Design of a stylus with variable tip compliance
Kara, Özdemir Can (2018) Design of a stylus with variable tip compliance. [Thesis]
Humans are known to modulate the impedance properties of their ﬁngers in order to physically interact with the environment. For instance, painting or palpating fragile objects require high compliance of the ﬁngers, while writing and measuring entails high precision position control, for which the stiﬀness of the ﬁngers is increased considerably. In this thesis, we present the design, modeling, implementation, characterization and user veriﬁcation of a stylus with variable tip compliance. In particular, we propose a variable stiﬀness mechanism as a compliant stylus that features an adjustable tip stiﬀness such that users can modulate compliance as needed to match the requirements of the task they perform. The variable stiﬀness of the stylus tip is achieved through transverse stiﬀness variations of axially loaded beams around their critical buckling load. Integrating an axially loaded beam with a compliant transmission mechanism, the stylus tip stiﬀness can be modulated over a large range. In particular, very low stiﬀness levels can be rendered with high ﬁdelity, without sacriﬁcing the mechanical integrity and load bearing capacity of the stylus. Compliant transmission mechanism of the stylus is analyzed through pseudo rigid body modeling which is a convenient and eﬃcient way of modeling ﬂexible elements exhibiting non-linear characteristics under large deﬂections. Furthermore, a novel pseudo rigid body model for a ﬁxed-guided buckling beam that captures the iii transverse stiﬀness variations around the ﬁrst critical buckling load is proposed and veriﬁed. These models are integrated to derive a lumped parameter model of the compliant stylus with adjustable tip stiﬀness. The lumped parameter model due to pseudo rigid body modeling promotes ease of analysis for design, by hiding the underlying modeling complexities of continuum mechanics from the designer. We provide experimental characterization results detailing the range of stiﬀness modulation achieved with several prototypes and verifying the accuracy of the equivalent pseudo rigid body model. We also present a set of human subject experiments that provide evidence in establishing the eﬃcacy of the modulated stylus stiﬀness on the human performance.
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