Fundamentals and Types of Mechanism

DIPLOMA IN Mechnical Engineering

2011-2012

Mr.Vaibhav V Naik

Mechanical Engineering

2011-2012

FUNDAMENTALS AND TYPE OF MECHANISM

THEORY OF MACHINE

FUNDAMENTALS AND TYPES OF MECHANISM Vaibhav Vithoba Naik

FUNDAMENTALS AND TYPES OF MECHANISMS

A. Kinematics of Machines: - Definition of Kinematics, Dynamics,

Statics, Kinetics, Kinematic link, Kinematic Pair and its types,

constrained motion and its types, Kinematic chain and its types,

Mechanism, inversion, machine and structure. (Marks- 6)

B. Inversions of Kinematic Chain. (Marks- 8)

Inversion of four bar chain,

Coupled wheels of Locomotive &

Pentograph.

Inversion of Single Slider Crank chain-

Rotary I.C. Engines mechanism,

Whitworth quick return mechanism,

Crank and Slotted lever quick return mechanism.

Inversion of Double Slider Crank Chain

Scotch Yoke Mechanism &

Oldham’s Coupling.

C. Common Mechanisms. (Marks- 4)

Bicycle free wheel Sprocket mechanism.

Geneva Mechanism.

Ackerman’s Steering gear mechanism.

Foot operated air pump mechanism.

THEORY OF MACHINE


THEORY OF MACHINE

Theory of machine is Branch of engineering science which deals with the

study of relative motion and forces between the various machine elements

:

Figure: Diagram of Theory of Machine

1. Statics

It is the branch of theory of machine, which deals with the forces and its effect on the machine part while the latter is at rest.

2. Dynamics of machine

It is the branch of theory of machine, which deals with the forces and

effect of forces on the machine component when they act on them.

3. Kinetics

It is the branch of theory of machine, which deals with the inertia forces,

which are formed due to combined action of mass and motion of

machine elements.

4. Kinematics of machine

It is the branch of theory of machine, which deals with the relative motion

between the various parts of the machine, without considering the forces

THEORY OF MACHINE

KINEMATICS DYNAMICS KINETICS STATICS

THEORY OF MACHINE


1. Kinematic Link

a. Links are individual parts of a mechanism. b. Each parts of a machine which has a relative motion to some other parts is

known as Kinematic link. Characteristics of the Kinematic link

1. It should have relative motion and

2. It should be a resistant body

Classification of the LINK

A. Depending upon the nature of the resistant bodies

1. Rigid link.

2. Flexible link.

3. Fluid link.

B. Depending upon the points at which the link is attached to mechanism 1. Binary link

2. Ternary link

3. Quaternary link

THEORY OF MACHINE


A. Depending upon the nature of the resistant bodies 1. Rigid link

The links which do not undergo appreciable transformation while transmitting

the required motion and forces is known as rigid link.

Example:

a. Piston,

b. Connecting Rod of Steam engine.

2. Flexible Link

The links which are partly deformed transformation while transmitting the

required motion and forces in such a way that they don effect the required

transmission of motion is known as Flexible link.

Example:

a. Chain,

b. Belt and Spring

3. Fluid Link

The link which transmit the motion by fluid pressure as compression are

called fluid link.

Example:

a. Liquid used in Hydraulic presses

THEORY OF MACHINE


B. Depending upon the points at which the link is attached to mechanism 1. Binary link

The link which is attached to two points in the mechanism is called Binary

link.

2. Ternary link The link which is attached to three points in the mechanism is called Ternary

link.

3. Quaternary link The link which is attached to four points in the mechanism is called

Quaternary link.

THEORY OF MACHINE


2. Kinematic Pair

The two links of the machine when in contact with each other are said to

form a pair if the relative motion between them is successfully constrained.

CLASSIFICATION OF KINEMATIC PAIR A. According to the relative motion between them

1. Sliding pair. S

2. Turning pair.

3. Rolling pair.

4. Screw pair.

5. Spherical pair.

B. According to Nature of the contact

1. Lower pair.

2. Higher pair.

C. According to type of closure

1. Self closed pair.

2. Force closed pair.

THEORY OF MACHINE


A. According to the relative motion between them

1. Sliding pair.

A sliding pair is said to be formed by two links such a manner that one link is

constrained to have a sliding motion relative to other link.

Example:

1. Piston and Cylinder,

2. Cross head and guides of Steam engine.

Figure: Sliding Pair

THEORY OF MACHINE


2. Turning pair

A turning pair is said to be formed by two links such a manner that one link is

constrained to turn or revolve relative to other link.

Example:

Shaft with collar in circular hole.

Figure: Turning Pair

THEORY OF MACHINE


3. Rolling pair.

A Rolling pair is said to be formed by two links such a manner that one link is

constrained to have a rolling motion over the other link.

Example:

Ball bearing forms Rolling pair.

Figure: Rolling Pair

THEORY OF MACHINE


4. Screw pair.

When the two elements of pairs are connected in such a way that one

element can turn about the other by means of screw threads is known as

Screw Pair.

Example:

Bolt and nut is example of Screw Pair.

Figure: Screw Pair

THEORY OF MACHINE


5. Spherical pair.

When the two elements of pairs are connected in such a way that one

element turn or swivels about the other fixed element, the pair formed is

known as Screw Pair.

Example:

Ball and socket is example of Spherical Pair.

Figure:Spherical Pair

THEORY OF MACHINE


B. According to Nature of the contact 1. Lower pair.

When the two element of a pair have a surface contact when the relative

motion takes place and the surface of one element slides over the other, the

pair forced is known as lower pair.

Example:

a. The motion of piston and cylinder in the engine.

b. Shaft rotating in a bearing and

c. Nut turning on a screw.

Figure: Lower Pair

THEORY OF MACHINE


2. Higher pair.

When the two element of a pair have a line or point contact when the

relative motion takes place and the motion between the two element is

partially turning and partly sliding then the pair formed is know as Higher

pair.

Example:

The motion of cam and follower

Figure: Higher Pair

THEORY OF MACHINE


C. Kinematic pairs according to nature of mechanical constraint 1. Self Closed pair

When the elements of a pair are held together mechanically in such a way

that only the required kind of relative motion occurs , all the lower pairs and

some of the higher pairs are closed pairs.

Example:

The lower pair is known as closed pair.

2. Force Closed pair or Unclosed pair

When two links of a pair are not connected mechanically but kept in contact

either due to force of gravity or some spring action, they constitute an

unclosed pairs.

Example:

The motion of cam and follower

THEORY OF MACHINE


TYPE OF CONSTARINED MOTIONS. 1. Completely constrained motion.

2. Incompletely constrained motion.

3. Successfully constrained motion.

1. Completely constrained motion.

When the motion between a pair is limited to definite direction irrespective of

the direction of force applied, then the motion is said to be a completely

constrained motion.

Example:

1. The motion of the square bar in square hole.

2. The motion of shaft with collars at each end in a circular hole.

Figure: Complete Constrained Motion

THEORY OF MACHINE


2. Incompletely constrained motion.

When the motion between a pair can take place in more than one direction,

then the motion is said to be a completely constrained motion.

Example:

1. The motion of the circular bar in circular hole.

Figure: Incomplete Constrained Motion

THEORY OF MACHINE


3. Successfully constrained motion

When the relative motion between the link is not completely constrained by

itself but it is made by some other means is called successfully constrained

motion.

Example:

1. Shaft in Footstep Bearing

2. The motion IC engine valve and piston in reciprocating inside an engine

cylinder.

Figure: Successfully Constrained Motion

THEORY OF MACHINE


3. Kinematic Chain

When the kinematic pairs are coupled in such a way that the last linked is

joined the first link to transmit the definite motion it is called a kinematic chain.

To determine the given assemblage of links forms the kinematic chain

or not:

The two equations are:

1. l = 2p - 4

2. J = 3/2 * l - 2

l = number of links

p = number of pairs

j = number of joints

Three possible cases are

1. If L.H.S=R.H.S then it is Constrained kinematic chain

2. If L.H.S>R.H.S then it is Locked Chain

3. If L.H.S<R.H.S then it is Unconstrained kinematic chain

THEORY OF MACHINE


1. Arrangement of three links

2. Arrangement of four links

Figure :Three Links

Figure :Four Links

THEORY OF MACHINE


3. Arrangement of five links

4. Arrangement of six links

Figure :Five Links

Figure :Sic Links

THEORY OF MACHINE


THEORY OF MACHINE


THEORY OF MACHINE


Types of Joints in the Chain

1. Binary joints

When the two links are joined at the same connections, the joint is known

as binary joint

W.Klien’s criterion of constraint

l = number of links

h = number of higher pairs

j = number of binary joints

j=4; l=4; h=0

j+h/2 = 3/2*l - 2

4+0 = 3/2*4 - 2

4 = 4

L.H.S=R.H.S

Figure: Binary Joints

THEORY OF MACHINE


2. Ternary Joints

When the three links are joined at the same connections, the joint is

known as ternary joints.

A.W.Klien’s criterion of constraint

l = number of links



j=7; l=6; h=0 j+h/2 =3/2*l – 2 7+0 =3/2*6 – 2 7 =7 L.H.S=R.H.S

Figure: Ternary Joints

THEORY OF MACHINE


3. Quaternary Joints

When the four links are joined at the same connections, the joint is known

as Quaternary joints.

W.Klien’s criterion of constraint

l = number of links



j=12; l=9; h=0

j+h/2 = 3/2*l – 2

12+0 = 3/2*9 – 2

12 = 11.5

L.H.S>R.H.S

Figure: Quaternary Joints

THEORY OF MACHINE


THEORY OF MACHINE


Types of Kinematic chain

1. Four bar chain

2. Single slider crank chain.

3. Double slider crank chain

Inversion of the following types 1. Four bar chain

a) Beam engine.

b) Coupling rod of Locomotives.

c) Watts’ indicator mechanism.

d) Pantograph.


a) Pendulum pump or Bull engine.

b) Oscillating cylinder engine.

c) Rotary IC engine.

d) Crank and slotted lever quick return mechanism.

e) With worth quick return mechanism.

3. Double slider crank chain.

a) Elliptical trammel

b) Scotch yoke mechanism.

c) Oldham’s coupling.

THEORY OF MACHINE


3. MECHANISM

a. When one of the links of a kinematic chain is fixed, the chain is known as

mechanism.

b. It may be used for transmitting or transforming motion.

Example:

1. Engine indicator,

2. Typewriter.

Types of Mechanism

a. Simple mechanism (a mechanism with four links)

b. Compound mechanism (a mechanism with more than four link)

Differentiate between Machine and Mechanism

NO

MACHINE

MECHANISM

1. It is like the human body, it transforms energy into useful work.

It is like a frame work and has a definite motion between various links.

2 It relates to energy only.

It relates to motion.

3 It has many link.

It also has many links.

4 Ex: lathe, shaper.

Ex. watt indicator,typwriter

5

THEORY OF MACHINE


4. Structure

It is the assemblage of a number of resistant bodies having no relative motion

between then and meant for carrying loads having a straining action.

Example:

1. A Railway bridge.

2. Roof Trusses

3. bridges,

4. buildings

5. machine frames

Figure: Structure

THEORY OF MACHINE


Differentiate between Machine and Structure.

NO

MACHINE

STRUCTURE

1 Has relative motion between the members

Has no relative motion

2 Transforms available energy into possible work.

Does not transform.

3 Members are meant to transmit motion and forces.

Members are meant to accept load

4 Example Shaper, lathe Example :Bridge.

5. Inversion

The method of obtaining the different mechanism by fixing the different links in

a kinematic chain is known as inversion of the mechanism.

THEORY OF MACHINE


Important Terminologies and Definition 1. Machine

It is device which takes in the available energy and converts it into useful work.

When the mechanism is required to transmit the power or to do some particular type of work, it then becomes a Machine.

Example: Shaper, Lathe machine 2. Mechanics( Theory of Machine)

Branch of engineering which deals with the relative motion and forces

between the various machine elements.

Kinematics of machine

Deals with the relative motion without considering the forces

Dynamics of machine

Deals with the forces and effect of forces on the machine component

when they act on them.

3. Kinetics of machine

Deals with the forces, which are formed due to combined action of mass and motion of machine elements.

4. Statics

Deals with the forces and its effect on the machine part while the latter is at rest.

5. Resistant body A

body is said to be resistant body if it is able to transmit the forces with the

least possible deformation.

Example: spring, belt oils in hydraulic presses

6. Kinematic Link

Links are individual parts of a mechanism.

Each parts of a machine which has a relative motion to some other parts is known as Kinematic link.

THEORY OF MACHINE


7. Kinematic Chain

When the kinematic pairs are coupled in such a way that the last linked is joined the first link to transmit the definite motion it is called a kinematic chain.

8. Kinematic Pair

The two links of the machine when in contact with each other are said to form a pair if the relative motion between them is successfully constrained.

9. Inversion

The method of obtaining the different mechanism by fixing the different links in a kinematic chain is known as inversion of the mechanism.

10. Structure

It is the assemblage of a number of resistant bodies having no relative motion between then and meant for carrying loads having a straining action. Example: a railway bridge.

11. Mechanism

When one of the links of a kinematic chain is fixed, the chain is known as

mechanism.

It may be used for transmitting or transforming motion.

Example: Engine indicator, Typewriter.

THEORY OF MACHINE


Grashof's Law The sum of the length of shortest and longest link must be equal or less

than the sum of the length of the other two link length, if there is to be a

continuous relative motion between the two links.

According to Grashofs law

s + l < p + q

l = length of the longest link.

s = length of the shortest link.

p & q = length of the other two

links

In a four-bar linkage, we refer to the line segment between hinges on a given link

as a bar where:

s = length of shortest bar

l = length of longest bar

p, q = lengths of intermediate bar

Grashof's theorem states that a four-bar mechanism has at least one revolving

link if

s + l <= p + q (1) and all three mobile links will rock if

s + l > p + q (2)

The inequality (1) is Grashof's criteria

The Link opposite to the frame is called Coupler Link and the link which are

hinged to the frame are called side link.

The link which is free to rotate through 3600 with respect to second link will be

said to revolve relative to the second link (not necessarily a frame).

THEORY OF MACHINE


If it is possible for all four bar to become simultaneously aligned, such a state

is called change point.

From the table we can see that for a mechanism to have a crank, the sum of the

length of shortest and longest link must be equal or less than the sum of the

length of the other two link.

However this condition is necessary but not sufficient. Mechanism satisfying this

condition falls into following three categories.

1) When the shortest link is the side link, the mechanism is crank rocker

mechanism. The shortest link is the CRANK in the mechanism.

2) When the shortest link is the Frame, the mechanism is double crank

mechanism.

3) When the shortest link is the coupler link, the mechanism is Double rocker

mechanism

Case

Criterion

Shortest link Category

1 s+l < p+q

frame double crank

2 s+l < p+q

slide crank rocker

3 s+l < p+q

coupler double rocker

4 s+l = p+q

any change point

5 s+l < p+q

any triple rocker

THEORY OF MACHINE


Inversion of the following types

1. Four bar chain

a. Beam engine.

b. Coupling rod of Locomotives.

c. Watts’ indicator mechanism.

d. Pantograph.


a. Pendulum pump or Bull engine.

b. Oscillating cylinder engine.

c. Rotary IC engine.

d. Crank and slotted lever quick return mechanism.

e. Whit worth quick return mechanism.

3. Double slider crank chain.

a. Elliptical trammel

b. Scotch yoke mechanism.

c. Oldham’s coupling.

THEORY OF MACHINE


INVERSION OF FOUR BAR CHAIN MECHANISM

THEORY OF MACHINE


a. BEAM ENGINE

1. Beam engine is also called as Crank and lever mechanism.

2. It consist of four link

a. Link A –Frame

b. Link AB –Crank

c. Link BC –Coupler

d. Link CE–Lever

3. In this mechanism, when the crank rotated about the fixed centre A,

the lever oscillates about the fixed center D.

4. The end E of the lever CDE is connected to piston rod which

reciprocates due to the rotation of the crank.

5. Purpose: Convert rotary motion into reciprocating motion.

Figure: Beam Engine

THEORY OF MACHINE


b. Coupling rod of locomotive

1. The coupling rod of the locomotive consists of four links as shown in figure.


a. Link AD – frame

b. Link AB –crank

c. Link BC –connecting rod

d. Link CD–crank

3. In this mechanism, the link AD and BC act as crank and are connected to

the respective wheel.

4. The link CD act as a coupling rod and the link AB is fixed in order to

maintain a constrain motion between them.

5. Purpose: meant for transmitting rotary motion from one wheel to another

wheel.

Figure: Coupling Rod of locomotive

THEORY OF MACHINE


c. Watts indicator mechanism

A watt indicator mechanism has a four link as shown in figure.

1. The four links are fixed link at A, link AC, link CE, and link BFD.

2. It may be noted that BF and FD forms one link because two parts have no

relative motion between them.

3. The link CE and BFD act as lever.

4. The displacement of link BFD is directly proportional to the pressure of gas

or steam which acts on the indicator plunger.

5. On any small displacement of the mechanism, the tracing point E at the end

of the link CE traces out approximately straight line.

6. The initial position of the mechanism is shown in full line whereas the dotted

lines shows the position of mechanism when the gas or steam pressure acts

on the indicator plunger.

Figure: Watts Indicator Mechanism

THEORY OF MACHINE


d. Pantograph

A pantograph is an instrument used to reproduce an enlarged or reduce scale

and as exactly as possible the path described by a given point.

1. It is a based on four based kinematic chain.

2. It consists of jointed parallelogram ABCD.

3. It is made up of bar connected by turning pair. It has a four turning pair.

4. Link BA and BC are extended to O and E respectively such that

OA/OE = AD/BE.

5. For all relative position of bars the triangle OAD and OBE are similar and

the point O,D,E are in straight line.

6. The point E describes the same path as described by point D.

Figure: Pantograph

THEORY OF MACHINE


INVERSION OF SINGLE SLIDER CRANK CHAIN

MECHANISM

1. A single slider crank chain is modification of the basic four bar chain.

2. It consist

a. One Sliding pair and

b. Three Turning pair

3. Link 1 - Frame of engine;

Link 2 - Crank

Link 3 - Connecting rod

Link 4 - Cross head

4. As the crank rotates the cross head reciprocates in the guides and

thus the piston reciprocates in the cylinder

5. It is usually found in reciprocating steam engine mechanism.

6. This type of mechanism converts rotary motion into reciprocating

motion and vice versa

Figure: Single Slider Crank Chain Mechanism

THEORY OF MACHINE


a. Pendulum pump or Bull engine.

1. In this mechanism, the inversion is obtained by fixing the link 4 or cylinder

(sliding pair).


a. Link 1 – Piston rod

b. Link 2 – AB-Crank

c. Link 3 -BC -connecting rod

d. Link 4 –Cylinder.

3. In this case, the crank rotates the connecting rod oscillates about the pin

pivoted to the fixed link.

4. The piston attached to the piston rod reciprocates inside the cylinder.

Figure: Pendulum pump or Bull engine

THEORY OF MACHINE


b. Oscillating cylinder engine.

1. In this mechanism, the inversion is obtained by fixing the link 3 or

connecting rod (turning pair).


e. Link 1 -AB- Piston rod

f. Link 2 -BD-Crank

g. Link 3 -AD -Connecting rod

h. Link 4 –Cylinder.

3. The link 3 (AD-connecting rod) is corresponds to the connecting rod of the

reciprocating steam engine mechanism.

4. When the link 2 rotates (BD-Crank) rotates, the piston attached to the

piston rod reciprocates and the cylinder oscillates about the pin pivoted to

the fixed link at A.

Figure: Oscillating Cylinder Engine

THEORY OF MACHINE


d. Rotary IC engine.

1. In this mechanism, the inversion is obtained by fixing the link 2 or crank.


a. Link 1 - Cylinder.

b. Link 2 -Fixed Crank

c. Link 3 -Piston

d. Link 4 – Connecting rod

3. The link 4 (AD-connecting rod) rotates, the piston reciprocates inside the

cylinder forming link1.

Figure: Rotary IC Engine

THEORY OF MACHINE


a. Crank and slotted lever quick return mechanism

1. In this mechanism, the inversion is obtained by fixing the link 3 or turning

pair.


a. Link 1 -Slider

b. Link 2 – Driving Crank

c. Link 3 -Fixed link

d. Link 4 –Slotted lever or Slotted bar

3. The driving crank AC revolves with uniform angular speed about fixed

centre.

4. The sliding bock is attached to crank pin at A slides in the slotted bar AP

and thus causes AP to oscillate about the point A.

5. A short link PR transmits the motion from AP to the Ram to which the

cutting tool is fixed

6. The motion of the tool is constrained along the line produced

Figure: Crank and slotted lever quick return mechanism

THEORY OF MACHINE


b. Whitworth quick return mechanism.

1. In this mechanism, the inversion is obtained by fixing the link 3 or turning

pair.


a. Link 1 -Slider

b. Link 2 - Crank

c. Link 3 -Fixed link

d. Link 4 –Slotted lever

3. The driving crank BC revolves with uniform angular speed about fixed

centre.

4. The sliding bock is attached to crank pin at B slides in the slotted bar AP

and thus causes AP to oscillate about the point A.

5. A short link PQ transmits the motion from AP to the Ram to which the

cutting tool is fixed

6. The motion of the tool is constrained along the line produced.

Figure: With worth Quick Return mechanism

THEORY OF MACHINE


INVERSION OF DOUBLE SLIDER CRANK CHAIN

MECHANISM

1. A kinematic chain which consists of two turning pair and two sliding

pair is called double slider crank chain.

2. It consist

a. Two Sliding pair and

b. Two Turning pair

3. The inversion of double slider crank chain mechanism are a. Elliptical trammel



THEORY OF MACHINE


a. Elliptical trammel

1. In this mechanism, the inversion is obtained by fixing the link 4 or slotted

plate.


a. Link 1 – Sliders

b. Link 2 – Bar

c. Link 3 – Sliders

d. Link 4 –Slotted Plate

3. The looted plate has two grooves cut in it at right angles to each other.

4. The link 1 and known as a sliders and form sliding pair with the link 4.

5. The link AB is a bar which forms the turning pair with the links 1 and link 3.

6. When the link 1 and link 3 slides along the respected grooves ,any point of

the link 2 such as point P traces out the ellipse on the surface.

Figure: Elliptical trammel

THEORY OF MACHINE



1. In this mechanism, the inversion is obtained by fixing link 1 or link3.


e. Link 1 – Fixed Link

f. Link 2 – Crank

g. Link 3 – Slider

h. Link 4 – Frame (Piston and Cylinder arrangement )

3. When the link 2 rotates about the about B as a centre the link 4

reciprocates.(Piston reciprocates inside the cylinder)

4. The fixed links guides the frame

.

Figure: Scotch Yoke Mechanism

THEORY OF MACHINE



1. In this mechanism, the inversion is obtained by fixing link 2.


a. Link 1 – Flanges

b. Link 2 – Supporting Frame

c. Link 3 – Flanges

d. Link 4 –Intermediate Piece.

3. The flanges (link 1 and link 3) forms turning pair with the link 2.

4. When the driving shaft is rotated, the flange (link 1) causes the

intermediated piece (link 4) to rotate at the same angle through which

the flange (link 1) is rotated.

5. It further rotates the flange (link 3) at the same angle through which the

flange (link 1) is rotated. Hence link 1,3,4, have same angular velocity.

6. A little consideration there is a sliding motion between link 4 and link 1

and 3.

Figure: Oldham’s Coupling

THEORY OF MACHINE


COMMON MECHANISM

1. BICYCLE FREE WHEEL SPROCKET MECHANISM

2. GENEVA MECHANISM

3. ACKERMAN’S STEERING GEAR MECHANISM

4. FOOT OPERATED AIR PUMP MECHANISM

THEORY OF MACHINE


1. BICYCLE FREE WHEEL SPROCKET MECHANISM

1. Mechanical or automotive engineering, a freewheel or overrunning clutch

is a device in a transmission that disengages the driveshaft from the

driven shaft when the driven shaft rotates faster than the driveshaft. An

overdrive is sometimes mistakenly called a freewheel, but is otherwise

unrelated.

2. The condition of a driven shaft spinning faster than its driveshaft exists in

most bicycles when the rider holds his or her feet still, no longer pushing

the pedals. Without a freewheel the rear wheel would drive the pedals

around.

Figure: Bicycle Free Wheel Sprocket Mechanism

http://en.wikipedia.org/wiki/Mechanical_engineering

http://en.wikipedia.org/wiki/Automotive_engineering

http://en.wikipedia.org/wiki/Transmission_%28mechanics%29

http://en.wikipedia.org/wiki/Driveshaft

http://en.wikipedia.org/wiki/Overdrive_%28mechanics%29

http://en.wikipedia.org/wiki/Bicycle

http://en.wikipedia.org/wiki/Pedal

THEORY OF MACHINE


3. In the past, such freewheel mechanisms have included an inner freewheel

body which engages threads on a rear wheel hub, and an outer freewheel

body, including an integral sprocket for engagement with the roller chain.

4. A pair of pawls, and at least one pawl spring have been disposed between

said inner and outer freewheel bodies, whereby forward rotation of the

outer freewheel body would cause the pawls to engage and drive the inner

freewheel body and rear wheel. Also, the pawls would allow the rear

wheel to rotate in a forward direction when the outer freewheel body was

rotating more slowly or was stopped.

THEORY OF MACHINE


2. GENEVA MECHANISM

1) In the mechanism shown in figure, link A is driver and it contains a pin

which engages with the slots in the driven link B.

2) The slots are positioned in such a manner, that the pin enters and leaves

them tangentially avoiding impact loading during transmission of motion.

3) In the mechanism shown, the driven member makes one-fourth of a

revolution for each revolution of the driver.

4) The locking plate, which is mounted on the driver, prevents the driven

member from rotating except during the indexing period.

Figure: Geneva mechanism

THEORY OF MACHINE


5. The Geneva mechanism is a timing device.

6. Geneva mechanism consists of a rotating disk with a pin and another

rotating disk with slots (usually four) into which the pin slides

7. In the most common arrangement, the driven wheel has four slots and

thus advances for each rotation of the drive wheel by one step of 90°.

If the driven wheel has n slots, it advances by 360/n° per full rotation of the

drive wheel.

8. One application of the Geneva drive is in movie projectors. Geneva

wheels having the form of the driven wheel were also used in mechanical

watches. Other applications of the Geneva drive include the pen change

mechanism in plotters, automated sampling devices, indexing tables in

assembly lines, tool changers for CNC machines, and so on.

Figure: Geneva mechanism

http://en.wikipedia.org/wiki/Degree_%28angle%29

http://en.wikipedia.org/wiki/Movie_projector

http://en.wikipedia.org/wiki/Plotter

http://en.wikipedia.org/wiki/CNC

THEORY OF MACHINE


3. Ackerman’s Steering Gear Mechanism.

1) The steering gear mechanism is used for changing the direction of two or

more of the wheel axles with reference to the chassis, so as to move the

automobile in any desired path.

2) When the vehicle takes a turn the front wheels along with the respective

axles turn about the respective pivoted points. The back wheels remain

straight and do not turn. Therefore steering is done by front wheels only.

3) In order to avoid skidding the two front wheels must turn about the same

Instantaneous center I which lies on the axis of the back axle. If the ICR of

the two front wheels do not coincide with the ICR of the back wheels

skidding will take place, which causes wear and tear of tires.

4) Thus the condition for correct steering is that the entire four wheel must

turn about the same ICR. The axis of the inner wheel makes a larger

turning angle θ than the angle Φ subtended by the axis of outer wheel.

Let

a= wheel track

b=wheel base

c=distance between the pivots A and b of the front axle

Now from triangle IBP

Cot θ=BP

IP

and from triangle IAP

Cot Φ = AP = AB + BP = AB + BP = c + Cot θ

IP IP IP IP b

Cot Φ - Cot θ =c/b

THEORY OF MACHINE


5) This is the fundamental equation for correct steering. If this condition is

satisfied there will be no skidding of the wheels when vehicle takes a turn.

6) In Ackerman steering gear the mechanism ABCD is a four bar crank

chain. The shorter link BC and AD are of equal length and are connected

by hinge joints with front wheel axle.The longer link AB and CD are of

unequal length.

Figure: Ackerman’s Steering gear Mechanism.

THEORY OF MACHINE


7) The following are three positions for correct steering

a. When vehicle moves along a straight path, the longer link AB and CD

are parallel and shorter link BC and AD are equally inclined to the

longitudinal axis of the vehicle.

b. When the vehicle is steering to the left, the position of the gear as

shown by dotted lines. In this position the lines of the front wheel axle

intersect on the back wheel axle at I for correct steering.

c. When the vehicle is steering to the right the similar position may be

obtained.

THEORY OF MACHINE


4. Foot operated Air Pump Mechanism.

1) It consists of a cylinder which can oscillate. A piston is mounted in the

cylinder. The cylinder is connected to the foot rest.

2) The arms connected to the foot rest can oscillate.

3) A retrieving spring can bring back the foot rest back to initial position’s the

foot rest is pressed the cylinder oscillates.

4) It creates reciprocating motion of the piston in the cylinder. Therefore

suction and delivery stroke can be obtained.

This is also called as oscillating cylinder mechanism.

Figure: Foot Operated Air Pump Mechanism

Documents

Fundamentals and Types of Mechanism