What Is a Linear Encoder?

A linear motor is a transmission that directly converts electrical energy into linear motion mechanical energy without the need for any intermediate conversion mechanism. It can be seen as a rotary electric machine cut in a radial direction and spread out into a plane.

Linear motor

The linear motor in this figure clearly shows the internal windings of the mover (forcer, rotor). The magnetic coil and the magnetic track. The mover is pressed into the coil with epoxy material. Moreover, the magnetic track is a magnet fixed to the steel.

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 to different lengths to ensure that the coupling between the primary and secondary remains unchanged within the required stroke range. Linear motors can be short primary long secondary, or long primary short secondary. Considering the manufacturing cost and operating cost, take a linear induction motor as an example: when AC power is applied to the primary winding, a traveling wave magnetic field is generated in the air gap, and the secondary is induced by the traveling wave magnetic field to generate an electromotive force and generate a current This electric current generates electromagnetic thrust when it interacts with the magnetic field in the air gap. If the primary is fixed, the secondary performs linear motion under thrust; otherwise, the primary performs linear motion. Drive control technology for linear motors A linear motor application system must not only have a linear motor with good performance, but also a control system that can achieve technical and economic requirements under safe and reliable conditions. With the development of automatic control technology and microcomputer technology, there are more and more linear motor control methods.

The research on linear motor control technology can be basically divided into three aspects: one is traditional control technology, the other is modern control technology, and the third is intelligent control technology. Traditional control technologies such as PID feedback control and decoupling control have been widely used in AC servo systems. Among them, PID control contains the information in the dynamic control process and has strong robustness. It is the most basic control method in AC servo motor drive system. In order to improve the control effect, decoupling control and vector control technology are often used. Under the condition that the object model is determined, does not change and is linear, and the operating conditions and operating environment are determined to be constant, it is simple and effective to use traditional control techniques. However, in high-performance applications with high-precision micro-feeding, it is necessary to consider changes in the object structure and parameters. Various non-linear effects, changes in the operating environment, and time-varying and uncertain factors such as environmental interference can achieve satisfactory control results. Therefore, modern control technology has attracted much attention in the research of linear servo motor control. Common control methods are: adaptive control, sliding mode variable structure control, robust control and intelligent control. It mainly combines existing mature control methods such as fuzzy logic, neural network, PID, H control, etc., to learn from each other to obtain better control performance.

A linear motor can be considered as a structural deformation of a rotary electric machine. It can be regarded as a rotary electric machine cut along its radial direction and then flattened and evolved. With the rapid development of automatic control technology and microcomputers, higher requirements are placed on the positioning accuracy of various automatic control systems. In this case, the traditional rotary motor plus a linear motion drive composed of a set of conversion mechanisms The device is far from meeting the requirements of modern control systems. For this reason, many countries in the world are researching, developing, and applying linear motors, making the field of linear motors more and more widely used.

Compared with rotary motors, linear motors mainly have the following features: First, the structure is simple. Because linear motors do not need to convert rotary motion into linear motion additional devices, the structure of the system itself is greatly simplified, and the weight and volume are greatly increased. The second is the 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 link. Therefore, the positioning accuracy is high. If microcomputer control is used, it can also be used. Greatly improve the positioning accuracy of the entire system; third, fast response, high sensitivity, good follow-up. Linear motors are easy to support their movers with magnetic suspension, so that a certain air gap is always maintained between the mover and the stator without contact, which eliminates the contact frictional resistance between the mover and the mover, thus greatly improving the system. Sensitivity, fastness and follow-up; the fourth is safe and reliable work and long life. Linear motors can achieve non-contact transmission force, and the mechanical friction loss is almost zero, so there are few failures and maintenance-free, so the work is safe, reliable and long life.

Linear motors are mainly used in three aspects: first, they are used in automatic control systems, and there are many such applications; secondly, they are used as driving motors for long-term continuous operation; third, they are used to provide huge linear motion in a short time and short distance Capable device.

High-speed maglev trains Maglev trains are the most typical examples of practical applications of linear motors. The United States, Britain, Japan, France, Germany, Canada and other countries are developing linear levitation trains, of which Japan has made the fastest progress.

Linear Motor Driven Elevator The first elevator in the world to be driven by a linear motor was installed in the Manse Building in Toshima, Tokyo, Japan in April 1990. The elevator has a load of 600 kg, a speed of 105 m / min, and a lifting height of 22.9 m. Since the linear motor-driven elevator has no traction unit, the machine room on the top of the building can be omitted. If the height of the building is increased to about 1000 meters, a wireless elevator must be used. This elevator is driven by a linear motor with high-temperature superconducting technology. The coil is installed in the hoistway. The high-performance permanent magnet material is installed outside the car, just like magnetic suspension Like a train, it is controlled by radio waves or light control technology.

When the ultra-high-speed motor rotates beyond a certain limit, the motor using rolling bearings will sinter and damage. A linear suspension motor (electromagnetic bearing) has been developed abroad. The suspension technology is used to suspend the motor's mover in the air, eliminating The mechanical contact and frictional resistance between the mover and the stator can reach a speed of more than 25,000 to 100,000 r / min, so it is widely used in high-speed motors and high-speed spindle components. For example, the newly developed 5-axis controllable electromagnetic high-speed spindle for multi-process automatic CNC lathes developed by Japan's Yaskawa Corporation uses two radial electromagnetic bearings and an axial thrust electromagnetic bearing, which can bear the load of the machine tool in any direction. In the middle of the shaft, in addition to a high-speed motor, it is also equipped with an automatic tool exchange mechanism that is compatible with a multi-process automatic CNC lathe.

Before the advent of practical and affordable linear motors, all linear motion had to be converted from rotating machinery through the use of balls or roller screws or belts or pulleys. For many applications, such as encountering heavy loads and

(1) Simple structure. The tubular linear motor does not need to go through the intermediate conversion mechanism to directly generate linear motion, which greatly simplifies the structure, reduces the motion inertia, greatly improves the dynamic response performance and positioning accuracy; it also improves reliability, saves costs, and makes manufacturing and maintenance more Easy. Its first level can be directly part of the organization, and this unique combination makes this advantage even more manifest.

(2) Suitable for high-speed linear motion. Because there is no constraint of centrifugal force, ordinary materials can reach higher speeds. And if the gap is saved by air cushion or magnetic cushion between the primary and secondary, there is no mechanical contact during the movement, so there is no friction and noise in the moving part. In this way, the transmission parts are not worn, which can greatly reduce the mechanical loss and avoid the noise caused by streamers, steel cables, gears and pulleys, thereby improving the overall efficiency.

(3) High primary winding utilization. In tube-type linear induction motors, the primary winding is pie type and there is no end winding, so the winding utilization rate is high.

(4) No lateral edge effect. The lateral effect refers to the weakening of the magnetic field at the boundary due to the lateral break, and the cylindrical linear motor has no break in the lateral direction, so the magnetic field is uniformly distributed in the circumferential direction.

(5) It is easy to overcome the problem of unilateral magnetic tension. The radial tensile forces cancel each other out, and there is basically no problem of unilateral magnetic tensile forces.

(6) Easy to adjust and control. By adjusting the voltage or frequency, or replacing the secondary materials, different speeds and electromagnetic thrusts can be obtained, which is suitable for low-speed reciprocating operation occasions.

(7) Strong adaptability. The primary iron core of a linear motor can be sealed into a whole with epoxy resin, which has good anti-corrosion and moisture-proof performance, and is easy to use in humid, dusty and harmful gas environments; and can be designed into a variety of structures to meet the needs of different situations .

(8) High acceleration. This is a linear motor drive, a significant advantage over other screw, timing belt and rack and pinion drives. ^[1]

Linear motor selection specifications are mainly for the selection of thrust, and software is usually used as an auxiliary tool. In order to accurately select the thrust of a linear motor, you need to know the load weight, effective stroke, maximum speed, and maximum acceleration. Auxiliary to the selection software, you can choose the appropriate thrust motor.