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Design and Analysis of Kinematic Couplings for Modular Machine ...

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tion. The serial multiplication <strong>of</strong> the HTM’s gives the total interface error at the TCP. First, the nominalgeometries <strong>of</strong> the interface plates, the kinematic couplings, <strong>and</strong> the measurement feature are specified. Theinterface plates are perturbed by error in placement <strong>of</strong> the coupling mounting holes (T holerror ), the kinematiccoupling is perturbed by <strong>for</strong>m error in machining (T <strong>for</strong>merror ), <strong>and</strong> the measurement feature (assumedmodular) is perturbed by <strong>for</strong>m error in machining (T ballerror ). Insertion error (T tballinsert ) between the measurementfeatures <strong>and</strong> the kinematic couplings, <strong>and</strong> between the kinematic couplings <strong>and</strong> the interfaceplates (T kcinsert ) is added next. The serial addition <strong>of</strong> these trans<strong>for</strong>mations represents the true interfacetrans<strong>for</strong>mation (T interface ), which when extended to the TCP can be compared in magnitude with <strong>and</strong> withoutcalibration. Assuming full measurement <strong>of</strong> the contact positions <strong>and</strong> orientations, the only differencebetween the true <strong>and</strong> the calibrated kinematic error <strong>of</strong> the interface comes from the error in the measurementfeature <strong>for</strong>m <strong>and</strong> <strong>of</strong>fset, the inaccuracy <strong>of</strong> the measurement system (T measerror ) itself, <strong>and</strong> the nonmodeledhigher-order effects.44

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