24 Jul 2024


Linear motors with magnet-free tracks cut costs

The linear motors with magnet-free tracks have special teeth shaped from a ferrous powder material. A magnetic field is generated in the teeth.

UK-based Motion Control Products (MCP) has announced what it claims are the first linear motors that do not have any magnets in their tracks, thus reducing the need for rare-earth materials and cutting costs, especially for long travel lengths. The motors are also said to be easier and safer to assemble, without the usual strong magnetic attraction between the track and the moving forcer.

Most conventional linear motors have magnets in the track, and coils in the forcer. When a current is applied to the coils, it creates an electromagnetic field. The linear track contains rare-earth magnets with alternating north and south pole segments along its length. The electromagnetic field generated by the coils interacts with the magnets in the track to move the forcer along the track.

Because the rare-earth magnets are powerful, care is needed when assembling and installing these motors, especially when they are close to other magnetic materials. In addition, sensitive or non-shielded electronic systems can be adversely affected by the strong magnetic fields.

MCP’s new MMF linear motors are based on the same “magnetic field modulation” principle as conventional linear motors and use it to control the interaction of the forcer with the teeth on the linear track. The teeth, moulded from a powdery ferrous material, are manufactured with a specific shape. When a current is applied to the coils, a magnetic field is generated in the teeth. By controlling the field induced in the teeth, it is possible to control the position of the forcer in relation to the track and thus to create motion. The only rare-earth magnets are inside the forcer and the number of magnets remains constant regardless of the length of travel.

MCP says that the performance of the MMF motor is comparable to that of a standard linear motor. There are two series of motors: one delivers acceleration up to 22G, speeds up to 30m/s, and thrust values up to 538N; the other produces acceleration up to 24G, speeds up to 15m/s, and thrust up to 1,076N.

The MMF motors have self-modulated ferrite alloy stators. Integrating the magnets with coils in the mover is said to result in a magnetic circuit that generates thrust smoothly. The easy-to-assemble motors are said to exhibit a high force densities, high operating speeds with precision movements. They also:
• are safer and easier to assemble because there is no magnetic field in the stator;
• exhibit low cogging forces and friction, increasing their life expectancy;
• produce significantly less electromagnetic interference in the platen;
• protect the forcer because fewer metallic particles are attracted by the magnetic field;
• offer improved thermal characteristics; and
• weigh less and have a simpler construction than conventional linear motors.

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