Analysis of Rocker Mechanism for Automobile Windscreen Wiper Applications

This paper presents the use of a computer oriented numerical approach in the characterization of the crank-double rocker mechanism of automobile windscreen wipers. The vector loop-closure technique, Newton-Raphson method for solution of nonlinear systems, and the concepts of velocity coefficients and velocity coefficient derivatives are used to formulate angular position, velocity and acceleration models for the kinematic analysis. The generalized energy-based equation of motion for single degree of freedom planar systems, the principles of virtual work, and those of force and moment equilibrium are used to formulate output torque, pin-joint or internal and reactive force models for the kinetostatic analysis. The effects of input speed, input torque and wiper contact friction on power transmission capability of the mechanism are studied in numerical experiments with the derived models, using ANOVA with repeated measures to establish these effects. It is found that the numerical models described, to acceptable levels, the kinematic and kinetostatic characteristics of the mechanism. The oscillatory or rocking motion is characteristic of the rockers, while the combined oscillatory and reciprocating motion is characteristic of the connecting links. Also, the input speed, input torque and friction factor have significant influence on the power transmission capability of first loop of the mechanism, whereas, only the friction factor has significant influence on the power transmission capability of second loop of the mechanism. The results showed that the derived models are quite suitable for the purpose of design and analysis of the mechanism and its extensions.