1. Introduction What is mechanisms Features of Mechanisms
Four different types of motion
Degree of Freedom 1

2. What is mechanisms
Mechanisms is a device which transmits energy in the form of movement.
A mechanisms changes an input force and movement into an output force and movement. 2

3. The combinations of mechanisms build mechanical systems which we call machine.
A machine is a device which does work by converting or transmitting energy.
e.g. bicycle, hand drill
A mechanisms transforms an input motion and force into a desired output motion and force.
e.g. gear, cam 3

4. Basic Machines Five basic Machines Screw Inclined plane pulley
Lever
Screw
Inclined plane
pulley
wheel and axle 4

5. Lever is a rigid rod pivoted about a fixed axis called a fulcrum.5

6. Screw mechanisms are used to enable heavy loads to be lifted.6

7. An inclined plane is a sloping surface used to gain mechanical advantage when raising a load.7

8. A pulley is a wheel with a grooved rim and used as lifting device.8

9. Wheels & axles are used to lift heavy load with small effort.9

10. Features of Mechanisms
Load & Effort
Load is the weight of the object need to move
Effort is the force applied to the mechanisms
Mechanical Advantage
Mechanical Advantage =
Load
Effort 10

11. Efficiency is less or equal to 1 (why?) Velocity ratio =
Distance moved by the effort
Distance moved by the load
Efficiency =
Mechanical Advantage
Velocity Ratio
X 100%
Efficiency =
Energy Output
Energy Input
X 100% 11

12. Types of Motion
Linear Motion
The motion in a straight line 12

13. Rotary motion
The motion in the circle 13

14. Oscillation Motion
The motion backwards and forwards in an arc. 14

15. Reciprocating motion
The motion backwards and forwards in a straight line
Mechanisms use one of these four basic movements, either on their own or combined. 15

16. Degree of Freedom Driving & Driven
In a mechanisms system, the first original device to generate motion is call driving device. It delivers the energy and motion to the devices connected to it.
The device follows the motion of the driving device is called driven device. 16

17. Degree of freedom of a rigid body is defined as the number of independent movements it has.
All motion can be regarded as a combination of translation and rotation.
Translation: movement alone one or more of the three axes.
Rotation: rotation about one or more of the axes. 17

18. In two dimensions, there 3 degree of freedom.X Y 18

19. What is the degree of freedom of a rigid body in three dimensions?X Z Y 19

20. There are six degree of freedom for an unrestrained rigid body in space:
Three translating motions along the x, y, z axes and three rotary motions around the x, y and z axes respectively. 20

21. Kinetic Constraints Rigid body system Kinetic constraints
Two or more rigid bodies in space are collectively called a rigid body system.
Kinetic constraints
Constraints between rigid bodies that result in the decrease of the degree of freedom of rigid body system 21

22. Kinetic pair Planar mechanisms
Kinetic constraints between rigid bodies.
Low pairs and High pairs.
Planar mechanisms
Two translational & one rotary motions
Lower pairs : Revolute & Prismatic pairs
ONLY ONE DEGREE OF FREEDOM 22

23. x y x y
Planar revolute pair
Planar prismatic pair 23

24. Kinetic Pairs in Spatial Mechanisms
Spherical pair DOF=3
Planar pair DOF=3
Cylindrical pair DOF=2 24

25. Revolute pair DOF=1
Prismatic pair DOF=1
Screw pair DOF=2 25

26. The influence of kinetic constraints in the motion of rigid body has two intrinsic aspects
Geometrical aspect
Physical aspect
The degree of freedom is important to the mechanisms due to the mechanisms is not a structure which has no motions.
Adding kinetic constraints between the rigid bodies will decrease the degree of freedom of the rigid body system 26

27. Degree of Freedom of Planar Mechanisms
Low pair : 1 degree of freedom
High pair : 2 degree of freedom
Equation for degree of freedom
F=3(n-1)-2L-H
Where F=total degree of freedom in the mechanisms
n=number of links (including the frame)
L=number of lower pairs (1 degree of freedom)
H=number of high pairs (2 degree of freedom) 27

28. Example 1
What is the degree of freedom in this mechanisms? 28

29. Answer
N=4 L=4 (at A, B, C, D) h=0
F = 3x(4-1)-2x4-1x0=1 29