The invention relates to a hip prosthesis having a shaft which is implantable in the femur, and having a ball head anchored on the shaft by a conical clamp, for example, and having a socket in which the ball head is movably supported. The multiple devices share multiple common voltage levels. The first period of the grating is taken as the minimum cycle period and includes two rows of grating structures having same grating pitch and same grating slit width. The hyrdraulic cylinders control the position of the crossbar assembly.