Shaft end adapter and ball screw assembly

Abstract

Shaft end adapter (20), comprising: a tube section (24) having an axial bore (26) defining an opening for receiving an end of a shaft element (10) at a free end of the tube section (24), the tube section (24) being formed at or adjacent to its free end portion with a circumferentially continuous portion (32) and with a slot (30) extending axially through a wall of the tube section (24) excluding the circumferentially continuous portion (32), the tube section (24) being formed at or adjacent to its free end in part with a large-diameter portion (24B); and a clamping element mounted on the pipe section (24) and suitable for narrowing the slot (30), wherein the clamping element comprises a fastening bolt (42) which is screwed into the tube section (24) and extends across the slot (30), wherein the large diameter section (24B) defines a bolt fastening recess (36) into which a bolt receiving hole (38) opens, and wherein the bolt receiving hole (38) is adapted such that the fastening bolt (42) is inserted into the bolt receiving hole (38) to be screwed into the tube section (24).

Description

TECHNICAL FIELDThe present invention relates to a shaft end adapter and a ball screw assembly, and more particularly to a shaft end adapter adapted to be fixed to an end of a shaft and a ball screw assembly incorporated in such a shaft end adapter.BACKGROUND OF THE INVENTIONThe ball screw shaft used in a lead screw mechanism is formed with a non-threaded mounting shaft portion at one of its ends for mounting a bearing member or a drive wheel thereon.The attachment shaft portion is usually formed integrally with the ball screw shaft, and it has been necessary to use a special machine tool and a jig for machining the attachment shaft portion. Even if the thread of the ball screw shaft is the same, the configuration of the attachment shaft portion may vary according to the user's need. Also, even if the configuration of the fastening shaft portion is the same, the length of the threaded shaft may vary. Such variations cause unavoidable bottleneckes in the manufacturing process. Further, the threaded shaft portion is quenched together with the mounting shaft portion, but the mounting shaft portion needs to be tempered because the quenched members cannot be easily worked.In connection with such a ball screw shaft, it is known to manufacture the mounting shaft portion (shaft end adapter) and the screw shaft portion as separate members, and integrally connect the two members together by brazing, welding or shrink fitting. See Patent Documents 1 and 2.PRIOR ART DOCUMENTSPATENT DOCUMENTSPatent Documents 1: JP2005-114081APatent Documents 2: JP2009-275914APatent Documents 3: DE 199 07 181 A1Patent Documents 4: DE 37 27 975 C2Patent Documents 5: DE 20 2007 004 690 U1Patent Documents 6: DE 927 061 BSUMMARY OF THE INVENTIONPROBLEM SOLVED BY THE INVENTIONWhen a shaft member such as the screw shaft portion is integrally connected to the fixing shaft portion, the coaxiality and straightness (face precision) of the both shaft portions can be easily secured by the available machine precision. However, when the screw shaft portion and the fixing shaft portion are made as two separate members and integrally joined together by brazing, welding or shrink fitting, the precision of joining the two shaft portions greatly affects the coaxiality and the straightness (run-flat precision) of the two shaft portions, in addition to the machine precision of the two shaft portions.In order to achieve required precision in the coaxiality and the straightness of the two shaft portions, when the screw shaft portion and the fastening shaft portion are manufactured as two separate members, it is necessary to improve the precision in the joining of the two shaft portions. However, a joining process based on brazing, welding or shrink fitting does not allow fine adjustment of coaxiality and straightness, and the inevitable thermal deformation prevents achievement of desired high precision in coaxiality and straightness. As a result, considerable differences between the products cannot be prevented.It is a main object of the present invention to effectively produce an assembly of a shaft member and a fixing shaft portion (shaft and adapter) which have been manufactured as two separate components with high precision in coaxiality and straightness.MEANS FOR ACHIEVING THE OBJECTThe present invention provides a shaft end adapter having the features of claim 1. Alternatively, the present invention provides a shaft end adapter having the features of claim 9.According to this arrangement, since the part of the pipe portion (24, 64) disposed adjacent to the open end (26B, 66B) of the axial bore (26, 66) defines a circumferentially continuous circumferential surface by the circumferentially continuous portion (32, 72), and has high rigidity due to its completely closed annular cross section, even if the pipe portion (24, 64) is caused to undergo elastic deformation toward the closed slit (30, 70), this part is less susceptible to elastic deformation and maintains a true circular configuration. Therefore, the assembly of the shaft member (10) and the shaft end adapter (20, 60) which are separately manufactured can be easily manufactured by operating the clamping member (42, 82, 90, 94) with high precision in coaxiality and straightness in an effective manner.Preferably, in the shaft end adapter of the present invention, it is provided that the circumferentially continuous portion (32, 72) defines a circumferentially continuous inner circumferential surface disposed adjacent an open end of the axial bore (26, 66).According to this arrangement, the axial bore (26, 66) is ensured to have a true circular configuration in this region, since the circumferentially continuous portion (32, 72) defines a circumferentially continuous surface adjacent the free end of the tubular portion (24, 64) having a same inner diameter as the axial bore (26, 66).Preferably, in the shaft end adapter of the present invention, it is provided that the circumferentially continuous portion (32, 72) is a part of an axial end surface (24D, 64D) of the pipe portion (24, 64) disposed at an open end of the pipe portion as a circumferentially continuous surface.According to this arrangement, the part of the axial bore ( 26, 66) disposed adjacent to the open end thereof is ensured to have a true circular configuration because the circumferentially continuous portion ( 32, 72) defines an axial end surface ( 24D, 64D) of the pipe portion ( 24, 64) as a circumferentially continuous surface.Preferably, in the shaft end adapter of the present invention, a plurality of threaded holes (44, 48) extend radially through the tubular portion (24) at circumferentially different positions, each defining an open end in the axial bore (26), and wherein when a screw member (46, 50) is threaded into each of the threaded holes (44, 48), an end of the screw member abuts an outer circumferential surface of the shaft member (10).According to this arrangement, by individually adjusting the thread feed of the screw members (46, 50) and thereby adjusting the radial pressures that the screw members (46, 50) exert on the shaft member (10), the tilt angle of the central axial line of the shaft member (10) with respect to the central axial line of the axial bore (26) can be finely adjusted, so that extremely high precision in straightness can be obtained.Preferably, in the shaft end portion of the present invention, it is provided that the shaft member comprises a ball screw shaft (10), and at least one of the screw members is adapted to engage with a threaded groove (12) of the ball screw shaft.According to this arrangement, the screw members (46, 50) also serve as stoppers for preventing the ball screw shaft (10) from slipping out of the axial bore (26).Preferably, in the shaft end adapter of the present invention, it is provided that a pipe portion side flange portion (104), a shaft portion (102), and a shaft side flange portion (100) connected to the pipe portion side flange portion (104) via the shaft portion (102) are integrally formed with a base side portion of the pipe portion (24) axially away from a free end thereof, a plurality of through holes (106) axially extend through the shaft side flange portion (100) at different circumferential positions, while the pipe portion side flange portion (104) is formed with a plurality of threaded holes (108) aligned with the respective through holes (106) of the shaft side flange portion (100) and opening to an end surface thereof, and each of the through holes (106) is inserted with a screw member (110), respectively, and screwed into the respective threaded hole (108).According to this arrangement, by individually adjusting the screw feed of the screw members (110) into the screw holes (108) and thereby causing a corresponding bending deformation of the shaft portion (102), the tilt angle of the major axis of the shaft member (10) with respect to the major axis of the axial bore (26) can be finely adjusted, so that an extremely high precision of straightness can be obtained.Preferably, in the shaft end adapter of the present invention, it is provided that a pipe portion side flange portion (104), a shaft portion (102), and a shaft side flange portion (100) connected to the pipe portion side flange portion (104) via the shaft portion (102) are integrally formed with a base side portion of the pipe portion (24), the base side being disposed axially away from a free end thereof of the pipe portion (24), and the pipe portion (104) is formed with a plurality of circumferentially disposed threaded holes (112) extending therethrough, and a screw member (114) is screwed into each of the threaded holes (112) so as to abut an end surface of the shaft side flange portion (100).According to this arrangement, by individually adjusting the screw feed of the screw members (110) into the screw holes (112) and thereby causing a corresponding bending deformation of the shaft portion (102), the tilt angle of the central axial line of the shaft member (10) with respect to the major axis of the axial bore (26) can be finely adjusted, so that an extremely high precision of straightness can be obtained.Preferably, in the shaft end adapter of the present invention, it is provided that the clamping element comprises two fastening bolts (42) which are screwed into the pipe section (24) and extend at two axial positions across the slot (30).According to this arrangement, narrowing of the slit (30) by the fastening bolt (42) can be achieved uniformly over the entire length of the slit (30), so that the tilt angle of the major axis of the shaft member (10) with respect to the central axial line of the axial bore (26) can be avoided, and high precision of coaxiality and axial straightness between the shaft member (10) and the shaft end adapter (20) can be achieved.In the alternative embodiment of the invention, it is contemplated that in the shaft end adapter of the present invention, an outer circumferential surface of the tubular portion (64) is formed with a conical outer circumferential surface (78, 80) at each of at least two of its axial positions, the clamping member including a clamping bushing (82, 90, 94) inserted onto the tubular portion and formed with a conical bore defining conical inner circumferential surfaces (84, 84A, 84B, 92, 96) for contacting the corresponding conical outer circumferential surfaces (78, 80).According to this arrangement, the slit (70) can be narrowed by the collet (82, 90, 94) over its entire axial length, so that tilting of the major axis of the shaft member (10) with respect to the major axis of the axial bore (66) can be avoided, and high precision of coaxiality and axial straightness between the shaft member (10) and the shaft end adapter (60) can be achieved.The present invention also provides a ball screw assembly comprising a shaft end adapter (20, 60) as defined above according to the present invention and a ball screw shaft (10) secured thereto.According to this arrangement, the assembling of the shaft member (10) and the shaft end adapter (20, 60) which are separately manufactured can be easily achieved by the operation of the clamping member (42, 82, 90, 94) with high precision in coaxiality and straightness in a highly efficient manner.EFFECT OF THE INVENTIONBecause the portion of the tubular portion (24, 64) disposed adjacent the open end (26B, 66B) of the axial bore (26, 66) defines a circumferentially continuous surface through the circumferentially continuous portion (32, 72) and demonstrates high rigidity due to its fully closed annular cross section, even when the tubular portion (24, 64) is caused to undergo elastic deformation in the closing direction of the slot (30, 70), this portion is less susceptible to elastic deformation and maintains a true circular configuration. Therefore, the assembling of the shaft member (10) and the shaft end adapter (20, 60) which are separately manufactured can be achieved easily by the operation of the clamping member (42, 82, 90, 94) with high precision in coaxiality and straightness in a highly efficient manner.BRIEF DESCRIPTION OF THE DRAWINGSNow, the present invention will be described below with reference to the accompanying drawings, in which:[FIG. 1 ] A perspective view showing the overall structure of the shaft end adapter and the ball screw assembly indicated as the first embodiment of the present invention.[FIG. 2 ] A perspective view of the shaft end adapter and the ball screw assembly of the first embodiment as viewed from the base side thereof.[FIG. 3 ] A perspective exploded view of the shaft end adapter and the ball screw assembly of the first embodiment as viewed from its free end.[FIG. 4 ] A side view of the shaft end adapter and the ball screw assembly of the first embodiment.[FIG. 5 ] A sectional view taken through the line V-V of FIG. 4.[FIG. 6 ] A sectional view taken through the line VI-VI of FIG. 5.[FIG. 7 ] A sectional view taken through the line VII-VII of FIG. 4.[FIG. 8 ] A perspective exploded view of the shaft end adapter and the ball screw assembly indicated as the second embodiment of the present invention.[FIG. 9 ] A sectional view of the shaft end adapter and the ball screw structure of the second embodiment.[FIG. 10 ] A perspective exploded view of the shaft end adapter and the ball screw assembly indicated as the third embodiment of the present invention.[FIG. 11 ] A sectional view of the shaft end adapter and the ball screw structure of the third embodiment.[FIG. 12 ] A perspective exploded view of the shaft end adapter and the ball screw assembly indicated as the fourth embodiment of the present invention.[FIG. 13 ] A sectional view of the shaft end adapter and the ball screw structure of the fourth embodiment.[FIG. 14 ] A diagram of the shaft end adapter and the ball screw assembly indicated as the fifth embodiment of the present invention.[FIG. 15 ] A side view of the shaft end adapter and the ball screw assembly of the fifth embodiment.[FIG. 16 ] A side view of the shaft end adapter and the ball screw assembly indicated as the sixth embodiment of the present invention.[FIG. 17 ] A magnified sectional view similar to the VII-VII sectional view of FIG. 4 showing the shaft end adapter and the ball screw structure of the seventh embodiment of the present invention.DESCRIPTION OF THE PREFERRED EMBODIMENT(S)The shaft end adapter and the ball screw structure indicated as the first embodiment of the present invention will be described below with reference to Figs. 1 to 7.The ball screw assembly 1 of the illustrated embodiment is an assembly of a ball screw shaft 10 and a shaft end adapter 20. A ball nut 14 is screwed onto the ball screw shaft 10 via balls (not shown in the drawings) rolling in the threaded groove 12.The shaft end adapter 20 is integrally formed in a coaxial and axially linear configuration with a mounting shaft portion 22 and a tube portion 24. The mounting shaft portion 22 is adapted to be supported by a fixed part (not shown in the drawings) by a bearing device typically equipped with a ball bearing (not shown in the drawings) in a rotatable manner about its main axis. The attachment shaft portion 22 may also be a shaft portion equipped with a gear or the like for transmitting an output torque of an electric motor not shown in the drawings.The pipe portion 24 has a pair of large diameter portions 24A and 24B arranged in spaced relationship on the side of the mounting shaft portion 22 (base side side) and corresponding to the side remote from the mounting shaft portion 22, and generally defines an outer profile consisting of the two large diameter portions 24A and 24B and a small cross-sectional portion 24C connecting the two large diameter portions 24A and 24B together.The tubular portion 24 is formed with an axial bore 26 for receiving one end of the ball screw shaft 10. The axial bore 26 is coaxial and axially linear with respect to the mounting shaft portion 22, and has a closed end, and opens only at the end face 24D on the free end of the tube portion 24. The axial bore 26 thus defines an open end 26B on the end surface 24D of the tubular portion 24.The axial bore 26 has a bottom surface 26A at an axial center of the large diameter portion 24A (need not be exactly half a length of the axial extension of the large diameter portion 24A). The bottom surface 26A preferably extends perpendicular to the major axis of the axial bore 26. in which case the free end surface 10A of the ball screw shaft 10 extends perpendicular to the major axis of the ball screw shaft 10 so that the ball screw shaft 10 can be threaded into the axial bore 26 until the free end surface 10A abuts the bottom surface 26A.The tubular portion 24 has a pair of axial slots 30 at an angular interval of 180 degrees about its major axis. Each slit 30 is defined by a pair of planar opposite side surfaces 30A and 30B while defining a small gap (a certain slit width) therebetween (as shown in FIGS. 4, 6 and 7) and opens on both of the outer circumferential surface of the pipe portion 24 and the inner circumferential surface of the pipe portion 24 defining the axial bore 26.The terms "adjacent to the free end" and "adjacent to the base side" as used herein include the free end itself and correspondingly the base side itself. The terms "adjacent to" and "adjacent" as used throughout the application should be understood in such a meaning.Specifically, the first continuous portion 32 defines a circumferentially continuous inner circumferential surface having the same inner diameter as the axial bore 26 and extending axially from the open end 26B of the axial bore 26 toward the bottom surface 26A for a relatively small distance a (see FIG. 5 ), and a circumferentially continuous flat end surface extending radially from the open end of the axial bore 26 at the end surface 24D of the pipe portion 24 for a relatively small distance b (see FIG. 5 ). Therefore, with respect to the axial direction of the pipe portion 24, the first continuous portion 32 is located only on the part adjacent to the open end 26B of the axial bore 26 and, with respect to the radial direction of the pipe portion 24, only on the marginal part of the open end 26B of the axial bore 26 without reaching the outer circumferential surface of the large diameter portion 24B. Therefore, each slit 30 on the outside of the large diameter portion 24B extends in the axial direction up to the end surface 24D.The second continuous portion 34 defines a circumferentially continuous surface having the same inner diameter as the first continuous portion 32 via a region axially extending between the terminal end of the slit 30 on the bottom surface 26A side of the axial bore 26 and the bottom surface 26A. This circumferentially continuous portion forms part of the axial bore 26 in the embodiment shown.Each of the large diameter portions 24A and 24B of the pipe portion 24 has a bolt fixing recess 36 for each slot 30. Each bolt mounting recess 36 has a seating surface 36A defined by a planar surface perpendicular to the widthwise extension of the slot 30 or parallel to the side surfaces 30A and 30B of the slot 30 (see FIGS. 3 and 7 ). The large diameter portions 24A and 24B of the pipe portion 24 have a total of four bolt receiving holes 38 (see FIG. 7 ), each extending from the corresponding seat surface 36A to the adjacent side surface 30A of the slot 30. The large diameter portions 24A and 24B of the pipe portion 24 have a total of four threaded holes 40 (see FIG. 7 ), each of which extends from the other side surface 30B of the slot 30 to the outer circumferential surface of the corresponding large diameter portion 24A, 24B in coaxial relation to the corresponding bolt receiving holes 38.A fastening bolt 42 consisting of a hexagon socket bolt is inserted into each of the bolt receiving holes 38. Each fastening bolt 42 is inserted transversely through the slot 30, a shoulder surface 42A (see FIG. 7 ) of the head of the fastening bolt 42 abuts against the corresponding shoulder surface 36A, and the threaded portion 42B at the free end portion of the fastening bolt 42 is screwed into the corresponding threaded hole 40 (see FIG. 7 ) transversely through the slot 30, so that the slot 30 is closed when the fastening bolts 42 are screwed into the threaded hole 40.The fastening bolts 42 provide a clamping action for the pipe portion 24 at the positions of the two large diameter portions 24A and 24B axially spaced apart from each other, in each case, on both sides of the pipe portion 24. In other words, the two clamping portions provided on the fastening bolts 42 are disposed adjacent to the axial terminal ends of the slits 30. Therefore, for example, when fastening bolts 42 are protruded as illustrated in FIG. 4, the fastening bolts 42 near the first continuous portion 32 are screwed into the corresponding threaded holes 40 in the large diameter portion 24B, which mainly causes a part of the pipe portion 24 where the continuous portion 32 is not provided to undergo elastic deformation in a closing direction of the slits 30 to narrow the slits to the extent that two parts of the pipe portion 24 are allowed to clamp the shaft member 10. Any other of these fastening bolts likewise provides a clamping action for the pipe section 24.The large diameter portion 24A is formed with a pair of threaded holes 44 extending through the thickness thereof and opening into the axial bore 26 in a 180 degree angular spacing relationship about the major axis. An adjusting screw 46 consisting of a hexagon socket screw is screwed into each threaded hole 44. The large diameter portion 24A is additionally formed with a pair of threaded holes 48 extending through its thickness and opening into the axial bore 26 in a 180 degree angular spaced relationship about the major axis and in an axially offset manner with respect to the threaded holes 44. An adjusting screw 50 consisting of a hexagon socket screw is screwed into each threaded hole 48.Each adjustment screw 46, 50 has a tapered, conical free end adapted to engage the outer circumferential surface of the ball screw shaft 10 received in the axial bore 26.When the pitch of the ball screw shaft 10 is 5 mm, the axial offset between the threaded holes 44 and 48 may be 2.5 mm. According to this arrangement, when the thread pitch of the ball screw shaft 10 is 5 mm, 10 mm, and so on without reference to the angular position of the ball screw shaft 10 relative to the shaft end adapter 20 about the main axis, one of the adjustment screws 46 and / or one of the adjustment screws 50 engages with the thread groove 12 of the ball screw shaft 10 (or an outer part thereof other than the thread groove 12) (see FIGS. 5 and 6 ). Thereby, the adjusting screws 46 and 50 provide the function of a stopper that prevents the ball screw shaft 10 from axially slipping out of the axial bore 26 during the assembly process.The axial offset between the threaded holes 44 and 48 may thus be one-fourth the pitch of the ball screw shaft 10. In this case, without reference to the thread pitch of the ball screw shaft 10, at least one of the adjustment screws 46 and at least one of the adjustment screws 50 engage with the thread groove 12 of the ball screw shaft 10, and an advantageous stopper effect can be obtained.The assembling operation of the ball screw shaft 10 and the shaft end adapter 20 will be described below.First, when all of the fastening bolts 42 and the adjusting screws 46 are not tightened, one end of the ball screw shaft 10 is inserted into the axial bore 26 from the open end 26B thereof until the free end surface 10A of the ball screw shaft 10 abuts the bottom surface 26A of the axial bore 26.The two fixing screws 42 of each large diameter portion 24A, 24B are then tightened. This allows the slots 30 to reduce their width due to the elastic deformation of the material of the pipe section 24 disposed adjacent to the slots 30. The resultant frictional engagement between the outer circumferential surface of the ball screw shaft 10 and the inner circumferential surface of the axial bore 26 clamps the end of the ball screw shaft 10 through the shaft end adapter 20 so that the ball screw shaft 10 is integrally connected to the shaft end adapter 20.The portions of the axial bore 26 adjacent the open end 26B and the bottom surface 26A thereof that are axially spaced apart from each other define a circumferentially continuous inner circumferential surface having a same inner diameter as the remaining portions of the axial bore 26 through the first continuous portion 32 and the second continuous portion 34, and demonstrate high stiffness due to their fully closed annular cross-section. Therefore, even if the pipe portion 24 makes elastic deformation in the closing direction of the slits 30, these continuous parts 32 and 34 maintain a substantially circular configuration.Therefore, the parts of the axial bore 26 that are located adjacent to the open end 26B thereof corresponding to the first continuous portion 32 and the bottom surface 26A corresponding to the second continuous portion 34 that are axially spaced from each other are secured with high precision in coaxiality and axial straightness achieved in the manufacture of the axial bore 26. This ensures high precision in coaxiality and axial straightness in assembling the ball screw shaft 10 and the shaft end adapter 20 made by inserting the ball screw shaft 10 into the axial bore 26.Since the first continuous portion 32 defines a circumferential inner surface continuous with the axial bore 26 and the same diameter as the inner circumferential surface of the axial bore 26 disposed adjacent to the free end of the tubular portion 24, circularity of the adjacent part of the axial bore 26 can be ensured in an advantageous manner. These factors contribute to the improvement of the precision in the coaxiality and the axial straightness of the assembly of the ball screw shaft 10 and the shaft end adapter 20.Since the fastening bolts 42 are provided in the two large diameter portions 24A and 24B that are disposed axially spaced apart from each other and disposed adjacent to the axial terminal end of the slot 30, the fastening bolts 42 are allowed to narrow the slot 30 uniformly over the entire axial length thereof. For this reason, tilting of the major axis of the ball screw shaft 10 with respect to the major axis of the axial bore 26 can be minimized, and high precision in coaxiality and axial straightness of assembling the ball screw shaft 10 and the shaft end adapter 20 can be ensured.If the desired precision in the straightness of assembly cannot be obtained in the assembly of the ball screw shaft 10 and the shaft end adapter 20 by the tightening of the fastening bolts 42, the four adjusting screws 46 and 50 disposed at an angular interval of 90 degrees around the major axis of the axial bore 26 can be rotated until the free ends of the adjusting screws 46 and 50 abut on the outer circumferential surface of the ball screw shaft 10. By individually changing the thread feed of each of the adjusting screws 46, 50, the radial pressure applied to the ball screw shaft 10 by the adjusting screws 46 and 50 at a 90 degree angular interval can be adjusted.Thereby, the tilting of the major axis of the ball screw shaft 10 with respect to the major axis of the axial bore 26 can be finely adjusted, so that high precision in the straightness of the assembly can be obtained.The ball screw shaft 10 and the shaft end adapter 20 manufactured as two separate members can be assembled in an efficient manner with high precision in coaxiality and straightness simply by adjusting the screws.The second embodiment of the shaft end adapter and ball screw assembly will be described below with reference to FIGS. 8 and 9.The ball screw structure of this embodiment is composed of assembling a ball screw shaft 10 and a shaft end adapter 60. The shaft end adapter 60 has a fixing shaft portion 62 and a pipe portion 64 formed integrally with each other in a coaxial and axially straight manner.The tubular portion 64 is formed with an axial bore 66 for receiving one end of the ball screw shaft 10. The axial bore 66 is coaxial and axially linear with respect to the attachment shaft portion 62, and has a closed end, and opens only at the end surface 64D on the free end of the pipe portion 64, and defines a bottom surface 66A on the base side side (the attachment shaft portion 62 side). The axial bore 66 thus defines an open end 66B on the end surface 64D of the tubular portion 64. Preferably, the bottom surface 66A also extends perpendicular to the major axis of the axial bore 66. the axial bore 66 has a circular cross-section with an inner diameter equal to or slightly greater than the outer diameter of the ball screw shaft 10.The tubular portion 64 has four axial slots 70 at an angular interval of 90 degrees about the major axis. Each slit 70 is defined by a pair of planar opposite side surfaces while defining a small gap (a certain slit width) therebetween, and opens on both the outer circumferential surface of the pipe portion 64 and the inner circumferential surface of the pipe portion 64 defining the axial bore 66. each slit 70 terminates at a circumferentially continuous portion 72 (first continuous portion 72) in the part adjacent to the free end of the pipe portion 64 and a circumferentially continuous portion 74 adjacent to the base side of the pipe portion 64 (second continuous portion 74).More specifically, the first continuous portion 72 defines a circumferentially continuous inner circumferential surface having the same inner diameter as the axial bore 66 adjacent the free end of the tubular portion 64, and a circumferentially continuous planar end surface 64D. The second continuous portion 74 defines a circumferentially continuous surface having the same inner diameter as the first continuous portion 72 via a region axially extending between the terminal end of the slit 70 on the bottom surface 66A side of the axial bore 66 and the bottom surface 66A.The outer circumferential surface of the tube portion 64 includes an externally threaded portion 76, a first conical outer circumferential surface 78, and a second outer circumferential surface 80 in this order as viewed from its free end. The first conical outer circumferential surface 78 and the second conical outer circumferential surface 80 are arranged axially spaced apart from each other and have the same slope tapering towards the free end side. The slots 70 extend the entire length of the first conical outer circumferential surface 78 and the second conical outer circumferential surface 80 In particular, the first conical outer circumferential surface 78 and the second conical outer circumferential surface 80 are provided in parts of the pipe portion 64 disposed adjacent the respective terminal ends of the slot 70.Sleeve 82 is slid onto the outer peripheral surface of tube portion 64 and includes a conical bore 85 defined by a conical inner peripheral surface 84 engaging first conical outer peripheral surface 78 and second conical outer peripheral surface 80. An internal thread portion 88 of the fastening nut 86 engages the external thread portion 76 in a screw-like manner.The assembling procedure for the ball screw shaft 10 and the shaft end adapter 60 will be described below.First, when the fixing nut 86 is not tightened, one end of the ball screw shaft 10 is inserted into the axial bore 66 from the open end 66B thereof until the free end surface 10A of the ball screw shaft 10 abuts against the bottom surface 66A of the axial bore 66.The fixing nut 86 is then fixed, with the result that the clamping bush 82 is pressed toward the base side side. Due to the cooperation of the conical inner circumferential surface 84 with the first conical outer circumferential surface 78 and the second conical outer circumferential surface 80, the parts of the pipe portion 64 arranged adjacent to the slots 70 execute an elastic deformation, so that the width of each slot 70 is reduced and the slots 70 narrow. The resulting frictional engagement between the outer circumferential surface of the ball screw shaft 10 and the inner circumferential surface of the axial bore 66 causes the end of the ball screw shaft 10 to be clamped by the shaft end adapter 60, so that the ball screw shaft 10 is integrally connected to the shaft end adapter 60.According to this embodiment, since the parts of the axial bore 66 disposed adjacent to the open end 66B and the bottom surface 66A that are spaced apart from each other are each defined by a circumferentially continuous surface having the same inner diameter as the axial bore 66, and have high rigidity due to the annular cross-sectional configuration, these parts are resistant to elastic deformation and can maintain an actually circular shape even when the pipe portion 64 is caused to undergo elastic deformation by the fixing nut 86 moved in the closing direction of the slits 70.The portions of the axial bore 66 adjacent to its open end 66B corresponding to the first continuous portion 72 and the bottom surface 66A corresponding to the second continuous portion 74 which are axially spaced from each other are provided with high precision in coaxiality and axial straightness as achieved in the manufacture of the axial bore 66. This ensures high precision in coaxiality and axial straightness for assembling the ball screw shaft 10 and the shaft end adapter 60 made by fitting the ball screw shaft 10 into the axial bore 66.Since the first conical outer circumferential surface 78 and the second conical outer circumferential surface 80 are disposed at two different axial positions and adjacent to terminal axial ends of the slots 70, the slots 70 are smoothly closed over their entire length by the cooperation between the clamping bush 82 and the fixing nut 86. This factor also contributes to improvement of the precision in the coaxiality and the axial straightness of the assembly of the ball screw shaft 10 and the shaft end adapter 60.Since the first continuous portion 72 has a circumferentially continuous surface having the same inner diameter as the axial bore 66 in its part disposed adjacent to the free end of the tubular portion 64, it can be ensured that the adjacent part of the axial bore 66 is truly circular. Also, because the first continuous portion 72 defines a circumferentially continuous surface in the end surface 64D of the tube portion 64 on the open end side, the axial bore 66 can be secured as being actually circular in its part disposed adjacent to its open end. These factors contribute to the improvement of the precision in the coaxiality and the axial straightness of the assembly of the ball screw shaft 10 and the shaft end adapter 60.The ball screw shaft 10 and the shaft end adapter 60, which are made as two separate members, can be assembled in a highly efficient manner with high precision in coaxiality and straightness simply by fastening the fastening nut 86.The third embodiment of the shaft end adapter and the ball screw assembly will be described below with reference to FIGS. 10 and 11. In FIGS. 10 and 11, the parts corresponding to the parts shown in FIGS. 8 and 9 are denoted by the same reference numerals without necessarily repeating the description of these parts.In this embodiment, the outer circumferential surface of the pipe portion 64 includes a first conical outer circumferential surface 78, an externally threaded portion 76, and a second conical outer circumferential surface 80 in this order as viewed from the base side side, and each slit is divided into a first slit 70A formed in the first conical outer circumferential surface 78 and a second slit 70B formed in the second conical outer circumferential surface 80. The inner circumferential surface of the collet 82 is divided into a first conical inner circumferential surface 84A engaging the first conical outer circumferential surface 78 and a second conical inner circumferential surface 84B engaging the second conical outer circumferential surface 80, and an externally threaded portion 88 is formed on the collet 82.This embodiment is otherwise similar to the second embodiment and therefore has similar advantages to the second embodiment.The fourth embodiment of the shaft end adapter and the ball screw assembly will be described below with reference to FIGS. 12 and 13. In FIGS. 12 and 13, the parts corresponding to the parts shown in FIGS. 8 and 9 are denoted by the same reference numerals without necessarily repeating the description of these parts.In this embodiment, the outer circumferential surface of the pipe portion 64 includes a first conical outer circumferential surface 78, a first male threaded portion 76A, a second male threaded portion 76B, and a second conical outer circumferential surface 80 in this order as viewed from the free end side. The collet is divided into a first collet 90 having a conical bore 93 defining a first conical inner circumferential surface 92 engaging the first conical outer circumferential surface 78, and a second collet 94 having a second conical inner circumferential surface 96 engaging the second conical outer circumferential surface 80. The first collet 90 is formed with a first internally threaded portion 98 that is threaded onto the first externally threaded portion 76A, and the second collet 94 is formed with a second internally threaded portion 99 that is threaded onto the second externally threaded portion 76B.In this embodiment, the two sets of slots 70A and 70B may be individually closed by the movement of the first clamping bushing 90 and the second clamping bushing 94, respectively. Therefore, the clamping force at the slots 70A and the slots 70B can be individually adjusted, so that the coaxiality and the axial straightness between the ball screw shaft 10 and the shaft end adapter 60 can be accurately adjusted.The fifth embodiment of the shaft end adapter and the ball screw assembly will be described below with reference to FIGS. 14 and 15. In Figs. 14 and 15, the parts corresponding to the parts shown in Figs. 1 to 7 are denoted by the same reference numerals without necessarily repeating the description of these parts.In this embodiment, a shaft side flange portion 100, a small diameter shaft portion 102, and a pipe portion side flange portion 104 are integrally formed between the fixing portion 22 and the pipe portion 24. In other words, the shaft side flange portion 100 is integrally formed with the pipe portion side flange portion 104, which is in turn formed on the base side of the pipe portion 24 via the small diameter shaft portion 102.The shaft side flange portion 100 is formed with four through holes 106 axially extending through the shaft side flange portion 100 and distributed at an angular interval of 90 degrees. The pipe portion side flange portion 104 has four threaded holes 108 axially parallel with the through holes 106 and opening from the end surface (the end surface on the base side of the pipe portion 24) of the pipe portion side flange portion 104 facing the shaft side flange portion 100.An adjusting screw 110 consisting of a hexagon socket screw is inserted into each of the through holes 106 from the side remote from the pipe portion side flange portion 104, and is screwed with its free end into the corresponding threaded hole 108.In this embodiment, the axial compressive forces acting on the four positions of the pipe portion side flange portion 104 and arranged according to the 90 degree angular interval can be adjusted by individually adjusting the thread feed of the adjusting screws 110 into the corresponding threaded holes 108.By causing a bending deformation of the small diameter shaft portion 102 according to the variations in the screw advances of the four adjusting screws 110 into the corresponding screw holes 108, similarly to the adjusting screws 46 and 50 of the first embodiment, the tilting of the major axis of the ball screw shaft 10 with respect to the major axis of the axial bore 26 can be finely adjusted, so that high precision in the straightness of the assembly can be obtained.This embodiment is otherwise similar to the first embodiment and therefore has similar advantages to the first embodiment.The sixth embodiment of the shaft end adapter and the ball screw assembly will be described below with reference to FIG. 16. In FIG. 16, the parts corresponding to the parts shown in FIGS. 14 and 15 are denoted by the reference numerals used in FIGS. 1 to 7 without necessarily repeating the description of these parts.In this embodiment, the shaft side flange portion 100 is formed with four threaded holes 112 axially extending through the shaft side flange portion 100 and spaced at an angular interval of 90 degrees. An adjusting screw 114 consisting of a hexagon socket screw is screwed into each threaded hole 112 from the side remote from the pipe portion side flange portion 104. The free end of the adjusting screw 114 abuts against the end surface (base side surface of the pipe portion 24) of the pipe portion side flange portion 104 facing the shaft side flange portion 100.In this embodiment, the axial pressures acting on the four positions of the pipe portion side flange portion 104 and arranged at an angular interval of 90 degrees can be adjusted by individually adjusting the thread feed of the adjusting screws 114 in the respective threaded holes 112.By causing a bending deformation of the small diameter shaft portion 102 according to the variations in the screw advances of the four adjusting screws 114 into the corresponding screw holes 112 similarly to the adjusting screws 46 and 50 of the first embodiment, the tilting of the major axis of the ball screw shaft 10 with respect to the major axis of the axial bore 26 can be finely adjusted, so that high precision in the straightness of the assembly can be obtained.This embodiment is otherwise similar to the first embodiment and therefore has similar advantages to the first embodiment.The seventh embodiment of the shaft end adapter and the ball screw assembly will be described below with reference to FIG. 17. In FIG. 17, the parts corresponding to the parts shown in FIG. 4 are denoted by the same reference numerals without necessarily repeating the description of these parts.In this embodiment, a differential screw mechanism is used as the fixing mechanism (clamping member) for the slots 30. The differential screw mechanism will be described below.For each slot 30, the pipe portion 24 has a first internal threaded hole 132 extending into the slot 30 from one side (lower side in FIG. 17 ) of the pipe portion 24 with respect to the slot 30, and a second internal threaded hole 134 having a larger diameter than the first internal threaded hole 132 extends from the other side (upper side in FIG. 17 ) of the pipe portion 24 with respect to the slot 30 into the slot 30 in a coaxial relationship to the first internal threaded hole 132.A first male threaded member 136 having a hex-engaging recess 138 is threaded into the female threaded hole 132. A second male threaded member 140 having a hex-engaging recess 144 is threaded into the second female threaded hole 134. The second male threaded member 140 is formed centrally with a third female threaded hole 142, and the first male threaded member 136 is screwed into the third female threaded hole 142.When the first female threaded member 136 is held in position in the hex engagement recess 138 by engagement of a wrench (not shown in the drawings), the second male threaded member 140 is rotated in the direction to increase the thread feed of the first male threaded member 136 with the third female threaded hole 142, for example, clockwise, thereby causing the second male threaded member 140 to move toward the slot 30 (or downward in FIG. 17 ).When the second male threaded member 140 advances by screwing, the part 24U of the pipe portion 24 on the other side (upper side in FIG. 17 ) of the slit 30 makes elastic in the opposite direction to the advancing direction of the second male threaded member 140, which results in the width of the slit 30 being increased and the pipe portion 24 being enlarged in the radial direction.Thereby, even if the fit between the axial bore and the ball screw shaft 10 is tight to achieve high precision in coaxiality, the ball screw shaft 10 can be easily inserted into the axial bore 26.Once the ball screw shaft 10 is fully inserted into the axial bore 26, the ball screw shaft 10 is secured to the shaft end adapter 20 as described below. When the first male threaded member 136 is held similar to the increase in diameter of the tubular portion 24, the second male threaded member 140 is rotated in the direction to reduce the thread feed of the first male threaded member 136 with the third female threaded member 142, for example, in the counterclockwise direction, thereby retracting the second male threaded member 140 from the slot 30 (or upward in FIG. 17 ).By such a retracting movement of the second male screw member 140, the elastic deformation of the part 24U of the pipe portion 24 disposed on the other side of the slit 30 is removed, and the width of the slit 30 is restored to its original size. As a result, the radial enlargement of the tubular portion 24 is canceled, and the resultant force restricting the slit 30 leads to fastening of the ball screw shaft 10 to the tubular portion 24.When the first female threaded member 136 is held, the second male threaded member 140 may be rotated in the direction for further retraction of the second male threaded member 140 (or for upward movement in FIG. 17 ), thereby elastically deforming the portion 24U of the pipe portion 24 disposed on the other side of the slot 30 in the direction opposite to the direction of retraction of the second male threaded member 140. This narrows the width of the slot 30 and the tubular portion 24 contracts in the radial direction. As a result, the ball screw shaft 10 is clamped to the shaft end adapter 20 with the clamping force described above. The final tightening torque should be controlled in proportion to the mechanical strength of the first male threaded member 136 so that the threaded engagement is not destroyed.Although the present invention has been described in terms of its preferred embodiment, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the present invention.For example, the inner diameter of the first continuous portions 32, 72 disposed adjacent the open end 26B, 66B of the axial bore 26, 66 and the second continuous portion 34, 74 disposed adjacent the bottom surface 26A, 66A may be smaller than the inner diameter of the remaining parts of the axial bore 26, 66. the second continuous portion 34 is not essential to the present invention, and high precision in the coaxiality and axial straightness of the ball screw shaft 10 and the shaft end adapter 20 obtained in the manufacture of the axial bore 26 may be achieved with the first continuous portion 32 alone. The first continuous portion 32 does not need to define a circumferential continuous surface at the end surface 24D of the pipe portion 24 adjacent to the open end 26B but at a part spaced from the end surface 24D toward the base side side.The number of the slits 30 and 70 is not limited to two or four, but may be one, three, or any other number. The fastening bolts 42 need not be provided at two locations, but may be provided at three or more locations. The number of the adjusting screws 46 and 50 is not limited to four, but may be two, three or more. The shaft element does not have to be a ball screw shaft, but can also be any other shaft element.The components shown in the foregoing embodiments are not necessarily essential to the present invention, but may be partly omitted or replaced without departing from the spirit of the present invention.LIST OF REFERENCE CHARACTERS1 Ball screw assembly 10 Ball screw shaft (shaft member) 10A Free end surface 12 Threaded member 14 Ball nut 20 Shaft end adapter 22 Fixing shaft portion 24 Pipe portion 24A Large diameter portion 24B Large diameter portion 24C Small cross-sectional portion 24D End surface 24U Part 24L Part 26 Axial bore 26A Bottom surface 26B Open end 30 Slit 32 First continuous portion 34 Second continuous portion 36 Bolt fixing recess 36A Seat surface (shoulder surface) 38 Bolt receiving hole 40 Threaded hole 42 Fixing bolt (clamping member) 42A Shoulder surface 42B Threaded portion 44 Threaded hole 46 Adjusting screw (screw member) 48 Threaded hole 50 Adjusting screw (screw member) 60 Shaft end adapter 62 Fixing shaft portion 64 Pipe portion 64D End surface 66 Axial bore 66A Bottom surface 66B Open end 70 Slit 70A First slit 70B Second slit 72 First continuous portion 74 Second continuous portion 76 External thread portion 76A First external thread portion 76B Second external thread portion 78 First conical outer circumferential surface 80 Second conical outer circumferential surface 82 Clamping bush (clamping member) 84 Conical inner circumferential surface 84A First conical inner circumferential surface 84B Second conical inner circumferential surface 85 Conical bore 86 Fixing nut (clamping member) 88 Internal thread portion 90 First clamping bush (clamping member) 92 First conical outer circumferential surface 93 Conical bore 94 Second clamping bush (clamping member) 96 Second conical inner circumferential surface 97 Conical bore 98 First internal thread portion 99 Second internal thread portion 100 Shaft side flange portion 102 Small diameter shaft portion 104 Pipe portion side flange portion 106 Through hole 108 Threaded hole 110 Adjusting screw (screw member) 112 Threaded hole 114 Adjusting screw (screw member) 132 First internally threaded hole 134 Second internally threaded hole 136 First externally threaded hole 138 Hexagonal engagement recess 140 Second internally threaded hole 142 Third internally threaded hole

Claims

A shaft end adapter (20) comprising: a tubular portion (24) having an axial bore (26) defining an opening for receiving an end of a shaft member (10) at a free end of the tubular portion (24), the tubular portion (24) being formed at or adjacent to its portion adjacent the free end with a circumferentially continuous portion (32) and with an extending slot (30) axially through a wall of the tubular portion (24) excluding the circumferentially continuous portion (32), the tubular portion (24) being formed at or adjacent to its free end in part with a large diameter portion (24B); and a clamping member mounted on the pipe portion (24) and adapted to narrow the slit (30), wherein the clamping member comprises a fastening bolt (42) screwed into the pipe portion (24) and extending across the slit (30), wherein the large diameter portion (24B) defines a bolt fastening recess (36) into which a bolt receiving hole (38) opens, and wherein the bolt receiving hole (38) is configured such that the fastening bolt (42) is inserted into the bolt receiving hole (38) to be screwed into the pipe portion (24).The shaft end adapter (20) of claim 1, wherein the circumferentially continuous portion (32) defines a circumferentially continuous inner circumferential surface disposed adjacent an open end (26B) of the axial bore (26).The shaft end adapter (20) according to claim 1, wherein the circumferentially continuous portion (32) is a part of an axial end surface (24D) of the pipe portion (24) disposed at or adjacent to a free end of the pipe portion (24) as a circumferentially continuous surface.The shaft end adapter (20) of any of claims 1 to 3, wherein a plurality of threaded holes (44, 48) extend radially through the tubular portion (24) at circumferentially different positions, each defining an open end in the axial bore (26), and wherein when a screw member (46, 50) is threaded into each of the threaded holes (44, 48), an end of the screw member (46, 50) abuts an outer circumferential surface of the shaft member (10).The shaft end adapter (20) of claim 4, wherein the shaft member (10) comprises a ball screw shaft, and at least one of the screw members (46, 50) is adapted to engage a threaded groove (12) of the ball screw shaft.The shaft end adapter (20) according to any one of claims 1 to 3, wherein a pipe portion side flange portion (104), a shaft portion (102), and a shaft side flange portion (100) connected to the pipe portion side flange portion (104) via the shaft portion (102) are integrally formed with a base side portion of the pipe portion (24) axially away from a free end thereof, and wherein a plurality of through holes (106) axially extend through the shaft side flange portion (100) at different circumferential positions, while the pipe portion side flange portion (104) is formed with a plurality of threaded holes (108) aligned with the corresponding through holes (106) of the shaft side flange portion (100) and opening toward an end surface thereof, and wherein each of the through holes (106) is inserted with a screw member (110), respectively, and screwed into the corresponding threaded hole (108).The shaft end adapter (20) according to any one of claims 1 to 3, wherein a pipe portion side flange portion (104), a shaft portion (102), and a shaft side flange portion (100) connected to the pipe portion side flange portion (104) via the shaft portion (102) are integrally formed with a base side portion of the pipe portion (24), the base side being disposed axially away from a free end thereof of the pipe portion (24), and the pipe portion side flange portion (104) is formed with a plurality of circumferentially disposed threaded holes (112) extending therethrough, and a screw member (114) is screwed into each of the threaded holes (112) so as to abut an end surface of the shaft side flange portion (100).The shaft end adapter (20) according to any one of claims 1 to 7, wherein the clamping element comprises two fastening bolts (42) screwed into the pipe section (24) and extending across the slot (30) at two axial positions.A shaft end adapter (60) comprising: a tubular portion (64) having an axial bore (66) defining an opening for receiving an end of a shaft member (10) at a free end of the tubular portion (64), the tubular portion (64) being formed at or adjacent to the portion thereof adjacent the free end with a circumferentially continuous portion (72) and with a slot (70) extending axially through a wall of the tubular portion (64) excluding the continuous portion (72); and a clamping member (82, 86, 90, 94) mounted on the pipe portion (64) and configured to narrow the slit (70), wherein an outer circumferential surface of the pipe portion (64) is formed with a conical outer circumferential surface (78, 80) at each of at least two of its axial positions, and wherein the clamping member comprises a clamping bushing (82, 90, 94) fitted on the pipe portion (64) and formed with a conical bore defining a conical inner circumferential surface (84, 84A, 84B, 92, 96) to come into contact with the corresponding conical outer circumferential surfaces.A ball screw assembly (1) comprising a shaft end adapter (20; 64) according to any one of claims 1 to 9 and a ball screw shaft secured thereto.

Images