Fig. 4. Measurements of the mechanical strength of the claw. (A) Principle of force measurements using the force tester Basalt-01 (Tetra GmbH, Ilmenau, Germany). The claw (CL) was glued to the platform (PF). The metal spring (MS) was driven downwards by the piezo-drive until the claw was broken. Displacement of the spring tip equipped with a mirror M was detected in the vertical direction by the fiber optical sensor (FOS). (B) Force—distance curve obtained in experiments with the claw and used to calculate breaking stress of the claw.