![cover image](https://wikiwandv2-19431.kxcdn.com/_next/image?url=https://upload.wikimedia.org/wikipedia/commons/thumb/7/7f/Watts_Parallel_Motion_Linkage.gif/640px-Watts_Parallel_Motion_Linkage.gif&w=640&q=50)
Parallel motion linkage
Six-bar straight-line mechanism / From Wikipedia, the free encyclopedia
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This article is about parallel motion in mechanics. For parallel motion in music, see Contrapuntal motion.
In kinematics, the parallel motion linkage is a six-bar mechanical linkage invented by the Scottish engineer James Watt in 1784 for the double-acting Watt steam engine. It allows a rod moving practically straight up and down to transmit motion to a beam moving in an arc, without putting significant sideways strain on the rod.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/7/7f/Watts_Parallel_Motion_Linkage.gif/640px-Watts_Parallel_Motion_Linkage.gif)
Dimensions (unit lengths a, b):
Link 2: a + a
Links 3 & 5: b + b, 2b
Links 4 & 6: a
Vertical distance between ground joints ≈ 2bHorizontal distance between ground joints ≈ 2a
Thus, link 1 (total distance between ground joints)