Slotted linear motors consist of a magnet track and a wire wound iron core. The iron helps channel and focus magnetic flux, increasing flux density, which results in higher force.

Slotted linear motors move with speed and precision, and are raising the bar on linear motion applications. They consist basically of magnets and windings. The magnets bond to an iron plate, forming a magnet-track assembly often called a " primary." The coils are wound in the teeth or slots on a laminated iron core, forming the "secondary" or forcer assembly. As in any motor, current applied to the coils controls speed, force (based on voltage), and direction (based on phase).

Slotted motors stack up well against the more common slotless types. They are less expensive, generate more force, and like their slotless counterparts, operate without backlash or contact. They also provide comparable speed and acceleration. On the downside, slotted linear motors exhibit a fair amount of cogging, limiting their use to point-topoint motion applications.

Skewing the magnets along the magnet assembly is one way to reduce cogging in slotted linear motors. It works by modifying the crossover point between the fields associated with the magnets and coils.

Software-based compensation offers almost an order of magnitude improvement in cogging compared to uncompensated motor output.

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Although there are various ways to limit the force "ripple" and velocity variations caused by cogging, most involve design changes that make slotted motors more expensive and less efficient. Another approach, which leaves the motor unchanged, is software-based compensation. In some cases, software compensation can reduce cogging by nearly an order of magnitude, making slotted motors a viable alternative for laser cutting, welding, scanning, and other processes requiring smooth motion.

For more information, contact Aerotech Inc. at (412) 963-7470, visit www.aerotech.com, or email the editor at ctelling@penton.com