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Ultrasonic processing method and apparatus with multiple frequency transducersRelated Patent Categories: Cleaning And Liquid Contact With Solids, Liquid Treating Forms And Mandrels, Including Application Of Electrical Radiant Or Wave Energy To WorkUltrasonic processing method and apparatus with multiple frequency transducers description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070283979, Ultrasonic processing method and apparatus with multiple frequency transducers. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATION [0001] This divisional application claims priority from U.S. patent application Ser. No. 10/983,183 filed Nov. 5, 2004 entitled ULTRASONIC PROCESSING METHOD AND APPARATUS WITH MULTIPLE FREQUENCY TRANSDUCERS which claims priority to U.S. Provisional Application No. 60/517,501, filed Nov. 5, 2003, entitled ULTRASONIC PROCESSING METHOD AND APPARATUS WITH MULTIPLE FREQUENCY TRANSDUCERS. These applications are expressly incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention relates generally to ultrasonic cleaning and liquid processing methods and apparatus and other uses involving two or more piezoelectric transducers, and relates more particularly to improving performance by using ultrasonic energy at multiple frequencies. [0004] 2. Description of the Relevant Art [0005] Ultrasonic devices are used in a variety of processes, including cleaning, emulsifying, and dispersing components or parts in a liquid medium, and other applications such as metal welding, plastic joining, and wire bonding. All these devices and processes use ultrasonic transducers to supply ultrasonic frequency sound waves to a liquid or solid medium. [0006] Cleaning parts in a liquid medium is one common use of ultrasonics. Cleaning with ultrasonics uses ultrasonic waves to generate and distribute cavitation implosions in a liquid medium. The released energies reach and penetrate deep into crevices, blind holes and areas that are inaccessible to other cleaning methods. [0007] Ultrasonic waves are pressure waves formed by actuating the ultrasonic transducers with high frequency, high voltage current generated by electronic oscillators (typically referred to as power supplies or generators). A typical industrial high power generator produces ultrasonic frequencies ranging from 20 to 300 kHz or more. Ultrasonic transducers typically include piezoelectric (PZT) devices that expand and contract when subjected to the oscillating driving signals supplied by generators. The transducers are normally mounted on the bottom and/or the sides of the cleaning tanks or immersed in the liquid. The generated ultrasonic waves propagate perpendicularly to the resonating surface. The waves interact with liquid media to generate cavitation implosions. High intensity ultrasonic waves create micro vapor/vacuum bubbles in the liquid medium, which grow to maximum sizes proportional to the applied ultrasonic frequency and then implode, releasing their energies. The higher the frequency, the smaller the cavitation size. [0008] The energy released from an implosion in close vicinity to the surface collides with and fragments or disintegrates the contaminants, allowing the detergent or the cleaning solvent to displace it. The implosion also produces dynamic pressure waves which carry the fragments away from the surface. The cumulative effect of millions of continuous tiny implosions in a liquid medium is what provides the necessary mechanical energy to break physically bonded contaminants, speed up the hydrolysis of chemically bonded ones and enhance the solubilization of ionic contaminants. [0009] In general, at low frequencies (20-30 kHz), a relatively smaller number of cavitations with larger sizes and more energy are generated. At higher frequencies, much denser cavitations with moderate or lower energies are formed. Low frequencies are more appropriate for cleaning heavy and large-size components, while higher frequency (60-80 kHz) ultrasonics is recommended for cleaning delicate surfaces and for the rinsing step. [0010] In some applications it is advantageous to use multiple transducers operating at different frequencies in combination. See, for example, U.S. Pat. No. 6,019,852 and U.K. Patent 1,488,252. These patents disclose cleaning apparatus with rectangular grids of two different frequency transducers, separately driven by two power supplies or generators. SUMMARY OF THE INVENTION [0011] One aspect of the present invention is an ultrasonic processing apparatus and method having multiple transducers of at least two different resonant frequencies supplying ultrasonic energy to a liquid filled tank containing components to be cleaned or processed ultrasonically. The transducers are preferably of a stacked construction and are arranged in equilateral triangular patterns along diagonal lines on the bottom wall or side walls of the tank so that each transducer has an adjacent transducer of a different frequency. [0012] A second aspect of the present invention is an ultrasonic processing apparatus and method having one or more rod transducers (push-pull or single-push types) with ultrasonic converters or transducers mounted on one or both aids and installed in a liquid-filled tank containing components to be cleaned or processed ultrasonically. The rod transducers have different resonant frequencies so that the apparatus provides a mixture of various frequencies of ultrasonic energy to the tank. [0013] A third aspect of the present invention is an ultrasonic processing apparatus and method having multiple transducers or piezoelectric crystals with different resonant frequencies and a generator or power supply that powers the transducers or piezoelectric crystals operating throughout a frequency range that spans the different resonant frequencies. Preferably,. the transducers or piezoelectric crystals are paired together and have at least a minimum difference in resonant frequencies. In other words, within the frequency range of driving signals supplied by the generator, there is a predetermined subrange in which none of the transducers or piezoelectric crystals have a resonant frequency. [0014] These aspects of the present invention provide, either individually or in combination, an improved performance ultrasonic cleaning and liquid processing method and apparatus. [0015] The features and advantages described in the specification are not all inclusive, and particularly, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification and claims hereof. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter, resort to the claims being necessary to determine such inventive subject matter. For example, the specification uses the terms transducer, converter, and piezoelectric crystals to refer to devices that generates ultrasonic vibrations in response to an electrical driving signal. Also, the term resonant frequency includes a fundamental harmonic frequency of a transducer or piezoelectric crystal, and also includes higher order harmonics. BRIEF DESCRIPTION OF THE DRAWINGS [0016] FIG. 1 is a view of an arrangement of two types of ultrasonic transducers on a tank wall according to one embodiment of the present invention. [0017] FIG. 2 is a view of an arrangement of three types of ultrasonic transducers on a tank wall according to another embodiment of the present invention. [0018] FIG. 3 is a view of an arrangement of two types of ultrasonic transducers and a center drain according to another embodiment of the present invention. [0019] FIG. 4 is a view of an arrangement of three types of ultrasonic transducers and a center drain according to another embodiment of the present invention. [0020] FIG. 5 is a view of the arrangement of two types of rod transducers on a tank wall according to another embodiment of the present invention. Continue reading about Ultrasonic processing method and apparatus with multiple frequency transducers... 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