Two-way travel

For the first time, standard linear motors can simultaneously provide movement along two axes, thus reducing the number of motors. Siobhan Wagner reports

A technique that for the first time allows standard linear motors to provide movement along two axes simultaneously could allow equipment designers to reduce the number of motors and electronic drive modules.

The ‘NForcer technology’ from Philips Applied Technologies in the Netherlands has the potential to simplify the overall mechanics of equipment such as pick-and-place machines used to assemble electronic printed circuit boards.

The technology could mean lower equipment cost, while the reduced number of moving parts will mean higher accelerations and operating speeds.

With the new technique, horizontally-mounted linear motors can generate lift and lateral motion with just one motor. Ordinary linear motors can also be used to produce precision magnetically- levitated platforms with 3D shifts and tilts.

According to Philips’ senior scientist Georgo Angelis: ‘The beauty of this is that it requires no modification to existing motor components. You just need to re-position them slightly and drive them in an intelligent way.’

Ironless, multi-phase linear motors use current-carrying conductors in a magnetic field to generate a Lorenz force — at right angles to the current and the magnetic field — that provides motion.

In a conventional linear motor, the current-carrying conductors are arranged in coils with only their vertical sides in the magnetic field. As a result, the motor only generates lateral motion.

The team achieved 2D motion from one motor by shifting the position of the coils so that the lower horizontal section of the coils also sits in the magnetic field. This generates force and consequent motion in the vertical direction.

‘It’s obvious that you can generate force by bringing the downside of the coil into the magnetic field, but up until now this was always considered to be a parasitic force and so all linear motor manufacturers kept them outside the magnet,’ said Angelis. ‘By getting the current to go through the coils in a more intelligent way we could decouple the two directions.’

The team did this by driving the motors with an added computational algorithm that altered the current going through the motors’ three coils. ‘With this, we are able to make the force directions independent and controllable,’ said Angelis.

One of the benefits of the NForcer is its ability to implement magnetic levitation. The researchers intend this to be used for the production of fully floating, bearing-free platforms that, unlike air-bearing technologies, can be used in a vacuum.

The design is simple. A floating, magnetically levitated platform with long x-axis strokes, short y and z strokes and tilt and turn movements would work with only four horizontal magnet stators and six rotors.

Fully functional prototypes of the technology have already been demonstrated in the US, where the team unveiled a pick-and-place mechanism with 20cm horizontal and 3cm vertical movements with a single rotor, and a magnetically levitated platform movable in six degrees of freedom with nanometre accuracy. Both prototypes were constructed from standard off-the-shelf motor components.

While the technology has direct applications in pick-and-place systems, it could also be used in areas such as product inspection and metrology which both require linear motion in multiple degrees of freedom.

The team will continue to research its technology and alter its ‘electromagnetic bearings’ with software to determine its limits of accuracy with increased speed. Research on faster acceleration will hopefully lead to improved technologies.