Prototyping the flexible solenoid-coil artificial muscle, for exoskeletal robots

Design approaches to exoskeletal robots traditionally aimed to achieve mechanical forces many times larger than the level achievable by the corresponding natural musculoskeletal system. This has often obstructed the user's muscles during physical rehabilitation. Moreover, mechanisms designed for excessive force generation are heavy and rigid structures with little compliance and thus are not suitable for many mobile applications. Here, we present a novel biomimetic flexible solenoid-coil artificial muscle (FSAM) fibre with inherent mechanical compliance, a high pulling stroke, and structural flexibility that suit a lightweight wearable exoskeletal robot for rehabilitation use. FSAM consists of a chain of specially designed bobbins of solenoid coils that can slide against each other. The chain allows FSAM to form an arch shape when the coils are energized; this is reminiscent of a natural muscle that bends a joint by a combined contraction of the muscle length and bending in an arch shape. This strategy of bending a joint not only reduces the need for linear contraction but also allows the exoskeletal to be compliant with the contraction morphology of natural muscle.