MEANS TO TRANSFORM A ROTATIONAL MOVEMENT OF A THREADED SPINDLE INTO AN AXIAL MOVEMENT OF A NUT

Abstract: Means for transforming rotary movement of a spindle (1) that has helical threads (2) to axial movement of a nut (3) embracing the spindle (1), and conversely for transforming axial movement of the nut to rotary movement of the spindle, comprises elements which are disposed between the spindle (1) and the nut (3) and which lie along at least two mutually parallel and mutually spaced peripheral lines around the spindle (1). Respective elements are comprised of a crown roller (11) which forms, on the one hand, a roller body-part (12) and, on the other hand, a ball race (13). The roller body-part (12) is adapted to engage the threads (2) of the spindle, and the ball race (13) is positioned so as to face away from the axis of the spindle (1) and lie in a plane which extends perpendicular to and has its rotational centre in a line passing through the spindle axis and the centre of the spherical part (12). Bearing balls (15) are disposed between the ball race (13) and the nut (3), and two mutually adjacent crown rollers (11) engage with mutually proximal or mutually distal thread flanks of the thread (2) or the threads.

Description: MEANS TO TRANSFORM A ROTATIONAL MOVEMENT OF A THREADED SPINDLE INTO AN AXIAL MOVEMENT OF A NUT The present invention relates to means according to the preamble of Claim 1. The invention provides a completely novel solution to transforming rotary movement of a threaded spindle to linear movement of a nut, or conversely for transforming linear nut movement to rotary spindle movement. The invention solves the problems hitherto encountered with known ball screws, i.e. problems such as high friction and therewith high heat generation, loud noise, restricted speed, relatively poor efficiency and the inability to take-up obliquely acting forces. The invention as defined in the characterizing clauses of respective Claims provides a means with which friction is restricted completely to purely rolling friction, i.e. negligible friction, and which withstands high rotary speeds and obliquely acting forces, which is silent and which can work in the total absence of axial play. The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings, in which Fig. 1 is a schematic part- sectional view of a spindle-nut with which the invention is applied; Fig. 2 is a part-sectional view seen in an axial direction along the line II-II in Fig. 1; Figs. 3 and 4 illustrate a crown roller in side view and from above respectively, said crown roller forming part of the inventive means; Fig. 5 is a partially sectioned side view of another embodiment of the crown roller; Fig. 6 is a side view of another crown roller embodiment; Fig. 7 illustrates a ball holder for the purpose of clarifying the invention; Fig. 8 is a view from one end of a member included in the described embodiment; Figs. 9 and 10 illustrate respectively two other embodiments of the invention; Fig. 11 illustrates very schematically an example of another form of crown roller; and Fig. 12 illustrates schematically examples of different arrangements of crown rollers along the spindle. Fig. 1 illustrates a spindle 1 having threads 2 and including one or more thread leads. The threads are only shown schematically in Figs. 1 and 2. The spindle 1 is embraced by a nut 3, which will be described in more detail hereinafter. The nut 3 shown in Fig. 1 includes two rings or sleeves 4 which include radially extending openings 5. These openings accommodate ball bearing rings 6 which are held radially outwards in place in the openings 5 with the aid of sleeves 7. As will be evident from Figs. 1 and 2, the ball bearing rings extend beyond the outer periphery of the rings 4, and the sleeves 7 are thus provided with corresponding recesses 8 which extend in the axial direction of the sleeves 7. When assembling the nut 3, the sleeve 7 is pushed in over the ring 4 with the recesses 8 engaging around the ball bearing rings 6. The rings 4 are held in place against each other with the aid of end-walls 9, which are locked to one another and to the nut by means of bolts 10 (Fig. 1) disposed uniformly around the end-walls. Disposed between the nut 3 and the spindle 1 are a number of elements which each including a crown roller 11. The crown roller is comprised of a hemispherical roller-body part 12 and a roller race 13 coaxial with said body-part 12. The crown roller 11 is rotatably mounted about its symmetry axis 14 (Figs. 3 and 6) in the nut 3 by means of ball bearing balls 15 which roll in the ball race 6. In the illustrated embodiment, the balls are separated with the aid of a ball holder 16. The crown roller 11 can be said to be planet-mounted by means of the ball bearing balls 15 in the nut 3. The crown rollers 11 of two mutually adjacent elements are intended to engage respective opposing flanks of the thread of the spindle, i.e. at points 17 shown in Figs. 1 and 9. Thus, in the illustrated case, the distance a. (Fig. 11) between the symmetry lines 14 of two mutually adjacent crown rollers will be smaller than the distance between the two illustrated thread grooves as measured along the line connecting said two points 17. It will be understood that the spherical parts of the crown rollers 11 may instead engage the mutually distal flanks of the thread grooves, i.e. the distance a. between the symmetry axes of two crown rollers will be greater than the distance between the threads as measured along said line through the points 17. The distance between the symmetry axes 14 of the crown rollers is defined by the mutual abutment of the rings 4. In order to achieve this precise distance between the ball bearing rings 6, and therewith between the crown rollers 11, by appropriate dimensioning of the rings 4 of the embodiment illustrated in Figs. 1 and 2, the sleeves 7 will be coaxially somewhat shorter than the rings 4 so as not to affect this distance, as indicated in Fig. 1. The distance or spacing between said elements may also be adjusted with the aid of washers for instance, which can be placed between the two rings 4 {this is not shown). Thus, as the spindle 1 rotates with the nut stationary, the crown roller 11 will roll along the generatrix of the point 7 and rotate about its symmetry axis 14 by virtue of its planet bearing in the nut 3, with the aid of the ball bearing balls 15 and the ball bearing rings 6. For clarifying purposes, Figs. 3 and 4 show respectively a crown roller from one side and from above, as described with reference to Figs. 1 and 2. Fig. 5 illustrates another embodiment of the crown roller. In this case, the crown roller is comprised of a ball 18 and a ball seating 19 which, in turn, includes the ball race 13. Fig. 6 illustrates an advantageous embodiment of the crown roller 11, in which the ball race 13 is formed directly in the hemi-spherical part of the crown roller, this configuration saving space and being beneficial from a manufacturing/technical aspect. To facilitate an understanding of the invention, Fig. 7 illustrates the ball holder 16 schematically from above. It will noted that the ball holder is not necessary to the function of the invention. Fig. 8 is an end view of a sleeve 7 and clearly shows the recesses 8 that accommodate the ball races 6. Fig. 9 is a schematic illustration of another proposed coupling of the rings 4, wherewith the crown rollers used are the crown rollers shown in Fig. 6. One of these has a peripherally outer left-hand thread 20 for instance, and the other an outer right- hand thread 21. A ring 22 having an inner right-hand thread and a left-hand thread respectively embraces the threaded parts of respective sleeve 4 and coacts with their threads 20 and 21. The sleeves 4 will be moved towards or away from each other as the ring 22 is turned, depending on the direction in which the ring 22 is turned. Thus, subsequent to mounting the nut 3 on the spindle 1, the distance between the elements can be set precisely with the aid of the ring 22, therewith completely avoiding any axial play. When mounted, the ring 22 can be locked in the position intended with the aid, e.g., of locking screws (not shown) , by locking the ring 22 between the sleeves 7 with the aid of bolts, e.g. 10, or by other means obvious to the skilled person. Alternatively, it is feasible to provide a common ring or sleeve 4 with two parallel, circumferentially extending rows of holes with a precise distance between the rows, for accommodating the ball races 6. There is no possibility of making adjustments between the rows of inventive elements in this particular case. Fig. 10 illustrates a further embodiment of a crown roller 11 used with the inventive means, said crown roller comprising a completely spherical ball in this case. The ball race 13 of the illustrated crown roller 11 is formed by the generatrix of the points at which the balls 15 of the ball bearings contact or roll on the ball 11. This crown roller embodiment is naturally an attractive solution from a technical aspect of manufacture and functions in the same way as the crown roller embodiments illustrated in Figs. 1 and 9, although it has a slightly lower bearing capacity at corresponding dimensions. Fig. 11 illustrates still another embodiment of the crown roller. Instead of being spherical in shape as in the aforedescribed embodiments, the rolling body-part of the crown roller has the form of a truncated conical roller. This crown roller coacts with a spindle 1 that has a trapezium thread. In order for the invention to function in this case, it is necessary that the thread flanks have a certain slope, which must not be exceeded. The thread flanks have a slope of 45° in the illustrated embodiment. As will be readily perceived, the root thread has a lower peripheral speed than the thread apex when the spindle rotates. The risk of the roller body-part slipping anywhere around its mantle surface can be eliminated, by using a truncated roller body-part and adapting the conicity so that the top part of the truncated comb will have the same peripheral speed as the thread flank at the thread bottom, and so that the base part of the truncated cone will have the same peripheral speed as the speed of the thread flank at the thread apex. Although the invention has been described and illustrated with reference to a nut that includes two rows of elements, it will be understood that three or more rows of elements may be used, depending on the desired load absorbing ability. It will also be understood that the number of crown rollers in each row can be optimized, as described with reference to Fig. 12. The inventive elements need only perform rotary movement in place in the nut, as opposed to the case in conventional ball screws, in which the balls roll with rotation of the screw, and the elements can be used with spindles that have right-hand and left- hand threads with one or more leads and different pitches. Depending on the geometry of the spindle for instance, the elements may either lie in a plane perpendicular to the spindle axis or along parallel lines that follow the spindle threads. Fig. 12 illustrates very schematically an example of different arrangements of the elements 11 in relation to the threads 2 which, extended, shall represent a threaded spindle having three leads. Shown at the bottom of the Figure is two rows of elements which lie in a plane perpendicular to the axis of the spindle. Because the spindle of the illustrated example has only three leads, only three elements can be arranged in each row or line. The penultimate part of the Figure illustrates the elements disposed in lines that follow the threads 2, wherewith two mutually adjacent elements in respective lines are directed along lines that extend parallel with the axis of the spindle. Because the placement of the elements follows the threads, a maximum number of elements can be used. The third part of the Figure as seen from the bottom thereof shows elements arranged along the threads, although in this case two mutually adjacent elements lying in their respective lines are directed on a line which extends perpendicular to the slope of the thread to the axis of the spindle. The uppermost part of Fig. 12 shows the elements running in only one thread. In this case, each alternate crown roller will lie against one flank of the thread and each other alternate crown roller will lie against the other flank of the thread, as indicated in this part of the Figure. The elements will, in this case, thus be disposed in a zig-zag pattern along the thread. It will be understood that the lines of elements may be disposed along more than one turn of the thread. This latter arrangement can be particularly appropriate in the case of spindles that have only one lead. It will be understood from the aforegoing and from Fig. 12 that the person skilled in this art has a high degree of freedom in arranging the inventive elements and also of using screw threads of varying profiles, including trapezium threads having sloping thread flanks, as earlier mentioned. It will be evident from the aforegoing that the invention provides a completely novel solution to problems encountered with ball screws and can be adapted to all types of threaded spindles, screw threads, ridges and grooves. It is emphasized that the construction of the nut itself and fitting of the ball races can be effected in many different ways and that the solution described and illustrated in this document is an advantageous technical solution.

Claims: CLAIMS 1. Means for transforming rotary movement of a spindle (1) that has helical threads (2) to axial movement of a nut (3) embracing said spindle, and conversely for transforming axial movement of said nut to rotary movement of said spindle, said means comprising elements which are disposed between the spindle (1) and the nut (3) and which lie along at least two mutually parallel and mutually separated peripheral lines around the spindle (1), characterized in that respective elements are comprised of a crown roller (11) which includes a roller body-part (12) and a ball race (13), wherewith the roller body-part (12) is adapted to engage the threads (2) of the spindle, and the ball race (13) is located so as to face away from the axis of the spindle ( 1 ) and to lie in a plane that extends perpendicularly to a line through the spindle axis and the rotational centre of the roller body- part (12); in that bearing balls (15) are disposed between the ball race (13) and the nut (3); and in that two mutually adjacent crown rollers (11) engage with mutually facing or mutually distal flanks of the threads (2) or the threads.? 2. Means according to Claim 1, characterized in that the crown roller (11) has the form of a unit. 3. Means according to Claim 2 , characterized in that the crown roller (11) has the form of a spherical ball and the ball race (13) is formed by the mantle surface of the sphere. 4. Means according to Claim 2, characterized in that the roller body-part (12) of the crown roller (11) has the form of a truncated conical roller and the threads (2) of the spindle (1) are trapezium threads. 5. Means according to Claim 2 or 4 , characterized in that the ball race (13) has the form of a sunken groove in the roller body-part ( 12 ) . 6. Means according to Claim 2 or 4 , characterized in that the ball race (13) is comprised of a groove built-on the roller body- part (12). 7. Means according to any one of the preceding Claims, charac- terized in that the peripheral lines lie in planes that extend perpendicular to the axis of the spindle (1). 8. Means according to any one of the preceding Claims, characterized in that the peripheral lines follow the threads (2) of the spindle. 9. Means according to any one of the preceding Claims, characterized in that the nut (3) carries ball bearing rings (6) against which the bearing balls (15) run. 10. Means according to any one of the preceding Claims, characterized in that the periphery of the nut (3) includes openings (5) in which the ball bearing rings (6) are received. 11. Means according to any one of the preceding Claims, characterized in that the nut (3) is divided and provided peripherally with a line of ball bearing rings (6) in each divided part; and in that the divided part can be adjusted axially in relation to each other and fixed (10) in their adjusted positions.?

Inventors: GRANBOM BO, GRANBOM, BO
Applicants: GRANBOM BO, KOLUNGEN AB, GRANBOM, BO
Application year: 1997
Main classification: F16H25
IPC codes: F16H15, F16H25