Title of Invention

A MACHINE TOOL FOR ADVANCING A TOOL

Abstract

ABSTRACT 632/MAS/96 The present invention relates to a machine tool for advancing a tool such as rotary cutting tool along at least three mutually transverse dais consists of a spindle for mounting the tool a frame for supporting the spindle, a vertical gantry connected to at least two frame members for slidable movement in, a saddle mounted on the gantry, a ram carried by the saddle, a first linear drive having at least one linear motor for moving the gantry a second linear drive having at least one linear motor for moving the saddle along the gantry and saddle and a third linear drive having at least one linear motor for moving the ram and spindle along tlie third axis.

Full Text

The present invention relates to machine tools driven by linear motors along a plurality of axes and, more particularly, to a machine tool supported in a frame and driven by linear motors for high speed movement of the tool along at least three (3) mutually transverse axes Background of the Invention The present invention is directed to a machine tool having three (3) axes of movement and a working element moved along these axes by linear motors. The working element is capable of moving in a work zone. The present invention is thus applicable to various machines of this type; but for sake of brevity, the invention will be described in connection to a cutting tool machine having a cutting tool. However, the invention is not to be limited as to only covering cutting tool machines. United States Patent 5,368,425 discloses a linear motor-driven, cutting tool machine, and as present in numerous conventional screw-driven cutting tool machines a vertical column is mounted on a slide to travel in a horizontal X-axis direction and a vertically-movable slide is slidable vertically along the column in the Y-axis direction. A spindle carrying a tool is mounted on the slide for sliding horizontally in a Z-axis direction at a location spaced above the X-axis and normal to both the X and Y axes, respectively. Each of these three axes is typically stacked one on another, resulting in the axis driving forces being offset from the spindle and cutting tool, e.g., a milling cutter, for cutting a piece of steel. This asymmetrical arrangement of the driving forces relative to the axis of the cutting tool results in deflections in the machine structure and inaccuracies in the cutting process. This is true whether the driving force is supplied by a servomotor and ball screw/nut combination or by way of linear motor drives, as in the '425 Patent. This asymmetrical arrangement results in: 1) structural deflections due to working forces or acceleration/deceleration forces, 2) in bending as experienced in the cantilevered load of the spindle slide and spindle, and 3) in less stiffness per unit of mass due to the large mass needed to achieve the necessary stiffness. United States Patent 5,368,425 discloses a cutting tool machine having its large upright column mounted for traversing in the X-direction along a large stationary, heavy base that supports the column. The driving force from the linear motors is applied only to the lower end of the column to propel it in the X-axis direction. The large stationary base provides the horizontal alignment of the respective X and Z-axis movements of the column and of the spindle slide and its tool spindle that travel vertically in the Y-axis direction along a vertical wall of the massive column. The spindle travels in a direction of the Z-axis and is carried on a cantilevered or overhung slide that travels along the vertical column wall. Thus, the machine alignment is predicated on the foundation remaining stable. If a corner of the foundation sinks or becomes misaligned, then the horizontal axes will be misaligned. Because of the space needed to support the column at its bottom end, and the size of the tool-carrying slide, the tool spindle and tool could not reach the bottom of a workpiece easily. To overcome this, the foundation required a pit to be dug to lower the spindle to reach a bottom portion of the workpiece to machine the same. Such foundation pits are expensive, as are the large and often custom-sized, foundations for the kind of machine tools illustrated in this patent. Further, adding to the size of the foundation and to the size of the machine, per se, are the covers for the ways which are bellow- shaped and which are located at the ends of the ways. These bellow-shaped covers are located at positions on the machine base at the ends of the column travel in the X-axis; and hence, add to the overall length footprint of the machine. The covers keep chips and metallic dust from the ways and from being magnetically attracted to the linear motor parts. To move the massive column in the X-axis in the machine disclosed in the aforesaid patent, there is a pair of linear motors with one-half of each linear motor being mounted on the stationary base and the other half being mounted on the X-axis carrier supporting the column. The one-half of each of these two motors on the column adds to its overall weight, and thereby requires more linear motor thrust for the column to be moved along the X-axis. In addition to this linear motor weight on the column, there is an attractive, magnetic force, i.e., a normal magnetic force component which, in this instance, is a downward magnetic force between the coils and magnets of these linear motors, e.g., 24,000 lbs. of downward force that causes an increase in friction that must be overcome to traverse the column-supporting carrier along the X-axis. If the column weighs 8,000 pounds, and a normal 24,000 lb. attractive, magnetic force is present, the latter adds significantly to the mass that needs to be overcome. The linear motors apply the thrust only to the bottom of the column. To resist deflection of the unsupported upper end of the column as the lower end accelerates, the column is formed with heavy structural members that add to the weight of the column. Hence, the linear motor force required to move the column at accelerations of one G or more is increased significantly from the force needed if the column were not driven only at its lower end, and if large no such attractive, magnetic, normal force was present. Generally speaking, at the present time, it takes about one pound of thrust from the linear motor to move about one pound of mass. The larger the thrust needed, the larger linear motor weight that must be added to the column. Stated differently, the effect is cumulative because the more force needed to be obtained from the linear motors, the heavier the linear motor is in weight, e.g., the coils on the column carrier and this weight increase adds more weight requiring more thrust. In the linear motor cutting machine, disclosed in the aforesaid patent, the massive column is constructed of lightweight materials and has a skeletized structure in order to reduce its weight; and thereby, reduces the linear thrust force needed to accelerate it rapidly and to reduce deflection of the upper end of the column relative to the lower end of the column, which is being propelled by the linear motors. The column is formed with an aluminum braced, trapezoidal-shaped frame and with an aluminum skin covering the skeleton frame and with a reinforcing ladder of frame elements thereon to add rigidity and stiffness to the column. Because one is machining metals, a high degree of stiffness is needed for the column which carries the cutting tool slide and spindle in order to obtain the precision needed for the cut workpiece surfaces. In the aforesaid patent, the spindle-carrying slide was overhung or cantilevered on the column to move vertically along a Y vertical axis. The column carried on three sides thereof, permanent magnets for three (3) linear motors used to accelerate and decelerate the spindle slide. The stator coils of the motors were on three sides of this slide and located closely adjacent to and traveling along the three, associated vertical rows of permanent magnets on the column. Three linear motors were needed to accelerate and decelerate the spindle slide vertically, and these three linear motors generated normal attractive, magnetic forces directed inwardly along three sides of the column. The spindle-carrying slide was cantilevered on the column and the weight of the ram and spindle as well as the applying of the thrust only to the side of the slide adjacent the column could cause bending and deflection and sufficient structural members had to be used in the slide to offset any such bending or deflection. The three linear motors not only applied their thrust to only one side of the slide adjacent the column wall, but these linear motors also increased the friction between the spindle slide and the column that had to be overcome. Thus, if 18,000 lbs. of normal attractive, magnetic force existed between the column and the ram, this increased frictional force generated thereby had to be overcome to accelerate the spindle slide in the Y-axis direction and the slide structure had to be reinforced with structural members to resist bending and deflection of the remote end of the cantilevered slide as the motor thrust was applied to the near side of the slide at the column wall. The size and weight of this spindle slide were quite large in order to support the three rows of coils for the three Y-axis motors and to provide a stiff, cantilever support for the slide and spindle thereon to provide the cutting tool with the necessary stiffness against the workpiece. The spindle slide, illustrated in this patent, had a ribbed structure that was quite large in cross-section and carried an outer aluminum skin about the ribs. The large size of the spindle slide meant that the tool could not be brought down as low as desired relative to the workpiece because the spindle slide's height below the spindle limited the amount of downward travel of the spindle. Summary of the Invention In accordance with the present invention, a machine tool for advancing a rotary cutting tool along at least three (3) mutually transverse axes and driven by linear motors is provided, which overcomes the aforementioned problems of the prior art. In accordance with the present invention, the machine tool has linear motor drives distributed symmetrically relative to at least two axes to minimize deflections that cause cutting process deviations and inaccuracies. By having the machine elements driven symmetrically on opposite sides of the cutting spindle axis, there has been achieved a reduction in structural deflection, a lighter weight machine having a high stiffness per mass unit, a balancing or cancelling of normal magnetic forces that would increase friction, and an elimination of bending from a cantilevered load. In accordance with the present invention, the structural member or gantry driven in the X-axis direction is driven by linear motors at both the upper and lower ends thereof, rather than only at the bottom thereof; and the spindle-carrying slide is driven in the Y-axis direction by linear motors on opposite sides of the slide rather than only at one side of the slide. By balancing these driving forces on opposite sides of the movable X and Y-axis structures, rather than applying these driving forces at one side of the movable X and Y-axis structures, as in the machine of the aforesaid patent, the structures may be of lighter weight construction by eliminating structural members added to resist deflection or bending of the side remote from the force application side. Hence, the present invention provides lighter weight X and Y-axis structures relative to the massive weights of the vertical column and of the cantilevered spindle slide, and reduces the friction by cancelling the effect of attractive forces. The X and Y linear motors are symmetrically arranged on opposite sides of the tool-carrying spindle to drive the X and Y moving machine elements with forces applied symmetrically on opposite sides of the tool-carrying spindle; and this results in a minimum of structural deflection from the motor attractive forces, acceleration forces and the cutting forces. This symmetrical machine structure eliminates Tiuch of the bending experienced in the asymmetrical Tiachine structure from the cantilevered loads. Preferably, the linear motors are distributed optimally Lhroughout the machine structure to balance loads and forces about the tool-carrying spindle, thereby Tiinimizing the cutting deviations and inaccuracies. By eliminating the need for many structural members used in the asymmetrical machines to resist bending and/or deflection, the symmetrical machine can be lighter in A^eight with a higher stiffness per unit of mass. Thus, it is possible to achieve higher accelerations and decelerations with less linear motors. In accordance with the present invention, the linear motor machine includes a slide-carrying gantry in ^hich the linear motors for moving the gantry are mounted DH opposite sides thereof to provide equal propelling forces on two sides of the gantry and to provide an attractive magnetic force balancing principle in which a reduced net downward force exists between the gantry and the underlying frame support member. Preferably, this is achieved by having the linear motor drive on one side of the gantry, e.g., the bottom side, pushing on the bottom side of the gantry in the X-direction and attracting downwardly and by having the linear motor drive on the Dther top side, pushing on the top side of the gantry in the X-direction and attracting oppositely, e.g., apwardly. This is in contrast to the aforementioned Tiachine in which the linear motors for shifting column all push on the lower end of the column and all attract in the same downward direction. Likewise, it is preferred that the tool-carrying slide or saddle (hereinafter called a "saddle") be driven by linear Tiotors mounted on opposite sides thereof, e.g., left and right vertical sides, rather than applying the motor driving force to only one side of the slide. Placing the linear motors on opposite sides of the saddle provides propelling forces in the Y-direction on opposite sides of the saddle and provides oppositely-directed, attractive motor forces in opposition with one another. This achieves a force-balancing principle that results in a reduced net magnetic, normal force, preferably about a zero (0) net magnetic, normal force in either the left or right direction. This is in contrast to the aforesaid patent wherein the illustrated machine has three (3) linear motors for moving the slide, all providing propelling forces on one side of the slide and all exerting inwardly-directed, magnetic normal forces against three sides of a vertical column. In the gantry, linear motor machine of the present invention, the tool-carrying spindle is supported on an underneath saddle that spans a pair of adjacent, vertical gantry frame members, rather than being cantilevered on one vertical wall of the column, as disclosed in the aforesaid patent. The underneath support of the saddle allows a large reduction in the size thereof relative to the size of the cantilevered ram. The reduction in size, and also of weight, results in less weight that needs to be moved in the Y-axis direction and less weight to be moved in the X-axis direction. The reduction in weight and size results in lower cost and less motor thrust needed. Indeed, the number of linear motors can be reduced from six or eight, in the aforesaid '425 Patent, to five, illustrated herein. In accordance with another aspect of the invention, the machine frame is box-like in configuration with upper and lower parallel, horizontal frame members and a pair of spaced vertical frame members joined to ends of the upper and lower frame members. There is no large foundation necessary for alignment of the machine; rather the frame members themselves provide the alignment. In theory, the machine tool can be rotated through 90°, 180° or 270° and still perform equally as well, which is not true of the column stack machine disclosed in the aforesaid patent. In the illustrated and preferred embodiment, the machine frame is a stationary box-type structure which encompasses the sides, rears, top and bottom of the movable, linear motor-driven, gantry traveling in the X-direction, the linear motor-driven saddle movable along the gantry in the Y-direction, and the linear motor-driven spindle movable along the saddle in the Z-direction. In this preferred embodiment, the gantry is supported on and is driven by top and bottom linear motor drives spaced on opposite sides of the spindle. Preferably, the upper and lower linear motors are substantially identical. Thus, the forces applied to the top and bottom of the gantry are substantially equal; and the opposed, normal magnetic forces between stator coils and magnets are self-cancelling. Thus, there is symmetry about the X-axis. In this illustrated and preferred embodiment of the invention, the spindle-carrying saddle is mounted to travel vertically in a slot at the vertical centerline of the gantry. The saddle is driven by left and right-hand, linear motors mounted on the gantry at opposite vertical sides of the slot. The linear motors are identical and are positioned so that the forces applied to the opposite sides of the saddle are substantially equal and so that the opposed right and left-hand, normal magnetic forces are self-cancelling. Thus, the Y-axis has symmetry as well as along the X-axis. The spindle and ram are mounted on the saddle to travel in the Z-direction. If desired, a linear motor may be mounted both above and below the same to drive the ram and spindle in the Z-direction and to provide symmetry. It is preferred, however, that a single linear motor be used either above or below the ram and extending in the Z-direction to reduce the weight of the ram and to provide an attractive "preload" on the ways of the ram and saddle for greater stability of the spindle. Accordmgly, the present invention provides a machine tool for advancing a tool along a plurality of mutually transverse axes for cutting a workpiece, the machine tool comprising: a rotary spindle having a cutting tool mounted thereon; a frame to support the spindle and cutting tool while cutting and being advanced along the transverse axes; a vertical gantry mounted for slidable movement in a first axis relative to the frame; a saddle mounted within the gantry and carried therewith and mounted for slidable movement along a second axis perpendicular to the first axis and along and witli the gantry; a ram carried by the saddle and mounted for slidable movement along, a third axis perpendicular to the second axis and carrying the spindle and rotary cutting tool for movement along the third axis; a first linear drive having first and second linear motors mounted between the gantry and frame and extending in the direction of tlie first axis for moving the gantry relative to the frame along the first axis; a second linear drive having first and second linear motors mounted on opposite sides within the gantry each extending in the direction of the second axis for moving the saddle along and within tlie gantry and along the second axis with magnetic force attractions being in opposite directions to provide symmetry; and a third linear drive having one or more linear motors mounted between the saddle and ram and extending in the direction of the third axis for moving tlie ram and spindle along the third axis. accompanying Brief Description of the/Prawinga FIG. 1 is a perspe,ctive view of a machine tool ■ movable in three axes and illustrating a box frame for supporting the three axis machine tool according to the invention; FIG. 2 is a front elevational view of the -nachine tool of FIG. 1 having a portion of the front face of the box frame removed to illustrate the vertical gantry, the saddle, and the ram and spindle arrangement; FIG. 3 is a cross-sectional view taken along Line 3-3 of FIG. 2 illustrating the vertical gantry, the saddle, and the ram and spindle and showing movement in Phantom of the ram along the Y-axis; FIG. 4 is an enlarged, exploded, perspective view of the ram and spindle assembly including permanent magnets of a linear motor associated with the ram and a wiper element; FIG. 5 is an enlarged, exploded perspective view of an alternatively shaped ram; FIG. 6 is an enlarged perspective view of a "doghouse" and bellow assembly for the ram of FIG. 5; F'IG. 7 is a front elevational view of the ram of FIG. 5; . FIG. 8 is a front elevational view of an alternative saddle and ram, similar to the ram of FIG. 4, with the ram being driven by linear motors at the top and bottom of the ram; FIG. 9 is a sectional end view of a prior art cantilevered ram and linear motors associated therewith; FIG. 10 is an enlarged, exploded perspective view of the vertical gantry; FIG. 11 is an enlarged, exploded perspective view of the saddle and coil stator sections of linear motors associated therewith and illustrates the detachable bottom plate and stator coils subassembly; FIG. 12 is a partially exploded perspective view of the box frame for housing the vertical gantry, the saddle, and the ram and spindle assembly; FIG. 13 is a sectional, side elevation view similar to FIG. 3, illustrating an alternative embodiment location for the gantry top guides and linear motor; Detailed Description of the Preferred Embodiments As shown in the drawings for purposes of illustration, the machine 10 has a frame 12 that supports a gantry 3 8 movable in a horizontal X-axis direction and slidable along an upper supporting, frame member 20 and a lower supporting, frame member 22. The gantry 38 carries a tool-carrying slide or saddle 56 that travels vertically in the Y-axis direction. The saddle 56 carries a reciprocating ram 68 and tool spindle 78 which has a tool 11 thereon for cutting a workpiece 3 0 mounted on a workpiece support 34. The gantry 38, saddle 56 and ram 68 are driven by linear motors, generally designated 108, and each having permanent magnets 110 and coil stator sections 112. In accordance with the present invention, upper and lower driving forces are applied to the upper and lower ends 3 8a and 3 8b of the gantry 3 8 by an upper linear motor 108b secured to the upper, horizontal frame member 20 and a lower linear motor 108a secured to the lower, horizontal frame member 22. As best seen in FIG. 2, the saddle 56 and the tool-carrying spindle 78 are both mounted between the upper and lower linear motors, 108b and 108a, respectively, so that there is symmetry about the spindle 78. This is in contrast to the asymmetrical machine disclosed in the aforesaid '425 Patent where the linear motors are all mounted at the bottom of the column and all push on the lower end of the column. In the machine 10, shown in FIGS. 2 and 3, WE CLAIM: 1. A machine tool for advancing a fool along a plurality of mutually transverse axes for cutting a workpiece the machine tool comprising: a rotary spindle having a cutting tool mounted thereon; a frame to support the spindle and cutting tool while cutting and being advanced along the transverse axes; a vertical gantry mounted for slidable movement in a first axis relative to the frame; a saddle mounted within the gantry and carried therewith and mounted for slidable movement along a second axis perpendicular to the first axis and along and with the gantry; a ram carried by the saddle and mounted for slidable movement along, a third axis perpendicular to the second axis and carrying the spindle and rotary cutting tool for movement along the third axis; a first linear drive having first and second linear motors mounted between the gantry and frame and extending in the direction of the first axis for moving the gantry relative to the frame along the first axis; a second linear drive having first and second linear motors mounted on opposite sides within the gantry each extending in the direction of the second axis for moving the saddle along and within the gantry and along the second axis with magnetic force attractions being in opposite directions to provide symmetry a third linear drive having one or more linear motors mounted between the saddle and ram and extending in the direction of the third axis for moving the ram and spindle along the third axis. 2. The machine tool as claimed in claim 1, wherein the frame comprises top and bottom frame members that are vertically spaced at a first predetermined distance and the frame comprises side frame members that are parallel and laterally spaced at a second predetermined distance with the first predetermined distance being approximately equal to or less than the second predetermined distance. 3. The machine tool as claimed in claim 1, wherein the frame, gantry, saddle and ram are formed from steel. 4. The machine tool as claimed in claim 1, wherein the frame members define an internal space with the gantry and saddle mounted relative to the frame in the internal space and the frame has means for substantially sealing and pressurizing the internal space to allow the ram and spindle to extend beyond the internal space while limiting workpiece chips generated and coolant used at the tool and workpiece interface from entering the internal space during a machining operation. 5. The machine tool as claimed in claim 4, wherein the sealing and pressurizing means comprises baffles for substantially blocking the central opening while allowing the ram to extend therethrough and a positive pressure means to supply air to pressurize the internal space. 6. The machine tool as claimed in claim 1, wherein the gantry has top, bottom and side walls and the saddle has spaced side walls and a bottom web wall extending therebetween to form a cradle for supporting the ram. 7. The machine tool as claimed in claim 6, wherein the gantry side walls Java first predetermined spacing and the saddle side walls have a second predetermined spacing slightly less than the first predetermined spacing to closely fit between the gantry side walls during sliding movement of the saddle in the second axis. 8. The machine tool as claimed in claim 1, wherein the linear motors each have a row of permanent magnets cooperating with a coil section and the first linear drive, first and second motors comprise symmetric linear motors having magnetic force attractions in opposite directions to offset their respective forces. 9. The machine tool as claimed in claim 6, wherein the second linear drive symmetric linear motors are each positioned between the gantry side walls and corresponding saddle side walls, respectively, for having magnetic force attractions in opposing directions to offset one against the other. 10. The machine tool as claimed in claim 6, wherein the ram has a bottom support plate with the third linear drive comprising a linear motor positioned between the ram bottom plate and saddle bottom web wall for shading movement of ram in the third axis. 11. The machine tool as claimed in claim 6, having bearing means to guide the sliding movement of the gantry, saddle and ram caused by their respective linear motors. 12. The machine tool as claimed in claim 11, wherein the bearing means has cooperating anti-friction slide rails and rail receiving trucks with the slide rails and trucks positioned between a pair of gantry walls and a pair of frame members, respectively. 13. The machine tool as claimed in claim 12, wherein the ram has a box-shaped body defining a spindle receiving bore and having slide rails mounted thereon, and means to limit the travel of workpiece chips generated and coolant used at the tool and workpiece interface during a machining operation from entering into the machine tool. 14. The machine tool as claimed in claim 1, wherein said frame is a box like frame having four frame members defining a central opening the gantry being located within the opening of said frame. 15. The machine tool as claimed in claim 1, wherein the frame, vertical gantry, saddle and ram are formed from steel and have a predetermined natural structural frequency and the linear drive means has a motor drive circuit having a preselected operating frequency range with the operating frequency being preselected such that the predetermined natural structural frequency is greater than the preselected operating frequency range of the motor drive circuit. 16. The machine tool as claimed in claim 1, wherein a plurality of resilient vibration absorbing pads are attached to the frame to mount the frame to a support surface and isolate the frame and support surface from each other. 17. The machine tool as claimed in claim 16, wherein three vibration pads are attached to the frame for three-point mounting of the frame to a support surface. 18. The machine tool as claimed in claim 1, wherein a saddle is mounted on the gantry for slidable movement with said gantry and a ram is carried by the saddle and is slidably mounted through the central opening. 19. The machine tool as claimed claim 1, wherein the third linear drive comprises a single linear motor mounted beneath the ram and spindle. 20. The machine tool as claimed in claim 1, wherein the third linear drive comprises a pair of linear motors each having a stator coil section and permanent magnet section mounted on opposite sides of the ram for moving the ram and spindle with magnetic force attractions being in opposite directions to provide symmetry. 21. A machine tool for advancing a tool substantially as herein described with reference to the accompanying drawings.

Documents:

632-mas-1996 others.pdf

632-mas-1996 abstract.pdf

632-mas-1996 assignment.pdf

632-mas-1996 claims.pdf

632-mas-1996 correspondence others.pdf

632-mas-1996 correspondence po.pdf

632-mas-1996 description (complete).pdf

632-mas-1996 drawings.pdf

632-mas-1996 form-2.pdf

632-mas-1996 form-26.pdf

632-mas-1996 form-4.pdf

632-mas-1996 form-6.pdf

632-mas-1996 petition.pdf