U.S. patent application number 09/879240 was filed with the patent office on 2002-01-10 for numerical control apparatus.
Invention is credited to Sagasaki, Masakazu, Yamada, Yoshinori.
Application Number | 20020003416 09/879240 |
Document ID | / |
Family ID | 14209690 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003416 |
Kind Code |
A1 |
Sagasaki, Masakazu ; et
al. |
January 10, 2002 |
Numerical control apparatus
Abstract
In a numerical control apparatus 1, a synchronous control
management unit 11 manages the dominant relation of plural axes to
be controlled synchronously. In case of the position control system
(synchronous control of axes), in the axis control unit which
controls the reference axis, a synchronous position calculation
processing unit 74 calculates the command position to the reference
axis, by adding the moving stroke of the reference axis calculated
in an axis control command value converting unit 72 to the
reference position of the reference axis. On the other hand, in the
axis control unit which control the synchronous axis, the
synchronous position calculation processing unit 74 calculates the
moving stroke per unit time of the synchronous axis from the moving
stroke received in a reference position input and output unit 73,
the gear ratio of synchronous axis to reference axis, and the
command unit time ratio, and adds the moving stroke to the
reference position of the synchronous axis, thereby calculating the
command position to the synchronous axis. One axis control unit
which controls the reference axis and plural axis control units for
controlling the synchronous axes issue the calculated command
positions, and control the individual corresponding motors, and
therefore control plural axes synchronously to one reference axis,
and further control other axis synchronously by reference to the
corresponding synchronous axis.
Inventors: |
Sagasaki, Masakazu; (Nagoya,
JP) ; Yamada, Yoshinori; (Tokyo, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEACK & SEAS
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037
US
|
Family ID: |
14209690 |
Appl. No.: |
09/879240 |
Filed: |
June 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09879240 |
Jun 6, 2001 |
|
|
|
PCT/JP98/05868 |
Dec 24, 1998 |
|
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Current U.S.
Class: |
318/600 |
Current CPC
Class: |
G05B 19/18 20130101;
G05B 19/414 20130101; G05B 2219/50216 20130101; G05B 19/4141
20130101; G05B 2219/50218 20130101 |
Class at
Publication: |
318/600 |
International
Class: |
G05B 019/29 |
Claims
1. A numerical control apparatus for synchronously controlling a
plurality of spindle motors or servo motors driven by a machine
tool according to a processing program, the numerical control
apparatus comprising: a memory unit which stores the processing
program; a synchronous control management unit which manages the
dominant relation of plural axes to be controlled synchronously;
and plural axis control units, having information about reference
axis as the reference of synchronous control and information about
synchronous axis for operating synchronously with the reference
axis stored according to the dominant relation of axes managed by
the synchronous control management unit, which control the
corresponding motors on the basis of the command position
calculated inside, wherein one axis control having set the
information about reference axis, and plural axis control units
having set the information about synchronous axis control the
individual corresponding motors, and the plural axes can be
controlled synchronously in relation to one reference axis, and
also other axis can be controlled synchronously on the basis of the
reference axis.
2. The numerical control apparatus according to claim 1, wherein
each one of the plural axis control units includes, an axis control
system changeover unit which changes over to either system of speed
control system for driving the corresponding motor depending on the
speed command value described in the processing program or the
position control system for driving depending on the moving stroke
per unit time converted from the speed command value; an axis
control command converting unit which calculates the moving stroke
per unit time from the speed command value with respect to the
reference axis; reference position input and output units which
issue the moving stroke per unit time of the reference axis
calculated in the axis control command value converting unit to
other axis control unit, or receive the moving stroke per unit time
of the reference axis calculated in other axis control unit; and a
synchronous position calculation processing unit which calculates
the command position corresponding to the pertinent axis, on the
basis of the moving stroke calculated by the axis control command
value converting unit or the moving stroke received in the
reference position input unit, wherein, in the position control
system, when controlling the reference axis, the synchronous
position calculation processing unit adds the moving stroke of the
reference axis calculated in the axis control command converting
unit to the reference position of the reference axis, and
calculates the command position to the reference axis, and when
controlling the synchronous axis, the synchronous position
calculation processing unit calculates the moving stroke per unit
time of the synchronous axis, from the moving stroke received in
the reference position input and output unit, the gear ratio of
synchronous axis to referenced axis, command rotation ratio, and
command unit time ratio, and adds the moving stroke to the
reference position of the synchronous axis, thereby calculating the
command position to the synchronous axis.
3. The numerical control apparatus according to claim 1, wherein
the axis control system changeover unit of the axis control unit
which control the synchronous axis calculates a theoretical command
position by subtracting the speed command value described in the
processing program, theoretical value of position deviation amount
calculated from the position control gain of the motor, and delay
amount corresponding to the sampling delay time of feedback
position, from the feedback position from the axis, and later
changes over from the ordinary speed control system to the position
control system in a contracted state of fluctuation of position
deviation amount.
4. The numerical control apparatus according to claim 1, wherein
each one of the plural axis control units further comprises a
synchronous position correction unit which corrects the fluctuation
of the axis by calculating the position correction amount form the
position deviation amount of reference axis and position deviation
amount of synchronous axis, and adding the position correction
amount to the command position of the synchronous axis.
5. The numerical control apparatus according to claim 1, wherein
the synchronous position correction unit in the axis control unit
which controls the synchronous axis multiplies the position
deviation amount of reference axis by the command rotation ratio of
reference axis and synchronous axis, and the command unit time
ratio, and calculates the difference between the calculation result
and the position deviation amount of the reference axis, then
determines the value of passing the obtained difference through the
primary delay filter according to a specific time constant
determined by the parameter as the position correction amount.
6. The numerical control apparatus according to claim 1, wherein
each one of the plural axis control units includes a theoretical
position deviation amount calculation processing unit which
calculates the theoretical position deviation amount from the speed
control value described in the processing program and the position
control gain of the motor, wherein, the synchronization position
correction unit in the axis control unit which controls the
synchronous axis calculates the difference between the theoretical
position deviation amount of the reference axis calculated in the
theoretical position deviation amount calculation processing unit
and the actual position deviation amount obtained from the
reference axis, and determines the value calculated from the
difference, the command rotation ratio of the synchronous axis to
the reference axis, and the command unit time ratio, as the
position correction amount.
7. The numerical control apparatus according to claim 1, wherein
each one of the axis control units includes a synchronous
correction amount fixing unit which calculates the average of the
position deviation amount in steady rotation on the reference axis
and synchronous axis for synchronous control, and further
calculates their difference, wherein, the synchronous position
correction unit in the axis control unit which controls the
synchronous axis determines the difference calculated in the
synchronous correction amount fixing unit as the position
correction amount.
8. The numerical control apparatus according to claim 1, wherein
the memory unit incorporates a synchronous correction coefficient
holding unit which calculates the average of the position deviation
amount in steady rotation on the reference axis and synchronous
axis for synchronous control, at the time of initial adjustment of
the machine tool, and holds the value obtained by dividing this
average by the speed control value as the coefficient for obtaining
the position deviation amount, wherein, the synchronous position
correction unit in the axis control unit which controls the
synchronous axis calculates the average of the position deviation
amount in steady rotation on the reference axis and synchronous
axis for synchronous control, by applying the speed command value
by the coefficient held in the synchronous correction coefficient
holding unit, and obtains this difference as the position
correction amount.
9. The numerical control apparatus according to claim 1, further
comprising a synchronous correction amount error canceling unit
which cancels the variation component of position deviation amount
caused by variation due to disturbance or the like, by subtracting
the difference between the average of the position deviation amount
in steady rotation on the axis for synchronous control and the
actual position deviation amount, temporarily from the position
correction amount.
10. The numerical control apparatus according to claim 1, further
comprising: a multi-level acceleration and deceleration parameter
memory unit which stores the multi-level acceleration an
deceleration speed generated by the acceleration and deceleration
pattern of ordinary speed control system, multi-level reference
acceleration and deceleration time constant, and multi-level
acceleration and deceleration time constant multiplying factor by
manipulating the parameter setting screen; a reference inclination
amount calculation unit which calculates the reference inclination
amount, as the acceleration and deceleration speed per unit time,
from the maximum rotating speed and multi-level reference
acceleration and deceleration time constant of the reference
spindle and synchronous spindle; a multi-level acceleration and
deceleration pattern calculation unit which calculates an
appropriate multi-level acceleration and deceleration pattern from
the set multi-level acceleration and deceleration pattern; and a
multi-level acceleration and deceleration decision unit which
determines the multi-level acceleration and deceleration pattern to
be noticed to the synchronous control management unit.
Description
TECHNICAL FIELD
[0001] The present invention in general relates to a numerical
control apparatus for synchronous control of two or more spindle
motors or servo motors driven in a machine tool. More particularly,
this invention relates to a numerical control apparatus capable of
realizing synchronous control of higher precision.
BACKGROUND ART
[0002] Some of the machine tools are hitherto capable of executing
synchronous control of two or more spindle motors or servo motors
to be driven. For example, the numerical control apparatus executes
the processing program commanded from a paper tape or the like,
that is, executes the numerical control process written in the
processing program, and the spindle motors or servo motors of the
machine tool are driven to process the work as commanded.
[0003] FIG. 12 is an essential block diagram showing an outline of
a conventional numerical control apparatus for driving spindle
motors or servo motors of a machine tool.
[0004] As shown in FIG. 12, the conventional machine tool comprises
a numerical control apparatus 101 for synchronously controlling a
motor for driving a reference axis of a lathe and a motor for
driving the synchronous axis, a processing program 102 in which a
program for numerical control processing is written, the reference
axis including a spindle amplifier 120, a spindle motor 121, a gear
122, a reference spindle 123, and an encoder 124, and the
synchronous axis including a spindle amplifier 140, a spindle motor
141, a gear 142, a synchronous spindle 143, and an encoder 144, and
the rotating speed of two spindles is synchronously controlled by
the numerical control apparatus 101, and further by closing chucks
125 and 145, a work 200 is held between the reference spindle 123
and synchronous spindle 143.
[0005] On the reference axis and synchronous axis, the spindle
amplifiers 120 and 140 are installed between the numerical control
apparatus 101 and spindle motor 121, and between the numerical
control apparatus 101 and spindle motor 121, respectively, and the
spindle amplifiers drive the corresponding spindle motors 121 and
141. The reference spindle 123 and synchronous spindle 143
installed by way of the gears 122 and 142 are controlled according
to the feedback position from the corresponding encoders 124 and
144. The numerical control apparatus 101 comprises, as shown in the
drawing, an analysis processing unit 103 for analyzing the
information about the reference axis and synchronous axis, an
interpolation processing unit 104 for issuing the interpolation
position command or rotating speed command analyzed in the analysis
processing unit 103 to subsequent circuits, a PLC circuit 105 for
issuing a specified signal, a machine control signal processing
unit 106 for processing the specified signal, a memory 107 for
storing a processing program 102, a parameter setting unit 108 for
setting parameters, a screen display unit 109 for displaying the
information in the memory 107 on a screen, axis control units 110a,
110b, 110c, . . . for issuing the information about the reference
axis and synchronous axis, interpolation position command, and
rotating speed command to the subsequent circuits depending on the
spindle to be driven, a reference axis control unit 111 which
controls the reference axis on the basis of the received
information, a synchronous axis control unit 112 which control the
synchronous axis on the basis of the received information, and a
data input/output circuit 113 for issuing various information to
the reference axis and synchronous axis.
[0006] The conventional numerical control apparatus will now be
explained in detail. Herein, in the spindle motor 121 for driving
the reference spindle 123 and the spindle motor 141 for driving the
synchronous spindle 143, the spindle synchronous control is
explained.
[0007] In FIG. 12, for example, the processing program 102 being
read in from a tape reader is read out and stored in the memory
107. Since the spindle synchronous control is a control executed by
the spindle synchronous command code, the spindle synchronous
command coded described in the processing program 102 is read out
into the analysis processing unit 103 in every block from the
memory 107.
[0008] The spindle synchronous command code thus being read out is
analyzed in the analysis processing unit 103, and the analysis
processing unit 103 notices its analysis result, that is, the
information about the reference axis and synchronous axis for
synchronous control to the interpolation processing unit 104.
[0009] Receiving this information, the interpolation processing
unit 104 notices information about the reference axis, for example,
to the axis control unit 110b (see FIG. 12) assigned to the
reference axis, out of the axis control units 110a, 110b, 110c, . .
. , and notices information about the synchronous axis to the axis
control unit 110c (see FIG. 12) assigned to the synchronous axis.
Herein, the spindle synchronous control is explained, but not in
case of spindle synchronous control, for example, information about
rotating speed is noticed to the axis control unit 110a (see FIG.
12) not assigned to either reference axis or synchronous axis. In
this case, therefore, information about rotating speed command is
directly noticed to the data input/output circuit 113, and the
spindle amplifier 120 receiving this rotating speed command
controls the speed of the spindle motor 121 according to this
command, and rotates the spindle 123.
[0010] The axis control units 110a, 110b, 110c, . . . are assigned
as shown in the diagram for the sake of convenience of explanation,
but each axis control unit operates similarly when assigned to the
reference axis, assigned to synchronous axis, or not assigned to
either.
[0011] Consequently, the axis control unit 110b notices information
about the reference axis, rotating speed command and other
information to the reference axis control unit 111 as shown in the
diagram, whereas the axis control unit 110c notices information
about the synchronous axis to the synchronous axis control unit
112. In the reference axis control unit 111, the command position
of the reference axis is calculated from the received rotating
speed command, and notices this command position to the data
input/output circuit 113 and synchronous axis control unit 112. The
synchronous axis control unit 112 calculates the command position
of the synchronous axis according to the command position of the
reference axis noticed from the referenced axis control unit 111
and the information about the synchronous axis is noticed to the
data input/output circuit 113.
[0012] Finally, the data input/output circuit 113 notices the
received position commands to the spindle amplifiers 120 and 140,
and the spindle amplifier 120 having received the command position
of reference axis rotates the reference spindle 123 by controlling
the speed of the spindle motor 121 according to the received
command position, and further the spindle amplifier 140 having
received the command position of synchronous axis rotates the
synchronization spindle 143 by controlling the speed of the spindle
motor 141 according to the received command position. Thus, in the
conventional numerical control apparatus, the synchronous axis
control unit 112 controls the command position of the synchronous
axis on the axis of the command position of the reference axis
calculated by the reference axis control unit 111, so that spindle
synchronous control is executed between one reference spindle 123
and one synchronous spindle 143.
[0013] In the conventional numerical control apparatus, however,
synchronous control about two spindles in the machine tool is
possible, but this control is limited within a set of reference
axis and synchronous axis. It means that three or more spindles
cannot be synchronously controlled at the same time.
[0014] The reason is as follows. For example, if each axis is
synchronized by noticing the command position, the axes are finally
converged at the specified position, but each axis of synchronous
control is different in the position control gain, speed and load,
and hence there is a position deviation amount, and the precision
of synchronism is lowered in an intermediate process. Accordingly,
in the conventional numerical control apparatus, for example, in
case of synchronous control of plural axes, one reference axis
monitors fluctuations of two or more synchronous axes, and
synchronous control is effected while correcting so as to decrease
the position deviation amount, and therefore the control is very
much complicated, and three or more spindles could not be
synchronously controlled at the same time.
[0015] Accordingly, in the machine tool conventionally used, in
order to perform spindle synchronous control on plural axes, it is
necessary to install plural numerical control apparatuses, and the
cost of the machine tool is higher. As a result, the control panel
for installing the numerical control apparatuses becomes larger in
size.
[0016] Further, in synchronous control of the conventional
numerical control apparatus, when grabbing one work between
spindles and closing the chuck, the axes may fluctuate due to
disturbance or the like. Thus, in a state having a stagnant
position deviation amount, when the reference axis and synchronous
axis are mechanically coupled through the work, each axis moves in
a direction for recovering the position deviation amount, and an
abnormal torque occurs, and the work may be flawed or
distorted.
[0017] It is an object of this invention to present a numerical
control apparatus capable of realizing synchronous control of two
or more spindles in a machine tool, realizing synchronous control
of three or more spindles at the same time, and also enhancing the
precision of synchronism more than in the conventional
apparatus.
DISCLOSURE OF THE INVENTION
[0018] The numerical control apparatus according one aspect of this
invention is for synchronously controlling a plurality of spindle
motors or servo motors driven by a machine tool according to a
processing program. This numerical control apparatus comprises a
memory unit (corresponding to a memory 7 described in an embodiment
later) which stores the processing program, a synchronous control
management unit (corresponding to synchronous control management
unit 11) which manages the dominant relation of plural axes to be
controlled synchronously, and plural axis control units
(corresponding to axis control units 10a, 10b, 10c, . . . ) having
information about reference axis as the reference of synchronous
control and information about synchronous axis for operating
synchronously with the reference axis stores according to the
dominant relation of axes managed by the synchronous control
management unit, for controlling the corresponding motors on the
basis of the command position calculated inside. In this
construction, one axis control unit stores information about
reference axis, and plural axis control units stores information
about synchronous axis control the individual motors, and the
plural axes can be controlled synchronously in relation to one
reference axis, and also other axis can be controlled synchronously
on the basis of the reference axis.
[0019] According to the above-mentioned aspect, the processing
program being read out from the tape reader or the like is stored
in the memory unit, and the information about the reference axis or
synchronous axis, and the information about the rotating direction
of synchronous axis, rotation ratio and others are analyzed inside,
for example, on the basis of the spindle synchronous command
described in the program, and the result is noticed to the
synchronous control management unit. In the synchronous control
management unit, combination of all axes for synchronous control is
management, and this information is noticed to the plural axis
control units, thereby setting one axis control unit which controls
the reference axis, and one or plural axis control units which
control the synchronous axis. Thus, the numerical control apparatus
of the invention realizes synchronous control of three or more
spindle motors or servo motors easily by management of the
synchronous control management unit. That is, for one reference
axis, plural axes (synchronous axes) can be control synchronously,
and also other axis can be controlled synchronously on the basis of
the synchronous axis.
[0020] Moreover, since combination of plural sets of synchronous
controls can be managed, wrong combination of synchronous controls
can be judged easily, and in the event of a wrong combination of
synchronous controls, it is noticed to the user by alarm or the
like, and the wrong combination still exists, by performing
synchronous control by exchanging the reference axis and
synchronous axis, synchronous control is possible in an arbitrary
combination without user's consciousness about reference axis and
synchronous axis.
[0021] Furthermore, in the numerical control apparatus, each one of
the plural axis control units comprises an axis control system
changeover unit (corresponding to an axis control system changeover
unit 71 described in embodiment below) which changes over to either
system of speed control system (speed control mode) for driving the
corresponding motor depending on the speed command value described
in the processing program or the position control system (position
control mode) for driving depending on the moving stroke per unit
time converted from the speed command value, an axis control
command converting unit (corresponding to an axis control command
converting unit 72) which calculates the moving stroke per unit
time from the speed command value with respect to the reference
axis, reference position input and output units (corresponding to
reference position input unit 73 and reference position output unit
75) which issues the moving stroke per unit time of the reference
axis calculated in the axis control command value converting unit
to other axis control unit, or for receiving the moving stroke per
unit time of the reference axis calculated in other axis control
unit, and a synchronous position calculation processing unit
(corresponding to synchronous position calculation processing unit
74) which calculates the command position corresponding to the
pertinent axis, on the basis of the moving stroke calculated in the
axis control command value converting unit or the moving stroke
received in the reference position input unit.
[0022] Thus, in synchronous control of axis (position control
system), when controlling the reference axis, the synchronous
position calculation processing unit adds the moving stroke of the
reference axis calculated in the axis control command converting
unit to the reference position of the reference axis, and
calculates the command position to the reference axis, and when
controlling the synchronous axis, on the other hand, the
synchronous position calculation processing unit calculates the
moving stroke per unit time of the synchronous axis, from the
moving stroke received in the reference position input and output
unit, the gear ratio of synchronous axis to referenced axis,
command rotation ratio, and command unit time ratio, and adds the
moving stroke to the reference position of the synchronous axis,
thereby calculating the command position to the synchronous axis.
As a result, on the reference axis and synchronous axis, an
accurate command position can be calculated, and the precision of
synchronous control of axis can be enhanced.
[0023] Furthermore, in the numerical control apparatus, the axis
control system changeover unit of the axis control unit which
control the synchronous axis calculates a theoretical command
position by subtracting the speed command value described in the
processing program, theoretical value of position deviation amount
calculated from the position control gain of the motor, and delay
amount corresponding to the sampling delay time of feedback
position, from the feedback position from the axis, and later
changes over from the ordinary speed control system to the position
control system in a contracted state of fluctuation of position
deviation amount.
[0024] Thus, since changeover from the speed control system of
spindle for synchronous control to position control system is
executed by calculating the theoretical command position in the
specified procedure (calculation by axis control system changeover
unit in the axis control unit which controls the synchronous axis),
and then contracting the fluctuation of of the position deviation
amount, the mode can be changed over to the synchronous control
mode (position control system) without causing any effect on the
operation of the reference axis. Therefore, since the
synchronization of the axis can be controlled without causing
effect on processing during processing at the reference axis side,
the processing cycle can be shortened.
[0025] Furthermore, in the numerical control apparatus, each one of
the plural axis control units further comprises a synchronous
position correction unit (corresponding to a synchronous position
correction unit 76 described in embodiment below) which corrects
the fluctuation of the axis by calculating the position correction
amount form the position deviation amount of reference axis and
position deviation amount of synchronous axis, and adding the
position correction amount to the command position of the
synchronous axis.
[0026] Thus, in case of synchronization control of axis, the axis
control unit which controls the reference axis calculates the
command position to the reference axis, and the plural axis control
units which control the synchronous axis calculate the command
position to the synchronous axis on the basis of the moving stroke
per unit time received from the axis control unit which controls
the reference axis. The synchronous position correction unit
corrects the fluctuation of the axis by adding the obtained
position correction amount only to the command position of the
synchronous axis. Therefore, since the axis can be controlled
simultaneously without causing effect on processing during
processing at the reference axis sided, the processing cycle can be
shortened, and further by correcting the command position of the
synchronous axis, the synchronous precision is enhanced.
[0027] Furthermore, in the numerical control apparatus, the
synchronous position correction unit in the axis control unit which
controls the synchronous axis multiplies the position deviation
amount of reference axis by the command rotation ratio of reference
axis and synchronous axis, and the command unit time ratio, and
calculates the difference between the calculation result and the
position deviation amount of the reference axis, then determines
the value of passing the obtained difference through the primary
delay filter according to a specific time constant determined by
the parameter as the position correction amount.
[0028] Thus, since the deviation occurring during synchronous
control is corrected by passing the difference between the
calculation result and position deviation amount of reference axis
through the primary delay filter, abrupt changes of command
position by correction do not occur, and occurrence of useless
alarm can be avoided.
[0029] Furthermore, in the numerical control apparatus, each one of
the plural axis control units comprises a theoretical position
deviation amount calculation processing unit (corresponding to an
theoretical position deviation amount calculation processing unit
77 described in embodiment below) which calculates the theoretical
position deviation amount from the speed control value described in
the processing program and the position control gain of the motor,
and the synchronization position correction unit, in the axis
control unit which control the synchronous axis, calculates the
difference between the theoretical position deviation amount of the
reference axis calculated in the theoretical position deviation
amount calculation processing unit and the actual position
deviation amount obtained from the reference axis, and determines
the value calculated from the difference, the command rotation
ratio of the synchronous axis to the reference axis, and the
command unit time ratio, as the position correction amount.
[0030] Thus, since the synchronous position correction unit of the
axis control unit which control the synchronous axis corrects the
deviation portion occurring in synchronous control by using the
actual delay amount to the theoretical position deviation amount of
the reference axis as the position correction amount, synchronism
deviation portion due to delay caused by cutting load or the like
can be easily corrected, and moreover since the position control
gain and load are different, even in case of synchronous control
between axes always having a difference in position deviation
amount, synchronous control of high precision can be realized
without causing improper torque by correction. As a result, flaw or
torsion of work can be prevented, so that processing of higher
precision is possible.
[0031] Furthermore, in the numerical control apparatus, each one of
the plural axis control units comprises a synchronous correction
amount fixing unit (corresponding to a synchronous correction
amount fixing unit 78 described in embodiment below) which
calculates the average of the position deviation amount in steady
rotation on the reference axis and synchronous axis for synchronous
control, and further calculates their difference, and the
synchronous position correction unit determines, in the axis
control unit which control the synchronous axis, the difference
calculated in the synchronous correction amount fixing unit as the
position correction amount.
[0032] Thus, since the synchronous position correction amount of
the axis control unit which control the synchronous axis corrects
the deviation portion occurring during synchronous control by using
the difference of the average values of position deviation amount
on the reference axis and synchronous axis for synchronous control
as the position correction amount, the position correction amount
is a fixed value, so that the load by calculation of the position
correction amount can be lessened.
[0033] Furthermore, in the numerical control apparatus, the memory
incorporates a synchronous correction coefficient holding unit
(corresponding to a synchronous correction coefficient holding unit
51 described in embodiment below) which calculates the average of
the position deviation amount in steady rotation on the reference
axis and synchronous axis for synchronous control, at the time of
initial adjustment of the machine tool, and holds the value
obtained by dividing this average by the speed control value as the
coefficient for obtaining the position deviation amount, and the
synchronous position correction unit calculates, in the axis
control unit which control the synchronous axis, the average of the
position deviation amount in steady rotation on the reference axis
and synchronous axis for synchronous control, by applying the speed
command value by the coefficient held in the synchronous correction
coefficient holding unit, and obtains this difference as the
position correction amount.
[0034] Thus, the synchronous position correction unit of the axis
control unit which control the synchronous axis calculates the
average of the position deviation amount on the reference axis and
synchronous axis for synchronous control, and the value obtained by
dividing this average by the speed command value is held in the
synchronous correction coefficient holding unit as the coefficient
for obtaining the position deviation amount. This held value is a
constant for obtaining the position deviation amount not depending
on the speed command value, and therefore if the speed command
value is different from the time of initial adjustment in
synchronous control, the position deviation amount in steady
rotation can be easily calculated by multiplying the coefficient by
the speed command value.
[0035] The numerical control apparatus may preferably further
comprise a synchronous correction amount error canceling unit
(corresponding to a synchronous correction amount error canceling
unit 79 described in embodiment below) which cancels the variation
component of position deviation amount caused by variation due to
disturbance or the like, by subtracting the difference between the
average of the position deviation amount in steady rotation on the
axis for synchronous control and the actual position deviation
amount, temporarily from the position correction amount.
[0036] Thus, when grabbing the work in a state changed in the
position deviation amount of the axis, the difference between the
average of the position deviation amount in steady rotation on the
synchronous axis for synchronous control and the actual position
deviation amount calculated preliminarily is subtracted temporarily
from the position correction amount applied on the synchronous
axis. As a result, variation component of the position deviation
amount caused by variation due to disturbance or the like can be
canceled, and synchronous control is realized at an optimum
position deviation amount.
[0037] The numerical control apparatus may preferably further
comprise a multi-level acceleration and deceleration parameter
memory unit (corresponding to a multi-level acceleration and
deceleration parameter memory unit 81 described in embodiment
below) which stores the multi-level acceleration an deceleration
speed generated by the acceleration and deceleration pattern of
ordinary speed control system, multi-level reference acceleration
and deceleration time constant, and multi-level acceleration and
deceleration time constant multiplying factor by manipulating the
parameter setting screen, a reference inclination amount
calculation unit (reference inclination amount calculation unit 83)
which calculates the reference inclination amount, as the
acceleration and deceleration speed per unit time, from the maximum
rotating speed and multi-level reference acceleration and
deceleration time constant of the reference spindle and synchronous
spindle, a multi-level acceleration and deceleration pattern
calculation unit (multi-level acceleration and deceleration pattern
calculation unit 84) which calculates an appropriate multi-level
acceleration and deceleration pattern from the set multi-level
acceleration and deceleration pattern, and a multi-level
acceleration and deceleration decision unit (multi-level
acceleration and deceleration decision unit 82) which determines
the multi-level acceleration and deceleration pattern to be noticed
to the synchronous control management unit.
[0038] Thus, in spindle control between two or more spindle motors,
when controlling the acceleration and deceleration of spindle
motors by the multi-level acceleration and deceleration pattern of
the position control system, the configuration for selecting an
appropriate multi-level acceleration and deceleration pattern is
designated. For example, if the multi-level acceleration and
deceleration pattern is different on each spindle, the multi-level
acceleration and deceleration time constant is determined on the
basis of the one of the largest inclination of acceleration and
deceleration, and other acceleration and deceleration patterns
defined by a constant multiple (1 or larger integer) of the
multi-level acceleration and deceleration time constant, and
therefore an appropriate multi-level acceleration and deceleration
pattern can be selected and judged by a simple process of
comparison of multi-level acceleration and deceleration time
constants.
[0039] For example, similarly, since an appropriate multi-level
acceleration and deceleration pattern is calculated from the ratio
of the multi-level acceleration and deceleration time constants
between spindles different in the multi-level acceleration and
deceleration pattern, if it is necessary to select the one of the
large inclination of acceleration and deceleration, it can be
easily corrected to an appropriate multi-level acceleration and
deceleration pattern.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 shows a configuration of a numerical control
apparatus according to a first embodiment;
[0041] FIG. 2 shows a configuration of axis control unit in the
numerical control apparatus;
[0042] FIG. 3 shows a synchronous control management matrix for
management of a set of synchronous control;
[0043] FIG. 4 is a flowchart for management of synchronous
control;
[0044] FIG. 5 shows a combination of synchronous control axes by
analysis of spindle synchronous control command;
[0045] FIG. 6 is a flowchart of axis control unit;
[0046] FIG. 7 shows configuration of a numerical control apparatus
according to a second embodiment;
[0047] FIG. 8 shows a specific example of multi-level acceleration
and deceleration pattern for synchronous control;
[0048] FIG. 9 is a diagram showing a method of calculation of
multi-level acceleration and deceleration time constant multiplying
factor;
[0049] FIG. 10 shows an example of setting of multi-level
acceleration and deceleration pattern for synchronous control;
[0050] FIG. 11 shows a method of selection and calculation of
multi-level acceleration and deceleration pattern; and
[0051] FIG. 12 shows a configuration of a conventional numerical
control apparatus.
BEST MODE FOR CARRYING OUT THE INVENTION
[0052] The invention is more specifically described below while
referring to the accompanying drawings. It must be noted, however,
that the invention is not limited to the illustrated embodiments
alone.
[0053] FIG. 1 is an essential block diagram of the numerical
control apparatus according to the first embodiment. This numerical
control apparatus is capable of driving spindle motors or servo
motors of a machine tool.
[0054] As shown in FIG. 1, the machine tool of the invention
comprises a numerical control apparatus 1 for synchronously
controlling a motor for driving a reference axis and a motor for
driving a synchronous axis, a processing program 2 storing a
program for numerical control process, a reference axis including a
spindle amplifier 20, a spindle motor 21, a gear 22, a reference
spindle 23, and an encoder 24, a first synchronous axis including a
a spindle amplifier 40, a spindle motor 41, a gear 42, a
synchronous spindle 43, and an encoder 44, and a second synchronous
axis including a spindle amplifier 60, a spindle motor 61, a gear
62, a synchronous spindle 63, and an encoder 64, in which the
rotating speed of the three spindles is synchronously controlled by
the numerical control apparatus 1, and a work 26 is held between
the reference spindle 23 and synchronous spindle 43 by-closing
chucks 25 and 45, and further a rotary tool 65 is rotated.
[0055] In the reference axis, first synchronous axis and second
synchronous axis, the spindle amplifiers 20, 40, and 60 are
installed respectively between the numerical control apparatus 1
and spindle motor 21, between the numerical control apparatus 1 and
spindle motor 41, and between the numerical control apparatus 1 and
spindle motor 61, and the spindle amplifiers are driving the
corresponding spindle motors 21, 41, and 61. The reference spindle
23, synchronous spindle 43, and synchronous spindle 63 installed
respectively by way of the gears 22, 42, and 62 are driven
according to the feedback position from the corresponding encoders
24, 44, and 64.
[0056] The numerical control apparatus 1 comprises, as shown in the
drawing, an analysis processing unit 3 for analyzing the
information about the reference axis and synchronous axes, an
interpolation processing unit 4 for transmitting the interpolation
position command and rotating speed command analyzed in the
analysis processing unit 3 to succeeding circuits, a PLC circuit 5
for issuing a specified signal, a machine control signal processing
unit 6 for processing the specified signal, a memory 7 storing the
processing program 2 and incorporating an synchronization
correction coefficient holding unit 51 described below, a parameter
setting unit 8 for setting various parameters by user s
manipulation, a screen display unit 9 for displaying the
information in the memory 7 on the screen, a synchronous control
management unit 11 for managing the combination of spindles for
synchronous control, axis control units 10a, 10b, 10c, . . . for
controlling the corresponding spindles by output of information
about reference axis and synchronous axes, command position, speed
command, etc., and a data input and output unit 13 for sending
various information to the reference axis and synchronous axes. In
this embodiment, for the sake of convenience of explanation, in
particular, synchronous control of three spindles is explained, but
the number of spindles for synchronous control is not limited, and
any plurality of spindles can be synchronously controlled by the
management of the synchronous control management unit 11.
[0057] FIG. 2 is an essential block diagram specifically describing
the axis control units 10a, 10b, 10c, . . . in FIG. 1.
[0058] As shown in FIG. 2, each axis control unit comprises an axis
control system changeover unit 71, an axis control command value
converting unit 72, a reference position input unit 73, a
synchronous position calculation processing unit 74, a reference
position output unit 75, a synchronous position correction unit 76,
an theoretical position deviation amount calculation processing
unit 77, a synchronous correction amount fixing unit 78, and a
synchronous correction amount error temporary canceling unit 79.
Each axis control unit can control either reference axis or
synchronous axis by the management of the synchronous control
management unit 11.
[0059] The axis control system changeover unit 71 changes over the
corresponding motor in either speed control system (speed control
mode: control in ordinary state) for driving according to the
command speed described in the processing program, or position
control system (position control mode: synchronous control) for
driving according to the moving stroke per unit time converted from
the corresponding speed command value. The axis control command
value converting unit 72 calculates the moving stroke per unit time
from the command speed to the reference axis. The reference
position input unit 73 receives the moving stroke per unit time of
the reference axis calculated in other axis control unit. The
synchronous position calculation processing unit 74 calculates the
command position to the corresponding axis on the basis of the
moving stroke calculated in the axis control command value
converting unit 72 or the moving stroke received in the reference
position input unit 73. The reference position output unit 75
issues the moving stroke per unit time of the reference axis
calculated in the axis control value converting unit 72 to other
axis control unit. The synchronous position correction unit 76
calculates the position correction amount from the position
deviation amount of the reference axis and position deviation
amount of synchronous axis, and corrects variation of axis by
adding the position correction amount to the command position of
the synchronous axis. The theoretical position deviation amount
calculation processing unit 77 calculates an ideal position
deviation amount from the speed command value described in the
processing program and the position control gain of the motor. The
synchronous correction amount fixing unit 78 calculates the average
of position deviation amount in steady rotation on the reference
axis and synchronous axis for synchronous control, further
calculates the difference thereof, and determines the result of
calculation as the fixed position correction amount. The
synchronous correction amount error temporary canceling unit 79
subtracts the difference of the average of position deviation
amount in steady rotation on the reference axis and synchronous
axis for synchronous control and the actual position deviation
amount, temporarily from the position correction amount, and
cancels the variation component of position deviation amount caused
by variation due to disturbance or the like.
[0060] The operation of the numerical control apparatus will be
explained below.
[0061] First, by the spindle synchronous command described in the
processing program 2, synchronous control of three spindles is
explained, assuming to control the spindle 23 as reference spindle
and spindle 43 as synchronous spindle, and further to control the
spindle 23 as reference spindle and spindle 43 as synchronous
spindle. In FIG. 1, the axis control unit 10a controls the spindle
23 through the spindle amplifier 20, the axis control unit 10b
controls the spindle 43 through the spindle amplifier 40, and the
axis control unit 10c controls the spindle 63 through the spindle
amplifier 60.
[0062] The processing program 2 being read out, for example, from a
tape reader is stored in the memory 7, and when executing the
processing program 2, the analysis processing unit 3 reads out the
processing program 2 block by block from the memory 7, and analyzes
the described spindle synchronous command. This spindle synchronous
command is analyzed by the analysis processing unit 3 as
information about reference axis and synchronous axes, rotating
direction and rotation ratio of synchronous axes, and noticed to
the interpolation processing unit 4. In the interpolation
processing unit 4, these items of information are noticed to the
synchronous control management unit 11.
[0063] In the synchronous control management unit 11, combination
of commanded synchronous control axes is managed, and the
information about the reference axis is noticed to the axis control
unit 10a responsible for control of reference axis, out of axis
control units 10a, 10b, 10c, . . . , or the information about
synchronous axes, and information of rotating direction and
rotation ratio of synchronous axes 43 and 63 to the reference axis
23 are noticed to the axis control units 10b, 10c responsible for
control of synchronous axes. Moreover, the reference position
output unit 75 of the axis control unit 10a and the reference
position input unit 73 of the axis control units 10b, 10c are
connected with each other, so that the synchronous control
reference moving stroke of the reference axis mentioned below may
be noticed to the synchronous axes.
[0064] Herein, the management method of combination of synchronous
control in the synchronous control management unit 11 is explained
according to the synchronous control management matrix shown in
FIG. 3.
[0065] In the case of synchronous control in combination of a
plurality of axes, all combinations are managed in the synchronous
control management unit 11, and it is required to perform
synchronous control according to the dominant relation thereof. In
the example shown in FIG. 3, spindle S1 is the reference spindle,
and spindle S2 is synchronously controlled, and further spindle S1
is the reference spindle, and spindle S3 is synchronously
controlled. By managing to control sequentially from the axis other
than the synchronous axis, a plurality of spindles are controlled
synchronously.
[0066] Further, by using the synchronous control management matrix,
unjust synchronous control pattern is checked. For example, in
principle, it is not allowed to combine one synchronous axis with
plural reference axes, and therefore if it is attempted to control
spindle S4 as reference axis and spindle S1 simultaneously during
synchronous control of spindle S2 with spindle S1 as reference
axis, in the synchronous control management unit 11, since spindle
S2 is already controlled synchronously with spindle S1 as reference
axis, synchronous control with spindle S4 as reference axis is
disabled. Therefore, such command is judged to be synchronous
control command of unjust combination. The synchronous control
management unit 11 develops such matrix on the memory, and realizes
a similar management.
[0067] By such management of the synchronous control management
unit 11, the following operation is carried out in the axis control
units 10a, 10b, 10c receiving such information.
[0068] The axis control system changeover unit 71 calculates a
theoretical value of position deviation amount from the command
speed described in the processing program and the position control
gain of the axis, and further calculates the moving stroke
corresponding to the sampling delay time of the feedback position
from this command speed, and subtracts these calculation results
from the feedback position from the spindle amplifier, and thereby
calculates the command position. In a contracted state of variation
of this position deviation amount, in order to change over the
effective command from the speed command value to the position
command value, checking for waiting time determined by the attained
speed or parameter, consequently, the control system to the spindle
is changed over from the ordinary speed control system to the
position control system of synchronous control.
[0069] In the axis control unit 10a of the reference axis change
over to the position control system, the axis control command value
converting unit 72 converts the speed command to the reference
spindle 23 to the moving stroke per unit time, and notices this
moving stroke to the synchronous position calculation processing
unit 74 as the synchronous control reference moving stroke.
Further, the synchronous position calculation processing unit 74
issues the synchronous control reference moving stroke to the axis
control units 10b, 10c responsible for control of synchronous axes
by way of the reference position output unit 75.
[0070] In this state, the synchronous position calculation
processing unit 74 adds the synchronous control reference moving
stroke to the synchronous control reference position, and issues
the result of addition to the synchronous position correction unit
76 as a new synchronous control reference position. In the
synchronous position correction unit 76, in order to control the
reference axis, the received synchronous control reference position
is used as the command value, and the command position is noticed
to the spindle amplifier 20 by way of the data input and output
circuit 13.
[0071] On the other hand, in the axis control units 10b, 10c of
synchronous axes changed over to the position control system, the
following operation is carried out.
[0072] First, in the synchronous axis 43 synchronized with the
reference axis 23, the reference position input unit 73 of the axis
control unit 10b receives the synchronous control reference moving
stroke issued from the reference position output unit 75 of the
axis control unit 10a for controlling the reference axis 23 related
by the synchronous control management unit 11, and notices to the
synchronous position calculation processing unit 74.
[0073] The synchronous position calculation processing unit 74
multiplies the received synchronous control reference moving stroke
by the gear ratio of the synchronous axis 43 to the reference axis
23, command rotation ratio, and command unit ratio, and determines
the product as the synchronous control reference moving stroke to
the synchronous axis 43. In the axis control unit 10b, since there
is no other axis for synchronous control with synchronous axis 43
as reference axis, the synchronous control reference moving stroke
is not issued to other axis control unit.
[0074] Afterwards, in the synchronous position calculation
processing unit 74, this synchronous control reference moving
stroke is added to the synchronous control reference position, and
the result of addition is noticed to the synchronous position
correction unit 76 as a new synchronous control reference position.
Consequently, the synchronous position correction unit 76
calculates the position correction amount in a method described
below from the position deviation amount of the reference axis 23
and the position deviation amount of the synchronous axis 43, and
adds it to the synchronous control reference position to obtain
command position, then notices the obtained command position to the
spindle amplifier 40 byway of the data input and output circuit 13.
In the synchronous axis 63 synchronized with the reference axis 23,
the operation of the axis control unit 10c for controlling the
synchronous axis 63 is same as mentioned above.
[0075] The method of calculation of the above position correction
amount is described in detail below.
[0076] In the synchronous position correction unit 76 of axis
control units 10b, 10c for controlling the synchronous axes, by the
spindle synchronous control described in the processing program 2,
the calculation method of position correction amount is selected
from the following two, and deviation component due to variation of
axis is synchronously corrected.
[0077] In a first calculation method of position correction amount,
the position deviation amount of reference axis is multiplied by
the command unit time ratio of reference axis to synchronous axis,
and command rotation ratio, the difference of this calculation
result and position deviation amount of synchronous axis is
calculated, and the delay amount of synchronous axis to the
position of reference axis is obtained. This difference is passed
through a primary delay filter according to a specific time
constant determined by the parameter in the memory 7, and the
position correction amount is obtained. This method is employed in
the case where the difference in the load between reference axis
and synchronous axis is not so much.
[0078] In a second calculation method of position correction
amount, the theoretical position deviation amount calculation
processing unit 77 of the axis control unit for controlling the
reference axis calculates a theoretical value of position deviation
amount of reference axis, from the command speed described in the
processing program and the position control gain of the axis, and
calculates the difference from the position deviation amount of
reference axis obtained through the data input and output circuit
13. This is multiplied by the command unit ratio and command
rotation ratio of synchronous axis to reference axis, and the
result of calculation is obtained as the position correction amount
in the synchronous axis. This method is employed when the
difference is large in the load between reference axis and
synchronous axis, and the difference of follow-up delay of
reference axis and follow-up delay of synchronous axis is always
large.
[0079] The synchronous position correction unit 76 of the axis
control units 10b, 10c of synchronous axes can temporarily fix the
position correction value by, for example, a specified signal from
the PLC circuit 5, or cancel the error of the position correction
amount.
[0080] In a method of temporarily fixing the position correction
amount, first, the average of position deviation amount in steady
rotation on reference axis and synchronous axis for synchronous
control is detected preliminarily. Closing the chucks mutually,
when the torque is transmitted to each other between axes for
synchronous control through the work or the like, for example, the
PLC circuit 75 issues a chuck close signal as the specified signal.
This chuck close signal is noticed to the synchronous correction
amount fixing unit 78 of the axis control unit of the synchronous
axis through the machine control signal processing unit 76, and in
the synchronous correction amount fixing part 78, at this time, the
difference between the average of the position deviation amount of
reference axis and average of position deviation amount of
synchronous axis is noticed to the synchronous position correction
unit 76 as position correction amount. The position correction
value obtained in this method is the difference between the average
of the position deviation amount of reference axis and average of
position deviation amount of synchronous axis, and is hence a fixed
value.
[0081] Meanwhile, in order to obtain the average of position
deviation amount in steady rotation on reference axis and
synchronous axis, at the time of initial adjustment of machine tool
beforehand, the average of position deviation amount in steady
rotation is detected, and divided by the command speed, and the
result is held, for example, in the synchronous correction
coefficient holding unit 51. At this time, the held value is the
coefficient for obtaining the position deviation amount not
depending on the command speed, and hence if the command speed of
ordinary operation is different from the command speed of initial
adjustment, by multiplying the coefficient by the command speed at
this time, the position deviation amount in steady rotation can be
calculated easily.
[0082] Calculating the difference of the average of position
deviation amount on reference axis and synchronous axis thus
calculated, together with the input of specified signal issued from
the PLC circuit 5, the difference of average of position deviation
amount of reference axis and synchronous axis is noticed to the
synchronous position correction unit 76 as position correction
amount. This method is employed when always working as synchronous
axis and correcting the guide bush spindle or the like for mutually
transmitting with reference axis through the work.
[0083] On the other hand, in a method of canceling the error of
position correction amount, assume to grab the work in a changed
state of position deviation amount of axis, due to variation caused
by operation. At this time, the synchronous correction error
canceling unit 79 calculates the difference between the average of
position deviation amount in steady rotation on reference axis and
synchronous axis calculated beforehand, and the actual position
deviation amount. As the specified signal issued from the PLC
circuit 5, together with the input of error cancel signal, the
error is temporarily subtracted from the position correction amount
applied on the synchronous axis, the variation component of
position deviation amount caused by variation due to disturbance or
the like is canceled, and the axes are controlled synchronously
with an optimum position deviation amount.
[0084] In the operation of the numerical control apparatus 1 of the
invention, by the spindle synchronous command described in the
processing program 2, synchronous control of three spindles is
explained, for example, supposing to control the spindle 23 as
reference spindle, spindle 43 as synchronous spindle, and spindle
63 as synchronous spindle. Explanation is omitted as for the
operation same as explained above.
[0085] After the same operation as explained above, the synchronous
control management unit 11 manages the combination of commanded
synchronous control axes, notices the information about reference
axis to the axis control unit 10a for controlling the reference
axis, out of axis control units 10a, 10b, 10c, . . . , and also
notices the information about synchronous axes and the information
about the rotating direction and rotation ratio of synchronous axes
43, 63 to the reference axis 23, to the axis control units 10b, 10c
for controlling the synchronous axes. Further, connecting the
reference position output unit 75 of the axis control unit 10a and
reference position input unit 73 of the axis control units 10b,
10c, the synchronous control reference moving stroke of reference
axis is noticed to the axis control unit 10b for controlling the
synchronous axis.
[0086] Next, the information about reference axis is noticed to the
axis control unit 10b, and the information about synchronous axis
and the information about the rotating direction and command
rotation ratio of the synchronous axis 63 to the reference axis 43
are noticed to the axis control unit 10c for controlling the
synchronous axis. Further, connecting the reference position output
unit 75 of the axis control unit 10b and reference position input
unit 73 of the axis control unit 10c, the synchronous control
reference moving stroke of reference axis is noticed to the axis
control unit 10c for controlling the synchronous axis.
[0087] In this state, in the axis control units 10a, 10b, and 10c
for reference axis and synchronous axes, the axis control system
changeover unit 71 changes over the axis control system from speed
control system to position control system.
[0088] In the axis control unit 10a of reference axis changed over
to the position control system, the axis control command value
converting unit 72 converts the speed command to the reference
spindle 23 to the moving stroke per unit time, and notices this
moving stroke as the synchronous control reference moving stroke to
the synchronous position calculation processing unit 74. In the
synchronous position calculation processing unit 74, further, the
synchronous control reference moving stroke is issued to the axis
control unit 10b for controlling the synchronous axis through the
reference position output unit 75.
[0089] In this state, the synchronous position calculation
processing unit 74 adds the synchronous control reference moving
stroke to the synchronous control reference position, and notices
the result of addition as a new synchronous control reference
position to the synchronous position correction unit 76. In the
synchronous position correction unit 76, in order to control the
reference axis, using the received synchronous control reference
position as command value, the command position is noticed to the
spindle amplifier 20 by way of the data input and output circuit
13.
[0090] Next, in the axis control unit 10b of reference axis changed
over to the position control system, the axis control command value
converting unit 72 converts the speed command to the reference
spindle 43 to the moving stroke per unit time, and notices this
moving stroke as the synchronous control reference moving stroke to
the synchronous position calculation processing unit 74. In the
synchronous position calculation processing unit 74, further, the
synchronous control reference moving stroke is issued to the axis
control unit 10c for controlling the synchronous axis through the
reference position output unit 75.
[0091] In this state, the synchronous position calculation
processing unit 74 adds the synchronous control reference moving
stroke to the synchronous control reference position, and notices
the result of addition as a new synchronous control reference
position to the synchronous position correction unit 76. In the
synchronous position correction unit 76, in order to control the
reference axis, using the received synchronous control reference
position as command value, the command position is noticed to the
spindle amplifier 40 by way of the data input and output circuit
13.
[0092] On the other hand, in the axis control unit 10c of reference
axis changed over to the position control system, the following
operation is carried out.
[0093] First, in the synchronous axis 63 synchronized with the
reference axis 43, the reference position input unit 73 of the axis
control unit 10c receives the synchronous control reference moving
stroke issued from the reference position output unit 75 of the
axis control unit 10b for controlling the reference axis 43 related
by the synchronous control management unit 11, and notices to the
synchronous position calculation processing unit 74.
[0094] The synchronous position calculation processing unit 74
multiplies the received synchronous control reference moving stroke
by the gear ratio of the synchronous axis 63 to the reference axis
43, command rotation ratio, and command unit ratio, and determines
the product as the synchronous control reference moving stroke to
the synchronous axis 63. In the axis control unit 10c, since there
is no other axis For synchronous control with synchronous axis 63
as reference axis, the synchronous control reference moving stroke
is not issued to other axis control unit.
[0095] Afterwards, in the synchronous position calculation
processing unit 74, this synchronous control reference moving
stroke is added to the synchronous control reference position, and
the result of addition is noticed to the synchronous position
correction unit 76 as a new synchronous control reference position.
Consequently, the synchronous position correction unit 76
calculates the position correction amount from the position
deviation amount of the reference axis 43 and the position
deviation amount of the synchronous axis 63, and adds it to the
synchronous control reference position to obtain command position,
then notices the obtained command position to the spindle amplifier
60 by way of the data input and output circuit 13. FIG. 4 is a
flowchart for managing the synchronous control in the numerical
control apparatus of the invention.
[0096] Referring to FIG. 4, the managing method of axis for
synchronous control and the managing method of processing sequence
in each axis control unit are explained below.
[0097] First, the processing program 2 is analyzed in the analysis
processing unit 3 (FIG. 4, S1), and if the information noticed to
the synchronous control management unit 11 is obtained by analyzing
the spindle synchronous control command as shown in FIG. 5 (S1,
Yes), referring to the data on the memory showing the synchronous
control management matrix shown in FIG. 3, it is judged if the
commanded command of synchronous control axes is correct or not
(S2). If the information is not obtained by analyzing the spindle
synchronous control command (S1, No), ordinary speed control is
executed.
[0098] In judgement at step S2, if not correct, it means the axis
newly commanded as synchronous axis has been already handled as
synchronous axis in any combination of synchronous control. For
example, if not correct (S2, No), the synchronous control
management unit 11 controls to issue an alarm (S7), and if correct
(S2, Yes), the information of synchronous control is newly set in
the data of synchronous control management matrix (S3).
[0099] Later, the synchronous control management unit 11 notices
the information about reference axis and synchronous control mode
request to the axis control unit (10a, 10b, . . . etc.) for
controlling the axis used as reference axis. Further, the
synchronous control management unit 11 also notices the information
about synchronous axis, synchronous control mode request, rotation
ratio and other information to the axis control unit (10a, 10b, . .
. etc.) of axis as synchronous axis (S5).
[0100] Finally, the synchronous control management unit 11 manages
the sequence of processing of axis control units on the basis of
the data of synchronous control management matrix (S6). The
sequence of management is from the axis not handled as synchronous
axis. That is, if the axis is being handled as the reference axis,
the next axis handled as synchronous axis is controlled, or if this
synchronous axis is also being handled as the reference axis, the
second axis handled as synchronous axis is controlled sequentially.
Thus, searching combinations of synchronous control in all axes, it
is possible to control in the sequence from reference axis to
synchronous axes.
[0101] FIG. 6 is a flowchart of the process performed by the axis
control units.
[0102] Referring to FIG. 6, the operation of each axis control unit
processed the sequence of management in the synchronous control
management unit 11 is explained.
[0103] First, in case of an axis not handled as synchronous axis,
this axis is an axis handled as spindle in ordinary speed control,
or an axis handled as reference axis of synchronous control.
Accordingly, the axis control unit checks if the corresponding
spindle is handled as reference axis or synchronous axis of
synchronous control (S11). In the case of the axis handled as
ordinary speed control spindle (S11, No), the axis control unit
issues the command speed to the corresponding spindle amplifier
through the data input and output circuit 13 (S24). On the other
hand, in case of reference axis (S11, Yes), the axis control unit
checks if the spindle motor control system has been changed over
from the speed control system to position control system or not
(S12).
[0104] If not changed over to the position control system (S12,
No), the control system of the spindle motor is changed over to the
position control system (S13). On the other hand, if already
changed over to the position control system (S12, Yes), the moving
stroke per unit time is calculated from the speed command to the
spindle, and the command position for position control is
calculated (S14).
[0105] Consequently, the axis control unit checks if the
corresponding axis is handled as synchronous axis of synchronous
control or not (S15). In this case, it is not handled as
synchronous axis, then it is checked if reference axis of
synchronous control or not (S18). Herein, being explained as
reference axis, the reference position moving stroke which is the
moving stroke per unit time of axis is issued to the axis control
unit of the axis to be synchronized (s19).
[0106] Again, checking if handled as synchronous axis of
synchronous control or not (S20), since the reference axis is
handled herein (S20, No), the axis command position is issued to
the data input and output processing unit 13 (S23), and the spindle
amplifier for controlling the reference axis controls the position
of the spindle according to the commanded command position.
[0107] Next, the synchronous axis of synchronous control is
explained. First, it is checked if the corresponding spindle is
handled as reference axis or synchronous axis of synchronous
control or not (S11) Being handled as synchronous axis herein (S11,
Yes), the axis control unit checks if the control system of the
spindle motor has been changed over from speed control system to
position control system or not by the synchronous control
(S12).
[0108] If not changed over to the position control system (S12,
No), the control system of the spindle motor is changed over to the
position control system (S13). On the other hand, if already
changed over to the position control system (S12, Yes), the
position moving stroke per unit time is calculated from the speed
command to the spindle, and the command position for position
control is calculated (S14).
[0109] Consequently, the axis control unit checks if handled as
synchronous axis of synchronous control or not (S15). In this case,
it is handled as synchronous axis (S15, Yes), and the axis control
unit checks if the reference axis is changed over to the position
control system to be in the synchronous control mode or not (S16).
If the reference axis is not changed over to the synchronous
control mode (S16, No), the process advances to step S18 in order
that the command of synchronous axis may be the one calculated at
step S14. On the other hand, when the reference axis has been
changed over to the synchronous control mode (S16, Yes), the moving
stroke per unit time of the axis synchronized with the reference
position moving stroke issued from step S19 of the reference axis
is calculated (S17). For example, assuming the position moving
stroke per unit time of reference axis to be La, the rotation ratio
to be reference axis rotation: synchronous axis rotation=Ra:Rb, the
command unit time of reference axis to be Ia, and the command unit
time of synchronous axis to be Ib, the position moving stroke per
unit time of the synchronous axis is expressed in the following
formula.
Lb=La.times.(Rb/Ra).times.(Ib/Ia)
[0110] Next, the axis control unit further checks if the
synchronous axis is the reference axis of synchronous control or
not (S18). If the synchronous control is executed in one set (S18,
No), this synchronous axis is not handled as reference axis, and
the process goes to step S20. If the synchronous control is
executed in two or more sets (S18, Yes), this synchronous axis can
be a reference axis of other set. Therefore, in case of reference
axis, the reference position moving stroke which is the moving
stroke per unit time of the axis is issued to the axis control unit
of the axis to be synchronized (S19). Again, checking if handled as
synchronous axis of synchronous control (S20), since it is handled
as synchronous axis of synchronous control (S20, Yes), the axis
control unit calculates the position correction amount (S21), and
further adds this position correction amount to the command
position, and calculates the corrected command position (S22).
[0111] Finally, the axis control unit issues the command position
of axis to the data input and output processing unit 13, and the
spindle amplifier for controlling the synchronous axis controls the
position of the spindle according to the commanded command position
(S23).
[0112] The numerical control apparatus of the invention thereafter
repeats the same operation according to the flowchart, and
synchronously controls a plurality of sets by normal combination
among arbitrary axes.
[0113] According to the numerical control apparatus of the
invention, synchronous control is realized in two or more spindles
in the machine tool, and synchronous control is simultaneously in
three or more spindles, and the precision of synchronism is higher
than in the prior art.
[0114] In the configuration of the invention, in spindle
synchronous control on plural axes, unlike the prior art, it is not
necessary to install plural numerical control apparatuses, so that
the cost of the machine tool can be curtailed. As a result, the
machine tool can be reduced in size.
[0115] Further, in the numerical control apparatus of the
invention, since the synchronous position correction unit 76 of the
axis control unit for controlling the synchronous axes corrects the
deviation component occurring during synchronous control,
off-synchronism component due to delay caused by cutting load or
the like can be easily corrected, or even in case of synchronous
control of axes involving difference always in the position
deviation amount due to difference in position control gain or
load, unjust torque due to correction does not take place, and
synchronous control of high precision is realized. As a result,
flaw or distortion of the work can be prevented, and processing of
higher precision is possible.
[0116] FIG. 7 is an essential block diagram of the numerical
control apparatus according to the second embodiment. This
numerical control apparatus, in addition to the components shown in
FIG. 1, comprises a multi-level acceleration and deceleration
parameter memory unit 81 for storing multi-level acceleration and
deceleration speed, multi-level reference acceleration and
deceleration time constant, and multi-level acceleration and
deceleration time constant multiplying factor described below,
generated according to the ordinary speed control acceleration and
deceleration pattern, by manipulating the parameter setting screen,
a reference inclination amount calculation unit 83 for calculating
the reference inclination amount which is the acceleration and
deceleration speed per unit time, from the maximum rotating speed
and multi-level reference acceleration and deceleration time
constant of reference spindle and synchronous spindle, a
multi-level acceleration and deceleration pattern calculation unit
84 for calculating an optimum multi-level acceleration and
deceleration pattern from the set multi-level acceleration and
deceleration parameter, and a multi-level acceleration and
deceleration decision unit 82 for determining the pattern of
acceleration and deceleration pattern, and noticing the pattern to
the synchronous control management unit. The components in the
second embodiment which are same as those in the first embodiment
are provided with the same reference characters, and their
description is omitted.
[0117] The operation of the numerical control apparatus according
to the second embodiment will be explained here.
[0118] First, setting of multi-level acceleration and deceleration
parameter from acceleration and deceleration speed, multi-level
reference acceleration and deceleration time constant, and
multi-level acceleration and deceleration time constant multiplying
factor is explained by referring to the essential block diagram in
FIG. 7, a specific example of multi-level acceleration and
deceleration pattern for synchronous control in FIG. 8, a diagram
showing calculation method of multi-level acceleration and
deceleration time constant multiplying factor in FIG. 9, and a
setting example of multi-level acceleration and deceleration
parameter for synchronous control in FIG. 10.
[0119] As shown in FIG. 8(a), usually, the spindle motor
accelerates and decelerates according to the acceleration and
deceleration pattern of speed control system, that is, along curve
1 shown in FIG. 8(a). However, the acceleration and deceleration
pattern by speed control system is a pattern at the time of maximum
torque output of spindle motor. Accordingly, in spindle synchronous
control of two or more spindle motors, in order to accelerate and
decelerate while maintaining the precision of synchronism, it is
necessary to accelerate and decelerate with plural acceleration and
deceleration patterns having a larger allowance (a smaller
inclination) than the acceleration and deceleration pattern of
speed control system, that is, by setting multi-level acceleration
and deceleration pattern.
[0120] The reason of multi-level setting of acceleration and
deceleration pattern is explained.
[0121] During high speed rotation, for example, at 7200 rpm to 8000
rpm in FIG. 8(a), the inclination of acceleration and deceleration
is very moderate. The spindle synchronous acceleration and
deceleration pattern {circle over (2)} in FIG. 8(a) must be set
with a larger allowance than the acceleration and deceleration
pattern of speed control due to the same reason as mentioned above,
and if set in one stage, the acceleration and deceleration time
becomes very long. Hence, by setting a multi-level acceleration and
deceleration pattern, the acceleration and deceleration operation
can be done efficiently in a short time form low speed rotation to
high speed rotation of the spindle motor (that is, acceleration and
deceleration closed to the acceleration and deceleration pattern of
speed control can be realized).
[0122] The parameter of multi-level acceleration and deceleration
pattern of spindle synchronous control is explained.
[0123] In FIG. 8(a), the acceleration and deceleration pattern of
speed control up to maximum rotating speed of 8000 rpm is divided
into seven sections. It is divided in a large section where the
acceleration and deceleration pattern of speed control system can
be approximately linearly, and in a small section where the curve
is large. For example, in FIG. 8(a), the former corresponds to
inclination 2, inclination 4, and inclination 7, and the latter
corresponds to inclination 1, inclination 3, inclination 5, and
inclination 6.
[0124] Determining the time constant at the largest inclination, it
is defined as the time until reaching the maximum rotating speed,
that is, the multi-level reference acceleration and deceleration
time constant. In the example in FIG. 8(a), inclination 2 is the
multi-level reference acceleration and deceleration time constant,
and it is calculated to be about 500 ms in the following
formula.
8000(rpm)/(4000(rpm)-500(rpm)).times.220(ms)=503(ms)
[0125] Next, the multi-level acceleration and deceleration time
constant multiplying factor is defined as the ratio to the
multi-level acceleration and deceleration time constant, and each
multi-level acceleration and deceleration time constant multiplying
factor the multi-level acceleration and deceleration pattern is
calculated as follows.
[0126] First, the method of determining the multi-level
acceleration and deceleration time constant multiplying factor of
inclination 1 is explained according to FIG. 9. For example, from
FIG. 1, the inclination (multi-level acceleration and deceleration
speed per unit time) is determined as follows:
500(rpm)/220(ms)=2.27(rpm/ms)
[0127] and the time to accelerate up to 8000 rpm is
8000(rpm)/2.27(rpm/ms)=3520(ms)
[0128] Finally, the ratio to the multi-level reference acceleration
and deceleration time constant (multi-level acceleration and
deceleration time constant multiplying factor) is calculated as
follows:
3520(ms)/500(ms)=7(times)
[0129] and hence the multi-level acceleration and deceleration time
constant multiplying factor 1 of inclination 1 is 7.
[0130] Similarly, the multi-level acceleration and deceleration
time constant multiplying factor 3, multi-level acceleration and
deceleration time constant multiplying factor 4, multi-level
acceleration and deceleration time constant multiplying factor 5,
multi-level acceleration and deceleration time constant multiplying
factor 6, and multi-level acceleration and deceleration time
constant multiplying factor 7 of inclination 3, inclination 4,
inclination 5, inclination 6, and inclination 7 are calculated, and
the parameters as shown in FIG. 10(a) are obtained. In FIGS. 8(b),
(c), and (d), each multi-level acceleration and deceleration time
constant multiplying factor is calculated, and patterns as shown in
FIGS. 10(b), (c), and (d) are obtained. Herein, since the
acceleration and deceleration pattern of the largest inclination is
defined as the multi-level reference acceleration and deceleration
time constant, the inclination is moderate in other acceleration
and deceleration patterns (that is, the multi-level acceleration
and deceleration time constant multiplying factor is larger than
1).
[0131] The parameters shown in FIG. 10 are stored in the
multi-level acceleration and deceleration parameter memory unit 81
in FIG. 7 through the parameter setting screen 8 by manipulating
the parameter setting screen not shown in the drawing.
[0132] FIG. 11 is a flowchart showing the method of selection and
calculation of multi-level acceleration and deceleration
pattern.
[0133] The selection method of multi-level acceleration and
deceleration pattern of synchronous control of three or more
spindles is explained by referring to FIG. 7, FIG. 8, FIG. 9, FIG.
10, and FIG. 11.
[0134] The acceleration and deceleration pattern in FIG. 8(a) shows
an acceleration and deceleration pattern of synchronous control of
reference spindle 23 and synchronous spindle 43. Herein, suppose
the synchronous spindle b63 is further synchronized with the
spindle synchronism of reference spindle 23 and synchronous spindle
43. As the acceleration and deceleration pattern of synchronous
spindle b63, three types are assumed as shown in the diagram. Ina
first type, the maximum rotating speed of the synchronous spindle
b63 is same as the maximum rotating speed of reference spindle 23
and synchronous spindle 43 (FIG. 8(b)), in a second type, the
maximum rotating speed of the synchronous spindle b63 is different
from that of the reference spindle 23 and synchronous spindle 43,
and the multi-level reference acceleration and deceleration time
constant (the time until reaching the maximum rotating speed) of
the synchronous spindle b63 is smaller than that of the reference
spindle 23 and synchronous spindle 43 (FIG. 8(c)), and in a third
type, the maximum rotating speed of the synchronous spindle b63 is
different from that of the reference spindle 23 and synchronous
spindle 43, and the multi-level reference acceleration and
deceleration time constant of the synchronous spindle b43 is larger
than that of the reference spindle 23 and synchronous spindle
43.
[0135] When three spindles, reference spindle 23, synchronous
spindle 43, and synchronous spindle b 63, start spindle
synchronism, the multi-level acceleration and deceleration decision
unit 82 compares, for example, the maximum rotating speed of the
reference spindle 23 and synchronous spindle 43 and the maximum
rotating speed of the synchronous spindle b63 (S31). At this time,
when the maximum rotating speed of the reference spindle 23 and
synchronous spindle 43 and the maximum rotating speed of the
synchronous spindle b63 are matched (S31, Yes), the multi-level
acceleration and deceleration decision unit 82 compares the
multi-level acceleration and deceleration time constants of the
reference spindle 23, synchronous spindle 43, and synchronous
spindle b63, and selects the multi-level acceleration and
deceleration pattern of the largest multi-level reference
acceleration and deceleration time constant, and notices the
selected multi-level acceleration and deceleration pattern to the
synchronous control management unit 11 (S32). Referring to the
example in FIG. 8, the reference spindle and synchronous spindle of
(a) and synchronous spindle b(1) of (b) correspond thereto, and the
multi-level reference acceleration and deceleration time constant
of the reference spindle and synchronous spindle of FIG. 8(a) is
500 ms, and the multi-level reference acceleration and deceleration
time constant of FIG. 8(b) is 600 ms. Therefore, in the multi-level
acceleration and deceleration decision unit 82, comparing the both
multi-level reference acceleration and deceleration time constants,
the multi-level acceleration and deceleration pattern of
synchronous spindle b(1) of FIG. 8(b) having the larger multi-level
reference acceleration and deceleration time constant is selected,
and the selected multi-level acceleration and deceleration pattern
is noticed to the synchronous control management unit 11 (S32).
[0136] On the other hand, when the maximum rotating speed of the
reference spindle 23 and synchronous spindle 43 and the maximum
rotating speed of the reference spindle b63 are not matched, the
multi-level acceleration and deceleration decision unit 82 compares
the maximum rotating speed of the reference spindle 23 and
synchronous spindle 43 and the maximum rotating speed of the
reference spindle b63, and selects the acceleration and
deceleration pattern of the spindle having the smaller maximum
rotating speed (S33) At this time, the multi-level acceleration and
deceleration decision unit 82 requests calculation of reference
inclination amount to the reference inclination amount calculation
unit 83. Herein, the reference inclination amount is the
multi-level acceleration and deceleration speed per unit time.
[0137] Being requested from the multi-level acceleration and
deceleration decision unit 82, the reference inclination amount
calculation unit 83 calculates the reference inclination amount as
follows from the maximum rotating speed of the designated spindle
and the multi-level reference acceleration and deceleration time
constant (S34).
Reference inclination amount=maximum rotating speed/multi-level
reference acceleration and deceleration time constant
[0138] The reference inclination amount calculation unit 83 notices
the result of calculation to the multi-level acceleration and
deceleration decision unit 82.
[0139] Receiving the calculation result from the reference
inclination amount calculation unit 83, the multi-level
acceleration and deceleration decision unit 802 checks if the
reference inclination amount of the spindle of the smaller maximum
rotating speed is less than the reference inclination amount of the
spindle of the larger maximum rotating speed or not (S35). At this
time, if the reference inclination amount of the spindle of the
smaller maximum rotating speed is less than the reference
inclination amount of the spindle of the larger maximum rotating
speed (S35, Yes), the multi-level acceleration and deceleration
decision unit 82 notices the acceleration and deceleration pattern
selected at step S33 directly to the synchronous control management
unit 11. Referring to the example in FIG. 8, the reference spindle
and synchronous spindle of (a) and the synchronous spindle b(2) of
(c) correspond thereto. Comparing the maximum rotating speed
between (a) and (c) in FIG. 8, (a) is 8000 rpm, and (c) is 4000
rpm, and the maximum rotating speed of (c) is smaller, and hence
the acceleration and deceleration pattern of synchronous spindle
b(2) of (c) is selected.
[0140] The reference inclination amount becomes, according to FIG.
8(a),
8000(rpm)/500(ms)=16(rpm/ms)
[0141] and becomes, according to FIG. 8(c),
4000(rpm)/400(ms)=10(rpm/ms).
[0142] Comparing the two, as shown below, since the reference
inclination amount of the synchronous spindle b(2) with smaller
maximum rotating speed is less than the reference inclination
amount of the reference spindle and synchronous speed with larger
maximum rotating speed,
10(rpm/ms)<16(rpm/ms)
[0143] the multi-level acceleration and deceleration decision unit
82 selects the acceleration and deceleration pattern of the
synchronous spindle b(2) with smaller maximum rotating speed.
[0144] On the other hand, when the reference inclination amount of
the spindle of the smaller maximum rotating speed is more than the
reference inclination amount of the spindle of the larger maximum
rotating speed (S35, No), the multi-level acceleration and
deceleration decision unit 82 requests calculation of multi-level
acceleration and deceleration pattern to the multi-level
acceleration and deceleration pattern calculation unit 84. Being
requested from the multi-level acceleration and deceleration
decision unit 82, the multi-level acceleration and deceleration
pattern calculation unit 84 calculates the multi-level reference
acceleration and deceleration time constant from the reference
inclination amount of reference spindle and synchronous spindle and
reference inclination amount of synchronous spindle b(2) calculated
by the reference inclination amount calculation unit 83 (S36).
[0145] Using the multi-level reference acceleration and
deceleration time constant calculated in the multi-level
acceleration and deceleration pattern calculation unit 84, and the
multi-level acceleration and deceleration parameter shown in FIG.
10, the multi-level acceleration and deceleration pattern is
calculated (S37), and noticed to the multi-level acceleration and
deceleration decision unit 82. The multi-level acceleration and
deceleration decision unit 82 notices the multi-level acceleration
and deceleration pattern calculated in the multi-level acceleration
and deceleration pattern calculation unit 84 to the synchronous
control management unit 11. Referring to the example in FIG. 8, the
reference spindle and synchronous spindle of (a) and the
synchronous spindle b(3) of (d) correspond thereto.
[0146] Calculating the reference inclination amount, in (a),
8000(rpm)/500(ms)=16(rpm/ms)
[0147] and in (d),
6000(rpm)/300(ms)=20(rpm/ms)
[0148] Comparing the two,
16(rpm/ms)<20(rpm/ms)
[0149] since the synchronous spindle b(3) with smaller maximum
rotating speed is larger in the reference inclination amount, the
multi-level acceleration and deceleration pattern calculation unit
84 calculates the multi-level reference acceleration and
deceleration time constant from the reference inclination amount of
reference spindle and synchronous spindle, and the reference
inclination amount of synchronous spindle b(2) calculated in the
reference inclination amount calculation unit 803. The result is as
follows.
300(ms).times.20(rpm/ms)/16(rpm/ms)=375(ms)
[0150] On the basis of this result of calculation, the multi-level
acceleration and deceleration pattern calculation unit 84
calculates the multi-level acceleration and deceleration pattern by
using the multi-level acceleration and deceleration parameter shown
in FIG. 10(d). Results of calculation are as follows.
1 Spindle rotating Acceleration and deceleration speed (rpm)
pattern (inclination: rpm/ms) 0-450 6000/(375 .times. 6.8) = 2.35
450-3000 6000/(375 .times. 1.0) = 16 3000-3500 6000/(375 .times.
4.6) = 3.48 3500-4500 6000/(375 .times. 5.0) = 3.2 4500-4900
6000/(375 .times. 7.1) = 2.25 4900-5400 6000/(375 .times. 7.5) =
2.13 5400-6000 6000/(375 .times. 15.0) = 1.07
[0151] The multi-level acceleration and deceleration pattern
calculation unit 84 notices the calculation results to the
multi-level acceleration and deceleration decision unit 82. The
multi-level acceleration and deceleration decision unit 82 notices
the multi-level acceleration and deceleration pattern calculated in
the multi-level acceleration and deceleration pattern calculation
unit 84 to the synchronous control management unit 11.
[0152] Thus, according to the numerical control apparatus of the
invention, an appropriate acceleration and deceleration pattern
maybe always noticed to the synchronous control management unit
11.
INDUSTRIAL APPLICABILITY
[0153] As described herein, the numerical control apparatus of the
invention is useful in a machine tool for synchronous control by
driving two or more spindle motors or servomotors, and is
particularly suited to synchronous control of higher precision.
* * * * *