Overview: This article explores the roles of sensors and actuators in embedded systems, detailing their functions, common types, and applications across various industries for effective environmental interaction.

The transition from centralized to cooperative systems is significant in various domains, including embedded systems, industrial automation, and software architectures. They have many benefits, such as adaptability to various environments, modularity, breakdown resistance, and less computational work. 

It is now possible to switch to a cooperative system that involves various processes.

  • Integrating actuator and sensors
  • Creating safe communication protocols 
  • Distributed control methods

This article provides an overview of actuators and sensors, as well as the numerous steps that are necessary for their integration and their applications.

What is an actuator?

An actuator is a machine or part of a machine that converts externally available energy into motion based on control signals, enabling a system to move or operate.

Types of actuators

Based on the type of motion, they are classified as:

  • Linear actuator
  • Rotary actuator

Linear actuator

Linear actuator enables movement back and forth in a set path in a straight motion. This type of motion allows the actuator to perform tasks such as pushing, pulling, lifting, dropping, sliding, adjusting, and tilting objects.

Rotary actuator

A rotary actuator produces rotational motion commonly used to power heavy machinery such as mixing, dumping, screw clamping, turning over, and providing constant tension. It performs tasks that require continuous or partial rotation.

Based on how the control signal and power source are provided, there are three types, which include:

  • Electrical actuators
  • Hydraulic actuators
  • Pneumatic actuators

All of these actuators are capable of linear and rotary motion.

Electrical actuator 

It is an electromechanical device that converts electrical energy into mechanical motion. The core of this actuator lies in its motor, controlled by an electronic control unit, which can produce either a quarter-turn (90-degree open used in valve control to open or close) or multiple rotations (multi-turn requiring continuous rotational motion, such as industrial machinery).

Pneumatic actuators 

These devices are prime movers that convert the energy of compressed air into mechanical motion. They are further classified based on the motion as linear or rotary. For example, linear pneumatic actuators include the spring diaphragm and piston. Examples of rotary pneumatic actuators include vane style, rack, and pinion style. 

Hydraulic actuator

The device changes the fluids' pressure energy into mechanical motion. Hydraulic systems use fluids like oil or water, which are nearly incompressible, and when pressure is applied, they are transmitted quickly and uniformly throughout the fluid. They are highly suited for high-force applications, as they can produce forces greater than pneumatic cylinders of equal size. A diagrammatic representation of a helical hydraulic rotary actuator is shown in Fig. 1

Fig. 1 Diagrammatic illustration of a helical hydraulic rotary actuator. Source: MDPI

A smart actuator is an advanced electromechanical device that integrates sensors, control electronics, and communication interfaces to actuate or move in response to sensed physical properties such as light, heat, humidity, or pressure. 

What is a sensor?

A sensor is a device that detects changes in physical, electrical, or chemical properties or environmental variables such as temperature, light, pressure, or motion into an electrical output. It produces data that can be interpreted by humans or machines.

Types of sensors

Based on external source or power to operate, they are classified as:

  • Active sensors
  • Passive sensors

Active sensors

Active sensors, also known as self-generating sensors, do not require an external power supply or excitation circuit to operate in response to changes in physical, chemical, or thermal properties. Examples of active sensors include thermocouples, piezoelectric sensors.

Passive sensors

Passive sensors, by contrast, require an external power supply or excitation circuit to produce a measurable change. Examples of passive sensors include resistance temperature detectors, and strain gauges.

Based on their functionality, they are classified into various types of sensors, including temperature, pressure, optical, mechanical, motion, position, proximity, ultrasonic, touch, analytical, level, flow, color, humidity, chemical sensors, etc.

A smart sensor is an advanced sensor that combines sensing capabilities with computing resources, such as a microprocessor or microcontroller. It gathers a large number of values with high resolution.

Integrating actuators and sensors

Sensor and actuator nodes work together to perceive their environment, make decisions, carry out tasks, and more. This integration comprises resource-rich devices with more processing and communication capabilities. Various steps involved in this integration are shown in Fig. 2 and are discussed below.

Fig. 2 Block diagram illustrating the integration of sensors and actuators within a wearable device. Source: MDPI

Data acquisition

When a sensor node detects an event, it first collects analog data from the environment, indicating the degree of changes such as temperature, motion, or pressure.

Signal processing 

The smart sensor interprets the data it collects, makes decisions, and even learns from patterns with high sensitivity and resolution.

Signal transmission

The analog signals are converted into digital signals using circuits or microchips, particularly in applications that require high sensitivity and resolution.

Actuator control

Control signals are sent to actuators to perform predefined specific actions based on the processed data. Smart actuators are advanced devices that combine mechanical actuation with digital communication, microprocessor-based control algorithms, and communication interfaces. It enables precise motion control, real-time monitoring, and enhanced operational efficiency.

Applications

Integrated systems containing sensors and actuators are important in automation because of enhanced processing capability. At the macro scale, they have enabled significant advancements in several fields, including smart grids, industrial IoT, industrial automation, sensor networks, autonomous vehicles, robotics, unmanned aerial vehicles, etc. A diagrammatic illustration of industrial automation is shown in Fig. 3.

At the micro-scale, they have been applied to Micro-Electro-Mechanical Systems, leading to innovative devices like micro-conveyors, micro-manipulators, micro-fluidic systems, reconfigurable structures, etc.

Fig. 3 Diagrammatic illustration of industrial automation. Source: MDPI

To conclude, integrated systems are important in achieving automation and preventive and predictive maintenance, enabling precision control, diagnostics, and monitoring capabilities.

Summarizing the key points

  • Sensors detect physical changes in the environment and convert them into electrical signals. Actuators convert electrical signals from a system into physical actions.
  • Integrating sensors and actuators in embedded systems enables effective environmental interactions and a wide range of applications across multiple industries.
  • Together, smart sensors and actuators improve automation in advanced systems like industrial IoT and robotics, providing significant advancements in monitoring, diagnostics, and operational precision.

Reference

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