Linear Motors

The linear motor has been a relatively recent addition to the electric motor world, considering the age of the ac motor is just about 100 years.  Linear motors have grown up primarily in the semiconductor industry where extraordinary precision and speed is required.  And as with all systems that offer the ultimate in performance, they have traditionally been very expensive.

But linear motors properties are quite unique and where many motion systems can achieve extreme precision, the tradoff is usually speed.  It’s hard to do both, and do them both well.  So the linear motor has carved it’s unique niche in the motion world.

But with time and applications, linear motors have become more cost effective, to the benefit of many new applications.  In addition to the sub-micron position accuracy, the technology has extraordinary speed and acceleration capability.

I had the opportunity to commission a linear motor for a unique requirement a few years ago.  We had some very tough constraints to deal with.  I did some calculations, and found that we were pulling 16 G’s of acceleration during portions of the motion cycle.

As with all systems, there are trade offs even with the most exotic systems.  There are several with linear motors as well.  They generate a great deal of heat.  High cycle rates and extreme acceleration profiles will often push the linear motors to their limits, and in response vendors have offered air and liquid cooling systems to offset the  thermal limit.

In some multi-axis applications, particularly Cartesian motion, the moving mass of one linear motor axis becomes part of the payload of the other axis.  This is very significant since motors are primarily iron cores with Neodymium Iron Boron magnets, all very dense materials.  This will cause a huge increase in the moving mass, increasing the power requirements dramatically.

And as with all linear motion, there are bearing considerations that must be accounted for.  Linear bearings are an integral part of the motor, necessary to maintain air gap between the stator and forcer, and ultimately attaching to the load.

Linear motors can be adapted to some very unique applications as has recently been shown through the use of curved actuators making hemispherical manipulators that can operate in large cylindrical envelopes.

Recent advances in linear motor systems include integrated off-the-shelf solutions from many vendors.  Since linear actuators are a combination of bearings, motors, feedback devices, amplifiers, etc., this complex system requires quite a bit of effort to integrate.  So making standard offering actuators helps control costs and makes integration for the user much quicker and more straightforward.  This creates a great opportunity for the many suppliers of linear motor technology to continue the trend forward and innovate great solutions.

As with all of electric motor history, every unique requirement leads to unique problem solving.  American innovation continues, at its finest.