S.No
CONTENTS
PAGE NO.
1.
Abstract
1
2.
Introduction to CAD SYSTEMS
2
2.1. Overview 2.2. Uses 3.
Introduction to AUTO CAD
6
2.1. History 2.2. Design 2.2.1. File formats and versions 2.2.2 Compatibility with other software 2.2.3 Extensions 2.2.4 Vertical integration 2.3. Variants 2.3.1 AutoCAD LT 2.3.2 Student versions 3.
Introduction to Oldham coupling
12
3.1 uses 4. Types of Couplings
21
4.1 Flexible 4.2 Constant velocity 5. Overview of Oldham coupling 5.1 Coupling maintenance and failure
30
5.2 Checking the coupling balance 5.3 Applications 5.4 Parts of Oldham coupling 6: Working & Advantages Conclusion
31
ABSTRACT An Oldham coupling has three discs, one coupled to the input, one coupled to the output, and a middle disc that is joined to the first two by tongue and groove. The tongue and groove on one side is perpendicular to the tongue and groove on the other. The middle disc rotates around its centre at the same speed as the input and output shafts. Its centre traces a circular orbit, twice per rotation, around the midpoint between input and output shafts. Often springs are used to reduce backlash of the mechanism. An advantage to this type of coupling, as compared to two universal joints, is its compact size. The coupler is named for John Oldham who invented it in Ireland, in 1821, to solve a paddle placement problem in a paddle steamer design. AutoCAD is
a software
application for 2D and 3D computer-aided
design
(CAD) and drafting — available since 1982 as a desktop application and since 2010 as a mobile web- and cloud-based application.
In this paper we draft/ draw the Oldham coupling of Orthographic views in the AutoCAD 2010 2D modelling Software.
CHAPTER-1:INTRODUCTION TO CAD SYSTEM Computer-aided design (CAD) is the use of computer systems to assist in the
creation, modification, analysis, or optimization of a design. CAD software is used to increase the productivity of the designer, improve the quality of design, improve communications through documentation, and to create a database for manufacturing. CAD output is often in the form of electronic files for print, machining, or other manufacturing operations. Computer-aided design is used in many fields. Its use in designing electronic systems is known as Electronic Design Automation, or EDA. In mechanical design it is known as Mechanical Design Automation (MDA) or computer-aided drafting (CAD), which includes the process of creating a technical drawing with the use of computer software. CAD software for mechanical design uses either vector-based graphics to depict the objects of traditional drafting, or may also produce raster graphics showing the overall appearance of designed
objects.
However,
it
involves
more
than
just
shapes.
As
in
the
manual drafting of technical and engineering drawings, the output of CAD must convey information, such as materials, processes, dimensions, and tolerances, according to application-specific conventions. CAD may be used to design curves and figures in two-dimensional (2D) space; or curves, surfaces, and solids in three-dimensional (3D) space. CAD is an important industrial art extensively used in many applications, including automotive,
shipbuilding,
and
aerospace
industries,
industrial
and
architectural
design, prosthetics, and many more. CAD is also widely used to produce computer animation for special effects in movies, advertising and technical manuals, often called DCC Digital content creation. The modern ubiquity and power of computers means that even perfume bottles and shampoo dispensers are designed using techniques unheard of by engineers of the 1960s. Because of its enormous economic importance, CAD has been a major driving force for research in computational geometry, computer graphics (both hardware and software), and discrete differential geometry.
The design of geometric models for object shapes, in particular, is occasionally called computer-aided geometric design (CAGD). While the goal of automated CAD systems is to increase efficiency, they are not necessarily the best way to allow newcomers to understand the geometrical principles of Solid Modeling. For this, scripting languages such as PLaSM (Programming Language of Solid Modeling) are more suitable. 1.1 Overview
Beginning in the 1980s computer-aided design programs reduced the need of draftsmen significantly, especially in small to mid-sized companies. Their affordability and ability to run on personal computers also allowed engineers to do their own drafting and analytic work, eliminating the need for entire departments. In today's world, many students in universities do not learn manual drafting techniques because they are not required to do so. The days of hand drawing for final drawings are virtually over. Universities no longer require the use of protractors and compasses to create drawings, instead there are several classes that focus on the use of CAD software. Current computer-aided design software packages range from 2D vector- based drafting systems to 3D solid and surface modelers. Modern CAD packages can also frequently allow rotations in three dimensions, allowing viewing of a designed object from any desired angle, even from the inside looking out. Some CAD software is capable of dynamic mathematical modeling, in which case it may be marketed as CADD. CAD is used in the design of tools and machinery and in the drafting and design of all types of buildings, from small residential types (houses) to the largest commercial and industrial structures (hospitals and factories). CAD is mainly used for detailed engineering of 3D models and/or 2D drawings of physical components, but it is also used throughout the engineering process from conceptual design and layout of products, through strength and dynamic analysis of assemblies to definition of manufacturing methods of components. It can also be used to design objects. Furthermore many CAD applications now offer advanced rendering and animation capabilities so engineers can better visualize their product designs.4D BIM is a type of virtual construction engineering simulation incorporating time or schedule related information for project management.
CAD has become an especially important technology within the scope of computer-aided technologies, with benefits such as lower product development costs and a greatly shortened design cycle. CAD enables designers to layout and develop work on screen, print it out and save it for future editing, saving time on their drawings. 1.2 Uses
Computer-aided design is one of the many tools used by engineers and designers and is used in many ways depending on the profession of the user and the type of software in question. CAD is one part of the whole Digital Product Development (DPD) activity within the Product Lifecycle Management (PLM) processes, and as such is used together with other tools, which are either integrated modules or stand-alone products, such as:
Computer-aided engineering (CAE) and Finite element analysis (FEA)
Computer-aided
manufacturing (CAM) including instructions to Computer Numerical
Control (CNC) machines
Photo realistic rendering
Document management and revision control using Product Data Management (PDM).
CAD is also used for the accurate creation of photo simulations that are often required in the preparation of Environmental Impact Reports, in which computer-aided designs of intended buildings are superimposed into photographs of existing environments to represent what that locale will be like were the proposed facilities allowed to be built. Potential blockage of view corridors and shadow studies are also frequently analyzed through the use of CAD. CAD has been proven to be useful to engineers as well. Using four properties which are history, features, parameterization, and high level constraints. The construction history can be used to look back into the model's personal features and work on the single area rather than the whole model. Parameters and constraints can be used to determine the size, shape, and other properties of the different modeling elements. The features in the CAD system can be used for the variety of tools for measurement such as tensile strength, yield strength, electrical or electro-magnetic properties. Also its stress, strain, timing or how the element gets affected in certain temperatures, etc.
CHAPTER 2: INTRODUCTION TO AUTOCAD
AutoCAD is
a software
application for 2D and 3D computer-aided
design
(CAD) and drafting — available since 1982 as a desktop application and since 2010 as a mobile web- and cloud-based app, currently marketed as AutoCAD 360. Developed and marketed by Autodesk, Inc. AutoCAD was first released in December 1982 — having been purchased a year prior in its original form by Autodesk founder John Walker.
The software is currently marketed in its eighteenth generation. As Autodesk's flagship product, by March 1986 AutoCAD had become the most ubiquitous microcomputer design program worldwide, with functions such as "polylines" and "curve fitting". Prior to the introduction of AutoCAD, most other CAD programs ran on mainframe computers or minicomputers, with each CAD operator (user) working at a graphical terminal or workstation. AutoCAD is used across a range of industries, including architects, project managers and engineers, among other professions, with 750 training centers established worldwide as of 1994. 2.1 History
AutoCAD was derived from a program begun in 1977 and released in 1979 called Interact CAD, also referred to in early Autodesk documents as MicroCAD, which was written prior to Autodesk's (then Marinchip Software Partners) formation by Autodesk cofounder Mike Riddle. The 2014 release marked the 28th major release for the AutoCAD for Windows. The 2014 release marked the fourth consecutive year for AutoCAD for Mac.
2.2 Design
2.2.1 File formats and versions
The native file format of AutoCAD is .dwg . This and, to a lesser extent, its interchange file format DXF , have become de facto, if proprietary, standards for CAD data interoperability. AutoCAD has included support for .dwg, a format developed and promoted by Autodesk, for publishing CAD data. 2.2.2 Compatibility with other software
ESRI ArcMap 10 permits export as AutoCAD drawing files. Civil 3D permits export as AutoCAD objects and as LandXML. Third-party file converters exist for specific formats such as Bentley MX GENIO Extension, PISTE Extension (France), ISYBAU (Germany), OKSTRA and Microdrainage (UK). 2.2.3 Extensions
AutoCAD
supports
a
number
of APIs for
customization
and
automation.
These
include AutoLISP, Visual LISP, VBA, .NET and ObjectARX. ObjectARX is a C++ class library, which was also the base for: (a) products extending AutoCAD functionality to specific fields; (b) creating products such as AutoCAD Architecture, AutoCAD Electrical, AutoCAD Civil 3D; or (c) third-party AutoCAD-based application. There is a large number of AutoCAD plugins (add-on applications) available on the application store Autodesk Exchange Apps . 2.2.4 Vertical integration
Autodesk has also developed a few vertical programs (AutoCAD Architecture, AutoCAD Civil 3D, AutoCAD Electrical, AutoCAD ecscad, AutoCAD Map 3D, AutoCAD Mechanical, AutoCAD MEP, AutoCAD Structural Detailing, AutoCAD Utility Design, AutoCAD P&ID and AutoCAD Plant 3D) for discipline-specific enhancements. For example, AutoCAD Architecture (formerly Architectural Desktop) permits architectural designers to draw 3D objects, such as walls, doors and windows, with more intelligent data associated with them rather than simple objects, such as lines and circles.
The data can be programmed to represent specific architectural products sold in the construction industry, or extracted into a data file for pricing, materials estimation, and other values related to the objects represented. Additional tools generate standard 2D drawings, such as elevations and sections, from a 3D architectural model. Similarly, Civil Design, Civil Design 3D, and Civil Design Professional support data-specific objects, facilitating easy standard civil engineering calculations and representations. Civil 3D was originally developed as an AutoCAD add-on by a company in New Hampshire called Softdesk (originally DCA). Softdesk was acquired by Autodesk, and Civil 3D was further evolved. 2.3 Variants
2.3.1 AutoCAD LT
AutoCAD LT is the lower cost version of AutoCAD, with reduced capabilities, first released in November 1993. Autodesk developed AutoCAD LT to have an entry-level CAD package to compete in the lower price level. AutoCAD LT, priced at $495, became the first AutoCAD product priced below $1000. It is sold directly by Autodesk and can also be purchased at computer stores (unlike the full version of AutoCAD, which must be purchased from official Autodesk dealers). As of the 2011 release the AutoCAD LT MSRP has risen to $1200. While there are hundreds of small differences between the full AutoCAD package and AutoCAD LT, currently there are a few recognized major differences in the software's features:
3D Capabilities: AutoCAD LT lacks the ability to create, visualize and render 3D models as well as 3D printing.
Network Licensing: AutoCAD LT cannot be used on multiple machines over a network.
Customization: AutoCAD LT does not support customization with LISP, ARX, and VBA.
Management and automation capabilities with Sheet Set Manager and Action Recorder.
CAD standards management tools.
AutoCAD 360
View 1
View 2
AutoCAD WS Mobile App (iOS) Formerly marketed as AutoCAD WS, AutoCAD 360 is an account-based mobile and web application enabling registered users to view, edit, and share AutoCAD files via mobile device and web using a limited AutoCAD feature set — and using cloud-stored drawing files. The program, which is an evolution and combination of previous products, uses a freemium business model with a free plan and two paid levels — marketed as Pro ($4.99 monthly or $49.99 yearly) and Pro Plus ($99.99 yearly) — including various amounts of storage, tools, and online access to drawings. 360 includes new features such as a "Smart Pen" mode and linking to third-party cloud-based storage such as Dropbox. Having evolved from Flash-based software, AutoCAD 360 uses HTML5 browser technology available in newer browsers including Firefox and Google Chrome.
AutoCAD WS began with a Flash-based version for the iPhone and subsequently expanded to include version for the iPod Touch, iPad, Android phones, and Android tablets. Autodesk
released
the iOS version
in
September
2010, following
with
the Android version on April 20, 2011. The program is available via download at no cost from the App Store (iOS), Google Play (Android) and Amazon Appstore (Android). In its initial iOS version, AutoCAD WS supported drawing of lines, circles, and other shapes; creation of text and comment boxes; and management of color, layer, and measurements — in both landscape and portrait modes. Version 1.3, released August 17, 2011, added support of unit typing, layer visibility, area measurement and file management. The Android variant
includes the iOS feature set along with such unique features as the ability to insert text or captions by voice command as well as manually. Both Android and iOS versions allow the user to save files on-line — or off-line in the absence of an Internet connection. In 2011, Autodesk announced plans to migrate the majority of its software to "the cloud", starting with the AutoCAD WS mobile application. According to a 2013 interview with IlaiRotbaein, an AutoCAD WS Product Manager for Autodesk, the name AutoCAD WS had no definitive meaning, and was interpreted variously as Autodesk Web Service, White Sheet or Work Space. 2.3.2 Student versions
AutoCAD is licensed at a significant discount over commercial retail pricing to qualifying students and teachers, with a 36-month license available. The student version of AutoCAD is functionally identical to the full commercial version, with one exception: DWG files created or edited by a student version have an internal bit-flag set (the "educational flag"). When such a DWG file is printed by any version of AutoCAD (commercial or student), the output includes a plot stamp / banner on all four sides.
Objects created in the Student Version cannot be used for commercial use. Student Version objects "infect" a commercial version DWG file if it is imported. The Autodesk Education Community provides registered students and faculty with free access to different Autodesk applications.
CHAPTER 3: INTRODUCING TO OLDHAM COUPLING An Oldham coupling has three discs, one coupled to the input, one coupled to the output, and a middle disc that is joined to the first two by tongue and groove. The tongue and groove on one side is perpendicular to the tongue and groove on the other. The middle disc rotates around its center at the same speed as the input and output shafts. Its center traces a circular orbit, twice per rotation, around the midpoint between input and output shafts. Often springs are used to reduce backlash of the mechanism. An advantage to this type of coupling, as compared to two universal joints, is its compact size. The coupler is named for John Oldham who invented it in Ireland, in 1821, to solve a paddle placement problem in a paddle steamer design.
Oldham coupling
A transmission apparatus to hold a lock core of a supplemental lock includes an inner housing, a lock coupler, a latch bolt coupler, a restitution element and a cover. The inner housing has a lock core chamber. The lock coupler is rotatably mounted in the lock core chamber and includes a rotatable outer disk coupler and two lock coupling arms. The outer disk coupler has a flat edge. The lock coupling arms connect to the lock core that rotates the outer disk coupler. The latch bolt coupler is rotated by the lock coupler and includes a latch coupling arm and a longitudinal tab. The restitution element is mounted around the latch coupling arm. The cover is attached to the rear of the inner housing.
Consequently, the flat edge abuts the longitudinal tab that rotates the latch coupling arm when the outer disk coupler is rotated. A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. By careful selection, installation and maintenance of couplings, substantial savings can be made in reduced maintenance costs and downtime. 3.1 Uses
Shaft couplings are used in machinery for several purposes, the most common of which are the following.
To provide for the connection of shafts of units that are manufactured separately such as a motor and generator and to provide for disconnection for repairs or alterations.
To provide for misalignment of the shafts or to introduce mechanical flexibility.
To reduce the transmission of shock loads from one shaft to another.
To introduce protection against overloads.
To alter the vibration characteristics of rotating units.
Chapter 4: Types of couplings Rigid
A rigid coupling is a unit of hardware used to join two shafts within a motor or mechanical system. It may be used to connect two separate systems, such as a motor and a generator, or to repair a connection within a single system. A rigid coupling may also be added between shafts to reduce shock and wear at the point where the shafts meet. When joining shafts within a machine, mechanics can choose between flexible and rigid couplings. While flexible units offer some movement and give between the shafts, rigid couplings are the most effective choice for precise alignment and secure hold. By precisely
aligning the two shafts and holding them firmly in place, rigid couplings help to maximize performance and increase the expected life of the machine. These rigid couplings are available in two basic designs to fit the needs of different applications. Sleeve-style couplings are the most affordable and easiest to use. They consist of a single tube of material with an inner diameter that's equal in size to the shafts. The sleeve slips over the shafts so they meet in the middle of the coupling. A series of set screws can be tightened so they touch the top of each shaft and hold them in place without passing all the way through the coupling. Clamped or compression rigid couplings come in two parts and fit together around the shafts to form a sleeve. They offer more flexibility than sleeved models, and can be used on shafts that are fixed in place. They generally are large enough so that screws can pass all the way through the coupling and into the second half to ensure a secure hold.Flanged rigid couplings are designed for heavy loads or industrial equipment. They consist of short sleeves surrounded by a perpendicular flange. One coupling is placed on each shaft so the two flanges line up face to face. A series of screws or bolts can then be installed in the flanges to hold them together. Because of their size and durability, flanged units can be used to bring shafts into alignment before they are joined together. Rigid couplings are used when precise shaft alignment is required; shaft misalignment will affect the coupling's performance as well as its life. Examples: Sleeve coupling A sleeve coupling consists of a pipe whose bore is finished to the required tolerance based on the shaft size. Based on the usage of the coupling a keyway is made in the bore in order to transmit the torque by means of the key. Two threaded holes are provided in order to lock the coupling in position. Sleeve couplings are also known as Box Couplings. In this case shaft ends are coupled together and abutted against each other which are enveloped by muff or sleeve. A gib head sunk keys hold the two shafts and sleeve together Clamp or split-muff coupling
A clamp coupling is different from the sleeve coupling in that the sleeve used in this type is split from one side.The shafts are entered and keyed to this sleeve and then split sides are screwed together. 4.1 Flexible
Flexible couplings are used to transmit torque from one shaft to another when the two shafts are slightly misaligned. Flexible couplings can accommodate varying degrees of misalignment up to 3° and some parallel misalignment. In addition, they can also be used for vibration damping or noise reduction. A beam coupling, also known as helical coupling, is a flexible coupling for transmitting torque between two shafts while allowing for angular misalignment, parallel offset and even axial motion, of one shaft relative to the other. This design utilizes a single piece of material and becomes flexible by removal of material along a spiral path resulting in a curved flexible beam of helical shape. Since it is made from a single piece of material, the Beam Style coupling does not exhibit the backlash found in some multi-piece couplings. Another advantage of being an all machined coupling is the possibility to incorporate features into the final product while still keeps the single piece integrity.
Beam coupling
Changes to the lead of the helical beam provide changes to misalignment capabilities as well as other performance characteristics such as torque capacity and torsional stiffness. It is even possible to have multiple starts within the same helix. The material used to manufacture the beam coupling also affects its performance and suitability for specific applications such as food, medical and aerospace. Materials are typically aluminum alloy and stainless steel, but they can also be made in acetal, maraging steel and titanium. The most common applications are attaching encoders to shafts and motion
control
for robotics.
4.2 Constant veloci ty
There are various types of constant-velocity (CV) couplings: Rzeppa joint, Double cardan joint, and Thompson coupling.
Diaphragm
Diaphragm couplings transmit torque from the outside diameter of a flexible plate to the inside diameter, across the spool or spacer piece, and then from inside to outside diameter. The deforming of a plate or series of plates from I.D. to O.D accomplishes the misalignment.
Disc
Disc couplings transmit torque from a driving to a driven bolt tangentially on a common bolt circle. Torque is transmitted between the bolts through a series of thin, stainless steel discs assembled in a pack. Misalignment is accomplished by deforming of the material between the bolts, Fluid
A gear coupling is a mechanical device for transmitting torque between two shafts that are not collinear. It consists of a flexible joint fixed to each shaft. The two joints are connected by a third shaft, called the spindle. Each joint consists of a 1:1 gear ratio internal/external gear pair. The tooth flanks and outer diameter of the external gear are crowned to allow for angular displacement between the two gears. Mechanically, the gears are equivalent to rotating splines with modified profiles. They are called gears because of the relatively large size of the teeth. Gear couplings and universal joints are used in similar applications. Gear couplings have higher torque densities than universal joints designed to fit a given space while universal joints induce lower vibrations. The limit on torque density in universal joints is due to the limited cross sections of the cross and yoke. The gear teeth in a gear coupling have high backlash to allow for angular misalignment. The excess backlash can contribute to vibration.
Gear coupling
Gear couplings are generally limited to angular misalignments, i.e., the angle of the spindle relative to the axes of the connected shafts, of 4-5°. Universal joints are capable of higher misalignments. Single joint gear couplings are also used to connected two nominally coaxial shafts. In this application the device is called a gear-type flexible, or flexible coupling. The single joint allows for minor misalignments such as installation errors and changes in shaft alignment due to operating conditions. These types of gear couplings are generally limited to angular misalignments of 1/4-1/2°. Rag joi nt
Rag joints are commonly used on automotive steering linkages and drive trains. When used on a drive train they are sometimes known as giubos.
Un iversal joi nt
Universal joints are also known as Cardan joints. Others
Bellows coupling — low backlash
Elastomeric coupling o
Bushed pin coupling
o
Donut coupling
o
Spider or jaw coupling (or lovejoy coupling)
Geislinger coupling
Resilient coupling
Roller chain and sprocket coupling
CHAPTER 5: OVERVIEW OF OLDHAM COUPLING Requirements of good shaft alignment / good coupling setup
It should be easy to connect or disconnect the coupling.
It does allow some misalignment between the two adjacent shaft rotation axes.
It is the goal to minimise the remaining misalignment in running operation to maximise power transmission and to maximise machine runtime (coupling and bearing and sealings lifetime).
it should have no projecting parts.
it is recommended to use manufacturer's alignment target values to set up the machine train to a defined non-zero alignment, due to the fact that later when the machine is at operation temperature the alignment condition is perfect
5.1 Coupli ng main tenance and fai lu re
Coupling maintenance is generally a simple matter, requiring a regularly scheduled inspection of each coupling. It consists of:
Performing visual inspections, checking for signs of wear or fatigue, and cleaning couplings regularly.
Checking and changing lubricant regularly if the coupling is lubricated. This maintenance is required annually for most couplings and more frequently for couplings in adverse environments or in demanding operating conditions.
Documenting the maintenance performed on each coupling, along with the date.
Even with proper maintenance, however, couplings can fail. Underlying reasons for failure, other than maintenance, include:
Improper installation
Poor coupling selection
Operation beyond design capabilities.
The only way to improve coupling life is to understand what caused the failure and to correct it prior to installing a new coupling. Some external signs that indicate potential coupling failure include:
Abnormal noise, such as screeching, squealing or chattering
Excessive vibration or wobble
Failed seals indicated by lubricant leakage or contamination.
5.2 Checki ng th e coupli ng balan ce
Couplings are normally balanced at the factory prior to being shipped, but they occasionally go out of balance in operation. Balancing can be difficult and expensive, and is normally done only when operating tolerances are such that the effort and the expense are justified. The amount of coupling unbalance that can be tolerated by any system is dictated by the characteristics of the specific connected machines and can be determined by detailed analysis or experience.
5.3 Applications:
It is used to transfer torque between two parallel but not collinear shafts.
Depending upon the matterial of the 3 discs , oldham coupling can be used in
many devices. They can easily be used in servo mechanisms.
Application of Oldhams coupling It was basically invented to connect two parallel non co axial shafts. It is a really good mechanism and transmits the same speed and same direction of rotation. It is not of much importance now as gears are being used.
An Oldham coupling is a flexible shaft coupling that consists of two hubs (each with a fin or tenon) and one midsection (with grooves that fit those fins, one on each side of the midsection, and perpendicular to one another).The Oldham coupling is an outstanding design for torque transmission between two shafts which might be slightly misaligned. The coupling accommodates this misalignment,
5.4 PARTS OF OLDHAM’S COUPLING
Two hubs:
It is the part which is connected to the ends of the shafts. It is a round circular shaped disk. The disk consists of groves in the center of them which is plugged into the projections of central disk.
Central disk:
It is the coupling part of two hubs. It consist of two projected bars on the both sides the disk which are perpendicularly plugged into the hubs. The center disk is press-fitted to eliminate backlash and also designed to act as a mechanical fuse. The disc slides to accommodate large parallel misalignment.
CHAPTER 6: WORKING
Oldham’s coupling is an example of third inversion of double -slider crank
mechanism. When link 3, of the double slider crank chain shown in fig. 1.28(c), is fixed and link 1 is free to move, third inversion is obtained which is shown in fig 1.30. In this case each of slide blocks (i.e. link 2 and link 4) can turn about the pins A and B. If one slide block (say link 2) is turned through a definite angle, the frame (i.e. link 1) and the other block (i.e. link 4) must turn through the same angle.
This inversion is used in Oldham’s coupling (shown in fig 1.31) which is used
for connecting two parallel shafts when the distance between the two shafts is small. The two shafts to be connected have flanges at their end which are rigidly fastened by forging to the shaft. This flanges from link 2 and 4. Each of these links forms a turning pair with link 3.there is diametrical slot cut in the inner face of these flanges. An intermediate piece is a circular disk (link 1) has two tongues T1 and T2 on each face at right angle to each other. These tongues can slide-fit in the slots in the two flanges (link 2 and 4). The link 1 can slide or reciprocate in the slots in the flanges. Frame and bearings form the link 3 which is fixed. When the driving shaft is rotated, the flange A (i.e. link 2) connected rigidly to the driving shaft also rotates by the same angle, the intermediate piece also rotate by the same angle through which flange A has rotated. Due to rotation of intermediate shaft, the flange B
(i.e. link 4) connected to the driven shaft, also rotate by the same angle. Hence link 2, 4and 1 have the same angular velocity at every instant. The distance between the axis of the shaft is constant and hence the center of the intermediate piece will describe a circle of diameter equal to the distance between the axes of the shafts. There is a sliding motion between the link 1 and each of the other link 2 and 4.
APPLICATIONS Oldham Coupling Lubrication Pump
The lubrication pump on GE Reciprocating compressors is usually Directly driven by the compressor Shaft through an Oldham coupling Which transmits the torque from the reciprocating compressor crankshaft to the lube oil pump. In larger and high-speed (>700 RPM) compressors, the power absorbed by the lube oil pump is very high and therefore, the coupling is a very critical item for compressor reliability.
ADVANTAGES OF OLDHAM’S COUPLING
Protects driven component by serving as a mechanical "fuse" - an inexpensive replaceable plastic midsection shears under excess load
Protects support bearings by exerting consistently low reactive forces, even under large misalignments
Homokinetic transmission - driving and driven shafts rotate at exactly the same speed at all times
Zero backlash and high torsional stiffness
Electrical insulation
Accommodates large radial misalignment in a short length
Easy installation in blind or difficult installations when through-bores are used
Economically priced compared to other couplings with similar performance characteristics
Inexpensive replaceable wear element
Low moment of inertia No velocity variation as with universal joints High lateral misalignments possible High torque capacity Ease of dismantling
DISADVANTAGES OF OLDHAM’S
Limited angular displacement of shafts Need for periodic lubrication due to relative sliding motion unless nylon or rubber construction is employed
Possible loss of loose members during disassembly
Accommodates a relatively small angular misalignment
Conclusion:
In this we develop drafting or drawing of orthogonal views(such as Front View & Top View) of a universal Joint or Coupling , by using commands in Autocad 2D Modeling software of version 2010 and fabrication of small non-linear Oldham coupling.
