An improved Geneva mechanism for optimal kinematic performance

Abstract

In this article, an alternative Geneva mechanism is presented and optimized. Unlike the original mechanism in which the driving pin operates at a fixed radius, the alternative mechanism benefits from a fixed groove cam which controls the radius of action of driving pin, resulting in continuous wheel acceleration and lower maximum velocity and acceleration. Apolynomial displacement function is adopted for the cam in the interval of engagement of driver and wheel. The problem of finding the coefficients of the polynomial is formulated as a constrained optimization problem in which the maximum acceleration of the Geneva wheel is to be minimized, while the motion of the pin is constrained to have zero velocity and zero acceleration at the beginning and end of the motion, respectively. Moreover, it is argued that since the objective function is highly sensitive to the variations of design variables, traditional search algorithms often fail to find its global optimum. To resolve this problem, a new hybrid genetic algorithm with a built-in adaptive local search is employed to find the coefficients of a polynomial that would define the optimal groove profile. The proposed approach is applied to the classical problems of designing a Geneva mechanism with four, five, and six grooves, and the results are compared with those obtained by other methods. The comparison shows that the proposed approach is capable of designing shock-free mechanisms with significantly reduced maximum angular velocity and acceleration of the Geneva wheel.