Stress wave gear, as well as flexspline for a stress wave gear, reference profile, gear manufacturing tool and method for manufacturing a flexspline for a stress wave gear

Abstract

The invention relates to a stress wave transmission (8), comprising a circular spline (4), a wave generator (6) and a flexspline (2) with an external toothing (14) with teeth, wherein the respective tooth satisfies a reference profile (16, 20, 24, 40, 48) which is parameterized in an xy plane as a reference profile curve according to x = b · (ϕ - a · sin (ϕ)), y = 0.5 · h · cos(ϕ), where b is a width factor, ϕ is a function parameter, a is a shape parameter and h is a reference profile height, and where -π <= ϕ <= π.

Description

[0001] The invention relates to a stress wave transmission comprising a wave generator, a circular spline, and a flexspline. It further relates to a flexspline, a reference profile for an external toothing of a flexspline, a transmission manufacturing tool, and a method for manufacturing a flexspline.

[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 positions on the flexspline in two areas of the circular spline. Such stress wave gears thus comprise three main components: the wave generator, the flexspline, and the circular spline.

[0003] When the strain 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] The wave generator usually consists of an elliptical steel disk and a thin-section roller bearing mounted on it. This component is used as the drive element in gear reduction mode. The circular spline is an internally toothed ring gear whose teeth mesh with the external teeth of the flexspline in the area of the major ellipse axis of the wave generator. The circular spline usually has two more teeth than the flexspline. The design of the flexspline allows for large elastic deformations in the radial direction. It is shaped into an elliptical shape by the wave generator. In the area of the major ellipse axis, the external teeth of the flexspline mesh with the internal teeth of the circular spline.

[0005] A disadvantage of external gearing of flexsplines of known tension shaft gears, especially roller tension shaft gears, is that the flexspline is subjected to high stress.

[0006] The invention is based on the object of providing a stress wave gear with a flexspline featuring improved external toothing. Furthermore, a flexspline, a reference profile, a gear manufacturing tool, and a method for manufacturing a flexspline are to be provided.

[0007] With regard to the stress wave transmission, this object is achieved according to the invention with the features of claim 1. The stress wave transmission comprises a circular spline, a wave generator and a flexspline with an external toothing with teeth, wherein the respective tooth satisfies a reference profile which is parameterized in an xy plane as a reference profile curve according to x = b · (ϕ - a · sin (ϕ)), y = 0.5 · h · cos(ϕ), where b is a width factor, ϕ is a function parameter, a is a shape parameter and h is a reference profile height, and where -π < = ϕ < = π.

[0008] In this application, the term "reference profile" and the specified calculation rules or formulas always refer to a standardized reference profile divided by π. A specific reference profile for a specific stress wave transmission is obtained by multiplying the standardized reference profile by a scaling factor (modulus).

[0009] In other words, the respective tooth satisfies a reference profile which is parameterized in an xy plane as a reference profile curve, whereby the x-value of the reference profile curve of the reference profile results from the difference of a functional parameter and a product of a shape parameter with the sine of the functional parameter multiplied by a width factor, and whereby the y-value of the reference profile curve of the reference profile results from the product of half a reference profile height and the cosine of the functional parameter, whereby the functional parameter lies in the interval of -Pi and +Pi.

[0010] Advantageous embodiments of the invention are the subject of the subclaims.

[0011] The invention is based on the consideration that in order to reduce the stress on the flexspline, the contact area between the teeth of the flexspline and the teeth of the circular spline or rollers in the case of a roller tension shaft gear should be increased in order to thereby reduce the load on the tooth flank and the wave generator bearing.

[0012] As has now been recognized, this can be achieved by using a specific profile or reference profile for the production of the external teeth of the flexspline, whose mathematical structure resembles the kinematics of the tooth mesh. The specific tooth profile, particularly through the use of parameters, can thus be more easily and accurately adapted to the kinematics of the tooth mesh of a roller HD gear.

[0013] The reference profile is described below in connection with Fig. 3 defined and explained.

[0014] The reference profile height is preferably between 0.8 and 1.5. The reference profile height should be as large as possible. It is limited by the permissible deformation of the flexspline.

[0015] The value of the shape parameter is preferably between 0.3 and 1.2, and particularly preferably between 0.4 and 0.8. The value of the shape parameter depends on the radial deformation of the flexspline. This factor allows the profile to be adapted to different deformations. The greater the relative deformation, the greater the value of the shape parameter.

[0016] The value of the width factor is preferably less than or equal to 0.5. The value of 0.5 is the upper limit of the width factor. In this case, the profile width corresponds exactly to one tooth pitch. If smaller values are selected, the reference profile must be supplemented with straight lines on both sides to achieve the tooth pitch. Smaller values result in a narrower tooth, which can reduce bending stress. The choice of the width factor improves the possibilities for adapting the profile to available roller diameters.

[0017] In a preferred embodiment, the parameterized curve is replaced by a geometric shape, particularly a circular segment, in a head region of the reference profile. This avoids excessively small radii at the head of the reference profile, as excessively small radii complicate manufacturing. Large values (close to 1) for the shape parameter a result in a peak or loop at the angle ϕ = 0. These inadmissible regions can be eliminated by a defined radius.

[0018] In a foot area of the reference profile, this is preferably extended laterally with a geometric shape, in particular straight sections.

[0019] In a preferred embodiment of the stress wave gear, the teeth of the circular spline are formed by rollers inserted in pockets.

[0020] With regard to the flexspline, the above-mentioned object is achieved according to the invention by a flexspline for a stress wave transmission with an external toothing with teeth, wherein the respective tooth satisfies a reference profile which is parameterized in an xy plane as a reference profile curve according to x = b · (ϕ - a · sin (ϕ)), y = 0.5 · h · cos(ϕ), where b is a width factor, ϕ is a function parameter, a is a shape parameter and h is a reference profile height, and where -π <= ϕ <= π.

[0021] In other words, the flexspline for a stress wave gear has an external toothing with teeth, wherein the respective tooth satisfies a reference profile which is parameterized in an xy plane as a reference profile curve, wherein the x-value of the reference profile curve of the reference profile results from the difference of a functional parameter and a product of a shape parameter with the sine of the functional parameter multiplied by a width factor, and wherein the y-value of the reference profile curve of the reference profile results from the product of half the reference profile height and the cosine of the functional parameter, wherein the functional parameter lies in the interval between -Pi and +Pi.

[0022] With regard to the reference profile, the above-mentioned object is achieved according to the invention by a reference profile for an external toothing of a flexspline for a stress wave transmission, which is parameterized in an xy plane as a reference profile curve according to x = b · (ϕ - a · sin (ϕ)), y = 0.5 · h · cos(ϕ), where b is a width factor, ϕ is a function parameter, a is a shape parameter and h is a reference profile height, where -π <= ϕ <= π.

[0023] With regard to the gearbox manufacturing tool, the above-mentioned object is achieved according to the invention by a gearbox manufacturing tool with a reference profile described above.

[0024] The gear manufacturing tool is advantageously designed as a grinding worm, grinding wheel, hob, cutting wheel, skiving wheel, planing comb or profile roller.

[0025] With regard to the method, the above-mentioned object is achieved according to the invention by using a gear manufacturing tool described above to form the external toothing of the flexspline.

[0026] The advantages of the invention lie in the fact that the proposed design of the flexspline's toothing, using a special reference profile, enables a torque increase of the corresponding gear by approximately 40-50%. By adapting the toothing to the specific tooth mesh, the reduced stress results in an increased service life of the gear. This enables improved use of the gear in continuous operation with optimized duty cycle and thermal limits.

[0027] The invention enables the construction of more powerful stress wave gears with small reduction ratios (80 and below). These can be used, for example, in the fields of robotics and service robotics, packaging machines, wheel drives for automated guided vehicles (AGVs), and machine tools.

[0028] 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 reference to one another.

[0029] Some of them show schematically: Fig. 1A shows a stress wave transmission in a preferred embodiment in a front view; Fig. 1B the stress wave transmission according to Fig. 1A in a section along the component axis; Fig. 2A shows a tension shaft gear, which is designed as a roller tension shaft gear, in a preferred embodiment in an end view; Fig. 2B the stress wave transmission according to Fig. 2A in a section along the component axis; Fig. 3 a representation of a spur gear and a rack; Fig. 4 three unmodified reference profiles for an external toothing of a flexspline, which differ in the shape parameter; Fig. 5 a reference profile modified in the head area, and Fig. 6 a reference profile modified in the head and foot areas.

[0030] 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.

[0031] One in Fig. 1A and Fig. The stress wave transmission 8 shown in Figure 1B comprises a flexspline 2 constructed in a silk-hat design, a circular spline 4 arranged coaxially thereto, and a wave generator 6. The circular spline 4 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 14. Located within the flexspline 2 is the wave generator 6, formed by a disk arranged in the center, the so-called plug 10, whose outer cross-section has an elliptical shape, and a rolling bearing 12 mounted on the outer surface of the plug 10. The cylindrical, thin-walled rings of the rolling bearing 12 and the flexspline 2 are elastically deformed into an elliptical cross-section by the plug 10. Due to the deformation, the external toothing 14 of the Flexspline 2 engages with the internal toothing 26 of the Circular Spline 4 in two areas on both sides of the major ellipse axis.

[0032] In the exemplary embodiment chosen here, the external toothing 14 of the flexspline 2 has two fewer teeth than the internal toothing 26 of the circular spline 4. When the plug 10 rotates around the gear axis, the tooth engagement areas shift in the circumferential direction following the major ellipse axis. Due to the different number of teeth of the flexspline 2 and the circular spline 4, the components rotate relative to each other by an angle of two tooth pitches with one rotation of the plug 10. Using the plug 10 as the input element and the circular spline 4 as the output, a transmission with a high reduction ratio in one stage is obtained.

[0033] One in Fig. 2A and Fig. The stress wave transmission 8 shown in Figure 2B is designed as a roller stress wave transmission. It comprises a flexspline 2 in a pot design, a circular spline 4 arranged coaxially thereto, and a wave generator 6. The flexspline 2 has, in some areas, the shape of a thin-walled hollow cylinder with external teeth 14. Located within the flexspline 2 is the wave generator 6, formed by a disk arranged in the center, the so-called plug 10, whose outer cross-section has an elliptical shape, and a roller bearing 12 mounted on the outer surface of the plug 10. The cylindrical, thin-walled rings of the roller bearing 12 and the flexspline 2 are elastically deformed into an elliptical cross-section by the plug 10. A plurality of rollers 58 are arranged in pockets 60 formed in the circular spline 4 and are in contact with the external teeth 14 of the flexspline 2. The rollers 58 form the teeth orInternal gearing of the circular spline 4.

[0034] In the exemplary embodiment chosen here, the external toothing 14 of the flexspline 2 has two fewer teeth than the number of rollers 58. When the plug 10 rotates around the gear axis, the tooth engagement areas shift in the circumferential direction following the major ellipse axis. Due to the different number of teeth on the flexspline 2 and the rollers 58, the components rotate relative to each other by an angle of two tooth pitches with one rotation of the plug 10. Using the plug 10 as the input element and the circular spline 4 as the output, a gear with a high reduction ratio in one stage is obtained.

[0035] In Fig. Figure 3 shows an example of a spur gear 62 and a rack 66. For spur gears 62, it is common to define tooth profiles by specifying the rack profile. A rack profile, also called a reference profile, is created from the spur gear 62 at the limit of the number of teeth and pitch circle toward infinity. The rack 66 is a lateral arrangement of a geometric structure (tooth) that repeats cyclically and infinitely at a pitch p. The pitch is the width of the structure in the direction of lateral extension. The geometric structure is the reference profile.

[0036] The tooth profile of any spur gear 62 is generated from the reference profile by generating in a rolling direction 82. During generating, the spur gear 62 rolls backlash-free on a pitch line 74 with a pitch circle 70. The pitch circle 70 is a virtual circle, concentric to the center axis of the spur gear 62 with a diameter of pitch x number of teeth / π. The pitch line 74 is a virtual straight line that runs in the direction of the lateral extension of the rack 66. It is parallel to the extreme tip or root points of the rack 66. Its position in the reference profile can be freely selected within reasonable limits. Reasonable limits depend on the specific profile and cannot be specified in general terms. The tooth profile of the spur gear 62 is formed from the enveloping sections of the rack 66. During generating, enveloping sections 78 are created in the spur gear 62.

[0037] Preferred embodiments of reference profiles for the external toothing 14 of the Flexspline 2 are explained with reference to the following figures.

[0038] All in the Fig. 4, Fig. 5 and Fig. The reference profiles 16, 20, 24, 40, and 48 shown in Figure 6 are standardized to a pitch of pi. This makes the coordinates dimensionless. Adaptation to a specific size (pitch) is achieved by multiplying by a scaling factor, which in gear technology is referred to as a module. The module has a dimension (unit of length, usually mm), which determines the size of the specific profile.

[0039] The Fig. Figure 4 shows three reference profiles 16, 20, 24 in a diagram. The respective reference profile 16, 20, 24 is parameterized as a reference profile curve, ie a pair of x-values and y-values. The x-values are in Fig. 2 on an x-axis 28 and the y-values on a y-axis 32. The respective profile 16, 20, 34 is in Fig. 4 and the Fig. 5, Fig. 6, Fig. 7 between the values -π / 2 and π / 2.

[0040] The three reference profiles 16, 20, 24 are parameterized as functions of a function parameter ϕ by the x-value according to x = b · (ϕ - a · sin (ϕ)) and the y-value according to y = 0.5 · h · cos(ϕ).

[0041] Here, b is a width factor, a is a shape parameter, and h is a reference profile height. The value of ϕ ranges from π to +π. The three reference profiles 16, 20, and 24 differ in the choice of the shape parameter a.

[0042] The value of the reference profile height h is preferably in a range between 0.8 and 1.5. The value of the shape parameter a is preferably in a range between 0.3 and 1.2. The value of the width factor b is preferably 0.5. If the profile is supplemented by a straight section 52, b is less than 0.5.

[0043] As mentioned above, the three differ in the Fig. 4 shown reference profiles 16, 20, 24 by the value of the shape parameter a. For the reference profile 16 this value is 0.3, for the reference profile 20 it is 0.5 and for the reference profile 20 it is 0.8. As in Fig. 4, the increase in the shape parameter a essentially leads to a constriction of the reference profile 16, 20, 24 with more pointed flanks.

[0044] All length dimensions are standardized to a pitch of π and are therefore dimensionless. Scaling to real values is achieved by multiplying the coordinates by a factor known in gear technology as the module. The width of the reference profile is also called the pitch and is calculated using the relationship module · π. If all length dimensions are represented in relation to the module, the width of the reference profile is always equal to π.

[0045] The profile is adapted to the design parameters of the gearbox using the reference profile height h and the shape parameter a, and the properties of the gearbox are optimized.

[0046] The reference profile 16, 20, 24 can also be adjusted in its head and / or foot area. Fig. 5 shows an example of a reference profile 40 which is a modification of the reference profile 20 according to Fig. 4. In a head region 36 of the reference profile 40, an area which would result from the parameterization of the x-coordinate and the y-coordinate is replaced by a circular arc 44 with a constant radius R inserted tangentially into the reference profile 40.

[0047] In the Fig. 6 shows an example of a further reference profile 48 which is modified in the head region 36 and in its foot region 52 compared to the reference profile 40. The modification in the head region 36 corresponds to the Fig. 5 shown modification by a circular arc. In the foot area 52 or in the area of the foot, the profile can be supplemented by other geometric elements. As in Fig. As shown in Figure 6, the reference profile 40 was extended by a straight line segment in each of the foot regions 52. The width factor b is then selected to be b = 0.5-s / π, where s is the length of the straight line segment or segment of the straight line. List of reference symbols 2 Flexsplines 4 Circular Spline 6 Wave Generator 8 stress wave gears 10 Plug 12 rolling bearings 14 External gearing 16 Reference profile 20 Reference profile 24 Reference profile 26 internal gearing 28 x-axis 32 y-axis 36 Head area 40 Reference profile 44 circular arcs 48 Reference profile 52 foot area 56 profile section 58 roll 60 bag 62 spur gear 66 rack 70 pitch circle 74 rolling lines 78 envelope cuts 82 Rolling direction P division a shape parameters b, s width factor h Reference profile height ra radius A, B point C, D point R radius

Claims

[1] Stress wave transmission (8), comprising a circular spline (4), a wave generator (6) and a flexspline (2) with an external toothing (14) with teeth, wherein the respective tooth satisfies a reference profile (16, 20, 24, 40, 48) which is parameterized in an xy plane as a reference profile curve according to x = b · (ϕ - a · sin (ϕ)), y = 0.5 · h · cos(ϕ), where b is a width factor, ϕ is a function parameter, a is a shape parameter and h is a reference profile height, and where -π <= ϕ <= π. [2] Stress wave transmission (8) according to claim 1, wherein the value of the reference profile height (h) is between 0.8 and 1.

5. [3] Stress wave transmission (8) according to claim 1 or 2, wherein the value of the shape parameter (a) is between 0.3 and 1.

2. [4] Stress wave transmission (8) according to one of the preceding claims, wherein the value of the width factor (b) is less than or equal to 0.

5. [5] Stress wave transmission (8) according to one of the preceding claims, wherein in a head region (36) of the reference profile (16, 20, 24, 40, 48) the parameterized curve is replaced by a geometric shape, in particular a circular segment (44). [6] Stress wave transmission (8) according to one of the preceding claims, wherein in a foot region (52) of the reference profile (16, 20, 24, 40, 48) this is laterally extended with a geometric shape, in particular straight sections. [7] Stress wave transmission (8) according to one of claims 1 to 6, wherein the teeth of the circular spline (4) are formed by rollers (58) inserted in pockets (60). [8] Flexspline (4) for a stress wave gear (8) with an external toothing (14) with teeth, wherein the respective tooth satisfies a reference profile (16, 20, 24, 40, 48) which is parameterized in an xy plane as a reference profile curve according to x = b · (ϕ - a · sin (ϕ)), y = 0.5 · h · cos(ϕ), where b is a width factor, ϕ is a function parameter, a is a shape parameter and h is a reference profile height, and where -π <= ϕ <= π. [9] Reference profile (16, 20, 24, 40, 48) for an external toothing (14) of a flexspline (2) for a stress wave transmission (8), which is parameterized in an xy plane as a reference profile curve according to x = b · (ϕ - a · sin (ϕ)), y = 0.5 · h · cos(ϕ), where b is a width factor, ϕ is a function parameter, a is a shape parameter and h is a reference profile height, where -π <= ϕ <= π. [10] Gear manufacturing tool with a reference profile (16, 20, 24, 40, 48) according to claim 9. [11] Gear manufacturing tool according to claim 10, which is designed as a grinding worm, grinding wheel, hob, cutting wheel, skiving wheel, planing comb, or profile roller. [12] Method for producing a flexspline (2) for a stress wave gear (8) with an external toothing (14), wherein a gear manufacturing tool according to claim 10 or 11 is used to form the external toothing (14).

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