When did the gear first appear?
The common line of the gear contact point must be connected through the center of the joint. When an auxiliary instantaneous center line rolls along the instantaneous center line (pitch circle) of the big wheel and the small wheel respectively, the auxiliary tooth shape which is fixed with the auxiliary instantaneous center line is formed on the big wheel and the small wheel, and the two tooth profile curves are mutually conjugate.In 1765, Euler clarified the relationship between the radius of curvature of the tooth profile and the center of curvature of the meshing gear. Savary then perfected the relationship and formed the Euler-Savary equation now in use. In 1873, Hoppe pointed out the involute profile of the gear with different teeth in the change of the pressure angle, thus laying the foundation of the gear shift gear. At the end of the nineteenth Century, the principle of fan cut method was adopted to make the involute profile eventually overcome the cycloid shape and go into mass production.In 1907, Frank Humphris proposed the circular arc tooth shape. Arc tooth profile has some advantages in service life and reducing size, so it has gradually played a role in modern industry.
In the early gear, there was no requirement of the tooth shape and the pitch of the teeth, so the continuous driving wheel could not make the passive wheel rotate continuously. In order to solve this problem, the tooth development is arc, and by decreasing the tooth distance so that the passive wheel to obtain continuous rotation, which makes the drawing device gear mechanism is very popular.Because of the appearance and popularity of clocks and watches, the demand for gear constant speed transmission has come into being. The basic law of gear meshing:The instantaneous speed ratio of a pair of tooth profiles is equal to the normal line of the instantaneous contact point, and the center line is inversely proportional to the two segment line.Constant condition of transmission ratio:The common line of the two tooth profile at the point of contact must be connected to the center line at a fixed point.The determined tooth profile is theoretically infinite, and Olaf Roemer discussed the cycloid tooth profile in 1674, while the Philipp de la Hire proposed the involute tooth profile in 1694. In 1733, Camus proposed the famous Camus theorem:
Human use of gear has a long history, there are historical records China is the first country in the world to use gear, 400 BC to 200 years ago in ancient China began to use gear [citation needed] China Shanxi province unearthed bronze gear gear is one of the oldest ever found. Zhang Heng Seimoscope, ancient India cotton nuclear elimination mechanism (now in Berlin Museum) contains a gear mechanism. The specific inventor of the gear has no Shi Ke test, and Aristotle may be considered the first person to systematically discuss the institution. But Archimedes not only has detailed discussion of gear and worm gear, but Pappus even records that Archimedes passed a worm gear and nine gear mechanism, so that a few slaves pushed the big ship "Syrakusia" into the sea.
