DC Motor Operation ME350 Current runs through conductor >Armature winding(电枢绕组) Winding placed in magnetic field >Generates a force =Causes it to rotate Armature Magnets (coil) Comutator (rotates) Brushes (stationary)
11 ME 350 DC Motor Operation • Current runs through conductor ¾Armature winding（电枢绕组） • Winding placed in magnetic field ¾Generates a force =Causes it to rotate
Mechanical“Brushes ME350 Armature Magnets (coil) Axis Comutator (rotates) Brushes (stationary) Brushes(电刷)and commutator(换向器)supply and switch current to armature while it rotates 12
12 ME 350 Mechanical “Brushes” Brushes(电刷) and commutator (换向器) supply and switch current to armature while it rotates
Electromotive Force ME350 A voltage is induced in a wire moved in a magnetic field >Generators(发电机) emd=(y×B)·l Induced Velocity of wire(m/s) voltage (volt) eind is also called electromotive force(EMF感应电动势) eind =vBl (7=the wire length) Vhat happens if a“free” current-carrying wire is placed in a magnetic field?
13 ME 350 • A voltage is induced in a wire moved in a magnetic field ¾Generators（发电机） B + + + v eind • l (l = the wire length) = ×Bv )( Induced voltage (volt) Velocity of wire (m/s) l --- eind =vBl eind is also called electromotive force (EMF感应电动势) eind What happens if a “free” current–carrying wire is placed in a magnetic field? Electromotive Force
Linear DC Motor ME350 i=ViR (Ohm's Law) B B is constant When the switch is on,the wire will experience a sudden increase of force from 0 to F v will increase. eind will be induced in the direction opposite to i. i will decrease F will decrease. Eventually v reaches to a v will decrease. constant velocity. 14
14 ME 350 Linear DC Motor R Vin i i e i ind l F, v x x x x B i = Vin/R (Ohm’s Law) B is constant When the switch is on, the wire will experience a sudden increase of force from 0 to F. v will increase. eind will be induced in the direction opposite to i. i will decrease. F will decrease. v will decrease. Eventually v reaches to a constant velocity
Linear DC Motor under External Load ME350 At steady-state,apply Fioad to slow down the wire. The net force will decrease.F-Foad v will decrease. eind will decrease. i will increase. F will increase. v will increase. Again,v eventually reaches a constant velocity.Vnew <v 15
15 ME 350 Linear DC Motor under External Load • At steady-state, apply Fload to slow down the wire. The net force will decrease. F - Fload v will decrease. i will increase. v will increase. F will increase. eind will decrease. Again, v eventually reaches a constant velocity. vnew < v R Vin l F, v x x x x B Fload i i i