Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2002-07-01
2004-09-28
Hail, III, Joseph J. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S008000, C451S009000, C451S047000, C451S900000
Reexamination Certificate
active
06796878
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an NC machine tool with a tiltable spindle unit. More specifically, the invention relates to an NC machine tool with a tiltable spindle unit for selectively using a vertical spindle and an inclined spindle in a tool mounting position.
2. Description of the Prior Art
In recent years, NC machine tools capable of shaping optical parts ultra-precisely, such as lenses, have been developed. An ultra-precise NC machine tool of this type can work a concave surface of a lens precisely by using a grindstone or end mill with a flat or spherical end. Conventional NC machine tools for shaping concave surfaces of lenses or the like include vertical spindle type machines, the tool mounting position of which extends in vertical directions, and inclined spindle type machines, the tool mounting position of which is inclined.
FIG. 6
a
schematically shows a concave surface grinding using a vertical spindle type machine,
FIG. 6
b
shows a concave surface grinding using an inclined spindle type machine.
As shown in
FIG. 6
a
, in a case where a concave surface of a workpiece W with a relatively small diameter is grinded by means of a grindstone
1
attached to a vertical spindle
3
, the vertical spindle
3
interferes with the outer circumferential edge portion on the concave surface of the workpiece W, if the radius of curvature on the concave surface of the workpiece W is large and if the spindle
3
having the grindstone
1
is relatively thick with respect to the radius of the grindstone
1
. To avoid the interference, the diameter of the spindle
3
must be as small as possible.
However, if the diameter of the workpiece W is 3 mm or less, the rigidity of the spindle
3
attached to the grindstone
1
is reduced, so that a precise working can not be achieved. In a case where a spindle
4
attached the grindstone
1
with a larger diameter having a high rigidity is tilted as shown in
FIG. 6
b
, it is possible to work the concave surface without interfering with the workpiece W. Thus, conventionally, the vertical spindle and the inclined spindle are selectively used for working the concave surface of a small work having a diameter of a few millimeters while insuring the rigidity of the spindles.
FIGS. 7 and 8
show a conventional NC machine tool capable of being used both as a vertical spindle type machine and an inclined spindle type machine in accordance with a work to be grinded or milled. In
FIG. 7
, a spindle is set to a vertical orientation. In
FIG. 7
, reference number
10
denotes a column with slide,
12
denotes a spindle unit for vertical oriented spindle, and
14
denotes a rotary unit for rotating a workpiece mounted thereon. The column with slide
10
is designed to be fed perpendicular to the plane of the figure by a control axis extending in directions of X-axis. The spindle unit
12
is detachably mounted on a slide
17
which is vertically movable along a slideway of the column with slide
10
via a vertical spindle mounting base
16
. The control axis for feeding the spindle
12
is Y-axis. A vacuum chuck
18
is mounted on the end portion of the rotating shaft of the rotary unit
14
, and the workpiece W is held on the vacuum chuck
18
via a fixture
19
by vacuuming air. The rotary unit
14
is installed on a table
22
. The table
22
is designed to be fed in directions of Z-axis as control axes, perpendicular to Y-axis and X-axis. The spindle unit
12
shown in
FIG. 7
includes a drive unit for a spindle
20
. On the top end of the spindle
20
, a tool, such as a grindstone or an end mill, is mounted.
On the other hand,
FIG. 8
shows a operating manner in which a spindle is changed to an inclined spindle type. The spindle can be changed to an inclined spindle type by replacing the spindle unit
12
for vertical spindle shown in
FIG. 7
with a spindle unit
24
for inclined spindle. In this case, the spindle unit
24
for inclined spindle is detachably mounted on the slide
17
via an inclined spindle mounting base
25
.
Such a conventional NC machine tool can work precisely the concave surface of the workpiece W by making replacement selectively between the spindle unit
12
for vertical spindle shaft with the spindle unit
24
for inclined spindle without changing other mechanical parts, such as the column with slide
10
and the rotary unit
14
.
In an NC machine tool of this type, it is required to measure a tool length, a tool diameter and a working point of the tool for preparations of the machining. Because the tool length, the tool diameter and so forth are data indispensable for grasping the working point of the tool precisely to conduct the position-control the spindle. In the case of the vertical spindle, it is easy to measure the tool length, the tool diameter and so forth, whereas in the case of the inclined spindle, it is very difficult to precisely measure the tool diameter and the working point the tool attached to the spindle
20
since the tool is inclined on the mounting position.
For that reason, in the case of the inclined shaft, it is the conventional practice that a tool wherein its diameter and so forth have been measured is mounted, and the measured values are used for preparing NC data, so that the alignment of a work piece with the tool is carried out on the basis of experience and practical sense after trial-and-error.
In the case of the inclined spindle, there is a problem in that it is very difficult to precisely carry out truing in addition to the problem on tool measurement, since the grindstone mounting position is inclined. Particularly, if the grindstone is eccentric, it is very difficult to carry out truing for correcting eccentricity.
Moreover, in
FIGS. 7 and 8
, it is assumed that the distance between the end face of the vacuum chuck
18
and the slide
17
of the column with slide
10
is L, the distance between the end face of the vacuum chuck
18
and the center of the tool is L1, and the distance between the center of the tool and the slide
17
is L2. In the case of the inclined spindle, the distance L1 between the end face of the vacuum chuck
18
and the center of the tool is far shorter than that in the case of the vertical spindle. Therefore, in order to insure a constant stroke in Z-axis in the case of the inclined shaft, the whole machine must be large, or the column with slide
10
must be replaced.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide an NC machine tool with tiltable spindle unit capable of being used both as vertical and inclined spindle type machine tools without restrictions on stroke and capable of easily carrying out tool measurement, alignment of a work piece with a tool, and truing.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention,
an NC machine tool with a tiltable spindle unit having a plurality of control axes, comprises: a spindle unit having a spindle serving both as a vertical spindle for keeping a tool in a vertical position and an inclined spindle for keeping the tool in a inclined position; a column for installing the spindle unit thereon; a table for supporting a workpiece; a turning shaft for pivotably supporting the spindle unit on a vertical plane, and a tilting means for changing the position of the spindle unit between the vertical position and the inclined position; wherein the turning shaft has a center of rotation which is arranged in the vicinity of a top end of the tool in alignment with a center line of the tool.
The tilting means part may comprises a mounting bracket mounted on a slide which vertically moves along a guide on a side of the column; a spindle unit bracket to which the spindle unit is fixed and which is connected to the turning shaft; a bearing, fixed to the mounting bracket, for horizontally supporting the turning shaft; and a positioning means for selectively positioning the spindle unit at the vertical position and the i
Mitsuzono Masaaki
Miura Kenji
Tsukita Yutaka
Hail III Joseph J.
Ojini Anthony
Pillsbury & Winthrop LLP
Toshiba Kikai Kabushiki Kaisha
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