Closed kinematic chains in mechanical systems represent a challenge for their motion analysis, and therefore, for path planning. Closed mechanisms appear in different areas where path planning algorithms are applied. We propose a method to handle them within Probabilistic RoadMap (PRM) techniques. This method is an extension of the approach proposed in [5]. Our main contribution concerns the generation of random configurations. The structure of the mechanism is analyzed in a preprocessing step. Then, in the roadmap construction phase, an algorithm called Random Loop Generator uses data from this analysis. This algorithm increases the probability of randomly generating valid configurations of the closed mechanism. Experimental results demonstrate the efficiency of the approach.