4 legged robot.docx

CHAPTER 1

INTRODUCTION

The pioneering works in the Þeld of legged robots were achieved around 1970 by two

famous researchers, Kato and Vukobratovic. Both works were characterized by the

design of relevant experimental systems. In Japan, the Þrst anthropomorphic robot,

WABOT 1, was demon-strated in 1973 by I. Kato and his team at Waseda University.

Using a very simple control scheme, it was able to realize a few slow steps in static

equilibrium. This achievement was the starting point of a proliÞc generation of legged

robots in Japan.

In parallel, M. Vukobratovic and his team were very involved in the problems

generated by functional re-habilitation. At the Mihailo Puppin Institute, Belgrade,

Yugoslavia, they designed the Þrst active exoskeletons, and several other devices such

as the Belgrade’s hand, but the most well-known outcome remains their analy-sis of

locomotion stability, which exhibited around 1972 the concept of zero-moment point

(ZMP), widely used since that time. This was the Þrst attempt to for-malize the need

for dynamical stability of legged robots; the idea was to use the dynamic wrench in

order to ex-tend a classical criterion of static balance (the center of mass should

project inside the convex hull of contact points). This important point will be detailed

later in this Chapter.And leds to creation of leg robot mechanism.

CHAPTER 2

A Brief History

In the next decade, the breakthroughs came from the United States. Following the

early work of R. McGhee in the 1960s at USC (University of Southern Califor-nia),

then in the 1970s at OSU (Ohio State University), which resulted in the Þrst

computer-controlled walk-ing machine, M. Raibert started to study dynamically stable

running at CMU (Carnegie Mellon University). Then, he launched the Massachusetts

Institute of Tech-nology (MIT) LegLab, where a sequence of active hopping robots,

with one, two or four legs were de-signed, with impressive results, among them a

famous ßip performed by a two-legged hopping machine. Simul-taneously, R.

McGhee and K. Waldron, after the building of some prototypes, achieved the design

of the largest hexapod in the world, called the adaptive suspension vehicle, a quasi-

industrial system able to walk on nat-ural irregular terrain, which was driven by a

human A third key period for research in legged robots was the early 1990s. Indeed,

the idea of studying purely passive mechanical systems was pioneered by McGeer [1.

In this seminal paper, McGeer intro-duces the concept of natural cyclic behavior, for a

class of very simple systems: a plane compass on an inclined plane. Stable walking

results from the balance between increase of the energy due to the slope and loss at the

im-pacts. However, what should be emphasized here is that McGeer popularized for

roboticists the analysis of such systems in terms of orbital stability using PoincarŽ

maps. Several researchers have followed the tracks open by McGeer, with many

extensions : adding trunk, feet and knees semipassive control, walking/running

underactuated systems like the Rabbit robot etc.

Finally, the end of the millennium was a period of in-tense technological activities.

Industrial breakthroughs showed to the world that building true humanoids was now

possible. In Japan, the Þrst humanoid robot, P2, was exhibited by Honda in 1996,

followed by several more. Presently, the most impressive technical achieve ments are

still realized by industrial companies: ASIMO (Honda), QRIO (Sony), HRP

(Kawada), being the ma-jor examples today, among others. In parallel, it should be

noticed that the market for small humanoid robots, mainly aimed at entertainment, has

grown steadily over the last decade.

While examining the history above and the present

state of the art, it is clear that roboticists are now facing a challenge. Very nice

technological achievements are available, especially biped robots. However, the

ability of these systems to walk truly autonomously on uneven and various terrains in

a robust way, i.e., in daily life, remains to be demonstrated. The goal of this chapter is

therefore to provide some keys in modeling and recent control advances, in order to be

able to design adequate and efÞcient control schemes when needed. This will be based

on two main classes of approaches: the use of so-called forward dynamics on one

hand, and the use of the ZMP on the other hand. The Chapter is organized as follows:

after a brief summary of the control principles used for hopping and passive robots,

we will focus on the issues needed for the control of biped robots from a dynamic

model scheme: modeling aspects, stability issues, trajectory generation, and control.

CHAPTER 3

Analysis Of Cycle Walking

A Few Points About Hopping Robot

Cyclic legged robots are those that reach, either naturally or with the help from a

control, a steady-state behavior characterized by a cycle in the phase plane. The

underly-ing assumption is that there exists in some sense a more or less hidden set of

optimal natural behaviors of the sys-tem. Within this class, hopping (or bouncing)

robots are interesting since they are generally unstable, but capable of high

performance in terms of velocities.

As mentioned, these robots have been widely stud-ied in the MIT LegLab. It is not the

goal of the Chapter to develop in depth the related design approaches and control

techniques, and we refer the reader to the excellent although ancient, book by Mark

Raibert on the subject

The basis of the work is in fact the planar one-leg hopping robot. Raibert proved that the

control of such system could be split into three separate compo-nents: the Þrst controls the

altitude by providing a Þxed thrust during each cycle; the second part controls the forward

velocity of the whole system by assigning to the foot, at each step, a given distance from the

hip when landing; and the last one controls the body atti-tude by servoing the hip during the

stance phase. The related algorithms are quite simple and allow a real-time implementation.

What is very interesting is that this simple approach applies almost straightforwardly to the

case of the three-dimensional (3-D) one-legged hopping robot , and moreover this three-part

control scheme can also be extended to biped or quadruped robots by adding techniques of

leg sequenc-ing and using the concept of a virtual leg when pairs of legs operate in unison.

Indeed, this interesting piece of work was not really followed up, but was surely the

inspiration for many re-searches on cyclic systems. Among these, purely passive walkers

have largely been considered, and we will now provide some insight into this area.

Stability of passive walking

The aim of this section is to present some basic facts and concepts related to passive

walking. Many more details may be found in the literature, for example in among

others. The issues considered here are mainly taken from [16.7]. We use the simplest

pos-sible model, an unactuated symmetric planar compass descending a slope of angle

φ. Masses are pin-point, and telescopic massless legs are only a way of ensuring foot

clearance. Several assumptions underlie the model. Among these, let us mention that

the swing phase is assumed to be slipless, and that the double stance phase, during

which the swing and support leg are exchanged, is instantaneous. The related impact

is slipless and inelastic.

The swing-stage equations of the robot, similar to those for a frictionless double

pendulum, can be written in the form of Lagrangian dynamicsThe speciÞcity of this

system with respect to, for example, manipulation robots, is that we have to com-plete

the continuous dynamics with equations describing the step transition.

We will encounter this requirement of separate modeling in legged

locomotion again when pre-senting the dynamics of bipedal walking.The pre- and the

post-impact conÞgurations of the robot can be related by q+ = Sq −, where S is a 2 × 2

antisymmetric matrix with unit elements. The principle of conservation of angular

momentum ap-plied to the robot gives Q−(α)q˙− = Q+(α)q˙+, from whichwe can obtain

the joint velocity relationship.

The periodic dynamic behavior of this system can be summarized in the phase portrait

where discontinuities result from impacts. The stability of this system can be analyzed

in terms of orbital stability. Intuitively, this means that, when the system deviates

from its trajectory in the phase plane within a certain domain (the basin of attraction),

its natural be havior is to return to this phase-plane trajectory, called the limit

cycle.The concept of orbital stability is well suited to the analysis of cyclic systems

such as steady-state walk-ing. Thus, the robustness of the obtained gait can be

assessed by measuring the size of the basin of attrac-tion. However, for a general

nonlinear system, the proof of the existence of a limit cycle, the analysis of its local

orbital stability, and the procedure to compute the cy-cle and its basin of attraction are

often difÞcult. For example, in the present case, the analysis would re-quire the

explicit integration of the dynamics during the swing phase. Nevertheless, it is

possible to test the local stability of a limit cycle, once it has been found. One method

to determine the stability of the robot gait is through the numerical computation of its

PoincarŽ.

CHAPTER 4

Biped Robots

The zero-moment point (ZMP) might be one of the most famous technical terms born

in robotics com-munity. Figure shows two important Þgures in the scene of ZMP-

based biped walking. Figure is WL-10RD, developed by Takanishi and Kato. This is

the Þrst ZMP-based robot, which successfully re-alized dynamic biped walking in

1985 [16.30]. It is a 12-degree-of-freedom (DOF) biped, 1.43 m high and weighing

84.5 kg, and driven by hydraulic actua-tors.

WL 10-RD ASIMO

Figure is ASIMO, a 26-DOF humanoid robot developed by Honda Motor Co. in 2000.

This is one of the most famous robots in public culture, and at the same time, its

superior performance of biped lo-comotion (walking and running) is well

acknowledged by specialists. According to the published papers and patents, ZMP

takes an important role in the walking control of ASIMO. In this section, we describe

the basic deÞnition, the calculation, and the usage of ZMP.

Mechanism

Figure shows recently developed biped robots con-trolled by the ZMP scheme. Figure

is a Johnnie, developed by Gienger et al. in 2001. It is a 1.80 m-high 17-DOF

humanoid weighing 40 kg, driven by direct-current (DC) servo motors with harmonic

drive gears and ball screws. Figure is HRP-2L, which was developed by Kaneko et

al. . It is a 1.41 m-high 12-DOF biped weighing 58.2 kg, driven by DC servo motors

with harmonic drive reduction gears.

Fig a Fig b

Fig C FIG D

Figure c is WL-16R, developed by Takanishi et al. as a walking chair that can carry a

human weighing up to 94 kg. It is a 1.29 m-high 12-DOF biped weighing 55 kg with

Stewart-platform-type legs driven by electric linear actuators. Figure d is HUBO, de-

veloped by Oh et al. It is a 1.25 m-high 41-DOF humanoid robot weighing 55

kg.Although these robots have different leg mechanism and outlook, they share some

common features:

1. there are at least six fully actuated joints for each leg,

2. the joints are position controlled,

3. the feet are equipped with force sensors, which are used to measure the ZMP.

As we will see in the following subsections, these are the fundamental requirements

for ZMP-based walking robots.

CHAPTER 5

Process used in making model

Basically there are four process used in making 4 wheel independent suspension sytem model

Welding

Grinding

Cutting

Drilling

Fastening

WELDING

Welding is a fabrication or sculptural process that joins materials, usually metals or ther

oplastics, by causing coalescence. This is often done by melting the workpieces and adding

a filler material to form a pool of molten material (the weld pool) that cools to become a

strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce

the weld. This is in contrast with soldering and brazing, which involve melting a lower-

melting-point material between the workpieces to form a bond between them, without

melting the work pieces. It is often used in construction engineering.

Some of the best known welding methods include:

Shielded metal arc welding (SMAW) - also known as "stick welding", uses

an electrode that has flux, the protectant for the puddle, around it. The electrode

holder holds the electrode as it slowly melts away. Slag protects the weld puddle

from atmospheric contamination.

Gas tungsten arc welding (GTAW) - also known as TIG (tungsten, inert gas), uses

a non-consumable tungsten electrode to produce the weld. The weld area is

protected from atmospheric contamination by an inert shielding gas such

as Argon or Helium.

Gas metal arc welding (GMAW) - commonly termed MIG (metal, inert gas), uses

a wire feeding gun that feeds wire at an adjustable speed and flows an argon-based

shielding gas or a mix of argon and carbon dioxide (CO2) over the weld puddle to

protect it from atmospheric contamination.

Flux-cored arc welding (FCAW) - almost identical to MIG welding except it uses

a special tubular wire filled with flux; it can be used with or without shielding gas,

depending on the filler.

Submerged arc welding (SAW) - uses an automatically fed consumable electrode

and a blanket of granular fusible flux. The molten weld and the arc zone are

protected from atmospheric contamination by being "submerged" under the flux

blanket.

Electroslag welding (ESW) - a highly productive, single pass welding process

for thicker materials between 1 inch (25 mm) and 12 inches (300 mm) in a

vertical or close to vertical position.

Many different energy sources can be used for welding, including a gas flame,

an electric arc, a laser, an electron beam, friction, and ultrasound. While often an

industrial process, welding may be performed in many different environments,

including in open air, under water, and in outer space. Welding is a hazardous

undertaking and precautions are required to avoid burns, electric shock, vision

damage, inhalation of poisonous gases and fumes, and exposure to intense ultraviolet

radiation.

Until the end of the 19th century, the only welding process was forge welding,

which blacksmiths had used for centuries to join iron and steel by heating and

hammering. Arc welding and oxyfuel welding were among the first processes to

develop late in the century, and electric resistance welding followed soon after.

Welding technology advanced quickly during the early 20th century as World War I

and World War II drove the demand for reliable and inexpensive joining methods.

Following the wars, several modern welding techniques were developed, including

manual methods like SMAW, now one of the most popular welding methods, as well

as semi-automatic and automatic processes such as GMAW, SAW, FCAW and ESW.

Developments continued with the invention of laser beam welding, electron beam

welding, magnetic pulse welding (MPW), and friction stir weldingin the latter half of

the century. Today, the science continues to advance. Robot welding is commonplace

in industrial settings, and researchers continue to develop new welding methods and

gain greater understanding of weld quality

History of Welding

The history of joining metals goes back several millennia. Called forge welding, the

earliest examples come from the Bronze and Iron Agesin Europe and the Middle East.

The ancient Greek historian Herodotus states in The Histories of the 5th century BC

that Glaucus of Chios "was the man who single-handedly invented iron

welding".Welding was used in the construction of the Iron pillar of Delhi, erected

inDelhi, India about 310 AD and weighing 5.4 metric tons.

The Middle Ages brought advances in forge welding, in which blacksmiths pounded

heated metal repeatedly until bonding occurred. In

1540, VannoccioBiringuccio published De la pirotechnia, which includes descriptions

of the forging operation. Renaissance craftsmen were skilled in the process, and the

industry continued to grow during the following centuries.In 1800, Sir Humphry

Davy discovered the short pulse electrical arc and presented his results in 1801. In

1802, Russian scientistVasilyPetrov also discovered the electric arc, and subsequently

published “News of Galvanic-Voltaic Experiments" in 1803, in which he described

experiments carried out in 1802. Of great importance in this work was the description

of a stable arc discharge and the indication of its possible use for many applications,

one being melting metals. In 1808, Davy, who was unaware of Petrov's work,

rediscovered the continuous electric arc. In 1881–82 inventors Nikolai

Benardos (Russian) and Stanisław Olszewski (Polish) created the first electric arc

welding method known as carbon arc welding using carbon electrodes. The advances

in arc welding continued with the invention of metal electrodes in the late 1800s by a

Russian, Nikolai Slavyanov (1888), and an American, C. L. Coffin (1890). Around

1900, A. P. Strohmenger released a coated metal electrode in Britain, which gave a

more stable arc. In 1905, Russian scientist Vladimir Mitkevich proposed using a three-

phase electric arc for welding. In 1919, alternating current welding was invented by C.

J. Holslag but did not become popular for another decade.

Resistance welding was also developed during the final decades of the 19th century,

with the first patents going to Elihu Thomson in 1885, who produced further advances

over the next 15 years. Thermite welding was invented in 1893, and around that time

another process, oxyfuel welding, became well established. Acetylene was discovered

in 1836 byEdmund Davy, but its use was not practical in welding until about 1900,

when a suitable torch was developed. At first, oxyfuel welding was one of the more

popular welding methods due to its portability and relatively low cost. As the 20th

century progressed, however, it fell out of favor for industrial applications. It was

largely replaced with arc welding, as metal coverings (known as flux) for the electrode

that stabilize the arc and shield the base material from impurities continued to be

developed.

World War I caused a major surge in the use of welding processes, with the various

military powers attempting to determine which of the several new welding processes

would be best. The British primarily used arc welding, even constructing a ship, the

"Fullagar" with an entirely welded hull. Arc welding was first applied to aircraft

during the war as well, as some German airplane fuselages were constructed using the

process.[16] Also noteworthy is the first welded road bridge in the world, the Maurzyce

Bridge designed by Stefan Bryła of the Lwów University of Technology in 1927, and

built across the river Słudwia near Łowicz, Poland in 1928.

During the 1920s, major advances were made in welding technology, including the

introduction of automatic welding in 1920, in which electrode wire was fed

continuously. Shielding gas became a subject receiving much attention, as scientists

attempted to protect welds from the effects of oxygen and nitrogen in the atmosphere.

Porosity and brittleness were the primary problems, and the solutions that developed

included the use of hydrogen, argon, and helium as welding atmospheres.[18] During

the following decade, further advances allowed for the welding of reactive metals

like aluminum and magnesium. This in conjunction with developments in automatic

welding, alternating current, and fluxes fed a major expansion of arc welding during

the 1930s and then during World War II.[19]

During the middle of the century, many new welding methods were invented. 1930

saw the release of stud welding, which soon became popular in shipbuilding and

construction. Submerged arc welding was invented the same year and continues to be

popular today. In 1932 a Russian,KonstantinKhrenov successfully implemented the

first underwater electric arc welding. Gas tungsten arc welding, after decades of

development, was finally perfected in 1941, and gas metal arc welding followed in

1948, allowing for fast welding of non-ferrous materials but requiring expensive

shielding gases. Shielded metal arc welding was developed during the 1950s, using a

flux-coated consumable electrode, and it quickly became the most popular metal arc

welding process. In 1957, the flux-cored arc welding process debuted, in which the

self-shielded wire electrode could be used with automatic equipment, resulting in

greatly increased welding speeds, and that same year, plasma arc welding was

invented. Electroslag welding was introduced in 1958, and it was followed by its

cousin, electrogas welding, in 1961.[20] In 1953 the Soviet scientist N. F. Kazakov

proposed the diffusion bonding method.

Other recent developments in welding include the 1958 breakthrough of electron

beam welding, making deep and narrow welding possible through the concentrated

heat source. Following the invention of the laser in 1960, laser beam welding debuted

several decades later, and has proved to be especially useful in high-speed, automated

welding.Magnetic pulse welding (MPW) is industrially used since 1967. Friction stir

welding was invented in 1991 by Wayne Thomas at The Welding Institute (TWI, UK)

and found high-quality applications all over the world.[22] All of these four new

processes continue to be quite expensive due the high cost of the necessary equipment,

and this has limited their applications

CHAPTER 6

Types of Welding

Arc

One of the most common types of arc welding is shielded metal arc

welding (SMAW); it is also known as manual metal arc welding (MMA) or stick

welding. Electric current is used to strike an arc between the base material and

consumable electrode rod, which is made of filler material (typically steel) and is

covered with a flux that protects the weld area from oxidation and contamination by

producing carbon dioxide (CO2) gas during the welding process. The electrode core

itself acts as filler material, making a separate filler unnecessary.The process is

versatile and can be performed with relatively inexpensive equipment, making it well

suited to shop jobs and field work.[28][29] An operator can become reasonably proficient

with a modest amount of training and can achieve mastery with experience. Weld

times are rather slow, since the consumable electrodes must be frequently replaced

and because slag, the residue from the flux, must be chipped away after welding.[28] Furthermore, the process is generally limited to welding ferrous materials, though

special electrodes have made possible the welding of cast iron, nickel,

aluminum, copper, and other metals.

Diagram of arc and weld area, in shielded metal arc welding

1. Coating Flow2.Rod3.Shield Gas 4.Fusion5.Base metal

6.Weld metal7. Solidified Slag

Gas metal arc welding (GMAW), also known as metal inert gas or MIG welding, is a

semi-automatic or automatic process that uses a continuous wire feed as an electrode

and an inert or semi-inert gas mixture to protect the weld from contamination. Since

the electrode is continuous, welding speeds are greater for GMAW than for SMAW.[30]

A related process, flux-cored arc welding (FCAW), uses similar equipment but uses

wire consisting of a steel electrode surrounding a powder fill material. This cored wire

is more expensive than the standard solid wire and can generate fumes and/or slag, but

it permits even higher welding speed and greater metal penetration.

Gas tungsten arc welding (GTAW), or tungsten inert gas (TIG) welding, is a manual

welding process that uses a nonconsumable tungstenelectrode, an inert or semi-inert

gas mixture, and a separate filler material.[32] Especially useful for welding thin

materials, this method is characterized by a stable arc and high quality welds, but it

requires significant operator skill and can only be accomplished at relatively low

speeds.

GTAW can be used on nearly all weldable metals, though it is most often applied

to stainless steel and light metals. It is often used when quality welds are extremely

important, such as in bicycle, aircraft and naval applications.[32] A related process,

plasma arc welding, also uses a tungsten electrode but uses plasma gas to make the

arc. The arc is more concentrated than the GTAW arc, making transverse control more

critical and thus generally restricting the technique to a mechanized process. Because

of its stable current, the method can be used on a wider range of material thicknesses

than can the GTAW process and it is much faster. It can be applied to all of the same

materials as GTAW except magnesium, and automated welding of stainless steel is

one important application of the process. A variation of the process is plasma cutting,

an efficient steel cutting process.

Submerged arc welding (SAW) is a high-productivity welding method in which the

arc is struck beneath a covering layer of flux. This increases arc quality, since

contaminants in the atmosphere are blocked by the flux. The slag that forms on the

weld generally comes off by itself, and combined with the use of a continuous wire

feed, the weld deposition rate is high. Working conditions are much improved over

other arc welding processes, since the flux hides the arc and almost no smoke is

produced. The process is commonly used in industry, especially for large products and

in the manufacture of welded pressure vessels.[34] Other arc welding processes

include atomic hydrogen welding, electroslag welding, electrogas welding, and stud

arc welding.

Gas welding

The most common gas welding process is oxyfuel welding, also known as

oxyacetylene welding. It is one of the oldest and most versatile welding processes,

but in recent years it has become less popular in industrial applications. It is still

widely used for welding pipes and tubes, as well as repair work.

The equipment is relatively inexpensive and simple, generally employing the

combustion of acetylene in oxygen to produce a welding flame temperature of about

3100 °C. The flame, since it is less concentrated than an electric arc, causes slower

weld cooling, which can lead to greater residual stresses and weld distortion, though it

eases the welding of high alloy steels. A similar process, generally called oxyfuel

cutting, is used to cut metals

Resistance spot welding

Resistance welding involves the generation of heat by passing current through the

resistance caused by the contact between two or more metal surfaces. Small pools of

molten metal are formed at the weld area as high current (1000–100,000 A) is passed

through the metal.In general, resistance welding methods are efficient and cause little

pollution, but their applications are somewhat limited and the equipment cost can be

high.

Spot welding

Spot welding is a popular resistance welding method used to join overlapping metal

sheets of up to 3 mm thick. Two electrodes are simultaneously used to clamp the

metal sheets together and to pass current through the sheets. The advantages of the

method include efficient energy use, limited workpiece deformation, high production

rates, easy automation, and no required filler materials. Weld strength is significantly

lower than with other welding methods, making the process suitable for only certain

applications. It is used extensively in the automotive industry—ordinary cars can have

several thousand spot welds made by industrial robots. A specialized process,

called shot welding, can be used to spot weld stainless steel.

Like spot welding, seam welding relies on two electrodes to apply pressure and

current to join metal sheets. However, instead of pointed electrodes, wheel-shaped

electrodes roll along and often feed the workpiece, making it possible to make long

continuous welds. In the past, this process was used in the manufacture of beverage

cans, but now its uses are more limited. Other resistance welding methods

include butt welding, flash welding, projection welding, and upset welding.

Energy Beam Welding

Energy beam welding methods, namely laser beam welding and electron beam

welding, are relatively new processes that have become quite popular in high

production applications. The two processes are quite similar, differing most notably in

their source of power. Laser beam welding employs a highly focused laser beam,

while electron beam welding is done in a vacuum and uses an electron beam. Both

have a very high energy density, making deep weld penetration possible and

minimizing the size of the weld area. Both processes are extremely fast, and are easily

automated, making them highly productive. The primary disadvantages are their very

high equipment costs (though these are decreasing) and a susceptibility to thermal

cracking. Developments in this area include laser-hybrid welding, which uses

principles from both laser beam welding and arc welding for even better weld

properties, laser cladding, and x-ray welding.

Solid-state welding

Like the first welding process, forge welding, some modern welding methods do not

involve the melting of the materials being joined. One of the most popular, ultrasonic

welding, is used to connect thin sheets or wires made of metal or thermoplastic by

vibrating them at high frequency and under high pressure. The equipment and

methods involved are similar to that of resistance welding, but instead of electric

current, vibration provides energy input. Welding metals with this process does not

involve melting the materials; instead, the weld is formed by introducing mechanical

vibrations horizontally under pressure. When welding plastics, the materials should

have similar melting temperatures, and the vibrations are introduced vertically.

http://en.wikipedia.org/wiki/File:Solid-state_welding_processes_-_AWS_A3.0_2001.svg

Ultrasonic welding is commonly used for making electrical connections out of

aluminum or copper, and it is also a very common polymer welding process.

Another common process, explosion welding, involves the joining of materials by

pushing them together under extremely high pressure. The energy from the impact

plasticizes the materials, forming a weld, even though only a limited amount of heat is

generated. The process is commonly used for welding dissimilar materials, such as the

welding of aluminum with steel in ship hulls or compound plates.Other solid-state

welding processes include friction welding (including friction stir welding), magnetic

pulse welding,co-extrusion welding, cold welding, diffusion bonding, exothermic

welding, high frequency welding, hot pressure welding, induction welding, and roll

welding

CHAPTER 7

Fastening

A fastener is a hardware device that mechanically joins or affixes two or more objects

together.

Fasteners can also be used to close a container such as a bag, a box, or an envelope; or

they may involve keeping together the sides of an opening of flexible material,

attaching a lid to a container, etc. There are also special-purpose closing devices, e.g.

abread clip. Fasteners used in these manners are often temporary, in that they may be

fastened and unfastened repeatedly.

Some types of woodworking joints make use of separate internal reinforcements, such

as dowels or biscuits, which in a sense can be considered fasteners within the scope of

the joint system, although on their own they are not general purpose fasteners.

Furniture supplied in flat-pack form often uses cam dowels locked by cam locks, also

known as conformat fasteners.

Items like a rope, string, wire (e.g. metal wire, possibly coated with plastic, or

multiple parallel wires kept together by a plastic strip coating), cable, chain, or plastic

wrap may be used to mechanically join objects; but are not generally categorized as

fasteners because they have additional common uses.

Likewise, hinges and springs may join objects together, but are ordinarily not

considered fasteners because their primary purpose is to allow articulation rather than

rigid affixment. Other alternative methods of joining materials

include: crimping, welding, soldering, brazing, taping, gluing, cementing, or the use of

other adhesives. The use of force may also be used, such as

with magnets, vacuum (like suction cups), or even friction.There are three major steel

fasteners used in industries: stainless steel, carbon steel, and alloy steel. The major

grade used in stainless steel fasteners: 200 series, 300 series, and 400 series.

CHAPTER 8

Drilling

Drilling is a cutting process that uses a drill bit to cut or enlarge a hole of

circular cross-section in solid materials. The drill bit is a rotarycutting tool, often

multipoint. The bit is pressed against the workpiece and rotated at rates from hundreds

to thousands of revolutions per minute. This forces the cutting edge against the

workpiece, cutting off chips (swarf) from the hole as it is drilled.

Exceptionally, specially-shaped bits can cut holes of non-circular cross-section;

a square cross-section is possible.

Drilled holes are characterized by their sharp edge on the entrance side and the

presence of burrs on the exit side (unless they have been removed). Also, the inside of

the usually has helical feed marks.

Drilling may affect the mechanical properties of the workpiece by creating

low residual stresses around the hole opening and a very thin layer of

highly stressed and disturbed material on the newly formed surface. This causes the

workpiece to become more susceptible to corrosion and crack propagation at the

stressed surface. A finish operation may be done to avoid these detrimental conditions.

For fluted drill bits, any chips are removed via the flutes. Chips may form long spirals

(undesirable)or small flakes, depending on the material, and process parameters. [3] The

type of chips formed can be an indicator of the machinability of the material, with

long chips suggesting poor material machinability.

When possible drilled holes should be located perpendicular to the workpiece surface.

This minimizes the drill bit's tendency to "walk", that is, to be deflected from the

intended center-line of the bore, causing the hole to be misplaced. The higher the

length-to-diameter ratio of the drill bit, the greater the tendency to walk. The tendency

to walk is also preempted in various other ways, which include:

Establishing a centering mark or feature before drilling, such as by:

Casting , molding, or forging a mark into the workpiece

Center punching

Spot drilling (i.e., center drilling)

Spot facing , which is facing a certain area on a rough casting or forging to

establish, essentially, an island of precisely known surface in a sea of

imprecisely known surface

Constraining the position of the drill bit using a drill jig with drill bushings

Surface finish produced by drilling may range from 32 to 500 microinches. Finish cuts

will generate surfaces near 32 microinches, and roughing will be near 500

microinches.

Cutting fluid is commonly used to cool the drill bit, increase tool life, increase speeds

and feeds, increase the surface finish, and aid in ejecting chips. Application of these

fluids is usually done by flooding the workpiece with coolant and lubricant or by

applying a spray mist.

In deciding which drill(s) to use it is important to consider the task at hand and

evaluate which drill would best accomplish the task. There are a variety of drill styles

that each serve a different purpose. The subland drill is capable of drilling more than

one diameter. The spade drill is used to drill larger hole sizes. The indexable drill is

useful in managing chips.

Drilling in metal

Under normal usage, swarf is carried up and away from the tip of the drill bit by the

fluting of the drill bit. The cutting edges produce more chips which continue the

movement of the chips outwards from the hole. This is successful until the chips pack

too tightly, either because of deeper than normal holes or insufficient backing

off (removing the drill slightly or totally from the hole while drilling). Cutting fluid is

sometimes used to ease this problem and to prolong the tool's life by cooling and

lubricating the tip and chip flow. Coolant may be introduced via holes through the

drill shank, which is common when using a gun drill.

High speed steel twist bit drilling into aluminium with methylated spirits lubricant

When cutting aluminum in particular, cutting fluid helps ensure a smooth and accurate

hole while preventing the metal from grabbing the drill bit in the process of drilling

the hole. When cutting brass, and other soft metals that can grab the drill bit and

causes "chatter", a face of approx. 1-2 millimeters can be ground on the cutting edge

to create an obtuse angle of 91 to 93 degrees. This prevents "chatter" during which the

drill tears rather than cuts the metal. However, with that shape of bit cutting edge, the

drill is pushing the metal away, rather than grabbing the metal. This creates high

friction and very hot swarf.

Different drill bits are used to drill metal depending upon hardness, thermal properties

of the metal and hole diameter required. Hole saw, Step drill, Countersink are some

among them. The drill speed is also adjusted depending upon the thermal properties

and hardness of metal. For example, when cutting stainless steel slower speed is

recommended than steel. Drilling too fast on stainless steel will heat it up easily and

make it hard quickly which makes it very difficult to drill.

For heavy feeds and comparatively deep holes oil-hole drills are used in the drill bit,

with a lubricant pumped to the drill head through a small hole in the bit and flowing

out along the fluting. A conventional drill press arrangement can be used in oil-hole

drilling, but it is more commonly seen in automatic drilling machinery in which it is

the workpiece that rotates rather than the drill bit.

http://en.wikipedia.org/wiki/File:HSS_Twist_Drill_into_Aluminium_with_Lubricant.jpg

In computer numerical control (CNC) machine tools a process called peck drilling,

or interrupted cut drilling, is used to keep swarf from detrimentally building up when

drilling deep holes (approximately when the depth of the hole is three times greater

than the drill diameter). Peck drilling involves plunging the drill part way through the

workpiece, no more than five times the diameter of the drill, and then retracting it to

the surface. This is repeated until the hole is finished. A modified form of this process,

called high speed peck drilling or chip breaking, only retracts the drill slightly. This

process is faster, but is only used in moderately long holes, otherwise it will overheat

the drill bit. It is also used when drilling stringy material to break the chips.

Drilling in wood

Wood being softer than most metals, drilling in wood is considerably easier and faster

than drilling in metal. Cutting fluids are not used or needed. The main issue in drilling

wood is assuring clean entry and exit holes and preventing burning. Avoiding burning

is a question of using sharp bits and the appropriate cutting speed. Drill bits can tear

out chips of wood around the top and bottom of the hole and this is undesirable in

fine woodworkingapplications.

The ubiquitous twist drill bits used in metalworking also work well in wood, but they

tend to chip wood out at the entry and exit of the hole. In some cases, as in rough

holes for carpentry, the quality of the hole does not matter, and a number of bits for

fast cutting in wood exist, including spade bits and self-feeding auger bits. Many types

of specialised drill bits for boring clean holes in wood have been developed, including

brad-point bits, Forstner bits and hole saws. Chipping on exit can be minimized by

using a piece of wood as backing behind the work piece, and the same technique is

sometimes used to keep the hole entry neat.

Holes are easier to start in wood as the drill bit can be accurately positioned by

pushing it into the wood and creating a dimple. The bit will thus have little tendency

to wander.

CHAPTER 9

Cutting

Cutting is the separation of a physical object, into two or more portions, through the

application of an acutely directed force.

Implements commonly used for cutting are the knife and saw, or in medicine and

science the scalpel and microtome. However, any sufficiently sharp object is capable

of cutting if it has a hardness sufficiently larger than the object being cut, and if it is

applied with sufficient force. Even liquids can be used to cut things when applied with

sufficient force (see water jet cutter).

Cutting is a compressive and shearing phenomenon, and occurs only when the

total stress generated by the cutting implement exceeds the ultimate strength of the

material of the object being cut. The simplest applicable equation is stress =

force/area: The stress generated by a cutting implement is directly proportional to the

force with which it is applied, and inversely proportional to the area of contact. Hence,

the smaller the area (i.e., the sharper the cutting implement), the less force is needed to

cut something. It is generally seen that cutting edges are thinner for cutting soft

materials and thicker for harder materials. This progression is seen from kitchen knife,

to clever, to axe, and is a balance between the easy cutting action of a thin blade vs

strength and edge durability of a thicker blade.

Metal Cutting

Cutting has been at the core of manufacturing throughout history. For metals many

methods are used and can be grouped by the physical phenomenon used.

Chip forming - sawing, drilling, milling, turning etc.

Shearing - punching, stamping, scissoring.

Abrading - Grinding, lapping, polishing; water-jet.

Heat - flame cutting, plasma cutting, laser cutting.

Electro-Chemical - Etching, Electrical discharge machining (EDM).

Every method has its limitations in accuracy, cost, and effect on the material. For

example: heat may damage the quality of heat treated alloys, and laser cutting is less

suitable for highly reflective materials such as aluminum

CHAPTER 10

Grinding

Grinding is an abrasive machining process that uses a grinding wheel as the cutting

tool.A wide variety of machines are used for grinding:

Hand-cranked knife-sharpening stones (grindstones)

Handheld power tools such as angle grinders and die grinders

Various kinds of expensive industrial machine tools called grinding machines

Bench grinders often found in residential garages and basements

Grinding practice is a large and diverse area of manufacturing and toolmaking. It can

produce very fine finishes and very accurate dimensions; yet in mass production

contexts it can also rough out large volumes of metal quite rapidly. It is usually better

suited to the machining of very hard materials than is "regular" machining (that is,

cutting larger chips with cutting tools such as tool bits or milling cutters), and until

recent decades it was the only practical way to machine such materials as hardened

steels. Compared to "regular" machining, it is usually better suited to taking very

shallow cuts, such as reducing a shaft’s diameter by half a thousandth of an inch or

12.7 μm.

Grinding is a subset of cutting, as grinding is a true metal-cutting process. Each grain

of abrasive functions as a microscopic single-point cutting edge (although of high

negative rake angle), and shears a tiny chip that is analogous to what would

conventionally be called a "cut" chip (turning, milling, drilling, tapping, etc.).

However, among people who work in the machining fields, the term cutting is often

understood to refer to the macroscopic cutting operations, and grinding is often

mentally categorized as a "separate" process. This is why the terms are usually used in

contradistinction in shop-floor practice, even though, strictly speaking, grinding is a

subset of cutting.

Surface grinding

Surface grinding uses a rotating abrasive wheel to remove material, creating a flat

surface. The tolerances that are normally achieved with grinding are ± 2 × 10−4 inches

for grinding a flat material, and ± 3 × 10−4 inches for a parallel surface (in metric units:

5 μm for flat material and 8 μm for parallel surface).

The surface grinder is composed of an abrasive wheel, a workholding device known

as a chuck, either electromagnetic or vacuum, and a reciprocating table.

Typical workpiece materials include cast iron and steel. These two materials do not

tend to clog the grinding wheel while being processed. Other materials are aluminum,

stainless steel, brass and some plastics.

Cylindrical grinding

Cylindrical grinding (also called center-type grinding) is used to grind the cylindrical

surfaces and shoulders of the workpiece. The workpiece is mounted on centers and

rotated by a device known as a drive dog or center driver. The abrasive wheel and the

workpiece are rotated by separate motors and at different speeds. The table can be

adjusted to produce tapers. The wheel head can be swiveled.

The five types of cylindrical grinding are: outside diameter (OD) grinding, inside

diameter (ID) grinding, plunge grinding, creep feed grinding, and centerless grinding.

A cylindrical grinder has a grinding (abrasive) wheel, two centers that hold the

workpiece, and a chuck, grinding dog, or other mechanism to drive the work. Most

cylindrical grinding machines include a swivel to allow for the forming of tapered

pieces. The wheel and workpiece move parallel to one another in both the radial and

longitudinal directions. The abrasive wheel can have many shapes. Standard disk-

shaped wheels can be used to create a tapered or straight workpiece geometry while

formed wheels are used to create a shaped workpiece. The process using a formed

wheel creates less vibration than using a regular disk-shaped wheel.

Tolerances for cylindrical grinding are held within five ten-thousandths of an inch (±

0.0005) (metric: ± 13 um) for diameter and one ten-thousandth of an inch(± 0.0001)

(metric: 2.5 um) for roundness. Precision work can reach tolerances as high as fifty

millionths of an inch (± 0.00005) (metric: 1.3 um) for diameter and ten millionths (±

0.00001) (metric: 0.25 um) for roundness. Surface finishes can range from 2 to 125

microinches (metric: 50 nm to 3 um), with typical finishes ranging from 8 to 32

microinches. (metric: 0.2 um to 0.8 um)

Creep-feed grinding

Creep-feed grinding (CFG) was invented in Germany in the late 1950s by Edmund

and Gerhard Lang. Unlike normal grinding, which is used primarily to finish surfaces,

CFG is used for high rates of material removal, competing with milling and turning as

a manufacturing process choice. Depths of cut of up to 6 mm (0.25 inches) are used

along with low workpiece speed. Surfaces with a softer-grade resin bond are used to

keep workpiece temperature low and an improved surface finish up to 1.6

micrometresRmax

With CFG it takes 117 sec to remove 1 in.3 of material, whereas precision grinding

would take more than 200 sec to do the same. CFG has the disadvantage of a wheel

that is constantly degrading, and requires high spindle power, 51 hp (38 kW), and is

limited in the length of part it can machine.[3]

To address the problem of wheel sharpness, continuous-dress creep-feed

grinding (CDCF) was developed in the 1970s. It dresses the wheel constantly during

machining, keeping it in a state of specified sharpness. It takes only 17 sec. to remove

1 in3 of material, a huge gain in productivity. 38 hp (28 kW) spindle power is required,

and runs at low to conventional spindle speeds. The limit on part length was erased.

High-efficiency deep grinding (HEDG) uses plated superabrasive wheels, which

never need dressing and last longer than other wheels. This reduces capital equipment

investment costs. HEDG can be used on long part lengths, and removes material at a

rate of 1 in3 in 83 sec. It requires high spindle power and high spindle speeds.

Peel grinding, patented under the name of Quickpoint in 1985 by Erwin Junker

Maschinenfabrik, GmbH in Nordrach, Germany, uses a tool with a with superabrasive

nose and can machine cylindrical parts.

VIPER (Very Impressive Performance Extreme Removal), 1999, is a process

patented by Rolls-Royce and is used in aerospace manufacturing to produce turbine

blades. It uses a continuously dressed aluminum oxide grinding wheel running at high

speed. CNC-controlled nozzles apply refrigerated grinding fluid during the cut.

VIPER is performed on equipment similar to a CNC machining center, and uses

special wheels.

Ultra-high speed grinding (UHSG) can run at speeds higher than 40,000 fpm (200

m/s), taking 41 sec to remove 1 in.3 of material, but is still in the R&D stage. It also

requires high spindle power and high spindle speeds.

CHAPTER 11

Construction of robot

To start with the construction there are following things which are required. List

of them are given below

Material PiecesBig Wheels

Screw and nuts

50 rpm motor

Black iron sheet

Soledring Iron

DPDT

4 meter Wire

PCB

Free rod

7 inch wood block

12 inch wood block

5 inch wood block

12 volt battery

Drilling machine

Drill bits

2 pieces

8-10 pieces

2 pieces

13x7 inch

1 piece

2piece

1 piece

1piece

2 piece

4 piece

2 piece

2 piece

1 piece

1piece

1set

Steps of construction

Now for the construction of frame following steps are followed

1. A Rectanglar piece of black iron sheet is cut out ( Dimention of piece 13 x 10)

2. Four holes of 14 mm each is done at four corner of the sheet.

3. A marking of 1.5 Inch from the width is done and then the sheet is folded,

before folding the sheet a cut has been given on the marking by the help of hand

cutting machine.

Construction of chasis

4. Coating of the upper side of the sheet with the help of black wiring tape is

done.

Chasis of robot

5. After making of chasis two motors of 50 rpm each are fitted on the front

wholes of therobot and two free rods are fitted at the end of the robot.

6. NOW cut out 4 blocks of wood of 7 inch and 2 blocks of wood of 5 inch and 2

blocks of wood of 12 inch, so that we use them as legs of robot.

7. Drill in the wooden block with the help of drilling machine. So that they can be

fitted in the motor shaft and they could be joint with the help of bolts and nuts.

LEGS OF ROBOT

Joints of robot

8. Now after Drilling fit the legs of the robot as given in the picture below.

Animated image of robot

9. Connect the battery and wire to the motor. Usea12 volt battery since the motor

used in the robot are D.C Geared motor (12 volt). We have connected three 4 volt

battries togetherin series to form a 12 volt battery.

BATTERY

CHAPTER 12

ASSEMBLY OF THE CONTROL BOX

We have used a wired control box. There are some materials required to make a

control box. These are as follows:-

1. PCB (Printed Circuit Board)

2. Three DPDT

3. Soldering Iron

4. Soldering Wire

5. Soldering Paste

6. 12 volt batery

PRECAUTION:- Be very careful while using soldering iron.

PCB AND DPDT CONNECTIONS

Constructional steps:-

1. Connect the dpdt’s with the pcb with the help of soldering iron, Connect the

dpdts permanently with the pcb. And see that there joint be no joints left.

2. After connecting the dpdt’s , connect a pair of wire with the dpdt coming from

the motors. Left motors with left dpdt and right motors with right dpdt. Use the

middle dpdt for the wire coming from upper motor. NOTE:- There are many types of

PCB’s you can use of your choice. Which you think is more suitable for your system.

FINAL IMAGE OF ROBOT

CHAPTER 13

FUTURE SCOPE

4 leg robot has a very great future scope. Since this robot does not use conventional

wheels. It can be used for following purposes:-

For spying

For military

For study of leg mechanism

It can be used for bringing images (it issmall in size so it can go through any

place)

4 legged robot.docx

Documents