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

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

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

Motion of Mechanism http://auto.howstuffworks.com/convertible2.htm

Motion of Mechanism

Position and Velocity analysis when R3= 30 in.

Position and Velocity analysis when R3= 35 in.

Position and Velocity analysis when R3= 40 in.

Dynamic Designer Convertible Animation 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.

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

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

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

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.

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

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

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)

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

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 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

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)

References 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].

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