Agonistic/Antagonistic Vsa - QB Robotics qbmove Advanced Kit User Manual

3.2.1

Agonistic/Antagonistic VSA

The qbmove Advanced embeds the features of a servo motor and, moreover, the possibility of
adjusting the output shaft stiffness.
The Figure 3-9 shows a scheme of the agonistic/antagonistic VSA principle, implemented in our
actuator. Basically, there are two motors connected at the output shaft by non-linear springs, so
the output position "x" and the stiffness "σ" depend on the motors' positions "q " and "q ", on
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the torque "τ" and on the mathematical model of the system.
Figure 3-9 Agonist/Antagonistic VSA model.
All these quantities are each other connected, then, to evaluate a proper mathematical model
experimental data are needed.
Using a pendulum structure, a sinusoidal movement with different frequencies, and different
stiffness presets, the obtained results can be synthetized in the graphic below; where the
deflection "δ" is the difference between the angular position of the output shaft δ = x - (q
+q )/2
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and the stiffness preset is (q - q )/2.
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Figure 3-10 Experimental Torque Deflection Characteristic.
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28 aprile 2021