4.a) List and explain the characteristics of actuators.
Answer:
Characteristics of actuators
The choice or selection of actuators is crucial in an IoT deployment, where a control mechanism is required after sensing and processing of the information obtained from the sensed environment. Actuators perform the physically heavier tasks in an IoT deployment; tasks which require moving or changing the orientation of physical objects, changing the state of objects, and other such activities. The correct choice of actuators is necessary for the long-term sustenance and continuity of operations, as well as for increasing the lifetime of the actuators themselves. A set of four characteristics can define all actuators:
1. Weight
- The physical weight of actuators limits its application scope.
- For example, the use of heavier actuators is generally preferred for industrial applications and applications requiring no mobility of the IoT deployment.
- In contrast, lightweight actuators typically find common usage in portable systems in vehicles, drones, and home IoT applications.
- It is to be noted that this is not always true. Heavier actuators also have selective usage in mobile systems, for example, landing gears and engine motors in aircraft.
2. Power Rating
- This helps in deciding the nature of the application with which an actuator can be associated.
- The power rating defines the minimum and maximum operating power an actuator can safely withstand without damage to itself. Generally, it is indicated as the power-toweight ratio for actuators.
- For example, smaller servo motors used in hobby projects typically have a maximum rating of 5 VDC, 500 mA, which is suitable for an operations-driven battery-based power source. Exceeding this limit might be detrimental to the performance of the actuator and may cause burnout of the motor.
- In contrast to this, servo motors in larger applications have a rating of 460 VAC, 2:5 A, which requires standalone power supply systems for operations. It is to be noted that actuators with still higher ratings are available and vary according to application requirements.
3. Torque to Weight Ratio
- The ratio of torque to the weight of the moving part of an instrument/device is referred to as its torque/weight ratio.
- This indicates the sensitivity of the actuator. Higher is the weight of the moving part; lower will be its torque to weight ratio for a given power.
4. Stiffness and Compliance
- The resistance of a material against deformation is known as its stiffness, whereas compliance of a material is the opposite of stiffness.
- Stiffness can be directly related to the modulus of elasticity of that material. Stiff systems are considered more accurate than compliant systems as they have a faster response to the change in load applied to it.
- For example, hydraulic systems are considered as stiff and non-compliant, whereas pneumatic systems are considered as compliant.