of two piezoelectric PZT actuators, through a serial line connection. The actuators are Queens Gate (QG) 17 μm capacity PZTs (Q1 and Q2 in Figure 2) and are mounted into machined holes within the structure of the micro-positioner. The actuators are equipped with embedded capacitive gauges, which measure the change in the length of the PZT stacks. This information is used by the QG controller to close the feedback loop. Our controller monitors and