Advantages, disadvantages and applications of linear motors

New generation of linear motor stages from Yaskawa

Figure 1: New generation of linear motor stages from Yaskawa.



Before the advent of practical and affordable linear motor, all linear motion had to be converted from rotating machinery through the use of ball or roller screws, belts or pulleys. For many applications, where large loads are encountered and the drive shaft is vertical, these methods are still the best.

However, linear motors have many unique advantages over mechanical systems. The following will give a more detailed description to the advantages and disadvantages of linear motors.

1. What are the advantages of a linear motor

1. Simple structure and small size. The linear motor achieves linear drive with fewer parts, which reduces the inertia of motion and greatly improves dynamic response and positioning accuracy. At the same time, it also improves reliability, saves costs, and makes manufacturing and maintenance easier.

2.Suitable for high-speed linear motion. Because there is no centrifugal force constraint, ordinary materials can also achieve higher speeds. Moreover, if the air cushion or magnetic cushion is used to keep the gap between the primary and secondary, there will be no mechanical contact during movement, so the moving part will have no friction and noise.
In this way, the transmission parts are not worn, which can greatly reduce the mechanical loss, avoid the noise caused by the towing cables, steel cables, gears and pulleys, etc., thereby improving the overall efficiency.

3. Unlimited running stroke. The running stroke is theoretically unlimited, and its performance will not be affected by the change of its stroke size.
4. Wide speed range. Its operation can provide a wide range of running speed, covering from several microns to several meters per second, especially at high speed, which is an outstanding advantage.
5. High acceleration, up to 10Kg. This is a significant advantage of linear motor drives over other screw, timing belt and rack and pinion drives.
6. Stable operation. The movement is smooth, because there is no other mechanical connection or conversion device except the linear guide rail or air bearing which play a supporting role.
7. High precision and repeatability. Because the intermediate link that affects the accuracy is eliminated, the accuracy of the system depends on the position detection element. With the right feedback device, its accuracy can reach sub-micron level.



Kollmorgen DDL direct drive linear motor with high performance

Figure 2: Kollmorgen DDL direct drive linear motor.



8. Simple maintenance. Because there are few parts and no mechanical contact during movement, thus greatly reducing the wear and tear of parts. It requires little or no maintenance, and has a long service life.
9. Strong adaptability. The primary iron core of the linear motor can be sealed with epoxy resin, which has good anti-corrosion and moisture-proof performance, and is convenient for use in the environment of humidity, dust and harmful gases. It can be designed into various structures to meet the needs of different situations.

2. What are disadvantages of linear motors

1. High power consumption. The power consumption of the linear motor is large. Especially in the case of high load and high acceleration motion, the instantaneous current of the machine tool brings a heavy load to the power supply system of the workshop.
2. High vibration. The dynamic rigidity of the linear motor is extremely low, and it cannot play the role of buffer damping. It is easy to cause resonance in other parts of the machine tool during high-speed motion.
3. High heat generation. The linear motor mover fixed at the bottom of the worktable is a high-heating component. The installation position is not conducive to natural heat dissipation, which poses a great challenge to the constant temperature control of the machine tool.
4. Unable of self-locking. In order to ensure reliable operation, the motion axis driven by the linear motor, especially the vertical motion axis, must be additionally equipped with a locking mechanism, which increases the complexity of the machine tool.



tubular linear motors

Figure 3: Tubular linear motors.

3. Where are linear motors used

In recent years, with the rapid development of automatic control technology and microcomputers, higher requirements have been placed on the positioning accuracy of various automatic control systems. Linear motors, relying on the characteristics of high speed, high acceleration, high precision, and unlimited travel, have got great attention in many fields. At present, the application of linear motor technology in countries around the world can be roughly divided into five aspects.

3.1 In Logistics Conveying System

At present, the logistics sorting and conveying line of express parcels can be driven by a linear motor and controlled by a computer, in addition to the chain drive or connecting rod through the rotating motor.
Compared with the traditional chain drive or connecting rod method, the logistics system driven by linear motor has the advantages of high efficiency, low noise, safety and reliability, and convenient maintenance.

In some novel three-dimensional warehouse handling systems and new automated garages, linear motors are also beginning to be used. Automated garages using linear motors install a series of longitudinal and transverse linear motor primary on the garage floor, and treat the vehicle carrier as the secondary. Through the computer, use the interaction between the primary and secondary of the linear motor to move the car in or out, providing high efficiency and utilization.



logistics sorting and conveying system

Figure 4: Logistics sorting and conveying system.

3.2 In Industrial Equipment

Because linear motors have their own unique advantages, they are widely used in mechatronics of mechanical equipment and machine tools, such as linear motor-driven punches, electromagnetic hammers, screw presses, die-casting machines, etc. X-Y tables driven by linear motors are also used in laser machinery and semiconductor manufacturing equipment.

3.3 In Information and Automation

The application of linear motor in information equipment is mainly reflected in computer equipment and its input and output equipment.

On the mainframe of the computer and in terms of hard disk devices, the linear servo motor was first used on the IBM2314 main optical drive, and later on the IBM333. Japan's Panasonic Corporation also uses linear servo motors on 3.5-inch disk drives, and Japan's Kobelco Electric Corporation and Fujitsu Corporation also manufacture linear stepper motors for floppy disk drives. After using the linear motor, the computer effectively shortens the access time and improves the work efficiency.

In addition, linear motors are also used in computer input and output devices. For example, Japan's Kobelco Electric Corporation and Fujitsu Corporation used linear stepper motors and linear DC motors for printers, respectively, and achieved improved resolution and stopping accuracy, as well as better acceleration characteristics.

Japan's Panasonic Corporation uses linear servo motors to drive digital scanners, which reduces the overall weight of the scanner and image fluctuations, and increases the starting thrust and the scanning speed by nearly 5 times.
As for the existing high-precision plane plotters at home and abroad, almost all of them use a flat linear stepper motor, which realizes the high speed, high precision, high reliability and durability of the plotter.

The applications of linear motors in automation equipment include new pen recorders, automatic winding machines, electromagnetic shutters for cameras, and automatic barcode readers.



Professional grade flat UV printer linear motor with high thrust

Figure 5: Flat UV printer linear motor.

3.4 Transportation and Civil Applications

Maglev trains have changed the way that traditional rail vehicles are propelled by wheel-rail friction, and use magnetic force to suspend the train body. Linear motor drive technology makes the train float and slide on the track, which is a major breakthrough in the history of transportation technology development. Linear motors are also used to drive subways, highway cars, and so on.

Linear motors have developed rapidly in civilian use, with relatively mature products and wide applications. At present, there are linear motor driven doors, windows, curtains, beds, cabinets, tables and chairs, and disc type linear motor driven washing machines, linear motor compressors for air conditioners and refrigerators, household knitting machines, sewing machines, and tea frying machines driven by linear motors, etc.
Especially the elevator driven by linear motor has the advantages of simple structure, material saving, space saving, high speed, low noise and energy saving, which has attracted great attention in the elevator industry.

3.5 Military and Other Applications

In military, medical and other aspects, linear motors have been applied to electromagnetic guns, submarines, military simulation facilities, and some linear motors have also been used in satellites and spacecraft. Linear motors have been used in medical instruments such as artificial hearts driven by linear motors, tactile simulators for blind people, and linear motors have also been used in massage and beating of electrotherapy and magnetic therapy. Linear motors have also been used in power tools, toys and construction pile drivers.

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