Method and apparatus for correcting deflection of a movable member

An apparatus for correcting a deflection caused in a cross beam, for use in a cantilever machine tool system, said cross beam extending in a horizontal direction, being supported movably in a vertical direction by a column disposed on a base of the machine tool system, and being coupled with a tool post movable in the horizontal direction, comprising:

• an auxiliary beam extending from an upper portion of the column in the horizontal direction, such that the cross beam is parallel to said auxiliary beam;
• a position detector device for detecting a position of the tool post;
• a first hydraulic cylinder for connecting an end of the cross beam and the auxiliary beam with a variable tension, said first hydraulic cylinder being arranged farther away from the column in the horizontal direction than the tool post;
• a second hydraulic cylinder for connecting the auxiliary beam and the base, said second hydraulic cylinder being closer to the column in the horizontal direction than the tool post;
• a hydraulic pressure controlling device for controlling hydraulic pressures of the first and second hydraulic cylinders;
• a controlling device, using a plurality of predetermined measurement positions at which deflections of the cross beams are to be measured, for respectively measuring the deflections of the cross beam at the plurality of measurement positions, obtaining correction values corresponding to the measurement positions, and storing the correction values, and for controlling the hydraulic pressure controlling device, based on the stored correction values, when the position of the tool post detected by the position detector device corresponds to one of the measurement positions, and based on an interpolation value, when the position of the tool post is between adjacent two of the measurement positions, said interpolation value being determined from a distance between the detected position of the tool post detected by the position detector device and one of the adjacent two measurement positions which is farther away from an end of the cross beam than the other, and from a difference between two of the correction values corresponding to the two adjacent measurement positions, and being an integral multiple of a minimum pressure unit equal to a smallest controllable pressure of the first cylinder.