Machine tool

Details Machine tool Machine tool

1998-11-19

2001-04-24

Briggs, William (Department: 3722)

Gear cutting, milling, or planing

Milling

Including means to infeed work to cutter

C029S02600B, C408S062000, C409S134000, C409S226000, C409S229000, C483S003000

Reexamination Certificate

active

06220799

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a machine tool.
BACKGROUND ART
In a conventional machine tool with a vertical spindle, the spindle is supported by a column in such a way that the spindle is movable along its axial direction or the Z-axis, and the column is either directly or indirectly supported on a base. In an exemplary arrangement shown in FIG.
21
(
a
), an X-axis table
72
being movable in the X-axis direction is mounted on a base
71
, and a column
73
serving as a Y-axis table being movable in the Y-axis direction is mounted on the X-axis table
72
. A spindle head
74
is supported by the column
73
movably along the Z-axis, and a work bed
75
is connected to the base
71
. In another arrangement shown in FIG.
21
(
b
), an X-axis table
76
serving as a work bed and the column
73
serving as a Y-axis table for movement in the Y-axis direction are mounted on the base
71
. The spindle head
74
is supported by the column
73
movably along the Z-axis direction. U.S. Pat. No. 5,439,431 typically discloses such type of machine tool, in which a spindle driven to move in Z-axis direction is mounted on a compound slide (corresponding to the column
73
in FIG.
21
(
b
)) which is moved in X- and/or Y-axis direction. In yet another arrangement shown in FIG.
21
(
c
), an X-axis table
78
serving as a work bed being movable in the X-axis direction is mounted on a Y-axis table
77
for movement in the Y-axis direction, which is disposed on the base
71
. A column
79
of an inverted L shape is vertically mounted on the base
71
, and a spindle head
80
having a built-in mechanism for movement in the Z-axis direction is mounted to the distal end of the column
79
. In a still further example shown in FIG.
21
(
d
), the Y-axis table
77
is mounted on the base
71
for movement in the Y-axis direction, and the X-axis table
78
serving as a work bed is mounted on the Y-axis table
78
for movement in the X-axis direction. A column
81
is vertically mounted on the base
71
, and the spindle head
74
is supported by the column
81
movably along the Z-axis.
Other types of machine tools such as the one employing a gate-like column (not shown) or the one having its spindle arranged horizontally have substantially the same configuration as described above.
The spindle head is generally cantilevered by the column in any of the prior arrangements described above. In order to variably determine the positional relationship between the spindle head and the workpiece, the mechanisms that link the spindle head and the work piece are constructed to detour the space therebetween. To accomplish high-speed and highly precise machining, the machine tool must meet two requirements. Firstly, the materials constituting the base, table, column, and other members should be given high rigidity. Secondly, the play between moving parts of each member should be minimized. To meet these requirements, relatively larger members precisely constructed are necessary, causing the entire machine to be larger, heavier, more expensive, and to occupy a larger space in a factory line for installation.
Another problem is attributable to the detoured structure and the large scale of the entire machine. Thermal deflection caused by changes in temperature has greater influence on the mechanisms, adversely affecting the precision of machining.
In view of the foregoing, it is an object of the present invention to provide a machine tool which accomplishes a high degree of precision in machining with minimized size, weight, and cost.
DISCLOSURE OF INVENTION
In order to accomplish the above-said object, a machine tool according to the present invention is characterized in that the spindle is supported at both sides within a stationary box-like body frame which constitutes a main frame of the machine body and located approximately at the center of the machine body, and that an X-axis table and a Y-axis table being respectively movable along X-axis and Y-axis directions are provided on a top face or one of four sides of the body frame and therewith in a plane, which lies orthogonal to the axis of the spindle in such a manner as to be cumulated on one another, the chuck means being mounted on the upper one of the X-axis table and Y-axis table.
Relative positions between the chuck means and the spindle is variably determined by moving the table disposed on one side of the body frame with respect to the axial center of the spindle disposed within the body frame. The mechanism for variably determining the positional relationship between the spindle and a workpiece held by the chuck means is comprised of the body frame and the table on one side thereof in abutment with each other, and includes no roundabout members such as a cantilevered column, providing no spaces between each member. The entire design of the machine tool can be thus compactly constructed with small and light parts yet keeping high rigidity. High-speed and highly accurate machining is thereby accomplished while minimizing the structure in size, weight, and cost. Further, the entire structure of the machine tool can be made approximately symmetrical around the spindle as the axis of symmetry, which restrains adverse effects of thermal deflection caused by changes in temperature which leads to errors in machining. It is to be understood that the axial center of the spindle may be arranged parallel as well as vertical to a horizontal plane.
In the above structure, the spindle is fixed to a Z-axis moving means which is slidably supported on guide rails within the body frame for moving the spindle in Z-axis direction. Since the spindle is movable in only one axial direction, the structure is simplified yet constructed with high rigidity and precision. The workpiece can also be accurately positioned by controlling each table.
The machine tool according to the present invention may further comprise a base plate provided on the top surface or the projected part of the base plate on one side of the body frame, contributing to a compact arrangement of the machine.
The machine tool according to the present invention may further comprise one or more tables disposed above the body frame, wherein the spindle is arranged to have the axial center thereof along a vertical direction and mounted with a cutting tool, and the chuck means is designed to hold the workpiece upside down. As the workpiece is held downward, chips created while machining flow down into an enclosed space in the body frame by gravity and effectively collected.
The spindle may be built in a high-speed motor as a rotary driver thereof and rotatably supported by non-contact type bearings. The machining force can be reduced by the high speed operation of about 40,000 rpm, and each member constituting the machine is required to have less rigidity yet assuring precise machining. The entire structure of the machine can be thereby minimized in size, weight, and cost.
The non-contact type bearings may be magnetic radial bearings. The spindle can be thereby readily and accurately supported by the control of electromagnet.
The machine tool may further comprise a means of correcting any errors in machining the workpiece by adjusting supporting position of the spindle by the non-contact type bearings. Errors created by inertial force when the X-axis or Y-axis table changes its directions or caused by backlash are preliminarily measured, so that the correction is made by the non-contact type bearings and it is unnecessary to correct numerical control data for machining.
A chuck rotating means may be provided to cause the chuck means to rotate around the axial center thereof. Circular parts of the workpiece can be precisely machined by rotating the workpiece instead of controlling the movement of the X-axis or Y-axis table.
The body frame may be constructed to have a U-shaped cross-section. The spindle or the rotary driver can be easily accessed from an opened side of the body frame for assembly or maintenance.
The machine tool may be provided with a position sensor for detecting positions of the

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