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group project

Duchenne muscular dystrophy (DMD) is a genetic disorder that results in the progressive degeneration of muscle cells[1]. People affected by DMD are unable to move their limbs, hands, and fingers once the disorder has progressed far enough. The inability to use most muscles means that these people lose their independence. As a result, it becomes difficult for people with DMD to socialize and connect with others through conventional means, such as playing games. In an interview with a person with late-stage DMD, it became clear that people with this condition want some of their independence back so that they can play games without help from their caretakers.

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Concept 1 is a serial robotic arm using three motors. The first DC motor is located at the base and is responsible for the rotation of the first arm segment along the XY plane, and similarly, the second motor at the first link rotates the second arm segment. Additionally, at the end effector, a servo motor is present which causes the end effector to rotate along the XZ plane, thereby lifting the pen off the canvas when required.

Concept 2 makes use of three DC motors and two gear belts to achieve the desired motion. The first motor situated in the base belt is responsible for moving the arm of the robot horizontally while the motor at the arm belt moves the pen holder across its length. The third motor located in the housing of the robot is meant to rotate the arm along the XY plane such that the pen can reach different areas of the canvas.

Concept 3 is a four-link parallel robot with a 3-DoF range of motion. There are two DC motors located at the base that are responsible for rotating the first segment of the arms along the XY plane. The second segment of the arms is connected freely to the first links and the end effector. A Servo motor rotates the end effector within the XZ plane. This allows the robot to lift the pen off the canvas so it can move around without making marks. Moreover, the holder was made adjustable to accommodate different sizes and weights of pens, markers, or brushes.

The coordinates of the end-effector, point C, can be derived using the formulas.

Due to time restraints, it was decided to not use a PID-controller to control the DC motors. Instead, a very naive controller was implemented. There is no attempt at doing error correction.

Once an angle has been set for the motors to turn, from the measured encoder value it is determined if the motor has turned enough. If the motor has turned enough the velocity is then set to zero bringing the motor to a stop. There is no continuous feedback to eliminate any errors and the robot cannot go back to its intended position if there are any physical disturbances.

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