SP2-Sensing: Development of sensing tools
Download SP2 presentation in pdf format: clic here
3.2 - Passibve levitation sensor [3] [4]
This sensor operates on the principle of passive levitation. The sensitive body consists of a glass
capillary maintained in levitation passively through a set of permanent magnets and diamagnetic graphite
(fig.2). The stiffness is provided by the magnetic forces. It is as if the capillary,
which is considered rigid, is connected to a magnetic spring acting in the horizontal direction. The measurement
is performed in this direction for one component of the effort.
Fig.2 - 1 glass capillary, 2 permanent magnets, 3 diamagnetic graphite plate,
4 laser sensor, 5 positioning device..
Features:
- stiffness between 0.02 and 0.04 N/m depending on the setting of permanent magnets,
- force measurement from 0 to 200 µN, with a resolution of 50 nN,
- filtering of the measurement by a Kalman filter (elimination of the dynamic component
due to the aceleration of the capillary), - measure one component of an horizontal force,
- calibration of stiffness by exciting the eigen mode in the direction of measurement.
Known limitations:
- bandwidth less than a few hertz,
- extreme sensitivity to vibration and surrounding air currents, especially in the range of LF.
The development and refinement of this sensor are funded by ANR Psirob Stilmicroforce.
3.3 - Femto tools sensor
This is a silicon sensor micro-machined by the society Femto Tools. The displacements of the sensitive
body are measured with a capacitive sensor integrated into the structure (fig.3).
Fig.3 - Femto tools sensor.
Features:
- stiffness of 1000 N/m,
- measurement from 0 to 2 mN with a resolution of 1µN,
- measure one component of an horizontal force.
Known limitations:
- range of force exceeding the range that of the sensors described above (section 3.1 and section 3.2),
- most suitable for measurement of surface tension or to apply important load.