Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority benefit of U.S. Provisional Patent Application No. 61/841,901, entitled “METHOD AND APPARATUS FOR HIGH SPEED PLASTIC STRAPPING WELDING” filed Jul. 1, 2013, by Pavlo Barsalov, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a process and an apparatus for welding straps made of thermoplastic plastics, particularly packaging straps made of polyester or the like. 
     BACKGROUND OF THE INVENTION 
     The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions. 
     Some prior art patents are U.S. Pat. No. 3,554,846 R. J. BILLETT 1971, U.S. Pat. No. 4,247,346 Kazuo Maehara, 1978, U.S. Pat. No. 4,858,815 Derek A. Roberts, 1989; EP 1824738 B1, Steve Aemisegger, 2005, U.S. Pat. No. 8,070,039 B1, Stephen A. Johnson 2010, U.S. Pat. No. 8,181,841 B2, Stephen A. Johnson 2011, U.S. Pat. No. 8,376,210 B2, Stephen A. Johnson 2012. 
     The welding process typically involves pressing one of the two strap portions against the other strap portion, so that the two strap portions overlap one another, with a force to create pressure holding the two strap portions together. One of the two straps is rapidly moved relative to the other strap to generate friction at the area of interface between the two straps. The pressure and movement generate sufficient heat to cause the components to begin to melt. Once the two straps are melted at the point of contact, the movement of the two straps is terminated, and the two straps are allowed to cool down while under a pressure pushing the two strap portions together. As the straps cool down in this static condition, a welded joint is formed at the interface where the two strap portions contact one another. The welding process may be applied to polyester strap with 16 mm width and 1 mm thickness and breaking strength about 650 kg, for example. 
     Conventionally produced welded joints in thermoplastic straps have found wide commercial acceptance in many applications. However, the welding process of creating such joints has limitations. Referring to  FIG. 1 , one of two straps typically, lower strap  41 , is the stationary strap, is loaded with tension force P during the welding operation. The conventional welding process requires a certain period of time to melt the material in the contact area. In that period of time, portions deep within the lower strap warm up, which reduces the cool cross section and therefore dramatically lowers breaking strength of the lower portion of the strap. Consequently, most plastic strapping apparatuses do not allow the strap to be tensioned more than 35% of the breaking strength of the strap and therefore do not utilize all of the capability of this expensive strap. 
     There are known methods and apparatuses that attempt to locate the welding surfaces in a predetermined position, by for example, using a combination of (1) forces of inertia to increase stroke from zero to a maximum and (2) a spring return mechanism to return to the initial position. However, this method is not entirely satisfactory since spring mechanisms are not able to consistently and accurately provide the alignment required. Also, there are methods of using forces of inertia without a spring return mechanism, but the welding mechanism is far less reliable and stable without the spring return mechanism. 
     Also there are some devices that have a very reliable stroke adjusting mechanism, but this kind of mechanism is too heavy in weight and is expensive to produce. As a result of the weight of the very reliable stroke adjusting mechanisms, the very reliable stroke adjusting mechanisms can only be implemented in stationary strapping machines and are not suitable for a mobile, handheld, or portable strapping apparatus. 
     All of the above-described examples utilize the same idea of adjusting stroke during the rotation of the driveshaft, which is still rotating is the same direction. 
     SUMMARY OF THE INVENTION 
     In an embodiment, an improved welding joint using a large stroke and high speed welding mechanism in conjunction with a reversible welding motor is provided. 
     In an embodiment, a welding mechanism with ability of align two straps in the beginning as well as in the end of the welding operation is provided. 
     In an embodiment, a method for stopping the relative motion with the plastic straps with respect to each other is provided. 
     In an embodiment, a method for keeping the straps oriented in the same relative positions at the end of the welding operation as at the beginning is provided. 
     In an embodiment, an apparatus is provided that includes a particular eccentric mechanism including at least a welding motor, a motor bushing, an eccentric shaft. The welding motor is mounted on a frame. The motor bushing is fixedly attached to the rotor of the welding motor. One side of the eccentric shaft is pivotally mounted on the frame. The other side of the eccentric shaft is also pivotally mounted on the motor bushing. The eccentric bushing is pivotally mounted on the eccentric shaft. The eccentric bushing is connected through the bearing to that connecting rod, which moves the upper strap. The motor bushing is connected to the eccentric bushing only in the circumferential direction and is able to transmit the torque from the motor to the eccentric bushing. The eccentric shaft is mounted in such a way that the eccentric shaft is permitted to assume either of two stable positions in accordance to the eccentric bushing. In the first position, the longitudinal eccentric axis of eccentric bushing is co-axial with longitudinal rotating axis of the eccentric shaft and the combined eccentricity in the first position of the eccentric bushing and the eccentric shaft is zero or relatively low. In second position, the eccentric shaft is turned to a particular angle, which for example may be 180 degrees. In an embodiment, when the eccentric shaft is turned to this particular angle, the distance between the rotation axis of the eccentric shaft and the eccentric axis of the eccentric bushing is at a maximum, which increases the eccentricity to a relatively high value or maximizes the eccentricity. Thus, in the first position, the rotation of the motor bushing does not move the connecting rod and consequently the straps continue to be aligned. In the second position, the rotation of the motor bushing results in the maximum oscillation of the eccentric bushing that is possible for the given eccentricity of the eccentric bushing and eccentric shaft, and consequently the reciprocation applied to the upper strap has the maximum amplitude that is possible for the combination of the eccentric bushing and eccentric shaft. Accordingly rotation of the motor shaft in first direction results in a stationary position of two straps and rotation of the motor shaft in second direction (which in an embodiment is opposite to the first direction) provides reciprocation of upper strap with a maximum amplitude and therefore high speed welding process. In an alternative embodiment, in the second position, the eccentric shaft is rotated to make an angle with the eccentric bushing that is sufficient to create enough reciprocation to weld the two straps, but is not the maximum angle and does not provide the maximum amplitude of oscillation. 
     It is preferable that in the low eccentricity configuration that the eccentricity be zero. The higher the eccentricity, the more misalignment of the straps in the joint. In prior art misalignment could be zero or maximum (that is about 1.2 mm) and the degree of misalignment is unpredictable. In an embodiment the value of eccentricity is certain value close to zero, and therefore the misalignment is zero or close to zero. 
     Also, the welding method provided may use a sequence of different directions of rotation of the motor shaft: 
     Rotation of the motor shaft in first direction provides neutral gripper positioning and at the same time engages the gripper under the pressure with the upper strap aligned with the lower strap. 
     Rotation of the motor shaft in the opposite (second) direction provides high speed welding process. 
     After the welding is complete, immediate rotation of the motor shaft back to the first direction provides a neutral position of the gripper engaged with the upper strap, at the same time keeping the welded joint under the pressure. After the material in the adjacent area solidifies and the welding joint is complete, the gripper is raised, and the strap (that until now was under tension) is released from the strapping tool. Now, the gripper, the eccentric shaft and eccentric bushing are in initial their initial positions and the device is ready for a new cycle. 
     The method and apparatus for high speed plastic strapping welding are explained in more detail with reference to examples of embodiments in the description given below with reference to the drawings. Any of the above embodiments may be used alone or together with one another in any combination. Inventions encompassed within this specification may also include embodiments that are only partially mentioned or alluded to or are not mentioned or alluded to at all in this brief summary or in the abstract. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following drawings like reference numbers are used to refer to like elements. Although the following figures depict various examples of the invention, the invention is not limited to the examples depicted in the figures. 
         FIG. 1  is a view schematically illustrating a conventional strapping tool and a strap tightened about article; 
         FIG. 2 a    is a schematic representation with broken-out section of part of the friction welding apparatus of the present invention in initial position; 
         FIG. 2 b    is a cross section of the friction welding means according to the present invention; 
         FIG. 2 c    is a cross section of the friction welding means in eccentric shaft area (eccentric area) in initial position; 
         FIG. 3 a    is a schematic representation with broken-out section of part of the friction welding apparatus of the present invention in an initial position; 
         FIG. 3 b    is a schematic representation with a broken-out section of part of the friction welding apparatus of the present invention in the beginning of welding process; 
         FIG. 3 c    is a schematic representation with broken-out section of part of the friction welding apparatus of the present invention during the welding process in maximum amplitude of oscillation shown; 
         FIG. 3 d    is a schematic representation with broken-out section of part of the friction welding apparatus of the present invention at the end of the welding process when the joint solidifies; 
         FIG. 3 e    is a schematic representation with broken-out section of part of the friction welding apparatus of the present invention in initial position with lock arms locked; 
         FIG. 4 a    is a cross section of the eccentric area in an initial position; 
         FIG. 4 b    is a cross section of the eccentric area at the beginning of the welding process; 
         FIG. 4 c    is a cross section of the eccentric area during the welding process; 
         FIG. 4 d    is a cross section of the eccentric area in the end of the welding process, while the joint is solidifying; 
         FIG. 4 e    is a cross section of the eccentric area in initial position with lock arms locked; 
         FIG. 5  is an exploded view of the friction welding apparatus; 
         FIG. 6 a    is an exploded view of the main elements of the eccentric mechanism in an initial position; 
         FIG. 6 b    is a cross section view of the main elements of the eccentric mechanism in an initial position; 
         FIG. 7 a    is an exploded view of the main elements of the eccentric mechanism during the welding process in maximum amplitude of oscillation shown; 
         FIG. 7 b    is an cross section view of the main elements of the eccentric mechanism during the welding process in maximum amplitude of oscillation shown; 
         FIG. 8 a    shows the mechanism for engaging and releasing gripper, in the engaged position, pushing the gripper onto a portion of the upper strap; 
         FIG. 8 b    shows the mechanism for engaging and releasing gripper, in the release position, allowing the welding apparatus to be removed from the strap; 
         FIG. 9 a    shows a cross sectional view of the mechanism for engaging and releasing gripper, in the engage position, pushing the gripper on a portion of the upper strap (along line  8 - 8  of  FIG. 8 a   ); 
         FIG. 9 b    shows a cross sectional view of the mechanism for engaging and releasing gripper, in the release position, allowing the welding apparatus to be removed from the strap (along line  8 - 8  of  FIG. 8 b   ); 
         FIG. 10 a    shows a perspective view of the mechanism for engaging and releasing gripper, in the engaged position, pushing the gripper on a portion of the upper strap; 
         FIG. 10 b    shows a perspective view of the mechanism for engaging and releasing gripper, in the released position, allowing the welding apparatus to be removed from the strap; 
         FIG. 11 a    shows a cross sectional view of the lock mechanism in unlocked position; 
         FIG. 11 b    shows a cross sectional view of the lock mechanism in locked position; 
         FIG. 12 a    shows an isometric view of the locked mechanism in unlock position; and 
         FIG. 12 b    shows an isometric view of the locked mechanism in lock position. 
     
    
    
     DETAILED DESCRIPTION 
     Although various embodiments of the invention may have been motivated by various deficiencies with the prior art, which may be discussed or alluded to in one or more places in the specification, the embodiments of the invention do not necessarily address any of these deficiencies. In other words, different embodiments of the invention may address different deficiencies that may be discussed in the specification. Some embodiments may only partially address some deficiencies or just one deficiency that may be discussed in the specification, and some embodiments may not address any of these deficiencies. 
     Rapid heating is a solution to solve the problem of the welding process lowering the breaking point of the strap, while at the same time consumes less energy and shortens the cooling time for the welded joint. 
     In order to attain the rapid heating, a given amount of heat must be applied within a minimal time window into a segment of the two straps that is bounded to be relatively close to the welded interface. High heat may be generated with the use of high frequency reciprocation (which is an oscillatory motion). However the high frequency reciprocation is usually limited by mechanical design and is not widely used in mobile strapping apparatuses. 
     Also the rapid heating can be achieved by increasing the pressure between two straps in the welded region, the amount of pressure is usually limited for some kinds of strap, such as polypropylene (and straps made from other similar compounds) due to molecular structure of the strap. 
     Although the stroke of reciprocation can be increased, the trailing edge of the vibrated strap exposes a portion of the stationary strap as the leading edge of the vibrated strap moves beyond the corresponding edge of the stationary strap. It is desirable that the plastic straps be oriented in the same relative positions at the end of the welding operation as at the beginning. However, if an increased stroke of reciprocation is applied, more attention needs to be paid to keep the straps aligned. 
       FIG. 1  schematically illustrates a conventional strapping tool during the operation of tightening and sealing the strap overlapped about an article. Typically, all strapping tools constructed with three major components, which includes a tightening device  1 , a sealing mechanism  2 , and a base  3 . The tightening device  1  includes a feedwheel  11  pivotally mounted on the pin  12 . The feedwheel interacts through the upper strap  41  and lower strap  42 , and gripper  13 . Gripper  13  is situated in the receptacle  32  of the base  31 .  FIG. 1  schematically shows the sealing mechanism  2  represented by upper gripper  21  and lower gripper  22  situated in the receptacle  33  of base  31  and a cutter  23  intended to cut free end  43  of the strap  4 . 
     During the tensioning process the gripper  13  holds the lower portion  42  of the strap  4  overlapped about the article  5 . Rotation of the feedwheel  11  causes tightening of the upper portion  41  of strap  4  therefore the lower portion  42  of the strap  4  is loaded with full amount of tension force P. 
       FIGS. 2 a -7 b    include the following components, welding motor  200 , a frame  201 , motor bushing  202 , motor shaft  203 , bearing  205 , bearing  206 , eccentric bushing  207 , bearing  208 , connecting rod  209 , pin  210 , vertical link  211 , pin  212 , gripper  213 , upper link  214 , pin  215 , pin  216 , main spring  217 , lock spring  220 , pin  221 , lock arm  222 , lock bracket  223 , clutch  224 , pin  225 , set screw  226 , eccentric axis  231 , eccentric shaft  240 , longitudinal rotation axis  241 , and longitudinal eccentric axis  242 . 
     Referring to  FIGS. 2 a  and 2 b   , the welding apparatus may include a welding motor  200  mounted on a frame  201 . The welding apparatus may also include a motor bushing  202  fixedly attached to the rotor  203  of the welding motor  200 . An eccentric shaft  240  is pivotally mounted on the frame  201  through the bearing  205  from one side (which is the left side of  FIG. 2 b   ). On the other side of the eccentric shaft  240  (which is towards the right side of  FIG. 2 b   ), the eccentric shaft  240  is pivotally mounted on the motor bushing  202  through the bearing  206 . Eccentric bushing  207  is pivotally mounted on the eccentric shaft  240 . The eccentric bushing  207  is connected through the bearing  208  to connecting rod  209 . Connecting rod  209  moves the upper strap through pin  210 , vertical link  211 , pin  212  and gripper  213 . The upper link  214  is pivotally mounted on the frame  201  through pin  215 , and the upper link  214  bears the vertical link  211  through pin  216  (see the right side of  FIG. 2 a   ). The upper link  214 , from another side (which is on the left side of  FIG. 2 a   ), is pressed against main spring  217 . 
     The apparatus shown in  FIG. 2 a    additionally has a lock constructed of lock spring  220 , pin  221 , lock arm  222 , and lock bracket  223 . Pin  221  rests on upper link  214 . The lock bracket  223  is connected to the lock arm  222  through pin  225  and to the eccentric shaft  204  through one way clutch  224 . The one way clutch  224  transmits a torque in a clockwise direction, when eccentric shaft  204  rotates. The one way clutch  224  transmits a torque in a counter clockwise direction, when lock bracket  223  rotates counter clockwise and permits rotation of the eccentric shaft  204  in counter clockwise direction. 
     The eccentric bushing  207  is pivoted about longitudinal eccentric axis  242  of the eccentric shaft  240 . So the longitudinal eccentric axis  242  of the eccentric shaft  240  is always co-axial with longitudinal rotation axis  230  of the eccentric bushing  207 . Consequently, when eccentric shaft  240  is in the position of  FIG. 4 a   , longitudinal rotation axis  241  of eccentric shaft  240  is co-axial with longitudinal eccentric axis  231  of the eccentric bushing  207 . When eccentric shaft is changing positions, eccentric bushing  207  rotates about eccentric axis  242  of the eccentric shaft  240 , so that after rotation 180 degrees, longitudinal rotation axis  241  of the eccentric shaft  240  is at maximum distance from longitudinal eccentric axis  231  of the eccentric bushing  207  causing longitudinal eccentric axis  231  of the eccentric bushing  207  to orbit as the motor turns motor bushing  202  about longitudinal rotation axis  241  of the eccentric shaft  240 . The orbiting of longitudinal eccentric axis  231  about longitudinal rotation axis  241  creates the oscillatory motion of eccentric bushing  207 , which is translated to gripper  213 . 
     Referring next to  FIG. 2 c   , the longitudinal rotation axis  241  of eccentric shaft  240  is co-axial with motor bushing  202 . The longitudinal eccentric axis  242  of eccentric shaft  240  is co-axial with longitudinal rotation axis  230  of eccentric bushing  207 . At the same time, longitudinal eccentric axis  231  of eccentric bushing  207  is concentric to the bearing  208  and therefore connecting rod  209 . The motor bushing  202  is connected to the eccentric bushing  207  only in the circumferential direction and is able to transmit the torque from the motor  200  to the eccentric bushing  207 . The eccentric shaft  240  is mounted in such a way that eccentric shaft  240  is permitted to assume either of two positions, in accordance to the eccentric bushing  207 . In first position ( FIG. 2 c   ), the longitudinal eccentric axis  231  of eccentric bushing  207  is co-axial with longitudinal rotation axis  241  of eccentric shaft  240 . In the configuration of  FIG. 2 c   , the combined eccentricity of eccentric bushing  207  and eccentric shaft  240  is minimal or zero, if the value of eccentricity for eccentric shaft  240  and eccentric bushing  207  are equal. In second position, the eccentric shaft  240  is turned to a particular angle, which may be 180 degrees from the initial orientation of the eccentric shaft, for example. Depending on the eccentric bushing  207  (as shown in  FIG. 4 c   ), after turning the eccentric shaft 180 degrees, the distance between the longitudinal rotation axis  241  and longitudinal eccentric axis  231  is maximized. Therefore, in the first position, the rotation of the motor bushing  202  does not move the connecting rod  209 . Since connecting rod  209  does not move in the first position, straps  41  and  42  remain aligned in neutral position. In the second position, the rotation of the motor bushing  202  causes a maximum amount of oscillation of the eccentric bushing  207 . As a result of the oscillation, the reciprocation applied to the upper strap with maximum amount of amplitude. Accordingly, the rotation of the motor shaft  203  in a first direction results in the two straps being held in fixed stationary neutral position and do not move with respect to one another. Rotation of the motor shaft  203  in the second direction (opposite to the first direction) causes reciprocation that is applied to upper strap  41  with maximum amplitude and therefore create sufficient heat to provide a high speed welding process. 
     The above described example of embodiment utilizes a method of operation according to this invention as follows: 
     After the strap  4  has been placed around the article  5 , and after the strap ends  41  and  42  have been inserted in the strapping tool, the strap is tensioned to a desired tension force, by tightening device with the gripper  213  in a raised position. After tensioning with the gripper in the raised position, the welding apparatus is in the position illustrated in  FIG. 3 a   . Lock arm  222  and lock bracket  223  are pressed by lock spring  220  in a counterclockwise direction, and form the lock. When lock arm  222  and lock bracket  223  are pressed by lock spring  220  in a counterclockwise direction, lock arm  222  and lock bracket  223  hold upper link  214  and therefore gripper  213  in raised position. When in the locked position, with gripper  213  raised, the eccentric shaft  240  is in the position illustrated in  FIG. 4 a    so that the eccentricity of the eccentric mechanism is zero. 
     In order to weld the strap ends  41  and  42 , the operation mode begins by turning the motor shaft  203  clockwise (first direction). As a result, the motor shaft  203  turns the lock bracket  223  through the motor bushing  202 , eccentric bushing  207 , eccentric shaft  240  and one way clutch  224 . The movement of the lock bracket  223  overcomes the torque of lock spring  220 , and causes the lock arm  222  to swivel in a clockwise direction. 
     The swivel of lock arm  222  produces the following effects: 
     The eccentric mechanism is placed into a neutral position. Having the eccentric mechanism in the neutral position ensures that gripper  213  is in a neutral position. 
     The lock is unlocked, and the upper link  214  is allowed to move clockwise. Moving the upper link  214  clockwise brings the gripper  213  in contact with upper strap  41  under the pressure of main spring  217  ( FIGS. 3 b  and 4 b   ). 
     After the gripper  213  is in contact with upper strap  41 , the welding process begins by turning motor shaft  203  counter clockwise (second direction) ( FIG. 3 c   ), which in turn puts eccentric shaft  240  in position illustrated in  FIG. 4 c    and therefore sets gripper in motion. Thus, welding process occurs with maximum amplitude of oscillation. 
     After welding is complete, but while the material in welded area is still soft, the motor shaft  203  immediately turns backward in the opposite direction, which is clockwise (first direction) (in  FIG. 3 d   ). Turning the motor shaft backwards—in first direction—causes the gripper  213  to be in a neutral position (as illustrated in  FIG. 4 d   ) in which gripper  213  is engaged with the upper strap. Placing gripper  213  so that gripper  213  is engaged with the upper strap  41  in neutral position sets the vertical alignment of upper strap  41  and lower strap  42  as the vertical alignment was in the beginning of the welding process. The welded joint is allowed to cool down under the pressure of gripper  213  until material in the joint area solidifies. 
     In order to free the strap  4 , gripper  213  rises up, upper link  214  swivels counter clockwise pressing down the main spring  217  until lock arm  222  (under the torque of the lock spring  220 ) moves to the locked position shown in  FIGS. 3 e  and 4 e   , which is the initial position. An operator can now remove the strap and the strapping tool is ready for a new cycle. 
       FIGS. 8 a  and 8 b    show the mechanism for engaging and releasing gripper  213 , in two positions. In  FIG. 8 a    the position of the mechanism corresponds with  FIG. 3 b    (and  3   d ). This is initial position for lifting the gripper  213  and compressing the spring  217 . In  FIG. 8 b    the position of the mechanism corresponds with  FIG. 2 a    (and  3   a ). An operator lifts the handle  14  and lever  15  moving up raises the right portion of the upper link  214  compressing the spring  217  by the left portion of upper link  214 . 
       FIG. 9 a    shows a cross sectional view of the mechanism for engaging and releasing gripper, in the engage position, pushing the gripper on a portion of the upper strap (along line  8 - 8  of  FIG. 8 a   ); 
       FIG. 9 b    shows a cross sectional view (along line  8 - 8  of  FIG. 8 b   ) of the mechanism for engaging and releasing the gripper, in the release position, allowing the welding apparatus to be removed from the strap.  FIG. 10 a    shows a perspective view of the mechanism for engaging and releasing gripper, in the engaged position, pushing the gripper on a portion of the upper strap.  FIG. 10 b    shows a perspective view of the mechanism for engaging and releasing gripper, in the released position, allowing the welding apparatus to be removed from the strap.  FIG. 11 a    shows a cross sectional view of the lock mechanism in unlocked position.  FIG. 11 b    shows a cross sectional view of the lock mechanism in locked position.  FIG. 12 a    shows an isometric view of the lock mechanism in an unlocked position.  FIG. 12 b    shows an isometric view of the lock mechanism in locked position. 
     It can be seen from the description above that using the high speed welding method and the welding apparatus of  FIGS. 2 a -11 b    gives numerous advantages including lower energy consumption by the welding process, which in turn, enables usage of lighter and cheaper batteries, and shortens cooling time of the welding joint thereby increasing productivity of the strapping tool. Also, as a result of having a shallower adjacent area of the welding joint that is heated, the threshold level of the strap tension increases, which allows a fuller utilization of the strap properties. Further, having a shallower area that is heated, enables usage of a narrower strap (as compared to were a deeper heating process used), without breaking. As a result of being able to use narrower or thinner straps, the entire packaging process is more economical and energy efficient. Also, in experiments applying the method to a polyester strap with 16 mm width and 1 mm thickness and breaking strength about 650 kg, the straps welding joint has up to a 95% of the breaking strength of the strap (compared to up to 80% in conventional tools), which in turn makes the packaging process more reliable. 
     This invention is not restricted to the embodiments that have been described and illustrated. Rather, numerous changes and additions are possible without departing from the scope of the invention. 
     Each embodiment disclosed herein may be used or otherwise combined with any of the other embodiments disclosed. Any element of any embodiment may be used in any embodiment. 
     Although the invention has been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, modifications may be made without departing from the essential teachings of the invention.

Technology Category: 7