Arrangement for keeping transverse beam of portal type milling machine in parallel displacement with itself

Claim 1

In a portal type milling machine having a beam adapted for displacement in parallelism with itself relative to a working region: a support carriage rigidly mounted on each end of the beam, a guide rail supportingly engaging each support carriage, said guide rails being parallel and extending at a predetermined angle relative to said beam, drive means including interengaging elements on each support carriage and the respective rails for driving the support carriages and beam along said rails, the interengaging elements on the support carriages being rotatable, a common drive member for said rotatable elements and respective drive trains leading from said drive member to each of said rotatable elements, surface means on one of said rails in a plane parallel to the direction of movement of said beam and angular to the plane of said rails, the support carriage on said one rail engaging said surface means so as to be nonlaterally movable on said one rail while being tiltable thereon in the plane of said rails if said support carriages fail to move in synchronism, a measure carriage on said one rail movable longitudinally of said one rail with the respective support carriage and engaging said surface means so as to be nontiltable on said one rail in the plane of the rails, cooperating elements of detecting means on said measuring carriage and the adjacent support carriage responsive to tilting of the support carriage on said one rail to develop signals, and control means under the control of said signals and operable for adjusting the relative positions of said support carriages on the respective rails so as to eliminate the tilting on said one rail of the support carriage thereon.