Stone working – Sawing – Endless
Reexamination Certificate
2000-01-27
2001-01-30
Banks, Derris H. (Department: 3723)
Stone working
Sawing
Endless
C451S005000, C125S016020
Reexamination Certificate
active
06178961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a wire saw control method and a wire saw for slicing a workpiece such as silicon, glass and ceramics, into a number of wafers.
2. Description of Related Art
A wire saw forms a wire row by winding a wire on a plurality of grooved rollers, and runs the wire at a high speed and presses a workpiece against the wire row to thereby slice the workpiece into wafers. When the wire saw slices a column-shaped workpiece, the slicing length varies according to the slicing positions such as a slicing start position, a slicing end position and a slicing intermediate position. This changes the cutting resistance to the wire and the wire deflection (a wire displacement in a workpiece feeding direction). The change in the wire deflection causes the wire to run unstably and deteriorates the workpiece slicing accuracy.
To address this problem, a conventional wire saw estimates the cutting resistance according to the workpiece slicing position, and controls a workpiece feed speed according to the estimated cutting resistance, thus preventing a change in the wire deflection.
The cutting resistance, however, varies according to a variety of conditions such as the shape of the workpiece and the workpiece feed speed, and thus, it is difficult to correctly estimate the cutting resistance. For this reason, the conventional wire saw cannot slice the workpiece accurately.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a wire saw control method and a wire saw for accurately slicing a workpiece.
The above object can be achieved by providing a wire saw control method, which comprises forming a wire row by winding a wire on a plurality of grooved rollers, running said wire, feeding a workpiece to said wire row and pressing said workpiece against said wire row while supplying a machining liquid to said wire row to thereby slice said workpiece into a number of wafers; said method comprising the steps of: measuring a displacement of said wire forming said wire row during the slicing of said workpiece; calculating a cutting load against said wire row in accordance with said measured displacement and an initial tension of said wire; and comparing said calculated cutting load with a preset reference value, and then slicing said workpiece while controlling a workpiece feed speed according to the results of the comparison.
The above object can also be achieved by providing a wire saw, which forms a wire row by winding a wire on a plurality of grooved rollers, runs said wire, feeds a workpiece to said wire row and presses said workpiece against said wire row while supplying a machining liquid to said wire row to thereby slice said workpiece into a number of wafers; said wire saw comprising: a sensor for measuring a displacement of said wire forming said wire row during the slicing of said workpiece; workpiece feeding means for moving said workpiece forward and backward with respect to said wire row; and control means for calculating a cutting load against said wire row in accordance with said displacement measured by said sensor and an initial tension of said wire, comparing said calculated cutting load with a preset reference value and controlling a workpiece feed speed of said workpiece feeding means according to the results of the comparison.
This invention controls the slicing of the workpiece in accordance with the cutting load in view of the fact that the wire deflection depends on the cutting load (the load on the workpiece in a direction opposite to a workpiece feed direction).
According to the present invention, the displacement of the wire is measured, and the cutting load on the wire is calculated according to the wire deflection and the initial tension of the wire. Then, the calculated cutting load is compared with the reference value, and the workpiece feed speed is controlled according to the results of the comparison. For example, if the cutting load is controlled to be always the preset value, the workpiece can be sliced accurately. Since the cutting load is calculated according to the displacement and the initial tension of the wire, the cutting load can be calculated correctly even if the initial tension of the wire is changed.
According to the present invention, the wire saw further comprises driving means for moving said sensor forward and backward with respect to said wire row and measuring means for measuring the movement amount of said sensor. The driving means moves said sensor forward and backward according to a position of said wire forming said wire row, and the movement amount measured by said measuring means is added to a measured value of said sensor to thereby calculate the displacement of said wire. This widens the measurement range of the wire displacement and enables the measurement of the displacement even if the wire is displaced widely.
According to the present invention, the sensor is arranged above the wire row, and this prevents the machining liquid supplied to the wire row, i.e., a slurry from adhering to the sensor. Thus, the sensor can measure the wire displacement without being affected by the slurry.
According to the present invention, the sensor is arranged opposite side of a side where the wire is displaced with respect to the wire row. This prevents the displaced wire from contacting with and damaging the sensor. The wire saw has moving means for moving back said sensor from said wire row, and said moving means moves back said sensor from said wire row when the sliced workpiece is moved back from said wire row. This prevents the wire, which is displaced in the opposite direction by being dragged by the moved-back wire, from contacting with and damaging the sensor.
According to the present invention, the sensor is detachably supported by a bracket rotatably supporting said plurality of grooved rollers. Therefore, the position of the sensor with respect to the wire row can be adjusted easily.
According to the present invention, a cover is attached to a sensing part of said sensor in order to protect said sensing part.
According to the present invention, the sensor is inclined in a wire displaced direction with respect to a wire row by a predetermined angle. For example, the sensor is inclined by half an angle between an unloaded wire and a wire with the allowable maximum load, if an eddy-current displacement meter is used as the sensor. The sensitivity of the sensor is usually lowered as the angle between the sensor and the wire is broadened. In this invention, the sensitivity of the sensor is not lowered even if the wire is displaced and the angle of the sensor is changed since the sensor is previously inclined to the wire displaced direction.
According to the present invention, the displacement of the wire measured by said sensor is corrected previously in accordance with a measured distance between said sensor and said wire. Conventionally, it is difficult to accurately measure the displacement of the wire because the area of the wire is smaller than a detection area for an ordinary non-contact sensor. A data table of the output values of the sensor and the displacement of the wire is previously produced from data obtained by sliding the sensor vertically in the state where the sensor is actually attached (same as the operation state). The output values are converted to the displacement of the wire according to the data table. Consequently, the distance between the wire and the sensor can be correctly measured, and the displacement of the wire can be measured accurately.
REFERENCES:
patent: 5628301 (1997-05-01), Katamachi
patent: 5937844 (1999-08-01), Kiuchi et al.
patent: 5944007 (1999-08-01), Miyoshi et al.
patent: 5947798 (1999-09-01), Toyama
patent: 1177509 (1999-03-01), None
Asakawa Keiichiro
Kawarai Hiroshi
Matsuzaki Junichi
Nagatsuka Shinji
Oishi Hiroshi
Banks Derris H.
Nixon & Peabody LLP
Safran David S.
Tokyo Seimitsu Co. Ltd.
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