# Application of Four-Bar Mechanisms in Cars

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Application of Four-Bar Mechanisms in Cars
Windshield Wiper Soft Top Mechanism Group A Christopher Back Josephashwin 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

Motion of Mechanism

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

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

Dynamic Designer Convertible Animation

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

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

Dynamic Designer Windshield Wiper Animation

Design Variation Animation
Varying ???

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

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?

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

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 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?

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

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

How is the difference of Rear wiper?
Rear windshield wiper Single application of Four-bar mechanism Similar to