Belts are used to mechanically link two or more rotating items. They may be used as a source of motion, to transmit power between two points, or to track relative movement. A belt may also be looped (or crossed) between two points so that the direction of rotation is reversed at the other point. Power transmission is achieved by specially designed belts and pulleys.
The demands on a belt drive system are large and this has led to many variations. The earliest was the Flat belt used with line shafting, it is a simple system of power transmission that was well suited to its time in history. The Industrial Revolution soon demanded more from the system as flat belt pulleys need to be carefully aligned to prevent the belt from slipping off, the flat belt also tends to slip on the pulley face when heavy loads are applied. Round belts are a circular cross section belt designed to run in a pulley with a circular (or near circular) groove. They are for use in low Torque situations and may be purchased in various lengths or cut to length and joined, either by a staple, glueing or welding (in the case of Polyurethane). The early sewing machines utilized a leather belt, joined either by a metal staple or glued, to great affect. V-belts (or wedge rope) are an early solution that solve the slippage and alignment problem. The V shape of the belt tracks in a mating groove in the pulley with the result that the belt cannot slip off, the belt also tends to wedge into the groove as the load increases (the greater the load, the greater the wedging action), improving the Torque transmission and making the vee belt an effective solution. They can be supplied at various fixed lengths or as a segmented section, where the segments are linked (spliced) to form a belt of the required length. Image:Timing_belt.jpg Timing_belts, (also known as Toothed, Notch or Cog) belts are a positive transfer belt and can track relative movement. These belts have teeth that fit into a matching toothed pulley. Correctly tensioned they have no slippage and are often used to transfer direct motion for indexing or timing purposes. The Camshaft of the automobile and Stepper_motors often utilize these belts.
Additional information and source: Belt