Traditional motors such as DC motor, synchronous motor, induction motor, and variable reluctance motor can be used as electromagnetic actuators, but using rotating motor as actuator has advantages and disadvantages. DC motor control is simple, but the existence of brush makes DC motor need to be maintained regularly and not suitable for vacuum working environment; induction motor control is more difficult; variable magnetism motor. The cogging force caused by the cogging of the resistance motor will bring the difficulty to precision positioning.
Synchronous motors are more suitable for lithographic operation. In order to avoid magnetic resistance and cogging force, they can adopt the structure without iron, cogging and winding surface mounting.
The traditional planar positioning system transforms the rotating motion of rotating motor into linear motion by gear, ball screw, and other transmission mechanisms. Because of the problems of backlash, friction and uncertain ball motion, it is difficult to carry out high precision positioning. As a result, technicians are forced to relocate on the workbench. A precise worktable is set up for micro-displacement correction. This kind of multi-action substructure positioning platform has a huge system and slow response.
In high precision plane motor control, compared with rotary motor drive, the direct drive of permanent magnet linear motor has the advantages of no mechanical noise and additional transmission error; no additional mass, such as lead screw, can obtain greater acceleration and faster response; linear motor can not only produce unilateral force but also can produce. The vertical force can be used as a two degree of freedom actuator. Ordinary permanent magnet linear motor only uses the single-layer primary magnet. The harmonic component of the magnetic field along the space is large and the amplitude of fundamental component is small, so it can not produce large electromagnetic force. Ordinary permanent magnet linear motor adopts three-phase control. The winding arrangement is complex, the winding end effect is large, and the cooling condition is poor, which affects the operation of the linear motor.
The magnetic field of Halbach permanent magnet array shows obvious unilateral characteristics. The magnetic field on one side is significantly enhanced, and on the other side is significantly weakened. The magnetic field on the strong side has good sinusoidal distribution characteristics, and the high-order harmonics are small. The linear motor with Halbach permanent magnet arrays can improve some shortcomings of ordinary permanent magnet linear motor.
The Neodymium Halbach Arrays are specialized magnetic assembly consisting of Neodymium Iron Boron (NdFeB, NIB, Neo) permanent magnets assembled in such a way as to provide a controlled (uniform and homogenous) and high magnetic field strength without the use of ferromagnetic materials.
This Halbach Array is a cylinder / ring-shape with a dipole (2 poles) pattern in the central air gap. The magnetic field within the ring is uniform (parallel field lines which are homogenous) across the entire central hole and of high strength (above 10000 Gauss or 1 Tesla), both being features of this style of Halbach Arrays.
The Neodymium Halbach Array ring magnet is made from 8 magnets (45-degree arc segments, each with a specific direction of magnetization). Each arc part has the direction of magnetization such that the magnetic field traverses the central air gap and is then ‘guided’ through and around the magnet material itself.