Abstract:
The present invention generally relates to medical systems and apparatus and uses thereof for treating obesity and/or obesity-related diseases, and more specifically, relates to systems and methods for energy recovery in a laparoscopically-placed gastric banding system operably coupled to a piezo actuator. The energy recovery may be obtained utilizing an energy recovery device, such as an inductor, coupled to the piezo actuator. The energy recovery device may utilize two circuits to facilitate energy recovery, and the two circuits may include diodes with opposite orientations to control current flow.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation in part of, and claims priority to and the benefit of U.S. patent application Ser. No. 12/859,196, entitled “POWER REGULATED IMPLANT” filed on Aug. 18, 2010, the entire disclosure of which is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present invention generally relates to medical systems and apparatus and uses thereof for treating obesity and/or obesity-related diseases, and more specifically, relates to systems and methods for energy recovery in a laparoscopically-placed gastric band operably coupled to a piezo actuator. 
       BACKGROUND 
       [0003]    Adjustable gastric banding apparatus have provided an effective and substantially less invasive alternative to gastric bypass surgery and other conventional surgical weight loss procedures. Despite the positive outcomes of invasive weight loss procedures, such as gastric bypass surgery, it has been recognized that sustained weight loss can be achieved through a laparoscopically-placed gastric band, for example, the LAP-BAND® (Allergan, Inc., Irvine, Calif.) gastric band or the LAP-BAND AP® (Allergan, Inc., Irvine, Calif.) gastric band. Generally, gastric bands are placed about the cardia, or upper portion, of a patient&#39;s stomach forming a stoma that restricts the food&#39;s passage into a lower portion of the stomach. When the stoma is of an appropriate size that is restricted by a gastric band, the food held in the upper portion of the stomach provides a feeling of satiety or fullness that discourages overeating. Unlike gastric bypass procedures, gastric band apparatus are reversible and require no permanent modification to the gastrointestinal tract. 
         [0004]    Over time, a stoma created by a gastric band may need adjustment in order to maintain an appropriate size, which is neither too restrictive nor too passive. Accordingly, prior art gastric band systems provide a subcutaneous fluid access port connected to an expandable or inflatable portion of the gastric band. By adding fluid to or removing fluid from the inflatable portion by means of a needle, such as a Huber needle inserted into the access port, the effective size of the gastric band can be adjusted to provide a tighter or looser constriction. 
         [0005]    Non-invasive adjustment systems and methods have also been proposed to change the constriction of a gastric band, for example, without the use of a needle. Some of these systems utilize implantable pumps to perform the constriction changes. However, the system specifications for these pumps, such as small size, power dissipation, flow rate, back pressure, and magnetic resonance imaging, result in challenging constraints for pump implementation. 
         [0006]    Thus, there continues to remain a need for more effective implantable pump systems for use with adjustable gastric bands, particularly such implantable pump systems with pumping capability that achieves the desired flow rate within other design parameters such as voltage and temperature. 
         [0007]    Further, there is a need for more effective implantable pump systems for adjustable gastric bands that are energy efficient and are capable of being optimized based on various factors. 
       SUMMARY 
       [0008]    Generally described herein are implantable pumping systems for implantable gastric banding systems driven by a piezoelectric element pump. The apparatus and systems described herein aid in facilitating obesity control and/or treating obesity-related diseases while being non-invasive once implanted. 
         [0009]    In an embodiment, a device for controlling a pump in an implantable gastric banding system comprises a positive terminal of a power source coupled via a first switch to a piezoelectric actuator, and a negative terminal of the power source coupled via a second switch to the piezoelectric actuator. The piezoelectric actuator may be coupled to an inductor to facilitate charging and discharging the piezoelectric actuator. The device for controlling a pump in an implantable gastric banding system may further comprise a first circuit comprising a first diode, a third switch, the inductor, and the piezoelectric actuator. The piezoelectric actuator may be operable to facilitate moving a fluid between a reservoir and an implantable portion of a gastric band. 
         [0010]    The device for controlling a pump in an implantable gastric banding system further comprises a second circuit comprising a second diode, a fourth switch, the inductor, and the piezoelectric actuator. The first diode and the second diode may comprise opposite operational orientations to facilitate discharging the piezoelectric actuator and to facilitate energy recovery in the implantable gastric banding system. The device for controlling a pump in an implantable gastric banding system further comprises a microcontroller operable to control the operation of at least one of the first switch, the second switch, the third switch, or the fourth switch, according to a dynamic algorithm to optimize the energy recovery of the implantable gastric banding system. The dynamic algorithm may compensate for at least one of the uniqueness of each system component or aging of the devices in the system. 
         [0011]    Further, in various embodiments, the system for energy recovery comprises at least one of a low voltage power supply, a high voltage power supply, an H bridge circuit, a sensor, or a power supply such as a battery. Additionally, a microcontroller may be configured to control the operation of at least one of the first switch or the second switch. 
         [0012]    In accordance with an embodiment, the inductance value of the inductor is selected based on at least one of the piezoelectric actuator operating period or the current output of the piezoelectric actuator. Further, the piezoelectric actuator may operate below the piezoelectric actuator resonant frequency. For example, the piezoelectric actuator may operate below about 50 KHz. 
         [0013]    Additionally, in various embodiments, a system for energy recovery in an implantable gastric banding system comprises a piezoelectric actuator for moving a fluid from a reservoir to an inflatable portion of a gastric band. A power supply is coupled to a terminal of the piezoelectric actuator, and an energy recovery device coupled to the terminal of the piezoelectric actuator. The system further comprises a first diode with a first orientation, and a first switch coupled to the first diode. A second switch is coupled to a second diode having a second orientation, and the second orientation is opposite the first orientation of the first diode. 
         [0014]    In various embodiments, the energy recovery device is coupled to a first diode terminal of the first diode and a second diode terminal of the second diode to facilitate recharging of the piezoelectric actuator. The recharging may occur in response to at least one of the first switch or the second switch being closed. In various embodiments, the energy recovery device comprises at least one of an inductor or a capacitor. 
         [0015]    Further, in accordance with an embodiment, a method for recovering energy from a piezoelectric actuator in an implantable gastric banding system comprises charging a piezoelectric actuator with a first magnitude of voltage of a first polarity from a power supply. The piezoelectric actuator may respond to the first magnitude of voltage to move a fluid from a reservoir to an inflatable portion of a gastric band of the implantable gastric banding system. The method for recovering energy may comprise discharging a flow of current of a first polarity from the piezoelectric actuator through an inductor coupled to a first diode comprising a first orientation. The flow of current may be discharged in response to closing a first switch coupled to the first diode, and the first switch may disconnect in response to a control signal being provided by a microcontroller. 
         [0016]    The method for recovering energy may further comprise recharging the piezoelectric actuator with a second magnitude of voltage of a second polarity from the inductor. The second polarity may be an opposite polarity from the first polarity. The method for recovering energy may comprise recharging the piezoelectric actuator with a third magnitude of voltage of the second polarity from the power supply. The method for recovering energy may comprise discharging a flow of current of the second polarity from the piezoelectric actuator through the inductor coupled to a second diode having a second orientation opposite the orientation of the first diode, and the discharging may occur in response to the closing of a second switch coupled to the second diode. The second switch may disconnect in response to a control signal provided by the microcontroller. 
         [0017]    Additionally, the method for recovering energy may comprise recharging the piezoelectric actuator with a fourth magnitude of voltage of the first polarity from the inductor. The method for recovering energy may comprise recharging the piezoelectric actuator with a fifth magnitude of the first polarity of voltage from the power supply. In various embodiments, the microcontroller is programmed with a dynamic algorithm. The dynamic algorithm may optimize operation of the system or compensate for at least one of the uniqueness of each system component or aging of the devices in the system. The dynamic algorithm may be implemented using software, hardware, or combinations thereof. 
         [0018]    In an embodiment, a system for energy recovery in an implantable gastric banding system is disclosed. The system for energy recovery comprises a piezoelectric actuator coupled to an inductor to facilitate charging and discharging of the piezoelectric actuator. The system for energy recovery further comprises a first circuit comprising a first diode, a first switch, the inductor, and the piezoelectric actuator. The piezoelectric actuator is operable to facilitate moving a fluid between a reservoir and an implantable portion of a gastric band. The system for energy recovery further comprises a second circuit comprising a second diode, a second switch, the inductor, and the piezoelectric actuator. The first diode and the second diode comprise opposite operational orientations to facilitate discharging the piezoelectric actuator and to facilitate energy recovery in the implantable gastric banding system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  illustrates a schematic view of an implantable pumping system according to an embodiment of the present invention. 
           [0020]      FIG. 2   a  illustrates a simplified circuit diagram according to an embodiment of the present invention. 
           [0021]      FIG. 2   b  illustrates the ideal voltage across the piezo electric actuator capacitive element (Vc) and the ideal current through the inductor of  FIG. 2   a  according to an embodiment of the present invention. 
           [0022]      FIG. 3  illustrates a simplified circuit diagram according to another embodiment of the present invention. 
           [0023]      FIG. 4  illustrates the functional blocks for a battery operated piezo actuator circuit according to an embodiment of the present invention. 
           [0024]      FIG. 5  illustrates a circuit diagram according to an embodiment of the present invention. 
           [0025]      FIG. 6  depicts an exemplary timing diagram of the microcontroller according to an embodiment of the present invention. 
           [0026]      FIG. 7  illustrates a flow chart representing a method of energy recovery according to an embodiment of the present invention. 
           [0027]      FIG. 8  depicts an exemplary embodiment of effective capacitance variation due to applied voltage according to an embodiment of the present invention. 
           [0028]      FIG. 9  illustrates a flow chart representing a method of adjusting the timing of the piezo actuator control waveforms to minimize power according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The present invention generally provides remotely adjustable gastric banding systems, for example, for treatment of obesity and obesity related conditions, as well as systems for controlling inflation of gastric banding systems. 
         [0030]    A remotely adjustable gastric band is a medical device which allows a healthcare worker to adjust a gastric band without utilizing needles to connect to an implanted access port. An external, handheld controller may be used to send radio frequency signals for powering and communicating with the implanted device. The implanted device may fill or drain the gastric band as requested by the healthcare worker via the handheld controller. The handheld controller may be a remote device configured to produce a telemetric signal that controls the various components of the gastric banding system. 
         [0031]    In various embodiments of the present invention, the filling and draining of the band is accomplished by a set of fluidic elements including pumps, valves, and sensors which monitor and/or move fluid between the gastric band and a reservoir. In accordance with various embodiments, different numbers, types, and orientations of the fluidic elements may be utilized to obtain the desired results. Any and/or all of these various components may be configured to be controlled by a remote transmitter, such as a handheld controller. 
         [0032]    For example, an implantable pump may be utilized to move the fluid through the adjustable gastric banding system. Considerations involved with the implantable pump include size, power dissipation, maintenance requirements, precision of operation, flow rate, back pressure, and effects on magnetic resonance imaging. Various embodiments of the present invention provide adjustable gastric banding systems that achieve the appropriate specifications for these and other considerations. 
         [0033]    Turning now to  FIG. 1 , an implantable pumping system  100 , according to an embodiment, comprises a piezo actuator based pump  130 . A voltage source, such as a high voltage source  105  is utilized to polarize the piezo actuators in the pump  130 . A voltage control circuit, such as a high voltage control circuit  110  is configured to increase or decrease the magnitude of the voltage. In various embodiments, the voltage may be in the range of approximately 20 volts to approximately 300 volts. In 
         [0000]        E=C*V   2   (2)
 
         [0034]    Upon fully charging the piezo actuator  240 , the energy stored in the capacitor may be half (½*C*V 2 ) the total energy where the other half of the energy may be dissipated in the circuit resistance. In one embodiment, after discharging, the piezo actuator&#39;s  240  stored energy may be dissipated in the circuit resistance. Stated another way, the energy put into the circuit is dissipated as heat and not as the useful work of piezo actuator  240  motion. 
         [0035]    In one embodiment, the energy stored in the piezo actuator  240  may be recovered, instead of being transferred into heat in the circuit resistance. Recovering the stored energy may lower the power input to the circuit from a power supply. In various embodiments, two types of electronic passive energy storage devices that may be utilized are (1) a capacitor and (2) an inductor. These devices may be used for energy recovery, alone or in combination. 
         [0036]    For example, in one embodiment, the charge stored in the piezo actuator  240  may be transferred to a second recovery capacitor during discharge of the piezo actuator  240 . Subsequently, such as on the next charge cycle of the piezo actuator  240 , the recovery capacitor may provide its stored energy back to the circuit. In another example, the resonance between a recovery inductor  250  and the piezo actuator  240  provides a mechanism for theoretically recovering substantially all of the energy of the piezo actuator  240 . 
         [0037]    The interaction of the inductor with other medical devices, such as interaction with magnetic resonance imaging devices, may be a factor in determining selection of passive energy storage devices. For instance, an inductor may have a composition that will interact with a magnetic field which may an embodiment, the piezoelectric actuator may operate below about 50 KHz. The piezoelectric actuator element displacement may be between about a nanometer and about a millimeter. 
         [0038]    In one embodiment, the piezo static capacitance is about 48 nF. In such an embodiment, the piezo actuator may be driven by a square wave with a 10 mS period, and an effective drive voltage of 210 volts. Components may be selected based on their size, cost, resistance, and ease of integration. 
         [0039]    With reference to  FIG. 2   a , a piezo actuator  240  associated with the piezoelectric actuator based pump  130  is depicted. When driven by a periodic voltage source at a frequency below the resonant frequency of the piezoelectric actuator  240 , the equivalent circuit model for the piezoelectric actuator  240  may be simplified to a single capacitor resulting in the equation: 
         [0000]        P=CV   2   F   (1)
 
         [0040]    Where the power (P) is determined by the product of the capacitance (C), the square of the voltage (V), and the driving frequency (F). The voltage, piezo capacitance (which is generally related to the actuator size), and driving frequency may not be capable of being reduced without adversely impacting proper operation of the piezoelectric actuator  240 . However, since the piezoelectric actuator  240  functionally operates as an energy storage device, energy may be recovered to reduce required power. Thus, references to a piezoelectric actuator or a piezo actuator encompass a piezoelectric actuator capacitance. 
         [0041]    Power dissipation due to charging and discharging the piezo actuator  240  may be significant. The charging of an initially discharged capacitance, C, from a constant voltage source, V, requires a total energy, E, expressed by the equation: create undesirable results. Thus, a capacitor selection over an inductor may be justified considering constraints of an MRI environment. 
         [0042]    With reference again to  FIG. 2   a  and  FIG. 2   b , and according to various embodiments, a diode  260 , a recovery inductor  250 , a piezo actuator  240 , and a switch  270  are illustrated. In one embodiment, for t&lt;0 the capacitance C of the piezo actuator  240  modeled as a capacitor is initially charged to voltage Vdd and no current is flowing in the circuit since the switch  270  is open. At t=0 the switch  270  is closed and current will start flowing from the piezo actuator  240  in the direction shown by the arrow. Under these conditions the diode  260  is considered an ideal short circuit. As current I L  flows, a magnetic field is induced in the recovery inductor  250  until the piezo actuator  240  is substantially fully discharged at Vc=0V. In response to the piezo actuator  240  being substantially fully discharged, the current in the recovery inductor  250  ramps down or is reduced as the magnetic field of the recovery inductor  250  collapses and, in the process, energy from the magnetic field is transferred back to the piezo actuator  240 . This process continues until the magnetic field has substantially fully dissipated and the piezo actuator  240  has been charged to −Vdd. Repeating or oscillating cycles do not occur due to the operation of diode  260 . The diode  260  may be considered an ideal open circuit completing one cycle of energy transfer. 
         [0043]    With renewed reference to  FIG. 2   b , and in accordance with an embodiment, the cycle for the recovery inductor  250  current and piezo actuator  240  voltage is depicted. The period of current flow in the circuit may be expressed as: 
         [0000]        T/ 2=1/(2*Freq)=π*( L*C ) 1/2   (3)
 
         [0044]    In an embodiment, the switch  270  is controlled in response to the algorithm programmed into a microcontroller  420  coupled to the system. In response to advantageously configured timing, when substantially full energy is transferred to the piezo actuator  240 , the algorithm directs the microcontroller to send a signal to the switch  270  to open. The operation of the microcontroller will be further discussed below. In one embodiment, switch  270  may automatically open when the substantially full energy transfer to the piezo actuator  240  occurs. 
         [0045]    Further, in one embodiment, losses due to resistance in the components, and non-ideal components may alter the previously presented equations. A power supply may be employed to inject power into the system to compensate for losses. Also, the power supply may be implemented to hold a voltage on the capacitance for substantially the full +Vdd to −Vdd voltage swing. The magnitude of the power transferred from the power supply may be proportional to and based on the loss in the circuit. 
         [0046]    In one embodiment, a simplified practical circuit for a repeating cycle of charging and discharging the piezo actuator  340  capacitance is shown in  FIG. 3 . For example, charging the piezo actuator  340  capacitance to a positive or negative Vdd may be accomplished with opposite diode  360 ,  365  orientations and using a shared recovery inductor  350 . The inductance value may be selected based on saturation point of the recovery inductor  350  relative to the full current of the piezo actuator  340  capacitance. Also, the inductance value may be selected so that time T/2 from the above equation is less than half the piezo actuator  340  operating period. The switches  370 ,  375 ,  380 , and  385  may be any suitable switch, such as a field effect transistor (FET), a bipolar junction transistor (BJT), (MOSFET), (HFET), (MESFET) and/or the like. 
         [0047]    With reference to  FIG. 4 , a diagram indicating the functional blocks for a piezo actuator  440  circuit is illustrated according to an embodiment of the present invention. In this embodiment, the power source is a DC battery  405 . Also, in various embodiments, a backup and/or a second battery may be coupled to the system. A low voltage power supply  410  may regulate the battery  405  to a specified voltage for the microcontroller  420  in the circuit. The low voltage supply  410  may be a linear regulator, a buck or boost switching regulator based on the battery  405  voltage. The high voltage supply  415  may generate the piezo actuator  440  electric field. The piezo actuator  440  electric field may be implemented with a boost topology switching regulator. 
         [0048]    In one embodiment, the microcontroller  420  may include a memory unit for storing the algorithms described herein. The microcontroller  420  and/or a processor may be used to execute the algorithms described herein. Other devices described herein may also be used to execute and/or store the algorithms described herein. 
         [0049]    In various embodiments, the microcontroller  420  may be any suitable microcontroller. The microcontroller  420  may be selected based on it being a low power device capable of generating the piezo actuator  440  operating frequency and providing control signals for the piezo driver  430  and efficiency circuit  435 . The piezo driver  430  may be configured to apply a voltage to the piezo actuator  440  with a proper phase and frequency. In various embodiments, the frequency may be in the range of approximately 10 Hz to approximately 1,000 Hz. Further, in various embodiments, the voltage applied to the pump  130  by the driver  120  may be in the range of approximately 20 volts to approximately 300 volts. 
         [0050]    With reference to  FIG. 5 , and in accordance with an embodiment, the simplified circuit depicted in  FIG. 3  is illustrated in more detail as implementing an H-bridge driver along with FETs  570 ,  575 ,  576 ,  577 ,  578 ,  579 ,  520 , and  521  to represent switches  370 ,  375 ,  380  and  385  from  FIG. 3 . The H-bridge may support the use of a single high voltage source  515  to oppositely polarize the piezo actuator  540  during each half of the operating period. In particular, the switch  380  of  FIG. 3  is represented by the current path enabled when the FET  578  and the FET  579  are on, while the switch  385  of  FIG. 3  is represented by the current path enabled when the FET  576  and the FET  577  are on. 
         [0051]    Though any suitable level translators may be utilized, R 1 , R 2 , and FET  520  are implemented as level translators interfacing between the high voltage associated with the FET  576  and the low voltage output of the microcontroller  420 . Similarly, R 3 , R 4  and FET  521  may be implemented as level translators interfacing between the high voltage associated with the FET  578  and the low voltage output of the microcontroller  420 . 
         [0052]    A diode D 1  may be utilized to prevent the piezo actuator  540  from discharging through the FET  577  instead of the intended path through the recovery inductor  550 , the diode  565 , and the FET  575 . A capacitor C 1  provides translation of a low going signal on SW 2  to a negative voltage to turn on the FET  575 . In an embodiment, the microcontroller orchestrates the control for each of the FETs  570 ,  575 ,  577 ,  579 ,  520 , and  521  gate signals to produce the sequence illustrated in  FIG. 6 . 
         [0053]    Further, in one embodiment, and with reference to  FIG. 7 , a method of operation of the switches and/or FETs is depicted. For simplicity, the switches depicted in  FIG. 3  are referenced. The microcontroller  420  and a dynamic algorithm associated therewith controls the operation of the switches and/or the FETs. 
         [0054]    At T=0, all switches are open ( 710 ). Subsequently, switch  380  is closed. At this point, the piezo actuator  340  is substantially fully charged via a terminal of the power source, such as the +Vdd terminal of the power source ( 715 ). 
         [0055]    All switches are then opened ( 720 ). Subsequently, switch  370  is closed, creating a complete electrical circuit from the piezo actuator  340  through the recovery inductor  350 , the diode  360 , and the switch  370  to ground ( 730 ). Resonance is created between the recovery inductor  350  and the piezo actuator  340 , thus reversing the polarity of the capacitive load from +Vdd to −Vdd. In one embodiment, a voltage equal to or a voltage between +Vdd to −Vdd may be represented as a first magnitude, second magnitude, third magnitude, fourth magnitude and fifth magnitude of voltage having a positive or negative polarity. Energy is initially stored in the recovery inductor  350  and then returned to the piezo actuator  340  with reversed polarity. 
         [0056]    A magnetic field is induced in the recovery inductor  350  due to the current passing through it. At T/4 the current is at a maximum. After T/4, the induced magnetic field begins to decay. At T/2 the polarity of the voltage in the capacitor is substantially reversed to −Vdd ( 735 ). 
         [0057]    All switches are then opened ( 740 ). Subsequently, switch  385  is closed and the piezo actuator  340  is substantially fully charged via a terminal of the power source, such as the −Vdd terminal of the power source to compensate for losses of the system ( 745 ). 
         [0058]    All switches are opened again ( 750 ). Subsequently, switch  375  is closed, creating a complete electrical circuit from the piezo actuator  340  through the recovery inductor  350 , the diode  365 , and the switch  375  to ground ( 755 ). Resonance is again created between the recovery inductor  350  and the piezo actuator  340 , thus reversing the polarity of the capacitive load from −Vdd to +Vdd ( 760 ). 
         [0059]    Again, all switches are then opened ( 765 ). Subsequently, switch  380  is closed and the piezo actuator  340  is substantially fully charged via a terminal of the power source due to losses of the system ( 770 ). This process may continue as desired. Although the method is described as initially putting a +Vdd polarity on the piezo actuator  340 , it is understood that a −Vdd polarity could be used in the alternative. 
         [0060]    In one embodiment, an algorithm controlling operation of the microcontroller may optimize the timing of the opening and closing of the switches in the system. For instance, minimizing the time between steps  740  and  745  may result in efficiencies. Also, determining T/2 and/or T/4 with increased precision may result in operational efficiencies of the system. 
         [0061]    This algorithm may be dynamic. As components of the system, such as the piezo actuator  340 , the recovery inductor  350 , the diodes or switches age, the timing of their operation may change. Alternatively, components may have different operational tendencies due to manufacturing irregularities and/or other material defects. The algorithm may be dynamically updated by self optimization to account for these changes in operation. Adding feedback, such as a power monitor, to the implementation previously described can provide further advantage for reducing the piezo pump power. In particular, variations in the piezo actuator due to manufacturing tolerances, aging, or applied voltage can be compensated by the algorithm of the micro-controller  420  that periodically adjusts the timing of the piezo actuator control waveforms to minimize the measured circuit power. 
         [0062]    An example of variation due to applied voltage is shown in  FIG. 8 . The power monitor, such as a sensor, may be implemented by measuring current into the piezo driver circuit, or by measuring other related parameters, such as a suitable voltage or temperature. Based on the feedback, the efficiency circuit  435  may adjust timing of the microcontroller  420  control signals to the switches to achieve greater operational efficiency and energy recovery. 
         [0063]    With reference to  FIG. 9 , and in accordance with an embodiment, a method for self-adjusting the timing of the control waveforms of the system to minimize power is illustrated. At the outset, the switch timing is formatted and initialized to established conditions ( 910 ). SwTime[N] is set to 0 ( 915 ). A measurement of the piezo driver input power is then taken ( 920 ). 
         [0064]    Next, a feedback loop is implemented to determine the minimum timing of switches  370 ,  375 ,  380 , and  385  by comparing the preset or previous timing and/or preset or previous measured piezo driver input power to the current measured timing and piezo driver input power ( 915 ,  920 ,  925 ,  930 ,  935 ,  940 ,  945 ,  950 ). For instance, the minimum pulse width of switches  370 ,  375 , the minimum on delays of the switch  385  and the minimum on delay of the positive terminal of the switch  380  are determined. Also, the minimum off delay of the negative terminal of switch  380  is determined. 
         [0065]    Again, a feedback loop is implemented to determine the maximum timing of the switches  380  and  385 . For instance, the maximum off delays of the switch  385  and the maximum off delay of the positive terminal of the switch  380  are determined. Also, the maximum on delay of the negative terminal of the switch  380  is determined ( 955 ,  960 ,  965 ,  970 ,  975 ,  980 ,  985 ). In response to the maximums and minimums of the switches  370 ,  375 ,  380 , and  385  being determined, the findings are applied and the switch timing in the microcontroller  420  is adjusted( 990 ). 
         [0066]    In one embodiment, a multi-piezo element pump may be implemented, such as a pump comprising multiple piezo elements within a single housing. For example, a 6 element piezo pump may be utilized in connection with a piezoelectric diaphragm and passive check valves to move fluid from a reservoir to a first pump chamber and then to a second pump chamber. A piezo actuator element mounted on a membrane may be deformed when voltage is applied. By the resulting downstroke associated with the deformation, the medium may be displaced out of the first pump chamber to a second pump chamber. When the voltage decreases, the corresponding deformation of the piezo element causes an upstroke of the membrane. This upstroke results in the first pump chamber being filled again. In some embodiments, check valves on both sides of the pump chamber may define the flow direction. In other embodiments, the elasticity of the system may cause the medium to flow in one direction while the pump is utilized to transfer medium in the opposite direction. 
         [0067]    Unless otherwise indicated, all numbers expressing quantities of ingredients, volumes of fluids, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. 
         [0068]    The terms “a,” “an,” “the” and similar referents used in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual 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 otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention. 
         [0069]    Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims. 
         [0070]    Certain embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than 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. 
         [0071]    Furthermore, certain references have been made to patents and printed publications throughout this specification. Each of the above-cited references and printed publications are individually incorporated herein by reference in their entirety. 
         [0072]    Specific embodiments disclosed herein may be further limited in the claims using consisting of or consisting essentially of language. When used in the claims, whether as filed or added per amendment, the transition term “consisting of” excludes any element, step, or ingredient not specified in the claims. The transition term “consisting essentially of” limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s). Embodiments of the invention so claimed are inherently or expressly described and enabled herein. 
         [0073]    In closing, it is to be understood that the embodiments of the invention disclosed herein are illustrative of the principles of the present invention. Other modifications that may be employed are within the scope of the invention. Thus, by way of example, but not of limitation, alternative configurations of the present invention may be utilized in accordance with the teachings herein. For instance, reference to a recovery inductor may be substituted with a recovery capacitor throughout. Accordingly, the present invention is not limited to that precisely as shown and described.