3.b) Explain the types of actuators.
Answer:
Types of actuators
Broadly, actuators can be divided into seven classes:
- Hydraulic actuators
- pneumatic actuators
- electrical actuators
- thermal/magnetic actuators
- mechanical actuators
- soft actuators
- shape memory polymers.
1. Hydraulic actuators
- A hydraulic actuator works on the principle of compression and decompression of fluids.
- These actuators facilitate mechanical tasks such as lifting loads through the use of hydraulic power derived from fluids in cylinders or fluid motors.
- The mechanical motion applied to a hydraulic actuator is converted to either linear, rotary, or oscillatory motion.
- The almost incompressible property of liquids is used in hydraulic actuators for exerting significant force.
- These hydraulic actuators are also considered as stiff systems.
2. Pneumatic actuators
- A pneumatic actuator works on the principle of compression and decompression of gases.
- These actuators use a vacuum or compressed air at high pressure and convert it into either linear or rotary motion.
- Pneumatic rack and pinion actuators are commonly used for valve controls of water pipes. Pneumatic actuators are considered as compliant systems.
- The actuators using pneumatic energy for their operation are typically characterized by the quick response to starting and stopping signals.
- Small pressure changes can be used for generating large forces through these actuators. Pneumatic brakes are an example of this type of actuator which is so responsive that they can convert small pressure changes applied by drives to generate the massive force required to stop or slow down a moving vehicle. Pneumatic actuators are responsible for converting pressure into force.
- The power source in the pneumatic actuator does not need to be stored in reserve for its operation.
3. Electric actuators
- Typically, electric motors are used to power an electric actuator by generating mechanical torque. This generated torque is translated into the motion of a motor’s shaft or for switching (as in relays).
- For example, actuating equipment’s such as solenoid valves control the flow of water in pipes in response to electrical signals.
- This class of actuators is considered one of the cheapest, cleanest and speedy actuator types available.
4. Thermal or magnetic actuators
- The use of thermal or magnetic energy is used for powering this class of actuators.
- These actuators have a very high-power density and are typically compact, lightweight, and economical.
- One classic example of thermal actuators is shape memory materials (SMMs) such as shape memory alloys (SMAs).
- These actuators do not require electricity for actuation. They are not affected by vibration and can work with liquid or gases.
- Magnetic shape memory alloys (MSMAs) are a type of magnetic actuators.
5. Mechanical actuators
- In mechanical actuation, the rotary motion of the actuator is converted into linear motion to execute some movement.
- The use of gears, rails, pulleys, chains, and other devices are necessary for these actuators to operate.
- These actuators can be easily used in conjunction with pneumatic, hydraulic, or electrical actuators.
- They can also work in a standalone mode.
- The best example of a mechanical actuator is a rack and pinion mechanism.
6. Soft actuators
- Soft actuators (e.g., polymer-based) consists of elastomeric polymers that are used as embedded fixtures in flexible materials such as cloth, paper, fiber, particles, and others.
- The conversion of molecular level microscopic changes into tangible macroscopic deformations is the primary working principle of this class of actuators.
- These actuators have a high stake in modern-day robotics.
- They are designed to handle fragile objects such as agricultural fruit harvesting or performing precise operations like manipulating the internal organs during robot- assisted surgeries.
7. Shape Memory Polymers
- Shape memory polymers (SMP) are considered as smart materials that respond to some external stimulus by changing their shape, and then revert to their original shape once the affecting stimulus is removed.
- Features such as high strain recovery, biocompatibility, low density, and biodegradability characterize these materials.
- Modern-day SMPs have been designed to respond to a wide range of stimuli such as pH changes, heat differentials, light intensity, and frequency changes, magnetic changes, and others.
- Photopolymer/light-activated polymers (LAP) are a particular type of SMP, which require light as a stimulus to operate. LAP-based actuators are characterized by their rapid response times. Using only the variation of light frequency or its intensity, LAPs can be controlled remotely without any physical contact. The development of LAPs whose shape can be changed by the application of a specific frequency of light have been reported. The polymer retains its shape after removal of the activating light. In order to change the polymer back to its original shape, a light stimulus of a different frequency has to be applied to the polymer.