Current Issue : July - September Volume : 2015 Issue Number : 3 Articles : 4 Articles
Friction is an inevitable nonlinear phenomenon existing in servomechanisms. Friction errors often affect their motion and contour\naccuracies during the reversemotion. To reduce friction errors, a novel time-varying friction compensation method is proposed to\nsolve the problem that the traditional friction compensation methods hardly deal with. This problem leads to an unsatisfactory\nfriction compensation performance and the motion and contour accuracies cannot be maintained effectively. In this method,\na trapezoidal compensation pulse is adopted to compensate for the friction errors. A generalized regression neural network\nalgorithm is used to generate the optimal pulse amplitude function.The optimal pulse duration function and the pulse amplitude\nfunction can be established by the pulse characteristic parameter learning and then the optimal friction compensation pulse can\nbe generated. The feasibility of friction compensation method was verified on a high-precision X-Y worktable. The experimental\nresults indicated that the motion and contour accuracies were improved greatly with reduction of the friction errors, in different\nworking conditions. Moreover, the overall friction compensation performance indicators were decreased by more than 54% and\nthis friction compensation method can be implemented easily on most of servomechanisms in industry....
Description of the transitional process from a static to a dynamic frictional\nregime is a fundamental problem of modern physics. Previously, we developed a model\nbased on the well-known Frenkel-Kontorova model to describe dry macroscopic friction.\nHere, this model has been modified to include the effect of dissipation in derived relations\nbetween the kinematic and dynamic parameters of a transition process. The main\n(somewhat counterintuitive) result is a demonstration that the rupture (i.e., detachment\nfront) velocity of the slip pulse which arises during the transition does not depend on\nfriction. The only parameter (besides the elastic and plastic properties of the medium)\ncontrolling the rupture velocity is the shear to normal stress ratio. In contrast to the rupture\nvelocity, the slip velocity does depend on friction. The model we have developed describes\nthese processes over a wide range of rupture and slip velocities (up to 7 orders of\nmagnitude) allowing, in particular, the consideration of seismic events ranging from\nregular earthquakes, with rupture velocities on the order of a few km/s, to slow slip events,\nwith rupture velocities of a few km/day....
The influence of temperature on the lubricating properties of neat water for\ntribopairs with varying bulk elasticity moduli and surface hydrophilicity, namely\nhard-hydrophobic interface (h-HB), hard-hydrophilic interface (h-HL), soft-hydrophobic\ninterface (s-HB), and soft-hydrophilic interface (s-HL), has been investigated. With\nincreasing temperature, the coefficients of friction generally increased due to the decreasing\nviscosity of water. This change was more clearly manifested from soft interfaces for more\nfeasible formation of lubricating films. Nevertheless, dominant lubrication mechanism\nappears to be boundary and mixed lubrication even for soft interfaces at all speeds (up to\n1200 mm/s) and temperatures (1 to 90 �°C) investigated. The results from this study are\nexpected to provide a reference to explore the temperature-dependent tribological behavior\nof more complex aqueous lubricants, e.g., those involving various additives, for a variety\nof tribosystems....
The vibration control and performance evaluation on a transmission-tower line system by using friction dampers subjected to\nwind excitations are carried out in this study. The three-dimensional finite element (FE) model of a transmission tower is firstly\nconstructed. A two-dimensional lumped mass model of a transmission tower is developed for dynamic analysis. The analytical\nmodel of transmission tower-line system is proposed by taking the dynamic interaction between the tower and the transmission\nlines into consideration. The mechanical model of passive friction damper is presented by involving the effects of damper axial\nstiffness. The equation of motion of the transmission tower-line system incorporated with the friction dampers disturbed by wind\nexcitations is established. A real transmission tower-line system is taken as an example to examine the feasibility and reliability of\nthe proposed control approach. An extensive parameter study is carried out to find the optimal parameters of friction damper and\nto assess the effects of slipping force axial stiffness and hysteresis loop on control performance. The work on an example structure\nindicates that the application of friction dampers with optimal parameters could significantly reduce wind-induced responses of\nthe transmission tower-line system....
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