Gears have a rich history and have been used by many cultures throughout the ages. In the West, ancient Greek philosophers like Aristotle and Archimedes explored the possibilities and limitations of bronze and cast iron gears for transmitting rotary motion. A Greek inventor named Guticibis came up with a clever mechanism involving pins and pin wheels that allowed for precise movement, which he used in his engraving work about 150 BC. Later, in 100 BC, an Alexandrian inventor named Herren used gears in his odometer. Even the famous Roman architect Bidobis utilized gears in his waterwheel pulverizer in the first century AD.
The practical applications for gears continued to expand throughout the centuries, and by the 14th century, they were being used in clocks and watches. It is interesting to note that the principles of gears are still used today in modern technology, from automobiles to industrial machinery. The development of gears over time has greatly impacted the progress of civilization, enabling precise movements and increased efficiency in many areas of life.
The gear transmission system has a long history in ancient China. Herringbone gears were already present in the early Eastern Han Dynasty, while the Guide Car and Jili Drum Car, which were invented during the Three Kingdoms Period, used this technology for their operation. The water rotary continuous mill also adopted gears to transfer the power of the water wheel to the stone mill during the Jin Dynasty. The Tang Dynasty saw the creation of the water transport armillary sphere, which was described as utilizing gear transmission. Later on, in the Northern Song Dynasty, the complex gear system of the water transport instrument stage was used. In the Ming Dynasty, the Wu Bei Zhi recorded a type of rack and pinion transmission device.
Archaeological remains have shown the existence of gears, with an iron spike gear from the Warring States Period to the Western Han Dynasty era found in Anwuji in Hebei Province. Similarly, a 40-tooth bronze spur gear was unearthed in Renjiaya in Shanxi Province, dating back to the Qin Dynasty or the early Western Han Dynasty. It is believed that these gears may have been used for braking to prevent the axle from reversing.
A highly significant find was made when a pair of bronze herringbone gears were discovered in Hongqing Village in Shaanxi Province, indicating the use of this technology as far back as the early Eastern Han Dynasty. With both wheels having 24 teeth and a diameter of about 15mm, similar herringbone gears were also found in Hengyang and other areas. Overall, the gear transmission system was a vital part of ancient Chinese technology, resulting in remarkable inventions that significantly contributed to the development of civilization.
As early as 1694, the French scholar PHILIPPE DE LA HIRE introduced the idea of using the involute as the tooth profile curve. This concept was further expanded upon in 1733 by French engineer M CAMUS, who proposed that the common normal of the gear tooth contact point should pass through the center line node. CAMUS theorem, which emerged from the rolling motion of an auxiliary instantaneous center line along the pitch circle of both the larger and smaller gears, established that the tooth profile curves formed by the auxiliary tooth are conjugate to each other. This theorem delves into the meshing state of the two tooth surfaces and provides a clear understanding of the contact point trajectory.
In 1765, Swiss mathematician L. EULER developed the mathematical foundation for the analytical study of involute tooth profiles. His work elucidated the relationship between the curvature radius of the tooth profile curve and the position of the curvature center in meshing gears. SAVARY later built upon this method, resulting in the EU-LET-SAVARY equation. ROTEFT WULLS contributed to the application of involute tooth profiles and highlighted the advantage of constant angular speed ratio exhibited by involute gears when the center distance varies.
German engineer HOPPE, in 1873, introduced the concept of involute profiles for gears with different numbers of teeth when the pressure angle changes. This groundbreaking idea laid the groundwork for modern modified gears.