U.S. patent application number 09/849269 was filed with the patent office on 2001-12-06 for machine tool.
This patent application is currently assigned to Mori Seiki Co., Ltd.. Invention is credited to Akamatsu, Yoshiaki, Fujishima, Makoto.
Application Number | 20010048858 09/849269 |
Document ID | / |
Family ID | 18642776 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010048858 |
Kind Code |
A1 |
Akamatsu, Yoshiaki ; et
al. |
December 6, 2001 |
Machine tool
Abstract
The present invention provides a machine tool which is adapted
to detect the end of the service life of a spring of a clamp unit
for fixing a tool to a spindle for systematic replacement of the
spring. The machine tool comprises a clamp unit (47) for fixing a
tool in a taper hole provided in a spindle, and a controlling
section (63) for controlling the operation of the clamp unit. The
clamp unit (47) includes a holder for holding a holder portion of
the tool, a driving rod coupled to the holder, a driver for moving
the driving rod along an axis thereof, and a spring for biasing the
driving rod in one direction along the axis thereof. The machine
tool further comprises a service life end detecting section (11)
for counting the number of times of actuation of the clamp unit
(47) and, when the count of the number reaches a predetermined
reference actuation number, judging that the service life of the
spring ends. With this arrangement, maintenance can systematically
be carried out by detecting the end of the service life of the
spring.
Inventors: |
Akamatsu, Yoshiaki;
(Yamatokoriyama-shi, JP) ; Fujishima, Makoto;
(Yamatokoriyama-shi, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN, HATTORI,
MCLELAND & NAUGHTON, LLP
1725 K STREET, NW, SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
Mori Seiki Co., Ltd.
Yamatokoriyama-shi
JP
|
Family ID: |
18642776 |
Appl. No.: |
09/849269 |
Filed: |
May 7, 2001 |
Current U.S.
Class: |
409/134 ;
409/233 |
Current CPC
Class: |
G05B 2219/35512
20130101; G05B 2219/37252 20130101; G05B 19/4065 20130101; Y10T
409/30392 20150115; G05B 2219/37251 20130101; Y10T 409/309464
20150115 |
Class at
Publication: |
409/134 ;
409/233 |
International
Class: |
B23C 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2000 |
JP |
2000-134509 |
Claims
What is claimed is:
1. A machine tool comprising: a spindle, a clamp unit for fixing a
tool in a taper hole provided in the spindle, the clamp unit
including a holder for holding a holder portion of the tool, a
driving rod coupled to the holder, a driver for moving the driving
rod along an axis thereof, and a spring for biasing the driving rod
in one direction along the axis thereof, whereby the driving rod is
moved along the axis thereof by the driver and the spring and the
tool is fixed in the taper hole of the spindle with the holder
portion thereof held by the holder; a controlling section for
controlling an operation of the clamp unit; and a service life end
detecting section for counting a number of times of actuation of
the clamp unit and, when a count of the number reaches a
predetermined reference actuation number, judging that a service
life of the spring ends.
2. A machine tool as set forth in claim 1, further comprising
display means for graphically displaying a ratio of the count of
the number to the reference actuation number.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a machine tool having a
spindle, a clamp unit for fixing a tool in a taper hole provided in
the spindle, and a controlling section for controlling the
operation of the clamp unit, wherein the clamp unit includes a
holder for holding a holder portion of a tool, a driving rod
coupled to the holder, a driver for driving the driving rod along
an axis thereof, and a spring for biasing the driving rod in one
direction along the axis thereof, whereby the driving rod is moved
along the axis thereof by the driver and the spring and the tool is
fixed in the taper hole of the spindle with the holder portion
thereof held by the holder.
[0003] 2. Description of Related Art
[0004] One exemplary machine tool having a clamp unit of the
aforesaid type will hereinafter be described with reference to
FIGS. 5 to 7. The machine tool 21 illustrated in FIG. 5 is a
so-called vertical machining center. The machine tool 21 includes:
a bed 22; a column 23 provided upright on the bed 22; a spindle
head 24 rotatably supporting a spindle 25 and supported by the
column 23 in a vertically movable manner; a table 26 provided below
the spindle head 24 on the bed 22; a tool magazine 30 provided on
the left side of the spindle head 24; an automatic tool changer 35
provided at a lower end of the tool magazine 30 for exchanging a
tool T attached to the spindle 25 with a tool T stored in the tool
magazine 30; a clamp unit 47 as shown in FIG. 6 for fixing the tool
T to a front end (lower end) of the spindle 25; and a numerical
controller 60 as shown in FIG. 7 for controlling the respective
components of the machine tool.
[0005] As shown in FIG. 6, the spindle head 24 includes the spindle
25, a housing 40 rotatably supporting the spindle 25 via a bearing
41, and a cover 42 provided at a front end of the housing 40. A
taper hole 25a for receiving the tool T is provided in the front
end of the spindle 25 (as seen in the direction of an arrow A).
[0006] As shown in FIG. 6, the clamp unit 47 includes a collet 48
provided in the spindle 25 for holding a pull stud (holder portion)
Ta of the tool T fitted in the taper hole 25a of the spindle 25, a
push-pull rod 49 engaged with the collet 48, a driving rod 50
coupled to the push-pull rod 49, coned disc springs 51 for biasing
the driving rod 50 in the direction of an arrow B, and a hydraulic
cylinder (not shown) for moving the driving rod 50 in the direction
of the arrow A.
[0007] As shown in FIG. 7, the numerical controller 60 includes a
CNC 61, a PLC 62, an input/output interface 65 and the like, and is
connected to an external control circuit 66 via the input/output
interface 65. The control circuit 66 is connected to an operation
panel 67, the clamp unit 47 and the like.
[0008] The CNC 61 executes a machining program stored therein to
control basic operations of the machine tool 21 such as axial
movements of the spindle head 24 and the table 26, and display of a
CRT 68. The PLC 62 includes a clamp controlling section 63 and the
like, and controls auxiliary operations of the machine tool 21 such
as operations of the tool magazine 30, the automatic tool changer
35 and the clamp unit 47. The CRT 68 typically displays the
machining program and the coordinates of the current position of
the tool.
[0009] As described above, the clamp controlling section 63
controls the operation of the clamp unit 47 via the control circuit
66. The clamp controlling section 63 usually drives the hydraulic
cylinder (not shown) of the clamp unit 47 to perform a tool
clamping or unclamping operation for clamping or unclamping the
tool T attached to the spindle 25 upon reception of a tool clamp
command or a tool unclamp command applied from the CNC 61 executing
the machining program. The tool clamp command or the tool unclamp
command can also be manually inputted from the operation panel 67
to cause the clamp unit 47 to perform the tool clamping or
unclamping operation. In this case, the tool clamp command or the
tool unclamp command inputted from the operation panel 67 is
transmitted to the CNC 61 via the control circuit 66, the
input/output interface 65 and the PLC 62, and then outputted from
the CNC 61 to the clamp controlling section 63. Upon reception of
the tool clamp command or the tool unclamp command, the clamp
controlling section 63 drives the clamp unit 47.
[0010] In the machine tool 21 having the aforesaid construction,
the tool T fixed to the spindle 25 is removed (unclamped) from the
spindle 25, and the tool T fitted in the taper hole 25a of the
spindle 25 is fixed (clamped) to the spindle 25 in the following
manner. It is herein assumed that the tool T, the driving rod 50,
the push-pull rod 49 and the collet 48 are respectively located in
positions as shown in FIG. 6, and the tool T is fixed to the
spindle 25.
[0011] First, a hydraulic pressure is supplied to the hydraulic
cylinder (not shown) to move the driving rod 50 in the direction of
the arrow A against a biasing force of the coned disc springs 51,
whereby the push-pull rod 49 and the collet 48 are moved in the
direction of the arrow A to open a front end of the collet 48 which
holds the pull stud Ta of the tool T. Thus, the tool T can be
withdrawn from the taper hole 25a of the spindle 25.
[0012] Where the tool T is fitted in the taper hole 25a of the
spindle 25 in the aforesaid state, the pull stud Ta of the tool T
is inserted in the collet 48. When the supply of the hydraulic
pressure to the hydraulic cylinder (not shown) is stopped in this
state, the driving rod 50 is moved in the direction of the arrow B
by the biasing force of the coned disc springs 51 to close the
collet 48, whereby the tool T attached to the spindle 25 is held by
the collet 48 with the pull stud Ta thereof inserted in the
direction of the arrow B. Thus, the tool T is fixed to the spindle
25.
[0013] As described above, the clamp unit 47 employs the coned disc
springs 51, which naturally have a limited fatigue durability
because the coned disc springs 51 are repeatedly subjected to a
load and, hence, have a finite service life. However, the
conventional machine tool 21 is not adapted to detect the end of
the service life of the coned disc springs 51. Therefore, the
service life of the coned disc springs 51 may end during the
operation of the machine tool 21, resulting in breakage of the
coned disc springs 51. Depending on operating conditions of the
machine tool 21 at the breakage, the time required for recovery
from the breakage is disadvantageously prolonged.
[0014] Where the coned disc springs 51 are broken, there is a
danger of breakage of other components depending on the conditions
of the breakage of the coned disc springs 51. The breakage of a
greater number of components prolongs the time required for repair
of the components. This disadvantageously reduces the availability
of the machine tool 21. If there are no spare coned disc springs
51, the machine tool 21 cannot be repaired until new coned disc
springs 51 are delivered. This further reduces the availability of
the machine tool 21.
[0015] In view of the foregoing, it is an object of the present
invention to provide a machine tool which is adapted to detect the
end of the service life of a spring of a clamp unit for fixing a
tool to a spindle for systematic replacement of the spring.
SUMMARY OF THE INVENTION
[0016] In accordance with the present invention to achieve the
aforesaid object, there is provided a machine tool, which
comprises: a clamp unit for fixing a tool in a taper hole provided
in a spindle, the clamp unit including a holder for holding a
holder portion of the tool, a driving rod coupled to the holder, a
driver for moving the driving rod along an axis thereof, and a
spring for biasing the driving rod in one direction along the axis
thereof, whereby the driving rod is moved along the axis thereof by
the driver and the spring and the tool is fixed in the taper hole
of the spindle with the holder portion thereof held by the holder;
a controlling section for controlling the operation of the clamp
unit; and a service life end detecting section for counting the
number of times of actuation of the clamp unit and, when the count
of the number reaches a predetermined reference actuation number,
judging that the service life of the spring ends.
[0017] In the machine tool according to the present invention, the
service life end detecting section counts the number of the times
of the actuation of the clamp unit and, when the count of the
number reaches the predetermined reference actuation number, judges
that the service life of the spring ends.
[0018] The end of the service life of the spring which repeatedly
operates under a constant repetitive load is detected on the basis
of the number of the times of the operation of the spring. The
number of the times that the spring is expected to operate before
the end of the service life thereof is typically determined as an
empirical value. Therefore, the end of the service life of the
spring can be detected by counting the number of the times of the
actuation of the clamp unit, more specifically, the number of the
times of the operation of the spring. In the present invention, the
known empirical value for the number of the times that the spring
is expected to operate before the end of the service life thereof
is employed as the reference actuation number. The number of the
times of the actuation of the clamp unit is counted and, when the
count of the number reaches the reference actuation number, it is
judged that the service life of the spring ends.
[0019] Since the end of the service life of the spring can be thus
detected by the service life end detecting section in accordance
with the present invention, maintenance can systematically be
carried out by preparing a spare spring and replacing the spring
with the spare spring before the end of the service life of the
spring. The availability of the machine tool can further be
improved by performing the maintenance operation during an idle
period of the machine tool in accordance with an operation plan of
the machine tool. Therefore, the reduction in the availability of
the machine tool can be prevented, because the breakage of the
spring due to the end of the service life thereof during the
operation of the machine tool can be prevented which may otherwise
require a prolonged time for the recovery from the breakage.
[0020] The ratio of the count of the number to the reference
actuation number may graphically be displayed on display means. By
graphically displaying the ratio of the count of the number to the
reference actuation number on the display means, an operator can
recognize the degree of the fatigue of the spring at a glance.
Through daily monitoring of the degree of the fatigue of the
spring, the end of the service life of the spring can easily be
predicted, so that a maintenance plan can easily be formulated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a block diagram illustrating a numerical
controller and the like of the machine tool according to one
embodiment of the present invention;
[0022] FIG. 2 is a characteristic diagram to be employed for
determination of a reference value in the embodiment;
[0023] FIG. 3 is a characteristic diagram showing a relationship
between the stress and the durability limit to be employed for the
determination of the reference value in the embodiment;
[0024] FIG. 4 is a diagram illustrating one exemplary display
screen to be displayed on a CRT in accordance with the
embodiment;
[0025] FIG. 5 is a front view illustrating a conventional machine
tool as a whole;
[0026] FIG. 6 is a sectional view illustrating a spindle head of
the machine tool shown in FIG. 5; and
[0027] FIG. 7 is a block diagram illustrating a numerical
controller and the like of the conventional machine tool.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] A preferred embodiment of the present invention will
hereinafter be described with reference to the attached drawings.
FIG. 1 is a block diagram illustrating a numerical controller and
the like of a machine tool according to this embodiment, and FIG. 4
is a diagram illustrating one exemplary display screen to be
displayed on a CRT. The machine tool according to this embodiment
is a modification of the conventional machine tool shown in FIGS. 5
to 7, and is different from the conventional machine tool in that
the numerical controller has a different construction. Therefore,
components equivalent to those of the conventional machine tool
shown in FIGS. 5 to 7 will not be explained in detail, and will be
denoted by like reference characters in FIGS. 1 and 4.
[0029] As shown in FIG. 1, the numerical controller 1 according to
this embodiment includes a PLC 6 which has a different construction
from the conventional PLC 62 in that the PLC 6 has additional
functions and further includes a display controlling section 12 and
a service life end detecting section 11.
[0030] The service life end detecting section 11 counts the number
of times of actuation of the clamp unit 47. More specifically, the
service life end detecting section 11 increments the count of the
number by one whenever receiving a tool clamp command or a tool
unclamp command applied from the CNC 61, and compares the count of
the number with a predetermined reference value to judge whether or
not the count of the number reaches the reference value. The count
of the number and the reference value and, if it is judged that the
count of the number reaches the reference value, a signal
indicative of the judgment (service life end detection signal) are
outputted to the display controlling section 12.
[0031] The reference value herein means the number of times that
the clamp unit 47 is expected to be actuated before the end of the
service life of the coned disc springs 51. The reference value is
determined in the following manner, and stored in the service life
end detecting section 11.
[0032] First, a mounting stress .sigma..sub.i exerted on the coned
disc springs 51 and a maximum stress .sigma..sub.m exerted on the
coned disc springs 51 under a maximum load are calculated from the
following equations (1) and (2) on the basis of a graph as shown in
FIG. 2. The equations (1) and (2) are Almen-Laszlo equations, and
the graph of FIG. 2 defines application ranges of the equations (1)
and (2). 1 t1 = 4 EC ( 1 - v 2 ) D 2 { - B ( h - 2 ) + t } ( 1 ) t2
= 4 EC ( 1 - v 2 ) D 2 { ( 2 - ) ( h - 2 ) + t } ( 2 )
[0033] wherein E is a Young's modulus, .nu. is a Poisson's ratio,
.delta. is the flexure of each coned disc spring 51, D is the outer
diameter of each coned disc spring 51, .beta. and .gamma. are
stress factors, h is the height of each coned disc spring 51, t is
the thickness of the coned disc springs 51, and C is a factor
obtained from an initial value.
[0034] Where a mounting load P.sub.1 and a maximum load P.sub.m are
610 kg and 840 kg, respectively, and the coned disc springs 51 each
have an outer diameter D of 54 mm, an inner diameter d of 25.4 mm,
a height of 1.1 mm with a total thickness of 3.0 mm, for example,
D/d and h/t are about 2.0 and about 0.37, respectively, which are
plotted at a point A in FIG. 2. The point A belongs to the
application range of the equation (1), so that the equation (1) is
employed for the calculation of the mounting stress .sigma..sub.i
and the maximum stress .sigma..sub.m. The results of the
calculation with the use of the equation (1) are shown in Table
1.
1 TABLE 1 Load P Flexure .delta. Stress .sigma. (kg) (mm)
(kg/mm.sup.2) Mounting (i) 610 0.39 63 Maximum (m) 840 0.55 92
[0035] Then, the number of the times that the coned disc springs 51
are expected to operate before the end of the service life thereof
is determined on the basis of the mounting stress .sigma..sub.i and
the maximum stress .sigma..sub.m thus calculated and a graph as
shown in FIG. 3. The graph of FIG. 3 is an empirically obtained
graph which indicates a durability limit determined on the basis of
the mounting stress .sigma..sub.i and the maximum stress
.sigma..sub.m.
[0036] Where the mounting stress .sigma..sub.i and the maximum
stress .sigma..sub.m are 63 kg/mm.sup.2 and 92 kg/mm.sup.2,
respectively, which are plotted at a point B in FIG. 3, for
example, the reference value (operation limit number) is
2.times.10.sup.6. The reference value thus determined is stored in
the service life end detecting section 11.
[0037] The display controlling section 12 receives the count of the
number and the reference value from the service life end detecting
section 11, and controls the CRT 68 via the CNC 61 to graphically
display the ratio of the count of the number to the reference value
as shown in FIG. 4. Further, the display controlling section 12
causes the CRT 68 to display a message requesting the replacement
of the coned disc springs 51 upon reception of the service life end
detection signal from the service life end detecting section 11. In
a display screen shown in FIG. 4, the reference value is displayed
as SERVICE LIFE and the count of the number is displayed as CURRENT
VALUE (%). Therefore, an operator can recognize the degree of the
fatigue of the coned disc springs 51 at a glance.
[0038] In the numerical controller 1 having the aforesaid
construction in accordance with this embodiment, the service life
end detecting section 11 increments the count of the number by one
whenever receiving the tool clamp command or the tool unclamp
command applied from the CNC 61 to the PLC 6 during the execution
of a machining program or by a manual operation. Then, the service
life end detecting section 11 compares the count of the number with
the predetermined reference value to judge whether or not the count
of the number reaches the reference value.
[0039] If the service life end detecting section 11 judges that the
count of the number reaches the reference value, the message
requesting the replacement of the coned disc springs 51 is
displayed on the CRT 68. Further, the ratio of the count of the
number to the reference value is graphically displayed on the CRT
68 as shown in FIG. 4, so that the operator can recognize the
degree of the fatigue of the coned disc springs 51 at a glance.
[0040] According to this embodiment, the end of the service life of
the coned disc springs 51 is detected by the service life end
detecting section 11. Therefore, maintenance can systematically be
carried out by preparing spare coned disc springs 51 and replacing
the coned disc springs 51 with the spare coned disc springs 51
before the end of the service life of the coned disc springs 51.
The availability of the machine tool 21 can further be improved by
performing the maintenance operation during an idle period of the
machine tool 21 in accordance with an operation plan of the machine
tool 21. Since the degree of the fatigue of the coned disc springs
51 is displayed on the CRT 68, the end of the service life of the
coned disc springs 51 can easily be predicted through daily
monitoring of the degree of the fatigue of the coned disc springs
51. Therefore, a maintenance plan can easily be formulated.
[0041] In this embodiment, the end of the service life of the coned
disc springs 51 is indicated by displaying the message requesting
the replacement of the coned disc springs 51 on the CRT 68, but may
be indicated by lighting an alarm lamp or beeping an alarm
beeper.
[0042] Although the coned disc springs 51 are employed as a spring
for the clamp unit 47 in the embodiment described above, any other
spring such as a coil spring may be employed instead of the coned
disc springs 51 in the present invention.
[0043] Further, the method for the determination of the reference
value (operation limit number) for the coned disc springs 51 is not
limited to that described above, but any other proper methods may
be employed for the determination of the reference value.
* * * * *