Puheelimet

Puheelimet are a category of simple machines consisting of a wheel (sheave) with a groove through which a rope, belt, or chain runs. They are used to change the direction of a force and, in configurations with multiple supporting rope sections, to gain a mechanical advantage. In Finnish, the term puheelimet refers to pulley systems used to lift and move loads.

Pulley configurations can be broadly categorized as fixed, movable, and compound arrangements. Fixed pulleys are mounted to a frame and change the direction of the force but provide little or no mechanical advantage. Movable pulleys attach to the load, reducing the required input force. When fixed and movable pulleys are combined in block-and-tackle arrangements, higher mechanical advantage can be achieved, at the cost of increased rope length and complexity.

The mechanical advantage in an ideal pulley system equals the number of rope sections supporting the load; in practice, friction, rope elasticity, and bearing losses reduce the actual advantage. Components include the wheel or sheave, axle, rope or belt, and the supporting frame. Pulleys can be made from metal, wood, or composites, and grooves are sized for specific ropes or belts.

Common applications include cranes, elevators, theatre rigging, sailing equipment, and various lifting devices in industrial and consumer contexts. History shows widespread use since ancient times, with significant improvements in bearings, materials, and rope technology during the Industrial Revolution and in modern machinery. Regular maintenance involves inspecting rope condition, ensuring proper alignment, lubricating bearings, and replacing worn pulleys to preserve efficiency and safety.