Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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Strain Wave Gear (SWG) or Harmonic Drive (HD) shows moderate performance under symmetrical involute teeth. Teeth interference, excessive teeth meshing, vibration due to improper teeth engagement are the major drawbacks of strain wave gear under symmetrical involute teeth. In the present paper, an attempt has been made to improve the performance of strain wave gear by replacing the symmetrical involute teeth with asymmetrical involute teeth. Present investigation finds that under ‘asymmetric toothed strain wave gear’, aspects such as teeth interference, teeth engagement and teeth contact stress of strain wave gear are improving clearly and as a consequence some other aspects such as individual teeth strength, load carrying capacity, tooth endurance are also improving inherently. In the present analysis for symmetrical teeth 20°–20° pressure angle and for asymmetrical teeth, three different combinations of pressure angles such as 25°–20°, 30°–20° and 35°–20° are taken. © IMechE 2021.

Department of Design and Automation

School of Mechanical Engineering

Vellore Campus

World University root node

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

Performance analysis of asymmetric toothed strain wave gear

The present investigation aims at analysing the effects of surface roughness (three possible types of roughness: isometric, longitudinal and transverse orientation of asperities) on lubrication mechanism at the coning gap which is formed between flexspline cup and cam interface in strain wave gear during assembly of its components. Investigation is further extended to analyse the effects of roughness on lubrication characteristics such as fluid flow speed, fluid flow force and fluid frictional force. In the present investigation at first, generalized Reynolds equation for hydrodynamic lubrication is modified to make it suitable for coning gap and then, micro-polar terms as well as surface roughness terms for all possible roughness (isometric, longitudinal and transverse) are incorporated into it. Conservative form of finite difference method is applied to solve the all three complicated Reynolds equation under suitable boundary conditions. The solution of Reynolds equation is further utilized to derive the lubrication characteristics like fluid flow speed, fluid flow force and fluid frictional force. Methods of finding lubrication pressure profiles and lubrication characteristics under micro-polar fluid with surface roughness are established. Effects of roughness terms on pressure profiles as well as on lubrication characteristics are also established. All analyses are done in dimensionless form. Originality of present investigation is lubrication analysis at the coning gap of strain wave gear under rough surfaces and the finding effects of roughness on it. © 2021 Author(s).

Department of Automotive Engineering

AIP Conference Proceedings

Lubrication mechanism and lubrication characteristics analysis at the critical interface of strain wave gear under different types of surface roughness assumptions

Present paper presents an approach for designing of regenerative braking system for human powered vehicles such as bicycle. Existing regenerative braking system is robust and its application is limited to fuelled vehicles only. Keeping size and weight constraints in mind, a lucid mechanism that incorporates a flat spiral spring, planetary gear system and a one-way clutch as the main components, is investigated here as regenerative braking system. This system stores the kinetic energy in the form of elastic potential energy and converts it back to kinetic energy. The design setup is pliable and can be incorporated with ease on a wheel hub. The mechanism is capable to work in extreme conditions. This system will prove to be cogent in assistance to the driver while acceleration, thus enhancing the overall efficiency of the system. © 2021 Author(s).

Spiral spring and planetary gear based regenerative braking system design for bicycles

The present paper aims at review on different aspects of harmonic drive gear to identify literature gap for future research. The present article is started first making the comparative study of harmonic drive gear over conventional gear, highlighting its historical background, its application, limitation etc. and then describing working principle of each and every components of it with detail dimensioning and modelling. The present article is further extended to study the different design aspects i.e. synthesis of tooth profiles, lubrication, stress, strain, torque, load sharing, kinematics error and vibration in details etc., identifying problems and then suggesting future perspective for the performance improvement of harmonic drive gear. © 2018 Author(s).

Design aspects of harmonic drive gear and performance improvement of its by problems identification: A review

In the present paper Reynolds equation of lubrication under micro-polar fluid for journal bearing is solved by direct-integration method under infinitely long and infinitely short journal bearing assumptions [1]. Infinitely long-bearing and infinitely short bearing solutions are the two available approximate closed form solutions for journal bearings. In the present investigation, solution of Reynolds equation i.e. pressure profile is compared with pressure profile obtained by previously used approximate method like finite difference method (FDM). Mentionable here that any approximation method needs lots of calculation and computer programing to get the result. In the present work it has been found that direct-integration method leads the almost same result as the conventionally used complex finite difference method. CFD analysis is also presented in the present work to justify the profile obtained by direct numerical method. It has seen here that theoretical and simulation results are in good agreement to each other’s.

Volume 2: Structures and Dynamics; Renewable Energy (Solar, Wind); Inlets and Exhausts; Emerging Technologies (Hybrid Electric Propulsion, UAV, ...); GT Operation and Maintenance; Materials and Manufacturing (Including Coatings, Composites, CMCs, Additive Manufacturing); Analytics and Digital Solutions for Gas Turbines/Rotating Machinery

Analysis of Infinitely Short and Infinitely Long Hydrodynamic Journal Bearings Under Micro-Polar Fluid by Direct Integration Method

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. © 2016 Emerald Publishing Limited.

Industrial Lubrication and Tribology

Analysis of coning and lubrication at flexspline cup and cam interface in conventional harmonic drives

In present study, the deformation behavior of copper containing 5.02 by weight percentage of zinc is investigated with strain rate of 1×10-1 to 1×10-3 s-1 at room temperature. Yield strength is found to vary from 260 to 335 MPa and ductility is found to increase from 38.66 to 44.31 %. It is also found that yield strength was highest for the sample tested with 1× 10-3 s-1 strain rate and lower yield strength was observed with strain rate 1×10-1 s-1. Optical images are included in the paper for gauge section of the test samples. It also found that as strain rate increases the nature of grains changes from fine (with strain rate 1×10-3 s-1) to coarser grains (with strain rate 1×10-1 s-1). Thus, an increase in strength of specimen can be attributed to decrease in grain size of the specimen. © IAEME Publication.

International Journal of Mechanical Engineering and Technology

Flow and fracture behavior of copper with different strain rate at room temperature

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 generating' oval-shaped cam. This is due to varying root deformations of teeth. In case of teeth with widely used involute profile, away from the contacts on line of action through pitch point, they definitely experience force closeness to or separation from the circular spline's (CS) originally conjugate tooth. We have estimated the deformed pitch distances at no load considering that FS teeth remain rigid while the rim deforms. The geometry of the oval-shaped pitch curve which is parallel to the elliptical outer profile of the cam is also defined. Similarly to maintain an elliptical pitch curve of FS, the oval cam is also defined. Both cases of tooth mesh of undeformed FS with CS and tooth mesh of deformed FS with CS, with involute teeth, are considered to find out tooth positions. Geometries of involute teeth profiles in mesh are examined and compared considering oval-shaped (on deformation) base drum of FS, whereas the base circle of the CS remained circular. © Institution of Mechanical Engineers.

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

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 characteristics and capacities in comparison to the conventional one of same size with oval-shaped strain wave generating cam. The cam profile has circular arcs at two working zones at 180 phases. The proposed profile shape is identified as the cause of trouble in assembly if the cam is made single piece. The split cam is made of two identical pieces having circular arc edges. These pieces constitute the cam in assembly after putting it inside the inner race of the flex bearing and adjusted by an adjuster. The design, kinematics, and the assembly method of the proposed split cam are presented in this article. The split cam arrangement not only solves the assembly problem but also gives a scope of fine adjustment of center distance (eccentricity). Such an adjustment is not possible in conventional oval wave generating cam. Stresses in flex gear cups assembled with both type cams at load and no-load conditions are estimated using finite element method. Some results are verified experimentally. Although the flex gear cup with the proposed split cam experiences lower stresses at load transmitting active gear contact zones, it shows higher stresses at some non-active zones (where teeth are free of load). It is apparent from results that stresses at those non-active zones do not increase substantially with the increase in torque, as they are away from active zones. © 2012 IMechE.

Design and development of strain wave generating cam for a new concept 'harmonic drive'

Circular pitches of flex spline teeth of a 'Strain Wave Gearing', also known as a 'Harmonic Drive', are deformed when the Strain Wave Generating Cam is inserted into the flex spline cup. In the present work the deformed pitch distances considering that flex spline teeth remain rigid while the rim deforms, are estimated. No applied load is considered. It is also shown that if the cam is elliptical then the pitch curve is not an ellipse and vice versa. Geometries of such curves can be defined following the analysis presented in this paper. Cases of both undeformed flex spline with circular spline and deformed flex spline with circular spline, with involute teeth, are considered to find out tooth positions. Geometries of involute teeth profiles in mesh are examined and compared considering oval shaped (on deformation) base drum of flex spline where as base circle of circular spline remained circular. Copyright © 2011 by ASME.