1. Field of the Invention
The present invention relates to ball screw modules, and more particularly, to a ball screw module having a circulating device mounted on a nut member thereof.
2. Description of the Prior Art
The operating principles of a conventional ball screw shaft involve providing balls between a screw shaft and a nut member so as to replace the sliding friction transmission of an outdated acme screw shaft (ACME) with ball rolling motion, thereby reducing friction-induced wear and tear greatly and maintaining high efficiency and high preciseness.
Balls are effective in enabling a screw shaft to move smoothly. However, adjacent balls are, in the course of rolling, likely to collide with each other and therefore produce much noise. The collision shortens the service life of the balls and therefore shortens the service life of the screw shaft.
To solve the problems, the prior art disclosed a connector whereby balls are fixed in position. U.S. Pat. No. 5,993,064 further provides an improved ball connector made of resilient material and comprising four belt members for fixing a plurality of balls in position in all directions, and a ball connector capable of bending freely in all directions and yet keeping the respective positions of the balls unchanged, such that the ball connector is applicable to linear sliding and ball screw shafts.
However, a ball screw module requires a circulating route for guiding the balls returning to a spiral-shaped groove so as to travel along a continuous ball track. A ball connector passing the circulating route has to change its direction of movement so as for the ball connector to follow a loop. An improperly designed circulating route is likely to prevent a ball connector from passing a circulating route smoothly and changing direction. Ball connectors disclosed in the prior art tend to sever when twisted and pulled unduly. Referring to
To solve the aforesaid problems, it is the primary objective of the present invention to provide a ball screw module comprising a ball connector revolving smoothly in a nut member so as to achieve high performance and high preciseness of the ball screw module.
Another objective of the present invention is to provide a ball screw module comprising a nut member, and a circulating device mounted on the nut member and configured to move a ball connector along a continuous circulating route (endless track).
The circulating device of the present invention at least comprises a guiding groove (preferably two guiding grooves) for guiding a ball connector, so as to guide the ball connector through revolutions smoothly. The length of the guiding grooves in each section approximates to the length of the center line of the circulating route such that, while the ball connector is turning around at a bend of the circulating route, the length of the center line of the ball connector approximates to the length of the guiding grooves laterally (or bilaterally) provided for the ball connector, thereby preventing the ball connector from being pushed or dragged which might otherwise occur in the presence of a great difference in length between the guiding grooves and the ball connector in a section. Hence, the present invention allows the ball connector to move smoothly without being dragged or pushed unduly.
A ball screw module of the present invention essentially comprises a screw shaft, a nut member, a ball connector, and a circulating device. The screw shaft has an outer surface provided with a spiral-shaped first load rolling groove. The nut member is circumferentially disposed around the screw shaft and has an inner surface provided with a spiral-shaped second load rolling groove corresponding in position to the first load rolling groove. The first and second load rolling grooves together form a spiral-shaped first rolling track. The first rolling track rolls in a first spiral direction. The aforesaid spiral direction is right-handed or left-handed. A right-handed spiral direction of advance is defined by the direction of the thumb of the right hand with the other four fingers of the right hand bending and pointing at the direction of revolution. Conversely, a left-handed spiral direction of advance is defined by the direction of the thumb of the left hand with the other four fingers of the left hand bending and pointing at the direction of revolution. The ball connector, which moves within the first rolling track, comprises a plurality of balls and a connector for carrying the balls. The connector further comprises a plurality of intervals and at least a linking strap. The connector is reinforced by means of two linking straps, namely a first linking strap and a second linking strap. The balls are fixed in position and spaced apart from each other by the intervals. The first linking strap and/or the second linking strap are configured to connect the intervals in series. The first linking strap and the second linking strap are spaced apart from each other by a distance, allowing the balls to be steadily positioned between the intervals, the first linking strap, and the second linking strap. The circulating device, which is mounted on the nut member, comprises a circulating route with two ends in communication with the first rolling track. The cross-sectional radius of the circulating route is slightly greatly than the radii of the balls so as to enable the ball connector to pass the circulating route. To guide the ball connector moving smoothly, the circulating route further comprises an intermediate route and connecting routes each having one end in communication with a corresponding one of the two ends of the intermediate route. The other end of each of the connecting routes is in communication with the first rolling track. The circulating route is further provided with a guiding groove formed along the circulating route. In the situation where the connector has two linking straps, the number of the guiding grooves must be two. The guiding grooves are configured to guide the first linking strap and/or the second linking strap of the ball connector. As disclosed in the present invention, construction and configuration of the guiding grooves are based on 3D geometrical analysis and are configured to guide the ball connector revolving, in the connecting route, relative to the center line of the circulating route and in the second spiral direction, wherein the second spiral direction is opposite to the first spiral direction in which the first rolling track rolls. If the first spiral direction is right-handed, the second spiral direction is left-handed. Conversely, if the first spiral direction is left-handed, the second spiral direction is right-handed. The guiding grooves guide the ball connector revolving, in the intermediate route, relative to the center line of the circulating route and in the third spiral direction, wherein the third spiral direction is the same as the first spiral direction. The ball connector take the course in the sequence “connecting route—intermediate route—connecting route” so as to go through all the bends and loops smoothly.
Compared to the prior art, the present invention has the following advantages. A circulating device of a ball screw module of the present invention is equipped with special guiding grooves twisted in different directions along a circulating route having connecting routes and an intermediate route, so as to guide a ball connector through bends and looping. The length of the guiding grooves bilaterally (or laterally) provided for the circulating route approximates to the length of the circulating route, and thus linking straps of the ball connector are unlikely to be dragged or pushed unduly while passing the circulating route.
The invention as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
The present invention is directed to a ball screw module which comprises a screw shaft, a nut member, and a circulating device and is based on mechanism transmission principles comprehensible to persons ordinarily skilled in the related art, and thus the related mechanism transmission principles are not described in detail hereunder. Also, the accompanying drawings solely serve an illustrative purpose and therefore are not drawn to scale.
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To enable the guiding grooves 416 to guide the ball connector 300 passing the connecting routes 414, the outer length of the guiding grooves 416 must decrease and the inner length of the guiding grooves 416 must increase such that, in the course of the turning of the connecting routes 414 entering the intermediate route 412, the guiding grooves 416 should equal the center line of the circulating route 410 in length as much as possible. The guiding grooves 416 guide the ball connector 300 revolving around the center of the circulating route in a second spiral direction S2/M2, allowing the ball connector 300 moving in a second moving direction M2 to revolve in a second screw direction S2, wherein the second spiral direction S2/M2 is opposite to the first spiral direction S1/M1 in which the first rolling track 230 rolls. In the first preferred embodiment, the second spiral direction S2/M2 is left-handed. It is because that the connecting routes 414 and the intermediate route 412 assume spherical three-dimensional configuration from a cross-sectional perspective, and thus the guiding grooves 416 should tilt toward the inside of a bend so as to decrease the length of the guiding grooves 416. Conversely, the guiding grooves 416 should tilt toward the outside of a bend so as to increase the length of the guiding grooves 416. Hence, the present invention teaches adjusting the length of the two guiding grooves 416 by means of the three-dimensional spatial characteristics. To enable the guiding grooves 416 to guide the ball connector 300 passing the intermediate route 412, the guiding grooves 416 guide the ball connector 300 revolving around the center of the circulating route in a third spiral direction S3/M3, allowing the ball connector 300 moving in a third moving direction M3 to revolve in a third screw direction S3, wherein the third spiral direction S3/M3 is the same as the first spiral direction S1/M1 in which the first rolling track 230 rolls. In the first preferred embodiment, the third spiral direction S3/M3 is right-handed.
The connector of the ball screw module is configured to carry the balls and space apart the intervals by a fixed distance so as to prevent the balls in motions from colliding with each other, thereby prolonging the service life the balls. Also, with the guiding grooves being formed in the circulating device, the ball connector changes its own direction while traveling along a specific route within the circulating device, thereby allowing the ball connector to revolve continuously. Since the length of the guiding grooves which flank the ball connector are equal and roughly amount to the length of the center line of the circulating route, the first linking strap and the second linking strap of the ball connector are unlikely to be dragged or pushed unduly in the turning sections, and in consequence the ball connector moves around within the ball screw module smoothly and efficiently.
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The foregoing specific embodiments are only illustrative of the features and functions of the present invention but are not intended to restrict the scope of the present invention. It is apparent to those skilled in the art that all equivalent modifications and variations made in the foregoing embodiment according to the spirit and principle in the disclosure of the present invention should fall within the scope of the appended claims.
Number | Date | Country | Kind |
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097133028 | Aug 2008 | TW | national |