Fig. 3. The dynamic properties of the force measurement system were verified by measuring the step response. (A) Before the step input. A 3 mN weight [load (I)] was loaded on the load cell, for the purpose of adjusting the weight condition to the experiments. In addition, a 5 mN weight [load (II)] and an electromagnet were prepared. Load (II) was iron, and pushed up the load cell by the magnetic force of the electromagnet. The magnetic force worked on load (II) was approximately 7 mN. Note that the magnitude of the additional force does not have an influence on the step response result. (B) After the step input. When the electromagnet was switched off, load (II) was immediately detached from the load cell, which signified the step input. Variations in the voltage of the electromagnet circuit and the output of the force measurement system were recorded at a sampling frequency of 10 kHz.