Patent ID: 8621893

Claim:
A method of controlling a drum type washing machine having a tub, a drum rotatably installed inside the tub, a motor rotating the drum, and a balancer installed on at least one of a front end and a rear end of the drum, the method comprising: sensing a rotational speed of a motor by a number sensing unit in a dehydration operation according to drive of the motor; determining whether or not the sensed rotational speed of the motor reaches a designated rotational speed by comparing the sensed rotational speed of the motor with the designated rotational speed; positioning balls in the balancer in a balancing position by maintaining the rotational speed of the motor at the designated rotational speed when it is determined that the sensed rotational speed of the motor reaches the designated rotational speed; measuring a time for maintaining the rotational speed of the motor at the designated rotational speed, and determining whether or not the measured time exceeds a designated time (t 1 ) that is calculated based on a time taken to reach a rotational speed of generating excessive vibration of the tub from the designated rotation speed; sensing, by a vibration sensing unit, vibration of the tub generated due to a difference between a rotational speed of the drum and a rotational speed of the balls when it is determined that the measured time exceeds the designated time (t 1 ); and increasing the rotational speed of the motor to a dehydrating rpm before a lowermost signal point at which a vibration frequency of the sensed vibration of the tub reaches a lowermost value, wherein in the maintaining the rotational speed of the motor at the designated rotational speed, the rotation speed of the motor is maintained at the designated rotation speed positioning the balls in the balancing position so as to pass a point at which the excessive vibration of the tub is generated in the dehydration operation, the designated rotation speed being prior to the point.