Patent Publication Number: US-8974020-B2

Title: Device for adjusting gap between platen and print head and inkjet printer using the device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 101126800, filed on Jul. 25, 2012. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention generally relates to a device for adjusting gap between platen and print head, and more particularly, to a device for adjusting gap between platen and print head which is able to adjust the distance between a print head and a platen. 
     2. Description of Related Art 
     Currently, before shipping out inkjet printers, it is required to appropriately adjust and calibrate them by staff, so that the distance between the print head (cartridge) of each inkjet printer and the platen helping the paper to be printed passing through can be kept within a specific range. However after shipping the printer, the thicknesses of the paper to be printed are different in the application practice, so that the distance between the print head and the platen is varied somehow. The above-mentioned distance is important to affect the printing resolution. In short, for a same printer, due to the different thickness of the paper to be printed, the printing quality on the printed paper would be affected. 
     In addition, the tolerance in the manufacture and the assembling of the components and sub-assemblies of the aforementioned inkjet printer may cause the distance between the print head and the paper to be printed varied, which also affects the printing quality so that a solution to overcome the above-mentioned problem is demanded. 
     SUMMARY OF THE INVENTION 
     Accordingly, the invention is directed to a device for adjusting gap between platen and print head configured to adjust the distance between the print head and the platen. 
     The invention is also directed to an inkjet printer using the above-mentioned device for adjusting gap between print head and platen. 
     The invention provides a device for adjusting gap between platen and print head, which includes a base, a printing unit, a platen and a pair of adjusting elements. The printing unit is located on the base and includes a print head. The platen is located between the printing unit and the base, in which the platen has a platen-portion and a pair of adjusting-portions, the adjusting-portions are disposed at opposite sides of the platen-portion, and each of the adjusting-portions has a step-guiding-surface. The adjusting elements are disposed beside the platen and correspondingly contact the step-guiding-surfaces of the adjusting-portions, in which the distance between the platen and the print head is varied with positions of the adjusting elements relative to the step-guiding-surfaces. 
     The invention also provides an inkjet printer, which includes a host and the above-mentioned device for adjusting gap between platen and print head, in which the host has a casing and the device for adjusting gap between platen and print head is disposed in the casing. The casing has the above-mentioned base and at least one of adjusting elements are exposed out of the casing. 
     Based on the description above, in the device for adjusting gap between platen and print head and the inkjet printer using the device of the invention, the adjusting elements are used to adjust the distance between the platen and the print head. Therefore, regardless thickness of the paper to be printed used by a terminal user, the distance between the paper sheet and the print head can be appropriately adjusted by the user to reach a good printing effect. 
     Other objectives, features and advantages of the present invention will be further understood from the further technological features disclosed by the embodiments of the present invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an inkjet printer according to the first embodiment of the invention. 
         FIG. 2  is a top-view diagram of the device for adjusting gap between platen and print head in the inkjet printer of  FIG. 1 . 
         FIGS. 3-5  are diagrams showing paper sheets are placed on the platen and the leaning-portion of the adjusting element leans against different step treading surfaces of a step-guiding-surface. 
         FIG. 6  is a schematic diagram shown a layout to enable a plurality of leaning-portions simultaneously acting. 
         FIGS. 7 and 8  are schematic diagrams of a device for adjusting gap between platen and print head according to the second embodiment of the invention. 
         FIG. 9  is a schematic diagram of a device for adjusting gap between platen and print head according to the third embodiment of the invention. 
         FIG. 10  is a schematic diagram of a device for adjusting gap between platen and print head according to the fourth embodiment of the invention. 
         FIG. 11  is a schematic diagram of a device for adjusting gap between platen and print head according to the fifth embodiment of the invention. 
         FIG. 12  is a schematic diagram of a device for adjusting gap between platen and print head according to the sixth embodiment of the invention. 
         FIG. 13  is a schematic diagram of a device for adjusting gap between platen and print head according to the seventh embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In general speaking, the printing resolution of every inkjet printer before shipping out from the manufactures has been roughly set, and the conventional inkjet printer today usually has a program for controlling the ink-throughput of the print head against different paper sheets so as to calibrate the printing quality. In comparison with the conventional inkjet printer, the scheme of the invention rests in that the distance between the platen and the print head is adjustable by a mechanism to optimize the printing quality. 
     In order to make the aforementioned and other features and advantages of the invention comprehensible, several exemplary embodiments accompanied with figures are described in detail below. 
     In addition, in the following, the depicted embodiments together with the included drawings are intended to explain the feasibility of the invention, wherein a same notation or a similar notation is for marking the same or the similar portions. Note that some of expression words hereinafter regarding direction or orientation, such as ‘up’, ‘down’, ‘left’, ‘right’, ‘above’, ‘below’, ‘towards left’, ‘towards right’ and the like, are to describe the relative positions, not to limit, the invention. 
     The First Embodiment 
       FIG. 1  is a schematic diagram of an inkjet printer according to the first embodiment of the invention and  FIG. 2  is a top-view diagram of the device for adjusting gap between platen and print head in the inkjet printer of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , an inkjet printer  100  of the embodiment includes a host  110  and a device  120  for adjusting gap between platen and print head, in which the device  120  for adjusting gap between platen and print head is installed in the casing (not marked) of the host  110  and the casing has the casing has a bottom-portion and a plurality of sidewalls vertically connecting the bottom-portion. 
     The device  120  for adjusting gap between platen and print head includes a base  122 , a printing unit  124 , a platen  126 , a pair of elastic elements  127  and a pair of adjusting elements  128 . The base  122  is the bottom-portion of the above-mentioned casing, and the printing unit  124  is located on the base  122  and includes a print head  124   a . The platen  126  is located between the inkjet unit  124  and the base  122  and has a platen-portion  126   a  and a pair of adjusting-portions  126   b . The adjusting-portions  126   b  are disposed at opposite sides of the platen-portion  126   a  and each of the adjusting-portions  126   b  has a step-guiding-surface  126   c . The elastic elements  127  are connected between the platen  126  and the base  122 , while the adjusting elements  128  are disposed beside the platen  126  and correspondingly contact the step-guiding-surfaces  126   c  of the adjusting-portions  126   b , in which the distance between the platen  126  and the print head  124   a  is varied with the positions of the adjusting elements  128  relative to the step-guiding-surfaces  126   c.    
     The above-mentioned distance d 1  between the platen  126  and the print head  124   a  means the distance d 1  between the surface  126   g  of the platen  126  facing the print head  124   a  and the nozzle  124   b  of the print head  124   a , not the distance d 2  between the tops (not marked) facing the print head  124   a  of the carry elements  129  disposed on the platen  126  and protruded from the surface  126   g  of the platen  126  and the nozzle  124   b  of the print head  124   a.    
     The printing unit  124  includes a shaft rod  124   c  and the above-mentioned print head  124   a , in which the shaft rod  124   c  is located on the platen  126 , and the print head  124   a  is pivoted on the shaft rod  124   c  and adapted to move along the axis direction A of the shaft rod  124   c . In addition, the elastic elements  127  of the embodiment are tension springs, the step-guiding-surfaces  126   c  face the base  122  and the steps-segment directions of the step-guiding-surfaces  126   c  located at both opposite sides of the platen  126  are opposite to each other. 
     It should be noted that the above-mentioned steps-segment means a plurality of treading surfaces  126   d ,  126   e  and  126   f  and guiding kick-off surfaces  126   h  of the step-guiding-surface  126   c , in which the treading surfaces  126   d ,  126   e  and  126   f  are parallel to the axis direction A of the shaft rod  124   c  and the guiding kick-off surfaces  126   h  have an angle towards the axis direction A and are connected between the treading surfaces  126   d  and  126   e  or between the treading surfaces  126   e  and  126   f . In the embodiment, the step-guiding-surface  126   c  has two guiding kick-off surfaces  126   h  and three treading surfaces  126   d ,  126   e  and  126   f , thus it is a 3-steps steps-segment. The steps-segment directions of the step-guiding-surfaces  126   c  located at both opposite sides of the platen  126  are opposite to each other, which means the closer to the platen  126  (i.e., the steps-segment faces down), the closer to the base  122  the treading surfaces of the step-guiding-surfaces  126   c  are. 
     At least one of the adjusting elements  128  has a push-button  128   a , each of the adjusting elements  128  has a leaning-portion  128   b , the push-button  128   a  is connected to the corresponding leaning-portion  128   b , the above-mentioned adjusting-portion  126   b  correspondingly leans against one of the treading surfaces  126   d ,  126   e  and  126   f  of the step-guiding-surface  126   c  of the adjusting-portion  126   b , and the treading surfaces  126   d ,  126   e  and  126   f  of the two adjusting-portions  126   b  leant by the two leaning-portions  128   b  respectively belong to the same step. In other words, the two leaning-portions  128   b  would simultaneously lean against the two treading surfaces  126   d . For operation convenience, the push-button  128   a  is exposed out of the host  110 . 
     It should be noted that in order to allow the leaning-portion  128   b  smoothly moving relative to the step-guiding-surface  126   c , the guiding kick-off surface  126   h  of the step-guiding-surface  126   c  has an angle towards the axis direction A and is connected between the two treading surfaces  126   d  and  126   e  or between the treading surfaces  126   e  and  126   f , so that while the leaning-portion  128   b  is approaching towards the direction relatively close to the platen-portion  126   a , the guiding inclined surfaces  128   c  of the leaning-portions  128   b  and the guiding kick-off surfaces  126   h  of the step-guiding-surface  126   c  would be guided by each other to help the leaning-portions  128   b  smoothly arriving at the next-step treading surface. 
       FIGS. 3-5  are diagrams showing paper sheets are placed on the platen and the leaning-portion of the adjusting element leans against different step treading surfaces of a step-guiding-surface. For simplicity and description convenience, the casing of the host  110  in  FIGS. 3-5  is omitted; instead, only the base  122  is directly illustrated. Referring to  FIG. 3 , in the embodiment, the leaning-portions  128   b  of the two adjusting elements  128  lean against two first-step treading surfaces  126   f  of the two step-guiding-surfaces  126   c  outmost relative to the platen  126 . In comparison with the other layout where the leaning-portions  128   b  of the adjusting elements  128  lean against the other treading surfaces  126   d  and  126   e  of the step-guiding-surface  126   c , in the embodiment, the leaning-portions  128   b  of the two adjusting elements  128  lean against the treading surfaces  126   f  of the two step-guiding-surface  126   c  outmost relative to the platen-portion  126   a  of the platen  126  so that the distance between the surface  126   g  of the platen  126  and the print head  124   a  is the maximal. 
     During printing of the inkjet printer  100 , the paper sheet P enters onto the platen  126  of the device  120  for adjusting gap between the platen  126  and print head  124   a  through a paper-feeding procedure and stays at the printing position. At the time, there is a paper-printhead space (PPS) between the print head  124   a  of the printing unit  124  and the paper sheet P. Since the paper sheet P is carried by the carry element  129  disposed on the platen  126 , the PPS between the paper sheet P and the print head  124   a  is less than the distance d 1  between the platen  126  and the print head  124   a.    
     Once the thickness of the paper sheet P conforms to the suggested thickness of the paper sheet P by the inkjet printer  100 , there is no need to adjust the distance d 1  between the platen  126  and the print head  124   a  for obtaining the optimum printing quality. 
     However, if the thickness of the paper sheet P to be printed is less than the suggested thickness of the paper sheet P by the inkjet printer  100 , the terminal user can push the push-button  128   a  with the finger to make the leaning-portions  128   b  move towards the platen-portion  126   a  so as to lean against the second-step treading surfaces  126   e  of the step-guiding-surfaces  126   c . At the time, the platen  126  is lifted relative to the base  122  and the elastic elements  127  produce a pre-stored elastic resuming force, as shown by  FIG. 4 . 
     In  FIG. 4 , the distance d 3  between the platen  126  and the print head  124   a  is less than the distance d 1  between the platen  126  and the print head  124   a  in  FIG. 3 . Thus, without adjusting the printing resolution by a program, although the thickness of the paper sheet P to be printed is less than the suggested thickness of the paper sheet P by the inkjet printer  100 , but the distance between the paper sheet P and the print head  124   a  gets smaller as well, so that the printing quality still is good. At the time, if the program is used to adjust the printing resolution (i.e., the ink throughput of the print head  124   a ), the printing quality would be better. 
     The user can further push the two adjusting elements  128  so that the leaning-portions  128   b  of the two adjusting elements  128  lean against the third-step treading surfaces  126   f  of the step-guiding-surfaces  126   c , so that the distance between the paper sheet P (shown by  FIG. 3 ) and the print head  124   a  gets the smallest. 
     It is clear, when the height of the carry element  129  relative to the surface  126   g  of the platen  126  and the height of the printing unit  124  keep unchanged, people skilled in the art should be aware of that when the distance d 1  between the platen  126  and the nozzle  124   b  of the print head  124   a  is adjusted and varied, the PPS between the paper sheet P carried on the platen  126  and the print head  124   a  would be accordingly varied, which can effectively control the printing quality. 
     Although in the embodiment, the above-mentioned description is against the example that the terminal user uses the finger to manually move the push-buttons  128   a  of the adjusting elements  128  to change the distance between the platen  126  and the print head  124   a , but any one skilled in the art can also change the push-button  128   a  into a press-button according to the demand so that the terminal user can manually press the press-button to start the program to control and adjust the distance between the platen  126  and the print head  124   a . The designer can also use a sensor (not shown) disposed in the casing of the host  110 , so that the sensor can automatically detect the thickness of the paper to decide whether or not adjusting the distance between the platen  126  and the print head  124   a . The time for adjusting the distance between the platen  126  and the print head  124   a  is determined by the design or the real application. For example, the paper thicknesses of various brands are normally marked on the package, so that the user can adjust the distance between the platen  126  and the print head  124   a  prior to printing according to the known information; or it is decided during printing to adjust the distance between the platen  126  and the print head  124   a  according to the thickness detection result of the sensor. 
       FIG. 6  is a schematic diagram shown a layout to enable a plurality of leaning-portions of the adjusting elements simultaneously acting. Referring to  FIG. 6 , the adjusting elements  128  in the embodiment move the leaning-portions  128   b  by the user to push the push-button  128   a , in which since only one of the adjusting elements  128  has the push-button  128   a , when the user pushes the push-button  128   a , the two leaning-portions  128   b  must simultaneously act to approach to the platen-portion  126   a  (shown by  FIG. 1 ). To make the two leaning-portions  128   b  simultaneously act in the embodiment, two racks  132  and  134  and a gear  140  are used, in which the push-button  128   a  is connected to the rack  132  and each of the racks  132  and  134  has a leaning-portion  128   b  and the racks  132  and  134  are engaged with the gear  140 . In the above-mentioned layout, when the user pushes the push-button  128   a , the leaning-portion  128   b  disposed on the same rack  132  as the push-button  128   a  would approach to the gear  140  and, together with the rack  132  connected to the push-button  128   a , simultaneously drives the gear  140  for rotation, which further brings the leaning-portion  128   b  of another rack  134  engaged with the gear  140  to approach to the gear  140 . In short, at the time, the two leaning-portions  128   b  are closed to each other. It is certainly to make the two adjusting elements  128  individually have a push-button  128   a  and the two adjusting elements  128  are subsequently pushed during adjusting the distance between the platen  126  and the print head  124   a , in which the adjusting elements  128  can be pushed manually by the user or by program control. 
     It can be seen the two adjusting elements  128  can move subsequently or simultaneously, and both can achieve the same goal. 
     To make the distance between the platen  126  and the print head  124   a  of the inkjet printer  100  larger than the distance of the previous state, the push-button  128   a  is pushed reversely to further move the leaning-portions  128   b . At the time, the pre-stored elastic resuming forces of the elastic elements  127  make the platen  126  close to the base  122 , which can adjust the distance between the platen  126  and the print head  124   a  to be larger than before. 
     Although the gap in the embodiment gets adjusted by a three-steps segment design composed of two guiding kick-off surfaces and three treading surfaces as an example, but people skilled in the art can also use multi segments design to adjust the gap in response to different thicknesses of the paper sheet P. For example, the more the number of the treading surfaces, the more the number of the adjustable segments of the gap is. 
     The Second Embodiment 
     The embodiment is basically the same as the first embodiment, and a same notation or a similar notation is for marking the same or the similar portions, in which the same content is omitted for simplicity. 
       FIGS. 7 and 8  are schematic diagrams of a device  120  for adjusting gap between a platen  126  and a print head  124   a  according to the second embodiment of the invention, in which the leaning-portions  128   b  in  FIGS. 7 and 8  are respectively located on different treading surfaces. Referring to  FIGS. 7 and 8 , in the embodiment, the steps-segment directions of the two step-guiding-surfaces  126   c  at opposite sides of the platen-portion  126   a  of the platen  126  are the same. 
     The same steps-segment directions of the two step-guiding-surfaces  126   c  at opposite sides of the platen-portion  126   a  of the platen  126  herein mean the treading surfaces of the two step-guiding-surfaces  126   c  at the two sides of the platen-portion  126   a  are more closed to the base  122  towards the right direction of the shaft rod  124   c , while the treading surfaces are more far away from the base  122  towards the left direction of the shaft rod  124   c.    
     It can be seen from  FIGS. 7 and 8  that when the leaning-portions  128   b  are located on the third-step treading surfaces  126   d  (shown by  FIG. 7 ), the distance between the platen  126  and the base  122  is larger so that the distance between the platen  126  and the print head  124   a  is smaller. When the leaning-portions  128   b  are located on the first-step treading surfaces  126   c  (shown by  FIG. 8 ), the distance between the platen  126  and the base  122  is smaller so that the distance between the platen  126  and the print head  124   a  is larger. It can be seen from  FIGS. 7 and 8  that when the leaning-portions  128   b  lean against different treading surfaces, the height of the platen  126  relative to the base  122  is different and, by using the feature, the distance between the platen  126  and the print head  124   a  can be adjusted. 
     The Third Embodiment 
     The embodiment is basically the same as the first and second embodiments, and a same notation or a similar notation is for marking the same or the similar portions, in which the same content is omitted for simplicity 
       FIG. 9  is a schematic diagram of a device  120  for adjusting gap between platen  126  and print head  124   a  according to the third embodiment of the invention. Referring to  FIG. 9 , in the embodiment, the elastic elements  127  are compression springs, the step-guiding-surfaces  126   c  face the printing unit  124  and the steps-segment directions of the two step-guiding-surfaces  126   c  at opposite sides of the platen-portion  126   a  of the platen  126  are opposite to each other, which means the more close to the platen-portion  126   a  of the platen  126 , the more far away from the base  122  the treading surfaces of the step treading surfaces  126   c  are. 
     Continuing to  FIG. 9 , the leaning-portions  128   b  lean against the step-guiding-surfaces  126   c  from the position above the step-guiding-surfaces  126   c  and, along the leaning-portions  128   b  approach to and lean against onto the second-step treading surfaces  126   e  from the first-step treading surfaces  126   d  of the step-guiding-surfaces  126   c , the platen  126  would be relatively closed to the base  122  (i.e., the platen  126  is more far away from the print head  124   a ), and at the time, the compression springs produce pre-stored elastic resuming forces. The more far away from the base  122  the treading surfaces are which the leaning-portion  128   b  lean against, the larger the pre-stored elastic resuming forces of the compression springs are. 
     It can be seen from the description above that the distance between the platen  126  and the print head  124   a  can be selected by multiple segments depending on the different steps of the treading surfaces which the leaning-portion  128   b  lean against, and the gaps can be adjusted according to the thickness of the paper sheet P. 
     The Fourth Embodiment 
     The embodiment is basically the same as the third embodiment, and a same notation or a similar notation is for marking the same or the similar portions, in which the same content is omitted for simplicity. 
       FIG. 10  is a schematic diagram of a device for adjusting gap between platen and print head according to the fourth embodiment of the invention. Referring to  FIG. 10 , in the embodiment, the steps-segment directions of the two step-guiding-surfaces  126   c  at opposite sides of the platen  126  are the same. The same steps-segment directions of the two step-guiding-surfaces  126   c  at opposite sides of the platen  126  herein mean the treading surfaces of the two step-guiding-surfaces  126   c  at the two sides of the platen-portion  126   a  are more close to the base  122  towards the right direction of the shaft rod  124   c , while the treading surfaces are more far away from the base  122  towards the left direction of the shaft rod  124   c    
     The Fifth Embodiment 
     The embodiment is basically the same as the above-mentioned four embodiments, and a same notation or a similar notation is for marking the same or the similar portions, in which the same content is omitted for simplicity. 
       FIG. 11  is a schematic diagram of a device for adjusting gap between platen and print head according to the fifth embodiment of the invention. Referring to  FIG. 11 , in the embodiment, there is further a body  125  between the two adjusting elements  128  and the body  125  is connected between the two leaning-portions  128   b . The body  125  can be connected between the two leaning-portions  128   b  in different ways of crossing the sides and the upper side of the platen  126  or crossing the sides and the lower side of the platen  126  according to the real demand of the elements of the inkjet printer  100 . In the embodiment, the push-button  128   a , the leaning-portions  128   b  and the body  125  can be integrally formed or assembled together, which the invention is not limited to. 
     In more details, the body  125  is used to connect the two adjusting elements  128  together to form a structure similar to a frame. In this way, only one push-button  128   a  enable to make the two adjusting elements  128  simultaneously act when the user pushes the push-button  128   a . In addition, the leaning-portions  128   b  lean against the step-guiding-surfaces  126   c  from the position below the adjusting-portion  126   b  so that the platen  126  is supported by the frame structure so as to save the elastic elements  127 . 
     The Sixth Embodiment 
     The embodiment is basically the same as the above-mentioned five embodiments, and a same notation or a similar notation is for marking the same or the similar portions, in which the same content is omitted for simplicity. 
       FIG. 12  is a schematic diagram of a device for adjusting gap between platen and print head according to the sixth embodiment of the invention. Referring to  FIG. 12 , in the embodiment, no elastic element is used to help adjusting the distance between the platen  126  and the print head  124   a  (shown by  FIG. 10 ). Instead, a magnet  152  is used and disposed on the surface (not shown) of the platen  126  facing the base  122 . Meanwhile, another magnet  154  is disposed on the surface (not shown) of the base  122  facing the platen  126 , in which the magnets  152  and  154  with corresponding positions are attractive by each other. 
     The Seventh Embodiment 
     The embodiment is basically the same as the sixth embodiment, and a same notation or a similar notation is for marking the same or the similar portions, in which the same content is omitted for simplicity. 
       FIG. 13  is a schematic diagram of a device for adjusting gap between platen and print head according to the seventh embodiment of the invention. Referring to  FIG. 13 , in the embodiment, no elastic element is used to help adjusting the distance between the platen  126  and the print head  124   a  (shown by  FIG. 10 ). Instead, a magnet  152  is used and disposed on the surface (not labelled) of the platen  126  facing the base  122 . Meanwhile, another magnet  154  is disposed on the surface (not labelled) of the base  122  facing the platen  126 , in which the magnets  152  and  154  with corresponding positions are attractive to each other. 
     In summary, in the device for adjusting gap between platen and print head and the inkjet printer using the device for adjusting gap between platen and print head of the invention, the adjusting elements in association with adjusting-portions of the platen are used to adjust the distance between the platen and the print head by the terminal user in response to the different thicknesses of the paper. Therefore, regardless thickness of the paper, a good printing quality is achieved. In short, the terminal user can independently adjust the inkjet printer to the optimum printing mode against different thicknesses of paper. 
     In addition, the unavoidable fabrication and assembling tolerances of the parts make the real distance between the nozzle of the print head and the platen varied, which further affects the distance between the nozzle and the paper sheet to be printed. However, by using the device for adjusting gap between platen and print head of the invention, the calibration stuff can adjust the distance between the nozzle of the print head and the platen to the predetermined value before shipping out from the manufactures. In comparison with the prior art where the distance between the nozzle of the print head and the platen in the printer is fixed so that the negative affecting of the varied distance between the nozzle of the print head and the platen caused by the tolerances of the components and sub-assemblies are unable reduced by the adjustment. In addition, the device for adjusting gap between platen and print head and the inkjet printer using the device for adjusting gap between platen and print head of the invention further have calibration convenience before the shipping out. 
     It will be apparent to those skilled in the art that the descriptions above are several preferred embodiments of the invention only, which does not limit the implementing range of the invention. Various modifications and variations can be made to the structure of the invention without departing from the scope or spirit of the invention. The claim scope of the invention is defined by the claims hereinafter.