With the continual developments of magnetic field modulation techniques and the introduction of powder magnetic materials, it has now been possible to produce a linear motor with zero magnets on the track, with magnets only in the forcer. This has the advantages of reducing the need for rare earth magnetic material in the construction of the product, therefore reducing the overall cost of the motor, particularly as the length of the system increases, so does the number of magnets that are required.
Linear Motors Technology and Development Histrory
Comparison of Standard Linear Motor with Magnet-Free Track Linear Motor
Since the 1970s, with the continual development of rare earth permanent magnet materials, vector control technology and power electronics technology getting smaller and more powerful, permanent magnet synchronous motors have appeared in the motion control industrial field. The synchronous belt, rack & pinion, lead screws and ball screws driven by the permanent magnet synchronous motor are quickly applied in the field of industrial control. Since around 2010, due to the development of the linear rail, linear encoder technology and motor packaging technology, linear motors have become more and more popular. After 2019, down to the theory of magnetic field modulation and the development of powder magnetic material, a magnet mounted on the linear motor mover, and a magnetic-track-free linear motor without magnets on the stator, has now been launched on the market to reduce the overall costs.
Conventional Linear Motor
A conventional linear motor has motor coils mounted in the forcer, so when a current is applied to the coils, this creates an electromagnetic field, so with the linear track consisting of range of rare earth magnetic of alternating N-pole and S-pole segments running the full length of travel, the interaction of the electromagnetic field generated by the coils and the magnets in the linear track, induces a magnetic field which pushes the forcer along the track creating motion.
With very strong rare earth magnets used in the construction of conventional linear motors, care must be used when installing the units in an application, especially when they are close to other magnetic materials. Coupled with the problem of sensitive or non-shielded electronic systems can be adversely affected by these strong magnetic fields.
MMF series ‘Magnet-free Track’ Linear Motor
The MMF linear motor uses the same ‘magnetic field modulation’ principle as conventional linear motors to control the interaction of the forcer with the teeth on the linear track. The teeth on the track are manufactured with a very specific shape and molded from powder ferrous material, so when a current is applied to the forcer coils and magnet, a magnetic field is generated in the teeth; by controlling the modulation of this magnetic field and the induced field within the teeth on the linear track, it is possible to control the position of the forcer in relation to the track and thus create motion.
The performance of the MMF linear motor is comparable to that of a standard linear motor. The price-to-performance ratio, compared to a conventional linear motor, can be greatly reduced because the track is magnet free. As the length of travel increases, only the rare earth magnets, used within the system, are inside the forcer and thus the number of magnets remains constant regardless of travel.
The track uses no magnets, and a magnetic field is only present when it interacts with the forcer, which leads to several benefits:
- Very low detent or cogging force*
- Ease of installation
- Reduced overall system cost
- Reduced weight
- Improved safety
- Less complex construction
- Improved thermal characteristics
* Cogging force is a result of the magnetic attraction between the “teeth,” or protrusions, of the iron lamination stack (forcer) and the permanent magnets of the magnet track
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