In a method for monitoring a stationary condition of a drive device, a monitoring device provides the drive device with a temporally varying monitoring signal which, when a sensor device connected to the drive device functions properly, modulates a sensor output signal of the sensor device in accordance with the monitoring input signal. The planetary gear mechanism comprises a sun gear, planetary gears supported on a carrier, and a ring gear having internal teeth and external teeth, the internal teeth engaging with the planetary gears. , cars, trucks, buses, aerospace vehicles including airplanes, and the like. Consequently, it is possible to prevent or suppress a reduction in print quality such as changes in density or the occurrence of voids due to displacement of the mounting positions of ejection heads in the overlapping range.