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MACHINE ELEMENTS AND DRIVES |
1.1 INTRODUCTION TO DRIVES
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In a machine, drives are required to transmit power from electric motor (usually) to various elements and from one element to others so that the various elements could perform their desired operations. Between any two elements of a machine, the one which drives the other is called ‘Driver’; and the other one is termed ‘Driven’. The power/motion is transmitted by means of various drives such as belts, chains and gears. The machine designer has the options of selecting the nature/type of drives. Different drives have certain advantages and limitations. The following factors have to be considered in selecting the natures of drives especially, gears, belts and chains: |
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Space constraint in housing the driver and driven elements. It is related to availability of space in the machine to house the drives. The compactness of the whole machine puts a limit on the availability of space in the machine. |
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Accuracy of speeds to be transmitted. In certain operations, the speed transmitted to an element must be very accurate. The speed variation must be kept within a very narrow limit due to process/product requirement. |
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The level of noise the drive system generates and that can be tolerated in the operating environment around the machine. |
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The level of vibrations/shocks the drives produce and their acceptability in terms of efficient functioning of the machines and quality of output from the machines. |
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Manufacturing accuracies of the drives and the cost associated with them. |
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The construction of flat-belt, v-belt, round belt, toothed belt, chain drives and various types of gears, analysis of forces, torque and power transmission, characteristics and applications of them are discussed in modules 2 to 5. The comparisons of these drives are also discussed. These modules help the reader on selecting a right type of drive for driving a specific machine element. |
The belts must be kept under required tension in order transfer optimum power. Various methods of controlling the belt tensions such as movable-swinging motor and tension pulley are discussed in module 2. The module 3 discusses about chain drives. The classification of chain drives, geometrical relationships, inherent speed variation in chain drives (polygonal effect), characteristics, selection and applications in textile machines are also covered in the module 3. |
Spur gears are extensively used in textile machines. The nomenclature used in spur gears and relationships between design parameters of spur gears, requirement of constant speed ratio (conjugate action), generation of involute teeth on spur gear, and effect of interference in gears on periodic drafting waves on fibre strands using roller drafting (drawing, roving and ring spinning machines), and elimination of interference are discussed in module 4. Derivatives of spur gears as internal gears, rack-and-pinion and their applications in textile machines are also discussed in this module. Parallel helical gears, crossed helical gears, different bevel gears and worm gears are used in textile machines. The geometry of these gears, thrust load acting on shaft mounted with these gears and applications are discussed in module 5. Gear trains (train of gears) widely used on machines to transfer motion from one element to many elements. Module 6 deals with many types of gear trains. |
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