Abstract:
FIG.  1  depicts a full view of the picnic table backrest. It shows the backrest, the bars that wrap around the bench to keep the back rest stable and the latch on the back of the rest that keeps the rest from slipping out. FIG.  2  shows a close up view of the latch on the rear of the backrest. The bar that holds the latch swivels upward to latch on to the top part of the backrest. This keeps the backrest from slipping out and also holds it in place so it doesn&#39;t shift while your sitting.

Description:
[0001]     This application is a Continuation-in-Part of application Ser. No. 10/919,579, filed on Aug. 17, 2004, now pending, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to tube apparatus such as tube sealers. More specifically, this invention relates to a method and apparatus for closing or severing a tube using a controllable force.  
       BACKGROUND OF THE INVENTION  
       [0003]     In a wide variety of applications and industries, there is a need to seal, connect, weld or otherwise manipulate tubes. For example, there is often a need to create a seal at a location along the length of a tube or a portion thereof. Such a seal may be desired to prevent or substantially reduce the flow of gaseous or liquid fluid between adjacent portions of a tube.  
         [0004]     One example of an application in which a tube may be desired to be sealed is the sealing of tubes that contain blood or other bodily fluids. For example, blood may be drawn from a donor from flexible tubing that extends into a plastic blood collection bag. Once the bag is filled to its capacity, it may be desired to seal the tubing in order to prevent leakage and/or contamination or deterioration of the collected blood. After such collection, the blood may need to be typed and/or tested under various criteria. In order to provide a representative supply of blood for such typing and test purposes, a plurality of segments of the tubing may be sealed from one another to provide multiple sealed samples. Such samples may later be separately opened for typing and/or testing purposes.  
         [0005]     The foregoing comments apply not only to dielectric tube sealers but also to any apparatus configured to connect, weld, or otherwise manipulate tubes using radio frequency, heat, mechanical elements, or any other known means for manipulating tubes.  
       SUMMARY OF THE INVENTION  
       [0006]     According to one aspect, this invention provides a tube apparatus configured to perform a tube operation on a tube portion. An exemplary embodiment of such a tube apparatus may include tube-contacting surfaces spaced from one another to receive the tube portion, at least one of the tube-contacting surfaces being movable with respect to another one of said tube-contacting surfaces to compress the tube portion, means for moving said at least one movable tube-contacting surface, and means for controlling a duty cycle of the moving means according to a compression profile of the moving means.  
         [0007]     According to another aspect, this invention provides a tube sealer to control a size of a seal formed in a tube portion. One exemplary embodiment of such a tube sealer may include a plurality of jaws mounted for movement with respect to each other, at least one of the jaws being coupled to an energy source to heat the tube portion, a solenoid coupled to a respective one of the jaws to move the respective one of the jaws to compress the tube portion, and a microprocessor configured to control the energy source and the solenoid, the microprocessor being programmable to select one or more periods during which heating of the tube portion is performed by the energy source and to select one or more compression periods, successive compression periods having a different duty cycle to supply power to the solenoid to adjust a compression action of the solenoid, thereby controlling the size of the seal formed in the tube portion.  
         [0008]     According to yet another aspect, this invention includes a method of controlling a tube apparatus configured to seal, weld or sever a tube portion, the tube apparatus including tube-contacting surfaces spaced from one another to receive the tube portion, at least one of said tube-contacting surfaces being movable with respect to another one of said tube-contacting surfaces to compress the tube portion, and an actuator coupled to said at least one movable tube-contacting surface. An exemplary method according to this aspect of the embodiment of the invention may include the steps of controlling a duty cycle of an actuator according to a compression profile of the actuator to compress the tube portion and to control an area of a seal formed in the tube portion and/or a thickness of the sealed tube portion.  
         [0009]     According to yet another aspect, this invention includes a method of controlling a tube sealer configured to seal a tube portion, the tube sealer having a heat source to selectively heat the tube portion and an actuator configured to compress the tube portion via at least one movable tube-contacting surface. An exemplary method according to this aspect of the invention may include the steps of selecting one mode of a plurality of selectable modes of operating the tube sealer, each of the modes having heating and compression profiles, the heating and compression profiles defining heating periods of the heat source for heating the tube portion and duty cycles of the actuator for compression of the tube portion, respectively, and during a plurality of periods defined by the selected mode, simultaneously heating and compressing the tube portion according to the heating and compression profiles of the selected mode.  
         [0010]     According to yet another aspect, this invention includes a method of controlling a tube sealer configured to seal a tube portion, the tube sealer having a heating source to selectively heat the tube portion and an actuator configured to compress the tube portion, compression by the actuator being controlled according to a duty cycle of the actuator. An exemplary method according to this aspect of the invention may include the steps of simultaneously heating and compressing the tube portion according to a mode selected by a user, each mode including a heating profile and a compression profile, the heating and compressing of the tube portion being adjusted based on a time to produce a measured compression of the tube portion.  
         [0011]     According to yet another aspect, this invention includes a computer readable medium to store program code for use in a microprocessor to control a tube sealer having an actuator for compressing a tube portion. An exemplary computer readable medium according to this aspect of an embodiment of the invention may include a program code segment for controlling a duty cycle of the actuator according to a compression profile to compress the tube portion, thereby controlling an area of a seal formed in the tube portion and or a thickness of the sealed tube portion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]     The invention will described with reference to the exemplary embodiments illustrated in the drawing, of which:  
         [0013]      FIGS. 1   a  and  1   b  are front and top views, respectively, of a tube portion sealed according to aspects of this invention.  
         [0014]      FIG. 2  is a cross-sectional end view of the tube portion illustrated in  FIGS. 1   a  and  1   b.    
         [0015]      FIG. 3  is a front perspective view of an embodiment of a tube sealer according to aspects of this invention.  
         [0016]      FIG. 4  is a top perspective view of the tube sealer shown in  FIG. 3 .  
         [0017]      FIG. 5  is a side perspective view of the tube sealer shown in  FIG. 3 .  
         [0018]      FIG. 6  is another top perspective view of the tube sealer shown in  FIG. 3 .  
         [0019]      FIG. 7  is a rear perspective view of an interior region of the tube sealer shown in  FIG. 3 .  
         [0020]      FIGS. 8   a  and  8   b  provide a flow diagram illustrating the use of an embodiment of a tube sealer according to aspects of this invention.  
         [0021]      FIG. 9  provides block diagram of a radio frequency amplifier according to aspects of this invention.  
         [0022]      FIG. 10  illustrates a circuit diagram for an embodiment of an exemplary radio frequency generator according to aspects of this invention.  
         [0023]      FIG. 11  illustrates a block diagram of an embodiment of a control circuit according to aspects of this invention.  
         [0024]      FIG. 12  illustrates an embodiment of a control board according to aspects of this invention.  
         [0025]      FIG. 13  provides a block diagram for an embodiment of a control unit according to aspects of this invention.  
         [0026]      FIGS. 14-17  are timing charts illustrating aspects of an exemplary control method according to aspects of this invention.  
         [0027]      FIGS. 18   a  and  18   b  provide a flow diagram illustrating the use of an embodiment of a tube apparatus according to aspects of this invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     Preferred features of exemplary embodiments of this invention will now be described with reference to the figures. It will be appreciated that the spirit and scope of the invention are not limited to the embodiments selected for illustration. Also, it should be noted that the drawings are not rendered to any particular scale or proportion. It is contemplated that any of the configurations and materials described hereafter can be modified within the scope of this invention.  
         [0029]     Generally, systems have been proposed to seal tubes using a pair of jaws, such as electrodes, for compressing tubing and applying radio frequency energy to melt the tubing and form a weld to effect a seal. Such systems typically may use a solenoid to compress the tubing as the RF radiation is applied. As the solenoid is activated a coil of the solenoid increases in temperature due to the current applied to the coil. A problem exist in these tube sealing systems that as the solenoid increases in temperature due to the current applied to the coil of the solenoid, compression force of the solenoid significantly decrease because resistance of the coil increases as temperature increases. Thus, frequent use of the tube sealing system, reduces the compression force to compress the tubing which significantly reduces the efficiency of the tube sealing system and produces an increased number of defective seals in the tubing being sealed.  
         [0030]     An improved tubing sealing apparatus is provided to reduce or substantially eliminate the compression force reduction in the solenoid when such a system is heavily (i.e., repeatedly) used.  
         [0031]     Exemplary tube sealers according to aspects of this invention can be adapted to seal tubes such as those illustrated in  FIGS. 1   a ,  1   b  and  2 . Referring to those figures, a tube portion  2  is illustrated with two (2) seals  4 , thereby separating an interior  6  of the tube portion  2  into multiple sections or compartments. As is illustrated in  FIGS. 1   a  and  1   b , the tube portion  2  may have a diameter D and a wall thickness T 1 . The dimensions of the tube portion  2  can be varied depending upon the nature of the tube and the use thereof.  
         [0032]     The tube portion  2  may be a tube used to collect a sample of blood from a donor. If so, the tube portion  2  may be formed from polyvinyl chloride (PVC) or any another suitable material. The seals  4  in the tube portion  2  are formed by compressing the tube so that its walls come into contact with one another and simultaneously subjecting the tube portion  2 , in the area of a seal  4 , to energy until a seal is formed by heating and softening or melting the tube such that a weld can be formed.  
         [0033]     Referring to  FIGS. 1   a ,  1   b  and  2 , the seals  4  formed in tube portion  2  will have a width W, a height H, and a thickness T 2 . It has been discovered that it may be desirable to modify, select, and/or control the “size” or “area” defined by one or more of the dimensions W, H, and T 2 . Generally, there is likely to be some limited flow of the material of the tube in the area of a seal during the formation of the seal. More specifically, the softening or melting of the material of the tube is likely to cause some migration of the material radially outwardly to arrive at a height H of the seal  4  that is greater than diameter D of the tube. Also, the width W of the seal  4  will result from some migration of the material of the tube along the axis of the tube.  
         [0034]     The dimensions W, H, and T 2  of each seal  4  are impacted by various parameters relating to the energy used to form the seal as well as the jaws of the sealer that directly form the seal. These parameters include the degree of compression imparted on the tube by the jaws (i.e., the minimum gap between the jaws), the duration of the compression (i.e., the time delay before the jaws are separated), and the duration over which the radio frequency energy is generated, among other parameters. It has been discovered that it may be beneficial to permit the adjustment of a tube sealer with respect to one or more of these parameters, as will be discussed later in greater detail.  
         [0035]     Referring again to  FIGS. 1   a  and  1   b , a “good” or “successful” weld or seal  4  across a tubing portion  2  will be likely to exist if the combination of melting of the tubing with the compressive force exerted by the jaws forming the seal force lateral flow of the plastic to develop ears or tab portions disposed on opposite sides of the tubing. Such ears or tabs may be indicative of an impermeable seal across the tubing.  
         [0036]     Generally referring to  FIGS. 3-7 , one aspect of this invention provides a dielectric tube sealer  8  adapted to limit radio frequency emissions or emanations during operation. The dielectric tube sealer  8  includes an enclosure such as a cabinet  10  and first and second jaws (i.e. first and second tube-contacting surfaces)  42  and  26 , respectively, oriented with respect to the cabinet  10  to receive a tube portion in a space therebetween. The first jaw  42  is fixed and is coupled to a radio frequency generator, and the second jaw  26  is movable with respect to the first jaw  42  and is coupled to ground potential. A shield  12  is positioned adjacent the cabinet  10  and configured to at least partially enclose the first and second jaws  42  and  26  yet permit the introduction of a tube portion to a position between the first and second jaws  42  and  26 . The shield  12  thereby reduces radio frequency emanations from the first jaw  42 , and the shield  12  can be movable with respect to the cabinet  10  to at least partially expose the first and second jaws  42  and  26 .  
         [0037]     According to another aspect of the invention, a dielectric tube sealer  8  is adapted to detect successful or failed seals. The dielectric tube sealer  8  includes jaws  26  and  42  mounted for movement with respect to one another between (1) a first position spaced from one another to receive a tube portion and (2) a second position proximal one another to compress the tube portion, wherein the jaws  26  and  42  in the second position define a gap selected to form a successful seal. The dielectric tube sealer  8  also includes a sensor  204  positioned to detect when the jaws  26  and  42  have moved into the second position. The dielectric tube sealer  8  also includes a timer electrically coupled to the sensor  204  for determining the time delay before the jaws  26  and  42  have moved into the second position. A time delay up to a predetermined time limit indicates a successful seal, and a time delay exceeding the predetermined limit indicates a failed seal.  
         [0038]     According to another aspect of the invention, a dielectric tube sealer  8  includes a radio frequency generator configured to generate radio frequency for a time period. Jaws  26  and  42  are mounted for movement with respect to one another, one of the jaws  26  or  42  being coupled to the radio frequency generator. The dielectric tube sealer  8  also includes a microprocessor or microcontroller  206  configured to control the radio frequency generator. The microcontroller  206  is programmable to select the time period or time periods during which radio frequency is generated by the radio frequency generator, thereby controlling the area of the seal formed in a tube.  
         [0039]     Referring to  FIGS. 3-7 , exemplary features of one embodiment of a tube sealer according to this invention will now be described. The dielectric tube sealer  8  includes a cabinet  10  to which a cover or shield  12  is removably mounted. The dielectric tube sealer  8  also includes a power switch  14  which acts as an on/off switch for the operation of the unit. The dielectric tube sealer  8  further includes a power indicator  16  and a seal indicator  18 , both of which may take the form of an LED according to one exemplary embodiment of the invention. The seal indicator  18  will be on when the solenoid is energized. When the shield  12  is off and the unit is inoperable, the seal indicator  18  will flash (except when the unit is in programming mode as will be described later).  
         [0040]     Referring specifically to  FIG. 4 , which reveals internal features of the dielectric tube sealer  8 , an actuator (e.g., solenoid  20 ) is mounted on a mounting platform  22  within an interior of the cabinet  10 . It will be noted that, although cabinet  10  is adapted as a table-top unit, cabinet  10  may also be reconfigured as a hand-held device that is remote from other components that are illustrated within the cabinet  10  in  FIGS. 3-7 . Coupled to the solenoid  20  is a ground jaw shaft  24  on which the ground jaw  26  is positioned. A flag  28  is provided as a part of the assembly of the ground jaw shaft  24  in order to actuate a stop sensor  204 , which will be described in further detail later.  
         [0041]     A fastener  30 , which may take the form of a cap-head screw or any other suitable fastener, is used to make a connection between a wire  32  leading to a radio frequency board ( FIG. 10 ) and the RF jaw  42  (see RF jaw  42  in  FIG. 5 , for example). A start lever  33  is also provided as a component of the dielectric tube sealer  8 . The start lever  33  has a proximal end  34  and a distal end  36 , wherein the proximal end  34  extends outwardly from the cabinet  10  and the distal end  36  extends inwardly into the interior of cabinet  10 . The proximal end  34  of the start lever  33  is depressed downwardly when a tube is introduced into a position between the ground jaw  26  and the RF jaw  42 , and the distal end  36  of the start lever  33  is pivoted upwardly. A flag (not shown) toward the distal end  36  of start lever  33  actuates a start sensor  205  ( FIG. 11 ), details of which will be provided later.  
         [0042]     The start lever  33 , ground jaw shaft  24 , and connection to the RF jaw  42  each passes through an insulator  40 . According to exemplary aspects of the invention, the insulator  40  is in the form of a block of insulating material. The insulating material may be DELRIN, for example, or any other suitable insulator. If DELRIN is used, it is preferably black to provide a UV protectant. The insulator  40  serves two (2) purposes according to exemplary features of this invention; namely, it isolates the radio frequency potential applied to the RF jaw from the ground potential of the ground jaw and it provides a low-friction surface through which moving parts (e.g., ground jaw shaft  24 ) can slide.  
         [0043]     Referring to  FIG. 5 , it will be seen that a portion of the RF jaw  42  extends outwardly beyond the surface of the insulator  40 , thereby exposing a surface of the RF jaw  42  for contact with a tube portion to be sealed. Also shown in  FIG. 5  is a power supply  44 , which is positioned under the mounting platform  22 . Although not shown in  FIG. 5 , it has been discovered that there is benefit in selecting a power supply  44  that incorporates a fan for heat dissipation. Heat will of course be generated within the cabinet  10  by virtue of the operation of the solenoid  20  and other components of the system. It has been discovered that the positioning of a power supply  44  toward the base of the cabinet  10  can help dissipate significant heat when the power supply  44  is provided with the fan. More specifically, the fan of the power supply  44  exhausts heat downwardly and outwardly through a base portion of the cabinet  10 .  
         [0044]     Referring still to  FIG. 5 , the RF jaw remains fixed with respect to the cabinet  10  and the ground jaw  26  moves with respect to the RF jaw  42  by virtue of sliding movement of ground jaw shaft  24  through an aperture in the insulator  40  and the action of the solenoid  20 . More specifically, upon actuation of the dielectric tube sealer  8  to seal a portion of a tube, the solenoid  20  will withdraw the ground jaw shaft  24  toward the interior of the cabinet  10 , thereby moving the ground jaw  26  closer the RF jaw  42 . In that manner, the jaws  26  and  42  have two (2) positions; namely, an open position in which the jaws  26  and  42  are separated from one another a distance sufficient to receive a tube, and a closed position in which the jaws  26  and  42  are proximal to one another such that a tube positioned therebetween will be in a compressed state. The gap between the jaws  26  and  42  when the jaws are in the closed position is selected to correspond substantially to the desired thickness T 2  of the seal  4  (see  FIG. 2 ).  
         [0045]     That gap can be periodically adjusted during calibration of the dielectric tube sealer  8  to ensure that an appropriate thickness T 2  is imparted to a seal. Also, the gap can be adjusted to avoid arcing between the jaws, which would otherwise occur if the jaws were too close together. On the other hand, if the jaws are too far apart, the seal of the tube might not be properly formed and might leak.  
         [0046]     When the jaws  26  and  42  are in the closed position (not shown), the flag  28  on the opposite end of the ground jaw shaft  24  will block an optical sensor such as stop sensor  204  to signal that the seal is virtually complete. Accordingly, the flag  28  is sized and positioned to actuate such a sensor as the jaws  26  and  42  enter the closed position. For example, when the gap between jaws  26  and  42  is reduced to a predetermined size (e.g., 0.1 mm-0.2 mm), the flag  28  will trigger the sensor to indicate full compression of the tubing.  
         [0047]     Although not shown in  FIGS. 3-7 , a controller board, such as the exemplary embodiment of a board shown in  FIG. 12 , is mounted in a horizontal position extending rearwardly from the top of the insulator block  40 . Standard fasteners can be used to fasten the board to the insulator block  40  or to otherwise mount the board within the cabinet  10 . The sensors for sensing the flags on the start lever  33  and the ground jaw shaft  24  are mounted to the controller board and are positioned on the board in locations selected to correspond to the respective flags on the start lever  33  and ground jaw shaft  24 .  
         [0048]     Referring now to  FIG. 6 , it will be seen that the RF jaw  42  is provided with a substantially flat surface  43  for contact with a tube portion to be sealed. Similarly, the ground jaw  26  is also provided with a substantially flat surface  27  for contact with the opposite side of the tube portion. These flat surfaces  27  and  43  are sized and oriented so as to impart a predetermined configuration to a seal  4  in a tube portion  2 . It will be appreciated that the widths and other dimensions of the flat surfaces  27  and  43  can be modified so as to alter the configuration of the seal  4 . More specifically, the surfaces  27  and  43  can be modified to impart functional or ornamental features to the surface of the seal, depending upon the particular application or preferences of the end user. Also, the texture or finish of the surfaces  43  and  27  can be modified to impart a particular surface feature to the seal.  
         [0049]     As shown in the figures, the ground jaw shaft  24  is substantially rounded in cross-sectional shape. For example, a cylindrical shape for ground jaw shaft  24  can be selected to correspond to a through-hole formed in the insulator  40 . Also, a cylindrical shaft or otherwise rounded shaft may be easier to clean in the instance of leaked fluids because the cylindrical shape will not encourage an accumulation of fluids on the ground jaw shaft  24 . The portion of ground jaw shaft  24  on which the ground jaw  26  is formed is also substantially cylindrical except for the flat surface  27  formed thereon.  
         [0050]     As is best illustrated in  FIG. 5 , it will be seen that the axis of the longitudinally extending portion of the ground jaw shaft  24  is spaced from, but substantially parallel to, the axis of the solenoid  20 . Also, the axis of the solenoid  20  corresponds to the position on the RF jaw  42  and ground jaw  26  that contact a tube portion to be sealed. In order to provide this feature, the ground jaw shaft  24  (extending all the way from the flag  28  extending upwardly beyond the axis of the solenoid to the top of the ground jaw  26 ) forms a substantially “U” shaped configuration. Such a configuration makes it possible to compress a tube portion along an axis of compression that is common to the axis of the solenoid  20 .  
         [0051]     The ground and RF jaws are, according to one exemplary embodiment, formed from a metal but can optionally be formed from any conductive material. The jaws can be formed from steel plate or rod by known forming techniques.  
         [0052]     It has been discovered that the configuration of the RF jaw as a fixed jaw at least partially insulated and located adjacent the cabinet  10  helps to reduce the radio frequency emanations from the dielectric tube sealer  8 . More specifically, the mounting of the RF jaw at least partially within an insulator block such as insulator  40  helps to shield the emanations of radio frequency energy. This can be accomplished by configuring the ground jaw  26  to be the moving jaw that extends outwardly from the cabinet  10 . By exposing the ground jaw  26  as the outer jaw, as opposed to the RF jaw  42 , the radio frequency emanations from the dielectric tube sealer  8  are further reduced. The configuration of the ground jaw shaft  42  as an exemplary “U” shaped configuration permits the orientation of the stationery RF jaw  42  in or near the cabinet with the ground jaw  26  extending outwardly beyond the RF jaw  42 .  
         [0053]     Referring now to  FIG. 7 , a magnet  46  is mounted to a portion of the shield  12 . Although not shown in  FIG. 7 , HALL effect sensor “H 1 ” on the control board shown on  FIG. 12  corresponds in position to the magnet  46  when the shield  12  is in place and the control board is mounted within the cabinet  10 . By virtue of the HALL effect sensor, therefore, the presence or absence of the magnet  46  (and therefore the presence or absence of the cover or shield  12 ) can be detected.  
         [0054]     It has been discovered that combined features of the exemplary dielectric tube sealer  8  cooperate to reduce emanations of radio frequency energy during operation of the sealer.  
         [0055]     Although each of the foregoing features helps to reduce radio frequency emanations, the combination of the shield  12 , the at least partial insulation of the stationery RF jaw  42 , and the outward positioning of the movable ground jaw  26  provide significant reductions in RF emanations.  
         [0056]     Also, the configuration of the jaws and the insulator with respect to one another helps to prevent arcing between the jaws (e.g., arcing between ground and RF potentials). More specifically, the extension of jaw  42  outwardly from the insulator  40  helps to prevent bridging of fluids such as blood between the RF jaw  42  and the ground jaw shaft  24 .  
         [0057]     In the exemplary embodiment illustrated in the figures, the shield  12  is removably mounted adjacent the cabinet  10 . Removal of the shield  12  facilitates cleaning and maintenance of the jaws and other components of the tube sealer  8 . As will be described later in greater detail, the removal of the shield  12  also facilitates the periodic calibration of the tube sealer to maintain an appropriate seal thickness and facilitates the programming of the tube sealer.  
         [0058]     While the exemplary shield  12  is removable and replaceable by virtue of a sliding engagement with the insulating block  40 , the tube sealer is configured to prevent its operation while the shield  12  is not in place. Contact between the shield  12  and the cabinet (e.g., by virtue of the flanges of the shield  12  extending between the insulator  40  and the cabinet  10 ) is optionally provided to ground the shield  12 .  
         [0059]     The shield  12  may be formed from a conductive material such as a metal. The slot (not numbered) in the shield  12  permits a user to insert a portion of the tube to be sealed between the jaws of the dielectric tube sealer  8 . The shape and configuration of the slot and the body of the shield are not important, however.  
         [0060]     Referring now to  FIGS. 8   a  and  8   b , a flow diagram illustrating operation of an exemplary embodiment of a tube sealer according to this invention will now be described. Steps  50 - 63  roughly correspond to an exemplary sealing operation of the unit, steps  64 - 67  illustrate exemplary operation of the system in connection with a failed seal, steps  68 - 73  illustrate an exemplary programming mode, and steps  74  and  75  illustrate an exemplary inoperable mode.  
         [0061]     Referring first to the exemplary sealing operation illustrated in steps  50 - 63  in  FIGS. 8   a  and  8   b , the unit is turned on in step  50 , which is followed by a query in step  51  as to whether the cover or shield  12  is in place. This query can be answered, for example, by use of a Hall sensor to detect the presence or absence of a magnet  46  on the shield  12 . In step  52 , the mode setting is read from the memory of the sealing unit, and the power LED is flashed in step  53  to indicate the mode selected. The number of flashed of the LED can indicate the mode. The mode may correspond, for example, to the time delay mode selected in steps  68 - 73  (described later). After the mode selected is indicated, the power LED is turned on in step  54 .  
         [0062]     In step  55 , a query asks whether the start switch has been activated. This query can be answered, for example, with the use of an optical sensor such as the start sensor  205  to detect the presence or absence of a flag on a distal end  36  of the start lever  33 , which would indicate that a tube portion has been inserted between the jaws of the sealer, thereby depressing the proximal end  34  of the start lever  33 . If the start switch has been activated, the solenoid and RF generator (and red seal LED) are turned on in step  56 . Step  57  queries whether the limit switch is activated, which can be answered, for example, depending on whether the flag  28  on the ground jaw shaft  24  is sensed by the optical sensor or stop sensor  204  on the control board. If so, the programmed time delay is read in step  58  and the RF generator is turned off after the programmed time delay elapses in step  59 . After a predetermined time (e.g., 500 ms), which may be selected based on the amount of time desired for the seal to cool adequately, the solenoid (and red seal LED) is turned off in step  60 , and a count is added to the memory for an updated count of complete seals in step  61 . The successful seal is then completed in step  62  and the unit can then be readied to create another seal at step  63 . If at any time during power “on” of the sealer the sealer cover  12  is removed, then the seal LED remains flashing and the unit will not respond to the start sensor  205 .  
         [0063]     Referring now to the exemplary failed seal mode in steps  64 - 67 , a query is made in step  64  to determine whether 3 seconds, or some other predetermined delay, has elapsed since the solenoid and RF generator were turned on in step  56 . If so, that means that too much time has elapsed since the start of the sealing process without a full seal being indicated by the limit switch. In other words, thereby indicating that the seal has not yet been made. If so, the RF generator and solenoid power are shut off in step  65 , and the seal LED flashes 3 times to indicate to the user of the sealer that the seal was unsuccessful in step  66 . If a buzzer is incorporated into the sealer system as an audible indicator to the user and the buzzer is programmed to activate, then the buzzer is sounded in step  66 . In step  67 , a count is added to the memory to updated the count of incomplete seals and the sealer is readied for another attempt at steps  62  and  63 .  
         [0064]     Referring now to the exemplary programming mode in steps  68 - 73 , if the cover is off (step  51 ) and the limit switch or stop sensor  204  is activated (step  68 ) during system start up, then the sealer unit scrolls through a menu of available delay times in step  69 . Accordingly, the programming mode in steps  68 - 73  is initiated by: (1) either removing the cover  12 , using start lever  33  to activate the limit switch or, otherwise, pushing the ground jaw  26  in to activate the limit switch, (2) turning the unit on, and (3) selecting a delay time. In step  70 , the power LED can flash as an indicator of a variety of selectable delay times and/or an audible alarm mode. In one embodiment, six (6) modes are available for selection.  
         [0065]     Program mode is initiated when the shield  12  is off, the limit switch is activated, and the power is then turned on. If the cover or shield is removed after power up and the limit switch is triggered, the unit will not enter program mode.  
         [0066]     For example, one flash may correspond to a particular mode with a delay time. As mentioned, the user of the system can activate the limit switch (step  68 ) by either using start lever  33  or, otherwise, pushing in the ground jaw shaft  24  or ground jaw  26  while the cover is off. While in the programming mode, the system will continue to scroll through the menu of possible delay times until the limit is switch is deactivated at step  71 . In other words, if the limit switch remains activated (e.g., by the user retaining the ground jaw shaft  24  in a closed position) then the system will continue to scroll delay times. Upon release of the ground jaw shaft  24  by the user, the limit switch will thereby be deactivated in step  71  and the delay mode selected by the user by deactivating the limit switch is then stored in the memory in step  72 .  
         [0067]     The various programmed modes may determine the delay times and/or the nature of the indicator with respect to failed and successful seals. For example, a menu of program modes can include modes configured to sound an audible alarm (e.g., a buzzer) in the event of a failed seal. Alternatively, modes can dictate a silent, visual alarm depending on the preferences of the end user.  
         [0068]     In one exemplary embodiment, six (6) modes are provided to offer three delay times with an audible indicator and three delay times without the audible indicator. The delay times can be, for example, 50 ms, 100 ms, and 150 ms, but a variety of delay times can be provided depending on the material to be sealed, the size of the tubing, the application for the tube sealer, and other factors.  
         [0069]     As indicated in step  72 , the delay mode selected by the user will correlate to a desired seal width. Generally, the longer the delay time (i.e., prior to turning off the RF generator), then the wider the seal may be. After step  72 , the programming mode is concluded at step  73 .  
         [0070]     Referring now to an exemplary inoperable mode of the dielectric tube sealer  8  in steps  74  and  75 , if the cover is off (step  51 ) and the limit switch is not activated (step  68 ), then the unit should not be operated by a user and a warning is delivered to the user in the form of the flashing of the seal LED in step  74 . As indicated in step  75 , further seal operation is prevented, and the system is returned to the query of whether or not the cover is on (step  51 ).  
         [0071]     Referring next to  FIG. 9 , there is shown an exemplary block diagram of a radio frequency (RF) energy generator, generally designated as  100 , for providing RF power to melt and weld a seal across a plastic tube. As shown, RF energy generator  100  includes RF amplifier  101 , coupling coil  107  and jaw/electrode  108 . RF amplifier  101  may include crystal oscillator  102 , monolithic amplifier  103 , current driver  104 , push/pull amplifier  105 , and filter network  106 . These are discussed below.  
         [0072]     An exemplary electrical circuit of RF amplifier  101  is shown in  FIG. 10 , and may include electrical components that are surface mountable on a single board. Referring to both  FIGS. 9 and 10 , there is shown crystal oscillator  102  capable of providing an RF signal at 40.68 MHz. The RF signal provided by crystal oscillator  102  may be filtered by a network of components (R 2 , C 1 , C 2 , C 3  and L 1 ) prior to amplification by monolithic amplifier  103 . The monolithic amplifier, designated as U 1  in  FIG. 10 , may be a MAV11 monolithic amplifier for providing an amplified RF output that may be adjustable by way of resistive components R 4 , R 5  and R 15 . The RF energy is adjustable largely by potentiometer R 5 . Alternatively, resistive components R 4  and R 5  can be removed, allowing the amplifier to run at maximum power, which will be controlled by fixed resistor R 3 .  
         [0073]     The crystal oscillator and monolithic amplifier may be turned on/off by way of switching transistors Q 6  and Q 2 . Upon activation by RF trigger input signal (provided from a control circuit, discussed below), transistors Q 6  and Q 2  may be turned on, thereby allowing voltage, +V, to saturate transistor Q 1  and start RF oscillation. Switching transistors Q 6  and Q 2  will activate monolithic amplifier U 1  to amplify the RF oscillation.  
         [0074]     The output energy from monolithic amplifier  103  may be filtered by various components including C 5 , C 7 , C 8 , L 2  and L 3 . The filtering advantageously prevents RF energy from feeding into the power supply and noise from reaching a microcontroller residing on the control circuit (discussed below). The output energy from monolithic amplifier  103  is further amplified by current driver  104  and push/pull amplifier  105 . Current driver  104  may include power amplifier Q 3  for driving step-down transformer L 4  (5T to 1T), which effectively lowers the output voltage and increases the current by a five-to-one ratio. The output of step-down transformer L 4  may be provided to push/pull amplifier  105 . In the exemplary embodiment of  FIG. 10 , the push/pull amplifier may have a configuration that includes transistors Q 4  and Q 5  for driving step-up transformer L 5  (1T to 3T).  
         [0075]     The amplified RF output signal from push/pull amplifier  105  may be low pass filtered by filter network  106  and may include components L 6 , L 7 , L 8 , C 13 , C 14 , C 15 , C 16  and C 17 . It will be appreciated that filter network  106  may provide a cut-off frequency for RF harmonics above the baseband frequency of crystal oscillator  102 .  
         [0076]     Completing description of RF amplifier  101 , additional filtering components may be included on the surface mountable RF board, such as D 1 , L 9 , C 11 , C 12  and C 18 . These additional filtering components may further prevent RF noise from reaching the power supply (+V, for example) and the microcontroller on the control circuit.  
         [0077]     In the embodiment shown, the amplified RF output signal is sent to coupling coil  107 , which may be mounted separately from RF amplifier  101 . Coupling coil  107  may be included to provide a matching impedance (50 ohms) between filter network  106  and jaw electrode  108 . In this manner, sufficient RF energy may be radiated from jaw electrode  108  to provide efficient melting and welding of the plastic tubing.  
         [0078]     In the RF circuit of  FIG. 10 , monolithic amplifier U 1 , may be configured to provide approximately 8-9 dB of amplification. Coupled between oscillator  102  and current amplifier Q 3 , the monolithic amplifier amplifies the low output signal from oscillator  102  and may achieve a maximum output power of 0.5 watts, for example. Sufficient gain is provided from the monolithic amplifier to directly drive current amplifier Q 3 .  
         [0079]     It will be appreciated that the monolithic amplifier is optionally utilized to provide gain in a single stage that conventionally may require three or more stages of amplification. The monolithic amplifier also requires less filtering. As a result, the RF circuit may be compact and small in size. The monolithic amplifier may, for example, be an MAV-11 amplifier manufactured by Mini-Circuits in Brooklyn, N.Y.  
         [0080]     Referring to  FIG. 11 , an exemplary embodiment of a control circuit, generally designated as  200 , will now be described.  
         [0081]     Control circuit  200  is adapted for monitoring and controlling the tube sealing operation. The control circuit may also provide status and alerts to the operator (or user). As shown, the heart of the control circuit is microcontroller  206 , and, for example, may be AVR microcontroller ATtiny 28L. In the embodiment shown, microcontroller  206  monitors sealer cover sensor  203 , stop sensor  204  and start sensor  205 . In response to these sensors and in response to a programmed method of operation, microcontroller  206  activates buzzer  214 , power on LED (green)  215 , seal indicator LED (red)  216 , solenoid  217  and RF trigger output to the RF amplifier board. Each of these elements may be activated by way of respective drivers  209 - 213 . Of course, a driver may be omitted, if the microcontroller is capable of directly driving the element.  
         [0082]     As shown, microcontroller  206  is coupled to memory  207 , which may be an EEPROM, such as FM 25160, and is capable of providing over a billion write operations. One such write operation may include microcontroller  206  storing “good/bad seal” status into memory  207 . Another write operation may include storing the modes of operation. Also included may be data port  208  for allowing the user to access memory  207  and obtain status information of a sealing operation.  
         [0083]     Control circuit  200  may also include voltage regulator  201  and reset monitor  202 . As shown, voltage regulator  201  regulates the V+voltage (for example 13.8 V) and provides Vcc voltage to both the microcontroller and the memory. Reset monitor  202  may also be included to continuously monitor the Vcc voltage from regulator  201 . If the voltage drops below a threshold (for example 4.68 V), microcontroller  206  may be reset by monitor  202 .  
         [0084]     Describing next the sensor signals provided to the microcontroller, there is shown sealer cover sensor  203 , which may be a Hall sensor adapted to sense magnetic fields emanating from a pole magnet  46  disposed on the cover or shield  12 . It will be appreciated that the placement of the Hall sensor may be such that if the magnetic fields are absent (or below a threshold), the Hall sensor may effectively alert the microcontroller that the sealer cover is not in a shielding position. In response to the Hall sensor alert, the microcontroller may be programmed to prevent activating the solenoid and the RF trigger signal.  
         [0085]     Start sensor  205  may include a combination of a transistor and a photodiode for sensing that the tube is in proper position for sealing. It will be appreciated that the microcontroller may be programmed to prevent activation of the solenoid and the RF energy until the tube is in proper position. In the example shown, start sensor  205  senses an absence of light that results from depression of a lever  33  after the tube has been placed in position. Depression of the lever  33 , in turn, raises a flag that blocks the light from reaching the photodiode. Blockage of the light may turn off the transistor and cause activation of a signal to inform the microcontroller that the tube is in position.  
         [0086]     In a similar manner, stop sensor  204  may include a similar combination of transistor and photodiode for sensing that a limit switch is to be activated. Activation of the limit switch may indicate that a preset jaw-gap has been reached (or a predetermined thickness of the seal has been reached). Activation of the limit switch may result from movement of a flag such as flag  28  of ground jaw shaft  24  into position to block light from reaching the photodiode of stop sensor  204 . Upon turning off the photodiode, the transistor may also be turned off, thereby providing an output signal to inform the microcontroller of the limit switch having been activated.  
         [0087]     Turning next to output signals that may be provided by microcontroller  206 , there is shown buzzer  214  that may be activated to alert the user that a step in the method is not successfully completed. For example, if sealing is not successfully completed, the buzzer may be activated. In another embodiment of the invention, the buzzer may be omitted.  
         [0088]     Power-on LED (green)  215  may be activated by the microcontroller to alert the user that the sealing unit is turned-on. The power-on LED may also be controlled from the microcontroller to flash on-and-off. The microcontroller may be programmed to cause the LED to flash a predetermined number of times to indicate a mode of operation (there may be, for example, six modes of operation corresponding to delay times, as discussed previously).  
         [0089]     Seal indicator LED (red)  216  may be activated by the microcontroller to alert the user that the RF energy and the solenoid is activated. The microcontroller may also be programmed to cause the seal indicator LED to flash, for example, if power to the unit is on and the shield cover  12  is not in position. In addition, the seal indicator LED may be programmed to flash a predetermined number of times to indicate, for example, that the RF energy and solenoid power are off.  
         [0090]     Completing the description of control circuit  200 , microcontroller  206  may be programmed to energize solenoid  217  (item  20  in  FIG. 5 ). The solenoid may be, for example, a 12 V solenoid energized by way of driver  212 . The driver may be a transistor-switch that when activated by the microcontroller places a ground potential at one end of the solenoid (the other end already having a 12 V potential).  
         [0091]     Microcontroller  206  may be programmed to generate the RF trigger signal for turning on the RF amplifier. Although shown as having driver  213  in the path between the microcontroller and switching transistor Q 6  ( FIG. 10 ), it will be appreciated that the AVR microcontroller ATtiny 28L may drive the transistor without need for a driver.  
         [0092]     Exemplary physical spacing among the components shown schematically in  FIG. 11  are provided in  FIG. 12 . The controller board may be positioned within the cabinet or other form of enclosure in such a way that the flags of the start lever and ground jaw correspond to the positions of the optical sensors and such that the position of the Hall sensor corresponds to the shield&#39;s magnet. A notch is provided in the insulator  40  at a location corresponding to the magnet  46  of the cover  12  to accommodate the Hall sensor.  
         [0093]     A connector (such as connector J 1  shown in  FIG. 12 ) can be provided for connection between the dielectric tube sealer  8  and an external computer or monitor. For example, a computer can be connected to the dielectric tube sealer  8  by means of the connector to download or upload information. In one exemplary embodiment, a Personal Digital Assistant (PDA) or other computer, communications, or reading device can be connected to download the counts of failed and successful seals. This count information can be used to monitor the amount of the use of the sealer, to schedule maintenance and calibration of the sealer, etc. Also, the recordation of the count helps to track the number of cycles a unit has completed, diagnose problems with the equipment, determine maintenance needs, and make accountings for billing purposes.  
         [0094]     Referring back to  FIG. 11 , microcontroller  206  may be programmed to output a pulse width modulated (PWM) signal to supply PWM power to solenoid  217 . That is, the PWM signal from microcontroller  206  may control a duty cycle of the power supplied to solenoid  217 . Solenoid  217  may be, for example, a 12 V or 13 V solenoid and may have a power rating in the range of 30-80 watts, preferably 60 to 70 watts, and a coil of solenoid  217  may have a DC resistance in the range of about 2.0-5.0 Ω. Moreover, the PWM signal may be at a frequency in the range of between about 250 Hz to 5 KHz.  
         [0095]     In a typical tube apparatus that does not include such a pulse width modulation operation, the solenoid heats up during continuous usage and the DC resistance increases at a result of such heating resulting in a reduction in current supplied to the solenoid and a corresponding reduction in compression force exerted by the jaws of the typical tube apparatus. Also the coil transfers heat to the plunger which would conduct unwanted heat to the movable ground jaw  26 .  
         [0096]     By controlling the duty cycle of the PWM power supplied to solenoid  217 , heating of solenoid  217  may be controlled (i.e., reduced or substantially eliminated) and instantaneous compression force produced during on cycles may remain substantially constant throughout all tubing operation of the tubing apparatus.  
         [0097]     Microcontroller  206  outputs the PWM signal to driver  212 . Driver  212  is connected with a DC voltage supply, for example, at Vcc voltage, such that the DC voltage supply switchably energizes solenoid  217  according to the PWM signal from microcontroller  206 . That is, driver  212  may be, for example, a switch switchably coupling the DC voltage supply to solenoid  217  such that microcontroller  206  may control the switch (driver  212 ) according to the PWM signal output from microcontroller  206 .  
         [0098]      FIG. 13  illustrates an alternative embodiment for duty cycle control of solenoid  217 .  
         [0099]     Referring to  FIG. 13 , a pulse width modulation (PWM) controller  300  maybe included in the tube apparatus. PWM controller  300  includes an input terminal  301  and an output terminal  302 . Input terminal  301  may be connected to any mode input device  303 . Mode input device  303  may provide, for example, an analog voltage proportional to the desired duty cycle. That is, for example, if a 10V signal from mode input device  303  represented a 100% duty cycle, then a 5V signal would represent a 50% duty cycle and soon on. Thus, mode input device  303  may be programmed with the selectable modes, and the selected mode selected by the user may be communicated directly to PWM controller  300  without affecting microcontroller  206 . In such a configuration, driver  212  would be coupled to output terminal  302  of PWM controller  300 , instead of microcontroller  206 . Driver  212  and solenoid  217  have the same functionality previously described. Moreover, a separate mode indicator  304  may be provided, such as an LED indicator, a display device or, otherwise, a wireless connectable device, such as a PDA (i.e., palm pilot) may be used to indicate the selectable modes and the selected mode.  
         [0100]      FIG. 14-17  illustrate an exemplary embodiment of four (4) pulse width modulated signals defining four different compression profiles and corresponding delay times defining corresponding heating profiles that are selectable modes by a user. These selectable modes are store in memory and are adjustable according to actual measured compression of the tube portion.  
         [0101]     A compression profile refers to establishing one or more periods, each having a successively different duty cycle such that the composite force (i.e., average force for that period) provided by solenoid  217  varies during the one or more periods.  
         [0102]     A heating profile refers to establishing one or more periods during which heating (e.g., by radio frequency source) of the tube portion occurs.  
         [0103]     Referring to  FIGS. 14-17 , the output of microcontroller  206  is represented by a control signal  120 ,  125 ,  130  or  135 . Control signals  120 ,  125 ,  130  or  135  corresponding to the duty cycle of solenoid  217  for four (4) different selectable modes (i.e., first through fourth modes). Each control signal  120 ,  125 ,  130  or  135  may be a pulse width modulated signal. That is, microcontroller  206  generates a control signal  120 ,  125 ,  130  or  135  according to a compression profile, to control the duty cycle of power supplied to solenoid  217  to actuate solenoid  217  and the coupled movable ground jaw  26 , thereby compressing the tube portion.  
         [0104]     Microcontroller  206  controls the duty cycle of power supplied to solenoid  217  for moving ground jaw  26  to adjust the area of the seal formed in the tube portion during compression and/or thickness T 2  of the sealed area. That is, by varying the composite force during the compression operation the area of the seal formed by the compression operation and/or the thickness T 2  of the sealed tube portion may be adjusted to produce improved seals.  
         [0105]     Moreover, the RF generator  100  may generate heat in the tube portion according to the heating profile simultaneously with the compressing of the tube portion to adjust the area of the seal tube portion and/or the thickness T 2  of the sealed tube portion.  
         [0106]     In an initial period TP 1 , a initial duty cycle of the control signal  120 ,  125 ,  130  or  135  is 100%. That is, solenoid  217  is fully turned on. The initial period TP 1  is for a time period that varies according to the mode selected and is in a range of about 70 to 200 milliseconds. After, initial period TP 1  is complete, a heating period TP 2  is commenced. The duration of the heating period TP 2  is based on activation of the limit switch (i.e., the duration of the heating period TP 2  is determined based on a time to produce a measured compression of the tube portion). The duration of the heating period T 2  is an indicator of a good tubing operation being accomplished by the tube apparatus. In the heating period TP 2 , the tube portion is simultaneously heated by RF generator  100  and compressed via solenoid  217 . After, the heating period TP 2  is complete, a sealing period TP 3  is commenced. The duration of the sealing period TP 3  varies according to the mode selected and may be in the range of about 0 to 200 milliseconds. In the sealing period TP 3 , the tube portion is simultaneously heated by the RF generator  100  and compressed via solenoid  217 , however, generally, composite compression force (i.e., the average force over the particular period, TP 3  in this case) is lower in the sealing period TP 3  than in the heating period TP 2 . That is, the duty cycle of solenoid  217  in the sealing period TP 3  is typically less than the duty cycle of solenoid in the heating period TP 2 . After the sealing period TP 3  is complete, a cooling period TP 4  is commenced. The duration of the cooling period TP 4  varies according to the mode selected and may be in the range of about 0 to 500 milliseconds. In the cooling period TP 4 , RF generator  100  is stopped and the composite compression force may remain the same as in the sealing period TP 3  (i.e., the duty cycle of solenoid  217  remains the same in the heating and cooling periods TP 3  and TP 4 ). After, the cooling period TP 4  is complete, power to solenoid  217  is stopped (see period TP 5 ).  
         [0107]     Microcontroller  206  may simultaneously control both the heating profile (e.g., a radio frequency energy profile) for heating of the tube portion and the compression profile for compressing of the tube portion to adjust the area or the thickness T 2  of the sealed tube portion.  
         [0108]     During the initial, heating and sealing periods TP 1 , TP 2  and TP 3 , simultaneously heating and compressing of the tube portion occurs and during the cooling period TP 4 , only compressing of the tube portion occurs.  
         [0109]     Although it is provided that the duration of the heating period TP 2  is based on a measure compression of the tube portion by activating the limit switch, it is contemplated that the measurement of compression may be provided by measuring impedance changes across ground and RF jaws  26  and  42 .  
         [0110]     Although an initial period TP 1  is shown, it is contemplated that for particular types of tube portions (for example, very thin walled tube portions) that the initial period TP 1  may be eliminated.  
         [0111]     For the four (4) exemplary selectable modes (i.e. first through fourth modes), in heating period TP 2 , the duty cycle of solenoid  217  may be 10%, 50%, 70% and 80%, respectively. For the first to fourth selectable modes, in sealing and cooling periods TP 3  and TP 4 , the duty cycle of solenoid  217  may be 40%, 40%, 48% and 64%, respectively. By providing different selectable modes, the user can select a mode to provide, for example, a particular width W and/or thickness T 2  of the sealed tube portion. That is, for a particular tube portion by selecting, for example, the fourth mode a wider sealed tube portion may be realized than, otherwise, if the first mode is selected.  
         [0112]     Although in the exemplary selectable modes specific values are provided for duty cycles in the various periods (i.e., the initial period TP 1 , the heating period TP 2 , the sealing period TP 3  and the cooling period TP 4 ), other duty cycles are possible as long as a good seal can be produced. The preferred ranges for duty cycles in the various periods are as follows: (1) in initial period TP 1 , the duty cycle of solenoid  217  is desirably in the range of about 90% to 100%; (2) in heating period TP 2 , the duty cycle of solenoid  217  is desirably in the range of about 10% to 90%; and (3) in third and fourth periods TP 3  and TP 4 , the duty cycle of solenoid  217  is desirably in the range of about 40% to 70%.  
         [0113]     Memory  207  may store the plurality of selectable modes in one or more tables. That is, memory  207  may include the one or more tables for storing the heating profiles and the compression profiles corresponding to the selectable modes. For example, for each selectable mode the one or more tables may include the programmed time delay that is used to turn off RF generator  100  after activation of the limit switch second and third duty cycle settings to set the duty cycle of solenoid  217  in the second and third periods TP 2  and TP 3 , respectively, and first, third and fourth duration settings to set the duration of the initial, cooling and sealing periods TP 1 , TP 3  and TP 4 .  
         [0114]     By controlling the duty cycle of solenoid  217 , power requirement for sealing the tube portion are reduced. Since power requirements are reduced, solenoid  217  may be configured to reduce or eliminate the affect of heating during heavy (e.g. continuous) usage. Thus, DC resistant of the coil of solenoid  217  may be keep substantially constant such that the instantaneous compression force exerted by movement of ground jaw  26  or the tube portion does not degrade (i.e., is not reduced) over time during heavy usage. If the tube apparatus is operated by battery power or uses a portable generator, this aspect of reducing the power requirements may be especially desirable.  
         [0115]     Since nonlinearities in compression force from solenoid  217  exist, it is contemplated that by varying the duty cycle of solenoid  217  that such nonlinearities may be compensated for, thereby producing a compression force from solenoid  217  that is equivalent to a linear compression force. That is, a typical solenoid has the least compression force for a particular input current when solenoid  217  is fully extended and the most compression force for the particular input current when solenoid  217  is fully retracted. Thus, using a varying duty cycle may allow for compensation of this effect to linearize the compression force of solenoid  217 .  
         [0116]     Microcontroller  206  or memory  207  may include program code stored therein for uses by microcontroller  206  to control the tube apparatus, the program code may include a program code segment for controlling the duty cycle of solenoid  217  according to the compression profile to compress the tube portion, thereby controlling the area of the seal formed in the tube portion and or thickness T 2  of the sealed tube portion.  
         [0117]     It is contemplated that the methods previously described may be carried out within microcontroller  206  or a general purpose computer system instructed to perform these functions by means of a computer-readable medium. Such computer-readable media include; integrated circuits, magnetic and optical storage media, as well as audio-frequency, radio frequency, and optical carrier waves.  
         [0118]     A plurality of user selectable modes which each may be defined by the heating profile, for example, the programmed delay time for turning off RF generator  100  and the compression profile, for example, the duty cycles of power supplied to solenoid  217 , may be programmed into microcontroller  206 . That is, the selectable modes set the delay time to shut off RF generator  100  after activation of the limit switch (for example, as shown in  FIGS. 8   a  and  8   b ), and, furthermore, set, for example, the duty cycle of solenoid  217 .  
         [0119]      FIGS. 18   a  and  18   b  which illustrate a flow diagram showing operation of an exemplary embodiment of a tube apparatus according to this invention will now be described.  
         [0120]     Now referring to  FIGS. 18   a  and  18   b , for brevity, only a brief review of steps which are common with those of  FIGS. 8   a  and  8   b  will be included below.  
         [0121]     Steps  64 - 67  which illustrate exemplary operation of the system in connection with a failed seal and steps  74  and  75  which illustrate an exemplary inoperable mode are common between this embodiment and that covered in  FIGS. 8   a  and  8   b  and will not be further discussed. Steps  50 - 55 ,  57 ,  61 - 63 , and  151 - 154  roughly correspond to another exemplary sealing operation of the apparatus. Further, steps  68 ,  70 - 71 ,  73 , and  155  and  156  illustrate another exemplary programming mode.  
         [0122]     Referring first to the exemplary sealing operation illustrated in steps  50 - 55 ,  57 ,  61 - 63 , and  151 - 154  of  FIGS. 18   a  and  18   b , steps  50 - 55  are common between this embodiment and that covered in  FIGS. 8   a  and  8   b  and will not be further discussed.  
         [0123]     After step  55  is complete, if the start switch has been activated, RF generator  100  (and red seal LED) may be turned on and solenoid  217  may be turned on (i.e., having a 100% duty cycle) for a predetermined time in step  150 . That is, RF generator  100  may be turned on and may remain on until the limit switch is activated or until an overall time period for making a seal elapse causing an indication of an unsuccessful seal (see steps  64  and  65  of  FIGS. 18   a  and  18   b ) and solenoid  217  may be turned on for a predetermined time in the range of about 0 to 200 milliseconds. By turning solenoid  217  on initially, a maximum force is applied to compress the tube portion when ground and RF jaws  26  and  42  are fully extended. This compensates for an affect that as solenoid  217  is extend the compression force produced by solenoid  217  is reduced for a constant input current level. After the predetermined time is completed, solenoid  217  is duty cycled (i.e., cycled on and off at a switching frequency in the range of about 250 Hz to 5 KHz) at a first duty cycle that is between about 10% and 90% according to the mode selected by the user in step  151 . Step  57  queries whether the limit switch is activated. If so, the programmed time delay of the selected mode is read in step  152 . In step  153 , solenoid  217  is duty cycled at a second duty cycle that is between about 40% and 64% according to the mode selected by the user. RF generator  100  is turned off after the programmed time delay of the set mode elapses in step  154 . After a predetermined time (e.g., 500 ms), which may be selected based on the amount of time desired for the seal to cool adequately, solenoid  217  (and red seal LED) is turned off in step  60 , and a count is added to memory  207  for an updated count of complete seals in step  61 . The successful seal is then completed in step  62  and the apparatus can then be readied to create another seal at step  63 .  
         [0124]     Referring now to the exemplary programming mode in steps  68 ,  70 ,  71 ,  73 ,  155  and  156 , if the cover is off (step  51 ) and the limit switch or stop sensor  204  is activated (step  68 ) during apparatus start up, then the apparatus scrolls through a menu of available modes in step  155 . Accordingly, the programming mode in steps  68 ,  70 ,  71 ,  73 ,  155  and  156  is initiated by: (1) removing the cover  12 , (2) either using start lever  33  to activate the limit switch or, otherwise, pushing ground jaw  26  in to activate the limit switch, (3) turning the apparatus on, and (4) selecting a mode. In step  70 , the power LED can flash as an indicator of a variety of selectable modes and/or an audible alarm mode. This embodiment includes four (4) modes available for selection. Each of these modes control both the timing of RF generation and the duty cycle of solenoid  217  during the sealing process of the tube portion received in the apparatus.  
         [0125]     Program mode is initiated when the shield  12  is off, the limit switch is activated, and the power is then turned on. If the cover or shield is removed after power up and the limit switch is triggered, the apparatus will not enter program mode.  
         [0126]     For example, one flash may correspond to a particular mode with a particular heating profile (e.g., a delay time to turn off RF generator  100  after the limit switch is activated) and a particular compression profile (e.g., a first duty cycle for cycling solenoid  217  after a full on predetermined period and a second duty cycle for cycling solenoid  217  after the limit switch is activated for another predetermined period).  
         [0127]     The user can activate the limit switch (step  68 ) by: either using start lever  33  to activate the limit switch or, otherwise, pushing in ground jaw shaft  24  or ground jaw  26  while the cover is off. While in the programming mode, the apparatus will continue to scroll through the menu of possible modes until the limit switch is deactivated at step  71 . In other words, if the limit switch remains activated (e.g., by the user retaining ground jaw shaft  24  in a closed position) then the apparatus will continue to scroll selectable modes. Upon release of ground jaw shaft  24  by the user, the limit switch will thereby be deactivated in step  71  and the mode selected by the user by deactivating the limit switch is then stored in the memory  207  as the selected mode in step  156 .  
         [0128]     The various programmed modes may determine the heating and compression profiles and/or the nature of the indicator with respect to failed and successful seals. For example, a menu of program modes can include modes configured to sound an audible alarm (e.g., a buzzer) in the event of a failed seal. Alternatively, modes can dictate a silent, visual alarm depending on the preferences of the end user.  
         [0129]     As indicated in step  155 , the mode selected by the user will correlate to a desired seal width. Generally, the longer the delay time (i.e., prior to turning off RF generator  100 ) and the larger the duty cycles of solenoid  217  (i.e., the higher the composite compression action of solenoid  217 ), the wider the seal may be. After step  155 , the programming mode is concluded at step  73 .  
         [0130]     Although in the embodiment shown includes four (4) user selectable modes, it is contemplated that any number of other user selectable modes may be implemented.  
         [0131]     Although in the embodiment shown the user selectable modes are preprogrammed (i.e., user selectable according to a scrolled menu), it is contemplated that an input device, such as a touch pad may be implemented to input setting to microcontroller  206  to set the mode according to unique requirements of the user by allowing the user to adjust any number of parameters established in a preprogrammed selectable mode or, otherwise, to establish a new mode for selection.  
         [0132]     Although exemplary embodiments of a tube sealer and method according to this invention have been described, there are others that support the spirit of the invention and are therefore within the contemplated scope of the invention. For example, although the dielectric tube sealer  8  is embodied as a tabletop unit, the jaw components of the system, and optionally the entire system, can be reconfigured as a hand-held unit to improve upon its portability. Also, the configuration of the jaws with respect to the cabinet can be modified. More specifically, although the jaws are shown to be extending outwardly from a cabinet  10  and covered by an external shield  12 , the jaws can be positioned entirely within the interior of a cabinet so long as access to the jaws can be provided for the insertion of a tube portion between them.  
         [0133]     Although the invention has been described with reference to tube sealers to illustrate exemplary features of the invention, this invention applies with equal benefit to all tube apparatus, whether such apparatus are used to seal, connect, weld, join, cut, or otherwise alter or manipulate tubing. For example, exemplary features of this invention can be applied to sterile tube welders or connection devices such as those used in blood bank or blood center applications.  
         [0134]     The foregoing is considered as illustrative only of the many possible variations in the illustrated configurations of the invention, and the foregoing recitation of variations should not be considered to be an exhaustive list. It will be appreciated, therefore, that other modifications can be made to the illustrated embodiment without departing from the scope of the invention. The scope of the invention is separately defined in the appended claims.