Stress wave gear and method for torque measurement on a stress wave gear

Abstract

A stress wave transmission (20) comprising a circular spline (1), a flex spline (2) formed with a base (30) and a wave generator (3), wherein a torque adapter (4, 11) is provided with a first section (24) which radially surrounds the flex spline (2) at least partially in the axial direction of the flex spline (2) and which has an internal toothing (27) which engages in a toothing area (8) with teeth of the external toothing (21) of the flex spline (2), wherein the number of teeth of the internal toothing of the torque adapter (4, 11) and of the external toothing (21) of the flex spline (2) is the same.

Description

[0001] The invention relates to a stress wave transmission comprising a circular spline, a flex spline formed with a base, and a wave generator. It further relates to a method for measuring torque on such a stress wave transmission.

[0002] Stress wave gears comprise a circular spline with internal teeth and a flexible flexspline with external teeth arranged within the circular spline. A wave generator is arranged within the flexspline to deform the flexspline in the radial direction. The deformation of the flexspline creates a positive, torque-transmitting connection between the circular spline and the flexspline at two opposite points on the flexspline, at two positions on either side of the contact with the circular spline. Such stress wave gears thus comprise three main components: the wave generator, the flexspline, and the circular spline.

[0003] When the wave gear is in reduction mode, i.e. when the speed is reduced, the elliptically shaped wave generator serves as the drive element. The wave generator (WG) uses a rolling bearing, in particular a thin-section rolling bearing, to deform the flexspline (FS), which is in mesh with the internally toothed ring gear, the circular spline (CS). When the wave generator rotates, the major axis of the ellipse shifts and with it the tooth meshing area. Since the flexspline has fewer teeth, in particular two teeth fewer, than the circular spline, the flexspline rotates relative to the circular spline during half a revolution of the wave generator, in particular by the angle of one tooth pitch, and during a full revolution by the angle of two tooth pitches. When the circular spline is stationary, the flexspline rotates in the opposite direction to the direction of rotation of the wave generator.

[0004] Measuring torque on stress wave gears always requires additional components and / or a complex sensor application. This typically requires additional installation space, particularly in the axial direction. Conventional methods measure the strains of the component caused by the applied torque. This inevitably results in a superposition of strains in different directions. This has a direct impact on the measured value determination, as the data from the sensor must be processed and filtered using complex algorithms.

[0005] It also plays a crucial role whether the component equipped with the sensor is implemented as "rotating" or "stationary" in the gear system. This can make connecting the sensor very complex and prone to errors.

[0006] In the state-of-the-art systems described above, an additional measuring flange is often used for torque measurement, which reduces the overall stiffness due to the series connection of the mechanical components and its position in the force flow.

[0007] From DE 10 2019 134 392 A1 a device for determining the torque between a first shaft and a second shaft, which are coupled relative to one another via a stress wave gear so as to be rotatable about an axis of rotation, is known, wherein the first shaft is designed as a hollow shaft and the second shaft is arranged coaxially in the first shaft, and wherein a first end region of the first shaft has a first measuring embodiment and a first end region of the second shaft has a second measuring embodiment, wherein the first measuring embodiment is scanned by a first sensor and the second measuring embodiment is scanned by a second sensor.

[0008] DE 10 2014 105 321 A1 discloses a drive device comprising an electric motor with a stator mounted in a motor housing and a rotor mounted radially to the stator for generating torque on a drive shaft connected to the input stage of a transmission mounted at the output end of the motor housing to form a motor-transmission unit. A torsion bar unit arranged outside the transmission is used for torque measurement.

[0009] From JP H07-103 291 A a method for measuring torque on a flexspline using a magnetostriction torque sensor is known.

[0010] Based on the disadvantages described above, the invention is therefore based on the object of enabling accurate torque measurement. In particular, the difficulties of application, data transmission, and signal processing are to be reduced.

[0011] With regard to the stress wave transmission, this object is achieved according to the invention by a stress wave transmission having the features of claim 1.

[0012] Advantageous embodiments of the invention are the subject of the subclaims.

[0013] The invention is based on the idea that in many applications of stress wave gears, precise knowledge of the applied torque is necessary. Conventional methods for determining torque measure component strain, which is only an imperfect measure of the actual torque.

[0014] As has now been recognized, the torque in a stress wave gear can be precisely determined by using an additional component, namely a torque adapter or measuring ring, which engages the flexspline in the area of ​​the external gear teeth. While the base of the flexspline is in the force path, this is not the case for the torque adapter.

[0015] Caused by the applied torque, a global twist occurs in the area between the flexspline external teeth and the flexspline base, due to the structural rigidity of the flexspline. By comparing the rotation of the flexspline base and the torque adapter, the torque can be accurately determined, taking into account the component stiffness of the flexspline.

[0016] The present invention thus describes a technical solution in which the global component twist, caused by the applied torque, is measured on a shaft gear. This does not involve strain detection, but rather a (torsion) angle measurement.

[0017] In a first preferred embodiment, the torque adapter is designed to be non-deformable, so that the flexspline engages with the internal toothing of the torque adapter only in the region of its vertical axis using teeth of the external toothing. The torque adapter or measuring ring has an identical number of teeth (and the same module) as the flexspline. As a result, the flexspline engages with the torque adapter in the region of its vertical axis and, due to the identical number of teeth on the flexspline and torque adapter, does not generate any relative movement between the two components. The torque adapter is preferably extended to a crossed roller bearing or the flexspline base. In this first preferred embodiment, the torque adapter is preferably made of steel.

[0018] In a second preferred embodiment, the torque adapter is designed to be deformable, so that the flexspline engages with all teeth of the external toothing into the internal toothing of the torque adapter. The torque adapter or measuring ring has the same number of teeth (and the same module) as the flexspline, but in this design, all teeth are in engagement with the toothing of the flexspline. The torque adapter follows the radial deformation of the flexspline. However, no deformation is transmitted through torsion. In this second preferred embodiment, the torque adapter is preferably made of plastic.

[0019] The steel version of the torque adapter requires more precision. The plastic version can be connected to the teeth of the flexspline without any play.

[0020] Caused by the applied torque, a global twist occurs in the area between the flexspline teeth and the flexspline base, due to the structural rigidity of the flexspline. The torque adapter is not in the force flow, is therefore force-free, and does not experience any torsion. Due to the resulting angular misalignment between the flexspline and the torque adapter, the torque can be determined based on the component stiffness of the flexspline.

[0021] The torque adapter is preferably firmly connected to the flexspline, in particular pressed into the teeth of the flexspline.

[0022] According to the invention, the torque adapter has a second section adjoining the first section, which is formed from an edge of the first section in the direction of the central axis of the stress wave gear substantially parallel to the bottom of the flexspline.

[0023] According to the invention, the stress wave transmission comprises an angle measuring system comprising a measuring scale mounted on the second section of the torque adapter and at least one sensor head mounted on an output flange of the stress wave transmission opposite the measuring scale. The measuring scale is the rotating component of the angle measuring system.

[0024] The angle measuring system preferably includes an angle measuring unit that is signal-connected to the sensor head. The torque adapter is not located in the force flow, is therefore force-free, and does not experience any torsion.

[0025] By measuring the angular offset between the torque adapter and the flexspline or output flange, taking into account the structural rigidity of the flexspline, the angle measuring unit determines the applied torque.

[0026] The angle measuring system is advantageously designed for measurement according to the optical, inductive or magnetic principle.

[0027] Preferably, the output flange is screwed to the bottom of the flexspline.

[0028] In a preferred embodiment, the stress wave gear has a bearing, in particular a plain bearing, roller bearing or ball bearing, which is provided between the torque adapter and the flexspline or output flange.

[0029] With regard to the method, the above-mentioned object is achieved according to the invention in that the torque is determined as a function of the angular offset between the torque adapter and the base of the flexspline and the structural rigidity of the flexspline with the aid of a torque adapter which is in engagement with the flexspline and which rotates with the flexspline.

[0030] The advantages of the invention lie in the fact that it enables precise torque determination on a stress wave gear without complex modifications. The present invention does not affect the overall rigidity of the stress wave gear, as the measuring flange is not located in the force flow. The invention has a beneficial effect on the required axial installation space.

[0031] The stress wave gearbox described can be used in robot axes, exoskeletons, machine tools, etc.

[0032] Further objects, advantages, features, and possible applications of the present invention will become apparent from the following description of an exemplary embodiment with reference to the drawing. All described and / or illustrated features, individually or in any meaningful combination, constitute the subject matter of the present invention, regardless of their summary in the claims or their interrelationship.

[0033] Some of them are shown schematically: Fig. 1 a stress wave transmission in a first preferred embodiment in a front view; Fig. 2 the stress wave gear according to Fig. 1 in a section along the component axis; Fig. 3 a stress wave transmission in a second preferred embodiment in a front view, and Fig. 4 the stress wave transmission according to Fig. 3 in a section along the component axis.

[0034] In the following figures of the drawing, identical or equivalent components are provided with reference numerals based on an embodiment in order to improve readability.

[0035] One in the Fig. 1 and Fig. The stress wave transmission 20 shown in Figure 2 comprises a pot-shaped flexspline 2 with a base 30, a circular spline 1 arranged coaxially thereto, and a wave generator 3. The circular spline 1 is designed as an internally toothed, cylindrical ring gear. The flexspline 2 has, in some areas, the shape of a thin-walled hollow cylinder with external teeth 21. Located within the flexspline 2 is the wave generator 3, formed by a disk arranged in the center, the so-called plug 23, whose outer cross-section has an elliptical shape, and a rolling bearing 25 mounted on the outer surface of the plug 23. The cylindrical, thin-walled rings of the rolling bearing 25 and the flexspline 2 are elastically deformed into an elliptical cross-section by the plug 23.Due to the deformation, the external toothing 21 of the flexspline 2 engages in a toothing area 9 with the internal toothing 28 of the circular spline 1 in two areas on both sides of the major ellipse axis.

[0036] In the embodiment chosen here, the external toothing 21 of the Flexspline 2 has two fewer teeth than the internal toothing 28 of the Circular Spline 1.

[0037] When the plug 23 rotates around the gear axis, the tooth engagement areas shift in the circumferential direction following the major axis of the ellipse. Due to the different number of teeth of the flexspline 2 and the circular spline 1, the components rotate relative to each other by an angle of two tooth pitches with one rotation of the plug 23. Using the plug 23 as the drive element and the circular spline 1 as the output, a gear with a high reduction ratio in one stage is obtained. The stress wave gear 20 has an output flange 7, which is firmly coupled to the base 30 of the flexspline 2. In this case, this is achieved by screwing the base 30 of the flexspline 2 to the output flange 7.

[0038] The stress wave gear 20 is equipped for torque measurement. For this purpose, it has a torque adapter 4, which is Fig. 1 and Fig. 2 is designed to be non-deformable. The torque adapter 4 is made of steel in the present case. The torque adapter 4 has a first section 24, which radially surrounds the flexspline 2 at least partially in the axial direction of the flexspline 2 and which has an internal toothing 27, which engages with teeth of the external toothing 21 of the flexspline 2 in a toothing region 8, which in this embodiment is free of play. The number of teeth of the internal toothing 27, of the torque adapter 4, and of the external toothing 21 of the flexspline 2 is the same.

[0039] Since the torque adapter 4 is designed to be non-deformable, the Flexspline 2 engages only in the area of ​​its vertical axis with teeth of the external toothing 21 in the internal toothing 27 of the torque adapter 4. In Fig. 2 also shows a bearing 10 of the torque adapter 4.

[0040] The stress wave gear 20 has an angle measuring system 22. The angle measuring system 22 comprises a measuring scale 5, which is mounted externally in the second region 26 of the torque adapter 4. The angle measuring system 22 further comprises a sensor head 6, which is attached to the output flange 7.

[0041] The sensor head 6 is connected to an angle measuring unit (not shown) for signal transmission. To measure the torque applied to the flexspline 2 or output flange 7 during operation of the stress wave gear 20, the angle measuring unit measures the angular offset or mutual rotation between the torque adapter 4 and the flexspline 2 or output flange 7. Taking into account the structural rigidity of the flexspline 2, the angle measuring unit calculates the applied torque.

[0042] In the Fig. 3 and Fig. Figure 4 shows a second preferred embodiment of a stress wave transmission 20. The circular spline 1, the flex spline 2 and the wave generator 3 are arranged as in the stress wave transmission 20 according to Fig. 1 and Fig. 2 and arranged relative to each other. The stress wave gear 20 according to the Fig. 3 and Fig. 4 differs from the stress wave gear 20 according to the Fig. 1 and Fig. 2 in the design of the torque adapter 11 and its arrangement or fastening in relation to the Flexspline 2.

[0043] The torque adapter 11 of the stress wave gear according to the Fig. 3 and Fig. 4 is designed to be deformable. In this embodiment, the torque adapter 4 is made of plastic. The torque adapter 11 has an internal toothing 27, which has the same number of teeth as the external toothing 21 of the flexspline 2. The torque adapter 11 is firmly connected to the flexspline 2; in particular, the internal toothing 27 of the torque adapter 11 is firmly pressed into the external toothing 21 of the flexspline 2 in the toothing area 8.

[0044] The stress wave gear 20 according to Fig. 3 and Fig. 4 has an angle measuring system 22 in the same way as the stress wave gear 20. As described above, the torque is determined by measuring the angular offset or the mutual rotation between the torque adapter 4 and the flexspline 2. Taking into account the structural rigidity of the flexspline 2, the angle measuring unit determines the applied torque. List of reference symbols 1 Circular Spline 2 Flexsplines 3 Wave Generator 4 torque adapters 5 Measurement embodiment 6 Sensor head 7 Output flange 8 Gearing area 9 Gearing area 10 Storage of the torque adapter 11 torque adapters 20 stress wave gears 21 External gearing 22 Angle measuring system 23 Plug 24 first section 25 rolling bearings 26 second section 27 Internal gearing 28 internal gearing 30 floor

Claims

[1] Stress wave transmission (20), comprising a circular spline (1), a flexspline (2) formed with a base (30) and a wave generator (3), wherein a torque adapter (4, 11) is provided with a first section (24) which surrounds the flexspline (2) radially at least partially in the axial direction of the flexspline (2) and which has an internal toothing (27) which engages in a toothing region (8) with teeth of the external toothing (21) of the flexspline (2), characterized byin that the number of teeth of the internal toothing of the torque adapter (4, 11) and the external toothing (21) of the flexspline (2) is the same, wherein the torque adapter (4, 11) has a second section (26) which adjoins the first section (24) and which is formed from an edge of the first section (24) in the direction of the central axis of the stress wave gear (20) substantially parallel to the base (30) of the flexspline (2), and wherein the stress wave gear (20) comprises an angle measuring system (22) which comprises a measuring embodiment (5) which is attached to the second section (26) of the torque adapter (4, 11), and which comprises at least one sensor head (6) which is attached to an output flange (7) of the stress wave gear (20) opposite the measuring embodiment (5). [2] Stress wave transmission (20) according to claim 1, wherein the torque adapter (4) is designed to be non-deformable, so that the flexspline (2) engages with the internal toothing (27) of the torque adapter (4) only in the region of its vertical axis with teeth of the external toothing (21). [3] Stress wave transmission (20) according to claim 1, wherein the torque adapter (11) is designed to be deformable, so that the flexspline (2) engages with all teeth of the external toothing (21) in the internal toothing (27) of the torque adapter (11). [4] Stress wave gear (20) according to claim 3, wherein the torque adapter (11) is firmly connected to the flexspline (2), in particular is pressed into the external toothing (21) of the flexspline (2). [5] Stress wave transmission (20) according to one of claims 1 to 4, wherein the angle measuring system (22) is designed for measurement according to the optical, inductive or magnetic principle. [6] Stress wave gear (20) according to one of claims 1 to 5, wherein the output flange (7) is screwed to the bottom (30) of the flexspline (2). [7] Stress wave gear (20) according to one of claims 1 to 6 with a bearing, in particular a plain bearing, roller bearing or ball bearing, which is provided between the torque adapter (4, 11) and the flexspline (2) or output flange (7). [8] Method for measuring torque on a stress wave transmission (20) according to one of claims 1 to 7, comprising a circular spline (1), a flexspline (2) with a base (30) and a wave generator (3), characterized by that with the aid of a torque adapter (4, 11) which is in engagement with the flexspline (2) and which rotates with the flexspline (2), the torque is determined as a function of the angular offset between the torque adapter (4, 11) and the base (30) of the flexspline (2) and the structural rigidity of the flexspline (2).

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