COMPUTER CONTROLLED MACHINE TOOL WITH TEMPERATURE ACCOMMODATION AND ALIGNMENT

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 60/914,725, filed April 28, 2007, herein incorporated by reference in its entirety for all purposes.

FIELD OF THE INVENTION

[0002] This invention pertains to machine tools and, more particularly, to computer controlled machine tools, such as lathes.

BACKGROUND OF THE INVENTION

[0003] Figure 1 is a side view illustrating one example of a conventional computer numerically controlled (CNC) lathe 10. In this example, the CNC lathe 10 has one main spindle 20 with a chuck 22 for mounting and rotating a workpiece in a Z axis. The main spindle is attached to a spindle head stock 2OA. A chuck is a "hand" for grabbing and securing the workpiece while a cutting process is performed, usually for a lathe or a machining center (computer controlled milling machine). Lathe 10 also includes a turret 30 that revolves to process the necessary cutting tools or cutlery for cutting the workpiece mounted to chuck 22. A turret is typically a rotational base in which a metal cutting tool can be attached. Turret 30 is mounted on a processing base or turret head stock 32 that, in this example, is able to move along an X axis and a Z axis in order to engage the workpiece being held by chuck 22 and rotated by spindle 20 mounted in spindle head stock 2OA. Figure 2 is a simplified end view of lathe 10 illustrating a relationship between spindle 20, which is fixedly attached to the machine base by bolts, in this example, and turret 30, which can move in the x axis to engage the workpiece held by chuck 22. In this example, lathe 10 includes a tail stock 42 that prevents a run off from the revolving center concentric to the direction of the main spindle when cutting a long cylindrical workpiece accurately, which is mounted in the Z axis. The spindle 20, turret 30 and turret head stock 32, and tail stock 42 are mounted on a machine base 40.

[0004] The conventional CNC lathe 10 operates by cutting a workpiece using a cutting tool as the workpiece is rotated. Chuck 22 holds the workpiece while spindle 20 rotates. Turret 30 rotates to present a cutting tool to the workpiece and turret head stock 32, in this example, moves to bring the cutting tool into contact with the rotating workpiece under precise computer control.

[0005] As spindle 20 rotates, it typically generates heat, which is transmitted to the machine base 40. As heat builds up in machine base 40, the machine base distorts, e.g. expands, and degrades the precision of the process, which reduces the quality of the resulting workpieces. In particular, the accuracy of the relationship between the main spindle 20 and the turret 30 is effected by the distortion. This is particularly the case when the machine is used to repetitively produce multiple workpieces. Also, heat may be transmitted from a cutting tool through turret 30 into turret head stock 32, which may also effect the accuracy of the process. The material cutoff from the workpiece during processing typically falls on the machine base 40 and further transmits heat to the machine base 40. Further inaccuracy may be introduced due to wear on the cutting tool mounted in turret 30.

[0006] Figures 3 and 4 illustrate another example of a conventional lathe 100, wherein the turret head stock 132 may be fixedly attached to the machine base 140, while the spindle head stock 120A is movably attached to the machine base 140, such as through the use of an X axis slide. The turret head stock 132 in Figure 3 is bolted to the machine base. Figure 4 illustrates the heat transfer for the conventional lathe 100. In this example, as in the previous example, the main heat source 150 for the machine is typically from rotation of the main spindle 120, the second heat source 152 is from the turret 130, and the third heat source 154 is from the cutout material from the workpiece scattered inside the machine. All these heat sources spread heat to the machine base 140 causing distortion that degrades the precision of the machine and reduces the accuracy and quality of the finished workpieces.

[0007] Figures 5 and 6 illustrate a further problem with some conventional CNC lathes relating to the centering the main spindle 120 with an X axis movable slide 160 providing for X axis movement, which are not always centered with one another. Because of the nature of a linear guide 164 for a movable axis, such as a box slide 160, it is difficult to center with a spindle 120. Because the center of a box slide 160 is typically covered, it is

difficult to align the center of the box slide 160 with the center of the main spindle 120. Also, as the machine performs repetitive processing steps, the center typically gets shifted by the motion of the spindle stock, which also degrades the precision of the machine tool.

[0008] Figures 7 and 8 illustrate another example of a conventional lathe 200 having a spindle head stock 220A with X axis movement and a turret head stock 232 with Z axis movement. This example is typically subject to the same problems discussed above.

BRIEF SUMMARY OF THE INVENTION

[0009] An embodiment of a machine tool 300 includes a movable slide 360 that is connected to the machine base through a linear guide 364 that maintains the alignment of a component, such as a turret or spindle, connected to the movable slide 360 through a head stock 320A along a first axis of movement. The slide 360 carrying the head stock 320A is also mounted to the machine base 340 at another point by an expansion mounting means 368, such as a tongue and groove, that provides for expansion and contraction of the slide 360 perpendicular to the first axis of movement established by the linear guide 364. A ball screw 366 is also attached between the slide 360 and the machine base 340 in order to provide computer controlled movement of the slide 360 relative to the machine base 340 along the first axis of movement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a side view of an example of a conventional lathe 10 that includes a turret head stock 32 having X and Z axis computer controlled movement;

[0011] Figure 2 is an end view of the lathe 10 of Figure 1;

[0012] Figure 3 is a top view of another example of a conventional lathe 100 that includes a spindle head stock 120A having X and Z axis computer controlled movement;

[0013] Figure 4 is a side view of the lathe 100 of Figure 3;

[0014] Figure 5 is a first end view of a misaligned spindle head stock 120;

[0015] Figure 6 is a second end view of a misaligned spindle head stock 120;

[0016] Figure 7 is a top view of another example of a conventional lathe 200 that includes a spindle head stock 220A having X axis computer controlled movement and a turret head stock 232 having Z axis computer controlled movement;

[0017] Figure 8 is a side view of the lathe 200 of Figure 7;

[0018] Figure 9 is an end view of an embodiment of a lathe 300 that includes a spindle head stock 320A having Z axis computer controlled movement that maintains an alignment of a spindle and accommodates expansion of a movable slide 360 along an X axis; and

[0019] Figure 10 is an end view of an embodiment of a lathe 400 that includes a turret head stock 432 having a first axis of computer controlled movement that maintains an alignment of a turret 430 and accommodates expansion of a movable slide 460 perpendicular to the first axis.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention is directed toward maintaining the accuracy of a machine, such as a CNC lathe, even as the temperature of the machine changes.

[0021] In a conventional lathe 10, the spindle-head-stock 2OA is typically directly connected to the machine base 40 of the machine so that when the spindle 20 rotates and generates heat, the heat is conducted from the spindle 20 through the spindle-head-stock 2OA to the machine base 40, which results in degradations of the machines precision.

[0022] Similarly, in a conventional CNC lathe 10, the turret-head-stock 32 is typically mounted onto the machine base 40 via X and Z axis slide devices or plates. The heat generated from the cutoff from the workpiece and the cutting tool is conducted to the machine base 40 as well as the turret-head-stock 32, which moves along the X and Z axes in order to process each workpiece. As the machine heats up, the machine base 40 and/or the turret-head-stock 32 distort and degrade the precision of the machine as repetitive processing in performed.

[0023] In one aspect of the present invention 300, a spindle is installed on a spindle head stock 320A that is mounted on a movable slide 360 that accommodates expansion due

to heat, but maintains the alignment of an active processing unit, e.g. spindle 322, relative to the machine base 340. In the embodiment of Figure 9, spindle 322 is mounted on a slide 360 that provides a first axis of motion, which is Z axis motion in the example shown. The slide 360 is attached to the machine base 340 at a point in alignment with the spindle center by a linear guide 364 that maintains the alignment of the spindle on the machine base. In the example shown, an axis perpendicular to slide 360 intersects both the spindle center and line guide 364. Linear guide 364 is preferably aligned with an operation center of the active unit, e.g. a rotational axis of a spindle, so that the weight of the active unit bears primarily on linear guide 364, which may require that a heavy duty linear guide device be utilized, and linear guide 364 primarily maintains the alignment of the active unit relative to machine base 340.

[0024] The slide 360 has a tendency to expand as heat is generated during processing and conducted into the machine base. The slide 360 is also mounted to the machine base 340 at another point by an expansion mounting 368, such as a tongue and groove, that provides for expansion and contraction of the slide 360 along an axis perpendicular to the first axis of motion, which is X axis expansion in the example shown. The expansion mounting 368 is fixedly secured to the machine base 340, such as by a bolt 380, and permits movement of slide 360, which is Z axis motion in the example shown. While one expansion mounting 368 is shown engaging one end of slide 360, an additional expansion mounting may be provided at the other end of the slide 360. Alternatively, the expansion mounting 368 may be positioned on the other end of slide 360.

[0025] In the embodiment shown, a ball screw 366 is also attached between the slide 360 and the machine base 340 in order to provide computer controlled Z axis movement of the slide 360 relative to the machine base 340. In other embodiments, ball screw 366 may be replaced by other devices capable of actuating linear movement under computer control. The linear actuator device, e.g. ball screw 366, is preferably positioned adjacent to linear guide 364 to reduce the amount of heat expansion that may occur in the portion of slide 360 between the point at which linear guide 364 is attached to the slide and the point at which ball screw 366 is attached.

[0026] In another embodiment 400, a turret head stock 432, e.g. another type of active unit or processing device, is provided with computer controlled linear movement that

maintains alignment and accommodates distortion due to heat fluctuations. Similarly to the embodiment of Figure 9, the turret head stock 432 of Figure 10 is attached to a movable slide 460. The movable slide 460, in turn, is connected to the machine base 440 through a linear guide 464 that maintains the alignment of a turret 430 connected to the turret head stock 432 along a first axis of movement. In this example, linear guide 464 is attached to slide 460 along an axis perpendicular to slide 460 that also intersects the plain of the face of turret 430, such that the weight of the active unit, e.g. turret 230, bears primarily on linear guide 464 and linear guide 464 primarily maintains the alignment of the active unit relative to machine base 440. The linear guide 464 may also be attached to slide 460 such that the axis perpendicular to slide 460 also intersects an operational axis of the active unit, e.g. a rotational axis of the turret 430.

[0027] The slide 460 carrying the turret head stock 432 is also mounted to the machine base 440 at another point by an expansion mounting 468, such as a tongue and groove, that provides for expansion and contraction of the slide 460 along an axis perpendicular to the first axis of movement established by the linear guide 464. An additional expansion mounting may be provided on a side of slide 460 opposite to the side where expansion mounting 468 engages slide 460. Alternatively, the expansion mounting 468 may be positioned on the other end of slide 460.

[0028] A ball screw 466 is also attached as a linear actuator between the slide 460 and the machine base 440 in order to provide computer controlled movement of the slide 460 relative to the machine base 440 along the first axis of movement. Preferably, ball screw 466 is mounted adjacent to linear guide 464 to reduce the distance, and, therefore, the amount of possible heat expansion, between the places where linear guide 464 and ball screw 466 are attached to slide 460.

[0029] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0030] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be

construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0031] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.