Background Art In general, a machine tool such as a polishing machine is used to polish partial surfaces of a workpiece into mirror planes after formation of the workpiece through molding, cold forging or blank molding.

The polishing operation is aimed to further miniaturize the surface coarseness of the workpiece formed through milling or grinding to smoothen the surface of the workpiece as a mirror plane and maintain its surface finish.

While various instruments such as home electronics and OA equipments are being shortened recently in their lifetime according to increasing consumer desires and the demand to molds owing to shortened lifetime is also continuously increasing, polishing as a final step of a mold fabrication process largely depends on manual works.

As an approach to solve this problem, the inventor of the application has filed Korean Patent Application No. 2002-0015836 (Mar 23,2002). This document proposes a polishing machine which includes a tool head unit both movable and tiltable in X-, Y-and Z-axis directions and an automatic

static pressure-adjusting means provided in the tool head unit capable of supplying a uniform workpiece-contact pressure to a grinder. As another approach, the inventor also filed Korean Registered Utility Model No. 20-0308643 (Dec 20,2002). This document proposes a tool head unit structure of a polishing machine which further simplifies both a power transmission structure for rotating a grinder and an air circuit of an automatic static pressure-adjusting means to maximize the efficiency of the polishing machine.

Although the tool head unit can be moved and tilted in X-, Y-and Z-axis directions in operation of the machine and the automatic static pressure-maintaining means can supply a uniform contact pressure to the workpiece, however, the above applications have a common drawback that angles of both the workpiece and the tool are adjusted manually in order to polish the workpiece.

Hereinafter a conventional machine tool will be described with reference to an accompanying drawing.

FIG. 1 is a perspective view of a general machine tool.

As shown in FIG. 1, a typical machine tool 1 includes a table 50 for seating a workpiece (not shown) on the top, a controller 10 arranged in a lateral portion of the machine tool 1 for controlling the operation of the machine tool 1, a control unit 12 arranged in a front portion of the machine tool 1 for controlling the controller 10 and X-, Y-and Z-axis carriers 20,30 and 40 arranged on a top portion of the machine tool 1 in particular above the table 50 for carrying a tool 62 mounted on a tool drive unit 60 on X-, Y-and Z-axes.

Herein, the X-axis carrier 20 is supported to a pair of columns 22 and 24 which are arranged in the top portion of the machine tool 1. The Y-axis carrier 30 is coupled on the X-axis

carrier 20 in a fashion movable along and across the longitudinal direction of the X-axis carrier 20. The Z-axis carrier 40 arranged at one end of the X-axis carrier 20 is movable in a vertical direction. The tool drive unit 60 mounted with the tool 62 for machining the workpiece is arranged at one end of the Z-axis carrier 40.

Further, the tool drive unit 60 includes a rotating section (not shown) coupled with the end of the Z-axis carrier 40 and functioning to set the operation angle of the tool drive unit 60, a static pressure-maintaining section (not shown) coupled with the rotating section for maintaining the workpiece under a uniform pressure from the tool 62 and an actuating section (not shown) functioning to rotate the tool 62 mounted thereon.

Although the tool drive unit 60 is rotatably mounted on the end of the Z-axis carrier 40 in the prior art, it is inconvenient to operate the machine tool. Before operating the machine tool, an operator personally sets the operation angle of the tool drive unit 60 to machine a portion of the workpiece corresponding to the operation angle. Then, the operator stops operation of the machine to adjust the angle of the tool drive unit 60 corresponding to a next portion of the workpiece to be machined before machining the next portion of the workpiece.

Further, because angles of the tool drive unit 60 are set separately corresponding to portions of the workpiece to be machined, it is not easy to machine regions adjacent to the machined portions and some of the adjacent regions are not or insufficiently machined.

Brief Description of the Drawings FIG. 1 is a perspective view of a general machine tool.

FIG. 2 is a side elevation view illustrating the structure

of a tool drive unit according to the invention.

FIG. 3 is front elevation view illustrating the structure of a tool drive unit according to the invention.

Disclosure of the Invention The present invention has been made to solve the foregoing problems and it is therefore an object of the present invention to provide a tool drive unit of a machine tool which can uniformly maintain a pressure applied to a tool while the tool mounted on the tool drive unit is being driven to machine the surface of a workpiece as well as adjust the rotating angle of the tool drive unit for rotating the tool corresponding to a set value so that a working process can be carried out without additionally setting the operation angle of the tool drive unit for respective regions of the workpiece to be machined, thereby simplifying the working process while preventing any un-machined regions in the workpiece.

According to an aspect of the invention for realizing the above objects, there is provided a tool drive unit provided at an end of a Z-axis carrier of a machine tool for machining a workpiece, in which the machine tool has X-and Y-axis carriers movable along X-and Y-axes together with the Z-axis carrier movable along a Z-axis, the tool drive unit comprising : a spindle section mounted with a tool for machining the workpiece and functioning to rotate the tool; a static pressure-maintaining section for moving the spindle section in response to a pressure applied to the tool fixed to the spindle section to uniformly maintain the pressure applied to the tool ; and a rotating section coupled to the end of the Z-axis carrier to rotate both the static pressure-maintaining section and the spindle section so that the tool is placed corresponding to regions of the workpiece

to be machined.

Preferably, the rotating section may include a servo motor inserted into and coupled with the Z-axis carrier and a decelerator for decelerating the rotating rate of the servo motor while increasing its rotating power.

And preferably, the static pressure-maintaining section may include a base coupled with the rotating section, an LM guide mounted to the base for guiding the passage of the spindle section and a double-acting air cylinder arranged above the base for shifting the spindle section along the LM guide.

And preferably, the spindle section may include a stationary bracket coupled to the static pressure-maintaining section, a spindle motor arranged on the stationary bracket for supplying rotating power to the tool and a spindle head connected to a rotating shaft of the spindle motor via a coupling, the spindle motor having a holder for being rotated with the tool mounted thereon.

Best Mode for Carrying Out the Invention Hereinafter a tool drive unit of a machine tool of the invention will be described in detail with reference to accompanying drawings.

In discussion of the present invention, several terms in the specification will be defined regarding their functions in the present invention. However, it is not to be understood that those terms limit technical features of the invention because they can be construed differently according to intentions of those skilled in the art or practices in this field.

FIG. 2 is a side elevation view illustrating the structure of a tool drive unit according to the invention, and FIG. 3 is front elevation view illustrating the structure of a tool drive

unit according to the invention.

First, the invention relates to rotation of the tool drive unit of a machine tool, in which those technical features substantially identical with those of previously filed technologies or known technologies will not be described hereinafter unless it makes the description of the invention vague.

As shown in FIGS. 2 and 3, a tool drive unit 60a of a machine tool according to the invention is provided at one end of a Z-axis carrier 40 of a machine tool 1 to machine the surface of a workpiece (not shown) fixed to a table 50. The tool drive unit 60a includes a spindle section 90 for fixing a tool 62 for machining the workpiece, a static pressure-maintaining section 80 for maintaining the workpiece under a uniform pressure from the tool 62 of the spindle section 90 and a rotating section 70 with one end fixed to the end of the Z-axis carrier 40 and the other end fixed to the tool drive unit 60a for rotating the tool drive unit 60a.

In the rotating section 70 having one end coupled to the end of the Z-axis carrier 40, a servo motor 72 is inserted into the Z-axis carrier 40 to supply power for rotating the tool drive unit 60a of the spindle section 90 and the static pressure-maintaining section 80, and a decelerator 74 is coupled to a rotating shaft of the servo motor 72 for decelerating the rotation rate of the servo motor 72 while increasing its torque to transmit the rotating power of the servo motor 72 in a direction perpendicular to the rotating shaft of the servo motor 72.

The static pressure-maintaining section 80 is provided with a n-shaped base 84 coupled to the rotating shaft of the decelerator 74. Over the base 84, there is provided a

double-acting air cylinder 82 for vertically shifting the spindle section 90 so that the tool 62 can apply a predetermined pressure to the workpiece in response to a pressure applied to the spindle section 90. An LM guide 86 is provided in a portion of the base 84 so that the spindle section 90 can be moved by the double-acting air cylinder 82.

As not shown in the drawings, the static pressure-maintaining section 80 includes a pressure sensor (not shown) for measuring the pressure within the double-acting air cylinder 82 in cooperation with the spindle section 90, a regulator (not shown) for feeding air under a predetermined pressure to the double-acting air cylinder 82 and a precision control regulator (not shown) for precisely controlling the pressurized air fed from the regulator.

The spindle section 90 is provided with a stationary bracket 91 fixed to a transport side of the LM guide 86. A spindle motor 92 for rotating the tool 62 is provided above the stationary bracket 91. A rotating shaft of the spindle motor 92 is connected to a spindle head 96 via a coupling 94, and a holder 97 for fixing the tool 62 for machining the workpiece is provided at one end of the spindle head 96.

The tool drive unit of a machine tool according to the invention can uniformly adjust the pressure of the tool 62 applied to the workpiece according to the pressure set to the controller 10 by manipulating the control unit 12. Also, the tool drive unit can control the servo motor 72 of the rotating section 70 according to a value set in the controller 10 to rotate the tool drive unit 60a instead of additionally rotating the tool drive unit 60a. As a result, the working process of the machine tool can be simplified.

Although the preferred embodiment of the present

invention has been disclosed in detail as set forth above, those skilled in the art will appreciate that various modifications, additions and substitutions can be made within the scope and spirit of the invention as disclosed in the accompanying claims.

Therefore, further changes to the embodiment of the invention will not depart from the scope of the invention.

Industrial Applicability As set forth above, the tool drive unit of a machine tool according to the invention can uniformly maintain the pressure applied to the tool while the tool mounted on the tool drive unit is being driven to machine the surface of a workpiece.

Further, the rotating angle of the tool drive unit for rotating the tool can be adjusted to a set value so that a working process can be carried out without additionally setting the operation angle of the tool drive unit for respective regions of the workpiece to be machined. As a result, the invention can simplify the working process while preventing any un-machined regions in the workpiece.