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Linear Motor

Linear Motor

Sep 1,2020
1. What is linear motor?

Linear motor is a transmission device that directly converts electrical energy into linear motion mechanical energy without any intermediate conversion mechanism. It can be seen as a rotating electric machine which is sectioned radially and expanded into a plane. The most commonly used linear motor types are flat and U-groove, and tubular. The typical composition of the coil is three-phase, and the Hall element realizes brushless commutation. 

2. How does the linear motor works?

Linear motors are often simply described as rotating motors being flattened, and the working principle is the same. The forcer rotor is made of epoxy material by compressing the coils together; the magnetic track is to fix the magnet (usually a high-energy rare earth magnet) to the steel. The forcer rotor of the motor includes coil winding, Hall element circuit board, thermistor (temperature sensor monitors the temperature) and electronic interface. In a rotating motor, the rotor and the stator need a rotating bearing to support the mover to ensure an air gap of the relative moving part. Similarly, linear motors require linear guides to maintain the position of the mover in the magnetic field generated by the magnetic track. As the encoder of a rotary servo motor installed on the shaft to feedback the position, the linear motor needs to feedback the linear position of the feedback device is the linear encoder, which can directly measure the position of the load to improve the position accuracy of the load.    

The side evolved from the stator is called the primary, and the side evolved from the rotor is called the secondary. In practical applications, the primary and secondary are manufactured into different lengths to ensure that the coupling between the primary and the secondary remains unchanged within the required stroke range. Linear motors can be short primary and long secondary, or long primary and short secondary. Considering the manufacturing cost and operating cost, take the linear induction motor as an example: when the primary winding is connected to AC power, a traveling wave magnetic field is generated in the air gap, and the secondary is cut by the traveling wave magnetic field, which induces electromotive force and generates current, the current interacts with the magnetic field in the air gap to produce electromagnetic thrust. If the primary is fixed, the secondary moves in a straight line under thrust; otherwise, the primary moves in a straight line.

3. Several common linear motors

A. Iron core linear motor

Advantages: large thrust, low cost, good heat dissipation

Disadvantages: There is suction, which is equivalent to 10 times the thrust of cogging or frustration

Iron core linear motor

Advantages: large thrust, low cost, good heat dissipation

Disadvantages: There is suction, which is equivalent to 10 times the thrust of cogging or frustration

Ironless linear motor

Advantages: no suction, no cogging, light mover

Disadvantages: poor heat dissipation, poor rigidity, low thrust

Slotless linear motor

It is a combination of iron core and ironless core

Magnetic shaft linear motor

Advantages: no magnetic slot, full use of magnetic lines, small size, good heat dissipation, simple process

Disadvantages: small thrust, poor rigidity, and limited length

4. Features and applications of linear motors

Compared with the rotary motor, the linear motor has the following characteristics:

Firstly, the structure is simple. Because the linear motor does not require an additional device to change the rotary motion into the linear motion, the structure of the system itself is greatly simplified, and the weight and volume are greatly reduced.;

Secondly,high positioning accuracy. Where linear motion is required, the linear motor can achieve direct transmission, which can eliminate various positioning errors caused by the intermediate links. Therefore, the positioning accuracy is high. If microcomputer control is used, it can be greatly improving the positioning accuracy of the entire system;

Thirdly, fast response, high sensitivity, and good follow-up. The linear motor is easy to support the mover with magnetic levitation, so that the mover and the stator always maintain a certain air gap without contact, which eliminates the contact friction resistance between the stator and the mover, thus greatly improving the system Sensitivity, rapidity and follow-up;

Fourthly, Safe and reliable work, long life. The linear motor can realize contactless transmission of force, and the mechanical friction loss is almost zero, so there are few failures and maintenance-free, so the work is safe and reliable, and the life is long.

Linear motors are mainly used in three aspects: one is used in automatic control systems, where there are many such applications; second, they are used as long-term continuous operation drive motors; third, It is used in devices that need to provide huge linear motion energy in a short time and a short distance.