Group AChristopher Back

Joseph Ashwin FranklinKwongvoon Wong

Chen Lin

•Windshield Wiper

• 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

Open Loop Four-bar

L= 4, J1= 3, J2= 0 DOF = M =3

Pantograph Linkage

L= 4, J1= 3, J2= 0 DOF = M = 1

http://auto.howstuffworks.com/convertible2.htm

Variation of design

Velocity Analysis and Limit Position Analysis with different R3 link length changing from 30 to 40 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.

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

Grashof Condition

S+L<P+QClass 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

Tandem system is widely used in the front windshield

One Motor runs both wipers

Parallelogram linkage translates motion to wipers

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.

Most Common Type of Windshield Mechanism

The coupler of the parallelogram linkage is in curvilinear translation

Remaining at the same angle while all points on it describe identical circular paths

Crank Rocker Input toWindshield Wiper

In above case,R7=0;Design variable:t3,t4,t5,t6,t7

R2Cos(Ө2) + R3Cos(Ө3) + R4Cos(Ө4) + R5Cos(Ө5) = ACos(ӨA)R2Sin(Ө2) + R3Sin(Ө3) + R4Sin(Ө4) + R5Sin(Ө5) = ASin(ӨA)

R2

R3

R4

R5

A

R2Cos(Ө2) + R3Cos(Ө3) + R6Cos(Ө6) + R7Cos(Ө7) = BCos(ӨB)R2Sin(Ө2) + R3Sin(Ө3) + R6Sin(Ө6) + R7Sin(Ө7) = BSin(ӨB)

R2

R3

R7

B

R6

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 Ө2 4

Ө3 (Ө3, Ө5, Ө6, Ө7)

Ө4 or = Ө6 +180o

Ө5

Ө6

Ө7

0 – 360(deg)

Windshield Wiper Animation

Wiper Angle Sweep

-Figures show the three angles swept by the windshield wiper for 3 chosen input link lengths

Analysis of Windshield Wiper

Delta Theta vs. Length of Input link

0

5

10

15

20

25

30

35

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Input Link Length (inch)

De

lta

Th

eta

(d

eg

ree

)

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)

How Windshield Wipers Work. (2006) In: How Stuff Works Available: <http://auto.howstuffworks.com/wiper2.htm> [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. 2006.

How soft top convertible works. (2006) In: How Stuff Works Available: <http://auto.howstuffworks.com/wiper2.htm> [2007, October 12].

Pantographs.(2006) In: Wikipedia The Free Encyclopedia:

<http://en.wikipedia.org/wiki/Pantograph> [2007, October 12].

• Questions?