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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.
- The physical specifications of the sensor are reported in Table 1.
Measurement frame specifications
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.
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]|
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
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.
There are three versions of the electronic board of the iCub's FT sensor: STRAIN (also known as STRAIN1), STRAIN1.5 or STRAIN2. All this electronic boards sample the analog strain gauges voltages, and expose the measurements over a CAN interface.
Low-level documentation and materials about the STRAIN board is available at here .
The user-manual for the STRAIN1 board is available at MU2007_RBCS_RC_STRAIN_0004.pdf . No user manual is currently available for the STRAIN1.5 and STRAIN2 boards.
Firmware source code for STRAIN1/STRAIN1.5 is available in the sensorReaderDspic30f4013/strain directory of the icub-firmware github repository, while the source code for the STRAIN2 is available in the emBODY/eBcode/arch-arm/board/strain2 directory of the icub-firmware github repository.
For info on how to load a new firmare build or a new calibration matrix on a sensor, please check the Firmware wiki page .
If you have access to iCub Facility's internal redmine, you can find more information about the FT sensor electronics at https://redmine.robotology.eu/projects/hardware/wiki/Force-Torque_sensors .
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