Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2001-03-08
2003-11-18
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S028000, C700S108000
Reexamination Certificate
active
06650960
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a machining control system for controlling machining state(s) of machine tools and, more particularly, to a machining control system made up of numerical controllers (NCs) which has functions of automatically determining machining conditions or automatic programming systems, or machining control systems made up of the combination of programming devices such as CAMs with numerical controllers.
In machining, it is not easy to determine the machining conditions such that the efficiency is high, the precision is high and no abnormality occurs because a large number of factors such as tools, workpieces to be machined (hereinafter referred to as workpieces), machines and coolants are complicatedly related to each other. For that reason, up to now, the machining conditions have been automatically determined by the following main two approaches.
One of those approaches is directed to a machining condition determining system disclosed in Japanese Patent Publication No. 7-41516 (refer to FIG.
13
), Japanese Patent Laid-Open No. 2-218538, Japanese Patent Laid-Open No. 10-86039, Japanese Patent Laid-Open No. 3-43132, and the like. This system mathematically represents and retains the knowledge of skilled men for determining the machining condition in accordance with various factors such as the tool and the workpiece which influence the machining so as to automatically determine the machining conditions. Further, it is general to provide a mechanism for additionally learning the knowledge for determining the machining condition. In this approach, the knowledge is normally acquired by the learning in an off-line manner, and this approach is mainly applied to CAD/CAM, an automatically programming system, or the like. In the following description, the approach of this type is called “first approach”.
Another approach is directed to an adaptive control system disclosed in Japanese Patent Laid-Open No. 62-292347 (refer to FIG.
14
), Japanese Patent Laid-Open No. 2-218538, Japanese Patent Laid-Open No. 6-8106, and the like. In this system, the machining states are monitored on the basis of signals obtained by sensors or the like and the machining conditions are changed in such a manner that an objective function is optimized while keeping given constraints, to thereby control the machining in an appropriate state. This approach changes the machining conditions at a real time in accordance with the actual machining states, and is mainly applied to the numerical controller or the like. In the following description, the approach of this type is called “second approach”.
Those conventional systems will be complementarily described in more detail.
FIG. 13
is a block diagram showing the structure of conventional system using the first approach (disclosed in Japanese Patent Publication No. 7-41516) among the above conventional approaches. In the figure, reference numerals
5
and
11
denote a spindle motor and a grinding motor which are to be controlled, respectively. Reference numeral
14
denotes a first RAM in which data related to the shape and material of the spindle (workpiece), etc., and data related to the tool and the machining method are stored. Reference numeral
15
denotes a second RAM for storing standard machining data which are set therein,
16
is an automatic machining condition setting circuit for automatically setting the machining condition on the basis of the data stored in the first and second RAMs,
18
is a CRT for displaying the machining condition which is automatically set, and
12
is a keyboard used in the case where an operator judges that the machining condition displayed on the CRT
18
is improper and corrects the machining condition. Further, in the figure, a portion “a” surrounded by a phantom line is means for storing a corrected rate as the coefficient every time when the operator corrects the machining condition and automatically correcting the machining condition by using the data in the next machining.
The operation of the conventional system shown in
FIG. 13
will be described in brief. In the automatic machining condition setting circuit
16
, the machining condition is automatically determined on the basis of the data retained in the first and second RAMs, and if a correction is necessary, the operator conducts the correction. In addition, when the correction has been conducted, the rate of the correction is retained as the coefficient, and the coefficient is used to conduct the automatic correction in the next machining.
Further,
FIG. 14
is a block diagram showing the structure of a conventional system using the second approach (disclosed in Japanese Patent Laid-Open No. 62-292347) among the above conventional approaches. In the figure, reference numeral
40
denotes machining load detecting means for detecting a machining load,
41
is standard machining load deriving means for sampling an output of the machining load detecting means
40
at the time of a model machining using a reference tool to derive the standard machining load on the basis of the sampled output, and
42
is machining condition setting means for setting the machining condition at the time of actual machining using a tool similar to the reference tool. Reference numeral
43
denotes target load calculating means for calculating a target load on the basis of the standard machining load derived by the standard machining load deriving means
41
and the machining condition at the time of actual machining which is set by the machining condition setting means
42
, and
44
is feed rate control means for increasing or decreasing a feed rate such that the machining load detected by the machining load detecting means
40
at the time of actual machining becomes the target load calculated by the target load calculating means
43
.
The operation of the conventional system shown in
FIG. 14
will be described below. The model machining is conducted on only the reference tool, and the machining load at the time of the model machining is detected by the machining load detecting means
40
, and the standard machining load deriving means
41
derives the standard machining load on the basis of the machining load thus detected. In the actual machining time, the target load calculating means
43
is actuated and calculates the target load on the basis of the machining condition at the time of actual machining which is set by the machining condition setting means
42
and the reference machining load derived at the time of model machining. The feed rate control means
44
compares the target load thus calculated with the actual machining load detected by the machining load detecting means
40
to change the feed rate such that the detected actual load approaches the calculated target load.
The conventional first approach is made provided that rules or models which determines the machining condition on the basis of the factors that basically influence the machining is identical with the actual machining environment and a fluctuation of the actual machining environment is sufficiently small. However, the above provision is hardly satisfied for the following reasons.
In general, in machining, there are many indefinite elements because the phenomenon is physically unclear, the phenomenon occurs only stochastically, much labor is required for making models, and the like. For example, in cast material, it has been known that variation of hardness by several tens of % cannot be prevented due to the metal composition, heat flow conditions, and the like at the time of manufacturing a casting. Similarly, in the tool, it has been known that the sharpness of the tool varies by several tens of % depending on the metal composition, coating state, grinding precision, and the like, even if a tool of the same model number is repeatedly used. In workpieces or tools which are manufactured at the same time, that is, of the same lot, the variation is somewhat improved, but slight variation cannot be prevented. There are many elements that are difficult to estimate
Fujishima Makoto
Kakino Yoshiaki
Nakagawa Hideo
Otsubo Hisashi
Sato Tomonori
Kakino Yoshiaki
Kosowski Alexander
Picard Leo
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