harmonic derives

when shafts are intersecting 
1.straight bevel gears
2.spiral bevel gears
Bevel gears are gears where the axes of the two shafts intersect and the tooth-bearing faces of the gears themselves are conically shaped.

1.Straight bevel gear

 Straight bevel
 have conical pitch surface and teeth are straight and tapering towards apex.straight bevel gears are used to transmit the power when the shafts are intersecting at an specific angle.they are basically used for perpendicular shafts but can designed for any specific angle.
2Q== harmonic derives 
spiral bevel gears
spiral bevel gears are use when the direction of the rotational shafts is required. these type of gears are mainly applicable in differential.design of the teeth are modified in the   helical form.the teeth are curve so the engagement of the teeth are much gradual.this mostly  reduces the noise and vibration in the system.however the design of the spiral gear is similar as the helical gears but the they have different functioning
1.helical gears are used to connect the parallel shafts but spiral bevel gears are used to connect two skew shafts.
2.helical gear is the part of cylinder but spiral bevel gears are the part of  Hyperboloid.
9k= harmonic derives
when the shafts are skew 
When the shaft s neither parallel nor intersecting …is known as skew shafts.                              1.Worm gears
2.Hypoid gears
1.Worm gears               
                                                                 
                                                                   

2Q== harmonic derives 

these are mainly used for large speed reduction.in this type of gear a screw type gear which is also known as worm on which the teeth are projected and another is a wheel which is also known as wheel.here the driving element is screw and driven element is helical wheel.
images?q=tbn:ANd9GcQciXIht16blvb2pVOkensjPWkao6JoVTmmt-MOp8aSt7ClLVxgSw harmonic derives

Advantages of Worm Gears

  1. Worm gear drives operate silently and smoothly.
  2. They are self-locking.
  3. They occupy less space.
  4. They have good meshing effectiveness.
  5. They can be used for reducing speed and increasing torque.
  6. High velocity ratio of the order of 100 can be obtained in a single step.

Disadvantages of Worm Gears

  1. Worm gear materials are expensive.
  2. Worm drives have high power losses and low transmission efficiency.
  3. They produce a lot of heat.

Applications of Worm Gear Drives:

Worm drives are used in:

  1. Steering system and Gate control mechanisms
  2. Hoisting machines
  3. Automobile steering mechanisms
  4. Lifts
  5. Conveyors
  6. Presses
2.Hypoid gears
images?q=tbn:ANd9GcTG5DDi8njbY7RyaiuZWk6JSz-RM-Zjmd5eMn6Nh1nciL3i3_4V harmonic derives
Hypoid gears are common in truck drive differentials, where high torque and an offset pinion are valued. However, an offset pinion does expend some mechanical efficiency. Hypoid gears are very strong and can offer a large gear reduction. Due to their exclusive arrangement, hypoid gears are typically produced in opposite-hand pairs (left and right handedness).

A hypoid gear is a style of spiral bevel gear whose main variance is that the mating gears’ axes do not intersect. The hypoid gear is offset from the gear center, allowing unique configurations and a large diameter shaft. The teeth on a hypoid gear are helical, and the pitch surface is best described as a hyperboloid. A hypoid gear can be considered a cross between a bevel gear and a worm drive.

Hypoid Gear – YouTube

                                  https://www.youtube.com/watch?v=nbaGh8aosEk

 

  Harmonic Drives

Harmonic drives are the special type of  gear system which is efficiently used to overcome the issues in normal or traditional types of gear system.these are invented  in 1957 by c.w musser.Harmonic drives are the strain wave gear.they are used in  large speed reduction in lower volume.

220px-Harmonic_drive_animation harmonic derives

Harmonic Drive – YouTube

https://www.youtube.com/watch?v=q1v7a0jsp1I

 

 

Mechanism

there are  some basic components

1.Wave generator
2.Flex spline
3Dynamic spline
4.circular spline
Wave Generator

it consist of a sun gear and two planet gears.sun gear is connected to the motor shaft and the planet gears are elastically deformable which are  internally engage with the flex spline.flexspline has outer teeth so it can also engage with circular spline and Dynamic spline.the shape of the wave generator is ellipse.

 Flex spline
The flexspline is made of special steel with a higher resistance to fatigue. these are also elastically deformable ring type gears which either has inner or outer teeth.it adopt the elliptical shape of the wave generator. these are externally engage with the circular or dynamic spline.

 circular spline
 circular spline has internal teeth.the difference between circular and flex spline is that circular spline is circular and the shape of the flex spline is elliptical.the circular spline keep two gear more than the flex spline.
 
 Dynamic spline
The Dynamic Spline is an internally toothed ring gear with the same number of teeth as the Flexspline. This component rotates in the same direction and with the same speed as the Flexspline and is used as output element when the gear is used as a speed reducer. 

principle of operation 
in this operation the wave generator acts as input element.because we know that the shape of  the wave generator is elliptical so it deforms the flex spline into the elliptical shape and so this is engage with both  circular and dynamic spline.in above moving image you can understand that as the planets are rotate in the clockwise direction then it press the elastical deformable  flexspline into the tooth of the fixed circular spline.
                                       
Because the Flexspline possesses two teeth less than the Circular Spline, for each 180° clockwise movement of the Wave Generator, the Flexspline moves counterclockwise by one tooth relative to the Circular Spline. Each complete clockwise rotation of the Wave Generator results in the Flexspline moving counterclockwise by two teeth from its previous position relative to the Circular Spline. The Dynamic Spline rotates in the same direction and with the same speed as the Flexspline and is used as the output element.

Characteristic  of the wave gear system
1.there is no backlash
2 .it light in weight
3.they are more efficient.The mating portion of each tooth is subjected to very little slide motion. Therefore, motion loss due to friction is reduced substantially. This is why the Harmonic Drive can maintain a high level of efficiency, allowing for the down sizing of driving motors as a result.
4.they have high torque capability
5.high gear reduction is possible in low volume space.
6.coaxial input and output shafts.
7. excellent repeatability when repositioning inertial loads.
8.small numbers of components and ease of assembly.
9 .Vibration free operation. With the Harmonic Drive, quiet and vibration-free operations are possible because the teeth do not come into rolling contact with one another, and since the circumferential speed of each tooth is low, the teeth provide a well-balanced force.
 

disavantage of the wave gear system
during the lower torque  region it include a tendency  for “Wind up”.
 


Application of the harmonic drive

  • Robotics
    Harmonic Drives offer robot manufacturers many benefits including zero backlash, high positional accuracy, low vibration and a compact design.   They can be used in any of the robot axes and their light weight design contributes minimal weight to the robotic arm which increases robot payload capacity.
  • Machine Tools
    Harmonic drives allow accurate control of the motions for axis positioning and for tool changing.
  • >

  • Medical
    Applications using harmonic drives include patient beds, rehabilitation equipment, and MRI / Cat scan gantries.
  • Military Aerospace
    The Harmonic Drives are used to accurately rotate and tilt the antennas and arrays.   They are also used for driving lunar vehicle motions and positioning aerials and telescopes e.g. Harmonic drives are used in the Hubble Telescope.


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