Conceptual Design and Prototyping of a Bi-Stable Magnetic Actuator

Prosthetics devices have open possibilities for the implementation of new technology that approximate the motion of human limbs. Nonetheless, some limitations are set by the weight and the complexity prostheses can have. Focusing on upper limb prostheses, a digital actuator with stable output positions could drive the system with lower energy requirements. The major achievements of this study are the conceptualization of an actuator that can harvest and store energy from the biomechanical motion of the hand; the implementation of permanent magnets as boundary constraints that can provide both holding or driving forces; and the use of slot Templates as geometric constraints to increase the mechanical advantage and reduce the energy requirement of an actuator driven by permanent magnets. The conceptual design presents the main components an energy harvesting-storage device may have in order to operate properly. To compensate the possible small amount of energy that may be harvested, permanent magnets represent an alternative to reduce the energy required to operate. Furthermore, the present study mathematically characterized the interaction between permanent magnets, explained its physical behavior and prototyped two actuators that represent the conceptual design with two and three stable output positions. The major impact of the prototype was a conceptual proof that the magnetic field of permanent magnets can be used as both holding and driving force. In conclusion, a bi-stable and a tri-stable magnetic actuators were prototyped proving that it is possible to drive a discrete angular joint by using magnetic constraints only, or by combining the magnetic and geometric constraints to move a pin through a slot, providing stable outputs where no energy is required to maintain the system at a stable position. The slot templates were implemented in order to increase the mechanical advantage and the range of forces the system can support. Future directions are proposed with conceptual design of elements of an energy harvesting-energy storage device that can indeed be implemented to activate the motion between permanent magnets and drive the system between output positions, which potentially could be used in prosthetic arm