When a traditional cutting machine for hard-and-brittle materials processes a cutting procedure on a hard-and-brittle material work-piece, such as: wafer, glass, or ceramic material, etc., it is easy to generate cutting-route fissures and breaking situation on the back of the work-piece. The reason: when the main-shaft processes a cutting-off procedure, it causes mistake of cutting-in position, instability of cutting route, and great variation of cutting force, because of the bias-and-swing of the main shaft of the cutting tool, assembling accumulation error of cutter and fixture, and entirety deformation under high speed; further, since the axial bias-and-swing bumps the edges of the cutting routes with high frequency at the side surface of the external edges of the cutting tool of cutting point, so that the cut work-piece generates a damage of brittleness.
In order to solve the problem of the vibration and the bias-and-swing generated by the cutting tools when the main shaft is rotated in high speed for processing a cutting-off procedure, a kind of gas-floating main-shaft device supplying more steady position of main shaft under the circumstance of rotation of high speed has been developed. The relative technique of this kind of gas-floating main-shaft device may be referred in the U.S. Pat. No. 5,997,223. However, although this kind of gas-floating main-shaft device may be provided for a higher stability of main shaft during the rotation of high speed, but even the stability of the main-shaft itself is increased greatly and, since the diameter of a common cutting tool formed as a disc shape is around 50˜100 mm, so the outer edge of the cutting tool itself may still generate a phenomenon of reciprocation of bias-and-swing, of which amplitude may reach around 10˜25 μm, when it is under the process of a cutting load of high-speed rotation (the rotation speed can exceed 10,000 rpm, even reach more than 60,000 rpm), such that the cutting tool will relatively cause an axial bump in bias-and-swing direction to the work-piece itself to be processed. Therefore, it is still impossible for this kind of rotational main-shaft device according to prior arts to avoid the generation of an axial displacement of bias-and-swing relative to the main shaft at the outer edge of the cutting tool, so that the fissures in cutting route and the damage phenomenon on the back of the work-piece described hereinbefore are still happened continuously.
Therefore, the Japanese factory—DISCO Company, of which the occupation rate in the global market of the cutting machine for the hard-and-brittle materials of wafer exceeds 60%, had developed a cutting machine in double axes aiming in solving such kind of problem (please refer to U.S. Pat. No. 6,102,023). Applying a cutting method of ladder or inverse angle in double axes for increasing the cutting quality, its first main-shaft processes a motion of cutting shallow trough for the purpose of guiding the second main-shaft to process in following to the fixed cutting-in position and cutting route of the shallow trough such that, when the second main-shaft is under the process of cut-off, the fissures of the edge of the cutting route and the damage on the back of the wafer created by the axial bias-and-swing of the main shaft are reduced. Its shortcomings: the work-piece needs two rounds of cutting processes, the cutting facilities are required for installing two sets of gas-floating main-shaft system, and the facility cost and the difficulty of system control are thereby multiplied relatively, so this is not a very good solution.
Another referring data may refer to U.S. Pat. Nos. 4,309,925 and 6,062,778 in addition. These two cases of prior arts are all relative to the technique and the device of the ┌Radial Position┘ of the ┌Boring Tool┘, which is different apparently from the axial positioning device and technique for cutting tool pursued by the present invention. However, claiming in advance, these two cases of prior arts, all processing the axial position of main shaft by sensing the bias of the ┌Main Shaft┘ itself, do not completely disclose the technical characteristics of the present invention.