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Similar to types of gears - bearings
types of gears - bearings
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- 2. Gears • Rugged • Durable •Can transmit power with up to 98% efficiency • Long service life
- 3. Motors • Motors convert electricalenergy to mechanical energy. • Mechanical energy moves our robot • Motors drive the gears http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LR9520&P=DS
- 4. Gears – Spur • Flat •Pinion – Bevel • Crown – Worm – Rack and Pinion – Differential www.mathworks.com
- 5. Gears • Toothed wheelsfixed to an axle. • Drive gear – connected to the input axle. • Driven gear – connected to the output axle. • Gear train – when an number of gears are connected together. Gear Ratio = Number of driven teeth (output) Number of driver teeth (input)
- 6. Gear and BearingAssemblies • Use as few views as possible – A full sectional view may be the only view necessary • Dimensions are normally omitted • Typically include balloons correlated with a parts list • May include torque data and lubricant information
- 7. Gear and BearingAssemblies
- 8. Applications of Gears •Control gears – long life, low noise, precision gears kinematic & stress analysis • Aerospace gears – light weight, moderate to high load kinematic & stress analysis • Power transmission – long life, high load and speed kinematic & stress analysis • Appliance gears – long life, low noise & cost, low to moderate load kinematic & some stress analysis • Toys and Small Mechanisms – small, low load, low cost kinematic analysis
- 9. Spur Gears – Straightteeth mounted on parallel shafts – Many used at once to create very large gear reductions • Flat • Pinion http://en.wikipedia.org/wiki/Gear#Worm_gear
- 10. Types of Gears KenYoussefi Mechanical Engineering Dept. 10 Spur gears – tooth profile is parallel to the axis of rotation, transmits motion between parallel shafts. Pinion (small gear) Gear (large gear) Internal gears – teeth are inclined to the axis of rotation, the angle provides more gradual engagement of the teeth during meshing, transmits motion between parallel shafts. Helical gears
- 11. Spur Gear Terminology •Teeth are straight and parallel to the gear shaft axis • Establish gear tooth profile using an involute curve • Basic rule: – No fewer than 13 teeth on the running gear and 26 teeth on the mating gear
- 12. Spur Gear Terminology •Pressure angle – 14.5°and 20°are standard • Diametral pitch • Gear accuracy – Maximum tooth-to-tooth tolerances allowed, as specified by the American Gear Manufacturers Association (AGMA) • Several additional formulas and specifications
- 13. Bevel Gears – Gearsthat mesh at an angle, usually 90° – Changes the direction of rotation http://science.howstuffworks.com/gear4.htm
- 14. Bevel Gears • Shaftsof the gear and pinion can intersect at 90°or any desired angle • Provide for a speed change between the gear and pinion, unless designed as miter gears
- 15. Types of Gears KenYoussefi Mechanical Engineering Dept. 15 Bevel gears – teeth are formed on a conical surface, used to transfer motion between non-parallel and intersecting shafts. Straight bevel gear Spiral bevel gear
- 16. Crown Gears – Specialform of bevel gear – Has right angles to the plane of the wheel http://www.plastic-gear-manufacturer.com/industrial-gear.htm
- 17. Worm Gears – Changesthe direction of turning motion by 90° – Decreases the speed of turning from screw to gear and increases the force http://blogs.toolbarn.com/brianm/labels/Tool%20Inner%20Workings.html
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- 19. Worm Gears • Usea worm and worm gear • Large speed reduction in a small space • Worm locks in place when not in operation
- 20. Rack and Pinion –Converts rotary motion to back and forth motion http://en.wikipedia.org/wiki/Gear#Worm_gear
- 21. Rack and Pinion •Spur pinion operating on a flat straight bar rack • Converts rotary motion into straight-line motion
- 23. Differential Gears – Splitstorque two ways, allowing each output to spin at a different speed http://nxtasy.org/wp-content/uploads/2006/08/Differential2-00.html
- 24. Spur Gears • Transmitmotion and power between parallel shafts • Two basic types: – External spur gears – Internal spur gears • Cluster gears
- 25. Spur Gears • Advantages: –Economical – Simple design – Ease of maintenance • Disadvantages: – Less load capacity – Higher noise levels
- 26. Helical Gears • Teethcut at an angle – Allows more than one tooth to be in contact
- 27. Crossed Helical Gears •Also known as: – Right angle helical gears – Spiral gears • Low load-carrying capabilities
- 28. Helical Gears • Carrymore load than equivalent-sized spur gears • Operate more quietly and smoothly • Develop end thrust – Can be eliminated using double helical gears, such as a herringbone gear
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- 30. Gear Assemblies – LEGO™Technic 1031 Gear Assembly Activity – Gearing up and Gearing down http://reprap.blogspot.com/2005_12_01_archiv
- 31. Cool Site • http://nxtasy.org/ –Includes plans! • NXT Aerial Ropeway • NXT Gymnast • NXTWay-G: Balancing with a Gyro Sensor February 19, 2007 Created by Dr. T.E. Varnado
- 32. GEARS-Wheel and Axel •Each gear in a series reverses the direction of rotation of the previous gear. The smaller gear will always turn faster than the larger gear.
- 36. Common Gear Materials •Cast iron • Steel • Brass • Bronze alloys • Plastic
- 37. Gear Selection andDesign • Often done through vendors’ catalogs or the use of standard formulas – American Gear Manufacturers Association (AGMA) • AGMA 2000-A88, Gear Classification and Inspection Handbook - Tolerances and Measuring Methods for Unassembled Spur and Helical Gears, including Metric Equivalents – American Society of Mechanical Engineers (ASME) • ASME Y14.7.1 Gear Drawing Standards - Part 1: For Spur, Helical, Double Helical and Rack • ASME Y14.7.2 Gear and Spline Drawing Standards - Part 2: Bevel and Hypoid Gears
- 38. Gear Train • Increaseor reduce speed • Change the direction of motion from one shaft to another
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- 40. Splines • Often usedwhen it is necessary for the gear or pulley to easily slide on the shaft • Can also be nonsliding • Stronger than keyways and keys
- 41. Intersecting Shafting Gears •Bevel gears • Face gears
- 42. Face Gears • Combinationof bevel gear and spur pinion, or bevel gear and helical pinion • Requires less mounting accuracy • Caries less load
- 43. Nonintersecting Shafting Gears •Crossed helical gears • Hypoid gears • Worm gears
- 44. Hypoid Gears • Offset,nonintersecting gear shaft axes • Very smooth, strong, and quiet
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- 47. Detailed Spur GearRepresentation
- 48. Showing a GearTooth Related to Another Feature
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- 50. Gear Trains • Transmitmotion between shafts • Decrease or increase the speed between shafts • Change the direction of motion
- 51. Gear Ratio • Importantwhen designing gear trains • Applies to any two gears in mesh • Expressed as a proportion, such as 2:1 or 4:1
- 52. Rack and PinionPrint
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- 54. Plastic Gears • Generallydesigned in the same manner as gears made from other materials • Glass fiber adds reinforcement and reduces thermal expansion • Additives that act as built-in lubricants and provide increased wear resistance: – Polytetrafluoroethylene (PTFE) – Silicones – Molybdenum disulphide
- 55. Advantages of MoldedPlastic Gears • Reduced cost • Increased efficiency • Self-lubrication • Increased tooth strength with nonstandard pressure angles • Reduced weight • Corrosion resistance • Less noise • Available in colors
- 56. Disadvantages of MoldedPlastic Gears • Lower strength • Greater thermal expansion and contraction • Limited heat resistance • Size change with moisture absorption
- 57. Planetary Gear Trains- Example Ken Youssefi Mechanical Engineering Dept. 57 For the speed reducer shown, the input shaft a is in line with output shaft b. The tooth numbers are N2=24, N3=18, N5=22, and N6=64. Find the ratio of the output speed to the input speed. Will both shafts rotate in the same direction? Gear 6 is a fixed internal gear. Train value = (-N2 / N3)(N5 / N6) = (-24/18)(22/64) = -.4583 -.4583 = (ωL – ωarm) / (ωF – ωarm) = (0 – ωarm) / (1 – ωarm) ωarm = .125, reduction is 8 to 1 Input and output shafts rotate in the same direction d2 + d3 = d6 – d5
- 58. Harmonic Drive Ken Youssefi MechanicalEngineering Dept. 58 The mechanism is comprised of three components: Wave Generator, Flexspline, and Circular Spline. Wave Generator Consists of a steel disk and a specially design bearing. The outer surface has an elliptical shape. The ball bearing conforms to the same elliptical shape of the wave generator. The wave generator is usually the input. Flexspline The Flexspline is a thin-walled steel cup with gear teeth on the outer surface near the open end of the cup. Flexspline is usually the output. Circular Spline Rigid internal circular gear, meshes with the external teeth on the Flexspline.
- 59. Harmonic Drive Ken Youssefi MechanicalEngineering Dept. 59 Teeth on the Flexspline and circular spline simultaneously mesh at two locations which are 180o apart. As the wave generator travels 180o , the flexspline shifts one tooth with respect to circular spline in the opposite direction. ω Circular Spline = 0 ω Flexspline = output ωWave Generator = input The flexspline has two less teeth than the circular spline. Gear Ratio = - (Nflex spline)/ 2 , ,
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- 61. Bearings • Two largegroups: – Plain bearings – Rolling element bearings • Accommodate either rotational or linear motion
- 62. Plain Bearings • Oftenreferred to as: – Sleeve bearings – Journal bearings – Bushings • Operation is based on a sliding action between mating parts • Clearance fit between the inside diameter of the bearing and the shaft is critical
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- 64. Rolling Element Bearings •Common classes: – Ball bearings – Roller bearings
- 65. Ball Bearings • Typicallyhave higher speed and lower load capabilities than roller bearings • May have a shield or seal
- 66. Typical Ball Bearings •Single-row ball bearings • Double-row ball bearings • Angular contact ball bearings • Thrust bearings
- 67. Roller Bearings • Moreeffective than ball bearings for heavy loads
- 68. Bearing Codes • Typicallyspecify: – Material – Bearing type – Bore size – Lubricant – Type of seals or shields
- 69. Bearing Selection • Avariety of bearing types are available depending on use requirements • Common classes: – Light bearings – Medium bearings – Heavy bearings
- 70. Bearing Bore, OutsideDiameters, and Width
- 71. Shaft and HousingFits • Important consideration – Tight fits can cause failure of the balls, rollers, lubricant, or overheating – Loose fits can cause slippage of the bearing in the housing, resulting in overheating, vibration, or excessive wear
- 72. Shaft and HousingFits • General shaft fits – Shaft diameter and tolerance are the same as the bearing bore diameter and tolerance • General housing fits – Minimum housing diameter is .0001 larger than the maximum bearing outside diameter – Maximum housing diameter is .0003 larger than the minimum housing diameter
- 73. The Shaft Shoulderand Housing Shoulder Dimensions • Shoulders should be large enough to rest flat on the face of the bearing and small enough to allow bearing removal
- 74. Surface Finish ofShaft and Housing • Shafts under 2 inches (50 mm) in diameter: – 32 microinches (0.80 micrometer) • Shafts over 2 inches in diameter – 63 microinch (1.6 micrometer) • Housing diameter: – 125 microinch (3.2 micrometer)
- 75. Bearing Lubrication • Necessaryrequirement based on: – Type of operation, such as continuous or intermittent – Service speed in rpm (revolutions per minute) – Bearing load, such as light, medium, or heavy
- 76. Oil Grooving ofBearings • Grooves for the proper flow of lubrication to the bearing surface – Help provide the proper lubricant between the bearing surfaces and maintain cooling • Several methods available
- 77. Sealing Methods • Staticsealing • Dynamic seals • Gaskets • Molded lip packings • Molded ring seals – Labyrinth – O-ring seal – Lobed ring seal • Felt seals and wool seals
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