DE102020132566A1 - Flat gear and cage for flat gear - Google Patents

Abstract

Flat gear (2) with at least one first ring gear (4) (Circular Spline) with internal teeth (8), a flexible spur gear (14) (Flexspline) arranged inside the ring gear (4) with external teeth (18) and a The shaft generator (20) arranged in the spur gear (14) for deforming the spur gear (14) in the radial direction, a torque-transmitting connection being established between the ring gear (4) and the spur gear (14) at two opposite points of the spur gear (14), and the shaft generator ( 20) a ring (24) with an elliptical outer circumference and two elliptically deformed roller bearings (28, 30) mounted on the outer circumference, with two outer rings (36, 38), two inner rings (32, 34) and each in a row between the outer ring (36, 38) and inner ring (32, 34) arranged rolling elements (42, 46), and wherein the wave generator (20) comprises two rows (40, 44) of rolling elements (40, 44), each row (40, 44) of Rolling elements (42, 46) each one of the b is assigned to two bearings (28, 30), and wherein the two rows (40, 44) of rolling bodies (42, 46) are arranged in a common cage (50) for both rows (40, 44).

Description

The invention relates to a flat gear with at least one first ring gear (circular spline) with internal teeth, a flexible spur gear (flex spline) with external teeth arranged inside the ring gear and a wave generator arranged inside the spur gear for deforming the spur gear in the radial direction, with between the ring gear and Spur gear at two opposite points of the spur gear, a torque-transmitting connection is made, and wherein the wave generator has a ring with an elliptical outer circumference.

Flat gears are known from the prior art, which represent a special design of strain wave gears. These flat gears usually comprise four components, namely two internally toothed ring gears (dynamic spline and circular spline), an externally toothed, thin-walled ring (flexspline) and a shaft generator. The drive component designed there as an elliptical wave generator deforms the transmission component designed as an externally toothed Flexspline via a ball bearing, which is located in the opposite areas of the large axis of the ellipse in engagement with the internally toothed wheel designed as a circular spline. Turning the wave generator shifts the large axis of the ellipse and thus the meshing area. Since the flexspline of the gear usually has two teeth fewer than the circular spline, a relative movement between the flexspline and circular spline of one tooth takes place during half a revolution of the wave generator and of two teeth during a complete revolution. With a fixed Circular Spline, for example, the Flexspline as a transmission element rotates the Dynamic Spline in the opposite direction to the drive. The circular spline can be arranged in a pivot bearing ring so that it can be fixed.

From the EP 2 676 019 B1 a harmonic drive in pot design is known, in which two sets of balls are offset in a bearing by half a pitch of the ball.

From the state of the art flat gears are known both with one and with two thin ring ball bearings arranged side by side on the elliptical disk. Flat gears with two bearings can transmit greater power with the same diameter of the toothed components. However, according to the current state of the art, they are wider than flat gears with one bearing. Flat gears with two bearings are previously only known in designs in which the ratio between the width of the flexspline and the pitch circle diameter of its teeth is greater than 0.3.

The invention is therefore based on the object of upgrading a flat gear to transmit higher power with narrower dimensions. Furthermore, a corresponding cage for a flat gear is to be provided.

With regard to the flat gear, this object is achieved according to the invention with two elliptically deformed rolling bearings mounted on the outer circumference with two outer rings, two inner rings and rolling elements arranged in a row between the outer ring and inner ring, the wave generator comprising two rows of rolling elements, each row of Rolling elements is assigned to one of the two bearings, and the two rows of rolling elements are arranged in a common cage for both rows.

Advantageous configurations of the invention are the subject matter of the dependent claims.

The invention is based on the consideration that flat gears, in particular due to their compact design, open up many areas of application in which the space available for a gear is very limited, for example in artificial joints or in robotics. However, the compact design of these flat gears also comes at the expense of their performance. Due to the narrow design, only one bearing is used, which limits the power that can be transmitted. It would therefore be desirable to increase the portability of benefits.

As has now been recognized, this transferability of power can be realized by using two narrower bearings arranged adjacent to one another with a common cage for rolling elements. The compact design can be maintained by using a common cage for both rows of rolling bodies, in which both rows of rolling bodies are arranged. The common cage guides the balls of the two roller bearings in such a way that they are offset from one another by half a pitch. Due to the staggered arrangement of the rolling elements and the common cage, the flat gear can be made narrower than previously known from the prior art.

Advantageously, the cage has a web and pockets for the rolling elements alternating on opposite sides. The balls or rolling bodies are thus arranged offset in both rows, so that the two rows of balls can be positioned very close together in the axial direction. This arrangement of the balls allows more balls to be accommodated in a comparable installation space, in which a bearing was previously arranged, and they can be used to support the flexspline cheaper, that is, axially offset from one another to arrange. In this way, a transmission of power or torque can be made possible with a very compact design. The axially arranged sets of balls and the alternating arrangement of the balls improve the radial support of the flexspline and the load distribution in the toothing.

The ratio between the width of the flexspline and the pitch circle diameter of its teeth is preferably less than or equal to 0.3.

The ball-shaped rolling elements are preferably arranged in the two rows by a predetermined ball offset relative to one another, i.e. the rolling elements are arranged at regular intervals in the cage or the pockets have the same distances from one another, as a result of which a uniform and stable functionality of the bearing is achieved.

The rolling bodies of the two rows advantageously have the same diameter, with the ball offset. This means that the distance between a ball in one row and an adjacent ball in the other row corresponds to half the pitch of the rolling elements.

In a preferred embodiment, the flat gear comprises a second ring gear (dynamic spline), the second bearing being arranged between the spur gear and the second ring gear.

The cage is preferably made of plastic. The plastic is preferably PA (polyamide). The use of a plastic is advantageous since plastic material has sufficient stability for the construction of the cage and at the same time allows complex shapes to be produced in a favorable manner. Alternatively, the cage can also be made from another material that is customary for bearing cages, such as steel, brass or bronze.

With regard to the cage, the above-mentioned object is achieved according to the invention with a cage that has pockets for rolling elements, alternating on opposite sides.

The cage is preferably made of plastic. The plastic is preferably PA. Alternatively, it can also be made of steel, brass or bronze.

The advantages of the invention are, in particular, that a narrower flat gear with a higher power transmission capacity can be designed in comparison to the known prior art by using two roller bearings arranged adjacent to one another in a compact design with a common cage. The self-supporting cage results in design advantages, since an additional shaped element to secure the cage is no longer required.

Further goals, advantages, features and application possibilities of the present invention result from the following description of an exemplary embodiment with reference to the drawing. All features described and/or illustrated form the subject matter of the present invention, either alone or in any meaningful combination, also independently of their summary in the claims or their references.

• 1 eine Vorderansicht eines Flachgetriebes in einer bevorzugten Ausführungsform;
• 2 einen Schnitt entlang der Getriebeachse durch das Flachgetriebe gemäß 1; und
• 3 ein Detail eines Käfigs des Flachgetriebes gemäß 1.

They show in a schematic representation:

• 1 a front view of a flat gear in a preferred embodiment;
• 2 according to a section along the gear axis through the flat gear 1 ; and
• 3 a detail of a cage of the flat gear according to 1 .

Identical parts are provided with the same reference symbols in all figures.

That in the 1 and 2 Flat gear 2 shown has two ring gears 4, 6 arranged side by side, ring gear 4 being the circular spline of flat gear 2 and ring gear 6 being the dynamic spline of flat gear 2. The ring gears 4, 6 each have internal teeth 8, 10. Flat gear 2 also has a flexible or elastically deformable spur gear 14 or a flex spline with external teeth 18 which can be engaged with internal teeth 8 , 10 of the respective ring gear 4 , 6 .

The spur gear 14 or the flexspline can be deflected into an approximately elliptical shape, it being possible for the elliptical deflection to be produced as a deformation running around the circumference of the flexspline. The Flexspline is located with its external toothing 18 only in the area of the large axis of the ellipse in engagement with the internal toothing 8, 10 of the respective ring gear 4, 6. The displacement of the elliptical deformation over the circumference of the Flexspline results in a rotational relative movement between the Flexspline and the circular splines.

The elliptical deformation of the flexspline takes place via a wave generator 20 or wave generator, which in the exemplary embodiment chosen here consists of a steel ring 24 with a central hub, the so-called plug, which has an elliptical contour on the outside, and two raised, elliptically deformable Wave generator bearings 28, 30 is formed. the Bearings 28, 30 of the wave generator 20 are each positioned on the inner lateral surface of the flexspline. The respective bearing 28, 30 has an inner ring 32, 34 and an outer ring 36, 38, between which the balls 42, 46, which form the corresponding rolling elements, run.

The shaft generator 20 as a driven component deforms the spur gear 14 or the flex spline via the bearings 28, 30, which is in engagement with the internally toothed circular spline (hollow gear 4) and dynamic spline (hollow gear 6) in the opposite areas of the large elliptical axis. When the shaft generator 20 rotates, the large axis of the ellipse and thus the meshing area shift.

In the exemplary embodiment selected here, the flexspline has two fewer teeth than the circular spline, so that after half a revolution of the wave generator, a relative movement between the flexspline and circular spline of one tooth and after a full revolution of two teeth takes place.

Flat gear 2 is implemented in a compact design with a width-to-diameter ratio (ratio between the width of the flexspline and the pitch diameter of its teeth) of less than or equal to 0.3. Compared to known versions of flat gears, the flat gear 2 described here can transmit higher power. This is made possible in the following way. As described above, the flat gear 2 shown has two bearings 28, 30, each having an inner ring 32, 34 and an outer ring 36, 38, between which a first row 40 of balls 42 and a second row 44 of balls 46 are arranged are.

A common cage 50, which is partially shown in 3 is shown, enables a close axial positioning of the balls 42, 46. The cage 50 has a central web 54 which is arranged in the assembled state of the flat gear 2 in the center plane of the gear 2 between the two bearings 28, 30. The cage 50 also has pockets 58 for the balls 42, 46 on both sides. The pockets 58 are designed in such a way that the rows of balls 40, 44 of the two bearings 28, 30 are arranged offset over the circumference of the two bearings 28, 30 by half a pitch, ie by half a rolling element pitch. In this way, the radial support of the Flexspline and the load distribution in the interlocking of Flexspline and Circular Spline or Dynamic Spline are improved.

In the exemplary embodiment shown, the cage 50 is made of plastic, in particular of PA.

Reference List

2

flat gear

4, 6

ring gear

8, 10

internal teeth

14

spur gear

18

external teeth

20

wave generator

24

steel ring

28, 30

warehouse

32, 34

inner ring

36, 38

outer ring

40

first row

42

Bullet

44

second row

46

Bullet

50

Cage

54

web

58

pocket

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 2676019 B1 [0003]

Claims (8)

Flat gear (2) with at least one first ring gear (4) (Circular Spline) with internal teeth (8), a flexible spur gear (14) (Flexspline) arranged inside the ring gear (4) with external teeth (18) and a The shaft generator (20) arranged in the spur gear (14) for deforming the spur gear (14) in the radial direction, a torque-transmitting connection being established between the ring gear (4) and the spur gear (14) at two opposite points of the spur gear (14), and the shaft generator ( 20) a ring (24) with an elliptical outer circumference and two elliptically deformed roller bearings (28, 30) mounted on the outer circumference, with two outer rings (36, 38), two inner rings (32, 34) and each in a row between the outer ring (36, 38) and inner ring (32, 34) arranged rolling elements (42, 46), and wherein the wave generator (20) comprises two rows (40, 44) of rolling elements (40, 44), each row (40, 44) of Rolling elements (42, 46) each one of the b is assigned to two bearings (28, 30), and wherein the two rows (40, 44) of rolling bodies (42, 46) are arranged in a common cage (50) for both rows (40, 44). Flat gear (2) after claim 1 , wherein the cage (50) has a web (54) and pockets (58) for the rolling elements (42, 46) alternating on opposite sides. Flat gear (2) after claim 2 , in which the ratio between the width of the flexspline and the pitch circle diameter of its teeth is less than or equal to 0.3. Flat gear (2) according to one of Claims 1 until 3 , wherein the ball-shaped rolling elements (42, 46) in the two rows (40, 44) are arranged by a predetermined ball offset to one another. Flat gear (2) according to one of Claims 1 until 4 , comprising a second ring gear (6) (dynamic spline), wherein the second bearing (30) between the spur gear (14) and the second ring gear (6) is arranged. Flat gear (2) according to one of Claims 1 until 5 , wherein the cage (50) is made of plastic. Flat gear (2) after claim 6 , where the plastic is PA. Cage (50) for flat gears (2), in particular for a flat gear (2) according to one of Claims 1 until 7 , which has alternating pockets (58) for rolling elements (42, 46) on opposite sides.

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