A novel vision-based position sensing solution to determine the accuracy of Optical and Electron microscopy stages and solve positioning issues

Session

Poster Session Three

Authors

Olivier Acher (1), Nguyên Thanh-Liêm (1), Philippe de Bettignies (1)

Affiliations

1. HORIBA France SAS

Keywords

optical microscopy, electron microscopy, moving stage, position accuracy, scale, encoder, drift, vibration

Abstract text

Summary:  A novel solution to determine the performance of microscopy stages is described. With this so-called nanoGPS OxyO solution, bidirectional reproducibility and positioning accuracy can be determined with a precision of 1nm and an accuracy better than 100nm. It also makes it easy to determine different angles that can be sources of errors: misalignement between stage and camera axes; deviation form orthogonality between X and Y axes; straightness error of translation stages. With this solution it is also possible to determine drifts (such as thermal-induced drifts due to the deformation of the microscope body with temperature), and vibrations (such as vibrations induced by stopping the stage translation).

Introduction:

A good accuracy of motorized stages is key to implement correlative microscopy workflows, automation, and for metrology. However, there is no convenient solution yet to allow on-site investigations of microscopy stage precision and accuracy. Recently, we introduced a position-sensing solution [1-3] suitable for optical and electron microscopy [1]. In this so-called nanoGPS-OxyO technology, a scale featuring a field of microscopic patterns looking like QR codes is placed on sample holder; images of the scale are recorded with the microscope; and a software interprets each image into in-plane coordinates and orientation. A precision of about 1nm and an accuracy better than 150nm over 800mm has been demonstrated [3]. The accuracy of angle measurement has been shown to be better than 100µrad [2].

Methods & Results:

Using nanoGPS-OxyO scales and software, we investigated the performance of the translation stages on three optical and two electron microscopes. We report the results for these 5 microscopes, in terms of X-Y accuracy, bidirectional reproducibility, and straightness.

We determined the deviation of the field of observation when switching the objective turret of an optical microscope. Since the nanoGPS measurement is simple to perform and precise, we were able to perform this experiment a number of time in order to obtain significant statistics. 

We also investigated experimentally positioning issues related to the stability of the microscope frame. We recorded the position obtained with nanoGPS at fixed stage position and evidenced the drift of the observation point with time. This provides a simple way to investigate the efficiency of methods to decrease the drift (such as improved air flow circulation or tighter thermal control). The nanoGPS technology can be very helpful to solve vibration issues on optical microscopes. Position determination with up to 300Hz frame rate is demonstrated with a normal microscopy camera. We report the experimental investigation of the response of a commercial microscope to external shocks. We also report the vibrations created by the internal shock associated to the stage stop. We determine experimentally the spatial blurring as a function of time after shock. It makes it easy to decide for a “wait time” after stage stop, or to tackle stage settings to decrease the vibrations created by the stage stop.

In conclusion, the observation of nanoGPS scales through a microscope provides accurate information on position and orientation of the field of view, in real-use conditions. It can be helpful to identify the limiting factors in positioning accuracy or stability for a given application and environment, and solve the issues.

References

[1] O. Acher, T.-L. Nguyên, A. Podzorov, M. Leroy, P.-A. Carles and S. Legendre, An efficient solution for correlative microscopy and co-localized observations based on multiscale multimodal machine-readable nanoGPS tags, Measurement Science and Technology 2021 Vol. 32 Issue 4 Pages 045402

[2] M. Pisani, M. Astrua, P.-A. Carles, S. Kubsky, T.-L. Nguyên and O. Acher, Characterization of Angle Accuracy and Precision of 3-Degree-of-Freedom Absolute Encoder Based on NanoGPS OxyO Technology, Sensors 2020 Vol. 20 Issue 12 Pages 3462

[3] O. Acher  and T.-L. Nguyên 2019 Turning a machine vision camera into a high precision position and angle encoder: nanoGPS-OxyO Proc.SPIE 11056 (2019)