  Soft actuators have drawn significant attention from researchers with an
inherently compliant design to address the safety issues in physical
human-robot interactions. However, they are also vulnerable and pose new
challenges in the design, fabrication, and analysis due to their inherent
material softness. In this paper, a novel hybrid actuator design is presented
with bio-inspirations from the lobster, or crustaceans in a broader
perspective. We enclose a soft chamber with rectangular cross-section using a
series of articulated rigid shells to produce bending under pneumatic input. By
mimicking the shell pattern of lobsters' abdomen, foldable rigid shells are
designed to provide the soft actuator with full protection throughout the
motion range. The articulation of the rigid shells predefines the actuator's
bending motions. As a result, the proposed design enables one to analyze this
hybrid actuator with simplified quasi-static models and rigid-body kinematics,
which are further validated by mechanical tests. This paper demonstrates that
the proposed hybrid actuator design is capable of bridging the major design
drawbacks of the entirely rigid and soft robots while preserving their
engineering merits in performance.
