A positioning device comprising an object table and a positioning module configured to position the object table. The positioning module comprises a first positioning module member configured to hold the object table, a second positioning module member configured to support the first positioning module member, and a support frame configured to support the second positioning module member. The positioning module also includes one or more actuators, a position measurement system configured to measure a position of the object table, and a control unit configured to control a position of the object table based on the measured position of the object table. The control unit is further configured to control a vertical position of the second position module member so as to maintain a top surface of the second positioning module member substantially parallel to a bottom surface of the first positioning module member.