AU730210B3 - Improved ultrasonic cleaning system - Google Patents

Description

P00012 Regulation 3.2 Revised 2/98

AUSTRALIA

Patents Act, 1990

ORIGINAL

COMPLETE SPECIFICATION PETTY PATENT TO BE COMPLETED BY THE APPLICANT NAME OF APPLICANT: ACTUAL INVENTORS: ADDRESS FOR SERVICE: INVENTION TITLE: DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO(S): NEW AGE AUTOMOTIVE PTY LIMITED (ACN 050 538 728) GERARD SYLVESTER MCGINTY and PETER FREDERICK SCHOENFELD Peter Maxwell Associates Level 6 Pitt Street SYDNEY NSW 2000 IMPROVED ULTRASONIC CLEANING

SYSTEM

PQ 1275 29 June 1999 Australia The following statement is a full description of this invention including the best method of performing it known to me:- The present invention relates to ultrasonic cleaning systems.

The use of ultrasonic waves propagating through a liquid cleaning medium is common for cleaning jewellery, watches and the like small objects.

However, these conventional ultrasonic cleaning systems are generally ill suited to clean industrial equipment which tend to accumulate higher levels of undesirable surface adhering substances. Paint is one example of a substance which undesirably adheres to the surface of paint spray guns and paint cans and which, hitherto, has never been easily removable therefrom using conventional physical and chemical treatments. Those who have endeavoured to use ultrasonic waves propagating through a liquid cleaning medium to more easily clean such industrial objects have failed in their attempts because they have generally embarked from the assumption that all that was required was to scale up the well known ultrasonic cleaning systems that apply to jewellery, watches and the like small objects to a level that will suit industrial objects.

The present inventors have realized that the problem with this simple scaling up approach is that industrial objects require a larger volume of liquid cleaning medium which exerts a much greater load on the ultrasonic wave generating system and that, to be effective, the ultrasonic wave generating system must generate ultrasonic waves over a broader than expected frequency range.

According to the present invention there is provided an ultrasonic cleaning system comprising a liquid cleaning medium for immersing at least one object to be cleaned, said liquid cleaning medium being contained within a vessel, a plurality of piezoelectric transducer means, each of which is secured via a metal plate to the said vessel and adapted to be driven asynchronously so as to generate ultrasonic waves that propagate through the liquid cleaning medium, each of the said piezoelectric transducer means generating ultrasonic waves at its unique resonant frequency by being subject to a load that is different to that on the other piezoelectric transducer means, the unique resonant frequencies provided by the plurality of piezoelectric transducer means being confined within a predetermined range of frequency sufficient to ultrasonically clean the at least one object, and wherein the load on each piezoelectric transducer means is adjustable.

In order that the invention may be readily understood and put into practical effect, reference will be made to the accompanying drawings, in which:- Fig 1 is a sectional side view of an ultrasonic cleaning system according to a preferred embodiment of the invention, Fig 2 is an isolated sectional view of the plurality of piezoelectric transducer means included in Fig 1, Fig 3 is bottom view of the plate of the ultrasonic cleaning system shown in Fig 1, on which plate the piezoelectric transducer means are secured, Fig 4 is an exploded view of one of the piezoelectric transducer means included in Figs 1, 2 and 3, and Fig 5 is a simplified circuit diagram of the means for driving each piezoelectric transducer means to vibrate its resonant frequency.

The ultrasonic cleaning system shown in the Figures comprises a vessel 12 within which is contained a liquid cleaning medium 14. One or more objects to be ultrasonically cleaned, such as the component parts of a paint spray gun that has been dismantled for cleaning, are immersed in the liquid cleaning medium 14 in the vessel 12.

Secured via a plate 15, which is fabricated of a suitable metal, such as aluminium, to the underside of the vessel 12 are a pair of piezoelectric >3 Z 1ST 7 transducer means 16, 18, each of which comprises a conductive brass shim sandwiched between a pair of piezoelectric crystals 22, 24, which are, in turn, sandwiched between the plate 15 and a steel washer body 26 by a high tensile cap screw 28 and steel insert The cap screw 28 has a head 29 and a partly threaded shaft 31 which secures all of the components of each piezoelectric transducer means 16, 18 together and to the plate 15 by passing through aligned holes formed centrally in each of the components of the piezoelectric transducer means 16, 18 and by screwably engaging the steel insert 30 having a collar 33 and a threaded bore 35. The head 29 of the cap screw 28 is partly sunk into a recess formed in the lower surface of the washer body 26, and the steel insert 30 has its collar 33 sunk into a recess formed in the upper surface of the plate The central holes through each of the piezoelectric crystals 22, 24 and brass shim 20 are larger in diameter than those in the washer body 26 and insert 30. An insulator ring 32 surrounds the portion of the cap screw shaft 31 adjacent to the piezoelectric crystals 22, 24 with brass shim 20 therebetween.

The brass shim 20 has a tongue portion 36 to which is connected electrical wiring feeding to a supply of current.

With regard to the electrical circuit shown in Fig 5, a transformer converts an AC mains voltage supply to two lower AC voltage supplies, namely a 15V AC supply and a 115V AC supply. The 15V AC and 115V AC supplies are rectified to generate a 20V DC unregulated supply and a 180V DC unregulated supply, respectively, by rectifiers 42, 43. The 20V DC unregulated supply is regulated down to a 15V DC supply by a regulator 44.

When an ON/OFF control 46 on a microprocessor control board is switched ON by the user, a "tuneable" oscillator 46 is activated to oscillate the DC supply into a square wave form signal 47. The square wave form signal 47 is converted by a signal converter 48 to repeating positive and negative spike signals 50, 51, which are, in turn, converted to a pair of out of phase switching signals 52, 53.

The switching signals 52, 53 are applied to two field effect transistors (FET's) 54, 55 and the arrival of the switching signal 52 corresponding to the positive spike causes the first FET 54 to be momentarily switched on (whilst the second FET is off) and the subsequent arrival of the switching signal 53 corresponding to the negative spike causes the second FET 55 to be momentarily switched on (after the first FET has switched off by the passing of the switching signal 52). In this way, the succession of switching signals 52, 53 sequentially open and close the switch of each FET 54, The 180V DC unregulated supply is controlled by the first FET 54 such that when the switch of the first FET 54 is closed, the 180V DC unregulated supply passes to an inductor coil 56 or choke which is connected in series to the brass shim 20 of one of the piezoelectric transducer means 16.

The alternating closing and opening of the switches of the first and second FET's 54, 55 switching events) charges and discharges the inductor coil 56. Each switching event experienced by the inductor coil 56 generates a high voltage or EMF of about 1 kV at or near the resonant frequency of the piezoelectric transducer means 16 so that it is excited to vibrate.

The vibration of the piezoelectric transducer means 16 is characteristic of its behaviour as a capacitative device. Each piezoelectric crystal 22, 24 is a capacitor, consisting of upper and lower surface coatings of silver conductive material between a dielectric material. The resonant frequency of each piezoelectric crystal 22, 24 is a function of its capacitance. Typically, the resonant frequency of each of the two piezoelectric crystals 22, 24 that are contained in each piezoelectric transducer means 16 is 25 kHz, but this frequency is varied upwardly or downwardly from that figure (say, anywhere between 23 kHz to 27 kHz) by adjusting the pressure on the piezoelectric crystals 22, 24 and brass shim 20 through manipulating the level to which the high tensile cap screw 28 is screwed against the aluminium plate There is a grounding point 64 for the electrical circuitry located at the underside of the plate 15 required to operate the ultrasonic cleaning system of this embodiment.

The use of a range of resonant frequencies, as provided by each of the piezoelectric transducer means 16, 18 generating ultrasonic waves at its unique resonant frequency, is advantageous in that the range of frequencies is more likely to spread the degree of agitation experienced by the objects being cleaned so that both large and small sized objects are effectively cleaned.

It is to be noted that, as with most ultrasonic cleaning systems presently in use, the piezoelectric transducer means 16, 18 are driven to their resonant frequency so as to achieve an optimal amplitude of vibration. However, unlike all prior art ultrasonic cleaning systems, the two or more piezoelectric transducer means used in the ultrasonic cleaning system of the present invention are driven asynchronously so as to generate ultrasonic waves of a unique resonant frequency by adjustment of the load thereon. The range of resonant frequencies swept through by a combination of all of the uniquely resonating piezoelectric transducer means in the ultrasonic cleaning system of the invention will cater for the variety of cleaning conditions possible and will compensate for the variations in tolerance of the piezoelectric transducer means.

Various other modifications may be made in details of design and construction without departing from the scope or ambit of the invention.

For example, an air charge may be delivered from a fitting at the floor of the vessel 12 through the cleaning medium 14 for 10 second durations at about 1 to 3 minute intervals, and at a pressure of 10 to 12 psi. The fitting, the access hole 60 for which is shown through the plate 15 in Fig 3, is a 3/8 inch fitting that enables air to be expelled in a direction radially outwardly therefrom and parallel to the floor of the vessel 12. The periodic air charges create a level of turbulence in the cleaning medium that improves the agitation of the objects being cleaned which, overall, enhances the cleaning effect of the ultrasonic waves propagating through the medium 14.

Also, the cleaning medium 14 may be maintained at a heated temperature of about 450C to optimize cleaning activity, with the use of a horseshoe shaped resistance heater element, the housing for which is secured to the underside of the plate 15 via threaded apertures 62. A negative temperature co-efficient resistor, serving as a temperature sensor, is connected to the floor of the vessel 12, the access hole 66 for which is shown in Fig 3.

Normally, the ultrasonic cleaning system of the present invention is incorporated into a washing station that is computer programable and can be operated through a digital control board and display.

Claims (2)

1. An ultrasonic cleaning system comprising a liquid cleaning medium for immersing at least one object to be cleaned, said liquid cleaning medium being contained within a vessel, a plurality of piezoelectric transducer means, each of which is secured via a metal plate to the said vessel and adapted to be driven asynchronously so as to generate ultrasonic waves that propagate through the liquid cleaning medium, each of the said piezoelectric transducer means generating ultrasonic waves at its unique resonant frequency by being subject to a load that is different to that on the other piezoelectric transducer means, the unique resonant frequencies provided by the plurality of piezoelectric transducer means being confined within a predetermined range of frequency sufficient to ultrasonically clean the at least one object, and wherein the load on each piezoelectric transducer means is adjustable.

2. The ultrasonic cleaning system of claim 1 wherein there are two piezoelectric transducer means secured to the said vessel. Dated this 7th day of December, 2000 New Age Automotive Pty Limited Patent Attorneys for the Applicant PETER MAXWELL ASSOCIATES '-V -o