Beam of a gantry-type stage structure

A beam of a gantry-type stage structure comprising:

• a lower plate elongated in a left-and-right direction to terminate at two lateral end edges, and having a lower front end edge and a lower rear end edge opposite to each other in a front-and-rear direction that is normal to the left-and-right direction;
• an upper plate elongated in the left-and-right direction, and disposed above and spaced apart from said lower plate in an upper-and-lower direction that is normal to both the left-and-right direction and the front-and-rear direction, said upper plate having an upper front end edge and an upper rear end edge opposite to each other in the front-and-rear direction;
• a front plate erected to interconnect said lower and upper front end edges;
• a rear plate erected from said lower rear end edge;
• two lateral plates erected from said lateral end edges, respectively, and each interconnecting said front and rear plates to cooperatively define an accommodating space thereamong;
• and
• a truss unit disposed in said accommodating space, and including a plurality of lower joint members which are disposed on an upper major surface of said lower plate and which are spaced apart from each other in the left-and-right direction, a plurality of first vertical members which are erected from said lower joint members, respectively, to said upper plate, a plurality of upper joint members which are disposed on a lower major surface of said upper plate, which are spaced apart from each other in the left-and-right direction, and which are arranged to alternate with said lower joint members in the left-and-right direction, a plurality of second vertical members which extend from said upper joint members, respectively, to said lower plate, and a plurality of diagonal members each of which extends to interconnect one of said lower joint members and an adjacent one of said upper joint members.