automatic screw jack

1. INTRODUCTION

1.1 Need for Introduction

Our survey in the regard in several users of vehicles, revealed the facts that

mostly some difficult methods were adopted in lifting the vehicles for reconditioning.

Now the project has mainly concentrated on this difficulty, and hence a suitable device

has been designed, such that the vehicle can be lifted from the floor land without

application of any impact force. The fabrication part of it has been considered with

almost case for its simplicity and economy, such that this can be accommodated as one of

the essential tools on automobile garages. The motorized screw jack has been developed

to cater to the needs of small and medium automobile garages, which are normally man

powered with minimum skilled labor. In most of the garages the vehicles are lifted by

using screw jack. This needs high man power and skilled labour. In order to avoid all

such disadvantages, the motorized jack has been designed in such a way that it can be

used to lift the vehicle very smoothly without any impact force. The operation is made

simple so that even unskilled labour can use it with ease. As automobile market is

growing, advance concepts are being implemented to make automobiles more and more

versatile and comfortable. Many concepts are implemented day to day to make

automobile better and better these days. One such concept is of variable height

adjustment in vehicle by adjusting its ground clearance,. In this way the vehicle becomes

more versatile and can be operated over variety of bad as well as good road conditions.

1.2 Necessity of Model

The design was focused on all the processes of conception, invention,

visualization, calculation, refinement and specification of details that determine the form

of the product. Hence, the said Motorized Screw Jack for Vehicles, specifically the

Scissors type has gone under force analysis so that its performance criterion will not fail

in any sense. The main physical parameters of the design are determined through the

appropriate calculations and practical considerations with reasonable assumptions.

1www.SeminarsTopics.com

Doing work in a bent or squatting position for a period of time is not ergonomic to

human body. It gives back ache problem in due of time. A mechanical jack is a device

which lifts heavy equipment and vehicles so that maintenance can be carried out

underneat. Car jacks usually use mechanical advantage to allow human being to lift a

vehicle. There are two types of automotive car jacks: Hydraulic and Screw types. Most

car jacks that are included with cars are screw types. These two categories also have

many subcategories of jacks. Hydraulic jacks have the shape of a bottle, or are built into a

trolley (the "floor jack") or the like. By operating the handle, which is a lever (a simple

machine), fluid is compressed and routed to an actuating cylinder. This results in lift.

A jackscrew is a type of jack which is operated by turning a lead screw. It is also

known as a screw jack, and is commonly used as car-jacks. In the case of a screw jack, a

small force applied in the horizontal plane is used to raise or lower large load. [Khurmi

and Gupta, 2010]. Of the screw-type mechanisms, there are scissor jacks, common in

newer cars, and bumper jacks, common in older cars. A jackscrew's compressive force is

obtained through the tension force applied by its lead screw. An Acme thread is most

often used, as this thread is very strong and can resist the large loads imposed on most

jackscrews while not being dramatically weakened by wear over many rotations. An

inherent advantage is that, if the tapered sides of the screw wear, the mating nut

automatically comes into closer engagement, instead of allowing backlash to develop

[Rajput, 2010]. These types are self-locking, which makes them intrinsically safer than

other jack technologies like hydraulic actuators which require continual pressure to

remain in a locked position. The correct projection of a screw thread is tedious and takes

a considerable time, so threads are shown conventionally on engineering drawings. Most

jackscrews are lubricated with grease. Ball screws are a more advanced screw

mechanisms that uses a recirculation-ball nut to minimize friction and prolong the life of

the screw threads. The thread profile of such screws is semicircular to properly mate with

the bearing balls. The disadvantage to this type of screw is that it is not self-locking. Jack

screws form vital components in equipment. For instance, the failure of a jackscrew on a

McDonnell Douglas MD80 due to a lack of grease resulted in the crash of Alaska

Airlines Flight 261 off the coast of California in 2000. Due to large numbers of examples


of compound stresses met with in engineering practice, the cause of “failure” or

permanent set under such conditions has attracted considerable attention [ Rajput, R.K.

2010]. So such type of motorized screw jack overcomes all limitations mention above

and hence model requirement is very necessary.

1.3 Today’s Importants for Model Design

When all the forces that act on a given part are known, their effect with respect to

the physical integrity of the part still must be determined. It would therefore be

reasonable to suppose that fatigue failure due to lack of allowance does not occur.

Screws Application is used in the elevation of vehicles or objects. The operation of the

screw jack is such that it comprises a handle for driving a bolt element (Lead Screw)

manually so as to adjust the height of the Jack to elevate a vehicle or the object. The

operation of the jack manually makes it difficult for most women and the elderly to

operate since much effort is needed to drive the screw jack which results in low linear

speed and time consuming. These presently available jacks further require the operator to

remain in prolonged bent or squatting position to operate the jack. Doing work in a bent

or squatting position for a period of time is not ergonomic to human body. It will give

back ache problem in due of time. Suppose car jacks must be easy to use by pregnant

women or whoever had problem with the tyres along the road.

The objective of this mode is therefore to modify the existing design of car jack

by incorporating an electric motor into the existing screw jack to make the operation

easier, safer faster and more reliable.


1.4 Background & Concept

1.4.1 History of screw jack

Screw type mechanical jacks were very common for jeeps and trucks of World

War II vintage. For example, the World War II jeeps were issued the "Jack, Automobile,

Screw type, Capacity 1 and 1/2 ton", Ordnance part number 41-J-66. This jacks, and

similar jacks for trucks, were activated by using the lug wrench as a handle for the jack's

ratchet action to of the jack. The 41-J-66 jack was carried in the jeep's tool compartment.

Screw type jack's continued in use for small capacity requirements due to low cost of

production raise or lower it. A control tab is marked up/down and its position determines

the direction of movement and almost no maintenance. The virtues of using a screw as a

machine, essentially an inclined plane wound round a cylinder, was first demonstrated by

Archimedes in 200BC with his device used for pumping water.

There is evidence of the use of screws in the Ancient Roman world but it was the

great Leonardo da Vinci, in the late 1400s, who first demonstrated the use of a screw jack

for lifting loads. Leonardo design used a threaded worm gear, supported on bearings, that

rotated by the turning of a worm shaft to drive a lifting screw to move the load - instantly

recognizable as the principle we use today. We can’t be sure of the intended application

of his invention, but it seems to have been relegated to the history books, along with the

helicopter and tank, for almost four centuries. It is not until the late 1800s that we have

evidence of the product being developed further. With the industrial revolution of the late

18th and 19th centuries came the first use of screws in machine tools, via English

inventors such as John Wilkinson and Henry Maudsley The most notable inventor in

mechanical engineering from the early 1800s was undoubtedly the mechanical genius

Joseph Whitworth, who recognized the need for precision had become as important in

industry as the provision of power. While he would eventually have over 50 British

patents with titles ranging from knitting machines to rifles, it was Whitworth work on

screw cutting machines, accurate measuring instruments and standards covering the angle

and pitch of screw threads that would most influence our industry today. Whitworth tools

had become internationally famous for their precision and quality and dominated the

market from the 1850s. Inspired young engineers began to put Whitworth’s machine


tools to new uses. During the early 1880s in Coaticook, a small town near Quebec, a 24-

year- old inventor named Frank Henry Sleeper designed a lifting jack. Like da Vinci’s

jack, it was a technological innovation because it was based on the principle of the ball

bearing for supporting a load and transferred rotary motion, through gearing and a screw,

into linear motion for moving the load. The device was efficient, reliable and easy to

operate. It was used in the construction of bridges, but mostly by the railroad industry,

where it was able to lift locomotives and railway cars. Local Coaticook industrialist,

Arthur Osmore Norton, spotted the potential for Sleeper’s design and in 1886 hired the

young man and purchased the patent. The Norton’s jack was born. Over the coming years

the famous Norton’s jacks were ma nufactured at plants in Boston, Coaticook and

Moline, Illinois. Meanwhile, in Alleghany County near Pittsburgh in 1883, an

enterprising Mississippi river boat captain named Josiah Barrett had an idea for a ratchet

jack that would pull barges together to form job. The idea was based on the familiar lever

and fulcrum principle and he needed someone to manufacture it. That person was Samuel

Duff, proprietor of a local machine shop.There was clearly potential for using this

technology for other applications and only 10 years later, in 1940, the first worm gear

screw jack, that is instantly recognizable today, was offered by Duff-Norton, for

adjusting the heights of truck loading platforms and mill tables. With the ability to be

used individually or linked mechanically and driven by either air or electric motors or

even manually, the first model had a lifting capacity of 10 tons with raises of 2” or 4”

Since then the product has evolved to push, pull, lift, lower and position loads of anything

from a few kilos to hundreds of tonnes. One of the biggest single screw jacks made to

date is a special Power Jacks E-Series unit that is rated for 350 tonnes even in earthquake

conditions for the nuclear industry. More recent developments have concentrated on

improved efficiency and durability, resulting in changes in both lead screw and gearbox

design options for screw jacks.


1.4.2 Types of screw jacks used

Jacks are of mainly two types- mechanical and hydraulic. They vary in size depending on

the load that they are used to lift.

(a) Mechanical jacks

A mechanical jack is a device which lifts heavy equipment. The most common

form is a car jack, floor jack or garage jack which lifts vehicles so that maintenance can

be performed. Car jacks usually use mechanical advantage to allow a human to lift a

vehicle by manual force alone. More powerful jacks use hydraulic power to provide more

lift over greater distances. Mechanical jacks are usually rated for maximum lifting

capacity. There are two types of mechanical jacks:

(b) Scissor jacks

Scissors jacks are also mechanical and have been in use at least since the 1930s. A

scissor jack is a device constructed with a cross-hatch mechanism, much like a scissor, to

lift up a vehicle for repair or storage. It typically works in just a vertical manner. The jack

opens and folds closed, applying pressure to the bottom supports along the crossed

pattern to move the lift. When closed, they have a diamond shape.

Photograph 1.1: Scissor Jack


Scissor jacks are simple mechanisms used to drive large loads short distances.

The power screw design of a common scissor jack reduces the amount of force required

by the user to drive the mechanism. Most scissor jacks are similar in design, consisting of

four main members driven by a power screw. A scissor jack is operated simply by turning

a small crank that is inserted into one end of the scissor jack. This crank is usually "Z"

shaped. The end fits into a ring hole mounted on the end of the screw, which is the object

of force on the scissor jack. When this crank is turned, the screw turns, and this raises the

jack. The screw acts like a gear mechanism. It has teeth (the screw thread), which turn

and move the two arms, producing work. Just by turning this screw thread, the scissor

jack can lift a vehicle that is several thousand pounds.

(c) Bottle (cylindrical) jacks

Bottle screws may operate by either

(i)Rotating the screw when the nut is fixed; or

(ii) Rotating the nut and preventing rotation of the screw.

Photograph 1.2: Bottle (cylindrical) Jacks

Bottle jacks mainly consist of a screw, a nut, thrust bearings, and a body. A stationary

platform is attached to the top of the screw. This platform acts as a support for the load


and also assists it in lifting or lowering of the load. These jacks are sturdier than the

scissor jacks and can lift heavier loads.

(d) Hydraulic jacks

Hydraulic jacks are typically used for shop work, rather than as an emergency

jack to be carried with the vehicle. Use of jacks not designed for a specific vehicle

requires more than the usual care in selecting ground conditions, the jacking point on the

vehicle, and to ensure stability when the jack is extended. Hydraulic jacks are often used

to lift elevators in low and medium rise buildings.

Photograph 1.3: Single piston hydraulic jack with a single manual screw extension.

Photograph 1.4: Hydraulic jack


A hydraulic jack uses a fluid, which is incompressible, that is forced into a

cylinder by a pump plunger. Oil is used since it is self lubricating and stable. When the

plunger pulls back, it draws oil out of the reservoir through a suction check valve into the

pump chamber. When the plunger moves forward, it pushes the oil through a discharge

check valve into the cylinder. The suction valve ball is within the chamber and opens

with each draw of the plunger. The discharge valve ball is outside the chamber and opens

when the oil is pushed into the cylinder. At this point the suction ball within the chamber

is forced shut and oil pressure builds in the cylinder. As we see that, up to the history

many types of screw jacks were used by users. This many types of screw jacks were

having their advantages but some types of disadvantages also occurs in them, and

limitations are overcome by designing of this type of screw jack.

1.4.3 Requirement of project model

As we see that, up to the history many types of screw jacks were used by users.

This many types of screw jacks were having their advantages but some types of

disadvantages also occurs in them, so this limitations are overcome by designing of this

type of screw jack. The mechanical and hydraulic jacks having some limitations and

given in following manner;

The Mechanical type screw jacks required high man power

For operating of such types of screw jack operator should having skilled of

operation

In case of hydraulic jack, they are oil based. The requirement of filtration of oils in hydraulic systems on a

regular basis to ensure that the hydraulic fluid contains no broken particles, as well as to eliminate harmful damaging air pockets.


2. SYSTEM MODELING

2.1 Construction & Working

In its simple construction the body is made up of combinations of various

components like connecting members, power screw, D. C. geared motor, switch,

connecting wire etc. and the motion of motorized screw jack i.e. forward and reverse is

control by using On-Off-On type toggle switch.

Photograph 2.1: Working Model

When electrical power flows through the cigarette lighter receptacle connected to

the motor, plugged to the automobile 12 V battery source to generate power for the prime

mover (motor), which transmits its rotating speed to the drive assembly connected to the


power screw to be rotated with required speed reduction and increased torque to drive the

power screw. The significance and purpose of this work is to modify the existing car jack

in order to make the operation easier, safer and more reliable in order to reduce health

risks especially back ache problems associated with doing work in a bent or squatting

position for a long period of time. The modified car jack is easy to use by pregnant

women, old age person or whoever had problem with the vehicle tyres along the road.

The designed motorized jack will also save time and requires less human energy to

operate.


The motorized screw jack has been developed to cater to the needs of small and medium

automobile garages and useful for old age persons, which are normally man powered

with minimum skilled labor. In most of the garages the vehicles are lifted by using screw

jack. This needs high man power and skilled labour. In order to avoid all such


disadvantages, the motorized jack has been designed in such a way that it can be used to

lift the vehicle very smoothly without any impact force. The operation is made simple so

that even unskilled labour can use it with ease .The d.c motor is coupled with the screw

jack by drive assembly. The screw jack shaft’s rotation depends upon the rotation of D.C

motor. This is a simple type of automation project. This is an era of automation where it

is broadly defined as replacement of manual effort by mechanical power in all degrees of

automation. The operation remains to be an essential part of the system although with

changing demands on physical input, the degree of mechanization is increased. Now the

project has mainly concentrated on this difficulty, and hence a suitable device has been

designed, such that the vehicle can be lifted from the floor land without application of

any impact force.

2.2 Need for Automation

Automation can be achieved through computers, hydraulics, pneumatics, robotics,

etc. Automation plays an important role in mass production. For mass production of the

product, the machining operations decide the sequence of machining. The machines

designed for producing a particular product are called transfer machines. The components

must be moved automatically from the bins to various machines sequentially and the final

component can be placed separately for packaging. Materials can also be repeatedly

transferred from the moving conveyors to the work place and vice versa. Nowadays,

almost all the manufacturing processes are being atomized in order to deliver the

products at a faster rate. The manufacturing operation is being atomized for the following

reasons:

(i) To achieve mass production

(ii) To reduce man power

(iii) To increase the efficiency of the plant

(iv)To reduce the work load

(v) To reduce the production cost


2.3 Components with Their Material Selection

The life span of the jack will depend greatly on the type of materials used for each

component to avoid failure. The whole performance of the jack model is depends on how

the material will select for jack and size of each components. For making of the model of

screw jack all components are given in following manner with their suitable material and

size.

Table 2.1 Components Part List

Sr.

No.

Description Material Size Quantity

1. Power screw High Strength Low-

Alloy Steel

13 cm Diameter 1

2. 3-Size angle M.S. 2.5 x 2.5 x 3 cm 1

3. 2-Size angle M.S. 2.5 x.2.5 cm 1

4. Button Switch _ On-off-On type 1

5. Wiper Motor _ Gear type 1

6. Nuts and Bolts M.S. 1.5 cm 2

7. Fixed type Rivets M.S. 8 mm 4

8. Cable _ 6 mm (9 ft.) 1

9. Cigarette Lighter _ 12 v operated 1


2.3.1 Power screw

A power screw is a mechanical device used for converting rotary motion into

linear motion and transmitting power. A power screw is also called translation screw. It

uses helical translatory motion of the screw thread in transmitting power rather than

clamping the machine components. Screws are used for power transmission or

transmission of force. A screw is a cylinder on whose surface helical projection is created

in form of thread. The thread will have specified width and depth, which bear some ratio

with the diameter of the cylinder. The screw rotates in a nut, which has corresponding

helical groove on the internal surface. Thus a nut and a screw make a connected pair in

which one remains stationary while other rotates and translates axially. The helical

surface of the screw thread makes surface contact with the helical groove surface of the

nut. If an axial force acts on, say screw moving inside stationary nut, the point of

application of the force will move as the screw advances in axial direction. This will

result in work being done and hence power being transmitted. Both types – one in which

screw rotates and advances in a stationary nut or one in which screw rotates between

fixed support and nut is free to move axially – are used in practice. In the latter case the

force acting on nut will move as nut translates. However, the friction between the

surfaces of contact will require some power to be overcome. Hence the power delivered

by the screw-nut pair will be less than the power supplied.

(A)Advantages

Power screws offer the following advantages:

1) Power screw has large load carrying capacity

2) The overall dimensions of the power screw are small, resulting in compact

construction.

3) Power screw is simple to design.

4) The manufacturing of power screw is easy without requiring specialized

machinery. Square threads are turned on lathe. Trapezoidal threads are

manufactured on thread milling machine.

5) Power screws give smooth and noiseless service without any maintenance.


6) Power screw can be designed with self-locking property. In screw-jack

application, self locking characteristic is required to prevent the load from

descending on its own.

7) There are only a few parts in power screw. This reduces cost and increases

reliability.

(B) Disadvantages

The disadvantages of power screws are as follows:

1) Power screws have very poor efficiency; as low as 40%.Therefore, it is not used

in continuous power transmission in machine tools, with the exception of the lead

screw. Power screws are mainly used for intermittent motion that is occasionally

required for lifting the load or actuating the mechanism.

2) ) High friction in threads causes rapid wear of the screw or the nut. In case of

square threads, the nut is usually made of soft material and replaced when worn

out. In trapezoidal threads, a split- type of nut is used to compensate for the wear.

Therefore, wear is a serious problem in power screws.

1.3.1.3 Terminology of power screw

Figure 2.1: Terminology of Power Screw


a) Pitch

The pitch is defined as the distance, measured parallel to the axis of the screw,

from a point on one thread to the corresponding point on the adjacent thread. It is denoted

by the letter‟p”.

b) Lead

The lead is defined as the distance, measured parallel to the axis of the screw, that

the nut will advance in one revolution of the screw. It is denoted by the letter “l”

c) Nominal diameter

It is the largest diameter of the screw. It is also called major diameter or outside

diameter and denoted by “D”. The half of nominal diameter is outer radius of screw and

denoted by “r0”.

d) Core diameter

It is the smallest diameter of the screw thread. It is also called minor diameter or

root diameter. It is denoted by the letter “dc”.

e) Helix angle

It is defined as the angle made by the helix of the thread with a plane perpendicular to the

axis of the screw. Helix angle is related to the lead and the mean diameter of the screw. It

is also called lead angle. It is denoted by θ.

tan (θ) = Lπd

2.3.1.4 Material selection for power screw

As per condition of material selection for power screw, the screw is subjected

tosional moment, bending moment and compressive force. For that purpose, High


Strength Low-Alloy Steel with 50 ksi (345 N/mm2) minimum yield point, 70 ksi (485

N/mm2) minimum tensile strength and 21 % elongation) is selected, due to the following

reasons:

1) Good Machinability

2) Good Ductility

3) High Strength

4) Wear Resistance

5) Ease of producing complicated parts

6) Economical, etc.

2.3.1.5 Forms of threads

Power screws are classified by the geometry of their thread. V-threads are less

suitable for Power screws than others such as Acme because they have more friction

between the threads. Their threads are designed to induce this friction to keep the fastener

from loosening. Power screws, on the other hand, are designed to minimize friction.

Therefore, in most commercial and industrial use, V-threads are avoided for Power screw

use. Nevertheless, V-threads are sometimes successfully used as Power screws, for

example on microlathes and micromills.

a) Square thread

Figure 2.2: Square thread


Square threads are named after their square geometry. They are the most efficient, having

the least friction, so they are often used for screws that carry high power. But they are

also the most difficult to machine, and are thus the most expensive.

b) Acme thread

Figure 2.3: Acme Thread

This is the most common form of thread used in power screws. This is a trapezoidal

thread type that has sloped sides. This thread is commonly used when a rapid movement

is required. They are cheap and easy to manufacture. The disadvantages of this thread

include its low efficiency and difficulty in predicting service life.

c) Buttress thread

Figure 2.4: Buttress Thread


Buttress threads are of a triangular shape. These are used where the load force on the

screw is only applied in one direction. They are as efficient as square threads in these

applications, but are not easier to manufacture.

2.3.1.6 Self locking condition of screw

The torque required to lower the load can be given by,

T = P * d2 = W tan (φ - α) *

d2

In the above expression, if φ < α, then torque required to lower the load will be negative.

In other words, the load will start moving down ward the application of any torque. Such

a condition is known as over hauling of screws. In however, φ > α, the torque required

to lower the load will be positive, indicating that an effort is applied to lower the load.

Such a screw is known as self locking screw. In other words, a screw will be locking if

the friction angle is greater than helix angle that is, tan φ > tan α.


Graph 2.1: Lead angle vs. Coefficient of Friction

2.3.1.7 Efficiency of square threaded screw

The efficiency of screw threaded screw may be defined as the ratio between the ideal

effort (i.e. the effort required to move the load , neglecting frication) to the actual effort

(i.e., the effort required to move the load taking friction into account ).

Efficiency, η = Ideal effortActual effort

= Po

P

= W tan(α )

W tan(α+ϕ)


η = tan(α )

tan(α+ϕ)

From above equation, the efficiency of screw threaded screw depends upon the helix

angle and friction angle. The following figure shows the variation of the efficiency of

square threaded screw against the helix angle for various values of coefficient of friction.

The graph is applicable when the load is lifted.

Graph 2.2: Graph between efficiency and helix (lead) angle.

2.3.2 Lifting members

These members are made from simple c-shapes. The web of the lifting members is cut

out near the pin connections to allow proper serviceability of the scissor jack at its

maximum and minimum heights. Members 12 and 15 have ideal connections to balance

the load between the left and right side. The lifting members having four in amount and

having c-shapes, used for lifting load. Hence it subjected compressive stress in it. For that

reason Grey cast iron is selected as the material for the lifting members. Cast iron is

cheap and it can be given any complex shape without involving costly machining

operations. Cast iron has higher compressive strength compared with steel. Therefore, it

is technically and economically advantageous to use cast iron for the lifting members.


Photograph 2.4 Lifting Member

2.3.3 D.C. gear motor

One of the first electromagnetic rotary motors was invented by Michael Faraday

in 1821 and consisted of a free-hanging wire dipping into a pool of mercury. A

permanent magnet was placed in the middle of the pool of mercury. When a current was

passed through the wire, the wire rotated around the magnet, showing that the current

gave rise to a circular magnetic field around the wire. This motor is often demonstrated in

school physics classes, but brine (salt water) is sometimes used in place of the toxic

mercury. This is the simplest form of a class of electric motors called homopolar motors.

A later refinement is the Barlow's Wheel. Another early electric motor design used a

reciprocating plunger inside a switched solenoid; conceptually it could be viewed as an

electromagnetic version of a two stroke internal combustion engine.


The modern DC motor was invented by accident in 1873, when Zénobe Gramme

connected a spinning dynamo to a second similar unit, driving it as a motor.The classic

DC motor has a rotating armature in the form of an electromagnet. A rotary switch called

a commutator reverses the direction of the electric current twice every cycle, to flow

through the armature so that the poles of the electromagnet push and pull against the

permanent magnets on the outside of the motor. As the poles of the armature

electromagnet pass the poles of the permanent magnets, the commutator reverses the

polarity of the armature electromagnet. During that instant of switching polarity, inertia

keeps the classical motor going in the proper direction. (See the diagrams below.) A

simple DC electric motor. When the coil is powered, a magnetic field is generated around

the armature. The left side of the armature is pushed away from the left magnet and

drawn toward the right; causing rotation.When the armature becomes horizontally

aligned, the commutator reverses the direction of current through the coil, reversing the

magnetic field. The process then repeats.

2.3.3.1 Principle of operation of D.C. motor

2.3.3..1.1 Fleming’s left hand rule

A uniform magnetic field in which a straight conductor carrying no current is

placed. The conductor is perpendicular to the direction of the magnetic field. The

conductor is shown as carrying a current away from the viewer, but the field due to the N

and S poles has been removed. There is no movement of the conductor during the above

two conditions. When the current carrying conductor is placed in the magnetic field, the

field due to the current in the conductor supports the main field above the conductor, but

opposes the main field below the conductor.


Figure 2.5: Principle of Operation of Dc Motor

The result is to increase the flux density in to the region directly above the conductor and

to reduce the flux density in the region directly below the conductor. It is found that a

force acts on the conductor, trying to push the conductor downwards as shown by the

arrow. If the current in the conductor is reversed, the strengthening of flux lines occurs

below the conductor, and the conductor will be pushed upwards. The N and S poles has

been removed. There is no movement of the conductor during the above two conditions.

When the current carrying conductor is placed in the magnetic field, the field due to the

current in the conductor supports the main field above the conductor, but opposes the

main field below the conductor.

Now consider a single turn coil carrying a current. In view of the reasons given above,

thone side of the coil will be forced to move downwards, whereas the other side will be


forced to move upwards. The forces acting on both the coil sides will be of same

magnitude. But their direction is opposite to one another. As the coil is wound on the

armature core which is supported by the bearings, the armature will now rotate. The

commutator periodically reverses the direction of current flow through the armature.

Therefore the armature will have a continuous rotation. A simplified model of such a

motor is shown in figure VI. The conductors are wound over a soft iron core. DC supply

is given to the field poles for producing flux. The conductors are connected to the DC

supply through brushes A simple 2-pole DC electric motor has 6 parts, as shown in the

diagram below.

1) The armature or rotor

2) A commutator

3) Brushes

4) An axle

5) A field magnet

6) A DC power supply of some sort

2.3.3.1.2 The armature


Figure 2.6: The Armature

The armature takes the place of the nail in an electric motor. The armature is an

electromagnet made by coiling thin wire around two or more poles of a metal core. The

armature has an axle, and the commutator is attached to the axle. In the diagram above

you can see three different views of the same armature: front, side and end-on. In the end-

on view the winding is eliminated to make the commutator more obvious. The

commutator is simply a pair of plates attached to the axle. These plates provide the two

connections for the coil of the electromagnet.

2.3.3.1.3 Electromagnets and motors

An electric motor is all about magnets and magnetism: a motor uses magnets to

create motion. Opposites attract and likes repel. So if there are 2 bar magnets with their

ends marked north and south, then the North end of one magnet will attract the South end

of the other. On the other hand, the North end of one magnet will repel the North end of

the other (and similarly south will repel south). Inside an electric motor these attracting

and repelling forces create rotational motion. In the diagram above, you can see two


magnets in the motor, the armature (or rotor) is an electromagnet, while the field magnet

is a permanent magnet (the field magnet could be an electromagnet as well, but in most

small motors it is not to save power). An electromagnet is the basis of an electric motor.

You can understand how things work in the motor by imagining the following scenario.

Say that you created a simple electromagnet by wrapping 100 loops of wire around a nail

and connecting it to a battery. The nail would become a magnet and have a North and

South pole while the battery is connected. Now say that you take your nail electromagnet,

run an axle through the middle of it, and you suspended it in the middle of a horseshoe

magnet as shown in the figure below. If you were to attach a battery to the electromagnet

so that the North end of the nail appeared as shown, the basic law of magnetism tells you

what would happen: The North end of the electromagnet would be repelled from the

north end of the horseshoe magnet and attracted to the south end of the horseshoe

magnet.

Figure 2.7: Electromagnets and Motors

2.3.3.1.4 The Commutator and brushes

The "flipping the electric field" part of an electric motor is accomplished by two

parts: the commutator and the brushes. The diagram at the right shows how the

commutator and brushes work together to let current flow to the electromagnet, and also

to flip the direction that the electrons are flowing at just the right moment. The contacts

of the commutator are attached to the axle of the electromagnet, so they spin with the


magnet. The brushes are just two pieces of springy metal or carbon that make contact

with the contacts of the commutator.

Photograph 2.5: D.C. Gear Motor (wiper)

Ratings:

System voltage: 12V

Polarity: Insult return or negative earth

Operating ambient temperature: -20ºC to + 90ºC

Characteristics:

Typical light running current (wet screen) :1.5 Amps (normal speed)2.5 Amps (high speed)

Rated torque (cold) at output gear: 18 - 29 Nm at 13.5 V

Operating Speed: normal

Normal speed: 41 rpm

High speed: 70 rpm

Angle of wipe: Max 120º,

Weight: 2 kg


Features:

This wiper motor has the capacitor connected in parallel to power supply to

minimize radio interference.

A thermal cut out is provided as a protective device to protect the armature

winding in the event of a blade block.

A ball bearing is provided on the commentator end of the armature to minimize

friction losses and thereby increase torque of the wiper motor.

2.3.3.1.5 Powering the motor

(a) Voltage: The standard voltage requirement for the wiper motor is 12 volts DC. The

electrical system in a running automobile usually puts out between 13 and 13.5 volts, so

it's safe to say the motor can handle up to 13.5 volts with no problem. I wouldn't

recommend any voltages higher than that.

(b) Wiring the motor: The Saturn wiper motor has a block with 5 electrical terminals.

One terminal goes to ground (Common), one is for high speed, one low speed and two for

a parking switch. It's important to note that the Common terminal is connected to the

motor casing. This could be a factor if you mount the motor to a metal. The parking

switch is used to bring the wiper blades to their "parked" position when used on a car.

During motor operation, the two terminals are connected to each other about 90% of each

rotation. They open during the other 10%. I haven't used this function, but it could be

used to "flash" a light or possibly in conjunction with a microcontroller to count

revolutions and make something happen every Nth revolution

(c) Speed control: This table shows some approximate motor speeds I've obtained by

varying the voltage going to the motor using two different wiring configurations. As

voltage goes down, so does the motor torque.


Table No. 2.2: Motor Speeds with Voltages

Voltage High Low12 70 rpm 41 rpm8 42 rpm 28 rpm5 26 rpm 16 rpm

3.3 13 rpm 10 rpm

(d) Gear mechanism in motor: Gears are used in tons of mechanical devices. They do

several important jobs, but most important, they provide a gear reduction in motorized

equipment. This is key because, often, a small motor spinning very fast can provide

enough power for a device, but not enough torque. For instance, an electric screwdriver

has a very large gear reduction because it needs lots of torque to turn screws, but the

motor only produces a small amount of torque at a high speed. With a gear reduction, the

output speed can be reduced while the torque is increased.

The gear mechanism in used gear wiper motor is worm gear type. Power from

motor is transfer to worm gear and then application. Worm gears are used when large

gear reductions are needed. It is common for worm gears to have reductions of 20:1, and

even up to 300:1 or greater. Many worm gears have an interesting property that no other

gear set has: the worm can easily turn the gear, but the gear cannot turn the worm. This is

because the angle on the worm is so shallow that when the gear tries to spin it, the

friction between the gear and the worm holds the worm in place. This feature is useful for

machines such as conveyor systems, in which the locking feature can act as a brake for

the conveyor when the motor is not turning. One other very interesting usage of worm

gears is in the differential, which is used on some high-performance cars and trucks.

There are a lot of intricacies in the different types of gears. In this article, we'll learn

exactly how the teeth on gears work, and we'll talk about the different types of gears you

find in all sorts of mechanical gadgets.


Photograph 2.6: Worm gear mechanism in motor


2.3.4 Cable and Cigarette Lighter (12V)

Control cables are used in order to connect the motor and switch. As the required

torque is very high, so control cables are having high amp up to 10-15 Amp. The

cigarette lighter receptacle in an automobile, initially designed to power an electrically

heated cigarette lighter, became a de facto standard DC connector to supply electrical

power for portable accessories used in or near an automobile. While the cigarette lighter

receptacle is a common feature of automobiles, as a DC power connector it has the

disadvantage of relatively low current rating and poor contact stability. Currently,

automobiles may provide several 12 V receptacles that are intended only to operate

accessories and that are not to be used with a cigarette lighter. Car manufacturers may

make a cigarette lighter an optional extra-cost accessory. Usually, only one 12 V

receptacle near the driver will accommodate an actual cigarette lighter, with other

receptacles designated as "12 V auxiliary power outlets" which are not physically able to

power a car lighter.

Photograph 2.6: 12 volt cigar lighter plug.


http://en.wikipedia.org/wiki/File:Car_12V_DC_plug.jpg

The traditional lighter is a metal or plastic cylinder containing a thin coil of nichrome

wire, through which high current (~10 amperes) passes when the device is activated,

usually by pushing it into the socket as though it were a button. When pushed in, the

lighter is held against the force of a spring by a hook attached to a bi-metallic strip.

heating element becomes glowing orange hot in seconds, causing the bimetallic strip to

bend and unhook the mechanism, and the handle pops out. If the lighter is then promptly

removed from its socket, it can light a cigarette, cigar or tinder.


2.3.5 Button Switch

A switch is used in order to start or stop the entire operation of the screw jack. The type

of switch that is used is known as a toggle switch. A toggle switch is a class of electrical

switches that are manually actuated by a mechanical lever, handle, or rocking

mechanism. Toggle switches are available in many different styles and sizes, and are

used in countless applications. Many are designed to provide, e.g., the simultaneous

actuation of multiple sets of electrical contacts, or the control of large amounts of electric

current or mains voltages.

Figure 2.8: On-Off-On type Switch


2.4 Applications

The following are the application of motorized screw jack This motorized screw jack is

used for lifting the vehicles. Thus it can be useful for the following types of vehicles in

future;

Maruti 800 and Alto

Ritz

Indica

Flat

All types of light vehicles

2.5 Advantages

Advantages of project model are given as follows;

1) The loaded light vehicles can be easily lifted.

2) Checking and cleaning are easy, because the main parts are screwed.

3) Handling is easy

4) No Manual power required.

5) Replacement of parts is easy.

2.6 Disadvantages

Some disadvantages of model occurs and given below

1) The limitation of this design is that it is only applicable to vehicles not weighing

above 1000 kg.

2) Care must be taken for the handling the equipment such as proper wiring

connection, battery charging checkup, etc.

3. DESIGN CALCULATION OF COMPONENTS


3.1 Design Calculations

The main physical parameters of the design are determined through the appropriate

calculations and practical considerations with reasonable assumptions. The purpose of the

design calculations is the assumptions and predictions of possible stresses or

deformations in the major parts and thereby chooses reasonable dimensions for those

parts of the machine so it will satisfy the design objectives and also attain its assumed

lifespan.

3.1.1 Force and stress analysis

The force analysis consideration is based on the assumption that the screw jack is loaded

vertically symmetrical.

Maximum Mass (m) = 1000 kg

F = (1000 kg * 9.81) = 9810 N

Figure 3.1: Force and Stress Analysis in Screw Jack members

Resolving vertical forces, fay + fby = F


And since, X1 = X2 , hence, fay = fby

At maximum raising height of the jack, θ =280

fa1= 4905cos (θ)

fa1= 4905cos (280)

fa1 = 5.555256 KN

Hence, (fa1 = fb1),

Also, fa = fa1 (sin280) + fa2 (sin280)

= 2 fa1 (sin280)

= [2 * 5555.256 (sin280)],

fa = fb = 5216 N

At minimum raising height of the jack,

θ = 55.770

fa1= fa ycos (θ)

fa1= 4905cos (55.77)

= 8.720 KN

fa = fa1 * sin (55.770) + fa2 * sin (55.770) ,

fa = fb = 14419.15 N (Tensile force in the Power Screw)

Since the maximum loading force will act at the minimum raising height of the jack, the design stresses will be analyzed at that point.

3.1.2 Design of the power screw


The design stress,

σ d= Tensile StrengthFactor of Safety (S . F .)

For 35% carbon steel, the tensile strength is 485 MN/m2, with yield strength of 345

MN/m2. Factor of Safety of 2.5 is chosen, because the material is known under

reasonably constant service conditions subjected to loads and stresses that can be

determined easily.

Design stress,

σ d=4852.5

=242.5 MNm2

Applying the design equation,

σd > σactual

σ actual= FA

σd =FA

A ≥ Fσd

A ≥ 14419.15

(242.5 X 106)

A = 0.05946 X 10−3

A = π4 d2

d = √ 4 Aπ


d = 0.0097280 m,

d ≥ 9.7280 mm.

For the sake of design convenience, the diameter of the power screw, d is chosen to be 13

mm, with a pitch of 2.54 mm.

3.1.3 Combined tensile and torsional stress in the power screw

Assuming a frictionless collar ,

Torsional stress, τ ≤16Tπ d3

≤ 16∗242.88π (0.013)3

τ = 563.03 Nm2

Tensile stress, σ x = (4∗14419.15)π ((0.013)2)

σ x = 108.63 MPa

Hence, the combined Tensile and Torsional stress is;

where, σ y = 0

σ1 = √σ x2−σ x∗σ y+σ y2+3 τ xy2

σ1 = √(108.63∗106)2−0+0+3∗(563.032)

σ1 = 108.63 MPa

Now, Yield Strength

Factor of Safety ,

Yield StrengthFactor of Safety = 345∗106

2.5 = 138 MPa


The power screw will not fail under yielding since,

Yield StrengthFacto r of Safety > σ1

3.1.4 Design of lifting members

Force in a lifting member, F = 8720N

Design stress,

σd = Yield StrengthFactor of Safety

σd = 138∗106

2.5 = 138 MPa

Design stress,

σd ≥ FA

A ≥ Fσd

= 8720

138∗106

A ≥ 63.188 * 10−5 mm2

For design consideration an area of 70 mm2will be chosen.

Tensile Stress, σ x ≥ F x

A

= 8720

70∗106 = 124.27 MPa


From the maximum distortion energy theorem; where σy = 0 and τ xy=0

σ1 = √σ x2−σ x∗σ y+σ y2+3 τ xy2

σ1 = √(124.27)2−0+0+0¿¿

σ1 = 124.27 MPa.

The lifting members will not fail due to yielding since,

Yield StrengthFactor of Safety > σ1

3.2 Cost Estimation


Cost estimation may be defined as the process of forecasting the expenses that

must be incurred to manufacture a product. These expenses take into a consideration all

expenditure involved in a design and manufacturing with all related services facilities

such as pattern making, tool making as well as a portion of the general administrative and

selling cost.

The machine tool designer must furnish the management with an idea of how

much cooling will cost and how much money the production methods save over specified

run. This information is generally furnished in a form of cost worksheets. By referring to

the cost worksheets the final cost of machine is calculated.

3.2.1 Purpose of cost estimation

To determine the selling price of a product for a quotation or contract so as to

insure a reasonable profit to the company.

Check the quotation supplied by vendors.

Determine the most economical process or material to manufacture the product.

To determine standards of production performance that may be used to control the

cost.

Initiate means of cost reduction in existing production facilities by using new

materials which result in saving due to lower scrap loss and revised method of

cooling and processing.

Decide whether a part or assembly is economical to be manufacture in the plant or

is to be purchased from outside.

Using the cost estimation the accurate idea about product making is done and

material required for that also given in that with their worth’s.


3.2.2 Material Cost

Material cost of different material is mention here for accurate taking cost of total

raw material required and given in the following table.

Table No 3.1: Material Cost

Sr.

No.

Component Material Quantity Cost (RS)

1 Power screw High Strength Low-

Alloy Steel

1 180 /-

2 3-Size angle M.S. 1 120 /-

3 2-Size angle M.S. 1 80 /-

4 Wiper Motor _ 1 720/-

5 Fixed type Rivets M.S. 4 40 /-

6 Nut and Bolts M.S. 2 30 /-

7 Cable _ 1 (9 ft) 125 /-

8 Cigarette Lighter _ 1 120 /-

9 Button Switch _ 1 65 /-

Total = 1480 /-

3.2.3. Machining cost

Here we have work on the different machines for having different operations so

the machine is being hired for that much period of time considering the depreciation

and the electric light bill along with the rent of the workshop or the initial investment,

the machining cost is calculated as follows:-

Table No 3.2: Machining Cost


Sr. No. Machine Operation Rupees

1. Cutting 110

2. Treading 120

3. Drilling 80

4. Welding 80

Total = 390 /-

Total Cost = Material Cost + Machining Cost

= 1480 + 390

= 1870 /-

4. CONCLSION


4.1 Conclusion

The existing design was modified by introduction of an electric motor in the

power screw, the cigarette lighter receptacle connected to the motor and plugged to the

automobile 12V battery source to generate power for the prime mover (motor), in order

to make load lifting easier. In this modified design, the power screw is rotated through its

drive assembly, when electrical power flows through it. The main advantages of the

modified design over the existing design are that the modified designed motorized jack

will save time, be faster and easier to operate and requires less human energy and

additional work to operate. There by effectively curb the problems associated with

Ergonomics - which is a fundamental concept of design process. The limitation of this

design is that it is only applicable to vehicles not weighing above 1000 kg.The design

was focused on all the processes of conception, invention, visualization, calculation,

refinement and specification of details that determine the form of the product. Hence, the

said Motorized Screw Jack for Vehicles, specifically the Scissors type has gone under

force analysis so that its performance criterion will not fail in any sense. The modified car

jack is easy to use by pregnant women or whoever had problem with the vehicle tyres

along the road. The designed motorized jack will also save time and requires less human

energy to operate. The main physical parameters of the design are determined through the

appropriate calculations and practical considerations with reasonable assumptions.


automatic screw jack

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