New Class of Linear Motors

November 16, 2009

New synchronous linear motor technology from Siemens that eliminates the magnets on the secondary track is opening the door to a new class of cost-effective, longer travel distance applications. Ideal target applications are systems with both long travel distances and demanding environments such as transportation systems, material handling, and laser or water cutting CNC machines.

The newly patented 1FN6 design offers the technical advantages of both a synchronous linear motor (higher dynamics, accuracies and force densities) along with a primary advantage of asynchronous linear motors - a non-magnetic secondary track.

The combination of no magnets on the secondary track, plus a 30 percent wider air gap, creates a robust design that is effective in dusty and dirty environments. But compared to asynchronous motors, the new design also offers 40-70 percent higher force densities and much higher dynamic response.

"With 1FN6 technology, users can get the advantages of a synchronous motor and the advantages of an induction motor without the magnets being on the secondary track. So it is really a combination of both designs, and combines the advantages of both," says Ralph Baran, product marketing manager for servo motors and cables for Siemens Industry Inc.

The key design innovation is a synchronous linear motor where the magnets are integrated directly into the lamination of the primary part along with the individual windings for each phase. The result is that the design of the secondary part is much simpler, and consists of milled steel with teeth that are used to control magnetic flow between the primary and secondary sections.

By commutating the current going into the primary section, the permanent magnet's magnetic field can be either strengthened or weakened to effectively guide the magnet flow so that it is always most concentrated on top of the teeth. Advanced commutation techniques are used to move the magnet flow up and down in the primary part, and the field generated by the current in the windings creates, in essence, a standing magnet field on the secondary part.

The traditional design of a permanent magnet or synchronous linear motor, such as Siemens' 1FN3 product, uses an electrically powered primary section that travels on a secondary magnet track. The secondary part consists of a steel plate with a series of permanent magnets mounted next to each other (north pole to south pole). The drive system provides current to the phases to generate a magnetic field, and implements sophisticated commutation algorithms to generate forces in either direction. The basic concept of a permanent magnet motor in a round design is a servomotor or, used in a linear design, you have a linear motor.

The key to lowering system costs for the 1FN6 is the limited use of magnet material which is very costly when laid out in a long magnet track. With secondary sections cut into lengths of about a foot and the travel distance laid out with a linear track where each segment has its own individual magnets, the longer you travel the more expensive the overall motor design gets.

With the 1FN6, because the secondary part

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