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Design Basics

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Principles of Linear Motion Newtons First Law If the net force acting on an object is zero: l An object at rest tends to remain at rest l An object in motion tends to remain in motion. Velocity = Distance / Time (ft/sec; miles/hr) Acceleration = Velocity / Time (ft/sec/sec or ft/sec 2 )

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Principles of Linear Motion Newtons Second Law If the net force acting on an object is not zero: l Object will accelerate in proportion to, and in the direction of, the net force, l Object will accelerate in inverse proportion to its mass. Force = Mass x Acceleration This implies: For swifter response l More Powerful prime movers (motors, pumps) must be used l Total weight of object must be minimized

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Principles of Rotary Motion Torque = Force x Radius Torque = Belt Pull x Radius Units: (lb.in.; lb.ft.)

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Principles of Work Work = Force x Distance Units: (in.lb; ft.lb.) NOTE: The distance traveled is independent of the Radius.

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Power / Horsepower hp = (Q ft )(rpm) / 5252 hp = (Q in )(rpm) / 63025 Power = Work / Time 1 Horsepower = 550 ft.lb./sec. Where: hp = Horsepower rpm = rev. per minute Q ft = Torque (lb.ft.) Q in = Torque (lb.in.)

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Torque / Speed Relationships For a Constant HP Load: Torque Increases as Speed Decreases OR Torque Decreases as Speed Increases This implies: If you want more pushing power (higher torque) you will need to sacrifice speed ie robot will move slower. hp = (Q. )(rpm) 63025 {Q in lb.in.} {Torque from 1 hp @ 1750 = 3 lb.ft.}

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Constant Torque vs. Constant HP Variable Speed Prime Movers Constant Torque (Reduced h.p. With Reduced Speed) l D.C. Motors ©Constant torque up to base speed (name plate speed) l A.C. Frequency Controlled Motors ©Constant torque up to 60 hz l Hydraulic Motors ©Configured for constant torque or constant HP

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Constant Torque vs. Constant HP Variable Speed Prime Movers Constant Horsepower (Increased Torque With Reduced Speed) l l D.C. Motors © Constant HP Above Base Speed (Name Plate Speed) l l A.C. Frequency Controlled Motors ©Constant HP Above 60 hz l l Hydraulic Motors ©Configured For Constant HP Or Constant Torque l l Mechanical Variable Speed Drives ©Constant HP Up To Maximum Power Capability

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Transmission Comparision Chart TypeRoller ChainTooth BeltV BeltSpur Gear SynchronizationGreatGreatPoorGreat Transmission EfficiencyGreatGreatPoorGreat Anti-ShockFairGoodGreatPoor Noise/VibrationFairGoodGreatPoor Surrounding Condition Avoid Water, Dust Avoid Heat, Oil, Water, Dust Avoid Water, Dust Space Saving (High Speed/ Low Load)PoorGreatGoodGood Space Saving (Low Speed/ High Load)Great Compact Fair Heavy Pulley Poor Wider Pulley Good Less Durability Due to Less Engagement Lubrication Poor Required Great Great No LubeGreat No Lube Poor Required Layout FlexibilityGreatGoodFairPoor Excess Load onto BearingGreatFairPoorGreat

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l Chain Drive is more suitable to long-term continuous running and power transmission with limited torque fluctuation. Gears are more fit to reversing or intermittent drives. l The greater the shaft center distance, the more practical the use of chain and belt, rather than gears. l Speed reduction/increase of up to seven to one can be easily accommodated. l Chain can accommodate long shaft-center distances (less than 4 m), and is more versatile. l It is possible to use chain with multiple shafts or drives with both sides of the chain. l Standardization of chains under the American National Standards Institute (ANSI), the International Standardization Organization (ISO), and the Japanese Industrial Standards (JIS) allow ease of selection. l It is easy to cut and connect chains. l The sprocket diameter for a chain system may be smaller than a belt pulley, while transmitting the same torque. l Sprockets are subject to less wear than gears because sprockets distribute the loading over their many teeth. Transmission Selection Criteria

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Mechanical Engineering: Motion Transmission

Mechanical Engineering: Motion Transmission

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