| Summary: | 博士 === 國立中央大學 === 機械工程研究所 === 92 === Friction is inherent in mechanisms. In this dissertation we study the dynamics of
pointing systems involving conspicuous friction. First we develop a general method
for the identification of systems with friction. Then an analytic algorithm for
simulation of discontinuous friction model is presented. In the proposed algorithm we
remove the requirement of the zero-velocity region in the Karnopp-like method and
develop a two-stage integration algorithm to solve the differential equations involving
a discontinuity at zero velocity. A procedure to estimate the Stribeck velocity, which
specifies how the friction force decreases in the range of very low velocities, is also
presented. Next we study the influence of presliding displacement on hunting.
Through experimental and numerical evaluations, we found that presliding
displacement could affect the stability of hunting. Such displacement is also crucial
to the performance of high-accuracy pointing applications. With this observation, we
propose a modified Coulomb friction model to increase its accuracy in the sticking
regime. Finally a controller consisting of three schemes, proportional gain, pulse, and
ramp (PPR), is proposed to achieve precise and fast pointing control under the presence
of friction. Design of the PPR controller is based on two distinctive features of
friction, the varying sticking force and presliding displacement of contacts. The latter
is the main idea behind the ramp scheme to replace integration control, which induces
slow dynamics in the sticking state. Experimental results demonstrate the robustness
and effectiveness of the proposed controller. Stability investigated by the Lyapunov
theorem is given in this dissertation.
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