Final Design

The overall design solution chosen for a 3- actuator mechanism capable of x- and y- translation as well as rotation, was a similar stage to the existing design solution, however while only using one actuator to translate the stage in the y-direction located in one side of the stage, instead of two actuators with one located in both sides of the stage. This method was supported by our simulation models, in which true x- and true y- translation were achievable, and findings through active prototype testing.

In order to actuate the stage given our small fitment requirements, shape memory alloy (SMA) wires were chosen for this task. Shape memory alloy works as a linear actuator that contracts when heat is applied to it. This is done in our design by running current through the wires which causes them to heat up and contract. This process is done indirectly, however, as copper clamps are used to act as electrical conductors to the wire as well as a method for fixing them at either end to the stage. Shape memory alloy must be coupled with springs when using this method, because the wire must be pulled taught when not being actuated in order to ensure proper control and that the mechanism will always return to the origin of the x, y stage after the alignment process. This coupled SMA/bias spring configuration is shown here:

Hall Effect sensors are used to record the position of these actuators for feedback control. These sensors use a small magnetic field that senses changes in magnetism. Therefore these sensors can be used as linear encoders when translated in reference to a magnet. The availability of these sensors and magnets, with compatible sensitivity for our required resolution, in small sizes makes them ideal encoders for feedback control in this project. The positions of these hall effect encoders in the 3-wire assembly are shown below:

    By performing a component analysis of different flexure designs (as seen below on the left) and later FEA analysis, cylindrical flexures were deemed the best fitting for our application. On the right is an isolated view of how these steel wires have been implemented in the final design.