WELCOME

A technical seminar on

“VELOCITY AND ACCELERATION ANALYSIS”

(GRAPHICAL METHOD)

BYN.SUDHEER

M.TECH-MACHINE DESIGN16481D1509

GUDLVAALLERU ENGINEERING COLLEGE

IMPORTANCE:

Design and analysis of machinery and mechanisms relies heavily on the skill and ability of a designer to visualize relative motion between machine components.

With the ever increasing use of high speed machines, velocity and acceleration analysis have become indispensible in machine design process.

VELOCITY ANALYSIS:

There are two methods to determine the velocity and acceleration of links in a mechanism by graphical analysis, namely:

1. Relative velocity method, and

2. Instantaneous centre method (I- centre method).

ABSOLUTE vs. RELATIVE VELOCITY:

1.ABSOLUTE VELOCITY:

An absolute velocity is the velocity of a point measured from a fixed point (normally the ground or anything rigidly attached to the ground and not moving).

2. RELATIVE VELOCITY:

Relative velocity is the velocity of a point measured relative to another point that may itself be moving.

MOTION OF LINK:

If the length of the link is r, then the velocity of point B relative to the point A is given by

VBA= r × ɷ

Steps to draw velocity diagram (graphical method):

The following points are to be considered while solving problems by this method:

Draw the configuration diagram to a suitable scale.

Locate all fixed points in the mechanism as a common point in velocity diagram.

Choose a suitable scale for the vector diagram of velocity.

Cond…

The velocity vector of each rotating link is r to the link.

Velocity of each link in mechanism has both magnitude and direction. Start from a point whose magnitude and direction is known.

The points of the velocity diagram are indicated by small letters.

Example problem:1

Solution:

Example problem:2

ACCELERATION ANALYSIS:

Acceleration is the rate of change of velocity with respect time.

When a body or link moves in a circular path it has

two components of acceleration namely, Tangential, and

Normal components of acceleration.

The rate of change of velocity of link along the circular rotational path is known as tangential component of acceleration, ft .

The tangential acceleration is always in a direction perpendicular to the radius of rotation and is thus tangent to the path of motion.

The rate of change of velocity of link normal to the direction of rotational path is known as normal component of acceleration or centripetal acceleration or radial acceleration, fn or fr or fc.

ACCELERATION OF A LINK:

Steps to draw acceleration diagram:

Choose the suitable scale for acceleration diagram.

Locate the fixed points as the common points in acceleration diagram.

The total acceleration of any point with respect to any other point is along the line joining them.

The radial component of acceleration of one point with respect to another point is along the line joining them, where as the tangential component is perpendicular to the line joining them.

If a point is moving along a straight line its radial component of acceleration is zero with respect to a point(which is on the same straight line).

Example:

Fig: Space and Velocity diagrams of Slider-crank mechanism

Fig: Acceleration diagram

CONCLUSION: Kinematic analysis of a mechanism consists of

calculating position, velocity and acceleration of any of its points or links. To carry out such an analysis, we have to know linkage dimensions as well as position, velocity and acceleration of as many points or links as degrees of freedom the linkage has.

After knowing the D.O.F’s, velocity and acceleration behavior only we may be able to design a mechanism for dynamic conditions.

THANK YOU