Team Members:

• Andrew Duenner (University of Texas at Austin)
• Ian Ladner (University of Texas at Austin)
• Nilabh Roy (University of Texas at Austin)
• Xiangzhi Yu (University of Rochester)

objective:

Construct a 2 degree-of-freedom stage to scan a small 2 mm square section of an artifact. An end effector to read the surface height will be provided. The objective is to output a surface height map of the scanned area. Students will work in groups of five. Teams must draw upon their precision engineering skills to solve a multi-disciplinary challenge covering mechanical, electrical, metrology, and controls. Teams will be judged based on originality, best performance, presentation and implementation of precision engineering principles. (ASPE.net)

Stage Design

Each team in the competition was provided one Motus Mechanical Mechblock kit. The kit contained structural pieces with holes on a 1" spacing, hardware, and thin spring steel strips to act as flexures. We started our design by designing a single-axis stage which utilized four of the flexure elements to provide highly repeatable (yet somewhat arcuate) linear motion. Our initial plan was to develop a fully-decoupled XY stage, but due to time limitations we opted for a simpler design with the axises in series. The stage was actuated by voice coils which were controlled by a linear servo amplifier. Due to the large moving mass the stage was expected to have a very low natural frequency. We utilized a vibration isolation table to minimize the introduction of vibrations from the environment and drove the stage at as high a frequency as possible.

Capacitance Probe Challenge

We were provided capacitance probes to provide positioning feedback for the voice coil actuators. The range of the probes was 2 mm while the actuation range was 4 mm. In order to solve this problem we measured displacement of a surface tilted off-axis relative to the direction of translation being measured. We measured displacement of the offset surface relative to the probe as a function of displacement of the surface in line with the translation direction over a 2mm range in order to calibrate the extended range capacitive probe. The correlation was highly linear and our creative solution was a hit with the crowd.

Data used to determine relationship between measured displacement and stage displacement

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