Patent ID: 8512476

Claim:
An ultrasonic cleaning method using an ultrasonic wave irradiation means for irradiating ultrasonic waves to a cleaning fluid retained in a cleaning bath, and a bubble supply means for supplying bubbles to said retained cleaning fluid, the method comprising: cleaning an article-to-be-cleaned immersed in said retained cleaning fluid by irradiating ultrasonic waves to said retained cleaning fluid by means of said ultrasonic wave irradiation means in a state where bubbles exist in said retained cleaning fluid by virtue of the operation of said bubble supply means, wherein the bubble supply means supplies bubbles to the retained cleaning fluid by circulating the retained cleaning fluid through a pump and mixing a gas into the cleaning fluid discharged from the pump; controlling an operation of said ultrasonic wave irradiation means by adjusting a combination of frequency and power to the ultrasonic wave irradiation means so as to materialize the relation represented by the following equation: 0.04 f− 20.0≦ P≦ 0.09 f− 7.5 where f (unit: kHz) is the frequency of the ultrasonic waves irradiated by said ultrasonic wave irradiation means, and P (unit: W/L) is the power per unit fluid volume obtained by dividing the power (unit: W) of the ultrasonic waves irradiated by said ultrasonic wave irradiation means by the volume (unit: L) of said retained cleaning fluid; and controlling the operation of said bubble supply means by adjusting a circulation flow rate of the cleaning fluid and a mixing flow rate of the gas so that a proportion of a brightness value of the cleaning fluid is 0.75 or less wherein the brightness value is determined by processing photographic images of the cleaning fluid to determine the proportion of the brightness value of the cleaning fluid after 5 seconds has passed since both said ultrasonic wave irradiation means and said bubble supply means are concurrently operating to a brightness value of the cleaning fluid when no bubbles exist in said retained cleaning fluid.