GB2131519A

GB2131519A - A ball-type transmission between two shaft-ends

Info

Publication number: GB2131519A
Application number: GB08330393A
Authority: GB
Inventors: Charles Favey
Original assignee: Centre Technique des Industries Mecaniques CETIM
Current assignee: Centre Technique des Industries Mecaniques CETIM
Priority date: 1982-12-06
Filing date: 1983-11-15
Publication date: 1984-06-20
Also published as: IT8323868A0; CH655160A5; DE3343826C2; GB2131519B; IT8323868A1; JPS6331006B2; FR2537227A1; JPS59113322A; IT1167271B; FR2537227B1; GB8330393D0; DE3343826A1

Abstract

In a ball-type rotary coupling between two non-aligned shaft-ends 1, 2, the extremity of one of the shaft-ends is provided with a female end-piece in the form of at least one cylindrical passage 4 displaced off-center and parallel to the axis of the end-piece. The extremity of the other shaft-end has an extension in the form of a male end-piece 5 provided in its outer face with a radial cylindrical recess 6 having the same diameter as the passage. A ball 7 inserted within the recess of the male end-piece and within the passage of the female end-piece provides a rotary coupling between the two shaft-ends. <IMAGE>

Description

SPECIFICATION A ball-type transmission between two shaftends This invention relates to the transmission of a movement of rotation or to the modification of relative orientation between two non-aligned rotating shafts.

The invention is more particularly directed to single and double universal-joint transmissions and to variable-angle universal joints.

Conventional universal joints usually comprise a central ball or a sliding shaft.

A single universal-joint comprises a minimum of two pivots and motion transmission in this case is not homocinetic.

For current uses, however, a single joint permits transmission of motion which is practically homocinetic by reason of internal play but which is limited to angles of 6 to 70. In the case of larger angular differences, it is the usual practice to make use of double joints which require equality of angles as well as identical orientation of pivot axes.

It is only on this condition that the transmission is homocinetic between the input shaft and the output shaft.

A transmission is known as homocinetic when the angles between the two driven shafts have exactly the same value with respect to a known origin.

Conventional universal joints employed in particular in automobiles and power transmissions can be of the spider type, one example of which is the Spicer-Glaenzer joint, or of the ball type such as the Weiss or Rzeppa systems which are joints having three pivots materialized by the balls which run in curved races. The machining of universal joints of this type, however, gives rise to major difficulties while offering only limited possibilities in regard to sliding motion and the angle between driving and driven shafts.

Another universal joint of conventional type is the so-called "Tripode" joint, this system being essentially composed of a shaft, three concurrent perpendicular pins which are fixed on said shaft and cylindrical or spherical rollers rotatably mounted on said pins, the complete assembly being capable of sliding within a female shaft or so-called "tulip".

This type of joint also involves considerable difficulties in machining and has a certain degree of fragility.

We have identified a need to provide a ball-type transmission which is not attended by the disadvantages of conventional universal joints, which is easy to machine and to assemble, has good sliding capabilities, permits a large angle of operation which can attain 200,for example, and which is particularly well-suited to the construction of homocinetic joints. An aim of the invention is to provide improvements in one or more of these respects.

There is disclosed below a ball-type mechanical transmission between two shaft-ends and is distinguished by the fact that the front extremity of a first shaft-end is hollowed-out so as to form a female end-piece having an axial housing. The transverse cross-section of said housing has at least one side-lobe forming a cylindrical passage of revolution which is not perpendicular to the axis of said first shaft-end, the transverse cross-section of said side-lobe being delimited by a horseshoe arch. A further distinguishing feature of the embodiment lies in the fact that the second shaftend has an extension in the form of at least one male end-piece whose width considered transversely to the axis of said second shaft-end is smaller than the width of the free opening of the horseshoe arch of the passage lobe associated with said end-piece.That wall of said male endpiece which is remote from the axis of the second shaft-end is hollowed-out near its extremity so as to form a cylindrical recess of revolution having the same diameter as the associated passage of the first shaft-end and having an axis which is not parallel to that of the second shaft-end, the transverse cross-section of said recess being limited by two diametrically opposite circular arcs.

Yet another feature of the invention lies in the fact that a coupling ball having a corresponding diameter with due allowance for clearance is inserted and maintained freely both within the passage of the first shaft-end and within the recess of the second shaft-end.

In one embodiment which is particularly advantageous, especially in regard to machining, the axis of the cylindrical recess of the male endpiece is perpendicular to the axis of the second shaft-end.

In the case of transmissions which operate within a relatively high power range, it is an advantage to provide the female housing of the first shaft-end with at least two radially spaced parallel cylindrical passages, the male end-piece of the second shaft-end being provided with a number of corresponding radial elements equal to the number of coupling balls and to the number of associated passage-eiement assemblies.

In this case the female housing preferably has an axial cylindrical passage of revolution with three lobes uniformly spaced in a star formation, the transverse cross-section of the male end-piece being in the shape of a Y having symmetrical arms spaced at angular intervals of 1200.

The invention is also directed to a double homocinetic ball-type mechanical transmission between two non-aligned rotary shaft-ends which may or may not be concurrent. Said transmission essentially comprises an intermediate shaft disposed freely between the two shaft-ends, a single universaidoint transmission in accordance with the invention being formed by each end of the intermediate shaft respectively with the associated shaft-end.

A homocinetic transmission of this type can be constructed with an intermediate shaft which is adapted to carry a male or female end-piece of the same type at each end, each shaft-end being provided with an end-piece of the same type and complementary to the end-pieces of the intermediate shaft.

The end-pieces at the ends of the intermediate shaft can be angularly displaced with respect to each other in parallel planes or else they can be aligned.

The intermediate shaft can be placed freely between the two shaft-ends but the displacements of said intermediate shaft can be limited by means of at least one resilient stop.

Thus in a double transmission in accordance with the invention, the two shaft-ends which carry respectively a male end-piece and a female endpiece are rotationally coupled by inserting within the female end-piece at least one coupling member having freedom of sliding motion both in a direction solely parallel to the axis of one of the shafts and angularly with respect to the axis of the other shaft.

In one application of the invention to a transmission which controls the relative inclination between two shafts, the free end of each radial element of the male end-piece which penetrates into the female end-piece is secured to a push-rod which slides in a direction parallel to the axis within an internal extension of each passage of the female end-piece and which can be actuated at will in order to modify the angle made by the axes of the two shaft-ends.

One embodiment of a transmission of this type which is particularly advantageous for the construction of a robot wrist comprises three parallel push-rods each connected respectively to one arm of the male end-piece by means of a linkarm.

These and other features of the invention will be more apparent upon consideration of the following description and accompanying drawings, wherein: ~Fig. 1 is a diagrammatic axial sectional view of a simplified ball transmission in accordance with the invention; ~Fig. 2 is an end view of the female end-piece of the transmission of Fig. 1; ~Fig. 3 is a plan view of the male end-piece of the transmission of Fig. 1; ~Fig. 4 is a diagrammatic axial sectional view of a double homocinetic mechanical ball-type transmission in accordance with the invention; ~Fig. 5 is a diagrammatic sectional view taken along line V-V of Fig. 4; ~Fig. 6 is a top view of the intermediate shaft of the transmission of Fig. 4:: ~Fig. 7 is a diagrammatic sectional view taken along line VIl-VIl of Fig. 6; ~Fig. 8 is an end view of the intermediate shaft of Fig. 6, looking in the direction of the arrow VIII; ~Fig. 9 is a schematic diagram in a plane located on line IX-IX of Fig. 4 and showing the displacements of the center of the balls within said transmission; ~Fig. 10 is a diagrammatic part-sectional view of a variable-angle transmission in accordance with the invention.

The single universal-joint transmission illustrated in Figs. 1 to 3 provides a rotational linkage between two angularly disposed shaftends 1 and 2.

The front extremity of the shaft-end 1 is hollowed-out so as to form a female end-piece provided with an axial housing 3. Said housing has a transverse cross-section in the shape of a keyhole and a side-lobe forming a cylindrical passage 4 of revolution which is parallel to the axis X-X of the shaft-end 1. The side-lobe which forms the cylindrical passage 4 has a transverse cross-section in the shape of a horseshoe arch, the edges of which are defined by a radial recess 40.

The second shaft-end 2 has an extension in the form of a male end-piece 5 of rectangular shape having a smaller width than that of the radial recess 40 in which said shaft-end is capable of moving freely.

A radial cylindrical recess 6 having the same diameter as the passage 4 of the shaft 1 is cut in the outer edge of said shaft-end 2.

Said recess 6 has a transverse cross-section which is limited by two diametrically opposite circular arcs.

A coupling ball 7 has a diameter which corresponds to that of the passage 4 and of the recess 6, with due allowance for clearance. Said ball is inserted both in the passage 4 and in the recess 6, thus providing a mechanical coupling between the two shaft-ends.

After rotation through one half revolution, the respective positions of the two shafts 1 and 2 are indicated in chain-dotted lines in Fig. 1. A simplified transmission system of this type does not permit transmission of substantial power but can serve for indexing movements or else for simple transmissions, especially for toys. This transmission is particularly easy to machine and can be formed by molding without any difficulty.

The system under consideration permits angular displacements between the axes X-X and Y-Y of the shafts 1 and 2 at least of the same order as conventional transmissions as well as a relatively substantial range of sliding motion of one shaft with respect to the other.

The homocinetic transmission illustrated in Figs. 4 to 8 is essentially constituted by two single ball-transmissions connected together by means of an intermediate shaft 50 which provides a coupling between the two shafts 20, 21, namely the shafts between which a movement of rotation is to be transmitted.

The shafts 20 and 21 are both hollowed-out so as to form female housings comprising three parallel passages 10, 11, 12 which are arranged radially in a star pattern around a cylindrical axial passage 19. In axial cross-section, the complete assembly has the shape of a clover-leaf.

The male end-piece is constituted by the intermediate shaft 50, the transverse crosssection of which has the shape of a Y having symmetrical arms 13, 14, 1 5 relatively displaced at angular intervals of 1200.

Each arm 13, 14, 1 5 is hollowed-out in the vicinity of each extremity so as to form two cylindrical housings 24, 25, 26, 27 and 28, 29 which have the same diameter as the passages 10,11, and in which are fitted six balls 16,17, 1 8, 30, 31. Said balls are intended to provide a coupling between the intermediate shaft 50 and the two shaft-ends 20, 21 by sliding within the passages 10, 11, 12 of each of the female endpieces of the shafts 20 and 21.

Two housings 32, 33 are formed respectively in each end face of the intermediate shaft 30 and receive thrust-bearing balls 34, 35 which are applied respectively against bearing plates 36, 37, said plates being urged elastically by a spring 22 and a rubber block 23.

The arrangement described in the foregoing prevents any accidental displacement of the intermediate shaft 50 between the two shaft ends 20, 21, especially for transmission of rotational motion at a given velocity.

In many practical applications, a single resilient stop proves sufficient whereas the other stop is constituted by a bearing face.

A bellows seal 38 which connects the two shaft-ends 20. 21 serves to protect the transmission against pollution.

A homocinetic transmission of this type permits the coupling of shafts having large angular differences and substantial deviations from parallel alignment as well as transmission of relatively high power at relatively high speeds of rotation. The transmission system remains homocinetic in all the angles of inclination.

A kinematic study of a double ball-type transmission of this type shows that, in contrast to conventional universal-joint transmissions, the axis of the intermediate shaft is never concurrent with the respective axes of the two shaft-ends coupled by said shaft unless the three axes are in alignment. In fact, when said axis is inclined and around its rotation, the center of the intermediate shaft describes an ellipse as shown in Fig. 9, in which the reference numeral 39 indicates the point at which the axis of the shaft 50 encounters the plane of the three balls 1 6, 1 7, 18. The curve 40 represents the path of the point 39. The curve 41 represents the path of the axis of the three balls 16,17,18.

By way of indication in the case of the balls 1 6, 1 7. 18 whose center is displaced radially to a distance of approximately 10 millimeters from the shaft 50, the dimensions of the ellipse are of the order of a few tenths of a millimeter, depending on the angle of inclination within parallel passages 49, 51, 52 of a three-lobed female housing which is similar to that of the shafts 20 and 21 of the example of Fig. 4 and which is hollowed-out in the second shaft-end 48. In the axial line of extension of each of the three passages 49, 51, 52 are formed housings 53 for push-rods 54, 55 each connected by means of a link-arm 56, 57 respectively to an arm 44, 45 of the male endpiece 43. Each push-rod 54, 55 can constitute the piston of a jack, the cylinder of which is formed by the associated housing 53.

As a result of controlled admission of a hydraulic fluid into each jack cylinder, the axis of the shaft 42 can be oriented at will with respect to the axis of the shaft 48.

By way of alternative, each push-rod can be actuated by any conventional means such as a screw jack, connecting-rod system or the like.

As will be readily apparent, the invention is not limited in any sense to the embodiments described in the foregoing with reference to the accompanying drawings. Depending on the applications considered, many alternative forms of construction within the capacity of those skilled in the art may accordingly be contemplated without thereby departing either from the scope or the spirit of the invention.

Claims

1. A ball-type mechanical transmission between two shaft-ends, characterized in that the front extremity of a first shaft-end is hollowed-out so as to form a female end-piece having an axial housing whose transverse cross-section has at least one side-lobe forming a cylindrical passage of revolution which is not perpendicular to the axis of said first shaft-end, the transverse cross-section of said side-lobe being delimited by a horseshoe arch, that the second shaft-end has an extension in the form of at least one male end-piece whose width considered transversely to the axis of said second shaft-end is smaller than the width of the free opening of the horseshoe arch of the passage lobe associated with said endpiece, the wall of said male end-piece which is remote from the axis of the second shaft-end being hollowed-out near its extremity so as to form a cylindrical recess of revolution having the same diameter as the associated passage of the first shaft-end and having an axis which is not parallel to that of the second shaft-end, the transverse cross-section of said recess being limited by two diametrically opposite circular arcs, and that a coupling ball having a corresponding diameter with due allowance for clearance is inserted and maintained freely both within the passage of the first shaftend and within the recess of the second shaft-end.

2. A transmission in accordance with claim 1, characterized in that the axis of the cylindrical recess of the male end-piece is perpendicular to the axis of the second shaft-end.

3. A transmission in accordance with claim 1 or claim 2, characterized in that the female housing of the first shaft-end is provided with at least two radially spaced parallel cylindrical passages, the male end-piece of the second shaft-end being provided with a number of corresponding radial elements equal to the number of coupling balls and to the number of associated passage-element assemblies.

4. A transmission in accordance with claim 3, characterized in that the female housing has an axial cylindrical passage of revolution with three lobes uniformly spaced in a star formation, the transverse cross-section of the male end-piece being in the shape of a Y having symmetrical arms spaced at angular intervals of 1200.

5. A double homocinetic ball-type mechanical transmission between two non-aligned rotary shaft-ends which may or may not be concurrent, characterized in that said transmission comprises an intermediate shaft disposed freely between the two shaft-ends, a ball-type transmission in accordance with any one of claims 1 to 4 being formed by each end of the intermediate shaft respectively with the associated shaft-end.

6. A transmission in accordance with claim 5, characterized in that the intermediate shaft is adapted to carry a male or female end-piece of the same type at each extremity, each shaft-end being provided with an end-piece of the same type and complementary to the end-pieces of the intermediate shaft.

7. A transmission in accordance with claim 5 or claim 6, characterized in that the end-pieces at the extremities of the intermediate shaft are angularly displaced with respect to each other in parallel planes.

8. A transmission in accordance with claim 5 or claim 6, characterized in that said transmission comprises at least one resilient stop for limiting the axial displacements of the intermediate shaft.

9. A transmission in accordance with claim 3 or claim 4, characterized in that the free extremity of each radial element of the male end-piece which penetrates into the female end-piece is secured to a push-rod which slides in a direction parallel to the axis within an internal extension of each passage of the female end-piece and which can be actuated at will in order to modify the angle made by the axes of the two shaft-ends.

10. A transmission in accordance with claim 4 and claim 9 especially for a robot wrist, characterized in that said transmission comprises three parallel push-rods each connected respectively to one arm of the male end-piece by means of a link-arm.

11. A ball-type mechanical transmission between two shaft-ends, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

12. A transmission in accordance with claim 1 substantially as described herein with reference to Figs 1 to 3 or Figs. 1 to 3 as modified by Figs. 4 to 9 or Fig. 10 of the accompanying drawings.

1 3. A robot wrist comprising a transmission in accordance with any one of the preceding claims.

14. A shaft coupling comprising any novel feature or combination of features disclosed in this application.