This document discusses the instantaneous center method for analyzing mechanisms. It defines key terms like instantaneous center, centrode, and axode. It explains how to determine the number and types of instant centers in a mechanism, including primary fixed/permanent centers and secondary centers. The document provides steps for locating all the instant centers using principles like Kennedy's theorem. It includes examples of applying the instant center method to determine velocities and angular velocities in different slider crank and linkage mechanisms.

1. INSTANTANEOUS CENTRE
METHOD
Combined motion of rotation & translation of
link AB: pure rotation about some center I,
instant center of rotation
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2. Introduction
Instantaneous center of a moving body:
center which keeps changing from
one instant to another
Centrode: locus of all such ICs
instantaneous axis: A line through an
IC & perpendicular to plane of motion
Axode: Locus of this axis
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3. Space and Body Centrodes
IC: a point in the body which may be
considered fixed at any particular moment
Space centrode: locus of IC in space
during a definite motion of the body
Body centrode: locus of IC relative to body
itself
Body centrode rolls without slipping over
space centrode.
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4. Methods for Determining the
Velocity of a Point on a Link
1. Instantaneous center method
2. Relative velocity method
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5. Number of Instant Centers in a
Mechanism

6. Types of Instant
Centers
a. Primary instant centers
1. Fixed instant centers
2. Permanent instant centers
b. Secondary instant centers
1. Neither fixed nor permanent instant
centers
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7. Types of Instantaneous
Centers
Fixed
ICs
,
I12
same place
configurations
& I14:
for all
of
mechanism
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8. Types of Instantaneous
Centers
I23 & I34, permanent
ICs: move when
mechanism moves,
but joints are of
permanent nature
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9. `
Types of Instantaneous
Centers
I13 & I24,
fixed
permanent
neither
no
r
ICs
:
vary with
configuration of
mechanism
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10. Location of Instantaneous Centers
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11. Arnold Kennedy Theorem
If 3 bodies move relative to each
other, they have 3 ICs that lie on a
straight line.
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12. Method of Locating ICs in a Mechanism
Fig. 6.8 (a)
1. Determine number of ICs (N)
2. Make a list of all instantaneous centers
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Links 1 2 3 4
Instantaneous
centers
12 23 34
13 24
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13. Method of Locating Instantaneous
Centers in a Mechanism
3. Locate fixed & permanent ICs by
inspection.
I12 & I14 are fixed Ics
I23 & I34 are permanent IC
The four bar mechanism has:
 four turning pairs
 four primary (fixed and permanent)
ICs located at centers of the pin joints

14. Method of Locating Instantaneous
Centers in a Mechanism
4. Locate remaining neither fixed nor
permanent ICs (secondary centers) by
Kennedy’s theorem
 Circle diagram Fig. 6.8 (b)
 Mark points on a circle equal to number of
links in a mechanism.
5. Join points by solid lines to show that these
centers are already found.
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15. Method of Locating Instantaneous
Centers in a Mechanism

16. Example 6.1
The crank AB rotates uniformly at 100 rpm.
Locate all instantaneous centers and find the
angular velocity of link BC.
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17. Example 6.2
Locate all ICs of the slider crank mechanism. If the crank
rotates cw with an angular velocity of 10 rad/s, find:
1. Velocity of slider A
2. Angular velocity of ConRod AB
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18. Example 6.3
A mechanism has the following dimensions: OA
= 200 mm; AB = 1500 mm; BC = 600 mm;
CD = 500 mm and BE = 400 mm. Locate all ICs.
If crank OA rotates uniformly at 120 rpm cw,
find:
1. velocity of B, C and D
2. angular velocity of links AB, BC and CD
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19. Example 6.3
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20. Example 6.4
The mechanism of a wrapping machine has the following
dimensions : O1A = 100 mm; AC = 700 mm; BC = 200
mm; O3C = 200 mm; O2E = 400 mm; O2D =
200 mm and BD = 150 mm. The crank O1A rotates at a
uniform speed of 100 rad/s. Find the velocity of point E of
the bell crank lever by IC method.
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21. Example 6.4
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22. Example 6.5
The figure shows a sewing needle
bar mechanism O1ABO2CD wherein
the different dimensions are as
follows: O1A = 16 mm;  = 45°;
Vertical distance between O1 & O2 =
40 mm; Horizontal distance between
O1 & O2 = 13 mm; O2B = 23 mm; AB
= 35 mm; O2BC = 90°;
BC = 16 mm; CD = 40 mm. D lies
vertically below O1. Find velocity of
needle at D for the given
configuration. Crank O1A rotates
at 400 rpm.
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23. Example 6.5

24. `
Example 6.6
The various dimensions of a
Whitworth quick return
motion mechanism are as
follows: OQ = 100 mm; OA
= 200 mm; QC = 150 mm;
and CD = 500 mm. The
crank OA rotates at 120 rpm
cw. Locate all ICs and find
the velocity of ram D.
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25. Example 6.6
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