Method for correcting thermal displacement in a machine tool

A method for estimating thermal displacement of a workpiece at a cutting edge position in estimating an amount of thermal displacement based on detected temperature obtained by detecting the temperature of each component of a machine tool and the workpiece, and the coordinate data of the cutting edge position, the method comprising the steps of:

• presetting the coordinate data of a positive end position as well as a negative end position of a cutting stroke, and the coordinate data of a fixed position of the workpiece on a table;
• finding an amount of displacement of the fixed position of the workpiece at the positive end position based on the detected temperature, the coordinate data of the fixed position and the coordinate data of the positive end position;
• finding an amount of displacement of the fixed position of the workpiece at the negative end position based on the detected temperature, the coordinate data of the fixed position and the coordinate data of the negative end position;
• computing the difference in the coordinate data between the fixed position of the workpiece and the positive end position, and between the fixed position of the workpiece and the negative end position respectively;
• finding an amount of displacement of the workpiece between the fixed position and the positive end position based on the detected temperature and the difference in the coordinate data between the fixed position of the workpiece and the positive end position;
• finding an amount of displacement of the workpiece between the fixed position and the negative end position based on the detected temperature and the difference in the coordinate data between the fixed position of the workpiece and the negative end position;
• computing a sum of an amount of displacement of the fixed position of the workpiece at the positive end position and an amount of displacement of the workpiece between the fixed position and the positive end position to define an estimated value at the positive end;
• computing a sum of an amount of displacement of the fixed position of the workpiece at the negative end position and an amount of displacement of the workpiece between the fixed position and the negative end position to define an estimated value at the negative end, and
• correcting thermal displacement by two-point correction function of a servo system based on the estimated values at the positive end as well as negative end.