DE102008014222B3 - Arrangement for wear compensation in particular consisting of plastic so-called. "Harmonic Drive" gears - Google Patents

Abstract

It is a gear consisting of - arranged coaxially to each other - a non-circular cross-section core (10), a fixed, provided with an internal toothing cylindrical inner surface having external toothed ring (20) and one between the core (10) and external toothed ring (20), in Substantially in the form of a hollow cylinder, elastically deformable intermediate toothed ring (30) with an existing at least in the region of one axial end of its outer surface outer toothing (31) with respect to their tooth dimensions of the internal toothing (21) of the outer toothed ring (20) corresponds, but over the circumference a smaller number of teeth than the internal toothing (21) of the outer toothed ring (20), wherein by means of at least one in the outer toothing (31) on the inside of the intermediate toothed ring (30) acting on the core (10) arranged Aufspannelementes (11) whose maximum radial Extension is greater than the inner radius of the intermediate toothed ring (30), the Zwis toothed ring (30) is deformed such that the outer toothing (31) of the intermediate toothed ring (30) only in one or more peripheral regions with the internal toothing (21) of the outer toothed ring (20) meshes (so-called. Harmonic drive gear) proposed in which to compensate for wear generated by play the intermediate toothed ring (30) is formed so that its outer surface at its from the outer toothing (31) remote other end regardless of the action of the at least one Aufspannelementes .. ,

Description

The The invention relates to means for ensuring freedom from play on a so-called harmonic drive transmission over its lifetime, in particular in such a transmission with a large hollow shaft and made of plastic.

Harmonic drive be made of steel for years use cases used, which require high accuracies and lifetimes (W. C. Musser: "The Harmonic Drive ", Machine Design, 1960).

So-called. Harmonic Drive transmissions basically consist of only three components: a non-circular core, the so-called WAVE GENERATOR, a flexible, external one toothed intermediate ring, the so-called FLEXSPLINE, and a fixed, internal toothed ring, the so-called CIRCULAR SPLINE.

One two diametrically opposite Core having clamping elements deformed as a driven part the intermediate tooth ring elliptical, so that this is in the opposite areas his big one Ellipse shaft with the internal toothed outer ring is engaged. At the Turning the core clockwise will displace the large ellipse axis and according to the tooth engagement portion of the intermediate toothed ring. Since the intermediate toothed ring has fewer teeth than the outer toothed ring, takes place per revolution of the core, a relative movement between the intermediate toothed ring and external teeth ring in the counterclockwise direction.

there the intermediate toothed ring is deformed, which is usually over Ball bearing takes place, whose outer ring is elastically deformable.

Of the Intermediate ring is at the predominant Number of harmonic drive gear designed as an elastic pot, At the bottom of the downforce attacks. Due to the deformation of the with the external tooth ring meshing Gearing bearing "pot edge" of such an intermediate toothed ring by means of the clamping elements of the core to the ellipse, the wall surface of the Potted complex deformed, taking a cut through the pot in the Axle of the large ellipse semiaxis of the core the shape of a symmetrical to the central axis of the pot Trapezes shows whose long side is on the "pot edge".

alternative the intermediate toothed ring may also have an outwardly directed flange instead of the bottom of the pot, hence the shape of a "cylinder hat without cover ". Again, the deformation of the pot wall is analogous.

at Such transmissions is currently on the entire life of the transmission on the one hand, the ball bearing has no significant wear, on the other possibly occurring, minimal wear in the Interlocking between intermediate toothed ring and external toothed ring due to the spring properties of the peripheral region of interest frustoconical widened and in the area of the toothing to the cylindrical outer tooth ring contiguous intermediate toothed ring is compensated.

For large quantities have been plastic Harmonic Drive gearboxes for several years now on the market.

Since a ball bearing is relatively expensive, alternative core designs are used here, which can be realized cheaper. For example, rolls (WC Musser: "The Harmonic Drive", Machine Design, 1960) or planetary precursors are used, and a particularly cost-effective design is a core with plain bearings, such as those from the GB 905015 A or the EP 0 743 474 B1 is known.

at Use of plain bearings on the core occurs at the sliding surface Core or its clamping elements and inner circumference of the intermediate toothed ring in the area of the toothing to a wear of the sliding surface, before especially on the core or the clamping elements (due to the higher surface pressure). At the same time the spring action of an intermediate toothed ring made of plastic significantly lower than that of a steel idler ring. By the Wear (abrasion) takes the Aufspannmaß the Kerns with increasing life off. At the same time they are wearing out Tooth flanks, resulting in larger tooth gaps. Because the intermediate toothed ring is less tensioned, its teeth grip less far in the extra enlarged tooth gaps of the Outside the ring gear one. This leads to play, and the accuracy of the transmission gets lost.

A compensation of the wear is possible by radially movable, sprung clamping elements on the core ( EP 0 743 474 B1 ). This ensures that worn clamping elements are radially tracked and thus the teeth of the intermediate gear ring are further pressed sufficiently into the tooth gaps of the outer ring gear. Thus, the freedom of play is largely restored. However, the means for achieving the radial bias require radial space, which may not be available in large hollow shaft applications.

Subject of the DE 195 20 555 A1 is a harmonic drive (harmonic drive gear), in which the intermediate toothed ring not directly but via a fle xible plug-in shaft connection with the output shaft is in communication. In a construction of a corrugated transmission according to this prior art, the actual intermediate toothed ring is deformed only elliptical and it is consequently always the entire tooth width of the teeth of external ring and intermediate toothed ring for power transmission available. By the known construction should also be achieved that a wear-related game extension automatically adjusts, but this can only apply to the game between the plug-in shaft connection and the actual intermediate gear ring and for their storage. A compensation of the wear due to wear of the teeth of external ring and intermediate ring expanding game is not expected. The plug-in shaft connection also requires additional parts and increased installation costs.

Of the Invention is based on the object, a simple and inexpensive way to compensate for the wear and to ensure freedom of movement over the life of Harmonic Drive gears, in particular of plastic, to create, as possible greater Hollow shaft diameter to be achieved.

These Task is according to the invention solved, by doing so Care is taken that the core or its Aufspannelemente - in the course the service life of the gearbox - axial moved or tracked so that the intermediate toothed ring increasingly clamped becomes.

With other words means this, that in the new state of the core or its clamping elements on one, "free", outside ring, elliptical strongly deformed end of the conical intermediate toothed ring are arranged. In the worn state, the core or the Clamping elements continue to the other, firmly clamped, essentially round or hollow cylindrical end of the intermediate toothed ring postponed. As a result, the Aufspannmaß regarding the intermediate toothed ring enlarged and the wear in the Area of the toothing between the intermediate toothed ring and the external toothed ring balanced.

Possible embodiments for one axial adjustment of the core or the clamping elements relative to Intermediate ring are explained below.

The axial displacement of the core and possibly according to the Aufspannelemente can be done by axial spring bias of the core relative to a housing. The springs can metallic or plastic and between the core and a housing or housing part inserted or formed directly on the core. This is special advantageous for small sizes and Plastic cores made by injection molding.

The axial displacement of the core or the clamping elements in comparison to the intermediate toothed ring can alternatively by a linear actuator, z. B. a pneumatic or Hydraulic cylinder done. This is particularly advantageous for larger sizes, at which requires a more accurate readjustment. The linear actuator can be controlled for example by a sensor signal, the z. B. output by a position, force or torque sensor becomes.

Advantages of the transmission design according to the invention are the following:
The axial relative displacement between the core or Aufspannelementen and intermediate toothed ring causes a clearance compensation and thus provides freedom from play over the entire life of the transmission, even with a cost-effective and compact design with plain bearings, clamping elements and / or plastic core.

After this the core or the clamping elements are moved axially instead to use radially movable clamping elements, simplifies the geometry of the core, especially in the area radially inside the clamping elements. It is also essential that less space is needed, leaving a larger hollow shaft at the same outer diameter is feasible.

Further Details of the invention will become apparent from the accompanying drawings.

1 shows in view according to II of 2 a harmonic drive transmission with clamping elements formed by semicircle-like projections 11 that at the core 10 instead of (known in the prior art) rollers are provided. The clamping elements 11 slide in the intermediate toothed ring 30 , As a carrier is an annular structure with a correspondingly large hollow shaft 12 provided, which in principle an outer geometry similar to that in the device according to EP 0 743 474 B1 can achieve.

2 and 3 each show in a section according to II-II of 1 through a harmonic drive gear with cup-shaped intermediate ring ( 30 ), wherein the embodiments of the 2 and 3 only by the design of the intermediate toothed ring 30 differ. This is according to 2 at its the external toothing 31 opposite end with a possibly an opening for an output shaft of the core 10 having ground 32 Mistake. In 3 is instead of a soil 32 a circumferential flange 33 intended.

The 1 to 3 show the basics The structure of a harmonic drive gearbox. This consists of three basic elements, which are arranged coaxially to one another, namely a core 10 in the form of a hollow shaft 12 with - in the embodiment two opposite - clamping elements 11 , an an end face 23 surrounding external teeth ring 20 and a substantially cup-shaped intermediate toothed ring 30 , The external teeth ring 20 is with an internal toothing 21 provided with one at the bottom 32 or flange 33 of the core 10 turned off end of the intermediate toothed ring 30 provided external toothing 31 meshes, but only in areas where the intermediate toothed ring 30 through the clamping elements 11 at the core 10 is widened.

The 4a to 4c show in sectional views accordingly 3 schematically three embodiments of a harmonic drive transmission according to the invention, in which the core 10 or the clamping elements 11 towards the ground 32 or flange 33 of the intermediate toothed ring 30 are biased.

Serve according to 4a one or more distributed over the circumference of the transmission, at the end face 23 and the core 10 or the clamping elements 11 supporting spring elements 40 ,

According to 4b are at a core 10 spring elements 13 attached. Preferably, the core exists 10 made of plastic and is integral with the spring elements 13 injected.

In the embodiment of the 4c the axial displacement of the core takes place 10 or the clamping elements 11 opposite the intermediate toothed ring 30 by means of a plunger 51 having linear actuator 50 , z. B. a pneumatic or hydraulic cylinder, which may be controlled by a sensor signal.

5 is a schematic representation illustrating the effect of wear. The illustration on the left in the drawing shows the outer tooth ring 20 and intermediate gear ring 30 when new, ie without wear-related game. The illustration on the right in the drawing shows the corresponding parts 20 . 30 in the worn state after appropriate running time. It can be seen that both the teeth 22a of the external tooth ring 20 as well as the clamping element 11a for the intermediate toothed ring 30 at the core 10 can be worn, creating a match between the outer ring 20 and intermediate gear ring 30 arises.

In 6 is finally schematic (corresponding to a section) 3 ) the axial displacement of the core 10 or the clamping elements 11 (Section through large ellipse half-axis) in a Harmonic Drive gear to compensate for wear and to avoid play between the teeth 21 . 31 of the external tooth ring 20 and the intermediate toothed ring 30 shown. In 6 left top left a gearbox is shown in new condition. 6 , top right, shows a worn gear with appropriate clearance between the teeth of the outer ring and the intermediate gear ring. The illustrations in 6 , Below, the positions of the parts of the transmission after displacement of the core (left) and the clamping elements (right) to the right in the drawing, whereby the pot of the intermediate toothed ring further widened and thereby the inherent game between the teeth is compensated.

10

core

11

clamping element

11a

clamping element at the core, worn

12

hollow shaft

13

Spring element, molded on the core

20

Outer ring gear

21

internal gearing on the outer ring

22

tooth the internal toothing on the outer tooth ring

22a

tooth the internal toothing on the outer tooth ring, worn

23

frontal Plate on the external teeth ring

30

Between annular gear

31

external teeth at the intermediate toothed ring

32

tooth the external toothing at the intermediate toothed ring

33

ground

34

flange

40

spring element

50

linear actuator

51

tappet

Claims (11)

Gear consisting of - coaxial to each other - a non-circular cross-section core (the so-called Wave Generator - 10 ), a fixed, one with an internal toothing ( 21 ) provided cylindrical inner surface having external tooth ring (the so-called. Circular Spline - 20 ) and one between core ( 10 ) and outer ring ( 20 ), substantially in the form of a hollow cylinder having, elastically deformable intermediate toothed ring (the so-called. Flexspline - 30 ) with an outer toothing present at least in the region of one axial end of its outer surface ( 31 ), which in terms of their tooth dimensions of the internal toothing ( 21 ) of the outer ring ( 20 ), but over the circumference a smaller number of teeth than the internal toothing ( 21 ) of the outer ring ( 20 ), wherein by means of at least one in the area the external toothing ( 31 ) on the inside of the intermediate toothed ring ( 30 attacking, at the core ( 10 ) arranged clamping element ( 11 ) whose maximum radial extent is greater than the inner radius of the intermediate toothed ring ( 30 ), the intermediate toothed ring ( 30 ) is deformed such that the external toothing ( 31 ) of the intermediate toothed ring ( 30 ) only in one or more peripheral regions with the internal toothing ( 21 ) of the outer ring ( 20 ) meshes so that upon rotation of the core ( 10 ) with the at least one clamping element ( 11 ) in relation to the external toothed ring ( 20 ) with an output shaft ( 12 ) connected toothed ring ( 30 ) with a relative to the angular velocity of the core ( 10 ) significantly reduced speed turns (so-called harmonic drive), characterized in that - the intermediate toothed ring ( 30 ) is formed so that its outer surface at its from the external toothing ( 31 ) remote other end regardless of the action of the at least one clamping element ( 11 ) at the core ( 10 ) substantially retains the hollow cylindrical shape - and that the at least one clamping element ( 11 ) within the intermediate toothed ring ( 30 ) Is arranged axially displaceable. Transmission according to claim 1, characterized in that the at least one clamping element ( 11 ) by means of spring force or an actuator axially in the direction of the other end of the intermediate toothed ring ( 30 ) is displaceable. Transmission according to claim 1 and 2, characterized in that on the core ( 10 ) is fixed a spring causing the axial displacement. Transmission according to claim 1 to 3, characterized in that to the core ( 10 ) or the clamping element ( 11 ) An axial displacement causing spring is formed. Transmission according to claim 1 and 2, characterized in that at least one of the axial displacement of the Aufspannelementes ( 11 ) causing spring between the core ( 10 ) and a housing part of the transmission is inserted. Transmission according to claim 1 and 2, characterized in that for the axial displacement at least one Aufspannelementes ( 11 ) a linear actuator, for example, a pneumatic or hydraulic cylinder is used. Transmission according to claim 6, characterized that the linear actuator is controlled by a sensor signal. Transmission according to one of the preceding claims, characterized in that the intermediate toothed ring ( 30 ) cup-shaped with a connection for an output shaft forming, circular or annular disk-shaped bottom is formed. Transmission according to claim 8, characterized in that the bottom of the intermediate toothed ring ( 30 ) projects beyond the shell of the hollow cylinder radially outward. Transmission according to one of the preceding claims, characterized in that the core ( 10 ) at least two equiangularly spaced, radially outwardly extending clamping elements ( 11 ), which with its outer ends, the external toothing ( 31 ) of the intermediate toothed ring ( 30 ) in the internal toothing ( 21 ) of the outer ring ( 20 ), and that the number of teeth of the outer toothing ( 31 ) of the intermediate toothed ring ( 30 ) by one of the number of clamping elements ( 11 ) corresponding number is less than the number of teeth of the internal toothing ( 21 ) of the outer ring ( 20 ). Transmission according to one of the preceding claims, characterized in that at least the core ( 10 ) with the clamping elements ( 11 ) and the intermediate toothed ring ( 30 ) consist of plastic.