This experiment investigates a digital control scheme using a Linear Quadratic Regulator (LQR) to control a rotary flexible link. The flexible link is a thin steel ruler approximately 20 inches long with a DC motor and a light sensor mounted at one end and a light source mounted on the other end The DC motor allows for rotational motion of the flexible link. The light sensor measures the amount of the tip deflection.

In this experiment, the DC motor end of the flexible link is required to track a desired trajectory, either a step or a sinusoidal reference. An experimental investigation easily reveals that the flexible link tip deflection with a position controller that neglects the flexible link dynamics is quite large. In comparison, a position controller that accounts for the flexible link dynamics significantly reduces the flexible link tip deflection.

The control panel on this page allows 5 LQR control gains for the flexible link system to be manipulated. It essentially consists of a set of PID control gains for the base dynamics and a set of PD control gains for the flexible link tip dynamics.

A switch is provided to change the reference signal from tracking a sinusoidal base trajectory to a step reference (by default, the switch off-light color is the step reference).

Finally, a control switch is provided to change the control design to either include the tip dynamics or to disregard the tip dynamics (default switch off-light color refers to the exclusion of the tip dynamics from the control).

  • To view the virtual flexible link model, first zoom forward the virtual object by holding ALT and moving back with the mouse. Next, click and hold the left mouse button to rotate the object to a desirable orientation.

  • Any changes in the sliders or knobs positions for first 5 seconds will not be reflected at the controller. This is an initialization state of the controller, allowing for the experiment to begin at a proper location.

  • Flexible link arm must not exceed 180 degrees from the initialized state on either side, otherwise the experiment will stop.

  • This experiment will stop 2 minutes after you click the start button.

A full description of the electro-mechanical modeling and controller design for the flexible link experiment can be accessed here.

To view a sample movie of the flexible link experiment, click on the following link:

Flexlink.mpg
File Size: 3.6M
Download Time: 19 seconds for T1 connection

Click on the following image to load the flexible link experiment.

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