Drive belt
A belt is a loop of flexible material used to link two or more rotating shafts mechanically, most often parallel. Belts may be used as a source of motion, to transmit power efficiently, or to track relative movement. Belts are looped over pulleys and may have a twist between the pulleys, and the shafts need not be parallel.
In a two pulley system, the belt can either drive the pulleys normally in one direction (the same if on parallel shafts), or the belt may be crossed, so that the direction of the driven shaft is reversed (the opposite direction to the driver if on parallel shafts). As a source of motion, a conveyor belt is one application where the belt is adapted to carry a load continuously between two points.
The mechanical belt drive, using a pulley machine, was first mentioned in the text the Dictionary of Local Expressions by the Han Dynasty philosopher, poet, and politician Yang Xiong (53–18 BC) in 15 BC, used for a quilling machine that wound silk fibers on to bobbins for weavers' shuttles. The belt drive is an essential component to the invention of the spinning wheel. The belt drive was not only used in textile technologies, it was also applied to hydraulic powered bellows dated from the 1st century AD.
Belts are the cheapest utility for power transmission between shafts that may not be axially aligned. Power transmission is achieved by specially designed belts and pulleys. The demands on a belt-drive transmission system are huge, and this has led to many variations on the theme. They run smoothly and with little noise, and cushion motor and bearings against load changes, albeit with less strength than gears or chains. However, improvements in belt engineering allow use of belts in systems that only formerly allowed chains or gears.
Power transmitted between a belt and a pulley is expressed as the product of difference of tension and belt velocity:
where, T1 and T2 are tensions in the tight side and slack side of the belt respectively. They are related as
where, μ is the coefficient of friction, and α is the angle (in radians) subtended by contact surface at the centre of the pulley.
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