Patent Publication Number: US-8973601-B2

Title: Liquid condition sensing circuit and method

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This patent application claims the benefit of U.S. Provisional Patent Application No. 61/300,211, filed Feb. 1, 2010, the entire teachings and disclosure of which are incorporated herein by reference thereto. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to ultrasonic cleaning systems, and, more particularly, to electronic systems used in the operation of ultrasonic cleaning systems. 
     BACKGROUND OF THE INVENTION 
     Ultrasonic energy is used in a variety of applications including, but not exclusive of, medical, industrial, and military applications. One common use for ultrasonic energy in manufacturing is for cleaning objects in liquids. In ultrasonic cleaning, a transducer, usually piezoelectric but sometimes magnetostrictive, is secured to or immersed in a cleaning tank to controllably impart ultrasonic vibration to the tank. The tank is filled with a cleaning liquid and parts are immersed into the liquid to be cleaned by ultrasonic agitation and cavitation. The ultrasonic energy itself can dislodge contaminants. Under certain conditions, the ultrasonic energy also creates cavitation bubbles within the liquid where the sound pressure exceeds the liquid vapor pressure. When the cavitation bubbles collapse, the interaction between the ultrasonically agitated liquid and the contaminants on the parts immersed in the liquid causes the contaminants to be dislodged. 
     In a typical ultrasonic cleaning system, the cleaning liquid is an aqueous solution, and parts immersed therein are cleaned via the aforementioned agitation and cavitation of the aqueous solution. Typically, the ultrasonic transducers transmit ultrasonic energy into the liquid-filled tank at frequencies of 18 kilohertz or greater, typically at a resonant frequency of the transducer and the load. The load includes the cleaning tank, the liquid in the tank, and the parts immersed in the liquid. When the ultrasonic transducer is driven at the resonant frequency of the load, the system is capable of delivering maximum power to the load. 
     The effectiveness of ultrasonic cleaning systems can be reduced by the presence of dissolved gases in the cleaning liquid. The presence of dissolved gases in the cleaning liquid used in ultrasonic cleaning systems may interfere with the cavitation that promotes the cleaning process. Typically, operators of ultrasonic cleaning systems will perform a degassing process for approximately ten minutes before commencing the actual cleaning. During this degassing process, the ultrasonic transducers are typically pulsed repeatedly for the entire ten minutes. Following the degassing process, the ultrasonic transducers can be switched to continuous operation needed for the cleaning operation. 
     Suboptimal liquid levels can also hinder the ultrasonic cleaning process. At certain liquid levels, the reflection of ultrasonic waves off of the surface of the liquid can create a destructive interference that reduces the energy effectively transferred from the ultrasonic transducers to the cleaning liquid. The ultrasonic energy which is transferred to the ultrasonic transducers, but which is not effectively transferred to the cleaning liquid is wasted. As a result, when suboptimal liquid levels are used, the cleaning times may need to be extended to achieve the same result that would be achieved in less time with optimal liquid levels. This increases cycle times and manufacturing costs for operators or ultrasonic cleaning systems. 
     It would therefore be desirable to have an ultrasonic cleaning system capable of providing the operator with an indication of the amount of dissolved gases in the cleaning liquid, and capable of indicating whether the cleaning liquid is at a suboptimal level. Embodiments of the invention provide such an ultrasonic cleaning system. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, embodiments of the invention provide a liquid condition sensor configured to monitor the condition of a liquid in an ultrasonic cleaning system tank, the liquid condition sensor including a first circuit configured to detect a signal transmitted from an ultrasonic generator to one or more ultrasonic transducers located in the tank. The liquid condition sensor further includes a second circuit coupled to the first circuit, the second circuit configured to determine if the signal is indicative of one of a suboptimal liquid level, and an unacceptably high concentration of dissolved gases in the cleaning liquid, and a third circuit coupled to the second circuit, the third circuit configured to provide a warning if one of a suboptimal liquid level, and an unacceptably high concentration of dissolved gases in the cleaning liquid is indicated by the second circuit. 
     In another aspect, embodiments of the invention provide a method of sensing the condition of liquid in an ultrasonic cleaning system tank, the method including detecting a signal being transmitted from an ultrasonic generator to an ultrasonic transducer, wherein the ultrasonic transducer is locating in a liquid-filled cleaning tank, and determining if the signal being transmitted is indicative of a suboptimal liquid level in the cleaning tank. The method of this embodiment further includes determining if the signal being transmitted is indicative of an unacceptably high concentration of dissolved gases in the cleaning liquid, providing a warning signal if it is determined that there is a suboptimal liquid level in the cleaning tank, and further providing a warning signal if it is determined that there is an unacceptably high concentration of dissolved gases in the cleaning liquid. 
     Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a schematic illustration of an exemplary ultrasonic cleaning system incorporating an embodiment of the invention; 
         FIG. 2  is a block diagram for a liquid condition sensing circuit according to an embodiment of the invention; 
         FIG. 3  is a schematic circuit diagram of a liquid condition sensing circuit, according to an alternate embodiment of the invention; 
         FIG. 4  is a graphical representation of an exemplary waveform for liquid in an ultrasonic cleaning tank at a suboptimal level or having suboptimal gas concentration; and 
         FIG. 5  is a graphical representation of an exemplary waveform for liquid having optimal gas concentration or for liquid at an optimal level in the cleaning tank; and 
         FIG. 6  is a plan view of an exemplary control panel which may be used with embodiments of the invention. 
     
    
    
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In an ultrasonic cleaning system having ultrasonic transducers coupled to a liquid-filled tank, several factors determine what portion of the energy from the ultrasonic transducers is actually directed toward cleaning, versus that portion of the energy which is wasted. One of these factors is the level of cleaning liquid in the tank. Another factor is the amount, or concentration, of gases dissolved in the cleaning liquid. In an embodiment of the invention, a liquid condition sensing circuit is coupled to the output transformer of an ultrasonic power generator. The liquid condition sensing circuit is configured to indicate whether an unacceptably high portion of the power from the ultrasonic transducer is being wasted. In so doing, it becomes possible to reduce the amount of wasted energy by adjusting two of the above-named factors to increase the overall efficiency of the cleaning process. 
       FIG. 1  is a schematic illustration of an exemplary ultrasonic cleaning system  10  incorporating an embodiment of the invention. The ultrasonic cleaning system  10  includes an ultrasonic generator  12 , which in one embodiment, supplies AC electrical power to a plurality of ultrasonic transducers  14  which are positioned in a cleaning tank  16 . Alternate embodiments of the invention include ultrasonic cleaning systems having a greater number or lesser number of ultrasonic transducers  14  than the three shown in  FIG. 1 . While the ultrasonic transducers  14  are shown as being positioned at the bottom of cleaning tank  16 , the ultrasonic transducers  14  could be mounted on the sides, bottom, or positioned at some other location within the cleaning tank  16 . An aqueous or semi-aqueous cleaning liquid  18  fills the cleaning tank  16  enough to sufficiently cover a plurality of parts  20  being cleaned. In another embodiment of the invention, the cleaning system  10  includes a connection (shown in phantom) from the circuitry driving the ultrasonic transducers  14  to a remote monitoring station  22  (shown in phantom). A controller  24  (shown in phantom) is also connected to the circuitry driving the ultrasonic transducers  14 , and is connected to the ultrasonic generator  12 . 
     In operation, power supplied to the ultrasonic transducers  14  by the electrical ultrasonic generator  12  causes the ultrasonic transducers to transmit acoustical energy into the cleaning liquid  18  thereby producing the agitation and cavitation in the cleaning liquid  18  that cleans the plurality of parts  20 . In at least one embodiment, the ultrasonic cleaning system includes a warning system configured to transmit a signal to the remote monitoring station  22 , such that one operator may monitor a number of such cleaning systems from a single location. Embodiments of the invention allow for such warnings to be transmitted in the event that the condition of the cleaning liquid is suboptimal for ultrasonic cleaning. For example, it is contemplated that the warning system may be coupled to a controller  24 , which upon receipt of a signal indicating that the cleaning liquid has an unacceptably high concentration of dissolved gases, may execute, for example, a degassing procedure. In the event that a warning is transmitted due to the cleaning liquid being at a suboptimal liquid level, the controller  24  may also be configured to terminate all power from the ultrasonic generator  12  to the ultrasonic transducers  14  until the liquid level is adjusted. 
       FIG. 2  is a block diagram illustrating an exemplary liquid condition sensing circuit  100 , according to an embodiment of the invention. The block diagram of  FIG. 2  shows that this embodiment of the liquid condition sensing circuit  100  includes a first circuit having a sensing coil  102  or generator output current pick-up (current transformer) on the output transformer of the ultrasonic generator. The sensing coil  102  is coupled to a second circuit which includes a demodulator filter  104 , buffer  106 , band-pass filter  108 , rectifier  110  and amplifer  112 . The demodulator filter  104  has an output which is fed into a buffer  106 . The buffer  106  is coupled to the band-pass filter  108 , whose output is coupled to the input of the rectifier  110 . The output of the rectifier  110  is amplified by amplifier  112 . The amplifier  112  output is routed to a third circuit that includes at least a portion of controller  114  and an LED driver  116 , which drives an LED display  118 . 
     The controller  114  is configured in one embodiment to implement a degassing process if the amplifier  112  signal indicated the need for degassing. Typically, degassing involves pulsing the ultrasonic transducer  14  (in  FIG. 1 ) repeatedly at regular intervals, for example on for 10 seconds then off for 10 seconds, for up to ten minutes to purge the dissolved gases from the cleaning liquid  18  (in  FIG. 1 ). Upon detection of high concentrations of dissolved gases in the cleaning liquid  18  as will be discussed below, the controller  114  is configured to automatically commence a degassing procedure that may last several minutes. The liquid condition sensing circuit  100 , either periodically or continuously, senses the condition (i.e., dissolved gas concentration) of the cleaning liquid  18  to determine if further or continuing degassing is required. This procedure is repeated until the liquid condition sensing circuit  100  determines an acceptable level of dissolved gases in the cleaning fluid  18 . 
     The controller  114  is configured to implement other control functions in addition to the degassing process in other embodiments. For example, in one embodiment the controller  114  is configured to shut off power to the transducers  14  (in  FIG. 1 ) if a suboptimal liquid level is indicated. In another embodiment of the invention, the controller  114  is configured to automatically adjust the level of cleaning liquid  18  (in  FIG. 1 ) in the tank  16 . The liquid condition sensing circuit  100  could then sense the level of the cleaning liquid  18  to determine if additional adjustment of the liquid level is required. The LED driver  116  is coupled to an LED display  118  and is configured to indicate to an operator when the liquid condition is or is not optimal for ultrasonic cleaning. However, in other embodiments of the invention, an audio warning system is employed in addition to, or instead of, a visual warning system, to alert operators when the liquid condition is or is not optimal for ultrasonic cleaning. 
       FIG. 3  is a schematic circuit diagram of an exemplary liquid condition sensing circuit  200 , according to an alternate embodiment of the invention. The circuit diagram of  FIG. 3  shows that the sensing coil  202 . The demodulation filter  204  includes a diode  222 . The diode  222  provides half-wave rectification of the AC signal from the sensing coil  202 . The diode  222  is coupled to a first active filter having a first op-amp circuit  224  configured to filter out signals of a given frequency. In at least one embodiment, the first active filter is configured to filter out signals at approximately 120 hertz. The first active filter is coupled to a second active filter having a second op-amp circuit  228  configured as a band-pass filter. In at least one embodiment, the second active filter is configured to pass signals at approximately three kilohertz. The second active [band-pass] filter is coupled to a first passive band-pass filter  254 . 
     The first passive band-pass filter  254  includes an inductor  256  and a capacitor  258 . In an embodiment of the invention, the band-pass filter  254  is configured to pass signals in the 38 kHz to 42 kHz range. The filtered signal is coupled to an input of a buffer  206 . Buffer  206  includes a third op-amp circuit  262  where the op-amp is configured for unity gain. The buffer  206  provides isolation of the electrical impedance at the buffer&#39;s output from the impedance at the buffer&#39;s input. The output of the buffer  206  is coupled to an input of an amplifier  212 . The amplifier  212  includes a fourth op-amp circuit  272 , which is configured such that the gain of the amplifier  212  is determined by a first variable resistor  274  and a resistor  276 . Using first variable resistor  274  allows the gain of the amplifier  212  to be adjusted as necessary. In an embodiment of the invention, the first variable resistor  274  can be adjusted to a value up to 100 kilohms, while the resistor  276  has a value of approximately one kilohm, giving the amplifier  212  a maximum gain of approximately 100. In operation, the resistance value of the variable resistor  276  is chosen such that the amplifier gain must be sufficient to supply the LED driver  216  with enough voltage to operate a bank of LEDs  296 . 
     The output of the amplifier  212  is coupled to a second passive band-pass filter. This second passive band-pass filter includes a capacitor  284 . In at least one embodiment of the invention, the second passive band-pass filter is configured to pass signals at approximately three kilohertz. The filtered signal from the second passive band-pass filter is input to a second diode  282 , which ensures the voltage to the LED driver  216  is positive, and to a second variable resistor  288 . The voltage across the second variable resistor  288  is used to drive the LED driver  216 , which powers an LED display  218  that includes the bank of LEDs  296 , which serve to warn the operator of suboptimal conditions in the cleaning liquid  18  (in  FIG. 1 ). 
       FIG. 4  is a graphical representation of an exemplary waveform  300  sensed by the liquid condition sensing circuit  200  (in  FIG. 3 ) for cleaning liquid  18  in an ultrasonic cleaning tank  16  (in  FIG. 1 ), when the liquid  18  is at a suboptimal liquid level or has an unacceptably high concentration of dissolved gases. The graphical representation of  FIG. 4  shows an exemplary first waveform  300  of the type that would be displayed by a spectrum analyzer attached to the output transformer (not shown) of an ultrasonic generator  12  (in  FIG. 1 ). The first waveform  300  of  FIG. 4  shows the signal from the output transformer of the ultrasonic generator in the frequency range of 38 kHz to 42 kHz. 
     As can be seen in  FIG. 4 , the first waveform  300 , which indicates a high concentration of dissolved gases in the cleaning liquid  18  (in  FIG. 1 ), is characterized by near-constant or very gradually changing peak amplitudes  302 . The near-constant peak amplitudes  302  shown here are characteristic of an absence of the cavitation normally present in the ultrasonic cleaning process. While the first waveform  300  shows that there is little or no cavitation in cleaning liquid  18 , the liquid itself may show evidence of disturbance at the surface. It is also typically the case that the output transformer of the ultrasonic generator  12  will generate a signal like that shown in first waveform  300  when the cleaning liquid  18  has a low concentration of dissolved gases, but is at a suboptimal liquid level. At certain liquid levels, ultrasonic waves in the cleaning liquid  18  reflect off of the surface and destructively interfere with other ultrasonic waves in the liquid. As a result, only a fraction of the ultrasonic energy transmitted by the transducers  14  (in  FIG. 1 ) is available to produce the cavitation in the cleaning liquid  18  that promotes the cleaning process. 
       FIG. 5  is a graphical representation of an exemplary second waveform  400  sensed by the liquid condition sensing circuit  200  (in  FIG. 3 ) for cleaning liquid  18  in an ultrasonic cleaning tank  16  (in  FIG. 1 ), when the liquid  18  at an optimal liquid level or has an acceptably low concentration of dissolved gases. The graphical representation of  FIG. 5  shows the second waveform  400  of the type that would be displayed by a spectrum analyzer attached to the output transformer (not shown) of an ultrasonic generator  12  (in  FIG. 1 ). The second waveform  400  of  FIG. 5  shows the signal from the output transformer of the ultrasonic generator  12  in the frequency range of 38 kHz to 42 kHz. 
     As can be seen in  FIG. 5 , the second waveform  400 , which indicates an acceptably low concentration of dissolved gases in the cleaning liquid (in  FIG. 1 ), is characterized by abrupt, seemingly random, changes in the peak amplitudes  402 . The abruptly-changing peak amplitudes  402  shown here are characteristic of the presence of cavitation in the cleaning liquid  18 , cavitation that is normally present in the ultrasonic cleaning process. In an embodiment of the invention, the peak amplitudes  402  have an average frequency of approximately three kilohertz. As a result, a liquid condition sensing circuit employing band pass filters configured to pass signals of approximately three kilohertz, would pass through these peak amplitudes  402 . 
     Those signals passing through the band-pass filters would drive, or light some number of the bank of LEDs  296 , thus indicating good cavitation in the cleaning liquid  18 . Depending on the magnitude of the peak amplitudes  302 , and on the resistance values chosen for the first and second variable resistors  274 ,  288 , the second waveform  400  could light one or all of the bank of LEDs  296 . While the waveform  400  shows that there is sufficient cavitation in the cleaning liquid  18 , the liquid itself may show little or no signs of disturbance at the surface. 
     In the first waveform  300  of  FIG. 4 , the lack of peak amplitudes like those in second waveform  400  means that there would be essentially no signal passing through the band-pass filters, and thus no signal to drive any of the bank of LEDs  296 . As such, none of the bank of LEDs  296  would light in the case of the first waveform  300 . In an embodiment of the invention, the first waveform  300  could trigger the controller  114  (in  FIG. 1 ) to automatically start a degassing procedure, in which the ultrasonic transducers are pulsed repeatedly until the waveform resembles the second waveform  400 . When the cleaning liquid  18  has been degassed, a waveform resembling the first waveform  300  could also alert the operator that the liquid level is suboptimal. In at least one embodiment of the invention, the controller  114  is configured to automatically adjust the water level until the waveform resembles the second waveform  400 . 
     In an alternate embodiment, the controller  114  (in  FIG. 1 ) is configured to automatically sense the level of parts loading in the cleaning tank  16 , and to adjust the power level accordingly. For example, when parts are removed from a fully loaded cleaning tank  16 , the peak amplitudes of the waveform sensed by the liquid condition sensing circuit  200  (in  FIG. 3 ) will become more random with more abrupt changes. If the part loading in the tank  16  is reduced such that the waveform shows more abruptly changing peak amplitudes than shown in the second waveform  400 , the controller  114  may determine, based on the waveform, that the power being supplied to the ultrasonic transducers  14  can be reduced without adversely affecting the cleaning process, thus saving energy. 
     Conversely, if parts are added increasing the load in the cleaning tank  16 , the peak amplitudes of the waveform sensed by the liquid condition sensing circuit  200  (in  FIG. 3 ) will become smoother and less random. When loading in the tank  16  increases to the point that the waveform resembles first waveform  300  (in  FIG. 4 ), the controller may determine, based on the waveform, that power to the ultrasonic transducers  14  needs to be increased to properly clean the parts in the tank  16 . Additionally, cycle time may be reduced by eliminating the need for the operator to adjust the power supplied to the ultrasonic transducers  14 . 
     In this manner, the controller  114  automatically adjusts the power to the ultrasonic transducers  14  based on a determination of the level of parts loading in the cleaning tank  16 , based on the peak amplitudes in the waveform sensed by the liquid condition sensing circuit  200  (in  FIG. 3 ), to increase efficiency and reduce cycle times. In an embodiment of the invention, the automatic power level adjustment is performed after completion of the above-mention degassing procedure and the optimal liquid level determination. 
       FIG. 6  is a plan view of an exemplary control panel  500  which may be used with embodiments of the invention. The control panel  500  includes a power button, and displays for a clock, timer and thermometer, along with control buttons to adjust time, the timer, and temperature. The control panel  500  further includes and intensity bar that includes the bank of LEDs  296  which alert the operator to the condition of the cleaning liquid  18  in the tank  16 . 
     All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.