Oct 7 2012
Actuators are broadly classified as follows: Motor control systems are commonly referred to as actuators. These motors use energy and a low power command to amplify a signal tha manifests as a desired output. They are usually used in high power hydraulic devices that help in operating control systems and flaps on valves, aircraft, and car steering as well as in low power switches.
Fluid mechanical actuators
- Pneumatic actuators
- Hydraulic actuators
- Electromagnetic actuators
- Electrodynamic actuators
Types of Actuators
Mechanical systems that are designed to move require actuators (e.g., robotic systems that are designed for functional capacity in manufacturing environments will require high-powered actuators to move an object). Actuators are mainly used to create motion in mechanical systems by the conversion of electrical energy into mechanical motion. Different types of actuators are discussed below in detail.
Solenoids are the most widely used actuators. The working principle of the solenoids is based around a piston which moves inside a wire coil. A spring is used to hold the piston outside the coil. A magnetic field is produced by the coil when a current is applied. The magnetic field produced attracts the piston and this manifests as a linear force.. Solenoids can be used in car door openers and pneumatic valves.
Solenoid controlled valves are used to control fluid and air flow. The central spool is moved to the left when the solenoid is actuated. Two ports at the top of the valve body are linked to a hydraulic cylinder. A single pressure line is present at the bottom of valve body and the power is made to pass from the center to the right hand cylinder port. The left hand cylinder port is passed through an exhaust port.
Different types of valves are:
- 2-way normally closed valve
- 2-way normally open valve
- 3-way normally closed valve
- 3-way normally open valve
- 3-way universal valve
- 4-way valve
The n-way represents the number of outlets and inlets connections.
Cylinders create linear force or motion by using pressurized air or fluid. When one side of the cylinder is pumped with fluid that side expands and a piston is moved. The fluid present on the other side of the piston should be moved out. The force produced by the cylinder is proportional to the cross sectional area of the cylinder (see video below).
P = F/A, so F = PA
- P represents pressure of the hydraulic fluid
- A represents an area of the piston
- F represents force produced from the piston rod
Principle of hydraulic lift
Hydraulics makes use of incompressible fluids to provide high force at limited motion ranges and low speed. The hydraulic system normally uses an oil as the hydraulic fluid. It is used to lubricate the components of the hydraulic system. This fluid is pressurized by a pump and then it is passed via valves and hoses in order to move the cylinders. A pump present at the center of the system produces high pressures, which are transferred to a cylinder and transformed into linear force and displacement. The hydraulic system can be mainly used in high power applications.
A pneumatic system and the hydraulic system are similar in many respects. With the pneumatic system, it avoids the use of reservoir as air is not collected and stored in the system. It is mainly used in low force applications.
The pneumatic system has following features:
- It is light in weight
- It produces pressures up to 85 psi
- Dampers are used to absorb the impact at ends of the cylinder
- It is provided with an additional equipment for pressurized air supply.
The operating environments should be verified with extreme care while designing the pneumatic system.
Motors are also commonly used actuators. However, they do not have significant properties for applications involving logical control. Low current motors are controlled by switching with a PLC and high power motors by using a motor starter or a relay.
Apart from the above, there are many other varieties of actuators such as heaters, lights, and sirens/horns. Heaters are switched on and off to maintain the temperature within a particular range. A relay is used to control the heaters. Lights are directly linked to the PLC and are found in all machines in order to give the proper feedback to operators and indicate the state of the machine. Sirens or horns are also linked to the PLC and are used for risky or unattended machines.
Actuators have the following applications:
Pneumatic Processing Centers
The pneumatic processing center has following functions:
- It carries out step-by-step rotation by using a rotary table
- It is used for cutting parts by using grinding, drilling, and milling tools
- It is used for reception, positioning and fixing a detail
- It is used for delivering the detail.
This system can be used for batching the fused metals and liquids in foundry manufacture. The power cylinder is used to actuate the lever with a ladle. The volume of the ladle corresponds to the needed doze of liquid entered into a top part of a rod of the cylinder. The liquid automatically flows into an accepting chamber from the ladle when the rods move to a bottom position.
Stationary and mobile robots can be developed with good functionalities using pneumatic actuators.
Stationary Robot - M¨I - 9˜N is the first stationary Russian serial pneumatic industrial robot. This robot has four degrees of mobility which is provided by vertical and horizontal power cylinders, a drive of fingers, and a turning drive of gripping device.
Mobile Robot - Includes two types of control modes. The first mode is referred as a transport mode. In this mode, the manipulators in the top position can be moved by the longitudinal cylinders at high speed. It leans on a moving surface using manipulators of the cross-section cylinder during this type of movement. The second mode is a mines detection mode. In this mode, a zone at a front part of a robot can be scanned by a detection block.