Material Selection and Incorporation 

The design goal for this project is to design an upper limb prothesis that can properly play the sport of volleyball, where a set, spike, and bump can be performed. 

The design of the upper limb prothesis for volleyball playing will involve a mixture of techniques and components resulted from 3D printing and EMG signaling. It will primarily be made out of titanium metal, known for its high strength to weight ratio which allows the prosthesis to be durable but maneuverable enough to perform quick movements in succession. Some delicate parts such as joints and fingers will be composed of polycarbonate plastic, which promotes easy maintenance and durability for the prosthesis users.  

The prothesis will consist of five main structural components. These components being: socket, forearm link (elbow), forearm, wrist, and sensor hand. The socket will be produced with the use of 3D-scanning software such as Reality Capture, which creates a 3D model of the patient’s residual limb. This 3D model will then be printed with a 3D printer. This will allow for the socket to be accurate and allows for a snug and comfortable fit. The hand will feature a silicone molded hand to resemble human tissue and skin. The membrane will allow for better grip and mitigate the force of the volleyball, extending the lifespan of the more delicate part of the prothesis such as the motors embedded in the fingers and the fingers themselves. 

EMG Signal Processing 

 To move and control the prothesis, we will utilize myoelectric technology. Myoelectric prothesis includes multi-channel detection systems, where the user input from their remaining upper limb can be monitored. Depending on the patient’s condition and status including age and muscle control, around 10 to 12 electrodes will be used. These electrodes are used to control the movements of the prosthetic arm needed for volleyball playing. These electrodes are attached to the supporting material or socket, stump, and surrounding tissues and muscles for accurate signal reading.  

To translate the information received by the EMG Electrodes into a list of commands for the prosthesis, we require the presence of a microprocessor. The primary objective of the microprocessor is to receive the signals from the electrodes placed onto the residual limb and command the motors within the prosthesis based on the information received. The control scheme of our prosthesis is that information is only translated if the EMG signals from the electrodes can pass an electronic threshold. This may be determined after individual tests of each user, as minimal threshold values can vary per individual. Our microprocessor will be able to control multiple joints simultaneously by overlapping electrical signals from different electrodes and pairing them with their desired function. For example, the appearance of several different electrical signal intensities from the residual limb could signify that the user wants to spike the volleyball. Our microprocessor will be able to recognize these trends with extended use for quicker reaction times. To help in receiving minute electrical signals, we will include an EMG Amplifier, which magnifies the general and musculoskeletal electrical activity and can monitor nerve action potentials. The microprocessor will be located above the forearm joint of our prosthesis and will be connected to the power source and EMG Amplifier.  

The electrical signals will then be classified into 3 different categories: set, spike, and bump. The signals placed into the set category will correspond to a hand motion of slightly contracted fingers as well as pulled back wrist. A spike will be a flat hand with all fingers straight out. A bump will be a loosely closed fist. 

Power Source 

The power source that will drive the translation of information from EMG signals to movements, is the lithium iron phosphate battery. These types of batteries allow for hundreds of cycles of use which translates into a long calendar life. In addition, lithium iron phosphate batteries typically have a lower energy output, which would help ensure full-day usage without need for recharge. The size and weight of the battery will vary depending on prosthesis size as it correlates to the user’s dimensions and age.  

The lithium iron phosphate battery will be connected to various motors placed throughout the prosthesis which contract and retract the joints the user requires. There will be an electrical motor placed above the elbow region that will control the folding of the arm on a single axis. There will be servo motors placed within each individual finger in order to perform functions such as pinching and grasping objects. This motor will also get its commands from the microprocessor. The forearm link will be located at the elbow and will connect the lower and upper extremities of our prosthesis. We will place the hand and elbow circuits within the forearm of the prostheses. This will include micro resistors, switches and regulators, which will ensure that the correct amount of current and voltage is dispersed to each device within the prosthesis. Finally, the user can have the option of covering the sensor hand with a silicone mold to resemble an actual human hand using  

The sum of all the materials and technology we will be incorporating into our design can be seen in the visual model in the figure below. We are confident that this prosthesis will be capable of allowing our users to play volleyball at an optimal level.  

Figure 1. Basic drawn layout of design idea                 Drawn By: Faheem Karim