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Hybrid Linear Actuator

This example shows a hybrid actuator consisting of a DC motor plus lead screw in series with a piezoelectric stack. The DC motor and lead screw combination supports large displacements (tens of millimeters), but is dynamically slow when tracking the reference demand x_ref. Conversely the piezoelectric stack only supports a maximum displacement of +-0.1mm, but has a very fast dynamic response. By combining the two actuator technologies, a large stroke actuator with precision control results.

An example application is antenna pointing control when tracking a satellite - large amplitude motion with time constants measured in a few seconds is required to move between satellites, whereas fine control is required to track a given non-geostationary satellite.

Run the model with the Manual Switch in the up position to see the tracking of a small demand. The Piezo Stack Demand scope shows that the initial motion is provided by the piezoelectric stack, and this is then washed out as the DC Motor rotor angle moves to the new operating point. Set the Manual Switch to the down position to run a larger step, and rescale the scopes.

If you have Simulink® Control Design™ installed, then a good way to understand the overall actuator performance is to plot a Bode plot. From the toolbar, select Tools->Control Design->Linear Analysis to open the Control and Estimation Tools Manager. Change the plot type to Bode response plot, and then click on Linearize Model. Note that the initial state on the current controller integrator has been set to a small non-zero number to avoid linearizing the Abs block around zero. You can disable the piezoelectric stack to generate a Bode plot for the DC Motor only by putting the Use Stack switch in the Position Controller subsystem to the down position.

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