In a method to regenerate during operation ink in nozzles of at least one inkjet print head operating according to drop on demand in an inkjet print apparatus, nozzles of the print head that generate print dots on a printing substrate are activated such that the nozzles output first ink droplets of a predetermined volume in a direction towards the printing substrate. The main bearing directly supports a torque inputting means and defines a rotational axis. The planar liquid crystal cell is sandwiched between the reflective electrode layer and the transparent conductive film. Further, small air circulation holes are provided above and below the annular projection of the shaft body, and the holes enable air to circulate through the inside of the shaft body. A surface layer region including the surface of the center electrode 3 which is exposed to the resistor 15 is a metallic layer 30 formed of a metal based on at least one of Zn, Sn, Pb, Rh, Pd, Pt, Cu, Au, Sb and Ag or a Ni alloy containing at least one of B and P, so that the center electrode 3 is provided in direct contact with the resistor 15 on the surface of the metallic layer 30.