A whisker sensor with a tetrapod particle-infused jamming actuator for extensive measurement range

The whisker sensor, with its long and slender shape, bends in response to external forces, enabling it to measure force or strain. To enhance sensitivity, it is advantageous for whiskers to bend easily, for which soft polymers are used. Since the bending magnitude changes with the Young’s modulus of the soft polymer, the measurement range of the sensor is determined by the material composing the whisker, assuming the structure remains the same. Meanwhile, the jamming effect, previously utilized to adjust the stiffness of soft actuators/grippers, involves the change in stiffness through the alteration of the spatial occupancy rate of spherical particles within a soft chamber, as the internal pressure is adjusted. For the first time, we applied the jamming effect to the whisker sensors, developing a whisker sensor with a variable stiffness that allows for a wide measurement range. Notably, using tetrapod particles instead of spherical ones increased the sensor’s measurement range by 2.7 times, maintaining an average sensitivity of $80 \mathrm{~mm} / \mathrm{N}$ within the measurement range. Particularly, to enhance the jamming effect, tetrapod particles, which have a higher contact area and thus greater friction between particles compared to spherical ones, were used in the jamming actuators. Consequently, the whisker sensor demonstrated the capability to measure with high sensitivity across a range of $0-240 \mathrm{mN}$ by effectively utilizing both soft and stiff modes. Therefore, the reported whisker sensor is expected to contribute to the improvement of sensor performance in measuring fine forces.