Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2002-02-22
2003-12-09
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S096000, C700S109000, C700S118000, C700S182000
Reexamination Certificate
active
06662073
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a machining simulation apparatus and method for NC machining and, more particularly, to an apparatus and a method for generating a numerical control command on the basis of a machining simulation performed on the basis of blank stock shape data, tool shape data and data specifying a workpiece shape.
BACKGROUND ART
An adaptive control command generating system for a conventional numerical control system will be described with reference to a block diagram in FIG.
1
.
An NC program for use in a machining operation to be performed is stored in an NC program memory
11
.
An NC program interpreting section
12
reads NC program blocks on a one-by-one basis from the NC program memory
11
, and interprets an NC program block to output an interpolation type, a target position and a feed rate specified in the current block or those specified on a modal basis in a previous block to an interpolating section
13
.
The interpolating section
13
calculates movement amounts &Dgr;x, &Dgr;y, &Dgr;z along the respective axes per unit time (interpolation cycle period) on the basis of the interpolation type, the target position and the feed rate, and outputs the movement amounts to a servo control section
14
.
The servo control section
14
controls the rotations of axial motors on the basis of the movement amounts &Dgr;x, &Dgr;y, &Dgr;z along the respective axes per unit time obtained from the interpolating section
13
to perform axial operations.
A cutting monitoring section
15
receives a spindle load and feed axis loads actually detected by the servo control section
14
, and outputs at least one of these loads to an adaptive control section
16
.
The adaptive control section
16
compares the spindle load and the feed axis loads obtained from the cutting monitoring section
15
with predetermined values. If the spindle load and the feed axis loads are greater than a predetermined overload judgment value, the adaptive control section
16
issues an alarm and outputs a command for stopping the axial operations to the interpolating section
13
. If the spindle load and the feed axis loads fall outside a predetermined rate control detection range, the adaptive control section
16
outputs a rate change command for increasing or reducing a feed rate to the interpolating section
13
. If the spindle load and the feed axis loads are lower than a predetermined air-cut judgment value, the adaptive control section
16
outputs a feed rate command suitable for air-cut to the interpolating section
13
.
On the basis of these commands, the interpolating section
13
re-calculates the movement amounts &Dgr;x, &Dgr;y, &Dgr;z along the respective axes per unit time (interpolation cycle period), and outputs the re-calculated movement amounts to the servo control section
14
.
The aforesaid process is repeated until the machining operation ends.
With reference to a block diagram in
FIG. 2
, an explanation will be given to a conventional NC program generating system.
An operator inputs information such as a tool type, a tool size, a blank stock material and a machining path required for the generation of an NC program to a machining data inputting section
21
. The input result is outputted to an NC program generating section
23
.
A cutting condition data table
22
is in a data table form which allows for determination of an optimum feed rate, an optimum spindle rotation speed and the like on the basis of the tool type, the tool size and the blank stock material and the like, and referred to by the NC program generating section
23
.
The NC program generating section
23
generates the NC program on the basis of machining data such as the tool type, the tool size, the blank stock material and the machining path outputted from the machining data inputting section
21
, and cutting conditions such as the feed rate and the spindle rotation speed read out of the cutting condition data table
22
on the basis of the tool type, the tool size, the blank stock material and the like.
A table data modifying section
24
outputs a command for modification of a relational table indicative of a relationship of the tool type, the tool size, the blank stock material and the like with the feed rate, the spindle rotation speed and the like.
An NC program editing section
25
allows the operator to directly edit the NC program.
In the NC program generating system having the aforesaid construction, the operator selects one of the following three methods for changing the feed rate or the like in the NC program.
The operator specifies the feed rate or the like directly from the machining data inputting section
21
. Alternatively, the operator inputs an instruction for modification of the relational table indicative of the relationship of the tool type, the tool size, the blank stock material and the like with the feed rate, the spindle rotation speed and the like in the table data modifying section
24
. Alternatively, the operator changes an F-command or the like in the NC program editing section
25
.
In the adaptive control command generating system for the conventional numerical control system, machining state information indicative of the spindle load, the feed axis loads and the like is fed back at a high speed but, even if so, a response delay is inevitable because of operating principles. Accordingly, there is no choice but to perform a “present” control operation on the basis of “old” information.
Where a machining operation with a small machining load follows a machining operation with a great machining load, the feed rate is controlled to be reduced even though the actual machining load is small. This results in a reduction in machining efficiency. Where a machining operation with a great machining load follows a machining operation with a small machining load, the feed rate is controlled to be increased even though the actual machining load is great. This results in an overload on a tool, failing to provide a proper surface roughness.
In the conventional NC program generating system, the cutting conditions such as the spindle rotation speed are specified by the operator according to his own judgment, or uniquely determined on the basis of the tool type, the tool size, the blank stock material and the like. Therefore, the cutting conditions are irrelevant to a forced-vibration frequency and a load variation frequency occurring due to interrupted cutting.
This makes it very difficult to continuously perform a cutting operation at an optimum spindle rotation speed or at an optimum cutting speed, leading to early tool wear and deterioration in machining accuracy and surface roughness. Where the interrupted-cutting forced-vibration frequency and load variation frequency, or harmonic frequencies thereof which are integral multiples thereof are close to the natural frequency of a machine, a tool, a jig, a workpiece or the like, chattering of several tens micrometers occurs due to resonance. As a result, periodic wave marks are formed on a surface of a workpiece thereby to deteriorate the surface roughness.
A conventional method to be taken when the chattering occurs is to change the frequency of the interrupted cutting (in general, the spindle rotation speed) so as to prevent the interrupted cutting frequency from being close to the natural frequency of the machine, the tool, the jig, the workpiece or the like.
However, this method heavily relies on a cut-and-try approach. Further, when the chattering is detected during a trial cutting operation, it is necessary to find conditions for elimination of the chattering. This operation is disadvantageously time-consuming even if performed by a skilled operator.
To overcome the aforesaid problem, it is an object of the present invention to provide a machining simulation apparatus and method for NC machining, wherein a machining simulation is performed on a graphic data basis prior to machining, and a spindle rotation speed is reflected on the actual machining and the generation of a machining program under conditions optimum
Fujishima Makoto
Fukaya Yasushi
Yamazaki Kazuo
Armstrong Westerman & Hattori, LLP
Masinick Michael D
Mori Seiki Co. Ltd.
Picard Leo
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