A network management apparatus and method reduces the number of events presented in an event list to a user. The method includes the recording of x-ray images at different relative positionings of the x-ray device, which contain the first and the second point respectively. In low-speed sensorless control, the magnetic salient pole of the motor is exploited, and the d-q axes are estimated by, for example, injection of a high-frequency rotating voltage. The electrode gap may be maintained by interposing a non-electrically conducting material between the electrodes. The hooks are placed at different intervals from the operating mechanism. The device is made of titanium with a native oxide layer on the surface.