Technology Elevates Linear Motors to Higher Plane

Oct 17, 2007 2:22 PM
By Mark Valentine, Technical Editor, Power Electronics Technology

Researchers at Philips Applied Technologies have developed an innovative technique that allows standard linear motors to simultaneously provide movement along two axes rather than along a single axis. This will allow designers to produce designs that achieve higher accelerations and operating speeds due to the reduced mass of the moving parts. It can also significantly lower equipment costs.

“The beauty of this new innovation in linear motor operation is that it requires absolutely no modification to existing motor components,” says Dr. Georgo Angelis, Senior Scientist at Philips Applied Technologies. “All you need to do is reposition the components slightly and drive them in an intelligent way.”

This simplified hardware aspect of the technology leverages the properties of conventional ironless multiphase linear motors. Specifically, the current-carrying conductors in conventional linear motors are arranged in coils and placed in a magnetic track, with only the vertical sides of the coils placed within the magnetic field. This arrangement limits the direction of the Lorentz force produced in the coils—and thus the motion of the coils—to the horizontal direction along the length of the magnetic track. However, in NForcer technology, the position of the coils with respect to the magnet track is shifted so that the lower horizontal section of the coils also sits in the magnetic field.

This repositioning allows the coils to generate a Lorentz force in the vertical as well as the horizontal direction with respect to the magnetic track. As a result, a single linear motor can produce swift, two-dimensional motion, such as that needed for pick-and-place machines (click here to download a video demonstration).

For example, in equipment such as the pick-and-place machines used to assemble pc boards, the technology will allow designers to reduce the number of motors and electronic drive modules required, as well as simplifying overall mechanical design. Philips has developed a pick-and-place demonstrator based on the technology that achieves 20-cm horizontal movement, and 3-cm vertical movement.

Figure 1: This magnetically levitated platform movable in six degrees of freedom with nanometer accuracy was constructed from standard off-the-shelf linear motor components.

In addition to generating both the lift and the lateral motion required in pick-and-place machines with only a single linear track and a single forcer (consisting of three coils), the technology also enables precision magnetically levitated platforms using only four horizontal magnet tracks and six forcers (see Figure 1). These fully floating, magnetically levitated platforms provide a long-stroke x-axis, short-stroke y- and z-axis movements, and a few milli-radians of tilt and turn. Furthermore, unlike air-bearing solutions, they can function in vacuum.

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