Electron microscopes from FEI use sophisticated computer-controlled mechatronic technology. These microscopes continue to evolve into industrial measuring machines.

Caged ball technology helps ensure smooth motion in low-speed applications by eliminating friction between the balls.

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With these tips and tactics, achieving slow motion is a walk in the park.

How would you like to move a row of 10 water molecules at the rate of human hair growth? If watching paint dry or grass grow is on your list of party favorites, this extreme slow-speed challenge might be right up your alley. If you have more practical concerns – for instance, precise industrial measuring applications – you'll want to know what's involved in this extraordinarily slow linear actuation.

Slow motion in the nanoworld

A trip to the nanoworld brings designers to the home of nanometers — tiny units of just a millionth of a millimeter. One of the most important tools for exploring this world is the electron microscope. Now, a joint project taking place in the Netherlands called "NewMotion," between microscope manufacturer FEI and Bosch Rexroth, has tightened new microscope process speeds to 1 nm per second. At the heart of these electron microscopes are FEI's mechatronic specimen-manipulator stages — and FEI's current goal is to design stages that will make it possible to manipulate the nanometer world in three dimensions. This new manipulator requires a movement and positioning accuracy down to the atomic level.

FEI already has their motion control system in place: a modular system made of various hardware and software packages from Bosch Rexroth's NYCe4000 industrial system. The Technical University of Eindhoven (TU/e, in the Netherlands) is aiding the project with research into the necessary control techniques. For this next step, TU/e is developing new measurement and control algorithms to be used in the motion control system for increased accuracy and fluid motion in the nm/sec range.

To do this, sensors and controls must constantly monitor, analyze, and correct the speed and position of several axes. As you might imagine, this places huge demands on the calculation capability and master control software tuned to do the job. Because only a small number of encoder steps are made per increment of time, the regulator in the control unit must be capable of generating a homogenous speed profile so that the actual speed of the sample being manipulated remains constant.

On the mechanical side, new mechatronic linear transducers are used to achieve virtually backlashfree power transmission with an accuracy of +/- 0.1 nm/min, with an ultrasonic piezomotor used as an actuator to achieve the super-slow rate of 1 nm/sec.

However, accuracy alone isn't good enough — the movement must be absolutely jerk free. So, FEI switched off mechatronic vibrations as much as possible, and uses the control system to compensate for any remaining vibration. Also in development is a balanced thermal-compensation system, which will hold temperature constant as a function of time.

Tips and tools

"To achieve smooth linear actuation at the sub-micron level, many factors must be considered, because everything becomes a potential system disturbance," says John Floresta, vice president of engineering at Anorad, a division of Rockwell Automation, Milwaukee, Wis. Here are some tips to keep in mind when tackling extremely slow motion applications, such as those found in semiconductor manufacturing.

What kind of feedback do you

"A good rule of thumb is that the feedback resolution should be 10 times the speed or resolution of what you're trying to move," advises Floresta. So, if you're trying to move at a rate of 100 nm/sec, you'll want 10 times that information coming back in order to accurately control the motion. High-resolution optical encoders or laser inferometers can work well to capture the data you'll need to make adjustments.