Introduction to flat pulleys:
Rotary motion is the most common type of motion for a shaft or an axle. One way in which an engineer uses rotary motion is by transmitting it from one shaft to another when the shafts are parallel. This can be done by using pulleys and belts. A pulley is a wheel which may or may not have a grooved rim.
The figure below shows a stacked vee pulleys and vee belts often used in car engines.
The main function of pulleys and belt systems are to transmit motion and torque from an engine to a machine. Various types of pulleys and belts are used on different machines. Machines used in the home, such as sewing machines, washing machines, spin dryers and vacuum cleaners. The picture below shows a flat belt and flat pulley used to transmit motion from an old heat engine.
In machines where a positive drive is essential and no slip between belt and pulleys can be accepted, a toothed belt and pulley is used. Toothed belts are mainly used for timing mechanisms, where quiet, positive (no slip) drive is required. The figure below shows a toothed belt and toothed pulleys used to drive a camshaft in a motor car engine.
Toothed belt and toothed pulleys
The gear wheel is a basic mechanism. Its purpose is to transmit rotary motion and force. A gear is a wheel with accurately machined teeth round its edge. A shaft passes through its center and the gear may be geared to the shaft. Gears are used in groups of two or more. A group of gears is called a gear train. The gears in a train are arranged so that their teeth closely interlock or mesh. The teeth on meshing gears are the same size so that they are of equal strength. Also, the spacing of the teeth is the same on each gear. An example of a gear train is shown below.
Single gear gear train
When two spur gears of different sizes mesh together, the larger gear is called a wheel, and the smaller gear is called a pinion. In a simple gear train of two spur gears, the input motion and force are applied to the driver gear. The output motion and force are transmitted by the driven gear. The driver gear rotates the driven gear without slipping.
The wheel or the pinion can be the driver gear. It depends on the exact function the designer wishes the mechanism to fulfill. When two spur gears are meshed the gears rotate in opposite directions, as shown in the figure below.
Wheel and pinion
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