A linear motor is a transmission that converts electrical energy directly into linear motion mechanical energy without the need for any intermediate conversion mechanism. It can be seen as a rotary motor cut in radial direction and developed into a plane. The side evolved from the stator is called the primary, and the side evolved from the rotor is called the secondary. In practice, the primary and secondary are manufactured to different lengths to ensure that the coupling between the primary and the secondary remains constant over the desired range of travel. The linear motor may be a short primary length secondary, or it may be a long primary short secondary. Taking into account the manufacturing costs, operating costs, generally adopt the short primary length secondary. The working principle of a linear motor is similar to that of a rotary motor. Take a linear induction motor as an example: When the primary winding is connected to an AC power source, a traveling wave magnetic field is generated in the air gap. Under the cutting of the traveling wave magnetic field, the secondary induces an electromotive force and generates a current. The current and the air gap The magnetic field acts to generate electromagnetic thrust. If the primary is fixed, the secondary performs a linear motion under the action of thrust; otherwise, the primary performs a linear motion. Linear motor drive control technology A linear motor application system must not only have a good linear motor, but also must have a control system that can achieve technical and economical requirements under safe and reliable conditions. With the development of automatic control technology and microcomputer technology, more and more linear motor control methods. The study of linear motor control technology can be basically divided into three aspects: First, the traditional control technology, the second is the modern control technology, and the third is the intelligent control technology. Traditional control techniques such as PID feedback control and decoupling control have been widely used in AC servo systems. The PID control contains past, present and future information in the dynamic control process, and the configuration is almost optimal and has strong robustness. It is the most basic control method in the AC servo motor drive system. In order to improve the control effect, decoupling control and vector control techniques are often used. Under the condition that the object model is determined, unchanged and linear, and the operating conditions and operating environment are fixed, the use of traditional control techniques is simple and effective. However, in high-performance applications where high-precision microfeeds are used, changes in the structure and parameters of the object must be considered. Various nonlinear effects, changes in the operating environment, and environmental disturbances such as time-varying and uncertain factors can achieve satisfactory control results. Therefore, modern control technology has attracted much attention in the research of linear servo motor control. Common control methods include: adaptive control, sliding mode variable structure control, robust control and intelligent control. In recent years, intelligent control methods such as fuzzy logic control and neural network control have also been introduced into the control of linear motor drive systems. At present, it mainly combines fuzzy logic, neural network, PID, H∞ control and other existing mature control methods to learn from each other to obtain better control performance.
Linear motors are also called linear motors, linear motors, and linear motors. The steady growth in practical industrial applications proves that linear motors can be used with confidence. The following is a brief description of the linear motor types and their differences from rotary motors. The most common types of linear motors are plate and U-slots, and tubing. The typical composition of the coil is three-phase, there is a Hall element for brushless commutation. The phase sequence and phase current of the HALL commutation for the linear motor are illustrated. The linear motor of this diagram clearly shows the internal winding of the rotor (rotor). Magnets and tracks. The mover uses epoxy to press the coil. Moreover, the magnetic track is to fix the magnet on the steel. In the past 10 years, linear motors have been truly matured after significant gains in practice and significant benefits from industrial applications. Linear motors are often simply described as rotating machines that are flattened and work in the same way. A forcer (rotor, rotor) is made by compressing coils together with an epoxy material. Moreover, the magnetic track is a magnet (usually a high-energy rare earth magnet) fixed on the steel. The motor's mover includes coil windings, Hall element circuit board, thermistor (temperature sensor monitoring temperature) and electronic interface. In a rotating electric machine, the mover and the stator require a rotary 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 track. Just like the encoder of the rotary servo motor is installed on the shaft, the linear motor needs to feedback the linear position feedback device--linear encoder, which can directly measure the position of the load to improve the position accuracy of the load. The linear motor controls the same as the rotary motor. Like a brushless rotary motor, the mover and the stator are not mechanically connected (brushless). Unlike the rotary motor, the mover rotates and the stator position remains fixed. The linear motor system can be either a magnetic track or a thrust coil (mostly positioning The system application is fixed track, thrust coil movement). In a motor that moves with a thrust coil, the weight and load ratio of the thrust coil is very small. However, there is a need for highly flexible cables and their management systems. Motion motors that use magnetic tracks not only have to bear the load but also have to bear the mass of the tracks, but they do not need a cable management system. Similar electromechanical principles are used on linear and rotary motors. The same electromagnetic force generates torque on the rotating motor and generates a linear thrust effect on the linear motor. Therefore, the linear motor uses the same control and programmable configuration as the rotary motor. The shape of the linear motor can be flat and U-slot, and tubular. Which configuration is most suitable depends on the specifications and working environment of the actual application.
Cylindrical moving magnet linear motor
Cylindrical moving magnet linear motor mover is a cylindrical structure. Move along a cylinder with a fixed magnetic field. This type of motor was originally found in commercial applications but could not be used in applications where space-saving flat and U-slot linear motors are required. The magnetic circuit of a cylindrical moving magnet linear motor is similar to a moving magnetic actuator. The difference is that the coil can be duplicated to increase the stroke. Typical coil windings are three-phase and use Hall devices for brushless commutation. The thrust coil is cylindrical and moves up and down along the magnet. This structure is not suitable for applications sensitive to flux leakage. Care must be taken to ensure that the fingers do not get caught between the magnet and the attractive side. One potential problem with the design of tubular linear motors arises from the fact that when the stroke increases, the only support points are at both ends because the motor is perfectly cylindrical and moves up and down along the magnet. It is always a limit to ensure that the radial deviation of the magnet bar does not cause the length of the magnet to contact the thrust coil.
U-slot linear motor
The U-slot linear motor has two parallel magnetic tracks that lie between the metal plates and face the coil mover. The mover is supported by the rail system in the middle of the two tracks. The mover is non-steel, meaning no suction and no interference force between the magnetic track and the thrust coil. Non-steel coil assemblies have a small inertia, allowing very high accelerations. The coils are generally three-phase, brushless commutation. The air cooling method can be used to cool the motor for performance enhancement. Water cooling is also used. This design can reduce magnetic flux leakage better because the magnets are mounted face to face in the U-shaped channel. This design also minimizes the damage caused by strong magnetic attraction. The magnetic track of this design allows the combination to increase the stroke length, limited only to the length of the cable management system that can be operated, the length of the encoder, and the ability of the mechanically configured large, flat structure.
Flat linear motor
There are three types of flat linear motors (brushless): no slots, no cores, no slots with cores and slots with cores. The selection needs to be based on an understanding of the application requirements. The slotless ironless flat motor is a series of coils mounted on an aluminum plate. Since the FOCER has no core, the motor has no suction and joint effect (the same as the U-slot motor). This design helps to extend bearing life in certain applications. The mover can be mounted from above or side to suit most applications. This type of motor is ideal for applications requiring smooth control of speed. Such as scanning applications, but the flat-rail design produces the lowest thrust output. In general, a flat magnetic track has a high magnetic flux leakage. Therefore, care must be taken to prevent the operator from being injured by magnetic attraction between them and other materials being sucked. Slotless cores: Slotless cored flat motors are similar in structure to non-slot coreless motors. In addition to the iron core installed in the steel lamination and then mounted on the aluminum backplate, the iron lamination structure is used to direct the magnetic field and increase the thrust. The suction force generated between the track and the mover is proportional to the thrust generated by the motor, and the lamination structure causes the joint force to be generated. When mounting the mover on the track, care must be taken to avoid injury from the suction between them. Slotless cores have greater thrust than non-slot coreless motors. Slotted core: This type of linear motor, the core coil is placed in a steel structure to produce a core coil unit. The core effectively enhances the thrust of the motor output magnetic field generated by the focusing coil. The strong attraction between the core armature and the magnetic track can be used as a preload for the air bearing system. These forces increase the wear of the bearing, and the phase difference of the magnet reduces the joint force.
summary
Prior to the emergence of practical and bought linear motors, all linear motion had to be converted from a rotating machine by using balls or roller screws or belts or pulleys. For many applications, 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, such as very high speed and very low speed, high acceleration, almost zero maintenance (without contact parts), high accuracy, and no time back. To perform a linear motion requires only the motor to eliminate the need for gears, couplings, or pulleys, which makes sense for many applications and removes unnecessary parts that reduce performance and shorten the mechanical life.
advantage
(1) The structure is simple. The tubular linear motor directly generates linear motion without intermediate conversion mechanisms, greatly simplifies the structure, reduces the movement inertia, greatly improves the dynamic response performance and positioning accuracy; at the same time, it also improves reliability, saves costs, and makes manufacturing and maintenance more efficient. Simple. Its initial sub-level can directly become a part of the organization. This unique combination makes this advantage further manifested.
(2) Suitable for high speed linear motion. Because there is no constraint of centrifugal force, ordinary materials can also achieve higher speeds. And if the gap between the primary and secondary air cushions or magnetic mats is preserved, there will be no mechanical contact during movement, and therefore the moving part will be free from friction and noise. In this way, the transmission components are not worn, which can greatly reduce the mechanical losses and avoid the noise caused by the streamers, cables, gears, pulleys, etc., thereby increasing the overall efficiency.
(3) High primary winding utilization. In the tube type linear induction motor, the primary winding is a cake type, there is no end winding, and thus the winding utilization is high.
(4) No lateral edge effect. The lateral effect refers to the weakening of the magnetic field at the boundary due to the transverse breaking, while the cylindrical linear motor does not open transversely, so the magnetic field is evenly distributed in the circumferential direction. (5) It is easy to overcome the problem of unilateral magnetic pull. Radial pull forces cancel each other out, basically there is no problem of unilateral magnetic pull force.
(6) Easy to adjust and control. By adjusting the voltage or frequency, or changing the secondary material, different speeds and electromagnetic thrusts can be obtained, suitable for low-speed reciprocating operation.
(7) strong adaptability. The primary core of the linear motor can be encapsulated with epoxy resin, has good anti-corrosion, moisture-proof performance, and is easy to use in the environment of moisture, dust and harmful gases; and it can be designed into a variety of structural forms to meet different conditions need.