Get acquainted with the types of actuators in IoT

How actuators are used in IoT

In IoT, actuators enable a physical action based on data that originates with one or more sensors.

The conversion of sensor data to activity follows this sequence:

1. Sensors detect an event in the physical environment.
2. The sensors convert that information about the event into electronic signals that travel to a control system, which has a scheme to determine when and what movement is needed.
3. The controller tells the actuator to take the desired action.
4. The actuator takes the action by turning energy into a physical force.

For example, an IoT deployment that regulates a refrigerator unit has sensors to read the temperature. The sensors send the temperature data to the control system as scheduled. The control system compares those temperature readings to the programmed desired temperature range. If the temperature moves outside that preprogrammed range, the control system sends a signal to an actuator to either turn on or off the refrigeration.

In many IoT deployments, the sensor, controller and actuator are physically different components that communicate via wireless or wired communication networks and an internet protocol. In other builds, a single physical device houses all three components. A smart valve, for example, generally contains a sensor, controller and actuator.

Some IoT deployments center around the actuators themselves. In such use cases, sensors monitor actuator performance, said Preston Johnson, senior solution manager for asset integrity and reliability at the intelligent edge at domain expert integrator CBT.

"In the old world, you would have to have someone inspect the actuators," Johnson said. "But, with the advent of IoT, we don't have to send inspectors in. We can get reports on how actuators are performing or whether they need mitigation."

Sensors can monitor, for example, the speed at which actuators open and close valves in pipes, with controllers that analyze the measurements to ensure the actuators properly work and to send an alert when there is a malfunction.

In the case of the smart valve that contains the sensor, controller and actuator in one part, the device could have a communications protocol to send data to a central server that analyzes valve performance, Johnson said.

Types of actuators

To enact movement, the actuator requires energy. The main types of energy sources are the following:

• electric
• hydraulic
• pneumatic
• thermal/magnetic

Each type comes with advantages and potential drawbacks.

Electric actuators, a common option for IoT devices, convert energy into mechanical torque. Electric energy is less noisy in operation than other actuator types. These actuators don't require fluid to run. Additionally, electric actuators offer high-control precision positioning due to programmability. But these actuators can be expensive. They also may not be suitable for extreme operating environments found in some manufacturing, aerospace and military use cases.

Hydraulic actuators can exert a large amount of force and move at a high speed. These characteristics suit use in construction and manufacturing equipment. But they have high maintenance requirements. For example, they can need noise mitigation, and fluid leaks can reduce their performance.

Pneumatic actuators, which use compressed air or gas for energy, have lower maintenance requirements and a longer life span than other types of actuators. They are durable and capable of working in extreme temperatures. This category can also quickly start and stop motion. But they still require some maintenance. For example, they demand a constant air supply, and their efficiency is affected by changes in air and gas pressure.

Thermal or magnetic actuators use energy gained from heating up a shape-memory alloy. They have a compact form factor, are lightweight and have high power density. It also removes the need for a temperature sensor when used in a thermal valve that integrates fluid control, actuation and temperature-sensing functions. Because this actuator uses heat to move, the actuator's piston can shift positions and cause a lag if the device is heating up or cooling down, which causes hysteresis. The actuator's metal can also suffer from structural and functional fatigue.

Actuator selection criteria

Another way to classify actuators is the type of motion they produce. The mechanical motions include rotary, linear and oscillating.

"The type of actuator you need is dependent on the work you need it to do," Johnson said.

A hydraulic actuator with linear movement meets the need to lift something heavy in a straight line up and down. Pneumatic actuators with rotary movement would be the likely choice for a robotic arm. Electric actuators are the most common type for IoT deployments, according to Chandler.

Although actuators are a component in many IoT use cases, enterprise IoT teams don't often directly select the type of actuator they deploy. Automation hardware vendors often select device components, including the actuator, and sell them as one packaged offering, Chandler said.

The more that IoT device design teams know about the components, the better informed they can be about how actuators might affect maintenance requirements, operating noise and product life span. Even if IoT product engineers don't directly purchase actuators from a supplier, they should still work with vendors to confirm they get the most suitable actuator as part of the technology offering and it supports the desired use case.