1. Application of Four-Bar Mechanisms in Cars
Windshield Wiper
Soft Top Mechanism
Group A
Christopher Back
Joseph Ashwin 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. Kinematic Diagram Open Loop Four-bar L= 4, J1= 3, J2= 0 DOF = M =3
Pantograph Linkage
DOF = M = 1

4. Motion of Mechanism

5. Motion of Mechanism

6. Position and Velocity analysis when R3= 30 in.

7. Position and Velocity analysis when R3= 35 in.

8. Position and Velocity analysis when R3= 40 in.

9. Dynamic Designer Convertible Animation
Variation of design
Velocity Analysis and Limit Position Analysis
with different R3 link length changing from 30 to units
Conclusion
With a constant input of theta2, the longer R3 is, the faster angle velocity of R4.
That means the soft top can open faster in this condition.

10. Dynamic Designer Convertible Animation
The proceeding figures shows ,when the R3 is longer, it has a smaller rotation range of output link R4.
That means :
For wider rotation angle of R4,we select R3 a bit shorter
Theta4 has the angle limit from 0 to Pi. It won’t work beyond this limit.
For a faster speed of R4,we select R3 a bit longer

11. 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

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

13. 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.

14. 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

15. Two Vector Loop Closure equations
In above case,R7=0;
Design variable:t3,t4,t5,t6,t7

16. Two Vector Loop Closure equations
R2Cos(Ө2) + R3Cos(Ө3) + R4Cos(Ө4) + R5Cos(Ө5) = ACos(ӨA)
R2Sin(Ө2) + R3Sin(Ө3) + R4Sin(Ө4) + R5Sin(Ө5) = ASin(ӨA)

17. Two Vector Loop Closure equationsB R3 R6 R2
R2Cos(Ө2) + R3Cos(Ө3) + R6Cos(Ө6) + R7Cos(Ө7) = BCos(ӨB)
R2Sin(Ө2) + R3Sin(Ө3) + R6Sin(Ө6) + R7Sin(Ө7) = BSin(ӨB)

18. Two Vector Loop Closure equations
R2Cos(Ө2) + R3Cos(Ө3) + R4Cos(Ө4) + R5Cos(Ө5) = ACos(ӨA)
R2Sin(Ө2) + R3Sin(Ө3) + R4Sin(Ө4) + R5Sin(Ө5) = ASin(ӨA)
R2Cos(Ө2) + R3Cos(Ө3) + R6Cos(Ө6) + R7Cos(Ө7) = BCos(ӨB)
R2Sin(Ө2) + R3Sin(Ө3) + R6Sin(Ө6) + R7Sin(Ө7) = BSin(ӨB)
Ө4 = Ө6 +180o
No. Equations Unknowns Total Unknowns
4 Ө
Ө (Ө3, Ө5, Ө6, Ө7)
Ө4 or = Ө6 +180o Ө5 Ө6 Ө7
0 – 360(deg)

19. Windshield Wiper Animation

20. Wiper Angle Sweep
-Figures show the three angles swept by the windshield wiper for 3 chosen input link lengths

21. Analysis of Windshield Wiper

22. Conclusions
The Four-bar linkage mechanism will still be used in this wiper system for a long time
It advantage includes
Utilize one motor to drive two wiper blade
Parametric changes gives different arc
Input link can be place in various location
ONE disadvantage commonly reported is Joint failure (joint dislocation)

23. 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].

24. Questions?