Introduction: The slip and creep in the belt or rope drives is a common phenomenon, in the transmission of motion or power between two shafts. The effect of slip is to reduce the velocity ratio of the drive. In precision machine, in which a definite velocity ratio is importance (as in watch mechanism, special purpose machines..etc), the only positive drive is by means of gears or toothed wheels.
TYPES OF GEARS
According to the position of axes of the shafts.
3.Rack and Pinion
c. Non-intersecting and Non-parallel
worm and worm gears
• Teeth is parallel to axis of rotation
• Transmit power from one shaft to another parallel shaft
• Used in Electric screwdriver, oscillating sprinkler, windup alarm clock, washing machine and clothes dryer
• The teeth on helical gears are cut at an angle to the face of the gear
• This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears
• One interesting thing about helical gears is that if the angles of the gear teeth are correct, they can be mounted on perpendicular shafts, adjusting the rotation angle by 90 degrees
To avoid axial thrust, two helical gears of opposite hand can be mounted side by side, to cancel resulting thrust forces
Herringbone gears are mostly used on heavy machinery.
Rack and pinion
• Rack and pinion gears are used to convert rotation (From the pinion) into linear motion (of the rack)
• A perfect example of this is the steering system on many cars
• Bevel gears are useful when the direction of a shaft’s rotation needs to be changed
• They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well
• The teeth on bevel gears can be straight, spiral or hypoid
• locomotives, marine applications, automobiles, printing presses, cooling towers, power plants, steel plants, railway track inspection machines, etc.
WORM AND WORM GEAR
• Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater
• Many worm gears have an interesting property that no other gear set has: the worm can easily turn the gear, but the gear cannot turn the worm
• Worm gears are used widely in material handling and transportation machinery, machine tools, automobiles etc