Abstract:
An electronic device that is driven by a battery and is capable of being attached to a power feeding device that feeds power to the electronic device, including: a surface opposite to the power feeding device when the electronic device is attached to the power feeding device; an electrode provided on the surface; and any one of a groove and a projection provided on the surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2015-051397 filed on Mar. 13, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    A certain aspect of the embodiments is related to an electronic device, a power feeding device and an electronic device system. 
       BACKGROUND 
       [0003]    Various electronic devices driven by batteries are used widely. A portable printer which is used to print a receipt and a check at a desired place is known as an example of such an electronic device. In addition, many portable information processing devices such as so-called hand held terminals are used. 
         [0004]    In these electronic devices, there are many devices equipped with charge-type batteries. To charge the battery of the electronic device, the electronic device is connected to a charging apparatus (i.e., a battery charger) which functions as a power feeding device. The electronic device can be seen as a device to be charged, and includes a charging electrode. On the other hand, a terminal that contacts the electrode of the electronic device is provided in the battery charger. 
         [0005]    A battery charger called a cradle is known as an example of the battery charger (see Japanese National Publication of International Patent Application No. 2014-521305). When the electronic device is charged, the electronic device is put on the cradle. Thereby, the electrode of the electronic device contacts the terminal provided in the cradle, and the charge to the electronic device is started. 
         [0006]    Here, the cradle is not necessarily used for a charge function. A cradle having a data transmission function between the cradle (or other electronic device to which the cradle is connected) and the electronic device exists. 
       SUMMARY 
       [0007]    According to a first aspect of the present invention, there is provided an electronic device that is driven by a battery and is capable of being attached to a power feeding device that feeds power to the electronic device, including: a surface opposite to the power feeding device when the electronic device is attached to the power feeding device; an electrode provided on the surface; and any one of a groove and a projection provided on the surface. 
         [0008]    According to a second aspect of the present invention, there is provided a power feeding device that feeds power to an electronic device, including: a surface opposite to the electronic device when the electronic device is attached to the power feeding device; a feeding terminal projected from the surface; and a projection projected from the surface. 
         [0009]    According to a third aspect of the present invention, there is provided an electronic device system including: an electronic device that is driven by a battery, and includes an electrode provided on a surface; a power feeding device to which the electronic device is capable of being attached, and that includes a feeding terminal contactable with the electrode, the feeding terminal being provided on another surface opposite to the surface of the attached electronic device; wherein one of the surface of the electronic device and the another surface of power feeding device includes a projection, the other of the surface of the electronic device and the another surface of power feeding device includes a groove into which the projection is inserted, and at least one of the electrode or the feeding terminal is projected from a corresponding surface. 
         [0010]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0011]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIGS. 1A and 1B  are diagrams illustrating a mounting state of an electronic device to a battery charger; 
           [0013]      FIGS. 2A and 2B  are diagrams illustrating a mounting state of the electronic device to another battery charger; 
           [0014]      FIG. 3  is an external view of a printer according to an embodiment; 
           [0015]      FIG. 4  is a perspective view illustrating a bottom surface of the printer; 
           [0016]      FIG. 5  is a perspective view illustrating a cross-section surface of the printer; 
           [0017]      FIG. 6  is a view illustrating a bottom surface of the printer; 
           [0018]      FIG. 7  is a view illustrating a cradle according to an embodiment; 
           [0019]      FIG. 8  is a perspective view illustrating an attachment portion of the cradle to which the printer is attached; 
           [0020]      FIG. 9  is a perspective view illustrating the attachment portion of the cradle as viewed from above. 
           [0021]      FIG. 10  is a partial enlarged view of the attachment portion of the cradle; 
           [0022]      FIG. 11  is a diagram illustrating a state before the printer is attached to the cradle; 
           [0023]      FIG. 12  is a diagram illustrating a state where the printer is attached to the cradle; 
           [0024]      FIG. 13  is a diagram illustrating a state where the printer is attached to the cradle; 
           [0025]      FIG. 14  is a diagram illustrating a first variation example of the printer and the cradle according to the embodiment; 
           [0026]      FIGS. 15A to 15C  are diagrams explaining an attachment process of the printer to the cradle according to a second variation example; 
           [0027]      FIGS. 16A to 16C  are diagrams explaining an attachment process of the printer to the cradle according to a third variation example; and 
           [0028]      FIGS. 17A to 17C  are diagrams explaining an attachment process of the printer to the cradle according to a fourth variation example. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0029]    When the charge terminal provided in the above-mentioned cradle is exposed, the charge terminal may be rubbed, which may cause contact failure of the charge terminal. 
         [0030]    A description will now be given of an embodiment of an electronic device according to the present invention. Hereinafter, a portable printer is explained as an example of the electronic device. Also, the embodiment described later is a single example. 
         [0031]    First, based on  FIGS. 1A and 1B , a description will be given of a situation where the electronic device that is a device to be charged is put on a battery charger (i.e., a cradle). 
         [0032]      FIGS. 1A and 1B  illustrate a situation where an electronic device  101  is charged by putting the electronic device  101  on a surface of a battery charger  102 . 
         [0033]    In  FIGS. 1A and 1B , a charge terminal  104  is provided on an upper surface of the battery charger  102 , and an electrode  103  is provided on a lower surface of the electronic device  101 . The electronic device  101  is put on the battery charger  102 , so that the electrode  103  contacts the charge terminal  104 . 
         [0034]    In the situation of  FIGS. 1A and 1B , the electrode  103  of the electronic device  101  is opposite to the charge terminal  104  in a direction where self-weight of the electronic device  101  is applied. Therefore, a shape of the battery charger  102  can be made simple. 
         [0035]    However, since the electronic device  101  is put on the upper surface of the battery charger  102 , a large installation area is required in order to put the battery charger  102 , particularly. For this reason, there is a possibility that a position where the electrode  103  of the electronic device  101  is provided is limited. 
         [0036]    In an example of  FIGS. 2A and 2B , a concave portion  205  for putting the electronic device  101  is formed on a battery charger  202 , and hence the electronic device  101  is vertically attached to the battery charger  202 . By making the battery charger  202  into such a shape, the installation area of the battery charger  202  can be reduced. 
         [0037]    In the example of  FIGS. 2A and 2B , the electrode  103  is provided at a right side of the electronic device  101  in a direction vertical to the direction where the self-weight of the electronic device  101  is applied. Correspondingly, a charge terminal  204  of the battery charger  202  is provided at a position, on a left surface of a right wall of the battery charger  202 , which is opposite to the electrode  103 . 
         [0038]    When the electronic device  101  is attached to the battery charger  202 , it is necessary to make the electrode  103  contact the charge terminal  204 . For this reason, the charge terminal  204  is slightly projected from a side surface (i.e., the left surface of the right wall) of the battery charger  202 . In such a shape of the charge terminal  204 , the charge terminal  204  is always exposed from the battery charger  202 . Therefore, when the electronic device  101  is attached to the battery charger  202 , the electronic device  101  is inserted into the concave portion  205  while rubbing against the charge terminal  204 . For this reason, the housing of the electronic device  101  may be damaged by the contact with the charge terminal  204 . Moreover, the charge terminal  204  rubbed by the electronic device  101  may be worn away. Also, a dust attaches to the exposed charge terminal  204 , and hence the contact failure between the charge terminal  204  and the electrode  103  may be caused. 
         [0039]    As measures to these problems, it is considered that provided in the battery charger is a mechanism which retracts the charge terminal into the wall surface of the battery charger when the electronic device is not attached to the battery charger, and projects the charge terminal from the wall surface of the battery charger when the electronic device is attached to the battery charger. In such a battery charger, a button member which is pushed by the self-weight of the attached electronic device is provided on the wall surface, and the charge terminal can be projected from the wall surface when the button member is pushed. 
         [0040]    By such a configuration, the charge terminal is not ordinarily exposed, and hence it is possible to prevent the electrode from rubbing against the charge terminal. However, the mechanism for putting the button member and the charge terminal in and out needs to be provided in the battery charger, and hence the structure of the battery charger becomes complicated. 
         [0041]      FIG. 3  is an external view of a printer according to the embodiment.  FIG. 4  is a perspective view illustrating a bottom surface of the printer illustrated in  FIG. 3 .  FIG. 5  is a perspective view illustrating a cross-section surface of the printer illustrated in  FIG. 4 .  FIG. 6  is a view illustrating the bottom surface of the printer.  FIG. 7  is a view illustrating a cradle according to the embodiment.  FIG. 8  is a perspective view illustrating an attachment portion of the cradle to which the printer is attached.  FIG. 9  is a perspective view illustrating the attachment portion of the cradle as viewed from above.  FIG. 10  is a partial enlarged view of the attachment portion of the cradle. 
         [0042]    Hereinafter, a description will be given of the printer and the cradle according to the embodiment, with reference to the drawings. 
         [0043]    A printer  1  which is an example of the electronic device according to the embodiment is a portable printer driven by a battery. Here, the following disclosure does not necessarily mean that the electronic device is limited to the printer. As illustrated in  FIG. 5 , provided in the printer  1  are a print head  15  composed of a thermal head and the like, a transfer portion that includes a platen roller  14  transferring a sheet, a storage portion  17  that stores a rolled paper (i.e., the sheet), and a control portion (not shown) that controls the printer  1 . A charge type battery  16  is stored into the printer  1 . 
         [0044]    The printer  1  can be put on a table by directing downward a bottom surface  11  illustrated in  FIG. 4 . At this time, projections which become legs are provided on the bottom surface  11  to stably support the printer  1 . 
         [0045]    The sheet stored into the storage portion  17  is conveyed, and data is printed on the sheet by the print head  15 . The sheet to be conveyed passes through a gap between the print head  15  and the platen roller  14 , and is ejected from a sheet ejection port provided on the printer  1 . 
         [0046]    On the bottom surface  11  of the printer  1 , two charge electrodes  13  are provided. These electrodes  13  are connected to the battery  16  in the inside of printer  1 . Here, as illustrated in  FIGS. 4 and 5 , portions of the bottom surface  11  on which the electrodes  13  are provided are concave portions, and the electrodes  13  are provided at deep positions from the bottom surface  11  of the printer  1 . 
         [0047]    In an example of  FIGS. 4 and 6 , two grooves  12  are formed on the bottom surface  11 . Looking from a lateral direction, each of the grooves  12  is formed in the shape of almost a trapezoid. Each groove  12  is formed so that a center part of the groove  12  is the deepest and a depth of the groove  12  gradually shallows toward both ends of the groove  12  (i.e. both ends in a right and left direction of  FIG. 6 ). In  FIG. 6 , the groove  12  is divided into three areas by lines drawn in an up-and-down direction. An area (i.e. a central area)  12   a  of the central part is a deepest area in the groove  12 . In the present embodiment, the central area  12   a  is flat and the depth of the central area  12   a  is equal anywhere. Areas  12   b  and  12   c  located in the right and the left of the central area  12   a  incline linearly so that the depths of the areas  12   b  and  12   c  become shallow as they are away from the central area  12   a.    FIG. 5  illustrates that a bottom surface of the groove  12  inclines. The two grooves  12  are arranged on the bottom surface  11  in parallel with each other. 
         [0048]    As illustrated in  FIG. 6 , a position of the deepest central area  12   a  in the groove  12  is adjacent to the positions where the electrodes  13  are provided. That is, the central areas  12   a  in the grooves  12  and the central parts of the two electrodes  13  are arranged on a straight line (not shown) extending up and down in  FIG. 6 . Here, the depth of each groove  12  on the central area  12   a  is formed deeper than a depth from the bottom surface  11  of the printer  1  to the electrodes  13 . 
         [0049]      FIG. 7  illustrates a cradle  2  according to the embodiment. In  FIG. 7 , a part of the internal structure of the cradle  2  is penetrated to make it easier to understand the internal structure of the cradle  2 . 
         [0050]    The cradle  2  functioning as the battery charger has a box-like shape. A hollow attachment portion  21  to which the printer  1  is attached is formed in the cradle  2 . A cross section of the attachment portion  21  becomes a shape corresponding to almost the cross section of the printer  1 . The printer  1  is attached to the cradle  2  from above the attachment portion  21 . Here, the attachment portion  21  is formed in a direction slightly inclined against a vertical direction of  FIG. 7 . 
         [0051]    As illustrated in  FIGS. 7 to 10 , two charge terminals  24  are provided on a surface  22  of the attachment portion  21 . The surface  22  is a surface to which the self-weight of the printer attached to the cradle  2  is applied. As illustrated in  FIGS. 9 and 10 , each of the charge terminals  24  is formed so as to project from the surface  22 . Moreover, the respective charge terminals  24  are provided at positions opposite to the electrodes  13  in a state where the printer  1  is attached to the cradle  2 . 
         [0052]    Also, two projections  23  are formed on the surface  22  of the cradle  2 . The two projections  23  are formed in parallel with each other. Specifically, as illustrated in  FIG. 10 , each of the projections  23  is formed in the shape of a trapezoid, and is mainly divided into three areas. In these areas, a central area  23   a  is the highest and the top of the central area  23   a  is flat. Areas  23   b  and  23   c  located in both sides of the central area  12   a  incline linearly so that the heights of the areas  23   b  and  23   c  reduce gradually toward both ends of each projection  23  from the central area  23   a.  The two respective projections  23  are provided at positions opposite to the grooves  12  in a state where the printer  1  is attached to the cradle  2 . Here, the central area  23   a  of each projection  23  is formed higher than the charge terminals  24 . 
         [0053]      FIG. 11  is a diagram illustrating a state before the printer  1  is attached to the cradle  2 .  FIGS. 12 and 13  are diagrams illustrating a state where the printer  1  is attached to the cradle  2 .  FIG. 13  is a partial transparent diagram. 
         [0054]    The printer  1  is attached to the attachment portion  21  of the cradle  2  so as to slightly incline to a right side of  FIG. 11  against the cradle  2 . In this case, the printer  1  gradually declines along the surface  22 . 
         [0055]    At this time, the bottom surface  11  of the declining printer  1  contacts the projections  23 . Thereby, the printer  1  is guided to the left side of  FIG. 11  by the projections  23 . Since the projections  23  are higher than the charge terminals  24 , a housing of the printer  1  lifted by the projections  23  does not contact the charge terminals  24 , which prevents the printer  1  from rubbing against the charge terminals  24 . 
         [0056]    Moreover, when the printer  1  declines, the projections  23  are fitted in the grooves  12 . Thereby, the upper surfaces of the projections  23  contact the bottom surfaces of the grooves  12 . Since the grooves  12  and the projections  23  are formed in the shape of a mountain, the printer  1  is guided by the projections  23  depending on the contact of the projections  23  and the grooves  12 , and the declining printer  1  gradually approaches the surface  22 . Then, when the highest parts (i.e., the central areas  23   a ) of the projections  23  reach the deepest positions (i.e., the central areas  12   a ) of the grooves  12 , the printer  1  gets closest to the surface  22 . 
         [0057]    The grooves  12  are formed deeper than the depths of the electrodes  13 . When the grooves  12  of the printer  1  reach the projections  23 , the electrodes  13  contact the charge terminals  24  and the charge to the printer  1  is started. 
         [0058]    When the printer  1  is removed from the cradle  2 , the contact positions of the projections  23  and the grooves  12  are changed by pulling out the printer  1  upward, and the printer  1  is gradually away from the surface  22 . Depending on this, the contact state of the electrodes  13  and the charge terminals  24  is also released. 
         [0059]    When the printer  1  is further pulled out upward, the projections  23  are removed from the grooves  12  and contact the bottom surface  11  of the printer  1 . Thereby, the printer  1  is further away from the surface  22 . The projections  23  guide the printer  1 , so that the printer  1  to be pulled out upward can be removed from the cradle  2  without contacting the charge terminals  24 . Therefore, it is possible to prevent the printer  1  from rubbing against the charge terminals  24 . 
         [0060]    The projections  23  have a function which guides the printer  1  so that the charge terminals  24  contact the electrodes  13  well. The width of the attachment portion  21  of the cradle  2  almost corresponds to the width of the printer  1 , but it is considered to make the width of the attachment portion  21  slightly larger than the width of the printer  1  so as to be able to attach the printer  1  more easily. In this case, the printer  1  to be attached to the cradle  2  deviates in the right and left direction, and there is a possibility that the charge terminals  24  do not contact the electrodes  13  well even when the printer  1  is attached to the cradle  2 . 
         [0061]    However, in the present embodiment, when the printer  1  is attached to the cradle  2 , the projections  23  come in the grooves  12 , the printer  1  is guided in the right and left direction by the projections  23 , and hence the printer  1  can be led to the positions where the electrodes  13  contact the charge terminals  24 . 
         [0062]    Here, the depths of the grooves  12  and the heights of the projections  23  may be formed so that the electrodes  13  and the charge terminals  24  can keep a good contact state when the highest parts of the projections  23  are located on the deepest parts of the grooves  12 . 
         [0063]    When a hardness of a material constituting a housing of the printer  1  is different from a hardness of a material constituting a housing of the cradle  2 , the printer  1  contacts the cradle  2  and rubs against the cradle  2  in attaching the printer  1  to the cradle  2 , and hence one of the housings may wear away. For this reason, it is desirable that the material constituting the housing of the printer  1  and the material constituting the housing of the cradle  2  have almost the same hardness as each other. 
         [0064]    In the above-mentioned embodiment, the grooves  12  and the projections  23  are formed in the shape of the trapezoid. However, as long as the charge terminals  24  do not contact the printer  1  in inserting the printer  1  into the cradle  2 , and the electrodes  13  contact the charge terminals  24  when the electrodes  13  of the printer  1  reach the positions of the charge terminals  24 , the grooves  12  and the projections  23  may be formed in a shape other than the trapezoid. The grooves  12  and the projections  23  can be arbitrarily formed in a shape, such as an arc-like shape including a semicircle, a triangle, a rectangle, or the like. The grooves  12  and the projections  23  do not necessarily have to be the same shape. If it is possible to prevent the charge terminals  24  from contacting the printer  1  needlessly, the shape of the projections  23  may be different from the shape of the grooves  12 . For example, the projections  23  may be the triangle, and the grooves  12  may be the rectangle. 
         [0065]    Moreover, in the above-mentioned embodiment, the two grooves  12  and the two projections  23  may be provided. However, if unnecessary contact of the charge terminals  24  to the printer  1  can be avoided, the number of grooves  12  and projections  23  does not need to be two. In this regard, when a single projection  23  supports the printer  1  to be attached to the cradle  2 , if a possibility that the printer  1  inclines in the attachment portion  21  and touches the charge terminals  24  is removed as much as possible, it is desirable that the plurality of projections  23  support the housing of the printer  1 . 
         [0066]      FIG. 14  schematically illustrates the printer and the cradle according to another example. As illustrated in  FIG. 14 , the projections  23  may be provided on the printer  1 , and the grooves  12  may be provided on the cradle  2 . Here, when the charge terminals  24  of the cradle  2  are projected and the electrodes  13  of the printer  1  are provided at the deep positions from the bottom surface  11  of the printer  1 , the grooves  12  to be formed on the cradle  2  are formed deeper than the depths of the electrodes  13 . Similarly, the projections  23  of the printer  1  are formed higher than the heights of the charge terminals  24  of the cradle  2 . Here, essentially, the electrodes  13  of the printer  1  may be projected and the charge terminals  24  of the cradle  2  may be provided at the deep positions from the surface  22  of the cradle  2 . 
         [0067]    In the above-mentioned embodiment, the projections  23  guide the printer  1  so that the printer  1  is away from the surface  22  on which the charge terminals  24  are provided. However, in order to attach the printer  1  to the cradle  2  without a trouble, a clearance  28  in which the printer  1  can move in a front-back direction is required in the front-back direction (i.e., a direction that intersects the surface  22  on which the charge terminals  24  are provided) of the attachment portion  21  (see  FIG. 13 ). When such a clearance  28  is provided in the attachment portion  21 , the printer  1  to be attached to the cradle  2  moves in the front-back direction in the attachment portion  21 , the contact state of the electrodes  13  and the charge terminals  24  is released, and hence the charge may not be performed appropriately. 
         [0068]    For this reason, a guide that guides the printer  1  to be attached to the cradle  2  toward the charge terminals  24  may be provided on another surface  26  of the cradle  2 . The guide can prevent the movement of the printer  1  in the front-back direction in the attachment portion  21 . 
         [0069]      FIGS. 15A to 15C  schematically illustrate an attachment state of the printer  1  to a cradle  31 .  FIG. 15A  illustrates a state before the start of the attachment of the printer  1  to the cradle  31 .  FIG. 15B  illustrates an ongoing state where the printer  1  is attached to the cradle  31 .  FIG. 15C  illustrates a state where the printer  1  has been attached to the cradle  31 . 
         [0070]    As illustrated in  FIGS. 15A to 15C , the printer  1  includes the grooves  12  and the electrodes  13 . Here, the numbers of grooves  12  and electrodes  13  are the same as those of  FIG. 4 . The cradle  31  includes: a hollow attachment portion  30  to which the printer  1  is attached; a surface  32  having charge terminals  34  and projections  33  to be got into the grooves  12 ; and a surface  35  that has a guide  36  and is opposite to the surface  32 . The guide  36  guides the printer  1  toward the projections  33 . The attachment portion  30  is surrounded with the surfaces  32  and  35 . 
         [0071]    By lowering the printer  1  from the state of  FIG. 15A , the projections  33  contact the housing of the printer  1  as illustrated in  FIG. 15B . Thereby, the printer  1  is guided in a direction away from the charge terminals  34 . Then, the projections  33  get into the grooves  12 , so that the printer  1  can be guided in a direction approaching the charge terminals  34 . 
         [0072]    At nearly the same timing as the projections  33  get into the grooves  12 , the mountain-like guide  36  provided on the surface  35  touches the housing of the printer  1 . The printer  1  is guided in the direction (i.e., a right direction of  FIG. 15 ) approaching the charge terminals  34  by the guide  36 , as illustrated by an arrow P of  FIG. 15C . 
         [0073]    When the printer  1  is attached to the cradle  31 , a highest portion X of the guide  36  contacts the printer  1 , and the position of the printer  1  is kept in the direction approaching the charge terminals  34 . Thereby, it is possible to keep the good contact state of the electrodes  13  and the charge terminals  34 . 
         [0074]    When the projections  33  interfere with the printer  1  at a stage where the insertion of the printer  1  into the attachment portion  30  is started, the attachment of the printer  1  is affected. Therefore, the width of the front-back direction (i.e., the right and left direction of  FIG. 15 ) of the attachment portion  30  needs to have a width corresponding to a total the height of the projections  33  and the width of the front-back direction of the printer  1 . However, after the projections  33  start to get into the grooves  12 , the printer  1  is brought close to the surface  32  side little by little. Therefore, the width of the front-back direction of the attachment portion  30  is gradually narrowed by the guide  36 , which can stably support the printer  1  in a state of  FIG. 15C . 
         [0075]    In the transparent diagrams of  FIGS. 7 and 13 , a surface  27  near a lower end of the surface  26  opposite to the surface  22  of the attachment portion  21  is formed in a tapered shape. Since the tapered surface  27  can be contacted with a lower end of the printer  1  depending on the shape of the tapered surface  27 , the tapered surface  27  can be provided with the same effect as the guide  36  of  FIG. 15 . The attachment portion  21  is surrounded with the surfaces  22 ,  26  and  27 . 
         [0076]      FIGS. 16A to 16C  are variation examples of  FIGS. 15A to 15C . A guide  62  is provided on the housing (i.e., a surface  19  opposite to the bottom surface  11 ) of the printer  1  in  FIGS. 16A to 16C . Therefore, an element corresponding to the guide is not provided on a cradle  41 . The printer  1  includes the grooves  12  and the electrodes  13 . The cradle  41  includes: a hollow attachment portion  40  to which the printer  1  is attached; a surface  42  having charge terminals  44  and projections  43  to be got into the grooves  12 ; and a surface  45  opposite to the surface  42 . The attachment portion  40  is surrounded with the surfaces  42  and  45 . 
         [0077]    As illustrated in  FIG. 16B , the guide  62  contacts the surface  45  of the cradle  41  depending on the grooves  12  reaching the positions of projections  43 . Then, the printer  1  is guided to the right side of  FIG. 16B  by the guide  62  contacting the surface  45  depending on the gradual lowering of the printer  1 . When the printer  1  becomes a state of  FIG. 16C , the printer  1  attached to the cradle  41  is supported appropriately. 
         [0078]      FIGS. 17A to 17C  are diagrams explaining the attachment of the printer to the cradle according to other examples. The printer  1  includes the grooves  12  and the electrodes  13 . The cradle  51  includes: a hollow attachment portion  50  to which the printer  1  is attached; a surface  52  having charge terminals  54  and projections  53  to be got into the grooves  12 ; and a surface  55  that is opposite to the surface  52  and has a biasing unit  56  which biases the printer  1  toward the charge terminal  54  side. The biasing unit  56  is an element which biases the printer  1  to the right side of  FIG. 17A  with an elastic body such as a spring. Here, the biasing unit  56  itself may be composed of a member having elasticity. The attachment portion  50  is surrounded with the surfaces  52  and  55 . 
         [0079]    As illustrated in  FIG. 17A , the printer  1  is inserted into the cradle  51 , so that the printer  1  contacts the biasing unit  56 . In this state, when the printer  1  is pushed downward, the projections  53  contact the printer  1  as illustrated in  FIG. 17B , the printer  1  is guided to the left side of  FIG. 17B , and the biasing unit  56  is pushed in a direction of an arrow Q of  FIG. 17B  by the printer  1 . 
         [0080]    When the printer  1  is additionally pushed downward, the projections  53  are fitted in the grooves  12  as illustrated in  FIG. 17C . In this case, the biasing unit  56  biases the printer  1  in a direction of an arrow R, so that the printer  1  is pushed against the surface  52 . Thereby, it is possible to keep the good contact state of the electrodes  13  and the charge terminals  54 . 
         [0081]    According to the above-mentioned embodiments, when the printer  1  is attached to the cradle  2  ( 31 ,  41  or  51 ), the projections  23  ( 33 ,  43  or  53 ) can prevent the contact of the housing of the printer  1  and the charge terminals  24  ( 34 ,  44  or  54 ). Moreover, according to the above-mentioned embodiments, when the electrodes  13  provided on the printer  1  reach the positions corresponding to the charge terminals  24  ( 34 ,  44  or  54 ), the electrodes  13  can be contacted with the charge terminals  24  ( 34 ,  44  or  54 ). 
         [0082]    When the projections  23  ( 33 ,  43  or  53 ) are formed near the charge terminals  24  ( 34 ,  44  or  54 ) of the cradle  2  ( 31 ,  41  or  51 ), the projections  23  ( 33 ,  43  or  53 ) can prevent foreign bodies from contacting the charge terminals  24  ( 34 ,  44  or  54 ). Especially, when metal objects, such as clips, fall in the cradle  2  ( 31 ,  41  or  51 ), the formation of the projections  23  ( 33 ,  43  or  53 ) can prevent the metal objects from contacting the charge terminals  24  ( 34 ,  44  or  54 ).