For my Biomedical Engineering bachelor assignment I created a 3D printed prosthetic arm that could be controlled using signals from my own muscles.
Duration: 10 weeks for the entire assignment, +/- 6 weeks for the arm itself
The elbow joint can flex and extend, the lower arm can rotate and the hand can grasp an object
First I designed the arm with three degrees of freedom. The elbow can flex and extend, the lower arm can rotate and the hand can grasp. The joints are controlled with electromyographic (EMG) signals from my biceps or triceps and with dorsal or palmair flexion of the hand. In combination with opposing my thumb, the signal would become 'negative' and result in the opposite motion. For example, closing the hand would become opening the hand.
Second, I calculated the torque that would be necesarry to grasp, lift and rotate a bottle of water with the arm and did some research into what motors I would have to buy to be able to facilitate this.
Elbow: Pololu D37 metal gearmotor + encoder and gearbox
Rotation: Pololu Micro Metal Gearmotor + encoder and gearbox
Hand: 3 TowerPro Servo's MG996R
To be able to filter the EMG signals properly and to control the motors a microcontroller and two shields have been used. They have been programmed with C++.
Microcontroller: Freedom Development Board (FRDM-K64F)
Motor shield: DFROBOT 2A Motor shield
EMG shield: OLIMEX SHIELD-EKG-EMG
The EMG signals are filtered with a Highpass, Notch and Lowpass filter. If these signals pass a certain threshold, a 'desired angle' value is send to the motors. The motors are controlled by a PID controller, which tries to get the actual angle as close as possible to the desired angle. This gets demonstrated it the next movie.
First the 'desired angle' is activated, after that the motor is activated. The actual angle of the motor will try to match the desired angle as fast and close as possible.
