Hybrid EEG-EMG signal controlled transhumeral prosthetic arm

In the world about 15% of the population lives with some kind of disability. Out of those most of them have lost their limbs due to reasons like to injuries, trauma and disease. Out of those a significant portion has lost their upper limb. Amputees who have lost the total function of their hands faces difficulties in performing common day to day tasks. It is challenging for them to carry out even the basic activities of daily living such as feeding themselves, cleaning, bathing, dressing etc. As they’ve lost their finger functions and also the ability to grip they are unable to hold objects and thy cant engage in activities like writing using a keyboard, cooking, sewing, etc.

In order to help those amputated people, researchers have developed prosthetic devices. Even though it is very difficult and hard thing to replicate the functionalities of the human limbs there are several type of commercially available products. First there are cosmetic hands. They only provide the appearance of the hand. Then there are body powered and the electrically powered hands. Considering those two types electronic hands have more functionality than the body powered hands. But those hands do cost a lot. Since most of the disabled persons are from the developing countries it is hard for the amputees to afford the cost of such prosthetic hand.

To cover come those difficulties modular type, low cost prosthetic arm was developed in the epartment of Mechanical Engineering, University of Moratuwa as the final year project of Janaka Subhodha, Kalinga Nisal and Isuru Ruhunage. I
t was developed under the guidance of department’s Senior Lecturer Dr. Thilina lalitaratna and Chamika perera a prost graduate student. The prosthetic hand is controlled by hybrid use of the brain and the muscle signals.
The prosthetic arm consist seven degrees of freedom (DOF). Six in the hand and one for the elbow joint. The controllers of the hand is embedded in the palm of the hand itself. It has the capability of the taking high level control signals from any method. Since this is modular type the trans-humeral as well as the trans-radial amputee can use this.

Most common way of controlling the prosthetic arms is the use of Electromyography (EMG) signals. Means the use of muscle signals. In a human arm the fingers and the gripping is controlled with the radialis muscles. But in case of a trans-humeral the radial
is muscles are not present. Due to that the using the EMG signals for the controlling of the gripping is difficult and not practical. Due to that the griping of the hand is controlled with the use of electroencephalography (EEG) signals.

The controlling signal for the hand is taken as steady state visual evoke potential (SSVEP) signals. A LED strip is attached at the wrist of the hand which blinks at the 6 Hz is used to take signal. By looking at the LED strip the control signal is generated and is send to the hand controller.

A trans-humeral amputee has the bicep and the tricep muscles in the stump. The signals from those muscles are used for the control of the elbow joint. The EMG signals are taken with the use of the Myo band. The signals are fed to a fuzzy-neuro algorithm which generate the required angle of the elbow joint. That generated angle is send to the motor controller of the motor at the elbow joint.

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