Sunday May 17, 2009 WorkShop sw-f1: Control Issues in the Micro/Nano-World

- Daniel Jasper

Division Microrobotics and Control Engineering (AMiR)
Department of Computing Science, University of Oldenburg,
D-26111 Oldenburg

Contact: daniel.jasper 'at' kisum.uni-oldenburg 'dot' de


Force control for nanohandling inside Scanning Electron Microscopes


In addition to reliable microrobot positioning, applying a controllable amount of force during a nanohandling or -assembly operation is essential for the reliability of the operation itself as well as the resulting product. E.g., excessive force generated by a nanogripper could damage the handled object and thus make the resulting product unusable. Insufficient force on the other hand can lead to improper gripping and thus misalignment or loss of the object.

Integrating force sensors into nanotools, however, is difficult. Due to the required small size, possible force sensing mechanisms such as piezoresistive feedback are noisy, have a limited dynamic range, could be in uenced if hit by the electron beam of a scanning electron microscope (SEM), and require tedious wiring.

Due to the required visual feedback, most nanoscale operations are currently performed in an SEM. With the approach presented in a previous work, it is possible to obtain highly dynamic position information using the SEM as position sensor. Simultaneously tracking a fixed point and the end of a well-known bending structure such as a cantilever or a gripper jaw, the applied force can also be measured with a high update rate (up to 1kHz) and high resolution (in the nN range, but only dependent on the bending structure). Thus, it is possible to integrate precise force sensors into virtually every nanotool used for SEMbased nanohandling without complicating the tool's manufacturing process or requiring additional cabling.

Preliminary tests with an electrothermal microgripper handling a multiwalled carbon nanotube have shown that a simple PID controller is sufficient to control the exerted force. The patterns required for position tracking could easily be created on the gripper using electron beam-induced deposition. A comparison to a cantilever with piezoresistive readout has shown the approach's advantages in terms of noise and accuracy.

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