in fact, i have to do an boundry condition which let free the rotation around the Z axe and the translation according to x and y axes and for the axe z, the motion should be free in one sens which is Z- so this boundry condition prohibit the translation in the sens of Z- and the rotation around x and y axes.( c'est une liaison apuui plan d'axe z un peu spcéciale ou l'interdiction de la translation suivant z se fait dans un seul sens)
plzz i need your ideas. it's for my end studies project
Beside the translation in Z you can do everything with regular boundary conditions.
The translation in -Z should be free and +Z is not allowed, right?
Well, that kind of difference within one degree of freedom cannot be defined directly. Actually that is a contact condition. So define a rigid plane, place it the correct location, constrain it and define a contact with your part.
The only other possibility is a connector element with a connector stop condition as behavior.