Nonlinear torsional compliance and hysteresis are associated with harmonic drives, and their accurate modeling is crucial for improving performance of the control system of harmonic drive-based devices such as robot joints. In this paper, a new approach is taken to model the torsional compliance and hysteresis behavior in harmonic drives. The proposed model is derived by modeling the compliance behavior of the flexspline and the wave generator instead of modeling the individual behaviors of the overall harmonic drive transmission. The hysteresis loss is captured by taking the wave generator torsional compliance into account. The proposed model is validated through numerical simulations and subsequently with experimental data.

Modeling of Torsional Compliance and Hysteresis Behaviors in Harmonic Drives

The use of bulk metallic glasses (BMGs) as the flexspline in strain wave gears (SWGs), also known as harmonic drives, is presented. SWGs are unique, ultra-precision gearboxes that function through the elastic flexing of a thin-walled cup, called a flexspline. The current research demonstrates that BMGs can be cast at extremely low cost relative to machining and can be implemented into SWGs as an alternative to steel. This approach may significantly reduce the cost of SWGs, enabling lower-cost robotics. The attractive properties of BMGs, such as hardness, elastic limit and yield strength, may also be suitable for extreme environment applications in spacecraft.

Castable Bulk Metallic Glass Strain Wave Gears: Towards Decreasing the Cost of High-Performance Robotics

On the eve of Human-Robot-Interaction (HRI) becoming customary in our lives, the performance of HRI robotic devices remains strongly conditioned by their gearboxes. In most industrial robots, two relatively unconventional transmission technologies – Harmonic Drives © and Cycloid Drives – are usually found, which are not so broadly used in other industries. Understanding the origin of this singularity provides valuable insights in the search for suitable, future robotic transmission technologies. In this paper we propose an assessment framework strongly conditioned by HRI applications, and we use it to review the performance of conventional and emerging robotic gearbox technologies, for which the design criterion is strongly shifted towards aspects like weight and efficiency. The framework proposes to use virtual power as a suitable way to assess the inherent limitations of a gearbox technologies to achieve high efficiencies. This paper complements the existing research dealing with the complex interaction between gearbox technologies and the actuators, with a new gearbox-centered perspective particularly focused on HRI applications.

/pdf/compact-gearboxes-for-modern-robotics-a-review-47xyfm0r69.pdf

Compact Gearboxes for Modern Robotics: A Review.

Considering the fact that load distribution of the flexspline under alternating dynamic loads is complicated, and it’s difficult to measure the stress of the flexspline by experiment, a d ynamic simulation model of harmonic gear drives is established to study the intensity of the flexspline in the operating process of harmonic gear drives based on finite element method. In order to decrease the force on flexspline, by means of conjugate method, the parameters of flexspline and circular spline’s tooth profiles are optimized. A D-100 harmonic drive is simulated based on the contact theory and the explicit algorithm of the finite element method. The parameterized finite element grid of the whole harmonic gear drive model is realized by Matlab, and then the assembly process of the wave generator is simulated by ABAQUS. Meanwhile, the distribution of the flexspline stress and the load characteristics of the flexspline tooth during dynamic transmission process of a harmonic gear with parameters, before and after optimization, are analyzed. The meshing characteristics of the tooth pairs with optimized parameters are improved significantly. The fatigue fracture position on the flexspline is forecasted according to the simulation results.

/pdf/dynamic-simulation-of-harmonic-gear-drives-considering-tooth-59f1ws8pka.pdf

Dynamic Simulation of Harmonic Gear Drives Considering Tooth Profiles Parameters Optimization

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...

An investigation on secondary force contacts of tooth pairs in conventional harmonic drives with involute toothed gear set

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.

The strain wave gearing

An external gear (13) of a strain wave gear device (11) is caused to deform into a shape that follows an elliptic curve by a wave generator (14). The external gear (13) is engaged with an internal gear (12) at the major axis positions of the elliptic curve. These two engagement positions (L1) gradually change in the circumferential direction of the two gears (12, 13) along a tooth trace direction (A). This allows for an increase in the number of external teeth (13e) of the external gear (13) involved in the engagement with the internal gear (12). The invention allows a strain wave gear device capable of having increased stiffness and reduced vibration noise to be achieved.

Strain wave gear device, friction engagement type strain wave device, and wave generator

An externally toothed gear of a strain wave gearing is made to flex into a shape conforming to an ellipsoidal curve. The externally toothed gear meshes with an internally toothed gear at the major-diameter position of the ellipsoidal curve. These two meshing positions gradually change in the circumferential direction of the both gears along the tooth trace direction. The number of external teeth of the externally toothed gear participating in meshing with the internally toothed gear can be increased. A strain wave gearing which has a high rigidity and is capable of reducing vibrational noise, can be realized.

Strain wave gearing, frictional engagement wave device, and wave generator

Ein ausen verzahntes Zahnrad (13) eines Verformungswellgetriebes (11) wird in eine Form verbogen, die mit einer elliptischen Kurve ubereinstimmt. Das ausen verzahnte Zahnrad (13) greift an den Hauptachsenpositionen der elliptischen Kurve in ein innen verzahntes Zahnrad (12) ein. Diese beiden Eingriffspositionen (L1) andern sich entlang der Zahnbahnrichtung (A) in der Umfangsrichtung der beiden Zahnrader (12, 13). Die Anzahl der auseren Zahne (13e) des ausen verzahnten Zahnrades (13), die am Eingreifen mit dem innen verzahnten Zahnrad (12) teilnehmen, kann vergrosert werden. Es kann ein Verformungswellgetriebe realisiert werden, dass eine hohe Steifigkeit hat, und das in der Lage ist, ein Vibrationsgerausch zu reduzieren.

Verformungswellgetriebe, Wellvorrichtung mit Reibungseingriff und Wellgenerator

First and second external tooth gear parts (7, 9) of a wave gear device (1) are bent in an elliptic shape by a wave generator (10) to engage with first and second internal tooth gears (2, 4), respectively. The first and second external tooth gear parts (7, 9) are bent so as to have elliptic shapes the phases of which are rotated 90 degrees from each other about a rotational center line (1a). A coupling external tooth gear part (8) that maintains a circular cross-sectional shape which does not deform is formed in between the first and second external tooth gear parts (7, 9). The coupling external tooth gear part (8) is maintained so as to be coupled with a coupling internal tooth gear (3) in an engaged manner. The strain wave gear device (1) has high engagement rigidity and is capable of transmitting large torque.

Masakatsu Sasahara

Papers

The strain wave gearing

Strain wave gear device, friction engagement type strain wave device, and wave generator

Strain wave gearing, frictional engagement wave device, and wave generator

Verformungswellgetriebe, Wellvorrichtung mit Reibungseingriff und Wellgenerator

Strain wave gear device