Nano-mechatronics: motion control system cuts system integration costs

Hoffman Estates, IL —In collaboration with Bosch Rexroth and the Technical University of Eindhoven , Netherlands (TU/e), electron microscope manufacturer FEI has embarked on a project called “NewMotion,” which aims to create a modular motion control system comprising various hardware and software packages from Bosch Rexroth’s NYCe4000 industrial motion control system. The system will be optimized for applications, such as microscopy, where extreme precision and stability are necessary, but rapidity of motion is not. The TU/e is aiding the project with research into the necessary new control techniques.

FEI has been in the microscopy business since 1949, when it produced the world’s first transmission electron microscope (TEM). FEI manufactures a full range of microscopes, including scanning (SEM) and TEM types, plus dual-beam lab-based and related equipment. The company’s tools, featuring focused ion- and electron-beam technologies, deliver 3D characterization, analysis, and modification capabilities with resolution down to the sub-Angstrom (0.1 nm) level.

With one of its major development facilities in Eindhoven (Netherlands), FEI is a close neighbor of Bosch Rexroth, which develops motion control systems for various applications in high-tech markets that include wafer handling in the semiconductor industry, the assembly of electronic components, special robots and handling systems, production systems for solar cells and the production of micro-electromechanical systems (MEMS).

FEI will equip high-precision mechatronic systems with the NewMotion system, and integrate them into electron microscopes. TU/e’s role is to study and develop new measurement and control algorithms in the field of motion control technology. It will develop new measurement and control principles that will be used in the motion control systems to increase the motion accuracy at the atomic level and achieve fluid motion in the nm/sec range.

Dr. Maarten Buijs, director of R&D Europe at FEI points out that machines capable of working on the nanometer scale increasingly are sold to customers in the industrial sector. Reducing system and integration costs, while increasing availability and service level become increasingly important as the electron microscope continues to evolve into an industrial measuring machine. “Achieving a breakthrough in cost reduction is the main driver,” admits Buijs, “but factors such as ease of use, high reproducibility of manipulations, and high throughput of samples all play an increasing role in our business.”

At the heart of an electron microscope are mechatronic specimen-manipulator stages, which FEI develops. The company is developing new stages that will make it possible to work in the 1 nm world in three dimensions. This new manipulator demands a movement and positioning accuracy down to the atomic level, which will be realized through a combination of special stage mechatronics and the new motion control system.

“Paradoxically,” Buijs points out, “the small world we are entering demands a different approach than the one required by manufacturers in other branches, who normally want high positional accuracy at the fastest possible speed. Samples must be handled with extreme precision. Rather than scanning at high speed, we require low-speed behavior for our application, which uses a fairly new type of actuator called an ultrasonic piezo motor .” At 1 nm per second, the slow-but-smooth motion required can be compared with the growth speed of a hair.

Expectations for the NewMotion project center on a new generation of motion control systems that will shift reliance from electronic hardware to software and system components. The collaborators also expect significant improvements in performance, functionality, and price savings.

The movement accuracy using the multi-axis manipulator on a TEM, for example, is critical for the quality of the electronic scan. This demands very slow movements at speeds of no more than 1 nm/s. In turn, this requires a high resolution with a step size of 1 nm. With this project, the targeted speeds are a 15-fold improvement on current capabilities. A big challenge to overcome is the achievement of shock-free movement. Since just a small number of encoder steps are made per increment of time, huge demands are placed on the regulator in the control unit. This must be able to generate a homogenous speed profile so that the actual speed of the sample being manipulated remains constant. In addition, there is always a certain amount of vibration in a mechatronic system that can affect the end position accuracy—a factor that is being taken into account in the design and construction phase.

Similarly, a new generation of manipulators with multiple axis coordinates will improve motion system performance and dynamic behavior by a factor of ten. The collaborators expect to achieve these results largely through new, balanced mechatronic constructions that make use of thermal compensation, vibration damping, and a new type of linear measurement scale coupled with play-free transmission. In concrete terms, this will deliver positional accuracy on the order of 100 nm with a relative accuracy of 10 nm and a drift of 0.1 nm/min. A special balanced thermal-compensation system, whereby temperature as a function of time is held constant, is being developed to achieve this extremely high level of stability.

Although slowness of motion appears more relevant than speed in microscopy applications, the manipulator’s measurement speed will improve by a factor of five to ten compared with existing systems. This raises the possibility to carry out measurements on multiple products in a reduced number of operations. The measurements in this case would take place sequentially, but samples would be placed in the measurement room in a single charge. All thermal and movement-critical effects would thus be much smaller than in the existing situation where just a single measurement sample is loaded at a time.

For its part, Bosch Rexroth is supplying hardware modules for various application areas, such as low power, high power, and piezo control—all with the electronic drive and the control in a single unit. The hardware architecture enables the required functionality to be developed with software. Similarly, software modules for applications, configuration, tuning, simulation, path generation, testing, and measurement are being developed to support the customer in implementing motion in a machine.

C.G. Masi , senior editor Control Engineering Machine Control eNewsletter

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