1： Advantages:

1. Wide feed speed range. From 1 (1) m / s to more than 20 m / min, the fast forward speed of machining center has reached 208 M / min, while the fast forward speed of traditional machine tools is less than 60 m / min, generally 20 ~ 30 m / min.

2. Good speed characteristic. The speed deviation is less than (1) 0.01%.

3. High acceleration. The large acceleration of linear motor can reach 30g, the feed acceleration of machining center has reached 3.24g, the feed acceleration of laser machining machine has reached 5g, while the feed acceleration of traditional machine tool is less than 1G, generally 0.3g.

4. High positioning accuracy. The positioning accuracy can reach 0.1-0.01 (1) mm by using grating closed-loop control. The linear motor drive system with feedforward control can reduce the tracking error by more than 200 times. Due to the good dynamic characteristics and sensitive response of the moving parts, and the refinement of interpolation control, the nano level control can be realized.

5. Unlimited travel. The traditional lead screw drive is limited by the manufacturing process of the lead screw, generally 4 ~ 6m, and the stroke needs to lengthen the lead screw, which is not ideal in terms of manufacturing process and performance. With linear motor drive, the stator can be infinitely lengthened, and the manufacturing process is simple. The x-axis of the existing large-scale high-speed machining center is more than 40m long.

6. Simple structure, smooth movement, low noise, small friction and wear of moving parts, long service life, safe and reliable.

2： Principle: linear motor is similar to ordinary motor in principle, it is only the expansion of motor cylindrical surface, and its types are the same as traditional motor, such as: DC linear motor, AC permanent magnet synchronous linear motor, AC induction asynchronous linear motor, stepping linear motor, etc. Like brushless rotary motor, there is no mechanical connection between motor and stator (brushless). Linear motors use the same control and programmable configuration as rotary motors. The shape of linear motor can be flat plate type, U-groove type and tube type. Which structure is suitable depends on the specifications and working environment of practical application.

3： The disadvantages of the linear motor are: (1) there is an inevitable "edge effect", that is, the distortion of the end magnetic field of the linear motor affects the integrity of the traveling wave magnetic field, increases the loss of the motor, reduces the thrust, and has a large thrust fluctuation（ 2) The change of load, the change of system parameters and all kinds of disturbances, including the end effect, directly affect the motor itself, without buffer link. If the robustness of the system is not strong, it will cause the instability and performance degradation of the system（ 3) Other disadvantages such as magnetic isolation, difficult installation and high cost.

4： Motor specifications: the motor with a stroke of 80mm has a total length of about 200 mm, a width of about 40 mm, a height of about 20 mm without seat, a price of 4000 / piece, and a force of about 20 N for 2 kg.

5、 Classification: linear motor is generally divided into linear DC motor, linear stepper motor, linear reluctance motor, linear induction motor and linear synchronous motor, but the development of various linear motors is not balanced, and the driving motors in linear servo system are mainly permanent magnet linear motor and linear induction motor. Permanent magnet linear motor and linear induction motor have their own advantages and disadvantages. The advantages of permanent magnet linear motor are: larger output per unit size; Less heating, low cooling requirements, long secondary does not need cooling. The existing problems are: the strong magnetic field produced by the permanent magnet makes its installation and operation more difficult; The permanent magnetic field attracts the iron chips, so it is difficult to remove the iron chips in the actual processing. The motor must be sealed tightly to prevent the iron chips from blocking the air gap or entering the moving pair; The position sensor is used to control the current commutation of the motor; Permanent magnets may demagnetize. The advantages of linear induction motor are: simple secondary structure, easy installation, maintenance and chip removal. Because expensive permanent magnets are not used, it is possible to reduce the cost in the application of long stroke (such as conveyor). The disadvantage lies in the use of electric excitation, so the efficiency is low, the heating is large, and the secondary also needs to be cooled; The air gap tolerance is strict, usually only 0.1 mm, which leads to poor processability and high processing cost; The control algorithm is much more complex than that of linear permanent magnet motor.