A differential-based parallel force/velocity actuation concept : theory and experiments

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Title: A differential-based parallel force/velocity actuation concept : theory and experiments
Author: Rabindran, Dinesh, 1978-
Abstract: Robots are now moving from their conventional confined habitats such as factory floors to human environments where they assist and physically interact with people . The requirement for inherent mechanical safety is overarching in such human -robot interaction systems . We propose a dual actuator called Parallel Force /Velocity Actuator (PFVA ) that combines a Force Actuator (FA ) (low velocity input ) and a Velocity Actuator (VA ) (high velocity input ) using a differential gear train . In this arrangement mechanical safety can be achieved by limiting the torque on the FA and thus making it a backdriveable input . In addition , the kinematic redundancy in the drive can be used to control output velocity while satisfying secondary operational objectives . Our research focus was on three areas : (i ) scalable parametric design of the PFVA , (ii ) analytical modeling of the PFVA and experimental testing on a single -joint prototype , and (iii ) generalized model formulation for PFVA -driven serial robot manipulators . In our analysis , the ratio of velocity ratios between the FA and the VA , called the relative scale factor , emerged as a purely geometric and dominant design parameter . Based on a dimensionless parametric design of PFVAs using power -flow and load distributions between the inputs , a prototype was designed and built using commercial -off -the -shelf components . Using controlled experiments , two performance -limiting phenomena in our prototype , friction and dynamic coupling between the two inputs , were identified . Two other experiments were conducted to characterize the operational performance of the actuator in velocity -mode and in what we call ‘torque -limited’ mode (i .e . when the FA input can be backdriven ) . Our theoretical and experimental results showed that the PFVA can be mechanical safe to both slow collisions and impacts due to the backdriveability of the FA . Also , we show that its kinematic redundancy can be effectively utilized to mitigate low -velocity friction and backlash in geared mechanisms . The implication at the system level of our actuator level analytical and experimental work was studied using a generalized dynamic modeling framework based on kinematic influence coefficients . Based on this dynamic model , three design case studies for a PFVA -driven serial planar 3R manipulator were presented . The major contributions of this research include (i ) mathematical models and physical understanding for over six fundamental design and operational parameters of the PFVA , based on which approximately ten design and five operational guidelines were laid out , (ii ) analytical and experimental proof -of -concept for the mechanical safety feature of the PFVA and the effective utilization of its kinematic redundancy , (iii ) an experimental methodology to characterize the dynamic coupling between the inputs in a differential -summing mechanism , and (iv ) a generalized dynamic model formulation for PFVA -driven serial robot manipulators with emphasis on distribution of output loads between the FA and VA input -sets .
URI: http : / /hdl .handle .net /2152 /6899
Date: 2010-02-05


A differential-based parallel force/velocity actuation concept : theory and experiments. Doctoral dissertation, The University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /6899 .

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