Measuring and testing – Surface and cutting edge testing
Patent
1995-03-24
1996-11-05
Raevis, Robert
Measuring and testing
Surface and cutting edge testing
G06F 1546
Patent
active
055719570
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of estimating the service life of a cutter, and more particularly to a method of estimating the service life of a cutter for automatically changing cutters in a numerically controlled machine tool.
BACKGROUND ART
Unmanned operation of a numerically controlled machine tool for a long period of time requires that the service life of a cutter be supervised precisely. If the cutter is used beyond its service life, it may often be broken. When the cutter in the form of a drill bit is broken, the broken drill bit remains stuck in a workpiece, making the workpiece useless. However, it is uneconomical to estimate the service life of a cutter to be too short. On the other hand, estimating the service life of a cutter to be longer than necessary tends to fracture the cutter when in use. Therefore, it is necessary to recognize the service life of a cutter exactly and replace the cutter before the service life expires.
It has been customary to count how many times a cutter has been used or accumulate periods of time in which it has been used, and to judge the cutter as reaching the end of its service life when the count or the accumulated periods of time exceed a predetermined reference value. According to an alternative procedure, the load current of a spindle motor coupled to a cutter is monitored, and the service life of the cutter is determined as having expired when the absolute value of the load current exceeds a predetermined reference value.
However, the above conventional processes are too simple to take into account any factors involved in an actual cutting process as affecting the service life of a cutter, and apply the same calculating procedure to the estimation of the service life of a cutter which has cut workpieces under a light load and the estimation of the service life of a cutter which has cut workpieces under a heavy load. The process of monitoring the load current of a spindle motor is disadvantageous in that widely different reference values are employed for different cutter types or machining conditions and make the entire process complex.
DISCLOSURE OF THE INVENTION
In view of the aforesaid problems, it is an object of the present invention to provide a method of estimating the service life of a cutter with very high accuracy.
To achieve the above object, there is provided in accordance with a first aspect of the present invention a method of estimating the service life of a cutter, comprising the steps of determining a corrective coefficient from a material coefficient determined by a material to be machined by the cutter and a machining condition coefficient determined by machining conditions, multiplying a period of usage of the cutter by the corrective coefficient thereby to correct the period of usage, and accumulating corrected periods of usage thereby to estimate the service life of the cutter with the accumulated corrected periods.
According to a second aspect of the present invention, there is provided a method of estimating the service life of a cutter, comprising the steps of determining a disturbant load torque imposed on the cutter with an observer, and integrating determined disturbant load torques thereby to estimate the service life of the cutter with the integrated disturbant load torques.
According to a third aspect of the present invention, there is provided a method of estimating the service life of a cutter, comprising the steps of determining a disturbant load torque imposed on the cutter with an observer, and determining a rate of change of the determined disturbant load torque thereby to estimate the service life of the cutter with the determined rate of change.
In the first aspect, a corrective coefficient, depending on the material of a workpiece to be machined and machining conditions for a cutter, is introduced to apply a load that is actually imposed on the cutter to the estimation of the service life of the cutter. Therefore, the service life of the cutter can be estimated highly accurately.
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REFERENCES:
patent: 4031368 (1977-06-01), Colding
patent: 4351029 (1982-09-01), Maxey et al.
patent: 4628458 (1986-12-01), Ohta et al.
patent: 5251144 (1993-10-01), Ramamurthi
Fanuc Limited
Raevis Robert
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