AXIAL ACTUATOR

Abstract: An axial actuator (1) wherein an output rod (5) is con­ trolled axially by a recirculating-ball screw-nut screw coupling (40), the screw of which is formed on the rod (5), and the nut screw (39) of which is supported in rotary and axially-fixed manner on a support (2) and rotated in relation to the same by a motor (6); the nut screw (39) constituting the intermediate ring of a double thrust bearing (42) mounted, via the inter­ position of a flexible support (49), between two opposite surfaces on the support (2).

Description: The present invention relates to an axial actuator. On known axial actuators, the output member comprises a screw designed to move axially by virtue of a nut screw mounted in axially-fixed manner on a support and rotated in relation to the same by a motor or other drive member directly or, as disclosed by EP-A-0 226 065, through a reduction gear. Known actuators of the aforementioned type usually present a relatively complex, high-cost structure, particularly as regards connection of the nut screw to the said support, which connection normally involves using taper roller bearings or a number of separate rolling bearings as disclosed in GB-A-1 183 720. The aim of the present invention is to provide an axial actuator of the type described above, that is of the type in which the nut screw is coupled to the relevant support by means of rolling bearing means, wherein connection of the nut screw and respective support is straightforward and cheap, and involves a minimum number of parts, thus enabling the formation of a highly compact, reliable assembly. With this aim in view, according to the present invention, there is provided an axial actuator comprising an axially-mobile output rod, and drive means for so moving the same, the said drive means comprising a support fitted through with the said rod; a screw-nut screw coupling wherein the screw is integral with the said rod, and the nut screw is supported in rotary and axially-fixed manner on the said support; and a motor connected to the said nut screw so as to turn it about it own axis; characterised by the fact that the said nut screw constitutes the intermediate ring of a double thrust rolling bearing mounted between two opposite faces on the said support. A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which : Fig.1 shows a partially-sectioned plan view of a preferred embodiment of the actuator according to the present invention; Fig.2 shows a section along line II-II in Fig.1; Fig.3 shows a section along line III-III in Fig.1; Fig.4 shows a section along line IV-IV in Fig.1; Fig.5 shows a section along line V-V in Fig.1; Fig.6 shows a section along line VI-VI in Fig.1. Number 1 in Fig.2 indicates an axial actuator comprising a box body 2 consisting of a cup-shaped body 3 closed by a cover 4. Actuator 1 also comprises a through output rod 5 extending through body 3 and cover 4, and powered axially by an electric motor 6 supported on a housing 7 connected to cover 4 and housing part of a drive 8 connecting motor 6 to rod 5. Body 3 comprises an end wall 9 and a side wall 10 defining a substantially cylindrical cavity 11 coaxial with rod 5; and an outer lateral appendix 12 integral with wall 10 and terminating with a flange 13 coplanar with the open end of cavity 11. Cover 4 is defined by a substantially flat plate extending in contact with both the free end of wall 10 and flange 13, so as to form a cover for casing 7. The said housing 7 comprises a cup-shaped body 14 contacting cover 4 and having its concave side facing that of the cup-shaped body 3, and is defined by a side wall 15 having an end flange 16, and by a flat end wall 17 parallel with cover 4 and supporting motor 6. As shown in Fig.s 1 and 6, from flange 16 there extend two locating pins 18, each of which engages a through hole 19 on cover 4, and a through hole 20 on flange 13. As shown in Fig.s 1 and 2, a number of screws 21 connect flanges 13 and 16 with cover 4 inbetween. As shown, particularly in Fig. 3, motor 6 is located over flange 13 and to the side of rod 5, and presents an output shaft extending inside housing 7 through hole 22 in wall 17, and fitted with a cylindrical gear 23 constituting the input member of drive 8. As shown, particularly in Fig.s 3, 4 and 5, drive 8 comprises a reduction gear 24 substantially housed inside housing 7 and in turn comprising a first shaft 25 mounted in idle manner, at one end, inside hole 26 through wall 17, and, at the other end, inside coaxial holes 27 and 28 through cover 4 and in flange 13. Shaft 25 is fitted with a cylindrical gear 29 connected to gear 23, and a second cylindrical gear 30 smaller in diameter than gear 29. Reduction gear 24 also comprises a second shaft 31 mounted in idle manner, at one end, inside hole 32 through wall 17, and, at the other end, inside a dead axial hole 33 in wall 10. Shaft 31 is parallel with shaft 25, and is fitted with a cylindrical gear 34 connected to gear 30, and a second cylindrical gear 35 smaller in diameter than gear 34 and housed in rotary manner partly inside through hole 36 in cover 4, and partly inside a groove 37 formed on the inner surface of wall 10 and communicating with cavity 11. Gear 35 constitutes the output member of reduction gear 24, and is connected to a gear 38 formed on the outer surface of a cylindrical coupling 39 constituting the nut screw of a recirculating-ball screw-nut screw coupling indicated as a whole by 40 and the screw 41 of which is formed along rod 5. As shown, particularly in Fig.s 2 and 5, coupling 39 constitutes the intermediate ring of a double thrust bearing 42, and presents, on its opposite axial ends, two tracks 43 for sets of balls 44 supporting coupling 39 in rotary manner on two outer rings 45 and 46. Ring 45 rests on the bottom of a cavity 47 formed in wall 9 and coaxial with hole 48 formed through wall 9 and engaged by rod 5. Via the interposition of a Belleville waser 49, ring 46 rests on the bottom of a cavity 50 formed in cover 4 and coaxial with hole 51 through cover 4, and hole 52 through wall 17, both engaged by rod 5. Formation of the nut screw on coupling 40 as an integral part of double thrust bearing 42 clearly provides for a highly reliable, straightforward, low-cost, compact structure designed, also by virtue of Belleville washer 49, to withstand continual reciprocating motion. Actuator 1 as described therefore provides an ideal, highly reliable solution for all applications requiring efficient, straightforward, low-cost control of reciprocating members.

Claims: An axial actuator comprising an axially movable output rod (5), and drive means for so moving the same, the said drive means comprising a support (2) fitted through with the said rod (5); a screw-nut screw coupling (40) wherein the screw (41) is integral with the said rod (5), and the nut screw is supported in rotary and axially-fixed manner on the said support (2); and a motor (6) connected to the said nut screw so as to turn it about its own axis; characterised by the fact that the said nut screw constitutes the intermediate ring (39) of a double thrust rolling bearing (42) mounted between two opposite faces on the said support (2). An actuator as claimed in Claim 1, characterised by the fact that the said coupling (40) is a recirculating-ball screw-nut screw coupling. An actuator as claimed in Claim 1 or 2, characterised by the fact that flexible thrust means (49) are provided between the said double bearing (42) and one of the said faces. An actuator as claimed in Claim 3, characterised by the fact that the said flexible thrust means (49) comprise a Belleville washer. An actuator as claimed in any one of the foregoing Claims, characterised by the fact that the said double bearing (42) comprises two end rings (45, 46), an intermediate ring, and a set of balls (44) between the said intermediate ring and each end ring (45, 46); the said intermediate ring comprising a cylindrical coupling (39) constituting the said nut screw and having, at each opposite axial end, a track (43) for a respective said set of balls (44). An actuator as claimed in any one of the foregoing Claims, characterised by the fact that the said motor (6) is located to the side of the said rod (5); drive means (8) being supported on the said support (2) for connecting the said motor (6) to the said nut screw. An actuator as claimed in Claim 6, characterised by the fact that the said drive means (8) comprise a reduction gear (24).

Inventors: BRUSASCO, ENZO
Applicants: ROLTRA-MORSE S.P.A.
Application year: 1988
Main classification: F16H25
IPC codes: F16H25