Ratchet movement

Manually adjusted screw or ratchet take-ups that adjust the position of the tail pulley to control belt tension can be used on relatively short, light duty conveyors. Automatic take-ups are used on conveyors over about 25 to 30 m long. The most common is the weighted automatic gravity take-up (see Fig. la). Other types of automatic take-ups have hydrauHc or pneumatic powered devices to adjust a snub pulley position and maintain a constant belt tension. The requited take-up movement varies according to the characteristics of the belt constmction and the belt length. Typically, take-up movements for pHed belts are 2% to 3% of the center distance between head and tail pulley, and about 0.5% for steel cable belts. The take-up movements requited for soHd woven belts are usually shorter because of the lower elastic stretch. Take-up requirements for a particular situation should be confirmed by the belt manufacturer. 

All of these devices show a certain degree of restriction in the movement of their molecular components, but rotation occurs randomly with no control over directionality. In an attempt to achieve directional motion Kelly investigated the dynamic behavior of a so-called molecular ratchet , 6 [21,22],... 

Indexing machines are characterized by a rigid chain of stations. The construction design depends mostly on the complexity of the product to be mounted. The main movements (drives for transfer systems) can be effected from an electrical motor via an adapted ratchet mechanism or cam and lever gears or can be implemented pneumatically and/or hydraulically. Secondary movements (clamping... 

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