Abstract:
Representative embodiments provide for a controller for use with a capacitive mat, the controller configured to selectively electrically energize a first node of the capacitive mat in response to an input. The controller is further configured to wait for a first predetermined period of time, and to electrically energize a second node of the capacitive mat after the first predetermined period time. A method of the present invention provides for controlling a capacitive mat, the method including receiving an input, (and electrically energizing a first node of the capacitive mat at a first predetermined potential. The method also includes waiting for a first predetermined period of time, and electrically energizing a second node of the capacitive mat after the first predetermined period of time.) This repeats the scenario stated in lines  5 - 7 . The abstract only mentions one of the three methods.

Description:
BACKGROUND  
       [0001]     Various kinds of imaging apparatuses that are configured to form images on sheet media are known. Some such apparatuses form images on sheet media in correspondence to an electronic document file, commonly referred to as a print job. Other types of imaging apparatus perform their imaging function in response to optically scanning an image-bearing sheet media. Thus, examples of imaging apparatuses include laser printers, inkjet printers, thermal imaging devices, photocopiers, etc.  
         [0002]     Generally, such imaging apparatuses temporarily secure the sheet media in a registered relationship with an imaging engine (i.e., inkjet print head, etc.) during the image forming process so as to achieve the desired image placement on the media. One kind of device used to temporarily secure sheet media is the capacitive mat. Broadly speaking, capacitive mat devices typically include a number of electrically charged conductors, usually arranged as a grid or matrix within a layer of nonconductive material, to support a sheet of media in registered orientation by way of capacitive (i.e., electrostatic) attraction.  
         [0003]     One generally undesirable aspect of capacitive mats is the tendency for the layer of nonconductive material to develop a residual electrostatic charge (known as polarization) over the course of operative time. This polarization tends to reduce the efficiency or ‘holding power’ of the capacitive mat with respect to the supported sheet media. Such loss of holding power can lead to movement and/or mis-registration of the sheet media supported by the capacitive mat during operation, resulting in undesirable or unacceptable imaging quality or media jams thereon.  
         [0004]     Therefore, it is desirable to provide methods and apparatus for use with capacitive mats that address the polarization problems discussed above.  
       SUMMARY  
       [0005]     One embodiment of the present invention provides a sheet media support apparatus, including a capacitive mat including electrical first and second nodes. The capacitive mat is configured to electrically attractingly support a sheet media. The apparatus further includes a controller, which is coupled to the first and second nodes of the capacitive mat. The controller is configured to selectively electrically energize the first node at a first predetermined potential in response to an input, and to wait for a first predetermined period of time. The controller is also configured to electrically energize the second node at a second predetermined potential after the first predetermined period of time.  
         [0006]     Another embodiment of the present invention provides for a sheet media support apparatus, including a capacitive mat. The capacitive mat includes electrical first and second nodes, and is configured to electrically attractingly support a sheet media. The apparatus further includes a controller coupled to the first and second nodes of the capacitive mat. The controller is, in turn, configured to selectively electrically energize the first node at a time-increasing positive potential in response to an input, and to electrically energize the second node at a time-increasing negative potential contemporaneous with the energizing the first node.  
         [0007]     Still another embodiment of the present invention provides a sheet media support apparatus, including a capacitive mat including electrical first and second nodes. The capacitive mat is configured to electrically attractingly support a sheet media. The apparatus also includes a controller coupled to the first and second nodes of the capacitive mat. The controller is configured to selectively electrically energize the first node at a first predetermined positive potential, and to electrically energize the second node at a first predetermined negative potential in response to an input. The controller is further configured to wait for a first predetermined period of time, and to electrically energize the first node at a second predetermined positive potential and electrically energize the second node at a second predetermined negative potential after the first predetermined period of time.  
         [0008]     Yet another embodiment provides for a method of controlling a capacitive mat, the method including receiving an input, and electrically energizing a first node of the capacitive mat at a first predetermined potential. The method further includes waiting for a first predetermined period of time, and electrically energizing a second node of the capacitive mat after the first predetermined period of time.  
         [0009]     These and other aspects and embodiments will now be described in detail with reference to the accompanying drawings, wherein: 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a side elevation sectional view depicting a capacitive mat according to the prior art.  
         [0011]      FIG. 2  is a block diagram depicting an imaging apparatus in accordance with an embodiment of the present invention.  
         [0012]      FIG. 3  is a perspective view depicting a capacitive mat in accordance with another embodiment of the present invention.  
         [0013]      FIG. 4  is a perspective view depicting a capacitive mat in accordance with yet another embodiment of the present invention.  
         [0014]      FIG. 5  is a signal timing diagram in accordance with still another embodiment of the present invention.  
         [0015]      FIG. 6  is a signal timing diagram in accordance with another embodiment of the present invention.  
         [0016]      FIG. 7  is a signal timing diagram in accordance with yet another embodiment of the present invention.  
         [0017]      FIG. 8  is a flowchart depicting a method in accordance with still another embodiment of the present invention.  
         [0018]      FIG. 9  is a flowchart depicting a method in accordance with another embodiment of the present invention.  
         [0019]      FIG. 10  is a flowchart depicting a method in accordance with yet another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0020]     In representative embodiments, the present teachings provide methods and apparatus for controlling a capacitive mat suitable for the registered support of a sheet media, typically within an imaging apparatus. In general, such methods of the present invention utilize any number of suitable sequences or signal patterns for energizing a capacitive mat and typically include such characteristics as one or more step changes in electrical potential, linear and/or non-linear ramping of (i.e., time-varying) electrical potential, or any suitable combination of these or other electrical energization characteristics. Such methods and apparatus of the present invention provide for the substantial elimination of the polarization problems described above.  
         [0021]     Turning now to  FIG. 1 , a side elevation sectional view depicts a capacitive mat  50  according to the prior art. The capacitive mat  50  includes a non-conductive base material (i.e., substrate)  52 . As depicted in  FIG. 1 , the substrate  52  supports a plurality of generally positive conductors  54  and a plurality of generally negative conductors  56 . The positive conductors  54  and the negative conductors  56  are assumed to extend away from the viewer, and are alternately arranged so as to generally define an inter-digitated, conductive grid or matrix on the substrate  52 . The pluralities of conductors  54  and  56  are electrically coupled to respective positive and negative electrical connections on a grid control circuit  58 .  
         [0022]     The capacitive mat  50  further includes a non-conductive (i.e., dielectric) cover material  60  that overlies and substantially encapsulates the pluralities of conductors  54  and  56  in generally fixed relationship with one another, the substrate  52 , and the cover material  60 . In this way, the positive conductors  54  and the negative conductors  56  are substantially isolated against contact with entities outside of the capacitive mat  50  (with the exception of electrical coupling to the grid control circuit  58 ). Further depicted in  FIG. 1  is a sheet of media  62 , which is generally supported on a surface  64  defined by the cover material  60 .  
         [0023]     Typical operation of the capacitive mat  50  is as follows: to begin, it is assumed that the sheet of media  62  is deposited (i.e., delivered) in resting support on the surface  64  of the capacitive mat  64  by way of a suitable delivery mechanism (not shown). The grid control circuit  58  then electrically energizes the positive conductors  54  and the negative conductors  56  such that a generally constant, predetermined electrical potential exists between these two respective pluralities.  
         [0024]     The electric field corresponding to the energized pluralities of conductors  54  and  56  causes a corresponding migration of electrical charge within the sheet media  62 , such that regions of positive charge  66  generally accumulate within the sheet media  62  over each of the negative electrodes  56 , while regions of negative charge  68  generally accumulate over each of the positive electrodes  54 . As a result, a capacitive (electrostatic) hold-down or ‘tacking’ force is exerted on the sheet media  62 , which serves to support the sheet media  62  in a substantially registered orientation with respect to the capacitive mat  50  and/or other entities (not shown).  
         [0025]     Eventually, the need to hold-down or register the sheet media  62  with the respect to the capacitive mat  50  ends. At such time, the grid control circuit  58  de-energizes the positive conductors  54  and the negative conductors  56 , resulting in the substantial release of the sheet media  62 .  
         [0026]     Over the course of time, the capacitive mat  50 , electrostatic charges (not shown) tend to accumulate within the dielectric cover material  60 . This charge accumulation within the cover material  60  is referred to as polarization. These polarization charges (not shown) generally mimic those that are induced within the sheet media  62  and are opposite the charges of the conductors  54  and  56  during operation.  
         [0027]     The polarization charges tend to oppose the accumulation of the charges  66  and  68 , thus resulting in a general decreasing of the tacking or hold-down force exerted on the sheet media  62  by the capacitive mat  50 . If the magnitude of the polarization becomes too severe, the hold-down force can become insufficient to maintain proper registration of the sheet media  62  during imaging or other associated operations. Undesirable degradation in imaging quality, media jams, or media crashing into the pens can, in turn, result.  
         [0028]     Methods and apparatus of the present invention, described hereafter, address this problem.  
         [0029]      FIG. 2  is a block diagram depicting an imaging apparatus  100  in accordance with an embodiment of the present invention. The imaging apparatus  100  includes an imaging apparatus controller (hereafter, controller)  102 . The controller  102  can typically include any controller suitable for controlling typical normal operation of the imaging apparatus  100 . As such, the controller  102  can include, for example: a microprocessor or microcontroller; a solid-state memory or other computer-accessible storage media; a state machine; digital, analog, and/or hybrid electronic circuitry; sensing instrumentation; etc. One of skill in the electronic control arts can appreciate that various embodiments of the controller  102  can be used in correspondence with differing embodiments of the imaging apparatus  100  and that further elaboration is not required for an understanding of the present invention.  
         [0030]     The imaging apparatus  100  also includes an imaging engine  104 . The imaging engine  104  is generally coupled in controlled relationship with the controller  102 . The imaging engine  104  can be defined by any such imaging engine suitable for selectively forming images on sheet media “S” (described in detail hereafter) under the control of the controller  102 . For example, the controller  104  can include an inkjet imaging engine, etc. Other suitable embodiments of the imaging engine  104  can also be used.  
         [0031]     The imaging apparatus  100  also includes a capacitive mat  106 . The capacitive mat  106  can be generally defined by any capacitive mat suitable for use with the present invention. The capacitive mat  106  is generally configured to controllably support a sheet media S in registered orientation with the imaging engine  104  (or other suitable elements of the imaging apparatus  100 , not shown) during normal operation. The capacitive mat  106  is configured to provide such registered support of the sheet media S by way of electrical (i.e., capacitive, or electrostatic) attraction under the control of a mat controller  108  (described hereafter). Further elaboration of the capacitive mat  106  is provided hereafter.  
         [0032]     The imaging apparatus  100  further includes the mat controller  108  of the present invention introduced above. The mat controller  108  can include any electronic circuitry suitable for electrically coupling the capacitive mat  106  to a source or sources of electrical energy (not shown) under the control signal influence of the controller  102  and in accordance with the methods of the present invention. Thus, the mat controller  108  can include, for example: digital, analog and/or hybrid electronic circuitry; signal amplifying circuitry; electrical switching devices; a microprocessor or microcontroller; etc.; or any combination of these or other suitable circuit elements. It can be appreciated by one of skill in the electrical arts that varying embodiments of the mat controller  108  can be used in accordance with the present invention, and that more particular elaboration is not required for purposes herein. It will also be appreciated that the mat controller  108  can be provided by components within the imaging apparatus controller  102 , described above.  
         [0033]     It is to be understood that the imaging apparatus  100  also typically includes other elements and devices not specifically shown in  FIG. 2 . Such other elements can include, for example: an electrical energy source or sources; an operator interface; input/output circuitry; optical scanning devices; sheet media transport and routing mechanisms; etc. These and other elements and devices can be selectively included in varying embodiments of the imaging apparatus  100  as required or desired for typical respective operation thereof.  
         [0034]     Normal operation of the imaging apparatus  100  is generally as follows: the controller  102 , in response to receiving an electronic document file (not shown), causes sheet media S to be drawn from an input tray  110  and routed to the capacitive mat  106 . The controller  102  then causes the mat controller  108  to energize (i.e., electrically couple an energy source or sources to) the capacitive mat  106  in accordance with the methods of the present invention. Energizing of the capacitive mat  106  by way of the mat controller  108  generally results in the capacitive (i.e., electrostatic) attraction of the sheet media S into supported registration with the imaging engine  104 . This capacitive attraction is generally referred to as hold-down or tacking force.  
         [0035]     The controller  102  then causes the imaging engine  104  to selectively form images on the registered, supported sheet media S in accordance with the electronic document file. The controller  102  thereafter causes the mat controller  108  to de-energize the capacitive mat  106 , effectively halting the capacitive attraction between the imaged sheet media S and the capacitive mat  106 . The controller  102  then causes the imaged sheet media S to be suitably transported generally out of the imaging apparatus  100 .  
         [0036]     The process described above is typically repeated, one sheet of media S at a time, until the electronic document file has been completely imaged on the sheet media S. The imaged sheet or sheets of media generally define an imaged document  112 .  
         [0037]     Because the capacitive mat  106  is controlled in accordance with the methods of the present invention (described in detail hereafter), the polarization effect described above in regard to the capacitive mat  50  of  FIG. 1  is substantially negated. Thus, the capacitive mat  106 , under the influence of the mat controller  108 , exerts a substantially controllable, non-degrading hold-down (tacking) force upon sheets of media S over the course of its useful life.  
         [0038]      FIG. 3  is a perspective view depicting a capacitive mat  206  in accordance with another embodiment of the present invention. The capacitive mat  206  can be used as the capacitive mat  106  of  FIG. 2 . The capacitive mat  206  includes a non-conductive (i.e., dielectric) substrate  220 . The substrate  220  can be formed from any suitable dielectric material, such as, for example, plastic, glass, silicon dioxide, etc. Other materials can also be used to form the substrate  220 .  
         [0039]     The capacitive mat  206  also includes a plurality of positive conductors  222 , and a plurality of negative conductors  224 . Each of the positive conductors  222  and the negative conductors  224  can be formed from any suitable electrically conductive material. Non-limiting examples of such electrically conductive material include copper, silver, conductively doped semiconductor, etc. Other suitable electrically conductive materials can also be used.  
         [0040]     As depicted in  FIG. 3 , the positive conductors  222  are arranged in alternating, spaced, parallel placement with the negative conductors  224 , such that a grid or matrix is defined and supported by the substrate  220 . Each of the plurality of positive conductors  222  is electrically coupled to one another so as to define a single positive node  230 . Similarly, each of the plurality of negative conductors  224  is electrically coupled to one another to define a single negative node  232 . Each of the positive conductors  222  and the negative conductors  224  extends substantially across a widthwise dimension “W” of the capacitive mat  206 . Furthermore, the particular count of positive conductors  222  and negative conductors  224  can vary selectively as desired in correspondence with different embodiments (not shown) of the capacitive mat  206 .  
         [0041]     The capacitive mat  206  further includes a dielectric cover material  226 . The dielectric cover material can be formed from any suitable electrically non-conductive material such as, for example, plastic, glass, silicon dioxide, etc. Other suitable materials can also be used to form the cover material  226 . The cover material  226  is configured to cooperate with the substrate  220  such that the positive conductors  222  and the negative conductors  224  are substantially encapsulated and isolated against physical contact with entities outside of the capacitive mat  206 . The cover material  226  is further configured to define a substantially planar support surface  228 .  
         [0042]     Further depicted in  FIG. 3  is a mat controller  208 . The mat controller  208  is electrically coupled to the positive node  230  and the negative node  232  of the capacitive mat  206 . The mat controller  208  can be defined by suitable mat controller in accordance with the present invention such as, for example, the mat controller  108  of  FIG. 2 . Thus, the mat controller  208  is generally configured to selectively energize the positive node  230  and the negative node  232  of the capacitive mat  206  in response to an appropriate input or signal, typically from an imaging apparatus controller (not shown, see the controller  102  of  FIG. 2 ), in accordance with the methods of the present invention.  
         [0043]     Typical operation of the capacitive mat  206  is generally as described above in regard to the capacitive mat  106  of  FIG. 2 . In this way, the capacitive mat  206  is generally configured to controllably exert an electrostatic hold-down force on a sheet of media (not shown) so as to maintain such a sheet of media in supportive registration during imaging operations within an imaging apparatus (not shown, see the imaging apparatus  100  of  FIG. 2 .).  
         [0044]      FIG. 4  is perspective view depicting a capacitive mat  306  in accordance with yet another embodiment of the present invention. The capacitive mat  306  includes a dielectric core or substrate  320 . The substrate  320  can be formed from any suitable non-conductive material such as, for example, plastic, glass, silicon dioxide, etc. Other materials suitable for forming substrate  320  can also be used. As depicted in  FIG. 4 , the substrate  320  substantially defines a hollow cylinder. Other suitable geometries can also be used.  
         [0045]     The capacitive mat  306  also includes a plurality of positive conductors  322 , and a plurality of negative conductors  324 . Each of the positive conductors  322  and the negative conductors  324  can be formed from any suitable electrically conductive material. Non-limiting examples of such electrically conductive material include copper, silver, conductively doped semiconductor, etc. Other suitable electrically conductive materials can also be used.  
         [0046]     As shown in  FIG. 4 , the positive conductors  322  are arranged in alternating, spaced, parallel placement with the negative conductors  324 , such that a grid or matrix is defined and supported by an outer surface of the generally cylindrical substrate  320 . In this way, substantially one-half of the substrate  320  outer surface area is utilized to support the positive conductors  322  and the negative conductors  324 . In another embodiment (not shown), a greater or lesser fraction of the substrate  320  outer surface area can be used to support conductors  322  and  324 . In such an embodiment (not shown), the count of positive conductors  322  and negative conductors  324  can also vary selectively.  
         [0047]     In any case, each of the plurality of positive conductors  322  is electrically coupled to one another so as to define a single positive node  330 . Similarly, each of the plurality of negative conductors  324  is electrically coupled to one another to define a single negative node  332 . Each of the positive conductors  322  and the negative conductors  324  extends substantially across a lengthwise dimension “L” of the capacitive mat  306 .  
         [0048]     The capacitive mat  306  further includes a dielectric cover material  326 . The dielectric cover material can be formed from any suitable electrically non-conductive material such as, for example, plastic, glass, silicon dioxide, etc. Other suitable materials can also be used to form the cover material  326 . The cover material  326  is configured to cooperate with the substrate  320  such that the positive conductors  322  and the negative conductors  324  are substantially encapsulated and isolated against physical contact with entities other than the capacitive mat  306 . The cover material  326  is further configured to define a substantially flat, smooth, generally cylindrical support surface  328 , in accordance with the geometry of the substrate (i.e., core)  320 .  
         [0049]     Further depicted in  FIG. 4  is a mat controller  308 . The mat controller  308  is electrically coupled to the positive node  330  and the negative node  332  of the capacitive mat  306 . The mat controller  308  can be defined by suitable mat controller in accordance with the present invention such as, for example, the mat controller  108  of  FIG. 2 . Thus, the mat controller  308  is generally configured to selectively energize the positive node  330  and the negative node  332  of the capacitive mat  206  in response to an appropriate input or signal, typically from an imaging apparatus controller (not shown, see the controller  102  of  FIG. 2 ), in accordance with the methods of the present invention.  
         [0050]     Typical operation of the capacitive mat  306  is substantially as described above in regard to the capacitive mat  106  of  FIG. 2 . However, in contrast to the substantially planar geometry of the capacitive mat  206  of  FIG. 3 , the capacitive mat  306  electrostatically supports a sheet media (not shown) on the support surface  328  in a correspondingly arced or curved registration thereon. This arced registration of the supported sheet media (not shown) is generally desirable in some usage environments such as, for example, during the deposition of imaging media (not shown) onto the supported sheet media within a inkjet printer type of imaging apparatus (not shown, see the imaging apparatus  100  of  FIG. 2 ). Other usage environments call for corresponding embodiments of capacitive mat (not shown) that include support surface geometries conducive to the particular environment.  
         [0051]      FIG. 5  is a signal timing diagram (hereafter, timing diagram)  400  in accordance with still another embodiment of the present invention. The timing diagram  400  depicts energization signals (described hereafter) for controllably operating a capacitive mat, such as, for example, the capacitive mats  106 ,  206  and  306  of respective  FIGS. 2, 3  and  4 , in accordance with the present invention. The energization signals of the timing diagram  400  are typically provided (i.e., generated or coupled) to a capacitive mat of the present invention by way of a mat controller of the present invention such as, for example, the mat controllers  108 ,  208  and  308  of respective  FIGS. 2, 3  and  4 .  
         [0052]     The timing diagram  400  includes a ground reference potential line  402 . The ground reference potential  402  is any suitable electrical potential or datum from which other relevant signals of the timing diagram  400  are referenced. For purposes herein, the ground reference potential  402  is considered a zero energy level or electrically de-energized state.  
         [0053]     The timing diagram  400  also includes an electrical positive node signal  404 . The positive node signal  404  is typically coupled to a positive node of a capacitive mat (e.g., positive node  230  of  FIG. 3 ) of the present invention. The timing diagram  400  further includes an electrical negative node signal  406 . The negative node signal  406  is typically coupled to a negative node of a capacitive mat (e.g., negative node  232  of  FIG. 3 ) of the present invention.  
         [0054]     Normal operation under the timing diagram  400  is as follows: the positive node signal  404  is electrically energized from ground reference potential  402  to a predetermined positive potential  408  at a time “T0”. The positive node signal  404  is substantially maintained at this positive potential  408  for a first predetermined period of time “P1”—that is, the period of time P1 can be considered as a wait or “dwell” period.  
         [0055]     Thereafter, at a time “T1”, the negative node signal  406  is electrically energized from ground reference potential  402  to a predetermined negative potential  410 . The positive node potential  404  and the negative node potential  410  are then respectively maintained during a second predetermined wait or dwell period of time “P2”.  
         [0056]     Thereafter, at a time “T2”, both the positive node signal  404  and the negative node signal  406  are substantially simultaneously electrically de-energized, typically by coupling both respective signals  404  and  406  to ground reference potential  402 . At this point, one energization cycle or iteration of the timing diagram  400  is considered complete.  
         [0057]     The timing diagram  400  provides one method of energizing a capacitive mat (i.e., capacitive mats  106 ,  206 ,  306  of respective  FIGS. 2, 3  and  4 ) in accordance with the present invention. In this way, the shifts in energization of the positive node signal  404  and negative node signal  406  that occur at times T0, T1 and T2, respectively, tend to permit an increase of the charge levels occurring on the capacitive mat, with a corresponding increased (i.e., generally sufficient) hold down force, even when some degree of polarization occurs.  
         [0058]      FIG. 6  is a signal timing diagram (hereafter, timing diagram)  500  in accordance with another embodiment of the present invention. The timing diagram  500  includes a ground reference potential line  502 , substantially as described above in regard to the ground reference potential line  402  of  FIG. 5 . Thus, the ground reference potential line  502  is considered a zero-energy reference level or datum within the context of the timing diagram  500 .  
         [0059]     The timing diagram  500  also includes an electrical positive node signal  504 . The positive node signal  504  is generally coupled to a positive node of a capacitive mat (e.g., positive node  230  of  FIG. 3 ) of the present invention. The timing diagram  500  also includes an electrical negative node signal  506 . The negative node signal  506  is typically coupled to a negative node of a capacitive mat (e.g., negative node  232  of  FIG. 3 ) of the present invention.  
         [0060]     Normal operation under the timing diagram  500  is as follows: the positive node signal  504  and the negative node signal  506  are substantially simultaneously electrically energized to predetermined initial positive and negative potentials  512  and  514 , respectively, at time “T0′”.  
         [0061]     Thereafter, the positive node signal  506  assumes a substantially linear, time-increasing positive potential  508  for a predetermined time period “P1′”. Also, the negative node signal  506  assumes a substantially linear, time-increasing negative potential  510  for the predetermined time period P1′. Thus, the respective electrical potentials of the positive node signal  504  and the negative node signal  506  are time-changing in a generally contemporaneous, mirror-image fashion with respect to the ground reference potential line  502 .  
         [0062]     Then, at a time “T1′”, both the positive node signal  504  and the negative node signal  506  are substantially simultaneously electrically de-energized. Generally, this can be accomplished by coupling both respective signals  504  and  506  to ground reference potential  502 . At this point, a single iteration of the timing diagram  500  is considered complete.  
         [0063]     The timing diagram  500  provides a method of energizing a capacitive mat (i.e., the capacitive mats  106 ,  206 ,  306  of respective  FIGS. 2, 3  and  4 ) in accordance with another embodiment of the present invention. The respective time-increasing electrical potentials of the positive node signal  504  and negative node signal  506  tend to substantially reduce the undesirable effects of polarization as described above. That is, generally sufficient hold down force results in accordance with the method as depicted by the timing diagram  500 .  
         [0064]      FIG. 7  is a signal timing diagram (hereafter, timing diagram)  600  in accordance with yet another embodiment of the present invention. The timing diagram  600  includes a ground reference potential line  602  substantially as described above in regard to the ground reference potential line  402  of  FIG. 5 .  
         [0065]     The timing diagram  600  also includes an electrical positive node signal  604 . The positive node signal  604  is typically coupled to a positive node of a capacitive mat (e.g., positive node  230  of  FIG. 3 ) of the present invention. The timing diagram  600  also includes an electrical negative node signal  606 . The negative node signal  606  is typically coupled to a negative node of a capacitive mat (e.g., negative node  232  of  FIG. 3 ) of the present invention.  
         [0066]     Normal operation under the timing diagram  600  is as follows: at an initial time “T0″”, the positive node signal  604  is electrically energized to a first predetermined positive potential  608 . Contemporaneously, the negative node signal  606  is electrically energized to a first predetermined negative potential  610 . Both the first predetermined positive potential  608  and the second predetermined negative potential  610  are maintained at substantially constant respective levels during a first predetermined time period (i.e., wait, or dwell period) “P1″”.  
         [0067]     Thereafter, at a time “T1″”, the positive node signal  604  is electrically energized (i.e., elevated) to a second predetermined positive potential  612 , and the negative node signal  606  is electrically energized to a second predetermined negative potential  614 . The second predetermined potentials  612  and  614  are respectively maintained during a second predetermined time period “P2″”.  
         [0068]     Then, at a later time “T2″”, both the positive node signal  604  and the negative node signal  606  are substantially simultaneously de-energized. Such de-energization is typically accomplished by coupling both the positive node signal  604  and the negative node signal  606  to ground reference potential  602 . At such a time, a single instance or iteration of the timing diagram  600  is considered complete.  
         [0069]     The timing diagram  600  provides a method of energizing a capacitive mat (i.e., capacitive mats  106 ,  206 ,  306  of respective  FIGS. 2, 3  and  4 ) in accordance with yet another embodiment of the present invention. The respective changes in the electrical potential of the positive node signal  604  and negative node signal  606  at times T0″, T1″ and T2″ serve to substantially mitigate the undesirable effects of any polarization which may occur within the dielectric cover material (such as, for example, the dielectric cover material  226  of  FIG. 3 ) of the particular capacitive mat controlled under the energization signal method described by the timing diagram  600 .  
         [0070]     Each of the timing diagrams  400 ,  500  and  600  described above provides (i.e., depicts) an energization signal method or format of the present invention for use with a capacitive mat (such as the capacitive mats  106 ,  206 ,  306  of respective  FIGS. 2, 3  and  4 ). Furthermore, each of the energization signal methods described in the timing diagrams  400 ,  500  and  600  can be implemented by way of a suitable embodiment of mat controller of the present invention, such as the mat controllers  108 ,  208 ,  308  of respective  FIGS. 2, 3  and  4 .  
         [0071]     In this way, the present invention provides a number of suitable control method (i.e., energization signal) embodiments for use in the registration and support of sheet media on a capacitive mat. It is to be understood that other embodiments of the present invention that correspond to other signal timing diagrams (not shown) for use with capacitive mats are also possible within the scope of the present invention.  
         [0072]     Such other embodiments of the present invention can include any suitable combination of the capacitive mat energization characteristics described above in regard to those of the timing diagrams  400 ,  500  and  600 , including, for example, step changes and/or time variations in electrical potential. Some of the embodiments of the present invention are further described in the context of sequential methodologies hereafter.  
         [0073]      FIG. 8  is a flowchart depicting a method  700  of controlling a capacitive mat in accordance with still another embodiment of the present invention. For clarity, the method  700  is described with reference to the imaging apparatus  100  of  FIG. 2  and the capacitive mat  206  of  FIG. 3 . It is to be understood, however, that the method  700  can be suitably used in conjunction with other embodiments of the present invention.  
         [0074]     In step  702  ( FIG. 8 ), it is assumed that a sheet of media S ( FIG. 2 ) is brought into resting support on the capacitive mat  106 .  
         [0075]     In step  704  ( FIG. 8 ), the mat controller  108  ( FIG. 2 ) receives a hold-down (or tacking) signal from the imaging apparatus controller  102 .  
         [0076]     In step  706  ( FIG. 8 ), the mat controller  108  ( FIG. 2 ) responds to the hold-down signal and energizes the first node  222  ( FIG. 3 ) of the capacitive mat  106  ( FIG. 2 ) at a predetermined positive potential or level.  
         [0077]     In step  708  ( FIG. 8 ), the mat controller  108  ( FIG. 2 ) continues to energize the first node  222  ( FIG. 3 ) as established in step  706  ( FIG. 8 ) above during a first wait or dwell period.  
         [0078]     In step  710  ( FIG. 8 ), the mat controller  108  ( FIG. 2 ) energizes a second node  224  ( FIG. 3 ) of the capacitive mat  106  ( FIG. 2 ) at a predetermined negative potential.  
         [0079]     In step  712  ( FIG. 8 ), the mat controller  108  ( FIG. 2 ) continues to energize both the first node  222  ( FIG. 3 ) and the second node  224  as established in steps  706  ( FIG. 8 ) and  710  above during a second predetermined wait period.  
         [0080]     In step  714  ( FIG. 8 ), the mat controller  108  ( FIG. 2 ) de-energizes both the first node  222  ( FIG. 3 ) and the second node  224  of the capacitive mat  106  ( FIG. 2 ). Typically, this is done by coupling the nodes  222  ( FIG. 3 ) and  224  to a ground reference potential. In any case, the method  700  is now considered complete.  
         [0081]      FIG. 9  is a flowchart depicting a method  800  of controlling a capacitive mat in accordance with still another embodiment of the present invention. In the interest of clarity, the method  800  is also described with reference to the imaging apparatus  100  of  FIG. 2  and the capacitive mat  206  of  FIG. 3 . It is to be understood, however, that the method  800  can be suitably used in conjunction with other embodiments of the present invention.  
         [0082]     In step  802  ( FIG. 9 ), a sheet of media S ( FIG. 2 ) is assumed to be brought into resting support with the capacitive mat  106 .  
         [0083]     In step  804  ( FIG. 9 ), the mat controller  108  ( FIG. 2 ) receives a hold-down signal from the imaging apparatus controller  102 .  
         [0084]     In step  806  ( FIG. 9 ), the mat controller  108  ( FIG. 2 ) responds to the hold-down signal by simultaneously energizing the first node  222  ( FIG. 3 ) and the second node  224  of the capacitive mat  106  ( FIG. 2 ) with respective first predetermined electrical potentials, with the first node  222  ( FIG. 3 ) potential being positive relative to that of the second node  224 . Immediately thereafter, the mat controller  108  ( FIG. 2 ) applies a time-increasing potential difference to the nodes  222  ( FIG. 3 ) and  224 . This application of time-increasing potential difference is continued by the mat controller  108  ( FIG. 2 ) for a predetermined period of time.  
         [0085]     In step  808  ( FIG. 9 ), the mat controller  108  ( FIG. 2 .) de-energizes both the first node  222  ( FIG. 3 ) and the second node  224  of the capacitive mat  106  ( FIG. 2 ). Generally, this is accomplished by coupling the nodes  222  ( FIG. 3 ) and  224  to a ground reference potential. The method  800  is now complete.  
         [0086]      FIG. 10  is a flowchart depicting a method  900  in accordance with yet another embodiment of the present invention. While the method  900  is described with reference to the imaging apparatus  100  of  FIG. 2  and the capacitive mat  206  of  FIG. 3 , it is to be understood that the method  900  can be suitably used in conjunction with other embodiments of the present invention.  
         [0087]     In step  902  ( FIG. 10 ), a sheet of media S ( FIG. 2 ) is brought into resting support on the capacitive mat  106 .  
         [0088]     In step  904  ( FIG. 10 ), the mat controller  108  ( FIG. 2 ) receives a hold-down signal from the imaging apparatus controller  102 .  
         [0089]     In step  906  ( FIG. 10 ), the mat controller  108  ( FIG. 2 ) responds to the hold-down signal by simultaneously energizing the first node  222  ( FIG. 3 ) and the second node  224  of the capacitive mat  106  ( FIG. 2 ) with respective first predetermined electrical potentials, with the first node  222  ( FIG. 3 ) potential being positive relative to that of the second node  224 .  
         [0090]     In step  908  ( FIG. 10 ), the mat controller  108  ( FIG. 2 ) waits for a first predetermined period of time. During this time the respective energization levels of the first node  222  ( FIG. 3 ) and the second node  224  are substantially maintained as established in step  906  ( FIG. 10 ) above.  
         [0091]     In step  910  ( FIG. 10 ), the mat controller  108  ( FIG. 2 ) simultaneously changes the energization of the first node  222  ( FIG. 3 ) and the second node  224  to second respective predetermined potential levels. In this way, the electrical potential between the first node  222  and the second node  224  is typically increased relative to that established in step  906  ( FIG. 10 ) above.  
         [0092]     In step  912  ( FIG. 10 ), the mat controller  108  ( FIG. 2 ) waits for a second predetermined period of time. During this time the respective energization levels of the first node  222  ( FIG. 3 ) and the second node  224  are maintained substantially as established in step  910  ( FIG. 10 ) above.  
         [0093]     In step  914  ( FIG. 10 ), the mat controller  108  ( FIG. 2 .) de-energizes both the first node  222  ( FIG. 3 ) and the second node  224  of the capacitive mat  106  ( FIG. 2 ). This is usually accomplished by coupling the nodes  222  ( FIG. 3 ) and  224  to a ground reference potential. The method  900  is now considered to be complete.  
         [0094]     While the methods  700 ,  800  and  900  of  FIGS. 8-10  above respectively describe particular method steps and order of execution, it is to be understood that other methods (not shown) consistent with other embodiments of the present invention can also be used. Other such methods (not shown) can include suitable combinations of these or other steps performed in correspondingly suitable orders of execution.  
         [0095]     Thus, the present invention provides a number of methods and apparatuses that are directed to substantially reducing polarization (i.e., electric charge accumulation) within the dielectric cover material of the capacitive mat thus controlled. In this way, the methods and apparatuses of the present invention provide for the ongoing controlled operation of capacitive mats in a manner that is generally free from a loss of hold-down or tacking force with respect to the supported sheet media.  
         [0096]     While the above methods and apparatus have been described in language more or less specific as to structural and methodical features, it is to be understood, however, that they are not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The methods and apparatus are, therefore, claimed in any of their forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.