Electric Rotary Actuators motors DC motors AC motors

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 • • Torque Speed Current Lead configuration

Torque/Speed

Series/Parallel Wiring

Step Motor Drives • • Resolution (full, half, microstepping) Current Limit (resistor or digital) AC powered or DC powered Pulse/Direction or Indexing

Resolution • Full step/Half step • Microstepping – x 2, x 4, x 5, x 8, x 10, x 16, x 25, x 32, x 50, x 64, x 125, x 128, x 250, x 2 56 common choices • Max step frequency – PLC: 7 k. Hz pulse rate => 2100 RPM at x 1, 8. 2 RPM at x 256 (1. 8 deg motor) – Compumotor 6104: 2 MHz pulse rate => 2300 RPM at x 256 • Resonance problems

Incremental Encoders

Incremental Encoders • Encoders typically run on +5 V, not +24 V • Outputs are typ. not 24 V 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 Resolution is ~. 001” with tupdate ~1 msec/in.

Magnetostrictive Sensor