Prosthesis

A Prosthetic Hand for Your Friend or Family.

Step-by-Step Manufacturing Process for the Prosthetic Arm

This guide outlines the entire process, from conceptualization to final assembly, ensuring functionality, durability, and user comfort.

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1. Design Phase

Step 1: Anatomical Measurements

• Use 3D scanning or manual measurement to capture the user’s forearm dimensions, wrist shape, and residual limb structure.
• Identify the precise locations of flexor and extensor muscles (e.g., flexor digitorum and extensor digitorum) for placing EMG sensors.

Step 2: Digital Modeling

• Create a 3D CAD model of the prosthesis using software like SolidWorks or Fusion 360:
  • Over Section: Encases the top of the forearm and houses the motors, actuators, and battery.
  • Under Section: Wraps under the forearm and secures the EMG sensors for muscle signal detection.
  • Include hollow channels for synthetic tendons, wiring, and actuation mechanisms.
  • Design modular, articulated fingers with joints to mimic natural hand movement.

Step 3: Material Selection

• Choose lightweight, durable materials:
  • Prosthetic Shell: Nylon (PA12) or carbon fiber-reinforced polymer.
  • Finger Components: TPU (flexible thermoplastic polyurethane) or reinforced ABS.
  • Synthetic Tendons: High-tensile-strength polymer or Kevlar-coated fiber.
  • Electronics Housing: Waterproof, shock-resistant polymer.

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2. Prototyping Phase

Step 4: 3D Printing

• Use SLS (Selective Laser Sintering) or FDM (Fused Deposition Modeling) for component fabrication:
  • Print the prosthetic shell, finger modules, and internal channels separately for modular assembly.
  • Ensure fine tolerances for moving parts like joints and tendon channels.

Step 5: EMG Circuit Prototyping

• Assemble an EMG sensor system:
  • Use medical-grade EMG pads to detect muscle activity.
  • Connect sensors to a microcontroller (e.g., Arduino Nano, ESP32) for signal processing.
• Develop and test firmware to translate muscle signals into motor commands.

Step 6: Actuator and Motor Testing

• Test servo motors or micro linear actuators to ensure they generate sufficient torque for finger movement:
  • Configure for pulling synthetic tendons to mimic flexion and extension.
  • Ensure smooth, proportional response to EMG signals.

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3. Assembly Phase

Step 7: Mounting EMG Sensors

• Install EMG sensors along the identified muscle activation points:
  • Use adjustable pads for secure placement and optimal signal detection.
  • Route sensor wiring through internal prosthetic channels to avoid tangling or damage.

Step 8: Installing Motors and Tendons

• Motor Mounting:
  • Secure motors in the over section of the prosthesis with vibration-dampening brackets.
• Tendon Routing:
  • Thread synthetic tendons through channels in the prosthetic fingers.
  • Attach tendons to motor spools for controlled flexion and extension.
  • Include tension-adjustment mechanisms for fine-tuning.

Step 9: Battery and USB-C Integration

• Battery Installation:
  • Mount a rechargeable lithium-ion battery (2000–3000 mAh) in a protected compartment.
  • Ensure thermal regulation and shock resistance.
• USB-C Port Setup:
  • Incorporate a retractable USB-C charging cable:
    • Use a spring-loaded mechanism for smooth extension and retraction.
    • Protect the cable with durable, flexible materials like reinforced silicone or TPU.
    • Integrate a tuck-away compartment to store the USB-C extension securely when not in use.

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4. Final Assembly

Step 10: Finger Mechanism Assembly

• Assemble finger segments using pivot joints:
  • Use metal pins or durable nylon hinges for joint articulation.
  • Install elastic bands or springs at each joint to assist in finger extension.

Step 11: Wiring and Electronics Integration

• Connect all components:
  • Route wiring for the EMG sensors, motors, and battery through internal channels.
  • Ensure secure connections and waterproofing for electrical components.

Step 12: Haptic Feedback (Optional)

• Install small vibration motors to provide tactile feedback for actions like gripping or releasing objects.

Step 13: External Finish

• Sand and polish 3D-printed surfaces for a smooth, professional appearance.
• Apply a protective coating to ensure durability and resistance to wear.

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5. Testing and Calibration Phase

Step 14: Functional Testing

• Test the prosthesis under real-world conditions:
  • Verify smooth, proportional finger movement in response to muscle signals.
  • Evaluate grip strength and responsiveness for various objects.

Step 15: User Adjustment and Training

• Fit the prosthesis to the user and adjust the tension of synthetic tendons.
• Train the user on using EMG signals to control the prosthetic hand effectively.

Step 16: Final Quality Checks

• Perform durability tests for all mechanical and electrical components.
• Ensure the battery system meets safety and longevity standards.

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This detailed process ensures a functional, durable, and user-friendly prosthetic arm that leverages modern materials and technologies while maintaining modularity for future upgrades or repairs.