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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.
The linkage actually used by Watt (also invented by him) in his later rotary beam engines was called the parallel motion linkage, a development of "Watt's linkage", but using the same principle. The piston of the engine is attached to the central point of the linkage, allowing it to act on the two outer beams of the linkage both by pushing and ...
Linkage mobility Locking pliers exemplify a four-bar, one degree of freedom mechanical linkage. The adjustable base pivot makes this a two degree-of-freedom five-bar linkage. It is common practice to design the linkage system so that the movement of all of the bodies are constrained to lie on parallel planes, to form what is known as a planar ...
The exception in this list is Watt's parallel motion, which combines Watt's linkage with another four-bar linkage – the pantograph – to amplify the existing approximate straight line movement. It is not possible to create perfectly straight line motion using a four-bar linkage, without using a prismatic joint. Watt's linkage (1784)
Six-bar linkage from Kinematics of Machinery, 1876. In mechanics, a six-bar linkage is a mechanism with one degree of freedom that is constructed from six links and seven joints. [1] An example is the Klann linkage used to drive the legs of a walking machine. In general, each joint of a linkage connects two links, and a binary link supports two ...
Another important invention, one which Watt was most proud of, was the parallel motion linkage, which was essential in double-acting engines as it produced the straight line motion required for the cylinder rod and pump, from the connected rocking beam, whose end moves in a circular arc. This was patented in 1784.
To bridge the conflicting actions of the beam and the piston, Watt developed his parallel motion. This device used a four bar linkage coupled with a pantograph to produce the required straight line motion much more cheaply than if he had used a slider type of linkage. He was very proud of his solution.
In the study of mechanisms, a four-bar linkage, also called a four-bar, is the simplest closed-chain movable linkage. It consists of four bodies, called bars or links, connected in a loop by four joints. Generally, the joints are configured so the links move in parallel planes, and the assembly is called a planar four-bar linkage. Spherical and ...