Patent ID: 7861560

Claim:
A drum type washing machine comprising: a cabinet body; a water tub installed in the cabinet body; a rotating drum installed in the water tub receiving laundry to be washed, the rotating drum including a front cover with an opening provided at a front side of a drum body to receive laundry and a rear cover provided at a rear side of the drum body; and a balancer to compensate for an imbalanced mass during rotation of the rotating drum, the balancer including a housing mounted on the rotating drum and a plurality of balls movably disposed within the housing, wherein a number of the balls (n) disposed in the housing of the balancer and the weight of each individual ball (m) disposed in the housing of the balancer are selected such that a mass imbalance of at least 300 grams is capable of being compensated by the balancer during the rotation of the rotating drum and such that the following conditions are satisfied: Ï*4/3Ï€( d/ 2)3=m, 12mm<d<30mm, ( d*n/R )*(180Â°/Ï€)=Î¸, 18.5Â°<Î¸<100Â°, and 3<n<43, wherein Ï is a specific gravity of the balls, d is a diameter of the balls installed in the housing of the balancer, and R is a radius of the balancer, m is the weight of a single ball, and Î¸is a central angle of a sector defined by the center of the balancer and the balls installed in the balancer, wherein an annular recess is formed in at least one of the front cover and the rear cover of the rotating drum to accommodate the balancer, wherein the balancer housing includes a first balancer housing section and a second balancer housing section, which are coupled to each other to define a race therebetween, and wherein the balancer housing is installed in the annular recess of the rotating drum such that the plurality of balls disposed completely within the balancer housing do not establish direct contact with any portion of the rotating drum including the annular recess.