1. Mechanical Engineering Dept.
Mechanism
Machines are mechanical devices used to accomplish work. A mechanism is a heart of a machine. It is the mechanical portion of the machine that has the function of transferring motion and forces from a power source to an output.
Mechanism is a system of rigid elements (linkages) arranged and connected to transmit motion and/or force in a predetermined fashion.
Mechanism consists of linkages (rigid bars, gears, belts & pulleys, chains & sprockets and cams) and joints.
Ken Youssefi
Mechanical Engineering Dept.

2. Mechanism Synthesis and Analysis
Synthesis – design a mechanism to perform a
desired function
Analysis – given a mechanism, perform kinematics
and kinetics analysis
Graphical techniques
Analytical methods

3. Mechanical Engineering Dept.
Four-Bar Linkage θ3 θ2 θ4
Ken Youssefi
Mechanical Engineering Dept.

4. The Slider-Crank Mechanism
Member 4 is converted to a slider
Input link, crank
Coupler link, connecting rod
Output link, piston (slider)
Ken Youssefi
Mechanical Engineering Dept.

5. Mechanical Engineering Dept.
Example of Mechanism
Can crusher 4
Simple press 5 3 4 2 1 6 2 3 1
Rear-window wiper 4 3 2 1
Ken Youssefi
Mechanical Engineering Dept.

6. Mechanical Engineering Dept.
Example of Mechanisms
Moves packages from an assembly bench to a conveyor 6 5 4 2 3
Six bar 1
Microwave carrier to assist people on wheelchair
Six bar 5 3 4 2 1 6
Lift platform
Six bar 5 3 4 2 1 6
Ken Youssefi
Mechanical Engineering Dept.

7. Mechanical Engineering Dept.
Example of Mechanisms
Lift platform
Front loader
Device to close the top flap of boxes
Ken Youssefi
Mechanical Engineering Dept.

8. Mechanical Engineering Dept.
Example of Mechanisms
Stair climbing mechanism
Airplane landing gear mechanism
A box that turns itself off
Ken Youssefi
Mechanical Engineering Dept.

9. Mechanical Engineering Dept.
Example of Mechanisms
Conceptual design for an exercise machine
Rowing type exercise machine
Ken Youssefi
Mechanical Engineering Dept.

10. Mechanical Engineering Dept.
Example of Mechanisms
6-Bar mechanism, automatic spoiler
Ken Youssefi
Mechanical Engineering Dept.

11. Mechanical Engineering Dept.
Example of Mechanisms
Extension position
Flexed position
Six-bar linkage prosthetic knee mechanism
Ken Youssefi
Mechanical Engineering Dept.

12. Four-Bar Linkage Categories
l = longest link
s = longest link
p and q = intermediate links
Case I shortest link + longest link < summation of the other two links
Shortest link is the driver with either one of the adjacent links as the ground link (fixed). The result is two different types of crank-rocker mechanisms, input link rotates 360 (crank) and output link oscillates (rocker)
fixed
Ken Youssefi
Mechanical Engineering Dept.

13. Four-Bar Linkage Categories
Case I shortest link + longest link < summation of the other two links
Shortest link is fixed. The result is a double-crank mechanism. Both, input and output links rotate 360.
Ken Youssefi
Mechanical Engineering Dept.

14. Four-Bar Linkage Categories
Case I shortest link + longest link < summation of the other two links
The longest link is fixed and either one of the intermediate links is the driver. The result is a double-rocker mechanism. Both, input and output links oscillate.
Grashof condition – one link rotates 360
Ken Youssefi
Mechanical Engineering Dept.

15. Four-Bar Linkage Categories
Case II shortest link + longest link > summation of the other two links
There are four possible mechanisms depending on which link is fixed. All mechanisms are double-rockers.
Case III shortest link + longest link = summation of the other two links
Same mechanisms as in case I with the addition of a branching point (all links become collinear).
Ken Youssefi
Mechanical Engineering Dept.

16. Mechanical Engineering Dept.
4-Bar mechanisms
Case I: s + l < p + q
Ken Youssefi
Mechanical Engineering Dept.

17. Mechanical Engineering Dept.
4-Bar mechanisms
S + l > p + q
4 double rocker mechanisms
8/26 mon
Ken Youssefi
Mechanical Engineering Dept.

18. The Slider-Crank Mechanism
Member 4 is converted to a slider
Input link, crank
Coupler link, connecting rod
Output link, piston (slider)
Ken Youssefi
Mechanical Engineering Dept.

19. Slider-Crank Mechanism
Offset slider-crank mechanism
Ken Youssefi
Mechanical Engineering Dept.

20. Slider-Crank Mechanism
The mechanism has a stroke B1B2 equal twice the crank length r2.
Locations B1 and B2 are called the extreme positions (limiting) of the slider
In-line slider crank mechanism
Ken Youssefi
Mechanical Engineering Dept.

21. The Slider-Crank Mechanism
Ken Youssefi
Mechanical Engineering Dept.

22. Slider-Crank Mechanism - Inversion
Ken Youssefi
Mechanical Engineering Dept.

23. Categories of Mechanisms
Function generation mechanisms
Output is a specified function of input
Motion generation mechanisms
The orientation of the object is important, rigid body guidance
Path generation mechanisms
A point on a link moves on a specified path
Ken Youssefi
Mechanical Engineering Dept.

24. Mechanical Engineering Dept.
Mechanism Categories
Function Generation Mechanisms
A function generator is a linkage in which the relative motion between links connected to the ground is of interest. 2 1 4 3
A four-bar hand actuated wheelchair brake mechanism
Ken Youssefi
Mechanical Engineering Dept.

25. Mechanical Engineering Dept.
Mechanism Categories
Function Generation Mechanisms
A four-bar linkage for a lawn sprinkler
Ken Youssefi
Mechanical Engineering Dept.

26. Mechanical Engineering Dept.
Mechanism Categories
Function Generation Mechanisms
A four-bar function generation mechanism to lower an attic stairway.
A four-bar function generation mechanism to operate an artificial hand used for gripping.
Ken Youssefi
Mechanical Engineering Dept.

27. Mechanical Engineering Dept.
Mechanism Categories
Motion Generation Mechanisms
In motion generation, the entire motion of the coupler link (3) is of interest (rigid body guidance). 2
Moving joints 3
Fixed pivot points 4
New Rollerblade brake system
Ken Youssefi
Mechanical Engineering Dept.

28. Mechanical Engineering Dept.
Mechanism Categories
Motion Generation Mechanisms
Four-bar automobile hood linkage design
Ken Youssefi
Mechanical Engineering Dept.

29. Mechanical Engineering Dept.
Mechanism Categories
Microwave carrier to assist people on wheelchair
Six bar 5 3 4 2 1 6
Lift platform
Six bar 5 3 4 2 1 6
Ken Youssefi
Mechanical Engineering Dept.

30. Mechanical Engineering Dept.
Mechanism Categories
Path Generation Mechanisms
In path generation, we are concerned only with the path of a tracer point and not with the motion (rotation) of the coupler link.
Crane – straight line motion
Ken Youssefi
Mechanical Engineering Dept.

31. Mechanical Engineering Dept.
Mechanism Categories
Path Generation Mechanisms with timing
A four-bar path generation mechanism to guide a thread in an automatic sewing machine
A four-bar path generation mechanism as part of an arm-actuated propulsion system for a wheelchair
Ken Youssefi
Mechanical Engineering Dept.

32. Primary Joints Lower Order Joints
Ken Youssefi
Mechanical Engineering Dept.

33. Mechanical Engineering Dept.
Higher Order Joints
Ken Youssefi
Mechanical Engineering Dept.

34. Motion Generation Mechanisms
Rotating an object into a storage position
Moving a storage bin from an accessible position to a stored position
Ken Youssefi
Mechanical Engineering Dept.

35. Motion Generation Mechanisms
Lifting a boat out of water
Moving a trash pan from the floor up over a trash bin and into a dump position
Ken Youssefi
Mechanical Engineering Dept.

36. Straight line Mechanisms
Ken Youssefi
Mechanical Engineering Dept.

37. Straight line Mechanisms
Ken Youssefi
Mechanical Engineering Dept.

38. Straight Line Mechanism
Ken Youssefi
Mechanical Engineering Dept.

39. Straight Line Mechanism - Application
Straight line mechanism with dwell
Ken Youssefi
Mechanical Engineering Dept.

40. Mechanical Engineering Dept.
Scotch Yoke Mechanism
Example – car window
Ken Youssefi
Mechanical Engineering Dept.

41. Mechanical Engineering Dept.
Geneva Mechanism
Ken Youssefi
Mechanical Engineering Dept.

42. Linear Geneva Mechanism
Ken Youssefi
Mechanical Engineering Dept.

43. Mechanical Engineering Dept.
Ratchet Mechanism
Ken Youssefi
Mechanical Engineering Dept.

44. Straight Beam Walking Mechanism
Ken Youssefi
Mechanical Engineering Dept.

45. Mechanical Engineering Dept.
Ken Youssefi
Mechanical Engineering Dept.

46. Roller and Flat Follower Cams
Ken Youssefi
Mechanical Engineering Dept.

47. Cylindrical Cam Mechanism
Ken Youssefi
Mechanical Engineering Dept.

48. Mechanical Engineering Dept.
Gears – Rack and Pinion
Ken Youssefi
Mechanical Engineering Dept.

49. Mechanical Engineering Dept.
Gears
Worm Gear Sets
Bevel gears
Planetary Gear set
Ken Youssefi
Mechanical Engineering Dept.

50. Mechanical Engineering Dept.
V-8 Engine
Ken Youssefi
Mechanical Engineering Dept.

51. Type of Motion and Mechanisms
Most power sources that are readily available today are either of the pure rotational motion type, such as electric motor or hand crank, or of the pure translational type, such as pneumatic or hydraulic cylinder, or linear actuators.
Translation to Translation
Ken Youssefi
Mechanical Engineering Dept.

52. Type of Motion and Mechanisms
Rotational to Rotational
Ken Youssefi
Mechanical Engineering Dept.

53. Type of Motion and Mechanisms
Rotation to Translation
Ken Youssefi
Mechanical Engineering Dept.

54. Mechanical Engineering Dept.
References
Mechanism Design, Analysis and Synthesis by Erdman and sander, fourth edition, Prentice-Hall,
Machines and Mechanisms by Uicker, Pennock and Shigley, third edition, Oxford
Machines and Mechanisms by Myszka, Prentice-Hall
Ken Youssefi
Mechanical Engineering Dept.