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DESCRIPTION
Field
5 [0001] The present invention relates to a numerical
control device that controls a machine tool.
Background
[0002] Conventionally, a numerical control (hereinafter,
10 referred to as NC) device reads a machining program
outputted from a CAD (Computer Aided Design) system or a
CAM (Computer Aided Manufacturing) system, and controls an
operation of a machine tool that machines a workpiece that
is a machining object. Machining patterns for which the NC
15 device controls a machine tool includes a pattern created
by a contour machining process for machining a contour
plane. In the contour machining, when a minute line
segment program for a contour machining process is
outputted from the CAD or CAM system, a minute movement
20 command toward an axis other than a contour plane is
sometimes erroneously outputted. The conventional NC
device cannot determine whether the minute movement command
is an erroneously outputted noise command, and thus outputs
a noise command according to erroneous program to a drive
25 unit of the machine tool.
[0003] The drive unit outputs a torque command to a
motor for each axis according to a movement command, and
moves a workpiece or the like with the motors to a
designated position. One of functions of the drive unit is
30 a lost motion compensation (hereinafter, referred to as
LMC) function. The LMC function is a function of
compensating a response delay caused by friction,
distortion, expansion and contraction, backlash, or the
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Z-axis direction is not outputted in the contour machining
mode of the X-Y plane as illustrated in FIG. 2(b).
Accordingly, application of excessive LMC can be avoided
and a workpiece can be prevented from being damaged.
5 [0015] Referring back to FIG. 1, in the NC device, a
program-input analysis unit 1 first reads a machining
program inputted from a CAD or CAM system (not illustrated),
and analyzes the machining program in units of blocks
constituting the machining program, that is, block by block.
10 After the analysis, the program-input analysis unit 1
stores data of a feeding speed per block, end point
coordinates on the respective axes, and respective modal
command flags in a data storage unit 2.
[0016] The data storage unit 2 is a storage unit in
15 which the program-input analysis unit 1 saves data of the
feeding speed, the end point coordinates on the respective
axes, and the respective modal command flags for the
analyzed block. While the data storage unit 2 is in form
of an independent configuration in FIG. 1, the embodiment
20 is not limited thereto. The data storage unit 2 may be
provided as an inside component of the program-input
analysis unit 1. A data table may be provided in the data
storage unit 2 to store the data on the data table.
[0017] After one block of the machining program is
25 analyzed in the program-input analysis unit 1, a pathcorrection
processing unit 3 determines whether the
analyzed block includes a noise command based on a noisecommand
allowable width stored in a parameter storage unit
4 in a case of the contour machining mode. When a noise
30 command is included in the block, the path-correction
processing unit 3 changes the end point coordinates and the
feeding speed obtained in the program-input analysis unit 1
and saved in the data storage unit 2 in order to correct
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machining program.
[0020] A method of setting a contour machining mode for
the NC device is described next. A user can create a
machining program to be read by the NC device, and set the
5 NC device to a contour machining mode according to a
program command in the machining program. For example,
four commands described below are registered in advance for
parameters of the machining program as selected-plane
notifying commands in respective contour machining modes
10 and a cancellation notifying command for the contour
machining modes. A number with M represents a command
number of an M code that is a command for an auxiliary
function to perform machining, and a content of a command
to be executed is represented beside the command number of
15 each M code.
[0021] M317 Contour machining mode (X-Y plane)
M318 Contour machining mode (Z-X plane)
M319 Contour machining mode (Y-Z plane)
M320 Contour machining mode cancellation
20 [0022] In the above examples of commands, when
instruction is made for any one of the contour machining
modes M317, M318 and M319 by the machining program, the NC
device is brought to the contour machining mode. The NC
device in the contour machining mode turns on a path25
correction request flag for a condition determination
process to determine whether or not path correction is
performed for a block including a movement command in a
direction of an axis not included in a selected plane in
the path-correction processing unit 3.
30 [0023] It is assumed here that an axis not included in a
selected plane is a command non-target axis. A command
non-target axis can be obtained in the NC device by
registering which plane is selected by each of the M code
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in the act of G17 plane selection and in the act of a
selected-plane notifying command for M317 (FIG. 6(a)).
Because the movement command in the Z-axis direction is not
a noise command, the path-correction processing unit 3 sets
5 the path based on the movement amount of the movement
command in the Z-axis direction (FIG. 6(b)) without
performing the path correction. Furthermore, the pathcorrection
processing unit 3 clears the ignored movement
amount ‘b’ to be set to "0" (zero), and uses the updated
10 ignored movement amount b=0 in the path correction process
for the next block (FIG. 6(c)).
[0040] As described above, according to the present
embodiment, when a machining program designates a contour
machining mode and a movement command in a direction of an
15 axis other than one included in a designated contour plane
is erroneously included in the machining program, the
numerical control device that controls a machine tool
regards the movement command in a direction of the axis
other than one included in the contour plane as a noise
20 command when the absolute value of a movement amount
according to the movement command in a direction of the
axis other than one included in the contour plane is
smaller than a noise-command allowable width set by a
parameter, and ignores the movement command that is the
25 noise command in a direction of the axis other than one
included in the contour plane and does not output that
command to the drive unit 6. Accordingly, even when a
contour-plane machining program created by CAD and CAM
includes a noise command, the numerical control device can
30 control an output of a movement command in a direction of
an axis not included in a designated machining plane, and
the drive unit 6 does not perform inappropriate LMC.
Therefore, a workpiece machined surface is avoided from
being damaged. Furthermore, man-hour of correcting noise
35 blocks can be reduced.
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[0041] In the present embodiment, the numerical control
device compares the absolute value of a movement amount
according to a movement command in a direction of an axis
other than one included in a contour plane and a noise5
command allowable width with each other. However, the
present invention is not limited thereto. For example, the
noise-command allowable width may have different allowable
widths between a positive direction and a negative
direction, and the numerical control device may determine
10 that a movement command is a noise command when a movement
amount according to the movement command in a direction of
an axis other than one included in a contour plane is
within an allowable range indicated by the positive and
negative noise-command allowable widths.
15 [0042] While a case of contour machining to machine a
contour plane has been described in the present embodiment,
the present invention is not limited thereto. The present
embodiment can be applied also to scanning-line machining
to machine a scanning-line plane, for example.
20 [0043] In the present embodiment, the numerical control
device is applied to a machine tool that operates a control
target on orthogonal three axes of an X axis, a Y axis and
a Z axis. However, this is merely one example, and the
numerical control device can also be applied to a machine
25 tool that operates it on three or more axes as long as
machining can be realized on orthogonal three axes of an X
axis, a Y axis, and a Z axis.
[0044] The configurations described in the embodiment
are only an example of the contents of the present
30 invention. The configurations can be combined with other
publicly-known techniques, and a part thereof can be
omitted or modified without departing from a scope of the
invention.
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We Claim :
1. A numerical control device controlling a machine tool,
the numerical control device comprising:
5 a parameter storage unit (4) to store therein a noisecommand
allowable width to be used for determining whether
to perform movement based on a movement command; and
a path-correction processing unit (3) to compare an
absolute value of a movement amount according to a movement
10 command in a command non-target axis direction that is a
direction of an axis not included in a designated plane
with the noise-command allowable width when a block of a
machining program includes a movement command in the
command non-target axis direction, determine the movement
15 command in the command non-target axis direction to be a
noise command when the absolute value of the movement
amount according to the movement command in the command
non-target axis direction is smaller than the noise-command
allowable width, and perform path correction to set a
20 movement amount according to the noise command to zero.
2. The numerical control device according to claim 1,
wherein
the path-correction processing unit (3)
25 stores therein an ignored movement amount obtained by
cumulatively adding movement amounts according to the noise
command when the movement amount of the noise command is
set to zero by the path correction, and
when a target block of next and following blocks of
30 the machining program includes a movement command in a
command non-target axis direction, adds a movement amount
according to the movement command in the command non-target
axis direction of the target block and the ignored movement
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amount to obtain a determination-target movement amount,
compares an absolute value of the determination-target
movement amount with the noise-command allowable width,
determines the movement command in the command non-target
5 axis direction in the target block to be a noise command
when the absolute value of the determination-target
movement amount is smaller than the noise-command allowable
width, and performs path correction to set a movement
amount according to the noise command to zero.
10
3. The numerical control device according to claim 2,
wherein the path-correction processing unit (3) compares
the absolute value of the determination-target movement
amount with the noise-command allowable width, and sets the
15 ignored movement amount to zero when the absolute value of
the determination-target movement amount is equal to or
larger than the noise-command allowable width.