BALL SCREW AND NUT MECHANISM

Abstract

A ball screw and nut mechanism has a screw in cooperation with a nut via balls that can circulate in a raceway formed by the opposing threads of the screw and nut. The nut has a recirculation insert passing therethrough from the outer face to the thread, the recirculation insert having a first end with a ball transfer groove turned towards the screw. The mechanism has a holding body for holding the recirculation insert in the housing, the recirculation insert having a second end with a shoulder bearing on the nut, the second end of the recirculation insert having an orientation lug having an angular position predetermined and fixed relative to the ball transfer groove, the orientation lug cooperating with a guide relief of the holding body to fix an orientation of the recirculation insert such that the transfer groove is adjusted to the raceway.

Claims

1. Ball screw and nut mechanism including a threaded screw and nut, the nut cooperating with the screw through an intermediary of balls able to circulate in a raceway formed by threads of the screw and the facing nut, the nut being furthermore provided with at least one recirculation insert inserted from the exterior face of the nut, in at least one cylindrical housing traversing the nut from the exterior face of the nut to the thread of the nut, the recirculation insert presenting a first end with a ball transfer groove turned towards the screw, characterized in that the mechanism includes a holding body for the recirculation insert, configured to keep the recirculation insert in its housing, the recirculation insert presents a second end with a supporting shoulder on a supporting area of the nut the second end of the recirculation insert includes an orientation lug presenting a predetermined and fixed angular position relative to the ball transfer groove, the orientation lug cooperating with at least one guide relief of the holding body to set an orientation of the recirculation insert in the housing, the orientation of the insert being set so that the transfer groove is adjusted to the raceway.

2. Mechanism according to claim 1, in which the orientation lug forms the supporting shoulder of the recirculation insert.

3. Mechanism according to claim 1, in which the support area is either the exterior face of the nut or a support area in an indentation made around the housing.

4. Mechanism according to claim 1, in which the holding body presents a bore hole suitable for receiving the nut, and in which at least one guide relief extends in parallel to an axis of the bore hole.

5. Mechanism according to claim 1, in which the guide relief is a depressed groove.

6. Mechanism according to claim 1, including a plurality of recirculation inserts of balls housed in a corresponding plurality of housings for inserts.

7. Mechanism according to claim 1, in which the holding body includes a plurality of guide reliefs, with uniform angular distribution, cooperating with a plurality of orientation lugs of a plurality of recirculation inserts.

8. Mechanism according to claim 1, in which each guide relief is adapted to receive a plurality of orientation lugs

9. Mechanism according to claim 1, featuring a plurality of recirculation inserts, the inserts being distributed in angular fashion around the nut and being spaced axially with respect to a distance corresponding to multiples of a thread pitch of the nut

10. Mechanism according to claim 1, featuring a plurality of recirculation inserts, the inserts being distributed in angular fashion around the nut and being spaced axially with respect to a distance corresponding to multiples of a thread pitch of the nut.

11. Mechanism according to claim 1, in which the recirculation insert presents at least one tab placed in proximity to the ball transfer groove and extending into the raceway in the direction of the screw, the guide tab presenting a stop edge for the balls.

12. Mechanism according to claim 11, in which the tab presents a stiffener opposite the stop edge, the stiffener protruding radially on the body of the recirculation insert, and extending into the raceway.

13. Mechanism according to claim 12, in which the recirculation insert presents a hollowing for radial extraction of the tab, the tab being connected to the body of the insert in a flexible manner with an amplitude of flexion in the direction of the retraction hollowing equal to a length of the protruding stiffener.

14. Portable power tool selected among pruning shears and scissors including a mobile blade, a rotary motor and a mobile drive element of the mobile blade driven by the motor and a ball screw-nut mechanism in accordance with claim 1, the nut of the ball screw-nut mechanism being connected to the mobile drive element of the blade and the screw being connected to the motor.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0054] The above aims, characteristics and advantages and still more, will become clearer in the description which follows and the drawings in which:

[0055] FIG. 1 is an exploded view of a ball screw-nut mechanism in accordance with the invention.

[0056] FIG. 2 is a perspective view of a holding body of the ball screw-nut mechanism of FIG. 1.

[0057] FIG. 3 is a partial cutaway drawing showing the assembly of the ball screw-nut mechanism.

[0058] FIG. 4 is an exploded view of the ball screw-nut mechanism.

[0059] FIG. 5 is a longitudinal section of the nut of FIG. 3 illustrating the recirculation of the balls.

[0060] FIG. 6 is a longitudinal section of the nut of FIG. 3 equipped with the screw of the ball screw-nut mechanism.

[0061] FIG. 7 is a cross section of a portion of the nut showing a detail of the positioning of a recirculation insert.

[0062] FIG. 8 is a cross section of a portion of the ball screw-nut mechanism around a recirculation insert.

[0063] FIG. 9 is a section of a portion of the ball screw-nut mechanism passing through a stiffener of a recirculation insert.

[0064] FIG. 10 is a perspective view of a recirculation insert.

[0065] FIG. 11 is a partial section of an electric pruning shear using the ball screw-nut mechanism in accordance with the invention.

DETAILED DESCRIPTION OF THE IMPLEMENTATION MODES OF THE INVENTION

[0066] Reference is made to the drawings to describe an interesting, although by no means limiting example of implementation of a ball screw-nut mechanism in accordance with the invention.

[0067] Identical or similar portions of the various figures are marked with the same reference signs so that one can refer from one figure to another. The various figures are shown in free-scale.

[0068] The ball screw-nut mechanism 10 of FIG. 1 includes a nut 12, received on screw 14. The nut and the screw are preferably made of metal. When the screw and the nut are assembled, the screw enters into a tapped hole 16 of the nut 12 provided with an interior thread 22. The interior thread of the nut 12 is better visible on FIGS. 5 and 7. The pitch of the interior thread 22 of the nut corresponds to the pitch of a thread 24 made on the screw. When the nut 12 and the screw 14 are assembled, the threads 22 and 24 are mutually opposite and form a raceway 26, visible on FIGS. 6, 8 and 9. The raceway receives a plurality of balls 28. The balls 28, the diameter of which is adapted

[0069] to that of the threads, keep the nut in a concentric position on the screw when the screw and the nut are assembled. They transmit the stresses of the movement of the screw towards the nut and reciprocally. The balls are preferably made of steel. The rotation of the screw 14 may be clockwise or counter-clockwise resulting either in a translation of the nut 12 in one direction or the other, along the axis of the screw.

[0070] In the implementation shown the nut presents an exterior cylindrical surface 18. It is noted that the exterior surface is not necessarily cylindrical. The nut can in effect present other shapes, for example a hexagonal shape.

[0071] A plurality of seats 30, in the form of radial bores are made in the nut 12, with a uniform angular distribution. The bore holes present a chamfer 31. The housings 30 traverse the nut from the exterior face 18 to the interior thread 22.

[0072] Each seat 30 is meant to receive a recirculation insert 32. As shown in FIGS. 1, 7 and 10 and in the particular example described, the inserts 32 present a general cylindrical shape with a first end 34 turned towards the screw 14, and provided with a transfer groove 36. A second end, opposite the first end, is provided with an orientation lug 38. The recirculation insert, and the orientation lug, formed preferably of a single piece, may consist of metal or plastic material. FIG. 8 shows that the recirculation insert is received with reduced play in its seat.

[0073] FIGS. 1, 3, 4, 5 and 6 show that the orientation lug 38 forms a shoulder which rests on a support area of the nut. In the example shown in FIGS. 1 to 6, the support area is formed by the exterior face 18 of the nut. The shoulder support permits fixing the extension of the recirculation insert in the housings 30. As FIGS. 5 to 8 also show, the length of the recirculation inserts is set so that the transfer groove 36 connects itself to the raceway 26 of the balls when the shoulder formed by the lug 38 rests on the supporting area of the nut.

[0074] A transfer groove 36 of the recirculation inserts is better visible on FIG. 5 which shows the recirculation of the balls 28. FIG. 5 is a section view of the nut 12 in which the screw has been removed. It shows in particular the end of four recirculation inserts in position in the nut. For the sake of clarity, the screw has been removed and the balls are only shown for two balls paths in the raceway. One can see that the balls 28 pass through the transfer groove 36 of the recirculation inserts of a row in the raceway 26, or of a row of the thread 22 of the nut, to the following or preceding row, depending on the sense of rotation.

[0075] Recirculation of the balls is also shown in FIG. 6 which is a cross-section of the nut 12 in which passes the non-sectioned screw 14. It is possible to observe that the balls travel along a raceway 26 which goes, respectively, from one row of threads of the screw and the nut to the next row. The balls 28 are then extracted from the raceway by the recirculation insert and pass into the transfer groove 36 of the recirculation insert, above the thread 24 of the screw 14. The balls are then reintroduced into the raceway 26 at the preceding or following row of the thread. depending on the sense of rotation. The two ball paths shown use a first recirculation insert upstream of the section plane which is not shown, and a second recirculation insert positioned in the cutting plane. The balls are not shown in the other paths, for the sake of clarity.

[0076] Returning to FIG. 1, it is possible to note that the ball screw-nut mechanism presents a holding body 40, preferably made of plastic, for the purpose of capping the nut 12. The holding body presents itself more exactly like a sleeve coming into contact with the exterior face 18 of the nut. In the example shown, where the nut 12 is of a general cylindrical shape, with a diameter adjusted to that of the nut. Other complementary shapes of the nut and the holding body may be envisaged.

[0077] As FIG. 3 shows, an essential function of the holding body is to keep the recirculation inserts 32 in their housings. The holding body rests in effect on the recirculation inserts 32 so as to press their shoulder against the nut.

[0078] FIG. 2 shows that the interior face of the bore 42 of the holding body 40 presents the guide reliefs 44. These are, in the example shown, grooves which extend in parallel to the axis of the bore.

[0079] The guide relief 44 presents a complementary shape to the orientation lugs 38. In the example shown, the orientation lugs present an oblong shape and the grooves of the guide relief have a width that corresponds to that of the lugs.

[0080] FIG. 3 shows the assembled mechanism of FIG. 1. The nut 12 is inserted in the holding body 40. It is possible to observe that the orientation lugs 38 are received and oriented in the grooves of the guide relief 44. This corresponds to the second function of the holding body which is to set and maintain the orientation of the recirculation inserts. The precise orientation of the recirculation inserts is essential because it permits adjusting the orientation of the transfer groove in relation to the ball race. A guide relief can be provided for each recirculation insert. It is also possible to envisage that a same guide relief cooperates with the lugs of several recirculation inserts aligned along the axis of the nut. It is possible to observe on FIGS. 1 and 4 that the orientation lugs 38 present a slightly tapered end. This makes it possible to summarily locate the orientation of the recirculation inserts at the time of their placement in their housings. Furthermore, the slightly tapered end facilitates the introduction of the lugs into the guide relief 44 at the time of the assembly. When the orientation lugs engage on the guide relief, orientation of the inserts adjusts itself automatically on the guide relief thanks to the rotational freedom of the recirculation inserts 32 in their housings 30. On the other hand, once the orientation lugs 38 are engaged with the guide relief, the rotation of the inserts in blocked.

[0081] FIGS. 1, 3, 4 and 5 also show a fastening bore hole 50 on the nut 12. The radial bore hole 50 traverses the nut through and through and is not

[0082] covered by the holding body 40. The bore hole 50 is provided for receiving fastening studs for connecting bars described below in reference to FIG. 1.

[0083] FIG. 4 shows the ball screw-nut mechanism just before installation of the holding body 40 on the nut 12. All recirculation inserts 32 are in place in their housings. The holding body 40 presents a segmented interior retainer ring, its segments 46 are engaged in a circular throat 48 provided on the exterior face 18 of the nut 12 for keeping the sleeve on the nut. The holding body 40 also presents a segmented shoulder 47 that abuts on a face 13 of the nut, next to the throat 48.

[0084] FIG. 10 shows, at a larger scale, a recirculation insert 32 of a general cylindrical shape. It is especially possible to observe the transfer groove 36 on the first end 34 of the insert, and the orientation lug 38 on the opposite end. In the particular implementation of the recirculation insert shown in FIG. 10, the transfer groove is extended by tabs 35. The purpose of the tabs 35 is to protrude into the raceway of the balls in order to stop the balls in circulation and to force them to leave the raceway to continue their path in the transfer groove 36. For this purpose, the tabs each present a ball stop edge indicated by the reference 37.

[0085] The ball stop edges 37 and the tabs 35 are subject to sustaining significant amounts of stress. Therefore, the insert 32 in this case presents stiffeners 39 opposite the stop edges 37.

[0086] The stiffeners 39 protrude radially on the cylindrical body of the recirculation insert. Also, to prevent the stiffeners 39 from hindering the installation of the recirculation insert in its housing, the insert is provided with a retraction hollowing 33. This is a longitudinal slot which opens into the raceway. The width of the slot is at the same time wide enough to permit the complete radial retraction of the stiffeners and is also sufficiently reduced so that the balls cannot enter. The slot forming the retraction hollowing 33 separates the end of the insert into two parts which constitute the flexion legs.

[0087] The retraction of the stiffeners 39 by flexion of the legs mentioned above is shown on FIG. 7. FIG. 7 shows, in cross section, a recirculation insert 32 at the time of its introduction into its housing 30.

[0088] When the recirculation insert is completely introduced, i.e. when the shoulder formed by the orientation lug 38 rests against the exterior face 18 of the nut 12, the flexion of the legs is released and the stiffeners place themselves in the raceway 26. It is possible to observe the position of the recirculation insert 32 and of the stiffeners 39 on FIG. 8. FIG. 8 shows in a section view a detail of the nut and of the screw in proximity of a recirculation insert, after its placement in its housing.

[0089] The stiffeners occupy a significant portion of the section of the raceway. However, the stiffeners are sized and held so that they touch neither the screw 14 nor the nut 12. A slight play is maintained in order to avoid any unnecessary friction. This aspect is illustrated by FIG. 9 which is a cross-section of the raceway passing through one of the stiffeners 39.

[0090] The ball screw-nut mechanism can be used for various applications. One particular application is shown in FIG. 1. It is an application on an electric pruning shear 60.

[0091] The pruning shear is provided with a rotary electric motor 62 and a ball screw-nut mechanism in accordance with the invention to transform a rotational movement of the motor into a translational movement. The motor 62 connected to the screw 14 of the ball screw-nut mechanism through the intermediary of a gear 63 to make the screw 14 turn clockwise or counter-clockwise, depending on a control applied to a trigger 66.

[0092] As described previously, the rotation of the screw 14 results in the displacement of the nut 12 parallel to the axis of the screw. The direction of displacement of the nut depends on the sense of rotation of the screw. A mobile drive element 68, for example an articulated rocker bar, is connected to the nut by means of an appropriate fastener, for example studs or pivot pins which are engaged in the fastening bore hole 50 mentioned in reference to FIGS. 1, 3, 4 and 5.

[0093] The opposite end of the mobile drive part is linked to a cam 72 of a mobile cam 70. in this manner, the translation movement of the nut 12 is transmitted to the cam and generates the pivoting of the mobile blade 70 around a pivot 74. Depending on the sense of rotation of the screw 14, the mobile blade 70 is raised or dropped on a fixed blade 76.