Actuation Methodsby Pauline Gill
Actuators are used on machinery, appliances, vehicles and medical devices to cause motion of one part relative to another. Examples include automatic openers on supermarket doors, solenoid operated power door locks, and fill valves on washing machines. Actuators are available for every range of linear and rotational movement and type of motive force that drives them. Actuators may have total movements from hundredths of an inch to many feet. Considerations for implementing actuator applications include range of motion, driving force, mounting options, materials and motive power methodology required.
Actuation Method Types
Actuation methods include mechanical, electro-magnetic, pneumatic, vacuum, hydraulic and thermal sealed systems. All usually use one form of energy to cause the release or movement of another form of energy.
Two Main Sections
All actuators consist of a motor section which is specifically adapted to the motive force and an output section which adapts the actuator to the task it is performing. On a washing machine fill valve, an electrical solenoid receives AC line voltage from the cycle timer and moves a small plunger connected to the actual valve, starting and stopping the water flow.
Mechanical actuators are many times driven by human power, such as lever hood or trunk openers on automobiles where the lever inside the car is connected to a cable which then pulls a spring loaded latch, releasing the hood for opening.
Electrical actuators include solenoids which create a magnetic field in the cylindrical opening inside a coil, drawing in an actuation plunger to create linear motion. Electrical solenoids are used on industrial machines, appliances, vending machines and in many areas of transportation including automotive starters, choking mechanisms, fuel injection systems and safety interlocks.
Pneumatic and Vacuum Actuators
Air driven actuators include pneumatic cylinders, bellows and vane motors. Large diaphragm motors open and close pneumatically actuated control valves or adjust their proportional position for throttling control. When combined with return springs, pneumatic actuators can be used to position dampers or to lift doors. Air brakes on large trucks use rugged diaphragm actuation motors. Automotive air conditioning and heating systems use manifold vacuum to energize small diaphragm actuators on air dampers and water valves.
Hydraulic actuators are used in all forms of transportation braking. One of the advantages of hydraulic braking is that brake fluid is incompressible and its force can be multiplied to thousands of pounds. Automotive disc brake calipers and brake cylinders are examples of hydraulic actuators. Actuators used in jacking, lifting and pressing all use hydraulic cylinders.
Thermal Sealed Systems
Thermal sealed systems filled with helium are used in domestic gas home heaters to allow fuel flow to the heater only when the unit has a proper flame. It uses a bellows actuated switch to enable the system.