Window cleaning apparatus and method of controlling the same

A window cleaning apparatus with a first cleaning unit and a second cleaning unit attached on opposite surfaces of a window, respectively, through a magnetic field, and moving or rotating in a first direction on the opposite surfaces of the window, the window cleaning apparatus comprising:

• a first magnetic module included in the first cleaning unit;
• a second magnetic module included in the second cleaning unit;
• a control part moving or rotating at least one of the first and second cleaning units in a second direction opposite to the first direction when the magnetic field between the first and second cleaning units is out of a normal range;
• and
• a magnetic sensor configured to sense the magnetic force between the first and second cleaning units,
• wherein, if the sensed magnetic force is weaker than a reference value by a moving or rotating one of the first and second cleaning units in a first moving or rotating direction, the control part is configured to move or rotate at least one of the first and second cleaning units in a second moving or rotating direction that is opposite to the first moving or rotating direction,
• wherein the first and second moving or rotating direction is parallel to the surface of a window.