Chapter 9 - Design for load compensation
Balanced Scan stage for in Electron microscope
Description
Delmic developed a confocal microscope in an electron microscope. The systems makes combined electron optical and optical images of a few square micrometers of biological samples.
The throughput of the system had to be increased by means of scanning over an area of 70 x 70 micrometer.
Therefor a dedicated flexure based scanning stage has been developed. The application is in UHV environment. Space was limited. Available height 14 mm. The stage developed is a feed forward controlled stage with an accuracy 10 nm. Feed forward model based control at 10 nm and high scan speed was possible due to a very high overall stiffness.
The design consists of a flexure system: 3 dof support by folded leafspring of sample holder Scanning is realized by 2 piezo. Step actuation is realized by a third piezo perpendicular on the scanning direction.
To eliminated reaction forces, balance masses have been implemented.
These balance masses are actuated by the same piezos but moving in the opposite direction by means of flexure based guiding and lever.
| Application: 2 DOF Scan stage in Electron Microscope in Ultra high vacuum | Realized: 14 mm thick flexure stage with balance masses and feed forward model based motion control | Principle: By 3 Folded leafspring suspended stage, 2 piezo’s in Y/ scan direction balanced with M1 + M2 and one piezo in step direction balanced by M3 + M4 |
Key Requirements
| Accuracy | 10 nm |
| Stroke | 70 x 70 micrometer |
| Scan speed | 20 Hz |
| First eigenfrequency | 1400 Hz |
| Reaction force reduction | >= 50 |
| UHV environment | 10-6 mbar |
| Clear optical aperture | 50 mm |
Development by:
- Hittech, TUDelft, Delmic
- Pjotr Sebek, Jesse van Koppen, Pieter Kappelhof, Just Herder
