Gear cutting – milling – or planing – Milling – With means to protect operative or machine
Reexamination Certificate
2001-05-07
2002-06-11
Howell, Daniel W. (Department: 3722)
Gear cutting, milling, or planing
Milling
With means to protect operative or machine
C409S233000, C700S177000
Reexamination Certificate
active
06402442
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Description of Related Art
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.
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
25
a
for receiving the tool T is provided in the front end of the spindle
25
(as seen in the direction of an arrow A).
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
25
a
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.
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.
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.
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
.
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
25
a
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
.
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
25
a
of the spindle
25
.
Where the tool T is fitted in the taper hole
25
a
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
.
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.
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
.
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
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
Akamatsu Yoshiaki
Fujishima Makoto
Howell Daniel W.
Mori Seiki Co., LTD
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