Abstract:
Acoustic Transfer Assist (ATA) systems are used in media printing devices to help transfer toner to paper by use of ultrasonic vibrations. The transducer is driven at its resonant frequency, though somewhat dampened. To shorten the decay time of the transducer when its vibration is not desired, a compensating signal is used. A reverse drive voltage is used during transducer shut-off. The reverse drive causes the transducer to vibrate at its normal resonant frequency, but at a 180° phase shift, causing the transducer to stop vibrating significantly faster than without a reverse drive. An open phase-locked loop system drives the transducer from resonance to rest. When the transducer stops vibrating, current to the reverse drive loop is cut off.

Description:
CROSS REFERENCE TO RELATED PATENTS AND APPLICATIONS 
   This application is an improvement of a device that employs an acoustic transfer system, such as the one described in U.S. Pat. No. 6,157,804 to Richmond, et al. 
   BACKGROUND 
   Acoustic Transfer Assist (ATA) devices are used to help transfer toner to paper through the use of ultrasonic vibrations. ATA is especially valuable when transferring toner to rough, embossed, or otherwise uneven papers. A piezoelectric transducer is driven at its resonant frequency, with appropriate damping. The transducer is a very high Q resonant electrical circuit driven at its resonant frequency. The factor “Q” is a measure of the rate at which a vibrating system dissipates its energy into heat. A higher Q indicates a lower rate of heat dissipation. The vibration in the transducer is electrically analogous to current in the resonant circuit, and like any very high Q circuit, the current rises and decays relatively slowly in reaction to application or removal of a drive signal. 
   At certain points in the printing process, it is desirable for the transducer to cease the vibrations to avoid print quality defects. For example, if the transducer is vibrating in certain areas, toner can be undesirably transferred to mechanical elements of the printer and then transferred to other images, resulting in errors in those images. Typically, to turn the transducer off, a drive signal is simply cut off from the transducer. This method of turn off is relatively slow. The transducer continues to vibrate for approximately 5 ms after the drive signal is cut off. This type of decay is typical with any oscillating mechanical system. The existing delay between signal shut-off and transducer inactivity can produce defects in current ATA systems. Because of this delay, the space between sheets of media needs to be extended so toner is not accidentally applied to areas where it should not be, ultimately effecting how many sheets of print media can be processed in any given time period. The time it takes for the transducer to decay ultimately effects the operating speed of the printer. For high speed ATA enabled machines, this decay time can represent a significant delay in job processing times. 
   INCORPORATION BY REFERENCE 
   U.S. Pat. No. 6,157,804 is hereby incorporated by reference in its entirety. 
   U.S. Pat. No. 6,205,315 is hereby incorporated by reference in its entirety. 
   U.S. Pat. No. 6,507,725 is hereby incorporated by reference in its entirety. 
   U.S. Pat. No. 6,579,405 is hereby incorporated by reference in its entirety. 
   BRIEF DESCRIPTION 
   In accordance with one aspect, a media output device is disclosed. The device includes a drive belt configured to propagate printable media along a print path, and a piezoelectric transducer for emitting ultrasonic vibrations that assist in adhering toner to the printable media. A transducer drive control circuit provides a drive signal to the transducer. The transducer drive control circuit includes an inverted drive portion that selectively inverts the drive signal to dampen vibrations of the transducer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a profile view of a media output device that employs an ATA system; 
       FIG. 2  is a circuit representation of a typical ATA drive circuit; 
       FIG. 3  shows a circuit representation of an ATA drive circuit that includes reverse resonance drive elements; and 
       FIG. 4  is a black box diagram of the circuit of  FIG. 3 . 
   

   DETAILED DESCRIPTION 
   With reference to  FIG. 1 , a typical xerographic device that employs an ATA system is depicted. A drive circuit  19 ′ causes a transducer  10  to vibrate at its normal resonant frequency, both with and without a 180° phase shift. This approach is effectively an open loop system based on a well behaved second order under damped system. The transducer  10  is used to assist in adhering toner to print media  12  as sheets of media pass by the transducer  10 . The transducer  10  produces ultrasonic vibrations in a direction perpendicular to a drive belt  14 . The vibrations of the transducer  10  are preferably about 62 kHz, but can be as much as 63.2 kHz, or more, or as low as 61 kHz, or less. This range of frequencies represents a typical range of resonant frequencies for transducers used in ATA devices, but it is to be understood that other frequency ranges are appropriate when using transducers with different resonant frequencies. A motorized drum  16  rotates the drive belt  14  that moves the print media by the transducer  10 . Control circuitry  19 ′ drives the transducer  10  and is described in more detail hereinbelow. Between each sheet of print media  12  is a patch of empty space in which a process control patch is developed after some delay following the training edge of the last prior sheet.  18 . The length of delay from the sheet trail edge to the process control patch  18  is dictated in part by a decay time of the transducer  10  after it has been activated. The longer it takes for the transducer  10  to become inactive, the longer the delay until the process control patch  18  has to be, so toner is not errantly applied to subsequent sheets of print media  12 . 
   With reference to  FIG. 2 , a circuit diagram portraying normal operation of a piezoelectric transducer driving circuit  19  is shown. A voltage phase detector  20  receives a voltage signal and a current signal and determines the phase between them. The voltage signal comes from a voltage comparator  22 , and the current signal comes from a current comparator  24 . The comparators  22 ,  24  are amplitude comparators whose outputs are digital signals with value of “1” when the input signal (current for comparator  24  and voltage for comparator  22 ) is greater than zero and “0” when the input signal is less than zero. Comparators  22  and  24  thus digitize the voltage into, and the current drawn by transducer  10 , respectively. The output from the phase detector  20  is a pulse-width modulated signal whose PWM duty cycle is proportional to the phase difference of the two inputs. In order to use the pulse-width modulated signal, it is first converted into an analog signal. A filter  26  takes the pulse-width modulated signal and outputs a phase dependent signal whose voltage is proportional to the detected phase. 
   From the filter  26 , the phase dependent signal is fed through a switch  46  into a voltage controlled oscillator  28 . The switch  46  is discussed in greater detail below. The frequency of the output of the voltage controlled oscillator  28  is dictated by the input voltage of the phase dependant signal. That is, the greater the input voltage, the higher the output frequency. So ultimately, the frequency of the signal output from the oscillator  28  is dependent on the phase detected by the phase detector  20 . 
   The signal from the oscillator  28  is then passed through a multiplication block  30 . The multiplication block  30  provides amplitude control for the driving signal output from the oscillator  28 . The desired, or control voltage  32  at which the transducer  10  will be driven is known, and the multiplication block  30 , working in conjunction with a power amplifier  34  either increases or decreases the voltage of the driving signal depending on how it compares to the desired driving (control) voltage  32 . The output signal from the amplifier  34  is applied via a standard buffering, filtering and rectifying feedback loop  36  to the multiplication block  30 . The feedback loop  36  includes its own multiplier  36   a  amplifiers  36   b  and a rectifier  36   c . In addition to being fed back to the multiplication block  30 , the drive signal from the amplifier  34  is also output to the transducer  10  to drive the vibrations of the transducer  10 . 
   The preferred transducer  10  includes a shunt capacitor  38  and a series resonant circuit  40  in parallel with the shunt capacitor  38 . It is to be understood that one skilled in the art will be aware of alternate working designs of the transducer  10 . The shunt capacitor  38  is tuned by a tuning inductor  42  in parallel with the shunt capacitor  38 . 
   A sweep generator  44  gradually sweeps the voltage of the input signal to find a point at which current becomes measurable. When current is detectable, the phase is close to the desired phase, and the switching circuitry  46  switches the input from the sweep generator  44  and hands control of the circuit over to the phase detector  20 . In other words, the sweep generator  44  narrows all possible frequencies to a narrow band of frequencies in which the resonant frequency of the transducer  10  is located. The circuit is then driven at the resonant frequency of the transducer  10  when toner is being applied to the print media  12 , and current does not flow through the circuit during times where no print media is present, such as between sheets, that is, over a process control patch  18 . In the above described situation, where the transducer  10  is allowed to naturally decay, the transducer  10  requires approximately 5 ms after the driving signal is shut off to become sufficiently inactive to the point where it will not help affix toner to a media surface. An inverted drive circuit reduces the time it takes for the transducer  10  to be dampened down to an inactive level. 
   Referring now to  FIG. 3 , an exemplary embodiment of a circuit  19 ′ showing an inverted drive circuit  50  is depicted. The circuit  19 ′, as depicted in  FIG. 3 , builds off of the circuit in  FIG. 2  by adding the inverted drive circuit  50  and supporting circuit elements that allow the inverted drive circuit to function. Generally, in periods where it is desirable to inactivate the transducer  10 , the inverted drive circuit  50  provides a signal that is 180° out of phase with the steady state driving signal. This dampens the transducer significantly faster than simply allowing it to decay naturally. The inverted drive circuit  50  includes an inverting amplifier  51 , and a drive switch  53 . The drive switch  53  includes an inversion side  53   a , and a steady state side  53   b . In accordance with concepts of the present application, a blanking signal  54  is applied to initiate the reverse drive of the inverted drive circuit  50 . 
   When the blanking signal  54  is applied to the circuit  19 ′, it activates the inversion side  53   a  of the drive switch  53 , which allows current to flow through the inverting amplifier  51 . The inverting amplifier  51  produces the drive signal that is 180° out of phase with the steady state operating signal. This inverted drive signal is applied to the transducer  10 , effecting a rapid decay of the transducer&#39;s oscillations. Once the transducer  10  has stopped oscillating, the inverted drive current is cut off. When the blanking signal  54  is not present, the steady state side  53   b  of the drive switch  53  is active, and current can flow normally to the power amplifier  34  and on to the transducer  10 . 
   With the addition of an exclusive OR (XOR) gate  52  between the voltage comparator  22  and the phase detector  20 , the circuit  19 ′ can be tricked into detecting a normal operating signal when the signal is actually 180° out of phase. One of the inputs of the XOR gate  52  is attached to the output of the voltage comparator  22 . The other input of the XOR gate  52  is attached to the blanking signal  54 . The input from the voltage comparator  22  is “on” when the circuit  19 ′ is operating. That is, there is a signal coming from the transducer drive portion of the circuit  19 ′, whether it is inverted or not. When the blanking signal  54  is applied, it activates the second input on the XOR gate  52 , which inverts the XOR gate&#39;s  52  output. Resultantly, the signal originating in the inverted drive circuit  50  voltage phase comparator  22  and ending at the output of the XOR gate  52  is doubly inverted, and the phase comparator  20  is fooled into thinking that drive signal is in phase the whole time. Beneficially, the circuit  19 ′ will continue to operate when a signal that is 180° out of phase with the resonant signal is applied to the transducer  10 . The 180° out of phase signal is triggered when the blanking signal  54  is introduced as an additional input signal. 
   If the inverted drive signal is allowed to persist, the transducer current (and thus vibration) will continue to go toward and then beyond zero. Since the object of this invention is to facilitate rapid decay to zero only of the transducer current the inverted signal must be cut-off from the transducer as it approaches the zero current state. When no measurable current is passing through the transducer  10  anymore, as measured across resistor  56 , circuit chain  58  detects the zero current and switches off the inverted current to the transducer  10 , resetting the circuit  19 ′ to normal operation. The circuit chain  58  includes a Zener diode  58   a , amplifiers  58   b , a rectifier  58   c , and an AND gate  58   d . The signal from the transducer  10  is fed into the circuit chain  58  and into the AND gate  58   d . The other input of the AND gate comes from the phase detector  20 . The signal from the circuit chain  58  is then fed into the switch  46 . With the addition of the inverted drive circuit  50  and supporting elements, the time of transducer  10  decay is reduced from approximately 5 ms to approximately 1 ms. 
   There are times when the drive circuit  19 ′ delivers no current to the transducer  10 . This is desirable, for example, when the output device is not in operation. More pertinent, however, the circuit  19 ′ does not supply the transducer  10  with any current in periods where there is no print media  12  present, for example, between sheets of media  12 , in a process control patch, or if the media sheet is currently being inverted in a duplex path, etc. Overall circuit  19 ′ operation is controlled by an AND gate  60 . The AND gate  60  must receive a signal at both of its inputs to activate the circuit  19 ′. One input of the AND gate  60  is attached to an enabling signal  62 . This enabling signal  62  is applied when a job commences, and is removed when the job is finished. In other words, the circuit  19 ′ is only active when a print job is proceeding, for instance, after a copy job has been programmed, and a user hits a start button. Regardless of the reason behind the enabling signal  62 , it is externally applied. 
   The AND gate  60  needs another signal, however, before it will activate the circuit  19 ′. The second signal comes from within the circuit  19 ′, that is, from an OR gate  64 . The OR gate  64  is active, and will provide the necessary signal to activate the AND gate  60  either when the blanking signal  54  is not asserted (indicating that normal operation of the circuit  19 ′ is desired) or when the circuit chain  58  is supplying a signal, indicating that there is measurable transducer  10  current. When there is measurable transducer  10  current, it is the case when the reverse drive is desired, that is, while the transducer  10  vibration is dying. If either of the blanking signal  54  or a signal from the circuit chain  58  is present, and the enabling signal  62  is present, the circuit will be in operation. Failing either or both of those conditions, the signal is run to ground  66 , and the circuit  19 ′ will not operate. 
   With reference now to  FIG. 4 , an overview of the circuit  19 ′ is provided. In the previous figures, an exemplary implementation has been described, but it is to be understood that the circuit  19 ′ can be described more generally. The circuit  19 ′ includes drive circuitry  70  that is capable of generating a transducer drive signal and an inverted drive signal. As previously discussed, the inverted drive signal is for producing vibrations in the transducer  10  at its resonant frequency that are 180° out of phase to actively dampen vibrations of the transducer  10 . 
   Generally, in order to enable the drive circuitry  70  to function as desired, the circuit  19 ′ has a double feedback loop architecture. The first feedback loop is a drive signal feedback loop  72  that involves feedback from the drive signal before it gets to the transducer  10 . The drive signal feedback loop  72  acts as quality control for the signals output by the drive circuitry  70 , ensuring that they stay within desired ranges. The second feedback loop includes a transducer activity detection feedback loop  74 . The transducer activity detection feedback loop  74 , working in concert with phase detection circuitry  76  and an inversion enabling signal  78  introduced from outside the circuit  19 ′, enables switching of the drive circuitry  70  from the drive signal to the inverted drive signal and back again. Switching circuitry  80  is used to process the inversion enabling signal  78  and the signals from the phase detection circuitry  76  and the transducer activity detection circuitry  74  to activate and deactivate the drive circuitry  70  as desired. 
   It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.