What Is a Linear Actuator?
A Linear Actuator is a device that generates power in a linear direction.
Generally, a rotating motor is converted to linear motion using mechanical components. In addition, there are pneumatic and hydraulic actuators that use cylinders to generate linear motion.
They are widely used as a drive source for parts that require linear motion, such as industrial machinery and computers.
Recently, Linear Actuators are used in industrial equipment and measuring instruments, where high speed and high positional accuracy are required due to their high performance.
Uses of Linear Actuators
Linear Actuators are used in parts that require linear power, such as industrial equipment, automobiles, and PC peripherals. The following are examples of applications where Linear Actuators are used:
- Opening and Closing Doors of Construction Machinery, Etc.
Linear actuators are used to open and close doors of heavy machinery such as construction equipment and to adjust the angle of mounted objects. Recently, electric actuators have been adopted, and they can be easily integrated with the control systems installed in construction machinery. - Throttle Control for Engines of Construction Machinery, Etc.
The throttle control system is used to control the throttle of engines of construction machinery. Compared to conventional hydraulic actuators, the linear actuator is smaller and lighter.
Principle of Linear Actuators
The principle of Linear Actuator can be mechanical, pneumatic, hydraulic, or electromagnetic. Each method is explained below:
- Mechanical Type
The rotational motion of a stepping motor is combined with a rack and pinion, ball screw, sliding screw, etc. to produce linear motion to obtain linear power. - Pneumatic Type
The pressure in a hollow cylinder is increased by a pump or compressor to raise or lower a piston, which moves the cylinder on the piston axis to generate linear power. - Hydraulic Type
Similar in structure to the pneumatic type, hydraulic pressure is used to raise and lower the piston in the cylinder and move the cylinder on the piston shaft to generate linear power. Compared to the pneumatic type, the hydraulic type is used at higher pressure. - Magnetic (Linear Motor)
Generates linear power by electromagnetic force. The structure consists of a magnet and a coil. When an electric current flows through the coil, it becomes an electromagnet, and the repelling and pulling forces from the magnet generate linear motion and power.
Types and Usage of Linear Actuators
The usage of Linear Actuator varies greatly depending on its structure
- Mechanical Type
Since the rotational motion of a stepping motor is mechanically converted into linear motion, the control and positioning methods are the same as those for stepping motors, and a power supply unit or controller for a stepping motor is used. The number of pulses input to the motor first determines the angle of rotation of the motor. With the mechanical origin as a reference, the diameter of the pinion and the number of teeth on both sides for a rack and pinion mechanism, and the pitch of the feed screw for a ball screw mechanism determine the amount of movement per rotation angle.
The motor can be stopped with high precision by stopping it at a position in the middle of the travel range, and the stepping motor can be used as a brake by applying an electric current to it. - Pneumatic Type
Compressed air is used as the working fluid, so an air compressor or existing compressed air piping is required, and a solenoid valve or speed controller is used for control.
Basically, the stop position is either at the fully extended position or at the fully retracted position, and it is difficult to control the machine to stop in the middle. By mechanically hitting the stopper, any position can be set as the end point.
There are two types: the double-acting type, which has a piping connection port at each of the front and rear and controls the position depending on the side to be pressurized, and the single-acting type, which has a connection port at only one end and uses a spring to determine a fixed position.If the compressed air pressure is too high, the cylinder may operate vigorously and dangerously.
In such cases, a speed controller is installed to control the operating speed by throttling the amount of air flowing into the cylinder to achieve the proper operating speed.
Since air is compressed when pressure is applied, it may not be able to produce the expected force when a large load is applied to the cylinder, etc. On the other hand, even if a fluid leakage occurs, since it is air, it is less likely to contaminate the surrounding area and the fluid can be released into the air after use. - Hydraulic Type
This type uses oil as the working fluid of the pneumatic type and is used when it is necessary to operate at higher pressure, i.e., with greater differential power. Oil is pressurized by a dedicated electric pump.
Since the operating principle is similar to that of the pneumatic type, it has the same characteristics, but since oil is not compressed even when pressure is applied, a larger differential force can be obtained.
Since the working fluid is oil, it can contaminate the surrounding area in the event of leakage.
Controlling Linear Actuators
In a mechanical Linear Actuator using a motor, the position is controlled by a contact input that indicates the position or by controlling the rotation of the motor.
Pneumatic and hydraulic types use valves or solenoid valves to switch compressed air or hydraulic circuits for position control.
Some have a built-in proximity switch or potentiometer as a sensor for position detection, which can be retrofitted for use if necessary.