a guided stage mechanism suitable for supporting a reticle in a photolithography machine includes a stage movable in the x - y directions on a base . laterally surrounding the stage is a rectangular window frame guide which is driven in the x - axis direction on two fixed guides by means of motor coils on the window frame guide co - operating with magnetic tracks fixed on the base . the stage is driven inside the window frame guide in the y - axis direction by motor coils located on the stage co - operating with magnetic tracks located on the window frame guide . forces from the drive motors of both the window frame guide and the stage are transmitted through the center of gravity of the stage , thereby eliminating unwanted moments of inertia . additionally , reaction forces caused by the drive motors are isolated from the projection lens and the alignment portions of the photolithography machine . this isolation is accomplished by providing a mechanical support for the stage independent of the support for its window frame guide . the window frame guide is a hinged structure capable of a slight yawing motion due to hinged flexures which connect the window frame guide members .