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Standard linear motors gain an extra dimension

16 October, 2007

Researchers at Philips Applied Technologies in the Netherlands have developed a technology that allows standard linear motors to provide movement simultaneously along two axes, rather than being restricted to a single axis. Philips says that the development will allow designers to cut the number of motors and electronic drive modules they need, as well as simplifying overall mechanical design in applications such as the pick-and-place systems.

Philips nforcer

Philips predicts that the patented technology, called NForcer, will cut equipment costs "significantly" and, by reducing the mass of moving parts, will also allow designers to produce designs that achieve higher accelerations and operating speeds.

The invention allows horizontally-mounted linear motors to generate lift as well as lateral motion, providing two axes of motion from just one motor. The technology can also be used to produce precision magnetically levitated platforms with six axes of controlled motion (3D shifts and tilts) using standard linear motors.

"The beauty of this innovation in linear motor operation is that it requires absolutely no modification to existing motor components," says Dr Georgo Angelis, a senior scientist at Philips Applied Technologies in Eindhoven. "All you need to do is re-position the components slightly, and drive them in an intelligent way."

Conventional iron-less, multi-phase linear motors rely on the fact that a current-carrying conductor placed in a magnetic field experiences a force perpendicular to the direction of the current and to the direction of the field. This phenomenon, known as the Lorentz force, creates the motion.

In a standard linear motor, the current-carrying conductors are arranged in coils, with only the vertical sides of the coils in the magnetic field. As a result, the motor only generates lateral motion. To achieve two-dimensional motion from one motor, the Philips researchers have shifted the position of the coils with respect to the magnetic track so that the lower horizontal section of the coils also sits in the magnetic field, where it generates force, and thus motion, in the vertical direction.

Philps nforcer platform

Because the technology can be used to achieve magnetic levitation, it can be harnessed to produce floating, bearing-less platforms (shown above) which, unlike air-bearings, can be used in vacuum. A magnetically levitated platform with a long-stroke x-axis, and short-stroke y- and z-axis movements, and a few milliradians of tilt and turn, can be implemented using just four horizontal magnet tracks (stators) and six forcers (rotors).

The development stems from Philips’ long history in developing advanced mechatronic systems, ranging from CD-ROM drive servo mechanisms, to precise positioning platforms for chip production.

Philips demonstrated the NForcer technology recently in the US. The demonstrations included a single-track roller bearing pick-and-place mechanism with 20cm horizontal and 3cm vertical movements, achieved using a single forcer, and a magnetically levitated platform movable in six degrees of freedom with nanometer accuracy. Both demonstrators were built using off-the-shelf motor components.

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