Download - Methods of exerting forces and displacements introduction to the design of „basic machine”
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Methods of exerting forces and displacements
introduction to the design of „basic machine”
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Levers
Drawings taken from: „Give me point of support and I will lift the Earth”Galileo
Is this true?
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Power screws (screw gears)
Torque that has to be applied to the nut (or screw head) in order to obtain force P
2'
2 221DPtgP
dMMM Tp
n
On the other side:Mn = Fhand x Lwrench
Screw with a nut is a basic machine able to achieve a large force in the
screw by multiplying the force applied to the nut
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Power screwsVarious configuration of mechanisms
Compound and differential screws (Hunter’s)
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Mechanizmy śruboweEvaluating torque and force
2'
2 221DPtgP
dMMM Tp
n
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Design of a power screw
Material selection + limited specific load:Cast iron 8-30 MPabrass 8-15 MPabronze 10-30 MPaAluminium bronze 10-40 MPa
seizure of the surfaces excessive wear
Screw under tension - break Screw under compression - exceeding allowable stress
- flexural buckling (wyboczenie)
Selection of thread1. Thread type – trapezoidal thread (Acme) or butress threadlub niesymetr.2. Minor diameter
3. Thread pitch – standard values selected to obtain required mechanical advantage and self-locking properties.A possibility to use differential and summing mech.
- destruction of the bolt shank
- Destruction of the thread
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Rope mechanisms
Pulley block (compound pulleys)
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Hydraulic devices
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Rack and pinion mechanism
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Transformation of rotational motion into linear motion
Cam mechanisms
Crank mechanism
Rack and pinion mechanismPush rodCam follower
crankshaft
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TransmissionsGear transmision
Belt transmision