Design and development of strain wave generating cam for a new concept ‘harmonic drive’
01 Aug 2013-Vol. 227, Iss: 8, pp 1870-1884
TL;DR: In this article, a split cam design is proposed to solve the problem of assembly of the single piece cam in the flexible raced bearing of an earlier proposed novel harmonic drive system, which shows better torque c...
Abstract: A split cam design is proposed to solve the problem of assembly of the single piece cam in the flexible raced bearing of an earlier proposed novel harmonic drive system, which shows better torque c...
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Patent•
24 Sep 2013
TL;DR: In this paper, ausen verzahnter Verzahnungsbereich (7, 9) werden so verbogen, dass sie elliptische Formen haben, deren Phasen um eine Rotationszentralachse (1a) um 90° gegeneinander verdreht sind.
Abstract: Ein erster und ein zweiter ausen verzahnter Verzahnungsbereich (7, 9) eines Verformungswellgetriebes (1) werden durch einen Wellgenerator (10) in eine elliptische Form verbogen, um in ein erstes bzw. in ein zweites innen verzahntes Zahnrad (2, 4) einzugreifen. Der erste und der zweite ausen verzahnte Verzahnungsbereich (7, 9) werden so verbogen, dass sie elliptische Formen haben, deren Phasen um eine Rotationszentralachse (1a) um 90° gegeneinander verdreht sind. Zwischen dem ersten und dem zweiten ausen verzahnten Verzahnungsbereich (7, 9) ist ein ausen verzahntes Kopplungsverzahnungsbereich (8) ausgebildet, der eine kreisformige Querschnittsform behalt, die sich nicht verbiegt. Der ausen verzahnte Kopplungsverzahnungsbereich (8) wird so auf eingreifende Art und Weise mit einem innen verzahnten Kopplungszahnrad (3) gekoppelt gehalten. Das Verformungswellgetriebe (1) hat eine hohe Eingriffssteifigkeit und ist in der Lage, ein groses Drehmoment zu ubertragen.
32 citations
01 Mar 2016
TL;DR: In this article, the authors describe variations in pitch lengths when teeth move on a strain wave geodesic bearing (SWG) on the flex spline of a Flex Spline.
Abstract: Originally fixed and uniform circular pitches of flex spline (FS) teeth of a ‘Strain Wave Gearing’ or ‘Harmonic Drive’ (HD) experience variations in pitch lengths when teeth move on ‘strain wave ge...
20 citations
TL;DR: In this article, the geometry of the coning gap and its variation with the strain wave generating (SWG) cam rotation are established. And the hydrodynamic lubrication equation is solved to get pressure profiles for this gap under suitable boundary conditions under non-Newtonian lubrication.
Abstract: Purpose
In a harmonic drive during assembly of its components like strain wave generating (SWG) cam, flexspline (FS) and circular spline, a gap is formed between the cam’s outer surface and the FS cup inner surface due to mismatching. This gap, which is known as “Coning”, plays a vital role in the flow of lubricant at that interface. This paper aims to analyse the coning phenomenon and the lubrication mechanism.
Design/methodology/approach
In the present investigation, the geometry of the coning gap and its variation with the SWG cam rotation are established. Essentially, the deflection of FS cup and deformation of SWG cam (bearing outer race) are derived to find the gap due to coning. Next, the hydrodynamic lubrication equation is solved to get pressure profiles for this gap under suitable boundary conditions assuming non-Newtonian lubrication.
Findings
Methods of estimating the coning gap and lubrication pressure profiles are established. Effects of non-Newtonian terms (coupling number and non-dimentionalized characteristic length) and SWG length (finite, long and short) on pressure profiles are also shown. All analyses are done in non-dimensionalized form.
Originality/value
Establishing the geometry of coning and non-Newtonian hydrodynamic lubrication aspects in the coning in the FS cup and SWG cam interface are the originality of the present investigation.
15 citations
01 Dec 2018
TL;DR: The failure process and failure mechanism of the flexspline in harmonic reducer system after 500h operation were analyzed in this article, where the microstructure, element composition and mechanical properties of flexpline were studied by optical microscope (OM), scanning electron microscope (SEM), atomic emission spectrometry (AES), infrared carbon sulfur analyzer and microhardness tester.
Abstract: The failure process and failure mechanism of the flexspline in harmonic reducer system after 500h operation were analyzed. The microstructure, element composition and mechanical properties of flexspline were studied by optical microscope (OM), scanning electron microscope (SEM), atomic emission spectrometry (AES), infrared carbon sulfur analyzer and microhardness tester. The stress distribution of the key parts of the flexspline was calculated by LS-DYNA finite element simulation software. The results revealed that the main reason for the failure of the flexspline was the local micro crack and the variation of the dimensional accuracy, the essential reason was grain and ferrite phase inappropriately. In addition, the stress of the failed flexspline was concentrated near the crack, the maximum stress was increased by 26%, which compared well with empirical conclusion. This work can offer a reference for the further improvement of the flexspline.
10 citations
14 Jun 2021
TL;DR: In this paper, the authors consider the influence of the tooth profile on the performance of a harmonic drive and design a tooth profile for each harmonic drive, based on the characteristics of the mesh.
Abstract: A tooth profile is of significant importance to the performance of a harmonic drive. Available studies about designing a tooth profile only consider the influence of the tooth profile on the meshin...
9 citations
References
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01 Jun 1996
TL;DR: This model was able to replicate many of the features observed in actual harmonic-drive dynamic response, and it seems unlikely that any comparably sufficient representation can be constructed with parameter values obtained from catalogs or simple experimental observations.
Abstract: Harmonic drives can exhibit very nonlinear dynamic behavior. In order to capture this behavior, not only must dynamic models include accurate representations of transmission friction, compliance, and kinematic error, but also important features of harmonic-drive gear-tooth geometry and interaction must be understood. In this investigation, experimental observations were used to guide the development of a model to describe harmonic-drive operation. Unlike less detailed representations, this model was able to replicate many of the features observed in actual harmonic-drive dynamic response. Unfortunately, since model parameters can only be derived from careful analysis of experimental dynamic response, it seems unlikely that any comparably sufficient representation can be constructed with parameter values obtained from catalogs or simple experimental observations.
197 citations
TL;DR: The results of this paper offer a new perspective in the understanding of the mechanism of kinematic error and will be valuable in the mechanical design of harmonic drive gears as well as in the dynamic modeling and precision control of harmonicDrive systems.
Abstract: Harmonic drive gears are widely used in space applications, robotics, and precision positioning systems because of their attractive attributes including near-zero backlash, high speed reduction ratio, compact size, and small weight. On the other hand, they possess an inherent periodic positioning error known as kinematic error responsible for transmission performance degradation. No definite understanding of the mechanism of kinematic error as well as its characterization is available in the literature. In this paper, we report analytical and experimental results on kinematic error using a dedicated research Harmonic Drive Test Apparatus. We first show that the error referred to in the literature as kinematic error actually consists of a basic component, representing ‘‘pure’’ kinematic error, colored with a second component resulting from inherent torsional flexibility in the harmonic drive gear. The latter component explains the source of variability in published kinematic error profiles. The decomposition of the kinematic error into a basic component and a flexibility related component is demonstrated experimentally as well as analytically by matching a mathematical model to experimental data. We also characterize the dependence of the kinematic error on inertial load, gear assembly, and rotational speed. The results of this paper offer a new perspective in the understanding of the mechanism of kinematic error and will be valuable in the mechanical design of harmonic drive gears as well as in the dynamic modeling and precision control of harmonic drive systems. @DOI: 10.1115/1.1334379#
124 citations
TL;DR: In this article, a wave generator is proposed to drive flex gears of harmonic drives with fully conjugate gear pairs of purely involute profiles, where the cam profile is made of circular arcs at the two diametrically opposite contact zones and shifted elliptical curves for the other two zones.
Abstract: Consider commercially available harmonic drives or strain wave gearings (all patented designs). The tooth profiles of the mating pairs of teeth of the noncircular (pitch curve) flex gear and circular (pitch circle) ring gears are nearly conjugate and noninvolute. Evidently none of them offers ideal gear kinematics. In this paper, we propose a new wave generator (or cam) to drive flex gears of harmonic drives with fully conjugate gear pairs of purely involute profiles. The cam profile is made of circular arcs at the two diametrically opposite contact zones and shifted elliptical curves for the other two zones. The geometric construction is done in such a way that tip interference is properly avoided for both engagement and disengagement with nominally stubbed or full depth tooth involute gears. We develop the theory of geometric and gearing conditions. We have also built a physical model in order to verify the geometry of tooth interference and other relevant gearing kinematics.
53 citations
TL;DR: In this article, the authors presented a rigorous analysis and description of the kinematics of planar harmonic drives, where the flexspline of a harmonic drive is assumed to be a ring without a cup.
Abstract: This paper presents the kinematic model and offers a rigorous analysis and description of the kinematics of planar harmonic drives. In order to reflect the fundamental kinematic principle of harmonic drives, the flexspline of a harmonic drive is assumed to be a ring without a cup. A tooth on the flexspline is a rigid body, and the motion of the tooth is fully governed by the wave generator and the nominal transmission ratio of the harmonic drive. The proposed model depicts the flexspline tooth and the wave generator as a cam-follower mechanism, with the follower executing a combined translating and oscillating motion. With the rigid tooth motion obtained, the conjugate condition between the flexspline and the circular spline is determined, from which the conjugate tooth profile can be derived. In this paper, the motion is governed by geometry, and the flexibility of the flexspline only serves as a spring to maintain the contact between the cam and the follower. For any wave generator and any transmission ratio, the explicit expression of the conjugate condition is presented. For a given circular or flexspline tooth profile, the exact conjugate tooth profile can be obtained. The phenomenon of twice engagement is discussed for the first time.
47 citations
41 citations
Additional excerpts
...Then, a circlip (4) is put to fix the subassembly....
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