A robot cleaner and a method for controlling a robot cleaner are provided. The method may include sensing a stored value of a pulse width modulation (PWM) duty ratio based on a voltage of a battery; comparing a measured value of the PWM duty ratio with the stored value to calculate a difference between the measured value and the stored value; upon determining that the difference between the measured value and the stored value is equal to or greater than a first set value, calculating a distributed value of acceleration on a substantially vertically extending axis of the robot cleaner; and, upon determining that the distributed value of acceleration deviates from a range of a second set values, increasing a force to suction foreign matter.