Fabrication and strength analysis of humanoid focusing mechanism
Date Issued
2010
Date
2010
Author(s)
Chung, Po-Keng
Abstract
When people stare on an object, different distances of the object will cause the lens accommodation of human eye to focus on this object. The human’s focusing mechanism is composed of a ring of zonular fibers connecting the ciliary muscle to the lens of the eyes. According the Helmholtz’s theory, when the ciliary muscle ring contracts, the displacement generates force on the lens through the zonular fibers and hence the contour of the lens changes. This shape change causes the power change of the lens. In this study, we demonstrated humanoid focusing mechanism that consists of parylene nanofibers and soft polymer lens.
Anodic aluminum oxide (AAO) is a film with arrays of nano-scale holes and used as a template to evaporate parylene C. The holes on the AAO was gradually filled with parylene during the deposition process. By etching the AAO, the parylene membrane with fibrillar structure was then obtained. By assembling this fibrillar membrane with pre-made soft lens and actuator, a bio-inspired lens accommodation system was completed.
For verifying the function of the fibrillar structure around the lens, we assumed that fibrillar structure has the stronger tensile strength than a plane surface. Using simple mechanics models, we found that the plane surface was prone to form crack than the fibrillar structure. An experiment stage was set up to test the tensile strength and to compare two bonding conditions. One of the conditions is the use of the fibrillar structure bonding on a flat polydimethylsiloxane (PDMS), and the other is a smooth plate bonding on the flat PDMS. We found that the bonding strength of the fibrillar structure is triple of the smooth one. This result proves the plane bonding is vulnerable to the crack and the fibrillar structure has stronger bonding strength than the plane one. This work implicitly explains the adoption of fibrillar structure which connects the lens to the ciliary muscle in human eyes.
Subjects
Humanoid lens
fibrillar structure
accommodation
soft lens
tensile strength
anodic aluminum oxide
Type
thesis
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