Development of Biomimetic Robot-eye System with Single Vari-focal Lens and winding-Type SMA Actuator
Based on the biomechanics of the human eye, this lens system consists of a biconvex PDMS lens, winding-type SMA actuator, and mechanical parts, such as grippers, load arms, an outer ring, and body. In contrast to other single vari-focal lenses, the proposed PDMS lens is a gel, thereby avoiding any deflection from gravity and external vibration. Plus, the PDMS lens is circularly enclosed and elongated by load arms joined to an outer ring that is operated by a winding-type SMA actuator. While the advantages of SMA wires are their light weight and high-power density, their deformation is small. Thus, to overcome this limitation, the lever principle is conversely applied to the load arms, allowing a large elongation of the PSMS lens to adjust its focal length, even though the SMA wire is only slightly deformed. Experimental video clips demonstrate the validity of the proposed system.
Development of liquid lens system using antagonistic winding-type SMA actuator
The new variable focal liquid lens system is developed using a SMA(shape memory alloy) actuator. Making a conventional variable focal liquid lens system small and light is difficult, due to the requirement of a large and heavy actuator, such as a pump or an electric motor, to distribute the liquid in the liquid lens. Plus, focal control is also difficult, due to a nonlinear focal variation in relation to a linear actuation. Thus, to solve these problems, a new actuation system is proposed for a liquid lens that uses a SMA wire and rotating piston mechanism, in which a cylindrical cam structure is adopted to create a linear relationship between the radius of the curvature of the lens and the displacement of the actuator. An antagonistic winding-type SMA actuator is also designed to produce a large displacement and fast response time. Experiments using a prototype demonstrate the efficiency of the proposed system.
