This paper represents a study of the context of improvement the parallel robots accuracy. We introduced, in the first hand, the different reasons of inaccuracy according to the different references mentioned in our paper as well as the methods used for the calibration and the accuracy improvement. In the other hand, we detailed the description of the direct and inverse geometric modeling of a biped robot with a rolling knee kinematic. The improvement of the accuracy of biped robots (moving with a high speed), while keeping the stability of the movement, and by exploiting the different models (geometric, kinematic and dynamic) as well as order, will be the target of our next publication.