me 143: mechanics of machinery-1aly/courses/me143/01_introd.pdf · me 143: mechanics of machinery-1...

ME 143: Mechanics of Machinery-1

Lecture 1

Introduction

Dr. Aly Mousaad Aly

Mechanical Engineering Department

Faculty of Engineering, Alexandria University

Policy

• Class attendance is very important.

• Come to the exercises prepared (your notes +

sketch + sheet + ruler + aristo + pencil +

eraser)

• If you don’t come, your class grade is zero

• You cannot be absent for more than 25%

Lecture 1, AM Aly 2

Grading

• Final project (20 Marks)

• Oral exam (10 Marks)

• Midterm exam (30 Marks)

• Final examination (90 Marks)

Lecture 1, AM Aly 3

Course objectives

• Develop the student's ability to analyze and

design planar machines.

• Analyzing motion of elements in machines

(disp., vel., acc., and forces).

• Understanding the terminology and

parameters of gears.

• Understanding various gear trains.

Lecture 1, AM Aly 4

Course Materials

Lecture Slides:

Will be available at the copy center + any other materials

References and Resources:

• R.S. Khurmi, J.K. Gupta "Theory of Machines"Chand (S.) & Co Ltd ,India, 2005

• Robert L. Norton "Design of Machinery”, 2nd ed, McGraw-Hill, 1999

Lecture 1, AM Aly 5

Course contents

• Joints

• Mechanisms

• Degrees of freedom

• Analysis of some applied mechanisms

• Graphical and analytical analyses of displacement, velocity and acceleration

• Gear geometry

• Gear trains

Lecture 1, AM Aly 6

What is Theory of Machines?

It is a branch of Engineering - Science, which

deals with the study of relative motion

between the various parts of machine, and

forces which act on them.

Knowledge of this subject is very essential for

an engineer in designing the various parts of a

machine.

Lecture 1, AM Aly 7

Sub-Divisions of Theory of Machines

Kinematics: describes the motion of bodies

without consideration of the forces that cause

the motion (i.e. disp., vel., acc.).

Dynamics:

a. Kinetics: describes the relation between

forces and motion (ma).

b. Statics: describes the relation between forces

at rest.

Lecture 1, AM Aly 8

Machine Element or Link

It is a part of machine which has a motion relative to some other part.

a.Tension link

A belt or a wire rope (tensile force)

Lecture 1, AM Aly 9


Lecture 1, AM Aly 10

b. Fluid link

Hydraulic jack



c. Rigid link

Links of different order

Kinematic Pairs: Lower Pairs

One relative motion

Sliding pair turning pair

pure rolling screw pair


Kinematic Pairs: Higher Pairs

Two motions

rolling + sliding

turning + sliding cam and follower


Kinematic chain

An assemblage of links and joints,

interconnected in a way to provide a

controlled output motion in response to a

supplied input motion.


Mechanism

A kinematic chain in which at least one link

has been "grounded," or attached, to th frame

of reference (which itself may be in motion).


Machine

A collection of mechanisms arranged to transmit

forces and to do work.


Degree of freedom (DOF)

Number of independent coordinates required

to define the position of a system (Mobility).



DOF = 3xN – 2xPl l l l – Phhhh

N: number of moving links

Pllll : number of lower pairs

Phhhh : number of higher pairs

OROROROR

DOF = 3x(L -1) – 2xPl l l l – Ph h h h Grübler's

equation

L: number of moving links


Mobility

• The mobility is the number of input parameters (usually pair variables) that must be independently controlled to bring the device into a particular position.

• The Kutzbach criterion, which is similar to Gruebler's equation, calculates the mobility.

• In order to control a mechanism, the number of independent input motions must equal the number of degrees of freedom of the mechanism.


Example

L = 4

Pl = 4

Ph = 0

DOF = 3x(L -1) – 2xPl – Ph

DOF = 3x(4 -1) – 2x4 – 0

= 1


Example


Example

L = 5; Pl = 5; Ph = 1

DOF = 3x(5 -1) – 2x5 – 1

= 1


Exercise


me 143: mechanics of machinery-1aly/courses/me143/01_introd.pdf · me 143: mechanics of machinery-1...

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