2021/04/01

Part 2: Components Of An Electric Linear Actuator

News and Articles

 

Welcome to part two of our six-part discussion on the basics of an electric actuator and factors to consider when purchasing an electric motion system. TiMOTION is a manufacturer of electric linear actuators and related components, with the ability to customize products to meet most specifications. To better understand how an actuation system works, let’s look at the components that manufacture an electric linear actuator.

 

A. Front / Rear Clevis

A clevis is a U-shaped metal piece with holes in each end through which a fastening device, a pin or bolt, is run. Clevis attachments on the front and rear of the actuator allow it to be mounted to the application. Attachment styles from TiMOTION include round, U-shaped (or slotted), or with a punched hole. TiMOTION can customize clevises to fit best the application in use. 

 

B. Outer Tube

Also known as the cover tube, this extruded aluminum tube protects the outside of the linear actuator and houses all of the actuator's inner components. 

 

C. Inner Tube 

Also known as the extension tube, drive tube, translating tube, or piston, the inner tube is usually made out of aluminum or stainless steel. While retracted, the inner tube is where the spindle is located. This tube is attached to the threaded drive nut and extends and retracts when the nut moves along the rotating spindle.   

 

D. Spindle

A spindle – also known as the lead screw, rotating screw, or lifting screw – is a long, straight rod that turns in a machine or tool. This linear actuator segment rotates, extending or retracting the nut/inner tube, which creates a linear motion. Our steel spindle ensures durability and strength. The spindle can be threaded in different ways for various load and speed capabilities. Additional details of this will be covered in another section.

 

E. Safety Stop

Located on the end of the spindle, the safety stop’s function is to prevent the inner tube’s overextension. 

 

F. Wiper

A wiper is a sealing component attached to the end of the outer tube, which prevents contaminants like dust and liquids from entering the actuator's spindle area. It also ensures a proper seal between the inner and outer tubes, influencing the linear actuator's IP rating. TiMOTION’s electric linear actuators can be rated anywhere between IP42, IP66, IP68, and IP69K.

 

G. Drive Nut

The nut, which can be acme or ball screws, is attached to the inner tube and travels along the spindle. The nut is the component that allows extension or retraction of the inner tube. It can be made of metal or plastic and is sometimes keyed to prevent inner tube rotation.

 

H. Limit Switches

Limit switches control the fully extended and retracted inner tube position by electrically cutting current to the motor. These switches prevent the actuator from overextending or over retracting. In addition to cutting current, limit switches can also be used as a signal sending device.

 

I. Gear

A gear is made of steel or plastic and mates with other gears to alter the relation between the speed of a driving mechanism (such as the engine of a vehicle) and the speed of the driven parts (the vehicle’s wheels). The gear connected to a power source, such as the motor, is called the "drive gear." TiMOTION has different gear options depending on the application (such as a worm gear or spur gear, covered in our “Part 1: What Is An Electric Linear Actuator And How To Choose It?” white paper).

 

J. Motor Housing

The motor housing contains all the internal parts to the gear motor without leaving anything exposed to external damage. TiMOTION's motor housing is typically made of high-quality plastic.

 

K. DC Motor

The DC (Direct Current) motor is where all of the electric linear actuator’s power is generated. There are several types of DC motors, but TiMOTION uses brushed DC motors, which are composed of:

 

Stator

This stationary, outside portion of the motor consists of the motor housing, two permanent magnets, and motor caps. The stator generates a stationary magnetic field that surrounds the rotor.

 

Rotor

The rotor – also known as the armature –is the inner part of the motor that rotates. It mainly consists of silicon steel laminate, motor shaft, commutator, and copper windings.

 

Commutator

The commutator is a pair of plates attached to the motor shaft. These plates provide two connections for the coil of the electromagnet. The commutator is used to reverse the motor's polarity and essentially keeps the motor rotating without losing torque.

 

Carbon brushes

Carbon brushes use sliding friction to transmit electrical current from the stator to the rotor in the motor.

 

Motor Shaft

The motor shaft connects the gear motor to the bottom of the stator on the DC motor. 

 

 

Note: Alternating Current Motors (AC Motors) is also an option that TiMOTION manufactures. This type of motor is an available option that can be seen in our MA1 Model.

 

L. Output/ Feedback Sensors

Output (or feedback) sensors are used to communicate the actuator's stroke position. The feedback that it gives is sent to the control box MCU (micro control unit). Linear actuators with position feedback are typically required when an application involves high-level functions such as synchronization and memory positioning. Output sensor options include:

 

Hall Effect Sensor

The output signal from a Hall Effect sensor is the function of magnetic field density around the device. When the sensor's magnetic flux density exceeds a certain pre-set threshold (set in the MCU), the sensor detects it and generates an output voltage called the Hall Voltage. A linear actuator with position feedback is important because of its reliability and accuracy, exactly what the Hall Sensor provides.

 

 

Potentiometer (POT) Sensor

A POT sensor consists of a wiper/slider and two end connections to change an electrical signal output. As the linear actuator lead screw (spindle) turns, the resistance between the wiper/slider and the two end connections will change. Each resistance value will correspond to a position in the actuator's stroke.

 

Reed Sensor

The reed sensor is a magnetic positional sensor. It is an electrical switch operated by an applied magnetic field. It consists of a pair of contacts on ferrous metal reeds in a sealed glass envelope. The contacts may be normally open but closing when a magnetic field is present (closing the circuit and cutting the actuator's power).

 

We hope that this has helped you develop a better understanding and foundation for electric linear actuators. Next, we will cover the safety feature options that can be added to an actuator. If you have further questions and/or would like help with your next application, Team TiMOTION would be glad to assist you. We specialize in partnering with our clients while providing quality solutions for their actuation needs.

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