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// Workers AI · dad joke modeWhat did the straight-line mechanism say? I'm on the right track.

From Wikipedia, the free encyclopedia
(Redirected from Straight line linkage)
An animation of Watt's Linkage.
An animation of Roberts Linkage.
Sarrus Linkage.
Parts of the same color are the same dimensions.
Peaucellier-Lipkin Inversor.
Links of the same color are the same length.

A straight-line mechanism is a mechanism that converts any type of rotary or angular motion to perfect or near-perfect straight-line motion, or vice versa. Straight-line motion is linear motion of definite length or "stroke", every forward stroke being followed by a return stroke, giving reciprocating motion. The first such mechanism, patented in 1784 by James Watt, produced approximate straight-line motion, referred to by Watt as parallel motion.

Straight-line mechanisms are used in a variety of applications, such as engines, vehicle suspensions, walking robots, and rover wheels.[citation needed]

History

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In the late eighteenth century, before the development of the planer and the milling machine, it was extremely difficult to machine straight, flat surfaces. During that era, much thought was given to the problem of attaining a straight-line motion, as this would allow the flat surfaces to be machined. To find a solution to the problem, the first straight-line mechanism was developed by James Watt, for guiding the pistons of early steam engines. Although it does not generate an exact straight line, a good approximation is achieved over a considerable distance of travel.

Perfect straight-line linkages were later discovered in the nineteenth century, but they were not as needed, as by then other techniques for machining had been developed.[citation needed]

List of linkages

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Approximate straight-line linkages

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These mechanisms often use four-bar linkages as they require very few pieces. These four-bar linkages have coupler curves that have one or more regions of approximately perfect straight-line motion. 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 perfect straight-line motion using a four-bar linkage, without using a prismatic joint.

Perfect straight-line linkages

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Eventually, perfect straight line motion was achieved. The Sarrus linkage was the first perfect linear linkage, made in 1853. However, it is a spatial linkage rather than a planar linkage. The first planar linkage would not be made until 1864.

Currently, all planar linkages which produce perfect linear motion utilize the inversion around a circle to produce a hypothetical circle of infinite radius, which is a line. This is why they are called inversors or inversor cells. The simplest solutions are Hart's W-frame–which uses 6-bars–and the quadruplanar inversors–Sylvester-Kempe and Kumara-Kampling, which also use 6-bars.

The Scott Russell linkage (1803) translates linear motion through a right angle, but is not a straight-line mechanism in itself. The Grasshopper beam/Evans linkage, an approximate straight-line linkage, and the Bricard linkage, an exact straight-line linkage, share similarities with the Scott Russell linkage and the Trammel of Archimedes.

Compound eccentric mechanisms with elliptical motion

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These mechanisms use the principle of a rolling curve instead of a coupler curve and can convert continuous, rather than just limited, rotary motion to reciprocating motion and vice versa via elliptical motion. The straight-line sinusoidal motion produces no second-order inertial forces, which simplifies balancing in high-speed machines.

  • Trammel of Archimedes. Originally an ellipsograph. Also known as the double-slider mechanism, it uses the fact that a circle and a straight line are special cases of an ellipse. It is based on much the same kinematic principle as Cardan's straight line mechanism (above) and could be considered as a spur gear with two teeth in a ring gear with four teeth. It has been used in the Baker-Cross engine.[3] It has been used in inverted form in Parsons' steam engine[4] and can still be found today in further inversions as the Oldham coupling and the scotch yoke mechanism.
MultiFAZE eccentric gear train for a 3-cylinder radial engine.[5]


Stiller-Smith eccentric gear train, core features, framed.[6]
  • MultiFAZE is an acronym for Multiple Fixed Axis Shaft Compound Eccentric. It refers to a mechanism that uses an eccentric gear train to interconvert reciprocating and rotary motions. History: A patent application for the mechanism[7] was filed by Michael Mayer as inventor in 1982. The application was published on 15 March 1984. On 6 July of the same year, West Virginia University (USA) filed a provisional patent application[8] for an engine with the same eccentric gear train, giving Profs. Alfred H. Stiller and James E. Smith as the inventors, without citing the Mayer patent. The MultiFAZE mechanism essentially became the Stiller-Smith mechanism. Stiller claimed to have got the idea from a “do-nothing machine”,[9] but the connection is not immediately apparent. The belt or chain drive[10] proposed as an alternative to the gear train suggests a poor grasp of basic mechanical principles. The mechanism became the subject of Prof. Smith's dissertation[11] and the start of his career. Two experimental Stiller-Smith engines were built at the University[12], accompanied by much publicity[9] and the hype typical of many a novel engine design.[13][14] However, most of the work was theoretical, centring on computer simulations and analyses of the mechanism. This spawned a string of technical reports and conference papers[15] and brought the University's College of Engineering its first million-dollar grant.[9] On 13 November 1989 the US Congress approved a grant of $1,760,000 for research into the engine's potential for future combat vehicles.[16]
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Approximate straight-line linkages

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Parts/links of the same color are the same dimensions.

Perfect straight-line linkages

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Parts/links of the same color are the same dimensions.

Tusi couple, elliptical motion: versions and inversions

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Compound eccentric mechanisms with elliptical motion

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See also

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Notes

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  1. 1 2 3 4 5 6 7 8 9 Linkage has unstable positions that are not accounted for. Mitigations for said unstable positions are not shown for the sake of clarity.

References

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  1. ↑ Kempe, Alfred Bray (1877). How to Draw a Straight Line: A Lecture on Linkages. Macmillan and Company. ISBN 978-1-4297-0244-7. {{cite book}}: ISBN / Date incompatibility (help)
  2. ↑ Artobolevsky, Ivan Ivanovich. Mechanisms in modern engineering design. ISBN 978-5-9710-5698-0.
  3. ↑ Four-cylinder, Four-cycle Engine With Two Reciprocating Components, A.J.S Baker, M.E Cross, The Institution of Mechanical Engineers, Automobile Division, Volume 188 38/74
  4. ↑ Parsons' epicyclic engine
  5. ↑ From Patent No. DE 3232974
  6. ↑ From Patent No. US 4641611. See also publications by J. Smith et al, e.g. Complete Balancing of the Stiller—Smith Engine: 4, 8, 12, 16 or More Cylinders
  7. ↑ Patent No. DE 3232974
  8. ↑ See Patent No. US 4641611
  9. 1 2 3 Chemical Engineering at West Virginia University: A Living History, page 79
  10. ↑ Part No. 40, front page, sheets 1, 4, claims 13, 15 of patent No. US4641611
  11. ↑ Smith, James E. "The dynamic analysis of an elliptical mechanism for possible application to an internal combustion engine with a floating crank". Dissertation. West Virginia University. 1984.
  12. ↑ The Stiller-Smith Engine - The Dewelopment (sic) of a New Environment for High-Tech Materials
  13. ↑ WVU professors design revolutionary engine, UPI Archives
  14. ↑ Clean engines - A combination of advanced materials and a new engine design, James E. Smith, Randolph A. Churchill, Jacky Prucz, West Virginia University, 1988
  15. ↑ See, for example, Researchgate(1) and Researchgate(2)
  16. ↑ November 13, 1989 CONGRESSIONAL RECORD - HOUSE Vol. 135 Part 20, P. 28453
  • Theory of Machines and Mechanisms, Joseph Edward Shigley
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