Concepts Flashcards
Sources of losses in electo mechanical devices
Losses in the electrical conductors
Losses in soft magnetic components (hysteresis and eddy losses)
Friction losses in mechanical system
What is the purpose of a gearbox attached to a motor
Step up or step down speed
Give a real life application of Lorentz magnetic force
Loudspeaker
Which part of a loudspeaker moves
The electrical coil
What assumptions would you make about the electric coil on a loud speaker
Uniformity- impedance, magnetic field
Displacement of the cone is proportional to applied force
Basic elements of a rotary actuator
Simple 2 pole single phase stator winding.
Moving element - iron core with permanent magnet or a single dc field coil
Uses of rotary actuators
Limited angle torque motors- scanning lasers and mirrors
How to tell current direction on a diagram
Arrow
X going into page
. Coming out of page
What equivalent represents back emf in a device
Capacitor
How does voltage across a capacitor rise
Exponentially slower
In a closed loop system how is the input to the servo amplifier calculated
Demand- Feedback= (error)
Basic components of Dc commutator motor
Permanent magnets produce a vertical field. Two conductor on the central rotor
At what point on a dc motor does the rotor have 0 torque
Perpendicular to the field
What is done to prevent net torque of one rotation of a dc motor
Switching the polarity of the current (commutation)
Advantages of DC motors
Very simple supply requirements
Straight forward control
Produce max torque at standstill
Low cost
Disadvantages of DC motors
Friction from brushes Sparking from commutator Brushes have to be periodically replaced Carbon deposits with machine Copper loss occurs on rotor
Increasing speed in a dc motor effect on armature current
Ia will reduce
Relationship between T and w in a dc machine
Negative linear. \
Tstall
Torque at 0 speed
Ability to Dissipate I^2*R loss in the armature
In practice is torque required to maintain a speed
Due to frictional losses yes
How does armature current/time compare to a torque/time graph (servo dc)
They look identical in theory but in practice it’s a slower rise with time constant L/R
What is the steady state equivalent servo circuit
Va-Ra-Ia-back emf-
