Oscillatory Circuit For Ultrasonic Cleaning Apparatus

Abstract

A high-efficient oscillatory circuit drives a piezoelectric crystal (transducer) which is coupled to an ultrasonic cleaning tank. The circuit includes a transistor switching means in the driver side of the oscillator. The primary winding of the transformer is coupled in parallel with a capacitor and forms a circuit having a resonant frequency which is a multiple even integer of the resonant frequency of the crystal which is coupled to the transformer secondary winding.

Description

The present invention refers to an oscillatory circuit for an ultrasonic cleaning apparatus and, more specifically, has reference to a simplified electronic circuit for driving an ultrasonic cleaning apparatus, particularly, an ultrasonic cleaning apparatus of the smaller type as used, for instance, in the laboratory, jewelry repair shops, home workshop, and the like.

The electrical circuit disclosed hereafter is characterized, quite specifically, by a high degree of efficiency, high reliability, by relatively few components and is, therefore, relatively simple and inexpensive as is a necessity when providing ultrasonic cleaning apparatus of the type indicated heretofore. Moreover, the high efficiency obtained is the result of a unique and novel circuit arrangement which provides for the conservation of stored energy.

The above indicated characteristics and advantages will be more clearly apparent from the following detailed description when considered in conjunction with the accompanying drawings, in which:

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

FIG. 2 is a schematic diagram of an electrical circuit employed embodying the present invention;

FIG. 3 is a schematic diagram of the wave shapes at certain points in FIG. 2, and

FIG. 4 is a schematic electrical circuit diagram of a further embodiment of the present invention.

Referring now to the figures, and FIG. 1 in particular, there is shown a skirt or enclosure 12 which supports therein a metal tank 14 which is filled with a cleaning liquid 16. The skirt 12 rests on a base 18 which is provided with a set of rubber feet 20.

A piezoelectric crystal 22, also called transducer, preferably of disk-shape, is bonded by means of a layer of epoxy resin material 24 to the underside of the tank 14 for imparting ultrasonic energy to the tank and to the cleaning liquid 16 in a manner that is well understood by those skilled in the art. The crystal 22 is connected by conductors 26 to an electronic circuit 28 which, in turn, by a power cord 30 can be connected to a standard 115 volts AC, 60 -cycle, power line.

The cleaning tank and the piezoelectric crystal attached thereto may take the form as shown for instance in U.S. Pat. No. 3,516,645 dated June 23, 1970 issued to J. P. Arndt et al., entitled "Ultrasonic Cleaner".

The novel, high-efficient and simple electronic circuit for setting the crystal 22 into resonance is shown in FIG. 2. The AC terminals 32 and 34 apply electrical power to a bridge-type rectifier 36 which is connected to a filter capacitor 38 in order to provide direct current energy. A transformer 40, preferably having a toroidal core, has a primary winding 42, a secondary winding 44, and a feedback winding 46. The primary winding 42 is coupled in parallel with a capacitor 43 and this parallel combination, forming an oscillatory circuit, is connected to a switching transistor 50 which is cyclically rendered conductive by the signal provided by the feedback winding 46. The capacitor 48 provides phase shift correction and the resistor 49, rectifier 52 and resistor 66 provide the normal biasing potential.

The piezoelectric crystal 22 is connected in parallel with an inductance 54 to the secondary transformer winding 44 and, thus, the crystal 22, inductance 54 and winding 44 form a parallel resonant circuit, causing the crystal to oscillate and impart the ultrasonic energy to the cleaning liquid. In a typical example, the crystal is selected to have a natural resonant frequency in the range from 40 to 60 kHz. It should be understood, however, that this frequency range is merely illustrative of a typical operating condition and that other frequencies may be used as well.

The driving portion of the circuit, that is the primary winding 42, the capacitor 43 and the reflected reactance, form an oscillatory circuit and the capacitor 43 is selected to cause the resonant frequency of this combination to be an even integer multiple of the resonant frequency of the transducer or crystal 22. In a typical example, the resonant frequency of the driving portion is four times that of the parallel resonant circuit which includes the piezoelectric crystal 22. Therefore, if the crystal is driven at its resonant frequency of, let us say 45 kHz., the primary side is tuned to exhibit a frequency of 180 kHz.

FIG. 3 shows the typical wave shapes which occur in the circuit per FIG. 2. The line 60 shows the transistor 50 being cyclically switched and when rendered conductive at time t.sub.l providing current flow from the DC power supply through the primary winding 42 and transistor 50 to ground. As the current conduction through the transistor ceases, time t.sub.o, the voltage across the capacitor 43 rises, voltage B-A, and the winding 42 together with the capacitor 43 and the reflected reactance of the other circuit components form an oscillatory circuit which has a fundamental frequency of four times the frequency of the oscillatory load circuit portion which includes the transducer 22.

The salient advantage of the present arrangement is seen at the time t.sub.l when the transistor is rendered conductive. The voltage across the primary transformer winding points B-A has reached a low state in its oscillation. As a result thereof, there is a minimum amount of energy stored in the resonant circuit. At this particular moment only this minimum amount of energy is conducted to ground by the transistor 50. Further, during the time interval in which the transistor is nonconductive, the high-frequency oscillation across the primary winding of the transformer is transferred to the load. These phenomena result, of course, in a higher degree of efficiency than the heretofore used circuits.

One further advantage of the present invention resides in the fact the transformer 40, on account of the frequency on the primary side of the circuit being higher than the frequency determined by the resonance of the crystal 22, can be made smaller and, therefore, is lighter and less expensive. Last but not least, since the electric energy stored is a minimum at the time the transistor is rendered conductive, current peaks during transistor switching are avoided and the transistor reliability is greatly improved.

A further improvement is incorporated in the circuit shown in FIG. 4. The circuit shown is identical with that in FIG. 2 except for the addition of inductance 62 and capacitor 64. The inductance 62 connected in series with the capacitor 43 delays momentarily the onset of heavy current flow through the transistor, permitting the transistor to attain its saturation level before heavy current is conducted therethrough. This arrangement prevents undue power dissipation by the transistor. Energy not dissipated in the transistor remains stored in the capacitor 38, thus contributing to greater efficiency. Because of the reduced stress on the transistor, the above circuit has been used successfully, for instance, to drive two transducers 22 with a single transistor 50.

The circuit per FIG. 4 shows a further improvement. A common cause of circuit defect is attributable to a failure of the transducer 22 caused, for instance, by cracking of the ceramic disk, conductor lead breakage, etc. When the transducer 22 fails in the circuit per FIG. 2, there no longer exists a parallel resonant circuit at the output side and, hence, the oscillations cease. Resistor 66 biases the transistor in the conductive condition and the collector current I.sub.C increases until the transistor 50 is destroyed. The parallel capacitor 64 added in FIG. 4 sustains the circuit in a higher frequency oscillatory mode when the transducer 22 fails. Hence, a transducer failure will no longer result in an electrical circuit failure.

Claims

What is claimed is:

1. An oscillatory circuit for an ultrasonic cleaning apparatus comprising:

a transformer having a primary winding and a secondary winding;

a capacitance coupled in parallel with said primary winding;

a source of direct current and a switching means coupled serially in circuit with said primary winding and parallel-coupled capacitance for cyclically providing current flow from said source through said winding;

said secondary winding coupled in parallel with an inductance and a piezoelectric element, the latter forming a part of said cleaning apparatus;

a further winding serving as a feedback means disposed on said transformer coupled to said switching means to cause said cyclic current flow, and

the combination of said primary winding and capacitance forming a resonant circuit having a resonant frequency which is an even integer multiple of the frequency of the oscillatory circuit comprising said secondary winding, said inductance and piezoelectric element.

2. An oscillatory circuit as set forth in claim 1, said primary winding and capacitance in combination having a resonant frequency which is four times higher than the resonant frequency determined by the oscillatory circuit comprising said secondary winding, said inductance and piezoelectric element.

3. An oscillatory circuit as set forth in claim 1, the combination of said secondary winding, said inductance and piezoelectric element being resonant at a frequency of at least 20 kHz.

4. An oscillatory circuit as set forth in claim 1, said switching means being a transistor.

5. An oscillatory circuit as set forth in claim 1, said piezoelectric element being a disk-type element coupled to an exterior surface of an ultrasonic cleaning tank.

6. An oscillatory circuit as set forth in claim 1, said primary, secondary and further windings being disposed on a toroidal transformer core.

7. An oscillatory circuit for an ultrasonic cleaning apparatus, said circuit comprising:

a driving portion which includes a source of direct current, a switching means, a first transformer winding, and a capacitance connected in parallel with said first winding so arranged that said switching means is adapted to cyclically provide current flow from said source through said winding;

a load portion which includes a second transformer winding inductively coupled to said first winding, a piezoelectric transducer, and an inductance coupled to said second winding and to said transducer; and

said driving portion being dimensioned to exhibit when said switching means inhibits current flow from said source to said first winding a fundamental resonant frequency which is an even integer multiple of the fundamental frequency of said transducer.

8. An oscillatory circuit for an ultrasonic cleaning apparatus comprising:

a transformer having a primary winding and a secondary winding;

the series combination of a capacitance and an inductance coupled in parallel with said primary winding;

a source of direct current and a switching means coupled serially in circuit with said primary winding and said parallel coupled series combination for cyclically providing current flow from said source through said winding;

said secondary winding coupled in parallel with an inductance and a piezoelectric element, the latter forming a part of said cleaning apparatus;

a further winding serving as a feedback means disposed on said transformer coupled to said switching means to cause said cyclic current flow, and

the combination of said primary winding and series combination forming a resonant circuit having a resonant frequency which is an even integer multiple of the frequency of the oscillatory circuit comprising said secondary winding, said inductance and piezoelectric element.

9. An oscillatory circuit as set forth in claim 8, said primary winding and series combination coupled in parallel in combination having a resonant frequency which is four times higher than the resonant frequency determined by the oscillatory circuit comprising said secondary winding, said inductance and piezoelectric element.

10. An oscillatory circuit as set forth in claim 8, the combination of said secondary winding, said inductance and piezoelectric element being resonant at a frequency of at least 20 kHz.

11. An oscillatory circuit as set forth in claim 8, said switching means being a transistor.

12. An oscillatory circuit as set forth in claim 8, said piezoelectric element being a disk-type element coupled to an exterior surface of an ultrasonic cleaning tank.

13. An oscillatory circuit as set forth in claim 8, said primary, secondary and further windings being disposed on a toroidal transformer core.

14. An oscillatory circuit as set forth in claim 8, and a capacitance coupled in parallel with said piezoelectric element.

15. An oscillatory circuit for an ultrasonic cleaning apparatus comprising:

a driving circuit portion;

an output circuit portion which includes a transducer having a predetermined resonant frequency;

means coupling said portions to each other, and

said driving circuit portion having a combination of circuit elements adapted to be resonant at a frequency which is an even integer multiple of said predetermined resonant frequency.