Toward a low hysteresis helical scale Jamming interface inspired by teleost fish scale morphology and arrangement

Inspired by teleost fish scale, this paper investigates the possibility of implementing stiffness control as a new source of robots dexterity and flexibility control. Guessing about the possibility of biological scale jamming in real fish, we try to understand the possible underlying actuation mechanism of such behavior by conducting experiments on a Cyprinus carpio fish skin sample. Bulking tests are carried out on an encapsulated skin sample, in thin latex rubber, for unjammed and vacuum jammed cases. For the first time, we observed biological scale jamming with very small hysteresis due to the unique scale morphology and jammed stacking formation. We call this unique feature 'Geometrical Jamming' where the resisting force is due to the stacking formation rather than the interlocking friction force. Inspiring by this unique morphology and helical arrangement of the scale, in this research, we investigate different possible design and actuation mechanisms for an integrable scale jamming interface for stiffness control of continuum manipulators. A set of curved scales are 3D printed which maintain a helix formation when are kept in place and jammed with two thin fishing steel wires. The non-self locking jagged contact surfaces replicate inclined stacking formation of the jammed fish scale resulting in the same reversible low hysteresis characteristics, in contrast to the available interlocking designs. The effectiveness of the designs are shown for uniaxial elongation experiments and the results are compared with similar research. The contact surfaces, in our design, can be lubricated for further hysteresis reduction to achieve smooth, repeatable and accurate stiffness control in dynamic tasks.