1. Application of Four-Bar Mechanisms in Cars
Windshield Wiper
Soft Top Mechanism
Group A
Christopher Back
Josephashwin Franklin
Kwongvoon Wong
Chen Lin

2. Components of Soft Top Mechanism
Cascading Four-bar Mechanisms
Open Loop Four-bar Configuration
Used in Industrial robots
Usually requires multiple actuators to control motion
Pantograph Linkage
Originally used in scaled diagrams
Linkages consist of Parallelograms

3. Motion of Mechanism

4. Kinematic Diagram Open Loop Four-bar L= 4, J1= 3, J2= 0 DOF = M =3
Pantograph Linkage
DOF = M = 1

5. Design Characteristics
Reason for Four-Bar Design
Pantograph serves as a locking mechanism
Use of Limiting Position simplifies complex motion
Parallel linkages prevent further motion when collinear

6. Dynamic Designer Convertible Animation

7. Windshield Wiper Mechanism
The four-bar linkage has been show as the simplest possible pin-jointed mechanism
Allows for single degree of freedom controlled motion

8. Variations of the Crank-Rocker in Windshield Wipers
Grashof Condition
S+L<P+Q
Class I case:
Ground either link adjacent to the shortest and you get a crank-rocker
The shortest link will fully rotate
the other link pivoted at the ground will oscillate

9. Tandem system Tandem system is widely used in the front windshield
One Motor runs both wipers
Parallelogram linkage translates motion to wipers

10. Most Common Type of Windshield mechanism
DOF= 3*(6-1)-2*7=1
Four and Six-bar is a parallelogram linkage.
Duplicate the rotary motion of the driver crank at the driven bar.

11. Crank Rocker Input to Windshield Wiper
The coupler of the parallelogram linkage is in curvilinear translation
Remaining at the same angle while all points on it describe identical circular paths

12. Dynamic Designer Windshield Wiper Animation

13. Design Variation Animation
Varying ???

14. Window Single Arm The slider-crank mechanism
Variations of grounding different links
Inversion D

15. Diagram of Rear Wiper DOF = 3*(4-1)-2*4= 1
We can imagine that the coupler link length is very small
How is the condition when driver link length change?

16. The Next Generation of Wipers
Flexblade(TM) Wiper .Its life can extend from months to years
The four-bar linkage mechanism will still be used in this wiper system for a long time

17. References
How Windshield Wipers Work. (2006) In: How Stuff Works Available: < [2007, October 12].
Norton, R.L. Design of Machinery: An Introduction to the Synthesis and Analysis of Mechanisms and Machines. 3rd ed. New York, McGraw-Hill Co
How soft top convertible works. (2006) In: How Stuff Works Available: < [2007, October 12].
Pantographs.(2006) In: Wikipedia The Free Encyclopedia:
< [2007, October 12].

18. Questions?

19. The crank-rocker system will change to be two crank system

20. Other Four-bars in Transportation
Contact points in trains
Linkages on locomotives
Pushrods mechanism
Car door linkages

21. How is the difference of Rear wiper?
Rear windshield wiper
Single application of
Four-bar mechanism
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