Introduction
In Julie Cimino’s art class, one of her physically-disabled students has little to no control over the actions of her limbs. As a result, she uses a wheelchair and has some ability to rock her upper body back and forth. Traditional art equipment is difficult to use, so we are setting out to build a sketching mechanism that she can interact with.
The basic black box model outlines the context of the mechanism. As shown on the right, the plan is to use accelerometer data from her movement to actuate a signal that drives a “sketching robot mechanism”. The use of the accelerometer provides a causality link between her actions and the output sketch which is important to making the mechanism engaging for the user.
The mechanism design concept is shown to the left. The outer and inner radii of the cam map to the desired x and y positions of the output joint, respectively. The motion of the output joint is then magnified using a pantograph mechanism shown at the top of the sketch. A pencil or pen is at the mechanism's end effector in order to draw the output path.
The cam will be actuated with constant angular velocity, ω, to avoid introducing jerky motion. To implement this, the DC motor and encoder will be implemented using a proportional controller in the control system to maintain velocity even with changing torque loads on the motor.