GB1559899A

GB1559899A - Recirculating ball screw-and-nut gear

Info

Publication number: GB1559899A
Application number: GB1476277A
Authority: GB
Original assignee: Politechnika Warszawska
Current assignee: Politechnika Warszawska
Priority date: 1976-04-10
Filing date: 1977-04-07
Publication date: 1980-01-30
Also published as: HU175282B; DE2715762A1; DD131277A5; IT1079598B

Description

(54) RECIRCULATING BALL SCREW-AND-NUT GEAR (71) We, POLITECHNIKA WARSZAWSKA, of Warszawa, 1 Jednosci Robotniczej Sq., a state enterprise organised and existing under the laws of Poland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to recirculating ball gears of the screw-and-nut type wherein the driving connection between a helically grooved screw member and a complementary nut member is effected by means of a train of spherical balls arranged to continuously circulate in predetermined convolutions formed jointly by the helical grooves of the screw and nut members, whereby rotary movement of either the screw or the nut is translated into axial displacement or linear movement of the other member, the balls being transferred or returned from a discharge point adjacent one convolution, to a selected inlet point adjacent a preceding convolution, so as to maintain a continuous circulation of balls within a predetermined helical path.

There has heretofore been proposed a recirculating ball gear of the screw-and-nut type wherein trains of balls under load continuously circulate in at least two helical paths with each of which is associated a separate ball-transfer element or insert attached to the nut member. Each ball-transfer element or insert has inwardly-projecting ball-directing lugs which are so arranged with respect to one another and to the convolutions of the screw member as to overlie a minimum in excess of one and one-half convolutions and less than two convolutions, and is designed to pick up the balls from one convolution and simultaneously initiate their transfer in a continuous circular movement. The required number of ball-transfer elements or inserts attached to the nut member depends upon the number of predetermined helical paths in which trains of balls circulate.

Disadvantages of said hitherto-proposed recirculating ball gear are that production of the gear is time-consuming and difficult and that the gear requires a considerable number of ball-transfer elements or inserts.

depending upon the increased number of groups of convolutions in which balls circulate. The object of the present invention is to provide a recirculating ball gear of the screw-and-nut type wherein the nut member has but one ball-transfer element or insert irrespective of the number of gear tracks provided by groups of convolutions.

According to the present invention we provide a recirculating ball gear of the screw-and-nut type wherein trains of balls under load continuously circulate in at least two helical paths and a single ball-transfer element or insert is secured to the nut member and fits flush against a flat surface area left through cutting away of a longitudinal portion of segmental section from the external surface of the nut, and said ball-transfer element or insert has in its flat inner surface a separate rectilinear groove for each of said helical paths and extending between an inlet to and a discharge from said helical path. The ends of each rectilinear groove in the ball-transfer element or insert preferably have in longitudinally section a curvilinear shape of radius greater than the diameter of the balls. The face of each groove is preferably coated with a plastics material having low coefficient of friction, preferably with polytetrafluoroethylene.

The gear according to the invention has small overall dimensions and a simple and functional design. Due to the coating with a plastics material having a low coefficient of friction of the faces of the grooves forming parts of the raceways for the balls, the frictional resistance is minimized and a smooth and uniform operation of the recirculating ball gear is ensured.

An embodiment of the invention will now be described in more detail, by way of example, with reference to the acc-ornpany- ing drawing, in which: Fig. 1 is an elevation from above, partly in section, of a recirculating ball gear according to the invention Fig. 2 is a section on the line A-A of Fig. l; Fig. 3 is an underneath plan view of the ball-transfer element or insert, the view being along the line B-B of Fig. 2; Fig. 4 is a section on the line C-C of Fig. 3; and Fig. 5 is a local section on the line D-D of Fig. 3.

Referring now to the drawings, as can be seen in Figs. 1 and 2, the recirculating ball gear has two trains of circulating balls 3 and consists of a screw 1 with external helical groove la and a nut 2 provided with a complementary, internal helical groove 2a, the two grooves la and 2a together forming a helical raceway for the balls 3. The nut 2 has a longitudinal portion of segmental section cut away from its external cylindrical surface to leave a flat surface area 2b from which extend cylindrical bores providing seats 2c for shaped lining elements forming guiding channels 4a which are the inlet to and the discharge or outlet from the individual gear tracks of the two trains of circulating balls 3. On the flat surface area 2b there is a cover plate 5 which fulfils the role of a ball-transfer element or insert. The cover plate 5 has therein two grooves Sa in its face continuous with the flat surface area 2b, each of the grooves 5a extending between the inlet and outlet guiding channels 4a of one of the gear tracks.

Moreover, the cover plate 5 is accurately positioned by means of pins 6 and is fastened to the nut 2 by means of screws 7.

In Fig. 3 of the drawing the cover plate 5 has two rectilinear grooves 5a forming the middle part of the guiding channel 4a, through which the rolling elements or balls 3 move, but it will be manifest that the number of grooves in the cover plate 5 corresponds to the number of individual gear tracks for independent trains of circulating ball 3 of the recirculating ball gear.

In Fig. 4 of the drawing each end of each of the two grooves Sa, each connecting together the inlet and outlet part of a channel 4a in the cover plate 5, has in longitudinal section a curvilinear contour of radius R greater than the diameter D of a ball 3.

Moreover, the faces of the grooves 5a are coated with polytetrafluoroethylene. As can be seen in Fig. 5 of the drawing the grooves 5a in the cover plate 5 are of Ushape in cross section, the bottoms thereof being rounded and both the depth and the width of each groove Sa being greater than the diameter D of the balls 3.

The described recirculating ball gear of the screw-and-nut type operates as follows: The screw 1 with the helical groove la and the nut 2 with the helical groove 2a together form a helical raceway track along which the balls move. The rolling motion of the balls 3 is due to a rotary motion or translation of the screw 1 or the nut 2.

The balls 3 moving along the helical raceway pass through the inlet to and outlet from the guiding channel 4a and the groove 5a forming the middle part of the guiding channel 4a of the individual gear tracks of the two trains of circulating balls. When the motion of the screw 1 is reversed relative to that of the nut 2, the inlet to each guiding channel 4a performs the function of the outlet from said channel and the outlet performs the function of the inlet.

In this way there is formed a closed track or raceway for the balls of each train of circulating balls. The ends of the grooves 5a enable a smooth movement of the balls 3 at the moment they pass through the inlet to the guiding channel 4a, therefrom to the grooves 5a and thence into the outlet of the guiding channel 4a, WHAT WE CLAIM IS: l. A recirculating ball gear of the screwand-nut type, wherein trains of balls under load continuously circulate in at least two helical paths and a single ball-transfer element or insert is secured to the nut member and fits flush against a flat surface area left through cutting away of a longitudinal portion of segmental section from the external surface of the nut, and said ball-transfer element or insert has in its flat inner surface a separate rectilinear groove for each of said helical paths and extending between an inlet to and a discharge from said helical path.

2. A recirculating ball gear as claimed in claim 1, wherein the ends of each rectilinear groove in the ball-transfer element or insert are of curvilinear contour in longitudinal section with a radius greater than the diameter of the balls.

3. A recirculating ball gear as claimed in claim l or 2, wherein the face of each groove in the ball-transfer element or insert is coated with a plastics material having a relatively low coefficient of friction.

4. A recirculating ball gear as claimed in claim 3, wherein the plastics material is polytetrafluorethylene.

5. A recirculating ball gear of the screwand-nut type substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

in section, of a recirculating ball gear according to the invention Fig. 2 is a section on the line A-A of Fig. l; Fig. 3 is an underneath plan view of the ball-transfer element or insert, the view being along the line B-B of Fig. 2; Fig. 4 is a section on the line C-C of Fig. 3; and Fig. 5 is a local section on the line D-D of Fig. 3.

Referring now to the drawings, as can be seen in Figs. 1 and 2, the recirculating ball gear has two trains of circulating balls 3 and consists of a screw 1 with external helical groove la and a nut 2 provided with a complementary, internal helical groove 2a, the two grooves la and 2a together forming a helical raceway for the balls 3. The nut 2 has a longitudinal portion of segmental section cut away from its external cylindrical surface to leave a flat surface area 2b from which extend cylindrical bores providing seats 2c for shaped lining elements forming guiding channels 4a which are the inlet to and the discharge or outlet from the individual gear tracks of the two trains of circulating balls 3. On the flat surface area 2b there is a cover plate 5 which fulfils the role of a ball-transfer element or insert. The cover plate 5 has therein two grooves Sa in its face continuous with the flat surface area 2b, each of the grooves 5a extending between the inlet and outlet guiding channels 4a of one of the gear tracks.

Moreover, the cover plate 5 is accurately positioned by means of pins 6 and is fastened to the nut 2 by means of screws 7.

In Fig. 3 of the drawing the cover plate 5 has two rectilinear grooves 5a forming the middle part of the guiding channel 4a, through which the rolling elements or balls 3 move, but it will be manifest that the number of grooves in the cover plate 5 corresponds to the number of individual gear tracks for independent trains of circulating ball 3 of the recirculating ball gear.

In Fig. 4 of the drawing each end of each of the two grooves Sa, each connecting together the inlet and outlet part of a channel 4a in the cover plate 5, has in longitudinal section a curvilinear contour of radius R greater than the diameter D of a ball 3.

Moreover, the faces of the grooves 5a are coated with polytetrafluoroethylene. As can be seen in Fig. 5 of the drawing the grooves 5a in the cover plate 5 are of Ushape in cross section, the bottoms thereof being rounded and both the depth and the width of each groove Sa being greater than the diameter D of the balls 3.

The described recirculating ball gear of the screw-and-nut type operates as follows: The screw 1 with the helical groove la and the nut 2 with the helical groove 2a together form a helical raceway track along which the balls move. The rolling motion of the balls 3 is due to a rotary motion or translation of the screw 1 or the nut 2.

The balls 3 moving along the helical raceway pass through the inlet to and outlet from the guiding channel 4a and the groove 5a forming the middle part of the guiding channel 4a of the individual gear tracks of the two trains of circulating balls. When the motion of the screw 1 is reversed relative to that of the nut 2, the inlet to each guiding channel 4a performs the function of the outlet from said channel and the outlet performs the function of the inlet.

In this way there is formed a closed track or raceway for the balls of each train of circulating balls. The ends of the grooves 5a enable a smooth movement of the balls 3 at the moment they pass through the inlet to the guiding channel 4a, therefrom to the grooves 5a and thence into the outlet of the guiding channel 4a, WHAT WE CLAIM IS: l. A recirculating ball gear of the screwand-nut type, wherein trains of balls under load continuously circulate in at least two helical paths and a single ball-transfer element or insert is secured to the nut member and fits flush against a flat surface area left through cutting away of a longitudinal portion of segmental section from the external surface of the nut, and said ball-transfer element or insert has in its flat inner surface a separate rectilinear groove for each of said helical paths and extending between an inlet to and a discharge from said helical path.
2. A recirculating ball gear as claimed in claim 1, wherein the ends of each rectilinear groove in the ball-transfer element or insert are of curvilinear contour in longitudinal section with a radius greater than the diameter of the balls.
3. A recirculating ball gear as claimed in claim l or 2, wherein the face of each groove in the ball-transfer element or insert is coated with a plastics material having a relatively low coefficient of friction.
4. A recirculating ball gear as claimed in claim 3, wherein the plastics material is polytetrafluorethylene.
5. A recirculating ball gear of the screwand-nut type substantially as hereinbefore described with reference to the accompanying drawing.