Frictional strain wave gear mechanism, and method

Abstract

The present invention relates to the field of strain wave gear mechanisms which are frequently also called "harmonic drive gear mechanisms". In order to provide a frictional strain wave gear mechanism which enables the deformation of the flexspline including the generation of the necessary pressing force in a simple, mechanical way, in order that technically utilizable forces can be transmitted without a great complexity being necessary for compensating for existing mechanical tolerances in the gear mechanism, a frictional strain wave gear mechanism is proposed with an outer cylinder, a flexspline and a wave generator, wherein the outer cylinder, the flexspline and the wave generator are in frictional contact for the transmission of force, which frictional contact is brought about by a pressing force, wherein at least one structure with an elastic shape is formed by the outer cylinder or a constituent part of the wave generator, which structure is hollow in the region of the frictional contact and has a wall thickness which is constant during a deformation of the shape, wherein the elastic structure is configured to apply the pressing force. The invention also relates to a frictional planetary gear mechanism.

Description

[0001] Friction stress wave gears and processes

[0002] Description

[0003] The present invention relates to the field of stress wave transmissions, often also called "Harmonie Drive transmissions," and in particular to a friction stress wave transmission, i.e., a stress wave transmission in which friction is used for power transmission. The present invention also relates to the field of a planetary transmission in which frictional engagement is used for power transmission.

[0004] A typical stress wave transmission, as described in US 1,906,143 A, has the following three elements.

[0005] 1 . a rigid cylinder 11 with an internal toothing 2. a deformable cylinder arranged concentrically to the rigid cylinder 1 i

[0006] (I2), also called Flexspline, with an external toothing whose number of teeth is less than the number of teeth of the rigid cylinder 11 and

[0007] 3. a wave generator I3, also arranged concentrically to the rigid cylinder 1 i, with a non-circular design.

[0008] These three elements of a known stress wave transmission are shown as an example in Fig. 1. The wave generator 13 acts on the flexspline 12 so that its external teeth engage with the internal teeth of the rigid cylinder 1 i in at least two areas. If the wave generator 1 3 is now rotated relative to the rigid cylinder 1 i around the common center, the areas in which the teeth are in engagement move with it. Since the number of teeth on the flexspline 12 is fewer than the number of teeth on the rigid cylinder 11, the flexspline 1 2 and the rigid cylinder 1 i perform a relative movement.

[0009] There are a variety of such stress wave gears, which differ in the design of the three elements and their interaction. These types of stress wave gears have disadvantages. One of them is that they cannot be built very small due to the necessary gearing – at least not without requiring very high and therefore expensive manufacturing effort.

[0010] If the torque to be transmitted via the gear becomes too great, damage occurs because the meshing teeth are destroyed.

[0011] In addition, gear transmissions generally run unevenly and therefore also generate noise during fast operation.

[0012] There is therefore an interest in realizing stress wave gears without gearing, based on friction.

[0013] The subject matter of the present invention belongs to this class of friction stress wave gears.

[0014] US 3,427,898 A describes a modification of a stress wave drive that does not use gears. Instead, the flexspline is locally deformed by one or more rollers and pressed against the inner surface of the rigid cylinder. The rollers can be rotated relative to the rigid cylinder, so that the deformation of the flexspline travels along the inner surface of the rigid cylinder. The contact force and the friction coefficient must be selected so that the force to be transmitted does not cause the components to slip against each other. Since the flexspline has a smaller circumference than the circumference of the inner surface of the rigid cylinder, each rotary pass of the flexspline's deformation results in a correspondingly smaller concentric rotation of the flexspline. In the description of US 3,427,898 A, the flexspline is fixed, and the input and output drive systems are located on the other two of the three elements.It is state of the art to be able to freely select which elements are fixed, which elements are driven, and which are used as output. The description of US 3,427,898 A does not explicitly explain how the contact force required for the drive is generated. However, based on the drawings, one can assume that the rollers are flexibly suspended on a flexible axle, so that the contact force is generated via this. US 3,427,898 A also proposes that the circumference of the flexspline be larger than the circumference of the inner surface of the rigid cylinder, which results in greater rotation of the flexspline.

[0015] A further modification was proposed in US 3,604,287 A. It also contains three elements (rigid cylinder, flexspline, and wave generator). The outer surface of the deformable cylinder (flexspline) is pressed against the inner surface of the rigid cylinder by a wave generator. Here, too, the circumference of the flexspline in frictional contact is smaller than the circumference of the inner surface of the rigid cylinder. In this case, the necessary contact force is generated by an elastomer arranged along the circumference of one of the surfaces in frictional contact. This is disadvantageous because such elastomers can only transmit small forces. In addition, the friction pairing is very susceptible to wear, so that only a short service life is to be expected, and dirt is generated in the form of abrasion.

[0016] A further modification of the friction stress wave drive is described in US 6,439,081 B1. The contact force is generated here via a Y-shaped support structure, possibly with the support of preload screws, which holds the rollers of the wave generator and can be rotated concentrically with the rigid cylinder together with the rollers. The rollers deform a flexspline. The flexspline, in turn, is pressed locally against the inner surfaces of the rigid cylinder via the rollers of the wave generator, with a force that allows a usable torque to be transmitted. Since the flexspline has a smaller circumference than the inner surface of the rigid cylinder, the flexspline rotates less with each complete revolution of the wave generator (consisting of the rollers and the Y-structures).

[0017] A further modification of the friction stress wave transmission is described in WO 2010 / 000302 A1. In this invention, the flexspline is not deformed by a mechanical device, but rather by circulating magnetic fields, which also generate the necessary contact force. Due to the exclusive use of magnetic fields, such a transmission cannot be significantly miniaturized if large torques are to be transmitted. The object of the present invention is to provide a friction stress wave transmission that enables the deformation of the flexspline and the generation of the necessary contact force in a simple, mechanical manner, so that technically usable forces can be transmitted, without requiring great effort to compensate for existing mechanical tolerances in the transmission.

[0018] According to a first aspect of the invention, a friction stress wave transmission is proposed as defined in claim 1, namely with an outer cylinder, a flex spine and a wave generator, wherein the outer cylinder, the flex spine and the wave generator are in frictional contact for power transmission, which is caused by a contact pressure, wherein at least one structure which is elastic in shape is formed by the outer cylinder or a component of the wave generator, which structure is hollow in the region of the frictional contact and has a constant wall thickness when the shape is deformed, wherein the elastic structure is designed to apply the contact pressure.

[0019] According to a second aspect of the invention, a kit or construction set for producing a friction stress wave transmission is proposed, as defined in claim 7, namely with an outer cylinder, a flexspine and a wave generator, wherein the outer cylinder has an inner radius which is smaller by a difference than the sum of the material thickness of the flexspine and the radius of the wave generator along its main axis, wherein the difference is dimensioned such that a structure formed by the outer cylinder or a component of the wave generator, which is elastic in its shape and which is hollow in an area intended for frictional contact between the outer cylinder, flexspine and wave generator for force transmission and has a wall thickness which is constant during deformation of the shape, is designed to provide a restoring force as a contact force during the corresponding deformation, which is for the transmission of force between the outer cylinder,Flexspine and Wave Generator is provided.

[0020] According to a third aspect of the invention, a method for transmitting a rotary movement with a friction stress wave gear is proposed, as defined in claim 8, wherein the friction stress wave gear comprises an outer cylinder, a flex spine and a wave generator, wherein the outer cylinder, the flex spine and the wave generator are in frictional contact for force transmission, which is caused by a contact pressure, wherein the contact pressure is applied by at least one structure which is elastic in its shape, which is hollow in the region of the frictional contact and has a wall thickness which is constant when the shape is deformed, wherein the elastic structure is formed by the outer cylinder or a component of the wave generator.According to a fourth aspect of the invention, a friction planetary gear is proposed as defined in claim 9, namely with: an outer cylinder and a revolving arrangement arranged in the outer cylinder with a sun gear and at least two planet gears, wherein the planet gears are each in frictional contact with the outer cylinder and the sun gear for power transmission, which is brought about by a contact pressure, wherein at least one structure which is elastic in its shape is formed by the outer cylinder and / or the sun gear, which structure is hollow in the region of the frictional contact and has a wall thickness which is constant when the shape is deformed, wherein the elastic structure is designed to apply the contact pressure.

[0021] Part of the background of the present invention can be found in the following considerations.

[0022] In the following description, unless stated otherwise, it is assumed that the outer cylinder is fixed while an inner cylinder is driven, so that a resulting, reduced movement can be detected in the flexspline. Those skilled in the art will know, in accordance with the prior art, that the configuration can also be selected differently. Depending on which component is fixed, which component is driven, and from which component the movement is detected, a different usable transmission ratio results. Even a differential gear can be realized in this way. The fact that the description assumes a fixed outer cylinder and an inner cylinder is driven does not mean that the invention is limited to this constellation. The other configurations are also intended to be encompassed by the present invention.

[0023] For the friction stress wave transmission according to the invention, the contact pressure between the friction partners is generated via the elastic deformation of the elastic structure (e.g., one or more radially elastic hollow cylinders with a constant material thickness across the contact pressure area), based on the restoring force of the at least one hollow cylinder. Such a very simple solution eliminates the need for complex mechanical preload structures, such as springs or deflection devices. This enables a particularly simple mechanical design, so that the transmission can be manufactured cost-effectively. In particular, the simple design according to the invention enables significant miniaturization.According to the present invention, an improved frictional stress wave transmission is described, which enables a high transmission or reduction ratio and, in a special design, a continuous change of the transmission or reduction ratio, even a reversal of the output direction without the drive having to change direction. Another advantage is that such a frictional stress wave transmission can be designed completely backlash-free, which is particularly necessary for precise applications.

[0024] The contact force F nThe friction between the contacting bodies must be large enough that, for a given coefficient of friction p, the tangential forces to be transmitted do not lead to sliding of the contacting surfaces, so that the rolling elements roll against each other. In a detailed analysis, the coefficient of sliding friction also plays a role, since the flattened areas created by the pressure generally lead to the formation of a friction and sliding zone, which, however, is not further relevant for the explanation of the transmission according to the invention.

[0025] The gearbox features inherent mechanical protection against overload, as excessive torque to be transmitted would cause the surfaces in frictional contact to slip without causing immediate damage to the components. Another advantage is that these gearboxes can be designed to be self-locking, eliminating the need for brakes. This is useful for use in robots, for example, as it allows for a simple overall design.

[0026] Features of advantageous embodiments of the invention are defined in particular in the subclaims, wherein further advantageous features, embodiments and configurations can also be gathered by the person skilled in the art from the above explanation and the following discussion.

[0027] In the following, the present invention is further illustrated and explained with reference to exemplary embodiments shown in the figures.

[0028] Fig. 1 is a schematic diagram illustrating an example of a conventional stress wave transmission,

[0029] Fig. 2 is a schematic representation of a first embodiment of the transmission according to the invention with flexible planetary gears in the wave generator,

[0030] Fig. 3 is a schematic representation of a second embodiment of the transmission according to the invention with only one flexible and at least one rigid planetary gear in the wave generator,

[0031] Fig. 4 is a schematic representation of a third embodiment of the transmission according to the invention with a flexible sun gear in the wave generator, Fig. 5 is a schematic representation of a fourth embodiment of the transmission according to the invention with a flexible, fixed cylinder,

[0032] Fig. 6 is a schematic representation of a friction stress wave transmission according to the invention with a planetary gear carrier,

[0033] Fig. 7 is a schematic representation of a friction stress wave transmission according to the invention with a driven outer cylinder,

[0034] Fig. 8 is a schematic representation of an embodiment of a friction stress wave transmission according to the invention with the potential of a particularly strong transmission,

[0035] Fig. 9 is a schematic representation of a friction stress wave transmission according to the invention, comparable to the embodiment of Fig. 8, but with a flexspline which has two diameters,

[0036] Fig. 10 is a schematic representation of a further modification of the embodiment of a friction stress wave transmission according to the invention as in Fig. 9, but with a flexspline which has a smaller outer diameter in the first stage than in the second stage,

[0037] Fig. 11 is a schematic representation of a further modification of the embodiment of a friction stress wave transmission according to the invention as in Fig. 9, but with planetary gears which have a smaller outer diameter in the first stage than in the second stage,

[0038] Fig. 12 is a schematic representation of a further modification of the embodiment of a friction stress wave transmission according to the invention as in Fig. 11, but with planetary gears which compensate for a difference in the inner diameters of the cylinders in the first and second stage via radial elasticity, so that no two radii in the planetary gears are necessary,

[0039] Fig. 13 is a schematic representation of a further modification of the embodiment of a friction stress wave transmission according to the invention as in Fig. 12, but with differently shaped planetary gears,

[0040] Fig. 14 is a schematic representation of an example of a cylinder with a variable inner diameter,

[0041] Fig. 15 is a schematic representation of an exemplary transmission according to the invention with a driven outer cylinder,

[0042] Fig. 16 is a schematic representation of exemplary designs of the hollow cylinders of a friction stress wave transmission according to the invention,

[0043] Fig. 17 is a schematic representation of an exemplary integration of a motor function in a frictional stress wave transmission according to the invention, Fig. 18 is a schematic representation of an embodiment of a frictional stress wave transmission according to the invention without a planetary gear-like wave generator,

[0044] Fig. 19 is a schematic representation of an embodiment of a friction stress wave transmission according to the invention, in which one of the components has a structured surface, and

[0045] Fig. 20 is a schematic representation of an embodiment of a friction planetary gear according to the invention.

[0046] In the accompanying drawings and the explanations to these drawings, corresponding or related elements are - where appropriate - identified by corresponding or similar reference numerals, even if they are found in different embodiments.

[0047] In a first embodiment, the at least one flexible hollow cylinder 2s is a component of the wave generator, wherein the wave generator essentially corresponds to the structure of a friction planetary gear, consisting of a sun gear 24 and the planet gears 23. Even if it is shown as a single-stage device, the wave generator can also be designed as a multi-stage planetary gear.

[0048] A first example of this embodiment is described below with reference to Fig. 2.

[0049] The driven sun gear 24 in the example is in frictional contact with at least two (in this specific example, three) planetary gears 2s. The planetary gears 2a are in direct frictional contact with a flexspline 22, which is deformed via the planetary gears 2s and pressed against the inner surface of the stationary cylinder 2i. The outer circumference of the flexspline is smaller than the inner circumference of the stationary cylinder 2i, which, in accordance with frictional stress wave gears, results in a reduction in speed such that when the wave generator rotates a full rotation, the flexspline rotates only a fraction of that rotation. Assuming that the flexspline is circular in its undeformed state, the gear ratio is as follows:

[0050] ADFS = Outer diameter of the Flexspline 22 nwG = Speed ​​of the Wave Generator nFs = Speed ​​of the Flexspline

[0051] IDz = inner diameter of the fixed cylinder 2i

[0052] IH = Gear ratio harmony = - nwc / nps = - (IDZ-ADFS)ZIDZ The negative sign indicates that the direction of rotation is reversed from the wave generator to the flexspline.

[0053] For the entire friction stress wave transmission, the ratio of the planetary gear in the wave generator is also added. ns = speed of the sun gear, rz = inner radius of the fixed cylinder, 2i h = thickness of the flexspline, 2i rs = radius of the sun gear, 24

[0054] IWG = translation in the wave generator = ns / nwG = (1 + r z -h) / rs

[0055] Thus, the total ratio of the transmission according to the invention is IG = IWG + IH

[0056] In the first embodiment according to the invention, the planetary gears are designed to be flexible (e.g., as a hollow cylinder). If such a hollow cylinder is clamped between the friction contacts, a deformation occurs, as shown in Fig. 2 b). If the inner radius of the stationary cylinder 2i is smaller than the sum of o rs, o ADp (diameter of a planetary gear 2s), and the o thickness h of the flexspline, then the radially flexible planetary gear 2a should be compressed in its inner and outer diameters by the difference. This situation is illustrated in Fig. 2 b) in an exaggerated manner. In a practical embodiment, such a deformation will hardly be visible to the naked eye. The two thick arrows indicate that a deforming force F nThe planetary gear is therefore no longer circular, but elastically deformed, takes on the shape of a slight ellipse. If the planetary gear 2a rolls on the sun gear 2, the diameter between the pressing points will always be smaller than in the areas where the sun gear is not pressed. The contact force always remains constant if the diameters and material thicknesses of the other components are also constant. If the contact force F nand the friction coefficient p is high enough, then the necessary torque can be transmitted via the friction gear according to the invention before the surfaces in frictional contact slip. In c) of Fig. 2, a frequently used embodiment of the flexspline is shown in cross-section when the gear is installed. The flexspline has a first flexible region, which is pressed in regions via the wave generator onto the inner surface of the stationary cylinder 2i. Another region of the flexspline is rigid, so that the rotation of the flexspline can be tapped from this region for technical use. According to the state of the art, there are various different designs of a flexspline, all of which can be used for the gear according to the invention.

[0057] In d) of Fig. 2, a modification of the transmission is shown which enables a continuously variable change of the transmission ratio. In the illustration, the fixed cylinder 2id has a conical shape on the inside (which is not absolutely necessary for the function). The flexspline 22d is also conical in the flexible area, the angle of which differs from the conical shape of the fixed cylinder 2id. Via the planetary gears 2ad, the flexspline is pressed onto the inner conical shape in the fixed cylinder at specific points. As already described, part of the transmission ratio of the friction stress wave transmission according to the invention is determined by

[0058] IH = Translation Harmony = nwc / nps = - (IDZ-ADFS)ZIDZ.

[0059] If only the flexspline 2zd is moved along the double arrow relative to the rest of the gearbox, then the ratio o of the diameter IDz (on the inner surface of the fixed cylinder, which is pressed onto the flexspline via the planetary gears), o to the diameter ADFS of the flexspline at this height changes.

[0060] This results in an adjustable change in the gear ratio IH. If the Flexspline22d is pushed far enough into the cylinder 2id that the inner diameter of the Flexspline corresponds to the inner diameter of the stationary cylinder, then the Flexspline rotates exactly with each revolution of the wave generator. If the Flexspline is pushed further along the double arrow so that the contacting outer diameter of the Flexspline (ADFS) becomes larger than the inner diameter (IDz) of the stationary cylinder (the Flexspline will then bulge along the surface), then the Flexspline rotates even faster than the wave generator. It is conceivable that a Flexspline could be designed adaptively, e.g. through the use of shape memory alloys (SMA) or electroactive polymers (EAP), so that its diameter can be varied when installed. This could enable a continuous change in the gear ratio.

[0061] If one of the components of the gear is not circular, which may be the case with a very elastic flexspline, for example, then the diameters of the components can be replaced with the corresponding circumferences when determining the gear ratios.

[0062] In the example of Figure 3, the structure corresponds to the example of Figure 2, with the difference that only one of the planetary gears, the planetary gear 34, is designed to be flexible. This is sufficient to achieve permanent preload of all components in the transmission according to the invention if the sun gear 3s can move slightly from the concentric position to the rigid cylinder 3i, so that a contact force can be distributed across all sun gears.

[0063] In the example shown in Fig. 4, it is not the planetary gears 4s that are designed to be flexible, but rather the sun gear 4, which can also be used to preload the components within the transmission according to the invention. Fig. 4 a) shows the appearance of such a transmission. Fig. 4 b) shows, in a highly exaggerated view, how such a sun gear is deformed when clamped in the friction stress wave transmission.

[0064] It can be seen that the wall thickness of the sun gear 44 is constant even when clamped, so that no change in the contact forces is to be expected when the planet gears 4a roll.

[0065] In an alternative embodiment (Figure 5), the fixed cylinder 5i is implemented as a flexible hollow cylinder with constant wall thickness.

[0066] In this case, the wave generator is implemented with exclusively non-compliant components (sun gear 54 and planet gears 5s). If the wave generator and the flexspline 52 are pressed into the cylinder 5i, the cylinder 5i deforms in such a way that the radius where the flexspline presses against the inner surface via the wave generator enlarges the inner surface, but becomes smaller in the remaining areas. This is shown exaggerated in Figure 5 b). In this way, a constant contact force can be achieved. For example, such a cylinder 5i can be implemented similarly to a flexspline, as can be seen from the section in Figure 5 c), but it should be significantly stiffer than the flexspline 52 so that technically usable forces can be transmitted.

[0067] In principle, the planetary gears can also be positioned relative to one another via a single-part or multi-part planetary gear carrier 65, as shown in Fig. 6.

[0068] When using a planetary carrier 65, ideally, care should be taken to ensure that the planetary gears 63 can still move somewhat relative to each other, so that the contact forces can always be distributed evenly across all friction contacts, even in the event of slight mechanical deviations in the rolling components of the friction gear. This is possible, for example, by making the planetary gear carrier, or components of the planetary gear carrier, elastic. Other means are also conceivable, such as mounting the planetary gears in the planetary gear carrier with some play.

[0069] A further exemplary embodiment (Fig. 7) demonstrates that the arrangement of the fixed and movable components for the friction-tension transmission according to the invention can be easily changed. Here, the flexspline 74 was arranged between the central gear 72 and the planetary gears. In the illustration, the transmission has a driven outer cylinder, and the transmitted movement of the transmission can be sensed at the gear 72.

[0070] If the outer cylinder 7i is rotated, the planet gears 73 (radially elastic in the example) roll on the flexspline 74. In the example, the flexspline 74 is secured against concentric twisting. The circumference on the inner surface of the flexspline 74 is larger than the outer circumference of the wheel 72. As a result, the planet gears rotating around the wheel 72 create waves in the flexspline 74 that move along with the planet gears. Due to the larger inner circumference of the flexspline compared to the outer circumference of the wheel 72, a rotary motion is created in the wheel 72 that counteracts the rotary motion of the planet gears. Other configurations are of course also conceivable, such as the wheel 72 being held fixed and a rotary motion being picked up on the flexspline 74. It is of course conceivable that only one of the planet gears is designed to be radially flexible.It is also conceivable for the cylinder 7i and / or the central wheel 72 to be designed to be flexible. A combination of flexibility in the various components is also conceivable. A special embodiment of the drive according to the invention allows unusually fine adjustment of the gear ratio. This embodiment is explained with reference to Fig. 8 to Fig. 15. For the sake of simplicity, an arrangement similar to the first exemplary embodiment in Fig. 2 is initially used for the purpose of explanation. The principle can of course also be applied to other exemplary embodiments and to variants not shown in this description. This means, for example, that the inventive principles described below can also be applied when other components of the transmission are driven or fixed.

[0071] As in the first embodiment, the sun gear 84 is driven and is in frictional contact with at least two (in this specific example, three) planetary gears 83. The planetary gears 83 are in direct frictional contact with a flexspline 82, which is deformed by the planetary gears 83 and, via their elastic deformation, is pressed with a sufficiently large force against the inner circumferential surface of the stationary cylinder 81. The outer circumference of the flexspline 82 is smaller than the inner circumference of the stationary cylinder 81, which, according to the friction stress wave gears, leads to a reduction ratio.

[0072] Unlike the first embodiment shown in Fig. 2, in the specific embodiment shown in Fig. 8, the transmitted movement is not already picked up at the flexspline 83, but rather at another rigid cylinder 85, which can be rotated concentrically to the bearing. In this embodiment, the planetary gears 83 press the flexspline 82 not only against the outer surface of the stationary, rigid cylinder 81, but also against the inner surface of the cylinder 85. This configuration allows—as explained below—a particularly wide transmission ratio and very fine adjustment of the transmission ratio.

[0073] As explained using the first embodiment, the transmission ratio IH in the first part of the stress wave gear results from the inner diameter IDz of the fixed, rigid cylinder 81 and the outer diameter of the flexspline 82. In the following, this is referred to as the first stage.

[0074] The ratio of the second stage of the IH2 gearbox (the rotationally movable cylinder 85 relative to the flexspline 82) depends on the inner diameter IDz2 of the cylinder 85 and the outer diameter of the flexspline 82. If the diameters of the components are identical to the first stage, then the ratio is identical; only the direction of rotation is reversed—compared to the first stage of the stress wave gearbox. Note that the corresponding circumferences can also be used to determine the ratio instead of the diameters, which may be useful if one of the components is not circular even when not clamped.

[0075] In the configuration shown in Fig. 8, where the cylinder inner and outer diameters IDz and IDZ2 are identical and the flexspline has the same outer circumference for both stages, cylinder 85 would not move relative to the fixed cylinder 81 upon rotation of sun gear 84, since the speeds nrs (speed of the flexspline) and nzz (speed of cylinder 85 relative to the flexspline) cancel each other out. They are equal but have a different sign.

[0076] In detail: The planetary gears 83 rotate at a speed nwc around the speed n srotating sun gear 84. Thus, the wave generated by the wave generator in the flexspline 82 travels at the speed nwc along the inner circumferential surfaces of the fixed, rigid cylinder 81 and the rotatable, rigid cylinder 85. Since the cylinder 81 is fixed, the flexspline rotates at the speed nps, as explained using the first exemplary embodiment. Since the cylinder 85, on the other hand, is rotationally movable, it is excited to a rotary movement relative to the flexspline due to the rotating shaft in the flexspline 82 in accordance with the principle of the stress wave drive. Since the inner diameters of the cylinders 81 and 85 are identical and the flexspline 82 has the same outer diameter everywhere, the speed of the cylinder 85 relative to the flexspline is -nps.Thus, the speed of the flexspline ( = nps) and the speed of the cylinder 85 relative to the flexspline 82 ( = -nps) cancel each other out, so that the cylinder 85 does not rotate during any rotation of the driving sun gear 84.

[0077] However, even small deviations in the diameters (or circumferences) can now produce very high transmission ratios and therefore high torques, as will be explained using a few examples. This is a major advantage over all previously described gears according to the invention, as the transmission ratio is no longer dependent on the difference between the circumference of the flexspline and the circumference of the outer surface (along which the shaft of the flexspline runs). This ratio cannot be adjusted very finely or even widely due to simple limitations. Based on the principle explained using the exemplary embodiments in Figs. 8 to 15, this limitation is lifted, as only the ratio of the circumferences (or diameters in the case of a circular design) of the cylinders and the flexspline in the first and second stages is relevant for the resulting transmission ratio. Example for Fig.9: If, with identical inner diameters of cylinders 9i and 9s, the flexspline in the first stage has a larger diameter (or a larger outer circumference) than in the second stage, then, as a result of a driven sun gear 94, the absolute speed nrs (speed of the flexspline) will be smaller than the absolute speed nz2 of cylinder 85 relative to the flexspline. Thus, for cylinder 9s relative to the fixed cylinder 9i, the speed n = nrs - nz2 results. Cylinder 9s is now rotating.

[0078] In the opposite direction, the movable cylinder I O5 rotates in the example according to Fig. 10, where in the first stage the outer diameter (or circumference) of the flexspline 2 is smaller than in the second stage.

[0079] However, even if the flexspline does not have a different diameter, a relative movement can be generated between the fixed and the movable cylinder, as explained in Fig. 11.

[0080] As can be seen in the left-hand part of Fig. 11, the flexspline H2 has a consistently identical outer diameter (or outer circumference). However, the fixed cylinder 111 has a smaller inner diameter than the movable cylinder 115. In this example, the planet gears 113 have a smaller diameter in the first stage than in the second stage. The planet gears 113 press the flexspline into the inner surfaces of the cylinders in both the first and second stages. In return, the flexspline is deformed less in the first stage than in the second stage. Accordingly, different ratios result in the first and second stages for the inner diameters of the cylinders 111 and 115 to the outer diameter of the flexspline 112, resulting in a rotation of the cylinder 115 relative to the fixed cylinder 111.Finally, in the first stage, the magnitude of the rotational speed nps of the flexspline 1 12 is lower than the magnitude of the rotational speed nz2 of the cylinder 115 relative to the flexspline.

[0081] As shown by way of example in Fig. 12, the planet gears do not necessarily have to have two diameters for the first and second stage. If the planet gears are designed to be radially elastic, as shown in the example in Fig. 2, then their elasticity will enable them to press the flexspline against the inner surfaces of the cylinders 12i and 12s, even if these have slightly different inner diameters. In Fig. 12, the different inner diameters are shown very large. For a very high gear ratio, it is advisable to keep this difference small. Fig. 13 shows an example identical to that in Fig. 12, with the difference that the planet gears 13s have a different design. Of course, these planet gears can have a wide variety of shapes, as long as they are able to press the flexspline 132 into the inner surfaces of the cylinders 13i and 13s.Multi-part radially elastic rolling elements are also conceivable.

[0082] The features of the examples shown in Figures 9 to 15 can, of course, be combined as desired. It is possible to produce the components with the two diameters as a single piece or in multiple pieces, although it is advantageous from a manufacturing perspective if the objects, such as the flexspline or the planetary gears, are made as a single piece.

[0083] If it is intended that the circumferences of the cylinders and / or the circumferences of the flexspline in the first and second stage can be changed when installed, this can enable a continuous change in the gear ratio and even a reversal of the direction of the movable cylinder relative to the fixed cylinder, even with a constant driving speed of the sun gear. Conventional techniques can be used for this, e.g., comparable to the technology explained in Fig. 2 d), by pushing variable circumferences into frictional contact, or by providing cylinder circumferences that are mechanically variable, as can be seen by way of example in Fig. 14. However, the use of actuators such as piezoceramics, shape-memory alloys (SMA), etc. is also possible to change the circumferences of the components when installed.

[0084] There are many ways to change the inner or outer diameter of a component belonging to the gear train (e.g. the cylinder or the flexspline). An example is briefly explained using Fig. 14. Here, the wall is perforated in a meandering shape in one section, resulting in interlocking crests in one area of ​​the circumference. If a force acts on the ring along the double arrows, the ring deforms, and the crests continue to interlock. The circumference inside the circle therefore becomes smaller. If it is now ensured that the flexspline is in frictional contact with at least one crest coming from the left and one from the right in the first and second stages, then a force can be transmitted continuously via the frictional contact. This type of continuously variable adjustment of the gear ratio can only be achieved with a friction gear train. As can be seen from the example in Fig.As shown in Figure 7, the arrangement of the fixed and movable components for the friction-tension drive according to the invention can be easily changed. This also applies to the friction-tension wave drives explained starting with Figure 8, as can be seen by way of example in Figure 15.

[0085] In the example of Fig. 15, gear 15i is fixed. A flexspline 152, which extends across the first and second stages of the transmission, is pressed locally against the outer surface of gear 15i via radially elastic planetary gears. When cylinder 154 is driven, the radially elastic planetary gears 15s pressed between the cylinder and the flexspline rotate together around the center of gear 15i, acting as a wave generator, causing a wave of the flexspline to travel around gear 15i. This traveling wave then generates a geared rotation of flexspline 152 in the first stage.If the flexspline 152 in the second stage has a different circumference than in the first stage, or, as shown in Fig. 15, the radius of the wheel 15s in the second stage is different from the radius of the wheel 15i of the first stage, then according to the principle described above, a relative movement occurs between the fixed wheel 15i and the movable wheel 15s.

[0086] For all configurations of a gear mechanism according to the invention, the contacting, non-toothed surfaces can be designed in a variety of ways. They can be very smooth, e.g., polished surfaces, which may or may not be lubricated. However, the surface can also be roughened to increase the coefficient of friction p, so that a greater tangential force can be transmitted for the same contact force.

[0087] Furthermore, the compressible elements, referred to here as "hollow cylinders," whose resilient properties generate the forces necessary to transmit the required tangential forces, can be designed in a variety of geometric configurations. Figure 16 shows some exemplary designs.

[0088] The hollow cylinders can be kept simple, as shown in Fig. 16 a) for example, or structural elements can be provided, as shown in Fig. 16 b), if, for example, the force needs to be transmitted very locally (as was also shown in Fig. 2 d) for example). So that the cylinders rolling against each other can guide each other, it is possible to incorporate structures (guide grooves) into their circumference, as shown in Fig. 16 c), or even guide tracks, as shown in Fig. 16 f). If the friction partners rolling against each other have matching guide grooves and guide tracks in their circumference, this prevents the components within the gearbox from performing an unwanted movement and possibly falling out of the gearbox.

[0089] If a driving or driving torque is to act on a hollow cylinder, it is possible to provide the hollow cylinder with a rigid area, as shown in Fig. 16 d). To prevent tilting of the contact surfaces, a symmetrical structure of the hollow cylinder including stiffening is also possible, as shown in Fig. 16 e). Such hollow cylinders can also be provided with structural elements and / or guide grooves, as shown in Fig. 16 f). All of these examples are mentioned only as examples, and a multitude of other single-part or multi-part hollow cylinders are conceivable. What all hollow cylinders have in common is that they have a constant wall thickness in the areas where the forces deforming the hollow cylinder act. In principle, the hollow cylinders can also be filled with a material, provided this does not prevent their flexibility.In principle, hollow cylinders can be made of any solid material that exhibits elastic behavior. In addition to plastics and ceramics, metals are particularly suitable as materials for hollow cylinders. Combinations of different materials are also conceivable.

[0090] The design of the inventive friction stress wave gear allows the construction of very small gears in the mm range - even in the sub-mm range (e.g. MEMS-based) - but it is also possible to build large gears with it - easily up to the meter range.

[0091] The radially flexible hollow cylinders allow tolerances, such as those caused by manufacturing inaccuracies or thermal deformation, to be compensated without compromising the functionality of the gearbox. In most cases, the hollow cylinders compensate for tolerances in the pm range. However, for very large gearboxes, this can be higher—in the mm range or even higher.

[0092] In the previous examples, radially elastic hollow cylinders were presented, each functioning as a sun gear, planet gear, and fixed cylinder. Of course, several of the components in a gearbox can also be designed as radially elastic hollow cylinders at the same time. A driving motor can be connected to the gearbox in any way. For example, it can be flange-mounted on the gearbox, built into the gearbox, or enclose the gearbox. It is also conceivable for parts of the gearbox to also be parts of the motor, e.g. if the rotor also represents the sun gear, or the stator is also the fixed cylinder. An example of integration of the motor function is shown in Fig. 17 using the exemplary embodiment from Fig. 15.

[0093] In this example, the function of a brushless direct current (BLDC) motor is integrated. A coil array 17s is connected to the stationary part 17i. An array of permanent magnets 17? is, in turn, connected to the ring 174, so that it can be excited to rotate. This rotation is then transferred to the wheel 17s by the friction wheels and the flexspline according to the principle already described, where the movement can then be tapped for technical use.

[0094] In principle, other types of wave generators can be used instead of a planetary gear-like wave generator, as long as the necessary contact force is generated via a radially elastic hollow cylinder. This is illustrated by an example in Fig. 18.

[0095] In this example, a radially elastic hollow cylinder 181 is held fixed. If the inner diameter of the inner cylinder is smaller than the sum of the internally arranged components of the main axis of the elliptical body 183 (twice the diameter of the rolling elements 184, and twice the material thickness of the flexspline 182), then the radially elastic cylinder 181 is elastically deformed. The restoring force generates the contact force required for the transmission between the contacting components.

[0096] In the example shown in Fig. 18, in addition to the fixed cylinder 181, a cylinder 185 that can be moved relative to it is also shown. A gear ratio can now be created according to the examples shown in Fig. 10 (and following) by either selecting different inner radii of the cylinders or by selecting different circumferences of the flexspline in the first stage than in the second stage. As in all previously shown examples, a flexspline can be constructed in one piece or consist of several interconnected components.

[0097] All transmissions according to the invention are friction gears, since the principle is not suitable for a transmission in which a defined gear meshes. However, a structure can be provided, as shown, for example, in the following Fig. 19.

[0098] In the embodiment shown in Fig. 19, the surface of the flexspline 192 is toothed. However, the teeth of the flexspline cannot engage with a counter-toothing in the inner circumference of the cylinder 19i, since such a toothing is not provided on the cylinder. This means that the friction gear according to the invention will still function even though one of the components has a toothing.

[0099] In a further embodiment which differs from the previous exemplary embodiments, as shown in Fig. 20, the friction gear also has two stages, each having an outer, radially flexible hollow cylinder 204 or 205. The gear has a sun gear 20i, which in the example is driven, without any teeth. The two or more planet gears 203, which also have no teeth, roll on the sun gear 20i. If it is stated here that no teeth are provided, this is to be understood to mean that the power is transmitted without any teeth, i.e. is based on friction. In this case, as shown in Fig. 19 and discussed above, the surface can certainly have a tooth structure or something similar.

[0100] The radius of the sun gear 20i plus the diameter of a sun gear 2O3 is larger than the inner radius of the hollow cylinder 2O5 and also larger than the inner radius of the hollow cylinder 2O4. The hollow cylinders do not have any internal teeth for engagement.

[0101] If the sun gear and planet gears are inserted into the cylinders, they will only fit into the interior of the cylinders if they deform, as shown exemplarily (and exaggeratedly) in section AA in Fig. 20. The dotted line shows the circumference of the non-deflected, circular cylinder 2O5, while the hatched area shows the cylinder 2O5 in radial deformation. The restoring force of this deflection generates the necessary normal forces that are required for the friction wheels to transmit the torque. The planet gears extend over both stages of the transmission, which means that both cylinders are subject to deformation due to the sun gear and the planet gears located inside. Even if it is not shown in Fig. 20, it is advisable to hold the planet gears in position relative to each other, for example bynon-engaging gears are placed between the planetary gears or a so-called planetary carrier - known from the state of the art of planetary gears - is provided.

[0102] In the exemplary embodiment, the radially flexible cylinder 204 is secured against rotation. If the sun gear 20i is now rotated, a joint rotation of the planet gears 203 around the sun gear is generated due to the fixed cylinder 20. If the inner radii of the cylinders 204 and 205 are identical, then the movable cylinder 205 will also not experience any rotation whatever with any drive of the sun gear 20i. If the radius of the cylinder 205 is smaller than the inner radius of the cylinder 204, then a rotation opposite to the direction of rotation of the planet gears rotating around the sun gear 20i is generated, since the sun gears 203 require fewer rotations on the inner surface of the cylinder 205 for a full revolution along the outer surface than on the inner surface of the cylinder 204. If the radius of the cylinder 205 is larger than the inner radius of the cylinder 204, then a rotation in the direction of rotation of the planet gears rotating around the sun gear 20i is generated.If the cylinder radii are different, a correspondingly strong reduction or transmission ratio results without the need for great mechanical effort.

[0103] Alternatively (or additionally), it is possible to design the sun gear with radial flexibility instead of cylinders 204 and 205, so that the necessary contact pressure is generated via the elastically deformed sun gear. To achieve this effectively, it is advisable to construct the sun gear in multiple parts rather than in one piece. This increases the complexity, which is why the design with a radially elastic outer cylinder is preferred.

[0104] If the inner diameters of cylinders 204 and 205 are kept identical, a reduction or transmission ratio can still be generated by having the planetary gear in the first stage with a radius that differs from the radius of this planetary gear inside the second stage and the planetary gears in the second stage with a radius that counteracts the difference. Even though various aspects or features of the invention are shown in combination in the figures, it will be apparent to those skilled in the art - unless otherwise stated - that the combinations shown and discussed are not the only possible ones. In particular, corresponding units or feature complexes from different exemplary embodiments can be interchanged.

[0105] In one embodiment of the invention, a friction stress wave transmission is provided, comprising a cylinder (which is stationary in use), a flexspline and a wave generator, wherein the wave generator has a sun gear and at least two planetary gears and wherein the inner radius of the (stationary) cylinder in the non-installed state is smaller than the sum of

[0106] Radius of the sun gear (in the non-installed state), the diameter of a planet gear (in the non-installed state) and the material thickness h of the flexspline, wherein the contact pressure for the components of the transmission is generated via the spring force of a flexible, essentially hollow-cylindrical structure with a wall thickness that is constant around the circumference of the friction contacts, wherein this hollow-cylindrical structure also contributes to the transmission of at least part of the tangential forces.

[0107] In a preferred variant of the above embodiment, the contact pressure is applied via at least one of the planetary gears of the wave generator, wherein this at least one planetary gear has a substantially radially elastic, hollow-cylindrical structure with a wall thickness that is constant in the circumference in the contact pressure area, the shape of which, in the installed state, is elastically deformed from the originally circular shape due to the undersize of the inner diameter of the fixed cylinder between the sun gear and the flexspline, so that a spring force acts which presses a flexspline against the inner surface of the fixed cylinder.

[0108] In another preferred variant of the above embodiment, the contact pressure is applied via the sun gear of the wave generator, wherein this sun gear has a radially elastic, substantially hollow-cylindrical structure with a wall thickness that is constant in the circumference in the contact pressure area, the shape of which, in the installed state, is elastically deformed from the originally circular shape due to the undersize of the inner diameter from the fixed cylinder via the sun gears, so that a spring force acts on the sun gears.In a further preferred variant of the above embodiment, the contact pressure is applied via the radially elastic, outer cylinder, said cylinder having a substantially hollow-cylindrical structure with a circumferentially constant wall thickness, the shape of which, in the installed state, is elastically deformed from the originally circular shape due to the undersize of the inner diameter by the fixed cylinder via the sun gears, so that a spring force acts on the sun gears.

[0109] In one of the friction stress wave gears explained here, a flexible area of ​​the flexspline can have a cone, so that a relative displacement of the flexspline to the fixed cylinder changes the ratio of the inner circumference of the fixed cylinder to the outer circumference of the flexspline, which allows a continuous adjustment of the gear ratio of the gear.

[0110] In one of the friction stress wave transmissions explained here, the outer cylinder can be movable and either the flexspline can be fixed, so that the wave generator is driven, or the wave generator can be fixed and the flexspline is driven. In a further development of a friction stress wave transmission, comprising at least one cylinder (stationary in use), at least one cylinder movable relative to the (stationary) cylinder, at least one flexspline and at least one wave generator, wherein the wave generator has at least one sun gear and at least two planet gears, and wherein the inner radius of the (stationary) cylinder in the non-installed state is smaller than the sum of

[0111] Radius of at least one sun gear (in the non-installed state), the diameter of a planet gear (in the non-installed state) and the material thickness h of the flexspline, and wherein the inner radius of the movable cylinder in the non-installed state is smaller than the sum of

[0112] Radius of the at least one sun gear (in the non-installed state), the diameter of a planet gear (in the non-installed state) and the material thickness h of the flexspline, the at least one flexspline extends over the first and second stage of the transmission and the contact force for the components of the transmission is generated via the spring force of a flexible, substantially hollow-cylindrical structure with a wall thickness constant in the circumference, wherein this hollow-cylindrical structure also contributes to the transmission of at least part of the tangential forces, wherein the transmission ratio of the transmission is defined by the relation, from o the ratio of the circumferences of the first stage

[0113] ■ Circumference of the inner surface of the fixed cylinder to the

[0114] ■ circumference of the flexspline o and the ratio of the circumferences in the second stage

[0115] ■ Circumference of the inner surface of the movable cylinder to the

[0116] ■ Scope of the flexspline

[0117] In a variant of the above design, with an identical circumference of the flexspline in the first and second stage, the circumference of the inner surface of the fixed cylinder differs from the inner circumference of the movable cylinder.

[0118] In another variant of the above design, with identical inner diameters of the fixed cylinder and the movable cylinder, the flexspline extending over both stages has a different circumference in the two stages.

[0119] In another variant of the above design, the inner diameters of the fixed cylinder and the movable cylinder differ, and the flexspline extending over both stages has a different circumference in the two stages.

[0120] In a further variant of the above design, one or both inner diameters of the cylinders can be changed in the installed state or the circumference of the flexspline can be changed in the first or second stage or in both stages in the installed state, so that a continuously adjustable transmission is produced.

[0121] In a further variant of the above design, the outer cylinder is movable and either the flexspline is fixed so that the wave generator is driven, or the wave generator is fixed and the flexspline is driven.

Claims

Claims 1. Friction stress wave transmission, comprising: an outer cylinder, a flex spine and a wave generator, wherein the outer cylinder, the flex spine and the wave generator are in frictional contact for power transmission, which is caused by a contact pressure, wherein the outer cylinder or a component of the wave generator forms at least one structure which is elastic in its shape and is hollow in the region of the frictional contact and has a constant wall thickness when the shape is deformed, wherein the elastic structure is designed to apply the contact pressure.

2. Frictional stress wave transmission according to claim 1, wherein the wave generator has a sun gear and at least two planet gears, wherein at least the sun gear and / or at least one of the planet gears form the elastic structure.

3. Friction stress wave transmission according to claim 1 or 2, wherein the flexspine and / or the outer cylinder comprises a cone, so that a change in a ratio of the inner circumference of the outer cylinder and the outer circumference of the flexspine can be effected by a relative displacement of the flexspine and the outer cylinder to one another in the axial direction.

4. Friction stress wave transmission according to one of the preceding claims, with a second outer cylinder, which is movable relative to the outer cylinder, wherein the second outer cylinder, the flex spine and the wave generator are in frictional contact for power transmission, which is brought about by a second contact pressure, wherein the elastic structure is designed to apply the second contact pressure and / or at least one second elastic structure is formed by the second outer cylinder or a component of the wave generator, which is hollow in the region of the frictional contact of the second outer cylinder and has a constant wall thickness when the shape is deformed, wherein the second elastic structure is designed to apply the second contact pressure.

5. Friction stress wave transmission according to claim 4, wherein the outer cylinder and the second outer cylinder have a different inner circumference.

6. Friction stress wave transmission according to claim 4 or 5, wherein the flex spine has a first outer circumference in the region of the outer cylinder and a second outer circumference in the region of the second outer cylinder, which are different from each other.

7. Kit for producing a friction stress wave transmission according to one of the preceding claims, with an outer cylinder, a flexspine and a wave generator, wherein the outer cylinder has an inner radius which is smaller by a difference than the sum of the material thickness of the flexspine and the radius of the wave generator along its main axis, wherein the difference is dimensioned such that a structure formed by the outer cylinder or a component of the wave generator, which is elastic in its shape and which is hollow in a region intended for frictional contact between the outer cylinder, flexspine and wave generator for force transmission and has a wall thickness which is constant when the shape is deformed, is designed to provide a restoring force as a contact pressure force when the corresponding deformation occurs, which is intended for force transmission between the outer cylinder, flexspine and wave generator.

8. A method for transmitting a rotary movement with a friction stress wave gear, wherein the friction stress wave gear comprises an outer cylinder, a flex spine and a wave generator, wherein the outer cylinder, the flex spine and the wave generator are in frictional contact for power transmission, which is caused by a contact force, wherein the contact force is applied by at least one structure which is elastic in shape, which is hollow in the region of the frictional contact and has a wall thickness which is constant when the shape is deformed, wherein the structure is formed by the outer cylinder or a component of the wave generator.

9. Friction planetary gear, comprising: an outer cylinder and a revolving arrangement arranged in the outer cylinder with a sun gear and at least two planet gears, wherein the planet gears are each connected to the outer cylinder and the sun gear to Power transmission is in frictional contact, which is caused by a contact pressure, wherein the outer cylinder and / or the sun gear form at least one structure which is elastic in its shape, which is hollow in the region of the frictional contact and has a constant wall thickness when the shape is deformed, wherein the elastic structure is designed to apply the contact pressure.

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