An apparatus for moving a mass, the apparatus having an arcuate track, a clamping member attached to a section of the arcuate track, an arm assembly pivotably connected to the clamping member, and a counterweight connected to the arm assembly. The rectifier circuit includes a plurality of diodes and is connected to the secondary coil to rectify a voltage outputted from the secondary coil. Thus, even if the bidirectional printing is displaced, printing widths are equally increased or reduced in the respective regions. The spring lock is adapted to engage the security pin when in an engaged position and release the security pin when in a released position. A threaded body in the boltnut connection is fixed, preferably plug welded, in the main part of the beam.