Ultrasound system
An ultrasound system for providing megasonics and ultrasonics to a liquid at different frequencies and/or sweeping frequencies with associated generators, transducers, operations between resonance and anti-resonance, non-resistive output with phase shift, multiple/sweep/single frequency modes, individually controlled sections, gate drive power control, variable inductive compensation for temperature changes, parallel inductor matching, stacked ceramics and non-volatile memory storage of fault, error and failure history.
This application is a division of commonly owned and co-pending U.S. patent application Ser. No. 11/827,288, filed Jul. 11, 2007. The entire contents of such application is incorporated herein by reference.
TECHNICAL FIELDThe present invention relates to megasonic and ultrasonic systems, and more particularly to systems for generating high power megasonic sound energy and introducing the megasonic sound energy into liquid media for the purpose of cleaning and/or processing.
BACKGROUND ARTFor years, megasonic energy has been used in manufacturing and processing plants to clean and/or otherwise process objects within liquids. It is well known that objects may be efficiently cleaned or processed by immersion in a liquid and subsequent application of megasonic energy to the liquid. Prior art megasonic systems include transducers, built by bonding piezoelectric ceramics to radiating membranes such as quartz, sapphire, stainless steel, titanium, tantalum, boron nitride, silicon carbide, silicon nitride, aluminum and ceramics, and generators designed to stimulate the transducers at a resonant or antiresonant frequency. The transducers are mechanically coupled to a tank containing a liquid that is formulated to clean or process the object of interest. The amount of liquid is adjusted to partially or completely cover the object in the tank, depending upon the particular application. When the transducers are stimulated by the output signal from the generator to spatially oscillate, they transmit megasonics into the liquid, and hence to the object. The interaction between the megasonic-energized liquid and the object creates the desired cleaning or processing action.
However, prior art megasonic systems lack optimum performance, are expensive and sometimes cause damage to the parts being cleaned or processed. The present invention improves performance of megasonic systems, reduces cost and minimizes damage caused by intense megasonic sound energy.
DISCLOSURE OF THE INVENTIONAs used herein, megasonics means sound energy with a fundamental frequency from about 350 kHz to about 15 MHz. As used herein, ultrasonics means sound energy with a fundamental frequency from about 18 kHz to about 350 kHz. The term ultrasound as used herein is defined to mean the complete range of ultrasonic and megasonic frequencies, from about 18 kHz to about 15 MHz.
With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, the present invention provides an improved megasonic system (2) for coupling megasonics to a liquid, comprising a megasonic transducer assembly of two or more megasonic transducers (10) having a first piezoelectric ceramic (11) bonded to a second piezoelectric ceramic (12), a megasonic generator (9) having a phase shift network (32) and an electronic bridge circuit (31) configured to selectively produce at least a first frequency of operation (64) and a second frequency of operation (67) and to selectively produce a driver signal characterized by a first frequency within a first frequency band (69) and to selectively produce a second frequency within a second frequency band (70) that is different from and non-contiguous to the first frequency band, the bridge circuit and phase shift network configured to provide an output voltage (36) and an output current (37), wherein the output voltage leads the output current by an angle (46) that is greater than 0 degrees and less than about 90 degrees into the phase shift network, the phase shift network having a non-resistive output circuit (100) having a Norton equivalent impedance (122) near infinity at the first frequency of operation, a transmission line (115) connecting the transducer assembly to the megasonic generator, at least one parallel inductor matching network (88) between the transmission line and the transducer assembly, at least one sensor (3) adapted to sense operating conditions of the megasonic system, a processor (4) communicating with the sensor, non-volatile memory (5) coupled to the processor, and the processor programmed to receive a signal from the sensor during operation of the megasonic system and to store the signal in the memory for access after operation of the megasonic system when the signal indicates a system error, fault or failure.
In another aspect, the invention also provides a megasonic transducer (10) comprising a first piezoelectric ceramic (11) with a positive polarity surface and a negative polarity surface opposite the positive surface, a second piezoelectric ceramic (12) with a positive polarity surface and a negative polarity surface opposite the positive surface, a resonator plate (15) having a first surface configured to couple megasonics to a liquid and a second surface, the negative polarity surface of the first piezoelectric ceramic bonded to the positive polarity surface of the second piezoelectric ceramic to form a megasonic piezoelectric assembly (14), and the negative polarity surface of the second piezoelectric ceramic bonded to the second surface of the resonator plate to form a megasonic transducer for producing multiple megasonic frequencies.
The invention also provides a megasonic transducer comprising a first piezoelectric ceramic having a positive polarity surface and a negative polarity surface opposite the positive surface, a second piezoelectric ceramic having a positive polarity surface and a negative polarity surface opposite the positive surface, a resonator plate having a first surface configured to couple megasonics to a liquid and having a second surface, the positive polarity surface of the first piezoelectric ceramic bonded to the negative polarity surface of the second piezoelectric ceramic to form a megasonic piezoelectric assembly, and the positive polarity surface of the second piezoelectric ceramic bonded to the second surface of the resonator plate to form a megasonic transducer for producing multiple megasonic frequencies.
The invention also provides an ultrasound system (30) comprising an electronic bridge circuit (31) that provides an operational frequency or operational bandwidth of frequencies and has a first output terminal (35) and a second output terminal (34) configured to provide an output voltage (36) and an output current (37), a phase shift network (32) having a first input terminal (38), a second input terminal (39), a first output terminal (40) and a second output terminal (41), the first output terminal of the bridge circuit coupled to the first input terminal of the phase shift network and the second output terminal of the bridge circuit coupled to the second input terminal of the phase shift network, an ultrasound transducer (33) having a first input terminal (42) and a second input terminal (43), the first output terminal of the phase shift network coupled to the first input terminal of the transducer and the second output terminal of the phase shift network coupled to the second input terminal of the transducer, the bridge circuit, the phase shift network and the transducer configured such that the output voltage leads the output current by an angle (46) that is greater than 0 degrees and less than about 90 degrees for the operational frequency or bandwidth of frequencies.
The operational bandwidth of frequencies may be the frequencies over which the transducer sweeps (69, 70). The electronic bridge circuit may comprise a loop inductance (50, 53) of between about 3 nanohenrys and about 27 nanohenrys and at least one gate drive dead time (49, 52) of between about 97 nanoseconds and about 787 nanoseconds. The electronic bridge circuit may also comprise at least one power MOSFET transistor as a switching device. The output voltage may lead the output current by an angle that is greater in a middle region of the operational bandwidth of frequencies than an angle at an end region of the operational bandwidth of frequencies and the output voltage may lead the output current by an angle that varies as a function g(f) of the frequency over the operational bandwidth of frequencies to produce a specified function h(f) for power versus frequency over the operational bandwidth of frequencies. The system may further comprise a phase lock loop (79, 80) controlling the operational bandwidth of frequencies. The transducer may be a megasonic transducer assembly.
The invention also provides a method of delivering multiple megasonic frequencies to a liquid, comprising the steps of (a) providing a liquid, (b) providing a megasonic transducer or assembly of megasonic transducers configured to selectively produce megasonic energy in the liquid at a first frequency (64) within a first frequency band (69) and at a second frequency (67) within a second frequency band (70) that is different from and non-contiguous to the first frequency band, (c) coupling the transducer to the liquid and (d) driving the transducer with a megasonics generator (9) configured to produce the first frequency and the second frequency.
The transducer may be configured to selectively produce megasonic energy in the liquid at sweeping frequencies within the first frequency band and may be configured to selectively produce megasonic energy in the liquid at sweeping frequencies within the second frequency band. The megasonic generator may be configured to selectively produce the sweeping frequencies in the first frequency band and to produce the sweeping frequencies in the second frequency band.
The invention also provides a method of delivering multiple megasonic frequencies to a liquid, comprising the steps of (a) providing a liquid, (b) providing a megasonic transducer or assembly of megasonic transducers configured to selectively produce megasonic energy in the liquid at a single frequency (64) within a first frequency band (69) and at sweeping frequencies in the first frequency band, (c) coupling the transducer to the liquid, and (d) driving the transducer with a megasonics generator (9) configured to produce the single frequency and the sweeping frequencies.
The invention also provides a megasonic system for coupling megasonics to a liquid, comprising a megasonic transducer adapted to couple to a liquid and configured and arranged so as to produce megasonics in the liquid at frequencies within at least a first frequency band and a second frequency band, a megasonic generator coupled to the transducer and configured and arranged to produce a driver signal to the megasonic transducer at one or more frequencies within each of the first and second frequency bands. The second frequency band may be different from and non-contiguous to the first frequency band. The transducer may comprise a first piezoelectric ceramic (11) with a positive polarity surface and a negative polarity surface opposite the positive surface, a second piezoelectric ceramic (12) with a positive polarity surface and a negative polarity surface opposite the positive surface, a resonator plate (15) having a first surface configured to couple megasonics to a liquid and a second surface, the negative polarity surface of the first piezoelectric ceramic bonded to the positive polarity surface of the second piezoelectric ceramic to form a megasonic piezoelectric assembly (14), and the negative polarity surface of the second piezoelectric ceramic bonded to the second surface of the resonator plate to form a megasonic transducer for producing multiple megasonic frequencies. The transducer may comprise a first piezoelectric ceramic having a positive polarity surface and a negative polarity surface opposite the positive surface, a second piezoelectric ceramic having a positive polarity surface and a negative polarity surface opposite the positive surface, a resonator plate having a first surface configured to couple megasonics to a liquid and having a second surface, the positive polarity surface of the first piezoelectric ceramic bonded to the negative polarity surface of the second piezoelectric ceramic to form a megasonic piezoelectric assembly, and the positive polarity surface of the second piezoelectric ceramic bonded to the second surface of the resonator plate to form a megasonic transducer for producing multiple megasonic frequencies. The transducer may have a resonance frequency and an anti-resonance frequency within the first frequency band, and the frequency within the first frequency band has a value that is greater than the resonance frequency and less than the anti-resonance frequency. The generator and transducer may be configured and arranged to produce sweeping frequencies within at least one of the frequency bands, and the frequency band may be the first frequency band, the transducer may have a resonance frequency and an anti-resonance frequency within the first frequency band, and the sweeping frequencies may be greater than the resonance frequency and less than the anti-resonance frequency.
The invention also provides a system for coupling megasonics to a liquid, comprising a megasonic transducer adapted to couple to a liquid and configured and arranged so as to produce megasonics in the liquid at a first frequency (64) within a first frequency band (69) and at sweeping frequencies in the first frequency band, a megasonic generator coupled to the transducer and configured and arranged to produce a driver signal to the megasonic transducer at the first frequency and at the sweeping frequencies. The predominant form of cavitation in the liquid may be stable cavitation when the megasonics is at the first frequency and the predominant form of cavitation in the liquid may be transient cavitation when the megasonics is at the sweeping frequencies. The transducer may have a resonance frequency and an anti-resonance frequency within the first frequency band, and the frequency within the first frequency band may have a value that is greater than the resonance frequency and less than the anti-resonance frequency. The transducer may have a resonance frequency and an anti-resonance frequency within the first frequency band, and the sweeping frequencies may be greater than the resonance frequency and less than the anti-resonance frequency.
The invention also provides a multiple frequency megasonic generator comprising an electronic bridge circuit (31) configured to selectively produce at least a first frequency of operation (64) and a second frequency of operation (67) and to selectively produce a driver signal characterized by a first frequency within a first frequency band (69) and to selectively produce a driver signal characterized by a second frequency within a second frequency band (70) that is different from and non-contiguous to the first frequency band, and a controller for generating the first frequency within the first frequency band during a first time period and for generating the second frequency within the second frequency band during a second time period different from and non-contiguous to the first time period. The bridge circuit may be a half bridge circuit. The electronic bridge circuit may be configured to selectively produce a driver signal characterized by sweeping frequencies within at least one of the frequency bands. The electronic bridge circuit may be configured to selectively produce a driver signal characterized by sweeping frequencies within the first frequency band and to selectively produce a driver signal characterized by sweeping frequencies within the second frequency band. The electronic bridge circuit (31) may have a first output terminal (35) and a second output terminal (34) configured to provide an output voltage (36) and an output current (37) and may further comprise a phase shift network (32) having a first input terminal (38), a second input terminal (39), a first output terminal (40), and a second output terminal (41), the first output terminal of the bridge circuit coupled to the first input terminal of the phase shift network and the second output terminal of the bridge circuit coupled to the second input terminal of the phase shift network, an ultrasound transducer (33) having an first input terminal (42) and a second input terminal (43), the first output terminal of the phase shift network coupled to the first input terminal of the transducer and the second output terminal of the phase shift network coupled to the second input terminal of the transducer, the bridge circuit, the phase shift network and the transducer configured such that the output voltage leads the output current by an angle (46) that is greater than 0 degrees and less than about 90 degrees for at least one of the frequencies. The transducer may be a megasonic transducer assembly. The electronic bridge circuit may comprise a loop inductance (50, 53) of between about 3 nanohenrys and about 27 nanohenrys; and at least one gate drive dead time (49, 52) of between about 97 nanoseconds and about 787 nanoseconds. The electronic bridge circuit may be configured to selectively produce a driver signal characterized by sweeping frequencies within at least one of the frequency bands and the output voltage leads the output current by an angle that is greater in a middle region of the sweeping frequencies than the angle at an end region of the sweeping frequencies. The output voltage may lead the output current by an angle (46) that is greater than 0 degrees and less than about 90 degrees for at least one of the frequency bands. The multiple frequency megasonic generator may further comprise a phase shift network having a non-resistive output circuit (100) with a Norton equivalent impedance (122) near infinity at the first frequency of operation. The multiple frequency megasonic generator may further comprise a transducer, a transmission line (115) between the transducer to the megasonic generator, and at least one parallel inductor matching network (88) between the transmission line and the transducer. The transducer may have a resonance frequency and an anti-resonance frequency within the first frequency band, and the frequency within the first frequency band may have a value that is greater than the resonance frequency and less than the anti-resonance frequency.
The invention also provides a method of delivering transient megasonic cavitation and stable megasonic cavitation to a liquid, comprising the steps of (a) providing a liquid, (b) providing a megasonic transducer or assembly of megasonic transducers configured to selectively produce megasonic energy in the liquid at single frequencies and at sweeping frequencies within a first frequency band (69), (c) coupling the transducer to the liquid, (d) driving the transducer with a megasonics generator (9) configured to produce substantially all of a range of frequencies within the frequency band, and (e) controlling the generator so as to produce megasonic sweeping frequencies that cause predominantly transient cavitation in the liquid during a first time period and so as to produce a megasonic frequency that causes predominantly stable cavitation during a second time period different from and non-contiguous to the first time period.
The invention also provides an ultrasound system comprising a generator for generating a driving signal to power an ultrasound transducer assembly, at least one sensor (3) adapted to sense operating conditions of the generator, a processor (4) communicating with the sensor, non-volatile memory (5) coupled to the processor, and the processor programmed to receive a signal from the sensor during operation of the generator and to store the signal in the memory for access after operation of the generator when the signal indicates a system error, fault or failure, whereby a history of the faults, errors or failures is available after the generator is powered down. The processor may be selected from a group consisting of digital integrated circuits, programmable logic controllers or computers commonly referred to as microprocessors, microcontrollers, CPUs, PICs, PLCs, PCs and microcomputers. The non-volatile memory may be selected from a group consisting of flash memory, EEPROM, magnetic memory and optical memory. The ultrasound transducer assembly may be configured and arranged to couple megasonics to liquid, to couple ultrasonics to liquid, to couple ultrasonics to solid, or to couple ultrasonics to a gas. The non-volatile memory may be RAM powered by a battery. The fault, error or failure may be selected from a group consisting of a low power line voltage condition, a high power line current draw, an over voltage power line condition, an over temperature condition, an over voltage ultrasound driving signal, an over current ultrasound driving signal, an under voltage ultrasound driving signal, an under current ultrasound driving signal, an unlocked PLL condition, an out of specification phase shift condition, an ultrasound drive frequency over a maximum limit, an ultrasound drive frequency under a minimum limit, an excessive reflected power condition, an open ultrasound transducer assembly, a shorted ultrasound transducer assembly, an ultrasound transducer assembly over a maximum capacitance value, an ultrasound transducer assembly under a minimum capacitance value, a high impedance ultrasound transducer assembly, a low impedance ultrasound transducer assembly, a missing interlock, incorrect output power, loss of closed loop output power control, a start up sequence error, an aborted start up sequence, and a shut down sequence error.
Thus, the general object of the invention is to provide a system for coupling megasonics with a liquid at multiple megasonic frequencies and/or sweeping frequencies.
Another object is to provide a transducer for megasonics at multiple frequencies and/or sweeping frequencies.
Another object is to provide a generator for driving at multiple megasonic frequencies and/or sweeping frequencies.
Another object is to provide a generator for driving between a resonance and anti-resonance frequency.
Another object is to provide an ultrasound generator having a phase shift network that provides voltage leading current.
Another object is to provide an inductor for compensating for changes in transducer capacitance.
Another object is to provide a system for individually controlling piezoelectric ceramic segments.
Another object is to provide an inductor matching network.
Another object is to provide a gate drive for power control.
Another object is to provide a system with near infinite output.
Another object is to provide a system having a transmission line with increased stability.
Another object is to provide an ultrasound generator system having non-volatile storage of fault, error and failure codes.
These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings and the appended claims.
At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.
Referring now to the drawings and more particularly to
As further identified herein, this system is also applicable in certain embodiments to ultrasonics. For example,
As shown in
With further reference to
Megasonic transducers as are known in the art are driven at a resonance frequency or at an anti-resonance frequency. In contrast, in the preferred embodiment the megasonic transducers are driven at a frequency between resonance and anti-resonance. Further, when a megasonic transducer consists of multiple piezoelectric ceramic segments in parallel, as is practiced in the prior art, and these multiple piezoelectric ceramic segments in parallel are driven by a generator with a phase lock loop (PLL) used to maintain operation at the anti-resonant frequency, because of an averaging effect, conventional state of the art generators drive some of the piezoelectric ceramic segments at a frequency higher than the anti-resonant frequency. This causes lower performance operation of those segments. This lower performance operation is overcome in the preferred embodiment because all of the piezoelectric ceramic segments are driven between their individual resonant and anti-resonant frequencies.
For megasonic systems where the PLL locks on the anti-resonant, four techniques are provided that accomplish the improved performance of driving every piezoelectric ceramic segment in any transducer assembly at a frequency between its individual resonant and anti-resonant frequencies. The first technique uses a matching network at the piezoelectric ceramic segments to cause zero phase shift at a frequency lower than the anti-resonant frequency of the lowest frequency piezoelectric segment. The second technique uses a network in the output of the megasonic generator to cause zero phase shift at a frequency lower than the anti-resonant frequency of the lowest frequency piezoelectric segment. The third technique uses a PLL designed to lock onto a non-zero phase shift condition, in this case, a phase angle occurring between resonance and anti-resonance. The fourth technique delays the true voltage signal prior to sending it to the phase detector of the PLL so that when the PLL locks onto zero phase shift, it is maintaining a condition where the true voltage leads the current, which is the condition for operation between resonance and anti-resonance with a PLL designed to search for the anti-resonant frequency.
For megasonic systems where the PLL locks onto the resonant frequency rather than the anti-resonant frequency, the improvement of driving at a frequency between resonance and anti-resonance still applies. However, there are several implementation changes that must be made because when a PLL controlled megasonic generator is designed to operate at the anti-resonant frequency, the PLL searches toward lower frequencies when the output current leads the output voltage and the PLL searches toward higher frequencies when the output voltage leads the output current. The operation is reversed when a PLL controlled megasonic generator is designed to operate at the resonant frequency. The PLL searches toward higher frequencies when the output current leads the output voltage and the PLL searches toward lower frequencies when the output voltage leads the output current. Four techniques that accomplish the improved performance of driving every piezoelectric ceramic segment in a transducer assembly at a frequency between its individual resonant and anti-resonant frequencies for PLL search arrangements designed to lock onto the resonant frequency may be used.
The first technique uses a matching network at the piezoelectric ceramic segments to cause zero phase shift at a frequency higher than the resonant frequency of the highest frequency piezoelectric segment. The second technique uses a network in the output of the megasonic generator to cause zero phase shift at a frequency higher than the resonant frequency of the highest frequency piezoelectric segment. The third technique uses a PLL designed to lock onto a non-zero phase shift condition, in this case, a phase angle occurring between resonance and anti-resonance. The fourth technique shifts the true voltage signal back in time prior to sending it to the phase detector of the PLL so that when the PLL locks on zero phase shift, it is maintaining a condition where the true voltage leads the current, which is the condition for operation between resonance and anti-resonance with a PLL designed to search for the resonant frequency.
In the first embodiment, a network 32 is placed between the electronic bridge circuit 31 (preferably a half bridge 48 or full bridge 51 topology) and the assembly of transducers 33 (preferably a transducer assembly that is a sweeping frequency or a transducer assembly that operates at various single frequencies within a PLL search bandwidth depending on the particular resonant frequency characteristics of the transducer assembly). The network is synthesized in combination with the transducer impedance characteristics such that the drive signal from the electronic bridge circuit always has the voltage leading the current by a phase angle between about one degree and about 89 degrees within the bandwidth of operation. This results in the simplest, least expensive, most reliable and most efficient sweeping frequency generator 9. A further improvement is to synthesize the network such that the magnitude of its phase shift is highest at the resonant frequency of the transducer assembly or in the middle region of the bandwidth of frequencies and decreases or approaches zero as the frequency sweeps to either end of the bandwidth. This adds a feature of a more constant power versus frequency over the sweep bandwidth. Data indicates that cleaning improves as the power versus frequency curve approaches a flat line. Although this network shows the greatest advantage at megasonic frequencies where losses are often higher than at lower ultrasonic frequencies, this phase shifting network is also applicable to other ultrasonic frequencies in the range from about 18 kHz up through the megasonic frequencies.
An electronic bridge circuit (a half bridge or full bridge topology) operates with current flowing forward through the switching devices and backwards through antiparallel or body diodes in parallel with the switching devices. When current through one of the diodes is reversed, the phase shift network in combination with the transducer impedance characteristics sets up a condition that the device that the diode is in parallel with is also on. This allows the reverse recovery current of the diode to flow with low voltage across the diode (i.e., the switching device on voltage). Therefore, there is insignificant power dissipation due to this reverse recovery current. Without the phase shift network in combination with the transducer impedance keeping the electronic bridge circuit output voltage leading the output current by an angle that is greater than 0 degrees and less than about 90 degrees, operational conditions occur where current through at least one of the diodes is reversed when the device that the diode is in parallel with is off. This causes the reverse recovery current of the diode to flow from the power supply voltage of the electronic bridge circuit to ground. Therefore, there is power dissipation due to this reverse recovery current equal to the power supply voltage times the reverse recovery current integrated and averaged over time. This power dissipation typically occurs every half cycle of the electronic bridge circuit resulting in significant power loss and inefficiency.
The preferred embodiment employs either a half bridge topology or a full bridge topology. An electronic bridge circuit 31 with an output supplying an output voltage 36 and an output current 37 and operational over a bandwidth of frequencies is provided. The electronic bridge circuit is coupled to a phase shift network 32 and the phase shift network is coupled to a transducer assembly 33. The electronic bridge circuit has output terminals from which the output voltage and the output current are supplied. The phase shift network has input terminals and output terminals, and the output terminals of the electronic bridge circuit are coupled to the input terminals of the phase shift network. The transducer assembly has input terminals, the output terminals of the phase shift network are coupled to the input terminals of the transducer assembly. The phase shift network coupled with the transducer assembly causes the output voltage of the electronic bridge circuit to lead the output current of the electronic bridge circuit by an angle greater than 0 degrees and less than about 90 degrees for all frequencies within the bandwidth of frequencies. An added enhancement to the operation of the electronic bridge circuit is to employ a loop inductance of between 3 nanohenrys and 27 nanohenrys and gate drive dead times between 97 nanoseconds and 787 nanoseconds to reduce spurious oscillations and to increase efficiency of the system.
The electronic bridge circuit with phase shift network and with transducer assembly can be used to produce a specific power curve versus frequency (P=h(f)) by synthesizing the phase shift network coupled with the transducer assembly such that the output voltage of the electronic bridge circuit leads the output current of the electronic bridge circuit by an angle that varies as a function of frequency g(f) over the bandwidth of frequencies to produce the specified function h(f) for the power versus frequency over the bandwidth of frequencies. The bandwidth of frequencies for the electronic bridge circuit are typically the set of lock frequencies for a phase lock loop which sets the system frequency or, if the system sweeps frequency, then the bandwidth of frequencies are the range of frequencies over which the system sweeps.
As shown in
As shown in
The phase of the voltage 36 and current 37 out of electronic bridge circuit 31 is determined by the impedance into terminals 38 and 39 of phase shift network 32. Since phase shift network 32 is coupled to ultrasound transducer assembly 33, the impedance into terminals 38 and 39 of phase shift network 32 is both a function of the phase shift network 32 impedance and the transducer assembly 33 impedance. This impedance into terminals 38 and 39 of phase shift network 32 is synthesized such that the voltage 36 leads the current 37 by a phase angle 46 of between about one degree and eighty nine degrees.
As mentioned above,
In the preferred embodiment, shown in
The megasonic generator of the preferred embodiment is designed to be capable of switching between single frequency operation and sweeping frequency operation. Generator 9 produces a process that is superior to conventional state of the art processes because it allows two distinct cavitation characteristics to be employed in the cleaning or processing operation. For example, a multiple frequency megasonic system operating at a phase lock loop frequency of 950 kHz or a phase lock loop frequency of 2.85 MHz is provided to also sweep frequency in a bandwidth around 950 kHz and in a second bandwidth around 2.85 MHz. A delicate part with critical cleaning requirements may require transient cavitation to remove some of the contamination, but the typical transient cavitation existing in a conventional state of the art 1 MHz megasonic system is too harsh and does damage to the part. With this embodiment of generator 9, the mode of sweeping frequency around 2.85 MHz is used for gentle transient cavitation, followed by single frequency 950 kHz, and followed by single frequency 2.85 MHz to produce stable cavitation of sizes appropriate for submicron particle removal.
As mentioned above, one of the preferred combinations of modes possible with system 2 is a process in which mode 68 is performed first, followed by mode 64, followed by a final process step of mode 67. This process is advantageous because a delicate part with critical cleaning requirements may require transient cavitation to remove some of the contamination, but the typical transient cavitation existing in a state of the art megasonic system is too harsh and does damage to the part. With this method, mode 68 sweeps at the third overtone frequency 70, which produces gentle transient cavitation. Mode 68 is then followed by a single frequency at the fundamental frequency 64 and is then followed by a single frequency at the third overtone 67 to produce stable cavitation of sizes appropriate for submicron particle removal.
Another combination of modes not available in state of the art megasonic systems is a multiple frequency process consisting of different megasonic frequencies produced by the same megasonic transducer assembly. For example, with system 2 capable of producing mode 64 and mode 67, a process is provided that employs this multiple megasonic frequency operation. The advantage to this system and process over state of the art megasonic systems is that each different frequency removes a different particle size most effectively. Therefore, a larger range of contamination can be cleaned in a shorter time by this process and system.
Another combination of modes is a significant advance over state of the art megasonic systems. This combination of modes does not require the capability of multiple frequencies, but rather uses sweeping frequency for one time period in one megasonic frequency band around one megasonic frequency, followed by single frequency operation for a second time period at the megasonic frequency. For example, system 2 may produce mode 65 and mode 64. Another example is to produce mode 68 and mode 67.
For larger systems having the modes shown in
In another embodiment, the megasonic generator is provided with multiple driver sections each with independent PLL (phase lock loop) and closed loop power control. Each of the multiple generator sections is configured and wired to drive one segment or section of piezoelectric ceramic transducer. This new system 83 gives the process engineer power control over each transducer segment or section while each segment or section is operating at an optimum closed loop frequency. The process engineer can then adjust each segment or section of a particular megasonic transducer for uniformity or for another specified power distribution curve that the process requires. The closed loop power control then maintains this condition for long term process optimization.
The system shown in
In the preferred embodiment, the generator 9, transducer 33 and transducer matching network 88 are configured for higher efficiency and lower cost than exists with state of the art megasonic systems. One conventional configuration is to connect the piezoelectric transducer to the generator through a cable. This is inefficient because the current flowing into and out of the capacitive component of the piezoelectric transducer causes heating of the cable and power loss. Another present day configuration is to use a transformer and reactive components at a piezoelectric megasonic transducer to match the impedance of the piezoelectric megasonic transducer to a coax cable impedance, typically 50 ohms. A coax cable of the proper impedance (typically 50 ohm RG-58 type coax cable) is used to connect this matched piezoelectric megasonic transducer to the generator. This is expensive because the matching transformer at megasonic frequencies is costly.
In the preferred embodiment, an inductor 89 (with a value in the range PI/(ŵ2*Co) to 1/(ŵ2*Co), where PI=3.14159, w=2PIf, Co is the parallel capacitance of the piezoelectric transducer, and f is the frequency of operation) is connected in parallel with the piezoelectric transducer at the transducer and uses any cable 115 to connect this assembly to the generator. The generator has a LC output network 100 which drives this cable, inductor 89 and piezoelectric transducer 33.
The cost reduction of a single inductor 89 versus a matching transformer 86 network 85 (prior art shown in
In another embodiment, a gate drive (where the duty cycle is non constant and the float side gate drive is the inverted ground side gate drive with dead times added) waveform for a half bridge is provided that will improve operation during power control when using gate duty cycle for the power control function in a megasonic generator. It eliminates the 3*Fo voltage changes that occur at the center of the half bridge when power is reduced. This improved gate drive still had a deficiency in that is was possible to have a condition where a forward biased antiparallel diode in one side of the half bridge could be reverse biased when the switching device is turned on in the other side of the half bridge. This condition dissipates energy and this impulse of energy in the circuitry causes noise and oscillations. Although this condition is common in state of the art ultrasonic generators, as frequency is raised to the 1 MHz range, this dissipation becomes a rather large problem. In this embodiment, the narrow gate pulses in the float side of the half bridge that meter the power to the load are always started when the current flowing from the center of the half bridge is negative, i.e., current flowing toward the half bridge typically through the ground side switching device. This solves the problems and results in a power control system that is small and low cost.
In another embodiment, the megasonic generator is designed and configured to have no resistive components or other lossy elements in the output stage. Unlike conventional state of the art megasonic generators where the output impedance matches the coax cable impedance, usually 50 ohms, this embodiment of the megasonic generator output stage does not have operating problems with mismatched loads or transducers because power reflected by the load or transducer is again reflected by the megasonic generator output stage back to the load or transducer. This results in a higher efficiency system when the transducer becomes mismatched due to temperature, age or other changes.
With reference to
In this embodiment, sensor 3 is a conventional temperature sensor that responds to an over temperature condition within the generator, processor 4 is a conventional PIC, and memory 5 is conventional EEPROM. The temperature sensor manufactured by Analog Devices and the PIC and EEPROM manufactured by Microchip may be used in the preferred embodiment.
While a temperature sensor, PIC and EEPROM are used in the preferred embodiment, it is contemplated that other sensors, processors or memory may be used. For example, it is contemplated that a digital integrated circuit, microprocessor, microcontroller, CPU, PLC, PC or microcomputer may be used as a processor. In addition, it is contemplated that a magnetic memory, flash memory or optically memory may be used as the memory element. In addition, it is contemplated that other sensors or an array of sensors may be used to sense a fault, error or failure. For example, sensors may be employed or adapted to determine a low power line voltage condition, a high power line current draw, an over voltage power line condition, an over temperature condition, an over voltage ultrasound driving signal, an over current ultrasound driving signal, an under voltage ultrasound driving signal, an under current ultrasound driving signal, an unlocked PLL condition, an out of specification phase shift condition, an ultrasound drive frequency over maximum limit, an ultrasound drive frequency under a minimum limit, an excessive reflected power condition, an open ultrasound transducer assembly, a shortened ultrasound transducer assembly, an ultrasound transducer assembly over a maximum capacitance value, an ultrasound transducer assembly under a minimum capacitance value, a high impedance ultrasound transducer assembly, a low impedance ultrasound transducer assembly, a missing interlock, incorrect output power, loss of closed loop output power control, a start up sequence error, an aborted start up sequence, or a shut down sequence error. Thus, system 7 may be used to determine and record the history of numerous different faults, errors and failures of interest with respect to troubleshooting and repair of the generator or system.
The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The present embodiments are therefore to be considered as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of the equivalency of the claims are therefore intended to be embraced therein. Accordingly, while the presently-preferred form of the system has been shown and described, and several embodiments discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.
Claims
1. A method of delivering multiple megasonic frequencies to a liquid, comprising the steps of:
- (a) providing a liquid;
- (b) providing a megasonic transducer or assembly of megasonic transducers configured to selectively produce megasonic energy in said liquid at a single megasonic frequency within a first megasonic frequency band and at sweeping frequencies in said first megasonic frequency band;
- (c) coupling said transducer to said liquid; and
- (d) driving said transducer with a megasonics generator configured to produce said single megasonic frequency and said sweeping frequencies.
2. A system for coupling megasonics to a liquid, comprising:
- a megasonic transducer adapted to couple to a liquid and configured and arranged so as to produce megasonics in said liquid at a first megasonic frequency within a first megasonic frequency band and at sweeping frequencies in said first megasonic frequency band;
- a megasonic generator coupled to said transducer and configured and arranged to produce a driver signal to said megasonic transducer at said first megasonic frequency and at said sweeping frequencies.
3. A system according to claim 2, wherein a predominant form of cavitation in said liquid is stable cavitation when said megasonics is at said first frequency and a predominant form of cavitation in said liquid is transient cavitation when said megasonics is at said sweeping frequencies.
4. A system according to claim 2, wherein said transducer has a resonance frequency and an anti-resonance frequency within said first frequency band, and said frequency within said first frequency band has a value that is greater than said resonance frequency and less than said anti-resonance frequency.
5. A system according to claim 2, wherein said transducer has a resonance frequency and an anti-resonance frequency within said first frequency band, and said sweeping frequencies are greater than said resonance frequency and less than said anti-resonance frequency.
6. A method of delivering transient megasonic cavitation and stable megasonic cavitation to a liquid, comprising the steps of:
- (a) providing a liquid;
- (b) providing a megasonic transducer or assembly of megasonic transducers configured to selectively produce megasonic energy in said liquid at single frequencies and at sweeping frequencies within a first megasonic frequency band;
- (c) coupling said transducer to said liquid; and
- (d) driving said transducer with a megasonics generator configured to produce substantially all of a range of frequencies within said megasonic frequency band;
- (e) controlling said generator so as to produce megasonic sweeping frequencies that cause predominantly transient cavitation in said liquid during a first time period and so as to produce a megasonic frequency that causes predominantly stable cavitation during a second time period different from and non-contiguous to said first time period.
Type: Application
Filed: Apr 24, 2009
Publication Date: Oct 1, 2009
Inventor: William L. Puskas (New London, NH)
Application Number: 12/386,910
International Classification: B08B 3/12 (20060101);