A New Solution to Coulomb Friction in Mechanism Bearings: Theory and Application

A new approximate closed form solution is presented for analyzing Coulomb friction in mechanism bearings. This is accomplished by linearizing the nonlinear terms of the equilibrium equations by a novel approach. The method, based on the traditional friction circle concepts, is particularly well suited to computers and proceeds to the solution without the need for any numerical methods or iterative steps as has previously been required. Further, only a pair of simultaneous equations is solved at a time, thus eliminating the need for a complete matrix inversion. It is believed that this simplified approach will be more readily usable in actual design situations where consideration of bearing friction is of considerable importance. A number of analytical validity checks were applied that successfully verified the adequacy of this new approach. As an example, the theory is applied to various models of a class of circuit breaker mechanisms, consisting of five four-bar linkages in series under different operating conditions. In all cases, the analytical results compare very favorably with the test data, thus establishing the method as a valuable practical design tool.