Distributed compliant model for efficient dynamic simulation of systems with frictional contacts.

ABSTRACT The use of Coulomb's friction law with the principles of classical rigid body dynamics introduces mathematical inconsistencies. Specifically, the forward dynamics problem can have no solutions or multiple solutions. In these situations an explicit model of the contact compliance at the contact point can resolve these difficulties. In this paper, we introduce a distributed compliant model for dynamic simulation. In contrast to the rigid body model and the lumped model, our approach models each contact as a finite patch and uses half space approximation to derive solutions for the small deformations and force distributions in the contact patch. This approach leads to a linear complementarity problem formulation for the contact dynamics. The existence of an unique solution can be proved for both the lumped model in the point contact case and the more accurate, distributed model. Simulation algorithm that incorporates compliant contact models and linear complementarity theory are created and demonstrated through numerical examples

IDETC2005-85471 MODELING AND ANALYSIS OF A VIBRATORY MICRO-PIN FEEDER USING IMPULSE-BASED SIMULATION

ABSTRACT A variety of methods exist for the assembly of microscale devices. One such strategy uses microscale force-fit pin insertion to assemble LIGA parts together. One of the challenges associated with this strategy is the handling of small pins which are 170 microns in diameter and with lengths ranging from 500 to 1000 microns. In preparation for insertion, a vibratory micro-pin feeder has been used to successfully singulate and manipulate the pins into a pin storage magazine. This paper presents the development of a deterministic model, simulation tool, and methodology in order to identify and analyze key performance attributes of the vibratory micro-pin feeder system. A brief parametric study was conducted to identify the effects of changing certain system parameters on the bulk behavior of the system, namely the capture rate of the pins. Results showing trends have been obtained for a few specific cases. These results indicate that different system parameters can be chosen to yield better system performance

Estimating Pose Statistics for Robotic Part Feeders

In automated assembly lines, part feeders often impose a bottleneck that restricts throughput. To facilitate the design of parts and assembly lines, we'd like to estimate feedrates based on CAD models of parts. A previous paper [8] described how to predict throughput for a vision-based robotic part feeder given the distribution of part poses when parts are randomly dropped on a conveyor belt. Estimating this distribution is also useful for the design of traditional feeders such as vibratory bowls. In this paper, we describe three algorithms for estimating pose distributions. We review the quasi-static estimate reported in [21] and introduce a refinement that takes into account some measure of dynamic stability. The perturbed quasi-static estimate can be computed very rapidly and is more accurate than the quasi-static. Still more accurate are estimates based on Monte Carlo simulation using Impulse [12; 13] , although the latter comes at the penalty of increased computation time. We com..