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FT sensor

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The F/T sensor of the iCub

The F/T sensor (6-dof) has also been specially designed to fit the iCub. However, the size of the sensor has been made compatible with an existing commercial product. On the other hand the signal conditioning electronics has been made to fit the sensor itself, consequently reducing the space required. The F/T sensor is based on a classical Wheatstone bridge design employing 12 semiconductor strain gauges arranged in a 6 half-bridges configuration.

Contents

Mechanical specifications

Physical specifications

  • The physical specifications of the sensor are reported in Table 1.
Weight 0.122[kg]
Diameter 45[mm]
Height 18.4[mm]
Table 1: Physical specifications of the sensor


Measurement frame specifications

FtsensorCoord.jpg

The F/T sensor reference frame. Please notice that key elements to localize the reference frame on the sensor are two: (1) the hole where the CAN exits the sensor and (2) the thick VS the thin sensor cover.

The sensor is calibrated to measure the Force/Torque applied by the upper (blue) part of the sensor on the lower (red) part of sensor, and express it on the F/T sensor reference frame.


Calibration specifications

The sensors are calibrated in order to obtain high resolution in typical operating regions. Typical values of the range and resolution for a sensor after the calibration procedure are reported in Table 2. The resolution is typical for most applications and can be improved with filtering. Resolutions quoted are the effective resolution after dropping three counts of noise.

Fx, Fy [N] Fz [N] Tx, Ty [Nm] Tz [Nm]
Range 2000 2000 40 30
Resolution 0.25 0.25 0.0049 0.0037
Table 2: typical values after sensor calibration

Creo CAD model

The CAD model of FTSens is available in the hardware repository of the iCub, for more information please check the hardware repository wiki page.

In particular the FT sensor assembly name is public/icub1_icub2/ftsensor45a.asm.1.

Additional info

Additional specification are reported in the document: FTSens.pdf .

For more info on how to load the firmware and the calibration matrix on a FT sensor, check the wiki page on Firmware.

Electronics

  • The F/T sensor electronics is called STRAIN and it is available from the iCubPlatform SVN module. In particular see here .
  • In iCub version 1.x there are four F/T sensors on the iCub located in the upper arms and upper legs respectively. In iCub version 2.x two additional F/T sensors are mounted in the ankle, for a total of six F/T sensors.
  • F/T sensors communicate via the CAN bus. The list of the CAN addresses employed on the iCub is reported here .
  • For info on how to load a new firmare build or a new calibration matrix on a sensor, please check the Firmware wiki page .

More information


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