Methods of exerting forces and displacements introduction to the design of „basic machine”

Levers Drawings taken from: „Give me point of support and I will lift the Earth” Galileo Is this true?

Power screws (screw gears) Torque that has to be applied to the nut (or screw head) in order to obtain force P On the other side: M n = F hand x L wrench 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

Power screws Various configuration of mechanisms Compound and differential screws (Hunter’s)

Mechanizmy śrubowe Evaluating torque and force

Design of a power screw Material selection + limited specific load: Cast iron 8-30 MPa brass 8-15 MPa bronze MPa Aluminium bronze10-40 MPa seizure of the surfaces excessive wear Screw under tension - break Screw under compression- exceeding allowable stress - flexural buckling (wyboczenie) Selection of thread 1. 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

Rope mechanisms Pulley block (compound pulleys)

Hydraulic devices

Rack and pinion mechanism

Transformation of rotational motion into linear motion Cam mechanisms Crank mechanism Rack and pinion mechanism Push rod Cam follower crankshaft

Transmissions Gear transmision Belt transmision