LINEAR MOTOR

A linear motor is a direct driven electric motor that produces a linear force in a straight line and converts electrical energy into mechanical energy as linear motion without extra transfer mechanism. We can think of it as cutting a rotating motor from radial direction and laying it out flat.

According to the magnetic way design, linear motors have two main types: iron core and ironless. Iron core linear motors are sometimes referred to as flat linear motors. Ironless linear motors are also called air core or U channel linear motors. HGT supply the linear motor secondary part, magnet assembly. A linear motor magnet assembly is a magnetic track with permanent magnets fixed on yoke plate(s). It can be considered as an unrolled rotor of a brushless DC rotary motor.

Because of magnetic attraction between iron lamination and permanent magnets, iron core linear motors can provide high thrust force. Due to open structure, they are easy to dissipate heat. With one row of magnets and simpler structure, they are usually cheaper. Iron core linear motors are suitable for pressing, molding. PCB drilling machines, printing, speed stability applications.

With primary coils encapsulated in epoxy instead of steel lamination stack, ironless linear motors have high smooth of motion and no cogging. Besides, they have lighter weight and lower setting times. Ironless linear motors are suitable for high speed assembly and transport, scanning, non-mechanical bearing, semiconductor, vacuum applications.

For different moving parts (moving coil and moving magnet track), there are two kinds of systems. Typically, the magnet track is the stationary part and the forcer containing coils is the moving part, for greater acceleration from the lower mass. But moving magnet motors are able to achieve higher precision. Shape of the linear motors could be manufactured as: a plate of surface-mounted track with a moving forcer (Flat linear motors), two parallel magnet tracks facing each other with the forcer in the middle of them (U-channel linear motors), or a forcer moves on a cylindrical bar that houses the magnets (Tubular linear motors). Specific configuration depends on the operating condition and particular application. Few types are followed.

Iron core linear motors consist of three-phase electromagnetic coils that are wound around the iron core (teeth) of laminations on forcer, and the iron core could increase the force output. However, there will also be cogging force and attractive force between forcer and track, affecting thrust force and bearing life.
Ironless linear motors are sometimes referred to as U-channel linear motor, and the windings are mounted in epoxy rather than iron lamination stack. Typically, the coil winding is three-phase, with brushless commutation. Zero cogging and attractive force extend the bearing life, but force output becomes smaller.

Slotless linear motors combine the design elements of iron core motors and ironless motors. The three-phase coils with back iron held together with epoxy over a single track. They have lower cost and better heat dissipation than U-channel ironless design, and lower attractive force and less cogging than iron core design.

The slotless-ironless flat motors consist of coils mounted to an aluminum base. While the slotless-iron flat motors consist of coils mounted to iron laminations, which are used to direct the magnetic field and increase the force, and then mounted to the aluminum base. Attractive force and cogging force are present in construction containing iron laminations, but this design produces more force than ironless design.

Tubular linear motors are another type of linear motors. The coil winding is typically three-phase, with brushless commutation using Hall effect devices, and those motors can be constructed with iron or ironless stators. The tubular linear motor has the coils surrounding cylinder-shaped magnets shaft. When current in the forcer is adjusted across the three-phase, magnetic fields are generated.

Voice coil motor, also known as non-commutated DC linear motor, is a single-phase tubular linear motor with moving coils or moving magnets. It consists of permanent magnetics and coils, and when the current flowing through the coil interacts with the permanent magnetic fields, the moving force is generated.