Transcript lecture_motors.ppt

Electric Rotary Actuators
(motors)
• DC motors
• AC motors
– stepper (2-phase synchronous)
– brushless (3-phase synchronous)
– induction
Step Motors
Step Motors
Step Motor
12 step/rev, 1 phase on
Step Motor
12 step/rev, 2 phase on
Step Motor
12 step/rev, half-stepping
Step Motors
Selecting Step Motors
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Torque
Speed
Current
Lead configuration
Torque/Speed
Series/Parallel Wiring
Step Motor Drives
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Resolution (full, half, microstepping)
Current Limit (resistor or digital)
AC powered or DC powered
Pulse/Direction or Indexing
Resolution
• Full step/Half step
• Microstepping
– x2,x4,x5,x8,x10,x16,x25,x32,x50,x64,x125,x128,x
250,x256 common choices
• Max step frequency
– PLC: 7kHz pulse rate => 2100 RPM at x1,
8.2RPM at x256 (1.8deg motor)
– Compumotor 6104: 2MHz pulse rate => 2300RPM
at x256
• Resonance problems
Incremental Encoders
Incremental Encoders
• Encoders typically
run on +5V, not
+24V
• Outputs are typ. not
24V compatible
either
Absolute Encoders
• doubling resolution requires adding
another photodiode/LED pair
• cost is much higher than incremental
• does not require seeking to establish
reference location
hybrid incr/absolute encoders
• add more information to index channel to
reduce amount of seeking required to find
reference position.
• interface requires lots of wires (parallel) or a
special comm. protocol
Potentiometer
• A potentiometer (or pot) is a variable
resistor wired to obtain a variable DC
voltage proportional to position
Magnetostrictive Pos. Sensor
• Pulse sent down magnetostrictive
material
• Pulse reflects off position magnet’s field
• Position is proportional to trcvd - tsent
• Pulse propagates at ~2800 m/s
Magnetostrictive Sensor