United States Patent 3596883

An ultrasonic cleaning apparatus has a plurality of electroacoustic transducers mounted to a container for providing ultrasonic energy to a liquid confined in the container. Each transducer is coupled to an individual electrical circuit for forming therewith a separate oscillatory circuit.

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Primary Class:
Other Classes:
134/184, 366/127
International Classes:
B06B1/02; B06B1/06; B08B3/12; (IPC1-7): B01F11/02
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Primary Examiner:
Machlin, Leon G.
What I claimed is

1. An ultrasonic cleaning apparatus comprising:

2. An ultrasonic cleaning apparatus comprising;

3. An ultrasonic cleaning apparatus as set forth in claim 2, each of said elctroacoustic transducers including a piezoelectric disk.

4. An ultrasonic cleaning apparatus as set forth in claim 2, said electroacoustic transducers and circuits operating substantially in the same frequency range.

5. An ultrasonic cleaning apparatus as set forth in claim 2, said electrical circuits being unitized assemblies, each assembly replaceable independent of other assemblies.

6. An ultrasonic cleaning apparatus as set forth in claim 5, said electrical circuits being mounted on respective circuit cards.

7. An ultrasonic cleaning apparatus as set forth in claim 2, each of said electrical circuits being provided with independent overload protection.

8. In ultrasonic cleaning apparatus comprising a cleaning tank having a chamber for holding a body of liquid and a plurality of electroacoustic transducers coupled to at least one wall of said chamber and responsive to the application thereto of oscillatory electrical voltage to produce sonic vibrations in said walls which are transmitted to said body of liquid from each of said transducers, the improvement comprising:

This invention refers to an ultrasonic apparatus and has particular reference to an ultrasonic apparatus usable for cleaning purposes. More specifically, this invention refers to an ultrasonic apparatus using a plurality of electroacoustic transducers which provide ultrasonic energy of a body, typically a quantity of liquid confined in a container.

Present ultrasonic cleaning apparatus, excepting small units, comprise a steel tank or container fitted with a plurality of electroacoustic transducers adapted to be energized by electrical high frequency energy. The transducers, in turn, impart sonic energy to a body of liquid in the container and cause cavitation in the liquid. Most frequently, the transducers are mounted to the exposed underside of to a sidewall of the container using mechanical fastening or adhesive bonding means, or alternatively, the transducers may be mounted also in a liquid-proof enclosure which is immersed in the liquid. The plurality of transducers, all connected electrically in parallel, are connected to a common electronic circuit which energizes the transducers and forms an oscillatory circuit therewith, Typically, an arrangement of this type may operate in the frequency range from 18 to 60 kHz. and provide sonic power from 500 watts to many kilowatts.

It will be apparent that the electronic circuit must be designed for the total power rating of the transducers and that there is a complete shutdown of such an ultrasonic cleaning apparatus if a single major component becomes defective. Moreover, since the various transducers are connected in parallel, they must be selected with regard to their natural mechanical resonance and with respect to their electrical impedance in order that these values match and be compatible. In a typical ultrasonic apparatus such a plurality of transducers may comprise from two to 24 transducers having a total power rating of many kilowatts. It will be apparent that the pretesting of each transducer and the selection of matched characteristics is time consuming and burdensome. Additionally, a "perfect" electrical and mechanical match is difficult to achieve and inevitably the best match is a compromise.

The invention described hereafter discloses a unitized design wherein each transducer of a plurality is coupled to its own electronic circuit and forms an independently operated oscillatory circuit. This arrangement has been made possible especially by the use of transistorized circuits designed to closely match the power capability of a transducer and by other constructional features which will be described hereafter. The main advantages achieved by this novel arrangement reside in the features that a particular circuit may be or become inoperable without affecting the performance of the other circuits, the possibility of almost instantaneous replacement of a complete electronic circuit and last, but not least, the individual transducers may vary with regard to their respective impedance value and natural mechanical resonant frequency, thus eliminating the need for a matched grouping.

It is obvious, therefore, that an ultrasonic cleaning unit constructed in accordance with this teaching is characterized by greater reliability, ease of maintenance and repair, and continued operation in the event that one or more of the individual circuits or transducers should become defective and inoperative.

One of the principal objects of this invention is, therefore, the provision of a new and improved ultrasonic apparatus.

Another important object of this invention is the provision of an ultrasonic apparatus using a plurality of electroacoustic transducers for providing energy to a body coupled to the transducers, and each transducer being individually connected to a separate electrical circuit, whereby such circuit in conjunction with the associated transducer forms an oscillatory circuit.

Further and still other objects of this invention will be more readily apparent by reference to the following description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic illustration of a typical ultrasonic cleaning apparatus;

FIG. 2 is a schematic illustration of a preferred mounting arrangement of an individual electronic circuit;

FIG. 3 is a schematic illustration indicating the electrical connection of a plurality of electronic circuits to a common alternating current input source, and

FIG. 4 is a schematic electrical circuit diagram of a typical circuit adapted to energize an electroacoustic transducer and form an oscillatory circuit therewith.

Referring now to the figures and FIG. 1 in particular, there is shown, as a typical example, an ultrasonic cleaning apparatus comprising a container 12 adapted to hold a quantity of liquid 14 into which an object 16 to be cleaned is immersed. The container 12, typically, is a stainless steel tank provided with a flange 13. The flange rests on the rim of a supporting enclosure 18 having a bottom plate 20.

The bottom of the container 12 is provided on its exterior surface with a plurality of piezoelectric disks 20a, 20b, and 20c, each of these disks being an electroacoustic transducer adapted to receive electrical energy and provide acoustic energy to the bottom of the tank 12 and the liquid 14 for causing cavitation. Typically, each transducer is made of lead zirconate-titanate (PZT) material 2" inches diameter by 0.100" inch thick and attached to the underside of the container 12 by means of a suitably epoxy resin, for instance Shell Chemical Company Epox Adhesive No 929. Alternatively, each piezoelectric disk may be attached first to a metallic resonator plate and the latter be bonded to the underside of the container 12 as disclosed in copending application for Letters Pat., Ser. No. 736,187 filed June 11, 1968, Kilian H. Brech, entitled "Sonic Energy Transducer" and now abandoned. Still further, each transducer may be of the clamped sandwich transducer construction as shown for instance in U.S. Pat. No. 3,066,232, to N. G. Branson, entitled "Ultrasonic Transducer," issued Nov. 27, 1962. Also, without deviating from the principle of this invention, each of the transducers 20a, 20b, and 20c may comprise a magnetostrictive transducer as illustrated for instance in U.S. Pat. No. 2,957,994 to C. W. Dickey, entitled "Magnetostrictive Transducer," dated Oct. 25, 1960.

The transducers attached to the tank are selected generally to have a natural mechanical resonant frequency which is within a predetermined range, for instance 45 to 46 kHz. but it will be appreciated that there may be instances where it is desired that the frequency of the individual transducers differs in order to set up multifrequency resonance conditions in the cleaning bath. Typically, a container may be provided with a first set of transducers and circuits for operation at 25 kHz. and a second set for operation at 50 kHz. Depending on the configuration and size of the charge to be cleaned, one or both of the oscillatory circuits and transducers can be activated. As is well understood by those skilled in the art, the transducers for different frequencies vary in size since the mechanical dimension of a transducer determines its mechanical resonance condition.

Each of the transducers, FIG. 1, is connected by suitable leads to an associated electrical circuit which, in the preferred embodiment, is mounted on a plug-in card, such as the cards 22a, 22b, and 22c, each card being mechanically supported in an associated rail 24a, 24b, and 24c. The individual circuit cards receive their input power from a common alternating current connector 30 which, via a cable 32 and a circuit switch 34, applies power to the individual circuits contained on the cards 22a, 22b, and 22c.

FIG. 2 is a schematic view of a circuit card, preferably of the type known as "printed circuit" card which contains all of the electrical components and electrical connections for energizing a single electroacoustic transducer. The circuit card 22a, as all of the other cards, is slidable with respect to the associated rail, such as rail 24a, and is constructed to plug-in into a stationary connector 23, there being one connector for each of the circuit cards.

FIG. 3 shows further, in schematic form, the plurality of circuit cards 22a, 22b, 22c, the associated plug-in connectors 23a, 23b, 23c and the electrical connection from these connectors to the common AC power line 32. The individual disk type piezoelectric transducers 20a, 20b, and 20c, may receive their electrical high frequency input energy directly from the respective circuit card, without going through the associated connector in order to avoid the additional capacitance provided by the interposition of a multicircuit connector. However, quick-disconnecting means are provided suitably in the leads between the circuit card and the associated electroacoustic transducer in order to obtain a quick connecting and disconnecting capability.

As illustrated in FIGS. 1, 3 and 4 forming a typical embodiment, the piezoelectric disks are connected to receive their electrical energy across their respective faces. The frequency of the alternating current electrical energy applied corresponds to the frequency which causes the respective transducer to resonate predominantly in its radial mode. This mode of operation is known also as the cross-connected coupling mode, and is revealed for instance in U.S. Pat. No. 2,741,754 issued to H. B. Miller, entitled "DIsk Transducer," dated Apr. 10, 1956. The purpose of this operating mode is to obtain a lower mechanical resonant frequency than that which would be obtained if the transducer disks were resonating at a frequency corresponding to the thickness dimension.

FIG. 4 is a schematic electrical circuit diagram of a transistorized class C oscillator adapted to drive piezolelectric disk transducer for causing vibratory energy to be imparted to the container 12 and from there to the liquid 14, producing cavitation in the liquid. The particular electrical circuit shown is only one of a variety of circuits which may be used and no limitation should be inferred. The electrical circuit contained within the dashed outline 44 is the electrical circuit which is contained on a particular circuit card, such as the card 22a, 22b, or 22c. Each circuit disposed on a card together with the associated electroacoustic transducer forms an independent oscillatory circuit.

The circuit contained on a respective card is independently fused, such as the fuse 29, FIG. 4. The alternating current input provided from the connector 30 via cable 32 reaches the fuse 29 and causes pulsating unidirectional current to flow through the diode 47, the primary winding 48 of the transformer T and through the transistor 50. The transistor 50 is gated by a feedback circuit which includes the feedback winding 51, the capacitor 52, and the rectifier 53. The piezoelectric transducer element 20a connected to this circuit is coupled in parallel with an inductance 54 across the secondary transformer winding 55, forming the oscillatory load circuit. The winding 56 and the diode 57 act as a clamping circuit during the nonconductive cycle of the transistor 50. This circuit can readily be mounted on a printed circuit card and thereby is quickly installed and replaced in case it becomes defective. Additionally, as will be apparent, if the fuse 29 of a respective circuit blows, the remaining circuits are not affected and continue to operate.

If magnetostrictive transducer means are used, the circuit is modified to provide for the energization of an electroacoustic transducer exhibiting an inductive reactance. Such circuits are well known, see for instance U.S. Pat. No. 3,177,416 issued to H.S.J. Pijls et al., Apr. 6, 1965, "Driving Oscillator for Producing Supersonic Oscillations."

In cases where the circuit dissipates more than a moderate amount of heat, forced air cooling may be provided and the circuit components may be mounted on a metallic surface which includes cooling fins or ribs.

It has been found that the unitized construction described hereinabove, that is, each individual transducer forming with an associated electrical circuit its own oscillatory circuit, is characterized by extreme simplicity, ease of manufacture and improved reliability. Importantly, however, each transducer and associated circuit is permitted to seek its own natural resonant frequency and is able to operate at this point, a condition which is not possible in the prior art arrangements. Thus, one transducer may resonate at a frequency of 45.1 kHz., another transducer at 45.3 kHz. and the like, rather than all transducers being forced to operate at a single frequency which is a compromise and determined essentially by the resultant characteristic of a group of transducers. Clearly, the arrangement described and tested by the applicant is one exhibiting improved operating efficiency and most favorable acoustic resonance condition.