In the paper a new approach to a design of fuzzy controllers is proposed, based on an automatic selection of membership functions shapes. The automatization is achieved by optimization using a genetic algorithm relative to a chosen system performance criterion. The software system for fuzzy control of the cart-ball system is also described. The described system is developed in such a way that modules are added to the previously existing system. Added modules are used for membership functions shapes optimization. Experimental results from experiments with the systems are given, some of them are improvements of earlier results. Directions for possible further work are pointed out.