The parallel motion was a mechanical linkage invented by James Watt in 1784 for his double-acting steam engine. The locking pliers is an example of a four-bar, one degree of freedom mechanical linkage; or a five-bar, two DOF linkage when the adjustment screw is considered. ... This article is about the Scottish engineer and inventor. ... 1784 was a leap year starting on Thursday (see link for calendar). ... A steam engine, once known as a fire and air engine, is a heat engine that makes use of the thermal energy that exists in steam, converting it to mechanical work. ...

In previous engines built by Newcomen and Watt, the piston pulled one end of the walking beam downwards during the power stroke using a chain, and the weight of the pump pulled the other end of the beam downwards during the recovery stroke using a second chain, the alternating forces producing the rocking motion of the beam. In Watt's new double-acting engine, the piston produced power on both the upward and downward strokes, so a chain could not be used to transmit the force to the beam. Watt designed the parallel motion to transmit force in both directions whilst keeping the piston rod vertical. Thomas Newcomen (baptized February 24, 1664 – August 5, 1729), blacksmith and inventor was born in Dartmouth, Devon, England. ... piston + connecting rod In general, a piston is a sliding plug that fits closely inside the bore of a cylinder. ... A chain can be any of the following: Look up Chain in Wiktionary, the free dictionary a flexible connection through multiple rigid links; applications include: pulling (it cannot be used for pushing) power transmission, as in roller chains (e. ...

Schematic of Watt's parallel motion

See the diagram on the right. A is the journal (bearing) of the walking beam ABC, which rocks up and down about A. H is the piston, which is required to move vertically but not horizontally. The heart of the design is the three-bar linkage consisting of AB, BE and EG. Point G is fixed to the framework of the engine. As the beam rocks, point F (which is drawn to aid this explanation, but which is not visible on the machine itself) describes an elongated figure-of-eight in mid-air. Since the motion of the walking beam is constrained to a small angle, F describes only a short section of the figure-of-eight, which is quite close to a vertical straight line. Image File history File links James Watts parallel motion linkage of 1784. ...

It would have been possible to connect F directly to the piston rod, but this would have made the machine an awkward shape, with G a long way from the end of the walking beam. To avoid this, Watt added the parallelogram linkage BCDE to form a pantograph. This guarantees that F always lies on a straight line between A and D, and therefore that the motion of D is a magnified version of the motion of F. D is therefore the point to which the piston rod DH is attached. This page is about the duplication instrument. ...

As already noted, the path of F is not a perfect straight line, but merely an approximation. Watt's design produced a deviation of about one part in 4000 from a straight line. Later, in the 19th century, perfect straight-line linkages were invented, beginning with the Peaucellier-Lipkin cell of 1864. Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ... The Peaucellier-Lipkin linkage (or Peaucellier-Lipkin cell), invented in 1864, was the first linkage capable of transforming rotary motion into perfect straight-line motion. ... 1864 was a leap year starting on Friday (see link for calendar). ...

References

• Linkages article in Encyclopedia Britannia, 1958.
• Parallel Motion article in Encyclopedia Britannia, 1911.
• Robert Stuart, A Descriptive History of the Steam Engine, London, J. Knight and H. Lacey, 1824.