Electricity: measuring and testing – A material property using electrostatic phenomenon
Reexamination Certificate
2000-08-31
2003-09-02
Patidar, Jay (Department: 2858)
Electricity: measuring and testing
A material property using electrostatic phenomenon
C324S453000, C324S456000
Reexamination Certificate
active
06614234
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an electric discharge machine, particularly to an electric discharge machine which, in case where the main body of the electric discharge machine is deformed by a reactive force caused by the electric discharge machining, controls the reactive force or a deformation of the main body of the electric discharge machine within a certain value or at a constant amount.
Discussion of Background
FIG. 6
is a structural view of a general type of a conventional electric discharge machine.
In
FIG. 6
, numeral
1
designates an electrode, numeral
2
designates a workpiece, numeral
3
designates a machining fluid, numeral
4
designates a machining tank, numeral
5
designates an electrode rotating device rotating the electrode
1
around a Z axis, numeral
6
designates a Y-axis table, numeral
7
designates a Y-axis driving device driving the Y-axis table, numeral
8
designates a X-axis table, numeral
9
designates a X-axis driving device driving the X-axis table, numeral
10
designates a Z-axis driving device driving the electrode rotating device
5
attached with the electrode
1
in Z-axis direction, numeral
11
designates an electric source supplying pulses between the electrode
1
and the workpiece
2
, numeral
12
designates a machining state detecting device detecting a machining state in machining, numeral
13
designates a machining fluid supplying device supplying the machining fluid to the gap of machining and numeral
14
designates a NC control device.
FIG. 7
is a block diagram for explaining the operation of the electric discharge machine shown in FIG.
6
. In
FIG. 7
, parts
11
,
12
,
13
and
14
are the same as those in FIG.
6
. Numeral
15
designates a machining condition setter setting various machining conditions to the electric source
11
, the machining fluid supplying device
13
, a machining path designator
16
, a jump motion controller
17
and a comparator
18
. The numeral
16
designates the machining path designator generating a path for machining the workpiece in a desired shape, an electrode planetary pattern and the like, the numeral
17
designates the jump motion controller for having the electrode
1
rise and fall during the machining operation, the numeral
18
is the comparator, a numeral
19
designates a machining controller and numeral
20
designates a machining/jump motion switcher. The operation of these parts
15
through
20
is generally realized by a program in the NC control device
14
. Numeral
21
designates an electrode driving device which is constituted by the electrode rotating device
5
, the respective axis tables and the respective axis driving devices
6
through
10
. Numeral
22
designates a discharge machining process indicating a discharge machining phenomenon caused between the electrode
1
and the workpiece
2
opposedly arranged in the machining fluid
3
.
Next, an explanation will be given of the operation.
In a normal electric discharge machine a gap distance control system is constituted for adjusting a gap between the electrode
1
and the workpiece
2
for machining the workpiece in a desired shape while maintaining a stable machining state. The control system compares a reference instruction value set by the machining condition setter
15
with a detected value indicating the electric discharge machining process
22
that is detected by the machining state detecting device
12
, by the comparator
18
, calculates a deviation and issues an electrode movement instruction based on an instruction from the machining path designator
16
such that the deviation is nullified by the machining controller to thereby control the gap between the electrode
1
and the workpiece
2
. Further, the machining is finished at a time point where the electrode movement instruction value becomes a final instruction value of the desired shape. In this case machining is selected in the machining/jump motion switcher
20
.
The NC control device
24
has a function of the jump motion control as well as a function of the gap distance control. In the jump motion the machining/jump motion switcher
20
forcibly switches the gap distance control to the jump motion whereby the electrode
1
is risen and fallen. This jump motion is important in view of stabilizing the machining state by evacuating debris from the gap of machining by its pumping operation.
However, in such an electric discharge machine a large positive pressure or negative pressure (hereinafter reactive force by working or working reaction) is operated on the electrode in rising or falling of the electrode in the jump motion, in case where the electrode is especially large or the gap of machining is very narrow as in a finishing operation or the depth of machining is large whereby the main body of the electric discharge machine is deformed and the machining accuracy is deteriorated. According to a research by Mohri et al at Toyoda Institute of Technology “Study on The Characteristics of Electrical Discharge Machining (EDM) in Real Operation”, Journal of the Japan Society of Electrical-Machining Engineers, vol. 20, No. 39, p.19-29, 1987, the above-mentioned force operating on the electrode is caused by the viscosity of a machining fluid and a force operating on the electrode when the electrode is falling, especially causes the deterioration of the machining accuracy.
FIGS. 8A
,
8
B and
8
C illustrate a main shaft displacement, a working reaction and a column displacement in a jump motion actually measured by Mohri et al. As is apparent from a portion A in the figures the working reaction is maximized when the electrode is falling. Incidentally, in these figures the main shaft designates the Z axis and the column indicates the main body of the machine supporting the Z axis, respectively and the working reaction is measured by a force sensor integrated in an electrode attaching jig.
To solve the above-mentioned problem Mohri et al proposed that the rigidity of the machine is to be enhanced by a planer-type structure and the working reaction is to be alleviated by reducing an electrode falling speed immediately before the falling of the electrode is finished to thereby decrease the deformation of the column.
A portion B in
FIG. 8
shows that the working reaction is smaller than that in the portion A and hence the amount of displacement of the column is reduced. This is due to the decelerated falling speed of the main shaft in the portion B that is a result supporting the proposal of Mohri et al.
Japanese Examined Patent Publication No. 31806/1992 discloses a method of controlling an electrode speed in the jump motion based on the same conception. As shown in
FIG. 9
in this method the speed is changed in rising and falling of the electrode in accordance with a distance between the electrode and the workpiece. In
FIG. 9
, in rising of the electrode the electrode rising speed is accelerated from v2 to v1 at a distance L1 between the electrode and the workpiece and in falling of the electrode the electrode falling speed is decelerated from v1 to v2 at the distance L1 between the electrode and the workpiece by which the positive pressure and the negative pressure operating on the electrode are alleviated.
Incidentally, in the paper of Mohri et al the area of the electrode is described only up to approximately 20 cm
2
.
FIGS. 10A and 10B
indicate the main shaft displacement and the column displacement in a finishing operation while performing a jump operation in which an electrode having the area of the electrode of approximately 1000 cm
2
is used. In the jump operation the electrode falling speed is controlled to decelerate immediately before the electrode falling is finished. Therefore, although a column displacement is caused in rising of the electrode, almost no column displacement is caused in falling the electrode. However, a noteworthy point in
FIG. 10
in comparison with
FIG. 8
is that a large column displacement is caused at portions C during time periods in which elec
Goto Akihiro
Imai Yoshihito
Magara Takuji
Miyake Hidetaka
Patidar Jay
Sughrue & Mion, PLLC
Teresinski John
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