Smart Rotary Electric Actuators

Smart electric actuators are devices that convert electrical energy into rotary torque which then can drive and automate various apparatus in industry.


With basic electrical actuators, the motor drives the equipment until the desired position is reached; this position is usually detected using a system of cams mounted to the actuator’s driveshaft, but can also be ascertained with magnetic digital position sensors linked with digital encoders, that when coupled with appropriate software or firmware stops the motor when a specific, usually pre-configured, angular position is reached.


The device’s motor usually drives the driveshaft via a planetary gearbox. This driveshaft then conects to the required apperatus, a valve for example, using a system defined in international standard ISO5211.

ISO5211 :2017

Control


The electrical and control connections vary substantially between applications and countries, ranging from traditional cable glands and cables connected to an internal terminal-strips, through to highly-sophisticated computerised data-bus connections over wired, or increasingly wireless, networks that has led to physical separation of control and manufacturing systems across the globe. This physical separation is especially useful for automated systems that span large geographical distances such as water or oil pipelines.

Modbus over TCP/IP, RS-232 or RS-485 is still one of the most widely used
Industrial Ethernet protocols currently in use today. The protocol fully complies with the standards defined in IEC 61158 and has become a de facto standard; this is despite it being originally propitiatory (Schneider Electric) and dating back to the late 1970s.

Types

There are generally four types of electric actuators, uni-directional, on-off, fail-safe and modulating.

  • Uni-directional actuators always rotate in the same direction with the motor being stopped at certain angular intervals (usually 90°).
  • On-off actuators drive the driveshaft from fully open to fully closed, or back as one movement.
  • Fail-safe actuators have a secondary power supply, this is usually a battery or increasingly a capacitor. This supply drives the actuator to a preset safe position on the loss of primary power.
  • Modulating actuators derive their drive-to angular position from either a digital or analogue input signal.
Copyright Journal for Control-Systems Engineering 2019
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