Prosthetic hands grip in various ways, depending on the type of prosthetic and the technology it uses.
Different prosthetic hand designs utilize various mechanisms to achieve grasping and manipulation. These mechanisms generally fall into two main categories: body-powered and externally powered (myoelectric, etc.).
Body-Powered Prosthetic Hands
Body-powered hands rely on the user's own body movements to control the grip.
- Mechanism: Users typically wear a harness connected by a cable to the prosthetic hand. Moving the shoulder, upper arm, or chest pulls the cable, which then activates the hand's grip. The strength of the grip is proportional to the force exerted on the cable.
- Attachment: As indicated in the reference, smaller body-powered devices, like fingertip or finger prosthetics, are attached with a band on the knuckle or wrist, allowing for controlled movement via tendon assistance.
- Control: Control is often limited to a single grip type (e.g., a pincer grip).
- Advantages: Durable, relatively inexpensive, and provides direct feedback.
- Disadvantages: Limited grip strength and dexterity, can be tiring to operate.
Externally Powered Prosthetic Hands
Externally powered hands use external power sources (batteries) and control systems to achieve grip.
- Myoelectric: These hands use electromyography (EMG) sensors to detect electrical signals generated by muscles in the residual limb. These signals are then processed to control the hand's movements and grip.
- Microprocessor-Controlled: Advanced prosthetic hands incorporate microprocessors and sophisticated algorithms to enable more natural and intuitive control. These hands may offer multiple grip patterns and varying grip strengths.
- Control Methods:
- Direct Control: The user directly controls the hand's movements through muscle contractions.
- Pattern Recognition: The system learns to recognize specific muscle activation patterns and associates them with desired grip types.
- Force Sensors: Some hands use force sensors in the fingers to provide feedback to the user, allowing for more precise grip control.
- Examples:
- Multi-articulating Hands: These hands have multiple joints in each finger, allowing for a wide range of grips and movements.
- Single-Grip Hands: These hands provide a single grip option, often a pinch grip or a power grip.
- Advantages: Greater dexterity, more natural movements, and stronger grip strength.
- Disadvantages: More expensive, heavier, and require more maintenance.
Hybrid Systems
Some prosthetic hands combine features of both body-powered and externally powered systems. For example, a hand might use myoelectric control for grip strength and a body-powered system for wrist rotation.
In summary, prosthetic hands grip using a variety of mechanisms, from simple cable-operated systems to complex microprocessor-controlled devices. The choice of prosthetic hand depends on the user's individual needs, preferences, and functional goals.
