GREATEST INDIAAAAAAAAAAAAAAAA

mech

jigarbhatiya — Wed, 13 Aug 2008 08:37:53 +0000

Linkage (mechanical)

From Wikipedia, the free encyclopedia

Locking pliers exemplify a four-bar, one degree of freedom mechanical linkage; or a five-bar, two DOF linkage when the adjustment screw is considered.

A mechanical linkage is a series of rigid links connected with joints to form a closed chain, or a series of closed chains. Each link has two or more joints, and the joints have various degrees of freedom to allow motion between the links. A linkage is called a mechanism if two or more links are movable with respect to a fixed link. Mechanical linkages are usually designed to take an input and produce a different output, altering the motion, velocity, acceleration, and applying mechanical advantage.

A linkage designed to be stationary is called a structure.

[hide]

[edit] History

A flyball governor for flow control. A water turbine spins the governor, which controls the water flow, which feeds the turbine, creating a speed-regulated machine.

Mechanical linkages are a fundamental part of machine design, and yet many simple linkages were not well understood nor invented until the 19^th century. Consider a stick: it has six degrees of freedom, three of which are the coordinates of its centre in space, the other three describing its rotation. Once nudged between a boulder and fulcrum it is constrained to a particular motion, to act as a lever to move the boulder. When more links are added and joined in various ways their collective motion can be further defined. Very complicated and precise motions can be designed into a linkage with only a few parts.

The Industrial Revolution was the golden age of mechanical linkages. Mathematical, engineering and manufacturing advances provided both the need and the ability to create new mechanisms. Many simple mechanisms that seem obvious today required some of the greatest minds of the era to create. Leonhard Euler was one of the first mathematicians to study linkage synthesis, and James Watt worked very hard to invent the Watt linkage to support his steam engine‘s piston. Chebyshev worked on mechanical linkage design for over thirty years, which led to his work on polynomials². New linkage inventions, designed by need, were instrumental in cloth making, power conversion and speed regulation. Even the ability of a mechanism to produce accurate linear motion, without a reference guide way, took years to solve.

Scientists, mostly German, Russian and English, have researched this domain over the last 200 years, so that today most traditional analysis or synthesis problems (e.g. planar movement) have been solved (see online libraries under External links). Recently, compliant structures have come to the fore.

Electronic technology has replaced many linkage applications taken for granted today, such as mechanical computation, typewriting and machining. However, modern linkage design continues to advance, and designs that used to occupy an engineer for days are now optimized with a computer in seconds.

Even though servomechanisms with digital control are common, and at first glance easy to use, some motion problems (especially for quick and accurate movements) are still only soluble using linkages and cams.

[edit] Theory

The most common linkages have one degree of freedom, meaning that there is one input motion that produces one output motion. Most linkages are also planar, meaning all the motion takes place in one plane. Spatial linkages (non-planar) are more difficult to design and therefore not as common.

Kutzbach-Gruebler’s equation is used to calculate the degrees of freedom of linkages. The number of degrees of freedom of a linkage is also called its mobility.

A simplified version of the Kutzbach-Gruebler’s equation for planar linkages :

= mobility = degrees of freedom

= number of links (including a single ground link)

= number of one-degree-of-freedom kinematic pairs (pin or slider joints)

A more general form of the Kutzbach-Gruebler equation for planar linkages involving more complex joints:

Or, for spatial linkages (linkages involving 3D motion):

= mobility (degrees of freedom)

= number of links (including a single ground link)

= number of total joints, regardless of connectivity or degree-of-freedom

= sum of each joint’s individual degree of freedom

The mobility of hydraulic machinery can easily be identified by counting the number of independently controlled hydraulic cylinders.

Simple linkages are capable of producing complicated motion.

Types of common joints:

Revolute or pin, one DOF rotation. Examples are; bushings, bearings, bolted joints, rivets and hinges.
Prismatic or slider, one or two DOF linear motion. Examples are; linear bearings, hydraulic cylinders, rollers and pistons.
Spherical or ball and socket, three DOF rotation, usually restricted to one DOF by other joints in the mechanism.

Designers will synthesize a linkage by starting with the required output motion, mechanical advantage, velocity and acceleration. A type of linkage is chosen and modified to deliver the required performance.

Each link is treated as a vector and the vectors can be combined into a system of equations because they form a loop. The matrix is solved to create a closed form equation that relates input motion to output motion. The same is done for mechanical advantage, or any other important quantity. The equations of motion are differentiated with respect to time to find velocity and acceleration of the mechanism parts.

[edit] Types of linkages

Four bar linkages are the simplest closed loop kinematic linkage. They perform a wide variety of motions with a few simple parts. They were also popular in the past due to the ease of calculations, prior to computers, compared to more complicated mechanisms.

Types of four bar linkages, s = shortest link, l = longest link

[edit] Uses

A spatial 3DOF linkage for joystick applications.

Linkages are primarily used as machine components and tools. Typical examples are automotive suspensions and bolt cutters. The internal combustion engine’s piston/rod/crank is a classic four-bar linkage with one degree of freedom. Linkages are often the simplest, least expensive and most efficient mechanism to perform complicated motions.

One highly visible application is the windshield wiper: a four bar linkage changes the motor’s rotary motion to oscillation. Some wipers also have a second set of four bar linkages to keep the wiper blades oriented correctly as they sweep. Another visible application is heavy equipment which makes extensive use of four and six bar linkages.

Spatial linkages are becoming more common due to computer aided design.

“The 4-Bar Linkage” is an adapted mechanical linkage used on bicycles. With a normal full-suspension bike the back wheel moves in a very tight arc shape. This means that more power is lost when going uphill. With a bike fitted with a 4-Bar Linkage, the wheel moves in such a large arc that it is moving almost vertically. This way the power loss is reduced by up to 30%.

[edit] References

Erdman, Arthur G.; Sandor, George N. (1984). Mechanism Design: Analysis and Synthesis. Prentice-Hall. ISBN 0-13-572396-5.
How to Draw a Straight Line, historical discussion of linkage design
What is a Watt I Linkage?

[edit] See also

Engineering mechanics
Cam
Kinematic pairs
Overconstrained mechanism
Machine
Three-point hitch
Lever
Parallel motion
Whippletree, a multi-bar linkage to evenly distribute force.

[edit] External links

Wikimedia Commons has media related to:

Linkage (mechanical)

How round is your circle? Contains a chapters on Watt’s and other linkages.
An (at present mainly German) online library about linkages and cams is available through Digital Mechanism and Gear Library (DMG-Lib) (in German: Digitale Mechanismen- und Getriebebibliothek)
With KMODDL there is also an English online library (contains foreign literature too)
Linkage calculations
Java animated linkages
Gif animated linkages
Introductory Linkage Lecture, 2MB PDF
Virtual Mechanisms Animated by Java
SAM User-friendly software for design, motion/force analysis & optimization of planar linkage, gear and belt mechanisms

Retrieved from “http://en.wikipedia.org/wiki/Linkage_%28mechanical%29“

Categories: Linkages

Views

Personal tools

Search

Toolbox

Languages

HISTORY OF INDIA

jigarbhatiya — Fri, 04 Apr 2008 05:20:10 +0000

India is a land of ancient civilization. India’s social, economic, and cultural configurations are the products of a long process of regional expansion. Indian history begins with the birth of the Indus Valley Civilization and the coming of the Aryans. These two phases are usually described as the pre-Vedic and Vedic age. Hinduism arose in the Vedic period. The fifth century saw the unification of India under Ashoka, who had converted to Buddhism, and it is in his reign that Buddhism spread in many parts of Asia. In the eighth century Islam came to India for the first time and by the eleventh century had firmly established itself in India as a political force. It resulted into the formation of the Delhi Sultanate, which was finally succeeded by the Mughal Empire, under which India once again achieved a large measure of political unity. It was in the 17th century that the Europeans came to India. This coincided with the disintegration of the Mughal Empire, paving the way for regional states. In the contest for supremacy, the English emerged ‘victors’. The Rebellion of 1857-58, which sought to restore Indian supremacy, was crushed; and with the subsequent crowning of Victoria as Empress of India, the incorporation of India into the empire was complete. It was followed by India’s struggle for independence, which we got in the year 1947.

National Flag

jigarbhatiya — Wed, 02 Apr 2008 09:10:35 +0000

The national flag of India is tricolor. It has deep saffron color strip at the top, white in the middle and dark green at the bottom in equal proportions. The width and length ratio of the National flag is two is to three. In the centre of the white strip, there is a wheel in navy blue color to indicate the Dharma Chakra, the wheel of law in the Sarnath Lion Capital. The diameter of the wheel approximates to the width of the white strip and has 24 spokes. The design of the national flag was adopted by the Constituent Assembly of India on 22nd July, 1947. The use and display of the National flag of India are regulated by a flag Code.

National Emblem

jigarbhatiya — Wed, 02 Apr 2008 09:08:00 +0000

The National Emblem of India has been taken from the Sarnath Lion capital erected by Ashoka. The national emblem of India was adapted by the Government of India on 26th January1950. In the National emblem only three lions are visible and the fourth one is hidden from the view. All the lions are mounted on an abacus. At the centre of the Abacus, there is a Chakra (wheel) which symbolizes the Dharma Chakra (Eternal wheel of law).

There is a bull, a galloping horse, an elephant and a lion, separated by intervening wheels over a bell shaped lotus. The word Satyameva Jayate (truth alone triumphs) have been inscribed in Devanagari script. The National emblem of India is the official seal of the President of India and Central and State Governments. The National emblem is used only for official purposes and commands highest respect and loyalty. It is also a symbol of independent India’s identity and sovereignty.

National Anthem

jigarbhatiya — Wed, 02 Apr 2008 09:05:34 +0000

The national anthem of India, Jana-gana-mana, was composed by the great poet Rabindranath Tagore and was adopted by the Constituent Assembly of India on January 24th 1950. Jana-gana-mana was first sung on 27th December, 1911 at the Calcutta Session of the Indian National Congress. The songs, Jana-gana-mana, consists of five stanzas. The first stanza constitutes the full version of the National Anthem. Playing time of the full version of the National Anthem is approximately 52 seconds. The national anthem of India is as follows-

“Jana-gana-mana-adhinaayaka, jaya he
Bhaarata-bhagya-vidhaataa
Punjab-Sindhu-Gujarata-Marathaa
Draavida-Utkala -Banga Vindhya-Himachala-Yamuna-Gangaa
Uchchala-Jaladhi-taranga
Tava shubha naame jaage
Tava shubha ashisha maange
Gaaye tab jaya gaatha
Jana-gana-mangala-daayaka jaya he
Bharata-bhagya-vidhataa
Jaya he, jaya he, jaya he
Jaya jaya, jaya, jaya he!! “

Here is Tagore’s English rendering of the stanza (Indian national anthem) – “Thou art the ruler of the minds of all people, dispenser of India’s destiny. Thy name rouses the hearts of Punjab, Sindh, Gujarat and Maratha, of the Dravida and Orissa and Bengal it echoes in the hills of the Vindhyas and Himalayas, Mingles in the music of Jamuna and Ganges and is chanted by the waves of the Indian Sea. They pray for thy blessings and sing thy praise. The saving of all people waits in thy hand, thou dispenser of India’s destiny victory, victory, victory, victory to thee.”

National Flower

jigarbhatiya — Wed, 02 Apr 2008 09:02:07 +0000

Lotus is the National flower of India. The Lotus symbolizes spirituality, fruitfulness, wealth, knowledge and illumination. The most important thing about lotus is that even after growing in murky water it is untouched by its impurity. On the other hand the lotus symbolizes purity of heart and mind. The National Flower ‘Lotus’ or water lily is an aquatic plant of Nymphaea species with broad floating leaves and bright aromatic flowers that grow only in shallow waters.

The leaves and flowers of the Lotus float and have long stems that contain air spaces in them. The lotus flowers have many petals overlapping in a proportional pattern. The root functions of lotus are carried out by rhizomes that fan out horizontally through the mud below the water. Lotuses, cherished for their tranquil beauty, are delightful to take a look at as their blossoms open on the pond’s surface.

National Animal

jigarbhatiya — Wed, 02 Apr 2008 08:58:37 +0000

Tiger (Panthera Tigris, Linnaeus) is the national animal of India. Tiger is also called the lord of Jungles. As the national animal of India, tiger symbolizes India’s wildlife wealth. The rare combination of grace, strength, agility and enormous power has earned the tiger great respect and high esteem. India is home to nearly half of the total population of tigers. The government of India launched the Project Tiger in 1973 to protect the royal animal.

Out of the eight races of the tiger, the Indian race, the Royal Bengal Tiger is found almost all over country (with the exception of the north-western region). With the launch of Project tiger in 1973, the tiger population showed a gradual increase and the census of 1993 puts the tiger population of the country at 3,750. Under Project tiger 23 tiger reserves have been established throughout the country, covering an area of 33,406 sq. km. Unfortunately due to negligence of authorities and poaching the tiger population of India is decreasing at an alarming rate. In fact, some of the tiger reserves do not have any tigers at all.

National Bird

jigarbhatiya — Wed, 02 Apr 2008 08:56:56 +0000

Peacock (Pavo cristatus), which is a symbol of grace, joy, beauty and love is the national bird of India. Peacock occupies a respectable position in Indian culture and is protected not only by religious sentiments but also by parliamentary statute. The Indian peacock is a colorful, swan-sized bird with a fan-shaped crest of feathers on its head, a white patch under the eye and a long-slender neck. The male peacock is more colorful than the female one.

The male peacock has a glossy blue breast and a magnificent bronze-green colored tail of around 200 extended feathers. The female peacock is brownish, slightly smaller than the male and does not have a tail. The dance of the male peacock by fanning out the tail and shaking the feathers is a treat top watch. In India the peacock is found in almost all parts and enjoys full protection under the Indian Wildlife (Protection) Act, 1972.

National Calendar

jigarbhatiya — Wed, 02 Apr 2008 08:53:37 +0000

The national calendar of India is based on the Saka Era with Chaitra as its first month and a normal year of 365 days. The national calendar of India was adopted on March 22nd 1957. Dates of the Indian national calendar have a permanent correspondence with the Gregorian calendar dates- 1 Chaitra falling on 22 March normally and on 21 March in leap year.

The national Calendar of India is used along with the Gregorian calendar for the following official purposes- (i) Gazette of India, (ii) news broadcast by All India Radio, (iii) calendars issued by the Government of India and (iv) Government communications addressed to the members of the public.

NATIONAL GAME-Hockey

jigarbhatiya — Wed, 02 Apr 2008 08:50:24 +0000

Hockey is the National Game of India. Hockey has been played in India for time immemorial. There was a golden period of Indian hockey when hockey stalwarts of India ruled the game. On the international scenario there were no competitors to match the magical hands of Indian hockey players. The might and power of Indian hockey made India synonymous with the game. Unmatched excellence and incomparable talent of Indian players became folklore. The ball-juggling feats of players like Major Dhyanchand made people to think that Indian players used some kind of black magic. The Golden Era of hockey in India was the period from 1928 – 1956 when India won 6 successive gold medals in the Olympic Games