GB2115733A - Threading head for a numerically controlled multiple spindlehead indexing machine tool - Google Patents

Abstract

A threading head for use on a numerically controlled multiple spindlehead machine tool includes a frame 12 having a hollow bore spindle 16 journaled therein so that the spindle extends therebeyond. The spindle is helically advanced out from and is retracted into the frame by the combination of a ball nut and a ball screw disposed between the spindle and the frame. The helical movement of the spindle is precisely controlled by a first servo-controlled motor 35 which rotatably drives the ball screw in response to numerical control commands. A cross block cutting tool 60 is slidably mounted on the face of the spindle distal from the frame and is displaced radially across the spindle face by a screw 44 journaled in the spindle perpendicular to the axis of the spindle so as to threadedly engage the cross block cutting tool, the screw being driven by a second servo controlled driver motor 54. Thus, by controlling the excitation of each of the two servo controlled drive motors, the length of the threads chased, the speed at which such threads are chased and the depth of threads cut can be controlled accordingly. <IMAGE>

Description

SPECIFICATION Threading head for a numerically controlled multiple spindlehead indexing machine tool In the production of machined parts by automatic machine tools, it is often desirable to achieve relatively high volume part production while retaining the flexibility to machine parts of different geometries. While automatic transfer line machine tools achieve high volume part production, the flexibility afforded by such automatic transfer line machine tools to accommodate different part geometries is often quite limited. On the other hand, a single numerically controlled machine tool, such as a horizontal or vertical spindle machining center, while offering great flexibility to machine parts of various different geometries, is usually capable of only low, or at most, mid-volume part production.

In an effort to achieve both high volume part production as well as the flexibility to machine parts of different geometries, multiple spindlehead machine tools have been developed. A typical multiple spindlehead machine tool, such as the Kearney & Trecker Model Milwaukee-FMS Head Indexer Module, comprises a power station which is operative to drive each of a set of multiple spindleheads when each is selectively indexed from a storage position to an operating position adjacent to the power station by a spindle-head indexing mechanism. Each spindlehead has one or more outwardly-extending spindles which may carry a drilling, reaming, milling or tapping tool therein.The spindles on each spindlehead are rotatably driven by an input shaft extending rearwardly from the spindlehead so as to engage the power station once the spindlehead is indexed to the operating position. After the selected spindlehead has been indexed to the operating position so that its input shank can be driven by the power station to enable the tool-carrying spindles to be driven thereby, then, a machining operation is commenced on an unfinished part by reciprocating the worktable in which the part is mounted, to and from the spindlehead along a path parallel to the axis of spindlehead rotation.

After a particular machining operation has been completed on the part by the tools carried in the spindles of the spindlehead then indexed to the operating station, then a different machining operation can be accomplished by indexing the appropriate spindlehead to the power station.

Upon completion of all the desired machining operations on the part then on the worktable, the just-machined part is shuttled off the worktable and a new part is shuttled thereon so that it may be machined in the manner set forth from above.

Although present day multiple spindlehead machine tools, such as the machine tool described above, are well suited for rapidly performing, drilling, milling reaming, and even tapping operations on a workpiece, heretofore, it has not been practical to employ a multiple spindlehead indexing machine tool to chase exterior or interior threads on a workpiece because of the inability to accurately coordinate the joint translational and rotational motion of the spindles of present day multiple spindle toolhead to perform a thread chasing operation.While it is true that thread chasing can be performed with a multiple spindlehead indexing machine tool by precisely controlling the rate of spindlehead rotation in unison with the rate of workpiece table movement, the threads chased in this manner usually do not have a constant pitch which may lead to cross threading when the threads chased in this fashion are mated with a complementary threaded element. In contrast, the present invention concerns a threading head specially adapted for use on a numerically controlled multiple spindlehead indexing machine tool for accurately chasing both interior and exterior threads on a workpiece.

It is an object of the present invention to provide a threading head for use on a numerically controlled, machine tool for accurately chasing exterior and interior threads on a machine part.

It is yet another object of the present invention to provide a threading head for use on a numerically controlled machine tool for accurately chasing threads on a machine part, the length and depth of such threads being controlled responsive to numerical control commands.

It is yet a further object of the present invention to provide a threading head for use on a numerically controlled machine tool for chasing interior or exterior threads in a machine part, the thread length, depth and pitch being controllable in response to numerical control commands.

Briefly, in accordance with the preferred embodiment of the invention, a threading head for use on a numerically controlled machine tool comprises a frame into which a tubular spindle is journaled for rotation about an axis and for movement along the axis out from and into the frame. The spindle is axially advanced out from and is retracted into the frame as it rotates by the combination of a ball nut and a ball screw secured between the frame and the spindle, the ball screw being rotatably threaded through the ball nut responsive to numerical control commands to impart a spiral orbit to a cross block cutting tool slidably carried at the end of the spindle distal from the frame.Means, including a threaded screw journaled into the end of the spindle for rotation about an axis perpendicular to the axis of spindle rotation, a servo controlled drive motor for rotatably driving the screw and a threaded block secured to the rearward end of the cross block cutting tool so as to be in threaded engagement with the screw, are provided for precisely controlling the orbit of the cross block cutting tool during spindle rotation.

In the presently preferred embodiment, the spindle comprises a pair of concentric sleeves, the outer sleeve being keyed to the frame so as to be axially movable out from and into the frame, while the inner sleeve is rotatably journaled within the outer sleeve. The ball nut is secured to the outer sleeve so as to be in threaded engagement with the ball screw which is rotatably journaled in the frame parallel to the inner and outer spindle sleeves. Both the inner spindle sleeve and the ball screw are jointly driven from a single servo drive motor through a gear train so that the inner and outer sleeves are extended and retracted as the inner sleeve rotates, thus imparting a spiral motion to the cross block cutting tool.The gear train includes shiftable members which permit the ratio of inner sleeve rotation to ball screw rotation to be varied to thus vary the lead of the threads being chased by the cross block cutting tool.

The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:: Fig. 1 is a longitudinal cross section of a preferred embodiment of a threading head for a numerically controlled multiple spindlehead indexing machine tool in accordance with the present invention; Fig. 2 is a cross sectional view of the threading head of Fig. 1 taken along lines 2-2 thereof; Fig. 3 is an end view of the threading head of Fig. 1 illustrating the mounting of the cross block cutting tool carried thereby; Fig. 4 is a cross sectional view taken along lines 4-4 of Fig. 3; Fig. 5 is a longitudinal cross section of an alternate preferred embodiment of a threading head constructed of the teachings of the present invention; Fig. 6 is a cross sectional view taken along lines 6-6 of Fig. 5; Fig. 7 is a longitudinal cross section of yet another alternate preferred embodiment of the threading head of the present invention;; Fig. 8 is a cross sectional view taken along lines 8-8 of Fig. 7; Fig. 9 is a cross sectional view taken along ;ines 9-9 of Fig. 8; Fig. 10 is an enlarged longitudinal cut away view of a modified version of the threading head of Fig. 7; and Fig. 11 is an end view of the threading head illustrated in Fig. 10 taken along lines 11-11 thereof.

Figure 1 illustrates a longitudinal cross section of a threading head 10 for a numerically controlled machine tool in accordance with the teachings of the present invention. Threading head 10 comprises a frame 12 which is mounted on a machine tool 14 for movement to an operating position directly opposite the machine tool workpiece holding table (not shown) which is movable to and from this operating position along a path, hereinafter designated as the Z axis, under command of the machine tool numerical control system (not shown).

Frame 12 has a passage through its forward (rightward) face which is dimensioned large enough to receive a tubular spindle 1 6 which is disposed through the passage so as to extend forwardly (rightwardly) beyond the frame. In the presently preferred embodiment, spindle 1 6 comprises a tubular ball screw which is threaded into a ball nut 1 8 secured to frame 12 by bolts 27 so as to threadedly journal the ball screw through the frame passage. As will be better understood hereinafter, the pitch of the ball screw threads is chosen to correspond to the desired pitch of the threads to be chased by the threading head.

Rotational energy is imparted to the ball screw to thread the ball screw through the ball nut by a gear 28 which is carried on the rearward end of the ball screw between a spacer 29, in abutment with a shoulder on the ball screw, and a nut 30, threadedly engaging the rearward end of the ball screw to urge gear 28 against spacer 29. A plurality of set screws (not shown) are radially threaded through nut 30 to prevent the nut from loosening during ball screw rotation.

Gear 28 is driven from a drive pinion 31 which is rotatably journaled into frame 12 parallel to ball screw 1 6 by bearings 32a and 32b so that the drive pinion meshingly engages gear 28. Drive pinion 31 has a bevel gear 33 secured to its rearward (leftward) end for meshing engagement with a bevel gear 34 carried on the shaft of a numerically controlled servo motor 35. Motor 35 is fastened to the top of frame 12 by bolts 36 so that the motor shaft extends downwardly into the frame through a bearing 38 seated in a passage in the top of the frame. The meshing engagement of gear 28 with drive pinion 31, and the meshing engagement of bevel gear 33 with bevel gear 34 are best illustrated by reference to Fig. 2 which is a cross sectional view taken along lines 2-2 of Fig. 1.

Numerically controlled servo motor 35 typically has an internal feedback transducer therein (not shown) for generating electrical signals indicative of the angular motor shaft position. The electrical signals from the internal feedback transducer within rnotor 35 are supplied to an N/C control circuit 39, such as are well known in the art. In accordance with the electrical signals provided by the motor internal feedback transducer, N/C control circuit 39 controls the excitation of servo motor 35 responsive to numerical control commands, such as are generated by a tape reader or the like (not shown) to precisely control ball screw 1 6 rotation. As ball screw 1 6 is rotatably threaded through ball nut 1 8 by servo motor 35 responsive to signals from N/C control circuit 39, the threaded engagement of the ball screw with ball nut 18, fastened to frame 12, causes the ball screw to be either extended out from or retracted into the frame as it rotates depending on the direction of ball screw rotation.

Because the ball screw translates as it rotates, drive pinion 31 thus must be dimensioned long enough so that gear 28 remains in constant meshing engagement with the drive pinion during the entire path of axial ball screw movement. In practice, the diameter of ball screw 1 6 and the pitch of the ball screw threads are selected such that five complete rotations of the ball screw causes the screw to be fully extended a distance of approximately 75 mm (3 inches) from the frame. Thus, when the ball screw is configured as described above, drive pinion 31 must likewise be 75 mm long to assure constant meshing engagement between drive pinion and gear 28.

Those skilled in the art, will, of course, recognize that by changing the diameter of a ball screw as well as by changing the pitch of ball screw threads, the length of ball screw advancement out from the frame after a set number of ball screw revolutions will vary accordingly and will thus necessitate that the drive pinion be dimensioned accordingly.

A housing 40 is secured to the end of ball screw 16 distal from the frame 12 by bolts 42 so that the housing rotates co-jointly with the ball screw. Within the housing is a screw 44 which is journaled in the housing by bearings 46a and 46b for rotation about an axis perpendicular to the axis of ball screw 1 6 rotation. Screw 44 has a bevel gear 48 integrated thereon for meshing engagement with a complementary bevel gear 50 journaled into the rearward wall of housing 40 so as to extend through the rearward housing wall into the hollow bore of ball screw 1 6 for coupling the forward end of a drive shaft 52 concentric within the bore of the ball screw.The rearward end of shaft 52 is attached to the shaft of a numerically controlled servo motor 54 which is attached to the rearward end of ball screw 1 6 by bolts 56 so that the motor is coaxial with the ball screw as illustrated in Fig. 2.

Referring now to Figs. 3 and 4, housing 40 has a channel 58 disposed in the forward face thereof so as to extend radially out from the ball screw for receiving a cross block cutting tool 60, the rearward end of the cross block cutting tool extending through the channel into the interior of the housing. Cross block cutting tool 60 slides within channel 58 along ways 62 (Fig. 4) which are each secured by fasteners (not shown) along the sides of the housing channel. A pair of guards 64 are each fastened by bolts 66 to the forward face of housing 40 to overlie ways 62 and thus retain the cross block cutting tool within the channel. Referring now to Figs. 1 and 4 jointly, a block 68 is fastened to the rear of cutting tool 60, and has a threaded bore vertically disposed therethrough to receive screw 44.In practice, block 68 and cross block cutting tool 60 are fabricated as a single integral unit. Fabricating cross block cutting tool 60 and block 68 of a single integral unit necessitates that housing 40 be provided with an opening in the top end thereof to facilitate threading of screw 44 into block 68.

An access plate 70 (Fig. 1) carrying bearing 46a (Fig. 1) is fastened to frame 40 so as to overlie the opening in the top thereof.

Servo controlled motor 54 of Fig. 1, like servo controlled motor 35, has a feedback transducer integral therein for generating electrical signals indicative of motor 54 shaft position. Electrical signals generated by the feedback transducer within servo control motor 54 are supplied to N/C control circuit 39, which, in response to numerical control commands, controls the excitation of motor 54 in accordance with the feedback signals generated by the motor feedback transducer to precisely control the rotation of shaft 52 and hence screw 44 since the screw is in constant engagement to shaft 52 by virtue of meshing engagement of bevel gear 48 on screw 44 with bevel gear 50 on shaft 52.The threaded engagement of shaft 44 with block 6s causes cutting tool 60 to be displaced radially outwardly from the ball screw or inwardly towards the ball screw responsive to shaft 52 rotation so that by controlling the excitation of motor 54, the orbit of cross block cutting tool 60, and hence, the depth of the threads chased thereby can be controlled accordingly. Although not shown, a slip ring arrangement, such as is well knovvn in the art, is provided for coupling electrical signals between N/C control circuit 39 and servo controlled motor 54 to maintain a constant electrical connection therebetween as motor 54 rotates co-jointiy with the spindle.

In operation, interior or exterior threads can be chased on a workpiece by cross block cutting tool 60 of threading head 10 by inputting the proper numerical control commands to N/C control circuit 39. In response to N/C control commands indicative of the length of the threads to be chased and the speed at which thread chasing is to occur, N/C control circuit 39 controls the excitation of motor 35 accordingly, while simultaneously controlling the excitation of motor 54 in response to N/C control commands indicative of the depth of thread cut.

Since the pitch of the threads chased by cross block cutting tool is fixed in accordance within the constant pitch of the threads on ball screw 1 6, which threads, in practice, are precision ground, it follows that the threads chased by the cross block cutting tool will be as precise as the ball screw threads, thereby eliminating the likelihood of cross threading when the workpiece threads chased by cross block cutting tool 60 are mated with a complementary threaded member.

Threading head 10 described above, while able to rapidly and accurately chase exterior or interior threads in a work-piece in accordance with the configuration of the cross block cutting tool, suffers from the drawback that it can only chase non-tapered threads of a single lead. In the production of certain machined parts, particularly oil well drilling pipe, it is often desirable to chase tapered threads, that is, threads whose width tapers, to assure a wedging action when such threads are mated with the threads of complementary threaded member. A threading head 10', capable of chasing such tapered threads on a workpiece is illustrated in cross section of Fig.

5. Threading head 10' illustrated in Fig. 5 is, in most respects, identical to threading head 10 illustrated in Figs. 1-4 and therefore, like numbers are employed in Fig. 5 to designate like elements which will not be described. For a description of these elements, reference should be had to Figs. 1-4. Threading head 10' of Fig. 5, while similar in many respects to threading head 10 of Figs. 1-4, differs in one major respect.

Unlike threading head 10 of Figs. 1-4 in which ball nut 18 is fixedly secured to frame 12 by fasteners 27, ball nut 18' of threading head 10' of Fig. 5 is journaled into an interior wall in frame 12 by a bearing 19' so as to be in threaded engagement with the ball screw for rotation about the ball screw. A gear 20', having a bore therethrough large enough to receive the ball screw, is fastened to the rightward face of ball nut 18' by bolts 21' so as to be coaxial with the ball screw. It is through gear 20' that rotational energy is transferred to the ball nut to rotate the ball nut independently of a ball screw in the manner described hereinafter to vary the taper, that is to say, the width of the threads chased by cross block cutting tool 60 of Fig. 5.

Referring jointly to Fig. 5 and to Fig. 6, which is a cross sectional view of threading head 10' of Fig. 5 taken along lines 6-6 thereof, gear 20' is rotatably driven by a drive pinion 22', which is journaled into frame 12 by bearing 23' (Fig. 5) for rotation about an axis parallel to the axis of ball screw 1 6 rotation. A first bevel gear 24a' is integrated to the right-hand end of drive pinion 22' and is dimensioned to meshingly engage a bevel gear 24b' carried on the shaft of a servo controlled motor 25' seated on the top of frame 1 2 so that the motor shaft extends vertically downward into the frame through bearing 26' which journals the motor shaft to an opening in the top of the frame. Bolts 27a' firmly secure the motor to the frame.To enable assembly of the rotatable ball nut into frame 12, the rightward (forward) end of the frame is provided with a large opening overlying which is a plate 27b' which is fastened to the frame by bolts 27c' as illustrated in Fig. 5.

Servo controlled motor 25' is configured identically to servo controlled motors 35 and 54 of Fig. 1, and includes an internal feedback transducer for generating electrical signals indicative of the angular position of the motor shaft and hence, the angular position of ball nut 1 8. A numerical control circuit (not shown) configured similarly to numerical control circuit 39 of Fig. 1, is supplied with the feedback transducer signals from servo controlled motor 25' and in response to numerical control command representing the thread taper. the numerical control circuit controls the excitation of motor 25' in accordance with its transducer feedback signals to precisely control the motor shaft and hence ball nut rotation.In addition, the N/C control circuit is also supplied with the feedback signals from the internal feedback transducers within servo controlled motors 35 and 54 and, in response to numerical control signals representing the thread length and speed of thread cut and numerical control signals representing the depth of thread cut, the N/C control circuit controls the excitation of servo motors 35 and 54, respectively, in accordance with the feedback signals generated by the respective motor feedback transducers to precisely control the rotation of ball screw 1 6 and screw 44, respectively, accordingly.

Threading head 10' of Fig. 5 operates in the same manner as threading head 10 of Fig. 1 in that the length of the threads chased by the cross block cutting tool 60 of Fig. 5 and the speed at which they are chased is varied by controlling the excitation of motor 35 of Fig. 5 in the same manner in which the length of the threads chased by the cross block cutting tool of threading head 10 of Figs. 1-4 and the speed at which such threads are chased is varied by controlling the excitation of motor 35 of Fig. 1. Likewise, the depth of the threads chased by the cross block cutting tool threading head 10' of Fig. 5 is controlled by controlling the excitation supplied to servo control motor 54 of Fig. 5 just as the depth of the threads chased by cross block cutting tool 60 of Fig. 1 is governed by the excitation supplied to servo motor 54 of Fig. 1.However, unlike threading head 10 of Figs. 1 --4, threading head 10' of Figs. 5 and 6 advantageously permits the width of the threads chased thereby to be varied by regulating the excitation of motor 25' of Fig. 5 responsive to numerical control commands to vary the rotation of rotation of ball nut 18' so as to impart a non-uniform spiral motion to the ball screw. This non-uniform spiral motion of the ball screw causes cross block cutting tool 60 of Fig. 5 to chase tapering width threads.

Yet another preferred embodiment of a threading head configured in accordance with the teachings of the present invention is illustrated in Fig. 7 and is identified generally by the reference number 1 00. Threading head 100 comprises a frame 112 which is affixed to a numerically controlled machine tool 114 for placement in an operating position directly opposite to the machine tool worktable (not shown) which is movable to and from the operating position along a path designated as the Z axis under command of the machine tool control system (not shown).

Frame 112 has a passage in the forward face thereof which is dimensioned thereof to receive a spindle 11 6 which extends forwardly beyond the frame. A seal 11 7a having a bore therethrough dimensioned to receive spindle 11 6, is fastened by bolts 11 7b to frame 112 so as to overlie the opening in the frame. In the presently preferred embodiment, spindle 11 6 comprises a pair of concentric sleeves 11 6a and 11 6b, sleeve 11 6b being rotatably journaled within sleeve 11 spa by a pair of bearings 11 6c which are each carried on the forward and rearward end of the sleeve 11 6b.

A key 11 7c is axially embedded into the periphery of sleeve 11 6a for engaging a complementary keyway inscribed in the frame passage. In this way, both sleeves 11 6a and 11 6b can be extended out from and into the frame along an axis parallel to the Z axis whereas only sleeve 11 6b can be rotated thereabout.

Sleeves 11 6a and 11 6b are displaced axially out from and into frame 112 by the combination of a ball nut 11 8, affixed to the outer periphery of sleeve 11 6a, and a ball screw 119 journaled in frame 114 by bearings 1 20a and 1 20b so as to be parallel to the sleeves and in threaded engagement with the ball nut. Ball screw 119 is rotatably driven by a gear 121 a which is keyed on the rearward end of the ball screw so as to be in meshing engagement with a complementary dimensioned gear 121b keyed on a shaft 122 journaled in frame 114 parallel to the ball screw by a pair of bearings 123 (only one of which is shown).Shaft 122 is splined to engage the splines on the interior bore of each of a pair of cluster gears 1 24a and 1 24b carried on the shaft. Each cluster gear has a separate one of shifter collars 124aa and 124bb, respectively, integrated to the leftward face of the gear for engaging a separate one of shifter forks 1 25a and 125b, respectively.

Each of shifter forks 1 25a and 1 25b is linked to a separate one of a pair of mechanical or hydraulic shifting mechanisms (not shown) such as are well known in the art. When each of shifter forks 1 25a and 1 25b is urged either rightwardly or leftwardly from its central most position by its corresponding shifter mechanism, the shifter fork biases a corresponding one of cluster gears 1 24a and 124b, respectively, either rightwardly or leftwardly.Cluster gear 124a, when urged either rightwardly or leftwardly from its central most position by shifter fork 125a, engages a separate one of gears 1 26a or 126b, respectively, which each are keyed in spaced apart relationship on a shaft 1 27a which is journaled into frame 112 parallel to shaft 122 by bearings 1 27b (only one of which is shown). Cluster gear 124b, when shifted rightwardly or leftwardly by its associated shifter fork, engages a separate one of gears 1 26c and 126d, respectively, which are keyed on shaft 1 27a in parallel spaced apart relationship with gears 1 26a and 126b.In practice, gears 1 26a-1 26d and cluster gears 1 24a and 1 24b are each dimensioned such that when cluster gear 1 24a is biased rightwardly and leftwardly to engage a separate one of gears 1 26a and 126b, respectively, shaft 127a, will undergo 1.5 and 2.0 revolutions, respectively, for each revolution of shaft 122. When cluster gear 1 24b engages a separate one of gears 1 26c and 126d, the ratio of shaft 1 27a rotation to 1 22 rotation becomes 3.0 to 1 and 4.0 to 1, respectively.As will become better understood hereinafter, when gears 1 26a-1 26d and cluster gears 1 24a and 1 24b are dimensioned to produce the above listed ratios, the pitch of the threads chased by the hereinafter described cross block cutting tool affixed to the distal end of sleeves 11 6a and 11 6b, will be 3, 4, 6 and 8 threads per unit, respectively. Those skilled in the art will recognize that by changing dimensions of cluster gears 1 24a and 1 24b and the dimensions of gears 1 26a and 1 26b and 1 26c and 126d, different pitch threads can be chased.

Sleeve 11 sub, which, as will be recalled, is journaled for rotation in sleeve 11 6a by bearings 11 6c, is rotatably driven by a gear 128 carried adjacent to the rearward end of sleeve 11 sub which extends rearwardly from sleeve 11 6a. Gear 128 is retained on sleeve 11 6b by virtue of being urged against a spacer 129, in abutment with the lower race of the lefthand one of bearings 11 6c, by a nut 1 30 in threaded engagement with the rearward end of the sleeve. A plurality of set screws (not shown) are radially threaded through nut 1 30 to secure the nut against rotation.

A drive pinion 131, dimensioned complementary to gear 128, isjournaled into frame 112 by bearings 1 32a and 1 32b so as to be parallel to and in meshing engagement with gear 130 as is best illustrated in Fig. 8. Like drive pinion 31 of threading head 10 of Fig. 1, drive pinion 131 of threading head 100 of Fig. 7 must be dimensioned long enough so as to remain in constant meshing engagement with gear 128 as sleeves 11 6a and 11 6b are advanced outwardly from the sleeves by virtue of ball screw 11 9 being threaded through ball nut 11 8. Drive pinion 131 has a bevel gear 133a and a spur gear 1 33b integrated on the rearward end thereof in parallel spaced apart relationship.Spur gear 133 b is dimensioned complementary to a spur gear 1 33c carried on shaft 1 27a for meshing engagement therewith. Thus when drive pinion 1 31 is driven through bevel gear 133a, rotational energy is transmitted through spur gear 1 33b and gear 1 33c (Fig. 7) to shaft 1 27a for transmission via a separate one of gears 1 26a through 1 26c and an associated one of cluster gears 1 24a and 1 24b to shaft 122 for transmission via gears 121 a and 121boo ball screw 119.Bevel gear 133a is dimensioned complementary to a bevel gear 1 34 carried on the downwardly extending shaft of a servo controlled motor 135 which is affixed to the top of frame 112 by bolts 136 so that the motor shaft extends into the frame through a bearing 138.

Servo controlled motor 1 35 is configured identically to servo controlled motor 35 of Fig.1 and like servo motor 35 of Fig. 1, servo controlled motor 135 of Fig. 7 has an internal feedback transducer integral for generating electrical signals indicative of motor shaft position. The electrical signals from the feedback transducer within motor 135 are supplied to a numerical control circuit 1 39 configured identically to numerical control circuit 39. Numerical control circuit 139 is responsive to numerical control signals, and in response to such numerical control signals, the numerical control circuit controls the excitation of motor 135 in accordance with the feedback signals generated by the internal feedback transducer to precisely control motor shaft 135 position.

As is best illustrated in Fig. 9, which is a cross sectional view of threading head 100 of Fig. 7 taken along lines 8-8 thereof, motor 135, when energized, drives pinion gear 131 through bevel gears 133 and 134 while at the same time driving ball screw 11 9 via one of cluster gears 1 24a and 1 24b when a separate one of the cluster gears is biased by a separate one of shifter forks 1 25a and 125b, respectively, into engagement with a corresponding one of gears 1 26a and 1 26b and 1 26c and 126d, respectively.The joint rotation of drive pinion 1 31 and ball screw 11 9 causes sleeve 11 6b (Fig. 7) to be axially advanced from the frame as it rotates, thus imparting a spiral motion to the sleeve. Since the distance of sleeves 11 6a and 11 6b are axially displaced from frame 112 during each revolution of sleeve 11 6b is determined by the ratio of ball screw 11 9 rotation to drive pinion 1 31 rotation, it can easily be seen that shifting cluster gears 1 24a and 1 24b to alter the ratio of shaft 1 27a rotation to shaft 122 rotation allows the effective orbit of the hereinafter described cutting tool affixed to sleeve 11 6b to be controlled accordingly to thus vary the lead of the threads chased thereby.

Referring back to Fig. 7, a housing 140 is affixed by bolts 142 to the face of sleeve 11 6b distal frorn frame 112 so as to rotate cojointly with the sleeve. Housing 1 40 is configured identically to housing 40 of Fig. 1 and has a screw 144 journaled in the housing by bearings 1 46a and 1 46b for rotation about an axis perpendicular to the axis of sleeve 11 6b rotation. Screw 144 carries a bevel gear 148 which is in meshing engagement with a complementary bevel gear 1 50 journaled into the rearward wall of housing 140 so as to extend therebeyond into sleeve 11 6b perpendicular to the axis of rotation of the screw.

A shaft 152, coaxial with and secured to bevel gear 1 50, extends rearwardly from the bevel gear for attachment to the shaft of a second servo controlled motor 1 54 which is secured to the rearward end of sleeve 11 6b by bolts 1 56 so as to be coaxial with sleeve 11 6b as illustrated in Fig. 8.

Servo controlled motor 154, like servo controlled motor 135, has an internal feedback transducer for generating electrical signals indicative of motor shaft rotation. The electrical signals from the internal feedback transducer of motor 1 54 are supplied via a slip ring arrangement (not shown) to N/C control circuit 139 (Fig. 7) which, in response to N/C commands, controls the excitation of motor 1 54 through the same slip ring arrangement in accordance with the feedback transducer signals to precisely control shaft 1 52 and screw 144 rotation.When screw 144 is rotatably driven via bevel gear 148 which is rotatably driven from servo controlled motor 1 54 via shaft 152, the screw displaces a cross block cutting tool 1 60 slidably mounted in the forward -Face of housing 140, radially across the housing by virtue of screw 144 being in threaded engagement with a block 1 68 extending rearwardly from the cross block cutting tool.

Threading head 100 operates in much the same manner as threading head 10 of Fig. 1 in that the length of threads chased by cross block cutting tool 1 60 and the speed at which they are chased are varied in response to numerical control commands received by N/C circuit 139 which, in turn, varies the excitation supplied to motor 135 accordingly. The depth of the threads chased by cutting tool 1 60 is controlled by the numerical control commands received by N/C control circuit 139 which varies the excitation provided to servo motor 154-accordingly.However, unlike threading head 10 of Fig. 1, threading head 100 of Fig. 7 advantageously enables the lead of the threads chased by the cross block cutting tool 1 60 to be changed by the shifting of cluster gears 1 24a and 1 24b so as to change the ratio of ball screw 11 9 rotation to sleeve 11 6b rotation.

It should be noted that the threads chased by cross block cutting tool 1 60 of threading head 100 of Fig. 7, like the threads chased by cross block cutting tool 60 of threading head 10 have a constant width unlike the threads chased by threading head 10' of Fig. 4 whose width can be varied by controlling the excitation of servo controlled motor 25' of Fig. 5. To enable threading head 100 of Fig. 7 to chase tapering width threads, threading head 100 can be modified as shown in Fig. 10 and 11, Fig. 10 being an enlarged cut away view showing a portion threading head 100 as modified and Fig. 11 being an end view taken along lines 11-11 of Fig. 10.

Referring to Figs. 10 and 11, threading head 100 as modified to chase tapered width threads, includes a flange 1 75 radially extending from sleeve 11 6a. Flange 175 has a hollow bore therethrough parallel to the axis of sleeve 11 6b rotation to receive a bearing 177 which journals ball nut 11 8 to flange 1 75 to permit the ball nut to rotate relative to ball screw 11 9 which threadedly engages the ball nut, in contrast to ball nut 118 of Fig. 7, which is fixedly mounted to sleeve 11 6b.

Ball nut 118 of Figs. 10 and 11 has a gear 179 coaxially mounted thereto by screws 1 79a so as to rotate co-jointly with the ball nut. Referring solely to Fig. 11, gear 179 and hence ball nut 118 are rotatably driven through an idler gear 180 which is affixed to a shaft 1 81 which is journaled in flange 1 75 parallel to the axis of rotation of ball nut 118 rotation so that gear 1 80 is in meshing engagement with gear 179 and a complementary dimensioned gear 1 82 carried on the shaft of the servo controlled motor 1 84 which is affixed by fasteners (not shown) to flange 1 75. Servo controlled motor 1 84 is configured identically to servo controlled motors 135 and 1 54 and includes an internal feedback transducer therein for generating electrical signals indicative of motor shaft and hence ball screw angular position. The signals from the feedback transducer integral with servo controlled motor 184 are supplied to a numerical control circuit, such as numerical control circuit 1 39 of Fig. 7 which, in accordance with the feedback signals generated by the feedback transducer integral with motor 184, controls motor 1 84 excitation responsive to numerical control commands to rotate ball nut 11 8 so as to achieve the desired thread width taper.

The foregoing describes an improved threading head for use with a numerically controlled multiple spindlehead indexing machine tool which is capable of accurately chasing interior or exterior threads on a workpiece of varying lead and of the varying width.

Although the illustrative embodiment of the invention has been described in considerable detail for the purpose of fully disclosing a practical operative structure incorporating the invention, it is to be understood that the particular apparatus shown and described is intended to be illustrative only and that various novel features of the invention may be incorporated in other structural forms without departing from the spirit and scope of the invention as defined in the subjoined claims.

Claims (13)

1. A threading head for use with a machine tool having a rotatably driven spindle for chasing threads on a workpiece comprising: a body adapted to be carried by the machine tool spindle for co-joint rotation; a housing; a cutting tool slidably carried by said housing for movement thereacross; means within said body for slidably moving said cutting tool across said housing: and means within said body and attached to said housing for advancing said housing out from and into said body as the machine tool spindle is rotatably driven to impart a spiral motion to said cutting tool.

2. A threading head for use on a numerically controlled machine tool comprising: a frame having a passage therein; a tubular spindle journaled in said frame for rotation about a first axis and for movement along said axis; a cross block cutting tool slidably mounted on the end of said spindle distal from said frame for radial movement across said spindle; means secured to said frame and coupled to said spindle for jointly rotating said spindle and advancing said spindle out from and into said frame responsive to numerical control commands so as to impart a helical orbit to said cross block cutting tool; and means affixed to said spindle for radially displacing said cross block cutting tool across said spindle responsive to numerical control commands to vary the helical orbit traversed by said cross block cutting tools and thus enable said cross block cutting tool to chase threads on a workpiece.

3. A head according to claim 2 wherein said spindle comprises 9 tubular ball screw and wherein said means advancing said spindle out from and for retracting said spindle into said frame comprises: a ball nut fixedly secured in said frame passage for threadedly engaging said tubular ball screw: a servo-controlled motor having a shaft coupled to said ball screw for precisely rotating said ball screw in response to electrical signals; numerical control means responsive to numerical control commands for supplying electrical signals to control the excitation of said servo-controlled motor in accordance with the motor shaft position; and a gear train disposed in said frame in engagement with said ball screw and said servocontrolled motor for coupling said servo-controlled motor to said tubular ball screw.

4. A head according to claim 2 wherein said spindle comprises a turbular ball screw and wherein said means for helically advancing said spindle out from and for retracting said spindle into said frame comprises: a ball nut rotatably journaled within said frame so as to be in threaded engagement within said ball screw; a first servo-controlled motor secured to said frame and coupled to said ball nut for precisely rotating said ball nut responsive to electrical signals representing a desired ball screw angular orientation; a second servo-controlled motor affixed to said frame for precisely rotating said ball screw in accordance with electrical signals indicative of the desired ball screw angular orientation;; a numerical control circuit responsive to numerical control commands for generating electrical signals to control said first and said second servo-controlled motors; and a gear train disposed in said frame in engagement with said ball screw and said second servo-controlled motor to couple said ball screw to said second servo-controlled motor.

5. A head according to claim 2, wherein said spindle comprises an outer and inner concentric sleeves disposed through said frame passage, said outer sleeve being keyed to said frame so as to be extendable out from and retractable into said frame and said inner sleeve being rotatably journaled within said outer sleeve so as to be rotatable about the common axis of said sleeves, said cross block cutting tool being affixed to the distal end of said inner sleeve and wherein said means for helically advancing said spindle out from or retracting said spindle into said frame comprises:: a ball screw rotatably journaled in said frame for rotation about an axis parallel to said axis of rotation of said inner sleeve; a ball nut secured to said outer sleeve so as to be in threaded engagement with said ball screw; a servo-controlled drive motor secured to said frame and having a rotary driven shaft for jointly rotating said inner sleeve and said ball screw in response to electrical signals supplied to said motor; numerical control means responsive to numerical control commands and to the motor position for supplying electrical signals to control said servo-controlled motor in accordance with said numerical control commands and the motor shaft position; a first gear train disposed in said frame for coupling said inner sleeve to said servo-controlled motor so that said inner sleeve can be rotatably driven therefrom; and a second gear train disposed in said frame in engagement with said first gear train and in engagement with said ball screw for rotatably driving said ball screw proportional to the rotation of said inner sleeve to impart a precise helical orbit to said cross block cutting tool.

6. A head according to claim 5, wherein said ball nut is rotatably journaled into said outer sleeve, and further including: a spur gear affixed to said ball nut; a servo-controlled motor affixed to said outer sleeve and having a rotary driven shaft for rotatably driving said ball nut; means journaled in said outer sleeve in engagement with said servo-controlled motor shaft and said spur gear for coupling said servocontrolled motor to said spur gear; and numerical control means coupled to said servocontrolled motor for controlling the excitation thereof in response to numerical control commands and the motor shaft position.

7. A head according to claim 5 or 6, wherein said second gear train comprises: a first shaft journaled in said frame for rotation about a first axis parallel to the axis of rotation of said inner sleeve; at least two gears keyed on said first shaft in spaced apart relationship so that one of said gears meshingly engages said first gear train; a second shaft journaled in said frame for rotation about an axis parallel to the axis of rotation of said inner sleeve and the axis of rotation of said first shaft; and at least two gears keyed on said second shaft so that one of said gears is in constant driving engagement with said ball screw and the other of said gears is slidable along said second shaft to meshingly engage either of said two gears on said first shaft.

8. A head according to claim 2 wherein said means for radially displacing said cross block cutting tool across said spindle to change the orbit of cross block cutting tool responsive to numerical control commands comprises: a screw journaled in said spindle perpendicular to the axis of spindle rotation; screw engaging means carried on said cross block cutting tool for threadedly engaging said screw; a drive shaft concentric within said spindle and in driving engagement with said screw for rotatably driving said screw so as to thread said screw through said screw engaging means so as to displace said cross block cutting tool radially across said spindle;; a servo-controlled motor secured to the rearward end of said spindle, said servo-controlled motor having a shaft in driving engagement with said drive shaft concentric within said spindle, for precisely rotating said drive shaft in response to electrical signals; and numerical control means coupled to said servo controlled motor for controlling the excitation thereof responsive to numerical control commands and the position of said motor shaft.

9. An improved threading head for-use on a numerically controlled machine tool comprising: a frame having a passage therein; a ball nut secured in said frame passage: a tubular ball screw disposed in said frame in threaded engagement with said ball nut so as to extend beyond said frame; first servo-controlled motor means secured to said frame and coupled to said ball screw for precisely rotating said ball screw responsive to numerical commands to spirally advance the ball screw out from and to spirally retract said ball screw into said frame; a cross block cutting tool slidably mounted in the end of said ball screw distal from said frame; and second servo-controlled motor means secured to the end of said spindle within said frame and linked to said cross block cutting tool for precisely displacing said cross block cutting tool radially across said ball screw responsive to numerical control of commands to vary the cross block cutting tool orbit so as to enable said cross block cutting tool to chase workpiece threads.

10. The invention according to claim 9 wherein each of said first and second servo controlled motor means includes: a servo-controlled motor having an internal feedback transducer therein for generating electrical signals indicative of motor shaft rotation; and a numerical control circuit responsive to numerical control commands for controlling the excitation of said servo-controlled motor in accordance with electrical signals from said motor feedback transducer.

11. An improved threading head for use on a numerically controlled machine tool comprising: a frame having a passage therein; a ball nut rotatably journaled in said frame in communication with said passage; first servo-controlled motor means attached to said frame and coupled to said ball nut for precisely rotating said ball nut responsive to numerical control commands; a tubular ball screw disposed into said frame through said passage so as to be in threaded engagement with said ball nut; second servo-controlled motor means disposed within said frame and coupled to said ball screw for precisely threading said ball screw through said ball nut responsive to numerical control commands; a cross block cutting tool slidably mounted in the end of said ball screw distal from said frame for radial movement thereacross; and third servo-controlled motor means secured to the end of said ball screw within said frame, said third servo controlled motor means being linked to the said cross block cutting tool for precisely displacing said cross block cutting tool radially across said ball screw to vary the cross block cutting tool orbit in accordance with numerical control commands.

12. A threading head for use on a numerically controlled machine tool comprising: a frame having a passage therein; a first sleeve disposed in said frame and being keyed thereto so as to be extendable out from and retractable into said frame without rotation relative to said frame; a second sleeve journaled concentrically within said first sleeve for rotation about the common axis of said sleeves; a ball nut secured to said first sleeve; a ball screw rotatably journaled in said frame parallel to said first and second sleeves so as to be in threaded engagement with said ball nut; a gear train for jointly rotating said second sleeve and said ball screw to advance said first and second sleeves out from said frame and retract said first and second sleeves into said frame while said second sleeve is undergoing rotation;; first servo-controlled motor means for precisely driving said gear train responsive to numerical control commands; a cross block cutting tool slidably mounted to the end of said outer sleeve distal from said frame for radial movement thereacross; and second servo-controlled motor means secured to the end of said first sleeve within said frame and linked to said cross block cutting tool for radially displacing said cross block cutting tool across the end of said first sleeve responsive to numerical control commands to vary the cross block cutting tool orbit to enable said cross block cutting tool to chase workpiece threads.

13. A threading head for use with a machine tool, such threading head being substantially as hereinbefore described with reference to, and as illustrated in, Figures 1 to 4, or Figures 5 and 6, or Figures 7 to 9 or Figures 10 and 11 of the accompanying drawings.